National Water-Quality Assessment (NAWQA) Program
U.S. GEOLOGICAL SURVEY
Water-Resources Investigations Report 98-4222
Sacramento, California, 1999
Figure 22. Monthly median concentrations of total herbicides and the six herbicides detected most frequently at the 37 agricultural indicator sites during a 1-year period. Each value represents the median concentration for 1 month. The annual median for each site is shown in red. Monthly median concentrations less than the detection limit are shown as points on the x-axis. For sites at which all 12 monthly values were below the detection limit, the annual median value is plotted on the x-axis. The sites are arranged by crop group classification an presented in the same order as in table 1. Site codes are defined in table 1 and crop group codes are define in table 4.