Isotopic Characterization for TCE Plume Discrimination and Monitored Natural Attenuation

Compound specific isotope analysis (CSIA) is an improved analytical procedure that allows isotopic characterization of individual compounds.  For this project, Kleinfelder teamed with the of and Zymax Forensics to generate CSIA characterization data at a confidential site in (Site).  The primary objective was to provide evidence for discrimination between sources of chlorinated solvents and to help identify the source of downgradient dissolved chlorinated aliphatic hydrocarbons (CAHs).  Chlorinated solvent releases have been identified in at least two locations that have resulted in a groundwater plume consisting of commingled dissolved perchloroethylene (PCE) and trichloroethylene (TCE) in a complex hydrogeologic environment.  CSIA data for carbon and chlorine isotopes did not vary significantly between the wells sampled and therefore does not currently provide evidence for discrimination between sources.  However, additional planned CSIA data collection from additional wells may provide evidence for source discrimination. 

A secondary objective of this study was to evaluate isotopic characterization data to ascertain whether or not natural attenuation through reductive dechlorination was occurring at the Site.  Results from isotopic characterization suggested that reductive dechlorination is not presently occurring at the Site.  It is anticipated that additional CSIA and geochemical data will be generated to continue monitoring for natural attenuation.  In the event that a more active remedial approach (e.g., enhanced or augmented bioremediation) is implemented, additional CSIA data and site-specific isotopic enrichment factors will be generated for performance monitoring.