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. 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 other than the carrying amount of the liability, we recognize a gain or loss on settlement.

We record all AROs for which we have legal obligations for land reclamation at estimated fair value. These AROs relate to our underlying land parcels, including both owned properties and mineral leases. ARO operating costs related to accretion of the liabilities and depreciation of the assets are as follows:



	Three Months Ended		Nine Months Ended
	September 30		September 30
in thousands	2020	2019	2020	2019
ARO Operating Costs
Accretion	$ 3,115	$ 2,744	$ 9,270	$ 8,194
Depreciation	2,123	1,720	6,022	5,361
Total	$ 5,238	$ 4,464	$ 15,292	$ 13,555

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



	Three Months Ended		Nine Months Ended
	September 30		September 30
in thousands	2020	2019	2020	2019
Asset Retirement Obligations
Balance at beginning of period	$ 263,748	$ 223,497	$ 210,323	$ 225,726
Liabilities incurred	353	0	353	263
Liabilities settled	(2,459)	(2,684)	(11,047)	(9,650)
Accretion expense	3,115	2,744	9,270	8,194
Revisions, net	(5,809)	510	50,049	(466)
Balance at end of period	$ 258,948	$ 224,067	$ 258,948	$ 224,067

ARO liabilities settled during the first nine months of 2020 and 2019 include $2,358,000 and $2,403,000, respectively, of reclamation activities required under a development agreement and conditional use permits at two adjacent aggregates sites on owned property in Southern California. The reclamation required under the development agreement will result in the restoration of 90 acres of previously mined property to conditions suitable for retail and commercial development.

ARO revisions during the first nine months of 2020 primarily include increases in estimated costs at three aggregates locations, including reclamation activities required under a development agreement at an aggregates site on owned property in Southern California. The reclamation required under the development agreement will result in the restoration of previously mined property to conditions suitable for retail and commercial development.