Formatted Title
Comparing the Sustainability of Active and Passive Groundwater Containment Systems for PFAS Plume Treatment
Background/Objectives
Background/Objectives. Very large, highly dilute plumes of per- and polyfluoroalkyl substances (PFAS) exist in groundwater worldwide. This is a result of the historic and ongoing use of PFAS-containing firefighting foam commonly discharged directly onto the ground.
Groundwater extraction and filtration/destruction (‘pump and treat’) has been considered effective for partial hazard removal in the circumstance of gross contamination depletion in source areas for contaminants such as petroleum hydrocarbons. However, it is well documented that physical removal of dilute contamination in the plume is ineffective due to low efficiency of removal and replenishment of aquifer contamination through ongoing desorption and back-diffusion. Therefore, although considered hazard removal by some, the inability of pump and treat systems to ‘flush clean’ the aquifer in a practical timeframe means the approach is more correctly categorized as risk pathway mitigation through hydraulic containment. This is particularly pertinent when considering PFAS plumes, which have very low concentrations (often µg/L) and even lower remedial targets of (perhaps ng/L).
An alternative passive PFAS plume containment approach employs the in situ emplacement of colloidal activated carbon (CAC) into PFAS-impacted groundwater to enhance PFAS retention and reduce mass flux. The PFAS influx is adsorbed by the CAC, providing a significant, long-term reduction in downgradient concentrations and mass discharge. Following installation, treatment through enhanced retention is designed to last decades and can be maintained through occasional re-application, or may be sufficient if application in the source area is also completed.
Approach/Activities
Approach/Activities. Using a real-world, full-scale application of a CAC injectable permeable reactive barrier (IPRB) on a PFAS-impacted site, a comparison was made between this approach and an equivalent pump and treat system. This comprised cost, carbon footprint and a sustainability assessment for the CAC and an active containment system with two filtration approaches.
A life cycle analysis (LCA) study was completed on the CAC material to show the environmental impacts into manufacturing, shipping and application of the product. The LCA boundary encompassed ‘cradle to grave’, including upstream sourcing of the material, core manufacturing processes and downstream transport and injection. The LCA was undertaken according to ISO14044/ISO14025 by using GaBi Professional software to meet EN15804 standards to create an Environmental Product Declaration (EPD).
The subject site comprised a commercial airport from which a PFAS plume was egressing the boundary and impacting off-site surface water. The 120-yd CAC IPRB was applied at the site boundary, immediately downgradient of the fire training area. A pump and treat system was then designed that could provide an alternative groundwater treatment along the same length, to achieve similar parameters over the same treatment period. A comparison was made between the two approaches using GaBi Professional software. The comparisons included greenhouse gas emissions, acidification, photochemical ozone formation, hazardous waste, slag/ashes, energy use, cost, and site disturbance. A life cycle cost analysis (LCCA) was completed using net present value. Finally, a Tier 2 sustainability assessment was completed using Ramboll’s SURE model, based on 15 sustainability indicators and compared for each remedial approach.
Results/Lessons Learned
Results/Lessons Learned. The site conditions, IPRB installation and pump and treat designs are explained. A description of the LCA, LCCA and Tier 2 sustainability assessment approach and results are shown. A comparison will be discussed and conclusions drawn on the relative sustainability and environmental impact of each process.