Dating groundwater in a limestone aquifer

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Arsenic contamination of groundwater and subsequently drinking water has become a problem of global proportions, likely affecting more than 100 million people. Except for a few cases of point source contamination the As is of geogenic origin, but released due to anthropogenic perturbations of hydrogeologic conditions. While there is good theoretical knowledge about the physicochemical conditions of As release from the aquifer matrix, only limited understanding exists of the how, when and why on a field scale. Here funds are requested to aid a study of anthropogenic induced As release in a limestone aquifer in central Florida. A substantial database of physicochemical parameters already exists for this site, however hydrogeologic conditions are rather complex, indicating at least two potentially connected aquifers. Thus dating of select samples in the study area using the tritium-helium method (T-He) should provide information necessary to better assess key questions such as: • Is there a correlation of age with predicted flow direction?• Is there an increase of ages with depths in the deep aquifer?• Is there a correlation of age with Arsenic concentration?• Is there young water in deeper aquifer?• Where are the pathways from upper to lower aquifer?Should the T-He dating prove successful in understanding (a) the hydrogeology of the study area and (b) delineating As release mechanisms and pathways, then a second step will be to put together a comprehensive study into As release and mobility in response to groundwater table fluctuations. The anticipated outcome of a second study would be a reactive transport model, applicable not only to central Florida, but to all areas with similar hydrogeologic conditions.