AN EVALUATION OF HYDROSTRATIGRAPHIC CHARACTERIZATION METHODS BASED ON WELL LOGS FOR GROUNDWATER MODELING OF THE HIGH PLAINS AQUIFER IN SOUTHWEST KANSAS

The Ogallala portion of the High Plains aquifer is the primary source of water for irrigation and municipal purposes in southwestern Kansas. The spatial variability and connectivity of permeable and non-permeable deposits influence local ground-water flow and availability. The complex distribution of lithology, as well as the limited quality and quantity of high-resolution data sources, present challenges for subsurface characterization. This study uses conditional rules based on regional hydrogeologic knowledge, and a relational well log database of over 4,000 carefully-screened drilling logs to consistently translate sediment descriptions into a form useful for 2D and 3D characterization of the High Plains aquifer framework. Methods used to approximate the spatial distribution of hydrogeologic units differ in function, application, computational requirements, and the amount and type of information needed. Semivariograms and transition probability geostatistics show that low permeability units are laterally extensive, and can be spatially correlated at distances up to 1 km across the study area. The modeling work described in this report incorporates various spatial approximations of hydraulic parameters to demonstrate the influence of heterogeneity on the ground-water flow system. The results of this study contribute to the conceptual understanding of local heterogeneity in the hydrostratigraphic framework