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43 <br />• to 5 mg/t (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 />tor between 0.5 and 1.0. The variability of the conversion <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 5%. <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 />Figure 8 is a plot of conductance versus temperature for a <br />0