Asset Retirement Obligations

Reconciliations of the Company’s asset retirement obligations are as follows:



	Successor						Predecessor
	Year Ended December 31, 2018			April 2 through December 31, 2017			January 1 through April 1, 2017
	(Dollars in millions)
Balance at beginning of period	$	691.1		$	664.2		$	758.8
Liabilities incurred or acquired	16.3			—			—
Liabilities settled or disposed	(57.8		)	(65.2		)	(2.7		)
Accretion expense	48.5			32.6			12.5
Revisions to estimates	52.1			59.5			(104.4		)
Balance at end of period	$	750.2		$	691.1		$	664.2
Less: Current portion (included in “Accounts payable and accrued expenses”)	63.8			34.1			31.1
Noncurrent obligation (included in “Asset retirement obligations”)	$	686.4		$	657.0		$	633.1
Balance at end of period — active locations	$	671.8		$	612.9		$	540.1
Balance at end of period — closed or inactive locations	$	78.4		$	78.2		$	124.1

During the year ended December 31, 2018, the Company acquired the Shoal Creek Mine and the related asset retirement obligations, as further discussed in Note 3. “Acquisition of Shoal Creek Mine.”

During the period April 2 through December 31, 2017, the Company sold its Burton Mine and the related asset retirement obligations, as further discussed in Note 22. “Other Events.” The changes in mine operations impacted reclamation estimates and are reflected in the asset retirement obligation asset and liability as of December 31, 2018 and 2017, respectively.

The credit-adjusted, risk-free interest rates utilized to estimate the Company’s asset retirement obligations ranged from 7.61% for life of mines 3 years or less to 11.54% for life of mines greater than 20 years for both U.S. and Australia reclamation obligations at December 31, 2018. The same rate was used for U.S. and Australia in 2018 as all cash collateral was converted to surety bonds, bank guarantees or letters of credit to secure reclamation obligations.

As of December 31, 2018 and 2017, the Company had $1,317.0 million and $1,136.8 million, respectively, in surety bonds and bank guarantees outstanding to secure reclamation obligations. Additionally, the Company had $142.3 million and $188.5 million, respectively, of letters of credit in support of reclamation obligations as of December 31, 2018 and 2017. The Company also had restricted cash and cash collateral of $205.2 million as of December 31, 2017 in support of reclamation obligations.