National Water-Quality Assessment (NAWQA) Program
U.S. GEOLOGICAL SURVEY
Water-Resources Investigations Report 98-4222
Sacramento, California, 1999
Figure 36. Concentrations of chlorpyrifos at two sites. The U.S. Environmental Protection Agency aquatic-life criterion value of 0.041 microgrm per liter is shown as a horizontal line. Concentrations reported as not detected were assigned a value of zero.