2002-12-12_REVISION - M2001085 (7)

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construction of the slurry wall and an excavation wall of less than 15 feet along the perimeter of the mining area. A minimum slope of 2 to 1 will be maintained on this temporary excavation wall. In Phase 1, mobile processing and washing equipment will be placed near to the center of the mining area. A temporary, overhead power line from 1201" Avenue (United Power) and a temporary, above ground water line from a hydrant on 1201h Avenue (South Adams County Water and Sanitation District) will be installed to provide power and water to the processing equipment. A standby generator will also be placed alongside processing equipment to supply electricity, if necessary. This equipment will be moved as little as possible during mining activity, and will be moved only to recover resources beneath it. In Phase 1, some unprocessed material from the originally permitted mining area will be moved by truck and stockpiled on the new mining area, as shown by the Mine Plan Map. The Applicant estimates that no more than 400,000 yards of material from the originally permitted area will be stockpiled at the new mining area. The purpose of this stockpiling activity will be to allow completion of mining and reclamation of the originally permitted area by the early summer of 2003. Phase 2 During Phase 2, a soil-bentonite slurry wall will be constructed and keyed into bedrock near the perimeter of the mining area, as shown by the Mine Plan Map. The purpose of the slurry wall will be to isolate the mining area from surrounding groundwater, so that mining activity has little or no impact on adjacent uses of shallow groundwater. The slurry wall will remain in place after mining and form, in part, the impermeable liner for the resulting water storage reservoir. As shown by the Mine Plan Map, the Applicant will construct the slurry wall from an elevation of approximately five feet above groundwater and key it into bedrock. It will be constructed in accordance with the Division's "Guide to Specification Preparation for Slurry Walls and Clay Liners as a Component of a Colorado Mined Land Reclamation Permit" (September 2000). The Applicant intends to construct the slurry wall between late fall and spring, when the Fulton Ditch is not flowing, and when there is minimal use of shallow groundwater in the area. A large (180,000 to 240,000 lb.), `super long reach' excavator, with an aggressive bucket to key into bedrock, will be used to dig the trench for placement of the slurry wall. A four to six percent bentonite slurry, prepared in a nearby mixing box, will be pumped into the trench, concurrently with digging, to provide stability within the trench. The large excavator will thus be digging trench and bringing up slurry material and placing it on the working bench, where a dozer or smaller excavator will be preparing the final backfill. Final backfill will include soil taken from the trench, a minimum of two percent bentonite, and twenty to forty percent fines. A small excavator will place the soil- bentonite backfill into the trench; and a noncompacted, temporary, soil cover will be Application to Amend -7- 124`h Estates Partners DMG 112 Reclamation Permit No. M-2001-085 124h Estates Sand and Gravel Mine Prepared by Scott Keen, December 2002 Henderson, Colorado