Geochemical and boron, strontium, and oxygen isotopic constraints on the origin of the salinity in groundwater from the Mediterranean coast of Israel

In order to identify the origin of the salinity and formation of saline plu mes in the central part of the Mediterranean coastal aquifer of Israel, we determined the elemental and boron, strontium, and oxygen isotopic composit ions of fresh and brackish groundwater (Cl up to 1500 mg/L). We distinguish between two key anthropogenic sources: (1) sewage effluents used for irrig ation with high Na/Cl, SO4/Cl, and B/Cl ratios and low Br/Cl ratios relativ e to seawater ratios, low delta(11)B values (0-10 parts per thousand) and h igh delta(18)O values (>-4 parts per thousand); and (2) imported water from the Sea of Galilee that is artificially recharged to the aquifer with high Br/Cl (3 x 10(-3)) and delta(18)O values (-1 parts per thousand) and a low Sr-87/Sr-86 ratio of 0.70753. The brackish groundwater from the saline plu mes have relatively low Na/Cl ratios (0.5-0.8) and high Ca/Mg, Mg/Cl, and C a/(SO4 + HCO3) (>1) ratios relative to seawater ratios; marine SO4/Cl and B r/Cl ratios; delta(11)B values of 24.8-49.9 parts per thousand; delta(18)O Of -2.95 parts per thousand to -4.73 parts per thousand; and Sr-87/Sr-86 ra tios of 0.708275-0.708532, The composition of most of the investigated grou ndwater from the saline plumes differs from those of the anthropogenic sour ces, imported water, fresh uncontaminated groundwater (Sr-87/Sr-86 of 0.708 66, delta(11)B of 20-30 parts per thousand), and saline water from the adja cent Eocene aquitard. Only in areas of artificial recharge does local groun dwater have high Br/Cl and delta(18)O values that are typical to the Sea of Galilee. The linear relationships between chloride and most of the ions, i ncluding B and Sr, the relatively high delta(11)B (>30 parts per thousand) and low delta(18)O (<-4 parts per thousand) values, and the chemical signat ure of the saline plumes (e.g., marine Br/Cl and SO4/Cl ratios), suggest th at (1) mixing processes control the chemical composition of the brackish wa ter within the aquifer, and (2) the saline postulated end-member has a chem ical composition that resembles modified seawater with a marine and higher delta(11)B values, and a Sr-87/Sr-86 ratio of <0.7083. We propose that most of the salinization phenomena and the formation of saline plumes in the in ner parts of the coastal aquifer are derived from upconing of underlying na tural saline water bodies and enhanced by overexploitation and draw-down of the overlying fresh groundwater.