Peak wet-weather flows posed a challenge for the Detroit Wastewater Treatment Plant. A state-issued discharge permit to the Detroit Water and Sewerage Department (DWSD) required the city spend over $2 billion for CSO detention basins.

Malcolm Pirnie assisted DWSD in negotiations with the state to craft a less costly short-term CSO demonstration program. The Pirnie team also helped develop a control plan that allowed DWSD to optimize the use of the existing system for storage, transport and treatment of wet-weather flows. The plan accounted for the design of sewage sampling stations to monitor sewage entering the system; installation of inflatable dams within the collection system piping network and upgraded regulating and control equipment to allow discharge flow rate flexibility and flow balancing within the system.

Conventional CSO control measures cost an estimated $4 billion. The Pirnie team’s long-term CSO Control Plan reduced the cost to $1 billion.