Sirens sounded for the last time around a Northwest chemical weapons depot on Tuesday, as workers incinerated the last of the chemical weapons stored in the region as part of the country's stockpile.

Sirens sounded for the last time around a Northwest chemical weapons depot on Tuesday, as workers incinerated the last of the chemical weapons stored in the region as part of the country's stockpile.

The Umatilla Chemical Depot in Hermiston once stored 12 percent of the United States' chemical weapons, including deadly VX nerve agent and blistering mustard agent.

Work to begin incinerating the weapons began seven years ago to meet a 2012 deadline imposed by the 1997 Chemical Weapons Convention, an international treaty. Depot employees watched on a closed-circuit television screen as the last ton-size container of mustard agent was incinerated, applauding when the job was done.

The completion of work there whittles the number of U.S. storage sites to three: Pueblo, Colo., Richmond, Ky., and the Deseret Chemical Depot in Tooele, Utah, which once held 40 percent of the U.S. stockpile but is expected to complete incineration in January. Once the Utah site completes operations, 90 percent of the U.S. stockpile will have been destroyed.

There once were nine U.S. chemical stockpiles scattered across the country.

"The end of nearly 50 years of chemical agents at Umatilla Chemical Depot has now come to a close," depot spokesman Michael Fletcher said in a telephone interview. "The local communities and the state of Oregon are a lot safer place now."

Umatilla County Commissioner Bill Hansell said, "it's been there virtually the entire life of everybody living in the area. We're glad it's gone."

Two months before the United States entered World War II in 1941, the federal government began storing conventional weapons across 30 square miles of northeast Oregon, a largely agricultural region 180 miles east of Portland, near the Washington state border. Weapons were stored in partly buried earthen bunkers, referred to as "igloos."

In 1962, the depot also began storing chemical weapons, and in 1994, conventional weapons were shipped offsite.

The international treaty to rid the world of chemical weapons shifted the focus to destroying the substances, rather than just safely storing them. That has meant big changes for northeast Oregon.

Thousands of tone-alert radios and shelter-in-place kits — containing duct tape, plastic sheeting and medical scissors — were distributed to residents to seal up a safe room in the event of a leak or accident at the site. Pressurized rooms were created as safety zones in schools, retirement homes and hospitals to protect the public.

Sirens were installed and tested in at least eight different communities in Oregon and Washington, and emergency management officials conducted emergency exercises each year. Those sirens sounded for the last time at noon Tuesday. They will be dismantled and sent to Oregon's coastal communities to enhance tsunami warning systems there.

The last official test for the 20,000 tone alert-radios that were distributed to residents and businesses will be Wednesday. Communities will then begin a recycling program for them.

The stockpile of deadly GB nerve agent, or sarin, and VX nerve agent already have been destroyed at the site. On Tuesday, workers incinerated the last of 2,635 ton-size containers of mustard agent, which causes blisters on skin, scars on the eyes and inflammation in airways.

Incinerators heat the chemicals and their containers to thousands of degrees, then run the exhaust through pollution-removing filters and afterburners.

More than $2.6 billion has been spent overall on construction and operations there.

"For decades, the residents of Eastern Oregon have been living next door to some of the most dangerous weapons the world has ever known, so dangerous that the world agreed they should be destroyed. Now they have been," U.S. Sen. Ron Wyden, D-Ore., said in a statement.

The destruction of these chemicals clears the way for the local community to begin turning the property into an asset that will create jobs and generate economic growth throughout the region, Wyden said. About 1,200 people work at the site, but that number will decline as some move to new sites and work to tear down buildings and clean up draws to an end over the next three or four years.

Hansell, the county commissioner, agreed that finding a future use for the site is equally as important as ridding it of dangerous chemicals. Plans have yet to be determined, but officials are hoping for some industrial development.

"We knew from the beginning that this was a project that was going to come to a close, that wasn't going to last forever," Hansell said. "Now the question is, 'What are we going to do with the program drawing to a close?' "