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i <br />3-8 <br /> <br />,• water level measured in the piezometer installed In alluvium (Sample Point 25) <br />showed a decline of 3.0 feet within three months of cutoff installation, as <br />shown in Figure 4. The water levels 1n the three adjacent piezometera (Sample <br />Points 29, 30 and 31), which are screened in rock, have not shown a similar <br />response. For example, sample point 31 has shown a slowly increasing level <br />with time, a level which is approximately 6 feet above the level at sample <br />point 25. Sample poinc 30 shows a similar trend. Sample Point 29, which is <br />the deepest of the three piezometers in rock, has shows a very slow recovery <br />since installation, presumably due to the tight nature of the rock around the <br />1 piezometer at depth. Prior to November of 1982, the water level in 29 was <br />below an elevation of 8820 feet. In November, it rose to level above sample <br />points 30 and 31, and in January it dropped to level between sample points 30 <br />and 31. The moat recent eater levels in sample Points 29, 30 and 31 (which <br />were installed at progressively shallower depths, see Appendix B) appear to <br />1 indicate a slight upward gradient, and therefore an upward flow of water in <br />1 the rock. Any upward flow which does exist, however, must be slight because <br />~• of the low water level in sample Point 25. An explanation for the slowly <br />~ rising water levels 1n Points 30 and 31 is not apparent. Potential explana- <br />tions are (a) natural ground water seepage is still occurring in the rock, or <br />(b) the time lag In response may result in slower changes in pressure in the <br />rock than in the alluvium. Further observation of these levels may provide <br />insight. <br />At the completion of construction on August 24, 1982, flow rates through the <br />two surface weirs and the pump-back system were measured. The old vein (90° V <br />notch) was flowing at a depth of 2-7/8 inches, or 33 gpm. The new weir (60° V <br />notch) vas flowing at a depth of 2-1/2 inches, or 13 gpm. The floe through <br />these two weirs is thus approximately 46 gpm. The pump back system was <br />returning eater to the pond at an average rate of approximately 95 gpm. The <br />surface floe rate (46 gpm) thus represents 48 percent of the pump-back rate. <br />Assuming that the subsurface seepage is the difference between the weir floe <br />rate aM the pump-back rate, or 49 gpm, the captured subsurface seepage <br />' represents 52 percent of the pump-back rate. <br />J• <br />_~ l~AP~~H.®1~T~ <br />