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to historic mining and processing operations in Grassy Valley. Additional discussion of <br />the flow and water quality conditions in Grassy Valley is presented in Appendices 1 and <br />2, Volume II. <br />4.6.2 Ground Water <br />Shallow ground water in the Cresson Project occurs at some locations in alluvial aquifers <br />associated with the surficial drainages or in shallow, fractured bedrock. Deeper ground <br />water in the District occurs in two distinct hydrologic zones that are strongly controlled <br />by the geologic setting: the volcanic diatreme and the surrounding granitic rocks. A <br />description of the general geology of the region, and specifically the geology beneath <br />project areas was previously provided in Section 4.4. The following summarizes the <br />ground water system with a complete description of the ground water system contained in <br />Appendix 2, Volume II of this document. <br />The volcanic diatreme that was emplaced into the Pikes Peak granite formed an inverted <br />cone of highly fractured volcanic rocks. The surrounding granite and gneiss is relatively <br />impervious, except in the immediate vicinity of the diatreme, where it was fractured <br />during the volcanic episodes. As a result, the brecciated rock within the diatreme filled <br />with water, receiving recharge from precipitation at the surface and storing it as ground <br />water in the faults, fractures, veins, joint structures, and underground workings. The <br />relatively impermeable Pikes Peak granite acted to hold this water in place within the <br />diatreme, although locally it may have flowed via springs at the boundary. A series of <br />drainage tunnels were created in the early 1900s as underground mining progressed in the <br />District. These tunnels drained the water within diatreme and lowered the regional <br />ground water system from the original elevation of approximately 9,500 feet amsl to a <br />level of approximately 7,000 feet amsl. The regional ground water system is intersected <br />by the Carlton Tunnel. <br />Recharge to the ground water system occurs by infiltration of precipitation in the spring, <br />summer, and fall months. Infiltrating water moves vertically downward through the <br />unsaturated portion of the system either through the brecciated diatreme country rock, <br />through subvertical fractures, through mined voids created during historic underground <br />mining, or a combination of these pathways. <br />Surface manifestation of the historical dewatering effects is apparent throughout the <br />District. Streams in the central and southern portions of the diatreme tend to be <br />ephemeral in nature, as most of the precipitation and snowmelt infiltrates into the porous <br />Cripple Creek & Victor Gold Mining Company <br />Cresson Project Mine Life Extension 2 <br />4 -13 <br />