CLH: Leadership change · Company disclosure

Item 5.02 Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers. On May 19, 2026, Alan S. McKim, serving in the capacities of Executive Chairman of the Board of Directors (the “Board”) and Chief Technology Officer, notified the Board of his intention to retire from the Board and his role as Chief Technology Officer, effective upon the Board’s appointment of a new Chairman. The appointment of an independent Chairman is anticipated to occur in the summer of 2026, as part of a planned leadership transition. Mr. McKim’s decision to retire from the Board and his role as Chief Technology Officer does not arise from, nor is it attributable to, any disagreement with the Company with respect to any matter pertaining to the Company's operations, policies, practices, or otherwise. Item 7.01 Regulation FD Disclosure. On May 20, 2026, the Company issued a press release announcing Mr. McKim’s retirement. A copy of the press release is furnished as Exhibit 99.1 hereto. Item 9.01 Financial Statements and Exhibits. (d) Exhibits Exhibit Number Description 99.1 Press Release dated May 20, 2026 (furnished herewith) 104 The cover page to this Current Report on Form 8-K, formatted in iXBRL (Inline eXtensible Business Reporting Language) 1 SIGNATURES Pursuant to the requirements of the Securities and Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized. Clean Harbors, Inc. (Registrant) May 20, 2026 /s/ Eric J. Dugas Executive Vice President and Chief Financial Officer 2