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Air and Radiation
EPA EPA's Map of Radon Zones
VIRGINIA
Printed on Recycled Paper
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EPA'S MAP OF RADON ZONES
VIRGINIA
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, Kcndell 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
ASSESSMENTSrINTRODUCnON
III. REGION 3 GEOLOGIC RADON POTENTIAL
SUMMARY
V. PRELIMINARY GEOLOGIC RADON POTENTIAL
ASSESSMENT OF VIRGINIA
V. EPA'S MAP OF RADON ZONES - VIRGINIA
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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-counry 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, USGS' 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.
1-1
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Purpose of the Map of Radon Zones
EPA's Map of Radon Zones (Figure 1) assigns each of the 3141 counties in the
United States to one of three zones:
o Zone 1 counties have a predicted average indoor screening level > than
4pCi/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.
Development 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
1-2
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Figure 1
EPA Map of Radon Zones
Zone designation for Puerto Rico is under development
Zone 2
Zone 3
Guam Preliminary Zone designation. f^ The purpose of this mop is to assist National, State and local organizations to target their resources and to implement radon-resistant building codes.
This map is not intended to be used to determine if a home in a given zone should be tested for radon. Homes with elevated levels of radon have been found
in all three zones. All homas should be tested, regardless of geographic location.
IMPORTANT: Consult the EPA Mop of Radon Zones document (EPA—402—R—93—071) before using this mop. This document contains information on radon potential variations within counties.
EPA also recommends that this mop be supplemented with any available local data in order to further understand and predict the radon potential of o specific area.
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Figure 2
GENERALIZED GEOLOGIC RADON POTENTIAL OF THE UNITED STATES
by the U.S. Geological Survey
^*i'-.-.sr &9^HV>^B
$&&$§&&&&&*&>
ScaJe
Continent^ United States
and Hawaii
500
Geologic Radon
Potential
(Predicted Average
Screening Measurement)
LOW (<2pCI/L)
1 MODERATE/VARIABLE
HIGH (>4pCI/L)
Miles
6/93
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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 Pai t II of this document
EPA subsequently developed the Map of Radon 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 basjc 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
The Map of Radon Zones is intended to be a starting point for characterizing radon
potential because our knowledge of radon sources and transport is always growing. Although
this effort represents the best data available at this time, EPA will continue to study these
parameters and others such as house construction, ventilation features and meteorology factors
in order to better characterize the presence of radon in U.S homes, especially in high risk
areas. These efforts will eventually assist EPA in refining and revising the conclusions of the
Map of Radon Zones. And although this map is most appropriately used as a targeting tool
by the aforementioned audiences — the Agency encourages all residents to test their homes
for radon, regardless of geographic location or the zone designation of the county in
which they live. Similarly, the Map of Radon Zones should not to be used in lieu of
testing during real estate transactions.
Review Process
The Map of Radon Zones has undergone extensive review within EPA and outside the
Agency. The Association of American State Geologists (AASG) played an integral role in
this review process. The AASG individual State geologists have reviewed their State-specific
information, the USGS Geologic Radon Province Map, and other materials for their geologic
content and consistency.
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Figure 3
Geologic Radon Potential Provinces for Nebraska
Li acola County
iteierttt
ton
Figure 4
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
*y
Linda C.S. Gtmdersen 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/or
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 genera! geology and geologic radon potential
of the EPA Region (Part III). The fourth component is an individual chapter for each state
(Part IV). Each state chapter discusses the state's specific geographic setting, soils, geologic
setting, geologic radon potential, indoor radon data, and a summary outlining the radon
potential rankings of geologic areas in the state. A variety of maps are presented in each
chapter—geologic, geographic, population, soils, aerial radioactivity, and indoor radon data by
county. Finally, the booklets contain EPA's map of radon zones for each state and an
accompanying description (Part V).
Because of constraints on the scales of maps presented in these reports and because the
smallest units used to present the indoor radon data are counties, some generalizations have
been made in order to estimate the radon potential of each area. Variations in geology, soil
characteristics, climatic factors, homeowner lifestyles, and other factors that influence radon
concentrations can be quite large within any particular geologic area, so these reports cannot
be used to estimate or predict the indoor radon concentrations of individual homes or housing
II-l Reprinted from USGS Open-File Report 93-292
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tracts. Within any area of a given geologic radon potential ranking, there are likely to be
areas where the radon potential is lower or higher than that assigned to the area as a whole,
especially in larger areas such as the large counties in some western states.
In each state chapter, references to additional reports related to radon are listed for the
state, and the reader is urged to consult these 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 (22iRn) is produced from the radioactive decay of radium (225Ra), which is, in turn,
a product of the decay of uranium (238U) (fig, 1). The half-life of 222Rn is 3,825 days. Other
isotopes of radon occur naturally, but, with the exception of thoron (JWRn), which occurs in
concentrations high enough to be of concern in a few localized areas, they are less important
in terms of indoor radon risk because of their extremely short half-lives and less common
occurrence. In general, the concentration and mobility of radon in soil are dependent on
several factors, the most important of which are the soil's radium content and distribution,
porosity, permeability to gas movement, and moisture content. These characteristics are, in
turn, determined by the soil's parent-material composition, climate, and the soil's age or
maturity. If parent-material composition, climate, vegetation, age of the soil, and topography
are known, the physical and chemical properties of a soil in a given area can be predicted.
As soils form, they develop distinct layers, or horizons, that are cumulatively called the
soil profile. The A horizon is a surface or near-surface horizon containing a relative
abundance of organic matter but dominated by mineral matter. Some soils contain an E
horizon, directly below the A horizon, that is generally characterized by loss of clays, iron, or
aluminum, and has a characteristically lighter color than the A horizon. The B horizon
underlies the A or E horizon. Important characteristics of B horizons include accumulation of
clays, iron oxides, calcium carbonate or other soluble salts, and organic matter complexes. In
drier environments, a horizon may exist within or below the B horizon that is dominated by
calcium carbonate, often called caliche or calcrete. This carbonate-cemented horizon is
designated the K horizon in modern soil classification schemes. The C horizon underlies the
B (or K) and is a zone of weathered parent material that does not exhibit characteristics of A
or B horizons; that is, it is generally not a zone of leaching or accumulation. In soils formed
in place from the underlying bedrock, the C horizon is a zone of unconsolidated, weathered
bedrock overlying the unweathered bedrock.
The shape and orientation of soil particles (soil structure) control permeability and affect
water movement in the soil. Soils with blocky or granular structure have roughly equivalent
permeabilities in the horizontal and vertical directions, and air and water can infiltrate the soil
relatively easily. However, in soils with platy structure, horizontal permeability is much
greater than vertical permeability, and air and moisture infiltration is generally slow. Soils
with prismatic or columnar structure have dominantly vertical permeability. Platy and
prismatic structures form in soils with high clay contents. In soils with shrink-swell clays, air
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Uranium-SOS
4.51 billion years
247,000 years
p \ProtactInlum-234
Uranlum-234
Lead-206
STABLE
138.4 days
Figure 1. The uranium-238 decay series, showing the half-lives of elements and their modes of decay (after Wanty and
Schoen, 1991). a denotes alpha decay, p denotes beta decay.
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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's meters), or about 2x10* inches—this is known as alpha
recoil (Tanner, 1980). Moisture in the soil lessens the chance of a recoiling radon atom
becoming imbedded in an adjacent grain. Because water is more dense than air, a radon atom
will travel a shorter distance in a water-filled pore than in an air-filled pore, thus increasing
the likelihood that the radon atom will remain in the pore space. Intermediate moisture levels
enhance radon emanation but do not significantly affect permeability. However, high
moisture levels can significantly decrease the gas permeability of the soil and impede radon
movement through the soil.
Concentrations of radon in soils are generally many times higher than those inside of
buildings, ranging from tens of pCi/L to more than 100,000 pCi/L, but typically in the range
of hundreds to low thousands of pCi/L. Soil-gas radon concentrations can vary in response to
variations in climate and weather on hourly, daily, or seasonal time scales. Schumann and
others (1992) and Rose and others (1988) recorded order-of-magnitude variations in soil-gas
radon concentrations between seasons in Colorado and Pennsylvania. The most important
factors appear to be (1) soil moisture conditions, which are controlled in large part by
precipitation; (2) barometric pressure; and (3) temperature. Washington and Rose (1990)
suggest that temperature-controlled partitioning of radon between water and gas in soil pores
also has a significant influence on the amount of mobile radon in soil gas.
Homes in hilly limestone regions of the southern Appalachians were found to have higher
indoor radon concentrations during the summer than in the winter. A suggested cause for this
phenomenon involves temperature/pressure-driven flow of radon-laden air from subsurface
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solution cavities in the carbonate rock into houses. As warm air enters solution cavities that
are higher on the hillslope than the homes, it cools and settles, pushing radon-laden air from
lower in the cave or cavity system into structures on the hillslope (Gammage and others,
1993). In contrast, homes built over caves having openings situated below the level of the
home had higher indoor radon levels in the winter., caused by cooler outside air entering the
cave, driving radon-laden air into cracks and solution cavities in the rock and soil, and
ultimately, into homes (Gammage and others, 1993).
RADON ENTRY INTO BUILDINGS
A driving force (reduced atmospheric pressure in the house relative to the soil, producing
a pressure gradient) and entry points must exist for radon to enter a building from the soil.
The negative pressure, caused by furnace combustion, ventilation devices, and the stack effect
(the rising and escape of warm air from the upper floors of the building, causing a
temperature and pressure gradient within the structure) during cold winter months are
common driving forces. Cracks and other penetrations through building foundations, sump
holes, and slab-to-foundation wall joints are common entry points.
Radon levels in the basement are generally higher than those on the main floor or upper
floors of most structures. Homes with basements generally provide more entry points for
radon, commonly have a more pronounced stack effect, and typically have lower air pressure
relative to the surrounding soil than nonbasement homes.. The term "nonbasement" applies to
slab-on-grade or crawl space construction.
METHODS AND SOURCES OF DATA
The assessments of radon potential in the booklets that follow this introduction were
made using five main types of data: (1) geologic (lithologic); (2) aerial radiometric; (3) soil
characteristics, including soil moisture, permeability, and drainage characteristics; (4) indoor
radon data; and (5) building architecture (specifically, whether homes in each area are built
slab-on-grade or have a basement or crawl space). These five factors were evaluated and .
integrated to produce estimates of radon potential. Field measurements of soil-gas radon or
soil radioactivity were not used except where such data were available in existing, published
reports of local field studies. Where applicable, such field studies are described in the
individual state chapters.
GEOLOGIC DATA
The types and distribution of lithologic units and other geologic features in an
assessment area are of primary importance in determining radon potential. Rock types that
are most likely to cause indoor radon problems include carbonaceous black shales, glauconite-
bearing sandstones, certain kinds of fluvial sandstones and fluvial sediments, phosphorites,
chalk, karst-productng 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
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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 (JHBi), 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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FLICOT LINE SPACING OF NUKE AERUI SURVEYS
2 KM (i KILE)
5 IH (3 MILES)
2 t 5 IU
ES 10 £11 {€ HUES)
5 4- 19 IH
NO DiTA
Figure 2. Nominal flightline spacings for NURE aerial gamma-ray surveys covering die
contiguous United States (from Duval and others, 1990). Rectangles represent I°x2° quadrangles.
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Figure 2 is an index map of NUKE 1° x 2° quadrangles showing the flight-line spacing
for each quadrangle. In general, the more closely spaced the flightlines are, the more area
was covered by the aerial gamma survey, and thus, more detail is available in the data set
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 in/hr are not truly units of permeability, these units are in widespread use and
are referred to as "permeability" in SCS soil surveys. The permeabilities listed in the SCS
surveys are for water, but they generally correlate well with gas permeability. Because data
on gas permeability of soils is extremely limited, data on permeability to water is used as a
substitute except in cases in which excessive soil moisture is known to exist. Water in soil
pores inhibits gas transport, so the amount of radon available to a home is effectively reduced
by a high water table. Areas likely to have high water tables include river valleys, coastal
areas, and some areas overlain by deposits of glacial origin (for example, loess).
Soil permeabilities greater than 6.0 in/hr may be considered high, and permeabilities less
than 0.6 in/hr may be considered low in terms of soil-gas transport. Soils with low
permeability may generally be considered to have a lower radon potential than more
permeable soils with similar radium concentrations. Many well-developed soils contain a
clay-rich B horizon that may impede vertical soil gas transport. Radon generated below this
horizon cannot readily escape to the surface, so it would instead tend to move laterally,
especially under the influence of a negative pressure exerted by a building.
Shrink-swell potential is an indicator of the abundance of smectitic (swelling) clays in a
soil. Soils with a high shrink-swell potential may cause building foundations to crack,
creating pathways for radon entry into the structure. During dry periods, desiccation cracks in
shrink-swell soils provide additional pathways for soil-gas transport and effectively increase
the gas permeability of the soil. Soil permeability data and soil profile data thus provide
important information for regional radon assessments.
INDOOR RADON DATA
Two major sources of indoor radon data were used. The first and largest source of data is
from the State/EPA Residential Radon Survey (Ronca-Battista and others, 1988; Dziuban and
others, 1990). Forty-two states completed EPA-sponsored indoor radon surveys between 1986
and 1992 (fig. 3). The State/EPA Residential Radon Surveys were designed to be
comprehensive and statistically significant at the state level, and were subjected to high levels
of quality assurance and control. The surveys collected screening indoor radon measurements,
defined as 2-7 day measurements using charcoal canister radon detectors placed in the lowest
livable area of the home. The target population for the surveys included owner-occupied
single family, detached housing units (White and others, 1989), although attached structures
such as duplexes, townhouses, or condominiums were included in some of the surveys if they
met the other criteria and had contact with the ground surface. Participants were selected
randomly from telephone-directory listings. In total, approximately 60,000 homes were tested
in the State/EPA surveys.
The second source of indoor radon data comes from residential surveys that have been
conducted in a specific state or region of the country (e.g. independent state surveys or utility
company surveys). Several states, including Delaware, Florida, Illinois, New Hampshire, New
Jersey, New York, Oregon, and Utah, have conducted their own surveys of indoor radon. The
quality and design of a state or other independent survey are discussed and referenced where
the data are used.
II-9 Reprinted from USGS Open-File Report 93-292
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Page Intentionally Blank
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The Slate*
These results arc based on 1-1 day screening
measurements in the lowest livable level and should not
be used to estimate annual averages or health risks.
Figure 3. Percent of homes tested in the State/EPA Residential Radon Survey with screening indoor radon levels exceeding 4 pCi/L.
-------
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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
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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
<2pO/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 4-2 points
MODERATE +1 point
LOW -2 points
No relevant geologic field studies 0 points
SCORING: Probable average screening
indoor radon for area
LOW
MODERATE/VARIABLE
HIGH
3-8 points
9-11 points
12-17 points
<2pCi/L
2-4pCi/L
>4pC3/L
POSSIBLE RANGE OF POINTS = 3 to 17
TABLE 2. CONFIDENCE INDEX MATRIX
INCREASING CONFIDENCE
FACTOR
INDOOR RADON DATA
AERIAL RADIOACTIVITY
GEOLOGIC DATA
SOIL PERMEABILITY
POINT VALUE
1
sparse/no data
questionable/no data
questionable
questionable/no data
2
fair coverage/quality
glacial cover
variable
variable
3
good coverage/quality
no glacial cover
proven geol. model
reliable, abundant
SCORING:
LOW CONFIDENCE
MODERATE CONFIDENCE
HIGH CONFIDENCE
4-6 points
7-9 points
10 -12 points
POSSIBLE RANGE OF POINTS « 4 to 12
n-12 Reprinted from USGS Open-File Report 93-292
-------
included as supplementary information and are discussed in the individual State chapters. If
the average screening indoor radon level for an area was less than 2 pCi/L, the indoor radon
factor was assigned 1 point, if it was between 2 and 4 pCi/L» it was scored 2 points, and if
the average screening indoor radon level for an area was greater than 4 pCi/L, the indoor
radon factor was assigned 3 RI points.
Aerial radioactivity data used in this report are from the equivalent uranium map of the
conterminous United States compiled from 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 'mv aerial
radiometric signature and score only one RI point in that category. However, data from
geologic field studies in North Dakota and Minnesota (Schumann and others, 1991) suggest
that eU is a poor predictor of geologic radon potential in this area because radionuclides have
11-13 Reprinted from USGS Open-File Report 93-292
-------
been leached from the upper soil layers but are present and possibly even concentrated in
deeper soil horizons, generating significant soil-gas radon. This positive supporting field
evidence adds two GFE points to the score, which helps to counteract the invalid conclusion
suggested by the radiometric data. No GFE points are awarded if there are no documented
field studies for the area.
"Soil permeability" refers to several soil characteristics that influence radon concentration
and mobility, including soil type, grain size, structure, soil moisture, drainage, slope, and
permeability. In the matrix, "low" refers to permeabilities less than about 0.6 in/hr; "high"
corresponds to greater than about 6.0 in/hr, in U.S. Soil Conservation Service (SCS) standard
soil percolation tests. The SCS data are for water permeability, which generally correlates
well with the gas permeability of the soil except when the soil moisture content is very high.
Areas with consistently high water tables were thus considered.to have low gas permeability.
"Low, "moderate", and "high" permeability were assigned 1, 2, and 3 points, respectively.
Architecture type refers to whether homes in the area have mostly basements (3 points),
mostly slab-on-grade construction (1 point), or a mixture of the'two. Split-level and crawl
space homes fall into the "mixed" category (2 points). Architecture information is necessary
to properly interpret the indoor radon data and produce geologic radon potential categories
that are consistent with screening indoor radon data.
The overall 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 on the basis of
the quality and quantity of the data used to complete the RI matrix.
Indoor radon data were evaluated based on the distribution and number of data points and
on whether the data were collected by random 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 geologH 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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Gundersen, L.C.S., eds., Geologic controls on radon: Geological Society of America
Special Paper 271, p. 65-72.
Sextro, R.G., Moed, B.A., Nazaroff, W.W., Revzan, K.L., and Nero, A.V., 1987,
Investigations of soil as a source of indoor radon, in Hopke, P.K., ed., Radon and its
decay products: American Chemical Society Symposium Series 331, p. 10-29.
Sterling, R., Meixel, G., Shen, L., Labs, K., and Bligh, T., 1985, Assessment of the energy
savings potential of building foundations research: Oak Ridge, 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, T.F.,
and Lowder, W.M. (eds), Natural radiation environment JH, Symposium proceedings,
Houston, Texas, v. 1, p. 5-56.
U.S. Department of Agriculture, 1987, Principal kinds of soils: Orders, suborders, and great
groups: U.S. Geological Survey, National Atlas of the United States of America, sheet
38077-BE-NA-07M-00, scale 1:7,500,000.
U.S. Department of Energy, 1976, National Uranium Resource Evaluation preliminary report,
prepared by the U.S. Energy Research and Development Administration, Grand Junction,
Colo.: GJO-11(76).
Wanty, Richard B., and Schoen, Robert, 1991, A review of the chemical processes affecting the
mobility of radionuclides in natural waters, with applications, in Gundersen, Linda C.S.,
and Richard B. Wanty, eds., Field studies of radon in rocks, soils, and water: U.S.
Geological Survey Bulletin no. 1971, p. 183-194.
Washington, J.W., and Rose, A.W., 1990, Regional and temporal relations of radon in soil gas to
soil temperature and moisture: Geophysical Research Letters, v. 17, p. 829-832.
White, S.B., Bergsten, J.W., Alexander, B.V., and Ronca-Battista, M., 1989, Multi-State
surveys of indoor 222Rn: Health Physics, v. 57, p. 891-896.
11-19 Reprinted from USGS Open-File Report 93-292
-------
Page Intentionally Blank
-------
APPENDIX A
GEOLOGIC TIME SCALE
Subdivisions (and their symbols)
Eon or
Eonothem
Phaneroioic*
Proteroioic
IP)
Archean
(Al
Era or
Erathem
Cenozoic 2
(Cx)
Mesozoic2
(Mi)
Paleozoic3
' lew.
M«OI»
PwiJeSeJW
AfWwJJlWl
MlOOK
Arah*«n(Vl
t»"y
Period, System,
Subporiod. Subsystem
Quaternary
(Q!
Neojene 2
Subceriod or
Tertiary Subsytttm (N!
j
Subetriodor
Subsytttm |Pi>
Cretaceous
Jurassic
(J)
Triassic
(TO
Permian
Pennsylvanian
Carboniferous (P)
'^-' Mississippian
(M)
Devonian
(D)
Silurian
Ordovician
•
Cambrian
tCJ
Epoch or Series
Hotocene
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
Uooer
Middle
Lower
Upper
Middle
Lower
Upper
Middle
Lower
Upper
Middle
Lower
None defined
None defined
None defined
None defined
None defined
None defined
pr^ArclM.n tpAl *
Age estimates
of boundaries
in mega-annum
(Mai1
^— ,,. J1A UAg_J^g^
-570s
reflect une*rtaint Decay constant* and ootoptc ratios ernployed va ctl»d in Sl»is*r *nd Jlgw (1ST?}. Dwignation m.y. ue*d tar an
int«rvej of lime.
*Modffi*rs (tow»r, middle, upper or early, middle, late) whin used with thts* Hems are informal division* of the larger unit; the
first totter of the modifier is lowercase.
'Racks elder than 570 Ma also called Pncambrian (p-C). a time term without spetifie rank.
'informal time term without apetific unk.
USGS Open-Hie Report 93-292
-------
Page Intentionally Blank
-------
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 pCS/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. Hie 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
men divided by the time (in hours) to determine the permeability. Soils range in permeability from
less than 0.06 in/hr to greater then 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-trade detector A passive radon measurement device consisting of a plastic film that is
sensitive to alpha particles. The film is etched with acid in a laboratory after it is exposed. The
etching reveals scratches, or "tracks", left by the alpha particles resulting from radon decay, which
can then be counted to calculate the radon concentration. Useful for long-term (1-12 months)
radon tests.
amphibolite A mafic metamorphic rock consisting mainly of pyroxenes and(or) amphibole and
plagioclase.
II-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, Le., 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 mat 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.
day A rock containing clay mineral fragments or material of any composition having a diameter
less man 1/256 mm.
day 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-Hie Repent 93-292
-------
delta, deltaic Referring to a low, flat, alluvial tract of land having a triangular or fan shape,
located at or near the month 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 Hie 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 mappablebpdy 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 tenses of different composition, giving the rock a striped or
"foliated" appearance.
granite Broadly applied, any coarsely crystalline, quartz- and feldspar-bearing igneous plutonic
rock. Technically, granites have between 10 and 50% quartz, and alkali feldspar comprises at least
65% of the total feldspar.
gravel An unconsolidated, natural accumulation of rock fragments consisting predominantly of
particles greater than 2 mm in size.
heavy minerals Mineral grains in sediment or sedimentary rock having higher than average
specific gravity. May form layers and lenses because of wind or water sorting by weight and size
11-23 Reprinted from USGS Open-File Report 93-292
-------
and may be referred to as a "placer deposit" Some heavy minerals are magnetite, garnet, zircon,
monazite, and xenotime.
igneous Said of a rock or mineral that solidified from molten or partly molten rock material. It is
one of the three main classes in.o which re. ~» are did ". Hie others tx..ng sedimentary and
mctamorphic.
intermontane A term that refers to an area between two mountains or mountain ranges.
intrusion, intrusive Hie 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
subbiturninous 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 man 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
PhylMte, 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.
JTJ-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 geomorpnic history, and whose topography or landforms differ
significantly from adjacent regions.
,>lacer deposit See heavy minerals
residual Formedby weathering of a material in place.
residuum Deposit of residual material.
rhyolite An extrusive igneous rock of volcanic origin, compositionally equivalent to granite.
sandstone A clastic sedimentary rock composed of sand-sized rock and mineral material mat is
more or less firmly cemented. Sand particles range from 1/16 to 2 mm in size.
schist A strongly foliated crystalline rock, formed by metamorphism, that can be readily split into
thin flakes or slabs. Contains mica; minerals are typically aligned.
screening level Result of an indoor radon test taken with a charcoal canister or similar device,
for a short period of time, usually less than seven days. May indicate the potential for an indoor
radon problem but does not indicate annual exposure to radon.
sediment Deposits of rock and mineral particles or fragments originating from material that is
transported by air, water or ice, or that accumulate by natural chemical precipitation or secretion of
organisms.
semiarid Refers to a climate mat 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 en the
earth's surface.
tablelands General term for a broad, elevated region with a nearly level surface of considerable
extent
IE-25 Reprinted from USGS Open-File Report 93-292
-------
terrace gravel Gravel-sized material that caps ridges and terraces, left behind by a stream as it
cute 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 mis report to refer to indoor radon dam 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.
1-26 Reprinted from USGS Open-File Report 93-292
-------
APPENDIX C
EPA REGIONAL OFFICES
EPA Regional Offices
State
EPA Region
EPA Region 1
JFK Federal Building
Boston, MA 02203
(617) 565-4502
EPA Region 2
(2AIR:RAD)
26 Federal Plaza
New York, NY 10278
(212) 264-4110
Region 3 (3AH14)
841 Chestnut Street
Philadelphia, PA 19107
(215) 597-8326
EPA Region 4
345 Courtland Street, RE.
Atlanta, GA 30365
(404) 347-3907
EPA Region 5 (5AR26)
77 West Jackson Blvd.
Chicago, IL 60604-3507
(312) 886-6175
EPA Region 6 (6T-AS)
1445 Ross Avenue.
Dallas, TX 75202-2733 .
(214) 655-7224
EPA Region 7
726 Minnesota Avenue
Kansas City, KS 66101
(913) 551-7604
EPA Region 8
(8HWM-RP)
999 18th Street
One Denver Place, Suite 1300
Denver, CO 80202-2413
(303) 293-1713
EPA Region 9 (A-3)
75 Hawthorne Street
San Francisco, CA 94105
(415) 744-1048
EPA Region 10
1200 Sixth Avenue
Seattle, WA 98101
(202) 442-7660
Alabama 4
Alaska 10
Arizona 9
Arkansas 6
California 9
Colorado 8
Connecticut 1
Delaware 3
District of Columbia 3
Florida 4
Georgia 4
Hawaii 9
Idaho 10
Illinois 5
Indiana 5
Iowa 7
Kansas : 7
Kentucky 4
Louisiana 6
Maine 1
Maryland..... 3
Massachusetts 1
Michigan 5
Minnesota 5
Mississippi 4
Missouri 7
Montana 8
Nebraska 7
Nevada 9
New Hampshire 1
New Jersey 2
New Mexico 6
New York 2
North Carolina 4
North Dakota 8
Ohio ....5
Oklahoma ...6
Oregon 10
Pennsylvania 3
Rhode Island 1
South Carolina 4
South Dakota 8
Tennessee 4
Texas '. 6
Utah 8
Vermont 1
Virginia 3
Washington 10
West Virginia 3
Wisconsin 5
Wyoming 8
n-27 Reprinted from USGS Open-File Report 93-292
-------
STATE RADON CONTACTS
May, 1993
Atahama 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
Alaska ChadesTedford
Department of Health and Social
Services
P.O. Box 110613
Juncau.AK 99811-0613
(907)465-3019
1-800-478-4845 in state
Arizona John Stewart
Arizona Radiation Regulatory Agency
4814 South 40th St.
Phoenix, AZ 85040
(602)255-4845
Arkansas LeeGershnei
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
Rpbert Davis
of Columbia DC Department of Consumer and
Regulatory Affairs
614 H Street NW
Room 1014
Washington, DC 20001
(202)727-71068
Honda N. Michael Gffley
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
Georgia Richard Schreiber
Georgia Department of Human . .
Resources
878 Peachtree St., Room 100
Atlanta, GA 30309
(404) 894-6644
1-800-745-0037 in state
Haaaii Russell Takata
Environmental Health Services
Division
591 Ala Moana Boulevard
Honolulu, HI 96813-2498
(808)5864700
E-28
Reprinted from USGS Open-File Report 93-292
-------
Idaho
Illinois
Indiana
Kansas
Kentucky
PalMcGavarn
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
017)633-8563
1-800-272-9723 to State
Donald A. Plater
Bureau of Radiological Health
Iowa Department of Public Health
Lucas State Office Building
Des Moines, IA 503194)075
(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
Topcka, 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 Bob Stilwell
Division of Health Engineering
Department of Human Services
State House, Station 10
Augusta, ME 04333
(207)289-5676
1-800-232-0842 in state
Maryland Leon J. Rachuba
Radiological Health Program
Maryland Department of the
Environment
2500 Broening Highway
Baltimore, MD 21224
(410)631-3301
1-800-872-3666 In State
Massachusetts William I. Bell
Radiation Control Program
Department of Public Health
23 Service Center
Northampton, MA 01060
(413)586-7525
1-800445-1255 in state
Michigan SueHendershott
Division of Radiological Health
Bureau of Environmental and
Occupational Health
3423 North Logan Street
P.O. Box 30195
Lansing, MI 48909
(517)335-8194
Minnesota Laura Oatmann
Indoor Air Quality Unit
925 Delaware Street, SB
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
-------
Mississii
Missouri;
Montana
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
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
Adrian C. Howe
Occupational Health Bureau
Montana Department of Health and
Environmental Sciences
Cogswell Building A113
Helena, MT 59620
(406)444-3671
Joseph Milone
Division of Radiological Health
Nebraska Department of Health
301 Centennial Mall, South
P.O. Box 95007
Lincoln, NE 68509
(402)471-2168
1-800-334-9491 In State
Stan Marshall
Department of Human Resources
505 East King Street
Room 203
Carson City.NV 89710
(702)687-5394
ftfga? Hampshire David Chase
Bureau of Radiological Health
Division of Public Health Services
Heal thandWelfere Building
Six Hazen Drive
Concord, NH 03301
(603)271-4674
1-800-852-3345 x4674
Nebraska
New Jersey Tonalee Carlson Key
Division of Environmental Quality
Department of Environmental
Protection
GN415
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 SL Francis Drive
Santa Fe,NM 87503
(505)827-4300
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 stale
North Carolina Dr. Felix Fong
Radiation Protection Division
Department of Environmental Health
and Natural Resources
701 Barbour Drive
Raleigh, NC 27603-2008
(919)571-4141
1-800462-7301 (recorded info x4 1%)
North Dakota Alien Jacobson
North Dakota Department of Health
1200 Missouri Avenue, Room 304
P.O. Box 5520
Bismarck, ND 58502-5520
(701)221-5188
Ohio Martie Matthews
Radiological Health Program
Department of Health
1224 Kinnear Road - Suite 120
Columbus, OH 43212
(614)644-2727
1-800-523-4439 in state
H-30
Reprinted from 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 In State
David SaWana
Radiological Health Division
GJP.O. Call Box 70184
Rio Piedras, Puerto Rico 00936
(809) 767-3563
Edmund Arcand
Division of Occupational Health and
Radiation
Department of Health
205 Cannon Building
Davis Street
Providence, RI02908
(401)277-2438
Bureau of Radiological Health
Department of Health and
Environmental Control
2600 Bull Street
Columbia, SC 29201
(803)734-4631
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, IN 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 JohnHultquist
Bureau of Radiation Control
Utah State Department of Health
288 North, 1460 West
P.O. Box 16690
Salt Lake City.UT 84116-0690
(801)536-4250
Vermont Paul demons
Occupational and Radiological Health
Division
Vermont Department of Health
10 Baldwin Street
Montpelier, VT 05602
(802)828-2886
1-800-640-0601 in state
Virgin Islands Contact the U.S. Environmental
Protection Agency, Region n
in New York
(212)264-4110
H-31
Reprinted from USGS Open-File Report 93-292
-------
Washington
West Virina
Wyoming
Shelly Ottenbnte
Bureau of Radiological Health
Department of Health
109 Governor Street
Richmond, VA 23219
(804) 786-5932
1-800-468-0138 In state
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
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 to State
Conrad Weiffenbach
Radiation Protection Section
Division of Health
Department of Health and Social
Services
P.O. Box 309
Madison, WI 53701-0309
(608)267-4796
1-800-798-9050 to state
Janet Hough
Wyoming Department of Health and
Social Services
Halhway Building, 4th Floor
Cheyenne, WY 82002-0710
(307)777-6015
1-800-458-5847 in state
11-32 Reprinted from USGS Open-Hie Report 93-292
-------
STATE GEOLOGICAL SURVEYS
May, 1993
Alabama Ernest A. Mancini
Geological Survey of Alabama
P.O. Box 0
420 Hackberry 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
Larry D. Fellows
Arizona Geological Survey
845 North Park Ave., Suite 100
Tucson, AZ 85719
(602)882-4795
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, DE19716-7501
(302)831-2833
Florida Walter Schmidt
Florida Geological Sr*vey
903 W. Tennessee St
Tallahassee, FL 32304-7700
(904)488-4191
William H. McLemore
Georgia Geologic Survey
Rm. 400
19 Martin Luther King Jr. Dr. SW
Atlanta, GA 30334
(404)656-3214
Hawaii Manabu Tagomori
Dent, 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
Morrill Hall, Rm. 332
Moscow, ID 83843
(208) 885-7991
Illinois Morris W. Leighton
Illinois State Geological Survey
Natural Resources Building
615 East Peabody Dr.
Champaign, IL 61820
(217)333^*747
Indiana Norman C. Hester
Indiana Geological Survey
611 Norm Walnut Grove
Bloomington, IN 47405
(812)855-9350
|owa Donald L.Koch
Iowa Department of Natural Resources
Geological Survey Bureau
109 Trowbridge Hall
Iowa City, JA 52242-1319
(319)335-1575
Kansas Lee C. Gerhard
Kansas Geological Survey
1930 Constant Ave., West Campus
University of Kansas
Lawrence, KS 66047
(913)864-3965
n-33
Reprinted from USGS Open-File Report 93-292
-------
Maine
Kentucky Donald CHaney
Kentucky Geological Sinvey
University of Kentucky
228 Mining & Mineral Resources
Building
. Lexington, KY 40506-0107
(606)257-5500
William E. Marsalis
Louisiana Geological Survey
P.O. Box 2827
University Station
Baton Rouge, LA 70821-2827
(504)388-5320
Walter A. Anderson
Maine Geological Survey
Department of Conservation
State House, Station 22
Augusta, ME 04333
(207)289-2801
Mayland Emery T. Cleaves
Maryland Geological Survey
2300 St. Paul Street
Baltimore, MD 21218-5210
(410)554-5500
Joseph A. Sinnott '
Massachusetts Office of
Environmental Affairs
100 Cambridge St., Room 2000
Boston, MA 02202
(617)727-9800
R. Thomas Segall
Michigan Geological Survey Division
Box 30256
Lansing, MI 48909
(517)334-6923
Minnesota Priscilla C. Grew
Minnesota Geological Survey
2642 University Ave.
St. Paul, MN 55114-1057
(612)627-4780
Mississippi S. Cragin Knox
Mississippi Office of Geology
P.O. Box 20307
Jackson, MS 39289-1307
(601)961-5500
Missouri James H. Williams
Missouri Division of Geology &
Land Survey
111 Fairgrounds Road
P.O. Box 250
Rolla, MO 65401
(314)368-2100
Montana Edward T.Ruppel
Montana Bureau of Mines & Geology
Montana College of Mineral Science
and Technology, Main Ball
Butte,MT 59701
(406)4964180
Nebraska
Perry B. Wigley
Nebraska Conservation & Survey
Division
113 Nebraska Hall
University of Nebraska
Lincoln, ME 68588-0517
(402)472-2410
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. Boudede
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
NewJSfexico Charles E. Chapin
New Mexico Bureau of Mines &
Mineral Resources
Campus Station
Socorro.NM 87801
(505)835-5420
NewYoifc Robert KLFakundiny
New York State Geological Survey
3136 Cultural Education Center
Empire State Plaza
Albany, NY 12230
(518)474-5816
1-34
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 I. Mankin
Oklahoma Geological Survey
loom N-131, Energy Center
KME.Boyd
Norman, OK 73019-0628
(405)325-3031
Oregon Donald A. Hull
DepL of Geology & Mineral IndusL
Suite 965
800 NE Oregon SL #28
Portland, OR 97232-2162
(503)731-4600
Pennsylvania Donald M. Hoskins
Dept. of Environmental Resources
Bureau of Topographic & Geologic
Survey
P.O. Box 2357
Harrisburg, PA 17105-2357
(717)787-2169
Puerto Rico Ramon M. Alonso
Puerto Rico Geological Survey
Division
Box 5887
Puerta de Tierra Station
San Juan, PJL 00906
(809)722-2526
Rhode Island J. Allan Cain
Department of Geology
University of Rhode Island
315 Green Hall
Kingston. RI02881
(401)792-2265
South Carolina Alan-Jon W. Zupan (Acting)
South Carolina Geological Survey
5 Geology Road
Columbia, SC 29210-9998
(803)737-9440
South Dakota CM. Christensen (Acting)
South Dakota Geological Survey
Science Center
University of South Dakota
VemiBIion, SD 57069-2390
(605)677-5227
Tennessee Edward T. Luther
Tennessee Division of Geology
13th Floor, L & C Tower
401 Church Street
Nashville, TN 37243-0445
(615)532-1500
Texas William L. Fisher
Texas Bureau of Economic Geology
University of Texas
University Station, Box X
Austin, TX 78713-7508
(512)471-7721
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 SL
Waterbury.VT 05671
(802)244-5164
Virginia Stanley S. Johnson
Virginia Division of Mineral
Resources
P.O. Box 3667
Charlottesvillc, 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
11-35 Reprinted from USGS Open-File Report 93-292
-------
West Virginia LanyD.Wopdfork
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
11-36 Reprinted from USGS Open-File Report 93-292
-------
EPA REGION 3 GEOLOGIC RADON POTENTIAL SUMMARY
by
Linda CJS. Gundersen, James K. Otton, and Sandra L. Szarzi
US. Geological Survey
EPA Region 3 includes the states of Delaware, Maryland, Pennsylvania, Virginia, and
West Virginia.. 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 pQ/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 3 is given in the individual state chapters. The individual chapters
describing the geology and radon potential of the states in EPA Region 3, 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.
Figure 1 shows a generalized map of the major physiographic/geologic provinces in EPA
Region 3. The summary of radon potential in Region 3 mat follows refers to these provinces.
Figure 2 shows average screening indoor radon levels by county. The data for Maryland,
Pennsylvania, Virginia, and West Virginia are from the State/EPA Residential Radon Survey. Data
for Delaware were compiled by the Delaware Department of Health and Social Services. Figure 3
shows the geologic radon potential areas in Region 3, combined and summarized from the
individual stale chapters in this booklet
DELAWARE
Piedmont
The Piedmont in Delaware has been ranked moderate in geologic radon potential; Average
measured indoor radon levels in the Piedmont vary from low (<2 pCi/L) to moderate (2-4 pCi/L).
Individual readings within the Piedmont can be locally very high (> 20 pCi/L), This is not
unexpected when a regional-scale look at the Atlantic coastal states shows that the Piedmont is
consistently an area of moderate to high radon potential. Much of the western Piedmont in
Delaware is underlain by the WissaMckon Formation, which consists predominantly of schist
This formation has moderate to locally high geologic radon potential. Equivalent schists in the
Piedmont of Maryland can have uranium concentrations of 3—5 ppm, especially where faulted.
The Wilmington Complex and James Run Formation, in the central and eastern portions of the
Delaware Piedmont, are variable in radon potential. In these units, the felsic gneiss and schist may
contribute to elevated radon levels, whereas mafic rocks such as amphibolite and gabbro, and
relatively quartz-poor granitic rocks such as charnocMte and diorite are probably lower in radon
potential. The average indoor radon is distinctly lower in parts of the Wilmington Complex than in
surrounding areas, particularly in areas underlain by the Bringhurst Gabbro and the Arden pluton.
The permeability of soils in the Piedmont is variable and dependent on the composition of the rocks
from which the soils are derived. Most soils are moderately permeable, with local areas of slow to
m-1 Reprinted from USGS Open-File Report 93-292-C
-------
Page Intentionally Blank
-------
100
miles
Figure 1. Geologic radon potential areas of EPA Region 3. 1-Central Lowland; 2-Glaciated Pittsburgh Plateau;
3-Pennsylvanian rocks of the Pittsburgh Low Plateau; 4-Permian rocks of the Pittsburgh Low Plateau; 5-High Plateau
Section; 6-Mountainous High Plateau; 7-Allegheny Plateau and Mountains; 8-Appalachian Mountains; 9-Glaciated
Low Plateau, Western Portion; IQ-Glaciated Pocono Plateau; 11-Glaciated Low Plateau, Eastern Portion;
12-Reading Prong; 13-Great Valley/Frederick Valley carbonates and elastics; 14-Blue Ridge Province;
15-Gettysburg-Newark Lowland Section (Newark basin) 16,34-Piedmonu 17-Atlantic Coastal Plain; 18-Central
Allegheny Plateau; 19-Cumberland Plateau and Mountains; ^-Appalachian Plateau; 21-Silurian and Devonian rocks
in Valley and Ridge; 22,23-Valley and Ridge (Appalachian Mountains); 24-Westem Piedmont Phyllite;
25-Culpeper, Gettysburg, and otter Mesozoic basins; 26-Mesozoic basins; 27-Eastem Piedmont, schist and gneiss;
28-lnner Piedmont; 29-Goochland Terrane; 30,31-Coastal Plain (Cretaceous, Quaternary, minor Tertiary sediments);
32-Carolina terrane; 33-Coastal Plain (Tertiary sediments); 35,37,38-Coastal Plain (quartz-rich Quaternary
sediments); 36-Glauconitic Coastal Plain sediments.
-------
100 Miles
indoor Radon Screening
Measurements: Average (pCi/L)
0.0 to 1.9
2.0 to 4.0
4.1 to 10.0
10.1 to 32.6
Missing Data
or < S measurements
Figure 2. Screening indoor radon averages for counties with 5 or more measurements in EPA
Region 3. Data for Maryland, Pennsylvania, Virginia, and West Virginia are from the State/EPA
Residential Radon Survey. Data for Delaware were compiled by the Delaware Department of
.Health and Social Services. Histograms in map legend show the number of counties in each
category.
-------
GEOLOGIC
.RADON POTENTIAL
| I LOW
HH MODERATE/VARIABLE
• HIGH
'• • ,*>—;V-»
• . « V* * » .' •
.,..„...»,. . £
100
milos
Figure 3. Geologic radon potential of EPA Region 3. For more detail, refer to individual state
radon potential chapters.
-------
Page Intentionally Blank
-------
rapid permeability. Limited aereal radioactivity data for the Delaware Piedmont indicates that
equivalent uranium is generally moderate (1.5-2.5 ppm).
CoastalPMn
Studies of radon and uranium in Coastal Plain sediments in New Jersey and Maryland
suggest that glauconitic marine sediments equivalent to those in the northern portion of the
Delaware Coastal Plain can cause elevated levels of indoor radon. Central New Castle County is
underlain by glauconitic marine sediments of Cretaceous and Tertiary age that have moderate to
locally high radon potential. Aerial radiometric data indicate that moderate concentrations of
uranium occur in rocks and soils associated with the Piedmont and parts of the Coastal Plain of
northern Delaware. Chemical analyses of Cretaceous and Tertiary glauconitic marine sediments
and fluvial sediments of the Columbia Formation performed by the Delaware geological survey
indicate variable but generally moderate concentrations of uranium, averaging 1.89 ppm or greater.
The permeability of soils in these areas is variable but generally moderate to high, allowing radon
gas to move readily through the soil. Data for New Castle County from the State indoor radon
survey shows that areas underlain by the Cretaceous fluvial sediments (not glauconitic) have lower
average indoor radon levels than the glauconitic parts of the upper Cretaceous and lower Tertiary
sequence to the south. Kent County and all of Sussex County are underlain by quartz-dominated
sands, silts, gravels, and clays with low radon potential. These sediments are low in radioactivity
and generally have a low percentage of homes with indoor radon levels greater than 4 pCi/L.
MARYLAND
CoastalPMn
The Western Shore of Maryland has been ranked moderate to locally high in radon potential
and the Eastern Shore has been ranked low in radon potential. The Coastal Plain Province is
underlain by relatively unconsolidated fluvial and marine sediments that are variably phosphatic
and glauconitic on the Western Shore, and dominated by quartz in the Eastern Shore.
Radioactivity in the Coastal Plain is moderate over parts of the Western Shore sediments,
particularly in the Upper Cretaceous and Tertiary sediments of Prince George's, Anne Arundel,
and northern Calvert counties. Moderate radioactivity also appears to be associated with the
Cretaceous and Tertiary sediments of the Eastern Shore where these sediments are exposed in
major drainages in Kent, Queen Anne's, and Talbot counties. Soil-gas radon studies in Prince
George's County indicate that soils formed from the locally phosphatic, carbonaceous, or
glauconitic sediments of the Calvert, Aquia, and Nanjemoy Formations can produce significantly
high radon (average soil radon > 1500 pCi/L). The Cretaceous Potomac Group had more
moderate levels of soil radon, averaging 800-900 pG/L, and the Tertiary-Cretaceous Brightseat
Formation and Monmouth Group had average soil radon of 1300 pCi/L. Soil permeability on the
Western Shore varies from low to moderate with some high permeability in sandier soils. Well-
developed clayey B horizons with low permeability are common. Indoor radon levels measured in
the State/EPA Residential Radon Survey are variable among the counties of the Western Shore but
are generally low to moderate. Moderate to high average indoor radon is found in most of the
Western Shore counties.
For this assessment we have ranked part of the Western Shore as high in radon potential,
including Calvert County, southern Anne Arundel County, and eastern Prince George's County.
This area has the highest radioactivity, high indoor radon, and significant exposure of Tertiary rock
m-5 Reprinted from USGS Open-File Report 93-292-C
-------
units. The part of the Western Shore ranked moderate consists of Quaternary sediments with low
radon potential, Cretaceous sediments with moderate radon potential, and lesser amounts of
Tertiary sediments with high radon potential. The Quaternary sediments of the Eastern Shore have
low radioactivity associated with them and are generally quartzose and thus low in uranium.
Heavy-mineral concentrations within these sediments may be very local sources of uranium.
Indoor radon appears to be generally low on the Eastern Shore with only a few measurements over
4 pCi/L reported.
Piedmont
Gneisses and schists in the eastern Piedmont, phyllites in the western Piedmont, and
Paleozoic metascdimentary rocks of the Frederick Valley are ranked high in radon potential.
Sedimentary and igneous rocks of the Mesozoic basins have been ranked moderate in radon
potential. Radioactivity in the Piedmont is generally moderate to high. Indoor radon is moderate
to high in the eastern Piedmont and nearly uniformly high in the western Piedmont. Permeabilily
is low to moderate in soils developed on the mica schists and gneisses of the eastern Piedmont,
Paleozoic sedimentary rocks of the Frederick Valley, and igneous and sedimentary rocks of the
Mesozoic Basins. Permeability is moderate to high in the soils developed on the phyllites of the
western Piedmont The Maryland Geological Survey has compared the geology of Maryland with
the Maryland indoor radon date. They report that most of the Piedmont rocks, with the exception
of ultramafic rocks, can contribute to indoor radon readings exceeding 4 pCi/L. Their data indicate
that the phyllites of the western Piedmont have much higher radon potential than the schists in the
east Ninety-five percent of the homes built on phyllites of the Gillis Formation had indoor radon
measurements greater than 4 pCi/L, and 47 percent of the measurements were greater than 20
pCi/L. In comparison, 80 percent of the homes built on the schists and gneiss of the Loch Raven
and Oclla Formations had indoor radon readings greater than 4 pCi/L, but only 9 percent were
greater than 20 pCi/L.
Studies of the phyllites in Frederick County show high average soil-gas radon (>1000
p Ci/L) when compared to other rock types in the county. Limestone and shale soils of the
Frederick Valley and some of the Triassic sedimentary rocks may be significant sources of radon
(500-2000 pG/L in soil gas). Because of the highly variable nature of the Triassic sediments and
the amount of area that the rocks cover with respect to the county boundaries, it is difficult to say
with confidence whether the high indoor radon in Montgomery, Frederick, and Carroll counties is
partly attributable to the Triassic sediments. In Montgomery County, high uranium concentrations
in fluvial crossbeds of the upper Manassas Sandstone containing gray carbonaceous clay intraclasts
and drapes have been documented. Similar lithologic associations are common in the upper New
Oxford Formation. Black shales and gray sandstones of the Heidlersburg Member are similar to
uranium-bearing strata in the Culpeper basin in Virginia and may be a source of radon. Black
shales in the overlying Gettysburg Formation may also be locally uranium rich. The lower New
Oxford Formation, the lower Manassas Sandstone, the lower Gettysburg Formation, and the Balls
Bluff Siltstone in Maryland are not likely to have concentrations of uranium except where altered
by diabase intrusives and/or faulted. The diabase bodies are low in radon potential.
Appalachian Mountains
The Appalachian Province is divided into the Blue Ridge, Great Valley, Valley and Ridge,
and Allegheny Plateau. Each of these areas is underlain by a distinct suite of rocks with a
particular geologic radon potential. The Blue Ridge is ranked low in radon potential but may be
ffl-6 Reprinted from USGS Open-Pile Report 93-292-C
-------
locally moderate to high. Hie Catoctin volcanic rocks that underlie a significant portion of the Blue
Ridge have low radioactivity, yield low soil radon and have low soil permeability. The quartzite
and conglomerates overlying the Catoctin also have low radioactivity and low soil-gas radon.
Further, the Pennsylvania Topographic and Geologic s«-»ey calculated the median uranium
content of 80 samples of Catoctin metabasalt and metadiabase to be less than 0.5 ppm. The
Harpers Formation phyllite bordering the Catoctin volcanic rocks yields high soil-gas radon
(>1000 pCi/L), has greater surface radioactivity than the surrounding rocks and is a potential
source of radon. The Precambrian gneiss that crops out in the Middletown Valley of the southern
Blue Ridge appears to have moderate radioactivity associated with it and yielded some high radon
in soil gas. It is difficult, given the constraints of the indoor radon data, to associate the high
average indoor radon in the part of Frederick County underlain by parts of Ms province with the
actual rocks. The Blue Ridge is provisionally ranked low in geologic radon potential, but this
cannot be verified with the presently existing indoor radon data.
Carbonates and black shales in the Great Valley in Maryland have been ranked high in
radon potential. Radioactivity is moderate to high over the Great Valley in Washington County.
Washington County has more than 100 indoor radon measurements, has an average indoor radon
concentration of 8.1 pCi/L in the State/EPA Survey, with over half of the readings greater than
4 pCi/L. To the north in Pennsylvania, carbonate rocks of the Great Valley and Appalachian
Mountain section have been the focus of several studies and the carbonate rocks in these areas
produce soils with high uranium and radium contents that generate high radon concentrations. In
general, indoor radon in these areas is higher than 4 pCi/L. Studies in the carbonates of the Great
Valley in West Virginia suggest that the deepest, most mature soils have the highest radium and
radon concentrations and generate moderate to high indoor radon. High radon in soils and high
indoor radon in homes over the black shales of the Martinsburg Formation of the Great Valley
were also measured in West Virginia.
The Silurian and Devonian rocks of the Valley and Ridge have been ranked moderate to
locally high in geologic radon potential. Indoor radon measurements are generally moderate to
high in Allegany County. Soil permeability is variable but is generally moderate. Radioactivity in
this part of the Valley and Ridge is moderate to locally high. The Tonoloway, Keyser, and Wills
Creek Formations, and Clinton and Hamilton Groups have high equivalent uranium associated
with them and the shales, limestone soils, and hematitic sands are possible sources of the high
readings over these units.
The Devonian through Permian rocks of the Allegheny Plateau are ranked moderate in
geologic radon potential. Indoor radon measurements are generally moderate to high.
Radioactivity in the Allegheny Plateau is low to moderate with locally high equivalent uranium
associated with the Pocono Group and Mauch Chunk Formation. Soil permeability is variable but
generally moderate.
PENNSYLVANIA
New England Province
The New England Province is ranked high in geologic radon potential. A number of
studies on the correlation of indoor radon with geology in Pennsylvania have been done. The
Reading Prong area in the New England Province is the most notable example because of the
national publicity surrounding a particularly severe case of indoor radon. These studies found that
shear zones within the Reading Prong rocks enhanced the radon potential of the rocks and created
ffl-7 Reprinted from USGS Open-File Report 93-292-C
-------
local occurrences of very high uranium and indoor radon. Several of the rock types in the Reading
Prong were found to be highly uraniferous in general and they are the source for high radon levels
throughout much of the province.
Piedmont
The Piedmont is underlain by metamorphic, igneous, and sedimentary rocks of
Precambrian to Mesozoic age that have generally moderate to high radon potential. Rock types in
the metamorphic crystalline portion of the Piedmont that have naturally elevated uranium
concentrations include granitic gneiss, biotite schist, and gray phyllite. Rocks that are known
sources of radon and have high indoor radon associated with them include phyllites and schists,
such as the Wissahickon Formation and Peters Creek Schist, shear zones in these rocks, and the
faults surrounding mafic bodies within these rocks.
Studies in the Newark Basin of New Jersey indicate that the black shales of the Lockatong
and Passaic Formations and fluvial sandstones of the Stockton Formation are a significant source
of radon in indoor air and in water. Where these rock units occur in Pennsylvania, they may be the
source of high indoor radon as well. Black shales of the Heidlersburg Member and fluvial
sandstones of the New Oxford Formation may also be sources of locally moderate to high indoor
radon in the Gettysburg Basin. Diabase sheets and dikes within the basins have low eU. The
Mesozoic basins as a whole, however, are variable in their geologic radon potential. The Narrow
Neck area is distinctly low in radioactivity and Montgomery County, which is underlain almost
entirely by Mesozoic basin rocks, has an indoor radon average less than 4 pCi/L. Other counties
underlain partly by the Mesozoic basin rocks, however, have average indoor radon greater than
4 pCi/L. The Newark basin is high in radon potential whereas the Gettysburg basin is low to
locally moderate. For the purposes of this report the basins have been subdivided along the
Lancaster-Berks county boundary. The Newark basin comprises the Mesozoic rocks east of this
county line.
Blue Ridge
The Blue Ridge Province is underlain by metasedimentary and metavolcanic rocks and is
generally an area of low radon potential. A distinct low area of radioactivity is associated with the
province on the map, although phyllite of the Harpers Formation may be uraniferous. Soils
generally have variable permeability. The metavolcanic rocks in this province have very low
uranium concentrations. It is difficult, given the constraints of the indoor radon data, to associate
the high average indoor radon in counties underlain by parts of this province with specific rock
units. When the indoor radon data are examined at the zip code level, it appears that most of the
high indoor radon is attributable to the Valley and Ridge soils and rocks. The conclusion is that the
Blue Ridge is provisionally ranked low in geologic radon potential although this cannot be verified
with the presently available indoor radon data.
Ridge and Valley and Appalachian Plateaus
Carbonate rocks of the Great Valley and Appalachian Mountain section have been the focus
of several studies and the carbonates in these areas produce soils with high uranium and radium
contents and soil radon concentrations. In general, indoor radon in these areas is higher than
4 pCi/L and the geologic radon potential of the area is high, especially in the Great Valley where
indoor radon is distinctly higher on the average than in surrounding areas. Soils developed on
ffl-8 Reprinted from USGS Open-File Report 93-292-C
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limestone and dolomite rock at the surface in the Great Valley, Appalachian Mountains, and
Piedmont are probably sources of high indoor radon.
The clastic rocks of the Ridge and Valley and Appalachian Plateaus province, particularly
the Ordovician through Pennsylvanian-age black to gray shales and fluvial sandstones, have been
extensively cited in the literature for their manium con^m. as well as their general uranium
potential. It appears from the uranium and radioactivity data and comparison with the indoor radon
data that the black shales of the Ordovician Martinsburg Formation, the lower Devonian black
shales, Peiuisylvanian black shales of the Allegheny Group, Conemaugh Group, and Monogahela
Group, and the fluvial sandstones of the Devonian Catskill and Mississippian Mauch Chunk
Formation may be the source of most moderate to high indoor radon levels in the Appalachian
Plateau and parts of the Appalachian Mountains section.
Only a few areas in these provinces appear to have geologically low to moderate radon
potential. The Greene Formation in Greene County appears to correlate with distinctly low
radioactivity. The indoor radon for Greene County averages less than 4 pCi/L for the few
measurements available in the State/EPA survey.
Somerset and Cambria Counties in the Allegheny Mountain section have indoor radon
averages less than 4 pCi/L, and it appears that low radioactivity and slow permeability of soils may
be factors in the moderate geologic radon potential of this area. These two counties ami most of
tiie Allegheny Mountain section are underlain by Pennsylvanian-age sedimentary rocks. The
radioactivity map shows low to moderate radioactivity for the Pennsylvanian-age rocks in the
Allegheny Mountain section and much higher radioactivity in the Pittsburgh Low Plateau section.
Most of the reported uranium occurrences in these rocks appear to be restricted to the north and
west of the Allegheny Mountain section. Approximately half of the soils developed on these
sediments have slow permeability and seasonally high water tables.
CoastalPlain
Philadelphia and Delaware Counties, in the southeastern corner of Pennsylvania, have
average indoor radon less than 4 pCi/L and have low radioactivity. Part of Delaware County and
most of Philadelphia County are underlain by Coastal Plain sediments with low uranium
concentrations. Soils developed on these sediments are variable, but a significant portion are
clayey with slow permeability.
Glaciated Areas of Pennsylvania
Radiometric lows and relatively lower indoor radon levels appear to be associated with the
glaciated areas of the State, particularly the eastern portion of the Glaciated Low Plateau and
Pocono Plateau in Wayne, Pike, Monroe, and Lackawanna Counties. Glacial deposits are
problematic to assess for radon. In some areas of the glaciated portion of the United States, glacial
deposits enhance radon potential, especially where the deposits have high permeability and are
derived from uraniferous source rocks. In other portions of the glaciated United States, glacial
deposits blanket more uraniferous rock or have low permeability and corresponding low radon
potential. The northeastern corner of Pennsylvania is covered by the Olean Till, made up of 80-90
percent sandstone and siltstone clasts with minor shale, conglomerate, limestone, and crystalline
clasts. A large proportion of the soils developed on this till have seasonally high water Miles and
poor drainage, but some parts of the till soils are stony and have good drainage and high
permeability. Low to moderate indoor radon levels and radioactivity in this area may be due to the
seasonally saturated pound and to the tills being made up predominantly of sandstones and
m-9 Reprinted fromUSGS Open-File Report 93-292-C
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siltstones with low uranium contents. A similar situation exists in the northwestern part of the
State, which is covered by a wide variety of tills, predominantly the Kent Till, which contains
mostly sandstone, sUtstone, and shale clasts. Many of the soils in this area also have low
permeabilities and seasonally high water tables. Where the tills are thinner, the western portion of
die Glaciated Low Plateau has higher indoor radon ana high radioactivity.
VIRGINIA
CoastalPlain
The Coastal Plain of Virginia is ranked low in geologic radon potential. Indoor radon is
generally low; however, moderate to high indoor radon can occur locally and may be associated
with phosphatic, glauconitic, or heavy mineral-bearing sediments. Equivalent uranium over the
Tertiary units of the Coastal Plain is generally moderate. Soils developed on the Cretaceous and
Tertiary units are slowly to moderately permeable. Studies of uranium and radon in soils indicate
that the Yorktown Formation could be a source for elevated levels of indoor radon. The
Quaternary sediments generally have low eU associated with them. Heavy mineral deposits of
monazite found locally within the Quaternary sediments of the Coastal Plain may have the potential
to generate locally moderate to high indoor radon.
Piedmont
The Goochland terrane and Inner Piedmont have been ranked high in radon potential.
Rocks of the Goochland terrane and Liner Piedmont have numerous well-documented uranium and
radon occurrences associated with granites; pegmatites; granitic gneiss; monazite-bearing
metasedimentary schist and gneiss; graphitic and carbonaceous slate, phyllite, and schist; and shear
zones. Indoor radon is generally moderate but significant very high radon levels occur in several
areas. Equivalent uranium over the Goochland terrane and Inner Piedmont is predominantly high
to moderate with areas of high eU more numerous in the southern part Permeability of soils
developed over the granitic igneous and metamorphic rocks of the Piedmont is generally moderate.
Within the Goochland terrane and Inner Piedmont, local areas of low to moderate radon potential
will probably be found over mafic rocks (such as gabbro and amphibolite), quartzite, and some
quartzitic schists. Mafic rocks have generally low uranium concentrations and slow to moderate
permeability in the soils they form.
The Carolina terrane is variable in radon potential but is generally moderate. Metavolcanic
rocks have low eU but the granites and granitic gneisses have moderate to locally high eU. Soils
developed over the volcanic rocks are slowly to moderately permeable. Granite and gneiss soils
have moderate permeability.
The Mesozoic basins have moderate to locally high radon potential. It is not possible to make
any general associations between county indoor radon averages and the Mesozoic basins as a
whole because of the limited extent of many the basins. However, sandstones and siltstones of the
Culpepcr basin, which have been lightly metamorphosed and altered by diabase intrusion, are
mineralized with uranium and cause documented moderate to high indoor radon levels in northern
Virginia. Lacustrine black shales and some of the coarse-grained gray sandstones also have
significant uranium mineralization, often associated with green clay clasts and copper. Equivalent
uranium over the Mesozoic basins varies among the basins. The Danville basin has very high eU
associated with it whereas the other basins have generally moderate eU. This radioactivity may be
related to extensive uranium mineralization along the Chatham fault on the west side of the Danville
ffl-10 Reprinted from USGS Open-File Report 93-292-C
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basin. Localized high eU also occurs over the western border fault of the Culpeper basin. Soils
are generally slowly to moderately permeable over the sedimentary and intrusive rocks of the
basins.
Valley and Ridge
The Valley and Ridge has been ranked high in geologic radon potential but some areas have
locally low to moderate radon potential. The VaUey and Ridge is underlain by Cambrian dolomite,
limestone, shale, and sandstone; Silurian-Ordovician limestone, dolomite, shale, and sandstone;
and Mississippian-Devonian sandstone, shale, limestone, gypsum, and coal. Soils derived from
carbonate rocks and black shales, and black shale bedrock may be sources of the moderate to high
levels of indoor radon in this province. Equivalent uranium over the Valley and Ridge is generally
low to moderate with isolated areas of high radioactivity. Soils are moderately to highly
permeable. Studies of radon in soil gas and indoor radon over the carbonates and shales of the
Great Valley in West Virginia and Pennsylvania indicate that the rocks and soils of this province
constitute a significant source of indoor radon. Sandstones and red siltstones and shales are
probably low to moderate in radon potential. Some local uranium accumulations are contained in
these rocks.
Appalachian Plateaus
The Appalachian Plateaus Province has been ranked moderate in geologic radon potential.
The plateaus are underlain by Pennsylvanian-age sandstone, shale, and coal. Black shales,
especially those associated with coal seams, are generally elevated hi uranium and may be the
source for moderate to high radon levels. The coals themselves may also be locally elevated in
uranium. The sandstones are generally low to moderate in radon potential but have higher soil
permeability than the black shales. Equivalent uranium of the province is low to moderate and
indoor radon is variable from low to high, but indoor radon data are limited in number.
WEST VIRGINIA
Allegheny Plateau
The Central Allegheny Plateau Province has moderate geologic radon potential overall, due
to persistently moderate eU values and the occurrence of steep, well-drained soils. However,
Brooke and Hancock counties, in the northernmost part of this province, have average indoor
radon levels exceeding 4 pCi/L. This appears to be related to underlying Conemaugh and
Monongahela Group sedimentary rocks which have elevated eU values in this area and in adjacent
areas of western Pennsylvania.
The Cumberland Plateau and Mountains Province has low radon potential. The eU values
for the province are low except in areas of heavy coal mining, where exposed shale-rich mine
waste tends to increase values. Indoor radon levels average less than 2 pCi/L in most counties.
The Eastern Allegheny Plateau and Mountains Province has moderate radon potential
overall. Locally high indoor radon levels are likely in homes on dark gray shales of Devonian age
and colluvium derived from them in Randolph County. The southern part of this province has
somewhat lower eU values and indoor radon averages.
m-11 Reprinted from USGS Open-File Report 93-292-C
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Ridge and Valley Province
The southern part of the Appalachian Ridge and Valley Province in West Virginia has
moderate radon potential overall. The eU signature for this province is elevated (> 2.5 ppm eU).
Locally high radon potential occurs in areas of deep residual soils developed on limestones of the
Mississippian Greenbrier Group, especially in central Greenbrier County, where eU values are
high. Elevated levels of radon may be expected in soils developed on dark shales in this province
or in colluvium derived from them.
The northern part of the Appalachian Ridge and Valley Province in West Virginia has high
geologic radon potential. The soils in this area have an elevated eU signature. Soils developed on
the Martinsburg Formation .and on limestones and dolomites throughout the Province contain
elevated levels of radon and a very high percentage of homes have indoor radon levels exceeding
4 pQ/L in this province. Karst topography and associated locally high permeability in soils
increases the radon potential. Structures sited on uraniferous black shales may have very high
indoor radon levels. Steep, well-drained soils developed on phyllites and quartzites of the Harpers
Formation in Jefferson County also produce high average indoor radon levels.
ffl-12 Reprinted fiomUSGS Open-File Report 93-292-C
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PRELIMINARY GEOLOGIC RADON POTENTIAL ASSESSMENT OF VIRGINIA
by
Linda C S. Gundersen
US. Geological Survey
INTRODUCTION
This is a generalized assessment of geologic radon potential of rocks, soils, and surficial
deposits of Virginia. 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 tiie 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
GEOGRAPHIC SETTING
The physiography of Virginia (fig. 1), to a large degree, reflects the underlying bedrock
geology (fig, 2). Virginia's elevation ranges from sea level to 5,729 feet The State has been
divided into five major physiographic regions: the Coastal Plain, the Piedmont, the Blue Ridge, the
Valley and Ridge, and the Appalachian Plateaus (fig. 1). For the purposes of this radon
assessment these provinces have also been subdivided based on geology.
The Coastal Plain is characterized by broad areas of low relief, averaging 100 feet above
sea level, and gently sloping downward from the Piedmont to the shoreline. It is underlain by
unconsolidated to partly consolidated sediments and has a maximum elevation of 300 feet above
sea level near the Fall Line. The Fall Line is the boundary between the Coastal Plain and the
Piedmont that is marked by a distinct change in river and stream water velocity, including the
occurrence of waterfalls. The Piedmont is characterized by gently rolling hills and is underlain by
a complicated sequence of metamorphic and igneous rocks. The land surface of the Piedmont
slopes gently to the east with a maximum elevation of 1350 feet in the west and a minimum
elevation of 300 feet in the east at the Fall Line. The topography of the Piedmont becomes more
hilly as it approaches the Blue Ridge to the west The Blue Ridge is a long narrow province that
extends from north to south across the State and is characterized by the most rugged topography in
Virginia. It contains the highest mountain in the State, Mount Rogers, at 5729 feet above sea level.
The Blue Ridge is underlain by igneous, metamorphic, and sedimentary rocks. To the west of the
Blue Ridge is the Valley and Ridge Province, the boundary of which is marked by a broad valley
underlain by carbonate rocks and shales. In the northern portion of the State, part of the Valley
and Ridge is referred to as the Great Valley and includes the Shenandoah Valley. The rest of the
Valley and Ridge consists of well-defined, parallel valleys and ridges underlain by folded
Paleozoic sedimentary rocks. More resistant sandstones and conglomerates form the ridges
whereas the valleys are underlain by carbonate rocks and shales. In the southwestern portion of
IV-1 Reprinted fromUSGS Open-File Report 93-292-C
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Page Intentionally Blank
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0
I-
100
Miles
Jff
Piedmont
— C0ast?l Plain
Figure 1. Physiographic/Geologic provinces of Virginia. Stippled areas indicate Mesozoic basins.
The Coastal Plain is labeled to show the age of sediments-1, Cretaceous sediments; 2, Tertiary
sediments; and 3, Quaternary sediments, (after Dietrich, 1970; Hatcher and others, 1990)
-------
Figure 2. Gene
Vkginia Division G
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Geologic Units for the General Geologic Map of Virginia
QUATERNARY
Quaternary - Beach sand; mud, sand, and silt of the marshes and tidal flats; fluvial sandy gravel, gravelly sand; silt, and
day; peat and peaty mud of swamps; and eolian dune sand. Tabb Formation - Sand, silt, clay, and peat Shirley
Formation - Gray and brown sand, gravel, silt, day, and peat Chuckatuck Formation - Reddish sand, silt, and clay
with minor peat Charles City Formation - Gray to reddish brown sand, silt, and clay. Windsor Formation - Gray to
reddish brown sand, gravel, silt, and clay. Kent bland Formation - Gray sand and sandy gravel grading upward into
silty and clayey sand. Wachapreagne Formation - Clayey and silty sand inteibedded with day and silt overiain by
gravelly sand. Nassawadox Formation - Sand and gravel. Joynes Neck Sand - Sandy gravel and gravelly sand grading
up into fine sand. Omar Formation - Gray to yellowish-orange sand, gravel, silt, clay, and peat
TERTIARY
Bacons Castle Formation - Gray quartzose sand, silt and clay.
Chesapeake Group: Chowan River Formation * Gray to green, clayey, silly, shelly sand with boulders and pebbles at
the base. Yorktown Formation - Gray, shelly sand that is in part glaiiconitic and phosphatic interbedded with sandy
and silty gray clay.. EastoverFormation-Gray, muddy, micaceous sand with sandy silt and clay. St Marys
Formation - Gray, muddy, fine sand and sandy silt-clay, locally shelly. Choptank Formation - Green-gray, shelly,
clayey and silty, fine sand with diatomaceous silt Calvert Formation - Gray-green, clayey and silty, shelly, fine sand
forming upward-fining sequences into diatomaceous silt
Pliocene Sand and Gravel -Orange to reddish-brown, locally cross-bedded gravelly sand, sandy gravel, and sand with
thin beds of clay and silt Miocene Sand and Gravel - Gray, sand, sandy gravel, silt, and clay with oxidized orange to
reddish brown pebbles and cobbles.
Old Church Formation - Shelly, sparsely glauconia'c quartz sand.
Lower Oligocene Beds - Gray-green, clayey, silty, micaceous, glauconitic sand.
Chickahominy Formation - Gray-green, glauconitic, micaceous clayey silt and silty day with basal sand and pebbles.
Pamunkey Group: Piney Point Formation - Gray-green, glauconitic, quartz sand interbedded with carbonate-
cemented sand and limestone. Namjemoy Formation - Gray-green and black, clayey and silty, glauconitic sand, locally
shelly and micaceous, pebbly at top. Marlboro Clay - Gray to reddish brown kaolinitic clay with silt and fine sand.
Aquia Formation - Gray-green, clayey and silty, locally shelly, glauconitic sand, calcareous at base with thin limestone
beds. Brightseat Formation - Gray to black, clayey and silty, micaceous quartz sand that is locally glauconitic.
CRETACEOUS
Potomac Formation - Cross-bedded, quartzo-feldspathic sand interbedded with gray and mottled red sandy clay and silt
Contains lesser amounts of clay-clast conglomerate and carbonaceous day and sOt
TRIASSIC-JURASSIC
Igneous rocks - Sills and dikes, diabase and gabbro
Newark Supergroup: Culpeper basin: Waterfall Formation - Red to gray arkosic sandstone, conglomerate, and
siltstone with black shale interbeds. Sander Basalt - Tholeiitic basalt interbedded with red sandstone and siltstone.
Turkey Run Formation - Red to gray arkosic sandstone, conglomerate, and siltstone with black shale interbeds.
Hickory Grove Basalt - Tholeiitic basalt inteibedded with red sandstone and siltstone; Midland Formation - Red to
gray arkosic sandstone, conglomerate, and siltstone with black shale interbeds. Mount Zion Church Basalt - Tholeiitic
basalt interbedded with red sandstone and siltstone. Catharpin Creek Formation - Red to gray arkosic sandstone,
conglomerate, and siltstone with black shale interbeds. Balls Bluff Siltstone - Red to gray arkosic siltstone, sandstone,
and conglomerate with black shale interbeds. Tibbstown Formation - Red to gray arkosic siltstone, sandstone, and
conglomerate with black shale interbeds. Manassas Sandstone - Red to gray arkosic sandstone and conglomerate.
BarboursviHe basin Balls Bluff Siltstone - Red arkosic siltstone, sandstone, and conglomerate. Tibbstown Formation
- Red arkosic siltstone, sandstone, and conglomerate. Manassas Sandstone - Red to gray arkosic sandstone and
conglomerate.
TaylorsviUe basin Doswell Formation - Red to gray arkosic sandstone, conglomerate, and siltstone with black shale
interbeds and some coal beds.
Richmond basin Otter-dale Sandstone - Arkosic sandstone and conglomerate. Venha beds - Black to green shale,
siltstone, and sandstone. Productive Coal Measures • Gray siltstone, shale, and sandstone with coal beds. Lower
Barren beds - Gray and black siltstone and shale with sandstone and conglomerate.
Danville basin Cedar Forest Formation - Red to gray arkosic sandstone, conglomerate, and siltstone with black shale
interbeds. Leakesvilte Formation - Red to gray arkosic siltstone, sandstone, and conglomerate with black shale
interbeds. Dry Fork Formation - Arkosic sandstone and conglomerate with red to gray siltstone and shale.
Other basins Triassic undifferentiated - Red arkosic sandstone, conglomerate, and siltstone with local gray to black
shale interbeds and coals. '..
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PENNSIrXVANIAN
Harlan Sandstone - Sandstone and shale with coal beds.
Wise Fonnation-Sandstone and shale with many coal beds.
Gladeville Sandstone - Sandstone, quartzose, gray, coarse-grained.
Norton Formation - Sandstone and shale with coal beds.
Lee Formation - Sandstone and shale with coal beds, conglomeratic at base.
5555:
•US?
MISSISSffHAN
Pennington Groap: Blutstone Formation-Shale and sandstone, some red shale in upper part. Princeton Sandstone-
Sandstone, conglomeratic. Hintoo Formation - Shale and siltstone, with sandstone, limestone, and dolomite.
Cove Creek Limestone - Limestone, argillaceous.
Fido Sandstone - Sandstone, argillaceous, calcareous in part
Newman Limestone - Limestone, oolitic or cherty.
Bluefield Formation - Shale, calcareous, with some limestone, siltstone and sandstone.
Greenbrkr Limestone-Limestone, oolitic^r cherty.
Maccradj Formation - Red shale and mudstone; red and green sandstone. Includes Little Valley Limestone at top locally.
Price Formation - Shale, fossiliferous, and sandstone with coal beds. Includes Grainger Formation in southwestern VA.
Pocono Formation - Sandstone and conglomerate with coal locally.
Mlxsissippian-Devonian shales - Shale and silstone, gray and greenish gray. Includes Chattanooga shale - black shale
DEVONIAN
Hampshire Formation - Shale and sandstone, red.
Chemung Formation - Shale and sandstone, mostly gray and greenish gray, fossiliferous.
Brallier Formation - Shale, greenish gray, siliceous; and sandstone, greenish, fine-grained.
Mahantango Formation, Marcellus Shak, Milboro Shale, Onondaga Formation, Needmore Shale, Huntersville Chert
-Blaci: to gray shale and siltstone with some limestone interbeds.
Ridgeley (Oriskany) Sandstone - Quartz sandstone.
Rocky Gap Sandstone - Quartz sandstone.
Licking Creek Limestone, HeUerberg Formation, New Scotland Limestone, Coeymans Limestone - Limestone with
some quartz sandstone in terbeds.
SILURIAN
Keyser Formation - Limestone, fossiliferous.
Cayuga Group; Hancock Dolomite - Dolomite and limestone. Tonoloway Formation, Wills Creek Formation -
Argillaceous limestone and dolomite. Bloomsburg Formation - Red siltstone, mudstone, and sandstone. McKenzie
Formation • Green siltstone, shale, and sandstone
Keefer Sandstone - sandstone with beds of fossiliferous, hematin'c sandstone.
Rose Hill Formation - Shale
Tuscarora Formation - Quartzite.
ORDOVIOAN
Sequatchie Formation - Limestone, argillaceous, and shale calcareous, mottled red and blue.
Juniata Formation and Oswego Sandstone - Fluvial sandstone.
ReedsviOe Shale - Shale, calcareous, olive-green.
Martinsburg Formation - Black shale with graywacke sandstone interbedsv—
Dot Limestone, Poteet Limestone, Rob Camp Limestone, Martin Creek Limestone, Hurricane Bridge Limestone,
Wood nay Limestone, Ben Hur Limestone, Hardy Creek Limestone, Moccasin Formation, Eggleston Formation, and
Trenton Limestone - Limestone, argillaceous limestone, calcareous shale, and shale.
Witten Limestone, Bowen Limestone, WardeU Limestone, Gratton Limestone, Benbolt Limestone, Effha Limestone,
Rye Cove Formation, Rockdell Limestone, Lincolnshire Formation, Lunch Formation, Five Oaks Limestone, Elway
Limestone, Blackford Formation • Limestone, argillaceous limestone, calcareous shale, and shale.
CoDierstown Limestone, Oranda Formation, Edinburg Formation, McGlone Formation, Big Valley Formation,
Lincolnshire Formation, Lurich Formation, New Market Limestone - Limestone, argillaceous limestone, calcareous
shale, and shale.
KHOX Group: Mascot Formation and Kingsport Formations - Dolomite and limestone. Copper Ridge Dolomite-
Dolomite with sandstone intcrbcds.
Beekmantown Formation - Limestone and dolomite. Includes Nittany and Betefonte Formations and Stonehenge
Limestone in northwestern Virginia.
Coep ul tepee Formation - Limestone and dolomite.
Arvonia Formation - Slate, phyllite and schist with garnet, conglomerate and quartzite.
Quantico Slate - Slate, in part graphitic, including rhyolite flows.
Evington Group; dandier Formation, Joshua Schist, Arch Marble, Pelrer Schist, Mount Athos Formation, and
Slippery Creek Greenstone - Muscovite, chlorite, paragonite. quartz phyllite and schist interbedded with graywacke,
volcanic greenstone, and marble.
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CAMBRIAN
Conasaoga Group: Nolichucky Formation, Maynardville Formation - Shale, olive, with thick beds of limestone.
Pumpkin Valley Shale, RuUedge Limestone, Rogersville Shale, and Maryville Limestone - Limestone and pay to
blade shale. Honaker Dolomite - Dolomite, locally argillaceous.
Conococheague Formation - Limestone and dolomite, contains beds of sandstone.
Elbrook Formation - Dolomite, shaly, argillaceous, some limestone.
Rome Formation - Shale and sandstone, variegated, with dolomite.
Shady Formation - Dolomite.with some limestone. In northern Loudoun County includes the Frederick Limestone.
Chilhowee Group: Erwin Formation - Sandstone and quartzite. Hampton Formation - Sandstone, shale, and
quartzite. Unicoi Formation - Conglomerate, shale and quartzite with basalt flows. Weverton Formation -
conglomerate, shale and quartzite.
Catoctin Formation - Basic lava flows, schist, gneiss, arkose, conglomerate and phylike.
Mount Rogers Volcanic Group - Rhyolite porphyry, arkose and tuff.
Swift Run Formation - Sandstone, graywacke, andesite tuff, and greenstone.
Mediums River Formation - Phyllite, quartzite, graywacke, and conglomerate.
PRECAMBRIAN
Lynchburg Formation - Phyllite, quaitzite, graywacke and conglomerate. Includes Alum Phyllite, Willis Phyllite,
Rockfish Conglomerate at base in Nelson and Albemarle counties, and Johnson Mill Formation and Charlottesville
Formation in Albemarle County.
Virginia Blue Ridge Complex: Lovingston Formation - Biotite granite, biotite gneiss and biotite, quartz monzonite.
Marshall Formation - Biotite, quartz, feldspar granite, gneiss and quartz monzonite. Moneta Gneiss - Biotite
hornblende gneiss. Old Rag Formation-Quartz, feldspar granite. Pedlar Formation - Granite, granodiorite,
hypersthene granodiorite, syenite, quartz diorite, anorthosite, and unakite. Robertston River Formation - Hornblende
granite and hornblende syenite. Roseland Anorthosite-Granular plagioclaserocL Striped Rock Granite - Biotite
granite and syenite.
GRANITE AND GNEISS OF UNCERTAIN AQB
Leatherwood Granite - Biotite, muscovite granite, locally porphyritic.
Melrose Granite - Biotite, muscovite granite and augen gneiss.
Petersburg Granite - Microcline, biotite granite and chloride granodiorite.
Redoak Granite - Biotite and muscovite granite, granite gneiss with feldspar phenocrysts, and chloride granodiorite.
Shelton Granite Gneiss - Granite gneiss, augen gneiss, and mylonite.
Columbia Granite: Biotite and muscovite granite, granodiorite, and quartz monzonite.
Carsonville Granite. Saddle Gneiss; Cattron Diorite; Beverdam Creek Augen Gneiss; Comers Granite Gneiss;
Grayson Granodiorite Gneiss; and Shoal Gneiss - Biotite and granitic gneiss and granite.
METAMORPHIC ROCKS AND IGNEOUS 1NTRUSIVES OF UNCERTAIN AGE
Amphibolite and Amphibole rich foliates includes Sabot amphibolite of Goochland terrane.
Granite gneiss - Biotite and muscovite granite gneiss, granodiorite gneiss.
Granite and hornblende gneiss - Interlayered mica, quartz, feldspar gneiss and hornblende, feldspar, mica gneiss.
Greenstone volcanics - Basic lava flows, tuff and slate commonly altered to chlorite bearing rocks.
Hornblende gabbro and gneiss - talc, amphibole chlorite schist, chloride hornblende gneiss; and some amphibolite,
cWoritic and hornblende diorite; and kyanite schist and quartzite.
Intrusive rocks - Granophyre, peridotite, and related rocks of possible Triassic age.
Metamorphosed sedimentary and volcanic rocks with minor igneous intrusives - Phyllite, schist, gneiss, slate,
greenstone, serpentinite, and quartzite, includes the State Farm Gneiss and Maidens Gneiss of the Goochland terrane,
the Chopawamsick Formation, Peters Creels: Formation, Bassett Formation, Fork Mountain Formation, and
E«ngton Group of the Inner Piedmont
Quartz diorite - Diorite with some blue quartz.
Limestone and marble - Includes equivalents of Cockeysville Marble in Loudoun and Fauquier counties, the Everona
Limestone in central Virginia, and limestone and marble in Pittsylvania County.
Virgilina Group - altered andesitic flows and tuffs; slate, quartz sericite schist, muscovite, quartz, paragonite phyllite,
and chloride arkose.
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the State is a small portion of the Appalachian Plateaus Province. It is highly dissected and
underlain by relatively fiat-lying sedimentary rocks.
Hie population of Virginia in 1990 was 6,187,358, including 66 percent urban population
(fig. 3). The average population density is 147 per square mile. The climate is moderate and
annual precipitation averages 32-48 inches (fig. 4). Agricultural products include tobacco,
soybeans, peanuts, wheat, corn, grain, fruit, and produce.
GEOLOGIC SETTING
The geology of Virginia is complex, and the names of rock formations and the way rocks
are grouped have changed with time. This description of the geology Hies to convey the major
rock types of an area, especially as they pertain to the radon problem. Descriptions in this report
are derived from the following references: Virginia Division of Mineral Resources (1963), Brown
(1970), Conley (1978), Patchen and others (1985), Krason and others (1988), Mixon and others
(1989), Hatcher and others (1989), and Smoot (1991). A general geologic map is given in figure
2. It is suggested, however, that the reader refer to the more detailed state geologic map (Virginia
Division of Mineral Resources, 1963) as well as the numerous detailed geologic maps available
from the Virginia Division of Mineral Resources (1988).
Coastal Plain
Sediments of the Coastal Plain range in age from Cretaceous to Quaternary, decreasing in
age from the Fall Line to the shoreline. The Cretaceous deposits are represented by the Potomac
Formation, which forms a thin band of outcrop from Washington D.C. south to Fredericksburg.
The Potomac Formation consists of fine- to coarse-grained quartzo-feldspathic sand of fluvial-
deltaic origin that is commonly crossbedded and interbedded with massive green sandy clay and
silt Lesser amounts of clay-clast conglomerate and carbonaceous clay and silt also form interbeds.
Tertiary deposits of Oligocene, Eocene, and Paleocene age, known as the Pamunky Group
and Old Church Formation, crop out along some of the major river drainages. These deposits are
characterized by fine- to coarse-grained glauconitic sand, clay, and silt, and sandy limestone.
Some units have abundant fossil shells and fish. Miocene-age sand and gravel crops out along the
fall line from Washington D.C. south to the state line. It consists of fine to coarse sand, sandy
gravel, silt, and clay, and is commonly oxidized. To the west of these deposits are similar
Pliocene-age deposits that cap the westernmost parts of the major drainage divides. They are
composed of oxidized gravelly sand, sandy gravel, fine- to coarse-grained crossbedded sands, and
thin beds of clay and silt
The Tertiary-age (upper Pliocene-lower Miocene) Chesapeake Group covers much of the
north-central part of the Coastal Plain and crops out along the major drainages. It is characterized
by shelly, sometimes diatomaceous, locally phosphatic, quartz sand, silt and clay, and is divided
up into a number of formations. These formations are the Calvert, Choptank, St Mary's,
Eastover, Yorktown, and the Chowan River Formations. The Bacons Castle Formation overlies
the Chesapeake Group and is upper Pliocene in age. The Bacons Castle is composed of sand,
gravel, silt and clay and covers much of the southwestern part of the Virginia Coastal Plain. It is
characterized by massive pebble and cobble gravel grading into crossbedded pebbly sand and
sandy, clayey silt In the northern part of the Virginia Coastal Plain, it crops out in the drainage
divides and consists of thin-bedded clayey silt and fine silty sand.
IV-7 Reprinted from USGS Open-File Report 93-292-C
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POPULATION (1990)
El 0 to 50000
C3 50001 to 100000
Ei 100001 to 250000
H 250001 to 500000
• 500001 to 818584
Figure 3. Population of counties in Virginia (1990 U.S. Census data).
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0 10 20 30 40 50
48"
48"
Figure 4. Average annual precipitation in Virginia (from Facts on File, 1984).
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At the top of the Tertiary section are the Moorings unit and Windsor Formation. The
Moorings unit forms discontinuous bodies west of the Surry scarp and is most extensive in the
north-central Coastal Plain. The Windsor Formation is upper Pliocene to lower Pleistocene in age
and crops out extensively, predominantly east of the Surrey scarp to the Quaternary/Tertiary
boundary near the shoreline. The Windsor Formation is comprised of crossbedded sand and
gravel grading upward to massive clayey silt and clay.
The Quaternary deposits of the Coastal Plain are subdivided into many formations and
generally represent nearshore sediments of beach, dune, river, estuary, terrace, swamp, lagoon,
and marsh origin. They are dominated by quartzose sand and gravel and often grade into silt and
clay or contain local deposits of silt, clay, and peat East of Chesapeake Bay in Northhampton and
Accomack Counties, the Quaternary section consists of the crossbedded sands, muddy sand, clay,
and silt of the Omar Formation; the fine to coarse sand and gravel of the Joynes Neck Sand; the
crossbedded sand and gravel deposits of the Nassawadox Formation; the interbedded clayey silty
sand, clayey silt, and gravelly sand of the Wachapreague Formation; and the coarse sand and
sandy gravel of the Kent Island Formation. West of Chesapeake Bay, the Quaternary sequence is
composed of sand, silt, and clay of the Charles City Formation; sand, silt, clay, and peat of the
Chuckatuck Formation; the sand, gravel, silt, clay, and peat of the Shirley Formation; and the
sand, silt, clay, and peat of the Tabb Formation.
ThePiedmont
The Piedmont is a complicated sequence of Precambrian to Paleozoic metasedimentary and
metavolcanic rocks intruded by igneous rocks of mafic to granitic composition. It has been
subdivided into several areas for the purpose of this report: the Goochland terrane, the Carolina
terrane, the Mesozoic basins, and the Inner Piedmont The geology of the Piedmont along the Fall
Line is dominated by numerous granitic intrusive rocks, including the Petersburg and Occoquan
Granites, the Mesozoic sedimentary and igneous rocks of the Richmond Basin (which will be
described in a following section), granitic gneiss and amphibolite of the Goochland terrane, and
minor diorite, metavolcanic rock, and gabbro. The Goochland terrane is bounded on the west by
the Spotsylvania and Nutbush Creek Faults. The terrane comprises some of the aforementioned
granites as well as the State Farm Gneiss, the Sabot amphibolite, the Maidens Gneiss, and the
Montpelier meta-anorthosite. The State Farm Gneiss is biotite-hornblende granitic gneiss that is
locally pegmatitic. The Sabot amphibolite overlies the State Farm Gneiss and is predominantly
amphibolite with minor biotite and granitic gneiss. The Maidens Gneiss includes biotite gneiss,
amphibolite layers, mica schist, calc-silicate layers, and granitic gneiss.
The Carolina terrane (Hatcher and others, 1989) extends from the Farmville basin south
between the Nutbush Creek Fault and the Danville Basin. It consists predominantly of
metavolcanic rocks that underlie large parts of Mecklenburg and Lunenburg Counties, the Virgilina
Group, the Shelton granite gneiss, granite and hornblende gneiss (especially in Halifax County),
the Redoak granite, and various granite gneiss, granitic bodies, mica schist, and minor hornblende
gneiss and gabbro. The Virgilina Group flanks the metavolcanic rocks to the west in Mecklenburg
and Halifax Counties and consists of volcanic rocks, slate, phyllite, schist and arkose.
The next terrane to the west is referred to as the Inner Piedmont (Hatcher and others,
1989). In the east the Inner Piedmont is underlain by metavolcanic rocks of the Chopawamsic
Formation which crop out in a wide band from northwestern Spotsylvania County south to
Buckingham County, where they are associated with the slate, phyllite, and schist of the Arvonia
Formation and Quantico Slate. Most of the Inner Piedmont is underlain by metamorphosed
IV-10 Reprinted from USGS Open-File Report 93-292-C
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sedimentary rocks, predominantly granitic gneiss, phyllite, and mica schist, including the Candler
Formation in the southern and central Inner Piedmont and die Peters Creek Formation in northern
Virginia. Some large areas of hornblende gneiss and gabbro crop out in the central part of the
Inner Piedmont in Appomattox and Buckingham Counties. The western edge of the Piedmont is
underlain by the sedimentary rocks of the Culpeper basin in the north, the Evington Group in the
central and south, and the Martinsville Igneous Complex, Bassett Formation, and Fork Mountain
Formation in the south. These last three rock types comprise the bulk of the Smith River allocthon
(Conley, 1978) which is bounded by the Bowens Creek fault and the Ridgeway fault The Bassett
Formation consists of biotite gneiss overlain by amphibolite, and the Fork Mountain Formation is
composed of mica schist and biotite gneiss. The Martinsville Igneous Complex is composed of the
Leatherwood Granite and the gabbro, norite, and diorite of the Rich Acres Formation. The
Evington Group is a broad band of metamorphic rocks that crop out from Campbell County north
to southwestern Fluvanna County. The group consists of mica schist and phyllite with graywacke,
greenstone, and marble.
Within the Piedmont, Late Triassic to early Jurassic continental sedimentary and igneous
rocks of the Newark Supergroup occur in ten basins that roughly form three northeast-trending
belts in east-central Virginia. The western belt includes the large Culpeper basin, which extends
into Maryland, the tiny Barboursville basin that is immediately south of the Culpeper, the tiny
Scottsville basin to the southwest of the Barboursville, and the large Danville basin, which is the
northern extension of the Dan River basin in North Carolina. The central belt consists of four
small basins, the largest being the northernmost Faimville basin, south of which is the Briery
Creek basin, the Roanoke basin, and the southernmost Scottsburg basin. The easternmost belt
consists of the small Richmond basin and the Taylorsville basin, which lies immediately north of
the Richmond basin. The strata in each basin dip northwest toward the faulted margin.
In the Culpeper basin, the basal Triassic Manassas Sandstone forms an outcrop belt along
the southeast margin of the basin that thins southward. The Manassas Sandstone consists of
arkosic sandstone, siltstone, and conglomerate. The Manassas Sandstone is overlain by a broad
belt of the Triassic Balls Bluff Siltstone. The Balls Bluff consists of fluvial red siltstones with thin
arkosic sandstones, overlain by lacustrine red and black shales and siltstones and fluvial
sandstones. Sandier parts of the upper Balls Bluff Siltstone in the southern part of the basin have
been assigned to the Tibbstown Formation by Lee and Froelich (1989). The Triassic Catharpin
Creek Formation in the northwestern part of the basin forms thick lenses of conglomerates and
sandstones that intertongue with the Balls Bluff lacustrine rocks to the south. A relatively narrow
belt of Jurassic basalts and sedimentary rocks occur in synclinal folds along the western quarter of
the basin. These rocks consist of the Mount Zion Church Basalt, the Midland Formation, the
Hickory Grove basalt, the Turkey Run Formation, the Sander Basalt, and the Waterfall Formation.
The Midland, Turkey Run, and Waterfall Formations consist of lacustrine black and red shales
interoedded with fluvial sandstones. Along the faulted northwestern margin of the basin, all of the
formations intertongue with alluvial fan conglomerates consisting of the older rocks immediately
outside of the basin. The Culpeper basin sedimentary rocks are intensively intruded by large
Jurassic diabase dikes and sheets mat are folded into broad dish-like synclines. The Barboursville
basin sedimentary sequence includes the Manassas Sandstone and the overlying Tibbstown
Formation. The Scottsville basin is mostly filled with Triassic conglomerates that reflect in their
composition the older rocks on the faulted side of the basin. Rocks in the Danville basin consist of
Triassic red and black shales and siltstones and arkosic sandstone and conglomerate. Jurassic
diabase intrudes the Triassic sedimentary rocks and the surrounding crystalline rocks.
IV-11 Reprinted from USGS Open-File Report 93-292-C
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The central belt of Newark Supergroup basins have no formal stratigraphic names. The
Farmville and Briery Creek basins have thin bands of Triassic arkosic sandstone along the eastern
margins that are overlain by a thick belt of lacustrine black shales and siltstones with coal seams
near the basal contact. The lacustrine rocks intertongue with conglomerates consisting of clasts of
the older rocks immediately outside of the basin near the northwestern border faults. The other
two basins consist predominantly of Triassic arkosic sandstones and conglomerates. Narrow
Jurassic diabase dikes cut the sedimentary rocks in these basins.
The eastern belt of Newark Supergroup basins is similar in character to the central belt
The Richmond basin consists of the basal Triassic Tuckahoe Formation, comprising a thin arkosic
fluvial sandstone (Lower Barren Beds Member) overlain by a black lacustrine shale with coal
seams (Productive Coal Measures Member). Both are restricted to a narrow belt on the eastern
edge of the basin and overlain by thick sequence of black shales (Vinita Beds Member) that
intertongue with conglomerates near the western border fault Outcrops of the Vinita Member are
restricted to a narrow band in the northern part of the basin by the overlying Triassic Turkey
Branch Formation, which consists of black to gray lacustrine shales and siltstones with abundant
sandstones near the base and top. The southern two-thirds of the basin is underlain by the Triassic
Otterdale Formation, which consists of sandstone and conglomerate. The exposed portion of the
Taylorsville basin consists of Triassic Doswell Formation. The basal Stagg Creek Member forms
a narrow outcrop band along the southern and eastern basin margin and consists of sandstones and
conglomerates. The Stagg Creek is overlain by the Falling Creek Member, which forms a parallel
narrow outcrop band. It consists of fine-grained fluvial and deltaic sandstones and lacustrine black
shales and coal seams. The uppermost Newfound Member covers most of the basin and consists
of fluvial sandstones and conglomerates. Some coarse conglomerates near the western border fault
are composed of clasts of the older rocks immediately outside of the basin. Narrow Jurassic
diabase dikes intrude the sedimentary rocks in these basins.
The Blue Ridge
The boundary between the Blue Ridge and Piedmont is represented in many different ways
on different maps. The physiographic Blue Ridge Province is only partly coincident with the
geologic Blue Ridge province. For the purposes of this report, the Blue Ridge is defined as the
rocks mapped as the Precambrian-Cambrian-Catoctin, SwiftRun, Lovingston, Mount Rogers, -
Mediums River, and Lynchburg Formations, Virginia Blue Ridge Complex and part of the
Chilhowee Group (Espenshade, 1970). The Chilhowee Group sedimentary rocks, which flank the
west limb of the Blue Ridge anticlinorium, are described with the Valley and Ridge Province.
However, rocks of the Chilhowee Group, especially the quartzite of the Weverton Formation, are
intimately associated with metavolcanic rocks, slate, and conglomerate of the Catoctin Formation in
the Blue Ridge. The eastern and western portions of the Blue Ridge in northern and central
Virginia are characterized by the Catoctin metavolcanic rocks. The Swift Run Formation underlies
the Catoctin on the western limb of the Blue Ridge anticlinorium, and the Lynchburg Formation,
which underlies the Catoctin, can be traced from Culpeper County to Patrick and Carroll Counties
in the south. The Catoctin Formation includes metabasalt, greenstone, and minor phyilite, arkose,
conglomerate, and schist On the western limb of the Blue Ridge anticlinorium it is underlain by
sandstone, conglomerate, graywacke, marble, and greenstone of the Swift Run Formation.
The Lynchburg Formation consists of biotite gneiss, graywacke, conglomerate, quartzite,
mica schist, and graphitic schist and phyilite. The lowest part of the Lynchburg, biotite-
hornblende gneiss of the Moneta Gneiss, crops out in eastern Bedford County. The Virginia Blue
IV-12 Reprinted tan USOS Open-File Report 93-292-C
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Ridge Complex is made up of granite, charnockite, granulite, and gneissic rocks of variable
composition that crop out in a broad belt that thins from Rappahannock County to Floyd County.
It includes the Roseland anorthosite, Striped Rock granite, Various granitic gneisses, and the
Marshall, Lovingston, Old Rag, Pedlar, and Robertson River Formations. The Old Rag
Formation is a quartz-feldspar granite that crops out in northern Madison County. The Pedlar
Formation is granodiorite, charnockite, granulite, syenite, diorite, and anorthosite that crops out
irregularly from southwestern Rappahannock County to Bedford County. The Robertson River
Formation and Mediums River Formation crop out in long linear bands within and on the eastern
edge of the Lovingston Formation from Rappahannock County south to Nelson County. The
Robertson River Formation is hornblende granite and syenite. The Mediums River Formation is
phyllite, quartzite, graywacke and conglomerate and the Lovingston Formation is biotite granite,
gneiss, and monzonite. Biotite granite, gneiss, and monzonite of the Marshall Formation crop out
to the south of the Lovingston Formation in Amherst County. The Roseland anorthosite is a small
body of plagioclase rock within the Marshall Formation.-; r
In the southernmost Blue Ridge to the west of the Lynchburg Formation, granite gneiss of
the Virginia Blue Ridge Complex and the Mount Rogers Formation underlies much of Grayson
County. The granite gneiss includes biotite gneiss, schist and quartzite and has several local names
including the Saddle gneiss, Cattron diorite, Beverdam Creek augen gneiss, Comers granite
gneiss, Grayson granodiorite gneiss, and Shoal gneiss. The gneiss is intruded by the Striped
Rock granite. The Mount Rogers Formation to the west comprises rhyolite, arkose, and tuff.
Valley and Ridge
The Valley and Ridge Province is underlain by a series of narrow, northeast-trending belts
of carbonate rocks, sandstone, and shale that are tightly folded and cut by faults. Valleys are
underlain by carbonate rocks and shale, whereas ridges are predominantly underlain by sandstones
and cherty carbonate strata.
The oldest rocks of the Valley and Ridge are Cambrian quartzites and shales of the
Chilhowee Group. These rocks form a prominent belt along the southeastern margin of the
province. In the southern Valley and Ridge, the Chilhowee Group consists of the basal Unicoi
Formation, a quartzite with conglomerate at the base and some basalt inter beds; the Hampton
Formation, which consists of green shales interbedded with quartzite and sandstone; and quartzite
of the Erwin Formation. In the northern Valley and Ridge, the Chilhowee Group consists of the
Weverton, Harpers, and Antietam Formations. The Chilhowee Group is overlain by a thick
sequence of Cambrian dolomite, limestone, and shale that forms several narrow belts in the
southern and western part of the province. The oldest Cambrian unit, the Shady Formation, is a
dolomite with limestone interbeds, similar to the younger Elbrook Formation. These units are
separated by the shaly Rome Formation which contains thin limestone interbeds. The
Conococheague Formation, consisting of limestone and dolomite, is Cambrian and Ordovician in
age and constitutes the top of the Cambrian sequence in the north. The Elbrook and
Conococheague Formations are interbedded with progressively more common shale units south
and westward. In northwestern and west-central Virginia, this rock progression includes the
Honaker Dolomite, overlain by green shale of the Nolichucky Formation, followed by the Copper
Ridge Dolomite. In southwestern Virginia, this progression consists of the Rowe Formation,
Pumpkin Valley Shale, Rufledge Limestone, Rogersville Shale, Marysville Limestone, and the
Nolichucky and Maynardville Formations, which are overlain by the Copper Ridge Dolomite.
IV-13 Reprinted from USGS Open-File Report 93-292-C
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Ordovician rocks underlie about a third of the province to the north and nearly half of it to
the south, but only occur in relatively small areas in the west central part of the province. The
lower Ordovician rocks are predominantly limestone with dolomite and shale. The oldest
Ordovician rocks in the province are the limestone and dolomite of the Chepultepec and
Bcckmantown Formations which are equivalent to the more dolomitic Mascot and Kingsport
Formations and the Knox Group in the southern part of the province. These are overlain by
narrow belts of limestone and shale that are subdivided into over 30 separately named units (please
see the geologic map explanation, figure 2, for the names of these units). This carbonate interval is
overlain by black shale and graywacke sandstone of the Martinsburg Formation in the north and
green shale and argillaceous limestone of the Reedsville Formation to the south. The Martinsburg
is overlain by red and green fluvial sandstone and shale of the Juniata Formation and Oswego
Sandstone to the north and the Reedsville is overlain by calcareous shale and limestone of the
Sequatchie Formation to the south.
Silurian rocks comprise only narrow belts in the northern, east-central, and southern parts
of the province. They comprise about one-fourth of the rocks underlying the west-central part of
the province. The basal Tuscorora Formation is a quartzite overlain by marine shale of the Rose
Hill Formation and the Keefer Sandstone, which includes beds of hematitic sandstone. These are
overlain by the Cayuga Group, which includes green marine shale and siltstone of the McKenzie
Formation, red sandstone and shale of the Bloomsburg Formation, and shaly limestone of the
Wills Creek and Tonoloway Formations, and by limestone of the Keyser Formation. The
Tuscorora Formation dominates the Silurian rocks exposed in the west-central part of the province.
Devonian rocks form a prominent belt along the northwestern and south-central portions of
the province and comprise most of the rocks underlying the west-central part of the province. The
lowermost Devonian rocks are dominated by limestone with some sandstone, including the
Cocymans, New Scotland, and Licking Greek Members of the Helderburg Formation. These are
overlain by green to black shales with some quartz sandstone and shaly limestone units near the
base and includes the Rocky Gap Sandstone, Ridgeley Sandstone, Huntersville Chert, Needmore
Shale, Onondaga Formation, the Millboro and MarceUus Shales, and the Mahantango, BralMer,
and Chemung Formations. In the northwestern portion of the province, the uppermost Devonian
rocks are red shale and sandstone of the Hampshire Formation.
Mississippian rocks are restricted to a few small-areas in the northern part of the province
and form prominent belts along the east-central, south-central, and southwestern portions of the
province. Mississippian rocks to the north consist of quartzose sandstone and conglomerate with
minor mudstone and coal beds of the Pocono Formation. To the south the oldest rocks are gray-
green shale and sandstone with minor coal beds of the Price Formation, overlain by red shale and
sandstone of the Maccrady Formation. These are overlain by the Greenbrier Limestone and to the
south by the Newman Limestone. These formations are overlain by shales, calcareous shale and
sandstone, and limestone of the Fido Sandstone, Cove Creek Limestone, and the Bluefield and
Hinton Formations. The Hinton Formation is combined with greenish sandstone, conglomeratic
sandstone, and green to red shale of the Princeton Sandstone and Bluestone Formation to form the
Pennington Group, which crops out along southwestern margin of the province and forms the
southernmost area of Mississippian rocks in Washington and Scott Counties.
IV-14 Reprinted from USGS Open-File Report 93-292-C
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Appalachian Plateaus -.
Rocks underlying the Appalachian Plateaus are predominantly Pennsylvania fluvial
sandstone, shale, and coal that form a broad syncline. These include the Lee and Norton
Formations, GladeviHe Sandstone, Wise Formation, and Harlan Sandstone. A few tiny outcrops
of Blusstone Formation green and red shale and sandstone occur along the northwestern margin of
the province.
SOILS
A generalized soil map for Virginia is given in figure 5. Soils of the Coastal Plain,
Piedmont, and lower mountains of the Blue Ridge are relatively deep and well oxidized, and
contain clay subsoils (Ultisols). Soils of the high mountains of the Blue Ridge, Valley and Ridge,
and Appalachian Plateau are shallower and less oxidized (Alfisols and Inceptisols). The following
discussion is condensed from U.S. Department of Agriculture (1979,1987) and Devereux and
others (1965). It is recommended that the reader consult these references, U.S. Soil Conservation
Service county soil surveys, and other publications for more detailed information.
Coastal Plain
Soils of the Cretaceous and Tertiary Coastal Plain are Ultisols comprising deep to very
deep, nearly level to sloping soils formed in unconsolidated marine sediments and alluvium derived
from Piedmont rocks on river terraces. These soils range from sands and sandy loams to clays and
clay loams, and they are generally poorly drained. Near the Piedmont, the Coastal Plain soils have
clay hardpans with low permeability (Devereux and others, 196S). Soils in the eastern part of the
Cretaceous and Tertiary Coastal Plain generally have moderate permeability. Alluvial soils in
stream valleys in the southern part of the Coastal Plain have high permeability, although they are
commonly poorly to moderately drained.
The Quaternary Coastal Plain is covered primarily by Ultisols, mature, deeply weathered
soils with prominent clay accumulations in the subsoil and often containing a moist or wet
substratum (U.S. Department of Agriculture, 1987). They are deep, generally poorly drained soils
with moderate permeability farmed in unconsolidated sediments. Coarse-textured, well-drained
soils with moderate permeability derived from Coastal Plain alluvial and estuarine materials occur
along the James and Meherrin Rivers (Devereux and others, 1965). Beach sands along the
shoreline have high permeability (U.S. Department of Agriculture, 1979). Several fairly large
areas are occupied by marshes, such as the Dismal Swamp. Histosols, poorly drained, commonly
wet, organic-rich soils, have formed in these environments.
Piedmont
Soils in the Piedmont are Ultisols, sandy, silty, and clayey loams with thin subsurface clay
horizons (U.S. Department of Agriculture, 1987). The soils of the Piedmont generally have a
light-colored surface and brownish to red subsoils; however, as one travels from south to north,
the soils become somewhat darker in the surface and subsoil and contain increasing amounts of
organic matter. Northern Piedmont soils also tend to be shallower and contain more friable
subsoils than southern Piedmont soils, although heavy plastic (clay-rich) soils occur in some
valleys in the northern Piedmont (Devereux and others, 1965). Most of the Piedmont is covered
by shallow to deep, moderately permeable soils formed in residuum from acidic rocks such as
granite, gneiss, and schist on gently to moderately sloping surfaces. Soils formed in residuum
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Figure 5. Generalized soils map of Virginia (after U.S. Department of Agriculture, 1979).
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GENERALIZED SOILS MAP OF VIRGINIA
EXPLANATION
APPALACHIAN PLATEAU & VALLEY AND RIDGE
Shallow to deep, moderately to highly permeable, steep to very steep soils formed mainly
in residuum from acid sandstone, shale, and phyllrtes; on mountains.
Moderately deep, moderately to highly permeable, gently sloping to steep soils formed in
residuum from acid shale; on uplands of dissected valleys.
Shallow to very deep, moderately permeable, gently sloping to steep soils formed in
residuum from limestone or interbedded limestone, sandstone, and shale; on uplands in
limestone valleys.
BLUE RIDGE MOUNTAINS
Shallow to deep, moderately to highly permeable, moderately steep to very steep soils
formed in residuum from sandstone, granite, or greenstone; on mountains.
Moderately deep to deep, moderately permeable, sloping to steep soils formed in
residuum from granite, gneiss, and greenstone; on mountains and ridges.
Shallow to deep, moderately to highly permeable, gently sloping to steep soils formed in
residuum from acidic or basic rocks; on uplands of the northern Blue Ridge.
Shallow to deep, moderately permeable, gently sloping and sloping soils formed in
residuum from acidic rocks on uplands of the Piedmont.
Shallow to deep, slowly to moderately permeable, nearly level and gently sloping soils
formed in residuum from basic rocks or mixed basic and acidic rocks on uplands of the
Piedmont.
Shallow to deep, slowly to moderately permeable, gently sloping soils formed in residuum
from sedimentary rocks in Triassic basins of the Piedmont.
Moderately deep to deep, slowly to moderately permeable, gently sloping to sloping soils
formed in residuum from igneous and metamorphic rocks or in associated coastal plain
sediments; on uplands of the upper Coastal Plain and Piedmont.
CRETACEOUS AND TERTIARY COASTAL PLAIN
Deep to very deep, slowly to moderately permeable, nearly level to sloping soils formed in
unconsolidated sediments of the Coastal Plain and river terraces; dominantly above 30
feet elevation. Alluvial soils of valleys in the southern part of this area are highly
permeable.
QUATERNARY COASTAL PLAIN
Deep, moderately permeable, nearly level and gently sloping soils formed in
unconsolidated sediments of the Coastal Plain or in organic materials; dominantly less
than 30 feet elevation.
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from basic rocks or mixed basic and acidic rocks on uplands of the Piedmont are shallow to deep,
relatively fine-textured soils with low to moderate permeability. In the southern Piedmont, these
soils are formed mainly on dark slate, greenstone, and metavolcanic rocks in Mecklenburg and
Halifax Counties (Devereux and others, 1965), and on amphibolite, serpentinite, and other
ultramafic rocks in the northern Piedmont. The Mesozoic Basins are covered by Alfisols (mineral
soils with argillic (clayey) subsurface horizons or fragipans, and which may contain iron-rich or
calcic horizons in the subsurface) and Ultisols, comprising shallow to deep, gently sloping, sandy,
silty, and clayey loams formed on red sandstone, siltstone, and shale, brown sandstone, some
conglomerate, and metasedimentary rocks. Because of their firm, clayey subsurface horizons,
these soils have low to moderate permeability. Along the eastern edge of the Piedmont, moderately
deep to deep, slowly to moderately permeable soils are formed in saprolite and residuum from
igneous and metamorphic rocks or in associated coastal plain sediments on gently to moderately
sloping uplands of the upper Coastal Plain and Piedmont
Blue Ridge
Soils of the Blue Ridge Mountains are mainly Ultisols and Alfisols. Mostly shallow to
locally deep, moderately steep to very steep, stony soils formed in residuum from sandstone,
granite, or greenstone have formed on the northwestern slopes of mountains in the western Blue
Ridge. These soils are well drained to excessively drained and have moderate to high permeability;
much of the area is rock outcrop. The southeastern slopes, eastern foot slopes, and smooth
mountain tops of the Blue Ridge are covered by moderately deep to deep, moderately permeable,
sloping to steep soils formed in saprolite and residuum from granite, gneiss, schist, mica schist,
and greenstone. The surface texture of most soils in this map unit are loam, silt loam, or clay
loam, and most of the soils are friable throughout the profile. The steep mountain slopes are
largely covered by thin, stony soils. On the mountaintops and in intermountain areas of the
southern Blue Ridge, the soils are deeper and better developed. Soils developed on weathered
mica schist have loose topsoils and clayey, red or brownish micaceous substrata (Devereux and
others, 1965) that have relatively low peimeabffity but are easily erodible. Gently to moderately
sloping upland areas in the northeastern part of the Blue Ridge are covered by shallow to deep,
moderately to highly permeable soils formed in residuum from acidic or basic rocks, primarily
metabasalt and granite. Also included in this map unit are moderately permeable-silt and clay loams
formed on schist and phyllite in the northern Piedmont (fig. 5).
Appalachian Plateaus and Valley and Ridge
The Appalachian Plateaus and Valley and Ridge are covered by Inceptisols and Ultisols.
Inceptisols are soils with weakly developed horizons in which materials have been altered or
removed and may contain horizons of accumulated silica, iron, or bases, but they generally do not
have clayey subsurface horizons. Ultisols are shallow to deep, moderately to highly permeable,
steep to very steep soils formed mainly in residuum from acid sandstone, shale and phyUites.
Soils of this type occur on mountains. Moderately deep, moderately to Mghly permeable, gently
sloping to steep soils formed in residuum from acid shale cover uplands of dissected valleys. In
many areas, rock fragments of various sizes are scattered across the surface and throughout the soil
(Devereux and others, 1965). The limestone valleys are covered by shallow to very deep, gently
sloping to steep soils formed in residuum from limestone or interbedded limestone, sandstone and
shale. Soils on ridges are usually derived from dolomitic limestone that contains significant
amounts of chert, and locally, sandstone and shale, which make the rock more resistant to erosion
IV-18 Reprinted from TJSGS Open-File Report 93-292-C
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(Devereux and others, 1965). Softs in the lower-lying limestone valleys are silt loams where the
soils are derived from limestone or shale, and sandy loams or loams where the soils are derived
from sandstone or mixtures of sandstone and limestone. Many of the shale or shaly limestone-
derived soils have plastic clay substrata that impart a low permeability to the soil. The remainder of
the soils in this map unit have moderate permeability.
RADIOACTIVITY
An aeroradiometric map of Virginia (fig. 6) was compiled from spectral gamma-ray data
acquired during the U.S. Department of Energy's National Uranium Resource Evaluation (NURE)
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 6, low eU appears to be associated with the
upper Tertiary and Quaternary sediments of the Coastal Plain; the metavolcanic rocks of the
Piedmont and Blue Ridge; the Virginia Blue Ridge Complex from southern Albermarle County to
Roanoke County; the Silurian sedimentary rocks of the Valley and Ridge; and parts of the
Devonian and Mississippian sedimentary rocks of the Valley and Ridge. Moderate eU is
associated with much of the Tertiary sediments of the Coastal Plain; the granitic schist, granite, and
gneiss of the Piedmont; granite and gneiss in the northern Blue Ridge; and many of the
sedimentary rocks in the Valley and Ridge and Appalachian Plateau. High eU is associated with
the Petersburg and Redoak Granites in the eastern and southern Piedmont; the Old Rag and Crozet
granites in the northern Blue Ridge; the Striped Rock granite in the southern Blue Ridge; the
schists and gneiss of the Goochland terrane; the faulted schist, gneiss, and granite in the
southwestern Piedmont, Triassic rocks of the Danville basin; and faulted Paleozoic elastics and
carbonates in the southern Valley and Ridge and Appalachian Plateau.
Many of the eU concentrations in the Piedmont, Blue Ridge, and parts of the Coastal Plain
(fig. 6) may be attributable to the mineral monazite, which, in the Piedmont and Blue Ridge, is
found in high-grade metamorphic rocks and late-stage granitic intrusive rocks. Monazite contains
significant amounts of uranium and thorium. Its resistance to weathering and high density result in
local concentrations of monazite in soils and as placer deposits in marine, fluvial, and alluvial
sediments. Several monazite "belts" in the Piedmont were defined by Mertie (1953); one of these
belts extends from the Raleigh Belt of North Carolina into the Goochland terrane of Virginia.
During the NURE program, stream sediment samples were analyzed for various elements. An
examination of the cerium data from these stream sediment samples can be used to verify whether
the source of radioactivity is monazite, as cerium is an element commonly found in monazite. A
map of the cerium concentrations exceeding 200 ppm in sediment samples for Virginia (Cook and
others, 1982) shows several distinct belts of cerium that correspond to the Grayson gneiss, parts
of the Virginia Blue Ridge Complex, the Leatherwood granite, parts of the Evington Group, the
Shelton granite gneiss, the schist, granite, and gneiss of the Goochland terrane, and scattered
anomalies throughout the Tertiary of the Piedmont and in the Quaternary east of Chesapeake Bay.
These belts correspond with several of the areas of high eU seen on the NURE aerial radiometric
map (fig. 6). However, uranium in other minerals, or by itself as an oxide, occurs in shear zones,
granite intrusives, pegmatites, granite gneiss, black shales, and soils formed from carbonate rocks.
These forms of uranium are also the source of much of the high radioactivity found in Virginia.
Granitic bodies and pegmatites may contain a number of uranium-bearing minerals, including
sphene, zircon, uraninite, allanite, and exotic uranium and thorium minerals, as well as monazite.
IV-19 Reprinted from USGS Open-FUe Report 93-292-C
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Uranium may also be finely disseminated in rocks and soils, such as in black shales, soils formed
from carbonate rocks, and graphitic schists and phyllites. Specific, known occurrences of uranium
in Virginia are discussed below. Hie source of uranium in the soils and rocks is important in
evaluating their radon potential. Uranium that is 'locked up" in mineral species as a trace element
will liberate less radon to pore spaces than uranium in uraninite, uranium oxidized with iron on
mineral grain surfaces, uranium on fracture and fault surfaces, or finely disseminated uranium in
graphitic phyllite or black shales.
There are numerous reports on uranium occurrences of Virginia. Grosz (1983) determined
that the Coastal Plain of Virginia was difficult to assess using aerial techniques because of the
cultural affects, such as that of agriculture, on surface radioactivity response. However, a regional
pattern of radioactivity from the NURE data (fig. 6), which is different from the data obtained by
Grosz, suggests that some of the Tertiary sediments have moderate radioactivity. Studies of
uranium and radon in the Coastal Plain of New Jersey, Alabama, and Texas by Gundersen and
others (1991) suggests that glauconitic, phosphatic, monazite-rich, and carbonaceous sediments
are the source of the moderate indoor radon measured in the Coastal Plain of these states.
Glauconite contains significant amounts of uranium (Gundersen and Schumann, 1989).
Phosphate is an effective scavenger of uranium and phosphatic deposits tend to have high uranium
concentrations, in many cases higher than in glauconitic sediments. The occurrence of fossils,
especially those high in phosphate such as shark teeth and whale bone, also correlates with
moderate to high soil radon concentrations. In a recent study of radon in soils developed from
Coastal Plain sediments in Virginia, Berquist and others (1990) found uranium in concentrations as
high as 1350 ppm in fossilized bone of the Yorktown Formation; the PaOs concentration was 32
percent (C.R. Berquist, oral comm.). They found that the average soil radon from their samples of
Virginia Coastal Plain sediments was generally 1000 pQ/L or less, the Yorktown sands having the
highest average radon concentration in sM gas, 959 pCi/L.
Uranium occurrences in the Piedmont and Blue Ridge appear to be associated most often
with uraniferous granites, pegmatites, monazite and other radioactive minerals in schist and gneiss,
phyllite, and fault zones (especially shear zones). In northern Virginia, Mose and others
(1988a, b), Otton and others (19S8), and Schumann and Owen (1988) noted that the highest aerial
radioactivity, soil-gas radon, and indoor radon levels are associated with phyllite and schist of the
Peters Creek Schist in Fairfax County. Neuschel and others (1971) reported elevated radioactivity
over a small quartz monzonite pluton northwest of Fredericksburg. Neuschel (1970) also
observed elevated radioactivity over granite and granite pegmatites in the area of Spotsylvania.
Several uranium and radon studies have been conducted in the Goochland terrane. Baillieul
and Dexter (1982) examined uranium anomalies found during the NURE program in the Hylas
fault zone and the Richmond basin west of Richmond. The Hylas zone is a mylonite developed
partly in the Petersburg Granite and partly in the Maidens Gneiss and State Farm Gneiss. Baillieul
and Dexter (1982) reported chemical uranium concentrations in the mylonite ranging 3-29 ppm
UsOg and pegmatite containing 450 ppm UsOg. In the Richmond basin, Triassic coaly shale
measured 5 ppm UsOg and feldspathic wacke measured 15 ppm UaOg. The Petersburg Granite
also showed anomalous gamma radioactivity. Radon and uranium studies of the Hylas zone by
Gates and others (1990) reported similar results but also showed that the Hylas zone mylonite
rocks can produce anomalously high radon in the overlying soils (up to 12,000 pCi/L). Uranium
in the Petersburg Granite and surrounding gneiss is distributed in a number of minerals. During
deformation these minerals were broken down and the uranium was redistributed into the foliation
of the mylonite. This uranium concentration mechanism may be common in most mylonites
IV-21 Reprinted firam USGS Open-File Report 93-292-C
-------
(Gunderscn, 1991). Gates and others (1990) found that the Sabot amphibolite had low uranium
(<1 ppm) and low soil radon (generally < 500 pQ/L). Soils developed on the Maidens and State
Farm Gneiss yielded moderate amounts of soil radon (generally in the 700-1000 pCi/L range).
Undcformed Petersburg Granite and the Triassic conglomerate (derived from granite and mylonite)
yielded moderate to high soil radon (generally 1000-2000 pCi/L). Soils over the pegmatite and
mylonite yielded the highest soil radon (generally > 2000 pCi/L). To the south in the Goochland
terrane, studies by Krason and others (1988) of anomalous radioactivity in the Powhatan area
suggest that the source of the radioactivity is accumulations of monazite in saprolite soils developed
on a monazite-rich layer of the Maidens Gneiss. The deposit also appears to be structurally
controlled since it corresponds to the crest of the Goochland anticline.
The Swanson uranium deposit in Pittsylvania County is a well known, fault-related
uranium deposit (Halladay, 1987). The deposit is located along the Chatham fault on the west side
of the Danville basin and is hosted in severely sheared and altered gneiss of the Fork Mountain
Formation. Aerial radiometric anomalies are associated with the main ore body and several other
anomalies are located to the north along the fault The ore body is described by Frishman and
others (1987) as a stockwork of U-bearing veinlets within the fault zone.
Grauch and Zarinsky (1976) report radioactivity in the Grayson gneiss, in schist near
Ridgeway in Henry County and near Woodville in Rappahannock County, in the Lovingston
Formation in Albermarle, Bedford, and Culpeper Counties, and in pegmatite in Amelia County.
Baillieul and Daddazio (1982) conducted field studies in the Lovingston Formation and found
numerous uranium occurrences and areas of very high radioactivity usually associated with shear
zones, highly altered schist and gneiss, vein fillings, and mineral accumulations in saprolite. They
also evaluated several igneous plutons and found elevated uranium associated with the Old Rag
Granite, the Crozet Granite, and where the Ellinsville granodiorite and Green Springs pluton
intrude the metamorphic rocks of the Candler and Chopawamsic Formations. They note that no
anomalous radioactivity was associated with the Pedlar, Swift Run, and Lynchburg Formations
but that the Mediums River Formation did have anomalous radioactivity associated with it
Sandstones and siltstones of the Culpeper basin which have been metamorphosed to
homfcls and altered by diabase intrusion are mineralized with uranium and cause documented
moderate to high radon levels in Virginia (Otton and others, 1988; Schumann and Owen, 1988).
Smootand Robinson (1988) examined th& base metal mineralization and conducted field studies of
the radioactivity in the Newark Supergroup and found several units with anomalous radioactivity,
especially black shales and reduced fluvial sandstones. Some coarse-grained gray sandstones have
significant radioactivity, often associated with green clay clasts and copper. The upper Manassas
Sandstone has anomalous radioactivity associated with fluvial crossbeds, with intraclasts, and with
lenses of gray carbonaceous silt, particularly in the northern half of the Culpeper basin. The fluvial
sandstone immediately below the Cow Branch Member in the Danville basin is similar to the upper
Manassas Sandstone and may also contain uranium mineralization. Black shales in the lower part
of the lacustrine portion of the Balls Bluff Siltstone are notably uranium-bearing. Border
conglomerates in the Danville and Richmond basins, consisting of blocks of mylonite, have high
radioactivity. Elevated radioactivity occurs where diabase bodies intrude limestone, limestone
conglomerates, or calcareous zones in siltstones and sandstones. Black shales in the Cow Branch
Member and immediately overlying lacustrine units are also likely to contain high uranium. Black
shales and gray sandstones in the upper Balls Bluff Siltstone, the finer-grained portions of the
Catharpin Creek Formation, the Waterfall, Turkey Run, and Midland Formations, the upper
IV-22 Reprinted from USGS Open-File Report 93-292-C
-------
portions of the Danville basin lacustrine sequence, and in the Vinita Beds Member of the Tuckahoe
Formation may all have locally elevated uranium (J.P. Smoot, oral comm.).
Sedimentary rocks of the Valley and Ridge and Appalachian Plateau have low to moderate
ell associated with them on the NURE map (fig. 6). To the north in Pennsylvania, carbonate
rocks of the Valley and Ridge and Great Valley have been the focus of several studies (van
Assendelft and Sachs, 1982; Gross and Sachs, 1982; Greeman and Rose, 1990; Luetzelschwab
and others, 1989) and the carbonate rocks in these areas produce soils with high uranium and
radium contents and high radon emanation. Carbonate rocks themselves are usually low in
radionuclide elements but the 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 base metals, including radionuclides. Studies in the carbonate
rocks and soils of the Great Valley in West Virginia suggest mat the deepest, most mature soils
have the highest radium and radon concentrations (Schultz and others, 1992). Rinds containing
high concentrations of uranium and uranium-bearing minerals can be formed on the surfaces of
rocks affected by CaCOs dissolution and karstification. Karst and cave morphology is also
thought to promote the flow and accumulation of radon. Schultz and others (1992) also measured
high radon concentrations in soils and high indoor radon levels in homes on the black shales of the
Martinsburg Formation. Analysis of the NUKE aerial radiometric data in Virginia (Texas
Instruments Incorporated, 1980) indicates that uranium anomalies are associated with Devonian
black shales, with the sandstones and shales of the Chemung Formation, shale and sandstone of
the Hampshire Formation, sandstone, shale, and coal of the Pocono Formation, limestone and
shale of the Greenbrier Group, and with some of the Pennsylvanian sandstones, shales, and coals.
However, Baillieul and Daddazio (1982) field checked some of these rock units in northern
Virginia and noted a striking contrast in radioactivity between the same rocks in Pennsylvania and
Virginia. They concluded that the upper Devonian-Pennsylvanian sandstone unite in Virginia have
only local areas of elevated radioactivity and do not appear to be as radioactive as their equivalents
in Pennsylvania.
INDOOR RADON
Indoor radon data from 1156 homes sampled in the State/EPA Residential Radon Survey
conducted in Virginia during the winter of 1991-92 are shown in figure 7 and Table 1. Data are
shown in figure 7 only for those counties and cities with 5 or more data values. A map of counties
is included for reference (fig. 8). The maximum value recorded in the survey was 81.5 pG/L in
Danville, in Pittsylvania County. The average for the State was 2.7 pQ/L and 17.6 percent of the
homes tested had indoor radon readings exceeding 4 pCi/L. Nonrandom commercial data
compiled by EPA Region 3 are shown in figure 9 for comparison purposes. Data are shown in
figure 9 only for those counties with 15 or more data values.
Both indoor radon data sets show a lack of data for significant parts of the Coastal Plain,
southern Piedmont, western Valley and Ridge, and Appalachian Plateaus. Available data are
concentrated in the northern and central portions of the State. The most obvious pattern that
emerges from these data sets is the abundance of counties that contain houses with high (>4 pCi/L)
indoor radon averages in the Valley and Ridge (fig. 7). Correspondingly, the commercial date
(fig. 9) show the greatest percentage of readings over 4 pCi/L concentrated in the Valley and Ridge
counties. Counties of the Blue Ridge and Piedmont have notably moderate (2-4 pQ/L) county
IV-23 Reprinted from USGS Open-File Report 93-292-C
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Bsmt. & 1st Floor Rn
%>4pO/L
48 L
OtolO
11to20
21 to 40
41 to 60
61 to 80
Missing Data
or < 5 measurements
46 L
Bsmt. & 1 st Floor Rn
Average Concentration (pCi/L)
0.0 to 1.9
2.0 to 4.0
4.1 to 10.0
10.1 to 135
Missing Data
or < 5 measurements
100 Miles
Figure 7. Screening indoor radon data from the EPA/State Residential Radon Survey of
Virginia, 1991-92, for counties with 5 or more measurements. Data are from 2-7 day charcoal
canister tests. Histograms in map legends show the number of counties in each category. The
number of samples in each county (See Table 1) may not be sufficient to statistically characterize
the radon levels of the counties, but they do suggest general trends. Unequal category intervals
were chosen to provide reference to decision and action levels.
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TABLE 1. Screening indoor radon data from the EPA/State Residential Radon Survey of
Virginia conducted during 1991-92. Data represent 2-7 day charcoal canister measurements
from the lowest level of each home tested.
COUNTY
ACCOMACK
ALBEMARLE
ALLEGHANY
AMELIA
AMHERST
APPOMATTOX
ARLINGTON
AUGUSTA
BATH
BEDFORD
BOTETOURT
BRUNSWICK
BUCHANAN
BUCKINGHAM
CAMPBELL
CAROLINE
CARROLL
CHARLES CITY
CHARLOTTE
CHESTERFIELD
CLARKE
CRAIG
CULPEPER
CUMBERLAND
DICKENSON
DINWIDDIE
ESSEX
FAIRFAX
FAUOWER
FLOYD
FLUVANNA
FRANKLIN
FREDERICK
GILES
GLOUCESTER
GOOCHLAND
GRAYSON
GREENE
GREENSVILLE
HALIFAX
HANOVER
NO. OF
MEAS.
5
12
5
4
14
5
14
19
2
15
9
3
3
4
17
3
11
1
4
-...459
3
2
6
2
6
6
2
70
9
5
2
7
9
8
3
3
6
1
2
2
13
MEAN
0.3
4.5
1.6
1.2
1.9
2.3
1.7
3.0
4.0
1.8
6.6
1.7
1.3
1.0
2.4
0.8
1.5
1.1
1.0
3;1
2.8
2.3
1.5
1.0
0.6
13.9
1.9
2.1
1.9
2.9
2.3
2.0
6.3
3.2
0.4
3.1
2.3
1.3
0.5
1.5
0.9
GEOM.
MEAN
0.2
1.7
1.4
0.6
1.1
1.5
1.1
1.8
3.3
1.0
4.2
1.6
1.2
0.5
1.5
0.5
0.9
1.1
0.7
1.1
1.8
0.7
0.9
1.0
0.4
1.3
1.6
1.4
1.2
2.6
2.3
1.1
2.1
1.1
0.4
1.3
1.3
1.3
0.2
1.4
0.7
MEDIAN
0.2
1.8
1.7
1.2
1.0
0.9
1.3
2.0
4.0
1.8
3.7
1.6
1.3
0.7
1.8
0.8
0.7
1.1
0.7
1.1
2.1
2.3
1.7
1.0
0.6
0.6
1.9
1.6
1.2
2.9
2.3
1.0
2.2
0.9
0.4
0.6
1.1
1.3
0.5
1.5
0.6
STD.
DEV.
0.3
8.5
0.7
1.0
2.1
2.4
1.5
3.1
3.0
1.9
6.7
0.7
0.7
1.0
2.5
0.7
1.3
0.0
1.1
7.2
2.7
3.1
1.2
0.0
0.4
31.7
1.2
2.0
2.4
1.3
0.0
2.9
12.2
4.8
0.2
4,4
2.8
0.0
0.6
0.5
0.7
MAXIMUM
0.8
30.7
2.3
2.5
7.4
6.1
4.9
13.4
6.1
7.8
20.8
2.4
2.0
2.4
9.7
1.5
4.3
1.1
2,6
49.9
5.7
4.5
3.4
1.0
1.1
78.6
2.7
9.2
7.9
4.9
2.3
8,5
38.5
12.0
0.6
8.1
7.6
1.3
0.9
1,8
2.0
%>4 pCi/L
0
25
0
0
14
20
14
32
50
7
44
0
0
0
12
0
9
0
0
17
33
50
0
0
0
17
0
10
11
20
0
14
33
25
0
33
17
0
0
0
0
%>20pCi/L
0
8
0
0
0
0
0
0
0
0
11
0
0
0
0
0
0
0
0
3
0
0
0
0
0
17
0
0
0
0
0
0
11
0
0
0
0
0
0
0
0
-------
TABLE 1 (continued). Screening indoor radon data for Virginia.
COUNTY
HBNRIOO
HENRY
ISLE OF WIGHT
JAMES CTIY
KING GEORGE
KING WILLIAM
LANCASTER
fjgB
LOUDOUN
LOUISA
LUNENBURG
MADISON
MATHEWS
MECKLENBURG
MIDDLESEX
MONTGOMERY
NELSON
NEW KENT
NORTHAMPTON
NORTHUMBERLAND
NOTTOWAY
ORANGE
PAGE
PATRICK
PITTS YLVANIA
POWHATAN
PRINCE EDWARD
PRINCE GEORGE
PRINCE WILLIAM
PULASKI
RAPPAHANNOCK
ROANOKE
ROCKBRIDGE
ROCJONGHAM
RUSSELL
SCOTT
SHENANDOAH
SMYTH
SOUTHAMPTON
SPOTSYLVANIA
STAFFORD
SURRY
SUSSEX
NO. OF
MEAS.
30
13
1
1
1
3
2
3
13
5
3
6
1
13
1
11
10
6
2
2
1
"1
5
8
21
3
4
3
16
11
7
12
6
15
9
4
15
14
2
7
11
1
2
MEAN
1.7
2.0
0.9
1.0
33
0.6
1.5
43
2.0
0.9
2,1
2.4
0.4
2.5
1.3
33
1.8
2.1
05
1.4
0.8
4.2
2.2
7.7
2.8
0.4
1.4
0.3
1.5
4.8
3.7
2.2
4.0
2.7
7.0
5.7
10.1
5.8
0.5
0.9
2.3
0.6
0.7
GEOM.
MEAN
0.9
1.5
0.9
1.0
33
0.4
12.
IS
1.3
0.8
0.7
1.3
0.4
1.4
1.3
1.7
1.4
1.7
0.4
1.3
0.8
1 :-"L7
1.9
5.7
1.8
0.4
0.8
0.2
1.0
2.8
2.4
1.1
3.0
1.6
2.3
2.7
3.2
2.6
0.4
0.5
1.3
0.6
0.7
MEDIAN
0.8
1.6
0.9
1.0
33
0.7
U
1.3
2.0
0.8
1.4
2.1
0.4
2.1
W
2.1
1.6
2.0
0.5
1.4
0.8
" ' IS
1.9
7.0
2.1
03
1.1
0,2
1.5
33
2.2
0.8
4.3
1.8
3.2
3.1
2.7
2.9
0.5
0.8
13
0.6
0.7
STD.
DEV.
2.7
1.5
0.0
0.0
0.0
0.5
13
5.2
1.4
0.4
2.6
1.8
0.0
2.5
0.0
3.4
1.3
1.4
0.2
0.1
0.0
6.8
1.0
6.6
2.7
0.2
13
0.4
1.1
4.8
3.9
23
2.5
3.0
13.4
7.1
19.7
8.5
0.1
0.8
2.5
0.0
0.1
MAXIMUM
14.9
5.7
0.9
1.0
33
1.0
2.4
103
4.1
1.4
5.0
4.8
0.4
8.5
13
10.9
5.1
4.5
0.6
1.4
0.8
19.4
33
21.8
12.2
0.6
3.1
0.8
4.1
153
11.9
6.1
6.7
11.7
42.4
15.8
77.2
33.1
0.5
2.0
8.2
0.6
0.8
%>4pCi/L
7
8
0
0
0
0
0
33
8
0
33
33
0
23
0
36
10
17
0
0
0
• - • u
0
63
24
0
0
0
6
36
29
25
50
13
44
50
40
43
0
0
27
0
0
%>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
0
13
0
0
0
0
0
0
0
0
0
0
11
0
13
7
0
0
0
0
0
-------
TABLE 1 (continued). Screening Indoor radon data for Virginia.
COUNTY
TAZEWELL
WARREN
WASHINGTON
WESTMORELAND
WISE
WYTHE
YORK
NO. OF
MEAS.
20
7
20
1
5
7
3
MEAN
5.2
2.6
3.4
U
5.8
4.9
0.6
GEQM.
MEAN
2.9
1.6
2.1
1.5
1.7
3.4
0.3
MEDIAN
2.8
1.1
2.1
1.5
1.0
2.9
0.4
STD.
DEV.
6.2
2.6
3.3
0.0
10.9
5.4
0.8
MAXIMUM
23.1
7.2
12.3
1.5
25.2
16.5
1.5
%>4pCI/L
35
29
35
0
20
29
0
%>20pCi/L
10
0
0
0
20
0
0
crrr
ALEXANDRIA CFTY
BEDFORD OTY
BRISTOL
BUENAVISTA
CHARLOTTESVILLE
CHESAPEAKE
CLIFTON FORGE
COLONIAL HEIGHTS
COVINGTON
DANVILLE
EMPORIA
FAIRFAX-CITY
FALLS CHURCH
FREDERICKSBURG
GALAX
HAMPTON
HARMSONBURG
HOPEWELL
LEXINGTON
LYNCHBURG
MANASSAS
MARTINSVILLE
NEWPORT NEWS
NORFOLK
PETERSBURG
POQUOSON
PORTSMOUTH
RADFORD
RICHMOND-CTTY
ROANOKE-CFTY
SALEM
SOUTH BOSTON
STAUNTON
SUFFOLK
VIRGINIA BEACH
12
5
6
5
15
23
1
5
1
14
2
21
2
?7
3
7
5
5
3
20
7
7
13
14
5
1
6
2
73
45
6
3
4
3
39
1.0
13.
7.0
3.0
1.3
0.3
0.8
2.4
3.1
8.7
0.5
2.1
1.3
2.8
5.8
0.3
1.8
0.6
4.0
2.9
1.7
2.3
0.7
0.8
1.1
0.4
0.4
3.9
1.4
4.3
5.5
1.1
7.3
0.1
0.5
0.5
1.0
2.5
2.3
0.8
0.2
0.8
2.0
3.1
2.3
0.4
1.3
1.2
2.1
4.8
0.3
1.4
0.4
3.9
2.3
1.3
O
0.5
0.4
1.0
0.4
0.2
2.1
0.9
3.0
2.8
0.5
5.8
0.1
0.3
0.5
1.1
2.2
2.7
1.0
0.2
0.8
2.0
3.1
2.3
0.5
1.6
1.3
2.7
6.8
0.3
1.1
0.4
4.2
2.6
1.1
1.6
0.5
0.6
1.2
0.4
0.4
3.9
0.9
3.0
12.
0.4
7.9
0
0.2
1.2
0.8
11.4
2.7
1.2
0.3
0.0
1.9
0.0
21.1
0.4
2.0
0.1
2.0
3.6
0.2
1.3
0.6
1,3
1.7
1.3
2.2
0.6
1.0
0.6
0.0
0.5
4.7
1.4
4.4
8.3
1.4
4.7
0.2
0.9
4.0
2.6
30.0
7.6
4.8
1.1
0.8
5.7
3.1
81.5
0.8
8.5
1,3
6.0
8.9
0.6
4.0
1.5
5.2
6.0
3.8
6.1
1.6
3.7
1.9
0.4
1.2
7.2
7.6
27.1
22.2
2.7
11.3
0.4
4.7
0
0
33
20
7
0
0
20
0
36
0
10
0
29
67
0
0
0
67
30
0
29
0
0
0
0
0
50
7
. 36
33
0
75
0
3
0
0
17
0
0
0
0
0
0
7
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
2
17
0
0
0
0
-------
TABLE 1 (continued). Screening indoor radon data for Virginia.
cnr
WAYM3SBORO
WMJAMSBURG
WINCHESTER
NO. OF
MEAS.
6
1
9
MEAN
5.7
1
3
GEOM.
MEAN
4.5
1
2.1
MEDIAN
4.2
1
2.4
STD.
DEV.
4.7
0
2.7
MAXIMUM
14.5
1
8.9
%>4pCi/L
50
0
33
%>20pCi/L
0
0
0
-------
Figure 8. Virginia counties (from Facts on File, 1984).
-------
PERCENTAGE OP RADON READINGS
ABOVE 4 pCi/1
B Over 60%
m 40% to 60%
m 20% to 40%
E3 0% lo 20%
Insuffic ienl Dala
Less Than 15 Readings
D
••MIM» dtla /rom VSCS
1:1.099.090 9LC. JUrfon tfid
/r«*i JTty Titknol
titCktk Int. «nd ^t R«4*ft
rr*jftl,
orir f»m it
Pttimltr fl, III!
/n/trm»H»n
•rinck
Predwctd for; IF4 Xffieii III -
4ir Fr«ft«nt fruntft
Priiit licit:
FUltttf:
Pr»dueirf iy;
Figure 9. Vendor screening indoor radon data for Virginia compiled by U.S. EPA Region IDL Total number of readings = 39,869.
-------
average indoor radon levels (fig. 7). The commercial data also show a distinct drop in the
percentage of readings exceeding 4 pQ/L in the Blue Ridge and Piedmont (fig. 9). The Coastal
Plain counties have moderate to low (< 2 pCi/L) indoor radon averages.
GEOLOGIC RADON POTENTIAL SUMMARY
For the purpose of this assessment, Virginia has been divided into eight geologic radon
potential areas and each area assigned a Radon Index (RI) and a Confidence Index (CI) score
(Table 2). These areas correspond to the areas delineated in figure 1. The RI is a relative measure
of radon potential based on geologic, soil, radioactivity, architecture, and indoor radon data, as
outlined in the preceding sections. The CI is a measure of the confidence of the RI assessment
based on the quality and quantity of the data used to assess die geologic radon potential. Please
refer to the introduction chapter of this regional book for a detailed discussion of the indexes.
As can be seen in Table 2, the radon potential of. rocks and soils in Virginia is variable from
low to high. In the following discussion, the factors for each ranking are briefly discussed and
local variations within each province or subdivision are indicated. Indoor radon data are clearly
lacking for parts of the Coastal Plain, southern Piedmont, and western Valley and Ridge and
Appalachian Plateaus. Please note that the confidence index score for the indoor radon factor in
these areas is low.
Coastal Plain
The Coastal Plain of Virginia is ranked low in geologic radon potential Indoor radon
levels are generally low; however, moderate to high indoor radon levels can occur locally and may
be associated with phosphatic, glauconitic, and heavy mineral-bearing sediments. Equivalent
uranium over the Tertiary units of the Coastal Plain is generally moderate. Soils developed on the
Cretaceous and Tertiary units are slowly to moderately permeable. Studies of uranium and radon
in soils indicate that the Yorktown Formation could be a source for elevated levels of indoor radon
(Berquist and others, 1990). The Quaternary sediments generally have low ell associated with
them. Heavy mineral deposits of monazite found locally within the Quaternary sediments of the
Coastal Plain may have the potential for creating locally moderate to high indoor radon levels.
Piedmont
The Goochland terrane and Inner Piedmont have been ranked high in radon potential. The
Carolina terrane has been ranked moderate in geologic radon potential. Rocks of the Goochland
terrane and Inner Hedmont have numerous well-documented uranium and radon occurrences
associated with granites; pegmatites; granitic gneiss; monazite-bearing metasedimentary schist and
gneiss; graphitic and carbonaceous slate, phyllite, and schist; and shear zones. Indoor radon levels
are generally moderate but significant very high radon levels occur in several areas. Equivalent
uranium (fig. 6) over the Goochland terrane and Inner Piedmont is predominantly high to moderate
with areas of high ell more numerous in the south. Permeability of soils developed over granitic
igneous and metamorphic rocks of the Piedmont is generally moderate. Within the Goochland
terrane and Inner Piedmont, local areas of low to moderate radon potential will probably be found
over mafic rocks (such as gabbro and amphibolite), quartzite, and some quartzitic schists. Mafic
rocks have generally low uranium concentrations and slow to moderate permeability in the soils
they form. The Carolina terrane is variable in radon potential but is generally moderate.
Metavolcanic rocks have low eU but the granites and granitic gneisses have moderate to locally
IV-31 Reprinted from USGS Open-FUe Report 93-292-C
-------
highcU. Soils developed over the volcanic rocks are slowly to moderately permeable. Granite
and gneiss soils have moderate permeability.
The Mesozoic basins have moderate to locally high geologic radon potential. It is not
possible to make any general associations between county indoor radon averages and the individual
Mesozoic basins because of the limited extent of many the basins. However, sandstones and
siltstoncs of the Culpeper basin, which have been lightly metamorphosed and altered by diabase
intrusion, are mineralized with uranium and cause documented moderate to high radon levels in
northern Virginia (Otton and others, 1988). Lacustrine black shales and some of the coarse-
grained gray sandstones also have significant uranium mineralization, often associated with green
clay clasts and copper. Equivalent uranium (fig. 6) over the Mesozoic basins varies among the
basins. The Danville basin has very high eU associated with it, whereas the other basins have
generally moderate eU. This radioactivity may be related to extensive uranium mineralization along
the Chatham fault on the west side of the Danville basin. Localized high eU also occurs over die
western border fault of the Culpeper basin. .Soils are generally slowly to moderately permeable
over the sedimentary and intrusive rocks of the basins.
Valley and Ridge
The Valley and Ridge has been ranked high in geologic radon potential, with local areas
having low to moderate radon potential. The Valley and Ridge is underlain by Cambrian dolomite,
limestone, shale, and sandstone; Silurian-Ordovician limestone, dolomite, shale, and sandstone;
and Mississippian-Devonian sandstone, shale, limestone, gypsum, and coal. Soils derived from
carbonate rocks and black shales, and black shale bedrock may be sources of the moderate to high
levels of indoor radon in this province. Equivalent uranium over the Valley and Ridge is generally
low to moderate, with isolated high-radioactivity areas. Soil permeability is moderate to high.
Studies of soil-gas and indoor radon over the carbonates and shales of the Great Valley in West
Virginia and studies in Pennsylvania indicate that the rocks and soils of this province constitute a
significant source of radon. Sandstones and red siltstones and shales probably have low to
moderate radon potential. Some local uranium accumulations are contained in these rocks.
Appalachian Plateaus
The Appalachian Plateaus Province has been ranked moderate in geologic radon potential.
The plateaus are underlain by Pennsylvanian sandstone, shale, and coal. Black shales, especially
those associated with coal seams, are generally elevated in uranium and may be sources of
moderate to high radon levels. The coals themselves may also be locally elevated in uranium. The
sandstones are generally low to moderate in radon potential but have higher soil permeability than
the black shales. Equivalent uranium (fig. 6) of the province is low to moderate, and indoor radon
is variable from low to high, but indoor radon data are limited in number.
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
HPl 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-32 Reprinted firom USGS Open-File Report 93-292-C
-------
TABLE 2. HI and CI scores for geologic radon potential areas of Virginia. See figure 1 for
locations of areas.
Appalachian Plateau
FACTOR RI CI
INDOOR RADON
RADIOACTIVITY
GEOLOGY
SOIL PERM.
ARCHITECTURE
Gra POINTS
TOTAL
FACTOR
INDOOR RADON
RADIOACTIVITY
GEOLOGY
SOIL PERM.
ARCHITECTURE
GFE POINTS
TOTAL
2
2
2
2
2
0
10
1
3
2
3
9
Mod Mod
Mesozoic Basins
RI CI
2
2
2
2
2
1
11
Mod
1
2
3
3
9
Mod
Valley and Ridge
RI Q
3
3
3
2
2
2
15
2
3
3
3
11
High High
Goochland
Terrane
RI a
2
3
2
2
2
2
13
High
1
2
3
3
9
Mod
Blue Ridge/
Carolina Terrane
RI CI
2
2
2
2
2
0
10
2
2
2
3
9
Mod Mod
Inner
Piedmont
RI CI
- 2
3
3
2
2
0
12
High
2
2
3
3
10
High
Cretaceous and Tertiary
Coastal Plain
FACTOR
INDOOR RADON
RADIOACTIVITY
GEOLOGY
SOIL PERM.
ARCHITECTURE
GFE POINTS
TOTAL
RI
1
2
2
2
1
0
8
Low
CI
1
2
3
3
.
-
9
Mod
Quaternary
Coastal Plain
RI
1
1
1
2
1
0
6
Low
a
1
2
3
3
.
-
9
Mod
RADON INDEX SCORING:
Radon potential category
LOW
MODERATE/VARIABLE
HIGH
Point range
3-8 points
9-11 points
> 11 points
Probable screening indoor
radon average for area
<2pO/L
2-4pO/L
>4pO/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-33 Reprinted from USGS Open-File Report 93-292-C
-------
REFERENCES CITED IN THIS CHAPTER
AND ADDITIONAL REFERENCES PERTAINING TO RADON IN VIRGINIA
Bailey, J.P., Mose, D.G., and Mushrush, G.W., 1989, Soil to indoor radon ratios and the
prediction of indoor radon: Geological Society of America, Abstracts with Programs,
v. 21, p. 3.
Baillieul, T.A. and Daddazio, P.L., 1982, National Uranium Resource Evaluation, Charlottesville
Quadrangle, Virginia and West Virginia: U.S. Department of Energy Report
PGJ/F-114(82).
Baillieul, T.A., and Dexter, JJ., 1982, Evaluation of uranium anomalies in the Hylas Stone and
the northern Richmond Basin, East-central Virginia, in C.S. Goodknight and J.A. Burger,
eds., Reports on investigations of uranium anomalies: U.S. Department of Energy,
National Uranium Resource Investigations Report GJBX-222(82), p. 1-16.
Betquist, Carl R., Jr., Cooper, J.M., and Goodwin, B.K., 1990, Radon from Coastal Plain
sediments, Virginia: Preliminary results: Geological Society of America, Abstracts with
Programs, v. 22, no. 2, p. 4-5.
Brown, W.R., 1970, Investigations of the sedimentary record in the Piedmont and Blue Ridge of
Virginia, in Fisher, G. W. and others, eds., Studies of Appalachian Geology-Central and
Southern: John Wiley and Sons, p. 199-212.
Cohen, B.L., 1990, Surveys of radon levels in homes by University of Pittsburgh Radon Project,
in Proceedings of the 1990 International Symposium on Radon and Radon Reduction
Technology, Vol. DJ: Preprints: U.S. Environmental Protection Agency Report
EPA/600/9-90/005C, Paper IV-3,17 p.
Cohen, B.L., and Gromicko, N., 1988, Variation of radon levels in U.S. homes with various
factors: Journal of the Air Pollution Control Association v. 38, p. 129-134.
Conley, J.F., 1978, Geology of the Piedmont of Virginia-Juiterpretations and problems, in
Contributions to Virginia geology-Hi: Virginia Division of Mineral Resources Publication
7, p. 115-149.
Cook, JJL, Fay, W.M., and Sargent, K.A., 1982, Data Report: Delaware, Maryland, Virginia,
and West Virginia, NURE Hydrogeochemical and stream sediment reconnaissance: U.S.
Department of Energy Report GJBX-103,44 p.
Devereux, R.E., Obenshain, S.S., Porter, H.C., and Epperson, G.R., 1965, Soils of Virginia:
Virginia Polytechnic Institute Agricultural Extension Service Bulletin 203,26 p.
Dribus, J.R., Hurley, B.W., Lawton, D.E., and Lee, C.H., 1982, Greensboro Quadrangle,
North Carolina and Virginia: U.S. Department of Energy National Uranium Resource
Investigations Report PGJ/F-063(82), 30 p.
IV-34 Reprinted from USGS Open-File Report 93-292-C
-------
Duval, J.S., Jones, W J., Higgle, F.R.," and PitMn, J.A., 1989, Equivalent uranium map of
conterminous United States: U.S. Geological Survey Open-Hie Report 89-478,10 p.
Espenshade, G.H., 1970, Geology of the northern part of the Blue Ridge Anticlinorium, in
Fisher, G. W. and others, eds., Studies of Appalachian Geology-Central and Southern:
John Wiley and Sons, p. 199-212.
Facts on File publications, 1984, State Maps on File: Southeast
Frishman, David, Halladay, C.R., Hauck, S.A., and Kendall, E.W., 1987, The Swanson
uranium deposit, Pittsylvania County, Virginia, USA: Stratigraphy, petrology, and ore
mineralogy, in Proceedings of the International Atomic Energy Agency Meeting, Uranium
Resources and Geology of North America, Saskatoon, Saskatchewan, Canada, IAEA-
TECDOC-500, p. 521-522.
Gates, A.E. and Gundersen, L.C.S., 1988, Soil radon as a function of shear strain in the
Brookneal zone, Va: Geological Society of America, Abstracts with Programs, v. 20,
p. 266.
Gates, AM., and Gundersen, L.C.S., 1989, Radon distribution around me Hylas Zone, VA; a
product of lithology and ductile shearing: Geological Society of America, Abstracts with
Programs, v. 21, p. 17.
Gates, A.E. and Gundersen, L.C.S., 1989, Role of ductile shearing in tiie concentration of radon
in the Brookneal Zone, Virginia: Geology, v. 17, p. 391-394.
Gates, A.E., Gundersen, LX1S., and Malizzi, L.D., 1990, Comparison of radioactive element
distribution between similar faulted crystalline terranes: Glaciated versus unglaciated:
Geophysical Research Letters, v. 17, no. 6, p. 813-816.
Grauch, R.I., and ZarinsM, K., 1976, Generalized descriptions of uranium-bearing veins,
pegmatites, and disseminations in non-sedimentary rocks, eastern United States: U.S.
Geological Survey Open-File Report 76-582,114 p.
Greeman, D.J., and Rose, A.W., 1990, Form and behavior of radium, uranium, and thorium in
central Pennsylvania soils derived from dolomite: Geophysical Research Letters, v. 17,
p. 833-836.
Gross, S., and Sachs, H.M., 1982, Regional (location) and building factors as determinants of
indoor radon concentrations in eastern Pennsylvania: Princeton University, Center for
Energy and Environmental Studies Report 146,117 p.
Grosz, AJL, 1983, Application of total-count aeroradiometric maps to the exploration for Heavy
Mineral Deposits in the Coastal Plain of Virginia: U.S. Geological Survey Professional
Paper 1263,20 p.
Gundersen, L.C.S., 1988, Radon production in shear zones of the Eastern United States:
Northeastern Environmental Science, v. 7, p. 6.
IV-35 Reprinted firom USGS Open-File Report 93-292-C
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Gundersen, L.C.S., 1991, Radon in sheared metamorphic and igneous rocks, In Gundersen,
L.C.S., and Wanty, R.B., eds., Field studies of radon in rocks, soils, and water: U.S.
Geological Survey Bulletin 1971, p. 39-50.
Gundersen, L.C.S., Peake, R.T., Latske, G.D., Hauser, L.M. and Wiggs, C.R., 1991, A
statistical summary of uranium and radon in soils from the Coastal Plain of Texas,
Alabama, and New Jersey, in Proceedings of the 1990 Symposium on Radon and Radon
Reduction Technology, Vol. 3: Symposium Poster Papers: Research Triangle Park,
N.C, U.S. Environmental Protection Agency Rept EPA600/9-91-026c, p. 6-35-6-47.
Gundersen, L.C.S., and Schumann, R.R., 1989, The importance of metal oxides in enhancing
radon emanation from rocks and soils (abs): Geological Society of America, Abstracts
with Programs, v.21, no. 6, p. A145.
Halladay, CJL, 1987, The Swanson uranium deposit, Virginia: A structurally controlled, U-P
albitite deposit, m Proceedings of the International Atomic Energy Agency Meeting,
Uranium Resources and Geology of North America, Saskatoon, Saskatchewan, Canada,
IAEA-TECDOC-500, p. 519.
Hammond, D.E., and Fuller, C, 1979, The use of radon-222 as a trace for vertical mixing rates
and exchange processes in the Potomac, in J.P. Bennett, ed., Proceedings of Seminar on
the water quality of the tidal Potomac River, Reston, VA, Dec. 6-7,1978: U. S.
Geological Survey Open-File Report 79-0158, p. 6-7.
Hatcher, R.D., Jr., Thomas, W.A., and Viele, G.W., 1989, The Appalachian-Ouachita Orogen in
the United States: Geological Society of America, Geology of North America, V. F-2,
767 p.
Kaiserman, R.K., Goodell, H.G., and Niemi, T.E., 1984, Lithologic controls on groundwater
chemistry in uranium-bearing rocks of the southern Culpeper and Dan River Triassic-
Jurassic basins, Virginia: Virginia Journal of Science, v. 35, p. 120.
Kline, S.W., and Mose, D.G., 1987, Predictive tools for indoor radon studies in Virginia:
Geological Society of America, Abstracts with Programs, v. 19, p. 729.
Krason, Jan, Johnson, S.S., Finley, P.D., and Marr, J.D., Jr., 1988, Geochemistry and
radioactivity in the Powhatan area, Virginia: Virginia Division of Mineral resources
Publication 78,60 p.
Lasch, D.K., 1988, On radon: Virginia Minerals, v. 34, p. 1-4.
Lee, K.Y., and Froelich, A.J., 1989, Triassic-Jurassic stratigraphy of the Culpeper and
Barboursville basins, Virginia and Maryland: U.S. Geological Survey Professional Paper
1472, 52 p.
Luetzelschwab, J.W., Berwick, K.L., and Hurst, K.A., 1989, Radon concentrations in five
Pennsylvania soils: Health Physics, v. 56, p. 181-188.
IV-36 Reprinted from USGS Open-File Report 93-292-C
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Mertie, J.B., Jr. 1953, Monazite deposits of the southeastern Atlantic states: U.S. Geological
Survey Circular 237,31p.
Mixon, R.B., Berquist, CJL, Jr., Newell, W.L., and Johnson, G.H., 1989, Geologic map and
generalized cross sections of the Coastal Plain and adjacent parts of the Piedmont, Virginia:
U.S. Geological Survey Miscellaneous Investigations Series, Map-I-2033, scale
1:250,000.
Mose, D.G., and Hall, S.T., 1987, Indoor radon survey; citizen response and preliminary
observations in Virginia and Maryland: Geological Society of America, Abstracts with
Programs, v. 19, p. 119.
Mose, D.G., and Hall, S.T., 1988, Effect of home construction and mitigation methods on indoor
radon; Virginia and Maryland homes during the winter of 1986-1987: Geological Society
of America, Abstracts with Programs, v. 20, p. 282.
Mose, D.G., and Mushrush, G.W., 1987, Correlation between indoor radon and geology in VA
& MD: Geological Society of America, Abstracts with Programs, v. 19, p. 779.
Mose, D., and Mushrush, G., 1988, Factors that determined indoor radon concentration in
Virginia and Maryland in 1987: Eos, Transactions, American Geophysical Union, v. 69,
p. 317.
Mose, D.G., and Mushrush, G., 1988, Comparison between activated charcoal and alpha-track
measurement of indoor radon in homes in Virginia and Maryland, 1986-1987: Geological
Society of America, Abstracts with Programs, v. 20, p. 282.
Mose, D.G., and Mushrush, G.W., 1988, Regional levels of indoor radon in Virginia and
Maryland: Environmental Geology and Water Sciences, v. 12, p. 197-201.
Mose, D.G., Mushrush, G.W., and Kline, S.W., 1988a, Geology and time dependent indoor
radon variations in V A and MD: Geological Society of America, Abstracts with Programs,
v. 20, p. 56-57.
Mose, D.G., Mushrush, G.W., and Kline, S.W., 1988b, The interaction of geology, weather and
home construction on indoor radon in northern Virginia and southern Maryland:
Northeastern Environmental Science, v. 7, p. 15-29.
Mose, D.G., Chrosniak, C.E., Mushrush, G.W. and Vitz, E., 1989, Cancer associated with
drinking radon enriched water: Geological Society of America, Abstracts with Programs,
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Neiheisel, J. and Battist, L., 1987, Conttibutary role of Mesozoic tectonic events to radon sources
in the Appalachian region: Geological Society of America, Abstracts with Programs,
v. 19, p. 120.
IV-37 Reprinted tan USGS Open-Ffle Report 93-292-C
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Ncuschcl, S.K., 1970, Correlation of aeromagnetics and aeroradioactivity with lithology in the
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potassium with aeroradioactivity in the Berea area, Virginia: Economic Geology, v. 66,
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Otton, J.K., and Gundersen, L.C.S., 1988, Geologic assessments of radon potential at county
scales; Northeastern Environmental Science, v. 7, p. 7-8.
Otton, J.K., Schumann, R.R., Owen, D.E., Thurman, N. and Duval, J.S., 1988, Map showing
radon potential of rocks and soils in Fairfax County, Virginia: U. S. Geological Survey
Miscellaneous Field Studies Map MF-2047, scale 1:62,500.
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IV-38 Reprinted from USGS Open-File Repent 93-292-C
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38077-BE-NA-07M-00, scale 1:7,500,000.
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Mineral Resources, 36 p.
IV-39 Reprinted from USGS Open-File Report 93-292-C
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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 USGS' 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.)
VIRGINIA MAP OF RADON ZONES
The Virginia Map of Radon Zones and its supporting documentation (Part IV of this
report) have received extensive review by Virginia geologists and radon program experts.
The map for Virginia 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.
Although the information provided in Part IV of this report — the State chapter entitled
"Preliminary Geologic Radon Potential Assessment of Virginia" — 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 3 EPA office or the
Virginia 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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VIRGINIA - EPA Map of Radon Zones
The purpose of this map Is to assist National, State and local organizations
to target their resources and to Implement radon-resistant building codes.
This map is not intended to determine H a home In a given zone should be tested
for radon. Homes w'rth elevated levels of radon have been found In all three
zones. All homes sftouM be Jested, regard/ess of zone designation.
nuNKUNcnv
Zone 1
Zone 2
ZoneS
IMPORTANT: Consult the publication entitled 'Preliminary Geologic Radon
Potential Assessment of Virginia' before using this map. This
document contains information on radon potential variations within counties.
EPA also recommends that this map be supplemented with any available
local data in order to further understand and predict the radon potential of a
specific area.
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