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81 <br />• certain this is immersed so that water temperatures rather <br />than air temperatures are recorded. <br />NONFILTERABLE RESIDUES <br />For these two measurements to be made by the standard <br />methods requires extensive laboratory equipment (13, 14). <br />What is developed in this section are suggestions for deter- <br />mining these solids concentrations with less expensive equip- <br />ment but the analyses require more time. Some objectives <br />behind the solids measurements need to be explained so that <br />the measurements can be put in proper context. <br />For dissolved solids, the conductivity reading is a good <br />method of measurement, but first, the empirical relation <br />between conductivity at 25°C and total dissolved solids levels <br />. has to be established by making measurements by both methods <br />on the different types of waters a number of times. Note <br />that the relationship may be different for different types <br />of water. If there are appreciable concentrations of vola- <br />tile species such as nitrates, carbonates or organics in <br />the water, making a precise determination of total dissolved <br />solids, is difficult. For waters associated with mining <br />operations, these constituents are usually not present so <br />the methods used can be a little less exacting. Again, it <br />is necessary to have a complete analysis of the water to <br />verify that volatile species are not in appreciable concen- <br />tration so that the methods used prove feasible. <br />In the case of suspended solids or nonfilterable residue, <br />• the concentrations are subject to compliance restrictions. <br />