Single Sample

E. coli standards comparisons: Single Sample Maximum Violations

Violations computed for the single sample maxima for current and two candidate E. coli standards are compared for each of the 15 Mad River sites. All 15 sites had violations of the current Vermont E. coli standard while 11 sites were in violation of the alternative single sample maximum and 9 sites had violations of the EPA single sample maximum. Most violations are located on the eastern side (sites 8-15) of the Mad River Valley which includes most of the agricultural land within the study area along with Warren village. The highest violation rate for all three standards occurred at site 11, the drainage area with the most agricultural use of all the sites. Violations were low for site 1, which includes residential development and Mad River Glen Ski Resort, and for site 3 which includes part of Sugarbush Ski Resort. Sites 6 and 7, also on the western side of the valley, are in the Green Mountain National Forest and have no development within their drainage areas and correspondingly low violation rates.

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 EFFECT

Streamflow level can have a dramatic effect on E. coli concentrations in streams. The current Vermont E. coli standard, alternative standard, and EPA standard are compared at three streamflow levels. Violations of E. coli single sample maxima were highest at peak flow with a high of 54% for the current standard, 35% for the alternative standard, and 28% for the EPA recommended standard. Violations for intermediate and low flow were less than 10% for all three standards.

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 gauging station.

Next, the violation rate for each of the 15 Mad River sties were calculated for each single sample maximum standard. The violation rates shown below are categorized by streamflow level (peak, intermediate, and low). At low flow, only one site (11) was in violation of all three standards; 10 sites had no violations. Sites 2, 4, 13, and 15 had one violation of the current Vermont standard with no violations of the alternative and EPA standards. At intermediate flow, 6 sites, all on the eastern side of the valley, were in violation of all three standards. Nine sites had no violations. Violations at peak flow are higher than at low and intermediate flows. At peak flow, all sites were in violation of the current Vermont standard. Eleven sites were also in violation of the alternative standard. Nine sites were in violation of all three standards. Most of the sites in violation of all three standards are on the eastern side of the valley.

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Standards Comparisons