Evaluation and mapping of Dead Sea coastal aquifers salinity using Transient Electromagnetic (TEM) resistivity measurements

Evaporite karst has intensively developed recently along the Dead Sea (DS) coastal area in Israel and Jordan. It takes place in very saline groundwater dissolving buried salt layers, causing collapse of the surface. In this paper, groundwater salinity throughout the DS coastal area is investigated using the Transient Electromagnetic (TEM) method. Twenty-eight TEM soundings along the DS coastal area were carried out close to observation boreholes to calibrate resistivity–salinity relationships. Groundwater electrical conductivity was measured in these boreholes, and its salinity was analyzed at the laboratory by the Geological Survey of Israel (GSI). Quantitative relationships between bulk resistivity (ρ_x), water resistivity (ρ_w) and chloride concentration (C_cl) were derived in the resistivity range less than 1.0 Ω·m that enabled to evaluate the salinity of the aquifer in in situ conditions. Average values of the effective porosity of sandy sediments, φ_e = 0.32, and of silty ones, φ_e = 0.44, were used to generate the corresponding Archie equations. The study has shown that a DS aquifer with bulk resistivity in the range of 0.55–1.0 Ω·m contains in pores brine with 50–110 g_chloride/l of (22–50% of that in saturated conditions, respectively), i.e. it keeps the potential to dissolve up to 114–174 g/l of salt.