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Harley Pit I, MLRB•ile 8 M-86-147 • Adequacy response continued Exhibit B (4) cont. very desireable for making asphalt. The lower strata is a clean sand and gravel that is good for concrete. Depending on the amount and demands for each material type it may be necessary to create two benches (excavation areas) since they would be mined at the same time. These benches would only be present during mining. The benches will be removed and the entire face sloped at 2h to lv at reclamation. The typical bench cross-section will better show what we foresee but the excavation areas may not be adjacent to each other as shown. a. Our best guess would be 100 feet wide. b. Access is from above, the elevation of the entrance is approximately that of the upper level of the mine. An interior pit road will be constructed into the first bench once it is opened. c. Enough material will be left so that regrading will be a cut/fill type of operation. 5) The side slopes will be native sand and gravel. This is a rather large deposit of Rocky Flats Alluvium material that extends beyond the permit boundary. Sterling will only be cutting into that deposit. As far as structural properties go, the side slopes will be in-situ material and should be as stable as undisturbed slopes would be. Please refer to the attached cross-section for a pictorial explanation of the geological setting. 6) That is correct. This material is a very porus sand and gravel and any water that might collect would tend to filter into the surrounding slopes or flow along the top of the shale into the surrounding terrace deposit. 7) Slopes surrounding the pit, ones that will not be continually disturbed will be graded accordingly and seeded with the approved seed mixture. We donot expect a problem with erosion on the site. The average annual rainfall is 14.7" an average of 1.23' per month, described previously the material is inherently absorbent. The source from this information is Climatology report 77-1, a Dept. of Atmospheric Science, CSU. 8) Since any water falling on the site will be directed into the mined area we may have to construct a small temporary settling pond from which it will either filter thru the terrace material or evaporate leaving the sediment material on site. It is entirely possible that no runoff will be encountered during the life of this Pit. Until the pit is opened the exact location of this pond will be unknown. 2