2013-05-09_HYDROLOGY - M2009048 - Laserfiche WebLink

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Mr. Ivan Geer May 3, 2013 Gunnison River Gravel Pit Nos. 1 & 5 Substitute Water Supply Plan Page 3 of 7 water will be consumed as product moisture on an annual basis at Pit No. 1 (production rate of 70,000 tons per year), and approximately 2.80 acre feet of water will be consumed as product moisture on an annual basis at Pit No. 5 (production rate of 250,000 tons per year). The anticipated net depletions for the first year of operation for Pit No. 1 total 3.43 acre -feet, which consists of 1.16 acre -feet of evaporative losses from 1.2 acres of exposed ground water, 1.52 acre -feet used for dust suppression, and 0.75 acre -feet for moisture retained in the mined product. The anticipated net depletions for the second year of operation for Pit No. 1 total 5.83 acre -feet, which consists of 3.56 acre -feet of evaporative losses from 2.4 acres of exposed ground water, 1.52 acre -feet used for dust suppression, and 0.75 acre -feet for moisture retained in the mined product. Evaporation amounts are based on the exposure of 0.1 acres of ground water for the mining period of June through August, and the exposure for the non mining months of September through May of 1.2 acres (year 1) and 2.4 acres (year 2). Anticipated net depletions for the first year of operation (water only projected to be used September through December for the first year) for Pit No. 5 total 5.02 acre -feet, which consists of 0.16 acre -feet of evaporative losses from 0.2 acres of exposed ground water, 3.74 acre -feet used for dust suppression, and 1.12 acre -feet for moisture retained in the mined product. The anticipated net depletions for the second year of operation for Pit No. 5 total 12.67 acre -feet, which consists of 0.77 acre -feet of evaporative losses from 0.2 acres of exposed ground water, 9.1 acre - feet used for dust suppression, and 2.80 acre -feet for moisture retained in the mined product. Evaporation amounts are based on the exposure of 0.2 acres of ground water for the entire mining period. The monthly distribution of consumptive losses for Pit Nos. 1 & 5 is shown on the attached Tables 2, 3, and 4. The timing of depletions to the Gunnison River from the consumptive uses described in this SWSP was estimated using Glover methodology and the following input parameters: Distance from the centroid of the exposed ground water pond to the river: 283 feet (Pit No. 1) and 303 feet (Pit No. 5); distance from the no -flow boundary to the river: 600 feet (Pit Nos. 1 and 5); transmissivity: 38,106 gpd /ft. (Pit No. 1) and 40,223 gpd /ft. (Pit No. 5), and specific yield: 0.2 (Pit Nos. 1 and 5). Lagged depletions are shown on the attached Tables 3 and 4. Dewatering will be accomplished by pumping water from each excavation at a maximum rate of 650 gallons per minute (gpm). A portion of the water generated during dewatering will be used to control fugitive dust on site roads and at the crusher facilities. The remainder of the water generated during dewatering will be discharged directly to the Gunnison River adjacent to each pit. Upon completion of operations at Pit No. 1 each year and at Pit No. 5 at the end of its three year mine life, the excavations will be filled by pumping water from the Gunnison River to each excavation at a rate sufficient to replace the volume of water in the first or intermittent fill (up to 850 gpm) within one month. Refilling of the dewatered mine sites is only proposed to occur at times that (1) there are no active calls on the river placed by a senior downstream water user, and based on discussions with the division engineer and water commissioner, there is no anticipation of a downstream call during the refilling period, or (2) sufficient excess replacement water, purchased as proposed in this SWSP, is available to cover potential out -of- priority depletions. REPLACEMENT WATER Replacement water for this SWSP will be provided by releases from Blue Mesa Reservoir. GJPS has obtained a contract with the U.S. Bureau of Reclamation for Blue Mesa Reservoir water