Comparing Bioretention Designs With and Without an Internal Water Storage Layer for Treating Highway Runoff

This study compares the performance of a field bioretention cell with and without an internal water storage (IWS) layer for treating highway runoff. Both synthetic and natural runoff tests were conducted. Hydraulic performances on peak discharge reduction and detention time extension were measured. Pollutant removal efficiencies were evaluated for total suspended solids (TSS), copper (Cu), lead (Pb), zinc (Zn), total nitrogen, nitrate, ammonia, total phosphorus, and orthophosphate phosphorus. Pollutants in soil media were measured. Results reveal that both IWS and non-IWS designs reduced peak discharge and extended detention time, while the IWS design performed better. For water quality performance, the non-IWS design removed TSS, Cu, Pb, Zn, and total phosphorus to varying degrees of efficiency, but total nitrogen removal was minimal. The IWS layer significantly improved removal efficiencies for TSS, Cu, Zn, nitrogen, and phosphorus. Soil media accumulated some metals over time.