The High Plains Aquifer, also known as the Ogallala Aquifer, has been used extensively for agricultural production in the Great Plains. It covers part of eight states, extending from west Texas to South Dakota (USGS 2011a). The High Plains Aquifer provides water for agricultural production and urban uses. In 2000, a total of 24.2 billion cubic meters of groundwater (or at a rate of 66.2 million cubic meters per day, m3/day) was pumped from the High Plains Aquifer (Maupin and Barber 2005), accounting for 30% of all groundwater used for irrigation in the United States (Guru and Horne 2000). Almost 97% of the pumped groundwater was used for irrigation; the remaining 3% was used for public, industrial, domestic, and other uses (Maupin and Barber 2005). In 2002, there were a total of 6.1 million ha of irrigated land in the High Plains area (USDA Census of Agriculture 2002; USGS 2011b), accounting for approximately one-‘fth of all cropland in the United States. Alfalfa, corn, cotton, sorghum, soybeans, peanuts, and wheat are major crops in the High Plains region. These crops provide Midwest cattle operations with enormous amounts of feed and account for 40% of the feedlot beef output here in the United States (Guru and Horne 2000). The use of groundwater from the High Plains Aquifer has transformed this area into an important agricultural region that sustains more than one-fourth of the nation’s agricultural production. Therefore, the current availability and future sustainable supply of high-quality groundwater are central to the overall health of the High Plains agricultural economy, the growth of its cities and rural communities, and the well-being of the ecosystem.