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t Letter to Richard Fanvo -3- February 20, 1996 acre-feet to facilitate comparison with volumes for the Hazel-A adit and tailing pond provided by COM, Inc.: Given Information: Average inflows to the Hazel-A adit over a 4 month period representative of low flow condition = 2425 gallons per day = .00744 ac-ft per day. Current storage available in the pond is .52 ac-ft to the elevation of the decant risers (primary spillway), and .76 ac- ft to the elevation of the dam crest. Storage capacity behind the Hazel-A bulkhead is .148 ac-ft. Inflow of .45 ac-ft to tailing pond would occur during the 100- yr, 24-hr storm event. Justified Asaumptiona: An increase in ground water inflow rates to the Hazel-A adit of 1 gallon per minute would result in an additional accumulation of 1440 gallons per day = .00442 ac-ft per day in the tailing pond (see discussion of evaporation above for justification). A 90 day period of accelerated ground water inflows to the Hazel-A adit may be anticipated due to snow melt and spring precipitation. This 90 day period would likely fall within a mid-March to mid-July time-frame. This assumption is based on stream flow data from USGS gauging stations in Boulder County, observations made by Division inspectors at the Gold Hill Mill during the spring of 1995, and climatological data provided by COM, Inc. SENSITIVITY ANALYSIS COMPARING GROUND WATER INFLOWS TO ACCUMULATION IN TAILING POND Inflow Increase 1 gpm = .00442 ac-ft/day 2 gpm = .00884 ac-ft/day 3 gpm = .0133 ac-ft/day 4 gpm = .0177 ac-ft/day 5 gpm = .0221 ac-ft/day 6 gpm = .0265 ac-ft/day 7 gpm = .0309 ac-ft/day 8 gpm = .0354 ac-ft/day 9 gpm = .0398 ac-ft/day x 90 days Accu .398 .796 1.19 1.59 1.99 2.39 2.78 3.18 3.58 nulation in Pond ac-ft ac-ft ac-ft ac-ft ac-ft ac-ft ac-ft ac-ft ac-ft