April 2008 monitoring report for Morrill, Kansas.

Abstract

In September 2005, the Commodity Credit Corporation of the U.S. Department of Agriculture (CCC/USDA) initiated periodic sampling of groundwater in the vicinity of a grain storage facility formerly operated by the CCC/USDA at Morrill, Kansas. The sampling at Morrill 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), to monitor levels of carbon tetrachloride contamination identified in the groundwater at this site (Argonne 2004, 2005a). This report provides results for the most recent monitoring event, in April 2008. Under the KDHE-approved monitoring plan (Argonne 2005b), groundwater was initially sampled twice yearly for a recommended period of two years (in fall 2005, in spring and fall 2006, and in spring and fall 2007). The samples were analyzed for volatile organic compounds (VOCs), as well as for selected geochemical parameters to aid in the evaluation of possible natural contaminant degradation (reductive dechlorination) processes in the subsurface environment. During the recommended two-year period, the originally approved scope of the monitoring was expanded to include vegetation sampling (initiated in October 2006) and surface water and stream bed sediment sampling (initiated in March 2007, after amore » visual reconnaissance along Terrapin Creek [Argonne 2007a]). The analytical results for groundwater sampling events at Morrill in September 2005, March 2006, September 2006, March 2007, and October 2007 were documented previously (Argonne 2006a,b, 2007b, 2008). Those results consistently demonstrated the presence of carbon tetrachloride contamination, at levels exceeding the KDHE Tier 2 risk-based screening level (5.0 {micro}g/L) for this compound, in a groundwater plume extending generally south-southeastward from the former CCC/USDA facility, toward Terrapin Creek at the south edge of the town. The results of those five monitoring events gave little indication of consistent changes in the contaminant concentrations at the individual monitoring points or of plume migration. Low levels (= 1.3 {micro}g/L) of carbon tetrachloride were persistently detected at monitoring well MW8S, however, on the bank of an intermittent tributary to Terrapin Creek. This observation suggested a possible risk of contamination of the surface waters of the creek. That concern became the driving force for ongoing monitoring and consideration of possible remedial options for Morrill. In light of the early findings, in 2006 the CCC/USDA recommended expansion of the approved monitoring program to include the collection and analysis of surface water samples along Terrapin Creek (Argonne 2006a). At the request of the KDHE (2007a), locations for both surface water and shallow sediment sampling were discussed with the KDHE in January 2007. An addendum to the existing monitoring plan and a standard operating procedure (SOP AGEM-15) for sediment sampling were submitted to the KDHE on the basis of these discussions (Argonne 2007c,d). To supplement the original scope of the monitoring, Argonne also sampled natural vegetation along Terrapin Creek in October 2006, April 2007, and July 2007 for analyses for VOCs. The results of the plant tissue analyses were reported previously (Argonne 2008). The April 2008 sampling event reported here represents a continuation of the two-year monitoring program, as requested by the KDHE (2007b). The sampling is presently conducted, in accord with the monitoring plan (Argonne 2005b) and the addendum to that plan (Argonne 2007a), in a network of 12 monitoring wells and 3 private wells (Figure 1.1), at locations approved by the KDHE. An event that affects the results of the April 2008 monitoring is the installation of an irrigation well, owned by Kent Grimm, on the south side of Terrapin Creek, near monitoring well MW6S. The WWC-5 well registration form (in Appendix A) indicates that the well diameter is 16 in., that artesian flow is occurring at a rate of 250 gpm, and that installation occurred on March 10, 2008.« less