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Cresson Project Hvdroaeochemistry AdrianBrown <br />2. REGIONAL HYDROLOGY EVALUATION <br />The regional ground water system associated with the District is dominated by the Diatreme, a volcanic <br />caldera approximately 7 square miles in area (Plate 3 and Plate 4). The Diatreme is located within the <br />host Precambrian -age granite, granodiorite, gneiss, and schist. The diatremal and adjacent rocks contain <br />the ore bodies in the District, and therefore contain most of the past and proposed mining activities. <br />The diatremal rocks are moderately permeable, while the surrounding Pikes Peak granite is of lower <br />permeability. As a result, the Diatreme is an enclosed regional ground water regime, with limited <br />hydrologic interaction with the surrounding rockmass. This has been observed from the earliest times of <br />evaluation of the hydrology of the area, as reported in a study performed by Lindgren and Ransome <br />(1906): <br />"The records of the various drainage tunnels all suggest the same conclusion, namely that the <br />volcanic neck, filled with breccia and eruptive rocks, contains a body of water which is <br />prevented from escaping into the streams of the region by the relatively impervious character of <br />the older crystalline rocks of the prevolcanic plateau. The relation is suggestive of a water - <br />soaked sponge set in a glass cup. <br />"For all practical purposes, therefore, the underground water of the central part of the Cripple <br />Creek district is to be regarded ... as an underground lake or pond bounded by the steep walls of <br />the old volcanic throat." <br />Historic drainage tunnels driven into the Diatreme in the 20 Century have drained the regional ground <br />water flow in the District from the Diatreme and the immediately adjacent granite. The Carlton Tunnel <br />is the deepest (approximate elevation 7,000 ft msl) and most recent (1941), and has created a reduction <br />in the ground water table in the diatremal rockmass to approximately 3,500 feet below the original <br />ground surface. <br />The source of ground water in the vicinity of the Diatreme is precipitation. The precipitation impinges <br />on the surface of the District and surrounding areas, and then runs off, evaporates, transpires, or <br />infiltrates. Percolating water within and immediately contiguous to the Diatreme moves vertically <br />downwards until it ultimately reaches the deep saturated regional ground water system, and then flows <br />laterally from the region through the Carlton Tunnel <br />The conceptual hydrologic flow model of the District is presented schematically in Plate 5. <br />2.1 Climate <br />The hydrologic system in the District and surrounding areas is controlled by precipitation. The <br />precipitation in the District has been measured since the current surface mining has been undertaken, <br />and is presented by month in Table 2. In the period 1992 -2011, the area received an average of 19.28 <br />inches per year of total precipitation; one quarter fell in the winter and spring (mostly as snow), and <br />three quarters fell in spring and summer. <br />1385L.20120125 <br />