Walker M. and Powell P. 2011, Radioactivity and groundwater in the Lahontan Valley, Extension | University of Nevada, Reno, FS-11-39

Groundwater sampling surveys in the Lahontan Valley found that 11 of 63 (17 percent) of private domestic wells that were more than 50 feet deep had alpha radioactivity that exceeded the federal drinking water standard. Radioactivity also occurred in wells less than 50 feet deep, though it was below the standard. Samples from wells in the basalt aquifer used for public water supplies for Fallon, Churchill County, the U.S. Naval Air Station and the Fallon Paiute-Shoshone Tribe also had radioactivity at levels below the federal standard. Based on these results, we recommend that households with wells deeper than 50 feet test their water. If the amount of radioactivity exceeds drinking water standards, we recommend that homeowners install a reverse osmosis system to treat water used for drinking and cooking. University of Nevada Cooperative Extension can provide bottles for sampling and arrange for transportation to the Nevada State Health Laboratory.

Background

Radioactivity in water in the United States:

Small amounts of radioactive elements are found in almost all soil, rock and water. Groundwater throughout the United States contains radioactivity and radioactive elements. This is especially true in the western United States, where geologic processes eroded mountain ranges and deposited sediments in downstream valleys.

Decaying elements such as uranium emit several kinds of radioactivity, including alpha and beta radiation. Alpha emitting elements include uranium and the elements formed when uranium decays, including radon-222 and polonium-210.

Water samples are often tested for “gross alpha radiation,” which is the total amount of alpha radiation emitted from all of the radiation sources in a sample. “Excess alpha radiation” is a measure of the gross alpha radiation in a water sample minus the amount due to uranium and radon. Public water supplies may not provide water that has more than 15 pico- Curies/Liter (piCi/L) of excess alpha radiation in water. A picoCurie is a measurement of radioactivity produced by the disintegration of unstable elements in a sample.

In Nevada, communities that pump groundwater for public water supply treat to remove radioactivity and other contaminants. If the gross alpha radiation levels exceed the standard of 15 piCi/L, a sample is usually tested further to determine how much uranium is present. The drinking water standard for uranium in water is 30 micrograms per liter. A microgram is 1/billionth of a gram. A gram is about the same as .002 pounds.

Health Risks:

Human skin protects the body against alpha radiation. Alpha radiation is cause for concern primarily when ingested in water or food. The drinking water standard is based on an assessment of the risk from drinking two liters of water (about two quarts) a day for a lifetime. If contaminated groundwater is consumed or used to prepare food, the circulatory system may transport radioactive elements to internal organs.

At low levels and over long periods of time, alpha radiation can damage cells and DNA, which can increase the risk for cancer. Radioactivity does not have a distinctive odor, taste or color. As with many contaminants at low concentrations, radioactivity in water is not indicated by taste, odor or color.

Public and private water supplies:

One of the biggest differences between public and private water supplies is that public water supplies are tested and managed to meet the requirements of the U.S. Safe Drinking Water Act. This ensures that these utilities deliver safe drinking water to consumers. Private wells, such as those that might serve a single household, are not regulated by the Safe Drinking Water Act. The standards that specify the allowable limits of chemicals and other contaminants in drinking water are only enforced for public water supplies. Therefore, private water supply owners must be responsible for checking their own water to ensure it meets drinking water standards.

Public water supplies are regulated by the Nevada Division of Environmental Protection, through the Bureau of Safe Drinking water (NDEP). Public water supplies are defined as those that “supply water for human consumption through pipes or other constructed conveyances, (and have) 15 or more service connections, as defined in NRS 445A.843, or regularly serve 25 or more persons …" (from the website cited above).

Public water supplies must be managed by a certified drinking water supply operator. Operators test the water regularly for contaminants and publish a summary of the test results.

Private water supplies are springs or wells that usually serve a single household. There are no requirements that private wells be tested for contaminants. Testing may occur as part of real estate transactions, or if the owner has an interest in water quality. In the discussion of results that follows, it is important to remember that the major sources of drinking water in the Lahontan Valley, the public water supplies, are required by law to test water and to inform customers if its water does not meet standards. Those who use private water supplies, such as domestic wells, do not have equivalent protection. However, private well owners can protect themselves by sampling their water.

Lahontan Valley

The Lahontan Valley has deep aquifers made of materials washed by rivers from eroded mountain ranges. These materials contain many substances, including radioactive elements, which dissolve in water. This historical photo shows the Carson River in the foreground, with arid desert in the background. Photo Courtesy of the Churchill County Museum Photo Collection

Radioactivity in Lahontan Valley Groundwater:

The U.S. Geological Survey tested 100 wells in Lahontan Valley for radioactivity (see the resources section for information on how to access a report on the results of that survey). These included eight wells used for public drinking water (for the City of Fallon, Churchill County, the Naval Air Station, and the Fallon Paiute-Shoshone Tribe). The U.S. Geological Survey also tested 92 private domestic wells used by homeowners in the rural areas around Fallon and the rest of the valley. Of these, 29 were less than 50 feet deep and 63 were more than 50 feet deep. The difference in depths is important. Studies completed by the U.S. Geological Survey have shown that the chemistry of water in the shallow wells (less than 50 feet below the land surface) can be very different than in the wells that are between 50 to 500 feet below the land surface.

Public water supplies had very low levels of radioactivity, as did water from domestic wells less than 50 feet deep. The wells most likely to have high levels of radioactivity were more than 50 feet deep. Eleven of 63 wells deeper than 50 feet had radioactivity that exceeded the federal standards for drinking water. Some of the radioactivity was from uranium decay products, including polonium-210.

What the results mean:

The results show that public water supplies for the City of Fallon, the Naval Air Station, Churchill County and the Fallon Paiute- Shoshone Tribe met the standards for alpha radiation. Wells less than 50 feet deep contained excess alpha radiation, but at levels below the drinking water standard of 15 pCi/L. In some domestic wells, especially those more than 50 feet deep, alpha radioactivity above acceptable levels for public water supplies was found. Some wells had levels more than 10 times the federal standard.

Recommendations:

If your domestic well is deeper than 50 feet, you should test a water sample for radioactivity. You may also wish to test for other chemicals that are commonly found in Churchill County’s groundwater, such as arsenic. If well water samples have excess alpha radiation levels greater than 15 pCi/L, the water should not be used for drinking or cooking until you install a treatment system and retest water to show that the radioactivity has been reduced to acceptable levels.

 Testing water:

If you plan to test your water, confirm that the laboratory that will do the test has been certified by the Nevada Division of Environmental Protection (NDEP) to analyze drinking water. NDEP maintains a list of certified laboratories at NDEP.

The Nevada State Health Laboratory on the University of Nevada campus in Reno is a certified drinking water analysis laboratory and can test samples for gross alpha radiation. If you plan to submit a water sample for testing for radioactivity, contact the laboratory that will do the analysis to obtain the proper bottles. Be sure to get instructions about how to collect, store and transport the sample to the laboratory. Also, be sure that you provide the laboratory with all necessary information, including your name, address, telephone number and email address.

University of Nevada Cooperative Extension can help you get the proper sample bottles and sampling instructions. The Churchill County Hospital can help transport your samples from Fallon to the Nevada State Health Laboratory in Reno. For more information, contact the Cooperative Extension office at 775-423-5121. The office is located at 111 Sheckler Road, Fallon, NV.

Treatment options:

No home treatment systems have been tested thoroughly enough to show that they remove radioactivity from water. However, preliminary tests have shown that reverse osmosis was effective in a few cases. Reverse-osmosis is essentially filtration at the molecular level. Large molecules are retained by the reverse osmosis membrane, and smaller molecules pass through.

Reverse-osmosis is very effective at removing metals such as arsenic, which have much smaller molecules than uranium and its decay byproducts. This indicates that reverse osmosis should improve drinking water supplies. However, if you plan to use reverse osmosis as a treatment, you should test the system after it is in place to be sure that it is removing radioactivity and other chemicals. This means testing water before and after you have installed the reverse osmosis system.

Remember that reverse osmosis systems require regular maintenance. Without proper maintenance, reverse osmosis systems eventually will fail to treat water. Check the manufacturer’s recommendations for maintenance procedures and schedules. For a list of products that have been tested to ensure that they work as advertised, use the National Sanitation Foundation’s website – NSF. Note that this website does not have specific information about radioactivity in water. It lists reverse osmosis systems that the foundation has certified to be effective for other chemicals, such as arsenic.

Useful Resources:

Seiler, R.L., 2007, Methods and data used to investigate polonium-210 as a source of excess gross-alpha radioactivity in groundwater, Churchill County, Nevada: U.S. Geological Survey Open-File Report 2007-1231, Nevada Water Science Center.

A description of the standard for alpha radiation in drinking water is available at Radionuclides Rule.

The Water Test Interpreter: Water Data Interpreter will help you understand the results of water tests. It is designed to be used with test results received from the Nevada State Health Laboratory.

A fact sheet on polonium-210 in Lahontan Valley ground water is available at CDC.

A fact sheet developed by the Nevada Division of Environmental Protection about sampling and polonium-210 is available at NDEP.

Answers to frequently asked questions about polonium-210 are available at CDC.

Information about reverse osmosis units (how they work, how to select the right unit and how to install them) can be found at Publications.

Reports prepared by USGS describing aquifers, groundwater and groundwater quality in the Lahontan Valley can be obtained by contacting the USGS Public Information Officer by Email.

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