Annual nitrate concentration (mg/L) in groundwater sources for Group A systems across Puget Sound (2011-2021). The yellow boxes illustrate the middle 50% of the concentration values, showing the first quartile (25th percentile), median (center), and third quartile (75th percentile). Whiskers are drawn to the 10th and 90th percentile; points outside the whisker boundaries represent outlier values. Blue reference lines are drawn at 2, 5 and 10 mg/L to show regulatory and health thresholds. Nitrate concentrations below 2 mg/L reflect levels found in natural groundwater. Concentrations above 2 mg/L indicate human activities contribute to contamination. When concentrations exceed 5 mg/L the frequency of sampling increases to better monitor concentrations. 10 mg/L is the EPA's maximum contaminant level for nitrate.
No targets are currently set for this indicator.
Washington State Department of Health, Water System Data Sentry Database