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                                                                    EXHIBIT 4.9

September 6, 1996



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:  Third Amendment to Financing Agreements - Issuance of City of Kimball,
          Nebraska Economic Development Revenue Bonds ("Third 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 arranged for the issuance of $10,000,000 of City of
Kimball, Nebraska Economic Development Revenue Bonds (Clean Harbors, Inc.),
Series 1996 (the "Bonds"), the proceeds of which will reimburse the Borrowers
for costs incurred in connection with the Kimball, Nebraska waste disposal
facility (the "Facility") owned by Clean Harbors Technology Corporation
("CHTC"). The proceeds of the Bonds less certain costs of issuance will be
$9,800,000. Upon such issuance, not less than $9,300,000 in proceeds are to be
immediately paid to the Lender and applied to the Obligations and up to $500,000
of additional proceeds will be subject to certain escrow conditions and will be,
once released by the Trustee for the Bonds, paid to Lender and applied to the
Obligations. In connection with the issuance of the Bonds, Borrowers have
requested that certain amendments be made in the Loan Agreement. Subject to the
terms and conditions hereof, the Lender agrees with the Borrowers as follows:

      (1) Section 1.31 of the Loan Agreement is deleted in its entirety and
replaced with the following:




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            "1.31 "Maximum Credit" shall mean $35,000,000.00.

      (2) 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
$24,500,000.00."


      (3) Notwithstanding the provisions of Section 9.8, the Lender consents to
the lease and leaseback of the Facility by CHTC pursuant to a certain Facilities
Lease (the "Facilities Lease") and Lease Agreement (the "Lease") between CHTC
and the City of Kimball, Nebraska, each dated as of September 1, 1996; provided,
that no mortgage, security interest or lien on the Facility or the assets of
CHTC, the Parent or the other Borrowers is granted to secure the repayment of
the Lease or the Bonds (other than a debt service reserve which the Parent and
Borrowers may be required to be fund with the Trustee under certain
circumstances for up to one year of maximum debt service on the Bonds) and the
Facilities Lease and Lease shall in all respects be subject to the Mortgage of
the Lender on the Facility and the real estate on which the Facility is located.
The Borrowers further covenant and agree that upon release from escrow of the
additional Bond proceeds and any release of funds from the above-described debt
service reserve or any other account maintained in respect of the Bonds or
Lease, Borrowers shall cause such funds to be paid to the Payment Account.

      (4) Notwithstanding the provisions of Section 9.9 and 9.10, the Lender
consents (a) to CHTC incurring the obligations under the Lease Agreement and (b)
to the other Borrowers and the Parent guarantying the obligations of CHTC
pursuant to the Lease Agreement; provided, that such obligations and guaranties
are and remain unsecured (except to the extent of the debt service reserve fund
described above) and subject to the provisions of Section 9.9.

      (5) Section 10.1 is amended by deleting the period at the end of clause
(o), inserting "; or" in place thereof and adding the following clause to the
end thereof as clause (p):

            "(p) there shall be a default under the Lease Agreement dated as of
September 1, 1996 between the CHTC and the City of Kimball, Nebraska or the City
of Kimball, Nebraska Economic Development Bonds (Clean Harbors, Inc.) Series,
1996 or under any of the agreements, instruments or documents relating thereto."

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




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            (a) The Bonds will be duly issued, all documentation necessary
therefor executed and delivered and all conditions thereto satisfied without
amendment or waiver and all of the proceeds thereof that are not subject to
escrow with the Trustee and, in any event, not less than $9,300,000, shall be
paid to Lender;

            (b) all requisite corporate action and proceedings of the Borrowers
in connection with this Third 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; and

            (c) Lender shall have received in form and substance satisfactory to
Lender, an opinion of counsel to Borrowers with respect to this Third Amendment.

      (7) 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 or as permitted under this Third Amendment), 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.

      (8) 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.

      (9) 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 





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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.

      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:
                                     ------------------------------------
                                      Name:
                                           ------------------------------
                                     Title:
                                           ------------------------------






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AGREED:
- -------

CLEAN HARBORS ENVIRONMENTAL
SERVICES, INC.


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


CLEAN HARBORS TECHNOLOGY
CORPORATION


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


CLEAN HARBORS KINGSTON FACILITY
CORPORATION

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


CLEAN HARBORS OF BRAINTREE, INC.


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


CLEAN HARBORS SERVICES, INC.


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


CLEAN HARBORS OF NATICK, INC.


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





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CLEAN HARBORS OF CONNECTICUT, INC.


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


MURPHY'S WASTE OIL SERVICE, INC.


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


CLEAN HARBORS OF CLEVELAND, INC.


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


MR. FRANK, INC.

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


SPRING GROVE RESOURCE RECOVERY, INC.

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


CLEAN HARBORS, INC.

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







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CLEAN HARBORS OF BALTIMORE, INC.


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












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