SIGNIFICANT ACCOUNTING POLICIES (Tables)

12 Months Ended

Dec. 31, 2015

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		30–40 years
Leasehold and building improvements		2–40 years
Camp equipment		8–15 years
Vehicles		3–12 years
Equipment
Capitalized software and computer equipment		3–5 years
Solar equipment		20 years
Containers and railcars		15–20 years
All other equipment		8–20 years
Furniture and fixtures		5–8 years

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



	December 31, 2015		December 31, 2014
Land	$	100,582	$	98,507
Asset retirement costs (non-landfill)	12,434		10,871
Landfill assets	136,624		110,984
Buildings and improvements	344,209		338,242
Camp equipment	149,361		180,575
Vehicles	500,619		471,615
Equipment	1,328,915		1,302,424
Furniture and fixtures	5,337		5,517
Construction in progress	113,657		45,605
	2,691,738		2,564,340
Less - accumulated depreciation and amortization	1,159,271		1,005,506
Total property, plant and equipment, net	$	1,532,467	$	1,558,834

Schedule of Property, Plant and Equipment, Landfill Assets

As of December 31, 2015, 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	6	686	—	686
Buttonwillow	California	20	7,023	—	7,023
Deer Park	Texas	7	268	—	268
Deer Trail	Colorado	28	1,932	—	1,932
Grassy Mountain	Utah	20	1,839	—	1,839
Kimball	Nebraska	9	243	—	243
Lambton	Ontario	37	5,062	—	5,062
Lone Mountain	Oklahoma	32	4,809	—	4,809
Ryley	Alberta	9	608	880	1,488
Sawyer	North Dakota	45	3,704	—	3,704
Westmorland	California	64	2,732	—	2,732
			28,906	880	29,786

Remaining Highly Probable Airspace

The following table presents the remaining highly probable airspace from January 1, 2013 through December 31, 2015 (in thousands of cubic yards):



	2015		2014		2013
Remaining capacity at January 1,	30,544		29,323		29,643
Addition of highly probable airspace, net	516		2,809		1,218
Consumed	(1,274	)	(1,588	)	(1,538	)
Remaining capacity at December 31,	29,786		30,544		29,323