Ground-Water Chemistry of the Coal-Bearing Upper Cretaceous Mesaverde Formation, Wind River Reservation, Wyoming

Abstract Ground-water samples were collected from several wells drilled in the coal-bearing Mesaverde Formation (Upper Cretaceous) on the Wind River Reservation, Wyoming. The samples were analyzed for major and minor cations and anions, as well as trace metals, and were found to be dominated by sodium and either carbonate or sulfate. The chemistry of ground water is an important factor to consider because any development of coalbed methane (CBM) resources would lead to production of byproduct water. This water must be treated, reinjected, or disposed of by some other method. Surface disposal is unlikely to be a reasonable handling method, as most of the waters sampled exceed permissible limits for total dissolved solids (>5000 ppm TDS for surface disposal), as well as concentrations of some individual elements. Mixing with more dilute waters thus would be a prerequisite to surface disposal. However, such dilute waters may not be available in adequate supply. Treatment methods may be costly because of the volume of water produced in CBM operations. Evaporation might be a feasible handling method because the relatively dry and windy climate would favor rapid evaporation. Calculations of likely evaporation products show that trona (Na3CO3HCO3·2H2O) and halite (NaCl) would be major products of the evaporation. These evaporation-product minerals may have some economic value if produced in great enough quantity.