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Letter to Richard Fanvo -4- February 14 1996 One measure of tolerable accumulation of water in the Gold Hill Mill tailing pond, would be accumulation to the elevation where there would still be sufficient freeboard to contain the 100-yr, 24-hr flood at the level of the decant risers, which are 6 inches below the dam crest. The following is a calculation of this tolerable accumulation scenario: Current available storage = Storage in pond + Storage in Hazel-A = .52 ac-ft + .15 ac-ft = .67 ac-ft Tolerable accumulation = Current available storage - Storm inflows _ .67 ac-ft - .45 ac-ft = .22 ac-ft Therefore, it is reasonable to conclude that an increase of ground water inflows to the Hazel-A of 1 gallon per minute may result in an unacceptable decrease in the freeboard or storage capacity in the tailing pond to contain a 100-yr, 24-hr storm event. It is also reasonable to conclude, based on the sensitivity analysis table above, that an increase in ground water inflows to the Hazel-A adit of just over 2 gallons per minute, may result in an exceedance of available storage capacity, and a discharge of process fluids from the system. Conclusions During the period from 9/17/95 to 1/17/96, the average inflow rate to the Hazel-A adit was 1.69 gallons per minute. Increased ground water inflows to the Hazel-A can anticipated during the period from about mid-March to mid-July. Such increased inflows were observed during an inspection of the Hazel-A adit conducted on June 7, 1995. Magnitudes for the increased inflows on the order of 1 to 2 gallons per minute or more could certainly occur. As examples, inflow rates for two underground mines where inflow rates have been quantified are presented here: Prior to 1978, inflow rates for the Terry Tunnel in San Juan County have been estimated to vary from 5 gpm in autumn to 100 gpm during spring runoff; after 1978 certain stopes connected to the Terry Tunnel were opened to the surface, and since that time Terry Tunnel inflows have ranged from 82 gpm in autumn to at least 1400 gpm during spring runoff. Inflow rates for the Climax Mine in Summit County during 1984 varied from approximately 600 gpm in January to approximately 4500 gpm during June and July. Clearly, neither the Terry Tunnel or the Climax Mine are comparable to the Hazel-A adit. These examples are provided to demonstrate the sorts of wide fluctuations in rates of ground water inflow that can occur, and that have occurred at these two sites where the inflows have been measured. In that the demonstrations provided in this letter indicate that exceedance of the Gold Hill Mill water storage capacities may occur as a result of relatively modest increases in the rate of ground water inflows to the Hazel-A adit, it is the Division's position that contingency measures need to be enacted to prevent unpermitted discharges from either the Hazel-A adit or the tailing pond, and that these contingency measures