Laserfiche WebLink
<br /> <br />unconsol i da Ced spo i 1 s .^a :a:^i 1; . :'ia ~ ~2-:ni .ii ng confined 'dadg~ and ri sh Creek <br />overburden aquifers have, therefore, been replaced with an unconfined spoils <br />aquifer in the mine pits. <br />Pre-mining recharge to the Wadge overburden aquifer occurs along the periphery <br />of the Twentymile Park structural basin. Snowmelt and precipitation provide <br />direct recharge to bedrock aquifers in the upland parts of the basin. Deep <br />percolation of ground water through overlying strata also provides recharge. <br />Water entering the bedrock aquifers moves downdip following permeable strata <br />in the unconfined recharge area. As the water migrates into the basin, less <br />permeable overlying rock layers confine the aquifer. The Wadge recharge area <br />has been extensively disturbed by previous mining in Eckman Park and Mine 1. <br />Spoils aquifers have developed in backfilled spoils throughout Eckman Park, <br />i4ine No. 1 and i4ine No. 2. The spoil material resaturates in the lowest part <br />of the pit adjacent to the downdip highwall. Recharge of the spoils is <br />primarily from surface infiltration and to a lesser extent from bedrock <br />contributions. <br />The spoils re saturate to an elevation slightly higher than the lowest part of <br />the highwall. Water not recharging the bedrock aquifer leaves the mine pit <br />area at the lowest part of the downdip mine highwall and is expressed on the <br />surface as springs. Previous mining has resulted in the creation of a series <br />of spoils springs throughout the Eckman Park complex. Springs exhibiting <br />spring peak flows of up to 1200 gpm have developed along the downdip highwall <br />of i4ine 1 and Eckman Park. Small springs and seeps are also present at Mine 2. <br />Water balance studies by Applied Hydrology Associates have estimated the <br />spoils spring discharges from Mine No. 1 and Eckman Park. No water balance <br />studies have been conducted at Mine No. 2. <br />The study assumed equilibrium conditions (ground water recharge equals ground <br />water discharge) and did not account for any ground water contribution to the <br />backfilled materials from bedrock aquifers. Recharge to the backfilled areas <br />was estimated at 0.25 ft/year. <br />The water balance study for i4ine No. 1 estimates approximately 1.16 x 107 <br />cubic feet (lb5 gpm) of water would discharge annually from Mine No. 1. Peak <br />discharges are estimated at approximately 2000 gpm. The discharge during <br />baseflow months is estimated to be 58 gpm. These estimated values are <br />reasonable when compared with observed spoils spring flows from i4ine No. 1. <br />A similar study was performed at Eckman Park. The annual discharge from <br />approximately 1950 acres of disturbed land was estimated to be 2.1 x 107 <br />cubic feet. Peak spoils spring discharges were estimated to be 2500 gpm. The <br />average discharge from Eckman Park is estimated to be 500 gpm. <br />Infiltration to ground water aquifers in the 'cckman Park Complex area is <br />estimated at 0.25 ft/year. Infiltration of the bedrock aquifers will result <br />in development of a salt effluent plume which will move through the Wadge <br />overburden aquifer toward the center of the Twentymile Park basin. This salt <br />plume will diffuse as it moves down-gradient from the mine site, improving in <br />?Y <br />