Palaeohydrogeology and water quality control of the tertiary aquifer, Kuwait

The State of Kuwait is located at the northwestern corner of the Arabian Gulf and covers an area of about approximate to 18,000 km2. The aquifer under investigation is the Eocene Dammam limestone aquifer. This paper discusses the hydrochemistry of the aquifer through the period 1972 - 2002 in order to identify the chemical and genetic types of groundwater, and to reveal the prevailing geochemical processes in the aquifer. Moreover, the spatial distribution of the brackish-brine groundwater is encountered to provide an overview of the regional scale hydrochemistry and to assess the possible factors controlling the aquifer quality. Accordingly, WATEQ4F program is used to compute the saturation indices of the minerals with respect to a state water composition. The Z- MAP and the STRATWORKS programs are used to construct the structural contour map and the subsurface geophysical logs of the Dammam Formation, respectively. The hydrochemical and geological investigations revealed that the Dammam limestone aquifer is occupied by a brackish-brine groundwater, with TDS values ranging from 2500 to 150,000 mg/l, which gradually increases towards the N - NE in the flow direction. The main recognized groundwater chemical types are: Na2SO4, CaSO4 and NaCl. Three groundwater genetic types Na-SO4, Mg-Cl, and Ca-Cl are dominant and indicate a continental-marine stagnant environment. Also, the study showed that the groundwater is oversaturated with respect to calcite and dolomite, and under-saturated with respect to gypsum. The calculated mean values of PCO2 range between 8.79 x 10-4 and 1.38 x 10-2 atm., which are above that of PCO2 of the earth's atmosphere. These high values of PCO2 suggest that the Dammam limestone aquifer represents a closed system with respect to CO2. The ion-exchange, reverse ion-exchange and dedolomitization are the main geochemical processes prevailing in the aquifer. Furthermore, the carbonate weathering is most likely to operate in the aquifer. Controls on the distribution of water qualities reflect the ancient marine depositional environment, water-rock interaction, aquifer flushing including ion exchange effect, and the structural feature related to the Persian Gulf synclinorium.