National Water-Quality Assessment (NAWQA) Project
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U.S. GEOLOGICAL SURVEY
Water-Resources Investigations Report 98-4222
Sacramento, California, 1999
Figure 15. Distributions of annual mean detection frequencies of the
most commonly detected compounds for each of the three types of sites.
Each boxplot represents the distribution of detection frequencies for a
specific compound among the sites in each group during a 1-year period.
Detection frequencies are based on a common reporting level of 0.01 microgram
per liter for all compounds.
(See figure 5A and associated text for
an explanation of boxplots.)