A Case Study of Natural Attenuation of Chlorinated Solvents Under Unstable Groundwater Conditions in Takahata, Japan
The natural attenuation behavior of chlorinated solvents and their risks to human health at a contaminated groundwater site in Takahata, Japan, were investigated. It was found that volatile organic compound (VOC) concentrations gradually decreased via two attenuation mechanisms, namely dilution and biodegradation. It was estimated that the VOC concentrations will be below the Japanese limits within 30 years after stopping the active remediation in 2003, which suggests that there is a high possibility that monitored natural attenuation can be adopted as the clean-up method at this contaminated site. The risk levels of VOCs at the present time are much lower than those at the time when the contamination was discovered. Vinyl chloride still presents a risk in some wells, and there were occasional unexpected increases in the risk levels of tetrachloroethylene, trichloroethylene, and cis-1,2-dichloloethylene, which means that continuous monitoring of the groundwater is necessary for forecasting risk levels.
KeywordsVolatile organic compounds (VOCs) Natural attenuation Biodegradation Groundwater Takahata
The authors are very thankful to Dr. Toshio Oiwa, Mr. Eiji Watanabe, Mr. Kazushige Nishizuka, and other staff at the Yamagata Environmental Science Research Center for their support in groundwater sampling. The authors would also like to thank Dr. Yasuhide Sakamoto and Ms. Yoshimi Ogamino at the National Institute of Advanced Industrial Science and Technology for their assistance in groundwater sampling and chemical analysis.
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