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	2019	2018	2019	2018
ARO Operating Costs
Accretion	$ 2,744	$ 2,684	$ 8,194	$ 8,036
Depreciation	1,720	1,512	5,361	4,192
Total	$ 4,464	$ 4,196	$ 13,555	$ 12,228

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	2019	2018	2019	2018
Asset Retirement Obligations
Balance at beginning of period	$ 223,497	$ 215,421	$ 225,726	$ 218,117
Liabilities incurred	0	0	263	0
Liabilities settled	(2,684)	(2,649)	(9,650)	(10,476)
Accretion expense	2,744	2,684	8,194	8,036
Revisions, net	510	10,628	(466)	10,407
Balance at end of period	$ 224,067	$ 226,084	$ 224,067	$ 226,084

ARO liabilities settled during the first nine months of 2019 and 2018 include $2,403,000 and $6,108,000, 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 reclamation agreement will result in the restoration of 90 acres of previously mined property to conditions suitable for retail and commercial development.