In September 2005, periodic sampling of groundwater was initiated by the Commodity Credit Corporation of the U.S. Department of Agriculture (CCC/USDA) in the vicinity of a grain storage facility formerly operated by the CCC/USDA at Centralia, Kansas. The sampling at Centralia is being performed on behalf of the CCC/USDA by Argonne National Laboratory, in accord with a monitoring program approved by the Kansas Department of Health and Environment (KDHE). The objective is to monitor levels of carbon tetrachloride contamination identified in the groundwater at Centralia (Argonne 2003, 2004, 2005a). Under a KDHE-approved monitoring plan (Argonne 2005b), the groundwater was sampled twice yearly (for a recommended period of two years) for analyses for volatile organic compounds (VOCs), as well as measurement of selected geochemical parameters to aid in the evaluation of possible natural contaminant degradation (reductive dechlorination) processes in the subsurface environment. The sampling in September 2007 represented the fifth and final monitoring event performed under the two-year twice yearly monitoring program (Argonne 2006a,b, 2007a, 2008a). The results from the two-year monitoring program demonstrated the presence of carbon tetrachloride contamination at levels exceeding the KDHE Tier 2 Risk-Based Screening Level of 5 {micro}g/L for this compound in a broad groundwater plume …