2011-01-10_HYDROLOGY - M2001022 - Laserfiche WebLink

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Ms. Cristyn R. Radabaugh Page 2 of 6 Green/Croissant Pit, M-2001-022 January 10, 2011 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. Since an application for approval of a permanent plan for augmentation was filed in case no. 09CW106 the DRMS letter's approach no. 2 is satisfied. Additionally, according to the SWSP request, up to 96 acre-feet of water is available through a lease with the City of Loveland to replace depletions from ground water evaporation in the event of abandonment of the Pit. Also, in accordance with approach nos.1 and 3, you have indicated that a bond has been obtained for $350,400 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 Net evaporative depletions were calculated using a gross annual evaporation of 40 inches from the exposed water surface, with a credit of 9.78 inches for effective precipitation. No credit was claimed for ice cover periods. According to the monthly breakdown you provided, 26.70 acres of ground water will be exposed to the atmosphere from January through March 2011, and 26.80 acres of ground water will be exposed to the atmosphere for the remainder of this plan period (April 2011 - December 2012). The net depletion of ground water due to evaporation was calculated to be 67.51 acre-feet for 2011 and 67.54 acre-feet for 2012. Operational losses at the site are anticipated to be the same for 2011 and 2012. The material mined at the Green/Croissant Pit will be below the ground water table and will have a moisture content of 4% by weight. The estimated annual aggregate production is 100,000 tons per year, resulting in 2.95 acre-feet of water retained in the mined product. The operator has estimated that 7.06 acre-feet of water will be required for dust suppression each year. The estimated annual concrete production is 200,000 cubic yards per year, resulting in an annual consumptive use of 18.41 acre-feet of water, based on 30 gallons of water consumed per cubic yard of concrete. Total annual operational losses were calculated to be 28.42 acre-feet for each year. The Green/Croissant Pit is located more than 100 feet from the Big Thompson River, therefore depletions to the river are not assumed to be instantaneous. The IDS AWAS stream depletion model was used to determine the lagged depletions to the Big Thompson River. The following parameters were used in the model: transmissivity (T) = 50,000 gallons per day per foot, specific yield (SY) = 0.2, the distance from the Big Thompson River to the edge of the alluvium = 2,910 feet, and the distance from the centroid of the exposed surface water areas to the Big Thompson River is approximately 1,450 feet. Lagged depletions are estimated to total 95.92 acre-feet for 2011 and 95.95 acre-feet for 2012. Cell 4 will be dewatered during active mining, which is anticipated to begin in May 2011 and continue through December 2012. Actual dewatering will occur at a rate between 50 and