CHARACTERIZATION OF SURFACE WATER/GROUND WATER INTERACTIONS ALONG THE TAR RIVER, NC USING GROUND PENETRATING RADAR

The distribution of floodplain and river channel sediments adjacent to coastal plain rivers is complex and requires numerous sediment cores to characterize, yet is very important to understanding river-ground water interactions and contaminant transport. Ground penetrating radar (GPR) may be an effective tool for subsurface characterization in these settings. Eighteen peizometers and 129 feet of split spoon cores and hand auger samples are being used to characterize the interaction of ground water and surface waters of a 10 mile stretch of the Tar River, eastern North Carolina, USA. Additionally, 2-D and 3-D GPR data are being collected using a GSSI SIR-2000 system with a 200 MHz antenna, to define the shallow stratigraphic framework. The ultimate goal is to use GPR to assess the hydraulic characteristics of floodplain and channel deposits. Ground water head data indicate that the shallow water table aquifer has a high degree of complexity on a local scale. Sediment samples and slug tests conducted in stream-channel piezometers indicate that the geology between the north and south sides of the river varies significantly, with a direct effect on the movement of ground water through the river channel. Ground water flux into and out of the channel varied between the north and south sides by as much as four orders of magnitude. The differences appear to be related to stratigraphic differences between the north and south sides of the river. GPR transects have successfully located key hydrogeologic elements such as clay layers (confining beds), sand lenses, and active channel bedforms, which have a direct impact on the movement of ground water. GPR may be a useful tool for the characterization of contaminant transport between the shallow water table aquifer and surface waters along coastal plain rivers.