MGE ENERGY INC

gencies.

a.

Environmental - MGE Energy and MGE.

Columbia

In February 2021, MGE and the other co-owners of Columbia announced plans to retire Units 1 and 2 at that facility. Effects of the environmental compliance requirements discussed below will depend upon the final Columbia retirement dates approved and required compliance dates.

Water Quality

Water quality regulations promulgated by the EPA and WDNR in accordance with the Federal Water Pollution Control Act, commonly known as the Clean Water Act, impose restrictions on discharges of various pollutants into surface waters. The Clean Water Act also regulates surface water quality issues that affect aquatic life, such as water temperatures, chemical concentrations, intake structures, and wetlands filling into Waters of the U.S., defined by EPA regulation. The Clean Water Act also includes discharge standards, which require the use of effluent-treatment processes equivalent to categorical "best practicable" or "best available" technologies. The Clean Water Act regulates discharges from "point sources," such as power plants, by establishing discharge limits via water discharge permits. MGE's power plants operate under Wisconsin Pollution Discharge Elimination System (WPDES) permits issued by the WDNR to ensure compliance with these discharge limits. Permits are subject to periodic renewal.

Effluent Limitations Guidelines and Standards for Steam Electric Power Generating Point Source Category

The EPA promulgated water Effluent Limitations Guidelines (ELG) and standards for steam electric power plants that focus on the reduction of metals and other pollutants in wastewater from new and existing power plants.

With the closure of the wet pond system in 2023 (as described in further detail in the CCR section below), Columbia complies with ELG requirements. With the installation of additional wastewater treatment equipment completed in 2023, the Elm Road Units comply with ELG requirements.

In May 2024, the EPA finalized the ELG rule that further regulates the wastewater discharges associated with coal-fired power plants. The rule focuses on wastewater discharges from flue gas desulfurization, combustion residual leachate, and bottom ash transport water. The rule includes reduced requirements for plants that have already installed pollution controls based on previous versions of the rule, and for plants that will be retiring or switching to natural gas by certain dates. Due to the installation of pollution control prevention equipment under previous versions of the rule and the planned fuel switching to natural gas, MGE believes it is likely the Elm Road Units will qualify for these reduced requirements. MGE and the operator of the Elm Road Units are evaluating operational options for Elm Road to be consistent with the requirements of the rule.

Cooling Water Intake Rules (Section 316(b))

The EPA's cooling water intake rules requires that cooling water intake structures at electric power plants meet best technology available (BTA) standards to reduce the mortality from entrainment (drawing aquatic life into a plant's cooling system) and impingement (trapping aquatic life on screens of cooling water intake structures).

Blount received its most recent WPDES permit from the Wisconsin Department of Natural Resources (WDNR) in October 2023. Blount's latest WPDES permit assumes that the plant meets BTA standards for entrainment for the duration of this permit which expires in 2028. The WDNR included a requirement to conduct an optimization study to demonstrate compliance with impingement BTA standards in the latest permit which needs to be completed by January 2028. Once the WDNR determines the impingement requirements at Blount, MGE will be able to determine any compliance costs of meeting Blount's permit requirements.

Intakes at Columbia are subject to this rule. The Columbia operator timely submitted its renewal application. BTA improvements required by the renewal permit will be coordinated with the owners' plan to retire both units by the end of 2029. MGE will continue to work with Columbia's operator to evaluate regulatory requirements in light of the planned retirement. MGE does not expect this rule to have a material effect on Columbia.

Air Quality

Federal and state air quality regulations impose restrictions on various emissions, including emissions of particulate matter (PM), sulfur dioxide (SO 2), nitrogen oxides (NOx), and other pollutants, and require permits for operation of emission sources. These permits have been obtained by MGE and must be renewed periodically. Current EPA initiatives under the Clean Air Act, including the Cross-State Air Pollution Rule (CSAPR) and National Ambient Air Quality Standards (NAAQS), have the potential to result in additional operating and capital expenditure costs for MGE.

Greenhouse Gas (GHG) Reduction Guidelines under the Clean Air Act 111(d) Rule

The Clean Air Act sets new source performance standards and emission guidelines for greenhouse gas (GHG) emissions from fossil fuel-fired electric generating units. These regulations apply to existing, new, and modified units and guide states in developing their emission control plans.

In May 2024, the EPA published its final performance standards and emission guidelines under section 111(b) of the Clean Air Act for carbon dioxide emissions from new combustion turbines and existing fossil-fuel fired boilers used to produce electricity. The final rule grants some emissions flexibility for existing coal-fired units that retire and/or fuel switch by certain dates. For existing natural gas boiler units, the final rule establishes a process where states must submit plans to the EPA for establishing standards. States will have two years from the publication date of these rules to submit plans to the EPA for review and approval. The EPA has indicated that it is separately developing performance standards and emission guidelines for GHG emissions from existing natural gas-fired combustion turbines. Preliminary evaluation of the final rule shows that MGE meets the requirements for the gas-fired boilers at Blount. Furthermore, MGE will meet the requirements for the coal-fired units at Columbia through planned unit retirements and the Elm Road Units through its transition to natural gas. MGE will monitor for upcoming rulemaking planned for gas-fired combustion turbines.

National Ambient Air Quality Standards (NAAQS) and Related Rules

The EPA's NAAQS regulations have been developed to set allowable ambient levels of six pollutants to protect sensitive human populations (primary NAAQS) and the environment (secondary NAAQS) from the negative effects of exposure to these pollutants. The Clean Air Act requires that the EPA periodically review, and adjust as necessary, the NAAQS for these six air pollutants. The EPA's NAAQS review can result in a lowering of the allowed ambient levels of a pollutant, a change in how the pollutant is monitored, and/or a change in which sources of that pollutant are regulated. States implement any necessary monitoring and measurement changes and recommend areas for attainment (meets the ambient requirements) or nonattainment (does not meet these standards). The EPA makes final attainment and nonattainment determinations. States must come up with a State Implementation Plan (SIP) to get nonattainment areas into attainment and maintain air quality in attainment areas Stationary sources of air emissions located in a nonattainment area will be most affected and may be subject to additional data submission and emission measurement requirements during permitting renewals, new emission limitations set by the SIP (which could result in significant capital expenditures), and additional expenses and/or permitting burdens for expanding existing facilities or building new facilities. The process, which starts with determining acceptable primary and/or secondary NAAQS and ends with executing SIPs can take years. Since the NAAQS regulations have the potential to affect both existing and new facilities, MGE continuously monitors changes to these rules to evaluate whether changes could impact its operations. In addition, the EPA has adopted interstate transport rules, such as CSAPR, to address contributions to NAAQS nonattainment from upwind sources in neighboring states. In the following paragraphs we discuss specific NAAQS and transport rule developments that may affect MGE.

Ozone NAAQS

The Elm Road Units are located in Milwaukee County, Wisconsin, a nonattainment area for the 2015 Ozone NAAQS. At this time, the operator of the Elm Road Units does not expect that the 2015 Ozone NAAQS or the Milwaukee County nonattainment designation will have a direct material effect on the Elm Road Units.

Fine Particulate Matter (PM2.5) NAAQS

In March 2024, the EPA published a final rule to lower the average annual PM2.5 NAAQS from 12 ug/m3 to 9 ug/m3, effective May 2024. The new annual PM2.5 NAAQS could impact Milwaukee County, where the Elm Road units are located, if the county is determined to be in nonattainment. A nonattainment designation would require the State of Wisconsin to develop a plan to get into attainment, which would likely include additional limitations for new and modified plants in the county.

The final impact of this rule will not be known until PM data from 2023 and 2024 is evaluated and approved, the EPA determines the attainment status of Wisconsin counties, and the State of Wisconsin develops an attainment implementation plan. MGE will continue to follow the rule's developments.

Rules regulating nitrogen oxide (NOx) and sulfur dioxide (SO 2) emissions, including the Cross State Air Pollution Rule (CSAPR) and Clean Air Visibility Rule

The EPA's CSAPR and its progeny are a suite of interstate air pollution transport rules designed to reduce ozone and PM2.5 ambient air levels in areas that the EPA has determined as being significantly impacted by pollution from upwind states. This is accomplished through a reduction in NOx and SO 2 from qualifying fossil-fuel fired power plants and industrial boilers in upwind "contributing" states. NOx and SO 2 contribute to fine particulate pollution and NOx contributes to ozone formation in downwind areas. Reductions are generally achieved through a cap-and-trade system. Individual plants can meet their caps through reducing emissions and/or buying allowances on the market.

In March 2023 (published June 2023), the EPA finalized its Federal Implementation Plan to address state obligations under the Clean Air Act "good neighbor" provisions for the 2015 Ozone NAAQS (FIP Rule). The FIP Rule impacts 23 states, including Wisconsin. For Wisconsin, the FIP Rule includes revisions to the current obligations for fossil-fuel power generation, which includes Blount, Columbia, the Elm Road Units, WCCF, West Riverside, and West Marinette. Emissions budgets can be met with planned retirements, fuel switching, and immediately available measures, including consistently operating emissions controls already installed at power plants. In 2026, additional obligations would go into effect, including a further reduction in emissions budgets. Wisconsin would need to submit a SIP to meet its obligations or accept the EPA's FIP Rule. Legal challenges to the FIP Rule are pending in the United States Court of Appeals for the

District of Columbia. In June 2024, the Supreme Court of the United States granted a request to stay the FIP Rule and block its enforcement pending judicial review by the U.S. Court of Appeals for the District of Columbia on the merits of petitioner's challenges to implementation of the rule. The EPA has temporarily halted the enforcement of the Good Neighbor Plan's requirements for all pollution sources in states affected by the plan, including Wisconsin. This action follows legal challenges to the plan. While the EPA addresses these concerns, interim rules have been implemented. In Wisconsin, these interim rules aim to ensure that obligations to address interstate ozone pollution with respect to the 2008 ozone NAAQS under the CSAPR Update Rule continue to be met, even though the Good Neighbor Plan is temporarily suspended. Based on our current evaluation, if the FIP goes into effect as-is, the 2026 additional emission reductions may impact the Elm Road Units, however, final impact of the rules will not be known until judicial reviews are completed and/or the EPA takes further action regarding the rule.

Clean Air Visibility Rule

Columbia is subject to the best available retrofit technology (BART) regulations, a subsection of Clean Air Visibility Rule, which may require pollution control retrofits. Columbia's existing pollution control upgrades, and the EPA's stance that compliance with the CSAPR satisfies the requirements of BART, should mean that Columbia will not need to do additional work to meet BART requirements. Wisconsin's 2021 SIP argues that Wisconsin will meet its current regional haze goals based on expected emissions reductions, which include the planned Columbia unit retirements. Given that the Wisconsin SIP recognizes the Columbia unit retirements as part of its emission reduction plan, MGE does not anticipate further obligations with respect to this rule at Columbia. MGE will continue to monitor legal developments and any future updates to this rule.

Solid Waste

Coal Combustion Residuals (CCR) Rule

The CCR rule regulates the disposal of solid waste coal ash and defines what ash use activities would be considered generally exempt beneficial reuse of coal ash. The CCR rule also regulates landfills, ash ponds, and other surface impoundments used for coal combustion residuals by regulating their design, location, monitoring, and operation. The CCR rule requires owners and operators of coal-fired power plants to stop transporting CCR and non-CCR wastewater to unlined surface impoundments. At Columbia, the coal combustion residuals system completed in 2023 replaced the unlined surface impoundment, and Columbia complies with this rule.

Review of the Elm Road Units has indicated that the costs to comply with the CCR rule are not expected to be significant.

In May 2024, the EPA published its final CCR Legacy Rule. The CCR Legacy Rule applies to previous closed disposal sites. In 2024, MGE recorded an asset retirement obligation for its estimated share of the legal liability associated with the effect of the CCR Legacy Rule for remediation and groundwater compliance monitoring. Actual costs of compliance may be different than the amount recorded due to potential changes in compliance strategies that will be used, as well as other potential changes in cost estimate. See Footnote 17 for further information on asset retirement obligations.

b.

Legal Matters -