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Enhancing Rain Garden Design to Promote Nitrate Removal: Testing a media carbon amendment
Citation:
STANDER, E. Enhancing Rain Garden Design to Promote Nitrate Removal: Testing a media carbon amendment. Presented at SER/ESA Mid-Atlantic Chapter Meeting, Ewing, NJ, March 13, 2009.
Impact/Purpose:
To inform the public.
Description:
Rain gardens effectively remove some stressors from stormwater, in particular heavy metals, phosphorus, and oil and grease, but in most cases they show much smaller removal rates of nitrate. This is likely due to the high sand and low organic matter content specified for rain garden media. These properties promote stormwater infiltration, but they inhibit nitrate removal by denitrification, a microbial process that requires anoxic conditions and a source of labile carbon. EPA’s pilot-scale research explores the use of shredded, unprinted newspaper as a carbon source to fuel denitrification. A bench-scale experiment was conducted to test the drainage capability of media containing shredded newspaper layers. Stormwater was introduced at low and high rates to bins containing zero, one, and two layers of newspaper at varying depths. While there were differences in effluent volumes and flow rates between control and newspaper treatments, surface ponding occurred in all three treatments, suggesting that some other factor besides the newspaper had an effect on drainage properties. Grain size and clay mineralogy analyses indicated the migration of finer particles into the deeper soils which could have inhibited drainage, particularly because one of the minerals contained in the clay, illite, may become gel-like when saturated. The larger, pilot-scale study is currently being designed to test the effects of shredded newspaper, the presence of a deep saturated zone, vegetation type, and hydraulic conductivity on the nitrate removal capacity of rain garden media.
