1990-01-09_REVISION - M1988112 (6)

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'90 P1~09 18:[l~ $ ~PJ 985 9947 Sks DEt~P BATTLE MOUN?AIN RESOURCES, SAN LUIS PROJECT CMLRD ADEQUACY LETTER RESPONSES Page 11 of 28 16. Section D.6.1 states that, during Phase 1, 33Y. of the ~ailings will be placed in the upper disposal area. Section D.6.5.3 states that, during Phase 1, the upper area will generate drainage at about 310 gpm, white the lower area will generate about 230 gpm. Please explain why the )esser volume of tailings generates 120 gpm more water. If these figures were used to evaluate the sizing and spat+al placement of the aD5 collector pipes, the design should be re-evaluated. It is essential that the drainage system be complete )y adeG~ate to transmit flows from the tolls to the Catchment basin white minimizing the hydraulic head within the facility. tiS?Dt!SE: Tiie quantity difference of 80 gpm is a result of the l~crger surface area of the upper area and thereby the drainage network under the upper area and is not related to the amount of tailings deposited. (he quantities were conservatively calculated assuming ghat the entire surface area for drainage network for both the upper and lower areas was covered with tailings which exhibited permeabilities similar to permeabilitiey expected after one year of deposition. First year tailings parmeabilities will decrease through consolidation over time. By assuming these high permeal,illties over the entire drainage network area and not ,lust the area of first year deposition, the ma~ci~.um flows were conservatively est•mated at 310 gpm for the upper area and 230 gp~a for the lower area 1~~ audition, the main collector pipes from the upper impoundment have Sea+~ designed to collect almost four times the conservatively calculated 310 gprr~ flow or 1200 gm. the main collector pipes from the lower Impoundment have been deigned to collect over three times the 540 gpm total flow or 1800 gpm. Additional capa=ity is also available in the drainage blanket surrounding the pipe network. The figures presented represent a conservative design for the pipe network utilizing non-pressurized flaw (zero head) and minimum graces. the elevations cuntairied on Figures D.6-3 through D.6-5 should be corrected, and the figures resubmitted. L'Sv~i~VS_~ The ela_vatiens an Figures D.6-3 through D.6-5 have been corrected and the corrected figures are included with this submittal. '. '. The pond cross-section shown on Figure C•8 indicates a six-inch PVC pipe will be used for the leak detactfon sump. The construction details provided in Appendix J state that an eight-fnch pipe will be used. Please c)arify. PCS~UNSE: The correct PVC pipe diameter shown on Figure C•8 should be 8" as stated in the construction details. The figure has been corrected. 94