The chemical evolution and hydrogeology of Al-Shagaya Field-B, Kuwait

The study area, Field-B, is located in the southwest of Kuwait. It is one of five water-well fields in the Al-Shagaya area, which supplies Kuwait with brackish ground water. This study was carried out at five-year intervals (during 1978, 1983, and 1989) to reveal the hydrochemical changes resulting from long duration production. Well-defined trends are observed in ion composition, as the groundwater exhibits high concentrations of Na+, Ca2+, SO42- and Cl-. The salinity of the Dammam Aquifer ranged from 2,684 to 4,897 mg/l during the study period, and shows a systematic increase in salinity with increased residence time. The recharged meteoric water rich in Na+ and SO42- entered the aquifer and displaced the preexisting water. The groundwater chemical types are: Na2SO4, CaSO4, NaCl and CaCl2. Some groundwater samples exhibited positive saturation index for calcite, aragonite, and dolomite, which indicates that the ground water of the carbonate aquifer is supersaturated with respect to these minerals, and undersaturated with respect to anhydrite, gypsum, and halite. Water movement generally follows the dip of the bedrock and moves toward north and northeast. The aquifer exhibits a semiconfining character. The transmissivity of the carbonate aquifer ranges from 32.9 to 2,606 m(2)/day. The chemical ratios of rK/rCl, rMg/rCl and rCa/rCl expressed in milliequivalent per mission (e.p.m.) of the study area attain higher values than those of normal sea water. This implies that the increase in the Mg2+ and Ca2+ ions is due to the leaching action of infiltrating meteoric water. On the other hand, the rSO(4)/rCl ratio attains high values in most of the studied samples, which suggests a reducing condition.