The City of Atchison had combined sanitary/storm sewers (CSS). Dry period wastewater flows flow uneventfully directly to the wastewater treatment plant. Rainfall contributed stormwater runoff to the CSS. The resulting combined flows can exceed the collection system capacity and the City is treating stormwater runoff at the wastewater treatment. During wet times the City was producing CSS overflows. The City is under Kansas Department of Health and Environment mandate to separate CSS flows to reduce or eliminate combined sewer overflows. 

Part of the watershed is controlled by Flood Retarding Dam #6. This project separated stormwater runoff from the CSS at Atchison Ave. and 16th Street and discharges it into White Clay Creek. This storm sewer consisted of 2,550 linear feet of 48” to 60” reinforced concrete pipe. The storm sewer was constructed in two phases. Phase 1 runs from the outfall at White Clay Creek north to the alley at 15th Street between Kansas Ave and Santa Fe Street; Phase 2 completed the storm sewer from the alley to Dam 6. 

This improvement conveyed the 1% SCS Type II, 24 hour rainfall event of 420 cubic feet per second to White Clay Creek.