SIGNIFICANT ACCOUNTING POLICIES (Tables)

12 Months Ended

Dec. 31, 2014

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		12–15 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, 2014		December 31, 2013
Land	$	98,507	$	99,794
Asset retirement costs (non-landfill)	10,871		10,938
Landfill assets	110,984		100,983
Buildings and improvements	338,242		327,956
Camp equipment	180,575		187,831
Vehicles	471,615		425,296
Equipment	1,302,424		1,201,296
Furniture and fixtures	5,517		5,260
Construction in progress	45,605		58,010
	2,564,340		2,417,364
Less - accumulated depreciation and amortization	1,005,506		815,194
Total property, plant and equipment, net	$	1,558,834	$	1,602,170

Schedule of Property, Plant and Equipment, Landfill Assets

As of December 31, 2014, 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	12	834	—	834
Buttonwillow	California	22	7,379	—	7,379
Deer Park	Texas	8	305	—	305
Deer Trail	Colorado	29	1,994	—	1,994
Grassy Mountain	Utah	17	1,921	—	1,921
Kimball	Nebraska	20	268	—	268
Lambton	Ontario	38	54	4,708	4,762
Lone Mountain	Oklahoma	33	2,301	2,650	4,951
Ryley	Alberta	9	735	880	1,615
Sawyer	North Dakota	14	3,783	—	3,783
Westmorland	California	64	2,732	—	2,732
			22,306	8,238	30,544

Remaining Highly Probable Airspace

The following table presents the remaining highly probable airspace from January 1, 2012 through December 31, 2014 (in thousands of cubic yards):



	2014		2013		2012
Remaining capacity at January 1,	29,323		29,643		27,557
Addition of highly probable airspace, net	2,809		1,218		3,598
Consumed	(1,588	)	(1,538	)	(1,512	)
Remaining capacity at December 31,	30,544		29,323		29,643