The Pueblo Chemical Depot’s mission is to ensure safe storage for part of the U.S. chemical weapons stockpile. The site, located about 14 miles east of Pueblo, Colorado, has been safely storing chemical weapons since the 1950s. The depot has 780,078 weapons with about 2,611 tons of mustard, a blister agent. This represents about 8.5 percent of the original U.S. chemical weapons stockpile. Pueblo Chemical Depot has 922 storage igloos, though only 102 store chemical weapons.
Military - Weapon Depots
I assume the secure compount on the north side is where the chemical weapons are stored.
Links: www.globalsecurity.org, en.wikipedia.org