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~- <br />The waste dump watershed is 243 acres, and runoff diversion requirements were <br />calculated using the following assumptions: <br />1.8" of rainfall - 10 year storm <br />1280 = 31% slope - steep designation <br />Runoff curve number 70 - "B" retardance <br />12.5 cfs - fair vegetative cover <br />3.0 ft./sec. velocity <br />Figure D.5-11 also shows the diversion conducting water from the natural drainages <br />through the waste dump to the valley floor. Rip-rap,to be gsed for velocity <br />reduction, will be required at the juncture of the waste dump and Monogram Mesa <br />with vegetative retardance employed for the diversion channels in the waste dump <br />and side slopes. As a temporary measure in years one through four, a diversion <br />at the waste dump and mesa interface will conduct water to the west and onto the <br />valley floor. This project will be undertaken as soon as practicable after the <br />waste has been placed and compacted. Vegetative retardance measures will be <br />employed in this channel. <br />Cotter will control erosion and resultant sediment loading by two methods: A <br />self-sustaining vegetative cover will be established in the flat and gently <br />sloping channels; and locally obtained rip-rap (or equivalent energy dissipation <br />method) will be used at the interface between the undisturbed, relatively steep, <br />drainage channels and the drainage channels constructed across the backfilled pit <br />and waste dump. <br />(This response will also address the questions and concerns raised in item <br />number 6 of the August 8, letter and item number 1 in the attached summary <br />Calculations of the premising ground water conditions are made using data derived <br />from observations of conditions in the underground mine presently operating at <br />the JD-7 site, and from gamma and lithic logs made during the surface drilling <br />operations. An analysis of premising hydrology will be submitted during the week <br />of September 17. <br />(a.) Premising ground water quality is summarized below: <br />The following data are lab analysis results of a sample taken from the <br />JD-7 underground mine and are indicative of the groundwater quality in <br />the adjacent proposed open pit. These results are from a sample <br />collected in April 1979. <br />Radium 226 <br />Uranium <br />Vanium <br />Selenium <br />Arsenic <br />Cyanide <br />S04 <br />PH <br />Total Suspended Solids <br />Total Dissolved Solids <br />Zinc <br />11.5+ - 1.2 pci/1 <br />0.0 mg/1 <br />0.11 mg/1 <br />0.0 mg/1 <br />0.0 mg/1 <br />0.0 mg/1 <br />2064 mg/1 <br />8.0 <br />3148 mg/1 <br />-3- <br />