Phase V West Ashley Sewer Tunnel & Influent Pump Station

OWNER: Charleston Water System

ENGINEER: Black and Veatch

SOUTHLAND HOLDINGS TEAM: Southland/Renda Joint Venture


This project serves to upgrade and replace the undersized existing sewer and increase pumping capacity to the overall wastewater system.  This project includes replacement of an existing sewer tunnel extending from the Croghan Spur in West Ashley to the Plum Island Wastewater Treatment Plant and construction of a new Influent Pump Station at the same location.

The most challenging aspects of this project was sinking a 60 ft. diameter concrete caisson shaft 150 ft. deep in mixed ground conditions for a 15 MGD Influent Pump Station and (2) ea 5’ diameter drilled piles 140 ft. deep.  The tunnel portion includes 8,300 LF of 86” tunnel for 54” fiberglass reinforced pipe (FRP) approximately 125 ft. below ground.  In addition, 1,200 LF of 48” pipe was installed above the marsh wetlands on pile bents.  Project is located on an estuary with fill, soils, and Cooper Marl.