Quality Water for Idaho Current Information Series No. 986

The Idaho Private Wellhead Sampling Program lets farmers and other rural residents with wells determine nitrate-nitrogen (nitrate-N, NO₃) levels in their drinking water. Initiated in 1990, this program provides nitrate-N values confidentially to Idaho residents.

Coordinated by the Idaho Farm Bureau Federation (IFB), the wellhead survey program eventually will cover most Idaho counties. From 1990 to 1992 a total of 1,849 samples from private wells and 1,162 quality control samples was collected in 14 Idaho counties (fig. 1). Initially, county selection was based on locations of highest risk in the state.

Fig. 1. Idaho counties surveyed for nitrates in wells from 1990 to 1992.

The program is a cooperative effort of the University of Idaho; the IFB, a private membership-oriented organization; and four government agencies. The Universityof Idaho Analytical Laboratory (UIAL) played a major role in planning and designing the quality assurance phase of the analytical part of the program. Also, the UIAL analyzed all samples for nitrates.

The Idaho Division of Environmental Quality (DEQ) designed the quality assurance plan for the field effort, the questionnaire, and sampling procedures. The Idaho Department of Agriculture (IDA), USDA-Soil Conservation Service (SCS), and United States Geological Survey (USGS) assisted with program logistics and sample bottle distribution and collection. The University of Idaho Cooperative Extension System (UI-CES) disseminated sampling results and helped with program logistics.

Why Conduct This Program?
A major potential groundwater contaminant is nitrate (NO₃^-). Humans ingest nitrate in both food and water. It is absorbed from the digestive tract and excreted rapidly in the urine of older children and adults. Healthy human adults can consume fairly large amounts of nitrate with no short-term adverse health effects. The health effects of chronic, long-term consumption of high dietary levels of nitrate are uncertain.

Infants younger than 6 months of age are susceptible to nitrate poisoning. Bacteria present in their digestive systems at birth can change nitrate to the more toxic nitrite (NO₂^-). Newborn infants have little acid in their digestive tracts, and they depend on these bacteria to help digest food. Usually, by the time infants reach 6 months of age, hydrochloric acid levels increase in their stomachs and kill most of the bacteria that convert nitrate to nitrite.

Once formed, the nitrite is absorbed and enters the bloodstream. There it reacts with the oxygen-carrying hemoglobin to form a new compound called "methemoglobin." This compound interferes with the blood's ability to carry oxygen. As oxygen levels decrease, a baby may show signs of suffocation. This condition is called "methemoglobinemia" or "blue baby syndrome." The major symptom of methemoglobinemia is bluish skin color, most noticeably around the eyes and mouth.

Infant deaths from methemoglobinemia are poorly documented and considered rare. Some documented deaths have been linked to high levels of nitrate in well water. doctors now recommend using bottled water to make formula when nitrate levels exceed the U.S. Public Health Service drinking water standard of 10 parts per million (ppm NO₃-N).

Besides causing problems in infants, nitrates are an indicator that other agrichemicals are present in groundwater. If nitrate levels are high, consider testing for the presence of mobile pesticides in groundwater. But, if nitrate values are low, groundwater contamination by pesticide leaching is less likely.

Groundwater monitoring surveys across the United States show that agrichemicals such as nitrogen fertilizers are contaminating many sources of groundwater. Idaho surveys show that nitrates are being found in several major aquifers.

The Idaho Division of Environmental Quality (DEQ) has identified many aquifers in the state as vulnerable groundwater resources. This is a major concern because groundwater is the source of drinking water for more than 90 percent of Idahoans. Some of the factors contributing to vulnerable areas in Idaho include:

• Numerous shallow aquifers.
• Large areas of sandy soil where leaching may occur (localized to southern Idaho).
• Excessive use of irrigation water that may flush nitrates into groundwater.
• Intensive and extensive N fertilizer use ranging from 50 to 300 pounds N per acre on cropland.
• Intensive animal operations producing large quantities of manure, that may contribute nitrates to the groundwater, in localized areas.
• Increasing numbers of rural septic tanks, which, if not maintained properly, may contribute nitrates to groundwater.

After collection, a preservative was added to the water sample before shipping to the UIAL in Moscow. Analyses were run in the laboratory within 72 hours of sample collection. Samples were tested for nitrate using EPA method 353.2, a cadmium reduction method by flow injection analysis. Because of this detailed protocol, we can place a high degree of confidence in this study's results.

Statewide Results
Six percent of the sampled wells in Idaho contained NO₃-N levels greater than 10 ppm, which is the state and U.S. Environmental Protection Agency (EPA) drinking water standard (fig. 2). More than 38 percent of the sampled wells contained less than 2.0 ppm NO₃-N. This study shows that:

• 6 percent of the wells contain more than 10.0 ppm nitrate-N and do not meet the drinking water standard.
• 94 percent of the sampled wells do not exceed the drinking water standard.

Fig. 2 Distribution of nitrate-N in well water samples from entire state from 1990 to 1992.

Man probably has impacted water quality where NO₃-N levels exceed 2.0 ppm. Several factors such as agriculture and poorly operating septic tanks may cause nitrate levels in groundwater to increase.

In areas where NO₃-N values range between 2.0 and 4.9 ppm (40 percent of sampled wells), agriculturalists should implement best management practices (BMPs) to prevent further increases in groundwater NO₃-N values. For more information see University of Idaho Current Information Series No. 962, Best Management Practices for Nitrogen Management to Protect Groundwater.

Where nitrate-N values range between 5.0 and 9.9 ppm NO₃-N (16 percent of sampled wells), the nitrate-N concentration is still safe and acceptable for human consumption. These wells should be sampled again within a 2- to 3-year period. Nitrogen fertilizer is the likely source of elevated N levels in groundwater in many Idaho areas. Also, animal wastes, septic systems, and plant residues may be responsible for elevated NO₃-N values. In these situations, you should consider changing N fertilizers and irrigation management.

Take action if your well contains more than 10.0 ppm NO₃-N. If an infant (<6 months of age) is living in a household with a well containing more than 10.0 ppm NO₃-N, consider alternative water sources or water treatment devices. Also, well owners should obtain additional analyses for potential agricultural chemicals.

Summary by Regions
Northern Idaho
According to this sampling, water quality is better in northern Idaho than other regions of the state. A total or 142 water samples was collected from wells in Benewah, Bonner, and Latah counties. Less than 3 percent of the wells contained NO₃-N values that exceeded the drinking water standard (fig. 3). In addition, 76 percent of the wells contained less than 2.0 ppm NO₃-N; 13 percent of the wells contained NO₃-N values between 2.0 and 5.0 ppm; and 11 percent had values greater than 5.0 ppm (50 percent of the drinking water standard).

Fig. 3. Distribution of nitrates in well water samples from northern Idaho.

Fig. 4. Distribution of nitrates in well water samples from southwestern Idaho.

Fig. 5. Distribution of nitrates in well water samples from southcentral and southeastern Idaho.

Fig. 6. County distribution of wells meeting federal drinking water standards (10.0 ppm) for nitrate-N.

Fig. 7. County distribution of percentage of wells sampled with elevated nitrate-N values (>5.0 ppm).

For the most part, these results are reassuring to Idahoans. To deal with specific and geographic problems, use proactive approaches that will protect and enhance water quality while ensuring the survival of Idaho's number one industry -- agriculture. Where NO₃-N levels are high, use BMPs to apply N-containing materials.

This program is one of the largest wellhead sampling programs in the United States. When completed in the next 2 to 3 years, it will provide an extensive data base for Idahoans to analyze effectively the quality of groundwater and plan for the future.

The Authors -- Robert L. Mahler, professor of soil science and Extension water quality specialist; Gregory Möller, technical director of the University of Idaho Analytical Laboratory; Kim A. Anderson, UIAL inorganic group leader, and Karen A. Mahler, water quality research associate, University of Idaho, Moscow.
Acknowledgments -- The authors thank Gerry Winter of the Idaho Division of Environmental Quality, and Jim Yost and Rayola Jacobson of the Idaho Farm Bureau, for their help with this project.

Issued in furtherance of cooperative extension work in agriculture and home economics, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, LeRoy D. Luft, Director of Cooperative Extension System, University of Idaho, Moscow, Idaho 83844. The University of Idaho provides equal opportunity in education and employment on the basis of race, color, religion, national origin, gender, age, disability, or status as a Vietnam-era veteran, as required by state and federal laws.

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Comments to author: karenl@uidaho.edu

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