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Whirlwind Mine Groundwater Characterization Report <br /> open workings. Even in the case of a fully saturated aquifer, the moderate permeability of the <br /> Top Rim sandstone would be expected to develop a cone of depression that is relatively <br /> compact(steep and narrow). It is likely that drawdown in the Salt Wash may not be measurable <br /> a few hundred feet from the workings. This is supported by the observation that the Top Rim of <br /> the Salt Wash as tested by Umetco in borehole BM00-1 did not produce any groundwater and <br /> this borehole was located only 200 ft away from the flooded workings of the Whirlwind Mine. <br /> This implies that the moderately low permeability of the Salt Wash prevents rapid infiltration <br /> from the flooded zone, and conversely, any groundwater withdrawals from the unit will impact a <br /> small area. <br /> It is expected that normal mine operations will utilize the minor amounts of water that may be <br /> produced in the mine workings. If excess water is produced, it will be pumped to the surface for <br /> treatment and discharge. <br /> A bulkhead seal has been designed for the Whirlwind Decline to isolate the Salt Wash mining <br /> zone from groundwater influx in the lower Brushy Basin after mine closure. This bulkhead will be <br /> constructed in an upper unmineralized portion of the Top Rim sandstone approximately 380 ft <br /> down the decline (west) of the groundwater seepage point in the lower Brushy Basin. The <br /> expected groundwater static level in the decline after the bulkhead is constructed is 15 ft above <br /> the current seepage point. This equates to approximately 680 linear ft of flooded decline above <br /> the bulkhead. <br /> The portion of decline that will be flooded after mine closure consists of lower Brushy Basin <br /> mudstone and the sandstone unit that is associated with the current seepage into the decline. <br /> While it is understood that not all underground hydraulic bulkheads are one hundred percent <br /> effective, it is assumed that any seepage around the bulkhead will be minimal. Published <br /> literature that has reported on the permeability of the mudstone units of the Brushy Basin was <br /> not located. Mudstones typically have a vertical permeability between 1 x 10-7 and 1 x 10-" cm/s <br /> (Freeze and Cherry,1979). Whole rock permeability including secondary porosity, such as <br /> fractures, could be orders of magnitude greater. However, since groundwater observed in the <br /> Whirlwind Decline is associated with a sandstone unit, and that the mudstone of the Brushy <br /> Basin is overall, not water bearing, it is safe to assume at this location, that the mudstones of <br /> the Brushy Basin are of low permeability. <br /> Western Water& Land, Inc. 57 <br />