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Response to DRMS Michael Cunningham <br /> CEMEX Sandstone Quarry Division of Reclamation Mining and Safety <br /> since 2008. The groundwater data provided by CEMEX shows that the water level has not <br /> exceeded an elevation of 5260.7 feet. The proposed pit bottom will rest at approximately 5350 <br /> feet at its lowest elevation, which is well above the observed groundwater elevation. In addition, <br /> the slope has not experienced any groundwater seepage during the life of the mine and no <br /> pumping has been necessary in the pit floor. <br /> Engineering Analytics has shown the area of the potential water ponding that would develop in <br /> the pit based on a 100 year storm event if the outlet pipe were to become completely plugged. <br /> This area if shown on Figure 3. The volume of water in the pit from the 100 year storm would <br /> be 6.1 acre/ft based on calculations completed by Water and Earth Technologies. The deepest <br /> depth of water in the pit would approximately 7 feet. EA updated our slope stability analyses to <br /> conservatively reflect a water depth of 7 feet across the entire pit floor. The results of our slope <br /> stability analyses indicated that the slopes have a factor of safety of 2.2 for static failure and 2.0 <br /> pseudostatic failure. <br /> 5. DRMS Comment: "Please provide comment on how surface water control will be <br /> established around the highwall." <br /> EA Response: Since there are no drainage features above the crest of the highwall, surface flow <br /> will be allowed to sheet flow over the crest of the highwall. The drainage area above the crest is <br /> approximately 30 acres. It is EA's understanding that the outlet in the south east corner of the pit <br /> has been sized by others to handle the surface flow. <br /> 6. DRMS Comment: "Please comment on how overall long-term highwall performance and <br /> stability will be determined and monitored". <br /> EA Response: Annual visual monitoring of the pit slope face and crest will be completed. A <br /> photographic record of the entire slope will be performed. The visual monitoring will consist of <br /> documenting any new tension cracks along the pit crest and providing a report to be kept at the <br /> CEMEX office. <br /> 4.0 REFERENCES <br /> Braddock,W., Houston, R.,Colton, R., and Cole, J. (1988). Geologic Map of Lyons Quadrangle, <br /> Boulder County, Colorado. U.S.Department of the Interior Geological Survey. <br /> Engineering Analytics, Inc. (2014). Lyons Sandstone Quarry, Slope Stability Analysis. March, <br /> 19 <br /> Hoek, E. (2007). Rock Mass Properties. Practical Rock Engineering: chapter 11. <br /> https://www.rocscience.com/education/hoeks—corner. <br /> Hoek, E., Carranza-Torres, C., Corkum, B. (2002).Hoek-Brown Failure Criterion. <br /> June 30, 2014 1 Engineering Analytics,Inc. <br />