The role of the overburden-bedrock contact and upper bedrock properties in the recharge and contamination of shallow bedrock aquifers

从断裂的基岩含水层中获得的地下水是世界上许多地方供水的重要来源。在一些地区，如安大略东部、大部分滨海地区、北欧的大部分地区、非洲的大部分地区和澳大利亚，基岩含水层是农村居民的唯一水源。典型的基岩含水层渗透性变化很大，储水能力很低，上覆覆层厚度往往很薄。因此，由于停留时间短，衰减最小，这些供水往往容易受到污染。雨水和/或污染渗入的主要途径是拦截覆盖层与基岩接触的垂直或次垂直裂缝。由于对这里的输送机制知之甚少，因此拟议工作的目标是进行详细的实地研究，以探索非饱和漂质与下垫基岩含水层之间流体和污染物的交换。本研究共涉及5项研究，涉及2名硕士生和3名博士生。研究将包括对结晶岩环境下上部基岩性质的详细水力评估，以及在结晶岩和碳酸盐岩环境下从地表到上部基岩的几次示踪剂迁移实验。分析结果将采用考虑多孔介质、离散裂隙岩石和非饱和-饱和流动和输运的有限元模型。拟议的工作将集中在三个一般的现场，这些地点只有薄薄的覆盖层，在基岩上有很好的钻孔仪器，并且有很好的水力特征。这项研究的结果将对市政供水和利用基岩含水层地下水的农村水井的管理具有重要意义。安大略省目前正在省内所有市政井，包括利用基岩含水层的井，建立井口保护区。这项研究的结果可以直接纳入对这些敏感含水层环境所采取的方法。研究结果也将有助于其他国际司法管辖区采取的办法。

Groundwater obtained from fractured bedrock aquifers is an important source of water supply in many parts of the world. In some areas such as eastern Ontario, most of the Maritimes, a good part of northern Europe, much of Africa, and Australia, bedrock aquifers are the only source of water for rural residents. Typical bedrock aquifers are highly variable in permeability, of very low storage capacity and often overlain by only a minimal thickness of overburden cover. As a consequence, these water supplies tend to be vulnerable to contamination as a result of short residence times and minimal attenuation. The principal pathway for infiltrating rainwater and/or contamination is the vertical or sub-vertical fractures that intercept the overburden-bedrock contact. As little is known about the transport mechanisms here, the objective of the proposed work is to conduct detailed field studies to explore the exchange of fluid and contaminants between unsaturated drift material and the underlying bedrock aquifer. A total of five studies involving two MASc and three PhD students are proposed. The studies will include a detailed hydraulic assessment of the properties of the upper bedrock in a crystalline rock setting, and several tracer migration experiments from ground surface to the upper bedrock in both crystalline and carbonate rock settings. Analysis of the results will be conducted using a finite-element model which accommodates porous media, discretely fractured rock and unsaturated-saturated flow and transport. The proposed work will be focused on three general field sites, which have only a thin veneer of overburden, are well instrumented with boreholes in the bedrock, and are well characterized, hydraulically. The results of this study will be of significant importance to the management of both municipal water supplies and rural wells that utilize groundwater from bedrock aquifers. The Province of Ontario is presently undertaking the establishment of well head protection areas at all municipal wells in the province, including those utilizing bedrock aquifers. The results from this study can be directly incorporated into the approach taken for these sensitive aquifer settings. The results will also contribute to the approach taken in other international jurisdictions.