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The physical±chemical characteristics of the groundwater in the Baza±Caniles detrital aquifer system indicate that a wide diversity of hydrochemical conditions exists in this semiarid region, de®ning geochemical zones with distinct groundwater types. The least mineralized water is found closest to the main recharge zones, and the salinity of the water increases signi®cantly with depth towards the center of the basin. Geochemical reaction models have been constructed using water chemistry data along¯ow paths that characterize the di erent sectors of the aquifer system, namely: Quaternary aquifer, uncon®ned sector and shallow and deep con®ned sectors of the Mio±Pliocene aquifer. Geochemical mass±balance calculations indicate that the dominant groundwater reaction throughout the detrital system is dedolomitisation (dolomite dissolution and calcite precipitation driven by gypsum dissolution); this process is highly developed in the central part of the basin due to the abundance of evaporites. Apart from this process, there are others which in¯uence the geochemical zoning of the system. In the Quaternary aquifer, which behaves as a system open to gases and which receives inputs of CO 2 gas derived from the intensive farming in the area, the interaction of the CO 2 with the carbonate matrix of the aquifer produces an increase in the alkalinity of the water. In the shallow con®ned sector of the Mio±Pliocene aquifer, the process of dedolomitisation evolves in a system closed to CO 2 gas. Ca 2+ /Na + cation exchange and halite dissolution processes are locally important, which gives rise to a relatively saline water. Finally, in the deep con®ned sector, a strongly reducing environment exists, in which the presence of H 2 S and NH + 4 in the highly mineralized groundwater can be detected. In this geochemical zone, the groundwater system is considered to be closed to CO 2 gas proceeding from external sources, but open to CO 2 from oxidation of organic matter. The geochemical modeling indicates that the chemical characteristics of this saline water are mainly due to SO 4 dissolution, dedolomitisation and SO 4 reduction, coupled with microbial degradation of lignite. #

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The present study concerns the application of a new numerical approach to describe the fresh‐water /sea‐water relationships in coastal aquifers. Essentially, a solution to the partial differential equation governing the regional motion of a phreatic surface and the resulting interface between fresh water and salt water is analyzed by a Galerkin finite‐element formulation. A single‐phase steady numerical model was applied to approximate, with simple triangular elements, the regional behavior of a coastal aquifer under appropriate sinks, sources, Neumann, outflow face, and open boundary conditions. On the one hand, outflow open boundaries at the coastline were not treated with other classical boundary conditions (Dirichlet or the outflow face approach), but instead with a formal numerical approach for open boundaries inspired in this particular case by the Dupuit approximation of horizontal outflow at the boundary. The solution to this numerical model, together with the Ghyben‐Herzberg principle, allows the correct simulation of fresh‐water heads and the position of the salt‐water interface for a steeply sloping coast. Although the solutions were precise and do not present classical numerical oscillations, this approach requires a previous solution with Dirichlet boundary conditions at the coastline in order to find a good convergence of the solution algorithm. On the other hand, the same precise results were obtained with a more restrictive open boundary condition, similar in a way to the outflow face approach, which required less computer time, did not need a prior numerical solution and could be extended to different coastline conditions. The steady‐state problem was solved for different hypothetical coastal aquifers and fresh‐water usage through three types of numerical tests. Calculated fresh‐water heads, interface positions and discharges show very precise results throughout the domain and especially at the coastline when compared to analytical, experimental, and numerically correct solutions. Therefore, interface positions, fresh‐water heads, and discharges originating from the steady regional behavior of coastal aquifers can be precisely predicted by numerical modeling when open boundaries towards the sea are properly treated for the likely conditions of the coastline.

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In July 1988, hydrocarbons were detected in wells in the urban area of Albolote, near Granada, Spain, near the border of the “Vega de Granada” alluvial aquifer. According to available hydrogeological data, the contamination was attributed to leaks in the underground pipelines of a nearby (300m) industrial factory, where the loss of 40,000 to 50,000 liters of gasoline had been detected some weeks before. A complete hydrogeological investigation was then undertaken, involving, among other techniques: (a) an inventory of the existing wells in the area; (b) the preparation of piezometric maps; (c) the application of electrical geophysical methods; (d) the drilling of piezometers and new pumping wells between the urbanized area and the leak point; (e) the improvement of the pluviometric and piezometric control by the installation of a pluviograph and several limnigraphs; (f) the sampling, initially daily and finally weekly, in a 20‐well observation network, also used for piezometric control; and (g) the geostatistical study of the analytical data. The contamination plume, extended in the direction of the flow lines, has a length of 500m and a width of less than 50m, and appears to have occurred mainly in a paleochannel. Hydrocarbons (1600 liters) were recovered by pumping and by using absorbent blankets, as well as by a gas and liquid suction method. Hydrocarbon concentrations have continuously decreased. However, sporadic increases, associated with rainfall, have been observed suggesting the presence of retained hydrocarbons in the unsaturated zone. The rate of decrease in hydrocarbon concentrations has currently slowed, particularly in the less affected zone. As a means of activating the cleaning up of the unsaturated zone, an artificial recharging method has been designed.