Electrical resistivity gradients as valuable tools for the parameterization of subterranean heterogeneity and aquifer vulnerability to contamination

This work demonstrates that electrical resistivity gradients are valuable for the characterization of subsurface heterogeneity and aquifer vulnerability to contamination. Field data was obtained via geo-electrostratigraphic techniques integrated with ground truth information from lithological boreholes. Vertical electrical soundings were undertaken along 19 profile lines and electrical resistivity tomography surveys were undertaken along 4 profile lines. The resistivity curves generated by WINRESIST described four geo-electrostratigraphic layers. The uppermost stratum (motley/heterogeneous topsoil) had resistivity measures of 95.2 - 1463.7 Ωm with a 0.6 - 6.6 m thickness. The second lithological layer (clayey sand) had resistivity values of 8.8 - 2485.1 Ωm with a thickness of 2.3-114.6 m. The third lithological stratum (fine/medium-grained sands) had resistivity values ranging from 72.5- 1332.7 Ωm with a thickness of 34.9 – 123.7 m. The fourth lithological stratum had resistivity measures of 82.0- 1808.6 Ωm. Mean values of electrical resistivity gradients for layers 1 and 2 were 411.42Ω and 53.22Ω, respectively. Iso-parametric maps of longitudinal conductance and electrical resistivity gradient (longitudinal resistance) indicated that the majority of the investigation area had weak aquifer protectivity. The transverse resistance, with a gamut of 3669.93 – 79868.18Ωm2 and a mean value of 20451.34 Ωm2, indicated that the region had prolific groundwater potential. The electrical resistivity gradient measures were integrated with measures of the electrical reflection coefficient, the goal being to investigate the degree of subsurface heterogeneity. The regression curves of the electrical reflection coefficients were 90o out of phase, indicating alternating beddings of diverse lithological facies. Utilization of electrical resistivity gradient and electrical reflection co-efficient measures generated information on subsurface heterogeneity with depth and aquifer vulnerability to contamination. This work has illustrated that measures of electrical resistivity gradient are valuable for parameterizing subterranean variability and groundwater susceptibility to toxicants.