FORMATION OF A SALT PLUME IN THE COASTAL-PLAIN AQUIFER OF ISRAEL - THE BEER-TOVIYYA REGION

The formation and development of a salt plume (salinity up to 800 mg C l l-1) in the inner part of the Coastal Plain aquifer of Israel is ana lyzed. Massive groundwater exploitation during the 1950s caused a larg e drop in the water level and formation of a hydrologic depression in the Be'er Toviyya-Kefar Warburg area. The depression reached a maximal depth during the late 1960s; thereafter a reduction in the rate of pu mpage led to restoration of water levels and shallowing of the depress ion, until its complete disappearance towards the end of the 1980s. A spot of high salinity first appeared in 1956, following a deep drawdow n in the water levels. This saline plume has been continuously expandi ng with increasing salinity concentrations (200-800 mg Cl l-1) in its center. The average rate of radial expansion was about 50 m year-1. Th e expansion and salinization did not cease as the depression disappear ed. Rather, equalization of water levels in wells situated within the plume area with those of situated along its margins resulted in the sa linization of the latter within a period of 1 year. Mass balances for water and chloride contents were made for the period 1967-1990. Taking into consideration the storage change, pumpage, natural replenishment and artificial recharge, the lateral inflow to the depression is esti mated as 60 x 10(6) m3. Upon addition of the chloride balance, and tak ing into consideration the chloride concentrations of the surrounding fresh water and the apparent possible end-member of the saline source (based on geochemical considerations), the saline inflow is estimated as (40-60) x 10(6). These estimates indicate that a large amount of sa linewater penetrated into the aquifer, of about half of the natural re plenishment of the study area, with an estimated salinity of 1900-2700 mg Cl l-1. It is suggested that the salt plume was formed as a result of a drop in water level combined with a flow of underlying saline wa ter bodies from deeper strata. The chemical composition of the groundw ater points to the existence of two saline water bodies of Ca-chloride composition and a marine Br/Cl ratio: (1) saline water with low Na/Cl (0.6), SO4/Cl, and B/Cl ratio; (2) saline water with higher Na/Cl (> 0.6), SO4/Cl, and B/Cl ratios. These chemical compositions resemble Ca -chloride saline waters found in other locations in the Coastal Plain aquifer and in underlying formations. The saline water bodies may occu r in either pockets at the bottom of the aquifer or lumachelle and san dstone layers of high hydraulic conductivity in underlying sediments.