Residence Time of Nubian Aquifer Ground Water Determined

地下水的地下停留时间的知识有许多重要的应用，既有科学的，也有实用的。 由于含水层性质、初始条件和水动力历史的不确定性，以及可能的地下生产或涉及用于滞留时间测定的同位素或化学示踪剂的水-岩相互作用，地下水滞留时间的测定充满了复杂性。 虽然有一些成熟的工具可以测定相对年轻的地下水的年代，但用于测定相对古老的地下水的年代的工具却很少。 测定古老地下水年代最常用的工具是基于加速器的质谱法， 36 Cl，然而，这种方法受到了最初的时间和地理变化的影响。 36 Cl/Cl比以及地下36 Cl产量的局部变化幅度。 一种比36 Cl更理想的工具，但由于分析困难而被忽视， 81 Kr磁光原子俘获方法的最新发展使得使用台式设备进行准确、精确的81 Kr分析成为可能。 我们建议使用原子阱痕量分析的原型仪器（由Z。T. Lu及其同事）对来自埃及西部沙漠努比亚含水层的非常古老的地下水进行了首次81 Kr测量。 由B从8，000 - 10，000 L样品中提取并纯化Kr。Lehmann和他的同事们开发了大样本惰性气体提取方法，用于地下沃茨的239 Ar分析。 这些81 Kr数据将与一套其他化学和同位素数据（包括溶质离子和溶解气体分析; H、C、N、O、S和Cl的稳定同位素;以及氚、放射性碳和放射性氯）一起获得，并用于解决有关地下水测年和努比亚含水层历史的基本问题。

126297SturchioKnowledge of the subsurface residence time of groundwater has a multitude of importantapplications, both scientific and utilitarian. The determination of groundwater residence time is fraught with complexity because of uncertainties in aquifer properties, initial conditions, and hydrodynamic history, as well as possible subsurface production or water-rock interactions involving the isotopic or chemical tracers used for residence time determination. Although there are a number of well-developed tools for dating relatively young groundwaters, there is a paucity of tools for dating relatively old groundwaters. The most commonly used tool for dating old groundwater is accelerator-based mass spectrometry of 36Cl, yet this approach is compromised by the temporal and geographic variability of the initial 36Cl/Cl ratio as well as the locally variable magnitude of subsurface 36CI production. A more ideal tool than 36Cl,, yet one which has been neglected because of analytical difficulties, is 81Kr Resent developments in magnetooptical atom-trapping methods have made accurate, precise 81Kr analysis possible by using a benchtop-scale apparatus. We propose to use the prototype instrument for atom-trap trace analysis (developed at Argonne National Laboratory by Z. T. Lu and colleagues) to perform the first 81Kr measurements of very old groundwater from the Nubian Aquifer of the Westem Desert of Egypt. The Kr will be extracted and purified from samples of 8,000-10,000 liters each by B. Lehmann and colleagues of the University of Bem who have developed large-sample noble gas extraction methods for 239Ar analysis of ground waters. These 81Kr data will be obtained in conjunction with a suite of other chemical and isotopic data (including solute ion and dissolved gas analyses; stable isotopes of H, C, N, 0, S, and Cl; and tritium, radiocarbon, and radiochlorine) and used to address fundamental questions about groundwater dating and the history of the Nubian aquifer.