Human health water-quality criteria are numeric values that are intended to limit chemical or microbiological pollutants in ambient water. Each state develops water-quality criteria based upon criteria determined under Section 304(a) of the Clean Water Act of 1972. These criteria are based solely on data and scientific judgment relative to pollutant concentrations and environmental and human health effects. The values of the standards must be established to support the predominate use of the water body. Such uses include drinking water, body contact recreation, fishing, and aquatic life maintenance. The standards developed by a state can be more stringent than the criteria but not more lenient.
The water-quality standard for the Escherichia coli indicator bacteria (E. coli) is 235 cells or colony forming units (CFU) per 100 mL of a single water sample, or 126 cells or CFU per 100 mL as a geometric mean from at least four water samples.
The USEPA has determined that higher E.coli bacteria counts indicate that people who come into contact with the water may have a greater probability of illness. But it is important to remember that as E.coli counts go up, it is the chance that someone will get sick that goes up - there are many other things that determine if a person will become sick:
When E. Coli counts exceed 235, there is a statistically greter risk that more than 8 people out of 1,000 people using the river will experience stomach illness.
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