Application of Modeling shows that Downspout Disconnect Program Can Eliminate Sensitive CSO

Field investigations in the Rockford Road service area of Wilmington revealed four engineered interconnections between a sanitary and storm sewer. These interconnections cause sanitary sewage to be diverted into the storm sewer system during precipitation events creating a “Combined Sewer Overflow” (CSO); discharging to the Brandywine Creek upstream of the City's water supply intake. Consistent with the objectives of the National CSO Policy for addressing CSOs in sensitive areas, a sewer separation project was determined to be necessary to eliminate overflows.For this project MOUSE, by the Danish Hydraulic Institute, was used to examine alternative separation approaches. The results of the 10-year model simulation were applied to the intensity-duration-frequency curves for the area to derive a correlation between the percentage of rooftop area disconnected and the level of protection against basement flooding provided. It was concluded that a roof leader separation program could be effective in eliminating the CSO for the most storm events.