Formatted Title
Can Permeability Enhancement Circumvent Back Diffusion, Rebound and Reduce Remediation Time at Low Permeability Sites?
Background/Objectives
Remediation in clay dominant environments often results in lengthy remediation programs, often with multiple injection or treatment events, occasionally requiring multiple iterations or applications of different technologies. During in situ injection applications, such site conditions commonly result in failed injections, excessive surfacing of injectate, minimal distribution, significant rebound post remediation, unidentified pockets of residual NAPL mass, and years to decades longer remediation timeframes. The primary limitation is diffusion and secondary permeability that is laterally discontinuous and isolated through the zone. There can be multiple objectives when performing permeability enhancement including increased distribution of injected reagents and creation of optimized injection wells for reinjection of liquid or soluble reagents. But can permeability enhancement also optimize diffusion rates by reducing the diffusive path lengths and achieve orders of magnitude reduction in time of remediation?
Approach/Activities
A numerical model for trichloroethylene back-diffusion, based on Fick’s Law of Diffusion, is applied to variable thickness low hydraulic conductivity clay in groundwater. The model is utilized to establish temporal minimums for baseline (no remedial action) conditions and then utilized to evaluate step-wise changes of diffusion rates resulting from changes in boundary conditions through mechanical manipulation (i.e., permeability enhancement) of the hydrogeologic conditions. The model is then utilized to evaluate step-wise changes in pore scale effects (i.e., micro scale mass flux) and potential influence of the temporal performance of active and non-reactive proppants that are combined with one or more remediation technologies including chemical oxidation, chemical reduction, sequestration, bioremediation and combinations there-of.
Results/Lessons Learned
Implications for Remediation Design
Model results present implications for the form, function, and longevity of remediation reagents that may be used as proppants, combined with proppants or combined with multiple technologies to achieve synergistic functions resulting in optimized remediation performance that may achieve increased rates of contaminant reduction in performance monitoring wells, reduction in quantity of injection events, and overall reduction in time of remediation to achieve target treatment goals.