"These projects are part of our closure mission and showcase the Army's commitment to the environment," Col. Mark B. Pomeroy, depot commander, said Monday in a prepared statement.
The mustard-filled munitions 11 rusted, nonexplosive 4.2-inch mortar cartridges were discovered in a landfill near the depot's southern edge, said spokeswoman Alaine Grieser. "We anticipate we'll find a few more."
The Army used a Portable Isotopic Neutron Spectroscopy (PINS) system, sort of like an X-ray, to detect the hazardous contents. The cartridges were packed in airtight containers, and at a later date will be loaded in to a portable "Explosive Destruction System," cracked open and chemically neutralized, Grieser said.
The Army is about halfway through the landfill and has removed about 40,000 munitions discarded between 1945 and 1978.
"Back then, it wasn't uncommon to dig trenches and take the munitions and dump them in there and light them on fire with diesel," said Brad Maulding, hazardous-waste facilities manager at the state Department of Environmental Quality (DEQ). "They didn't question the long-term environmental effects or whether burning was adequate."
The depot's environmental legacy isn't fully known, but Maulding said the decomposing weapons pose no direct threat to the community.
"No one could have stumbled across them," he said, noting the depot is surrounded by barbed-wire fences and patrolled by security officers.
To date, no munitions chemicals have been found in the groundwater, but some wells have tested positive for industrial pollutants from old plant operations, such as the solvent carbon tetrachloride, Maulding said.
Environmental groups say the landfills should remind future generations of how something dangerous is easily mishandled.
"We have to realize that Utah is a place where lots of materials like this gets brought," said Matt Pacenza, policy director for HEAL Utah. "Whether it's nuclear waste or chemical weapons, we need to be constantly vigilant and skeptical when companies say, 'Don't worry about it. It's safe.' "
Cleanup at the depot is expected to continue through 2014.