(5) Property and Equipment

The Partnership’s investment in property and equipment for the periods presented is as follows:


	Estimated	December 31,
(in thousands)	useful lives	2017		2018
Land	n/a	$	15,382		18,649
Gathering systems and facilities	50 years(1)		1,781,386		2,175,500
Fresh water permanent buried pipelines and equipment	20 years		472,810		523,488
Wastewater treatment facility	30 years		—		300,064
Fresh water surface pipelines and equipment	5 years		46,139		62,683
Landfill	n/a(2)		—		60,950
Heavy trucks and equipment	5 years		—		4,831
Above ground storage tanks	10 years		4,301		4,824
Construction-in-progress(3)	n/a		654,904		306,759
Total property and equipment			2,974,922		3,457,748
Less accumulated depreciation			(369,320)		(499,333)
Property and equipment, net		$	2,605,602		2,958,415

⁽¹⁾

In accordance with its policy, the Partnership evaluates the reasonableness of the estimated useful lives of its fixed assets and determined that the actual lives of the gathering systems and facilities were longer than the estimated useful lives used in calculating depreciation expense. On October 1, 2018, the Partnership increased the useful lives of the gathering systems and facilities from 20 years to 50 years based on a change in the expected period that our systems and facilities will be used to support Antero Resources’ producing wells. For the year ended December 31, 2018, the change in estimate decreased depreciation by $18 million, increased net income and comprehensive income by $18 million and increased basic and diluted net income per limited partner unit by $0.10.

⁽²⁾

Amortization of landfill costs is recorded over the life of the landfill on a units-of-consumption basis.

⁽³⁾

As of December 31, 2017, construction-in-progress included $355 million for the construction of the wastewater treatment facility and landfill, which was placed in service in 2018.

The Partnership capitalized interest of $4 million, $12 million and $4 million for the years ended December 31, 2016, 2017 and 2018, respectively for the construction of the wastewater treatment facility.

Net operating expenses incurred during wastewater treatment facility commissioning were capitalized. Due to delays in reaching contractual treatment capacity of the wastewater treatment facility, the Partnership has and continues to accrue for liquidated damages from the vendor. At December 31, 2018, the Partnership had accrued $21 million for liquidated damages as a current asset and reduction in cost of the facility.

The Partnership recorded impairment charges of $23 million and $6 million in the years ended December 31, 2017 and 2018, respectively. The impairment charge for the year ended December 31, 2017 related to condensate gathering lines which Antero Resources no longer uses. During the year ended December 31, 2018, the impairment charge is due to the impairment of gathering assets acquired from Antero Resources at the time of its IPO related to well pads Antero Resources no longer has plans to drill and complete. The Partnership’s gathering and compression agreement with Antero Resources provides that for certain gathering assets the Partnership constructs after receiving notice from Antero Resources, and are subsequently delayed or cancelled, Antero Resources is required to repurchase the assets at 115% of the cost. This resulted in a gain of $583 thousand during the year ended December 31, 2018.