METHODS DOCUMENTATION FOR APPENDIX GRAPHS
NAWQA Study-Unit Summary Reports, 2004
Description of Graphs
The graphs are designed to compare each NAWQA Study Unit's data to national data. The national
dataset consists of data from 52 NAWQA Study Units, 20 of which began their study in 1991,
16 of which began in 1994, and 16 of which began in 1997. Data were collected in several media:
surface water, ground water, bed sediment, and fish tissue.
Surface water and ground water data are shown together in the same graphs, and bed
sediment and tissue are shown together. Semi-volatile organic compounds are
shown only in bed sediment. Trace elements are shown only in ground water.
Volatile organic compounds are shown in ground water and
urban surface water only.
Each medium is broken down into three land use categories:
- Agriculture
- Urban
- Mixed land use (surface water)/Major aquifers (ground water)
Each category shows a national distribution as a colored boxplot, with a study unit's
detections plotted over the colored bar
as black diamond symbols. The colored boxplot bars are thicker for the middle
50 percent (the 25th - 75th percentile range) of the national detections,
and thinner (whiskers) for the uppermost and lowermost
quartiles of the national dataset.
These national boxplot bars are calculated only from detections; that is,
all nondetections are excluded from the national percentiles and range.
Selected Water Quality Benchmarks
(Maximum Contaminant Levels and health advisories for drinking water,
criteria for the protection of
aquatic life, and criteria for the protection of fish-eating wildlife), are plotted as vertical
lines overlying the national bars and the study unit detections.
To the left of the concentration graphs are two columns of detection
frequencies. For each land use bar, the
left number is the uncensored frequency of detection for the study unit,
and the right number is the uncensored frequency of detection from the national dataset.
To the right of the concentration graphs is another column of numbers,
which represent the number of study unit samples represented in that row
of the graph, i.e., for that medium and land use.
NAWQA home page
- USGS Water Resources
- USGS Home
The URL for this page is http://oregon.usgs.gov/sumrpt/descr_of_grphs.html
Contact Ken Skach, 503-251-3285, with your comments and questions.
Last Modified: Fri Jun 25, 2004