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• <br />~~ CONDUCTANCE <br />Method 120.1 (Specific Conductance, umhos at 25°C) <br />STOREY NO. 00095 <br />1. Scope and Application <br />1.1 This method is applicable to drinking, surface, and saline waters, domestic and industrial <br />wastes. <br />2. Summary of Method <br />2.1 The specific conductance of a sample is measured by use of aself-contained conductivity <br />meter, Wheatstone bridge-type, or equivalent. <br />2.2 Samples are preferably analyzed at 25°C. If not, temperature corrections are made and <br />results reported at 25°C. <br />3. Comments <br />3.1 Instrument must be standardized with KCl solution before daily use. <br />3.2 Conductivity cell must be kept clean. <br />3.3 Field measurements with comparable instruments are reliable. <br />4. Precision and Accuracy <br />4.1 Forty-one analysts in l7 laboratories analyzed six synthetic water samples containing <br />increments of inorganic salts, with the following results: <br />Increment as Precision as Accuracy as <br />Specific Conductance Standard Deviation Bias, Bias, <br /> % umhos/cm <br />100 7.55 -2.02 -2.0 <br />106 8.14 -0.76 -0.8 <br />808 66.1 -3.63 -29.3 <br />848 79.6 x.54 -38.5 <br />1640 106 -5.36 -87.9 <br />1710 119 -5.08 -86.9 <br />(FWPCA Method Study I, Mineral and Physical Analyses.) <br />4.2 In a single laboratory (EMSL) using surface water samples with an average conductivity <br />of 536 umhos/cm at 25°C, the standard deviation was t6. <br />5. References <br />5.1 The procedure to be used for this determination is found in: <br />Annual Book of ASTM Standards, Part 3l, "Water", Standard D 1125-64, p 120 (1976). <br />Standard Methods for the Examination of Water and Wastewater, 14th Edition, p 71, <br />Method 205, (1975). <br />Approved for NPDES <br />Issued 1971 <br />120.1-1 <br /> <br />