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

Topic Area: 7p. PFAS: Groundwater Treatment Case Studies

Formatted Title:

In Situ Destructive Treatment of PFAS Using Sonolysis within a Horizontal Treatment Well

Background/Objectives:

InSRT (in situ Remediation Technology) is an innovative technology for destruction of PFAS in impacted groundwater in situ using sonolysis. InSRT is deployed within a horizontal well that focuses the flow of upgradient groundwater into the well for a capture zone many times the well’s diameter. PFAS in groundwater is treated by InSRT within the well, making the approach well-suited for a site where mass discharge control is a priority. It also eliminates pumping groundwater to the surface for ex situ treatment, which is expensive and energy-intensive. Furthermore, the destructive treatment process eliminates the need to dispose of or recharge/replacement of PFAS-laden spent sorbent media. InSRT is connected to an aboveground ultrasound generator and its design allows multiple reactors to be placed in-line. The flow rate through the reactor can be controlled using a low-flow inline pump within the well. The focus of this presentation will be on the design, implementation, and results of InSRT’s first field demonstration, currently taking place at Peterson Space Force Base (PSFB) in Colorado Springs, CO, funded by the DoD’s Environmental Security Technology Certification Program (ESTCP, Project ER-21-5045).

Approach/Activities:

At the time of this submission, October 2023, InSRT is awaiting installation within an existing horizontal well that contains carbon cartridges for PFAS treatment (Arcadis’ HRX Well® technology) at PSFB. The team is onsite preparing to remove a single carbon cartridge and to place InSRT downgradient of the remaining cartridges, along with a low-flow pump to control the rate of water moving through InSRT, and tubing to sample directly up- and downgradient of the reactor. Groundwater flow will be controlled at multiple different rates to assess treatment rates relative to residence times. Samples will be collected at selected time points for three reactor volumes of throughput at each flow rate, with demonstration completion in December 2023. The well’s hydraulic capture, PFAS treatment efficiency, and mass discharge reduction will be measured and compared to model-predicted performance. The overall treatment performance, sustainability, and installation methodology of InSRT will also be assessed.

Results/Lessons Learned:

InSRT treatability tests were conducted with PFAS-contaminated groundwater from PSBS prior to this field demonstration. Results demonstrated over three orders of magnitude of removal for measured compounds. Laboratory results indicate PFAS concentrations in the low parts per trillion or below detection within the reactor retention times that will be tested in this field demonstration. We, therefore, anticipate achieving these values during the field demonstration. Challenges associated with in situ destructive treatment using sonolysis that have been overcome with InSRT’s design have included (1) managing heat within the reactor body, (2) providing a robust frame for delicate reactor components that is suitable for in situ installation by a drill rig, and (3) providing the appropriate site-specific retention time via low-flow in-well pumping and/or by daisy-chaining multiple in-line reactors in sequence. An existing user-friendly HRX Well design tool, which has been adapted for destructive PFAS treatment using InSRT, will be updated and presented, along with guidance that addresses technology applicability and limitations, anticipated performance, design and installation considerations, and lifecycle costs.

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Mike Riggle