The folks at the Deseret Chemical Depot in Tooele County have been busy. Having destroyed much of the nation's deadly arsenal of nerve gas by burning it in a high-tech incinerator, they have turned their attention to mustard weapons.

But there is a problem. The Army has discovered that some of the mustard agent contains elevated levels of mercury, a nasty metal that is toxic in some forms that you don't want escaping into the air from the incinerator stack. In addition, some of the chemical witch's brew has hardened into huge hockey pucks (the Army calls them heels) that won't burn in the furnaces, which are designed to incinerate liquids.

So the Army and its contractors are busy sorting through the thousands of one-ton containers of mustard agent and artillery shells, punching holes in them and sampling the contents for high levels of mercury and heels. Those that have neither are being incinerated. The problem is what to do with the others.

The Army has a plan. It wants to place new filters on the incinerator stacks to eliminate about 90 percent of the mercury, which an environmental assessment says should bring the emissions well within environmental rules. It wants to use a hot-water process to wash out the containers and neutralize the heels.

But a couple of environmental groups aren't sure that's the best way to go. They've never been fans of burning chemical weapons, arguing for decades that neutralization is safer than burning the stuff and risking the toxic pollution that could go up the stack despite all the Army's precautions. Their activism helped persuade the Army to abandon incineration for neutralization at four of its eight chemical weapons sites. But not in Utah.

One of these environmental watchdogs, the Chemical Weapons Working Group, hired an engineer to study whether a retrofit of the Utah incinerators or construction of new facilities, both to accommodate neutralization, would be technically and financially feasible and timely. (The Army needs to get the job done in time to comply with a treaty.) But he could not reach final conclusions, saying that he needed unclassified information that the Army was unwilling to provide.

HEAL Utah, another environmental group, shares the CWWG's concerns and has asked Utah's U.S. senators to intervene. It has not, however, formally petitioned the Army for the information the CWWG says it needs, and the CWWG says its requests have been fruitless.

Meantime, the Army says its plan is best.

Nevertheless, we urge the Army to provide the information the CWWG seeks. Where expert opinion is concerned, more is better. Especially when Utah's waters, which already are tainted by methyl mercury, are on the line.