Nitrates in Groundwater

Mapping Nitrate Contamination in California’s Groundwater Aquifers

These maps developed by CCKA, using U.S. Geological Survey (USGS) data, provide a picture of nitrate contamination in the aquifers of central California.  The wells mapped are domestic, private water supply wells, and the water quality data taken at these wells are intended to provide an indication of the drinking water quality of Californians that rely on private domestic wells for drinking water.  Data points are largely clustered in the Central Valley because this is where USGS studies have focused in California. 

The primary source of nitrate contamination in California is agriculture. Commercial fertilizers and animal wastes release highly soluble nitrates, which then leach through the soil from land application or run off into surface waters and eventually work their way down into groundwater aquifers. The U.S. Environmental Protection Agency’s (EPA) Maximum Contaminant Level (MCL) for nitrates is 10 milligrams per liter (mg/L), though nitrate concentrations far less than that can damage aquatic species. Infants and children are particularly susceptible to illness from nitrate contamination: immature human digestive systems convert nitrate into nitrites, which enters the bloodstream and reduces the ability of blood to carry oxygen. This can lead to the potentially fatal "blue baby syndrome". The maps below show that numerous areas of the state have groundwater concentrations of nitrates above or near the maximum contaminant level, even in areas where residents’ primary source of drinking water is groundwater.  Visit CCKA’s Groundwater Page to learn more about pollution in California’s aquifers.

Pick a Map to View
Wells and Agricultural Irrigation  
Wells and Domestic Groundwater Withdrawals
Wells and Land Cover