Minnesota Department of Transportation
A field-monitoring program began in the spring of 2000 to test the ability of a grassy swale at removing pollutants in stormwater. In 2001, a check dam was designed in conjunction with Minnesota Department of Transportation (Mn/Dot) engineers and installed into the vegetative swale. The check dam system incorporated some unique design features including a peat filter to trap nutrients and metals; and a low rock pool to trap water for biological processing. The check dam was designed for cost effectiveness and simple installation. The entire system was quantified and evaluated hydrologically and qualitatively both before and after the check dam installation. Pollutants monitored included total suspended solids, total phosphorus, and orthophosphorus. The average pollutant removal rates for the three storms following the installation of the check dam were 54 percent total phosphorus, 47 percent orthophosphorus, and 50 percent total suspended solids. The results suggest that properly designed short vegetative strips and swales, which include peat and rock check dams can substantially reduce pollutant levels from the stormwater exiting roadways.
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