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CNAPTERFIVE Draft EIS Recisions <br />hydraulic conductiviri of the Mahoeanv Zone A schematic representation of groundwater flow <br />in the basin is provided in Figure 3.4-3. <br />Infiltrating precipitation is the main source of Proundwater recharge within the basin. Areas of <br />hieher elevations alone the southern eastern and western mazeins of the basin typically receive <br />more precipitation usually in the form of snow which results in meltwater. Consequently. <br />s~nificant eroundwater rechazee occurs alone the basin mazein azeas. <br />Groundwater dischazees from the bedrock aquifers by the followine mechanisms: <br />• duect dischazee to surface flow in Piceance Creek, Yellow Creek, and tributaries <br />• dischazee to alluvial aquifers in the maior stream valleys <br />• evapotranspiration from veeetation and wet soil located primarily in stream valleys <br />Robson and Sauhuer (19801 and Tobin (1987) estimated that approximately 80 percent of surface <br />water flow in the basin is supplied by eroundwater dischazee. <br />3.4.1.3 Groundwater Quality <br />Concentrations of total dissolved solids (TDS) in the Upper and Lower Aquifer range from <br />approximately 400 milligrams per liter (mgA) neaz the basin mazgins to 40,000 mg/I in the north- <br />central part of the basin. Increases in TDS with depth also occur within the basin (Robson and <br />Saulnier 1980). These lateral and vertical variations in water quality occur as a result of <br />geochemical changes taking place along the groundwater flow path from recharge areas near the <br />basin margins to dischazge azeas along the major streams (e.g., Piceance Creek and Yellow <br />Creek}. Figure 3.4-1.3, showing idealized groundwater flow paths within the basin, indicates the <br />potential for water from the Lower Aquifer, which is typically high in TDS and of poorer quality, <br />to flow upwazd into the Upper Aquifer and ultimately to dischazge to creeks. <br />Groundwater in the Lower Aquifer is generally classified as a sodium =bicazbonate-chloride type <br />with TDS concentrations ranging from approximately 600 mg/1 along the basin mazgins to <br />greater than 45,000 mgp in the northern part of the basin. In the Project Area TDS values range <br />from approximately 830 to 9,700 mg/1(Robson and Saulnier 1980). Site evaluation studies for <br />the U.S. Bureau of Mines experimental oil shale mine in Rio Blanco County included one site <br />located in close proximity to the proposed project. TDS iso-concentration maps produced for <br />that study showed ~ T'DS values for the Upper and Lower Aquifers similaz to those <br />described by Robson and Saulnier (1980) in the vicinity of the proposed project. Salinity and <br />TDS increase rapidly within the Lower Aquifer as the Dissolution Surface is approached (Welder <br />and Saulnier 1978). <br />I3S~VlL <br />Pse 3-18 <br />... Resources State Engineer's office. A summary of the well seazch for the three azeas as well as <br />location maps for the wells aze presented in Appendix C. These mans also include wells <br />identified in a seazch of the USGS database. The State En ing eer's well summary includes the <br />township, range and section of each well, the owner of the well, the well use, and, if available, <br />the geologic aquifer, well yield, well depth, and water level. Well use included the following <br />categories: municipal, domestic, crop irrigation, livestock, industrial, commercial, and <br />5-9 <br />