National Water-Quality Assessment (NAWQA) Program
U.S. GEOLOGICAL SURVEY
Water-Resources Investigations Report 98-4222
Sacramento, California, 1999
Figure 24. Examples of temporal concentration patterns at eight agricultural indicator sites. The upper plot for each site shows total herbicide concentrations, and the lower plot shows total insecticide concentrations. The concentration of total herbicides is shown on the left axis, and the concentration of total insecticides is shown on the right axis. The same 2-year period is shown for each site. Samples with no detections of either herbicides or insecticides were assigned a concentration of zero.