Stormwater Impacts on Ground Water Quality via Detention Basins

Use of stormwater retention and detention basins has become a popular method for managing urban and suburban stormwater runoff. Infiltration of stormwater through these basins, however, may increase the risk to ground-water quality, especially in areas like the Coastal Plain of southern New Jersey, where the soil is sandy and the water table shallow, and contaminants may not have a chance to degrade or sorb onto soil particles before reaching the saturated zone. Ground water from monitoring wells installed in basins in Camden and Gloucester Counties, New Jersey, was sampled and analyzed for volatile organic compounds (VOCs), pesticides, nutrients, and major ions. Results of analysis of these detention-basin samples were compared to "background" ground-water quality at sites in areas of "new-ruban" land use. Initial results show elevated concentrations of some ions and nutrients, but VOC and pesticide concentrations did not differ greatly from background concentrations found elsewhere in the area. Dissolved-oxygen concentrations in detention-basin samples were considerably lower than background levels.