Updating a CSO Facility with New Technology and No Interruption in Service

The Milk River Retention Treatment Basin (RTB) was originally constructed in 1958 to reduce untreated discharges of combined sewage. The facility went through significant upgrades in 1994 to meet the State of Michigan's CSO Control Policy. Since the 1994 construction, many components of the system had aged and required improvement. Additionally, technology has changed and has made some working features outdated. In 2017, construction began on extensive retrofits (current construction contract value is $41 million) to replace aging equipment and modify process components, improving operation and maintenance. The current construction upgrades for the facility are essentially complete. This paper describes modifications in system components to take advantage of new technology, changes made to simplify operations, changes made to improve performance, and implementation of the upgrades in a manner that allowed for continuous facility operation. The old versus new process systems are compared, reasons identified for the modifications desired after 25 years of operation are provided, and challenges with the construction process are discussed. This case study provides insights into design enhancements that could be considered for new CSO facilities or other CSO facility upgrades.