Surface Water Treatment Plant Preliminary Design

Waterworks facilities at the Surface Water Treatment Plant (SWTP) site on Portsmouth Ave were first developed in 1886, with plant upgrades completed in 1905, 1924, 1972, 1992, and 2019 to improve efficiency and meet evolving drinking water regulations and standards. The current SWTP plant treats raw water from the Exeter Reservoir, Exeter River (via pump station), and Skinner Springs (located in Stratham). The river is the primary source of water from mid-spring through mid-autumn, while the reservoir, located behind the plant, supplies water during the remaining months of the year.

The Town completed an assessment of its surface water and groundwater supplies and projected future water demand in 2020 which determined the need for additional sources. In response to a recommended roadmap to address this, the Town is in the process of pursuing development of a new groundwater source of Drinkwater Road. Planning and preliminary design of a new SWTP is the next recommended course of action. Due to the age of the SWTP facilities, process limitations, site constraints, and flooding history, replacement of the SWTP at a new location is the preferred option.

An early estimate of the required future production capacity of the SWTP is 1.3 to 1.5 Million Gallons per Day, about half of the capacity of the SWTP that was proposed and designed in the early 2000’s and failed to receive voter support. Since that time, the Great Dam has been removed, which has reduced the total yield of the Exeter River. Therefore, a planning/preliminary design effort is necessary to re-evaluate the river supply yield, determine and evaluate potential sites, establish the required plant capacity, investigate appropriate treatment processes, and refine project costs.