IDENTIFYING SUBSURFACE STRATIGRAPHY OF ALLUVIAL TERRACES USING GEOPHYSICAL, GEOCHEMICAL, AND HYDROGEOLOGIC TOOLS FOR WELL SITE DETERMINATION

The University of Tennessee Institute of Agriculture East Tennessee AgResearch and Education Plant Sciences Unit (ETREC-PSU) is located along alluvial terraces adjacent to the Tennessee River about 5 miles south of campus. The alluvial terrace silts, sands, and gravels were deposited onto and possibly reworked portion of the Ottosee Shale (Chickamauga Group, Valley and Ridge Province), a unit consisting of shales, siltstones, sandstones, and limestones. Core samples from the lower terrace were collected during the construction of the Hydrogeology Teaching Site (~1997), with well completion occurring in different aquifer units representing a range of hydraulic conductivities (10^-6 to 10^-8 m/s). This work seeks to extend the utility of teaching site to include strata on the terrace above. To identify potential sites for monitoring well installation, a surface geophysical survey (June 2024) indicated that the upper terrace units potentially extend to the lower terrace. Initial seismic and resistivity analysis revealed discontinuous portions of higher resistivity units underlying the surface of both terraces, suspected to be associated with increased gravel content. Geochemical analysis of existing well sites showed chloride and total dissolved solids varied across and between units along the lower terrace; however, these differences were not great enough to result in the differences in resistivity. Downhole geophysical data from new and existing wells will help calibrate survey geophysical techniques. Combination of these datasets will be used to identify locations for installation of additional monitoring wells, verify predicted stratigraphy columns, distinguish important aquifer units, and constrain the uppermost portion of the seismic results.