Formatted Title
Demonstrating the Effectiveness of Intraplex®-Carbon for In Situ Immobilization of PFAS Plumes at Airport Sites
Background/Objectives
The oil- and water-repellent properties of per- and polyfluorinated alkyl substances (PFAS) ensure their widespread use in many everyday and industrial goods. Their use in fire extinguishing agents is of particular environmental relevance. The extensive use of PFAS, which are considered carcinogenic, has led to widespread groundwater contamination requiring appropriate efforts for their remediation as a large number of PFAS are extremely mobile in soil and groundwater.
If PFAS molecules have been transported through the unsaturated soil zone into the groundwater, then no efficient remediation approach is currently available to sustainably limit the further spreading of PFAS throughout the aquifers. Therefore, Intrapore put considerable effort over the last years into a new generation of colloidal activated carbon for the in situ immobilization of PFAS in aquifers and has tested it on several airport sites.
Approach/Activities
The new material, Intraplex® carbon, a novel generation of specialized colloidal activated carbon, was synthesized by a unique activation process and characterized for its specific surface area, pore size distribution, and adsorption capacity for PFAS. Results showed a significantly higher specific surface area and improved adsorption capacity compared to conventional (colloidal) activated carbon. Intraplex® carbon was then applied in real-world PFAS-contaminated aquifers and showed significant and sustained reduction of PFAS concentrations almost instantly after injection.
The first test site was a former military airport in Germany where exercises with PFAS-containing fire extinguishers were carried out in the area of a firefighting training site for decades. The PFAS eventually entered the groundwater, which led to the formation of a plume. The PFAS concentration was 100 ng/L in the immediate downstream groundwater below the firefighting training site (sum of 27 PFAS). The pollutant inventory identified mainly included H4PFOS and PFOA in the vicinity of the source, as well as PFHxS in the downstream. The second test site was also located at a fire-fighting training area in a large European airport. There, the PFAS concentration were up to 70,000 ng/L (sum of 35 PFAS) with PFOS being the main compound.
After an extensive analysis of the spatial distribution of local groundwater flow directions and velocities with Intrasense®, Intraplex® carbon was injected across the main downstream direction using permanent injection points and direct push injections.
Results/Lessons Learned
At both sites an overall PFAS reduction of more than 95% could be achieved over the course of months. These studies demonstrate the potential of the new colloidal activated carbon for efficient and cost-effective in situ PFAS remediation. In particular, the material showed an excellent performance also at large airport sites where PFAS contamination from firefighting training areas pose a serious threat. Results revealed the high removal efficiency of PFAS and a rapid reduction of PFAS concentrations to values below regulatory thresholds. This suggests that the new colloidal activated carbon is a promising solution for the remediation of PFAS contaminated groundwater at large airports, industrial sites, infrastructure or military sites.