The distribution of saline groundwater and its relation to the hydraulic conditions of aquifers and aquitards: examples from Israel

The effect of separation by aquitard layers on the distribution of saline groundwater in coastal aquifers has been demonstrated in two Israeli coastal aquifers: the Mediterranean and the Dead Sea aquifers. There is vertical separation in the Dead Sea area, even where the clayey aquitard layers are <1 m thick, exhibited by large differences in hydraulic head (2–5 m), salinity (TDS of 50–340 g/L) and chemical composition (e.g. Na/Cl range 0.28–0.55). Similar features are found in the Mediterranean coastal aquifer, where the separating aquitard layers are thicker (∼5–10 m). Here, the different subaquifers host fresh and saline groundwater of different ages (tritium and ¹⁴C ages range from tens to thousands of years), as well as different chemical compositions. This high resolution of results can be obtained only by drilling without fluids; otherwise, the spatial information may lead to incorrect representation of the studied aquifer. This is especially important in saline systems where only partial flushing occurs and, thus, large variations in salinity and chemical composition are expected. The main factors controlling the salinity of groundwater in subaquifers in coastal aquifers are their connection to the sea or saline lakes, existence of brines, salinization and flushing rates, and separation by aquitard layers.