Is nitrate contamination expected to continue in deep groundwater that may be used as a drinking water supply in the future?
Nitrate concentrations are likely to increase in deep aquifers typically used for drinking-water supplies during the next decade, despite nutrient reduction strategies, as shallow groundwater with high nitrate concentrations moves downward to deeper aquifers. USGS findings show that the percentage of sampled wells with nitrate concentrations greater than the USEPA drinking-water standard increased from 16 to 21 percent since the early 1990s. Nitrate can persist in groundwater for years or decades and may continue to be present at high concentrations because of previous land uses and nutrient sources, such as fertilizers, manure, and septic systems. A national statistical model was developed to assess the vulnerability of relatively deep groundwater (more than 164 feet below land surface) to nitrate contamination. Model simulations predict moderate (greater than 5 but less than 10 milligrams per liter) to severe (greater than 10 milligrams per liter) nitrate contamination in groundwater
