Asset Retirement Obligations

9 Months Ended

Sep. 30, 2017

Asset Retirement Obligation Disclosure [Abstract]

In the third quarter of 2017, an updated decommissioning study was completed for the Navajo Generating Station, which resulted in an increase to the asset retirement obligation ("ARO") in the amount of $22 million.

The following schedule shows the change in our asset retirement obligations for the nine months ended September 30, 2017 (dollars in thousands):



Asset retirement obligations at January 1, 2017	$	624,475
Changes attributable to:
Accretion expense	24,170
Estimated cash flow revisions	22,211
Asset retirement obligations at September 30, 2017	$	670,856

In accordance with regulatory accounting, APS accrues removal costs for its regulated utility assets, even if there is no legal obligation for removal. See detail of regulatory liabilities in Note 3.