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- 24 - <br />Data from 224 exploratory holes used in.our analysis are shown on <br />Fig. 6. Most of the holes have been drilled into the lower portion of <br />the Morrison Formation. Drilling was generally terminated about 20 to <br />120 feet below the level of the mine workings. Ground water was <br />encountered in approximately 45% of the holes. Ground water levels in <br />the holes are erratic due to the lenticular nature of the pervious <br />beds and the various depth of hole completions. Of the holes which <br />encountered water, water levels in approximately 90% ranged from 40 to <br />130 feet below the mine workings. Ninety -five percent of the holes <br />had water levels greater than 10 feet below the mine workings, and <br />water levels in 5% of the holes were within 10 feet of the workings. <br />The variation in water level in the test holes is attributable to <br />the lenticular and discontinuous nature of the pervious beds. Ground <br />water in the Salt Wash Member at the mine is unconfined and occurs as <br />isolated perched zones where pervious sandstone overlies very <br />impervious nudstones. Continuity between pervious zones does not <br />appear to be good. Similar occurrences of ground water have been <br />described in the Morrison Formation elsewhere in the Colorado Plateau <br />Region, Phoenix (1959). <br />At the mine site, the Salt Wash Member of the Morrison Formation <br />is underlain by relatively impermeable beds of Summerville Formation. <br />The Summerville Formation is probably about 80 feet thick in this area <br />old is underlain by the Entrada Sandstone which was discussed in the <br />,,eding paragraphs. Two potential aquifers of low hydraulic <br />ctivity underlie the Entrada Sandstone. These potential aquifers <br />ie Kayenta Formation and the Wingate Sandstone. It is not known <br />