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Show Chapter 2 Watershed Characteristics and Uses because coliform tend to exist in high quantities within fecal matter ( 100 to 400 billion per day discharge by humans1), and thus provide a good indication or warning of possible contamination by other fecal born species. Some water borne pathogens are difficult to detect or the tests may be complex, time consuming, and often not sufficiently sensitive or selective. Coliform testing is relatively simple and inexpensive, thus rendering it the method of choice for many years. SOURCES AND FATE OF TOTAL COLIFORM BACTERIA " The coliform group of bacteria includes all aerobic and facultative anaerobic, gram- negative, nonspore- forming rod- shaped bacteria mat ferment lactose with gas formation." 2 Included in the coliform class of bacteria are the genera Escherichia and Aerobacter. Coliform bacteria have been found to increase in viable bacterial numbers under favorable conditions in pipe distribution systems. 3 According to the American Water Works Association, " Finding coliform densities ranging from 1 to 150 organisms per 100 mL may be possible with their occurrence widespread in the distribution system/' 4 There is a possibility that coliform could colonize in streams within the slower moving areas. Porous media such as rocks may provide a good surface to which the bacteria can attach and colonize. Total coliform life expectancies are on the order of days. Based on the results of deep well studies, many coliforms live well in colder waters. Coliform life expectancies have not been verified in open stream flows. " The use of coliforms as indicator organisms is complicated by the fact the Aerobacter and certain Escherichia can grow in soil. Thus, the presence of coliforms does not always mean contamination with human wastes. Apparently, Escherichia coli ( E. coli) are entirely of fecal origin. There is difficulty in determining E. coli to the exclusion of the soil coliforms; as a result, the entire coliform group is used as an indicator of fecal pollution." 5 Therefore, total coliform presence in water is not proof of fecal contamination, however, total coliform will always be present when there is fecal contamination. Though the significance of coliform occurrences should not be ignored because they may indicate a potential pathway for pathogen penetration into the water supply, sole reliance on coliform occurrence may not be adequate in defining the source of the contamination. If coliforms occur repeatedly at levels higher than background, then perhaps a more stringent monitoring program should be employed in order to determine for certain that there is human- based contamination. Page 12 |