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Evaporative Losses <br /> The NOAA Technical Report NWS 33, 'Evaporation Atlas for the Contiguous 48 United <br /> States', published by the U.S. Department of Commerce was used to determine the <br /> amount of evaporation. The annual evaporation is 42.0 inches at the subject location. <br /> Precipitation at the site was found by using data from the publication, 'Climatography of <br /> the United States No. 81'. The precipitation at the mine site is estimated to be the same <br /> as that found at the nearest weather station which is located in Greeley. The annual <br /> mean precipitation is 12.68 inches/year. <br /> Effective precipitation was determined in order to compute the net lake evaporation. <br /> Effective precipitation was computed as 70% of the total precipitation. Effective <br /> precipitation was then subtracted from the gross evaporation to obtain the net <br /> evaporation. The net annual evaporation from a lake surface at the subject site is 2.76 <br /> ft (33.1 inches). <br /> The calculation of future evaporation should also be reduced due to the freezing of the } <br /> gravel pit lakes during the months of January and February. After elimination of <br /> evaporation during January and February the net evaporation is equal to 2.61 ft (31.3 <br /> inches). <br /> Mining <br /> The only groundwater exposed to the atmosphere during the excavation process will be <br /> water in the dewatering trench, sump pond, and the settling ponds at the north end of the <br /> site. The total area exposed in the dewatering operation is expected to be 0.4 acres in <br /> the trenches and 0.3 acres in the sump pond and settling ponds. <br /> The total lake surface at the site will be 0.7 acres, which is the total area for the <br /> dewatering operation. Therefore, the total net annual evaporation is 1.8 acre-feet during <br /> the mining operation. <br /> Post Mining <br /> The proposed mining operation would create a lake with a water surface area of <br /> approximately 29.9 acres. This would be the final configuration and would only occur <br /> after the dewatering pumps had been stopped and the lake allowed to refill. <br /> Senate Bill 120 requiring the augmentation of evaporative losses from sand and gravel <br /> operations allows for various reductions on the calculation of the amount of annual <br /> evaporation. <br /> G-2 <br />