EXHIBIT 4.6

                              November 21, 1995


CLEAN HARBORS ENVIRONMENTAL
     SERVICES, INC.
CLEAN HARBORS TECHNOLOGY
     CORPORATION
CLEAN HARBORS KINGSTON FACILITY
     CORPORATION
CLEAN HARBORS OF BRAINTREE, INC.
CLEAN HARBORS OF CHICAGO, 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:  Additional Revolving Loans and Cash Collateral
          ---------------------------------------------- 

Gentlemen:

          Reference is made to the Loan and Security Agreement dated May 8,
1995, as amended, between you and the undersigned (the "Loan Agreement").  We
have received $2,000,000 in cash collateral (the "Cash Collateral") from Alan
McKim (the "Pledgor") pursuant to a Cash Collateral Agreement of even date.  All
capitalized terms not otherwise defined herein shall have the meanings given
such terms in the Loan Agreement.

          The Lender agrees with the Borrowers as follows:

          (1) Subject to the provisions of Section 4.2 of the Loan Agreement, we
agree to make additional Revolving Loans to Borrowers on a dollar for dollar
basis with the Cash Collateral provided that such Cash Collateral is at all
times fully available to Lender as collateral security for the Obligations
pursuant to the Cash Collateral Agreement.

          (2) The Lender agrees to make additional Revolving Loans to Borrowers
in excess of the limits set forth in section 2 of the Loan Agreement and in
paragraph (1) of this letter agreement, in an aggregate amount not exceeding
$2,000,000 (the "Overadvance Limit") at any time, with such Overadvance Limit to
be reduced each week by $200,000 and the amount of Revolving Loans in excess of
the Overadvance Limit, as so reduced, repaid to such level commencing on
November 27, 1995 and on the Monday of each calendar week thereafter, with the
full amount of the Revolving Loans 

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made under this paragraph (2) plus accrued and unpaid interest thereon to be due
and payable on January 29, 1996.

          (3) For the period ending 90 days from the date hereof, Lender waives
the limitation set forth on Schedule 9.11 to the Loan Agreement requiring that
the Borrowers maintain Excess Availability of not less than $4,500,000 before
making any distributions to Parent but solely with respect to distributions to
Parent that pay obligations described in clauses (a) and (e) of Schedule 9.11.

          (4) The Borrowers shall pay the Lender an overadvance fee of $30,000,
which overadvance fee shall be fully earned and payable upon Borrowers'
execution of this letter agreement.

          This letter agreement shall be deemed to be a Financing Agreement and
incorporates by reference all the terms of the Loan Agreement.  All Revolving
Loans made hereunder shall be deemed to be Obligations incurred under and
subject to the benefits of the Financing Agreements including, without
limitation, that such loans shall be secured by a first priority lien on all the
Collateral.

          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/ Marc E. Swartz
                                          ---------------------------
                                          Name: Marc E. Swartz 
                                               ----------------------
                                          Title: Vice President
                                                ---------------------

AGREED:
- ------ 

CLEAN HARBORS ENVIRONMENTAL
SERVICES, INC.


By: /s/ Stephen Moynihan
   --------------------------
   Name: Stephen Moynihan
        ---------------------
   Title: Vice President
         --------------------

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CLEAN HARBORS TECHNOLOGY
CORPORATION


By: /s/ Stephen Moynihan
   --------------------------
   Name: Stephen Moynihan
        ---------------------
   Title: Vice President
         --------------------


CLEAN HARBORS KINGSTON FACILITY
CORPORATION


By: /s/ Stephen Moynihan
   --------------------------
   Name: Stephen Moynihan
        ---------------------
   Title: Vice President
         --------------------


CLEAN HARBORS OF BRAINTREE, INC.


By: /s/ Stephen Moynihan
   --------------------------
   Name: Stephen Moynihan
        ---------------------
   Title: Vice President
         --------------------


CLEAN HARBORS OF CHICAGO, INC.


By: /s/ Stephen Moynihan
   --------------------------
   Name: Stephen Moynihan
        ---------------------
   Title: Vice President
         --------------------


CLEAN HARBORS OF NATICK, INC.


By: /s/ Stephen Moynihan
   --------------------------
   Name: Stephen Moynihan
        ---------------------
   Title: Vice President
         --------------------



CLEAN HARBORS OF CONNECTICUT, INC.


By: /s/ Stephen Moynihan
   --------------------------
   Name: Stephen Moynihan
        ---------------------
   Title: Vice President
         --------------------

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MURPHY'S WASTE OIL SERVICE, INC.


By: /s/ Stephen Moynihan
   --------------------------
   Name: Stephen Moynihan
        ---------------------
   Title: Vice President
         --------------------


CLEAN HARBORS OF CLEVELAND, INC.


By: /s/ Stephen Moynihan
   --------------------------
   Name: Stephen Moynihan
        ---------------------
   Title: Vice President
         --------------------


MR. FRANK, INC.


By: /s/ Stephen Moynihan
   --------------------------
   Name: Stephen Moynihan
        ---------------------
   Title: Vice President
         --------------------


SPRING GROVE RESOURCE RECOVERY, INC.


By: /s/ Stephen Moynihan
   --------------------------
   Name: Stephen Moynihan
        ---------------------
   Title: Vice President
         --------------------

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