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Eeb 28 2001 12 06PM TUTTLE APPLEGATE No 3552 P. 3/7 UPDATED CONSUMPTfVE USE Water use at the site will include evaporation from the dewatering trench and collection area, dust control of haul roads and stockpiles, and water retained in material removed from the site. Evaporative Losses The NOAA Technical Report NWS 33, Evaporation Atlas for the Contigntous 48 United States (U.S. Deparnnent of Commerce) was used to determine gross evaporation. For this location, the annual evaporation is 44.0 inches. Montlily evaporation percentages as suggested by the Office of the State Engineer were used to calculate monthly evaporation. Precipitation was estimated using Colorado Climate Center Website data. Annual precipitation at this site was assumed to be equal to that at the neazest station. The site lies between the Brighton and the Denver WSFO Weather Station, and these values were averaged for the Howe Pit site. The averaged mean precipitation is 14.44 inches. Effective precipitation was calculated as 70% of total precipitation. Net evaporation was then computed as the difference between gross evaporation and effective precipitation Net evaporation at the site was calculated to be 2.8 feet. Figure 2 is a September 30, 1999 aerial photo of the Howe Pit site. There are currently 17.0 acres exposed at the site. The mining operation will intercept the alluvial aquifer that supplies water to the South Platte River. In order to allow for dry osirtirtg of the material, a dewatering trench will be excavated around the site and be approximately I O,ti501inear feet and 5 feet wide, which will expose approximately 1.2 acres with a 0.1 collection azea. The total of 18.3 acres is exposed at the Howe Pit. As mentioned in the (/27/98 SEO approval, the Howe Pit has 26.6 exposed acres that were created pn-1981 and do not require augmentation. Since the pre-1981 acreage exceeds the currenily exposed area, no evaporative consumptive use at the site requires augmentation. Operational Losses The operator anticipates that 925,000 tons of material will be mined and washed from the azea annually. At 4% moisttm content by weight as suggested by the SEO, the depletion would total 27.2 acre-feet per yeaz (Table 2). The estimated consumptive use for dust control of haul roads and stockpiles is 4.0 acre-feet per year (Table 2). The consumptive use was distributed throughout the year in the same percentages as the material produced. Concrete is also produced on the site.llte applicant estimates an average production of 400 cubic yards of concrete per day which requires approximately 40 gallons of water per cubic yard. If Page 2