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Sewage overflows reported in Merrimack River

This week’s heavy rains led at least two wastewater treatment plants to discharge sewage into the Merrimack River.

On Tuesday, Haverhill and the Greater Lawrence Sanitary District — which serves Lawrence, Andover, North Andover, Methuen and Salem N.H. — reported releasing sewage overflows into the Merrimack. Neither plant stated how much sewage was discharged into the river. Haverhill reported that .71 inches of rain fell.

The two plants have a voluntary agreement with the Merrimack River Watershed Council to provide reports of sewage overflows. Two other plants along the Merrimack typically release sewage during rainstorms — the plants in Lowell and Manchester N.H. Those plants do not make public notifications when they release sewage, however the Merrimack River Watershed Council is working with them to release this information to the public in a timely manner.

In a typical year, about a half billion gallons of sewage is dumped into the Merrimack during rainstorms. The Greater Lawrence plant releases about 35 million gallons of sewage into the river, while Lowell and Manchester release over 200 million gallons each. Haverhill releases about 21 million gallons of partially treated sewage annually.

These sewage discharges — called Combined Sewage Overflow events — frequently occur during moderate to heavy rainstorms. In many cities, street drains that collect rainwater are connected to sewer lines. When rainwater collects in sewer pipes, the volume overwhelms the capacity of the sewage plant to process the wastewater, and as a result untreated or partially treated sewage is released into the river. All sewage treatment plants are required by the federal government to disconnect stormwater drains from their sewage systems, however the task is expensive and each plant is working under a multi-year timeline to complete the disconnections.

Currently, Massachusetts lawmakers are considering a law that would require sewage treatment plants to make timely public reports of the CSO events. The plants are currently not required to alert the general public. Under the proposed law, the plants would provide reports to the state, which would then post them on a dedicated website. There is also some thought being given to creating a phone alert system that would send text or message alerts to people whenever CSO events occur.

The Merrimack River Watershed Association supports the legislation. Many people use the Merrimack for boating, fishing, and swimming, however they are not alerted when the river is experiencing CSO events. Untreated sewage contains pathogens that can be dangerous to the health of humans and animals. A 2015 medical study found a correlation between CSO events and increased hospital admissions for intestinal disorders in the Merrimack Valley. The pathogens often remain in the river for days after the CSO events occur, and solid waste that is released can remain lodged along the riverbanks for longer periods of time.