EXHIBIT 4.7
 
                              March 20, 1996


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:  Second Amendment to Financing Agreements - Term Loan Refunding
          --------------------------------------------------------------
          ("Second 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 that the principal amount of the Term Loan be
increased to $15,000,000.00 and that the difference between the outstanding
principal amount of the original Term Loan ($8,333,333.33) and $15,000,000 be
funded to the Borrowers and used to repay outstanding Revolving Loans.  Subject
to the terms and conditions hereof, the Lender agrees with the Borrowers as
follows:

          (1) Section 1.48 of the Loan Agreement is deleted in its entirety and
replaced with the following:
 
              "1.48 "Revolving Credit Limit" shall mean the amount of
$30,000,000.00."

          (2) Section 2.3 of the Loan Agreement is deleted in its entirety and
replaced with the following:

                                       1

 
              "2.3  Term Loan.  Effective upon the date of the Second Amendment,
                    ---------                                                   
Lender is making a Term Loan to Borrowers in the original principal amount of
$15,000,000.00.  The outstanding principal amount on the $10,000,000 Term Loan
made as of May 8, 1995 shall be converted into the Term Loan made under the
Second Amendment and the balance shall be applied to repay outstanding Revolving
Loans.  The Term Loan is (a) evidenced by an Amended and Restated Term
Promissory Note in the original principal amount of $15,000,000.00 duly executed
and delivered by the Borrowers to Lender; (b) to be repaid, together with
interest and other amounts, in accordance with this Agreement, the Amended and
Restated Term Promissory Note, and the other Financing Agreements and (c)
secured by all the Collateral."

          (3) The Lender agrees to make the Term Loan to Borrowers upon the
satisfaction of the conditions set forth in Section 4.2 of the Loan Agreement
and the following additional conditions:

              (a) all requisite corporate action and proceedings of the
Borrowers in connection with this Second Amendment and the Amended and Restated
Term Promissory Note 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) Lender shall have received in form and substance satisfactory
to Lender, an opinion of counsel to Borrowers with respect to this Second
Amendment and the Amended and Restated Secured Promissory Term Note;

              (c) 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

              (d) Borrowers shall pay to Lender, and directs Lender to debit its
loan account for, an additional facility fee equal to $33,333.33, which fee
shall be fully earned and non-refundable on the date hereof.

          (4) For the period ending 60 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.

          (5) Section 12.9 is amended by adding the following sentence to the
end thereof:  "For purposes hereof, the Proportionate Share of a Borrower shall
mean the actual amount of Loans made to such Borrower and Letter of Credit
Accommodations 

                                       2

 
issued for the account of such Borrower, based upon the lending formula and
other provisions of Section 2 hereof."

          (6) 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.

          (7) 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.

          (8) 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

 
   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
                                      ------------------------

                                       4

 
AGREED:
- ------ 

CLEAN HARBORS ENVIRONMENTAL
SERVICES, INC.


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

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

                                       5

 
CLEAN HARBORS OF CONNECTICUT, INC.


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


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



CLEAN HARBORS, INC.


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

                                       6

 
CLEAN HARBORS OF BALTIMORE, INC.


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

                                       7