DRY WEATHER INFILTRATION AND INFLOW EVALUATION CHALLENGES IN A LARGE URBAN COMBINED SEWER SYSTEM

摘要

Flow Monitoring and Infiltration and Inflow (I/I) evaluations in urban combined sewer systems have historically focused on determining the quantity of rainfall induced infiltration and inflow (RDI/I). Less common are large-scale efforts to quantify the constituent components of dry weather flows. Dry weather evaluations have unique characteristics and present different challenges than those present in wet weather studies. rnFaced with estimated “unaccounted for” flows comprising approximately 30 percent of incoming flows to the City of Detroit WWTP during dry weather conditions, leading to disputes with wholesale customers over sewer rates, the Detroit Water and Sewerage Department (DWSD) embarked on a significant evaluation to locate, quantify and develop cost effective measures for, elimination of excessive dry weather Infiltration and Inflow (DWI/I) from the City of Detroit portion of the Greater Detroit Regional Sewer System (GDRSS). This major undertaking was broken down into over ten total tasks. Included in these tasks were the following key subtasks: rn1. Extensive records review complemented by targeted field investigations to delineate appropriately sized dry weather sewersheds (meter districts), select suitable flow monitoring sites, and prepare sites for temporary flow monitor installation. rn2. Cleaning of selected sewers and manholes to remove sediment and debris from key meter sites in advance of flow monitoring. rn3. Installation, calibration, confirmation, maintenance and data download of ten (10)-minute interval depth and velocity reads for 193 meters installed and concurrently operational for a 45-day flow monitoring period. rn4. Compiling population, employment, Significant Industrial User (SIU), and water consumption data for the entire study area, and employing Geographical Information System (GIS) tools to allocate the various parameters to the project-specific meter districts.