Comprehensive Assessment of Applying Modified Clays using Jet Grouting for In-situ Isolation versus Stabilization of PFAS Source Zones

Chadi El Mohtar | University of Texas at Austin

ER21-5229

Objective

The goal of this project is to field-validate the use of jet grouting with modified clays as a technology for in situ per- and polyfluoroalkyl substances (PFAS) source zone stabilization. Historically, modified clays have been implemented at the field scale for environmental remediation of various constituents, but not for PFAS on a large scale and not in combination with jet grouting. Recent work has shown successful application of modified clays to stabilize PFAS in bench-scale simulations and a small-scale field trial. In this project, jet grouting with modified clay will be used to establish precision-placed isolation cutoff elements (walls and flooring) around the PFAS hot spot compared to stabilizing the entire PFAS source zone with traditional mixing. A comprehensive field-scale trial at a Department of Defense (DoD) site will be conducted to achieve the following technical objectives:

  • Evaluate the performance of modified clay to stabilize PFAS using conventional soil mixing;
  • Evaluate the performance of isolation cutoff elements; 
  • Evaluate the potential to establish the continuity of the isolation cutoff elements using non-destructive underground three-dimensional (3D) imaging through geophysical testing;
  • Assess the stability of PFAS within the spoils from both field treatments;
  • Provide DoD with a PFAS hot spot remediation technology that can be applied at facilities with deep groundwater table where the majority of the PFAS is present in unsaturated soil; and
  • Develop a comparative evaluation of the different PFAS source zone treatments.

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Technology Description

Both modified clays and jet grouting technologies are mature technologies in their respected fields. This innovative approach combines the two for a cost-effective low-environmental-impact PFAS source zone treatment. Employing non-destructive 3D underground imaging to investigate the integrity of the isolation elements will help the DoD better assess risk of continued PFAS transfer into the groundwater through potential points of discontinuity in the modified clay treatment (i.e., "defects"). For this project, Fluoro-SorbĀ® will be used as the modified clay for PFAS treatment. Recent bench-scale and limited field-scale testing demonstrated the ability of Fluoro-Sorb to stabilize PFAS within impacted soils and reduced leaching to below relevant screening criteria. The Fluoro-Sorb particle size makes it a feasible option to be applied in the field using either jet grouting or soil mixing. Additionally, it can be combined with other additives to achieve the required slurry rheological and internal stability properties to sustain the high pressure and flow rates associated with jet grouting.

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Benefits

The PFAS source zone technology will provide a method to mitigate future groundwater impacts and reduce the DoD's cost of managing the long-term liability and cleanup associated with impacted groundwater. Additionally, the approach is applicable to remediate facilities with deep groundwater tables for which current technologies for stopping plume migration would not be practical. Currently, there are limited commercially available technologies for reliable, cost-effective treatment of PFAS impacted source zones. This project will provide the DoD with the necessary information for assessing the effectiveness and cost/benefit of the approaches compared to existing methods along with recommendations for future applications based on the lessons learned from this field demonstration. The use of soil stabilization within shallow PFAS source zones may be particularly beneficial at deep groundwater sites because current technologies focused on sequestering PFAS plume migration within the saturated zone may be challenged with depth.

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Points of Contact

Principal Investigator

Dr. Chadi El Mohtar

University of Texas at Austin

Phone: 512-471-3695

Program Manager

Environmental Restoration

SERDP and ESTCP

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