Abstract
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 δ13C of CBs + benzene (δ13Csum). Upgradient of the HB, the average δ13Csum of −25.6‰ and −29.4‰ were measured for plumes within the eastern and western sectors, respectively. Similar values were observed for the potential sources, with δ13Csum values of −26.5‰ for contaminated soils and −29.8‰ 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 δ13Csum values between −24.5‰ and −25.9‰ were measured. Moreover, contaminated soils showed a similar δ13Csum signature of −24.5‰, thus suggesting that the plumes likely originate from past activities located in the downgradient of the HB. Within the industrial property, significant δ13C 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.
Highlights
Chlorinated solvents pose significant risks to human health, and contaminated sites entail tremendous management costs [1,2]
The present study examines the potential of compound-specific stable isotope analysis (CSIA) for chlorinated benzenes (CBs), DCBs
The proposed approach using CSIA supported by hydrogeological, concentration and redox data proved to be an effective tool for detailed site characterization
Summary
Chlorinated solvents pose significant risks to human health, and contaminated sites entail tremendous management costs [1,2]. The application of new approaches for the correct identification of the polluter is necessary in the presence of potential multiple sources/polluters, and especially at mega-sites such as industrial areas or petrochemical plants [4]. After remediation actions (e.g., plume or source containment by physical or hydraulic barriers (HBs)), a downgradient contamination can still be detected [10], and often it is crucial to understand the reasons for the ongoing contamination. Studies including SA may provide an understanding of whether the downgradient pollution is due to a failure of the remediation system, for example, failure of containment of the contaminants by the barrier [11,12], or rather is related to other external sources undiscovered during the characterization of the contaminated site belonging to some other industrial sites
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