2009-01-09_REPORT - M2007044 - Laserfiche WebLink

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were all determined to be installed at the correct elevations and dimensions. See revised Pond Design Sheets I and 2 in Appendix A. I made three site visits during the construction season: August 21, October I and October 21, 2008. On the October 1 and October 21 visits, I observed the following pond related items: pond excavation, fill material, keyway construction, primary pipe installation, seep collars, fill compaction and stockpiling of topsoil and extra fill. I observed no issue which would compromise the design and long term functionality of the pond. In my opinion, as a professional engineer with over 30 years experience in pond design, fill compaction and slope stability, I believe the pond is well constructed and meets all requirements of sound engineering. The As Built Site Map dated December 2008 shows the pond and all other installed structures, which is attached to this report in Appendix C. B) Mine Ditch System As shown on Map C-6 of the approved permit, the initial site construction was to be based on the plan view titled Phase I Hydrology. It was determined that more room was needed for initial waste storage, therefore, the diversion on the east side of the disturbed area was moved further east, which is more representative of the location shown in the Phase 2 Hydrology view in Map C- 6. Based on the actual location, the flow capacity needed was determined from the existing hydrologic calculations for the Interim Diversion. The exact location of the As Built Interim Diversion is shown on the As Built Site Map of December 2008. Ditch cross sectional areas were checked and found to be adequate for the final design based on the Phase 2 Hydrology. However, in order that the diversion drain downhill to 5/10 Road, a cut of up to 7 feet was needed in the original ground to get through a natural mound in the terrain. Also, since this cut area is also located in the steep area, no rip rap lining was needed since the cut was made in rock. A picture enclosed in Appendix D shows the excavation that was made in this area. A small area of 0.23 acres immediately east of the diversion was stripped of vegetation and has been reseeded and mulched. Since this area cannot drain to the sediment pond, it will be handled as a small area exemption until the waste area is further expanded. This area has been controlled from erosion by silt fence along the downhill side of the area. The changes to the layout of the sediment pond and the mine stockpiles led to minor changes to the layout of the collection ditches. All collection ditches from the disturbed area are delivered to the twin set of 24" diameter CMP's located as shown on the As Built Map. The original plan for the Phase 1 Hydrology was based on 4.24 acres draining to the culverts with a peak flow of 13.28 cfs. The As Built Plan has 7.25 acres draining to the same set of culverts. The peak flow for this case is approximately 22.9 cfs. There is approximately 2.0 feet of height above the culverts as fill to determine the headwater depth under inlet control. Based on this information and the conservative case of the culvert projecting from the fill, the culvert capacity, as shown on the chart below, is 17 cfs each, or 34 cfs total, which is more than adequate. For the recommended Whirlwind Portal Area As Built Report 3