Characterizing vertical contaminant distribution in a thick unconfined aquifer,Hanford site,Washington, USA |
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| Authors: | Bruce A Williams Charissa J Chou |
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| Institution: | (1) Pacific Northwest National Laboratory, PO Box 999, Richland, WA, USA |
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| Abstract: | Drilling-intensive aquifer characterization techniques have been used to obtain depth-discrete water samples from a thick,
hydrogeologically continuous unconfined aquifer system; groundwater results indicate that carbon tetrachloride contamination
is widespread and extends deeper and at concentrations much higher than detected in monitoring networks at the water table.
Carbon tetrachloride, a legacy waste, was used in the plutonium extraction process at the Hanford site in south-central Washington
State. Vertical, depth-discrete groundwater samples were collected during well drilling throughout a 28-km2 region to determine the concentration of carbon tetrachloride present as a dissolved phase in the aquifer. Results indicate
that high concentrations of carbon tetrachloride, three orders of magnitude above the allowable regulatory limit, are present
at depths greater than 25 m beneath the water table. In support of future efforts to remediate the carbon tetrachloride contamination,
it is imperative to locate the remaining chemical inventory, determine the vertical as well as the lateral distribution of
this contaminant and its physical form. Depth-discrete aquifer characterization throughout the uppermost-unconfined aquifer
system is providing this information and improving the understanding of the contaminant distribution and the hydrogeologic
framework through which it moves.
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| Keywords: | DNAPL Hydrostratigraphy Groundwater contamination Carbon tetrachloride Deep unconfined aquifer Vadose zone |
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