Results of Operations and Financial Condition On July 29, 2026, Clean Harbors, Inc. (the “Company”) issued a press release announcing the Company’s results of operations for the second quarter ended June 30, 2026. A copy of that press release is furnished with this report as Exhibit 99.1.

Executive Chairman of the Board and Chief Technology Officer — Alan S. McKim: Mr. McKim is retiring from the Board and his role as Chief Technology Officer, with a planned leadership transition.

Other Events. On May 14, 2026, Clean Harbors, Inc. issued a press release announcing the completion of its acquisition of Terra Nova Solutions. A copy of the press release is furnished as Exhibit 99.1 to this Current Report on Form 8-K and is incorporated herein by reference.

Results of Operations and Financial Condition On May 6, 2026, Clean Harbors, Inc. (the “Company”) issued a press release announcing the Company’s results of operations for the first quarter ended March 31, 2026. A copy of that press release is furnished with this report as Exhibit 99.1.

Results of Operations and Financial Condition On February 18, 2026, Clean Harbors, Inc. (the “Company”) issued a press release announcing the Company’s results of operations for the fourth quarter and year ended December 31, 2025. A copy of that press release is furnished with this report as Exhibit 99.1.

Results of Operations and Financial Condition On October 29, 2025, Clean Harbors, Inc. (the “Company”) issued a press release announcing the Company’s results of operations for the third quarter ended September 30, 2025. A copy of that press release is furnished with this report as Exhibit 99.1.

Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant. The information set forth under

Entry into a Material Definitive Agreement. Issuance of 5.750% Senior Notes due 2033 On October 9, 2025, Clean Harbors, Inc. (the “Company”), issued $745.0 million aggregate principal amount of 5.750% senior notes due 2033 (the “Notes”). The Company used a portion of the net proceeds from the offering of Notes and $1,260.0 million in borrowings under the Amended Credit Agreement (defined below) to refinance all of the approximately $1,457.3 million aggregate principal amount of secured senior…

Other Events. On September 25, 2025, Clean Harbors, Inc. (the “Company”) issued a press release announcing that it had commenced a private offering of senior notes due 2033 to persons reasonably believed to be “qualified institutional buyers” in the United States, as defined in Rule 144A under the Securities Act of 1933, as amended (the “Securities Act”), and to certain non-U.S. persons outside the United States in offshore transactions pursuant to Regulation S under the Securities Act. On Se…

Results of Operations and Financial Condition On July 30, 2025, Clean Harbors, Inc. (the “Company”) issued a press release announcing the Company’s results of operations for the second quarter ended June 30, 2025. A copy of that press release is furnished with this report as Exhibit 99.1.

Results of Operations and Financial Condition On April 30, 2025, Clean Harbors, Inc. (the “Company”) issued a press release announcing the Company’s results of operations for the first quarter ended March 31, 2025. A copy of that press release is furnished with this report as Exhibit 99.1.

Results of Operations and Financial Condition On February 19, 2025, Clean Harbors, Inc. (the “Company”) issued a press release announcing the Company’s results of operations for the fourth quarter and year ended December 31, 2024. A copy of that press release is furnished with this report as Exhibit 99.1.

Results of Operations and Financial Condition On October 30, 2024, Clean Harbors, Inc. (the “Company”) issued a press release announcing the Company’s results of operations for the third quarter ended September 30, 2024. A copy of that press release is furnished with this report as Exhibit 99.1.

Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant. The discussion of the Sixth Amendment set forth under

Entry into a Material Definitive Agreement. On October 8, 2024, Clean Harbors, Inc. (the “Company”) entered into Amendment No. 6 (the “Sixth Amendment”) to the Credit Agreement, dated as of June 30, 2017, among the Company, the subsidiaries of the Company identified therein and Goldman Sachs Lending Partners LLC, as administrative agent and collateral agent, and the lenders party thereto (such Credit Agreement, as previously amended and further amended by the Sixth Amendment, the “Credit Agre…

Director — Michael Battles and Eric Gerstenberg: The filing discloses the election of existing Co-CEOs to the Board of Directors, which is a routine governance action and not a departure of an executive.

Results of Operations and Financial Condition On July 31, 2024, Clean Harbors, Inc. (the “Company”) issued a press release announcing the Company’s results of operations for the second quarter ended June 30, 2024. A copy of that press release is furnished with this report as Exhibit 99.1.

Entry into a Material Definitive Agreement. On June 28, 2024, Clean Harbors, Inc. (the “Company”) and one of the Company’s Canadian subsidiaries (the “Canadian Borrower”) entered into a seventh amended and restated credit agreement ( the “Amended Credit Agreement”) with Bank of America, N.A. (“BofA”), as administrative agent (the “Agent”), and the lenders party to the Amended Credit Agreement. The Amended Credit Agreement amends and restates the sixth amended and restated credit agreement dat…

Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant. The information set forth above in

The filing discloses the approval of an Employee Stock Purchase Plan (ESPP), which is a compensatory arrangement rather than a change in management or board composition.

Results of Operations and Financial Condition On May 1, 2024, Clean Harbors, Inc. (the “Company”) issued a press release announcing the Company’s results of operations for the first quarter ended March 31, 2024. A copy of that press release is furnished with this report as Exhibit 99.1.

Entry into a Material Definitive Agreement. On March 22, 2024, Clean Harbors, Inc., (the “Company”) a Massachusetts corporation, and substantially all of the Company’s domestic subsidiaries as guarantors, entered into Incremental Facility Amendment No. 5, dated as of March 22, 2024 (“Incremental Facility Amendment No. 5”) to the Company’s existing Credit Agreement, dated as of June 30, 2017 (as previously amended and further amended by Incremental Facility Amendment No. 5, the “Term Loan Agre…

Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant. The information set forth under

Other Events. On March 22, 2024, the Company completed its previously announced proposed acquisition of Hepaco Blocker, Inc. and its subsidiaries (collectively, “HEPACO”) from Gryphon Investors (the “Seller”). HEPACO is a leading U.S. provider of specialized environmental and emergency response services in the Eastern United States. The acquisition was completed in accordance with the purchase agreement with the Seller dated as of February 2, 2024. Under that agreement, the Company paid an al…