Refer to the Environmental Science & Technology (Jan. 2005) study of the MTBE contamination in New Hampshire wells, Exercise 2.12. Consider only the data for those wells with detectable levels of MTBE. The MINITAB printout below gives summary statistics for MTBE levels (micrograms per liter) of public and private wells.
a. Find an interval that will contain most (about 95%) of the MTBE values for private New Hampshire wells.
b. Find an interval that will contain most (about 95%) of the MTBE values for public New Hampshire wells.
Data from Exercise 2.12
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 Hampshire wells. Data were collected for 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 micrograms per liter.) The data for 10 selected wells are shown in the accompanying table. Use graphical methods to describe each of the three qualitative variables for all 223 wells.
