2002-12-12_REVISION - M2001085 (7)

Home Browse Search

I Exhibit D - Mining Plan Overview The Applicant intends to recover approximately two million yards of sand and gravel resources, over a five year period, from an area of approximately 38.3 acres. Soil borings show the mining area to have overburden of three to six feet of native clay soils, underlain by native sands and gravels, which are underlain in turn by interbedded claystone and sandstone bedrock at depths of 25 to 64 feet. Before excavation occurs below the water table, a soil-bentonite slurry wall will be constructed near the perimeter of the mining area to isolate it from surrounding groundwater. Dry mining methods will be employed; and recovered material will be transported directly from the site, or it will be processed and washed before being hauled offsite. Hours of operation will be limited from 6 am through 7 pm; and the Applicant expects that a maximum of 200 trucks per day will access the site during periods of peak activity. Excavation walls will be reclaimed to slopes of 3:1, and claystone material, ripped from bedrock, will be added on top of the slurry wall to provide an impermeable liner for the reclaimed use of water storage. Attachment l of these application materials contains a report of November 8 and a supplemental letter report of November 27, 2002, both prepared by Ground Engineering Consultants (Ground) These reports provide a summary of soil conditions for the mining area and have been used by the Applicant to develop the Mining Plan and to define mining setbacks that will assure stability of structures within 200 feet of the mining area (Exhibit S). Mining Sequence After removal of topsoil and overburden and the placement of a mobile processing plant near the center of the mining area, initial mining activity will be accomplished with scrapers and loaders to recover sand and gravel resources over the entire mining area to an elevation approximately 5 feet above the water table. The resulting platform will allow construction of a soil-bentonite slurry wall, keyed into bedrock, around the perimeter of the mining area, to isolate the mining area from surrounding groundwater. During early stages of mining, some material from the previously permitted area of the 124th Estates Sand and Gravel Mine will also be stockpiled in this new mining area. The Applicant expects that up to 400,000 cubic yards of this material could be stockpiled at one time, as shown by Exhibit C-1. After completion of the slurry wall, a dewatering pit will be excavated along the north boundary of the site, and water contained within the isolated mining area will be pumped into the adjacent pond of the Henderson Water Ski Club. Mining activity below the historic water table, to bedrock, will begin in the southwest portion of the mine. Subsequent stages of site activity will include the completion of mining, generally in a counter clockwise direction around the mining area. Reclamation will begin in the Application to Amend -5- 124'h Estates Partners DMG 1 12 Reclamation Permit No. M-2001-085 120 Estates Sand and Gravel Mine \ Prepared by Scott Keen, December 2002 Henderson, Colorado _t