(5) Property, Plant and Equipment, net

Property, plant and equipment consists of the following:

 

		December 31,
		2013				2012
Land		$	10,640			$	8,469
Buildings and improvements			40,465				32,699
Pipelines			74,817				76,667
Disposal wells			71,860				79,344
Landfill			27,828				—
Machinery and equipment			39,011				94,982
Equipment under capital leases			18,475				20,771
Motor vehicles and trailers			159,992				148,555
Rental equipment			167,912				137,084
Office equipment			4,976				4,214
			615,976				602,785
Less accumulated depreciation			(137,318	)			(61,242	)
Construction in process			19,883				37,479
Property, plant and equipment, net		$	498,541			$	579,022

During the year ended December 31, 2013, the Company recorded impairment of property, plant and equipment of $107.4 million (Note 7). Depreciation expense for the years ended December 31, 2013, 2012 and 2011 was $78.8 million, $40.1 million and $21.4 million, respectively.