CLEAN HARBORS INC

During the quarter ended September 30, 2026, no director or “officer” (as defined in Rule 16a-1(f)) of Clean Harbors, Inc. adopted, modified orterminated a “Rule 10b5-1 trading arrangement” or “non-Rule 10b5-1 trading arrangement,” as each term is defined in Item 408(a) of Regulation S-K.

Disclosure in Lieu of Current Report on Form 8-K

We are providing the following disclosure in lieu of filing a Current Report on Form 8-K relating to Item 5.02 - Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers:

On October 28, 2026, the Company announced that Eric W. Gerstenberg, currently Co-Chief Executive Officer and Co-President of the Company, will serve as sole Chief Executive Officer and President (and, as a result, as the sole “principal executive officer” of the Company), effective as of January 1, 2027. Mr. Gerstenberg’s biographical information is set forth in the Company’s Definitive Proxy Statement filed with the Securities and Exchange Commission on April 10, 2026, and such information is incorporated herein by reference. In connection with the transition, and as of January 1, 2027, Mr. Gerstenberg will receive an annual base salary of $1,200,000, a target annual incentive cash opportunity equal to 150% of his annual base salary, and an annual long-term incentive with a target value of $8,000,000 (consisting of 60% performance-based restricted stock and 40% time-based restricted stock). In addition, upon the start date in his new role, Mr. Gerstenberg will receive a one-time restricted stock award with a target value of $5,000,000. Such restricted stock award will cliff vest on the fifth anniversary of the grant date, subject to Mr. Gerstenberg’s continued employment with the Company through such date, and will include a relative total shareholder return performance modifier. There are no other arrangements or understandings between Mr. Gerstenberg and any other person pursuant to which Mr. Gerstenberg was named as sole Chief Executive Officer and President of the Company. Mr. Gerstenberg is not a party to any transaction that would require disclosure under Item 404(a) of Regulation S-K.

Michael L. Battles, currently Co-Chief Executive Officer and Co-President of the Company, will transition from such roles, effective as of December 31, 2026. In connection with the transition, on October 26, 2026, Mr. Battles entered into a Retirement and Transition Agreement with the Company (the “Retirement Agreement”), which constituted notice of his retirement in accordance with the Company’s retirement policy, with a retirement date of December 31, 2027. During 2027, Mr. Battles will serve as a part-time employee of the Company in a Senior Advisor role reporting to the Company’s Board of Directors (the “Board”) and providing strategic advice and transition assistance as requested and, in such capacity, he will receive an annual base salary of $200,000. Mr. Battles will remain eligible to receive an annual bonus under the Company’s Management Incentive Plan (the “MIP”) for the 2026 plan year consistent with other senior executives of the Company and, while he remains an employee of the Company, his existing restricted stock awards will be eligible for continued vesting in accordance with their terms. Mr. Battles will not be eligible to participate in the MIP for the 2027 plan year or receive an annual equity award during 2027. In accordance with the terms of the Company’s retirement policy, if Mr. Battles satisfies the conditions set forth in the Retirement Agreement, he will be entitled to the accelerated vesting of 75% of any unvested time-based restricted stock awards and earned but unvested performance-based restricted stock awards outstanding as of his retirement date. All other restricted stock awards held by Mr. Battles that remain unvested as of his retirement date will be forfeited. The Retirement Agreement also contains a reaffirmation of Mr. Battles’ confidentiality obligations to the Company and other restrictive covenants, as well as a general release of claims by Mr. Battles. The foregoing description of the Retirement Agreement is qualified in its entirety by reference to the full text of the Retirement Agreement, a copy of which will be filed as an exhibit to the Company’s Annual Report on Form 10-K for the year ended December 31, 2026.

In addition, on October 26, 2026, Mr. Battles resigned from the Board, effective as of December 31, 2026.