Hydrogeologic Characterization of Fractured Rock Formations: A Guide for Groundwater Remediators

A field site was developed in the foothills of the Sierra Nevada, California, to develop and test a multidisciplinary approach to the characterization of ground-water flow and transport in fractured rocks. Nine boreholes were drilled into the granitic bedrock, and a wide variety of instruments and methodologies were tested. Fracture properties were measured on outcrops and in boreholes using acoustic televiewer, digital borehole color scanner, and by down-hole camera logs. Conventional geophysical logs were collected. In addition, thermal-pulse and impeller flowmeter logging, fluid replacement and conductivity logging, packer-injection profiling tests, and ordinary open-hole pumping tests were conducted. Transmissive fractures were identified by integrating results from hydrologic and geophysical measurements, and the hydrogeologic structure of the formation was hypothesized. Cross-hole seismic surveys yielded tomograms of interborehole rock properties. Visualization software was used in combination with geophysical logs to interpolate interborehole properties, and a detailed 3-D model of the subsurface was constructed. Other referenced work at the site includes cross-hole hydrologic EPA/600/S-96/001 May 1996 tomography, tracer tests, fracturespecific morphology studies, and development of an automated data acquisition system used to collect data and monitor and control test parameters during borehole testing. A novel aspect of the project report is its guidebook format. A description of each tool and methodology, the strengths and shortcoming of each, how they compare with one another, and suggestions of how best to analyze and integrate data are presented. The Project Summary was developed by the National Risk Management Research Laboratory's Subsurface Protection and Remediation Division, Ada, OK, to announce key findings of the research project that is fully documented in a separate report (see Project Report ordering information at the back). The reader is encouraged to visit the Internet Web page for further information: http://www.epa.gov/ada/kerrlab.html