Technical justification for a request to reclassify the former CCC/USDA facility at Canada, Kansas.

[摘要] Contamination in groundwater at Canada, Kansas, was discovered in 1997, during limited private well sampling near former grain storage facilities of the Commodity Credit Corporation, U.S. Department of Agriculture (CCC/USDA). Subsequent investigations by the Kansas Department of Health and Environment (KDHE) confirmed carbon tetrachloride and nitrate concentrations in groundwater above the respective maximum contaminant levels (MCLs) of 5.0 {micro}g/L and 10.0 mg/L. The KDHE investigations identified both the former CCC/USDA grain storage facility and a private grain storage facility as likely sources for the carbon tetrachloride contamination. The CCC/USDA funded extension of a rural water district line to provide a permanent alternate water supply, and the KDHE has conducted long-term monitoring under the State Water Plan. This document presents an analysis of the available information for the Canada site, acquired in previous investigations and the long-term KDHE monitoring. This analysis forms the technical justification for a request to reclassify the former CCC/USDA grain storage facility at Canada as a site requiring no further action under the Intergovernmental Agreement (IGA) between the KDHE and the USDA's Farm Service Agency. The KDHE's long-term water level monitoring results indicate a consistent groundwater flow direction to the east-southeast. Consequently, the wells with the highest overall concentrations of carbon tetrachloride are downgradient from the private grain storage facility but not downgradient from the former CCC/USDA facility. The KDHE criterion for reclassification of a site is that contamination there should not pose an unacceptable risk, on the basis of analytical results for four consecutive, equally timed, sequenced sampling episodes over a period of no less than two years. In seven KDHE sampling events over a period of six years (2001-2007), the concentrations of carbon tetrachloride in the monitoring well on the former CCC/USDA property at Canada have ranged from 0.63 {micro}g/L to 2.9 {micro}g/L. These seven results are all below the MCL of 5.0 {micro}g/L, and they demonstrate that groundwater on the former CCC/USDA property has met the standard for carbon tetrachloride in drinking water since 2001 and does not pose a significant human health threat. Except for a two-year interval between sampling events in December 2003 and December 2005, the monitoring occurred at approximately annual intervals. The results warrant a request for reclassification of the Canada site to Resolved status on the KDHE's Identified Sites List, under Section III (Other Considerations) of KDHE policy BER-RS-024, Rev. 2001.

[发布日期] 2007-12-21

[学科分类] 环境科学（综合）

[关键词] KANSAS;CARBON TETRACHLORIDE;CONTAMINATION;DRINKING WATER;MONITORING;NITRATES;SAMPLING;STORAGE FACILITIES;GROUND WATER;WATER WELLS