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.