Enhancing Rain Garden Design to Promote Nitrate Removal

Rain gardens effectively remove some stressors from stormwater, but in most cases they show much smaller removal rates of nitrate, likely due to the media's high sand and low organic matter content that inhibit nitrate removal by denitrification. 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 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 that migration of finer particles into the deeper soils could have inhibited drainage.