Idaho Wellhead Sampling Program Nitrate Sampling Cumulative Results 1990-99

Water Quality
Water is the lifeblood of Idaho! Idaho ranks second in the United States in water use, only to California. Our traditional industries such as agriculture, forestry, and mining are all water dependent. And a large portion of tourist revenues in Idaho are tied to attractions with water. In addition to the economy, high quality water is essential to Idaho's recreational opportunities and wildlands. We must protect water quality to maintain our high standard of living and uniquely rich quality of life in Idaho.

Over 90 percent of Idahoans rely on groundwater for their drinking water. Surveys in Idaho have generally shown that groundwater quality is not a widespread problem.

The Program
The Idaho Private Wellhead Sampling Program was initiated and coordinated by the Idaho Farm Bureau Federation (IFB). In conjunction with local county Farm Bureau branches, 2,524 private wellhead samples have been collected from farmers and rural residents in 25 counties between 1990 and 1999.

This program has truly been a cooperative effort as several different government agencies and the Idaho Farm Bureau Federation, a private membership-oriented organization, united to make the program a success. The Idaho Department of Agriculture (IDA), Natural Resource Conservation Service (NRCS), local Health Districts, and the University of Idaho Cooperative Extension System (UI CES) assisted with program logistics, sample bottle distribution, and dissemination of information. The University of Idaho College of Agriculture's Analytical Laboratory (UI LAB) had major roles in planning and designing the quality assurance phase of the analytical part of the program and 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 for the public. The United States Geological Survey (USGS) assisted with the collection of samples for quality assurance.

Why Conduct This Program?
Groundwater monitoring surveys across the U.S. have shown 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 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.

The Sampling
A total of 2,524 samples was collected from farmers and rural residents between 1990 and 1999.

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. Forty-four 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.

The wells containing less than 2.0 ppm NO₃-N are in excellent shape. There is no reason to believe that man-induced practices are adding nitrates to groundwater in these areas since low levels of NO₃-N (0.5 to 2.0 ppm) may be natural in some parts of the aquifers.

Man probably has adversely impacted water quality where NO₃-N levels exceed 2.0 ppm. Several factors such as animal waste, excessive fertilizer use, 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 (34 percent of sampled wells), agriculturalists should implement best management practices (BMPs) to prevent further increases in groundwater NO₃-N values.

Where nitrate-N values range between 5.0 and 9.9 ppm NO₃-N (15 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. However, animal wastes, septic systems, and plant residues may be responsible for elevated NO₃-N values. In situations where fertilizers and/or animal wastes may be impacting nitrate levels in groundwater you should consider changes in N fertilization and/or 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 to detect the presence of other agricultural chemicals.

Summary by Regions
Northern Idaho
A total of 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. 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 4.9 ppm; and 11 percent had values greater than 5.0 ppm (50 percent of the drinking water standard).

Southwestern Idaho
Nitrate values in groundwater were higher in southwestern Idaho than other regions of the state. Still, 91 percent of the samples did not exceed the drinking water standard. A total of 1,206 samples was collected from Ada, Canyon, Elmore, Gem, Owyhee, Payette, and Washington counties. About 9 percent of the wells exceeded the 10.0 ppm NO₃-N drinking water standard. More than 59 percent of the wells had NO₃-N levels between 2.0 and 4.9 ppm; and 25 percent of the wells had values greater than 5.0 ppm.

Southcentral Idaho
A total of 542 water samples was collected from wells in Cassia, Jerome, Minidoka, and Twin Falls counties. About 4 percent of the wells contained NO₃-N values that exceeded the drinking water standard. Conversely, 21 percent of the wells contained NO₃-N values between 2.0 and 5.0 ppm; and 25 percent had values greater than 5.0 ppm. Ninety-six percent of the wells meet the drinking water standard in the region. However, using the 2.0 ppm value, humans have impacted the nitrate content in 79 percent (above 2.0 ppm) of the wells.

Southeastern Idaho
Nitrate values in groundwater were lower in southeastern Idaho than in southwestern or southcentral Idaho as 97 percent of the samples did not exceed the drinking water standard. A total of 480 samples was collected from Bonneville, Caribou, Franklin, Fremont, Jefferson, Madison, Oneida, and Teton counties. About 3 percent of the wells exceeded the 10.0 ppm NO₃-N drinking water standard. More than 39 percent of the wells had NO₃-N levels above 2.0 ppm; 26 percent contained NO₃-N levels between 2.0 and 4.9 ppm; and 13 percent of the wells had values greater than 5.0 ppm.

Mountain Idaho
From this sampling, water quality appears better in the mountainous region of Idaho than other areas of the state. A total of 212 water samples was collected from wells in Butte, Custer, and Lemhi counties. Only 1 percent of the wells contained NO₃-N values that exceeded the drinking water standard. In addition, 82 percent of the wells contained less than 2.0 ppm NO₃-N; 14 percent contained NO₃-N values between 2.0 and 4.9 ppm; and 4 percent had values greater than 5.0 ppm.

Quality Assurance
Quality control in this sampling project was the top priority. Blind spiked samples and blanks were randomly dispersed with farmer-provided samples to assure top quality. In addition, in some cases, duplicate farm wellhead samples were included. Over 1,300 quality control samples were part of this study. Nitrates were determined on water samples by the University of Idaho College of Agriculture's Analytical Laboratory in Moscow.

Summary
According to this survey, the majority of Idaho's wells (94 percent) are producing water that meets the state and U.S. EPA drinking water standard for nitrate-N.

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.

The University of Idaho Cooperative Extension System has over 140 faculty strategically located throughout the state, including 84 agricultural educators stationed in 42 of 44 counties. In addition, faculty (specialists) are located on campus in Moscow and at research and extension centers in Aberdeen, Caldwell, Idaho Falls, Kimberly, Parma, Sandpoint, Tetonia, and Twin Falls.

This brochure, WQ-39, was prepared by R. L. Mahler and K. A. Loeffelman, Soil Science Division, University of Idaho, Moscow, Idaho 83844.
1,000, 8-99

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Revised: January 3, 2003

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