Stormwater infiltration BMP impacts on groundwater quality

Project Status

In cooperation with DelDOT, DGS is monitoring groundwater at stormwater infiltration best management practices (BMPs) to characterize the fate and transport of chloride in stormwater BMPs. The goal is to characterize the potential risks to groundwater quality from de-icing practices at a DelDOT BMP and a shared use BMP (receiving runoff from roadways, businesses, schools, etc.). This project arose because of increasing chloride concentrations observed in a number of groundwater-supplied public water systems in New Castle County. Increased concentrations of radionuclides and radiation are observed in some of the impacted water sources.

During the first phase of this project GIS analysis and field visits to a number of stormwater management facilities were done. Field visits included water sampling. This work led to the selection of two stormwater management sites for site characterization and monitoring. Water sampling is building empirical relationships between inexpensive field measurements of electrical conductivity and more time consuming and expensive laboratory measured chloride concentrations.

A site near Summit Bridge has been selected and is co-located with a pavement runoff and soil amendment project established by Dr. Paul Imhoff of the UD Department of Civil and Environmental Engineering. Four shallow monitoring wells and two runoff collectors with automated water level, temperature, and salinity monitoring systems were installed in March 2019 to characterize properties of roadway runoff and salinity of shallow groundwater. A second site near Middletown is located in a stormwater basin. Seventeen monitoring wells, and stormwater inlet and outlet monitoring systems have been installed. The monitoring wells are installed in clusters finished at different depths and equipped with automated water level, temperature, and salinity monitoring systems to characterize infiltration and salt movement. Stormwater inlet pipes and the basin outflow weir are equipped with flow and salinity monitoring systems.

The next phase of the project will continue an enhanced field monitoring study that includes operation of the automated monitoring systems and sampling of wells and runoff. Data from this work will support development of statistical and simulation tools to evaluate the risks of de-icing practices on groundwater.