Spatial delineation of groundwater salinity using deep time domain electromagnetic geophysical measurements: A feasibility study

The objective of this study was to delineate the spatial distribution of fresh, brackish, and saline groundwater bodies, as well as brine, beneath the Judea Desert, Israel. We used the deep time domain electromagnetic (TDEM) geophysical system, Cycle-5M, which provides the maximum exploration capability, to depths ∼1.5-2 km below land surface. The study was conducted at 21 locations at the desert plateau, where fresh groundwater flows through the upper aquifers from the replenishment area at the Judea Mountains toward the Dead Sea springs. In deeper aquifers, brackish and saline groundwater bodies exist, which originated from lakes and lagoons that existed at the Dead Sea Rift valley during the Pleistocene and Pliocene, respectively. It was found that within carbonate formations, fresh groundwater (C < 10³ ppm total dissolved solids (TDS)) is characterized by a resistivity of more than 15 Ω m, brackish groundwater (10³ < C < 10⁴ ppm TDS) is characterized by 5-15 Ω m, saline groundwater (10⁴ < C < 10⁵ ppm TDS) is characterized by 0.5-5 Ω m, and brine (10⁵ < C ppm TDS) is characterized by less than 0.5 Ω m.