Theme: 07. Per- and Polyfluorinated Alkyl Substances (PFAS)

Topic Area: 7m. PFAS Site Characterization

Formatted Title:

Assessing PFAS Risk in Drinking Water with High Resolution Site Characterization Technology

Background/Objectives:

Military bases are often major contributors to per- and polyfluoroalkyl substances (PFAS) contamination due to the use of firefighting foam for training and testing exercises. Unfortunately, this contamination also affects groundwater and drinking water supplies in communities surrounding these contaminated bases. Though these chemicals are highly effective in being resistant to heat, stains, and water, PFAS, now coined “forever chemicals”, are linked to cancer, kidney disease, birth defects, decreased immunity, liver problems and a range of other serious diseases.

United States (U.S.) Army Corps of Engineers (USACE) and the Department of the Air Force (DAF) conducted a non-time-critical removal action (NTCRA) at an Air Force base. The NTCRA was to address the probable releases from Air Force activities of PFAS, including perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), that contribute to the contamination of groundwater potentially used as a drinking water source in downgradient areas on-base and off-base. High resolution site characterization (HRSC) was conducted to map subsurface features with the goal of assessing drinking water contamination risk.

Approach/Activities:

This investigation included advancing 62 hydraulic profiling tool-electrical conductivity (HPT-EC) borings and 15 groundwater sampler (GWS) borings to depths ranging from approximately 60-75 feet below ground surface (bgs). The HPT-GWS allows for the collection of hydrogeological data in real-time, enabling the ability to identify and define potential migratory pathways and confining intervals throughout groundwater sample collection. Subsurface imaging began using the hydraulic profiling tool (HPT) system in conjunction with an EC measurement. The HPT technology is an excellent indicator of formation permeability and assists the prediction of the position of the water table. This data along with the flow rate can then be used to calculate an estimate of hydraulic conductivity (K) in the saturated formation. Obtaining an understanding of soil conductance and permeability along with the contaminant information enables the discovery of prominent migration pathways. Discrete groundwater sampling was performed using the GWS at 15 of the boring locations. High resolution sampling enhances the ability to make the HRSC data semi-quantitative. Applying the HPT-EC technology along with the GWS, it is possible to identify potential migratory pathways and confining intervals in real time as the tool is advanced through the subsurface, while maintaining the ability to collect discrete groundwater samples.

Results/Lessons Learned:

Based on the HSCR data collected, the client was able to understand the subsurface geology and lithology features to define potential migratory pathways. The site subsurface knowledge gained allows for a better, informed risk assessment of PFAS-contaminated groundwater entering drinking water sources. Additionally, the discrete water samples benefited the client in delineating the PFAS plume and creating a precise and effective remedial strategy.

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Ed Coggin