Talen Energy, owner of the Brunner Island coal-fired plant in York County, has agreed to pay Pennsylvania $1 million as part of a legal settlement over coal ash that seeped into the groundwater and ultimately the Susquehanna River and two tributaries.

It marks the largest coal ash related penalty in Pennsylvania history. The company will also pay an additional $100,000 toward projects aimed at reducing pollution in nearby waterways.

The settlement between Talen, three environmental groups, and the state Department of Environmental Protection is the result of a notice of intent to sue filed by the groups.

The 1,422-megawatt Brunner Island power plant in York Haven, Pa., is comprised of three coal-fired units. It has been in operation since 1961 and creates tons of ash and other coal combustion wastes annually. In recent years, Talen, which took over operation of the plant in 2016, has added capacity to burn natural gas.

“This enforcement action is one of historic proportions, since it’s the largest penalty ever assessed at a coal ash pollution site in Pennsylvania history,” said David Masur, executive director of PennEnvironment. “We are glad to see the DEP working with citizen groups to reach this important settlement for the good of the commonwealth.”

The other groups involved were the Lower Susquehanna Riverkeeper Association and Waterkeeper Alliance. The three organizations, working as part of the Environmental Integrity Project, contended that actions at Brunner Island violated the federal Clean Water Act and Pennsylvania’s Clean Streams Law by dumping coal ash waste in seven unlined ponds and a lined landfill over 367 acres bordered by the Susquehanna and two tributaries, Black Gut and Conewago Creek.

The Brunner Island operation generated residual wastes as the byproduct of coal combustion. Those byproducts include fly ash, a light form of coal ash that floats, and bottom ash, which is heavier and settles on the ground in disposal areas. The DEP said both types of contaminants have been leaking into groundwater around the facility.

Mary Greene, deputy director of the Environmental Integrity Project, credited Talen for cooperating and called the settlement “amicable.”

The groups said some coal ash disposal sites lacked liners that prevent leakage. As a result, pollutants such as arsenic, boron, and lithium infiltrated groundwater. Although six of the plant’s waste sites are now closed, Talen still disposes of ash in the lined landfill, which is leaking, and in an unlined pond, legal documents said.

Talen released a statement saying the settlement resolves all legal claims against it by the DEP and the groups.

“We are pleased to have reached agreement and appreciate the hard work and collaborative efforts of PaDEP, EIP and all stakeholders to resolve this matter," Debra Raggio, a senior vice president at Talen, said in the statement. "Talen is committed to complying with all environmental regulations and will continue to focus on the safe, efficient and reliable operation of our plants.”

As part of the settlement, Brunner Island also agreed to investigate and clean up groundwater in certain areas of the ash basins. Talen calls the pollution the result of “legacy” issues from prior to its ownership. It is currently phasing out coal and switching to natural gas.

The settlement, part of a consent decree, is pending approval by U.S. District Court for the Middle District of Pennsylvania.

The DEP said Talen will be required to continue to “inspect, monitor, and remediate” any potential seeps from the area as part of the settlement.

“We are confident that the work to be performed as spelled out in this consent decree will be for the betterment of all involved — the environment and area residents,” DEP Secretary Patrick McDonnell said in a statement.