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z <br /> suffers from the inflow of irrigation tail water from farming practices along valleys of the surface <br /> drainages. <br /> Water quality in Yellow Creek, including all tributaries from the source to Stinking Spring, is <br /> protected in accordance with the Colorado Water Quality Standards for only the designated use of <br /> agriculture (CDPHE, 1997). <br /> The USGS conducts water quality analyses on water collected at the gauging station in Corral <br /> Gulch and the gauging station in Yellow Creek described above. Those data are reported by the <br /> USGS in the annual "Water Resources Data, Colorado. Volume 2." A summary of selected <br /> parameters from those analyses for the 1998 water year is presented in Table G-1. <br /> G-2.2 GROUND WATER <br /> The principal water-bearing bedrock units within the Piceance Basin include the Uinta and upper <br /> most members of the Green River Formations. The underlying Wasatch Formation and lower most <br /> members of the Green River Formation consists of low-permeability clays, shales, and lenticular <br /> sandstone and forms an aquitard. The ground water system within the Piceance Basin is typically <br /> divided into three acquifers: 1) Alluvial, 2) Upper, and 3) Lower which are based on hydraulic and <br /> water chemistry characteristics. Alluvial sediments found within major drainages can provide locally <br /> important sources of ground water. Communication occurs between the Upper and Lower Aquifers <br /> which are separated by the leaky semi-confining upper portion of the Mahogany Zone (Daub et. al., <br /> 1985). The general arrangement for the aquifer system on the Rock School Sodium Lease is <br /> shown in Figure G-2 and described below. Wells which have been sampled in the Lease area are <br /> shown on Figure G-3. <br /> G-2.2.1 Alluvial Aquifer <br /> Alluvial Aquifers occur in the main valley bottoms to the north, east, and south of the Lease <br /> area. In general, the saturated thickness ranges from a few feet up to 100 feet in the Piceance <br /> Basin (Weeks and Welder, 1974). Water levels in wells in local alluvial aquifers exhibit <br /> seasonal trends: rising during spring snowmelt runoff periods and declining the remainder of <br /> the year (BLM, 1985). Ground water in the alluvial aquifer can occur in both confined and <br /> unconfined conditions. <br /> Ground water in the alluvial acquifers in the Piceance Basin are classified as a sodium <br /> bicarbonate type, with total dissolved solids (TDS) concentrations ranging from 470 to 6,720 <br /> G:%LMlM78545.00ZRodamatioMRedamexh.DOC G-4 <br />