Detection of shallow and deep conductive zones using direct current resistivity and time-domain electromagnetic methods, west El-Minia, Egypt

Abstract

Direct current (DC) resistivity and time-domain electromagnetic (TEM) methods were used to distinguish between saturated and dry zones and in an evaluation of groundwater resources in the western desert of Egypt. DC-resistivity method was used to evaluate the shallow section while TEM method was used for the shallow and deep aquifer sections. In the decay (voltage) curves, the last parts of the early stage and the intermediate stage refer to the shallow aquifer while the late stage indicates the deep aquifer. The effect of ramp-off time was studied. The shallow unrecorded depths of the high current diffusion speed and first and last diffusion depths were determined. The resistivity and thickness of surface deposits and loop side length are the prime influences on diffusion, investigation, and shallow unrecorded depths. By combining the two methods, the subsurface layers were classified into eight conductive and resistive zones. The third (15-75.5 O m), sixth (55-124 O m), and seventh (35-54 O m) are high conductively zones that corresponds to the shallow and deep aquifers, respectively. The TEM method delineated the sedimentary basin and the maximum penetration depth was ∼1300 m. The complementary of two methods confirmed that the resistivity method is sensitive to shallow conductive and resistive zones while the TEM method is sensitive to shallow and deep conductive and resistive zones. The TEM method assisted in identifying the shallow unrecorded depths, the effect of ramp-off time, diffusion depths, and the effect of shallow resistive depths on diffusion depths.