Annual report of groundwater monitoring at Centralia, Kansas, in 2010.

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 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 the KDHE-approved monitoring plan (Argonne 2005b), the groundwater was sampled twice yearly from September 2005 until September 2007 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 processes (reductive dechlorination) in the subsurface environment (Argonne 2006, 2007a, 2008a). The results from the two-year sampling program demonstrated the presence of carbon tetrachloride contamination at levels exceeding the KDHE Tier 2 risk-based screening level (RBSL) of 5 {micro}g/L for this compound, in a localized groundwater plume that has shown little movement. The relative concentrations of chloroform, the primary degradation product of carbon tetrachloride, suggested that some degree of reductive dechlorination or natural biodegradation was talking place in situ at the former CCC/USDA facility on a localized scale. The CCC/USDA subsequently developed an Interim Measure Conceptual Design (Argonne 2007b), proposing a pilot test of the Adventus EHC technology for in situ chemical reduction (ISCR). The proposed interim measure (IM) was approved by the KDHE in November 2007 (KDHE 2007). Implementation of the pilot test occurred in November-December 2007. The objective was to create highly reducing conditions that would enhance both chemical and biological reductive dechlorination in the injection test area (Argonne 2009a). The KDHE (2008a) requested that sitewide monitoring continue until a final remedy is selected (as part of a Corrective Action Study [CAS] evaluation) and implemented. In response to this request, the established sampling across the site and additional sampling in the IM pilot test area continued in 2008 (Argonne 2008b, 2009a,b). On the basis of results of the 2005-2008 sitewide monitoring and the 2008 IM pilot test monitoring, the CCC/USDA recommended a revised sampling program for both the wider site and the IM pilot test area (Section 4.2 in Argonne 2009b). The elements of this interim monitoring plan are as follows: (1) Annual sampling of twelve monitoring points across the site (Figure 1.1) and five outlying IM pilot test monitoring points (PMP4, PMP5, PMP6, PMP7, PMP9; Figure 1.2); and (2) Twice yearly sampling of five IM pilot test monitoring points inside the injection area (PMP1-PMP3, PMP8, MW02; Figure 1.2). With the approval of the KDHE (2009), the initial groundwater sampling for VOCs and geochemical analyses under the interim monitoring plan outlined above was conducted in 2009 (Argonne 2010). The present report documents the findings of the 2010 monitoring events, conducted on April 5 and September 19-21, 2010