A Modeling Based Assessment of Groundwater Quality Impacts Under Low Impact Development

Permeable pavements are a low impact development approach that is used to reduce surface water runoff in urbanized watersheds.  One objective is to increase the infiltration into the soils in urban areas by increasing the permeability of the pavements.  The overall goal in many low impact development projects is to ensure that the post-development hydrograph as closely mimics the pre-development hydrograph.  While  surface water runoff and the associated pollutant loading is diminished.  It is likely that these pollutants will infiltrate the subsurface and have the potential to reach the water table.  The filtering capacity of the vadose zone therefore becomes a critical factor in ensuring that this low impact development option does not lead to contamination of the shallow aquifer.  A modeling based investigation is carried out to evaluate important factors such as pollutant infiltration rates, vadose zone assimilative capacity, water-table depths to evaluate conditions when permeable pavements pose a threat to aquifer resources.  In addition, the study also evaluated certain design characteristics such as the permeability of the pavement and the thickness of the pavement sub-base on aquifer vulnerability.  Design modifications such as addition of sorbents to trap pollutants in the pavement sub-base were also evaluated as part of the study.