The release of per- and polyfluoroalkyl substances (PFAS) has occurred at sites across the United States. PFAS-impacted soil can result in persistent groundwater plumes. Increasingly stringent state and federal regulatory requirements are being instated on PFAS-impacted soil for groundwater protection. The highest PFAS concentrations are typically observed in shallow soils, which are often excavated and stockpiled. Once PFAS-impacted soil is excavated, off-site disposal is currently the most developed option for removal from sites.

Due to concerns associated with off-site disposal, a significant need exists for alternative on-site treatment approaches. The project objective is to demonstrate ex situ thermal treatment of PFAS applying thermal conduction heating (TCH) in an above-grade constructed treatment cell. This field demonstration will evaluate PFAS reduction in soil and effective treatment of vapors extracted from the ex situ cell during heating. This TCH thermal desorption demonstration is intended to provide an alternative to off-site transport of PFAS-impacted soil.

Schematic Diagram of Thermal Conduction Heating for PFAS Treatment System with Heaters Arranged in Triangular Arrays

This project will result in design guidance for larger scale TCH PFAS treatment applications, through the following objectives:

1. Determine ex situ cell heating effectiveness through continuous temperature monitoring across the cell;
2. Determine soil remediation effectiveness by measuring PFAS concentrations in discrete and composite soil samples, before and after thermal conduction heating;
3. Determine effectiveness of vapor and process water treatment through evaluating PFAS concentration in extracted vapor and process water samples, before and after treatment; and
4. Determine energy efficiency by establishing an energy balance for the ex situ cell, and tracking energy usage.

Vapors extracted from the ex situ cell will be transferred to an above-ground treatment system where vapors will be cooled, and condensed steam will be separated from the vapor stream. Granular activated carbon (GAC) will be used for treatment of the vapor and process water streams. The project team will implement an analytical approach to quantify PFAS in soil before and after heating, as well as vapors and process water before and after GAC treatment. Energy application to the ex situ cell and temperature at each soil sample location will be monitored during system operations to determine energy efficiency.

A key advantage of TCH is its ability to reach temperatures high enough for effective PFAS removal within three to six months of heating. Ex situ treatment allows for stockpiled soil to be treated on site, eliminating the need for transportation and disposal. This can reduce the overall liability when PFAS-impacted soil is managed. (Anticipated Project Completion - 2025)