US Ecology (ECOL) 10-K 2 Mar 20 2019 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Feb. 26, 2020	Jun. 30, 2019
Document Information
Document Type	10-K
Document Annual Report	true
Document Transition Report	false
Document Period End Date	Dec. 31, 2019
Entity File Number	001-39120
Entity Registrant Name	US ECOLOGY, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	84-2421185
Entity Address, Address Line One	101 S. Capitol Blvd., Suite 1000
Entity Address, City or Town	Boise
Entity Address, State or Province	ID
Entity Address, Postal Zip Code	83702
City Area Code	208
Local Phone Number	331-8400
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
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		31,516,432
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Entity Central Index Key	0001783400
Amendment Flag	false
Entity Public Float			$ 1,300
Common Stock
Document Information
Title of 12(b) Security	Common Stock
Trading Symbol	ECOL
Security Exchange Name	NASDAQ
Warrants
Document Information
Title of 12(b) Security	Warrants to Purchase Common Stock
Trading Symbol	ECOLW

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current Assets:
Cash and cash equivalents	$ 41,281	$ 31,969
Receivables, net	255,310	144,690
Prepaid expenses and other current assets	25,136	10,938
Income taxes receivable	11,244	7,071
Total current assets	332,971	194,668
Property and equipment, net	478,768	258,443
Operating lease assets	57,396
Restricted cash and investments	5,069	4,941
Intangible assets, net	574,902	279,666
Goodwill	766,980	207,177
Other assets	15,158	3,003
Total assets	2,231,244	947,898
Current Liabilities:
Accounts payable	46,906	17,754
Deferred revenue	14,788	10,451
Accrued liabilities	65,869	35,524
Accrued salaries and benefits	29,653	16,732
Income taxes payable	726	505
Current portion of long-term debt	3,359
Current portion of closure and post-closure obligations	2,152	2,266
Current portion of operating lease liabilities	17,317
Total current liabilities	180,770	83,232
Long-term debt	765,842	364,000
Long-term closure and post-closure obligations	84,231	76,097
Long-term operating lease liabilities	39,954
Other long-term liabilities	20,722	2,146
Deferred income taxes, net	128,345	63,206
Total liabilities	1,219,864	588,681
Commitments and contingencies (See Note 18)
Stockholders' Equity:
Common stock $0.01 par value per share, 50,000 authorized; 31,461 and 22,040 shares issued and outstanding, respectively	315	220
Additional paid-in capital	816,345	183,834
Retained earnings	206,574	189,324
Treasury stock, at cost, 0 and 8 shares, respectively		(370)
Accumulated other comprehensive loss	(11,854)	(13,791)
Total stockholders' equity	1,011,380	359,217
Total liabilities and stockholders' equity	$ 2,231,244	$ 947,898

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares shares in Thousands	Dec. 31, 2019	Dec. 31, 2018
CONSOLIDATED BALANCE SHEETS
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	50,000	50,000
Common stock, shares issued	31,461	22,040
Common stock, shares outstanding	31,461	22,040
Treasury stock, shares	0	8

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
CONSOLIDATED STATEMENTS OF OPERATIONS
Revenue	$ 685,509	$ 565,928	$ 504,042
Direct operating costs	475,675	395,834	350,915
Gross profit	209,834	170,094	153,127
Selling, general and administrative expenses	141,123	92,340	84,466
Goodwill and intangible asset impairment charges		3,666	8,903
Operating income	68,711	74,088	59,758
Other income (expense):
Interest income	605	215	62
Interest expense	(19,239)	(12,130)	(18,157)
Foreign currency gain (loss)	(733)	55	516
Other	455	2,630	791
Total other expense	(18,912)	(9,230)	(16,788)
Income before income taxes	49,799	64,858	42,970
Income tax expense (benefit)	16,659	15,263	(6,395)
Net income	$ 33,140	$ 49,595	$ 49,365
Earnings per share:
Basic (in dollars per share)	$ 1.41	$ 2.27	$ 2.27
Diluted (in dollars per share)	$ 1.40	$ 2.25	$ 2.25
Shares used in earnings per share calculation:
Basic (in shares)	23,521	21,888	21,758
Diluted (in shares)	23,749	22,047	21,902

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME
Net income	$ 33,140	$ 49,595	$ 49,365
Other comprehensive income (loss):
Foreign currency translation gain (loss)	3,772	(6,094)	4,046
Net changes in interest rate hedge, net of taxes of $(488), $375 and $985, respectively	(1,835)	1,407	1,575
Comprehensive income, net of tax	$ 35,077	$ 44,908	$ 54,986

CONSOLIDATED STATEMENTS OF CO_2

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Other comprehensive income (loss):
Net changes in interest rate hedge, tax	$ (488)	$ 375	$ 985

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net income	$ 33,140	$ 49,595	$ 49,365
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization of property and equipment	41,423	29,207	28,302
Amortization of intangible assets	15,491	9,645	9,888
Accretion of closure and post-closure obligations	4,388	3,707	3,026
Property and equipment impairment charges	25
Goodwill and intangible asset impairment charges		3,666	8,903
Unrealized foreign currency loss (gain)	(666)	1,211	(1,283)
Deferred income taxes	6,601	5,906	(25,309)
Share-based compensation expense	5,544	4,366	3,933
Share-based payments of business development and integration expenses	3,717
Unrecognized tax benefits	(238)	485
Net loss on disposition of assets	426	370	408
Gain on insurance proceeds from damaged property and equipment	(12,366)	(347)	(1,313)
Amortization and write-off of debt issuance costs	1,007	810	6,009
Amortization and write-off of debt discount	27		667
Change in fair value of contingent consideration	349
Changes in assets and liabilities (net of effects of business acquisitions):
Receivables	(9,357)	(32,301)	(13,861)
Income taxes receivable	(4,163)	(7,072)	4,121
Other assets	(2,163)	(1,187)	(1,328)
Accounts payable and accrued liabilities	(10,706)	14,301	2,012
Deferred revenue	967	2,059	617
Accrued salaries and benefits	8,326	2,476	3,420
Income taxes payable	(244)	(3,512)	3,921
Closure and post-closure obligations	(1,912)	(1,900)	(1,795)
Net cash provided by operating activities	79,616	81,485	79,703
Cash flows from investing activities:
Business acquisitions (net of cash acquired)	(399,599)	(108,382)
Purchases of property and equipment	(58,100)	(40,757)	(36,240)
Insurance proceeds from damaged property and equipment	12,714		1,313
Minority interest investment	(7,870)
Proceeds from sale of property and equipment	1,182	493	974
Payment of acquired contingent consideration liabilities	(4,000)
Purchases of restricted investments	(1,197)	(1,023)	(800)
Proceeds from sale of restricted investments	1,145	910	835
Net cash used in investing activities	(455,725)	(148,759)	(33,918)
Cash flows from financing activities:
Proceeds from long-term debt	491,875	87,000	281,000
Payments on long-term debt	(80,000)		(287,040)
Payments on short-term borrowings	(77,997)		(13,438)
Proceeds from short-term borrowings	77,997		11,260
Dividends paid	(15,890)	(15,804)	(15,711)
Deferred financing costs paid	(9,416)		(2,967)
Payment of equipment financing obligations	(1,539)	(448)	(377)
Proceeds from exercise of stock options	319	2,427	1,050
Other	(915)	(314)	(121)
Net cash provided by (used in) financing activities	384,434	72,861	(26,344)
Effect of foreign exchange rate changes on cash	1,062	(1,633)	636
Increase in Cash and cash equivalents and restricted cash	9,387	3,954	20,077
Cash and cash equivalents and restricted cash at beginning of year	32,753	28,799	8,722
Cash and cash equivalents and restricted cash at end of year	$ 42,140	$ 32,753	$ 28,799

CONSOLIDATED STATEMENTS OF CA_2

CONSOLIDATED STATEMENTS OF CASH FLOWS - (Restricted cash and investments) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Cash and cash equivalents and restricted cash
Cash and cash equivalents	$ 41,281	$ 31,969	$ 27,042	$ 7,015
Restricted cash	859	784	1,757	1,707
Cash and cash equivalents and restricted cash	$ 42,140	$ 32,753	$ 28,799	$ 8,722

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($)	Common Stock	Additional Paid-In Capital	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Total
Beginning balances at Dec. 31, 2016	$ 218	$ 172,704,000	$ 121,879,000	$ (52,000)	$ (14,725,000)	$ 280,024,000
Balance (in shares) at Dec. 31, 2016	21,779,716
Increase (Decrease) in Stockholders' Equity
Net income			49,365,000			49,365,000
Other comprehensive income (loss)					5,621,000	5,621,000
Share-based compensation		3,933,000				3,933,000
Dividends paid			(15,711,000)			(15,711,000)
Stock option exercises		1,047,000				1,047,000
Stock option exercises (in shares)	43,175
Repurchase of common stock				(121,000)		(121,000)
Issuance of restricted common stock		(81,000)				(81,000)
Issuance of restricted common stock (in shares)	26,274
Issuance of restricted common stock from treasury shares		(105,000)		105,000
Ending balances at Dec. 31, 2017	$ 218	177,498,000	155,533,000	(68,000)	(9,104,000)	324,077,000
Balance (in shares) at Dec. 31, 2017	21,849,165
Increase (Decrease) in Stockholders' Equity
Net income			49,595,000			49,595,000
Other comprehensive income (loss)					(4,687,000)	(4,687,000)
Share-based compensation		4,366,000				4,366,000
Dividends paid			(15,804,000)			(15,804,000)
Stock option exercises	$ 1	2,428,000				2,429,000
Stock option exercises (in shares)	143,220
Repurchase of common stock				(313,000)		(313,000)
Issuance of restricted common stock	$ 1	(278,000)				(277,000)
Issuance of restricted common stock (in shares)	44,949
Issuance of restricted common stock from treasury shares		(11,000)		11,000
Issuance of performance common stock		(169,000)				(169,000)
Issuance of performance common stock (in shares)	2,810
Ending balances at Dec. 31, 2018	$ 220	183,834,000	189,324,000	(370,000)	(13,791,000)	$ 359,217,000
Balance (in shares) at Dec. 31, 2018	22,040,144					22,040,000
Increase (Decrease) in Stockholders' Equity
Net income			33,140,000			$ 33,140,000
Other comprehensive income (loss)					1,937,000	1,937,000
Share-based compensation		5,544,000				5,544,000
Dividends paid			(15,890,000)			(15,890,000)
Share-based payments of business development and integration expenses		3,717,000				3,717,000
Stock option exercises		319,000				319,000
Stock option exercises (in shares)	8,235
Repurchase of common stock				(916,000)		(916,000)
Issuance of restricted common stock	$ 2	(1,516,000)				(1,514,000)
Issuance of restricted common stock (in shares)	78,175
Issuance of restricted common stock from treasury shares		(514,000)		514,000
Issuance of performance common stock		(634,000)				(634,000)
Issuance of performance common stock (in shares)	9,540
Common stock issued in NRC Merger	$ 93	581,008,000				581,101,000
Common stock issued in NRC Merger (in shares)	9,337,949
Replacement warrants, restricted stock and stock options issued in NRC Merger		45,359,000				45,359,000
Cancellation of treasury shares		(772,000)		$ 772,000
Cancellation of treasury shares (in shares)	(13,359)
Ending balances at Dec. 31, 2019	$ 315	$ 816,345,000	$ 206,574,000		$ (11,854,000)	$ 1,011,380,000
Balance (in shares) at Dec. 31, 2019	31,460,684					31,461,000

CONSOLIDATED STATEMENTS OF ST_2

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY
Repurchase of common stock, number of shares	14,462	5,564	2,502

DESCRIPTION OF BUSINESS

DESCRIPTION OF BUSINESS	12 Months Ended
	Dec. 31, 2019
DESCRIPTION OF BUSINESS
DESCRIPTION OF BUSINESS	NOTE 1. DESCRIPTION OF BUSINESS US Ecology Holdings, Inc., the predecessor to the Company (“Predecessor US Ecology”), was incorporated as a Delaware corporation in March 1987 as American Ecology Corporation. On February 22, 2010, Predecessor US Ecology changed its name from American Ecology Corporation to US Ecology, Inc. On November 1, 2019, in connection with the Company’s acquisition of NRC Group Holdings Corp. (“NRC”), a new parent entity of US Ecology completed a merger transaction with Predecessor US Ecology and became the successor to Predecessor US Ecology and changed its name to “US Ecology, Inc.” In connection with the closing of the NRC Merger (as defined below), Predecessor US Ecology changed its name to “US Ecology Holdings, Inc.” US Ecology, Inc., through its subsidiaries, is a leading North American provider of environmental services to commercial and government entities. The Company addresses the complex waste management needs of its customers, offering treatment, disposal and recycling of hazardous and radioactive waste, as well as a wide range of complementary field and industrial services. US Ecology, Inc. and its predecessors have been protecting the environment since 1952, with operations primarily in the United States, Canada, the Europe, Middle East, and Africa (“EMEA”) region and Mexico. Throughout these consolidated financial statements words such as “we,” “us,” “our,” “US Ecology” and the “Company” refer to US Ecology, Inc. and its subsidiaries. On November 1, 2019, pursuant to and subject to the conditions set forth in the Agreement and Plan of Merger (the “Merger Agreement”) by and among the Company, NRC, Predecessor US Ecology, Rooster Merger Sub, Inc. (“NRC Merger Sub”), and ECOL Merger Sub, Inc. (“ECOL Merger Sub”), ECOL Merger Sub merged with and into Predecessor US Ecology, with Predecessor US Ecology continuing as the surviving company and as a wholly-owned subsidiary of the Company. Substantially concurrently therewith, NRC Merger Sub merged with and into NRC, with NRC continuing as the surviving company and as a wholly-owned subsidiary of the Company. Following the completion of the mergers (collectively, the “NRC Merger”), the Company contributed all of the issued and outstanding equity interests of NRC to Predecessor US Ecology so that, after such contribution, NRC became a wholly-owned subsidiary of Predecessor US Ecology. ​ Effective as of November 1, 2019, the Company changed its name from “US Ecology Parent, Inc.” to “US Ecology, Inc.,” the Company’s common stock and warrants began trading on Nasdaq under the symbol “ECOL” and “ECOLW,” respectively. The Company identified itself as the successor issuer to Predecessor US Ecology pursuant to Rule 12g-3(c) under the Securities Exchange Act of 1934, as amended. Our operations are managed in two reportable segments reflecting our internal management reporting structure and nature of services offered as follows: Environmental Services Field & Industrial Services

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2019
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	NOTE 2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Principles of Consolidation The accompanying financial statements are prepared on a consolidated basis. All inter-company balances and transactions have been eliminated in consolidation. Our year-end is December 31. Cash and Cash Equivalents Cash and cash equivalents consist primarily of cash on deposit, money market accounts or short-term investments with original maturities of 90 days or less at the date of acquisition. Cash and cash equivalents totaled $41.3 million and $32.0 million at December 31, 2019 and 2018, respectively. At December 31, 2019 and 2018, we had $35.2 million and $19.4 million, respectively, of cash at our operations outside the United States. Receivables Our receivables include invoiced and unbilled amounts where the Company has an unconditional right to payment. ​ Receivables are stated at an amount management expects to collect. Based on management’s assessment of the credit history of the customers having outstanding balances and factoring in current economic conditions, management has concluded that potential unidentified losses on balances outstanding at year-end will not be material. ​ Unbilled receivables are recorded for work performed under contracts that have not yet been invoiced to customers and arise due to the timing of billings. Substantially all unbilled receivables at December 31, 2019, were billed in the following month. ​ Restricted Cash and Investments Restricted cash and investments of $5.1 million and $4.9 million at December 31, 2019 and 2018, respectively, represent funds held in third-party managed trust accounts as collateral for our financial assurance obligations for post-closure activities at our non-operating facilities. These funds are invested in fixed-income U.S. Treasury and government agency securities and money market accounts. The balances are adjusted monthly to fair market value based on quoted prices in active markets for identical or similar assets. Revenue Recognition Revenues are recognized when control of the promised services is transferred to our customers, in an amount that reflects the consideration we expect to be entitled to in exchange for those services. ​ We recognize revenue from three primary sources: (1) waste treatment, recycling and disposal services, (2) field and industrial waste management services, and (3) waste transportation services. Our waste treatment and disposal customers are legally obligated to properly treat and dispose of their waste in accordance with local, state, and federal laws and regulations. As our customers do not possess the resources to properly treat and dispose of their waste independently, they contract with the Company to perform these services. Waste treatment, recycling, and disposal revenue results primarily from fixed fees charged to customers for treatment and/or disposal or recycling of specified wastes. Waste treatment, recycling, and disposal revenue is generally charged on a per-ton or per-yard basis based on contracted prices and is recognized over time as the services are performed. Our treatment and disposal services are generally performed as the waste is received and considered complete upon final disposal. Field and industrial waste management services revenue results primarily from specialty onsite services such as high-pressure cleaning, tank cleaning, decontamination, remediation, transportation, spill cleanup and emergency response at refineries, chemical plants, steel and automotive plants, and other government, commercial and industrial facilities. We also provide hazardous waste packaging and collection services and total waste management solutions at customer sites and through our 10-day transfer facilities. These 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. Generally, the pricing in these types of contracts is fixed, but the quantity of services to be provided during the contract term is variable and revenues are recognized over the term of the agreements or as services are performed. As we have a right to consideration from our customers in an amount that corresponds directly with the value to the customer of the Company’s performance completed to date, we have applied the practical expedient to recognize revenue in the amount to which we have the right to invoice. Additionally, we have customers that pay annual retainer fees, primarily for our standby services, under long-term or evergreen contracts. Such retainer fees are recognized over time as the services are performed and it is probable that a significant reversal in the amount of cumulative revenue recognized on the contracts will not occur. Transportation and logistics revenue results from delivering customer waste to a disposal facility for treatment and/or disposal or recycling. Transportation services are generally not provided on a stand-alone basis and instead are bundled with other Company services. However, in some instances we provide transportation and logistics services for shipment of waste from cleanup sites to disposal facilities operated by other companies. For such arrangements, we allocate revenue to each performance obligation based on its relative standalone selling price. We generally determine standalone selling prices based on the prices charged to customer or using expected cost plus margin. Transportation revenue is recognized over time as the waste is transported. Taxes and fees collected from customers concurrent with revenue-producing transactions to be remitted to governmental authorities are excluded from revenue. Our Richland, Washington disposal facility is regulated by the Washington Utilities and Transportation Commission (“WUTC”), which approves our rates for disposal of low-level radioactive waste (“LLRW”). Annual revenue levels are established based on a rate agreement with the WUTC at amounts sufficient to cover the costs of operation, including facility maintenance, equipment replacement and related costs, and provide us with a reasonable profit. Per-unit rates charged to LLRW customers during the year are based on our evaluation of disposal volume and radioactivity projections submitted to us by waste generators. Our proposed rates are then reviewed and approved by the WUTC. If annual revenue exceeds the approved levels set by the WUTC, we are required to refund excess collections to facility users on a pro-rata basis. Refundable excess collections, if any, are recorded in Accrued liabilities in the consolidated balance sheets. The current rate agreement with the WUTC was extended in 2019 and is effective until December 31, 2025. Deferred Revenue We record deferred revenue when cash payments are received, or advance billings are charged, prior to performance of services, such as waste that has been received but not yet treated or disposed, and is recognized when these services are performed. During the year ended December 31, 2019 and 2018, we recognized $10.4 million and $8.4 million of revenue that was included in the deferred revenue balance at the beginning of each year, respectively. ​ Property and Equipment Property and equipment are recorded at cost and depreciated on the straight-line method over estimated useful lives. Replacements and major repairs of property and equipment are capitalized and retirements are made when assets are disposed of or when the useful life has been exhausted. Minor components and parts are expensed as incurred. Repair and maintenance expenses were $20.5 million, $17.5 million and $14.8 million for the years ended December 31, 2019, 2018 and 2017, respectively. We assume no salvage value for our depreciable fixed assets. The estimated useful lives for significant property and equipment categories are as follows: ​ ​ ​ ​ ​ ​ ​ ​ Useful Lives Vehicles, vessels and other equipment 3 to 10 years Disposal facility and equipment 3 to 20 years Buildings and improvements 5 to 40 years Railcars ​ ​ 40 years ​ Disposal Cell Accounting Qualified disposal cell development costs such as personnel and equipment costs incurred to construct new disposal cells are recorded and capitalized at cost. Capitalized cell development costs, net of recorded amortization, are added to estimated future costs of the permitted disposal cell to be incurred over the remaining construction of the cell, to determine the amount to be amortized over the remaining estimated cell life. Estimates of future costs are developed using input from independent engineers and internal technical and accounting managers. We review these estimates at least annually. Amortization is recorded on a unit of consumption basis, typically applying cost as a rate per cubic yard disposed. Disposal facility costs are expected to be fully amortized upon final closure of the facility, as no salvage value applies. Costs associated with ongoing disposal operations are charged to expense as incurred. We have material financial commitments for closure and post-closure obligations for certain facilities we own or operate. We estimate future cost requirements for closure and post-closure monitoring based on RCRA and conforming state requirements and facility permits. RCRA requires that companies provide the responsible regulatory agency acceptable financial assurance for closure work and subsequent post-closure monitoring of each facility for 30 years following closure. Estimates for final closure and post-closure costs are developed using input from our technical and accounting managers as well as independent engineers and are reviewed by management at least annually. These estimates involve projections of costs that will be incurred after the disposal facility ceases operations, through the required post-closure care period. The present value of the estimated closure and post-closure costs are accreted using the interest method of allocation to direct costs in our consolidated statements of operations so that 100% of the future cost has been incurred at the time of payment. Business Combinations We account for business combinations under the acquisition method of accounting. The cost of an acquired company is assigned to the tangible and identifiable intangible assets purchased and the liabilities assumed on the basis of their fair values at the date of acquisition. Any excess of purchase price over the fair value of net tangible and intangible assets acquired is assigned to goodwill. The transaction costs associated with business combinations are expensed as they are incurred. Goodwill Goodwill represents the excess of the fair value of the consideration transferred over the fair value of the underlying identifiable assets and liabilities acquired. Goodwill is not amortized, but instead is assessed for impairment annually in the fourth quarter as of October 1 and also if an event occurs or circumstances change that may indicate a possible impairment. In the event that we determine that the value of goodwill has become impaired, we will incur an accounting charge for the amount of impairment during the period in which the determination has been made. See Note 3 for additional information related to the use of estimates in the Company’s goodwill impairment tests and Note 13 for additional information related to our annual assessment of goodwill. Intangible Assets Intangible assets are stated at the fair value assigned in a business combination net of amortization. We amortize our amortizing intangible assets using the straight-line method over their estimated economic lives ranging from 1 to 60 years. We review intangible assets with indefinite useful lives for impairment during the fourth quarter as of October 1 of each year. We also review both non-amortizing and amortizing intangible assets for impairment whenever events or changes in circumstances indicate that the carrying value of an intangible asset may not be recoverable. See Note 3 for additional information related to the use of estimates in the Company’s intangible assets impairment tests and Note 13 for additional information related to our annual assessment of non-amortizing intangible. Our acquired permits and licenses generally have renewal terms of approximately 5-10 years. We have a history of renewing these permits and licenses as demonstrated by the fact that each of the sites’ treatment permits and licenses have been renewed regularly since the facility began operations. We intend to continue to renew our permits and licenses as they come up for renewal for the foreseeable future. Costs incurred to renew or extend the term of our permits and licenses are recorded in Selling, general and administrative expenses in our consolidated statements of operations. Impairment of Long-Lived Assets Long-lived assets consist primarily of property and equipment facility development costs and amortizing intangible assets. The recoverability of long-lived assets is evaluated periodically through analysis of operating results and consideration of other significant events or changes in the business environment. If an operating unit had indications of possible impairment, we would evaluate whether impairment exists on the basis of undiscounted expected future cash flows from operations over the remaining amortization period. If an impairment loss were to exist, the carrying amount of the related long-lived assets would be reduced to their estimated fair value. Debt Issuance Costs & Debt Discount Debt issuance costs and debt discount are amortized over the scheduled maturity of the underlying debt instrument. Amortization of debt issuance costs and debt discount is included as a component of interest expense in the consolidated statements of operations. Unamortized debt discount and debt issuance costs associated with our Term Loan were $7.8 million at December 31, 2019 and have been recorded as a reduction of the Current portion of long-term debt and Long-term debt in the consolidated balance sheets. Unamortized debt issuance costs associated with our Revolving Credit Facility were $4.7 million and $2.7 million at December 31, 2019 and 2018, respectively, and have been recorded in Prepaid expenses and other current assets and Other assets in the consolidated balance sheets. The Company wrote off certain unamortized debt issuance costs associated with the 2014 Credit Agreement that were to be amortized to interest expense in future periods through a charge of $5.5 million to Interest expense in 2017. Derivative Instruments In order to manage interest rate exposure, we entered into an interest rate swap agreement in October 2014 that effectively converts a portion of our variable-rate debt to a fixed interest rate. Changes in the fair value of the interest rate swap are recorded as a component of accumulated other comprehensive income within stockholders’ equity, and are recognized in interest expense in the period in which the payment is settled. The interest rate swap has an effective date of December 31, 2014 in an initial notional amount of $250.0 million. The Company does not hold or issue derivative financial instruments for trading or speculative purposes. Foreign Currency The assets, liabilities and results of operations of certain of our foreign subsidiaries are measured using their functional currency which is the currency of the primary foreign economic environment in which they operate. Assets and liabilities are translated to U.S. dollars (“USD”) 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 our foreign subsidiaries into USD are included in stockholders’ equity as a component of Accumulated other comprehensive income. Gains and losses resulting from foreign currency transactions are recognized in the consolidated statements of operations. Recorded balances that are denominated in a currency other than the functional currency are re-measured to the functional currency using the exchange rate at the balance sheet date and gains or losses are recorded in the statements of operations. Income Taxes We account for income taxes using an asset and liability method, which requires the recognition of taxes payable or refundable for the current year and deferred tax assets and liabilities for the expected future tax consequences of temporary differences that currently exist between the tax basis and the financial reporting basis of our taxable subsidiaries’ assets and liabilities using the enacted tax rates in effect for the year in which the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in operations in the period that includes the enactment date. The measurement of deferred tax assets is reduced, if necessary, by the amount of any tax benefits that, based on available evidence, are not expected to be realized. We regularly assess the need for a valuation allowance against our deferred tax assets. In making that assessment, we consider both positive and negative evidence related to the likelihood of realization of the deferred tax assets on a jurisdictional basis to determine, based on the weight of available evidence, whether it is more-likely-than-not that some or all of the deferred tax assets will not be realized. Examples of positive and negative evidence include future growth, forecasted earnings, future taxable income, the mix of earnings in the jurisdictions in which we operate, historical earnings, taxable income in prior years, if carryback is permitted under the law and prudent and feasible tax planning strategies. In the event we were to determine that we would not be able to realize all or part of our net deferred tax assets in the future, an adjustment to the deferred tax assets valuation allowance would be charged to earnings in the period in which we make such a determination, or goodwill would be adjusted at our final determination of the valuation allowance related to an acquisition within the measurement period. If we later determine that it is more-likely-than-not that the net deferred tax assets would be realized, we would reverse the applicable portion of the previously-provided valuation allowance as an adjustment to earnings at such time. We account for unrecognized tax benefits using a more-likely-than-not threshold for financial statement recognition and measurement of tax positions taken or expected to be taken in a tax return. We establish reserves for tax-related uncertainties based on estimates of whether, and the extent to which, additional taxes will be due. We record an income tax liability, if any, for the difference between the benefit recognized and measured and the tax position taken or expected to be taken on our tax returns. At December 31, 2019, our estimated gross unrecognized tax benefits were $8.3 million, of which $236,000, if recognized, would favorably impact our future earnings. We recognize interest assessed by taxing authorities or interest associated with uncertain tax positions as a component of interest expense. We recognize any penalties assessed by taxing authorities or penalties associated with uncertain tax positions as a component of selling, general and administrative expenses. To the extent that the assessment of such tax positions change, the change in estimate is recorded in the period in which the determination is made. The reserves are adjusted in light of changing facts and circumstances, such as the outcome of a tax audit. The provision for income taxes includes the impact of reserve provisions and changes to reserves that are considered appropriate. Insurance Accrued costs for our self-insured healthcare coverage were $1.0 million and $826,000 at December 31, 2019 and 2018, respectively. Earnings Per Share Basic earnings per share is calculated based on the weighted-average number of outstanding common shares during the applicable period. Diluted earnings per share is based on the weighted-average number of outstanding common shares plus the weighted-average number of potential outstanding common shares. Potential common shares that would increase earnings per share or decrease loss per share are anti-dilutive and are excluded from earnings per share computations. Earnings per share is computed separately for each period presented. Treasury Stock Shares of common stock repurchased by us are recorded at cost as treasury stock and result in a reduction of stockholders’ equity in our consolidated balance sheets. Treasury shares are reissued using the weighted average cost method for determining the cost of the shares reissued. The difference between the cost of the shares reissued and the issuance price is added or deducted from additional paid-in capital. Recently Issued Accounting Pronouncements In August 2018, the SEC adopted the final rule under SEC Release No. 33-10532, “Disclosure Update and Simplification,” adopting amendments to certain disclosure rules that were redundant, duplicative, overlapping, outdated, or superseded, in light of other SEC disclosure requirements, GAAP or changes in the information environment. In addition, the amendments expanded the disclosure requirements relating to the analysis of equity for interim financial statements. Under the amendments, an analysis of the changes in each caption of shareholders’ equity and noncontrolling interests presented in the balance sheet must be provided in a note or separate statement. The analysis must present a reconciliation of the beginning balance to the ending balance of each period for which a statement of earnings is required to be filed. The final rule became effective on November 5, 2018. The Company adopted the final rule effective for the first quarter of 2019. The adoption of the final rule did not have an impact on the Company’s consolidated financial position or results of operations. ​ In August 2017, the FASB issued ASU No. 2017-12, Derivatives and Hedging (Topic 815). This ASU amends the guidance in ASC 815 to better align an entity’s risk management activities and financial reporting for hedging relationships through changes to both the designation and measurement guidance for qualifying hedging relationships and the presentation of hedge results. The guidance is effective for annual and interim reporting periods beginning after December 15, 2018, with early adoption permitted. The Company adopted ASU 2017-12 on January 1, 2019 and the standard did not have a material impact on its consolidated financial statements. ​ In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). The ASU significantly changes the accounting model used by lessees to account for leases, requiring that all material leases be presented on the balance sheet. Lessees will recognize substantially all leases on the balance sheet as a right-of-use asset and a corresponding lease liability. The Company adopted ASU 2016-02 on January 1, 2019 utilizing the modified retrospective transition method and elected not to recast comparative periods. We elected the package of practical expedients, which allows the Company not to reassess (1) whether any expired or existing contracts as of the adoption date are or contain a lease, (2) lease classification for any expired or existing leases as of the adoption date and (3) initial direct costs for any existing leases as of the adoption date. We also elected the practical expedient related to land easements, allowing us to carry forward our accounting treatment for land easements on existing agreements. The Company did not elect to apply the hindsight practical expedient when determining lease term and assessing impairment of right-of-use assets. ​ Adoption of ASU 2016-02 resulted in the recognition of right-of-use assets ​ In December 2019, the FASB issued ASU No. 2019-12, “Income Taxes” (Topic 740): Simplifying the Accounting for Income Taxes (“ASU 2019-12”), which is intended to simplify various aspects related to accounting for income taxes. ASU 2019-12 removes certain exceptions to the general principles in Topic 740 and also clarifies and amends existing guidance to improve consistent application. This guidance is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020, with early adoption permitted. The Company is currently evaluating the impact of this standard on its consolidated financial statements and related disclosures. In June 2016, the FASB issued ASU No. 2016-13, “Financial Instruments - Credit Losses” (Topic 326), which is effective for reporting periods beginning after December 15, 2019. The standard replaces the incurred loss impairment methodology under current GAAP with a methodology that reflects expected credit losses and requires the use of a forward-looking expected credit loss model for accounts receivables, loans, and other financial instruments. The standard requires a modified retrospective approach through a cumulative-effect adjustment to retained earnings as of the beginning of the first reporting period in which the guidance is effective. We plan to adopt the new credit loss standard effective January 1, 2020 and do not expect the impact of this standard to have a material impact on our consolidated financial statements.

USE OF ESTIMATES

USE OF ESTIMATES	12 Months Ended
	Dec. 31, 2019
USE OF ESTIMATES
USE OF ESTIMATES	NOTE 3. USE OF ESTIMATES The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements, as well as the reported amounts of revenue and expenses during the reporting period. Listed below are the estimates and assumptions that we consider to be significant in the preparation of our consolidated financial statements. ● Allowance for Doubtful Accounts - We estimate losses for uncollectible accounts based on the aging of the accounts receivable and an evaluation of the likelihood of success in collecting the receivable. ● Recovery of Long-Lived Assets - We evaluate the recovery of our long-lived assets periodically by analyzing our operating results and considering significant events or changes in the business environment. ● Income Taxes - We assume the deductibility of certain costs in our income tax filings, and estimate our income tax rate and future recovery of deferred tax assets. ● Legal and Environmental Accruals - We estimate the amount of potential exposure we may have with respect to litigation and environmental claims and assessments. ● Disposal Cell Development and Final Closure/Post-Closure Amortization - We expense amounts for disposal cell usage and closure and post-closure costs for each cubic yard of waste disposed of at our operating facilities. In determining the amount to expense for each cubic yard of waste disposed, we estimate the cost to develop each disposal cell and the closure and post-closure costs for each disposal cell and facility. The expense for each cubic yard is then calculated based on the remaining permitted capacity and total permitted capacity. Estimates for closure and post-closure costs are developed using input from third-party engineering consultants, and our internal technical and accounting personnel. Management reviews estimates at least annually. Estimates for final disposal cell closure and post-closure costs consider when the costs would actually be paid and, where appropriate, inflation and discount rates. ● Business Acquisitions - The Company records assets and liabilities of the acquired business at their fair values. Acquisition-related transaction and restructuring costs are expensed rather than treated as part of the cost of the acquisition. Goodwill represents the excess of the cost of an acquired business over the fair value of the identifiable tangible and intangible assets acquired and liabilities assumed in a business acquisition. ● Contingent Consideration – The Company records liabilities for the estimated fair value of potential future payments the Company may be required to remit under the terms of historical purchase agreements, entered into by NRC, prior to the NRC Merger. The payments are contingent on the acquired business’ achievement of annual earnings targets in certain years and other events considered in the purchase agreement. ● Goodwill - We assess goodwill for impairment during the fourth quarter as of October 1 of each year or sooner if an event occurs or circumstances change that would more likely than not reduce the fair value of a reporting unit below its carrying amount. The assessment consists of comparing the estimated fair value of the reporting unit to the carrying value of the net assets assigned to the reporting unit, including goodwill. Fair values are generally determined by using both the market approach, applying a multiple of earnings based on guideline for publicly traded companies, and the income approach, discounting projected future cash flows based on our expectations of the current and future operating environment. The rates used to discount projected future cash flows reflect a weighted average cost of capital based on our industry, capital structure and risk premiums including those reflected in the current market capitalization. Estimating future cash flows requires significant judgment about factors such as general economic conditions and projected growth rates, and our estimates often vary from the cash flows eventually realized. Failure to execute on planned growth initiatives within the related reporting units, coupled with the other factors mentioned above, could lead to the impairment of goodwill and other long-lived assets in future periods. ● Intangible Assets - We review intangible assets with indefinite useful lives for impairment during the fourth quarter as of October 1 of each year. Fair value is generally determined by considering an internally-developed discounted projected cash flow analysis. If the fair value of an asset is determined to be less than the carrying amount of the intangible asset, an impairment in the amount of the difference is recorded in the period in which the annual assessment occurs. We also review amortizing intangible assets for impairment whenever events or changes in circumstances indicate that the carrying value of an intangible asset may not be recoverable. In order to assess whether a potential impairment exists, the assets’ carrying values are compared with their undiscounted expected future cash flows. Estimating future cash flows requires significant judgment about factors such as general economic conditions and projected growth rates, and our estimates often vary from the cash flows eventually realized. Impairments are measured by comparing the fair value of the asset to its carrying value. Fair value is generally determined by considering: (i) the internally-developed discounted projected cash flow analysis; (ii) a third-party valuation; and/or (iii) information available regarding the current market environment for similar assets. If the fair value is determined to be less than the carrying amount of the intangible assets, an impairment in the amount of the difference is recorded in the period in which the events or changes in circumstances that indicated the carrying value of the intangible assets may not be recoverable occurred. Actual results could differ materially from the estimates and assumptions that we use in the preparation of our consolidated financial statements. As it relates to estimates and assumptions in amortization rates and environmental obligations, significant engineering, operations and accounting judgments are required. We review these estimates and assumptions no less than annually. In many circumstances, the ultimate outcome of these estimates and assumptions will not be known for decades into the future. Actual results could differ materially from these estimates and assumptions due to changes in applicable regulations, changes in future operational plans and inherent imprecision associated with estimating environmental impacts far into the future.

REVENUES

REVENUES	12 Months Ended
	Dec. 31, 2019
REVENUES
REVENUES	NOTE 4. REVENUES ​ Adoption of ASC Topic 606, “Revenue from Contracts with Customers” ​ As of January 1, 2018, we adopted Topic 606 using the modified retrospective method applied to those contracts which were not completed as of January 1, 2018. Results for reporting periods beginning after January 1, 2018 are presented under Topic 606, while prior period amounts are not adjusted and continue to be reported in accordance with our historic accounting under Revenue Recognition (Topic 605). ​ Adoption of the guidance did not materially affect the timing or amount of revenue recognized, and no cumulative effect adjustment was recognized as a result of initially applying Topic 606. ​ Disaggregation of Revenue ​ Our operations are managed in two reportable segments, Environmental Services and Field & Industrial Services, reflecting our internal reporting structure and nature of services offered. See Note 21 for additional information on our operating segments. ​ Effective January 1, 2019, Emergency Response revenues, formerly classified as Other, are now presented as a discrete service line. We also conformed the allocation of intercompany revenues between Treatment & Disposal Revenue and Services Revenue to be consistent across both segments. Throughout this Annual Report on Form 10-K, our disaggregated revenues for all periods presented have been recast to reflect these changes. ​ The following table presents our revenue disaggregated by our reportable segments and service lines: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 ​ ​ ​ ​ Field & ​ ​ ​ ​ ​ Environmental ​ Industrial ​ ​ ​ $s in thousands Services Services Total Treatment & Disposal Revenue (1) ​ $ 365,886 ​ $ 18,480 ​ $ 384,366 Services Revenue: ​ ​ ​ ​ ​ ​ ​ ​ ​ Transportation and Logistics (2) ​ ​ 87,221 ​ ​ 40,833 ​ ​ 128,054 Industrial Services (3) ​ ​ — ​ ​ 38,865 ​ ​ 38,865 Small Quantity Generation (4) ​ ​ — ​ ​ 37,471 ​ ​ 37,471 Total Waste Management (5) ​ ​ — ​ ​ 33,792 ​ ​ 33,792 Remediation (6) ​ ​ — ​ ​ 13,288 ​ ​ 13,288 Emergency Response (7) ​ ​ — ​ ​ 26,737 ​ ​ 26,737 Domestic Standby Services (8) ​ ​ — ​ ​ 14,249 ​ ​ 14,249 Other (9) ​ ​ — ​ ​ 8,687 ​ ​ 8,687 Revenue ​ $ 453,107 ​ $ 232,402 ​ $ 685,509 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2018 ​ ​ ​ ​ Field & ​ ​ ​ ​ ​ Environmental ​ Industrial ​ ​ ​ $s in thousands Services Services Total Treatment & Disposal Revenue (1) ​ $ 320,045 ​ $ 11,736 ​ $ 331,781 Services Revenue: ​ ​ ​ ​ ​ ​ ​ ​ ​ Transportation and Logistics (2) ​ ​ 80,633 ​ ​ 33,037 ​ ​ 113,670 Industrial Services (3) ​ ​ — ​ ​ 24,155 ​ ​ 24,155 Small Quantity Generation (4) ​ ​ — ​ ​ 34,571 ​ ​ 34,571 Total Waste Management (5) ​ ​ — ​ ​ 41,729 ​ ​ 41,729 Remediation (6) ​ ​ — ​ ​ 10,139 ​ ​ 10,139 Emergency Response (7) ​ ​ — ​ ​ 7,513 ​ ​ 7,513 Other (9) ​ ​ — ​ ​ 2,370 ​ ​ 2,370 Revenue ​ $ 400,678 ​ $ 165,250 ​ $ 565,928 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2017 ​ ​ ​ ​ Field & ​ ​ ​ ​ ​ Environmental ​ Industrial ​ ​ ​ $s in thousands Services Services Total Treatment & Disposal Revenue (1) ​ $ 299,403 ​ $ 10,404 ​ $ 309,807 Services Revenue: ​ ​ ​ ​ ​ ​ ​ ​ ​ Transportation and Logistics (2) ​ ​ 66,905 ​ ​ 21,899 ​ ​ 88,804 Industrial Services (3) ​ ​ — ​ ​ 19,121 ​ ​ 19,121 Small Quantity Generation (4) ​ ​ — ​ ​ 29,934 ​ ​ 29,934 Total Waste Management (5) ​ ​ — ​ ​ 38,628 ​ ​ 38,628 Remediation (6) ​ ​ — ​ ​ 14,241 ​ ​ 14,241 Emergency Response (7) ​ ​ — ​ ​ 3,214 ​ ​ 3,214 Other (9) ​ ​ — ​ ​ 293 ​ ​ 293 Revenue ​ $ 366,308 ​ $ 137,734 ​ $ 504,042 (1) We categorize our treatment and disposal revenue as either “Base Business” or “Event Business” based on the underlying nature of the revenue source. We define Event Business as non-recurring projects that are expected to equal or exceed 1,000 tons, with Base Business defined as all other business not meeting the definition of Event Business. For the years ended December 31, 2019, 2018 and 2017, 22% , 20% and 22% , respectively, of our treatment and disposal revenue, excluding NRC, was derived from Event Business projects. Base Business revenue accounted for 78% , 80% and 78% of our treatment and disposal revenue, excluding NRC, for the years ended December 31, 2019, 2018 and 2017, respectively. (2) Includes collection and transportation of non-hazardous and hazardous waste. (3) Includes industrial cleaning and maintenance for refineries, chemical plants, steel and automotive plants, marine terminals and refinery services such as tank cleaning and temporary storage. (4) Includes retail services, laboratory packing, less-then-truck-load service and household hazardous waste collection. Contracts for Small Quantity Generation may extend beyond one year and a portion of the transaction price can be fixed. (5) Through our TWM program, customers outsource the management of their waste compliance program to us, allowing us to organize and coordinate their waste management disposal activities and environmental compliance. TWM contracts may extend beyond one year and a portion of the transaction price can be fixed. (6) Includes site assessment, onsite treatment, project management and remedial action planning and execution. Contracts for Remediation may extend beyond one year and a portion of the transaction price can be fixed. (7) Includes spill response, waste analysis and treatment and disposal planning. (8) We provide government-mandated, commercial standby oil spill compliance solutions to companies that store, transport, produce or handle petroleum and certain nonpetroleum oils on or near U.S. waters. Our standby services customers pay annual retainer fees under long-term or evergreen contracts for access to our regulatory certifications, specialized assets and highly trained personnel. When a customer with a retainer contract experiences a spill incident, we coordinate and manage the spill response, which results in incremental revenue for the services provided, in addition to the retainer fees. (9) Includes equipment rental and other miscellaneous services. ​ We provide services primarily in the United States, Canada and the EMEA region. The following table presents our revenue disaggregated by our reportable segments and geographic location where the underlying services were performed: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 ​ 2018 ​ 2017 ​ ​ ​ ​ Field & ​ ​ ​ ​ ​ ​ Field & ​ ​ ​ ​ ​ ​ Field & ​ ​ ​ ​ ​ Environmental ​ Industrial ​ ​ ​ ​ Environmental ​ Industrial ​ ​ ​ ​ Environmental ​ Industrial ​ ​ ​ $s in thousands Services Services Total Services Services Total Services Services Total United States ​ $ 367,185 ​ $ 221,942 ​ $ 589,127 ​ $ 329,918 ​ $ 165,250 ​ $ 495,168 ​ $ 296,777 ​ $ 137,734 ​ $ 434,511 Canada ​ 85,922 ​ 2,577 ​ 88,499 ​ 70,760 ​ — ​ 70,760 ​ 69,531 ​ — ​ 69,531 EMEA ​ ​ — ​ ​ 5,079 ​ ​ 5,079 ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ — Other (1) ​ ​ — ​ ​ 2,804 ​ ​ 2,804 ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ — Total revenue ​ $ 453,107 ​ $ 232,402 ​ $ 685,509 ​ $ 400,678 ​ $ 165,250 ​ $ 565,928 ​ $ 366,308 ​ $ 137,734 ​ $ 504,042 ​ (1) Includes Mexico, Asia Pacific, and Latin America and Caribbean geographical regions. ​ Principal versus Agent Considerations ​ The Company commonly contracts with third-parties to perform certain waste-related services that we have promised in our customer contracts. We consider ourselves the principal in these arrangements as we direct the timing, nature and pricing of the services ultimately provided by the third-party to the customer. ​ Costs to Obtain a Contract ​ The Company pays sales commissions to employees, which qualify as costs to obtain a contract. Sales commissions are expensed as incurred as the commissions are earned by the employee and paid by the Company over time as the related revenue is recognized. Other commissions and incremental costs to obtain a contract are not material. ​ Practical Expedients and Optional Exemptions ​ Our payment terms may vary based on type of service or customer; however, we do not adjust the promised amount of consideration in our contracts for the time value of money as payment terms extended to our customers do not exceed one year and are not considered a significant financing component in our contracts. ​ We do not disclose the value of unsatisfied performance obligations as contracts with an original expected length of more than one year and contracts for which we do not recognize revenue at the amount to which we have the right to invoice for services performed is insignificant and the aggregate amount of fixed consideration allocated to unsatisfied performance obligations is not material.

BUSINESS COMBINATIONS

BUSINESS COMBINATIONS	12 Months Ended
	Dec. 31, 2019
BUSINESS COMBINATIONS
BUSINESS COMBINATIONS	NOTE 5. BUSINESS COMBINATIONS NRC Group Holdings Corp. On November 1, 2019, the Company completed its merger with NRC, a provider of comprehensive environmental, compliance and waste management services to the marine and rail transportation, general industrial and energy industries. The addition of NRC’s substantial service network strengthens and expands US Ecology’s suite of environmental services, including new oil and gas exploration and production landfill disposal capabilities, and provides expanded opportunities to establish US Ecology as a leader in standby and emergency response services. The total merger consideration was $1,024.8 million, comprised of the following: ​ ​ ​ ​ ​ ​ ​ November 1, $s in thousands 2019 Fair value of US Ecology common stock issued (1) ​ $ 581,101 Fair value of replacement warrants issued (2) ​ 44,858 Fair value of replacement restricted stock units issued (3) ​ 141 Fair value of replacement stock options (4) ​ 360 Repayment of NRC’s term loan and revolving credit facility ​ 398,373 Total merger consideration ​ $ 1,024,833 (1) The fair value of US Ecology common stock issued was calculated based on 9,337,949 shares of US Ecology common stock multiplied by the closing price of US Ecology common stock of $62.23 per share on October 31, 2019, the day immediately preceding the closing of the NRC Merger. (2) The fair value of replacement warrants issued was calculated based on 3,772,753 replacement warrants multiplied by the fair value per warrant of $11.89 . The fair value per warrant was based on the closing price of the replaced NRC warrants (NYSE: NRCG.WS) of $2.33 on October 31, 2019, the day immediately preceding the closing of the NRC Merger, divided by the exchange ratio of 0.196 pursuant to the Merger Agreement. (3) The fair value of replacement restricted stock units issued was calculated based on 118,239 replacement restricted stock units multiplied by the closing price of US Ecology common stock of $62.23 per share on October 31, 2019, the day immediately preceding the closing of the NRC Merger, further multiplied by the ratio of the precombination service period to the remaining vesting period, or approximately 1.9% . (4) The fair value of replacement stock options issued was calculated based on 29,400 replacement stock options multiplied by the fair value per option of $12.26 . The fair value per option was calculated using the Black-Scholes option pricing model, with the following weighted-average assumptions: strike price of $52.30 per option, dividend yield of 1.2% ; expected volatility of 28.9% ; average risk-free interest rate of 1.5% ; and an expected term of 1 year. The replacement stock options became fully vested at the merger date therefore the entire fair value is considered merger consideration. The payment of transaction fees and expenses and repayment of $398.4 million of NRC’s debt were funded using proceeds from a new $450.0 million seven-year term loan. Refer to “Note 16. Debt” for more information. We have recognized the assets and liabilities of NRC based on our preliminary estimates of their acquisition date fair values. The purchase price allocations are preliminary and subject to change. We continue to gather information relevant to our determination of the fair value of acquired assets and liabilities primarily related to, but not limited to, property and equipment, identifiable intangible assets and deferred income taxes. Any adjustments to the purchase price allocations are made as soon as practicable but no later than one year from the merger date. The following table summarizes the merger consideration and the preliminary fair value estimates of assets acquired and liabilities assumed at the merger date: ​ ​ ​ ​ ​ ​ ​ November 1, $s in thousands 2019 Current assets ​ $ 131,653 Property and equipment ​ ​ 197,045 Identifiable intangible assets ​ ​ 303,600 Other assets ​ ​ 41,687 Current liabilities ​ ​ (83,460) Deferred income tax liabilities ​ ​ (56,596) Other liabilities ​ ​ (57,581) Total identifiable net assets ​ ​ 476,348 Goodwill ​ ​ 548,485 Total purchase price ​ $ 1,024,833 ​ Goodwill of $548.5 million arising from the acquisition is primarily attributable to the assembled workforce of NRC and expected synergies from combining operations. $308.9 million of the goodwill recognized was allocated to our Environmental Services segment and $239.6 million of the goodwill recognized was allocated to Field & Industrial Services segment. We expect $33.3 million of the acquired goodwill to be deductible for income tax purposes. The preliminary fair value of identifiable intangible assets related to the acquisition of NRC by major intangible asset class and corresponding weighted average amortization period are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Average ​ ​ ​ ​ ​ Amortization $s in thousands ​ ​ Fair Value ​ Period (Years) Amortizing intangible assets: ​ ​ ​ ​ ​ Customer relationships - noncontractual ​ $ 193,700 ​ 14 Customer relationships - contractual ​ ​ 34,400 ​ 7 Permits and licenses ​ ​ 8,700 ​ 16 Tradenames ​ ​ 6,100 ​ 2 Non-compete agreements ​ ​ 3,300 ​ 2 Total identified amortizing intangible assets ​ ​ 246,200 ​ ​ Non-amortizing intangible assets: ​ ​ ​ ​ ​ Permits and licenses ​ ​ 57,400 ​ n/a Total identified intangible assets ​ $ 303,600 ​ ​ ​ The following unaudited pro forma financial information presents the combined results of operations as if NRC had been combined with US Ecology as of January 1, 2018. The pro forma financial information includes the accounting effects of the business combination, including the amortization of intangible assets, depreciation of property, plant and equipment, and interest expense. The unaudited pro forma financial information is presented for informational purposes only and is not indicative of the results of operations that would have been achieved if the acquisition had taken place at the beginning of the periods presented, nor should it be taken as indication of our future consolidated results of operations. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (unaudited) $s in thousands ​ ​ 2019 ​ ​ 2018 Pro forma combined: ​ ​ ​ ​ ​ ​ Revenue ​ $ 1,048,745 ​ $ 923,947 Net income (loss) ​ $ 11,775 ​ $ (12,296) ​ The amounts of revenue and operating loss from NRC included in the Company’s consolidated statements of operations for the year ended December 31, 2019 was $70.2 million and $9.1 million, respectively. NRC Merger-related business development and integration expenses of $24.4 million are included in Selling, general and administrative expenses in the Company’s consolidated statements of operations for the year ended December 31, 2019. W.I.S.E. Environmental Solutions Inc. On August 1, 2019, we acquired 100% of the outstanding shares of W.I.S.E. Environmental Solutions Inc. (“US Ecology Sarnia”), an equipment rental and waste services company based in Sarnia, Ontario, Canada for 23.5 million Canadian dollars, which translated to $17.9 million at the time of transaction and was funded with borrowings under the Credit Agreement. US Ecology Sarnia is reported as part of our Field & Industrial Services segment. The Company assessed the revenues, net income, earnings per share and total assets of US Ecology Sarnia and concluded they are not material to our consolidated financial position or results of operations. As such, pro forma financial information has not been provided. We allocated the purchase price to the assets acquired and liabilities assumed based on estimates of the fair value at the date of the acquisition, resulting in $7.7 million allocated to goodwill and $6.2 million allocated to intangible assets (primarily customer relationships) to be amortized over a weighted average life of approximately 14 years. The purchase price allocation is preliminary, as estimates and assumptions are subject to change as more information becomes available. Goodwill of $7.7 million arising from the acquisition is attributable to the assembled workforce and the future economic benefits of synergies with our other regional facilities and expansion into new markets. All of the goodwill recognized was assigned to our Field & Industrial Services segment and is not expected to be deductible for income tax purposes. ES&H of Dallas, LLC On August 31, 2018, the Company acquired ES&H of Dallas, LLC (“ES&H Dallas”), which provides emergency and spill response, light industrial services and transportation and logistics for waste disposal and recycling from locations in Dallas and Midland, Texas. The total purchase price was $21.3 million and was funded with cash on hand. The ES&H Dallas facilities are reported as part of our Field and Industrial Services segment. The Company assessed the revenues, net income, earnings per share and total assets of ES&H Dallas and concluded they are not material to our consolidated financial position or results of operations either individually or when aggregated with other acquisitions completed in 2018. As such, pro forma financial information has not been provided. ​ We allocated the purchase price to the assets acquired based on preliminary estimates of the fair value at the date of acquisition, resulting in $10.0 million allocated to property and equipment and other current assets, $7.1 million allocated to goodwill and $4.2 million allocated to intangible assets (consisting primarily of customer relationships) to be amortized over a weighted average life of approximately 13 years. No liabilities were assumed in the acquisition. Goodwill of $7.1 million arising from the acquisition is attributable to the assembled workforce and the future economic benefits of synergies with our other Texas facilities and expansion into new markets. All of the goodwill recognized was assigned to our Field & Industrial Services segment and is expected to be deductible for income tax purposes over a 15-year Ecoserv Industrial Disposal, LLC On November 14, 2018, the Company acquired Ecoserv Industrial Disposal, LLC (“Winnie”), which provides non-hazardous industrial wastewater disposal solutions and employs deep-well injection technology in the southern United States. The total purchase price was $87.2 million and was funded with $87.0 million in borrowings under the Credit Agreement and cash on hand. Winnie is reported as part of our Environmental Services segment. The Company assessed the revenues, net income, earnings per share and total assets of Winnie and concluded they are not material to our consolidated financial position or results of operations either individually or when aggregated with other acquisitions completed in 2018. As such, pro forma financial information has not been provided. ​ We allocated the purchase price to the assets acquired and liabilities assumed based on estimates of the fair value at the date of acquisition. The following table summarizes the consideration paid for Winnie and the fair value estimates of assets acquired and liabilities assumed, recognized at the acquisition date, with purchase price allocation adjustments since the preliminary purchase price allocation as previously disclosed as of December 31, 2018: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Purchase Price Allocation ​ ​ December 31, ​ ​ ​ ​ December 31, $s in thousands 2018 ​ Adjustments ​ 2019 Current assets ​ $ 1,923 ​ $ (63) ​ $ 1,860 Property and equipment ​ ​ 6,300 ​ ​ (2,601) ​ ​ 3,699 Identifiable intangible assets ​ ​ 66,600 ​ ​ (100) ​ ​ 66,500 Current liabilities ​ ​ (755) ​ ​ — ​ ​ (755) Other liabilities ​ ​ (512) ​ ​ — ​ ​ (512) Total identifiable net assets ​ ​ 73,556 ​ ​ (2,764) ​ ​ 70,792 Goodwill ​ ​ 13,573 ​ ​ 2,863 ​ ​ 16,436 Total purchase price ​ $ 87,129 ​ $ 99 ​ $ 87,228 ​ Purchase price allocation adjustments relate primarily to the receipt of additional information regarding the fair values of property and equipment and a post-closing price adjustment based on working capital requirements. ​ The fair value of identifiable intangible assets related to the acquisition of Winnie consisted of $54.7 million in permits to be amortized over a life of 60 years, and $11.8 million in customer relationships to be amortized over a life of 15 years. Goodwill of $16.4 million arising from the acquisition is attributable to the future economic benefits of expansion into the deep-well injection market and the assembled workforce. All of the goodwill recognized was assigned to our Environmental Services segment and is expected to be deductible for income tax purposes over a 15-year

ACCUMULATED OTHER COMPREHENSIVE

ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS)	12 Months Ended
	Dec. 31, 2019
ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS).
ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS)	NOTE 6. ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) Changes in accumulated other comprehensive income (loss) (“AOCI”) consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Foreign ​ Unrealized Gain ​ ​ ​ ​ ​ Currency ​ (Loss) on Interest ​ ​ ​ $s in thousands Translation Rate Hedge Total Balance at December 31, 2017 ​ $ (8,603) ​ $ (501) ​ $ (9,104) Other comprehensive income (loss) before reclassifications, net of tax ​ ​ (6,094) ​ ​ 1,111 ​ ​ (4,983) Amounts reclassified out of AOCI, net of tax (1) ​ — ​ 296 ​ 296 Other comprehensive income (loss), net ​ ​ (6,094) ​ ​ 1,407 ​ ​ (4,687) Balance at December 31, 2018 ​ $ (14,697) ​ $ 906 ​ $ (13,791) Other comprehensive income (loss) before reclassifications, net of tax ​ 3,772 ​ (1,700) ​ 2,072 Amounts reclassified out of AOCI, net of tax (2) ​ — ​ (135) ​ (135) Other comprehensive income (loss), net ​ 3,772 ​ (1,835) ​ 1,937 Balance at December 31, 2019 ​ $ (10,925) ​ $ (929) ​ $ (11,854) (1) Before-tax reclassifications of $375,000 ( $296,000 after-tax) for the year ended December 31, 2018 were included in Interest expense in the Company’s consolidated statements of operations. Amount relates to the Company’s interest rate swap which is designated as a cash flow hedge. Changes in fair value of the swap recognized in AOCI are reclassified to interest expense when hedged interest payments on the underlying long-term debt are made. (2) Before-tax reclassifications of $170,000 ( $135,000 after-tax) for the year ended December 31, 2019 were included as a reduction of Interest expense in the Company’s consolidated statements of operations. Amount relates to the Company’s interest rate swap which is designated as a cash flow hedge. Changes in fair value of the swap recognized in AOCI are reclassified to interest expense when hedged interest payments on the underlying long-term debt are made. Amounts in AOCI expected to be recognized as interest expense over the next 12 months total approximately $523,000 ( $413,000 after tax).

DISCLOSURE OF SUPPLEMENTAL CASH

DISCLOSURE OF SUPPLEMENTAL CASH FLOW INFORMATION	12 Months Ended
	Dec. 31, 2019
DISCLOSURE OF SUPPLEMENTAL CASH FLOW INFORMATION
DISCLOSURE OF SUPPLEMENTAL CASH FLOW INFORMATION	NOTE 7. DISCLOSURE OF SUPPLEMENTAL CASH FLOW INFORMATION ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the Year Ended December 31, $s in thousands 2019 2018 2017 Income taxes and interest paid: ​ ​ ​ ​ ​ ​ ​ ​ ​ Income taxes paid, net of receipts ​ $ 14,777 ​ $ 19,580 ​ $ 10,714 Interest paid ​ 17,204 ​ 11,246 ​ 11,364 Non-cash investing and financing activities: ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value of equity issued for acquisition of NRC ​ 626,460 ​ — ​ — Closure/Post-closure retirement asset ​ (221) ​ 99 ​ (352) Capital expenditures in accounts payable ​ 2,882 ​ 1,601 ​ 2,302 Acquisition of equipment with financing arrangements ​ ​ 2,481 ​ ​ 747 ​ ​ 531 Restricted stock issuances from treasury shares ​ 514 ​ 11 ​ 105 ​

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	12 Months Ended
	Dec. 31, 2019
FAIR VALUE MEASUREMENTS
FAIR VALUE MEASUREMENTS	NOTE 8. FAIR VALUE MEASUREMENTS Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Assets and liabilities recorded at fair value are categorized using defined hierarchical levels directly related to the amount of subjectivity associated with the inputs to fair value measurements, as follows: ● Level 1 - Quoted prices in active markets for identical assets or liabilities; ● Level 2 - Inputs other than quoted prices included within Level 1 that are either directly or indirectly observable; ● Level 3 - Unobservable inputs in which little or no market activity exists, requiring an entity to develop its own assumptions that market participants would use to value the asset or liability. The Company’s financial instruments consist of cash and cash equivalents, accounts receivable, restricted cash and investments, accounts payable and accrued liabilities, debt, interest rate swap agreements and contingent consideration. The estimated fair value of cash and cash equivalents, accounts receivable, accounts payable and accrued liabilities approximate their carrying value due to the short-term nature of these instruments. On September 19, 2019, the Company invested $7.9 million in the preferred stock of a privately held company which is included in Other assets in the Company’s consolidated balance sheets. The investment does not have a readily determinable fair value therefore the investment is valued at cost, less impairment, plus or minus observable price changes of an identical or similar investment of the same issuer, if any. As of December 31, 2019, there have been no identified events or changes in circumstances that would indicate the cost method investment should be impaired nor have there been any observable price changes of an identical or similar investment of the same issuer. The Company estimates the fair value of its variable-rate debt using Level 2 inputs, such as interest rates, related terms and maturities of similar obligations. At December 31, 2019, the fair value of the Company’s variable rate term loan was estimated to be $454.5 million, and the carrying value of the Company’s variable-rate revolving credit facility approximates fair value due to the short-term nature of the interest rates. The Company estimates the fair value of its contingent consideration liabilities using Level 3 inputs, including both observable and unobservable inputs. As a result, unrealized gains and losses may include changes in fair value that are attributable to both observable (e.g., changes in market interest rates) and unobservable (e.g., changes in unobservable long-dated volatilities) inputs. The Company’s assets and liabilities measured at fair value on a recurring basis at December 31, 2019 and 2018 consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 ​ ​ Quoted Prices in ​ Other Observable ​ Unobservable ​ ​ ​ ​ ​ Active Markets ​ Inputs ​ Inputs ​ ​ ​ $s in thousands (Level 1) (Level 2) (Level 3) Total Assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fixed-income securities (1) ​ $ 2,380 ​ $ 1,830 ​ $ — ​ $ 4,210 Money market funds (2) ​ ​ 859 ​ ​ — ​ ​ — ​ ​ 859 Total ​ $ 3,239 ​ $ 1,830 ​ $ — ​ $ 5,069 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Liabilities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Interest rate swap agreement (3) ​ $ — ​ $ 1,176 ​ $ — ​ $ 1,176 Contingent consideration (4) ​ ​ — ​ ​ — ​ ​ 8,283 ​ ​ 8,283 Total ​ $ — ​ $ 1,176 ​ $ 8,283 ​ $ 9,459 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2018 ​ ​ Quoted Prices in ​ Other Observable ​ Unobservable ​ ​ ​ ​ ​ Active Markets ​ Inputs ​ Inputs ​ ​ ​ $s in thousands (Level 1) (Level 2) (Level 3) Total Assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fixed-income securities (1) ​ $ 1,561 ​ $ 2,596 ​ $ — ​ $ 4,157 Money market funds (2) ​ ​ 784 ​ ​ — ​ ​ — ​ ​ 784 Interest rate swap agreement (3) ​ ​ — ​ ​ 1,147 ​ ​ ​ ​ ​ 1,147 Total ​ $ 2,345 ​ $ 3,743 ​ $ — ​ $ 6,088 (1) We invest a portion of our Restricted cash and investments in fixed-income securities, including U.S. Treasury and U.S. agency securities. We measure the fair value of U.S. Treasury securities using quoted prices for identical assets in active markets. We measure the fair value of U.S. agency securities using observable market activity for similar assets. The fair value of our fixed-income securities approximates our cost basis in the investments. (2) We invest a portion of our Restricted cash and investments in money market funds. We measure the fair value of these money market fund investments using quoted prices for identical assets in active markets. Money market funds are considered restricted cash for purposes of reconciling the beginning-of-period and end-of-period amounts presented in the Company’s consolidated statements of cash flows. (3) In order to manage interest rate exposure, we entered into an interest rate swap agreement in October 2014 that effectively converts a portion of our variable-rate debt to a fixed interest rate. The swap is designated as a cash flow hedge, with gains and losses deferred in other comprehensive income to be recognized as an adjustment to interest expense in the same period that the hedged interest payments affect earnings. The interest rate swap has an effective date of December 31, 2014 with an initial notional amount of $250.0 million. The fair value of the interest rate swap agreement represents the difference in the present value of cash flows calculated at the contracted interest rates and at current market interest rates at the end of the period. We calculate the fair value of the interest rate swap agreement quarterly based on the quoted market price for the same or similar financial instruments. The fair value of the interest rate swap agreement is included in Other long-term liabilities and Other assets in the Company’s consolidated balance sheets as of December 31, 2019 and 2018, respectively. (4) Our contingent consideration liabilities represent the estimated fair value of potential future payments the Company may be required to remit under the terms of historical purchase agreements entered into by NRC prior to the NRC Merger. The payments are contingent on the acquired businesses’ achievement of annual earnings targets in certain years and other events considered in the purchase agreements. The fair value of our contingent consideration liabilities are calculated using either a Monte Carlo simulation or modified Black-Scholes analyses based on earnings projections for the respective earn-out periods, corresponding earnings thresholds, and approximate timing of payments as outlined in the purchase agreements. The analyses utilize the following assumptions: (i) expected term; (ii) risk-adjusted net sales or earnings; (iii) risk-free interest rate; and (iv) expected volatility of earnings. Estimated payments, as determined through the respective models, are discounted by a credit spread assumption to account for credit risk. The fair value of our contingent consideration liabilities are included in Accrued liabilities and Other long-term liabilities. At December 31, 2019, balances of $6.6 million and $1.7 million were included in Accrued liabilities and Other long-term liabilities, respectively. We revalue our contingent consideration payments each period and any increases or decreases to fair value are included in Selling, general and administrative expenses in our consolidated statements of operations. Fair values may be impacted by certain unobservable inputs, most significantly with regard to discount rates, expected volatility and historical and projected performance. Significant changes to these inputs in isolation could result in a significantly different fair value measurement. ​ Changes in Level 3 liabilities measured at fair value for the years ended December 31, 2019 and 2018 are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value $s in thousands (Level 3) Balance at December 31, 2017 ​ $ — Balance at December 31, 2018 ​ $ — Fair value of contingent consideration acquired ​ 11,859 Change in fair value of contingent consideration ​ ​ 349 Foreign currency translation ​ ​ 75 Contingent consideration paid ​ (4,000) Balance at December 31, 2019 ​ $ 8,283 ​

CONCENTRATIONS AND CREDIT RISK

CONCENTRATIONS AND CREDIT RISK	12 Months Ended
	Dec. 31, 2019
CONCENTRATIONS AND CREDIT RISK
CONCENTRATIONS AND CREDIT RISK	NOTE 9. CONCENTRATIONS AND CREDIT RISK Major Customers No customer accounted for more than 10% of total revenue for the years ended December 31, 2019, 2018 or 2017. No customer accounted for more than 10% of total receivables as of December 31, 2019 or 2018. Credit Risk Concentration We maintain most of our cash and cash equivalents with nationally recognized financial institutions. Substantially all balances are uninsured and are not used as collateral for other obligations. Concentrations of credit risk on accounts receivable are believed to be limited due to the number, diversification and character of the obligors and our credit evaluation process. Credit risk associated with a portion of the Company’s trade receivables is reduced by our ability to submit claims to the Oil Spill Liability Trust Fund (“OSLTF”) for reimbursement of unpaid customer receivables related to services regulated under the provisions of the Oil Pollution Act of 1990 (“OPA 90”). As of December 31, 2019, the Company did not have any trade receivables that are eligible for submission to the OSLTF for reimbursement. Labor Concentrations As of December 31, 2019, approximately 523 of our employees (approximately 14% of our employees), were covered by collective bargaining agreements with various labor unions. Approximately 37% of these employees are covered by collective bargaining agreements that expire within one year of December 31, 2019.

RECEIVABLES

RECEIVABLES	12 Months Ended
	Dec. 31, 2019
RECEIVABLES
RECEIVABLES	NOTE 10. RECEIVABLES Receivables as of December 31, 2019 and 2018 consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ $s in thousands ​ 2019 2018 Trade ​ $ 196,593 ​ $ 118,909 Unbilled revenue ​ 54,727 ​ 26,538 Other ​ 7,000 ​ 2,241 Total receivables ​ 258,320 ​ 147,688 Allowance for doubtful accounts ​ (3,010) ​ (2,998) Receivables, net ​ $ 255,310 ​ $ 144,690 ​ The allowance for doubtful accounts is a provision for uncollectible accounts receivable and unbilled receivables. The allowance is evaluated and adjusted to reflect our collection history and an analysis of the accounts receivables aging. The allowance is decreased by accounts receivable as they are written off. The allowance is adjusted periodically to reflect actual experience. The change in the allowance during 2019, 2018 and 2017 was as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Charged ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance at ​ (Credited) to ​ Recoveries ​ ​ ​ ​ ​ ​ ​ ​ Beginning of ​ Costs and ​ (Deductions/ ​ ​ ​ ​ Balance at $s in thousands Period Expenses Write-offs) Adjustments End of Period Year ended December 31, 2019 ​ $ 2,998 ​ $ 226 ​ $ (439) ​ $ 225 ​ $ 3,010 Year ended December 31, 2018 ​ $ 2,796 ​ $ 436 ​ $ (213) ​ $ (21) ​ $ 2,998 Year ended December 31, 2017 ​ $ 2,334 ​ $ 704 ​ $ (255) ​ $ 13 ​ $ 2,796 ​

PROPERTY AND EQUIPMENT

PROPERTY AND EQUIPMENT	12 Months Ended
	Dec. 31, 2019
PROPERTY AND EQUIPMENT
PROPERTY AND EQUIPMENT	NOTE 11. PROPERTY AND EQUIPMENT Property and equipment as of December 31, 2019 and 2018 consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ $s in thousands 2019 2018 Cell development costs ​ $ 174,561 ​ $ 146,155 Land and improvements ​ 52,909 ​ 50,481 Buildings and improvements ​ 109,580 ​ 91,358 Railcars ​ 17,299 ​ 17,299 Vehicles, vessels and other equipment ​ 317,472 ​ 154,014 Construction in progress ​ 61,537 ​ 14,554 Total property and equipment ​ 733,358 ​ 473,861 Accumulated depreciation and amortization ​ (254,590) ​ (215,418) Property and equipment, net ​ $ 478,768 ​ $ 258,443 ​ Depreciation and amortization expense was $41.4 million, $29.2 million and $28.3 million for the years ended December 31, 2019, 2018 and 2017, respectively.

LEASES

LEASES	12 Months Ended
	Dec. 31, 2019
LEASES
LEASES	​ NOTE 12. LEASES We lease certain facilities, office space, land and equipment. Our lease payments are primarily fixed, but also include variable payments that are based on usage of the leased asset. Initial lease terms range from one to one lease up ​ Leases with an initial term of 12 months or less are not recorded on the balance sheet and expense is recognized on a straight-line basis over the lease term. We combine lease and non-lease components in our leases. We use the rate implicit in the lease, when available, to discount lease payments to present value. However, many of our leases do not provide a readily determinable implicit rate and we estimate our incremental borrowing rate to discount payments based on information available at lease commencement. ​ Lease assets and liabilities consisted of the following: ​ ​ ​ ​ ​ $s in thousands December 31, 2019 Assets: ​ ​ ​ Operating right-of-use assets (1) ​ $ 57,396 Finance right-of-use assets (2) ​ ​ 20,499 Total ​ $ 77,895 ​ ​ ​ ​ Liabilities: ​ ​ ​ Current: ​ ​ ​ Operating (3) ​ $ 17,317 Finance (4) ​ ​ 4,128 Long-term: ​ ​ ​ Operating (5) ​ ​ 39,954 Finance (6) ​ ​ 16,308 Total ​ $ 77,707 (1) Included in Operating lease assets in the Company’s consolidated balance sheets. (2) Included in Property and equipment, net in the Company’s consolidated balance sheets. Finance right-of-use assets are recorded net of accumulated amortization of $2.7 million as of December 31, 2019. (3) Included in Current portion of operating lease liabilities in the Company’s consolidated balance sheets. (4) Included in Accrued liabilities in the Company’s consolidated balance sheets. (5) Included in Long-term operating lease liabilities in the Company’s consolidated balance sheets. (6) Included in Other long-term liabilities in the Company’s consolidated balance sheets. ​ Lease expense consisted of the following: ​ ​ ​ ​ ​ ​ ​ Year Ended $s in thousands December 31, 2019 Operating lease cost (1) ​ $ 9,144 Finance lease cost: ​ ​ ​ Amortization of leased assets (2) ​ ​ 1,641 Interest on lease liabilities (3) ​ ​ 332 Total ​ $ 11,117 (1) Included in Direct operating costs and Selling, general, and administrative expenses in the Company’s consolidated statements of operations. Operating lease cost includes short-term leases, excluding expenses relating to leases with a term of one month or less, which are not material. Operating lease cost excludes variable lease costs which are not material. (2) Included in Direct operating costs in the Company’s consolidated statements of operations. (3) Included in Interest expense in the Company’s consolidated statements of operations. ​ Supplemental cash flow information related to our leases is as follows: ​ ​ ​ ​ ​ ​ ​ Year Ended $s in thousands December 31, 2019 Cash paid for amounts included in the measurement of lease liabilities: ​ ​ ​ Operating cash flows from operating leases ​ $ 8,656 Operating cash flows from finance leases ​ ​ 332 Financing cash flows from finance leases ​ ​ 1,298 ​ ​ ​ ​ Non-cash investing and financing activities: ​ ​ ​ Right-of-use assets obtained in exchange for new operating lease liabilities ​ $ 7,380 Right-of-use assets obtained in exchange for new finance lease liabilities ​ ​ 2,481 ​ Other information related to our leases is as follows: ​ ​ ​ ​ ​ ​ ​ December 31, 2019 Weighted-average remaining lease term (years): ​ ​ ​ ​ Operating leases ​ ​ 4.4 ​ Finance leases ​ ​ 4.5 ​ Weighted-average discount rate: ​ ​ ​ ​ Operating leases ​ ​ 3.80 % Finance leases ​ ​ 5.07 % ​ The Company’s maturity analysis of its lease liabilities as of December 31, 2019 is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Operating ​ Finance ​ ​ $s in thousands Leases ​ Leases ​ Total 2020 ​ $ 18,007 ​ $ 4,742 ​ $ 22,749 2021 ​ ​ 14,935 ​ ​ 4,699 ​ ​ 19,634 2022 ​ 11,210 ​ 4,315 ​ 15,525 2023 ​ 8,643 ​ 4,400 ​ 13,043 2024 ​ 4,885 ​ 2,714 ​ 7,599 Thereafter ​ 5,025 ​ 2,853 ​ 7,878 Total ​ $ 62,705 ​ $ 23,723 ​ $ 86,428 Less: Interest ​ ​ 5,434 ​ ​ 3,287 ​ ​ 8,721 Present value of lease liabilities ​ $ 57,271 ​ $ 20,436 ​ $ 77,707 ​ As previously disclosed in the Company’s 2018 Form 10-K, which followed the lease accounting standards in effect prior to adoption of ASC 842, future minimum lease payments on non-cancellable operating leases as of December 31, 2018 were as follows: ​ ​ ​ ​ ​ $s in thousands Payments 2019 ​ $ 5,638 2020 ​ 3,644 2021 ​ 3,184 2022 ​ 1,885 2023 ​ 1,457 Thereafter ​ 5,065 ​ ​ $ 20,873 ​ Rental expense under operating leases was $7.4 million and $7.6 million for the years ended December 31, 2018 and 2017, respectively.

GOODWILL AND INTANGIBLE ASSETS

GOODWILL AND INTANGIBLE ASSETS	12 Months Ended
	Dec. 31, 2019
GOODWILL AND INTANGIBLE ASSETS
GOODWILL AND INTANGIBLE ASSETS	NOTE 13. GOODWILL AND INTANGIBLE ASSETS Changes in goodwill for the years ended December 31, 2019 and 2018 were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Field & ​ ​ ​ ​ ​ Environmental ​ Industrial ​ ​ ​ ​ Services ​ Services ​ ​ ​ ​ ​ ​ ​ Accumulated ​ ​ ​ Accumulated ​ ​ ​ $s in thousands ​ Gross ​ Impairment ​ Gross ​ Impairment ​ Total Balance at December 31, 2017 ​ $ 150,699 ​ $ (5,457) ​ $ 44,131 ​ $ — ​ $ 189,373 ES&H Dallas acquisition ​ ​ — ​ ​ — ​ ​ 7,100 ​ ​ — ​ ​ 7,100 Winnie acquisition ​ ​ 13,573 ​ ​ — ​ ​ — ​ ​ — ​ ​ 13,573 Impairment charges ​ ​ — ​ ​ (1,413) ​ — ​ ​ — ​ ​ (1,413) Foreign currency translation ​ ​ (1,456) ​ ​ — ​ — ​ ​ — ​ ​ (1,456) Balance at December 31, 2018 ​ $ 162,816 ​ $ (6,870) ​ $ 51,231 ​ $ — ​ $ 207,177 NRC Merger ​ ​ 308,856 ​ ​ — ​ ​ 239,629 ​ ​ — ​ ​ 548,485 US Ecology Sarnia acquisition ​ ​ — ​ ​ — ​ ​ 7,668 ​ ​ — ​ ​ 7,668 Winnie purchase price allocation adjustment ​ ​ 2,863 ​ ​ — ​ ​ — ​ ​ — ​ ​ 2,863 Foreign currency translation ​ 736 ​ ​ — ​ 51 ​ ​ — ​ 787 Balance at December 31, 2019 ​ $ 475,271 ​ $ (6,870) ​ $ 298,579 ​ $ — ​ $ 766,980 ​ We assess goodwill for impairment during the fourth quarter as of October 1 of each year, and also if an event occurs or circumstances change that would more likely than not reduce the fair value of a reporting unit below its carrying amount. The assessment consists of comparing the fair value of the reporting unit to the carrying value of the net assets assigned to the reporting unit, including goodwill. Fair values are generally determined by using a market approach, applying a multiple of earnings based on guideline for publicly traded companies, an income approach, discounting projected future cash flows based on our expectations of the current and future operating environment, or a combination thereof. Estimating future cash flows requires significant judgment about factors such as general economic conditions and projected growth rates, and our estimates often vary from the cash flows eventually realized. The rates used to discount projected future cash flows reflect a weighted average cost of capital based on our industry, capital structure and risk premiums including those reflected in the current market capitalization. The result of the annual assessment of goodwill undertaken in the fourth quarter of 2019 indicated that the fair value of each of our reporting units was in excess of its respective carrying value. In connection with our annual budgeting process commencing in the third quarter of 2018 and review of the projected future cash flows of our reporting units used in our annual assessment of goodwill, it was determined that the projected future cash flows of our Mobile Recycling reporting unit (described below), which is part of our Environmental Services segment, indicated that the fair value of the reporting unit may be below its carrying amount. Accordingly, we performed an interim assessment of the reporting unit’s goodwill as of September 30, 2018. Based on the results of that assessment, goodwill was deemed impaired and we recognized an impairment charge of $1.4 million in the third quarter of 2018, representing the reporting unit’s entire goodwill balance. The factors contributing to the $1.4 million goodwill impairment charge principally related to declining business and cash flows, which negatively impacted the reporting unit’s prospective financial information in its discounted cash flow model and the reporting unit’s estimated fair value as compared to previous estimates. ​ The result of the annual assessment of goodwill undertaken in the fourth quarter of 2018 indicated that the fair value of each of our reporting units was in excess of its respective carrying value. Intangible assets as of December 31, 2019 and 2018 consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 ​ 2018 ​ ​ ​ ​ ​ Accumulated ​ ​ ​ ​ ​ ​ ​ Accumulated ​ ​ ​ $s in thousands Cost Amortization Net Cost Amortization Net Amortizing intangible assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Permits, licenses and lease ​ $ 174,339 ​ $ (18,707) ​ $ 155,632 ​ $ 164,840 ​ $ (14,804) ​ $ 150,036 Customer relationships ​ ​ 333,090 ​ ​ (35,254) ​ ​ 297,836 ​ ​ 99,241 ​ ​ (25,676) ​ ​ 73,565 Technology - formulae and processes ​ 6,964 ​ (2,013) ​ 4,951 ​ 6,672 ​ (1,714) ​ 4,958 Customer backlog ​ 3,652 ​ (2,022) ​ 1,630 ​ 3,652 ​ (1,656) ​ 1,996 Tradename ​ 10,390 ​ ​ (4,832) ​ ​ 5,558 ​ ​ 4,290 ​ ​ (4,290) ​ ​ — Developed software ​ ​ 2,895 ​ ​ (1,884) ​ ​ 1,011 ​ ​ 2,884 ​ ​ (1,581) ​ ​ 1,303 Non-compete agreements ​ 5,455 ​ (1,694) ​ 3,761 ​ 1,542 ​ (875) ​ 667 Internet domain and website ​ ​ 536 ​ ​ (156) ​ ​ 380 ​ ​ 536 ​ ​ (128) ​ ​ 408 Database ​ ​ 388 ​ ​ (191) ​ ​ 197 ​ ​ 384 ​ ​ (167) ​ ​ 217 Total amortizing intangible assets ​ 537,709 ​ (66,753) ​ 470,956 ​ 284,041 ​ (50,891) ​ 233,150 Non-amortizing intangible assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Permits and licenses ​ 103,816 ​ ​ — ​ 103,816 ​ 46,391 ​ ​ — ​ 46,391 Tradename ​ 130 ​ ​ — ​ ​ 130 ​ 125 ​ ​ — ​ ​ 125 Total intangible assets ​ $ 641,655 ​ $ (66,753) ​ $ 574,902 ​ $ 330,557 ​ $ (50,891) ​ $ 279,666 ​ We review non-amortizing intangible assets for impairment during the fourth quarter as of October 1 of each year. Fair value is generally determined by considering an internally-developed discounted projected cash flow analysis. Estimating future cash flows requires significant judgment about factors such as general economic conditions and projected growth rates, and our estimates often vary from the cash flows eventually realized. If the fair value of an asset is determined to be less than the carrying amount of the intangible asset, an impairment in the amount of the difference is recorded in the period in which the annual assessment occurs. The result of the annual assessment of non-amortizing intangible assets undertaken in the fourth quarter of 2019 indicated no impairment charges were required. In connection with the interim goodwill impairment assessment of the Mobile Recycling reporting unit, we also assessed the reporting unit’s non-amortizing permit intangible asset and other amortizing tangible and intangible assets for impairment as of September 30, 2018. Based on the results of that assessment, the carrying amounts of the non-amortizing permit intangible asset and other amortizing intangible assets exceeded their estimated fair values and, as a result, we recognized a $2.3 million impairment charge in the third quarter of 2018. The factors and timing contributing to the non-amortizing intangible asset and the other amortizing intangible assets impairment charges were the same as the factors and timing described above with regards to the Mobile Recycling reporting unit goodwill impairment charge. The result of the annual assessment of non-amortizing intangible assets undertaken in the fourth quarter of 2018 indicated no impairment charges were required. On November 1, 2019, the Company completed the NRC Merger and recorded $548.5 million of goodwill, $246.2 million of amortizing intangible assets (consisting primarily of customer relationships) and $57.4 million of non-amortizing intangible assets (consisting of permits and licenses) as a result of the acquisition. See Note 5 for additional information. On August 1, 2019, the Company acquired US Ecology Sarnia and recorded $7.7 million of goodwill and $6.2 million of amortizing intangible assets (consisting primarily of customer relationships) as a result of the acquisition. See Note 5 for additional information. On August 31, 2018, the Company acquired ES&H Dallas and recorded $7.1 million of goodwill and $4.2 million of amortizing intangible assets (consisting primarily of customer relationships) as a result of the acquisition. See Note 5 for additional information. On November 14, 2018, the Company acquired Winnie and recorded $16.4 million of goodwill and $66.5 million of amortizing intangible assets (consisting of permits and customer relationships) as a result of the acquisition. See Note 5 for additional information. Amortization expense relating to intangible assets was $15.5 million, $9.6 million and $9.9 million for the years ended December 31, 2019, 2018 and 2017, respectively. Foreign intangible asset carrying amounts are affected by foreign currency translation. Future amortization expense of amortizing intangible assets is expected to be as follows: ​ ​ ​ ​ ​ ​ ​ Expected $s in thousands Amortization 2020 ​ $ 36,737 2021 ​ 33,948 2022 ​ 30,840 2023 ​ 30,684 2024 ​ 30,302 Thereafter ​ 308,445 ​ ​ $ 470,956 ​

EMPLOYEE BENEFIT PLANS

EMPLOYEE BENEFIT PLANS	12 Months Ended
	Dec. 31, 2019
EMPLOYEE BENEFIT PLANS
EMPLOYEE BENEFIT PLANS	NOTE 14. EMPLOYEE BENEFIT PLANS Defined Contribution Plans We maintain the US Ecology, Inc., 401(k) Savings and Retirement Plan (“the Plan”) for employees who voluntarily contribute a portion of their compensation, thereby deferring income for federal income tax purposes. Participants may contribute a percentage of salary up to the IRS limitations. The Company contributes a matching contribution equal to 55% of participant contributions up to 6% of eligible compensation. The Company contributed matching contributions to the Plan of $3.0 million, $2.5 million and $2.1 million in 2019, 2018 and 2017, respectively. The Company also maintains 401(k) savings and retirement plans (“the NRC Plans”) for the employees that joined the Company through the NRC Merger. Participants may contribute a percentage of salary up to the IRS limitations. The Company contributes a matching contribution equal to 50% of participant contributions up to 6% of eligible compensation. The deferred amount cannot exceed 25% of the annual aggregate salaries of those employees eligible for participation. The Company contributed matching contributions to the NRC Plans of $325,000 in 2019. We also maintain the Stablex Canada Inc. Simplified Pension Plan (“the SPP”). This defined contribution plan covers substantially all of our employees at our Blainville, Québec facility in Canada. Employees represented by the Communications, Energy and Paperworkers Union of Canada receive a Company contribution equal to 9.0% of eligible compensation. Employees not represented by the union receive a base Company contribution equal to 5% of eligible compensation and an additional matching contribution in an amount up to 2% of eligible compensation. The Company contributed $692,000, $653,000 and $556,000 to the SPP in 2019, 2018 and 2017, respectively. Multi-Employer Defined Benefit Pension Plans Certain of the Company’s wholly-owned subsidiaries participate in a total of five multi-employer defined benefit pension plans under the terms of collective bargaining agreements covering most of the subsidiaries’ union employees. Contributions are determined in accordance with the provisions of negotiated labor contracts and are generally based on stipulated rates per hours worked. Benefits under these plans are generally based on compensation levels and years of service. The financial risks of participating in multi-employer plans are different from single employer defined benefit pension plans in the following respects: ● Assets contributed to the multi-employer plan by one employer may be used to provide benefits to employees of other participating employers. ● If a participating employer discontinues contributions to a plan, the unfunded obligations of the plan may be borne by the remaining participating employers. ● If a participating employer chooses to stop participating in a plan, a withdrawal liability may be created based on the unfunded vested benefits for all employees in the plan. Information regarding significant multi-employer pension benefit plans in which the Company participates is shown in the following table: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Pension ​ ​ ​ ​ ​ ​ Protection Act ​ ​ ​ ​ ​ ​ Certified ​ ​ Plan Employer ​ Plan ​ Zone Status Name of Plan ID Number Number 2019 2018 Operating Engineers Local 324 Pension Fund ​ 38-1900637 ​ 001 ​ Red ​ Red ​ The Company contributed $1.0 million to the Operating Engineers Local 324 Pension Fund (the “Local 324 Plan”) in both 2019 and 2018. The Company also contributed $281,000 and $242,000 to other multi-employer plans in 2019 and 2018, respectively, which are excluded from the table above as they are not individually significant. Based on information as of April 30, 2019 and 2018, the year end of the Local 324 Plan, the Company’s contributions made to the Local 324 Plan represented less than 5% of total contributions received by the Local 324 Plan during the 2019 and 2018 plan years. The certified zone status in the table above is defined by the Department of Labor and the Pension Protection Act of 2006 and represents the level at which the plan is funded. Plans in the red zone are less than 65% funded; plans in the yellow zone are less than 80% funded; and plans in the green zone are at least 80% funded. The certified zone status is as of the Local 324 Plan’s year-end of April 30, 2019 and 2018.

CLOSURE AND POST-CLOSURE OBLIGA

CLOSURE AND POST-CLOSURE OBLIGATIONS	12 Months Ended
	Dec. 31, 2019
CLOSURE AND POST-CLOSURE OBLIGATIONS
CLOSURE AND POST-CLOSURE OBLIGATIONS	NOTE 15. CLOSURE AND POST-CLOSURE OBLIGATIONS Our accrued closure and post-closure liability represents the expected future costs, including corrective actions, associated with closure and post-closure of our operating and non-operating disposal facilities. We record the fair value of our closure and post-closure obligations as a liability in the period in which the regulatory obligation to retire a specific asset is triggered. For our individual landfill cells, the required closure and post-closure obligations under the terms of our permits and our intended operation of the landfill cell are triggered and recorded when the cell is placed into service and waste is initially disposed in the landfill cell. The fair value is based on the total estimated costs to close the landfill cell and perform post-closure activities once the landfill cell has reached capacity and is no longer accepting waste. We perform periodic reviews of both non-operating and operating facilities and revise accruals for estimated closure and post-closure, remediation or other costs as necessary. Recorded liabilities are based on our best estimates of current costs and are updated periodically to include the effects of existing technology, presently enacted laws and regulations, inflation and other economic factors. We do not presently bear significant financial responsibility for closure and/or post-closure care of the disposal facilities located on state-owned land at our Beatty, Nevada site, provincial-owned land in Blainville, Québec; or state-leased federal land on the Department of Energy Hanford Reservation near Richland, Washington. The states of Nevada and Washington and the province of Québec collect fees from us based on the waste received on a quarterly or annual basis. Such fees are deposited in dedicated, government-controlled funds to cover the future costs of closure and post-closure care and maintenance. Such fees are periodically reviewed for adequacy by the governmental authorities. We maintain a surety bond for closure costs associated with the Stablex facility. Our lease agreement with the province of Québec requires that the surety bond be maintained for 25 years after the lease expires. We also maintain surety bonds for closure costs associated with our energy waste landfills in Texas. Under the terms of our waste disposal permits for these landfills, financial security must be provided to the Railroad Commission of Texas in an amount necessary to close the facility. At December 31, 2019 we had $12.8 million in commercial surety bonds dedicated for closure obligations at our operating and non-operating disposal facilities. In accounting for closure and post-closure obligations, which represent our asset retirement obligations, we recognize a liability as part of the fair value of future asset retirement obligations and an associated asset as part of the carrying amount of the underlying asset. This obligation is valued based on our best estimates of current costs and current estimated closure and post-closure costs taking into account current technology, material and service costs, laws and regulations. These cost estimates are increased by an estimated inflation rate, estimated to be 2.6% at December 31, 2019. Inflated current costs are then discounted using our credit-adjusted risk-free interest rate, which approximates our incremental borrowing rate, in effect at the time the obligation is established or when there are upward revisions to our estimated closure and post-closure costs. Our weighted-average credit-adjusted risk-free interest rate at December 31, 2019 approximated 5.9%. Changes to reported closure and post-closure obligations for the years ended December 31, 2019 and 2018, were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $s in thousands 2019 2018 Closure and post-closure obligations, beginning of year ​ $ 78,363 ​ $ 76,088 Liabilities assumed in the NRC Merger ​ ​ 5,691 ​ ​ — Accretion expense ​ 4,388 ​ 3,707 Payments ​ (1,913) ​ (1,388) Adjustments ​ (221) ​ 99 Foreign currency translation ​ 75 ​ (143) Closure and post-closure obligations, end of year ​ 86,383 ​ 78,363 Less current portion ​ (2,152) ​ (2,266) Long-term portion ​ $ 84,231 ​ $ 76,097 ​ Adjustment to the obligations represents changes in the expected timing or amount of cash expenditures based upon actual and estimated cash expenditures. The adjustments in 2019 were primarily attributable to a $393,000 decrease in closure and post-closure obligations at our Robstown, Texas operating facility and a $272,000 decrease in closure and post-closure obligations at our Blainville, Québec, Canada operating facility due to changes in closure timing, partially offset by a $422,000 increase to the obligation for our Blainville, Québec, Canada operating facility associated with a newly-constructed disposal cell. The adjustments in 2018 were primarily attributable to a $1.1 million decrease in closure and post-closure obligations at our Grand View, Idaho operating facility due to a change in closure timing, partially offset by a $511,000 increase to the obligation for the acquired deep-well at our Winnie facility and a $472,000 increase to the obligation at our Belleville, Michigan operating facility due to changes in both estimated closure costs and closure timing. Changes in the reported closure and post-closure asset, recorded as a component of Property and equipment, net, in the consolidated balance sheets, for the years ended December 31, 2019 and 2018 were as follows: ​ ​ ​ ​ ​ ​ ​ ​ $s in thousands 2019 2018 Net closure and post-closure asset, beginning of year ​ $ 19,510 ​ $ 20,495 Asset acquired in the NRC Merger ​ ​ 4,857 ​ ​ — Additions or adjustments to closure and post-closure asset ​ (221) ​ 99 Amortization of closure and post-closure asset ​ (1,298) ​ (805) Foreign currency translation ​ 36 ​ (279) Net closure and post-closure asset, end of year ​ $ 22,884 ​ $ 19,510 ​

DEBT

DEBT	12 Months Ended
	Dec. 31, 2019
DEBT
DEBT	​ NOTE 16. DEBT Long-term debt consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, $s in thousands 2019 2018 Revolving credit facility ​ $ 327,000 ​ $ 364,000 Term loan ​ ​ 450,000 ​ ​ — Unamortized term loan discount and debt issuance costs ​ ​ (7,799) ​ ​ — Total debt ​ ​ 769,201 ​ ​ 364,000 Current portion of long-term debt ​ ​ (3,359) ​ ​ — Long-term debt ​ $ 765,842 ​ $ 364,000 ​ Future maturities of long-term debt, excluding unamortized discount and debt issuance costs, as of December 31, 2019 consisted of the following: ​ ​ ​ ​ ​ $s in thousands Maturities 2020 ​ $ 4,500 2021 ​ ​ 4,500 2022 ​ ​ 4,500 2023 ​ ​ 4,500 2024 ​ ​ 331,500 Thereafter ​ ​ 427,500 ​ ​ $ 777,000 ​ Credit Agreement ​ On April 18, 2017, Predecessor US Ecology, a wholly-owned subsidiary of the Company, entered into a new senior secured credit agreement (the “Credit Agreement”) with Wells Fargo Bank, National Association (“Wells Fargo”), as administrative agent for the lenders, swingline lender and issuing lender, and Bank of America, N.A., as an issuing lender, that provides for a $500.0 million, five-year revolving credit facility (the “Revolving Credit Facility”), including a $75.0 million sublimit for the issuance of standby letters of credit and a $40.0 million sublimit for the issuance of swingline loans used to fund short-term working capital requirements. The Credit Agreement also contains an accordion feature whereby Predecessor US Ecology may request up to $200.0 million of additional funds through an increase to the Revolving Credit Facility, through incremental term loans, or some combination thereof. As described below, the Credit Agreement was amended in November 2019 in connection with the NRC Merger. In addition, as a result of the consummation of the NRC Merger, the borrower under the Credit Facility is Predecessor US Ecology, a wholly-owned subsidiary of the Company. In connection with Predecessor US Ecology’s entry into the Credit Agreement, Predecessor US Ecology terminated its existing credit agreement with Wells Fargo, dated June 17, 2014 (the “2014 Credit Agreement”). Immediately prior to the termination of the 2014 Credit Agreement, there were $278.3 million of term loans and no revolving loans outstanding under the 2014 Credit Agreement. No early termination penalties were incurred as a result of the termination of the 2014 Credit Agreement. Predecessor US Ecology wrote off certain unamortized deferred financing costs and original issue discount associated with the 2014 Credit Agreement that were to be amortized to interest expense in future periods through a non-cash charge of $5.5 million to interest expense in 2017. ​ The Revolving Credit Facility provides up to $500.0 million of revolving credit loans or letters of credit with the use of proceeds restricted solely for working capital and other general corporate purposes (including acquisitions and capital expenditures). Under the Revolving Credit Facility, revolving credit loans are available based on a base rate (as defined in the Credit Agreement) or LIBOR, at the Company’s option, plus an applicable margin which is determined according to a pricing grid under which the interest rate decreases or increases based on our ratio of funded debt to consolidated earnings before interest, taxes, depreciation and amortization (as defined in the Credit Agreement), as set forth in the table below: ​ Total Net Leverage Ratio LIBOR Rate Loans Interest Margin Base Rate Loans Interest Margin Equal to or greater than 3.25 to 1.00 2.00% 1.00% Equal to or greater than 2.50 to 1.00, but less than 3.25 to 1.00 1.75% 0.75% Equal to or greater than 1.75 to 1.00, but less than 2.50 to 1.00 1.50% 0.50% Equal to or greater than 1.00 to 1.00, but less than 1.75 to 1.00 1.25% 0.25% Less than 1.00 to 1.00 1.00% 0.00% ​ During the year ended December 31, 2019, the effective interest rate on the Revolving Credit Facility, after giving effect to the impact of our interest rate swap and the amortization of the loan discount and debt issuance costs, was 3.98%. Interest only payments are due either quarterly or on the last day of any interest period, as applicable. ​ In October 2014, Predecessor US Ecology entered into an interest rate swap agreement, effectively fixing the interest rate on $150.0 million, or 46%, of the Revolving Credit Facility borrowings as of December 31, 2019. The interest rate swap agreement continued in place following the termination of the 2014 Credit Agreement. The critical terms of the interest rate swap and the forecasted transaction (periodic interest payments on the Predecessor US Ecology’s variable-rate debt) did not change as a result of the refinancing therefore the interest rate swap continues to qualify as a highly-effective cash flow hedge, with gains and losses deferred in accumulated other comprehensive income to be recognized as an adjustment to interest expense in the same period that the hedged interest payments affect earnings. ​ Predecessor US Ecology is required to pay a commitment fee ranging from 0.175% to 0.35% on the average daily unused portion of the Revolving Credit Facility, with such commitment fee to be reduced based upon Predecessor US Ecology’s total net leverage ratio (as defined in the Credit Agreement). The maximum letter of credit capacity under the Revolving Credit Facility is $75.0 million and the Credit Agreement provides for a letter of credit fee equal to the applicable margin for LIBOR loans under the Revolving Credit Facility. At December 31, 2019, there were $327.0 million of revolving credit loans outstanding on the Revolving Credit Facility. These revolving credit loans are due upon the earliest to occur of (a) November 1, 2024 (or, with respect to any lender, such later date as requested by us and accepted by such lender), (b) the date of termination of the entire revolving credit commitment (as defined in the Credit Agreement) by us, and (c) the date of termination of the revolving credit commitment and are presented as long-term debt in the consolidated balance sheets. ​ Predecessor US Ecology has entered into a sweep arrangement whereby day-to-day cash requirements in excess of available cash balances are advanced to the Company on an as-needed basis with repayments of these advances automatically made from subsequent deposits to our cash operating accounts (the “Sweep Arrangement”). Total advances outstanding under the Sweep Arrangement are subject to the $40.0 million swingline loan sublimit under the Revolving Credit Facility. Predecessor US Ecology’s revolving credit loans outstanding under the Revolving Credit Facility are not subject to repayment through the Sweep Arrangement. As of December 31, 2019, there were no amounts outstanding subject to the Sweep Arrangement. ​ As of December 31, 2019, the availability under the Revolving Credit Facility was $166.3 million with $6.7 million of the Revolving Credit Facility issued in the form of standby letters of credit utilized as collateral for closure and post-closure financial assurance and other assurance obligations. ​ Predecessor US Ecology may at any time and from time to time prepay revolving credit loans and swingline loans, in whole or in part, without premium or penalty, subject to the obligation to indemnify each of the lenders against any actual loss or expense (including any loss or expense arising from the liquidation or reemployment of funds obtained by it to maintain a LIBOR rate loan (as defined in the Credit Agreement) or from fees payable to terminate the deposits from which such funds were obtained) with respect to the early termination of any LIBOR rate loan. The Credit Agreement provides for mandatory prepayment at any time if the revolving credit outstanding exceeds the revolving credit commitment (as such terms are defined in the Credit Agreement), in an amount equal to such excess. Subject to certain exceptions, the Credit Agreement provides for mandatory prepayment upon certain asset dispositions, casualty events and issuances of indebtedness. ​ Pursuant to (i) an unconditional guarantee agreement and (ii) a collateral agreement, each entered into by Predecessor US Ecology and its domestic subsidiaries on April 18, 2017, Predecessor US Ecology’s obligations under the Credit Agreement are (or will be) jointly and severally and fully and unconditionally guaranteed on a senior basis by all of the Company’s existing and certain future domestic subsidiaries and are secured by substantially all of the assets of Predecessor US Ecology and the Company’s existing and certain future domestic subsidiaries (subject to certain exclusions), including 100% of the equity interests of the Company’s domestic subsidiaries and 65% of the voting equity interests of the Company’s directly owned foreign subsidiaries (and 100% of the non-voting equity interests of the Company’s directly owned foreign subsidiaries). ​ The Credit Agreement contains customary restrictive covenants, subject to certain permitted amounts and exceptions, including covenants limiting the ability of the Company to incur additional indebtedness, pay dividends and make other restricted payments, repurchase shares of our outstanding stock and create certain liens. Upon the occurrence of an event of default (as defined in the Credit Agreement), among other things, amounts outstanding under the Credit Agreement may be accelerated and the commitments may be terminated. ​ The Credit Agreement also contains financial maintenance covenants, a maximum consolidated total net leverage ratio and a consolidated interest coverage ratio (as such terms are defined in the Credit Agreement). Our consolidated total net leverage ratio as of the last day of any fiscal quarter, commencing with the fiscal quarter ending June 30, 2017, may not exceed 4.00 to 1.00, subject to certain exceptions. Our consolidated interest coverage ratio as of the last day of any fiscal quarter, commencing with the fiscal quarter ending June 30, 2017, may not be less than 3.00 to 1.00. ​ At December 31, 2019, we were in compliance with all of the financial covenants in the Credit Agreement. ​ Amendments to the Credit Agreement ​ On August 6, 2019, Predecessor US Ecology entered into the first amendment (the “First Amendment”) to the Credit Agreement, by and among Predecessor US Ecology, the subsidiaries of Predecessor US Ecology party thereto, the lenders referred to therein and Wells Fargo, as issuing lender, swingline lender and administrative agent. Effective November 1, 2019, the First Amendment, among other things, extended the expiration of the Revolving Credit Facility to November 1, 2024, permitted the issuance of a $400.0 million incremental term loan to be used to refinance the indebtedness of NRC and pay related transaction expenses in connection with the NRC Merger, modified the accordion feature allowing Predecessor US Ecology to request up to the greater of (x) $250.0 million and (y) 100% of consolidated EBITDA plus certain additional amounts, increased the sublimit for the issuance of swingline loans to $40.0 million and increased the maximum consolidated total net leverage ratio to 4.00 to 1.00. ​ On November 1, 2019, Predecessor US Ecology entered into the lender joinder agreement and second amendment (the “Second Amendment”) to the Credit Agreement. Effective November 1, 2019, the Second Amendment, among other things, amended the Credit Agreement to increase the capacity for incremental term loans by $50.0 million and provided for Wells Fargo lending $450.0 million in incremental term loans to Predecessor US Ecology to pay off the existing debt of NRC in connection with the NRC Merger, to pay certain fees, costs and expenses incurred in connection with the NRC Merger and to repay outstanding borrowings under the Revolving Credit Facility. The seven-year incremental term loan matures November 1, 2026, requires principal repayment of 1% annually, and bears interest at LIBOR plus 2.25% or a base rate plus 1.25% (with a step-up to LIBOR plus 2.50% or a base rate plus 1.50% in the event that US Ecology credit ratings are not BB (with a stable or better outlook) or better from S&P and Ba2 (with a stable or better outlook) or better from Moody’s). The effective interest rate on the term loan, including the impact of the amortization of debt issuance costs, was 4.45% from the issue date through December 31, 2019. ​ 2014 Credit Agreement ​ On June 17, 2014, Predecessor US Ecology entered into a $540.0 million senior secured credit agreement with a syndicate of banks comprised of a $415.0 million term loan (the “Former Term Loan”) with a maturity date of June 17, 2021 and a $125.0 million revolving line of credit (the “Former Revolving Credit Facility”) with a maturity date of June 17, 2019. ​ The Former Term Loan provided an initial commitment amount of $415.0 million and bore interest at a base rate (as defined in the 2014 Credit Agreement) plus 2.00% or LIBOR plus 3.00%, at Predecessor US Ecology’s option. ​ The Former Revolving Credit Facility provided up to $125.0 million of revolving credit loans or letters of credit with the use of proceeds restricted solely for working capital and other general corporate purposes. Under the Former Revolving Credit Facility, revolving loans were available based on a base rate (as defined in the 2014 Credit Agreement) or LIBOR, at Predecessor US Ecology’s option, plus an applicable margin which was determined according to a pricing grid under which the interest rate decreased or increased based on our ratio of funded debt to consolidated earnings before interest, taxes, depreciation and amortization (as defined in the 2014 Credit Agreement). The maximum letter of credit capacity under the Former Revolving Credit Facility was $50.0 million and the 2014 Credit Agreement provided for a letter of credit fee equal to the applicable margin for LIBOR loans under the Former Revolving Credit Facility.

INCOME TAXES

INCOME TAXES	12 Months Ended
	Dec. 31, 2019
INCOME TAXES
INCOME TAXES	NOTE 17. INCOME TAXES The domestic and foreign components of income (loss) before income taxes consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $s in thousands 2019 2018 2017 Domestic $ 30,706 $ 46,147 $ 26,051 Foreign ​ 19,093 ​ 18,711 ​ 16,919 Income before income taxes ​ $ 49,799 ​ $ 64,858 ​ $ 42,970 ​ The components of the income tax expense (benefit) consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $s in thousands 2019 2018 2017 Current: ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. Federal ​ $ 3,120 ​ $ 2,239 ​ $ 11,157 State ​ 1,547 ​ 2,368 ​ 2,482 Foreign ​ 5,426 ​ 4,746 ​ 5,398 Total current ​ 10,093 ​ 9,353 ​ 19,037 Deferred: ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. Federal ​ 5,977 ​ 5,675 ​ (27,029) State ​ 714 ​ 172 ​ 2,323 Foreign ​ (125) ​ 63 ​ (726) Total deferred ​ 6,566 ​ 5,910 ​ (25,432) Income tax (benefit) expense ​ $ 16,659 ​ $ 15,263 ​ $ (6,395) ​ On December 22, 2017, the Tax Act was signed into law, making significant changes to the Internal Revenue Code. Changes include, but are not limited to, a corporate tax rate decrease from 35% to 21% effective for tax years beginning after December 31, 2017, the transition of U.S. international taxation from a worldwide tax system to a territorial system, and a one-time transition tax on the mandatory deemed repatriation of cumulative foreign earnings as of December 31, 2017. In accordance with the Tax Act, we recorded $23.8 million as additional income tax benefit in the fourth quarter of 2017, the period in which the legislation was enacted. The total benefit included $25.2 million related to the re-measurement of certain deferred tax assets and liabilities partially offset by $1.4 million of expense related to one-time transition tax on the mandatory deemed repatriation of foreign earnings. As of December 22, 2018, we completed our accounting for the income tax effects of the Tax Act as of the enactment date, which resulted in a net benefit for measurement period adjustments of $193,000 for the year ended December 31, 2018. The total tax provision benefit included a $2.2 million benefit related to the re-measurement of certain deferred tax assets and liabilities offset by $2.0 million of expense related to adjustments to the transition tax. The completion of the Company’s accounting for the enactment of the Tax Act reflects, among other things, (i) the issuance of guidance by the U.S. Treasury regarding provisions of the Tax Act, (ii) certain elections and accounting policy decisions pursuant to the Tax Act, (iii) adjustments to historic foreign earnings and profits or the associated tax credit pools which are significant factors in the calculation of the repatriation tax, and (iv) changes in interpretations and assumptions that we have made. We note that final guidance and regulations surrounding the implementation of all provisions in the Tax Act have not been issued to date. This guidance, once issued, may materially affect our conclusions regarding the net related effects of the Tax Act on our financial statements. A reconciliation between the statutory federal income tax rate and the effective income tax rate is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 2018 2017 Taxes computed at federal statutory rate 21.0 % 21.0 % 35.0 % Impairment and loss on divestiture ​ — ​ 0.5 ​ 4.4 ​ State income taxes (net of federal income tax benefit) 5.7 ​ 5.1 ​ 2.9 ​ Share-based compensation ​ (0.4) ​ (1.3) ​ — ​ Research and development credits ​ (0.8) ​ (2.0) ​ — ​ Non-deductible transaction costs ​ 3.4 ​ — ​ — ​ Global intangible low taxed income ​ 1.1 ​ — ​ — ​ Tax Cuts and Jobs Act of 2017 ​ — ​ (0.3) ​ (55.4) ​ Foreign rate differential 2.5 ​ 1.7 ​ (2.9) ​ State deferred rate differential ​ (1.6) ​ — ​ — ​ Other 2.6 ​ (1.2) ​ 1.1 ​ ​ 33.5 % 23.5 % (14.9) % ​ The components of the total net deferred tax assets and liabilities as of December 31, 2019 and 2018 consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ $s in thousands 2019 2018 Deferred tax assets: ​ ​ ​ ​ ​ ​ Net operating losses ​ $ 14,121 ​ $ — Operating leases ​ ​ 14,034 ​ ​ — Foreign tax credit and capital loss carry forwards ​ ​ 4,705 ​ ​ 5,165 Accruals, allowances and other ​ 8,966 ​ 5,041 Environmental compliance and other site related costs ​ 9,203 ​ 8,580 Business interest expense ​ ​ 6,498 ​ ​ — Unrealized foreign exchange gains and losses ​ ​ 962 ​ ​ 1,550 Total deferred tax assets ​ 58,489 ​ 20,336 Less: valuation allowance ​ (4,965) ​ (4,791) Net deferred tax assets ​ 53,524 ​ 15,545 Deferred tax liabilities: ​ ​ ​ ​ ​ ​ Property and equipment ​ (53,540) ​ (26,145) Intangible assets ​ (112,446) ​ (51,081) Operating leases ​ ​ (14,034) ​ ​ — Unrealized gains and losses on interest rate hedge ​ ​ — ​ ​ (241) Other ​ (1,849) ​ (1,284) Total deferred tax liabilities ​ (181,869) ​ (78,751) Net deferred tax liability ​ $ (128,345) ​ $ (63,206) ​ All deferred tax assets and liabilities are recorded in Deferred income taxes, net on the consolidated balance sheets as of December 31, 2019 and 2018. The Company acquired U.S. federal and state net operating loss and business interest expense carryforwards of NRC upon the acquisition of that entity in November 2019, subject to the ownership change limitations. Acquired U.S. federal net operating losses, state net operating losses, and business interest expense carryforwards from NRC total approximately $95.1 million, $43.8 million and $38.2 million, respectively, net of amounts unavailable due to previous ownership change limitations, which are included in the total Net operating losses and Business interest expense above. Utilization of the Company’s net operating loss and business interest expense carryforwards may be subject to a substantial annual limitation due to the ownership change limitations provided by the Internal Revenue Code and similar state provisions. Such an annual limitation could result in the expiration or elimination of the net operating loss and business interest expense carryforwards before utilization. Management believes that the limitation will not limit utilization of the carryforwards prior to their expiration based on the historic profitability of the Company and certain favorable adjustments available to the annual limitation calculations. As of December 31, 2019, we had approximately $92.3 million, $2.7 million, and $42.4 million of federal, foreign, and state and local net operating losses (“NOLs”), respectively. A portion of the federal NOLs begin to expire in 2029 and the remaining federal NOLs have no expiration date. Foreign NOLs are indefinite lived and therefore have no expiration date. State and local NOLs expire between 2020 and 2039. We have historically recorded a valuation allowance for certain deferred tax assets due to uncertainties regarding future operating results and limitations on utilization of state and local NOLs for tax purposes. At December 31, 2019 and 2018, we maintained a valuation allowance of approximately $260,000 and $73,000, respectively, for state and local NOLs that are not expected to be utilizable prior to expiration. The valuation allowance as of December 31, 2019 and 2018 was primarily related to foreign tax credit and capital loss carryforwards that, in the judgment of management, were not more likely than not to be realized. In assessing the realizability of deferred tax assets, management considers whether it is more likely than not that some or all of the deferred tax assets will not be realized. The ultimate realization of deferred tax assets depends on the generation of future taxable income during the periods in which those temporary differences are deductible. Management considers the scheduled reversal of deferred tax liabilities (including the impact of available carryback and carryforward periods), projected taxable income, and tax-planning strategies in making this assessment. The net valuation allowance increased $174,000 for the year ended December 31, 2019 compared to December 31, 2018. Changes to unrecognized tax benefits for the years ended December 31, 2019, 2018 and 2017, were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $s in thousands 2019 2018 2017 Unrecognized tax benefits, beginning of year ​ $ 555 ​ $ — ​ $ — Gross increases - tax positions in prior period ​ ​ 8,088 ​ ​ 494 ​ ​ — Gross decreases - tax positions in prior period ​ ​ (9) ​ ​ — ​ ​ — Gross increases - tax positions in current period ​ ​ 52 ​ ​ 61 ​ ​ — Settlements ​ ​ (284) ​ ​ — ​ ​ — Lapse of statute of limitations ​ ​ (67) ​ ​ — ​ ​ — Unrecognized tax benefits, end of year ​ $ 8,335 ​ $ 555 ​ $ — ​ We apply the provisions of ASC 740 related to income tax uncertainties which clarifies the accounting for income taxes by prescribing a minimum recognition threshold a tax position is require to meet before being recognized in the consolidated financial statements. The unrecognized tax benefits that are not expected to result in payment or receipt of cash within one year are classified as “Other long-term liabilities” in the Consolidated Balance Sheets. At December 31, 2019, the total amount of unrecognized tax benefits was $8.3 million, of which $236,000, if recognized, would favorably impact our future earnings. The remaining $8.1 million of which is related to the acquired NRC net operating losses and is recorded as a reduction to our net operating losses deferred tax asset. We do not anticipate that the amount of existing unrecognized tax benefits will significantly increase or decrease within the next 12 months. Accrued interest and penalties related to unrecognized tax benefits are recorded as interest expense and selling, general and administrative expenses, respectively. The total accrued interest related to unrecognized tax benefits as of December 31, 2019 and December 31, 2018 were not significant. There is no accrual for penalties. As of December 31, 2019, the Company had accumulated undistributed earnings generated by our foreign subsidiaries of approximately $49.0 million. Any additional taxes due with respect to such earnings or the excess of the amount for financial reporting over the tax basis of our foreign investments would generally be limited to foreign withholding taxes and state income taxes. We intend, however, to indefinitely reinvest these earnings and expect future U.S. cash generation to be sufficient to meet future U.S. cash needs. The Company files income tax returns in the U.S. Federal and various state, local and foreign jurisdictions. The Company is subject to examination by the IRS for tax years 2016 through 2019. The 2014 through 2019 state tax returns are subject to examination by state tax authorities. US Ecology Sarnia is currently under examination by the Canadian Revenue Agency for the pre-acquisition years 2016 and 2017. The tax years 2015 through 2019 remain subject to examination in our significant foreign jurisdictions. The Company does not anticipate any material change as a result of any current examinations in progress.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	12 Months Ended
	Dec. 31, 2019
COMMITMENTS AND CONTINGENCIES
COMMITMENTS AND CONTINGENCIES	NOTE 18. COMMITMENTS AND CONTINGENCIES Litigation and Regulatory Proceedings In the ordinary course of business, we are involved in judicial and administrative proceedings involving federal, state, provincial or local governmental authorities, including regulatory agencies that oversee and enforce compliance with permits. Fines or penalties may be assessed by our regulators for non-compliance. Actions may also be brought by individuals or groups in connection with permitting of planned facilities, modification or alleged violations of existing permits, or alleged damages suffered from exposure to hazardous substances purportedly released from our operated sites, as well as other litigation. We maintain insurance intended to cover property and damage claims asserted as a result of our operations. Periodically, management reviews and may establish reserves for legal and administrative matters, or other fees expected to be incurred in relation to these matters. In December 2010, National Response Corporation, a subsidiary of NRC acquired by the Company in the NRC Merger, was named as one of many “Dispersant Defendants” in multi-district litigation, arising out of the explosion of the BP Deepwater Horizon (“BP”) oil rig, filed in the U.S. District Court for the Eastern District of Louisiana (“ In re Deepwater Horizon In January 2019, Kevin Sullivan, a driver for NRC from May 1, 2018 to August 22, 2018 filed a class action complaint against NRC in California Superior Court ( Kevin Sullivan et. Al. v. National Response Corp., NRC Environmental Services, Inc. and Paul Taveira et al. claim only, absent any individual or class claims against the Company or NRC. While the Company believes that Mr. Sullivan’s claims lack merit, the Company is currently unable to estimate the range of possible losses associated with this proceeding. On November 17, 2018, an explosion occurred at our Grand View, Idaho facility, resulting in one employee fatality and injuries to other employees. The incident severely damaged the facility’s primary waste-treatment building as well as surrounding waste handling, waste storage, maintenance and administrative support structures, resulting in the closure of the entire facility that remained in effect through January 2019. We resumed limited operations at our Grand View, Idaho facility in February 2019 and regained additional capabilities throughout the remainder of 2019. In addition to initiating and conducting our own investigation into the incident, we fully cooperated with IDEQ, the USEPA and OSHA to support their comprehensive and independent investigations of the incident. On January 10, 2020, we entered into a settlement agreement with OSHA settling a complaint made by OSHA relating to the incident for $50,000. On January 28, 2020, the Occupational Safety and Health Review Commission issued an order terminating the proceeding relating to such OSHA complaint. We have not otherwise been named as a defendant in any action relating to the incident. We maintain workers’ compensation insurance, business interruption insurance and liability insurance for personal injury, property and casualty damage. We believe that any potential third-party claims associated with the explosion, in excess of our deductibles, are expected to be resolved primarily through our insurance policies. Although we carry business interruption insurance, a disruption of our business caused by a casualty event, including the full and partial closure of our Grand View, Idaho facility, may result in the loss of business, profits or customers during the time of such closure. Accordingly, our insurance policies may not fully compensate us for these losses. The Company is actively working with its insurance companies on comprehensive property and business interruption insurance claims related to the incident at our Grand View, Idaho facility in the fourth quarter of 2018. The Company received $12.7 million of property-related insurance payments in 2019 and recognized $12.4 million of property-related insurance recovery gains during 2019. The Company has also recognized insurance recoveries of $5.0 million in 2019 related to expenses incurred to continue limited operations at the facility and $4.7 million in 2019, related to lost profits as a result of lost business or customers. Other than as described above, we are not currently a party to any material pending legal proceedings and are not aware of any other claims that could, individually or in the aggregate, have a materially adverse effect on our financial position, results of operations or cash flows.

EQUITY

EQUITY	12 Months Ended
	Dec. 31, 2019
EQUITY
EQUITY	NOTE 19. EQUITY Equity-Based Purchase Consideration Pursuant to the Merger Agreement, on November 1, 2019 the Company paid $626.5 million of the purchase price in equity-based consideration comprising 9,337,949 newly-issued shares of US Ecology common stock, 3,772,753 replacement warrants, 118,239 replacement restricted stock units and 29,400 replacement stock options. Stock Repurchase Program On June 1, 2016, the Company’s Board of Directors authorized the repurchase of $25.0 million of the Company’s outstanding common stock. On May 29, 2018, the repurchase program was extended and will remain in effect until June 6, 2020, unless further extended by our Board of Directors. On December 30, 2019, the Company’s Board of Directors authorized the repurchase of $25.0 million of the Company’s outstanding warrants (such dollar amount considered in the aggregate with the dollar amount of shares of common stock repurchased by the Company, if any, under the Company’s share repurchase program) as part of the Company’s share repurchase program. Repurchases may be made from time to time in the open market or through privately negotiated transactions. The timing of any repurchases of common stock or warrants will be based upon prevailing market conditions and other factors. The Company may from time to time also consider other options for repurchasing some or all of its warrants, including but not limited to a tender offer for all of the outstanding warrants. The Company did not repurchase any shares of common stock under the repurchase program during the year ended December 31, 2019. Omnibus Incentive Plan On May 27, 2015, the stockholders of Predecessor US Ecology approved the Omnibus Incentive Plan (as amended, “Omnibus Plan”), which was approved by Predecessor US Ecology’s Board of Directors on April 7, 2015. In connection with the closing of the NRC Merger, the Company assumed the Omnibus Plan by adopting the Amended and Restated US Ecology, Inc. Omnibus Incentive Plan for the purposes of issuing replacement awards to award recipients under the Omnibus Plan pursuant to the Merger Agreement and for the issuance of additional awards in the future. The Omnibus Plan was developed to provide additional incentives through equity ownership in US Ecology and, as a result, encourage employees and directors to contribute to our success. The Omnibus Plan provides, among other things, the ability for the Company to grant restricted stock, performance stock, options, stock appreciation rights, restricted stock units, performance stock units and other share-based awards or cash awards to officers, employees, consultants and non-employee directors. The Omnibus Plan expires on April 7, 2025 and authorizes 1,500,000 shares of common stock for grant over the life of the Omnibus Plan. As of December 31, 2019, 725,966 shares of common stock remain available for grant under the Omnibus Plan. Subsequent to the approval of the Omnibus Plan by Predecessor US Ecology in May 2015, we stopped granting equity awards under our 2008 Stock Option Incentive Plan (“2008 Stock Option Plan”). However, in connection with the closing of the NRC Merger, the Company assumed the 2008 Stock Option Plan for the purpose of issuing replacement awards to award recipients thereunder and will remain in effect solely for the settlement of awards granted under such plan. No shares that are reserved but unissued under the 2008 Stock Option Plan or that are outstanding under the 2008 Stock Option Plan and reacquired by the Company for any reason will be available for issuance under the Omnibus Plan. In addition, in connection with the closing of the NRC Merger, the Company assumed the NRC Group Holdings Corp. 2018 Equity Incentive Plan previously maintained by NRC by adopting the Amended and Restated US Ecology, Inc. 2018 Equity and Incentive Compensation Plan. Like the 2008 Stock Option Plan, the NRC Group Holdings Corp. 2018 Equity Incentive Plan was assumed by the Company solely for the purpose of issuing replacement awards to award recipients pursuant to the Merger Agreement, and no future grants may be made under the 2018 Equity and Incentive Compensation Plan. Performance Stock Units (PSUs) We have PSU awards outstanding under the Omnibus Plan. Each PSU represents the right to receive, on the settlement date, one share of the Company’s common stock. The total number of PSUs each participant is eligible to earn ranges from 0% to 200% of the target number of PSUs granted in 2018 and 2017. The actual number of 2018 and 2017 PSUs that will vest and be settled in shares is determined based on total stockholder return relative to a set of peer companies, over a three-year performance period. The total number of PSUs each participant is eligible to earn ranges from 0% to 300% of the target number of PSUs granted in 2019. The actual number of 2019 PSUs that will vest and be settled in shares is determined based on achievement of certain Company financial performance metrics and total stockholder return relative to a set of peer companies, over a three-year performance period. Compensation expense is recorded over the awards’ three-year vesting period. A summary of our PSU activity is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ Average ​ ​ ​ ​ Grant Date ​ ​ Units ​ Fair Value Outstanding as of December 31, 2018 ​ 39,200 ​ $ 55.48 Granted ​ 17,111 ​ ​ 58.20 Vested ​ (13,600) ​ ​ 41.22 Outstanding as of December 31, 2019 ​ 42,711 ​ $ 61.11 ​ The fair value of PSUs is estimated as of the date of grant using a Monte Carlo simulation model. The grant date fair value of PSUs granted during 2019, 2018 and 2017 was $58.20, $63.56. and $62.45 per unit, respectively. Assumptions used in the Monte Carlo simulation to calculate the fair value of the PSUs granted are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 2018 ​ 2017 ​ Stock price on grant date ​ $ 58.40 ​ $ 51.00 ​ $ 49.15 ​ Expected term ​ 3.0 years ​ 3.0 years ​ 3.0 years Expected volatility ​ ​ 30 % ​ 30 % ​ 31 % Risk-free interest rate ​ 2.5 % ​ 2.0 % ​ 1.5 % Expected dividend yield ​ 1.1 % ​ 1.4 % ​ 1.5 % ​ During 2019, 13,600 PSUs vested and PSU holders earned 19,414 shares of the Company’s common stock. Stock Options We have stock option awards outstanding under the 2008 Stock Option Plan and the Omnibus Plan. Stock options expire ten years from the date of grant and generally vest over a period of three years from the date of grant. Vesting requirements for non-employee directors are contingent on attending a minimum of 75% of regularly scheduled board meetings during the year. Upon the exercise of stock options, common stock is issued from treasury stock or, when depleted, from new stock issuances. A summary of our stock option activity is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ Weighted ​ ​ ​ ​ Average ​ ​ ​ ​ Average ​ Aggregate ​ Remaining ​ ​ ​ ​ Exercise ​ Intrinsic ​ Contractual ​ Shares Price Value Term (Years) Outstanding as of December 31, 2018 236,503 ​ $ 44.93 ​ ​ ​ ​ ​ Granted 70,500 ​ ​ 58.75 ​ ​ ​ ​ ​ Exercised (11,875) ​ 45.42 ​ ​ ​ ​ ​ Cancelled, expired or forfeited (1,540) ​ 43.55 ​ ​ ​ ​ ​ Outstanding as of December 31, 2019 293,588 ​ $ 48.23 ​ $ 2,841 ​ 6.1 Exercisable as of December 31, 2019 212,527 ​ $ 44.89 ​ $ 2,767 5.2 ​ The weighted average grant date fair value of all stock options granted during 2019, 2018 and 2017 was $14.26, $11.64 and $10.92 per share, respectively. The total intrinsic value of stock options exercised during 2019, 2018 and 2017 was $152,000, $6.6 million and $1.0 million, respectively. During 2019, option holders tendered 3,640 options in connection with options exercised via net share settlement. The fair value of each stock option is estimated as of the date of grant using the Black-Scholes option-pricing model. Expected volatility is estimated based on an average of actual historical volatility and implied volatility corresponding to the stock option’s estimated expected term. We believe this approach to determine volatility is representative of future stock volatility. The expected term of a stock option is estimated based on analysis of stock options already exercised and foreseeable trends or changes in behavior. The risk-free interest rates are based on the U.S. Treasury securities maturities as of each applicable grant date. The dividend yield is based on analysis of actual historical dividend yield. The significant weighted-average assumptions relating to the valuation of option grants are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 2018 2017 ​ Expected life 2.7 years 3.8 years 3.8 years Expected volatility 30 % 30 % 31 % Risk-free interest rate 2.1 % 2.0 % 1.5 % Expected dividend yield 1.2 % 1.5 % 1.7 % ​ Restricted Stock We have restricted stock awards outstanding under the Omnibus Plan. Generally, restricted stock awards vest annually over a three-year period. Vesting of restricted stock awards to non-employee directors is contingent on the non-employee director attending a minimum of 75% of regularly scheduled board meetings and 75% of the meetings of each committee of which the non‐employee director is a member during the year. Upon the vesting of restricted stock awards, common stock is issued from treasury stock or, when depleted, from new stock issuances. A summary of our restricted stock activity is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ Average ​ ​ ​ ​ Grant Date ​ Shares Fair Value Outstanding as of December 31, 2018 74,988 ​ $ 46.74 Granted 28,900 ​ ​ 62.59 Vested (39,234) ​ 43.77 Outstanding as of December 31, 2019 64,654 ​ $ 55.62 ​ The total fair value of restricted stock vested during 2019, 2018 and 2017 was $2.5 million, $2.2 million and $868,000, respectively. Restricted Stock Units We have restricted stock unit awards outstanding under the Omnibus Plan. Each restricted stock unit represents the right to receive, on the settlement date, one share of the Company’s common stock. Generally, restricted stock unit awards vest annually over a three-year period. Upon the vesting of restricted stock unit awards, common stock is issued from treasury stock or, when depleted, from new stock issuances. A summary of our restricted stock unit activity is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ Average ​ ​ ​ ​ Grant Date ​ ​ Units ​ Fair Value Outstanding as of December 31, 2018 ​ 66,785 ​ $ 53.77 Granted ​ 151,263 ​ ​ 60.92 Vested ​ (85,014) ​ 58.35 Cancelled, expired or forfeited ​ (1,835) ​ 52.87 Outstanding as of December 31, 2019 ​ 131,199 ​ $ 59.05 ​ The total fair value of restricted stock units vested during 2019, 2018 and 2017 was $4.8 million, $967,000 and $314,000, respectively. Treasury Stock During 2019 prior to the NRC Merger, Predecessor US Ecology issued 8,900 shares of restricted stock under the Omnibus Plan, from our treasury stock at an average cost of $57.77 per share and repurchased 14,462 shares of the Predecessor US Ecology’s common stock in connection with the net share settlement of employee equity awards at an average cost of $63.34 per share. In connection with the closing of the NRC Merger, the outstanding treasury stock of Predecessor US Ecology was cancelled. Share-Based Compensation Expense All share-based compensation is measured at the grant date based on the fair value of the award, and is recognized as an expense in earnings over the requisite service period. The components of pre-tax share-based compensation expense (primarily included in Selling, general and administrative expenses in our consolidated statements of operations) and related tax benefits were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $s in thousands 2019 2018 2017 Share-based compensation from: ​ ​ ​ ​ ​ ​ ​ ​ ​ Stock options ​ $ 575 ​ $ 727 ​ $ 1,141 Restricted stock ​ 1,662 ​ 1,590 ​ 1,505 Restricted stock units (1) ​ ​ 6,193 ​ ​ 1,324 ​ ​ 716 Performance stock units ​ ​ 831 ​ ​ 725 ​ ​ 571 Total share-based compensation ​ 9,261 ​ 4,366 ​ 3,933 Income tax benefit ​ (3,098) ​ (1,027) ​ (1,403) Share-based compensation, net of tax ​ $ 6,163 ​ $ 3,339 ​ $ 2,530 (1) 2019 share-based compensation from restricted stock units includes $3.7 million of compensation expense related to the accelerated vesting of restricted stock unit awards upon the termination of former employees of NRC subsequent to the NRC Merger in accordance with change-in-control provisions of their respective employment agreements. The accelerated vesting and resulting share-based compensation expense recognition was attributable entirely to the NRC Merger therefore the Company has classified this portion of share-based compensation expense as business development and integration expenses within Selling, general and administrative expenses in our consolidated statements of operations. ​ The tax benefits from stock options exercised during 2019, 2018 and 2017 were $321,000, $1.4 million and $129,000, respectively. Unrecognized Share-Based Compensation Expense As of December 31, 2019, there was $8.3 million of unrecognized compensation expense related to unvested share-based awards granted under our share-based award plans. The expense is expected to be recognized over a weighted average remaining vesting period of approximately two years. Warrants At December 31, 2019, there were a total of 3,772,753 warrants outstanding. Each warrant entitles the holder thereof to purchase one share of common stock at a price of $58.67 per share, subject to certain adjustments. The warrants may be exercised only for a whole number of shares of common stock. No fractional shares will be issued upon exercise of the warrants. The warrants will expire at 5:00 p.m. New York City time on October 17, 2023, or earlier upon redemption or liquidation. The warrants are listed on the Nasdaq Capital Market under the symbol “ECOLW”. The Company may call the warrants for redemption, in whole and not in part, at a price of $0.01 per warrant, upon not less than 30 days’ prior written notice of redemption to each warrant holder, if, and only if, the reported last sale price of Common Stock equals or exceeds $91.84 per share on each of 20 trading days within the 30 trading-day period ending on the business day prior to the date on which notice of the redemption is given and provided that there is an effective registration statement covering the shares of Common Stock issuable on exercise of the warrants and subject to the satisfaction of certain other requirements. The warrants were determined to be equity classified in accordance with ASC 815, Derivatives and Hedging

EARNINGS PER SHARE

EARNINGS PER SHARE	12 Months Ended
	Dec. 31, 2019
EARNINGS PER SHARE
EARNINGS PER SHARE	NOTE 20. EARNINGS PER SHARE ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 ​ 2018 ​ 2017 $s and shares in thousands, except per share amounts Basic Diluted Basic Diluted Basic Diluted Net income ​ $ 33,140 ​ $ 33,140 ​ $ 49,595 ​ $ 49,595 ​ $ 49,365 ​ $ 49,365 Weighted average basic shares outstanding ​ 23,521 ​ 23,521 ​ 21,888 ​ 21,888 ​ 21,758 ​ 21,758 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Dilutive effect of share-based awards and warrants ​ ​ ​ ​ 228 ​ ​ ​ ​ 159 ​ ​ ​ ​ 144 Weighted average diluted shares outstanding ​ ​ ​ ​ 23,749 ​ ​ ​ ​ 22,047 ​ ​ ​ ​ 21,902 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Earnings per share ​ $ 1.41 ​ $ 1.40 ​ $ 2.27 ​ $ 2.25 ​ $ 2.27 ​ $ 2.25 Anti-dilutive shares excluded from calculation ​ ​ ​ ​ 90 ​ ​ ​ ​ 46 ​ ​ ​ ​ 103 ​

SEGMENT REPORTING

SEGMENT REPORTING	12 Months Ended
	Dec. 31, 2019
SEGMENT REPORTING
OPERATING SEGMENTS	NOTE 21. SEGMENT REPORTING Financial Information by Segment Our operations are managed in two reportable segments reflecting our internal management reporting structure and nature of services offered as follows: Environmental Services Field & Industrial Services The operations not managed through our two reportable segments are recorded as “Corporate.” Corporate selling, general and administrative expenses include typical corporate items such as legal, accounting and other items of a general corporate nature. Income taxes are assigned to Corporate, but all other items are included in the segment where they originated. Inter-company transactions have been eliminated from the segment information and are not significant between segments. Summarized financial information of our reportable segments for the years ended December 31, 2019, 2018 and 2017 is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 ​ ​ ​ ​ Field & ​ ​ ​ ​ ​ ​ ​ ​ Environmental ​ Industrial ​ ​ ​ ​ ​ ​ $s in thousands Services Services Corporate Total Revenue ​ $ 453,107 ​ $ 232,402 ​ $ — ​ $ 685,509 Depreciation, amortization and accretion ​ $ 44,535 ​ $ 15,007 ​ $ 1,760 ​ $ 61,302 Capital expenditures ​ $ 47,593 ​ $ 5,986 ​ $ 4,521 ​ $ 58,100 Total assets ​ $ 1,290,304 ​ $ 865,540 ​ $ 75,400 ​ $ 2,231,244 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2018 ​ ​ ​ ​ Field & ​ ​ ​ ​ ​ ​ ​ ​ Environmental ​ Industrial ​ ​ ​ ​ ​ ​ $s in thousands Services Services Corporate Total Revenue ​ $ 400,678 ​ $ 165,250 ​ $ — ​ $ 565,928 Depreciation, amortization and accretion ​ $ 35,195 ​ $ 6,304 ​ $ 1,060 ​ $ 42,559 Capital expenditures ​ $ 31,735 ​ $ 7,430 ​ $ 1,592 ​ $ 40,757 Total assets ​ $ 701,267 ​ $ 169,066 ​ $ 77,565 ​ $ 947,898 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2017 ​ ​ ​ ​ Field & ​ ​ ​ ​ ​ ​ ​ ​ Environmental ​ Industrial ​ ​ ​ ​ ​ ​ $s in thousands Services Services Corporate Total Revenue ​ $ 366,308 ​ $ 137,734 ​ $ — ​ $ 504,042 Depreciation, amortization and accretion ​ $ 35,137 ​ $ 5,578 ​ $ 501 ​ $ 41,216 Capital expenditures ​ $ 28,783 ​ $ 4,206 ​ $ 3,251 ​ $ 36,240 Total assets ​ $ 609,174 ​ $ 125,110 ​ $ 67,792 ​ $ 802,076 ​ Management uses Adjusted EBITDA as a financial measure to assess segment performance. Adjusted EBITDA is defined as net income before interest expense, interest income, income tax expense, depreciation, amortization, share-based compensation, accretion of closure and post-closure liabilities, foreign currency gain/loss, non-cash property and equipment impairment charges, non-cash goodwill and intangible asset impairment charges, gain on property insurance recoveries, business development and integration expenses and other income/expense. In 2019, we updated our Adjusted EBITDA definition to include adjustments for business development and integration expenses and gain on property insurance recoveries. Throughout this Annual Report on Form 10-K, our Adjusted EBITDA results for all periods presented have been recast to reflect these adjustments. Adjusted EBITDA is a complement to results provided in accordance with GAAP and we believe that such information provides additional useful information to analysts, stockholders and other users to understand the Company’s operating performance. Since Adjusted EBITDA is not a measurement determined in accordance with GAAP and is thus susceptible to varying calculations, Adjusted EBITDA as presented may not be comparable to other similarly titled measures of other companies. Items excluded from Adjusted EBITDA are significant components in understanding and assessing our financial performance. Adjusted EBITDA should not be considered in isolation or as an alternative to, or substitute for, net income, cash flows generated by operations, investing or financing activities, or other financial statement data presented in the consolidated financial statements as indicators of financial performance or liquidity. Adjusted EBITDA has limitations as an analytical tool and should not be considered in isolation or a substitute for analyzing our results as reported under GAAP. Some of the limitations are: ● Adjusted EBITDA does not reflect changes in, or cash requirements for, our working capital needs; ● Adjusted EBITDA does not reflect our interest expense, or the requirements necessary to service interest or principal payments on our debt; ● Adjusted EBITDA does not reflect our income tax expenses or the cash requirements to pay our taxes; ● Adjusted EBITDA does not reflect our cash expenditures or future requirements for capital expenditures or contractual commitments; ● Although depreciation and amortization charges are non-cash charges, the assets being depreciated and amortized will often have to be replaced in the future, and Adjusted EBITDA does not reflect any cash requirements for such replacements; and ● Adjusted EBITDA does not reflect our business development and integration expenses. A reconciliation of Net income to Adjusted EBITDA for the years ended December 31, 2019, 2018 and 2017 is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $s in thousands 2019 2018 2017 Net income ​ $ 33,140 ​ $ 49,595 ​ $ 49,365 Income tax expense (benefit) ​ ​ 16,659 ​ ​ 15,263 ​ ​ (6,395) Interest expense ​ ​ 19,239 ​ ​ 12,130 ​ ​ 18,157 Interest income ​ ​ (605) ​ ​ (215) ​ ​ (62) Foreign currency (gain) loss ​ ​ 733 ​ ​ (55) ​ ​ (516) Other income ​ ​ (455) ​ ​ (2,630) ​ ​ (791) Property and equipment impairment charges ​ ​ 25 ​ ​ — ​ ​ — Goodwill and intangible asset impairment charges ​ ​ — ​ ​ 3,666 ​ ​ 8,903 Depreciation and amortization of plant and equipment ​ ​ 41,423 ​ ​ 29,207 ​ ​ 28,302 Amortization of intangible assets ​ ​ 15,491 ​ ​ 9,645 ​ ​ 9,888 Share-based compensation ​ ​ 5,544 ​ ​ 4,366 ​ ​ 3,933 Accretion and non-cash adjustment of closure & post-closure liabilities ​ ​ 4,388 ​ ​ 3,707 ​ ​ 3,026 Gain on property insurance recoveries ​ ​ (12,366) ​ ​ (347) ​ ​ (1,313) Business development and integration expenses ​ ​ 26,150 ​ ​ 748 ​ ​ 500 Adjusted EBITDA ​ $ 149,366 ​ $ 125,080 ​ $ 112,997 ​ Adjusted EBITDA, by operating segment, for the years ended December 31, 2019, 2018 and 2017 is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $s in thousands ​ 2019 2018 2017 Environmental Services $ 187,759 ​ $ 160,179 ​ $ 145,058 Field & Industrial Services 26,707 ​ 18,457 ​ 14,709 Corporate (65,100) ​ (53,556) ​ (46,770) Total $ 149,366 ​ $ 125,080 ​ $ 112,997 ​ Property and Equipment and Intangible Assets Outside of the United States We provide services primarily in the United States, Canada and the EMEA region. Long-lived assets, comprised of property and equipment and intangible assets net of accumulated depreciation and amortization, by geographic location as of December 31, 2019 and 2018 are as follows: ​ ​ ​ ​ ​ ​ ​ ​ $s in thousands 2019 2018 United States ​ $ 954,102 ​ $ 480,322 Canada ​ 70,691 ​ 57,787 EMEA ​ ​ 23,587 ​ ​ — Other (1) ​ ​ 5,290 ​ ​ — Total long-lived assets ​ $ 1,053,670 ​ $ 538,109 ​ (1) Includes Mexico, Asia Pacific, and Latin America and Caribbean geographical regions.

QUARTERLY FINANCIAL DATA (unaud

QUARTERLY FINANCIAL DATA (unaudited)	12 Months Ended
	Dec. 31, 2019
QUARTERLY FINANCIAL DATA (unaudited)
QUARTERLY FINANCIAL DATA (unaudited)	NOTE 22. QUARTERLY FINANCIAL DATA (unaudited) The unaudited consolidated quarterly results of operations for 2019 and 2018 were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three-Months Ended ​ ​ ​ $s and shares in thousands, except per share amounts Mar. 31, June 30, Sept. 30, Dec. 31, Year 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenue ​ $ 131,037 ​ $ 155,802 ​ $ 167,402 ​ $ 231,268 ​ $ 685,509 Gross profit ​ 35,241 ​ 49,583 ​ 56,540 ​ 68,470 ​ 209,834 Operating income ​ 14,936 ​ 25,534 ​ 23,211 ​ 5,030 ​ 68,711 Net income (loss) ​ 8,043 ​ 15,491 ​ 13,070 ​ (3,464) ​ 33,140 Earnings (loss) per share—diluted (1) ​ $ 0.36 ​ $ 0.70 ​ $ 0.59 ​ $ (0.12) ​ $ 1.40 Weighted average common shares outstanding used in the diluted earnings per share calculation ​ 22,197 ​ 22,208 ​ 22,231 ​ 27,916 ​ 23,749 Dividends paid per share ​ $ 0.18 ​ $ 0.18 ​ $ 0.18 ​ $ 0.18 ​ $ 0.72 2018 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenue ​ $ 120,059 ​ $ 136,912 ​ $ 151,416 ​ $ 157,541 ​ $ 565,928 Gross profit ​ 35,671 ​ 41,448 ​ 47,300 ​ 45,675 ​ 170,094 Operating income ​ 13,439 ​ 20,292 ​ 19,985 ​ 20,372 ​ 74,088 Net income ​ 9,243 ​ 13,220 ​ 13,427 ​ 13,705 ​ 49,595 Earnings per share—diluted (1) ​ $ 0.42 ​ $ 0.60 ​ $ 0.61 ​ $ 0.62 ​ $ 2.25 Weighted average common shares outstanding used in the diluted earnings per share calculation ​ 21,957 ​ 22,024 ​ 22,099 ​ 22,109 ​ 22,047 Dividends paid per share ​ $ 0.18 ​ $ 0.18 ​ $ 0.18 ​ $ 0.18 ​ $ 0.72 (1) Diluted earnings (loss) per common share for each quarter presented above is based on the respective weighted average number of common shares for the respective quarter therefore the sum of the diluted earnings (loss) per share for each respective quarter may not necessarily be equal to the full year diluted earnings (loss) per common share amount .

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	12 Months Ended
	Dec. 31, 2019
SUBSEQUENT EVENTS
SUBSEQUENT EVENTS	NOTE 23. SUBSEQUENT EVENT On January 2, 2020, the Company declared a dividend of $0.18 per common share for stockholders of record on January 17, 2020. The dividend was paid from cash on hand on January 24, 2020 in an aggregate amount of $5.7 million. Holders of our warrants are not entitled to receive dividends.

SUMMARY OF SIGNIFICANT ACCOUN_2

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2019
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
Principles of Consolidation	Principles of Consolidation The accompanying financial statements are prepared on a consolidated basis. All inter-company balances and transactions have been eliminated in consolidation. Our year-end is December 31.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents consist primarily of cash on deposit, money market accounts or short-term investments with original maturities of 90 days or less at the date of acquisition. Cash and cash equivalents totaled $41.3 million and $32.0 million at December 31, 2019 and 2018, respectively. At December 31, 2019 and 2018, we had $35.2 million and $19.4 million, respectively, of cash at our operations outside the United States.
Receivables	Receivables Our receivables include invoiced and unbilled amounts where the Company has an unconditional right to payment. ​ Receivables are stated at an amount management expects to collect. Based on management’s assessment of the credit history of the customers having outstanding balances and factoring in current economic conditions, management has concluded that potential unidentified losses on balances outstanding at year-end will not be material. ​ Unbilled receivables are recorded for work performed under contracts that have not yet been invoiced to customers and arise due to the timing of billings. Substantially all unbilled receivables at December 31, 2019, were billed in the following month. ​
Restricted Cash and Investments	Restricted Cash and Investments Restricted cash and investments of $5.1 million and $4.9 million at December 31, 2019 and 2018, respectively, represent funds held in third-party managed trust accounts as collateral for our financial assurance obligations for post-closure activities at our non-operating facilities. These funds are invested in fixed-income U.S. Treasury and government agency securities and money market accounts. The balances are adjusted monthly to fair market value based on quoted prices in active markets for identical or similar assets.
Revenue Recognition	Revenue Recognition Revenues are recognized when control of the promised services is transferred to our customers, in an amount that reflects the consideration we expect to be entitled to in exchange for those services. ​ We recognize revenue from three primary sources: (1) waste treatment, recycling and disposal services, (2) field and industrial waste management services, and (3) waste transportation services. Our waste treatment and disposal customers are legally obligated to properly treat and dispose of their waste in accordance with local, state, and federal laws and regulations. As our customers do not possess the resources to properly treat and dispose of their waste independently, they contract with the Company to perform these services. Waste treatment, recycling, and disposal revenue results primarily from fixed fees charged to customers for treatment and/or disposal or recycling of specified wastes. Waste treatment, recycling, and disposal revenue is generally charged on a per-ton or per-yard basis based on contracted prices and is recognized over time as the services are performed. Our treatment and disposal services are generally performed as the waste is received and considered complete upon final disposal. Field and industrial waste management services revenue results primarily from specialty onsite services such as high-pressure cleaning, tank cleaning, decontamination, remediation, transportation, spill cleanup and emergency response at refineries, chemical plants, steel and automotive plants, and other government, commercial and industrial facilities. We also provide hazardous waste packaging and collection services and total waste management solutions at customer sites and through our 10-day transfer facilities. These 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. Generally, the pricing in these types of contracts is fixed, but the quantity of services to be provided during the contract term is variable and revenues are recognized over the term of the agreements or as services are performed. As we have a right to consideration from our customers in an amount that corresponds directly with the value to the customer of the Company’s performance completed to date, we have applied the practical expedient to recognize revenue in the amount to which we have the right to invoice. Additionally, we have customers that pay annual retainer fees, primarily for our standby services, under long-term or evergreen contracts. Such retainer fees are recognized over time as the services are performed and it is probable that a significant reversal in the amount of cumulative revenue recognized on the contracts will not occur. Transportation and logistics revenue results from delivering customer waste to a disposal facility for treatment and/or disposal or recycling. Transportation services are generally not provided on a stand-alone basis and instead are bundled with other Company services. However, in some instances we provide transportation and logistics services for shipment of waste from cleanup sites to disposal facilities operated by other companies. For such arrangements, we allocate revenue to each performance obligation based on its relative standalone selling price. We generally determine standalone selling prices based on the prices charged to customer or using expected cost plus margin. Transportation revenue is recognized over time as the waste is transported. Taxes and fees collected from customers concurrent with revenue-producing transactions to be remitted to governmental authorities are excluded from revenue. Our Richland, Washington disposal facility is regulated by the Washington Utilities and Transportation Commission (“WUTC”), which approves our rates for disposal of low-level radioactive waste (“LLRW”). Annual revenue levels are established based on a rate agreement with the WUTC at amounts sufficient to cover the costs of operation, including facility maintenance, equipment replacement and related costs, and provide us with a reasonable profit. Per-unit rates charged to LLRW customers during the year are based on our evaluation of disposal volume and radioactivity projections submitted to us by waste generators. Our proposed rates are then reviewed and approved by the WUTC. If annual revenue exceeds the approved levels set by the WUTC, we are required to refund excess collections to facility users on a pro-rata basis. Refundable excess collections, if any, are recorded in Accrued liabilities in the consolidated balance sheets. The current rate agreement with the WUTC was extended in 2019 and is effective until December 31, 2025.
Deferred Revenue	Deferred Revenue We record deferred revenue when cash payments are received, or advance billings are charged, prior to performance of services, such as waste that has been received but not yet treated or disposed, and is recognized when these services are performed. During the year ended December 31, 2019 and 2018, we recognized $10.4 million and $8.4 million of revenue that was included in the deferred revenue balance at the beginning of each year, respectively.
Property and Equipment	Property and Equipment Property and equipment are recorded at cost and depreciated on the straight-line method over estimated useful lives. Replacements and major repairs of property and equipment are capitalized and retirements are made when assets are disposed of or when the useful life has been exhausted. Minor components and parts are expensed as incurred. Repair and maintenance expenses were $20.5 million, $17.5 million and $14.8 million for the years ended December 31, 2019, 2018 and 2017, respectively. We assume no salvage value for our depreciable fixed assets. The estimated useful lives for significant property and equipment categories are as follows: ​ ​ ​ ​ ​ ​ ​ ​ Useful Lives Vehicles, vessels and other equipment 3 to 10 years Disposal facility and equipment 3 to 20 years Buildings and improvements 5 to 40 years Railcars ​ ​ 40 years
Disposal Cell Accounting	Disposal Cell Accounting Qualified disposal cell development costs such as personnel and equipment costs incurred to construct new disposal cells are recorded and capitalized at cost. Capitalized cell development costs, net of recorded amortization, are added to estimated future costs of the permitted disposal cell to be incurred over the remaining construction of the cell, to determine the amount to be amortized over the remaining estimated cell life. Estimates of future costs are developed using input from independent engineers and internal technical and accounting managers. We review these estimates at least annually. Amortization is recorded on a unit of consumption basis, typically applying cost as a rate per cubic yard disposed. Disposal facility costs are expected to be fully amortized upon final closure of the facility, as no salvage value applies. Costs associated with ongoing disposal operations are charged to expense as incurred. We have material financial commitments for closure and post-closure obligations for certain facilities we own or operate. We estimate future cost requirements for closure and post-closure monitoring based on RCRA and conforming state requirements and facility permits. RCRA requires that companies provide the responsible regulatory agency acceptable financial assurance for closure work and subsequent post-closure monitoring of each facility for 30 years following closure. Estimates for final closure and post-closure costs are developed using input from our technical and accounting managers as well as independent engineers and are reviewed by management at least annually. These estimates involve projections of costs that will be incurred after the disposal facility ceases operations, through the required post-closure care period. The present value of the estimated closure and post-closure costs are accreted using the interest method of allocation to direct costs in our consolidated statements of operations so that 100% of the future cost has been incurred at the time of payment.
Business Combinations	Business Combinations We account for business combinations under the acquisition method of accounting. The cost of an acquired company is assigned to the tangible and identifiable intangible assets purchased and the liabilities assumed on the basis of their fair values at the date of acquisition. Any excess of purchase price over the fair value of net tangible and intangible assets acquired is assigned to goodwill. The transaction costs associated with business combinations are expensed as they are incurred.
Goodwill	Goodwill Goodwill represents the excess of the fair value of the consideration transferred over the fair value of the underlying identifiable assets and liabilities acquired. Goodwill is not amortized, but instead is assessed for impairment annually in the fourth quarter as of October 1 and also if an event occurs or circumstances change that may indicate a possible impairment. In the event that we determine that the value of goodwill has become impaired, we will incur an accounting charge for the amount of impairment during the period in which the determination has been made. See Note 3 for additional information related to the use of estimates in the Company’s goodwill impairment tests and Note 13 for additional information related to our annual assessment of goodwill.
Intangible Assets	Intangible Assets Intangible assets are stated at the fair value assigned in a business combination net of amortization. We amortize our amortizing intangible assets using the straight-line method over their estimated economic lives ranging from 1 to 60 years. We review intangible assets with indefinite useful lives for impairment during the fourth quarter as of October 1 of each year. We also review both non-amortizing and amortizing intangible assets for impairment whenever events or changes in circumstances indicate that the carrying value of an intangible asset may not be recoverable. See Note 3 for additional information related to the use of estimates in the Company’s intangible assets impairment tests and Note 13 for additional information related to our annual assessment of non-amortizing intangible. Our acquired permits and licenses generally have renewal terms of approximately 5-10 years. We have a history of renewing these permits and licenses as demonstrated by the fact that each of the sites’ treatment permits and licenses have been renewed regularly since the facility began operations. We intend to continue to renew our permits and licenses as they come up for renewal for the foreseeable future. Costs incurred to renew or extend the term of our permits and licenses are recorded in Selling, general and administrative expenses in our consolidated statements of operations.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets Long-lived assets consist primarily of property and equipment facility development costs and amortizing intangible assets. The recoverability of long-lived assets is evaluated periodically through analysis of operating results and consideration of other significant events or changes in the business environment. If an operating unit had indications of possible impairment, we would evaluate whether impairment exists on the basis of undiscounted expected future cash flows from operations over the remaining amortization period. If an impairment loss were to exist, the carrying amount of the related long-lived assets would be reduced to their estimated fair value.
Debt Issuance Costs & Debt Discount	Debt Issuance Costs & Debt Discount Debt issuance costs and debt discount are amortized over the scheduled maturity of the underlying debt instrument. Amortization of debt issuance costs and debt discount is included as a component of interest expense in the consolidated statements of operations. Unamortized debt discount and debt issuance costs associated with our Term Loan were $7.8 million at December 31, 2019 and have been recorded as a reduction of the Current portion of long-term debt and Long-term debt in the consolidated balance sheets. Unamortized debt issuance costs associated with our Revolving Credit Facility were $4.7 million and $2.7 million at December 31, 2019 and 2018, respectively, and have been recorded in Prepaid expenses and other current assets and Other assets in the consolidated balance sheets. The Company wrote off certain unamortized debt issuance costs associated with the 2014 Credit Agreement that were to be amortized to interest expense in future periods through a charge of $5.5 million to Interest expense in 2017.
Derivative Instruments	Derivative Instruments In order to manage interest rate exposure, we entered into an interest rate swap agreement in October 2014 that effectively converts a portion of our variable-rate debt to a fixed interest rate. Changes in the fair value of the interest rate swap are recorded as a component of accumulated other comprehensive income within stockholders’ equity, and are recognized in interest expense in the period in which the payment is settled. The interest rate swap has an effective date of December 31, 2014 in an initial notional amount of $250.0 million. The Company does not hold or issue derivative financial instruments for trading or speculative purposes.
Foreign Currency	Foreign Currency The assets, liabilities and results of operations of certain of our foreign subsidiaries are measured using their functional currency which is the currency of the primary foreign economic environment in which they operate. Assets and liabilities are translated to U.S. dollars (“USD”) 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 our foreign subsidiaries into USD are included in stockholders’ equity as a component of Accumulated other comprehensive income. Gains and losses resulting from foreign currency transactions are recognized in the consolidated statements of operations. Recorded balances that are denominated in a currency other than the functional currency are re-measured to the functional currency using the exchange rate at the balance sheet date and gains or losses are recorded in the statements of operations.
Income Taxes	Income Taxes We account for income taxes using an asset and liability method, which requires the recognition of taxes payable or refundable for the current year and deferred tax assets and liabilities for the expected future tax consequences of temporary differences that currently exist between the tax basis and the financial reporting basis of our taxable subsidiaries’ assets and liabilities using the enacted tax rates in effect for the year in which the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in operations in the period that includes the enactment date. The measurement of deferred tax assets is reduced, if necessary, by the amount of any tax benefits that, based on available evidence, are not expected to be realized. We regularly assess the need for a valuation allowance against our deferred tax assets. In making that assessment, we consider both positive and negative evidence related to the likelihood of realization of the deferred tax assets on a jurisdictional basis to determine, based on the weight of available evidence, whether it is more-likely-than-not that some or all of the deferred tax assets will not be realized. Examples of positive and negative evidence include future growth, forecasted earnings, future taxable income, the mix of earnings in the jurisdictions in which we operate, historical earnings, taxable income in prior years, if carryback is permitted under the law and prudent and feasible tax planning strategies. In the event we were to determine that we would not be able to realize all or part of our net deferred tax assets in the future, an adjustment to the deferred tax assets valuation allowance would be charged to earnings in the period in which we make such a determination, or goodwill would be adjusted at our final determination of the valuation allowance related to an acquisition within the measurement period. If we later determine that it is more-likely-than-not that the net deferred tax assets would be realized, we would reverse the applicable portion of the previously-provided valuation allowance as an adjustment to earnings at such time. We account for unrecognized tax benefits using a more-likely-than-not threshold for financial statement recognition and measurement of tax positions taken or expected to be taken in a tax return. We establish reserves for tax-related uncertainties based on estimates of whether, and the extent to which, additional taxes will be due. We record an income tax liability, if any, for the difference between the benefit recognized and measured and the tax position taken or expected to be taken on our tax returns. At December 31, 2019, our estimated gross unrecognized tax benefits were $8.3 million, of which $236,000, if recognized, would favorably impact our future earnings. We recognize interest assessed by taxing authorities or interest associated with uncertain tax positions as a component of interest expense. We recognize any penalties assessed by taxing authorities or penalties associated with uncertain tax positions as a component of selling, general and administrative expenses. To the extent that the assessment of such tax positions change, the change in estimate is recorded in the period in which the determination is made. The reserves are adjusted in light of changing facts and circumstances, such as the outcome of a tax audit. The provision for income taxes includes the impact of reserve provisions and changes to reserves that are considered appropriate.
Insurance	Insurance Accrued costs for our self-insured healthcare coverage were $1.0 million and $826,000 at December 31, 2019 and 2018, respectively.
Earnings Per Share	Earnings Per Share Basic earnings per share is calculated based on the weighted-average number of outstanding common shares during the applicable period. Diluted earnings per share is based on the weighted-average number of outstanding common shares plus the weighted-average number of potential outstanding common shares. Potential common shares that would increase earnings per share or decrease loss per share are anti-dilutive and are excluded from earnings per share computations. Earnings per share is computed separately for each period presented.
Treasury Stock	Treasury Stock Shares of common stock repurchased by us are recorded at cost as treasury stock and result in a reduction of stockholders’ equity in our consolidated balance sheets. Treasury shares are reissued using the weighted average cost method for determining the cost of the shares reissued. The difference between the cost of the shares reissued and the issuance price is added or deducted from additional paid-in capital.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In August 2018, the SEC adopted the final rule under SEC Release No. 33-10532, “Disclosure Update and Simplification,” adopting amendments to certain disclosure rules that were redundant, duplicative, overlapping, outdated, or superseded, in light of other SEC disclosure requirements, GAAP or changes in the information environment. In addition, the amendments expanded the disclosure requirements relating to the analysis of equity for interim financial statements. Under the amendments, an analysis of the changes in each caption of shareholders’ equity and noncontrolling interests presented in the balance sheet must be provided in a note or separate statement. The analysis must present a reconciliation of the beginning balance to the ending balance of each period for which a statement of earnings is required to be filed. The final rule became effective on November 5, 2018. The Company adopted the final rule effective for the first quarter of 2019. The adoption of the final rule did not have an impact on the Company’s consolidated financial position or results of operations. ​ In August 2017, the FASB issued ASU No. 2017-12, Derivatives and Hedging (Topic 815). This ASU amends the guidance in ASC 815 to better align an entity’s risk management activities and financial reporting for hedging relationships through changes to both the designation and measurement guidance for qualifying hedging relationships and the presentation of hedge results. The guidance is effective for annual and interim reporting periods beginning after December 15, 2018, with early adoption permitted. The Company adopted ASU 2017-12 on January 1, 2019 and the standard did not have a material impact on its consolidated financial statements. ​ In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). The ASU significantly changes the accounting model used by lessees to account for leases, requiring that all material leases be presented on the balance sheet. Lessees will recognize substantially all leases on the balance sheet as a right-of-use asset and a corresponding lease liability. The Company adopted ASU 2016-02 on January 1, 2019 utilizing the modified retrospective transition method and elected not to recast comparative periods. We elected the package of practical expedients, which allows the Company not to reassess (1) whether any expired or existing contracts as of the adoption date are or contain a lease, (2) lease classification for any expired or existing leases as of the adoption date and (3) initial direct costs for any existing leases as of the adoption date. We also elected the practical expedient related to land easements, allowing us to carry forward our accounting treatment for land easements on existing agreements. The Company did not elect to apply the hindsight practical expedient when determining lease term and assessing impairment of right-of-use assets. ​ Adoption of ASU 2016-02 resulted in the recognition of right-of-use assets ​ In December 2019, the FASB issued ASU No. 2019-12, “Income Taxes” (Topic 740): Simplifying the Accounting for Income Taxes (“ASU 2019-12”), which is intended to simplify various aspects related to accounting for income taxes. ASU 2019-12 removes certain exceptions to the general principles in Topic 740 and also clarifies and amends existing guidance to improve consistent application. This guidance is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020, with early adoption permitted. The Company is currently evaluating the impact of this standard on its consolidated financial statements and related disclosures. In June 2016, the FASB issued ASU No. 2016-13, “Financial Instruments - Credit Losses” (Topic 326), which is effective for reporting periods beginning after December 15, 2019. The standard replaces the incurred loss impairment methodology under current GAAP with a methodology that reflects expected credit losses and requires the use of a forward-looking expected credit loss model for accounts receivables, loans, and other financial instruments. The standard requires a modified retrospective approach through a cumulative-effect adjustment to retained earnings as of the beginning of the first reporting period in which the guidance is effective. We plan to adopt the new credit loss standard effective January 1, 2020 and do not expect the impact of this standard to have a material impact on our consolidated financial statements.

SUMMARY OF SIGNIFICANT ACCOUN_3

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	12 Months Ended
	Dec. 31, 2019
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
Schedule of property and equipment	​ ​ ​ ​ ​ ​ ​ ​ Useful Lives Vehicles, vessels and other equipment 3 to 10 years Disposal facility and equipment 3 to 20 years Buildings and improvements 5 to 40 years Railcars ​ ​ 40 years

REVENUES (Tables)

REVENUES (Tables)	12 Months Ended
	Dec. 31, 2019
REVENUES
Schedule of disaggregation of revenues	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 ​ ​ ​ ​ Field & ​ ​ ​ ​ ​ Environmental ​ Industrial ​ ​ ​ $s in thousands Services Services Total Treatment & Disposal Revenue (1) ​ $ 365,886 ​ $ 18,480 ​ $ 384,366 Services Revenue: ​ ​ ​ ​ ​ ​ ​ ​ ​ Transportation and Logistics (2) ​ ​ 87,221 ​ ​ 40,833 ​ ​ 128,054 Industrial Services (3) ​ ​ — ​ ​ 38,865 ​ ​ 38,865 Small Quantity Generation (4) ​ ​ — ​ ​ 37,471 ​ ​ 37,471 Total Waste Management (5) ​ ​ — ​ ​ 33,792 ​ ​ 33,792 Remediation (6) ​ ​ — ​ ​ 13,288 ​ ​ 13,288 Emergency Response (7) ​ ​ — ​ ​ 26,737 ​ ​ 26,737 Domestic Standby Services (8) ​ ​ — ​ ​ 14,249 ​ ​ 14,249 Other (9) ​ ​ — ​ ​ 8,687 ​ ​ 8,687 Revenue ​ $ 453,107 ​ $ 232,402 ​ $ 685,509 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2018 ​ ​ ​ ​ Field & ​ ​ ​ ​ ​ Environmental ​ Industrial ​ ​ ​ $s in thousands Services Services Total Treatment & Disposal Revenue (1) ​ $ 320,045 ​ $ 11,736 ​ $ 331,781 Services Revenue: ​ ​ ​ ​ ​ ​ ​ ​ ​ Transportation and Logistics (2) ​ ​ 80,633 ​ ​ 33,037 ​ ​ 113,670 Industrial Services (3) ​ ​ — ​ ​ 24,155 ​ ​ 24,155 Small Quantity Generation (4) ​ ​ — ​ ​ 34,571 ​ ​ 34,571 Total Waste Management (5) ​ ​ — ​ ​ 41,729 ​ ​ 41,729 Remediation (6) ​ ​ — ​ ​ 10,139 ​ ​ 10,139 Emergency Response (7) ​ ​ — ​ ​ 7,513 ​ ​ 7,513 Other (9) ​ ​ — ​ ​ 2,370 ​ ​ 2,370 Revenue ​ $ 400,678 ​ $ 165,250 ​ $ 565,928 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2017 ​ ​ ​ ​ Field & ​ ​ ​ ​ ​ Environmental ​ Industrial ​ ​ ​ $s in thousands Services Services Total Treatment & Disposal Revenue (1) ​ $ 299,403 ​ $ 10,404 ​ $ 309,807 Services Revenue: ​ ​ ​ ​ ​ ​ ​ ​ ​ Transportation and Logistics (2) ​ ​ 66,905 ​ ​ 21,899 ​ ​ 88,804 Industrial Services (3) ​ ​ — ​ ​ 19,121 ​ ​ 19,121 Small Quantity Generation (4) ​ ​ — ​ ​ 29,934 ​ ​ 29,934 Total Waste Management (5) ​ ​ — ​ ​ 38,628 ​ ​ 38,628 Remediation (6) ​ ​ — ​ ​ 14,241 ​ ​ 14,241 Emergency Response (7) ​ ​ — ​ ​ 3,214 ​ ​ 3,214 Other (9) ​ ​ — ​ ​ 293 ​ ​ 293 Revenue ​ $ 366,308 ​ $ 137,734 ​ $ 504,042 (1) We categorize our treatment and disposal revenue as either “Base Business” or “Event Business” based on the underlying nature of the revenue source. We define Event Business as non-recurring projects that are expected to equal or exceed 1,000 tons, with Base Business defined as all other business not meeting the definition of Event Business. For the years ended December 31, 2019, 2018 and 2017, 22% , 20% and 22% , respectively, of our treatment and disposal revenue, excluding NRC, was derived from Event Business projects. Base Business revenue accounted for 78% , 80% and 78% of our treatment and disposal revenue, excluding NRC, for the years ended December 31, 2019, 2018 and 2017, respectively. (2) Includes collection and transportation of non-hazardous and hazardous waste. (3) Includes industrial cleaning and maintenance for refineries, chemical plants, steel and automotive plants, marine terminals and refinery services such as tank cleaning and temporary storage. (4) Includes retail services, laboratory packing, less-then-truck-load service and household hazardous waste collection. Contracts for Small Quantity Generation may extend beyond one year and a portion of the transaction price can be fixed. (5) Through our TWM program, customers outsource the management of their waste compliance program to us, allowing us to organize and coordinate their waste management disposal activities and environmental compliance. TWM contracts may extend beyond one year and a portion of the transaction price can be fixed. (6) Includes site assessment, onsite treatment, project management and remedial action planning and execution. Contracts for Remediation may extend beyond one year and a portion of the transaction price can be fixed. (7) Includes spill response, waste analysis and treatment and disposal planning. (8) We provide government-mandated, commercial standby oil spill compliance solutions to companies that store, transport, produce or handle petroleum and certain nonpetroleum oils on or near U.S. waters. Our standby services customers pay annual retainer fees under long-term or evergreen contracts for access to our regulatory certifications, specialized assets and highly trained personnel. When a customer with a retainer contract experiences a spill incident, we coordinate and manage the spill response, which results in incremental revenue for the services provided, in addition to the retainer fees. (9) Includes equipment rental and other miscellaneous services. ​ We provide services primarily in the United States, Canada and the EMEA region. The following table presents our revenue disaggregated by our reportable segments and geographic location where the underlying services were performed: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 ​ 2018 ​ 2017 ​ ​ ​ ​ Field & ​ ​ ​ ​ ​ ​ Field & ​ ​ ​ ​ ​ ​ Field & ​ ​ ​ ​ ​ Environmental ​ Industrial ​ ​ ​ ​ Environmental ​ Industrial ​ ​ ​ ​ Environmental ​ Industrial ​ ​ ​ $s in thousands Services Services Total Services Services Total Services Services Total United States ​ $ 367,185 ​ $ 221,942 ​ $ 589,127 ​ $ 329,918 ​ $ 165,250 ​ $ 495,168 ​ $ 296,777 ​ $ 137,734 ​ $ 434,511 Canada ​ 85,922 ​ 2,577 ​ 88,499 ​ 70,760 ​ — ​ 70,760 ​ 69,531 ​ — ​ 69,531 EMEA ​ ​ — ​ ​ 5,079 ​ ​ 5,079 ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ — Other (1) ​ ​ — ​ ​ 2,804 ​ ​ 2,804 ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ — Total revenue ​ $ 453,107 ​ $ 232,402 ​ $ 685,509 ​ $ 400,678 ​ $ 165,250 ​ $ 565,928 ​ $ 366,308 ​ $ 137,734 ​ $ 504,042 ​ (1) Includes Mexico, Asia Pacific, and Latin America and Caribbean geographical regions. ​

BUSINESS COMBINATIONS (Tables)

BUSINESS COMBINATIONS (Tables)	12 Months Ended
	Dec. 31, 2019
Summary of total merger consideration	​ ​ ​ ​ ​ ​ ​ November 1, $s in thousands 2019 Fair value of US Ecology common stock issued (1) ​ $ 581,101 Fair value of replacement warrants issued (2) ​ 44,858 Fair value of replacement restricted stock units issued (3) ​ 141 Fair value of replacement stock options (4) ​ 360 Repayment of NRC’s term loan and revolving credit facility ​ 398,373 Total merger consideration ​ $ 1,024,833 (1) The fair value of US Ecology common stock issued was calculated based on 9,337,949 shares of US Ecology common stock multiplied by the closing price of US Ecology common stock of $62.23 per share on October 31, 2019, the day immediately preceding the closing of the NRC Merger. (2) The fair value of replacement warrants issued was calculated based on 3,772,753 replacement warrants multiplied by the fair value per warrant of $11.89 . The fair value per warrant was based on the closing price of the replaced NRC warrants (NYSE: NRCG.WS) of $2.33 on October 31, 2019, the day immediately preceding the closing of the NRC Merger, divided by the exchange ratio of 0.196 pursuant to the Merger Agreement. (3) The fair value of replacement restricted stock units issued was calculated based on 118,239 replacement restricted stock units multiplied by the closing price of US Ecology common stock of $62.23 per share on October 31, 2019, the day immediately preceding the closing of the NRC Merger, further multiplied by the ratio of the precombination service period to the remaining vesting period, or approximately 1.9% . (4) The fair value of replacement stock options issued was calculated based on 29,400 replacement stock options multiplied by the fair value per option of $12.26 . The fair value per option was calculated using the Black-Scholes option pricing model, with the following weighted-average assumptions: strike price of $52.30 per option, dividend yield of 1.2% ; expected volatility of 28.9% ; average risk-free interest rate of 1.5% ; and an expected term of 1 year. The replacement stock options became fully vested at the merger date therefore the entire fair value is considered merger consideration.
Schedule of preliminary fair value of identifiable intangible assets related to the acquisition of NRCG	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 ​ 2018 ​ ​ ​ ​ ​ Accumulated ​ ​ ​ ​ ​ ​ ​ Accumulated ​ ​ ​ $s in thousands Cost Amortization Net Cost Amortization Net Amortizing intangible assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Permits, licenses and lease ​ $ 174,339 ​ $ (18,707) ​ $ 155,632 ​ $ 164,840 ​ $ (14,804) ​ $ 150,036 Customer relationships ​ ​ 333,090 ​ ​ (35,254) ​ ​ 297,836 ​ ​ 99,241 ​ ​ (25,676) ​ ​ 73,565 Technology - formulae and processes ​ 6,964 ​ (2,013) ​ 4,951 ​ 6,672 ​ (1,714) ​ 4,958 Customer backlog ​ 3,652 ​ (2,022) ​ 1,630 ​ 3,652 ​ (1,656) ​ 1,996 Tradename ​ 10,390 ​ ​ (4,832) ​ ​ 5,558 ​ ​ 4,290 ​ ​ (4,290) ​ ​ — Developed software ​ ​ 2,895 ​ ​ (1,884) ​ ​ 1,011 ​ ​ 2,884 ​ ​ (1,581) ​ ​ 1,303 Non-compete agreements ​ 5,455 ​ (1,694) ​ 3,761 ​ 1,542 ​ (875) ​ 667 Internet domain and website ​ ​ 536 ​ ​ (156) ​ ​ 380 ​ ​ 536 ​ ​ (128) ​ ​ 408 Database ​ ​ 388 ​ ​ (191) ​ ​ 197 ​ ​ 384 ​ ​ (167) ​ ​ 217 Total amortizing intangible assets ​ 537,709 ​ (66,753) ​ 470,956 ​ 284,041 ​ (50,891) ​ 233,150 Non-amortizing intangible assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Permits and licenses ​ 103,816 ​ ​ — ​ 103,816 ​ 46,391 ​ ​ — ​ 46,391 Tradename ​ 130 ​ ​ — ​ ​ 130 ​ 125 ​ ​ — ​ ​ 125 Total intangible assets ​ $ 641,655 ​ $ (66,753) ​ $ 574,902 ​ $ 330,557 ​ $ (50,891) ​ $ 279,666
Schedule of unaudited pro forma financial information for EQ	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (unaudited) $s in thousands ​ ​ 2019 ​ ​ 2018 Pro forma combined: ​ ​ ​ ​ ​ ​ Revenue ​ $ 1,048,745 ​ $ 923,947 Net income (loss) ​ $ 11,775 ​ $ (12,296)
Winnie
Summary of preliminary fair value estimates of assets acquired and liabilities assumed	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Purchase Price Allocation ​ ​ December 31, ​ ​ ​ ​ December 31, $s in thousands 2018 ​ Adjustments ​ 2019 Current assets ​ $ 1,923 ​ $ (63) ​ $ 1,860 Property and equipment ​ ​ 6,300 ​ ​ (2,601) ​ ​ 3,699 Identifiable intangible assets ​ ​ 66,600 ​ ​ (100) ​ ​ 66,500 Current liabilities ​ ​ (755) ​ ​ — ​ ​ (755) Other liabilities ​ ​ (512) ​ ​ — ​ ​ (512) Total identifiable net assets ​ ​ 73,556 ​ ​ (2,764) ​ ​ 70,792 Goodwill ​ ​ 13,573 ​ ​ 2,863 ​ ​ 16,436 Total purchase price ​ $ 87,129 ​ $ 99 ​ $ 87,228
NRC
Summary of preliminary fair value estimates of assets acquired and liabilities assumed	​ ​ ​ ​ ​ ​ ​ November 1, $s in thousands 2019 Current assets ​ $ 131,653 Property and equipment ​ ​ 197,045 Identifiable intangible assets ​ ​ 303,600 Other assets ​ ​ 41,687 Current liabilities ​ ​ (83,460) Deferred income tax liabilities ​ ​ (56,596) Other liabilities ​ ​ (57,581) Total identifiable net assets ​ ​ 476,348 Goodwill ​ ​ 548,485 Total purchase price ​ $ 1,024,833
Schedule of preliminary fair value of identifiable intangible assets related to the acquisition of NRCG	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Average ​ ​ ​ ​ ​ Amortization $s in thousands ​ ​ Fair Value ​ Period (Years) Amortizing intangible assets: ​ ​ ​ ​ ​ Customer relationships - noncontractual ​ $ 193,700 ​ 14 Customer relationships - contractual ​ ​ 34,400 ​ 7 Permits and licenses ​ ​ 8,700 ​ 16 Tradenames ​ ​ 6,100 ​ 2 Non-compete agreements ​ ​ 3,300 ​ 2 Total identified amortizing intangible assets ​ ​ 246,200 ​ ​ Non-amortizing intangible assets: ​ ​ ​ ​ ​ Permits and licenses ​ ​ 57,400 ​ n/a Total identified intangible assets ​ $ 303,600 ​ ​

ACCUMULATED OTHER COMPREHENSI_2

ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Tables)	12 Months Ended
	Dec. 31, 2019
ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS).
Schedule of changes in accumulated other comprehensive income (loss)	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Foreign ​ Unrealized Gain ​ ​ ​ ​ ​ Currency ​ (Loss) on Interest ​ ​ ​ $s in thousands Translation Rate Hedge Total Balance at December 31, 2017 ​ $ (8,603) ​ $ (501) ​ $ (9,104) Other comprehensive income (loss) before reclassifications, net of tax ​ ​ (6,094) ​ ​ 1,111 ​ ​ (4,983) Amounts reclassified out of AOCI, net of tax (1) ​ — ​ 296 ​ 296 Other comprehensive income (loss), net ​ ​ (6,094) ​ ​ 1,407 ​ ​ (4,687) Balance at December 31, 2018 ​ $ (14,697) ​ $ 906 ​ $ (13,791) Other comprehensive income (loss) before reclassifications, net of tax ​ 3,772 ​ (1,700) ​ 2,072 Amounts reclassified out of AOCI, net of tax (2) ​ — ​ (135) ​ (135) Other comprehensive income (loss), net ​ 3,772 ​ (1,835) ​ 1,937 Balance at December 31, 2019 ​ $ (10,925) ​ $ (929) ​ $ (11,854) (1) Before-tax reclassifications of $375,000 ( $296,000 after-tax) for the year ended December 31, 2018 were included in Interest expense in the Company’s consolidated statements of operations. Amount relates to the Company’s interest rate swap which is designated as a cash flow hedge. Changes in fair value of the swap recognized in AOCI are reclassified to interest expense when hedged interest payments on the underlying long-term debt are made. (2) Before-tax reclassifications of $170,000 ( $135,000 after-tax) for the year ended December 31, 2019 were included as a reduction of Interest expense in the Company’s consolidated statements of operations. Amount relates to the Company’s interest rate swap which is designated as a cash flow hedge. Changes in fair value of the swap recognized in AOCI are reclassified to interest expense when hedged interest payments on the underlying long-term debt are made. Amounts in AOCI expected to be recognized as interest expense over the next 12 months total approximately $523,000 ( $413,000 after tax).

DISCLOSURE OF SUPPLEMENTAL CA_2

DISCLOSURE OF SUPPLEMENTAL CASH FLOW INFORMATION (Tables)	12 Months Ended
	Dec. 31, 2019
DISCLOSURE OF SUPPLEMENTAL CASH FLOW INFORMATION
Schedule of disclosure of supplemental cash flow information	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the Year Ended December 31, $s in thousands 2019 2018 2017 Income taxes and interest paid: ​ ​ ​ ​ ​ ​ ​ ​ ​ Income taxes paid, net of receipts ​ $ 14,777 ​ $ 19,580 ​ $ 10,714 Interest paid ​ 17,204 ​ 11,246 ​ 11,364 Non-cash investing and financing activities: ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value of equity issued for acquisition of NRC ​ 626,460 ​ — ​ — Closure/Post-closure retirement asset ​ (221) ​ 99 ​ (352) Capital expenditures in accounts payable ​ 2,882 ​ 1,601 ​ 2,302 Acquisition of equipment with financing arrangements ​ ​ 2,481 ​ ​ 747 ​ ​ 531 Restricted stock issuances from treasury shares ​ 514 ​ 11 ​ 105

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	12 Months Ended
	Dec. 31, 2019
FAIR VALUE MEASUREMENTS
Schedule of assets and liabilities measured at fair value on a recurring basis	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 ​ ​ Quoted Prices in ​ Other Observable ​ Unobservable ​ ​ ​ ​ ​ Active Markets ​ Inputs ​ Inputs ​ ​ ​ $s in thousands (Level 1) (Level 2) (Level 3) Total Assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fixed-income securities (1) ​ $ 2,380 ​ $ 1,830 ​ $ — ​ $ 4,210 Money market funds (2) ​ ​ 859 ​ ​ — ​ ​ — ​ ​ 859 Total ​ $ 3,239 ​ $ 1,830 ​ $ — ​ $ 5,069 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Liabilities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Interest rate swap agreement (3) ​ $ — ​ $ 1,176 ​ $ — ​ $ 1,176 Contingent consideration (4) ​ ​ — ​ ​ — ​ ​ 8,283 ​ ​ 8,283 Total ​ $ — ​ $ 1,176 ​ $ 8,283 ​ $ 9,459 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2018 ​ ​ Quoted Prices in ​ Other Observable ​ Unobservable ​ ​ ​ ​ ​ Active Markets ​ Inputs ​ Inputs ​ ​ ​ $s in thousands (Level 1) (Level 2) (Level 3) Total Assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fixed-income securities (1) ​ $ 1,561 ​ $ 2,596 ​ $ — ​ $ 4,157 Money market funds (2) ​ ​ 784 ​ ​ — ​ ​ — ​ ​ 784 Interest rate swap agreement (3) ​ ​ — ​ ​ 1,147 ​ ​ ​ ​ ​ 1,147 Total ​ $ 2,345 ​ $ 3,743 ​ $ — ​ $ 6,088 (1) We invest a portion of our Restricted cash and investments in fixed-income securities, including U.S. Treasury and U.S. agency securities. We measure the fair value of U.S. Treasury securities using quoted prices for identical assets in active markets. We measure the fair value of U.S. agency securities using observable market activity for similar assets. The fair value of our fixed-income securities approximates our cost basis in the investments. (2) We invest a portion of our Restricted cash and investments in money market funds. We measure the fair value of these money market fund investments using quoted prices for identical assets in active markets. Money market funds are considered restricted cash for purposes of reconciling the beginning-of-period and end-of-period amounts presented in the Company’s consolidated statements of cash flows. (3) In order to manage interest rate exposure, we entered into an interest rate swap agreement in October 2014 that effectively converts a portion of our variable-rate debt to a fixed interest rate. The swap is designated as a cash flow hedge, with gains and losses deferred in other comprehensive income to be recognized as an adjustment to interest expense in the same period that the hedged interest payments affect earnings. The interest rate swap has an effective date of December 31, 2014 with an initial notional amount of $250.0 million. The fair value of the interest rate swap agreement represents the difference in the present value of cash flows calculated at the contracted interest rates and at current market interest rates at the end of the period. We calculate the fair value of the interest rate swap agreement quarterly based on the quoted market price for the same or similar financial instruments. The fair value of the interest rate swap agreement is included in Other long-term liabilities and Other assets in the Company’s consolidated balance sheets as of December 31, 2019 and 2018, respectively. (4) Our contingent consideration liabilities represent the estimated fair value of potential future payments the Company may be required to remit under the terms of historical purchase agreements entered into by NRC prior to the NRC Merger. The payments are contingent on the acquired businesses’ achievement of annual earnings targets in certain years and other events considered in the purchase agreements. The fair value of our contingent consideration liabilities are calculated using either a Monte Carlo simulation or modified Black-Scholes analyses based on earnings projections for the respective earn-out periods, corresponding earnings thresholds, and approximate timing of payments as outlined in the purchase agreements. The analyses utilize the following assumptions: (i) expected term; (ii) risk-adjusted net sales or earnings; (iii) risk-free interest rate; and (iv) expected volatility of earnings. Estimated payments, as determined through the respective models, are discounted by a credit spread assumption to account for credit risk. The fair value of our contingent consideration liabilities are included in Accrued liabilities and Other long-term liabilities. At December 31, 2019, balances of $6.6 million and $1.7 million were included in Accrued liabilities and Other long-term liabilities, respectively. We revalue our contingent consideration payments each period and any increases or decreases to fair value are included in Selling, general and administrative expenses in our consolidated statements of operations. Fair values may be impacted by certain unobservable inputs, most significantly with regard to discount rates, expected volatility and historical and projected performance. Significant changes to these inputs in isolation could result in a significantly different fair value measurement.
Schedule of changes in Level 3 liabilities measured at fair value	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value $s in thousands (Level 3) Balance at December 31, 2017 ​ $ — Balance at December 31, 2018 ​ $ — Fair value of contingent consideration acquired ​ 11,859 Change in fair value of contingent consideration ​ ​ 349 Foreign currency translation ​ ​ 75 Contingent consideration paid ​ (4,000) Balance at December 31, 2019 ​ $ 8,283

RECEIVABLES (Tables)

RECEIVABLES (Tables)	12 Months Ended
	Dec. 31, 2019
RECEIVABLES
Schedule of receivables	​ ​ ​ ​ ​ ​ ​ ​ $s in thousands ​ 2019 2018 Trade ​ $ 196,593 ​ $ 118,909 Unbilled revenue ​ 54,727 ​ 26,538 Other ​ 7,000 ​ 2,241 Total receivables ​ 258,320 ​ 147,688 Allowance for doubtful accounts ​ (3,010) ​ (2,998) Receivables, net ​ $ 255,310 ​ $ 144,690
Schedule of change in the allowance for doubtful accounts receivable	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Charged ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance at ​ (Credited) to ​ Recoveries ​ ​ ​ ​ ​ ​ ​ ​ Beginning of ​ Costs and ​ (Deductions/ ​ ​ ​ ​ Balance at $s in thousands Period Expenses Write-offs) Adjustments End of Period Year ended December 31, 2019 ​ $ 2,998 ​ $ 226 ​ $ (439) ​ $ 225 ​ $ 3,010 Year ended December 31, 2018 ​ $ 2,796 ​ $ 436 ​ $ (213) ​ $ (21) ​ $ 2,998 Year ended December 31, 2017 ​ $ 2,334 ​ $ 704 ​ $ (255) ​ $ 13 ​ $ 2,796

PROPERTY AND EQUIPMENT (Tables)

PROPERTY AND EQUIPMENT (Tables)	12 Months Ended
	Dec. 31, 2019
PROPERTY AND EQUIPMENT
Schedule of property and equipment	​ ​ ​ ​ ​ ​ ​ ​ $s in thousands 2019 2018 Cell development costs ​ $ 174,561 ​ $ 146,155 Land and improvements ​ 52,909 ​ 50,481 Buildings and improvements ​ 109,580 ​ 91,358 Railcars ​ 17,299 ​ 17,299 Vehicles, vessels and other equipment ​ 317,472 ​ 154,014 Construction in progress ​ 61,537 ​ 14,554 Total property and equipment ​ 733,358 ​ 473,861 Accumulated depreciation and amortization ​ (254,590) ​ (215,418) Property and equipment, net ​ $ 478,768 ​ $ 258,443

LEASES (Tables)

LEASES (Tables)	12 Months Ended
	Dec. 31, 2019
LEASES
Summary of leased assets and liabilities	​ ​ ​ ​ ​ $s in thousands December 31, 2019 Assets: ​ ​ ​ Operating right-of-use assets (1) ​ $ 57,396 Finance right-of-use assets (2) ​ ​ 20,499 Total ​ $ 77,895 ​ ​ ​ ​ Liabilities: ​ ​ ​ Current: ​ ​ ​ Operating (3) ​ $ 17,317 Finance (4) ​ ​ 4,128 Long-term: ​ ​ ​ Operating (5) ​ ​ 39,954 Finance (6) ​ ​ 16,308 Total ​ $ 77,707 (1) Included in Operating lease assets in the Company’s consolidated balance sheets. (2) Included in Property and equipment, net in the Company’s consolidated balance sheets. Finance right-of-use assets are recorded net of accumulated amortization of $2.7 million as of December 31, 2019. (3) Included in Current portion of operating lease liabilities in the Company’s consolidated balance sheets. (4) Included in Accrued liabilities in the Company’s consolidated balance sheets. (5) Included in Long-term operating lease liabilities in the Company’s consolidated balance sheets. (6) Included in Other long-term liabilities in the Company’s consolidated balance sheets.
Summary of lease cost	​ ​ ​ ​ ​ ​ ​ Year Ended $s in thousands December 31, 2019 Operating lease cost (1) ​ $ 9,144 Finance lease cost: ​ ​ ​ Amortization of leased assets (2) ​ ​ 1,641 Interest on lease liabilities (3) ​ ​ 332 Total ​ $ 11,117 (1) Included in Direct operating costs and Selling, general, and administrative expenses in the Company’s consolidated statements of operations. Operating lease cost includes short-term leases, excluding expenses relating to leases with a term of one month or less, which are not material. Operating lease cost excludes variable lease costs which are not material. (2) Included in Direct operating costs in the Company’s consolidated statements of operations. (3) Included in Interest expense in the Company’s consolidated statements of operations.
Schedule of cash flow supplemental information	​ ​ ​ ​ ​ ​ ​ Year Ended $s in thousands December 31, 2019 Cash paid for amounts included in the measurement of lease liabilities: ​ ​ ​ Operating cash flows from operating leases ​ $ 8,656 Operating cash flows from finance leases ​ ​ 332 Financing cash flows from finance leases ​ ​ 1,298 ​ ​ ​ ​ Non-cash investing and financing activities: ​ ​ ​ Right-of-use assets obtained in exchange for new operating lease liabilities ​ $ 7,380 Right-of-use assets obtained in exchange for new finance lease liabilities ​ ​ 2,481
Summary of weighted-average remaining lease term and discount rate	​ ​ ​ ​ ​ ​ ​ December 31, 2019 Weighted-average remaining lease term (years): ​ ​ ​ ​ Operating leases ​ ​ 4.4 ​ Finance leases ​ ​ 4.5 ​ Weighted-average discount rate: ​ ​ ​ ​ Operating leases ​ ​ 3.80 % Finance leases ​ ​ 5.07 %
Summary of future maturity of lease liability and its present value	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Operating ​ Finance ​ ​ $s in thousands Leases ​ Leases ​ Total 2020 ​ $ 18,007 ​ $ 4,742 ​ $ 22,749 2021 ​ ​ 14,935 ​ ​ 4,699 ​ ​ 19,634 2022 ​ 11,210 ​ 4,315 ​ 15,525 2023 ​ 8,643 ​ 4,400 ​ 13,043 2024 ​ 4,885 ​ 2,714 ​ 7,599 Thereafter ​ 5,025 ​ 2,853 ​ 7,878 Total ​ $ 62,705 ​ $ 23,723 ​ $ 86,428 Less: Interest ​ ​ 5,434 ​ ​ 3,287 ​ ​ 8,721 Present value of lease liabilities ​ $ 57,271 ​ $ 20,436 ​ $ 77,707
Schedule of future minimum lease payments on non-cancelable operating leases	​ ​ ​ ​ ​ $s in thousands Payments 2019 ​ $ 5,638 2020 ​ 3,644 2021 ​ 3,184 2022 ​ 1,885 2023 ​ 1,457 Thereafter ​ 5,065 ​ ​ $ 20,873

GOODWILL AND INTANGIBLE ASSETS

GOODWILL AND INTANGIBLE ASSETS (Tables)	12 Months Ended
	Dec. 31, 2019
GOODWILL AND INTANGIBLE ASSETS
Schedule of changes in goodwill	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Field & ​ ​ ​ ​ ​ Environmental ​ Industrial ​ ​ ​ ​ Services ​ Services ​ ​ ​ ​ ​ ​ ​ Accumulated ​ ​ ​ Accumulated ​ ​ ​ $s in thousands ​ Gross ​ Impairment ​ Gross ​ Impairment ​ Total Balance at December 31, 2017 ​ $ 150,699 ​ $ (5,457) ​ $ 44,131 ​ $ — ​ $ 189,373 ES&H Dallas acquisition ​ ​ — ​ ​ — ​ ​ 7,100 ​ ​ — ​ ​ 7,100 Winnie acquisition ​ ​ 13,573 ​ ​ — ​ ​ — ​ ​ — ​ ​ 13,573 Impairment charges ​ ​ — ​ ​ (1,413) ​ — ​ ​ — ​ ​ (1,413) Foreign currency translation ​ ​ (1,456) ​ ​ — ​ — ​ ​ — ​ ​ (1,456) Balance at December 31, 2018 ​ $ 162,816 ​ $ (6,870) ​ $ 51,231 ​ $ — ​ $ 207,177 NRC Merger ​ ​ 308,856 ​ ​ — ​ ​ 239,629 ​ ​ — ​ ​ 548,485 US Ecology Sarnia acquisition ​ ​ — ​ ​ — ​ ​ 7,668 ​ ​ — ​ ​ 7,668 Winnie purchase price allocation adjustment ​ ​ 2,863 ​ ​ — ​ ​ — ​ ​ — ​ ​ 2,863 Foreign currency translation ​ 736 ​ ​ — ​ 51 ​ ​ — ​ 787 Balance at December 31, 2019 ​ $ 475,271 ​ $ (6,870) ​ $ 298,579 ​ $ — ​ $ 766,980
Schedule of intangible assets, net	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 ​ 2018 ​ ​ ​ ​ ​ Accumulated ​ ​ ​ ​ ​ ​ ​ Accumulated ​ ​ ​ $s in thousands Cost Amortization Net Cost Amortization Net Amortizing intangible assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Permits, licenses and lease ​ $ 174,339 ​ $ (18,707) ​ $ 155,632 ​ $ 164,840 ​ $ (14,804) ​ $ 150,036 Customer relationships ​ ​ 333,090 ​ ​ (35,254) ​ ​ 297,836 ​ ​ 99,241 ​ ​ (25,676) ​ ​ 73,565 Technology - formulae and processes ​ 6,964 ​ (2,013) ​ 4,951 ​ 6,672 ​ (1,714) ​ 4,958 Customer backlog ​ 3,652 ​ (2,022) ​ 1,630 ​ 3,652 ​ (1,656) ​ 1,996 Tradename ​ 10,390 ​ ​ (4,832) ​ ​ 5,558 ​ ​ 4,290 ​ ​ (4,290) ​ ​ — Developed software ​ ​ 2,895 ​ ​ (1,884) ​ ​ 1,011 ​ ​ 2,884 ​ ​ (1,581) ​ ​ 1,303 Non-compete agreements ​ 5,455 ​ (1,694) ​ 3,761 ​ 1,542 ​ (875) ​ 667 Internet domain and website ​ ​ 536 ​ ​ (156) ​ ​ 380 ​ ​ 536 ​ ​ (128) ​ ​ 408 Database ​ ​ 388 ​ ​ (191) ​ ​ 197 ​ ​ 384 ​ ​ (167) ​ ​ 217 Total amortizing intangible assets ​ 537,709 ​ (66,753) ​ 470,956 ​ 284,041 ​ (50,891) ​ 233,150 Non-amortizing intangible assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Permits and licenses ​ 103,816 ​ ​ — ​ 103,816 ​ 46,391 ​ ​ — ​ 46,391 Tradename ​ 130 ​ ​ — ​ ​ 130 ​ 125 ​ ​ — ​ ​ 125 Total intangible assets ​ $ 641,655 ​ $ (66,753) ​ $ 574,902 ​ $ 330,557 ​ $ (50,891) ​ $ 279,666
Schedule of future amortization expense of amortizing intangible assets	​ ​ ​ ​ ​ ​ ​ Expected $s in thousands Amortization 2020 ​ $ 36,737 2021 ​ 33,948 2022 ​ 30,840 2023 ​ 30,684 2024 ​ 30,302 Thereafter ​ 308,445 ​ ​ $ 470,956

EMPLOYEE BENEFIT PLANS (Tables)

EMPLOYEE BENEFIT PLANS (Tables)	12 Months Ended
	Dec. 31, 2019
EMPLOYEE BENEFIT PLANS
Schedule of information regarding significant multi-employer pension benefit plans	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Pension ​ ​ ​ ​ ​ ​ Protection Act ​ ​ ​ ​ ​ ​ Certified ​ ​ Plan Employer ​ Plan ​ Zone Status Name of Plan ID Number Number 2019 2018 Operating Engineers Local 324 Pension Fund ​ 38-1900637 ​ 001 ​ Red ​ Red

CLOSURE AND POST-CLOSURE OBLI_2

CLOSURE AND POST-CLOSURE OBLIGATIONS (Tables)	12 Months Ended
	Dec. 31, 2019
CLOSURE AND POST-CLOSURE OBLIGATIONS
Schedule of changes to reported closure and post closure obligations	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $s in thousands 2019 2018 Closure and post-closure obligations, beginning of year ​ $ 78,363 ​ $ 76,088 Liabilities assumed in the NRC Merger ​ ​ 5,691 ​ ​ — Accretion expense ​ 4,388 ​ 3,707 Payments ​ (1,913) ​ (1,388) Adjustments ​ (221) ​ 99 Foreign currency translation ​ 75 ​ (143) Closure and post-closure obligations, end of year ​ 86,383 ​ 78,363 Less current portion ​ (2,152) ​ (2,266) Long-term portion ​ $ 84,231 ​ $ 76,097
Schedule of changes in the reported closure and post-closure asset recorded as a component of Property and equipment, net	​ ​ ​ ​ ​ ​ ​ ​ $s in thousands 2019 2018 Net closure and post-closure asset, beginning of year ​ $ 19,510 ​ $ 20,495 Asset acquired in the NRC Merger ​ ​ 4,857 ​ ​ — Additions or adjustments to closure and post-closure asset ​ (221) ​ 99 Amortization of closure and post-closure asset ​ (1,298) ​ (805) Foreign currency translation ​ 36 ​ (279) Net closure and post-closure asset, end of year ​ $ 22,884 ​ $ 19,510

DEBT (Tables)

DEBT (Tables)	12 Months Ended
	Dec. 31, 2019
DEBT
Schedule of long-term debt	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, $s in thousands 2019 2018 Revolving credit facility ​ $ 327,000 ​ $ 364,000 Term loan ​ ​ 450,000 ​ ​ — Unamortized term loan discount and debt issuance costs ​ ​ (7,799) ​ ​ — Total debt ​ ​ 769,201 ​ ​ 364,000 Current portion of long-term debt ​ ​ (3,359) ​ ​ — Long-term debt ​ $ 765,842 ​ $ 364,000
Schedule of future maturities of long-term debt, excluding the unamortized discount and debt issuance costs	​ ​ ​ ​ ​ $s in thousands Maturities 2020 ​ $ 4,500 2021 ​ ​ 4,500 2022 ​ ​ 4,500 2023 ​ ​ 4,500 2024 ​ ​ 331,500 Thereafter ​ ​ 427,500 ​ ​ $ 777,000
Schedule of interest margins based on the total net leverage ratio	​ Total Net Leverage Ratio LIBOR Rate Loans Interest Margin Base Rate Loans Interest Margin Equal to or greater than 3.25 to 1.00 2.00% 1.00% Equal to or greater than 2.50 to 1.00, but less than 3.25 to 1.00 1.75% 0.75% Equal to or greater than 1.75 to 1.00, but less than 2.50 to 1.00 1.50% 0.50% Equal to or greater than 1.00 to 1.00, but less than 1.75 to 1.00 1.25% 0.25% Less than 1.00 to 1.00 1.00% 0.00%

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2019
INCOME TAXES
Schedule of domestic and foreign components of Income (loss) before income taxes	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $s in thousands 2019 2018 2017 Domestic $ 30,706 $ 46,147 $ 26,051 Foreign ​ 19,093 ​ 18,711 ​ 16,919 Income before income taxes ​ $ 49,799 ​ $ 64,858 ​ $ 42,970
Schedule of components of the income tax expense	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $s in thousands 2019 2018 2017 Current: ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. Federal ​ $ 3,120 ​ $ 2,239 ​ $ 11,157 State ​ 1,547 ​ 2,368 ​ 2,482 Foreign ​ 5,426 ​ 4,746 ​ 5,398 Total current ​ 10,093 ​ 9,353 ​ 19,037 Deferred: ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. Federal ​ 5,977 ​ 5,675 ​ (27,029) State ​ 714 ​ 172 ​ 2,323 Foreign ​ (125) ​ 63 ​ (726) Total deferred ​ 6,566 ​ 5,910 ​ (25,432) Income tax (benefit) expense ​ $ 16,659 ​ $ 15,263 ​ $ (6,395)
Schedule of reconciliation between the effective income tax rate and the applicable statutory federal and state income tax rate	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 2018 2017 Taxes computed at federal statutory rate 21.0 % 21.0 % 35.0 % Impairment and loss on divestiture ​ — ​ 0.5 ​ 4.4 ​ State income taxes (net of federal income tax benefit) 5.7 ​ 5.1 ​ 2.9 ​ Share-based compensation ​ (0.4) ​ (1.3) ​ — ​ Research and development credits ​ (0.8) ​ (2.0) ​ — ​ Non-deductible transaction costs ​ 3.4 ​ — ​ — ​ Global intangible low taxed income ​ 1.1 ​ — ​ — ​ Tax Cuts and Jobs Act of 2017 ​ — ​ (0.3) ​ (55.4) ​ Foreign rate differential 2.5 ​ 1.7 ​ (2.9) ​ State deferred rate differential ​ (1.6) ​ — ​ — ​ Other 2.6 ​ (1.2) ​ 1.1 ​ ​ 33.5 % 23.5 % (14.9) %
Schedule of components of the total net deferred tax assets and liabilities	​ ​ ​ ​ ​ ​ ​ ​ $s in thousands 2019 2018 Deferred tax assets: ​ ​ ​ ​ ​ ​ Net operating losses ​ $ 14,121 ​ $ — Operating leases ​ ​ 14,034 ​ ​ — Foreign tax credit and capital loss carry forwards ​ ​ 4,705 ​ ​ 5,165 Accruals, allowances and other ​ 8,966 ​ 5,041 Environmental compliance and other site related costs ​ 9,203 ​ 8,580 Business interest expense ​ ​ 6,498 ​ ​ — Unrealized foreign exchange gains and losses ​ ​ 962 ​ ​ 1,550 Total deferred tax assets ​ 58,489 ​ 20,336 Less: valuation allowance ​ (4,965) ​ (4,791) Net deferred tax assets ​ 53,524 ​ 15,545 Deferred tax liabilities: ​ ​ ​ ​ ​ ​ Property and equipment ​ (53,540) ​ (26,145) Intangible assets ​ (112,446) ​ (51,081) Operating leases ​ ​ (14,034) ​ ​ — Unrealized gains and losses on interest rate hedge ​ ​ — ​ ​ (241) Other ​ (1,849) ​ (1,284) Total deferred tax liabilities ​ (181,869) ​ (78,751) Net deferred tax liability ​ $ (128,345) ​ $ (63,206)
Schedule of changes to unrecognized tax benefits	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $s in thousands 2019 2018 2017 Unrecognized tax benefits, beginning of year ​ $ 555 ​ $ — ​ $ — Gross increases - tax positions in prior period ​ ​ 8,088 ​ ​ 494 ​ ​ — Gross decreases - tax positions in prior period ​ ​ (9) ​ ​ — ​ ​ — Gross increases - tax positions in current period ​ ​ 52 ​ ​ 61 ​ ​ — Settlements ​ ​ (284) ​ ​ — ​ ​ — Lapse of statute of limitations ​ ​ (67) ​ ​ — ​ ​ — Unrecognized tax benefits, end of year ​ $ 8,335 ​ $ 555 ​ $ —

EQUITY (Tables)

EQUITY (Tables)	12 Months Ended
	Dec. 31, 2019
Summary of stock option activity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ Weighted ​ ​ ​ ​ Average ​ ​ ​ ​ Average ​ Aggregate ​ Remaining ​ ​ ​ ​ Exercise ​ Intrinsic ​ Contractual ​ Shares Price Value Term (Years) Outstanding as of December 31, 2018 236,503 ​ $ 44.93 ​ ​ ​ ​ ​ Granted 70,500 ​ ​ 58.75 ​ ​ ​ ​ ​ Exercised (11,875) ​ 45.42 ​ ​ ​ ​ ​ Cancelled, expired or forfeited (1,540) ​ 43.55 ​ ​ ​ ​ ​ Outstanding as of December 31, 2019 293,588 ​ $ 48.23 ​ $ 2,841 ​ 6.1 Exercisable as of December 31, 2019 212,527 ​ $ 44.89 ​ $ 2,767 5.2
Schedule of significant weighted-average assumptions relating to the valuation of option grants	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 2018 2017 ​ Expected life 2.7 years 3.8 years 3.8 years Expected volatility 30 % 30 % 31 % Risk-free interest rate 2.1 % 2.0 % 1.5 % Expected dividend yield 1.2 % 1.5 % 1.7 %
Schedule of components of pre-tax share-based compensation expense (primarily included in Selling, general and administrative expenses in our consolidated statements of operations) and related tax benefits	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $s in thousands 2019 2018 2017 Share-based compensation from: ​ ​ ​ ​ ​ ​ ​ ​ ​ Stock options ​ $ 575 ​ $ 727 ​ $ 1,141 Restricted stock ​ 1,662 ​ 1,590 ​ 1,505 Restricted stock units (1) ​ ​ 6,193 ​ ​ 1,324 ​ ​ 716 Performance stock units ​ ​ 831 ​ ​ 725 ​ ​ 571 Total share-based compensation ​ 9,261 ​ 4,366 ​ 3,933 Income tax benefit ​ (3,098) ​ (1,027) ​ (1,403) Share-based compensation, net of tax ​ $ 6,163 ​ $ 3,339 ​ $ 2,530
PSUs
Schedule of assumptions for determining the fair value for PSU awards using Monte Carlo simulation models	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 2018 ​ 2017 ​ Stock price on grant date ​ $ 58.40 ​ $ 51.00 ​ $ 49.15 ​ Expected term ​ 3.0 years ​ 3.0 years ​ 3.0 years Expected volatility ​ ​ 30 % ​ 30 % ​ 31 % Risk-free interest rate ​ 2.5 % ​ 2.0 % ​ 1.5 % Expected dividend yield ​ 1.1 % ​ 1.4 % ​ 1.5 %
Summary of PSU, restricted stock and RSU activity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ Average ​ ​ ​ ​ Grant Date ​ ​ Units ​ Fair Value Outstanding as of December 31, 2018 ​ 39,200 ​ $ 55.48 Granted ​ 17,111 ​ ​ 58.20 Vested ​ (13,600) ​ ​ 41.22 Outstanding as of December 31, 2019 ​ 42,711 ​ $ 61.11
Restricted stock
Summary of PSU, restricted stock and RSU activity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ Average ​ ​ ​ ​ Grant Date ​ Shares Fair Value Outstanding as of December 31, 2018 74,988 ​ $ 46.74 Granted 28,900 ​ ​ 62.59 Vested (39,234) ​ 43.77 Outstanding as of December 31, 2019 64,654 ​ $ 55.62
RSUs
Summary of PSU, restricted stock and RSU activity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ Average ​ ​ ​ ​ Grant Date ​ ​ Units ​ Fair Value Outstanding as of December 31, 2018 ​ 66,785 ​ $ 53.77 Granted ​ 151,263 ​ ​ 60.92 Vested ​ (85,014) ​ 58.35 Cancelled, expired or forfeited ​ (1,835) ​ 52.87 Outstanding as of December 31, 2019 ​ 131,199 ​ $ 59.05

EARNINGS PER SHARE (Tables)

EARNINGS PER SHARE (Tables)	12 Months Ended
	Dec. 31, 2019
EARNINGS PER SHARE
Schedule of earnings per share	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 ​ 2018 ​ 2017 $s and shares in thousands, except per share amounts Basic Diluted Basic Diluted Basic Diluted Net income ​ $ 33,140 ​ $ 33,140 ​ $ 49,595 ​ $ 49,595 ​ $ 49,365 ​ $ 49,365 Weighted average basic shares outstanding ​ 23,521 ​ 23,521 ​ 21,888 ​ 21,888 ​ 21,758 ​ 21,758 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Dilutive effect of share-based awards and warrants ​ ​ ​ ​ 228 ​ ​ ​ ​ 159 ​ ​ ​ ​ 144 Weighted average diluted shares outstanding ​ ​ ​ ​ 23,749 ​ ​ ​ ​ 22,047 ​ ​ ​ ​ 21,902 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Earnings per share ​ $ 1.41 ​ $ 1.40 ​ $ 2.27 ​ $ 2.25 ​ $ 2.27 ​ $ 2.25 Anti-dilutive shares excluded from calculation ​ ​ ​ ​ 90 ​ ​ ​ ​ 46 ​ ​ ​ ​ 103

SEGMENT REPORTING (Tables)

SEGMENT REPORTING (Tables)	12 Months Ended
	Dec. 31, 2019
SEGMENT REPORTING
Summary of financial information of our reportable segments	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 ​ ​ ​ ​ Field & ​ ​ ​ ​ ​ ​ ​ ​ Environmental ​ Industrial ​ ​ ​ ​ ​ ​ $s in thousands Services Services Corporate Total Revenue ​ $ 453,107 ​ $ 232,402 ​ $ — ​ $ 685,509 Depreciation, amortization and accretion ​ $ 44,535 ​ $ 15,007 ​ $ 1,760 ​ $ 61,302 Capital expenditures ​ $ 47,593 ​ $ 5,986 ​ $ 4,521 ​ $ 58,100 Total assets ​ $ 1,290,304 ​ $ 865,540 ​ $ 75,400 ​ $ 2,231,244 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2018 ​ ​ ​ ​ Field & ​ ​ ​ ​ ​ ​ ​ ​ Environmental ​ Industrial ​ ​ ​ ​ ​ ​ $s in thousands Services Services Corporate Total Revenue ​ $ 400,678 ​ $ 165,250 ​ $ — ​ $ 565,928 Depreciation, amortization and accretion ​ $ 35,195 ​ $ 6,304 ​ $ 1,060 ​ $ 42,559 Capital expenditures ​ $ 31,735 ​ $ 7,430 ​ $ 1,592 ​ $ 40,757 Total assets ​ $ 701,267 ​ $ 169,066 ​ $ 77,565 ​ $ 947,898 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2017 ​ ​ ​ ​ Field & ​ ​ ​ ​ ​ ​ ​ ​ Environmental ​ Industrial ​ ​ ​ ​ ​ ​ $s in thousands Services Services Corporate Total Revenue ​ $ 366,308 ​ $ 137,734 ​ $ — ​ $ 504,042 Depreciation, amortization and accretion ​ $ 35,137 ​ $ 5,578 ​ $ 501 ​ $ 41,216 Capital expenditures ​ $ 28,783 ​ $ 4,206 ​ $ 3,251 ​ $ 36,240 Total assets ​ $ 609,174 ​ $ 125,110 ​ $ 67,792 ​ $ 802,076
Reconciliation of Net Income to Adjusted EBITDA and adjusted EBITDA by operating segment	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $s in thousands 2019 2018 2017 Net income ​ $ 33,140 ​ $ 49,595 ​ $ 49,365 Income tax expense (benefit) ​ ​ 16,659 ​ ​ 15,263 ​ ​ (6,395) Interest expense ​ ​ 19,239 ​ ​ 12,130 ​ ​ 18,157 Interest income ​ ​ (605) ​ ​ (215) ​ ​ (62) Foreign currency (gain) loss ​ ​ 733 ​ ​ (55) ​ ​ (516) Other income ​ ​ (455) ​ ​ (2,630) ​ ​ (791) Property and equipment impairment charges ​ ​ 25 ​ ​ — ​ ​ — Goodwill and intangible asset impairment charges ​ ​ — ​ ​ 3,666 ​ ​ 8,903 Depreciation and amortization of plant and equipment ​ ​ 41,423 ​ ​ 29,207 ​ ​ 28,302 Amortization of intangible assets ​ ​ 15,491 ​ ​ 9,645 ​ ​ 9,888 Share-based compensation ​ ​ 5,544 ​ ​ 4,366 ​ ​ 3,933 Accretion and non-cash adjustment of closure & post-closure liabilities ​ ​ 4,388 ​ ​ 3,707 ​ ​ 3,026 Gain on property insurance recoveries ​ ​ (12,366) ​ ​ (347) ​ ​ (1,313) Business development and integration expenses ​ ​ 26,150 ​ ​ 748 ​ ​ 500 Adjusted EBITDA ​ $ 149,366 ​ $ 125,080 ​ $ 112,997 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $s in thousands ​ 2019 2018 2017 Environmental Services $ 187,759 ​ $ 160,179 ​ $ 145,058 Field & Industrial Services 26,707 ​ 18,457 ​ 14,709 Corporate (65,100) ​ (53,556) ​ (46,770) Total $ 149,366 ​ $ 125,080 ​ $ 112,997
Schedule of long-lived assets by geographic location	​ ​ ​ ​ ​ ​ ​ ​ $s in thousands 2019 2018 United States ​ $ 954,102 ​ $ 480,322 Canada ​ 70,691 ​ 57,787 EMEA ​ ​ 23,587 ​ ​ — Other (1) ​ ​ 5,290 ​ ​ — Total long-lived assets ​ $ 1,053,670 ​ $ 538,109 ​ (1) Includes Mexico, Asia Pacific, and Latin America and Caribbean geographical regions.

QUARTERLY FINANCIAL DATA (una_2

QUARTERLY FINANCIAL DATA (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2019
QUARTERLY FINANCIAL DATA (unaudited)
Schedule of unaudited consolidated quarterly results of operations	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three-Months Ended ​ ​ ​ $s and shares in thousands, except per share amounts Mar. 31, June 30, Sept. 30, Dec. 31, Year 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenue ​ $ 131,037 ​ $ 155,802 ​ $ 167,402 ​ $ 231,268 ​ $ 685,509 Gross profit ​ 35,241 ​ 49,583 ​ 56,540 ​ 68,470 ​ 209,834 Operating income ​ 14,936 ​ 25,534 ​ 23,211 ​ 5,030 ​ 68,711 Net income (loss) ​ 8,043 ​ 15,491 ​ 13,070 ​ (3,464) ​ 33,140 Earnings (loss) per share—diluted (1) ​ $ 0.36 ​ $ 0.70 ​ $ 0.59 ​ $ (0.12) ​ $ 1.40 Weighted average common shares outstanding used in the diluted earnings per share calculation ​ 22,197 ​ 22,208 ​ 22,231 ​ 27,916 ​ 23,749 Dividends paid per share ​ $ 0.18 ​ $ 0.18 ​ $ 0.18 ​ $ 0.18 ​ $ 0.72 2018 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenue ​ $ 120,059 ​ $ 136,912 ​ $ 151,416 ​ $ 157,541 ​ $ 565,928 Gross profit ​ 35,671 ​ 41,448 ​ 47,300 ​ 45,675 ​ 170,094 Operating income ​ 13,439 ​ 20,292 ​ 19,985 ​ 20,372 ​ 74,088 Net income ​ 9,243 ​ 13,220 ​ 13,427 ​ 13,705 ​ 49,595 Earnings per share—diluted (1) ​ $ 0.42 ​ $ 0.60 ​ $ 0.61 ​ $ 0.62 ​ $ 2.25 Weighted average common shares outstanding used in the diluted earnings per share calculation ​ 21,957 ​ 22,024 ​ 22,099 ​ 22,109 ​ 22,047 Dividends paid per share ​ $ 0.18 ​ $ 0.18 ​ $ 0.18 ​ $ 0.18 ​ $ 0.72 (1) Diluted earnings (loss) per common share for each quarter presented above is based on the respective weighted average number of common shares for the respective quarter therefore the sum of the diluted earnings (loss) per share for each respective quarter may not necessarily be equal to the full year diluted earnings (loss) per common share amount .

DESCRIPTION OF BUSINESS (Detail

DESCRIPTION OF BUSINESS (Details)	12 Months Ended
	Dec. 31, 2019segment
DESCRIPTION OF BUSINESS
Number of Reportable Segments	2

SUMMARY OF SIGNIFICANT ACCOUN_4

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash and Cash Equivalents
Cash and Cash Equivalents, at Carrying Value	$ 41,281	$ 31,969	$ 27,042	$ 7,015
Non-US Operations
Cash and Cash Equivalents
Cash	$ 35,200	$ 19,400

SUMMARY OF SIGNIFICANT ACCOUN_5

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Restricted Cash and Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Restricted Cash and Investments
Restricted cash and investments	$ 5,069	$ 4,941

SUMMARY OF SIGNIFICANT ACCOUN_6

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Deferred Revenue (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019USD ($)item	Dec. 31, 2018USD ($)
Revenue Recognition
Number of primary sources for revenue recognition | item	3
Deferred revenue recognized in revenue | $	$ 10.4	$ 8.4

SUMMARY OF SIGNIFICANT ACCOUN_7

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Property and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property and Equipment
Repair and maintenance expenses	$ 20.5	$ 17.5	$ 14.8
Salvage value for the depreciable fixed assets	$ 0
Vehicles, vessels and other equipment | Minimum
Property and Equipment
Useful Lives	3 years
Vehicles, vessels and other equipment | Maximum
Property and Equipment
Useful Lives	10 years
Disposal facility and equipment | Minimum
Property and Equipment
Useful Lives	3 years
Disposal facility and equipment | Maximum
Property and Equipment
Useful Lives	20 years
Buildings and improvements | Minimum
Property and Equipment
Useful Lives	5 years
Buildings and improvements | Maximum
Property and Equipment
Useful Lives	40 years
Railcars
Property and Equipment
Useful Lives	40 years

SUMMARY OF SIGNIFICANT ACCOUN_8

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Disposal Cell Accounting (Details)	12 Months Ended
	Dec. 31, 2019
Disposal Cell Accounting
Period of acceptable financial assurance for closure and post-closure monitoring of each facility as per RCRA requirements	30 years

SUMMARY OF SIGNIFICANT ACCOUN_9

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Intangible Assets (Details)	12 Months Ended
	Dec. 31, 2019
Minimum
Intangible Assets
Estimated economic lives	1 year
Maximum
Intangible Assets
Estimated economic lives	60 years
Permits and licenses | Minimum
Intangible Assets
Renewal terms of acquired intangible assets	5 years
Permits and licenses | Maximum
Intangible Assets
Renewal terms of acquired intangible assets	10 years

SUMMARY OF SIGNIFICANT ACCOU_10

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Debt Issuance Costs & Debt Discount (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018
Debt Issuance Costs & Debt Discount
Unamortized discount and debt issuance costs		$ 7,799
2014 Credit Agreement
Debt Issuance Costs & Debt Discount
Write off unamortized debt issuance costs	$ 5,500
Term Loan
Debt Issuance Costs & Debt Discount
Unamortized discount and debt issuance costs		7,800
Revolving credit facility
Debt Issuance Costs & Debt Discount
Unamortized debt issuance costs		$ 4,700	$ 2,700

SUMMARY OF SIGNIFICANT ACCOU_11

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Derivative Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2014
Derivative Instruments
Initial notional amount	$ 250	$ 250

SUMMARY OF SIGNIFICANT ACCOU_12

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Income Taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
Unrecognized tax benefits	$ 8,335	$ 555
Unrecognized tax benefits, if recognized, would favorably impact future earnings	$ 236

SUMMARY OF SIGNIFICANT ACCOU_13

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Insurance (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Insurance
Accrued costs for self-insured health care coverage	$ 1,000,000	$ 826,000

SUMMARY OF SIGNIFICANT ACCOU_14

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Recently Issued Accounting Pronouncements (Details) - USD ($) $ in Thousands	Jan. 01, 2019	Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, right-of-use asset		$ 57,396
Operating lease liability		$ 57,271
ASU 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Practical expedients - Package	true
Practical expedients - Land easements	true
Practical expedients - Hindsight	false
Operating lease, right-of-use asset	$ 18,100
Operating lease liability	$ 18,100

REVENUES (Details)

REVENUES (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019USD ($)	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2019USD ($)segment	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Disaggregation of revenue
Number of reportable segments | segment									2
Revenue	$ 231,268	$ 167,402	$ 155,802	$ 131,037	$ 157,541	$ 151,416	$ 136,912	$ 120,059	$ 685,509	$ 565,928	$ 504,042
Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue											504,042
Treatment and disposal
Disaggregation of revenue
Revenue									384,366	331,781
Treatment and disposal | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue											309,807
Transportation and Logistics
Disaggregation of revenue
Revenue									128,054	113,670
Transportation and Logistics | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue											88,804
Industrial Services
Disaggregation of revenue
Revenue									38,865	24,155
Industrial Services | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue											19,121
Small Quantity Generation
Disaggregation of revenue
Revenue									37,471	34,571
Small Quantity Generation | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue											29,934
Total Waste Management
Disaggregation of revenue
Revenue									33,792	41,729
Total Waste Management | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue											38,628
Remediation
Disaggregation of revenue
Revenue									13,288	10,139
Remediation | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue											14,241
Emergency Response
Disaggregation of revenue
Revenue									26,737	7,513
Emergency Response | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue											3,214
Domestic Standby Services
Disaggregation of revenue
Revenue									14,249
Other
Disaggregation of revenue
Revenue									8,687	2,370
Other | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue											293
Operating Segment | Environmental Services
Disaggregation of revenue
Revenue									453,107	400,678	366,308
Operating Segment | Field and Industrial Services
Disaggregation of revenue
Revenue									232,402	165,250	137,734
Operating Segment | Calculated under Revenue Guidance in Effect before Topic 606 | Environmental Services
Disaggregation of revenue
Revenue											366,308
Operating Segment | Calculated under Revenue Guidance in Effect before Topic 606 | Field and Industrial Services
Disaggregation of revenue
Revenue											137,734
Operating Segment | Treatment and disposal | Environmental Services
Disaggregation of revenue
Revenue									365,886	320,045
Operating Segment | Treatment and disposal | Field and Industrial Services
Disaggregation of revenue
Revenue									18,480	11,736
Operating Segment | Treatment and disposal | Calculated under Revenue Guidance in Effect before Topic 606 | Environmental Services
Disaggregation of revenue
Revenue											299,403
Operating Segment | Treatment and disposal | Calculated under Revenue Guidance in Effect before Topic 606 | Field and Industrial Services
Disaggregation of revenue
Revenue											10,404
Operating Segment | Transportation and Logistics | Environmental Services
Disaggregation of revenue
Revenue									87,221	80,633
Operating Segment | Transportation and Logistics | Field and Industrial Services
Disaggregation of revenue
Revenue									40,833	33,037
Operating Segment | Transportation and Logistics | Calculated under Revenue Guidance in Effect before Topic 606 | Environmental Services
Disaggregation of revenue
Revenue											66,905
Operating Segment | Transportation and Logistics | Calculated under Revenue Guidance in Effect before Topic 606 | Field and Industrial Services
Disaggregation of revenue
Revenue											21,899
Operating Segment | Industrial Services | Field and Industrial Services
Disaggregation of revenue
Revenue									38,865	24,155
Operating Segment | Industrial Services | Calculated under Revenue Guidance in Effect before Topic 606 | Field and Industrial Services
Disaggregation of revenue
Revenue											19,121
Operating Segment | Small Quantity Generation | Field and Industrial Services
Disaggregation of revenue
Revenue									37,471	34,571
Operating Segment | Small Quantity Generation | Calculated under Revenue Guidance in Effect before Topic 606 | Field and Industrial Services
Disaggregation of revenue
Revenue											29,934
Operating Segment | Total Waste Management | Field and Industrial Services
Disaggregation of revenue
Revenue									33,792	41,729
Operating Segment | Total Waste Management | Calculated under Revenue Guidance in Effect before Topic 606 | Field and Industrial Services
Disaggregation of revenue
Revenue											38,628
Operating Segment | Remediation | Field and Industrial Services
Disaggregation of revenue
Revenue									13,288	10,139
Operating Segment | Remediation | Calculated under Revenue Guidance in Effect before Topic 606 | Field and Industrial Services
Disaggregation of revenue
Revenue											14,241
Operating Segment | Emergency Response | Field and Industrial Services
Disaggregation of revenue
Revenue									26,737	7,513
Operating Segment | Emergency Response | Calculated under Revenue Guidance in Effect before Topic 606 | Field and Industrial Services
Disaggregation of revenue
Revenue											3,214
Operating Segment | Domestic Standby Services | Field and Industrial Services
Disaggregation of revenue
Revenue									14,249
Operating Segment | Other | Field and Industrial Services
Disaggregation of revenue
Revenue									$ 8,687	$ 2,370
Operating Segment | Other | Calculated under Revenue Guidance in Effect before Topic 606 | Field and Industrial Services
Disaggregation of revenue
Revenue											$ 293

REVENUES - Treatment and Dispos

REVENUES - Treatment and Disposal Revenue (Details) - T	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Total Waste Management | Minimum
Disaggregation of revenue
Revenue Contract Term	1 year
Event Business | Treatment and disposal
Disaggregation of revenue
Threshold Tons of Non-recurring projects	1,000
Revenue (in percent)	22.00%	20.00%	22.00%
Base Business | Treatment and disposal
Disaggregation of revenue
Revenue (in percent)	78.00%	80.00%	78.00%

REVENUES - Geography (Details)

REVENUES - Geography (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of revenue
Revenue	$ 231,268	$ 167,402	$ 155,802	$ 131,037	$ 157,541	$ 151,416	$ 136,912	$ 120,059	$ 685,509	$ 565,928	$ 504,042
Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue											504,042
United States
Disaggregation of revenue
Revenue									589,127	495,168
United States | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue											434,511
Canada
Disaggregation of revenue
Revenue									88,499	70,760
Canada | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue											69,531
EMEA
Disaggregation of revenue
Revenue									5,079
Other
Disaggregation of revenue
Revenue									2,804
Operating Segment | Environmental Services
Disaggregation of revenue
Revenue									453,107	400,678	366,308
Operating Segment | Environmental Services | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue											366,308
Operating Segment | Environmental Services | United States
Disaggregation of revenue
Revenue									367,185	329,918
Operating Segment | Environmental Services | United States | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue											296,777
Operating Segment | Environmental Services | Canada
Disaggregation of revenue
Revenue									85,922	70,760
Operating Segment | Environmental Services | Canada | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue											69,531
Operating Segment | Field and Industrial Services
Disaggregation of revenue
Revenue									232,402	165,250	137,734
Operating Segment | Field and Industrial Services | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue											137,734
Operating Segment | Field and Industrial Services | United States
Disaggregation of revenue
Revenue									221,942	$ 165,250
Operating Segment | Field and Industrial Services | United States | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue											$ 137,734
Operating Segment | Field and Industrial Services | Canada
Disaggregation of revenue
Revenue									2,577
Operating Segment | Field and Industrial Services | EMEA
Disaggregation of revenue
Revenue									5,079
Operating Segment | Field and Industrial Services | Other
Disaggregation of revenue
Revenue									$ 2,804

REVENUES - Practical Expedients

REVENUES - Practical Expedients (Details)	12 Months Ended
	Dec. 31, 2019
REVENUES
Revenue, Practical Expedient, Financing Component	true
Revenue, Practical Expedient, Initial Application and Transition, Nonrestatement of Modified Contract	true

BUSINESS COMBINATIONS - Merger

BUSINESS COMBINATIONS - Merger consideration (Details) $ / shares in Units, $ in Thousands	Nov. 01, 2019USD ($)$ / sharesY	Nov. 01, 2019USD ($)$ / sharesYshares	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Oct. 31, 2019$ / shares
Business Acquisition [Line Items]
Total merger consideration	$ 1,024,800
Proceeds from term loan			$ 491,875	$ 87,000	$ 281,000
Term of long term debt	7 years	7 years
NRC
Business Acquisition [Line Items]
Fair value of US Ecology common stock issued			$ 626,460
Repayment of NRC's term loan and revolving credit facility	$ 398,373	$ 398,373
Total merger consideration	1,024,833
Proceeds from term loan	450,000
NRC | Common Stock
Business Acquisition [Line Items]
Fair value of US Ecology common stock issued	581,101	$ 581,101
Shares Issued | shares		9,337,949
Closing share price | $ / shares						$ 62.23
NRC | Warrants
Business Acquisition [Line Items]
Fair value of replacement warrants issued	$ 44,858	$ 44,858
Shares Issued | shares		3,772,753
Fair value per warrant | $ / shares	$ 11.89	$ 11.89
Closing share price | $ / shares						$ 2.33
Exchange ratio	0.196	0.196
NRC | RSUs
Business Acquisition [Line Items]
Fair value of replacement RSUs issued	$ 141	$ 141
Shares Issued | shares		118,239
Ratio of precombination service period to vesting period	1.90%
NRC | Stock options
Business Acquisition [Line Items]
Fair value of replacement stock options	$ 360	$ 360
Shares Issued | shares		29,400
Fair value per option | $ / shares	$ 12.26	$ 12.26
Strike price | $ / shares	$ 52.30	$ 52.30
NRC | Stock options | Dividend yield
Business Acquisition [Line Items]
Fair value of option	1.2	1.2
NRC | Stock options | Expected volatility
Business Acquisition [Line Items]
Fair value of option	28.9	28.9
NRC | Stock options | Risk free rate
Business Acquisition [Line Items]
Fair value of option | $ / shares	1.5	1.5
NRC | Stock options | Expected term
Business Acquisition [Line Items]
Fair value of option | Y	1	1

BUSINESS COMBINATIONS - Prelimi

BUSINESS COMBINATIONS - Preliminary fair value estimates of assets acquired and liabilities assumed recognized (Details) $ in Thousands, $ in Millions	Nov. 01, 2019USD ($)	Aug. 01, 2019USD ($)	Aug. 01, 2019CAD ($)	Nov. 14, 2018USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Consideration paid and the fair value of assets acquired and liabilities assumed
Goodwill					$ 766,980	$ 207,177	$ 189,373
Field and Industrial Services
Consideration paid and the fair value of assets acquired and liabilities assumed
Goodwill	$ 239,600				298,579	51,231	44,131
Environmental Services
Consideration paid and the fair value of assets acquired and liabilities assumed
Goodwill	308,900				475,271	162,816	$ 150,699
NRC
Consideration paid and the fair value of assets acquired and liabilities assumed
Current assets	131,653
Property and equipment	197,045
Identifiable intangible assets	303,600
Other assets	41,687
Current liabilities	(83,460)
Deferred income tax liabilities	(56,596)
Other liabilities	(57,581)
Total identifiable net assets	476,348
Goodwill	548,485
Total purchase price	1,024,833
Goodwill expected to be deductible for income tax purposes	$ 33,300
US Ecology Sarnia
Consideration paid and the fair value of assets acquired and liabilities assumed
Identifiable intangible assets		$ 6,200
Goodwill		7,700
Total purchase price		$ 17,900	$ 23.5
Winnie
Consideration paid and the fair value of assets acquired and liabilities assumed
Current assets					1,860	1,923
Property and equipment					3,699	6,300
Identifiable intangible assets				$ 66,500	66,500	66,600
Current liabilities					(755)	(755)
Other liabilities					(512)	(512)
Total identifiable net assets					70,792	73,556
Goodwill				16,400	16,436	$ 13,573
Total purchase price				87,200
Adjustments
Current assets - adjustment					(63)
Property and equipment - adjustment					(2,601)
Identifiable intangible assets - adjustment					(100)
Total identifiable net assets - adjustment					(2,764)
Goodwill - adjustment					2,863
Total purchase price - adjustment					99
Winnie | Permit
Consideration paid and the fair value of assets acquired and liabilities assumed
Identifiable intangible assets				54,700
Winnie | Customer relationships
Consideration paid and the fair value of assets acquired and liabilities assumed
Identifiable intangible assets				$ 11,800
Winnie | Environmental Services
Adjustments
Goodwill - adjustment					$ 2,863

BUSINESS COMBINATIONS - preli_2

BUSINESS COMBINATIONS - preliminary fair value of identifiable intangible assets (Details) - NRC $ in Thousands	Nov. 01, 2019USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total identified intangible assets	$ 246,200
Total identified intangible assets	303,600
Customer relationships - noncontractual
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total identified intangible assets	$ 193,700
Average Amortization Period	14 years
Customer relationships - contractual
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total identified intangible assets	$ 34,400
Average Amortization Period	7 years
Permits and licenses
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total identified intangible assets	$ 8,700
Average Amortization Period	16 years
Tradename
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total identified intangible assets	$ 6,100
Average Amortization Period	2 years
Non-compete agreements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total identified intangible assets	$ 3,300
Average Amortization Period	2 years
Permits and licenses
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-amortizing intangible assets	$ 57,400

BUSINESS COMBINATIONS - Pro for

BUSINESS COMBINATIONS - Pro forma information (Details) - NRC - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Pro forma combined:
Revenue	$ 1,048,745	$ 923,947
Net income (loss)	$ 11,775	$ (12,296)

BUSINESS COMBINATIONS - 2018 (D

BUSINESS COMBINATIONS - 2018 (Details) $ in Thousands, $ in Millions	Aug. 01, 2019USD ($)	Aug. 01, 2019CAD ($)	Nov. 14, 2018USD ($)	Aug. 31, 2018USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Nov. 01, 2019USD ($)
Acquisition
Payment to acquire business, net of cash acquired					$ 399,599	$ 108,382
Consideration paid and the fair value of assets acquired and liabilities assumed
Goodwill					766,980	207,177	$ 189,373
Additional information
Acquisition-related costs included in selling, general and administrative expenses					26,150	748	500
Field and Industrial Services
Consideration paid and the fair value of assets acquired and liabilities assumed
Goodwill					298,579	51,231	$ 44,131	$ 239,600
Winnie
Acquisition
Payment to acquire business					87,228	87,129
Acquisition price			$ 87,200
Consideration paid and the fair value of assets acquired and liabilities assumed
Current assets					1,860	1,923
Property and equipment					3,699	6,300
Identifiable intangible assets			66,500		66,500	66,600
Current liabilities					(755)	(755)
Other liabilities					(512)	(512)
Total identifiable net assets					70,792	73,556
Goodwill			16,400		16,436	$ 13,573
Total purchase price			$ 87,200
Adjustments
Current assets - adjustment					(63)
Property and equipment - adjustment					(2,601)
Identifiable intangible assets - adjustment					(100)
Total identifiable net assets - adjustment					(2,764)
Goodwill - adjustment					2,863
Total purchase price - adjustment					$ 99
Additional information
Amortization period of goodwill recognized and expected to be deductible for income tax purposes			15 years
Winnie | Credit agreement
Acquisition
Amount of term loan which was used to funded acquisition			$ 87,000
Winnie | Customer relationships
Consideration paid and the fair value of assets acquired and liabilities assumed
Identifiable intangible assets			$ 11,800
Additional information
Weighted average amortization period			15 years
Winnie | Permit
Consideration paid and the fair value of assets acquired and liabilities assumed
Identifiable intangible assets			$ 54,700
Additional information
Weighted average amortization period			60 years
US Ecology Sarnia
Acquisition
Percentage of outstanding shares acquired	100.00%
Acquisition price	$ 17,900	$ 23.5
Consideration paid and the fair value of assets acquired and liabilities assumed
Identifiable intangible assets	6,200
Goodwill	7,700
Total purchase price	$ 17,900	$ 23.5
Additional information
Weighted average amortization period	14 years	14 years
ES&H Dallas
Acquisition
Payment to acquire business				$ 21,300
Consideration paid and the fair value of assets acquired and liabilities assumed
Property and equipment				10,000
Identifiable intangible assets				4,200
Goodwill	$ 7,700			$ 7,100
Additional information
Weighted average amortization period				13 years
Amortization period of goodwill recognized and expected to be deductible for income tax purposes				15 years

BUSINESS COMBINATIONS - Additio

BUSINESS COMBINATIONS - Additional Information (Details) $ in Thousands, $ in Millions	Nov. 01, 2019USD ($)	Aug. 01, 2019USD ($)	Aug. 01, 2019CAD ($)	Nov. 14, 2018USD ($)	Aug. 31, 2018USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Acquisition
Goodwill						$ 766,980	$ 207,177	$ 189,373
Additional information
Acquisition-related costs included in selling, general and administrative expenses						26,150	748	500
Field and Industrial Services
Acquisition
Goodwill	$ 239,600					298,579	51,231	44,131
Environmental Services
Acquisition
Goodwill	308,900					475,271	162,816	$ 150,699
NRC
Acquisition
Acquisition price	1,024,833
Goodwill	548,485
Identifiable intangible assets	303,600
Property and equipment	$ 197,045
Additional information
Revenue since acquisition included in consolidated statements of operations						70,200
Operating loss since acquisition included in consolidated statements of operations						9,100
Acquisition-related costs included in selling, general and administrative expenses						24,400
US Ecology Sarnia
Acquisition
Percentage of outstanding shares acquired		100.00%
Acquisition price		$ 17,900	$ 23.5
Goodwill		7,700
Identifiable intangible assets		$ 6,200
Additional information
Weighted average amortization period		14 years	14 years
ES&H Dallas
Acquisition
Payment to acquire business					$ 21,300
Goodwill		$ 7,700			7,100
Identifiable intangible assets					4,200
Property and equipment					$ 10,000
Additional information
Weighted average amortization period					13 years
Amortization period of goodwill recognized and expected to be deductible for income tax purposes					15 years
Winnie
Acquisition
Payment to acquire business						87,228	87,129
Acquisition price				$ 87,200
Goodwill				16,400		16,436	13,573
Identifiable intangible assets				$ 66,500		66,500	66,600
Property and equipment						$ 3,699	$ 6,300
Additional information
Amortization period of goodwill recognized and expected to be deductible for income tax purposes				15 years
Winnie | Credit agreement
Acquisition
Amount of term loan which was used to funded acquisition				$ 87,000
Winnie | Customer relationships
Acquisition
Identifiable intangible assets				$ 11,800
Additional information
Weighted average amortization period				15 years
Winnie | Permit
Acquisition
Identifiable intangible assets				$ 54,700
Additional information
Weighted average amortization period				60 years

ACCUMULATED OTHER COMPREHENSI_3

ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Changes in AOCI (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated other comprehensive income (loss)
Beginning balances	$ 359,217	$ 324,077	$ 280,024
Other comprehensive income, (loss), net	1,937	(4,687)	5,621
Ending balances	1,011,380	359,217	324,077
Foreign Currency Translation
Accumulated other comprehensive income (loss)
Beginning balances	(14,697)	(8,603)
Other comprehensive income (loss) before reclassifications, net of tax	3,772	(6,094)
Other comprehensive income, (loss), net	3,772	(6,094)
Ending balances	(10,925)	(14,697)	(8,603)
Unrealized Gain (Loss) on Interest Rate Hedge
Accumulated other comprehensive income (loss)
Beginning balances	906	(501)
Other comprehensive income (loss) before reclassifications, net of tax	(1,700)	1,111
Amounts reclassified out of AOCI, net of tax	(135)	296
Other comprehensive income, (loss), net	(1,835)	1,407
Ending balances	(929)	906	(501)
Accumulated Other Comprehensive Income (Loss)
Accumulated other comprehensive income (loss)
Beginning balances	(13,791)	(9,104)	(14,725)
Other comprehensive income (loss) before reclassifications, net of tax	2,072	(4,983)
Amounts reclassified out of AOCI, net of tax	(135)	296
Other comprehensive income, (loss), net	1,937	(4,687)	5,621
Ending balances	$ (11,854)	$ (13,791)	$ (9,104)

ACCUMULATED OTHER COMPREHENSI_4

ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) -Reclassifications Line Items (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reclassification adjustments
Interest expense	$ 19,239,000	$ 12,130,000	$ 18,157,000
Unrealized Gain (Loss) on Interest Rate Hedge | Interest rate swap agreement
Reclassification adjustments
Amounts in AOCI expected to be recognized over the next 12 months before tax	523,000
Amounts in AOCI expected to be recognized over the next 12 months, net of taxes	413,000
Unrealized Gain (Loss) on Interest Rate Hedge | Interest rate swap agreement | Reclassification out of accumulated other comprehensive income
Reclassification adjustments
Interest expense	170,000	375,000
Interest expense, net of tax	$ 135,000	$ 296,000

DISCLOSURE OF SUPPLEMENTAL CA_3

DISCLOSURE OF SUPPLEMENTAL CASH FLOW INFORMATION (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income taxes and interest paid:
Income taxes paid, net of receipts	$ 14,777	$ 19,580	$ 10,714
Interest paid	17,204	11,246	11,364
Non-cash investing and financing activities:
Closure/Post-closure retirement asset	(221)	99	(352)
Capital expenditures in accounts payable	2,882	1,601	2,302
Acquisition of equipment with financing arrangements	2,481	747	531
Restricted stock issued from treasury shares	514	$ 11	$ 105
NRC
Non-cash investing and financing activities:
Fair value of equity issued for acquisition of NRC	$ 626,460

FAIR VALUE MEASUREMENTS (Detail

FAIR VALUE MEASUREMENTS (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 19, 2019	Dec. 31, 2018	Dec. 31, 2014
Assets measured at fair value on a recurring basis
Initial notional amount	$ 250,000			$ 250,000
Equity securities without readily determinable fair value
Variable rate	454,500
Preferred Stock | Other Assets
Equity securities without readily determinable fair value
Investment in privately held company		$ 7,900
Level 3 | Contingent Consideration | Accrued Liabilities
Assets measured at fair value on a recurring basis
Liabilities fair value disclosure	6,600
Level 3 | Contingent Consideration | Other long-term liabilities
Assets measured at fair value on a recurring basis
Liabilities fair value disclosure	1,700
Recurring
Assets measured at fair value on a recurring basis
Assets fair value disclosure	5,069		$ 6,088
Liabilities fair value disclosure	9,459
Recurring | Interest rate swap agreement
Assets measured at fair value on a recurring basis
Assets fair value disclosure			1,147
Liabilities fair value disclosure	1,176
Recurring | Fixed-income securities
Assets measured at fair value on a recurring basis
Assets fair value disclosure	4,210		4,157
Recurring | Money market funds
Assets measured at fair value on a recurring basis
Assets fair value disclosure	859		784
Recurring | Contingent Consideration
Assets measured at fair value on a recurring basis
Liabilities fair value disclosure	8,283
Recurring | Quoted Prices in Active Markets (Level 1)
Assets measured at fair value on a recurring basis
Assets fair value disclosure	3,239		2,345
Recurring | Quoted Prices in Active Markets (Level 1) | Fixed-income securities
Assets measured at fair value on a recurring basis
Assets fair value disclosure	2,380		1,561
Recurring | Quoted Prices in Active Markets (Level 1) | Money market funds
Assets measured at fair value on a recurring basis
Assets fair value disclosure	859		784
Recurring | Other Observable Inputs (Level 2)
Assets measured at fair value on a recurring basis
Assets fair value disclosure	1,830		3,743
Liabilities fair value disclosure	1,176
Recurring | Other Observable Inputs (Level 2) | Interest rate swap agreement
Assets measured at fair value on a recurring basis
Assets fair value disclosure			1,147
Liabilities fair value disclosure	1,176
Recurring | Other Observable Inputs (Level 2) | Fixed-income securities
Assets measured at fair value on a recurring basis
Assets fair value disclosure	1,830		$ 2,596
Recurring | Level 3
Assets measured at fair value on a recurring basis
Liabilities fair value disclosure	8,283
Recurring | Level 3 | Contingent Consideration
Assets measured at fair value on a recurring basis
Liabilities fair value disclosure	$ 8,283

FAIR VALUE MEASUREMENTS - Chang

FAIR VALUE MEASUREMENTS - Changes in Level 3 liabilities measured at fair value (Details) - Level 3 - Recurring $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of contingent consideration acquired	$ 11,859
Change in fair value of contingent consideration	349
Foreign currency translation	(75)
Contingent consideration paid	(4,000)
Balance at end of period	$ 8,283

CONCENTRATIONS AND CREDIT RISK

CONCENTRATIONS AND CREDIT RISK (Details)	12 Months Ended
	Dec. 31, 2019employee
Workforce Subject to Collective Bargaining Arrangements
CONCENTRATIONS AND CREDIT RISK
Number of employees covered under collective bargaining agreements	523
Workforce Subject to Collective Bargaining Arrangements | Labor Force Concentration Risk
CONCENTRATIONS AND CREDIT RISK
Concentration of risk (as a percent)	14.00%
Workforce Subject to Collective Bargaining Arrangements Expiring within One Year | Labor Force Concentration Risk
CONCENTRATIONS AND CREDIT RISK
Concentration of risk (as a percent)	37.00%

RECEIVABLES (Details)

RECEIVABLES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018
RECEIVABLES
Trade				$ 196,593	$ 118,909
Unbilled revenue				54,727	26,538
Other				7,000	2,241
Total receivables				258,320	147,688
Allowance for doubtful accounts	$ (2,998)	$ (2,998)	$ (2,334)	(3,010)	(2,998)
Receivables, net				$ 255,310	$ 144,690
Change in the allowance for doubtful accounts receivable
Balance at Beginning of Period	2,998	2,796	2,334
Charged (Credited) to Costs and Expenses	226	436	704
Recoveries (Deductions/Write-offs)	(439)	(213)	(255)
Adjustments	225	(21)	13
Balance at End of Period	$ 3,010	$ 2,998	$ 2,796

PROPERTY AND EQUIPMENT (Details

PROPERTY AND EQUIPMENT (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
PROPERTY AND EQUIPMENT
Total property and equipment	$ 733,358	$ 473,861
Accumulated depreciation and amortization	(254,590)	(215,418)
Property and equipment, net	478,768	258,443
Depreciation and amortization of plant and equipment	41,423	29,207	$ 28,302
Cell development costs
PROPERTY AND EQUIPMENT
Total property and equipment	174,561	146,155
Land and improvements
PROPERTY AND EQUIPMENT
Total property and equipment	52,909	50,481
Buildings and improvements
PROPERTY AND EQUIPMENT
Total property and equipment	109,580	91,358
Railcars
PROPERTY AND EQUIPMENT
Total property and equipment	17,299	17,299
Vehicles, vessels and other equipment
PROPERTY AND EQUIPMENT
Total property and equipment	317,472	154,014
Construction in progress
PROPERTY AND EQUIPMENT
Total property and equipment	$ 61,537	$ 14,554

LEASES (Details)

LEASES (Details)	12 Months Ended
	Dec. 31, 2019
Leases
Operating lease - existence of option to renew	true
Finance lease - existence of option to renew	true
Minimum
Leases
Operating lease - term	1 year
Finance lease - term	1 year
Maximum
Leases
Operating lease - term	15 years
Operating lease - renewal term	40 years
Finance lease - term	15 years
Finance lease - renewal term	40 years

LEASES - Leased assets and liab

LEASES - Leased assets and liabilities (Details) $ in Thousands	Dec. 31, 2019USD ($)
Assets:
Operating lease assets	$ 57,396
Finance right-of-use lease assets	$ 20,499
Finance Lease, Right-of-Use Asset	us-gaap:PropertyPlantAndEquipmentNet
Total	$ 77,895
Finance leased assets - accumulated amortization	2,700
Liabilities:
Operating lease, current	17,317
Finance lease, current	$ 4,128
Finance Lease, Liability, Current	us-gaap:AccruedLiabilitiesCurrent
Long-term operating lease liabilities	$ 39,954
Finance lease, long term	$ 16,308
Finance Lease, Liability, Noncurrent	us-gaap:OtherLiabilitiesNoncurrent
Total	$ 77,707

LEASES - Lease cost (Details)

LEASES - Lease cost (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)
Lease cost
Operating lease cost	$ 9,144
Amortization of leased assets	1,641
Interest on lease liabilities	332
Total	$ 11,117

LEASES - Supplemental Cash Flow

LEASES - Supplemental Cash Flow information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)
LEASES
Operating cash flows from operating leases	$ 8,656
Operating cash flows from finance leases	332
Financing cash flows from finance leases	1,298
Right-of-use assets obtained in exchange for new operating lease liabilities	7,380
Right-of-use assets obtained in exchange for new finance lease liabilities	$ 2,481

LEASES - Weighted-average remai

LEASES - Weighted-average remaining lease term and discount rate (Details)	Dec. 31, 2019
LEASES
Weighted-average remaining lease term, operating leases	4 years 4 months 24 days
Weighted-average remaining lease term, finance leases	4 years 6 months
Weighted-average discount rate, operating leases	3.80%
Weighted-average discount rate, finance leases	5.07%

LEASES - Maturity analysis of o

LEASES - Maturity analysis of operating and finance lease liabilities (Details) $ in Thousands	Dec. 31, 2019USD ($)
Operating Leases
2020	$ 18,007
2021	14,935
2022	11,210
2023	8,643
2024	4,885
Thereafter	5,025
Total	62,705
Less: Interest	5,434
Present Value of Lease Liabilities	57,271
Finance Leases
2020	4,742
2021	4,699
2022	4,315
2023	4,400
2024	2,714
Thereafter	2,853
Total	23,723
Less: Interest	3,287
Present Value of Lease Liabilities	20,436
Operating And Finance Leases
2020	22,749
2021	19,634
2022	15,525
2023	13,043
2024	7,599
Thereafter	7,878
Total	86,428
Less: Interest	8,721
Present Value of Lease Liabilities	$ 77,707

LEASES - Future minimum lease p

LEASES - Future minimum lease payments on non-cancellable operating leases (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Future minimum lease payments on non-cancellable operating leases
2019	$ 5,638
2020	3,644
2021	3,184
2022	1,885
2023	1,457
Thereafter	5,065
Total	20,873
Rental expense under operating leases	$ 7,400	$ 7,600

GOODWILL AND INTANGIBLE ASSET_2

GOODWILL AND INTANGIBLE ASSETS - Goodwill (Details) - USD ($) $ in Thousands	Nov. 14, 2018	Aug. 31, 2018	Sep. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Nov. 01, 2019	Aug. 01, 2019	Dec. 31, 2018	Nov. 14, 2018	Aug. 31, 2018
Changes in goodwill
Balance at the beginning of the period				$ 207,177	$ 189,373
Goodwill				207,177	189,373	$ 766,980			$ 207,177
Foreign currency translation				787	(1,456)
Balance at the end of the period				766,980	207,177
Accumulated Impairment
Impairment charges					(1,413)
ES&H Dallas
Changes in goodwill
Goodwill		$ 7,100						$ 7,700			$ 7,100
Acquisition		7,100			7,100
Balance at the end of the period		$ 7,100
Identifiable intangible assets											$ 4,200
NRC
Changes in goodwill
Goodwill							$ 548,485
Acquisition				548,485
Identifiable intangible assets							303,600
Total identified intangible assets							246,200
NRC | Permits and licenses
Changes in goodwill
Non-amortizing intangible assets							57,400
US Ecology Sarnia
Changes in goodwill
Goodwill								7,700
Acquisition				7,668
Identifiable intangible assets								$ 6,200
Winnie
Changes in goodwill
Balance at the beginning of the period				13,573
Purchase price allocation adjustment				2,863
Goodwill	$ 16,400			16,436	13,573	16,436			13,573	$ 16,400
Acquisition	16,400				13,573
Balance at the end of the period	$ 16,400			16,436	13,573
Identifiable intangible assets						66,500			66,600	$ 66,500
Environmental Services
Changes in goodwill
Balance at the beginning of the period				162,816	150,699
Goodwill				475,271	162,816	475,271	308,900		162,816
Foreign currency translation				736	(1,456)
Balance at the end of the period				475,271	162,816
Accumulated Impairment
Accumulated impairment at the beginning				(6,870)	(5,457)
Impairment charges					(1,413)
Accumulated impairment at the ending				(6,870)	(6,870)
Environmental Services | NRC
Changes in goodwill
Acquisition				308,856
Environmental Services | Winnie
Changes in goodwill
Purchase price allocation adjustment				2,863
Acquisition					13,573
Environmental Services | Mobile Recycling
Accumulated Impairment
Impairment charges			$ (1,400)
Field and Industrial Services
Changes in goodwill
Balance at the beginning of the period				51,231	44,131
Goodwill				298,579	51,231	$ 298,579	$ 239,600		$ 51,231
Foreign currency translation				51
Balance at the end of the period				298,579	51,231
Field and Industrial Services | ES&H Dallas
Changes in goodwill
Acquisition					$ 7,100
Field and Industrial Services | NRC
Changes in goodwill
Acquisition				239,629
Field and Industrial Services | US Ecology Sarnia
Changes in goodwill
Acquisition				$ 7,668

GOODWILL AND INTANGIBLE ASSET_3

GOODWILL AND INTANGIBLE ASSETS - Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2019	Sep. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Nov. 01, 2019	Aug. 01, 2019	Nov. 14, 2018	Aug. 31, 2018
Intangible Assets
Amortizing intangible assets, Cost	$ 537,709		$ 537,709	$ 284,041
Accumulated amortization	(66,753)		(66,753)	(50,891)
Amortizing intangible assets, Net	470,956		470,956	233,150
Total intangible assets, cost	641,655		641,655	330,557
Total intangible assets, net	574,902		574,902	279,666
Indefinite lived intangible asset impairment	0
Amortization of intangible assets			15,491	9,645	$ 9,888
Goodwill	766,980		766,980	207,177	189,373
Permits and licenses
Intangible Assets
Non-amortizing intangible assets	103,816		103,816	46,391
Tradename
Intangible Assets
Non-amortizing intangible assets	130		130	125
Permits, licenses and lease
Intangible Assets
Amortizing intangible assets, Cost	174,339		174,339	164,840
Accumulated amortization	(18,707)		(18,707)	(14,804)
Amortizing intangible assets, Net	155,632		155,632	150,036
Customer relationships
Intangible Assets
Amortizing intangible assets, Cost	333,090		333,090	99,241
Accumulated amortization	(35,254)		(35,254)	(25,676)
Amortizing intangible assets, Net	297,836		297,836	73,565
Technology - formulae and processes
Intangible Assets
Amortizing intangible assets, Cost	6,964		6,964	6,672
Accumulated amortization	(2,013)		(2,013)	(1,714)
Amortizing intangible assets, Net	4,951		4,951	4,958
Customer backlog
Intangible Assets
Amortizing intangible assets, Cost	3,652		3,652	3,652
Accumulated amortization	(2,022)		(2,022)	(1,656)
Amortizing intangible assets, Net	1,630		1,630	1,996
Tradename
Intangible Assets
Amortizing intangible assets, Cost	10,390		10,390	4,290
Accumulated amortization	(4,832)		(4,832)	(4,290)
Amortizing intangible assets, Net	5,558		5,558
Developed software
Intangible Assets
Amortizing intangible assets, Cost	2,895		2,895	2,884
Accumulated amortization	(1,884)		(1,884)	(1,581)
Amortizing intangible assets, Net	1,011		1,011	1,303
Non-compete agreements
Intangible Assets
Amortizing intangible assets, Cost	5,455		5,455	1,542
Accumulated amortization	(1,694)		(1,694)	(875)
Amortizing intangible assets, Net	3,761		3,761	667
Internet domain and website
Intangible Assets
Amortizing intangible assets, Cost	536		536	536
Accumulated amortization	(156)		(156)	(128)
Amortizing intangible assets, Net	380		380	408
Database
Intangible Assets
Amortizing intangible assets, Cost	388		388	384
Accumulated amortization	(191)		(191)	(167)
Amortizing intangible assets, Net	197		197	217
ES&H Dallas
Intangible Assets
Goodwill							$ 7,700		$ 7,100
Winnie
Intangible Assets
Goodwill	16,436		16,436	13,573				$ 16,400
US Ecology Sarnia
Intangible Assets
Goodwill							$ 7,700
Environmental Services
Intangible Assets
Goodwill	475,271		475,271	162,816	150,699	$ 308,900
Field and Industrial Services
Intangible Assets
Goodwill	$ 298,579		$ 298,579	$ 51,231	$ 44,131	$ 239,600
Mobile Recycling | Environmental Services
Intangible Assets
Impairment of intangible assets		$ 2,300

GOODWILL AND INTANGIBLE ASSET_4

GOODWILL AND INTANGIBLE ASSETS - Future amortization expense (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Expected future amortization expense of amortizing intangible assets
2020	$ 36,737
2021	33,948
2022	30,840
2023	30,684
2024	30,302
Thereafter	308,445
Amortizing intangible assets, Net	$ 470,956	$ 233,150

EMPLOYEE BENEFIT PLANS (Details

EMPLOYEE BENEFIT PLANS (Details)	12 Months Ended
	Dec. 31, 2019USD ($)plan	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
The Plan
Defined contribution plans
Entity's matching contribution (as a percent)	55.00%
Company's contribution as a percentage of eligible compensation	6.00%
Entity's matching contributions to the Plan	$ 3,000,000	$ 2,500,000	$ 2,100,000
NRC Savings And Retirement Plan [Member]
Defined contribution plans
Entity's matching contribution (as a percent)	50.00%
Company's contribution as a percentage of eligible compensation	6.00%
Entity's matching contributions to the Plan	$ 325,000
NRC Savings And Retirement Plan [Member] | Maximum
Defined contribution plans
Employer Matching Contribution Deferred Amount, Percent Of Employees' Gross Pay	25.00%
The SPP
Defined contribution plans
Entity's matching contributions to the Plan	$ 692,000	653,000	$ 556,000
Multi-employer defined benefit pension plans
Defined contribution plans
Number of multi-employer plans | plan	5
Communications, Energy and Paperworkers Union of Canada
Defined contribution plans
Company's contribution as a percentage of eligible compensation	9.00%
Labor Force Concentration Risk | The SPP
Defined contribution plans
Company's contribution as a percentage of eligible compensation	5.00%
Labor Force Concentration Risk | The SPP | Maximum
Defined contribution plans
Entity's matching contribution (as a percent)	2.00%
Operating Engineers Local 324 Pension Fund
Defined contribution plans
Total contributions made	$ 1,000,000	1,000,000
Contributions to multi-employer plans not individually significant
Defined contribution plans
Total contributions made	$ 281,000	$ 242,000

CLOSURE AND POST-CLOSURE OBLI_3

CLOSURE AND POST-CLOSURE OBLIGATIONS (Details) - Surety bond $ in Millions	12 Months Ended
	Dec. 31, 2019USD ($)
Closure obligations
Period for which the guarantee obligation is required to be maintained	25 years
Carrying value of Commercial bonds dedicated for closure obligations	$ 12.8

CLOSURE AND POST-CLOSURE OBLI_4

CLOSURE AND POST-CLOSURE OBLIGATIONS - FAIR VALUE ASSUMPTIONS (Details) - Asset retirement obligations	12 Months Ended
	Dec. 31, 2019
Fair value of future asset retirement obligations
Estimated inflation rate (as a percent)	2.60%
Risk free rate | Weighted-average
Fair value of future asset retirement obligations
Measurement input	5.9

CLOSURE AND POST-CLOSURE OBLI_5

CLOSURE AND POST-CLOSURE OBLIGATIONS - Rollforward (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Changes to reported closure and post-closure obligations
Closure and post-closure obligations, beginning of period	$ 78,363,000	$ 76,088,000
Liabilities assumed in the NRC Merger	5,691,000
Accretion expense	4,388,000	3,707,000	$ 3,026,000
Payments	(1,913,000)	(1,388,000)
Adjustments	(221,000)	99,000
Foreign currency translation	75,000	(143,000)
Closure and post-closure obligations, end of period	86,383,000	78,363,000	$ 76,088,000
Less current portion	(2,152,000)	(2,266,000)
Long-term portion	84,231,000	76,097,000
Additions or adjustments to closure and post-closure asset	(221,000)	99,000
Grand View, Idaho | Operating disposal facilities
Changes to reported closure and post-closure obligations
Adjustments		(1,100,000)
Belleville, Michigan | Operating disposal facilities
Changes to reported closure and post-closure obligations
Adjustments		472,000
Winnie | Operating disposal facilities
Changes to reported closure and post-closure obligations
Adjustments		$ 511,000
Robstown Texas Operating Facility
Changes to reported closure and post-closure obligations
Additions or adjustments to closure and post-closure asset	(393,000)
Blainville, Quebec, Canada
Changes to reported closure and post-closure obligations
Additions or adjustments to closure and post-closure asset	(272,000)
Increase to the obligation	$ 422,000

CLOSURE AND POST-CLOSURE OBLI_6

CLOSURE AND POST-CLOSURE OBLIGATIONS - CHANGES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Changes in the reported closure and post-closure asset, recorded as a component of Property and equipment, net
Net closure and post-closure asset, beginning of year	$ 19,510	$ 20,495
Asset Acquired In NRC Merger	4,857
Amortization of closure and post-closure asset	(1,298)	(805)
Foreign currency translation	36	(279)
Net closure and post-closure asset, end of year	$ 22,884	$ 19,510

DEBT - Schedule (Details)

DEBT - Schedule (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Long-term debt
Loan amount	$ 777,000
Unamortized discount and debt issuance costs	(7,799)
Total debt	769,201	$ 364,000
Current portion of long-term debt	(3,359)
Long-term debt	765,842	364,000
Credit agreement
Long-term debt
Loan amount	327,000	$ 364,000
Term Loan
Long-term debt
Loan amount	450,000
Unamortized discount and debt issuance costs	$ (7,800)

DEBT - Future Maturities (Detai

DEBT - Future Maturities (Details) $ in Thousands	Dec. 31, 2019USD ($)
Future maturities of long-term debt, excluding unamortized net discount
2020	$ 4,500
2021	4,500
2022	4,500
2023	4,500
2024	331,500
Thereafter	427,500
Term loan	$ 777,000

DEBT - Paragraph (Details)

DEBT - Paragraph (Details) $ in Thousands	Nov. 01, 2019USD ($)	Aug. 06, 2019	Apr. 18, 2017USD ($)	Jun. 17, 2014USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2018USD ($)	Apr. 17, 2017USD ($)
DEBT
Loan amount					$ 777,000
Sweep Arrangements
DEBT
Advances outstanding					0
Interest Expense.
DEBT
Amortization of Financing Costs and Discounts						$ 5,500
2014 Credit Agreement
DEBT
Maximum borrowing capacity				$ 540,000
Early termination penalties incurred			$ 0
2014 Term Loan
DEBT
Maximum borrowing capacity				$ 415,000
Amount outstanding								$ 278,300
2014 Term Loan | LIBOR
DEBT
Percentage points added to the reference rate				3.00%
2014 Term Loan | Base rate
DEBT
Percentage points added to the reference rate				2.00%
2014 Revolving Credit Facility
DEBT
Maximum borrowing capacity				$ 125,000
Amount outstanding								$ 0
2014 Letter of credit
DEBT
Maximum borrowing capacity				$ 50,000
Credit agreement
DEBT
Maximum borrowing capacity			$ 500,000
Loan amount					$ 327,000		$ 364,000
Contractual term			5 years
Accordion feature	$ 250,000		$ 200,000
Percentage of EBITDA plus certain additional amounts used to determine additional borrowing capacity	100.00%
Effective interest rate (as a percent)					3.98%
Amount of debt hedged					$ 150,000
Debt instrument, aggregate annual amortization as a percentage of original principal amount					46.00%
Availability for borrowings under line of credit					$ 166,300
Equity interest in domestic subsidiaries pledged as security (as a percent)			100.00%
Voting equity interest in foreign subsidiaries pledged as security (as a percent)			100.00%
Non-voting equity interest in foreign subsidiaries pledged as security (as a percent)			65.00%
Minimum consolidated senior secured leverage ratio			3
Total leverage ratio		4	4
Credit agreement | Minimum
DEBT
Commitment fee (as a percent)					0.175%
Credit agreement | Maximum
DEBT
Commitment fee (as a percent)					0.35%
Credit agreement | Equal To Or Greater Than 3.25 to 1.00
DEBT
Minimum consolidated senior secured leverage ratio			3.25
Credit agreement | Equal To Or Greater Than 2.50 to 1.00, But Less Than 3.25 to 1.00
DEBT
Minimum consolidated senior secured leverage ratio			2.50
Maximum consolidated senior secured leverage ratio			3.25
Credit agreement | Equal To Or Greater Than 1.75 to 1.00, But Less Than 2.50 to 1.00
DEBT
Minimum consolidated senior secured leverage ratio			1.75
Maximum consolidated senior secured leverage ratio			2.50
Credit agreement | Equal To Or Greater Than 1.00 to 1.00, But Less Than 1.75 to 1.00
DEBT
Minimum consolidated senior secured leverage ratio			1
Maximum consolidated senior secured leverage ratio			1.75
Credit agreement | Less Than 1.00 to 1.00
DEBT
Maximum consolidated senior secured leverage ratio			1
Credit agreement | LIBOR | Equal To Or Greater Than 3.25 to 1.00
DEBT
Percentage points added to the reference rate					2.00%
Credit agreement | LIBOR | Equal To Or Greater Than 2.50 to 1.00, But Less Than 3.25 to 1.00
DEBT
Percentage points added to the reference rate					1.75%
Credit agreement | LIBOR | Equal To Or Greater Than 1.75 to 1.00, But Less Than 2.50 to 1.00
DEBT
Percentage points added to the reference rate					1.50%
Credit agreement | LIBOR | Equal To Or Greater Than 1.00 to 1.00, But Less Than 1.75 to 1.00
DEBT
Percentage points added to the reference rate					1.25%
Credit agreement | LIBOR | Less Than 1.00 to 1.00
DEBT
Percentage points added to the reference rate					1.00%
Credit agreement | Base rate | Equal To Or Greater Than 3.25 to 1.00
DEBT
Percentage points added to the reference rate					1.00%
Credit agreement | Base rate | Equal To Or Greater Than 2.50 to 1.00, But Less Than 3.25 to 1.00
DEBT
Percentage points added to the reference rate					0.75%
Credit agreement | Base rate | Equal To Or Greater Than 1.75 to 1.00, But Less Than 2.50 to 1.00
DEBT
Percentage points added to the reference rate					0.50%
Credit agreement | Base rate | Equal To Or Greater Than 1.00 to 1.00, But Less Than 1.75 to 1.00
DEBT
Percentage points added to the reference rate					0.25%
Credit agreement | Base rate | Less Than 1.00 to 1.00
DEBT
Percentage points added to the reference rate					0.00%
Credit Agreement, Letter Of Credit
DEBT
Maximum borrowing capacity			$ 75,000
Line of credit issued in the form of a standby letters of credit					$ 6,700
Credit Agreement, Swingline Loans
DEBT
Maximum borrowing capacity	$ 40,000		$ 40,000
Credit Agreement, Swingline Loans | Sweep Arrangements
DEBT
Maximum borrowing capacity					40,000
Incremental Term Loans
DEBT
Increase in capacity	50,000
Maximum borrowing capacity	$ 450,000
Loan amount					$ 400,000
Contractual term	7 years
Required annual principal repayment (as a percent)	1.00%
Effective interest rate					4.45%
Incremental Term Loans | LIBOR
DEBT
Percentage points added to the reference rate	2.25%
Incremental Term Loans | LIBOR | Step Up Rate Based on Credit Ratings
DEBT
Percentage points added to the reference rate	2.50%
Incremental Term Loans | Base rate
DEBT
Percentage points added to the reference rate	1.25%
Incremental Term Loans | Base rate | Step Up Rate Based on Credit Ratings
DEBT
Percentage points added to the reference rate	1.50%

INCOME TAXES (Details)

INCOME TAXES (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Domestic and foreign components of Income (loss) before income taxes
Domestic		$ 30,706	$ 46,147	$ 26,051
Foreign		19,093	18,711	16,919
Income before income taxes		49,799	64,858	42,970
Current:
U.S. Federal		3,120	2,239	11,157
State		1,547	2,368	2,482
Foreign		5,426	4,746	5,398
Total current		10,093	9,353	19,037
Deferred:
U.S. Federal		5,977	5,675	(27,029)
State		714	172	2,323
Foreign		(125)	63	(726)
Total deferred		6,566	5,910	(25,432)
Income tax (benefit) expense		$ 16,659	15,263	$ (6,395)
Net income tax (benefit) expense	$ (23,800)
Tax benefit related to the remeasurement of certain deferred tax assets and liabilities	(25,200)
Foreign earnings	$ 1,400
Tax benefit from the 2017 Tax Act			193
Benefit from re-measurement of certain deferred tax assets and liabilities			2,200
Adjustments to the transition tax			$ 2,000
Reconciliation between the effective income tax rate and the applicable statutory federal and state income tax rate
Taxes computed at federal statutory rate		21.00%	21.00%	35.00%
Impairment and loss on divestiture			0.50%	4.40%
State income taxes (net of federal income tax benefit)		5.70%	5.10%	2.90%
Share-based compensation		(0.40%)	(1.30%)
Research and development credits		(0.80%)	(2.00%)
Non-deductible transaction costs		3.40%
Global intangible low taxed income		1.10%
Tax Cuts and Jobs Act of 2017			(0.30%)	(55.40%)
Foreign rate differential		2.50%	1.70%	(2.90%)
State deferred rate differential		(1.60%)
Other		2.60%	(1.20%)	1.10%
Total (as a percent)		33.50%	23.50%	(14.90%)

INCOME TAXES - DEFERRED TAX ASS

INCOME TAXES - DEFERRED TAX ASSETS AND LIABILITIES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Net operating losses	$ 14,121
Operating leases	14,034
Foreign tax credit and capital loss carry forwards	4,705	$ 5,165
Accruals, allowances and other	8,966	5,041
Environmental compliance and other site related costs	9,203	8,580
Business interest expense	6,498
Unrealized foreign exchange gains and losses	962	1,550
Total deferred tax assets	58,489	20,336
Less: valuation allowance	(4,965)	(4,791)
Net deferred tax assets	53,524	15,545
Deferred tax liabilities:
Property and equipment	(53,540)	(26,145)
Intangible assets	(112,446)	(51,081)
Operating leases	(14,034)
Unrealized gains and losses on interest rate hedge		(241)
Other	(1,849)	(1,284)
Total deferred tax liabilities	(181,869)	(78,751)
Net deferred tax liability	(128,345)	(63,206)
Valuation allowance increased	174
Accumulated undistributed earnings generated by foreign subsidiaries	49,000
Foreign
Deferred tax liabilities:
Operating Loss Carryforwards	2,700
State
Deferred tax liabilities:
Valuation allowance for certain deferred tax assets	260	$ 73
Operating Loss Carryforwards	42,400
Federal
Deferred tax liabilities:
Operating Loss Carryforwards	92,300
NRC
Deferred tax liabilities:
State and local net operating loss carry forward	43,800
Federal net operating loss carry forward	95,100
Business Interest expense carryforwards	$ 38,200

INCOME TAXES - DOMESTIC AND FOR

INCOME TAXES - DOMESTIC AND FOREIGN COMPONENTS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Changes to unrecognized tax benefits (excluding related penalties and interest)
Unrecognized tax benefits, beginning of year	$ 555
Gross increases - tax positions in prior period	8,088	$ 494
Gross decreases - tax positions in prior period	(9)
Gross increases - tax positions in current period	52	61
Settlements	(284)
Lapse of statute of limitations	(67)
Unrecognized tax benefits, end of year	8,335	$ 555
Change in net operating losses deferred tax asset	(8,100)
Unrecognized tax benefits, if recognized, would favorably impact future earnings	236
Penalties accrued on unrecognized tax benefits	$ 0

COMMITMENTS AND CONTINGENCIES -

COMMITMENTS AND CONTINGENCIES - Litigation and Regulatory Proceedings (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Nov. 17, 2018item
Litigation and Regulatory Proceedings
Insurance proceeds from damaged property and equipment	$ 12,714		$ 1,313
Property insurance recoveries	12,366	$ 347	$ 1,313
Explosion at the Grand View, Idaho Facility
Litigation and Regulatory Proceedings
Number of fatalities | item				1
Insurance proceeds from damaged property and equipment	12,700
Property insurance recoveries	12,400
Continued limited operations insurance recoveries	5,000
Lost profits insurance recoveries	4,700
Occupational Safety and Health Review Commission
Litigation and Regulatory Proceedings
Estimated liability	$ 50

EQUITY - Equity Based Purchase

EQUITY - Equity Based Purchase Consideration (Details) - NRC $ in Millions	Nov. 01, 2019USD ($)shares
Business Acquisition [Line Items]
Purchase price in equity-based consideration | $	$ 626.5
Common Stock
Business Acquisition [Line Items]
Shares Issued	9,337,949
Warrants
Business Acquisition [Line Items]
Shares Issued	3,772,753
RSUs
Business Acquisition [Line Items]
Shares Issued	118,239
Stock options
Business Acquisition [Line Items]
Shares Issued	29,400

EQUITY - Stock Repurchase Progr

EQUITY - Stock Repurchase Program (Details) - USD ($) $ in Millions	Dec. 31, 2019	Jun. 01, 2016
Repurchase of Common Stock
Authorized repurchase amount of outstanding common stock		$ 25
Warrants
Repurchase of Common Stock
Authorized repurchase amount of outstanding common stock	$ 25

EQUITY - Omnibus Incentive Plan

EQUITY - Omnibus Incentive Plan (Details) - Omnibus Plan - shares	Dec. 31, 2019	May 27, 2015
Stock-Based Compensation Plans
Number of shares authorized for grant		1,500,000
Number of shares available for future grant	725,966

EQUITY - PSUs, Restricted Stock

EQUITY - PSUs, Restricted Stock and RSU (Details) - USD ($)	12 Months Ended			24 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018
Stock-Based Compensation Plans
Number of common stock shares each RSUs represents (in shares)	1
Assumptions used in Monte Carlo simulation
Common stock, shares issued	31,461,000	22,040,000		22,040,000
PSUs
Stock-Based Compensation Plans
Number of common shares each PSU represents (in shares)	1
Vesting period	3 years			3 years
Shares
Outstanding at the beginning of the year (in shares)	39,200
Granted (in shares)	17,111
Vested (in shares)	(13,600)
Outstanding at the end of the year (in shares)	42,711	39,200		39,200
Weighted Average Grant Date Fair Value
Outstanding at the beginning of the period (in dollars per share)	$ 55.48
Granted (in dollars per share)	58.20
Vested (in dollars per share)	41.22
Outstanding at the end of the period (in dollars per share)	$ 61.11	$ 55.48		$ 55.48
Additional disclosures
Total fair value of restricted stock vested	$ 58.20	$ 63.56	$ 62.45
Assumptions used in Monte Carlo simulation
Stock price on grant date	$ 58.40	$ 51	$ 49.15	$ 51
Expected term (years)	3 years	3 years	3 years
Expected volatility (as a percent)	30.00%	30.00%	31.00%
Risk-free interest rate (as a percent)	2.50%	2.00%	1.50%
Expected dividend yield (as a percent)	1.10%	1.40%	1.50%
Common stock, shares issued	19,414
PSUs | Minimum
Stock-Based Compensation Plans
Percentage payout rate	0.00%	0.00%		0.00%
PSUs | Maximum
Stock-Based Compensation Plans
Percentage payout rate	300.00%	200.00%		200.00%
Restricted stock
Stock-Based Compensation Plans
Vesting period	3 years
Shares
Outstanding at the beginning of the year (in shares)	74,988
Granted (in shares)	28,900
Vested (in shares)	(39,234)
Outstanding at the end of the year (in shares)	64,654	74,988		74,988
Weighted Average Grant Date Fair Value
Outstanding at the beginning of the period (in dollars per share)	$ 46.74
Granted (in dollars per share)	62.59
Vested (in dollars per share)	43.77
Outstanding at the end of the period (in dollars per share)	$ 55.62	$ 46.74		$ 46.74
Additional disclosures
Total fair value of restricted stock vested	$ 2,500,000	$ 2,200,000	$ 868,000
RSUs
Stock-Based Compensation Plans
Vesting period	3 years
Shares
Outstanding at the beginning of the year (in shares)	66,785
Granted (in shares)	151,263
Vested (in shares)	(85,014)
Cancelled, expired or forfeited (in shares)	(1,835)
Outstanding at the end of the year (in shares)	131,199	66,785		66,785
Weighted Average Grant Date Fair Value
Outstanding at the beginning of the period (in dollars per share)	$ 53.77
Granted (in dollars per share)	60.92
Vested (in dollars per share)	58.35
Cancelled, expired or forfeited (in dollars per share)	52.87
Outstanding at the end of the period (in dollars per share)	$ 59.05	$ 53.77		$ 53.77
Additional disclosures
Total fair value of restricted stock vested	$ 4,800,000	$ 967,000	$ 314,000
Director Plan | Restricted stock | Minimum | Non-employee directors
Stock-Based Compensation Plans
Vesting requirement condition, percentage of attendance in regularly scheduled board meetings	75.00%
Vesting requirement condition, percentage of attendance in regularly scheduled committee meetings that they are a member of	75.00%

EQUITY - Stock Options (Details

EQUITY - Stock Options (Details) - Stock options - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stock-Based Compensation Plans
Expiration term	10 years
Performance period	3 years
Shares
Outstanding at the beginning of the period (in shares)	236,503
Granted (in shares)	70,500
Exercised (in shares)	(11,875)
Cancelled, expired or forfeited (in shares)	(1,540)
Outstanding at the end of the period (in shares)	293,588	236,503
Exercisable at the end of the period (in shares)	212,527
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 44.93
Granted (in dollars per share)	58.75
Exercised (in dollars per share)	45.42
Cancelled, expired or forfeited (in dollars per share)	43.55
Outstanding at the end of the period (in dollars per share)	48.23	$ 44.93
Exercisable at the end of the period (in dollars per share)	$ 44.89
Aggregate Intrinsic Value
Outstanding at the end of the year (in dollars)	$ 2,841
Exercisable at the end of the year (in dollars)	$ 2,767
Weighted Average Remaining Contractual Term (Years)
Outstanding at the end of the year	6 years 1 month 6 days
Exercisable at the end of the year	5 years 2 months 12 days
Additional disclosures
Weighted average grant date fair value (in dollars per share)	$ 14.26	$ 11.64	$ 10.92
Intrinsic value of stock options exercised	$ 152	$ 6,600	$ 1,000
Number of options exercised via net share settlement	3,640
Assumptions used in Monte Carlo simulation
Expected term (years)	2 years 8 months 12 days	3 years 9 months 18 days	3 years 9 months 18 days
Expected volatility (as a percent)	30.00%	30.00%	31.00%
Risk-free interest rate (as a percent)	2.10%	2.00%	1.50%
Expected dividend yield (as a percent)	1.20%	1.50%	1.70%
Minimum | Non-employee directors
Stock-Based Compensation Plans
Vesting requirement condition, percentage of attendance in regularly scheduled board meetings	75.00%

EQUITY - Treasury Stock (Detail

EQUITY - Treasury Stock (Details)	12 Months Ended
	Dec. 31, 2019$ / sharesshares
Treasury Stock
Repurchase of common stock (in shares) | shares	14,462
Average cost of repurchase (in dollars per share) | $ / shares	$ 63.34
Restricted stock
Treasury Stock
Issuance of restricted stock from treasury stock (in shares) | shares	8,900
Average cost (in dollars per share) | $ / shares	$ 57.77

EQUITY - Share-based Compensati

EQUITY - Share-based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-Based Compensation Expense
Total share-based compensation	$ 9,261	$ 4,366	$ 3,933
Income tax benefit	(3,098)	(1,027)	(1,403)
Share-based compensation, net of tax	6,163	3,339	2,530
Tax benefits from stock options exercised	321	1,400	129
Unrecognized Share-Based Compensation Expense
Unrecognized compensation expense related to unvested share-based awards granted	$ 8,300
Weighted average remaining vesting period over which expense is expected to be recognized	2 years
Stock options
Share-Based Compensation Expense
Total share-based compensation	$ 575	727	1,141
Restricted stock
Share-Based Compensation Expense
Total share-based compensation	1,662	1,590	1,505
RSUs
Share-Based Compensation Expense
Total share-based compensation	6,193	1,324	716
Share-based Payment Arrangement, Accelerated Cost	3,700
PSUs
Share-Based Compensation Expense
Total share-based compensation	$ 831	$ 725	$ 571

EQUITY - Warrants (Details)

EQUITY - Warrants (Details)	12 Months Ended
	Dec. 31, 2019$ / sharesshares
Warrants
Number of warrants (in shares) | shares	3,772,753
Number of shares each warrant is entitled to purchase | shares	1
Exercise price	$ 58.67
Redemption price of warrants	$ 0.01
Minimum number of day for written prior notice for redemption	30 days
Share price of common stock required for redemption	$ 91.84
Number of trading days share price equals or exceeds required price within 30 consecutive trading days for redemption	20 days
Number of consecutive trading days	30 days

EARNINGS PER SHARE (Details)

EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
EARNINGS PER SHARE
Net income	$ (3,464)	$ 13,070	$ 15,491	$ 8,043	$ 13,705	$ 13,427	$ 13,220	$ 9,243	$ 33,140	$ 49,595	$ 49,365
Basic
Weighted average basic shares outstanding									23,521	21,888	21,758
Earnings per share-Basic (in dollars per share)									$ 1.41	$ 2.27	$ 2.27
Diluted
Net income, diluted									$ 33,140	$ 49,595	$ 49,365
Dilutive effect of share-based awards and warrants (in shares)									228	159	144
Weighted average diluted shares outstanding	27,916	22,231	22,208	22,197	22,109	22,099	22,024	21,957	23,749	22,047	21,902
Earnings (loss) per share-Diluted (in dollars per share)	$ (0.12)	$ 0.59	$ 0.70	$ 0.36	$ 0.62	$ 0.61	$ 0.60	$ 0.42	$ 1.40	$ 2.25	$ 2.25
Anti-dilutive shares excluded from calculation									90	46	103

SEGMENT REPORTING - Summarized

SEGMENT REPORTING - Summarized Financial Information (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019USD ($)	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2019USD ($)segment	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
OPERATING SEGMENTS
Number of reportable segments | segment									2
Revenue	$ 231,268	$ 167,402	$ 155,802	$ 131,037	$ 157,541	$ 151,416	$ 136,912	$ 120,059	$ 685,509	$ 565,928	$ 504,042
Depreciation, amortization and accretion									61,302	42,559	41,216
Capital expenditures									58,100	40,757	36,240
Total assets	2,231,244				947,898				2,231,244	947,898	802,076
Treatment and disposal
OPERATING SEGMENTS
Revenue									384,366	331,781
Transportation and Logistics
OPERATING SEGMENTS
Revenue									128,054	113,670
Remediation
OPERATING SEGMENTS
Revenue									13,288	10,139
Other
OPERATING SEGMENTS
Revenue									8,687	2,370
Corporate
OPERATING SEGMENTS
Depreciation, amortization and accretion									1,760	1,060	501
Capital expenditures									4,521	1,592	3,251
Total assets	75,400				77,565				75,400	77,565	67,792
Environmental Services | Operating Segment
OPERATING SEGMENTS
Revenue									453,107	400,678	366,308
Depreciation, amortization and accretion									44,535	35,195	35,137
Capital expenditures									47,593	31,735	28,783
Total assets	1,290,304				701,267				1,290,304	701,267	609,174
Environmental Services | Operating Segment | Treatment and disposal
OPERATING SEGMENTS
Revenue									365,886	320,045
Environmental Services | Operating Segment | Transportation and Logistics
OPERATING SEGMENTS
Revenue									87,221	80,633
Field and Industrial Services | Operating Segment
OPERATING SEGMENTS
Revenue									232,402	165,250	137,734
Depreciation, amortization and accretion									15,007	6,304	5,578
Capital expenditures									5,986	7,430	4,206
Total assets	$ 865,540				$ 169,066				865,540	169,066	$ 125,110
Field and Industrial Services | Operating Segment | Treatment and disposal
OPERATING SEGMENTS
Revenue									18,480	11,736
Field and Industrial Services | Operating Segment | Transportation and Logistics
OPERATING SEGMENTS
Revenue									40,833	33,037
Field and Industrial Services | Operating Segment | Remediation
OPERATING SEGMENTS
Revenue									13,288	10,139
Field and Industrial Services | Operating Segment | Other
OPERATING SEGMENTS
Revenue									$ 8,687	$ 2,370

SEGMENT REPORTING - Reconciliat

SEGMENT REPORTING - Reconciliation of EBITDA (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of Net Income to Adjusted EBITDA
Net income	$ (3,464)	$ 13,070	$ 15,491	$ 8,043	$ 13,705	$ 13,427	$ 13,220	$ 9,243	$ 33,140	$ 49,595	$ 49,365
Income tax expense (benefit)									16,659	15,263	(6,395)
Interest expense									19,239	12,130	18,157
Interest income									(605)	(215)	(62)
Foreign currency (gain) loss									733	(55)	(516)
Other income									(455)	(2,630)	(791)
Property and equipment impairment charges									25
Goodwill and intangible asset impairment charges										3,666	8,903
Depreciation and amortization of plant and equipment									41,423	29,207	28,302
Amortization of intangibles assets									15,491	9,645	9,888
Share-based compensation									5,544	4,366	3,933
Accretion and non-cash adjustment of closure & post-closure liabilities									4,388	3,707	3,026
Gain on property insurance recoveries									(12,366)	(347)	(1,313)
Business development and integration expenses									26,150	748	500
Adjusted EBITDA									149,366	125,080	112,997
Operating Segment | Environmental Services
Reconciliation of Net Income to Adjusted EBITDA
Adjusted EBITDA									187,759	160,179	145,058
Operating Segment | Field and Industrial Services
Reconciliation of Net Income to Adjusted EBITDA
Adjusted EBITDA									26,707	18,457	14,709
Corporate
Reconciliation of Net Income to Adjusted EBITDA
Adjusted EBITDA									$ (65,100)	$ (53,556)	$ (46,770)

SEGMENT REPORTING - Revenue and

SEGMENT REPORTING - Revenue and Long-lived Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Revenue and Long-Lived Assets Outside of the United States
Total long- lived assets	$ 1,053,670	$ 538,109
United States
Revenue and Long-Lived Assets Outside of the United States
Total long- lived assets	954,102	480,322
Canada
Revenue and Long-Lived Assets Outside of the United States
Total long- lived assets	70,691	$ 57,787
EMEA
Revenue and Long-Lived Assets Outside of the United States
Total long- lived assets	23,587
Other
Revenue and Long-Lived Assets Outside of the United States
Total long- lived assets	$ 5,290

QUARTERLY FINANCIAL DATA (una_3

QUARTERLY FINANCIAL DATA (unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
QUARTERLY FINANCIAL DATA (unaudited)
Revenue	$ 231,268	$ 167,402	$ 155,802	$ 131,037	$ 157,541	$ 151,416	$ 136,912	$ 120,059	$ 685,509	$ 565,928	$ 504,042
Gross profit	68,470	56,540	49,583	35,241	45,675	47,300	41,448	35,671	209,834	170,094	153,127
Operating income	5,030	23,211	25,534	14,936	20,372	19,985	20,292	13,439	68,711	74,088	59,758
Net income (loss)	$ (3,464)	$ 13,070	$ 15,491	$ 8,043	$ 13,705	$ 13,427	$ 13,220	$ 9,243	$ 33,140	$ 49,595	$ 49,365
Earnings (loss) per share-Diluted (in dollars per share)	$ (0.12)	$ 0.59	$ 0.70	$ 0.36	$ 0.62	$ 0.61	$ 0.60	$ 0.42	$ 1.40	$ 2.25	$ 2.25
Weighted average common shares outstanding used in the diluted earnings per share calculation	27,916	22,231	22,208	22,197	22,109	22,099	22,024	21,957	23,749	22,047	21,902
Dividends paid per share (in dollars per share)	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.72	$ 0.72

SUBSEQUENT EVENTS (Details)

SUBSEQUENT EVENTS (Details) - USD ($) $ / shares in Units, $ in Thousands	Jan. 24, 2020	Jan. 02, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Subsequent events
Quarterly dividend declared (in dollars per share)			$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.72	$ 0.72
Dividend paid in cash											$ 15,890	$ 15,804	$ 15,711
Subsequent events
Subsequent events
Quarterly dividend declared (in dollars per share)		$ 0.18
Dividend paid in cash	$ 5,700