How does NAWQA assess potential effects on human health?
Concentrations of nutrients in drinking water are regulated by U.S. Environmental Protection Agency (USEPA) under the Safe Drinking Water Act (SDWA). To evaluate the potential significance of nutrient concentrations to human health, concentration in streams and groundwater samples are compared to regulatory Maximum Contaminant Levels (MCLs). MCLs are referred to as human-health benchmarks in this study. The USEPA drinking-water standard (MCL) for nitrate is 10 mg/L as nitrogen. Concentrations greater than benchmarks are potential human-health concerns, but do not mean that adverse effects are certain to occur because the benchmarks are conservatively protective, and most samples were collected prior to any treatment or blending of water that potentially could alter contaminant concentrations.
