Multi-element isotopic fingerprinting on aqueous-phase chloroethenes derived from chlorinated pitches

Compound Specific Isotope Analysis (CSIA) is an effective tool in order to apportion the source of groundwater contamination. Isotopic signature may reflect the production process of a compound or the origin of raw materials used in the production. Nijenhuis et al. (2013) demonstrated that PCE and TCE, as by-products of the distillation of chloromethanes via thermal chlorination, show strongly depleted δ13C, with values ranging between -87 and -65‰ for PCE and between -79 and -64‰ for TCE. This finding was related to a field study in Northern Italy (Ferrara). In order to strengthen the investigation tool, the presented study involves a multi-element and multi-site approach by taking into account the same industrial process of chloromethanes production and nearby dumping in different sites (in charge of different producers and in different hydrogeological settings). In particular, the δ13C, δ37Cl and δ2H were analyzed in the molecules of PCE, TCE and 1,2 DCE dissolved in groundwater at two distinct locations in Italy. The existing fingerprinting of δ13C in Ferrara site was complemented by δ37Cl and δ2H analyzed in some selected boreholes from the previous survey. The second investigated site is known as the Bussi site (Central Italy). Contaminated groundwater was sampled at the two sites in two distinct sampling rounds, for a total of 30 boreholes (the second sampling round is being performed in 2017). The geological settings are different at the two sites: a large alluvial plain (Ferrara site) and a narrow valley with macroclastic alluvial deposits and travertines (Bussi site). The following issues will be targeted during the presentation: can we apply the CSIA approaches for source apportionment in different hydrogeological settings with different potential producers of chlorinated aliphatic hydrocarbons (CAH)? Is it feasible to define a multi element fingerprinting for CAH derived from chlorinated pitches, and how does the fractionation of the different stable isotopes respond to production, dumping and biodegradation? The research will show that the multi-isotope approach can help addressing liability of contamination events in urban and periurban areas, where the pattern of contaminant distribution and concentration in groundwater does not allow identification of the polluter. References. Nijenhuis, I., Schmidt, M., Pellegati, E., Paramatti, E., Richnow, H.H., Gargini, A. 2013. A stable isotope approach for source apportionment of chlorinated ethenes plumes at a complex multi-contamination events urban site. Journal of Contaminant Hydrology, 153, 92–105.