Stratigraphic Control on CCl4 and CHCl3 Concentrations in the 200 West Area, Hanford Site
An extensive subsurface contaminant plume of carbon tetrachloride (CCl4) is the focus of a remedial effort in the 200 West Area of Washington State’s Hanford Site. Remediation requires a high-resolution model of the region’s spatially variable lithofacies and of the effect these units have on CCl4 migration through the unconfined aquifer. To increase detail of previous models, a transect was chosen along the primary groundwater flow path in the most heavily contaminated area. Borehole logs of wells along this 3.7 km-long transect were systematized and used to create a cross section displaying lithofacies depth and continuity. Natural and spectral gamma geophysical logs were examined to pinpoint the depths of geologic units. Depth discrete concentrations of CCl4 and its reductive dechlorination product, chloroform (CHCl3), were overlain on this cross section. Comparison of stratigraphy to contaminant levels shows that peaks in CCl4 concentration occur in thin, fine-grained layers and other that fine-grained layers frequently form lower boundaries to regions of high concentration. Peaks in CCl4 concentrations are frequently located at different depths from those of CHCl3, suggesting that these concentrations are affected by dechlorination of CCl4. Transformation of CCl4 to CHCl3 appears to be more prevalent within reduced, iron-containing sediments. Influence of thin, fine-grained layers within the larger aquifer unit indicates that characterization of contamination in this locality should consider subsurface geology with at least as much resolution as provided in this study.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 958515
- Report Number(s):
- PNNL-SA-55088; KL0101000; TRN: US201002%%183
- Journal Information:
- Journal of Undergraduate Research, VIII:144-149, Vol. 8
- Country of Publication:
- United States
- Language:
- English
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