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

Suny At Buffalo, Amherst NY

Investigators

Abstract

Becker 0207720 It 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.