A Colorado company said it has been awarded a contract for up to $4.6 million to destroy 71 recovered chemical weapons at Schofield Barracks.

Denver-based CH2M Hill said it will set up its portable "controlled detonation chamber" technology at Schofield, provide technical support during operations, and disassemble and remove the system once the project is completed.

The Army is in the process of completing an environmental assessment for the weapons disposal.

In early 2006, the Army said it had destroyed six rounds containing chloropicrin, an asphyxiator used in World War I.

Army officials said 152 suspect rounds were discovered during the cleanup of an old range that was to be used for the Stryker brigade.

Seventy-one of the rounds were determined to contain either chloropicrin or phosgene, both choking agents. The rest of the rounds were not chemical munitions, the Army said yesterday.

The reason for the old weapons' presence was a mystery, but Kendrick Washington, a spokesman at the time, said, "We suspect that these rounds were used for military training or quality-control testing during World War II."

The Army has historical evidence indicating that chemical munitions were stored, used and disposed of in the theater.

The unexploded ordnance cleanup also yielded other potentially dangerous surprises for the Army, including depleted uranium used in aiming rounds from a 1960s nuclear weapon system called the Davy Crockett.

CH2M Hill said its system is the only transportable detonation chamber approved by the Defense Department's Explosives Safety Board for the destruction of munitions, including those labeled "Munitions and Explosives of Concern."

The company said more than 1,500 sites across the United States, encompassing an estimated 15 million acres, may contain such munitions, and that growing concern about traditional open burn and open detonation destruction led to the environmentally friendly detonation chamber system.

Schofield spokeswoman Stefanie Gardin said the technology uses a combination of explosives to destroy the agent, and gas treatment to process any remaining residuals.

"All of this takes place in a completely monitored environment in which the air is filtered twice before release," Gardin said in an e-mailed statement.

"The system has been operated in the United Kingdom, processing chemical agents — to include chloropicrin and phosgene with complete success."

Initial X-rays of some of the old chemical weapons found at Schofield showed they were filled with liquid and had unstable fuses that made some unsafe to move.

Experts from the 22nd Chemical Battalion's Technical Escort Unit reported finding 4.2-inch mortars, 155 mm projectiles, 81 mm mortars, 75 mm projectiles, 4-inch Stokes mortars, a Livens Projector and a 105 mm projectile.

Reach William Cole at wcole@honoluluadvertiser.com.