Sanitary Sewer and Underdrain Separation

Abstract

The Newton Sanitary Sewer and Underdrain Separation project is the largest cured-in-place-lining project undertaken in New England. The project utilizes a multi-faceted approach to remove infiltration and inflow (I/I) from the sanitary sewer while simultaneously reducing the potential for sanitary contamination of local receiving waters. The project area consists of approximately 27,432 meters (90,000 feet) of 30.48 centimeters (12″) to 60.96 cm x 91.44 cm (24' x 36') sanitary sewer lines with 15.24 cm to 45.72 cm (6″ to 18″) underdrains. Constructed in the late 1800s, the underdrains were originally used for de-watering during construction. Underdrains are pipes with open joints that were installed beneath the sewer line to convey groundwater to a local drain or water body. These underdrains are connected to the sanitary sewer through access points located inside sanitary manholes. The access points were built to provide locations to perform maintenance on the underdrain piping system. Over time, these access points deteriorated, resulting in a direct connection between the sanitary sewer and underdrain. The direct connection allowed sanitary flow to enter the underdrain system and groundwater from the underdrain system to enter the sanitary system. This mixing of flows between the two (2) systems results in sewer overflows during extreme wet weather events, increased sewer user costs, and contamination of local receiving waters.