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Sewer Separation and Infrastructure Improvements

The City has a combined sewer system that carries both sanitary and storm water. During severe rainstorms the interceptor sewers were unable to carry the combined flows to the wastewater treatment plant. Seven relief points in the system, known as combined sewer overflows (CSOs), allowed untreated combined flows to be discharged into the Mascoma and Connecticut Rivers. The City came under an EPA Administrative Order to eliminate the CSOs. 

Wright Pierce was hired to develop a master plan to address the CSO issue. Based on an evaluation of the sewer system and the aquatic environment, Wright-Pierce developed alternative solutions to the CSO problem. Three solutions were proposed; they included a partial sewer separation, a full scale sewer separation, and the use of satellite treatment facilities to provide partial treatment and disinfection prior to discharge. It was concluded that the most cost effective solution was to continue to separate the sewer system. The report was submitted to the DES and EPA and is in the implementation phase.

The original sewer system included 12 miles of pipe ranging from 6-inches to 24-inches in diameter. Each of the 8 construction contracts will include new sanitary sewers, new storm drain lines, replacement of water lines where appropriate, new sidewalks, new granite curbing, and all new curb-to-curb street reconstruction.

Five contracts have been awarded for a total construction cost of approximately $11 million. Construction of the entire project will be extended over several years with the total cost estimated at $40 million.

The project is funded through a combination of grants from NHDES, USEPA, the Army Corps of Engineers, and a CDBG grant.

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Project Highlights
  • The EPA ordered the City to evaluate and correct a CSO problem.
  • Wright-Pierce was retained to evaluate the existing sewer system and develop a phased master plan to address the CSO issue.
  • The master plan outlined various solutions including a partial sewer separation, a full scale sewer separation, and the use of satellite treatment facilities to provide partial treatment and disinfection prior to discharge.
  • Based on the master plan, the City opted to continue the separate sewer system.
  • Five contracts have been awarded for a total construction cost of approximately $11 million.
  • Construction of the entire project will be extended over several years with the total cost estimated at $40 million