impose the model of private property and subsistence farming, thinking to encourage assimilation of the tribes to the majority type farm. It registered all members of the tribes and allotted individual 160-acre plots of land to each household. Given the arid local conditions, these allotments were generally too small to support subsistence agriculture. The government declared the remainder of the formerly communal land to be "surplus" and sold much of it to European-American settlers. Some members of the tribes later sold their plots because they were too small to be successfully farmed, leading to the tribes' losing control of more lands. 20th century to present In 1934 during the Franklin D. Roosevelt administration, the US Congress passed the Indian Reorganization Act, created in part to end the allotment process and encourage tribes to re-establish self-government and to stabilize their land bases. In 1936 these two tribes reorganized, wrote a common constitution and established their own elected government. They have managed to retain most of their lands since that time. During World War II, however, the US government assumed control of a 3,300-acre tract within the reservation, which it developed for use as an air base. Federal officials had told the tribe they would return the land to them after the war. Instead, the federal government sold the property for $1 to nearby Pocatello, a city about to the east, which developed it as a regional airport. In the 21st century, there continue to be conflicts over development at the airport without consultation with the tribe. (See material below). FMC Corporation operated a phosphate mine and plant under a lease at the Fort Hall Reservation. Between 1949 and 2001, it produced an estimated 250 million pounds of elemental phosphorus annually. It has had serious adverse environmental effects. In 1989, as part of what is termed the Eastern Michaud Flats Contamination, its 1500-acre plant site was designated by EPA under CERCLA as a Superfund site because of extensive water and land pollution caused by these operations, including degradation of the Portneuf River. The J.R. Simplot Company also operated on and near the reservation for decades. Their sites have been designated by the EPA as Superfund sites. Although some mitigation has been accomplished, scientists estimate the pollution will be hazardous for a very long time. As a result of this case, EPA has worked with the Tribes to develop the Clean Air Act’s