Residence Time of Nubian Aquifer Ground Water Determined

[126297]地下水在地下停留时间的知识有许多重要的科学和实用的应用。地下水停留时间的确定充满了复杂性，因为含水层性质、初始条件和水动力历史的不确定性，以及用于停留时间确定的同位素或化学示踪剂可能涉及的地下产量或水岩相互作用。虽然有许多成熟的工具来测定相对较年轻的地下水的年代，但测定相对较老的地下水的年代的工具却很少。最常用的地下水测年工具是基于加速器的36Cl质谱法，但这种方法受到初始36Cl/Cl比值的时间和地理变化以及地下36CI产量的局部变化的影响。比36Cl更理想的工具是81Kr，但由于分析困难而被忽视，最近磁光原子捕获方法的发展使得使用台式设备进行精确的81Kr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zz . T. Lu及其同事在阿贡国家实验室开发）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第一次81Kr测量。本姆大学的B. Lehmann和他的同事开发了用于地下水239Ar分析的大样本稀有气体提取方法，他们将从8000 - 10000升的样品中提取和纯化氪。这些81Kr数据将与一系列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、0、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定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.