Laserfiche WebLink
CG� <br />June 28, 2011 <br />Division of Reclamation, Mining and Safety (Division) <br />1313 Sherman Street, Room 215 <br />Denver, Colorado 80203 <br />Attn: Mr. Michael Cunningham <br />RE: Varra Great Western Sugar Project <br />Response to Division Letter <br />DRMS File No. M- 2010 -049 — Slope Stability Review <br />CGRS No. 1- 135- 12539aa <br />Dear Mr. Cunningham: <br />The following provides responses to Mr. Cazier's comments of June 17, 2011. <br />Item 1— This issue is addressed by Varra Companies. <br />ENVIRONMENTAL OINU© <br />Item 2(b) — This is a confusing response and appears that we are being asked to justify why we <br />used field or laboratory measured values instead of table values. Varra performed direct shear <br />testing on sand deposits at the Durham facility, which is adjacent to the proposed mine. The <br />testing results are attached. A review of the data shows that the strength properties are much <br />greater than those presented in the March 2003 table presented by the Division. Penetration <br />resistance data also indicate strength values very close to those presented by Terracon for the <br />Great Western Sugar site. <br />We ran simulations using the table value data for the upper two soil profiles and strength <br />properties for the lower three profiles as reported by Terracon. A safety factor of greater than <br />1.2 was calculated for this scenario. We also ran simulations using the table values for all soil <br />profiles and obtained a safety factor of slightly greater than 1. Plates depicting the simulations <br />are also presented as an attachment to this letter. <br />Item 6 — Our analysis using the table values presented by the Division indicates a safety factor of <br />greater than one. The Divisions memo, relied upon by the Division, clearly states that the table <br />values represent the worst case for critical structures and "any safety factor in excess of one <br />should be protective of critical structures." We contend that additional studies are not <br />warranted for the existing mine plan. <br />Varra Companies conducted a geotechnical investigation, by a respected contractor, so that its <br />slope failure analysis would reflect actual conditions. The Division's response appears to ignore <br />field conditions and even contradicts its own recommendations. If the Division conducts its own <br />analysis using the best available data and still concludes the FoS values are insufficient we agree <br />to further analysis. <br />P.O. Box 1489 Fort Collins, CO 80522 T 800 - 288 -2657 F 970 - 493 -7986 www.cgrs.com <br />1 <br />