Origin and residence time of salinity in the Aspo groundwater system

The origin of salinity within the Aspo groundwater system is investigated b y combining interpretations of conservative dissolved ions and of stable is otope ratios in water. The interpretation concludes that the groundwater sa linity results from a mixing between Baltic Sea water intrusion and a deep seated saline groundwater of marine origin. This conclusion supports the ge ochemical model developed for the Aspo site. The residence time of the deep salinity is assessed by comparing the Cl-36 content of dissolved salt at d ifferent depths and the secular equilibrium value of the host rock. The Cl- 36 of deepest levels corresponding to the highest salinity, is in equilibri um with rock, suggesting a penetration of the deep salinity into the host r ock more than 1.5 Ma ago. (C) 1999 Elsevier Science Ltd. All rights reserve d.