United States
Environmental Protection
Agency
Air and Radiation
(6604J)
4O2-R-S3-053
September 1993
vvEPA EPA's Map of Radon Zones
NORTH CAROLINA
Recycled/Recyclable
Printed on paper thai contains
at least 50% recycled fiber
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EPA'S MAP OF RADON ZONES
NORTH CAROLINA
RADON DIVISION
OFFICE OF RADIATION AND INDOOR AIR
U.S. ENVIRONMENTAL PROTECTION AGENCY
SEPTEMBER, 1993
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ACKNOWLEDGEMENTS
This document was prepared by the U.S. Environmental Protection- Agency's (EPA's)
Office of Radiation and Indoor Air (ORIA) in conjunction with the U.S. Geological Survey
(USGS). Sharon W. White was the EPA project manager. Numerous other people in ORIA
were instrumental in the development of the Map of Radon Zones, including Lisa Ratcliff,
Kirk Maconaughey, R. Thomas Peake, Dave Rowson, and Steve Page.
EPA would especially like to acknowledge the outstanding effort of the USGS
radon team — Linda Gundersen, Randy Schumann, Jim Otton, Doug Owen, Russell
Dubiel, Kendell Dickinson, and Sandra Szarzi ~ in developing the technical base for the
Map of Radon Zones.
ORIA would also like to recognize the efforts of all the EPA Regional Offices in
coordinating the reviews with the State programs and the Association of American State
Geologists (AASG) for providing a liaison with the State geological surveys. In addition,
appreciation is expressed to all of the State radon programs and geological surveys for their
technical input and review of the Map of Radon Zones.
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I. OVERVIEW
II. THE USGS/EPA RADON POTENTIAL
ASSESSMENTSiINTRODUCTION
III. REGION 4 GEOLOGIC RADON POTENTIAL
SUMMARY
V. PRELIMINARY GEOLOGIC RADON POTENTIAL
ASSESSMENT OF NORTH CAROLINA
V. EPA'S MAP OF RADON ZONES -
NORTH CAROLINA
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OVERVIEW
Sections 307 and 309 of the 1988 Indoor Radon Abatement Act (IRAA) direct EPA to
identify areas of the United States that have the potential to produce elevated levels of radon.
EPA, the U.S. Geological Survey (USGS), and the Association of American State Geologists
(. iASG) have worked closely over the past several y.ars to produce a series of .naps and
documents which address these directives. The EPA Map of Radon Zones is a compilation of
that work and fulfills the requirements of sections 307 and 309 of IRAA.- The Map of Radon
Zones identifies, on a county-by-county basis, areas of the U.S. that have the highest potential
for elevated indoor radon levels (greater than 4 pCi/L).
The Map of Radon Zones is designed to assist national, State and local governments
and organizations to target their radon program activities and resources. It is also intended to
help building code officials determine areas that are the highest priority for adopting radon-
resistant building practices. The Map of Radon Zones should not be used to determine if
individual homes in any given area need to be tested for radon. EPA recommends that all
homes be tested for radon, regardless of geographic location or the zone designation of
the county in which they are located.
This document provides background information concerning the development of the
Map of Radon Zones. It explains the purposes of the map, the approach for developing the
map (including the respective roles of EPA and USGS), the data sources used, the conclusions
and confidence levels developed for the prediction of radon potential, and the review process
that was conducted to finalize this effort.
BACKGROUND
Radon (Rn222) is a colorless, odorless, radioactive gas. It comes from the natural
decay of uranium that is found in nearly all soils. It typically moves through the ground to
the air above and into homes and other buildings through cracks and openings in the
foundation. Any home, school or workplace may have a radon problem, regardless of
whether it is new or old, well-sealed or drafty, or with or without a basement. Nearly one out
of every 15 homes in the U.S. is estimated to have elevated annual average levels of indoor
radon.
Radon first gained national attention in early 1984, when extremely high levels of
indoor radon were found in areas of Pennsylvania, New Jersey, and New York, along the
Reading Prong-physiographic province. EPA established a Radon Program in 1985 to assist
States and homeowners in reducing their risk of lung cancer from indoor radon.
Since 1985, EPA and USGS have been working together to continually increase our
understanding of radon sources and the migration dynamics that cause elevated indoor radon
levels. Early efforts resulted in the 1987 map entitled "Areas with Potentially High Radon
Levels." This map was based on limited geologic information only because few indoor radon
measurements were available at the time. The development of EPA's Map of Radon Zones
and its technical foundation, USGS1 National Geologic Radon Province Map, has been based
on additional information from six years of the State/EPA Residential Radon Surveys,
independent State residential surveys, and continued expansion of geologic and geophysical
information, particularly the data from the National Uranium Resource Evaluation project.
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Purpose of the Map of Radon Zones
EPA's Map of Radon Zones (Figure 1) assigns each of the 3141 counties in the
United States to one of three zones:
o Zone 1 counties have a predicted average indoor screening level > than
4 pCi/L
o Zone 2 counties have a predicted average screening level > 2 pCi/L and
< 4 pCi/L
o Zone 3 counties have a predicted average screening level < 2 pCi/L
The Zone designations were determined by assessing five factors that are known to be
important indicators of radon potential: indoor radon measurements, geology, aerial
radioactivity, soil parameters, and foundation types.
The predictions of average screening levels in each of the Zones is an expression of
radon potential in the lowest liveable area of a structure. This rnap is unable to estimate
actual exposures to radon. EPA recommends methods for testing and fixing individual homes
based on an estimate of actual exposure to radon. For more information on testing and fixing
elevated radon levels in homes consult these EPA publications: A Citizen's Guide to Radon.
the Consumer's Guide to Radon Reduction and the Home Buyer's and Seller's Guide to
Radon.
EPA believes that States, local governments and other organizations can achieve
optimal risk reductions by targeting resources and program activities to high radon potential
areas. Emphasizing targeted approaches (technical assistance, information and outreach
efforts, promotion of real estate mandates and policies and building codes, etc.) in such areas
addresses the greatest potential risks first.
EPA also believes that the use of passive radon control systems in the construction of
new homes in Zone 1 counties, and the activation of those systems if necessitated by follow-
up testing, is a cost effective approach to achieving significant radon risk reduction.
The Map of Radon Zones and its supporting documentation establish no regulatory
requirements. Use of this map by State or local radon programs and building code officials is
voluntary. The information presented on the Map of Radon Zones and in the supporting
documentation is not applicable to radon in water.
Development of the Mao of Radon Zones
The technical foundation for the Map of Radon Zones is the USGS Geologic Radon
Province Map. In order to examine the radon potential for the United States, the USGS
began by identifying approximately 360 separate geologic provinces for the U.S. The
provinces are shown on the USGS Geologic Radon Province Map (Figure 2). Each of the
geologic provinces was evaluated by examining the available data for that area: indoor radon
measurements, geology, aerial radioactivity, soil parameters, and foundation types. As stated
previously, these five factors are considered to be of basic importance in assessing radon
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potential and some data are available for each of these factors in every geologic province. The
province boundaries do not coincide with political borders (county and state) but define areas
of general radon potential. The five factors were assigned numerical values based on an
assessment of their respective contribution to radon potential, and a confidence level was
assigned to each contributing variable. The approach used by USGS to estimate the radon
potential for each province is described in Part II of mis document.
EPA subsequently developed the Map of Radon Zones by extrapofating from the
province level to the county level so that all counties in the U.S. were assigned to one of
three radon zones. EPA assigned each county to a given zone based on its provincial radon.
potential.. For example, if a county is located within a geologic province that has a predicted
average screening level greater than 4 pCi/L, it was assigned to Zone 1. Likewise, counties
located in provinces with predicted average screening levels > 2 pCi/L and < 4 pCi/L, and
less than 2 pCi/L, were assigned to Zones 2 and 3, respectively.
If the boundaries of a county fall in more than one geologic province, the county was
assigned to a zone based on the predicted radon potential of the province in which most of
the area lies. For example, if three different provinces cross through a given county, the
county was assigned to the zone representing-the radon potential of the province containing
most of the county's land area. (In this case, it is not technically correct to say that the
predicted average screening level applies to the entire county since the county falls in
multiple provinces with differing radon potentials.)
Figures 3 and 4 demonstrate an example of how EPA extrapolated the county zone
designations for Nebraska from the USGS geologic province map for the State. As figure 3
shows, USGS has identified 5 geologic provinces for Nebraska. Most of the counties are
extrapolated "straight" from their corresponding provinces, but there are counties "partitioned"
by several provinces -- for example, Lincoln County. Although Lincoln county falls in
multiple provinces, it was assigned to Zone 3 because most of its area falls in the province
with the lowest radon potential.
It is important to note that EPA's extrapolation from the province level to the
county level may mask significant "highs" and "lows" within specific counties. In other
words, within-county variations in radon potential are not shown on the Map of Radon
Zones. EPA recommends that users who may need to address specific within-county
variations in radon potential (e.g., local government officials considering the
implementation of radon-resistant construction codes) consult USGS' Geologic Radon
Province Map and the State chapters provided with this map for more detailed
information, as well as any locally available data.
Map Validation
The Map of Radon Zones is intended to represent a preliminary assessment of radon
potential for the entire United States. The factors that are used in this effort -indoor radon
data, geology, aerial radioactivity, soils, and foundation type ~ are basic indicators for radon
potential. It is important to note, however, that the map's county zone designations are not
"statistically valid" predictions due to the nature of the data available for these 5 factors at the
county level. In order to validate the map in light of this lack of statistical confidence, EPA
conducted a number of analyses. These analyses have helped EPA to identify the best
situations in which to apply the map, and its limitations.
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Figure 3
Geologic Radon Potential Provinces for Nebraska
Lincoln County
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Figure 4
NEBRASKA - EPA Map of Radon Zones
Lincoln County
Zone 1 Zone 2 Zone 3
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One such analysis involved comparing county zone designations to indoor radon
measurements from the State/EPA Residential Radon Surveys (SRRS). Screening averages
for counties with at least 100 measurements were compared to the counties' predicted'radon
potential as indicated by the Map of Radon Zones. EPA found that 72% of the county
screening averages -were correctly reflected by the appropriate zone designations on the Map.
In all other cases, they only differed by 1 zone.
Another accuracy analysis used the annual average data from the National Residential
Radon Survey (NRRS). The NRRS indicated that approximately 6 million homes in the
United States have.annual averages greater than or equal to 4 pCi/L. By cross checking the
county location of the approximately 5,700 homes which participated in the survey, their
radon measurements, and the zone designations for these counties, EPA found that
approximately 3.8 million homes of the 5.4 million homes with radon levels greater than or
equal to 4 pCi/L will be found in counties designated as Zone 1. A random sampling of an
equal number of counties would have only found approximately 1.8 million homes greater
than 4 pCi/L. In other words, this analysis indicated that the map approach is three times
more efficient at identifying high radon areas than random selection of zone designations.
Together, these analyses show that the approach EPA used to develop the Map of
Radon Zones is a reasonable one. In addition, the Agency's confidence is enhanced by results
of the extensive State review process — the map generally agrees with the States' knowledge
of and experience in their own jurisdictions. However, the accuracy analyses highlight two
important points: the fact that elevated'levels will be found in Zones 2 and 3, and that there
will be significant numbers of homes with lower indoor radon levels in all of the Zones. For
these reasons, users of the Map of Radon Zones need to supplement the Map with locally
available data whenever possible. Although all known "hot spots", i.e., localized areas of
consistently elevated levels, are discussed in the State- •
specific chapters, accurately defining the boundaries of the "hot spots" on this scale of map is
not possible at this time. Also, unknown "hot spots" do exist.
The Map of Radon Zones is intended to be a starting point for characterizing radon
potential because our knowledge of radon sources and transport is always growing. Although
this effort represents the best data available at this time, EPA will continue to study these
parameters and others such as house construction, ventilation features and meteorology factors
in order to better characterize the presence of radon in U.S homes, especially in high risk
areas. These efforts will eventually assist EPA in refining and revising the conclusions of the
Map of Radon Zones. And although this map is most appropriately used as a targeting tool
by the aforementioned audiences — the Agency encourages all residents to test their homes
for radon, regardless of geographic location or the zone designation of the county in
which they live. Similarly, the Map of Radon Zones should not to be used in lieu of
testing during real estate transactions.
Review Process
The Map of Radon Zones has undergone extensive review within EPA and outside the
Agency. The Association of American State Geologists (AASG) played an integral role in
this review process. The AASG individual State geologists have reviewed their State-specific
information, the USGS Geologic Radon Province Map, and other materials for their geologic
content and consistency.
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In addition to each State geologist providing technical comments, the State radon
offices were asked to comment on their respective States' radon potential evaluations.. In
particular, the States were asked to evaluate the data used to assign their counties to specific
zones. EPA and USGS worked with the States to resolve any issues concerning county zone
designations. In a few cases, States have requested changes in county zone designations. The
requests were based on additional data from the State on geology, indoor radon
measurements, population, etc. Upon reviewing the data submitted by the States, EPA did
make some changes in zone designations. These changes, which do not strictly follow the
methodology outlined in this document, are discussed in the respective State chapters.
EPA encourages the States and counties to conduct further research and data collection
efforts to refine the Map of Radon Zones. EPA would like to be kept informed of any
changes the States, counties, or others make to the maps. Updates and revisions will be
handled in a similar fashion to the way the map was developed. States should notify EPA of
any proposed changes by forwarding the changes through the Regional EPA offices that are
listed in Part II. Depending on the amount of new information that is presented, EPA will
consider updating this map periodically. The State radon programs should initiate proper
notification of the appropriate State officials when the Map of Radon Zones is released and
when revisions or updates are made by the State or EPA.
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THE USGS/EPA RADON POTENTIAL ASSESSMENTS: AN INTRODUCTION
by
Linda C.S. Gundersen and R. Randall Schumann
U.S. Geological Survey
and
Sharon W. White .
U.S. Environmental Protection Agency
BACKGROUND
The Indoor Radon Abatement Act of 1988 (15 U.S.C. 2661-2671) directed the U.S.
Environmental Protection Agency (EPA) to identify areas of the United States that have the
potential to produce harmful levels of indoor radon. These characterizations were to be based
on both geological data and on indoor radon levels in homes and other structures. The EPA
also was directed to develop model standards and techniques for new building constructs
that would provide adequate prevention or mitigation of radon entry. As part of"an
Interagency Agreement between the EPA and the U.S. Geological Survey (USGS) the USGS
has prepared radon potential estimates for the United States. This report is one of ten
booklets that document this effort. The purpose and intended use of these reports is to help
identify areas where states can target their radon program resources, to provide guidance in
selecting the most appropriate building code options for areas, and to provide general
information on radon and geology for each state for federal, state, and municipal officials
dealing with radon issues. These reports are noi intended to be used as a substitute Jar
indoor radon testing, and they cannot and should not be used to estimate or predict the
indoor radon concentrations of individual homes, building sites, or housing tracts. Elevated
levels of indoor radon have been found in every State, and EPA recommends that all homes
be tested for indoor radon.
Booklets detailing the radon potential assessment for the U.S. have been developed for
each State USGS geologists are the authors of the geologic radon potential booklets. Each
booklet consists of several components, the first being an overview to the mapping project
(Part I) this introduction to the USGS assessment. (Part II), including a general discussion of
radon (occurrence, transport, etc.), and details concerning the types of data used The third
component is a summary chapter outlining the general geology and geologic radon potential
of the EPA Region (Part III). The fourth component is an individual chapter for each state
(Part IV) Each state chapter discusses the state's specific geographic setting, soils, geologic
setting geologic radon potential, indoor radon data, and a summary outlining the radon
potential rankings of geologic areas in the state. A variety of maps are presented in each
chapter-geologic, geographic, population, soils, aerial radioactivity, and indoor radon data by
county. Finally, the booklets contain EPA's map of radon zones for each state and an
accompanying description (Part V).
Because of constraints on the scales of maps presented in these reports and because the
smallest units used to present the indoor radon data are counties, some generalizations have
been made in order to estimate the radon potential of each area. Variations in geology soil
characteristics, climatic factors, homeowner lifestyles, and other factors that influence radon
concentrations can be quite large within any particular geologic area, so these reports cannot
be used to estimate or predict the indoor radon concentrations of individual homes or housing
II-l Reprinted from USGS Open-File .Report 93-292
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tracts. Within any area of a given geologic radon potential ranking, there are likely to be
areas where the radon potential is lower or higher than that assigned to the area as a whole,
especially in larger areas such as the large counties in some western states.
In each state chapter, references to additional reports related to radon are listed for the
state, and the reader is urged to consult these reports for more detailed information. In most
cases the best sources of information on radon for specific areas are state and local
departments of health, state departments responsible for nuclear safety or environmental
protection, and U.S. EPA regional offices. More detailed information on state or local
geology may be obtained from the state geological surveys. Addresses and telephone
numbers of state radon contacts, geological surveys, and EPA regional offices are listed in
Appendix C at the end of this chapter.
RADON GENERATION AND TRANSPORT IN SOILS
Radon (:"Rn) is produced from the radioactive decay of radium (~6Ra), which is, in turn,
a product of the decay of uranium (23SU) (fig. 1). The half-life of :"Rn is 3.825 days. Other
isotopes of radon occur naturally, but, with the exception of thoron (2-°Rn), which occurs in
concentrations high enough to be of concern in a few localized areas, they are less important
in terms of indoor radon risk because of their extremely short half-lives and less common
occurrence. In general, the concentration and mobility of radon in soil- are dependent on
several factors, the most important of which are the soil's radium content and distribution,
porosity, permeability to gas movement, and moisture content. These characteristics are, in
turn, determined by the soil's parent-material composition, climate, and the soil's age or
maturity. If parent-material composition, climate, vegetation, age of the soil, and topography
are known, the physical and chemical properties of a soil in a given area can be predicted.
As soils form, they develop distinct layers, or horizons, that are cumulatively called the
soil profile. The A horizon is a surface or near-surface horizon containing a relative
abundance of organic matter but dominated by mineral matter. Some soils contain an E
horizon, directly below the A horizon, that is generally characterized by loss of clays, iron, or
aluminum, and has a characteristically lighter color than the A horizon. The B horizon
underlies the A or E horizon. Important characteristics of B horizons include accumulation of
clays, iron oxides, calcium carbonate or other soluble salts, and organic matter complexes. In
drier environments, a horizon may exist within or below the B horizon that is dominated by
calcium carbonate, often called caliche or calcrete. This carbonate-cemented horizon is
designated the K horizon in modern soil classification schemes. The C horizon underlies the
B (or K) and is a zone of weathered parent material that does not exhibit characteristics of A
or B horizons; that is, it is generally not a zone of leaching or accumulation. In soils formed
in place from the underlying bedrock, the C horizon is a zone of unconsolidated, weathered
bedrock overlying the unweathered bedrock.
The shape and orientation of soil particles (soil structure) control permeability and affect
water movement in the soil. Soils with blocky or granular structure have roughly equivalent
permeabilities in the horizontal and vertical directions, and air and water can infiltrate the soil
relatively easily. However, in soils with platy structure, horizontal permeability is much
greater than vertical permeability, and air and moisture infiltration is generally slow. Soils
with prismatic or columnar structure have dominantly vertical permeability. Platy and
prismatic structures form in soils with high clay contents. In soils with shrink-swell clays, air
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and moisture infiltration rates and depth of wetting may be limited when trie cracks in the
surface soil layers swell shut. Clay-rich B horizons, particularly those with massive or platy
structure, can form a capping layer that impedes the escape of soil gas to the surface
(Schumann and others, 1992). However, the shrinkage of clays can act to open or widen
cracks upon drying, thus increasing the soil's permeability to gas flow during drier periods.
Radon transport in soils occurs by two processes: (1) diffusion and (2) flow (Tanner,
1964). Diffusion is the process whereby radon atoms move from areas of higher
concentration to areas of lower concentration in response to a concentration gradient. Flow is
the process by which soil air moves through soil pores in response to differences in pressure
within the soil or between the soil and the atmosphere, carrying the radon atoms along with it.
Diffusion is the dominant radon transport process in soils of low permeability, whereas flow
tends to dominate in highly permeable soils (Sextro and others, 1987). In low-permeability
soils, much of the radon may decay before it is able to enter a building because its transport
rate is reduced. Conversely, highly permeable soils, even those that are relatively low in
radium, such as those derived from some types of glacial deposits, have been associated with
high indoor radon levels in Europe and in the northern United States (Akerblom and others,
1984; Kunz and others, 1989; Sextro and others, 1987). In areas of karst topography formed
in carbonate rock (limestone or dolomite) environments, solution cavities and fissures can
increase soil permeability at depth by providing additional pathways for gas flow.
Not all radium contained in soil grains and grain coatings will result in mobile radon
when the radium decays. Depending on where the radium is distributed in the soil, many of
the radon atoms may remain imbedded in the soil grain containing the parent radium atom, or
become imbedded in adjacent soil grains. The portion of radium that releases radon into the
pores and fractures of rocks and soils is called the emanating fraction. When a radium atom
decays to radon, the energy generated is strong enough to send the radon atom a distance of
about 40 nanometers (1 nm = 10"* meters), or about 2x\0'c' inches—this is known as alpha
recoil (Tanner, 1980). Moisture in the soil lessens the chance of a recoiling radon atom
becoming imbedded in an adjacent grain. Because water is more dense than air, a radon atom
will travel a shorter distance in a water-filled pore than in an air-filled pore, thus increasing
the likelihood that the radon atom will remain in the pore space. Intermediate moisture levels
enhance radon emanation but do not significantly affect permeability. However, high
moisture levels can significantly decrease the gas permeability of the soil and impede radon
movement through the soil.
Concentrations of radon in soils are generally many times higher than those inside of
buildings, ranging from tens of pCi/L to more than 100,000 pCi/L, but typically in the range
of hundreds to low thousands of pCi/L. Soil-gas radon concentrations can vary in response to
variations in climate and weather on hourly, daily, or seasonal time scales. Schumann and
others (1992) and Rose and others (1988) recorded order-of-magnitude variations in soil-gas
radon concentrations between seasons in Colorado and Pennsylvania. The most important
factors appear to be (1) soil moisture conditions, which are controlled in large part by
precipitation; (2) barometric pressure; and (3) temperature. Washington and Rose (1990)
suggest that temperature-controlled partitioning of radon between water and gas in soil pores
also has a significant influence on the amount of mobile radon in soil gas.
Homes in hilly limestone regions of the southern Appalachians were found to have higher
indoor radon concentrations during the summer than in the winter. A suggested cause, for this
phenomenon involves temperature/pressure-driven flow of radon-laden air from subsurface
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solution cavities in the carbonate rock into houses. As warm air enters solution cavities that
are higher on the hillslope than the homes, it cools and settles, pushing radon-laden air from
lower in the cave or cavity system into structures on the hillslope (Gammage and others,
1993). In contrast, homes built over caves having openings situated below the level of the
home had higher indoor radon levels in the winter, caused by cooler outside air entering the
cave, driving radon-laden air into cracks and solution cavities in the rock and soil, and
ultimately, into homes (Gammage and others, 1993).
RADON ENTRY INTO BUILDINGS
A driving force (reduced atmospheric pressure in the house relative to the soil, producing
a pressure gradient) and entry points must exist for radon to enter a building from the soil.
The negative pressure caused by furnace combustion, ventilation devices, and the stack effect
(the rising and escape of warm air from the upper floors of the building, causing a
temperature and pressure gradient within the structure) during cold winter months are
common driving forces. Cracks and other penetrations through building foundations, sump
holes, and slab-to-foundation wall joints are common entry points.
Radon levels in the basement are generally higher than those on the main floor or upper
floors of most structures. Homes with basements generally provide more entry points for
radon, commonly have a more pronounced stack effect, and typically have lower air pressure
relative to the surrounding soil than nonbasement homes. The term "nonbasement" applies to
slab-on-grade or crawl space construction.
METHODS AND SOURCES OF DATA
The assessments of radon potential in the booklets that follow this introduction were
made using five main types of data: (1) geologic (lithologic); (2) aerial radiometric; (3) soil
characteristics, including soil moisture, permeability, and drainage characteristics; (4) indoor
radon data; and (5) building architecture (specifically, whether homes in each area are built
slab-on-grade or have a basement or crawl space). These five factors were evaluated and
integrated to produce estimates of radon potential. Field measurements of soil-gas radon or
soil radioactivity were not used except where such data were available in existing, published
reports of local field studies. Where applicable, such field studies are described in the
individual state chapters.
GEOLOGIC DATA
The types and distribution of lithologic units and other geologic features in an
assessment area are of primary importance in determining radon potential. Rock types that
are most likely to cause indoor radon problems include carbonaceous black shales, glauconite-
bearing sandstones, certain kinds of fluvial sandstones and fluvial sediments, phosphorites,
chalk, karst-producing carbonate rocks, certain kinds of glacial deposits, bauxite, uranium-rich
granitic rocks, metamorphic rocks of granitic composition, silica-rich volcanic rocks, many
sheared or faulted rocks, some coals, and certain kinds of contact metamorphosed rocks.
Rock types least likely to cause radon problems include marine quartz sands, non-
carbonaceous shales and siltstones, certain kinds of clays, silica-poor metamorphic and
II-5 Reprinted from USGS Open-File Report 93-292
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igneous rocks, and basalts. Exceptions exist within these general lithologic groups because of
the occurrence of localized uranium deposits, commonly of the hydrothermal type in
crystalline rocks or the "roll-front" type in sedimentary rocks. Uranium and radium are
commonly sited in heavy minerals, iron-oxide coatings on rock and soil grains, and organic
materials in soils and sediments. Less common are uranium associated with phosphate and
carbonate complexes in rocks and soils, and uranium minerals.
Although many cases of elevated indoor radon levels can be traced to'high radium and
(or) uranium concentrations in parent rocks, some structural features, most notably faults and
shear zones, have been identified a§ sites of localized uranium concentrations (Deffeyes and
MacGregor, 1980) and have'been associated with some of the highest reported indoor radon
levels (Gundersen, 1991). The two highest known indoor radon occurrences are associated
with sheared fault zones in Boyertown, Pennsylvania (Gundersen and others, 1988a; Smith
and others, 1987), and in Clinton, New Jersey (Henry and others, 1991; Muessig and Bell,
1988).
NURE AERIAL RADIOMETRIC DATA
Aerial radiometric data are used to quantify the radioactivity of rocks and soils.
Equivalent uranium (eU) data provide an estimate of the surficial concentrations of radon
parent materials (uranium, radium) in rocks and soils. Equivalent uranium is calculated from
the counts received by a gamma-ray detector from the 1.76 MeV (mega-electron volts)
emission energy corresponding to bismuth-214 (2l4Bi), with the assumption that uranium and
its decay products are in secular equilibrium. Equivalent uranium is expressed in units of
parts per million (ppm). Gamma radioactivity also may be expressed in terms of a radium
activity; 3 ppm eU corresponds to approximately 1 picocurie per gram (pCi/g) of radium-226.
Although radon is highly mobile in soil and its concentration is affected by meteorological
conditions (Kovach, 1945; Klusman and Jaacks, 1987; Schery and others, 1984; Schumann
and others, 1992), statistical correlations between average soil-gas radon concentrations and
average eU values for a wide variety of soils have been documented (Gundersen and others,
1988a, 1988b; Schumann and Owen, 1988). Aerial radiometric data can provide an estimate
of radon source strength over a region, but the amount of radon that is able to enter a home
from the soil is dependent on several local factors, including soil structure, grain size
distribution, moisture content, and permeability, as well as type of house construction and its
structural condition.
The aerial radiometric data used for these characterizations were collected as part of the
Department of Energy National Uranium Resource Evaluation (NURE) program of the 1970s
and early 1980s. The purpose of the NURE program was to identify and describe areas in the
United States having potential uranium resources (U.S. Department of Energy, 1976). The
NURE aerial radiometric data were collected by aircraft in which a gamma-ray spectrometer
was mounted, flying approximately 122 m (400 ft) above the ground surface. The equivalent
uranium maps presented in the state chapters were generated from reprocessed NURE data in
which smoothing, filtering, recalibrating, and matching of adjacent quadrangle data sets were
performed to compensate for background, altitude, calibration, and other types of errors and
inconsistencies in the original data set (Duval and others, 1989). The data were then gridded
and contoured to produce maps of eU with a pixel size corresponding to approximately 2.5 x
2.5 km (1.6 x 1.6 mi).
II-6 Reprinted from USGS Open-File Report 93-292
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FLIGHT LINE SPACING OF NUKE AERIAL SURVEYS
2 k'U (1 HUE)
5 KM (3 MILES)
2 k 5 O
E3 10 111 (6 U1LES)
5 & 10 IK
NO DATA
Figure 2. Nominal fliehtUne spacings for NURE aerial gamma-ray surveys covering the
contiguous United States (from Duval and others, 1990). Rectangles represent I°x2° quadrangles.
-------
Figure 2 is an index map of NUKE 1° x 2° quadrangles showing the flight-line spacing
for each quadrangle. In general, the more closely spaced the flightlines are, the more area
was covered by the aerial gamma survey, and thus, more detail is available in the data set.
^o- an altitude of 400 ft above the ground surface a-d with primary flightline -pacing
typically between 3 and 6 miles, less than 10 percent of the ground surface of the United
States was actually measured by the airborne gamma-ray detectors (Duval and others, 1989),,
although some areas had better coverage than others due to the differences in flight-line
spacing between areas (fig. 2). This suggests that some localized uranium anomalies may not
have been detected by the aerial surveys, but the good correlations of eU patterns with
geologic outcrop patterns indicate that, at relatively small scales (approximately 1:1,000,000
or smaller) the National eU map (Duval and others, 1989) gives reasonably good estimates of
average surface uranium concentrations and thus can assist in the prediction of radon potential
of rocks and soils, especially when augmented with additional geologic and soil data.
The shallow (20-30 cm) depth of investigation of gamma-ray spectrometers, either
ground-based or airborne (Duval and others, 1971; Durrance, 1986), suggests that gamma-ray
data may sometimes underestimate the radon-source strength in soils in which some of the
radionuclides in the near-surface soil layers have been transported downward through the soil
profile. In such cases the concentration of radioactive minerals in the A horizon would be
lower than in the B horizon, where such minerals are typically concentrated. The
concentration of radionuclides in the C horizon and below may be relatively unaffected by
surface solution processes. Under these conditions the surface gamma-ray signal may indicate
a lower radon source concentration than actually exists in the deeper soil layers, which are
most likely to affect radon levels in structures with basements. The redistribution of
radionuclides in soil profiles is dependent on a combination of climatic, geologic, and
geochemical factors. There is reason to believe that correlations of eU with actual soil
radium and uranium concentrations at a depth relevant to radon entry into structures may be
regionally variable (Duval, 1989; Schumann and Gundersen, 1991). Given sufficient
understanding of the factors cited above, these regional differences may be predictable.
SOIL SURVEY DATA
Soil surveys prepared by the U.S. Soil Conservation Service (SCS) provide data on soil
characteristics, including soil-cover thickness, grain-size distribution, permeability, shrink-
swell potential, vegetative cover, generalized groundwater characteristics, and land use. The
reports are available in county formats and State summaries. The county reports typically
contain both generalized and detailed maps of soils in the area.
Because of time and map-scale constraints, it was impractical to examine county soil
reports for each county in the United States, so more generalized summaries at appropriate
scales were used where available. For State or regional-scale radon characterizations, soil
maps were compared to geologic maps of the area, and the soil descriptions, shrink-swell
potential, drainage characteristics, depth to seasonal high water table, permeability, and other
relevant characteristics of each soil group noted. Technical soil terms used in soil s«»-veys are
generally complex; however, a good summary of soil engineering terms and the national
distribution of technical soil types is the "Soils" sheet of the National Atlas (U.S. Department
of Agriculture, 1987).
II-8 Reprinted from USGS Open-File Report 93-292
-------
Soil permeability is commonly expressed in SCS soil surveys in terms of the speed, in
inches per hour (in/hr), at which water soaks into the soil, as measured in a soil percolation
test. Although in/hr are not truly units of permeability, these units are in widespread use and
are referred to as "permeability" in SCS soil surveys. The permeabilities listed in the SCS
surveys are for water, but they generally correlate well with gas permeability. Because data
on gas permeability of soils is extremely limited, data on permeability to water is used as a
substitute except in cases in which excessive soil moisture is known to exist. Water in soil
pores inhibits gas transport, so the amount of radon available to a home is effectively reduced
by a high-water table. Areas likely to have high water tables include river valleys, coastal
areas, and some areas overlain by deposits of glacial origin (for example, loess).
Soil permeabilities greater than 6.0 in/hr may be considered high, and permeabilities less
than 0.6 in/hr may be considered low in terms of soil-gas transport. Soils with low
permeability may generally be considered to have a lower radon potential than more
permeable soils with similar radium concentrations. Many well-developed soils contain a
clay-rich B horizon that may impede vertical soil gas transport. Radon generated below this
horizon cannot readily escape to the surface, so it would instead tend to move laterally,
especially under the influence of a negative pressure exerted by a building.
Shrink-swell potential is an indicator of the abundance of smectitic (swelling) clays in a
soil. Soils with a high shrink-swell potential may cause building foundations to crack,
creating pathways for radon entry into the structure. During dry periods, desiccation cracks in
shrink-swell soils provide additional pathways for soil-gas transport and effectively increase
the gas permeability of the soil. Soil permeability data and soil profile data thus provide
important information for regional radon assessments.
INDOOR RADON DATA
Two major sources of indoor radon data were used. The first and largest source of data is
from the State/EPA Residential Radon Survey (Ronca-Battista and others, 1988; Dziuban and
others, 1990). Forty-two states completed EPA-sponsored indoor radon surveys between 1986
and 1992 (fig. 3). The State/EPA Residential Radon Surveys were designed to be
comprehensive and statistically significant at the state level, and were subjected to high levels
of quality assurance and control. The surveys collected screening indoor radon measurements,
defined as 2-7 day measurements using charcoal canister radon detectors placed in the lowest
livable area of the home. The target population for the surveys included owner-occupied
single family, detached housing units (White and others, 1989), although attached structures
such as duplexes, townhouses, or condominiums were included in some of the surveys if they
met the other criteria and had contact with the ground surface. Participants were selected
randomly from telephone-directory listings. In total, approximately 60,000 homes were tested
in the State/EPA surveys.
The second source of indoor radon data comes from residential surveys that have been
conducted in a specific state or region of the country (e.g. independent state surveys or utility
company surveys). Several states, including Delaware, Florida, Illinois, New Hampshire, New
Jersey, New York, Oregon, and Utah, have conducted their own surveys of indoor radon. The
quality and design of a state or other independent survey are discussed and referenced where
the data are used.
II-9 Reprinted from USGS Open-File Report 93-292
-------
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Data for only those counties with five or more measurements are shown in the indoor
radon maps in the state chapters, .although data for all counties with a nonzero number of
measurements are listed in the indoor radon data tables in each state chapter. In total, indoor
radon data from more than 100,000 homes nationwide were used in the compilation of these
assessments. Radon data from State or regional indoor radon surveys, public health
organizations, or other sources are discussed in addition to the primary data sources where
they are available. Nearly all of the data used in these evaluations represent short-term (2-7
day) screening measurements from the lowest livable space of the homes. Specific details .
concerning the nature and use of indoor radon data sets other than the State/EPA Residential
Radon Survey are discussed in the individual State chapters.
RADON INDEX AND CONFIDENCE INDEX
Many of the geologic methods used to evaluate an area for radon potential require
subjective opinions based on the professional judgment and experience of the individual
geologist. The evaluations are nevertheless based on established scientific principles that are
universally applicable to any geographic area or geologic setting. This section describes the
methods and conceptual framework used by the U.S. Geological Survey to evaluate areas for
radon potential based on the five factors discussed in the previous sections. The scheme is
divided into two basic parts, a Radon Index (RI), used to rank the general radon potential of
the area, and the Confidence Index (CI), used to express the level of confidence in the
prediction based on the quantity and quality of the data used to make the determination. This
scheme works best if the areas to be evaluated are delineated by geologically-based
boundaries (geologic provinces) rather than political ones (state/county boundaries) in which
the geology may vary across the area.
Radon Index. Table 1 presents the Radon Index (RI) matrix. The five factors—indoor
radon data, geology, aerial radioactivity, soil parameters, and house foundation type—were
quantitatively ranked (using a point value of 1, 2, or 3) for their respective contribution to
radon potential in a given area. At least some data for the 5 factors are consistently available
for every geologic province. Because each of these main factors encompass a wide variety of
complex and variable components, the geologists performing the evaluation relied heavily on
their professional judgment and experience in assigning point values to each category and in
determining the overall radon potential ranking. Background information on these factors is
discussed in more detail in the preceding sections of this introduction.
Indoor radon was evaluated using unweighted arithmetic means of the indoor radon data
for each geologic area to be assessed. Other expressions of indoor radon levels in an area
also could have been used, such as weighted averages or annual averages, but these types of
data were not consistently available for the entire United States at the time of this writing, or
the schemes were not considered sufficient to provide a means of consistent comparison
across all areas. For this report, charcoal-canister screening measurement data from the
State/EPA Residential Radon Surveys and other carefully selected sources were used, as
described in the preceding section. To maintain consistency, other indoor radon data sets
(vendor, state, or other data) were not considered in scoring the indoor radon factor of the
Radon Index if they were not randomly sampled or could not be statistically combined with
the primary indoor radon data sets. However, these additional radon data sets can provide a
means to further refine correlations between geologic factors and radon potential, so they are
II-11 Reprinted from USGS Open-File Report 93-292
-------
TABLE 1. RADON INDEX MATRIX, "ppm eU" indicates parts per million of equivalent
uranium, as indicated by NURE aerial radiometric data. See text discussion for details.
FACTOR
ssg~— jggg™5^^g9gs55S^^^£33^S3™S^S^S^3I^^S3i^S5
INDOOR RADON (average)
AERIAL RADIOACTIVITY
GEOLOGY*
SOIL PERMEABILITY
ARCHITECTURE TYPE
POINT VALUE
1
============
<2pCi/L
< 1.5 ppm eU
negative
low
mostly slab
2
2-4pCi/L
1.5 - 2.5 ppm eU
variable
moderate
mixed
3
>4pCi/L
> 2.5 ppm eU
positive
high
mostly basement
'GEOLOGIC FIELD EVIDENCE (GFE) POINTS: GFE points are assigned in addition to points
for the "Geology" factor for specific, relevant geologic field studies. See text for details.
Geologic evidence supporting:
HIGH radon +2 points
MODERATE +1 point
LOW -2 points
No relevant geologic field studies 0 points
SCORING:
Radon potential category
Point range
LOW
MODERATE/VARIABLE
HIGH
3-8 points
9-11 points
12-17 points
Probable average screening
indoor radon for area
<2pCi/L
2-4pCi/L
>4pCi/L
POSSIBLE RANGE OF POINTS = 3 to 17
TABLE 2. CONFIDENCE INDEX MATRIX
INCREASING CONFIDENCE
FACTOR
••»•••••••••••••••»••••••••••
INDOOR RADON DATA
AERIAL RADIOACI'I V1T V
GEOLOGIC DATA
SOIL PERMEABILITY
POINT VALUE
1
•••••»•••••••»•••«•»
sparse/no data
questionable/no data
questionable
2
••••»•••»•""••••••»•
fair coverage/quality
glacial cover
variable
variable
3
^iM.BMBa-31— =====
good coverage/quality
no glacial cover
proven geol. model
reliable, abundant
SCORING:
LOW CONFIDENCE
MODERATE CONFIDENCE
HIGH CONFIDENCE
4-6 points
7-9 points
10 - 12 points
POSSIBLE RANGE OF POINTS = 4 to 12
n-12 Reprinted from USGS Open-File Report 93-292
-------
included as supplementary information and are discussed in the individual State chapters. If
the average screening indoor radon level for an area was less than 2 pCi/L, the indoor radon
factor was assigned. 1 point, if it was between 2 and 4 pCi/L, it was scored 2 points, and if
the average screening indoor radon level for an area was greater than 4 pCi/L, the indoor
radon factor was assigned 3 RI points.
Aerial radioactivity data used in this report are from the equivalent uranium map of the
conterminous United States .compiled from MURE aerial gamma-ray surveys (Duval and
others, 1989). These data indicate the gamma radioactivity from approximately the upper 30
cm of rock and soil, expressed in units of ppm equivalent uranium. An approximate average
value of eU was determined visually for each area and point values assigned based on
whether the overall eU for the area falls below 1.5 ppm (1 point), between 1.5 and 2.5 ppm
(2 points), or greater than 2.5 ppm (3 points).
The geology factor is complex and actually incorporates many geologic characteristics. In
the matrix, "positive" and "negative" refer to the presence or absence and distribution of rock
types known to have high uranium contents and to generate elevated radon in soils or indoors.
Examples of "positive" rock types include granites, black shales, phosphatic rocks, and other
rock types described in the preceding "geologic data" section. Examples of "negative" rock
types include marine quartz sands and some clays. The term "variable" indicates that the
geology within the region is variable or that the rock types in the area are known or suspected
to generate elevated radon in some areas but not in others due to compositional differences,
climatic effects, localizeddistribution of uranium, or other factors. Geologic information
indicates not only how much uranium is present in the rocks and soils but also gives clues for
predicting general radon emanation and mobility characteristics through additional factors
such as structure (notably the presence of faults or shears) and geochemical characteristics
(for example, a phosphate-rich sandstone will likely contain more uranium than a sandstone
containing little or no phosphate because the phosphate forms chemical complexes with
uranium). "Negative", "variable", and "positive" geology were assigned 1, 2, and 3 points,
respectively.
In cases where additional reinforcing or contradictory geologic evidence is available,
Geologic Field Evidence (GFE) points were added to or subtracted from an area's score
(Table 1). Relevant geologic field studies are important to enhancing our understanding of
how geologic processes affect radon distribution. In some cases, geologic models and
supporting field data reinforced an already strong (high or low) score; in others, they provided
important contradictory data. GFE points were applied for geologically-sound evidence that
supports the prediction (but which may contradict one or more factors) on the basis of known
geologic field studies in the area or in areas with geologic and climatic settings similar
enough that they could be applied with full confidence. For example, areas of the Dakotas,
Minnesota, and Iowa that are covered with Wisconsin-age glacial deposits exhibit a low aerial
radiometric signature and score only one RI point in that category. However, data from
geologic field studies in North Dakota and Minnesota (Schumann and others, 1991) suggest
that eU is a poor predictor of geologic radon potential in this area because radionuclides have
11-13 Reprinted from USGS Open-File Report 93-292
-------
been leached from the upper soil layers but are present and possibly even concentrated in
deeper soil horizons, generating significant soil-gas radon. This positive supporting field
evidence adds two GFE points to the score, which helps to counteract the invalid conclusion
suggested by the radiometric data. No GFE points are awarded if there are no documented _
field studies for the area.
"Soil permeability" refers to several soil characteristics that influence radon concentration
and mobility, including soil type, grain size, structure, soil moisture, drainage, slope, and
permeability. In the matrix, "low" refers to permeabilities less than about 0.6 in/hr; "high"
corresponds to greater than about 6.0 in/hr, in U.S. Soil Conservation Service (SCS) standard
soil percolation tests. The SCS data are for water permeability, which generally correlates
well with the gas permeability of the soil except when the soil moisture content is very high.
Areas with consistently high water tables were thus considered to have low gas permeability.
"Low, "moderate", and "high" permeability were assigned 1, 2, and 3 points, respectively.
Architecture type refers to whether homes in the area have mostly basements (3 points),
mostly slab-on-grade construction (1 point), or a mixture of the'two. Split-level and crawl
space homes fall into the "mixed" category (2 points). Architecture information is necessary
to properly interpret the indoor radon data and produce geologic radon potential categories
that are consistent with screening indoor radon data.
The overall RJ for an area is calculated by adding the individual RI scores for the 5
factors, plus or minus GFE points, if any. The total RI for an area falls in one of three
categories—low, moderate or variable, or high. The point ranges for the three categories were
determined by examining the possible combinations of points for the 5 factors and setting
rules such that a majority (3 of 5 factors) would determine the final score for the low and
high categories, with allowances for possible deviation from an ideal score by the other two
factors. The moderate/variable category lies between these two ranges. A total deviation of 3
points from the "ideal" score was considered reasonable to allow for natural variability of
factors—if two of the five factors are allowed to vary from the "ideal" for a category, they
can differ by a minimum of 2 (1 point different each) and a maximum of 4 points (2 points
different each). With "ideal" scores of 5, 10, and 15 points describing low, moderate, and
high geologic radon potential, respectively, an ideal low score of 5 points plus 3 points for
possible variability allows a maximum of 8 points in the low category. Similarly, an ideal
high score of 15 points minus 3 points gives a minimum of 12 points for the high category.
Note, however, that if both other factors differ by two points from the "ideal", indicating
considerable variability in the system, the total point score would lie in the adjacent (i.e.,
moderate/variable) category.
Confidence Index. Except for architecture type, the same factors were used to establish a
Confidence Index (CI) for the radon potential prediction for each area (Table 2). Architecture
type was not included in the confidence index because house construction data are readily and
reliably available through surveys taken by agencies and industry groups including the
National Association of Home Builders, U.S. Department of Housing and Urban
Development, and the Federal Housing Administration; thus it was not considered necessary
11-14 Reprinted from USGS Open-File Report 93-292
-------
te question the quality or validity of these data. The other factors were scored on the basis of
the quality and quantity of the data used to complete the RI matrix.
Indoor radon data were evaluated based on the distribution and number of data points and
on whether the data were collected by random sar... j (State/EPA Residential Radon Survey
or other state survey data) or volunteered vendor data (likely to be nonrandom and biased
toward population centers and/or high indoor radon levels). The categories listed in the CI .
matrix for indoor radon data ("sparse or no data", "fair coverage or quality", and "good
coverage/quality") indicate the sampling density and statistical robustness of an indoor radon
data set.. Data from the State/EPA Residential Radon Survey and statistically valid state
surveys were typically assigned 3 Confidence Index points unless the data were poorly
distributed or absent in the area evaluated.
Aerial radioactivity data are available, for all but a few areas of the continental United
States and for part of Alaska. An evaluation of the quality of the radioactivity data was based
on whether there appeared to be a good correlation between the radioactivity and the actual
amount of uranium or radium available to generate mobile radon in the rocks and soils of the
area evaluated. In general, the greatest problems with correlations among eU, geology, and
soil-gas or indoor radon levels were associated with glacial deposits (see the discussion in a
previous section) and typically were assigned a 2-point Confidence Index score. Correlations
among eU, geology, and radon were generally sound in unglaciated areas and were usually
assigned 3 CI points. Again, however, radioactivity data in some unglaciated areas may have
been assigned fewer than 3 points, and in glaciated areas may be assigned only one point, if
the data were considered questionable or if coverage was poor.
To assign Confidence Index scores for the geologic data factor, rock types and geologic
settings for which a physical-chemical, process-based understanding of radon generation and
mobility exists were regarded as having "proven geologic models" (3 points); a high
confidence could be held for predictions in such areas. Rocks for which the processes are
less well known or for which data are contradictory were regarded as "variable" (2 points),
and those about which little is known or for which no apparent correlations have been found
were deemed "questionable" (1 point).
The soil permeability factor was also scored based on quality and amount of data. The
three categories for soil permeability in the Confidence Index are similar in concept, and
scored similarly, to those for the geologic data factor. Soil permeability can be roughly
estimated from grain size and drainage class if data from standard, accepted soil percolation
tests are unavailable; however, the reliability of the data would be lower than if percolation
test figures or other measured permeability data are available, because an estimate of this type
does not encompass all the factors that affect soil permeability and thus may be inaccurate in
some instances. Most published soil permeability data are for water; although this is
generally closely related to the air permeability of the soil, there are some instances when it
may provide an incorrect estimate. Examples of areas in which water permeability data may
not accurately reflect air permeability include areas with consistently high levels of soil
moisture, or clay-rich soils, which would have a low water permeability but may have a
»
11-15 Reprinted from USGS Open-File Report 93-292
-------
significantly higher air permeability when dry due to shnnkage cracks m the soil. These
additional factors were applied to the soil permeability factor when assigning the RI score, but
may have less certainty in some cases and thus would be assigned a lower CI score
The Radon Index and Confidence Index £ive a general indication of the relative
contributions of the interrelated geologic factors influencing radon generation and transport m
rocks and soils, and thus, of the potential for elevated indoor radon level* to occur ma
particular are, However, because these reports are somewhat generated to cover re.at vely
large areas of States, it is highly recommended that more detailed studies be performed in
local areas-of interest, using the methods and general informal in these booklets as a guide.
*-~~ U?
-------
REFERENCES CITED
Akerblom, G., Anderson, P., and Clavensjo, B., 1984, Soil gas radon~A source for indoor radon
daughters: Radiation Protection Dosimetry, v. 7, p. 49-54.
Deffeyes, K.S., and MacGregor, I.D., 1980, World uranium resources: Scientific American,
v. 242, p. 66-76.
Durrance, E.M., 1986, Radioactivity in geology: Principles and applications: New York, N.Y.,
Wiley and Sons, 441 p.
Duval, J.S., 1989, Radioactivity and some of its applications in geology: Proceedings of the
symposium on the application of geophysics to engineering and environmental problems
(SAGEEP), Golden, Colorado, March 13-16,1989: Society of Engineering and Mineral
Exploration Geophysicists, p. 1-61.
Duval, J.S., Cook, E.G., and Adams^ J.A.S., 1971, Circle of investigation of an airborne
gamma-ray spectrometer: Journal of Geophysical Research, v. 76, p. 8466-8470.
Duval, J.S., Jones, W.J., Riggle, F.R., and Pitkin, J.A., 1989, Equivalent uranium map of
conterminous United States: U.S. Geological Survey Open-File Report 89-478,10 p.
Duval, J.S., Reimer, G.M., Schumann, R.R., Owen, D.E., and Otton, J.K., 1990, Soil-gas
radon compared to aerial and ground gamma-ray measurements at study sites near Greeley
and Fort Collins, Colorado: U.S. Geological Survey Open-File Report 90-648,42 p.
Dziuban, J.A., Clifford, M.A., White, S.B., Bergstein, J.W., and Alexander, B.V., 1990,
Residential radon survey of twenty-three States, in Proceedings of the 1990 International
Symposium on Radon and Radon Reduction Technology, Vol. HI: Preprints: U.S.
Environmental Protection Agency report EPA/600/9-90AX)5c, Paper IV-2,17 p.
Gammage, R.B., Wilson, D.L., Saultz, R.J., and Bauer, B.C., 1993, Subtereanean transport of
radon and elevated indoor radon in hilly karst terranes: Atmospheric Environment
(in press).
Gundersen, L.C.S., Reimer, G.M., and Agard, S.S., 1988a, Correlation between geology, radon
in soil gas, and indoor radon in the Reading Prong, in Marikos, M.A., and Hansman,
R.H., eds., Geologic causes of natural radionuclide anomalies: Missouri Department of
Natural Resources Special Publication 4, p. 91-102.
Gundersen, L.C.S, Reimer, G.M., Wiggs, C.R., and Rice, C.A., 1988b, Map showing radon
potential of rocks and soils in Montgomery County, Maryland: U.S. Geological Survey
Miscellaneous Field Studies Map MF-2043, scale 1:62,500.
Gundersen, Linda C.S., 1991, Radon in sheared metamorphic and igneous rocks, in Gundersen,
Linda C.S., and Richard B. Wanty, eds., Field studies of radon in rocks, soils, and water:
U.S. Geol. Survey Bulletin no. 1971, p. 39-50.
II-17 Reprinted from USGS Qpen-FUe Report 93-292
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Henry, Mitchell E., Kaeding, Margret E., and Monteverde, Donald, 1991, Radon in soil gas and
gamma-ray activity of rocks and soils at the Mulligan Quarry, Clinton, New Jersey, in
Gundersen, Linda C.S., and Richard B. Wanty, eds., Field studies of radon in rocks,
soils, and water: U.S. Geol. Survey Bulletin no. 1971, p. 65-75.
Klusman, R. W., and Jaacks, J. A., 1987, Environmental influences upon mercury, radon, and
helium concentrations in soil gases at a site near Denver, Colorado: Journal of
Geochemical Exploration, v. 27, p. 259-280.
Kovach, E.M., 1945, Meteorological influences upon the radon content of soil gas: Transactions,
American Geophysical Union, v. 26, p. 241-248.
Kunz, C., Laymon, C.A., and Parker, C., 1989, Gravelly soils and indoor radon, in Osborne,
M.C., and Harrison, J., eds., Proceedings of the 1988 EPA Symposium on Radon and
Radon Reduction Technology, Volume 1: U.S. Environmental Protection Agency Report
EPA/600/9-89/006A, p. 5-75-5-86.
Muessig, K., and Bell, C., 1988, Use of airborne radiometric data to direct testing for elevated
indoor radon: Northeastern Environmental Science, v. 7, no. 1, p. 45-51.
Ronca-Battista, M., Moon, M., Bergsten, J., White, S.B., Holt, N, and Alexander, B., 1988,
Radon-222 concentrations in the United States—Results of sample surveys in five states:
Radiation Protection Dosimetry, v. 24, p. 307-312.
Rose, A.W., Washington, J.W., and Greeman, D.J., 1988, Variability of radon with depth and
season in a central Pennsylvania soil developed on limestone: Northeastern Environmental
Science, v. 7, p. 35-39.
Schery, S.D., Gaeddert, D.H., and Wilkening, M.H., 1984, Factors affecting exhalation of radon
from a gravelly sandy loam: Journal of Geophysical Research, v. 89, p. 7299-7309.
Schumann, R.R., and Owen, D.E., 1988, Relationships between geology, equivalent uranium
concentration, and radon in soil gas, Fairfax County, Virginia: U.S. Geological Survey
Open-File Report 88-18,28 p.
Schumann, R.R., and Gundersen, L.C.S., 1991, Regional differences in radon emanation
coefficients in soils: Geological Society of America Abstracts With Programs, v. 23,
no. 1, p. 125.
Schumann, R.R., Peake, R.T., Schmidt, K.M., and Owen, D.E., 1991, Correlations of soil-gas
and indoor radon with geology in glacially derived soils of the northern Great Plains, in
Proceedings of the 1990 International Symposium on Radon and Radon Reduction
Technology, Volume 2, Symposium Oral Papers: U.S. Environmental Protection Agency
report EPA/600/9-9 l/026b, p. 6-23-6-36.
JJ-18 Reprinted from USGS Open-File Report 93-292
-------
Schumann, R.R., Owen, D.E., and Asher-Bolinder, S., 1992, Effects of weather and soil
characteristics on temporal variations in soil-gas radon concentrations, in Gates, A.E., and
Gundersen, L.C.S., eds., Geologic controls on radon: Geological Society of America
Special Paper 271, p. 65-72.
Sextro, R.G., Moed, B.A., Nazaroff, W.W., Revzan, K.L., and Nero, A.V., 1987,
Investigations of soil as a source of indoor radon, in Hopke, P.K., ed., Radon and its
decay products: American Chemical Society Symposium Series 331, p. 10-29.
Sterling, R., Meixel, G., Shen, L., Labs, K., and Bligh, T., 1985, Assessment of the energy
savings potential of building foundations research: Oak Ridge, Term., U.S. Department of
Energy Report ORNL/SUB/84-0024/1.
Smith, R.C., JJ, Reilly, M.A., Rose, A.W., Barnes, J.H., and Berkheiser, S.W., Jr., 1987,
Radon: a profound case:-Pennsylvania Geology, v. 18, p. 1-7.
Tanner, A.B., 1964, Radon migration in the ground: a review, in Adams, J.A.S., and Lowder,
W.M., eds., The natural radiation environment: Chicago, HI., University of Chicago
Press, p. 161-190.
Tanner, A.B., 1980, Radon migration in the ground: a supplementary review, in Gesell, T.F.,
and Lowder, W.M. (eds), Natural radiation environment HI, Symposium proceedings,
Houston, Texas, v. 1, p. 5-56.
U.S. Department of Agriculture, 1987, Principal kinds of soils: Orders, suborders, and great
groups: U.S. Geological Survey, National Atlas of the United States of America, sheet
38077-BE-NA-07M-00, scale 1:7,500,000.
U.S. Department of Energy, 1976, National Uranium Resource Evaluation preliminary report,
prepared by the U.S. Energy Research and Development Administration, Grand Junction,
Colo.: GJO-11(76).
Wanty, Richard B., and Schoen, Robert, 1991, A review of the chemical processes affecting the
mobility of radionuclides in natural waters, with applications, in Gundersen, Linda C.S.,
and Richard B. Wanty, eds., Field studies of radon in rocks, soils, and water: U.S.
Geological Survey Bulletin no. 1971, p. 183-194.
Washington, J.W., and Rose, A.W., 1990, Regional and temporal relations of radon in soil gas to
soil temperature and moisture: Geophysical Research Letters, v. 17, p. 829-832.
White, S.B., Bergsten, J.W., Alexander, B.V., and Ronca-Battista, M., 1989, Multi-State
surveys of indoor 222Rn: Health Physics, v. 57, p. 891-896.
JI-19 Reprinted from USGS Open-File Report 93-292
-------
-------
APPENDIX A
GEOLOGIC TIME SCALE
Subdivisions {and their symbols)
Eon or
Eonothem
Phaneroioic2
Proierozoic
(E)
Archean
(A)
Era or
Erathem
Cenozoic
(Cz)
Mesozoic2
(Md
Paleozoic
(Pd
feu!™* IZ)
M«30I»
E«ny
— ss
Mioait
t«rty
Period, System,
Subperiod, Subsystem
Quaternary
(Q)
Neocene 2
Subperiod or
T.«:.,y Subsystem (N)
_ Paieogene2
>" Subperiod or
Subsystem (Pi)
Cretaceous
(K)
Jurassic
(J)
Triassic
OH
Permian
(P)
Pennsylvanian
Carboniferous 'P'
(C) Mississippian
(M)
Devonian
(0)
Silurian
(S)
Ordovician
-------
-------
APPENDIX B
GLOSSARY OF TERMS
Units of measure
pCi/L (picocuries per liter)- a unit of measure of radioactivity used to describe radon
concentrations in a volume of air. One picocurie (10"12 curies) is equal to about 2.2 disintegrations
of radon atoms per minute. A liter is about 1.06 quarts. The average concentration of radon in
U.S. homes measured to date is between 1 and 2 pQ/L.
Bq/m3 (Becquerels per cubic meter)- a metric unit of radioactivity used to describe radon
concentrations in a volume of air. One becquerel is equal to one radioactive disintegration per
second. One pCi/L is equal to 37 Bq/m3.
ppm (parts per million)- a unit of measure of concentration by weight of an element in a
substance, in this case, soil or rock. One ppm of uranium contained in a ton of rock corresponds
to about 0.03 ounces of uranium. The average concentration of uranium in soils in the United
States is between 1 and 2 ppm.
in/hr (inches per hour)- a unit of measure used by soil scientists and engineers to describe the
permeability of a soil to water flowing through it It is measured by digging a hole 1 foot (12
inches) square and one foot deep, filling it with water, and measuring the time it takes for the water
to drain from the hole. The drop in height of the water level in the hole, measured in inches, is
then divided by the time (in hours) to determine the permeability. Soils range in permeability from
less than 0.06 in/hr to greater than 20 in/hr, but most soils in the United States have permeabilities
between these two extremes.
Geologic terms and terms related to the study of radon
aerial radiometric, aeroradiometric survey A survey of radioactivity, usually gamma rays,
taken by an aircraft carrying a gamma-ray spectrometer pointed at the ground surface.
alluvial fan A low, widespread mass of loose rock and soil material, shaped like an open fan
and deposited by a stream at the point where it flows from a narrow mountain valley out onto a
plain or broader valley. May also form at the junction with larger streams or when the gradient of
the stream abruptly decreases.
alluvium, alluvial General terms referring to unconsolidated detiital material deposited by a
stream or other body of running water.
alpha-track detector A passive radon measurement device consisting of a plastic film that is
sensitive to alpha particles. The film is etched with acid in a laboratory after it is exposed. The
etching reveals scratches, or "tracks", left by the alpha particles resulting from radon decay, which
can then be counted to calculate the radon concentration. Useful for long-term (1-12 months)
radon tests.
amphibolite A mafic metamorpnic rock consisting mainly of pyroxenes and(or) amphibole and
plagioclase.
11-21 Reprinted from USGS Open-File Report 93-292
-------
argillite, argillaceous Terms referring to a rock derived from clay or shale, or any sedimentary
rock containing an appreciable amount of clay-size material, i.e., argillaceous sandstone.
arid Term describing a climate characterized by dryness, or an evaporation rate that exceeds the
amount of precipitation.
basalt A general term for a dark-colored mafic igneous rocks that may be of extrusive origin,
such as volcanic basalt flows, or intrusive origin, such as basalt dikes.
batholith A mass of plutonic igneous rock that has more than 40 square miles of surface
exposure and no known bottom.
carbonate A sedimentary rock consisting of the carbonate (COs) compounds of calcium,
magnesium, or iron, e.g. limestone and dolomite.
carbonaceous Said of a rock or sediment that is rich in carbon, is coaly, or contains organic
matter.
charcoal canister A passive radon measurement device consisting of a small container of
granulated activated charcoal that is designed to adsorb radon. Useful for short duration (2-7 days)
measurements only. May be referred to as a "screening" test
chert A hard, extremely dense sedimentary rock consisting dominantly of interlocking crystals of
quartz. Crystals are not visible to the naked eye, giving the rock a milky, dull luster. It may be
white or gray but is commonly colored red, black, yellow, blue, pink, brown, or green.
clastic pertaining to a rock or sediment composed of fragments that are derived from preexisting
rocks or minerals. The most common clastic sedimentary rocks are sandstone and shale.
clay A rock containing clay mineral fragments or material of any composition having a diameter
less than 1/256 mm.
clay mineral One of a complex and loosely defined group of finely crystalline minerals made up
of water, silicate and aluminum (and a wide variety of other elements). They are formed chiefly by
alteration or weathering of primary silicate minerals. Certain clay minerals are noted for their small
size and ability to absorb substantial amounts of water, causing them to swell. The change in size
that occurs as these clays change between dry and wet is referred to as their "shrink-swell"
potential.
concretion A hard, compact mass of mineral matter, normally subspherical but commonly
irregular in shape; formed by precipitation from a water solution about a nucleus or center, such as
a leaf, shell, bone, or fossil, within a sedimentary or fractured rock.
conglomerate A coarse-grained, clastic sedimentary rock composed of rock and mineral
fragments larger than 2 mm, set in a finer-grained matrix of clastic material.
cuesta A hill or ridge with a gentle slope on one side and a steep slope on the other. The
formation of a cuesta is controlled by the different weathering properties and the structural dip of
the rocks forming the hill or ridge.
daughter product A nuclide formed by the disintegration of a radioactive precursor or "parent"
atom.
n-22 Reprinted from USGS Open-File Report 93-292
-------
delta, deltaic Referring to a low, flat, alluvial tract of land having a triangular or fan shape,
located at or near the mouth of a river. It results from the accumulation of sediment deposited by a
river at the point at which the river loses its ability to transport the sediment, commonly where a
river meets a larger body of water such as a lake or ocean.
dike A tabular igneous intrusion of rock, younger than the surrounding rock-; that commonly cuts
across the bedding or foliation of the rock it intrudes.
diorite A plutonic igneous rock that is medium in color and contains visible dark minerals that
make up less than 50% of the rock. It also contains abundant sodium plagioclase and minor
quartz.
dolomite A carbonate sedimentary rock of which more than 50% consists of the mineral dolomite
(CaMg(CO3)2), and is commonly white, gray, brown, yellow, or pinkish in color.
drainage The manner in which the waters of an area pass, flow off of, or flow into the soil.
Also refers to the water features of an area, such as lakes and rivers, that drain it
eolian Pertaining to sediments deposited by the wind.
esker A long, narrow, steep-sided ridge composed of irregular beds of sand and gravel deposited
by streams beneath a glacier and left behind when the ice melted.
evapotranspiration Loss of water from a land area by evaporation from the soil and
transpiration from plants.
extrusive Said of igneous rocks that have been erupted onto the surface of the Earth.
fault A fracture or zone of fractures in rock or sediment along which there has been movement.
fluvial, fluvial deposit Pertaining to sediment that has been deposited by a river or stream.
foliation A linear feature in a rock defined by both mineralogic and structural characteristics. It
may be formed during deformation or metamorphism.
formation A mappable body of rock having similar characteristics.
glacial deposit Any sediment transported and deposited by a glacier or processes associated
with glaciers, such as glaciofluvial sediments deposited by streams flowing from melting glaciers.
gneiss A rock formed by metamorphism in which bands and lenses of minerals of similar
composition alternate with bands and lenses of different composition, giving the rock a striped or
"foliated" appearance.
granite Broadly applied, any coarsely crystalline, quartz- and feldspar-bearing igneous plutonic
rock. Technically, granites have between 10 and 50% quartz, and alkali feldspar comprises at least
65% of the total feldspar.
gravel An unconsolidated, natural accumulation of rock fragments consisting predominantly of
particles greater than 2 mm in size.
heavy minerals Mineral grains in sediment or sedimentary rock having higher than average
specific gravity. May form layers and lenses because of wind or water sorting by weight and size
11-23 Reprinted from USGS Open-File Report 93-292
-------
and may be referred to as a "placer deposit" Some heavy minerals are magnetite, garnet, zircon,
monazite, and xenotime.
igneous Said of a rock or mineral that solidified from molten or partly molten rock material. It is
one of the three main classes into which ro<*s are tfvW. the others b*mg sedimentary and
metamorphic.
intermontane A term that refers to an area between two mountains or mountain ranges.
intrusion, intrusive The processes of emplacement or injection of molten rock into pre-existing
rock. Also refers to the rock formed by intrusive processes, such as an intrusive igneous rock .
kame A low mound, knob, hummock, or short irregular ridge formed by a glacial stream at the
margin of a melting glacier; composed of bedded sand and gravel.
karst terrain A type of topography that is formed on limestone, gypsum and other rocks by
dissolution of the rock by water,' forming sinkholes and caves.
lignite A brownish-black coal that is intermediate in coalification between peat and
subbituminous coal.
limestone A carbonate sedimentary rock consisting of more than 50% calcium carbonate,
primarily in the form of the mineral calcite (CaCOs).
lithology The description of rocks in hand specimen and in outcrop on the basis of color,
composition, and grain size.
loam A permeable soil composed of a mixture of relatively equal parts clay, silt, and sand, and
usually containing some organic matter.
loess A fine-grained eolian deposit composed of silt-sized particles generally thought to have
been deposited from windblown dust of Pleistocene age.
mafic Term describing an igneous rock containing more than 50% dark-colored minerals.
marine Term describing sediments deposited in the ocean, or precipitated from ocean waters.
metamorphic Any rock derived from pre-existing rocks by mineralogical, chemical, or structural
changes in response to changes in temperature, pressure, stress, and the chemical environment
PhylUte, schist, amphibolite, and gneiss are metamorphic rocks.
moraine A mound, ridge, or other distinct accumulation of unsorted, imbedded glacial material,
predominantly till, deposited by the action of glacial ice.
outcrop That part of a geologic formation or structure that appears at the surface of the Earth, as
in "rock outcrop".
percolation test A term used in engineering for a test to determine the water permeability of a
soil. A hole is dug and filled with water and the rate of water level decline is measured.
permeability The capacity of a rock, sediment or soil to transmit liquid or gas.
phosphate, phosphatic, phosphorite Any rock or sediment containing a significant amount
of phosphate minerals, i.e., minerals containing PO4.
IL-24 Reprinted from USGS Open-File Report 93-292
-------
physiographic province A region in which all parts are similar in geologic structure and
climate, which has had a uniform geomorphic history, and whose topography or landforms differ
significantly from adjacent regions.
nlacer deposit See heavy minerals
residual Formed by weathering of a material in place.
residuum Deposit of residual material. -
rhyolite An extrusive igneous rock of volcanic origin, compositionally equivalent to granite.
sandstone A clastic sedimentary rock composed of sand-sized rock and mineral material that is
more or less firmly cemented. Sand particles range from 1/16 to 2 mm in size.
schist A strongly foliated crystalline rock, formed by metamorphism, that can be readily split into
thin flakes or slabs. Contains mica; minerals are typically aligned.
screening level Result of an indoor radon test taken with a charcoal canister or similar device,
for a short period of time, usually less than seven days. May indicate the potential for an indoor
radon problem but does not indicate annual exposure to radon.
sediment Deposits of rock and mineral particles or fragments originating from material that is
transported by air, water or ice, or that accumulate by natural chemical precipitation or secretion of
organisms.
semiarid Refers to a climate that has slightly more precipitation than an arid climate.
shale A fine-grained sedimentary rock formed from solidification (lithification) of clay or mud.
shear zone Refers to a roughly linear zone of rock that has been faulted by ductile or non-ductile
processes in which the rock is sheared and both sides are displaced relative to one another.
shrink-swell clay See clay mineral.
siltstone A fine-grained clastic sedimentary rock composed of silt-sized rock and mineral
material and more or less firmly cemented. Silt particles range from 1/16 to 1/256 mm in size.
sinkhole A roughly circular depression in a karst area measuring meters to tens of meters in
diameter. It is funnel shaped and is formed by collapse of the surface material into an underlying
void created by the dissolution of carbonate rock.
slope An inclined part of the earth's surf ace.
solution cavity A hole, channel or cave-like cavity formed by dissolution of rock.
stratigraphy The study of rock strata; also refers to the succession of rocks of a particular area.
surficial materials Unconsolidated glacial, wind-, or waterborne deposits occurring on the
earth's surface.
tablelands General term for a broad, elevated region with a nearly level surface of considerable
extent
IE-25 Reprinted from USGS Open-File Report 93-292
-------
terrace gravel Gravel-sized material that caps ridges and terraces, left behind by a stream as it
cuts down to a lower level.
terrain A tract or region of the Earth's surface considered as a physical feature or an ecological
environment
till Unsorted, generally unconsolidated and unbedded rock and mineral material deposited directly
adjacent to and underneath a glacier, without reworking by meltwater. Size of grains varies greatly
from clay to boulders.
uraniferous Containing uranium, usually more than 2 ppm.
vendor data Used in this report to refer to indoor radon data collected and measured by
commercial vendors of radon measurement devices and/or services.
volcanic Pertaining to the activities, structures, and extrusive rock types of a volcano.
water table The surface forming the boundary between the zone of saturation and the zone of
aeration; the top surface of a body of unconfined groundwater in rock or soil.
weathering The destructive process by which earth and rock materials, on exposure to
atmospheric elements, are changed in color, texture, composition, firmness, or form with little or
no transport of the material.
n-26 Reprinted from USGS Open-File Report 93-292
-------
APPENDIX C
EPA REGIONAL OFFICES
EPA Regional Offices
State
EPA Region
EPA Region 1
JFK Federal Building
Boston, MA 02203
(617) 565-4502
EPA Region 2
(2AIR:RAD)
26 Federal Plaza
New York, NY 10278
(212) 264-4110
Region 3 (3AH14)
S41 Chestnut Street
Philadelphia, PA 19107
(215) 597-8326
EPA Region 4
345 Courtland Street, N.E.
Atlanta, GA 30365
(404) 347-3907
EPA Region 5 (5AR26)
77 West Jackson Blvd.
Chicago, IL 60604-3507
(312) 886-6175
EPA Region 6 (6T-AS)
1445 Ross Avenue
Dallas, TX 75202-2733
(214) 655-7224
EPA Region 7
726 Minnesota Avenue
Kansas City, KS 66101
(913) 551-7604
EPA Region 8
(8HWM-RP)
999 18th Street
One Denver Place, Suite 1300
Denver, CO 80202-2413
(303) 293-1713
EPA Region 9 (A-3)
75 Hawthorne Street
San Francisco, CA 94105
(415) 744-1048
EPA Region 10
1200 Sixth Avenue
Seattle, WA 98101
(202) 442-7660
Alabama .' 4
Alaska..... 10
Arizona 9
Arkansas 6
California 9
Colorado 8
Connecticut 1
Delaware 3
District of Columbia 3
Florida 4
Georgia 4
Hawaii 9
Idaho 10
Illinois 5
Indiana 5
Iowa 7
Kansas : 7
Kentucky 4
Louisiana 6
Maine 1
Maryland 3
Massachusetts 1
Michigan 5
Minnesota 5
Mississippi 4
Missouri 7
Montana. 8
Nebraska 7
Nevada 9
New Hampshire 1
New Jersey 2
New Mexico 6
New York 2
North Carolina 4
North Dakota 8
Ohio 5
Oklahoma 6
Oregon 10
Pennsylvania 3
Rhode Island 1
South Carolina 4
South Dakota 8
Tennessee 4
Texas 6
Utah 8
Vermont 1
Virginia 3
Washington 10
West Virginia 3
Wisconsin 5
Wyoming 8
IE-27 Reprinted from USGS Open-File Report 93-292
-------
STATE RADON CONTACTS
May, 1993
Alabama James McNees
Division of Radiation Control
Alabama Department of Public Health
State Office Building
Montgomery, AL 36130
(205)242-5315
1-800-582-1866 in state
AJasJsa Charles Tedford
Department of Health and Social
Services
P.O. Box 110613
Juneau.AK 99811-0613
(907)465-3019
1-800-478-4845 in state
Arizona John Stewart
Arizona Radiation Regulatory Agency
4814 South 40th St.
Phoenix, AZ 85040
(602) 255-4845
Arkansas LeeGershner
Division of Radiation Control
Department of Health
4815 Markham Street, Slot 30
Little Rock, AR 72205-3867
(501) 661-2301
California J. David Quinton
Department of Health Services
714 P Street, Room 600
Sacramento, CA 94234-7320
(916) 324-2208
1-800-745-7236 in state
Colorado Linda Martin
Department of Health
4210 East llth Avenue
Denver, CO 80220
(303)692-3057
1-800-846-3986 in state
Connecticut Alan J. Siniscalchi
Radon Program
Connecticut Department of Health
Services
150 Washington Street
Hartford, CT 06106-4474
(203) 566-3122
Delaware Marai G. Rejai
Office of Radiation Control
Division of Public Health
P.O. Box 637
Dover, DE 19903
(302) 736-3028
1-800-554-4636 In State
District Robert Davis
of Columbia DC Department of Consumer and
Regulatory Affairs
614 H Street NW
Room 1014
Washington, DC 20001
(202) 727-71068
Florida N. Michael Gilley
Office of Radiation Control
Department of Health and
Rehabilitative Services
1317 Winewood Boulevard
Tallahassee, FL 32399-0700
(904)488-1525
1-800-543-8279 in state
Richard Schreiber
Georgia Department of Human
Resources
878 Peachtree St., Room 100
Atlanta, GA 30309
(404) 894-6644
1-800-745-0037 in state
Hawaii Russell Takata
Environmental Health Services
Division
591 Ala Moana Boulevard
Honolulu, ffl 96813-2498
(808)5864700
n-28
Reprinted from USGS Open-File Report 93-292
-------
Idaho
Illinois
Indiana
Iowa
Kansas
Kentucky
PatMcGavam
Office of Environmental Health
450 West State Street
Boise, ID 83720
(208) 334-6584
1-800-445-8647 in state
Richard Allen
Illinois Department of Nuclear Safety
1301 Outer Park Drive
Springfield, IL 62704
(217) 524-5614
1-800-325-1245 in state
Lorand Magyar
Radiological Health Section
Indiana State Department of Health
1330 West Michigan Street
P.O. Box 1964
Indianapolis, IN 46206
(317)633-8563
1-800-272-9723 In State
Donald A. Hater
Bureau of Radiological Health
Iowa Department of Public Health
Lucas State Office Building
Des Moines, IA 50319-0075
(515)281-3478
1-800-383-5992 In State
Harold Spiker
Radiation Control Program
Kansas Department of Health and
Environment
109 SW 9th Street
6th Floor Mills Building
Topeka, KS 66612
(913)296-1561
JeanaPhelps
Radiation Control Branch
Department of Health Services
Cabinet for Human Resources
275 East Main Street
Frankfort, KY 40601
(502)564-3700
Louisiana Matt Schlenker
Louisiana Department of
Environmental Quality
P.O. Box 82135
Baton Rouge, LA 70884-2135
(504)925-7042
1-800-256-2494 in state
Maine BobStilwell
Division of Health Engineering
Department of Human Services
State House, Station 10
Augusta, ME 04333
(207)289-5676
1-800-232-0842 in state
Maryland Leon J. Rachuba
Radiological Health Program
Maryland Department of the
Environment
2500 Broening Highway
Baltimore, MD 21224
(410)631-3301
1-800-872-3666 In State
Massachusetts William J. Bell
Radiation Control Program
Department of Public Health
23 Service Center
Northampton, MA 01060
(413)586-7525
1-800-445-1255 in state
Michigan SueHendershott
Division of Radiological Health
Bureau of Environmental and
Occupational Health
3423 North Logan Street
P.O. Box 30195
Lansing, MI 48909
(517) 335-8194
Minnesota Laura Oatrnann
Indoor Air Quality Unit
925 Delaware Street, SE
P.O. Box 59040
Minneapolis, MN 55459-0040
(612)627-5480
1-800-798-9050 in state
n-29
Reprinted from USGS Open-File Report 93-292
-------
Mississippi Silas Anderson
Division of Radiological Health
Department of Health
3150 Lawson Street
P.O. Box 1700
Jackson, MS 39215-1700
(601) 354-6657
1-800-626-7739 in state
Missouri Kenneth V. Miller
Bureau of Radiological Health
Missouri Department of Health
1730 East Elm
P.O. Box 570
Jefferson City, MO 65102
(314)751-6083
1-800-669-7236 In State
Montana Adrian C. Howe
Occupational Health Bureau
Montana Department of Health and
Environmental Sciences
Cogswell Building A113
Helena, MT 59620
(406)444-3671
Joseph Milone
Division of Radiological Health
Nebraska Department of Health
301 Centennial Mall, South
P.O. Box 95007
Lincoln, NE 68509
(402)471-2168
1-800-334-9491 In State
Nevada Stan Marshall
Department of Human Resources
505 East King Street
Room 203
Carson City,NV 89710
(702) 687-5394
New Hampshire David Chase
Bureau of Radiological Health
Division of Public Health Services
Health and Welfare Building
Six Hazen Drive
Concord, NH 03301
(603)271-4674
1-800-852-3345 x4674
. New Jersey Tonalee Carlson Key
Division of Environmental Quality
Department of Environmental
Protection
CN415
Trenton, NJ 08625-0145
(609)987-6369
1-800-648-0394 in state
New Mexico. William M. Floyd
Radiation Licensing and Registration
Section
New Mexico Environmental
Improvement Division
1190 St. Francis Drive
Santa Fe,NM 87503
(505) 827-4300
New York William J. Condon
Bureau of Environmental Radiation
Protection
New York State Health Department
Two University Place
Albany, NY 12202
(518)458-6495
1-800-458-1158 in state
North Carolina Dr. Felix Fong
Radiation Protection Division
Department of Environmental Health
and Natural Resources
701 Barbour Drive
Raleigh, NC 27603-2008
(919) 571-4141
1-800-662-7301 (recorded info x4196)
North Dakota Arlen Jacobson
North Dakota Department of Health
1200 Missouri Avenue, Room 304
P.O. Box 5520
Bismarck, ND 58502-5520
(701)221-5188
Ohio Marcie Matthews
Radiological Health Program
Department of Health
1224 Kinnear Road - Suite 120
Columbus, OH 43212
(614)644-2727
1-800-523-4439 in state
n-30 Reprinted from USGS Open-File Report 93-292
-------
Oklahoma
Pennsylvania
Puerto Rico
Rhode Island
South Carolina
Gene Smith
Radiation Protection Division
Oklahoma State Department of
Health
P.O. Box 53551
Oklahoma City, OK 73152
(405)271-5221
George Toombs
Department of Human Resources
Health Division
1400 SW 5th Avenue
Portland, OR 97201
(503) 731^014
Michael Pyles
Pennsylvania Department of
Environmental Resources
Bureau of Radiation Protection
P.O. Box 2063
Harrisburg, PA 17120
(717) 783-3594
1-800-23-RADON Li State
David Saldana
Radiological Health Division
G.P.O. Call Box 70184
Rio Piedras, Puerto Rico 00936
(809) 767-3563
Edmund Arcand
Division of Occupational Health and
Radiation
Department of Health
205 Cannon Building
Davis Street
Providence, RI02908
(401) 277-2438
Bureau of Radiological Health
Department of Health and
Environmental Control
2600 Bull Street
Columbia, SC 29201
(803)734^631
1-800-768-0362
South Dakota MikePochop
Division of Environment Regulation
Department of Water and Natural
Resources
Joe Foss Building, Room 217
523 E. Capitol
Pierre, SD 57501-3181
(605)773-3351
Tennessee Susie Shimek
Division of Air Pollution Control
Bureau of the Environment
Department of Environment and
Conservation
Customs House, 701 Broadway
Nashville, TN 37219-5403
(615) 532-0733
1-800-232-1139 in state
Texas Gary Smith
Bureau of Radiation Control
Texas Department of Health
1100 West 49th Street
Austin, TX 78756-3189
(512) 834-6688
Utah John Hultquist
Bureau of Radiation Control
Utah State Department of Health
288 North, 1460 West
P.O. Box 16690
Salt Lake City, UT 84116-0690
(801) 536-4250
Vermont Paul demons
Occupational and Radiological Health
Division
Vermont Department of Health
10 Baldwin Street
Montpelier, VT 05602
(802) 828-2886
1-800-640-0601 in state
Virgin Islands Contact the U.S. Environmental
Protection Agency, Region n
in New York
(212)264^110 i
11-31 Reprinted from USGS Open-File Report 93-292
-------
Virginia Shelly Ottenbrite
Bureau of Radiological Health
Department of Health
109 Governor Street
Richmond, VA 23219
(804)786-5932
1-800-468-0138 in state
Washington KateColeman
Department of Health
Office of Radiation Protection
Airdustrial Building 5, LE-13
Olympia,WA 98504
(206)753-4518
1-800-323-9727 In State
West Virginia Beanie L. DeBoid
Industrial Hygiene Division
West Virginia Department of Health
151 llth Avenue
South Charleston, WV 25303
(304)558-3526
1-800-922-1255 In State
Wisconsin Conrad Weiffenbach
Radiation Protection Section
Division of Health
Department of Health and Social
Services
P.O. Box 309
Madison, WI53701-0309
(608)267-4796
1-800-798-9050 in state
Wyoming Janet Hough
Wyoming Department of Health and
Social Services
Hathway Building, 4th Floor
Cheyenne, WY 82002-0710
(307) 777-6015
1-800-458-5847 in state
H-32 Reprinted from USGS Open-File Report 93-292
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STATE GEOLOGICAL SURVEYS
May, 1993
Alabama Ernest A. Mancini
Geological Survey of Alabama
P.O. Box 0
420 Hackbeny Lane
Tuscaloosa, AL 35486-9780
(205)349-2852
Alaska Thomas E. Smith
Alaska Division of Geological &
Geophysical Surveys
794 University Ave., Suite 200
Fairbanks, AK 99709-3645
(907)479-7147
Arizona Larry D. Fellows •
Arizona Geological Survey
845 North Park Ave., Suite 100
Tucson, AZ 85719
(602) 882-4795
Arkansas Norman F. Williams
Arkansas Geological Commission
Vardelle Parham Geology Center
3815 West Roosevelt Rd.
Little Rock, AR 72204
(501) 324-9165
California James F. Davis
California Division of Mines &
Geology
801 K Street, MS 12-30
Sacramento, CA 95814-3531
(916)445-1923
Colorado Pat Rogers (Acting)
Colorado Geological Survey
1313 Sherman St., Rm 715
Denver, CO 80203
(303)866-2611
Connecticut Richard C. Hyde
Connecticut Geological & Natural
History Survey
165 Capitol Ave., Rm. 553
Hartford, CT 06106
(203) 566-3540
Delaware Robert R. Jordan
Delaware Geological Survey
University of Delaware
101 Penny Hall
Newark, DE 19716-7501
(302)831-2833
Idaho
Florida Walter Schmidt
Florida Geological Survey
903 W. Tennessee Su
Tallahassee, FL 32304-7700
(904)488^191
William H. McLemore
Georgia Geologic Survey
Rm. 400
19 Martin Luther King Jr. Dr. S W
Atlanta, GA 30334
(404) 656-3214
Manabu Tagomori
Dept. of Land and Natural Resources
Division of Water & Land Mgt
P.O. Box 373
Honolulu, HI 96809
(808) 548-7539
Earl H. Bennett
Idaho Geological Survey
University of Idaho
Morrill Hall, Rm. 332
Moscow, ID 83843
(208) 885-7991
Illinois Morris W. Leighton
Illinois State Geological Survey
Natural Resources Building
615 East Peabody Dr.
Champaign, IL 61820
(217) 333^747
Norman C. Hester
Indiana Geological Survey
611 North Walnut Grove
Bloomington, IN 47405
(812) 855-9350
Donald L. Koch
Iowa Department of Natural Resources
Geological Survey Bureau
109 Trowbridge Hall
Iowa City, IA 52242-1319
(319) 335-1575
LeeC. Gerhard
Kansas Geological Survey
1930 Constant Ave., West campus
University of Kansas
Lawrence, KS 66047
(913)864-3965
Iowa
Kansas
11-33 Reprinted from USGS Open-File Report 93-292
-------
Kentucky Donald C. Haney
Kentucky Geological Survey
University of Kentucky
. 228 Mining & Mineral Resources
Building
Lexington, KY 40506-0107
(606)257-5500
Louisiana William E. Marsalis
Louisiana Geological Survey
P.O. Box 2827
• University Station
Baton Rouge, LA 70821-2827
(504) 388-5320
Maine Walter A. Anderson
Maine Geological Survey
Department of Conservation
State House, Station 22
Augusta, ME 04333
(207) 289-2801
Maryland Emery T. Cleaves
Maryland Geological Survey
2300 St. Paul Street
Baltimore, MD 21218-5210
(410) 554-5500
Massachusetts Joseph A. Sinnott
Massachusetts Office of
Environmental Affairs
100 Cambridge SL, Room 2000
Boston, MA 02202
(617)727-9800
Michigan R. Thomas Segall
Michigan Geological Survey Division
Box 30256
Lansing, MI 48909
(517) 334-6923
Minnesota Priscilla C. Grew
Minnesota Geological Survey
2642 University Ave.
St Paul, MN 55114-1057
(612)627-4780
Mississippi S. Cragin Knox
Mississippi Office of Geology
P.O. Box 20307
Jackson, MS 39289-1307
(601)961-5500
Missouri James H. Williams
Missouri Division of Geology &
Land Survey
111 Fairgrounds Road
P.O. Box 250
Rolla, MO 65401
(314) 368-2100
Montana Edward T.Ruppel
Montana Bureau of Mines & Geology
Montana College of Mineral Science
and Technology, Main Hall
Butte, MT 59701
.(406)496-4180
Nebraska Perry B. Wigley
Nebraska Conservation & Survey
Division
113 Nebraska Hall
University of Nebraska
Lincoln, ME 68588-0517
(402)472-2410
Nevada Jonathan G. Price
Nevada Bureau of Mines & Geology
Stop 178
University of Nevada-Reno
Reno, NV 89557-0088
(702) 784-6691
New Hampshire Eugene L. Boudette
Dept. of Environmental Services
117 James Hall
University of New Hampshire
Durham, NH 03824-3589
(603)862-3160
New Jersey Haig F. Kasabach
New Jersey Geological Survey
P.O. Box 427
Trenton, NJ 08625
(609)292-1185
New Mexico Charles E. Chapin
New Mexico Bureau of Mines &
Mineral Resources
Campus Station
Socorro.NM 87801
(505)835-5420
New York Robert H. Fakundiny
New York State Geological Survey
3136 Cultural Education Center
Empire State Plaza
Albany, NY 12230
(518)474-5816
H-34 Reprinted from USGS Open-File Report 93-292
-------
North Carolina Charles H. Gardner
North Carolina Geological Survey
P.O. Box 27687
Raleigh, NC 27611-7687
(919)733-3833
North Dakota John P. Bluemle
North Dakota Geological Survey
600 East Blvd.
Bismarck, ND 58505-0840
(701) 224-4109
Ohio Thomas M. Berg
Ohio DepL of Natural Resources
Division of Geological Survey
4383 Fountain Square Drive
Columbus, OH 43224-1362
(614) 265-6576
Oklahoma Charles J. Mankin
Oklahoma Geological Survey
Room N-131, Energy Center
lOOE.Boyd
Norman, OK 73019-0628
(405)325-3031
Oregon Donald A. Hull
DepL of Geology & Mineral Indust.
Suite 965
800 NE Oregon St. #28
Portland, OR 97232-2162
(503) 731-4600
Pennsylvania Donald M. Hoskins
Dept. of Environmental Resources
Bureau of Topographic & Geologic
Survey
P.O. Box 2357
Harrisburg, PA 17105-2357
(717) 787-2169
Puerto Rico Ramon M. Alonso
Puerto Rico Geological Survey
Division
Box 5887
Puerta de Tierra Station
San Juan, P.R. 00906
(809)722-2526
Rhode Island J. Allan Cain
Department of Geology
University of Rhode Island
315 Green Hall
Kingston, RI02881
(401)792-2265
South Carolina Alan-Jon W. Zupan (Acting)
South Carolina Geological Survey
5 Geology Road
Columbia, SC 29210-9998
(803)737-9440
South Dakota C.M. Christensen (Acting)
South Dakota Geological Survey
Science Center
University of South Dakota
Vermillion, SD 57069-2390
(605) 677-5227
Tennessee Edward T.Luther
Tennessee Division of Geology
13th Floor, L & C Tower
401 Church Street
Nashville, TN 37243-0445
(615)532-1500
Texas William L. Fisher
Texas Bureau of Economic Geology
University of Texas
University Station, Box X
Austin, TX 78713-7508
(512)471-7721
Utah M. Lee Allison
Utah Geological & Mineral Survey
2363 S. Foothill Dr.
Salt Lake City, UT 84109-1491
(801)467-7970
Vermont Diane L. Conrad
Vermont Division of Geology and
Mineral Resources
103 South Main St.
Waterbury,VT 05671
(802)244-5164
Virginia Stanley S. Johnson
Virginia Division of Mineral
Resources
P.O. Box 3667
Charlottesvffle, VA 22903
(804)293-5121
Washington Raymond Lasmanis
Washington Division of Geology &
Earth Resources
Department of Natural Resources
P.O. Box 47007
Olympia, Washington 98504-7007
(206)902-1450
n-35 Reprinted from USGS Open-File Report 93-292
-------
West Virginia Larry D. Woodfoik
West Virginia Geological and
Economic Survey
Mont Chateau Research Center
P.O. Box 879
Morgantown.WV 26507-0879
(304) 594-2331
Wisconsin James Robertson
Wisconsin Geological & Natural
History Survey
3817 Mineral Point Road
Madison, WI 53705-5100
(608)263-7384
Wyoming Gary B. Glass
Geological Survey of Wyoming
University of Wyoming
Box 3008, University Station
Laramie, WY 82071-3008
(307)766-2286
n-36 Reprinted from USGS Open-Hie Report 93-292
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EPA REGION 4 GEOLOGIC RADON POTENTIAL SUMMARY
by
Linda C.S. Gundersen, James K. Otton, andR. Randall Schumann
U.S. Geological Survey
EPA Region 4 includes the states of Alabama, Florida, Georgia, Kentucky, Mississippi,
North Carolina, South Carolina, and Tennessee. For each state, geologic radon potential areas '
were delineated and ranked on the basis of geologic, soil, housing construction, and other factors.
Areas in which the average screening indoor radon level of all homes within the area is estimated to
be greater than 4 pCi/L were ranked high. Areas in which the average screening indoor radon
level of all homes within the area is estimated to be between 2 and 4 pCi/L were ranked
moderate/variable, and areas in which the average screening indoor radon level of all homes within
the area is estimated to be less than 2 pCi/L were ranked low. Information on the data used and on
the radon potential ranking scheme is given in the introduction to this volume. More detailed
information on the geology and radon potential of each state in Region 4 is given in the individual
state chapters. The individual chapters describing the geology and radon potential of the states in
EPA Region 4, though much more detailed than this summary, still are generalized assessments
and there is no substitute for having a home tested. Within any radon potential area homes with
indoor radon levels both above and below the predicted average will likely be found.
Major geologic/physiographic provinces for Region 4 are shown in figure 1 and are
referred to in the summary that follows. The moderate climate, use of air conditioning, evaporative
coolers, or open windows for ventilation, and the small proportion of homes with basements
throughout much of Region 4 contribute to generally low indoor radon levels in spite of the fact
that this area has substantial areas of high surface radioactivity.
Maps showing arithmetic means of measured indoor radon levels are shown in figure 2.
Indoor radon data for Alabama, Georgia, Kentucky, Mississippi, North Carolina, South Carolina,
and Tennessee are from the State/EPA Residential Radon Survey. Data for Florida are from the
Florida Statewide Radon Study. County screening indoor radon averages range from less than 1
pCi/L to 4.6 pCi/L. The geologic radon potential areas in Region 4 have been summarized from
the individual state chapters and are shown in figure 3.
ALABAMA
The Plateaus
The Interior Low Plateaus have been ranked high in geologic radon potential. The
Mississippian carbonate rocks and shales that underlie this province appear to have high (>2.5 ppm
eU) to moderate (1.5-2.5 ppm eU) radioactivity associated with them. The carbonates and shales
are also associated with most of the highest county indoor radon averages for the State, particularly
in Colbert, Madison, Lawrence, and Lauderdale Counties. The geologic units that may be the
source of these problems, as indicated by the radioactivity, appear to be parts of the Fort Payne
Chert, the Tuscumbia Limestone, the Monteagle, Bangor, Pride Mountain, and Parkwood
Formations, and the Floyd Shale. Indoor radon levels in homes built on the St. Genevieve
Limestone, Tuscumbia Limestone, and Fort Payne Chert averaged between 3.0 and 4.3 pCi/L.
Soils developed from carbonate rocks are often elevated in uranium and radium. Carbonate soils
are derived from the dissolution of the CaCOs that makes up the majority of the rock. When the
CaCO3 has been dissolved away, the soils are enriched in the remaining impurities, predominantly
ffl-1 Reprinted from USGS Open-File Report 93-292-D
-------
Figure 1. Geologic radon potential areas of EPA Region 4. See next page for names of
numbered areas.
-------
Figure 1 (continued). Geologic radon potential areas of EPA Region 4. Note: although some
areas, for example, the Coastal Plain, are contiguous from state to state, they are sometimes
referred to by slightly different names or are subdivided differently in different states, thus are
numbered and labelled seperately on this figure.
1-Jackson Purchase (Coastal Plain)
2-Westem Coalfield
3-Mississippian Plateau
4-Eastern Pennyroyal
5-New Albany Shale
6-Outer Bluegrass
7-InnerBluegrass
8-Cumberland Plateau (Appalachian Plateau)
9-Mississippi alluvial plain
10-Loess-covered Coastal Plain
11-Eastern Coastal Plain
12-Cherty Highland
13-Highland Rim
14-Nashville Basin
15-Appalachian Plateau
16-Ridge and Valley
17-Unaka Mountains
18-Blue Ridge Belt
19-Brevard Fault Zone
20-Chauga Belt
21-Inner Piedmont
22-Kings Mountain Belt
23-Dan River Basin
24-Milton Belt
25-Charlotte Belt
26-Carolina Slate Belt
27-Wadesboro sub-basin
28-Sanfoid-Durham sub-basins
29-Raleigh Belt
30-Eastem Slate Belt
31-Inner Coastal Plain
32-Outer Coastal Plain
33-Jackson Prairies
34-Loess Hills
35-North Central Hills
36-Flatwoods
37-Pontotoc Ridge
38-Black Prairies
39-Tombigbee Hills
40-Coastal Pine Meadows
41-Pine Hills
42-Interior Low Plateaus
43-Inner Coastal Plain (Cretaceous)
44-Northern Piedmont (faults, phylite and granite rocks)
45-Wedowee and Emuckfaw Groups
46-Inner Piedmont/Dadeville Complex
47-Southern Piedmont
48-Inner and Outer Coastal Plain (Tertiary Rocks)
49-Rome-Kingston Thrust Stack
50-Georgiabama Thrust Stack (north of Allatoona Fault)
51-Georgiabama Thrust Stack (south of Allatoona Fault)
52-Litde River Thrust Stack
53-Coastal Plain (Cretaceous/Tertiary)
54-Coastal Plain (Quaternary/Pliocene-Pleistocene gravels)
55-Upper Coastal Plain
56-Middle Coastal Plain
57-Lower Coastal Plain
58-Highlands
59-Lowlands
60-Dade County anomalous area.
ffl-3 Reprinted from USGS Open-File Report 93-292-D
-------
Indoor Radon Screening
Measurements: Average (pCi/L)
0.0 to 1.9
2.0 to 4.0
4.1 to 6.0
6.1 to 13.8
Missing Data
or < 5 measurements
Figure 2. Screening indoor radon averages for counties with 5 or more measurements in EPA
Region 4. Data for all states in Region4 except Florida from the State/EPA Residential Radon
Survey. Data for Florida are from the Florida Statewide Radon Study. Histograms in map
legend show the number of counties in each category.
-------
GEOLOGIC
RADON POTENTIAL
| | LOW
[H] MODERATE/VARIABLE
HIGH
Figure 3. Geologic radon potential areas of EPA Region 4. For more detail, refer to individual
state radon potential chapters.
-------
base metals, including uranium. Rinds containing high concentrations of uranium and uranium
minerals can be formed on the surfaces of rocks affected by CaCOs dissolution and karstification.
Karst and cave morphology is also thought to promote the flow and accumulation of radon.
Because carbonate soils are clayey, they have a tendency to crack when they dry and may develop
very high permeability from the fractures. Under mu*.... .nditions, however, the soils derived
from carbonates have generally low permeability.
The Appalachian Plateaus region is ranked moderate in radon potential. Indoor radon is
generally low (< 2 pCi/L) to moderate (2-4 pCi/L). Radioactivity is low to moderate and soil
permeability is moderate. The sandstone of the Pottsville Formation is not noted for being
uranium-bearing, but uraniferous carbonaceous shales interbedded with the sandstone may be the
cause of locally moderate to high (>4 pCi/L) indoor radon. Cullman County had several indoor
radon measurements greater than 4 pCi/L, including one measurement of 19.8 pCi/L. Winston and
Walker Counties also had several indoor radon levels greater than 4 pCi/L in the Alabama
Department of Public Health data set
Valley and Ridge
The Valley and Ridge province has been ranked moderate in geologic radon potential.
Radioactivity is generally moderate in the Valley and Ridge, with high radioactivity occurring along
the southeastern border with the Piedmont. Indoor radon is highly variable, with generally low
county averages and one high county average. Most of the counties had a few readings greater
than 4 pCi/L. The soils of the Valley and Ridge have low to moderate permeability. The
permeability may be locally high in dry clayey soils and karst areas. Carbonate soils derived from
Cambrian-Ordovician rock units of the Valley and Ridge province cause known indoor radon
problems in eastern Tennessee, western New Jersey, western Virginia, eastern West Virginia and
central and eastern Pennsylvania. Further, the Devonian Chattanooga Shale crops out locally in
parts of the Valley and Ridge. This shale is widely known to be highly uraniferous and has been
identified as a source of high indoor radon in Kentucky.
Piedmont
Where it is possible to associate high radioactivity and/or high indoor radon levels with
particular areas, parts of the Piedmont have been ranked moderate to high in radon potential.
Radiometric anomalies occur over the Talladega Fault zone, which separates the Paleozoic
carbonates from the metamorphic rocks. Some of the metamorphic rocks in the Northern
Piedmont, including the Poe Bridge Mountain Group, the Mad Indian Group, parts of the
Wedowee Group, and the Higgins Ferry Group, also have high radioactivity associated with them.
In many cases the radiometric anomalies appear to be associated with rocks in fault zones, graphitic
schists and phyllites, felsic gneiss, and other granitic rocks. Furthermore, Talladega, Calhoun,
Cleburne, and Randolph Counties all have some high indoor radon measurements. Uranium in
graphitic phyllite with an assay value of 0.076 percent UsOg has been reported from Cleburne
County and similar graphitic phyllites from the Georgia Piedmont average 4.7 ppm uranium.
Graphitic phyllites and schists in other parts of the Piedmont are known sources of radon and have
high indoor radon levels associated with them. Another source of uranium in Piedmont
metamorphic rocks is monazite, which contains high amounts of both uranium and thorium. It is a
common accessory mineral in gneisses and granites throughout the Piedmont and its resistance to
weathering and high density result in local monazite concentrations in saprolite. A uraniferous
monazite belt that crosses the Piedmont in northern Chambers and Tallapoosa County may provide
ffl-6 Reprinted from USGS Open-File Report 93-292-D
-------
a source of radon. Soils of the Northern and Southern Piedmont have moderate to high
permeability, whereas soils developed from mafic rocks of the Dadeville Complex have low
permeability. Because the Dadeville Complex consists primarily of mafic rocks with low
radioactivity and low permeability, the Dadeville Complex was ranked separately from other
Piedmont rocks and is ranked low in geologic radon potential.
Coastal Plain
More than half of Alabama is covered by the sediments of the Coastal Plain. Indoor radon
levels are generally less than 4 pCi/L and commonly less than 2 pCi/L in this province. Soil
permeability is variable-generally low in clays and moderate to high in silts and sands. A distinct
radiometric high is located over the central belt of marly sandy clay and chalk known as the Selma
Group. Within the Selma Group high radioactivity is associated with the Demopolis Chalk,
Mooreville Chalk, Prairie Bluffs Chalk, and the Ripley Formation in central and western Alabama.
In eastern Alabama and into Georgia these rocks are dominated by the glauconitic sands and clays
of the Providence Sand, Cusseta Sand, and Blufftown Formation. These units have overall
moderate geologic radon potential.
As part of a study by the U.S. Geological Survey and the U.S. EPA to assess the radon
potential of the Coastal Plain sediments in the United States, data on radon in soil gas, surface
gamma-ray activity, and soil permeability were collected and examined. Data were collected in the
Alabama Coastal Plain along a transect running from just north of Montgomery, Alabama, to just
south of De Funiak Springs, Florida. The highest soil-gas radon concentrations and equivalent
uranium were found in the Cretaceous Mooreville Chalk, carbonaceous sands and clays of the
Providence Sand, and the glauconitic sands of the Eutaw and Ripley Formations. However,
permeability in many of these units is slow—generally less than IxlO-12 cm2, and soil-gas radon
was difficult to collect. Geologic units that have the lowest soil-gas radon concentrations and eU
include the quartz sands of the Cretaceous Gordo Formation and quartz sands and residuum of the
undifferentiated upper Tertiary sediments. Low to moderate radon and uranium concentrations
were measured in the glauconitic sands and clays of the Tertiary Porters Creek Formation and in
the glauconitic sands, limestones, and clays of the Tertiary Nanafalia, Lisbon Formation, and the
Tuscahoma Sand. The indoor radon in some counties underlain by the Selma Group is in the 2-4
pCi/L range with a few measurements greater than 4 pCi/L, higher than in most other parts of the
Alabama Coastal Plain. High uranium and radon concentrations in the sediments of the Jackson
Group, locally exceeding 8 ppm U, but generally in the 1-4 ppm U range, and high soil-gas radon
concentrations, are associated with faults and oil and gas wells in Choctaw County. Indoor radon
measurements are generally low in these areas, but may be locally high.
FLORIDA
Florida lies entirely within the Coastal Plain, but there are six distinctive areas in Florida for
which geologic radon potential may be evaluated—the Northern Highlands, Central Highlands, the
Central and Northern Highlands anomalous areas, the Gulf Coastal Lowlands, Atlantic Coastal
Lowlands, and an area here termed the Dade County anomalous area.
The Northern Highlands province has generally low geologic radon potential. All counties
entirely within this province have average indoor radon levels less than 1 pCi/L. Leon County
averaged 1.7 and 1.8 pCi/L in the two surveys of the Florida Statewide Radon Study. Most of
these data likely come from Tallahassee, which lies within an area of moderately elevated eU. This
m-7 Reprinted from USGS Open-File Report 93-292-D
-------
area and those parts of southern Columbia, western Union, and northern Alachiia County which
are underlain by phosphatic rocks, and limited areas where coarse gravels occur in river terraces in
the western panhandle, are likely to have elevated radon potential.
The Central Highlands province has variable geologic radon potential. Generally low
radon potential occurs in low eL areas in tl.«. eastern ai ^uthern parts ^f this province. Moderate
radon potential occurs in the western part of this province where uraniferous phosphatic rocks are
close to the surface. Localized areas in which uranium contents of soils and shallow subsoils
exceed 100 ppm are likely, and indoor radon levels may exceed 20 pCi/L or more where this
occurs. Alachua (lies in both the Central and Northern Highlands), Marion, and Sumter Counties
report indoor radon values exceeding 20 pCi/L. Excessively well-drained hillslopes may also
contribute to higher radon potential.
The Gulf Coastal Lowland Province generally has low radon potential. High rainfall and
high water tables cause very moist soils which inhibit radon movement. Equivalent uranium is low
in most areas except in some coastal bay areas of western peninsular Florida. Some isolated areas
of elevated radon potential may occur in these areas of higher eU.
The Atlantic Coastal Lowland area generally has low radon potential. High rainfall and
high water tables cause very rnoist soils that inhibit radon movement Equivalent uranium is low in
most areas. In some beach sand areas in northern Florida, elevated eU seems to be associated with
heavy minerals; however, there is no evidence to suggest that elevated indoor radon occurs in these
areas.
An area in southwestern Dade County, underlain by thin sandy soils covering shallow
limestone bedrock, has equivalent uranium values as high as 3.5 ppm. Unusually high levels of
radium are present in soils formed on the Pleistocene Key Largo Limestone and perhaps on other
rock formations in certain areas of the Florida Keys and in southwestern Dade County. Areas of
elevated eU and elevated indoor radon in Dade County are likely related to these unusual soils.
These soils may be responsible for the modestly elevated eU in soils and for the elevated indoor
radon levels, and they may extend into Collier County as well.
GEORGIA
Piedmont and Blue Ridge
The oldest rocks in Georgia form the mountains and rolling hills of the Blue Ridge
Province and most of the Piedmont Province. These highly deformed rocks are separated by a
series of thrust faults superimposing groups of older rocks over younger rocks, comprising the
Georgiabama Thrust Stack. The igneous and metamorphic rocks in the Georgiabama Thrust Stack
north of the Altoona Fault have been ranked moderate overall in geologic radon potential, but the
radon potential of the area is variable. Mafic rocks are expected to have low radon potential
whereas phylUte, slate, some metagraywacke, granitic gneiss and granite have moderate to high
radon potential. Soil permeability is slow to moderate in most soils. Counties in this area have
average indoor radon levels that vary from low to high (< 1 pCi/L to > 4 pCi/L), but the
measurements are predominantly in the moderate range. The highest indoor radon reading, 18.7
pCi/L, was measured in the northern Blue Ridge in Fannin County, which is underlain
predominantly by metagraywacke, slate, phyllite, and mica schists. Equivalent uranium
concentrations in rocks and soils of this area are moderate to high.
The Georgiabama Thrust Stack south of the Alatoona Fault has also been ranked moderate
in geologic radon potential. The majority of this part of the Georgiabama Thrust Stack is underlain
m-8 Reprinted from USGS Open-File Report 93-292-D
-------
by schist and amphibolite of the Zebulon sheet, which have generally low radioactivity where not
intruded by granites or where not highly sheared, particularly south of the Towaliga Fault An area
with distinctly low aeroradiometric readings which is underlain by mafic metamorphic rocks lies
between the Brevard and Allatoona Faults in the northwestern Georgiabama Thrust Stack. All of
mese rocks have slow to moderate permeability, and indoor radon values are generally low to
moderate. A central zone of biotite gneiss, granitic gneiss, and granite has elevated uranium
concentrations and high equivalent uranium (>2.5 ppm) on the NURE map. Soil permeability is
generally low to locally moderate. Indoor radon levels are generally moderate. Recent soil-gas -
radon studies in the Brevard zone and surrounding rocks show that this zone may yield unusually
high soil-gas radon where the zone crosses the Ben Hill and Palmetto granites. Surface gamma-
ray spectrometer measurements yielded equivalent uranium from 4 to 17 ppm over granite and
granitic biotite gneiss (Lithonia gneiss). Soil-gas radon concentrations commonly exceeded 2,000
pCi/L and the highest soil-gas radon measured was 26,000 pCi/L in faulted Ben Hill granite.
Undeformed Lithonia gneiss had average soil radon of more than 2,000 pCi/L. Mica schist
averaged less than 1,000 pCi/L where it is undeformed. The Stone Mountain granite and mafic
rocks yielded low soil-gas radon. The Grenville Basement granite and granite gneiss have
moderate to locally high radon potential. Radioactivity is generally moderate to high and soil
permeability is generally moderate.
The Little River Thrust Stack is generally low to moderate in geologic radon potential. It is
underlain primarily by mafic metamorphic rocks with low radon potential, but each belt contains
areas of rocks with moderate to locally high radon potential. Metadacites have moderate radon
potential and moderate radioactivity. Faults and shear zones have local areas of mineralization and
locally high permeability. Granite intrusives may also have moderate radon potential.
Aeroradioactivity is generally low and soil permeability is generally moderate.
Ridge and Valley
The Rome-Kingston Thrust Stack is ranked low in geologic radon potential; however,
some of the limestones and shales in this area may have moderate to high radon potential. Indoor
radon is variable but generally low to moderate. Permeability of the soils is low to moderate.
Equivalent uranium is moderate to locally high, especially along the Carters Dam and Emerson
faults. Carbonate soils of the Valley and Ridge Province are likely to cause indoor radon
problems. The Devonian Chattanooga Shale, which crops out locally in parts of the Valley and
Ridge, is highly uraniferous and has been identified as a source of high indoor radon levels in
Kentucky. Numerous gamma radioactivity anomalies are associated with the Pennington
Formation, Bangor Limestone, Fort Paine Chert, Chattanooga Shale, Floyd Shale, the Knox
Group, and the Rome Formation.
Appalachian Plateau
The Appalachian Plateau has been ranked low in geologic radon potential. Sandstone is the
dominant rock type and it generally has low uranium concentrations. Equivalent uranium is low to
moderate. Permeability of the soils is moderate and indoor radon levels are low.
Coastal Plain
The Coastal Plain has been ranked low in radon potential, but certain areas of the Coastal
Plain in which glauconitic, carbonaceous, and phosphatic sediments are abundant may have
moderate geologic radon potential. The highest soil-gas radon concentrations (>1000 pCi/L) and
ffl-9 Reprinted from USGS Open-File Report 93-292-D
-------
equivalent uranium (eU) concentrations (>2 ppm) in studies of radon in soil-gas in the Coastal
Plain of Alabama were found in the carbonaceous sands and clays of the Providence Sand and the
glauconitic sands of the Eutaw and Ripley Formations. .Low to moderate soil-gas radon and
uranium concentrations were measured in the glauconitic sands, limestones, and clays of the
Tertiary Nanafalia and Lisbon Formations, and the Tuscahoma Sand. Equivalent rock units in
Georgia are also likely to be sources of high radon levels. Equivalent uranium is moderate in the
Cretaceous and Tertiary-age sediments and low, with local highs, in the Quaternary sediments.
Radioactivity highs in much of the Coastal Plain are related to phosphate and heavy-mineral
concentrations. In the shoreline complexes and in several sediment units such as the Hawthorn
Formation, the phosphate concentrations are naturally occurring. In the Black Lands and in many
portions of the central Coastal Plain that have abundant agricultural activity, the radioactivity may
be related to the use of phosphate fertilizers. Indoor radon in the Coastal Plain is generally low.
KENTUCKY
Three primary areas in Kentucky are identified as being underlain by rock types and
geologic features suspected of producing elevated radon levels: (1) areas underlain by Devonian
black shales in the Outer Bluegrass region; (2) areas underlain by the Ordovician Lexington
Limestone, particularly the Tanglewood Member, in the Inner Bluegrass region; and (3) areas of
the Mississippian Plateau underlain by karsted limestones or black shales. In addition, some
homes underlain by, or in close proximity to, major faults in the Western Coalfield and Inner
Bluegrass regions may have locally elevated indoor radon levels due to localized concentrations of
radioactive minerals and higher permeability in fault and fracture zones.
Appalachian Plateau
The black shale and limestone areas in the Mississippian Plateau region have associated
high surface radioactivity, and the Western Coalfield contains scattered radioactivity anomalies.
The arcuate pattern of radioactivity anomalies along the southern edge of the Outer Bluegrass
region corresponds closely to the outcrop pattern of the New Albany Shale. A group of
radiometric anomalies in the vicinity of Warren and Logan counties appears to correspond to
outcrops of the Mississippian Ste. Genevieve and St. Louis Limestones. The clastic sedimentary
rocks of the Cumberland Plateau region are characterized by relatively low surface radioactivity and
generally have low indoor radon levels.
In the Mississippian Plateau Region, locally elevated indoor radon levels are likely in areas
with high soil permeability, solution cavities, or localized concentrations of radioactive minerals in
karst regions, and in areas underlain black shale along the State's southern border. Of particular
concern are the Devonian-Mississippian Chattanooga Shale (equivalent to the New Albany Shale),
limestones in the Mississippian Fort Payne Formation, and the Mississippian Salem, Warsaw,
Harrodsburg, St. Louis, and Ste. Genevieve Limestones in south-central Kentucky.
Caves, produced by limestone solution and relatively common in central Kentucky, are
natural concentrators of radon and can be a local source of high radon levels. Levels of radon
decay products approaching a maximum of 2.0 working levels (WL), which corresponds to about
400 pCi/L of radon (assuming that radon and its decay products are in 50 percent equiUbrium), and
averaging about 0.70 WL, or about 140 pCi/L of radon, have been recorded in Mammoth Cave.
Although these levels are not considered hazardous if the exposure is of short duration, such as
would be experienced by a visitor to the cave, it could be of concern to National Park Service
employees and other persons that spend longer periods of time in the caves. Another potential
hazard is the use of cave air for building air temperature control, as was formerly done at the
m-10 Reprinted from USGS Open-File Report 93-292-D
-------
Mammoth Cave National Park visitor center. The cave air, which averages 54°F, was pumped into
the visitor center for cooling, but this process has been discontinued due to the relatively high
radioactivity associated with the cave air.
Coastal Plain
The majority of homes in the Jackson Purchase Region (Coastal Plain) have low indoor
radon levels, although the area is underlain in part by loess with an elJ signature in the 2.0-3.0
ppm range. The poor correspondence with surface radioactivity in this area appears to be due to a
combination of low soil permeability and high water tables. The Coastal Plain is the only part of
the State in which seasonal high water tables were consistently listed in the SCS soil surveys as
less than 6 ft, and commonly less than 2 ft.
MISSISSIPPI
Examination of the available data reveals that Mississippi is generally an area of low radon
potential. Indoor radon levels in Mississippi are generally low; however, several counties had
individual homes with radon levels greater than 4 pCi/L. Counties with maximum levels greater
than 4 pCi/L are concentrated in the northeastern part of the State within the glauconitic and
phosphatic sediments of the Tombigbee Hills and Black Prairies. Readings greater than 4 pCi/L
also occur in the Mississippi Alluvial Plain, the eastern part of the Pine Hills Province, and in
loess-covered areas. Glauconitic and phosphatic sediments of the Coastal Plain, particularly the
Cretaceous and lower Tertiary-age geologic units located in the northeastern portion of the State,
have some geologic potential to produce radon. Based on radioactivity and studies of radon in
other parts of the Coastal Plain, the Black Prairies and Pontotoc Ridge have been assigned
moderate geologic radon potential; all other parts of Mississippi are considered to be low in
geologic radon potential. The climate, soil, and lifestyle of the inhabitants of Mississippi have
influenced building construction styles and building ventilation which, in general, do not allow
high concentrations of radon to accumulate.
Coastal Plain
A study of the radon in the Coastal Plain of Texas, Tennessee, and Alabama suggests that
glauconitic, phosphatic, and carbonaceous sediments and sedimentary rocks, equivalent to those in
Mississippi, can cause elevated levels of indoor radon. Ground-based surveys of radioactivity and
radon in soils in that study indicate that the Upper Cretaceous through Lower Tertiary Coastal Plain
sediments are sources of high soil-gas radon (> 1,000 pCi/L) and soil uranium concentrations.
The high equivalent uranium found over the Coastal Plain sediments in northeastern Mississippi
supports the possibility of a similar source of high radon levels. Chalks, clays and marls tend to
have low permeability when moist and higher permeability when dry due to desiccation fractures
and joints.
The youngest Coastal Plain sediments, particularly Oligocene and younger, have
decreasing amounts of glauconite and phosphate and become increasingly siliceous and therefore
less likely to be significant sources of radon. Some carbonaceous units may be possible radon
sources.
Loess in Tennessee, and probably elsewhere, is known to generate high levels of radon in
both dry and saturated soils. Both thin and thick loess units can easily be traced on the
m-11 Reprinted from USGS Open-FUe Report 93-292-D
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radioactivity map of Mississippi by following the highest of the moderate equivalent uranium
anomalies. Loess tends to have low permeability when moist and higher permeability when dry.
Mississippi Alluvial Plain
The Mississippi Alluvial Plain contains several areas with locally high eU, as well as
having moderate radioactivity overall. These high eU areas are located close to the river in Bolivar
and Washington Counties. The highest indoor radon level recorded in Mississippi in the
State/EPA Residential Radon Survey (22.8 pCi/L) occurs within Bolivar County and the second
highest radon level of homes measured to date in the State (16.1 pCi/L) occurs in Washington
County. It is not apparent from the data available whether the high eU and indoor radon levels are
correlative, and only a few indoor radon readings in each county are greater than 4 pCi/L. The
geology of the region is not generally conducive to high uranium concentrations, except possibly in
heavy-mineral placer deposits. Further, elevated radioactivity in the Mississippi Alluvial Plain may
be due in part to uranium in phosphatic fertilizers. Locally high soil permeability in some of the
alluvial sediments may allow locally high indoor radon levels to occur.
The southeastern half of Mississippi has low radioactivity and low indoor radon levels.
The few indoor radon readings greater than 4 pCi/L were between 4.1 and 5.8 pCi/L The lowest
eU is associated with the coastal deposits and the CitroneUe Formation, which are predominantly
quartz sands with low radon potential. Slightly higher eU, though still low overall, is associated
with the Pascagoula and Hattiesburg Formations and Catahoula Formation. Soils in this area are
variably poorly to well drained with slow to moderate permeabilities.
The Chattanooga Shale and related sedimentary rocks in the northeastern part of the State
have the potential to be sources of high indoor radon levels, In Tennessee and Kentucky the
Chattanooga Shale has high uranium concentrations and is associated with high indoor radon levels
in those states. The extent of these rocks in Mississippi is minor.
NORTH CAROLINA
*The Blue Ridge has been ranked moderate overall in geologic radon potential, but it is
actually variably moderate to high in radon potential. The province has highly variable geology
and because of the constraints imposed by viewing the indoor radon data at the county level, it is
impossible to assign specific geologic areas of the Blue Ridge to specific moderate or high indoor
radon levels. Average indoor radon levels are moderate (2-4 pCi/L) in the majority of counties.
However two counties have indoor radon averages between 4.1 and 6 pCi/L (Cherokee and
Buncomb Counties) and three counties in the northern Blue Ridge (Alleghany, Watauga, and
Mitchell) have indoor radon averages greater than 6 pCi/L. These three counties are generally
underlain by granitic gneiss, mica schist, and minor amphibolite and phyllite. Transylvania and
Henderson Counties, which are underlain by parts of the Blue Ridge and Inner Piedmont, also
have indoor radon averages greater than 6 pCi/L. The Brevard fault zone, Henderson Gneiss, and
Ceasars Head Granite are possible sources of high indoor radon in these two counties. Equivalent
uranium is variable from low to high in the Blue Ridge. The highest eU appears to be associated
with the Ocoee Supergroup in the southern Blue Ridge, rocks in the Grandfather Mountain
Window, and metamorphic rocks in parts of Haywood and Buncomb Counties. Soils are
generally moderate in permeability.
ffl-12 Reprinted from USGS Open-File Report 93-292-D
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The Chauga belt and Brevard fault zone are ranked high in geologic radon potential. The
Chauga belt consists predominantly of the Henderson Gneiss. High eU and high uranium in
stream sediments appears to be associated with the Brevard fault zone, Henderson Gneiss, and
Ceasars Head Granite in this area. Average indoor radon levels in the two counties that the main
part of the Chauga belt and the southern portion of the Brevard fault zone passes through are high.
The soils have moderate permeability.
Piedmont
The Inner Piedmont and Kings Mountain belts have been ranked moderate in geologic
radon potential. Indoor radon levels are generally moderate. Granitic plutons, granitic gneiss,
monazite-rich gneiss and schist, pegmatites, and fault zones appear to have high eU and high
uranium concentrations in stream sediment samples. Many of the granitic plutons are known to be
enriched in uranium and recent studies suggest that the soils developed on many of the uraniferous
granitic plutons and related fault zones in the Blue Ridge and Piedmont are possible sources of
radon. Measured soil-gas radon concentrations commonly exceeded 1,000 pCi/L in soils
developed on the Cherryville Granite, Rolesville Suite, and the Sims, Sandy Mush, and Castalia
plutons. Soils developed on the Rocky Mount, Spruce Pine, Toluca, Mt. Airy, and Stone
Mountain plutons had relatively low soil-gas radon concentrations. Soil permeabilities in the Inner
Piedmont, Brevard fault zone, and Kings Mountain belt are variably low to moderate which,
together with the large proportion of homes without basements, may account for the abundance of
moderate indoor radon levels.
Most shear zones in the Piedmont and Blue Ridge should be regarded as having the
potential to produce very localized moderate to high indoor radon levels. Geochemical and
structural models developed from studies of shear zones in granitic metamorphic and igneous rocks
from the Reading Prong in New York to the Piedmont in Virginia indicate that uranium
enrichment, the redistribution of uranium into the rock foliation during deformation, and high
radon emanation, are common to most shear zones. Because they are very localized sources of
radon and uranium, shear zones may not always be detected by radiometric or stream sediments
surveys.
The Charlotte belt has been ranked low in geologic radon potential but it is actually quite
variable-dominantry low in the southern portion of the belt and higher in the northern portion of
the belt Equivalent uranium is generally low, with locally high eU occurring in the central and
northern portions of the belt, associated with the Concord and Salisbury Plutonic Suites.
Permeability of the soils is generally low to moderate and indoor radon levels are generally low.
The Carolina slate belt has been ranked low in radon potential where it is underlain
primarily by metavolcanic rocks. Where it crops out east of the Mesozoic basins it has been ranked
moderate. Aeroradioactivity over the Carolina slate belt, uranium in stream sediment samples, and
indoor radon levels are markedly low. Permeability of many of the metavolcanic units is generally
low to locally moderate. East of the Wadesboro subbasin in Anson and Richmond Counties lies a
small area of the slate belt that is intruded by the Lilesville Granite and Peedee Gabbro. It has high
eU and high uranium concentrations in stream sediments, and moderate to high permeability in the
soils, and is a likely source of moderate to high indoor radon levels.
The Raleigh belt has been ranked moderate in geologic radon potential. Equivalent uranium
in the Raleigh belt is generally moderate to high and appears to be associated with granitic intrusive
rocks, including the Castalia and Wilton plutons and the Rolesville Suite. A belt of monazite-
bearing rocks also passes through the Raleigh belt and may account for part of the observed high
m-13 Reprinted from USGS Open-File Report 93-292-D
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radioactivity. Soils have variably low to moderate permeability. Indoor radon levels are generally
moderate.
Coastal Plain
In the Coastal Plain province, moderate to higi. _ ^ is associated with the Cretaceous and
Tertiary sediments of the Inner Coastal Plain. Permeability of the soils is highly variable but
generally moderate to low, and may be locally high in sands and gravels. Seasonally high water
tables are common. Indoor radon levels in the Coastal Plain are generally low. The Inner Coastal
Plain is ranked low in geologic radon potential but may be locally moderate to high, especially in
areas underlain by Cretaceous sediments. Glauconitic, phosphatic, monazite-rich, and
carbonaceous sediments and sedimentary rocks in the Coastal Plain of Texas, New Jersey, and
Alabama, similar to some Coastal Plain sediments in North Carolina, are the source for moderate
indoor radon levels seen in parts of the Inner Coastal Plain of these states.
The Outer Coastal Plain has low eU, low indoor radon levels, and is generally underlain by
sediments with low uranium concentrations. Soil permeability is variable but generally moderate.
Seasonally high water tables are common. A few isolated areas of high radioactivity in the Outer
Coastal Plain may be related to heavy mineral and phosphate deposits in the shoreline sediments.
The area has been ranked low in geologic radon potential, but may have local moderate or high
indoor radon occurrences related to heavy minerals or phosphate deposits.
SOUTH CAROLINA
Blue Ridge and Piedmont
The Blue Ridge and Piedmont Provinces have moderate geologic radon potential. Possible
sources of radon include uraniferous granites, biotite and granitic gneiss, and shear zones. Soils
developed on many of the uraniferous granitic plutons and some fault zones within the Piedmont
and Blue Ridge of North and South Carolina yield high soil-gas radon (>1,000 pCi/L). In the
Blue Ridge, sheared graphitic rocks may be a local source for high indoor radon concentrations.
More than 10 percent of the homes tested in Greenville and Oconee Counties, in the Blue
Ridge and Piedmont, have indoor radon levels greater than 4 pCi/L. Greenville County also has
the highest indoor radon measurement in the State, 80.7 pCi/L, the highest radioactivity, associated
with the Silurian-Devonian Ceasers Head Granitic Gneiss, and with biotite gneiss in the Carolina
monazite belt. In Oconee County, the Toxaway Gneiss and graphitic rocks in the Brevard Fault
Zone may account for the higher incidence of indoor radon levels exceeding 4 pCi/L and the higher
overall indoor radon average of the county. Average indoor radon levels in the Blue Ridge and
Piedmont are generally higher than in the rest of the State, and moderate to high radioactivity is
common. Most of the soils formed on granitic rocks have moderate permeability and do not
represent an impediment to radon mobility. Mafic rocks in the Blue Ridge and Piedmont have low
radon potential. These rocks have low concentrations of uranium, and soils formed from them
have low permeability.
Coastal Plain
In the Coastal Plain Province, moderate to high radioactivity is associated with the
Cretaceous and Tertiary sediments of the upper Coastal Plain. Glauconitic, phosphatic, monazite-
rich, and carbonaceous sediments and sedimentary rocks in the Coastal Plain of Texas, New
Jersey, and Alabama, similar to some of those in South Carolina, cause elevated levels of indoor
m-14 Reprinted from USGS Open-File Report 93-292-D
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radon. Orangeburg County is the only other county besides Greenville and Oconee Counties that
has an average indoor radon level greater than 2 pCi/L. It is underlain by Lower Tertiary
sediments in an extremely dissected part of the Coastal Plain. Radioactivity is moderate to low.
Soils are highly variable in the county because of the complicated erosion patterns. The few high
values of indoor radon for this county create an overall higher indoor radon ajyerage for the county.
These locally high readings may be due to local accumulations of monazite, glauconite, or
phosphate that can occur within these particular sediments.
The lower Coastal Plain has low to locally high radioactivity and low indoor radon levels:
Most of the sediments have low uranium concentrations with the exception of the uraniferous,
phosphatic sediments of the Cooper Group and local, heavy-mineral placer deposits within some
of the Quaternary units. The area has been ranked low in geologic radon potential overall, but the
radon potential may be locally high in areas underlain by these uraniferous sediments.
TENNESSEE
Coastal Plain and Mississippi Alluvial Plain
The Mississippi Alluvial Plain has low geologic radon potential. The high soil moisture,
high water tables, and the lack of permeable soils lower the radon potential in spite of moderate eU
values. Some areas with very sandy or excessively-drained soils may cause homes to have indoor
radon levels exceeding 4 pCi/L.
The loess-covered parts of the Coastal Plain have low radon potential in spite of moderate
eU values and elevated soil-gas radon concentrations. The radon potential is lowered by the high
moisture content and low permeability of the soils. The lack of basements in homes also lowers
the potential. If prolonged dry periods were to occur in this area, some homes might see a
significant increase in indoor radon, especially those with basements or crawl spaces. The eastern
Coastal Plain has moderate geologic radon potential. NURE data show elevated eU values
compared to the rest of the Coastal Plain. Soil-gas radon levels are locally elevated.
Highland Rim and Nashville Basin
The Highland Rim and Nashville Basin are underlain by sedimentary rocks of Paleozoic
age, principally limestone, shale, chert, and dolostone. The part of the Highland Rim that is
underlain by cherty limestone (Fort Payne Formation) has high geologic radon potential. This area
has moderate to locally high eU and soils that are cherty and excessively well drained. The
limestone and shale part of the Highland Rim has moderate radon potential. The Nashville Basin
has high geologic radon potential. The elevated eU, the presence of abundant phosphatic soils,
local karst, and the presence of generally well-drained soils all contribute to this high geologic
radon potential. Very high (>20 pCi/L) to extreme indoor radon values (>200 pCi/L) are possible
where homes are sited on soils developed on the Chattanooga shale, on phosphate-rich residual
soils, or on karst pinnacles.
Appalachian Plateau
Sandstones and shales underlie most of the Appalachian Plateau, which generally has
moderate geologic radon potential. These rocks are typically not good sources of radon and values
for eU are among the lowest in the State. However, many sandy, well-drained to excessively-
drained soils are present in this region, and may be a source of locally elevated radon levels
because of their high permeability.
m-15 Reprinted from USGS Open-File Report 93-292-D
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Ridge and Valley
Folded and faulted Paleozoic limestone, shale, chert, dolostone, and sandstone underlie
most of the Ridge and Valley region, with sandstone and cherry dolostone forming most of the
ridges and limestone and shale terming mo*~ of the \ al ,.,. The Ridge «nd Valley region has high
geologic radon potential because of elevated ell values, karst, and well drained soils. Very high
(>20 pCi/L) to extreme indoor radon values (>200 pCi/L) are possible where homes are sited on
soils developed on black shales, phosphate-rich residual soils, or karst pinnacles. Homes with
basements are more likely to yield elevated indoor radon levels than homes with slab-on-grade
construction.
Unaka Mountains
The Unaka Mountains are underlain by siltstone, sandstone, conglomerate, quartzite,
phyllite, gneiss, granite, and metamorphosed volcanic rocks of Precambrian and Paleozoic age that
have moderate geologic radon potential. Values of eU are generally moderate, although they are
locally high. Some very high (>20 pCi/L) to extreme (>200 pCi/L) indoor radon levels are
possible where homes are sited on phosphate-rich residual soils developed on phosphatic carbonate
rocks, or on pegmatite in the metamorphic rock areas, but the former are much less common in this
region than in the Nashville Basin and the Ridge and Valley region.
ffl-16 Reprinted from USGS Open-File Report 93-292-D
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PRELIMINARY GEOLOGIC RADON POTENTIAL ASSESSMENT OF NORTH CAROLINA
by
Linda C.S. Gundersen
US Geological Survey
INTRODUCTION
This is a generalized assessment of geologic radon potential of rocks, soils, and surficial
deposits of North Carolina. The scale of this assessment is such that it is inappropriate for use in
identifying the radon potential of small areas such as neighborhoods, individual building sites, or
housing tracts. Any localized assessment of radon potential must be supplemented with additional
data and information from the locality. Within any area of a given radon potential ranking, there
are likely to be areas with higher or lower radon levels than characterized for the area as a whole.
Indoor radon levels, both high and low, can be quite localized, and there is no substitute for testing
individual homes. Elevated levels of indoor radon have been found in every State, and the U.S.
Environmental Protection Agency (EPA) recommends that all homes be tested. For a free brochure
on radon, EPA has established the National Radon Hotline (1-800-767-7236). The North Carolina
Cooperative Extension Service at North Carolina State University also has a free tape information
service that has information on radon (1-800-662-7301 in North Carolina; tapes 4196,4197,
4198). The Cooperative Extension Service and North Carolina Division of Radiation Protection
publish a quarterly newsletter entitled "Radon News in North Carolina" as well as conducting
workshops, indoor radon surveys, and supplying information on radon risks, mitigation, and
school testing. For more information, the reader is urged to consult the State radon program or
U.S. EPA at the numbers listed above or in chapter 1 of this booklet.
PHYSIOGRAPHIC AND GEOGRAPHIC SETTING
In general, the physiography of North Carolina (fig. 1) is a reflection of the underlying
bedrock geology of the State (fig. 2). North Carolina has three distinct physiographic provinces:
the Blue Ridge, the Piedmont, and the Atlantic Coastal Plain. The rugged Blue Ridge province is
characterized by deeply dissected mountains with steep ridges, intermontane basins, and deep
valleys. Elevations reach more than 6000 feet, including Mount Mitchell, which at 6684 feet is the
highest peak in eastern North America. About ten percent of the State is covered by the Blue Ridge
Mountains.
The Piedmont province covers about 45 percent of the State. It is bounded on the east by
the fall line, defined by rapids where local streams and rivers descend into the tidal estuaries of the
Coastal Plain, and on the west by the Blue Ridge scarp, a prominent topographic feature that rises
1500-2500 feet above the Piedmont Near the fall line, elevations are 300 to 600 feet above sea
level and at the foot of the Blue Ridge, the elevation is about 1500 feet above sea level. Most of
the Piedmont landscape is characterized by gently rolling hills and long, low ridges and valleys,
with a local relief of several hundred feet. Several monadnocks, or erosional remnants, form
prominent isolated mountains in the Piedmont
About 45 percent of the State is covered by the Atlantic Coastal Plain province, which is
underlain by relatively unconsolidated marine and fluvial sediments. A chain of dune-covered
islands known as the Outer Banks marks the coastline with the Atlantic Ocean. Westward from the
shoreline is a swampy tidewater area; this area, together with the Outer Banks, forms the Outer
IV-1 Reprinted from USGS Open-File Report 93-292-D
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North Carolina Geologic Mao Kev
ERA
CODE
LITHOLOGIC DESCRIPTION
to Early Paleozo
Proterozo
La
Sedimentary and Metamorphic Rocks
Sedimentary rocks - sandstone, dolomite, shale and
siltstone.
Metasedimentary and metavolcanic rocks of the
Kings Mountain belt - schist, phyllite, marble,
metavolcanic rock, quartzite and gneiss.
Metamorphic rocks of the Inner Piedmont, Milton
belt and Raleigh belt - gneiss, schist and
amphibolite.
Metavolcanic rocks of the Carolina slate belt
and eastern slate belt - felsic metavolcanic
rock with mafic and intermediate volcanic rock.
Metasedimentry rocks of the Carolina slate belt
and eastern slate belt - metamudstone,
argillite and epiclastic rock.
tero
Late
Clastic and carbonate metasedimentary rocks of the
Murphy belt - schist, phyllite, quartzite, marble,
slate and metasiltstone.
Brevard fault zone - schist, marble and
phyllonite.
Clastic metasedimentary and metavolcanic rocks of
the Ocoee Supergroup, Grandfather Mountain
Formation, Mount Rogers Formation and
quartzite of the Sauratown Mountains
anticlinorium - slate, metasiltsone, schist,
metagraywacke, calc-silicate granofels, quartzite
and felsic metavolcanic rocks.
Clastic metasedimenatary rocks and mafic and
felsic metavolcanic rock of the Ash
Metamorphic Suite, Tallulah Falls
Formation and Alligator Back Formation -
gneiss, schist, metagraywacke, amphibolite and
calc-silicate granofels.
-------
ERA
Middle Proterozoic
Middle Paleozoic to
Late Paleozoic
Late Proterozoic to Middle Paleozoic
CODE
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LTIHOLOGIC DESCRIPTION
Sedimentary and Metamorphic Rocks continued...
Felsic gneiss derived from sedimentary and igneous-
rocks in the northern outcrop area; biotite gneiss .
in the southern outcop area; locally migmatitic
and mylonitic. Locally and variably interlayered
with amphibolite, calc-silicate granofels and rare
marble. Intruded by Late Proterozoic mafic and
felsic plutons.
Intrusive Rocks
Granitic rocks - unfoliated to weakly foliated.
Syenite - Concord ring dike.
Metamorphosed gabbro and diorite - foliated to
weakly foliated.
Metamorphosed granitic rocks - foliated to weakly
foliated; locally migmatic.
Henderson Gneiss - uneven-grained monzonitic to
granodioritic.
Meta-ultramafic rocks.
-------
ERA
CODE
LITHOLOGIC DESCRIPTIONS
I?
03
I
a
Sedimentary Rocks
Surficial deposits, undivided - sand, clay and gravel.
(Shown only below 25 feet of elevation.)
Pinehurst Formation - unconsolidated sand.
Terrace deposits and upland sediment - gravel,
clayey sand and sand.
Waccamaw Formation - fossiliferous sand with
silt and clay.
Yorktown Formation and Duplin Formation,
undivided. Yorktown Formation- fossiliferous
clay and sand. Duplin Formation- shelly sand,
sandy marl and limestone.
Belgrade Formation, undivided-JP0//0<±yvj7/e
Member- oyster-shell mounds in sand matrix.
Haywood Landing Member- fossiliferous clayey
sand.
River Bend Formation - sandy, molluscan-mold
limestone.
Castle Hayne Formation- Spring Garden Member-
molluscan-mold limestone.
Comfort Member and New Hanover Member,
undivided. Comfort Member - limestone with
bryozoan and echinoid skeletons. New Hanover
Member - phosphate-pebble conglomerate.
Beaufort Formation, undivided. Unnamed upper
member - glauconitic, fossiliferous sand and silty
clay. Jericho Run Member - siliceous mudstone
with sandstone lenses.
-------
ERA
Cretaceous
Triassic
CODE
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LITHOLOGIC DESCRIPTION
Sedimentary Rocks continued...
Peedee Formation - marine sand, clayey sand and
clay.
Black Creek Formation - lignitic sand and clay.
Middendorf Formation - sand, sandstone and clay.
Cape Fear Formation - sandstone and sandy
mudstone.
Dan River Group, undivided . Stoneville
Formation - conglomerate, sandstone and
mudstone. Cow Branch Formation - mudstone.
Pine Hall Formation - sandstone, mudstone and
conglomerate.
Chatham Group, undivided . Sanford Formation -
conglomerate, sandstone and mudstone. Cumnock
Formation - sandstone and mudstone. Pekin
Formation - conglomerate, sandstone and
mudstone.
-------
Coastal Plain. Farther inland is the gently rolling Inner Coastal Plain and an area along the fall line
known as the Sand Hills. Elevations in the Coastal Plain range from sea level at the coast and rise
westward to about 600 feet in the Sand Hills.
Population distribution and land use in North Carolina is influenced greatly by the geology
topography, and climate of the State. The population was 6,628,637 in 1990, including 43 percent
urban population (fig. 3). The climate is sub-tropical in the southeast to temperate in the
mountains. The mean annual temperature ranges from 66° F in the coastal area to 55° F in the Blue
Ridge. Annual precipitation ranges from 46 to 72 inches (fig. 4). Hurricanes occur seasonally in
the coastal region and may occasionally affect other parts of the State.
Agricultural products include tobacco, soybeans, corn, peanuts, sweet potatoes, feed
grains, vegetables, and fruits, and dairy farming. Principal businesses include manufacturing
tobacco, technology, and tourism.
GEOLOGIC SETTING
North Carolina has been divided into several major geologic belts (fig. 1). These will be
described from west to east across the State. The geologic map descriptions that follow are derived
from several sources, including the North Carolina Geological Survey (1985,1991) and Horton
and Zullo (1991). A general geologic map is given for reference in figure 2. It is suggested
however, that the reader refer to the published Geologic Map of North Carolina (North Carolina
Geological Survey, 1985). Soil descriptions are from Tant and others (1974); Richmond and
others, (1986,1987,1991); and selected Soil Conservation Service County soil survey reports
Because there are so many igneous plutons in the Blue Ridge and Piedmont provinces, not all of
them are named and described in this geologic section and only those plutons which are of
importance to the radon problem are discussed in the radioactivity and radon potential sections of
this report
The Blue Ridge
The Blue Ridge belt consists of a rugged mountainous terrain underlain by metamorphic
igneous, and sedimentary rocks of Proterozoic to Cambrian age. The rocks have been complexly
folded and faulted during several orogenies. The belt is bounded on the southeast and northwest
by major fault systems that transported the rocks of the Blue Ridge northwestward to its present
site in a series of thrust sheets.
Late Proterozoic rocks of sedimentary and volcanic origin that crop out in the westernmost
Blue Ridge or in isolated windows include the Ocoee Supergroup, the Grandfather Mountain
Formation, and the Mount Rogers Formation. The Mount Rogers Formation consists of two
distinct Late Proterozoic units: a metafelsite and a metagraywacke with interlayered
metaconglomerate, metasiltstone, slate, and minor calcareous metasandstone, greenstone, and
metarhyolite. The Grandfather Mountain Formation crops out in Grandfather Mountain window
and is composed of meta-arkose, greenstone, phyllitic to schistose felsic metavolcanic rock, and
metamorphosed siltstone, dolomite and graywacke. The Ocoee Supergroup includes the Walden
Creek Group, the Great Smoky Group, and the Snowbird Group. Slates, metasiltstone,
metaconglomerates, metasandstone, quartzite, and metalimestone characterize the Walden Creek
Group. Metagraywacke, metasiltstone, and graphitic and sulfidic slates and schists make up the
Great Smoky Group. The Snowbird Group includes metamorphosed sandstone, siltstone, and
limestone, as well as quartzite, slate, phyllite, and schist.
IV-8 Reprinted from USGS Open-File Report 93-292-D
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Within the southwestern Blue Ridge is a series of metasedimentary rocks that lie
stratigraphically above the Great Smoky Group and form the Murphy belt. The Brasstown
Formation is biotite schist with micaceous quartzite and the Nantahala Formation is sulfidic slate
grapluuc schist, metasiltstone, and quartzite. These two formations have been grouped into the '
Hiwassee River Group by Tull and others (1991) and form the base of the Murphy belt sequence
The Murphy Marble is a thin calcareous to dolomitic marble overlying the Hiwassee Group The'
Mineral Bluff Group (Tull and others, 1991) lies unconformably above the Murphy Marble'and
consists of quartz-chlorite-sericite schist and phyllite with thin layers of quartzite and minor
graphitic, calc-silicate, and aluminous schists and slate. It is surrounded by a thin layer of
amphibolite, possibly of Late Proterozoic to Cambrian in age.
Late Proterozoic rocks of sedimentary and volcanic origin that crop out in the eastern Blue
Ridge include the Alligator Back Formation, the Ashe Metamorphic Suite and the Tallulah Falls
Formation. Devonian-age quartz diorite and granodiorite intrude into several parts of these units
The Alligator Back Formation crops out in the east-central and northeastern Blue Ridge and
consists of finely laminated to massive gneiss, micaceous conglomerate, mica schist, phyllite and
minor amphibolite. The Ashe Metamorphic Suite and Tallulah Falls Formation consist of '
metagraywacke; muscovite-biotite schist with minor amphibolite and hornblende gneiss- sulfidic
and graphitic mica schist, mica gneiss and amphibolite; and biotite gneiss with interlayers of
amphibolite and biotite-and-garnet schists.
Between the two Late Proterozoic belts of metasedimentary and metavolcanic rocks is a
region of Middle Proterozoic felsic gneiss derived from sedimentary and igneous rocks and Middle
to Late Proterozoic-age metamorphic rocks of the Coweeta Group. These rocks are intruded by
various Late Proterozoic mafic and felsic plutons. The Coweeta Group consists of a quartz-dioritic
gneiss with metasandstone, quartzite, amphibolite, and variable biotite gneiss and schist- a biotite
gneiss with interfered biotite garnet gneiss and amphibolite; and a massive to well-foliated
amphibolite. Abundant intrusions of Devonian to Silurian-age granitic pegmatites occur within the
biotite gneiss. The Middle Proterozoic felsic gneisses include granodioritic gneiss, the Toxaway
Gneiss, biotite granite gneiss that is mylonitized in places, migmatitic biotite-hornblende gneiss
and amphibolite. 6 '
The Piedmont
u v- Th^Piedmont Province includes several major geologic belts including the Inner Piedmont
the Kings Mountain, the Milton, the Charlotte, the Carolina slate, the Raleigh, and the Eastern '
Mate belts as well as the Mesozoic Basins. Many of these belts are separated by major fault
systems and consist of several series of thrust sheets.
The Inner Piedmont is the most intensely deformed and metamorphosed part of the
Piedmont The majority of the Inner Piedmont is underlain by Proterozoic through Cambrian-age
metamorphic rocks—the most areally extensive of these are biotite gneiss and schist, and mica
schist. These gneisses and schists are locally variable and can contain abundant feldspar garnet
aluminosilicate minerals, and layers of quartzite, calc-silicate rock, amphibolite, and small masses
of granitic rocks. The Inner Piedmont is separated from the Blue Ridge by the Brevard fault zone
a shear zone characterized by metasandstone, marble, graphitic schist and phyllonite. Along the '
Brevard fault zone, in the southwestern Inner Piedmont, lies the Cambrian Henderson Gneiss a
large body of monzomtic to granodioritic gneiss that underlies the eastern halves of Henderson and
Transylvania Counties and comprises much of the Chauga belt East of the Henderson Gneiss are
several small granite bodies, grouped under the name Ceasars Head Granite, which intrude older
IV-11 Reprinted from USGS Open-File Report 93-292-D
-------
theSe r™Se Milton belt is on the northeastern side of the Inner Piedmont, east of *e Danvme
northeastern half of the belt
W-12 Reprinted from USGS Open-File Report 93-292-D
-------
along the southeast margin of the basin. The Pine Hall consists mainly of fluvial arkosic sandstone
and siltstone that is conglomeratic near the contact with older crystalline rocks to the southeast
The Pine Hall is overlain by the lacustrine shales and siltstones of the Cow Branch Formation.
The Cow Branch is overlain by the Stoneville Formation, which forms a single band of outcrop on
the northwestern edge of the basin. It consists of lacustrine siltstones near the center of the basin
and alluvial fan and deltaic sandstone and conglomerate near the border fault
The Davie County basin is a small half graben located southwest of the Dan River basin. It is
filled with fluvial arkosic sandstone, siltstone, and alluvial fan conglomerates. Jurassic diabase
dikes intrude the sedimentary rocks of both basins.
The Deep River basin forms a long narrow band in the eastern part of the Piedmont province
and extends into South Carolina along the western edge of the Carolina slate belt. It is divided into
three subbasins which are named, from north to south, the Durham, Sanford, and Wadesboro
subbasins. Each subbasin is connected to the next by a narrow segment of sedimentary rock. The
sedimentary fill of the Deep River basin comprises the Chatham Group. In the Sanford subbasin,
the basal Triassic Pekin Formation forms a narrow band of outcrop along the northwestern margin.
It consists of fluvial lithic and arkosic sandstone, siltstone, and conglomerate that is more
conglomeratic near the contact with older rocks to the northwest The Pekin Formation is overlain
by the Triassic Cumnock Formation, which thins to the northeast and southwest The Cumnock
Formation consists of black shales and siltstones with local deltaic sandstone lenses and coal beds
near the base. The Cumnock is overlain by the Triassic Sanford Formation, which occupies most
of the width of the Sanford subbasin. It consists of fluvial arkosic red sandstone, siltstone, and
conglomerate. In the Durham subbasin, the formations of the Chatham Group are not
differentiated. In the Wadesboro subbasin, the Pekin Formation equivalent continues along the
length of the basin as a narrow band of outcrop and the Cumnock-equivalent black shales extend a
short distance into the basin before pinching out. Sanford-equivalent sandstones and siltstones
make up the greatest part of the sedimentary package. All of the formations intertongue with
conglomerates whose clasts are derived from older rocks immediately outside of the basin to the
southeast. Jurassic diabase dikes and sheets intrude the sedimentary rocks in all of the subbasins.
The tiny Ellerbe basin, which lies east of the northern part of the Wadesboro subbasin is filled with
conglomerates.
The Raleigh belt is just east of the Carolina slate belt and the Durham subbasin. It underlies
parts of Warren, Vance, Franklin, Wake, Johnston, Nash, Halifax, and Northampton Counties.
Metamorphic rocks make up about half of the belt and consist of Proterozoic through Cambrian-
age biotite gneiss and mica schist with lesser amounts of amphibolite, hornblende gneiss, graphitic
schist, quartzite, and phyllite. Phyllonite and sheared metasedimentary and metavolcanic rock
occur along the western edge of the belt. The metamorphic rocks are intruded by several kinds of
igneous rocks, primarily Pennsylvanian to Permian-age granite. These in turn are intruded by
Jurassic rhyolite dikes. Biotite gneiss and schist along the western edge of the largest granite body
are intruded by dikes and sills of granite, pegmatite, and aplite. Minor bodies of gabbro, diorite,
and ultramafic rocks occur mainly in the western part of the belt
The Eastern Slate belt lies to the east of the Raleigh belt and contains several of the same
intrusive rocks. Proterozoic to Cambrian metamudstone and argillite, interbedded with
metamorphosed sandstone, conglomerate, and volcanic rock, underlies much of the area.
Metamorphosed felsic to mafic volcanic rocks are associated with these metasediments. The
northern and eastern parts of the belt are intruded by Pennsylvanian to Permian granite and older
gabbro and diorite. Intruded biotite gneiss and granite also occur in association with the granite.
IV-13 Reprinted from USGS Open-File Report 93-292-D
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•The Coastal Plain
The Coastal Plain of North Carolina is part of the Atlantic Coastal Plain. It is a thick
accumulation of mostly Cretaceous and younger sediments that form a wedge-shaped mass of
relatively flat-lying strata. It varies in thickness from several feet at the fall line to nearly 10,000
feet at the Outer Banks. These sediments and sedimentary rocks occur in broad outcrop belts that
are roughly parallel to the coastline. Cretaceous and Tertiary-age sediments characterize the Inner
Coastal Plain and Quaternary and younger sediments make up the Outer Coastal Plain.
The Cretaceous Cape Fear Formation is the oldest unit exposed in the North Carolina
Coastal Plain, and is only exposed in major river drainages. The Cretaceous succession is thought
to be initially deltaic in the older units such as the Cape Fear and Middendorf Formations, and then
gradational to marine shelf in the Black Creek and Peedee Formations (Sohl and Owens, 1991).
The Cape Fear Formation consists of fine to coarse sands and sandstones interbedded with sandy
mudstone and clay. Local pebble and gravel beds occur in the upper part of the formation. The
sands are principally quartzitic to feldspathic with local accumulations of heavy minerals (ilmenite
being the most common).
The Middendorf Formation forms a broad outcrop band in the southwestern part of the
Coastal Plain. It is composed of quartz sandstone, sand, and clay, with local concentrations of
clay-clast conglomerates and iron-oxide-cemented concretions. The Middendorf Formation in
South Carolina has high concentrations of radioactive monazite and zircon (Owens and others,
1989). High concentrations of these radioactive minerals in the Middendorf Formation of North
Carolina have recently been documented by Grosz and others (in preparation).
The Black Creek Formation overlies the Middendorf Formation and crops out just to the
east of it It is a gray to black lignitic clay with thin beds and laminae of fine micaceous sand and
thick lenses of cross-bedded sand. Glauconitic, fossiliferous, clayey sand lenses occur in the
upper part of the formation. The Peedee Formation overlies the Black Creek Formation and crops
out in an irregular band to the east The contact between the two is a disconformity containing
medium to coarse grained sand, abundant phosphate pebbles, bone, and shelly material. The
Peedee Formation is locally calcareous and fossiliferous, glauconitic sandstone, sand, clayey sand,
and clay. Sandy fossiliferous limestones occur at the top of this unit
The Beaufort Formation, at the base of the Tertiary succession, occurs in a few small
surface outcrops in the southern part of the Coastal Plain. It consists of siliceous mudstone and
sandstone at the base of the section and glauconitic, fossiliferous sand and silty clay at the top.
The Castle Hayne Formation crops out to the east of the Peedee Fm, and consists of several
members: the Spring Garden Member-sandy limestone and fossiliferous sand; the Comfort
Member-skeletal, partially dolomitic limestone; and, at the base of the formation, the New
Hanover Member-a phosphate pebble conglomerate. Outcropping to the east and overlying the
Castle Hayne Formation is sandy limestone of the River Bend Formation. This unit is succeeded
by the fossiliferous clayey sands of the Belgrade Formation.
The next youngest Tertiary-age sediments cover much of the northern half of the Coastal
Plain. The Yorktown and Duplin Formations are shown undivided on .the map. TheDuplin
Formation consists of medium- to coarse-grained fossiliferous sand, sandy marl, and limestone.
The Yorktown Formation is a fossiliferous clay with minor sand. A phosphatic gravelly sand unit
in the lower part of the Yorktown is a potential phosphate resource (Feiss and others, 1989).
Exposures of the Waccamaw Formation occur to the south of the exposures of the Peedee
Formation, near Cape Fear in the southernmost part of the Coastal Plain. It is a fossiliferous sand
with silt and clay, and its age straddles the Pleistocene-Pliocene boundary.
IV-14 Reprinted from USGS Open-File Report 93-292-D
-------
*~ Tertiary terrace deposits and upland sediments crop out in a string of small exposures along
the northern part of the fall line. These deposits consist of gravel, sand, and clayey sands with
minor oxide-cemented sandstone. Unconsolidated sand deposits of the Pinehurst Formation form
scattered exposures in the southern Coastal Plain in the Middendorf Formation outcrop belt
The Outer Coastal Plain is characterized, by unconsolidated surficial deposits of sand, clay,
gravel, and peat These deposits are marine, fluvial, eolian, and lacustrine irrorigin, reflecting
sedimentation of the tidewater and beach areas. Shoreline deposits in this part of the Coastal Plain
are hosts to local heavy-mineral deposits that include radioactive monazite and zircon. These occur
along Holocene and Pleistocene shorelines.
SOILS
A generalized soil map for North Carolina is shown in figure 5. Because of the warm,
temperate climate and moderately high rainfall, the soils of the Inner Coastal Plain, Piedmont, and
lower mountains of the Blue Ridge are relatively deep, well oxidized, and contain clay subsoils
(Ultisols). The cooler climate and steep slopes in the high mountains of the Blue Ridge and the
young sediments of the Coastal Plain produce shallower, less oxidized, and organic-rich soils
(Inceptisols, Entisols, and Histosols).
The Blue Ridge
Ultisols and Inceptisols are the principal soil orders of the Blue Ridge. Inceptisols have
modest subsoil development and are formed on steep slopes of the high mountains where the rate
of erosion is, in general, nearly equivalent to that of soil development Shallow loams and sandy
loams with loam and clay loam subsoils form on the granites, granitic gneisses, schists, and clastic
metasediments where these rocks occur on steep slopes. These soils generally have moderate
permeability. Ultisols are more mature, deeply-weathered soils with prominent clay accumulations
in the subsoil. In valleys and on less steep slopes, deep loams, sandy loams, and silty loams with
clay or clay loam subsoils form on very micaceous schists, metavolcanic rocks, and felsic to mafic
igneous and metamorphic rocks. Permeabilities range from low to moderate.
The Piedmont
Soils of the Piedmont are primarily Ultisols and Alfisols. Soils formed on gneiss, schist,
amphibolite, metasedimentary rocks, and metavolcanic rocks of the Inner Piedmont belt Charlotte
belt and Carolina slate belt (western and central Piedmont) are sandy and silty loams with firm red
clay subsoils that have low to moderate permeability. Soils formed on gabbro and diorite in the
central Piedmont are shallow, clay loams with firm clay substrata and slow permeability. In the
eastern Piedmont sandy loams with firm clayey subsoils have formed on the sandstones,
siltstones, and shales of the Mesozoic basins. Because of their clayey subsurface horizons, these
soils have low to moderate permeability.
The Inner Coastal Plain
Soils on dissected uplands on the western edge of the Coastal Plain are Entisols,
comprising sands and sandy loams formed mostly on sandstone, sand, and sandy clay. Where
these soils are formed on sandy clays or clayey sands they have moderate permeability, whereas
the soils formed on sands and sandstones have high permeability. The remainder of the Inner
Coastal Plain is covered by loams and sandy loams with clayey or loamy subsoils belonging to the
IV-15 Reprinted from USGS Open-File Report 93-292-D
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GENERALIZED SOIL. MAP OF NORTH CAROLINA EXPLANATION
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Soils of the Blue Ridge Mountains i ;j,
1. Shallow loams and sandy loams formed mainly on granitic and metamorphic rocks, moderate permeability.
2. Moderately deep and deep loams, sandy loams, and silty loams with clay or clay loam subsoils, formed on felsic and
mafic igneous and metamorphic rocks, moderate permeability.
Soils of the Southern Piedmont
3. Shallow to deep sandy to clayey loams with clay and clay loam subsoils, formed mainly on diorites and mafic
metamorphic rocks, low permeability.
4. Sandy loams with clayey subsoils formed on sandstone, siltstone, and shale, low to moderate permeability.
5. Sandy and silty loams with clay or clay loam subsoils formed on gneiss, schist, slate, and granite, generally low to
moderate permeability.
Soils of the Inner Coastal Plain
6. Sands and sandy loams of dissected uplands, moderate to high permeability.
7. Loamy sands and sandy loams with loam or clay loam subsoils, moderate permeability.
8. Loams and sandy loams with clay or clay loam subsoils of lowlands and stream terraces, moderate to high
permeability— commonly wet.
Soils of the Outer Coastal Plain.
9. Mucky soils of shallow lake beds and river swamps, moderate permeability-- typically wet.
10. Clayey and mucky soils of coastal marshes and dunes, low to moderate permeability- wet in low-lying areas.
11. Sandy and loamy soils on broad ridge crests, moderate permeability- commonly wet.
12. Loams, loamy soils, and clay loams in lowlands along stream valleys, moderate to high permeability- typically
13. Sand, loamy sand and sandy loam soils of uplands, mostly high permeability.
14. Sandy and silty loam soils of wet lowlands, clay loam subsoils, moderate permeability- includes marine terraces
coastal lowlands and marshes.
-------
commonly wet
RADIOACTIVITY
describes the available radioactivity data by province and geologic belt
IV-18 Reprinted from USGS Open-File Report 93-292-D
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Graphitic and suffidic schist and slate in the unit are one possible source of the elevated uranium.
Lesure and Chatman (1983) noted that graphitic slate of the Wehutty Formation of the Great ;
Smoky Group was slightly more radioactive than surrounding rocks, and analyses of uranium in
the slates varied from 1 to 6 ppm. Carbonaceous, suffidic, and graphite-bearing metasedimentary
rocks characteristically have radioactivity and uranium occurrences associated with them in the
Appalachians from Georgia to Maine (Grauch and Zarinski, 1976; McConnell and Costello 1980;
Ratte and Vancek, 1980; Gundersen and others, 1988). The Alligator Back Formation north of the
Bowens Creek Fault (northern extension of the Brevard fault zone) also has an area of high eU
(fig 6) associated with it, especially along the fault This area of high radioactivity, however, is
notreflected in the uranium analyses of stream sediment samples from the area and may be an
artifact of the low relief and the altitude at which the gamma-ray survey was flown.
The Piedmont , ..
Much of the radioactivity in the Piedmont may be attributable to the mineral monazite,
which is found in high-grade metamorphic rocks and late-stage granitic intrusive rocks.
Monazite's high density and resistance to weathering result in local monazite concentrations in soils
and as placer deposits in marine and alluvial sediments. Two monazite "belts" in the Piedmont
were defined by Mertie (1953): the western monazite belt extends from Stokes and Surry Counties,
North Carolina, southwest through the Inner Piedmont to South Carolina, and the eastern monazite
belt extends from Rolesville in Wake County, North Carolina, northeast through the Raleigh belt
into Virginia Monazite is most abundant in the sillimanite-bearing schists and gneisses of the
Inner Piedmont, high grade metamorphic rocks of the Blue Ridge, and in the kyamte-staurolite-
bearing metamorphic rocks and the RolesvOle Suite of the Raleigh belt Monazite is also
concentrated in the Coastal Plain sediments and is discussed in the Coastal Plain section below.
Uranium in shear zones, granite intrusives, pegmatites, and granite gneiss may also be
sources of the radioactivity observed in the Piedmont Granitic bodies and pegmatites in North
Carolina may contain a number of uranium-bearing minerals including sphene, zircon, ^ani™te>
allanite and exotic uranium and thorium minerals, as well as monazite (Costain and others, 1986).
An examination of the stream sediment concentrations of cerium can be used to verify whether the
source of radioactivity is monazite. Cerium is an element commonly found in monazite. Reid (in
revision) reports that the cerium concentrations are relatively high in the belts defined by Mertie
(1953), in the metasedimentary rocks of the Alligator Back Formation, in various biotite gneisses
of the Blue Ridge, and in the Cretaceous and Tertiary Coastal Plain sediments. Cerium
concentrations are much lower in areas with suspected uranium mineralization from other sources,
such as in the Brevard fault zone and in the Hendersen Gneiss in Transylvania and Henderson
Counties. The source of uranium in the soil and rocks is important in evaluating their radon
potential Uranium locked up in mineral species as a trace element will emanate less radon than
uranium in uraninite, uranium oxidized with iron on mineral surfaces, on fracture and fault
surfaces, as finely disseminated uranium in graphitic phyllite, or uranium adsorbed onto clays.
Several plutons and granitic gneisses are clearly delineated by areas of eU greater than 2.5
ppm on figure 6. In the Inner Piedmont, several Ordovician-Cambrian metamorphosed granite
plutons have high eU; these include the Brooks Crossroads pluton, the Rocky Face pluton, the
Toluca Granite, and the Sandy Mush pluton. The Cherryville Granite, Ceasars Head Granite, and
Henderson Gneiss also have high eU associated with them. Uranium enrichment (>7.5 ppm) is
seen in stream sediment samples in much of the Inner Piedmont, with distinctly lower uranium
concentrations in stream sediments in the Sauratown Mountains of the northern Inner Piedmont
IV-20 Reprinted from USGS Open-File Report 93-292-D
-------
(Reid, in revision). Parts of the Brevard fault zone, which separates the Piedmont and Blue Ridge,
appear to have high eU (fig. 6) associated with it in Transylvania, Henderson, and McDoweU
Counties, and where several faults intersect in Wilkes and Yadkin Counties. Rocks of the Brevard
fault zone include graphitic metasedimentary rocks in the southern portion that are the probable
source of uranium, as well as uranium introduced into the fault zone during deformation.
The Kings Mountain shear zone, along the southeastern boundary of the Kings Mountain
belt, contains highly faulted and sheared metamorphic rocks that are intruded by the High Shoals
Granite and the Sunnyside pluton. Some of the metamorphic rocks include biotite gneiss, phyllite
and graphitic schist. Studies of uranium in the area (Sargent and others, 1982) indicate that the
Cherryyille Granite, occurring to the west of the zone, contains some uranium, whereas the
Sunnyside pluton within the Kings Mountain belt itself and the Kings Mountain shear zone do not
appear to have high uranium associated with them. Data in Reid (in revision) indicate that stream
sediment samples with uranium concentrations greater than 7.5 ppm are associated with the
Cherryville Granite and, to a lesser extent, with the High Shoals Granite. The equivalent uranium
map (fig. 6) shows high eU in the northern part of the Kings Mountain belt in Gaston County and
also associated with the High Shoals Granite.
The Charlotte belt has generally low eU with small areas of locally high eU (fig. 6). High
eU (fig. 6) and uranium in stream sediment samples (>7.5 ppm) are associated with the Concord
and Salisbury Plutonic Suites. Ground-based surveys of radioactivity using a gamma-ray
spectrometer (Carpenter, 1981) confirm the high radioactivity associated with these plutons as well
as with the syenite ring around the Concord Gabbro. Low equivalent uranium (fig. 6) is
associated with the many mafic intrusive rocks and metavolcanic rocks in the Charlotte belt.
Aeroradioactivity over the Carolina slate belt is markedly low. The metamorphosed mafic
metavolcanic and volcaniclastic rocks such as the meta-argillite are poor uranium sources. Some
moderate equivalent uranium is found in the southern portion of the belt over the Cid Formation.
Data in Reid (in revision) indicates that some uranium enrichment in stream sediment samples
(>7.5 ppm) appears to be associated with the Parks Crossroads pluton and granitic rocks north of
it Most of the stream sediment samples in the belt contain less than 2.2 ppm uranium. A small
area of the slate belt is intruded by the Lilesville Granite and Peedee Gabbro in Anson and
Richmond Counties east of the Wadesboro subbasin. It has a distinct radiometric high (fig. 6) and
a number of stream sediment uranium concentrations are greater than 7.5 ppm.
Aeroradioactivity over the Mesozoic basins is generally moderate with locally high and low
eU (fig. 6). High eU occurs in Dan River basin and in the northern Durham subbasin. Uranium
concentrations are contained in conglomerates in the Danville basin in Virginia and are derived
from the adjacent mylonite zone (J.P. Smoot oral communication, 1992). In Reid (in revision)
uranium enrichment in stream sediment samples (>7.5 ppm) is seen along part of the northern
border fault of the Dan River basin. Black shales in the Cow Branch Formation and the lower part
of the Stonevffle Formation are similar to uranium-bearing black shales in the Newark basin, and
may also be uranium enriched. Uranium enrichment in stream sediment samples occurs in the
northern parts of the Durham and Wadesboro subbasins (Reid, in revision). Black shales in the
Cumnock Formation may have small local uranium concentrations, particularly in association with
coal beds and fluvial sandstones with carbonaceous debris in the upper Pekin Formation and upper
Pine Hall Formation (J.P. Smoot, oral communication, 1992). The lower Pekin and Pine Hall
Formations and the Sanford Formation are not likely to have uranium enrichment
High equivalent uranium in the Raleigh belt appears to be associated with granitic intrusive
rocks, including the Castalia and Wise plutons and the Rolesville Suite. Mertie's (1953) eastern
IV-21 Reprinted from USGS Open-File Report 93-292-D
-------
rocks.
Coastal Plain may host heavy mineral concentrations, i o minerals are
" rhd0^±^^oC^S,ran]ultv; Sverifled iy ground-based
radioactivity in the Outer Coastal Plain
INDOORRADON
most of the Coastal Plain.
IV-22 Reprinted from USGS Open-File Report 93-292-D
-------
to
-------
TABLE 1 Summary of screening indoor radon data in North Carolina from die
EPA/State Residential Radon Survey, the North Carolina Cooperative Extension
Service Radon Survey, and non-random data collected from vendors of charcoal
canister radon detectors. Data represent 2-7 day screening tests.
COUNTY
Alamance
Alexander
-------
TABLE 1 (continued). Random and nonrandom screening indoor radon data for North
Carolina.
COUNTY
Guilford
Halifax
Harnett
Haywood
Henderson
Hertford
Hyde
Iredell
Jackson
Johnston
Jones
Lee
Lenoir
Lincoln
McDowell
Macon
Madison
Martin
Mecklenburg
Mitchell
Montgomery
Moore
Nash
New Hanover
Northampton
Onslow
Orange
Pamlico
Pasquotank
Fender
Perquimans
Person
Pitt
Polk
Randolph
Richmond
Robeson
Rockingham
Rowan
Rutherford
Sampson
Scotland
NO. OF MEAS.
338
17
19
130
225
8
6
85
48
14
-63
135
18
50
38
70
15
11
257
22
14
41
100
70
22
44
99
68
13
11
6
15
42
25
49
16
25
74
49
149
20
9
AVERAGE
1.8
1.6
0.6
3.5
7.1
0.3
0.1
2.3
2.5
0.4
1.0
1.2
0.4
3.3
3.1
2.8
1.5
0.7
1.1
8.1
1.5
2.0
1.0
0.6
2.8
0.9
2.0
0.8
0.3
1.1
0.1
2.4
0.6
3.3
1.7
1.0
0.6
5.4
1.2
2.7
0.7
1.2
MINIMUM
0.0
0.0
0.0
0.0
0.4
0.0
0.0
0.0
0.0
0.0
0.2
0.0
0.0
0.1
0.3
0.3
0.0
0.1
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.3
0.0
0.2
0.0
0.0
0.0
0.1
0.0
0.0
0.1
0.1
MAXIMUM
21.0
" 7.0
• 1.4
37.0
51.7
0.8
0.4
9.5
11.9
2.2
4.4
6.0
1.0
36.2
8.7
10.8
7.1
4.3
8.3
25.5
5.9
20.7
5.1
4.0
16.8
7.4
14.0
2.6
0.9
5.2
0.2
6.9
4.1
17.3
8.0
3.5
2.3
61.5
8.0
27.1
1.5
2.4
-------
TABLE 1 (continued). Random and nonrandom screening indoor radon data for North
Carolina.
COUNTY
Stanly
Stokes
Surry
Swain
Transylvania
Tyrrell
Union
Vance
Wake
Warren
Washington
Watauga
Wayne
Wilkes
Wilson
Yadkin
Yancey
STATEWIDE
NO. OF MEAS.
22
120
99
26
44
6
23
33
755
5
7 '
85
11
51
101
30
11
6825
AVERAGE
1.7
2.8
2.2
3.5
6.8
0.2
1.0
2.1
2.5
4.1
0.6
7.0
1.1
2.8
1.3
2.4
2.7
2.5
MINIMUM
0.0
0.0
0.0
0.0
0.3
0.0
0.1
0.0
0.0
0.1
0.0
0.0
0.0
0.2
0.0
0.0
0.1
0.0
MAXIMUM
8.7
15.3
11.9
11.4
31.4
0.3
6.0
9.5
30.0
12.8
1.5
52.6
2.1
11.1
6.6
8.1
4.9
100.0
-------
a
OQ
I
OO
O
O
Et.
I
O
vo
OO
-------
GEOLOGIC RADON POTENTIAL
For the purpose of this assessment, North Carolina has been divided into 14 geologic
radon potential areas and each area assigned a Radon Index (RI) and a Confidence Index CI) score
(Table 2) The RI is a relative measure of geologic radon potential based on geology, soils,
radioactivity, architecture, and indoor radon, as outlined in the preceding sections. The CI is a
measure of the confidence of the RI assessment based on the quality and quantity of the dato used
to assess geologic radon potential (please refer to the introduction at the beginning of this regional
boot for fdetaled discussion of the indexes). The geologic radon potential areas are shown in
figure 9.' Much of North Carolina has been ranked moderate to low in geologic radon P^aL
Theprevalence of non-basement homes contributes greatly to the low and moderate rankings. In
AefoUowing discussion, the factors contributing to each ranking, and local variations within each
PrOV*C™^
moderate to high in radon potential. The province has highly variable geology, and because of the
cTsfcaints imposed by viewing the indoor radon data at the county level it is impossible to assign
sSTgeologic areas of the Blue Ridge to specific moderate or high indoor radon measurements.
Sge indoor radon is moderate (2-4 PCi/L) in the majority of counties, but two counties
Cherokee and Buncomb) have indoor radon averages between 4.1 and 6 pCi/L and three counties
ta£nShern Blue Ridge (Alleghany, Watauga, and Mitchell) have indoor radon averages greater
man 6 PCi/L. These three counties are underlain primarily by granitic gneiss mica schist and
minor Lphibolite and phyllite. Transylvania and Henderson Counties which are parts o^e
Blue Ridge and Inner Piedmont, also have indoor radon averages over 6 pCi/L. The Brevarfault
zone, Henderson Gneiss, and Ceasars Head Granite are possible sources of ^a^"°n
levels in these two counties. Equivalent uranium is variable from low to high m uie Blue Ridge.
The highest eU appears to be associated with the Ocoee Supergroup in the southern Blue Ridge,
rocksTthe Grandfather Mountain Window, and metamorphic rocks in parts of Haywood and
Buncomb Counties. Soils have generally moderate permeability. H«« ««i«itial
The Chauga belt and Brevard fault zone have been ranked high in geologic radon potential.
The Chauga belt consists predominantly of the Henderson Gneiss. High eU (fig. 6]) and high
uranium concentrations in stream sediments appear to be associated with the Brevard fault zone
Henderson Gneiss, and Ceasars Head Granite in this area. Indoor radon averages are highin_ the
two counties that the main part of the Chauga belt and the southern portion of the Brevard fault
zone pass through. Soils have moderate permeability.
Tlie Inner Piedmont and Kings Mountain belts have been ranked moderate in geologic
radon potential. Indoor radon levels are generally moderate. Grardtic plutons gramtic gne^s,
monazite-rich gneiss and schist, pegmatites, and fault zones appear to have high eU and high
SaS concentrations in stream" sediment sample, Many of tiie granitic plutons are *™*
enriched in uranium and recent work by Speer and others (1992) and f^*™*"^*
the soUs developed on many of the uraniferous granitic plutons and related faultzone^ *e
R\dge and Redmont are possible sources of high radon levels. Sod-gas radon concentrations
measured by the authors commonly exceeded 1000 pCi/L in the Cherryvule Granite, Rolesvi
Sr^d me Sims, Sandy Mush, and Castalia, plutons. The Rocky Mount, Spruce Pine Toluca,
MtAfc? and Stonefountain plutons had relatively low soil-gas radon concentrations. The soil
perartfifty of the Inner Piedmont, Brevard fault zone, and Kings Mountain belt are variably low
IV-28 Reprinted from USGS Open-File Report 93-292-D
-------
to moderate which, together with the large proportion of homes without basements, may account
for the abundance of moderate indoor radon measurements.
Most shear zones in the Piedmont and Blue Ridge should be regarded as having the
potential for producing very local moderate to high indoor radon levels. Studies of shear zones in
granitic metamorphic and igneous rocks from the Reading Prong in New York to the Piedmont in
Virginia (Gundersen, 1991) indicate that shear zones can be the source of high indoor radon levels.
Geochemical and structural models developed from these studies indicate that uranium enrichment,
the redistribution of uranium into the rock foliation during deformation, and relatively high radon
emanation coefficients are common to most shear zones. Because they are very localized sources
of radon and uranium, uranium concentrations in shear zones may not always be detected by
radiometric or stream sediment surveys.
The Charlotte belt has been ranked low in geologic radon potential but it is actually quite
variable-^rimarily low in the southern portion of the belt, and higher in the northern portion of the
belt Equivalent uranium is generally low with locally high eU in the central and northern portions
of the belt, associated with the Concord and Salisbury Plutonic Suites. Permeability of the soils is
generally low to moderate and indoor radon levels are generally low.
The Carolina slate belt has been ranked low in geologic radon potential where it is underlain
primarily by metavolcanic rocks. Where it crops Out east of the Mesozoic basins it has been ranked
moderate. Aeroradioactivity over the Carolina slate belt, uranium in stream sediment samples, and
indoor radon levels are markedly low. Permeability of soils developed on many of the
metavolcanic units is generally low to locally moderate. A small area of the slate belt is intruded
by the Lilesville Granite and Peedee Gabbro in Anson and Richmond Counties, east of the
Wadesboro subbasin. It has high eU and high uranium concentrations in stream sediments, and
moderate to high permeability in the soils. This area has locally high geologic radon potential.
The Raleigh belt has been ranked moderate in geologic radon potential. Equivalent uranium
in the Raleigh belt is generally moderate to high and appears to be associated with granitic intrusive
rocks, including the Castalia and Wilton plutons and the Rolesville Suite. Mertie's (1953) eastern
monazite belt also passes through the Raleigh belt and may account for part of the radioactivity.
The soils have low to moderate permeability. Indoor radon levels are generally moderate.
In the Coastal Plain province, moderate to high eU is associated with the Cretaceous and
Tertiary sediments of the Inner Coastal Plain. Permeability of the soils is highly variable but is
generally moderate to low, and may be locally high in sands and gravels. Seasonally high water
tables are common. Indoor radon levels in the Coastal Plain are generally low. The Inner Coastal
Plain has been ranked low in radon potential but may be locally moderate to high, especially in
areas underlain by Cretaceous sediments. A study of the radon in the Coastal Plain of Texas, New
Jersey, and Alabama (Gundersen and Peake, 1992) suggests that glauconitic, phosphatic,
monazite-rich, and carbonaceous sediments and sedimentary rocks, similar to some Coastal Plain
sediments in North Carolina, are the sources for moderate indoor radon levels observed in parts of
the Inner Coastal Plain of these states.
The Outer Coastal Plain has low eU, low indoor radon averages, and is generally underlain
by sediments with low uranium concentrations. Soil permeability is variable but generally
moderate. Seasonally high water tables are common. A few isolated areas of high radioactivity in
the Outer Coastal Plain may be related to heavy mineral and phosphate deposits in the shoreline
sediments. The area has been ranked low in geologic radon potential, but may have local moderate
or high indoor radon occurrences related to heavy minerals or phosphate lands.
IV-29 Reprinted from USGS Open-File Report 93-292-D
-------
This is a generalized assessment of the State's geologic radon potential and there is no
substitute for having a home tested. The conclusions about radon potential presented in this report
cannot be applied to individual homes or building sites. Indoor radon levels, both high and low,
can be quite localized, and within any radon potential area there will likely be areas with higher or
lower radon potential than assigned to the area as a whole. Any local decisions about radon should
DPI be made without consulting all available local data. For additional information on radon and
how to test, contact your State radon program or EPA regional office. Addresses and phone
numbers for these agencies are listed in chapter 1 of this booklet.
IV-30 Reprinted from USGS Open-File Report 93-292-D
-------
TABLE 2. RI and CI scores for geologic radon potential areas of North Carolina.
FACTOR
INDOOR RADON
RADIOACTIVITY
GEOLOGY
SOIL PERM.
ARCHITECTURE
GFE POINTS
TOTAL
Blue
Ridge
RI CI
2
2
2
2
2
0
10
2
3
1
3
.
-
9
Chaugabelt,
Brevard fault zone
RI CI
3
3
2
2
2
0
12
2
3
3
2
.
-
10
Inner Piedmont, Kings
Mountain, Milton belts
RI CI
2
3
2
2
2
0
11
3
3
3
2
.
11
Charlotte
belt
RI CI
1
1
2
2
2
0
8
3
3
3
2
.
-
11
Mod Mod
High High
Mod High
Low High
FACTOR
INDOOR RADON
RADIOACTIVITY
GEOLOGY
SOIL PERM.
ARCHITECTURE
GFE POINTS
TOTAL
Carolina Carolina slate belt
slate belt east of the Mesozoic basins
RI CI RI CI
1
1
1
2
1
0
6
Low
3
3
2
3
11
High
1
3
2
2
1
. 0
9
Mod
1
3
2
3
9
Mod
Mesozoic
basins
RI CI
1
2
2
2
1
0
8
Low
1
2
2
3
8
Mod
Raleigh
belt
RI CI
2
3
3
2
1
0
11
Mod
3
3
3
3
12
High
Eastern Slate belt
Inner Coastal Plain
Outer Coastal Plain
FACTOR
RI
CI
RI
CI
RI
CI
INDOOR RADON
RADIOACnVITY
GEOLOGY
SOIL PERM.
ARCHITECTURE
GFE POINTS
TOTAL
1
2
2
2
1
0
8
Low
2
3
2
2
.
-
9
Mod
1
2
2
2
1
0
8
Low
2
3
2
2
- -
-
9
Mod
1
1
2
2
1
0
7
Low
2
3
2
3
-
-
10
High
RADON INDEX SCORING:
Radon potential category
Probable screening indoor
Point range radon average for area
LOW " 3-8 points <2pCi/L
MODERATE/VARIABLE 9-11 points 2 - 4 pCi/L
HIGH > 11 points > 4 pCi/L
Possible range of points = 3 to 17
CONFIDENCE INDEX SCORING:
LOW CONFIDENCE
MODERATE CONFIDENCE
HIGH CONFIDENCE
4-6 points
7-9 points
10- 12 points
Possible range of points = 4 to 12
IV-31 Reprinted from USGS Open-File Report 93-292-D
-------
09
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-------
REFERENCES CITED IN THIS REPORT
AND GENERAL REFERENCES RELEVANT TO RADON IN NORTH CAROLINA
Berquist, Carl R., Jr., Cooper, J. M., and Goodwin, B. K., 1990, Radon from Coastal Plain
sediments, Virginia: Preliminary results: Geological Society of America, Abstracts with
Programs, v. 22, no. 2, p. 4-5.
Carpenter, R.H., 1981, An evaluation of the uranium geochemical anomalies in the Charlotte I°x2°
NTMS quadrangle: U.S. Department of Energy Report GJBX-25(82).
Costain, J.K., Speer, J.A., Glover, L., IE, Perry, L., Dashevsky, S., and McKinney, M.,'1986,
Heat flow in the Piedmont and Atlantic Coastal Plain of the southeastern United States:
Journal of Geophysical Research, v. 91, p. 2123-2135.
Dribus, J.R., Hurley, B.W., Lawton, D.E., and Lee, C.H., 1982, Greensboro Quadrangle,
North Carolina and Virginia: U.S. Department of Energy National Uranium Resource
Evaluation Report PGJ/F-063(82), 30 p.
Duval, J.S., Jones, W.J., Riggle, F.R., and Pitkin, J.A., 1989, Equivalent uranium map of
conterminous United States: U.S. Geological Survey Open-File Report 89-478,10 p.
Epperson, G.L., Johnson, G.L., Davis, J.M., and Robinson, P.J., 1988, Weather and climate in
North Carolina: North Carolina State University Agricultural Extension Service
Publication AG-375,48 p.
Facts on File Publications, 1984, State Maps on File: Southeast
Feiss, P.G., Maybin, A.H., m, Riggs, S.R., and Grosz, A.E., 1991, Mineral resources of the
Carolinas, in Horton Jr., J.W., and Zullo, V. A., eds., The Geology of the Carolinas:
Knoxville, University of Tennessee Press, p. 319-345.
Grauch, R.I., and Zarinski, K., 1976, Generalized descriptions of uranium-bearing veins,
pegmatites, and disseminations in non-sedimentary rocks, eastern United States: U.S.
Geological Survey Open-File Report 76-582,114 p.
Grosz, A.E., San Juan, F., and Reid, J.C., in preparation, Gamma-ray aeroradiometric anomalies
on Cretaceous age sediments in North Carolina: Implications for placer mineral resources.
Gundersen, L.C.S., and Peake, R.T., 1992, Radon in the Coastal Plain of Texas, Alabama, and
New Jersey, in Gates, A.E., and Gundersen, L.C.S., eds., Geologic controls on radon:
Geological Society of America Special Paper 271, p. 53-64.
Gundersen, L.C.S, Reimer, G.M., Wiggs, C.R., and Rice, C.A., 1988, Map showing radon
potential of rocks and soils in Montgomery County, Maryland: U.S. Geological Survey
Miscellaneous Field Studies Map MF-2043, scale 1:62,500.
Gundersen, L.C.S., 1991, Radon in sheared metamorphic and igneous rocks, in Gundersen,
L.C.S., and Wanty, R.B., eds., Field studies of radon in rocks, soils, and water: U.S.
Geological Survey Bulletin 1971, p. 39-50.
IV-33 Reprinted from USGS Open-File Report 93-292-D
-------
Horton Jr., J.W., and Zullo, V. A., eds., 1991, The Geology of the Carolinas: Knoxvffle,
University of Tennessee Press, 406 p.
Lee, R.D., Watson, I.E., Jr., and Fong, S.W., 1979, An assessment of radium in selected North
Carolina drinking water supplies: Health Physics, v. 37, p. 777-77y.
Lesure, F.G., and Chatman, M.L., 1983, Mineral resource map of the Snowbird roadless area,
Graham County, North Carolina: U.S. Geological Survey Miscellaneous Field
Investigations Map MF-1587-C, scale varies.
LKB Resources, 1979, National Uranium Resource Evaluation aerial gamma-ray and magnetic
reconnaissance survey, Blue Ridge area, KnoxviUe and Charlotte quadrangles: U.S.
Department of Energy, Narrative Report GJBX-57-79, v. 1.
Loomis, D., 1987, Radon-222 concentration and aquifer lithology in North Carolina: Ground
Water Monitoring Review, v. 7, p. 33.
Loomis, D.P., Watson, J.E., Jr., and Crawford-Brown, D J 1988, ftefct^he1t°.cc™ce of
radon-222 in groundwater supplies: Environmental Geochemistry and Health, v. 10,
p. 41-50.
McConnell, K.I., and Costello, J.O., 1980, Uranium evaluation of graphitic phyllites and other
selected rocks in the Georgia Piedmont and Blue Ridge: Georgia Geological Survey, Open
File Report 80-5,41 p.
Mertie, J.B., Jr. 1953, Monazite deposits of the southeastern Atlantic states: U.S. Geological
'Survey Circular 237,31 p.
Mitsch, B.F., Watson, J.E., Jr. and Hayes, J.A., 1984, A study of radium-226 and radon-222
concentrations in ground water near a phosphate mining and manufacturing facility with
emphasis on the hydrogeologic characteristics of the area: University of North Carolina
Water Resources Research Institute Report 216,69 p.
North Carolina Geological Survey, 1985, Geologic Map of North Carolina, scale 1:500,000.
North Carolina Geological Survey, 1991, Generalized Geologic Map of North Carolina, scale
approx. 1:2,000,000.
Owens, J.P., Grosz, A.E., and Fisher, J.C., 1989, Aeroradiometric map and geologic
interpretation of part of the Florence-Georgetown I°x2° quadrangles South Carolina. U.S.
Geological Survey Miscellaneous Investigations Map I-1948-B, scale 1:250,UUU.
Ratte", C., and Vanacek, D., 1980, Radioactivity Map of Vermont: Vermont Geological Survey,
File No. 1980-1, rev.3,3 plates with text.
Reid, J.C., in revision, A Geochemical Atlas of North Carolina: North Carolina Geological Survey
Bulletin 93,54 plates with text
Richmond, G.M., Fullerton, D.S., and Christiansen, A.C., eds., 1991, Quaternary geologic map
of tiie Blue Ridge 4°x6° quadrangle, United States: U.S. Geological Survey Miscellaneous
Investigations Series Map 1-1420 (NJ-17), scale 1:1,000,000.
IV-34 Reprinted from USGS Open-File Report 93-292-D
-------
Richmond, G.M., Fullerton, D.S., and Weide, D.L., eds., 1986, Quaternary geologic map of the
Hatteras 4°x6° quadrangle, United States: U.S. Geological Survey Miscellaneous
Investigations Series Map 1-1420 (NI-18), scale 1:1,000,000.
Richmond, G.M., Fullertdn, D.S., and Weide, D.L., eds., 1987, Quaternary geologic map of the
Savannah 4°x6° quadrangle, United States: U.S. Geological Survey Miscellaneous
Investigations Series Map 1-1420 (NI-17), scale 1:1,000,000.
Sargent, K.A., Price, Van, Jr.,. and Karfunkel, B.S., 1982, Evaluation of uranium geochemical
anomalies in the Kings Mountain area, Charlotte I°x2° quadrangle: U.S. Department of
Energy Report GJBX-102(82), 31 p.
Sasser, M.K., and Watson, J.E., Jr., 1978, An evaluation of the radon concentration in North
Carolina ground water supplies: Health Physics, v. 34, p. 667-671.
Sohl, N.F., and Owens, J.P., 1991, Cretaceous Stratigraphy of the Carolina Coastal Plain, in
Horton, J.W., Jr., and Zullo, V. A., eds., The Geology of the Carolinas: Knoxville,
University of Tennessee Press, 406 p.
Speer, J.A., 1992, Radon potential of uraniferous granites and the relationship among the
geochemistry of the granites, heat production, heat flow, and soil radon: USGS-NC State
University Cooperative 14-08-000 l-AO742,unpub. file report, 67 p.
Speer, J.A., Burtwell, G.T., and Douglas, T.J., 1992, Radon in soils derived from post-
metamorphic granitoids of North and South Carolina: Geological Society of America,
Abstracts with Programs, v. 24, no. 2, p. 45.
Spruill, R.K., and Tarravechia, R.J., 1989, An evaluation of Rn-222 levels in groundwater from
granite and sedimentary cover, with results of an in-situ remediation technique : Geological
Society of America, Abstracts with Programs, v. 21, p. 59.
Strain, C, Watson, J.E., Jr., and Fong, S.W., 1979, An evaluation of 226Ra and 222Rn
concentrations in ground and surface water near a phosphate mining and manufacturing
facility: Health Physics, v. 37, p. 779-783.
Tant, P.L., Byrd, H.J., and Horton, R.E., 1974, General soil map of North Carolina: U.S. Soil
Conservation Service map, scale 1:1,000,000.
Tull, J.F., Thompson, T.W., Groszos, M.S., Aylor, J.G., Jr., and Kish, S.A., 1991, Murphy
belt lithostratigraphic nomenclature, in Kish, S.A., ed., Studies of Precambrian and
Paleozoic stratigraphy in the western Blue Ridge: Carolina Geological Society, Field Trip
Guidebook, p. 79-86.
Watson, J.E., Jr. and Mitsch, B.F., 1987, Ground-water concentrations of 226Ra and 222Rn in
North Carolina phosphate lands: Health Physics, v. 52, p. 361-365.
IV-35 Reprinted from USGS Open-File Report 93-292-D
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APPENDIX A. Screening indoor radon data from the EPA/State Residential Radon Survey and
the North Carolina Cooperative Extension Service Radon Survey conducted during 1989-90.
Data represent randomly-sampled, 2-7 day charcoal canister measurements.
COUNTY
ALAMANCE
ALEXANDER
ALLEGHANY
ANSON
ASHE
AVERY
BEAUFORT
BERTIE
BLADEN
BRUNSWICK
BUNCOMBE
BURKE
CABARRUS
CALDWELL
CAMDEN
CARTERET
CASWELL
CATAWBA
CHATHAM
CHEROKEE
CHOWAN
CLAY
CLEVELAND
COLUMBUS
CRAVEN
CUMBERLAND
cuRRrrucK
DARE
DAVIDSON
DAVIE
DUPLIN
DURHAM
EDGECOMBE
FORSYTH
FRANKLIN
GASTON
GATES
GRAHAM
GRANVTLLE
GREENE
GUILFORD
NO. OF
ME AS.
12
15
9
89
9
7
7
91
2
4
94
33
13
38
1
7
89
62
5
8
2
6
41
9
4
13
2
3
20
17
7
11
4
118
8
157
68
5
8
1
123
MEAN
0.6
2.1
2.5
1.3
4.0
3.8
0.4
1.0
0.4
0.6
2.2
2.1
1.1
1.9
0.0
0.2
2.7
1.3
0.4
3.4
0.3
2.1
1.7
0.3
0.9
1.1
0.4
0.0
0.8
1.9
0.6
0.8
0.3
4.0
1.3
1.9
1.0
2.4
0.6
0.0
1.7
GEOM.
MEAN
0.1
1.3
0.5
0.9
0.7
2.6
0.1
0.8
0.4
0.6
1.3
0.8
0.1
1.3
0.0
0.0
1.6
0.4
0.1
1.7
0.2
1.4
1.2
0.1
0.8
0.4
0.3
0.0
0.2
0.7
0.1
0.1
0.0
2.4
0.4
0.8
0.8
0.2
0.1
0.0
0.7
MEDIAN
0.6
1.4
1.2
1.1
1.5
4.2
0.5
0.8
0.4
0.6
1:5
1.8
0.8
1.3
0.0
0.2
1.7
1.0
0.3
1.4
0.3
1.0
1.3
0.3
0.9
0.6
0.4
0.0
0.5
0.9
0.2
0.5
0.3
2.6
1.3
1.2
0.8
0.5
0.3
0.0
0.9
STD.
DEV.
0.4
2.6
3.3
0.9
5.0
3.0
0.3
0.8
0.0
0.2
2.0
2.0
-1.3
2.2
***
0.3
3.1
1.2
0.4
6.1
0.1
2.0
1.9
0.2
0.4
1.1
0.3
0.1
0.9
1.9
0.9
1.3
0.2
4.1
0.8
2.3
0.7
3.7
0.7
***
2.5
MAXIMUM
1.2
8.9
8.6
4.9
13.5
9.0
0.8
4.6
0.4
0.7
10.4
10.1
4.2
12.0
0.0
0.8
20.0
5.3
0.9
18.6
0.3
5.4
10.7
0.7
1.2
3.4
0.6
0.1
3.2
6.3
2.7
4.6
0.6
23.1
2.3
15.4
3.8
8.8
2.1
0.0
21.0
%>4 pCi/L
0
13
22
1
33
57
0
1
0
0
20
12
8
8
0
0
19
6
0
13
0
17
10
0
0
0
0
0
0
12
0
9
0
32
0
13
0
20
0
0
8
%>20pCi/L
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
2
0
0
0
0
0
0
1
-------
APPENDIX A. (continued). Screening indoor radon data for North Carolina.
COUNTY
HALIFAX
HARNETT
HAYWOOD
HENDERSON
HERTFORD
HOKE
HYDE
nmnnrj.
JACKSON
JOHNSTON
JONES
LEE
LENOIR
LINCOLN
MCDOWELL
MACON
MADISON
MARTIN
MECKLENBURG
MITCHELL
MONTGOMERY
MOORE
NASH
NEW HANOVER
NORTHAMPTON
ONSLOW
ORANGE
PAMLICO
PASQUOTANK
PENDER
PEROUIMANS
PERSON
PITT
POLK
RANDOLPH
RICHMOND
ROBESON
ROCKINGHAM
ROWAN
RUTHERFORD
SAMPSON
NO. OF
MEAS.
3
6
103
124
3
1
1
52
13
9
64
103
3
29
15
14
6
3
55
5
3
5
91
10
4
5
13
63
4
5
1
1
10
9
8
5
10
10
10
114
5
MEAN
1.0
0.4
2.8
6.4
0.4
0.2
0.0
1.9
1.7
0.3
I'.O
1.3
0.2
2.8
2.7
2.0
2.3
0.4
0.7
1.8
0.8
0.4
1.1
0.3
0.4
0.6
1.1
0.8
0.3
0.4
0.2
1.2
0.6
2.9
0.4
0.4
0.4
1.9
0.4
2.4
0.6
GEOM.
MEAN
0.1
0.0
1.0
3.9
0.3
0.2
0.0
0.7
0.6
0.0
0.7
0.9
0.0
1.3
1.9
0.9
0.4
0.3
0.3
0.3
0.0
0.0
0.7
0.0
0.0
0.1
1.0
0.5
0.0
0.1
0.2
1.2
0.0
1.2
0.1
0.1
0.1
1.4
0.0
1.6
0.6
MEDIAN
1.2
0.4
1.6
4.0
0.2
0.2
0.0
1.3
1.3
0.1
0.8
1.2
0.0
1.3
1.7
1.4
1.7
0.5
0.5
1.6
0.3
0.3
0.8
0.3
0.3
0.4
0.9
0.7
0.3
0.1
0.2
1.2
0.1
1.1
0.4
0.2
0.4
1.6
0.5
1.6
0.6
STD.
DEV.
0.9
0.4
3.6
7.3
0.4
***
***
2.0
1.6
0.3
0.9
0.9
0.3
3.9
2.3
1.5
2.5
0.3
0.7
1.3
1.1
0.4
0.9
0.4
0.5
0.6
0.7
•0.6
0.3
0.6
***
***
1.3
5.4
0.4
0.4
0.3
1.3
0.4
3.1
0.3
MAXIMUM
1.8
0.7
21.3
44.3
0.8
0.2
0.0
9.5
5.4
0.8
4.4
6.0
0.5
18.8
7.4
4.9
7.1
0.6
3.6
3.5
2.0
1.0
5.1
1.2
1.2
1.5
2.7
2.6
0.6
1.5
0.2
1.2
4.1
17.3
1.2
1.1
1.0
4.4
0.9
27.1
1.0
%>4pCi/L
0
0
22
50
0
0
0
10
8
0
3
1
0
21
27
14
17
0
0
0
0
0
2
0
0
0
0
0
0
0
0
0
10
11
0
0
0
10
0
13
0
%>20 pCi/L
0
0
1
5
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
-------
APPENDIX A. (continued). Screening indoor radon data for North Carolina.
COUNTY
SCOTLAND
STANLY
STOKES
SURRY
SWAIN
TRANSYLVANIA
TYR1?FT.T.
UNION
VANCE
WAKE
WASHINGTON
WATAUGA
WAYNE
WELKES
WILSON
YADKIN
YANCEY
NO. OF
MEAS.
1
8
104
36
2
17
1
7
3
53
1
18
3
23
79
12
5
MEAN
1.7
1.4
2.8
2.3
3.0
4.4
0.0
0.6
1.6
1.8
0.0
5.3
0.3
2.7
1.3
0.9
2.3
GEOM.
MEAN
1.7
1.1
2.1
1.1
• 3.0
2.3
0.0
0.1
0.1
0.5
0.0
1.7
0.0
1.9
0.7
0.4
1.2
MEDIAN
1.7
1.4
2.0
1.8
3.0
2.4
0.0
0.2
0.6
1.0
0.0
3.7
0.2
2.2
1.0
0.8
2.5
STD.
DEV.
***
1.0
2.5
2.4
0.1
4.7
***
0.7
2.2
. 2.4
***
6.0
0.3
1.9
1.3
0.5
2.0
MAXIMUM
1.7
2.8
15.3
9.8
3.1
15.4
0.0
1.6
4.1
12.4
0.0
23.9
0.6
7.3
6.6
1.9
4.9
%>4 pCi/L
0
0
27
17
0
35
0
0
33
13
0
50
0
26
5
0
20
%>20pCi/L
0
0
0
0
0
0
0
0
0
0
0
6
0
0
0
0
0
-------
-------
EPA's Map of Radon Zones
The USGS' Geologic Radon Province Map is the technical foundation for EPA's Map
of Radon Zones. The Geologic Radon Province Map defines the radon potential for
approximately 360 geologic provinces. EPA has adapted this information to fit a county
boundary map in order to produce the Map of Radon Zones.
The Map of Radon Zones is based on the same range of predicted screening levels of
indoor radon as USGS1 Geologic Radon Province Map. EPA defines the three zones as
follows: Zone One areas have an average predicted indoor radon screening potential greater
than 4 pCi/L. Zone Two areas are predicted to have an average indoor radon screening
potential between 2 pCi/L and 4 pCi/L. Zone Three areas are predicted to have an average
indoor radon screening potential less than 2 pCi/L.
Since the geologic province boundaries cross state and county boundaries, a strict
translation of counties from the Geologic Radon Province Map to the Map of Radon Zones
was not possible. For counties that have variable radon potential (i.e., are located in two or
more provinces of different rankings), the counties were assigned to a zone based on the
predicted radon potential of the province in which most of its area lies. (See Part I for more
details.)
NORTH CAROLINA MAP OF RADON ZONES
The information presented in this report on North Carolina is not endorsed by the
North Carolina Department of Environment, Health and Natural Resources. Although both
the radon program and geological survey of this department were available for technical
consultation during the development of this information, North Carolina feels that additional
work needs to be done on the methodology to appropriately characterize radon potential for
North Carolina. EPA is providing this information on North Carolina independent of the
Department of Environment, Health, and Natural Resources. However, both EPA and North
Carolina are committed to continuing to work together to improve upon this information.
Although the information provided in Part IV of this report — the State chapter entitled
"Preliminary Geologic Radon Potential Assessment of North Carolina" — may appear to be
quite specific, it cannot be applied to determine the radon levels of a neighborhood, housing
tract, individual house, etc. Despite the differences in opinion in the methodology for
developing this map, EPA and North Carolina agree that THE ONLY WAY TO
DETERMINE IF A HOUSE HAS ELEVATED INDOOR RADON IS TO TEST.
Contact the Region 4 EPA office or the North Carolina radon program for information on
testing and fixing homes. Telephone numbers and addresses can be found in Part II of this
report.
V-l
-------
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