Annual report of monitoring at Morrill, Kansas, in 2009 .

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 2005), to monitor levels of carbon tetrachloride contamination identified in the groundwater at this site (Argonne 2004, 2005a). This report provides results for monitoring events in April and September 2009. Under the KDHE-approved monitoring plan (Argonne 2005b), groundwater was initially sampled twice yearly for a 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. The analytical results for groundwater sampling events at Morrill from September 2005 to October 2008 were documented previously (Argonne 2006a,b, 2007, 2008a,b, 2009). Those results consistently demonstrated the presence of carbon tetrachloride contamination, at levels exceeding the KDHE Tier 2 risk-based screening level of 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. Low levels ({le} 1.3 {micro}g/L) of carbon tetrachloride were persistently detected at monitoring well MW8S, 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 is the regulatory driver for ongoing monitoring. 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 (Appendix A) and a standard operating procedure (SOP AGEM-15; Appendix B) for sediment sampling were submitted to the KDHE on the basis of these discussions and were subsequently approved (KDHE 2008b). Results of sediment sampling prior to 2009 were reported previously (Argonne 2008a,b; 2009). 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 these plant tissue analyses were reported previously (Argonne 2008a, 2009). The April and September 2009 sampling events reported here represent a continuation of the two-year monitoring program, as requested by the KDHE (2007b). The groundwater sampling is presently conducted, in accord with the monitoring plan (Argonne 2005b) and the addendum to that plan (Appendix A in this report), in a network of 12 monitoring wells and 3 private wells (Figure 1.1), at locations approved by the KDHE (2008b). The findings of the April and September 2009 monitoring events at Morrill support the following conclusions: (1) Groundwater flow during the early spring and the later part of this review period was predominantly to the south-southeast, from the vicinity of the former CCC/USDA facility toward Terrapin Creek. In late spring, a slight shift occurred toward more southerly groundwater flow (possibly southwesterly in the immediate vicinity of the intermittent tributary that flows into Terrapin Creek). This shift in the late spring reflected transient seasonal precipitation and recharge that resulted in higher groundwater levels at this time. (2) No significant changes were observed in the levels or distribution of carbon tetrachloride in the groundwater at Morrill during the current review period, or in comparison to the results of the spring and fall 2008 monitoring events. A maximum carbon tetrachloride concentration of 28-30 {micro}g/L was identified in groundwater - at well MW3S - during both the April and September 2009 sampling events. (3) No carbon tetrachloride contamination was detected in surface waters or shallow streambed sediments sampled at five locations along Terrapin Creek, downgradient from the former CCC/USDA facility. (4) Sampling of tree branch tissues from existing trees for VOCs analyses can be an indicator of shallow subsurface groundwater contamination. Detections of carbon tetrachloride in vegetation at the Morrill site to date have been generally consistent with the documented location of the groundwater plume