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

Topic Area: 7h. PFAS Fate and Transport

Formatted Title:

Use of Lysimeters to Estimate Site-Specific Soil Standards for PFAS

Background/Objectives:

As part of PFAS investigations across the country, soil impacts are being evaluated to determine risk. One of the primary pathways driving risk to human health in soil is the soil to groundwater or soil leaching pathway. Therefore, it is vitally important to understand leaching behavior to properly identify affect property and/or exceedance zones requiring remedial action. However, the sorptive and leaching behavior of PFAS is a highly complex process due to the unique physiochemical properties of these compounds. Due to these chemical properties, traditional risk-based techniques for estimating leach-based soil standards are not adequate.

Approach/Activities:

During remedial investigations at Department of Defense facilities, lysimeters were employed to evaluate the soil to groundwater leaching pathway for PFAS. Lysimeters provide a direct measurement of PFAS concentrations in porewater, which is compared to a developed porewater comparison level to determine if vertical mass discharge is currently contributing to the groundwater plume at unacceptable levels. Site-specific leach-based soil standards were developed using lysimeter data as described above and/or calculated using site specific inputs to evaluate this human health exposure pathway.

Results/Lessons Learned:

A variety of lessons were learned throughout the installation and sampling process due to regional environmental factors at the sites. Remedies included soil moisture meters usage, target installation depth and lithology adjustment, and sample procedure alteration were deployed to achieve sample collection.

Calculated, site-specific soil leaching thresholds were developed for each compound at areas where soil and groundwater results exceed default standards. In general, calculated leach-based thresholds are higher than default values, shrinking the exceedance zone footprint and reducing the volume of soil requiring remedy.

Site conclusions will be compared to evaluate leaching consistency across sites considering varying source and environmental factors. Results from lysimeters installed in different soil types will also be compared to evaluate differences in leachability by compound and compound class.

Matthew Zenker

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Use of Lysimeters to Estimate Site-Specific Soil Standards for PFAS