An Investigation of Infiltration in a Constructed Stormwater Wetland and Implications for Groundwater Quality

Traditionally, detention basins and constructed stormwater wetlands (CSW) have been used primarily for peak flow reduction and water quality improvement and are assumed to possess negligible infiltrative capabilities. However, the potential for storm water infiltration within these structures and the associated non-point source pollution of groundwater can not be ignored based on untested assumptions. The purpose of this research was to assess the infiltration capacity of a mature CSW on Villanova University's campus, in Villanova, Pennsylvania. Piezometers located within the CSW were monitored to develop a water budget and a chloride mass balance. The vertical gradients in the piezometers alternated between recharge and discharge patterns, with downward recharge gradients for baseflow conditions and upward discharge gradients after rainfall events. Preliminary water budget and chloride mass balance analyses suggest considerable reductions in volume and chloride load over a 6.5 day baseflow period in December, 2008. Although these findings suggest infiltration contributes to the water budget, it is unclear whether other explanations (e.g. perched water table or chloride stratification) could account for these patterns. Infiltration may be the most parsimonious explanation, but further research needs to be conducted to determine whether the negligible infiltration assumption is valid.