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.

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

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

Well Class Aquifer Detect MTBE?

Private Bedrock Below Limit Private Bedrock Below Limit Public Unconsolidated Detect Public Unconsolidated Below Limit Public Unconsolidated Below Limit Public Unconsolidated Below Limit Public Unconsolidated Detect Public Unconsolidated Below Limit Public Unconsolidated Below Limit Public Bedrock Detect Public Bedrock Detect

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

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