Ground water salinization caused by residual neogene and pliocene sea water - An example from the Judea group aquifer, southern Israel

The Judea Group Aquifer of late Albian-Turonian age is mainly composed of k arstic 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 so uthern part of the basin. Fresh ground water (46 to 200 mg/L Cl) flows nort hward from the south and southeast, Saline ground water (1200 to 8350 mg/L Cl), which occurs irregularly in the midst of this flowpath, severely jeopa rdizes the development and exploitation of this aquifer. By defining the hy drochemical typology and applying mass balance considerations, it was found that the saline mater is derived from two endmembers designated as the "La hish" and "Hazerim" water types. The Lahish water type is generally respons ible for salinization of the lower portion of the Judea Group Aquifer, It a pparently evolved from transgressing Messinian sea water which penetrated i nland 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 Haz erim water type infiltrated into the Judea Group Aquifer through the overly ing Avedat and Mt. Scopus rock successions. It appears that the Hazerim wat er developed from the transgressing Pliocene sea which percolated through t hese low-permeability rock units. Subsequent rain percolated through these formations, dissolved evaporites that are mainly concentrated in the shallo w layers and mixed with residual sea water of Pliocene age, which became mo re diluted over time. Geological studies revealed that during the Neogene a ge, the back-cut incision of channels into the Coastal plain facilitated in land ingression of the sea and dissolution of evaporites. The Pliocene mari ne transgression deposited a thick sequence of clay that sealed the underly ing beds, This process resulted in trapping and pressurizing the saline wat er landward along pre-existing fault lines. These findings contribute to th e formulation of an updated ground water exploitation scheme that avoids su bsurface fault systems, which act as conduits of brines. The geological pro cesses occurred during the Neogene and Pliocene. This case study could help solve similar problems in the eastern Mediterranean region which experienc ed similar geological events.