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Section 4.4. A description of the ground water system is contained in Appendix <br />• 1, Volume II of this document. <br />The volcanic diatreme that was emplaced into the Pikes Peak granite <br />formed an inverted cone of highly fractured volcanic rocks. The surrounding <br />granite and gneiss is relatively impervious, except in the immediate vicinity of the <br />diatreme, where it was fractured during the volcanic episodes. As a result, the <br />brecciated rock within the diatreme filled with water, receiving recharge from <br />precipitation at the surface and storing it as ground water in the faults, fractures, <br />veins, joint structures, and underground workings. The relatively impermeable <br />Pikes Peak granite acted to hold this water in place within the diatreme, although <br />locally it may have flowed via springs at the boundary. A series of drainage <br />tunnels were created in the early 1900s as underground mining progressed in the <br />area. These tunnels drained the diatreme and lowered the ground water system <br />from the original elevation of approximately 9,500 feet amsl to a level of <br />• approximately 7,000 feet amsl. The Carlton Tunnel is the primary point of water <br />outflow from the diatreme and surrounding area. <br />Recharge to the ground water system occurs by infiltration of precipitation <br />in the spring, summer, and fall months. Infiltrating water moves vertically <br />downward through the unsaturated portion of the system either through the <br />brecciated diatreme country rock, through subvertical fractures, through mined <br />voids created during historic underground mining, or a combination of these <br />pathways. <br />Surface manifestation of the dewatering effects of the Carlton Tunnel is <br />appazent throughout the District. Streams in the central and southern portions of <br />the diatreme tend to be ephemeral in nature, as most of the precipitation and <br />snowmelt infiltrates into the porous rock and is drained by the tunnel. Exploration <br />drill holes and development wells drilled within the caldera tend to be dry or have <br />• low yields. Present mining by CC&V has not encountered significant ground <br />27 <br />