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Page 3 <br />Homestake Tailings Dam <br />Meeting Notes - 6/I2/80 <br />E. Seismic zone classification 3 (Corp of Engineers) applies an acceleration <br />of O.I gravity as an appropriate pseudo static coefficient. <br />4. No hydraulic link ascertained between the various units during pumping <br />tests. Colorado Health Department reminded applicant the necessity of <br />properly plugging and sealing the exploratory test holes. Applicant recognizes <br />obligation. <br />5. Geotechnics of Dam Design (Curt Seally) <br />A. A11 alluvial deposits and weathered materials being removed to avoid dif <br />faential settlement of embankment and liner. <br />B. Proposed to use excavated alluvium and weathered materials as topsoil for <br />reclamation. <br />C. Tuffaceous materials appear appropriate as core material for dam embank- <br />ment, Liquid limits 30 through 70 with very highly plastic clay fraction <br />varying from 20 to 60~ by weight. <br />D. Safety factor calculations for embankment as designed using Bishop's method <br />of slices. <br />1.7 in static, 1.2 'in pseudo static. <br />E. Minimal seepage anticipated. Testing on core material determined perme-~ <br />ability of .06 gallons per foot square per day under 175 foot hydraulic <br />head, anticipated total reservoir heighth. <br />F. Liquifaction potential tests as virtually non-existent. <br />G. Clays for use as liner of reservoir test having permeability of 10-8 <br />centimeters per second. <br />H. Over drain system consists of 6" open joint pipe laid in a filter bed, <br />designed in accordance with Corps of Engineer's criteria. Three layered <br />extremely expensive filter design using natural materials. Materials to <br />be processed and manufactured on site. Filter cloths will not work, with <br />plug in year or two. <br />I. Strength testing for tailings. 50 PSF sheer strength equals , <br />300 PSF total bearing strength. In order to reclaim tailings, applicant <br />intends to spray sand over tailings surface until firm enough to work with <br />light weight track vehicle. Wi11 then apply additional layers of sand <br />covered with 3 foot thick clay liner, covered in turn with random material <br />and finely topsoiled. Total thickness of tailings cover to be at least <br />20 feet. <br />6. Application for Health Department to be submitted by end of June. Appropriate <br />applications to be submitted to MLRD by Jvly 15th. <br />Geohydrology (Envirologic Systems - Jim Rouse) <br />Z. Groundwater regime <br />A. Synclinal paleozolic zone basin with recharge to the northeast (towards mine <br />area) and discharge to the southwest (near junction of Marshal and Indian Creeks). <br />High quality artisian wells occur in areas of discharge downstream from tailings <br />embankment. <br />B. Volcanics (Tuffs, andesites and alluvium/colluvium) in filling sinclinal basins. <br />