Question

The Environmental Protection Agency (EPA) requires that cities monitor over 80 contaminants in their drinking water. Samples from the Lake Huron Water Treatment Plant gave the results shown here. Only the range is reported, not the mean (presumably the mean would be the midrange). Substance MCLG Range Detected Allowable MCLG 100 Origin of Substance Discharge from steel and pulp mills, natural erosion Discharge from drilling wastes metal refineries, natural erosion Natural erosion, water additive discharge from fertilizer and aluminum factories Chromium 0.41 to 0.70 0.004 to 0.020 1.09 to 1.15 Barium Fluoride 4 MCLG Maximum contaminant level goal For each substance, estimate the standard deviation ơ by assuming uniform distribution and normal distribution shown in Table 8.11 in Section 8.8. (Round your answers to 4 decimal places.) Uniform Distribution Normal Distribution Chromium Barium Fluoride

Answer 1

for uniform distribution ; std deviation =range/sqrt(12)

from Conservative method: for normal distribution ; std deviation =range/4

		unifom		normal
chromium		0.0837		0.0725
Barium		0.0046		0.0040
Fluroide		0.0173		0.0150