MULTI-FACETED HYDRAULIC CHARACTERIZATION OF AN ISOLATED BEDROCK FRACTURE

Previous research conducted at the Fractured Rock research Site (FRS) in Floyd County, Virginia has revealed important information concerning the structure and behavior of crystalline bedrock aquifers in the Blue Ridge physiographic province. While researchers have conducted significant work over the extent of this aquifer, little has been done to investigate processes at the single fracture scale. The current study focuses on determining the hydraulic characteristics of a fracture connection between two wells at FRS using a variety of hydrogeological tests and identifying regionally significant implications.

Using a combination of optical televiewer and heat-pulse flow meter logs, fractures intersecting the borehole walls are identified both visually and hydraulically. A series of rising and falling head slug tests are performed using packers to evaluate the near-borehole hydraulic conductivity, which fluctuates in the presence of non-Darcian flow and remains constant during Darcian flow, for various applied heads. Isolation of the fracture of interest at each well with packers during aquifer testing allows for the determination of cross-borehole hydraulic conductivity and storativity, as well as an estimation of the fracture aperture. Finally, a pair of forced gradient tracer tests is used to investigate the behavior of contaminants within the fracture. Using both a conservative saline tracer and a non-conservative heat tracer, travel time between wells is calculated. In addition, details about a contaminant’s preferred pathway are identified using the shape of the breakthrough curves and a numerical model of an equivalent homogeneous medium.

By combining the data collected from multiple tests, we obtain a comprehensive description of the fracture and its hydraulic characteristics. This study is also important for evaluating the effectiveness of techniques for analyzing fractures in both the Blue Ridge province and other localities of fractured crystalline rock.