Since the early 1990s, the City of Wilmington, Delaware, has been outlining a Long Term Control Plan (LTCP) to initiate a series of improvement projects aimed at reducing combined sewer overflow events and increasing the annual average flow intercepted at the city’s wastewater treatment plant from 50 percent to more than 87 percent.

One of the key developments in this LTCP was the implementation of a coordinated systemwide real-time control (RTC) solution, which consisted of building five control stations, controlling three existing siphons, and implementing an extensive network of data collection and monitoring sites. In addition, all of the local stations were linked to a central station via a telemetry system.

By optimizing the use of the existing sewer system capacity, the coordinated systemwide RTC system developed by Tetra Tech has enabled the City of Wilmington to maximize its system performance at minimal cost. Specifically, when considering conventional approaches for addressing the LTCP objectives such as storage tanks or increasing conveyance capacity (estimated at $114 million), the cost of the RTC solution was significantly more attractive at $27 million.

Furthermore, with a lower startup investment, the coordinated systemwide RTC approach has been implemented more quickly, thus providing environmental benefits sooner than conventional solutions.