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III IIIIIIII I ~P~ ~ ~ <br />Doc Date:12/11/2001 <br />• 6.0 OBSERVED IMPACTS ON THE HYDROLOGIC SYSTEMS <br />OF THE TRAPPER 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 were observed in QR aquifer <br />wells GD-2 and GF-6, along with associated backfill wells GD-3 and GF-11. Wells GD-2 and <br />GF-6 are fairly close to mined areas but the 2000 gradual water-level decline observed in <br />these four wells is mainly due to a decline in recharge. The increased recharge due to <br />higher precipitation over the prior years had caused water-level increases and gradual <br />water-level declines have occurred with the lower precipitation rates the last three years. <br />These wells are located near the downgradient toes of D and E pits and/or at the interface <br />of upgradient backfill and the downgradient native QR aquifer. These well locations seem <br />•': <br />to be relating to changes in precipitation with very little lag in time. <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 aquifer. Water levels in welts GD-2, GD-3, GF-6 and GF-il are thought <br />to be at or above the baseline levels for this reason. The slightly higher water levels in <br />well GD-Z in 1998 than those observed in 1986 after six wet years indicates the post-mine <br />• <br />6-1 <br />