Eliminating Risk of PFAS Contamination: Low Cost In Situ Remediation with Colloidal Activated Carbon

Colloidal activated carbon is emerging as a low cost in situ method to eliminate the risk associated with PFAS compounds in groundwater. By coating flux zones of an aquifer with colloidal activated carbon a permeable sorption barrier is created in situ, purifying groundwater as it passively migrates. PFAS constituents from up-gradient source zones are rapidly sorbed to the carbon and removed from the mobile dissolved phase. By removing PFAS from the mobile phase, the route of exposure to down-gradient receptors is eliminated, thereby eliminating the down-gradient public health risk associated with PFAS.

PFAS as a group are not ameable to destructive biodegradation. The retardation of migrating species by colloidal activated carbon is therefore finite – albeit variable with carbon dose, placement dimensions, and the concentration, nature and mix of the PFAS species. Retardation factors in the order of thousands may nevertheless be secured using colloidal activated carbon placements representing a fraction of soil mass in the order of 0.001 to 0.01 (a similar range to natural foc.) Impact on groundwater flow is therefore negligible, whereas capture / retardation is significant.

Colloidal carbon isotherm data and sorption test data are presented for specific PFAS compounds indicating excellent sorption capability and increased performance with decreasing carbon particle size. The potential for competitive sorption/elution is discussed. Plume modeling is presented indicating longevity of in situ colloidal carbon treatment for PFAS to be on the order of multiple decades before reapplication is required.

Data are presented from an actual field case site where a single application of colloidal activated carbon resulted in orders of magnitude reduction in PFAS groundwater concentrations to below USEPA health advisory levels. Design considerations for plume management are discussed including amending existing pump & treat systems to reduce project cost and to eliminate down-gradient risk to public health.