Extrapolation of Available Monitoring Data to Facilitate Long-Term Continuous Simulation Modeling

Abstract

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 (H&H) computer 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 control facilities to select 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 and utilized. The accurate representation of the diurnal and seasonal variation in dry weather (or base) flows is an important component of an accurate continuous simulation model. Imprecision related to the representation of wastewater base flow conditions can translate into inaccuracies associated with simulation of wet weather peak flows and volumes and can result in potential errors in the selection and design of control facilities.