When the Metropolitan St. Louis Sewer District (MSD) embarked on its first true design-build project, they turned to the trusted team of CMT and Goodwin Brothers Construction. The project involved the installation of a 1-million-gallon below-grade sanitary sewer overflows (SSOs) relief storage tank, diversion structure, submersible pump station, real-time controls, odor control system, and tank cleaning system.

The station is designed to intercept wet weather event flows by monitoring collection system levels at critical manholes. Excess flows are diverted into the influent pump station and pumped into the storage tank until the event ends. As capacity becomes available in the collection system, stored contents are strategically released to expedite drainage without surcharging the system. Once drained, tanks are automatically cleaned with a high-pressure spray wash system and put back into service for the next wet weather event.

Despite initial budget estimates of $8 million, the design-build team was able to optimize the tank orientation and design to fit on the small site with the Federal Emergency Management Agency (FEMA) floodway limits restrictions. This led to a fixed-price bid of just under $6.7 million, saving MSD $1.3 million (16%).