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Fig. 1. Concentrations of herbicides measured in ground water at individual sites during the NAWQA investigation, in relation to drinking-water quality criteria (USEPA, 2000). Lifetime health advisory level (HAL) shown for herbicides for which no maximum contaminant level (MCL) has been established. (Neither criterion has yet been established for acetochlor.) Overall percentage of sites with no detections given above the not detected symbols for each herbicide. Number of sites sampled for each study component given in Fig. 2. LUSs, land-use studies; SUSs, subunit surveys.
