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Monitoring engineered remediation with borehole radar

By John W. Lane, Jr., Frederick D. Day-Lewis, and Peter K. Joesten
U.S. Geological Survey, Office of Ground Water, Branch of Geophysics, 11 Sherman Place, Unit 5015, Storrs, CT 06269

Abstract

The success of engineered remediation is predicated on correct emplacement of either amendments (e.g., vegetable-oil emulsion, lactate, molasses, etc.) or permeable reactive barriers (e.g., vegetable oil, zero-valent iron, etc.) to enhance microbial breakdown of contaminants and treat contaminants. Currently, site managers have limited tools to provide information about (1) the distribution of injected materials; (2) the existence of gaps or holes in barriers; and (3) breakdown or transformation of injected materials over time. Current technologies for evaluating or confirming the success of emplacements primarily rely on direct measurements from wells. Such measurements are invasive, expensive, time consuming, and provide only limited spatial and temporal information. Given that microbial activity can be highly localized and conventional fluid sampling is sparse (in space and time), new approaches are required for cost-effective verification of engineered remediation. In this article, we discuss the application of borehole-radar techniques to monitor engineered remediation. We review the basis for cross-hole radar monitoring of remediation processes and provide two case studies. In the first study, borehole radar was used to evaluate the emplacement of vegetable oil emulsion in a pilot study to promote biodegradation of chlorinated solvents. In the second study, borehole radar was used to monitor the installation of a permeable reactive iron wall, again part of a pilot study to remediate chlorinated solvents. Our results demonstrate that radar data can provide information to (1) improve or extend the interpretation of conventional geochemical samples, and (2) optimize selection of locations for additional geochemical sampling or drilling.

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Final copy as submitted to The Leading Edge for publication as: Lane, J.W., Jr., Day-Lewis, F.D., and Joesten, P.K., 2007, Monitoring engineered remediation with borehole radar: The Leading Edge, v.26, no. 8, p. 1032-1035.