A New Framework for Accelerated Site Closure: Dynamic Remedy Implementation

A decade ago, a resurgence in the field of hydrogeology began as groundwater remediation practitioners and researchers re-examined solute transport processes from the perspective of groundwater remediation. This re-evaluation led to better framework of the solute transport phenomena, recognizing that plume development and transport are mostly influenced by advection and diffusion, rather than advection and dispersion. These observations changed how we investigate sites; now focusing on high-resolution characterization to locate zones where contaminant mass is moving and zones where mass is stored. Remediation strategies have also changed, particularly at large sites, where combined remedies, tailored to hydrogeology, sources, and scale are the norm. However, challenges still exist, in particular how we extrapolate local data to larger scales. Consider remediation systems, technology aside; asymptotic performance is usually observed within a few years following startup. System optimization is to be expected, but the question remains the same, what drives lulls in performance.

The presented case study illustrates the application and performance of Directed Groundwater Recirculation (DGR). The most important difference between DGR and conventional P&T is the reliance on the CSM to develop a hydraulic flushing framework, a dynamic operation plan, and the approach for continuous adaption based on actual remedial performance. The DGR system is operating at 65gpm to remediate the diffuse plume and overcome the challenges of advection and stagnation. The system began operation in December 2014 with 29-extraction-wells and 58-extraction-wells with contractually driven goals, to allow property transfer within 18 months, and regulatory goals thereafter. The DGR system removed most of mass within 8 months, meeting contractual obligations for property transfer everywhere. Regulatory criteria in the shallow portion of the aquifer have been met. Details will be presented to discuss lingering, low-concentration exceedances in deep portions of the aquifer, required further efforts to achieve stringent criteria for vinyl chloride (2µg/L).