PROPERTY, PLANT AND EQUIPMENT

12 Months Ended

Dec. 31, 2022

PROPERTY, PLANT AND EQUIPMENT

PROPERTY, PLANT AND EQUIPMENT

7.PROPERTY, PLANT AND EQUIPMENT

Property, plant and equipment consist of the following:

	December 31,
	2022		2021
	(in thousands)
Mining equipment and processing facilities	$	1,927,603	$	1,896,470
Land and coal mineral rights		499,950		458,440
Oil & gas mineral interests		740,635		647,864
Buildings, office equipment, improvements and other miscellaneous equipment		300,436		282,902
Construction, mine development and other projects in progress		99,042		44,217
Mine development costs		289,724		278,454
Property, plant and equipment, at cost		3,857,390		3,608,347
Less accumulated depreciation, depletion and amortization		(2,040,468)		(1,909,669)
Total property, plant and equipment, net	$	1,816,922	$	1,698,678

Depreciation, depletion and amortization expense related to property, plant and equipment was $270.9 million, $256.9 million and $297.0 million for the years ended December 31, 2022, 2021 and 2020, respectively.

At December 31, 2022 and 2021, land and coal mineral rights above include $29.9 million and $37.4 million, respectively, of carrying value associated with coal mineral reserves and resources attributable to properties where we or a third party to which we lease coal mineral reserves and resources are not currently engaged in mining operations or leasing to third parties, and therefore, the coal mineral reserves are not currently being depleted.  We believe that the carrying value of these coal mineral reserves will be recovered.  

At December 31, 2022 and 2021, our oil & gas mineral interests noted in the table above includes the carrying value of our unproved oil & gas mineral interests totaling $383.6 million and $355.1 million, respectively. As discussed in Note 2 – Summary of Significant Accounting Policies, we generally do not record depletion expense for our unproved oil & gas mineral interests; however, we do review for impairment as needed throughout the year.

During 2022, we incurred $11.3 million in mine development costs, primarily related to Hamilton and River View Coal, LLC ("River View") mine. During 2021, we did not incur material mine development costs. All past capitalized mine development costs are associated with other mines that shifted to the production phase in past years and we are amortizing these costs accordingly.  We believe that the carrying value of the past development costs will be recovered.

See Note 2 – Summary of Significant Accounting Policies for more information on our accounting policy for property, plant and equipment.