Dispersion of Water Age in Aquifer Systems and in Groundwater Samples

0208492Fogg使用各种环境示踪剂方法估计的地下水年龄日期越来越多地被要求解决地下水质量问题和了解地下水系统的许多其他方面。 然而，缺乏对地下水年龄含义的系统分析，这可能会限制其应用，或导致严重的误解。 PI最近的工作表明，对估计地下水年龄的常见解释取决于对分散和混合的假设，而这些假设在许多（也许是大多数）情况下是不合适的。 PI发现，虽然大多数年龄数据被认为是代表水样中的所有水分子，但如果井筛不是太长，则该样品中的实际年龄可能差异很大（从100到102 + yr）。在典型的异构系统中。 虽然一些地下水文学家已经预料到这一点，但评估地下水年龄的科学基础仍然不发达和模糊。 这反过来又导致了水资源管理者和研究人员的极端解释和假设。 在这里，PI提出了一个理论上准确的，测试模拟方法，提供有史以来第一次定量评估的作用，非均质性，井筒混合，井筛深度和长度，含水层参数，地下水年龄的变化在空间和时间上的地质现实的冲积含水层系统的边界条件。 特别是，该研究将调查水“粒子”的年龄如何在空间和时间上在具有不同程度异质性的地下单个水样中变化。 通过建模和现场测试，PI还提出了一个新的假设，即在长期抽水井的年龄日期的变化提供了一个信号指示含水层的异质性和脆弱性。了解控制地下水年龄和年龄分布的主要因素是任何基于示踪剂的年龄测定数据的应用的先决条件。 地下水年龄随空间和时间变化的波动可以用来探索地下水的水文过程，远远超过传统的静态地下水年龄测定方法。 上述假设的拟议测试提供了一种可能性，即地下水年龄测定方法可以从依赖于模糊的、未经检验的假设的定性程序转变为以以前未预料到的方式定量（或半定量）评估地下水状况的强大表征工具。 PI显示了丰富的初步模拟结果，以支持这个问题的陈述，并证明了可行性的一般approach.Keywords：地下水，污染，运输，含水层脆弱性，建模，年龄。

0208492FoggGroundwater age dates estimated using various environmental tracer methods is being increasingly called upon to address groundwater quality problems and to understand many other aspects of subsurface systems. However, systematic analysis of the meaning of groundwater age dates is lacking, which may limit the application, or result in serious misinterpretations. The PI's recent work indicates that common interpretations of estimated groundwater ages are dependent on assumptions about dispersion and mixing that are not appropriate in many, perhaps most, cases. The PI finds that, while most age dates are thought to be representative of all the water molecules in the water sample if the well screen is not too long, actual ages within that sample can vary significantly (from IO0 to 102+ yr.) in typically heterogeneous systems. Although some subsurface hydrologists already anticipated this, the scientific basis for evaluating groundwater age dates remains undeveloped and vague. This in turn has led to an extreme range of interpretations and assumptions by both water managers and researchers. Herein the PI proposes a theoretically accurate, tested simulation approach to provide the first ever quantitative evaluation of the roles of heterogeneity, well-bore mixing, well screen depth and length, aquifer parameters, and boundary conditions on groundwater age variations in space and time in geologically realistic alluvial aquifer systems. In particular, the research will investigate how ages of water "particles" can be expected to vary within individual water samples in space and time in subsurface with different degrees of heterogeneity. Through both modeling and field-testing the PI also proposes to explore a new hypothesis that variation in age dates during long-term pumping of a well provides a signal indicative of aquifer heterogeneity and vulnerability. Understanding of the main factors controlling groundwater ages and age distributions is a prerequisite for any application of tracer-based age-dating data. Fluctuations in groundwater age as a function of space and time may be used to explore subsurface hydrologic processes far beyond the traditional static groundwater age dating method. Proposed testing of the above hypothesis holds out the possibility that groundwater age dating approaches can be transformed from qualitiative procedures dependent on vague, untested assumptions to powerful characterization tools for quantitatively (or semiquantitatively) assessing groundwater conditions in previously unanticipated ways. The PI shows abundant preliminary simulation results to support this problem statement and to demonstrate feasibility of the general approach.Key words: groundwater, contamination, transport, aquifer vulnerability, modeling, ageDate.