Effect of source variability and transport processes

which should be used for any reference to this work 1occurs during dissolution of TCE (0.26x), which is consistent with field observations. At most sampling points, the y13C of dissolved TCE was similar to that of the DNAPL except for a few sampling points at the bottom of the aquifer close to the underlying aquitard. At these points, a 13C enrichment of up to 2.4x was observed, which was likely due to biodegradation and possibly preferential diffusion of TCE with 12C into the aquitard. In contrast to the TCE site, several distinct zones of high concentration were observed at the PCE site and from zones to zone, the y13C values varied substantially from 24.3x to 33.6x. Comparison of the y13C values in the high concentration zones made it possible to divide the plume in the three different domains, each probably representing a different episode and location of DNAPL release. The three different zones could still be distinguished 220 m from the DNAPL sources. This demonstrates that carbon isotope ratios can be used to differentiate between different zones in chlorinated ethene plumes and to link plume zones to their sources. In addition, subtle variations in y13C at plume fringes provided insight into mechanisms of plume spreading in transverse vertical direction. These variations were identified because of the high-resolution provided by the monitoring network.on carbon isotope ratios of TCE and PCE in two sandy aquifer