Rethinking Traditional Treatment Systems for
PFAS Remediation

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By Ed Coggin, P.E.

At two U.S. Air Force bases impacted by historical releases of aqueous film-forming foam, innovative methods in treating PFAS in both surface water and groundwater provide examples of success in safeguarding health for military personnel and nearby communities.

Just west of downtown Sumter, S.C., Shaw AFB has served as an active flying field for the U.S. Air Force since its establishment in 1941. A sprawling installation covering 3,570-acre, the base boasts a diverse landscape that includes airstrips, fuel depots, aviation equipment storage hangars, residential buildings, and recreational spaces. Notably, it serves as the home of the 20th Fighter Wing (the Air Force’s premier combat F-16 wing) and provides combat ready airpower and airmen to meet any challenge, anytime, anywhere.

Some 560 miles northwest, Wright-Patterson AFB, outside Dayton, Ohio, is divided into two sections by State Route 444: 2,400-acre Wright Field and 5,200-acre Patterson Field. With a workforce exceeding 30,000, including military personnel, civilians, and contractors, Wright-Patterson is Ohio’s largest single-site employer and instrumental to the regional economy. The installation houses many critical centers and laboratories, including Air Force Materiel Command, Air Force Lifecycle Management Center, Air Force Research Laboratory, Air Force Institute of Technology, and National Air & Space Intelligence Center.

At both Shaw and Wright-Patterson, due to past uses of aqueous film-forming foams to extinguish fuel fires, PFAS chemicals were released into the environment, entering into soil, groundwater, and surface water, as confirmed by site inspection sampling.

Today, innovative approaches for removing PFAS from groundwater are being leveraged at both sites. The ongoing work involves both building on proven methodologies and introducing innovative engineering and scientific technologies to create new novel treatment trains—demonstrating effective environmental stewardship and community protection efforts.

Addressing Health Risks

Wright-Patterson AFB, following the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), identified PFAS impacts across multiple media in two areas, which prompted interim removal actions. These steps are helping mitigate health risks while the CERCLA process continues to identify any additional actions necessary for complete site cleanup. At Area 1 and Area 21 (measuring 13-acres and 7-acres, respectively) it was determined that PFAS-impacted surface water and groundwater were migrating into the Great Miami Buried Aquifer. This complex aquifer system supplies drinking water to Wright-Patterson and nearby cities, potentially impacting the water supply for more than 400,000 people. Similarly, Shaw AFB identified PFAS in groundwater from a trio of former fire training areas. The impacted groundwater was detected in water supply wells both on the base and privately owned real estate.

To address the contamination at both installations, the Omaha District of the U.S. Army Corps of Engineers issued two time-sensitive contracts to the Weston-ER Federal Services joint venture.

Characterizing Impacts

At Wright-Patterson, 300 samples were collected at Area 1 and Area 21 to define the extent of PFAS in the soil, groundwater, and surface water. Following completion of site characterization at Area 21, a six-month pilot treatment study of impacted groundwater was performed to assess pretreatment requirements and to develop design parameters for adsorptive treatment media. Field personnel evaluated three types of media: granular activated carbon, ion-exchange resin, and organoclay.

The evaluation of PFAS treatment media then was conducted using two criteria: effluent concentration at increasing flow rates and absorption capacity. Organoclay treated the highest number of treatment bed volumes of water (65,000) and had the highest adsorption capacity. As a result, it was selected as the primary PFAS treatment media for system design.

Meanwhile, the data gap investigation at Shaw AFB involved drilling 24 monitoring wells and collecting over 280 soil and groundwater samples from three source areas to evaluate interim remedial action alternatives. From the data gap investigation, appropriate design criteria were established; then, environmental sequence stratigraphy geologic formation characterization enhanced the conceptual site models for the source areas. Engineers also used high-resolution site characterization technologies to supplement the investigation. This provided data-driven graphics to better assess the remedial designs. Analytical results demonstrated that the highest PFAS concentrations in groundwater were greater than 15,000 times the established federal drinking water maximum contaminant levels. This warranted removal actions to mitigate potential health threats.

Gravity Flow Benefits

Concurrent with the treatability study at Wright-Patterson, engineering evaluations/cost analysis reports assessed the effectiveness and feasibility of various technologies associated with a groundwater extraction and treatment system. The recommended alternative for each area went through the CERCLA approval process, and the action memorandums were signed.

The project team utilized the first-ever gravity upflow basin system as a cost-effective approach for removing PFAS from surface water and groundwater using FLUORO-SORB FS-400 organoclay media. This advancement marks a significant development in the field, as it uses basin systems for collecting impacted groundwater, eliminating the need for pressurized vessels in temperature-controlled buildings. Benefits include a shorter construction timeline, expedited schedule, and significant cost savings.

The Area 1 alternative involves groundwater capture with a 400-ft long interceptor trench and surface water capture with a 100,000-gal detention pond and water treatment in a 500-gal/min passive (gravity flow) basin system. The discharge of treated water is sent to a National Pollutant Discharge Elimination System.

The Area 21 alternative involves groundwater capture with seven extraction wells and water treatment in a 250-gal/min gravity flow basin system. The passive filtration system, which uses organoclay media, is uniquely scalable, offers an accelerated construction period, protection from biofouling typically associated with surface water treatment, and long-term effectiveness.

Installing Systems

Construction on Area 1 and Area 21 at Wright-Patterson began in fall 2023, focusing first on installing the treatment basins and underground piping at Area 1 and then moving onto Area 21.

At Area 1, the treatment system began operations in interim mode while long-lead time components required for fully operational mode were procured. Using this approach, approximately 100,000-gal/day of PFAS-impacted water has been treated to non-detect levels. The Area 21 treatment system is scheduled to be operational in early 2025.

Hydraulic Capture

At Shaw AFB, the complex geologic structure underlying the site led to inconsistent PFAS migration. This variability prompted an optimized design for a groundwater remediation system using an extracting and reinjection trench design for hydraulic capture to directly target areas of contamination. The approach shifted the groundwater capture design from several extraction wells to a centralized trench configuration. This optimized results. The water collected in the trench undergoes pretreatment through bag filters for particulate removal before being treated in a centralized 1,000-gal/min treatment system employing granular-activated carbon for volatile organic compound removal and ion exchange media for PFAS removal.

The project team used a groundwater fate and transport flow model from the U.S. Geological Survey, MODFLOW-2005 to refine existing 3D models and optimize the system design. Using various groundwater extraction and reinjection scenarios, the model predicted PFAS reductions over time as the system flushes the aquifer.

The next step was the planning, design, and execution of hydraulic capture and groundwater treatment. The site design includes 45-ft-deep, 300-ft-long extraction/reinjection trenches at each source area that provide a continuous permeable wall with an in-built perforated pipe to completely capture groundwater. Due to potential gaps for plume migration between individual extraction wells, the trench design increases hydraulic capture from 80 percent to 100 percent, cuts installation and maintenance costs, and improves long-term operations. The trench design at Shaw also requires fewer pumps.

The central groundwater treatment system receives discharge from the trenches at the three source areas and pre-treats extracted groundwater using bag filters for removal of solid materials. Then, the water is treated with granular activated carbon to remove chlorinated solvents and explosives, and ion exchange media to remove PFAS. Afterward, the water is reinjected into the source area trenches.

Proving Technologies

The success of the groundwater remediation projects at Shaw AFB and Wright-Patterson in treating PFAS reinforces the need for innovative designs that takes long-term goals into consideration.

The composition of these new systems allows for treating contamination at the source, reducing additional spread, and limiting further impacts to water supplies—both on the military installations and in the surrounding communities.

Ed Coggin, P.E., is Technical Director, Weston Solutions; ed.coggin@westonsolutions.com.

Published in the January-February 2025 issue of The Military Engineer