Contaminant transport from stormwater management areas to a freshwater karst spring in Florida: Results of near-surface geophysical investigations and tracer experiments

Abstract

Study region: Silver Springs is a karst spring in north-central Florida. As landuses in the springshed have urbanized in recent decades, concentrations of contaminants, including nitrate, have increased in spring water, causing environmental concerns. Study focus: Pathways of groundwater movement from stormwater management areas to Silver Springs were investigated using ground-based geophysical surveys (ground penetrating radar and frequency domain electromagnetics) accompanied by tracer tests in the Upper Floridan Aquifer (UFA) and surficial aquifer. Results indicated heterogeneous near-surface and deep karst conditions, where stormwater runoff may be transported quickly through groundwater to the spring. A wide range of groundwater velocities (10−6 to 10−3 ms−1) were observed in the surficial aquifer, where faster flow speeds were associated with subsurface anomalies and preferential flow. However, tracer injected into the UFA was observed in the spring hours later, suggesting possible maximum groundwater velocities on the order of 10−1 ms−1 in the karst aquifer. Series of tracer pulses in the spring highlight the complexity of flow pathways to Silver Springs. New hydrological insights for the region: The rapid transport of tracer from stormwater basins to Silver Springs suggests that stormwater infiltration basins may be hotspots for potential aquifer and spring contamination in karst areas. Development of stormwater best management practices (BMPs) that integrate heterogeneous karst transport processes may enhance spring and groundwater quality in Silver Springs and other karst regions.

Keywords

• Karst
• Hydrogeology
• Stormwater runoff
• GPR
• Electromagnetic
• Tracer