Formatted Title
Remedial Approaches for Management of PFAS-Contaminated Lagoon Sediments and Soils at Buick City Site
Background/Objectives
A former aeration lagoon as well as adjacent stockpiled soils located at the historic Buick City site in Flint, Michigan, contained PFOS at concentrations from up to 6,000 parts per trillion (ppt) in sediments, 9,200 ppt in stockpiled soils and even higher concentrations in phragmites surrounding the pond area. RACER Trust, an entity established to address historic GM properties like Buick City, managed the project. The lagoon was first dewatered using granular activated carbon (GAC) treatment and discharge to the local POTW, followed by backfilling the lagoon with treated soils, sediments and phragmites using six different stabilizing binding agents. This was possible because the lagoon was determined to have a competent clay bottom, which would limit potential leaching of PFAS from any of the stabilized/immobilized materials placed in the lagoon. The goal was not to reduce soil leaching to 12 ppt PFOS but rather implement source control/source reduction to prevent PFAS releases over 12 ppt from reaching the nearby river.
Approach/Activities
Standing water (about 6.6 M gallons - average over 1000 ppt of PFAS) was removed and treated with GAC vessels to empty the former lagoon. PFAS-contaminated sediments, stockpiled soils (6000 yards) and an extensive growth of phragmites and soils surrounding the lagoon were contaminated with elevated levels of PFAS. Due to recent overflows from the lagoon and potential impacts to a nearby river, an immediate response required solutions be developed rapidly. The need for a timely cost-effective strategy required multiple unconventional approaches. Treatment to immobilize PFOS involved the use of a combination of RemBind (76,000 lbs.) and Powdered Activated Carbon (PAC) (54,000 lbs.) for the stockpiled soils. PAC was used to treat a combination of clay soils and phragmites, Recycled GAC (30,000 lbs. from the water treatment system) was used to treat clay and phragmites, Portland Cement (490 tons) was used to treat granular surface soils, and Holcim EnviroSet (325 tons) was used to treat granular soils, and finally the wet sediments at the base of the lagoon, following de-watering were treated with a Bentonite/PAC blend (21,000 lbs.).
Results/Lessons Learned
The presentation will provide an overview of how the remediation was executed (i.e., field mixing methods) along with preliminary sampling data that demonstrate relative effectiveness of the binding agents. Samples of treated materials were collected at the time of treatment and about 10 months after treatment and placement in the lagoon. An overview of the effectives of this work will be reviewed and reported. Practical recommendations based on this work to date will be summarized.