Deactivated Minuteman installations (Ellsworth AFB area, South Dakota, Whiteman AFB area, Missouri, Grand Forks AFB area, North Dakota) were rendered incapable of being used as ICBM launchers again via the Strategic Arms Reduction Treaty (START-I) and for many years it was forbidden to disturb the soil at these sites. The silos (and their support structures) were imploded meaning that any missile silo today is merely a space of ground with a lot of concrete and rebar chunks to be found if one dug deep enough. The Missile Alert Facilities meanwhile were left intact (save for the 564th Missile Squadron sites in Montana that were demolished) however the elevator shaft was filled with debris and capped with concrete. There has been at least one instance of a landowner removing debris from the elevator shaft and accessing the underground Launch Control Center and Launch Control Equipment Building, however all that was left below were the blast doors and some metal racks. The understanding was the Air Force was okay with ground disturbance after 2009 although the Environmental Protection Agency was involved due to reports at some sites of PCB (polychlorinated biphenyls) and diesel contamination.