An Economic Approach to Off-Line Storage: A Means of Mitigating SSOs

This paper reports on the use of a two cell 30-million-gallon (MG) equalization basin and diesel engine-driven pump station as a means of mitigating sanitary sewer overflows (SSOs). The ultimate capacity of the pump station, which utilizes vertical turbine solids handling pumps (VTSH) arranged in a self-cleaning trench-style wet well, is 68 million gallons per day (MGD). Configuring the pump station with diesel engine-driven pumps provided a 20-year, 1 million present worth savings in comparison to a conventional electrical motor driven pump station arrangement. The use of diesel engine-driven pumps eliminated the peak electrical usage of 450- horsepower (HP) electrical motors, as well as the need for variable frequency drives and redundant power generation needs during electrical outage time periods. A supplemental 150- kilowatt (kW) generator was installed to provide emergency power needs for SCADA, seal water systems, influent screen, and a 50-HP maintenance pump for wetwell cleaning.