Hydrologic-system analysis of the Wind River Formation with special reference to underground mining in the Shirley Basin area, Wyoming

Abstract

The Wind River Formation in the Shirley Basin area of southcentral Wyoming is a series of conglomeratic sand lenses interbedded with clay and silt lenses0 The sediments for the most part are unconsolidated0 Large quantities of ground water are found in the formation under both artesian and water-table conditions0 The sand, silt, and clay sequence forming the upper part of the formation contains water under nonartesian conditions0 The lower ore-bearing sand is an artesian aquifer. The lower sand averages 80 feet in thickness and is overlain and underlain by clay lenses averaging 15 and 50 feet, respectively. The aquifer is bounded on the east by a subsurface ridge formed by the relatively impervious Wall Creek Member of the Frontier Formation (Cretaceous). Pumping tests of the lower sand aquifer indicate that the coefficient of transmissibility ranges from 23, 000 to 29, 000 gpd/ft, and the coefficient of storage ranges from 0 00006 to 0 22. The Thiem and Theis mathematical models used in these computations are limited by a number of assumptions0 One of these assumptions is that the aquifer is infinite0 The Wall Creek ridge is known to limit the extent of the aquifer0 The method of images was used to reproduce the hydrologic control established by this aquifer boundary0 Results of this study indicate that the aquifer characteristics are about 25, 000 gpd/ft for transmissibility and 0 0001 for storage0 Using these values and the appropriate boundary control, the size and shape of the computed drawdown closely approximates the drawdown observed in the field0 The data upon which these results are based are very limited. To further verify the results, exploratory drilling and construction of additional observation wells are recommended0 The results of this additional study should be evaluated before plans for a dewatering pumping regimen are undertaken.