Subsurface barrier verification technology

Subsurface Barrier Verification Technologies

John H. Heiser
Environmental and Waste Technology Center
Brookhaven National Laboratory

Abstract
One of the more promising remediation options available to the DOE waste management community is subsurface barriers. Some of the uses of subsurface barriers include surrounding and/or containing buried waste, as secondary confinement of underground storage tanks, to direct or contain subsurface contaminant plumes and to restrict remediation methods, such as vacuum extraction, to a limited area. To be most effective the barriers should be continuous and depending on use, have few or no breaches. A breach may be formed through numerous pathways including: discontinuous grout application, from joints between panels and from cracking due to grout curing or wet-dry cycling. The ability to verify barrier integrity is valuable to the DOE, EPA, and commercial sector and will be required to gain full public acceptance of subsurface barriers as either primary or secondary confinement at waste sites.

It is recognized that no suitable method exists for the verification of an emplaced barrier's integrity (see Needs Statement IS-9). The large size and deep placement of subsurface barriers makes detection of leaks challenging. This becomes magnified if the permissible leakage from the site is low. Detection of small cracks (fractions of an inch) at depths of 100 feet or more has not been possible using existing surface geophysical techniques. Compounding the problem of locating flaws in a barrier is the fact that no placement technology can guarantee the completeness or integrity of the emplaced barrier. This report summarizes several commonly used or promising technologies that have been or may be applied to in-situ barrier continuity verification.

Most methods presently being employed for in situ characterization of the subsurface can be defined as well logging technologies. This report gives brief discussions of some of the commonly used logging techniques and the limitation(s) of the methodology when used to verify grout continuity. These methods include well logging technologies such as; neutron logging, gamma logging, electrical resistance tomography, radio imaging method, ground penetrating radar, acoustic logging, seismic tomography, and thermal logging. Also discussed are tracer technologies including a promising new technology for characterization of the subsurface using perfluorocarbon tracers.

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Last Modified: January 31, 2008
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