The storage vaults at the Rocky Flats Plant are unique in construction. The walls of the vaults are constructed of reinforced concrete approximately 14 ' in thickness and are buried 15' underground. At other Department of Energy weapons production facilities, storage vault walls are generally constructed only 2 to 3' thick. Building 996 is an underground vault, rectangular in shape. The vault is 60' x 68' and 10' high.
Heavy walls divide the vault into five, nearly equal, rooms and an entry hall.
The underground vault is constructed of thick, reinforced concrete. Air is supplied to the vault through an air supply plenum, and air is exhausted through the air filter plenum in Building 985. Building 996 is located northwest of Building 991, and is connected to the northwest corner of the building by underground Tunnel 996. Tunnel 996 is 10 to 12' wide x 11 to 13' high and approximately 25 yards long. Building 997 is at the western-most end of Tunnel 997, and Building 999 is on the north side approximately midway along Tunnel 997.