ASSET RETIREMENT OBLIGATIONS

3 Months Ended

Mar. 31, 2024

Asset Retirement Obligation Disclosure [Abstract]

Asset retirement obligations (AROs) are legal obligations associated with the retirement of long-lived assets resulting from the acquisition, construction, development and/or normal use of the underlying assets, including legal obligations for land reclamation. Recognition of a liability for an ARO is required in the period in which it is incurred at its estimated fair value. The associated asset retirement costs are capitalized as part of the carrying amount of the underlying asset and depreciated over the estimated useful life of the asset. The liability is accreted through charges to operating expenses. If the ARO is settled for a value other than the carrying amount of the liability, we recognize a gain or loss on settlement.

ARO operating costs related to accretion of the liabilities and depreciation of the assets are as follows:


	Three Months Ended March 31
in millions	2024		2023
Accretion	$	3.5	$	3.4
Depreciation	2.4		2.2
Total	$	5.9	$	5.6

ARO operating costs are reported in cost of revenues. AROs are reported within other noncurrent liabilities in our accompanying Condensed Consolidated Balance Sheets.

Reconciliations of the carrying amounts of our AROs are as follows:


	Three Months Ended March 31
in millions	2024		2023
Balance at beginning of period	$	324.1	$	311.3
Liabilities incurred	0.0		0.0
Liabilities settled	(1.8)		(2.9)
Accretion expense	3.5		3.4
Revisions, net	(0.1)		0.1
Balance at end of period	$	325.7	$	311.9