Clean Harbors (CLH) 10-K 19 Feb 25 2024 FY Annual report Financial data

Cover

Cover - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2024	Feb. 12, 2025	Jun. 28, 2024
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2024
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-34223
Entity Registrant Name	CLEAN HARBORS, INC.
Entity Incorporation, State or Country Code	MA
Entity Tax Identification Number	04-2997780
Entity Address, Address Line One	42 Longwater Drive
Entity Address, City or Town	Norwell
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02061-9149
City Area Code	781
Local Phone Number	792-5000
Title of 12(b) Security	Common Stock, $0.01 par value
Trading Symbol	CLH
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Document Financial Statement Error Correction	false
Entity Shell Company	false
Entity Public Float			$ 11.5
Entity Common Stock, Shares Outstanding		53,856,836
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Portions of the registrant’s proxy statement for the 2025 Annual Meeting of Shareholders are incorporated by reference in Part III of this Form 10-K to the extent described herein.
Entity Central Index Key	0000822818
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	FY
Amendment Flag	false

Audit Information

Audit Information	12 Months Ended
	Dec. 31, 2024
Audit Information [Abstract]
Auditor Firm ID	34
Auditor Name	Deloitte & Touche LLP
Auditor Location	Boston, Massachusetts

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Current assets:
Cash and cash equivalents	$ 687,192	$ 444,698
Short-term marketable securities	102,634	106,101
Accounts receivable, net of allowances aggregating $47,242 and $42,209, respectively	1,015,357	983,111
Unbilled accounts receivable	162,215	107,859
Inventories and supplies	384,657	327,511
Prepaid expenses and other current assets	81,741	82,939
Total current assets	2,433,796	2,052,219
Property, plant and equipment, net	2,447,941	2,193,318
Other assets:
Operating lease right-of-use assets	250,853	187,060
Goodwill	1,477,199	1,287,736
Permits and other intangibles, net	701,987	602,797
Other long-term assets	65,502	59,739
Total other assets	2,495,541	2,137,332
Total assets	7,377,278	6,382,869
Current liabilities:
Current portion of long-term debt	15,102	10,000
Accounts payable	487,286	451,806
Deferred revenue	88,545	95,230
Accrued expenses and other current liabilities	419,445	397,157
Current portion of closure, post-closure and remedial liabilities	20,625	26,914
Current portion of operating lease liabilities	71,663	56,430
Total current liabilities	1,102,666	1,037,537
Other liabilities:
Closure and post-closure liabilities, less current portion of $10,304 and $13,556, respectively	119,484	105,044
Remedial liabilities, less current portion of $10,321 and $13,358, respectively	101,424	97,885
Long-term debt, less current portion	2,771,117	2,291,717
Operating lease liabilities, less current portion	182,883	131,743
Deferred tax liabilities	363,623	353,107
Other long-term liabilities	162,552	118,330
Total other liabilities	3,701,083	3,097,826
Commitments and contingent liabilities (See Note 18)
Stockholders' equity:
Authorized 80,000,000 shares; issued and outstanding 53,832,692 and 53,929,703 shares, respectively	538	539
Additional paid-in capital	421,749	459,728
Accumulated other comprehensive loss	(213,635)	(175,339)
Retained earnings	2,364,877	1,962,578
Total stockholders' equity	2,573,529	2,247,506
Total liabilities and stockholders' equity	$ 7,377,278	$ 6,382,869

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Statement of Financial Position [Abstract]
Account receivable, allowances aggregating	$ 47,242	$ 42,209
Closure and post-closure liabilities, current portion	10,304	13,556
Remedial liabilities, current portion	$ 10,321	$ 13,358
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, authorized shares (in shares)	80,000,000	80,000,000
Common stock, issued shares (in shares)	53,832,692	53,929,703
Common stock, outstanding shares (in shares)	53,832,692	53,929,703

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Revenues:
Total revenues	$ 5,889,952	$ 5,409,152	$ 5,166,605
Cost of revenues: (exclusive of items shown separately below)
Total cost of revenues	4,065,713	3,746,124	3,543,930
Selling, general and administrative expenses	739,629	671,161	627,391
Accretion of environmental liabilities	13,456	13,667	12,943
Depreciation and amortization	400,922	365,761	347,594
Income from operations	670,232	612,439	634,747
Other (expense) income, net	(1,454)	2,315	2,472
Loss on early extinguishment of debt	(371)	(2,880)	(422)
Gain on sale of business	0	0	8,864
Interest expense, net of interest income of $19,437, $11,930 and $4,607, respectively	(134,964)	(108,595)	(107,663)
Income before provision for income taxes	533,443	503,279	537,998
Provision for income taxes	131,144	125,423	126,254
Net income	$ 402,299	$ 377,856	$ 411,744
Earnings per share:
Basic (in dollars per share)	$ 7.46	$ 6.99	$ 7.59
Diluted (in dollars per share)	$ 7.42	$ 6.95	$ 7.56
Shares used to compute earnings per share — Basic (in shares)	53,902	54,071	54,223
Shares used to compute earnings per share — Diluted (in shares)	54,199	54,382	54,487
Service revenues
Revenues:
Total revenues	$ 4,928,023	$ 4,449,542	$ 4,133,184
Cost of revenues: (exclusive of items shown separately below)
Total cost of revenues	3,370,231	3,054,594	2,892,726
Product revenues
Revenues:
Total revenues	961,929	959,610	1,033,421
Cost of revenues: (exclusive of items shown separately below)
Total cost of revenues	$ 695,482	$ 691,530	$ 651,204

CONSOLIDATED STATEMENTS OF OP_2

CONSOLIDATED STATEMENTS OF OPERATIONS (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Income Statement [Abstract]
Interest income	$ 19,437	$ 11,930	$ 4,607

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Statement of Comprehensive Income [Abstract]
Net income	$ 402,299	$ 377,856	$ 411,744
Other comprehensive (loss) income, net of tax:
Unrealized gain (loss) on available-for-sale securities	37	559	(413)
Unrealized gain on fair value of interest rate hedges	12,056	5,163	61,124
Reclassification adjustment for interest rate hedge amounts realized in net income	(14,295)	(16,425)	(683)
Reclassification adjustment for settlement of interest rate hedges	0	(5,905)	0
Pension adjustments	269	(550)	318
Foreign currency translation adjustments	(36,363)	9,000	(31,515)
Other comprehensive (loss) income, net of tax	(38,296)	(8,158)	28,831
Comprehensive income	$ 364,003	$ 369,698	$ 440,575

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Cash flows from operating activities:
Net income	$ 402,299	$ 377,856	$ 411,744
Adjustments to reconcile net income to net cash from operating activities:
Depreciation and amortization	400,922	365,761	347,594
Allowance for doubtful accounts	8,129	5,956	7,783
Amortization of deferred financing costs and debt discount	6,321	5,309	6,301
Accretion of environmental liabilities	13,456	13,667	12,943
Changes in environmental liability estimates	4,139	4,828	8,272
Deferred income taxes	18,437	12,685	17,549
Other expense (income), net	1,454	(2,315)	(2,472)
Stock-based compensation	27,981	20,703	26,844
Loss on early extinguishment of debt	371	2,880	422
Gain on sale of business	0	0	(8,864)
Environmental expenditures	(27,522)	(28,960)	(13,946)
Changes in assets and liabilities, net of acquisitions:
Accounts receivable and unbilled accounts receivable	(28,822)	2,453	(201,087)
Inventories and supplies	(49,588)	(4,312)	(74,547)
Other current and non-current assets	(57,220)	(22,645)	(17,303)
Accounts payable	12,327	(27,425)	74,460
Other current and long-term liabilities	45,087	8,111	30,521
Net cash from operating activities	777,771	734,552	626,214
Cash flows used in investing activities:
Additions to property, plant and equipment	(432,241)	(422,300)	(345,056)
Proceeds from sale and disposal of fixed assets	9,099	9,650	8,779
Acquisitions, net of cash acquired	(478,011)	(119,596)	(86,278)
Proceeds from sale of business, net of transaction costs	750	750	16,811
Additions to intangible assets including costs to obtain or renew permits	(9,607)	(2,649)	(1,966)
Purchases of available-for-sale securities	(117,861)	(158,264)	(49,845)
Proceeds from sale of available-for-sale securities	124,197	117,359	68,611
Net cash used in investing activities	(903,674)	(575,050)	(388,944)
Cash flows from (used in) financing activities:
Change in uncashed checks	(1,473)	2,759	552
Tax payments related to withholdings on vested restricted stock	(13,759)	(13,838)	(8,801)
Repurchases of common stock	(55,178)	(51,164)	(50,183)
Deferred financing costs paid	(8,954)	(6,736)	(410)
Payments on finance leases	(30,886)	(15,937)	(12,821)
Proceeds from employee stock purchase plan	3,009	0	0
Principal payments on debt	(15,102)	(623,975)	(115,652)
Proceeds from issuance of debt, net of discount	499,375	500,000	0
Borrowing from revolving credit facility	0	114,000	0
Payment on revolving credit facility	0	(114,000)	0
Net cash from (used in) financing activities	377,032	(208,891)	(187,315)
Effect of exchange rate change on cash	(8,635)	1,484	(9,927)
Increase (decrease) in cash and cash equivalents	242,494	(47,905)	40,028
Cash and cash equivalents, beginning of year	444,698	492,603	452,575
Cash and cash equivalents, end of year	687,192	444,698	492,603
Cash payments for interest and income taxes:
Interest paid	153,059	114,560	105,643
Income taxes paid, net of refunds	130,606	132,314	78,526
Non-cash investing activities:
Property, plant and equipment accrued	43,750	52,376	30,950
Remedial liability assumed in acquisition of property, plant and equipment	$ 0	$ 0	$ 8,092

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Retained Earnings
Beginning balance (in shares) at Dec. 31, 2021		54,419,000
Beginning balance at Dec. 31, 2021	$ 1,513,887	$ 544	$ 536,377	$ (196,012)	$ 1,172,978
Increase (Decrease) in Stockholders' Equity
Net income	411,744				411,744
Other comprehensive income (loss)	28,831			28,831
Stock-based compensation	26,844		26,844
Issuance of common stock for restricted share vesting, net of employee tax withholding (in shares)		183,000
Issuance of common stock for restricted share vesting, net of employee tax withholdings	$ (8,801)	$ 2	(8,803)
Repurchases of common stock (in shares)	(500,000)	(537,000)
Repurchases of common stock	$ (50,183)	$ (5)	(50,178)
Ending balance (in shares) at Dec. 31, 2022		54,065,000
Ending balance at Dec. 31, 2022	1,922,322	$ 541	504,240	(167,181)	1,584,722
Increase (Decrease) in Stockholders' Equity
Net income	377,856				377,856
Other comprehensive income (loss)	(8,158)			(8,158)
Stock-based compensation	20,703		20,703
Issuance of common stock for restricted share vesting, net of employee tax withholding (in shares)		193,000
Issuance of common stock for restricted share vesting, net of employee tax withholdings	$ (13,838)	$ 1	(13,839)
Repurchases of common stock (in shares)	(300,000)	(328,000)
Repurchases of common stock	$ (51,379)	$ (3)	(51,376)
Ending balance (in shares) at Dec. 31, 2023	53,929,703	53,930,000
Ending balance at Dec. 31, 2023	$ 2,247,506	$ 539	459,728	(175,339)	1,962,578
Increase (Decrease) in Stockholders' Equity
Net income	402,299				402,299
Other comprehensive income (loss)	(38,296)			(38,296)
Stock-based compensation	27,981		27,981
Issuance of common stock for restricted share vesting, net of employee tax withholding (in shares)		125,000
Issuance of common stock for restricted share vesting, net of employee tax withholdings	$ (13,759)	$ 1	(13,760)
Repurchases of common stock (in shares)	(200,000)	(237,000)
Repurchases of common stock	$ (55,211)	$ (2)	(55,209)
Employee stock purchase plan (in shares)		15,000
Employee stock purchase plan	$ 3,009		3,009
Ending balance (in shares) at Dec. 31, 2024	53,832,692	53,833,000
Ending balance at Dec. 31, 2024	$ 2,573,529	$ 538	$ 421,749	$ (213,635)	$ 2,364,877

CONSOLIDATED STATEMENTS OF ST_2

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (PARENTHETICAL) - $ / shares	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Statement of Stockholders' Equity [Abstract]
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01	$ 0.01

OPERATIONS

OPERATIONS	12 Months Ended
	Dec. 31, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
OPERATIONS	OPERATIONS Clean Harbors, Inc., through its subsidiaries (collectively, the "Company"), is a leading provider of sustainable environmental and industrial services throughout North America. The Company is also the largest re-refiner and recycler of used oil and the premier provider of parts cleaning and related environmental services to commercial, industrial and automotive customers in North America.

SIGNIFICANT ACCOUNTING POLICIES

SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2024
Accounting Policies [Abstract]
SIGNIFICANT ACCOUNTING POLICIES	SIGNIFICANT ACCOUNTING POLICIES The accompanying consolidated financial statements of the Company reflect the application of certain significant accounting policies as described below: Principles of Consolidation The accompanying consolidated financial statements include the accounts of Clean Harbors, Inc. and its majority-owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation. Use of Estimates The preparation of consolidated financial statements in conformity with U.S. Generally Accepted Accounting Principles (GAAP), requires management to make estimates and assumptions about future events that affect the amounts reported in the consolidated financial statements and the accompanying notes. Management bases its estimates on historical experience and other assumptions that it believes to be reasonable at the time. Actual results could differ from those estimates, and any such differences may be material to the consolidated financial statements. Estimates and assumptions are reviewed periodically and the effects of changes, if any, are reflected in our consolidated financial statements in the period they are determined. Cash, Cash Equivalents, Marketable Securities and Uncashed Checks Cash consists primarily of cash on deposit and money market accounts. The Company, through its wholly-owned captive insurance subsidiary, invests in cash equivalents and marketable securities. Marketable securities with maturities of three months or less from the date of purchase are classified as cash equivalents. As of December 31, 2024 and 2023, the Company had total marketable securities as follows (in thousands): December 31, 2024 December 31, 2023 Commercial paper $ 4,035 $ 27,542 Total cash equivalents 4,035 27,542 Commercial paper 17,489 56,172 Corporate notes and bonds 85,145 49,929 Total marketable securities 102,634 106,101 Total $ 106,669 $ 133,643 Realized gains and losses on sales of available-for-sale marketable securities in the years presented were immaterial. The majority of the marketable securities have a remaining maturity of less than one year and fair value approximates cost. The Company's cash management program with its revolving credit lender allows the Company to maintain a zero balance in the U.S. bank disbursement accounts that are used to issue vendor and payroll checks. When checks are presented to the bank for payment, cash deposits in amounts sufficient to fund the checks are made, at the Company's discretion, either from funds provided by other accounts or under the terms of the Company's revolving credit facility. Checks that have been written to vendors or employees but have not yet been presented for payment at the Company's bank are classified as uncashed checks in accounts payable and changes in the balance are reported as a financing activity in the consolidated statements of cash flows. Allowance for Doubtful Accounts and Revenue Allowance On a regular basis, the Company evaluates its accounts receivable and establishes the allowance for doubtful accounts based on an evaluation of certain criteria and evidence of collection uncertainty including historical collection trends, reasonable expectations of future collections, current economic trends and changes in customer payment patterns. Past-due receivable balances are written off when the Company's collection efforts have been deemed unsuccessful in collecting the outstanding balance due. Due to the nature of the Company's businesses and the invoices that result from the services provided, customers may withhold payments and attempt to renegotiate amounts invoiced. In addition, for some of the services provided, the Company's invoices are based on quotes that, in limited instances, can result in adjustments to revenue subsequent to billing. Based on industry knowledge and historical trends, the Company records a revenue allowance in anticipation of these expected adjustments. This practice causes the volume of activity flowing through the revenue allowance during the year to be higher than the balance at the end of the year. The revenue allowance is intended to cover the net amount of revenue adjustments that may need to be credited to customers' accounts in future periods. Management determines the appropriate total revenue allowance by evaluating the following factors on an invoice-by-invoice basis as well as on a consolidated level: trends in adjustments to previously billed amounts, existing economic conditions, communications with customers and other information as deemed applicable. Revenue allowance estimates can differ from the actual adjustments, but historically the revenue allowance has been sufficient to cover the net amount of the reserve adjustments issued in subsequent reporting periods. The following table reflects the activity in the allowance for doubtful accounts and revenue allowance (in thousands): Allowance for Doubtful Accounts Revenue Allowance 2024 2023 2022 2024 2023 2022 Balance at January 1, $ 22,568 $ 24,659 $ 24,136 $ 19,641 $ 20,594 $ 16,004 Additions charged to earnings 8,129 5,956 7,783 48,301 46,467 54,836 Deductions from reserves, net of recoveries (7,789) (8,047) (7,260) (43,608) (47,420) (50,246) Balance at December 31, $ 22,908 $ 22,568 $ 24,659 $ 24,334 $ 19,641 $ 20,594 Credit Concentration Concentration of credit risks in accounts receivable is limited due to the large number of customers comprising the Company's customer base throughout North America. The Company maintains policies over credit extension that include credit evaluations, credit limits and collection monitoring procedures on a customer-by-customer basis. However, the Company generally does not require collateral before services are performed. No individual customer accounted for more than 10% of accounts receivable or more than 10% of total third-party revenues in the periods presented. Inventories and Supplies Inventories are stated at the lower of cost or net realizable value. The cost of oil and oil products as well as the cost of supplies and drums, solvent and solution and other inventories is principally determined on a first-in, first-out ("FIFO") basis. The Company continually reviews its inventories for obsolete or unsalable items and adjusts its carrying value to reflect estimated realizable values. Property, Plant and Equipment, net (excluding landfill assets and finance lease right-of-use assets) Property, plant and equipment, net is stated at cost less accumulated depreciation. Expenditures for major renewals and improvements which extend the life or usefulness of the asset are capitalized. Items of an ordinary repair or maintenance nature are charged directly to operating expense as incurred. During the construction and development period of an asset, the costs incurred, including interest expense, are classified as construction-in-progress. When the asset is ready for its intended use, the asset is reclassified to an appropriate asset classification and depreciation or amortization commences. The Company depreciates and amortizes the capitalized cost of these assets, using the straight-line method as follows: Asset Classification Estimated Useful Life Buildings and building improvements Buildings 20-42 years Leasehold and building improvements 2-45 years Vehicles 2-15 years Equipment Capitalized software and computer equipment 3-5 years Containers and railcars 8-16 years All other equipment 4-30 years Furniture and fixtures 5-8 years Gains and losses on the sale of property, plant and equipment are included in Other (expense) income, net. Fully depreciated assets are retained in property, plant and equipment and accumulated depreciation until they are removed from service. The Company tests asset groups for impairment whenever events or changes in circumstances indicate that the carrying value may not be recoverable. An impairment in the carrying value of long-lived assets is recognized if the expected future undiscounted cash flows derived from the assets, or group of assets, are less than their carrying value. The Company did not record any impairment charges related to long-lived assets in the periods presented. Business Combinations In accordance with the acquisition method of accounting, the purchase price paid for an acquisition is allocated to the assets and liabilities acquired based upon their estimated fair values as of the acquisition date, with the excess of the purchase price over the net assets acquired recorded as goodwill. As required, a preliminary fair value is determined once a business is acquired, with the final determination of the fair value being completed no later than one year from the date of acquisition. Goodwill Goodwill is comprised of the purchase price of business acquisitions in excess of the fair value of the net assets acquired. Goodwill is reviewed for impairment annually as of December 31 or when events or changes in the business environment indicate the carrying value of a reporting unit may exceed its fair value. This review is performed by comparing the fair value of each reporting unit to its carrying value, including goodwill. If the fair value is less than the carrying amount, a loss is recorded for the excess of the carrying value over the fair value up to the carrying amount of goodwill. The Company determines its reporting units by identifying the components of each operating segment. As of December 31, 2024, the Company had four reporting units consisting of, Environmental Sales and Service, Industrial Services, Environmental Facilities and Safety-Kleen Sustainability Solutions ("SKSS"). See Note 8, "Goodwill and Other Intangible Assets," for additional information related to the Company's goodwill impairment tests. Permits and Other Intangibles Costs related to acquiring licenses, permits and intangible assets, such as legal fees, site surveys, engineering costs and other expenditures are capitalized. Other intangible assets consist primarily of customer and supplier relationships, trademarks and trade names and developed technology. Permits relating to landfills are amortized on a units-of-consumption basis. All other permits are amortized over periods ranging from five two All finite-lived intangible assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying value may not be recoverable. When such factors and circumstances exist, management compares the projected undiscounted future cash flows associated with the related asset or group of assets to the carrying amount. The impairment loss, if any, is measured as the excess of the carrying amount over the fair value of the asset or group of assets. Indefinite-lived intangible assets are not amortized but are reviewed for impairment annually as of December 31, or when events or changes in the business environment indicate that the carrying value may be impaired. If the fair value of the asset is less than the carrying amount, the impairment loss is measured as the excess of the carrying value of the asset over its fair value. Landfill Accounting The Company amortizes landfill improvements and certain landfill-related permits over the estimated useful lives. The units-of-consumption method is used to amortize land, landfill cell construction, asset retirement costs and remaining landfill cells and sites. The Company also utilizes the units-of-consumption method to record closure and post-closure obligations for landfill cells and sites. Under the units-of-consumption method, the Company includes future estimated construction and asset retirement costs, as well as costs incurred to date, in the amortization base of the landfill assets. Additionally, where appropriate, as described below, the Company includes probable expansion airspace that has yet to be permitted in the calculation of the total remaining useful life of the landfill. If it is determined that expansion capacity should no longer be considered in calculating the recoverability of a landfill asset, the Company may be required to recognize an asset impairment or incur significantly higher amortization expense. If at any time the Company makes the decision to abandon the expansion effort, the capitalized costs related to the expansion effort are expensed immediately. Landfill assets —Landfill assets include the costs of landfill site acquisition, permits and cell construction incurred to date. These amounts are recorded at cost, which includes capitalized interest as applicable. Landfill assets, net of amortization, are combined with management's estimate of the costs required to complete construction of the landfill to determine the amount to be amortized over the remaining estimated useful economic life of a site. Amortization of landfill assets is recorded on a units-of-consumption basis, such that the landfill assets should be completely amortized at the date the landfill ceases accepting waste. Amortization totaled $10.6 million, $18.6 million and $16.2 million for the years ended December 31, 2024, 2023 and 2022, respectively. Changes in the determination of when the landfill will cease accepting waste, either through a business decision by the Company, determination that expansion capacity should no longer be considered probable or changes in estimates on annual airspace consumption, will impact the amortization expense of the landfill assets. Changes in estimated costs to complete construction are applied prospectively to the amortization rate. Landfill capacity —Landfill capacity, which is the basis for the amortization of landfill assets and for the accrual of final closure and post-closure obligations, represents total permitted airspace plus unpermitted airspace that management believes is highly probable of ultimately being permitted. As of December 31, 2024, there were no unpermitted expansions included in the Company's landfill accounting model. If actual expansion airspace is significantly different from management's estimate of expansion airspace, the amortization rates used for the units-of-consumption method would change, therefore impacting the Company's profitability. As of December 31, 2024, the Company had eight active landfill sites (including the Company's non-commercial landfill), which have estimated remaining lives (based on anticipated waste volumes and the remaining highly probable airspace) as follows: Facility Name Location Remaining Permitted Remaining Highly Probable Airspace Buttonwillow California 21 4,909 Deer Trail Colorado 17 1,347 Grassy Mountain Utah 37 4,253 Kimball Nebraska 22 520 Lambton Ontario, Canada 46 4,218 Lone Mountain Oklahoma 13 2,913 Ryley Alberta, Canada 40 5,594 Sawyer North Dakota 61 3,197 26,951 At December 31, 2024 and 2023, the Company had no cubic yards of permitted, but not highly probable, airspace. The following table presents the remaining highly probable airspace from January 1, 2023 through December 31, 2024 (in thousands of cubic yards): 2024 2023 Remaining capacity, beginning of year 27,753 28,270 Changes in highly probable airspace, net — 464 Consumed (802) (981) Remaining capacity, end of year 26,951 27,753 In the year ended December 31, 2023 the Company received a permit for expansion of its Kimball, Nebraska landfill. Amortization of cell construction costs and accrual of cell closure obligations —Landfills are typically comprised of a number of cells, which are constructed within a defined acreage (or footprint). The cells are typically discrete units, which require both separate construction and separate capping and closure procedures. Cell construction costs are the costs required to excavate and construct the landfill cell. These costs are typically amortized on a units-of-consumption basis, such that they are completely amortized when the specific cell ceases accepting waste. In some instances, the Company has landfills that are engineered and constructed as "progressive trenches." In progressive trench landfills, a number of contiguous cells form a progressive trench. In those instances, the Company amortizes cell construction costs over the airspace within the entire trench, such that the cell construction costs will be fully amortized at the end of the trench useful life. The design and construction of a landfill does not create a landfill asset retirement obligation. Rather, the asset retirement obligation for cell closure (the cost associated with capping each cell) is incurred in relatively small increments as waste is placed in the landfill. Therefore, the cost required to construct the cell cap is capitalized as an asset retirement cost and a liability of an equal amount is established, based on the discounted cash flow associated with each capping event, as airspace is consumed. Spending for cell capping is reflected as environmental expenditures within operating activities in the consolidated statements of cash flows. Landfill final closure and post-closure liabilities —The balance of landfill final closure and post-closure liabilities was $59.4 million at both December 31, 2024 and 2023 respectively. The Company has material financial commitments for the costs associated with requirements of the Environmental Protection Agency ("EPA") and the comparable regulatory agency in Canada for landfill final closure and post-closure activities. The Company develops estimates for the cost of these activities based on an evaluation of site-specific facts and circumstances, including the Company's interpretation of current regulatory requirements and proposed regulatory changes. Such estimates may change in the future due to various circumstances including, but not limited to, permit modifications, changes in legislation or regulations, technological changes and results of environmental studies. Final closure costs are the costs incurred after the site ceases to accept waste, but before the landfill is certified as closed by the applicable state regulatory agency. These costs generally include the costs required to cap the final cell of the landfill (if not included in cell closure), the costs required to dismantle certain structures for landfills and other landfill improvements, and regulation-mandated groundwater monitoring and leachate management. Post-closure costs involve the maintenance and monitoring of a landfill site that has been certified closed by the applicable regulatory agency. These costs generally include groundwater monitoring and leachate management. Regulatory post-closure periods are generally 30 years after landfill closure. Final closure and post-closure obligations are accrued on a units-of-consumption basis, such that the present value of the final closure and post-closure obligations are fully accrued at the date the landfill ceases accepting waste. Cell closure, final closure and post-closure costs (also referred to as "asset retirement obligations") are calculated by estimating the total obligation in current dollars, adjusted for future inflation estimates and discounted at the Company's credit-adjusted risk-free interest rate (6.57% and 6.51% during 2024 and 2023, respectively). Non-Landfill Closure and Post-Closure Liabilities The balance of non-landfill closure and post-closure liabilities at December 31, 2024 and 2023 was $70.4 million and $59.2 million, respectively. Non-landfill closure and post-closure obligations arise when the Company commences non-landfill facility operations and include costs required to dismantle and decontaminate certain structures and other costs incurred during the closure process. Post-closure costs, if required, include associated maintenance and monitoring costs as required by the closure permit. Post-closure periods are performance-based and are not typically specified in terms of years in the closure permit, but generally range from 10 to 30 years or more. The Company records its non-landfill closure and post-closure liability by: (i) estimating the current cost of closing a non-landfill facility and the post-closure care of that facility, if required, based upon the closure plan that the Company is required to follow under its operating permit, or in the event the facility operates with a permit that does not contain a closure plan, based upon legally enforceable closure commitments made by the Company to various government agencies; (ii) estimates as to when future operations may cease; (iii) cost estimates of closing the non-landfill facility using the inflation rate to the time of closing; and (iv) discounting the future value back to the present using the credit-adjusted risk-free interest rate. The estimates for non-landfill closure and post-closure liabilities are inherently uncertain due to the possibility that permit and regulatory requirements will change in the future, impacting the estimation of total costs and the timing of the expenditures. Management reviews non-landfill closure and post-closure liabilities for changes to key assumptions that would impact the amount of the recorded liabilities. Changes that would prompt management to revise a liability estimate include changes in legal requirements that impact the Company's expected closure plan or scope of work, in the market price of a significant cost item, in the estimate as to when future operations at a location might cease or in the expected timing of the costs. Changes in estimates for non-landfill closure and post-closure events immediately impact the liability and the value of the corresponding asset. If a change is made to a fully-amortized asset, the adjustment is charged immediately to expense. When a change in estimate relates to an asset that has not been fully amortized, the adjustment to the asset is recognized in income prospectively as a component of amortization. Historically, changes to non-landfill closure and post-closure estimates have not been material. Remedial Liabilities The balance of remedial liabilities at December 31, 2024 and 2023 was $111.7 million and $111.2 million, respectively. Remedial liabilities, including Superfund liabilities, include the costs of removal or containment of contaminated material, treatment of potentially contaminated groundwater and maintenance and monitoring costs necessary to comply with regulatory requirements. Most of the Company's remedial liabilities relate to the active and inactive hazardous waste treatment and disposal facilities which the Company acquired and Superfund sites owned by third-parties for which the Company, or the prior owners of certain of the Company's facilities for which the Company may have certain indemnification obligations, have been identified as potentially responsible parties ("PRPs") or potential PRPs. The Company's estimate of remedial liabilities involves an analysis of such factors as: (i) the nature and extent of environmental contamination (if any); (ii) the terms of applicable permits and agreements with regulatory authorities as to cleanup procedures and whether modifications to such permits and agreements will likely need to be negotiated; (iii) the cost of performing anticipated cleanup activities based upon current technology; and (iv) in the case of Superfund and other sites where other parties will also be responsible for a portion of the cleanup costs, the likely allocation of such costs and the ability of such other parties to pay their share. The measurement of remedial liabilities is reviewed at least quarterly and changes in estimates are recognized in the consolidated statements of operations when identified. Where the Company concludes that it is probable that a liability has been incurred and an amount can be estimated, a liability is recognized. Remedial liabilities are inherently difficult to estimate. Estimating remedial liabilities requires that the existing environmental contamination be understood. There are risks that the actual quantities of contaminants differ from the results of the site investigation, and that contaminants exist that have not been previously identified. In addition, the value of the remedial liabilities is dependent on the remedial method selected. There is a risk that funds will be expended on a remedial solution that is not successful, which could result in the Company incurring the incremental costs of an alternative solution. Such estimates, which are subject to change, are subsequently revised if and when additional or new information becomes available. Remedial liabilities are discounted when the timing of the payments is determinable and the amounts are estimable. In the case of remedial liabilities assumed in connection with acquisitions, acquired liabilities are recorded at fair value as of the dates of the acquisitions calculated by inflating costs in current dollars using an estimate of future inflation rates as of the respective acquisition dates until the expected time of payment, and then discounting the amount of the payments to their present value using a risk-free discount rate as of the acquisition dates. Discount rates used in the present value determination of the Company's remedial liabilities range from 1.37% to 4.90%. Self-Insurance Liabilities The Company self-insures a significant portion of expected losses related to workers' compensation, employee medical, comprehensive general liability and vehicle liability. Liabilities associated with these losses are recorded based on the Company's estimates of the ultimate cost to settle incurred claims. These recorded liabilities are estimated based on independent actuarial estimates and judgments which consider the frequency and settlement amount of historical claims data and are discounted to present value using a risk-free interest rate. Revenue Recognition The Company recognizes revenue when control of the promised goods or services is transferred to the Company's customers, in an amount that reflects the consideration the Company expects to be entitled to in exchange for those goods or services. The majority of the Company’s revenues are for services, which are recognized based on time and materials incurred at contractually agreed-upon rates. Product revenues are recognized when the products are delivered and control transfers to the customer. The Company’s payment terms vary by the type of customers and the products or services offered. The periods between invoicing and when payments are due are not significant. Amounts billed to customers related to shipping and handling are classified as revenue, and the Company's shipping and handling costs are included in costs of revenues. In the course of operations, the Company collects sales tax and other excise taxes from its customers and recognizes a current liability, which is then relieved when the taxes are remitted to the appropriate government authorities. The Company excludes sales and other excise taxes that it collects from customers from its revenues. Foreign Currency The Company has international operations in Canada and administrative support services located in India. The functional currencies of foreign operations are the local currency and therefore assets and liabilities of those foreign operations are translated to U.S. Dollars at the exchange rate in effect at the balance sheet date and revenue and expenses at the average exchange rate for the period. Gains and losses from the translation of the consolidated financial statements of foreign subsidiaries into U.S. Dollars are included in stockholders' equity as a component of accumulated other comprehensive loss. Gains and losses from transactions not denominated in the functional currency of an entity are recognized in the consolidated statements of operations. Recorded balances that are denominated in a currency other than the functional currency are remeasured to the functional currency using the exchange rate at the balance sheet date and gains or losses are recorded in the consolidated statements of operations. Defined Contribution Plan The Company has defined contribution plans under which eligible employees may contribute up to the maximum amount as provided by law. The Company matches a portion of these employee contributions and contributed $30.9 million, $28.8 million and $25.3 million in 2024, 2023 and 2022 respectively. Advertising Expense Advertising costs are expensed as incurred. Advertising expense was $11.4 million in 2024, $10.9 million in 2023 and $9.4 million in 2022. Stock-based Compensation Stock-based compensation cost is measured at the grant date based on the fair value of the award and is recognized as expense over the requisite service period, which generally represents the vesting period. In addition, the Company issues awards with performance targets established prior to or at the grant date. The expense for these awards is recognized over the requisite service period when management believes it is probable those performance targets will be achieved. The fair value of the Company's grants under the 2020 Stock Incentive Plan are based on the closing price of the Company's common stock on the respective dates of grant. The fair value of shares issued under the Company’s 2024 Employee Stock Purchase plan are valued using the Black-Scholes option pricing model, which requires management to make assumptions with respect to the fair value of our common stock on the grant date, including the expected volatility of our stock, calculated based on a period of time generally commensurate with the expected term of the award and risk-free interest rates. Forfeitures are recognized as they occur. Stock-based compensation is recognized in selling, general and administrative expense. Interest Rate Derivatives The Company enters into interest rate derivative agreements as part of the overall strategy to hedge against fluctuations in variable interest rates. These interest rate derivatives swap a variable interest rate for a fixed interest rate and have been designated as cash flow hedges. The Company assesses the hedge’s effectiveness at the inception of the hedge and at regular intervals throughout the life of the derivative. To the extent that the interest rate swap is highly effective, changes in fair value are recorded in stockholders’ equity as a component of accumulated other comprehensive loss. Amounts are reclassified from accumulated other comprehensive loss into interest expense on the consolidated statement of operations in the same period or periods during which the hedged transactions affect earnings. Although it was determined that the interest rate swaps will be a highly effective hedge, any portion of the interest rate swaps subsequently determined to be ineffective will be recognized in earnings. Further, if it becomes probable that a forecasted transaction designated as the hedged item will not occur, any gain or loss deferred is recognized in interest expense at that time. The fair value of the interest rate swaps is calculated using discounted cash flow valuation methodologies based upon the one-month variable rate yield curves that are observable at commonly quoted intervals for the full term of the interest rate swaps and as such is considered a Level 2 measure according to the fair value hierarchy. The Company recognizes the fair value of the derivative instruments by counterparty as either a net asset, included in Other long-term assets, or net liability, included in Accrued expenses and other current liabilities, on the consolidated balance sheets. Income Taxes Current income tax expense approximates cash to be paid or refunded for taxes for the applicable period. Deferred tax expense or benefit is the result of changes between deferred tax assets and liabilities. Deferred tax assets and liabilities are determined based upon the temporary differences between the financial statement basis and tax basis of assets and liabilities as well as from net operating loss and tax credit carryforwards as measured by the enacted tax rates which will be in effect when these differences reverse. The effect of a change in tax rates on deferred tax assets and liabilities is generally recognized in income in the period that includes the enactment date. The Company evaluates the recoverability of future tax deductions and credits and a valuation allowance is established by tax jurisdiction when, based on an evaluation of both positive and negative objective verifiable evidence, it is more likely than not that some portion or all of deferred tax assets will not be realized. The Company recognizes and measures a tax benefit from uncertain tax positions when it is more likely than not that the tax position will be sustained upon examination by the taxing

REVENUES

REVENUES	12 Months Ended
	Dec. 31, 2024
Revenue from Contract with Customer [Abstract]
REVENUES	REVENUES The Company generates revenues through the following operating segments: Environmental Services and SKSS. The Company’s Environmental Services operating segment generally has four sources of revenue and the SKSS operating segment has two sources of revenue. The Company disaggregates third-party revenues by geographic location and source of revenue as management believes these categories depict how revenue and cash flows are affected by economic factors. The tables below present revenue billed to outside customers by a particular segment. Should it be necessary, there will be intercompany transactions to present the direct revenues in the appropriate segment results. The Company’s significant sources of revenue include: Technical Services —Technical Services contribute to the revenues of the Environmental Services operating segment. Revenues for these services are generated from fees charged for waste material management and disposal services including onsite environmental management services, collection and transportation, packaging, recycling, treatment and disposal of waste and remediation projects. These services handle hazardous and/or non-hazardous waste, including per- and polyfluoroalkyl substances (“PFAS”). Revenue is primarily generated by short-term projects, most of which are governed by master service agreements that are long-term in nature. These master service agreements are typically entered into with the Company’s larger customers and outline the pricing and legal frameworks for such arrangements. Services are provided based on purchase orders or agreements with the customer and include prices based upon units of volume of waste, material and personnel costs as well as transportation and other fees. Collection and transportation revenues are recognized over time, as the customer receives and consumes the benefits of the services as they are being performed and the Company has a right to payment for performance completed to date. The Company uses the input method to recognize revenue over time, based on time and materials incurred as a basis for measuring the satisfaction of the performance obligation. Revenues for treatment and disposal of waste are recognized upon completion of treatment, final disposition, or when the waste is shipped to a third-party for processing and disposal. The Company periodically enters into bundled arrangements for the collection and transportation and disposal of waste. For such arrangements, transportation and disposal are considered distinct performance obligations and the Company allocates revenue to each based on the relative standalone selling price (i.e., the estimated price that a customer would pay for the services on a standalone basis). Revenues and the related costs from waste that is not yet completely processed and disposed of are deferred. The deferred revenues and costs are recognized when the services are completed. The period between collection and transportation and the final processing and disposal ranges depending on the location of the customer, but generally is measured in days. Industrial Services —Industrial Services contribute to the revenues of the Environmental Services operating segment. These revenues are primarily generated from industrial and specialty services provided to refineries, chemical plants, manufacturing facilities, power generation companies and other industrial customers throughout North America. Services include in-plant cleaning and maintenance services, plant outage and turnaround services, specialty cleaning services including chemical cleaning, pigging and high and ultra-high pressure water cleaning, leak detection and repair, daylighting, production services and upstream energy services. Services are provided based on purchase orders or agreements with the customer and include prices based upon daily, hourly or job rates for equipment, materials and personnel. The Company recognizes revenue for these services over time, as the customer receives and consumes the benefits of the services as they are being performed and the Company has a right to payment for performance completed to date. The Company uses the input method to recognize revenue over time, based on time and materials incurred. Field and Emergency Response Services —Field and Emergency Response Services, which includes contributions from the acquisition of HEPACO Blocker, Inc. and its subsidiaries (collectively, “HEPACO”) in 2024, contribute to the revenues of the Environmental Services operating segment. Field Services revenues are generated from cleanup services at customer sites, including those managed by municipalities and utility providers, or other locations on a scheduled or emergency response basis. Services include confined space entry for tank cleaning, site decontamination, environmental remediation, railcar cleaning, manhole/vault clean outs, product recovery and transfer and vacuum services. Additional services include filtration, water treatment services and wetland restoration. Response services for environmental emergencies of any scale range from man-made disasters such as oil spills to natural disasters like hurricanes. Emergency response services also include spill cleanup on land and water, as well as contagion disinfection, decontamination and disposal services. Field and emergency response services are provided based on purchase orders or agreements with customers and include prices generally based upon daily, hourly or job rates for equipment, materials and personnel. The Company recognizes revenue for these services over time, as the customer receives and consumes the benefits of the services as they are being performed and the Company has a right to payment for performance completed to date. The Company uses the input method to recognize revenue over time, based on time and materials incurred. The duration of such services can be over a number of hours, several days or even months for larger scale projects. Safety-Kleen Environmental Services —Safety-Kleen Environmental Services revenues contribute both to the Environmental Services operating segment and the SKSS operating segment. Revenues from providing containerized waste handling and disposal services, parts washer services and vacuum services, referred to collectively as the Safety-Kleen branches’ core service offerings, contribute to the revenues of the Environmental Services operating segment. In addition, sales of packaged blended oil products and other complementary product sales contribute to the revenues of the Environmental Services operating segment. Revenues generated from waste oil, anti-freeze and oil filter collection services, sales of bulk blended oil products and sales of automotive fluids contribute to the SKSS operating segment. Due to the complementary nature of these products and services and their customer base, there are some cross-overs of Safety-Kleen Environmental Services revenue streams between Environmental Services and SKSS operating segments. Generally, the revenue from services is recognized over time, as the customer receives and consumes the benefits of the services as they are being performed and the Company has a right to payment for performance completed to date. The duration of such services can be over a number of hours or several days. The Company uses the input method to recognize revenue over time, based on time and materials incurred. Product revenue is recognized upon the transfer of control whereby control transfers when the products are delivered to the customer. Containerized waste services consist of profiling, collecting, transporting and recycling or disposing of a wide variety of waste. Related collection and transportation revenues are recognized over time, as the customer receives and consumes the benefits of the services as they are being performed and the Company has a right to payment for performance completed to date. Parts washer services include customer use of the Company’s parts washer equipment, cleaning and maintenance of the parts washer equipment and removal and replacement of used cleaning fluids. Parts washer services are considered a single performance obligation due to the highly integrated and interdependent nature of the arrangement. Revenue from parts washer services is recognized over the service interval as the customer receives the benefit of the services. Safety-Kleen Oil —Safety-Kleen Oil related sales contribute to the revenues of the SKSS segment. These revenues are generated from bulk sales of high-quality base and blended lubricating oils to many industries, including major oil brands, lubricant blenders and manufacturers, blended lubricant distributors and government agencies. The business also sells recycled fuel oil to asphalt plants, industrial plants and pulp and paper companies. The used oil is also processed into vacuum gas oil which can be further re-refined into lubricant base oils or sold directly into the marine diesel oil fuel market. By-products coming off the refinery are a mixture of light end distillates and asphalt flux that are sold into various markets. Revenue for oil products is recognized at a point in time, upon the transfer of control. Generally, control transfers when the products are delivered to the customer. The following tables present the Company’s third-party revenue disaggregated by source of revenue and geography (in thousands): For the year ended December 31, 2024 Environmental Services Safety-Kleen Sustainability Solutions Corporate Total Primary Geographical Markets United States $ 4,510,845 $ 841,171 $ 407 $ 5,352,423 Canada 449,480 88,049 — 537,529 Total third-party revenues $ 4,960,325 $ 929,220 $ 407 $ 5,889,952 Sources of Revenue Technical Services $ 1,733,550 $ — $ — $ 1,733,550 Industrial Services and Other 1,377,502 — 407 1,377,909 Field and Emergency Response Services 895,120 — — 895,120 Safety-Kleen Environmental Services 954,153 229,730 — 1,183,883 Safety-Kleen Oil — 699,490 — 699,490 Total third-party revenues $ 4,960,325 $ 929,220 $ 407 $ 5,889,952 For the year ended December 31, 2023 Environmental Services Safety-Kleen Sustainability Solutions Corporate Total Primary Geographical Markets United States $ 4,022,394 $ 846,339 $ 447 $ 4,869,180 Canada 447,515 92,457 — 539,972 Total third-party revenues $ 4,469,909 $ 938,796 $ 447 $ 5,409,152 Sources of Revenue Technical Services $ 1,563,847 $ — $ — $ 1,563,847 Industrial Services and Other 1,418,938 — 447 1,419,385 Field and Emergency Response Services 609,913 — — 609,913 Safety-Kleen Environmental Services 877,211 224,830 — 1,102,041 Safety-Kleen Oil — 713,966 — 713,966 Total third-party revenues $ 4,469,909 $ 938,796 $ 447 $ 5,409,152 For the year ended December 31, 2022 Environmental Services Safety-Kleen Sustainability Solutions Corporate Total Primary Geographical Markets United States $ 3,675,880 $ 899,780 $ 507 $ 4,576,167 Canada 469,093 121,345 — 590,438 Total third-party revenues $ 4,144,973 $ 1,021,125 $ 507 $ 5,166,605 Sources of Revenue Technical Services $ 1,495,264 $ — $ — $ 1,495,264 Industrial Services and Other 1,311,072 — 507 1,311,579 Field and Emergency Response Services 575,300 — — 575,300 Safety-Kleen Environmental Services 763,337 199,360 — 962,697 Safety-Kleen Oil — 821,765 — 821,765 Total third-party revenues $ 4,144,973 $ 1,021,125 $ 507 $ 5,166,605 Contract Balances (in thousands) December 31, 2024 December 31, 2023 Receivables $ 1,015,357 $ 983,111 Contract assets (unbilled receivables) 162,215 107,859 Contract liabilities (deferred revenue) 88,545 95,230 The timing of revenue recognition, billings and cash collections results in billed accounts receivable, unbilled receivables (contract assets) and customer advances and deposits or deferred revenue (contract liabilities) on the consolidated balance sheet. Generally, billing occurs subsequent to revenue recognition, as a right to payment is not just subject to passage of time, resulting in contract assets, which are generally classified as current. The Company sometimes receives advances or deposits from its customers before revenue is recognized, resulting in contract liabilities. These assets and liabilities are reported on the consolidated balance sheet on a contract-by-contract basis at the end of each reporting period. The contract liability balances at the beginning of each period presented are generally fully recognized in the subsequent three-month period. Variable Consideration The nature of the Company's contracts give rise to certain types of variable consideration, including in limited cases volume discounts. Accordingly, management establishes a revenue allowance to cover the estimated amounts of revenue that may need to be credited to customers' accounts in future periods. The Company estimates the amount of variable consideration included in the estimated transaction price based on historical experience, anticipated performance and management's best judgment at the time. The Company includes estimated amounts in the transaction price to the extent it is probable that a significant reversal of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is resolved. There have been no material changes in estimates of variable consideration in the periods presented. Contract Costs Contract costs include direct and incremental costs to obtain or fulfill a contract. Parts washer costs include costs of solvent, commissions paid relating to revenue generated from parts washer services, and transportation costs associated with transferring the product picked up from the service as it is brought to the Company’s facilities or third-party sites. Costs related to the treatment of waste include costs for waste receiving, drum movement and storage, waste consolidation and transportation between facilities. The Company’s contract costs that are subject to capitalization are comprised of costs associated with parts washer services and with the treatment and disposal of waste. As of December 31, 2024 and 2023, the Company's deferred contract costs totaled $28.2 million and $29.9 million, respectively. Deferred parts washer costs are recognized over the service interval as the customer receives the benefit of the services, and deferred costs related to treatment and disposal of waste are recognized when the corresponding waste is disposed. Deferred costs are included within prepaid expenses and other current assets in the Company’s consolidated balance sheets. The deferred contract cost balances at the beginning of each period presented were fully recognized in cost of revenue in the subsequent three-month period.

BUSINESS COMBINATIONS

BUSINESS COMBINATIONS	12 Months Ended
	Dec. 31, 2024
Business Combination, Asset Acquisition, and Joint Venture Formation [Abstract]
BUSINESS COMBINATIONS	BUSINESS COMBINATIONS 2024 Acquisitions On March 22, 2024, the Company completed its acquisition of HEPACO for an all-cash purchase price of $392.2 million, net of cash acquired and after the settlement of working capital in the third quarter of 2024. The operations of HEPACO expand the Environmental Services segment’s field services business. The preliminary allocation of the purchase price is provisional and was based on estimates of the fair value of assets acquired and liabilities assumed as of March 22, 2024. The Company continues to obtain information to complete the valuation of these balances and the associated income tax accounting. Measurement period adjustments will reflect new information obtained about facts and circumstances that existed as of the acquisition date. The following table summarizes the preliminary determination and recognition of assets acquired and liabilities assumed (in thousands): At Acquisition Date As Reported December 31, 2024 Accounts receivable, including unbilled receivables $ 69,072 Inventories and supplies 384 Prepaid expenses and other current assets 4,383 Property, plant and equipment 47,125 Permits and other intangibles 130,500 Operating lease right-of-use assets 9,385 Other long-term assets 5,712 Accounts payable (30,602) Accrued expenses and other current liabilities (16,005) Current portion of operating lease liabilities (2,758) Operating lease liabilities, less current portion (6,627) Closure and post-closure liabilities (2,492) Remedial liabilities (2,435) Other long-term liabilities (374) Total identifiable net assets 205,268 Goodwill 186,911 Total purchase price $ 392,179 Other intangible assets acquired include customer relationships and trademarks/trade names and are anticipated to have estimated useful lives of between seven and 20 years with a weighted average useful life of approximately 19 years . The excess of the total purchase price, which includes the aggregate cash consideration paid in excess of the fair value of the tangible and intangible assets acquired and liabilities assumed, was recorded as goodwill. The goodwill recognized is attributable to the operating synergies, assembled workforce and growth potential that the Company expects to realize from the acquisition. Goodwill generated from the acquisition is not deductible for tax purposes. The operations included in the Company’s financial statements for the period ended December 31, 2024 , and pro forma revenue and earnings amounts on a combined basis as if this acquisition had been completed on January 1, 2023 are immaterial to the consolidated financial statements of the Company. On March 1, 2024, the Company acquired Noble Oil Services, Inc. and its subsidiaries (collectively “Noble”) for an all-cash purchase price of $68.7 million, net of cash acquired and after the settlement of working capital in the second quarter of 2024. The acquisition of Noble expands the SKSS segment’s oil collection operations in the southeastern region of the United States while also adding incremental production from the re-refinery owned and operated by the acquired company. The preliminary allocation of the purchase price is provisional and was based on estimates of the fair value of assets acquired and liabilities assumed as of March 1, 2024. The Company continues to obtain information to complete the valuation of these balances and the associated income tax accounting. Measurement period adjustments will reflect new information obtained about facts and circumstances that existed as of the acquisition date. The following table summarizes the preliminary determination and recognition of assets acquired and liabilities assumed (in thousands): At Acquisition Date As Reported December 31, 2024 Accounts receivable, including unbilled receivables $ 5,855 Inventories and supplies 6,598 Prepaid expenses and other current assets 408 Property, plant and equipment 55,615 Permits and other intangibles 14,500 Operating lease right-of-use assets 3,615 Other long-term assets 92 Accounts payable (7,752) Accrued expenses and other current liabilities (1,145) Current portion of operating lease liabilities (1,823) Operating lease liabilities, less current portion (1,792) Closure and post-closure liabilities (8,929) Remedial liabilities (2,757) Total identifiable net assets 62,485 Goodwill 6,257 Total purchase price $ 68,742 Other intangible assets acquired include customer relationships and trademarks/trade names and are anticipated to have estimated useful lives of between seven . The excess of the total purchase price, which includes the aggregate cash consideration paid in excess of the fair value of the tangible and intangible assets acquired and liabilities assumed, was recorded as goodwill. The goodwill recognized is attributable to the operating synergies and assembled workforce that the Company expects to realize from the acquisition. Goodwill generated from the acquisition is deductible for tax purposes. The operations included in the Company’s financial statements for the period ended December 31, 2024 , and pro forma revenue and earnings amounts on a combined basis as if this acquisition had been completed on January 1, 2023 are immaterial to the consolidated financial statements of the Company. During 2024, the Company completed the acquisition of three additional privately-owned business for $17.1 million in total cash consideration. The operations were consolidated into the Environmental Services and SKSS segments. The acquisitions of the acquired businesses were not material in 2024 to the consolidated financial statements of the Company. 2023 Acquisition On March 31, 2023, the Company acquired Thompson Industrial Services, LLC (“Thompson Industrial”) for an all-cash purchase price of $110.9 million, net of cash acquired. The operations of Thompson Industrial expand the Environmental Services segment’s industrial service operations in the southeastern region of the United States. The Company finalized the purchase accounting for this acquisition in the first quarter of 2024. The preliminary allocation of the purchase price was based on estimates of the fair value and assets acquired and liabilities assumed as of March 31, 2023. The following table summarizes the preliminary and final determination and recognition of assets acquired and liabilities assumed (in thousands): Preliminary Allocation As Reported December 31, 2023 Measurement Period Adjustments Final Allocation as Reported December, 31, 2024 Accounts receivable, including unbilled receivables $ 25,233 $ (73) $ 25,160 Inventories and supplies 228 — 228 Prepaid expenses and other current assets 1,302 — 1,302 Property, plant and equipment 26,719 — 26,719 Permits and other intangibles 28,900 — 28,900 Operating lease right-of-use assets 4,716 — 4,716 Other long-term assets 72 — 72 Accounts payable (7,185) (55) (7,240) Accrued expenses and other current liabilities (3,200) (90) (3,290) Current portion of operating lease liabilities (1,653) — (1,653) Operating lease liabilities, less current portion (3,063) — (3,063) Other long-term liabilities (560) — (560) Total identifiable net assets 71,509 (218) 71,291 Goodwill 39,346 218 39,564 Total purchase price $ 110,855 $ — $ 110,855 Permits and other intangible assets acquired include customer relationships, trademarks/trade names and non-compete agreements and are anticipated to have estimated useful lives of between five The operations included in the Company’s financial statements for the period ended December 31, 2024 , and pro forma revenue and earnings amounts on a combined basis as if this acquisition had been completed on January 1, 2022 are immaterial to the consolidated financial statements of the Company. 2022 Acquisitions On June 17, 2022, the Company acquired a privately-owned company for an all-cash purchase price of approximately $78.9 million, net of cash acquired. The operations of the newly acquired company expand the SKSS segment’s waste oil collection capabilities and re-refining business throughout the southeastern region of the United States, including the addition of a re-refinery in Georgia. The Company finalized the purchase accounting for this acquisition in the second quarter of 2023. The allocation of the purchase price was based on estimates of the fair value and assets acquired and liabilities assumed as of June 17, 2022. The following table summarizes the final determination and recognition of assets acquired and liabilities assumed (in thousands): Final Allocation Accounts receivable $ 1,089 Inventories and supplies 5,745 Prepaid expenses and other current assets 144 Property, plant and equipment 22,231 Permits and other intangibles 23,500 Operating lease right-of-use assets 585 Other long-term assets 13 Accrued expenses and other current liabilities (3,375) Current portion of operating lease liabilities (186) Operating lease liabilities, less current portion (399) Other long-term liabilities (2,681) Total identifiable net assets 46,666 Goodwill 32,212 Total purchase price $ 78,878 Permits and other intangible assets acquired include supplier relationships, permits, customer relationships and trademarks/trade names and are anticipated to have estimated useful lives of between five The operations included in the Company’s financial statements for the period ended December 31, 2022 and pro forma revenue and earnings amounts on a combined basis as if this acquisition had been completed on January 1, 2022 were not material to the consolidated financial statements of the Company. On December 9, 2022, the Company acquired a privately-owned business for $12.6 million cash consideration. The acquired company expands the SKSS segment’s oil collection operations in the southeastern United States. In connection with this acquisition, goodwill of $2.7 million was recognized. The results of operations for the acquired business were not material in 2022 to the consolidated financial statements of the Company.

DISPOSITION OF BUSINESS

DISPOSITION OF BUSINESS	12 Months Ended
	Dec. 31, 2024
Discontinued Operations and Disposal Groups [Abstract]
DISPOSITION OF BUSINESS	DISPOSITION OF BUSINESS On June 30, 2022, the Company completed the sale of a line of business as part of its continuous focus on divesting certain non-core operations. The divested line of business was previously included within the Environmental Sales & Service reporting unit of the Environmental Services segment. The Company determined that the disposition did not constitute a strategic shift and that the impact on the Company's overall operations and financial results was not material. Accordingly, the operations associated with the disposal were not reported in discontinued operations. The final purchase price, after settling working capital, for the line of business was $18.8 million, of which $1.5 million was held in escrow and received by the Company in equal parts in 2023 and 2024. The gain on sale of $8.9 million, after accounting for the assets sold, liabilities transferred upon sale and transaction costs, was included in gain on sale of business in the Company's consolidated statement of operations for the year ended December 31, 2022.

INVENTORIES AND SUPPLIES

INVENTORIES AND SUPPLIES	12 Months Ended
	Dec. 31, 2024
Inventory Disclosure [Abstract]
INVENTORIES AND SUPPLIES	INVENTORIES AND SUPPLIES Inventories and supplies consisted of the following (in thousands): December 31, 2024 December 31, 2023 Supplies $ 200,905 $ 177,217 Oil and oil related products 152,992 118,600 Solvent and solutions 12,458 11,795 Other 18,302 19,899 Total inventories and supplies $ 384,657 $ 327,511

PROPERTY, PLANT, AND EQUIPMENT

PROPERTY, PLANT, AND EQUIPMENT	12 Months Ended
	Dec. 31, 2024
Property, Plant and Equipment [Abstract]
PROPERTY, PLANT, AND EQUIPMENT	PROPERTY, PLANT AND EQUIPMENT Property, plant and equipment consisted of the following (in thousands): December 31, 2024 December 31, 2023 Land $ 184,191 $ 174,891 Asset retirement costs (non-landfill) 38,705 27,167 Landfill assets 258,138 253,180 Buildings and improvements (1) 719,439 630,525 Vehicles (2) 1,455,530 1,276,567 Equipment (3) 2,600,085 2,388,370 Construction in progress 70,305 213,601 5,326,393 4,964,301 Less - accumulated depreciation and amortization 2,878,452 2,770,983 Total property, plant and equipment, net $ 2,447,941 $ 2,193,318 ___________________________________ (1) Balances inclusive of gross ROU assets classified as finance leases of $8.0 million in both periods. (2) Balances inclusive of gross ROU assets classified as finance leases of $230.5 million and $151.7 million, respectively. (3) Balances inclusive of gross ROU assets classified as finance leases of $9.2 million in both periods. Depreciation expense, inclusive of landfill and finance lease amortization was $346.5 million, $315.5 million and $297.4 million for the years ended December 31, 2024, 2023 and 2022, respectively. The Company recorded $11.2 million, $6.6 million and $3.4 million of capitalized interest in 2024, 2023 and 2022, respectively, mainly due to the construction of the new incinerator in Kimball, Nebraska .

GOODWILL AND OTHER INTANGIBLE A

GOODWILL AND OTHER INTANGIBLE ASSETS	12 Months Ended
	Dec. 31, 2024
Goodwill and Intangible Assets Disclosure [Abstract]
GOODWILL AND OTHER INTANGIBLE ASSETS	GOODWILL AND OTHER INTANGIBLE ASSETS The changes in goodwill for the years ended December 31, 2024 and 2023 were as follows (in thousands): Environmental Services Safety-Kleen Sustainability Solutions Total Balance at January 1, 2023 $ 1,071,846 $ 175,032 $ 1,246,878 Increase from current period acquisitions 39,346 — 39,346 Measurement period adjustments from prior period acquisition — 360 360 Foreign currency translation 821 331 1,152 Balance at December 31, 2023 $ 1,112,013 $ 175,723 $ 1,287,736 Increase from current period acquisitions 186,911 6,457 193,368 Measurement period adjustments from prior period acquisitions 218 — 218 Foreign currency translation (2,938) (1,185) (4,123) Balance at December 31, 2024 $ 1,296,204 $ 180,995 $ 1,477,199 The Company assesses goodwill for impairment on an annual basis as of December 31 or at an interim date when it is more likely than not that events or changes in the business environment (“triggering events”) would reduce the fair value of a reporting unit below its carrying value. The Company did not identify any triggering events in the years presented. Goodwill is also tested for impairment annually. The Company conducted its annual impairment test of goodwill as of December 31, 2024 and determined that no adjustment to the carrying value of goodwill for any reporting unit was then necessary because the fair values of the reporting units exceeded their respective carrying values. The fair value of all reporting units was determined using an income approach based upon estimates of future discounted cash flows. The resulting estimates of fair value were validated through the consideration of other factors such as the fair value of comparable companies to the reporting units and a reconciliation of the sum of all estimated fair values of the reporting units to the Company’s overall market capitalization. In all cases, the estimated fair values of the reporting units significantly exceeded the respective carrying values. Significant judgments and unobservable inputs, categorized as Level 3 in the fair value hierarchy, are inherent in the impairment tests performed and include assumptions about the amount and timing of expected future cash flows, growth rates, and the determination of appropriate discount rates. Level 3 inputs are unobservable inputs for the asset or liability in which there is little, if any, market activity for the asset or liability at the measurement date. The Company believes that the assumptions used in its impairment tests are reasonable, but variations in any of the assumptions may result in different measurements of fair values. The impacts of any adverse business and market conditions which may impact the overall performance of the Company's reporting units will continue to be monitored. If the Company's reporting units do not achieve the financial performance that the Company expects, or if there is a significant prolonged change in demand for the Company's products and services, it is possible that goodwill impairment charges may result. Therefore, there can be no assurance that future events will not result in an impairment of goodwill. As of December 31, 2024 and 2023, the Company's intangible assets consisted of the following (in thousands): December 31, 2024 December 31, 2023 Cost Accumulated Net Cost Accumulated Net Permits $ 191,921 $ 123,939 $ 67,982 $ 191,747 $ 117,556 $ 74,191 Customer and supplier relationships 697,326 256,657 440,669 604,994 258,879 346,115 Other intangible assets 120,316 46,490 73,826 100,068 37,862 62,206 Total amortizable permits and other intangible assets 1,009,563 427,086 582,477 896,809 414,297 482,512 Trademarks and trade names 119,510 — 119,510 120,285 — 120,285 Total permits and other intangible assets $ 1,129,073 $ 427,086 $ 701,987 $ 1,017,094 $ 414,297 $ 602,797 During the periods presented, there were no events or changes in circumstances which would indicate that the carrying values of the Company's asset groups would not be recoverable and thus no impairment charges were recorded . If expectations of future cash flows were to decrease in the future as a result of worse than expected or prolonged periods of depressed activity, future impairments may become evident. Amortization expense of permits, customer and supplier relationships and other intangible assets for the years ended December 31, 2024, 2023 and 2022 were $54.4 million, $50.3 million and $50.2 million, respectively. The expected amortization of the net carrying amount of finite-lived intangible assets at December 31, 2024 was as follows (in thousands): Years ending December 31, Expected 2025 $ 53,335 2026 51,297 2027 49,221 2028 47,916 2029 46,763 Thereafter 333,945 $ 582,477

ACCRUED EXPENSES AND OTHER CURR

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES	12 Months Ended
	Dec. 31, 2024
Payables and Accruals [Abstract]
ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES	ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES Accrued expenses and other current liabilities consisted of the following (in thousands): December 31, 2024 December 31, 2023 Accrued compensation and benefits $ 134,458 $ 113,236 Accrued insurance 112,367 107,658 Accrued interest 33,259 33,857 Accrued income, real estate, sales and other taxes 35,394 44,752 Accrued other 103,967 97,654 $ 419,445 $ 397,157

CLOSURE AND POST-CLOSURE LIABIL

CLOSURE AND POST-CLOSURE LIABILITIES	12 Months Ended
	Dec. 31, 2024
Asset Retirement Obligation Disclosure [Abstract]
CLOSURE AND POST-CLOSURE LIABILITIES	CLOSURE AND POST-CLOSURE LIABILITIES The changes to closure and post-closure liabilities (also referred to as "asset retirement obligations") from January 1, 2023 through December 31, 2024 were as follows (in thousands): Landfill Non-Landfill Total Balance at January 1, 2023 $ 62,251 $ 56,550 $ 118,801 Liabilities assumed in acquisitions — 574 574 Measurement period adjustments from prior period acquisitions — 3,015 3,015 New asset retirement obligations 3,092 — 3,092 Accretion 4,958 4,519 9,477 Changes in estimates recorded to consolidated statement of operations 1,147 53 1,200 Changes in estimates recorded to consolidated balance sheet (3,706) 1,600 (2,106) Environmental expenditures (8,478) (7,206) (15,684) Currency translation and other 179 52 231 Balance at December 31, 2023 59,443 59,157 118,600 Liabilities assumed in acquisitions — 11,421 11,421 New asset retirement obligations 2,118 — 2,118 Accretion 5,069 4,489 9,558 Changes in estimates recorded to consolidated statement of operations 70 (295) (225) Changes in estimates recorded to consolidated balance sheet 4,335 402 4,737 Environmental expenditures (11,210) (4,466) (15,676) Currency translation and other (425) (320) (745) Balance at December 31, 2024 $ 59,400 $ 70,388 $ 129,788 In the year ended December 31, 2024, there were no significant benefits or charges resulting from changes in estimates for closure and post-closure liabilities. In 2024 and 2023, the Company has been executing upon the planned closure activities at the Company’s non-commercial landfill at the Deer Park, Texas incinerator facility after the site reached its permitted capacity, in early 2023. There have been no changes to the estimated closure costs related to this location. Anticipated payments (based on current estimated costs and anticipated timing of necessary regulatory approvals to commence work on closure and post-closure activities) for each of the next five years and thereafter are as follows (in thousands): Years ending December 31, 2025 $ 10,304 2026 14,457 2027 12,485 2028 14,127 2029 3,224 Thereafter 278,762 Undiscounted closure and post-closure liabilities 333,359 Less: Discount at credit-adjusted risk-free rate (119,353) Less: Undiscounted estimated closure and post-closure liabilities relating to airspace not yet consumed (84,218) Present value of closure and post-closure liabilities $ 129,788

REMEDIAL LIABILITIES

REMEDIAL LIABILITIES	12 Months Ended
	Dec. 31, 2024
Environmental Remediation Obligations [Abstract]
REMEDIAL LIABILITIES	REMEDIAL LIABILITIES The changes to remedial liabilities Remedial Remedial Remedial Total Balance at January 1, 2023 $ 1,824 $ 59,749 $ 54,717 $ 116,290 Accretion 89 2,540 1,561 4,190 Changes in estimates recorded to consolidated statement of operations 19 1,713 1,896 3,628 Environmental expenditures (52) (3,840) (9,384) (13,276) Currency translation and other — 115 296 411 Balance at December 31, 2023 1,880 60,277 49,086 111,243 Liabilities assumed in acquisitions — — 5,192 5,192 Accretion 92 2,292 1,514 3,898 Changes in estimates recorded to consolidated statement of operations 29 573 3,762 4,364 Expenditures (53) (6,078) (5,715) (11,846) Currency translation and other — (28) (1,078) (1,106) Balance at December 31, 2024 $ 1,948 $ 57,036 $ 52,761 $ 111,745 In the year ended December 31, 2024, the Company increased its remedial liabilities for an existing Superfund site by $2.9 million related to new information on the ultimate remediation of this site. Anticipated payments at December 31, 2024 (based on current estimated costs and anticipated timing of necessary regulatory approvals to commence work on remedial activities) for each of the next five years and thereafter were as follows (in thousands): Years ending December 31, 2025 $ 10,321 2026 17,391 2027 11,259 2028 10,972 2029 8,745 Thereafter 70,610 Undiscounted remedial liabilities 129,298 Less: Discount at risk free rates (17,553) Total remedial liabilities $ 111,745 The following table presents the Company's estimated remedial liabilities and reasonably possible additional liabilities as of December 31, 2024 disaggregated by facility/site type (in thousands, except percentages): Type of Facility or Site Remedial % of Total Reasonably Possible Additional Liabilities (1) Inactive facilities not used in active conduct of the Company's business, most of which were assumed through prior period acquisitions (25 facilities) $ 56,976 51.0 % $ 10,765 Facilities now used in active conduct of the Company's business (62 facilities, including 24 acquired by the Company through acquisitions in 2024) 46,131 41.3 9,497 Superfund sites (12 sites) 8,638 7.7 1,296 Total $ 111,745 100.0 % $ 21,558 ___________________________________ (1) Amounts represent the high end of the range of management's best estimate of the reasonably possible additional liabilities. The following table presents the Company's estimated remedial liabilities and reasonably possible additional liabilities as of December 31, 2024 disaggregated by facilities/sites which represent at least 5% of the total and with all other facilities/ sites combined (in thousands, except percentages): Location Type of Facility or Site Remedial Liabilities (1) % of Total Reasonably Possible Additional Liabilities (2) Baton Rouge, LA Closed incinerator and landfill $ 25,578 22.9 % $ 4,303 Bridgeport, NJ Closed incinerator 17,417 15.6 3,254 Mercier, Quebec Idled incinerator 10,826 9.7 1,631 Linden, NJ Operating solvent recycling center 9,434 8.4 2,148 Various All other incinerators, landfills, wastewater treatment facilities and service centers (83 facilities, including 24 acquired by the Company through acquisitions in 2024) 39,852 35.7 8,926 Various Superfund sites (each representing less than 5% of total liabilities) (12 sites) 8,638 7.7 1,296 Total $ 111,745 100.0 % $ 21,558 _________________________________ (1) $23.3 million of the $111.7 million remedial liabilities include estimates related to the legal and administrative proceedings discussed in Note 18, "Commitments and Contingencies." (2) Amounts represent the high end of the range of management's best estimate of the reasonably possible additional liabilities. Revisions to remediation reserve requirements may result in upward or downward adjustments to income from operations in any given period. The Company believes that its extensive experience in the environmental services business, as well as its involvement with a large number of sites, provides a reasonable basis for estimating its aggregate liability. It is possible, however, that future changes in available technology, regulatory or enforcement developments, the results of environmental studies or other factors could necessitate the recording of additional liabilities or the revision of currently recorded liabilities that could be material. Since the Company's satisfaction of the liabilities will occur over many years, the Company cannot reasonably predict the nature or extent of possible future events or the impact that those events, if any, might have on the current estimates of remedial liabilities.

FINANCING ARRANGEMENTS

FINANCING ARRANGEMENTS	12 Months Ended
	Dec. 31, 2024
Debt Disclosure [Abstract]
FINANCING ARRANGEMENTS	FINANCING ARRANGEMENTS Long-term Debt The following table is a summary of the Company's long-term debt (in thousands): December 31, 2024 December 31, 2023 Current Portion of Long-Term Debt: Secured senior term loans $ 15,102 $ 10,000 Long-Term Debt: Secured senior term loans due October 8, 2028 1,449,796 970,000 Unsecured senior notes, at 4.875%, due July 15, 2027 ("2027 Notes") 545,000 545,000 Unsecured senior notes, at 5.125%, due July 15, 2029 ("2029 Notes") 300,000 300,000 Unsecured senior notes, at 6.375%, due February 1, 2031 ("2031 Notes") 500,000 500,000 Long-term debt, at par 2,794,796 2,315,000 Unamortized debt issuance costs and discount, net (23,679) (23,283) Long-term debt, at carrying value $ 2,771,117 $ 2,291,717 As of December 31, 2024 and 2023, the estimated fair value of the Company’s outstanding long-term debt, including the current portion, was $2.8 billion and $2.3 billion, respectively. The Company’s estimates of fair value of its long-term debt, including the current portion, are based on quoted market prices or other available market data which are considered Level 2 measures according to the fair value hierarchy. Level 2 utilizes quoted market prices in markets that are not active, broker or dealer quotation or alternative pricing sources with reasonable levels of price transparency for similar assets and liabilities. The sections below will outline the key terms of the outstanding debt, including any changes occurring during the period: Secured Senior Term Loans As of December 31, 2024, the Company had an aggregate principal amount outstanding of $1,464.9 million under the Sixth Amendment to the Company's existing Credit Agreement dated as of June 30, 2017 (the "Term Loan Agreement"). As of December 31, 2023, the Company had an aggregate principal amount outstanding of $980.0 million under Fourth Amendment to the Term Loan Agreement. On March 22, 2024, the Term Loan Agreement was amended (the “Fifth Amendment”), to provide for the incurrence of additional term loans (the “2024 Incremental Term Loans”) under the Term Loan Agreement in the aggregate principal amount of $500.0 million. Proceeds from the issuance of the 2024 Incremental Term Loans were $491.1 million after debt discount and debt issuance costs, and were used to fund the acquisition of HEPACO, with the excess increasing the Company’s cash balances. The 2024 Incremental Term Loans are in addition to the aggregate of $980.0 million of term loans (the “Existing Term Loans”) which were outstanding prior to the issuance of the 2024 Incremental Term Loans. The total amount outstanding under the Term Loans as December 31, 2024 will mature on October 8, 2028, and may be prepaid at any time without premium or penalty other than customary breakage costs. Interest under the Term Loan Agreement is paid monthly. On October 8, 2024, the Company entered into the Sixth Amendment to the Term Loan Agreement (the “Sixth Amendment”). The Sixth Amendment (i) eliminated the Term SOFR adjustment of 0.11448% per annum and (ii) reset the six month soft call period for a repricing of the 2028 Term Loans. Under the Sixth Amendment, the applicable interest rate margins for the Term Loans is either 1.75% for Term SOFR borrowings or 0.75% for base rate borrowings, at the Company’s election. The Term Loans may be prepaid at any time without premium or penalty other than customary breakage costs or if the Company engages in certain repricing transactions before April 8, 2025, in which event a 1.0% prepayment premium would be due. The Term SOFR Rate is subject to a floor of 0.00% and the Base Rate is subject to a floor of 1.00%. The Term Loan Agreement provides for Term SOFR adjustments for other interest periods; however, the Company elects one-month Term SOFR for interest payments on that debt resulting in total interest on the 2028 Term Loans of one-month Term SOFR plus 1.75%. Prior to the Sixth Amendment on October 8, 2024, the margin on the Term Loans also included a credit spread adjustment of 0.11448% for all one-month Term SOFR payments. Additionally, prior to December 27, 2023, the interest rate margins for the Term Loans were 0.25% higher. The rates were lowered by 25 basis points through the Fourth Amendment of the Term Loans. Each of these amendments resulted in minimal amounts being recognized as a loss on the early extinguishment of debt in the Company’s Consolidated Statement of Operations. The Company's obligations under the Term Loan Agreement are guaranteed by all of the Company's domestic restricted subsidiaries and secured by the liens on substantially all of the assets of the Company and the guarantors. Unsecured Senior Notes On July 2, 2019, the Company completed a private placement of $545.0 million aggregate principal amount of 2027 Notes and $300.0 million aggregate principal amount of 2029 Notes. The 2027 Notes will mature on July 15, 2027 and the 2029 Notes will mature on July 15, 2029. Interest payments on the 2027 and 2029 Notes are paid semiannually on January 15 and July 15. On January 24, 2023, the Company completed a private placement of $500.0 million aggregate principal amount of 2031 Notes which will mature on February 1, 2031 (collectively referred to with the 2027 Notes and 2029 Notes as the "Notes"). The proceeds from this were used toward the repayment of the Term Loans outstanding at the time. The interest rate on the 2031 Notes is paid semiannually on February 1 and August 1 of each year and commenced on August 1, 2023. The tables below depict the redemption prices of the Notes if redeemed during the twelve-month period commencing on the dates below, plus accrued and unpaid interest, if any, to but not including the redemption date. 2027 Notes Percentage July 15, 2024 and thereafter 100.000 % 2029 Notes Percentage July 15, 2024 102.563 % July 15, 2025 101.281 % July 15, 2026 and thereafter 100.000 % 2031 Notes Percentage February 1, 2026 103.188 % February 1, 2027 101.594 % February 1, 2028 and thereafter 100.000 % The Company may also redeem all or any portion of the 2031 Notes prior to February 1, 2026, at a redemption price equal to 100% of the principal amount redeemed plus a make whole premium as of the date of redemption including accrued and unpaid interest, if any, up to but not including the date of redemption. Additionally, subject to certain limitations, prior to February 1, 2026, the Company may use net cash proceeds of one or more equity offerings to redeem up to 40% in aggregate principal of the 2031 Notes at a redemption price equal to 106.375% of the principal amount thereof plus accrued and unpaid interest thereon, if any, up to but not including the date of redemption. The Notes and the related indentures contain various customary non-financial covenants and are guaranteed by substantially all of the Company’s current and future domestic subsidiaries. The Notes are effectively subordinated to the Company's Term Loans, revolving credit facility and finance lease obligations to the extent of the value of the assets securing such secured indebtedness. The Notes are also effectively subordinated to all indebtedness and other liabilities of the Company's subsidiaries that are not guarantors of the Notes. Revolving Credit Facility. On June 28, 2024, 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., as administrative agent, and the lenders party to the Amended Credit Agreement. The Amended Credit Agreement amended and restated the sixth amended and restated credit agreement dated October 28, 2020 (the “Prior Credit Agreement”). Under the Amended Credit Agreement, the Company has the right to obtain revolving loans and letters of credit for a combined maximum of up to $550.0 million (with a sub-limit of $250.0 million for letters of credit) and the Canadian Borrower has the right to obtain revolving loans and letters of credit for a combined maximum of up to $50.0 million. The maximum borrowing amount of $600.0 million under the Amended Credit Agreement is increased from $400.0 million under the Prior Credit Agreement. Borrowings by the Company under the Amended Credit Agreement will bear interest at the Company’s option, at either (i) the sum of Term SOFR plus a SOFR Adjustment of 0.1% plus 1.5% per annum, or (ii) the U.S. Base Rate, plus 0.5% per annum, and borrowings by the Canadian Borrower will bear interest, at the Company’s option, at either (i) the sum of Term CORRA plus a Term CORRA adjustment of either 0.29547% or 0.32138% for the one or three month interest period respectively, plus 1.5% per annum, (ii) the Canadian Prime Rate, plus 0.5% per annum, or (iii) the Canadian Base Rate, plus 0.5% per annum, as those terms are defined in the Amended Credit Agreement. Other terms under the Amended Credit Agreement are substantially the same as under the Prior Credit Agreement. Subject to certain customary conditions, the facility will expire on June 28, 2029. On April 28, 2023, the Company entered into an amendment to the credit agreement for the revolving credit facility. As amended, the terms of the agreement are substantially the same as prior to the amendment except for certain updates required to transition the agreement to include a defined LIBOR successor rate. Under the amended agreement, borrowings under the revolving credit facility will bear interest at a rate, at the Company’s option, of either (i) “Term SOFR” (as defined in the amended agreement) plus an applicable margin ranging from 1.50% to 1.75% per annum based primarily on the level of the Company’s average liquidity for the most recent 30 day period or (ii) BofA’s base rate plus an applicable margin ranging from 0.50% to 0.75% per annum based primarily on such average liquidity. The amended agreement also continues to provide (i) for an unused line fee payable to the lenders, calculated on the then unused portion of the lenders’ $400.0 million maximum commitments, ranging from 0.25% to 0.375% per annum of the unused commitment, and (ii) for outstanding letters of credit, a fee payable to the lenders equal to the then applicable margin for Term SOFR borrowings described above, and to the issuing banks a standard fronting fee and customary fees and charges in connection with all amendments, extensions, draws and other actions with respect to letters of credit. Letters of credit issued under the revolving credit facility are utilized primarily as security for the Company's insurance program that includes casualty and financial assurance. The Company’s obligations under the revolving credit facility (including revolving loans and reimbursement obligations for outstanding letters of credit) are guaranteed by substantially all of the Company’s U.S. subsidiaries and secured by a first lien on the Company’s and its U.S. subsidiaries’ accounts receivable. The Canadian Borrower’s obligations under the facility are guaranteed by substantially all of the Company’s Canadian subsidiaries and secured by a first lien on the accounts receivable of the Canadian subsidiaries. As of December 31, 2024, the revolving credit facility had no outstanding loan balances, $470.0 million available to borrow and outstanding letters of credit of $130.0 million. The Company also had no outstanding loan balances as of December 31, 2023. Cash Flow Hedges The Company's strategy to hedge against fluctuations in variable interest rates involves entering into interest rate derivative agreements. 2022 Swap Arrangement In 2022, the Company entered into interest rate swap agreements with a notional amount of $600.0 million ("2022 Swaps") to effectively fix the interest rate on $600.0 million principal of the outstanding 2028 Term Loans. Under the terms of the 2022 Swaps' agreements, the Company receives interest based upon the variable rates on the 2028 Term Loans and pays a fixed amount of interest. The fixed rate on these instruments was 0.931% through June 30, 2023 which, together with the original 2.00% interest rate margin for the 2028 Term Loans, resulted in an effective annual interest rate of approximately 2.931%. The fixed rate on these instruments increased to 1.965% on July 1, 2023 and the variable rate became linked to Term SOFR to mirror the variable interest payments for the 2028 Term Loans. Including the 2.00% interest rate margin for borrowings on the 2028 Term Loans and the 0.11448% SOFR adjustment per the 2028 Term Loans, in effect at the time of this change, beginning July 1, 2023, the effective annual interest rate of this $600.0 million increased to 4.07898%. With the Fourth Amendment on December 27, 2023 the margin on the 2028 Term Loans decreased from 2.00% to 1.75%, and the effective annual interest rate on the swapped portion of 2028 Term Loans outstanding decreased to 3.82898%. With the Sixth Amendment on October 8, 2024 the SOFR adjustment was eliminated, and the effective annual interest rate on the swapped portion of 2028 Term Loans outstanding decreased to 3.71450%. The changes to the 2028 term loans described herein are discussed in the Secured Senior Term Loans section above. The 2022 Swaps expire September 30, 2027. 2018 Swap Arrangement In 2018, the Company effectively fixed the interest rate on $350.0 million principal of the previously outstanding 2024 Term Loans by entering into interest rate swap agreements with a notional amount of $350.0 million ("2018 Swaps"). On January 24, 2023, concurrently with the repayment of the 2024 Term Loans, the Company received a settlement payment of $8.3 million from the 2018 Swap counterparties. As a result of the settlement, the Company also reclassified the amounts previously deferred in accumulated other comprehensive loss and recognized a settlement gain of $8.3 million in interest expense in 2023. At the inception of these instruments, the Company designated both the 2018 Swaps and the 2022 Swaps (collectively referred to as the “Swaps”) as cash flow hedges. As of December 31, 2024 the Company recorded a derivative asset with a fair value of $32.4 million. The balance in the derivative asset as of December 31, 2023 was $35.5 million, which included both of the Swaps. The balance in both periods is comprised only of the 2022 Swaps, given that the 2018 Swaps were settled in early 2023, as noted above. No ineffectiveness has been identified on the Swaps and, therefore the change in fair value is recorded in stockholders' equity as a component of accumulated other comprehensive loss. Amounts are reclassified from accumulated other comprehensive loss into interest expense on the consolidated statement of operations in the same period or periods during which the hedged transactions affect earnings.

INCOME TAXES

INCOME TAXES	12 Months Ended
	Dec. 31, 2024
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES The domestic and foreign components of income before provision for income taxes were as follows (in thousands): For the years ended December 31, 2024 2023 2022 Domestic $ 444,118 $ 401,912 $ 406,206 Foreign 89,325 101,367 131,792 Total $ 533,443 $ 503,279 $ 537,998 The provision for income taxes consisted of the following (in thousands, except percentages): For the years ended December 31, 2024 2023 2022 Current: Federal $ 68,321 $ 64,164 $ 52,237 State 27,649 25,496 26,980 Foreign 16,737 23,078 29,488 112,707 112,738 108,705 Deferred Federal 20,669 18,251 32,199 State (4,415) (9,049) (2,432) Foreign 2,183 3,483 (12,218) 18,437 12,685 17,549 Provision for income taxes $ 131,144 $ 125,423 $ 126,254 Effective tax rate 24.6% 24.9% 23.5% The Company's effective income tax rate varied from the amount computed using the statutory federal income tax rate of 21% as follows (in thousands): For the years ended December 31, 2024 2023 2022 Tax expense at U.S. statutory rate $ 112,023 $ 105,689 $ 112,980 State income taxes, net of federal benefit 18,555 18,067 19,831 Foreign rate differential 3,965 4,213 6,196 Valuation allowance (6,485) (7,699) (18,769) Uncertain tax position interest and penalties (1,773) (7) (2,454) Tax credits 2,694 1,653 2,768 Non-deductible compensation 2,211 2,898 2,754 Other (46) 609 2,948 Provision for income taxes $ 131,144 $ 125,423 $ 126,254 In 2024, $4.1 million in fully reserved for foreign tax credits expired. In the table above, the expiration is included in the tax credits line and the write off of the valuation allowance is contributing to the valuation allowance benefit, however the foreign tax credit expiration and associated valuation allowance write-off had no net impact to the provision for income tax. The remaining valuation allowance benefit in 2024 is the result of profitable earnings at certain Canadian entities which utilized previously reserved for operating losses. The valuation allowance benefits recognized in 2023 are predominately the result of cumulative profitable earnings at certain US entities with historical state operating losses. As of December 31, 2023, management determined that there is sufficient positive evidence to conclude that it is more likely than not that additional deferred taxes associated with these State net operating losses are realizable. Therefore the valuation allowance was reduced accordingly. The valuation allowance benefits recognized in 2022 were the result of cumulative profitable earnings at certain Canadian entities with historic operating losses. The 2022 earnings were sufficient to utilize substantially all of the net operating losses, and as of December 31, 2022, the Company released any remaining valuation allowances associated with these entities, which were nominal. The components of the total net deferred tax assets and liabilities as of December 31, 2024 and 2023 were as follows (in thousands): 2024 2023 Deferred tax assets: Provision for doubtful accounts $ 14,808 $ 10,882 Closure, post-closure and remedial liabilities 32,189 31,944 Operating lease liabilities 60,929 46,784 Accrued expenses 14,749 14,963 Accrued compensation and benefits 16,876 15,058 Net operating loss carryforwards (1) 48,331 39,042 Excess business interest (2) 22,078 — Tax credit carryforwards 2,619 6,531 Stock-based compensation 4,877 3,516 Other 2,565 4,843 Total deferred tax assets 220,021 173,563 Deferred tax liabilities: Property, plant and equipment (311,546) (284,997) Operating lease right-of-use assets (59,999) (46,584) Interest rate swap asset (8,748) (9,576) Permits and other intangible assets (158,905) (130,391) Prepaid expenses (10,881) (12,372) Total deferred tax liabilities (550,079) (483,920) Total net deferred tax liability before valuation allowance (330,058) (310,357) Less valuation allowance (27,232) (35,272) Net deferred tax liabilities $ (357,290) $ (345,629) ___________________________________ (1) As of December 31, 2024, the net operating loss carryforwards included (i) gross state net operating loss carryforwards of $290.7 million which will begin to expire in 2025, (ii) gross federal net operating loss carryforwards of $79.3 million which will begin to expire in 2025 and (iii) gross foreign net operating loss carryforwards of $64.3 million which will begin to expire in 2025. The increase in the state and federal net operating loss carryforward from the prior year is predominately due to assets acquired in the HEPACO transaction. See Note 4, "Business Combinations" for more information on the related transaction. (2) Deferred tax asset acquired in the HEPACO transaction. See Note 4, "Business Combinations" for more information on the related transaction. The Company previously recognized the U.S. federal income taxes related to the operations in Canada and has not accrued for any remaining undistributed foreign earnings. These amounts continue to be indefinitely reinvested. The amount of tax associated with those unrepatriated earnings is not expected to be material. A valuation allowance is required to be established when, based on an evaluation of available evidence, it is more likely than not that some portion or all of the deferred tax assets will not be realized. The components of the total valuation allowance as of December 31, 2024 and 2023 were as follows (in thousands): 2024 2023 Allowance related to: Foreign tax credits $ 346 $ 4,422 Federal net operating losses 3,783 3,783 State net operating loss carryforwards 4,734 4,809 Foreign net operating loss carryforwards 14,543 17,464 Deferred tax assets of a Canadian subsidiary 3,521 4,489 Realized and unrealized capital losses 305 305 Total valuation allowance $ 27,232 $ 35,272 The Company files U.S. federal income tax returns as well as income tax returns in various states and foreign jurisdictions. The Company may be subject to examination by the Internal Revenue Service for calendar years 2018 through 2022. The Company may be subject to examination by Canadian federal and provincial authorities for calendar years 2016 through 2022 and by state and local revenue authorities for calendar years 2017 through 2022. The Company has ongoing U.S., state and local jurisdictional audits, as well as Canadian federal and provincial audits, all of which the Company believes will not result in material liabilities. The Company has not identified any material uncertain tax positions in the periods presented.

EARNINGS PER SHARE

EARNINGS PER SHARE	12 Months Ended
	Dec. 31, 2024
Earnings Per Share [Abstract]
EARNINGS PER SHARE	EARNINGS PER SHARE The computation of basic earnings per share (EPS) is based on the weighted-average number of our common shares outstanding. The computation of diluted EPS is based on the weighted-average number of our common shares outstanding and potential dilutive common shares during the period as determined by using the treasury stock method. The following are computations of basic and diluted earnings per share (in thousands, except for per share amounts): For the years ended December 31, 2024 2023 2022 Numerator for basic and diluted earnings per share: Net income $ 402,299 $ 377,856 $ 411,744 Denominator: Weighted-average shares outstanding, basic 53,902 54,071 54,223 Dilutive impact of equity awards 297 311 264 Weighted-average shares outstanding, diluted 54,199 54,382 54,487 Basic earnings per share $ 7.46 $ 6.99 $ 7.59 Diluted earnings per share $ 7.42 $ 6.95 $ 7.56 In the table above, potentially dilutive shares outstanding include the dilutive effect of unvested restricted stock awards. Shares under the Employee Stock Purchase Plan (“ESPP”) which commenced in 2024 were issued on the last day of the year and therefore are included in the weighted-average shares outstanding when issued. Potentially dilutive shares whose effect would have been antidilutive have been excluded from the computation of diluted earnings per share. The Company included all outstanding performance awards and restricted stock awards in the calculation of diluted earnings per share except as shown in the table below (in thousands): For the years ended December 31, 2024 2023 2022 Antidilutive restricted stock awards 10 12 10 Performance stock awards for which performance criteria was not attained at reporting date 39 89 —

STOCKHOLDERS' EQUITY

STOCKHOLDERS' EQUITY	12 Months Ended
	Dec. 31, 2024
Equity [Abstract]
STOCKHOLDERS' EQUITY	STOCKHOLDERS' EQUITY The Company’s Board of Directors has authorized the repurchase of up to $1.1 billion of the Company’s common stock. The repurchase program authorizes the Company to purchase the Company's common stock on the open market or in privately negotiated transactions periodically in a manner that complies with applicable U.S. securities laws. The number of shares purchased and the timing of the purchases have depended and will depend on a number of factors including share price, cash required for future business plans, trading volume and other conditions. The Company has no obligation to repurchase stock under this program and may suspend or terminate the repurchase program at any time. During the years ended December 31, 2024, 2023 and 2022, the Company repurchased and retired a total of 0.2 million, 0.3 million and 0.5 million shares, respectively, of the Company's common stock for total costs of $55.0 million, $51.2 million and $50.2 million, respectively. As of December 31, 2024, an additional $499.1 million remained available to repurchase shares under this program.

ACCUMULATED OTHER COMPREHENSIVE

ACCUMULATED OTHER COMPREHENSIVE LOSS	12 Months Ended
	Dec. 31, 2024
Equity [Abstract]
ACCUMULATED OTHER COMPREHENSIVE LOSS	ACCUMULATED OTHER COMPREHENSIVE LOSS The changes in accumulated other comprehensive loss by component and related tax impacts for the years ended December 31, 2024, 2023 and 2022 were as follows (in thousands): Foreign Currency Translation Adjustments Unrealized (Loss) Gain on Available-For-Sale Securities Unrealized (Loss) Gain on Fair Value of Interest Rate Hedges Unrealized Loss on Pension Total Balance at January 1, 2022 $ (177,824) $ (150) $ (17,383) $ (655) $ (196,012) Other comprehensive (loss) income before reclassifications (31,515) (523) 78,711 415 47,088 Amounts reclassified out of accumulated other comprehensive loss — — (683) — (683) Tax benefit (provision) — 110 (17,587) (97) (17,574) Other comprehensive (loss) income (31,515) (413) 60,441 318 28,831 Balance at December 31, 2022 (209,339) (563) 43,058 (337) (167,181) Other comprehensive income (loss) before reclassifications 9,000 708 5,094 (741) 14,061 Amounts reclassified out of accumulated other comprehensive loss — — (30,273) — (30,273) Tax (provision) benefit — (149) 8,012 191 8,054 Other comprehensive income (loss) 9,000 559 (17,167) (550) (8,158) Balance at December 31, 2023 (200,339) (4) 25,891 (887) (175,339) Other comprehensive (loss) income before reclassifications (36,363) 47 16,515 339 (19,462) Amounts reclassified out of accumulated other comprehensive loss — — (19,582) — (19,582) Tax (provision) benefit — (10) 828 (70) 748 Other comprehensive (loss) income (36,363) 37 (2,239) 269 (38,296) Balance at December 31, 2024 $ (236,702) $ 33 $ 23,652 $ (618) $ (213,635) The amounts realized in the consolidated statements of operations during the years ended December 31, 2024, 2023 and 2022 which were reclassified out of accumulated other comprehensive loss were as follows (in thousands): For the years ended December 31, Other Comprehensive Loss Component 2024 2023 2022 Location Unrealized (Loss) Gain on Fair Value of Interest Rate Hedges (1) $ 19,582 $ 30,273 $ 683 Interest expense, net of interest income ___________________________________ (1) For the year ended December 31, 2023, the balance is inclusive of an $8.3 million gain realized in connection with the settlement of certain interest rate swaps. For more information on this transaction, see Note 12, "Financing Arrangements."

STOCK-BASED COMPENSATION

STOCK-BASED COMPENSATION	12 Months Ended
	Dec. 31, 2024
Share-Based Payment Arrangement [Abstract]
STOCK-BASED COMPENSATION	STOCK-BASED COMPENSATION Stock-based Compensation In 2020, the Company's shareholders approved the Clean Harbors, Inc. 2020 Stock Incentive Plan (the "2020 Plan"). The 2020 Plan provides for future awards of up to 2.5 million shares of the Company’s common stock (subject to certain anti-dilution adjustments) in the form of stock options, stock appreciation rights, restricted stock, restricted stock units and other stock-based awards. The 2020 Plan is administered by the Compensation and Human Capital Committee of the Company’s Board of Directors. The Company grants restricted stock awards and performance stock awards. The restricted stock awards generally vest over three Total stock-based compensation cost recognized for the years ended December 31, 2024, 2023 and 2022 was $28.0 million, $20.7 million and $26.8 million, respectively. The total income tax benefit recognized in the consolidated statements of operations from stock-based compensation expense was $5.1 million, $3.5 million and $5.0 million for the years ended December 31, 2024, 2023 and 2022, respectively. Restricted Stock Awards The following table summarizes information about restricted stock awards for the year ended December 31, 2024: Restricted Stock Number of Weighted Average Balance at January 1, 2024 414,623 $ 114.02 Granted 148,941 189.39 Vested (150,097) 107.23 Forfeited (25,507) 142.80 Balance at December 31, 2024 387,960 $ 143.69 As of December 31, 2024, there was $39.5 million of total unrecognized compensation cost arising from restricted stock awards. This cost is expected to be recognized over a weighted average period of 2.7 years. The total fair value of restricted stock vested during 2024, 2023 and 2022 was $31.9 million, $26.5 million and $16.4 million, respectively. Performance Stock Awards The following table summarizes information about performance stock awards for the year ended December 31, 2024: Performance Stock Number of Weighted Average Balance at January 1, 2024 181,284 $ 114.10 Granted 79,738 173.45 Vested (38,882) 104.69 Forfeited (62,944) 128.99 Balance at December 31, 2024 159,196 $ 102.09 As of December 31, 2024, there was $5.7 million of total unrecognized compensation cost arising from unvested performance stock awards deemed probable of vesting. This cost is expected to be recognized over a weighted average period of 2.4 years. The total fair value of performance awards vested during 2024, 2023 and 2022 was $8.6 million, $17.0 million and $11.1 million, respectively. Employee Stock Purchase Plan On May 22, 2024, the Company’s shareholders approved the Clean Harbors Employee Stock Purchase Plan (the “ESPP”). The ESPP provides a means for eligible employees of the Company to authorize after-tax payroll deductions on a voluntary basis to be used for the periodic purchase of the Company's common stock at a 10% discount to its fair market value. The purchase price paid by the employees will be 90% of the lower of the closing price of the Company's common stock on (i) the first trading day of the offering period or (ii) the last trading day of the offering period. A total of 500,000 shares of common stock are reserved for issuance under the ESPP. As of December 31, 2024, 15,435 shares have been issued under the plan. For the year ended December 31, 2024 total stock-based compensation cost recognized for the ESPP was $0.7 million.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	12 Months Ended
	Dec. 31, 2024
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES The Company and its subsidiaries are subject to legal proceedings and claims arising in the ordinary course of business. Actions filed against the Company arise from commercial and employment-related claims including alleged class actions related to sales practices and wage and hour claims. The plaintiffs in these actions may be seeking damages or injunctive relief or both. These actions are in various jurisdictions and stages of proceedings, and some are covered in part by insurance. In addition, the Company’s waste management services operations are regulated by federal, state, provincial and local laws enacted to regulate discharge of materials into the environment, remediation of contaminated soil and groundwater or otherwise protect the environment. This ongoing regulation results in the Company frequently becoming a party to legal or administrative proceedings involving all levels of government authorities and other interested parties. The issues involved in such proceedings generally relate to alleged violations of existing permits and licenses or alleged responsibility under federal or state Superfund laws to remediate contamination at properties owned either by the Company or by other parties (“third-party sites”) to which either the Company or the prior owners of certain of the Company’s facilities shipped waste. At December 31, 2024 and 2023, the Company had recorded reserves of $29.8 million and $32.4 million, respectively, for actual or probable liabilities related to the legal and administrative proceedings in which the Company was then involved, the principal of which are described below. As of December 31, 2024 and 2023, the $29.8 million and $32.4 million, respectively, of reserves consisted of (i) $23.3 million and $25.0 million, respectively, related to pending legal or administrative proceedings, including Superfund liabilities, which were included in remedial liabilities on the consolidated balance sheets, and (ii) $6.5 million and $7.4 million, respectively, related to federal, state and provincial enforcement actions as well as legal claims, which were included in accrued expenses on the consolidated balance sheets. In management's opinion, it is not reasonably possible that the potential liability beyond what has been recorded, if any, that may result from these actions, either individually or collectively, will have a material effect on the Company's financial position, results of operations or cash flows. The Company periodically adjusts the aggregate amount of these reserves when actual or probable liabilities are paid or otherwise discharged, new claims arise, or additional relevant information about existing or probable claims becomes available. Legal or Administrative Proceedings As of December 31, 2024, the principal legal and administrative proceedings in which the Company was involved, or which had been terminated during 2024, relate to Safety-Kleen product liability cases and Superfund proceedings. Safety-Kleen Product Liability Cases: Safety-Kleen, Inc. ("Safety-Kleen"), which is a legal entity acquired by the Company in 2012, has been named as a defendant in certain product liability cases that are currently pending in various courts and jurisdictions throughout the United States. As of December 31, 2024, there were approximately 68 proceedings (excluding cases which have been settled but not formally dismissed) wherein persons claim personal injury resulting from the use of Safety-Kleen's parts cleaning equipment or cleaning products. These proceedings typically involve allegations that the solvent used in Safety-Kleen's parts cleaning equipment contains contaminants and/or that Safety-Kleen's recycling process does not effectively remove the contaminants that become entrained in the solvent during their use. In addition, certain claimants assert that Safety-Kleen failed to warn adequately the product user of potential risks, including a historic failure to warn that solvent contains trace amounts of toxic or hazardous substances such as benzene. The Company maintains insurance that it believes will provide coverage for these product liability claims (over amounts accrued for self-insured retentions and deductibles in certain limited cases), except for punitive damages to the extent not insurable under state law or excluded from insurance coverage. The Company historically has vigorously defended, and intends to continue to vigorously defend, itself and the safety of its products against all of these claims. Such matters are subject to many uncertainties and outcomes are not predictable with assurance. Consequently, the Company is unable to ascertain the ultimate aggregate amount of monetary liability or financial impact with respect to these matters as of December 31, 2024. From January 1, 2024 to December 31, 2024, 18 product liability claims were settled or dismissed. Due to the nature of these claims and the related insurance, the Company did not incur any expense as insurance provided coverage in full for all such claims. Safety-Kleen may be named in similar, additional lawsuits in the future, including claims for which insurance coverage may not be available. Superfund Proceedings: The Company has been notified that either the Company (which, since December 28, 2012, has included Safety-Kleen) or the prior owners of certain of the Company's facilities for which the Company may have certain indemnification obligations have been identified as PRPs or potential PRPs in connection with 131 sites which are subject to or are proposed to become subject to proceedings under federal or state Superfund laws. Of the 131 Superfund related sites, six involve facilities that are now owned or leased by the Company and 125 involve third-party sites to which either the Company or the prior owners of certain of the Company’s facilities shipped waste. Of the 125 third-party sites, 30 are now settled, 12 are currently requiring expenditures on remediation and 83 are not currently requiring expenditures on remediation. In connection with each site, the Company has estimated the extent, if any, to which it may be subject, either directly or as a result of any indemnification obligations, for cleanup and remediation costs, related legal and consulting costs associated with PRP investigations, settlements and related legal and administrative proceedings. The amount of such actual and potential liability is inherently difficult to estimate because of, among other relevant factors, uncertainties as to the legal liability (if any) of the Company or the prior owners of certain of the Company's facilities to contribute a portion of the cleanup costs, the assumptions that must be made in calculating the estimated cost and timing of remediation, the identification of other PRPs and their respective capability and obligation to contribute to remediation efforts and the existence and legal standing of indemnification agreements (if any) with prior owners, which may either benefit the Company or subject the Company to potential indemnification obligations. The Company believes its potential monetary liability could exceed $1.0 million at three of the 131 Superfund related sites. Of the 125 third-party sites at which the Company has been notified it is a PRP or potential PRP or may have indemnification obligations, the Company has indemnification agreements at a total of 17 sites. These agreements indemnify the Company (which now includes Safety-Kleen) with respect to any liability at the 17 sites for waste disposed prior to the Company's (or Safety-Kleen's) acquisition of the former subsidiaries of Waste Management and McKesson which had shipped waste to those sites. Accordingly, the indemnifying parties are paying all costs of defending those subsidiaries in those 17 cases, including legal fees and settlement costs. However, there can be no guarantee that the Company's ultimate liabilities for those sites will not exceed the amount recorded or that indemnities applicable to any of these sites will be available to pay all or a portion of related costs. Except for those indemnification agreements discussed, the Company does not have an indemnity agreement with respect to any of the 125 third-party sites discussed above. Federal, State and Provincial Enforcement Actions From time to time, the Company pays fines or penalties in regulatory proceedings relating primarily to waste treatment, storage or disposal facilities. As of December 31, 2024, there were two proceedings for which the Company believes it is possible that the sanctions could equal or exceed $1.0 million. The Company believes that the fines or other penalties in this or any of the other regulatory proceedings will, individually or in the aggregate, not have a material effect on its financial condition, results of operations or cash flows. Self-Insurance Liabilities Under the Company's insurance programs, coverage is obtained for catastrophic exposures, as well as those risks required to be insured by law or contract. The Company's policy is to retain a significant portion of certain expected losses related to workers' compensation, employee medical, comprehensive general liability and vehicle liability. A portion of these self-insured liabilities are managed through its wholly-owned captive insurance subsidiary. Provisions for losses expected under these programs are recorded based upon the Company's estimates of the aggregate liability for claims. The current deductible per participant per year for the employee medical insurance policy is $2.0 million. The current deductible per occurrence for workers' compensation is $1.0 million, general liability is $2.0 million and vehicle liability is $2.0 million. The retention per claim for the environmental impairment policy is $1.0 million. At December 31, 2024 and 2023, the Company had accrued $83.7 million and $82.7 million, respectively, for its self-insurance liabilities (exclusive of employee medical insurance) using a risk-free discount rate of 4.14% and 4.86%, respectively. Anticipated payments for contingencies related to workers' compensation, comprehensive general liability and vehicle liability related claims at December 31, 2024 for each of the next five years and thereafter were as follows (in thousands): Years ending December 31, 2025 $ 25,855 2026 21,083 2027 16,622 2028 11,720 2029 4,692 Thereafter 14,074 Undiscounted self-insurance liabilities 94,046 Less: Discount (10,374) Total self-insurance liabilities (included in accrued expenses and other current liabilities) $ 83,672

LEASES

LEASES	12 Months Ended
	Dec. 31, 2024
Leases [Abstract]
LEASES	LEASES The Company’s lease portfolio is predominately operating leases for real estate, vehicles and industrial equipment utilized in operations and rail cars. The Company presents operating lease balances separately on the consolidated balance sheets. The Company's finance leases relate to vehicles, rail cars and certain real estate. The following table presents the Company's finance lease balances and their classification on the consolidated balance sheets (in thousands): Finance Lease Balances (Classification) December 31, 2024 December 31, 2023 ROU assets (Property, plant and equipment, net) $ 182,532 $ 126,292 Current portion of lease liabilities (Accrued expenses and other current liabilities) 25,330 16,975 Long-term portion of lease liabilities (Other long-term liabilities) 161,375 113,486 The Company’s lease expense was as follows (in thousands): For the years ended December 31, 2024 2023 2022 Operating lease cost $ 81,688 $ 69,156 $ 59,041 Finance lease cost: Amortization of ROU assets 25,985 17,183 13,239 Interest on lease liabilities 7,066 4,051 3,011 Total finance lease cost 33,051 21,234 16,250 Short-term lease cost 199,516 167,379 158,736 Variable lease cost 5,187 4,887 4,353 Total lease cost $ 319,442 $ 262,656 $ 238,380 Other information related to leases was as follows: Weighted Average Remaining Lease Term (years) December 31, 2024 December 31, 2023 Operating leases 4.3 3.8 Finance leases 6.8 7.1 Weighted Average Discount Rate December 31, 2024 December 31, 2023 Operating leases 5.20 % 4.68 % Finance leases 4.84 % 3.96 % For the years ended December 31, Supplemental Cash Flow Related Disclosures (in thousands) 2024 2023 2022 Cash paid for amounts related to lease liabilities: Operating cash flows from operating leases $ 84,932 $ 71,185 $ 61,014 Operating cash flows from finance leases 7,066 4,051 3,011 Financing cash flows from finance leases 30,886 15,937 12,821 ROU assets obtained in exchange for operating lease liabilities 123,938 82,392 58,230 ROU assets obtained in exchange for finance lease liabilities 78,455 47,238 29,205 At December 31, 2024, the Company's future lease payments under non-cancelable leases that have lease terms in excess of one year were as follows (in thousands): Years ending December 31, December 31, 2024 Operating Leases Finance Leases 2025 $ 82,873 $ 36,230 2026 66,702 35,228 2027 54,242 35,217 2028 37,291 31,244 2029 20,357 27,084 Thereafter 25,064 58,522 Total future lease payments 286,529 223,525 Amount representing interest (31,983) (36,820) Total lease liabilities $ 254,546 $ 186,705 At December 31, 2024, none of the Company's executed leases that had not yet commenced will create significant rights or obligations in the future and sublease transactions are not material. Additionally, the Company does not have any related party leases, and there were no restrictions or covenants imposed by its leases.
LEASES	LEASES The Company’s lease portfolio is predominately operating leases for real estate, vehicles and industrial equipment utilized in operations and rail cars. The Company presents operating lease balances separately on the consolidated balance sheets. The Company's finance leases relate to vehicles, rail cars and certain real estate. The following table presents the Company's finance lease balances and their classification on the consolidated balance sheets (in thousands): Finance Lease Balances (Classification) December 31, 2024 December 31, 2023 ROU assets (Property, plant and equipment, net) $ 182,532 $ 126,292 Current portion of lease liabilities (Accrued expenses and other current liabilities) 25,330 16,975 Long-term portion of lease liabilities (Other long-term liabilities) 161,375 113,486 The Company’s lease expense was as follows (in thousands): For the years ended December 31, 2024 2023 2022 Operating lease cost $ 81,688 $ 69,156 $ 59,041 Finance lease cost: Amortization of ROU assets 25,985 17,183 13,239 Interest on lease liabilities 7,066 4,051 3,011 Total finance lease cost 33,051 21,234 16,250 Short-term lease cost 199,516 167,379 158,736 Variable lease cost 5,187 4,887 4,353 Total lease cost $ 319,442 $ 262,656 $ 238,380 Other information related to leases was as follows: Weighted Average Remaining Lease Term (years) December 31, 2024 December 31, 2023 Operating leases 4.3 3.8 Finance leases 6.8 7.1 Weighted Average Discount Rate December 31, 2024 December 31, 2023 Operating leases 5.20 % 4.68 % Finance leases 4.84 % 3.96 % For the years ended December 31, Supplemental Cash Flow Related Disclosures (in thousands) 2024 2023 2022 Cash paid for amounts related to lease liabilities: Operating cash flows from operating leases $ 84,932 $ 71,185 $ 61,014 Operating cash flows from finance leases 7,066 4,051 3,011 Financing cash flows from finance leases 30,886 15,937 12,821 ROU assets obtained in exchange for operating lease liabilities 123,938 82,392 58,230 ROU assets obtained in exchange for finance lease liabilities 78,455 47,238 29,205 At December 31, 2024, the Company's future lease payments under non-cancelable leases that have lease terms in excess of one year were as follows (in thousands): Years ending December 31, December 31, 2024 Operating Leases Finance Leases 2025 $ 82,873 $ 36,230 2026 66,702 35,228 2027 54,242 35,217 2028 37,291 31,244 2029 20,357 27,084 Thereafter 25,064 58,522 Total future lease payments 286,529 223,525 Amount representing interest (31,983) (36,820) Total lease liabilities $ 254,546 $ 186,705 At December 31, 2024, none of the Company's executed leases that had not yet commenced will create significant rights or obligations in the future and sublease transactions are not material. Additionally, the Company does not have any related party leases, and there were no restrictions or covenants imposed by its leases.

SEGMENT REPORTING

SEGMENT REPORTING	12 Months Ended
	Dec. 31, 2024
Segment Reporting [Abstract]
SEGMENT REPORTING	SEGMENT REPORTING Segment reporting is prepared on the same basis that the Company's chief operating decision maker ("CODM"), which is a committee comprised of the Company's Co-Chief Executive Officers, manages the business, makes operating decisions and assesses performance. The Company is managed and reports as two operating segments; (i) the Environmental Services segment and (ii) the Safety-Kleen Sustainability Solutions segment. Third-party revenue is revenue billed to outside customers by a particular segment. Direct revenue is revenue allocated to the segment providing the product or service. Intersegment revenues represent the sharing of third-party revenues among the segments based on products and services provided by each segment as if the products and services were sold directly to the third-party. The intersegment revenues are shown net. The operations not managed through the Company’s operating segments described above are recorded as “Corporate.” Although such transactions are excluded from the business segment results, they are included in reported consolidated earnings. The following tables reconcile third-party revenues to direct revenues by Reportable Segment (in thousands): For the year ended December 31, 2024 Environmental Safety-Kleen Sustainability Solutions Total Segment Revenues Corporate Total Consolidated Revenues Third-party revenues $ 4,960,325 $ 929,220 $ 5,889,545 $ 407 $ 5,889,952 Intersegment revenues (expense), net 44,422 (44,422) — — — Direct revenues $ 5,004,747 $ 884,798 $ 5,889,545 $ 407 $ 5,889,952 For the year ended December 31, 2023 Environmental Safety-Kleen Sustainability Solutions Total Segment Revenues Corporate Total Consolidated Revenues Third-party revenues $ 4,469,909 $ 938,796 $ 5,408,705 $ 447 $ 5,409,152 Intersegment revenues (expense), net 41,533 (41,533) — — — Direct revenues $ 4,511,442 $ 897,263 $ 5,408,705 $ 447 $ 5,409,152 For the year ended December 31, 2022 Environmental Safety-Kleen Sustainability Solutions Total Segment Revenues Corporate Total Consolidated Revenues Third-party revenues $ 4,144,973 $ 1,021,125 $ 5,166,098 $ 507 $ 5,166,605 Intersegment revenues (expense), net 26,733 (26,733) — — — Direct revenues $ 4,171,706 $ 994,392 $ 5,166,098 $ 507 $ 5,166,605 The primary financial measure by which the CODM evaluates the performance of its segments is Adjusted EBITDA, which consists of net income plus accretion of environmental liabilities, stock-based compensation, depreciation and amortization, net interest expense, loss on early extinguishment of debt and provision for income taxes and excludes other transactions not deemed representative of fundamental segment results and other (income) expense, net. Transactions between the segments are accounted for at the Company’s best estimate based on similar transactions with outside customers. The CODM uses Adjusted EBITDA to enhance their understanding of segment operating performance, which represents the Company’s performance in the ordinary, ongoing and customary course of operations. The reportable segment operating performance Adjusted EBITDA is used by the CODM to make key operating decisions such as the allocation of resources. Total assets by segment are not used by the CODM to assess the performance of, or allocate resources to, the Company’s segments, therefore total assets by segment are not disclosed. The tables below present total Reportable Segment Adjusted EBITDA and the relevant significant segment expenses provided to the CODM by reported segment (in thousands): For the year ended December 31, 2024 Environmental Services Safety-Kleen Sustainability Solutions Total Reportable Segments Direct Revenues $ 5,004,747 $ 884,798 $ 5,889,545 Cost of Revenues 3,366,022 659,217 4,025,239 Selling, General and Administrative Expenses 371,263 78,575 449,838 Total Reportable Segment Adjusted EBITDA $ 1,267,462 $ 147,006 $ 1,414,468 For the year ended December 31, 2023 Environmental Services Safety-Kleen Sustainability Solutions Total Reportable Segments Direct Revenues $ 4,511,442 $ 897,263 $ 5,408,705 Cost of Revenues 3,063,043 646,301 3,709,344 Selling, General and Administrative Expenses 346,791 78,089 424,880 Total Reportable Segment Adjusted EBITDA $ 1,101,608 $ 172,873 $ 1,274,481 For the year ended December 31, 2022 Environmental Services Safety-Kleen Sustainability Solutions Total Reportable Segments Direct Revenues $ 4,171,706 $ 994,392 $ 5,166,098 Cost of Revenues 2,902,979 615,303 3,518,282 Selling, General and Administrative Expenses 315,674 72,762 388,436 Total Reportable Segment Adjusted EBITDA $ 953,053 $ 306,327 $ 1,259,380 The following table presents Total Reportable Segment Adjusted EBITDA reconciled to income from operations before provision for income taxes (in thousands): For the years ended December 31, 2024 2023 2022 Adjusted EBITDA: Environmental Services $ 1,267,462 $ 1,101,608 $ 953,053 Safety-Kleen Sustainability Solutions 147,006 172,873 306,327 Total Reportable Segment Adjusted EBITDA 1,414,468 1,274,481 1,259,380 Reconciliation to Consolidated Statements of Operations: Corporate Costs (1) 297,534 261,911 237,252 Accretion of environmental liabilities 13,456 13,667 12,943 Stock-based compensation 27,981 20,703 26,844 Depreciation and amortization 400,922 365,761 347,594 Kimball startup costs 4,343 — — Income from operations 670,232 612,439 634,747 Other expense (income), net 1,454 (2,315) (2,472) Loss on early extinguishment of debt 371 2,880 422 Gain on sale of business — — (8,864) Interest expense, net of interest income 134,964 108,595 107,663 Income from operations before provision for income taxes $ 533,443 $ 503,279 $ 537,998 ___________________________________ (1) Corporate Costs include the revenue, cost of revenues and selling, general and administrative expenses not managed through the Company’s operating segments. These costs are not captured within the Company’s Reportable Segment Adjusted EBITDA but are included in the Company’s total Adjusted EBITDA balances. The following table presents assets by reported segment and in the aggregate (in thousands): December 31, 2024 December 31, 2023 Property, plant and equipment, net Environmental Services $ 1,865,611 $ 1,651,026 Safety-Kleen Sustainability Solutions 463,538 411,415 Corporate 118,792 130,877 Total property, plant and equipment, net $ 2,447,941 $ 2,193,318 Goodwill and Permits and other intangibles, net Environmental Services Goodwill $ 1,296,204 $ 1,112,013 Permits and other intangibles, net 549,482 454,919 Total Environmental Services 1,845,686 1,566,932 Safety-Kleen Sustainability Solutions Goodwill $ 180,995 $ 175,723 Permits and other intangibles, net 152,505 147,878 Total Safety-Kleen Sustainability Solutions 333,500 323,601 Total $ 2,179,186 $ 1,890,533 Geographic Information As of December 31, 2024 and 2023, the Company had property, plant and equipment, net of depreciation and amortization and permits and other intangible assets, net of amortization in the following geographic locations (in thousands): December 31, 2024 December 31, 2023 Total % of Total Total % of Total Property, plant and equipment, net United States $ 2,249,155 91.9 % $ 1,972,221 89.9 % Canada and other foreign 198,786 8.1 221,097 10.1 Total property, plant and equipment, net $ 2,447,941 100.0 % $ 2,193,318 100.0 % Permits and other intangibles, net United States $ 674,246 96.0 % $ 570,049 94.6 % Canada 27,741 4.0 32,748 5.4 Total permits and other intangibles, net $ 701,987 100.0 % $ 602,797 100.0 % The following table presents the total assets by geographical area (in thousands): December 31, 2024 December 31, 2023 United States $ 6,756,813 $ 5,786,937 Canada and other foreign 620,465 595,932 Total $ 7,377,278 $ 6,382,869

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Pay vs Performance Disclosure
Net income	$ 402,299	$ 377,856	$ 411,744

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Dec. 31, 2024
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

Insider Trading Policies and Pr

Insider Trading Policies and Procedures	12 Months Ended
	Dec. 31, 2024
Insider Trading Policies and Procedures [Line Items]
Insider Trading Policies and Procedures Adopted	true

Cybersecurity Risk Management a

Cybersecurity Risk Management and Strategy Disclosure	12 Months Ended
	Dec. 31, 2024
Cybersecurity Risk Management, Strategy, and Governance [Line Items]
Cybersecurity Risk Management Processes for Assessing, Identifying, and Managing Threats [Text Block]	Reporting to the CIO, the CISO manages Cybersecurity at Clean Harbors and is a Certified Informational Systems Security Professional. The CISO leads the Clean Harbors’ cybersecurity response program based on the National Institute of Standards and Technology (“NIST”) Cybersecurity Framework providing a collaborative, balanced risk based approach to securing and defending the Company. The CISO leverages open source and private threat intelligence sources to remain current about the latest developments in cybersecurity, including potential threats and risk management techniques. The CISO implements and oversees processes and technologies for regular monitoring of our information systems. Third party cybersecurity advisory services are employed to consult on, monitor, respond and/or assess our IT landscape and cybersecurity response. The CISO is also responsible for the ongoing cybersecurity awareness, training and education of the employees of Clean Harbors and any other parties that may interact with the Company’s information technology systems. Awareness activities include cybersecurity training, simulated exercises, cross functional tabletop exercises and internal communication updates. In the event of a cybersecurity incident, the CISO is equipped with a well-defined incident response plan which has been communicated to the IT and operational organization. This plan includes immediate actions to mitigate the impact, solutions to enable the restoration of business critical technology and long-term strategies for remediation and prevention of future incidents. Risks from Cybersecurity Threats
Cybersecurity Risk Management Processes Integrated [Flag]	true
Cybersecurity Risk Management Processes Integrated [Text Block]	Clean Harbors recognizes the critical importance of developing, implementing and maintaining cybersecurity measures to safeguard our information technology. The Company has integrated cybersecurity risk management into our overall risk management framework to collectively assess and respond to operational, financial and cybersecurity risks.
Cybersecurity Risk Management Third Party Engaged [Flag]	true
Cybersecurity Risk Third Party Oversight and Identification Processes [Flag]	true
Cybersecurity Risk Materially Affected or Reasonably Likely to Materially Affect Registrant [Flag]	false
Cybersecurity Risk Board of Directors Oversight [Text Block]	The Board of Directors is acutely aware of the critical nature of managing risks associated with cybersecurity threats. The Board, led by the Executive Chairman Alan McKim, who is also the Chief Technology Officer of the Company, has primary oversight responsibilities for cybersecurity risks and therefore has established oversight mechanisms to ensure effective governance in managing risks associated with cybersecurity threats. We have a special subcommittee of the Board of Directors with the goal of reviewing the Company’s overall cybersecurity risk and response landscape. The special Cybersecurity subcommittee is comprised of board members with diverse expertise including risk management, technology and finance, with two members holding Cybersecurity Oversight Certificates issued by the National Association of Corporate Directors and Carnegie Mellon University. The Chief Information Security Officer (“CISO”) and Chief Information Officer (“CIO”) provide comprehensive briefings throughout the year to the Cybersecurity subcommittee, which meets quarterly. The chair of the Cybersecurity subcommittee provides updates on the subcommittee’s activities to the Board of Directors and, from time to time as warranted, the CISO and CIO will present to the full Board of Directors as well. The briefings include the current landscape of cybersecurity risks and emerging threats, relevant Company infrastructure and tools employed to address these risk and threats, status of ongoing initiatives, incident reports and learnings and compliance with regulatory requirements and industry standards.
Cybersecurity Risk Board Committee or Subcommittee Responsible for Oversight [Text Block]	The Board of Directors is acutely aware of the critical nature of managing risks associated with cybersecurity threats. The Board, led by the Executive Chairman Alan McKim, who is also the Chief Technology Officer of the Company, has primary oversight responsibilities for cybersecurity risks and therefore has established oversight mechanisms to ensure effective governance in managing risks associated with cybersecurity threats.
Cybersecurity Risk Process for Informing Board Committee or Subcommittee Responsible for Oversight [Text Block]	The Chief Information Security Officer (“CISO”) and Chief Information Officer (“CIO”) provide comprehensive briefings throughout the year to the Cybersecurity subcommittee, which meets quarterly. The chair of the Cybersecurity subcommittee provides updates on the subcommittee’s activities to the Board of Directors and, from time to time as warranted, the CISO and CIO will present to the full Board of Directors as well. The briefings include the current landscape of cybersecurity risks and emerging threats, relevant Company infrastructure and tools employed to address these risk and threats, status of ongoing initiatives, incident reports and learnings and compliance with regulatory requirements and industry standards.
Cybersecurity Risk Role of Management [Text Block]	Reporting to the CIO, the CISO manages Cybersecurity at Clean Harbors and is a Certified Informational Systems Security Professional. The CISO leads the Clean Harbors’ cybersecurity response program based on the National Institute of Standards and Technology (“NIST”) Cybersecurity Framework providing a collaborative, balanced risk based approach to securing and defending the Company. The CISO leverages open source and private threat intelligence sources to remain current about the latest developments in cybersecurity, including potential threats and risk management techniques. The CISO implements and oversees processes and technologies for regular monitoring of our information systems. Third party cybersecurity advisory services are employed to consult on, monitor, respond and/or assess our IT landscape and cybersecurity response. The CISO is also responsible for the ongoing cybersecurity awareness, training and education of the employees of Clean Harbors and any other parties that may interact with the Company’s information technology systems. Awareness activities include cybersecurity training, simulated exercises, cross functional tabletop exercises and internal communication updates. In the event of a cybersecurity incident, the CISO is equipped with a well-defined incident response plan which has been communicated to the IT and operational organization. This plan includes immediate actions to mitigate the impact, solutions to enable the restoration of business critical technology and long-term strategies for remediation and prevention of future incidents.
Cybersecurity Risk Management Positions or Committees Responsible [Flag]	true
Cybersecurity Risk Management Positions or Committees Responsible [Text Block]	The Chief Information Security Officer (“CISO”) and Chief Information Officer (“CIO”) provide comprehensive briefings throughout the year to the Cybersecurity subcommittee, which meets quarterly. The chair of the Cybersecurity subcommittee provides updates on the subcommittee’s activities to the Board of Directors and, from time to time as warranted, the CISO and CIO will present to the full Board of Directors as well. The briefings include the current landscape of cybersecurity risks and emerging threats, relevant Company infrastructure and tools employed to address these risk and threats, status of ongoing initiatives, incident reports and learnings and compliance with regulatory requirements and industry standards.
Cybersecurity Risk Management Expertise of Management Responsible [Text Block]	Reporting to the CIO, the CISO manages Cybersecurity at Clean Harbors and is a Certified Informational Systems Security Professional.
Cybersecurity Risk Process for Informing Management or Committees Responsible [Text Block]	The Chief Information Security Officer (“CISO”) and Chief Information Officer (“CIO”) provide comprehensive briefings throughout the year to the Cybersecurity subcommittee, which meets quarterly. The chair of the Cybersecurity subcommittee provides updates on the subcommittee’s activities to the Board of Directors and, from time to time as warranted, the CISO and CIO will present to the full Board of Directors as well. The briefings include the current landscape of cybersecurity risks and emerging threats, relevant Company infrastructure and tools employed to address these risk and threats, status of ongoing initiatives, incident reports and learnings and compliance with regulatory requirements and industry standards.
Cybersecurity Risk Management Positions or Committees Responsible Report to Board [Flag]	true

SIGNIFICANT ACCOUNTING POLICI_2

SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2024
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with U.S. Generally Accepted Accounting Principles (GAAP), requires management to make estimates and assumptions about future events that affect the amounts reported in the consolidated financial statements and the accompanying notes. Management bases its estimates on historical experience and other assumptions that it believes to be reasonable at the time. Actual results could differ from those estimates, and any such differences may be material to the consolidated financial statements. Estimates and assumptions are reviewed periodically and the effects of changes, if any, are reflected in our consolidated financial statements in the period they are determined.
Cash, Cash Equivalents, Marketable Securities and Uncashed Checks	Cash, Cash Equivalents, Marketable Securities and Uncashed Checks
Cash, Cash Equivalents, Marketable Securities and Uncashed Checks	Realized gains and losses on sales of available-for-sale marketable securities in the years presented were immaterial. The majority of the marketable securities have a remaining maturity of less than one year and fair value approximates cost. The Company's cash management program with its revolving credit lender allows the Company to maintain a zero balance in the U.S. bank disbursement accounts that are used to issue vendor and payroll checks. When checks are presented to the bank for payment, cash deposits in amounts sufficient to fund the checks are made, at the Company's discretion, either from funds provided by other accounts or under the terms of the Company's revolving credit facility. Checks that have been written to vendors or employees but have not yet been presented for payment at the Company's bank are classified as uncashed checks in accounts payable and changes in the balance are reported as a financing activity in the consolidated statements of cash flows.
Allowances for Doubtful Accounts	Allowance for Doubtful Accounts and Revenue Allowance On a regular basis, the Company evaluates its accounts receivable and establishes the allowance for doubtful accounts based on an evaluation of certain criteria and evidence of collection uncertainty including historical collection trends, reasonable expectations of future collections, current economic trends and changes in customer payment patterns. Past-due receivable balances are written off when the Company's collection efforts have been deemed unsuccessful in collecting the outstanding balance due. Due to the nature of the Company's businesses and the invoices that result from the services provided, customers may withhold payments and attempt to renegotiate amounts invoiced. In addition, for some of the services provided, the Company's invoices are based on quotes that, in limited instances, can result in adjustments to revenue subsequent to billing. Based on industry knowledge and historical trends, the Company records a revenue allowance in anticipation of these expected adjustments. This practice causes the volume of activity flowing through the revenue allowance during the year to be higher than the balance at the end of the year. The revenue allowance is intended to cover the net amount of revenue adjustments that may need to be credited to customers' accounts in future periods. Management determines the appropriate total revenue allowance by evaluating the following factors on an invoice-by-invoice basis as well as on a consolidated level: trends in adjustments to previously billed amounts, existing economic conditions, communications with customers and other information as deemed applicable. Revenue allowance estimates can differ from the actual adjustments, but historically the revenue allowance has been sufficient to cover the net amount of the reserve adjustments issued in subsequent reporting periods.
Revenue Allowance	Allowance for Doubtful Accounts and Revenue Allowance On a regular basis, the Company evaluates its accounts receivable and establishes the allowance for doubtful accounts based on an evaluation of certain criteria and evidence of collection uncertainty including historical collection trends, reasonable expectations of future collections, current economic trends and changes in customer payment patterns. Past-due receivable balances are written off when the Company's collection efforts have been deemed unsuccessful in collecting the outstanding balance due. Due to the nature of the Company's businesses and the invoices that result from the services provided, customers may withhold payments and attempt to renegotiate amounts invoiced. In addition, for some of the services provided, the Company's invoices are based on quotes that, in limited instances, can result in adjustments to revenue subsequent to billing. Based on industry knowledge and historical trends, the Company records a revenue allowance in anticipation of these expected adjustments. This practice causes the volume of activity flowing through the revenue allowance during the year to be higher than the balance at the end of the year. The revenue allowance is intended to cover the net amount of revenue adjustments that may need to be credited to customers' accounts in future periods. Management determines the appropriate total revenue allowance by evaluating the following factors on an invoice-by-invoice basis as well as on a consolidated level: trends in adjustments to previously billed amounts, existing economic conditions, communications with customers and other information as deemed applicable. Revenue allowance estimates can differ from the actual adjustments, but historically the revenue allowance has been sufficient to cover the net amount of the reserve adjustments issued in subsequent reporting periods.
Credit Concentration	Credit Concentration Concentration of credit risks in accounts receivable is limited due to the large number of customers comprising the Company's customer base throughout North America. The Company maintains policies over credit extension that include credit evaluations, credit limits and collection monitoring procedures on a customer-by-customer basis. However, the Company generally does not require collateral before services are performed. No individual customer accounted for more than 10% of accounts receivable or more than 10% of total third-party revenues in the periods presented.
Inventories and Supplies	Inventories and Supplies Inventories are stated at the lower of cost or net realizable value. The cost of oil and oil products as well as the cost of supplies and drums, solvent and solution and other inventories is principally determined on a first-in, first-out ("FIFO") basis. The Company continually reviews its inventories for obsolete or unsalable items and adjusts its carrying value to reflect estimated realizable values.
Property, Plant and Equipment, net (excluding landfill assets and finance lease right-of-use assets)	Property, Plant and Equipment, net (excluding landfill assets and finance lease right-of-use assets) Property, plant and equipment, net is stated at cost less accumulated depreciation. Expenditures for major renewals and improvements which extend the life or usefulness of the asset are capitalized. Items of an ordinary repair or maintenance nature are charged directly to operating expense as incurred. During the construction and development period of an asset, the costs incurred, including interest expense, are classified as construction-in-progress. When the asset is ready for its intended use, the asset is reclassified to an appropriate asset classification and depreciation or amortization commences. The Company depreciates and amortizes the capitalized cost of these assets, using the straight-line method as follows: Asset Classification Estimated Useful Life Buildings and building improvements Buildings 20-42 years Leasehold and building improvements 2-45 years Vehicles 2-15 years Equipment Capitalized software and computer equipment 3-5 years Containers and railcars 8-16 years All other equipment 4-30 years Furniture and fixtures 5-8 years Gains and losses on the sale of property, plant and equipment are included in Other (expense) income, net. Fully depreciated assets are retained in property, plant and equipment and accumulated depreciation until they are removed from service.
Business Combinations	Business Combinations
Goodwill	Goodwill Goodwill is comprised of the purchase price of business acquisitions in excess of the fair value of the net assets acquired. Goodwill is reviewed for impairment annually as of December 31 or when events or changes in the business environment indicate the carrying value of a reporting unit may exceed its fair value. This review is performed by comparing the fair value of each reporting unit to its carrying value, including goodwill. If the fair value is less than the carrying amount, a loss is recorded for the excess of the carrying value over the fair value up to the carrying amount of goodwill.
Permits and Other Intangibles	Permits and Other Intangibles Costs related to acquiring licenses, permits and intangible assets, such as legal fees, site surveys, engineering costs and other expenditures are capitalized. Other intangible assets consist primarily of customer and supplier relationships, trademarks and trade names and developed technology. Permits relating to landfills are amortized on a units-of-consumption basis. All other permits are amortized over periods ranging from five two All finite-lived intangible assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying value may not be recoverable. When such factors and circumstances exist, management compares the projected undiscounted future cash flows associated with the related asset or group of assets to the carrying amount. The impairment loss, if any, is measured as the excess of the carrying amount over the fair value of the asset or group of assets.
Landfill Accounting	Landfill Accounting The Company amortizes landfill improvements and certain landfill-related permits over the estimated useful lives. The units-of-consumption method is used to amortize land, landfill cell construction, asset retirement costs and remaining landfill cells and sites. The Company also utilizes the units-of-consumption method to record closure and post-closure obligations for landfill cells and sites. Under the units-of-consumption method, the Company includes future estimated construction and asset retirement costs, as well as costs incurred to date, in the amortization base of the landfill assets. Additionally, where appropriate, as described below, the Company includes probable expansion airspace that has yet to be permitted in the calculation of the total remaining useful life of the landfill. If it is determined that expansion capacity should no longer be considered in calculating the recoverability of a landfill asset, the Company may be required to recognize an asset impairment or incur significantly higher amortization expense. If at any time the Company makes the decision to abandon the expansion effort, the capitalized costs related to the expansion effort are expensed immediately. Landfill assets —Landfill assets include the costs of landfill site acquisition, permits and cell construction incurred to date. These amounts are recorded at cost, which includes capitalized interest as applicable. Landfill assets, net of amortization, are combined with management's estimate of the costs required to complete construction of the landfill to determine the amount to be amortized over the remaining estimated useful economic life of a site. Amortization of landfill assets is recorded on a units-of-consumption basis, such that the landfill assets should be completely amortized at the date the landfill ceases accepting waste. Amortization totaled $10.6 million, $18.6 million and $16.2 million for the years ended December 31, 2024, 2023 and 2022, respectively. Changes in the determination of when the landfill will cease accepting waste, either through a business decision by the Company, determination that expansion capacity should no longer be considered probable or changes in estimates on annual airspace consumption, will impact the amortization expense of the landfill assets. Changes in estimated costs to complete construction are applied prospectively to the amortization rate. Landfill capacity —Landfill capacity, which is the basis for the amortization of landfill assets and for the accrual of final closure and post-closure obligations, represents total permitted airspace plus unpermitted airspace that management believes is highly probable of ultimately being permitted. As of December 31, 2024, there were no unpermitted expansions included in the Company's landfill accounting model. If actual expansion airspace is significantly different from management's estimate of expansion airspace, the amortization rates used for the units-of-consumption method would change, therefore impacting the Company's profitability. As of December 31, 2024, the Company had eight active landfill sites (including the Company's non-commercial landfill), which have estimated remaining lives (based on anticipated waste volumes and the remaining highly probable airspace) as follows: Facility Name Location Remaining Permitted Remaining Highly Probable Airspace Buttonwillow California 21 4,909 Deer Trail Colorado 17 1,347 Grassy Mountain Utah 37 4,253 Kimball Nebraska 22 520 Lambton Ontario, Canada 46 4,218 Lone Mountain Oklahoma 13 2,913 Ryley Alberta, Canada 40 5,594 Sawyer North Dakota 61 3,197 26,951 At December 31, 2024 and 2023, the Company had no cubic yards of permitted, but not highly probable, airspace. The following table presents the remaining highly probable airspace from January 1, 2023 through December 31, 2024 (in thousands of cubic yards): 2024 2023 Remaining capacity, beginning of year 27,753 28,270 Changes in highly probable airspace, net — 464 Consumed (802) (981) Remaining capacity, end of year 26,951 27,753 In the year ended December 31, 2023 the Company received a permit for expansion of its Kimball, Nebraska landfill. Amortization of cell construction costs and accrual of cell closure obligations —Landfills are typically comprised of a number of cells, which are constructed within a defined acreage (or footprint). The cells are typically discrete units, which require both separate construction and separate capping and closure procedures. Cell construction costs are the costs required to excavate and construct the landfill cell. These costs are typically amortized on a units-of-consumption basis, such that they are completely amortized when the specific cell ceases accepting waste. In some instances, the Company has landfills that are engineered and constructed as "progressive trenches." In progressive trench landfills, a number of contiguous cells form a progressive trench. In those instances, the Company amortizes cell construction costs over the airspace within the entire trench, such that the cell construction costs will be fully amortized at the end of the trench useful life. The design and construction of a landfill does not create a landfill asset retirement obligation. Rather, the asset retirement obligation for cell closure (the cost associated with capping each cell) is incurred in relatively small increments as waste is placed in the landfill. Therefore, the cost required to construct the cell cap is capitalized as an asset retirement cost and a liability of an equal amount is established, based on the discounted cash flow associated with each capping event, as airspace is consumed. Spending for cell capping is reflected as environmental expenditures within operating activities in the consolidated statements of cash flows. Landfill final closure and post-closure liabilities —The balance of landfill final closure and post-closure liabilities was $59.4 million at both December 31, 2024 and 2023 respectively. The Company has material financial commitments for the costs associated with requirements of the Environmental Protection Agency ("EPA") and the comparable regulatory agency in Canada for landfill final closure and post-closure activities. The Company develops estimates for the cost of these activities based on an evaluation of site-specific facts and circumstances, including the Company's interpretation of current regulatory requirements and proposed regulatory changes. Such estimates may change in the future due to various circumstances including, but not limited to, permit modifications, changes in legislation or regulations, technological changes and results of environmental studies. Final closure costs are the costs incurred after the site ceases to accept waste, but before the landfill is certified as closed by the applicable state regulatory agency. These costs generally include the costs required to cap the final cell of the landfill (if not included in cell closure), the costs required to dismantle certain structures for landfills and other landfill improvements, and regulation-mandated groundwater monitoring and leachate management. Post-closure costs involve the maintenance and monitoring of a landfill site that has been certified closed by the applicable regulatory agency. These costs generally include groundwater monitoring and leachate management. Regulatory post-closure periods are generally 30 years after landfill closure. Final closure and post-closure obligations are accrued on a units-of-consumption basis, such that the present value of the final closure and post-closure obligations are fully accrued at the date the landfill ceases accepting waste. Cell closure, final closure and post-closure costs (also referred to as "asset retirement obligations") are calculated by estimating the total obligation in current dollars, adjusted for future inflation estimates and discounted at the Company's credit-adjusted risk-free interest rate (6.57% and 6.51% during 2024 and 2023, respectively).
Non-Landfill Closure and Post-Closure Liabilities	Non-Landfill Closure and Post-Closure Liabilities The balance of non-landfill closure and post-closure liabilities at December 31, 2024 and 2023 was $70.4 million and $59.2 million, respectively. Non-landfill closure and post-closure obligations arise when the Company commences non-landfill facility operations and include costs required to dismantle and decontaminate certain structures and other costs incurred during the closure process. Post-closure costs, if required, include associated maintenance and monitoring costs as required by the closure permit. Post-closure periods are performance-based and are not typically specified in terms of years in the closure permit, but generally range from 10 to 30 years or more. The Company records its non-landfill closure and post-closure liability by: (i) estimating the current cost of closing a non-landfill facility and the post-closure care of that facility, if required, based upon the closure plan that the Company is required to follow under its operating permit, or in the event the facility operates with a permit that does not contain a closure plan, based upon legally enforceable closure commitments made by the Company to various government agencies; (ii) estimates as to when future operations may cease; (iii) cost estimates of closing the non-landfill facility using the inflation rate to the time of closing; and (iv) discounting the future value back to the present using the credit-adjusted risk-free interest rate. The estimates for non-landfill closure and post-closure liabilities are inherently uncertain due to the possibility that permit and regulatory requirements will change in the future, impacting the estimation of total costs and the timing of the expenditures. Management reviews non-landfill closure and post-closure liabilities for changes to key assumptions that would impact the amount of the recorded liabilities. Changes that would prompt management to revise a liability estimate include changes in legal requirements that impact the Company's expected closure plan or scope of work, in the market price of a significant cost item, in the estimate as to when future operations at a location might cease or in the expected timing of the costs. Changes in estimates for non-landfill closure and post-closure events immediately impact the liability and the value of the corresponding asset. If a change is made to a fully-amortized asset, the adjustment is charged immediately to expense. When a change in estimate relates to an asset that has not been fully amortized, the adjustment to the asset is recognized in income prospectively as a component of amortization. Historically, changes to non-landfill closure and post-closure estimates have not been material.
Remedial Liabilities	Remedial Liabilities The balance of remedial liabilities at December 31, 2024 and 2023 was $111.7 million and $111.2 million, respectively. Remedial liabilities, including Superfund liabilities, include the costs of removal or containment of contaminated material, treatment of potentially contaminated groundwater and maintenance and monitoring costs necessary to comply with regulatory requirements. Most of the Company's remedial liabilities relate to the active and inactive hazardous waste treatment and disposal facilities which the Company acquired and Superfund sites owned by third-parties for which the Company, or the prior owners of certain of the Company's facilities for which the Company may have certain indemnification obligations, have been identified as potentially responsible parties ("PRPs") or potential PRPs. The Company's estimate of remedial liabilities involves an analysis of such factors as: (i) the nature and extent of environmental contamination (if any); (ii) the terms of applicable permits and agreements with regulatory authorities as to cleanup procedures and whether modifications to such permits and agreements will likely need to be negotiated; (iii) the cost of performing anticipated cleanup activities based upon current technology; and (iv) in the case of Superfund and other sites where other parties will also be responsible for a portion of the cleanup costs, the likely allocation of such costs and the ability of such other parties to pay their share. The measurement of remedial liabilities is reviewed at least quarterly and changes in estimates are recognized in the consolidated statements of operations when identified. Where the Company concludes that it is probable that a liability has been incurred and an amount can be estimated, a liability is recognized. Remedial liabilities are inherently difficult to estimate. Estimating remedial liabilities requires that the existing environmental contamination be understood. There are risks that the actual quantities of contaminants differ from the results of the site investigation, and that contaminants exist that have not been previously identified. In addition, the value of the remedial liabilities is dependent on the remedial method selected. There is a risk that funds will be expended on a remedial solution that is not successful, which could result in the Company incurring the incremental costs of an alternative solution. Such estimates, which are subject to change, are subsequently revised if and when additional or new information becomes available. Remedial liabilities are discounted when the timing of the payments is determinable and the amounts are estimable. In the case of remedial liabilities assumed in connection with acquisitions, acquired liabilities are recorded at fair value as of the dates of the acquisitions calculated by inflating costs in current dollars using an estimate of future inflation rates as of the respective acquisition dates until the expected time of payment, and then discounting the amount of the payments to their present value using a risk-free discount rate as of the acquisition dates. Discount rates used in the present value determination of the Company's remedial liabilities range from 1.37% to 4.90%.
Self-Insurance Liabilities	Self-Insurance Liabilities The Company self-insures a significant portion of expected losses related to workers' compensation, employee medical, comprehensive general liability and vehicle liability. Liabilities associated with these losses are recorded based on the Company's estimates of the ultimate cost to settle incurred claims. These recorded liabilities are estimated based on independent actuarial estimates and judgments which consider the frequency and settlement amount of historical claims data and are discounted to present value using a risk-free interest rate.
Revenue Recognition	Revenue Recognition The Company recognizes revenue when control of the promised goods or services is transferred to the Company's customers, in an amount that reflects the consideration the Company expects to be entitled to in exchange for those goods or services. The majority of the Company’s revenues are for services, which are recognized based on time and materials incurred at contractually agreed-upon rates. Product revenues are recognized when the products are delivered and control transfers to the customer. The Company’s payment terms vary by the type of customers and the products or services offered. The periods between invoicing and when payments are due are not significant. Amounts billed to customers related to shipping and handling are classified as revenue, and the Company's shipping and handling costs are included in costs of revenues. In the course of operations, the Company collects sales tax and other excise taxes from its customers and recognizes a current liability, which is then relieved when the taxes are remitted to the appropriate government authorities. The Company excludes sales and other excise taxes that it collects from customers from its revenues. The Company generates revenues through the following operating segments: Environmental Services and SKSS. The Company’s Environmental Services operating segment generally has four sources of revenue and the SKSS operating segment has two sources of revenue. The Company disaggregates third-party revenues by geographic location and source of revenue as management believes these categories depict how revenue and cash flows are affected by economic factors. The tables below present revenue billed to outside customers by a particular segment. Should it be necessary, there will be intercompany transactions to present the direct revenues in the appropriate segment results. The Company’s significant sources of revenue include: Technical Services —Technical Services contribute to the revenues of the Environmental Services operating segment. Revenues for these services are generated from fees charged for waste material management and disposal services including onsite environmental management services, collection and transportation, packaging, recycling, treatment and disposal of waste and remediation projects. These services handle hazardous and/or non-hazardous waste, including per- and polyfluoroalkyl substances (“PFAS”). Revenue is primarily generated by short-term projects, most of which are governed by master service agreements that are long-term in nature. These master service agreements are typically entered into with the Company’s larger customers and outline the pricing and legal frameworks for such arrangements. Services are provided based on purchase orders or agreements with the customer and include prices based upon units of volume of waste, material and personnel costs as well as transportation and other fees. Collection and transportation revenues are recognized over time, as the customer receives and consumes the benefits of the services as they are being performed and the Company has a right to payment for performance completed to date. The Company uses the input method to recognize revenue over time, based on time and materials incurred as a basis for measuring the satisfaction of the performance obligation. Revenues for treatment and disposal of waste are recognized upon completion of treatment, final disposition, or when the waste is shipped to a third-party for processing and disposal. The Company periodically enters into bundled arrangements for the collection and transportation and disposal of waste. For such arrangements, transportation and disposal are considered distinct performance obligations and the Company allocates revenue to each based on the relative standalone selling price (i.e., the estimated price that a customer would pay for the services on a standalone basis). Revenues and the related costs from waste that is not yet completely processed and disposed of are deferred. The deferred revenues and costs are recognized when the services are completed. The period between collection and transportation and the final processing and disposal ranges depending on the location of the customer, but generally is measured in days. Industrial Services —Industrial Services contribute to the revenues of the Environmental Services operating segment. These revenues are primarily generated from industrial and specialty services provided to refineries, chemical plants, manufacturing facilities, power generation companies and other industrial customers throughout North America. Services include in-plant cleaning and maintenance services, plant outage and turnaround services, specialty cleaning services including chemical cleaning, pigging and high and ultra-high pressure water cleaning, leak detection and repair, daylighting, production services and upstream energy services. Services are provided based on purchase orders or agreements with the customer and include prices based upon daily, hourly or job rates for equipment, materials and personnel. The Company recognizes revenue for these services over time, as the customer receives and consumes the benefits of the services as they are being performed and the Company has a right to payment for performance completed to date. The Company uses the input method to recognize revenue over time, based on time and materials incurred. Field and Emergency Response Services —Field and Emergency Response Services, which includes contributions from the acquisition of HEPACO Blocker, Inc. and its subsidiaries (collectively, “HEPACO”) in 2024, contribute to the revenues of the Environmental Services operating segment. Field Services revenues are generated from cleanup services at customer sites, including those managed by municipalities and utility providers, or other locations on a scheduled or emergency response basis. Services include confined space entry for tank cleaning, site decontamination, environmental remediation, railcar cleaning, manhole/vault clean outs, product recovery and transfer and vacuum services. Additional services include filtration, water treatment services and wetland restoration. Response services for environmental emergencies of any scale range from man-made disasters such as oil spills to natural disasters like hurricanes. Emergency response services also include spill cleanup on land and water, as well as contagion disinfection, decontamination and disposal services. Field and emergency response services are provided based on purchase orders or agreements with customers and include prices generally based upon daily, hourly or job rates for equipment, materials and personnel. The Company recognizes revenue for these services over time, as the customer receives and consumes the benefits of the services as they are being performed and the Company has a right to payment for performance completed to date. The Company uses the input method to recognize revenue over time, based on time and materials incurred. The duration of such services can be over a number of hours, several days or even months for larger scale projects. Safety-Kleen Environmental Services —Safety-Kleen Environmental Services revenues contribute both to the Environmental Services operating segment and the SKSS operating segment. Revenues from providing containerized waste handling and disposal services, parts washer services and vacuum services, referred to collectively as the Safety-Kleen branches’ core service offerings, contribute to the revenues of the Environmental Services operating segment. In addition, sales of packaged blended oil products and other complementary product sales contribute to the revenues of the Environmental Services operating segment. Revenues generated from waste oil, anti-freeze and oil filter collection services, sales of bulk blended oil products and sales of automotive fluids contribute to the SKSS operating segment. Due to the complementary nature of these products and services and their customer base, there are some cross-overs of Safety-Kleen Environmental Services revenue streams between Environmental Services and SKSS operating segments. Generally, the revenue from services is recognized over time, as the customer receives and consumes the benefits of the services as they are being performed and the Company has a right to payment for performance completed to date. The duration of such services can be over a number of hours or several days. The Company uses the input method to recognize revenue over time, based on time and materials incurred. Product revenue is recognized upon the transfer of control whereby control transfers when the products are delivered to the customer. Containerized waste services consist of profiling, collecting, transporting and recycling or disposing of a wide variety of waste. Related collection and transportation revenues are recognized over time, as the customer receives and consumes the benefits of the services as they are being performed and the Company has a right to payment for performance completed to date. Parts washer services include customer use of the Company’s parts washer equipment, cleaning and maintenance of the parts washer equipment and removal and replacement of used cleaning fluids. Parts washer services are considered a single performance obligation due to the highly integrated and interdependent nature of the arrangement. Revenue from parts washer services is recognized over the service interval as the customer receives the benefit of the services. Safety-Kleen Oil —Safety-Kleen Oil related sales contribute to the revenues of the SKSS segment. These revenues are generated from bulk sales of high-quality base and blended lubricating oils to many industries, including major oil brands, lubricant blenders and manufacturers, blended lubricant distributors and government agencies. The business also sells recycled fuel oil to asphalt plants, industrial plants and pulp and paper companies. The used oil is also processed into vacuum gas oil which can be further re-refined into lubricant base oils or sold directly into the marine diesel oil fuel market. By-products coming off the refinery are a mixture of light end distillates and asphalt flux that are sold into various markets. Revenue for oil products is recognized at a point in time, upon the transfer of control. Generally, control transfers when the products are delivered to the customer.
Foreign Currency	Foreign Currency The Company has international operations in Canada and administrative support services located in India. The functional currencies of foreign operations are the local currency and therefore assets and liabilities of those foreign operations are translated to U.S. Dollars at the exchange rate in effect at the balance sheet date and revenue and expenses at the average exchange rate for the period. Gains and losses from the translation of the consolidated financial statements of foreign subsidiaries into U.S. Dollars are included in stockholders' equity as a component of accumulated other comprehensive loss. Gains and losses from transactions not denominated in the functional currency of an entity are recognized in the consolidated statements of operations. Recorded balances that are denominated in a currency other than the functional currency are remeasured to the functional currency using the exchange rate at the balance sheet date and gains or losses are recorded in the consolidated statements of operations.
Defined Contribution Plan	Defined Contribution Plan
Advertising Expense	Advertising Expense
Stock-based Compensation	Stock-based Compensation Stock-based compensation cost is measured at the grant date based on the fair value of the award and is recognized as expense over the requisite service period, which generally represents the vesting period. In addition, the Company issues awards with performance targets established prior to or at the grant date. The expense for these awards is recognized over the requisite service period when management believes it is probable those performance targets will be achieved. The fair value of the Company's grants under the 2020 Stock Incentive Plan are based on the closing price of the Company's common stock on the respective dates of grant. The fair value of shares issued under the Company’s 2024 Employee Stock Purchase plan are valued using the Black-Scholes option pricing model, which requires management to make assumptions with respect to the fair value of our common stock on the grant date, including the expected volatility of our stock, calculated based on a period of time generally commensurate with the expected term of the award and risk-free interest rates. Forfeitures are recognized as they occur. Stock-based compensation is recognized in selling, general and administrative expense.
Interest Rate Derivatives	Interest Rate Derivatives The Company enters into interest rate derivative agreements as part of the overall strategy to hedge against fluctuations in variable interest rates. These interest rate derivatives swap a variable interest rate for a fixed interest rate and have been designated as cash flow hedges. The Company assesses the hedge’s effectiveness at the inception of the hedge and at regular intervals throughout the life of the derivative. To the extent that the interest rate swap is highly effective, changes in fair value are recorded in stockholders’ equity as a component of accumulated other comprehensive loss. Amounts are reclassified from accumulated other comprehensive loss into interest expense on the consolidated statement of operations in the same period or periods during which the hedged transactions affect earnings. Although it was determined that the interest rate swaps will be a highly effective hedge, any portion of the interest rate swaps subsequently determined to be ineffective will be recognized in earnings. Further, if it becomes probable that a forecasted transaction designated as the hedged item will not occur, any gain or loss deferred is recognized in interest expense at that time.
Income Taxes	Income Taxes Current income tax expense approximates cash to be paid or refunded for taxes for the applicable period. Deferred tax expense or benefit is the result of changes between deferred tax assets and liabilities. Deferred tax assets and liabilities are determined based upon the temporary differences between the financial statement basis and tax basis of assets and liabilities as well as from net operating loss and tax credit carryforwards as measured by the enacted tax rates which will be in effect when these differences reverse. The effect of a change in tax rates on deferred tax assets and liabilities is generally recognized in income in the period that includes the enactment date. The Company evaluates the recoverability of future tax deductions and credits and a valuation allowance is established by tax jurisdiction when, based on an evaluation of both positive and negative objective verifiable evidence, it is more likely than not that some portion or all of deferred tax assets will not be realized. The Company recognizes and measures a tax benefit from uncertain tax positions when it is more likely than not that the tax position will be sustained upon examination by the taxing authorities, based on the technical merits of the position. The Company recognizes a liability for unrecognized tax benefits resulting from uncertain tax positions taken or expected to be taken in a tax return. The Company adjusts these liabilities when its judgment changes as a result of the evaluation of new information not previously available. Due to the complexity of some of these uncertainties, the ultimate resolution may result in a payment that is materially different from the current estimate or future recognition of an unrecognized benefit. These differences will be reflected as increases or decreases to income tax expense in the period in which they are determined. Liabilities for unrecognized tax benefits are included within other long-term liabilities in the consolidated balance sheets.
Earnings per Share ("EPS")	Earnings per Share ("EPS") Basic EPS is calculated using the treasury stock method by dividing net income by the weighted average number of common shares outstanding during the period. Diluted EPS gives effect to all potentially dilutive common shares that were outstanding during the period.
Leases	Leases The Company’s leases predominately relate to real estate, equipment, such as vehicles and industrial equipment utilized in operations, and rail cars utilized in connection with the Company’s transportation needs. Contracts are reviewed at inception to determine if the arrangement is a lease and, if so, whether it is an operating or finance lease. For all of its leases, the Company has elected not to separate lease and nonlease components, such as common area maintenance. The Company generally enters into long-term real estate leases with two three Certain of the Company's real estate leases contain escalating future lease payments. Escalating lease payments that are based upon explicit amounts contained in the lease or an index (e.g., consumer price index) are included in the Company's determination of future lease payments to determine the ROU asset and lease liability recognized at the commencement date. Any differences in the future lease payments from initial recognition are not anticipated to be material and will be recorded as variable lease cost in the period incurred. The variable lease cost will also include the Company’s portion of property tax, utilities and common area maintenance. A significant portion of the Company’s real estate lease agreements include renewal periods at the Company’s option. The Company includes these renewal periods in the lease term only when renewal is reasonably certain based upon facts and circumstances specific to the lease and known by the Company. Certain of the equipment and rail car leases transfer ownership upon the conclusion of the lease term and as such, are classified as finance leases. Leases containing purchase options are classified as finance leases only when it is reasonably certain that the Company will execute such options. The Company uses its incremental borrowing rate on collateralized debt based on the information available at the lease commencement date in determining the present value of future lease payments as the implicit rate is typically not readily determinable. For operating leases, lease cost is recognized on a straight-line basis over the lease term and is included in cost of revenues or selling, general and administrative expenses depending on the use of the asset. For finance leases, ROU assets are amortized on a straight-line basis and interest expense is recognized based on the incremental borrowing rate. Finance lease amortization is recognized in depreciation and amortization and finance lease related interest expense is recognized in interest expense, net of interest income.
Recent Accounting Pronouncements	Recent Accounting Pronouncements Accounting Pronouncements Adopted In November 2023, the Financial Accounting Standards Board ("FASB") issued ASU No. 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures , which requires an enhanced disclosure of significant segment expenses on an annual and interim basis. The Company adopted ASU No. 2023-07 for the year ended December 31, 2024. The only significant impact from the adoption of this standard relates to incremental disclosures now required. Accounting Pronouncements Not Yet Adopted In December 2023, the FASB issued ASU No. 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures , which enhances income tax disclosures related to the tax rate reconciliation and income taxes paid. This guidance will be effective for the annual periods beginning the year ended December 31, 2025. Early adoption is permitted. Upon adoption, the guidance can be applied prospectively or retrospectively. The Company is currently evaluating the impact of adopting this new pronouncement on its consolidated financial statements disclosures. In November 2024, the FASB issued ASU No. 2024-03, Income Statement—Reporting Comprehensive Income—Expense Disaggregation Disclosures (Subtopic 220-40) , which requires disaggregated disclosure of income statement expenses. This guidance will be effective for annual periods beginning the year ended December 31, 2027. Early adoption is permitted. Upon adoption, the guidance can be applied prospectively or retrospectively. The Company is currently evaluating the impact of adopting this new pronouncement on its consolidated financial statements disclosures.

SIGNIFICANT ACCOUNTING POLICI_3

SIGNIFICANT ACCOUNTING POLICIES (Tables)	12 Months Ended
	Dec. 31, 2024
Accounting Policies [Abstract]
Schedule of Marketable Securities	As of December 31, 2024 and 2023, the Company had total marketable securities as follows (in thousands): December 31, 2024 December 31, 2023 Commercial paper $ 4,035 $ 27,542 Total cash equivalents 4,035 27,542 Commercial paper 17,489 56,172 Corporate notes and bonds 85,145 49,929 Total marketable securities 102,634 106,101 Total $ 106,669 $ 133,643
Schedule of Activity in Allowance for Doubtful Accounts	The following table reflects the activity in the allowance for doubtful accounts and revenue allowance (in thousands): Allowance for Doubtful Accounts Revenue Allowance 2024 2023 2022 2024 2023 2022 Balance at January 1, $ 22,568 $ 24,659 $ 24,136 $ 19,641 $ 20,594 $ 16,004 Additions charged to earnings 8,129 5,956 7,783 48,301 46,467 54,836 Deductions from reserves, net of recoveries (7,789) (8,047) (7,260) (43,608) (47,420) (50,246) Balance at December 31, $ 22,908 $ 22,568 $ 24,659 $ 24,334 $ 19,641 $ 20,594
Schedule of Activity in Revenue Allowance	The following table reflects the activity in the allowance for doubtful accounts and revenue allowance (in thousands): Allowance for Doubtful Accounts Revenue Allowance 2024 2023 2022 2024 2023 2022 Balance at January 1, $ 22,568 $ 24,659 $ 24,136 $ 19,641 $ 20,594 $ 16,004 Additions charged to earnings 8,129 5,956 7,783 48,301 46,467 54,836 Deductions from reserves, net of recoveries (7,789) (8,047) (7,260) (43,608) (47,420) (50,246) Balance at December 31, $ 22,908 $ 22,568 $ 24,659 $ 24,334 $ 19,641 $ 20,594
Schedule of Asset Classification and Estimated Useful Life	The Company depreciates and amortizes the capitalized cost of these assets, using the straight-line method as follows: Asset Classification Estimated Useful Life Buildings and building improvements Buildings 20-42 years Leasehold and building improvements 2-45 years Vehicles 2-15 years Equipment Capitalized software and computer equipment 3-5 years Containers and railcars 8-16 years All other equipment 4-30 years Furniture and fixtures 5-8 years Property, plant and equipment consisted of the following (in thousands): December 31, 2024 December 31, 2023 Land $ 184,191 $ 174,891 Asset retirement costs (non-landfill) 38,705 27,167 Landfill assets 258,138 253,180 Buildings and improvements (1) 719,439 630,525 Vehicles (2) 1,455,530 1,276,567 Equipment (3) 2,600,085 2,388,370 Construction in progress 70,305 213,601 5,326,393 4,964,301 Less - accumulated depreciation and amortization 2,878,452 2,770,983 Total property, plant and equipment, net $ 2,447,941 $ 2,193,318 ___________________________________ (1) Balances inclusive of gross ROU assets classified as finance leases of $8.0 million in both periods. (2) Balances inclusive of gross ROU assets classified as finance leases of $230.5 million and $151.7 million, respectively. (3) Balances inclusive of gross ROU assets classified as finance leases of $9.2 million in both periods.
Schedule of Active Landfill Sites	As of December 31, 2024, the Company had eight active landfill sites (including the Company's non-commercial landfill), which have estimated remaining lives (based on anticipated waste volumes and the remaining highly probable airspace) as follows: Facility Name Location Remaining Permitted Remaining Highly Probable Airspace Buttonwillow California 21 4,909 Deer Trail Colorado 17 1,347 Grassy Mountain Utah 37 4,253 Kimball Nebraska 22 520 Lambton Ontario, Canada 46 4,218 Lone Mountain Oklahoma 13 2,913 Ryley Alberta, Canada 40 5,594 Sawyer North Dakota 61 3,197 26,951
Schedule of Remaining Highly Probable Airspace	The following table presents the remaining highly probable airspace from January 1, 2023 through December 31, 2024 (in thousands of cubic yards): 2024 2023 Remaining capacity, beginning of year 27,753 28,270 Changes in highly probable airspace, net — 464 Consumed (802) (981) Remaining capacity, end of year 26,951 27,753

REVENUES (Tables)

REVENUES (Tables)	12 Months Ended
	Dec. 31, 2024
Revenue from Contract with Customer [Abstract]
Schedule of Disaggregation of Revenue	The following tables present the Company’s third-party revenue disaggregated by source of revenue and geography (in thousands): For the year ended December 31, 2024 Environmental Services Safety-Kleen Sustainability Solutions Corporate Total Primary Geographical Markets United States $ 4,510,845 $ 841,171 $ 407 $ 5,352,423 Canada 449,480 88,049 — 537,529 Total third-party revenues $ 4,960,325 $ 929,220 $ 407 $ 5,889,952 Sources of Revenue Technical Services $ 1,733,550 $ — $ — $ 1,733,550 Industrial Services and Other 1,377,502 — 407 1,377,909 Field and Emergency Response Services 895,120 — — 895,120 Safety-Kleen Environmental Services 954,153 229,730 — 1,183,883 Safety-Kleen Oil — 699,490 — 699,490 Total third-party revenues $ 4,960,325 $ 929,220 $ 407 $ 5,889,952 For the year ended December 31, 2023 Environmental Services Safety-Kleen Sustainability Solutions Corporate Total Primary Geographical Markets United States $ 4,022,394 $ 846,339 $ 447 $ 4,869,180 Canada 447,515 92,457 — 539,972 Total third-party revenues $ 4,469,909 $ 938,796 $ 447 $ 5,409,152 Sources of Revenue Technical Services $ 1,563,847 $ — $ — $ 1,563,847 Industrial Services and Other 1,418,938 — 447 1,419,385 Field and Emergency Response Services 609,913 — — 609,913 Safety-Kleen Environmental Services 877,211 224,830 — 1,102,041 Safety-Kleen Oil — 713,966 — 713,966 Total third-party revenues $ 4,469,909 $ 938,796 $ 447 $ 5,409,152 For the year ended December 31, 2022 Environmental Services Safety-Kleen Sustainability Solutions Corporate Total Primary Geographical Markets United States $ 3,675,880 $ 899,780 $ 507 $ 4,576,167 Canada 469,093 121,345 — 590,438 Total third-party revenues $ 4,144,973 $ 1,021,125 $ 507 $ 5,166,605 Sources of Revenue Technical Services $ 1,495,264 $ — $ — $ 1,495,264 Industrial Services and Other 1,311,072 — 507 1,311,579 Field and Emergency Response Services 575,300 — — 575,300 Safety-Kleen Environmental Services 763,337 199,360 — 962,697 Safety-Kleen Oil — 821,765 — 821,765 Total third-party revenues $ 4,144,973 $ 1,021,125 $ 507 $ 5,166,605
Schedule of Contract Balances	Contract Balances (in thousands) December 31, 2024 December 31, 2023 Receivables $ 1,015,357 $ 983,111 Contract assets (unbilled receivables) 162,215 107,859 Contract liabilities (deferred revenue) 88,545 95,230

BUSINESS COMBINATIONS (Tables)

BUSINESS COMBINATIONS (Tables)	12 Months Ended
	Dec. 31, 2024
Business Combination, Asset Acquisition, and Joint Venture Formation [Abstract]
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed	The following table summarizes the preliminary determination and recognition of assets acquired and liabilities assumed (in thousands): At Acquisition Date As Reported December 31, 2024 Accounts receivable, including unbilled receivables $ 69,072 Inventories and supplies 384 Prepaid expenses and other current assets 4,383 Property, plant and equipment 47,125 Permits and other intangibles 130,500 Operating lease right-of-use assets 9,385 Other long-term assets 5,712 Accounts payable (30,602) Accrued expenses and other current liabilities (16,005) Current portion of operating lease liabilities (2,758) Operating lease liabilities, less current portion (6,627) Closure and post-closure liabilities (2,492) Remedial liabilities (2,435) Other long-term liabilities (374) Total identifiable net assets 205,268 Goodwill 186,911 Total purchase price $ 392,179 At Acquisition Date As Reported December 31, 2024 Accounts receivable, including unbilled receivables $ 5,855 Inventories and supplies 6,598 Prepaid expenses and other current assets 408 Property, plant and equipment 55,615 Permits and other intangibles 14,500 Operating lease right-of-use assets 3,615 Other long-term assets 92 Accounts payable (7,752) Accrued expenses and other current liabilities (1,145) Current portion of operating lease liabilities (1,823) Operating lease liabilities, less current portion (1,792) Closure and post-closure liabilities (8,929) Remedial liabilities (2,757) Total identifiable net assets 62,485 Goodwill 6,257 Total purchase price $ 68,742 Preliminary Allocation As Reported December 31, 2023 Measurement Period Adjustments Final Allocation as Reported December, 31, 2024 Accounts receivable, including unbilled receivables $ 25,233 $ (73) $ 25,160 Inventories and supplies 228 — 228 Prepaid expenses and other current assets 1,302 — 1,302 Property, plant and equipment 26,719 — 26,719 Permits and other intangibles 28,900 — 28,900 Operating lease right-of-use assets 4,716 — 4,716 Other long-term assets 72 — 72 Accounts payable (7,185) (55) (7,240) Accrued expenses and other current liabilities (3,200) (90) (3,290) Current portion of operating lease liabilities (1,653) — (1,653) Operating lease liabilities, less current portion (3,063) — (3,063) Other long-term liabilities (560) — (560) Total identifiable net assets 71,509 (218) 71,291 Goodwill 39,346 218 39,564 Total purchase price $ 110,855 $ — $ 110,855 Final Allocation Accounts receivable $ 1,089 Inventories and supplies 5,745 Prepaid expenses and other current assets 144 Property, plant and equipment 22,231 Permits and other intangibles 23,500 Operating lease right-of-use assets 585 Other long-term assets 13 Accrued expenses and other current liabilities (3,375) Current portion of operating lease liabilities (186) Operating lease liabilities, less current portion (399) Other long-term liabilities (2,681) Total identifiable net assets 46,666 Goodwill 32,212 Total purchase price $ 78,878

INVENTORIES AND SUPPLIES (Table

INVENTORIES AND SUPPLIES (Tables)	12 Months Ended
	Dec. 31, 2024
Inventory Disclosure [Abstract]
Schedule of Inventories	Inventories and supplies consisted of the following (in thousands): December 31, 2024 December 31, 2023 Supplies $ 200,905 $ 177,217 Oil and oil related products 152,992 118,600 Solvent and solutions 12,458 11,795 Other 18,302 19,899 Total inventories and supplies $ 384,657 $ 327,511

PROPERTY, PLANT, AND EQUIPMENT

PROPERTY, PLANT, AND EQUIPMENT (Tables)	12 Months Ended
	Dec. 31, 2024
Property, Plant and Equipment [Abstract]
Schedule of Property, Plant and Equipment	The Company depreciates and amortizes the capitalized cost of these assets, using the straight-line method as follows: Asset Classification Estimated Useful Life Buildings and building improvements Buildings 20-42 years Leasehold and building improvements 2-45 years Vehicles 2-15 years Equipment Capitalized software and computer equipment 3-5 years Containers and railcars 8-16 years All other equipment 4-30 years Furniture and fixtures 5-8 years Property, plant and equipment consisted of the following (in thousands): December 31, 2024 December 31, 2023 Land $ 184,191 $ 174,891 Asset retirement costs (non-landfill) 38,705 27,167 Landfill assets 258,138 253,180 Buildings and improvements (1) 719,439 630,525 Vehicles (2) 1,455,530 1,276,567 Equipment (3) 2,600,085 2,388,370 Construction in progress 70,305 213,601 5,326,393 4,964,301 Less - accumulated depreciation and amortization 2,878,452 2,770,983 Total property, plant and equipment, net $ 2,447,941 $ 2,193,318 ___________________________________ (1) Balances inclusive of gross ROU assets classified as finance leases of $8.0 million in both periods. (2) Balances inclusive of gross ROU assets classified as finance leases of $230.5 million and $151.7 million, respectively. (3) Balances inclusive of gross ROU assets classified as finance leases of $9.2 million in both periods.

GOODWILL AND OTHER INTANGIBLE_2

GOODWILL AND OTHER INTANGIBLE ASSETS (Tables)	12 Months Ended
	Dec. 31, 2024
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Changes to Goodwill	The changes in goodwill for the years ended December 31, 2024 and 2023 were as follows (in thousands): Environmental Services Safety-Kleen Sustainability Solutions Total Balance at January 1, 2023 $ 1,071,846 $ 175,032 $ 1,246,878 Increase from current period acquisitions 39,346 — 39,346 Measurement period adjustments from prior period acquisition — 360 360 Foreign currency translation 821 331 1,152 Balance at December 31, 2023 $ 1,112,013 $ 175,723 $ 1,287,736 Increase from current period acquisitions 186,911 6,457 193,368 Measurement period adjustments from prior period acquisitions 218 — 218 Foreign currency translation (2,938) (1,185) (4,123) Balance at December 31, 2024 $ 1,296,204 $ 180,995 $ 1,477,199
Schedule of Finite-Lived Intangible Assets by Major Class	As of December 31, 2024 and 2023, the Company's intangible assets consisted of the following (in thousands): December 31, 2024 December 31, 2023 Cost Accumulated Net Cost Accumulated Net Permits $ 191,921 $ 123,939 $ 67,982 $ 191,747 $ 117,556 $ 74,191 Customer and supplier relationships 697,326 256,657 440,669 604,994 258,879 346,115 Other intangible assets 120,316 46,490 73,826 100,068 37,862 62,206 Total amortizable permits and other intangible assets 1,009,563 427,086 582,477 896,809 414,297 482,512 Trademarks and trade names 119,510 — 119,510 120,285 — 120,285 Total permits and other intangible assets $ 1,129,073 $ 427,086 $ 701,987 $ 1,017,094 $ 414,297 $ 602,797
Schedule of Indefinite-Lived Intangible Assets	As of December 31, 2024 and 2023, the Company's intangible assets consisted of the following (in thousands): December 31, 2024 December 31, 2023 Cost Accumulated Net Cost Accumulated Net Permits $ 191,921 $ 123,939 $ 67,982 $ 191,747 $ 117,556 $ 74,191 Customer and supplier relationships 697,326 256,657 440,669 604,994 258,879 346,115 Other intangible assets 120,316 46,490 73,826 100,068 37,862 62,206 Total amortizable permits and other intangible assets 1,009,563 427,086 582,477 896,809 414,297 482,512 Trademarks and trade names 119,510 — 119,510 120,285 — 120,285 Total permits and other intangible assets $ 1,129,073 $ 427,086 $ 701,987 $ 1,017,094 $ 414,297 $ 602,797
Schedule of Expected Amortization for the Net Carrying Amount of Finite Lived Intangible Assets	The expected amortization of the net carrying amount of finite-lived intangible assets at December 31, 2024 was as follows (in thousands): Years ending December 31, Expected 2025 $ 53,335 2026 51,297 2027 49,221 2028 47,916 2029 46,763 Thereafter 333,945 $ 582,477

ACCRUED EXPENSES AND OTHER CU_2

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES (Tables)	12 Months Ended
	Dec. 31, 2024
Payables and Accruals [Abstract]
Schedule of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following (in thousands): December 31, 2024 December 31, 2023 Accrued compensation and benefits $ 134,458 $ 113,236 Accrued insurance 112,367 107,658 Accrued interest 33,259 33,857 Accrued income, real estate, sales and other taxes 35,394 44,752 Accrued other 103,967 97,654 $ 419,445 $ 397,157

CLOSURE AND POST-CLOSURE LIAB_2

CLOSURE AND POST-CLOSURE LIABILITIES (Tables)	12 Months Ended
	Dec. 31, 2024
Asset Retirement Obligation Disclosure [Abstract]
Schedule of Closure and Post-Closure Liabilities	The changes to closure and post-closure liabilities (also referred to as "asset retirement obligations") from January 1, 2023 through December 31, 2024 were as follows (in thousands): Landfill Non-Landfill Total Balance at January 1, 2023 $ 62,251 $ 56,550 $ 118,801 Liabilities assumed in acquisitions — 574 574 Measurement period adjustments from prior period acquisitions — 3,015 3,015 New asset retirement obligations 3,092 — 3,092 Accretion 4,958 4,519 9,477 Changes in estimates recorded to consolidated statement of operations 1,147 53 1,200 Changes in estimates recorded to consolidated balance sheet (3,706) 1,600 (2,106) Environmental expenditures (8,478) (7,206) (15,684) Currency translation and other 179 52 231 Balance at December 31, 2023 59,443 59,157 118,600 Liabilities assumed in acquisitions — 11,421 11,421 New asset retirement obligations 2,118 — 2,118 Accretion 5,069 4,489 9,558 Changes in estimates recorded to consolidated statement of operations 70 (295) (225) Changes in estimates recorded to consolidated balance sheet 4,335 402 4,737 Environmental expenditures (11,210) (4,466) (15,676) Currency translation and other (425) (320) (745) Balance at December 31, 2024 $ 59,400 $ 70,388 $ 129,788
Schedule of Expected Payments Related to Asset Retirement Obligations	Anticipated payments (based on current estimated costs and anticipated timing of necessary regulatory approvals to commence work on closure and post-closure activities) for each of the next five years and thereafter are as follows (in thousands): Years ending December 31, 2025 $ 10,304 2026 14,457 2027 12,485 2028 14,127 2029 3,224 Thereafter 278,762 Undiscounted closure and post-closure liabilities 333,359 Less: Discount at credit-adjusted risk-free rate (119,353) Less: Undiscounted estimated closure and post-closure liabilities relating to airspace not yet consumed (84,218) Present value of closure and post-closure liabilities $ 129,788

REMEDIAL LIABILITIES (Tables)

REMEDIAL LIABILITIES (Tables)	12 Months Ended
	Dec. 31, 2024
Environmental Remediation Obligations [Abstract]
Schedule of Changes to Remedial Liabilities	The changes to remedial liabilities Remedial Remedial Remedial Total Balance at January 1, 2023 $ 1,824 $ 59,749 $ 54,717 $ 116,290 Accretion 89 2,540 1,561 4,190 Changes in estimates recorded to consolidated statement of operations 19 1,713 1,896 3,628 Environmental expenditures (52) (3,840) (9,384) (13,276) Currency translation and other — 115 296 411 Balance at December 31, 2023 1,880 60,277 49,086 111,243 Liabilities assumed in acquisitions — — 5,192 5,192 Accretion 92 2,292 1,514 3,898 Changes in estimates recorded to consolidated statement of operations 29 573 3,762 4,364 Expenditures (53) (6,078) (5,715) (11,846) Currency translation and other — (28) (1,078) (1,106) Balance at December 31, 2024 $ 1,948 $ 57,036 $ 52,761 $ 111,745
Schedule of Remedial Liabilities Anticipated Payments for Each of the Next Five Years	Anticipated payments at December 31, 2024 (based on current estimated costs and anticipated timing of necessary regulatory approvals to commence work on remedial activities) for each of the next five years and thereafter were as follows (in thousands): Years ending December 31, 2025 $ 10,321 2026 17,391 2027 11,259 2028 10,972 2029 8,745 Thereafter 70,610 Undiscounted remedial liabilities 129,298 Less: Discount at risk free rates (17,553) Total remedial liabilities $ 111,745
Schedule of Environmental Exit Costs by Cost	The following table presents the Company's estimated remedial liabilities and reasonably possible additional liabilities as of December 31, 2024 disaggregated by facility/site type (in thousands, except percentages): Type of Facility or Site Remedial % of Total Reasonably Possible Additional Liabilities (1) Inactive facilities not used in active conduct of the Company's business, most of which were assumed through prior period acquisitions (25 facilities) $ 56,976 51.0 % $ 10,765 Facilities now used in active conduct of the Company's business (62 facilities, including 24 acquired by the Company through acquisitions in 2024) 46,131 41.3 9,497 Superfund sites (12 sites) 8,638 7.7 1,296 Total $ 111,745 100.0 % $ 21,558 ___________________________________ (1) Amounts represent the high end of the range of management's best estimate of the reasonably possible additional liabilities. The following table presents the Company's estimated remedial liabilities and reasonably possible additional liabilities as of December 31, 2024 disaggregated by facilities/sites which represent at least 5% of the total and with all other facilities/ sites combined (in thousands, except percentages): Location Type of Facility or Site Remedial Liabilities (1) % of Total Reasonably Possible Additional Liabilities (2) Baton Rouge, LA Closed incinerator and landfill $ 25,578 22.9 % $ 4,303 Bridgeport, NJ Closed incinerator 17,417 15.6 3,254 Mercier, Quebec Idled incinerator 10,826 9.7 1,631 Linden, NJ Operating solvent recycling center 9,434 8.4 2,148 Various All other incinerators, landfills, wastewater treatment facilities and service centers (83 facilities, including 24 acquired by the Company through acquisitions in 2024) 39,852 35.7 8,926 Various Superfund sites (each representing less than 5% of total liabilities) (12 sites) 8,638 7.7 1,296 Total $ 111,745 100.0 % $ 21,558 _________________________________ (1) $23.3 million of the $111.7 million remedial liabilities include estimates related to the legal and administrative proceedings discussed in Note 18, "Commitments and Contingencies." (2) Amounts represent the high end of the range of management's best estimate of the reasonably possible additional liabilities.

FINANCING ARRANGEMENTS (Tables)

FINANCING ARRANGEMENTS (Tables)	12 Months Ended
	Dec. 31, 2024
Debt Disclosure [Abstract]
Schedule of Long-term Debt	The following table is a summary of the Company's long-term debt (in thousands): December 31, 2024 December 31, 2023 Current Portion of Long-Term Debt: Secured senior term loans $ 15,102 $ 10,000 Long-Term Debt: Secured senior term loans due October 8, 2028 1,449,796 970,000 Unsecured senior notes, at 4.875%, due July 15, 2027 ("2027 Notes") 545,000 545,000 Unsecured senior notes, at 5.125%, due July 15, 2029 ("2029 Notes") 300,000 300,000 Unsecured senior notes, at 6.375%, due February 1, 2031 ("2031 Notes") 500,000 500,000 Long-term debt, at par 2,794,796 2,315,000 Unamortized debt issuance costs and discount, net (23,679) (23,283) Long-term debt, at carrying value $ 2,771,117 $ 2,291,717
Schedule of Redemption Prices	The tables below depict the redemption prices of the Notes if redeemed during the twelve-month period commencing on the dates below, plus accrued and unpaid interest, if any, to but not including the redemption date. 2027 Notes Percentage July 15, 2024 and thereafter 100.000 % 2029 Notes Percentage July 15, 2024 102.563 % July 15, 2025 101.281 % July 15, 2026 and thereafter 100.000 % 2031 Notes Percentage February 1, 2026 103.188 % February 1, 2027 101.594 % February 1, 2028 and thereafter 100.000 %

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2024
Income Tax Disclosure [Abstract]
Schedule of Income before Income Tax, Domestic and Foreign	The domestic and foreign components of income before provision for income taxes were as follows (in thousands): For the years ended December 31, 2024 2023 2022 Domestic $ 444,118 $ 401,912 $ 406,206 Foreign 89,325 101,367 131,792 Total $ 533,443 $ 503,279 $ 537,998
Schedule of Components of Provision for Income Taxes	The provision for income taxes consisted of the following (in thousands, except percentages): For the years ended December 31, 2024 2023 2022 Current: Federal $ 68,321 $ 64,164 $ 52,237 State 27,649 25,496 26,980 Foreign 16,737 23,078 29,488 112,707 112,738 108,705 Deferred Federal 20,669 18,251 32,199 State (4,415) (9,049) (2,432) Foreign 2,183 3,483 (12,218) 18,437 12,685 17,549 Provision for income taxes $ 131,144 $ 125,423 $ 126,254 Effective tax rate 24.6% 24.9% 23.5%
Schedule of Effective Income Tax Rate Reconciliation	The Company's effective income tax rate varied from the amount computed using the statutory federal income tax rate of 21% as follows (in thousands): For the years ended December 31, 2024 2023 2022 Tax expense at U.S. statutory rate $ 112,023 $ 105,689 $ 112,980 State income taxes, net of federal benefit 18,555 18,067 19,831 Foreign rate differential 3,965 4,213 6,196 Valuation allowance (6,485) (7,699) (18,769) Uncertain tax position interest and penalties (1,773) (7) (2,454) Tax credits 2,694 1,653 2,768 Non-deductible compensation 2,211 2,898 2,754 Other (46) 609 2,948 Provision for income taxes $ 131,144 $ 125,423 $ 126,254
Schedule of Deferred Tax Assets and Liabilities	The components of the total net deferred tax assets and liabilities as of December 31, 2024 and 2023 were as follows (in thousands): 2024 2023 Deferred tax assets: Provision for doubtful accounts $ 14,808 $ 10,882 Closure, post-closure and remedial liabilities 32,189 31,944 Operating lease liabilities 60,929 46,784 Accrued expenses 14,749 14,963 Accrued compensation and benefits 16,876 15,058 Net operating loss carryforwards (1) 48,331 39,042 Excess business interest (2) 22,078 — Tax credit carryforwards 2,619 6,531 Stock-based compensation 4,877 3,516 Other 2,565 4,843 Total deferred tax assets 220,021 173,563 Deferred tax liabilities: Property, plant and equipment (311,546) (284,997) Operating lease right-of-use assets (59,999) (46,584) Interest rate swap asset (8,748) (9,576) Permits and other intangible assets (158,905) (130,391) Prepaid expenses (10,881) (12,372) Total deferred tax liabilities (550,079) (483,920) Total net deferred tax liability before valuation allowance (330,058) (310,357) Less valuation allowance (27,232) (35,272) Net deferred tax liabilities $ (357,290) $ (345,629) ___________________________________ (1) As of December 31, 2024, the net operating loss carryforwards included (i) gross state net operating loss carryforwards of $290.7 million which will begin to expire in 2025, (ii) gross federal net operating loss carryforwards of $79.3 million which will begin to expire in 2025 and (iii) gross foreign net operating loss carryforwards of $64.3 million which will begin to expire in 2025. The increase in the state and federal net operating loss carryforward from the prior year is predominately due to assets acquired in the HEPACO transaction. See Note 4, "Business Combinations" for more information on the related transaction. (2) Deferred tax asset acquired in the HEPACO transaction. See Note 4, "Business Combinations" for more information on the related transaction.
Schedule of Valuation Allowance	The components of the total valuation allowance as of December 31, 2024 and 2023 were as follows (in thousands): 2024 2023 Allowance related to: Foreign tax credits $ 346 $ 4,422 Federal net operating losses 3,783 3,783 State net operating loss carryforwards 4,734 4,809 Foreign net operating loss carryforwards 14,543 17,464 Deferred tax assets of a Canadian subsidiary 3,521 4,489 Realized and unrealized capital losses 305 305 Total valuation allowance $ 27,232 $ 35,272

EARNINGS PER SHARE (Tables)

EARNINGS PER SHARE (Tables)	12 Months Ended
	Dec. 31, 2024
Earnings Per Share [Abstract]
Schedule of Reconciliation of Basic and Diluted Earnings Per Share Computations	The following are computations of basic and diluted earnings per share (in thousands, except for per share amounts): For the years ended December 31, 2024 2023 2022 Numerator for basic and diluted earnings per share: Net income $ 402,299 $ 377,856 $ 411,744 Denominator: Weighted-average shares outstanding, basic 53,902 54,071 54,223 Dilutive impact of equity awards 297 311 264 Weighted-average shares outstanding, diluted 54,199 54,382 54,487 Basic earnings per share $ 7.46 $ 6.99 $ 7.59 Diluted earnings per share $ 7.42 $ 6.95 $ 7.56
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	The Company included all outstanding performance awards and restricted stock awards in the calculation of diluted earnings per share except as shown in the table below (in thousands): For the years ended December 31, 2024 2023 2022 Antidilutive restricted stock awards 10 12 10 Performance stock awards for which performance criteria was not attained at reporting date 39 89 —

ACCUMULATED OTHER COMPREHENSI_2

ACCUMULATED OTHER COMPREHENSIVE LOSS (Tables)	12 Months Ended
	Dec. 31, 2024
Equity [Abstract]
Schedule of Reclassification of Accumulated Other Comprehensive Income (Loss)	The changes in accumulated other comprehensive loss by component and related tax impacts for the years ended December 31, 2024, 2023 and 2022 were as follows (in thousands): Foreign Currency Translation Adjustments Unrealized (Loss) Gain on Available-For-Sale Securities Unrealized (Loss) Gain on Fair Value of Interest Rate Hedges Unrealized Loss on Pension Total Balance at January 1, 2022 $ (177,824) $ (150) $ (17,383) $ (655) $ (196,012) Other comprehensive (loss) income before reclassifications (31,515) (523) 78,711 415 47,088 Amounts reclassified out of accumulated other comprehensive loss — — (683) — (683) Tax benefit (provision) — 110 (17,587) (97) (17,574) Other comprehensive (loss) income (31,515) (413) 60,441 318 28,831 Balance at December 31, 2022 (209,339) (563) 43,058 (337) (167,181) Other comprehensive income (loss) before reclassifications 9,000 708 5,094 (741) 14,061 Amounts reclassified out of accumulated other comprehensive loss — — (30,273) — (30,273) Tax (provision) benefit — (149) 8,012 191 8,054 Other comprehensive income (loss) 9,000 559 (17,167) (550) (8,158) Balance at December 31, 2023 (200,339) (4) 25,891 (887) (175,339) Other comprehensive (loss) income before reclassifications (36,363) 47 16,515 339 (19,462) Amounts reclassified out of accumulated other comprehensive loss — — (19,582) — (19,582) Tax (provision) benefit — (10) 828 (70) 748 Other comprehensive (loss) income (36,363) 37 (2,239) 269 (38,296) Balance at December 31, 2024 $ (236,702) $ 33 $ 23,652 $ (618) $ (213,635)
Schedule of Reclassification out of Accumulated Other Comprehensive Income	The amounts realized in the consolidated statements of operations during the years ended December 31, 2024, 2023 and 2022 which were reclassified out of accumulated other comprehensive loss were as follows (in thousands): For the years ended December 31, Other Comprehensive Loss Component 2024 2023 2022 Location Unrealized (Loss) Gain on Fair Value of Interest Rate Hedges (1) $ 19,582 $ 30,273 $ 683 Interest expense, net of interest income ___________________________________ (1) For the year ended December 31, 2023, the balance is inclusive of an $8.3 million gain realized in connection with the settlement of certain interest rate swaps. For more information on this transaction, see Note 12, "Financing Arrangements."

STOCK-BASED COMPENSATION (Table

STOCK-BASED COMPENSATION (Tables)	12 Months Ended
	Dec. 31, 2024
Share-Based Payment Arrangement [Abstract]
Schedule of Restricted Stock	The following table summarizes information about restricted stock awards for the year ended December 31, 2024: Restricted Stock Number of Weighted Average Balance at January 1, 2024 414,623 $ 114.02 Granted 148,941 189.39 Vested (150,097) 107.23 Forfeited (25,507) 142.80 Balance at December 31, 2024 387,960 $ 143.69
Schedule of Performance Stock Awards	The following table summarizes information about performance stock awards for the year ended December 31, 2024: Performance Stock Number of Weighted Average Balance at January 1, 2024 181,284 $ 114.10 Granted 79,738 173.45 Vested (38,882) 104.69 Forfeited (62,944) 128.99 Balance at December 31, 2024 159,196 $ 102.09

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Tables)	12 Months Ended
	Dec. 31, 2024
Commitments and Contingencies Disclosure [Abstract]
Schedule of Self-Insurance Liabilities Anticipated Payments	Anticipated payments for contingencies related to workers' compensation, comprehensive general liability and vehicle liability related claims at December 31, 2024 for each of the next five years and thereafter were as follows (in thousands): Years ending December 31, 2025 $ 25,855 2026 21,083 2027 16,622 2028 11,720 2029 4,692 Thereafter 14,074 Undiscounted self-insurance liabilities 94,046 Less: Discount (10,374) Total self-insurance liabilities (included in accrued expenses and other current liabilities) $ 83,672

LEASES (Tables)

LEASES (Tables)	12 Months Ended
	Dec. 31, 2024
Leases [Abstract]
Schedule of Supplemental Lease Balance Sheet Information	The following table presents the Company's finance lease balances and their classification on the consolidated balance sheets (in thousands): Finance Lease Balances (Classification) December 31, 2024 December 31, 2023 ROU assets (Property, plant and equipment, net) $ 182,532 $ 126,292 Current portion of lease liabilities (Accrued expenses and other current liabilities) 25,330 16,975 Long-term portion of lease liabilities (Other long-term liabilities) 161,375 113,486
Schedule of Lease Expense and Other Information	The Company’s lease expense was as follows (in thousands): For the years ended December 31, 2024 2023 2022 Operating lease cost $ 81,688 $ 69,156 $ 59,041 Finance lease cost: Amortization of ROU assets 25,985 17,183 13,239 Interest on lease liabilities 7,066 4,051 3,011 Total finance lease cost 33,051 21,234 16,250 Short-term lease cost 199,516 167,379 158,736 Variable lease cost 5,187 4,887 4,353 Total lease cost $ 319,442 $ 262,656 $ 238,380 Other information related to leases was as follows: Weighted Average Remaining Lease Term (years) December 31, 2024 December 31, 2023 Operating leases 4.3 3.8 Finance leases 6.8 7.1 Weighted Average Discount Rate December 31, 2024 December 31, 2023 Operating leases 5.20 % 4.68 % Finance leases 4.84 % 3.96 % For the years ended December 31, Supplemental Cash Flow Related Disclosures (in thousands) 2024 2023 2022 Cash paid for amounts related to lease liabilities: Operating cash flows from operating leases $ 84,932 $ 71,185 $ 61,014 Operating cash flows from finance leases 7,066 4,051 3,011 Financing cash flows from finance leases 30,886 15,937 12,821 ROU assets obtained in exchange for operating lease liabilities 123,938 82,392 58,230 ROU assets obtained in exchange for finance lease liabilities 78,455 47,238 29,205
Schedule of Operating Lease Maturity	At December 31, 2024, the Company's future lease payments under non-cancelable leases that have lease terms in excess of one year were as follows (in thousands): Years ending December 31, December 31, 2024 Operating Leases Finance Leases 2025 $ 82,873 $ 36,230 2026 66,702 35,228 2027 54,242 35,217 2028 37,291 31,244 2029 20,357 27,084 Thereafter 25,064 58,522 Total future lease payments 286,529 223,525 Amount representing interest (31,983) (36,820) Total lease liabilities $ 254,546 $ 186,705
Schedule of Finance Lease Maturity	At December 31, 2024, the Company's future lease payments under non-cancelable leases that have lease terms in excess of one year were as follows (in thousands): Years ending December 31, December 31, 2024 Operating Leases Finance Leases 2025 $ 82,873 $ 36,230 2026 66,702 35,228 2027 54,242 35,217 2028 37,291 31,244 2029 20,357 27,084 Thereafter 25,064 58,522 Total future lease payments 286,529 223,525 Amount representing interest (31,983) (36,820) Total lease liabilities $ 254,546 $ 186,705

SEGMENT REPORTING (Tables)

SEGMENT REPORTING (Tables)	12 Months Ended
	Dec. 31, 2024
Segment Reporting [Abstract]
Schedule of Reconciliation of Third Party Revenues to Direct Revenues	The following tables reconcile third-party revenues to direct revenues by Reportable Segment (in thousands): For the year ended December 31, 2024 Environmental Safety-Kleen Sustainability Solutions Total Segment Revenues Corporate Total Consolidated Revenues Third-party revenues $ 4,960,325 $ 929,220 $ 5,889,545 $ 407 $ 5,889,952 Intersegment revenues (expense), net 44,422 (44,422) — — — Direct revenues $ 5,004,747 $ 884,798 $ 5,889,545 $ 407 $ 5,889,952 For the year ended December 31, 2023 Environmental Safety-Kleen Sustainability Solutions Total Segment Revenues Corporate Total Consolidated Revenues Third-party revenues $ 4,469,909 $ 938,796 $ 5,408,705 $ 447 $ 5,409,152 Intersegment revenues (expense), net 41,533 (41,533) — — — Direct revenues $ 4,511,442 $ 897,263 $ 5,408,705 $ 447 $ 5,409,152 For the year ended December 31, 2022 Environmental Safety-Kleen Sustainability Solutions Total Segment Revenues Corporate Total Consolidated Revenues Third-party revenues $ 4,144,973 $ 1,021,125 $ 5,166,098 $ 507 $ 5,166,605 Intersegment revenues (expense), net 26,733 (26,733) — — — Direct revenues $ 4,171,706 $ 994,392 $ 5,166,098 $ 507 $ 5,166,605
Schedule of Reconciliation to Consolidated Statements of Income to Adjusted EBITDA	The tables below present total Reportable Segment Adjusted EBITDA and the relevant significant segment expenses provided to the CODM by reported segment (in thousands): For the year ended December 31, 2024 Environmental Services Safety-Kleen Sustainability Solutions Total Reportable Segments Direct Revenues $ 5,004,747 $ 884,798 $ 5,889,545 Cost of Revenues 3,366,022 659,217 4,025,239 Selling, General and Administrative Expenses 371,263 78,575 449,838 Total Reportable Segment Adjusted EBITDA $ 1,267,462 $ 147,006 $ 1,414,468 For the year ended December 31, 2023 Environmental Services Safety-Kleen Sustainability Solutions Total Reportable Segments Direct Revenues $ 4,511,442 $ 897,263 $ 5,408,705 Cost of Revenues 3,063,043 646,301 3,709,344 Selling, General and Administrative Expenses 346,791 78,089 424,880 Total Reportable Segment Adjusted EBITDA $ 1,101,608 $ 172,873 $ 1,274,481 For the year ended December 31, 2022 Environmental Services Safety-Kleen Sustainability Solutions Total Reportable Segments Direct Revenues $ 4,171,706 $ 994,392 $ 5,166,098 Cost of Revenues 2,902,979 615,303 3,518,282 Selling, General and Administrative Expenses 315,674 72,762 388,436 Total Reportable Segment Adjusted EBITDA $ 953,053 $ 306,327 $ 1,259,380 The following table presents Total Reportable Segment Adjusted EBITDA reconciled to income from operations before provision for income taxes (in thousands): For the years ended December 31, 2024 2023 2022 Adjusted EBITDA: Environmental Services $ 1,267,462 $ 1,101,608 $ 953,053 Safety-Kleen Sustainability Solutions 147,006 172,873 306,327 Total Reportable Segment Adjusted EBITDA 1,414,468 1,274,481 1,259,380 Reconciliation to Consolidated Statements of Operations: Corporate Costs (1) 297,534 261,911 237,252 Accretion of environmental liabilities 13,456 13,667 12,943 Stock-based compensation 27,981 20,703 26,844 Depreciation and amortization 400,922 365,761 347,594 Kimball startup costs 4,343 — — Income from operations 670,232 612,439 634,747 Other expense (income), net 1,454 (2,315) (2,472) Loss on early extinguishment of debt 371 2,880 422 Gain on sale of business — — (8,864) Interest expense, net of interest income 134,964 108,595 107,663 Income from operations before provision for income taxes $ 533,443 $ 503,279 $ 537,998 ___________________________________ (1) Corporate Costs include the revenue, cost of revenues and selling, general and administrative expenses not managed through the Company’s operating segments. These costs are not captured within the Company’s Reportable Segment Adjusted EBITDA but are included in the Company’s total Adjusted EBITDA balances.
Schedule of Segment Reporting Information, by Segment	The following table presents assets by reported segment and in the aggregate (in thousands): December 31, 2024 December 31, 2023 Property, plant and equipment, net Environmental Services $ 1,865,611 $ 1,651,026 Safety-Kleen Sustainability Solutions 463,538 411,415 Corporate 118,792 130,877 Total property, plant and equipment, net $ 2,447,941 $ 2,193,318 Goodwill and Permits and other intangibles, net Environmental Services Goodwill $ 1,296,204 $ 1,112,013 Permits and other intangibles, net 549,482 454,919 Total Environmental Services 1,845,686 1,566,932 Safety-Kleen Sustainability Solutions Goodwill $ 180,995 $ 175,723 Permits and other intangibles, net 152,505 147,878 Total Safety-Kleen Sustainability Solutions 333,500 323,601 Total $ 2,179,186 $ 1,890,533
Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas	As of December 31, 2024 and 2023, the Company had property, plant and equipment, net of depreciation and amortization and permits and other intangible assets, net of amortization in the following geographic locations (in thousands): December 31, 2024 December 31, 2023 Total % of Total Total % of Total Property, plant and equipment, net United States $ 2,249,155 91.9 % $ 1,972,221 89.9 % Canada and other foreign 198,786 8.1 221,097 10.1 Total property, plant and equipment, net $ 2,447,941 100.0 % $ 2,193,318 100.0 % Permits and other intangibles, net United States $ 674,246 96.0 % $ 570,049 94.6 % Canada 27,741 4.0 32,748 5.4 Total permits and other intangibles, net $ 701,987 100.0 % $ 602,797 100.0 %
Schedule of Long-lived Assets by Geographic Areas	The following table presents the total assets by geographical area (in thousands): December 31, 2024 December 31, 2023 United States $ 6,756,813 $ 5,786,937 Canada and other foreign 620,465 595,932 Total $ 7,377,278 $ 6,382,869

SIGNIFICANT ACCOUNTING POLICI_4

SIGNIFICANT ACCOUNTING POLICIES - Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Marketable Securities [Line Items]
Total cash equivalents	$ 4,035	$ 27,542
Total marketable securities	102,634	106,101
Total	106,669	133,643
Commercial paper
Marketable Securities [Line Items]
Total marketable securities	17,489	56,172
Corporate notes and bonds
Marketable Securities [Line Items]
Total marketable securities	85,145	49,929
Commercial paper
Marketable Securities [Line Items]
Total cash equivalents	$ 4,035	$ 27,542

SIGNIFICANT ACCOUNTING POLICI_5

SIGNIFICANT ACCOUNTING POLICIES - Cash, Cash Equivalents and Uncashed Checks (Details)	Dec. 31, 2024 USD ($)
Accounting Policies [Abstract]
Bank disbursement account balance	$ 0

SIGNIFICANT ACCOUNTING POLICI_6

SIGNIFICANT ACCOUNTING POLICIES - Allowances for Doubtful Accounts And Revenue Allowance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Allowance for Doubtful Accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at January 1,	$ 22,568	$ 24,659	$ 24,136
Additions charged to earnings	8,129	5,956	7,783
Deductions from reserves, net of recoveries	(7,789)	(8,047)	(7,260)
Balance at December 31,	22,908	22,568	24,659
Revenue Allowance
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at January 1,	19,641	20,594	16,004
Additions charged to earnings	48,301	46,467	54,836
Deductions from reserves, net of recoveries	(43,608)	(47,420)	(50,246)
Balance at December 31,	$ 24,334	$ 19,641	$ 20,594

SIGNIFICANT ACCOUNTING POLICI_7

SIGNIFICANT ACCOUNTING POLICIES - Property, Plant and Equipment, net (Details) - USD ($)	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Impairment charges related to long-lived assets	$ 0	$ 0	$ 0
Minimum | Buildings
Property, Plant and Equipment [Line Items]
Weighted average remaining useful life (in years)	20 years
Minimum | Leasehold and building improvements
Property, Plant and Equipment [Line Items]
Weighted average remaining useful life (in years)	2 years
Minimum | Vehicles
Property, Plant and Equipment [Line Items]
Weighted average remaining useful life (in years)	2 years
Minimum | Capitalized software and computer equipment
Property, Plant and Equipment [Line Items]
Weighted average remaining useful life (in years)	3 years
Minimum | Containers and railcars
Property, Plant and Equipment [Line Items]
Weighted average remaining useful life (in years)	8 years
Minimum | All other equipment
Property, Plant and Equipment [Line Items]
Weighted average remaining useful life (in years)	4 years
Minimum | Furniture and fixtures
Property, Plant and Equipment [Line Items]
Weighted average remaining useful life (in years)	5 years
Maximum | Buildings
Property, Plant and Equipment [Line Items]
Weighted average remaining useful life (in years)	42 years
Maximum | Leasehold and building improvements
Property, Plant and Equipment [Line Items]
Weighted average remaining useful life (in years)	45 years
Maximum | Vehicles
Property, Plant and Equipment [Line Items]
Weighted average remaining useful life (in years)	15 years
Maximum | Capitalized software and computer equipment
Property, Plant and Equipment [Line Items]
Weighted average remaining useful life (in years)	5 years
Maximum | Containers and railcars
Property, Plant and Equipment [Line Items]
Weighted average remaining useful life (in years)	16 years
Maximum | All other equipment
Property, Plant and Equipment [Line Items]
Weighted average remaining useful life (in years)	30 years
Maximum | Furniture and fixtures
Property, Plant and Equipment [Line Items]
Weighted average remaining useful life (in years)	8 years

SIGNIFICANT ACCOUNTING POLICI_8

SIGNIFICANT ACCOUNTING POLICIES - Goodwill (Details)	12 Months Ended
	Dec. 31, 2024 reporting_unit
Accounting Policies [Abstract]
Number of reporting units	4

SIGNIFICANT ACCOUNTING POLICI_9

SIGNIFICANT ACCOUNTING POLICIES - Permits and Other Intangibles (Details)	Dec. 31, 2024
Minimum | Permits
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life (in years)	5 years
Minimum | Other intangible assets
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life (in years)	2 years
Maximum | Permits
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life (in years)	30 years
Maximum | Other intangible assets
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life (in years)	25 years

SIGNIFICANT ACCOUNTING POLIC_10

SIGNIFICANT ACCOUNTING POLICIES - Landfill Accounting and Non-Landfill Closure and Post-Closure Liabilities (Details) $ in Millions	12 Months Ended
	Dec. 31, 2024 USD ($) cubic_yard landfill_site	Dec. 31, 2023 USD ($) cubic_yard	Dec. 31, 2022 USD ($) cubic_yard
Property, Plant and Equipment [Line Items]
Landfill sites | landfill_site	8
Permitted, but not highly probable airspace (cubic yards)	0	0
Remaining Airspace Capacity [Roll Forward]
Remaining capacity, beginning of period (cubic yards)	27,753,000	28,270,000
Changes in highly probable airspace, net (cubic yards)	0	464,000
Consumed (cubic yards)	(802,000)	(981,000)
Remaining capacity, end of period (cubic yards)	26,951,000	27,753,000	28,270,000
Landfill final closure and post-closure liabilities | $	$ 59.4	$ 59.4
Regulatory post-closure period for landfill (in years)	30 years
Asset retirement obligations, risk free rate (as a percent)	6.57%	6.51%
Non-landfill closure and post-closure liabilities | $	$ 70.4	$ 59.2
Minimum
Remaining Airspace Capacity [Roll Forward]
Non-landfill closure and post-closure liabilities, period (in years)	10 years
Maximum
Remaining Airspace Capacity [Roll Forward]
Non-landfill closure and post-closure liabilities, period (in years)	30 years
Buttonwillow | California
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	21 years
Deer Trail | Colorado
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	17 years
Grassy Mountain | Utah
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	37 years
Kimball | Nebraska
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	22 years
Lambton | Ontario, Canada
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	46 years
Lone Mountain | Oklahoma
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	13 years
Ryley | Alberta, Canada
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	40 years
Sawyer | North Dakota
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	61 years
Landfill assets
Property, Plant and Equipment [Line Items]
Amortization | $	$ 10.6	$ 18.6	$ 16.2
Permitted
Property, Plant and Equipment [Line Items]
Permitted Remaining Highly Probable Airspace (cubic yards)	26,951,000
Permitted | Buttonwillow | California
Property, Plant and Equipment [Line Items]
Permitted Remaining Highly Probable Airspace (cubic yards)	4,909,000
Permitted | Deer Trail | Colorado
Property, Plant and Equipment [Line Items]
Permitted Remaining Highly Probable Airspace (cubic yards)	1,347,000
Permitted | Grassy Mountain | Utah
Property, Plant and Equipment [Line Items]
Permitted Remaining Highly Probable Airspace (cubic yards)	4,253,000
Permitted | Kimball | Nebraska
Property, Plant and Equipment [Line Items]
Permitted Remaining Highly Probable Airspace (cubic yards)	520,000
Permitted | Lambton | Ontario, Canada
Property, Plant and Equipment [Line Items]
Permitted Remaining Highly Probable Airspace (cubic yards)	4,218,000
Permitted | Lone Mountain | Oklahoma
Property, Plant and Equipment [Line Items]
Permitted Remaining Highly Probable Airspace (cubic yards)	2,913,000
Permitted | Ryley | Alberta, Canada
Property, Plant and Equipment [Line Items]
Permitted Remaining Highly Probable Airspace (cubic yards)	5,594,000
Permitted | Sawyer | North Dakota
Property, Plant and Equipment [Line Items]
Permitted Remaining Highly Probable Airspace (cubic yards)	3,197,000

SIGNIFICANT ACCOUNTING POLIC_11

SIGNIFICANT ACCOUNTING POLICIES - Remedial Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Regulatory Liabilities [Line Items]
Accrual for environmental loss contingencies	$ 111,745	$ 111,243	$ 116,290
Minimum
Regulatory Liabilities [Line Items]
Remedial liabilities at acquisition, risk-free interest rate (as a percent)	1.37%
Maximum
Regulatory Liabilities [Line Items]
Remedial liabilities at acquisition, risk-free interest rate (as a percent)	4.90%

SIGNIFICANT ACCOUNTING POLIC_12

SIGNIFICANT ACCOUNTING POLICIES - Defined Contribution Plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Accounting Policies [Abstract]
Employer discretionary contribution	$ 30.9	$ 28.8	$ 25.3

SIGNIFICANT ACCOUNTING POLIC_13

SIGNIFICANT ACCOUNTING POLICIES - Advertising Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Accounting Policies [Abstract]
Advertising expense	$ 11.4	$ 10.9	$ 9.4

SIGNIFICANT ACCOUNTING POLIC_14

SIGNIFICANT ACCOUNTING POLICIES - Leases (Details)	Dec. 31, 2024
Real Estate | Minimum
Property, Plant and Equipment [Line Items]
Lessee term	2 years
Real Estate | Maximum
Property, Plant and Equipment [Line Items]
Lessee term	10 years
Non-Real Estate | Minimum
Property, Plant and Equipment [Line Items]
Lessee term	3 years
Non-Real Estate | Maximum
Property, Plant and Equipment [Line Items]
Lessee term	7 years

REVENUES - Narrative (Details)

REVENUES - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2024 USD ($) source	Dec. 31, 2023 USD ($)
Disaggregation of Revenue [Line Items]
Deferred contract cost, recognition period	3 months
Deferred contracts costs | $	$ 28.2	$ 29.9
Environmental Services
Disaggregation of Revenue [Line Items]
Number of revenue sources	4
Safety-Kleen Sustainability Solutions
Disaggregation of Revenue [Line Items]
Number of revenue sources	2

REVENUES - Disaggregation of Re

REVENUES - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Disaggregation of Revenue [Line Items]
Total revenues	$ 5,889,952	$ 5,409,152	$ 5,166,605
Technical Services
Disaggregation of Revenue [Line Items]
Total revenues	1,733,550	1,563,847	1,495,264
Industrial Services and Other
Disaggregation of Revenue [Line Items]
Total revenues	1,377,909	1,419,385	1,311,579
Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total revenues	895,120	609,913	575,300
Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total revenues	1,183,883	1,102,041	962,697
Safety-Kleen Oil
Disaggregation of Revenue [Line Items]
Total revenues	699,490	713,966	821,765
United States
Disaggregation of Revenue [Line Items]
Total revenues	5,352,423	4,869,180	4,576,167
Canada
Disaggregation of Revenue [Line Items]
Total revenues	537,529	539,972	590,438
Environmental Services
Disaggregation of Revenue [Line Items]
Total revenues	5,004,747	4,511,442	4,171,706
Safety-Kleen Sustainability Solutions
Disaggregation of Revenue [Line Items]
Total revenues	884,798	897,263	994,392
Operating segments | Environmental Services
Disaggregation of Revenue [Line Items]
Total revenues	4,960,325	4,469,909	4,144,973
Operating segments | Environmental Services | Technical Services
Disaggregation of Revenue [Line Items]
Total revenues	1,733,550	1,563,847	1,495,264
Operating segments | Environmental Services | Industrial Services and Other
Disaggregation of Revenue [Line Items]
Total revenues	1,377,502	1,418,938	1,311,072
Operating segments | Environmental Services | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total revenues	895,120	609,913	575,300
Operating segments | Environmental Services | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total revenues	954,153	877,211	763,337
Operating segments | Environmental Services | Safety-Kleen Oil
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0
Operating segments | Environmental Services | United States
Disaggregation of Revenue [Line Items]
Total revenues	4,510,845	4,022,394	3,675,880
Operating segments | Environmental Services | Canada
Disaggregation of Revenue [Line Items]
Total revenues	449,480	447,515	469,093
Operating segments | Safety-Kleen Sustainability Solutions
Disaggregation of Revenue [Line Items]
Total revenues	929,220	938,796	1,021,125
Operating segments | Safety-Kleen Sustainability Solutions | Technical Services
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0
Operating segments | Safety-Kleen Sustainability Solutions | Industrial Services and Other
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0
Operating segments | Safety-Kleen Sustainability Solutions | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0
Operating segments | Safety-Kleen Sustainability Solutions | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total revenues	229,730	224,830	199,360
Operating segments | Safety-Kleen Sustainability Solutions | Safety-Kleen Oil
Disaggregation of Revenue [Line Items]
Total revenues	699,490	713,966	821,765
Operating segments | Safety-Kleen Sustainability Solutions | United States
Disaggregation of Revenue [Line Items]
Total revenues	841,171	846,339	899,780
Operating segments | Safety-Kleen Sustainability Solutions | Canada
Disaggregation of Revenue [Line Items]
Total revenues	88,049	92,457	121,345
Corporate
Disaggregation of Revenue [Line Items]
Total revenues	407	447	507
Corporate | Technical Services
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0
Corporate | Industrial Services and Other
Disaggregation of Revenue [Line Items]
Total revenues	407	447	507
Corporate | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0
Corporate | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0
Corporate | Safety-Kleen Oil
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0
Corporate | United States
Disaggregation of Revenue [Line Items]
Total revenues	407	447	507
Corporate | Canada
Disaggregation of Revenue [Line Items]
Total revenues	$ 0	$ 0	$ 0

REVENUES - Contract Balances (D

REVENUES - Contract Balances (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Revenue from Contract with Customer [Abstract]
Receivables	$ 1,015,357	$ 983,111
Contract assets (unbilled receivables)	162,215	107,859
Contract liabilities (deferred revenue)	$ 88,545	$ 95,230

BUSINESS COMBINATIONS - Additio

BUSINESS COMBINATIONS - Additional Information (Details) $ in Thousands						12 Months Ended
	Mar. 22, 2024 USD ($)	Mar. 01, 2024 USD ($)	Mar. 31, 2023 USD ($)	Dec. 09, 2022 USD ($)	Jun. 17, 2022 USD ($)	Dec. 31, 2024 USD ($) business	Dec. 31, 2023 USD ($)	Jun. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)
Business Acquisition [Line Items]
Number of businesses acquired | business						3
Goodwill						$ 1,477,199	$ 1,287,736		$ 1,246,878
HEPACO
Business Acquisition [Line Items]
Purchase price to acquire business	$ 392,200
Weighted average useful life of acquired intangible assets (in years)	19 years
Goodwill						186,911
HEPACO | Minimum
Business Acquisition [Line Items]
Finite-lived intangible asset, useful life (in years)	7 years
HEPACO | Maximum
Business Acquisition [Line Items]
Finite-lived intangible asset, useful life (in years)	20 years
Noble Oil Services , Inc. Acquisition
Business Acquisition [Line Items]
Purchase price to acquire business		$ 68,700
Weighted average useful life of acquired intangible assets (in years)		13 years
Goodwill						6,257
Noble Oil Services , Inc. Acquisition | Minimum
Business Acquisition [Line Items]
Finite-lived intangible asset, useful life (in years)		7 years
Noble Oil Services , Inc. Acquisition | Maximum
Business Acquisition [Line Items]
Finite-lived intangible asset, useful life (in years)		15 years
Series of Individually Immaterial Business Acquisitions
Business Acquisition [Line Items]
Purchase price to acquire business						17,100
Thompson Industrial
Business Acquisition [Line Items]
Purchase price to acquire business			$ 110,900
Weighted average useful life of acquired intangible assets (in years)			13 years
Goodwill						$ 39,564	$ 39,346
Thompson Industrial | Minimum
Business Acquisition [Line Items]
Finite-lived intangible asset, useful life (in years)			5 years
Thompson Industrial | Maximum
Business Acquisition [Line Items]
Finite-lived intangible asset, useful life (in years)			15 years
June 17, 2022 Acquisition
Business Acquisition [Line Items]
Purchase price to acquire business					$ 78,900
Weighted average useful life of acquired intangible assets (in years)					18 years
Goodwill								$ 32,212
June 17, 2022 Acquisition | Minimum
Business Acquisition [Line Items]
Finite-lived intangible asset, useful life (in years)					5 years
June 17, 2022 Acquisition | Maximum
Business Acquisition [Line Items]
Finite-lived intangible asset, useful life (in years)					20 years
December 9, 2022 Acquisition
Business Acquisition [Line Items]
Purchase price to acquire business				$ 12,600
Goodwill				$ 2,700

BUSINESS COMBINATIONS - Assets

BUSINESS COMBINATIONS - Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Jun. 30, 2023	Dec. 31, 2022
Business Acquisition [Line Items]
Goodwill	$ 1,477,199	$ 1,287,736		$ 1,246,878
Measurement Period Adjustments, Goodwill	218	360
HEPACO
Business Acquisition [Line Items]
Accounts receivable, including unbilled receivables	69,072
Inventories and supplies	384
Prepaid expenses and other current assets	4,383
Property, plant and equipment	47,125
Permits and other intangibles	130,500
Operating lease right-of-use assets	9,385
Other long-term assets	5,712
Accounts payable	(30,602)
Accrued expenses and other current liabilities	(16,005)
Current portion of operating lease liabilities	(2,758)
Operating lease liabilities, less current portion	(6,627)
Closure and post-closure liabilities	(2,492)
Remedial liabilities	(2,435)
Other long-term liabilities	(374)
Total identifiable net assets	205,268
Goodwill	186,911
Total purchase price	392,179
Noble Oil Services , Inc. Acquisition
Business Acquisition [Line Items]
Accounts receivable, including unbilled receivables	5,855
Inventories and supplies	6,598
Prepaid expenses and other current assets	408
Property, plant and equipment	55,615
Permits and other intangibles	14,500
Operating lease right-of-use assets	3,615
Other long-term assets	92
Accounts payable	(7,752)
Accrued expenses and other current liabilities	(1,145)
Current portion of operating lease liabilities	(1,823)
Operating lease liabilities, less current portion	(1,792)
Closure and post-closure liabilities	(8,929)
Remedial liabilities	(2,757)
Total identifiable net assets	62,485
Goodwill	6,257
Total purchase price	68,742
Thompson Industrial
Business Acquisition [Line Items]
Accounts receivable, including unbilled receivables	25,160	25,233
Inventories and supplies	228	228
Prepaid expenses and other current assets	1,302	1,302
Property, plant and equipment	26,719	26,719
Permits and other intangibles	28,900	28,900
Operating lease right-of-use assets	4,716	4,716
Other long-term assets	72	72
Accounts payable	(7,240)	(7,185)
Accrued expenses and other current liabilities	(3,290)	(3,200)
Current portion of operating lease liabilities	(1,653)	(1,653)
Operating lease liabilities, less current portion	(3,063)	(3,063)
Other long-term liabilities	(560)	(560)
Total identifiable net assets	71,291	71,509
Goodwill	39,564	39,346
Total purchase price	110,855	$ 110,855
Measurement Period Adjustments, Accounts receivable	(73)
Measurement Period Adjustments, Accounts payable	(55)
Measurement Period Adjustments, Accrued expenses and other current liabilities	(90)
Measurement Period Adjustments, Total identifiable net assets	(218)
Measurement Period Adjustments, Goodwill	218
Measurement Period Adjustments, Total purchase price	$ 0
June 17, 2022 Acquisition
Business Acquisition [Line Items]
Accounts receivable, including unbilled receivables			$ 1,089
Inventories and supplies			5,745
Prepaid expenses and other current assets			144
Property, plant and equipment			22,231
Permits and other intangibles			23,500
Operating lease right-of-use assets			585
Other long-term assets			13
Accrued expenses and other current liabilities			(3,375)
Current portion of operating lease liabilities			(186)
Operating lease liabilities, less current portion			(399)
Other long-term liabilities			(2,681)
Total identifiable net assets			46,666
Goodwill			32,212
Total purchase price			$ 78,878

DISPOSITION OF BUSINESS (Detail

DISPOSITION OF BUSINESS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Jun. 30, 2022
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale of business	$ 0	$ 0	$ 8,864
Disposal Group, Disposed of by Sale, Not Discontinued Operations | June 30, 2022 Disposition
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from disposition of business				$ 18,800
Consideration held in escrow				$ 1,500
Gain on sale of business			$ 8,900

INVENTORIES AND SUPPLIES (Detai

INVENTORIES AND SUPPLIES (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Inventory [Line Items]
Inventories and supplies	$ 384,657	$ 327,511
Supplies
Inventory [Line Items]
Inventories and supplies	200,905	177,217
Oil and oil related products
Inventory [Line Items]
Inventories and supplies	152,992	118,600
Solvent and solutions
Inventory [Line Items]
Inventories and supplies	12,458	11,795
Other
Inventory [Line Items]
Inventories and supplies	$ 18,302	$ 19,899

PROPERTY, PLANT AND EQUIPMENT -

PROPERTY, PLANT AND EQUIPMENT - Schedule of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 5,326,393	$ 4,964,301
Less - accumulated depreciation and amortization	2,878,452	2,770,983
Total property, plant and equipment, net	2,447,941	2,193,318
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	184,191	174,891
Asset retirement costs (non-landfill)
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	38,705	27,167
Landfill assets
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	258,138	253,180
Buildings and improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	719,439	630,525
Right-of-use assets, finance leases	8,000	8,000
Vehicles
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,455,530	1,276,567
Right-of-use assets, finance leases	230,500	151,700
Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,600,085	2,388,370
Right-of-use assets, finance leases	9,200	9,200
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 70,305	$ 213,601

PROPERTY, PLANT AND EQUIPMENT_2

PROPERTY, PLANT AND EQUIPMENT - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Abstract]
Depreciation expense, inclusive of landfill and finance lease amortization	$ 346.5	$ 315.5	$ 297.4
Interest costs capitalized	$ 11.2	$ 6.6	$ 3.4

GOODWILL AND OTHER INTANGIBLE_3

GOODWILL AND OTHER INTANGIBLE ASSETS - Changes to Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Goodwill [Roll Forward]
Goodwill, beginning of period	$ 1,287,736	$ 1,246,878
Increase from current period acquisitions	193,368	39,346
Measurement period adjustments from prior period acquisition	218	360
Foreign currency translation	(4,123)	1,152
Goodwill, end of period	1,477,199	1,287,736
Environmental Services
Goodwill [Roll Forward]
Goodwill, beginning of period	1,112,013	1,071,846
Increase from current period acquisitions	186,911	39,346
Measurement period adjustments from prior period acquisition	218	0
Foreign currency translation	(2,938)	821
Goodwill, end of period	1,296,204	1,112,013
Safety-Kleen Sustainability Solutions
Goodwill [Roll Forward]
Goodwill, beginning of period	175,723	175,032
Increase from current period acquisitions	6,457	0
Measurement period adjustments from prior period acquisition	0	360
Foreign currency translation	(1,185)	331
Goodwill, end of period	$ 180,995	$ 175,723

GOODWILL AND OTHER INTANGIBLE_4

GOODWILL AND OTHER INTANGIBLE ASSETS - Finite-lived and Indefinite Lived Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Finite-lived intangible assets
Finite-lived intangible assets, cost	$ 1,009,563	$ 896,809
Accumulated Amortization	427,086	414,297
Finite-lived intangible assets, net	582,477	482,512
Total permits and other intangible assets, cost	1,129,073	1,017,094
Total permits and other intangible assets, net	701,987	602,797
Trademarks and trade names
Finite-lived intangible assets
Trademarks and trade names	119,510	120,285
Permits
Finite-lived intangible assets
Finite-lived intangible assets, cost	191,921	191,747
Accumulated Amortization	123,939	117,556
Finite-lived intangible assets, net	67,982	74,191
Customer and supplier relationships
Finite-lived intangible assets
Finite-lived intangible assets, cost	697,326	604,994
Accumulated Amortization	256,657	258,879
Finite-lived intangible assets, net	440,669	346,115
Other intangible assets
Finite-lived intangible assets
Finite-lived intangible assets, cost	120,316	100,068
Accumulated Amortization	46,490	37,862
Finite-lived intangible assets, net	$ 73,826	$ 62,206

GOODWILL AND OTHER INTANGIBLE_5

GOODWILL AND OTHER INTANGIBLE ASSETS - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization expense of permits and other intangible assets	$ 54.4	$ 50.3	$ 50.2

GOODWILL AND OTHER INTANGIBLE_6

GOODWILL AND OTHER INTANGIBLE ASSETS - Expected Amortization (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Expected amortization
2025	$ 53,335
2026	51,297
2027	49,221
2028	47,916
2029	46,763
Thereafter	333,945
Finite-lived intangible assets, net	$ 582,477	$ 482,512

ACCRUED EXPENSES AND OTHER CU_3

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Payables and Accruals [Abstract]
Accrued compensation and benefits	$ 134,458	$ 113,236
Accrued insurance	112,367	107,658
Accrued interest	33,259	33,857
Accrued income, real estate, sales and other taxes	35,394	44,752
Accrued other	103,967	97,654
Total accrued expenses	$ 419,445	$ 397,157

ACCRUED EXPENSES AND OTHER CU_4

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES - Additional Information (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Payables and Accruals [Abstract]
Accrued insurance, employee medical insurance costs	$ 23.9	$ 22.8
Accrual loss for workers' compensation, comprehensive general liability and vehicle liability self-insurance programs	$ 83.7	$ 82.7

CLOSURE AND POST-CLOSURE LIAB_3

CLOSURE AND POST-CLOSURE LIABILITIES - Changes in Post-Closure Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Changes to post-closure liabilities
Balance at the beginning of the period	$ 118,600	$ 118,801
Liabilities assumed in acquisitions	11,421	574
Measurement period adjustments from prior period acquisitions		3,015
New asset retirement obligations	2,118	3,092
Accretion	9,558	9,477
Changes in estimates recorded to consolidated statement of operations	(225)	1,200
Changes in estimates recorded to consolidated balance sheet	4,737	(2,106)
Environmental expenditures	(15,676)	(15,684)
Currency translation and other	(745)	231
Balance at the end of the period	129,788	118,600
Landfill Retirement Liability
Changes to post-closure liabilities
Balance at the beginning of the period	59,443	62,251
Liabilities assumed in acquisitions	0	0
Measurement period adjustments from prior period acquisitions		0
New asset retirement obligations	2,118	3,092
Accretion	5,069	4,958
Changes in estimates recorded to consolidated statement of operations	70	1,147
Changes in estimates recorded to consolidated balance sheet	4,335	(3,706)
Environmental expenditures	(11,210)	(8,478)
Currency translation and other	(425)	179
Balance at the end of the period	59,400	59,443
Non-Landfill Retirement Liability
Changes to post-closure liabilities
Balance at the beginning of the period	59,157	56,550
Liabilities assumed in acquisitions	11,421	574
Measurement period adjustments from prior period acquisitions		3,015
New asset retirement obligations	0	0
Accretion	4,489	4,519
Changes in estimates recorded to consolidated statement of operations	(295)	53
Changes in estimates recorded to consolidated balance sheet	402	1,600
Environmental expenditures	(4,466)	(7,206)
Currency translation and other	(320)	52
Balance at the end of the period	$ 70,388	$ 59,157

CLOSURE AND POST-CLOSURE LIAB_4

CLOSURE AND POST-CLOSURE LIABILITIES - Anticipated Payments (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Environmental Property Sale, Disposal or Abandonment Costs
2025	$ 10,304
2026	14,457
2027	12,485
2028	14,127
2029	3,224
Thereafter	278,762
Undiscounted closure and post-closure liabilities	333,359
Less: Discount at credit-adjusted risk-free rate	(119,353)
Less: Undiscounted estimated closure and post-closure liabilities relating to airspace not yet consumed	(84,218)
Present value of closure and post-closure liabilities	$ 129,788	$ 118,600	$ 118,801

REMEDIAL LIABILITIES - Changes

REMEDIAL LIABILITIES - Changes in Remedial Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Site Contingency [Line Items]
Environmental Loss Contingency, Current, Statement of Financial Position [Extensible Enumeration]	Current portion of closure, post-closure and remedial liabilities	Current portion of closure, post-closure and remedial liabilities
Changes to remedial liabilities
Balance at the beginning of the period	$ 111,243	$ 116,290
Accretion	3,898	4,190
Changes in estimates recorded to consolidated statement of operations	4,364	3,628
Environmental expenditures	(11,846)	(13,276)
Currency translation and other	(1,106)	411
Liabilities assumed in acquisitions	5,192
Balance at the end of the period	111,745	111,243
Remedial Liabilities for Landfill Sites
Changes to remedial liabilities
Balance at the beginning of the period	1,880	1,824
Accretion	92	89
Changes in estimates recorded to consolidated statement of operations	29	19
Environmental expenditures	(53)	(52)
Currency translation and other	0	0
Liabilities assumed in acquisitions	0
Balance at the end of the period	1,948	1,880
Remedial Liabilities for Inactive Sites
Changes to remedial liabilities
Balance at the beginning of the period	60,277	59,749
Accretion	2,292	2,540
Changes in estimates recorded to consolidated statement of operations	573	1,713
Environmental expenditures	(6,078)	(3,840)
Currency translation and other	(28)	115
Liabilities assumed in acquisitions	0
Balance at the end of the period	57,036	60,277
Remedial Liabilities (Including Superfund) for Non-Landfill Operations
Changes to remedial liabilities
Balance at the beginning of the period	49,086	54,717
Accretion	1,514	1,561
Changes in estimates recorded to consolidated statement of operations	3,762	1,896
Environmental expenditures	(5,715)	(9,384)
Currency translation and other	(1,078)	296
Liabilities assumed in acquisitions	5,192
Balance at the end of the period	$ 52,761	$ 49,086

REMEDIAL LIABILITIES - Addition

REMEDIAL LIABILITIES - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Site Contingency [Line Items]
Remedial liabilities	$ 4,364	$ 3,628
Remedial Liabilities for Superfund Site
Site Contingency [Line Items]
Remedial liabilities	$ 2,900

REMEDIAL LIABILITIES - Anticipa

REMEDIAL LIABILITIES - Anticipated Payments (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Accrual for Environmental Loss Contingencies, Net [Abstract]
2025	$ 10,321
2026	17,391
2027	11,259
2028	10,972
2029	8,745
Thereafter	70,610
Undiscounted remedial liabilities	129,298
Less: Discount at risk free rates	(17,553)
Total remedial liabilities	$ 111,745	$ 111,243	$ 116,290
Environmental Loss Contingency, Statement of Financial Position [Extensible Enumeration]	Remedial liabilities, less current portion of $10,321 and $13,358, respectively, Current portion of closure, post-closure and remedial liabilities

REMEDIAL LIABILITIES - Estimate

REMEDIAL LIABILITIES - Estimates (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2024 USD ($) facility business	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Site Contingency [Line Items]
Number of businesses acquired | business	3
Accrual for environmental loss contingencies	5%
Accrual for environmental loss contingencies	$ 111,745	$ 111,243	$ 116,290
% of Total	100%
Reasonably possible additional liabilities	$ 21,558
Loss contingency accrual	29,800	32,400
Total remedial liabilities	111,745	111,243	$ 116,290
Legal and Administrative Proceedings
Site Contingency [Line Items]
Loss contingency accrual	$ 23,300	$ 25,000
Inactive facilities not used in active conduct of the Company's business, most of which were assumed through prior period acquisitions (25 facilities)
Site Contingency [Line Items]
Number of facility by type | facility	25
Accrual for environmental loss contingencies	$ 56,976
% of Total	51%
Reasonably possible additional liabilities	$ 10,765
Total remedial liabilities	$ 56,976
Facilities now used in active conduct of the Company's business (62 facilities, including 24 acquired by the Company through acquisitions in 2024)
Site Contingency [Line Items]
Number of facility by type | facility	62
Number of businesses acquired | business	24
Accrual for environmental loss contingencies	$ 46,131
% of Total	41.30%
Reasonably possible additional liabilities	$ 9,497
Total remedial liabilities	$ 46,131
Superfund sites (12 sites)
Site Contingency [Line Items]
Number of facility by type | facility	12
Accrual for environmental loss contingencies	$ 8,638
% of Total	7.70%
Reasonably possible additional liabilities	$ 1,296
Total remedial liabilities	$ 8,638
Superfund sites (12 sites) | Various
Site Contingency [Line Items]
Number of facility by type | facility	12
Accrual for environmental loss contingencies	$ 8,638
% of Total	7.70%
Reasonably possible additional liabilities	$ 1,296
Total remedial liabilities	8,638
Closed incinerator and landfill | Baton Rouge, LA
Site Contingency [Line Items]
Accrual for environmental loss contingencies	$ 25,578
% of Total	22.90%
Reasonably possible additional liabilities	$ 4,303
Total remedial liabilities	25,578
Closed incinerator | Bridgeport, NJ
Site Contingency [Line Items]
Accrual for environmental loss contingencies	$ 17,417
% of Total	15.60%
Reasonably possible additional liabilities	$ 3,254
Total remedial liabilities	17,417
Idled incinerator | Mercier, Quebec
Site Contingency [Line Items]
Accrual for environmental loss contingencies	$ 10,826
% of Total	9.70%
Reasonably possible additional liabilities	$ 1,631
Total remedial liabilities	10,826
Operating solvent recycling center | Linden, NJ
Site Contingency [Line Items]
Accrual for environmental loss contingencies	$ 9,434
% of Total	8.40%
Reasonably possible additional liabilities	$ 2,148
Total remedial liabilities	$ 9,434
All other incinerators, landfills, wastewater treatment facilities and service centers (83 facilities, including 24 acquired by the Company through acquisitions in 2024) | Various
Site Contingency [Line Items]
Number of facility by type | facility	83
Accrual for environmental loss contingencies	$ 39,852
% of Total	35.70%
Reasonably possible additional liabilities	$ 8,926
Total remedial liabilities	$ 39,852

FINANCING ARRANGEMENTS - Schedu

FINANCING ARRANGEMENTS - Schedule of Long-term Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Debt Instrument [Line Items]
Current portion of long-term debt	$ 15,102	$ 10,000
Long-term debt, at par	2,794,796	2,315,000
Unamortized debt issuance costs and discount, net	(23,679)	(23,283)
Long-term debt, at carrying value	2,771,117	2,291,717
Secured debt | Secured senior term loans due October 8, 2028
Debt Instrument [Line Items]
Current portion of long-term debt	15,102	10,000
Long-term debt, at par	1,449,796	970,000
Unsecured debt | Unsecured senior notes, at 4.875%, due July 15, 2027 ("2027 Notes")
Debt Instrument [Line Items]
Long-term debt, at par	$ 545,000	545,000
Interest rate (as a percent)	4.875%
Unsecured debt | Unsecured senior notes, at 5.125%, due July 15, 2029 ("2029 Notes")
Debt Instrument [Line Items]
Long-term debt, at par	$ 300,000	300,000
Interest rate (as a percent)	5.125%
Unsecured debt | Unsecured senior notes, at 6.375%, due February 1, 2031 ("2031 Notes")
Debt Instrument [Line Items]
Long-term debt, at par	$ 500,000	$ 500,000
Interest rate (as a percent)	6.375%

FINANCING ARRANGEMENTS - Additi

FINANCING ARRANGEMENTS - Additional Information (Details) - USD ($)

6 Months Ended

12 Months Ended

Oct. 08, 2024

Jun. 28, 2024

Mar. 22, 2024

Dec. 27, 2023

Apr. 28, 2023

Jan. 24, 2023

Dec. 31, 2023

Dec. 31, 2024

Dec. 31, 2023

Dec. 31, 2022

Jun. 27, 2024

Dec. 26, 2023

Jul. 01, 2023

Jun. 30, 2023

Jul. 02, 2019

Dec. 31, 2018

Financing arrangements

Fair value of long-term obligations, including current portion

$ 2,300,000,000

$ 2,800,000,000

$ 2,300,000,000

2022 Swaps

Financing arrangements

Derivative notional amount

$ 600,000,000

2018 Swaps

Financing arrangements

Derivative notional amount

$ 350,000,000

Reclassification of gain from accumulated other comprehensive loss to interest expense

$ 8,300,000

8,300,000

Interest rate swap

Financing arrangements

Reclassification of gain from accumulated other comprehensive loss to interest expense

19,582,000

30,273,000

$ 683,000

Derivative asset

35,500,000

32,400,000

35,500,000

Term CORRA Adjustment 1 | Revolving credit facility

Financing arrangements

Basis spread on variable rate (as a percent)

0.29547%

Term CORRA Adjustment 2 | Revolving credit facility

Financing arrangements

Basis spread on variable rate (as a percent)

0.32138%

Line of credit

Financing arrangements

Period for measurement of average liquidity (in days)

30 days

Line of credit | Minimum

Financing arrangements

Commitment fee per annum of the unused commitment

0.25%

Line of credit | Maximum

Financing arrangements

Commitment fee per annum of the unused commitment

0.375%

Line of credit | Revolving credit facility

Financing arrangements

Debt outstanding

0

0

0

Credit facility, maximum borrowing capacity

$ 600,000,000

$ 400,000,000

Revolving credit facility, available borrowing capacity

470,000,000

Letters of credit outstanding, amount

$ 130,000,000

Line of credit | Revolving credit facility | U.S. Borrower

Financing arrangements

Credit facility, maximum borrowing capacity

550,000,000

Line of credit | Revolving credit facility | Canadian Subsidiaries

Financing arrangements

Credit facility, maximum borrowing capacity

50,000,000

Line of credit | Letters of credit

Financing arrangements

Credit facility, maximum borrowing capacity

$ 250,000,000

Line of credit | Secured Overnight Financing Rate (SOFR) | Minimum

Financing arrangements

Basis spread on variable rate (as a percent)

1.50%

Line of credit | Secured Overnight Financing Rate (SOFR) | Maximum

Financing arrangements

Basis spread on variable rate (as a percent)

1.75%

Line of credit | Base rate | Minimum

Financing arrangements

Basis spread on variable rate (as a percent)

0.50%

Line of credit | Base rate | Maximum

Financing arrangements

Basis spread on variable rate (as a percent)

0.75%

Line of credit | Base rate | Revolving credit facility

Financing arrangements

Basis spread on variable rate (as a percent)

0.50%

Line of credit | Secured Overnight Financing Rate (SOFR) Adjustment | Revolving credit facility

Financing arrangements

Basis spread on variable rate (as a percent)

0.10%

Line of credit | SOFR Adjustment and Base Rate | Revolving credit facility

Financing arrangements

Basis spread on variable rate (as a percent)

1.50%

Line of credit | Canadian Rate | Revolving credit facility

Financing arrangements

Basis spread on variable rate (as a percent)

0.50%

Unsecured debt

Financing arrangements

Redemption percentage of principal amount

100%

Term Loans | Secured debt

Financing arrangements

Debt outstanding

$ 980,000,000

$ 980,000,000

$ 1,464,900,000

$ 980,000,000

Aggregate principal amount

500,000,000

Proceeds from issuance of secured debt

$ 491,100,000

Soft call repricing term

6 months

Prepayment premium percentage

1%

Decrease of interest rate margin

0.25%

Effective interest rate (as a percent)

3.7145%

3.82898%

4.07898%

Term Loans | Secured debt | Term SOFR Adjustment

Financing arrangements

Basis spread on variable rate (as a percent)

0.11448%

0.11448%

Term Loans | Secured debt | Secured Overnight Financing Rate (SOFR)

Financing arrangements

Debt, interest margin

1.75%

1.75%

2%

2%

Debt, floor interest rate

0%

Variable rate, percentage

0.25%

Term Loans | Secured debt | Base rate

Financing arrangements

Debt, interest margin

0.75%

Debt, floor interest rate

1%

Unsecured senior notes, at 4.875%, due July 15, 2027 ("2027 Notes") | Unsecured debt

Financing arrangements

Aggregate principal amount

$ 545,000,000

Unsecured senior notes, at 5.125%, due July 15, 2029 ("2029 Notes") | Unsecured debt

Financing arrangements

Aggregate principal amount

$ 300,000,000

Unsecured senior notes, at 6.375%, due February 1, 2031 ("2031 Notes") | Unsecured debt

Financing arrangements

Aggregate principal amount

$ 500,000,000

Redemption percentage of principal amount

106.375%

Debt instrument, redemption price, percentage of principal amount redeemed

40%

Secured senior term loans due June 30, 2024 ("2024 Term Loans") | Secured debt | 2018 Swaps

Financing arrangements

Debt outstanding

$ 350,000,000

Existing Term Loans | Secured debt | 2022 Swaps

Financing arrangements

Aggregate principal amount

$ 600,000,000

Effective interest rate (as a percent)

2.931%

Existing Term Loans | Secured debt | 2022 Swaps | Through June 30, 2023

Financing arrangements

Derivative, fixed interest rate

0.931%

Existing Term Loans | Secured debt | 2022 Swaps | From July 1, 2023 through September 30, 2027

Financing arrangements

Derivative, fixed interest rate

1.965%

FINANCING ARRANGEMENTS - Sche_2

FINANCING ARRANGEMENTS - Schedule of Redemption Prices (Details) - Unsecured debt	12 Months Ended
	Dec. 31, 2024
Debt Instrument, Redemption [Line Items]
Redemption percentage of principal amount	100%
2031 Notes
Debt Instrument, Redemption [Line Items]
Redemption percentage of principal amount	106.375%
Debt Instrument, Redemption, Period One | 2029 Notes
Debt Instrument, Redemption [Line Items]
Redemption percentage of principal amount	102.563%
Debt Instrument, Redemption, Period One | 2031 Notes
Debt Instrument, Redemption [Line Items]
Redemption percentage of principal amount	103.188%
Debt Instrument, Redemption, Period Two | 2029 Notes
Debt Instrument, Redemption [Line Items]
Redemption percentage of principal amount	101.281%
Debt Instrument, Redemption, Period Two | 2031 Notes
Debt Instrument, Redemption [Line Items]
Redemption percentage of principal amount	101.594%
Debt Instrument, Redemption, Period Three | 2027 Notes
Debt Instrument, Redemption [Line Items]
Redemption percentage of principal amount	100%
Debt Instrument, Redemption, Period Three | 2029 Notes
Debt Instrument, Redemption [Line Items]
Redemption percentage of principal amount	100%
Debt Instrument, Redemption, Period Three | 2031 Notes
Debt Instrument, Redemption [Line Items]
Redemption percentage of principal amount	100%

INCOME TAXES - Provision for Ta

INCOME TAXES - Provision for Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Noncontrolling Interest [Abstract]
Domestic	$ 444,118	$ 401,912	$ 406,206
Foreign	89,325	101,367	131,792
Income before provision for income taxes	533,443	503,279	537,998
Current:
Federal	68,321	64,164	52,237
State	27,649	25,496	26,980
Foreign	16,737	23,078	29,488
Current income taxes	112,707	112,738	108,705
Deferred
Federal	20,669	18,251	32,199
State	(4,415)	(9,049)	(2,432)
Foreign	2,183	3,483	(12,218)
Deferred income taxes	18,437	12,685	17,549
Provision for income taxes	$ 131,144	$ 125,423	$ 126,254
Effective tax rate	24.60%	24.90%	23.50%
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Tax expense at U.S. statutory rate	$ 112,023	$ 105,689	$ 112,980
State income taxes, net of federal benefit	18,555	18,067	19,831
Foreign rate differential	3,965	4,213	6,196
Valuation allowance	(6,485)	(7,699)	(18,769)
Uncertain tax position interest and penalties	(1,773)	(7)	(2,454)
Tax credits	2,694	1,653	2,768
Non-deductible compensation	2,211	2,898	2,754
Other	(46)	609	2,948
Provision for income taxes	$ 131,144	$ 125,423	$ 126,254

INCOME TAXES - Additional Infor

INCOME TAXES - Additional Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2024 USD ($)
Income Tax Disclosure [Abstract]
Expiration of tax credits	$ 4.1

INCOME TAXES - Deferred Tax Ass

INCOME TAXES - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Deferred tax assets:
Provision for doubtful accounts	$ 14,808	$ 10,882
Closure, post-closure and remedial liabilities	32,189	31,944
Operating lease liabilities	60,929	46,784
Accrued expenses	14,749	14,963
Accrued compensation and benefits	16,876	15,058
Net operating loss carryforwards	48,331	39,042
Excess business interest	22,078	0
Tax credit carryforwards	2,619	6,531
Stock-based compensation	4,877	3,516
Other	2,565	4,843
Total deferred tax assets	220,021	173,563
Deferred tax liabilities:
Property, plant and equipment	(311,546)	(284,997)
Operating lease right-of-use assets	(59,999)	(46,584)
Interest rate swap asset	(8,748)	(9,576)
Permits and other intangible assets	(158,905)	(130,391)
Prepaid expenses	(10,881)	(12,372)
Total deferred tax liabilities	(550,079)	(483,920)
Total net deferred tax liability before valuation allowance	(330,058)	(310,357)
Less valuation allowance	(27,232)	(35,272)
Net deferred tax liabilities	(357,290)	$ (345,629)
State net operating loss carryforwards, begin to expire in 2025	290,700
Federal operating loss carryforwards, begin to expire in 2025	79,300
Foreign net operating loss carryforwards, begin to expire in 2025	$ 64,300

INCOME TAXES - Valuation Allowa

INCOME TAXES - Valuation Allowance (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Foreign tax credits	$ 346	$ 4,422
Federal net operating losses	3,783	3,783
State net operating loss carryforwards	4,734	4,809
Foreign net operating loss carryforwards	14,543	17,464
Deferred tax assets of a Canadian subsidiary	3,521	4,489
Realized and unrealized capital losses	305	305
Total valuation allowance	$ 27,232	$ 35,272

EARNINGS PER SHARE - Reconcilia

EARNINGS PER SHARE - Reconciliation of Basic and Diluted Earnings Per Share Computations (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Numerator for basic and diluted earnings per share:
Net income, basic	$ 402,299	$ 377,856	$ 411,744
Net income, diluted	$ 402,299	$ 377,856	$ 411,744
Denominator:
Weighted-average shares outstanding basic (in shares)	53,902	54,071	54,223
Dilutive impact of equity awards (in shares)	297	311	264
Weighted-average shares outstanding, diluted (in shares)	54,199	54,382	54,487
Basic earnings per share (in dollars per share)	$ 7.46	$ 6.99	$ 7.59
Diluted earnings per share (in dollars per share)	$ 7.42	$ 6.95	$ 7.56

EARNINGS PER SHARE - Antidiluti

EARNINGS PER SHARE - Antidilutive Securities Excluded from Computation of Earnings Per Share (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Performance stock awards for which performance criteria was not attained at reporting date (in shares)	39	89	0
Restricted Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive restricted stock awards (in shares)	10	12	10

STOCKHOLDERS' EQUITY (Details)

STOCKHOLDERS' EQUITY (Details) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Equity [Abstract]
Stock repurchase program, authorized amount	$ 1,100
Repurchase of common stock (in shares)	0.2	0.3	0.5
Repurchases of common stock, excluding exercise tax	$ 55	$ 51.2	$ 50.2
Stock repurchase program, remaining authorized repurchase amount	$ 499.1

ACCUMULATED OTHER COMPREHENSI_3

ACCUMULATED OTHER COMPREHENSIVE LOSS - Components of AOCI (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 2,247,506	$ 1,922,322	$ 1,513,887
Other comprehensive (loss) income before reclassifications	(19,462)	14,061	47,088
Amounts reclassified out of accumulated other comprehensive loss	(19,582)	(30,273)	(683)
Tax (provision) benefit	748	8,054	(17,574)
Other comprehensive (loss) income, net of tax	(38,296)	(8,158)	28,831
Ending balance	2,573,529	2,247,506	1,922,322
Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(175,339)	(167,181)	(196,012)
Other comprehensive (loss) income, net of tax	(38,296)	(8,158)	28,831
Ending balance	(213,635)	(175,339)	(167,181)
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(200,339)	(209,339)	(177,824)
Other comprehensive (loss) income before reclassifications	(36,363)	9,000	(31,515)
Amounts reclassified out of accumulated other comprehensive loss	0	0	0
Tax (provision) benefit	0	0	0
Other comprehensive (loss) income, net of tax	(36,363)	9,000	(31,515)
Ending balance	(236,702)	(200,339)	(209,339)
Unrealized (Loss) Gain on Available-For-Sale Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(4)	(563)	(150)
Other comprehensive (loss) income before reclassifications	47	708	(523)
Amounts reclassified out of accumulated other comprehensive loss	0	0	0
Tax (provision) benefit	(10)	(149)	110
Other comprehensive (loss) income, net of tax	37	559	(413)
Ending balance	33	(4)	(563)
Unrealized (Loss) Gain on Fair Value of Interest Rate Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	25,891	43,058	(17,383)
Other comprehensive (loss) income before reclassifications	16,515	5,094	78,711
Amounts reclassified out of accumulated other comprehensive loss	(19,582)	(30,273)	(683)
Tax (provision) benefit	828	8,012	(17,587)
Other comprehensive (loss) income, net of tax	(2,239)	(17,167)	60,441
Ending balance	23,652	25,891	43,058
Unrealized Loss on Pension
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(887)	(337)	(655)
Other comprehensive (loss) income before reclassifications	339	(741)	415
Amounts reclassified out of accumulated other comprehensive loss	0	0	0
Tax (provision) benefit	(70)	191	(97)
Other comprehensive (loss) income, net of tax	269	(550)	318
Ending balance	$ (618)	$ (887)	$ (337)

ACCUMULATED OTHER COMPREHENSI_4

ACCUMULATED OTHER COMPREHENSIVE LOSS - Reclassification out of AOCI (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Interest rate swap
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Unrealized (loss) gain on fair value of interest rate hedges	$ 19,582	$ 30,273	$ 683
Certain Interest Rate Swaps
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Unrealized (loss) gain on fair value of interest rate hedges		$ 8,300

STOCK-BASED COMPENSATION - Addi

STOCK-BASED COMPENSATION - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 28	$ 20.7	$ 26.8
Total income tax benefit from stock-based compensation	$ 5.1	$ 3.5	$ 5
Minimum | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period (in years)	3 years
Maximum | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period (in years)	5 years
2020 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized (in shares)				2,500,000

STOCK-BASED COMPENSATION - Rest

STOCK-BASED COMPENSATION - Restricted Stock Awards (Details) - Restricted Stock - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Number of Shares
Beginning balance (in shares)	414,623
Granted (in shares)	148,941
Vested (in shares)	(150,097)
Forfeited (in shares)	(25,507)
Ending balance (in shares)	387,960	414,623
Weighted Average Grant-Date Fair Value
Beginning balance (in shares)	$ 114.02
Granted (in dollars per share)	189.39
Vested (in dollars per share)	107.23
Forfeited (in dollars per share)	142.80
Ending balance (in shares)	$ 143.69	$ 114.02
Unrecognized compensation cost	$ 39.5
Period for recognition (in years)	2 years 8 months 12 days
Fair value of share-based payment awards	$ 31.9	$ 26.5	$ 16.4

STOCK-BASED COMPENSATION - Perf

STOCK-BASED COMPENSATION - Performance Stock Awards (Details) - Performance Stock Awards - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Number of Shares
Beginning balance (in shares)	181,284
Granted (in shares)	79,738
Vested (in shares)	(38,882)
Forfeited (in shares)	(62,944)
Ending balance (in shares)	159,196	181,284
Weighted Average Grant-Date Fair Value
Beginning balance (in shares)	$ 114.10
Granted (in dollars per share)	173.45
Vested (in dollars per share)	104.69
Forfeited (in dollars per share)	128.99
Ending balance (in shares)	$ 102.09	$ 114.10
Unrecognized compensation cost	$ 5.7
Period for recognition (in years)	2 years 4 months 24 days
Fair value of share-based payment awards	$ 8.6	$ 17	$ 11.1

STOCK-BASED COMPENSATION - Empl

STOCK-BASED COMPENSATION - Employee Stock Purchase Plan (Details) - USD ($) $ in Millions		12 Months Ended
	May 22, 2024	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 28	$ 20.7	$ 26.8
Employee Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
ESPP discount percentage from fair market value	10%
ESPP purchase price of common stock, percent of closing price	90%
Shares originally authorized for issuance (in shares)	500,000
Shares issued under ESPP (in shares)		15,435
Stock-based compensation expense		$ 0.7

COMMITMENTS AND CONTINGENCIES_2

COMMITMENTS AND CONTINGENCIES (Details) $ in Millions	12 Months Ended
	Dec. 31, 2024 USD ($) site claim proceeding	Dec. 31, 2023 USD ($)
Loss Contingencies [Line Items]
Loss contingency accrual	$ 29.8	$ 32.4
Retention for environmental impairment	1
Self-insurance liabilities	$ 83.7	$ 82.7
Weighted average risk free discount rate for self insurance liabilities	4.14%	4.86%
Safety-Kleen Sustainability Solutions
Loss Contingencies [Line Items]
Deductible per occurrence for workers compensation	$ 1
Deductible per occurrence for general liability	2
Deductible per occurrence for vehicle liability	2
Minimum
Loss Contingencies [Line Items]
Deductible medical insurance policy	$ 2
Product Liability Cases
Loss Contingencies [Line Items]
Number of proceedings | proceeding	68
Loss contingency, claims settled and dismissed, claims | claim	18
Legal and Administrative Proceedings
Loss Contingencies [Line Items]
Loss contingency accrual	$ 23.3	$ 25
Federal, State, and Provincial Enforcement Actions
Loss Contingencies [Line Items]
Loss contingency accrual	$ 6.5	$ 7.4
Number of proceedings | proceeding	2
Superfund Proceedings
Loss Contingencies [Line Items]
Number of sites subject to proceedings under federal or state superfund laws | site	131
Number of sites owned by the entity subject to proceedings under federal or state superfund laws | site	6
Number of sites owned by third parties subject to proceedings under federal or state superfund laws | site	125
Number of sites for which environmental remediation expense is settled | site	30
Third party sites requiring expenditure on remediation | site	12
Number of sites for which environmental remediation expense is not required | site	83
Number of sites which potential liability could exceed $1.0 million | site	3
Safety-Kleen Sustainability Solutions
Loss Contingencies [Line Items]
Notices received from owners of third party sites seeking indemnification from the company | site	17

COMMITMENTS AND CONTINGENCIES -

COMMITMENTS AND CONTINGENCIES - Schedule of Self-Insurance Liabilities Anticipated Payments (Details) $ in Thousands	Dec. 31, 2024 USD ($)
Commitments and Contingencies Disclosure [Abstract]
2025	$ 25,855
2026	21,083
2027	16,622
2028	11,720
2029	4,692
Thereafter	14,074
Undiscounted self-insurance liabilities	94,046
Less: Discount	(10,374)
Total self-insurance liabilities (included in accrued expenses and other current liabilities)	$ 83,672

LEASES - Schedule of Supplement

LEASES - Schedule of Supplemental Finance Lease Balance Sheet information (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
ROU assets:
ROU assets (Property, plant and equipment, net)	$ 182,532	$ 126,292
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Property, plant and equipment, net	Property, plant and equipment, net
Current portion of lease liabilities:
Current portion of lease liabilities (Accrued expenses and other current liabilities)	$ 25,330	$ 16,975
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	Accrued expenses and other current liabilities	Accrued expenses and other current liabilities
Long-term portion of lease liabilities:
Long-term portion of lease liabilities (Other long-term liabilities)	$ 161,375	$ 113,486
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Other long-term liabilities	Other long-term liabilities

LEASES - Lease Expense (Details

LEASES - Lease Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Leases [Abstract]
Operating lease cost	$ 81,688	$ 69,156	$ 59,041
Finance lease cost:
Amortization of ROU assets	25,985	17,183	13,239
Interest on lease liabilities	7,066	4,051	3,011
Total finance lease cost	33,051	21,234	16,250
Short-term lease cost	199,516	167,379	158,736
Variable lease cost	5,187	4,887	4,353
Total lease cost	$ 319,442	$ 262,656	$ 238,380

LEASES - Other Information rela

LEASES - Other Information related to Leases (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Weighted Average Remaining Lease Term (years)
Operating lease (in years)	4 years 3 months 18 days	3 years 9 months 18 days
Finance lease (in years)	6 years 9 months 18 days	7 years 1 month 6 days
Weighted Average Discount Rate
Operating lease (as a percentage)	5.20%	4.68%
Finance lease (as a percentage)	4.84%	3.96%
Cash paid for amounts related to lease liabilities:
Operating cash flows from operating leases	$ 84,932	$ 71,185	$ 61,014
Operating cash flows from finance leases	7,066	4,051	3,011
Financing cash flows from finance leases	30,886	15,937	12,821
ROU assets obtained in exchange for operating lease liabilities	123,938	82,392	58,230
ROU assets obtained in exchange for finance lease liabilities	$ 78,455	$ 47,238	$ 29,205

LEASES - Schedule of Future Lea

LEASES - Schedule of Future Lease Payments (Details) $ in Thousands	Dec. 31, 2024 USD ($)
Operating Leases
2025	$ 82,873
2026	66,702
2027	54,242
2028	37,291
2029	20,357
Thereafter	25,064
Total future lease payments	286,529
Amount representing interest	(31,983)
Total lease liabilities	254,546
Finance Leases
2025	36,230
2026	35,228
2027	35,217
2028	31,244
2029	27,084
Thereafter	58,522
Total future lease payments	223,525
Amount representing interest	(36,820)
Total lease liabilities	$ 186,705

SEGMENT REPORTING - Additional

SEGMENT REPORTING - Additional Information (Details)	12 Months Ended
	Dec. 31, 2024 segment
Segment Reporting [Abstract]
Number of operating segments	2

SEGMENT REPORTING - Reconciliat

SEGMENT REPORTING - Reconciliation of Third Party Revenues to Direct Revenues (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting Information [Line Items]
Total revenues	$ 5,889,952	$ 5,409,152	$ 5,166,605
Total Segment Revenues
Segment Reporting Information [Line Items]
Total revenues	5,889,545	5,408,705	5,166,098
Environmental Services
Segment Reporting Information [Line Items]
Total revenues	5,004,747	4,511,442	4,171,706
Safety-Kleen Sustainability Solutions
Segment Reporting Information [Line Items]
Total revenues	884,798	897,263	994,392
Intersegment revenues (expense), net | Environmental Services
Segment Reporting Information [Line Items]
Total revenues	44,422	41,533	26,733
Intersegment revenues (expense), net | Safety-Kleen Sustainability Solutions
Segment Reporting Information [Line Items]
Total revenues	(44,422)	(41,533)	(26,733)
Operating Segments | Total Segment Revenues
Segment Reporting Information [Line Items]
Total revenues	5,889,545	5,408,705	5,166,098
Operating Segments | Environmental Services
Segment Reporting Information [Line Items]
Total revenues	4,960,325	4,469,909	4,144,973
Operating Segments | Safety-Kleen Sustainability Solutions
Segment Reporting Information [Line Items]
Total revenues	929,220	938,796	1,021,125
Corporate
Segment Reporting Information [Line Items]
Total revenues	$ 407	$ 447	$ 507

SEGMENT REPORTING - Adjusted EB

SEGMENT REPORTING - Adjusted EBITDA and Significant Segment Expense Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting Information [Line Items]
Direct Revenues	$ 5,889,952	$ 5,409,152	$ 5,166,605
Cost of Revenues	4,065,713	3,746,124	3,543,930
Selling, general and administrative expenses	739,629	671,161	627,391
Total Reportable Segments
Segment Reporting Information [Line Items]
Direct Revenues	5,889,545	5,408,705	5,166,098
Cost of Revenues	4,025,239	3,709,344	3,518,282
Selling, general and administrative expenses	449,838	424,880	388,436
Total Reportable Segment Adjusted EBITDA	1,414,468	1,274,481	1,259,380
Environmental Services
Segment Reporting Information [Line Items]
Direct Revenues	5,004,747	4,511,442	4,171,706
Cost of Revenues	3,366,022	3,063,043	2,902,979
Selling, general and administrative expenses	371,263	346,791	315,674
Total Reportable Segment Adjusted EBITDA	1,267,462	1,101,608	953,053
Safety-Kleen Sustainability Solutions
Segment Reporting Information [Line Items]
Direct Revenues	884,798	897,263	994,392
Cost of Revenues	659,217	646,301	615,303
Selling, general and administrative expenses	78,575	78,089	72,762
Total Reportable Segment Adjusted EBITDA	$ 147,006	$ 172,873	$ 306,327

SEGMENT REPORTING - Reconcili_2

SEGMENT REPORTING - Reconciliation to Consolidated Statements of Income to Adjusted EBITDA (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Reconciliation to Consolidated Statements of Operations:
Corporate Costs	$ 297,534	$ 261,911	$ 237,252
Accretion of environmental liabilities	13,456	13,667	12,943
Stock-based compensation	27,981	20,703	26,844
Depreciation and amortization	400,922	365,761	347,594
Kimball startup costs	4,343	0	0
Income from operations	670,232	612,439	634,747
Other expense (income), net	1,454	(2,315)	(2,472)
Loss on early extinguishment of debt	371	2,880	422
Gain on sale of business	0	0	(8,864)
Interest expense, net of interest income	134,964	108,595	107,663
Income before provision for income taxes	533,443	503,279	537,998
Environmental Services
Segment Reporting Information [Line Items]
Total Reportable Segment Adjusted EBITDA	1,267,462	1,101,608	953,053
Safety-Kleen Sustainability Solutions
Segment Reporting Information [Line Items]
Total Reportable Segment Adjusted EBITDA	147,006	172,873	306,327
Operating segments
Segment Reporting Information [Line Items]
Total Reportable Segment Adjusted EBITDA	1,414,468	1,274,481	1,259,380
Operating segments | Environmental Services
Segment Reporting Information [Line Items]
Total Reportable Segment Adjusted EBITDA	1,267,462	1,101,608	953,053
Operating segments | Safety-Kleen Sustainability Solutions
Segment Reporting Information [Line Items]
Total Reportable Segment Adjusted EBITDA	$ 147,006	$ 172,873	$ 306,327

SEGMENT REPORTING - Schedule of

SEGMENT REPORTING - Schedule of Segment Reporting Information, by Segment (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 2,447,941	$ 2,193,318
Goodwill	1,477,199	1,287,736	$ 1,246,878
Permits and other intangibles, net	701,987	602,797
Total	2,179,186	1,890,533
Environmental Services
Segment Reporting Information [Line Items]
Goodwill	1,296,204	1,112,013	1,071,846
Safety-Kleen Sustainability Solutions
Segment Reporting Information [Line Items]
Goodwill	180,995	175,723	$ 175,032
Operating segments | Environmental Services
Segment Reporting Information [Line Items]
Property, plant and equipment, net	1,865,611	1,651,026
Goodwill	1,296,204	1,112,013
Permits and other intangibles, net	549,482	454,919
Total	1,845,686	1,566,932
Operating segments | Safety-Kleen Sustainability Solutions
Segment Reporting Information [Line Items]
Property, plant and equipment, net	463,538	411,415
Goodwill	180,995	175,723
Permits and other intangibles, net	152,505	147,878
Total	333,500	323,601
Corporate
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 118,792	$ 130,877

SEGMENT REPORTING - Assets by G

SEGMENT REPORTING - Assets by Geographical Area (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 2,447,941	$ 2,193,318
Percent of property, plant and equipment, net	100%	100%
Permits and other intangibles, net	$ 701,987	$ 602,797
Percent of permits and other intangibles, net	100%	100%
Assets	$ 7,377,278	$ 6,382,869
United States
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 2,249,155	$ 1,972,221
Percent of property, plant and equipment, net	91.90%	89.90%
Permits and other intangibles, net	$ 674,246	$ 570,049
Percent of permits and other intangibles, net	96%	94.60%
Assets	$ 6,756,813	$ 5,786,937
Canada and other foreign
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 198,786	$ 221,097
Percent of property, plant and equipment, net	8.10%	10.10%
Assets	$ 620,465	$ 595,932
Canada
Segment Reporting Information [Line Items]
Permits and other intangibles, net	$ 27,741	$ 32,748
Percent of permits and other intangibles, net	4%	5.40%