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Asset Retirement Obligations | 12 Months Ended
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Dec. 31, 2024
Asset Retirement Obligation Disclosure [Abstract] |
Asset Retirement Obligations | Asset Retirement Obligations We have recognized asset retirement obligations (AROs) related to our coal-fired generation plants, natural gas combustion turbines, solar facility and wind turbines. The cost of AROs include items such as site restoration, closure or removal of ash pits and removal of certain structures, generators, asbestos and storage tanks. We have other legal obligations associated with the retirement of a variety of other long-lived tangible assets used in electric operations where the estimated settlement costs are individually and collectively immaterial. We have no assets legally restricted for the settlement of any AROs. As of December 31, 2024 and 2023, $0.1 million and $0.1 million, respectively, was included in other current liabilities and $42.1 million and $36.4 million, respectively, was included in other noncurrent liabilities in the consolidated balance sheets related to AROs. A reconciliation of the carrying amounts of AROs for the years ended December 31, 2024 and 2023 is as follows:
(in thousands) | 2024 |  | 2023
Beginning Balance | $ | 36,477 |  |  | $ | 25,182 |
New Obligations Recognized | 2,991 |  |  | 4,506 |
Adjustments Due to Revisions in Cash Flow Estimates | 1,098 |  |  | 8,394 |
Accrued Accretion | 1,676 |  |  | 1,191 |
Settlements | (79) |  |  | (2,796) |
Ending Balance | $ | 42,163 |  |  | $ | 36,477 |
Coal Combustion Residual Regulations In May 2024, the Environmental Protection Agency (EPA) published a final rule amending coal combustion residual (CCR) regulations. The final rule introduces new requirements for the management of coal ash at active coal-fired power plants and inactive coal-fired power plants with a legacy surface impoundment. The regulations impose new requirements including groundwater monitoring, closure standards, post-closure care obligations and potential remediation activities. At this time, we do not believe there are any significant new requirements which are applicable to our coal-fired power plants, except for Big Stone Plant. During the fourth quarter of 2024, a site evaluation was performed at Big Stone Plant to assess the presence and estimated volumes of coal ash stored at the facility. Based on this and our assessment of the regulations, we believe the plant will be impacted by the new requirements. As of December 31, 2024, we recognized $3.0 million of additional liabilities for new obligations resulting from the EPA's final CCR rule for costs associated with coal ash removal and groundwater monitoring we expect to incur in the future. The final rule requires facility evaluations to be performed in the future. Revisions to our estimated compliance costs or further obligations could be identified through the process of performing the additional evaluations. Should such revisions be necessary or if additional cost obligations are identified, we will update our cash flow estimates and resulting retirement obligation at that time.

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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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