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The Judea Group Aquifer of late Albian‐Turonian age is mainly composed of karstic limestone and dolomite. In the western part of Israel it is known as the Yarkon‐Taninim ground water basin. The study area is located in the southern part of the basin. Fresh ground water (46 to 200 mg/L Cl) flows northward from the south and southeast. Saline ground water (1200 to 8350 mg/L Cl), which occurs irregularly in the midst of this flowpath, severely jeopardizes the development and exploitation of this aquifer. By defining the hydrochemical typology and applying mass balance considerations, it was found that the saline water is derived from two endmembers designated as the “Lahish” and “Hazerim” water types. The Lahish water type is generally responsible for salinization of the lower portion of the Judea Group Aquifer. It apparently evolved from transgressing Messinian sea water which penetrated inland through prior incised Neogene erosional channels. Upon inundation, it dissolved halite and gypsum from the Mavqi'im Formation. This was followed by massive bacterial reduction of sulfates in the presence of oil. The Hazerim water type infiltrated into the Judea Group Aquifer through the overlying Avedat and Mt. Scopus rock successions. It appears that the Hazerim water developed from the transgressing Pliocene sea which percolated through these low‐permeability rock units. Subsequent rain percolated through these formations, dissolved evaporites that are mainly concentrated in the shallow layers and mixed with residual sea water of Pliocene age, which became more diluted over time. Geological studies revealed that during the Neogene age, the back‐cut incision of channels into the Coastal Plain facilitated inland ingression of the sea and dissolution of evaporites. The Pliocene marine transgression deposited a thick sequence of clay that sealed the underlying beds. This process resulted in trapping and pressurizing the saline water landward along pre‐existing fault lines. These findings contribute to the formulation of an updated ground water exploitation scheme that avoids subsurface fault systems, which act as conduits of brines. The geological processes occurred during the Neogene and Pliocene. This case study could help solve similar problems in the eastern Mediterranean region which experienced similar geological events.

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