Fecal coliform bacteria indicate the presence of
human and animal waste in the water. Fecal coliform levels in the bays and
rivers rise after heavy rainstorms for several reasons, including storm runoff
and combined sewer overflows (CSOs). Stormwater
running off yards, parking lots and streets also affects fecal coliform levels
because it carries pollution, such as animal or bird waste into the water. CSOs
happen when rainwater overwhelms the sewer pipes
causing a mixture of rainwater and sewage to
overflow into a river or bay. The NBC is currently working on a project to end
CSO discharges.
People who swim in or eat fish or shellfish from waters with high levels of bacteria may become ill. In seawater, acceptable levels of fecal coliform bacteria are less than a geometric mean of 14 MPN/100ml. In freshwater, acceptable concentrations of fecal coliform is less than the geometric mean of 20 MPN/100ml. To see the fecal coliform levels in Narragansett Bay click here. Total coliform bacteria are a collection of relatively harmless microorganisms that live in large numbers in the intestines of man and warm- and cold-blooded animals. They aid in the digestion of food. A specific subgroup of this collection is the fecal coliform bacteria, the most common member being Escherichia coli. These organisms may be separated from the total coliform group by their ability to grow at elevated temperatures and are associated only with the fecal material of warm-blooded animals. Methodology: Membrane filtration is the method of choice for the analysis of fecal coliforms in water. Samples to be tested are passed through a membrane filter of particular pore size (generally 0.45 micron). The microorganisms present in the water remain on the filter surface. When the filter is placed in a sterile petri dish and saturated with an appropriate medium, growth of the desired organisms is encouraged, while that of other organisms is suppressed. Each cell develops into a discrete colony which can be counted directly and the results calculated as microbial density. Sample volumes of 1 ml and 10 ml will be used for the ambient water testing, with the goal of achieving a final desirable colony density range of 20-60 colonies/filter. Excessively contaminated sources may require dilution to achieve a "countable" membrane. Environmental Impact: The presence of fecal coliform bacteria in aquatic environments indicates that the water has been contaminated with the fecal material of man or other animals. At the time this occurred, the source water may have been contaminated by pathogens or disease producing bacteria or viruses which can also exist in fecal material. Some waterborne pathogenic diseases include typhoid fever, viral and bacterial gastroenteritis and hepatitis A. The presence of fecal contamination is an indicator that a potential health risk exists for individuals exposed to this water. Fecal coliform bacteria may occur in ambient water as a result of the overflow of domestic sewage or nonpoint sources of human and animal waste. The following are fecal coliform transport models using ASA's WQMAP. A storm frequency is how frequent the storm is expected. Next to the frequency is how many inches of rain are expected within a certain amount of time.
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