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• • the well field needed to dewater the backfill already exists in the form of the backfill <br />monitoring wells installed as part of the TR-15 Response Plan <br />• the backfill is sufficiently permeable that the majority of the water pumped would <br />derive from dewatering of the backfill <br />• the water quality of the pumped water will be more concentrated, which is <br />advantageous from the standpoint of efficiency of water treatment <br />• dewatering approximately 15 feet of the backfill will result in a water table elevation <br />that more closely corresponds to the water level assumed for the backfill design in <br />TR-18 <br />• the final, steady-state water level elevation in the West Pit would remain in the Santa <br />Fe Formation backfill material, as planned in TR-18, and would not fluctuate with <br />time (minimizing the potential for additional oxidation) <br />• adequate dewatering can be achieved in less than 1 yeaz, which would result in long- <br />term pumping rates approximately equal to the estimated rate of groundwater <br />recharge to the backfill (approximately 100 gpm) <br />• • measurement of water level in the West Pit, to ensure that the water level is lower <br />than the Rito Seco, will provide a rapid and effective measure of the performance of <br />the water management system. <br />The diagrammatic cross sections shown on Figure 6-1 depict the conceptual flow relationships <br />between backfill, alluvium, and the Rito Seco for current conditions and conditions that will <br />prevail after dewatering is initiated. Note that groundwater flow rates shown on the figure and <br />discussed below aze based on available information and professional judgment. The flow rates <br />should not be considered final design values. <br />For current conditions, the assumption was made that steady-state flow prevails in the combined <br />backfill -alluvial groundwater system (Figure 6-la). The backfill receives rechazge equal to <br />approximately 80 gpm, which is also the rate of groundwater flow through the zone of outflow <br />from the West Pit and into the Rito Seco alluvial aquifer (see Section 3.1.2.1). <br /> <br />Barlle Mountain Resources, lnc. <br />pal00167IreporrslmnrchrprVrl6wrrmngrmarch.Aoc 65 March 27, 1999 <br />