Sewage flowed into the Merrimack River for 13 hours after the powerful storm early Monday knocked out electricity to a treatment plant and pump station in North Andover, officials said.
The Greater Lawrence Sanitary District facilities came to a stop around 1:30 a.m. Monday. When they couldn’t keep up with the water flowing in, sewage began overflowing at various outlets along the Merrimack, the district said.
“We lost all power to our pumping station, which is off site, and the main plant, which is where all of the treatment happens,” sanitary district executive director Cheri Cousens said in a telephone interview.
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“We couldn’t power up the pumps . . . and eventually as waste water continues to enter the system it no longer can accommodate it.”
Cousens said she did not know how much sewage entered the river. The Eagle-Tribune of Lawrence reported the amount was 8 million gallons. The district processes around 17 million gallons of storm water and sanitary sewage daily, officials said.
A generator at the treatment facility did start up after the power outage, providing “preliminary treatment along with disinfection and dechlorination” of sewage “before discharging the effluent to the Merrimack River,” the district said in a statement.
The treatment plant and pump station handle the sewer systems for the communities of Lawrence, Methuen, Andover, North Andover, Dracut, and Salem, N.H.
Massachusetts Department of Environmental Protection spokesman Edmund J. Coletta Jr. said in an e-mail Tuesday that heavy rain caused an 8-foot rise in river elevation during the past five days, meaning the “volume of flow in the river increased dramatically, diluting any discharge to the river and quickly carrying the discharge out to the ocean.”
The sewage is not expected to affect drinking water supply, said Coletta. He said there were no “drinking water intakes” below the area where the sewage flowed into the river.
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The state is working with the sanitary district and the US Environmental Protection Agency to consider both short-term and long-term measures that could prevent such an incident in the future, Coletta said.
He could not verify how many millions of gallons of sewage flowed into the river, deferring comment to the sanitary district. Messages left with the EPA were not immediately returned Tuesday afternoon.
Another backup generator was on its way to the facility Monday, which could have helped, officials said, but delivery was delayed because of a chemical fire in a truck on Interstate 495. The facilities were eventually fully working around 2:30 p.m. Monday, the district said.
Danny McDonald of Globe staff contributed to this report.