National Water-Quality Assessment (NAWQA) Project
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By Robert J. Gilliom and Gail P. Thelin
U.S. Geological Survey Circular 1131
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U.S. Department of the Interior | U.S. Geological Survey URL: http://water.usgs.gov/nawqa/pnsp/pubs/circ1131/fig1.html Page Contact Information: gs-w_nawqa_whq@usgs.gov Page Last Modified: Tuesday, 04-Mar-2014 14:44:19 EST