A judge has ordered a new review of whether an incinerator is safe enough to destroy 2,300 tons of mercury-bearing mustard gas at the Umatilla Chemical Depot.

The decision could mean a delay in the work, which might have begun next year.

Multnomah County Circuit Court Judge Michael Marcus did not halt the work under way at the plant near Hermiston. The Army is burning artillery shells containing GB, or sarin, at the site near Hermiston. Last year, it finished destroying rockets containing the nerve agent.

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Chemical weapons are stored in earth-covered igloos shown in this file photo at the Umatilla Chemical Depot in Umatilla, Ore.

But before the plant starts burning mustard gas, Marcus said Tuesday, the state Department of Environmental Quality must consider changes in the plant's design and operations made since the incinerator was approved in 1997.

"I don't think under this ruling they could start the mustard processing," said Mick Harrison, an Indiana lawyer who worked on the case for environmental groups including GASP, an Oregon group opposed to incineration. "It's a substantial victory."

Harrison and Portland lawyer Stuart Sugarman said that it would be safer to treat the mustard gas with a water neutralization process. That creates liquid waste to be disposed of, but it would not incinerate the mercury.

Marcus' ruling said the DEQ could still reasonably decide to incinerate the mustard gas and some secondary waste, such as chemical protection suits, after a more thorough look at the best options for disposing of those items.

That review probably couldn't be completed until 2008, said Rich Duvall, administrator of the state environmental department's Chemical Demilitarization Program.

But he said the facility might have to delay processing mustard gas, work that otherwise might have started in late 2008.

Mercury is found naturally and introduced into the environment through processes such as coal burning and chemical processing.

Mustard gas, first used during World War I, causes severe blisters and internal and external bleeding, strips the mucus membranes from airways and may increase the risk of cancer and birth defects. Exposure is often fatal.

Umatilla is one of seven Army facilities that have been destroying chemical weapons under terms of a 1997 treaty. The deadline for the work is April 29, but the United States and Russia are seeking five-year extensions.