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Peter Foster and Jonah Howe, Wright Water Engineers Page 3 of 14 <br /> Re: Gunnison West Gravel Pit SWSP, Amendment No. 1 <br /> December 12, 2025 <br /> Evaporation <br /> Evaporation calculations are shown on attached Table 1A. <br /> Pre-1981 Area <br /> According to the information from the SWSP request, a total of 13.7 acres of pond surface <br /> was exposed within the Gunnison West Pit reclamation permit boundary prior to January 1, <br /> 1981, as shown on attached Figure 4. Of this area, approximately 10.6 acres remain exposed <br /> today. Based on the Division 1 Water Court decision in case no. 2009CW49, the replacement <br /> of evaporative depletions is not required for groundwater exposed to the atmosphere prior <br /> to January 1, 1981 through open mining of sand and gravel, regardless of whether open <br /> mining operations continued or were reactivated on or after that date. The Water Court <br /> effectively held that Senate Bill 120 of 1989, as amended in Senate Bill 93-260, exempted all <br /> pre-1981 exposed groundwater regardless of whether open mining operations continued or <br /> were reactivated on or after January 1, 1981. <br /> For the 40.1 acres of groundwater that are proposed to be exposed during the term of this <br /> SWSP, 10.6 acres (the amount remaining of the 13.7 acres originally exposed pre-1981) were <br /> exposed prior to January 1, 1981, which leaves 29.5 acres exposed after December 31, 1980. <br /> Replacement of evaporative depletions is only required from the 29.5 acres exposed after <br /> December 31, 1980. The area exposed prior to 1981 ("Pre-1981 Area") is shown on attached <br /> Figure 2. The offset for the Pre-1981 Area is tied to the location identified on Figure 2 and <br /> may not be re-allocated to other areas of groundwater exposure within the gravel pit permit <br /> boundary. <br /> Ice Cover <br /> Computation of evaporation under this SWSP was reduced during the ice-covered period. Ice <br /> cover was assumed during the months of November through March based on the average <br /> monthly temperatures of 27.9°F for November, 13.5°F for December, 9.2°F for January, <br /> 14.6°F for February, and 26.6°F for March. Temperature data were obtained from the <br />