Hydrologic evaluation of the Arikaree Formation near Lusk, Niobrara and Goshen counties, Wyoming

The Arikaree Formation of early Miocene age is an aquifer of large areal extent and is composed of very fine grained, poorly bedded, loosely to moderately cemented sandstone and interbedded silt, limestone, and many concretionary layers. The area studied is about 800 square miles in southern Niobrara and northern Goshen Counties of Wyoming. Long-term average annual recharge to the aquifer from streams and precipitation is estimated to total about 24,270 acre-feet. Pumpage from public-supply and irrigation wells is estimated to have totaled about 48,000 acre-feet from 1938 through 1972. This pumpage did not cause any noticeable decrease in natural discharge and it is assumed there has been no significant change in ground-water storage. Pumpage is estimated to total about 39,500 acre-feet for the 3-year period 1973 through 1975. A digital model was developed to simulate the ground-water system in the Arikaree Formation. The model can be used to indicate the general effect of applying hydraulic stresses to the aquifer. (Woodard-USGS)