2009-05-19_REVISION - M1981021 (36)

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Section 7 Groundwater Information Cater (1955), because these features have a potential to influence groundwater flow at a larger scale. The effect of major fracture zones on groundwater flow is dependent on the rheological characteristics of the displaced rock units. Fault zones within relatively brittle rocks such as massive sandstone are more likely to include zones of closely spaced and interconnected fractures forming a fracture zone. The fracture zones may have a marked influence of hydrogeologic characteristics. Fault zones within shale units such as the bentonite-rich Brushy Basin Member are less likely to influence groundwater, because the shale deforms plastically reducing permeability of the fault zone as compared to the more brittle units (Weir et al. 1983). The interpretive hydrogeologic framework cross-sections presented previously (Figures 7-6 to 7-9) provide information regarding the relative permeability of the fault zones. A hatched pattern identifies portions of faults where two shale units are juxtaposed on either side of the fault. These are areas where the fault is less likely to have a major effect on groundwater flow. Fault zones that are not hatched identify areas where significant fracture zones are more likely to be associated with the fault. These are areas where the fault zone would be more likely to affect groundwater flow. 7.4 Direction and Rate of Groundwater Flow 7.4.1 Area of Underground Workings Although the regional direction of groundwater flow is towards the Dolores River, the direction and rate of groundwater flow in the area of the Sunday Mines Group is perturbed by the presence of the underground mine workings and integral activities associated with mining such as dewatering and ventilation. Available data regarding the rate and direction of groundwater flow in the interconnected Sunday-Carnation- St. Jude-West Sunday mine workings, the Topaz Mine underground workings suggests the following: ¦ The direction of groundwater flow in the vicinity of the West Sunday Mine underground workings is into the mine; ¦ The direction of groundwater flow in the area of the Sunday mine underground workings has been into the mine during periods of active dewatering prior to 1991 and during recovery of the water table since 1991--it is unknown if groundwater is still flowing into the Sunday mine; and ¦ The direction of groundwater flow in the areas of the Topaz, Carnation, and St. Jude mines is currently unknown. Mine water pumped from the underground mines is not pumped to the surface and discharged. All of this water is used within the mines for dust control and drilling purposes. It is currently thought that this water evaporates and is exhausted from the mine in the ventilation circuit. This process can result in removal of large quantities of water from underground mines (Younger et al. 2002). This process causes the underground mines to act as a local groundwater sink, which causes local 7-6 T:t64986-Denison Mines7ask Order 4 - EPP Sunday Mines GroupTINAL EPPTINAL - Environmental Protection Plan Sunday Mines.doc