13C and 37Cl characterization of PCE and application to contamination of the Harrison Landfill: Tucson, Arizona

Abstract

Tetrachloroethene (PCE) contamination of groundwater and soil air underneath Harrison Landfill in Tucson, Arizona, likely occurred by downward vapor phase transport of PCE dumped in the landfill. This study has explored the possibility of using isotopic techniques to better understand this process. The author designed and used a technique for the extraction of PCE vapors from soil air, for 6 13C and 637C1 analysis. It involved collecting PCE vapors by passing soil air through PCE adsorbent traps, then processing and transferring the PCE to a combustion tube. The author also measured for 6 13C and 637C1 values from manufactured trichloroethene (TCE, same as measured by another lab) and PCE samples. An additional experiment measured the 6 13C and 837C1 values of the liquid PCE residual after evaporating various fractions of PCE. 8 13C and 837Cl values of the TCE samples previously described were similar to the earlier values, indicating that 8 13C and 637C1 measurements of solvents (including PCE) were reproducible. Successive evaporation of PCE followed a Rayleigh trend, indicating a values of 1.0006 for carbon and 0.9992 for chlorine. The author simulated the PCE soil vapor sampling in the laboratory, achieving high yields and good separation of PCE. 8 13C values from Harrison soil PCE vapors ranged from — 27.3 to —25.1 0/00 and were within previous values for PCE. 637C1 values were at least 2.3 0/00 higher than any previously reported for PCE samples. 637C1 values for PCE, indicated that either the PCE in Harrison landfill became fractionated in situ, or was already 37C1 rich when dumped at the site.