Asset Retirement Obligations

12 Months Ended

Dec. 31, 2012

Asset Retirement Obligations

Asset Retirement Obligations

13. Asset Retirement Obligations

        Changes in the carrying amount of our AROs were as follows (in thousands):

	2012			2011
Balance at January 1	$	199,633		$	188,757
Accretion expense		13,189			12,469
Revisions to estimated cash flows		33,444			5,913
Payments		(5,632	)		(7,506	)
Balance at December 31		240,634			199,633
Less: current portion		(1,643	)		(6,926	)
Asset retirement obligation, net of current portion	$	238,991		$	192,707

        The above amounts exclude $8.6 million and $5.3 million of concurrent reclamation for the years ended December 31, 2012 and 2011, respectively.

        Revisions to estimated cash flows pertain to revisions in the estimated amount and timing of legally required reclamation activities throughout the lives of the respective mines and reflect changes in estimates of closure volumes, disturbed acreages, and third-party unit costs as of December 31, 2012 and 2011. The successful federal coal lease awards during 2011 are included in the revisions to estimated cash flows as our Antelope mine's life is now expected to be approximately 12 years longer, which reduced the discounted value of the future liability. Reductions to AROs resulting from such revisions generally result in a corresponding reduction to the related asset retirement cost in property, plant and equipment, net. However, during the three months ended June 30, 2011, the increased life of the Antelope mine resulting from the WAII LBAs caused a decrease to the ARO liability that exceeded the carrying amount of the related asset retirement cost. The resulting non-cash credit reduced depreciation and depletion expense on the consolidated statements of operations by $15.7 million for the year ended December 31, 2011.