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。除了少数情况下的点源污染的As是地质起源，但释放由于人为扰动的水文地质条件。虽然有很好的理论知识的物理化学条件下释放的含水层基质，只有有限的理解存在的方式，何时以及为什么在现场规模。在这里，资金要求援助的研究，人为引起的释放在石灰岩含水层中的佛罗里达。该场址已有大量的物理化学参数数据库，但水文地质条件相当复杂，表明至少有两个潜在相连的含水层。因此，使用氚-氦法（T-He）对研究区域的选定样品进行定年，应能提供必要的信息，以更好地评估关键问题，如：· 年龄是否与预测的流向相关？· 深层含水层的年龄是否随深度增加？ 年龄与砷浓度是否存在相关性？ 深层含水层是否有年轻水？ 从上层到下层的通道在哪里？如果氚-氦测年证明成功地了解（a）研究区的水文地质和（B）划定作为释放机制和途径，那么第二步将是把一个全面的研究到作为释放和流动性的地下水位波动。第二项研究的预期成果将是一个反应性运输模型，不仅适用于佛罗里达中部，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.