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• 6.2 Brushy Basin Aquifers <br />Three water-bearing sandstone units were encountered in the Brushy Basin member during the drilling <br />and testing of Boring BM00-1. These units, herein referred to as the Upper, Middle, and Lower <br />Sandstones were encountered at depths of 121 to 135 feet bgs, 242 to 264 feet bgs, and from 360 to <br />428 feet bgs (see Figure GS). These sandstone units are separated by thick sequences of mudstone. <br />As discussed in Dick White's January 8, 2008 memorandum titled "Geological Interpretation of <br />Beaver Mesa Water-Bearing Zones Based on Exploration Drilling Results", the sandstone lenses <br />within the Brushy Basin member of the 1Vlorrison Formation were formed by ancient stream and river <br />channels flowing across a slowly subsiding plain. This resulted in the creation of isolated sandstone <br />lenses within the massive mudstone deposits of the Brushy Basin. These lenses are irregular in shape <br />and size and seldom continuous over a large area because the stream locations usually shifted over <br />time. Ground water, if encountered, is typically found along the base of the sandstone lenses and is <br />unconfined (under no pressure). In these cases, ground water recharge is very limited because the <br />overlying mudstones and shales prevent ground water from percolating downward to the sandstone <br />• lenses. Mr. White's memorandum and supporting information is included in its entirety as Part 2 of <br />Appendix D. <br />Water analyses of the samples collected from BM00-1 and from other available sources indicate that <br />the water quality in the Brushy Basin changes with depth. The Upper Sandstone ground water is <br />similar in quality to the Burro Canyon aquifers with acalcium-bicarbonate chemical signature (see <br />Trilinear Diagram or Piper Plot in Figure G6)) and low levels of radionuclides. The Middle Sandstone <br />ground water also has low levels of radionuclides; however, calcium has been partially replaced by <br />sodium and potassium as shown on the Piper Plot. The ground water in the lowest sandstone unit, in <br />contrast, contains some radionuclides above regulatory standards and is a sodium and potassium- <br />bicarbonate water with almost no calcium. <br />The change in water quality with depth is attributable to the formation's origin and chemical <br />characteristics. Much of the Brushy Basin is mudstone, claystone, and siltstone composed of clays <br />derived from detrital glassy volcanic debris. Devitrification of this volcanic ash is believed to be the <br />Whirlwind Mine 07 (rev. April 08) G-10 <br />