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56 <br />should be ,fudged. The quality of the Stonewall waters has been used as the s <br />J <br />base in this report because of the interest 1n presenting a worst case esti- <br />1 mate. A similar analysis using the water quality and discharge at: Madrid <br />J would indicate undetectable increases in mean annual concentrations for nearly <br />all parameters. <br />~~ HYDROLOGIC BALANCE <br />i <br />Bedrock Groundwater <br />~' Mining will create a drawdown of the piezometric surface 1n a.nd around <br />the mine. Following the cessation of mining, the underground workings will <br />be filled with water and the piezometric surface will recover towards its <br />original position. The extent to which the effect of mining on the piezo- <br />metric surface will spread during the active mining phase is estimated <br />from <br />1 xc•Bln('SO~ <br />sc -, <br />i <br />1 where xc is the distance from the mine face to the point where the drawdown <br />is some arbitrarily small value given by sc. This formula is based upon <br />the same theory as previously used in this report to estimate mine inflows. <br />The computations are made with sc 0.005 so which corresponds to a drawdown <br />of slightly more than ohe foot. The estimates of the distance from the mine <br />face to points where the drawdown is negligible for the three case:> defined <br />previously are given in;Tabie 15. <br />i <br />TABLE 15 Extent of Drarrdown Of Piezometric Surface During Mining-Maxwell Mine <br />B xc Distance From Center Of Mine' <br />ft ft ft <br />Case I 781 4100 11,400 <br />Case II 1457 7700 15,000 <br />i Case III 1166 6200 13,500 <br />'Mean distance from center of mine to face is 7300 ft. for Maxwell Mine of , <br />6 sq. miles. <br /> <br />