The Metropolitan St. Louis Sewer District (MSD) is undertaking a long-term program called “MSD Project Clear” to improve water quality for the St. Louis region by reducing the occurrence of basement backups and overflows caused by excessive wet weather sanitary and combined sewage flows. The Gravois Trunk Sanitary Storage Facility, one of the larger projects in the program, was recently completed to relieve sanitary sewer overflows (SSOs) and basement backups within the Gravois Creek watershed. Working through MSD’s prime consultant, Burns & McDonnell, Wade Trim provided planning and design services for the new facility including storage sizing and hydraulics evaluation, civil, structural, and process mechanical, as well as construction phase services and startup assistance.

The Gravois Trunk Sanitary Storage Facility increases the collection system’s capacity during heavy rains, storing up to 8 MG of sewage until the Gravois Trunk Sewer has adequate capacity to accept the flow, and eliminates two constructed SSO outfalls. Wade Trim’s hydraulic evaluation of storage requirements included continuous simulation of historic rainfall records to assess hydraulic performance of the facility using a calibrated XPSWMM model of the Gravois Creek watershed. To best fit the project site, two, 4-MG, above-ground storage tanks were designed. Special care was taken in design of the tank façades, landscaping, and fencing to address stakeholder concerns about aesthetics.

The project also features an influent pump station and wash water cleaning system. The pump station conveys the peak 54-MGD wet weather flow diverted from the existing Gravois trunk sewer to the storage tanks. Submersible pumps and valving enable pumping of flows to either tank. Wade Trim provided design services for the diversion structure, influent and effluent sewers, pumping systems, storage tanks, odor control, tank and wet well cleaning systems, and process control. The wash water cleaning system for the tanks and pump station wet well uses a cistern to store rainwater collected from tank roofs, a vertical turbine pumping station, piping, and nozzles. The pumps also provide water to the yard hydrants.