Milk River CSO Facility Modernization

The Milk River CSO Facility (located in St. Clair Shores, Michigan) was originally constructed in 1958 to reduce untreated discharges of combined sewage. The facility was significantly upgraded in 1994 and again in 2021. Upgrades include incorporation of new technology and replacement of aging systems. As other CSO facilities age, they will need to undergo similar upgrades and improvements while continuing to be available for wet weather event management. The Milk River facility provides a case study of issues to be considered in these upgrades and provides insight into design considerations for newer facilities. This presentation will discuss 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 paper and presentation will compare and contrast the old versus new process systems, modifications desired after 25 years of operation, and challenges with the construction process. BACKGROUND The Milk River CSO facility serves a combined tributary area of approximately 4,000 acres, including the majority of the communities of Harper Woods and Grosse Pointe Woods, MI. All flows tributary to the facility are pumped. The pump station provides 10,000 gpm (14.4 MGD) of dry weather capacity discharging to the interceptor and 862,000 gpm (1240 MGD) of wet weather capacity. Process elements include bar racks, storage, disinfection, aeration, recirculation pumping and flushing systems. The original 1958 storage capacity was 3 MG. This was expanded to 19 MG in the 1994 upgrades. The historic Milk River was almost completely replaced by the combined sewer system service area. The remaining river remnant functions as an estuary of Lake St. Clair. A vast majority of the flow that enters this remnant river is treated CSO discharge. This results in several unique challenges and facility components, including a river recirculation system (with aeration) to prevent dissolved oxygen depletion and hydraulic impacts related to the high Great Lake levels with are impacting the outlet conditions at the facility. MODERNIZATION AND EQUIPMENT REPLACEMENT At the time of the current project, components of the facility dated from either 1958 (pump station and many buildings), or 1994 (storage basins, flushing system, disinfection and aeration elements). Improvements were designed throughout the entire facility that would result in improved pollutant removal, ease of operations and improved efficiency. such that the aged buildings and infrastructure would be renewed with limited anticipated upgrades over the next generation. Improvements included: · Flushing system upgrades included conversion of the nozzle based flushing system to the use of flushing gates. The modification required reconfiguration of the storage compartment floor, with the modification of floor slope and the addition of flushing lanes. This issue needed to be addressed at the regulatory level because the volume available in the basin would actually decrease with the new flushing methodology. · The disinfection system was upgraded to refine the dosing of sodium hypochlorite and improve the reliability of the system. This work included new pumps and piping for disinfection and rehabilitation of the chemical storage tanks. · Modifications to improve dewatering were implemented. Recent consolidation of basin operations with other CSO facilities in the tributary area further coordinates with and makes better use of the available space in the interceptor. The dewatering system needed to be able to operate at a greater range of flow conditions. Changes included the replacement of dewatering pumps and the addition of grit pumps to handle the increased removal of solids. In addition, the automation of the facility was tied back to interceptor levels so that the basin could be dewatered sooner than previously possible. · Improvements were provided to the aeration system to improve blower operation. · New chemical feed improvements were provided with, new and a new zebra mussel control feed system. · Pumping station upgrades included reconditioning of 6 wet weather 'storm' pumps and motors. To keep the station in operation, a detailed construction sequencing plan was provided to ensure that firm capacity was maintained throughout the construction period. The dry weather 'sanitary' pump station improvements required influent sewer access structure, bypass pumping and a new stoplog structure to isolate the sanitary wet well and allow for continual dry weather flow into the Detroit Interceptor. · A new concrete bridge and loading/unloading platform was designed for storm pump removal and maintenance. The structural platform was designed over the top of the existing basin requiring unique structural support while allowing for ease of access to all pumps. · Upgrades were designed for the recirculation pumping system that provides fresh water to the Milk River channel from Lake St. Clair. The intake piping and force main were inspected and found to require removal of sediment and rehabilitation. Zebra and other mussels were infesting the intake and improvements were necessary to clean, repair, and provide for future mussel control. · Other upgrades included heating and ventilation improvements for energy efficiency; and a complete electrical upgrade. Energy efficient lighting and controls were added. The building architecture was reconditioned, including aesthetic and safety improvements. Automation of the facility allows for a reduction in staffing levels and coordination with other CSO facilities in the area. CONCLUSION This presentation will highlight lessons learned in an existing CSO facility that are being addressed through upgrades. The project and its components will inform other facility design, both for existing and proposed facilities. These improvements will aid in operation and maintenance, as well as process performance and reliability.