The Oglala Aquifer is a huge aquifer that spans an area from Texas to Colorado and Nebraska. The oldest water deposited in the aquifer is over one million years old, and only a very small amount of water is added each year. The Oglala Aquifer is being pumped rapidly by the farms in the region, causing a reduction in the amount of water in the aquifer. Consequently, wells have to be continually deepened so that they can continue to pump water.