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46 <br />2. In a specific situation, if the composition of the <br />water is well known, conductivity will be a good <br />indicator test of changes in concentration of <br />specific elements. <br />The second conclusion needs more explanation. Figure <br />10 is a graph of conductivity vs. concentration for Fe, <br />Cd, Zn, and Na for the Argo Tunnel data in Table VI. For <br />those cations that are primarily derived from the sulfide <br />minerals, the changes in concentration correlate well with <br />conductivity. For those elements that are derived from <br />the rock forming minerals, the concentration doesn't <br />change at all. Consequently, when the compositional changes <br />in the water are well known, there is an excellent chance <br />that conductivity will serve as a good indicative test <br />of concentration changes. <br />TESTS FOR THE NATURE OF THE WATER <br />In this area there are two objectives for the tests: <br />1. Is the water of an acid mine drainage type or is <br />it weathering more typical types of rock? <br />2. Is the aquifer a diffuse or conduit type? <br />To answer the first question tests of pH and conductivity <br />should be mde. Acid mine water of poor quality will have a <br />pH below 3 and a specific conductance above 2000 umho/cm at <br />25°C. A pH of 4-5 and specific conductance of 1000-2000 is <br />suspect. If the pH is between 6 and 9 and the specific con- <br />ductance is below 1000 the water probably has not weathered <br />• <br />k