Compound-Specific Isotope Analysis (CSIA) Application for Source Apportionment and Natural Attenuation Assessment of Chlorinated Benzenes

In light of the complex management of chlorobenzene (CB) contaminated sites, at which a hydraulic barrier (HB) for plumes containment is emplaced, compound-specific stable isotope analysis (CSIA) has been applied for source apportionment, for investigating the relation between the upgradient and downgradient of the HB, and to target potential CB biodegradation processes. The isotope signature of all the components potentially involved in the degradation processes has been expressed using the concentration-weighted average C-13 of CBs + benzene (C-13(sum)). Upgradient of the HB, the average C-13(sum) of -25.6 parts per thousand and -29.4 parts per thousand were measured for plumes within the eastern and western sectors, respectively. Similar values were observed for the potential sources, with C-13(sum) values of -26.5 parts per thousand for contaminated soils and -29.8 parts per thousand for the processing water pipeline in the eastern and western sectors, respectively, allowing for apportioning of these potential sources to the respective contaminant plumes. For the downgradient of the HB, similar CB concentrations but enriched C-13(sum) values between -24.5 parts per thousand and -25.9 parts per thousand were measured. Moreover, contaminated soils showed a similar C-13(sum) signature of -24.5 parts per thousand, thus suggesting that the plumes likely originate from past activities located in the downgradient of the HB. Within the industrial property, significant C-13 enrichments were measured for 1,2,4-trichlorobenzene (TCB), 1,2-dichlorobenzene (DCB), 1,3-DCB, and 1,4-DCBs, thus suggesting an important role for anaerobic biodegradation. Further degradation of monochlorobenzene (MCB) and benzene was also demonstrated. CSIA was confirmed to be an effective approach for site characterization, revealing the proper functioning of the HB and demonstrating the important role of natural attenuation processes in reducing the contamination upgradient of the HB.