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40. Page 6 -10, Section 6.3.2 — The High Grade Mill Facility will hold, convey, contain, and/or transport <br />designated chemicals used in the extractive metallurgical process. Pursuant to Rule 6.4.21(10)(a), the <br />Applicant must provide design specifications certified by a licensed professional engineer for all <br />Environmental Protection Facilities intended for that purpose. There is not an engineer's stamp and signature <br />on the preliminary design summary presented in Appendix 10, Volume VI — Design Summary Squaw Gulch <br />High Grade Mill Facilities. Please have the responsible engineer from FL Smidth stamp and seal the last page <br />of the design summary that precedes the series of drawings in Appendix 10, Volume VI. (Note: Colorado <br />statutes require the certifying engineer to be licensed in Colorado). <br />RESPONSE. As requested, CC &V provides within Attachment 9 stamp and seal last pages of the design <br />summary that precedes the series of drawings in Appendix 10, Volume VI from the responsible engineer from <br />FL Smidth. <br />41. Page 7 -8, 1" paragraph — the "post - closure" pregnant solution storage area (PSSA) drains are to be drilled a <br />minimum of 10 feet into the diatreme (note: this is also discussed in the last paragraph on p. 7 -10). Based on <br />Figure 3 (Appendix 9) the drilled shafts under the PSSA originate approximately 180 horizontal feet outside <br />the diatreme. Please provide some discussion addressing: <br />a. The selection of a minimum 10 -foot penetration into the diatreme, <br />RESPONSE. CC &V selected 10 foot penetration into the Diatreme as a means to ensure water at closure of <br />the SGVLF that will be from the closure drain will be directed directly into the Diatreme. <br />b. How it will be verified that the drilled shafts are terminated the proposed minimum 10 feet into the <br />diatreme, and <br />RESPONSE: CC &V will use on -site CC &V geologist that are familiar with rock characteristic of the <br />Diatreme to insure 10 foot penetration into the Diatreme and that verification will be included as part of the <br />third party CQA report submitted to the Division for review following construction activities. <br />C. How an angle for the drilled shafts will be selected to ensure the hydraulic gradient of the shaft will <br />sufficiently compensate for the permeability of the material encountered in the first 180 horizontal feet <br />of the proposed shaft. <br />RESPONSE: AMEC is preparing supporting calculations to respond to this inquiry, and will provide an <br />answer by Friday, August 24, 2012. <br />42. Page 7 -9, last paragraph — There are some areas within the SGVLF footprint with 1H:1 V side slopes. How <br />does the Applicant intend to keep drain cover fill (DCF) stable on a 1H:1V slope after construction and prior <br />to ore loading? <br />RESPONSE: To address the 2H.•1 V slopes, AMEC has changed the design of the liner system outside of the <br />PSSA from an 80 -mil smooth LLDPE geomembrane to an 80 -mil double -sided textured LLDPE geomembrane <br />to improve the friction angle between the DCF and the liner, and to improve safety during construction. <br />Secondly, CC &V is proposing to phase the installation of the DCF based on the schedule of the advancement <br />of the ore. This will minimize the time the DCF is exposed to the elements and reduce the risk of future <br />sloughing. <br />43. Page 7 -10, 5h Para rg aph — A three -foot layer of structural fill (and possibly geogrid and/or geotextile) is <br />proposed to control differential settlement of the SGVLF over portions of the regraded SGOSA. Furthermore, <br />section 7.2.7.1 (reference pp.7 -15 — 16) states settlements will likely range from 2.4 to 29 inches. Please <br />substantiate how the liner can tolerate 29 inches of differential settlement. <br />RESPONSE: The performance of the liner system on the SGVLF foundation was analyzed using a numerical <br />code, Plaxis, as detailed in Appendix C6, using material properties that are considered typical for the CC &V <br />area (based on experience at the site). The results of the model indicate that the amount of anticipated <br />settlement varies between 2.4 to 29 inches. It is important to note that these settlement values are not <br />differential settlement, but total vertical settlement. Differential settlement is addressed in Appendix B.6 in the <br />form of shear strain, which directly relates to the strain the geomembrane will be exposed to under load. As <br />presented, the maximum shear strain (differential) is less than 4 percent (elongation). For reference, the yield <br />strain for High Density Polyethylene (HDPE) is 12 % while LLDPE does not have a definite yield point and <br />has been observed to strain 140% without failure (Peggs, Schmucker, and Carey, 2005). In addition, Touze- <br />