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Design, Installation and Monitoring of Subsurface Treatment System to Reduce Phosphorus Loading from Tile Drains

Once dismissed as negligible, phosphorus levels in subsurface tile drain flow are now recognized as significant. Phosphorus removal systems installed at the outlets of tile drains that direct flow through filtering media have the potential to significantly reduce P loads to drainage ditches and receiving waters. Stone and the Friends of Northern Lake Champlain (FNLC) implemented Vermont’s interim practice standard (Phosphorus Removal System, Code 782) for the first time. Stone designed and constructed a phosphorus removal system on a farm in Franklin, Vermont designed to capture phosphorus via sorptive media immediately before it discharged to surface waters as a pollutant, and return it to cropland in a soil amendment for beneficial reuse. This practice has been successfully employed to treat water in drainage ditches, as well as runoff from agricultural and residential land uses. Stone evaluated a variety of media and selected a limestone bedding sand from a Swanton quarry and drinking water treatment residuals from Champlain Water District.