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~~ <br />~ 6.0 OBSERVED IMPACTS ON THE HYDROLOGIC SYSTEMS OF THE TRAPPER <br />MINE <br />6.1 GROUND WATER <br />Water-level changes in the last few years for the QR aquifer are mainly due to <br />natural variations in the recharge rate. Water-level changes in QR aquifer wells GA-1, GD- <br />2, and GF-6, along with associated backfill wells GD-3 and GF-11, are close to active <br />mining and have been influenced by mining activities in addition to natural variations. The <br />water levels in these wells increased or remained steady in 1996. The increases are in <br />response to above average precipitation during the last two years, which resulted in <br />increased recharge_These wells are located near the downgradient toes of D and E pits <br />andlor at the interface of upgradient backfill and the downgradient native QR aquifer. <br />These positions tend to amplify water-level variations. <br />Upgradient mining can cause water-level rises in wells downgradient of the mining <br />by allowing ground water to flow to the downgradient end of mining quicker. Also, the <br />backfill aquifers are generally more permeable than the native aquifer which also allows <br />ground water to flow faster through the backfill material resulting in more water in the <br />aquifer at this location. The input of additional water to the native aquifer at the north end <br />(toe} of the mining has decreased the effects mine dewatering has had on water levels in <br />this portion of the aquif_ er. _- <br />The water-level changes for the HI aquifer have also been influenced by v~tions <br />in recharge during the last few years. The mining upgradient of HI wells GB-5 and GF-4, <br />which occurred several years ago, has been long enough in the past to allow water to reach <br />fairly stable levels. The water levels in these HI aquifer wells seem to be varying only with <br />changes in recharge rates. Water levels are not likely to ever recover to their pre-mine <br />6-1 <br />