Officials closed the Rocky Mountain Arsenal Wildlife Refuge to the public Thursday after revealing workers at an adjacent cleanup site had unearthed a potentially deadly chemical warfare agent.

The workers detected the agent, a mustard-gas-like chemical called lewisite, late Wednesday, the Colorado Department of Public Health and Environment said in a statement.

They were digging trenches as part of the cleanup effort of the arsenal's Superfund site, which is contained within the wildlife refuge but is separate from the refuge and not open to the public.

Ned Calonge, Colorado's chief medical officer, said that the workers reported no symptoms as a result of the exposure and that air sampling showed the contamination to be limited.

Calonge said the wildlife refuge was closed as a precaution. 

"This is really confined to the site," he said. "There's no expectation that beyond the arsenal or the refuge that there is any hazard."

The Rocky Mountain Arsenal encompasses about 17,000 acres northeast of downtown Denver and was used for years by the Army to make chemical weapons.

About 12,500 of those acres have been certified clean and were turned into a national wildlife refuge. Several thousand acres remain on the Superfund list, and a final transfer is expected by 2011, according to the U.S. Fish and Wildlife Service. Some of the most polluted acreage will remain under the control of the Army.

The workers were digging trenches designed to be filled with slurry to encapsulate pits where the Army dumped chemical agents, possibly including lewisite, said Mark Salley, spokesman for the Colorado Department of Public Health and Environment.

"Pretty nasty stuff"

The workers, who were wearing protective clothing, may have uncovered lewisite trapped in the soil or may have broken open a container of the chemical, Calonge said.

Lewisite causes

The chemical, which is sometimes called the "dew of death," was manufactured at the arsenal in 1943, Calonge said.

"It's pretty nasty stuff," Calonge said. "It does the same thing as mustard gas, which is another blistering agent. It's just worse."

The arsenal has had chemical-weapons scares in the past.

In 2000, workers discovered several bomblets filled with deadly sarin gas, prompting officials to cancel tours of the wildlife refuge.

What it is

Lewisite is a powerful chemical that causes immediate blistering of the skin and mucous membranes on contact.

Uses

It has been used only as a chemical-warfare agent. It has no medical or practical use.

Description

An oily, colorless liquid that contains arsenic. Can appear black in impure form. Smells like geraniums.

Exposure

May be spread through the air or water.

Source: Centers for Disease Control and Prevention

About the arsenal

Located about 11 miles northeast of downtown Denver, the refuge is the largest contiguous open space in the metro area.

Before World War II, the arsenal was farmland. Settlers began breaking the shortgrass prairie sod, planting trees and crops and bringing irrigation to the area in the 1880s.

In 1942, the Army bought 30 square miles of farmland for the Rocky Mountain Arsenal, a chemical weapons factory.

In 1986, while investigating the extent of the pollution and ways to clean it up, biologists discovered the arsenal was home to a large population of wintering bald eagles.

Source, Rocky Mountain Arsenal Wildlife Refuge

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