Formatted Title
Meeting the Site Requirements: Full-Scale, In Situ PFAS Treatment Unlocks Redevelopment and Protects Offsite Receptors
Background/Objectives
Background/Objectives. Groundwater at an airport in the UK was impacted by per- and polyfluoroalkyl substances (PFAS) due to the use of aqueous film-forming foams (AFFF). PFOS and PFOA were the target contaminants with concentrations ranging from 200 – 1,000 ng/L, while the sum of 19 PFAS compounds was approximately 30,000 ng/L. The remediation at this site was being driven by land divestment to allow for the development of residential housing; with this change of land use there was a need to meet regulatory ‘planning’ conditions before proceeding. As part of these requirements, PFAS remediation needed to be proven by a pilot study and a subsequent full-scale design must have been accepted by the authorities to allow the divestment to take place. A ‘pump and treat’ approach was rejected due to cost and disturbance to the future housing development and an in-situ solution using the injection of colloidal activated carbon (CAC) was chosen.
Approach/Activities
Approach/Activities. Prior to application, design verification testing (DVT) was conducted at this site to confirm a series of design assumptions regarding the flux of PFAS and to confirm suitability of the in situ barrier of CAC approach. The DVT included installing passive flux meters, soil logging, permeability testing, additional sampling to test for non-target organic species that can compete for sorption sites, total oxidizable precursor (TOP) analysis for PFAS, and clean water injection testing. Following the DVT, a pilot trial was conducted, where a 10m long barrier of CAC was installed from 3-11m bgs through 12 direct push locations. After 8 months of monitoring the pilot trial, the full-scale application was then implemented. The full scale comprised of a 277m (295 yd) CAC barrier installed via 400 injection points with a total of 477,000L of diluted CAC (as PlumeStop®) injected. The landowner required cost certainty for the treatment to reach an agreement for divestment as so a warranty was provided ensuring ongoing efficacy of the barrier.
Results/Lessons Learned
Results/Lessons Learned. This presentation will show validation results and lessons learned from the single application of CAC in both the pilot and full-scale phases. The work at this site was completed simply and safely at an active airport, with no on-going site activity required. All data showed immediate and sustained decreases of PFAS groundwater concentrations, leading to project closure in October 2022, with planned annual verification testing. The successful implementation of this remedial approach allowed residential properties to be built in this location, thereby meeting the driving goal for the site. This site was selected as the winner of the Best Application of Remediation Techniques at the 2023 Brownfields Awards.