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Page 4 <br />Homestake Tailings Dam <br />Meeting Notes - 6/12/80 <br />C. Studies have been performed on vertical component on permeability by <br />observing standing head conditions in varying depth bore holes. Nested wells <br />measured heads, and allowed pumping tests to check vertical connection of <br />various wells. <br />D. No vertical connection detected between the younger volcanic materials <br />and the basement paleozoic limestones. (Head differentials of 150 to 250 <br />feet observed) Paleozoics and upper volcanics have parallel hydraulic <br />gradients dipping toward the southwest, but no direct connections, therefore <br />little if any contamination potential. <br />E. A11 of the existing holes have been cased and grouted in order to <br />prevent any possibility of cross contamination of different deposits. <br />F. No evidence of radio nuclide transport in either the paleozoics or <br />volcanics. Radio nuclides apparently geochemically absorbed or precipitated. <br />G. Gradient in volcanics only very locally affected by the strain and <br />sized into the deposit. <br />H. Highest absorbed permeability in area observed in 55 foot deep well <br />into volcanics below dam embankment site (K=16:130 gpd/foot2). <br />Next highest permeability was observed in the paleozoic section, an' <br />aquifer of very high quality (.7:1.5 gpd/foot 2) <br />Deepest strata of tertiary volcanic section is extremely impermeable, <br />accounting for Zack of hydraulic connection between paleozoics and volcanic <br />sections. <br />Monitoring System <br />R. Two holes drilled to paleozoic section several hundred feet downstream <br />from dam embankment's toe, to observe water qualities in paleozoics. <br />B. A1I quality testing should utilize continuous pumping samples. Thief <br />samples believed non-indicative of actual water quality. <br />C. Wing of wells into near surface volcanics installed surrounding <br />reservoir area to assure good quality control of water within volcanic aquifer. <br />D. Consultant proposes installation of low capacity constant pump in one of <br />the wells below the dam embankment. Purpose to establish cone of depression. <br />and to allow constant monitoring. Cone of depression would capture any <br />escaping contaminant. <br />E. Monitor well also be installed upgrading from reservoir for comparison. <br />F. Underdrains will keep water table below the Liner at all times. Anticipate <br />at steady state condition, approximately 5 gpm outflow from drain system. Easy <br />to monitor at out fall. <br />G. Underdrains will prevent osmotic uptake of water from below liner into <br />tailings. <br />Geochemistry (Roman Pyrah and Associates) <br />1. Chemical interactions between tailings and clay liner. <br />A. Ca (?) tests of clay act in containers exposed to tailings solutions. <br />B. Collect and test effluence forced through column using 200 PSI head, <br />difficult to collect because of extremely low permeabilities. <br />C. First throughput volume equals volume of fluid equivalent to the original <br />poor water contents of the sample. Samples compacted containing only natural <br />moisture included in sample. <br />D. Second throughput volume equals volume of tailings liquor cycled through <br />the column sample. <br />