How were these guidelines developed?
National Recommendations
The Environmental Protection Agency’s (EPA) bacteria criteria was established in the early 1980’s based on two studies, one in Oklahoma and one in Pennsylvania. These studies established a relationship between exposure to swimming waters contaminated with E. coli and gastrointestinal illness. Based on these studies, EPA recommends a single sample maximum E. coli standard of 235/100 ml, which corresponds to 8 illnesses per 1,000 swimmers. In addition, EPA recommends a geometric mean of 126 E. coli per 100 ml (a little less than half a cup). If E. coli counts are above either of the standards, the beach is closed.
Vermont Guidelines
There is currently no required national standard for E. coli in swimming areas. Though many states use the standards developed by the EPA, Vermont’s standard differs in significant ways. Vermont's Water Resources Board established a single sample maximum E. coli standard of 77/100 ml in 1990. This level corresponds to an illness rate of 6 per 1,000 swimmers and was selected to be approximately comparable in its level of protection to the previous water quality standard, 200 fecal coliform bacteria per 100 ml. In reality, Vermont’s current standard is more conservative than that level. Vermont currently has no geometric mean standard; such a standard requires several samples to be taken and can be difficult to implement. Because Vermont’s single sample standard is strict compared with other states and the EPA, Vermont doesn’t have a criterion value for beach closings. The group or municipality monitoring the swimming area may choose to keep the beach open even if E. coli levels exceed 77/100 ml.
