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MEMORANDUM At <br /> AdrianBrown <br /> Based on oxidation,the pre-mining water table appears to have been located between 9,400 ft amsl and 9,650 <br /> ft amsl in the locations where oxidation data was available.This is consistent with the results of the <br /> groundwater analysis above. <br /> Areal Variation <br /> The geochemical data collected during drilling at Cripple Creek allows an evaluation of the change in the water <br /> table over the diatremal area.To illustrate I have chosen to use the oxidation data,and to identify the lower <br /> limit of the zone of oxidation in all 1000 ft x 1000 ft squares within the diatreme by averaging the oxidation in 50 <br /> foot elevation increments. I then plotted the resulting elevations of the base of oxidation on the plan of Cripple <br /> Creek Mining district, which is presented as Plate 11.The following comments are germane: <br /> 1. The base of the zone of oxidation slopes generally downward from approximately 9,700 ft amsl on the <br /> east side of the diatreme, to approximately 9,400 ft amsl on the west side of the diatreme. <br /> 2. The areal coverage of wells, and data, is skewed to the west. In particular,there are a limited number of <br /> wells in the far east of the diatreme (because this area is "dead"with respect to gold mineralization, and <br /> hence not the target of a significant number of exploration boreholes). <br /> 3. There is a significant "hole" in the base of oxidation in the vicinity of the Cresson Pipe,just south of <br /> Granite Island,which is both the most heavily altered part of the diatremal rockmass, and the site of the <br /> most intensive mining.This may be a result of post-mining oxidation (which the geologic loggers are <br /> directed to identify and ignore), deep penetration of oxygen in natural groundwater flow, or alteration <br /> mistakenly logged as oxidation. It is not considered to be indicative of the pre-mining water table <br /> elevation. <br /> Geochemical Water Table Elevation <br /> Based on the geochemical evaluation above,the geological water table is considered to slope from 9,700 ft amsl <br /> in the east of the diatreme, a little below the overflow point at Grassy Valley(9,750 ft amsl),to 9,400 ft amsl at <br /> the west of the diatreme, discharging at the Squaw Gulch overflow point (9,350 ft amsl).These results are <br /> similar to and generally confirmatory of the results obtained from consideration of the pre-mining water levels <br /> reported by Lindgren and Ransome (1906), reported above, and plotted on Plate 11 for reference. <br /> Post-Mining Groundwater Elevation <br /> Underground mining in the Cripple Creek district began in 1891,and by 1895 was encountering increasingly wet <br /> conditions, requiring dewatering.To assist in dewatering the underground mines a series of drainage tunnels <br /> have been installed in the district, all penetrating the diatremal rocks and removing water.The major drainage <br /> tunnels that have been installed are described below,and are shown on Plate 12: <br /> 1. Moffat Tunnel. The Moffat Tunnel (also known as the Ophelia Tunnel) enters the granite at the west <br /> base of Gold Hill at an elevation of 9,268 feet. In December, 1896, this tunnel was 2,600 feet in length, <br /> Page 6 <br /> Adrian Brown Consultants, Inc. <br /> 130 W.4th Ave., Denver CO 80223 <br /> 303-698-9080 www.abch2o.com <br />