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Ewing Gravel Mine Substitute Water Supply Plan Page 2 of 7 <br /> March 25, 2024 <br /> assumed to be equal to the effective precipitation, based on an average precipitation of 12 inches per <br /> year from the Fort Lupton and Brighton weather stations (1950-2018). <br /> Computation of evaporation under this SWSP was reduced during the ice-covered period. The Applicant <br /> has assumed the ice-covered period will occur during the months of December and January based on <br /> average monthly temperatures less than 32°F taken from the Fort Lupton and Brighton weather stations <br /> (1950-2018). However, for the purpose of this SWSP, the Applicant shall replace the net evaporation <br /> depletions from the exposed groundwater surface area that may occur during the assumed ice-covered <br /> period (the months of December and January) for any time that the pit is not completely covered by ice. <br /> If the Applicant is claiming in the accounting that no evaporation is occurring on a specific day, the <br /> Applicant must include in their accounting verification that the pit has been observed on that day and the <br /> pit is completely covered by ice. Computation of the net evaporation during any time that the pit is not <br /> completely covered by ice shall be determined as the pro-rata amount of the monthly gross evaporation <br /> rate distribution amount identified in the State Engineer's General Guidelines for Substitute Supply Plans <br /> for Sand and Gravel Pits, subtracting the pro-rata amount of the effective precipitation for that period. <br /> The maximum anticipated exposed groundwater surface area is 5.18 acres, up to 2.93 acres for the silt <br /> storage and freshwater pond in the northeast and up to 2.25 acres for the dewatering trenches and <br /> sumps, though the total surface area will vary from month to month. This results in 2.8 acre-feet/acre/ <br /> year of evaporative losses or 15.2 acre-feet for this SWSP period accounting for ice cover. A summary of <br /> the evaporative depletions is shown on attached Table 1. <br /> Water Lost with Mined Product <br /> Material mined below the groundwater table has a 4% moisture content. Therefore, depletions are 4% of <br /> the material mined by weight. The Applicant proposes to mine approximately 1,000,000 tons of material <br /> per year or 1,639,360 tons for this SWSP period, which results in 48.2 acre-feet of depletions for this <br /> SWSP period. A summary of depletions from mined product is shown on attached Table 2a. <br /> Slurry Wall Construction and Dust Control <br /> A total of 10.5 acre-feet (3.5 acre-feet/month for 3 months) will be used for the slurry wall construction. <br /> A total of 4.8 acre-feet (0.24 acre-feet/month for 20 months) will be used for dust control. A summary of <br /> these depletions is shown on attached Table 2a. <br /> DewaterinQ <br /> Approximately 2,025 acre-feet are anticipated to be dewatered from the pit until a slurry liner is <br /> installed. Since dewatering water will be returned through a combination of water delivered directly to <br /> the river and through recharge as shown on attached Figure 2, dewatering credit to depletions will be <br /> applied. Approximately 89 acre-feet will be returned directly to the river and 1,936 acre-feet (242 <br /> acre-feet/month for 8 months) will be delivered to recharge for this SWSP period. <br /> The total unlagged evaporative and operational depletions are approximately 78.7 acre-feet (15.2 <br /> acre-feet of evaporative losses, 48.2 acre-feet lost with mined product, 10.5 acre-feet for the slurry wall <br /> construction, and 4.8 acre-feet for dust control). Total unlagged depletions, including dewatering, are <br /> 2,103.7 acre-feet. A summary of these depletions is shown on attached Table 2b. <br />