Phase V West Ashley Sewer Tunnel & Influent Pump Station
Charleston, SC

From 2002 to 2008, Hussey Gay Bell was involved in Phases II-IV leading up to the Phase V West Ashley Sewer Tunnel & Influent Pump Station. The $50.8 million fifth and final phase of CWS’s 15-year+ sewer tunnel improvements program, replaced an existing deep tunnel from the Croghan Spur to the Plum Island Wastewater Treatment Plant (PIWWTP) with a new tunnel 120-foot-deep, 1.6 mile long tunnel from Albemarle Road, under the Wappoo Cut, to the PIWWTP. Other improvements consisted of a new 60 MGD influent pump station, new pile-supported 48-in. force main, new 3,200-sf pump control building at the treatment plant, installation of near surface connection at the PIWWTP, two shaft sites and surface collection improvements in the Country Club of Charleston and along Harborview Road. The shafts consist of a 60-ft ID at PIWWTP and 20-ft ID at Croghan, both built using the caisson sinking method, and 30-in. drop pipe at Porter Gaud. The 8,300 ft tunnel was excavated with an 86-inch diameter single shield tunnel boring machine and supported with ribs and lagging boards.