SIGNIFICANT ACCOUNTING POLICIES (Tables)

12 Months Ended

Dec. 31, 2016

Schedule of Asset Classification and Estimated Useful Life

The Company depreciates and amortizes the cost of these assets, using the straight-line method as follows:



Asset Classification		Estimated Useful Life
Buildings and building improvements
Buildings		30–42 years
Leasehold and building improvements		2–45 years
Camp equipment		8–15 years
Vehicles		3–15 years
Equipment
Capitalized software and computer equipment		3–5 years
Solar equipment		30 years
Containers and railcars		15–20 years
All other equipment		8–25 years
Furniture and fixtures		5–8 years

Property, plant and equipment consisted of the following (in thousands):



	December 31, 2016		December 31, 2015
Land	$	120,575	$	100,582
Asset retirement costs (non-landfill)	14,567		12,434
Landfill assets	139,708		136,624
Buildings and improvements	373,160		344,209
Camp equipment	152,740		149,361
Vehicles	541,022		500,619
Equipment	1,483,736		1,328,915
Furniture and fixtures	5,492		5,337
Construction in progress	146,904		113,657
	2,977,904		2,691,738
Less - accumulated depreciation and amortization	1,366,077		1,159,271
Total property, plant and equipment, net	$	1,611,827	$	1,532,467

Schedule of Active Landfill Sites

As of December 31, 2016, the Company had 11 active landfill sites (including the Company's two non-commercial landfills), which have estimated remaining lives (based on anticipated waste volumes and remaining highly probable airspace) as follows:



		Remaining Lives (Years)	Remaining Highly Probable Airspace (cubic yards) (in thousands)
Facility Name	Location	Remaining Lives (Years)	Permitted	Unpermitted	Total
Altair	Texas	4	562	—	562
Buttonwillow	California	26	6,760	—	6,760
Deer Park	Texas	6	230	—	230
Deer Trail	Colorado	29	1,862	—	1,862
Grassy Mountain	Utah	55	375	4,830	5,205
Kimball	Nebraska	18	232	—	232
Lambton	Ontario	38	4,973	—	4,973
Lone Mountain	Oklahoma	31	4,627	—	4,627
Ryley	Alberta	14	494	880	1,374
Sawyer	North Dakota	82	3,671	—	3,671
Westmorland	California	64	2,732	—	2,732
			26,518	5,710	32,228

Remaining Highly Probable Airspace

The following table presents the remaining highly probable airspace from January 1, 2014 through December 31, 2016 (in thousands of cubic yards):



	2016		2015		2014
Remaining capacity at January 1,	29,786		30,544		29,323
Addition of highly probable airspace, net	3,464		516		2,809
Consumed	(1,022	)	(1,274	)	(1,588	)
Remaining capacity at December 31,	32,228		29,786		30,544