5-Year Continuous SWMM Simulation: 17 Gig of Data, 1600 Hours Computer Time, and Updates to the Indianapolis LTCP Configuration

The City of Indianapolis is currently implementing a 20-year, 1.7 billion Combined Sewer Overflow Long-Term Control Plan (CSO LTCP). Indianapolis is pursuing a variety of control measures to implement the LTCP, including deep tunnel storage, treatment plant expansions, consolidation sewers, satellite storage and treatment, and local sewer separation. The LTCP configuration was developed from planning-level modeling performed in 2004. Since 2004, Indianapolis has made a significant investment in the collection of flow monitoring and field surveying data, expansion of its hydraulic model in both the combined and sanitary sewer areas, and detailed calibrations of the combined sewer area and sanitary sewer interceptors. In 2009, the Indianapolis Clean Stream Team completed a 5-year continuous simulation of its expanded SWMM model of the collection system to re-evaluate the planning-level modeling performed in 2004. The continuous simulation included an evaluation of planned interceptor improvement projects outside the combined sewer area, and an evaluation of the potential impact of high river stages on the combined sewer system. Upon completion of the long-term simulation using a detailed (∼ 7,000 node) model, a post-processing database tool was developed to compare the average annual CSO frequency and discharge volume determined in 2004, assess the CSO storage tunnel requirements determined in 2004, and assess the advanced wastewater treatment (AWT) plant improvements determined in 2004.The completed 5-year continuous simulation and associated post-processing determined significant reductions in average annual CSO volume, CSO storage tunnel requirements, and identified an opportunity to optimize the configuration of the Southport AWT plant. The analysis also identified several CSO structures with the strong potential for river infiltration. The potential modifications to the Indianapolis LTCP were presented to U.S. EPA Region V in May 2009.