Crawford, Murphy & Tilly (CMT) served as the prime consultant for both the pre-design study and for the final design of the Coldwater Wet Weather Storage Facility Tank “A” project for the Metropolitan St. Louis Sewer District (MSD). The project included hydraulic modeling to determine the best alternative to eliminate sanitary sewer overflows (SSOs) and basement back-ups in an area served by a 9.4-mile-long section of the Coldwater Creek trunk sewer. We developed a flow equalization/storage tank solution that proved to be a more optimal strategy than the previously conceived tunnel concept and resulted in a cost savings in excess of $80 million over a traditional deep tunnel relief sewer. Continued modeling during design, allowed for further value enhancements that saved money on construction.

The main features include a six million gallon concrete wet weather storage tank, a diversion structure, an influent pump station with six submersible pumps to accommodate a wide range of flows with a firm capacity of 30,000 GPM, and a SCADA system for real-time monitoring of wet weather levels in the trunk sewer and controlling the diversion of flow into and out of the wet weather storage tank.

Given the location of the tank facility within a residential community, a context-sensitive design approach was essential. CMT and MSD worked with a citizens’ committee to address concerns that the facilities would be obtrusive and unsightly. An Exterior Insulation Finishing System was used to create faux windows and other aesthetic features on the tank surface to make it resemble an office building. Green features were incorporated, including a unique rain water harvesting design for the tank’s spray wash system. A rain garden was also designed for on-site groundwater infiltration.