Subtle Geochemical Adjustments in Native Aquifer Soils – In Situ Groundwater Treatment Strategies for Cobalt at Coal Combustion Residual Sites

Subtle Geochemical Adjustments in Native Aquifer Soils – In Situ Groundwater Treatment Strategies for Cobalt at Coal Combustion Residual Sites

Grand Rapids, Michigan

Subtle Geochemical Adjustments in Native Aquifer Soils – In Situ Groundwater Treatment Strategies for Cobalt at Coal Combustion Residual Sites Authors Mr. David Collins - United States - Stantec Mr. Jim Finley - United States - Stantec Abstract Cobalt is frequently observed above the groundwater protection standard (GWPS) downgradient of CCR units. Native aquifer soils have the capacity to influence groundwater geochemistry and play an important role in attenuation of cobalt and other CCR constituents. Geochemical modeling confirmed by bench-scale treatability testing has shown cobalt responds favorably to enhanced attenuation by relatively minor in situ adjustments of geochemical conditions in these soils. This presentation will summarize geochemical modeling and treatability testing results for multiple reagents to reduce dissolved cobalt below the GWPS and minimize mobilization of other constituents. Remedial evaluations identified treatment of groundwater downgradient of CCR units is most effective via a permeable reactive barrier (PRB). As such, cost-effective and industry accepted deployment methods to establish a PRB for in situ adjustment of groundwater will be presented. This alternatives analysis will focus specifically on design considerations particular to CCR sites, advantages and challenges associated with each, relative cost, and schedule implications. A case study will be presented to summarize the site-specific treatability testing results, deployment method alternatives analysis process, the selected site-specific technology including a preliminary conceptual design, and results of pilot testing that was conducted to confirm bench-scale treatability testing and evaluate parameters for full-scale design.