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Memo to Erica Crosby 3 January 16, 2004 Duckworth Pit Setbacks and Ditch Seeoaee Permit No. M-2003-091 The permit application does not provide the easement width for Idaho Creek through the proposed permit area. For the most part, the setbacks described and illustrated above are adequate to assure the structural stability of the ditches and the other manmade facilities around the pit. However, the ten-foot setback from the Smith and Emmons Ditch easement line results in a setback distance that is less than two times the maximum 25-foot pit depth. This setback is not in accord with Applicant's engineering analysis provided in Exhibit S, and the DMG would not accept this setback distance without further analysis. The Operator must specify which of the various proposed setbacks will be the enforceable permit conditions for the operation of the Duckworth Pit. In selecting the setback distance requirements, the Operator should consider their rights to mine within any easements. If the Operator selects setback distances that indicate mining will take place within easements, proof of legal right of entry will be required. The Operator must further specify the angle at which the pit slope will be excavated as mining approaches a structure or a setback line, must specify landmarks from which setback distances will be measured, e.g., from the top of the ditch bank or from the ditch centerline, from a property or easement line or from the edge of the structure itself? And the Operator must specify how and when the setback lines will be located and marked. The permit application commits to a 10-foot mining setback from the west property line. The DMG has previously approved the installation of a slurry wall 23-feet further to the west of that same property line. The slurry wall approval was made under the auspices of reclamation permit M-1994-027 held by Aggregate Industries. This means that mining of the Duckworth Pit could occur as close as 33-feet to the location of the proposed slurry wall, as illustrated in the following cross section. Mined Face Approx. ' "'y"`y 25-feet Line Slurry Wall The proposed ten-foot setback from the west property line results in a setback from the slurry wall that is less than two times the maximum 25-foot pit depth. This setback is not in accord with Applicant's engineering analysis provided in Exhibit S, and the DMG would not accept this setback distance without further analysis. The DMG would accept a 30-foot setback for the west property line as being protective of the proposed slurry wall. The Ditch Company has provided DMG with written comments expressing concern with the potential for increased seepage losses from the Smith and Emmons Ditch during the dewatering and excavation ofthe Duckworth Pit. The DMG concurs with the Ditch Company's position that this is a legitimate