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

在世界许多地方，从断裂基岩含水层获得的地下水是重要的供水来源。在某些地区，如安大略东部、滨海地区大部分地区、北方大部分地区、非洲大部分地区和澳大利亚，基岩含水层是农村居民唯一的水源。典型的基岩含水层渗透性变化很大，蓄水能力很低，而且往往只有极薄的覆盖层覆盖。因此，由于停留时间短和衰减最小，这些供水往往容易受到污染。雨水和/或污染物渗透的主要途径是拦截覆盖层-基岩接触面的垂直或近垂直裂缝。由于对这里的输运机制知之甚少，拟议工作的目标是进行详细的实地研究，以探索不饱和漂流物和下伏基岩含水层之间的流体和污染物交换。共有五项研究，涉及两个硕士和三个博士生提出。这些研究将包括对结晶岩环境中上部基岩的特性进行详细的水力评估，以及在结晶岩和碳酸盐岩环境中进行从地表到上部基岩的几个示踪剂迁移实验。将使用有限元模型对结果进行分析，该模型适用于多孔介质、离散裂隙岩石和非饱和-饱和流动和运输。拟议工作将集中在三个一般现场，这些现场只有薄薄的覆盖层，在基岩中有很好的钻孔仪器，并且具有很好的水力特性。这项研究的结果将是非常重要的管理城市供水和农村威尔斯，利用地下水从基岩含水层。安大略省目前正在该省所有市政威尔斯水井，包括那些利用基岩含水层的水井，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采取的办法。研究结果也将有助于其他国际司法管辖区采取的做法。

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.