What is a Sanitary Sewer Overflow?
Average, daily flow of water through a community’s Sanitary Sewer system can be very different than the flow seen during a large rain storm or in Spring during high snowmelt runoff. This increase in water does not mean that residents are suddenly creating more wastewater (water that goes down drains and toilets). It usually means that “extra” “clear” water is getting into the sanitary sewer system through the process of Inflow and Infiltration. Wastewater plants are sized to handle much more than “average” daily flow. In Duluth, average daily flow to the Western Lake Superior Sanitary District is about 48 million gallons per day. The treatment facility can handle up to about 120 million gallons per day. On rainy days, this flow may rise to well over 100 million gallons per day, and in extreme situations, considerably more. See what happened at WLSSD from a huge storm on July 3, 2003. How can this happen? When a lot of “extra” water that should be handled by the storm sewer system, that
