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1 <br /> <br />56 <br />should be judged. The quality of the Stonewall waters has been used as the • <br />base in this report because of the interest in presenting a worst case esti- <br />mate. A similar analysis using the water quality and discharge at ~4adrid <br />would indicate undetectable increases in mean annual concentrations for nearly <br />all parameters. <br />HYDROLOGIC BALANCE <br />C <br />Bedrock Groundwater <br />Mining will create a drawdown of the piezometric surface in and 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 />so <br />xc=6 ]n (' ~ <br />5~ <br />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 one foot. The estimates of the distance from the mine <br />face to points where the drawdown is negligible for the three cases defined <br />previously are given in Table 15. <br />TABLE 15 Extent of Orawdawn Of Piezometric Surface During Mining-Maxwell Mine <br />B <br />ft <br />Case I 781 <br />Case II 1457 <br />Case III 1166 <br />xc Distance from Center Of Mine* <br />ft ft <br />4100 11,400 <br />7700 15,000 <br />6200 13,500 <br />*Mean distance from center of mine to face is 7300 ft. for t4axwell Mine of <br />6 sq. miles. <br />