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EPA?S MAP OF RADON ZONES
SOUTH 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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TABLE OF CONTENTS
I. OVERVIEW
II. THE USGS/EPA RADON POTENTIAL
ASSESSMENTSiINTRODUCTION
III. REGION 4 GEOLOGIC RADON POTENTIAL
SUMMARY
V. PRELIMINARY GEOLOGIC RADON POTENTIAL
ASSESSMENT OF SOUTH CAROLINA
V. EPA'S MAP OF RADON ZONES -
SOUTH 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
(AASG) have worked closely over the past several years to produce a series of maps 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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nf thft 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 map 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.
of the Map 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 this document.
EPA subsequently developed the Map of Rauon Zones by extrapolating 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.
1-5
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Figure 3
Geol-ogic Radon Potential Provinces for Nebraska
Lincoln County
Bigk Uoiettte Low
Figure 4
NEBRASKA - EPA Map of Radon Zones
Lincoln County
Zoae 1 Zooe 2 Zone 3
1-6
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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.
1-7
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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 H 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 construction
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 not intended to be used as a substitute for
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
H-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 report* 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 (226Ra), which is, in turn,
a product of the decay of uranium (M8U) (fig. 1). The half-life of "2Rn is 3.825 days. Other
isotopes of radon occur naturally, but, with the exception of tho'ron (KORn), 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
II-2 Reprinted from USGS Open-File Report 93-292
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and moisture infiltration rates and depth of wetting may be limited when the 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 = 10'9 meters), or about 2x1 O* 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
II-4 Reprinted from USGS Open-File Report 93-292
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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 g/adient) 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
H-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 as 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 (2HBi), 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 AEKlAL SURVEYS
2 KM (1 MILE)
5 IV. {3 MILES)
2 i 5 XII
E3 10 IU (6 HUES)
5 i 10 III
NO DATA
Figure 2. Nominal flighdine 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 NURE 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.
For an altitude of 400 ft above the ground surface and with primary flightline spacing
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 surveys 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
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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 ih/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 pppularion 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.
H-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.
INCREASING RADON POTENTIAL
FACTOR
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
Probable average screening
Point ranee indppr radon for area
LOW
MODERATE/VARIABLE
HIGH
3-8 points
9-11 points
12-17 points
<2pCi/L
2-4pCi/L
>4pCi/L
POSSIBLE RANGE OF POINTS = 3 to 17
TABLE 2. CONFIDENCE INDEX MATRIX
INCREASING CONFIDENCE
FACTOR
INDOORRADONDATA
AERIAL RADIOACTIVITY
GEOLOGIC DATA
SOIL PERMEABILITY
1
sparse/no data
questionable/no data
questionable
POINT VALUE
2
fair coverage/quality
glacial cover
variable
variable
3
good coverage/quality
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 fiom 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
+he average screening indoor radon level for an are? 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 NURE 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 'c\v 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 horizonsj 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 poims 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; "high1"
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 RI 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
-------
to question the quality or validity of these data. The other factors were scored oh 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 sampling (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 shrinkage cracks in 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 give a general indication of the relative
contributions of the interrelated geologic factors influencing radon generation and transport in
rocks and soils, and thus, of the potential for elevated indoor radon levels to occur in a
particular area. However, because these reports are somewhat generalized to cover relatively.
large areas of States, it is highly recommended that more detailed studies be performed in
local areas of interest, using the methods and general information in these booklets as a guide.
11-16 Reprinted from USGS Open-File Report 93-292
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Deffeyes, K.S., and MacGregor, ID., 1980, World uranium resources: Scientific American
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Durrance, E.M., 1986, Radioactivity in geology: Principles and applications: New York, N.Y.,
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Duval, J.S., 1989, Radioactivity and some of its applications in geology: Proceedings of the
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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.
II-18 Reprinted from USGS Open-File Report 93-292
-------
Schumann, R.R., Owen, D.E., and Asher-Bolinder, S., 1992, Effects of weather arid 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. 6^-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, Tenn., U.S. Department of
Energy Report ORNL/SUB/84-0024/1.
Smith, R.C., H, 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, TJ7.,
and Lowder, W.M. (eds), Natural radiation environment IE, 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 Adas 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.
n-19 Reprinted from USGS Open-File Report 93-292
-------
APPENDIX A
GEOLOGIC TIME SCALE
Subdivisions (and their symbols)
Eon or
Phanerozoic2
Proterozoic
(E)
Archean
(A)
Era or
Erathem
Canozoic 2
(Cz>
Mesozoic2
(Mi)
Paleozoic2
(Pd
MiOfll*
**"*• »
MiOOl*
t«ny
Period, System.
Subperiod, Subsystem
Quaternary 2
(Q)
Neogene 2
Subperiod or
-rf^-f Subsystem (N)
m Paieogene
111 Subperiod or
Subsystem (Pi)
Cretaceous
(K)
Jurassic
(J)
Trisssic
CR)
Permian
(P)
Pennsylvanian
Carboniferous 'P'
(C) Mississippian
(M)
Devonian
(D)
Silurian
(S)
Ordovician
(Q)
Cambrian
tC)
Epoch or Series
Holocene
Pleistocene
Pliocene
Miocene
Oligocene
Eocene
Paleocene
Late
Early
Late
Middle
Early
Late
Middle
Early
Late
Early
Late
Middle
Early
Late
Early
Late
Middle
Early
Late
Middle
Early
Late
Middle
Early
Late
Middle
Early
Upper
Lower
Upper
Middle
Lower
Upper
Middle
Lower
Upper
Lower
Upper
Middle
Lower
Upper
Lower
Upper
Middle
Lower
Upper
Middle
Lower
Upper
Middle
Lower
Upper
Middle
Lower
None defined
None defined
None defined
Age estimates
of boundaries
in mega-annum
(Ma)1
5 (4 9-5.3)
24 (23-26)
66 (63-66)
138 (135-141)
205 (200-215)
240
290 (290-305)
360 (360-365)'
410 (405-415)
435 (435-440)
500 (495-510)
.570'
900
1600
2500
3000
3400
3800?
of teoiopfc and bto«r.tioraphic age assignmenta. Ao« bound.ri.. not ete««ly br.ck.t.d by existing
•*» taSie ratio, .mptey* «. d.ad in Sfioer and Jlo« (1977). Donation m.y. us* tor an
r. mkW... upper or M*. midc*. ta.e) whan uaed «* the,. H.ms «. inform^ drviaten, of ft. Uro^ unK: th,
I^«nlxto ,
'miermal tlm« tam> without apedfie nwk.
USGS Open-FDe Report 93-292
-------
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 pCi/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 detrital 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.
ampnibolite A mafic metamorphic 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
tt-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 rnineral that solidified from molten or partly molten rock material. It is
one of the three main classes into which rocks are divided, the others being 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
Phylfite, 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.
11-24 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.
placer 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, compositionaUy 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
lor 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 surface.
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. fe
tablelands General term for a broad, elevated region with a nearly level surface of considerable
extent.
11-25 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 imbedded 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.
11-26 Reprinted ftom USGS Open-File Report 93-292
-------
APPENDIX C
EPA REGIONAL OFFICES
EPA Regional Offices
State
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)
841 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 JQ
Arizona 9
Arkansas g
California 9
Colorado g
Connecticut i
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 '. j
Maryland 3
Massachusetts i
Michigan 5
Minnesota. „ 5
Mississippi 4
Missouri ; 7
Montana g
Nebraska 7
Nevada 9
New Hampshire l
New Jersey 2
New Mexico 6
New York 2
North Carolina 4
North Dakota g
Ohio 5
Oklahoma 6
Oregon JQ
Pennsylvania 3
Rhode Island l
South Carolina 4
South Dakota g
Tennessee 4
Texas "g
Utah ]g
Vermont l
Virginia , 3
Washington 10
West Virginia 3
Wisconsin 5
Wyoming g
n-27 Reprinted fiom 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
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)255^845
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 MaraiG. 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, HI 96813-2498
(808) 586-4700
n-28 Reprinted from USGS Open-File Report 93-292
-------
Idato
Illinois
Indiana
Iowa
Kansas
Kentucky
PatMcGavarh
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. Plater
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 LeonJ.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 Sue Hendershott
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 Oatmann
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
Nebraska 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) 8274300
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) 5714141
1-800-662-7301 (recorded info x4196)
North Dakota Aden 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
11-30 Reprinted fiom USGS Open-File Report 93-292
-------
Oklahoma
Oregon
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)731-4014
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)7344631
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
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
inNewYork
(212)264^110
11-31 Reprinted from USGS Open-File Report 93-292
-------
Virginia Shelly Ottenhrite
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
W^st Virginia Beanie L. DeBord
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
-------
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
801K 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 -
Walter Schmidt
Florida Geological Survey
903 W. Tennessee St
Tallahassee, FL 32304-7700
(904)4884191
William H. McLemore
Georgia Geologic Survey
Rm. 400
19 Martin Luther King Jr. Dr. SW
Aflanta,GA 30334
(404)656-3214
Hawaii ManabuTagomori
Dept. of Land and Natural Resources
Division of Water & Land Mgt
P.O. Box 373
Honolulu, HI 96809
(808) 548-7539
Idaho Earl H. Bennett
Idaho Geological Survey
University of Idaho
Merrill 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) 333-4747
Indiana Norman C. Hester
Indiana Geological Survey
611 North Walnut Grove
Bloomington, IN 47405
(812)855-9350
Iowa Donald L. Koch
Iowa Department of Natural Resources
Geological Survey Bureau
109 Trowbridge Hall
Iowa City, IA 52242-1319
(319)335-1575
Kansas LeeC.Gerhard
Kansas Geological Survey
1930 Constant Ave., West Campus
University of Kansas
Lawrence, KS 66047
(913)864-3965
H-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 SL Paul Street
Baltimore, MD 21218-5210
(410) 554-5500
Massachusetts Joseph A. Sinnott
Massachusetts Office of
Environmental Affairs
100 Cambridge St, 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.
SL 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)4964180
Nebraska Perry B. Wigley
Nebraska Conservation & Survey
Division
113 Nebraska Hall
University of Nebraska
Lincoln, NE 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 Ramdn 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
Utah
South Carolina Alan-Jon W. Zupan (Acting)
South Carolina Geological Survey
5 Geology Road
Columbia, SC 29210-9998
(803)7: '-9440
South Dakota CM. Christensen (Acting)
South Dakota Geological Survey
Science Center
University of South Dakota
Vermfflion, SD 57069-2390
(605)677-5227
Tennessee Edward T.Luther
Tennessee Division of Geology
13th Hoor, L & C Tower
401 Church Street
Nashville, TN 37243-0445
(615) 532-1500
William L. Fisher
Texas Bureau of Economic Geology
University of Texas
University Station, Box X
Austin, TX 78713-7508
(512)471-7721
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
Charlottesville, 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
H-35 Reprinted from USGS Open-File Report 93-292
-------
West Virginia Larry D.Woodfork
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 fitom USGS Open-File Report 93-292
-------
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
CaCOs has been dissolved away, the soils are enriched in the remaining impurities, predominantly
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-Eastem Pennyroyal
5-New Albany Shale
6-OuterBluegrass
7-InnerBluegrass
8-Cumberland Plateau (Appalachian Plateau)
9-Mississippi alluvial plain
10-Loess-covered Coastal Plain
11-Eastern Coastal Plain
12-Cherty Highland
13-HighlandRim
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-Sanford-Durham sub-basins
29-Raleigh Belt
30-Eastern 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-Southem 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-Lktle River Thrust Stack
53-Coastal Plain (Cretaceous/Tertiary)
54-Coastal Plain (Quaternary/Ph'ocene-Pleistocene gravels)
55-Upper Coastal Plain
56-Middle Coastal Plain
57-Lower Coastal Plain
58-Highlands
59-Lowlands
60-Dade County anomalous area.
m-3 Reprinted from USGS Open-File Report 93-292-D
-------
Indoor Radon Screening
Measurements: Average (pCi/L)
0.0to1.9
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 Honda 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
j j LOW
j£l MODERATE/VARIABLE
HIGH
Mividual
-------
base metals, including uranium. Rinds containing high concentrations of uranium and uranium
minerals can be formed oh 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 mo^ Conditions, 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 PottsvUle 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
than4pCi/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,
Clebume, 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 Clebume
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 IxlO12 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-FUe Report 93-292-D
-------
area and those parts of southern Columbia, western Union, and northern Alachua 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 e'U areas in uic eastern a^ ^outhern parts of 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 elJ.
The Atlantic Coastal Lowland area generally has low radon potential. High rainfall and
high water tables cause very moist 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 cU 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 phyllite, 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
ffl-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
tnese 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
m-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 equilibrium), 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
ffl-10 Reprinted from USGS Open-FUe Report 93-292-D
-------
Mammoth Cave National Park visitor center. The cave air, which averages 54°F was DumDed into
ft™ center for cooling, tat this process has been discontinued duel the reiativelyZh
radioactivity associated with the cave air. y 8
Coastal Plain
«,/ i™?™?!^^0™68™*^^
radon levels, although the area is underlain in part by loess with an eU 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
S, ihf ^^ SeaSOnal1hif water *"«« were consistently listed in the SCS soil surveys as
less than 6 ft, and commonly less than 2 ft.
MISSISSIPPI
™H .reveals ** Mississippi is generally an area of low radon
>h°n r f m f^iPPi are generally low; however, several counties had
n™ ^ radon/evels «««« ta 4 pCi/L. Counties with maximum levels greater
^*^ T concentrated in the northeastern part of the State within the glauconitic and
phosphauc sediments of the Tombigbee Hills and Black Prairies. Readings greater than 4 pCi/L
ako occur in the Mississippi AUuvial Plain, the eastern part of the Pine MsSnce "and 1 S
^ess-covered areas. Glauconitic and phosphatic sediments of the Coastal Plain, partic^ly the
C^ceous and lower Tertiary-age geologic units located in the northeastern portion of T State,
oAer nan! gf^T ^'T^ tO ^^ rad°n' BaSed On ^ioactivity and sLies of radon in
, H Plam' ** BfeCk Rairics ^ P°ntotoc ^ge have been assigned
geologic radon potential; all other parts of Mississippi are considered to be low in
°" P0tenbal- T* climate> "3. ^d lifestyle of ^inhabitants of Mississippi have
111" C ti°n StylCS "* bUndin Ventil
cont on Which'
nigh concentrations of radon to accumulate.
Coastal Plain
elauconftiflof i?^ rad°? " ?6 CoaStal Hain °f TeXES' Tenness^ and Alabama suggests that
glauconitic phosphatic, and carbonaceous sediments and sedimentary rocks, equivalenUo those in
^ssissippi can cause elevated levels of indoor radon. Ground-baSi survey^ Activity "
^don in soUs in that study indicate that the Upper Cretaceous through Lower Tertiary Coastal
^diments are sources of high soil-gas radon (> 1,000 PCi/L) and soil uranium concentrations.
^SffST^TT1 Ufd °Ver ±C C°aStal Plain Sediments in northeastern Mississippi
have^^S^t^ °H a SlmUar SO,Te °f Wgh rad°n levels' Chalks' clays *« marls tend to
a^d jobTte m01St ghef peraieabaity wh«n dry due to desiccation fractures
The youngest Coastal Plain sediments, particularly Oligocene and younger, have
^Sft^^glT0nite and ^hosPhate and become increasingly siliceous and therefore
less likely to be significant sources of radon. Some carbonaceous units may be possible radon
•
• sources*
hnth H Tennfssef ' md 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
-------
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 Citronelle 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
Blue Ridge
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-FUe Report 93-292-D
-------
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 metamprphic 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-dominantiy 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
ffl-13 Reprinted from USGS Open-FUe Report 93-292-D
-------
radioactivity. Soils have variably low to moderate permeability. Indoor radon levels are generally
moderate. ' . •
Coastal Plain
In the Coastal Plain province, moderate to higu oc 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.
CoastalPlain
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
ffl-14 Reprinted from USGSOpen-FUe Report 93-292-D
-------
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 average 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 USGSOpen-FUe 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 cherty dolostone forming most of the
ridges and limestone and shale rorming moj>i of the vzu^ *. The Ridge and Valley region has high
geologic radon potential because of elevated eU 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.
Vnaka 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 (>2QO 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.
m-16 Reprinted from USGS Open-File Report 93-292-D
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PRELIMINARY GEOLOGIC RADON POTENTIAL ASSESSMENT OF SOUTH CAROLINA
. • by
Linda C.S. Gundersen '
US. Geological Survey
INTRODUCTION
Indoor radon measurements of 1089 homes sampled in the State of South Carolina for the
State/EPA Residential Radon Survey have an average of 1.1 pCi/L. Only a few geologic units in
the State have high radioactivity and the potential to produce indoor high radon levels. These
include granitic rocks and sheared fault zones in the Blue Ridge and Piedmont Provinces and some
of the Cretaceous and lower Tertiary-age geologic units located in the Coastal Plain. Further, the
climate and lifestyle of the inhabitants have influenced building construction styles and building
ventilation characteristics, which, in general, do not allow high concentrations of radon to
accumulate.
This is a generalized assessment of geologic radon potential of rocks, soils, and surficial
deposits of South 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 EPA
recommends that all homes be tested. For more information on radon, the reader is urged to
consult the local or State radon program or EPA regional office. More detailed information on state
or local geology may be obtained from the state geological survey. Addresses and phone numbers
for these agencies are listed in chapter 1 of this booklet
PHYSIOGRAPHIC AND GEOGRAPHIC SETTING
The physiography of South Carolina (fig. 1) is in part a reflection of the underlying
bedrock geology (fig. 2). South Carolina has three major physiographic regions: the Blue Ridge
the Piedmont, and the Coastal Plain. Each of these regions is subdivided geologically in figure l'
and these divisions will be referred to throughout the text The Blue Ridge, in northwestern South
Carolina, covers approximately 2 percent of the State and contains the highest elevation found in
South Carolina—3,560 feet above sea level. Crystalline rocks make up the rugged mountains and
narrow valleys of this province. Local relief is several hundred feet to several thousand feet from
valley floor to ridge crest The Piedmont is just east of the Blue Ridge and covers about 35 percent
of the State. It is underlain by complexly deformed igneous and metamorphic rocks that form
gentiy rolling to hilly slopes and narrow stream valleys. Elevation in the province increases
gradually from southeast to northwest, with local relief of several hundred feet The boundary
between the Piedmont and Coastal Plain is defined by the fall line zone, which marks the distinct
change in stream and river velocity from the Piedmont to the Coastal Plain. This zone is
characterized by rapids. The Coastal Plain Province covers approximately two-thirds of the State
and varies from steeply sloping uplands in the Upper Coastal Plain, near the fall line, to nearly
level ground surface in the Lower Coastal Plain near the shoreline. The province is underlain by
IV-1 Reprinted from USGS Open-File Report 93-292-D
-------
-------
-------
GENERALIZED GEOLOGIC MAP OF SOUTH CAROLINA
EXPLANATION
Coastal Plain
Quaternary
Nearshore dune, beach, and marine sediments, predominantly very coarse to fine sand
interbedded with clay and silt. Carolina bays at surface.
Pliocene
Duplin and Bear Bluff Formations. Duplin Formation consists of nearshore beach and
marine sediments, fossiliferous sand with Carolina bays. The Bear Bluff Formation is
fossiliferous with thick clayey to sandy silt and Carolina bays.
Miocene
Pinehurst Formation: Windblown sand deposits, loose, crossbedded quartz sands with
abundant heavy minerals. Upland unit: Crossbedded quartz sand in clay matrix, clay clasts,
cobble deposits, and masses of clay.
Upper Oligocene
Chandler Bridge Formation: Fine grained, phosphatic sand with minor clay. Ashley
Formation of the upper Cooper Group: Clayey, phosphatic, calcareous, fine grained sand.
Eocene
Lower Cooper Group: Parkers Ferry and Harleyville Formations: Harleyville Formation is
phosphatic, calcareous clay. (Parkers Ferry is not exposed at the surface.) Barnwell Group:
Dry Branch Formation and Tobacco Road Sand. Dry Branch Formation is calcareous,
fossiliferous sand with clay interbeds, coarse grained pebbly sand with local thin clay
laminae, and laminated clays and thin sands. Tobacco Road Sand is a medium to very coarse
sand, locally pebbly and clayey.
Orangeburg Group: Huber Formation comprises kaolin deposits and cross-bedded coarse
sands. Grades down dip to the Congaree Formation, which is made up of coarse sands with
locally indurated claystone beds. Wharley Hill Formation is quartzose and glauconitic sand,
glauconitic silt, and interbedded clays and marl. McBean Formation is micaceous, locally
fossiliferous and glauconitic, quartz sand with abundant heavy minerals and minor calcareous
clays, and marls.
Paleocene to Lower Eocene
I' Black Mingo Group: Clay, feldspathic, micaceous, clayey quartz sand overlain by pebbly,
local
Cretaceous
III
locally glauconitic, quartz sand, with thin interbeds of black clay.
Middendorf, Black Creek, and Peedee Formations. Middendorf is quartz sandstone, sand,
and clay with clay-clast conglomerates, iron-cernented concretions, and high concentrations
of radioactive monazite and zircon. Black Creek Formation is gray to black lignitic clay
-------
with thin, fine micaceous sand and thick lenses of cross-bedded sand. Glauconitic,
fossiliferous, clayey sand lenses in the upper part of the formation. Peedee Formation is
locally calcareous and fossiliferous, glauconitic sandstone, sand, clayey sand, and clay.
phosphate pebbles, bone, and shelly material at base
Blue Ridge and Piedmont
Proterozoic-Paleozoic
Granite and granite gneiss: Plutons range in age from Proterozoic to Permian and include
the Toxaway, Ceasars Head, Gray Court, Cherryville, Liberty Hill, Bald Rock, Newberry,
Cuffytown Geek, Yorktown, Clover, Clouds Creek and Ogden plutons.
Brevard Fault Zone: graphitic phyllonite, blastomylonite, and sheared biotite gneiss and
schist.
Hornblende gneiss, amphibolite, diorite, gabbro, and serpentinite includes plutonic,
metasedimentary, and metavolcanic.
Precambrian-Cambrian
Henderson Gneiss of the Inner Piedmont monzonitic to granodioritic gneiss.
Metamorphic rocks in the Blue Ridge and Inner Piedmont: biotite gneiss, biotite schist,
and mica schist Gneisses and schists are locally variable and can contain abundant
feldspar, garnet, aluminosilicate minerals, and layers of quartzite, calc-silicate rock,
amphibolite, monazite and small masses of granitic rocks. Metamorphic rocks in the the
Kings Mountain Belt: metasedimentary and metavolcanic rocks, biotite gneiss, phyllite,
graphitic schist, quartzite, marble, amphibolite, metaconglomerate, and metavolcanic rock.
Metamorphic rocks in the Charlotte Belt biotite gneiss and schist, metavolcanic rocks,
granitic gneiss, mica gneiss. Metamorphic rocks in the Carolina Slate Belt amphibolite,
granitic gneiss, quartzite, muscovite schist, and meta-argillite, metavolcanic rocks:
Metavolcanic rocks: Felsic to mafic metavolcanic rocks. In the Carolina Slate belt
includes meta-argillite interbedded with metamorphosed sandstone, conglomerate,
metamorphosed graywacke, volcanic sandstone, siltstone, and interbedded felsic to mafic
metavolcanic rocks.
-------
relatively unconsolidated sediments of marine and fluvial origin. Local relief is on the order of tens
of feet in the Upper Coastal Plain.
In 1990, .the population of South Carolina was 3,486,703, with 54 percent of the
population living in urban regions (fig. 3). The average population density is approximately 112
per square mile. The climate is humid sub-tropical. Average annual precipitation is about 48
inches (fig. 4). More than half of South Carolina is forested.
GEOLOGIC SETTING
The State has been divided into major geologic provinces and subdivided into geologic
belts (fig. 1), and will be described from west to east across the State. The geologic map
descriptions that follow are derived from several sources, including Overstreet and Bell (1965a, b),
Sheridan and Grow (1988), Bennison (1989), and Horton and Zullo (1991). A generalized
geologic map is given for reference in figure 2..
Blue Ridge
The Blue Ridge province consists of rugged mountainous terrain underlain by metamorphic
rocks of Proterozoic to Cambrian age. The rocks have been complexly folded and faulted during
several orogenies. Biotite schist and gneiss, locally containing garnet, muscovite, and pegmatites,
underlie most of the area. The Toxaway Gneiss, a granitic gneiss, occurs along the northern part
of the province and is possibly igneous in origin (McSween and others, 1991). The boundary
between the Piedmont and Blue Ridge is the Brevard fault zone, a wide zone of graphitic
phyllonite, blastomylonite, and sheared biotite gneiss and schist
Piedmont
The Piedmont province comprises four major geologic belts including the Inner Piedmont,
Kings Mountain, Charlotte, and Carolina slate belts, and two minor belts, the Kiokee and Belair.
The belts consist of metasedimentary and metavolcanic rocks of Precambrian to Cambrian age that
are intruded by various granitic to mafic igneous rocks. Mesozoic basins, very small fault-
bounded basins in the northern part of the Carolina slate belt, consist of conglomerate, sandstone,
and siltstone that are intruded by mafic dikes.
The majority of the Inner Piedmont is underlain by Proterozoic through Cambrian-age
metamorphic rocks. The most areally extensive of these are biotite gneiss, biotite 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 Cambrian-age Henderson Gneiss, a large body of monzonitic to
granodioritic gneiss, lies along the Brevard fault zone. Hornblende gneiss with amphibolite,
diorite, gabbro, and serpentinite forms several bands east of and within the Henderson Gneiss. A
large body of Silurian-Devonian biotite granite and granite gneiss, called the Ceasars Head Granite,
intrudes these rocks and underlies much of Greenville County and parts of Anderson and Pickens
Counties. Several Silurian-Devonian granites, including the Gray Court Granite, the Late
Paleozoic Cherryville Monzonite, and granites and granitic gneisses of unknown age, are found as
irregular masses throughout the western Inner Piedmont
The Kings Mountain belt is just east of the Inner Piedmont and is separated from it by the
Kings Mountain Shear Zone. It consists of Proterozoic through Cambrian-age metasedimentary
and metavolcanic rocks intruded by younger granites. The metamorphic rocks include biotite
IV-6 Reprinted from USGS Open-File Report 93-292-D
-------
POPULATION (1990)
0 to 10000
10001 to 25000
25001 to 50000
50001 to 100000
100001 to 320167
Figure 3. Population of counties in South Carolina (1990 U.S. Census data).
-------
e
•o
a
I
i
§
O
I
o
CO
.s
c
o
o
c
at
-------
gneiss, phyllite, graphitic schist, quartzite, marble, amphibolite, metaconglomerate, and
metavolcanic rock. The Chenyvffle Granite crops out to the west of these rocks. To the south, the
Lowndesville Shear Zone separates the Inner Piedmont from the Charlotte belt
The Charlotte belt comprises many different kinds of igneous rocks including granite,
gabbro, and diorite, as well as granitic gneiss and, to a lesser extent, biotite schist, biotite gneiss,
and metavolcanic rocks. The northern half of the Charlotte belt is predominantly Proterozoic-
Cambrian granitic gneiss and metavolcanic rocks that are intruded by numerous Paleozoic gabbros
and granites. Notable large granite plutons include the Newberry and Bald Rock Granites in the
central and northern part of the belt, in Newberry, Fairfield, Union, and Cherokee Counties. The
southern half of the belt is predominantly Proterozoic-Cambrian biotite gneiss and schist,
metavolcanic rocks, granitic gneiss, and a lesser amount of Proterozoic-Paleozoic gabbroic and
granitic intrusives.
The Carolina slate belt consists of interbedded metavolcanic and metasedimentary rocks. In
west-central South Carolina, the slate belt has been subdivided in to the Persimmon Fork
Formation, the Ashbill Pond Formation, and the Richtex Formation (Butler and Secor, 1991).
Felsic tuff of the Persimmon Fork Formation contains lenses and layers of metasedimentary rocks,
including sandstone and massive mudstone. The Ashbill Pond Formation is predominantly
metasedimentary, with locally interbedded felsic to intermediate volcanic rocks. Fine-grained
quartz sandstone grades into mudstone, graywacke, and feldspathic sandstone in the Ashbill Pond
Formation. The Richtex Formation consists of mudstone, siltstone, graywacke and greenstone.
The Lincolnton metadacite, which is composed of metadacite interbedded with felsic and mafic
tuff, graywacke, argillite, and chert, is exposed in the southwestern portion of the Carolina slate
belt Quartzite, sericite schist and meta-argillite also occur in the Carolina slate belt Late
Paleozoic granite intrusives are common throughout the Carolina slate belt in Chesterfield,
Kershaw, Lancaster, Fairfield, Richland, Saluda, and Edgefield Counties.
The Coastal Plain
The Coastal Plain of South Carolina is part of the Atlantic Coastal Plain and is divided into
three sections: the upper, middle, and lower Coastal Plain. Stratigraphy of the South Carolina
Coastal Plain is complicated and is the subject of much debate. It is beyond the scope of this report
to resolve any stratigraphic questions and usage of specific formation names. The terminology
used here has been derived from several of the papers pertaining to Coastal Plain geology in
Horton and Zullo (1991), especially Nystrom and others (1991) and Owens (1989).
The upper Coastal Plain of South Carolina is bounded on the northwest by crystalline rocks
of the Piedmont and on the southeast by the Orangeburg Scarp. It consists in part of Upper
Cretaceous sediments that are generally micaceous, locally glauconitic to lignitic, kaolinitic sands,
with lenses of clay. The quartzose sands are medium- to coarse-grained, locally pebbly, and
locally cemented with iron oxide or silica. Three formations are recognized in the section the
Middendorf, the Black Creek, and the Peedee, Formations. The Middendorf Formation is
composed of quartz sandstone, sand, and clay with local concentrations of clay-clast
conglomerates, iron-cemented concretions, and high concentrations of radioactive monazite and
zircon (Owens and others, 1989). The Black Creek Formation overlies the Middendorf Formation
and is a gray to black lignitic clay with thin beds and laminae of fine micaceous sand and thick
lenses of crossbedded sand. Glauconitic, fossiliferous, clayey sand lenses occur in the upper part
of the formation. The Peedee Formation overlies the Black Creek Formation and the contact
between the two is a disconformity consisting of medium- to coarse-grained sand, abundant
IV-9 Reprinted from USGS Open-File Report 93-292-D
-------
phosphate pebbles, bone, and shelly material along the contact The Peedee Formation comprises
locally calcareous and fossiliferous, glauconitic sandstone, sand, clayey sand, and clay.
The base.of the Tertiary section, consisting of Paleocene to lower Eocene sediments,
occurs in a few small surface outcrops north of the Santee river and in a few major drainages of the
Coastal Plain, and is referred to as the Black Mingo Group. It consists of clay and feldspathic,
micaceous, clayey quartz sand, overlain by pebbly, locally glauconitic, quartz sand, with thin
interbeds of black clay.
Middle Eocene-age sediments of the Coastal Plain are very limited in surface outcrop
(predominantly in the major drainages of the Coastal Plain) and are placed in the Qrangeburg
Group by Nystrom and others (1991). This includes the formations known as the Huber,
Congaree, Warley Hill and McBean Formations. The Huber Formation comprises kaolin deposits
and crossbedded coarse sands. This grades downdip to the Congaree Formation, which is made
up of coarse sands with locally indurated claystone beds. The Warley Hill Formation is composed
of quartzose and glauconitic sand, glauconitic silt, and interbedded clay and marl. The Warley Hill
crops out in Calhoun and Qrangeburg Counties and includes the Santee Limestone, a fossiliferous
biomicrite. The McBean Formation is micaceous, locally fossiliferous and glauconitic, quartz sand
with abundant heavy minerals and minor calcareous clays and marls.
Upper Eocene sediments of the Coastal Plain crop out extensively in the southern hah7 of
the Upper Coastal Plain. They are referred to as the Bamwell Group and consist of the Dry
Branch Formation and Tobacco Road Sand. The Dry Branch Formation is characterized by
calcareous, fossiliferous sand with clay interbeds, coarse-grained pebbly sand with local thin clay
laminae, and laminated clays and thin sands. The Tobacco Road Sand is a medium- to very
coarse-grained sand that is locally pebbly and clayey.
Possible Miocene-age fluvial sediments blanket the uplands of the southern half of the
upper Coastal Plain. The Upland unit exposures consist of coarse, crossbedded quartz sand in a
clay matrix, clay clasts, cobble deposits, and masses of clay. Possible Late Miocene windblown
sand deposits known as the Pinehurst Formation are irregularly distributed throughout the upper
Coastal plain, particularly towards the fall line. These deposits are loose, crossbedded quartz
sands containing abundant heavy minerals.
The middle Coastal Plain is underlain primarily by deeply weathered Pliocene sediments of
the Duplin and Bear Bluff Formations. The Duplin consists of nearshore beach and marine
sediments, mostly fossiliferous sand with a distinct surface of Carolina bays. The Bear Bluff
Formation is also fossiliferous with thick clayey to sandy silt and Carolina bays.
The lower Coastal Plain is underlain by nearshore dune, beach, and marine sediments,
predominantly very coarse to fine sand interbedded with clays and silts. Carolina bays are also
numerous on the surface of the lower Coastal Plain. The Waccamaw Formation is the oldest of the
Quaternary units (Pleistocene) and lies adjacent to the Bear Bluff Formation. It is composed
predominantly of fine- to coarse-grained barrier sands, locally with backbarrier clayey silts and
clayey sands. The next younger sequence is called the Penholoway Formation and it is similar to
the Waccamaw, but the barriers are typically smaller than in the Waccamaw and back-barrier
sediments are more predominant The Canepatch Formation crops out discontinuously in the
central and southern portions of the lower Coastal Plain and consists of fluvial sands, backbarrier
muds, and barrier sands. The Socastee Formation lies seaward of the Penholoway and Canepatch
Formations and is the next youngest unit It contains gravel and sand with shells and wood at the
base, followed by interbedded sands and peaty clays. The Wando Formation is the youngest of
the Pleistocene barrier sands and does not have Carolina Bays developed on it The youngest
IV-10 Reprinted from USGS Open-FUe Report 93-292-D
-------
sediments of the Coastal Plain are Holocene in age and include alluvial sand, silt, and elay in the
major drainages, and modern beach and barrier sands.
Upper Oligocene and Eocene sediments of the Cooper Group crop out in Dorchester,
Charleston, and Berkeley Counties, along stream drainages in the lower Coastal Plain. The lower
part of the Cooper Group is divided into the Eocene-age Parkers Ferry and Harleyville Formations.
The Harleyville Formation consists of phosphatic, calcareous clay that is overlain by glauconitic,
clayey, fossiliferous limestone of the Parkers Ferry Formation. The Parkers Ferry Formation is
not exposed at the surface. The upper part of the Cooper Group consists of clayey, phosphatic,
calcareous, fine-grained sand known as the Ashley Formation. The Chandler Bridge Formation
disconformably overlies the Ashley Formation and consists of fine-grained, phosphatic sand with
minor clay.
SOILS
A generalized soil map for South Carolina is shown in figure 5. Because of the warm,
temperate climate and moderately high rainfall, the soils of the upper Coastal Plain, Piedmont, and
lower mountains of the Blue Ridge are relatively deep and well oxidized, and some contain clay
subsoils (Ultisols). The young sediments of the middle and lower Coastal Plain and in alluvial
valleys produce shallower, less oxidized, more organic-rich soils (Inceptisols, Entisols, Alfisols,
and Spodosols). Ultisols cover about 85-90 percent of the State's area, the remainder being
covered by soils of the other four orders listed above. The following discussion is condensed
from Smith and Hallbick (1979); the reader is referred to this and U.S. Soil Conservation Service
county soil surveys for more detailed information on soils in South Carolina.
Soils of the Blue Ridge are moderately deep to deep, well drained, clayey sandy loams,
silty sandy loams, and sandy loams formed on saprolite derived from gneiss, schist, and phyllite.
The subsoils contain some clay but the soils are generally moderately permeable.
Soils of the Piedmont are moderately deep to deep, well drained, silty and clayey loams.
Soils over most of the Piedmont are firm, acidic, clay loams derived from gneiss, schist, granite,
and argillite (fig. 5). These soils contain firm, non-swelling clays and are moderately permeable.
Areas in Cherokee, Chester, York, and Fairfield counties in the northern Piedmont, and in
McCormick and Abbeville counties in the southern Piedmont, are covered by slightly acid to
slightly alkaline, fine-silty clay loams to clays derived from diorite, gabbro, and hornblende schist
(fig. 5). These soils contain plastic, swelling clays and have low permeability.
The Sandhills is an area of gently sloping to steeply sloping uplands that forms a transition
between the Piedmont and the Coastal Plain. The area is geologically and physiographically
similar to the upper Coastal Plain, and it is included in the upper Coastal Plain on most
physiographic maps of South Carolina. Soils of the Sandhills are deep, moderately to well-
drained, sands and sandy loams derived from silty and sandy Coastal Plain sediments and
windblown sand. Some of these soils are formed on clayey residuum and consequently have
clayey horizons with low permeability at depth (Richmond and others, 1987). Soils of this unit
that are developed on sandy sediments have moderate to locally high permeability. Soils of the
Sandhills cover slightly less than half of the upper Coastal Plain. The rest of the upper Coastal
Plain is covered by deep, poorly drained to moderately well drained, loamy and clayey soils
developed on mostly silty and clayey Coastal Plain sediments. Local relief is on the order of tens
of feet and the drainage characteristics of the soils depend largely on their position on the slopes,
IV-11 Reprinted from USGS Open-FUe Report 93-292-D
-------
-------
GENERALIZED SOIL MAP OF SOUTH CAROLINA
EXPLANATION
(After Smith and Hallbick, 1979)
SOILS OF THE BLUE RIDGE MOUNTAINS
E3 Moderately deep and deep, fine- to coarse-loamy soils with moderate permeability
and low shnnk-sweU potential; derived from gneiss, schist, phyllite, and granite.
SOILS OF THE SOUTHERN PIEDMONT
Fine silty to clayey soils with low permeability and medium to high shrink-swell
potential; derived mainly from diorite, gabbro, and hornblende schist
Firm clayey soils with moderate permeability and low shrink-swell potential-
derived mainly from gneiss, schist, granite, and Carolina slate.
SOILS OF THE CAROLINA AND GEORGIA SANDHILLS
Sandy and loamy soils with low to moderate permeability and low shrink-swell
potential; derived from silty and sandy sediments.
SOILS OF THE INNER COASTAL PLAIN
££iil Loamy and clayey soils with low to moderate permeability, low shrink-swell
potential, and locally high water tables; derived from clayey and silty sediments.
SOILS OF THE OUTER COASTAL PLAIN (FLATWOODS)
Loamy and clayey soils of wet lowlands, with low to moderate permeability
low to moderate shrink-swell potential, and typically high water tables; derived
from clayey to sandy sediments.
Wet, loamy and sandy soils of broad ridges, with moderate to high permeability
low•shrink-swell potential, and typically high water tables; derived from silty and
sandy sediments. *
Fine- to coarse-loamy and sandy soils of floodplains, with low to moderate
permeability, low to moderate shrink-swell potential, and typically high water
tables; derived from silty and clayey sediments.
I 1 Clayey, organic-rich marsh sediments and beach sand dunes; marshes have low
permeability and are typically wet; beach sands have high permeability and may
be locally or ocassionally wet
-------
with upland soils being better drained than soils in valley bottoms. These soils have low to
moderate permeability, and soils in low-lying areas are subject to high water tables.
Soils of the lower Coastal Plain are dominated by deep,'loamy and clayey soils with low to
moderate permeability developed on sandy, silty, and clayey sediments. Relief in the lower
Coastal Plain is in the range of 1-2 ft to no more than 20 ft, and most of the soils are classified as
wet Areas along the coastline and an area in Hampton, Jasper, and Colleton counties (fig. 5) are
covered by deep, wet, sandy and loamy soils developed on broad, low, sandy ridges. These soils
have moderate to high permeability but they typically have high water tables. Beaches and tidal
marsh zones are among the lowest-lying areas in the State. The soils of this map unit (fig. 5) are
poorly developed and range from sand to organic-rich muck. Permeabilities range from low in
clay-rich mucks to high in beach sands; however, all of the marsh soils and many of the beach
sands are classified as wet
Alluvial soils are formed on floodplains of wide stream valleys throughout the Coastal
Plain. The soils are deep, generally poorly drained, fine- to coarse-loamy and sandy soils derived
from clayey, silty, and sandy alluvial sediments. They have low to moderate permeability but
valley-bottom soils are subject to seasonal or occasional high water tables and flooding.
INDOOR RADON DATA
Indoor radon data from 1089 homes sampled in the State/EPA Residential Radon Survey
conducted in South Carolina during the winter of 1990 are shown in figure 6 and Table 1. A map
of counties is included for reference (fig. 7). Indoor radon was measured by charcoal canister and
data are shown on figure 6 only for those counties with 5 or more data values. The maximum
value recorded in the survey was 80.7 pCi/L in Greenville County. The average for the State was
1.1 pCi/L and 3.7 percent of the homes tested had indoor radon levels exceeding 4 pCi/L.
Greenville, Oconee, and Orangeburg were the only counties with average indoor radon levels
greater than 2 pCi/L.
RADIOACTIVITY
An aeroradiometric map of South Carolina (fig. 8) was compiled from spectral gamma-ray
data acquired during the U.S. Department of Energy's National Uranium Resource Evaluation
(NUKE) program (Duval and others, 1989). For the purposes of this report, low equivalent
uranium (eU) is defined as less than 1.5 parts per million (ppm), moderate eU is defined as
1.5-2.5 ppm, and high eU is defined as greater than 2.5 ppm. In figure 8, low eU is found
throughout much of the middle and lower Coastal Plain, and parts of the Blue Ridge, Charlotte
belt, and Carolina slate belt Moderate eU is characteristic of the upper Coastal Plain and parts of
the Charlotte belt High eU is associated with the granites, granitic gneisses, and faults in the Blue
Ridge, Inner Piedmont Charlotte belt and Carolina slate belt as well some of the Cretaceous and
Tertiary sediments of the Coastal Plain. Occurrence of the uraniferous mineral monazite in the
Inner Piedmont gneisses of South Carolina is well documented. Analyses of monazite from
Greenville and Cherokee counties yielded 0.3 percent U3Og (Mertie, 1953). Monazite is found
throughout the Piedmont in metamorphic rocks (Feiss and others, 1991) and in parts of the Coastal
Plain, particularly the Middendorf Formation (Owens and others, 1989). Its resistance to
weathering and high density result in local monazite concentrations in saprolite and as placers in
marine and alluvial deposits. Monazite concentrations probably account for much of the
IV-14 Reprinted from USGS Open-File Report 93-292-D
-------
Bsmt. 1st Floor Rn
%>4pCi/L
38 »"-*-* * * "• *
OtolO
11 to 13
14 to 16
Missing Data
or < 5 measurements
100 Miles
Bsmt. & 1st Floor Rn
Average Concentration (pCi/L)
28 I*-**
0.0 to 1.0
1.1 to 2.0
2.1 to 3.0
Missing Data
or < 5 measurements
o iSSwfi radon date from the EPA/State Residential Radon Survey of South
Carolina, 1989-90, for counties with 5 or more measurements. Data are from 2-7 dav charcoal
camster tests, ftstognuns in map legends show the number of counties in e?ch cateJory Se
S£CfT ea°h C-°Un?(S^ Table 1} ^ not te sufficient to statisticaU^Sacterize
Une.ualcatego^intervals
-------
TABLE 1. Screening indoor radon data from the EPA/State Residential Radon Survey of
South Carolina conducted during 1990-91. Data represent 2-7 day charcoal canister measurement
from the lowest level of each home tested.
COUNTY
ABBEVILLE
AIKEN
ALI.ENDAT.F,
ANDERSON
BAMBERG
BARNWELL
BEAUFORT
PRPKTPT.T7V
CALHOUN
CHARLESTON
PHnRROTCKR
CHESTER
L'HbSTBKf'JJaUJ
CLARENDON
COLLETON
DARLINGTON
DILLON
DORCHESTER
EPGBFJ^'tt
FAIRFIELD
FLORENCE
GEORGETOWN
GREENVILLE
GREENWOOD
HAMPTON
HORRY
KERSHAW
LANCASTER
LAURENS
LEE
LEXINGTON
MARION
MARLBORO
MCCORMICK
NEWBERRY
OCONEE
ORANGEBURG
PICKENS
RICHLAND
SALUDA
SPARTANBURG
NO. OF
MEAS.
7
49
3
56
2
6
26
24
4
74
10
14
14
6
11
23
4
28
5
6
37
15
102
24
6
48
9
18
19
7
62
10
5
2
11
27
27
31
87
5
78
MEAN
0.6
0.8
1.1
1.0
0.2
1.0
0.6
0.5
0.5
0.4
1.6
0.9
0.9
0.4
0.2
1.0
0.4
0.4
0.7
1.2
0.5
0.3
3.0
0.5
0.5
0.4
1.4
0.0
1.2
0.8
1.0
0.7
0.2
0.3
1.0
2.1
2.4
1.6
0.7
0.5
1.5
GEOM.
MEAN
0.3
0.5
0.5
0.6
0.2
0.4
0.3
0.3
0.4
0.2
1.0
0.3
0.6
0.3
0.2
0.4
0.2
0.3
0.7
0.8
0.3
0.2
1.2
0.3
0.3
0.3
1.2
0.1
0.6
0.6
0.5
0.5
0.1
0.3
0.6
1.0
0.5
0.8
0.4
0.3
1.0
MEDIAN
0.5
0.7
0.4
0.8
0.2
0.7
. 0.5
0.5
0.5
0.2
0.9
0.6
0.8
0.4
0.1
0.5
0.3
0.4
0.7
1.0
0.4
0.1
1.4
0.5
0.5
0.3
1.4
0.0
0.9
1.0
0.5
0.4
0.1
0.3
0.9
1.0
0.5
1.1
0.4
0.5
1.2
STD.
DEV.
0.6
0.9
1.4
1.0
0.6
1.6
0.6
0.5
0.2
0.8
1.5
1.3
0.8
0.4
0.3
1.5
0.5
0.6
0.1
1.3
0.5
0.8
8.4
0.5
0.6
0.7
0.8
0.4
2.1
0.7
1.5
0.7
0.3
0.1
0.7
3.4
8.8
1.7
0.9
0.7
1.5
MAXIMUM
1.5
3.4
2.7
4.7
0.6
4.0
2.2
1.7
0.6
3.6
4.0
3.8
2.6
0.8
0.8
6.4
1.1
2.4
0.8
3.3
1.9
2.1
80.7
1.6
1.7
3.3
2.8
1.1
9.4
2.0
7.3
2.3
0.7
0.4
2.1
15.1
46.2
7.8
5.7
1.4
9.6
%>4pCi/L
0
0
0
4
0
0
0
0
0
0
0
0
0
0
0
4
0
0
0
0
0
0
16
0
0
0
0
0
5
0
6
0
0
0
0
11
4
6
1
0
6
%>20 pCi/L
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
2
0
0
0
0
0
0
0
0
0
0
0
0
0
4
0
0
0
0
-------
TABLE 1 (continued). Screening indoor radon data for South Carolina.
COUNTY
SUMTER
UNION
WILLIAMSBURG
YORK
NO. OF
MEAS.
19
13
11
44
MEAN
1.1
1.1
0.2
1.4
GEOM.
MEAN
0.8
0.8
0.1
0.6
MEDIAN
0.9
1.0
0.1
0.7
STD.
DEV.
1.0
0.9
0.4
1.8
MAXIMUM
3.9
3.5
0.7
8.6
%>4pCi/L
0
0
0
9
%>20nCi/L
0
0
0
0
-------
oo
ON
I
1
o
f
o
CO
00
ffi
-------
Figure 8. Aerial radiometric map of South Carolina (after Duval and others, 1989). Contour lines
at 1.5 and 2.5 ppm equivalent uranium (eU). Pixels shaded at 0.5 ppm eU increments.
-------
radioactivity observed on the map. In the granite plutons, however, such as the Liberty Hill in the
Carolina slate belt, or the Ceasars Head in the Piedmont, the granites carry a number of uranium-
bearing minerals that vary from pluton to phrton. These minerals include sphene, zircon, uramnite,
allanite, and exotic uranium and thorium minerals, as well as monazite (Costain and others, 1986).
The most uraniferous plutons are clearly outlined on the radiometric map (fig. 8).
In the lower Coastal Plain of South Carolina, highly uraniferous phosphate deposits are
found in the Cooper Group (Force and others, 1978). Fresh sediments from me Cooper Group
average 14.5 ppm uranium for the Oligocene-age samples and 5.6 ppm uranium for the Eocene-age
samples. Secondary enrichment zones in.the Cooper Group contain an average of 60 ppm
uranium. High eU in the vicinity of Charleston and north of the city are probably due to surface
outcrops of, and quarries in, the Cooper Group.
GEOLOGIC RADON POTENTIAL
The Blue Ridg'e'and Piedmont Provinces appear to have moderate geologic radon potential.
Possible sources of radon include uraniferous granites, biotite and granitic gneiss, and shear
zones. Recent work by Speer and others (1992) arid Speer (1992) show that the soils developed
on many of the uraniferous granitic plutons and some fault zones within the Piedmont and Blue
Ridge of North and South Carolina yielded high soil-gas radon concentrations (>1000 pCi/L). Jn
the Blue Ridge, sheared graphitic rocks may be a local source of high radon concentrations.
Graphitic phyllites and schists in other parts of the Piedmont (Maryland and Georgia) are sources
of uranium (McConnell and Costello, 1980) and have high indoor radon levels associated with
them, especially where they are sheared (Gundersen, 1989).
£ Greenville and Oconee Counties, in the Blue Ridge and Piedmont, more than 10 percent
of the homes tested had 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 (fig. 8)
associated with the Ceasers Head Granitic Gneiss of Silurian-Devonian age, and the Carolina
monazite belt within biotite gneiss. 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 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 (fig. 8) 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 geologic radon potential. The rocks have low concentrations of uranium
and soils formed from them have low permeability.
Coastal Plain
uoasiai nam . .. ,
In the Coastal Plain Province, moderate to high radioactivity is associated with the
Cretaceous and Tertiary sediments of the Upper Coastal Plain. A study of the radon in the Coastal
Plain of Texas, New Jersey, and Alabama (Gundersen and Peake, 1992) suggests that glaucomtic,
phosphatic, monazite-rich, and carbonaceous sediments and sedimentary rocks, similar to some of
those in South Carolina, can cause elevated levels of indoor radon. Orangeburg County is the only
other county besides Greenville and Oconee Counties that has an average indoor radon level greater
than 2 pO/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
IV-20 Reprinted from USGS Open-File Report 93-292-D
-------
the? complicated erosion patterns. The few high levels of indoor radon for this county cause the
indoor radon average for the county to be higher overall. These locally high readings may be due
to local accumulations of monazite, glauconite, or phosphate that can occur within these particular
sediments. . F
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
pho^hauc 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 may be
locally high in areas underlain by these uraniferous sediments.
SUMMARY
For the purpose of this assessment, South Carolina has been divided into 6 geologic radon
potential areas and each area assigned a Radon Index (RI) and a Confidence Index (O) score
(Table 2). The RI is a relative measure of radon potential based on geology, soils, radioactivity
architecture, and indoor radon, as outlined in the preceding sections. The CI is a measure of the'
f*f\nfin£*v\f*& f^f +1*4^ KjT —— * i j _ j* •«•. .• _ _ _
discussion of the indexes).
Examination of the indoor radon datareveals that South Carolinais generally an area of low
to moderate radon potential. The Blue Ridge and Piedmont provinces have moderate radon
potential overall; however, highly uraniferous granites, monazite-bearing biotite and granitic
gneiss^ and fault zones of the Blue Ridge and Piedmont may be the source of locally high indoor
radon levels. Other metasedimentary and metavolcanic rocks of the Blue Ridge and Piedmont have
low to moderate potential to produce radon. Sediments of the Coastal Plain have low radon
^ ™^ however monazite-bearing, glauconitic, and phosphatic sediments of the upper
mia^e,andlowerCoastalPlainmaybethesourceoflocallyhighradonlevelsandrnaybe '
responsible for the few elevated indoor radon levels reported in some counties. The climate and
Mestyle of the inhabitants of South Carolina have influenced building construction styles and
building ventilation which, in general, do not allow high concentrations of radon to accumulate
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
not 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. More detailed information
on state or local geology may be obtained from the state geological survey. Addresses and phone
numbers for these agencies are listed in chapter 1 of this booklet.
IV-21 Reprinted from USGS Open-FUe Report 93-292-D
-------
TABLE 2. RI and CI scores for geologic radon potential areas of South Carolina.
Blue Ridge
Piedmont
Charlotte and Carolina
slate belt granites
FACTOR RI
INDOOR RADON 2
RADIOACTIVITY 3
GEOLOGY 2
SOIL PERM. 2
ARCHITECTURE 1
GFE POINTS 0
TOTAL 10
CI
2
3
3
3
11
Mod High
Charlotte and Carolina
slate belt metamorphic rocks
FACTOR RI CI
INDOOR RADON 1
RADIOACTIVITY 2
GEOLOGY 2
SOIL PERM. 2
ARCHITECTURE 1
GFE POINTS 0
Low
2
3
3
3
High
RI
2
3
3
2
1
0
11
a
3
3
3
11
Mod High
Upper
Coastal Plain
RI Q
1
2
2
2
1
0
Low
2
3
3
3
High
RI CI
3 3
3 3
2 3
1
0
11 11
Mod High
Middle and Lower
Coastal Plain
RI CI
1 2
1 3
2 3
2 3
1
0
7 11
RADON INDEX SCORING:
Radon potential category
LOW
MODERATE/VARIABLE
HIGH
Point ranee
3-8 points
9-11 points
> 11 points
Probable screening indoor
radon average for area
<2pCi/L
2-4pCi/L
>4pCi/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-22 Reprinted from USGS Open-File Report 93-292-D
-------
REFERENCES CITED IN THIS REPORT
AND GENERAL REFERENCES PERTAINING TO RADON IN SOUTH CAROLINA
Bennison, A.P., compiler, 1989, Geological Highway Map of the Mid-Atlantic Region: Tulsa,
Oklahoma, American Association of Petroleum Geologists, scale 1:2,000,000.
Butler, J.R., 1991, Metamorphism, in Horton, J.W., Jr., and Zullo, V.A., eds., The Geology of
the Carolinas: Knoxville, University of Tennessee Press, p. 127-141.
Butier, J.R., and Secor, Jr., D.T., 1991, The central Piedmont, in Horton, J.W., Jr., and Zullo,
V.A., eds., The Geology of the Carolinas: Knoxville, University of Tennessee Press
p. 59-78.
Costain, J.K., Speer, J.A., Glover HI, L., 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.
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.
Facts on File Inc., 1984, State Maps on File: Southeast
Feiss, P.G., Maybin, A.H., HI, Riggs, S.R., and Grosz, A.E., 1991, Mineral Resources of the
Carolinas, in Horton, J.W., Jr., and Zullo, V.A., eds., The Geology of the Carolinas:
Knoxville, University of Tennessee Press, p. 319-345.
Force, E.R., Gohn, G.S., Force, L.M., and Higgins, B.B., 1978, Uranium and phosphate
resources in the Cooper Formation of the Charleston Region, South Carolina: South
Carolina Geological Survey, Geological Notes, v. 22, no. 1, p. 17-31.
Gundersen, L. C. S., 1989, Anomalously High Radon in Shear Zones, in Proceedings of the
1988 Symposium on Radon and Radon Reduction Technology, Volume 1, oral
presentations: U.S. Environmental Protection Agency Report EPA/600/9-89/006A
p. 5-27 to 5-44.
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.
Horton Jr., J.W., and Zullo, V. A., eds., 1991, The Geology of the Carolinas: Knoxville,
University of Tennessee Press, 406 p.
King, P.T., Michel, J., and Moore, W.S., 1981, 228R&j 226Ra? and 222^ ^ South Carolina
ground water; lithology controlled isotope distributions: Eos, Transactions, American
Geophysical Union, v. 62, p. 287.
IV-23 Reprinted from USGS Open-FUe Report 93-292-D
-------
Loomis, D.P., Watson, J.E., Jr. and Crawford-Brown, DJ., 1987, Predicting the occurrence of
radon-222 in North Carolina groundwater: University of North Carolina Water Resources
Research Institute Report 230,52 p.
McConnell, K.L, and CosteUo, 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.
McSween, H.Y., Jr., Speer, J.A., and Fullgar, P.D., 1991, Pluronic Rocks, in Horton, J.W.,
Jr., and Zullo, V.A., eds., The Geology of the Carolinas: Knoxville, University of
Tennessee Press, p. 109-126.
Mertie, J.B., Jr. 1953, Monazite deposits of the southeastern Atlantic states: U.S. Geological
Survey Circular 237,31 p.
Nystrom, P.G., Jr., Willoughby, R.H., and Price, L.K., 1991, Cretaceous and Tertiary
Stratigraphy of the upper Coastal Plain, South Carolina, in Horton, J.W., Jr., and Zullo,
V.A., eds., The Geology of the Carolinas: Knoxville, University of Tennessee Press,
p. 221-240.
Overstreet, W.C., and Bell, H., HI, 1965a, The Crystalline Rocks of South Carolina: U.S.
Geological Survey Bulletin, 1183,126p., 4 plates.
Overstreet, W.C., and Bell, H., m, 1965b, The Crystalline Rocks of South Carolina: U.S.
Geological Survey Miscellaneous Investigations Map 1-413, scale 1:250,000.
Owens, J.P., Grosz, A.E., and Fisher, J.C., 1989, Aeroradiometric map and geologic
interpretation of part of the Florence-Georgetown 1° x 2° quadrangles, South Carolina:
U.S. Geological Survey Miscellaneous Investigations Map I-1948-B, scale 1:250,000.
Owens, J.P., 1989, Geologic map of the Cape Fear region, Florence 1X2 Quadrangle and
northern half of the Georgetown 1X2 Quadrangle, North Carolina and South Carolina:
U.S. Geological Survey Miscellaneous Investigations Map I-1948-A, scale 1:250,000.
Richmond, G.M., Fullerton, D.S., and Weide, D.L., editors, 1987, Quaternary geologic map of
the Savannah 4° x 6° quadrangle, United States: U.S. Geological Survey Miscellaneous
Investigations Map 1-1420 (NI-17), scale 1:1,000,000.
Sheridan, R.E. and Grow, J.A., 1988, The Atlantic Coastal Margin: US: The Geology of North
America, Volume 1-2: Geological Society of America, 610 p.
Smith, B.R., and Hallbick, D.C., 1979, General soil map of South Carolina: South Carolina
Agricultural Experiment Station Soil Map 48, scale 1:750,000.
Seller, D.R., and Mills, H.H., 1991, Surficial Geology and Geomorphology, in Horton, J.W.,
Jr., and Zullo, V.A., eds., The Geology of the Carolinas: Knoxville, University of
Tennessee Press, p. 290-308.
IV-24 Reprinted from USGS Open-FHe Report 93-292-D
-------
Sohl, N.F., and Owens. J.P., 1991, Cretaceous Stratigraphy of the Carolina Coastal Plain, in
Horton,J.W., Jr.,. and ZuUo,V.A.,eds., The Geology of the Carolinas: Knoxville,
University of Tennessee Press, p. 191-220. '
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 14-08-0001-AO742,unpub. file report, 67 p.
Speer, J.A., Burtwell, G.T., and Doulgas, 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.
Talwani, P., and Van Nieuwenhuise, R.E., 1981, Water level and geochemical anomalies at Lake
Jocassee, South Carolina: Eos, Transactions, American Geophysical Union, v 62
p. 1035.
IV-25 Reprinted from USGS Open-File Report 93-292-D
-------
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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.)
SOUTH CAROT.TNA MAP OF PAr»r>N 7Q>TFc;
The South Carolina Map of Radon Zones and its supporting documentation (Part IV of
this report) have received extensive review by South Carolina geologists and radon program
experts. The map for South Carolina generally reflects current State knowledge about radon
for its counties. Some States have been able to conduct radon investigations in areas smaller
than geologic provinces and counties, so it is important to consult locally available data
One county designation does not strictly follow this methodology for adapting the
geologic provinces to county boundaries. EPA and the South Carolina Department of Health
and Environmental Control have decided to designate Greenville county as Zone 1 because
many elevated levels of indoor radon have been recorded from this county. Also, some areas
of Greenville county have significant surficial radioactivity readings from the NURE data that
can cause elevated indoor radon levels.
Although the information provided in Part IV of this report - the State chapter entitled
Preliminary Geologic Radon Potential Assessment of South Carolina" ,- may appear to be
quite specific, it cannot be applied to determine the radon levels of a neighborhood housing
tract, individual house, etc. THE ONLY WAY TO DETERMINE IF A HOUSE?HAS
ELEVATED INDOOR RADON IS TO TEST. Contact the Region 4 EPA office or the
South 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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