Scientific Investigations Report 2007–5179
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2007–5179
Figure 13. Relation between ranked nitrate concentrations and ranked well, aquifer, and land-use characteristics in agricultural areas within regional National Water-Quality Assessment Program study units in the arid to semiarid Western United States, 1993–2004. See figure 1 for definitions of study unit abbreviations.