2011-03-14_HYDROLOGY - M2009048 - Laserfiche WebLink

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n Mr. William G. Merrill March 10, 2011 Gunnison River Gravel Pit Nos. 1 & 5 Substitute Water Supply Plan Page 2 of 7 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. The DRMS letter identifies four approaches to satisfy this requirement and requests the operator provide this information to DRMS by April 30, 2011. It is our understanding that a financial warranty is proposed to be utilized for Pits Nos. 1 and 5 to comply with this requirement. Please confirm by April 30, 2011 if this is correct, or if another approach will be utilized. If this requested information is not provided to the Division of Water Resources, any future SWSP may limit the mining operation so that additional ground water cannot be exposed, beyond that specified in this SWSP. 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 water will be consumed as product moisture on an annual basis at Pit No. 1 (production rate of