2017-11-17_HYDROLOGY - M1997054 - Laserfiche WebLink

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Mr. Stephen Buechner, P.E. November 17, 2017 Page 2 of 6 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 $1,174,724 through DRMS to assure that depletions from groundwater evaporation do not occur in the unforeseen event, or events, which would lead to the abandonment of the Pit. In addition, Front Range Aggregates owns and has dedicated five shares of Twin Lakes Reservoir and Canal Company to cover these potential long term depletions. Front Range Aggregates must continue to commit those shares to this plan until such time as the State Engineer authorizes the release of this commitment. DEPLETIONS The depletions that result from the mining operation over the period of this SWSP include evaporation from exposed ground water, dust suppression, dewatering, and water lost with the mined product. Evaporation losses will result from the exposure of ground water in the settling ponds, a gravel washing pond, dewatering trenches and two small sumps. The maximum exposed water surface area during this SWSP period will be approximately 4.0 acres. The 4.0 acres of exposed surface area, shown on the attached Figure 2, will consist of 3.4 acres in the settling ponds and the gravel washing pond, 0.4 acres in a small sump, and 0.2 acres in the dewatering trenches. Gross annual evaporation at the gravel pit location is estimated to be 46.0 inches per year and the monthly distribution is as depicted on the attached Table 1. Net evaporation is defined as gross evaporation less the consumptive use of water by vegetation that naturally occurred at the site prior to construction of the pit. The historical consumptive use was assumed to be equal to the effective precipitation, which was estimated as 70% of the 12.51 inches of average annual precipitation based on data from the Cañon City weather station over the period 1893 through 2016. The net evaporation for the exposed water surface is 37.32 inches per year with a monthly distribution as shown on the attached Table 1. The total annual stream depletion resulting from the exposure of groundwater is estimated to be 11.29 acre-feet. Computation of evaporation under this SWSP was also reduced during the ice covered period. You have assumed the ice covered period will occur during the months of December, January, and February based on the Cañon City weather station average temperatures of 22.5°F for December, 26.23°F for January, and 24.13°F for February. 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 (the months of December, January, and February) for any time that the exposed ground water in the pit is not completely covered by ice. Computation of the net evaporation during any time that the pond is not completely covered by ice shall be determined as the pro-rata amount of the monthly gross evaporation rate distribution amount identified in the State Engineer’s General Guidelines for Substitute Supply Plans for Sand and Gravel Pits, subtracting the pro-rata amount of the effective precipitation for that period. You have provided a monthly breakdown of the depletions under this SWSP on the attached Table 2, which includes 11.29 acre-feet of net evaporative loss, 15.03 acre-feet of water lost in product, and 9.20 acre-feet for on-site dust control, for a total consumptive use of 35.52 acre-feet. The Applicant anticipates that 570,400 tons of aggregate will be mined at the site