2014-05-15_REVISION - M1977361 - Laserfiche WebLink

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AVCOLORADO Division of Reclamation, Mining and Safety Department of Natural Resources 1313 Sherman Street, Room 215 Denver, CO 80203 May 15, 2014 To: Michael Cunningham, DRMS From: TC Wait, DRMS Re: Review of Stability Exhibit, Cemex Sandstone Quarry M- 1977 -361 Per your request, I have reviewed the Stability Exhibit dated March 21, 2014 by Engineering Analytics, Inc. that was submitted to DRMS as part of the March 2014 Amendment for the Cemex Sandstone Quarry in Lyons, CO. The amendment is to update the mining and reclamation plans, clarify the affected land boundary, and update the post- mining land use. The Stability Exhibit analyses the final grading plan for the west side highwall, which will be between 60 and 120 feet high and sloped at a 1v:0.5h grade. A fence and 10v:15h foot bench at the top of the highwall will be placed for safety. The comments below should be considered as part of the adequacy response for DRMS. The slope stability evaluation is based on one cross section through the highwall, using generalized material strength data from a national reference. The quarry is located in the Plainview Sandstone member of the South Platte Formation east of Lyons. This sandstone is noted as being thinly bedded carbonaceous fine grained sandstone to a non - carbonaceous mudstone. The geologic quadrangle (USGS GQ -1629) shows a north -south trending fault location just west of the quarry. Based on the bedding and likely jointing and possible presence of a shear zone, it seems that the strength data used, while within the general range of global sandstone materials, may not be a conservative estimate for the conditions at this specific site. • Please give rationale for the use of the strength parameters used, and address bedding and jointing that may be present in the rockmass. Figures 4 and 5 show the cross section A -A' that was analyzed for stability. The cross section for Figures 4 and 5 is approximately 2100 feet long and does not match the cross section shown on figure 3 (approximately 120 feet long). • Please revise Figure 3 to reflect the entire cross section that was analyzed. • Please indicate on Figures 4 and 5 where the affected area boundary lies. The stability evaluation does not make mention of the depth to water and assumes dry conditions in the slope. There is a swale that drains toward the southern part of oFco� J0 1313 Sherman Street, Room 215, Denver, CO 80203 P 303.866.3567 F 303.832.8106 http: / /mining.state.co.us John W. Hickenlooper, Governor I Mike King, Executive Director I Virginia Brannon, Director