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Sent By: TUTTLE APPLEOATE INC U; 30345227593034526611;Sep-25-00 10:38; Pege 3 Mr. Bill Mc%tyre -• Sepleerbald,T000 Pege d rjS Evapo-atlve Lossu During mining, groundwater will be exposed in a dowatering trench, a collection basin and settling ponds. The total exposed ground water surface area due to mining is approximate]y 3.U acres. The NOAH Technical Report NWS 33, Evaporation Atlas for the ontiguous 481Jnited States (U.S. Department of Commerce) was used to determine gross evaporation. For this locatioq the annual cvaporplion was estimated at 43.0 inches. Monthly evaporation percentages, as suggested by the Office of the State Engineer for elevations below 6.500 feet. were used to calculate monthly evaporation. The Colorado Climate Crater monttily clunatic date for Brighton, station 50950, was used to estimate precipitation. Effective monthly ptt:cipilation was assumed to be 7(1% of uveragc monthly ptecipimtion. Evaporative losses are detailed in Tahlo-l . Net evaporation is difference between gross evaporation and effective precipitation. The total evaporative loss is the product of net _, evaportion and the total exposed ground water surface. Tho annual evaporative loss is 8.2U acrwfeet Operations! Lossrs Operational losses are detailed in Table-2. The moistum content of the material hauled off the site was assumed to be 4 percent by weight The ermual amount of mined product for the pit is estimated at 700,000 tons. This tesult+ in an annual amount of 20.60 acre-feet of watcT retained in Ute product. Since the thine is producing yeu round, dust control is requited during all months. Production rates are highest dttriag the months ofMay-September, and, in combination witt- the weathor, this period requires the greatest amount of dust control. The annual amount of water use For dust control is estimated at 2.0 acre-feat, and use is diroctly related to production rates. Thercforc, total annual operational losses of 22.60 aae-feu are prorated throughout the year based on production rates. Projected stnearre depietlons Since the site is more than Il2fl feet from the South Platte River, the total consumptive uses were pot assumed to be inatautaneow depktiona in the river. A stream depletion modal utilizing a stream depletion factor (SDF) of 10 days was completed for the Hammer Pit to determine the lagged effect of the consumptive uses.