The Ogallala is an unconfined fresh-water aquifer extending from just north of the Nebraska-South Dakota border to the southern edge of the Texas High Plains. The areal extent of the aquifer includes the eastern tier of counties in Colorado and New Mexico, the western third of Kansas, three counties in Oklahoma, the greater part of the state of Nebraska and the Texas "panhandle." The area assumed to overlie the aquifer adjusted to county lines is shown in Figure 1! Discontinuous segments of the Ogallala Aquifer have also been identified in other areas such as central Kansas and south-eastern Colorado and Wyoming. The aquifer may also stretch into counties adjoining the study area; the northern edge of the aquifer, for example, is actually located in South Dakota but the aquifer is of minor economic significance in these regions.