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' San Luis Mine Phase D, Raise 2 Design Report ' 3.0 EMBANKMENT DESIGN The total remaining ore production as of June 1, 1995 is estimated to be approximately 4.07 million ' tons. At an overall average density of 99.2 pcf, as presented in Section 2.1 for the operations to date, the required future disposal capacity is approximately 82.1 million cubic ft. This disposal capacity can be achieved by raising the embankment crest approximately 9 ft in an upstream fashion. Analyses conducted and submitted to the Division of Minerals and Geology in conjunction withn ' TR-016 indicate that the entire 100-yr 24-hr design storm event and the maximum operating water pool can be fully contained on the tailings surface without coming into contact wiEh the embankment, ' Accordingly, a final raise height of 9 ft is indicated. However, in order to provide additional capacity for potentially larger storm inflows and contingency for lower tai]&ngs densities, the embankment crest will be raised 15 ft during Raise 2 construction consistent with the Amendment. ' The design of the second embankment raise is consistent with the conceptual raise design presented in the Amendment. The raise will be constructed using upstream construction methods to increase the embanlanent crest elevation from 8605 to 8620 ft. Drawings 14729-101 and 14729-102 included with this report depict the embankment raise in plan and profile. ' As shown on the Drawings, the raise will have a downstream slope of 3H:1V, an upstream slope of 2.SH:1V and a crest width of 30 ft. The downstream toe of the raise will be located at the t , centerline of the existing Raise 1 embankment crest to create a 15 ft wide bench at this location. The upstream portions of the raise will be founded on tailings which are anticipated to be at ' elevation 8600 at the time of raise construction. As per the Amendment, the raise will be constructed as a loosely compacted, homogenous earthfill structure utilizing silty sandy gravel and gravelly silty sand inorganic soils selectively borrowed from on site sources. The fill material wiil primarily consist of decomposed gneiss overburden from the ' mine pit. Where constructed directly on tailings, a geotextile filter fabric will ugderlie the raise fill. At each abutment, the raise will underlain by VLDPE geomembrane liner and a drainage layer as ' described in the Amendment. This liner was previously installed during Raise 1 construction and the associated disposal area expansion. Details of this construction are documented in the report titled "San Luis Project Tailings Disposal Area, Phase II, Raise 1 Final Construction Report" ' prepared by SRK dated May 16, 1994 and previously submitted to the State. The Technical Specifications for Raise 2 construction are included as Appendix A to this report. r u y 3-i ro~ect o.