Concept Design of the DC Water Tunnel Dewatering Pump Station

The District of Columbia Water and Sewer Authority is currently implementing a long-term control plan (LTCP) to address combined sewer overflows (CSOs). Major components of the LTCP include a tunnel system that will collect and convey CSOs to a tunnel dewatering pump station (TDPS) and enhanced clarification facility (ECF) located at the Blue Plains Advanced Wastewater Treatment Plant (Blue Plains AWTP). The TDPS is comprised of two shafts, a surge/screening shaft, and dry well dewatering shaft. TDPS technical elements and challenges addressed through completion of concept design and preparation of design-build procurement documents include depth of station, limited footprint, egress and ventilation, intermittent duty systems (requiring simple, robust, reliable approach), controlling a wide variations in flow and head conditions, motor voltage, and single point of failure analysis to identify risks and risk mitigation for system components.