Destroying Mustard Gas

The discovery of high levels of mercury in its mustard gas stocks at Tooele, Utah, is forcing the Army to make more than $50 million in modifications to its incinerator-based destruction facility. Despite the changes, the Army claims it will be able to meet its 2007 deadline for destroying all chemical weapons stored at Tooele, if processing mustard gas begins in spring 2005.

Nearly half of Tooele’s original 13,500-ton stockpile is mustard gas. Most of the mustard gas—about 92%—is stored in 6,4001-ton containers, and 75% of these hold mercury-free agent.

The bulk containers storing mercury-tainted mustard gas came from the Army’s Rocky Mountain Arsenal, where the agent was produced. The Army believes this mustard agent was stored in recycled but incompletely cleaned containers that had previously been used to deliver mercuric chloride for other production processes.

Bulk containers with no or low levels of mercury will be processed using the incineration method currently being employed to destroy the nerve agent VX. This same method has already destroyed all of Tooele’s sarin nerve gas.

The approximately 1,600 containers storing mercury-contaminated mustard agent will be processed differently. First, the containers will be drained of agent and then washed out. The drained agent will be destroyed in one of Tooele’s two liquid incinerators that has been fitted with a mercury filtration system to prevent release of mercury to the air.

Mercury will be removed from the so-called washout water and sent to a regulated commercial hazardous waste facility for disposal. The washout water containing diluted mustard agent will then be neutralized and the hydrolysates destroyed in the modified incinerator.

According to Gregory Mahall, spokesman for the Army’s Chemical Materials Agency, modification of the liquid incinerator “will begin this fall and will be completed by spring 2005.” Once the Army receives the modified operating permits that it needs from Utah, it will begin destroying mustard agent, a process it expects to complete by December 2007. “When all the mustard agent is destroyed, all of Tooele’s stockpile will be gone,” Mahall says.

In addition to mercury-tainted agent, some of the problematic 1-ton containers may, after 50 years of storage, also contain gelled mustard agent and/or sulfur-containing sludge, which the Army calls “heels.” These heels will be disposed of using the modified incinerator.

The metal containers themselves will be destroyed in a metal parts furnace, which will have to be modified to accept containers tainted with mercury or sludge. For example, water sprays for combustion control and airflows will have to be upgraded. These upgrades also will require a state-approved modified operating permit to allow for the increased feed limits that will be needed.

The Army will also have to get Utah-approved modified operating permits for the liquid incinerator fitted with mercury filters and for the neutralization process. According to Mahall, the Army could request permit modifications as early as this summer.

Dale Ormond, the Army’s site manager at Tooele, has already briefed Utah regulators and state and local officials about the Army’s plans for destroying mustard gas. Ormond will address Utah’s Citizens’ Advisory Commission next month.