Systemwide Operation Planning as an Integral Aspect of Specific CSO Facility Designs

In 1994, the City of Portland signed an Amended Stipulation Final Order (ASFO) with the State of Oregon Department of Environmental Quality, agreeing to control combined sewer overflows (CSOs) on the Willamette River by 2011. To achieve the goal of controlling CSO volume by 97 percent, the City has embarked on a series of projects consisting of the expansion of wet-weather treatment capacity at the Columbia Boulevard wastewater treatment plant (CBWTP) and the construction of interceptors, tunnels, and pump stations. This paper focuses on the interconnected Westside and Eastside CSO tunnels. The Westside tunnel is currently being designed and the Eastside CSO tunnel is in the predesign phase. The subject of this paper is the series of analyses performed to ensure that the tunnel designs:Incorporate real-time facilities to optimize operation of the tunnels themselvesInclude planning for future real-time control (RTC) activity that is in harmony with other attributes of the overall CSO program to be completed by 2011The analyses included comprehensive hydrologic and hydraulic modeling of the combined sewer drainage system and the tunnel system, RTC simulation of gates, weirs, and pumping facilities, and planning for instrumentation, monitoring, operation, control, and maintenance.Hydraulic modeling software was used to evaluate and determine the feasibility of a number of operational scenarios and strategies for a variety of objectives. The analysis focused on operating the system in real time to ensure adequate velocities for flushing, maximizing use of the system for storing flows (controlling filling and evacuation), optimizing power consumption at pumping stations, minimizing sharp changes in flow rate arriving at the CBWTP, and controlling the amount of “first-flush ”separate stormwater accepted into the tunnel system.An evaluation matrix was developed to summarize the RTC scenarios and their performance relative to criteria and objectives. Recommendations were then made to the tunnel design steering committee on measures and facilities to incorporate into the design.