Drilling is stopped after leaks develop along Mariner East pipeline. One is affecting Chester’s Marsh Creek Lake.

Drilling fluid used in Sunoco Pipeline LP’s Mariner East project in Chester County leaked into Marsh Creek Lake in a state park of the same name on Monday — one of three incidents in recent days along the pipeline construction project route.

Virginia Cain, a spokesperson for the Pennsylvania Department of Environmental Protection, said the agency is investigating the three incidents, which occurred at two project sites, in West Whiteland and Upper Uwchlan Townships.

The DEP said the first leak occurred on the 100 block of Shoen Road in West Whiteland on Saturday. Both the DEP and the Fish and Boat Commission responded and tested water to see if it contained drilling fluids. Drilling was stopped to await an analysis of the liquid.

If the liquid is found to be that used for drilling, which typically contains bentonite clay and water, the site will be shut down until an application to restart is filed. Usually, the liquid is injected into a bore during the horizontal drilling process. The mixture is not normally hazardous, though environmental groups say it could contain other chemicals.

On Sunday, the same agencies were called after discharges related to the same site were reported “at multiple areas in the West Whiteland Apartment Complex.” The DEP is reviewing permits and plans Sunoco filed pertaining to the location to see if regulations were followed.

Then, on Monday, the DEP was called to another drill site off Green Valley Road in Marsh Creek State Park in Upper Uwchlan. There, drilling fluid leaked into wetlands and a tributary to Marsh Creek Lake, then finally into the lake.

Sunoco is working on a cleanup in coordination with the two state agencies.

Environmental groups and residents who have been battling the pipeline for years were outraged. When complete, the pipeline will transport gas liquids, such as propane, ethane, and butane.

The Clean Air Council estimated that 1,000 gallons of the drilling fluid were released into Marsh Creek Lake, which also serves as a drinking water reservoir. The nonprofit environmental organization said the fluid contains chemical additives and can “smother aquatic life.” The group said photographs show “a large plume of gray water snaking hundreds of feet into the lake.”

The potential impact on the overall health of the lake was not immediately clear as of Tuesday.

Environmental groups in the past have urged the DEP to prevent Sunoco from drilling near the park because of the risk of spills.

“Sunoco again has failed to take seriously the danger its construction poses to drinking water supplies and other water resources,” the Clean Air Council said in a statement.

Alex Bomstein, an attorney at Clean Air Council, said a Sunoco geologist had included in a previous report before drilling began that there was a “moderate to high risk of a spill” in the area.

West Whiteland Residents for Pipeline Safety, a citizens group, posted a picture of muddied water and what it identified as Sunoco workers at the scene.

Ginny Kerslake, a member of the West Whiteland group, said she was at the lake Monday night and again Tuesday.

“I have seen it firsthand,” she said of the spill. “Like many people, we frequently enjoy that lake. It’s devastating this has been allowed to happen.”

Marsh Creek State Park is in north-central Chester County. The 1,784-acre park contains the 535-acre Marsh Creek Lake, widely used for fishing and boating.

The pipeline has caused a number of incidents over the years. In July, inspectors found a new series of sinkholes that have opened up along the pipeline’s route in Chester County after cracks were reported in the pavement of Business Route 30 in Exton.