Eversource Energy and solar energy developer CS Energy have agreed to pay up to $310,000 to settle allegations that they allowed stormwater and sediment from a solar array construction site to flow into surrounding wetlands in Southampton, Mass.

Under state law, developers must implement erosion and stormwater controls. Massachusetts Attorney General Maura Healey alleged that Eversource and CS Energy did not adequately implement controls for the 11.7-acre solar array. The attorney general said that the companies received repeated warnings from the project’s environmental monitor that stormwater was flowing into Moose Brook, a cold-water fishery, and its tributaries and wetlands.

According to Eversource spokesperson Priscilla Ress, the utility evaluated all its solar sites after the incident in Southampton in 2018 to “help strengthen and inform best practices” after “unanticipated stormwater impacts in this case.”

CS Energy did not respond to requests for comment.

Erosion and stormwater runoff are concerns for any large development, but Heidi Ricci, director of policy at Mass Audubon, said they are a particular concern for solar array development because so much forest is cleared.

This is not the first erosion and stormwater runoff incident that has warranted state action. A Pennsylvania-based solar array developer agreed to pay approximately $1.14 million to settle allegations that it damaged protected wetlands and polluted the Mill River in Williamsburg after violating federal stormwater requirements.

Developer Dynamic Energy Solutions built the 18.5-acre solar array on a steep hillside above the river, according to Healey’s office. The complaint, filed last year, alleges the stormwater eroded the hillside, uprooted trees, destroyed stream beds and filled in wetlands with sediment that turned the river brown.

In the Southampton project, the sediment-laden stormwater clogged one of the streams, dumped sediment into a bordering wetlands area and turned Moose Brook’s water cloudy downstream of the array, according to the attorney general’s office.

CS Energy and Eversource together will pay a civil penalty of up to $240,000, and CS Energy will also spend up to $70,000 to preserve an 8.7-acre Easthampton property located along the Manhan River near Moose Brook. The area is an important habitat for wood turtles and creeper freshwater mussels.

“Solar energy is an important part of our state’s thriving clean energy economy, but developers must construct these projects in a way that complies with state laws and does not harm our natural resources,” Healey said in a statement.

Working with Clark University, Mass Audubon created a GIS map of all solar projects across the state. They found that 7,700 acres of land have been dedicated to solar energy projects and at least half of that land used to be forest.

Mass Audubon supports the state’s goal to be carbon neutral by 2050, but the state needs to develop a plan to encourage solar arrays in the built environment, Ricci said.

Forests store carbon, stabilize the soil and support fishing streams. But large-scale solar developers are running into complex administrative barriers at the local level that deter them from siting in parking lots or school buildings.

“Clean water is important for people and wildlife,” Ricci said. “That’s why we have laws to protect it.”