Groundwater contamination in wells. Refer to the Environmental Science&Technology (Jan...

Groundwater contamination in wells. Refer to the Environmental Science&Technology (Jan. 2005) study of the factors related to MTBE contamination in 223 New Hampshire wells, presented in Exercise . The data are saved in the MTBE file. Two of the many quantitative variables measured for each well are the pH level (standard units) and the MTBE level (micrograms per liter).

a. Construct a histogram for the pH levels of the sampled wells. From the histogram, estimate the proportion of wells with pH values less than 7.0.

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b. For those wells with detectible levels of MTBE, construct a histogram for the MTBE values. From the histogram, estimate the proportion of contaminated wells with MTBE values that exceed 5 micrograms per liter.

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c. Find the mean and standard deviation for the pH levels of the sampled wells, and construct the interval x ± 2 s. Estimate the percentage of wells with pH levels that fall within the interval. What rule did you apply to obtain the estimate? Explain.

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d. Find the mean and standard deviation for the MTBE levels of the sampled wells, and construct the interval . Estimate the percentage of wells with MTBE levels that fall within the interval. What rule did you apply to obtain the estimate? Explain.

Groundwater contamination in wells. In New Hampshire, about half the counties mandate the use of reformulated gasoline. This has led to an increase in the contamination of groundwater with methyl tert-butyl ether (MTBE). Environmental Science&Technology (Jan. 2005) reported on the factors related to MTBE contamination in public and private New Hamsphire wells. Data were collected on a sample of 223 wells. These data are saved in the MTBE file. Three of the variables are qualitative in nature: well class (public or private), aquifer (bedrock or unconsolidated), and detectable level of MTBE (below limit or detect). [Note: A detectable level of MTBE occurs if the MTBE value exceeds .2 microgram per liter.] The data on 11 selected wells are shown in the accompanying table.

(11 selected observations from 223)

Based on Ayotte, J. D., Argue, D. M., and McGarry, F. J. “Methyl tert -Butyl ether occurrence and related factors in public and private wells in southeast New Hampshire.” Environmental Science&Technology, Vol. 39, No. 1, Jan. 2005, pp. 9–16.

a. Use graphical methods to describe each of the three qualitative variables for all 223 wells.

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b. Use side-by-side bar charts to compare the proportions of contaminated wells for private and public well classes.

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c. Use side-by-side bar charts to compare the proportions of contaminated wells for bedrock and unconsolidated aquifiers.

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d. What inferences can be made from the bar charts of parts a–c?