The wettest summer on record in New Hampshire resulted in historic levels of raw sewage and stormwater runoff flowing into the Merrimack River last year, data obtained by Merrimack River Watershed Council shows.
More than 2 billion gallons of Combined Sewer Overflow (CSO) — raw sewage mixed with runoff from urban street drains — were discharged into the river from five cities along the Merrimack.
Merrimack River Watershed Council (MRWC) has been keeping records since 2013, the first year CSO data from all five locations became publicly available.
The previous record, set in 2021, was 823 million gallons. In an average year, about 550 million gallons of CSO waste is discharged.
Manchester was tops in terms of sewer overflow with 875 million gallons, followed by Lowell, Mass., with 850 million gallons. The two cities accounted for 86% of the total volume of sewer overflow last year, MRWC said in a release.
The other three cities included two in Massachusetts — Greater Lawrence with 164 million gallons and Haverhill with an estimated 97 million gallons — and Nashua with 20 million gallons.
“The enormous amount of rain we received last year was the primary reason why we had such an astonishingly high volume of CSO waste discharged into the river,” said John Macone, MRWC’s policy and education specialist. “I heard many complaints and concerns from people throughout the region about the unhealthy appearance of the river last year, and the new data helps to verify that we experienced an unusual bad year for CSO events.
“Climate change scientists have been predicting that the Northeast will witness a substantial increase in heavy rainstorms, and in 2021 and 2023, we certainly saw that in the Merrimack Valley.”
The summer of 2023 was the wettest on record in New Hampshire, according to data shared by the National Oceanic and Atmospheric Administration (NOAA).
The Granite State received 21.11 inches of rain across June, July and August, records available online at www.ncei.noaa.gov show. That represents the most rainfall across the three-month summer time frame since record keeping began in 1895, and about 8 inches more than average.
Concord saw 15.52 inches of rain in the summer of 2023, placing it No. 13 overall for the state’s capital.
Summer 2023 also broke records at the Mount Washington Observatory.
The 43 inches of rain recorded at the weather station at the mountain’s summit surpassed a 1998 record. Records at the observatory go back to 1932.
In June, the observatory reported precipitation on 24 of 30 days. In July, precipitation was reported on 22 of 31 days.
CSOs can contain high levels of harmful bacteria that can cause rashes, infections and intestinal problems for people and animals. CSOs can also be harmful to fish due to reduced oxygen levels. The New Hampshire Department of Health advises people to avoid direct contact with river water for 48 hours after CSO events occur.
Of the 61 days in June and July, the Merrimack River was under “no contact” CSO-related advisories for 39 days.
Currently, both Lowell and Manchester are embarking on massive projects that will reduce their CSO volumes.
In Manchester, a 20-year, $300 million project is underway. One of its key components is digging a 2-mile-long tunnel to separate stormwater and sewage. The tunnel is deep — up to 80 feet underground in some spots. When finished, it is expected to reduce the city’s CSO outflow by 80%, according to a 2020 agreement announced by the U.S. Environmental Protection Agency and Justice Department.
The agreement focuses on the sewer system, which provides sewage treatment to most of the city as well as portions of Bedford, Goffstown and Londonderry.
During heavy rainfalls, stormwater overwhelms the capacity of antiquated sewer systems to handle both stormwater and sewage, causing raw sewage to be discharged directly into the river.
In 1999, the EPA ordered Manchester to address the problem. In 2009, Manchester completed a $58 million Phase I project that covered the West Side.
