Hydrochemical considerations for identifying water from basaltic aquifers: The Israeli experience

Study region: Yizre'el-Harod-Bet She'an valley, Lower Galilee and Golan Heights, Israel. Study focus: Identification of pure groundwater that infiltrated the widespread alkali olivine basalts in the replenishment areas of the study region. New hydrological insights for the region: The groundwater is characterized by equivalent ratios such as Na/Cl>1; Na/HCO₃^-<1; SO₄^2--fraction<0.1; HCO₃^-/(Ca+Mg+Na)≥0.7; HCO3^-/(Ca+Mg)>1; 1000Br/Cl in the range of 1-2.5; δ³⁴S_sulfate<5‰ (CDT). Bowl-shaped-normalized REY distribution patterns are indicative for recharge over basaltic outcrops. These aquifers are recharged not only by direct precipitation on volcanic exposures but also by water from underlying confined limestone aquifers. Groundwater from the limestone aquifers is characterized by Na/Cl<1; HCO₃^-/(Ca+Mg)<1; HCO₃^-/(Ca+Mg+Na)<0.7; 1000Br/Cl in the range of 1.6-10; δ³⁴S_sulfate range from 20 to 25‰ (CDT). The wide spread of these parameters characterizes mixing of groundwater from both limestone catchments and aquifers in different stages of hydochemical evolution. The REY patterns of these groundwaters resemble those of limestones. If δ³⁴S_sulfate and/or REY distribution patterns are not available, the unmixed water from basaltic-rock aquifers show up in the field of HCO₃^-/(Ca+Mg)>1 and HCO₃^-/(Ca+Mg+Na+K)>0.7. Application of these parameters to analyses showing only the main constituents of groundwater reveals that in the study area the contribution of unmixed groundwater from basaltic catchments is largely restricted to the Golan Heights. Mixing of groundwater by interaquifer flow is a common phenomenon all over the area.