A properly designed, operated and maintained sanitary sewer system is meant to collect and convey all of the sewage that flows into it to a wastewater treatment plant. However, occasional unintentional discharges of raw sewage from municipal sanitary sewers – called sanitary sewer overflows (SSOs) – occur in many systems.
Rainfall-derived infiltration and inflow (RDII) into sanitary sewer systems has long been recognized as a major source of operating problems, causing poor performance of many sewer systems. RDII is the main cause of SSOs to customer basements, streets or nearby streams and can also cause serious operating problems at wastewater treatment facilities. There is a need to develop proven methodologies and computer tools to assist communities in developing SSO control plans that are in line with their projected annual capital budgets and provide flexibility in future improvements.
To accomplish this goal, the U.S. EPA entered into a cooperative research and development agreement (CRADA) in 2003 with Camp Dresser & McKee Inc. (CDM) to develop a public-domain Sanitary Sewer Overflow Analysis and Planning (SSOAP) Toolbox. The CRADA also included preparation of a technical guide for analyzing RDII, performing capacity analyses of sanitary sewer systems and developing SSO control plans using the toolbox. The U.S. EPA published this technical guide in October 2007 (EPA/600/R-07/111) and plans to release a beta version of the Toolbox to the public in the spring of 2008.
The Toolbox contains five primary tools: (1) Data Management Tool to store and organize data and serve as the command center of the Toolbox; (2) RDII Analysis Tool to perform the wastewater flow decomposition and determine R, T, K parameter values that provides reasonable fit between the computed RDII hydrograph and RDII hydrograph derived from the monitored data; (3) RDII Hydrograph Generation Tool to generate the RDII hydrograph of a sewershed for the selected rainfall events using its physical characteristics (e.g., sewer areas and land uses); (4) SWMM5 Interface Tool to incorporate the inflow hydrograph (RDII plus dry-weather flow) from a sewershed into the SWMM5 input file; and (5) SWMM5 to perform the actual dynamic flow routing through a sewer system and export the output data for further analysis.
The conference presentation will provide the status of the SSOAP Toolbox development and an overview of various functional tools within the Toolbox.