2002-12-12_REVISION - M2001085 (7)

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placed over each backfilled section. Fines, material passing #200 seive, will be taken from site overburden materials or will be imported, if necessary. Also during Phase 2 of mining activity, stockpiled material from the originally permitted mining area will be processed and/or transported offsite. Dewatering trenches from the processing area to a rinsewater lagoon, adjacent to processing equipment will be constructed, as necessary. Phase 2 activity will be completed in approximately 4 months. Phase 3 Following completion of the slurry wall, a dewatering sump will be excavated, to a depth approaching bedrock, in the northern portion of the mining area, as shown by the Mine Plan Map. Dewatering trenches from the mining areas to this sump will be constructed and maintained, as necessary, depending on rain and snowfall conditions. Groundwater, isolated within the mining area, will be pumped to the lake of the Henderson Water Ski Club, located immediately north of the mining area. As the mining area is dewatered, mining below the historic water table will begin in the southwest portion of the site, identified as Area 1 on the Mine Plan Map. Excavation walls will be maintained at a minimum slope of 2 to 1; and at the closest point, near the top of the slurry wall, mining will be setback at least 15 feet from the slurry wall. Mining will proceed in a counter clockwise direction and will be completed in Area 1 in approximately one year. Phase 4 During Phase 4, mining will continue in Area 2, in a counter clockwise direction. Excavation walls, which will be temporary, will be maintained at a minimum slope of 2 to 1. When adequate operating space is created, and concurrently with mining activity in Area 2, slopes in Area 1 will be backfilled to create reclaimed slopes of 3 to 1, and claystone bedrock will be ripped from the floor of the mine to create a clay liner on top of the slurry wall, as shown by the Reclamation Plan Map in Exhibit F. The Applicant will use overburden, characterized as alluvial/eolian clays, for initial backfill material and will use compacted claystone material to replace the temporary soil cover on top of the slurry wall. Compacted claystone material will also be used to complete the clay liner above the slurry wall and result in a 20 foot final bench around the mined area, as shown by the Reclamation Plan Map. The reports by Ground Engineering Consultants indicate that claystone bedrock generally falls within the Division's parameters for plasticity and gradation for liner material and demonstrates a hydraulic conductivity on the order of 1.4 x 10"7 cm/s, below the State Engineer's standard of 1 x 10"6 cm/s. Phase 4 activity is expected to take eighteen months for completion. Phase 5 Application to Amend -8- 124' Estates Partners DMG 112 Reclamation Permit No. M-2001-085 124`h Estates Sand and Gravel Mine Prepared by Scott Keen, December 2002 Henderson, Colorado