Cleaning up: Promising pilot test destroying groundwater contamination in Spokane Valley

Kaiser Aluminum’s Trentwood facility is in the early phases of testing new technology that destroys over 90 percent of polychlorinated biphenyl (PCB) contamination in water at their facility in the Spokane Valley.

The Trentwood facility has produced specialized aluminum products for more than 75 years and, like many facilities around the country, used PCB-containing oils in an effort to safely and efficiently operate some industrial equipment. Over the years, some of the PCB oil leaked, contaminating groundwater under the aluminum-casting building near the Spokane River.

Kaiser has been researching and implementing technologies to address the contaminated groundwater, and is now examining two processes to see which will more effectively reduce the threat posed by the PCBs.

Walnut shells and castor oil, or ultraviolet light and hydrogen peroxide?

Walnut shell filtration system with one large tank for treatment and nearby water tanks to hold treated water.

The walnut shell and castor oil system Kaiser's operated since 2015 removes 70 percent of PCBs from water.

For the past five years, Kaiser has been running a pilot project, filtering contaminated water through a walnut-shell pump-and-treat system. In this system, a small amount of castor bean oil is added to contaminated water, and the water is then filtered through crushed walnut shells. The PCB clings to the oil, which is then removed by the walnut filter. While this system removes about 70 percent of PCB from extracted groundwater, it only captures the PCB, which creates a waste stream of the contaminated castor oil and walnut shells that has to be further treated or properly disposed at a licensed landfill.

Before drafting the plan for full-scale cleanup, we asked Kaiser if any new technologies might be available to more effectively treat the groundwater contamination. A few weeks later, Kaiser sent us research that showed PCBs in water could be destroyed using ultraviolet (UV) light and a little hydrogen peroxide.​ We agreed to wait until they could determine which technology worked better and was more cost effective.

Beaker with UV light treating PCB-contaminated water in a laboratory.

Kaiser first first started testing in a bench-scale format to replicate exactly what was in the research.

Kaiser has since successfully completed a laboratory bench-scale test and pilot-tested two small flow-through UV light systems that can process about five gallons of contaminated water per minute. The pilot systems remove more than 90 percent of the PCBs from the groundwater, and the treated water coming out of the UV light system is meeting drinking water standards. Kaiser is now constructing a 50-gallon per minute flow-through system, which could be the first of several, if testing goes well.

Ecology’s site manager Jeremy Schmidt recently visited the facility and answered questions about the cleanup for Inlander reporter Samantha Wohlfeil. You can learn more in her Nov. 25 article “Kaiser Aluminum experiments with a new way to break down toxic chemicals” and on our Kaiser Aluminum cleanup website.

The deadline to decide on the final cleanup method is February 2022, and Kaiser will implement a full-scale cleanup system within a year after.