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<br />Gold Hill Mill 9 March 27. 1995 <br />tailing and to provide the necessary freeboard: <br />(a) If upstream raises are to be utilized, COM, Inc. will need to <br />characterize the suitability of existing tailing as a foundation <br />material. Include an analysis of in-situ density, in-place tailing <br />stratigraphy, grain size, plasticity, shear strength, pore pressures <br />(this can be determined using a cone penetrometer, or other types of <br />testing), consolidation or settlement potential, and liquefaction <br />potential under seismic loading. <br />(b) Specify source locations and characterize the material that the <br />raise is to be constructed from in terms of the Unified Soil <br />Classification System. The shear strength of the borrow material <br />should also be determined. Raise construction specifications will <br />have to be developed and approved by the Division in terms of <br />acceptable grain size range for the dam raise fill, plasticity of <br />the fill, lift thickness and preparation, as well as moisture <br />content and compaction. Quality assurance and quality control must <br />be incorporated into the specifications, including a description of <br />the types and frequencies of testing to be conducted to verify that <br />the specifications are met. <br />(c) Describe, using cross-sections, the final and all interim <br />embankment configurations. <br />(d) Describe how the liner will be extended on the upstream face of <br />the dam as it is raised, and how the liner will be extended at the <br />back and on the sides of the impoundment. Include liner <br />installation and subgrade preparation specifications. The <br />specifications must include the frequency and types of quality <br />assurance/quality control tests to be conducted during liner <br />installation. The Division will further require that quality <br />control testing be conducted on samples of existing liner materials <br />that will remain in the impoundment and have been exposed to the <br />elements for long periods. This testing is needed to assure that <br />the liner has not been degraded by ultra-violet radiation. Describe <br />how the decant system will be extended as the embankment is raised <br />and the impoundment enlarged. <br />(e) Provide an analysis of bulk embankment stability for all stages <br />of the designed impoundment life. In order to complete such an <br />analysis, you will need to determine the shear strength of all <br />impoundment materials, including interfacial shearing resistance for <br />critical liner-soil interfaces. The embankment must be stable with <br />a minimum safety factor of 1.5 for the static case, and must be <br />stable with a minimum safety greater than 1.0 under maximum <br />anticipated seismic shaking (maximum credible earthquake). <br />(f) Describe tailing impoundment operating parameters, particularly <br />in terms of tailing deposition protocol and water management. <br />