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Peter Foster and Jonah Howe, Wright Water Engineers Page 4 of 14 <br /> Re: Gunnison West Gravel Pit SWSP <br /> December 8, 2025 <br /> surface area that may occur during the assumed ice-covered period (November through <br /> March) for any time that the pits are not completely covered by ice. <br /> Pre-existing Vegetative Consumptive Use (CU) Credit <br /> Computation of evaporation under this SWSP was also reduced by CU for the elimination of <br /> pre-existing native vegetation on lands inundated by the post-1981 exposed groundwater in <br /> the gravel pit. Potential consumptive use without precipitation was modeled using StateCU <br /> and the Upper Gunnison High Elevation Calibration Coefficient for grass, resulting in 2.2 <br /> acre-feet/acre of CU credit. For months where native evapotranspiration CU was greater <br /> than gross evaporation, gross evaporation was used instead for evaporative depletions. <br /> Net Evaporative Depletions <br /> Evaporative depletions associated with the 29.5 acres of exposed groundwater was <br /> determined using gross evaporative rates from the NOAA Technical Report NWS 33 and the <br /> SEO monthly percentages for elevations above 6,500 feet. This was then reduced for ice <br /> cover during the months November through March and for pre-existing vegetative CU, which <br /> resulted in a net evaporation of 17.4 acre-feet/year, as shown on attached Table 1A. <br /> Dust Suppression <br /> Water used for dust suppression is one hundred percent (100%) depletive with no measurable <br /> return flows to the river. Water use for dust control is estimated at 70,000 gallons per month <br /> applied to the haul roads during the period from May through October. Dust control at the <br /> site is estimated to be 1.3 acre-feet/ year, as shown on attached Table 2. <br /> Aggregate Production <br /> A maximum of 100,000 tons of aggregate will be mined per year. Aggregate will be mined in <br /> a dewatered state and washed; therefore, product moisture loss is assumed to be four <br /> percent (4%) by weight of the mined material. Water lost in mined product and from washing <br /> is 2.9 acre-feet/year, as shown on attached Table 2. <br />