Integrating Hydraulic, Tracer, and Geophysical Methods to Image Flow-Channeling Behavior in Fractured Bedrock

长期以来，人们一直假设地下水以沟道化的方式流经基岩裂隙，这意味着受污染的地下水可能很难检测或预测。到目前为止，仅在井眼或隧道中检测到了现场规模的水流通道。这项研究将第一次产生断裂面中通道的地图图像。盐水示踪剂将被注入到单一饱和的亚水平层面裂缝中，并将使用高分辨率探地雷达绘制其分布图。实验将在一个石灰岩采石场的底板上进行，这样地下水位就会很浅，没有覆盖层会阻碍雷达信号。将使用几种强制梯度液压配置，以允许盐分示踪剂的低分辨率时变成像和高分辨率时不变成像。监测孔将同时检测盐水浓度，从而可以评估在存在导流的情况下井眼监测的效果。最后，将荧光染料注入裂缝中，并移除裂缝上方的岩石，以便可以直接绘制流动通道图。将使用探地雷达、监测井浓度、染料分布和水力测试来校准有限差分地下水流动和传输模型。这个模型将被用来调查与监测地下水污染有关的误差，并设计水力和示踪剂测试来表征裂隙基岩中的有效孔隙度。尽管这项研究中使用的地球物理技术对大多数污染场地并不实用，但从该项目开发的示踪剂和水力方法可能会对如何监测、表征和修复破碎基岩中的污染场地产生重大影响。

Becker0207720It has long been hypothesized that ground water flows through bedrock fractures in a channelized manner, implying that contaminated ground water may be very difficult to detect or predict. To date, flow channeling at the field scale has been detected only in boreholes or tunnels. This research will yield, for the first time, map-view images of channeling in a fracture plane. Saline tracer will be injected into a single saturated sub-horizontal bedding-plane fracture, and its distribution will be mapped using high-resolution ground-penetrating radar. Experiments will be conducted in floor of a limestone quarry so that the water table is shallow and there is no overburden to obstruct the radar signal. Several forced gradient hydraulic configurations will be used to allow both low-resolution time-variant and high-resolution time-invariant imaging of saline tracer. Monitoring holes will simultaneously detect saline concentration, so that the efficacy of borehole monitoring in the presence of channeling can be evaluated. Finally, fluorescent dye will be injected into the fracture and the rock above the fracture removed so that flow channeling can be mapped directly. Ground penetrating radar, monitoring well concentrations, dye distribution, and hydraulic testing will be used to calibrate a finite difference ground-water flow and transport model. This model will be used to investigate errors associated with monitoring ground-water pollution and design hydraulic and tracer tests to characterize effective porosity in fractured bedrock. Although the geophysical techniques employed in this research are not practical for most contaminated sites, tracer and hydraulic methods developed from this project could have a significant impact on how contaminated sites in fractured bedrock are monitored, characterized, and remediated.