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Christine Johnston. Kent Gorham, Jim Pendleton <br />September 18, 1995 <br />• Page 3 <br />]. See pages 2.05-134 through 138 for rationale for streams. <br />2. There aze 18 stream channel crossings of panels in the Apache Rocks permit revision <br />azea. At each such crossing, as shown on page 2.05-135, the channel has a <br />probability of 0.2 percent (.002) of encountering a surface crack. This leads to o <br />cumulative probability of a stream channel encountering a surface crack in the <br />Apache Racks permit revision area of 3.6 percent (0.036j, calculated via (18 <br />crossings) x (.011) = 0.0036. <br />3. Per Richard Dunrud, "typical" crack dimensions would be, conservatively, 200 feet <br />long, 100 feet deep and 0.5 feet wide (on the average) for a total volume of 0.23 acre- <br />feet per crack. <br />4. Assume, conservatively, that there will be enough snowmelt runoff and rainfall-runoff <br />events to produce measurable flows five times each year. <br />5. Assume that during each runoff event, conservatively, the runoff "hydrograph" will <br />last long enough to enable 25 "crack volumes" of water to infiltrate into the relative <br />• formations. Given the low permeability of the formations and the tendency for <br />internal "healing" to occur, this is conservative. <br />6. Based upon all of the factors listed above, the avenge annual stream channel loss in <br />the Apache Rocks permit revision area can be calculated via Equation 2, which yields <br />an average loss of approximately 1 acre-foot per year. <br />(18 crossings) (.002)(0.23 AF)(5 times/year)(25 crack volumes/time) = 1.0 AF/yeaz <br />GROUNDWATER <br />1. Page 2.04-98 states: "Observations within the B-Seam mine workings show that the <br />average annual inflow to the mine is approximately 12 gpm." <br />2. Page 2.05-161 states: "Average mine water inflow over 11 years (1983-1993) is 12 <br />acre-feet per year. <br />3. Statement number 1 refers to B-Seam inflows only while statement no. 2, above, <br />• refers to inflows for both the F and B-seams. If these two values are averaged, an <br />average mine water inflow of 16 acre-feet jgr year results. <br />