Predicting longevity of iron permeable reactive barriers using multiple iron deactivation models

Area of Science:

• Environmental Engineering
• Geochemistry
• Contaminant Hydrogeology

Background:

• Permeable reactive barriers (PRBs) are engineered systems for in-situ groundwater remediation.
• Predicting the long-term efficiency of PRBs is crucial for effective site management.
• Lab-scale experiments under accelerated conditions can provide insights but may introduce uncertainties.

Purpose of the Study:

• To investigate model uncertainties in predicting long-term PRB remediation efficiency.
• To evaluate the performance of a lab-scale PRB column experiment.
• To assess the impact of different reactive surface models on long-term performance predictions.

Main Methods:

• A lab-scale column experiment simulating a PRB (20% iron, 80% sand) was conducted for one year.
• Contaminated groundwater with chlorinated solvents was pumped at an accelerated velocity (3.7 E-1 m d(-1)).
• A multi-component reactive transport model was calibrated using measured contaminant and inorganic concentrations, then used to predict performance under reduced flow conditions (1.4 E-3 m d(-1)).

Main Results:

• All tested models reasonably reproduced the column experiment data.
• Extrapolated long-term PRB efficiency predictions varied significantly among the four different iron reactive surface models.
• Model predictions diverged considerably when simulating reduced, field-representative flow rates.

Conclusions:

• Significant model uncertainties exist when extrapolating long-term PRB performance from lab-scale experiments.
• These uncertainties must be addressed during the PRB design phase.
• Further research, including independent experiments and field observations, is needed to better understand reactive surface deactivation mechanisms in iron PRBs.