Picher is a ghost town and former city in Ottawa County, Oklahoma, United States. Formerly a major national center of lead and zinc mining at the heart of the Tri-State Mining District, over a century of unrestricted subsurface excavation dangerously undermined most of Picher's town buildings and left giant piles of toxic metal-contaminated mine tailings (known as chat) heaped throughout the area. The discovery of the cave-in risks, groundwater contamination and health effects associated with the chat piles and subsurface shafts—particularly an alarming 1996 study which showed lead poisoning in 34% of the children in Picher—eventually prompted a mandatory evacuation and buyout (via eminent domain) of the entire township by the Environmental Protection Agency and the incorporation of the town (along with the similarly contaminated satellite towns of Treece and Cardin) into the Tar Creek Superfund site. A 2006 Army Corps of Engineers study showed 86% of Picher's buildings (including the town school) were badly undermined and subject to collapse at any time. An F4 tornado which destroyed or damaged 150 homes in May 2008 accelerated the exodus. The town ceased official operations on September 1, 2009 and the population plummeted from 1,640 at the 2000 census to just 20 at the 2010 census. As of January 2011, only six homes and one business remain, their owners having refused to leave at any price; the rest of the town's buildings (excepting designated historical structures) are scheduled to be demolished by the end of the year. Picher is one of only a few locations in the world (along with others such as Gilman, Colorado and Wittenoom, Western Australia) to be evacuated and declared uninhabitable due to environmental and health damage caused by the mines the town once serviced.