2009-09-25_PERMIT FILE - M2009076 (31)

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• 6.4.20(8)(a) On a map generated from the CO Division of Water Resources in the appendix of Exhibit C is shown water resources, consisting of surface water and groundwater wells, within a specific local regime approximately within 2 miles of the proposed affected area. 6.4.20(8)(b) There are no perched zones or traditionally defined aquifers in this mountainous area. The site is completely composed of crystalline Precambrian rocks, i.e. gneisses and schists, and tertiary intrusive rocks such as quartz monzonites overlain by 0-24" of unconsolidated material. Unconsolidated materials, soils, of between 0 and 18"-24" overlay the crystalline rocks. The rocks themselves have essentially no porosity or permeability. Random, in-identifiable fractures due to jointing and faulting provide the only groundwater transmissivity and relative porosity. The site is underlain by numerous mine openings, the most important of which is the workings of the Shafter Mine. The vein of the Shafter Mine outcrops within 100 yards of the proposed disposal area, strikes N 40-60° W and dips 78-80° NW. The Shafter vein (along with the Great American and Edgar) is cut by the Big Five Tunnel at 4,250 feet from the portal, and at a depth of 893 feet on the dip of the vein. The mine workings effectively drain the area underneath the site. Refer to USGS Bulletin 1208, Plate 3, Geologic Section Alone the Big Five Tunnel. Idaho Springs District. Colorado in the appendix of Exhibit C. Another example supporting this is the Colorado School of Mines Edgar Mine Facility (approx. 350' south of the proposed Tailings Impoundment). After a meeting with them on August 31, 2009, it was learned that their mine is "dry". So "dry" in fact that they are working on permitting a well on premises to supply a marginal water supply for drilling operations to keep the dust down. The starting elevation of their well is 7,793' and the borehole was drilled to-254'. Water was determined at -172'. This elevation, 7,621', just so happens to match the Big 5 Tunnel elevation. Safe to say another example of the drainage in this area. A copy of this well log is attached in the • appendix of Exhibit C. Hydraulic conductivity for the undisturbed rock types present at the site, in-situ before mining, ranges from 10"2 - 10' gallons per day per square foot (as reported by Freeze and Cherry (1979)) due to joints and fractures in the rock. These joints and fractures will be sealed with hydraulically applied clay that is part of the waste stream. The existence of the underground mine workings provide a direct hydraulic conduit for groundwater beneath the site. The Big Five tunnel, the major drainage for the area, lies 1,000 feet directly below the site. The Big Five Tunnel drainage is monitored, collected, and pumped to the Argo Tunnel Treatment Facility located in Idaho Springs. It produces on average, 35 gallons per minute. 6.4.20(8)(c) The regional and local geological structure can be described as follows (excerpt from USGS Bulletin 1208, Economic Geology of the Idaho Springs District - Clear Creek and Gilpin Counties Colorado Moench, Robert H. and Drake, Avery Ala, Jr., 1966): GENERAL GEOLOGY The Idaho Springs district is underlain dominantly by gneissic, granitic, and pegmatitic rocks of Precambrian age (pl. 2), which constitute part of the core of the Front Range. These rocks are intruded by numerous small porphyritic dikes and irregular plutons of early Tertiary age and are cut by numerous faults. Some faults possibly originated in Precambrian time, but most formed near the close of the emplacement period of the early Tertiary magma sequence. Physical character and structure of the Precambrian and Tertiary rocks had a marked influence on the formation of the fault patterns. Accordingly, a brief description of the rock types and the structure of these rocks is given in the pages that follow. A more comprehensive report on the Precambrian rocks has been published separately (Moench, 1964). The petrography and structure of the Tertiary intrusive rocks in this district and adjoining ones were reported in detail by Wells (1960).