Dating groundwater in a limestone aquifer

地下水和随后的饮用水的砷污染已成为一个全球性问题，可能影响到1亿多人。除少数点源污染外，砷均为地质成因，但由于水文地质条件的人为扰动而释放。虽然关于砷从含水层基质中释放的物理化学条件有很好的理论知识，但在油田规模上，对砷如何、何时以及为什么释放的理解有限。在这里，基金被要求帮助在佛罗里达州中部的石灰岩含水层中进行人为诱发的砷释放的研究。这个地点已经有了大量的物理化学参数数据库，但是水文地质条件相当复杂，表明至少有两个潜在的连接含水层。因此，使用氚氦法（T-He）对研究区域的选定样品进行定年应该提供必要的信息，以更好地评估关键问题，例如：•年龄与预测的流动方向是否存在相关性？•在深层含水层中，年龄是否随着深度的增加而增加？•年龄与砷浓度有相关性吗？•在更深的含水层中有年轻的水吗？•从上到下含水层的通道在哪里？如果T-He定年法能够成功地理解(a)研究区域的水文地质和(b)划定砷的释放机制和途径，那么第二步将是对地下水位波动对砷释放和迁移的响应进行全面研究。第二项研究的预期结果将是一个反应输送模型，不仅适用于佛罗里达州中部，而且适用于具有类似水文地质条件的所有地区。

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.