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provide for additional storage capacity within the South Platte River floodplain, thereby <br />reducing downstream flood risk. <br />Specific engineering stability analyses for specific proposed excavation and <br />reclamation slopes are not included because shallow excavations less than approximately <br />25 ft deep are planned at conventional excavation and reclamation backfill slope angles <br />of 1:1 (H:V) and 3:1 to 2:1, respectively, proven to be effective and stable during twenty <br />years of mining at the site to date. A general global stability analysis was performed <br />previously for existing Ready Mixed Pit No. 1 (M-1985-017) along its southern <br />boundary, which abuts "Tower Lake". This analysis was submitted to DRMS in a letter <br />dated October 2007 and is discussed further below and attached. The analysis was used <br />to confirm that previously assumed reasonable geotechnical setbacks of 25 ft were indeed <br />appropriate for the sensitive third party structures to avoid off-site impacts. Reasonable <br />mining offsets have been established from typical property boundaries where no <br />structures exist. Conservative setbacks of 50 ft (two times the analyzed case) have been <br />established from the edges of the McCann Ditch and Third Creek, and from Brighton <br />Road to protect these structures. The minimum 25 ft setback is established from the <br />Spier property inholding that is surrounded by proposed new mining on three of four <br />sides, but this includes over 70 ft of separation from any structures on the property, <br />except for the perimeter fencing. <br />Simple Spencer "method of slices" stability analysis of a greater than 25 ft deep, 1:1 <br />excavation slope with a minimum offset distance from the crest of slope to a property <br />boundary resulted in a Safety Factor of greater than 1.3. Further, existing temporary <br />mine slopes at 1:1 or steeper at the site have been observed to be stable over long periods <br />of time and are considered more of a safety hazard for activity at the toe of slope than <br />globally unstable to beyond the setback distances employed. Typical hard rock mining <br />slope design is typically done at a much less conservative Safety Factors of <br />approximately 1.0 to 1.1, where limited failures are considered necessary (to maximize <br />extraction) and acceptable (due to controlled access and lack of public safety concerns at <br />a private facility). <br />Off-site impacts due to failure of geologic structures or constructed earthen facilities <br />are not anticipated. Such structures will only include the reclaimed earthen slopes <br />68