South Boston has beautiful beaches, but for years, their appeal was tainted by water pollution (flowing from wastewater systems and combined sewer overflow [CSO]). The Massachusetts Water Resource Authority (MWRA) started the North Dorchester Bay project to keep the beaches naturally appealing so community members could enjoy them indefinitely.
Our team handled design and construction-phase services for part of this project, which called for a pumping station, ventilation building, force main, and new gravity sewers. The 15-million-gallon-per-day (56-million-litre-per-day) station is designed to dewater the storage tunnel (the project’s key element) following storm events.
Created in the dry-pit style with submersible pumps, the station extends 68 feet (21 metres) below ground and includes a slurry wall to support excavation (as per our geotechnical investigation). The station’s three raw wastewater pumps empty the tunnel. One of the pumps is a stand-by (per regulations), whereas a smaller, fourth pump is used for dewatering; it pumps infiltration entering the storage tunnel which flows to the station.
Through this work, we’re helping MWRA eliminate CSO discharges to the beaches in up to a 25-year storm event and eliminating separate stormwater discharges in up to a five-year storm event.