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the Uravan area. In descending order the units are: t) sandstones and shales of the Jurassic Salt Wash Member of the Morrison Formation, 2) shales and siltstones of the Jurassic Summerville Formation, 3) sandstones of the Jurassic Entrada, 4) sandstones of the Triassic Kayenta, and 5) sandstones of the Triassic Wingate Formation. The Kayenta/Wingate Formation is the uppermost aquifer beneath the Uravan area. The aquifer is unconfined with an average hydraulic conductivity of 0.12 fUday (4.2 x 10-5 cm/sec). Primary recharge to the Kayenta/Wingate aquifer is northeast of the San Miguel River along the Uncompahgre Plateau. Secondary recharge to the Wingate portion of the aquifer is from the Paradox Valley southwest of the site. Ground water levels in the Kayenta/Wingate show flow directions toward the San Miguel River. In the Uravan area a ground water trough exists just southwest and parallel to the river. Discharge from the aquifer is to the San Miguel River. Ground water chemistry of the aquifer is different on each side of the river. Ground water derived from the Uncompahgre Plateau is a magnesium chloride type water low in Total Dissolved Solids (TDS). Ground water under Club Mesa, derived from the Paradox Valley is a sodium chloride . type water much higher in TDS. Club Mesa is underlain by approximately 600 feet of unsaturated sandstone, siltstone and shale. The Summerville Formation, composed of shale and siltstone, has a hydraulic conductivity of less than 0.01 fUyr (1.0 x 10-a crn/sec). This 90-foot thick layer, the top of which outcrops along the canyon walls, effectively isolates any potential seepage from the repositories to the Kayenta/Wingatesquifer. In the river valley,'the Summerville Formation is not present- Therefore, seepage from the Club Ranch Ponds has impacted rho Kayenta/Wingatc aquifer on the northeast side of the San Miguel River. Groundwater remediation activities has decreased the size of the contaminant plume and reduced contaminant concentrations. 5.3 Club Mesa HydrogeoloRy Hydrologic units of interest on Club Mesa include the Salt Wash Sandstone and the Kayenta/Wingate aquifer. Perched raffinate liquid is present at the bast of the Salt Wash Sandstone. This perched zone resulted from the migration of liquids from the tailings piles and Club Mesa Spray area. The Kayenta/Wingate Formations comprise the first aquifer beneath Club Mesa. The hydrogeology of Club Mesa is evaluated through wells completed in the Salt Wash Member of the Morrison Formation (V-762, V-763S, V-7645, V-770, V-771, and V.772) and wells completed in the Kayenta/Wingate aquifer (V-768, V-769, CRP-15, CRP-16, V-766, CM- 93-1, CM-93-2, and CM-93-3). Club Mesa hydrogeology is dominated by unsaturated conditions in the 400 to 600-foot thick strata above the Kayenta/Wingate aquifer. Unsaturated flow is controlled by deep infiltration (percolation) in the Bushy Hasin shalt and Salt Wash Sandstone that cap the mesa. The Salt Wash Member of the Morrison Formation is dominantly sandstone; however, shale lenses are present. These shale layers comprise approximately 25 percent of the formation in the Uravan area. Salt Wash Sandstones have hydraulic conductivities that range from 0.051 ft/day (1.8 x 10'5 cm/sec) to 0.027 fUday (9.7 x 10'6 cm/sec). The Salt Wash Formation is unsaturated with an average sandstone porosity of about 17.6 percent and a moisture content of 4.4 percent and average shale porosity of 16.3 percent and a moisture content of 9.5 percent. Umsco-Uravan DA February 11.2000 39dd C~Of1N db00 b31100 to LSLL0980L6 9Z=L[ L00L/S[(90