CSO Characterization
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The NetSTORM module of the program has been used by Manchester, New Hampshire, Philadelphia and Pittsburgh, Pennsylvania, and Indianapolis, Indiana for computing average annual CSO statistics. In Manchester, the program has been used for 2002 and 2003 USEPA National Pollution Discharge Elimination System (NPDES) compliance reports. While Manchester developed a detailed SWMM model of the collection system in the mid-1990s, that model has not been updated in recent years to maintain currency with extensive sewer separation work performed to reduce CSO activity. In 2003, CDM recalibrated an existing NetSTORM model that had been developed and calibrated in the mid-1990s. Runoff parameters were adjusted as appropriate in basins where separation work had been performed. The recalibration used year-round digital hourly data from a pumping station that services one-third of the sewered area, as well as hourly data from the wastewater treatment plant (WWTP) and from a CSO located immediately upgradient of the WWTP. Groundwater infiltration into the system was mimicked by extracting the four-day minimum flow from the WWTP inflow time series. Diurnal variation in sanitary flow was similarly computed from the filtered WWTP flow data. While only daily precipitation data for Manchester were available, hourly data were obtained for Concord, New Hampshire, located 25 km (15 miles) to the north. The daily data for Manchester were synthetically disaggregated based on the Concord records on a storm-by-storm basis. The resulting hourly precipitation data was thus accurate on a daily basis, but not robust on an hourly basis. The resulting model nonetheless yielded reasonable estimates of flow to the WWTP, and was judged to be reasonable for estimating citywide CSO.


The NetSTORM applications in Philadelphia, Pittsburgh, and Indianapolis have been used for similar purposes. Each model was developed in tandem with a SWMM model of the collection system, but the NetSTORM models were able to be more rapidly deployed. The NetSTORM models could also perform long simulations based on 50 to 100 years of precipitation data, whereas the SWMM models could not practically be run for more than one year until recently. Although it would have been possible to develop moderately fast SWMM models using kinematic wave routing in SWMM Transport, NetSTORM has much simpler input requirements and is custom-designed to produce annual average CSO statistics needed for CSO facilities planning and NPDES reporting. The Indianapolis NetSTORM model is presented as a case study in USEPAs CSO monitoring and modeling guidance document (USEPA, 1999).