Field Tests of a DNAPL Characterization System Using Cone Penetrometer-Based Raman Spectroscopy

• Published in: Ground water monitoring & remediation 2000, Vol.20 (4), p.72-81
• Main Authors: Rossabi, J., Riha, B.D., III, J.W. Hass, Eddy-Dilek, C.A., Lustin, A.G., Carrabba, M., Hyde, W.K., Bello, J.
• Format: Article
• Language: English
• Subjects: USA, South Carolina, Aiken
• ISSN: 1069-3629; 1745-6592
• DOI: 10.1111/j.1745-6592.2000.tb00291.x

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.