Assessment of Trichloroethene Source Zone and Plume Evolution in a Fractured Dolostone Aquifer Due to Natural Attenuation Processes

Olesiuk, Joanna B.
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University of Guelph

A detailed study of an aged trichloroethene source zone and plume in fractured dolostone in Guelph, Ontario was undertaken to assess bulk scale behaviour due to natural attenuation. Long term groundwater quality data from an established monitoring network indicate spatially heterogeneous conditions. Decreasing TCE concentration trends occur at over 80% of locations. Degradation products cis-DCE, VC, ethene and ethane are present. Within shallow bedrock, where bulk of the mass resides, 46%, 74% and 86% reduction in TCE plume area, average concentration and mass, occurred between 2003 and 2013. Results of Compound Specific Isotope Analysis show TCE 13C enrichment and increasing concentrations of dissolved gases, providing evidence that complete biodegradation, specifically where favourable redox conditions exist, is occurring and increasing. Although the centre of mass is near stationary, plume front position is retreating toward the source area and groundwater concentrations are strongly attenuating due to continued matrix diffusion, sorption and degradation.

Trichloroethene, Fractured rock, Natural attenuation, Plume evolution, Dolostone, Bedrock aquifer, CSIA, Biodegradation