Chlorinated Ethene Degradation Rate Coefficients Simulated with Intact Sandstone Core Microcosms.

Area of Science:

• Environmental Science
• Geochemistry
• Chemical Engineering

Background:

• Abiotic transformation of trichloroethene (TCE) in fractured porous rock is difficult to quantify.
• Understanding these processes is crucial for effective groundwater remediation strategies.

Purpose of the Study:

• To estimate pseudo first-order abiotic reaction rate coefficients for TCE in diffusion-dominated intact core microcosms.
• To investigate the impact of lactate amendment on TCE abiotic transformation rates.

Main Methods:

• Intact sandstone core microcosms were established to simulate clean groundwater flow adjacent to a TCE-contaminated rock matrix.
• A numerical model was calibrated to monitoring data to assess rate coefficients.
• ¹³C enrichment data and gas formation were used to evaluate dechlorination extent.

Main Results:

• Average initial abiotic transformation rate coefficients for TCE to acetylene, ethene, and ethane were 0.019 y⁻¹ (unamended) and 0.024 y⁻¹ (lactate-amended).
• ¹³C enrichment data yielded moderately higher coefficients (0.026 y⁻¹ unamended, 0.035 y⁻¹ lactate-amended).
• Rate coefficients decreased significantly after ~25 days in unamended microcosms, attributed to reductive capacity depletion.

Conclusions:

• Intact core microcosms provide reliable estimates for abiotic TCE transformation rates in sandstone.
• Lactate amendment showed a modest increase in initial TCE abiotic transformation rates.
• Reductive capacity is a limiting factor for long-term abiotic TCE degradation in these systems.