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Asset Retirement Obligations | 12 Months Ended
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Dec. 31, 2023
Asset Retirement Obligation Disclosure [Abstract] |
Asset Retirement Obligations | NOTE 11. ASSET RETI REMENT OBLIGATIONS The Company has recorded liabilities for future AROs to: • restore coal ash containment ponds and coal holding areas at Colstrip, • cap a landfill at the Kettle Falls Plant, and • remove plant and restore the land at the Coyote Springs 2 site at the termination of the land lease. Due to an inability to estimate a range of settlement dates, the Company cannot estimate a liability for the: • removal and disposal of certain transmission and distribution assets, and • abandonment and decommissioning of certain hydroelectric generation and natural gas storage facilities. In 2015, the EPA issued a final rule regarding CCRs. Colstrip produces this byproduct. The CCR rule has been the subject of ongoing litigation. In August 2018, the D.C. Circuit struck down provisions of the rule. The rule includes technical requirements for CCR landfills and surface impoundments. The Colstrip owners developed a multi-year compliance plan to address the CCR requirements and existing state obligations. The actual asset retirement costs related to the CCR rule requirements may vary substantially from the estimates used to record the ARO due to the uncertainty and evolving nature of the compliance strategies that will be used and the availability of data used to estimate costs, such as the quantity of coal ash present at certain sites and the volume of fill that will be needed to cap and cover certain impoundments. The Company updates its estimates as new information becomes available. The Company expects to seek recovery of costs related to complying with the CCR rule through the ratemaking process. In addition to the above, under a 2018 Administrative Order on Consent and ongoing negotiations with the Montana Department of Ecological Quality, the owners of Colstrip are required to provide financial assurance, primarily in the form of surety bonds, to secure each owner's pro-rata share of various anticipated closure and remediation of the ash ponds and coal holding areas. The amount of financial assurance required of each owner may, like the ARO, vary substantially due to the uncertainty and evolving nature of anticipated closure and remediation activities, and as those activities are completed over time. The following table documents the changes in the Company’s asset retirement obligation during the years ended December 31 (dollars in thousands):
|  | 2023 |  |  | 2022 |  |  | 2021 |
Asset retirement obligation at beginning of year |  | $ | 15,783 |  |  | $ | 17,142 |  |  | $ | 17,194 |
Liabilities incurred |  |  | 1,927 |  |  |  | — |  |  |  | 825 |
Liabilities settled |  |  | (232 | ) |  |  | (1,964 | ) |  |  | (1,541 | )
Accretion expense |  |  | 580 |  |  |  | 605 |  |  |  | 664 |
Asset retirement obligation at end of year |  | $ | 18,058 |  |  | $ | 15,783 |  |  | $ | 17,142 |

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- Definition The entire disclosure for an asset retirement obligation and the associated long-lived asset. An asset retirement obligation is a legal obligation associated with the disposal or retirement from service of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 410 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147481850/410-20-50-1 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 410 -SubTopic 20 -Name Accounting Standards Codification -Publisher FASB -URI https://asc.fasb.org//410-20/tableOfContent Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name Accounting Standards Codification -Section 50 -Paragraph 2 -SubTopic 20 -Topic 410 -Publisher FASB -URI https://asc.fasb.org//1943274/2147481850/410-20-50-2 + Details
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