Sanitary Sewer OverflowsThe Duluth Sanitary Sewer Collection System has the capacity to contain a specified volume of wastewater within the system. The capacity is more than enough to handle dry weather flow. However wet weather and snow melt may cause excess water to enter the sanitary collection system though leaks or illegal connections, roof drain connections or footing drains. This excess water, in turn, causes the system to overload resulting in system back up and overflows at certain locations. These overflows are referred to as Sanitary Sewer Overflows (SSO). WLSSD and the City are co-permittees on a National Pollution Discharge Elimination system (NPDES) Collection System Permit. The permit addresses problems the systems have encountered with overfills that spill sewage into the environment. The permit requires the permittees to control or eliminate all overflows by 2007. Overflows occur during wet weather when storm water (clean water) enters the system (this is called “inflow and infiltration� of the system). The clear water from storms finds its way into the system through old connections to roof and footing drains, broken or cracked lateral piping from homes and businesses, defects in the infrastructure or through illicit connections. Other overflows occur as the result of pipe breakages or blockages during dry weather. In order to eliminate the problem these situations must be minimized.
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