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KERB COAL COMPANY <br />720 PIT DISCHARGE ESTIMATE <br />Present Volume of Water Accumulation in 720 Pit <br />• Pit bottom elevation (estimated from pit angles and coal thickness in developing <br />topography and volumetric from 4/89 aerial flight) - 7,940' <br />• Pit bottom area (digitized from 4/89 topographic projection of pit configuration <br />below waterline taking into account plunge of coal seam) - 3,900 ft' <br />• Water level elevation (conservative estimate bazed on 4/89 measured water level <br />of 8,022' and observations over intervening years of minor water level <br />fluctuations) - 8,020' <br />• Surface azea of ponded a-ater (digitized area at elevation 8,020' from 4/89 aerial <br />mapping) - 226,500 ftz = 5.2 acres <br />• Maximum water dep[h - (8,020' - 7,940') = 80' <br />• Calculated water volume - (3,900 ftt + 226,500 fr)/2 x 80' = 9,063,900 ft' <br />= 208 ac-ft <br />Runoff Inflows During Reclamation Period <br />• Drainage area (digitized a-atershed area from surface topography map) - 182 acres <br />• Assume that runoff would occur during the period from June through October <br />and that runoff R•ould equal 82 percent of precipitation (based on calculations for <br />resaturation of spoils, page 780-115aa of permit, which assumes 18 percent <br />infiltration) <br />• Precipitation (averages from Table 15 of permit) <br />June - 0.80" <br />July - 0.96" <br />Aug. - 1.16" <br />Sep[. - 0.78" <br />Oct. - 0.84" <br />To[al 4.54" <br />• Calculated runoff inflow - (182 ac. x 4.54"/12) x 0.82 = 56 ac-ft <br />Evaporative Losses During Reclamation Period <br />• Assume evaporation over same period that runoff would occur ~une - October) <br />• Average annual evaporation ra[e is approximately 30 inches <br />C:\..VJCTRIO.DOC <br />oviavs~ Wm ACZ /nc. "P.O. Boz 774018 • Stcamlxwr Spnng; Colorado 80477 • (303f 8796160 <br />