FIRST AMENDMENT TO

Exhibit 4.25A

FIRST AMENDMENT TO

FINANCING AGREEMENT

THIS FIRST AMENDMENT TO FINANCING AGREEMENT (this “Amendment”) is entered into as of May 20, 2003, by and among Clean Harbors, Inc., a Massachusetts corporation (the “Parent”), each subsidiary of the Parent listed as a “Borrower” on the signature pages to the Financing Agreement (together with the Parent, each a “Borrower” and collectively, the “Borrowers”), each subsidiary of the Parent listed as a “Guarantor” on the signature pages to the Financing Agreement (each a “Guarantor” and collectively, the “Guarantors”; together with the Borrowers, the “Loan Parties”), the financial institutions from time to time party to the Financing Agreement (each a “Lender” and collectively, the “Lenders”), and Ableco Finance LLC, a Delaware limited liability company (“Ableco”), as agent for the Lenders (in such capacity, the “Agent”).

W I T N E S S E T H

WHEREAS, the Loan Parties, the Lenders and the Agent are parties to a Financing Agreement, dated as of September 6, 2002 (as amended, modified or supplemented from time to time, the “Financing Agreement”), pursuant to which the Lenders have made certain terms loans to the Borrowers in an aggregate principal amount at any time not to exceed the aggregate amount of the Commitments (as defined in the Financing Agreement) set forth therein;

WHEREAS, the Loan Parties, the Lenders and the Agent desire to amend certain terms and provisions of the Financing Agreement to reflect, among other things, a modification of (i) the financial covenants set forth in Section 7.03 thereof and (ii) the applicable interest rates set forth in Section 2.04 thereof. In addition, the Borrowers have advised the Agent that the Borrowers are in default, among other things, under the financial covenants set forth in Section 7.03 of the Financing Agreement and have requested the Lenders to waive such defaults, and the Lenders have agreed to such waiver, subject to (i) the execution and delivery of this Amendment by the Loan Parties, and (ii) the other terms and conditions set forth in this Amendment; and

WHEREAS, the Agent and the Lenders are willing to amend the Financing Agreement to provide for such amendments, subject to the execution and delivery of this Amendment by the Loan Parties; and.

NOW, THEREFORE, in consideration of the premises and of the mutual covenants, agreements and conditions hereinafter set forth, and for other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, the parties hereto hereby agree as follows:

1. Capitalized Terms. All capitalized terms used in this Amendment and not otherwise defined shall have their respective meanings set forth in the Financing Agreement.

2. Consolidated Net Income. The definition of the term “Consolidated Net Income” set forth in Section 1.01 of the Financing Agreement is hereby amended by (i) deleting the word “and” at the end of clause (d) thereof, (ii) deleting the period at the end of clause (e) thereof and inserting “,” at the end thereof and (iii) inserting new clauses (f), (g) and (h) therein to read as follows:

“, (f) non-cash gains or losses reflecting the cumulative effect of adoption of changes in GAAP, (g) accretion expense (provided that such expense is non-cash) applicable to environmental liabilities to the extent such expense would not have been recorded under GAAP as used in the preparation of the Financial Statements and (h) non-cash gains or losses reflecting adjustments to the estimated value of the embedded derivative associated with the Parent’s outstanding Series C convertible preferred stock.”

3. Term Loan A Interest. Section 2.04(a) of the Financing Agreement is hereby amended in its entirety to read as follows:

“(a) The Term Loan A shall be a LIBOR Loan, except as otherwise provided in Section 2.09. The portion of the Term Loan A that is a LIBOR Loan shall bear interest on the principal amount thereof from time to time outstanding, from the date of the Term Loan A until such principal amount becomes due, at a rate per annum equal to the LIBOR Rate for the Interest Period in effect for such portion of the Term Loan A plus 7.75%, provided, however, that if the Consolidated EBITDA of the Parent and its Subsidiaries for the Fiscal Year ending on December 31, 2003 is equal to or exceeds $90,000,000, such percentage shall be 7.25% effective upon the Agent’s receipt of the audited financial statements of the Parent and its Subsidiaries delivered to the Agent in accordance with Section 7.01(a)(ii) hereof. The portion of the Term Loan A that is a Reference Rate Loan shall bear interest on the principal amount thereof from time to time outstanding, from the date of the Term Loan A until such principal amount becomes due, at a rate per annum equal to the Reference Rate plus 5.00%; provided, however, that if the Consolidated EBITDA of the Parent and its Subsidiaries for the Fiscal Year ending on December 31, 2003 is equal to or exceeds $90,000,000, such percentage shall be 4.50% effective upon the Agent’s receipt of the audited financial statements of the Parent and its Subsidiaries delivered to the Agent in accordance with Section 7.01(a)(ii) hereof.”

4. Term Loan B Interest. Section 2.04(b) of the Financing Agreement is hereby amended in its entirety to read as follows:

“(b) Term Loan B. The Term Loan B shall bear interest on the principal amount thereof from time to time outstanding, from the date of the Term Loan B until such principal amount becomes due, at a rate per annum equal to 22.50%; provided, however, that, (i) if the Consolidated EBITDA of the Parent and its Subsidiaries for the Fiscal Year ending on December 31, 2003 is equal to or exceeds $90,000,000, such rate shall be 22% effective upon the Agent’s receipt of the audited financial statements of the Parent and its Subsidiaries delivered to the

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Agent in accordance with Section 7.01(a)(ii) hereof and (ii) so long as no Event of Default has occurred and is continuing, interest on the outstanding principal amount of the Term Loan B at a per annum rate equal to 11% shall, in the absence of an election by the Administrative Borrower to pay such interest in cash, be paid by capitalizing such interest and adding such capitalized interest to the then outstanding principal amount of the Term Loan B. Any interest to be capitalized shall be capitalized on the date such interest is to be paid pursuant to Section 2.04(d) and added to the then outstanding principal amount of the Term Loan B and thereafter shall bear interest as provided hereunder as if it had originally been part of the outstanding principal of the Term Loan B.”

5. Hiring of Consultant. Section 7.01 of the Financing Agreement is hereby amended by inserting a new Section 7.01(q) therein immediately after Section 7.01(p) to read as follows:

“(q) Hiring of Consultant. At the written request of the Required Lenders, the Borrowers shall, at Borrowers’ expense, promptly (but in any event within fifteen (15) days of such request) engage a financial consultant reasonably acceptable to the Required Lenders pursuant to terms and with a scope of duties and responsibilities reasonably acceptable to the Required Lenders.”

6. Restricted Payments. Section 7.02(h) of the Financing Agreement is hereby amended in its entirety to read as follows:

“(h) Restricted Payments. (i) Declare or pay any dividend or other distribution, direct or indirect, on account of any Capital Stock of any Loan Party or any of its Subsidiaries, now or hereafter outstanding, (ii) make any repurchase, redemption, retirement, defeasance, sinking fund or similar payment, purchase or other acquisition for value, direct or indirect, of any Capital Stock of any Loan Party or any direct or indirect parent of any Loan Party, now or hereafter outstanding, (iii) make any payment to retire, or to obtain the surrender of, any outstanding warrants, options or other rights for the purchase or acquisition of shares of any class of Capital Stock of any Loan Party, now or hereafter outstanding, (iv) return any Capital Stock to any shareholders or other equity holders of any Loan Party or any of its Subsidiaries, or make any other distribution of property, assets, shares of Capital Stock, warrants, rights, options, obligations or securities thereto as such or (v) pay any management fees or any other fees or expenses (including the reimbursement thereof by any Loan Party or any of its Subsidiaries) pursuant to any management, consulting or other services agreement to any of the shareholders or other equityholders of any Loan Party or any of its Subsidiaries or other Affiliates, or to any other Subsidiaries or Affiliates of any Loan Party; provided, however, (A) any Loan Party may pay dividends to the Parent, (B) any Subsidiary of any Borrower may pay dividends to such Borrower and (C) the Parent may pay dividends in the form of common Capital Stock, provided that in each case of clauses (A) through (C) above, at the election of the Agent, which the Agent may and, upon the direction of the Required Lenders, shall make by notice to the Administrative Borrower, no such payment shall be made if

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an Event of Default shall have occurred and be continuing or would result from the making of any such payment.”

7. Financial Covenants. Section 7.03 of the Financing Agreement is hereby amended in its entirety to read as follows:

“Section 7.03 Financial Covenants .. So long as any principal of or interest on any Loan or any other Obligation (whether or not due) shall remain unpaid or any Lender shall have any Commitment hereunder, each Loan Party shall not, unless the Required Lenders shall otherwise consent in writing:

(a) Leverage Ratio . Permit the ratio of Consolidated Funded Indebtedness to (i) for any fiscal quarter ending on June 30, 2003, Consolidated Annualized EBITDA of the Parent and its Subsidiaries and (ii) for each fiscal quarter ending thereafter, Consolidated EBITDA of the Parent and its Subsidiaries as of the end of each period of four (4) consecutive fiscal quarters of the Parent and its Subsidiaries for which the last quarter ends on a date set forth below, to be greater than the applicable ratio set forth below:

(b) Fixed Charge Coverage Ratio. Permit the Fixed Charge Coverage Ratio of the Parent and its Subsidiaries for each period of four (4) consecutive fiscal quarters (or, in the case of each fiscal quarter ending on June 30, 2003, such lesser number of consecutive fiscal quarters as shall then have been completed since the fiscal quarter commencing on October 1, 2002) of the Parent and its Subsidiaries for which the last quarter ends on a date set forth below to be less than the amount set forth opposite such date:

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(c) Consolidated EBITDA. Permit (i) for any fiscal quarter ending on June 30, 2003, Consolidated Annualized EBITDA of the Parent and its Subsidiaries and (ii) for each fiscal quarter ending thereafter, Consolidated EBITDA of the Parent and its Subsidiaries for the four fiscal quarters ending as of the end of the applicable fiscal quarter set forth below, to be less than the applicable amount set forth below:

8. Amendment Fee. The Borrowers hereby agree that, in consideration of the Lenders’ willingness to enter into this Amendment, the Borrowers shall pay to the Agent, for the ratable benefit of the Lenders, in immediately available funds, a nonrefundable amendment fee (the “Amendment Fee”) equal to $400,000, which Amendment Fee shall be fully earned on the Amendment Effective Date (as defined herein) and payable on the first day of each month following the Amendment Effective Date in increments of $100,000 until such Amendment Fee is paid in full.

9. Conditions to Effectiveness. This Amendment shall become effective only upon satisfaction in full, in a manner satisfactory to the Agent, of the following conditions precedent (the first date upon which all such conditions shall have been satisfied being herein called the “Amendment Effective Date”), provided that the amendments set forth in Sections 3 and 4 of this Amendment shall be deemed effective as of April 1, 2003 but shall not apply to periods prior to April 1, 2003:

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(a) The representations and warranties contained in Article VI of the Financing Agreement and in each other Loan Document, certificate or other writing delivered on or on behalf of any Loan Party to the Agent or any Lender pursuant to the Financing Agreement or any other Loan Document on or prior to the Amendment Effective Date are true and correct on and as of such date as though made on and as of such date, and, subject to Section 11 hereof, no Default or Event of Default has occurred and is continuing on the Amendment Effective Date or would result from this Amendment becoming effective in accordance with its terms.

(b) Delivery of Documents. The Agent shall have received on or before the Amendment Effective Date counterparts to this Amendment signed by each of the Loan Parties, the Lenders and the Agent, in form and substance satisfactory to the Agent and dated the Amendment Effective Date.

(c) All legal matters incident to this Amendment shall be satisfactory to the Agent and its counsel.

10. Representations and Warranties. Each Loan Party that is a party to the Financing Agreement hereby represents and warrants to the Agent and the Lenders as follows:

(a) Representations and Warranties; No Event of Default. The representations and warranties herein, in Article VI of the Financing Agreement and in each other Loan Document, certificate or other writing delivered on or on behalf of any Loan Party to the Agent or any Lender pursuant to the Financing Agreement or any other Loan Document on or prior to the Amendment Effective Date are true and correct on and as of such date as though made on and as of such date, and, subject to Section 11 hereof, no Default or Event of Default has occurred and is continuing as of the Amendment Effective Date or would result from this Amendment becoming effective in accordance with its terms.

(b) Organization, Good Standing, Etc. Each Loan Party (i) is a corporation, limited liability company or limited partnership duly organized, validly existing and in good standing under the laws of the state or jurisdiction of its organization, (ii) has all requisite power and authority to conduct its business as now conducted and as presently contemplated, and to execute and deliver this Amendment, and to consummate the transactions contemplated hereby and by the Financing Agreement, as amended hereby, and (iii) is duly qualified to do business and is in good standing in each jurisdiction in which the character of the properties owned or leased by it or in which the transaction of its business makes such qualification necessary, except where the failure to be so qualified and in good standing could not reasonably be expected to have a Material Adverse Effect.

(c) Authorization, Etc. The execution, delivery and performance of this Amendment and each other Loan Document being executed in connection with this Amendment by each Loan Party that is a party thereto, and the performance of the Financing Agreement as amended hereby (i) have been duly authorized by all necessary action, (ii) do not and will not contravene such Loan Party’s charter or by-laws, its limited liability company or operating agreement or its certificate of partnership or partnership agreement, as applicable, or any applicable law or any Transaction Document, any Material Contract or any other contractual restriction binding on or otherwise affecting it or any of its properties, (iii) do not and will not

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result in or require the creation of any Lien (other than pursuant to any Loan Document) upon or with respect to any of its properties, and (iv) do not and will not result in any default, noncompliance, suspension, revocation, impairment, forfeiture or nonrenewal of any permit, license, authorization or approval applicable to its operations or any of its properties.

(d) Governmental Approvals. No authorization or approval or other action by, and no notice to or filing with, any Governmental Authority is required in connection with the due execution, delivery and performance by any Loan Party of this Amendment or any other Loan Document to which it is a party being executed in connection with this Amendment, or for the performance of the Financing Agreement, as amended hereby.

(e) Enforceability of Loan Documents. Each of this Amendment, the Financing Agreement, as amended hereby, and each other Loan Document to which such Loan Party is a party is a legal, valid and binding obligation of such Loan Party, enforceable against such Loan Party in accordance with its terms, except as may be limited by applicable bankruptcy, insolvency, reorganization, moratorium or other similar laws.

11. Waiver and Consent.

(a) Pursuant to the request of the Borrowers, the Lenders hereby consent to and waive any Event of Default that would arise under Section 9.01(c) or 9.01(d) of the Financing Agreement as a result of (i) the Borrowers’ failure to deliver the financial statements for the fiscal month and quarter ending March 31, 2003 in accordance with Section 7.01(a)(i) and (iii) of the Financing Agreement and (ii) the Borrowers’ failure to satisfy each of the financial covenants set forth in Section 7.03 of the Financing Agreement for the fiscal quarter ended March 31, 2003.

(b) The Lenders’ consent and waiver of any Event of Default relating to the events set forth in paragraph (a) above:

i. shall be effective only in this specific instance and for the specific purposes set forth herein, and

ii. does not allow for any other or further departure from the terms and conditions of the Financing Agreement or any other Loan Documents, which terms and conditions shall continue in full force and effect.

12. Continued Effectiveness of Financing Agreement. Each Loan Party hereby (i) confirms and agrees that each Loan Document to which it is a party is, and shall continue to be, in full force and effect and is hereby ratified and confirmed in all respects except that on and after the Amendment Effective Date all references in any such Loan Document to “the Financing Agreement”, “thereto”, “thereof”, “thereunder” or words of like import referring to the Financing Agreement shall mean the Financing Agreement as amended by this Amendment, and (ii) confirms and agrees that to the extent that any such Loan Document purports to assign or pledge to the Agent, or to grant to the Agent, a Lien on any collateral as security for the Obligations of the Borrowers from time to time existing in respect of the Financing Agreement and the Loan Documents, such pledge, assignment and/or grant of a Lien is hereby ratified and confirmed in all respects.

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13. Miscellaneous.

(a) This Amendment may be executed in any number of counterparts and by different parties hereto in separate counterparts, each of which shall be deemed to be an original, but all of which taken together shall constitute one and the same agreement.

(b) Section and paragraph headings herein are included for convenience of reference only and shall not constitute a part of this Amendment for any other purpose.

(c) This Amendment shall be governed by, and construed in accordance with, the laws of the State of New York.

(d) Each Loan Party hereby acknowledges and agrees that this Amendment constitutes a “Loan Document” under the Financing Agreement. Accordingly, it shall be an Event of Default under the Financing Agreement if (i) any representation or warranty made by a Loan Party under or in connection with this Amendment shall have been untrue, false or misleading in any material respect when made, or (ii) a Loan Party shall fail to perform or observe any term, covenant or agreement contained in this Amendment.

(e) Notwithstanding anything to the contrary, except as specifically provided herein, this Amendment is not, and shall not be deemed to be, a waiver of, or a consent to any Event of Default, event with which the giving of notice or lapse of time or both may result in an Event of Default, or other noncompliance now existing or hereafter arising under the Financing Agreement and the other Loan Documents.

14. The Borrowers will pay on demand all reasonable out-of-pocket costs and expenses of the Agent and the Lenders in connection with the preparation, execution and delivery of this Amendment, including, without limitation, the reasonable fees, disbursements and other charges of Schulte Roth & Zabel LLP, counsel to the Agent.

15. THE LOAN PARTIES, THE AGENT AND THE LENDERS EACH HEREBY IRREVOCABLY WAIVE ALL RIGHT TO TRIAL BY JURY IN ANY ACTION, PROCEEDING OR COUNTERCLAIM (WHETHER BASED ON CONTRACT, TORT OR OTHERWISE) ARISING OUT OF OR RELATING TO THIS AMENDMENT OR THE ACTIONS OF THE AGENT OR THE LENDERS IN THE NEGOTIATION, ADMINISTRATION, PERFORMANCE OR ENFORCEMENT HEREOF.

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IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be executed by their respective officers thereunto duly authorized, as of the date first above written.

    BORROWERS:

    CLEAN HARBORS, INC.

    ALTAIR DISPOSAL SERVICES, LLC

    BATON ROUGE DISPOSAL, LLC

    BRIDGEPORT DISPOSAL, LLC

    CLEAN HARBORS ANDOVER, LLC

    CLEAN HARBORS ANTIOCH, LLC

    CLEAN HARBORS ARAGONITE, LLC

    CLEAN HARBORS ARIZONA, LLC

    CLEAN HARBORS BATON ROUGE, LLC

    CLEAN HARBORS BDT, LLC

    CLEAN HARBORS BUTTONWILLOW, LLC

    CLEAN HARBORS CHATTANOOGA, LLC

    CHEMICAL SALES, LLC

    CLEAN HARBORS COFFEYVILLE, LLC

    CLEAN HARBORS COLFAX, LLC

    CLEAN HARBORS DEER PARK, L.P.

    CLEAN HARBORS DEER TRAIL, LLC

    CLEAN HARBORS DISPOSAL SERVICES, INC.

    CLEAN HARBORS FINANCIAL SERVICES

        COMPANY

    CLEAN HARBORS FLORIDA, LLC

    CLEAN HARBORS GRASSY MOUNTAIN, LLC

    CLEAN HARBORS KANSAS, LLC

    CLEAN HARBORS LAPORTE, L.P.

    CLEAN HARBORS LAUREL, LLC

    CLEAN HARBORS LONE MOUNTAIN, LLC

    CLEAN HARBORS LONE STAR CORP.

    CLEAN HARBORS LOS ANGELES, LLC

    CLEAN HARBORS OF TEXAS, LLC

    CLEAN HARBORS PECATONICA, LLC

    CLEAN HARBORS PLAQUEMINE, LLC

    CLEAN HARBORS PPM, LLC

    CLEAN HARBORS REIDSVILLE, LLC

    CLEAN HARBORS SAN JOSE, LLC

    CLEAN HARBORS TENNESSEE, LLC

    CLEAN HARBORS WESTMORLAND, LLC

    CLEAN HARBORS WHITE CASTLE, LLC

    CROWLEY DISPOSAL, LLC

    DISPOSAL PROPERTIES, LLC

    GSX DISPOSAL, LLC