Carbon and Chlorine Isotope Ratios of Chlorinated Ethenes Migrating through a Thick Unsaturated Zone of a Sandy Aquifer

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• 作者：Daniel Hunkeler ; Ramon Aravena ; Orfan Shouakar-Stash ; Noam Weisbrod ; Ahmed Nasser ; Lior Netzer ; Daniel Ronen
• 刊名：Environmental Science & Technology
• 出版年：2011
• 出版时间：October 1, 2011
• 年：2011
• 卷：45
• 期：19
• 页码：8247-8253
• 全文大小：937K
• 年卷期：v.45,no.19(October 1, 2011)
• ISSN：1520-5851

文摘

Compound-specific isotope analysis (CSIA) can potentially be used to relate vapor phase contamination by volatile organic compounds (VOCs) to their subsurface sources. This field and modeling study investigated how isotope ratios evolve during migration of gaseous chlorinated ethenes across a 18 m thick unsaturated zone of a sandy coastal plain aquifer. At the site, high concentrations of tetrachloroethene (PCE up to 380 渭g/L), trichloroethene (TCE up to 31,600 渭g/L), and cis-1,2-dichloroethene (cDCE up to 680 渭g/L) were detected in groundwater. Chlorinated ethene concentrations were highest at the water table and steadily decreased upward toward the land surface and downward below the water table. Although isotopologues have different diffusion coefficients, constant carbon and chlorine isotope ratios were observed throughout the unsaturated zone, which corresponded to the isotope ratios measured at the water table. In the saturated zone, TCE became increasingly depleted along a concentration gradient, possibly due to isotope fractionation associated with aqueous phase diffusion. These results indicate that carbon and chlorine isotopes can be used to link vapor phase contamination to their source even if extensive migration of the vapors occurs. However, the numerical model revealed that constant isotope ratios are only expected for systems close to steady state.