The Army plans to leave in place depleted uranium discovered in 2005 at a Schofield Barracks firing range from a Cold War weapon that could fire a nuclear warhead, saying it poses no health risk.

The weakly radioactive heavy metal was used in aiming rounds for the Davy Crockett, a 1960s weapon intended to be used as a last-ditch effort against masses of Soviet soldiers in the event of war.

At a news conference yesterday at Fort Shafter, Army officials — flanked by representatives of the Nuclear Regulatory Commission and state Health Department — revealed the results of a "human health risk assessment" for depleted uranium on about 430 acres of a 2,650-acre ordnance impact area.

"The Army has concluded that the (depleted uranium) levels are safe at Schofield Barracks based on the national standards for measuring this type of hazard," said Col. Howard Killian, deputy region director for Installation Management Command Pacific.

A shipping list showed that 714 of the spotting rounds, containing about 298 pounds of depleted uranium, were sent to Hawai'i between 1962 and 1968, the Army said.

The approximately 7-inch aiming rounds were launched by a gas piston. The device was attached to a recoilless rifle that could fire a 76-pound nuclear bomb.

The weapon could be fired up to three miles but likely would have irradiated the soldiers using it. Then-Attorney General Robert F. Kennedy witnessed a test fire and detonation of a Davy Crockett — at the time a classified weapon system — in Nevada in 1962.

NO EXPOSURE RISKS

Depleted uranium was used in spotting rounds because of its weight. The projectile, which gave off smoke on impact, was used in training to simulate the trajectory of the weapon's nuclear warhead.

The spotting rounds are believed to have been fired mainly at Schofield Barracks and Pohakuloa Training Area on the Big Island, but the Army said they also may have been used at Makua Military Reservation.

Assessments of Pohakuloa and Makua are ongoing as part of the $2.4 million effort.

"We know the community was very concerned about depleted uranium and we wanted to address that as quickly as possible," Killian said. "We also have a population of soldiers who are in the midst of training as they get ready to deploy to Iraq again this fall."

Part of the study was intended to look at health risks that the soldiers and their families might face, Killian added.

Only about 30 tailfin assemblies were found at the Schofield impact area, meaning there are likely more. Yesterday, Greg Komp, chief of health physics at Walter Reed Army Medical Center, said, "We did the study using radiation detectors, so we have a big picture of what's actually out there on the ground."

Depleted uranium fragments and fine particulate matter were observed throughout the Schofield impact area, which officials noted will remain a restricted area.

The Army report released yesterday said 1,226 soil samples were collected at 645 locations. Testing exposures for site workers found no adverse risks expected from either chemical or radiological exposure to the depleted uranium.

Surface water sampling indicated that the concentration of uranium was less than the drinking water standard for uranium, and depleted uranium was not detected at all in the samples, according to the report.

Additionally, the risks for a subsistence farmer living less than a mile from the impact area for radiological and chemical levels were found to be within the U.S. Environmental Protection Agency "acceptable" risk range.

According to the World Health Organization, a radiation dose from depleted uranium would be about 60 percent of that from purified natural uranium with the same mass.

HEAVY METAL

Due to its high density — about twice that of lead — depleted uranium, or DU, is used for counterweights in aircraft and radiation shields.

DU is used in armor-penetrating military ordnance because of its density. It can ignite on impact if the temperature exceeds 600 degrees Celsius. The Army said it does not train in Hawai'i with depleted uranium.

Some Big Island residents were worried that fine particulate DU would be spread by wind and inhaled. According to the World Health Organization, "very large amounts of dust" would have to be inhaled for there to be an additional risk of lung cancer.

CONTINUAL MONITORING

The Army said there has been no measurable migration of the DU at Schofield, and monitoring will continue in the future.

Russell Takata, program manager for the state Health Department's Noise, Radiation and Indoor Air Quality branch, yesterday said he was "satisfied thus far with their (the Army's) processes and direction they are taking."

A helicopter survey of the impact area at Pohakuloa was conducted last August as part of the search for DU. Surveys are continuing there and at Makua, where heavy vegetation and the presence of old unexploded ordnance, including cluster bombs, has made searching difficult.