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Environ Sci Technol

Title:		Can soil gas VOCs be related to groundwater plumes based on their isotope signature?
Author(s):		Jeannottat S; Hunkeler D;
Address:		"Centre for Hydrogeology & Geothermics (CHYN), University of Neuchatel , Rue Emile Argand 11, CH-2000 Neuchatel, Switzerland"
Journal Title:		Environ Sci Technol
Year:		2013
Volume:		20131024
Issue:		21
Page Number:		12115 - 12122
DOI:		10.1021/es4010703
ISSN/ISBN:		1520-5851 (Electronic) 0013-936X (Linking)
Abstract:		"The isotope evolution of tetrachloroethene (PCE) during its transport from groundwater toward the soil surface was investigated using laboratory studies and numerical modeling. During air-water partitioning, carbon and chlorine isotope ratios evolved in opposite directions, with a normal isotope effect for chlorine (epsilon = -0.20 per thousand) and an inverse effect for carbon (epsilon = +0.46 per thousand). During the migration of PCE from groundwater to the unsaturated zone in a 2D laboratory system, small shifts of carbon and chlorine isotope ratios (+0.8 per thousand) were observed across the capillary fringe. Numerical modeling showed that these shifts are due to isotope fractionation associated with air-water partitioning and gas-phase diffusion. Carbon and chlorine isotope profiles were constant throughout the unsaturated zone once a steady state was reached. However, depending on the thickness of the unsaturated zone and its lithology, depletion in heavy isotopes may occur with distance during the transient migration of contaminants. Additionally, variations of up to +1.5 per thousand were observed in the unsaturated zone for chlorine isotopes during water table fluctuations. However, at steady state, it is possible to link a groundwater plume to gas-phase contamination and/or to differentiate sources of contamination based on isotope ratios"
Keywords:		"Carbon Isotopes/*analysis Chemical Fractionation Chlorine/*analysis/chemistry Diffusion Gases/chemistry Groundwater/analysis/*chemistry Isotopes/analysis/chemistry Models, Chemical Models, Theoretical Soil/*chemistry Tetrachloroethylene/*analysis/chemistr;"
Notes:		"MedlineJeannottat, S Hunkeler, D eng Research Support, Non-U.S. Gov't 2013/09/24 Environ Sci Technol. 2013; 47(21):12115-22. doi: 10.1021/es4010703. Epub 2013 Oct 24"