Portland, OR (AHN) - A judge has delayed the disposal of thousands of tons of chemical weapons being stored at the Umatilla Chemical Depot, located in the eastern Oregon desert near the small town of Hermiston.

Capping a decade-long court battle, Multnomah County Judge Michael Marcus ruled this week that before 2,300 tons of mustard gas can be destroyed, the Oregon Department of Environmental Quality must reassess the U.S. Army's incinerator, which was originally approved in 1997.

The judge's order, which comes after revelations that mustard gas may contain higher concentrations of mercury than previously believed, does not affect the facility's on-going disposal of 155mm sarin-containing artillery shells, reported the Portland Oregonian.

Mick Harrison, an Indiana lawyer who worked on the case for environmental groups, told the Associated Press that the ruling marks a "substantial victory" for those opposed to the project.

Opened in 1941, the 19,728-acre Umatilla Chemical Depot is one of seven U.S. military facilities destroying chemical weapons under the terms of a 1997 disarmament treaty.

On March 27, a monitoring crew found trace amounts of sarin vapor with the "igloo" structure the nerve agent was stored. Sarin, an odorless, colorless, and tasteless liquid, is deadly.

Originally developed as a pesticide in Germany in 1938, an impure form of the chemical was used in terror attacks in Japan in 1994 and 1995.