2009-05-19_REVISION - M1981021 (36)

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Section 7 Groundwater Information confining units restrict groundwater flow between aquifers, unless the aquifers are directly adjacent as a result of fault displacements. 7.2.3 West Sunday Mine An interpretive hydrogeologic cross-section showing the West Sunday mine is included as Figure 7-8. The West Sunday Mine affected area is located east of the series of faults on the periphery of the Gypsum Valley anticline, and the development rock storage area overlies the Burro Canyon Formation. Where saturated, the Burro Canyon Formation is part of the Dakota aquifer, and there is potential for groundwater recharge to the Dakota aquifer from the mine affected area. The Salt Wash and Navajo aquifers are overlain by the Brushy Basin Member shale, and therefore significant recharge from the mine affected area to those aquifers is unlikely. The cross-section shows the West Sunday mine decline extending to the south towards Disappointment Valley. Groundwater is present in the base of the West Sunday mine, which is south of the groundwater divide between Disappointment Valley to the South and Big Gypsum Valley to the north. Therefore, groundwater in the underground mining area would be expected to flow southward into Disappointment Valley. 7.2.4 Topaz Mine An interpretive hydrogeological cross-section showing the Topaz Mine affected area is included as Figure 7-9. The Topaz Mine affected area overlies the Salt Wash Member of the Morrison Formation. Based on the interpretive hydrogeological framework, this portion of the Salt Wash Member may be saturated, and therefore the Salt Wash aquifer could be present in this area. The Salt Wash Member in this area is truncated to the north by the Brushy Basin Member of the Morrison Formation, which is a confining layer of low permeability shale. There is potential for infiltration from the mine affected area to recharge the Salt Wash aquifer. Flow of this water towards the north into Big Gypsum Valley would be unlikely based on the fault contact juxtaposing the Salt Wash Member against the Brushy Basin Member. However, the potential for westerly flow towards the Dolores River is plausible considering the surficial geology. The Topaz mine decline is also shown on the section. The decline extends toward the south to access mining areas located south of the groundwater divide between Disappointment Valley to the south and Big Gypsum Valley to the north. This orientation is similar to that observed at other Sunday Mines Group where groundwater flow from areas of underground mining is interpreted to be south into Disappointment Valley. 7.3 Potentially Water-Bearing Fracture Zones Potentially water-bearing fracture zones range in size from very small-scale features that primarily influence only the permeability of the rock, to large-scale features that extend for miles and could potentially influence groundwater-flow paths. This section focuses on identifying large scale fracture zones associated with the faults mapped by 7-5 T:t649WDenison MinesWask Order 4 - EPP Sunday Mines GroupTINAL EPPTINAL - Environmental Protection Plan Sunday Mines.doc