Property, Plant and Equipment

6 Months Ended

Jun. 30, 2019

Property, Plant and Equipment [Abstract]

Property, Plant and Equipment

7. PROPERTY, PLANT AND EQUIPMENT

A summary of the historical cost of property, plant and equipment is as follows:

thousands	Estimated Useful Life	June 30,   2019		December 31,   2018
Land	n/a	$	8,863	$	5,298
Gathering systems – pipelines	30 years	4,938,224		4,764,099
Gathering systems – compressors	15 years	1,839,353		1,712,939
Processing complexes and treating facilities	25 years	2,952,268		2,844,337
Transportation pipeline and equipment	6 to 45 years	172,807		172,558
Produced water disposal systems	20 years	697,949		629,946
Assets under construction	n/a	660,397		604,265
Other	3 to 40 years	582,297		525,331
Total property, plant and equipment		11,852,158		11,258,773
Less accumulated depreciation		3,058,512		2,848,420
Net property, plant and equipment		$	8,793,646	$	8,410,353

The cost of property classified as “Assets under construction” is excluded from capitalized costs being depreciated. These amounts represent property that is not yet suitable to be placed into productive service as of the respective balance sheet date.

Impairments. During the six months ended June 30, 2019, the Partnership recognized impairments of $1.2 million.

During the year ended December 31, 2018, the Partnership recognized impairments of $230.6 million, including impairments of $125.9 million at the Third Creek gathering system and $8.1 million at the Kitty Draw gathering system. These assets were impaired to their estimated salvage values of $1.8 million and zero, respectively, using the market approach and Level 3 fair value inputs, due to the shutdown of the systems in May 2018. Also during 2018, the Partnership recognized impairments of $38.7 million and $34.6 million at the Hilight and MIGC systems, respectively. These assets were impaired to their estimated fair values of $4.9 million and $15.2 million, respectively, using the income approach and Level 3 fair value inputs, due to a reduction in estimated future cash flows. The remaining $23.3 million of impairments was primarily related to (i) a $10.9 million impairment at the GNB NGL pipeline, which was impaired to its estimated fair value of $10.0 million using the income approach and Level 3 fair value inputs, and (ii) a $5.6 million impairment related to an idle facility at the Chipeta complex, which was impaired to its estimated salvage value of $1.5 million using the market approach and Level 3 fair value inputs.