2013-07-03_REVISION - M1985112 (3)

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M -1985-112 — Loloff Construction, Inc. — Loloff Pit — Technical Revision Request No. 1 July 3, 2013 IM Earth Moving Equipment Dozers, loaders, scrapers, excavators, and compactors will be used for mining and earth moving operations. Miscellaneous Equipment Dewatering pumps, electrical trailer, generator trailer, small portable generators and watering trucks will be used as needed. As mining progresses, topsoil and overburden will be stripped with scrapers to expose the aggregate product below. All soil and overburden material will be used on -site for reclamation; so long -term stockpiling of these materials is not anticipated. Overburden stockpiles will be located within the proposed mining area and placed so that they do not impede potential floodwaters. The stockpiles will be placed outside the floodplain where possible. Mining of the aggregate will progress down to the underlying bedrock. Since reclamation will occur concurrently with mining, it is not anticipated that bedrock material will be stockpiled long -term prior to use if it is used in the reclamation slopes. During mining and at the completion of reclamation, the mining face will have a 3HAV slope. The aggregate material will be temporarily stockpiled near the portable plant site outside the floodplain where possible until mining has progressed where stockpiles as well as the portable plant site can be placed below the existing grade within the mining boundary. Loloff Construction, Inc. recently received an inspection report from you regarding the dewatering of the Loloff Pit and we addressed the complaint from Mr. and Mrs. Lary Monroe. Since that time we have included calculations to estimate the effects of the dewatering. The methodology presented in "Groundwater and Wells - Second Edition" by Fletcher G. Driscoll, for wells in an unconfined aquifer that are pumped at a constant rate and have reached equilibrium conditions, was used to estimate the limits of the cone of depression /radius of influence (Equation 9.1). Attached are excerpts of this reference that give the details of the methodology used and a figure showing the typical hydraulic conductivity values for soils of this type in an unconfined aquifer (Figure 5.14). The cone of depression /radius of influence from the mining limits has been estimated using the known pumping rate for the mining dewatering activities, the known depth of dewatering from the normal groundwater level, an estimated radius of the pit that the mining perimeter of those phases represents, and an estimated value of hydraulic conductivity for the type of soils found in this aquifer. The cone of depression /radius of influence was estimated for two conditions: Full depth dewatering of the pit with no aquifer recharge and the following assumptions: A constant dewatering pumping rate = 3,000 gpm Dewatering depth = 37 ft Radius of the pit = 600 ft A hydraulic conductivity value of 1000 gpd /sq -ft was assumed for the soil types found on this site. The inflow to the pit through the mining slopes was assumed to be supplied solely by the groundwater present in the aquifer, hence the full hydraulic conductivity value of 1000 gpd /sq -ft was used. v M 305 Denver Avenue - Suite D • Fort Lupton CO 80621 • Ph: 303 - 857 -6222 • Fax: 303 - 857 -6224