Impacts of Stormwater Infiltration on Groundwater

The infiltration of stormwater has become a popular tool for stormwater management; however relatively little research has examined the impact of infiltration on groundwater. This research presents a case study of the impacts of stormwater infiltration on a shallow unconfined aquifer at a bioinfiltration Best Management Practice (BMP) on the campus of Villanova University. The study site is a vegetated infiltration basin with a 1.3 acre drainage area consisting of parking areas and recreational fields with approximately 35% directly connected impervious area. The study utilizes continuous monitoring of groundwater elevation, temperature and conductivity in conjunction with hydrologic monitoring to assess the transport of chloride and conductivity and to examine the extent of groundwater mounding. Results indicate a direct impact on groundwater chloride concentration and conductivity near the BMP, but also show significant attenuation of influent concentrations. Regarding groundwater mounding, it is observed that following precipitation of less than approximately 0.75 inches, the upgradient control well presents larger increases in groundwater elevation than other wells, but for storms larger than 0.75 inches, the well adjacent to the site displays increased mounding. Groundwater elevation monitoring indicates that the extent of groundwater mounding is localized and is related to infiltration rate and groundwater temperature. This study demonstrates the utility of groundwater monitoring for the purpose of BMP performance assessment. It is suggested that groundwater monitoring be considered for site monitoring plans and as a tool for BMP site selection.