HERMISTON -- An Oregon judge has sided with the state of Oregon and the Army, ending a lawsuit by activists who challenged whether incineration was the best way to destroy mustard agent at the Umatilla Chemical Depot.

Judge Michael Marcus of the Oregon Circuit Court in Portland signed a summary judgment ruling Thursday. Barring any appeals, his ruling ended the lawsuit filed a year ago by the Government Accountability Project on behalf of the Oregon environmental group GASP, the Oregon Wildlife Federation, the Sierra Club and others.

Plaintiffs argued that chemical neutralization would release significantly less contaminants than incineration of 4.7 million pounds of weapons mustard agent stored at the chemical depot. They were particularly concerned about unknown amounts of mercury in the weapons agent.

"Our use of incineration has a proven track record in terms of safety and agent destruction," said Conrad F. Whyne, director of the U.S. Army Chemical Materials Agency, in a statement Thursday. The Army was a co-defendant in the case with the state of Oregon, which regulates the destruction of chemical weapons at the depot.

The Army has experience in Utah dealing with mercury in munitions and has applied what it learned there to incineration in Oregon, Whyne said.

"When we discovered the mercury issue, we took additional steps to ensure that the mercury found in the agent is contained within our agent destruction system," he said.

Marcus's ruling allows the Umatilla Chemical Agent Disposal Facility to continue destruction of ton containers filled with mustard agent. Nerve agent once stored at the depot already has been destroyed, leaving only weapons mustard agent in depot storage igloos yet to be incinerated.

The judge also agreed with the state's determination that the filters being used in the incinerators were the best available.

He did find that the state should have decided sooner whether to issue an air quality permit. However, the issue is moot because Oregon issued it last week, the judge ruled.

Destruction of the first ton container with mustard in the Umatilla Chemical Agent Disposal Facility began June 11, as part of a planned slow and deliberate startup. At the time, depot officials estimated the mustard agent all would be destroyed by sometime between summer 2010 and summer 2011.

However, it since has adjusted that date to sometime between January 2011 and late summer to early fall 2011 because of a slower than expected startup. The incineration campaign still is in the "shakedown" phase before going to a trial burn phase, said depot spokesman Bruce Henrickson.

Work slowed initially over state concerns that a small cloud of sulfur dioxide sometimes would be released from containers after they came out of the furnace. That's been controlled by spraying water on the container to cool it down.

Then incineration stopped about a week ago because of concerns over carbon monoxide. A restart of mustard processing has not been scheduled.