Springfield, Ill.-based engineer Crawford, Murphy & Tilly Inc. (CMT) has a transformative effect on the design issues it encounters.
To contend with sanitary sewer overflows in an area served by a 9.4-mile-long section of trunk sewer, Metropolitan St. Louis Sewer District (MSD) initially considered constructing a $120-million to $160-million deep tunnel relief sewer until, during a predesign study, client and CMT began to brainstorm.
"Our rule is, there's no crazy idea. Put everything on the table," says CMT project manager Raed Armouti.
In all, discussions generated 14 feasible alternatives, though one in particular resonated. What if MSD instead constructed as many as four flow-equalization tanks to store sewage during a rain event, then release it into the system once conditions stabilized? In theory, the alternative could yield considerable savings, assuming it was executed in combination with upgrades to existing pipe that reduced infiltration and inflow.
In subsequent sessions, CMT performed hydraulic modeling to vet the concept, evaluating design flows, sewer sizes, storage volumes and placement of the tanks within the sewer system, all while calculating costs of candidate configurations.
The upshot: Only two storage tanks were needed rather than four, bringing total cost savings to more than $80 million.
As designed by CMT, the first of the two tanks, a 6-million-gallon concrete structure, is supported by a diversion structure and six submersible pumps to accommodate a range of flows, with a firm capacity of 30,000 gpm. During rainfalls, a real-time SCADA system monitors water levels in the trunk sewer while controlling diversion of flow into and out of the tank, a solution that minimized storage requirements.
The project, completed last year, was the first of its kind for MSD.
For CMT, a firm of 260 employees, firsts are second nature. "We're not a firm that holds box lunch meetings to discuss how to innovate," says Roger Austin, CMT vice president and marketing director. "It's in our DNA. We're a medium-size firm that brings a small firm's perspective to client needs. We don't bring cookie-cutter concepts to the table."
Nor are designers constrained by layers of management. Across 10 regional offices and four operating groups, including aviation, highways and bridges, water resources and civil site services, "the project manager is king," says the firm's president, Dan Meckes, who is based in the firm's St. Louis office. "Organizationally, we're flat. We believe in empowering our designers and letting them lead in our collaborations with clients."