Comparisons of E.
coli Standards 
The current E. coli water quality standard for
swimming (class B) waters in Vermont is 77 organisms/100 mla single
sample maximum. There are no criteria for number of samples nor
sampling conditions. Although standards approved in June of 1999,
effective July of 2000, maintain the same standard, discussion regarding
modification of the recreational water quality standard for E. coli
continues. In order to illustrate the potential impact of changing the
current water quality standard, three scenarios are compared using the current Vermont standard (77 organisms/100 ml), an
alternative standard (geometric
mean of 77 organisms/100 ml with a single sample maximum of 143
organisms/100 ml), and the EPA recommended standard (geometric mean of 126
organisms/100 ml with a single sample maximum of 235 organisms/100
ml). Data used for these comparisons were collected weekly at 15
sites in tributaries of the Mad River
from May 2November 3, 1998. Total number of violations and number
of sites in violation of geometric mean and single sample standards are summarized
below. Violations of the single sample maximum for each of three standards is compared by
site and for all sites. The effects of streamflow on the violation rate of three
single sample maxima and two geometric mean standards are also
analyzed. Finally, the number of violations are calculated for a geometric
mean based on three time periods (30, 60, and 90 days).

