In late June, a Navy contractor began the month-long process of injecting over 180,000 gallons of activated carbon solution into the ground at Alameda Point to prevent a hazardous substance called PFAS (Perfluoroalkyl and Polyfluoroalkyl Substances) from entering the Oakland Estuary.
PFAS is a group of chemicals made by humans. It has been used in many consumer products and industrial processes since the 1950s because the chemicals resist heat, grease, and water. PFAS began being phased out more than a decade ago, according to a U.S. Environmental Protection Agency (EPA) fact sheet, but unacceptable amounts are still in the environment.
Navy firefighters used fire suppression foam containing PFAS during training exercises near one of the aircraft runways that ended up in soil and groundwater. PFAS cleanup at Alameda Point was not dealt with until now because it was not yet mandated by the EPA under the Superfund cleanup rules. Up until a new ruling in 2021, the EPA classified PFAS chemicals only as “pollutants,” but not as “hazardous.” A classification of “hazardous” would have required a remediation plan long ago. The Department of Defense, on its own initiative, started taking action in 2016 to limit PFAS exposure and investigate contamination at military bases.
An assessment of PFAS at Alameda Point, completed in May 2021, identified 11 contamination sites based on historical use. The firefighter training area has been singled out for immediate action, with lessons learned to be applied at the other sites. Detailed soil and groundwater data was collected in 2022 to fine tune the formula for the carbon solution.
Cleaning up PFAS contamination has been a challenge because the compound is virtually impossible to destroy, which is why it has been dubbed a “forever chemical.” Since it can’t be broken up and rendered harmless in soil and groundwater, the next best thing is isolating it and preventing it from moving. That’s where a form of charcoal—activated carbon—comes in. PFAS chemicals coming in contact with activated carbon become permanently bonded to the carbon.
Fun Science Fact: The process of trapping the PFAS in a carbon matrix is called adsorption, which means it is locked together like Velcro® and won’t come loose. It sounds like a similar process called absorption, which is what a cleaning sponge will do. But dirt absorbed into a sponge can be rinsed out.
While the in-ground carbon filter concept is elegantly simple, Regenesis, the manufacturer of the product being used at Alameda Point, had to address two important challenges before implementing the system. First, the carbon molecules had to be ground extremely fine—to the size of red blood cells at 1 to 2 microns—so that they would disperse evenly through openings between soil particles and coat the soil particles like a blanket. A similar form of charcoal, called granulated activated charcoal, is used for such applications as large-scale municipal water treatment systems, aquariums, and coffee water filters, but the grain size of up to 300 microns makes it unworkable for injecting into soil for contamination treatment.
The second challenge was that simply mixing superfine charcoal dust with water and pumping it into the ground led to clumping of the product. To allow for uniform dispersion and no clumping, Regenesis developed a special biodegradable polymer to mix with the powdered charcoal. This proprietary mixture is called a colloid, in which one substance is suspended in another, hence the name colloidal activated carbon.
Some 19,000 gallons of the Regenesis product called PlumeStop® has been delivered to the site in 275-gallon tanks. The product is being mixed on-site with hydrant water in a trailer and injected 15 feet deep at 288 different points along a 720-foot strip parallel to the shoreline. As groundwater naturally flows toward the shoreline and passes through the carbon barrier, PFAS molecules become trapped. The product is considered food-grade and harmless to the environment.
A groundwater monitoring program will begin at the end of August 2023 and continue until July 2025 to evaluate the effectiveness of the treatment.
PFAS Science Fact: “PFAS molecules are made up of a chain of carbon and fluorine atoms linked together. Because the carbon-fluorine bond is one of the strongest ever created, these chemicals do not degrade in the environment. In fact, PFAS products remain in the environment for so long that scientists are unable to estimate an environmental half-life, or the amount of time it takes for 50 percent of the chemical to disappear.” Source: National Institute of Environmental Health Sciences, National Institutes of Health information bulletin, March 2019.
According to the Centers for Disease Control and Prevention, exposure to high levels of PFAS may impact the immune system.
For more info, see our previous story “Navy to Lock Down PFAS in Groundwater with Carbon.”
Contributing writer Richard Bangert posts stories and photos about environmental issues on his blog Alameda Point Environmental Report, https://alamedapointenviro.com/. His writing is collected at AlamedaPost.com/Richard-Bangert.
