From January through August of this year, combined sewer overflows in the Massachusetts Water Resources Authority (MWRA) service zone discharged more than twice as much sewage and runoff into public waterways than was expelled throughout all of 2020.
Parts of Massachusetts have combined sewer systems, in which stormwater runs through the same pipes that carry sewage. Heavy and persistent rains can overwhelm the systems. To prevent sewage backups into homes and streets, combined sewer overflows (CSOs) discharge some of the sewage and rainwater into the nearest rivers or lakes.
Through last month, there had been 80 discharges totaling 594 million gallons at CSOs that the MWRA meters, according to the Executive Office of Energy and Environmental Affairs. In all of 2020, there were 58 discharges at those same MWRA-metered CSOs that emptied a total of 259 million gallons.
Last year, all but one million gallons of the sewage and runoff discharged by the MWRA was treated before it was dumped into a waterway, EEA said.
Boston just "wrapped up the third wettest meteorological summer ever recorded" and the region had already received more precipitation (40.17 inches) by Sept. 2 than during all of 2020 (37.54 inches), according to WBZ-TV's meteorology team.
The overall amount of rain is a major factor in CSO discharges, but officials said 2021 has also seen more of the large storms that increase the need for CSO discharges. After last week's heavy rains from the remnants of Hurricane Ida, the Department of Environmental Protection worked with wastewater system operators to assess CSO discharges into water bodies across the Bay State.
In addition to the MWRA service area, CSO discharges are a major concern along the Merrimack River.