LAIDLAW ENVIRONMENTAL SERVICES INC
S-4, 1997-11-13
HAZARDOUS WASTE MANAGEMENT
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<PAGE>   1
 
   AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON NOVEMBER 13, 1997
 
                                                     REGISTRATION NO. 333-
================================================================================
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                             ---------------------
                                    FORM S-4
                             REGISTRATION STATEMENT
                                     UNDER
                           THE SECURITIES ACT OF 1933
                             ---------------------
                      LAIDLAW ENVIRONMENTAL SERVICES, INC.
             (Exact name of Registrant as specified in its charter)
                             ---------------------
 
<TABLE>
<C>                               <C>                               <C>
            DELAWARE                            4953                           51-0228924
  (State or other jurisdiction      (Primary Standard Industrial            (I.R.S. Employer
      of incorporation or           Classification Code Number)           Identification No.)
          organization)
</TABLE>
 
 1301 GERVAIS STREET, SUITE 300, COLUMBIA, SOUTH CAROLINA 29201, (803) 933-4200
  (Address, including zip code, and telephone number, including area code, of
                   Registrant's principal executive offices)
 
                               KENNETH W. WINGER
                      LAIDLAW ENVIRONMENTAL SERVICES, INC.
                        1301 GERVAIS STREET, SUITE 300,
                        COLUMBIA, SOUTH CAROLINA 29201,
                                 (803) 933-4200
  (Name and address, including zip code, and telephone number, including area
                          code, of agent for service)
 
                                    COPY TO:
 
                            HERBERT S. WANDER, ESQ.
                             KATTEN MUCHIN & ZAVIS
                       525 WEST MONROE STREET, SUITE 1600
                          CHICAGO, ILLINOIS 60661-3693
                                 (312) 902-5200
 
     APPROXIMATE DATE OF COMMENCEMENT OF PROPOSED SALE TO THE PUBLIC: As soon as
practicable after the effective date of this Registration Statement.
 
     If the securities being registered on this Form are being offered in
connection with the formation of a holding company and there is compliance with
General Instruction G, check the following box.  [ ]
                             ---------------------
 
                        CALCULATION OF REGISTRATION FEE
 
<TABLE>
<CAPTION>
=========================================================================================================================
                                                            PROPOSED MAXIMUM      PROPOSED MAXIMUM
      TITLE OF EACH CLASS OF            AMOUNT TO BE         OFFERING PRICE      AGGREGATE OFFERING        AMOUNT OF
    SECURITIES TO BE REGISTERED         REGISTERED(1)           PER UNIT              PRICE(2)        REGISTRATION FEE(2)
- -------------------------------------------------------------------------------------------------------------------------
<S>                                  <C>                  <C>                   <C>                   <C>
Common Stock, $1.00 par value per
  share and associated Stock
  Purchase Rights(3), of Laidlaw
  Environmental Services, Inc......      150,862,632              N/A               $771,992,375           $233,938
========================================================================================================================
</TABLE>
 
(1) Represents the maximum amount of Common Stock, par value $1.00 per share, of
    Laidlaw Environmental Services, Inc., a Delaware corporation ("Laidlaw
    Environmental") issuable upon the consummation of the exchange offer for
    shares of Common Stock, par value $0.10 per share (the "Shares") of
    Safety-Kleen Corp., a Wisconsin corporation ("Safety-Kleen"), together with
    associated stock purchase rights. According to Safety-Kleen's Form 10-Q for
    the period ended September 6, 1997, as of September 6, 1997, there were
    issued and outstanding 58,400,729 Shares of which 601,100 Shares were owned
    by a wholly-owned subsidiary of Laidlaw Environmental as of the date of the
    filing of this Registration Statement. Based on the foregoing and assuming
    that (i) no shares have been issued since September 6, 1997 and (ii) no
    options or shares have been issued other than the 5,059,801 options to
    purchase shares reported in Safety-Kleen's Form 10-K for the period ended
    December 28, 1996, the maximum number of Shares to be received in exchange
    would be 62,859,430. The actual number of Shares will depend on the facts
    that exist on the date of the exchange.
(2) Pursuant to Rules 457(f)(1) and 457(c) under the Securities Act of 1933, as
    amended, and solely for the purposes of calculating the registration fee,
    the registration fee was computed on the basis of $26.28125 per Share, the
    average of the high and low prices of Safety-Kleen Common Stock as reported
    on New York Stock Exchange on November 7, 1997.
(3) Stock Purchase Rights are attached to and trade with Laidlaw Environmental
    Common Stock. Value attributable to such rights, if any, is reflected in the
    market price of the Laidlaw Environmental Common Stock.
                             ---------------------
 
     THE REGISTRANT HEREBY AMENDS THIS REGISTRATION STATEMENT ON SUCH DATE OR
DATES AS MAY BE NECESSARY TO DELAY ITS EFFECTIVE DATE UNTIL THE REGISTRANT SHALL
FILE A FURTHER AMENDMENT WHICH SPECIFICALLY STATES THAT THIS REGISTRATION
STATEMENT SHALL THEREAFTER BECOME EFFECTIVE IN ACCORDANCE WITH SECTION 8(A) OF
THE SECURITIES ACT OF 1933 OR UNTIL THE REGISTRATION STATEMENT SHALL BECOME
EFFECTIVE ON SUCH DATE AS THE SECURITIES AND EXCHANGE COMMISSION, ACTING
PURSUANT TO SAID SECTION 8(A), MAY DETERMINE.
================================================================================
<PAGE>   2
 
     INFORMATION CONTAINED HEREIN IS SUBJECT TO COMPLETION OR AMENDMENT. A
     REGISTRATION STATEMENT RELATING TO THE SECURITIES HAS BEEN FILED WITH THE
     SECURITIES AND EXCHANGE COMMISSION. THESE SECURITIES MAY NOT BE SOLD NOR
     MAY OFFERS TO BUY BE ACCEPTED PRIOR TO THE TIME THE REGISTRATION STATEMENT
     BECOMES EFFECTIVE. THIS PROSPECTUS SHALL NOT CONSTITUTE AN OFFER TO SELL OR
     THE SOLICITATION OF AN OFFER TO BUY NOR SHALL THERE BE ANY SALE OF THE
     SECURITIES IN ANY STATE IN WHICH SUCH OFFER, SOLICITATION OR SALE WOULD BE
     UNLAWFUL PRIOR TO REGISTRATION OR QUALIFICATION UNDER THE SECURITIES LAWS
     OF ANY SUCH STATE.
 
                SUBJECT TO COMPLETION, DATED NOVEMBER   , 1997.
PROSPECTUS
                       OFFER TO EXCHANGE EACH OUTSTANDING
                                  COMMON SHARE
                (INCLUDING THE ASSOCIATED SHARE PURCHASE RIGHTS)
 
                                       OF
 
                               SAFETY-KLEEN CORP.
                                      FOR
 
                          $14.00 NET PER SHARE IN CASH
 
                                      AND
 
                           2.4 SHARES OF COMMON STOCK
 
                                       OF
 
                      LAIDLAW ENVIRONMENTAL SERVICES, INC.
 
     THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 5:00 P.M., NEW YORK CITY
TIME, ON             , 1997, UNLESS THE OFFER IS EXTENDED (THE "EXPIRATION
DATE"). SHARES WHICH ARE TENDERED PURSUANT TO THE OFFER MAY BE WITHDRAWN AT ANY
TIME PRIOR TO THE EXPIRATION DATE.
 
     Laidlaw Environmental Services, Inc., a Delaware corporation ("Laidlaw
Environmental"), and LES Acquisition, Inc., a Delaware corporation and indirect
wholly-owned subsidiary of Laidlaw Environmental ("LES Acquisition"), hereby
offer, upon the terms and subject to the conditions set forth herein and in the
related Letter of Transmittal (collectively, the "Offer"), to exchange $14.00
net in cash and 2.4 shares of Common Stock, par value $1.00 per share, of
Laidlaw Environmental ("Laidlaw Environmental Common Stock"), for each
outstanding Common Share, par value $0.10 per share (each, a "Share" and
collectively, the "Shares"), of Safety-Kleen Corp., a Wisconsin corporation
("Safety-Kleen"), including (unless and until Laidlaw Environmental and LES
Acquisition declare that the Rights Condition (as defined below) is satisfied)
the associated Common Share Purchase Rights (each, a "Right" and collectively,
the "Rights") issued pursuant to the Rights Agreement, dated as of November 9,
1988, between Safety-Kleen and First National Bank of Chicago, as Rights Agent,
as amended by a First Amendment to Rights Agreement, dated as of August 10, 1990
(as so amended, the "Rights Agreement"), validly tendered on or prior to the
Expiration Date and not properly withdrawn. Unless the context otherwise
requires and unless and until the Rights are redeemed, all references to Shares
shall include the associated Rights. All references herein to Rights shall
include all benefits that may inure to holders of the Rights pursuant to the
Rights Agreement. Each Share validly tendered on or prior to the Expiration Date
and not properly withdrawn will be entitled to receive $14.00 net in cash (the
"Cash Consideration") and 2.4 shares of Laidlaw Environmental Common Stock (the
"Stock Consideration," and, together with the Cash Consideration, the "Offer
Consideration").
 
                                                   (Continued on following page)
  THESE SECURITIES HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE SECURITIES AND
 EXCHANGE COMMISSION OR ANY STATE SECURITIES COMMISSION, NOR HAS THE SECURITIES
   AND EXCHANGE COMMISSION OR ANY STATE SECURITIES COMMISSION PASSED UPON THE
ACCURACY OR ADEQUACY OF THIS PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY IS A
                               CRIMINAL OFFENSE.
                      THE DEALER MANAGER FOR THE OFFER IS:
                            BEAR, STEARNS & CO. INC.
                                245 PARK AVENUE
                            NEW YORK, NEW YORK 10167
               THE DATE OF THIS PROSPECTUS IS             , 1997.
<PAGE>   3
 
(continued from previous page)
 
     LAIDLAW ENVIRONMENTAL'S OBLIGATION TO EXCHANGE THE OFFER CONSIDERATION FOR
SHARES PURSUANT TO THE OFFER IS CONDITIONED UPON, AMONG OTHER THINGS, THE
SATISFACTION OR, WHERE APPLICABLE, WAIVER OF THE FOLLOWING CONDITIONS: (I) THERE
BEING VALIDLY TENDERED AND NOT WITHDRAWN PRIOR TO THE EXPIRATION DATE A NUMBER
OF SHARES WHICH, TOGETHER WITH SHARES OWNED BY LAIDLAW ENVIRONMENTAL AND ITS
AFFILIATES, CONSTITUTE AT LEAST TWO THIRDS OF THE TOTAL NUMBER OF OUTSTANDING
SHARES ON A FULLY DILUTED BASIS (AS THOUGH ALL OPTIONS OR OTHER SECURITIES
CONVERTIBLE INTO OR EXERCISABLE OR EXCHANGEABLE FOR SHARES (OTHER THAN THE
RIGHTS) HAD BEEN SO CONVERTED, EXERCISED OR EXCHANGED) AS OF THE DATE THE SHARES
ARE ACCEPTED FOR EXCHANGE BY LAIDLAW ENVIRONMENTAL PURSUANT TO THE OFFER (THE
"MINIMUM TENDER CONDITION"), (II) THE AUTHORIZATION TO INCREASE THE NUMBER OF
SHARES OF LAIDLAW ENVIRONMENTAL COMMON STOCK AND THE APPROVAL OF THE ISSUANCE OF
SHARES OF LAIDLAW ENVIRONMENTAL COMMON STOCK IN CONNECTION WITH THE OFFER AND
THE MERGER BY HOLDERS OF THE REQUISITE NUMBER OF SHARES OF LAIDLAW ENVIRONMENTAL
COMMON STOCK NECESSARY FOR THE AUTHORIZATION AND ISSUANCE (THE "LAIDLAW
ENVIRONMENTAL STOCKHOLDER APPROVAL CONDITION"), (III) THE SAFETY-KLEEN BOARD
HAVING REDEEMED THE RIGHTS OR AMENDED THE RIGHTS AGREEMENT SO THAT THE RIGHTS
ARE INAPPLICABLE TO THE ACQUISITION OF SHARES PURSUANT TO THE OFFER, OR LAIDLAW
ENVIRONMENTAL BEING OTHERWISE SATISFIED IN ITS SOLE DISCRETION THAT THE RIGHTS
ARE INVALID OR ARE NOT APPLICABLE TO THE ACQUISITION OF SHARES PURSUANT TO THE
OFFER (THE "RIGHTS PLAN CONDITION"), (IV) LAIDLAW ENVIRONMENTAL BEING SATISFIED,
IN ITS SOLE DISCRETION, EITHER THAT THE PROVISIONS OF SECTIONS 180.1141 AND
SECTION 180.1150 OF THE WISCONSIN STATUTES (THE "WISCONSIN STATUTES") ARE
INAPPLICABLE TO LAIDLAW ENVIRONMENTAL, LES ACQUISITION AND THE TRANSACTIONS
CONTEMPLATED HEREIN, OR THAT (A) FULL VOTING RIGHTS FOR ALL SHARES TO BE
ACQUIRED BY LAIDLAW ENVIRONMENTAL AND LES ACQUISITION PURSUANT TO THE OFFER HAVE
BEEN RESTORED BY THE SHAREHOLDERS OF SAFETY-KLEEN PURSUANT TO THE WISCONSIN
STATUTES, AND (B) THE WISCONSIN STATUTES WILL NOT PROHIBIT FOR ANY PERIOD OF
TIME THE CONSUMMATION OF THE MERGER OR ANY OTHER "BUSINESS COMBINATION" (AS
DEFINED IN SUCH STATUTES) INVOLVING SAFETY-KLEEN AND LAIDLAW ENVIRONMENTAL OR
LES ACQUISITION, OR ANY OF THEIR RESPECTIVE AFFILIATES (THE "WISCONSIN STATUTORY
CONDITIONS") AND (V) ALL REGULATORY APPROVALS REQUIRED TO CONSUMMATE THE OFFER
HAVE BEEN OBTAINED AND REMAIN IN FULL FORCE AND EFFECT, ALL STATUTORY WAITING
PERIODS IN RESPECT THEREOF HAVING EXPIRED AND NO SUCH APPROVAL CONTAINING ANY
CONDITIONS OR RESTRICTIONS WHICH THE LAIDLAW ENVIRONMENTAL BOARD OF DIRECTORS
(THE "LAIDLAW ENVIRONMENTAL BOARD") DETERMINES WILL OR COULD BE EXPECTED TO
MATERIALLY IMPAIR THE STRATEGIC AND FINANCIAL BENEFITS EXPECTED TO RESULT FROM
THE OFFER (THE "REGULATORY APPROVAL CONDITION"). THE MINIMUM TENDER CONDITION,
THE LAIDLAW ENVIRONMENTAL STOCKHOLDER APPROVAL CONDITION, THE RIGHTS PLAN
CONDITION, THE WISCONSIN STATUTORY CONDITIONS, THE REGULATORY APPROVAL CONDITION
AND THE OTHER CONDITIONS SET FORTH UNDER THE CAPTION "THE OFFER -- CONDITIONS OF
THE OFFER -- CERTAIN OTHER CONDITIONS OF THE OFFER" SHALL BE REFERRED TO
COLLECTIVELY AS THE "OFFER CONDITIONS." TERMS USED BUT NOT DEFINED ABOVE ARE
DEFINED HEREINAFTER.
 
     THIS PROSPECTUS AND THE OFFER MADE HEREBY DO NOT CONSTITUTE SOLICITATION OF
ANY PROXIES. ANY SUCH SOLICITATIONS WILL BE MADE ONLY PURSUANT TO
 
                                       ii
<PAGE>   4
 
SEPARATE PROXY MATERIALS COMPLYING WITH THE REQUIREMENTS OF SECTION 14(A) OF THE
SECURITIES EXCHANGE ACT OF 1934, AS AMENDED.
 
     THIS PROSPECTUS CONTAINS CERTAIN ANALYSES AND STATEMENTS WITH RESPECT TO
THE FINANCIAL CONDITION, RESULTS OF OPERATIONS AND BUSINESS OF LAIDLAW
ENVIRONMENTAL FOLLOWING THE CONSUMMATION OF THE OFFER AND THE MERGER, INCLUDING
STATEMENTS RELATING TO THE COST SAVINGS OR SYNERGIES THAT MAY BE REALIZED FROM
THE MERGER. SEE "PROSPECTUS SUMMARY -- REASONS FOR THE OFFER -- ENHANCED
BUSINESS OPPORTUNITIES" AND "BACKGROUND OF OFFER." THESE ANALYSES AND STATEMENTS
INCLUDE FORWARD-LOOKING STATEMENTS WITH RESPECT TO, AMONG OTHER THINGS, EXPECTED
COST SAVINGS FROM THE MERGER, FUTURE BUSINESS DECISIONS, AND OTHER UNCERTAINTIES
WHICH, ALTHOUGH CONSIDERED REASONABLE BY LAIDLAW ENVIRONMENTAL, ARE SUBJECT TO
UNCERTAINTIES AND INVOLVE MATTERS THAT ARE BEYOND LAIDLAW ENVIRONMENTAL'S
CONTROL AND DIFFICULT TO PREDICT. SEE "CAUTIONARY STATEMENT REGARDING
FORWARD-LOOKING STATEMENTS." FURTHER INFORMATION AND OTHER FACTORS WHICH COULD
AFFECT THE FINANCIAL RESULTS OF LAIDLAW ENVIRONMENTAL AFTER THE MERGER ARE
INCLUDED IN THE FILINGS WITH THE SECURITIES AND EXCHANGE COMMISSION INCORPORATED
BY REFERENCE HEREIN.
                             ---------------------
 
     Laidlaw Environmental is unable to predict the amount of time necessary to
obtain, among other things, the shareholder, governmental and regulatory
approvals and consents required to complete the Offer and the transactions
contemplated herein. However, the time necessary to obtain such approvals and
consents may extend beyond the Expiration Date, and Laidlaw Environmental
reserves the right to extend the Offer from time to time in its sole discretion.
                             ---------------------
 
                                   IMPORTANT
 
     Any Safety-Kleen Shareholder desiring to tender all or any portion of his
or her Shares and the associated Rights should either (a) complete and sign the
Letter of Transmittal or a facsimile copy thereof in accordance with the
instructions in the Letter of Transmittal, and mail or deliver the Letter of
Transmittal or such facsimile and any other required documents to IBJ Schroder
Bank & Trust Company (the "Exchange Agent") and either deliver the certificates
for such Shares and, if separate, certificates for the Rights to the Exchange
Agent along with the Letter of Transmittal, deliver such Shares (and Rights, if
applicable) pursuant to the procedures for book-entry transfer set forth herein
(in the case of Rights, only if such procedures are available) or comply with
the guaranteed delivery procedures set forth below or (b) request his or her
broker, dealer, commercial bank, trust company or other nominee to effect the
transaction for such Safety-Kleen Shareholder. Any Safety-Kleen Shareholder
having Shares and, if applicable, Rights registered in the name of a broker,
dealer, commercial bank, trust company or other nominee is urged to contact such
broker, dealer, commercial bank, trust company or other nominee if he or she
desires to tender such Shares and, if applicable, Rights.
 
     Safety-Kleen Shareholders will be required to tender one Right for each
Share tendered in order to effect a valid tender of Shares, unless and until
Laidlaw Environmental declares that the Rights Plan Condition is satisfied or
waived. Unless and until the Safety-Kleen Distribution Date (as defined herein)
occurs, a tender of Shares will constitute a tender of the associated Rights.
 
     A Safety-Kleen Shareholder that desires to tender Shares and, if
applicable, Rights and whose certificates for such Shares and, if applicable,
Rights are not immediately available or who cannot comply with the procedures
for book-entry transfer on a timely basis or who cannot deliver all required
documents to the Exchange Agent prior to the Expiration Date, may tender such
Shares and, if applicable, Rights, by following the procedure for guaranteed
delivery.
 
                                       iii
<PAGE>   5
 
     Questions and requests for assistance may be directed to the Information
Agent or to the Dealer Manager at their respective addresses and telephone
numbers set forth on the back cover of this Prospectus. Requests for additional
copies of this Prospectus and the Letter of Transmittal may be directed to the
Information Agent or to brokers, dealers, commercial banks or trust companies.
 
     NO PERSON HAS BEEN AUTHORIZED TO GIVE ANY INFORMATION OR MAKE ANY
REPRESENTATION IN CONNECTION WITH THE OFFER OTHER THAN THOSE CONTAINED OR
INCORPORATED BY REFERENCE IN THIS PROSPECTUS, AND, IF GIVEN OR MADE, SUCH
INFORMATION OR REPRESENTATION MUST NOT BE RELIED UPON AS HAVING BEEN AUTHORIZED
BY LAIDLAW ENVIRONMENTAL OR BEAR, STEARNS & CO. INC. (THE "DEALER MANAGER").
THIS PROSPECTUS DOES NOT CONSTITUTE AN OFFER OR A SOLICITATION TO ANY PERSON IN
ANY JURISDICTION IN WHICH SUCH OFFER OR SOLICITATION IS UNLAWFUL. THE OFFER IS
NOT BEING MADE TO, NOR WILL TENDERS BE ACCEPTED FROM OR ON BEHALF OF,
SAFETY-KLEEN SHAREHOLDERS IN ANY JURISDICTION IN WHICH THE MAKING OR ACCEPTANCE
THEREOF WOULD NOT BE IN COMPLIANCE WITH THE LAWS OF SUCH JURISDICTION. HOWEVER,
LAIDLAW ENVIRONMENTAL MAY, IN ITS SOLE DISCRETION, TAKE SUCH ACTION AS IT MAY
DEEM NECESSARY TO MAKE THE OFFER IN ANY SUCH JURISDICTION AND EXTEND THE OFFER
TO SAFETY-KLEEN SHAREHOLDERS IN SUCH JURISDICTION. NEITHER THE DELIVERY OF THIS
PROSPECTUS NOR ANY EXCHANGE HEREUNDER SHALL UNDER ANY CIRCUMSTANCES CREATE ANY
IMPLICATION THAT THERE HAS BEEN NO CHANGE IN THE AFFAIRS OF LAIDLAW
ENVIRONMENTAL OR SAFETY-KLEEN SINCE THE DATE AS OF WHICH INFORMATION IS
FURNISHED OR THE DATE HEREOF.
 
     IN ANY JURISDICTION WHERE THE SECURITIES, BLUE SKY OR OTHER LAWS REQUIRE
THE OFFER TO BE MADE BY A LICENSED BROKER OR DEALER, THE OFFER SHALL BE DEEMED
TO BE MADE ON BEHALF OF LAIDLAW ENVIRONMENTAL BY BEAR STEARNS AS DEALER MANAGER,
OR ONE OR MORE REGISTERED BROKERS OR DEALERS LICENSED UNDER THE LAWS OF SUCH
JURISDICTION.
 
                                       iv
<PAGE>   6
 
                               TABLE OF CONTENTS
 
<TABLE>
<CAPTION>
                                                              PAGE
                                                              -----
<S>                                                           <C>
AVAILABLE INFORMATION.......................................  v
INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE.............  vi
SAFETY-KLEEN INFORMATION....................................  vii
PROSPECTUS SUMMARY..........................................  1
REASONS FOR THE OFFER.......................................  14
BACKGROUND OF THE OFFER.....................................  14
THE OFFER...................................................  21
THE MERGER..................................................  39
INFORMATION REGARDING LAIDLAW ENVIRONMENTAL.................  41
UNAUDITED PRO FORMA COMBINED FINANCIAL INFORMATION..........  47
NOTES TO UNAUDITED PRO FORMA COMBINED FINANCIAL
  INFORMATION...............................................  49
DESCRIPTION OF LAIDLAW ENVIRONMENTAL CAPITAL STOCK..........  53
COMPARISON OF THE RIGHTS OF HOLDERS OF SHARES AND LAIDLAW
  ENVIRONMENTAL COMMON STOCK................................  54
COMPARISONS OF DELAWARE AND WISCONSIN LAW -- SIMILARITIES...  54
COMPARISON OF DELAWARE AND WISCONSIN LAW -- DIFFERENCES.....  56
MARKET PRICES...............................................  61
VALIDITY OF LAIDLAW ENVIRONMENTAL COMMON STOCK..............  61
EXPERTS.....................................................  61
SCHEDULE A -- DIRECTORS AND EXECUTIVE OFFICERS OF LAIDLAW
  ENVIRONMENTAL.............................................  A-1
SCHEDULE B -- OWNERSHIP OF SHARES BY CERTAIN BENEFICIAL
  OWNERS AND SAFETY-KLEEN MANAGEMENT........................  B-1
</TABLE>
 
                             AVAILABLE INFORMATION
 
     Laidlaw Environmental and Safety-Kleen are subject to the informational
requirements of the Exchange Act, and in accordance therewith file reports,
proxy statements and other information with the Securities and Exchange
Commission (the "Commission"). Reports, proxy statements and other information
filed by Laidlaw Environmental and Safety-Kleen with the Commission may be
inspected and copied at the public reference facilities maintained by the
Commission at Judiciary Plaza, 450 Fifth Street, N.W., Room 1024, Washington,
D.C. 20549 and at the public reference facilities in the Commission's Regional
Offices at Seven World Trade Center, 13th Floor, New York, New York 10048 and
Citicorp Center, 500 West Madison Street, Suite 1400, Chicago, Illinois 60661.
Copies of information may be obtained from the Public Reference Section of the
Commission at 450 Fifth Street, N.W., Washington, D.C. 20549 at prescribed
rates. Because Laidlaw Environmental and Safety-Kleen each file certain
documents electronically with the Commission, reports, proxy and information
statements and other information regarding Laidlaw Environmental and
Safety-Kleen may also be accessed through the Commission's Web site,
http//:www.sec.gov. Laidlaw Environmental Common Stock and the Shares are listed
and traded on the NYSE, and Laidlaw Environmental Common Stock is also traded on
the Pacific Exchange, Inc. Reports, proxy statements and other information filed
by Laidlaw Environmental and Safety-Kleen with the Commission may be inspected
at the offices of the NYSE, 20 Broad Street, New York, New York 10005, and in
the case of Laidlaw Environmental, at the offices of the Pacific Exchange at 301
Pine Street, San Francisco, California 94104.
 
     This Prospectus does not contain all of the information set forth in the
Registration Statement on Form S-4 (together with all amendments and exhibits
thereto, the "Registration Statement"), covering the Laidlaw Environmental
Common Stock offered hereby, which has been filed with the Commission, certain
 
                                        v
<PAGE>   7
 
portions of which have been omitted pursuant to the rules and regulations of the
Commission, and to which portions reference is hereby made for further
information with respect to Laidlaw Environmental and Safety-Kleen and the
securities offered hereby. Statements contained herein concerning the provisions
of certain documents are not necessarily complete and, in each instance,
reference is made to the copies of such documents filed as exhibits to the
Registration Statement or otherwise filed with the Commission, for a more
complete description of the matter involved. Each such statement is qualified in
its entirety by such reference.
 
     Not later than the date of commencement of the Offer, Laidlaw Environmental
and LES Acquisition will file with the Commission a statement on Schedule 14D-1
pursuant to Rule 14d-3 under the Exchange Act furnishing certain information
with respect to the Offer. Such Schedule and any amendments thereto should be
available for inspection and copying as set forth above (except that such
Schedules and any amendments thereto will not be available at the regional
offices of the Commission).
 
     Pursuant to Rule 409 promulgated under the Securities Act and Rule 12b-21
promulgated under the Exchange Act, Laidlaw Environmental will request that
Safety-Kleen and its independent public accountants, Arthur Andersen LLP,
provide to Laidlaw Environmental the information required for complete
disclosure concerning the business, operations, financial condition and
management of Safety-Kleen. Laidlaw Environmental will provide any and all
information that it receives from Safety-Kleen or Arthur Andersen LLP prior to
the expiration of the Offer and that Laidlaw Environmental deems material,
reliable and appropriate in a subsequently prepared amendment or supplement
hereto.
 
                INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE
 
     THIS PROSPECTUS INCORPORATES BY REFERENCE DOCUMENTS NOT PRESENTED HEREIN OR
DELIVERED HEREWITH. THESE DOCUMENTS (NOT INCLUDING EXHIBITS TO SUCH DOCUMENTS
THAT ARE NOT SPECIFICALLY INCORPORATED BY REFERENCE INTO SUCH DOCUMENTS) ARE
AVAILABLE WITHOUT CHARGE UPON REQUEST TO: CORPORATE SECRETARY, LAIDLAW
ENVIRONMENTAL SERVICES, INC., 1301 GERVAIS STREET, SUITE 300, COLUMBIA, SOUTH
CAROLINA 29201. TELEPHONE REQUESTS MAY BE DIRECTED TO THE CORPORATE SECRETARY'S
DEPARTMENT AT (803) 933-4200. IN ORDER TO ENSURE TIMELY DELIVERY OF SUCH
DOCUMENTS, ANY REQUEST FOR DOCUMENTS SHOULD BE SUBMITTED NOT LATER THAN FIVE
BUSINESS DAYS PRIOR TO THE EXPIRATION DATE.
 
     The following documents filed with the Commission by Laidlaw Environmental
(File No. 1-8368) are incorporated herein by reference:
 
          (a) Laidlaw Environmental Form 10-K for the fiscal year ended August
     31, 1997 (the "Laidlaw Environmental 1997 Form 10-K");
 
          (b) Laidlaw Environmental Proxy Statement, dated October 28, 1997, for
     Laidlaw Environmental's annual meeting to be held on November 25, 1997 (the
     "Laidlaw Environmental 1997 Annual Meeting Proxy Statement"); and
 
          (c) Laidlaw Environmental Form 8-K, dated November 5, 1997 (the
     "Laidlaw Environmental Form 8-K").
 
     The following documents filed with the Commission by Safety-Kleen (File No.
1-6513) are incorporated herein by reference:
 
          (a) Safety-Kleen Form 10-K for the fiscal year ended December 28, 1996
     (the "Safety-Kleen 1996 Form 10-K);
 
          (b) Safety-Kleen Forms 10-Q for the quarterly periods ending March 22,
     June 14 and September 6, 1997 (the "Safety-Kleen Forms 10-Q");
 
          (c) Safety-Kleen Proxy Statement, dated March 28, 1997, for the
     Safety-Kleen annual meeting held May 9, 1997 (the "Safety-Kleen Annual
     Meeting Proxy Statement"); and
 
                                       vi
<PAGE>   8
 
          (d) Safety-Kleen Form 8-K, dated August 8, 1997 (the "Safety-Kleen
     Form 8-K").
 
     All documents filed by either Laidlaw Environmental or Safety-Kleen
pursuant to Section 13(a), 13(c), 14 or 15(d) of the Exchange Act subsequent to
the date hereof and prior to the date the Offer is terminated or the Shares are
accepted for exchange shall be deemed to be incorporated herein by reference and
to be a part hereof from the date of such filing. See "Available Information."
Any statement contained herein or in a document incorporated or deemed to be
incorporated herein by reference shall be deemed to be modified or superseded
for purposes hereof to the extent that a statement contained herein or in any
other subsequently filed document which also is, or is deemed to be,
incorporated herein by reference modifies or supersedes such statement. Any such
statement so modified or superseded shall not be deemed to constitute a part
hereof, except as so modified or superseded.
 
                            SAFETY-KLEEN INFORMATION
 
     While Laidlaw Environmental has included information concerning
Safety-Kleen insofar as it is known or reasonably available to Laidlaw
Environmental, Safety-Kleen is not affiliated with Laidlaw Environmental and
Safety-Kleen has not to date permitted access by Laidlaw Environmental to
Safety-Kleen's books and records for the purpose of preparing this Prospectus.
Therefore, information concerning Safety-Kleen that has not been made public was
not available to Laidlaw Environmental for the purpose of preparing this
Prospectus. Although Laidlaw Environmental has no knowledge that would indicate
that statements relating to Safety-Kleen contained or incorporated by reference
in this Prospectus in reliance upon publicly available information are
inaccurate or incomplete, Laidlaw Environmental was not involved in the
preparation of such information and statements and, for the foregoing reasons,
is not in a position to verify any such information or statements.
 
                                       vii
<PAGE>   9
 
                               PROSPECTUS SUMMARY
 
     The information below is qualified in its entirety by the more detailed
information and financial statements appearing elsewhere in this Prospectus,
including the documents incorporated in this Prospectus by reference.
Safety-Kleen Shareholders are urged to read this Prospectus and the attachments
hereto, and the documents incorporated herein by reference, in their entirety.
As used in this Prospectus, the terms "Laidlaw Environmental" and "Safety-Kleen"
refer to such entity and, unless the context otherwise requires, its
subsidiaries.
 
                         LAIDLAW ENVIRONMENTAL BUSINESS
 
     Laidlaw Environmental provides hazardous and industrial waste management
services throughout North America. Laidlaw Environmental collects, transports,
treats and disposes of waste by incineration, landfilling and other methods at
its facilities located in the United States and Canada. Laidlaw Environmental
also operates waste processing, recycling and repackaging facilities and has
analytical laboratories at its facilities in several states.
 
     On May 15, 1997, pursuant to a February 6, 1997, stock purchase agreement
(the "Stock Purchase Agreement") between Rollins Environmental Services, Inc.
("Rollins") and Laidlaw Inc. ("Laidlaw"), Rollins acquired the hazardous and
industrial waste operations of Laidlaw ("Old LESI") (the "Acquisition"). The
Acquisition was accounted for as a reverse acquisition using the purchase method
of accounting. Rollins issued 120 million Common Shares and a $350 million 5%
subordinated convertible pay-in-kind debenture, and paid $349.1 million in cash
($400 million, less assumed debt of $50.9 million), to Laidlaw to consummate the
Acquisition. Concurrent with the closing of the Acquisition, the continuing
legal entity changed its name from Rollins Environmental Services, Inc. to
Laidlaw Environmental Services, Inc. As a result of the Acquisition, Laidlaw
owns approximately 67% of the issued common shares of Laidlaw Environmental.
Laidlaw Environmental accordingly adopted Old LESI's fiscal year-end of August
31.
 
     Old LESI consisted of all direct and indirect subsidiaries of Laidlaw
engaged in the hazardous and industrial waste business, other than JTM
Industries, Inc. and its subsidiary, KBK Enterprises, Inc. Prior to the
Acquisition, Old LESI provided hazardous and industrial waste services from 85
service locations in 26 states and seven Canadian provinces. Although Old LESI
was a conglomerate of separate entities, these entities conducted such services
primarily under the name "Laidlaw Environmental Services."
 
     Laidlaw Environmental, in providing hazardous and industrial waste
services, is engaged in five primary lines, or classes, of business: (a) service
center; (b) landfill; (c) incineration; (d) transportation; and (e) specialty
services, including polychlorinated biphenyl ("PCB") management, wastewater
treatment and other specialty services.
 
     Laidlaw Environmental's revenues and income are derived from one industry
segment principally in the United States, which includes the collection,
transportation, processing/recovery and disposal of hazardous and industrial
wastes. This segment renders services to a variety of commercial, industrial,
governmental and residential customers. Substantially all revenues represent
income from unaffiliated customers.
 
     Laidlaw Environmental was incorporated in Delaware in 1968. Its principal
executive office is located at 1301 Gervais Street, Suite 300, Columbia, South
Carolina 29201 and its telephone number is 803-933-4200.
 
     LES Acquisition is a newly-formed Delaware corporation, indirectly
wholly-owned by Laidlaw Environmental. LES Acquisition has no operations other
than in connection with Laidlaw Environmental's efforts to acquire Safety-Kleen.
 
SAFETY-KLEEN BUSINESS
 
     The following information concerning Safety-Kleen is excerpted from the
Safety-Kleen 1996 Form 10-K and other publicly available information.
                                        1
<PAGE>   10
 
     Safety-Kleen was incorporated in July, 1963 under the laws of the State of
Wisconsin. The Company's principal executive office is located at 1 Brinckman
Way, Elgin, Illinois 60123, and its telephone number is (847) 697-8460.
 
     Safety-Kleen groups its operations geographically into North America and
Europe. Safety-Kleen further segregates its North American services into four
broad categories: industrial services; automotive/retail repair services; oil
recovery services; and other services. Safety-Kleen performed nearly 5 million
individual services and reclaimed more than 300 million gallons of contaminated
fluid through a network of 230 branches worldwide in 1996. The Company collects
and recycles used products at thirteen recycling centers, two lube oil
refineries, and three fuel blending facilities.
 
     Safety-Kleen operates in the continental United States, Canada, the United
Kingdom, the Republic of Ireland, Puerto Rico, Belgium, France, Italy, Spain and
Germany. Safety-Kleen has licensee operations in Japan and Korea.
 
     On August 8, 1997 Safety-Kleen announced the resignation of John G.
Johnson, Jr., President and Chief Executive Officer of Safety-Kleen. Donald W.
Brinckman, Chairman of Safety-Kleen's Board of Directors, who had previously
served as Safety-Kleen's Chief Executive Officer from 1968 until December 31,
1994, was appointed Chief Executive Officer. Safety-Kleen also announced that
its Board of Directors had engaged the services of William Blair & Company
("William Blair") to act as advisor to Safety-Kleen and manage the process of
exploring strategic options for enhancing shareholder value.
 
REASONS FOR THE OFFER
 
     Offer Premium.  The purpose of the Offer is for Laidlaw Environmental to
obtain control of Safety-Kleen and ultimately to obtain the entire equity
interest in Safety-Kleen. Laidlaw Environmental presently intends, as soon as
practicable after consummation of the Offer, to propose and seek to have
Safety-Kleen effect a merger (the "Merger") of LES Acquisition with and into
Safety-Kleen pursuant to the provisions of the Wisconsin Statutes and the
Delaware General Corporation Law (the "DGCL"). The consideration per Share in
the Merger would be identical to the Offer Consideration. Safety-Kleen has not
provided Laidlaw Environmental with information that might be relevant to the
structuring of the Merger. Laidlaw Environmental therefore reserves the right to
change the structure of the Merger upon receipt of such information.
 
     Laidlaw Environmental believes that the Offer is in the best interests of
the Safety-Kleen Shareholders because, among other things, the Offer
Consideration represents a 45.1% premium to the per Share closing price on the
NYSE on August 7, 1997, the day before Safety-Kleen announced the retention of
William Blair, and a 17.8% premium to the per Share closing price on the NYSE on
November 3, 1997, the last trading day prior to the public announcement of
Laidlaw Environmental's intention to make the Offer in each case taken from
August 7. See "Reasons for the Offer -- Offer Premium". In developing its belief
that the Offer is in the best interests of Safety-Kleen Shareholders, Laidlaw
Environmental possessed limited information with respect to the particular
circumstances, from a tax standpoint, of individual Safety-Kleen Shareholders.
Laidlaw Environmental therefore cannot make a conclusive determination as to the
tax impact of the Offer and the Merger on all Safety-Kleen Shareholders.
 
     Enhanced Business Opportunities.  Laidlaw Environmental believes that
Safety-Kleen Shareholders will benefit in several ways in addition to the
significant premium. Upon consummation of the Offer, Laidlaw Environmental
intends to build upon Safety-Kleen's leading market presence and quality brand
equity. In addition, significant cost savings would result from the combination
of the two companies due to an anticipated elimination of duplicative general
and administrative and other public company costs, the closure of overlapping
service center facilities, the increased utilization of those facilities that
remain open, and the internalization of various waste streams. Laidlaw
Environmental's acquisition of Safety-Kleen will result in a further
strengthening of Laidlaw Environmental's market position by: (i) providing
additional service center market coverage in key geographic regions including
Kentucky, Minnesota, and New Jersey; (ii) introducing a smaller-sized customer
base to complement Laidlaw Environmental's existing customer base of medium-and
large-sized customers; (iii) allowing for increased internalization using
Laidlaw Environmental facilities
                                        2
<PAGE>   11
 
to process waste streams collected by Safety-Kleen Service Centers; and (iv)
providing significant expansion into the solvent recycling market.
 
     If the Merger is consummated, Laidlaw Environmental will consider the sale
of two assets of the combined business: (i) Safety-Kleen's European operations
and (ii) Safety-Kleen's Oil Recovery Services business. These divestitures (and
possibly other divestitures) will be further assessed as additional information
becomes available. See "Reasons for the Offer -- Enhanced Business
Opportunities."
 
BACKGROUND OF THE OFFER
 
     On August 8, 1997 Safety-Kleen announced the resignation of John G.
Johnson, Jr., President and Chief Executive Officer of Safety-Kleen. Donald W.
Brinckman, Chairman of Safety-Kleen's Board of Directors, who had previously
served as Safety-Kleen's Chief Executive Officer from 1968 until December 31,
1994, was appointed Chief Executive Officer. Safety-Kleen also announced that
its Board of Directors had engaged the services of William Blair to act as
advisor to Safety-Kleen and manage the process of exploring strategic options
for enhancing shareholder value.
 
     On August 8, 1997, William Blair sent a copy of the Safety-Kleen
Confidentiality Letter to one of Laidlaw Environmental's investment bankers, Mr.
David E. Thomas, Jr. of Raymond James & Associates, Inc. ("Raymond James") and
stated that an offering circular would be available early in the week of August
18, 1997, and that such circular would be distributed to parties that have
executed a confidentiality agreement. Laidlaw Environmental did not respond to
this letter and William Blair called Laidlaw Environmental's representative and
asked that Laidlaw Environmental sign the confidentiality agreement. Laidlaw
Environmental was willing to sign a confidentiality agreement, but not the one
proposed by Safety-Kleen, which contained a two year standstill provision.
 
     In mid September 1997, there were further discussions between the two
investment banks in which Laidlaw Environmental's representatives requested a
meeting of the two companies and their advisors so that Laidlaw Environmental
could fully describe why a business combination was in both companies' best
interests. Safety-Kleen's representative continued to request that Laidlaw
Environmental sign the Confidentiality Agreement containing the two year
standstill provision. He also stated that if Laidlaw Environmental would submit
its proposal in writing, Safety-Kleen would consider a meeting with Laidlaw
Environmental.
 
     On September 24, 1997, Mr. Thomas, delivered a letter to Mr. Jeffrey W.
Corum of William Blair, informing Mr. Corum of Laidlaw Environmental's interest
in pursuing negotiations with Safety-Kleen. In particular, Mr. Thomas' letter
requested a meeting between the management of Laidlaw Environmental and the
management of Safety-Kleen and pointed out several unique features of Laidlaw
Environmental's proposed transaction including the cost synergies available from
combining the operations of Laidlaw Environmental and Safety-Kleen which would
result in an anticipated annual cost savings of $100 to $130 million. Mr.
Thomas' letter suggested structuring the transaction as a reverse merger in
which Safety-Kleen would issue one share of its stock for every three shares of
Laidlaw Environmental stock. The full text of Mr. Thomas' letter is set forth
below under the heading "Reasons for the Offer -- Background of the Offer."
 
     Shortly thereafter Mr. Corum responded to Mr. Thomas' letter by telephone
stating that only upon Laidlaw Environmental's delivery of a confidentiality and
standstill agreement acceptable to Safety-Kleen, would Safety-Kleen meet with
Laidlaw Environmental. Subsequent to their telephone conversations, Mr. James R.
Bullock, Chairman of Laidlaw Environmental, attempted to call Mr. Brinckman, who
did not return his call. Mr. Bullock then called Mr. E. David Coolidge of
William Blair in an effort to arrange a meeting with Safety-Kleen. Mr. Coolidge
repeated Safety-Kleen's refusal to meet with Laidlaw Environmental in the
absence of a confidentiality and standstill agreement.
 
     On November 3, 1997, the Laidlaw Environmental Board of Directors met and
determined to proceed with the Offer as well as to retain Bear, Stearns & Co.
Inc. ("Bear Stearns") to work together with Raymond James. Laidlaw Environmental
management had previously retained Katten Muchin & Zavis to serve as legal
counsel. Also on November 3, 1997, in a letter to Mr. Brinckman, Mr. Bullock
informed Mr. Brinckman and the Safety-Kleen Board of Directors of Laidlaw
Environmental's intention to acquire Safety-Kleen, that
                                        3
<PAGE>   12
 
Laidlaw Environmental was willing to execute a confidentiality agreement
provided such agreement did not contain a standstill provision, and that Laidlaw
Environmental continued to believe that annual cost savings and synergies
resulting from a combination of the two companies would exceed $100 million
annually. For these and other reasons, Laidlaw Environmental would consider and
pursue various options with respect to an acquisition of Safety-Kleen
notwithstanding Safety-Kleen's refusal to meet with representatives of Laidlaw
Environmental. The letter also informed Mr. Brinckman that Laidlaw Environmental
had executed a commitment letter with Toronto-Dominion Bank to provide all
necessary financing for the Offer and the Merger and again encouraged Mr.
Brinckman and the Safety-Kleen Board of Directors to meet with representatives
of Laidlaw Environmental to discuss the possibility of a mutually beneficial
negotiated transaction. The full text of Mr. Bullock's letter is set forth below
under the heading "Reasons for the Offer -- Background of the Offer."
 
     On November 3, 1997 after receipt of Mr. Bullock's letter, Mr. Brinckman
delivered a letter to Mr. Bullock requesting that Laidlaw Environmental execute
a confidentiality and standstill agreement and informing Mr. Bullock that the
Safety-Kleen Board of Directors would fully consider Laidlaw Environmental's
proposal along with others received by Safety-Kleen. In addition, Mr. Brinckman
stated that representatives of Safety-Kleen, together with its financial
advisors, would meet with representatives of Laidlaw Environmental, together
with its financial advisors, to discuss information concerning Laidlaw
Environmental and the estimated cost savings and synergies. The full text of Mr.
Brinckman's letter is set forth below under the heading "Reasons for the
Offer -- Background of the Offer."
 
     On November 4, 1997, Laidlaw Environmental publicly announced its intention
to pursue the Offer and the Merger.
 
     On November 5, 1997, Mr. Bullock and a representative of Bear Stearns met
with Mr. Brinckman and Mr. Joseph Chalhoub, Senior Vice President of
Safety-Kleen, and representatives of William Blair to discuss preliminary
potential synergies that could be achieved through a combination of the two
companies and ways the parties could work together. Mr. Bullock stated that
Laidlaw Environmental was prepared to sign a mutual confidentiality agreement
that did not contain a standstill provision so that Laidlaw Environmental and
Safety-Kleen could share information with each other. Safety-Kleen again
repeated that it insisted Laidlaw Environmental sign a confidentiality and
standstill agreement.
 
     Subsequent to the November 5th meeting, the representatives of the parties
exchanged correspondence reiterating their positions with respect to the
confidentiality and standstill agreement.
 
MARKET PRICES
 
     The Shares are listed and traded on the NYSE under the symbol "SK." The
Laidlaw Environmental Common Stock is listed and traded on the NYSE under the
symbol "LLE," and is also traded on the Pacific Exchange, Inc. See "Market
Prices" below for historical information regarding the market price per share of
the Shares and the Laidlaw Environmental Common Stock. On August 7, 1997, the
date prior to the date Safety-Kleen announced its retention of William Blair,
the closing price per Share, as reported on the NYSE Composite Tape, was
$17.8125, and the closing price per share of Laidlaw Environmental Common Stock,
as reported on the NYSE Composite Tape, was $3.1875. On November 3, 1997, the
date prior to the date of the public announcement of Laidlaw Environmental's
intention to acquire Safety-Kleen, the closing price per Share, as reported on
the NYSE Composite Tape, was $21.9375, and the closing price per share of
Laidlaw Environmental Common Stock, as reported on the NYSE Composite Tape, was
$4.9375. On             , 1997, the date prior to the date of this Prospectus,
the closing price per Share, as reported on the NYSE Composite Tape, was
$          , and the closing price per share of Laidlaw Environmental Common
Stock, as reported on the NYSE Composite Tape, was $          . Shareholders are
urged to obtain current market information for Laidlaw Environmental Common
Stock and the Shares. No assurance can be given as to market prices of Laidlaw
Environmental Common Stock and the Shares at the Expiration Date of the Offer.
The market value of the shares of Laidlaw Environmental Common Stock that
holders of Shares will receive upon consummation of the Offer may vary from the
market value of shares of Laidlaw Environmental
                                        4
<PAGE>   13
 
Common Stock that holders of Shares would receive if the Offer were consummated
on the date of this Prospectus.
 
                                   THE OFFER
 
     General.  Laidlaw Environmental hereby offers, upon the terms and subject
to the conditions set forth herein and in the related Letter of Transmittal, to
exchange the Offer Consideration for each outstanding Share (and the
accompanying Rights, if any) validly tendered on or prior to the Expiration Date
and not properly withdrawn. The Offer Consideration consists of $14.00 net in
cash and 2.4 shares of Laidlaw Environmental Common Stock. The term "Expiration
Date" shall mean 5:00 p.m., New York City time on             , 1997, unless and
until Laidlaw Environmental extends the period of time for which the Offer is
open, in which event the term "Expiration Date" shall mean the latest time and
date at which the Offer, as so extended by Laidlaw Environmental, shall expire.
No certificates representing fractional shares of Laidlaw Environmental Common
Stock will be issued pursuant to the Offer. Each tendering Safety-Kleen
Shareholder who would otherwise be entitled to a fractional share of Laidlaw
Environmental Common Stock will receive cash in lieu thereof. See "The
Offer -- Cash in Lieu of Fractional Shares of Laidlaw Environmental Common
Stock." On             , 1997, the closing price of the Laidlaw Environmental
Common Stock on the NYSE was $          . A registration statement relating to
the Laidlaw Environmental Common Stock to be exchanged in the Offer has been
filed with the Commission. See "The Offer -- General."
 
     Conditions of the Offer.  Laidlaw Environmental's obligation to exchange
the Offer Consideration for Shares pursuant to the Offer is conditioned upon,
among other things, the satisfaction or, where applicable, waiver of each of the
Offer Conditions. Subject to the applicable rules and regulations of the
Commission, Laidlaw Environmental expressly reserves the right, in its sole
discretion, at any time or from time to time, to delay acceptance for exchange
or, regardless of whether such Shares were theretofore accepted for exchange,
exchange of any Shares pursuant to the Offer or to amend or terminate the Offer
and not accept for exchange or exchange any Shares not theretofore accepted for
exchange or exchanged, upon the failure of any of the conditions to the Offer to
be satisfied. Laidlaw Environmental reserves the absolute right to waive any
defect or irregularity in the tender of any securities and to waive any of the
Offer Conditions (other than the Laidlaw Environmental Stockholder Approval
Condition, the Regulatory Approval Condition and the condition related to the
effectiveness of the Registration Statement). Although Laidlaw Environmental
reserves the right to do so, Laidlaw Environmental does not currently intend to
waive the Minimum Tender Condition, the Wisconsin Statutory Conditions or the
Rights Plan Condition. See "The Offer -- Conditions of the Offer -- Minimum
Tender Condition," "-- Laidlaw Environmental Stockholder Approval Condition,"
"-- Rights Plan Condition," "-- Wisconsin Statutory Conditions," "-- Regulatory
Approval Condition," and "-- Certain Other Conditions of the Offer." Waiver or
amendment of any of these conditions may require an extension of the Offer.
 
     Regulatory Approvals.  The acquisition of Shares by Laidlaw Environmental
pursuant to the Offer is subject to the Hart-Scott-Rodino Act (the "HSR Act")
and the rules (the "Rules") that have been promulgated thereunder. Laidlaw Inc.
will file with the Antitrust Division of the Department of Justice (the
"Antitrust Division") and the Federal Trade Commission (the "FTC") a
Hart-Scott-Rodino Notification and Report Form with respect to the Offer to
acquire up to 100% of the outstanding Shares, and Laidlaw Environmental and LES
Acquisition will not acquire any Shares until the applicable waiting period for
such acquisition has expired or been terminated.
 
     European Regulatory Approvals.  The acquisition of Shares by Laidlaw
Environmental pursuant to the Offer is subject to prior notification
requirements of several of the member countries of the European Union in which
Safety-Kleen operates. Based on the limited information concerning Safety-Kleen
that is available to Laidlaw Environmental, filings will be necessary in the
Republic of Ireland and Federal Republic of Germany. In addition, filings may
also be necessary in Italy and Belgium. The necessary filings must be made in
sufficient time to allow the passing of a one month waiting period before
Laidlaw Environmental's acquisition of Shares pursuant to this Offer may be
completed. No pre-merger notification under the European Economic Community's
Merger Control Regulation is required for the proposed transaction.
                                        5
<PAGE>   14
 
     Canadian Competitive Act.  Under the Canadian federal Competitive Act (the
"Competition Act") acquisition transactions, insofar as they relate to the
acquisition of such Canadian subsidiaries, qualify as a "merger" if they are of
sufficient size to be subject to the notification and waiting period
requirements of the competition Act. The Competition Act is administered by the
Canadian Director of Investigation and Research appointed under the Competition
Act (the "Competition Act Director"). Laidlaw Environmental believes that the
proposed transaction requires notification and intends to file the required
information with the Competition Act Director.
 
     Under separate "merger" provisions of the Competition Act, which operate
independently of its notification and waiting period requirements, if an
acquisition is likely to give rise to a substantial prevention or lessening of
competition in a market in Canada, the Competition Act Director may apply for a
remedial order (such as an injunction or an order to divest specified assets or
securities) to be issued by a qualsi-judicial body (the "Competition tribunal").
 
     Timing of the Offer.  The Offer is currently scheduled to expire on
            , 1997; however, it is Laidlaw Environmental's current intention to
extend the Offer from time to time as necessary until all conditions to the
Offer have been satisfied or waived. See "The Offer -- Extension, Termination
and Amendment." Laidlaw Environmental has received a commitment letter from
Toronto-Dominion Bank in which it states that it will provide or arrange credit
facilities in the amount necessary to fund payment of the Cash Consideration.
See "The Offer -- Source and Amount of Funds." Laidlaw Environmental has
obtained the commitment for the financing for the Cash Consideration; however,
in the unlikely event that the financing is not available, Laidlaw Environmental
currently intends to extend the Offer to ensure that five business days remain
for Safety-Kleen Shareholders to tender their Shares in the Offer subsequent to
obtaining such financing. See "The Offer -- Source and Amount of Funds." Laidlaw
Environmental expects that the Laidlaw Environmental Stockholder Approval
Condition will be satisfied on or about             , 1997, the date on which it
plans to call a special meeting of its stockholders (the "Laidlaw Environmental
Special Meeting"), to approve the increase in the number of authorized shares of
Laidlaw Environmental Common Stock from 350,000,000 to 750,000,000, and the
issuance of shares of Laidlaw Environmental Common Stock in connection with the
Offer and the Merger.
 
     Extension, Termination and Amendment.  Laidlaw Environmental expressly
reserves the right (but will not be obligated), in its sole discretion, at any
time or from time to time, and regardless of whether any of the events set forth
in "The Offer -- Conditions of the Offer" shall have occurred or shall have been
determined by Laidlaw Environmental to have occurred, (a) to extend the period
of time during which the Offer is open by giving oral or written notice of such
extension to the Exchange Agent, which extension will be announced no later than
9:00 a.m., New York City time, on the next business day after the previously
scheduled Expiration Date, and (b) to amend the Offer in any respect (including,
without limitation, by decreasing or increasing the consideration offered in the
Offer to holders of Shares and/or by increasing or decreasing the number of
Shares being sought in the Offer) by giving oral or written notice of such
amendment to the Exchange Agent. The rights reserved by Laidlaw Environmental in
this paragraph are in addition to Laidlaw Environmental's right to terminate the
Offer as described in "The Offer -- Extension, Termination and Amendment." There
can be no assurance that Laidlaw Environmental will exercise its right to extend
the Offer. However, it is Laidlaw Environmental's current intention to extend
the Offer until all Offer Conditions have been satisfied or waived. See "The
Offer -- Extension, Termination and Amendment." During any such extension, all
Shares previously tendered and not withdrawn will remain subject to the Offer,
subject to the right of a tendering Safety-Kleen Shareholder to withdraw his or
her Shares. See "The Offer -- Withdrawal Rights."
 
     Exchange of Shares; Delivery of Laidlaw Environmental Common Stock and Cash
Consideration. Upon the terms and subject to the conditions of the Offer
(including, if the Offer is extended or amended, the terms and conditions of any
such extension or amendment), Laidlaw Environmental will accept for exchange,
and will exchange, Shares (and Rights, if applicable) validly tendered and not
properly withdrawn as promptly as practicable following the Expiration Date. See
"The Offer -- Exchange of Shares; Delivery of Laidlaw Environmental Common Stock
and Cash Consideration."
                                        6
<PAGE>   15
 
     Withdrawal Rights.  Tenders of Shares (and Rights, if applicable) made
pursuant to the Offer are irrevocable, except that Shares (and Rights, if
applicable) tendered pursuant to the Offer may be withdrawn at any time prior to
the Expiration Date, and, unless theretofore accepted for exchange and exchanged
by Laidlaw Environmental for the Offer Consideration pursuant to the Offer, may
also be withdrawn at any time after             , 1997. See "The
Offer -- Withdrawal Rights."
 
     Procedure for Tendering Shares.  For a Safety-Kleen Shareholder to validly
tender Shares (and Rights, if applicable) pursuant to the Offer, (i) a properly
completed and duly executed Letter of Transmittal (or manually executed
facsimile thereof), together with any required signature guarantees, or an
Agent's Message (as defined herein) in connection with a book-entry transfer,
and any other required documents, must be transmitted to and received by the
Exchange Agent at one of its addresses set forth on the back cover of this
Prospectus and either certificates for tendered Shares (and Rights, if
applicable) must be received by the Exchange Agent at such address or such
Shares (and Rights, if applicable) must be tendered pursuant to the procedures
for book-entry transfer (in the case of Rights, if available) set forth under
"The Offer -- Procedure for Tendering" (and a confirmation of receipt of such
tender received), in each case, prior to the Expiration Date, or (ii) such
Safety-Kleen Shareholder must comply with the guaranteed delivery procedure set
forth under "The Offer -- Procedure for Tendering."
 
     Safety-Kleen Shareholders will be required to tender one Right for each
Share tendered in order to effect a valid tender of Shares, unless the Rights
Plan Condition has been satisfied or waived. Unless the Safety-Kleen
Distribution Date occurs, a tender of Shares will constitute a tender of the
associated Rights.
 
     THE METHOD OF DELIVERY OF SHARE CERTIFICATES (AND RIGHTS CERTIFICATES, IF
APPLICABLE) AND ALL OTHER REQUIRED DOCUMENTS, INCLUDING DELIVERY THROUGH ANY
BOOK-ENTRY TRANSFER FACILITY, IS AT THE OPTION AND RISK OF THE TENDERING
SHAREHOLDER, AND THE DELIVERY WILL BE DEEMED MADE ONLY WHEN ACTUALLY RECEIVED BY
THE EXCHANGE AGENT. IF DELIVERY IS BY MAIL, REGISTERED MAIL WITH RETURN RECEIPT
REQUESTED, PROPERLY INSURED, IS RECOMMENDED. IN ALL CASES, SUFFICIENT TIME
SHOULD BE ALLOWED TO ENSURE TIMELY DELIVERY.
 
THE MERGER
 
     The purpose of the Offer is to enable Laidlaw Environmental to acquire
control of, and ultimately the entire equity interest in, Safety-Kleen. Laidlaw
Environmental presently intends, following consummation of the Offer, to propose
and seek to have LES Acquisition merge with Safety-Kleen. In the Merger, each
then outstanding Share (other than Shares owned by Laidlaw Environmental or any
of its affiliates, and Shares held in the treasury of Safety-Kleen (if
Safety-Kleen is so authorized) or by any subsidiary of Safety-Kleen) would be
cancelled in exchange for the right to receive the Offer Consideration.
Safety-Kleen has not agreed to provide Laidlaw Environmental with information
that might be relevant to the structuring of the Merger. Laidlaw Environmental
therefore reserves the right to change the structure of the Merger upon receipt
of such information.
 
     If the Minimum Tender Condition and other Offer Conditions are satisfied,
and the Offer is consummated, Laidlaw Environmental and its affiliates will own
not less than two-thirds of the outstanding Shares. Accordingly, Laidlaw
Environmental and its affiliates will at such time have sufficient voting power
in Safety-Kleen to approve the Merger independently of the votes of any other
Safety-Kleen Shareholders. Laidlaw Environmental presently intends to vote any
and all Shares owned by Laidlaw Environmental and its affiliates following
consummation of the Offer to approve the Merger.
 
     Safety-Kleen Shareholders will have appraisal rights under Wisconsin law in
connection with the Merger. See "-- Appraisal Rights."
                                        7
<PAGE>   16
 
CERTAIN FEDERAL INCOME TAX CONSEQUENCES
 
     The exchange of Shares for Laidlaw Environmental Common Stock and cash
pursuant to the Offer and Merger will be a taxable transaction for U.S. federal
income tax purposes and may also be taxable under applicable state, local and
foreign tax laws. If the Board of Safety-Kleen agrees to the Offer, the Merger
may be restructured to be a partially tax-free merger for U.S. federal income
tax purposes.
 
     All Safety-Kleen Shareholders should carefully read the summary of the
federal income tax consequences of the Offer and the Merger under "The Offer --
Certain Federal Income Tax Consequences" and are urged to consult with their own
tax advisors as to the federal, state, local and foreign tax consequences in
their particular circumstances.
 
EFFECT OF OFFER ON MARKET FOR SHARES; REGISTRATION UNDER THE EXCHANGE ACT
 
     The exchange of Shares pursuant to the Offer will reduce the number of
holders of Shares and the number of Shares that might otherwise trade publicly
and, depending upon the number of Shares so purchased, could adversely affect
the liquidity and market value of the remaining Shares held by the public.
 
     The Shares are listed and traded on the NYSE. Depending upon the number of
Shares acquired pursuant to the Offer, following consummation of the Offer, the
Shares may no longer meet the requirements of the NYSE for continued listing and
the Shares may no longer constitute "margin securities" for the purposes of the
Federal Reserve Board's margin regulations, in which event the Shares would be
ineligible as collateral for margin loans made by brokers. For a description of
the treatment of Shares in the Merger, see "The Merger."
 
DISSENTER RIGHTS
 
     Holders of shares do not have appraisal rights as a result of the Offer.
However, in the event the Merger is consummated, the Safety-Kleen shareholders
would have appraisal rights with respect to the Merger under Section 180.1302 of
the Wisconsin Statutes.
 
COMPARISON OF THE RIGHTS OF HOLDERS OF SHARES AND LAIDLAW ENVIRONMENTAL COMMON
STOCK
 
     As a consequence of the exchange of Shares for shares of Laidlaw
Environmental Common Stock in the Offer and the cancellation of Shares as a
result of the Merger, shareholders of Safety-Kleen, a corporation incorporated
under the laws of Wisconsin, would become shareholders of Laidlaw Environmental,
a Delaware corporation. Such holders would have certain rights as Laidlaw
Environmental shareholders that are different from the rights they currently
have in Safety-Kleen, both because of the differences between the Laidlaw
Environmental Certificate of Incorporation (the "Laidlaw Environmental
Certificate") and Laidlaw Environmental's by-laws (the "Laidlaw Environmental
By-laws"), on the one hand, and the Safety-Kleen Articles of Incorporation (the
"Safety-Kleen Articles") and by-laws (the "Safety-Kleen By-Laws"), on the other
hand, and because of differences between Wisconsin and Delaware corporation law.
For a comparison of the charter and by-law provisions of Laidlaw Environmental
and Safety-Kleen and of Wisconsin and Delaware law, see "Comparison of the
Rights of Holders of Shares and Laidlaw Environmental Common Stock."
 
DESCRIPTION OF LAIDLAW ENVIRONMENTAL CAPITAL STOCK
 
     The authorized capital stock of Laidlaw Environmental consists of
350,000,000 shares of Laidlaw Environmental Common Stock, par value $1.00 per
share and 1,000,000 shares of preference stock, $1.00 par value. As of October
14, 1997, there were 180,549,911 shares of Laidlaw Environmental Common Stock
issued and outstanding. No preferred stock has been issued.
 
     Holders of shares of Laidlaw Environmental Common Stock are entitled to one
vote per share for each share held. Subject to the rights of holders of shares
of outstanding Laidlaw Environmental Preferred Stock (if any), holders of shares
of Laidlaw Environmental Common Stock have equal rights to participate in
dividends when declared and, in the event of liquidation, in the net assets of
Laidlaw Environmental available for distribution to shareholders.
                                        8
<PAGE>   17
 
     For information relating to ownership of Laidlaw Environmental Common Stock
by certain beneficial owners and directors and executive officers of Laidlaw
Environmental, see the Laidlaw Environmental 1997 Annual Meeting Proxy
Statement. As of October 14, 1997, as a group, Laidlaw Environmental's
directors, executive officers and their affiliates (including Laidlaw Inc.)
beneficially owned approximately 70.29% of the outstanding shares of Laidlaw
Environmental Common Stock.
 
     For additional information concerning the capital stock of Laidlaw
Environmental, see "Description of Laidlaw Environmental Capital Stock."
 
THE EXCHANGE AGENT
 
     IBJ Schroder Bank & Trust Company has been appointed Exchange Agent in
connection with the Offer. A duly executed Letter of Transmittal (or facsimile
copies thereof), together with any required signature guarantees, or an Agent's
Message in connection with a book-entry transfer, and certificates for Shares
(and Rights, if applicable) should be sent by each tendering Safety-Kleen
Shareholder or his or her broker, dealer, bank or nominee to the Exchange Agent
at the addresses set forth on the back cover of this Prospectus.
 
REQUEST FOR ASSISTANCE AND ADDITIONAL COPIES
 
     Requests for information or assistance concerning the Offer may be directed
to the Dealer Manager or the Information Agent at their respective addresses set
forth on the back cover of this Prospectus. Requests for additional copies of
this Prospectus and the Letter of Transmittal should be directed to the
Information Agent.
 
LAIDLAW ENVIRONMENTAL AND SAFETY-KLEEN COMPARATIVE PER SHARE DATA
 
     The following table sets forth comparative per share data of Laidlaw
Environmental and Safety-Kleen on both a historical and pro forma combined
basis. This table should be read in conjunction with each entity's historical
financial statements and notes thereto as set forth in the filings incorporated
by reference herein (but which in the case of Safety-Kleen are not covered by
the report of Safety-Kleen's independent accountants for purposes of this
Prospectus), and in conjunction with the unaudited pro forma combined financial
information appearing elsewhere in this Prospectus. See "Laidlaw Environmental
and Safety-Kleen Unaudited Pro Forma Combined Financial Information."
 
     The Merger will be accounted for as a purchase and the pro forma
information set forth below presents pro forma combined information for the
fiscal year of Laidlaw Environmental ended August 31, 1997. This information
does not reflect the estimated cost savings that Laidlaw Environmental believes
may result from the Merger. The pro forma combined per share data is not
necessarily indicative of actual results had the Merger occurred on such dates
or of future expected results.
 
<TABLE>
<CAPTION>
                                                                                 LAIDLAW
                                                                              ENVIRONMENTAL/
                                                  LAIDLAW                      SAFETY-KLEEN    SAFETY-KLEEN
                                               ENVIRONMENTAL   SAFETY-KLEEN     PRO FORMA        PRO FORMA
                                                HISTORICAL      HISTORICAL     COMBINED(1)     EQUIVALENT(2)
                                               -------------   ------------   --------------   -------------
<S>                                            <C>             <C>            <C>              <C>
Book value per common share:
  August 31, 1997............................     $ 1.82          $8.49           $ 3.20          $ 7.68
Year ended August 31, 1997:
  Income (loss) per common share from
     continuing operations...................      (1.33)          1.04            (.675)          (1.63)
  Cash dividends.............................          0            .36                0               0
</TABLE>
 
- ---------------
 
(1) See "Selected Pro Forma Financial Information."
(2) The Safety-Kleen pro forma equivalent represents the Laidlaw
    Environmental/Safety-Kleen pro forma combined book value, dividends and
    income (loss) per common share multiplied by an assumed Exchange Ratio of
    2.4.
                                        9
<PAGE>   18
 
SELECTED FINANCIAL DATA
 
     The summary below sets forth selected historical financial data and
selected unaudited pro forma combined financial data. This financial data should
be read in conjunction with the historical financial statements and notes
thereto contained in the filings incorporated by reference herein (but which, in
the case of Safety-Kleen, are not covered by the report of Safety-Kleen's
independent accountants for purposes of this Prospectus), and in conjunction
with the unaudited pro forma combined financial information and notes thereto
appearing elsewhere in this Prospectus. See "Laidlaw Environmental and
Safety-Kleen Unaudited Pro Forma Combined Financial Information."
 
SELECTED HISTORICAL FINANCIAL DATA OF LAIDLAW ENVIRONMENTAL
 
     The selected historical financial data of Laidlaw Environmental set forth
below has been derived from financial statements of Laidlaw Environmental as
they appeared in the Laidlaw Environmental 1997 Form 10-K. The Laidlaw
Environmental 10-K should be read in conjunction with Laidlaw Environmental's
selected historical financial data.
 
<TABLE>
<CAPTION>
                                                        YEAR ENDED AUGUST 31,
                                      ----------------------------------------------------------
                                         1997         1996         1995        1994       1993
                                      ----------   ----------   ----------   --------   --------
                                              ($ IN THOUSANDS, EXCEPT PER SHARE AMOUNTS)
<S>                                   <C>          <C>          <C>          <C>        <C>
STATEMENT OF INCOME DATA:
Revenues............................  $  678,619   $  652,973   $  599,241   $517,804   $511,554
Operating income before
  restructuring charge(1)...........  $   66,983   $   57,319   $   59,859   $ 45,548   $ 52,400
Applicable margin(1)................         9.9%         8.8%        10.0%       8.8%      10.2%
Income (loss) from continuing
  operations(1).....................  $ (183,452)  $    6,714   $   16,765   $ 22,531   $ 11,654
Income (loss) per share from
  continuing operations(1)..........      (1.329)       0.056        0.140      0.188      0.097
Cash dividends per common share.....          --           --           --         --         --
BALANCE SHEET DATA:
Working capital.....................      76,095       40,617       60,075     90,831    119,522
Total assets........................   1,610,878    1,491,294    1,367,411    974,053    947,976
Long-term debt......................     540,096       55,838       64,256     18,454     24,253
Stockholders' equity................     327,965    1,094,777    1,056,266    798,597    795,887
Weighted average common and common
  stock equivalents outstanding
  (000's)...........................     138,033      120,000      120,000    120,000    120,000
</TABLE>
 
- ---------------
 
(1) Fiscal year 1997 includes restructuring charge, net of tax benefit, of $200
    million ($332 million pre-tax) or $1.45 per share.
                                       10
<PAGE>   19
 
SELECTED HISTORICAL FINANCIAL DATA OF SAFETY-KLEEN
 
     The selected historical financial data of Safety-Kleen set forth below has
been derived from financial statements of Safety-Kleen as they appeared in
Safety-Kleen's Form 10-K filed with the Commission for each of the five fiscal
years in the period ended December 28, 1996 and the Safety-Kleen Form 10-Q for
the period ended September 6, 1997. The Safety-Kleen 1996 Form 10-K should also
be read in conjunction with Safety-Kleen's selected historical financial data.
 
<TABLE>
<CAPTION>
                             36 WEEKS ENDED                                    FISCAL YEAR
                       ---------------------------   ---------------------------------------------------------------
                       SEPTEMBER 6,   SEPTEMBER 7,
                           1997           1996          1996         1995        1994         1993         1992(3)
                       ------------   ------------   ----------   ----------   ---------   ----------     ----------
                                                ($ IN THOUSANDS, EXCEPT PER SHARE AMOUNTS)
<S>                    <C>            <C>            <C>          <C>          <C>         <C>            <C>
STATEMENT OF INCOME
  DATA:
Revenues.............   $  680,172      $626,176     $  923,126   $  859,251   $ 791,267   $  795,508     $  794,542
Operating income
  before
  restructuring
  charge.............   $   76,450      $ 80,008     $  119,490   $  108,463   $  99,324   $   70,656(1)  $   85,537
Applicable margin....         11.2%         12.8%          12.9%        12.6%       12.6%         8.9%(1)       10.8%
Income (loss) from
  continuing
  operations.........   $   40,297      $ 40,685     $   61,109   $   53,303   $  50,094   $ (101,346)(1) $   45,637(2)
Net income (loss) per
  share from
  continuing
  operations.........   $     0.69      $   0.70     $     1.05   $     0.92   $    0.87   $    (1.76)(1) $     0.79(2)
Cash dividends per
  common share.......   $     0.27      $   0.27     $     0.36   $     0.36   $    0.36   $     0.36     $     0.34
BALANCE SHEET DATA:
Working capital......   $   74,795                   $   72,340   $   43,532   $  31,766   $   53,472     $   47,729
Total assets.........   $1,037,192                   $1,044,823   $1,009,050   $ 973,444   $  950,664     $1,006,446
Long-term debt.......   $  246,080                   $  276,954   $  283,715   $ 284,125   $  288,633     $  300,724
Stockholders'
  Equity.............   $  495,718                   $  480,290   $  433,435   $ 396,336   $  362,664     $  492,095
Weighted average
  common and common
  stock
 equivalents(000's)..       58,490        58,078         58,152       57,857      57,741       57,679         57,768
</TABLE>
 
- ---------------
 
(1) Includes restructuring and special charges, net of tax benefit, of $136
    million ($229 million pre-tax) or $2.36 per share.
(2) Includes $300,000 ($.01 per share) increase in net earnings from cumulative
    effect of prior years effect of adopting Statement of Financial Accounting
    Standards (SFAS) No. 106 on accounting for post-retirement benefits and SFAS
    No. 109 on accounting for income taxes.
(3) Fiscal year 1992 was a fifty-three week year. All other years presented were
    fifty-two weeks.
(4) Thirty-six weeks ending September 7, 1997.
                                       11
<PAGE>   20
 
LAIDLAW ENVIRONMENTAL AND SAFETY-KLEEN SELECTED UNAUDITED PRO FORMA COMBINED
FINANCIAL INFORMATION
 
     The following selected unaudited pro forma combined financial information
combines the consolidated balance sheets and income statements of Laidlaw
Environmental and Safety-Kleen as if the Offer, Merger and the transactions
herein had occurred for all periods presented. These statements are prepared on
the basis of accounting for the Merger as a purchase and are based on the
assumptions set forth in the notes thereto. These statements do not reflect the
estimated cost savings Laidlaw Environmental believes will result from the
Merger. The following information is not necessarily indicative of the financial
position or the actual results of operation that would have occurred had the
transactions assumed here occurred on such dates or of expected future results.
See "Laidlaw Environmental and Safety-Kleen Unaudited Pro Forma Combined
Financial Information." This information should be read in conjunction with and
is qualified in its entirety by the consolidated financial statements and
accompanying notes of Laidlaw Environmental and Safety-Kleen included in the
documents described under "Incorporation of Certain Documents by Reference" (but
which, in the case of Safety-Kleen, are not covered by the reports of
Safety-Kleen's independent accountants for purposes of this Prospectus) and the
pro forma combined financial statements and accompanying discussion and notes
set forth under "Unaudited Pro Forma Combined Financial Information."
 
<TABLE>
<CAPTION>
                                                                 PRO FORMA
                                                                 COMBINED
                                                              ---------------
                                                                YEAR ENDED
                                                              AUGUST 31, 1997
                                                              ---------------
                                                                (UNAUDITED)
                                                                   ($ IN
                                                                THOUSANDS,
                                                                EXCEPT PER
                                                                   SHARE
                                                                 AMOUNTS)
<S>                                                           <C>
STATEMENT OF INCOME DATA:
Revenue.....................................................    $1,655,741
Income (loss) from continuing operations....................      (186,723)
Income (loss) from discontinued operations..................            20
Net income (loss)...........................................      (186,703)
PER SHARE DATA:
Income (loss) from continuing operations....................        (0.675)
Income (loss) from discontinued operations..................          .000
Net income (loss)...........................................        (0.675)
Weighted average common and common stock equivalents
  (000).....................................................       276,752
</TABLE>
 
<TABLE>
<CAPTION>
                                                                 PRO FORMA
                                                                 COMBINED
                                                              ---------------
                                                                   AS OF
                                                              AUGUST 31, 1997
                                                              ---------------
                                                                (UNAUDITED)
                                                                   ($ IN
                                                                THOUSANDS)
<S>                                                           <C>
BALANCE SHEET DATA:
Assets
  Total current assets......................................    $  491,921
  Total assets..............................................     4,225,103
Liabilities
  Total current liabilities.................................       412,945
  Long term debt............................................     1,563,072
  Subordinated convertible debenture........................       350,000
  Total liabilities.........................................     3,203,541
Stockholders' Equity........................................     1,021,562
</TABLE>
 
                                       12
<PAGE>   21
 
           CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS
 
     Certain statements contained in "Prospectus Summary," "-- Reasons for the
Offer," "-- Certain Federal Income Tax Consequences," and "-- Background of the
Offer," "-- Reasons for the Offer -- Enhanced Business Opportunities,"
"Background of the Offer," "The Offer -- Certain Federal Income Tax
Consequences," "The Merger -- General," and "Unaudited Pro Forma Combined
Financial Incorporation" including any forecasts, projections and descriptions
of anticipated synergies referred to therein, and certain statements
incorporated by reference from documents filed with the Commission by Laidlaw
Environmental and Safety-Kleen, including any statements contained herein or
therein regarding the development or possible assumed future results of
operations of Laidlaw Environmental's and Safety-Kleen's businesses, the markets
for Laidlaw Environmental's and Safety-Kleen's services and products,
anticipated capital expenditures, regulatory developments and the effects of the
Offer and the Merger, any statements preceded by, followed by or that include
the words "believes," "expects," "anticipates," or similar expressions, and
other statements contained or incorporated by reference herein regarding matters
that are not historical facts, are or may constitute forward-looking statements
(as such term is defined in the Private Securities Litigation Reform Act of
1995). Because such statements are subject to risks and uncertainties, actual
results may differ materially from those expressed or implied by such
forward-looking statements. The risks and uncertainties that may cause actual
results to differ include, among others, general economic conditions, risks
associated with acquisitions, fluctuations in operating results because of
acquisitions and variations in stock prices, changes in applicable federal,
state and local laws and regulations, especially environmental regulations,
alternate and emerging technologies, competition and pricing pressures,
overcapacity in the industry, seasonal fluctuations due to weather,
uncertainties of litigation, and risks associated with the operation, growth and
integration of the newly acquired businesses. As a result of these factors,
Laidlaw Environmental's revenue and income could vary significantly from quarter
to quarter, and past financial performance should not be considered a reliable
indicator of future performance. All subsequent written and oral forward-looking
statements attributable to Laidlaw Environmental or persons acting on its behalf
are expressly qualified in their entirety by the cautionary statements set forth
or referred to above in this paragraph. Investors are cautioned not to place
undue reliance on such statements, which speak only as of the date hereof.
Laidlaw Environmental undertakes no obligation to release publicly any revisions
to these forward-looking statements to reflect events or circumstances after the
date hereof or to reflect the occurrence of unanticipated events.
                                       13
<PAGE>   22
 
                             REASONS FOR THE OFFER
 
OFFER CONSIDERATION AND PREMIUM
 
     Pursuant to the Offer, each Share will be exchanged for $14.00 net in cash
and 2.4 shares of Laidlaw Environmental Common Stock. Accordingly, the per Share
price premium which Safety-Kleen Shareholders will receive in the Offer will
depend on the Laidlaw Common Stock trading price at the time of consummation of
the Offer.
 
     Laidlaw Environmental believes that the Offer is in the best interests of
Safety-Kleen Shareholders because, among other things, the Offer Consideration
represents a 45.1% premium to the closing price per Share on August 7, 1997, the
date prior to the announcement of William Blair's retention, and a 17.8% premium
to the closing price per Share on November 3, 1997, the last trading day prior
to the public announcement of Laidlaw Environmental's intent to acquire
Safety-Kleen (in each case, based on the closing price of Laidlaw Environmental
Common Stock). In developing its belief that the Offer is in the best interests
of Safety-Kleen Shareholders, Laidlaw Environmental possessed limited
information with respect to the particular circumstances, from a tax standpoint,
of individual Safety-Kleen Shareholders. Laidlaw Environmental therefore cannot
make a conclusive determination as to the tax impact of the Offer and the Merger
on all Safety-Kleen Shareholders. The following table shows the premium of the
Offer Consideration over the closing per Share price on the NYSE on the last
trading day immediately prior to the public announcement of the Offer.
 
<TABLE>
<CAPTION>
                                                              OFFER    SAFETY-KLEEN      PERCENT
                                                              PRICE*   SHARE PRICE    DIFFERENTIAL**
                                                              ------   ------------   --------------
<S>                                                           <C>      <C>            <C>
August 7, 1997, the date prior to public announcement of
  William Blair's retention.................................  $25.85     $17.8125          45.1%
November 3, 1997, the last trading day before the public
  announcement of Laidlaw Environmental's intention to
  acquire Safety-Kleen......................................  $25.85     $21.9375          17.8%
</TABLE>
 
- ---------------
 
 * Assumes the Offer Consideration per share is $14.00 net in cash and 2.4
   shares of Laidlaw Environmental Common Stock multiplied by the closing price
   of $4.9375 on November 3, 1997.
** Based on the closing prices of Shares on the indicated dates.
 
ENHANCED BUSINESS OPPORTUNITIES
 
     In addition to the per Share price premium provided by the Offer, Laidlaw
Environmental believes that the Safety-Kleen Shareholders will also benefit from
the Offer as a result of becoming shareholders of Laidlaw Environmental. Laidlaw
Environmental has carefully studied the potential benefits of the combination of
the businesses of Laidlaw Environmental and Safety-Kleen and believes that such
a combination will result in a further strengthening of Laidlaw Environmental's
market position by: (i) providing additional service center market coverage in
key geographic regions including Kentucky, Minnesota, and New Jersey; (ii)
introducing a smaller-sized customer base to complement Laidlaw Environmental's
existing customer base of medium-and large-sized customers; (iii) allowing for
the internalization of waste streams collected by the service centers; and (iv)
providing significant expansion into the solvent recycling market.
 
                            BACKGROUND OF THE OFFER
 
     On August 8, 1997 Safety-Kleen announced the resignation of John G.
Johnson, Jr., President and Chief Executive Officer of Safety-Kleen. Donald W.
Brinckman, Chairman of Safety-Kleen's Board of Directors, who had previously
served as Safety-Kleen's Chief Executive Officer from 1968 until December 31,
1994, was appointed Chief Executive Officer. Safety-Kleen also announced that
its Board of Directors had engaged the services of William Blair to act as
advisor to Safety-Kleen and manage the process of exploring strategic options
for enhancing shareholder value.
 
                                       14
<PAGE>   23
 
     On August 8, 1997, William Blair sent a copy of the Safety-Kleen
Confidentiality Letter to one of Laidlaw Environmental's investment bankers, Mr.
David E. Thomas, Jr. of Raymond James & Associates, Inc. and stated that an
offering circular would be available early in the week of August 18, 1997, and
that such circular would be distributed to parties that have executed a
confidentiality agreement. Laidlaw Environmental did not respond to this letter
and William Blair called Laidlaw Environmental's representative and asked that
Laidlaw Environmental sign the confidentiality agreement. Laidlaw Environmental
was willing to sign a confidentiality agreement, but not the one proposed by
Safety-Kleen, which contained a two year standstill provision.
 
     In mid September 1997, there were further discussions between the two
investment banks in which Laidlaw Environmental's representatives requested a
meeting of the management of the two companies and their advisors so that
Laidlaw Environmental could fully describe why a business combination was in
both companies' best interests. Safety-Kleen's representative continued to
request that Laidlaw Environmental sign the confidentiality agreement containing
the two year standstill provision. He also stated that if Laidlaw Environmental
would submit its proposal in writing, Safety-Kleen would consider a meeting with
Laidlaw Environmental.
 
     On September 24, 1997, Mr. David E. Thomas, Jr. of Raymond James, financial
advisor to Laidlaw Environmental, delivered a letter to Mr. Jeffrey W. Corum of
William Blair, informing Mr. Corum of Laidlaw Environmental's interest in
pursuing negotiations with Safety-Kleen. In particular, Mr. Thomas' letter
requested a meeting between management of Laidlaw Environmental and management
of Safety-Kleen and pointed out several unique features of Laidlaw
Environmental's proposed transaction including the cost synergies available from
combining the operations of Laidlaw Environmental and Safety-Kleen which would
result in an anticipated annual savings of $100 to $130 million. Mr. Thomas'
letter suggested structuring the transaction as a reverse merger in which
Safety-Kleen would issue one share of its stock for every three shares of
Laidlaw Environmental stock.
 
                                       15
<PAGE>   24
 
     The text of the September 24 letter is as follows:
 
                 Letterhead of Raymond James & Associates, Inc.
 
                                                              September 24, 1997
 
Mr. Jeffrey W. Corum
William Blair & Company
222 West Adams Street
Chicago, Illinois 60606
 
Dear Jeff:
 
    As we have discussed, our client, Laidlaw Environmental Services Inc.
("LESI") is interested in pursuing a transaction with Safety-Kleen Corp. ("SK").
We would hope to have a meeting between top management of LESI, Laidlaw, Inc.
and SK to outline our proposed structure and discuss the advantages to SK
shareholders in depth. In anticipation of this meeting we would like to outline
that structure and the benefits.
 
    We propose a reverse merger in which SK would issue one share of its stock
for three shares of LESI stock. The resultant company would have approximately
120 million shares outstanding, approximately half-owned by each of the
precedent company's existing shareholders. Surviving senior management would be
the existing LESI management team, although we would certainly envision that the
best of the combined teams would stay with the combined company.
 
    The key initial advantage of the transaction lies in the tremendous cost
synergies available from combining the operations of SK and LESI. Our estimates
are that these savings could range from $100-$130 million annually. These would
arise from the elimination of duplicate general and administrative and other
public company costs, from the closure of overlapping service center facilities,
from increased utilization of those facilities that remain open, and from the
internalization of various waste streams. Our experience with the merger of
Rollins' and Laidlaw's hazardous waste businesses, in which ultimate realizable
savings will exceed our originally projected $75 million annually (now expected
to be approximately $90 million), gives us a high level of confidence that we
can achieve these synergies.
 
    Your client's board and shareholders should find this to be a very
compelling opportunity. They would have ownership of a company with tremendous
economic opportunity via the increased earnings available from cost savings. Our
estimates show an accretion in SK's EPS from $1.05 to $1.25, which would yield
an additional $4 in value at SK's existing multiple. We believe it likely the
combined companies would trade at an even higher level, reflecting LESI's
multiple or a blend of the LESI and SK multiples. The company would be driven by
a management team with a proven record of achieving similar consolidation
savings and increasing shareholder value, as evidenced by the doubling of LESI's
share price since the date of the Rollins transaction earlier this year.
 
    We would point out several unique features in our proposed transaction that
we believe distinguishes it from other alternatives:
 
        (i) the annual potential savings of $130 million
 
        (ii) the relative ease of completing the transaction based on Laidlaw
    Inc.'s ownership position (66 1/2% in LESI);
 
        (iii) the absence of any new funding requirements by the combined
    company; and
 
        (iv) the financial strength of the combined balance sheet, cash flow,
    and operating margins.
 
        We would like to explore this with you in more detail. We will call you
    later today or tomorrow to set up a meeting between our clients.
 
                                          Sincerely,
 
                                          David E. Thomas, Jr.
                                          Senior Managing Director
cc: Kenneth W. Winger
   James R. Bullock
 
attachment:  Forbes article dated October 6, 1997
 
                                       16
<PAGE>   25
 
     Shortly thereafter, Mr. Corum responded to Mr. Thomas' letter by telephone
stating that only upon Laidlaw Environmental's delivery of a confidentiality and
standstill agreement acceptable to Safety-Kleen, would Safety-Kleen commence
negotiations with Laidlaw Environmental. Subsequent to their telephone
conversations, Mr. James R. Bullock, Chairman of Laidlaw Environmental,
attempted to call Mr. Brinckman, who did not return his call. Mr. Bullock then
called Mr. E. David Coolidge, III of William Blair in an effort to arrange a
meeting with Safety-Kleen. Mr. Coolidge repeated Safety-Kleen's refusal to meet
with Laidlaw Environmental in the absence of a confidentiality and standstill
agreement.
 
     On November 3, 1997, the Laidlaw Environmental Board of Directors met and
determined to proceed with the Offer as well as to retain Bear Stearns to work
together with Raymond James as financial advisors to Laidlaw Environmental.
Laidlaw Environmental management had previously retained Katten Muchin & Zavis
to serve as legal counsel. Also on November 3, 1997, in a letter to Mr.
Brinckman, Mr. James R. Bullock, Chairman of Laidlaw Environmental, informed Mr.
Brinckman and the Safety-Kleen Board of Directors of Laidlaw Environmental's
intention to pursue the Offer, that Laidlaw Environmental was willing to execute
a confidentiality agreement provided such agreement did not contain a standstill
provision, and that Laidlaw Environmental continued to believe that annual cost
savings and synergies resulting from a combination of the two companies would
exceed $100 million annually. For these and other reasons, Laidlaw Environmental
would consider and pursue various options with respect to an acquisition of
Safety-Kleen notwithstanding Safety-Kleen's refusal to meet with representatives
of Laidlaw Environmental. The letter also informed Mr. Brinckman that Laidlaw
Environmental had executed a commitment letter with Toronto-Dominion Bank to
provide all necessary financing for the Offer and the Merger and again
encouraged Mr. Brinckman and the Safety-Kleen Board to meet with representatives
of Laidlaw Environmental to discuss the possibility of a mutually beneficial
negotiated transaction.
 
                                       17
<PAGE>   26
 
     The text of Mr. Bullock's November 3 letter is as follows:
 
                        LETTERHEAD FOR JAMES R. BULLOCK
 
                                          November 3, 1997
Mr. Donald W. Brinckman
Chairman & Chief Executive Officer
Safety-Kleen Corp.
900 North Randall Road
Elgin, Illinois
USA 60123
 
Dear Mr. Brinckman:
 
    I am writing to you in my capacity as Chairman of Laidlaw Environmental
Services, Inc. Since your August 8th announcement that you would explore
strategic alternative to enhance shareholder value, we have sought
unsuccessfully, directly through phone calls to you and indirectly through your
advisors, to meet with you to pursue the combination of our companies. Six weeks
ago, at the request of your financial advisor, we submitted a preliminary merger
proposal to which you have yet to respond. Needless to say, we are frustrated by
your continuing unwillingness to engage in constructive dialogue.
 
    As you are aware, your advisors have insisted that we sign an agreement that
would permit us to propose strategic alternatives that maximize value for your
shareholders only if you "shall have requested in writing in advance the
submission of such proposal". We have made clear on numerous occasions our
willingness to sign a confidentiality agreement that protects nonpublic
information you choose to share with us. In light of our experience to date,
however, we will not sign any agreement that does not ensure that your
shareholders have the opportunity to consider our offer and to maximize the
value of their stock.
 
    In response to your continuing unwillingness to meet or commence discussions
with us in a meaningful way, our Board of Directors today authorized and
directed senior management of Laidlaw Environmental Services, Inc. to pursue the
acquisition of Safety-Kleen Corp. We have executed commitment letters with the
Toronto-Dominion Bank to provide all the necessary financing for this
acquisition. We have engaged Bear Stearns & Co., Inc. and Raymond James and
Associates Inc. to serve as our financial advisors and Katten Muchin and Zavis
to serve as our legal counsel.
 
    Our offer for each share of Safety-Kleen Corp. is a combination of $14.00 in
cash and 2.4 common shares of Laidlaw Environmental Services, Inc. stock. This
represents approximately an 18.2% premium to Safety-Kleen's closing price on
Friday and a 46% premium to Safety-Kleen's trading price prior to your August
8th announcement. Please note that our offer is not subject to due diligence or
a financing contingency. We have fully committed financing sufficient to
complete the combination. We believe our offer represents a full and fair price
based on the publicly available information we have reviewed. However, should
you be willing to meet with us, we are prepared to consider any additional
information you may wish to provide that demonstrates that a higher valuation is
warranted. We continue to prefer a negotiated transaction.
 
    Together our companies can create greater shareholder value than can either
of us alone. We estimate annual cost savings and synergy's will exceed $90
million. We believe the stock market will embrace this transaction and will
reward the combined company with enhanced stock performance. Our offer ensures
your shareholders participate in this exciting future.
 
    We believe it is in the best interests of our companies to proceed
immediately to negotiate a definitive agreement, containing customary public
company terms and conditions, and to consummate a transaction by year-end. Given
the importance we place on this combination, we are prepared to commit the
resources necessary to see its timely completion. We and our advisors would be
pleased to meet you and your advisors in Chicago either later today or tomorrow
to complete the necessary papers.
 
    In recognition of the strategic nature and compelling financial benefits of
our proposed combination to your shareholders and our willingness to consider
modifications to our offer as warranted, we expect you not to enter into any
binding merger or similar agreement with any other party without first exploring
with us the full merits of combining our two companies.
 
    Our Board of Directors unanimously supports this merger. We trust you and
the other members of Safety-Kleen's Board of Directors will consider the best
interests of Safety-Kleen's shareholders and will agree to meet with us promptly
to achieve a mutually beneficial transaction.
 
    We look forward to hearing from you later today.
                                          Sincerely,
 
                                          James R. Bullock, Chairman
cc: Safety-Kleen, Board of Directors
    Laidlaw Environmental Services, Inc., Board of Directors
    Douglas T. Lake, Bear Stearns & Co. Inc.
    David E. Thomas, Jr., Raymond James & Associates Inc.
    Herbert S. Wander, Katten, Muchin & Zavis
    William Blair & Company, LLC
 
                                       18
<PAGE>   27
 
     On November 3, 1997 after receipt of Mr. Bullock's letter, Mr. Brinckman
delivered a letter to Mr. Bullock requesting that Laidlaw Environmental execute
a confidentiality and standstill agreement and informing Mr. Bullock that the
Board of Directors of Safety-Kleen would fully consider Laidlaw Environmental's
proposal along with other proposals received by Safety-Kleen. In addition, Mr.
Brinckman stated that representatives of Safety-Kleen, together with its
financial advisors, would meet with representatives of Laidlaw Environmental,
together with its financial advisors, to discuss information concerning Laidlaw
Environmental and the estimated cost savings and synergies.
 
          The text of Mr. Brinckman's November 3 letter is as follows:
 
                                          November 3, 1997
VIA FACSIMILE
 
Mr. James R. Bullock
Chairman
Laidlaw Environmental Services, Inc.
3221 North Service Road
P.O. Box 5028
Burlington, Ontario
Canada L7R 3Y8
 
Dear Mr. Bullock:
 
     Thank you for your letter of November 3, 1997.
 
     As you know, we are engaged in a process of exploring strategic
alternatives for enhancing shareholder value. That process includes a possible
sale of the Company. Every prospective purchaser engaged in that phase of the
process has signed a confidentiality and standstill agreement that is designed
to produce even-handed treatment of participants. We urge you -- as we have
previously -- to sign that agreement and participate in this process on the same
basis as each of the other potential bidders.
 
     In any event, our Board of Directors will fully consider your proposal
along with others that we receive. For purposes of furthering our understanding
and evaluation of your proposal, our financial advisors, William Blair &
Company, together with representatives of the Company, would be pleased to meet
with you in Chicago at a mutually convenient time so that you can furnish us
with information concerning Laidlaw Environmental Services and your estimated
cost savings and synergies. Please call John Carton of William Blair
(312/364-8426) to arrange for this meeting. In addition, if you execute our
confidentiality and standstill agreement accepting the same ground rules as our
other potential bidders, arrangements will be made to promptly provide you with
non-public information concerning the Company.
 
     We appreciate your interest in Safety-Kleen and look forward to hearing
from you.
 
                                          Sincerely,
 
                                          Donald W. Brinckman
 
DWB/mb
 
     On November 4, 1997, Laidlaw Environmental publicly announced its intention
to commence the Offer and pursue the Merger.
 
     On November 5, 1997, Mr. Bullock and a representative of Bear Stearns met
with Mr. Brinckman and Mr. Joseph Chalhaub, Senior Vice President of
Safety-Kleen, and representatives of William Blair to discuss
 
                                       19
<PAGE>   28
 
preliminary potential synergies that could be achieved through a combination of
the two companies and ways the parties could work together. Mr. Bullock stated
that Laidlaw Environmental was prepared to sign a mutual confidentiality
agreement that did not contain a standstill provision so that Laidlaw
Environmental and Safety-Kleen could share information with each other.
 
                                       20
<PAGE>   29
 
                                   THE OFFER
 
GENERAL
 
     Laidlaw Environmental hereby offers, upon the terms and subject to the
conditions set forth herein and in the related Letter of Transmittal, to
exchange the Offer Consideration for each outstanding Share validly tendered on
or prior to the Expiration Date and not properly withdrawn. The Offer
Consideration per Share (and accompanying Rights) consists of $14.00 net in cash
and 2.4 shares of Laidlaw Environmental Common Stock. On November 10, 1997, the
closing price of Laidlaw Environmental Common Stock on the NYSE was $4.875.
Based on such closing price, each Share would be converted into $14.00 net in
cash and Laidlaw Environmental Common Stock having a market value of $11.70. The
value of the Offer Consideration will fluctuate as the market price of the
Laidlaw Common Stock changes.
 
     Tendering shareholders will not be obligated to pay any charges or expenses
of the Exchange Agent or any brokerage commissions. Except as set forth in the
Instructions to the Letter of Transmittal, transfer taxes on the exchange of
Shares pursuant to the Offer will be paid by or on behalf of Laidlaw
Environmental.
 
     The purpose of the Offer is to enable Laidlaw Environmental to obtain
control of, and ultimately the entire common equity interest in, Safety-Kleen.
Laidlaw Environmental presently intends, as soon as practicable after
consummation of the Offer, to propose and seek to have Safety-Kleen effect the
Merger. In the Merger, each outstanding Share (other than Shares owned by
Laidlaw Environmental or any of its affiliates, Shares held in the treasury of
Safety-Kleen (if Safety-Kleen is so authorized) or by any subsidiary of
Safety-Kleen and Shares owned by Safety-Kleen Shareholders who perfect appraisal
rights under Wisconsin law) would be cancelled in exchange for the right to
receive the Offer Consideration. See "The Merger."
 
     In the event that Laidlaw Environmental obtains all of the Shares pursuant
to the Offer and/or the Merger, former holders of Shares (other than Laidlaw
Environmental) would own approximately 43.4% of the outstanding shares of
Laidlaw Environmental Common Stock, based on the number of shares of Laidlaw
Environmental Common Stock outstanding on October 14, 1997.
 
     Laidlaw Environmental's obligation to exchange the Offer Consideration for
Shares pursuant to the Offer is subject to satisfaction or waiver of the Minimum
Tender Condition, the Laidlaw Environmental Stockholder Approval Condition, the
Rights Plan Condition, the Wisconsin Statutory Conditions and the Regulatory
Approval Condition (in each case as defined on the cover page of this
Prospectus) and the other conditions set forth under "-- Conditions of the
Offer."
 
     According to the Safety-Kleen September 6, 1997 Form 10-Q, as of September
6, 1997, there were 58,400,729 Shares outstanding. As of October 29, 1997,
Laidlaw Environmental beneficially owned 601,100 Shares, or approximately 1.03%
of the outstanding Shares.
 
     Requests have been made to Safety-Kleen pursuant to Rule 14d-5 promulgated
under the Exchange Act, for the use of Safety-Kleen's shareholder lists and
security position listings for the purpose of communicating with Safety-Kleen
Shareholders and disseminating the Offer to holders of Shares. This Prospectus
and the related Letter of Transmittal and other relevant materials will be
mailed to registered holders of Shares and will be furnished to brokers,
dealers, commercial banks, trust companies and similar persons whose names, or
the names of whose nominees, appear on such shareholder lists, or, if
applicable, who are listed as participants in a clearing agency's security
position listing for subsequent transmittal to beneficial owners of Shares by
Laidlaw Environmental following receipt of such list or listings from
Safety-Kleen.
 
SAFETY-KLEEN RIGHTS
 
     No separate payment will be made by Laidlaw Environmental for the Rights
pursuant to the Offer. The Rights are presently evidenced by the certificates
for the Shares and the tender by a Safety-Kleen Shareholder of his or her Shares
prior to the Distribution Date (as defined below) will also constitute a tender
of the associated Rights. Upon the earlier to occur of (i) 10 days following a
public announcement that a person has acquired beneficial ownership of 20% or
more of the outstanding Shares (an "Acquiring Person") or (ii) 10 business days
(or such later date as may be determined by action of the Safety-Kleen Board
prior to such time
 
                                       21
<PAGE>   30
 
as any person or group becomes an Acquiring Person) following the commencement
of, or announcement of an intention to make, a tender offer or exchange offer
which would result in the person making the offer becoming an Acquiring Person
(the earlier of such dates being called the "Distribution Date"), separate
certificates evidencing the Rights will be mailed to holders of record of the
Shares as of the close of business on the Distribution Date and such separate
Rights certificates alone will evidence the Rights.
 
     If the Distribution Date occurs and separate certificates representing the
Rights are distributed by Safety-Kleen or the Rights Agent to holders of Shares
prior to the time a holder's Shares are tendered pursuant to the Offer,
certificates representing a number of Rights equal to the number of Shares
tendered must be delivered to the Exchange Agent, or, if available, a book-entry
confirmation received by the Exchange Agent with respect thereto, in order for
such Shares to be validly tendered. If a Distribution Date occurs and separate
certificates representing the Rights are not distributed prior to the time
Shares are tendered pursuant to the Offer, Rights may be tendered prior to a
Safety-Kleen Shareholder receiving the certificates for Rights by use of the
guaranteed delivery procedure described under "-- Procedure for Tendering"
below.
 
TIMING OF THE OFFER
 
     The Offer is currently scheduled to expire on             , 1997; however,
it is Laidlaw Environmental's current intention to extend the Offer from time to
time as necessary until all conditions to the Offer have been satisfied or
waived. See "-- Extension, Termination and Amendment." Laidlaw Environmental has
received a commitment letter from Toronto-Dominion Bank stating that it will
provide or arrange credit facilities in the amount necessary to fund payment of
the Cash Consideration. See "-- Source and Amount of Funds." In the unlikely
event that Laidlaw Environmental has not obtained financing for the Cash
Consideration prior to five business days before the Expiration Date, Laidlaw
Environmental currently intends to extend the Offer to ensure that five business
days remain for Safety-Kleen Shareholders to tender their Shares in the Offer
subsequent to obtaining financing. See "-- Source and Amount of Funds." Laidlaw
Environmental expects that the Laidlaw Environmental Stockholder Approval
Condition will be satisfied on or about             , 1997, the date on which it
plans to call the Laidlaw Environmental Special Meeting, to approve the issuance
of shares of Laidlaw Environmental Common Stock in connection with the Offer and
the Merger.
 
EXTENSION, TERMINATION AND AMENDMENT
 
     Laidlaw Environmental expressly reserves the right (but will not be
obligated), in its sole discretion, at any time or from time to time, and
regardless of whether any of the events set forth in "-- Conditions of the
Offer" shall have occurred or shall have been determined by Laidlaw
Environmental to have occurred, to extend the period of time during which the
Offer is to remain open by giving oral or written notice of such extension to
the Exchange Agent, which extension will be announced no later than 9:00 a.m.,
New York City time, on the next business day after the previously scheduled
Expiration Date. There can be no assurance that Laidlaw Environmental will
exercise its right to extend the Offer. However, it is Laidlaw Environmental's
current intention to extend the Offer until all Offer Conditions have been
satisfied or waived. During any such extension, all Shares previously tendered
and not withdrawn will remain subject to the Offer, subject to the right of a
tendering Safety-Kleen Shareholder to withdraw his or her Shares. See
"-- Withdrawal Rights."
 
     Subject to the applicable rules and regulations of the Commission, Laidlaw
Environmental also reserves the right, in its sole discretion, at any time or
from time to time, (i) to delay acceptance for, exchange of, or, regardless of
whether such Shares (and Rights, if applicable) were theretofore accepted for
exchange, exchange of any Shares (and Rights, if applicable) pursuant to the
Offer, or to terminate the Offer and not accept for exchange or exchange any
Shares (and Rights, if applicable) not theretofore accepted for exchange, or
exchanged, upon the failure of any of the conditions of the Offer to be
satisfied and (ii) to waive any condition (other than the Laidlaw Environmental
Stockholder Approval Condition, the Regulatory Approval Condition and the
condition relating to the effectiveness of the Registration Statement) or
otherwise amend the Offer in any respect, by giving oral or written notice of
such delay, termination or amendment to the Exchange Agent and by making a
public announcement thereof. Any such extension, termination, amendment or delay
will be followed as promptly as practicable by public announcement thereof, such
announcement in the case of an extension to be issued no later than 9:00 a.m.,
New York City time, on the next business day
 
                                       22
<PAGE>   31
 
after the previously scheduled Expiration Date. Subject to applicable law
(including Rules 14d-4(c) and 14d-6(d) under the Exchange Act, which require
that any material change in the information published, sent or given to
Safety-Kleen Shareholders in connection with the Offer be promptly disseminated
to Safety-Kleen Shareholders in a manner reasonably designed to inform
Safety-Kleen Shareholders of such change) and without limiting the manner in
which Laidlaw Environmental may choose to make any public announcement, Laidlaw
Environmental shall have no obligation to publish, advertise or otherwise
communicate any such public announcement other than by making a release to the
Dow Jones News Service.
 
     Laidlaw Environmental confirms that if it makes a material change in the
terms of the Offer or the information concerning the Offer, or if it waives a
material condition of the Offer, Laidlaw Environmental will extend the Offer to
the extent required under the Exchange Act. If, prior to the Expiration Date,
Laidlaw Environmental shall increase or decrease the percentage of Shares being
sought or the consideration offered to holders of Shares, such increase or
decrease shall be applicable to all holders whose Shares are accepted for
exchange pursuant to the Offer, and, if at the time notice of any such increase
or decrease is first published, sent or given to holders of Shares, the Offer is
scheduled to expire at any time earlier than the tenth business day from and
including the date that such notice is first so published, sent or given, the
Offer will be extended until the expiration of such ten business day period. For
purposes of the Offer, a "business day" means any day other than a Saturday,
Sunday or a federal holiday and consists of the time period from 12:01 a.m.
through 12:00 midnight, New York City time.
 
EXCHANGE OF SHARES; DELIVERY OF OFFER CONSIDERATION
 
     Upon the terms and subject to the conditions of the Offer (including, if
the Offer is extended or amended, the terms and conditions of any such extension
or amendment), Laidlaw Environmental will accept for exchange, and will
exchange, Shares (and Rights, if applicable) validly tendered and not properly
withdrawn as promptly as practicable following the Expiration Date. In addition,
subject to applicable rules of the Commission, Laidlaw Environmental expressly
reserves the right to delay acceptance of or the exchange of Shares (and Rights,
if applicable) in order to comply with any applicable law. In all cases,
exchange of Shares (and Rights, if applicable) tendered and accepted for
exchange pursuant to the Offer will be made only after receipt by the Exchange
Agent of certificates for such Shares (and Rights, if applicable) (or a
confirmation of a book-entry transfer of such Shares (and Rights, if applicable)
in the Exchange Agent's account at The Depository Trust Company (the "Book-Entry
Transfer Facility")), a properly completed and duly executed Letter of
Transmittal (or facsimile thereof) and any other required documents.
 
     For purposes of the Offer, Laidlaw Environmental will be deemed to have
accepted for exchange Shares (and Rights, if applicable) validly tendered and
not withdrawn as, if and when Laidlaw Environmental gives oral or written notice
to the Exchange Agent of its acceptance of the tenders of such Shares (and
Rights, if applicable) pursuant to the Offer. Delivery of Laidlaw Environmental
Common Stock and Cash Consideration in exchange for Shares (and Rights, if
applicable) pursuant to the Offer and cash in lieu of fractional shares of
Laidlaw Environmental Common Stock will be made by the Exchange Agent as soon as
practicable after receipt of such notice. The Exchange Agent will act as agent
for tendering Safety-Kleen Shareholders for the purpose of receiving Laidlaw
Environmental Common Stock, the Cash Consideration and cash to be paid in lieu
of fractional shares of Laidlaw Environmental Common Stock from Laidlaw
Environmental and transmitting such Laidlaw Environmental Common Stock and cash
to tendering Safety-Kleen Shareholders. Under no circumstances will interest be
paid by Laidlaw Environmental by reason of any delay in making such exchange.
 
     If any tendered Shares are not accepted for exchange pursuant to the terms
and conditions of the Offer for any reason, or if certificates are submitted for
more Shares than are tendered, certificates for such unexchanged Shares will be
returned without expense to the tendering Safety-Kleen Shareholder or, in the
case of Shares tendered by book-entry transfer of such Shares into the Exchange
Agent's account at a Book-Entry Transfer Facility pursuant to the procedures set
forth below under "-- Procedure for Tendering," such Shares will be credited to
an account maintained within such Book-Entry Transfer Facility as soon as
practicable following expiration or termination of the Offer.
 
                                       23
<PAGE>   32
 
CASH IN LIEU OF FRACTIONAL SHARES OF LAIDLAW ENVIRONMENTAL COMMON STOCK
 
     No certificates representing fractional shares of Laidlaw Environmental
Common Stock will be issued pursuant to the Offer. In lieu thereof, each
tendering shareholder who would otherwise be entitled to a fractional share of
Laidlaw Environmental Common Stock will receive cash in an amount equal to such
fraction (expressed as a decimal and rounded to the nearest 0.01 of a share)
times the closing price for shares of Laidlaw Environmental Common Stock on the
NYSE Composite Tape on the date such Safety-Kleen Shareholder's Shares are
accepted for exchange by Laidlaw Environmental.
 
WITHDRAWAL RIGHTS
 
     Tenders of Shares (and Rights, if applicable) made pursuant to the Offer
are irrevocable, except that Shares (and Rights, if applicable) tendered
pursuant to the Offer may be withdrawn pursuant to the procedures set forth
below at any time prior to the Expiration Date, and, unless theretofore accepted
for exchange and exchanged by Laidlaw Environmental for the Offer Consideration
pursuant to the Offer, may also be withdrawn at any time after             .
 
     For a withdrawal to be effective, a written or facsimile transmission
notice of withdrawal must be timely received by the Exchange Agent at one of its
addresses set forth on the back cover of this Prospectus, and must specify the
name of the person having tendered the Shares (and Rights, if applicable) to be
withdrawn, the number of Shares (and Rights, if applicable) to be withdrawn and
the name of the registered holder, if different from that of the person who
tendered such Shares (and Rights, if applicable).
 
     The signature(s) on the notice of withdrawal must be guaranteed by a
financial institution (including most banks, savings and loan associations and
brokerage houses) which is a participant in the Securities Transfer Agents
Medallion Program, the New York Stock Exchange Medallion Signature Program or
the Stock Exchange Medallion Program (an "Eligible Institution") unless such
Shares (and Rights, if applicable) have been tendered for the account of any
Eligible Institution. If Shares (and Rights, if applicable) have been tendered
pursuant to the procedures for book-entry tender as set forth below under
"-- Procedure for Tendering," any notice of withdrawal must specify the name and
number of the account at the Book-Entry Transfer Facility to be credited with
the withdrawn Shares (and Rights, if applicable) and must otherwise comply with
such Book-Entry Transfer Facility's procedures. If certificates have been
delivered or otherwise identified to the Exchange Agent, the name of the
registered holder and the serial numbers of the particular certificates
evidencing the Shares (and Rights, if applicable) withdrawn must also be
furnished to the Exchange Agent as aforesaid prior to the physical release of
such certificates.
 
     All questions as to the form and validity (including time of receipt) of
any notice of withdrawal will be determined by Laidlaw Environmental, in its
sole discretion, which determination shall be final and binding. Neither Laidlaw
Environmental, the Exchange Agent, the Information Agent, the Dealer Manager nor
any other person will be under any duty to give notification of any defects or
irregularities in any notice of withdrawal or will incur any liability for
failure to give any such notification. Any Shares (and Rights, if applicable)
properly withdrawn will be deemed not to have been validly tendered for purposes
of the Offer. However, withdrawn Shares (and Rights, if applicable) may be
retendered by following one of the procedures described under "-- Procedure for
Tendering" at any time prior to the Expiration Date.
 
     A withdrawal of Shares shall also constitute a withdrawal of the associated
Rights. Rights may not be withdrawn unless the associated Shares are also
withdrawn.
 
PROCEDURE FOR TENDERING
 
     For a Safety-Kleen Shareholder to validly tender Shares (and Rights, if
applicable) pursuant to the Offer, (i) a properly completed and duly executed
Letter of Transmittal (or manually executed facsimile thereof), together with
any required signature guarantees, or an Agent's Message (as defined below) in
connection with a book-entry transfer, and any other required documents, must be
transmitted to and received by the Exchange Agent at one of its addresses set
forth on the back cover of this Prospectus and either certificates for tendered
Shares (and Rights, if applicable) must be received by the Exchange Agent at
such
 
                                       24
<PAGE>   33
 
address or such Shares (and Rights, if applicable) must be tendered pursuant to
the procedures for book-entry transfer set forth below (and a confirmation of
receipt of such tender received (such confirmation, a "Book-Entry
Confirmation")), in each case prior to the Expiration Date, or (ii) such
Safety-Kleen Shareholders must comply with the guaranteed delivery procedure set
forth below.
 
     The term "Agent's Message" means a message, transmitted by a Book-Entry
Transfer Facility to, and received by, the Exchange Agent, and forming a part of
a Book-Entry Confirmation, which states that such Book-Entry Transfer Facility
has received an express acknowledgment from the participant in such Book-Entry
Transfer Facility tendering the Shares (and Rights, if applicable) that such
participant has received and agrees to be bound by the terms of the Letter of
Transmittal and that Laidlaw Environmental may enforce such agreement against
such participant.
 
     Safety-Kleen Shareholders will be required to tender one Right for each
Share tendered in order to effect a valid tender of Shares, unless the Rights
Plan Condition has been satisfied or waived. Unless the Safety-Kleen
Distribution Date occurs, a tender of Shares will constitute a tender of the
associated Rights. If the Safety-Kleen Distribution Date occurs and separate
certificates representing the Rights are distributed by Safety-Kleen or the
Rights Agent to holders of Shares prior to the time a holder's Shares are
tendered pursuant to the Offer, certificates representing a number of Rights
equal to the number of Shares tendered must be delivered to the Exchange Agent,
or, if available, a Book-Entry Confirmation received by the Exchange Agent with
respect thereto, in order for such Shares to be validly tendered. If the
Safety-Kleen Distribution Date occurs and separate certificates representing the
Rights are not distributed prior to the time Shares are tendered pursuant to the
Offer, Rights may be tendered prior to a shareholder receiving the certificates
for Rights by use of the guaranteed delivery procedure described below. If
Rights certificates are distributed but are not available to a shareholder prior
to the time Shares are tendered pursuant to the Offer, a tender of Shares
constitutes an agreement by the tendering shareholder to deliver to the Exchange
Agent pursuant to the guaranteed delivery procedure described below, prior to
the expiration of the period to be specified in the Notice of Guaranteed
Delivery and the related Letter of Transmittal for delivery of Rights
certificates or a Book-Entry Confirmation for Rights (the "Rights Delivery
Period"), Rights certificates representing a number of Rights equal to the
number of Shares tendered. Laidlaw Environmental reserves the right to require
that it receive such Rights certificates (or a Book-Entry Confirmation with
respect to such Rights) prior to accepting Shares for exchange. If Rights
certificates are distributed, Laidlaw Environmental will distribute a separate
letter of transmittal for such Rights certificates. If Rights certificates are
tendered separately from Shares, then a properly completed letter of transmittal
for Rights certificates (or manually executed facsimile thereof) must be
submitted with respect to such Rights. Laidlaw Environmental reserves the right
to require that it receive such Rights certificates (or a Book-Entry
Confirmation with respect to such Rights) prior to accepting Shares for
exchange.
 
     Nevertheless, Laidlaw Environmental will be entitled to accept for exchange
Shares tendered by a shareholder prior to receipt of the Rights certificates
required to be tendered with such Shares or a Book-Entry Confirmation with
respect to such Rights and either (i) subject to complying with applicable rules
and regulations of the Commission, withhold payment for such Shares pending
receipt of the Rights certificates or a Book-Entry Confirmation for such Rights
or (ii) exchange Shares accepted for exchange pending receipt of the Rights
certificates or a Book-Entry Confirmation for such Rights in reliance upon the
guaranteed delivery procedure described below. In addition, after expiration of
the Rights Delivery Period, Laidlaw Environmental may instead elect to reject as
invalid a tender of Shares with respect to which Rights certificates or a Book-
Entry Confirmation for an equal number of Rights have not been received by the
Exchange Agent. Any determination by Laidlaw Environmental to make payment for
Shares in reliance upon such guaranteed delivery procedure or, after expiration
of the Rights Delivery Period, to reject as invalid, shall be made, subject to
applicable law, in the sole and absolute discretion of Laidlaw Environmental.
 
     The Exchange Agent will establish accounts with respect to the Shares at
the Book-Entry Transfer Facility for purposes of the Offer within two business
days after the date of the mailing of the final Prospectus, and any financial
institution that is a participant in any of the Book-Entry Transfer Facility
systems may make book-entry delivery of the Shares by causing the Book-Entry
Transfer Facility to transfer such Shares into the Exchange Agent's account in
accordance with the Book-Entry Transfer Facility's procedure for such transfer.
 
                                       25
<PAGE>   34
 
However, although delivery of Shares may be effected through book-entry at the
Book-Entry Transfer Facility, the Letter of Transmittal (or facsimile thereof),
with any required signature guarantees, or an Agent's Message in connection with
a book-entry transfer, and any other required documents, must, in any case, be
transmitted to and received by the Exchange Agent at one or more of its
addresses set forth on the back cover of this Prospectus prior to the Expiration
Date, or the guaranteed delivery procedure described below must be complied
with. No assurance can be given, however, that book-entry delivery of Rights
will be available. If book-entry delivery is not available, a tendering
shareholder will be required to tender Rights by means of delivery of Rights
certificates or pursuant to the guaranteed delivery procedure set forth below.
 
     No signature guarantee is required on the Letter of Transmittal in cases
where (a) the Letter of Transmittal is signed by the registered holder(s) of the
Shares (including any participant in the Book-Entry Transfer Facility whose name
appears on a security position listing as the owner of Shares) tendered
therewith and such holder(s) have not completed the instruction entitled
"Special Issuance Instructions" on the Letter of Transmittal or (b) such Shares
are tendered for the account of an Eligible Institution. Otherwise, all
signatures on the Letter of Transmittal must be guaranteed by an Eligible
Institution. If the certificates for Shares or Rights (if any) are registered in
the name of a person other than the signer of the Letter of Transmittal, or if
certificates for unexchanged Shares or Rights (if any) are to be issued to a
person other than the registered holder(s), the certificates must be endorsed or
accompanied by appropriate stock powers, in either case signed exactly as the
name or names of the registered owner or owners appear on the certificates, with
the signature(s) on the certificates or stock powers guaranteed as aforesaid.
 
     THE METHOD OF DELIVERY OF SHARE CERTIFICATES AND ALL OTHER REQUIRED
DOCUMENTS, INCLUDING DELIVERY THROUGH THE BOOK-ENTRY TRANSFER FACILITY, IS AT
THE OPTION AND RISK OF THE TENDERING SHAREHOLDER, AND THE DELIVERY WILL BE
DEEMED MADE ONLY WHEN ACTUALLY RECEIVED BY THE EXCHANGE AGENT. IF DELIVERY IS BY
MAIL, REGISTERED MAIL WITH RETURN RECEIPT REQUESTED, PROPERLY INSURED, IS
RECOMMENDED. IN ALL CASES, SUFFICIENT TIME SHOULD BE ALLOWED TO ENSURE TIMELY
DELIVERY.
 
     TO PREVENT BACKUP FEDERAL INCOME TAX WITHHOLDING WITH RESPECT TO CASH
CONSIDERATION AND CASH RECEIVED IN LIEU OF FRACTIONAL SHARES OF LAIDLAW
ENVIRONMENTAL COMMON STOCK, A SHAREHOLDER MUST PROVIDE THE EXCHANGE AGENT WITH
HIS OR HER CORRECT TAXPAYER IDENTIFICATION NUMBER AND CERTIFY WHETHER SUCH
SHAREHOLDER IS SUBJECT TO BACKUP WITHHOLDING OF FEDERAL INCOME TAX BY COMPLETING
THE SUBSTITUTE FORM W-9 INCLUDED IN THE LETTER OF TRANSMITTAL. CERTAIN
SHAREHOLDERS (INCLUDING, AMONG OTHERS, ALL CORPORATIONS AND CERTAIN FOREIGN
INDIVIDUALS) ARE NOT SUBJECT TO THESE BACKUP WITHHOLDING AND REPORTING
REQUIREMENTS. IN ORDER FOR A FOREIGN INDIVIDUAL TO QUALIFY AS AN EXEMPT
RECIPIENT, THE SHAREHOLDER MUST SUBMIT A FORM W-8, SIGNED UNDER PENALTIES OF
PERJURY, ATTESTING TO THAT INDIVIDUAL'S EXEMPT STATUS.
 
     If a Safety-Kleen Shareholder desires to tender Shares (and Rights, if
applicable) pursuant to the Offer and such shareholder's certificates are not
immediately available or such shareholder cannot deliver the certificates and
all other required documents to the Exchange Agent prior to the Expiration Date
or such shareholder cannot complete the procedure for book-entry transfer on a
timely basis, such Shares (and Rights, if applicable) may nevertheless be
tendered, provided that all of the following conditions are satisfied:
 
          (a) such tenders are made by or through an Eligible Institution;
 
          (b) a properly completed and duly executed Notice of Guaranteed
     Delivery, substantially in the form made available by Laidlaw
     Environmental, is received by the Exchange Agent as provided below on or
     prior to the Expiration Date; and
 
          (c) the certificates for all tendered Shares (or a confirmation of a
     book-entry transfer of such securities into the Exchange Agent's account at
     a Book-Entry Transfer Facility as described above), in
 
                                       26
<PAGE>   35
 
     proper form for transfer, together with a properly completed and duly
     executed Letter of Transmittal (or facsimile thereof), with any required
     signature guarantees (or, in the case of a book-entry transfer, an Agent's
     Message) and all other documents required by the Letter of Transmittal are
     received by the Exchange Agent within three NYSE trading days after the
     date of execution of such Notice of Guaranteed Delivery.
 
     The Notice of Guaranteed Delivery may be delivered by hand or transmitted
by facsimile transmission or mail to the Exchange Agent and must include a
guarantee by an Eligible Institution in the form set forth in such Notice.
 
     In all cases, exchanges of Shares (and Rights, if applicable) tendered and
accepted for exchange pursuant to the Offer will be made only after timely
receipt by the Exchange Agent of certificates for Shares (and Rights, if
applicable) (or timely confirmation of a book-entry transfer of such securities
into the Exchange Agent's account at a Book-Entry Transfer Facility as described
above), properly completed and duly executed Letter(s) of Transmittal (or
facsimile(s) thereof), or an Agent's Message in connection with a book-entry
transfer, and any other required documents. Accordingly, tendering Safety-Kleen
Shareholders may be paid at different times depending upon when certificates for
Shares (and Rights, if applicable) or confirmations of book-entry transfers of
such Shares (and Rights, if applicable) are actually received by the Exchange
Agent.
 
     By executing a Letter of Transmittal as set forth above, the tendering
Safety-Kleen Shareholder irrevocably appoints designees of Laidlaw Environmental
as such shareholder's attorneys-in-fact and proxies, each with full power of
substitution, to the full extent of such shareholder's rights with respect to
the Shares (and Rights, if applicable) tendered by such shareholder and accepted
for exchange by Laidlaw Environmental and with respect to any and all other
Shares (and Rights, if applicable) and other securities issued or issuable in
respect of the Shares (and Rights, if applicable) on or after             ,
1997. Such appointment is effective, and voting rights will be affected, when
and only to the extent that Laidlaw Environmental deposits the shares of Laidlaw
Environmental Common Stock and Cash Consideration for Shares tendered by such
shareholder with the Exchange Agent. All such proxies shall be considered
coupled with an interest in the tendered Shares and therefore shall not be
revocable. Upon the effectiveness of such appointment, all prior proxies given
by such shareholder will be revoked, and no subsequent proxies may be given
(and, if given, will not be deemed effective). Laidlaw Environmental's designees
will, with respect to the Shares for which the appointment is effective, be
empowered, among other things, to exercise all voting and other rights of such
shareholder as they, in their sole discretion, deem proper at any annual,
special or adjourned meeting of Safety-Kleen Shareholders, by written consent in
lieu of any such meeting or otherwise. Laidlaw Environmental reserves the right
to require that, in order for Shares to be deemed validly tendered, immediately
upon Laidlaw Environmental's exchange of such Shares, Laidlaw Environmental must
be able to exercise full voting rights with respect to such Shares.
 
     All questions as to the validity, form, eligibility (including time of
receipt) and acceptance for exchange of any tender of Shares (and Rights, if
applicable) will be determined by Laidlaw Environmental, in its sole discretion,
which determination shall be final and binding. Laidlaw Environmental reserves
the absolute right to reject any and all tenders of Shares (and Rights, if
applicable) determined by it not to be in proper form or the acceptance of or
exchange for which may, in the opinion of Laidlaw Environmental's counsel, be
unlawful. Laidlaw Environmental also reserves the absolute right to waive any of
the conditions of the Offer (other than the Laidlaw Environmental Stockholder
Approval Condition, the Regulatory Approval Condition and the condition relating
to the effectiveness of the Registration Statement), or any defect or
irregularity in the tender of any Shares (and Rights, if applicable). No tender
of Shares (and Rights, if applicable) will be deemed to have been validly made
until all defects and irregularities in tenders of Shares have been cured or
waived. Neither Laidlaw Environmental, the Exchange Agent, the Information
Agent, the Dealer Manager nor any other person will be under any duty to give
notification of any defects or irregularities in the tender of any Shares or
will incur any liability for failure to give any such notification. Laidlaw
Environmental's interpretation of the terms and conditions of the Offer
(including the Letter of Transmittal and instructions thereto) will be final and
binding.
 
                                       27
<PAGE>   36
 
     The tender of Shares and Rights (if any) pursuant to any of the procedures
described above will constitute a binding agreement between the tendering
Safety-Kleen Shareholder and Laidlaw Environmental upon the terms and subject to
the conditions of the Offer.
 
CERTAIN FEDERAL INCOME TAX CONSEQUENCES
 
     The following is a summary of certain federal income tax consequences of
the Offer and the Merger and represents the opinion of Katten Muchin & Zavis,
counsel to Laidlaw Environmental. It does not address any tax consequences of
the Offer and the Merger to persons who exercise appraisal rights, if any, to
the Merger. This summary may not apply to certain classes of persons subject to
special tax treatment, such as foreign persons, insurance companies, tax-exempt
organizations, financial institutions, dealers in securities, persons who
acquired Shares pursuant to the exercise of employee stock options or rights or
otherwise as compensation and persons who hold Shares as part of a straddle or
conversion transaction. This summary is based upon laws, regulations, rulings
and decisions, all of which are subject to change (possibly with retroactive
effect), and no ruling has been or will be requested from the Internal Revenue
Service (the "Service") on the tax consequences of the Offer and the Merger.
 
     The exchange of Shares for Laidlaw Environmental Common Stock and cash
pursuant to the Offer and Merger will be a taxable transaction for U.S. federal
income tax purposes and may also be taxable under applicable state, local and
foreign tax laws. In general, for U.S. federal income purposes, each
Safety-Kleen Shareholder will realize gain or loss equal to the difference
between (x) the amount of cash and the fair market value of the shares Laidlaw
Environmental Common Stock received and (y) the Safety-Kleen Shareholder's
adjusted tax basis in the Shares exchanged therefor. Such gain or loss will be
capital gain or loss if the Safety-Kleen Shareholder holds the Shares as a
capital asset and will be long-term gain or loss if the Safety-Kleen
Shareholder's holding period for the Shares is more than eighteen months. The
Safety-Kleen Shareholder will have a tax basis in the Laidlaw Environmental
Common Stock received equal to the fair market value thereof and the
shareholder's holding period for the Laidlaw Environmental Common Stock will
begin on the day following the date of the exchange.
 
     If the Board of Safety-Kleen agrees to the Offer, the Merger may be
restructured as a partially tax-free merger for U.S. federal income tax
purposes. If the Merger is structured to qualify as a partially tax-free merger
for U.S. federal income tax purposes, the material federal income tax
consequences to the Safety-Kleen Shareholders will be as follows:
 
          1. No gain or loss will be recognized or be included in the income of
     a Safety-Kleen Shareholder to the extent that a Safety-Kleen Shareholder
     exchanges Shares for Laidlaw Environmental Common Stock in the Merger.
 
          2. A Safety-Kleen Shareholder will recognize taxable income to the
     extent that the Safety-Kleen Shareholder receives cash in the Merger in an
     amount equal to the lesser of (i) the amount of cash received in the
     Merger, or (ii) an amount equal to the difference between (a) the amount of
     cash and the fair market value of the shares of Laidlaw Environmental
     Common Stock received and (b) the Safety-Kleen Shareholder's adjusted tax
     basis in the Shares exchanged therefor. Such gain generally will be
     long-term capital gain if the Safety-Kleen Shareholder's holding period for
     the shares is more than eighteen months.
 
          3. Assuming that a Safety-Kleen Shareholder holds the Shares as a
     capital asset, such Shareholder's holding period for the Laidlaw
     Environmental Common Stock received in the Merger will include the period
     during which such Shares were held; and
 
          4. The tax basis of the Laidlaw Environmental Common Stock received in
     the Merger will be equal to the tax basis a Safety-Kleen Shareholder has in
     Shares immediately before the Merger, decreased by the amount of cash
     received in the Merger, and increased by the amount of gain recognized by a
     Safety-Kleen Shareholder in the Merger.
 
     This summary relates to some of the anticipated federal income tax
consequences of the Offer and the Merger. The analysis contain herein does not
address state, local or foreign tax consequences of the Offer and
 
                                       28
<PAGE>   37
 
the Merger, and is not intended as a substitute for careful tax planning,
particularly since certain of the tax consequences of the Offer and the Merger
will not be the same for all taxpayers. Consequently, each holder should consult
such holder's own tax advisor as to the specific tax consequences of the Offer
and the Merger to such holder.
 
EFFECT OF OFFER ON MARKET FOR SHARES; REGISTRATION UNDER THE EXCHANGE ACT
 
     The exchange of Shares pursuant to the Offer will reduce the number of
holders of Shares and the number of Shares that might otherwise trade publicly
and, depending upon the number of Shares so purchased, could adversely affect
the liquidity and market value of the remaining Shares held by the public.
 
     The Shares are listed and traded on the NYSE. Depending upon the number of
Shares acquired pursuant to the Offer, following consummation of the Offer, the
Shares may no longer meet the requirements of such exchanges for continued
listing. For example, published guidelines of the NYSE indicate that the NYSE
would consider delisting the outstanding Shares if, among other things, (i) the
number of publicly held Shares (exclusive of holdings of officers, directors and
members of their immediate families and other concentrated holdings of 10% or
more) should fall below 600,000, (ii) the number of record holders of 100 or
more Shares should fall below 1,200 or (iii) the aggregate market value of
publicly held Shares should fall below $5 million. According to the Safety-Kleen
Form 10-Q for quarter ended September 6, 1997, there were, as of September 6,
1997, 58,400,729 Shares outstanding. As of December 28, 1996 there were 8,042
holders of record of Shares.
 
     If the NYSE were to delist the Shares, the market therefor could be
adversely affected. It is possible that the Shares would be traded on other
securities exchanges or in the over-the-counter market, and that price
quotations would be reported by such exchanges, or through the National
Association of Securities Dealers, Inc., Automated Quotations System ("Nasdaq")
or by other sources. The extent of the public market for the Shares and the
availability of such quotations would, however, depend upon the number of
holders and/or the aggregate market value of the Shares remaining at such time,
the interest in maintaining a market in the Shares on the part of securities
firms, the possible termination of registration of Shares under the Exchange
Act, as described below, and other factors.
 
     The Shares are presently "margin securities" under the regulations of the
Federal Reserve Board, which has the effect, among other things, of allowing
brokers to extend credit on the collateral of such Shares. Depending on factors
similar to those described above with respect to listing and market quotations,
following consummation of the Offer the Shares may no longer constitute "margin
securities" for the purposes of the Federal Reserve Board's margin regulations,
in which event the Shares would be ineligible as collateral for margin loans
made by brokers.
 
     The Shares are currently registered under the Exchange Act. Such
registration may be terminated by Safety-Kleen upon application to the
Commission if the outstanding Shares are not listed on a national securities
exchange and if there are fewer than 300 holders of record of Shares.
Termination of registration of the Shares under the Exchange Act would reduce
the information required to be furnished by Safety-Kleen to its shareholders and
to the Commission and would make certain provisions of the Exchange Act, such as
the short-swing profit recovery provisions of Section 16(b) and the requirement
of furnishing a proxy statement in connection with shareholders' meetings
pursuant to Section 14(a) and the related requirement of furnishing an annual
report to shareholders, no longer applicable with respect to the Shares.
Furthermore, the ability of "affiliates" of Safety-Kleen and persons holding
"restricted securities" of Safety-Kleen to dispose of such securities pursuant
to Rule 144 under the Securities Act may be impaired or eliminated. If
registration of the Shares under the Exchange Act were terminated, the Shares
would no longer be eligible for Nasdaq reporting or for continued inclusion on
the Federal Reserve Board's list of "margin securities."
 
     The Rights currently are registered under the Exchange Act and are listed
on the NYSE, but currently are attached to the outstanding Shares and are not
separately transferable. If the Distribution Date occurs, the Rights may become
transferable apart from the Shares, unless previously redeemed. If the Rights
are not redeemed or invalidated and Laidlaw Environmental waives the Rights Plan
Condition, then the foregoing
 
                                       29
<PAGE>   38
 
discussion with respect to the effect of the Offer on the Shares would be
similarly applicable to the Rights (although the continued listing criteria are
different).
 
PURPOSE OF THE OFFER; THE MERGER
 
     The purpose of the Offer is to enable Laidlaw Environmental to obtain
control of, and ultimately the entire equity interest in, Safety-Kleen.
 
     The Offer, as the first step in the acquisition of Laidlaw Environmental,
is intended to facilitate the acquisition of all Shares. Laidlaw Environmental
presently intends, following consummation of the Offer, to propose and seek to
have Safety-Kleen effect the Merger. In the Merger, each outstanding Share
(other than Shares owned by Laidlaw Environmental or any of its affiliates,
Shares held in the treasury of Safety-Kleen or by any subsidiary of Safety-Kleen
and Shares owned by Safety-Kleen Shareholders who perfect dissenter rights under
Wisconsin law) would be canceled in exchange for the right to receive the Offer
Consideration. Assuming the conditions to the Offer are satisfied or waived and
Laidlaw Environmental consummates the Offer, Laidlaw Environmental would
consummate the Merger without any additional vote of the holders of Laidlaw
Environmental Common Stock or the vote of any other Safety-Kleen Shareholder.
 
     It is Laidlaw Environmental's current intention to consummate the Offer as
soon as the conditions to the Offer are satisfied and to consummate the Merger
in               .
 
CONDITIONS OF THE OFFER
 
     Minimum Tender Condition.  The Offer is conditioned upon, among other
things, there being validly tendered and not withdrawn prior to the Expiration
Date a number of Shares which, together with Shares owned by Laidlaw
Environmental and its affiliates, will constitute at least two-thirds of the
total number of outstanding Shares on a fully diluted basis (as though all
options or other securities convertible into or exercisable or exchangeable for
Shares, other than the Rights, had been so converted, exercised or exchanged) as
of the date the Shares are accepted for exchange by Laidlaw Environmental
pursuant to the Offer. Based upon information set forth in the Safety-Kleen Form
10-Q for quarter ended September 6, 1997, as of September 6, 1997, there were
58,400,729 Shares outstanding. As of October 29, 1997, Laidlaw Environmental
owned 601,100 Shares, or approximately 1.03% of the outstanding Shares. Based on
the foregoing, Laidlaw Environmental believes that the Minimum Tender Condition
would be satisfied if at least an aggregate of 42,302,789 Shares (or 66 2/3%) of
the Shares expected to be outstanding immediately prior to the consummation of
the Offer had been validly tendered pursuant to the Offer and not withdrawn.
Laidlaw Environmental reserves the right (but shall not be obligated), subject
to the rules and regulations of the Commission, to waive or amend the Minimum
Tender Condition and to exchange fewer than such number of Shares as would
satisfy the Minimum Tender Condition pursuant to the Offer; provided, however,
that, in the event of such waiver or amendment, the Offer shall expire no sooner
than ten business days from the date of such waiver or amendment.
 
     Laidlaw Environmental Stockholder Approval Condition.  The Offer is
conditioned, among other things, upon the satisfaction of the Laidlaw
Environmental Stockholder Approval Condition. The authorization to increase the
number of shares of Laidlaw Environmental Common Stock to 750,000,000 must be
approved by a majority of the outstanding shares of Laidlaw Environmental Common
Stock. The issuance of Laidlaw Environmental Common Stock pursuant to the Offer
and the Merger must be approved by the holders of a majority of the shares of
Laidlaw Environmental Common Stock voted at a meeting of such holders at which
the total number of votes cast represents over 50% in interest of all shares of
Laidlaw Environmental Common Stock outstanding on the applicable record date.
Laidlaw Environmental intends to seek such approvals at the Laidlaw
Environmental Special Meeting to be held on or about             , 1997.
Laidlaw, which presently owns 67% of Laidlaw Environmental Common Stock, intends
to vote its shares to approve the increase in the number of shares of Laidlaw
Environmental Common Stock and the issuance of Laidlaw Environmental Common
Stock pursuant to the Offer and the Merger.
 
     Rights Plan Condition.  The Offer is conditioned upon, among other things,
the satisfaction of the Rights Plan Condition. The Rights Plan Condition may be
satisfied in several ways, including the current
 
                                       30
<PAGE>   39
 
Safety-Kleen Board may (a) amend the Rights Agreement so that the Rights would
not be triggered by the Offer and the Merger or (b) redeem the Rights.
 
     Set forth below is certain additional information concerning the Rights
Agreement. This information is based upon information included in Safety-Kleen's
publicly filed documents.
 
     On November 9, 1988, the Safety-Kleen Board declared a dividend of one
common share purchase right ("Right") on each outstanding Share payable to
Safety-Kleen Shareholders of record on November 21, 1988 (the "Record Date").
Each Right entitles the holder thereof to buy one Share at an exercise price of
$73.33, subject to adjustment. The terms of the Rights are set forth in the
Rights Agreement. The following description of the Rights does not purport to be
complete and is qualified in its entirety by reference to the Rights Agreement
which is filed as an exhibit to the Safety-Kleen Registration Statement on Form
8-A dated December 28, 1988, as amended on August 27, 1990.
 
     Until the earlier to occur of (i) 10 days following a public announcement
that a person or group of affiliated or associated persons (an "Acquiring
Person") has acquired beneficial ownership of 20% or more of the outstanding
Shares or (ii) 10 business days (or such later date as may be determined by
action of the Safety-Kleen Board prior to such time as any person or group
becomes an Acquiring Person) following the commencement of, or announcement of
an intention to make, a tender offer or exchange offer the consummation of which
would result in the beneficial ownership by a person or group of 20% or more of
such outstanding Shares (the earlier of such dates being called the
"Distribution Date"), the Rights will be evidenced by Share certificates.
 
     The Rights Agreement provides that, until the Distribution Date, the Rights
will be transferred with and only with the Shares. Until the Distribution Date
(or earlier redemption or expiration of the Rights), new Share certificates
issued after the Record Date will contain a notation incorporating the Rights
Agreement by reference. Until the Distribution Date (or earlier redemption or
expiration of the Rights), the surrender for transfer of any certificates for
Shares will also constitute the transfer of the Rights associated with the
Shares represented by such certificate. As soon as practicable following the
Distribution Date, separate certificates evidencing the Rights ("Right
Certificates") will be mailed to holders of record of the Shares as of the close
of business on the Distribution Date and such separate Right Certificate alone
will evidence the Rights.
 
     The Rights are not exercisable until the Distribution Date. The Rights will
expire on November 21, 1998 (the "Final Expiration Date"), unless the Rights are
earlier redeemed by Safety-Kleen, as described below.
 
     A person shall not be deemed to have become an "Acquiring Person" for any
purposes if, as determined in good faith by the Safety-Kleen Board, he
inadvertently becomes an Acquiring Person and promptly thereafter divests
himself of sufficient Shares to no longer be an "Acquiring Person".
 
     The Purchase Price payable, and the number of Shares or other securities or
property issuable, upon exercise of the Rights are subject to adjustment from
time to time to prevent dilution (i) in the event of a stock dividend on, or a
subdivision, combination or reclassification of, the Shares, (ii) upon the grant
to holders of the Shares of certain rights or warrants to subscribe for or
purchase Shares at a price, or securities convertible into Shares with a
conversion price, less than the then current market price of the Shares or (iii)
upon the distribution to holders of the Shares of evidences of indebtedness or
assets (excluding regular periodic cash dividends paid out of earnings or
retained earnings or dividends payable in Shares) or of subscription rights or
warrants (other than those referred to above). With certain exceptions, no
adjustment in the Purchase Price will be required until cumulative adjustments
require an adjustment of at least 1% in such Purchase Price. No fractional
Shares will be issued and in lieu thereof, an adjustment in cash will be made
based on the market price of the Shares on the last trading day prior to the
date of exercise.
 
     If any person becomes an Acquiring Person, each holder of a Right, other
than Rights beneficially owned by the Acquiring Person (which will be void),
will have the right to receive upon exercise of such Right that number of Shares
having a market value of two times the exercise price of the Right.
 
     In addition, if Safety-Kleen is acquired in a merger or other business
combination transaction or 50% or more of its consolidated assets or earning
power are sold, proper provision will be made so that each holder of a
 
                                       31
<PAGE>   40
 
Right will thereafter have the right to receive, upon the exercise thereof at
the then current exercise price of the Right, that number of shares of common
stock of the acquiring company which at the time of such transaction will have a
market value of two times the exercise price of the Right.
 
     At any time after the acquisition by a person or group of affiliated or
associated persons of beneficial ownership of 20% or more of the outstanding
Shares and prior to the acquisition by such person or group of 50% or more of
the outstanding Shares, the Safety-Kleen Board may exchange the Rights (other
than Rights owned by such person or group which have become void), in whole or
in part, at an exchange ratio of one Share per Right (subject to adjustment).
 
     At any time prior to the acquisition by a person or group of affiliated or
associated persons of beneficial ownership of 20% or more of the outstanding
Shares, the Safety-Kleen Board may redeem the Rights in whole, but not in part,
at a price of $.01 per Right, subject to adjustment (the "Redemption Price").
The redemption of the Rights may be made effective at such time, on such basis
and with such conditions as the Safety-Kleen Board in its sole discretion may
establish; provided, however, that no redemption will be permitted or required
after the acquisition by any person or group of affiliated or associated persons
of beneficial ownership of 20% or more of the outstanding Shares. Immediately
upon any redemption of the Rights, the right to exercise the Rights will
terminate and the only right of the holders of the Rights will be to receive the
Redemption Price.
 
     The terms of the Rights may be amended by the Safety-Kleen Board without
the consent of the holders of the Rights including an amendment to lower the
threshold for exercisability of the Rights from 20% to not less than the greater
of (i) any percentage greater than the largest percentage of the outstanding
Shares then known to Safety-Kleen to be beneficially owned by any person or
group of affiliated or associates persons and (ii) 10%, except that from and
after such time as any person becomes an Acquiring Person no such amendment may
adversely affect the interests of the holders of the Rights.
 
     Until a Right is exercised, the holder thereof, as such, will have no
rights as a shareholder of Safety-Kleen including, without limitation, the right
to vote or to received dividends.
 
     The Rights have certain anti-takeover effects. The Rights will cause
substantial dilution to a person or group of persons that attempts to acquire
Safety-Kleen in a manner which causes the Rights to become exercisable.
 
     Wisconsin Statutory Conditions.  The Offer is conditioned upon, among other
things, Laidlaw Environmental being satisfied, in its sole discretion, either
that the provisions of Section 180.1141 and Section 180.1150 of the Wisconsin
Statutes are inapplicable to Laidlaw Environmental, LES Acquisition and the
transactions contemplated herein, or that (i) full voting rights for all Shares
to be acquired by Laidlaw Environmental and LES Acquisition pursuant to the
offer have been restored by approval of the shareholders of Safety-Kleen
pursuant to the Wisconsin Statutes, and (ii) the Wisconsin Statutes will not
prohibit for any period of time the consummation of the Merger or any other
"business combination" (as defined in such statutes) involving Safety-Kleen and
Laidlaw Environmental or LES Acquisition, or any of their respective affiliates.
 
     Section 180.1141 of the Wisconsin Statutes ("Wisconsin Business Combination
Statute") prohibits certain business combinations involving a Wisconsin
"resident domestic corporation" (as defined in Section 180.1140(9)(a) of the
Wisconsin Statutes). This portion of the Wisconsin Statutory Condition may be
satisfied by (i) the Safety-Kleen Board of Directors approving the Offer for the
purposes of Section 180.1141 prior to the consummation of the offer or (ii)
Laidlaw Environmental being satisfied, in its sole discretion, that Safety-Kleen
is not a "resident domestic corporation" as defined in Section 180.1140(9)(a) of
the Wisconsin Statutes. For a Summary of the Business Combination Statute, see
"Comparison of the Rights of Holders of Shares and Laidlaw Environmental Common
Stock -- Comparison of Delaware and Wisconsin Law-Differences -- Anti-Takeover
Statutes."
 
     Section 180.1150 of the Wisconsin Statutes ("Wisconsin Control Share
Statute") limits the voting power of shares of a "resident domestic corporation"
(as defined in Section 180.1150(1)(c)) of the Wisconsin Statutes) that are held
by certain persons holding in excess of 20% of the voting power of such shares
in the
 
                                       32
<PAGE>   41
 
election of the directors. This portion of the Wisconsin Statutory Condition may
be satisfied by (i) the affirmative vote of a majority of the voting power of
shares represented and entitled to vote at a special meeting of Safety-Kleen
Shareholders to restore regular voting power of the Shares to be acquired by
Laidlaw Environmental, or (ii) Laidlaw Environmental being satisfied, in its
sole discretion, that the provisions of the Wisconsin Control Share Acquisition
Statute do not in any way restrict Laidlaw Environmental's and LES Acquisition's
ability to consummate the Merger. For a summary of the Wisconsin Control Share
Acquisition Statute, see "Comparison of the Rights of Holders of Shares and
Laidlaw Environmental Common Stock -- Comparison of Delaware and Wisconsin
Law-Differences -- Anti-Takeover Statutes."
 
     Laidlaw Environmental and LES Acquisition are requesting that Safety
Kleen's Board of Directors take appropriate action so that the Wisconsin
Business Combination Law is not applicable to the acquisition of Shares pursuant
to the Offer or a subsequent business combination involving Laidlaw
Environmental or LES Acquisition and Safety-Kleen. There can be no assurance
that the Safety-Kleen Board of Directors will do so.
 
     The Wisconsin Statutes contain certain other provisions restricting certain
business combinations and other transactions with significant shareholders under
certain circumstances. Section 180-1150 of the Wisconsin Statutes limits, under
certain circumstances, the voting power of a shareholder that holds in excess of
20% of the voting power of certain corporations. See "Comparison of Delaware and
Wisconsin Law -- Differences."
 
     Regulatory Approval Condition.  The Offer is conditioned upon, among other
things, all regulatory approvals required to consummate the Offer (the
"Requisite Regulatory Approvals") having been obtained and remaining in full
force and effect, all statutory waiting periods in respect thereof having
expired and no such approval containing any conditions or restrictions which the
Laidlaw Environmental Board determines will or reasonably could be expected to
materially impair the strategic and financial benefits expected to result from
the Offer. Laidlaw Environmental will use its reasonable best efforts to obtain
the Requisite Regulatory Approvals. As described below, applications and notices
seeking the Requisite Regulatory Approvals have been or will be promptly filed.
The Offer cannot proceed in the absence of the Requisite Regulatory Approvals.
Although no assurances can be given, Laidlaw Environmental anticipates that it
will receive all regulatory approvals on a timely basis.
 
     Antitrust.  Under the HSR Act, and the Rules that have been promulgated
thereunder, certain acquisition transactions may not be consummated unless
certain information has been furnished to the Antitrust Division of the
Department of Justice ("DOJ") and the Federal Trade Commission ("FTC") and
certain waiting period requirements have been satisfied. The acquisition of
Shares by Laidlaw Environmental pursuant to the Offer is subject to the
expiration of the statutory waiting period under the HSR Act.
 
     Laidlaw intends to file with the DOJ and the FTC a Hart-Scott-Rodino
Notification and Report Form (the "Notification Form") with respect to the
Offer. Under the applicable provisions of the HSR Act, the purchase of Shares
under the Offer could not be consummated until the expiration of a 30-day
waiting period following the filing of the Notification Form by Laidlaw, unless
Laidlaw receives a request for additional information or documentary material or
the DOJ and the FTC terminate the waiting period thereto. If, within such 30-day
waiting period, either the DOJ or the FTC requests additional information or
material from Laidlaw and/or Safety-Kleen concerning the Offer, the waiting
period will be extended for an additional 20 days after Laidlaw has
substantially complied with such request. Only one extension of the waiting
period pursuant to a request for additional information is authorized by the HSR
Act. Thereafter, the waiting period may be extended only by court order or with
the consent of Laidlaw.
 
     Laidlaw Environmental will not accept for exchange Shares tendered pursuant
to the Offer unless and until the waiting period requirements imposed by the HSR
Act with respect to the Offer have been satisfied.
 
     Federal and state antitrust enforcement agencies frequently scrutinize,
under the antitrust laws, transactions such as Laidlaw Environmental's
acquisition of Shares pursuant to the Offer. At any time before or after Laidlaw
Environmental's acquisition of Shares, any such agency could take such action
under the antitrust laws as it deems necessary or desirable in the public
interest, including seeking to enjoin the acquisition of Shares pursuant to the
Offer or otherwise or seeking divestiture of Shares acquired by Laidlaw
 
                                       33
<PAGE>   42
 
Environmental or divestiture of substantial assets of Laidlaw Environmental
and/or Safety-Kleen. Private parties may also bring legal action under the
antitrust laws under certain circumstances.
 
     Based upon an examination of publicly available information relating to the
businesses in which both Laidlaw Environmental and Safety-Kleen are engaged,
Laidlaw Environmental believes that the Offer will not violate the antitrust
laws. Nevertheless, there can be no assurance that a challenge to the Offer on
antitrust grounds will not be made or that, if such a challenge is made, Laidlaw
Environmental will prevail.
 
     The Antitrust Division and the FTC are referred to herein as the
"Regulatory Commissions."
 
     Canadian Competition Act.  Under the Canadian Federal Competition Act (the
"Competition Act"), acquisition transactions, insofar as they relate to the
acquisition of such Canadian subsidiaries, qualify as a "merger" if they are of
sufficient size to be subject to the notification and waiting period
requirements of the Competition Act. The Competition Act is administered by the
Canadian Director of Investigation and Research appointed under the Competition
Act (the "Competition Act Director"). Laidlaw Environmental believes that the
proposed transaction requires notification and intends to file the required
information with the Competition Act Director.
 
     Under separate "merger" provisions of the Competition Act, which operate
independently of its notification and waiting period requirements, if an
acquisition is likely to give rise to a substantial prevention or lessening of
competition in a market in Canada, the Competition Act Director may apply for a
remedial order (such as an injunction or an order to divest specified assets or
securities) to be issued by a quasi-judicial body (the "Competition Tribunal").
 
     Europe.  The acquisition of Shares by Laidlaw Environmental pursuant to the
Offer is subject to prior notification requirements of several of the member
countries of the European Union in which Safety-Kleen operates. Based on the
limited information concerning Safety-Kleen that is available to Laidlaw
Environmental, filings will be necessary in the Republic of Ireland and Federal
Republic of Germany. In addition, filings may also be necessary in Italy and
Belgium. The necessary filings must be made in sufficient time to allow the
passing of a one month waiting period before Laidlaw Environmental's acquisition
of shares pursuant to the Offer may be completed. No pre-merger notification
under the European Economic Community's Merger Control Regulation is required
for the proposed transaction.
 
     General.  Except as set forth above, based upon an examination of publicly
available information filed by Safety-Kleen with the Commission and other
publicly available information with respect to Safety-Kleen, Laidlaw
Environmental is not aware of (a) any license or regulatory permit which appears
to be material to the business of Safety-Kleen and its subsidiaries, taken as a
whole, and which is likely to be adversely affected by Laidlaw Environmental's
acquisition of Shares pursuant to the Offer or (b) any approval or other action
by any state, federal or foreign governmental administrative or regulatory
agency or authority that would be required prior to the acquisition of Shares
pursuant to the Offer. Laidlaw Environmental presently intends to take such
actions with respect to any approvals as will enable it to consummate the Offer.
In this regard, Laidlaw Environmental expressly reserves the right to challenge
the validity and applicability of any state, foreign or other statutes or
regulations purporting to require approval of the consummation of the Offer.
 
     There can be no assurance that any license, permit, approval or other
action, if needed, would be obtained, or would be obtained without substantial
conditions, or, if so obtained, when it would be obtained, or that adverse
consequences might not result to Safety-Kleen, Laidlaw Environmental or their
respective businesses in the event of adverse regulatory action or inaction.
 
     THE OFFER IS CONDITIONED UPON, AMONG OTHER THINGS, LAIDLAW ENVIRONMENTAL
HAVING RECEIVED ALL NECESSARY OR DESIRABLE GOVERNMENTAL AND REGULATORY APPROVALS
AND CONSENTS FOR THE ACQUISITION OF SHARES PURSUANT TO THE OFFER AND THE OTHER
TRANSACTIONS CONTEMPLATED HEREIN, INCLUDING APPROVALS AND CONSENTS FROM THE
REGULATORY COMMISSIONS AND SUCH APPROVALS AND CONSENTS HAVING BECOME FINAL
ORDERS AND SUCH FINAL ORDERS NOT HAVING IMPOSED TERMS OR CONDITIONS WHICH, IN
THE AGGREGATE, WOULD HAVE OR, INSOFAR AS REASONABLY CAN BE FORESEEN, COULD HAVE
A
 
                                       34
<PAGE>   43
 
MATERIAL ADVERSE EFFECT ON THE BUSINESS, ASSETS, FINANCIAL CONDITION, OR RESULTS
OF OPERATIONS OF LAIDLAW ENVIRONMENTAL, SAFETY-KLEEN AND THEIR RESPECTIVE
SUBSIDIARIES TAKEN AS A WHOLE.
 
     Certain Other Conditions of the Offer.  Notwithstanding any other provision
of the Offer and subject to any applicable rules and regulations of the
Commission, including Rule 14e-1(c) under the Exchange Act (relating to Laidlaw
Environmental's obligation to exchange or return tendered Shares promptly after
the termination or withdrawal of the Offer), Laidlaw Environmental shall not be
required to accept for exchange or exchange any Shares, may postpone the
acceptance for exchange or exchange for tendered Shares and may, in its sole
discretion, terminate or amend the Offer as to any Shares not then exchanged if
at the Expiration Date any of the Offer Conditions have not been satisfied or
waived or if on or after the date of this Prospectus and on or prior to the
Expiration Date any of the following events shall not have occurred:
 
          (a) The shares of Laidlaw Environmental Common Stock (and accompanying
     Rights) which shall be issued to the Safety-Kleen Shareholders in the Offer
     and the Merger shall have been authorized for listing on the NYSE, subject
     to official notice of issuance.
 
          (b) The Registration Statement shall have become effective under the
     Securities Act, and no stop order suspending the effectiveness of the
     Registration Statement shall have been issued and no proceedings for that
     purpose shall have been initiated or threatened by the Commission.
 
          (c) No order, injunction or decree issued by any court or agency of
     competent jurisdiction or other legal restraint or prohibition preventing
     the consummation of the Offer and/or the Merger or any of the other
     transactions contemplated by this Prospectus shall be in effect. No
     statute, rule, regulation, order, injunction or decree shall have been
     enacted, entered, promulgated or enforced by any court, administrative
     agency or commission or other governmental authority or instrumentality
     which prohibits, restricts or makes illegal the consummation of the Offer
     and/or the Merger.
 
          (d) There shall not have occurred or been threatened (i) any general
     suspension of trading in, or limitation on times or prices for, securities
     on any national securities exchange or in the over-the-counter market in
     the United States, (ii) any significant adverse change in interest rates,
     the financial markets or major stock exchange indices in the United States
     or abroad or in the market price of Shares, including, without limitation,
     a decline of at least 10% in either the Dow Jones Average of Industrial
     Stocks or the Standard & Poor's 500 Index from that existing at the close
     of business on                , 1997, (iii) any change in the general
     political, market, economic, regulatory or financial conditions in the
     United States or abroad that could, in the reasonable judgment of Laidlaw
     Environmental, have a material adverse effect upon the business,
     properties, assets, liabilities, capitalization, stockholders' equity,
     condition (financial or otherwise), operations, licenses or franchises,
     results of operations or prospects of Safety-Kleen or any of its
     subsidiaries or the trading in, or value of, the Shares, (iv) any material
     change in United States currency exchange rates or any other currency
     exchange rates or a suspension of, or limitation on, the markets therefor,
     (v) a declaration of a banking moratorium or any suspension of payments in
     respect of banks in the United States, (vi) any limitation (whether or not
     mandatory) by any government, domestic, foreign or supranational, or
     governmental entity on, or other event that in the reasonable judgment of
     Laidlaw Environmental might affect, the extension of credit by banks or
     other lending institutions, (vii) a commencement of a war or armed
     hostilities or other national or international calamity directly or
     indirectly involving the United States or (viii) in the case of any of the
     foregoing existing at the time of the commencement of the Offer, a material
     acceleration or worsening thereof.
 
     The foregoing conditions are for the sole benefit of Laidlaw Environmental
and may be asserted by Laidlaw Environmental regardless of the circumstances
giving rise to any such conditions (including any action or inaction by Laidlaw
Environmental) or may be waived by Laidlaw Environmental in whole or in part
(other than the Laidlaw Environmental Stockholder Approval Condition, the
Regulatory Approval Condition and the condition relating to effectiveness of the
Registration Statement). The determination as to whether any condition has been
satisfied shall be in the sole judgment of Laidlaw Environmental and will be
final and binding on all parties. The failure by Laidlaw Environmental at any
time to exercise any of the foregoing rights shall not be deemed a waiver of any
such right, and each such right shall be deemed a continuing right which
 
                                       35
<PAGE>   44
 
may be asserted at any time and from time to time. Notwithstanding the fact that
Laidlaw Environmental reserves the right to assert the failure of a condition
following acceptance for exchange but prior to exchange in order to delay
exchange or cancel its obligation to exchange properly tendered Shares, Laidlaw
Environmental will either promptly exchange such Shares or promptly return such
Shares.
 
SOURCE AND AMOUNT OF FUNDS
 
     Laidlaw Environmental estimates that the total amount of funds required
pursuant to the Offer to pay for the Cash Consideration in connection with the
exchange of all Shares outstanding on a fully diluted basis, to refinance
Laidlaw Environmental's existing bank debt, to refinance Safety-Kleen's existing
and outstanding indebtedness and to pay fees and expenses related to the Offer
will be approximately $1.5 billion. See "The Offer -- Fees and Expenses."
Laidlaw Environmental plans to obtain the outside funds necessary to finance the
Cash Consideration pursuant to credit facilities to be arranged by TD Securities
(USA), Inc. ("TDSI"). Laidlaw Environmental has received a written financing
commitment (the "Commitment Letter") from TDSI and Toronto-Dominion Bank ("TD")
to provide senior secured credit facilities in the aggregate principal amount of
up to $1.8 billion (the "Senior Credit Facilities"). The terms of the definitive
agreement for the Senior Credit Facilities (the "Loan Agreement") have not yet
been finalized. The following is a summary of the anticipated principal terms of
the Senior Credit Facilities based upon the Commitment Letter. This summary is
subject to finalization of the Loan Agreement and is qualified in its entirety
by reference to the Commitment Letter, which is filed as Exhibit   hereto.
 
     The Credit Facilities will consist of four parts: (i) a $400,000,000 6-year
Senior Secured Revolving Credit Facility with a $200,000,000 letter of credit
sublimit (the "Revolving Credit Facility" or "Facility A"), (ii) a $500,000,000
6-year Senior Secured Amortizing Term Loan ("Facility B"), (iii) a $450,000,000
Minimally Amortizing 7-year Senior Secured Term Facility ("Facility C") and (iv)
a $450,000,000 Minimally Amortizing 8-year Senior Secured Term Loan ("Facility
D"); (Facility B, Facility C and Facility D, collectively, the "Term Loans").
The Credit Facilities will be secured by all of the tangible assets of the
combined companies to the extent required by the syndicate of banks and other
financial institutions (collectively, the "Lenders") acceptable to Laidlaw
Environmental and the Agent that will make the loans pursuant to the Credit
Facilities. All of the capital stock of Laidlaw Environmental's subsidiaries,
including the acquired Safety-Kleen subsidiaries, will be pledged as part of
such security for the Credit Facilities, and such subsidiaries will guaranty the
obligations of Laidlaw Environmental to the Lenders. The Term Loans will be
drawn in full on the closing date. The Revolving Credit Facility will be
available commencing on the closing date at which time $200,000,000 will be
available for letters of credit and $250,000,000 will be available for loans,
subject to an aggregate maximum of $400,000,000.
 
     Facility A will have no scheduled amortization. The Term Loans will require
aggregate principal repayments of $84 million in each of years 1, 2, 3 and 4,
$109 million in each of years 5 and 6, $428 million in year 7 and $419 million
in year 8.
 
     Borrowings under the Senior Credit Facilities will bear interest at a
floating rate based upon, at LES Acquisition's option, (i) the higher of the TD
prime rate and the federal funds rate plus 0.50% per annum, or (ii) the London
Interbank Offered Rate ("LIBOR") adjusted for reserves, in each case plus a
margin based upon the total leverage ratio of LES Acquisition. LES Acquisition
also will pay administration fees, commitment fees, re-syndication fees (under
certain circumstances), certain expenses and provide certain indemnities, all of
which LES Acquisition believes to be customary for commitments of this type. The
commitment fees have been paid or will be payable, as applicable, in stages,
beginning with the execution of the Commitment Letter and ending with a final
payment upon consummation of the financing. The Commitment Letter may be
extended beyond its expiration date of [March 31, 1998] upon payment of an
additional fee.
 
     The Loan Agreement will contain conditions precedent, representations and
warranties, covenants (including financial covenants), events of default and
other provisions customary for such financings.
 
     TD's commitment to provide the Senior Credit Facilities is conditioned on,
among other things, the following: the negotiation, execution and delivery of
the Loan Agreement; receipt of all necessary or desirable
 
                                       36
<PAGE>   45
 
governmental, shareholder and third party consents; the absence of a material
adverse change in the business assets, operations, condition (financial or
otherwise), or prospects of LES Acquisition, Safety-Kleen and their respective
subsidiaries on a consolidated basis; the execution of definitive agreements
relating to the Merger and the Offer; satisfactory completion of due diligence
examinations; prior or contemporaneous repayment in full of all existing
indebtedness of each of LES Acquisition and Safety-Kleen; and the successful
syndication of $400 million of the $1.8 billion commitment; and after
consummation of the transactions at closing, either (i) Laidlaw Environmental
shall hold a sufficient number of shares to effect the Merger or (ii) the Merger
shall have been or, concurrently with the closing, shall be, consummated, and
the surviving corporation shall be a wholly-owned subsidiary of LES Acquisition.
 
     It is anticipated that the indebtedness incurred through borrowings under
the Senior Credit Facilities will be repaid from funds generated internally by
LES Acquisition and its subsidiaries, and from other sources. No final decisions
have been made concerning the method LES Acquisition will employ to repay such
indebtedness. Such decisions when made will be based on LES Acquisition 's
review from time to time of the advisability of particular actions, as well as
on prevailing interest rates and financial and other economic conditions.
 
CERTAIN DEBT INSTRUMENTS OF SAFETY-KLEEN
 
     The total long term debt of Safety-Kleen as of September 6, 1997 totaled
$246,080,000. This long term debt is comprised of (i) 9 1/4% Senior Notes due in
1999 (the "9 1/4% Notes"); (ii) 8 1/2% Senior Notes due in 1998 (the "8 1/2%
Notes"), together with the 9 1/4% Notes, (the "Notes"); and (iii) unsecured
notes payable to banks under revolving lines of credit and uncommitted lines of
credit.
 
     Upon the occurrence of a downgrade in a credit agency's rating of the
9 1/4% Notes in conjunction with a change of control, each holder of the Notes
may require the repurchase of all or part of such holder's Notes at a price
equal to the principal amount plus accrued interest.
 
RELATIONSHIPS WITH SAFETY-KLEEN
 
     Except as to the transactions described below effected on the New York
Stock Exchange by a wholly owned subsidiary of Laidlaw Environmental, neither
Laidlaw Environmental nor, to the best of its knowledge, any of the persons
listed on Schedule A hereto nor any associate or majority-owned subsidiary of
any of the foregoing, beneficially owns or has a right to acquire any equity
securities of Safety-Kleen nor have they effected any transaction in such equity
securities during the last 60 days.
 
<TABLE>
<CAPTION>
                                                                NUMBER OF        PRICE
DATE PURCHASED                                                SHARES BOUGHT    PER SHARE
- --------------                                                -------------    ---------
<S>                                                           <C>              <C>
  10/02/97..................................................         100       $23.8750
  10/28/97..................................................      78,000       $20.5000
  10/28/97..................................................      85,000       $20.7500
  10/28/97..................................................      43,000       $21.5000
  10/28/97..................................................      23,000       $19.7500
  10/28/97..................................................      10,000       $20.2600
  10/28/97..................................................       2,000       $19.5000
  10/29/97..................................................     191,000       $22.0000
  10/29/97..................................................      91,000       $21.9375
  10/29/97..................................................      25,100       $21.8750
  10/29/97..................................................      38,200       $21.8125
  10/29/97..................................................       9,700       $21.7500
  10/29/97..................................................       5,000       $21.6250
</TABLE>
 
     Neither Laidlaw Environmental nor, to the best of its knowledge, any of the
persons listed on Schedule A hereto has (i) any contract, arrangement,
understanding or relationship with any other person with respect to any
securities of Safety-Kleen, including, but not limited to, any contract,
arrangement, understanding or relationship concerning the transfer or the voting
of any such securities, joint ventures, loan or option
 
                                       37
<PAGE>   46
 
arrangements, puts or calls, guaranties of loans, guaranties against loss or the
giving or withholding of proxies; (ii) had any contacts or negotiations with
Safety-Kleen or its affiliates concerning a merger, consolidation or
acquisition, a tender offer or other acquisition of securities, an election of
directors, or a sale or other transfer of a material amount of assets, except as
described herein; or (iii) has had any transaction with Safety-Kleen or any of
its executive officers, directors or affiliates that would require disclosure
under the rules and regulations of the Commission applicable to the Offer except
existing and present business relationships (e.g., providing services to each
other or considering the purchase or sale of discrete assets or operations or
alliances) in the ordinary course of business none of which are material, the
sale of certain assets of a Laidlaw Environmental subsidiary to Safety-Kleen in
February 1996 and the accompanying cooperative services agreement which is in
the process of being terminated.
 
FEES AND EXPENSES
 
     Laidlaw Environmental has retained Morrow & Co., Inc. ("Information Agent")
to act as Information Agent in connection with the Offer. The Information Agent
may contact holders of Shares by mail, telephone, electronic mail and personal
interviews and may request brokers, dealers and other nominee shareholders to
forward the Offer materials to beneficial owners of Shares. The Information
Agent will be paid a customary fee of up to $          for such services, plus
reimbursement of out-of-pocket expenses, and Laidlaw Environmental will
indemnify the Information Agent against certain liabilities and expenses in
connection with the Offer, including liabilities under federal securities laws.
 
     Bear Stearns is acting as financial advisor to Laidlaw Environmental in
connection with its effort to acquire Safety-Kleen, for which services Laidlaw
Environmental has paid to Bear Stearns aggregate fees equal to $1,500,000, and
has agreed to pay additional amounts to Bear Stearns (up to a maximum of
$3,250,000).
 
     Raymond James is acting as financial advisor to Laidlaw Environmental in
connection with its effort to acquire Safety-Kleen, for which services, and for
assistance rendered by Raymond James in connection with prior purchases of
Shares by Laidlaw, Laidlaw has agreed to pay Raymond James aggregate fees up to
a maximum of $1,000,000 (all of which is contingent upon consummation of the
Merger).
 
     Laidlaw Environmental has also agreed to reimburse each of the Financial
Advisors for necessary and reasonable advisor, consultant, and attorney's fees
incurred in connection with its engagement, and has agreed to indemnify each of
Bear Stearns and Raymond James and certain related persons and entities against
certain liabilities and expenses in connection with their respective
engagements, including certain liabilities under the federal securities laws. In
connection with each of Bear Stearns' and Raymond James' engagement, Laidlaw
Environmental anticipates that certain employees of Bear Stearns and Raymond
James may communicate in person, by telephone or otherwise with a limited number
of institutions, brokers or other persons who are Safety-Kleen Shareholders.
Neither Bear Stearns nor Raymond James will receive any fee for or in connection
with such solicitation activities by its employees apart from the fees it is
otherwise entitled to receive as described above.
 
     In addition to the fees to be received by each of Bear Stearns and Raymond
James in connection with its engagement as financial advisor to Laidlaw
Environmental, Raymond James has in the past rendered various investment banking
and financial advisory services for Laidlaw Environmental for which it has
received customary compensation. Both Bear Stearns and Raymond James may in the
future render services to Laidlaw Environmental for which they will receive
customary fees.
 
     Laidlaw Environmental will pay the Exchange Agent reasonable and customary
compensation for its services in connection with the Offer, plus reimbursement
for out-of-pocket expenses, and will indemnify the Exchange Agent against
certain liabilities and expenses in connection therewith, including liabilities
under the federal securities laws. Laidlaw Environmental will not pay any fees
or commissions to any broker or dealer or other person (other than the Dealer
Manager and the Information Agent) for soliciting tenders of Shares pursuant to
the Offer. Brokers, dealers, commercial banks and trust companies will be
reimbursed by Laidlaw Environmental for customary mailing and handling expenses
incurred by them in forwarding material to their customers.
 
                                       38
<PAGE>   47
 
ACCOUNTING TREATMENT
 
     Laidlaw Environmental will account for the acquisition of Shares pursuant
to the Offer and the Merger using the purchase method of accounting.
Accordingly, the purchase price will be allocated to assets acquired and
liabilities assumed based on their estimated fair values at the acquisition
date. Safety-Kleen's financial position and results of operations will not be
included in Laidlaw Environmental's consolidated accounts prior to the
consummation date of the Merger.
 
STOCK EXCHANGE LISTING
 
     The Laidlaw Environmental Common Stock (with accompanying Rights) is listed
on the NYSE and the Pacific Exchange, Inc. (the "Pacific Exchange"). Application
will be made to list the Laidlaw Environmental Common Stock to be issued
pursuant to the Offer and the Merger on the NYSE and the Pacific Exchange. As
described above under "The Offer -- Conditions of the Offer -- Laidlaw
Environmental Shareholder Approval Condition," pursuant to the rules of the
NYSE, the issuance of Laidlaw Environmental Common Stock in the Offer and the
Merger must be approved by the holders of a majority of the shares of Laidlaw
Environmental voting stock, voting as a single class, voted at a meeting of such
holders at which the total number of votes cast represents over 50% in interest
of all shares of Laidlaw Environmental voting stock outstanding on the
applicable record date.
 
     Wisconsin State Laws.  Although Laidlaw Environmental and LES Acquisition
consider it unlikely, it is possible that the Offer may be subject to Chapter
552 of the Wisconsin Statutes (the "Wisconsin Corporate Take-Over Law"). The
Wisconsin Corporate Take-Over Law makes it unlawful, under certain
circumstances, for any person to make a take-over offer involving a target
company in Wisconsin, which meets certain criteria, or to acquire any equity
securities of such a target company pursuant to the take-over offer, unless a
registration statement has been filed with the Wisconsin Division of Securities
ten days prior to the commencement of the take-over offer and has become
effective or such take-over is exempted by rule or order of the Wisconsin
Division of Securities. The Wisconsin Corporate Take-Over Law also imposes
certain reporting and filing requirements on persons making such a take-over
offer and makes unlawful certain fraudulent and deceptive practices, all of
which provisions may be applicable to the Offer. The applicability of the
Wisconsin Corporate Take-Over Law depends on the percentage of Safety-Kleen's
outstanding common shares held of record by residents of Wisconsin, which is not
determinable with certainty from publicly available information. Laidlaw
Environmental and LES Acquisition intended to apply to the Wisconsin Division of
Securities an exemption order permitting the Offer to be made without prior
registration, provided that no Shares are purchased or taken up pursuant to the
Offer unless a registration is effective or registration is found not to be
required after the information necessary to make this determination is obtained
from Safety-Kleen. If it is found that compliance is required, Laidlaw
Environmental and LES Acquisition presently intend to comply with the Wisconsin
Corporate Take-Over Law, including making any required filings. Laidlaw
Environmental and LES Acquisition both have reserved their rights to challenge
the constitutionality of the Wisconsin Corporate Take-Over Law or its
applicability to them.
 
                                   THE MERGER
 
GENERAL
 
     If the Minimum Tender Condition and other Offer Conditions are satisfied
and the Offer is consummated, Laidlaw Environmental and its affiliates will own
two-thirds of the outstanding Shares. Accordingly, Laidlaw Environmental and its
affiliates will at such time have sufficient voting power in Safety-Kleen to
approve the Merger independently of the votes of any other Safety-Kleen
Shareholders, and Laidlaw Environmental presently intends to vote any and all
Shares then owned by Laidlaw Environmental and its affiliates to approve the
Merger.
 
     Rule 13e-3 of the General Rules and Regulations under the Exchange Act,
which Laidlaw Environmental does not believe would be applicable to the Merger
as long as the Merger occurred within one year of consummation of the Offer,
would require, among other things, that certain financial information concerning
 
                                       39
<PAGE>   48
 
Safety-Kleen, and certain information relating to the fairness of the proposed
transaction and the consideration offered to Safety-Kleen Shareholders therein,
be filed with the Commission and disclosed to Safety-Kleen Shareholders prior to
consummation of the Merger.
 
     Laidlaw Environmental reserves the right to acquire, following the
consummation or termination of the Offer, additional Shares through open-market
purchases, privately negotiated transactions, a tender offer or exchange offer,
or otherwise, upon such terms and at such prices as it shall determine, which
may be more or less favorable than those of the Offer. Laidlaw Environmental and
its affiliates also reserve the right to dispose of any or all Shares acquired
by them pursuant to the Offer or otherwise, upon such terms and at such prices
as they shall determine.
 
     In connection with the Offer, Laidlaw Environmental has reviewed, and will
continue to review, on the basis of available information, various possible
business strategies that it might consider in the event that it acquires all or
substantially all of the common equity interest in Safety-Kleen. Laidlaw
Environmental also intends to conduct a detailed review of Safety-Kleen and its
assets, corporate structure, capitalization, operations, properties, policies,
management and personnel and consider which changes, if any, would be desirable
in light of the circumstances which then exist. Such strategies could include,
among other things, changes in Safety-Kleen's business, corporate structure,
capitalization, the Safety-Kleen Board or management, and consideration of
disposition of certain assets or lines of business of Safety-Kleen.
 
     If the Merger is consummated, Laidlaw Environmental will consider the sale
of two assets after the Merger: (i) Safety-Kleen's European operations and (ii)
Safety-Kleen's Oil Recovery Services business. Laidlaw Environmental will fully
assess these potential divestitures, and possibly other potential divestitures,
as additional information regarding Safety-Kleen becomes available.
 
     Except as noted herein, Laidlaw Environmental does not have any present
plans or proposals that would result in an extraordinary corporate transaction,
such as a merger, reorganization or liquidation, or sale or transfer of a
material amount of assets, involving Safety-Kleen or any of its subsidiaries, or
any material changes in Safety-Kleen's corporate structure or business. However,
because Laidlaw Environmental has not had access to Safety-Kleen's books and
records, additional changes may be made after a full review of Safety-Kleen's
operations is completed.
 
DISSENTER RIGHTS
 
     Holders of Shares do not have appraisal rights as a result of the Offer.
However, in the event the Merger is consummated, the Safety-Kleen Shareholders
would have dissenter rights with respect to the Merger under the Wisconsin
Statutes Section 180.1302.
 
                       INFORMATION REGARDING SAFETY-KLEEN
 
     The following information is taken from the Safety-Kleen Annual Report on
Form 10-K for the fiscal year ending December 28, 1996.
 
     Safety-Kleen is a leader in servicing the recycling and waste needs of
companies in the automotive/retail repair, industrial, imaging and other
business sectors. Over 2,800 Safety-Kleen specialists service customers from a
branch network that extends across North America and Western Europe.
 
     Focusing primarily on the needs of smaller businesses, Safety-Kleen
performed nearly five million individual services and reclaimed more than 300
million gallons of contaminated fluid through a network of 230 branches
worldwide in 1996. Safety-Kleen collects and recycles used products at thirteen
recycle centers, two lube oil re-refineries, and three fuel-blending facilities.
 
     Safety-Kleen operates in the continental U.S., Canada, the United Kingdom,
the Republic of Ireland, Puerto Rico, Belgium, France, Italy, Spain and Germany.
Safety-Kleen has licensee operations in Japan and Korea. Safety-Kleen Corp. was
incorporated in July, 1963 under the laws of the State of Wisconsin.
 
                                       40
<PAGE>   49
 
                  INFORMATION REGARDING LAIDLAW ENVIRONMENTAL
 
     The following describes the business and management of Laidlaw
Environmental. Additional information regarding Laidlaw Environmental is
contained in its filings with the Commission pursuant to the Exchange Act. See
"Available Information" and "Incorporation of Certain Documents by Reference."
 
BUSINESS OF LAIDLAW ENVIRONMENTAL
 
     Laidlaw Environmental provides hazardous and industrial waste management
services throughout North America. Laidlaw Environmental collects, transports,
treats and disposes of waste by incineration, landfilling and other methods at
its facilities located in the United States and Canada. Laidlaw Environmental
also operates waste processing, recycling and repackaging facilities and has
analytical laboratories at its facilities in several states.
 
     On May 15, 1997, pursuant to a February 6, 1997, stock purchase agreement
(the "Stock Purchase Agreement") between Rollins Environmental Services, Inc.
("Rollins") and Laidlaw Inc. ("Laidlaw"), Rollins acquired (the "Acquisition")
the hazardous and industrial waste operations of Laidlaw ("Old LESI" or the
"Accounting Acquirer"). The business combination was accounted for as a reverse
acquisition using the purchase method of accounting. Rollins issued 120 million
Common Shares and a $350 million 5% subordinated convertible debenture, and paid
$349.1 million in cash ($400 million, less debt of $50.9 million assumed), to
Laidlaw to consummate the Acquisition. Concurrent with the closing of the
Acquisition, the continuing legal entity changed its name from "Rollins
Environmental Services, Inc." to "Laidlaw Environmental Services, Inc." As a
result of the Acquisition, Laidlaw owns 67% of the issued common shares of
Laidlaw Environmental. Laidlaw Environmental accordingly adopted the Accounting
Acquirer's fiscal year-end of August 31.
 
     Old LESI consisted of all direct and indirect subsidiaries of Laidlaw
engaged in the hazardous and industrial waste business, other than JTM
Industries, Inc. and its subsidiary, KBK Enterprises, Inc. Prior to the
Acquisition, Old LESI provided hazardous and industrial waste services from 85
service locations in 26 states and seven Canadian provinces. Although Old LESI
was a conglomerate of separate entities, these entities conducted such services
primarily under the name "Laidlaw Environmental Services."
 
     Laidlaw Environmental was incorporated in Delaware in 1968. Its principal
executive office is located at 1301 Gervais Street, Suite 300, Columbia, South
Carolina 29201 and its telephone number is 803-933-4200.
 
     Laidlaw Environmental, in providing hazardous and industrial waste
services, is engaged in five primary lines, or classes, of business: (a) service
center, (b) landfill, (c) incineration, (d) transportation and (e) specialty
services, including polychlorinated biphenyl ("PCB") management, wastewater
treatment and other specialty services.
 
     The percentages of Laidlaw Environmental's gross revenue contributed by its
business classes for the last three fiscal years ended August 31, were as
follows:
 
<TABLE>
<CAPTION>
                                                              1997   1996   1995
                                                              ----   ----   ----
<S>                                                           <C>    <C>    <C>
Service Centers.............................................   38%    39%    41%
Landfill....................................................   22     25     21
Incineration................................................   11      4      4
Transportation..............................................   12     12     15
Specialty Services..........................................   17     20     19
                                                              ---    ---    ---
          Total Revenue.....................................  100%   100%   100%
                                                              ===    ===    ===
</TABLE>
 
SERVICE CENTERS
 
     Service centers across the United States and Canada work in partnership
with Laidlaw Environmental's treatment and disposal facilities to provide an
integrated service delivery system. Waste materials are transported from a
customer site to a service center, where they are temporarily stored or
consolidated with
 
                                       41
<PAGE>   50
 
compatible waste streams for more efficient transportation to final treatment
and/or disposal destinations. All of Laidlaw Environmental's service centers in
the United States have Part B permits under the United States Resource
Conservation and Recovery Act ("RCRA") that, among other things, allow Laidlaw
Environmental to store waste for up to one year for bulking and/or transfer
purposes. Additionally, Laidlaw Environmental operates smaller satellite
locations which act as local collection points for the service centers. Through
its service center network, Laidlaw Environmental can access its customers
quickly in order to collect their waste streams, thus enabling customers to
remain in compliance with on-site storage regulations.
 
     Laidlaw Environmental also has on-site field operations headquartered at
its service centers, including lab-packing services, field services and
household hazardous waste collection programs.
 
     Laidlaw Environmental performs a variety of resource recovery processes at
many of its service centers. Resource recovery involves the distillation of used
solvents to remove contaminants and then the return of the material to the
market as a solvent or for use as fuel. Most of these hazardous materials come
from the aerospace and transportation industries and the metals finishing
industries. Fuel substitution, mainly, in the energy intensive cement
manufacturing process, is the most prevalent form of resource recovery.
 
LANDFILLS
 
     Laidlaw Environmental operates 12 landfills located throughout the United
States and Canada. A total of eight landfills are designed and permitted for the
disposal of hazardous wastes. Four landfills are operated for non-hazardous
industrial waste disposal, and to a lesser extent, municipal solid waste.
 
     Laidlaw Environmental operates eight of the 23 permitted hazardous waste
landfills in North America, with 52 million cubic yards of remaining permitted
capacity (which at current fill rates represents in excess of 50 years of
capacity). Of these facilities, six are located in the United States and two in
Canada.
 
     In the United States, Laidlaw Environmental's hazardous waste landfills
have been issued RCRA Subtitle C permits. The EPA's permitting process for RCRA
Subtitle C landfills is very rigorous. Before a permit can be issued, the
applicant must provide detailed waste analysis, spill prevention and control
counter-measure plans, detailed design specifications (which include liner
design, leak detection systems and rainwater removal systems), groundwater
monitoring, employee training and geologic/hydrogeologic investigations.
Furthermore, the applicant must post financial assurance instruments for
landfill cell and site closure and post-closure care. All six of Laidlaw
Environmental's United States hazardous waste landfills have received Part B
landfill permits and meet or exceed Subtitle C requirements. These permits are
generally issued for periods of five or ten years, after which the permit must
be reviewed by state and/or federal regulators before the permit can be renewed
for additional terms. Management is not aware of any issues at any of Laidlaw
Environmental's sites that would preclude the renewal of its Part B landfill
permits. During the last 12 months, approximately 0.9 million cubic yards of
hazardous wastes were disposed of in these landfills.
 
     In addition to its hazardous waste landfill sites, Laidlaw Environmental
operates four nonhazardous industrial landfills with over 209 million cubic
yards of remaining permitted capacity. Laidlaw Environmental's non-hazardous
landfill facilities are permitted to accept commercial industrial waste,
including wastes from foundries, demolition and construction, machine shops,
automobile manufacturing, printing, metal fabrications and recycling. Laidlaw
Environmental's facility in Carbon County, Utah also accepts municipal solid
waste. During the last 12 months, 1.4 million cubic yards of non-hazardous
wastes were disposed of in these landfills.
 
INCINERATION
 
     Laidlaw Environmental offers a wide range of technological capabilities and
locations to customers through a collection of incineration facilities.
Incineration is the preferred method for the treatment of organic hazardous
waste, because it effectively destroys the contaminants at temperatures in
excess of 2,000 degrees Fahrenheit. High temperature incineration effectively
eliminates organic wastes such as herbicides, plastics, halogenated solvents,
pesticides, pharmaceutical and refinery wastes, regardless of whether they are
gases,
 
                                       42
<PAGE>   51
 
liquids, sludges or solids. Federal and state incineration regulations require a
destruction and removal efficiency of 99.99% for most organic wastes and
99.9999% for PCBs and dioxin.
 
     Laidlaw Environmental operates four United States-based solids and liquids
capable incinerators with annual capacity of over 250,000 tons, two hazardous
waste liquid injection incinerators in Canada, and one in the United States, and
two lower volume specialty incineration facilities in the United States.
 
     Laidlaw Environmental's incineration facilities in Bridgeport, New Jersey;
Deer Park, Texas; Coffeyville, Kansas, and Aragonite, Utah, are designed to
process liquid organic wastes, sludges, solids, soil and debris. The Deer Park
facility has two kilns and a rotary reactor. Additionally, the Deer Park
facility has an on-site landfill for the disposal of ash and other waste
material produced as a result of the incineration process. The landfill is built
and permitted to RCRA hazardous waste standards.
 
     Laidlaw Environmental's incineration facilities in Roebuck, South Carolina,
Mercier, Quebec and Sarnia, Ontario are liquid injection incinerators, designed
primarily for the destruction of liquid organic waste. The Mercier facility also
has a system to blend and destroy pumpable sludges. Typical wastestreams include
wastewater containing concentrated organic levels not amenable to conventional
physical/chemical waste treatment, pesticide and herbicide waste, waste with
high chlorinated organic concentrations and flammable materials.
 
     All but one of Laidlaw Environmental's United States incineration
facilities have received Part B permits under RCRA. The facility in Roebuck,
South Carolina has received EPA approval for that portion of the Part B permit
under EPA authority; however, the required state permit which was originally
issued in 1987 is currently under appeal. Part B permits are generally issued
for periods of five or ten years, after which the permit must be reviewed by
state and/or federal regulators before the permit can be renewed for additional
terms. Management is not aware of any issues at any of Laidlaw Environmental's
sites that would preclude the renewal of any of its Part B permits.
 
     During fiscal year 1997, Laidlaw Environmental closed its incinerators at
Baton Rouge, Louisiana, and Clive, Utah, reducing utilization of less efficient
and redundant facilities. During fiscal year 1998, Laidlaw Environmental plans
to close its incinerators at Coffeyville, Kansas, and Roebuck, South Carolina,
reducing excess capacity. These four closures will eliminate approximately
244,000 tons of practical capacity from the off-site commercial incineration
market. The industry's total off-site commercial incinerator practical capacity
was estimated at 1.26 million tons in 1996, according to EI Digest.
 
TRANSPORTATION
 
     Laidlaw Environmental's transportation operations facilitate the movement
of materials between locations, which is key to the operation of Laidlaw
Environmental's network of hazardous and industrial waste facilities.
Transportation may be accomplished by truck, rail, or other mode, with
company-owned assets or in conjunction with third party transporters.
 
     Specially designed containment systems, vehicles and other equipment
permitted for hazardous waste transport, along with drivers trained in
transportation skills and hazardous waste procedures, provide for the movement
of customer waste streams.
 
SPECIALTY SERVICES
 
     Other specialty services provided by Laidlaw Environmental include PCB
management services, wastewater treatment, harbor and channel dredging, remedial
construction and consulting, industrial services, analytical services,
biological treatment, and paint and solvent recovery.
 
     Laidlaw Environmental recycles PCB contaminated oils and reclaims metals
from PCB contaminated equipment. Laidlaw Environmental accomplishes this
recycling and reclamation through a de-chlorination process operated from seven
facilities mainly in the eastern United States and Canada.
 
     Laidlaw Environmental provides field services for industrial customers at
their sites and at government installations, federal and state Superfund sites,
laboratories and schools across North America. These
 
                                       43
<PAGE>   52
 
activities range from typical environmental remediation and construction to
specialized services. Laidlaw Environmental recently adopted its INSITE program,
an environmental outsourcing program that allows companies to achieve their
environmental goals while focusing on their core business.
 
     Laidlaw Environmental also offers a range of wastewater treatment
technology, facilities and customer services. Wastewater treatment is provided
from four facilities and consists of four basic business lines: hazardous
wastewater treatment, mobile treatment, sludge dewatering/drying and
nonhazardous wastewater treatment. These services include the reduction,
treatment and disposal of both hazardous and non-hazardous wastewater, sludges
and solids for both bulk and drummed waste. Laidlaw Environmental removes
hazardous components from hazardous industrial liquids and/or
chemically/physically makes hazardous industrial liquids non-hazardous through
blending and treatment technology. Specialized techniques reduce residues by
recycling/reusing spent products. Batch treatment technologies also enable
Laidlaw Environmental to handle hard-to-treat wastewater streams.
 
     Hazardous wastewater treatment involves the safe detoxification of
hazardous components from liquid waste streams. The hazardous properties are
neutralized (pH adjustment) and/or reduced to non-leachable state, through a
multistep treatment process. The resulting treated effluent is tested prior to
discharge to ensure compliance with discharge limits, while the sludge is
dewatered and tested to ensure that it meets the requirements for off-site
disposal as a nonhazardous waste. Because certain wastes carry hazardous waste
designation throughout the treatment system, these wastes are treated separately
to minimize dewatered sludge disposal costs. Laidlaw Environmental's wastewater
treatment facilities are fully-permitted and approved under applicable
regulations.
 
     Mobile wastewater treatment and dewatering equipment is used to dewater
industrial sludges at the generators' sites. Turn-key services include
laboratory, trained operators, treatment supplies and equipment, dewatering and
stabilization technology -- all designed to provide optimal treatment chemistry
that reduces the volume of sludge generated for off-site disposal.
 
     Sludge drying uses transportable equipment that reduces the amount of
entrained liquid in dewatered sludge. This process is particularly effective for
organic sludges that must be incinerated at high cost. Drying greatly reduces
ultimate disposal and transportation costs by minimizing the volume of waste
sent off-site for treatment.
 
     Laidlaw Environmental treats non-hazardous waste streams at all of its
hazardous wastewater plants and operates a facility specifically designed for
non-hazardous wastewater and consumer goods destruction in Chattanooga,
Tennessee.
 
     In connection with the Acquisition, Laidlaw Environmental's hazardous
wastewater facility in Nashville, Tennessee was closed in May of 1997.
 
COMPETITION
 
     The hazardous and industrial waste management industry is highly
competitive. The sources of competition vary by locality and by type of service
rendered, with competition coming from the other major waste services companies
and thousands of privately owned firms in North America which offer waste
services. Laidlaw Environmental also competes with municipalities and larger
plants which provide their own waste services. In acquiring new contracts and
maintaining business, Laidlaw Environmental experiences competition primarily in
the areas of pricing and service.
 
     Total hazardous waste industry revenues for 1995 were estimated to have
been approximately $3 billion. Prior to the Acquisition, Old LESI, Rollins and
three other large waste management companies accounted for 65% of the hazardous
waste management industry's revenues in 1995, according to EI Digest (October
1996). The pro forma combined revenues of Laidlaw Environmental for the year
ended August 31, 1996, would have given Laidlaw Environmental a 30% market share
of the hazardous waste industry revenues for 1995.
 
     Service center competition consists of two companies with national coverage
providing varying forms of waste collection assets or facilities. A number of
companies also compete on a local and regional basis.
 
                                       44
<PAGE>   53
 
     Ten of the 15 hazardous waste landfills not operated by Laidlaw
Environmental are operated by three competitors with landfill facilities spread
throughout the United States.
 
     Competitors operate large-scale incinerators at eight locations throughout
North America. Other companies have applied for or received permits to construct
and operate hazardous waste incinerators. Competition is also encountered from
cement kilns, which use hazardous waste-derived fuel as a supplemental fuel
source.
 
CUSTOMERS
 
     Laidlaw Environmental conducts business with more than 18,000 customers.
These customers represent diverse industries, including automotive manufacturers
and suppliers, chemical and petrochemical, computer and micro-processor
manufacturers, primary metals, paper, furniture, aerospace and pharmaceutical,
and are located throughout the United States and Canada. During fiscal 1997 no
one customer accounted for more than six percent of Laidlaw Environmental's
consolidated revenues.
 
     The hazardous waste management business is cyclical to the extent that it
is dependent upon a stream of waste from cyclical industries. If those cyclical
industries slow significantly, the business that Laidlaw Environmental receives
from those industries is likely to slow.
 
SEASONALITY
 
     Adverse winter weather moderately affects some of Laidlaw Environmental's
operations, particularly during the second fiscal quarters. The main reason for
this effect is reduced volumes of waste being received at Laidlaw
Environmental's facilities and higher operating costs associated with operating
in sub-freezing weather and high levels of snowfall.
 
REGULATIONS
 
     The collection and disposal of solid and hazardous wastes are subject to
the laws and regulations promulgated by United States, Canadian or other
foreign, state, territorial, federal, provincial or local courts, executive
offices, legislatures, governmental agencies or ministries, commissions or
administrative, regulatory or self-regulatory authorities or instrumentalities
which regulate health, safety, the environment, zoning and land-use.
Environmental laws and regulations require hazardous waste disposal facilities
to obtain permits, which generally outline the procedures under which the
facilities must be operated. Governmental authorities have the power to enforce
compliance with these, regulations, and violations of permit conditions, or of
the regulations, even if unintentional, may result in fines, shutdowns, remedial
work or revocation of the permit. Regulations vary but generally govern
collection, storage and disposal activities and the location and use of
facilities and impose restrictions to prohibit or minimize air and water
pollution.
 
     Laidlaw Environmental's business is significantly affected by federal,
state, provincial and local environmental law, including RCRA, the Toxic
Substances Control Act, CERCLA, the Clean Water Act and the Clean Air Act, and
corresponding state laws and related regulations and enforcement practices.
Safety standards under the Occupational Safety and Health Act are also
applicable to Laidlaw Environmental's business.
 
     RCRA provides for the establishment of a national hazardous waste
management program through a comprehensive regulatory system. Among other
things, it defines hazardous wastes and provides standards for generators,
transporters and disposers of hazardous wastes, and for the issuance of permits
for sites where such material is treated, stored or disposed. These regulations
also require Laidlaw Environmental's facilities to demonstrate financial
assurance for sudden and accidental and, in the case of land based treatment
facilities, non-sudden and gradual pollution occurrences. Financial assurance
for future closure and post-closure expenses must also be maintained. Laidlaw
Environmental believes that each facility operating under interim status will be
issued its final RCRA permit and that each permit will be renewed at the end of
its existing term. However, any such issuance or renewal could include
conditions requiring further capital expenditures or corrective actions.
Although Laidlaw Environmental also believes that each of its operating
facilities complies in all material respects with the applicable requirements of
RCRA, it may be necessary to expend considerable time, effort and money to keep
existing or acquired facilities of Laidlaw Environmental in compliance with
 
                                       45
<PAGE>   54
 
applicable requirements, including new regulations, to maintain existing permits
and approvals and to obtain the permits and approvals necessary to increase
their capacity.
 
     CERCLA, among other things, imposes financial liability for damages and the
cleanup of sites from which there is a release or threatened release of
hazardous substances into the environment. Present and past owners and operators
of sites which release hazardous substances, as well as generators and
transporters of the waste material, are jointly and severally liable for
remediation costs and environmental damages. Given the substantial costs
involved in a CERCLA cleanup and the difficulty of obtaining insurance for
environmental impairment liability, such liability could have a material impact
on Laidlaw Environmental's business, financial condition and future prospects.
 
     The Clean Water Act regulates the discharge of pollutants into surface
waters and sewers from a variety of sources, including disposal sites and
treatment facilities. Laidlaw Environmental is required to obtain discharge
permits and conduct sampling and monitoring programs. The Clean Air Act
regulates the emission of certain potentially harmful substances into the air.
These regulations also impact Laidlaw Environmental's operations. Laidlaw
Environmental believes each of its operating facilities complies in all material
respects with the applicable requirements.
 
ENVIRONMENTAL LIABILITIES AND CAPITAL EXPENDITURES
 
     A portion of Laidlaw Environmental's capital expenditures are related to
compliance with environmental laws and regulations. Laidlaw Environmental
estimates capital spending of approximately $1 million for fiscal year 1998, and
$3 million in the aggregate for the fiscal years 1999 through 2001 in order to
comply with RCRA, the Clean Air Act and other environmental laws and regulations
currently in effect.
 
     In addition to these capital expenditures, Laidlaw Environmental may incur
costs in connection with closure activities at certain of its sites. When
Laidlaw Environmental discontinues using or changes the use of a hazardous waste
management unit, formal closure procedures must be followed, and such procedures
must be approved by federal or state environmental authorities. In some cases,
costs are incurred to complete remedial cleanup work at the site. In addition at
certain of Laidlaw Environmental's other operating sites, remedial cleanup work
is required as part of the RCRA Corrective Action Program or other state and
federal programs. As shown in Laidlaw Environmental's Consolidated Balance Sheet
and more fully described in Note 6 of the Notes to Consolidated Financial
Statements, incorporated herein by reference, Laidlaw Environmental has recorded
liabilities of $183.1 million as of August 31, 1997, for remedial cleanup work,
Superfund site liability, closure activities and certain other environmental
expenses related to its operating and previously closed sites.
 
     With respect to various operating facilities, Laidlaw Environmental is
required to provide financial assurance with respect to certain statutorily
required closure and post-closure obligations totaling $450 million at August
31, 1997. Historically, Laidlaw provided certain of these financial assurances
in the form of parental guaranties. As a result of the Acquisition, Laidlaw
Environmental will be obligated to provide most of these financial assurances.
Laidlaw Environmental intends to provide the required financial assurance
through a combination of letters of credit and insurance policies, as allowed by
the applicable regulatory authorities.
 
EMPLOYEES
 
     As of August 31, 1997, 4,500 employees provided Laidlaw Environmental's
hazardous waste services, of whom 1,500 were executive, supervisory, clerical
and sales personnel. Approximately 12% of Laidlaw Environmental's employees were
represented by various collective bargaining groups. Management believes that
its relations with its employees are excellent.
 
MANAGEMENT
 
     Certain information regarding the directors and executive officers of
Laidlaw Environmental is set forth on Schedule A annexed hereto.
 
                                       46
<PAGE>   55
 
               UNAUDITED PRO FORMA COMBINED FINANCIAL INFORMATION
 
     The following selected unaudited pro forma combined financial information
combines the consolidated balance sheets and income statements of Laidlaw
Environmental and Safety-Kleen as if the Offer, Merger and the transactions
herein had occurred for all periods presented. These statements are prepared on
the basis of accounting for the Merger as a purchase and are based on the
assumptions set forth in the notes thereto. These statements do not reflect the
estimated cost savings Laidlaw Environmental believes will result from the
Merger. The following information is not necessarily indicative of the financial
position or the actual results of operation that would have occurred had the
transactions assumed here occurred on such dates or of expected future results.
This information should be read in conjunction with and is qualified in its
entirety by the consolidated financial statements and accompanying notes of
Laidlaw Environmental and Safety-Kleen included in the documents described under
"Incorporation of Certain Documents by Reference" (but which, in the case of
Safety-Kleen, are not covered by the reports of Safety-Kleen's independent
accountants for purposes of this Prospectus) and the pro forma accompanying
discussion and notes set forth under this Section.
 
     The following information is being presented for illustrative purposes only
and is not necessarily indicative of the financial position or operating results
that would have occurred had the Merger been consummated at the beginning of the
periods for which the Merger is being given effect, nor is it necessarily
indicative of future operating results or financial position.
 
                     LAIDLAW ENVIRONMENTAL AND SAFETY-KLEEN
 
                     PRO FORMA COMBINED STATEMENT OF INCOME
                       FOR THE YEAR ENDED AUGUST 31, 1997
 
<TABLE>
<CAPTION>
                                    HISTORICAL     HISTORICAL   PRO FORMA ADJUSTMENTS
                                      LAIDLAW       SAFETY-     ---------------------      PRO FORMA
                                   ENVIRONMENTAL     KLEEN         DR           CR          COMBINED
                                   -------------   ----------   --------      -------      ----------
                                                              (UNAUDITED)
                                               ($ IN THOUSANDS, EXCEPT PER SHARE AMOUNTS)
<S>                                <C>             <C>          <C>           <C>          <C>
Revenues.........................    $ 678,619      $977,122    $     --      $    --      $1,655,741
Expenses:
  Operating......................      485,062       645,488          --           --       1,130,550
  Depreciation and
     amortization................       53,506        77,741      27,474(D1)       --         158,721
  Selling, general and
     administrative..............       73,068       137,961          --           --         211,029
  Restructuring charge...........      331,697            --          --           --         331,697
                                     ---------      --------    --------      -------      ----------
          Total expenses.........      943,333       861,190      27,474           --       1,831,997
                                     ---------      --------    --------      -------      ----------
Operating income (loss)..........     (264,714)      115,932      27,474           --        (176,256)
Allocated interest expense.......       24,030            --          --           --          24,030
Interest expense.................       20,243        18,504      82,458(D2)       --         121,205
Other income.....................        2,865         1,587          --           --           4,452
                                     ---------      --------    --------      -------      ----------
Income (loss) from continuing
  operations before income tax...     (306,122)       99,015     109,932                     (317,039)
Income tax expense (benefit).....     (122,789)       38,294          --       45,940(D3)    (130,435)
                                     ---------      --------    --------      -------      ----------
Income (loss) from continuing
  operations before minority
  interest.......................     (183,333)       60,721     109,932       45,940        (186,604)
Minority interest (net of tax)...         (119)           --          --           --            (119)
                                     ---------      --------    --------      -------      ----------
Income (loss) from continuing
  operations.....................     (183,452)       60,721     109,932       45,940        (186,723)
Income from discontinued
  operations (net of tax)........           20            --          --           --              20
                                     ---------      --------    --------      -------      ----------
          Net income (loss)......    $(183,432)     $ 60,721    $109,932      $45,940      $ (186,703)
                                     =========      ========    ========      =======      ==========
Net income (loss) per share (Note
  D5)............................    $  (1.329)                                            $   (0.675)
Weighted average common and
  common stock equivalents
  outstanding (000s).............      138,033                                                276,752(D4)
</TABLE>
 
 See Accompanying Notes to Unaudited Pro Forma Combined Financial Information.
 
                                       47
<PAGE>   56
 
                      LAIDLAW ENVIRONMENTAL SERVICES, INC.
 
                        PRO FORMA COMBINED BALANCE SHEET
                             AS OF AUGUST 31, 1997
 
<TABLE>
<CAPTION>
                                        HISTORICAL     HISTORICAL      PRO FORMA ADJUSTMENTS
                                          LAIDLAW       SAFETY-     ---------------------------       PRO FORMA
                                       ENVIRONMENTAL     KLEEN          DR               CR            COMBINED
                                       -------------   ----------   ----------       ----------       ----------
                                                                      (UNAUDITED)
                                                                   ($ IN THOUSANDS)
<S>                                    <C>             <C>          <C>              <C>              <C>
                                                     ASSETS
Current assets
  Cash and cash equivalents..........   $   11,160     $   13,273   $                $                $   24,433
  Trade and other accounts
    receivable.......................      210,914        141,597           --               --          352,511
  Inventories........................        7,927         48,853           --               --           56,780
  Other current assets...............       21,539         36,658           --               --           58,197
                                        ----------     ----------   ----------       ----------       ----------
         Total current assets........      251,540        240,381           --               --          491,921
                                        ----------     ----------   ----------       ----------       ----------
Property, plant and equipment, net...    1,236,569        629,561    1,295,644(D6)           --        3,161,774
Goodwill.............................       70,527        136,479      288,025(D7)           --          495,031
Other assets.........................       52,242         30,771                         6,636(D8)       76,377
                                        ----------     ----------   ----------       ----------       ----------
         Total assets................   $1,610,878     $1,037,192   $1,583,669       $    6,636       $4,225,103
                                        ==========     ==========   ==========       ==========       ==========
 
                                                  LIABILITIES
Current liabilities
  Accounts payable...................   $   48,148     $   63,563   $                $                $  111,711
  Accrued liabilities................      115,211        102,023           --               --          217,234
  Current portion of long-term
    debt.............................       12,086             --           --           71,914(D10)      84,000
                                        ----------     ----------   ----------       ----------       ----------
         Total current liabilities...      175,445        165,586           --           71,914          412,995
                                        ----------     ----------   ----------       ----------       ----------
Deferred items Income taxes..........       49,790         57,361                       518,258       $  625,409
  Other..............................      179,668         72,447           --                           252,115
Long-term debt.......................      528,010        246,080           --          788,982        1,563,072
Subordinated convertible debenture...      350,000             --           --                           350,000
                                        ----------     ----------   ----------       ----------       ----------
         Total liabilities...........    1,282,913        541,474                     1,379,154        3,203,541
 
                                              STOCKHOLDERS' EQUITY
Common stock.........................      180,435          5,839           --          132,880(D11)     319,154
Additional paid-in capital...........      385,200        194,977           --          359,901(D12)     940,078
Retained earnings (accumulated
  deficit)...........................     (237,670)       294,902      294,902(D13)          --         (237,670)
                                        ----------     ----------   ----------       ----------       ----------
         Total stockholders'
           equity....................      327,965        495,718      294,902          492,781        1,021,562
                                        ----------     ----------   ----------       ----------       ----------
         Total liabilities and
           stockholders' equity......   $1,610,878     $1,037,192   $  294,902       $1,871,935       $4,225,103
                                        ==========     ==========   ==========       ==========       ==========
</TABLE>
 
 See Accompanying Notes to Unaudited Pro Forma Combined Financial Information.
 
                                       48
<PAGE>   57
 
          NOTES TO UNAUDITED PRO FORMA COMBINED FINANCIAL INFORMATION
 
A.  SUMMARY OF OFFER
 
     Laidlaw Environmental hereby offers, upon the terms and subject to the
conditions set forth herein and in the related Letter of Transmittal, to
exchange the Offer Consideration for each outstanding Share validly tendered on
or prior to the Expiration Date and not properly withdrawn. The Offer
Consideration per share consists of $14.00 net in cash and 2.4 shares of Laidlaw
Environmental Common Stock.
 
     According to the Safety-Kleen Form 10-Q for the period ended September 6,
1997, as of September 6, 1997, there were 58,400,729 Shares outstanding. Laidlaw
Environmental beneficially owns 601,100 Shares, or approximately 1.03% of the
outstanding Shares.
 
     In contemplation of the Merger, Laidlaw has received a commitment letter
from The Toronto Dominion Bank (the "Agent") to provide the Credit Facilities.
The Credit Facilities will consist of four parts: (i) a $400,000,000 6-year
Senior Secured Revolving Credit Facility with a $200,000,000 letter of credit
sublimit (the "Revolving Credit Facility" or "Facility A"), (ii) a $500,000,000
6-year Senior Secured Amortizing Term Loan ("Facility B"), (iii) a $450,000,000
Minimally Amortizing 7-year Senior Secured Term Loan ("Facility C") and (iv) a
$450,000,000 Minimally Amortizing 8-year Senior Secured Term Loan ("Facility
D"); (Facility B, Facility C and Facility D, collectively, the "Term Loans").
The Credit Facilities will be secured by all of the tangible assets of the
combined companies to the extent required by the syndicate of banks and other
financial institutions (collectively, the "Lenders") acceptable to Laidlaw
Environmental and the Agent that will make the loans pursuant to the Credit
Facilities. All of the capital stock of Laidlaw Environmental's subsidiaries,
including the acquired Safety-Kleen subsidiaries, will be pledged as part of
such security for the Credit Facilities, and such subsidiaries will guaranty the
obligations of Laidlaw Environmental to the Lenders. The Term Loans will be
drawn in full on the closing date. The Revolving Credit Facility will be
available commencing on the closing date at which time $200,000,000 will be
available for letters of credit and $250,000,000 will be available for loans,
subject to an aggregate maximum of $400,000,000. Interest per annum on the
Credit Facilities will vary depending on the particular Credit Facility, whether
Laidlaw Environmental chooses to borrow under Eurodollar or non-Eurodollar loans
and, with respect to Facilities A and B the current total leverage ratio. Under
the terms of the Credit Facilities, Laidlaw Environmental will be required to
use interest rate swaps to manage the risk of interest rate fluctuations. The
terms of such interest rate swaps have not been established.
 
                                       49
<PAGE>   58
 
B.  ACCOUNTING TREATMENT ($ IN THOUSANDS)
 
     If the Merger is consummated, it will be accounted for using the purchase
method of accounting applied in accordance with generally accepted accounting
principles. Accordingly, the assets and liabilities of Safety-Kleen will be
recorded at their estimated fair value, with any difference between the amount
of such fair value and the purchase price being recorded as goodwill. The
operating results of the combined company will include the results of operations
of Safety-Kleen from and after the closing date.
 
     The aggregate merger purchase price totals $1,554,493 and is comprised as
follows:
 
<TABLE>
<S>                                                           <C>           <C>
Safety-Kleen Shares outstanding at September 6, 1997
  according to Safety-Kleen's September 6, 1997 Form 10-Q...                58,400,729
Safety-Kleen Shares previously acquired by Laidlaw
  Environmental.............................................                  (601,100)
                                                                            ----------
Safety-Kleen Shares remaining to acquire....................                57,799,629
                                                                            ----------
Cash cost at $14.00 per Safety-Kleen Share..................                $  809,196
Cost of additional Laidlaw Environmental Shares to be issued
  Number of Laidlaw Environmental Shares to be issued.......  138,719,110
Price per Share.............................................        $5.00
          Total cost........................................                   693,597
                                                                            ----------
                                                                             1,502,793
Cost of Safety-Kleen Shares previously acquired by Laidlaw
  Environmental.............................................                    13,000
Cost of "in-the-money" Safety-Kleen stock options that are
  assumed to fully vest.....................................                    38,700
                                                                            ----------
          Total merger purchase price.......................                $1,554,493
                                                                            ==========
</TABLE>
 
     The price per share of the additional Laidlaw Environmental shares to be
issued of $5.00 is the average of the closing NYSE market price for the five
trading days before and after November 4, 1997, the date of the public
announcement of the Offer.
 
     The purchase price has been allocated to the assets acquired and
liabilities assumed based on estimated fair values at August 31, 1997, as
follows:
 
<TABLE>
<S>                                                           <C>
Current assets..............................................  $  240,381
Property, plant and equipment...............................   1,925,205
Goodwill....................................................     424,504
Other assets................................................      24,135
Current liabilities.........................................    (165,586)
Deferred income taxes.......................................    (575,619)
Other deferred items........................................     (72,447)
Long-term debt..............................................    (246,080)
                                                              ----------
Merger purchase price.......................................  $1,554,493
                                                              ==========
</TABLE>
 
C.  BASIS OF PRESENTATION
 
     The accompanying unaudited pro forma combined balance sheet gives effect to
the Merger as if it had occurred on August 31, 1997. The unaudited pro forma
combined statement of income for the year ended August 31, 1997 gives effect to
the Merger as if it had occurred as of September 1, 1996. During the report
periods there were no material transactions between Laidlaw Environmental and
Safety-Kleen.
 
        The unaudited pro forma combined balance sheet at August 31, 1997
includes the balance sheet of Laidlaw Environmental at August 31, 1997 and the
balance sheet of Safety-Kleen at September 6, 1997. The unaudited pro forma
combined statement of income for the year ended August 31, 1997 includes Laidlaw
Environmental for the year ended August 31, 1997 and for Safety-Kleen the
aggregate of the 16 weeks ended December 28, 1996 plus the 36 weeks ended
September 6, 1997.
 
                                       50
<PAGE>   59
 
     The effects of the Merger have been presented using the purchase method of
accounting. Accordingly, the purchase price was allocated to the assets acquired
and liabilities assumed based upon management's best preliminary estimate of
their fair values, based upon publicly available documents and information. The
preliminary allocation of the purchase price will be subject to further
adjustments, as Laidlaw Environmental finalizes the allocation of the purchase
price in accordance with generally accepted accounting principles. The goodwill
acquired is being amortized over 40 years on a straight-line basis.
 
     The unaudited combined pro forma financial information does not purport to
be indicative of the combined financial position or combined results of
operations of Laidlaw Environmental and Safety-Kleen had the transactions
assumed therein occurred on the dates specified, nor are they indicative of
future financial position or results of operations. The unaudited pro forma
financial information does not give effect to certain cost savings that Laidlaw
Environmental management believes may be realized as a result of the Merger.
There can be no assurances that such cost savings, if any, will be achieved.
 
     The unaudited pro forma financial information should be read in conjunction
with the historical consolidated financial statements of Laidlaw Environmental
and the notes thereto and the historical consolidated financial statements of
Safety-Kleen and the notes thereto included elsewhere herein.
 
D.  PRO FORMA ADJUSTMENTS ($ AND SHARES IN THOUSANDS)
 
     The following adjustments and elimination entries have been made to the
unaudited pro forma combined statement of income to reflect the acquisition of
Safety-Kleen by Laidlaw Environmental using the purchase method of accounting
for the Merger:
 
          1. To adjust depreciation and amortization expense to reflect the fair
     value adjustment of property, plant and equipment and the effect of the
     Merger on goodwill amortization, as follows:
 
<TABLE>
<CAPTION>
 
<S>                                                           <C>
To eliminate Safety-Kleen's estimated historical intangible
  and other asset amortization expense......................  $(15,531)
To record amortization expense related to goodwill arising
  as a result of the Merger.................................    10,613
To record depreciation expense related to certain
  Safety-Kleen property, plant and equipment written up to
  estimated fair value......................................    32,392
                                                              --------
          Total adjustment..................................  $ 27,474
                                                              ========
</TABLE>
 
          2. To adjust interest expense for the impact of the additional
     long-term debt associated with the Merger, as follows:
 
<TABLE>
<CAPTION>
 
<S>                                                           <C>
To eliminate historical Safety-Kleen interest expense.......  $(18,504)
To record interest expense on $1,106,976(1) of borrowings at
  9.00% (2) under the Senior Credit Facilities..............   100,962
                                                              --------
          Total adjustment..................................  $ 82,458
                                                              ========
</TABLE>
 
- ---------------
 
        (1) Includes additional long-term debt associated with Merger (Note D10)
            and anticipated refinancing of Safety-Kleen historical long-term
            debt.
        (2) At current rates pursuant to the terms of the Senior Credit
            Facilities.
 
          3. To adjust income taxes (benefits) to record the pro forma income
     taxes (benefits) as computed under SFAS 109 on pro forma pre-tax income
     (loss).
 
                                       51
<PAGE>   60
 
          4. Pro forma weighted average common and common stock equivalents
     outstanding comprise:
 
<TABLE>
<S>                                                           <C>
Laidlaw Environmental historical for year ended August 31,
  1997......................................................  138,033
Additional Laidlaw Environmental shares to be issued in
  connection with the Merger (see Note B)...................  138,719
                                                              -------
          Pro forma total...................................  276,752
                                                              =======
</TABLE>
 
          5. Fully diluted earnings per share amounts, which would include the
     dilutive effect of the subordinated convertible debenture, have not been
     included as the effect of such inclusion would be to increase earnings per
     share, and thus be anti-dilutive.
 
             The following adjustments and elimination have been made to the
     unaudited pro forma combined balance sheet to reflect the acquisition of
     Safety-Kleen by Laidlaw Environmental using the purchase method of
     accounting for the Merger:
 
          6. To writeup certain Safety-Kleen property, plant and equipment to
     fair value.
 
          7. To eliminate the historical book value of Safety-Kleen's intangible
     assets and record the goodwill resulting from the Merger as follows:
 
<TABLE>
<S>                                                           <C>
Eliminate historical Safety-Kleen intangible assets.........  $(136,479)
Record goodwill arising from the Merger (See Note A)........    424,504
                                                              ---------
          Net goodwill adjustment...........................  $ 288,025
</TABLE>
 
          8. To write-off the estimated book value of Safety-Kleen's other
     assets.
 
          9. Laidlaw Environmental's management estimates that approximately
     $100 million of costs related to facility closures, severance costs and
     other direct acquisition costs would be incurred in connection with the
     Merger; these estimates of costs are not yet based on sufficient factual
     information so as to be included as pro forma adjustments and are subject
     to change as additional information becomes available.
 
          10. To record the additional long-term debt associated with the Merger
     (see Note B), as follows:
 
<TABLE>
<S>                                                           <C>
Cash component of acquiring outstanding Safety-Kleen
  shares....................................................  $809,196
Cost of Safety-Kleen shares previously acquired.............    13,000
Cost of stock options.......................................    38,700
                                                              --------
Total long-term debt adjustment.............................  $860,896
Less: current portion adjustment............................   (71,914)
                                                              --------
          Net long-term debt adjustment.....................  $788,982
                                                              --------
</TABLE>
 
          11. To record the additional common stock associated with the Merger,
     as follows:
 
<TABLE>
<S>                                                           <C>
Eliminate historical Safety-Kleen common stock..............  $ (5,839)
Issuance of additional Laidlaw Environmental common stock
  (Note B)..................................................   138,719
                                                              --------
          Total common stock adjustment.....................  $132,880
                                                              ========
</TABLE>
 
          12. To record the impact on additional paid-in capital associated with
     the Merger, as follows:
 
<TABLE>
<S>                                                           <C>
Eliminate historical Safety-Kleen additional paid-in
  capital...................................................  $(194,977)
Issuance of additional Laidlaw Environmental common stock
  (Note B)..................................................    554,878
                                                              ---------
          Total additional historical paid-in capital
            adjustment......................................  $ 359,901
                                                              =========
</TABLE>
 
          13. To eliminate historical Safety-Kleen retained earnings.
 
          14. To record the incremental change in the Laidlaw Environmental tax
     liability and benefit which results from the adjustment of certain assets
     and the recording of certain liabilities utilizing the Federal statutory
     rate of 35% plus an effective state rate of 5%.
 
                                       52
<PAGE>   61
 
E. ADDITIONAL ACQUISITION PRO FORMA INFORMATION
 
     As disclosed in "Prospectus Summary -- Laidlaw Environmental Business,"
Rollins Environmental Services, Inc. ("Rollins"), on May 15, 1997, acquired the
hazardous and industrial waste operations of Laidlaw Inc. As a result of this
acquisition being accounted for as a reverse acquisition, the historical
financial information of Laidlaw Environmental included in this unaudited pro
forma combined financial information is that of the accounting acquirer, Old
LESI, and includes the results of operations of Rollins from the date of
acquisition, May 15, 1997.
 
     Condensed unaudited pro forma combined statement of income data, as if this
reverse acquisition had occurred as of September 1, 1996, is as follows ($ in
thousands, except per share amounts):
 
<TABLE>
<CAPTION>
                                                                YEAR ENDED
                                                              AUGUST 31, 1997
                                                              ---------------
<S>                                                           <C>
REVENUE:....................................................    $1,802,627
  Income (loss) from continuing operations..................      (225,443)
  Income (loss) from discontinued operations................            20
          Net income (loss).................................    $ (225,413)
Per share data:
  Income (loss) from continuing operations..................    $   (0.698)
  Income (loss) from discontinued operations................          .000
  Net income (loss).........................................    $   (0.698)
  Weighted average common and common stock equivalents
     (000)..................................................       323,163
</TABLE>
 
               DESCRIPTION OF LAIDLAW ENVIRONMENTAL CAPITAL STOCK
 
     The authorized capital stock of Laidlaw Environmental consists of
350,000,000 shares of Laidlaw Environmental Common Stock, par value $1.00 per
share, and 1,000,000 shares of Laidlaw Environmental Preferred Stock, par value
$1.00 per share (the "Laidlaw Environmental Preferred Stock").
 
LAIDLAW ENVIRONMENTAL COMMON STOCK
 
     As of October 14, 1997, there were 180,549,911 shares of Laidlaw
Environmental Common Stock issued and outstanding. The holders of Laidlaw
Environmental Common Stock are entitled to one vote per share on all matters
requiring stockholder action. The holders of the Laidlaw Environmental Common
Stock participate ratably in liquidation, subject to the payment to the holders
of any outstanding class of Laidlaw Environmental Preferred Stock of the
preferential amounts to which they are entitled.
 
     Dividends on the Laidlaw Environmental Common Stock may be declared and
paid only out of surplus or net profits legally available for the payment of
dividends.
 
LAIDLAW ENVIRONMENTAL PREFERRED STOCK
 
     Laidlaw Environmental is authorized to issue 1,000,000 shares of Laidlaw
Environmental Preferred Stock, which may be issued from time to time in one or
more series, each such series to have such distinctive designation or title as
may be fixed by the Laidlaw Environmental Board of Directors prior to the
issuance of any shares thereof. Each series may differ from each other series
already outstanding as may be declared from time to time by the Laidlaw
Environmental Board of Directors in the following respects: (i) the rate of
dividend; (ii) the amount per share, if any, which the Laidlaw Environmental
Preferred Stock shall be entitled to receive upon redemption, liquidation,
distribution or sale of assets, dissolution or winding up of Laidlaw
Environmental; (iii) terms and conditions of conversions, if any; and (iv) terms
of sinking fund, redemption or purchase account, if any. As of November 10,
1997, Laidlaw Environmental had no Laidlaw Environmental Preferred Stock
outstanding.
 
                                       53
<PAGE>   62
 
                 COMPARISON OF THE RIGHTS OF HOLDERS OF SHARES
                     AND LAIDLAW ENVIRONMENTAL COMMON STOCK
 
     As a consequence of the exchange of Shares for shares of Laidlaw
Environmental Common Stock in the Offer and the cancellation of Shares as a
result of the Merger, shareholders of Safety-Kleen, a company incorporated under
the laws of the State of Wisconsin, would become shareholders of Laidlaw
Environmental, a Delaware corporation. The rights of Safety-Kleen Shareholders
are currently governed by Wisconsin law (including the Wisconsin Statutes), the
Safety-Kleen Articles and the Safety-Kleen By-Laws. Upon the exchange of Shares
for Laidlaw Environmental Common Stock, the rights of Safety-Kleen Shareholders
will be governed by Delaware law (including the DGCL), the Laidlaw Environmental
Certificate and the Laidlaw Environmental By-laws.
 
     The following is a summary of certain similarities and material differences
between the rights of holders of Shares and the rights of holders of Laidlaw
Environmental Common Stock. The following summary does not purport to be a
complete statement of the rights of Safety-Kleen Shareholders under Wisconsin
law, the Safety-Kleen Articles, the Safety-Kleen By-Laws and the Rights
Agreement as compared with the rights of Laidlaw Environmental stockholders
under Delaware law, the Laidlaw Environmental Certificate and the Laidlaw
Environmental By-laws, or a complete description of the specific provisions
referred to herein. The summary discusses certain material aspects of the
above-mentioned corporate laws and instruments but is qualified in its entirety
by reference to such laws and instruments, including the aforementioned
instruments of Safety-Kleen and Laidlaw Environmental. Complete copies of all
such laws and instruments may be obtained in the manner set forth above under
the caption "Available Information."
 
           COMPARISONS OF DELAWARE AND WISCONSIN LAW -- SIMILARITIES
 
     Modern corporation laws have evolved to the point where the laws of most
states contain substantially similar provisions regarding major features of
corporate existence. Certain relevant similarities between the DGCL and the
Wisconsin Statutes are described below:
 
          Classified Board of Directors; Removal of Directors.  Both the DGCL
     and the Wisconsin Statutes allow the Board of Directors to be divided into
     two or three classes. Under the DGCL, absent a provision to the contrary in
     a corporation's certificate of incorporation, directors on a classified
     board can be removed only for cause. The Wisconsin Statutes allows for the
     removal of directors on a classified board with or without cause unless the
     articles of incorporation or by-laws provide that the directors may be
     removed only for cause.
 
     Pursuant to the Laidlaw Environmental Certificate, Laidlaw Environmental's
Board of Directors is divided into three classes, with each class serving a
three-year term. Any director of Laidlaw Environmental may be removed at any
time by the stockholders, but only for cause, and only at a meeting of the
stockholders called for that purpose by the affirmative vote of the holders of
75% or more of the Shares of Laidlaw Environmental entitled to vote at an
election of directors. The Safety-Kleen Articles provide that the Safety-Kleen
Board of Directors will be divided into three classes, with each class serving a
three-year term. Safety-Kleen directors may be removed only for cause and only
by a vote of holders of not less than two-thirds of the issued and outstanding
shares of Safety-Kleen.
 
          Preferred Stock.  The DGCL permits the Board of Directors to decrease
     the number of authorized shares of any series of preferred stock (but not
     below the number of shares then outstanding). The Wisconsin Statutes,
     however, does not permit a Board of Directors to decrease the number of
     shares in a series of preferred stock.
 
     Laidlaw Environmental has one million shares of "blank check" preferred
stock authorized, none of which is issued. Safety-Kleen has one million shares
of "blank check" preferred stock authorized, none of which (according to
Safety-Kleen's public filings), is issued.
 
          Required Vote for Authorization of Certain Actions.  Both the DGCL and
     the Wisconsin Statutes permit the authorization of a merger, dissolution or
     disposition of substantially all the assets of
 
                                       54
<PAGE>   63
 
     corporations by the holders of a majority of the outstanding shares of
     capital stock entitled to vote. Under the Wisconsin Statutes, this majority
     shareholder vote also applies to a share exchange.
 
     Pursuant to the Laidlaw Environmental Certificate, any merger, sale, lease,
exchange, transfer or other disposition of assets of Laidlaw Environmental
having an aggregate fair market value of $5,000,000, or the issuance of
securities of Laidlaw Environmental having an aggregate fair market value of
$5,000,000, shall, if such transaction is to be consummated with an "Interested
Stockholder," require the affirmative vote of not less than 75% of the
outstanding Common Stock of Laidlaw Environmental. For purposes of the Laidlaw
Environmental Certificate, an "Interested Stockholder" is a stockholder that
owns, or upon consummation of the transaction, will own, in excess of 30% of the
voting securities of Laidlaw Environmental, or is an affiliate of Laidlaw
Environmental and at any time within two years prior to the date of the
transaction was a beneficial owner of not less than 20% of the voting securities
of Laidlaw Environmental. Pursuant to the Safety-Kleen Articles, the affirmative
vote of not less than two-thirds of all outstanding voting securities of
Safety-Kleen is required for any merger, consolidation, sale, lease, exchange or
other disposition of all or substantially all of the property or assets of
Safety-Kleen.
 
          Shareholder Action by Consent.  Under the DGCL, unless the certificate
     of incorporation provides otherwise, any action which may be taken by the
     stockholders at a meeting may also be taken without a meeting by written
     consent by the holders of such number of shares as, if present at a
     meeting, could have so acted by vote. Under the Wisconsin Statutes,
     shareholders may take action without a meeting by unanimous written
     consent, or, if a Wisconsin corporation so elects in its articles of
     incorporation, by less than unanimous written consent.
 
     The Laidlaw Environmental By-Laws specifically deny stockholders the right
to take action without a meeting by written consent. The Safety-Kleen articles
do not permit action by written consent of the shareholders with less than
unanimous written consent, and accordingly action by written consent of the
shareholders of Safety-Kleen would require unanimous consent.
 
          Interested Director Transactions.  Under both the DGCL and the
     Wisconsin Statutes, contracts or transactions in which one or more of the
     corporation's directors has an interest are not void or voidable solely
     because of such interest or because such director was present at the
     directors' or shareholders' meeting where such contract or transaction was
     approved, if certain conditions are met. Under the laws of both Wisconsin
     and Delaware, if the director's interest is fully disclosed and a vote is
     taken in good faith, such contracts or transactions may be approved by a
     majority vote of the shareholders (excluding under the Wisconsin Statutes
     shares held by the interested director or entities controlled by the
     interested director) or of the disinterested directors. If the contracts or
     transactions are shown to be fair and reasonable as to the corporation at
     the time that they are authorized, approved or ratified by the board of
     directors, then separate shareholder or disinterested director approval is
     not required.
 
          Under the DGCL, a quorum for a separate determination by the board is
     a majority of the total number of directors, with the interested director
     counted for purposes of determining whether a quorum exists. Under
     Wisconsin Statutes, a quorum is deemed to exist if a majority of directors
     who have no interest in the transaction vote to authorize it; no separate
     quorum determination is made. Finally, under Wisconsin Statutes shares
     owned by or voted under control of an interested director or an entity in
     which the interested director has a material financial interest or of which
     he or she is a general partner may not be "counted" for purposes of a
     shareholder vote respecting the transaction in which the director has an
     interest.
 
          Indemnification of Directors and Officers.  Under the DGCL,
     indemnification provisions are strictly elective. The Wisconsin Statutes
     provides for mandatory indemnification of a director or officer against
     certain liabilities and expenses (i) to the extent such officers or
     directors are successful in the defense of a proceeding (whether brought VX
     or by a third party) and (ii) in proceedings in which the director or
     officer is not successful in the defense thereof, unless (in the latter
     case only) it is determined that the director or officer breached or failed
     to perform his or her duties to the corporation and such breach or failure
     constituted (a) a willful failure by the director or officer to deal fairly
     with the corporation or its shareholders in connection with a matter in
     which the director or officer had a material conflict of
 
                                       55
<PAGE>   64
 
     interest; (b) a violation of the criminal law, unless the director or
     officer had reasonable cause to believe his or her conduct was lawful or
     had no reasonable cause to believe his or her conduct was unlawful; (c) a
     transaction from which the director or officer derived an improper personal
     profit; or (d) willful misconduct. The Wisconsin Statutes specifically
     states that it is the public policy of Wisconsin to require or permit
     indemnification in connection with a proceeding involving securities
     regulation, as described therein, to the extent otherwise required or
     permitted under the Wisconsin Statutes as described above. The Wisconsin
     Statutes also does not limit indemnification of expenses in connection with
     a claim by or on behalf of the corporation as is mandated by the DGCL.
 
          The DGCL permits a corporation to adopt a provision in its certificate
     of incorporation that limits the monetary liability of the corporation's
     directors to the corporation or its stockholders for a breach of the
     director's fiduciary duty of care. The Laidlaw Environmental Certificate
     contains such a provision. Under the DGCL, a corporation may not limit a
     director's monetary liability for (i) any breach of the director's duty of
     loyalty to the corporation or its stockholders; (ii) an act or omission not
     in good faith or involving intentional misconduct or knowing violation of
     law; (iii) the payment of unlawful dividends or unlawful stock repurchases
     or redemptions; or (iv) any transaction in which the director received an
     improper personal benefit.
 
          Unlike the DGCL, the Wisconsin Statutes automatically limits the
     liability of directors of Wisconsin corporations statutorily, without
     requiring a provision in a corporation's articles of incorporation. Under
     the Wisconsin Statutes, the personal liability of a director to the
     corporation and its shareholders is eliminated, except where (a) the
     liability is based on a breach of the director's duty (whether duty of care
     or duty of loyalty) to the corporation and its shareholders and (b) such
     breach constitutes (i) the director's willful failure to deal fairly with
     the corporation or its shareholders in connection with a matter in which
     the director had a material conflict of interest; (ii) a violation of
     criminal law, unless the director had reasonable cause to believe that his
     or her conduct was lawful or no reasonable cause to believe his or her
     conduct was unlawful; (iii) a transaction from which the director derived
     an improper personal profit; or (iv) willful misconduct. The DGCL does not
     specifically define the type of conduct that constitutes a breach of a
     director's "duty of loyalty," while clauses (i) and (iii) above define the
     specific types of behavior under the Wisconsin Statutes that constitutes a
     breach of a director's duty of loyalty that would preclude elimination of
     personal liability. Because of the vagaries of the DGCL in this regard, it
     is possible that a broad interpretation of a breach of a director's duty of
     loyalty under the DGCL could result in the imposition of personal liability
     on a director under the DGCL when such conduct would be shielded from
     liability under the Wisconsin Statutes. A director may also be found
     personally liable to a corporation for the amount of a distribution made in
     violation of the Wisconsin Statutes if the director's vote constitutes
     conduct described in the preceding sentence.
 
          Both the Safety-Kleen By-Laws and the Laidlaw Environmental By-Laws
     provide for indemnification to the fullest extent permitted by law.
 
            COMPARISON OF DELAWARE AND WISCONSIN LAW -- DIFFERENCES
 
     Although it is impractical to note all of the differences between the
corporation laws of Delaware and Wisconsin, the following is a summary of the
significant differences between the DGCL and the Wisconsin Statutes as
applicable to the Offer and the Merger:
 
          Corporate Franchise Taxes.  Under ff Delaware law, corporations are
     assessed a franchise tax based upon the "assumed par value" of their
     outstanding shares or total shares issued, whichever is less. Wisconsin has
     no comparable tax for domestic corporations.
 
          Special Meetings of Shareholders.  Under Delaware law, a special
     meeting of stockholders may be called only by the Board of Directors. Under
     Wisconsin law, a special meeting of shareholders must also be called by the
     Board of Directors pursuant to a written demand of the holders of not less
     than one-tenth of the votes entitled to be cast at such meeting or by such
     other person as may be designated in the articles or by-laws.
 
                                       56
<PAGE>   65
 
          The Laidlaw Environmental Certificate provides that special meetings
     of the stockholders may be called only by the Chairman of the Board of
     Directors, the President of Laidlaw Environmental or the Chairman of the
     Executive Committee of the Board of Directors of Laidlaw Environmental. The
     Safety-Kleen By-Laws provide that special meetings of the shareholders may
     be called by the Chairman of the Board of Directors, the Board of
     Directors, or the President of Safety-Kleen at the request of holders of at
     least 10% of all votes entitled to be cast at a meeting of the
     shareholders, if such shareholders meet certain notice requirements in
     requesting a meeting.
 
          Inspection of Corporate Records.  The DGCL permits any stockholder of
     record to inspect the corporate records of a corporation upon a good faith
     showing of a proper purpose, and the stockholder list must be made
     available for inspection at least 10 days before a stockholders' meeting
     and may be inspected by any stockholder. By contrast, under the Wisconsin
     Statutes, in order to inspect and copy the corporate records of a
     corporation, including the shareholder list, a shareholder must be a
     shareholder of record and either has been a shareholder of record of the
     corporation for at least 6 months before making a demand or holds at least
     5% of the outstanding shares of the corporation. Under the Wisconsin
     Statutes, a shareholder's demand must also be made for a proper purpose. In
     addition, under the Wisconsin Statutes, all shareholders may inspect the
     shareholder list for a meeting beginning two business days after the notice
     of a meeting of shareholders is given and ending at the conclusion of the
     meeting.
 
          Dividends.  Under the DGCL, a corporation may pay dividends and
     repurchase stock out of surplus and any net profits for the fiscal year in
     which the dividend was declared or for the preceding fiscal year provided
     that no payment may reduce capital below the amount of capital represented
     by all classes of shares having a preference upon the distribution of
     assets. Under the Wisconsin Statutes, the board of directors may authorize
     and the corporation may make distributions to its shareholders unless after
     such distribution the corporation would not be able to pay its debts as
     they become due or its total assets after the distribution would be less
     than the sum of its total liabilities, plus, unless the articles of
     incorporation provide otherwise, the amount that would be needed, if the
     corporation were to be dissolved at the time of the distribution, to
     satisfy the preferential rights upon dissolution of shareholders whose
     preferential rights are superior to those receiving the distribution.
 
          Dissenters' Rights.  Under both Delaware and Wisconsin law, a
     shareholder is entitled to receive payment of the fair value of the
     shareholder's common stock if the shareholder dissents from a proposed
     merger or consolidation. Under the DGCL, dissenters' rights are not
     available in the case of a sale of all or substantially all of the assets
     of a corporation. Dissenters' rights also are not available for
     stockholders of the surviving corporation if the merger did not require the
     approval of the stockholders of the surviving corporation or if the shares
     of the Delaware corporation that is party to a merger or consolidation are
     listed on a national securities exchange or designated as a national market
     system security on an interdealer quotation system by the National
     Association of Securities Dealers, Inc., or are held of record by not less
     than 2,000 persons and in the merger or consolidation stockholders receive
     shares of stock of the corporation surviving or resulting from the merger
     or consolidation and/or shares of stock of any other corporation that are
     either listed on a national securities exchange or designated as a national
     market system security on an interdealer quotation system by the National
     Association of Securities Dealers, Inc. or held of record by more than
     2,000 persons and/or cash in lieu of fractional shares of the foregoing or
     any combination of the foregoing.
 
          In addition to being applicable in the case of a merger, under the
     Wisconsin Statutes, dissenters' rights are available in the case of a share
     exchange or sale of all or substantially all of the assets of a Wisconsin
     corporation. Dissenters' rights may also be made applicable by affirmative
     provision in the articles of incorporation, by-laws or a board of
     directors' resolution in the case of certain amendments to the articles of
     incorporation or other actions requiring a shareholder vote. Under the
     Wisconsin Statutes, holders of record and beneficial owners of the Shares
     may be entitled to dissenters' rights to object to the Merger and demand
     payment of the "fair value" of their Shares in cash, if they properly
     exercise such rights in connection with the consummation of the Merger in
     accordance with the provisions of the Wisconsin Statutes. Such dissenters'
     rights will not be available if the Shares are registered on a national
     securities exchange or quoted on the National Association of Securities
     Dealers, Inc., automated
 
                                       57
<PAGE>   66
 
     quotations system on the record date fixed to determine the shareholders of
     the Company entitled to notice of a shareholders' meeting at which
     shareholders are to vote on the Merger, unless the Merger would be a
     "business combination" as defined in Section 180.1130(3) of the Wisconsin
     Statutes. The Merger would not be a "business combination" if, among other
     things, it is consummated as a short-form merger under the Wisconsin
     Statutes (where Laidlaw Environmental owns 90% or more of each class of
     outstanding shares of a subsidiary corporation, it may merge the subsidiary
     corporation into itself upon adoption of a merger agreement by the board of
     directors of a parent corporation and upon complying with certain notice
     requirements, but without approval of the shareholders of the parent or the
     subsidiary) or, at the time, Safety-Kleen does not have a class of equity
     securities held of record by 500 or more persons and at least 100
     shareholders of record who have unlimited voting rights and who are
     residents of the State of Wisconsin. "Fair Value" of the Shares would be
     determined immediately before the consummation of the Merger, excluding any
     appreciation or depreciation in anticipation of the Merger unless such
     exclusion would be inequitable; provided, however, that if the Merger is a
     business combination, "fair value" will be determined pursuant to Section
     180.1130(9)(a) of the Wisconsin Statutes with reference to the public
     market price of the Shares if available or, if not available, by a good
     faith determination of the Company's Board of Directors. The "fair value"
     as so determined, could be equal to, more or less than the value per Share
     to be paid pursuant to the Offer and the Merger.
 
          The foregoing summary of the rights of dissenting shareholders does
     not purport to be a complete statement of the procedures to be followed by
     shareholders desiring to exercise their dissenters' rights in connection
     with the Merger. The preservation and exercise of dissenters' rights are
     conditioned on strict adherence to the applicable provisions of the
     Wisconsin Statutes.
 
          Director and Officer Discretion.  Under the provisions of Section
     180.0827 of the Wisconsin Statutes (the "Wisconsin Stakeholder
     Provisions"), in discharging his or her duties to the corporation and in
     determining what he or she believes to be in the best interests of the
     corporation, a director or officer may, in addition to considering the
     effects of any action on shareholders, consider the effects of the action
     on employees, suppliers, customers, the communities in which the
     corporation operates and any other factors that the director or officer
     considers pertinent. Under Delaware law, the consideration that a board may
     give to nonstockholder constituencies is less clear. Under Delaware
     judicial doctrine, a director may generally consider the effect of a
     proposed action on nonstockholder constituencies when these interests are
     not adverse to the interests of stockholders.
 
          Anti-Takeover Statutes.  DGCL Section 203 (the "Delaware Business
     Combination Statute") applies to certain business combinations involving a
     corporation and certain of its stockholders. Unless the corporation's
     certificate of incorporation expressly provides that Section 203 of the
     DGCL shall not apply, the Delaware Business Combination Statute prevents an
     "Interested Stockholder" (defined generally as a person with 15% or more of
     the corporation's outstanding voting stock) from engaging in a "Business
     Combination" (defined to include a variety of transactions, including the
     sale of assets, mergers and almost any related party transaction) with a
     Delaware corporation for three years following the date such person became
     an Interested Stockholder, unless (i) before such person became an
     Interested Stockholder, the board of directors of the corporation approved
     the transaction in which the Interested Stockholder became an Interested
     Stockholder or approved the Business Combination; (ii) upon consummation of
     the transaction which resulted in the Interested Stockholder becoming an
     Interested Stockholder, the Interested Stockholder owned at least 85% of
     the voting stock of the corporation outstanding at the time the transaction
     commenced (excluding stock held by directors who are also officers of the
     corporation and by certain employee stock ownership plans); or (iii)
     following the transaction in which such person became an Interested
     Stockholder, the Business Combination is approved by the board of directors
     of the corporation and authorized at a meeting of stockholders by the
     affirmative vote of the holders of two-thirds of the outstanding voting
     stock of the corporation not owned by the Interested Stockholder. The
     Delaware Business Combination Statute currently applies to Laidlaw
     Environmental.
 
          Sections 180.1140 to 180.1144 of the Wisconsin Statutes (the
     "Wisconsin Business Combination Statute") regulate a broad range of
     "business combinations" between a Wisconsin corporation and an
 
                                       58
<PAGE>   67
 
     "interested stockholder." The Wisconsin Business Combination Statute
     defines a "business combination" to include a merger or share exchange,
     sale, lease, exchange, mortgage, pledge, transfer or other disposition of
     assets equal to at least 5% of the market value of the stock or assets of
     the company or 10% of its earning power, or issuance of stock or rights to
     purchase stock with a market value equal to at least 5% of the outstanding
     stock, adoption of a plan of liquidation and certain other transactions
     involving an "interested stockholder." An "interested stockholder" is
     defined as a person who beneficially owns, directly or indirectly, 10% of
     the voting power of the outstanding voting stock of a corporation or who is
     an affiliate or associate of the corporation and beneficially owned 10% of
     the voting power of the then outstanding voting stock within the last three
     years. The Wisconsin Business Combination Statute prohibits a corporation
     from engaging in a business combination (other than a business combination
     of a type specifically excluded from the coverage of the statute) with an
     interested stockholder for a period of three years following the date such
     person becomes an interested stockholder, unless the board of directors
     approved the business combination or the acquisition of the stock that
     resulted in a person becoming an interested stockholder before such
     acquisition. Business combinations after the three-year period following
     the stock acquisition date are permitted only if (i) the board of directors
     approved the acquisition of the stock prior to the acquisition date; (ii)
     the business combination is approved by a majority of the outstanding
     voting stock not beneficially owned by the interested stockholder; or (iii)
     the consideration to be received by shareholders meets certain requirements
     of the statute with respect to form and amount. Unlike the prohibition on
     business combinations in the Delaware Business Combination Statute, which
     is inapplicable if the interested stockholder acquires at least 85% of the
     outstanding voting stock at the time of becoming an interested stockholder
     or if during the three-year period of the prohibition the board of
     directors and holders of two-thirds of the unaffiliated shares approve the
     business combination, the Wisconsin Business Combination Statute's
     prohibition on business combinations applies for three years after the
     acquisition of at least 10% of the outstanding shares without regard to the
     percentage of shares owned by the interested stockholder and cannot be
     avoided by subsequent action of the board of directors or shareholders. As
     presently constituted, the staute only applies to a resident domestic
     corporation that does not have a class of voting stock that is registered
     or traded on a national securities exchange or that is registered under
     Section 12(g) of the Securities Exchange Act.
 
          Sections 180.1130 to 180.1132 of the Wisconsin Statutes provide that
     certain mergers, share exchanges or sales, leases, exchanges or other
     dispositions of assets in a transaction involving a "significant
     shareholder" and an issuing public corporation are subject to a
     supermajority vote of shareholders (the "Wisconsin Fair Price Statute"), in
     addition to any approval otherwise required. A "significant shareholder" is
     defined as a person who beneficially owns, directly or indirectly, 10% or
     more of the voting stock of a corporation or an affiliate of the
     corporation which beneficially owned, directly or indirectly, 10% or more
     of the voting stock of the corporation within the last two years. Such
     business combination must be approved by 80% of the voting power of the
     corporation's stock and at least two-thirds of the voting power of the
     corporation's stock not beneficially held by the significant shareholder
     who is party to the relevant transaction or any of its affiliates or
     associates, in each case voting together as a single group, unless the
     following fair price standards have been met: (i) the aggregate value of
     the per share consideration is equal to the higher of (a) the highest price
     paid for any common shares of the corporation by the significant
     shareholder in the transaction in which it became a significant shareholder
     or within two years before the date of the business combination; (b) the
     market value of the corporation's shares on the date of commencement of any
     tender offer by the significant shareholder, the date on which the person
     became a significant shareholder or the date of the first public
     announcement of the proposed business combination, whichever is higher; or
     (c) the highest liquidation or dissolution distribution to which holders of
     the shares would be entitled; and (ii) either cash, or the form of
     consideration used by the significant shareholder to acquire the largest
     number of shares, is offered. However, the impact of the Wisconsin Fair
     Price Statute is limited because the statute does not prohibit an acquirer
     from effecting a second step transaction as a "reverse stock split" without
     complying with the statute.
 
          Under Section 180.1150 (the "Wisconsin Control Share Statute") of the
     Wisconsin Statutes, the voting power of shares, including shares issuable
     upon conversion of convertible securities or exercise of options or
     warrants, of an "issuing public corporation" held by any person or persons
     acting as a group in
 
                                       59
<PAGE>   68
 
     excess of 20% of the voting power in the election of directors is limited
     to 10% of the full voting power of those shares, unless the articles of
     incorporation otherwise provide. This restriction does not apply to shares
     acquired directly from the issuing public corporation, in certain specified
     transactions, or in a transaction in which the corporation's shareholders
     have approved restoration of the full voting power of the otherwise
     restricted shares. As presently constituted, the statute only applies to a
     resident domestic corporation that does not have a class of voting stock
     that is registered or traded on a national securities exchange or that is
     registered under Section 12(g) of the Securities Exchange Act. The DGCL
     does not have a similar provision.
 
          Section 180.1134 (the "Wisconsin Defensive Action Restrictions") of
     the Wisconsin Statutes provides that in addition to the vote otherwise
     required by law or the articles of incorporation of an issuing public
     corporation the approval of the holders of a majority of the shares
     entitled to vote is required before such a corporation can take certain
     action while a takeover offer is being made or after the takeover offer has
     been publicly announced and before it is concluded. Under the Wisconsin
     Defensive Action Restrictions, shareholder approval is required for the
     corporation to (i) acquire more than 5% of the outstanding voting shares at
     a price above the market price from any individual or organization that
     owns more than 3% of the outstanding voting shares and has held such shares
     for less than two years, unless an equal offer is made to acquire all
     voting shares; or (ii) sell or option assets of the corporation which
     amount to at least 10% of the market value of the corporation, unless in
     the case of this clause (ii) the corporation has at least three independent
     directors and a majority of the independent directors vote to opt out of
     this provision. The DGCL does not have a similar provision.
 
          Statutory Shareholder Liability.  Wisconsin law provides that
     shareholders of Wisconsin domestic corporations and foreign corporations
     registered to do business in Wisconsin are personally liable, up to the
     value of the consideration paid to the corporation for their shares, for
     certain debts owed to employees for services performed. While the Wisconsin
     Statutes specifies that such liability is limited to the par value of the
     shares, this has been interpreted by at least one Wisconsin trial court to
     mean the consideration paid to a corporation for shares. This decision was
     affirmed by a split decision of the Wisconsin Supreme Court with one
     justice abstaining. As a result, the affirmance is without precedential
     effect. Delaware has no comparable provision.
 
          "Going Private" Transactions.  The securities regulations of the State
     of Wisconsin (Wisconsin Administrative Code Section DFI -- Sec. 6.05)
     contain provisions that under certain circumstances may require a filing in
     connection with the fairness of certain "going private" transactions.
     Laidlaw Environmental believes such provisions are not applicable to the
     Offer or the Merger.
 
OTHER COMPARISONS
 
     Preemptive Rights.  No shareholder of Safety-Kleen or Laidlaw Environmental
has preemptive rights with regard to shares of common or preferred stock.
 
     Shareholder Rights Plan.  As described above in "The Offer -- Conditions of
the Offer -- Rights Agreement," Safety-Kleen has entered into the Rights
Agreement pursuant to which Shares in issue on or after November 9, 1988 entitle
the holder thereof to one Right, subject to certain exceptions.
 
     Laidlaw Environmental is a party to a similar agreement which is triggered
by a tender offer for or acquisition of 15% or more of the issued and
outstanding Laidlaw Environmental Common Stock.
 
                                       60
<PAGE>   69
 
                                 MARKET PRICES
 
     The Laidlaw Environmental Common Stock is listed and principally traded on
the NYSE. The Shares are listed and traded on the NYSE. The following table sets
forth the range of high and low sales prices as reported on the NYSE Composite
Tape.
 
<TABLE>
<CAPTION>
                                                         LAIDLAW
                                                      ENVIRONMENTAL          SAFETY-KLEEN
                                                    ------------------    ------------------
                                                       PRICE RANGE           PRICE RANGE
                                                    ------------------    ------------------
                                                     HIGH        LOW       HIGH        LOW
                                                    -------    -------    -------    -------
<S>                                                 <C> <C>    <C> <C>    <C> <C>    <C> <C>
1995
First Quarter.....................................    5 1/2      4         17 7/8     14 1/2
Second Quarter....................................    5          4 1/8     18 1/8     15
Third Quarter.....................................    5 1/4      4 1/4     18         12 7/8
Fourth Quarter....................................    4 1/2      2 3/4     15 3/4     13 3/4
1996
First Quarter.....................................    3 1/8      2         15 7/8     13 3/8
Second Quarter....................................    4 1/2      2 1/4     17 1/2     14 1/2
Third Quarter.....................................    4 1/2      2 5/8     18 5/8     15 1/8
Fourth Quarter....................................    2 7/8      1 5/8     17 1/4     14 3/4
1997
First Quarter.....................................    3 3/8      1 3/4     18 3/8     14 1/2
Second Quarter....................................    5 1/4      2 5/8     17 11/16   14 1/8
Third Quarter.....................................    5 15/16    2 7/8     26         16
Fourth Quarter (through November   , 1997)........
</TABLE>
 
     On November 3, 1997, the last trading day prior to the public announcement
of Laidlaw Environmental's offer to acquire Safety-Kleen, the closing sales
price per Share was $22.125, and the closing sales price per share of Laidlaw
Environmental Common Stock was $4.9375. On             , 1997, the last trading
day prior to the date of the Prospectus, the closing price per Share was
$          , and the closing price per share of Laidlaw Environmental Common
Stock was $          . Past price performance is not necessarily indicative of
likely future price performance. Holders of Shares are urged to obtain current
market quotations for shares of Laidlaw Environmental Common Stock.
 
     According to the Safety-Kleen 1996 Form 10-K, there were, as of December
28, 1996, 8,042 holders of record of Shares. As of October 7, 1997, there were
6,234 holders of record of shares of Laidlaw Environmental Common Stock.
 
     According to the Safety-Kleen Form 8-K filed November 10, 1988, the Rights
are listed on the NYSE, but are currently attached to all outstanding Shares and
may not be traded separately. Upon the occurrence of the Safety-Kleen
Distribution Date, the Rights are to trade separately from the Shares.
 
                 VALIDITY OF LAIDLAW ENVIRONMENTAL COMMON STOCK
 
     The validity of the shares of Laidlaw Environmental Common Stock offered
hereby will be passed upon for Laidlaw Environmental by Katten Muchin & Zavis,
525 West Monroe Street, Chicago, Illinois 60661.
 
                                    EXPERTS
 
     The consolidated balance sheets as of August 31, 1997 and 1996 and the
consolidated statements of income, shareholders' equity and cash flows for each
of the three years in the period ended August 31, 1997, of Laidlaw Environmental
incorporated by reference in this prospectus and elsewhere in the Registration
Statement have been incorporated herein in reliance on the report of Coopers &
Lybrand L.L.P. independent accountants, given on the authority of that firm as
experts in accounting and auditing.
 
                                       61
<PAGE>   70
 
                                                                      SCHEDULE A
 
           DIRECTORS AND EXECUTIVE OFFICERS OF LAIDLAW ENVIRONMENTAL
 
     Directors and Executive Officers of Laidlaw Environmental.  The name,
business address, present principal occupation or employment and five-year
employment history of each of the directors and executive officers of Laidlaw
Environmental are set forth below. Unless otherwise indicated, each occupation
set forth opposite an individual's name refers to employment with Laidlaw
Environmental. Unless otherwise indicated, each director and executive officer
listed below is a citizen of the United States.
 
<TABLE>
<CAPTION>
                                                  PRINCIPAL OCCUPATION OR EMPLOYMENT DURING THE
NAME AND BUSINESS ADDRESS              AGE      LAST FIVE YEARS, DIRECTORSHIPS OF PUBLIC COMPANIES
- -------------------------              ---      --------------------------------------------------
<S>                                    <C>   <C>
Kenneth W. Winger....................  59    President, Chief Executive Officer and Director of
  President, Chief Executive Officer         Laidlaw Environmental since May 15, 1997; President,
  and Director of Laidlaw                    Chief Operating Officer and sole director of Laidlaw
  Environmental since May 1997               Environmental Services (US), Inc. from July 1995 until
  Laidlaw Environmental Services,            May 1997; Executive Vice President for Business
  Inc.                                       Development of Laidlaw Waste Systems, Ltd. from January
  1301 Gervais Street, Suite 300             1995 until July 1995; from May 1991 until December 1994,
  Columbia, S.C. 29201                       Senior Vice President for Corporate Development of
                                             Laidlaw Inc. Mr. Winger also is a director of ViroGroup,
                                             Inc. Non- U.S. citizen.
James R. Bullock.....................  53    President and Chief Executive Officer of Laidlaw Inc.
  Director of Laidlaw Environmental          since October 1993; for more than a year prior thereto,
  and Chairman of the Board since May        President and Chief Executive Officer of Cadillac
  1997                                       Fairview Corporation Limited. Mr. Bullock also is a
  Laidlaw Inc.                               director of Laidlaw Inc. Non-U.S. citizen.
  3221 North Service Road
  Burlington, Ontario L7R 3Y8
John R. Grainger.....................  48    Executive Vice President and Chief Operating Officer of
  Director of Laidlaw Environmental          Laidlaw Inc. since September 1997; President and Chief
  since May 1997                             Operating Officer of Laidlaw Transit, Inc. since May
  Laidlaw Inc.                               1992. Mr. Grainger currently serves as Chairman of the
  3221 North Service Road                    Human Resources and Compensation Committee. Non-U.S.
  Burlington, Ontario L7R 3Y8                citizen.
Leslie W. Haworth....................  54    Senior Vice President and Chief Financial Officer of
  Director of Laidlaw Environmental          Laidlaw Inc. for more than five years. Mr. Haworth
  since May 1997                             currently serves as Chairman of the Audit Committee.
  Laidlaw Inc.                               Non-U.S. citizen.
  3221 North Service Road
  Burlington, Ontario L7R 3Y8
John W. Rollins, Sr..................  80    Chairman of the Board and Chief Executive Officer of
  Director of Rollins since 1982             Rollins Truck Leasing Corp. for more than five years.
  Rollins Truck Leasing Corp.                Mr. Rollins was Chairman of the Board and Chief
  2200 Concord Pike                          Executive Officer of Rollins from 1988 until May 15,
  One Rollins Plaza                          1997. Mr. Rollins also is a director of Matlack Systems,
  Wilmington, DE 19803                       Inc., Rollins, Inc., RPC, Inc. and Dover Downs En-
                                             tertainment, Inc. Mr. Rollins is the father of John W.
                                             Rollins, Jr.
</TABLE>
 
                                       A-1
<PAGE>   71
<TABLE>
<CAPTION>
                                                  PRINCIPAL OCCUPATION OR EMPLOYMENT DURING THE
NAME AND BUSINESS ADDRESS              AGE      LAST FIVE YEARS, DIRECTORSHIPS OF PUBLIC COMPANIES
- -------------------------              ---      --------------------------------------------------
<S>                                    <C>   <C>
John W. Rollins, Jr..................  55    President and Chief Operating Officer and a director of
  Director of Rollins since 1982             Rollins Truck Leasing Corp. for more than five years;
  Rollins Truck Leasing Corp.                Chairman of the Board of Matlack Systems, Inc. for more
  2200 Concord Pike                          than five years. Mr. Rollins was Senior Vice Chairman of
  One Rollins Plaza                          the Board of Rollins from 1988 until May 15, 1997. Mr.
  Wilmington, DE 19803                       Rollins also is a director of Dover Downs Entertainment,
                                             Inc. Mr. Rollins is a member of the Human Resources and
                                             Compensation Committee. Mr. Rollins is the son of John
                                             W. Rollins, Sr.
David E. Thomas, Jr..................  40    Senior Managing Director and the Head of the Investment
  Director of Laidlaw Environmental          Banking Group of Raymond James since July 1996; from
  since June 1997                            1991 until July 1996, Managing Director of Raymond
  Raymond James & Associates, Inc.           James. Mr. Thomas also is a director of Reynolds, Smith
  880 Carillon Parkway                       and Hills, Inc. Mr. Thomas is a member of the Human
  St. Petersburg, FL 33716                   Resources and Compensation Committee.
Henry B. Tippie......................  70    For more than five years, Chairman of the Board and
  Director of Rollins since 1982             President of Tippie Services; for more than five years,
  Tippie Service, Inc.                       Chairman of the Executive Committee and Vice Chairman of
  3420 Executive Center Drive, NW            the Board of Rollins Truck Leasing Corp. Mr. Tippie was
  Suite 163                                  Chairman of the Executive Committee of Rollins from 1988
  Austin, TX 78731                           until May 15, 1997. Mr. Tippie also is a director of
                                             Matlack Systems, Inc., Dover Downs Entertainment, Inc.,
                                             RPC, Inc. and Rollins Inc. Mr. Tippie is a member of the
                                             Audit Committee.
James L. Wareham.....................  58    President of AK Steel Corporation since March 1997; from
  Director of Laidlaw Environmental          1992 until 1996, Chief Executive Officer of
  since June 1997                            Wheeling-Pittsburgh Steel Corporation. Mr. Wareham is a
  AK Steel Corporation                       member of the Audit Committee.
  703 Curtis Street
  Middleton, OH 45043
Grover C. Wrenn......................  54    Chairman and Chief Executive Officer of Better Health
  Director of Laidlaw Environmental          Network, Inc. since June 1996; Chief Executive Officer
  since July 1997                            of EnSys Environmental Products, Inc. from April 1995
  4 Wolfe Street                             through December 1996; and President and Chief Executive
  Alexandria, VA 22314                       Officer of Applied Bioscience International from 1991
                                             through March 1995. Mr. Wrenn also is a director of
                                             Strategic Diagnostics, Inc. and Pharmakinetics Labora-
                                             tories, Inc.
Michael A. Bragagnloo................  51    Executive Vice President and Chief Operating Officer of
  Executive Vice President and Chief         Laidlaw Environmental Services, Inc. since May 15, 1997;
  Operating Officer of Laidlaw               Executive Vice President and Chief Operating Officer of
  Environmental since May 1997               Laidlaw Environmental Services (US), Inc. from January
  Laidlaw Environmental Services,            1997 until May 1997; Executive Vice President of United
  Inc.                                       States Operations of Laidlaw Waste Systems, Inc. from
  1301 Gervais Street, Suite 300             September 1993 until January 1997; Vice President of
  Columbia, SC 29201                         Strategic Analysis and Planning of Laidlaw Waste
                                             Systems, Inc. from December 1991 until September 1993.
                                             Non- U.S. Citizen.
</TABLE>
 
                                       A-2
<PAGE>   72
<TABLE>
<CAPTION>
                                                  PRINCIPAL OCCUPATION OR EMPLOYMENT DURING THE
NAME AND BUSINESS ADDRESS              AGE      LAST FIVE YEARS, DIRECTORSHIPS OF PUBLIC COMPANIES
- -------------------------              ---      --------------------------------------------------
<S>                                    <C>   <C>
Henry H. Taylor......................  53    Vice President, General Counsel and Secretary of Laidlaw
  Vice President, General Counsel and        Environmental Services, Inc. since May 15, 1997; Vice
  Secretary of Laidlaw Environmental         President of Legal and Regulatory Affairs and Secretary
  since May 1997.                            of Laidlaw Environmental Services (US), Inc. September
  Laidlaw Environmental Services,            1995 until May 1997; Vice President of Legal Affairs of
  Inc.                                       Laidlaw Environmental Services (US), Inc. May 1990 until
  1301 Gervais Street, Suite 300             January 1995.
  Columbia, SC 29201
Paul R. Humphreys....................  38    Senior Vice President of Finance and Chief Financial
  Senior Vice President, Finance and         Officer of Laidlaw Environmental Services, Inc. since
  Chief Financial Officer of Laidlaw         May 15, 1997; Vice President of Finance for Laidlaw
  Environmental since May 1997               Environmental Services (US), Inc. January 1995 until May
  Laidlaw Environmental Services,            1997; Manager of Finance for Laidlaw Inc. from 1988
  Inc.                                       until January 1995. Non-U.S. Citizen
  1301 Gervais Street, Suite 300
  Columbia, SC 29201
</TABLE>
 
                                       A-3
<PAGE>   73
 
                                                                      SCHEDULE B
 
                OWNERSHIP OF SHARES BY CERTAIN BENEFICIAL OWNERS
                          AND SAFETY-KLEEN MANAGEMENT
 
     The following table and notes thereto, which, other than information
regarding Laidlaw Environmental, are reproduced from the Safety-Kleen Proxy
Statement, set forth certain information with respect to beneficial ownership of
Shares as of March 28, 1997 by (a) all directors of Safety-Kleen, (b) the named
directors and officers of Safety-Kleen, including the executive officers of
subsidiaries of Safety-Kleen and (c) all directors and executive officers of
Safety-Kleen as a group. The following table also sets forth certain information
with respect to beneficial ownership of Shares by Laidlaw Environmental as of
the date of this Prospectus. An asterisk indicates ownership of less than one
percent of outstanding Shares.
 
<TABLE>
<CAPTION>
                                                                                     PERCENTAGE OF
                                                           NUMBER OF SHARES           OUTSTANDING
NAME                                                     BENEFICIALLY OWNED(1)      COMMON STOCK(2)
- ----                                                     ---------------------     -----------------
<S>                                                      <C>                       <C>
Donald W. Brinckman....................................          869,156(3)              1.48%
Joseph Chalhoub........................................          350,683(4)            *
David A. Dattilo.......................................          119,972(5)            *
Richard T. Farmer......................................           42,750(6)            *
Russell A. Gwillim.....................................          197,981(7)            *
F. Henry Habicht II....................................           42,226(8)            *
Edgar D. Jannotta......................................           67,500(6)            *
John G. Johnson, Jr....................................           91,513(9)            *
Karl G. Otzen..........................................        1,480,581(12)             2.54%
Paul D. Schrage........................................           31,180(6)
Marcia E. Williams.....................................            8,500(10)           *
W. Gordon Wood.........................................           70,805(6)            *
</TABLE>
 
- ---------------
 
   * Denotes less than one percent of shares outstanding.
 (1) Under regulations of the Securities and Exchange Commission, persons who
     own or have the power to vote or dispose of shares, either alone or jointly
     with others, are deemed to be the beneficial owners of such shares. Such
     persons are also deemed to be the beneficial owners of shares beneficially
     owned by certain close family members.
 (2) Shares subject to options exercisable within 60 days of February 26, 1997
     are considered outstanding for the purpose of determining the percent of
     the class held by the holder of such option, but not for the purpose of
     computing the percentage held by others.
 (3) Includes 73 shares owned by his wife, 431,091 shares subject to options
     exercisable within 60 days of February 26, 1997 and 1,033 shares held in
     the Company's 401(k) plan as to which he does not have voting control.
 (4) Includes 275,000 shares owned by Breslube Industries, Ltd. of which 100% is
     owned by Mr. Chalhoub. Also included are 59 shares owned by his wife, 75
     shares owned by his son and 75,549 shares subject to options exercisable
     within 60 days of February 26, 1997.
 (5) Includes 88,627 shares subject to options exercisable within 60 days of
     February 26, 1997.
 (6) Includes 30,000 shares subject to options exercisable within 60 days of
     February 26, 1997.
 (7) Includes 30,223 shares owned by his wife and 30,000 shares subject to
     options exercisable within 60 days of February 26, 1997. Mr Gwillim is also
     a co-trustee for 45,827 shares held in an irrevocable trust for which he
     has no beneficial ownership; such shares are not included in the table.
 (8) Includes 39,712 shares subject to options exercisable within 60 days of
     February 26, 1997 and 114 shares held in the Company's 401(i) plan as to
     which he does not have voting control.
 (9) Includes 700 shares owned by his wife, 81,962 shares subject to options
     exercisable within 60 days of February 26, 1997 and 322 shares held in the
     Company's 401(k) plan as to which he does not have voting control.
(10) Includes 7,500 shares subject to options exercisable within 60 days of
     February 26, 1997.
(11) Includes 1,537,470 shares subject to options exercisable within 60 days of
     February 26, 1997 and 1,798 shares held in the Company's 401(k) plan as to
     which they do not have voting control.
(12) Karl G. Otzen and Lucy T. Otzen (the "Otzens") are husband and wife. For
     purposes of this table, each is deemed to own shares owned by the other,
     and accordingly the same shares are shown opposite each of their names. In
     December 1992, the Otzens caused 683,760 of the shares shown opposite each
     of
 
                                       B-1
<PAGE>   74
 
     their names to be contributed to Circle L Limited Partnership. The general
     partner which controls the Partnership is a corporation in which Karl G.
     Otzen, Luch T. Otzen, Joan Emery Lammers and her husband (the "Lammers")
     each own 25% of the voting stock and each occupies one of the four
     positions on the Board of Directors. Because the Otzens and Lammers share
     voting power over all of the shares held by the Partnership, each of them
     may be deemed to "own" all shares in the partnership under the criteria
     governing this table. To enhance clarity of presentation, however, the
     shares contributed to the Partnership by Joan Emery Lammers are shown
     opposite the Otzens' names also include: 757,721 shares owned by trustees
     of which the Otzens are co-trustees, 9,100 shares owned by a trust of which
     The Northern Trust Company is trustee and 30,000 shares subject to options
     exercisable by Karl G. Otzen within 60 days of February 26, 1997.
 
                                       B-2
<PAGE>   75
 
     Manually signed facsimile copies of the Letter of Transmittal will be
accepted. The Letter of Transmittal, certificates for Shares and any other
required documents should be sent or delivered by each Safety-Kleen Shareholder
or his or her broker, dealer, commercial bank, trust company or other nominee to
the Exchange Agent at one of its addresses set forth below.
 
                       IBJ SCHRODER BANK & TRUST COMPANY
 
<TABLE>
<S>                             <C>                             <C>
            BY HAND                  BY OVERNIGHT COURIER                   BY MAIL
 
        1 State Street                  1 State Street                    P.O. Box 84
   New York, New York 10004        New York, New York 10004          Bowling Green Station
      Attn: Reorg. Dept.              Attn: Reorg. Dept.           New York, New York 10004
     Securities Processing           Securities Processing            Attn: Reorg. Dept.
          Window SC-1                     Window SC-1                Securities Processing
                                                                          Window SC-1
      By Facsimile Transmission                     Telephone Number
  (for Eligible Institutions only)           For information call collect:
           (212) 858-2611                            (212) 858-2100
Confirm by telephone: (212) 858-2013
</TABLE>
 
Any questions or requests for assistance or additional copies of the Prospectus,
the Letter of Transmittal and the Notice of Guaranteed Delivery may be directed
to the Information Agent or the Dealer Manager at their respective telephone
numbers and locations listed below. You may also contact your local broker,
commercial bank, trust company or nominee for assistance concerning the Offer.
 
                    The Information Agent for the Offer is:
 
                               MORROW & CO., INC.
                                909 Third Avenue
                                   20th Floor
                               New York, NY 10022
                                  212/754-8000
                             Toll Free 800/566-9061
 
                              Banks and Brokerage
                               Firms please call:
                                  800/662-5200
 
                      The Dealer Manager for the Offer is:
 
                            BEAR, STEARNS & CO. INC.
                                245 Park Avenue
                               New York, NY 10167
                                  212/272-2000
                             Toll Free 800/999-2000
<PAGE>   76
 
                                    PART II
 
                     INFORMATION NOT REQUIRED IN PROSPECTUS
 
ITEM 20.  INDEMNIFICATION OF DIRECTORS AND OFFICERS
 
     Laidlaw Environmental is incorporated under the laws of the State of
Delaware. Section 145 of the DGCL, inter alia ("Section 145") provides that a
Delaware corporation may indemnify any person who were, are or are threatened to
be made, parties to any threatened, pending or completed action, suit or
proceeding, whether civil, criminal, administrative or investigative (other than
an action by or in the right of such corporation), by reason of the fact that
such person is or was an officer, director, employee or agent of such
corporation, or is or was serving at the request of such corporation as a
director, officer, employee or agent of another corporation or enterprise. The
indemnity may include expenses (including attorneys' fees), judgments, fines and
amounts paid in settlement actually and reasonably incurred by such person in
connection with such action, suit or proceeding, provided such person acted in
good faith and in a manner he reasonably believed to be in or not opposed to the
corporation's best interests and, with respect to any criminal action or
proceeding, had no reasonable cause to believe that his conduct was illegal. A
Delaware corporation may indemnify any persons who are, were or are threatened
to be made, a party to any threatened, pending or completed action or suit by or
in the right of the corporation by reason of the fact that such person was a
director, officer, employee or agent of such corporation, or is or was serving
at the request of such corporation as a director, officer, employee or agent of
another corporation or enterprise. The indemnity may include expenses (including
attorneys' fees) actually and reasonably incurred by such person in connection
with the defense or settlement of such action or suit, provided such person
acted in good faith and in a manner he reasonably believed to be in or not
opposed to the corporation's best interests, provided that no indemnification is
permitted without judicial approval if the officer, director, employee or agent
is adjudged to be liable to the corporation. Where an officer, director,
employee or agent is successful on the merits or otherwise in the defense of any
action referred to above, the corporation must indemnify him against the
expenses which such officer or director has actually and reasonably incurred.
 
     The Laidlaw Environmental Certificate of Incorporation provides that, to
the fullest extent permitted by the DGCL as the same exists or may hereafter be
amended, a director of Laidlaw Environmental shall not be liable to Laidlaw
Environmental or its stockholders for monetary damages for a breach of fiduciary
duty as a director.
 
     Section 145 further authorizes a corporation to purchase and maintain
insurance on behalf of any person who is or was a director, officer, employee or
agent of the corporation, or is or was serving at the request of the corporation
as a director, officer, employee or agent of another corporation or enterprise,
against any liability asserted against him and incurred by him in any such
capacity, arising out of his status as such, whether or not the corporation
would otherwise have the power to indemnify him under Section 145.
 
     [ALL OF THE LAIDLAW ENVIRONMENTAL DIRECTORS AND OFFICERS ARE COVERED BY
INSURANCE POLICIES MAINTAINED AND HELD IN EFFECT BY LAIDLAW ENVIRONMENTAL
AGAINST CERTAIN LIABILITIES FOR ACTIONS TAKEN IN SUCH CAPACITIES, INCLUDING
LIABILITIES UNDER THE SECURITIES ACT OF 1933.]
 
                                      II-1
<PAGE>   77
 
ITEM 21.  EXHIBITS AND FINANCIAL STATEMENT SCHEDULES
 
<TABLE>
<CAPTION>
EXHIBIT
NUMBER                                      DESCRIPTION
- -------                                     -----------
<C>            <C>  <S>
   (3)(a)       --  Restated Certificate of Incorporation of the Company dated
                    May 13, 1997, and Amendment to Certificate of Incorporation
                    dated May 15, 1997, filed as Exhibit 3(a) to the
                    Registrant's Form 10-Q for the Quarter ended May 31, 1997,
                    and incorporated herein by reference.
   (3)(a)(1)    --  Certificate of Correction Filed to Correct a Certain Error
                    in the Restated and Amended Certificate of Incorporation of
                    the Company dated October 15, 1997, filed as Exhibit 3(a)(i)
                    to the Registrant's Form 10-K for the Fiscal Year ended
                    August 31, 1997, and incorporated herein by reference.
   (3)(b)       --  Bylaws of the Company filed as Exhibit 4(ii) to the
                    Registrant's Current Report on Form 8-K dated July 29, 1997,
                    and incorporated herein by reference.
   (4)(a)       --  Rights Agreement dated as of June 14, 1989 between the
                    Company and First Chicago Trust Company as successor to
                    Registrar and Transfer Company, as Rights Agent filed as an
                    Exhibit to the Registrant's Form 8-K filed on June 13, 1995
                    and incorporated herein by reference.
   (4)(b)       --  Amendment No. 1 dated as of March 31, 1995 to the Rights
                    Agreement between the Company and First Chicago Trust
                    Company as successor to Registrar and Transfer Company, as
                    Rights Agent filed as an Exhibit to the Registrant's Form
                    8-K filed on June 13, 1995 and incorporated herein by
                    reference.
   (4)(c)       --  Credit Agreement among Laidlaw Chem-Waste, Inc., Laidlaw
                    Environmental Services (Canada) Ltd., Toronto Dominion
                    (Texas) Inc., The Toronto-Dominion Bank, TD Securities (USA)
                    Inc., the Bank or Nova Scotia, NationsBank, N.A. and The
                    First National Bank of Chicago and NationsBank, N.A. as
                    Syndication Agent dated as of May 9, 1997, filed as Exhibit
                    4(c) to the Registrant's Form 10- Q for the Quarter ended
                    March 31, 1997, and incorporated herein by reference.
   (4)(d)       --  $350,000,000 5% Subordinated Convertible Pay-In-Kind
                    Debenture due 2009 issued by Registrant on May 15, 1997 to
                    Laidlaw Inc. the form of which was included as an appendix
                    to the Registrant's Definitive Proxy Statement on Form DEF
                    14A, filed on May 1, 1997 and incorporated herein by
                    reference.
   (4)(e)       --  Registration Rights Agreement dated May 15, 1997 between
                    Registrant, Laidlaw Transportation, Inc. and Laidlaw Inc.
                    included as appendix to the Registrant's Definitive Proxy
                    Statement on Form DEF 14A, the form of which was filed on
                    May 1, 1997 and incorporated herein by reference.
   (4)(f)       --  Indenture dated as of May 1, 1993 between the Industrial
                    Development Board of the Metropolitan Government of
                    Nashville and Davidson County (Tennessee) and NationsBank of
                    Tennessee, N.A., filed as Exhibit 4(f) to the Registrant's
                    Form 10-Q for the Quarter ended May 31, 1997, and
                    incorporated herein by reference.
   (4)(g)       --  Indenture of Trust dated as of February 1, 1995 between
                    Carbon County, Utah and West One Bank, Utah, now known as
                    U.S. Bank, as Trustee, filed as Exhibit 4(g) to the
                    Registrant's Form 10-Q for the Quarter ended May 31, 1997,
                    and incorporated herein by reference.
   (4)(h)       --  Indenture of Trust dated as of August, 1995 between Tooele
                    County, Utah and West One Bank, Utah, now known as U.S.
                    Bank, as Trustee, filed as Exhibit 4(h) to the Registrant's
                    Form 10-Q for the Quarter ended May 31, 1997, and
                    incorporated herein by reference.
   (4)(i)       --  Indenture of Trust dated as of July 1, 1997 between Carbon
                    County, Utah and U.S. Bank, a national banking association,
                    as Trustee, filed as Exhibit 4(i) to the Registrant's Form
                    10-Q for the Quarter ended May 31, 1997, and incorporated
                    herein by reference.
   (4)(j)       --  Indenture of Trust dated as of July 1, 1997 between Tooele
                    County, Utah and U.S. Bank, a national banking association,
                    as Trustee, filed as Exhibit 4(j) to the Registrant's Form
                    10-Q for the Quarter ended May 31, 1997, and incorporated
                    herein by reference.
</TABLE>
 
                                      II-2
<PAGE>   78
<TABLE>
<CAPTION>
EXHIBIT
NUMBER                                      DESCRIPTION
- -------                                     -----------
<C>            <C>  <S>
   (4)(k)       --  Indenture of Trust dated as of July 1, 1997 between
                    California Pollution Control Financing Authority and U.S.
                    Bank, a national banking association, as Trustee, filed as
                    Exhibit 4(k) to the Registrant's Form 10-Q for the Quarter
                    ended May 31,1997, and incorporated herein by reference.
   (4)(l)       --  Stock Purchase Agreement between Westinghouse Electric
                    Corporation (Seller) and Rollins Environmental Services,
                    Inc. (Buyer) for National Electric, Inc. dated March 7,
                    1995, filed as an Exhibit to the Registrant's Form 8-K filed
                    on June 13, 1995, and incorporated herein by reference.
   (4)(m)       --  Second Amendment to Stock Purchase Agreement (as referenced
                    in Exhibit (4)(1) above, dated May 15, 1997, among
                    Westinghouse Electric Corporation, Rollins Environmental
                    Services, Inc. and Laidlaw Inc., filed as Exhibit 4(m) to
                    the Registrant's Form 10-Q for the Quarter ended May 31,
                    1997, and incorporated herein by reference.
   (4)(n)       --  Promissory Note dated May 15, 1997 for $60,000,000 from
                    Laidlaw Environmental Services, Inc. to Westinghouse
                    Electric Corporation, filed as Exhibit 4(n) to the
                    Registrant's Form 10-Q for the Quarter ended May 31, 1997,
                    and incorporated herein by reference.
   (4)(o)       --  Guaranty Agreement dated May 15, 1997 by Laidlaw Inc. to
                    Westinghouse Electric Corporation guaranteeing Promissory
                    Note dated May 15, 1997 (as referenced in Exhibit (4)(n))
                    from Laidlaw Environmental Services, Inc. to Westinghouse
                    Electric Corporation, filed as Exhibit 4(o) to the
                    Registrant's Form 10-Q for the Quarter ended May 31, 1997,
                    and incorporated herein by reference.
   (4)(p)       --  Commitment letter of October 31, 1997 between the
                    Toronto-Dominion Bank, TD Securities Inc. and Laidlaw
                    Environmental Services Inc.
   (5)          --  Opinion of Katten Muchin & Zavis as to the legality of the
                    shares of common stock being offered.*
  (10)(a)       --  Rollins Environmental Services, Inc. 1982 Incentive Stock
                    Option Plan, filed with Amendment No. 1 to the Company's
                    Registration Statement No. 2-84139 on Form S-1 dated June
                    24, 1983 and incorporated herein by reference.
  (10)(b)       --  Rollins Environmental Services, Inc. 1993 Stock Option Plan,
                    filed with the Company's Proxy Statement for the Annual
                    Meeting of Stockholders held January 28, 1994 and
                    incorporated herein by reference.
  (10)(c)       --  Stock Purchase Agreement dated February 6, 1997, among the
                    Registrant, Laidlaw Inc., and Laidlaw Transportation, Inc.
                    included as an appendix to the Registrant's Definitive Proxy
                    Statement on Form DEF 14A, filed on May 1, 1997, and
                    incorporated herein by reference.
  (10)(e)       --  Management Incentive Plan for fiscal year 1996, filed as
                    Exhibit 10(e) to the Registrant's Form 10-Q for the Quarter
                    ended May 31, 1997, and incorporated herein by reference.
  (11)          --  Statement regarding computation of earnings per share.*
  (12)          --  Computation of ratio of earnings to fixed charges, filed as
                    Exhibit (12) to the Registrant's form 10-K for the year
                    ended August 31, 1997, and incorporated herein by reference.
  (21)          --  Subsidiaries of the Registrant, filed as Exhibit (20) to the
                    Registrant's Form 10-K for the year ended August 31, 1997,
                    and incorporated herein by reference.
  (23)(a)       --  Consent of Coopers & Lybrand, independent accountants.
  (23)(b)       --  Consent of Katten Muchin & Zavis (included in Exhibit (5).
  (24)          --  Power of Attorney (included on the signature page of this
                    registration statement).
</TABLE>
 
- ---------------
* To be filed by amendment.
 
                                      II-3
<PAGE>   79
 
ITEM 22.  UNDERTAKINGS
 
     The undersigned Registrant hereby undertakes:
 
          (1) That, for purposes of determining any liability under the
     Securities Act of 1933, each filing of the registrant's annual report
     pursuant to Section 13(a) or Section 15(d) of the Securities Exchange Act
     of 1934 (and, where applicable, each filing of an employee benefit plan's
     annual report pursuant to Section 15(d) of the Securities Exchange Act of
     1934) that is incorporated by reference in the registration statement shall
     be deemed to be a new registration statement relating to the securities
     offered therein, and the offering of such securities at that time shall be
     deemed to be the initial bona fide offering thereof.
 
          (2) To deliver or cause to be delivered with the prospectus, to each
     person to whom the prospectus is sent or given, the latest annual report to
     security holders that is incorporated by reference in the prospectus and
     furnished pursuant to and meeting the requirements of Rule 14a-3 or Rule
     14c-3 under the Securities Exchange Act of 1934; and, where interim
     financial information is required to be presented by Article 3 of
     Regulations S-X is not set forth in the prospectus, to deliver, or cause to
     be delivered to each person to whom the prospectus is sent or given, the
     latest quarterly report that is specifically incorporated by referenced to
     provide such interim financial information.
 
          (3) Insofar as indemnification for liabilities arising under the
     Securities Act of 1933 may be permitted to directors, officers and
     controlling persons of the Registrant pursuant to the foregoing provisions,
     or otherwise, the Registrant has been advised that in the opinion of the
     Securities and Exchange Commission such indemnification is against public
     policy as expressed in the Act and is, therefore, unenforceable. In the
     event that a claim for indemnification against such liabilities (other than
     the payment by the Registrant of expenses incurred by a director, officer
     or controlling person of the Registrant in the successful defense of any
     action, suit or proceeding) is asserted by such director, officer or
     controlling person in connection with the securities being registered, the
     Registrant will, unless in the opinion of its counsel the matter has been
     settled by controlling precedent, submit to a court of appropriate
     jurisdiction the question whether such indemnification by it is against
     public policy as expressed in the Act and will be governed by the final
     adjudication of such issue.
 
          (4) The undersigned Registrant hereby undertakes to respond to
     requests for information that is incorporated by reference into the
     prospectus pursuant to Items 4, 10(b), 11 or 13 of this Form within one
     business day of receipt of such request, and to send the incorporated
     documents by first class mail or other equally prompt means. This includes
     information contained in documents filed subsequent to the effective date
     of the registration statement through the date of responding to the
     request.
 
          (5) The undersigned Registrant hereby undertakes to supply by means of
     a post-effective amendment all information concerning a transaction, and
     the company being acquired involved therein, that was not the subject of
     and included in the registration statement when it became effective.
 
                                      II-4
<PAGE>   80
 
     SIGNATURES PURSUANT TO THE REQUIREMENTS OF THE SECURITIES ACT OF 1933
 
     Pursuant to the requirements of the Securities Act of 1933, the Registrant
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-4 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the City of Columbia, and State of South Carolina on the 13th day
of November, 1997.
 
                                          Laidlaw Environmental Services, Inc.
 
                                          By:     /s/ KENNETH W. WINGER
                                            ------------------------------------
                                                     Kenneth W. Winger
                                               President and Chief Executive
                                                           Officer
 
                               POWER OF ATTORNEY
 
     Each person whose signature appears below hereby constitutes and appoints
James R. Bullock, Kenneth W. Winger, Ivan R. Cairns, Henry H. Taylor and Herbert
S. Wander and, each of them, his true and lawful attorneys-in-fact and agents,
with full power of substitution and revocation, to sign on his behalf,
individually and in each capacity stated below, this Registration Statement and
all amendments to this Registration Statement and to file the same, with all
exhibits thereto and any other documents in connection therewith, with the
Securities and Exchange Commission under the Securities Act of 1933, granting
unto each such attorney-in-fact and agent full power and authority to do and
perform each and every act and thing requisite and necessary to be done in and
about the premises, as fully to all intents and purposes as such person might or
could do in person, hereby to all intents and purposes as such person might or
could do in person, hereby ratifying and confirming each act that said
attorneys-in-fact and agents may lawfully do or cause to be done by virtue
thereof.
 
     Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed below by the following persons in the
capacities indicated on November 13th, 1997.
 
<TABLE>
<CAPTION>
                      SIGNATURE                                            TITLE
                      ---------                                            -----
<C>                                                    <S>
 
                /s/ JAMES R. BULLOCK                   Chairman of the Board and Director
- -----------------------------------------------------
                  James R. Bullock
 
                /s/ KENNETH W. WINGER                  President, Chief Executive Officer and
- -----------------------------------------------------    Director
                  Kenneth W. Winger
 
                /s/ PAUL R. HUMPHREYS                  Senior Vice President, Finance and Chief
- -----------------------------------------------------    Financial Officer
                  Paul R. Humphreys
 
                /s/ JOHN R. GRAINGER                   Director
- -----------------------------------------------------
                  John R. Grainger
 
                /s/ LESLIE W. HAWORTH                  Director
- -----------------------------------------------------
                  Leslie W. Haworth
 
              /s/ JOHN W. ROLLINS, SR.                 Director
- -----------------------------------------------------
                John W. Rollins, Sr.
</TABLE>
 
                                      II-5
<PAGE>   81
 
<TABLE>
<CAPTION>
                      SIGNATURE                                            TITLE
                      ---------                                            -----
<C>                                                    <S>
 
                                                       Director
              /s/ JOHN W. ROLLINS, JR.
- -----------------------------------------------------
                John W. Rollins, Jr.
 
              /s/ DAVID E. THOMAS, JR.                 Director
- -----------------------------------------------------
                David E. Thomas, Jr.
 
                                                       Director
- -----------------------------------------------------
                   Henry B. Tippie
 
                /s/ JAMES L. WAREHAM                   Director
- -----------------------------------------------------
                  James L. Wareham
 
                 /s/ GROVER C. WRENN                   Director
- -----------------------------------------------------
                   Grover C. Wrenn
</TABLE>
 
                                      II-6
<PAGE>   82
 
                               INDEX TO EXHIBITS
 
<TABLE>
<CAPTION>
EXHIBIT
NUMBER                                   DESCRIPTION
- -------                                  -----------
<C>         <C>  <S>
   (3)(a)    --  Restated Certificate of Incorporation of the Company dated
                 May 13, 1997, and Amendment to Certificate of Incorporation
                 dated May 15, 1997, filed as Exhibit 3(a) to the
                 Registrant's Form 10-Q for the Quarter ended May 31, 1997,
                 and incorporated herein by reference.
   (3)(a)(1)  -- Certificate of Correction Filed to Correct a Certain Error
                 in the Restated and Amended Certificate of Incorporation of
                 the Company dated October 15, 1997, filed as Exhibit 3(a)(i)
                 to the Registrant's Form 10-K for the Fiscal Year ended
                 August 31, 1997, and incorporated herein by reference.
   (3)(b)    --  Bylaws of the Company filed as Exhibit 4(ii) to the
                 Registrant's Current Report on Form 8-K dated July 29, 1997,
                 and incorporated herein by reference.
   (4)(a)    --  Rights Agreement dated as of June 14, 1989 between the
                 Company and First Chicago Trust Company as successor to
                 Registrar and Transfer Company, as Rights Agent filed as an
                 Exhibit to the Registrant's Form 8-K filed on June 13, 1995
                 and incorporated herein by reference.
   (4)(b)    --  Amendment No. 1 dated as of March 31, 1995 to the Rights
                 Agreement between the Company and First Chicago Trust
                 Company as successor to Registrar and Transfer Company, as
                 Rights Agent filed as an Exhibit to the Registrant's Form
                 8-K filed on June 13, 1995 and incorporated herein by
                 reference.
   (4)(c)    --  Credit Agreement among Laidlaw Chem-Waste, Inc., Laidlaw
                 Environmental Services (Canada) Ltd., Toronto Dominion
                 (Texas) Inc., The Toronto-Dominion Bank, TD Securities (USA)
                 Inc., the Bank or Nova Scotia, NationsBank, N.A. and The
                 First National Bank of Chicago and NationsBank, N.A. as
                 Syndication Agent dated as of May 9, 1997, filed as Exhibit
                 4(c) to the Registrant's Form 10- Q for the Quarter ended
                 March 31, 1997, and incorporated herein by reference.
   (4)(d)    --  $350,000,000 5% Subordinated Convertible Pay-In-Kind
                 Debenture due 2009 issued by Registrant on May 15, 1997 to
                 Laidlaw Inc. the form of which was included as an appendix
                 to the Registrant's Definitive Proxy Statement on Form DEF
                 14A, filed on May 1, 1997 and incorporated herein by
                 reference.
   (4)(e)    --  Registration Rights Agreement dated May 15, 1997 between
                 Registrant, Laidlaw Transportation, Inc. and Laidlaw Inc.
                 included as appendix to the Registrant's Definitive Proxy
                 Statement on Form DEF 14A, the form of which was filed on
                 May 1, 1997 and incorporated herein by reference.
   (4)(f)    --  Indenture dated as of May 1, 1993 between the Industrial
                 Development Board of the Metropolitan Government of
                 Nashville and Davidson County (Tennessee) and NationsBank of
                 Tennessee, N.A., filed as Exhibit 4(f) to the Registrant's
                 Form 10-Q for the Quarter ended May 31, 1997, and
                 incorporated herein by reference.
   (4)(g)    --  Indenture of Trust dated as of February 1, 1995 between
                 Carbon County, Utah and West One Bank, Utah, now known as
                 U.S. Bank, as Trustee, filed as Exhibit 4(g) to the
                 Registrant's Form 10-Q for the Quarter ended May 31, 1997,
                 and incorporated herein by reference.
   (4)(h)    --  Indenture of Trust dated as of August, 1995 between Tooele
                 County, Utah and West One Bank, Utah, now known as U.S.
                 Bank, as Trustee, filed as Exhibit 4(h) to the Registrant's
                 Form 10-Q for the Quarter ended May 31, 1997, and
                 incorporated herein by reference.
   (4)(i)    --  Indenture of Trust dated as of July 1, 1997 between Carbon
                 County, Utah and U.S. Bank, a national banking association,
                 as Trustee, filed as Exhibit 4(i) to the Registrant's Form
                 10-Q for the Quarter ended May 31, 1997, and incorporated
                 herein by reference.
   (4)(j)    --  Indenture of Trust dated as of July 1, 1997 between Tooele
                 County, Utah and U.S. Bank, a national banking association,
                 as Trustee, filed as Exhibit 4(j) to the Registrant's Form
                 10-Q for the Quarter ended May 31, 1997, and incorporated
                 herein by reference.
</TABLE>
<PAGE>   83
<TABLE>
<CAPTION>
EXHIBIT
NUMBER                                   DESCRIPTION
- -------                                  -----------
<C>         <C>  <S>
   (4)(k)    --  Indenture of Trust dated as of July 1, 1997 between
                 California Pollution Control Financing Authority and U.S.
                 Bank, a national banking association, as Trustee, filed as
                 Exhibit 4(k) to the Registrant's Form 10-Q for the Quarter
                 ended May 31,1997, and incorporated herein by reference.
   (4)(l)    --  Stock Purchase Agreement between Westinghouse Electric
                 Corporation (Seller) and Rollins Environmental Services,
                 Inc. (Buyer) for National Electric, Inc. dated March 7,
                 1995, filed as an Exhibit to the Registrant's Form 8-K filed
                 on June 13, 1995, and incorporated herein by reference.
   (4)(m)    --  Second Amendment to Stock Purchase Agreement (as referenced
                 in Exhibit (4)(1) above, dated May 15, 1997, among
                 Westinghouse Electric Corporation, Rollins Environmental
                 Services, Inc. and Laidlaw Inc., filed as Exhibit 4(m) to
                 the Registrant's Form 10-Q for the Quarter ended May 31,
                 1997, and incorporated herein by reference.
   (4)(n)    --  Promissory Note dated May 15, 1997 for $60,000,000 from
                 Laidlaw Environmental Services, Inc. to Westinghouse
                 Electric Corporation, filed as Exhibit 4(n) to the
                 Registrant's Form 10-Q for the Quarter ended May 31, 1997,
                 and incorporated herein by reference.
   (4)(o)    --  Guaranty Agreement dated May 15, 1997 by Laidlaw Inc. to
                 Westinghouse Electric Corporation guaranteeing Promissory
                 Note dated May 15, 1997 (as referenced in Exhibit (4)(n))
                 from Laidlaw Environmental Services, Inc. to Westinghouse
                 Electric Corporation, filed as Exhibit 4(o) to the
                 Registrant's Form 10-Q for the Quarter ended May 31, 1997,
                 and incorporated herein by reference.
   (4)(p)    --  Commitment letter of October 31, 1997 between the
                 Toronto-Dominion Bank, TD Securities Inc. and Laidlaw
                 Environmental Services Inc.
   (5)       --  Opinion of Katten Muchin & Zavis as to the legality of the
                 shares of common stock being offered.*
  (10)(a)    --  Rollins Environmental Services, Inc. 1982 Incentive Stock
                 Option Plan, filed with Amendment No. 1 to the Company's
                 Registration Statement No. 2-84139 on Form S-1 dated June
                 24, 1983 and incorporated herein by reference.
  (10)(b)    --  Rollins Environmental Services, Inc. 1993 Stock Option Plan,
                 filed with the Company's Proxy Statement for the Annual
                 Meeting of Stockholders held January 28, 1994 and
                 incorporated herein by reference.
  (10)(c)    --  Stock Purchase Agreement dated February 6, 1997, among the
                 Registrant, Laidlaw Inc., and Laidlaw Transportation, Inc.
                 included as an appendix to the Registrant's Definitive Proxy
                 Statement on Form DEF 14A, filed on May 1, 1997, and
                 incorporated herein by reference.
  (10)(e)    --  Management Incentive Plan for fiscal year 1996, filed as
                 Exhibit 10(e) to the Registrant's Form 10-Q for the Quarter
                 ended May 31, 1997, and incorporated herein by reference.
  (11)       --  Statement regarding computation of earnings per share.*
  (12)       --  Computation of ratio of earnings to fixed charges, filed as
                 Exhibit (12) to the Registrant's form 10-K for the year
                 ended August 31, 1997, and incorporated herein by reference.
  (21)       --  Subsidiaries of the Registrant, filed as Exhibit (20) to the
                 Registrant's Form 10-K for the year ended August 31, 1997,
                 and incorporated herein by reference.
  (23)(a)    --  Consent of Coopers & Lybrand, independent accountants.
  (23)(b)    --  Consent of Katten Muchin & Zavis (included in Exhibit (5).
  (24)       --  Power of Attorney (included on the signature page of this
                 registration statement).
</TABLE>
 
- ---------------
* To be filed by amendment.

<PAGE>   1
                                                                October 31, 1997

                                        
                                   LESI, Inc.
                     Senior Secured Bank Credit Facilities
                               Commitment Letter


Laidlaw Environmental Services, Inc.
LESI, Inc.
1301 Gervais Street
Columbia, South Carolina 29211

Attention: Mr. Kenneth W. Winger
           President and Chief Executive Officer

Ladies and Gentlemen:

         You have advised The Toronto-Dominion Bank ("TD") and TD Securities
(USA), Inc. ("TDSI") that Laidlaw Environmental Services, Inc., a Delaware
corporation ("LESI"), through its wholly owned subsidiary LESI, Inc., a
Delaware corporation (the "Borrower"), is interested in acquiring (the
"Acquisition") an entity you have identified in writing to TD and TDSI (the
"Acquired Company"). We understand that the Acquisition would be accomplished
by means of either (i) a tender offer followed by a merger between the Acquired
Company and a wholly owned subsidiary of the Borrower or (ii) a merger between
the Acquired Company and a wholly owned subsidiary of the Borrower. As
consideration for the Acquisition, the shareholders of the Acquired Company
will receive consideration in the form of cash (in an aggregate amount not
exceeding $900,000,000) and common stock of LESI, and after giving effect to
the Acquisition, the Acquired Company will be a wholly owned subsidiary of the
Borrower. In that connection, you have requested that TDSI agree to structure,
arrange and syndicate senior secured credit facilities to be made available to
the Borrower in an aggregate amount of up to $1,800,000,000 (the "Facilities")
and that TD commit to provide $1,400,000,000 of the Facilities and to serve as
administrative agent for the Facilities. The Facilities would be used to
finance the Acquisition and related costs and expenses, to refinance and
restate the Borrower's existing Credit Agreement, dated as of May 9, 1997 under
which Toronto Dominion (Texas), Inc. is General Administrative Agent (the
"Existing Credit Agreement"), and to finance the working capital and general
corporate needs of the Borrower and its subsidiaries following the Acquisition.

         TDSI is pleased to advise you that it is willing to act as exclusive
advisor and arranger for the Facilities.

         Furthermore, TD is pleased to advise you of its commitment to provide
$1,400,000,000 of the Facilities upon the terms and subject to the conditions
set forth or
<PAGE>   2
Laidlaw Environmental                  -2-                      October 31, 1997
 Services, Inc.


referred to in this commitment letter (the "Commitment Letter") and in the
Summary of Terms and Conditions attached hereto as Exhibit A (the "Term
Sheet"). Furthermore, TDSI is pleased to advise you that it will use its
reasonable best efforts to syndicate the remaining $400,000,000 of the
Facilities on the terms and conditions set forth herein and in the Term Sheet
(the $1,400,000,000 commitment of TD hereunder being subject to the successful
syndication of such remaining $400,000,000).

         It is agreed that TD will act as the sole and exclusive Administrative
Agent, and that TDSI will act as the sole and exclusive advisor and arranger,
for the Facilities, and each will, in such capacities, perform the duties and
exercise the authority customarily performed and exercised by it in such roles.
You agree that no other agents, co-agents or arrangers will be appointed, no
other titles will be awarded and no compensation (other than that expressly
contemplated by the Term Sheet and the Fee Letter referred to below) will be
paid in connection with the Facilities unless you and we shall so agree.

         We intend to syndicate the Facilities (including, in our discretion,
all or part of TD's commitment hereunder) to a group of financial institutions
(together with TD, the "Lenders") identified by us in consultation with you.
TDSI intends to commence syndication efforts to a small group of institutions
approved by you promptly upon the execution of this Commitment Letter, and
retains the right to commence the general syndication at any time TDSI deems
appropriate, provided, that TDSI shall give you at least five business days'
prior notice of its intention to commence a general syndication, during which
time you have the right to terminate the commitments of TD hereunder. You agree
to actively assist TDSI in completing a syndication satisfactory to it. Such
assistance shall include (a) your using commercially reasonable efforts to
ensure that the syndication efforts benefit materially from the Borrower's
existing lending relationships and, to the extent practicable, the existing
lending relationships of the Acquired Company, (b) direct contact between
senior management and advisors of the Borrower and the proposed Lenders, (c)
assistance in the preparation of a Confidential Information Memorandum and
other marketing materials to be used in connection with the syndication and (d)
the hosting, with TDSI, of one or more meetings of prospective Lenders.

         TDSI will manage all aspects of the syndication, including decisions
as to the selection of institutions to be approached and when they will be
approached, when their commitments will be accepted, which institutions will
participate, the allocations of the commitments among the Lenders and the amount
and distribution of fees among the Lenders. To assist TDSI in its syndication
efforts, you agree promptly to prepare and provide to TDSI and TD all
information with respect to the Borrower, the Acquired Company, the Acquisition
and the other transactions contemplated hereby, including all financial
information and projections (the "Projections"), as we may reasonably request in
<PAGE>   3
Laidlaw Environmental              -3-                      October 31, 1997
 Services, Inc.


connection with he arrangement and syndication of the Facilities.  You hereby
represent and covenant that (a) all information other than the Projections (the
"Information") that has been or will be made available to TD or TDSI by you or
any of your representatives is or will be, when furnished, complete and correct
in all material respects and does not or will not, when furnished, contain any
untrue statement of a material fact or omit to state a material fact necessary
in order to make the statements contained therein not materially misleading in
light of the circumstances under which such statements are made and (b) the
Projections that have been or will be made available to TD or TDSI by you or
any of your representatives have been or will be prepared in good faith based
upon reasonable assumptions.  You understand that in arranging and syndicating
the Facilities we may use and rely on the Information and Projections without
independent verification thereof.

     As consideration for TD's commitment hereunder and TDSI's agreement to
perform the services described herein, you agree to pay to TD the nonrefundable
fees set forth in the Fee Letter dated the date hereof and delivered herewith
(the "Fee Letter").

     TD and TDSI shall be entitled, with your consent (which shall not be
unreasonably withheld), to change the structure, terms, pricing or amount of,
or to eliminate, any of the Facilities if TD and TDSI determine that such
changes are advisable in order to ensure a successful syndication or an optimal
credit structure and if the aggregate amount of the Facilities shall remain
unchanged.

     TD's commitment hereunder and TDSI's agreement to perform the services
described herein are subject to (a) there not occurring or becoming known to us
any material adverse condition or material adverse change in or affecting the
business, operations, property, condition (financial or otherwise) or prospects
of the Borrower and its subsidiaries, taken as a whole, or the Acquired Company
and its subsidiaries taken as a whole, (b) our completion of and satisfaction in
all respects with a due diligence investigation of the Borrower and the Acquired
Company, (c) our not becoming aware after the date hereof of any information or
other matter affecting the Borrower, the Acquired Company, or the transactions
contemplated hereby which is inconsistent in a material and adverse manner with
any such information or other matter disclosed to us prior to the date hereof,
(d) there not having occurred a material disruption of or material adverse
change in financial, banking or capital market conditions that, in our judgment,
could materially impair the syndication of the Facilities, (e) our satisfaction
that prior to and during the syndication of the Facilities there shall be no
compelling offering, placement or arrangement of any debt securities or bank
financing by or on behalf of the Borrower or any affiliate thereof without prior
consultation with and consent of TD and TDSI, (f) the negotiation, execution and
delivery on or before March 31, 1998 (or such later date, if any, that may be
agreed to by the parties hereto as provided in the Fee Letter) of definitive
documentation with respect to the Facilities satisfactory to TD and its

<PAGE>   4
Laidlaw Environmental                 -4-                     October 31, 1997
 Services, Inc.


counsel and (g) the other conditions set forth or referred to in the Term
Sheet.  The terms and conditions of TD's commitment hereunder and of the
Facilities are not limited to those set forth herein and in the Term Sheet.
Those matters that are not covered by the provisions hereof and of the Term
Sheet are subject to the approval and agreement of TD, TDSI and the Borrower.

     YOU agree (a) to indemnify and hold harmless TD, TDSI, their affiliates
and their respective officers, directors, employees, advisors, and agents
(each, and "indemnified person") from and against any and all losses, claims,
damages and liabilities to which any such indemnified person may become subject
arising out of or in connection with this Commitment Letter, the Facilities,
the use of the proceeds thereof, the Acquisition or any related transaction or
any claim, litigation, investigation or proceeding relating to any of the
foregoing, regardless of whether any indemnified person is a party thereto, and
to reimburse each indemnified person upon demand for any legal or other
expenses incurred in connection with investigating or defending any of the
foregoing, provided that the foregoing indemnity will not, as to any
indemnified person, apply to losses, claims, damages, liabilities or related
expenses to the extent they arise from the willful misconduct or gross
negligence of such indemnified person, and (b) to reimburse TD, TDSI and their
affiliates on demand for all out-of-pocked expenses (including due diligence
expenses, syndication expenses, consultant's fees and expenses, travel
expenses, and reasonable fees, charges and disbursements of counsel) incurred
in connection with the Facilities and any related documentation (including
this Commitment Letter, the Term Sheet, the Fee Letter and the definitive
financing documentation) or the administration, amendment, modification or
waiver thereof.  No indemnified person shall be liable for any indirect or
consequential damages in connection with its activities related to the
Facilities.

     This Commitment Letter shall not be assignable by you without the prior
written consent of TD and TDSI (and any purported assignment without such
consent shall be null and void), is intended to be solely for the benefit of
the parties hereto and is not intended to confer any benefits upon, or create
any rights in favor of, any person other than the parties hereto.  This
Commitment Letter may not be amended or waived except by an instrument in
writing signed by you, TD and TDSI.  This Commitment Letter may be executed in
any number of counterparts, each of which shall be an original, and all of
which, when taken together, shall constitute one agreement.  Delivery of an
executed signature page of this Commitment Letter by facsimile transmission
shall be affective as delivery of a manually executed counterpart hereof.  This
Commitment Letter and the Fee Letter are the only agreements that have been
entered into among us with respect to the Facilities and set forth the entire
understanding of the parties with respect thereto.  This Commitment Letter
shall be governed by, and construed in accordance with, the laws of the State
of New York.


<PAGE>   5
Laidlaw Environmental                  -5-                      October 31, 1997
 Services, Inc.


         This Commitment Letter is delivered to you on the understanding that
neither this Commitment Letter, the Term Sheet or the Fee Letter nor any of
their terms or substance shall be disclosed, directly or indirectly, to any
other person except (a) to your officers, agents and advisors who are directly
involved in the consideration of this matter, including parties to the
Acquisition, or (b) as may be compelled in a judicial or administrative
proceeding or as otherwise required by law (in which case you agree to inform
us promptly thereof), provided, that the foregoing restrictions shall cease to
apply (except in respect of the Fee Letter and its terms and substance) after
this Commitment Letter has been accepted by you.

         The compensation, reimbursement, indemnification and confidentiality
provisions contained herein and in the Fee Letter shall remain in full force
and effect regardless of whether definitive financing documentation shall be
executed and delivered and notwithstanding the termination of this Commitment
Letter or TD's commitment hereunder.

         If the foregoing correctly sets forth our agreement, please indicate
your acceptance of the terms hereof and of the Term Sheet and the Fee Letter
by returning to us executed counterparts hereof and of the Fee Letter, together
with the amounts agreed upon pursuant to the Fee Letter to be payable upon the
acceptance hereof, not later than 5:00 p.m., New York City time, on October 31,
1997. TD's commitment and TDSI's agreements herein will expire at such time in
the event TD has not received such executed counterparts and such amounts in
accordance with the immediately preceding sentence.
<PAGE>   6
Laidlaw Environmental                  -6-                      October 31, 1997
 Services, Inc.


         We are pleased to have been given the opportunity to assist you in
connection with this financing.

                                        Very truly yours,

                                        THE TORONTO-DOMINION BANK


                                        By: /s/ Wade C. Jacobson
                                           -------------------------------------
                                           Title: Managing Director

                                        TD SECURITIES (USA) INC.


                                        By: /s/ Wade C. Jacobson
                                           -------------------------------------
                                           Title: Managing Director



Accepted and agreed to
as of the date first
written above by:

LAIDLAW ENVIRONMENTAL SERVICES, INC.

By: /s/
   --------------------------
   Title:

LESI, INC.


By: /s/
   --------------------------
   Title:
<PAGE>   7
                                                                       EXHIBIT A



                      LAIDLAW ENVIRONMENTAL SERVICES, INC.
                                   LESI, INC.


               $1,800,000,000 Senior Secured Bank Credit Facility

                        Summary of Terms and Conditions

                                October 31, 1997

     Laidlaw Environmental Services, Inc., a Delaware corporation ("LESI"),
through its wholly owned subsidiary LESI, Inc., a Delaware corporation (the
"Borrower"), is interested in acquiring (the "Acquisition") an entity (the
"Acquired Company") previously identified in writing to The Toronto-Dominion
Bank and TD Securities (USA) Inc. The Acquisition would be accomplished by
means of either (i) a tender offer (the "Tender Offer") followed by a merger
(the "Back-End Merger") between the Acquired Company and a wholly owned
subsidiary of the Borrower or (ii) a merger (the "One Step Merger") between the
Acquired Company and a wholly owned subsidiary of the Borrower. As
consideration for the Acquisition, the shareholders of the Acquired Company
will receive consideration in the form of cash (in an aggregate amount not
exceeding $900,000,000) and common stock of LESI, and after giving effect to
the Acquisition, the Acquired Company will be a wholly owned subsidiary of the
Borrower. This Summary of Terms and Conditions sets forth certain terms and
conditions of proposed credit facilities to be used to finance the Acquisition
and other purposes, including the refinancing of the Borrower's existing Credit
Agreement, dated as of May 9, 1997 under which Toronto Dominion (Texas), Inc.
is the General Administrative Agent (the "Existing Credit Agreement").

THE CREDIT FACILITIES:    $1,800,000,000 Senior Secured Credit Facilities
                          composed of four facilities; a $400,000,000 6-year
                          Senior Secured Revolving Credit Facility with a
                          $200,000,000 Letter of Credit sublimit, a $500,000,000
                          6-year Senior Secured Amortizing "A" Term Loan
                          Facility, a $450,000,000 Minimally Amortizing 7-year
                          Senior Secured Term "B" Loan Facility, and a
                          $450,000,000 Minimally Amortized 8-year Senior Secured
                          Term "C" Loan Facility (collectively, the "Credit
                          Facilities"; the Loans thereunder, the "Loans").

BORROWER:                 LESI, Inc., a Delaware corporation (the "Borrower").

ADVISOR AND ARRANGER:     TD Securities (USA) Inc. ("TDSI" or the "Arranger").

ADMINISTRATIVE AGENT:     The Toronto-Dominion Bank ("TD") and/or one of its
                          affiliates (in such capacity, the "Agent").
 
LENDERS:                  TD and a syndicate of banks and other financial
                          institutions (collectively, the "Lenders") acceptable
                          to the Borrower and TD.
<PAGE>   8
                                                                               2


LETTER OF CREDIT FRONTING          TD or one of its affiliates.
BANK:

CREDIT FACILITIES:                 A)  $400,000,000 Senior Secured Revolving 
                                       Working Capital Credit Facility.
                                   B)  $500,000,000 Senior Secured Amortizing
                                       "A" Term Loan Facility.
                                   C)  $450,000,000 Senior Secured Minimally 
                                       Amortizing "B" Term Loan Facility.
                                   D)  $450,000,000 Senior Secured Minimally 
                                       Amortizing "C" Term Loan Facility.

CLOSING DATE:                      The date on or before March 31, 1998, on 
                                   which a Credit Agreement is signed and the
                                   conditions to the initial extension of 
                                   credit thereunder are satisfied.

FINAL MATURITY:                    A,B) Six (6) years from the Closing Date.
                                   C)   Seven (7) years from the Closing Date.
                                   D)   Eight (8) years from the Closing Date.

USE OF PROCEEDS:                   Proceeds from the Credit Facilities may be 
                                   used as follows:
                                   (a)  Finance the Acquisition.
                                   (b)  Refinance existing indebtedness of the 
                                        Borrower and the Acquired Company,
                                        including indebtedness of the Borrower
                                        under the Existing Credit Agreement.
                                   (c)  Fund certain capital expenditures, 
                                        working capital and permitted 
                                        acquisitions, as well as transaction 
                                        fees and expenses associated with the
                                        Acquisition.
                                   (d)  Provide for up to $200,000,000 of 
                                        letters of credit.

GUARANTORS:                        LESI and all material subsidiaries of the 
                                   Borrower (the "Guarantors", together
                                   with the Borrower, the "Credit Parties").

COLLATERAL:                        The obligations of each Credit Party in 
                                   respect of the Credit Facilities shall be 
                                   secured by a perfected first priority 
                                   security interest in all of its tangible and
                                   intangible assets including, without 
                                   limitation, intellectual property, real 
                                   property (at the sole discretion of the 
                                   Agent) and all of the capital stock of each
                                   of its direct and indirect subsidiaries. If
                                   the Acquisition is accomplished by means of
                                   the Tender Offer followed by the Back-End
                                   Merger, all stock of the Acquired Company
                                   purchased in the Tender Offer will constitute
                                   collateral until the Back-End Merger, at
                                   which time (i) the surviving corporation of
                                   the Back-End Merger will be a wholly owned
                                   subsidiary to the Borrower, (ii) 100% of the
                                   stock of such surviving corporation will
                                   constitute collateral and (iii) all assets of
                                   such surviving corporation will constitute
                                   collateral. If the Acquisition is
                                   accomplished by means of the One Step Merger,
                                   100% of the stock of the surviving
                                   corporation of the One Step 
<PAGE>   9
                                                                               3


                         Merger will constitute collateral and all assets of
                         such surviving corporation will constitute collateral.

 AVAILABILITY:           A)  Commencing on the Closing Date, Loans may be
                             borrowed, repaid and reborrowed from time to time
                             prior to the date which is five years after the
                             Closing Date. Up to $200,000,000 of the commitment
                             amount shall be available for the issuance of
                             letters of credit and $250,000,000 for loans. At
                             no time may the amount of all Loans and letters of
                             credit under the Facility exceed $400,000,000.
                         B)  Available in one borrowing on the Closing Date;
                             provided that if the Acquisition is accomplished
                             by means of the Tender Offer followed by the
                             Back-End Merger, a portion of this Facility will be
                             available on the closing date of the Tender Offer,
                             with the remainder being available on the closing
                             date of the Back-End Merger.
                         C)  Available in one borrowing on the Closing Date;
                             provided that if the Acquisition is accomplished by
                             means of the Tender Offer followed by the Back-End
                             Merger, a portion of this Facility will be
                             available on the closing date of the Tender Offer,
                             with the remainder being available on the closing
                             date of the Back-End Merger.
                         D)  Available in one borrowing on the Closing Date;
                             provided that if the Acquisition is accomplished by
                             means of the Tender Offer followed by the Back-End
                             Merger, a portion of this Facility will be
                             available on the closing date of the Tender Offer,
                             with the remainder being available on the closing
                             date of the Back-End Merger.

<TABLE>
<CAPTION>
MINIMUM DRAWDOWN         A)  Type of     Min. Initial   Additional     Days
AMOUNTS:                     Advance     Draw           Increment      Notice
                             ------------------------------------------------
                             <S>         <C>            <C>            <C>
                             LIBOR       $5,000,000     $1,000,000       3
                             Base Rate   $1,000,000     $  500,000       1
</TABLE>

SCHEDULED AMORTIZATION:  A)  N/A.
                         B)  The "A" Term Loan Facility shall be payable in each
                             year in quarterly principal installments in annual
                             amounts as follows:

<TABLE>
<CAPTION>
                                                           Annual Principal 
                                   Year                             Payment
                                   ----------------------------------------
                                   <S>                     <C>
                                   1998                               $75MM
                                   1999                               $75MM
                                   2000                               $75MM
                                   2001                               $75MM
                                   2002                              $100MM
                                   2003                              $100MM
</TABLE>

<PAGE>   10
                                                                               4


                          C)  The "B" Term Loan Facility shall be payable in
                              each year in quarterly principal installments in
                              annual amounts as follows:

<TABLE>
<CAPTION>
                                   Year           Annual Principal
                                                           Payment
                                   -------------------------------
                                   <S>            <C>
                                   1998                $  4.5 MM   
                                   1999                $  4.5 MM   
                                   2000                $  4.5 MM   
                                   2001                $  4.5 MM   
                                   2002                $  4.5 MM   
                                   2003                $  4.5 MM   
                                   2004                $423.0 MM   
</TABLE>

                          D)  The "C" Term Loan Facility shall be payable in
                              each year in quarterly principal installments in
                              annual amounts as follows:

<TABLE>
<CAPTION>
                                   Year           Annual Principal
                                                           Payment
                                   -------------------------------
                                   <S>            <C>
                                   1998                $  4.5 MM  
                                   1999                $  4.5 MM  
                                   2000                $  4.5 MM  
                                   2001                $  4.5 MM  
                                   2002                $  4.5 MM  
                                   2003                $  4.5 MM  
                                   2004                $  4.5 MM  
                                   2005                $418.5 MM
</TABLE>

OPTIONAL COMMITMENT      The Borrower may terminate the unused portion of the
REDUCTION:               Revolving Credit Facility Commitment in amounts of at 
                         least $5,000,000 (and in increments of $1,000,000 in
                         excess thereof) at any time on three business days'
                         irrevocable written notice without penalty. Such
                         reductions shall be permanent.

MANDATORY COMMITMENT 
REDUCTIONS/PREPAYMENT:   The Borrower shall prepay the "A" Term Loan Facility,
                         the "B" Term Loan Facility and the "C" Term Loan
                         Facility in amounts equal to the following:

                         (a)  100% of net proceeds from permitted asset sales
                              and sale/leasebacks.
                         (b)  50% of the net cash proceeds from any equity
                              issuance of the Borrower or LESI, including
                              proceeds from the exercise of warrants, excluding
                              those warrants attached to LESI's 5% Convertible
                              Subordinated Debenture due 2009 and excluding
                              common stock of LESI issued as a part of the
                              consideration for the Acquisition.
                         (c)  100% of the net cash proceeds form issuance of
                              debt of the Borrower or LESI.
                         (d)  75% of the Excess Cash Flow, if any.
<PAGE>   11
                                                                               5

                         Mandatory prepayments shall be applied, on a pro rata
                         basis, to prepay installments of the "A" Term Loan
                         Facility, the "B" Term Loan Facility and the "C" Term
                         Loan Facility over the remaining maturities. If there
                         are no outstandings under the "A" Term Loan Facility,
                         the "B" Term Loan Facility and the "C" Term Loan
                         Facility, mandatory prepayments shall permanently
                         reduce availability and outstandings under the
                         Revolving Credit Facility. Notwithstanding the
                         foregoing, mandatory prepayments shall not be required
                         to reduce letters of credit issued under the Revolving
                         Credit Facility.

                         Such reductions shall be permanent.

OPTIONAL PREPAYMENTS:    At its option, the Borrower may prepay Loans under the
                         Credit Facility in amounts of at least $3,000,000,
                         without premium or penalty; however, prepayments of
                         borrowings must be accompanied by payments of all
                         breakage costs and funding losses, if any.

RATES OF INTEREST:       At the Borrower's option, Loans shall bear interest at
                         a rate per annum equal to either:

                         (a)  Alternate Base Rate plus Applicable Margin; or
                         (b)  Eurodollar Rate plus Applicable Margin.

                         The Alternate Base Rate is defined as the higher of (i)
                         the applicable prime rate of TD and (ii) the Federal
                         Funds rate + 1/2 of 1%.

                         The Eurodollar Rate shall be the London Interbank
                         Offered Rate ("LIBOR") as determined by TD for the
                         respective interest period.

                         Applicable Margin for Revolving Credit Facility and "A"
                         Term Loan Facility:

                         The Applicable Margin shall be determined by reference
                         to the Total Leverage Ratio as set forth below:

<TABLE>
<CAPTION>
                         Total Leverage      Base Rate      LIBOR
                         Ratio               Margin         Margin
                         -----------------------------------------
                         <S>                 <C>            <C>
                         >=4.00x <4.50x       137.5          237.5
                         >=3.50x <4,00x       125.0          225.0
                         >=3.25X <3.50x       100.0          200.0
                         >=3.00x <3.25x        87.5          187.5
                         >=2.50x <3.00x        50.0          150.0
                         >=2.00x <2.50x        12.5          112.5
                         >=1.50x <2.00x         0.0           87.5
                         <1.50x                 0.0           62.5
</TABLE>

<PAGE>   12
                                                                               6

                         Notwithstanding the foregoing, the Applicable Margins
                         on the Revolving Credit Facility and the "A" Term Loan
                         Facility shall be at least 2.25% for LIBOR Loans and at
                         least 1.25% for Base Rate Loans during the fist six
                         months following the Closing Date.

                         Applicable Margin for "B" Term Loan Facility:
                              LIBOR Margin:  262.5
                              Base Rate Margin:   162.5
                              The LIBOR or Base Rate Margin will decrease by 25
                              bps if the Total Leverage Ratio declines below
                              3.0x, but in no event will such decrease occur
                              prior to twelve months after the Closing date.

                         Applicable Margin for "C" Term Loan Facility:
                              LIBOR Margin   287.5
                              Base Rate Margin    187.5
                              The LIBOR or Base Rate Margin will decrease by 25
                              bps (if the Total Leverage Ratio declines below
                              3.0x, but in no event will such decrease occur
                              prior to twelve months after the Closing Date.

DEFAULT RATE:            During the continuance of a payment default, all 
                         Applicable Margins shall increase by 2.00% per annum.

INTEREST PERIODS:        Interest periods for LIBOR Loans shall be, at the 
                         Borrower's option, one, two, three or six months (and
                         nine and twelve months if available).

INTEREST PAYMENT DATES:  Interest on LIBOR Loans shall be payable at the end of
                         each applicable Interest Period or every 90 days, if 
                         earlier. Interest on Base Rate Loans shall be payable 
                         quarterly in arrears.

LETTER OF CREDIT FEES:   Letter of Credit Fees shall accrue at a rate per annum
                         equal to the Applicable LIBOR Margin for the Revolving
                         Credit Facility and the "A" Term Loan Facility in
                         effect from time to time. Letter of Credit Fees shall
                         be payable quarterly in arrears calculated on the basis
                         of a 360-day year. TD shall retain 0.25% of the Letter
                         of Credit Fee as a fronting fee.

COMMITMENT FEES:

<TABLE>
<CAPTION>
                         Total Leverage         Commitment
                         Ratio                         Fee
                         ---------------------------------
                         <S>                    <C>
                         >=4.00x <4.50x               50.0
                         >=3.50x <4.00x               50.0
                         >=3.00x <3.50x               37.5
                         >=2.50x <3.00x               37.5
                         >=2.00x <2.50x               25.0
</TABLE>
<PAGE>   13
                                                                               7


<TABLE>
                              <S>                           <C>
                              >= 1.50x < 2.00x              25.0
                              < 1.500x                      15.0
</TABLE>

                         Commitment fees are calculated on the unused portion of
                         the Revolving Credit Facility and are payable quarterly
                         in arrears. If the Acquisition is to be accomplished by
                         means of the Tender Offer followed by the Back-End
                         Merger, commitment fees will be payable on the portions
                         of the "A" Term Loan Facility, the "B" Term Loan
                         Facility and the "C" Term Loan Facility not drawn on
                         the Closing Date, and will accrue until the closing
                         date of the Back-End Merger.


INCREASED COSTS/CHANGE 
CIRCUMSTANCE:            The Credit Agreement governing the Credit Facilities
                         shall include standard protective provisions for such
                         matters as unavailablity of funding, increased costs,
                         funding losses, capital adequacy requirements,
                         illegality and withholding taxes.

CONDITIONS PRECEDENT:    Customary for the type of transaction proposed, and
                         others to be reasonably specified by the Agent
                         including, without limitation, the following:

                         (a)  Execution and delivery of a satisfactory credit
                              agreement (the "Credit Agreement") and
                              satisfactory security, guarantee, and other
                              related documentation embodying the structure,
                              terms and conditions contained herein (together
                              with the Credit Agreement, the "Credit
                              Documentation").
                         (b)  The Agent shall have satisfactorily completed a
                              due diligence review of (i) the assets,
                              liabilites, business, operations, conditions,
                              prospects and environmental condition and
                              litigation of the Borrower and the Acquired
                              Company and (ii) the legal and tax issues
                              regarding the proposed security for the Credit
                              Facilities. Included in this review will be an
                              environmental audit in respect of facilities owned
                              or operated by the Acquired Company and the
                              Borrower to be performed by a third party
                              satisfactory to the Agent, of a scope deemed
                              necessary by the Agent for a business fo this
                              type.
                         (c)  Prior or contemporaneous repayment in full of all
                              amounts outstanding in respect of existing debt of
                              the Borrower and the Acquired Company, including
                              letters of credit, other than permitted debt and
                              permitted assumed debt (to be defined in the
                              Credit Agreement). On the Closing Date, the
                              Existing Credit Agreement will be amended and
                              restated by the Credit Agreement, and all amounts
                              outstanding under the Existing Credit Agreement
                              will be repaid in full and refinanced with
                              borrowings under the Credit Agreement.
<PAGE>   14
                                                                               8


                          (d)  The Borrower and the Acquired Company shall have
                               entered into definitive documentation providing
                               for the Acquisition, which shall be satisfactory
                               in form and substance to the Lenders; no material
                               provision of such documentation shall have been
                               amended, waived or otherwise modified without the
                               consent of the Lenders; the Board of Directors of
                               the Acquired Company shall have approved the
                               Acquisition and shall not have withdrawn such
                               approval; and all required actions shall have
                               been taken so that the provisions of Section
                               180.1141 of the Wisconsin Business Corporation
                               Law shall be inapplicable to the Acquisition, and
                               so that any preferred stock purchase rights or
                               other "poison pill" arrangements shall not have
                               become, and shall not become, exercisable. 
                          (e)  On the Closing Date (i) if the Acquisition is to
                               be accomplished by means of the Tender Offer
                               followed by the Back-End Merger, the Borrower
                               shall have acquired pursuant to the Tender Offer
                               at least the minimum number of shares required to
                               effect the Back-End Merger and (ii) if the
                               Acquisition is to be accomplished by means of the
                               One Step Merger, the One Step Merger shall have
                               been consummated and after giving effect thereto
                               the surviving corporation of such transaction
                               shall be a wholly owned subsidiary of the
                               Borrower. The Lenders shall be satisfied that the
                               Acquisition and the financing thereof do not
                               violate Regulations G, T, U, or X of the Board of
                               Governors of the Federal Reserve System.
                          (f)  All documents and materials filed publicly by the
                               Borrower, LESI or the Acquired Company in
                               connection with the Acquisition shall have been
                               furnished to the Agent and shall be reasonably
                               satisfactory to the Agent.
                          (g)  All necessary or required governmental and third
                               party consents and approvals (including
                               Hart-Scott-Rodino clearance) in connection with
                               the Acquisition and the financing contemplated
                               hereby shall have been obtained and shall be in
                               full force and effect. There shall be in effect
                               no injunction or other prohibition on the
                               Acquisition or the financing contemplated hereby,
                               and no litigation or proceeding pending or
                               threatened which seeks to enjoin the Acquisition
                               or the other transactions contemplated hereby or
                               which could reasonably be expected to have a
                               material adverse effect on the Borrower and its
                               subsidiaries taken as a whole.
                          (h)  Review of and reasonable satisfaction by the
                               Agent and its counsel with the Borrower's
                               existing and proposed capital structure (both
                               debt and equity) and corporate structure and all
                               other matters relating to the financial and
                               operating condition of the Borrower and the
                               Acquired Company and its subsidiaries, including
                               unaudited 
<PAGE>   15
                                                                               9


                               consolidating financial statements, and with the
                               terms and provisions of the Borrower's and the
                               Acquired Company's material contracts.
                          (i)  The Lenders shall have received perfected
                               security interests and guarantees as contemplated
                               under "Guarantors" and "Collateral" above,
                               together with evidence satisfactory that all
                               necessary or appropriate actions have been taken
                               and/or obtained in connection with the creation
                               and perfection of such security interest, and the
                               Agent shall be satisfied with the tax, legal and
                               environmental liability implications, if any, of
                               the same. In general, security interests will not
                               be created in real property interests of the
                               Borrower and its subsidiaries, except as required
                               by the Agent.
                          (j)  In the reasonable and good faith determination of
                               the Agent, there shall have been no material
                               adverse change in the business, assets, financial
                               condition, operations or prospects of the
                               Borrower or the Acquired Company or any of their
                               subsidiaries.
                          (k)  Receipt of corporate resolutions, corporate
                               documents, closing certificates, opinions of
                               counsel, etc. customary for the type of
                               transaction proposed, to the reasonable
                               satisfaction of the Agent and its counsel.
                          (l)  Receipt by the Lenders of a solvency certificate
                               from an authorized financial officer of the
                               Borrower upon the consummation of the
                               Acquisition, reasonably acceptable in form, scope
                               and substance to the Agent and its counsel.
                          (m)  All representations and warranties in the Credit
                               Documentation shall be true and correct, and no
                               Default or Event of Default shall be in
                               existence.

REPRESENTATIONS AND 
WARRANTIES:               Customary for the type of transaction proposed and
                          others to be reasonably specified by the Agent
                          (applicable, as appropriate, to the Borrower, the
                          Acquired Company and their respective subsidiaries),
                          including, without limitation:

                          (a)  Due organization and authorization for
                               contemplated transactions.
                          (b)  The Borrower and its subsidiaries are in
                               substantial compliance with all relevant laws,
                               including environmental laws and ERISA
                               provisions. The transaction will not violate any
                               laws, including margin regulations.
                          (c)  Absence of material adverse litigation or
                               arbitration with respect to the Borrower, the
                               Acquired Company or any of their subsidiaries.
                          (d)  Possession of all material permits, licenses,
                               trademarks, and other intangibles necessary to
                               conduct business.
 

<PAGE>   16
                                                                              10


                         (e)  Absence of default.
                         (f)  No material adverse change in financial
                              condition, business, affairs or properties of the 
                              Borrower and its subsidiaries or the Acquired 
                              Company and its subsidiaries.
                         (g)  Fair presentation of financial statements of the
                              Borrower and all its subsidiaries.
                         (h)  Solvency of the Borrower and its subsidiaries.
                         (i)  Accuracy of disclosure.
                         (j)  Security documents.

Affirmative Covenants:   Customary for the type of transactions proposed 
                         and others to be reasonably specified by the Agent,
                         including, without limitation, the following:

                         (a)  Maintenance of corporate existence and
                              qualifications, compliance in all material
                              respects with all applicable legal requirements
                              (including environmental laws), and maintenance of
                              material privileges, permits, licenses and other
                              rights necessary to conduct business as presently
                              conducted.
                         (b)  Delivery of quarterly unaudited and annual audited
                              consolidated financial statements of the Borrower
                              and its subsidiaries together with an officer's
                              certificate demonstrating compliance with the
                              financial covenants and a certificate of no
                              default.
                         (c)  Delivery of financial projections and budgets as
                              mutually agreed upon.
                         (d)  Maintenance of insurance.
                         (e)  The Agent, at its discretion, shall have the right
                              to inspect the facilities and records of the
                              Borrower.
                         (f)  While the Borrower's Leverage Ratio is greater
                              than 2.5:1.0, Laidlaw, Inc. shall retain at least
                              a 20% equity interest in the Borrower, and, in any
                              case, at all times there shall be at least one
                              member of the Board of Directors of the Borrower
                              who is a designee of Laidlaw, Inc. and Laidlaw,
                              Inc. shall remain a primary shareholder of LESL.
                         (g)  The Agent and the banks shall approve the
                              environmental and financial condition of a
                              company, business or asset acquired by the
                              Borrower if the operation of such company,
                              business or asset requires a hazardous waste
                              permit issued by the applicable State
                              environmental authority.
                         (h)  If the Acquisition is accomplished by means of the
                              Tender Offer followed by the Back-End Merger, the
                              Borrower will covenant to consummate the Back-End
                              Merger as promptly as practicable, and in any
                              event within 60 days after the Closing Date.
<PAGE>   17
                                                                              11


                          (i)  The Borrower shall obtain interest rate
                               protection satisfactory to the Agent in respect
                               of at least 40% of its floating rate debt for a
                               period of at least 2 years.

NEGATIVE COVENANTS:       Customary for the type of transaction proposed and 
                          others to be mutually agreed upon by the Borrower 
                          and the Agent, including, without limitation, 
                          the following:

                          (a)  Limitations on intercompany debt, with exceptions
                               to be negotiated.
                          (b)  Restrictions on the incurrence of liens or other
                               encumbrances on the assets of the Borrower and
                               its Subsidiaries, subject to mutually agreed upon
                               categories of permitted liens and encumbrances.
                          (c)  Restrictions on the sale of assets or similar
                               transfers, other than those made in the ordinary
                               course of business.
                          (d)  Restrictions on acquisitions and investments
                               (with a basket of $100,000,000 during the term of
                               the Facility).
                          (e)  Prohibition on the payment of dividends.
                          (f)  Restrictions on the repurchase of capital stock.
                          (g)  Restrictions on guarantees of debt.
                          (h)  Restrictions on mergers and other fundamental
                               changes.
                          (i)  Restrictions on changes in lines of business.
                          (j)  Restrictions on optional prepayments and
                               amendments of debt instruments.
                          (k)  Restrictions on negative pledge clauses and
                               similar restrictions.

FINANCIAL COVENANTS:      Customary for the type of transaction proposed 
                          and others to be reasonably specified by the 
                          Agent including, without limitation, as set 
                          forth below (final financial covenant levels
                          subject to negotiation):

                                    (a)  Total Leverage Ratio shall not at any
                                         time exceed the following:

<TABLE>
                                         <S>            <C>
                                         1998           4.50x 
                                         1999           3.75x
                                         2000           3.25x
                                         2001           2.75x 
                                         2002           2.50x
                                         2003+          2.00x
</TABLE>

 

<PAGE>   18
                                                                              12


                         (b)  Fixed Charge Coverage Test shall be a minimum of 
                              the following:

<TABLE>
                              <S>            <C>
                              1998           1.25x
                              1999           1.25x
                              2000           1.50x
                              2001           1.50x
                              2002           1.50x
                              2003+          1.50x
</TABLE>

                         (c)  Interest Coverage Ratio shall be a minimum of the
                              following:

<TABLE>
                              <S>            <C>
                              1998           2.00x
                              1999           2.50x
                              2000           3.00x
                              2001           3.00x
                              2002           3.00x
                              2003+          3.00x
</TABLE>

                         (d)  Maximum Contingent Obligation to Operating Cash
                              Flow Ratio: not to be greater than 1.0:1.0.

                         Note: Financial terms will be defined substantially as
                         in the Existing Credit Agreement.

EVENTS OF DEFAULT:       Customary for the type of transaction proposed and
                         others to be reasonably specified by the Agent
                         including, without limitation, nonpayment of principal,
                         interest or other fees when due, breach of
                         representations, warranties or convenants, breach of
                         other material agreements, material undischarged
                         judgments or fines, ERISA, bankruptcy or insolvency,
                         change of control, and cross default to other
                         indebtedness of the Borrower and any of its
                         subsidiaries (subject in certain cases to notice, grace
                         and cure provisions to be determined).

ASSIGNMENTS AND 
PARTICIPATIONS:          The Borrower may not assign its rights or obligations
                         under the Credit Facilities without prior written
                         consent of the Lendors. The Lendors shall be permitted
                         to assign and participate Loans, Letters of Credit and
                         Commitments, provided that each assignment and
                         participation shall be in minimum principal amounts of
                         $5,000,000. Assignments shall 
<PAGE>   19
                                                                              13


                         be subject to certain other conditions, including
                         approval of the Borrower (other than assignments to
                         other Lenders, affiliates of a Federal Reserve Bank or
                         if the Borrower is in default), such approval not to be
                         unreasonably withheld.

REQUIRED LENDERS:        66-2/3%

EXPENSES:                The Borrower shall pay (and shall indemnify the Agent
                         for) all of the Agent's fees and other out-of-pocket
                         expenses (including reasonable legal and other
                         out-of-pocket expenses of the Agent's counsel, and the
                         reasonable fees and out-of-pocket expenses of any local
                         counsel retained by them following consultation with
                         the Borrower and the fees and out-of-pocket expenses of
                         an environmental consultant) arising out of or in
                         connection with the Credit Facilities and the
                         syndication thereof, the Commitment Letter, this Term
                         Sheet or the credit documentation, including any such
                         fees and expenses which may arise from or in connection
                         with any action, suit or proceeding (whether or not an
                         indemnified party is a party or is subject thereto).

INDEMNIFICATION:         The Borrower will indemnify, defend, and hold the
                         Lenders and their shareholders, directors, officers,
                         employees and agents harmless from and against all
                         costs, liability and expense (including interest,
                         penalties, attorneys' fees and amounts paid in
                         settlement) to which any of them may become subject
                         arising out of or based upon the Credit Facilities. The
                         Credit Agreement will also contain standard indemnities
                         in respect of environmental matters.

GOVERNING LAW:           Laws of the State of New York.

WAIVER OF JURY TRIAL:    To be included in the Credit Agreement.

<PAGE>   20
[TD SECURITIES LETTERHEAD]





Laidlaw Environmental Services, Inc.
LESI, Inc.
1301 Gervais Street
Columbia, South Carolina 29211

Attention: Mr. Kenneth W. Winger
           President and Chief Executive Officer

Dear Sirs:

Please be advised that TD Securities (USA), Inc. has successfully completed the
initial syndication of $400,000,000 of the senior secured credit facilities in
accordance with the Commitment Letter dated October 31, 1997. Laidlaw
Environmental Services, Inc. and LESI, Inc. now have available to them the
$1,800,000,000 necessary to go forward with the intended Acquisition.

If you require any further detail, please feel free to contact me.

Yours truly,


/s/ Wade C. Jacobson
Wade C. Jacobson
Managing Director

<PAGE>   1
                       CONSENT OF INDEPENDENT ACCOUNTANTS

     We consent to the incorporation by reference in this registration statement
on Form S-4 (File No.  ) of our report dated October 7, 1997, on our audits of
the consolidated financial statements and financial statement schedules of
Laidlaw Environmental Services, Inc, which report is incorporated by reference
in the Annual Report on Form 10k. We also consent to the references to our firm
under the captions "Experts."



                                   Coopers & Lybrand L.L.P.

Charlotte, North Carolina
November 13, 1997


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