Analytical and Numerical Modeling of Solute Intrusion,Recovery, and Rebound in Fractured Bedrock |
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| Authors: | Ranjeet M Nagare Young-Jin Park Trevor Butterfield Chad Belenky Sheldon Scyrup |
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| Institution: | 1. ARKK Engineering Corporation, Sherwood Park, AB, T8H 2K8, Canada;2. University of Waterloo, Waterloo, Ontario, Canada;3. Advisian, WorleyParsons Group, Edmonton, Alberta, Canada;4. Parkvalley Consulting Inc., Calgary, Alberta, Canada;5. Chevron Canada Resources, Calgary, Alberta, Canada |
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| Abstract: | Contaminated groundwater in fractured bedrock can expose ecosystems to undesired levels of risk for extended periods due to prolonged back-diffusion from rock matrix to permeable fractures. Therefore, it is key to characterize the diffusive mass loading (intrusion) of contaminants into the rock matrix for successful management of contaminated bedrock sites. Even the most detailed site characterization techniques often fail to delineate contamination in rock matrix. This study presents a set of analytical solutions to estimate diffusive mass intrusion into matrix blocks, it is recovered by pumping and concentration rebound when pumping ceases. The analytical models were validated by comparing the results with (1) numerical model results using the same model parameters and (2) observed chloride mass recovery, rebound concentration, and concentration in pumped groundwater at a highly fractured bedrock site in Alberta, Canada. It is also demonstrated that the analytical solutions can be used to estimate the total mass stored in the fractured bedrock prior to any remediation thereby providing insights into site contamination history. The predictive results of the analytical models clearly show that successful remediation by pumping depends largely on diffusive intrusion period. The results of initial mass from the analytical model was used to successfully calibrate a three-dimensional discrete fracture network numerical model further highlighting the utility of the simple analytical solutions in supplementing the more detailed site numerical modeling. Overall, the study shows the utility of simple analytical methods to support long-term management of a contaminated fractured bedrock site including site investigations and complex numerical modeling. |
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