Sewer Collection System

The City of Portsmouth is a regional provider of wastewater collection and treatment services to the City of Portsmouth, Town of New Castle and portions of the Towns of Greenland and Rye. The City has two wastewater collection systems that convey wastewater to separate wastewater treatment facilities (WWTF) at the Peirce Island WWTF and the Pease International Tradeport WWTF. The collection systems for the Pierce Island WWTF and Pease International Tradeport WWTF are shown in the figure below and services downtown Portsmouth and the client communities.

The Peirce Island WWTF collection system dates back to the 1800’s. The sewer collection system originally included pipelines that collected wastewater and discharged it directly and untreated to the South Mill Pond, North Mill Pond and the Piscataqua River. The collection system was a completely combined collection system carrying both wastewater and stormwater in the same pipe. A solution to the water quality issues this caused were not implemented until the 1970’s after the City constructed the Peirce Island WWTF and the City began constructing collection system improvements. These changes included constructing wastewater pumping stations at low points in the collection system, separating the stormwater from the sewage (sewer separation) by constructing separate sewer and drainage pipes and installing combined sewer overflows to provide relief points in the collection system. In the 1970’s there were fourteen (14) combined sewer overflows (CSO). Through additional work in the collection system as part of the City’s program to reduced combined sewer overflow discharges the number of CSO outfalls was reduced to 3 in the 1980’s. These three combined sewer overflows remain in the system today.

The current Peirce Island WWTF Collection System consists of 99 miles of sewer main, 8.6 miles of forcemain, and 19 wastewater pumping stations. The collection system is approximately 80% separated with the oldest parts of the system still combined (~20%). Some of the pipelines are greater than 100 years old and pipe materials include brick, reinforced concrete, vitrified clay, asbestos cement, cast iron, ductile iron, PVC and HDPE.  

The collection system for the Pease International Tradeport WWTF consists of 11 miles of sewer main, 0.5 miles of forcemain, and 1 pumping station.  This collection system was constructed as part of the Pease Air Force Base construction and serves only the area of the existing Pease International Tradeport. The collection system is a completely separate system and there are separate pipes for the stormwater drainage system. The pipelines were constructed in the 1950’s and pipe materials include vitrified clay, asbestos cement and PVC.