E. coli standards comparisons: Geometric Mean
The geometric mean was calculated for 27 samples for each site. No sites were in violation of either the alternative standard or the EPA standard.
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| Data and analysis by Deb Sargent under the direction of Dr. Leslie Morrissey, School of Natural Resources, University of Vermont. Cooperator: Friends of the Mad River. Streamflow data: USGS, Mad River gaging station. |
STREAMFLOW EFFECTThe geometric mean was also calculated for all sites by streamflow level. There were no violations of either the alternative or EPA geometric mean standard when calculated for intermediate or low flows. All violations of these two standards occur at peak flow. Violations of the alternative E. coli standard at peak flow occurred at 8 sites while 6 sites were in violation of the EPA standard. Streamflow conditions at sampling time have a pronounced effect on E. coli concentrations in stream water. Calculating a geometric mean of data at mixed flow conditions can mask high E. coli counts as shown by the number of violations for all samples. When all water samples are combined for all streamflow levels, the number of violations for both standards is zero.
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