Rainfall-derived infiltration and inflow (RDII) into sanitary sewer systems has long been recognized as a source of operating problems in sewerage systems. RDII is the main cause of sanitary sewer overflows (SSOs) to basements, streets, or nearby receiving waters and can also cause serious operating problems at wastewater treatment facilities. Thus, there is a need to develop proven methodologies and computer tools to assist SSO communities in developing an optimal capital improvement program that is in line with the projected annual capital budget and provides flexibility for future improvements. To assist municipalities in developing plans to mitigate SSO problems, the United States Environmental Protection Agency (USEPA) developed a public-domain Sanitary Sewer Overflow Analysis and Planning (SSOAP) toolbox. The SSOAP toolbox is a suite of computer software tools used for quantification of RDII and facilitating capacity analysis of sanitary sewer systems. This toolbox includes USEPA Storm Water Management Model Version 5 (SWMM5) for performing dynamic routing of flows through the sanitary sewer systems.
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