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Peter Foster and Jonah Howe, Wright Water Engineers Page 4 of 14 <br /> Re: Gunnison West Gravel Pit SWSP, Amendment No. 1 <br /> December 12, 2025 <br /> Gunnison 1 N weather station. The ice-covered periods may be used to reduce the amount of <br /> evaporative losses that need to be replaced; however, for the purpose of this SWSP, the <br /> Applicant must replace the net evaporation depletions from the exposed groundwater <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 <br />