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Show Salt Lake City Watershed Management Plan ' 99 SOURCES AND FATE OF FECAL COLIFORM BACTERIA Fecal coliforms are a subgroup of total coliforms, and are usually found in much lower numbers. They are more indicative of contamination from a warm- blooded animal source. Therefore, they can come from both humans as well as animals. However, even though fecal coliform testing may rule out soil borne coliforms, they may be from any warm- blooded animal source, as discussed previously, and not necessarily an indicator of a human source. " In many situations where human pollution is suspected on the basis of [ fecal] coliform test results, the actual pollution may, in fact, be caused by animal discharges/' 6 Fecal coliform density per gram of feces and average contribution per capita per day is provided on Table 1 for human beings and some warm blooded animals. Table 1 Fecal Coliform Contribution Per Capita From Human Beings And Some Animals ( After Tchobanolglous, 1987) 7 Average indicator density/ g of feces Average contribution/ capita/ day Fecal Coliform ( 106) Fecal Coliform ( 106) Human 13.0 2,000 Chicken 1.3 240 Cow 0.23 5,400 Duck 33.0 11,000 Pig 3.3 8,900 Sheep 16.0 18,000 Turkey 0.29 130 As can be seen from the table above, many animals have a higher fecal coliform production than humans. Therefore, relying solely on fecal coliform counts as an indicator of human contamination may not be correct. Fecal coliform may be expected to live in a cold water environment for at least the duration of water flow from the upper reaches of the canyon to the canyon mouth in any of the Wasatch Canyons. Coliforms survive well in cold water ( the colder the better) with a survival time on the order of days. 8 In order to minimize differential death rates, samples should be taken no further down stream than 24 hours of flow time from the source of pollution. 9 With these two items in mind, and the fact that these creeks take less than 24 hours to flow from top to bottom, survival of coliform from any source in the canyon is possible. Page 13 |