The Merrimack River Watershed Council says 896 million gallons of untreated sewage were released last year along the Merrimack River—about 30% above the average amount in the previous 10 years.
In a statement, Watershed Council Executive Director Curt Rogers reported Tuesday the amount does not account for additional partially treated sewage discharged and street sewer overflows. While Massachusetts law requires sewer treatment plants to publicly report when they release sewage into the river, “the river’s complex flow and currents can make that advisory inaccurate.”
CSO testing last year by the Merrimack River Watershed Council showed that while 48 hours was more than enough time for the plume of bacteria to flow downstream, the plume often persisted longer than the recommended window and flowed further downstream than expected. Jose Tapia, the Council’s water quality project manager, says they are working to better understand the overflows’ effect on the river.
“Questions asked this year will include how long do plumes of bacteria survive in the river following a CSO and for how many miles downstream can they pose a risk to people’s health?” He says.
During the testing season, which runs April through September, volunteers and staff collect water samples from 15 locations from Manchester to Salisbury Beach and Plum Island. The samples are analyzed in the Watershed Council’s lab and results posted at merrimack.org.
Combined sewage overflows, known as CSOs, come from “antiquated sewer lines that become overfilled during rainstorms” from five cities—Manchester, Nashua, Lowell, Lawrence and Haverhill. Last year, more than 90% of the untreated volume came from Manchester and Lowell.
Testing is paid by a state Department of Environmental Protection budget line item championed by Sen, Bruce E. Tarr and Rep. Tram T. Nguyen and supported by multiple Merrimack Valley lawmakers. The Council warns, however, continued testing beyond June 30 depends on lawmakers renewing the money.