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43 <br />0 to 5 mg/Q (34). Conductivity is an indicator of the dis- <br /> solved ionic species, so its measurement is indicative of <br /> the amount of dissolved ionic material in the water. Recent <br /> advances in instrumentation allow portable measurements to <br /> be made easily and precisely (see the Appendix). Thus, <br /> conductivity is a sensitive indicator of the level of total <br /> dissolved solids and hardness in water. <br /> Hem (7) suggests that typically the relation between <br /> conductivity and total dissolved solids follows a simple <br /> straight line relation <br /> K A = S <br /> where K is conductivity in micro mho/cm, S is total dissolved <br /> solids in milligrams per liter and A is some conversion fac- <br /> i <br /> on <br />tor between 0.5 and 1.0. The variability of the convers <br /> factor A usually renders this equation useful for making only <br /> estimates. But Hem (7) goes on to show that in particular <br /> situations, the relation holds true to the extent that total <br /> dissolved solids and major element concentration can be <br /> estimated with conductance measurements to better than 50. <br /> Ramirez (35) has shown that for mine drainage effluents which <br /> have S04 as the dominant anion, the conductance is an excel- <br /> lent indicator of total dissolved solids, and iron and sulfate <br /> concentrations. To do this, certain procedures have to be <br /> followed. <br /> The first detail that should be resolved for good con- <br /> ductivity data is that the parameter changes with temperature. <br /> <br /> Figure 8 is a plot of conductance versus temperature for a