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Cross-borehole flow tests and insights into hydraulic connections in fractured mudstone and sandstone

John H. Williams,
U. S. Geological Survey, Troy, NY

Pierre J. Lacombe,
U. S. Geological Survey, West Trenton, NJ

Carole D. Johnson,
U. S. Geological Survey, Storrs, CT

Abstract

Cross-borehole flow tests provided insights into hydraulic connections in fractured and dipping mudstone and sandstone that were consistent with the lithostratigraphic and structural framework of a VOC-contaminated bedrock research site in west-central New Jersey. Two cross-borehole flow tests were completed. Each test involved measurement and analysis of transient flow in a newly installed deep corehole with a long open interval during short-term pumping and recovery in an adjacent shallow well with a short open interval. The cross-borehole flow test in the mudstone identified a hydraulic connection through a dipping fractured bed between the pumped interval in the well and a flow zone at an intermediate depth in the corehole. The presence of a hydraulic connection between the pumped well and the corehole was not obvious because the water-level response in the corehole was dominated by a shallow zone of high transmissivity, which was hydraulically isolated from the pumped interval. In the sandstone, the cross-borehole flow test identified a hydraulic connection along dipping fractured beds as well as a connection to a deep high-angle fracture that cuts across bedding. These results suggest that application of cross-borehole flow tests at other contaminated fractured-bedrock sites could provide insights into hydraulic connections useful the design and implementation of monitoring and remediation programs.

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Final copy as submitted to SAGEEP for publication as: Williams, J.H., Lacombe, P.J., Johnson, C.D., and Paillet, F.L., 2007, Cross-borehole flow tests and insights into hydraulic connections in fractured mudstone and sandstone, in Symposium on the Application of Geophysics to Engineering and Environmental Problems, April 1-5, 2007, Denver, Colorado, Proceedings 2007: Denver, Colorado, Environmental and Engineering Geophysical Society, CD-ROM, p. 1140-1152.