In 2023, the Company revised its cost estimates for existing Asset Retirement Obligations (“ARO”) for the following:

•Cholla coal-fired power plant related to the closure of ponds and facilities, which resulted in an increase to the ARO of approximately $71 million, primarily due to changes in the planned pond closure methodology and increased corrective action cost estimates associated with the CCR Rule. See Note 10.

•Four Corners coal-fired power plant, which resulted in a decrease of approximately $7 million.

•Navajo coal-fired plant, which resulted in an increase of approximately $8 million.

•Palo Verde received a new decommissioning study, which resulted in an increase to the ARO in the amount of $63 million, an increase in the plant in service of $59 million and a decrease in the regulatory liability of $4 million.

In 2022, APS did not revise any cost estimates related to existing AROs, and no new AROs were necessary.

The following table shows the change in our AROs (dollars in thousands):


	2023		2022
Asset retirement obligations at the beginning of year	$	797,762	$	767,382
Changes attributable to:
Accretion expense	44,269		41,240
Settlements	(14,039)		(10,860)

Estimated cash flow revisions	135,323		—
Newly incurred obligation	2,686		—
Asset retirement obligations at the end of year	$	966,001	$	797,762

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.