Description The Sale Drinking Water Act. which was passed in I974. 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' taps. These contaminants include microorganhtms, organic chemicals. and inorganic chemicals. such as cyanide. Cyanide's presence in drinking water is the result of discharges lrom 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 includ an analysis of the results shown in the gure at the right. The gure shows the point estimates for the population mean concentration and die 95% confidence intervals for n for cyanide over a three-year period. The data are based on random water samples taken by the city's three water treatment plants. Cyanide (in parts per million) Mean concentration level Year 1 Year 2 Year 3 YearExercises 1. Interpreting the Results Use the figure to determine whether there has been a change in the mean concentration level of cyanide for each time period. Explain your reasoning. b. From Year 1 to Year 2 c. From Year 2 to Year 3 d. From Year 1 to Year 3 2. What Can You Conclude? Using the results of Exercise 1, what can you conclude about the concentrations of cyanide in the drinking water? 3. What Do You Think? The confidence interval for Year 2 is much larger than that for the other years. What do you think may have caused this larger confidence level