For the soil copper data of Example 8.4 in Section 8.5, statistical tests are to be performed to determine whether the site soil copper concentrations should be of environmental concern. The Action Level for soil copper is 600 mg/kg based on ecological criteria. (A) Graphically explore the site and the background soil copper distributions using the box plot, probability plot, quantile–quantile plot, and double quantile plot, as described in Example 20.1 in Section 20.4 of this chapter. Any initial conclusions based on the graphical reviews? (B) Example 8.4 indicates that the logarithms of both the site and background copper are normally distributed (which should also be confirmed from the graphical tests, and quantitative normality tests if necessary) and have equal population variances. Therefore, compute a two-sample t test and quantile test using ProUCL to compare the site and background copper populations. Assume the width of the gray region, that is, S, is zero; (C) UsingProUCL, compute a one-sample sign test to compare the site data with the Action Level of 600, noting that this is a fully nonparametric test that makes no assumptions regarding the data distribution (i.e., no need to transform the data), as long as the data are independent and free of trend; (D) Using ProUCL’s (Version 4) UCL -> All menu, compute the 95% upper confidence limit on the population mean site copper concentration and compare that value with the Action Level. Note also that there is no need to transform the site data, as ProUCL uses a suite of parametric and nonparametric methods to determine the appropriate UCL on the mean; (E) Overall, would you characterize the copper at this site as a contaminant of potential concern?
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