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渠化的方式流经基岩裂缝，这意味着受污染的地下水可能很难检测或预测。迄今为止，仅在井眼或隧道中检测到现场尺度的流动通道。这项研究将首次产生裂缝平面内通道的地图视图图像。盐水示踪剂将注入一条饱和的亚水平层状面裂缝中，并利用高分辨率探地雷达绘制裂缝的分布。实验将在一个石灰岩采石场的底板进行，以便地下水位较浅，没有覆盖层阻碍雷达信号。几种强制梯度水力配置将用于低分辨率时变和高分辨率时不变盐水示踪剂成像。监测孔将同时检测盐水浓度，从而可以评估存在窜流的井眼监测效果。最后，将荧光染料注入裂缝，并去除裂缝上方的岩石，这样就可以直接绘制出流动通道。探地雷达、监测井浓度、染料分布和水力测试将用于校准有限差分地下水流动和输送模型。该模型将用于研究与监测地下水污染相关的误差，并设计水力和示踪剂测试，以表征裂缝性基岩的有效孔隙度。尽管本研究中使用的地球物理技术对大多数污染场地并不实用，但该项目开发的示踪剂和水力方法可能对如何监测、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.