Application of geochemistry and radioactivity in the hydrogeological investigation of carbonate aquifers (Sierras Blanca and Mijas, southern Spain)

The chemical characteristics, H-3 contents and radioactivity of groundwater s from the Sierras Blanca and Mijas (Southern Spain) have been studied in r elation to the chemical composition and radioactivity of the aquifer host r ocks, and the residence time of the water. The Sierras Blanca and 1Mijas ar e made up of calcitic and dolomitic marbles of Triassic age. The groundwate rs that drain the calcitic marbles (which outcrop principally in the wester n Sierra Blanca) have less mineralization, which descreases quickly with re charge (as does the H-3 content), and the gross alpha and beta activities a re below detection limit. This is due to the short residence time of water inside the aquifers which are conduit flow systems. The waters of the dolom itic marbles (eastern Sierra Blanca and Sierra Mijas) have higher and less variable mineralization and contain greater concentrations of Mg2+, SiO2 an d SO42- (ions normally associated with slow flows). The H-3 contents are mo re uniform with time (indicating an older age) and there is detectable natu ral radioactivity, because the waters have a longer residence time in the a quifers, which are diffuse flow systems. (C) 1999 Elsevier Science Ltd. All rights reserved.