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Cone penctrometer test (CPT) based Raman spectroscopy was used to identify separate phase tetrachloroethylene (PCE) and trichlorocthylene (TCE) contamination in the subsurface at two locations during field tests conducted at the U.S. Department of Energy's (DOE) Savannah River site. Clear characteristic Raman spectral peaks for PCE and TCE were observed at two sites and several depths during CPT deployment. Because of the uniqueness of a Raman spectrum for a given compound, these data are compelling evidence of the presence of the two compounds. The Raman spectral results correlated with high PCE and TCE concentrations in soil samples collected from the same subsurface zones, confirming that the method is a viable dense nonaqueous phase liquid (DNAPL) characterization technique. The Raman spectroscopic identification of PCE and TCE in these tests represents the first time that DNAPLs have been unequivocally located in the subsurface by an in situ technique. The detection limit of the Raman spectroscopy is related to the probability of contaminant droplets appearing on the optical window in the path of the probe light. Based on data from this fieldwork the Raman technique may require a threshold quantity of DNAPL to provide an adequate optical cross section for spectroscopic response. The low aqueous solubility of PCE and TCE and relatively weak optical intensity of the Raman signal precludes the detection of aqueous phase contaminants by this method, making it selective for DNAPL contaminants only.

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The MicroBlower Sustainable Soil Vapor Extraction System is a cost-effective device specifically designed for remediation of organic compounds in the vadose zone. The system is applicable for remediating sites with low levels of contamination and for transitioning sites from active source technologies such as active soil vapor extraction to natural attenuation. It can also be a better choice for remediating small source zones that are often found in "tight zones" that are controlled by diffusion rate. The MicroBlower was developed by the Savannah River National Laboratory at the US Department of Energy's Savannah River Site to address residual volatile organic compound (VOC) contamination after shutdown of active soil vapor extraction systems. In addition, the system has been deployed to control recalcitrant sources that are controlled by diffusion rates. O Braden H. Rambo is a senior field scientist at CRB Geological and Environmental Services, Inc., and he has worked in the environmental industry since 2004; for most of his career, he has studied and applied techniques for biodegradation of chlorinated solvents. He received a BS in geology and a minor in environmental engineering from Clemson University. During an internship at SRS, he assisted groundwater and vadose-zone remediation efforts. Rambo is pursuing an MBA through the University of Florida and plans to qualify as a professional geologist within the year.

Nonlinear complex-resistivity (NLCR) cross-hole imaging of the vadose zone was performed at the A-014 Outfall at the Savannah River Site, Aiken, SC. The purpose of this experiment was to fieldtest the ability of this method to detect dense nonaqueous phase liquids (DNAPLs), specifically tetrachloroethene (PCE), known to contaminate the area. Five vertical electrode arrays (VEAs) were installed with~15-ft (3 m) separations in and around the suspected source zone to depths of 72 ft (22 m), and measurements were carried out at seven nearest-neighbor panels. Amplitude and phase data were edited for quality and then inverted to form three-dimensional (3D) images. The comparatively small magnitude of the nonlinear resistivity Hilbert distortion allowed approximate linearized imaging of the 3D distribution of this quantity as well. Laboratory analysis of nearby soil contaminated in situ indicated that the NLCR response to the PCE-clay reaction is maximized near 50 mHz, leading to the development of a metric involving the phase and resistivity Hilbert distortion to infer the 3D distribution of PCE. Variations in PCE content were independently detailed at three drilling locations within the NLCR survey area using direct penetration-based soil-collection tools. Approximately 400 soil samples were collected and analyzed for chlorinated solvent mass composition at 1-ft (0.3-m) vertical intervals to compare with the NLCR-predicted distribution of DNAPL. The optimum performance for 1,000 mg/kg PCE was~80% detection (true positives) with~30% false alarms (false positives) at an effective resolution of 4 ft (1.2 m), or~1/4 of the interwell separation. When smoothed to 12-ft (3.7 m) resolution (comparable to well spacing), detection was 100% with just 12% false alarms. NLCR successfully predicted the general distribution of PCE at parts-perthousand soil-mass fractions, specifically widespread near-surface contamination and a zone of discontinuous stringers and pods below the source.