Peirce Island WWTF Resiliency

Project Update: December 6, 2024:

FEMA and the NH Department of Homeland Security completed a walk-through of the completed project with AECOM, DPW and the Portsmouth Fire Chief.

In September 2023, the City of Portsmouth was notified that it had received $965,333 in Congressionally Directed Spending (CDS) from the Federal Pre-Disaster Mitigation (PDM) Grant Program through the NH Department of Homeland Security and Emergency Management for the Peirce Island Road Resiliency Project. The City matched 25 percent of the grant. Work on the project started the week of April 15, 2024.

The project was designed to raise a 400-foot-long section of Peirce Island Road and the adjacent parking area to three feet above the current 100-year floodplain. Additionally, a portion of the packed gravel parking area was replaced with grass pavers and vegetation to improve stormwater management. 

The City applied for the grant to provide consistent access to the Pierce Island Wastewater Treatment Facility (WWTF), a critical municipal service. Pierce Island Road, the sole access road to the critical infrastructure facility, currently floods during spring high tides and storm events. Raising the road approximately 3 feet above its current lowest point elevated it above the 100-year flood line and protected it against predicted sea level rise. The raised road also offers greater protection to the force mains under the road that carry wastewater to the WWTF.

The project had no impact on the rocky shore, salt marsh or marsh elder and the City complied with the conditions set forth in the NH Department of Environmental Services (NH DES) Wetlands Permit to minimize any potential impacts to nearby wetlands. The project maintained the existing walking trail and vegetation north of the road and supplemented the existing site with a narrow buffer of stone and upland plantings between the trail and the road to protect the road from high water and wave action during storms. The previous parking area was raised and the gravel was replaced with a more permeable reinforced turf parking area and a grass paver driveway. These surfaces decrease runoff by promoting absorption of stormwater.