Through its long-term water quality improvement program “MSD Project Clear,” the Metropolitan St. Louis Sewer District (MSD) completed the Gravois Trunk Sanitary Storage Facility to relieve sanitary sewer overflows (SSOs) and basement backups in the Gravois Creek watershed. Wade Trim worked with prime consultant Burns & McDonnell to provide planning and design services for the new facility including storage sizing; hydraulics evaluation; civil, structural, and process mechanical engineering; construction phase services; and startup assistance. The project, which increased the MSD collection system’s capacity by 8 million gallons (MG) and eliminated two SSO outfalls, has received an Honor Award through the American Council of Engineering Companies (ACEC) of Missouri’s 2022 Engineering Excellence Awards Competition.

Two 4-MG above-ground storage tanks provide additional storage capacity during heavy rains and were designed to best fit the project site. 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. Special care was taken in design of the tank façades, landscaping, and fencing to address stakeholder concerns about aesthetics.

An influent pump station was necessary to convey peak 54-MGD wet weather flow diverted from the existing Gravois trunk sewer to the storage tanks via submersible pumps and valving. Wade Trim designed the diversion structure, influent and effluent sewers, pumping systems, storage tanks, odor control, tank and wet well cleaning systems, and process control for the pump station. A wash water cleaning system for the tanks and pump station wet well, also a feature of the larger project, uses a cistern to store rainwater collected from tank roofs, a vertical turbine pumping station, piping, and nozzles.

Wade Trim’s John Weiland (left), and Burns and McDonnell Project Manager Curt Kimmel accepted the Honor Award on February 24 at the ACEC of Missouri Awards Banquet in Kansas City.