The Allegheny County Sanitary Authority (ALCOSAN) is implementing a regional plan to control Combined Sewer Overflow (CSO) and Sanitary Sewer Overflow (SSO) discharges into receiving water bodies within the greater Pittsburgh region. In order to develop and evaluate alternative conveyance and control facilities to regulate the frequency and volume of CSO and SSO discharges, ALCOSAN has developed detailed hydrologic and hydraulic simulation models. These models are used to quantify and characterize the amount of flow conveyed by tributary service communities and guide the decision making process by evaluating various alternative solutions to choose the most viable and cost effective solutions. To adequately account for seasonal and annual variability on system-wide flow from the regional collection systems, a long-term continuous simulation modeling approach has been selected.
This paper will demonstrate the innovative methods and techniques used to accurately characterize and quantify spatially and temporally varied dry and wet weather flow for a 6-year simulation period. Seasonal and annual variability for base wastewater flow has a significant impact on available release rates from a proposed regional network of flow equalization facilities. There are over 400 points of connection to the ALCOSAN interceptor system. Many have physical conditions that make it infeasible to provide accurate and reliable flow monitoring and it would be cost prohibitive and unnecessary to monitor for the entire 6-year analysis period. To perform multi-year continuous simulations, analytical results from monitored dry weather flow periods and monitored storms events are extrapolated and applied to locations and simulation periods for which there is no directly monitored wastewater flow data available.