		June 30,			December 31,
		2016			2015
Asset retirement obligation, beginning of period	$	8,573		$	5,683
Revision of estimate		-			877
Aquried in asset acquisitions or business combinations		5,454			2,145
Accretion of liabilities		351			494
Settlements		(698	)		(626	)
Asset retirement obligation, end of period	$	13,680		$	8,573
Asset retirement obligation:
Current	$	305		$	1,000
Non-current		13,375			7,573
Asset retirement obligation, end of period	$	13,680		$	8,573

Revision of estimates is as a result of a change in estimates of the amount or timing of cash flows to settle asset retirement obligations. Changes to the asset retirement obligations are recorded in profit and loss.

The asset retirement obligations of the Company are subject to legal and regulatory requirements. Estimates of the costs of reclamation are reviewed periodically by the applicable regulatory authorities. The above provision represents the Company’s best estimate of the present value of future reclamation costs, discounted using credit adjusted risk-free interest rates ranging from 9.5% to 11.5% and an inflation rate of 2.0% (December 31, 2015 – 2.0%) . The total undiscounted decommissioning liability at June 30, 2016 is $41.23 million (December 31, 2015 - $32.30 million). Reclamation costs are expected to be incurred between 2016 and 2038 in the following manner: 2016 – 2020 - $4.67 million, 2021 – 2025 - $9.41 million, 2026 – 2030 - $2.69 million, 2031 – 2035 - $8.78 million, 2036 – 2038 - $15.67 million.

The Company has cash, cash equivalents and fixed income securities as collateral for various bonds posted in favor of the State of Utah, the State of Wyoming, the applicable state regulatory agencies in Colorado and Arizona and the U.S. Bureau of Land Management for estimated reclamation costs associated with the White Mesa mill and mining properties. Cash equivalents are short-term highly liquid investments with original maturities of three months or less. The restricted cash will be released when the Company has reclaimed a mineral property or restructured the surety and collateral arrangements. See Note 12 for a discussion of the Company’s surety bond commitments.