The incineration plant at the Umatilla Chemical Depot plans to lay off 100 people Thursday.
The project had 830 employees when the last of the chemical weapons stored at the depot were destroyed in late 2011, with about half of those employees commuting across the state line from Washington.
After this week’s layoff, 165 employees will remain.
Last month the plant, the Umatilla Chemical Agent Disposal Facility, cut 200 positions.
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Primarily operations and maintenance workers for contractor URS will lose their jobs this week.
The layoff also will include 18 employees of Southwest Research Institute, the subcontractor that operates the project’s laboratory.
The contractor hired to demolish the building where the chemical weapons were processed and also the associated pollution control systems is staging its equipment at the site now.
Northwest Demolition of Tigard, Ore., plans to begin demolition Aug. 15.
The next major staff reduction is expected in March when 80 positions will be cut as the “demolition complete” milestone is completed.