Chapter 6, Problem 2RSRD

The Safe Drinking Water Act, which was passed in 1974, allows the Environmental Protection Agency (EPA) to regulate the levels of contaminants in drinking water. The EPA requires that water utilities give their customers water quality reports annually. These reports include the results of daily water quality monitoring, which is performed to determine whether drinking water is safe for consumption.

A water department tests for contaminants at water treatment plants and at customers laps. These contaminants include microorganisms, organic chemicals, and inorganic chemicals such as cyanide. Cyanide’s presence in drinking water is the result of discharges from Steel, plastics, and fertilizer factories. For drinking water, the maximum contaminant level of cyanide is 0.2 part per million.

As part of your job for your city’s water department, you are preparing a report that includes an analysis of the results shown in the figure at the right. The figure shows the point estimates for the population mean concentration and the 95% confidence intervals for μ for cyanide over a three-year period. The data are based on random water samples taken by the city’s three water treatment plants.

2. What Can You Conclude?

Using the results of Exercise 1, what can you conclude about the concentrations of cyanide in the drinking water?