2012-07-03_HYDROLOGY - M1977023 - Laserfiche WebLink

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Mr. Peter Foster, P.E. Page 2 June 28, 2012 Figure 4. The credits for the pre -1981 area are tied to the location identified on Figure 4 and may not be re- allocated to other areas of ground water exposure within the gravel pit permit boundary. 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, you have indicated that a bond has been obtained for $155,814 through the Division of Reclamation, Mining, and Safety ( "DRMS "). This bond is for reclamation requirements under the current mining permit but may not be sufficient for lining or backfilling the pit to ensure that depletions from groundwater evaporation do not occur in the unforeseen event, or events, that would lead to the abandonment of the Pit. Future SWSPs for this site will not authorize any expansion of the area of exposed ground water until the Applicant provides documentation that a bond sufficient to cover lining or backfilling of the pit has been obtained. Depletions You have provided a monthly breakdown of the annual depletions totaling 10.37 acre - feet of evaporative Toss from 17.2 acres of exposed surface area, 0.7 acre -feet of water lost with mined product associated with 24,000 tons of aggregate, and 1.30 acre -feet of water used for dust control. Consumptive use at the pit totals 12.37 acre -feet per year. Computation of evaporation under this plan was reduced during the ice covered period. You have assumed the ice covered period to occur during the months of November, December, January, February and March based on the average monthly temperatures of 27.9 °F for November, 13.45 °F for December, 9.15 °F for January, 14.6 °F for February and 26.6 °F for March. Temperature data were obtained from the Gunnison SW weather station. The ice covered periods may be used to reduce the amount of evaporative losses that need to be replaced; however, for the purpose of this SWSP, the Applicant shall replace the net evaporation depletions from the exposed ground water surface area that may occur during the assumed ice covered period (November, December, January, February and March) for any time that the pit is not completely covered by ice. Computation of evaporation under this plan was also reduced by the dry-up credits from the existing pits (17.2 acres post -1981) formerly irrigated by the Seventy -Five Ditch. The dry-up calculation for the inundated areas is shown in Table 2A (attached). Using the State Consumptive Use model with the Upper Gunnison High Elevation Calibration Coefficient with no effective precipitation, the Unit Potential Consumptive Use was determined to be 2.21 acre -feet per acre. Thus the dry-up credits for the irrigated area under the pits equal 38.08 acre -feet (17.2x2.21).