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Parsons Mine SWSP June 30, 2017 <br />Plan ID 5822 Page 2 of 10 <br /> <br />Office of the State Engineer <br />1313 Sherman Street, Room 821, Denver, CO 80203 P 303.866.3581 <br />www.water.state.co.us <br /> <br /> <br />Depletions <br /> Depletions at the Parsons Mine during the term of this SWSP will consist of evaporation from <br />exposed groundwater, water lost with the mined product, and dust suppression. You have <br />anticipated that beginning in June 2017, 0.85 acres of ground water will be exposed at the site in <br />dewatering trenches (7,400 feet long × 5 feet wide) around Phase 1A. In addition, it is anticipated <br />that water will be sent to a silt pond constructed in Phase 1C beginning in June 2017. For the <br />purposes of this SWSP, you have assumed that the silt pond will be filled to its maximum surface <br />area of 12.7 acres for the entire plan period. Beginning in August 2017, it is anticipated that 0.47 <br />acres of ground water will be exposed at the site in dewatering trenches (4,100 feet long × 5 feet <br />wide) around Phase 1B. <br />Net evaporative depletions were calculated using a gross annual evaporation of 3.51 feet <br />(42.12 inches) from the exposed water surface, with a credit of 0.84 feet (10.08 inches) for <br />effective precipitation, based on average annual precipitation of 1.20 feet (14.42 inches) for the <br />Greeley UNC weather station. Computation of evaporation under this plan was reduced during the <br />ice covered period. You have assumed the ice covered period to occur during the months of <br />December and January based on below-freezing average monthly temperatures for the Greeley UNC <br />weather station. The ice covered periods may be used to reduce the amount of evaporative losses <br />that need to be replaced; however, for the purpose of this SWSP, the Applicant shall replace the <br />net evaporation depletions from the exposed ground water surface area that may occur during the <br />assumed ice covered period (December through January) for any time that the exposed ground <br />water surface is not completely covered by ice. Computation of the net evaporation during any <br />time that the exposed ground water surface is not completely covered by ice shall be determined <br />as the pro-rata amount of the monthly gross evaporation rate distribution amount identified in the <br />State Engineer’s General Guidelines for Substitute Supply Plans for Sand and Gravel Pits, <br />subtracting the pro-rata amount of the effective precipitation for that period. The net depletion of <br />ground water due to evaporation is projected to total 34.87 acre-feet during this plan period, as <br />shown on the attached Table 1. <br /> Operational losses associated with mining activities will include water removed with the <br />mined product and water used for dust control. Up to 742,000 tons of material is projected to be <br />mined during this plan period. Of the total amount of mined material, 412,550 tons of aggregate is <br />anticipated to be crushed (not washed) and 329,450 tons is anticipated to be washed. All of the <br />material will be mined below the ground water table, but in a dewatered state. The water <br />retained by the crushed aggregate is considered to be 2% of the mined material by weight, and the <br />water retained by the washed material is considered to be 4% of the mined material by weight. <br />This results in a total groundwater loss of 15.76 acre-feet. <br /> The Applicant has estimated that a total of 23.71 acre-feet of water will be required for <br />dust control purposes at the site during this plan period. MM plans to pump all dust suppression <br />water from the dewatering trenches of the Phase 1A mining area. MM also has an agreement with <br />the North Weld County Water District which allows MM to pump municipal water from a nearby <br />hydrant to use for dust suppression purposes if necessary. However, for the purposes of this SWSP, <br />you have assumed that all water for dust suppression purposes will be ground water pumped from <br />the dewatering trenches of Phase 1A. Water used for dust control purposes is assumed to be 100% <br />consumed. <br />The total consumptive use at this site during the period of this SWSP is 74.34 acre-feet. A <br />monthly breakdown of evaporative and operational consumptive use is given in the attached Table <br />1.