Formatted Title
Colloidal Activated Carbon Treats PFAS Impacts at AFFF Training Areas at Three Regional Airports
Background/Objectives
Background/Objectives. Per- and polyfluoroalkyl substances (PFAS) are a group of contaminants found in groundwater at airports worldwide, primarily from the use of aqueous film-forming foams (AFFF) for firefighting and training activities. PFAS compounds belong to a family of thousands of chemicals known for their risk to both human health and the environment. PFAS are known to be resistant to biological breakdown, chemical degradation, or physical destruction.
An environmentally sustainable strategy to address PFAS risk involves the use of colloidal activated carbon (CAC) to enhance the natural attenuation of PFAS in situ by engineering the distribution coefficient (Kd) of the subsurface, resulting in a significantly increased adsorption capacity. CAC consists of exceptionally fine particles of activated carbon suspended in a polymer and injected into the aquifer under low pressure or mixed into source area soils. The CAC binds to the soil matrix and serves as an in situ filter to effectively remove PFAS from groundwater as it encounters the activated carbon particles. It also is used to reduce the mass discharge of PFAS into groundwater from impacted vadose soils. The use of one or both applications virtually eliminates further discharge of PFAS mass into aquifers, making PFAS adsorption a cost-effective, sustainable approach with a proven record of success.
Approach/Activities
Approach/Activities. The presentation will provide a review of three regional airport sites that employed CAC to address PFAS impacts in groundwater due to the use of AFFF onsite. These pilot studies were designed as microcosms of a full-scale application and are in areas of high importance. In each case, the use of AFFF onsite has led to a situation where risk to sensitive receptors has been established. In two cases, the PFAS plume has migrated into residential areas where municipal water is unavailable, and PFAS has impacted private potable water wells. In the third case, the PFAS plume has migrated into a watershed which provides municipal water to a major metropolitan area. In each case, conditions exist where the most cost-effective and expedient solution is needed to eliminate risk to the public. Additionally, public perception and involvement are major factors for each of these projects. The size and scope of the CAC pilot projects vary, along with the injection treatment configurations, including barrier geometry, monitoring arrays, and application techniques. Groundwater was primarily targeted for treatment in these pilot studies. Prior to the implementation of the CAC, design verification testing (DVT), mass flux measurements, and predictive competitive sorption modeling were conducted to refine the site conceptual models. Furthermore, during the application process, field placement validation steps, such as soil cores and piezometers, were used to observe and assure proper CAC distribution.
Results/Lessons Learned
Results/Lessons Learned. The results of the three pilot studies demonstrate that CAC was effectively distributed within the aquifers and resulted in consistently meeting stringent remedial standards, often falling below laboratory detection limits, with contaminant reductions typically exceeding 95%. Furthermore, advanced modeling demonstrated theoretical PFAS retardation spanning decades from a one-time treatment of CAC. These pilot studies support the approach for using in situ CAC applications to enhance the attenuation of PFAS compounds and are a viable and environmentally sustainable approach to reduce the risk associated with the AFFF-impacted areas at these airports. It is anticipated that larger scale treatments with CAC will be completed at each of these locations.