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North Carolina Radon-in-Water Advisory Committee Report



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    Radon-222 (radon) is a naturally occurring radioactive gas and human carcinogen found in groundwater drinking supplies in some parts of North Carolina (NC) at levels that may pose a public health risk. Radon is produced during the decay of uranium-238, an element common in many rocks throughout the Piedmont and mountains of NC. In some areas, dissolved radon concentrations are among the highest in the United States (Hess and others, 1985; Horton, 1983; 1985). This is problematic because about 40 percent of North Carolinians use groundwater as their principal drinking supply. Radon is the leading cause of lung cancer among non-smokers and one of the leading environmental causes of cancer mortality in the United States (Field, 2010). The primary risk associated with radon in water is from inhalation (lung cancer) of radon gas released during household water use; a minor secondary risk is from ingestion (stomach cancer). Increased cancer risks associated with radon in water are greater - in some cases by an order of magnitude or more - than a large number of Environmental Protection Agency (EPA) and State (15A NCAC 02L .0200) regulated contaminants at their respective maximum contaminant levels (MCLs), including benzene, trichloroethylene, tetrachloroethylene, ethylene dibromide, vinyl chloride, combined radium, uranium, and others. Generally, the risks associated with radon in water are relatively small when compared to the risks associated with radon from soil and rock. In 1991, the U.S. Environmental Protection Agency (EPA) proposed an MCL of 300 picocuries per liter1 (pCi/L) for radon in community water supplies. In 1999, EPA proposed an alternate MCL of 4,000 pCi/L (Federal Register, November, 1999) for water suppliers with a multimedia radon mitigation program that included reduction of airborne radon exposure. These levels were designed to prevent additional cancer incidents resulting from exposure to radon in water. To date, these standards have not been enacted, and many states have established their own radon-in-water advisories at levels ranging from 800 to 10,000 pCi/L. Geology is the primary influence on dissolved radon levels in NC (Loomis, 1987; Campbell, 2006, 2008). About 25 percent of the Piedmont and mountains of NC are underlain with rocks commonly associated with elevated radon in water, namely granites and granitic gneisses. Based on geology and radon-in-water data collected to date, seven areas in the state are considered to be particularly susceptible to elevated radon in water and are mapped in this report. These areas comprise part of 19 counties, including Buncombe, Caldwell, Catawba, Cleveland, Franklin, Gaston, Henderson, Jackson, Lincoln, McDowell, Mecklenburg, Mitchell, Rutherford, Transylvania, Vance, Wake, Watauga, Wilkes, and Yancey Counties. Many of these areas are also associated with elevated indoor air radon. Surface water supplies in general, and groundwater supplies in the Coastal Plain, tend to be relatively low in dissolved radon. Radon-in-water data are lacking in many counties that contain rock units commonly associated with elevated radon in water, and an ongoing sampling program (NC Division of Water Quality) is helping to fill these gaps. Private bedrock wells sampled within seven areas of particular susceptibility to dissolved radon (n = 358; median radon = 4,680 pCi/L) show that 99% contained radon above 300 pCi/L, 57% above 4,000 pCi/L, and 19% above 10,000 pCi/L. The estimated increased lifetime cancer mortality risk associated with these radon levels is 2, 27, and 67 deaths in 10,000, respectively, for a mixed population of ever and never smokers. These risks well exceed the typical EPA risk tolerance range of 1 in 10,000 to 1 in 1,000,000. The vast majority of wells across NC contain radon above the proposed EPA MCL of 300 pCi/L. For practical and economic reasons, agencies generally have been willing to tolerate a larger risk for radon in water than for other dissolved contaminants. The North Carolina Radon-in-Water Advisory Committee was formed to evaluate radon-inwater occurrence and exposure in North Carolina, review peer-reviewed scientific literature on radon risks, and recommend a level of radon in water above which treatment should be considered. The committee was established by the NC Department of Environment and Natural Resources (DENR) (Division of Environmental Health and Division of Water Quality) and NC Department of Health and Human Services (DHHS) (Division of Public Health), and members include scientists from universities and from state and county government. The advisory level recommended by the Committee is not intended to be a regulatory standard. Rather, it is intended to be a guideline for well owners and state and local officials responsible for drinking water supplies and public health, education, and planning. The Committee's approach to radon in water is as follows (fig. 1). The Committee recommends an indoor air radon test for all occupied dwellings in NC. The Committee also recommends a radon-in-water test for all homeowners on a potable well that meet either of two criteria: (1) the home has an indoor air radon test result, after mitigation, above 4 pCi/L, or (2) the home has an indoor air radon test result above 2 pCi/L and is located within an area of moderate to high susceptibility to elevated radon in water as identified by the DWQ's program to map naturally occurring contaminants (currently identified areas are mapped in this report). The primary purpose of the radon-in-water test is to determine whether water is a significant contributor to indoor air radon levels. While the Committee does not ignore the ingestion risk, it focuses primarily on the much larger inhalation risk. In keeping with the EPA goal of limiting indoor air radon to 4 pCi/L (the current EPA action level), the Committee seeks to address the combined sources of radon (radon from soil gas and radon released from water) by limiting the combined exposure level to no more than 4 pCi/L. The Committee also recognizes the benefit of achieving an even lower exposure level and the associated reduced risk, and suggests that homeowners consider, as an option, a mitigation goal for combined sources of radon of between 2 and 4 pCi/L. The Committee recommends a radon-in-water advisory be set at two levels. At the moderate level, concentrations between 4,000 and 10,000 pCi/L in water, treatment is considered optional. At the elevated level, concentrations at or above 10,000 pCi/L in water, treatment should be considered in conjunction with the treatment of indoor air radon released from soil gas. In most cases, mitigation of soil gas radon will have the greatest impact on reducing overall radon exposure and will usually take precedence over treatment of radon in water. Testing well water for radon is easy and costs about $20 to $75. Bubble aeration systems effectively remove radon in water and range in price from about $2000 to $4000. Somewhat less expensive, whole house granular activated carbon filtration systems may be appropriate when radon levels do not exceed about 5,000 pCi/L3 Testing well water for radon is easy and costs about $20 to $75. Bubble aeration systems effectively remove radon in water and range in price from about $2000 to $4000. Somewhat less expensive, whole house granular activated carbon filtration systems may be appropriate when radon levels do not exceed about 5,000 pCi/L3. A program of additional sampling of radon in water is recommended in areas that lack adequate data, particularly in areas that contain rock units commonly associated with elevated radon in water. [Description provided by NIOSH]
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  • Document Type:
    Text
  • Funding:
    Grant
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  • Location:
  • Pages in Document:
    1-30
  • NIOSHTIC Number:
    nn:20063841
  • Citation:
    Final Report of the NC Radon-in-Water Advisory Committee, 2011 Mar; :1-30
  • Contact Point Address:
    Ted Campbell, MS, Committee Chair, North Carolina Department of Environment and Natural Resources, Division of Water Quality, Raleigh, NC
  • CAS Registry Number:
  • Federal Fiscal Year:
    2011
  • Performing Organization:
    University of Iowa
  • Peer Reviewed:
    False
  • Start Date:
    20050701
  • Source Full Name:
    Final Report of the NC Radon-in-Water Advisory Committee
  • End Date:
    20290630
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  • Main Document Checksum:
    urn:sha-512:b0bfe6f149aaea6fdda8ca19906a8c20429d566be3924bcbafe21a7a753ac4e7b42cbc3053c77bfa8cbb1ffa786d42e8e738854e601ea1333c53649cd8920324
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  • File Type:
    Filetype[PDF - 626.33 KB ]
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