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GEOTECHNICAL STABILITY EXHIBIT <br />This information is presented to address the plan to mine within <br />200 feet of the structures listed in Exhibit S. This analysis is <br />presented in leu of obtaining agreements from the numerous owners <br />of the noted structures. McAtee Construction Company, has <br />committed to mining slope adjacent to structures at their final <br />slope rate. Under the approved plan this would be 3:1 from the <br />original land surface to the mine floor. This leaves a stable <br />slope of undisturbed gravel adjacent to the structure. <br />To do this Suburban will have any buried structures (i.e., <br />communication lines, etc.) located by the Colorado Call One <br />locate service and then apply a 25 foot setback from the markers. <br />For above ground structures the setback will be staked prior to <br />mining in those areas. For example, as mining begins near a <br />fence the 10 foot setback will be staked. A second line will be <br />staked from this setback line a distance equal to the mine depth <br />time 3. This establishes the toe of the slope line. This leaves <br />a slope envelope where mining would be done to create the slopes <br />without backfilling. The three cross-sections on Figure 1 show <br />what is explained above. In Section A, a vertical face is being <br />excavated as mining approaches the structure (gasline) and the <br />slope distances have been staked. In Section B the mining has <br />shifted from working a vertical face and is transitioning into <br />the slope mining method. In Section C the final slopes are <br />completed. <br />This method of creating slopes leaves a stable slope requir- <br />ing no backfilling or other work once complete. Over the years <br />we have found that the natural angle of repose for most gravel is <br />approximately 2:1 so it would be possible to mine within 80 feet <br />of a structure with a vertical face and be assured that no damage <br />would occur to the structure by a slope failure. Instead and for <br />safety reasons McAtee Construction company has chosen to use the <br />method described above. This will entail more work on their part <br />but when done will have created stable slope that protects the <br />structures. <br />29 <br />