Geohydrology of the Big Creek Alluvial Aquifer of Hays and Vicinity, Ellis County, Kansas

To define the extent of the Big Creek alluvial aquifer in the Hays area (Ellis County, Kansas) hydrogeologic maps and cross-sections were constructed. The maps are based on data from 354 wells and include a surficial geologic map; a contour map of the buried surface of the Blue Hill Shale (Cretaceous bedrock); an isopach map of the aquifer; a generalized contour map of the water-table surface; water-table contour maps for 1981, 1983, and 1985; and a water-well distribution map. Unconsolidated alluvial deposits of Quaternary age underlie the Hays area. Sands and gravels characterize the basal part of the alluvial deposits and fill channels carved in the bedrock; these sands and gravels make up the unconfined and heterogeneous Big Creek aquifer. Thickness of the aquifer varies from 0 to 42 feet (0 -12.8 meters). Yields of wells range from 5 to 450 gallons per minute (0.31 to 28.4 liters per second). Flow lines indicate a general southwestern groundwater flow direction. The water table fluctuates in response to precipitation and rate of pumpage changes. There are more than 1,000 wells in the study area. At some sites, where water wells are very close to each other, well interference is suggested. At other sites, where the buried channels are deepest and the density of wells is lower, the aquifer may provide high yields for new wells