Design and Performance of Multipurpose Constructed Wetland and Flow Equalization Basin

DavidE.Schaad,Ph.D.,P.E.
Walter“Brent”Chambers
JamesM.Halley,P.E.
ScottDenson

Abstract: Storm water runoff from a portion of a 273 ha (675 acres) Midwestern rail yard contacts industrial facilities including fuel storage tanks and fueling and servicing operation areas. Stormwater draining from a smaller 64 ha (159acres) sub-basin containing the industrial facilities previously flowed into a retention pond within the rail yard. The retention pond had a surface area of 607m (0.15 acre) and a maximum storage capacity of 1.4 million L (370,000 gal). Given the large drainage area of the pond the retention time within the pond was shorter than optimal, limiting its potential effectiveness for improving water quality. To address these issues the pond was redesigned to havea 6.25million L (1.65 million gal) storage capacity and configured into a constructed wetland to control a 50-year storm event and increase its ability to treat stormwater runoff. A network of riparian plants (5,700) was placed within the stormwater wetland to treat runoff prior to discharge off-site. Evaluating the performance of both the former and current retention basins revealed significant improvements in the retention and treatmentability when comparing the two structures. Mean total suspended solid concentrations and oil and grease concentrations were reduced approximately 45% when comparing pre-and postconstruction flow analysis. This innovative multiuse approach has demonstrated effectiveness in controlling storm flows and treating runoff from the rail yard.

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