2020-03-30_HYDROLOGY - M1981021 - Laserfiche WebLink

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SUNDAY MINE COMPLEX-HYDROGEOLOGIC REPORT connected to overlying water bearing units besides the Salt Wash Member Top Rim Sandstone. Possible overlying water-bearing units include the Burro Canyon Formation, which forms bedrock at the MW-SUN2 location, the 40-foot lens of conglomerate that is located in the Brushy Basin Member above the Salt Wash Member (as shown in page 2 of 2 of Figure 11-1), or other water bearing units in the Salt Wash. This may be occurring because of an inadequate well completion (leaking annular seal, or cracked well casing). This is also the same well that experienced difficulties in obtaining a packer seal, as discussed previously in Section 9.1.2. Because water levels of well MW-SUN2 do not appear to be representative of the Salt Wash aquitard, water levels from this well were not used in the consideration of a general potentiometric surface map for the SMC area. Similar to well MW-SUN2, but to a lesser degree, the observed water levels in well MW-SUN1 are also not particularly agreeable with a conventional model that would propose a uniform potentiometric surface in the SMC area. But this depends also on how one interprets rising water levels observed in the underground workings and that of well MW-SUN 1. For example, the head measured in well MW-SUN1 may be representative of the confined conditions at that location, and the head in upgradient areas may be more transient and rising toward the MW- SUN1 water levels. In addition, open historic drill holes that penetrated water bearing units in the Brushy Basin Member and were later mined through in the Top Rim of the Salt Wash Member may be contributing additional water and hydraulic head at some locations within the mine workings. Water levels recently collected in several vent shafts as well as historical levels observed in underground workings have contributed to an understanding of groundwater conditions in the Salt Wash further northeast of the monitoring wells. Water levels measured at vent shafts have been used to project the current mine potentiometric surface and indicate the level of flooded mine workings. Observations by Denison in 2009 during underground well installations in the West Sunday Mine indicated that saturation of the Top Rim Sandstone occurred below the flooded level in the mine, but not upgradient of this location. Miners also have made comments that mining in most of the worked areas yielded no to very little groundwater (Rutter, 2020). After periods of inactive mining operations, the deepest workings flood from groundwater inflow. There is no detailed information on the character of mine inflow, but flow originates from the deepest workings, not from upgradient areas inside the mines. Western Water& Land, Inc. 41