Sewer Inflow/Infiltration Reduction Project

Project overview

The City of Dover owns and operates a wastewater collection and treatment system serving more than 31,000 residents. The collection system includes approximately 115 miles of sanitary sewer (8 to 40 inches in diameter) and 23 pumping stations. All flows are conveyed to the Dover Wastewater Treatment Facility (WWTF) on Middle Road for treatment and discharge to the Piscataqua River.

In 2000, the City of Dover launched Phase I of an Infiltration and Inflow (I/I) Study to identify areas with high I/I and to develop a plan to reduce peak flows in the wastewater collection system. Since then, the City has continued to pursue projects that remove existing I/I sources and prevent new I/I from entering the system.

To help reduce peak flows during wet-weather events, the City is identifying potential direct connections to the wastewater collection system. Common sources include roof drains on flat roofs and roof gutters.

As part of this ongoing effort, the City and their consultant will conduct a drone flyover during the week of May 18, 2026 weather permitting, to identify roof drains on flat roofs. The photo below shows a drone similar to the one that will be used to capture images. The drone is expected to remain over any individual rooftop for no more than 5 to 10 minutes, depending on roof size, before moving on.

• Map of Project Area

When excessive stormwater or groundwater enters the sanitary sewer system during rain events, it strains the wastewater treatment facility operations. Since 2000, the city has been working to identify and correct inflow and infiltration into the system.

The greatest flow-reductions have been by reducing illegal, direct connections into the sewer system, known as the “inflow” of the I/I acronym. These include roof drains, catch basins, and residential sump pumps. “Infiltration” is the other part of the acronym which refers to water seeping through cracked pipes, broken maintenance holes, or utility cover access hatch openings.

A comprehensive follow-up I/I flow study in 2019 identified areas of high-flow inputs in various sub-drainage sheds of the sanitary sewer system, including in and around Bellamy Road, Knox Marsh Road, and Mount Vernon Street.

The city uses multiple methods to identify and eliminate I/I, including maintenance hole inspections, closed-circuit TV inspections on the interior of piping, dye-testing, and smoke-testing.

For more information, contact Community Services at 603-516-6450.