Used to be stored at Dugaway Proving Grounds. Most met the incinerator at Anniston.
"The Chemical Munitions Storage Area is located along the northern boundary of PCD within the Chemical Demilitarization reuse area. Mustard chemical munitions are stored in above the ground surface, concrete, and earth-covered igloos. The munitions were first stored in C-Block igloos and moved to G-Block in 1979. Munitions are inspected regularly...
"The Army currently is assessing viable technologies other than incineration to dispose of chemical weapons at Pueblo. Until this assessment is complete, the Armys plans to construct an incinerator at Pueblo are on hold. The facility will destroy 8.5% of the nation's original chemical stockpile including Mustard agent in projectiles and mortars. The decision about which technology will be used to dispose of Pueblo's stockpile of chemical weapons has not been made, but the path of the two Environmental Impact Statements will lead the Army to that ultimate decision...."