Bentonite Spill Under Marsh Creek Lake Delays Winter Drawdown

DOWNINGTOWN, PA — A 10-acre bed of bentonite material at the bottom of Marsh Creek Lake has delayed the usual winter drawdown of the reservoir's level because if it's exposed, it's an "inhalation risk," according to the DCNR.

The Pennsylvania Department of Conservation and Natural Resources has had to manage its winter water drawdown in stages because of Sunoco's Aug. 10 spill of drilling fluid that contained bentonite into the park's waters. The bentonite has settled over a 10-acre area under the 535-acre reservoir. If water levels get low enough for the material to become dry and be inhaled, it represents a health risk, the DCNR said in a Dec. 23 release.

Sunoco was forced to halt drilling after the spill and has since formed a plan to reroute its Mariner East II pipeline around the wetlands. Sunoco and the Pennsylvania Environmental Protection Agency have since been embroiled in a legal tug-of-war over the plan and permits.

The Pennsylvania Department of Conservation and Natural Resources explained in a news release that the normal seasonal drawdown prevents damage to park facilities, increases flow capacity so water can be stored as winter storms come, and reduces risk to downstream communities and possible damage to infrastructure like dams.

But it had to be done in stages this year because of the bentonite left behind by Sunoco's spill in August. Marsh Creek State Park officials announced Wednesday that water levels of the reservoir at the park will soon return to "normal summer pool levels," after residents noticed the lake level seemed very high. Some contacted their state representative.

The DCNR clarified the reason for the altered water management plan, in a Dec. 23 news release.

"A three-foot drawdown would expose 10 acres of bentonite deposited in the lake during an inadvertent return associated with the Sunoco Mariner East II pipeline construction project on Aug. 10, 2020," the DCNR said.

"Hazard Communication Safety Data Sheets for the bentonite material notes inhalation risk from dry material," the DCNR said.

State Rep. Danielle Friel Otten (D-155th) said she'd heard from constituents who were concerned about unusually high water levels at Marsh Creek State Park.

"This year, the standard drawdown practice has been delayed and complicated by the presence of bentonite material on the lake floor resulting from Sunoco's August 2020 spill of drilling fluid into a tributary of Marsh Creek Lake," Friel Otten told residents of the area.

On Thursday, the Pennsylvania Department of Conservation and Natural Resources
initiated a one-foot drawdown of the lake, with a goal of reaching the standard three-foot drawdown later in the winter.

The cove affected by the bentonite spill is marked by buoys and is closed to the public, and park officials request that visitors also avoid the shoreline areas along the cove "to reduce exposure to any exposed bentonite material," the DCNR said.

The stages of the water drawdown are being announced. "Staff at Marsh Creek State Park will be opening a 42-inch valve on Jan. 7 in order to return the reservoir to normal summer pool levels," park staff said Wednesday.

They explained that opening the valve can cause the East Branch Brandywine Creek to rise rapidly.

They also alerted residents that additional valve openings will be required after Jan.7 for a one-foot drawdown at Marsh Creek State Park reservoir.