2016-12-13_HYDROLOGY - M1997054 - Laserfiche WebLink

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Mr. Stephen Buechner, P.E. December 8, 2016 Page 2 of 6 occur in the unforeseen event, or events, that 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 shared 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 the SWSP period will be approximately 7.0 acres in October 2016, 5.0 _ - -acres in November 2016, and 4.0 acres the remainder of the SWSP. The 4.0 acres of exposed surface area for the majority SWSP period will consist of 3.4 acres in the settling ponds and the gravel washing pond, 0.4 acres in the two small sumps 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 based on the data from the Canon City weather station. The net evaporation for the exposed water surface is 37.2 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 13.19 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 Canon 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 13.19 acre-feet of net evaporative loss, 13.66 acre-feet of water lost in product, and 8.88 acre-feet for on-site dust control, for a total consumptive use of 35.73 acre-feet. The Applicant anticipates that 540,700 tons of aggregate will be mined at the site during this SWSP period, of which 387,500 tons will be washed material and 153,200 tons will be unwashed material. The washed material will be charged a depletion of 4 percent by weight of the material, and the unwashed material will be charged a depletion of 2 percent by weight of the material. The IDS Alluvial Water Accounting System ("AWAS") stream depletion model was used to determine the tagged depletions from dewatering, evaporation and operational losses to the Arkansas River. The aquifer characteristics used in the model are: transmissivity (T) = 55,000 gallons per day per foot and specific yield (SY) - 0.2, the distance of the exposed ground water to the stream = 1,400 Office of the State Engineer eti��'$ 1313 Sherman Street,Room 821,Denver,CO 80203 P 303.866.3581 �y( www.water.statexo.us `�*�\ ' �a76 f