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Whirlwind Mine Groundwater Characterization Report <br /> canyons that drain in many directions; the canyons near the mine drain to the Dolores River <br /> only a few miles to the east. All of these canyons exhibit ephemeral flow. The mesa was the site <br /> of multiple uranium mines during the 1950s through the 1990's. <br /> The geology of the project area consists of Mesozoic sedimentary rocks that gently dip to the <br /> northeast. One normal fault, the Lumsden fault trends west through the axis of upper Lumsden <br /> Canyon and into the eastern portion of Beaver Mesa. <br /> The hydrostratigraphic units of interest consist from youngest to oldest: the Burro Canyon <br /> Formation of Cretaceous age, consisting of conglomeritic sandstone that is approximately 100 ft <br /> thick; the Brushy Basin Member of the Morrison Formation of Jurassic age, consisting of <br /> interbedded mudstones and lenticular sandstone beds and is approximately 400 ft thick; and the <br /> Salt Wash Member of Morrison Formation, consisting largely of sandstone units with some <br /> interbeds of shale and mudstone and is approximately 300 ft thick. The stratigraphically highest <br /> sandstone unit in the Salt Wash is referred to as the Top Rim sandstone that hosts the uranium <br /> mineralization; it ranges from 30 to 105 ft thick. <br /> The Burro Canyon forms a discontinuous, thin, unconfined aquifer on Beaver Mesa. The overall <br /> thickness of the Burro Canyon is approximately 100-foot thick with a saturated thickness of <br /> approximately 10 ft. This aquifer is at an elevation 400 ft higher than the Whirlwind Decline <br /> portal. The aquifer has the best water quality in the study area but due to its discontinuous and <br /> thin nature, and the lack of private lands in the area, the aquifer is not commonly used as water <br /> supply; only one rarely used BLM production well exists upgradient of the mine area. <br /> The underlying Brushy Basin is known to contain two to three isolated or perched aquifers <br /> associated with sandstone units; the upper, middle, and lower sandstones. However, since <br /> these sandstones are lenticular in nature, they are not continuous across the project area. The <br /> sandstones range from a few feet to approximately 40 ft thick. The interbedded mudstones have <br /> not been shown to be water-bearing and are considered confining units of low permeability. This <br /> characteristic is best observed in the Whirlwind Decline where the lower sandstone unit seeps <br /> groundwater into the lower decline. The Brushy Basin hydrostratigraphy has been studied and <br /> confirmed through one hydraulically tested borehole (BM00-1), numerous exploration holes, an <br /> EFR Monitoring Well (W-1), and the Whirlwind Decline. Water quality of the Brushy Basin is <br /> generally poor, and the unit does contain spotty mineralized zones. <br /> Western Water& Land, Inc. 60 <br />