Denver Basin ground-water has been the subject of many past and current investigations by the U.S. Geological Survey. Past investigations from 1978 to 1998 included hydrogeologic mapping, geophysical logging, aquifer testing, water quality sampling, and ground-water modeling. Recent investigations since 1998 include the Front Range Infrastructure Resources Project (FRIRP), the Kiowa Core Project, and, currently, the National Water Quality Assessment (NAWQA) Program in the South Platte River Basin. The FRIRP included geologic mapping of Denver Basin bedrock and surficial aquifers to define the bedrock-outcrop areas, and extent, thickness, and water-table altitude of surficial aquifers. Lithologic and hydrologic data from more than 10,000 wells were used to prepare surficial aquifer maps, and geophysical data from about 1700 oil, gas, and water wells were used to prepare bedrock-aquifer outcrop maps. The Kiowa Core Project included drilling a 2,256-foot-deep corehole to the base of the Denver Basin aquifers to determine the thickness, lithology, and hydraulic properties of the aquifers near the center of the basin. Four ground-water studies are in progress as part of the South Platte NAWQA study: 1) resampling of about 30 monitoring wells completed in the South Platte alluvium in areas of irrigated corn agriculture; 2) an agricultural land-use study in areas of wheat farming east of Denver, Colorado; 3) an urban land-use study in recently urbanized areas of southern metropolitan Denver; and 4) a topical research study entitled “Transport of Anthropogenic and Natural Contaminants to Public-Supply and Domestic Wells.” The research study will focus on water quality in the Dawson aquifer.