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

Topic Area: 7e. Ex Situ PFAS Treatment: Soils/Solids and Other Waste Streams

Formatted Title:

Stabilizing PFAS-Contaminated Water, Sediments, and 6,000 yd³ Soil with Six Different Amendments (Buick City, Michigan)

Background/Objectives:

Approximately 6.6 million gallons of standing water in a lagoon at the Buick City, Michigan Site, with average concentrations over 1,000 ppt of PFAS was treated with granular activated carbon (GAC) to empty a former lagoon. The PFAS-contaminated sediments in the lagoon (with average concentrations over 10,000 ppt PFAS), soil surrounding the lagoon itself, plus over 6,000 yd³ of stockpiled soils from different sources at the Buick City site, were treated with stabilization and stabilization/solidification amendments. An extensive growth of invasive Phragmites australis in and surrounding the lagoon was suspected of having significant concentrations of PFAS absorbed to its various tissues. There was an immediate need to stop the lagoon from overflowing and for an impromptu solution to reduce PFAS leaching from relocated PFAS-contaminated stockpiled soil, surface the soil surrounding the lagoon and the P. australis itself. The solution selected for the stockpiled soils was stabilization, using a combination of Rembind^TM (76,000 lbs) and powdered activated carbon (PAC) (54,000 lbs). PAC was used to treat a combination of clay soils from the lagoon and the co-existing P. australis. Recycled (i.e., “spent) GAC (30,000 lbs) from the system treating the lagoon and groundwater was used as a stabilization amendment for the lagoon clays and P. australis. Portland Cement (490 tons) and Holcim EnviroSet (325 tons) were used to treat stockpiled, coarser-grained soils, A 50/50 Bentonite/PAC blend (21,000 lbs) was used to treat the wet sediments.

The remediation goal was not to reduce PFAS in leachate to the 12 ppt PFOS (the drinking water standard set by Michigan EGLE), but rather to significantly reduce leaching from the various source materials and to prevent PFAS releases from a low-permeability, clay-lined lagoon near the Flint River.

Approach/Activities:

The effectiveness of this approach will be presented and discussed. Samples of treated materials were collected at the time of treatment and 6 months after stabilization/solidification treatment and placement in the lagoon. These implemented in the field were also tested in bench studies on samples taken from the site. Groundwater samples pre- and post-treatment will be collected, analyzed, and discussed. This study is the largest stabilization/solidification (S/S) effort implemented for PFAS anywhere in the world and includes results on reduced leaching (using SPLP) achieved with different S/S amendments, and data on the PFAS sorption capacities of many materials (e.g., P. australis, spent GAC, spent GAC size-reduced to PAC) not yet published on. Various tissues of P. australis were tested for their ability to adsorb PFAS.

Results/Lessons Learned:

All the S/S amendments tested significantly reduced PFAS leaching in the treated materials. Reducing spent GAC to PAC increased the Kd values by an order of magnitude. One surprising result from both the field and bench studies was that the leaf tissues of P. australis showed a greater concentration of PFAS, and a greater ability to adsorb PFAS compared to other tissues than expected (i.e., rhizomes, stems, roots).

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Daniel Cassidy

Biography