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Show Chapter 2 Watershed Characteristics and Uses pathogenic organisms may not come into contact with the disinfectant. That is to say, that the organisms may be shielded within or by a particle. The amount of raw water turbidity ( suspended solids) may also determine the type of treatment required. Water with consistently high turbidity ( greater than 5 NTU) requires conventional treatment like coagulation, flocculation, sedimentation, and filtration. Water with consistently low turbidity ( less than 5 NTU) may be treated by direct filtration, which is basically conventional treatment without sedimentation. Direct filtration treatment plants are less costly to construct than conventional plants. This is currently not an issue for Salt Lake City because all of the City's treatment plants are conventional plants. However, turbidity can be a significant issue with respect to operation costs. Higher turbidity requires higher dosages of coagulating chemicals, more frequent backwashing, and it produces greater quantities of sludge for disposal. In addition, fluctuating turbidity levels ( spikes) are difficult for plant operators to manage since fluctuating turbidity requires fluctuating levels of chemical feed. Watershed management practices that lower and stabilize turbidity levels are very important with respect to water treatment. METALS SOURCES AND FATE Trace quantities of many metals are important in most waters and are required for biological growth. Some of these trace quantities include metals such as nickel ( Ni), lead ( Pb), manganese ( Mn), cadmium ( Cd), chromium ( Cr), zinc ( Zn), iron ( Fe), copper ( Cu), and mercury ( Hg). However, a few of these metals are classified as heavy metals. Heavy metals are listed in Table 2 along with associated health concerns resulting from elevated concentrations. Table 2 Heavy Metals Metal Health Concern Barium ( Ba) Increase blood pressure and nerve block Cadmium ( Cd) Carcinogen Page 16 |