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Magazine Chapter 2: Q17E (page 75)
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 Hampshire wells. Data were collected for a sample of 223 wells. Three of the variables are qualitative in nature: well class (public or private), aquifer (bedrock or unconsolidated), and detectible level of MTBE (below limit or detect). [Note: A detectible level of MTBE occurs if the MTBE value exceeds .2 micrograms per liter.] The data for 11 selected wells are shown in the accompanying table.
Source: Based on J. D. Ayotte, D. M. Argue, and F. J. McGarry, 鈥淢ethyl tert-Butyl Ether Occurrence and Related Factors in Public and Private Wells in Southeast New Hampshire,鈥� Environmental Science & Technology, Vol. 39, No. 1, Jan. 2005, pp. 9鈥�16
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.
c. Use side-by-side bar charts to compare the proportions of contaminated wells for bedrock and unconsolidated aquifers.
d. What inferences can be made from the bar charts, parts a鈥揷?
Short Answer
a) Three qualitative variables are the well class (public or private), aquifer (bedrock or unconsolidated), and detectible level of MTBE (below limit or detect).
b) The proportions of contaminated wells for private and public well classes are below the limit or detected.
c) The proportions of contaminated wells for bedrock and unconsolidated aquifers are below the limit or detected.
d) We can infer that there are relatively equal numbers of public and private wells
Step by step solution
(a) Three qualitative variables
The three qualitative variables are the well class (public or private), aquifer (bedrock or unconsolidated), and detectible level of MTBE (below limit or detect).
The aquifer class frequencies are depicted in the bar chart (bedrock or unconsolidated).
The bar chart describes class frequencies for detectible levels of MTBE (below limit or detected).
(b) The proportions of contaminated wells for private and public well classes
The proportions of contaminated wells for private and public well classes are below the limit or detected.
(c) The proportions of contaminated wells for bedrock and unconsolidated acquirers
The proportions of contaminated wells for bedrock and unconsolidated aquifers are below the limit or detected.
(d) Inferences
According to the class frequency bar charts, there are similar numbers of public and private wells (54% vs. 46%). Most aquifers (90%) are bedrock, and the majority of wells (69%) have MTBE levels below the limit. In addition, public wells (40%) are more polluted than private wells (21%). Ultimately, bedrock aquifers are only 20% polluted, but unconsolidated aquifers are 100% contaminated. Unconsolidated aquifers are only found in public wells.
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