Unit Process Modeling of Stormwater Flow and Pollutant Sorption in a Bioretention Cell

Bioretention is a mulch/soil/plant-based low impact development facility employed to collect, store, infiltrate and treat urban stormwater runoff. This work focuses on modeling to describe the fate of stormwater and the adsorption of pollutants in bioretention facilities. A two dimensional Variable Saturated Flow and Transport Model is developed based on partial differential equation modes in COMSOL Multiphysics, in which both fluid flow and solute transport are under transient analysis. Model results indicate that the outflow volume is less than the inflow due to the storage and the extent of initial unsaturation in the media. The outflow volume from loamy sand media (with larger K^s) is larger than that from sandy loam media. The flow peak is reduced. Concentrations of naphthalene (NP) and pyrene (PY) in runoff vary with depth and most NP and PY (> 90%) is removed within about 3 cm media depth.