Topic Area: 4b. Innovative Treatment Technologies for PFAS Ex Situ

Formatted Title:

Soil Washing of PFAS-Contaminated Soil Stockpiles: A High-Throughput Success

Background/Objectives:

During construction of new facilities and infrastructure at a Department of Defense (DoD) installation in Alaska, potentially per- and polyfluoroalkyl substances (PFAS)-impacted soil was excavated for building foundations, site grading, and utility installation. To avoid construction delays, the DoD stockpiled 145,793 cubic yards (CY) of soil on Base. Through characterization in 2021, approximately 139,000 CY were determined to be impacted with PFAS and co-contaminants above Alaska Department of Environmental Conservation (ADEC) target cleanup levels (TCLs). The DoD disposed 11,972 CY of PFAS-impacted soil offsite and in 2022 awarded Brice a contract to process the remaining 127,126 CY through its patented soil washing process with an objective to reduce levels to below ADEC TCLs.

Approach/Activities:

Soil washing uses attrition and segregation of soil fractions through aggressive contact with wash water treated in a closed-loop water treatment system. During soil washing, PFAS partitions from the soil into the water phase due to its preference for the water/air interface, including the fines fraction. Soil washing is a very effective and efficient solution to bulk treatment, providing an opportunity for full-scale implementation at a high throughput to significantly reduce the volume requiring further treatment. Washed soils meeting the TCLs can be beneficially reused on site, while the reduced volume not meeting TCLs after the first wash can be re-washed to meet TCLs, disposed of offsite, or treated through subsequent destructive treatment technologies. In the end, the vast reduction in PFAS-impacted soil quantities that remain after soil washing makes high-energy/high-electricity-demand destructive technologies – and eliminating off-site disposal - more viable. Much like the treatment of other legacy contaminants, treatment trains of multiple treatment methods should be implemented to provide a complete solution to the PFAS-impacted soil stockpile issues that many DoD installations are facing.

Rob Singer

Affiliation

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Soil Washing of PFAS-Contaminated Soil Stockpiles: A High-Throughput Success