Kaiser Aluminum & Chemical Corporation

Kaiser Aluminum & Chemical Corporation’s Trentwood facility (Kaiser Trentwood) produces aluminum sheet, plate, and coil for aerospace and general engineering applications.

The federal government built the facility during World War II, and it first produced aluminum sheet in 1943. After the war ended, the facility was sold to private interests and has processed aluminum since.

Materials used in past aluminum production included polychlorinated biphenyl (PCB) oil, petroleum fuels, solvents, and chromium. Wastes generated as a result of past or present operations are wastewaters, chrome sludge, paint and solvent wastes, and black dross.

Several releases of contamination have occurred at the Kaiser Trentwood site due to historical operations. Kaiser investigated the contamination and completed interim cleanup actions to address groundwater and soil contamination coming from these releases. Full-scale testing of a treatment system that uses ultraviolet light and an advanced oxidation process to destroy PCBs in groundwater is ongoing. The results will inform the final cleanup plan.

Remedial investigation and feasibility study

In 2010, Kaiser investigated nine areas at the site to better understand contaminants in soil and groundwater, where they were located, and how much was present at the site.

Since completing the investigations, Ecology requested more information about the west discharge ravine area, where wastewater was formerly discharged to the Spokane River. This investigation more clearly defined possible sources of PCB contamination in groundwater.

The feasibility study evaluated information from the investigations and outlined cleanup options for contaminants in soil and groundwater at the site.

• Please visit the Technical Reports section of the site documents to view the multi-volume remedial investigation and feasibility study that was completed in 2012.

Interim cleanup actions and groundwater tests leading to final cleanup plan

Kaiser has completed many interim cleanup actions, including removing petroleum on groundwater and excavating or capping contaminated soil. PCB contamination in groundwater is the primary remaining issue.

To find the most effective method, Kaiser pilot tested the following ways to remove PCBs from groundwater from 2013–2022:

1. Walnut-shell filtration
2. Algae filtration
3. Solvent extraction with zero-valent metal treatment
4. Ultraviolet light/advanced oxidation (adding hydrogen peroxide, basically) process, or UV/AOP

The first three methods only captured PCBs and created a new waste stream to be managed and disposed, along with other technical issues, while UV/AOP was highly efficient at destroying PCBs. In 2022, Ecology and Kaiser agreed to move forward with full-scale implementation of UV/AOP. You can learn more in the Interim Action Completion Report.

In June 2024, Kaiser began operating a full-scale UV/AOP system. Ecology’s legal agreement with Kaiser requires the full-scale system to extract contaminated groundwater at rates that protect the Spokane River. It also requires they improve and expand the system, as necessary. Kaiser will operate the full-scale system for several years. Ecology will write the draft cleanup action plan after we assess the results of the testing and the system’s ability to meet state standards. The draft plan will be available for public review before becoming final.