Optimizing Capacity Management to Mitigate Flooding and CSOs in St. Louis, MO

Combined Sewer Overflows (CSOs) are a major water pollution and public health concern that affect nearly 700 communities across the United States (US EPA, 2024). Sewer separation is an effective CSO mitigation strategy but is costly and disruptive. Detention systems offer a more cost-effective alternative, capturing and gradually releasing stormwater to reduce flooding and CSOs. Historically, passive detention systems have limited wet weather capture rates (10-20%). However, the advent of 'smart data infrastructure,' as defined by the USEPA, has enabled the development of real-time control systems like Continuous Monitoring and Adaptive Control (CMAC) (US EPA, 2018). CMAC integrates sensor data and forecasts to actively manage stormwater storage and flows. This dynamic approach can significantly increase capture rates to over 90% for both new and existing detention systems. By optimizing release timing based on downstream capacity, CMAC prevents overflows, minimizes flooding, and enhances collection system efficiency. This presentation will demonstrate the effectiveness of predictive wet weather capacity management and optimization using CMAC technology to mitigate Combined Sewer Overflows (CSOs). This technology can provide a cost-effective and sustainable alternative to expensive and disruptive solutions like sewer separation, offering improved system resilience, reduced environmental impact, and enhanced water quality. The case study will focus on the North Pointe detention basin in St. Louis, Missouri, where the implementation of an Opti CMAC system significantly increased stormwater capture and reduced peak flows compared to traditional passive detention systems. In St. Louis, the Metropolitan St. Louis Sewer District (MSD) implemented an Opti CMAC system at the North Pointe detention basin with the objective of enhancing CSO compliance and flood mitigation via system optimization. This pilot project integrated digital solutions from Opti (adaptive control technology) with ADS Environmental Services (ADS) (continuous flow and level monitoring). The CMAC system, hosted on a robust software platform, includes real-time data visualization and field monitoring to optimize stormwater retention and outflow management. The primary goal is to minimize runoff entering the MSD combined sewer system by strategically managing stormwater releases during and after rainfall events. The control valve is proactively and automatically adjusted before, during, and after storms to prevent overflows and maximize detention time. This predictive control strategy reduces peak flow discharges and improves stormwater management effectiveness. Over a 5-month optimization period, the Opti CMAC system at North Pointe detention basin handled 14 storm events, capturing 1.8 million gallons of stormwater, or 82% of the wet weather flow volume. This is significantly higher than the modeled 10% capture rate of a passive system. Additionally, the CMAC system achieved an 85% reduction in peak flow rates released from the basin compared to the passive design. The system was designed to capture up to a 1-inch storm event, and successfully retained this volume during a March 25, 2024 storm without discharging (as shown in Figure 1). The system's pre-event drawdown, initiated 3 hours before rainfall, created enough storage capacity for incoming runoff. During the storm, the valve closed to retain water, preventing stormwater release into the downstream sewer system. The system significantly reduced the risk of combined sewer overflows (CSOs) by retaining runoff from its contributing area during the September 2024 storm event. The successful implementation of the Opti CMAC system at the North Pointe detention basin demonstrates the significant potential of predictive wet weather capacity management and optimization for CSO mitigation. By leveraging smart data infrastructure and real-time control, the CMAC system achieved a substantial increase in wet weather capture and a significant reduction in peak flows compared to traditional passive systems. This case study demonstrates the feasibility and effectiveness of CMAC technology as a sustainable and cost-effective solution for enhancing stormwater management and reducing CSOs in urban environments. Expanding this approach to a network of connected detention basins offers the potential for even greater benefits, enabling coordinated release strategies and further minimizing the risk of CSOs.