C and Cl-CSIA for Elucidating Chlorinated Methanes Biotic and Abiotic Degradation at a Polluted Bedrock Aquifer

In this study,concentration and δ13C and δ37Cl values of chloroform (CF) and carbon tetrachloride (CT) measured in groundwater samples are related to redox conditions to elucidate natural attenuation processes in a polluted site. Shifts in δ13C and δ37Cl of CF and CT were detected over time.δ13CCF values found in the potential sources were -34.5 ± 0.6 ‰ (tank near S3 well), -37.3 ± 0.6 ‰ (in a fracture near S1 well) and -46.2± 0.4 ‰ (barrels) in 2004, whereas in later sampling campaigns, δ13CCF enriched values such as -25.2 ± 0.5 ‰ were measured in S3 in 2013. 2D plots (δ13CCFvs δ37ClCF) showed different isotopic patterns in different wells and depths. δ37ClCF values let distinguish that the former sources evolved towards completely different isotopic signatures, whilst δ37ClCF values of +1.3 ± 0.3 ‰ were reached in 2013 for S3,S1 moved towards more depleted δ37ClCF values (down to -3.9 ± 0.6‰). These data indicate that differentreductive dechlorination processes might occur.