What is the significance of concentrations greater than one-tenth of MCLs or HBSLs?
For individual contaminants, concentrations within one-tenth of a human-health benchmark are often used to identify contaminants that may warrant additional monitoring, to analyze trends in their occurrence, and to provide an early indication of contaminant concentrations that approach their benchmarks. Early attention to potential ground-water contamination, in particular, is warranted because the movement of ground water is usually slow and contamination is difficult to reverse. As a result, the presence of contaminants at concentrations less than, but approaching benchmarks can inform water-resource managers about needs for preventive actions for sources of these contaminants. Federal and state agencies use the criteria of one-tenth of a human-health benchmark for a variety of purposes—examples include: (1) reporting contaminant occurrence in ground water (New Jersey Department of Environmental Protection, 2003), (2) reporting pesticide detections in water to USEPA under the Federal
