Integration of Water Billing Records in Estimating Base Wastewater Flow Rates to Support Large-Scale Sewer System Computer Modeling

The Metropolitan Sewer District of Greater Cincinnati (MSDGC) is developing a computer model of its collection system, referred to as the System Wide Model (SWM). The model will be used to characterize and evaluate nearly 90 sanitary sewer overflows (SSOs) and approximately 230 Combined Sewer Overflows (CSOs), address wet-weather problems related to SSOs and CSOs, and ultimately evaluate the use of real-time sewer system controls (RTC). One of the key elements of the SWM development is integration of detailed water billing records to establish the base flow rates for the dry-weather model simulations. This paper describes how more than 225,000 water billing records were integrated in base flow estimates for 30,000 catchment areas, and demonstrates how this approach for base flow estimation impacted the dry-weather model calibrations.In lieu of using typical unit wastewater flow rates correlated to land use and population data to estimate the BWF, water billing/use records were used to estimate the BWF in the pipes throughout the study area. Using the water billing records as a basis to estimate DWF, the SWM was calibrated to within approximately five percent of the measured flow rates for the entire MSDGC service area. The authors concluded that the use of water billing records provided a reliable basis for establishing the base flows in the sewer system.