2012-10-01_REVISION - M1977305 (16)

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warning system were problematic at best and not representative of subsurface conditions at worst. Cotter instructed crews drilling exploration holes to delineate ore deposits, and to note zones of "moisture." Figure U2 shows a 3 -D diagram of the site topography and geology, including the location of exploration borings that targeted the ore - producing zone in the Salt Wash sandstone. This moisture data provides valuable insights on the hydrogeology of the region. The upper surface of Figure U2 shows the topography of the site, the middle layer is the ore zones within the upper sandstone unit of the Salt Wash Member of the Morrison Formation, and the lower layer is the Entrada Sandstone based on structural contours shown on the Geologic Map for the Uravan Quadrangle (Cater et al, 1955). These test borings were drilled with air rotary drilling rigs and the drillers were instructed to note wet or moist zones based on observations of the drill cuttings. While this is a subjective observation and the results are not indicative of saturated conditions, it does indicate where water, under either saturated or unsaturated conditions, is located in the subsurface. However, it provides no indication of the mobility of the groundwater. These "moist" zones, based on the drill logs, are shown on Figure U2 as blue ovals. While the exploration holes targeted the ore zone, numerous borings continued through the ore zone and into the upper portion of the Salt Wash Formation. While the majority of the exploration holes are dry, there are numerous "moist" zones located above the ore horizon in the Brushy Basin Formation and below the ore zone in the Salt Wash Formation. In hydrogeologic terms, the Brushy Basin Member is defined as an aquitard - a term coined to describe the less - permeable beds in a stratigraphic sequence (Freeze and Cherry, 1979). This is a classic definition of a geologic unit incapable of providing a pathway for environmental exposure or recharge to the underlying Salt Wash sandstones. As previously noted, the Brushy Basin is a rock unit dominantly comprised of bentonitic shales (impermeable) with discontinuous lenses of low- permeable sandstones and conglomerates. Any water in this formation would cause the bentonite shales to swell and isolate lenses of sandstone and conglomerate where water could potentially accumulate. Any fractures in the bentonite shales would seal with moisture due to the expansive nature of the shales. Since meteoric water that accumulated in isolated lenses of sandstone and conglomerate had to move through impermeable bentonitic shale that dominates the lithology, the evidence suggests that this water is connate. The definition of connate water is water trapped in sediments at the time of their deposition (Freeze and Cherry, 1979). If this analysis is correct, the data suggest that the water in the Brushy Basin was deposited in the Jurassic Period of earth's history indicating that the age of the water is at least 145 million years old. This is a clear indication that the Brushy Basin is not a pathway for exposure or recharge for the underlying Salt Wash sandstones. The distribution of moisture data from the borings shows limited vertical and horizontal extent of water - bearing zones indicating that if saturated conditions occur in the subsurface, these zones are isolated. Sandstone beds below the ore horizon in the Salt Wash Member show several "moist" zones. These continuous sandstone units, if saturated, would show horizontal continuity. However, this is not the case as the moisture zones show a random distribution. O'Connor Design Group Inc. U - 15