City to spend $231 million over 20 years to reduce sewage overflow into Merrimack River

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Merrimack River. Photo, Carol Robidoux

MANCHESTER, NH – The city will spend $231 million over the next 20 years to reduce sewer system overflows into the Merrimack River, the source of drinking water for more than 500,000 people, according to a settlement agreement with the U.S. Environmental Protection Agency (EPA).

The proposed settlement, filed Monday in U.S. District Court in Concord, also involved the U.S. Department of Justice and the State of New Hampshire, which joined the U.S. government as a co-plaintiff on the agreement that resolves alleged violations of the Clean Water Act by the city.

“This agreement means a healthier Merrimack River and cleaner water for the communities along the river in both New Hampshire and Massachusetts,” said EPA New England Regional Administrator Dennis Deziel in a news release.   “EPA has long been committed to working with our state and federal partners and cities like Manchester to improve water quality along the Merrimack, which is an important source of drinking water and recreation destination.”

“This agreement demonstrates a recognition by all parties of the importance of maintaining our clean waters,” said Bob Scott, Commissioner of the NH Department of Environmental Services. “NHDES looks forward to continuing to work with Manchester, both in terms of financing the projects and ensuring they are successful.”

Over the past decade, the city has spent nearly $41 million to upgrade the sewer system.  However, Manchester’s combined sewer system, when overwhelmed by rain and stormwater, still discharges raw sewage, industrial waste, nitrogen, phosphorus and polluted stormwater into the Merrimack River and its tributaries. 

According to the EPA, about 280 million gallons of raw sewage and other pollutants from the city’s sewer system end up in the river each year, nearly half of the combined sewage discharge volume from all communities along the Merrimack River.

Under the proposed consent decree, Manchester will implement combined sewer overflow (CSO) abatement controls and upgrades at its wastewater treatment facilities that are expected to reduce the city’s total annual combined sewer discharge volume by approximately 74 percent from approximately 280 million gallons to 73 million gallons.

The two major components of the CSO abatement controls will disconnect Cemetery Brook in Manchester, the largest of the local five significant connected brooks, from the city’s combined sewer system. Manchester will design and construct a new 2.5-mile drain for Cemetery Brook from Mammoth Road to the Merrimack River to convey both the brook’s and storm drainage flows. The city will also design and construct projects to separate the combined sewers for areas adjacent to the Cemetery Brook drain. These drainage and sewer separation projects will together address the largest drainage basin in the city and produce the greatest volume of CSO reduction.

The work under the proposed consent decree also includes the construction of a new drain and sewer separation in the Christian Brook drainage basin, which will remove the third-largest brook from the wastewater collection system.

The proposed consent decree also requires the city to implement a CSO discharge monitoring and notification program, which will include direct measurement of all discharges from six CSO outfalls estimated to be more than 99% of all of the city’s total CSO discharge volumes. The city will be required to provide initial and supplemental notification to the public 

In addition to the 20-year control plan, the proposed settlement also requires the upgrades to improve the handling of solid waste at the wastewater treatment plant to reduce discharges of phosphorous.

Many of the communities in the Merrimack River watershed are environmental justice communities with large numbers of minority and low-income residents.

The projects are expected to result in the following annual reductions in pollutants:  

  • 1,814,450 pounds of total suspended solids;
  • 535,695 pounds of biochemical oxygen demand;
  • 881,304 pounds of chemical oxygen demand;
  • 16,416 pounds of total nitrogen; and
  • 3,283 pounds of total phosphorus.

The proposed consent decree is subject to a 30-day public comment period and court approval after it is published in the Federal Register. It will be available for viewing on the DOJ’s website:

For more information on this settlement, visit:

The 83-page settlement document is below: