An analysis was made of baseline groundwater quality data from oil shale lease tract C-a, managed by Rio Blanco Oil Shale Company. The data are limited in several respects. All conclusions drawn from the data must be qualified with these limitations. Baseline conditions were determined by analyzing data from wells in the upper bedrock and lower bedrock aquifers and from the alluvial wells. Baseline data were considered all data collected before mining operations began. The water quality was then evaluated using the 1987 Colorado State Basic Standards for Ground Water as a basis. The maximum baseline values for several parameters in each aquifer exceed the standard values. The quality of the upper lower bedrock aquifers varies from region to region within the site. Data on the lower bedrock aquifer are insufficient for speculation on the cause of the variations. Variations in the upper bedrock aquifer are possibly caused by leakage of the lower bedrock aquifer. 16 refs., 9 figs., 9 tabs.