2017-06-20_HYDROLOGY - M2016080 - Laserfiche WebLink

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Trout Valley Ranch SWSP June 19, 2017 Plan ID 5900 Page 2 of 7 Depletions The Applicant proposes to excavate a small ground water pond, known as the “Freshwater Pond”, to supply water for mining operations at the site. The material excavated from below the ground water table will create a ground water depletion due to the “first fill”. The “first fill” is the water that fills an unlined pit or pond and occupies the volume previously occupied by the removed sand, gravel, or other solid material. The Freshwater Pond is anticipated to be excavated to a depth of 10 feet below the ground water table, with a surface area of 0.49 acres (21,344 square feet) and a porosity of 0.3. A depletion of 3.43 acre-feet for the first fill is accounted for in this SWSP. Evaporation from the 0.49-acre Freshwater Pond and the 1.10-acre Recirculation Pond was calculated using a gross annual evaporation of 35 inches from the exposed water surface, with a credit of 9.15 inches for effective precipitation, based on an average annual precipitation of 13.07 inches obtained from the Western Regional Climate Center. The resulting net evaporation is more conservative than the net evaporative loss estimated by DWR and therefore is acceptable for the purposes of this SWSP. Computation of evaporation under this plan was reduced during the ice covered period. You have assumed the ice covered period to occur during the period of December through February based on average monthly temperatures obtained from the Western Regional Climate Center. 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 water surface area that may occur during the assumed ice covered period (December through February) for any time that the ponds are not completely covered by ice. Net evaporative depletions from ground water are estimated to total 1.02 acre-feet per year for the Freshwater Pond and 2.29 acre-feet per year for the Recirculation Pond. You have estimated that 750,000 tons of mined material will be removed from the site each year, of which 475,000 tons will be washed. The material mined above the water table and not washed has a moisture content of 2% of the mined material by weight, but none of the moisture is a ground water diversion. The material mined above the water table that is washed will have a 4% moisture content, of which 2% is from the soil profile and 2% is from the ground water used for washing. This results in a consumptive use of approximately 4.79 gallons per ton, or 6.99 acre-feet for the 475,000 tons of washed material per year. Dust control during crushing and screening will use approximately 2.28 gallons of ground water per ton, or 5.24 acre-feet of water per year for 750,000 tons of material. You have estimated that an additional 9.68 acre-feet of water will be required for dust control along unpaved roads, stockpiles, and disturbed areas during 2017, and 10.73 acre-feet will be required per year thereafter. All water used for dust control purposes is assumed to be 100% consumed. Total out-of-priority diversions are projected to be 28.45 acre-feet for 2017, and 26.27 acre-feet per year thereafter. The monthly ground water depletions were lagged from the Freshwater Pond to the Middle Fork of the South Platte River in Section 2, T10S, R77W, using the Alluvial Water Accounting System (AWAS) program developed by the Integrated Decision Support (IDS) Group at Colorado State University with the following parameters: