2,000,000 Shares CLEAN HARBORS, INC. Common Stock UNDERWRITING AGREEMENT

QuickLinks -- Click here to rapidly navigate through this document

Exhibit 1.1

2,000,000 Shares
CLEAN HARBORS, INC.
Common Stock
UNDERWRITING AGREEMENT

December [ ], 2005

Credit Suisse First Boston LLC,
As Representative of the Several Underwriters,
Eleven Madison Avenue,
New York, N.Y. 10010-3629

Dear Sirs:

1. Introductory. Clean Harbors, Inc., a Massachusetts corporation ("Company"), proposes to issue and sell 2,000,000 ("Firm Securities") shares of its common stock, $0.01 par value per share ("Securities"), and also proposes to sell to the Underwriters, at the option of the Underwriters, an aggregate of not more than 300,000 additional shares ("Optional Securities") of its Securities, as set forth below. The Firm Securities and the Optional Securities are herein collectively called the "Offered Securities". The Company hereby agrees with the several Underwriters named in Schedule A hereto ("Underwriters") as follows:

2. Representations and Warranties of the Company. (a) The Company represents and warrants to, and agrees with, the several Underwriters that:

(i) A registration statement (No. 333-129346) relating to the Offered Securities, including a form of prospectus, has been filed with the Securities and Exchange Commission ("Commission") and either (A) has been declared effective under the Securities Act of 1933 ("Act") and is not proposed to be amended or (B) is proposed to be amended by amendment or post-effective amendment. If such registration statement (the "initial registration statement") has been declared effective, either (A) an additional registration statement (the "additional registration statement") relating to the Offered Securities may have been filed with the Commission pursuant to Rule 462(b) ("Rule 462(b)") under the Act and, if so filed, has become effective upon filing pursuant to such Rule and the Offered Securities all have been duly registered under the Act pursuant to the initial registration statement and, if applicable, the additional registration statement or (B) such an additional registration statement may be proposed to be filed with the Commission pursuant to Rule 462(b) and, if so filed, will become effective upon filing pursuant to such Rule and upon such filing the Offered Securities will all have been duly registered under the Act pursuant to the initial registration statement and such additional registration statement. If the Company does not propose to amend the initial registration statement or if an additional registration statement has been filed and the Company does not propose to amend it, and if any post-effective amendment to either such registration statement has been filed with the Commission prior to the execution and delivery of this Agreement, the most recent amendment (if any) to each such registration statement has been declared effective by the Commission or has become effective upon filing pursuant to Rule 462(c) ("Rule 462(c)") under the Act or, in the case of the additional registration statement, Rule 462(b). For purposes of this Agreement, "Effective Time" with respect to the initial registration statement or, if filed prior to the execution and delivery of this Agreement, the additional registration statement means (A) if the Company has advised the Representative that it does not propose to amend such registration statement, the date and time as of which such registration statement, or the most recent post-effective amendment thereto (if any) filed prior to the execution and delivery of this Agreement, was declared effective by the Commission or has become effective upon filing pursuant to Rule 462(c), or (B) if the Company

has advised the Representative that it proposes to file an amendment or post-effective amendment to such registration statement, the date and time as of which such registration statement, as amended by such amendment or post-effective amendment, as the case may be, is declared effective by the Commission. If an additional registration statement has not been filed prior to the execution and delivery of this Agreement but the Company has advised the Representative that it proposes to file one, "Effective Time" with respect to such additional registration statement means the date and time as of which such registration statement is filed and becomes effective pursuant to Rule 462(b). "Effective Date" with respect to the initial registration statement or the additional registration statement (if any) means the date of the Effective Time thereof. The initial registration statement, as amended at its Effective Time, including all material incorporated by reference therein, including all information contained in the additional registration statement (if any) and deemed to be a part of the initial registration statement as of the Effective Time of the additional registration statement pursuant to the General Instructions of the Form on which it is filed and including all information (if any) deemed to be a part of the initial registration statement as of its Effective Time pursuant to Rule 430A(b) ("Rule 430A(b)") under the Act, is hereinafter referred to as the "Initial Registration Statement". The additional registration statement, as amended at its Effective Time, including the contents of the initial registration statement incorporated by reference therein and including all information (if any) deemed to be a part of the additional registration statement as of its Effective Time pursuant to Rule 430A(b), is hereinafter referred to as the "Additional Registration Statement". The Initial Registration Statement and the Additional Registration Statement are herein referred to collectively as the "Registration Statements" and individually as a "Registration Statement". The form of prospectus relating to the Offered Securities, as first filed with the Commission pursuant to and in accordance with Rule 424(b) ("Rule 424(b)") under the Act or (if no such filing is required) as included in a Registration Statement, including all material incorporated by reference in such prospectus, is hereinafter referred to as the "Prospectus". No document has been or will be prepared or distributed in reliance on Rule 434 under the Act.

(ii) If the Effective Time of the Initial Registration Statement is prior to the execution and delivery of this Agreement: (A) on the Effective Date of the Initial Registration Statement, the Initial Registration Statement conformed in all respects to the requirements of the Act and the rules and regulations of the Commission ("Rules and Regulations") and did not include any untrue statement of a material fact or omit to state any material fact required to be stated therein or necessary to make the statements therein not misleading, (B) on the Effective Date of the Additional Registration Statement (if any), each Registration Statement conformed or will conform, in all respects to the requirements of the Act and the Rules and Regulations and did not include, or will not include, any untrue statement of a material fact and did not omit, or will not omit, to state any material fact required to be stated therein or necessary to make the statements therein not misleading, and (C) on the date of this Agreement, the Initial Registration Statement and, if the Effective Time of the Additional Registration Statement is prior to the execution and delivery of this Agreement, the Additional Registration Statement each conforms, and at the time of filing of the Prospectus pursuant to Rule 424(b) or (if no such filing is required) at the Effective Date of the Additional Registration Statement in which the Prospectus is included, each Registration Statement and the Prospectus will conform, in all respects to the requirements of the Act and the Rules and Regulations, and neither of such documents includes, or will include, any untrue statement of a material fact or omits, or will omit, to state any material fact required to be stated therein or necessary to make the statements therein not misleading. If the Effective Time of the Initial Registration Statement is subsequent to the execution and delivery of this Agreement: on the Effective Date of the Initial Registration Statement, the Initial Registration Statement and the Prospectus will conform in all respects to the requirements of the Act and the Rules and Regulations, neither of such documents will include any untrue statement of a material fact or will

omit to state any material fact required to be stated therein or necessary to make the statements therein not misleading, and no Additional Registration Statement has been or will be filed. The two preceding sentences do not apply to statements in or omissions from a Registration Statement or the Prospectus based upon written information furnished to the Company by any Underwriter through the Representative specifically for use therein, it being understood and agreed that the only such information is that described as such in Section 7(c) hereof.

(iii) The Company has been duly incorporated and is an existing corporation in good standing under the laws of the Commonwealth of Massachusetts, with power and authority (corporate and other) to own its properties and conduct its business as described in the Prospectus; and the Company is duly qualified to do business as a foreign corporation in good standing in all other jurisdictions in which its ownership or lease of property or the conduct of its business requires such qualification.

(iv) Each subsidiary of the Company has been duly incorporated or organized, as the case may be, and is an existing corporation or other entity in good standing under the laws of the jurisdiction of its incorporation or formation, with power and authority (corporate and other) to own its properties and conduct its business as described in the Prospectus; and each subsidiary of the Company is duly qualified to do business as a foreign corporation or organization in good standing in all other jurisdictions in which its ownership or lease of property or the conduct of its business requires such qualification; all of the issued and outstanding capital stock of each subsidiary of the Company has been duly authorized and validly issued and is fully paid and nonassessable; and the capital stock of each subsidiary owned by the Company, directly or through subsidiaries, is owned free from liens, encumbrances and defects, except for liens permitted under (i) the Company's amended and restated loan and security agreement (the "Credit Facility"), among the Company, Credit Suisse First Boston, acting through one or more of its branches or affiliates, as administrative agent for the letter of credit facility, Bank of America, N.A., as administrative agent for the revolving facility, the lenders party thereto from time to time and the other persons party thereto from time to time and (ii) the indenture dated June 30, 2004 governing the Company's 11¹/4% Senior Secured Notes due 2012 (the "Existing Notes").

(v) The Offered Securities and all other outstanding shares of capital stock of the Company have been duly authorized; all outstanding shares of capital stock of the Company are, and, when the Offered Securities have been delivered and paid for in accordance with this Agreement on each Closing Date (as defined below), such Offered Securities will have been, validly issued, fully paid and nonassessable and conform to the description thereof contained in the Prospectus; and the stockholders of the Company have no preemptive rights with respect to the Securities.

(vi) Except as disclosed in the Prospectus, there are no contracts, agreements or understandings between the Company and any person that would give rise to a valid claim against the Company or any Underwriter for a brokerage commission, finder's fee or other like payment in connection with this offering.

(vii) Except for the Investors Rights Agreement, dated June 30, 2004, by and among the Company and the investors party thereto relating to the Company's common stock purchase warrants ("Investors Rights Agreement"), there are no contracts, agreements or understandings between the Company and any person granting such person the right to require the Company to file a registration statement under the Act with respect to any securities of the Company owned or to be owned by such person or to require the Company to include such securities in the securities registered pursuant to a Registration Statement or in any securities being registered pursuant to any other registration statement filed by the Company under the Act.

(viii) The Securities are listed on the Nasdaq Stock Market's National Market.

(ix) No consent, approval, authorization, or order of, or filing with, any governmental agency or body or any court is required to be obtained or made by the Company for the consummation of the transactions contemplated by this Agreement in connection with the issuance and sale of the Offered Securities, except such as have been obtained and made under the Act and such as may be required under state securities laws.

(x) The execution, delivery and performance of this Agreement, and the consummation of the transactions herein contemplated will not result in a breach or violation of any of the terms and provisions of, or constitute a default under, any statute, any rule, regulation or order of any governmental agency or body or any court, domestic or foreign, having jurisdiction over the Company or any subsidiary of the Company or any of their properties, or any agreement or instrument to which the Company or any such subsidiary is a party or by which the Company or any such subsidiary is bound or to which any of the properties of the Company or any such subsidiary is subject, or the charter or by-laws of the Company or any such subsidiary, and the Company has full power and authority to authorize, issue and sell the Offered Securities as contemplated by this Agreement.

(xi) This Agreement has been duly authorized, executed and delivered by the Company.

(xii) Except as disclosed in the Prospectus, the Company and its subsidiaries have good and marketable title to all real properties and all other properties and assets owned by them, in each case free from liens, encumbrances and defects that would materially affect the value thereof or materially interfere with the use made or to be made thereof by them; and except as disclosed in the Prospectus, the Company and its subsidiaries hold any leased real or personal property under valid and enforceable leases with no exceptions that would materially interfere with the use made or to be made thereof by them.

(xiii) The Company and its subsidiaries possess adequate certificates, authorities or permits issued by appropriate governmental agencies or bodies necessary to conduct the business now operated by them and have not received any notice of proceedings relating to the revocation or modification of any such certificate, authority or permit that, if determined adversely to the Company or any of its subsidiaries, would individually or in the aggregate have a material adverse effect on the condition (financial or other), business, properties or results of operations of the Company and its subsidiaries taken as a whole ("Material Adverse Effect").

(xiv) No labor dispute with the employees of the Company or any subsidiary exists or, to the knowledge of the Company, is imminent that might have a Material Adverse Effect.

(xv) The Company and its subsidiaries own, possess or can acquire on reasonable terms, adequate trademarks, trade names and other rights to inventions, know-how, patents, copyrights, confidential information and other intellectual property (collectively, "intellectual property rights") necessary to conduct the business now operated by them, or presently employed by them, and have not received any notice of infringement of or conflict with asserted rights of others with respect to any intellectual property rights that, if determined adversely to the Company or any of its subsidiaries, would individually or in the aggregate have a Material Adverse Effect.

(xvi) Except as disclosed in the Prospectus and as would not reasonably be expected to, individually or in the aggregate, have a Material Adverse Effect, (A) each of the Company and its subsidiaries is in compliance with, and not subject to liability under, Environmental Law (as defined below), (B) each of the Company and its subsidiaries has made all filings, and provided all financial assurances and notices, required under Environmental Law, and has, and is in compliance with, all permits required under Environmental Law and each of them is in full force and effect, (C) there is no civil, criminal or administrative action, suit, demand, claim, hearing, written notice of violation, proceeding, notice or demand letter or written request for information pending or, to

the knowledge of the Company, threatened, or, to the knowledge of the Company, investigation threatened or pending, against the Company or any of its subsidiaries under Environmental Law, (D) no lien, charge, encumbrance or restriction has been recorded under any Environmental Law with respect to any asset, facility or property owned, operated, leased or controlled by the Company or any of its subsidiaries, (E) neither the Company nor any of its subsidiaries has received notice that it has been identified as a potentially responsible party under the Comprehensive Environmental Response, Compensation and Liability Act of 1980, as amended ("CERCLA"), or any comparable Environmental Law, (F) no property or facility of the Company or any of its subsidiaries is (i) listed or proposed for listing on the National Priorities List promulgated pursuant to CERCLA, (ii) listed in the Comprehensive Environmental Response, Compensation and Liability Information System List promulgated pursuant to CERCLA, or (iii) listed on any comparable list of sites known or suspected to be contaminated with Hazardous Material (as defined below) as maintained by any governmental authority, (G) neither the Company nor any of its subsidiaries is conducting or financing an investigation, or response, corrective or other action pursuant to Environmental Law at any site or facility, nor is any of them subject to or party to any order, judgment, decree, contract or agreement which obligates it to conduct or finance any such action nor has any of them assumed by contract or agreement or otherwise any obligation or liability under Environmental Law, and (H) there are no past or present events, activities, operations, occurrences or conditions which could reasonably be expected to prevent or interfere with compliance by the Company or any of its subsidiaries with, or result in liability of any of them under, Environmental Law (including, without limitation, any capital or operating expenditures required for cleanup, closure or compliance with Environmental Law, any constraints on operating activities and any potential liability to third parties).

For purposes of this Agreement, "Environmental Law" means the common law and all applicable federal, provincial, state and local laws or regulations, codes, ordinances, orders, decrees, judgments or injunctions issued, promulgated, approved or entered thereunder, relating to pollution or protection of public or employee health and safety, the environment or natural resources, including, without limitation, those relating to (i) emissions, discharges, releases or threatened releases of Hazardous Material in or into the environment (including, without limitation, ambient air, surface water, groundwater, drinking water, land surface or subsurface strata, and natural resources such as wetlands, flora and fauna) or exposure thereto, (ii) the manufacture, processing, distribution, use, generation, treatment storage, disposal, transport, handling or recycling of Hazardous Material, (iii) zoning, facility siting, financial assurance, environmental impact assessment or review, reclamation or land use and (iv) underground or aboveground storage tanks and related piping, and emissions, discharges, releases or threatened releases therefrom. "Hazardous Material" means any substance, material, pollutant, contaminant, chemical, constituent or waste, in any form, including without limitation, petroleum and petroleum products, subject to regulation under or which could give rise to liability under Environmental Law.

(xvii) Except as disclosed in the Prospectus, there are no pending actions, suits or proceedings against or affecting the Company, any of its subsidiaries or any of their respective properties that, if determined adversely to the Company or any of its subsidiaries, would individually or in the aggregate have a Material Adverse Effect, or would materially and adversely affect the ability of the Company to perform its obligations under this Agreement, or which are otherwise material in the context of the sale of the Offered Securities; and no such actions, suits or proceedings are threatened or, to the Company's knowledge, contemplated.

(xviii) The financial statements included in each Registration Statement and the Prospectus present fairly the financial position of the Company and its consolidated subsidiaries as of the dates shown and their results of operations and cash flows for the periods shown and, except as

otherwise disclosed in the Prospectus, such financial statements have been prepared in conformity with the generally accepted accounting principles in the United States applied on a consistent basis and the schedules included in each Registration Statement present fairly the information required to be stated therein; and the assumptions used in preparing the pro forma financial statements included in each Registration Statement and the Prospectus provide a reasonable basis for presenting the significant effects directly attributable to the transactions or events described therein, the related pro forma adjustments give appropriate effect to those assumptions, and the pro forma columns therein reflect the proper application of those adjustments to the corresponding historical financial statement amounts.

(xix) Except as disclosed in the Prospectus, since the date of the latest audited financial statements included in the Prospectus there has been no material adverse change, nor any development or event involving a prospective material adverse change, in the condition (financial or other), business, properties or results of operations of the Company and its subsidiaries taken as a whole, and, except as disclosed in or contemplated by the Prospectus, there has been no dividend or distribution of any kind declared, paid or made by the Company on any class of its capital stock.

(xx) The Company is subject to the reporting requirements of either Section 13 or Section 15(d) of the Securities Exchange Act of 1934 and files reports with the Commission on the Electronic Data Gathering, Analysis, and Retrieval (▇▇▇▇▇) system.

(xxi) The Company is not and, after giving effect to the offering and sale of the Offered Securities and the application of the proceeds thereof as described in the Prospectus, will not be an "investment company" as defined in the Investment Company Act of 1940.

3. Purchase, Sale and Delivery of Offered Securities. On the basis of the representations, warranties and agreements herein contained, but subject to the terms and conditions herein set forth, the Company agrees to sell to each Underwriter, and each Underwriter agrees, severally and not jointly, to purchase from the Company, at a purchase price of $[ ] per share, the respective number of Firm Securities set forth opposite the name of such Underwriter in Schedule A hereto.

The Company will deliver the Firm Securities to the Representative for the accounts of the Underwriters, at the office of the Representative, against payment of the purchase price in Federal (same day) funds by official bank check or checks or wire transfer to an account at a bank acceptable to Credit Suisse First Boston LLC ("CSFB") drawn to the order of the Company at the office of ▇▇▇▇▇▇ ▇▇▇▇▇▇ & ▇▇▇▇▇▇▇ LLP, ▇▇ ▇▇▇▇ ▇▇▇▇▇▇, ▇▇▇ ▇▇▇▇, ▇▇▇ ▇▇▇▇ ▇▇▇▇▇, at [9:30] A.M., New York time, on [ ], 2005, or at such other time not later than seven full business days thereafter as CSFB and the Company determine, such time being herein referred to as the "First Closing Date". For purposes of Rule 15c6-1 under the Securities Exchange Act of 1934, the First Closing Date (if later than the otherwise applicable settlement date) shall be the settlement date for payment of funds and delivery of securities for all the Offered Securities sold pursuant to the offering. The certificates for the Firm Securities so to be delivered will be in definitive form, in such denominations and registered in such names as CSFB requests and will be made available for checking and packaging at the above office at least 24 hours prior to the First Closing Date.

In addition, upon written notice from CSFB given to the Company from time to time not more than 30 days subsequent to the date of the Prospectus, the Underwriters may purchase all or less than all of the Optional Securities at the purchase price per Security to be paid for the Firm Securities. The Company agrees to sell to the Underwriters the number of shares of Optional Securities specified in such notice and the Underwriters agree, severally and not jointly, to purchase such Optional Securities. Such Optional Securities shall be purchased for the account of each Underwriter in the same proportion as the number of Firm Securities set forth opposite such Underwriter's name bears to the total number of Firm Securities (subject to adjustment by CSFB to eliminate fractions) and may be

purchased by the Underwriters only for the purpose of covering over-allotments made in connection with the sale of the Firm Securities. No Optional Securities shall be sold or delivered unless the Firm Securities previously have been, or simultaneously are, sold and delivered. The right to purchase the Optional Securities or any portion thereof may be exercised from time to time and to the extent not previously exercised may be surrendered and terminated at any time upon notice by CSFB to the Company.

Each time for the delivery of and payment for the Optional Securities, being herein referred to as an "Optional Closing Date", which may be the First Closing Date (the First Closing Date and each Optional Closing Date, if any, being sometimes referred to as a "Closing Date"), shall be determined by CSFB but shall be not later than five full business days after written notice of election to purchase Optional Securities is given. The Company will deliver the Optional Securities being purchased on each Optional Closing Date to the Representative for the accounts of the several Underwriters against payment of the purchase price therefor in Federal (same day) funds by official bank check or checks or wire transfer to an account at a bank acceptable to CSFB drawn to the order of the Company, at the above office of ▇▇▇▇▇▇ ▇▇▇▇▇▇ & ▇▇▇▇▇▇▇ LLP. The certificates for the Optional Securities being purchased on each Optional Closing Date will be in definitive form, in such denominations and registered in such names as CSFB requests upon reasonable notice prior to such Optional Closing Date and will be made available for checking and packaging at the above office of ▇▇▇▇▇▇ ▇▇▇▇▇▇ & ▇▇▇▇▇▇▇ LLP at a reasonable time in advance of such Optional Closing Date.

4. Offering by Underwriters. It is understood that the several Underwriters propose to offer the Offered Securities for sale to the public as set forth in the Prospectus.

5. Certain Agreements of the Company. The Company agrees with the several Underwriters that:

(a) If the Effective Time of the Initial Registration Statement is prior to the execution and delivery of this Agreement, the Company will file the Prospectus with the Commission pursuant to and in accordance with subparagraph (1) (or, if applicable and if consented to by CSFB, subparagraph (4)) of Rule 424(b) not later than the earlier of (A) the second business day following the execution and delivery of this Agreement or (B) the fifteenth business day after the Effective Date of the Initial Registration Statement. The Company will advise CSFB promptly of any such filing pursuant to Rule 424(b). If the Effective Time of the Initial Registration Statement is prior to the execution and delivery of this Agreement and an additional registration statement is necessary to register a portion of the Offered Securities under the Act but the Effective Time thereof has not occurred as of such execution and delivery, the Company will file the additional registration statement or, if filed, will file a post-effective amendment thereto with the Commission pursuant to and in accordance with Rule 462(b) on or prior to 10:00 P.M., New York time, on the date of this Agreement or, if earlier, on or prior to the time the Prospectus is printed and distributed to any Underwriter, or will make such filing at such later date as shall have been consented to by CSFB.

(b) The Company will advise CSFB promptly of any proposal to amend or supplement the initial or any additional registration statement as filed or the related prospectus or the Initial Registration Statement, the Additional Registration Statement (if any) or the Prospectus and will not effect such amendment or supplementation without CSFB's consent; and the Company will also advise CSFB promptly of the effectiveness of each Registration Statement (if its Effective Time is subsequent to the execution and delivery of this Agreement) and of any amendment or supplementation of a Registration Statement or the Prospectus and of the institution by the Commission of any stop order proceedings in respect of a Registration Statement and will use its best efforts to prevent the issuance of any such stop order and to obtain as soon as possible its lifting, if issued.

(c) If, at any time when a prospectus relating to the Offered Securities is required to be delivered under the Act in connection with sales by any Underwriter or dealer, any event occurs as a result of which the Prospectus as then amended or supplemented would include an untrue statement of a material fact or omit to state any material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading, or if it is necessary at any time to amend the Prospectus to comply with the Act, the Company will promptly notify CSFB of such event and will promptly prepare and file with the Commission, at its own expense, an amendment or supplement which will correct such statement or omission or an amendment which will effect such compliance. Neither CSFB's consent to, nor the Underwriters' delivery of, any such amendment or supplement shall constitute a waiver of any of the conditions set forth in Section 6.

(d) As soon as practicable, but not later than the Availability Date (as defined below), the Company will make generally available to its securityholders an earnings statement covering a period of at least 12 months beginning after the Effective Date of the Initial Registration Statement (or, if later, the Effective Date of the Additional Registration Statement) which will satisfy the provisions of Section 11(a) of the Act. For the purpose of the preceding sentence, "Availability Date" means the 45th day after the end of the fourth fiscal quarter following the fiscal quarter that includes such Effective Date, except that, if such fourth fiscal quarter is the last quarter of the Company's fiscal year, "Availability Date" means the 90th day after the end of such fourth fiscal quarter.

(e) The Company will furnish to the Representative copies of each Registration Statement (two of which will be signed and will include all exhibits), each related preliminary prospectus, and, so long as a prospectus relating to the Offered Securities is required to be delivered under the Act in connection with sales by any Underwriter or dealer, the Prospectus and all amendments and supplements to such documents, in each case in such quantities as CSFB requests. The Prospectus shall be so furnished on or prior to 3:00 P.M., New York time, on the business day following the later of the execution and delivery of this Agreement or the Effective Time of the Initial Registration Statement. All other such documents shall be so furnished as soon as available. The Company will pay the expenses of printing and distributing to the Underwriters all such documents.

(f) The Company will arrange for the qualification of the Offered Securities for sale under the laws of such jurisdictions as CSFB designates and will continue such qualifications in effect so long as required for the distribution.

(g) For the period specified below (the "Lock-Up Period"), the Company will not offer, sell, contract to sell, pledge or otherwise dispose of, directly or indirectly, or file with the Commission a registration statement under the Act relating to, any additional shares of its Securities or securities convertible into or exchangeable or exercisable for any shares of its Securities, or publicly disclose the intention to make any such offer, sale, pledge, disposition or filing, without the prior written consent of CSFB, except issuances pursuant to the exercise of warrants outstanding on the date hereof or conversion of shares of the Company's Series B convertible preferred stock outstanding on the date hereof, or pursuant to the terms of the Company's employee benefit plans and employee stock purchase plan as in effect on the date hereof. The initial Lock-Up Period will commence on the date hereof and will continue and include the date 90 days after the date hereof or such earlier date that CSFB consents to in writing; provided, however, that if (1) during the last 17 days of the initial Lock-Up Period, the Company releases earnings results or material news or a material event relating to the Company occurs or (2) prior to the expiration of the initial Lock-Up period, the Company announces that it will release earnings results during the 16-day period beginning on the last day of the initial Lock-Up Period, then in each case the Lock-Up Period will be extended until the expiration of the 18-day period beginning on the date of release of the

earnings results or the occurrence of the material news or material event, as applicable, unless CSFB waives, in writing, such extension. The Company will provide CSFB with notice of any announcement described in clause (2) of the preceding sentence that gives rise to an extension of the Lock-up Period.

(h) The Company will pay all expenses incident to the performance of its obligations under this Agreement, for any filing fees and other expenses (including fees and disbursements of counsel) in connection with qualification of the Offered Securities for sale under the laws of such jurisdictions as CSFB designates and the printing of memoranda relating thereto, for the filing fee incident to the review by the National Association of Securities Dealers, Inc. of the Offered Securities, for any travel expenses of the Company's officers and employees and any other expenses of the Company in connection with attending or hosting meetings with prospective purchasers of the Offered Securities, including the cost of any aircraft chartered in connection with attending or hosting such meetings, and for expenses incurred in distributing preliminary prospectuses and the Prospectus (including any amendments and supplements thereto) to the Underwriters.

6. Conditions of the Obligations of the Underwriters. The obligations of the several Underwriters to purchase and pay for the Firm Securities on the First Closing Date and the Optional Securities to be purchased on each Optional Closing Date will be subject to the accuracy of the representations and warranties on the part of the Company herein, to the accuracy of the statements of Company officers made pursuant to the provisions hereof, to the performance by the Company of its obligations hereunder and to the following additional conditions precedent:

(a) The Representative shall have received a letter, dated the date of delivery thereof (which, if the Effective Time of the Initial Registration Statement is prior to the execution and delivery of this Agreement, shall be on or prior to the date of this Agreement or, if the Effective Time of the Initial Registration Statement is subsequent to the execution and delivery of this Agreement, shall be prior to the filing of the amendment or post-effective amendment to the registration statement to be filed shortly prior to such Effective Time), of each of PricewaterhouseCoopers LLP and Deloitte & Touche LLP confirming that they are each independent public accountants within the meaning of the Act and stating such other matters in form and substance satisfactory to the Representative concerning certain financial information with respect to the Company set forth and incorporated by reference in the Registration Statement.

(b) If the Effective Time of the Initial Registration Statement is not prior to the execution and delivery of this Agreement, such Effective Time shall have occurred not later than 10:00 P.M., New York time, on the date of this Agreement or such later date as shall have been consented to by CSFB. If the Effective Time of the Additional Registration Statement (if any) is not prior to the execution and delivery of this Agreement, such Effective Time shall have occurred not later than 10:00 P.M., New York time, on the date of this Agreement or, if earlier, the time the Prospectus is printed and distributed to any Underwriter, or shall have occurred at such later date as shall have been consented to by CSFB. If the Effective Time of the Initial Registration Statement is prior to the execution and delivery of this Agreement, the Prospectus shall have been filed with the Commission in accordance with the Rules and Regulations and Section 5(a) of this Agreement. Prior to such Closing Date, no stop order suspending the effectiveness of a Registration Statement shall have been issued and no proceedings for that purpose shall have been instituted or, to the knowledge of the Company or the Representative, shall be contemplated by the Commission.

(c) Subsequent to the execution and delivery of this Agreement, there shall not have occurred (i) any change, or any development or event involving a prospective change, in the condition (financial or other), business, properties or results of operations of the Company and its

subsidiaries taken as one enterprise which, in the judgment of a majority in interest of the Underwriters including the Representative, is material and adverse and makes it impractical or inadvisable to proceed with completion of the public offering or the sale of and payment for the Offered Securities; (ii) any downgrading in the rating of any debt securities or preferred stock of the Company by any "nationally recognized statistical rating organization" (as defined for purposes of Rule 436(g) under the Act), or any public announcement that any such organization has under surveillance or review its rating of any debt securities or preferred stock of the Company (other than an announcement with positive implications of a possible upgrading, and no implication of a possible downgrading, of such rating); (iii) any change in U.S. or international financial, political or economic conditions or currency exchange rates or exchange controls as would, in the judgment of a majority in interest of the Underwriters including the Representative, be likely to prejudice materially the success of the proposed issue, sale or distribution of the Offered Securities, whether in the primary market or in respect of dealings in the secondary market; (iv) any material suspension or material limitation of trading in securities generally on the New York Stock Exchange, or any setting of minimum prices for trading on such exchange; (v) any suspension of trading of any securities of the Company on any exchange or in the over-the-counter market; (vi) any banking moratorium declared by U.S. Federal or New York authorities; (vii) any major disruption of settlements of securities or clearance services in the United States; or (viii) any attack on, outbreak or escalation of hostilities or act of terrorism involving the United States, any declaration of war by Congress or any other national or international calamity or emergency if, in the judgment of a majority in interest of the Underwriters including the Representative, the effect of any such attack, outbreak, escalation, act, declaration, calamity or emergency makes it impractical or inadvisable to proceed with completion of the public offering or the sale of and payment for the Offered Securities.

(d) The Representative shall have received an opinion, dated such Closing Date, of ▇▇▇▇▇, ▇▇▇▇ & ▇'▇▇▇▇▇▇▇▇, P.C., counsel for the Company, to the effect that:

(i): The Company has been duly incorporated and is an existing corporation in good standing under the laws of the Commonwealth of Massachusetts, with corporate power and authority to own its properties and conduct its business as described in the Prospectus; and the Company is duly qualified to do business as a foreign corporation in good standing in all other jurisdictions in which its ownership or lease of property or the conduct of its business requires such qualification, except where failure to be so qualified or to be in good standing would not individually or in the aggregate have a material adverse effect on the condition (financial or other), business, properties or results of operations of the Company and its subsidiaries taken as a whole;
(ii): Each subsidiary of the Company has been duly incorporated and is an existing corporation in good standing under the laws of the jurisdiction of its incorporation, with power and authority (corporate and other) to own its properties and conduct its business as described in the Prospectus; and each subsidiary of the Company is duly qualified to do business as a foreign corporation in good standing in all other jurisdictions in which its ownership or lease of property or the conduct of its business requires such qualification, except where failure to be so qualified or to be in good standing would not individually or in the aggregate have a material adverse effect on the condition (financial or other), business, properties or results of operations of the Company and its subsidiaries taken as a whole; all of the issued and outstanding capital stock of each subsidiary of the Company has been duly authorized and validly issued and is fully paid and nonassessable; and the capital stock of each subsidiary owned by the Company, directly or through subsidiaries, is owned free from liens, encumbrances and defects,

except for liens permitted under the Credit Facility and the indenture governing the Existing Notes.

(iii): The Offered Securities delivered on such Closing Date and all other outstanding shares of the Common Stock of the Company have been duly authorized and validly issued, are fully paid and nonassessable and conform to the description thereof contained in the Prospectus; and the stockholders of the Company have no preemptive rights with respect to the Securities;
(iv): To their knowledge, except for the Investors Rights Agreement, there are no contracts, agreements or understandings known to such counsel between the Company and any person granting such person the right to require the Company to file a registration statement under the Act with respect to any securities of the Company owned or to be owned by such person or to require the Company to include such securities in the securities registered pursuant to the Registration Statement or in any securities being registered pursuant to any other registration statement filed by the Company under the Act;
(v): No consent, approval, authorization or order of, or filing with, any governmental agency or body or any court is required to be obtained or made by the Company for the consummation of the transactions contemplated by this Agreement in connection with the sale of the Offered Securities, except such as have been obtained and made under the Act and such as may be required under state securities laws;
(vi): The execution, delivery and performance of this Agreement and the consummation of the transactions herein contemplated will not result in a breach or violation of any of the terms and provisions of, or constitute a default under, any statute, any rule, regulation or order of any governmental agency or body or any court having jurisdiction over the Company or any subsidiary of the Company or any of their properties, or any agreement or instrument to which the Company or any such subsidiary is a party or by which the Company or any such subsidiary is bound or to which any of the properties of the Company or any such subsidiary is subject, or the charter or by-laws of the Company or any such subsidiary, and the Company has full power and authority to authorize, issue and sell the Offered Securities as contemplated by this Agreement;
(vii): The Initial Registration Statement was declared effective under the Act as of the date and time specified in such opinion, the Additional Registration Statement (if any) was filed and became effective under the Act as of the date and time (if determinable) specified in such opinion, the Prospectus either was filed with the Commission pursuant to the subparagraph of Rule 424(b) specified in such opinion on the date specified therein or was included in the Initial Registration Statement or the Additional Registration Statement (as the case may be), and, to the best of the knowledge of such counsel, no stop order suspending the effectiveness of a Registration Statement or any part thereof has been issued and no proceedings for that purpose have been instituted or are pending or contemplated under the Act, and each Registration Statement and the Prospectus, and each amendment or supplement thereto, as of their respective effective or issue dates, complied as to form in all material respects with the requirements of the Act and the Rules and Regulations; such counsel have no reason to believe that any part of a Registration Statement or any amendment thereto, as of its effective date or as of such Closing Date, contained any untrue statement of a material fact or omitted to state any material fact required to be stated therein or necessary to make the statements therein not misleading; or that the Prospectus or any amendment or supplement thereto, as of its issue date or as of such Closing Date, contained any untrue statement of a

material fact or omitted to state any material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading; the descriptions in the Registration Statements and Prospectus of statutes, legal and governmental proceedings and contracts and other documents are accurate and fairly present the information required to be shown; and such counsel do not know of any legal or governmental proceedings required to be described in a Registration Statement or the Prospectus which are not described as required or of any contracts or documents of a character required to be described in a Registration Statement or the Prospectus or to be filed as exhibits to a Registration Statement which are not described and filed as required; it being understood that such counsel need express no opinion as to the financial statements or other financial data contained in the Registration Statements or the Prospectus; and

(viii): This Agreement has been duly authorized, executed and delivered by the Company.

(e) The Representative shall have received from ▇▇▇▇▇▇ ▇▇▇▇▇▇ & ▇▇▇▇▇▇▇ LLP, counsel for the Underwriters, such opinion or opinions, dated such Closing Date, with respect to the Registration Statements, the Prospectus and other related matters as the Representative may require, and the Company shall have furnished to such counsel such documents as they request for the purpose of enabling them to pass upon such matters.

(f) The Representative shall have received a certificate, dated such Closing Date, of the President or any Vice President and a principal financial or accounting officer of the Company in which such officers, to the best of their knowledge after reasonable investigation, shall state that: the representations and warranties of the Company in this Agreement are true and correct; the Company has complied with all agreements and satisfied all conditions on its part to be performed or satisfied hereunder at or prior to such Closing Date; no stop order suspending the effectiveness of any Registration Statement has been issued and no proceedings for that purpose have been instituted or are contemplated by the Commission; the Additional Registration Statement (if any) satisfying the requirements of subparagraphs (1) and (3) of Rule 462(b) was filed pursuant to Rule 462(b), including payment of the applicable filing fee in accordance with Rule 111(a) or (b) under the Act, prior to the time the Prospectus was printed and distributed to any Underwriter; and, subsequent to the respective dates of the most recent financial statements in the Prospectus, there has been no material adverse change, nor any development or event involving a prospective material adverse change, in the condition (financial or other), business, properties or results of operations of the Company and its subsidiaries taken as a whole except as set forth in the Prospectus or as described in such certificate.

(g) The Representative shall have received a letter from each of PricewaterhouseCoopers LLP and Deloitte & Touche LLP, dated such Closing Date, both of which meet the requirements of subsection (a) of this Section, except that the specified date referred to in such subsection will be a date not more than three days prior to such Closing Date for the purposes of this subsection.

(h) On or prior to the date of this Agreement, the Representative shall have received lockup letters from each of executive officers and directors of the Company.

(i) The amendment and restatement of the Credit Facility described under "Description of Certain Indebtedness" in the Prospectus shall have become effective on terms and conditions satisfactory to the Representative.

(j) The Company shall have delivered an irrevocable notice of redemption to the trustee under the indenture governing the Existing Notes, pursuant to which the Company shall redeem Existing Notes in an aggregate principal amount equal to the lesser of (x) $52.5 million and (y) the net cash proceeds received by the Company from the offering contemplated by this Agreement.

The Company will furnish the Representative with such conformed copies of such opinions, certificates, letters and documents as the Representative reasonably requests. CSFB may in its sole discretion waive on behalf of the Underwriters compliance with any conditions to the obligations of the Underwriters hereunder, whether in respect of an Optional Closing Date or otherwise.

7. Indemnification and Contribution. (a) The Company will indemnify and hold harmless each Underwriter, its partners, members, directors, officers, affiliates and each person, if any who controls such Underwriter within the meaning of Section 15 of the Act, against any losses, claims, damages or liabilities, joint or several, to which such Underwriter may become subject, under the Act or otherwise, insofar as such losses, claims, damages or liabilities (or actions in respect thereof) arise out of or are based upon any untrue statement or alleged untrue statement of any material fact contained in any Registration Statement, the Prospectus, or any amendment or supplement thereto, or any related preliminary prospectus, or arise out of or are based upon the omission or alleged omission to state therein a material fact required to be stated therein or necessary to make the statements therein not misleading, and will reimburse each Underwriter for any legal or other expenses reasonably incurred by such Underwriter in connection with investigating or defending any such loss, claim, damage, liability or action as such expenses are incurred; provided, however, that the Company will not be liable in any such case to the extent that any such loss, claim, damage or liability arises out of or is based upon an untrue statement or alleged untrue statement in or omission or alleged omission from any of such documents in reliance upon and in conformity with written information furnished to the Company by any Underwriter through the Representative specifically for use therein, it being understood and agreed that the only such information furnished by any Underwriter consists of the information described as such in subsection (b) below.

(b) Each Underwriter will severally and not jointly indemnify and hold harmless the Company, its directors and officers and each person, if any, who controls the Company within the meaning of Section 15 of the Act, against any losses, claims, damages or liabilities to which the Company may become subject, under the Act or otherwise, insofar as such losses, claims, damages or liabilities (or actions in respect thereof) arise out of or are based upon any untrue statement or alleged untrue statement of any material fact contained in any Registration Statement, the Prospectus, or any amendment or supplement thereto, or any related preliminary prospectus, or arise out of or are based upon the omission or the alleged omission to state therein a material fact required to be stated therein or necessary to make the statements therein not misleading, in each case to the extent, but only to the extent, that such untrue statement or alleged untrue statement or omission or alleged omission was made in reliance upon and in conformity with written information furnished to the Company by such Underwriter through the Representative specifically for use therein, and will reimburse any legal or other expenses reasonably incurred by the Company in connection with investigating or defending any such loss, claim, damage, liability or action as such expenses are incurred, it being understood and agreed that the only such information furnished by any Underwriter consists of the following information in the Prospectus furnished on behalf of each Underwriter: the concession and reallowance figures appearing in the fourth paragraph under the caption "Underwriting" and the information contained in the tenth and twelfth paragraphs under the caption "Underwriting".

(c) Promptly after receipt by an indemnified party under this Section of notice of the commencement of any action, such indemnified party will, if a claim in respect thereof is to be made against an indemnifying party under subsection (a) or (b) above, notify the indemnifying party of the commencement thereof; but the failure to notify the indemnifying party shall not relieve it from any liability that it may have under subsection (a) or (b) above except to the extent that it has been materially prejudiced (through the forfeiture of substantive rights or defenses) by such failure; and provided further that the failure to notify the indemnifying party shall not relieve it from any liability that it may have to an indemnified party otherwise than under subsection (a) or (b) above. In case any such action is brought against any indemnified party and it notifies an indemnifying party of the

commencement thereof, the indemnifying party will be entitled to participate therein and, to the extent that it may wish, jointly with any other indemnifying party similarly notified, to assume the defense thereof, with counsel satisfactory to such indemnified party (who shall not, except with the consent of the indemnified party, be counsel to the indemnifying party), and after notice from the indemnifying party to such indemnified party of its election so to assume the defense thereof, the indemnifying party will not be liable to such indemnified party under this Section for any legal or other expenses subsequently incurred by such indemnified party in connection with the defense thereof other than reasonable costs of investigation. No indemnifying party shall, without the prior written consent of the indemnified party, effect any settlement of any pending or threatened action in respect of which any indemnified party is or could have been a party and indemnity could have been sought hereunder by such indemnified party unless such (i) settlement includes an unconditional release of such indemnified party from all liability on any claims that are the subject matter of such action and (ii) does not include a statement as to, or an admission of, fault, culpability or a failure to act by or on behalf of an indemnified party.

(d) If the indemnification provided for in this Section is unavailable or insufficient to hold harmless an indemnified party under subsection (a) or (b) above, then each indemnifying party shall contribute to the amount paid or payable by such indemnified party as a result of the losses, claims, damages or liabilities referred to in subsection (a) or (b) above (i) in such proportion as is appropriate to reflect the relative benefits received by the Company on the one hand and the Underwriters on the other from the offering of the Securities or (ii) if the allocation provided by clause (i) above is not permitted by applicable law, in such proportion as is appropriate to reflect not only the relative benefits referred to in clause (i) above but also the relative fault of the Company on the one hand and the Underwriters on the other in connection with the statements or omissions which resulted in such losses, claims, damages or liabilities as well as any other relevant equitable considerations. The relative benefits received by the Company on the one hand and the Underwriters on the other shall be deemed to be in the same proportion as the total net proceeds from the offering (before deducting expenses) received by the Company bear to the total underwriting discounts and commissions received by the Underwriters. The relative fault shall be determined by reference to, among other things, whether the untrue or alleged untrue statement of a material fact or the omission or alleged omission to state a material fact relates to information supplied by the Company or the Underwriters and the parties' relative intent, knowledge, access to information and opportunity to correct or prevent such untrue statement or omission. The amount paid by an indemnified party as a result of the losses, claims, damages or liabilities referred to in the first sentence of this subsection (d) shall be deemed to include any legal or other expenses reasonably incurred by such indemnified party in connection with investigating or defending any action or claim which is the subject of this subsection (d). Notwithstanding the provisions of this subsection (d), no Underwriter shall be required to contribute any amount in excess of the amount by which the total price at which the Securities underwritten by it and distributed to the public were offered to the public exceeds the amount of any damages which such Underwriter has otherwise been required to pay by reason of such untrue or alleged untrue statement or omission or alleged omission. No person guilty of fraudulent misrepresentation (within the meaning of Section 11(f) of the Act) shall be entitled to contribution from any person who was not guilty of such fraudulent misrepresentation. The Underwriters' obligations in this subsection (d) to contribute are several in proportion to their respective underwriting obligations and not joint.

(e) The obligations of the Company under this Section shall be in addition to any liability which the Company may otherwise have and shall extend, upon the same terms and conditions, to each person, if any, who controls any Underwriter within the meaning of the Act; and the obligations of the Underwriters under this Section shall be in addition to any liability which the respective Underwriters may otherwise have and shall extend, upon the same terms and conditions, to each director of the Company, to each officer of the Company who has signed a Registration Statement and to each person, if any, who controls the Company within the meaning of the Act.

8. Default of Underwriters. If any Underwriter or Underwriters default in their obligations to purchase Offered Securities hereunder on either the First or any Optional Closing Date and the aggregate number of shares of Offered Securities that such defaulting Underwriter or Underwriters agreed but failed to purchase does not exceed 10% of the total number of shares of Offered Securities that the Underwriters are obligated to purchase on such Closing Date, CSFB may make arrangements satisfactory to the Company for the purchase of such Offered Securities by other persons, including any of the Underwriters, but if no such arrangements are made by such Closing Date, the non-defaulting Underwriters shall be obligated severally, in proportion to their respective commitments hereunder, to purchase the Offered Securities that such defaulting Underwriters agreed but failed to purchase on such Closing Date. If any Underwriter or Underwriters so default and the aggregate number of shares of Offered Securities with respect to which such default or defaults occur exceeds 10% of the total number of shares of Offered Securities that the Underwriters are obligated to purchase on such Closing Date and arrangements satisfactory to CSFB and the Company for the purchase of such Offered Securities by other persons are not made within 36 hours after such default, this Agreement will terminate without liability on the part of any non-defaulting Underwriter or the Company, except as provided in Section 9 (provided that if such default occurs with respect to Optional Securities after the First Closing Date, this Agreement will not terminate as to the Firm Securities or any Optional Securities purchased prior to such termination). As used in this Agreement, the term "Underwriter" includes any person substituted for an Underwriter under this Section. Nothing herein will relieve a defaulting Underwriter from liability for its default.

9. Survival of Certain Representations and Obligations. The respective indemnities, agreements, representations, warranties and other statements of the Company or its officers and of the several Underwriters set forth in or made pursuant to this Agreement will remain in full force and effect, regardless of any investigation, or statement as to the results thereof, made by or on behalf of any Underwriter, the Company or any of their respective representatives, officers or directors or any controlling person, and will survive delivery of and payment for the Offered Securities. If this Agreement is terminated pursuant to Section 8 or if for any reason the purchase of the Offered Securities by the Underwriters is not consummated, the Company shall remain responsible for the expenses to be paid or reimbursed by them pursuant to Section 5 and the respective obligations of the Company and the Underwriters pursuant to Section 7 shall remain in effect, and if any Offered Securities have been purchased hereunder the representations and warranties in Section 2 and all obligations under Section 5 shall also remain in effect. If the purchase of the Offered Securities by the Underwriters is not consummated for any reason other than solely because of the termination of this Agreement pursuant to Section 8 or the occurrence of any event specified in clause (iii), (iv), (vi), (vii) or (viii) of Section 6(c), the Company will reimburse the Underwriters for all out-of-pocket expenses (including fees and disbursements of counsel) reasonably incurred by them in connection with the offering of the Offered Securities.

10. Notices. All communications hereunder will be in writing and, if sent to the Underwriters, will be mailed, delivered or telegraphed and confirmed to the Representative, Eleven Madison Avenue, New York, N.Y. 10010-3629, Attention: Transactions Advisory Group, or, if sent to the Company, will be mailed, delivered or telegraphed and confirmed to it at Clean Harbors, Inc., ▇▇▇▇ ▇▇▇▇▇▇▇▇▇▇ ▇▇., ▇▇▇▇▇▇▇▇▇, ▇▇ ▇▇▇▇▇-▇▇▇▇, Attention: Chief Financial Officer; provided, however, that any notice to an Underwriter pursuant to Section 7 will be mailed, delivered or telegraphed and confirmed to such Underwriter.

11. Successors. This Agreement will inure to the benefit of and be binding upon the parties hereto and their respective successors and the officers and directors and controlling persons referred to in Section 7, and no other person will have any right or obligation hereunder.

12. Representation. The Representative will act for the several Underwriters in connection with the transactions contemplated by this Agreement, and any action under this Agreement taken by the Representative will be binding upon all the Underwriters.

13. Counterparts. This Agreement may be executed in any number of counterparts, each of which shall be deemed to be an original, but all such counterparts shall together constitute one and the same Agreement.

14. Absence of Fiduciary Relationship. The Company acknowledges and agrees that:

(a): the Representative has been retained solely to act as underwriter in connection with the sale of the Offered Securities and that no fiduciary, advisory or agency relationship between the Company, on the one hand, and the Representative, on the other, has been created in respect of any of the transactions contemplated by this Agreement, irrespective of whether the Representative has advised or is advising the Company on other matters;
(b): the price of the Offered Securities set forth in this Agreement was established by Company following discussions and arm's-length negotiations with the Representative and the Company are capable of evaluating and understanding and understand and accept the terms, risks and conditions of the transactions contemplated by this Agreement;
(c): it has been advised that the Representative and its affiliates are engaged in a broad range of transactions which may involve interests that differ from those of the Company and that the Representative has no obligation to disclose such interests and transactions to the Company by virtue of any fiduciary, advisory or agency relationship; and
(d): it waives, to the fullest extent permitted by law, any claims it may have against the Representative for breach of fiduciary duty or alleged breach of fiduciary duty and agrees that the Representative shall have no liability (whether direct or indirect) to the Company in respect of such a fiduciary duty claim or to any person asserting a fiduciary duty claim on behalf of or in right of the Company, including stockholders, employees or creditors of the Company.

14. Applicable Law. This Agreement shall be governed by, and construed in accordance with, the laws of the State of New York, without regard to principles of conflicts of laws.

The Company hereby submits to the non-exclusive jurisdiction of the Federal and state courts in the Borough of Manhattan in The City of New York in any suit or proceeding arising out of or relating to this Agreement or the transactions contemplated hereby.

If the foregoing is in accordance with the Representative's understanding of our agreement, kindly sign and return to the Company one of the counterparts hereof, whereupon it will become a binding agreement among the Company and the several Underwriters in accordance with its terms.

		Very truly yours,
		CLEAN HARBORS, INC.
		By
				Name: Title:

The foregoing Underwriting Agreement is hereby confirmed and accepted as of the date first above written.

CREDIT SUISSE FIRST BOSTON LLC
By
		Name: Title:

Acting on behalf of itself and as the
Representative of the several Underwriters.

SCHEDULE A

Underwriter		Number of Firm Securities to be Purchased
Credit Suisse First Boston LLC
▇▇▇▇▇▇▇ & Company, LLC
Wedbush ▇▇▇▇▇▇ Securities Inc.
CJS Securities, Inc.

Total		2,000,000

QuickLinks

Exhibit 1.1

SCHEDULE A

2,000,000 Shares CLEAN HARBORS, INC. Common Stock UNDERWRITING AGREEMENT

Document Metadata

Document Metadata

Table of Contents