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SUNDAY MINE COMPLEX-HYDROGEOLOGIC REPORT <br /> Currently, groundwater elevations in the West Sunday and Sunday Mines are interpreted to be <br /> at approximately 5,490 ft amsl. Current ground water elevations at wells MW-SUN1 and MW- <br /> SUN3, although perhaps not static, are at 5,571.36 and 5,494.05 ft amsl, respectively. The <br /> elevation of the Dolores River several miles to the west of the SMC is approximately 5,500 ft <br /> amsl. Collectively, these elevation heads, if part of the same potentiometric surface, indicate a <br /> relatively flat hydraulic gradient in the Salt Wash Member in the vicinity of the SMC, including <br /> Disappointment Valley. This flat gradient is supported by work done by Weir in 1983 (Plate 2). <br /> The currently observed rise in water levels in vent shafts and in wells MW-SUN1 and MW-SUN3 <br /> may be related to the ongoing slow movement of groundwater to a representative static level <br /> within the wells and the mine workings. The low permeability of the Top Rim Sandstone may <br /> explain this slow"recovery" phenomenon. <br /> Conceptually, it is uncertain whether groundwater flow in the Salt Wash Member is to or from <br /> the Dolores River, which acts as a constant head boundary in the region. River discharge <br /> records indicate that generally the Dolores River is a slightly gaining stream in the area, but <br /> these findings are complicated by irrigation diversions. The river could be gaining from other <br /> source aquifers in area. Given the limited recharge capacity of the Salt Wash Member in the <br /> SMC area and its very low permeability, its potential discharge to the river would be relatively <br /> minor. Alternatively, the river could act as the most influential source to controlling head in the <br /> Salt Wash by recharging or maintaining head in the aquitard over time. <br /> 11.3 Mine Inflow <br /> As interpreted, groundwater in the Salt Wash is confined in Disappointment Valley, downdip of <br /> the SMC area. Indications are that the Salt Wash is variably saturated to unsaturated in the <br /> upper mine workings, and groundwater that may occur in these updip locations is either not <br /> present or unconfined. Groundwater has been seeping into the mine workings since before <br /> 1991 at the lower elevations (i.e., those locations that fall below the projected potentiometric <br /> surface shown on Figure 8-1). Groundwater influx to the deeper mine workings occurs because <br /> of the low atmospheric pressure in the workings compared to the confined pore pressure within <br /> the aquitard. The mine workings provide a highly transmissive conduit for upward movement of <br /> groundwater under confining pressures into previously unsaturated areas. The overall influx (or <br /> inflow) rate is small because of the low permeability of the Top Rim Sandstone unit. The Top <br /> Rim unit would have remained essentially unsaturated in the area of the mine workings if the <br /> workings did not exist. <br /> Western Water& Land, Inc. 42 <br />