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
<br />• dip of the vein. The aline workings effectively drain the area underneath the site. Refer to USGS Bulletin 1208,
<br />Plate 3, Geologic Section Along the Big Five Tunnel Idaho Springs District Colorado in the appendix of Exhibit C.
<br />Another example supporting this is the Colorado School of Mines Edgar Mine Facility (approx. 350' south of the
<br />proposed Tailings Impoundment). After a meeting with them on August 31, 2009, it was learned that their mine is
<br />"dry". So "dry" in fact that they are working on permitting a well on premises to supply a marginal water supply for
<br />drilling operations to keep the dust down. The starting elevation of their well is 7,793' and the borehole was drilled
<br />to-254'. Water was detennined at -172'. This elevation, 7,621', just so happens to match the Big 5 Tunnel
<br />elevation. Safe to say another example of the drainage in this area. A copy of this well log is attached in the
<br />appendix of EAubit C.
<br />Hydraulic conductivity for the undisturbed rock types present at the site, in-situ before mining, ranges from 10-2 -
<br />10+2 gallons per day per square foot (as reported by Freeze and Cherry (1979)) due to joints and fractures in the
<br />rock. These joints and fractures will be sealed with hydraulically applied clay that is part of the waste stream. The
<br />existence of the underground mine workings provide a direct hydraulic conduit for groundwater beneath the site.
<br />The Big Five tunnel, the major drainage for the area, lies 1,000 feet directly below the site. The Big Five Tunnel
<br />drainage is monitored, collected, and pumped to the Argo Tunnel Treatment Facility located in Idaho Springs. It
<br />produces on average, 35 gallons per minute.
<br />6.4.20(8)(c)
<br />The regional and local geological structure can be described as follows (excerpt from USGS Bulletin 1208,
<br />Economic Geology of the Idaho Springs District - Clear Creek and Gilpin Counties, Colorado, Moench, Robert H.
<br />and Drake, Avery Ala, Jr., 1966):
<br />GENERAL GEOLOGY
<br />The Idaho Springs district is underlain dominantly by gneissic, granitic, and pegmatitic rocks of
<br />Precambrian age (pl. 2), which constitute part of the core of the Front Range. These rocks are intruded by
<br />numerous small porphyritic dikes and irregular plutons of early Tertiary age and are cut by numerous faults.
<br />Some faults possibly originated in Precambrian time, but most formed near the close of the emplacement period
<br />of the early Tertiary magma sequence.
<br />Physical character and structure of the Precambrian and Tertiary rocks had a marked influence on the
<br />formation of the fault patterns. Accordingly, a brief description of the rock types and the structure of these rocks
<br />is given in the pages that follow. A more comprehensive report on the Precambrian rocks has been published
<br />separately (Moench, 1964). The petrography and structure of the Tertiary intrusive rocks in this district and
<br />adjoining ones were reported in detail by Wells (1960).
<br />PRECAMBRIAN ROCKS
<br />The Precambrian rocks are a generally conformable succession of interlayered gneissic, granitic, and
<br />pegmatitic units. The gneissic rocks, which are dominantly metamorphosed sedimentary rocks, are the oldest
<br />and by far the most widespread and abundant rocks in the district. These rocks have been invaded by three
<br />varieties of granitic rock (from oldest to youngest) : granodiorite, quartz diorite, and biotile-muscovite granite.
<br />Several types of small pegmatite bodies are interlayered with and locally cut the gneissic and granitic rocks.
<br />The major gneissic rock units are interlayered biotite gneisses, granite gneiss, and microcline-quartz-
<br />plagioclase-biotite gneiss, which, for convenience, in most of the text are called, respectively, biotite gneiss,
<br />granite gneiss, and microcline gneiss. The biotite gneiss and granite gneiss are intermixed in layers that range
<br />from a fraction of an inch to several hundred feet in thickness. The thicker layers can be mapped individually at
<br />1 : 6,000, but on plate 2 these two rock types are combined so that the major units shown are microcline gneiss
<br />and a mixture of biotite gneiss and granite gneiss. Within the latter mixed unit, granite gneiss increases in
<br />abundance southwestward across the district, apparently at the expense of the biotite gneiss. Thinly layered
<br />rocks that consist of roughly equal proportions of biotite gneiss and granite gneiss are termed mignnatite. Small
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