Wastewater Treatment Facility Plan

WWTF Plan and Long-Term Control Plan Update

Weston & Sampson was part of a project team selected by the City of Portsmouth to develop an overall wastewater master plan. Historically an excellent steward of the environment, the city, in the 1960s, was one of the first communities of its size to construct a primary wastewater treatment facility (WWTF) to treat combined sewer flows. The city also reduced the number of combined sewer overflow (CSO) locations from 14 to 3 during a permit renewal process.

During its NPDES permit renewal, the city was notified that it would be required to meet a minimum of secondary treatment with the potential for nutrient limits at Peirce Island. The new secondary permit, along with the potential for more stringent future nutrient limits and the magnitude of the remaining CSO mitigation work, led the city to engage in a two-pronged planning process: a facilities plan focusing on the need to provide secondary treatment at the Pierce Island WWTF, and an update of the CSO long term control plan (LTCP).

Weston & Sampson completed the initial phases of the project including the development of a detailed flow and pollutant loading technical memorandum that evaluated current, future, and build-out wastewater flows and regional flows for the city. The memorandum included loading projections for biosolids, septage, and fats/oils/grease (FOG). The project team worked with state and federal regulators to identify and evaluate all appropriate technologies for meeting the new permit limits. The evaluation also includes an overall siting assessment that may allow Peirce Island, which is a scenic and historic artifact, to be used for recreational purposes.

The project required a detailed alternatives evaluation with respect to meeting stringent nutrient limits. The results of this combined effort has provided the city with a wastewater infrastructure roadmap for decades.


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