2008-04-15_REVISION - M1980244 (325)

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9 • 3.0 MAIN PROJECT AREA HYDROLOGIC CONDITIONS This section provides a description of the hydrologic and hydrogeologic conditions in the drainages of the main project area. Conditions within the Grassy Valley drainage are discussed in Section 4.0. The hydrologic monitoring program for the main project area is described, and data collected through January 2008 are presented. General hydrology and hydrogeology are described for main project area, followed by a drainage-by- drainage description of Cripple Creek, Arequa Gulch, Wilson Creek, Poverty Gulch, Squaw Gulch, Vindicator Valley, and Gold Run. 3.1 Main project area general hydrology Surface water flows in the drainages of the main project area are seasonal and generally low. Flows, if observed, occur in the spring due to snowmelt runoff and/or in the summer due to seasonal rains and runoff. In many locations, continuous flows do not occur along surface water drainages. Due to the relatively high transmissivity of the diatreme and the lowering of the regional groundwater table by historical underground drainage tunnels within the District, any sporadic surface and/or shallow groundwater flows generally percolate into the deeper diatreme system and become part of the regional groundwater system that is intersected by the Carlton Tunnel (Adrian Brown Consultants, 1998 and Adrian Brown, 2008). 3.2 Main project area general hydrogeology Shallow groundwater in the main project area occurs at some locations in alluvial aquifers associated with the surficial drainages or in shallow, fractured bedrock. Deep groundwater occurs in two distinct hydrologic zones that are strongly controlled by the geologic setting, the volcanic diatreme, and the surrounding granitic and gneissic rocks. The volcanic diatreme that was emplaced in the Pikes Peak Granite formed a complex of feeders of highly fractured volcanic rocks within the relatively impervious surrounding granite and gneiss. Prior to mining, the diatreme was saturated with water from infiltrating precipitation that was stored predominantly in the faults, fractures, and other secondary geological features in the rock. The relatively impermeable surrounding granite held the water in place within the diatreme until a series of drainage tunnels were created in the period 1895-1941 as historical underground mining progressed deeper in the District. The development of these tunnels drained the diatreme and progressively lowered the groundwater table from an original elevation of ,approximately 9,600 feet amsl (measured in 1890) to the present day level of approximately 7,200 feet amsl. 2736 ~ Cripple Creek & Victor Gold Mining Company Water Management Consultants