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<br />Letter to Richard Fanvo -4- February 20, 1996 <br />One measure of tolerable accumulation of water in the Gold Hill Mill <br />tailing pond, would be accumulation to the elevation where there would <br />still be sufficient freeboard to contain the 100-yr, 24-hr flood at the <br />level of the decant risers, which are 6 inches below the dam crest. The <br />following is a calculation of this tolerable accumulation scenario: <br />Current available storage = Storage in pond + Storage in Hazel-A = <br />.52 ac-ft + .15 ac-ft = .67 ac-ft <br />Tolerable accumulation = Current available storage - Storm inflows <br />_ .67 ac-ft - .45 ac-ft = .22 ac-ft <br />Therefore, it is reasonable to conclude that an increase of ground water <br />inflows to the Hazel-A of 1 gallon per minute, and subsequent pumping of <br />this water to the pond, will result in an unacceptable decrease in the <br />freeboard or storage capacity in the tailing pond to contain a 100-yr, 24- <br />hr storm event. It is also reasonable to conclude, based on the <br />sensitivity analysis table above, that an increase in ground water inflows <br />to the Hazel-A adit of just over 2 gallons per minute, will exceed <br />available storage capacity, and a discharge of process fluids from the <br />adit may result. <br />Conclusions <br />During the period from 9/17/95 to 1/17/96, the average inflow rate to the <br />Hazel-A adit is estimated to be 1.69 gallons per minute. Increased ground <br />water inflows to the Hazel-A can be anticipated during the period from <br />about mid-March to mid-July. Such increased inflows were observed during <br />an inspection of the Hazel-A adit conducted on June 7, 1995. Magnitudes <br />for the increased inflows on the order of 1 to 2 gallons per minute or <br />more could occur. it is the Division's understanding that COM, Inc. <br />recognizes, and does not dispute, the potential for increased ground water <br />inflows to the Hazel-A adit as a result of spring precipitation and <br />snowmelt. <br />The demonstrations provided in this letter indicate that the Gold Hill <br />Mill water storage capacities may be exceeded as a result of relatively <br />modest increases in the rate of ground water inflows to the Hazel-A adit. <br />It is the Division's position that contingency measures need to be enacted <br />to prevent unpermitted discharges from either the Hazel-A adit or the <br />tailing pond, and that these contingency measures must be enacted in <br />preparation for this year's spring runoff. We have discussed a variety <br />of possible contingency measures in general terms during past meetings, <br />and in more comprehensive terms during a meeting held February 26, 1996. <br />Criteria for potential contingency measures were established during the <br />February 26, 1996 meeting, and it was agreed that COM, Inc. would provide <br />a progress report on the development of contingency measures and <br />implementation timeframes no later than March 4, 1996. <br />