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McChord Airbridge PFAS Investigation

The McChord Airbridge Repair project was a large-scale emergency repair at McChord Airfield, part of Joint Base Lewis-McChord (JBLM). The project was initiated due to the structural failure of culverts beneath the runways, which significantly impacted mission capabilities. Managed by the USACE-Seattle District and implemented by Brice Civil Constructors (Brice) as the prime contractor, the project aimed to replace the failing twin corrugated metal culverts from the 1950s with a new 1,800 linear foot-long buried reinforced concrete bridge/culvert. This replacement was critical to restore the airfield’s full operational capabilities while ensuring compliance with state and federal environmental regulations.

KEMRON Environmental Services performed all environmental work, including a site investigation, waste characterization, groundwater extraction, treatment, effluent monitoring, and surface water monitoring. The goal was to ensure compliance with established environmental requirements and JBLM General NPDES discharge limits. Clover Creek, which flows beneath the airfield, contains sensitive fish species such as Coho, Steelhead, and Coastal Cutthroats. The reroute and new construction had to comply with the 2011 National Marine Fisheries Service Anadromous Salmonid Passage Facility Design and the 2013 Washington Department of Fish and Wildlife Water Crossing Design Guidelines.

The bridge construction site is hydrogeologically downgradient from a fire training area where aqueous film forming foam (AFFF) was historically used, contaminating the soil and groundwater with PFAS compounds. The shallow groundwater at the site is perched on a low permeability aquitard, which overlies the primary aquifer. The groundwater dynamics are complex, as the upper aquifer is hydraulically connected to Clover Creek, which can experience varying flow conditions depending on precipitation and water levels.

Dewatering was essential for the installation of the new airbridge footings. The dewatering design and construction methods ensured that the excavation did not breach the aquitard, preventing cross-contamination and loss of creek flow. Given the presence of PFAS in the groundwater, dewatering presented unique challenges.

KEMRON’s key activities included performing a site investigation to characterize the shallow groundwater for PFAS and other contaminants to support the design of the dewatering system water treatment plant for discharge to Clover Creek, monitoring PFAS concentrations in the extracted groundwater and the effluent for performance and compliance, and characterizing contaminant concentrations in excavated soil for proper management in compliance with RCRA and JBLM soil reuse requirements. KEMRON prepared a Site Safety and Health Plan (SSHP) and an expedited Uniform Federal Policy Quality Assurance Project Plan (UFP-QAPP). The site investigation involved installing new monitoring wells, sampling groundwater at existing and new wells, and soil sampling. Samples were analyzed for TPH, VOCs, metals, and PFAS. Surface water samples from Clover Creek were analyzed for various parameters, providing baseline values.

The dewatering and treatment system included over 680 dewatering wells and five pumps. Groundwater was treated using a multi-stage activated carbon system to address PFAS contamination. The system processed nearly 800 million gallons of groundwater over six months, maintaining a flow rate of approximately 6,000 gallons per minute. Weekly VOC and PFAS sampling ensured continuous compliance with established effluent thresholds. KEMRON’s approach ensured 100% compliance with surface water parameters throughout the project. The data collected allowed for real-time adjustments to the treatment system, maintaining its effectiveness. Weekly updates provided insights into PFAS concentrations and trends, supporting timely decisions on system reconfiguration, backflushing, and GAC unit change-outs.

Soil sampling of a 25,000 cubic yard stockpile was conducted per the UFP-QAPP. Samples were analyzed for BTEX, TPH-GRO, TPH-DRO/ORO, and RCRA metals to determine the disposition of soils for off-site disposal or reuse at JBLM. KEMRON’s environmental expertise and effective project management were crucial in addressing the complex challenges of the McChord Airbridge Repair project, ensuring regulatory compliance and the successful restoration of the airfield’s mission capabilities.¬†

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