INDIANAPOLIS (AP) — The Indianapolis utility that operates a large southwestern Indiana power plant environmentalists call a “super polluter” plans to retire two of the station’s four coal-fired units by 2023, continuing its shift away from coal power.

Indianapolis Power & Light Co. officials outlined their plans for shuttering two units at the utility’s massive Petersburg Generating Station as part of a 20-year strategy plan for power generation that all electric utilities are required to file every three years.

All four units at the Petersburg station, located about 120 miles (193 kilometers) southwest of Indianapolis, have run afoul of environmental regulations. The station has racked up more than a dozen environmental violations in the past five years, emitting excess sulfur dioxide, nitrous oxide particulate matter and sulfuric mist, the Indianapolis Business Journal reported.

IPL’s tentative plans for retiring half of the station’s units represent the utility’s latest move to reduce its coal footprint. In recent years, IPL stopped using coal at two of its plants — its Harding Street station in Indianapolis and its Eagle Valley station in Martinsville — in favor of natural gas.

The Petersburg station is IPL’s largest generating station, with a generating capacity of 1,700 megawatts — enough to light up factories, homes and shopping centers across central Indiana. It contains the utility’s only remaining coal-consuming power plants.

IPL president's and CEO, Vince Parisi, said in written comments that the utility used economics, flexibility, grid reliability and other factors to support “our decision to invest in a more balanced energy mix, which minimizes risk to our customers and takes into account a rapidly-changing energy landscape.”

The utility, which is a unit of Arlington, Virginia-based AES Corp., has about 490,000 customers in its service territory of Indianapolis and some nearby areas.

The Sierra Club environmental group praised IPL’s announcement, but also said that it would push for the utility to stop using coal entirely at its Petersburg station by 2028 and to “clean up its widespread toxic pollution.”

“It’s good that IPL is moving to get rid of two units at this outdated, massive Super Polluter, but we can’t tiptoe our way out of the climate crisis,” Wendy Bredhold, senior campaign representative for the Sierra Club’s Beyond Coal campaign in Indiana, said in a statement. “Southwest Indiana’s families and children living with health impacts from the Petersburg plant need bold plans to move rapidly away from dangerous fossil fuels that are poisoning our air and water and threatening our health.”

The Citizens Action Coalition of Indiana, a consumer group, said it appreciated IPL’s decision to retire a portion of Petersburg’s coal-burning capacity, but added that it was “disheartening” that the utility will continue burning coal at the power plant for decades to come.

“IPL’s plan does not have the urgency to swiftly transition to clean energy that the climate crisis demands,” said Kerwin Olson, the group’s executive director.

In 2017, the Indianapolis City-County Council passed a resolution that called for a reduction in carbon emissions, increased energy efficiency and renewable energy use. City officials later created a plan for the city to be powered by 100% renewable energy by 2050.

Other Indiana utilities also are moving to retire old coal-fired units. In July, Duke Energy Indiana, the state’s largest electric utility, said it wants to retire all nine of its coal-fired units by 2038 and build two large natural gas plants, along with 700 megawatts of wind energy and 1,650 megawatts of solar energy.