About 1.5 million gallons of partially treated sewage spilled into a wooded area at a wastewater treatment plant in Prince George’s County, Maryland, officials said on Thursday.

The incident at the Piscataway Wastewater Treatment Plant started at approximately 3:50 p.m. Wednesday, May 4 and ended Thursday, May 5 at 7:15 a.m.

Luis Maya, a spokesman for the Washington Suburban Sanitary Commission (WSSC), told the Washington Post that the spill occurred when workers tried to change the flow of the sewage during an ongoing construction project at the plant.

The sewage spilled from a manhole cover that was pushed open by the water flow. It had already gone through the first stage of the treatment process, Maya said.

The overflow was contained within the facility grounds, and no sewage entered any storm drains or waterways, according to the WSSC, which provides water and wastewater services in Prince George’s and Montgomery counties.

Following the spill, crews were working to clean up the site and recover as much of the partially treated wastewater as possible to pump back into the plant drain sewer for full treatment.

The utility notified the Maryland Department of the Environment and the Prince George’s County Health Department about the incident and has posted signs around the area as a precaution.