The southeastern Uinta Basin of Utah and Colorado includes an area of 3,000 square miles containing large oilshale deposits. Future mining and retorting of the oil shale in northeastern Utah is expected to impact the area's water resources. In order to determine premining conditions, streamflow and water-quality data were collected during 1974-79. These data plus all other available information were used to define baseline conditions for streamflow and water-quality characteristics. The data and interpretations will provide a basis for evaluating impacts of future mining.

Areal and time variances in streamflow and waterquality characteristics were determined for the major rivers (Green and White) and the intra-area streams (streams that originate within the study area). The streamflow characteristics defined are average streamflow and low- and highflow extremes. Graphs of frequency curves, duration curves, and draft-storage relations are presented for selected gaging stations. Areal variances in average and peak flows are illustrated. Water-quality characteristics are summarized according to the following categories: general waterquality characteristics, major dissolved constituents, trace elements, nutrients, pesticides, and sediment, biological, organic, and radiochemical characteristics. The means and ranges in values are discussed for the major rivers and the intra-area streams. The water-quality constituents are compared to water-quality criteria of the Environmental Protection Agency.

The major rivers flowing into the area convey an average of 5,900 cubic feet per second from a total drainage area of about 34,000 square miles. This is more than 100 times as much runoff as originates within the study area. The average flow for the major rivers is 0.17 cubic foot per second per square mile and does not vary significantly from one location to another within the study area. The flows of the intra-area streams vary from less than 0.001 to more than 0.10 cubic foot per second per square mile. Evapotranspiration losses can exceed inflow; thus average flows of some intra-area streams decrease in a downstream direction.

The quality of streamflow varies considerably between the major rivers and the intra-area streams. In the major rivers, the concentrations vary seasonally but do not vary significantly from one location to another. In the intra-area streams, concentrations vary both seasonally and from one location to another. The water quality in the major rivers generally is better than that in the intra-area streams. Dissolved-solids concentrations average 572 milligrams per liter for the Green River and 500 milligrams per liter for the White River, whereas mean concentrations for the intraarea streams range from 549 milligrams per liter in ephemeral streams to 5,320 milligrams per liter in Bitter Creek. Concentrations of major constituents generally do not exceed water-quality criteria of the Environmental Protection Agency except for hardness and sulfate. Several trace elements exceed water-quality criteria in intra-area streams. Dissolved-solids concentrations in base flow in short reaches of Bitter Creek can exceed 10,000 milligrams per liter.