Nitrates In Groundwater: A Persistent Nationwide Problem

USGS Map of Nitrate in Shallow Groundwater

One of the great accomplishments of the environmental movement in the US has been to secure clean drinking water for the vast majority of Americans and to protect the waterways and aquifers that serve as sources of clean drinking water. In fact, The Clean Water Act of 1972 and The Safe Drinking Water Act (SDWA) of 1974 are considered two of a handful of federal laws that ushered in the modern era of environmental protection. Considering all the progress that has been made, it is easy to forget that the work of the SDWA is not done. It is not just third-world problem: many folks right here in the U.S. still lack access to safe drinking water. A recent article in the New York Times entitled, Safe Drinking Water Elusive for Many in California tells the tale of a small agricultural community in the Central Valley of California that has unsafe drinking water due to elevated levels of nitrates from fertilizer use in surrounding agricultural areas. Septic systems and animal feedlots (also called concentrated animal feeding operations or CAFOs) are also sources of nitrate contamination to the environment.

 We often consider petroleum hydrocarbons and industrial solvents when thinking of groundwater contamination, and these are certainly serious issues. However, nitrate is one of the most common groundwater contaminants in the nation, especially in rural areas. As seen on the attached map, wide regions of the country are vulnerable to nitrate contamination in shallow groundwater. This is because nitrate contamination is associated with agricultural fertilizer use and because many rural communities rely on local groundwater for their drinking water. Nitrate in drinking water is a health risk, especially for infants and young children primarily because it reacts with hemoglobin and compromises the ability of blood to transport oxygen throughout the body. Nitrate can also be an indicator for the presence of other contaminants, such as bacteria or pesticides.

 As discussed by the US Geological Survey in the recent journal article, “Vulnerability of Streams to Legacy Nitrate Sources” (Environmental Science & Technology, 2013, v. 47, pp. 3623-3629; subscription required) nitrates can take decades to migrate in groundwater to a stream or lake or water well, thus even if fertilizer application is managed responsibly today, the legacy of past practices will be with us for decades to come.