QUANTIFYING THE VOLUMETRIC TRANSPORT OF HEAVY METALS ALONG THE GROUNDWATER-SURFACE WATER INTERFACE OF A SEMIDIURNAL ESTUARY

Understanding contaminant transport processes in the near surface of the Earth is essential for effective waste and water management practices. Near surface groundwater flowpaths can have profound impacts on the transport processes of contaminants from source zones to surface waters. In this study, localized groundwater seepage was characterized surrounding the contaminant source zone of McAllister Point Landfill, located on the coastline of the Narragansett Bay. We used the thermal and electrical conductivity signals of groundwater from the source zone at a variety of scales to characterize seepage locations and magnitude. Thermal infrared (TIR) imagery at aerial and handheld scales yielded evidence of cooler thermal signatures from groundwater seepage during the summer season. TIR methods further showed evidence for both localized, and expansive matrix seepage along the McAllister Point coastline. Localized seepage points were investigated further using point temperature and specific conductance measurements. These point measurements were repeated over time during variable climatic conditions, yielding insight into the dependence of groundwater seepage on local precipitation. Electrical conductivity variations with depth were investigated using waterborne electromagnetic induction (EMI) and electrical resistivity imaging (ERI) surveys. Seeps identified from the temperature and conductivity characterization methods were sampled for heavy metals to determine contaminants transported at this site. Future work at the McAllister Point source zone will involve the targeted deployment of 20 vertical temperature profilers arranged in a grid to determine the volumetric flux of groundwater along an expansive seepage zone of the coastline. Research shows the efficient and effective deployment of paired thermal characterization with electrical geophysical methods to delineate contaminant transport pathways at the groundwater-surface water interface.