Removal of Heavy Metal Pollutants (Copper, Chromium and Lead) by a Bi-Phasic Rain Garden Ecosystem

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Rain gardens are a relatively new best management practice (BMP) to treat urban stormwater runoff while additionally providing for an aesthetically pleasing landscape. The runoff, diverted from the storm sewer, is treated in the rain garden before recharging the groundwater. Heavy metals in urban areas are a concern due to both their persistence in the environment and potentially adverse health effects. Three replicated rain gardens were constructed using a novel bi-phasic design that consists of both an anaerobic (oxygen-deprived) and an aerobic (oxygen-rich) zone. A field study was conducted whereby multiple rainfall events were applied to collect simulated stormwater runoff from a concrete pad. During each simulated rain, water samples were collected at three sampling points: 1) the inlet to the rain garden, 2) the interface between the anaerobic and aerobic zone, and 3) at the final discharge of the aerobic zone. The water samples were analyzed for copper (Cu), chromium (Cr) and lead (Pb) to determine removal efficiency. Initial concentrations of the metals in the water entering the rain gardens were in excess of the legally enforceable Environmental Protection Agency’s (EPA) Maximum Contamination Level standards (MCL) by at least 7.5 times. The rain gardens were effective in removing metals with results showing a decrease in the heavy metal concentrations at both sampling points 2 and 3; overall, the removal was a greater than 99%. Of the 36 samples analyzed from the aerobic (final) discharge pipe, all were also below the MCL.



Rain Garden, Biorention, Heavy Metals, runoff pollutants