Pollution of both surface and ground waters by two major contaminants – nitrogen and phosphorus – has failed to improve or has gotten worse since the early 1990s, a major new study by the U.S. Geological Survey reports.
The new study, released Thursday, Sept. 23, contained compelling evidence about the widespread nitrate contamination of shallow aquifers, the source of water for many people who rely on private wells.
The study, which examined results from multiple tests of streams and groundwater between 1992 and 2004, found:
- Nitrate concentrations in 7 percent of about 2,400 private wells across the country exceeded the national health standard for drinking water.
- In agricultural areas, water from more than 20 percent of the shallow private wells tested exceeded the health standard.
- In deeper wells used for public water supply systems, about 3 percent of the water tested exceeded the limit.
- In streams in agricultural and urban areas, levels of nitrogen and phosphorus were two to 10 times greater than Environmental Protection Agency criteria set for protecting the health of plants and other organisms.
Elevated levels of nitrate can be caused by fertilizers, runoff from feedlots and septic systems. High levels of nitrate in drinking water are especially harmful for infants, causing a condition known as methemoglobinemia or “blue baby syndrome.”
Phosphorus from fertilizers and naturally occurring organic sources feeds nuisance algae growth. High levels of nitrogen and phosphorus contribute to oxygen-deprived “dead zones” in the Gulf of Mexico and other waters.
The USGS report, titled Elevated Nitrogen and Phosphorus Still Widespread in Much of the Nation’s Streams and Groundwater, is available at www.usgs.gov.
In a news release announcing the report’s release, Mathew C. Larsen, the USGS associate director for water, said: “Despite major federal, state and local efforts and expenditures to control sources and movement of nutrients within our nation’s watersheds, national-scale progress was not evident in this assessment, which is based on thousands of measurements and hundreds of studies across the country from the 1990s and early 2000s.”
In Minnesota, a random test of water quality in about 700 private wells in the mid-90s by the state Health Department, found that 5.8 percent exceeded the health standard for nitrate.
In Dakota County, where the county aggressively samples water from private wells, about one in every four wells violates the health standard for nitrate, according to Jill Trescott, the county’s supervisor for groundwater protection.
“It’s definitely worse in the rural parts of the county, particularly in the east and the south,” Trescott said. And she added: “It’s the older wells we see problems with.” Newer wells, drilled since about 1989, are much less likely to exceed the nitrate standard because wells since then have been drilled deeper, she said.