DETROIT'S LARGEST CSO CONTROL FACILITY: A MAJOR STRUCTURAL UNDERTAKING

In response to the requirements outlined in the National Pollutant Discharge Elimination System (NPDES) permit issued by the Michigan Department of Environmental Quality (MDEQ), the Detroit Water and Sewerage Department (DWSD) developed a Long-Term Combined Sewer Overflow (CSO) Control Planthat addresses the control of discharges from combined sewer outfalls to the Detroit River and the Rouge River. One component of the plan was to construct the Conner Creek CSO Control Facility (facility).Emerging at the head of Conner Creek, the facility was constructed partially inside the existing creek and partially on its west bank. The overall facility is approximately 1,220 feet long and consists of various reinforced concrete structural systems. It was constructed in approximately five years at a construction cost of about 187 million and is the largest CSO control facility in Michigan. Approximately 6,700 concrete filled pipe piles were used to support the facility against gravity and buoyant forces. Over 110,000 cubic yards of cast-in-place concrete and 16,000 tons of reinforcing steel were used in its construction.Several challenges were addressed in the design and construction of the facility as follows:The facility's special hydraulic requirements led to a complex facility configuration.Constraints imposed by the geotechnical conditions led to the multi-staged construction of the retention basin.Site constraints and a potential need for future expansion required locating the facility partially in the creek and partially on land.A requirement for uninterrupted operation of existing infrastructure led to a design requiring multi-staged construction of the basin's influent channels to make connection to the existing outfalls.Special requirements stipulated in the code for environmental facilities (ACI-350R) had to be met.The paper focuses on the design approach used to overcome the above challenges while also meetingthe facility's other design requirements.