Exhibit 4.12







                                    June 23, 1998


CLEAN HARBORS ENVIRONMENTAL 
     SERVICES, INC.
CLEAN HARBORS TECHNOLOGY
     CORPORATION
CLEAN HARBORS KINGSTON FACILITY 
     CORPORATION
CLEAN HARBORS OF BRAINTREE, INC.
CLEAN HARBORS SERVICES, INC.
CLEAN HARBORS OF NATICK, INC.
CLEAN HARBORS OF CONNECTICUT, INC.
MURPHY'S WASTE OIL SERVICE, INC.
CLEAN HARBORS OF CLEVELAND, INC.
MR. FRANK, INC.
SPRING GROVE RESOURCE RECOVERY, INC.

     Re:  Sixth Amendment to Financing Agreements ("Sixth Amendment")

Gentlemen:

     Reference is made to the Loan and Security Agreement dated May 8, 1995, 
as amended, between you and the undersigned (the "Loan Agreement").  All 
capitalized terms not otherwise defined herein shall have the meanings given 
such terms in the Loan Agreement.

     Borrowers have requested an extension of the term of the Financing 
Agreements to May 8, 2000.  Subject to the terms and conditions hereof, the 
Lender agrees with the Borrowers as follows:

     (1)  The first sentence of Section 12.1(a) of the Loan Agreement is 
deleted and replaced with the following sentence:

     "This Agreement and the other Financing Agreements shall become 
     effective as of the date set forth on the first page hereof and shall 
     continue in full force and effect for a term ending on the 



June 24, 1998
Page 2


     date five (5) years from the date hereof (the "Renewal Date"), and from 
     year to year thereafter, unless sooner terminated pursuant to the terms 
     hereof; provided, that, Lender may, at its option, extend the Renewal 
     Date to the date six (6) years from the date hereof by giving Borrower 
     notice at least one hundred twenty (120) days prior to the fifth 
     anniversary of this Agreement."

     (2)  Section 12.1(c) of the Loan Agreement is deleted in its entirety 
and replaced with the following:

     "If for any reason this Agreement is terminated prior to the end of the 
     then current term or renewal term of this Agreement, in view of the 
     impracticality and extreme difficulty of ascertaining actual damages and 
     by mutual agreement of the parties as to a reasonable calculation of 
     Lender's lost profits as a result thereof, Borrower agrees to pay to 
     Lender, upon the effective date of such termination, an early 
     termination fee in the amount of 1/2% of the Revolving Credit Limit if 
     such termination is effective in the period May 9, 1998 to and including 
     May 8, 2000.  Such early termination fee shall be presumed to be the 
     amount of damages sustained by Lender as a result of such early 
     termination and Borrower agrees that it is reasonable under the 
     circumstances currently existing.  The refinancing and repayment of the 
     Term Loan through the issuance of pollution control authority industrial 
     revenue bonds shall not trigger the payment of the early termination 
     fee.  The early termination fee provided for in this Section 12.1 shall 
     be deemed included in the Obligations."

     (3)  This Sixth Amendment and the Lender's obligations hereunder shall 
not be effective until each of the following conditions are satisfied:

          (a)  all requisite corporate action and proceedings of the 
Borrowers in connection with this Sixth Amendment shall be satisfactory in 
form and substance to Lender and Lender shall receive certified copies of 
such corporate action and proceedings as Lender may request;

          (b)  no material adverse change shall have occurred in the assets, 
business or prospects of any Borrower since the date of the most recent 
financial statements furnished to Lender pursuant to the Loan Agreement and 
no change or event shall have occurred which would impair the ability of any 
Borrower or any Obligor to perform its obligations under the Loan Agreement 
or any of the other Financing Agreements or of Lender to enforce the 
Obligations or to realize upon the Collateral; and

          (c)  Borrowers shall pay to Lender, and directs Lender to debit its 
loan account for, an additional facility fee equal to $50,000.00, which fee 
shall be fully earned and non-refundable on the date hereof.

                                                                           2



July 24, 1998
Page 3


     (4)  Each Borrower confirms and agrees that (a) all representations and 
warranties contained in the Loan Agreement and in the other Financing 
Agreements are on the date hereof true and correct in all material respects 
(except for changes that have occurred as permitted by the covenants in 
Section 9 of the Loan Agreement), and (b) it is unconditionally and jointly 
and severally liable for the punctual and full payment of all Obligations, 
including, without limitation, all charges, fees, expenses and costs 
(including attorneys' fees and expenses) under the Financing Agreements, and 
that no Borrower has any defenses, counterclaims or setoffs with respect to 
full, complete and timely payment of all Obligations.

     (5)  Each Guarantor, for value received, hereby assents to the 
Borrowers' execution and delivery of this Amendment, and to the performance 
by the Borrowers of their respective agreements and obligations hereunder.  
This Amendment and the performance or consummation of any transaction or 
matter contemplated under this Amendment, shall not limit, restrict, 
extinguish or otherwise impair any of the Guarantor's liability to Lender 
with respect to the payment and other performance obligations of the 
Guarantors pursuant to the Guarantees, dated May 8, 1995 executed for the 
benefit of Lender.  Each Guarantor acknowledges that it is unconditionally 
liable to Lender for the full and complete payment of all Obligations 
including, without limitation, all charges, fees, expenses and costs 
(including attorney's fees and expenses) under the Financing Agreements and 
that such Guarantor has no defenses, counterclaims or setoffs with respect to 
full, complete and timely payment of any and all Obligations.

     (6)  Borrowers hereby agree to pay to Lender all reasonable attorney's 
fees and costs which have been incurred or may in the future be incurred by 
Lender in connection with the negotiation and preparation of this Amendment 
and any other documents and agreements prepared in connection with this 
Amendment.  The undersigned confirm that the Financing Agreements remain in 
full force and effect without amendment or modification of any kind, except 
for the amendments explicitly set forth herein.  The undersigned further 
confirm that no Event of Default or events which with notice or the passage 
of time or both would constitute an Event of Default have occurred and are 
continuing.  The execution and delivery of this Amendment by Lender shall not 
be construed as a waiver by Lender of any Event of Default under the 
Financing Agreements.  This Amendment shall be deemed to be a Financing 
Agreement and, together with the other Financing Agreements, constitute the 
entire agreement between the parties with respect to the subject matter 
hereof and supersedes all prior dealings, correspondence, conversations or 
communications between the parties with respect to the subject matter hereof.

                                                                           3



June 24, 1998
Page 4


     If you accept and agree to the foregoing please sign and return the 
enclosed copy of this letter.  Thank you.

                                 Very truly yours,

                                 CONGRESS FINANCIAL CORPORATION
                                 (NEW ENGLAND)


                                 By: /s/ KATHLEEN J. MERRITT     
                                    ----------------------------
                                    Name: Kathleen J. Merritt
                                    Title: Vice President

AGREED:
- -------

CLEAN HARBORS ENVIRONMENTAL 
     SERVICES, INC.
CLEAN HARBORS TECHNOLOGY
     CORPORATION
CLEAN HARBORS KINGSTON FACILITY 
     CORPORATION
CLEAN HARBORS OF BRAINTREE, INC.
CLEAN HARBORS SERVICES, INC.
CLEAN HARBORS OF NATICK, INC.
CLEAN HARBORS OF CONNECTICUT, INC.
MURPHY'S WASTE OIL SERVICE, INC.
CLEAN HARBORS OF CLEVELAND, INC.
MR. FRANK, INC. 
SPRING GROVE RESOURCE RECOVERY, INC.


By: /s/ STEPHEN MOYNIHAN
   ----------------------------
   Name: Stephen Moynihan
   Title: Senior Vice President

GUARANTORS:

CLEAN HARBORS, INC.

By: /s/ STEPHEN MOYNIHAN
   ----------------------------
   Name: Stephen Moynihan
   Title: Senior Vice President


                                                                           4



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Page 5


CLEAN HARBORS OF BALTIMORE, INC.


By: /s/ STEPHEN MOYNIHAN
   ----------------------------
   Name: Stephen Moynihan
   Title: Senior Vice President









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