Asset Retirement Obligations:

12 Months Ended

Dec. 31, 2021

Asset Retirement Obligation Disclosure [Abstract]

ASSET RETIREMENT OBLIGATIONS

We have identified legal obligations related to reclamation of mining sites; removal of fuel tanks, transformers containing polychlorinated biphenyls, and an evaporation pond; and reclamation of wind turbine sites at our Electric Utilities segment. In addition, we have identified legal obligations related to retirement of gas pipelines and wells at our Gas Utilities and removal of asbestos at our Utilities. We periodically review and update estimated costs related to these AROs. The actual cost may vary from estimates due to regulatory requirements, changes in technology and increased labor, materials and equipment costs.

The following tables present the details of AROs which are included on the accompanying Consolidated Balance Sheets in Other deferred credits and other liabilities (in thousands):


	December 31, 2020		Liabilities Incurred		Liabilities Settled		Accretion		Revisions to Prior Estimates		December 31, 2021
Electric Utilities	$	29,157	$	—	$	(978)	$	1,315	$	595	$	30,089
Gas Utilities (a)	42,274		—		(66)		1,733		1,514		45,455
Total	71,431		$	—	$	(1,044)	$	3,048	$	2,109	$	75,544


	December 31, 2019		Liabilities Incurred		Liabilities Settled		Accretion		Revisions to Prior Estimates		December 31, 2020
Electric Utilities (b) (c)	$	28,120	$	1,217	$	(185)	$	1,230	$	(1,225)	$	29,157
Gas Utilities (d)	36,085		4,782		(132)		1,539		—		42,274
Total	$	64,205	$	5,999	$	(317)	$	2,769	$	(1,225)	$	71,431

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(a) The Revisions to Prior Estimates were primarily driven by changes in estimates associated with natural gas wells.

(b) Liabilities incurred were related to new wind assets.

(c) The Revisions to Prior Estimates were primarily driven by changes in estimated costs associated with back-filling the pit with overburden removed during the mining process.

(d) Liabilities incurred were driven by an increase in gas pipeline miles; which increases our legal liability for retirement of gas pipelines, specifically to purge and cap these lines in accordance with federal regulations.

We also have legally required AROs related to certain assets within our electric transmission and distribution systems. These retirement obligations are pursuant to an easement or franchise agreement and are only required if we discontinue our utility service under such easement or franchise agreement. Accordingly, it is not possible to estimate a time period when these obligations could be settled, and therefore, a liability for the cost of these obligations cannot be measured at this time.