September 2008 monitoring results for Centralia, Kansas.

Abstract

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 plumemore » 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 taking 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 in situ chemical reduction technology, that was approved by the KDHE in November 2007 (KDHE 2007). Implementation of the proposed interim measure occurred in 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 2009). The KDHE has requested that sitewide monitoring continue at Centralia until a final remedy has been implemented and a comprehensive program of performance and compliance monitoring has been established for this site (KDHE 2008a). The groundwater sampling events at Centralia in March 2008 (Argonne 2008b) and September 2008 were performed in response to this request. The present report documents the results of groundwater sampling conducted in September 2008, in the network of 10 monitoring wells and 6 piezometers (Figure 1.1) previously approved by the KDHE for extended monitoring of the groundwater contamination at Centralia (KDHE 2005a,b). Sampling of additional piezometers specifically installed to monitor the progress of the interim measure pilot test (PMP1-PMP9; Figure 1.2) was also performed in September 2008; the results of these analyses are reported and discussed separately (Argonne 2009).« less