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 2 of 7 ponds with up to 3.6 acres of ground water exposed in Pit No. 1 and up to 6.8 acres of ground water exposed in Pit No. 5. Both pits will be dewatered during pit operations. At Pit No. 1, dewatering is proposed to be performed from June through August; at Pit No. 5, dewatering is proposed to continue throughout the life of the mining operation. In accordance with the letter dated April 30, 2010 (copy attached) from the Colorado Division of Reclamation, Mining, and Safety ( "DRMS "), all sand and gravel mining operators must comply with the requirements of the Colorado Reclamation Act and the Mineral Rules and Regulations for the protection of water resources. The April 30, 2010 letter from DRMS requires that you provide information to DRMS to demonstrate you can replace long term injurious stream depletions that result from mining related exposure of ground water. In accordance with approach nos. 1 and 3, a bond has been obtained for $88,767.00 through the Division of Reclamation, Mining, and Safety ( "DRMS ") to assure that depletions from groundwater evaporation do not occur in the unforeseen event, or events, that would lead to the abandonment of the Pit. Depletions Depletions at Pit Nos. 1 and 5 will occur as a result of evaporation from exposed ground water, dust suppression, water removed with the mined product, dewatering, and water filling the gravel pit as a result of material removal. Net evaporative depletions were calculated using a gross annual evaporation of 55 inches from the exposed water surface, and an effective precipitation amount of 6.2 inches. Based on monthly average temperatures reported for the Grand Junction 6 ESE weather station, you have estimated ice cover will occur on the ponds during the months of December and January; therefore no evaporative consumptive use was estimated for those months. For the purposes of this SWSP, the Applicant shall replace the net evaporative depletions from the exposed ground water surface area that may occur during the assumed ice cover period (December and January) for any time that the pits are not completely covered by ice. Net pond evaporation was calculated to be 46.25 inches per year (3.85 feet per year) as shown on the attached Table 1. Ground water will be used for dust suppression on the haul roads at the gravel pit sites and for dust suppression purposes for the rock crusher operations. At Pit No. 1, you have estimated 0.34 acre -feet of water will be used per month for the three -month operating period (typically June through August) for dust suppression on the haul roads, and 0.5 acre -foot of water will be used during the month of July for dust suppression purposes at the rock crusher operation. At Pit No. 5, you have estimated 0.81 acre -feet of water will be used per month for the ten -month operating period (typically January through June and September through December) for dust suppression on the haul roads, and 0.5 acre -foot of water will be used during the months of March and September for dust suppression purposes at the rock crusher operation. The amount of water retained in the material removed from each pit was calculated using a value of 2 percent (by weight) for all sand /gravel mined below the water table because material removed from the pits will not be washed and each pit will be in a dewatered state when material is mined below the groundwater table. It is estimated that 72 percent of the sand and gravel deposit will be excavated below the water table at Pit No. 1, and 76 percent of the sand and gravel deposit will be excavated below the water table at Pit No. 5. Accordingly, approximately 0.75 acre feet of