Hydrologic information and analysis aid in decisions to lease federally owned coal and to prepare necessary Environmental Assessments and Impact Study reports. This need has become even more critical with the enactment of Public Law 95-87, the "Surface Mining Control and Reclamation Act of 1977." This act requires an appropriate regulatory agency to issue permits, based on the review of permit-application data to assess hydrologic impacts. This report, which partially fulfills this requirement, is one in a series of nationwide coal province reports that present information thematically, through the use of a brief text and accompanying maps, graphs, charts, or other illustrations for single hydrologic topics. The report broadly characterizes the hydrology of Area 59 in north-central Colorado and southeastern Wyoming. The report area, located within the South Platte River basin, covers a 16,000-square-mile area of diverse geology, topography, and climate. This diversity results in contrasting hydrologic characteristics. Hydrologic problems related to surface mining are erosion, sedimentation, decline in water levels, disruption of aquifers, and degradation of water quality. Because the semiarid mine areas have very little runoff, and the major streams have large buffer and dilution capacities, the effects of mining on surface water is minimal. However, effects on ground water may be much more severe and long-lasting.

The U.S. Geological Survey, in cooperation with the Metro Wastewater Reclamation District, studied the groundwater quality effects of the application of anaerobic digested municipal sewage sludge at agronomic rates to farmland near Platteville. Beginning in the fall of 1985, the sludge was injected annually into the sandy farmland in a 1-square-mile area. Generally, water-quality samples were collected from observation wells two or three times during each irrigation season from 1985 through 1990 and once each winter or late spring from 1987 through early 1991. Water levels were measured, and water-quality, soil and soil-moisture samples, and precipitation data were collected at selected sites throughout the study area. This report presents the data collected during 1985-91 from observation wells, irrigation wells, domestic wells, and other selected sites in the study area.

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