United Siatos
Environmental Protection
Agency
Air and Radiation
(6604J)
<&EPA EPA's Map of Radon Zones
TEXAS
402-H-93-063
September 1993
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EPA'S MAP OF RADON ZONES
TEXAS
RADON DIVISION
OFFICE OF RADIATION AND INDOOR AIR
U.S. ENVIRONMENTAL PROTECTION AGENCY
SEPTEMBER, 1993
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ACKNOWLEDGEMENTS
This document was prepared by the U.S. Environmental Protection Agency's (EPA's)
Office of Radiation and Indoor Air (ORIA) in conjunction with the U.S. Geological Survey
(USGS). Sharon W. White was the EPA project manager. Numerous other people in ORIA
were instrumental in the development of the Map of Radon Zones, including Lisa Ratcliff,
Kirk Maconaughey, R. Thomas Peake, Dave Rowson, and Steve Page.
EPA would especially like to acknowledge the outstanding effort of the USGS
radon team Linda Gundersen, Randy Schumann, Jim Otton, Doug Owen, Russell
Dubiel, Kendell Dickinson, and Sandra Szarzi in developing the technical base for the
Map of Radon Zones.
ORIA would also like to recognize the efforts of all the EPA Regional Offices in
coordinating the reviews with the State programs and the Association of American State
Geologists (AASG) for providing a liaison with the State geological surveys. In addition,
appreciation is expressed to all of the State radon programs and geological surveys for their .
technical input and review of the Map of Radon Zones.
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TABLE OF CONTENTS
I. OVERVIEW
II. THE USGS/EPA RADON POTENTIAL
ASSESSMENTS: INTRODU CTION
III. REGION 6 GEOLOGIC RADON POTENTIAL
SUMMARY
V. PRELIMINARY GEOLOGIC RADON POTENTIAL
ASSESSMENT OF TEXAS
V. EPA'S MAP OF RADON ZONES - TEXAS
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Page Intentionally Blank
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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 thj Association of American State Geologists
(AASG) have, worked closely over the past several years to produce a series of maps and
documents which address these directives. The EPA Map of Radon Zones is a compilation of
that work and fulfills the requirements of sections 307 and 309 of IRAA. The Map of Radon
Zones identifies, on a county-by-county basis, areas of the U.S. that have the highest potential
for elevated indoor radon levels (greater than 4 pCi/L).
The Map of Radon Zones is designed to assist national, State and local governments
and organizations to target their radon program activities and resources. It is also intended to
help building code officials determine areas that are the highest priority for adopting radon-
resistant building practices. The Map of Radon Zones should not be used to determine if
individual homes in any given area need to be tested for radon. EPA recommends that all
homes be tested for radon, regardless of geographic location or the zone designation of
the county in which they are located.
This document provides background information concerning the development of the
Map of Radon Zones. It explains the purposes of the map, the approach for developing the
map (including the respective roles of EPA and USGS), the data sources used, the conclusions
and confidence levels developed for the prediction of radon potential, and the review process
that was conducted to finalize this effort. ,
BACKGROUND
i
Radon (Rir22) 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 Man of Radon Zones
EPA's Map of Radon Zones (Figure 1) assigns each of the 3141 counties in the
United States to one of three zones:
o Zone 1 counties have a predicted average indoor screening level > than
4 pCi/L
o Zone 2 counties have a predicted average screening level > 2 pCi/L and
< 4 pCi/L
o Zone 3 counties have a predicted average screening leyel < 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
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Figure 1
EPA Map of Radon Zones
1
llWIissfa
Mar^^ss-a^i
LTCSi
l~zi '¦-*<&
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LEGEND
Zone 1
Zone 3
Zone designation, for Puerto Rico is vnder development
Guam - Preliminary Zone designation. ^ The purpose of this mop. is to assist Notional, Stote and local organizations to target their resources and to implement radon-resistant building codes.
This mop 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 oil three zones. All homes should be tested, regardless of geographic location.
Consult the EPA Map of Radon Zones document (EPA-402-R-93-07I) before using. this map. 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 a specific area.
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Figure 2
GENERALIZED GEOLOGIC RADON POTENTIAL OF THE UNITED STATES
by the U.S. Geological Survey
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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 Part 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 hoiw EPA extrapolated the county zone
designations for Nebraska from the USGS geologic province map for the State. As figure 3
shows, USGS has identified 5 geologic provinces for Nebraska. Most of the counties are
extrapolated "straight" from their corresponding provinces, but there are counties "partitioned"
by several provinces ~ for example, Lincoln County. Although Lincoln county falls in
multiple provinces, it was assigned to Zone 3 because most of its area falls in the province
with the lowest radon potential. ...
It is important to note that EPA's extrapolation from the province level to the
county level may mask significant "highs" and "lows" within specific counties. In other
words, within-county variations in radon potential are not shown on the Map of Radon
Zones. EPA recommends that users who may need to address specific within-county
variations in radon potential (e.g., local government officials considering the
implementation of radon-resistant construction codes) consult USGS' Geologic Radon
Province Map and the State chapters provided with this map for more detailed
information, as well as any locally available data.
Map Validation
The Map of Radon Zones is intended to represent a preliminary assessment of radon .
potential for the entire United States. The factors that are used in this effort indoor radon
data, geology, aerial radioactivity, soils, and foundation type are basic indicators for radon
potential. It is important to note, however, that the map's county zone designations are not
"statistically valid" predictions due to the nature of the data available for these 5 factors at the
county level. In order to validate the map in light of this lack of statistical confidence, EPA
conducted a number of analyses. These analyses have helped EPA to identify the best
situations in which to apply the map, and its limitations.
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Figure 3
Geologic Radon Potential Provinces for Nebraska
Lincoln County
Uotf e r *t e
Figure 4
NEBRASKA
mmmM
.LifeStfJ
Lincoln County
Zoic 2
1-6
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One such analysis involved comparing county zone designations to indoor radon
measurements from the State/EPA Residential Radon- Surveys (SRRS). Screening averages
for counties with at least 100 measurements were compared to the counties' predicted radon
potential as indicated by. the Map of Radon Zones. EPA found that 72% of the county
screening averages were correctly reflected by the appropriate zone designations on the Map.
In all other cases, they only differed by 1 zone.
Another accuracy analysis used the annual average data from the National Residential
Radon Survey (NRRS). The NRRS indicated that approximately 6 million homes in the
United States have annual averages greater than or equal to 4 pCi/L. By cross checking the
county location of the approximately 5,700 homes which participated in the survey, their
radon measurements, and the zone designations for these counties, EPA found that
approximately 3.8 million fyomes of the 5.4 million homes1 with radon levels greater than or
equal to 4 pCi/L will be found in counties designated as Zone 1. A random sampling of an
equal number of counties would have only found approximately 1.8 million homes greater
than 4 pCi/L. In other words, this analysis indicated that the map approach is three times
more efficient at identifying high radon areas than random selection of zone designations.
Together, these analyses show that the approach EPA used to develop the Map of
Radon Zones is a reasonable one. In addition, the Agency's confidence is enhanced by results
of the extensive State review process the map generally agrees with the States' knowledge
of and experience in their own jurisdictions. However, the accuracy analyses highlight two
important points: the fact that elevated levels will be found in Zones 2 and 3, and that there
will be significant numbers of homes with lower indoor radon levels in all of the Zones. For
these reasons, users of the Map of Radon Zones need to supplement the Map with locally
available data whenever possible. Although all known "hot spots", i.e., localized areas of
consistently elevated levels, are discussed in the State-
specific chapters, accurately defining the boundaries of the "hot spots" on this scale of map is
not possible at this time. Also, unknown "hot spots" do exist.
The Map of Radon Zones is intended to be a starting point for characterizing radon
potential because our knowledge of radon sources and transport is always growing. Although
this effort represents the best data available at this time, EPA will continue to study these
parameters and others such as house construction, ventilation features and meteorology factors
in order to better characterize the presence of radon in U.S homes, especially in high risk
areas. These efforts will eventually assist EPA in refining and revising the conclusions of the
Map of Radon Zones. And although this map is most appropriately used as a targeting tool
by the aforementioned audiences the Agency encourages all residents to test their homes
for radon, regardless of geographic location or the zone designation of the county in
which they live. .Similarly, the Map of Radon Zones should not to be used in lieu of
testing during real estate transactions.
Review Process
The Map of Radon Zones has undergone extensive review within EPA and outside the
Agency. The Association of American State Geologists (AASG) played an integral role in
this review process. The AASG individual State geologists have reviewed their State-specific
information, the USGS Geologic Radon Province Map, and other materials for their geologic
content and consistency.
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In addition to each State geologist providing technical comments, the State radon
offices were asked to comment on their respective States' radon potential evaluations. In
particular, the States were asked to evaluate the data used to assign their counties to specific
zones. EPA and USGS worked with the States to resolve any issues concerning county zone
designations. In a few cases, States have requested changes in county zone designations. The
requests were based on additional data from the State on geology, indoor radon
measurements, population, etc. Upon reviewing the data submitted by the States, EPA did
make some changes in zone designations. These changes, which do not strictly follow the
methodology outlined in this document, are discussed in the respective State chapters.
EPA encourages the States and counties to conduct further research and data collection
efforts to refine the Map of Radon Zones. EPA would like to be kept informed of any
changes the States, counties, or others make to the maps. Updates and revisions will be
handled in a similar fashion to the way the map was developed. States should notify EPA of
any proposed changes by forwarding the changes through the Regional EPA offices that are
listed in ParJ II. Depending on the amount of new information that is presented, EPA will
consider updating this map periodically. The State radon programs should initiate proper
notification of the appropriate State officials when the Map of Radon Zones is released and
when revisions or updates are made by the State or EPA.
1-8
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THE USGS/EPA RADON POTENTIAL ASSESSMENTS: AN INTRODUCTION
by
Linda C.S. Gimdersen and R. Randall Schumann
U.S. Geological Sun>ey
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 niodel standards and techniques for new building construction
that would provide adequate prevention or mitigation of radon entry. As part of an
Interagency Agreement between the EPA and the U.S. Geological Survey (USGS), the USGS
has prepared radon potential estimates for the United States. This report is one of ten
booklets that document this effort. The purpose and intended use of these reports is to help
identify areas where states can target their radon program resources, to provide guidance in
selecting the most appropriate building code options for areas, and to provide general
information on radon and geology for each state for federal, state, and municipal officials
dealing with radon issues. These reports are not intended to be used as a substitute for
indoor radon testing, and they cannot and should not be used to estimate or predict the
indoor radon concentrations of individual homes, building sites, or housing tracts. Elevated
levels of indoor radon have been found in every State, and EPA recommends that all homes
be tested for indoor radon.
Booklets detailing the radon potential assessment for the U.S. have been developed for
each State. USGS geologists are the authors of the geologic radon potential booklets. Each
booklet consists of several components, the first being an overview to the mapping project
(Part I), this introduction to the USGS assessment (Part II), including a general discussion of
radon (occurrence, transport, etc.), and details concerning the types of data used. The third
component is a summary chapter outlining the general geology and geologic radon potential
of the EPA Region (Part III). The fourth component is an individual chapter for each state
(Part IV). Each state chapter discusses the state's specific geographic setting, soils, geologic
setting, geologic radon potential, indoor radon data, and a summary outlining the radon
potential rankings of geologic areas in the state. A. variety of maps are presented in each
chaptergeologic, 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-1 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
wtJue, and the reader is urged to consult these report, for more deiailed inform, rion. In most
cases the best sources of information on radon for specific areas are state and local
departments of health, state departments responsible for nuclear safety or environmental
protection, and U.S. EPA regional offices. More detailed information on state or local
geology may be obtained from the state geological surveys. Addresses and telephone
numbers of state radon contacts, geological surveys, and EPA regional offices are listed in
Appendix C at the end of this chapter.
RADON GENERATION AND TRANSPORT IN SOILS
Radon (":Rn) is produced from the radioactive decay of radium (~6Ra), which is, in turn,
a product of the decay of uranium (:5SU) (fig. 1). The half-life of -"Rn is 3.825 days. Other
isotopes of radon occur naturally, but, with the exception of tho'ron ("°Rn), which occurs in
concentrations high enough to be of concern in a few localized areas, they are less important
in terms of indoor radon risk because of their extremely short half-lives and less common
occurrence. In general, the concentration and mobility of radon in soil are dependent on
several factors, the most important of which are the soil's radium content and distribution,
porosity, permeability to gas movement, and moisture content. These characteristics are, in
turn, determined by the soil's parent-material composition, climate, and the soil's age or
maturity. If parent-material composition, climate, vegetation, age of the soil, and topography
are known, the physical and chemical properties of a soil in a given area can be predicted.
As soils form, they develop distinct layers, or horizons, that are cumulatively called the
soil profile. The A horizon is a surface or near-surface horizon containing a relative
abundance of organic matter but dominated by mineral matter. Some soils contain an E
horizon, directly below the A horizon, that is generally characterized by loss of clays, iron, or
aluminum, and has a characteristically lighter color than the A horizon. The B horizon
underlies the A or E horizon. Important characteristics of B horizons include accumulation of
clays, iron oxides, calcium carbonate or other soluble salts, and organic matter complexes. In
drier environments, a horizon may exist within or below the B horizon that is dominated by
calcium carbonate, often called caliche or calcrete. This carbonate-cemented horizon is
designated the K horizon, in modern soil classification schemes. The C horizon underlies the
B (or K) and is a zone of weathered parent material that does not exhibit characteristics of A
or B horizons; that is, it is generally not a zone.of leaching or accumulation. In soils formed
in place from the underlying bedrock, the C horizon is a zone of unconsolidated,, weathered
bedrock overlying the unweathered bedrock.
The shape and orientation of soil particles (soil structure) control permeability and affect
water movement in the soil. Soils with blocky or granular structure have roughly equivalent
permeabilities in the horizontal and vertical directions, and air and water can infiltrate the soil
relatively easily. However, in soils with platy structure, horizontal permeability is w.uch
greater than vertical permeability, and air and moisture infiltration is generally slow. Soils
with prismatic or columnar structure have dominantly vertical permeability. Platy and .
prismatic structures form in soils with high clay contents. In soils with shrink-swell clays, air
II-2 Reprinted from USGS Open-File Report 93-292
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Uranlum-238
4.51 billion years
Thorlum-234
24.1 days
Uranlum-234
247,000 years
Thorlum-230
80,000 years
Radium-226 Fa
1602 years
Radon-222
3.82 days
Polonlum-218
3.05 mln.
ead-214
27 mln.
Blsmuth-214
19.7 mln.
Polonlum-214
164 usee.
Lead-210
19.4 years
Blsmuth-210
olonlum-210
138.4 days
Lead-206
STABLE
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"9 meters), or about 2xl0'6 inchesthis 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 highei
indoor radon concentrations during the summer than in the winter. A suggested cause for this
phenomenon involves temperature/pressure-driven flow of radon-laden air from subsurface
II-4
Reprinted from USGS Open-File Report 93-292
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solution cavities in the carbonate rock into houses. As warm air enters solution cavities that
are higher on the hillslope than the homes, it cools arid settles, pushing radon-laden air from
lower in the cave or cavity system into structures on the hillslope (Gammage and others,
1993). In contrast, homes built over caves having openings situated below the level of the
home had higher indoor radon levels in the winter, caused by cooler outside air entering the
cave, driving radon-laden air into cracks and solution cavities in the rock and soil, and
ultimately, into homes (Gammage and others, 1993).
RADON ENTRY INTO BUILDINGS
A driving force (reduced atmospheric pressure in the house relative to the soil, producing
a pressure gradient) and entry points must exist for radon to enter a building from the soil.
. The negative pressure caused by furnace combustion, ventilation devices, and the stack effect
(the rising and escape of warm air from the upper floors of the building, causing a
temperature and pressure gradient within the structure) during cold winter months are
common driving forces. Cracks and other penetrations through building foundations, sump
holes, and slab-to-foundation wall joints are common entry points.
Radon levels in the basement are generally higher than those on the main floor or upper
floors of most structures. Homes with basements generally provide more entry points for
radon, commonly have a more pronounced stack effect, and typically have lower air pressure
relative to the surrounding soil than nonbasement homes. - The term "nonbasement" applies to
slab-on-grade or crawl space construction.
METHODS AND SOURCES OF DATA
The assessments of radon potential in-the booklets that follow this introduction were
made using five main types of data: (1) geologic (lithologic); (2) aerial radiometric; (3) soil
characteristics, including soil moisture, permeability, and drainage characteristics; (4) indoor
radon data; and (5) building architecture (specifically, whether homes in each area are built
slab-on-grade or have a basement or crawl space). These five factors were evaluated and
integrated to produce estimates of radon potential. Field measurements of soil-gas radon or
soil radioactivity were not used except where such data were available in existing, published
reports of local field studies. Where applicable, such field'studies are described in the
individual state chapters.
Geologic Data
The types and distribution of lithologic units and other geologic features in an
assessment area are of primary importance in determining radon potential. Rock types that
are most likely to cause indoor radon problems include carbonaceous black shales, glauconite-
bearing sandstones, certain kinds of fluvial sandstones and fluvial sediments, phosphorites,
chalk, karst-producing carbonate rocks, certain kinds of glacial deposits, bauxite, uranium-rich
granitic rocks, metamorphic rocks of granitic composition, silica-rich volcanic rocks, many
sheared or faulted rocks, some coals, and certain kinds.of contact metamorphosed rocks.
Rock types least likely to cause radon problems include marine quartz sands, non-
carbonaceous shales and siltstones, certain kinds of clays, silica-poor metamorphic and
\
II-5 Reprinted from USGS Open-File Report 93-292
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igneous rocks, and basalts. Exceptions exist within these general lithologic groups because of
the occurrence of localized uranium deposits, commonly of the hydrothermal type in
crystalline rocks or the "roll-front" type in sedimentary rocks. Uranium and radium are
commonly sited in heavy minerals, iron-oxide coatings on rock and soil grains, and organic
materials in soils and sediments. Less common are uranium associated with phosphate and
carbonate complexes in rocks and soils, and uranium minerals.
Although many cases of elevated indoor radon levels can be traced to high radium and
(or) uranium concentrations in parent rocks, some structural features, most notably faults and
shear zones, have been identified 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 (:MBi), 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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FLICHT LINE SPACING OF SURE AERIAL SUKVEYS
^ 2 k'U (1 KILE]
@ 5 IW (3 MILES)
^ 2 1 3 U
SSS 10 KU (6 UILES)
^3 S k 10. KM
¦1 NO .DATA
Figure 2. Nominal flightline spacings for NURE aerial gamma-ray surveys covering the
contiguous United States (from Duval and others, 1990). Rectangles represent l°x2° quadrangles.
-------
Figure 2 is an index map of NURE 1° x 2° quadrangles showing the flight-line spacing
for each quadrangle. In general, the more closely spaced the flightlines are, the more area
was covered by the aerial gamma survey, and thus, more detail is available in the data set.
For an altitude of 400 ft above the ground surface and with primary flightline spacing
typically between 3 and 6 miles, less than 10 perc<^ 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 d'ata.
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, arid 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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STATE/EPA RESIDENTIAL RADON
ST1RVRY .9r.RFP.NINr, MF.A.9I IRRMRNT5?
Estimated Percent of Houses with Screening Levels Greater than 4 pCi/L
20 and >
The Slates of Dn.11 Jfl I.NJ.NY, andIUT
have conducted their own surveys. OR A
SD declined to participate in the SRRS.
These results arc based on 2-7 day screening
measurements in the lowest livable level ana 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.
-------
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 indooi 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 rnake 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 factorsindoor
radon data, geology, aerial radioactivity, soil parameters, and house foundation typewere
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 hot 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-1 1 Reprinted from USGS Open-File Report 93-292
-------
TABLE 1. RADON INDEX MATRIX, "ppm eU" indicates parts per million of equivalent
uranium, as indicated by NURE aerial radiometric data. See text discussion for details.
INCREASING RADON POTENTIAL ^
FACTOR
POINT VALUE
1
2
3
INDOOR RADON (average)
< 2 pCi/L
2-4 pCi/L
> 4 pCi/L
AERIAL RADIOACTIVITY
<1.5 ppm eU
1.5 - 2.5 ppm eU
> 2.5 ppm eU
GEOLOGY*
negative
variable
positive
SOIL PERMEABILITY
low
moderate
high
ARCHITECTURE TYPE
mostly slab
mixed
mostly basement
'GEOLOGIC FIELD EVIDENCE (GFE) POINTS: GFE points are assigned in addition to points
for the "Geology" factor for specific, relevant geologic field studies. See text for details.
Geologic evidence supporting: HIGH radon +2 points
MODERATE +1 point
LOW -2 points
No relevant geologic field studies 0 points
SCORING: Probable average screening
Radon potential category Point range indoor radon for area
LOW 3-8 points <2pCi/L
MODERATE/VARIABLE 9-11 points 2-4pCi/L
HIGH . 12-17 points >4 pCi/L
POSSIBLE RANGE OF POINTS = 3 to 17
TABLE 2. CONFIDENCE INDEX MATRIX
INCREASING CONFIDENCE
FACTOR
POINT VALUE
1
2
3
INDOOR RADON DATA
sparse/no data
fair coverage/quality
good coverage/quality
AERIAL RADIOACTIVITY
questionable/no data
glacial cover
no glacial cover
GEOLOGIC DATA
questionable
variable
»
proven geol. model
SOIL PERMEABILITY
questionable/no data
variable
reliable, abundant
SCORING: LOW CONFIDENCE 4-6 points
MODERATE CONFIDENCE 7-9 points
HIGH CONFIDENCE 10 -12 points
POSSIBLE RANGE OF POINTS = 4 to 12
H-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, arid 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 arfe 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 ,
-------
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 (SOS) 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 fail 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
categorieslow, 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
factorsif 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 allow;s 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 nonrandpm 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 sojl permeability in the Confidence Index are similar in concept, and
scored similarly, to those for the geologic data factor.. Soil permeability .can be roughly
estimated from grain size and drainage class if data from standard, accepted soil percolation
tests are unavailable; however, the reliability of the data would be lower than if percolation
test figures or other measured permeability data are available, because an estimate of this type
does not encompass all the factors that affect soil permeability and thus may be inaccurate in
some instances. Most published soil permeability data are for water; although this is
generally closely related to the air permeability of the soil, there are some instances when it
may provide an incorrect estimate. Examples of areas in which water permeability data may
not accurately reflect air permeability include areas with consistently high levels of soil
moisture, or clay-rich soils, which would have a low water permeability but may have a
11-15- Reprinted from USGS Open-File Report 93-292
-------
significantly higher air permeability when dry due to shrinkage cracks in the soil. These
additional factors were applied to the soil permeability factor when assigning the RI score, but
may have less certainty in some cases and thus would be assigned a lower CI score.
The Radon Index and Confidence Index give a general indication of the relative
contributions of the interrelated geologic factors influencing radon generation and transport in
rocks and soils, and thus, of the potential for elevated indoor radon levels to occur in a
particular area. However, because these reports are somewhat generalized to cover relatively
large areas of States, it is highly recommended that more detailed studies be performed in
local areas of interest, using the methods and general information in these booklets as a guide.
Reprinted from USGS Open-File Report 93-292
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REFERENCES CITED
Akerblom, G., Anderson, P., and Clavensjo, B., 1984, Soil gas radon--A source for indoor radon
daughter^: Radiation Protection Dosimetry, v. 7, p. 49-54.
Deffeyes, K.S., and MacGregor, I.D., 1980, World uranium resources: Scientific American,
v. 242, p. 66-76.
Durrance, E.M., 1986, Radioactivity in geology: Principles and applications: New York, N.Y.,
Wiley and Sons, 441 p.
s
Duval, J.S., 1989, Radioactivity and some of its applications in geology: Proceedings of the
symposium on the application of geophysics to engineering and environmental problems
(SAGEEP), Golden, Colorado, March 13-16, 1989: Society of Engineering and Mineral
Exploration Geophysicists, p. 1-61.
Duval, J.S., Cook, B.G., and Adams, J.A.S., 1971, Circle of investigation of an airborne
gamma-ray spectrometer: Journal of Geophysical Research, v. 76, p. 8466-8470.
Duval, J.S., Jones, W.J., Riggle, F.R., and Pitkin, J.A., 1989, Equivalent uranium map of
conterminous United States: U.S. Geological Survey Open-File Report 89-478,10 p.
Duval, J.S., Reimer, G.M., Schumann, R.R., Owen, D.E., and Otton, J.K., 1990, Soil-gas
radon compared to aerial and ground gamma-ray measurements at study sites near Greeley
and Fort Collins, Colorado: U.S. Geological Survey Open-File Report 90-648,42 p.
Dziuban, J.A., Clifford, M.A., White, S.B., Bergstein, J.W., and Alexander, B.V., 1990,
Residential radon survey of twenty-three States, in Proceedings of the 1990 International
Symposium on Radon and Radon Reduction Technology, Vol. HI: Preprints: U.S.
Environmental Protection Agency report EPA/600/9-90/005c, Paper IV-2,17 p.
Gammage, R.B., Wilson, D.L., Saultz, R.J,, and Bauer, B.C., 1993, Subtereanean transport of
radon and elevated indoor radon in hilly karst terranes: Atmospheric Environment
(in press).
Gundersen, L.C.S., Reimer, G.M., and Agard, S.S., 1988a, Correlation between geology, radon
in soil gas, and indoor radon in the Reading Prong, in Marikos, M. A., and Hansman,
R.H., eds., Geologic causes of natural radionuclide anomalies: Missouri Department of
Natural Resources Special Publication 4, p. 91-102.
Gundersen, L.C.S, Reimer, G.M., Wiggs, C.R., and Rice, C.A., 1988b, Map showing radon
potential of rocks and soils in Montgomery County, Maryland: U.S. Geological Survey
Miscellaneous Field Studies Map MF-2043, scale 1:62,500.
Gundersen, Linda C.S., 1991, Radon in sheared metamorphic and igneous rocks, in Gundersen,
Linda C.S., and Richard B. Wanty, eds., Field studies of radon in rocks, soils, and water:
U.S. Geol. Survey Bulletin no. 1971, p. 39-50.
II-17 Reprinted from USGS Open-File Report 93-292
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Henry, Mitchell E., Kaeding, Margret E., and Monteverde, Donald, 1991, Radon in soil gas and
gamma-ray activity of rocks and soils at the Mulligan Quarry, Clinton, New Jersey, in
Gundersen, Linda C.S., and Richard B. Wanty, eds., Field studies of radon in rocks,
soils, and water: U.S. Geol. Survey Bulletin no. 1971, p. 65-75:
Klusman, R. W., and Jaacks, J. A., 1987, Environmental influences upon mercury, radon, and
helium concentrations in soil gases at a site near Denver, Colorado: Journal of
Geochemical Exploration, v. 27, p. 259-280.
Kovach, E.M., 1945, Meteorological influences upon the radon content of soil gas: Transactions,
American Geophysical Union, v. 26, p. 241-248.
Kunz, C., Laymon, C.A., and Parker, C., 1989, Gravelly soils and indoor radon, in Osborne,
M.C., and Harrison, J., eds., Proceedings of the 1988 EPA Symposium on Radon and
Radon Reduction Technology, Volume 1: U.S. Environmental Protection Agency Report
EPA/600/9-89/006A, p. 5-75-5-86.
Muessig, K., and Bell, C., 1988, Use of airborne radiometric data to direct testing for elevated
indoor radon: Northeastern Environmental Science, v. 7, no. 1, p. 45-51.
Ronca-Battista, M., Moon, M., Bergsten, J., White, S.B., Holt, N., and Alexander, B., 1988,
Radon-222 concentrations in the United StatesResults of sample surveys in five states:
Radiation Protection Dosimetry, v. 24, p. 307-312.
Rose, A.W., Washington, J.W., and Greeman, D.J., 1988, Variability of radon with depth and
season in a central Pennsylvania soil developed on limestone: Northeastern Environmental
Science, v. 7, p. 35-39.
Schery, S.D., Gaeddert, D.H., and Wilkening, M.H., 1984, Factors affecting exhalation of radon
from a gravelly sandy loam: Journal of Geophysical Research, v. 89, p. 7299-7309.
Schumann, R.R., and Owen, D.E., 1988, Relationships between geology, equivalent uranium
concentration, and radon in soil gas, Fairfax County, Virginia: U.S. Geological Survey
Open-File Report 88-18,28 p.
»
Schumann, R.R., and Gundersen, L.C.S., 1991, Regional differences in radon emanation
coefficients in soils: Geological Society of America Abstracts With Programs, v. 23,
no. 1, p. 125.
Schumann, R.R., Peake, R.T., Schmidt, K.M., and Owen, D.E., 1991, Correlations of soil-gas
and indoor radon with geology in glacially derived soils of the northern Great Plains, in
Proceedings of the 1990 International Symposium on Radon and Radon Reduction
Technology, Volume 2, Symposium Oral Papers: U.S. Environmental Protection Agency
report EPA/600/9-9 l/026b, p. 6-23-6-36.
11-18
Reprinted from USGS Open-File Report 93-292
-------
Schumann, R.R., Owen, D.E., and Asher-Bolinder, S., 1992, Effects of weather and soil
characteristics on temporal variations in soil-gas radon concentrations, in Gates, A.E., and
Gundersen, L.C.S., eds., Geologic controls on radon: Geological Society of America
Special Paper 271, p. 65-72.
Sextro, R.G., Moed, B.A., Nazaroff, W.W., Revzan, K.L., and Nero, A.V., 1957,
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., II, 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, 111., 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 III, 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 Schod'n, 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.
H-19
Reprinted from USGS Open-File Report 93-292
-------
APPFNDTY A
GEOLOGIC TIME SCALE
Subdivisions {and their symbols)
Eon or
Eonothem
Era or
Erathem
Period, System.
Subperiod, Subsystem
Epoch or Series
Age estimates
of boundaries
in mega-annum
(Ma)1
Phanerozoic*
Cenozoic 2
(Cz)
Mesczoic
(MxJ
Quaternary'
(Q)
Holocene
Tertiary
m
Pleistocene
Neog«ne 2
Subperiod or
Subsystem IN)
Pliocene
Miocene
Paleogene
Suboenod or
Subsystem (Pi!
Oligocene
Eocene
Pa (eocene
Cretaceous
CK)
Late
Early
Jurassic
(J)
Triassic
nu
Late
Middle
Early
Late
Middle
Paleozoic'
(Pi)
Proterozoic
(B)
L«l»
fe>o«c
Froi»re>0»C fVl
£»rty
Archean
(A)
L4!«
Archeen fWl
MiO0>»
tiny
Permian
(P)
Carboniferous
Systems
(C)
Pennsylvanian
(P!
Mississippian
(M!
Devonian
(D)
Silurian
(S>
Early
Late
Early
Late
Middle
Early
Late
Early
Late
Middle
Early
Late
Middle
Early
Ordovician
(O)
Cambrian
- fC)
Late
Middle
Early
Late
Middle
Early
None defined
None defined
None defined
None defined
None defined
None defined
pr*
-------
APPENDIX B
GLOSSARY OF TERMS
Units of measure
pCi/L (picocuries per liter)- a unit of measure of radioactivity used to describe radon
concentrations in a volume of air. One picocurie (10"12 curies) is equal to about 2.2 disintegrations
of radon atoms per minute. A liter is about 1.06 quarts. The average concentration of radon in
U.S. homes measured to date is between 1 and 2 pCi/L.
Bq/m3 (Becquerels per cubic meter)- a metric unit of radioactivity used to describe radon
concentrations in a volume of air. One becquerel is equal to one radioactive disintegration per
second. One pCi/L is equal to 37 Bq/m3.
ppm (parts per million)- a unit of measure of concentration by weight of an element in a
substance, in this case, soil or rock. One ppm of uranium contained in a ton of rock corresponds
to about 0.03 ounces of uranium.. The average concentration of uranium in soils in the United
States is between 1 and 2 ppm.
in/hr (inches per hour)- a unit of measure used by soil scientists and engineers to describe the
permeability of a soil to water flowing through it It is measured by digging a hole 1 foot (12
inches) square and one foot deep, filling it with water, and measuring the time it takes for the water
to drain from the hole. The drop in height of the water level in the hole, measured in inches, is
then divided by the time (in hours) to determine the permeability. Soils range in permeability from
less than 0.06 in/hr to greater than 20 in/hr, but most soils in the United States have permeabilities
between these two extremes.
Geologic terms and terms related to the study of radon
aerial radiometric, aeroradiometric survey A survey of radioactivity, usually gamma rays,
taken by an aircraft carrying a gamma-ray spectrometer pointed at the ground surface.
alluvial fan A low, widespread mass of loose rock and soil material, shaped like an open*fan
and deposited by a stream at the point where it flows from a narrow mountain valley out onto a
plain or broader valley. May also form at the junction with larger streams or when the gradient of
the stream abruptly decreases.
alluvium, alluvial General terms referring to unconsolidated detrital material deposited by a
stream or other body of running water.
alpha-track detector A passive radon measurement device consisting of a plastic film that is
sensitive to alpha particles. The film is etched with acid in a laboratoiy 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.
H-21 Reprinted from USGS Open-File Report 93-292
-------
argillite, argillaceous Terms referring to a rock derived from clay or shale, or any sedimentary
rock containing an appreciable amount of clay-size material, i.e., argillaceous sandstone.
arid Term describing a climate characterized by dryness, or an evaporation rate that exceeds the
amount of precipitation.
basalt A general term for a dark-colored mafic igneous rocks that may be of extrusive origin,
such as volcanic basalt flows, or intrusive origin, such as basalt dikes.
batholith A mass of plutonic igneous rock that has more than 40 square miles of surface
exposure and no known bottom.
carbonate' A sedimentary rock consisting of the carbonate (CO3) compounds of calcium,
magnesium, or iron, e.g. limestone and dolomite.
carbonaceous Said of a rock or sediment that is rich in carbon, is coaly, or contains organic
matter.
charcoal canister A passive radon measurement device consisting of a small container of
granulated activated charcoal that is designed to adsorb radon. Useful for short duration (2-7 days)
measurements only. May be referred to as a "screening" test
chert A hard, extremely dense sedimentary rock consisting dominantly of interlocking crystals of
quartz. Crystals are not visible to the naked eye, giving the rock a milky, dull luster. It may be
white or gray but is commonly colored red, black, yellow, blue, pink, brown, or green.
clastic pertaining to a rock or sediment composed of fragments that are derived from preexisting
rocks or minerals. The most common clastic sedimentary rocks are sandstone and shale.
clay A rock containing clay mineral fragments or material of any composition having a diameter
less than 1/256 mm.
clay mineral One of a complex and loosely defined group of finely crystalline minerals made up
of water, silicate and aluminum (and a wide variety of other elements). They are formed chiefly by
alteration or weathering of primary silicate minerals. Certain clay minerals are noted for their small
size and ability to absorb substantial amounts of water, causing them to swell. The change in size
that occurs as these clays change between dry and wet is referred to as their "shrink-swell"
potential.
concretion A hard, compact mass of mineral matter, normally subspherical but commonly
irregular in shape; formed by precipitation from a water solution about a nucleus or center, such as
a leaf, shell, bone, or fossil, within a sedimentary or fractured rock.
conglomerate A coarse-grained, clastic sedimentary rock composed of rock and mineral
fragments larger than 2 mm, set in a finer-grained matrix of clastic material.
cuesta A hill or ridge with a gentle slope on one side and a steep slope on the other. The
formation of a cuesta is controlled by the different weathering properties and the structural dip of
the rocks forming the hill or ridge.
daughter product A nuclide formed by the disintegration of a radioactive precursor or "parent"
atom.
n-22 Reprinted from 1JSGS Open-File Report 93-292
-------
delta, deltaic Referring to a low, flat, alluvial tract of land having a triangular or fan shape,
located at or near the mouth of a river. It results from the accumulation of sediment deposited by a
river at the point at which the river loses its ability to transport the sediment, commonly where a
river meets a larger body of water such as a lake or ocean.
dike A tabular igneous intrusion of rock, younger than the surrounding rock, that commonly cuts
across the bedding or foliation of the rock it intrudes.
diorite A plutonic igneous rock that is medium in color and contains visible dark minerals that
make up less than 50% of the rock. It also contains abundant sodium plagioclase and minor
quartz.
\
dolomite A carbonate sedimentary rock of which more than 50% consists of the mineral dolomite
(CaMg(C03)2), and is commonly white, gray, brown, yellow, or pinkish in color.
drainage The manner in which the waters of an area pass, flow off of, or flow into the soil.
Also refers to the water features of an area, such as lakes and rivers, that drain it
eolian Pertaining to sediments deposited by the wind.
esker A long, narrow, steep-sided ridge composed of irregular beds of sand and gravel deposited
by streams beneath a glacier and left behind when the ice melted.
evapotranspiration Loss of water from a land area by evaporation from the soil and
transpiration from plants.
extrusive Said of igneous rocks that have been erupted onto the surface of the Earth.
fault A fracture or zone of fractures in rock or sediment along which there has been movement.
fluvial, fluvial deposit Pertaining to sediment that has been deposited by a river or stream.
foliation A linear feature in a rock defined by both mineralogic and structural characteristics. It
may be formed during deformation or metamoiphism.
formation A mappable body of rock having similar characteristics.
glacial deposit Any sediment transported and deposited by a glacier or processes associated
with glaciers, such as glaciofluvial sediments deposited by streams flowing from melting glaciers.
gneiss A rock formed by metamorphism in which bands and'lenses of minerals of similar
composition alternate with bands and lenses of different comppsition, giving the rock a striped or
"foliated" appearance.
granite Broadly applied, any coarsely crystalline, quartz- and feldspar-bearing igneous plutonic
rock. Technically, granites have between 10 and 50% quartz, and alkali feldspar comprises at least
65% of the total feldspar.
gravel An unconsolidated, natural accumulation of rock fragments consisting predominantly of
particles greater than 2 mm in size.
heavy minerals Mineral grains in sediment or sedimentary rock having higher than average
specific gravity. May form layers and lenses because of wind or water, sorting by weight and size
11-23 Reprinted from USGS Open-File Report 93-292
-------
and may be referred" to as a "placer deposit." Some heavy minerals are magnetite, garnet, zircon,
monazite, and xenotime.
igneous Said of a rock or mineral that solidified from molten or partly molten rock material. It is
one of the three main classes into which rocks are divided, the others being sedimentary and
metamorphic.
intermontane A term that refers to an area between two mountains or mountain ranges.
intrusion, intrusive The processes of emplacement or injection of molten rock into pre-existing
rock. Also refers to the rock formed by intrusive processes, such as an "intrusive igneous rock".
kame A low mound, knob, hummock, or short irregular ridge formed by a glacial stream at the
margin of a melting glacier; composed of bedded sand and gravel.
karst terrain A type of topography that is formed on limestone, gypsum and other rocks by
dissolution of the rock by water, forming sinkholes and caves.
lignite A brownish-black coal that is intermediate in coalification between peat and
subbituminous coal.
limestone A carbonate sedimentary rock consisting of more than 50% calcium carbonate,
primarily in the form of the mineral calcite (CaC03).
lithology The description of rocks in hand specimen and in outcrop on the basis of color,
composition, and grain size.
loam A permeable soil composed of a mixture of relatively equal parts clay, silt, and sand, and
usually containing some organic matter.
loess A fine-grained eolian deposit composed of silt-sized particles generally thought to have
been deposited from windblown dust of Pleistocene age.
mafic Term describing an igneous rock containing more than 50% dark-colored minerals.
marine Term describing sediments deposited in the ocean, or precipitated from ocean waters.
metamorphic Any rock derived from pre-existing rocks by mineralogical, chemical, or structural
changes in response to changes in temperature, pressure, stress, and the chemical environment
Phyllite, schist, amphibolite, and gneiss are metamorphic rocks.
moraine A mound, ridge, or other distinct accumulation of unsorted, unbedded 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.
H-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 geomoiphic history, and whose topography or landforms differ
significantly from adjacent regions.
placer deposit See heavy minerals
residual Formed by weathering of a material in place. .
residuum Deposit of residual material.
rhyolite An extrusive igneous rock of volcanic origin, compositionally equivalent to granite.
sandstone A clastic sedimentary rock composed of sand-sized rock and mineral material that is
more or less firmly cemented. Sand particles range from 1/16 to 2 mm in size.
schist A strongly foliated crystalline rock, formed by metamorphism, that can be readily split into
thin flakes or slabs. Contains mica; minerals are typically aligned.
screening level Result of an indoor radon test taken with a charcoal canister or similar device,
for a short period of time, usually less than seven days. May indicate the potential for an indoor
radon problem but does not indicate annual exposure to radon.
sediment Deposits of rock and mineral particles or fragments originating from material that is
transported by air, water or ice, or that accumulate by natural chemical precipitation or secretion of .
organisms.
semiarid Refers to a climate that has slightly more precipitation than an arid climate.
shale A fine-grained sedimentary rock formed from solidification (lithification) of clay or mud.
shear zone Refers to a roughly linear zone of rock that has been faulted by ductile or non-ductile
processes in which the rock is sheared and both sides are displaced relative to one another.
shrink-swell clay See clay mineral.
siltstone A fine-grained clastic sedimentary rock composed of silt-sized rock and mineral
material and more or less firmly cemented. Silt particles range from 1/16 to 1/256 mm in size.
sinkhole A roughly circular depression in a karst area measuring meters to tens of meters in
diameter. It is funnel shaped and is formed by collapse of the surface material into an underlying
void created by the dissolution of carbonate rock.
slope An inclined part of the earth's surface.
solution cavity A hole, channel or cave-like cavity formed by dissolution of rock.
stratigraphy The study of rock strata; also refers to the succession of rocks of a particular area.
surficial materials Unconsolidated glacial, wind-, or waterborne deposits occurring on the
earth's surface. -
tablelands General term for a broad, elevated region with a nearly level surface of considerable
extent
13-25 Reprinted from USGS Open-File Report 93-292
-------
terrace gravel Gravel-sized material that caps ridges and terraces, left behind by a stream as it
cuts down to a lower level.
terrain A tract or region of the Earth's surface considered as a physical feature or an ecological
environment.
till Unsorted, generally unconsolidated and unbedded rock and mineral material deposited directly
adjacent to and underneath a glacier, without reworking by meltwater. Size of grains varies greatly
from clay to boulders.
uranlferous Containing uranium, usually more than 2 ppm.
vendor data Used in this report to refer to indoor radon data collected and measured by
commercial vendors of radon measurement devices and/or services. .
volcanic Pertaining to the activities, structures, and extrusive rock types of a volcano.
water table The surface forming the boundary between the zone of saturation and the zone of
aeration; the top surface of a body of unconfined groundwater in rock or soil.
weathering The destructive process by which earth and rock materials, on exposure to
atmospheric elements, are changed in color, texture, composition, firmness, or form with little or
no transport of the material.
11-26 Reprinted from USGS Open-File Report 93-292
-------
APPENDIX C
EPA REGIONAL OFFICES
EPA Regional Qfffcw Stale EPA Region
EPA Region 1 Alabama 4
JFK Federal Building Alaska 1.......10
Boston, MA 02203 Arizona i 9
(617) 565-4502 Arkansas 6
California.' 9
¦ EPA Region 2 Colorado 8
(2 AIR:RAD) Connecticut i 1
26 Federal Plaza Delaware 3
New York, NY 10278 District of Columbia . 3
(212) 264-4110 Florida 4
Georgia 4
Region 3 (3AH14) Hawaii 9
841 Chestnut Street Idaho 10
Philadelphia, PA 19107 Illinois...... ....... 5
(215) 597-8326 Indiana. 5
Iowa....' 7
EPA Region 4 Kansas : 7
345 Courtland Street, N.E. Kentucky 4
Atlanta, GA 30365 Louisiana 6
(404) 347-3907 Maine : 1
Maryland.... 3
EPA Region 5 (5AR26) Massachusetts 1
77 West Jackson Blvd. Michigan 5
Chicago, IL 60604-3507 Minnesota 5
(312) 886-6175 Mississippi 4
Missouri 7
' EPA Region 6 (6T-AS) Montana... 8
1445 Ross Avenue Nebraska 7
Dallas, TX 75202-2733 Nevada 9
(214) 655-7224 New Hampshire 1
. New Jersey 2
EPA Region 7 New Mexico 6
726 Minnesota Avenue New York 2
Kansas City, KS 66101 North Carolina A
(913) 551-7604 North Dakota 8
Ohio 5
EPA Region 8 Oklahoma 6
(8HWM-RP) Oregon 10
999 18th Street Pennsylvania 3
One Denver Place, Suite 1300 Rhode Island 1
Denver, CO 80202-2413 South Carolina ....4
(303) 293-1713 South Dakota ....: 8
Tennessee., 4
EPA Region 9 (A-3) Texas. ...6
75 Hawthorne Street Utah ' 8
San Francisco, CA 94105 Vermont. 1
(415) 744-1048 Virginia.... ; 3
Washington 10
EPA Region 10 West Virginia 3
1200 Sixth Avenue Wisconsin 5
Seattle, WA 98101 Wyoming 8
(202) 442-7660
H-27 Reprinted from USGS Open-File Report 93-292
-------
STATE RADON CONTACTS
May, 1993
James McNees
Division of Radiation Control
Alabama Department of Public Health
State Office Building
Montgomery, AL 36130
(205)242-5315
1-800-582-1866 in state
Charles Tedford
Department of Health and Social
Services
P.O. Box 110613
Juneau, AK 99811-0613
(907)465-3019
1-800-478-4845 in state .
John Stewart
Arizona Radiation Regulatory Agency
4814 South 40th St
Phoenix, AZ 85040
(602) 255-4845
Lee Gershner
Division of Radiation Control
Department of Health
4815 Markham Street, Slot 30
Little Rock, AR 72205-3867
(501) 661-2301
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
Linda Martin
Department of Health
4210 East 11th 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 061064474
(203) 566-3122
Regulatory Affairs
614 H Street NW
Room 1014
Washington, DC 20001
(202)727-71068
Florida N. Michael Gilley
Office of Radiation Control
Department of Health and
Rehabilitative Services
1317 Winewood Boulevard
Tallahassee, FL 32399-0700
(904)488-1525
1-800-543-8279 in state
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
Hawaii Russell Takata
Environmental Health Services
Division
591 Ala Moana Boulevard
Honolulu, HI 96813-2498
(808)586-4700
Delaware MaraiG. Rejai
Office of Radiation Control
Division of Public Health
P.O. Box 637
Dover, DE 19903
(302)736-3028
1-800-554-4636 In State
District Robert Davis
of Columbia DC Department of Consumer and
n-28 Reprinted from USGS Open-File Report 93-292
-------
I&hQ
Pat McGavarn
Office of Environmental Health
450 West State Street
Boise, ID 83720
(208) 334-6584
1-800-445-8647 in state
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
Illinois
Richard Allen
Illinois Department of Nuclear Safety
1301 Outer Park Drive
Springfield, IL 62704
(217)524-5614
1-800-325-1245 in state
Maim*. 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
In
-------
Mississippi Silas Anderson
Division of Radiological Health
Department of Health
3150 Lawson Street
P.O. Box 1700
Jackson, MS 39215-1700
(601) 354-6657
1-800-626-7739 in state
New Jersey
Missouri Kenneth V. Miller
Bureau of Radiological Health
Missouri Department of Health
1730 East Elm
P.O. Box 570
Jefferson City, MO 65102
(314)751-6083
1-800-669-7236 In State
New Mexico
Montana Adrian C. Howe
Occupational Health Bureau
Montana Department of Health and
Environmental Sciences
Cogswell Building A113
Helena, MT 59620
(406)444-3671
New Yoik
Nebraska Joseph Milone
Division of Radiological Health
Nebraska Department of Health
301 Centennial Mall, South
P.O. Box 95007
Lincoln, NE 68509
(402)471-2168
1-800-334-9491 In State
North Carolina
Nevada Stan Marshall North Dakota
Department of Human Resources
505 East King Street
Room 203
Carson City, NV 89710
(702)687-5394
New Hampshire David Chase Ohio
Bureau of Radiological Health
Division of Public Health Services
Health and Welfare Building
Six Hazen Drive
Concord, NH 03301
(603) 271-4674
1-800-852-3345 x4674
Tonalee Carlson Key
Division of Environmental Quality
Department of Environmental
Protection
CN 415
Trenton, NJ 08625-0145
(609) 987-6369
1-800-648-0394 in state
William M. Floyd
Radiation Licensing and Registration
Section
New Mexico Environmental
Improvement Division
1190 St. Francis Drive
Santa Fe, NM 87503
(505) 8274300
William J. Condon
Bureau of Environmental Radiation
Protection
New York State Health Department
Two University Place
Albany, NY 12202
(518)458-6495
1-800-458-1158 in state .
Dr. Felix Fong
Radiation Protection Division
Department of Environmental Health
and Natural Resources
701 Baibour Drive
Raleigh, NC 27603-2008 .
(919) 571-4141
1-800-662-7301 (recorded info x4196)
Arlen Jacobson
North Dakota Department of Heal th
1200 Missouri Avenue, Room 304
P.O. Box 5520
Bismarck, ND 58502-5520
(701)221-5188
Maicie Matthews
Radiological Health Program
Department of Health
1224 Kinnear Road - Suite 120
Columbus, OH 43212
(614)644-2727
1-800-523-4439 in state
11-30 Reprinted from USGS Open-File Report 93-292
-------
Oklahoma
Qn?gpn
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
Hekth Division
1400 SW 5th Avenue
Portland, OR 97201
(503)731-4014
South Dakota MikePochop
Division of Environment Regulation
Department of Water and Natural
Resources
Joe FOi. Building, Room 217.
523 E. Capitol
Pierre, SD 57501-3181
(605)773-3351
Tennessee Susie Shimek
Division of Air Pollution Control
. Bureau of the Environment
Department of Environment and
Conservation
Customs House, 701 Broadway
Nashville, TN 37219-5403
(615)532-0733
1-800-232-1139 in state ¦.
Pennsylvania Michael Pyles
Pennsylvania Department of
Environmental Resources
Bureau of Radiation Protection
P.O. Box 2063
Hanisburg, PA 17120
(717)783-3594
1-800-23-RADON In State
Texas Gary Smith
Bureau of Radiation Control
Texas Department of Health
1100 West 49th Street
Austin, TX 78756-3189
(512) 834-6688
Puerto Rico
Rhode Island
South Carolina
David Saldana
Radiological Health Division
G.P.O. Call Box 70184
Rio Piedras, Puerto Rico 00936
(809) 767-3563
Edmund Arcand
Division of Occupational Health and
Radiation
Department of He'alth
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
Utah John Hultquist
Bureau of Radiation Control
Utah State Department of Health
288 North, 1460 West
P.O. Box 16690
Salt Lake City, UT 84116-0690
(801) 536-4250
Vermont Paul Clemons
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 II
in New York
(212) 264-4110
II-31 Reprinted from USGS Open-File Report 93-292
-------
Virginia Shelly Ottenbrite
Bureau of Radiological Health
Department of Health
109 Governor Street
Richmond, VA 23219
(804) 786-5932
1-800-468-0138 in state
Washington Kate Coleman
Department of Health
Office of Radiation Protection
Airdustrial Building 5, LE-13
Olympia, WA 98504
(206) 753-4518
1-800-323-9727 In State
West Virginia BeattieL.DeBord
Industrial Hygiene Division
West Virginia Department of Health
15111th Avenue
South Charleston, WV 25303
(304) 558-3526
1-800-922-1255 In State
Wisconsin Conrad Weiffenbach
Radiation Protection Section
Division of Health
Department of Health and Social
Services
P.O. Box 309
Madison, WI53701-0309
(608) 267-4796
1-800-798-9050 in state
Wyoming Janet Hough
Wyoming Department of Health and
Social Services
Hathway Building, 4th Floor
Cheyenne, WY 82002-0710
(307) 777-6015
1-800-458-5847 in state
n-32 Reprinted from USGS Open-File Report 93-292
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STATE GEOLOGICAL SURVEYS
May, 1993
Alahama 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
Arizona Larry D. Fellows
Arizona Geological Survey
845 North Park Ave., Suite 100
Tucson, AZ 85719
(602) 882-4795
Arkansas Norman F. Williams
Arkansas Geological Commission
Vardelle Parham Geology Center
3815 West Roosevelt Rd.
Little Rock, AR 72204
(501)324-9165
California James F. Davis
California Division of Mines' &
Geology
801 K Street, MS 12-30
Sacramento, CA 95814-3531
(916)445-1923
Colorado Pat Rogers (Acting)
Colorado Geological Survey
1313 Sherman St., Rm 715
Denver, CO 80203
(303)866-2611
Connecticut Richard C. Hyde
Connecticut Geological & Natural
History Survey
165 Capitol Ave., Rm. 553
Hartford, CT 06106
(203)566-3540
Delaware Robert R. Jordan
Delaware Geological Survey
University of Delaware
101 Penny Hall
Newaik, DE 19716-7501
(302)831-2833
Florida Walter Schmidt
Florida Geological Survey
903 W. Tennessee St.
Tallahassee, FL 32304-7700
(904)488-4191
Georgia William H. McLemore
Georgia Geologic Survey
Rm. 400
19 Martin Luther King Jr. Dr. SW
Atlanta, GA 30334
(404) 656-3214
Hawaii Manabu Tagomori
Dept. of Land and Natural Resources
Division of Water & Land Mgt
P.O. Box 373
Honolulu, HI 96809
(808)548-7539
Mi?. EariH. 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) 333-4747
Indiana Norman C. Hester
Indiana Geological Survey
611 North Walnut Grove
Bloomingtori, IN 47405
' (812) 855-9350
Iowa Donald L. Koch
Iowa Department of Natural Resources
Geological Survey Bureau
109 Trowbridge Hall
Iowa City, IA 52242-1319
(319)335-1575
Kansas Lee C. Gerhard
Kansas Geological Survey
1930 Constant Ave., West Campus
University of Kansas
Lawrence, KS 66047
(913) 864-3965
11-33 Reprinted from USGS Open-File Report 93-292
-------
Kentucky Donald C. Haney
Kentucky Geological Survey
University of Kentucky
228 Mining & Mineral Resources
Building
Lexington, KY 40506-0107
(606) 257-5500
Louisiana William E. Marsalis
Louisiana Geological Survey
P.O. Box 2827
University Station
Baton Rouge, LA 70821-2827
(504)388-5320
Maine Walter A. Anderson
Maine Geological Survey
Department of Conservation
State House, Station 22
Augusta, ME 04333
(207) 289-2801
Maryland Emery T. Cleaves
Maryland Geological Survey
2300 St. Paul Street
Baltimore, MD 21218-5210
(410) 554-5500
Massachusetts Joseph A. Sinnott
Massachusetts Office of
Environmental Affairs
100 Cambridge St., Room 2000
Boston, MA 02202
(617) 727-9800
Michigan R. Thomas Segall
Michigan Geological Survey Division
Box 30256
Lansing, MI 48909
(517) 334-6923
Minnesota Priscilla C. Grew
Minnesota Geological Survey
2642 University Ave.
St. Paul, MN 55114-1057
(612) 627-4780
Mississippi S. Cragin Knox
Mississippi Office of Geology
P.O. Box 20307
Jackson, MS 39289-1307
(601)961-5500
Missouri James H. Williams
Missouri Division of Geology &
Land Survey
111 Fairgrounds Road
P.O. Box 250
Rolla, MO 65401
(314) 368-2100
Montana Edward T.Ruppel
Montana Bureau of Mines & Geology
Montana College of Mineral Science
and Technology, Main Hall
Butte, MT 59701
(406)496-4180
Nebraska Perry B.Wigley
Nebraska Conservation & Survey
Division
113 Nebraska Hall
University of Nebraska
Lincoln, NE 68588-0517
(402)472-2410
Nevada Jonathan G. Price
Nevada Bureau of Mines & Geology
Stop 178
University of Nevada-Reno
Reno, NV 89557-0088
(702) 784-6691
New Hampshire Eugene L. Boudette
Dept. of Environmental Services
117 James Hall
University of New Hampshire
Durham, NH 03824-3589
(603)862-3160
New Jersey Haig F. Kasabach
New Jersey Geological Survey
P.O. Box 427
Trenton, NJ 08625
(609)292-1185
New Mexico Charles E. Chapin
New Mexico Bureau of Mines &
Mineral Resources
Campus Station
Socorro, NM 87801
(505) 835-5420
New York Robert H. Fakundiny
" New York State Geological Survey
3136 Cultural Education Center
Empire State Plaza
Albany, NY 12230
.(518)474-5816
H-34 Reprinted from USGS Open-File Report 93-292
-------
North Carolina Charles H. Gardner
North Carolina Geological Survey
P.O. Box 27687
Raleigh, NC 27611-7687
(919) 733-3833
North Dakota John P. Bluemle
North Dakota Geological Survey
600 East Blvd.
Bismarck, ND 58505-0840
(701)224-4109
Ohio Thomas M. Berg
Ohio Dept of Natural Resources
Division of Geological Survey
4383 Fountain Square Drive
Columbus, OH 43224-1362
(614) 265-6576
Oklahoma Charles J. Mankin
Oklahoma Geological Survey
Room N-131, Energy Center
100 E.Boyd
Norman, OK 73019-0628
(405)325-3031
Oregon Donald A. Hull
Dept. of Geology & Mineral Indust.
Suite 965
800 NE Oregon St. #28
Portland, OR 97232-2162
(503) 731-4600
Pennsylvania Donald M. Hoskins
Dept. of Environmental Resources
Bureau of Topographic & Geologic
Survey
P.O. Box 2357,
Harrisburg, PA 17105-2357
(717) 787-2169
Puerto Rico Ram6n M. Alonso
Puerto Rico Geological Survey
Division
Box 5887
Puerta de Tiena Station
San Juan, P.R. 00906
(809)722-2526
Rhode Island J. Allan Cain
Department of Geology
University of Rhode Island
315 Green Hall
Kingston, RI 02881
(401) 792-2265
South Carolina Alan-Jon W. Zupan (Acting)
South Carolina Geological Survey
5 Geology Road
Columbia, SC 29210-9998
(803)737-9440
South Dakota C.M. Christensen (Acting)
South Dakota Geological Survey
Science Center
University of South Dakota
Vermillion, SD 57069-2390
(605)677-5227
Tennessee Edward T. Luther
Tennessee Division of Geology
. 13th Floor, L & C Tower
401 Church Street
Nashville, TN 37243-0445
(615) 532-1500
Texas William L. Fisher
Texas Bureau of Economic Geology
University of Texas
University Station, Box X
Austin, TX 78713-7508
(512)471-7721
Utah M. Lee Allison
Utah Geological & Mineral Survey
2363 S. Foothill Dr.
Salt Lake City, UT 84109-1491
(801)467-7970
Vermont Diane L. Conrad
Vermont Division of Geology and
Mineral Resources
103 South Main St.
Waterbury,VT 05671
(802)244-5164
Virginia Stanley S. Johnson
Virginia Division of Mineral
Resources
P.O. Box 3667
Charlottesville, VA 22903
(804)293-5121
Washington Raymond Lasmanis
Washington Division of Geology &
Earth Resources
Department of Natural Resources
P.O. Box 47007
Olympia, Washington 98504-7007
(206)902-1450
H-35 . Reprinted from USGS Open-File Report 93-292
-------
West Virginia Larry D.Woodfork
West Virginia Geological and
Economic Survey
Mont Chateau Research Center
P.O. Box 879
Morgantown, WV 26507-0879
(304) 594-2331
Wisconsin James Robertson
Wisconsin Geological & Natural
History Survey
3817 Mineral Point Road
Madison, WI 53705-5100
(608)263-7384
Wyoming Gary B. Glass
Geological Survey of Wyoming
University of Wyoming
Box 3008, University Station
Laramie, WY 82071-3008
(307)766-2286
H-36
Reprinted from USGS Open-File Report 93-292
-------
EPA REGION 6 GEOLOGIC RADON POTENTIAL SUMMARY
by .
Linda C.S. Gundersen, James K. Otton, Russell F. Dubiel, and Sandra L. Szarzi
U.S. Geological Survey
EPA Region 6 includes the states Arkansas, Louisiana, New Mexico, Oklahoma, and
Texas. For each state, geologic radon potential areas were delineated and ranked on the basis of
geology, soils, housing construction, indoor radon, and other factors. Areas in which the average
screening indoor radon level of all homes within the area is estimated to be greater than 4 pCi/L
were ranked high. Areas in which the average screening indoor radon level of all homes within the
area is estimated to be between 2 and 4 pCi/L were ranked moderate/variable, and areas in which
the average screening indoor radon level of all homes within the area is estimated to be less than
2 pCi/L were ranked low. Information on the data used and on the radon potential ranking scheme
is given in the introduction to this volume. More detailed information on the geology and radon
potential of each state in Region .6 is given in the individual state chapters. The individual chapters
describing the geology and radon potential of the states in Region 6, 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 likely will be found.
Figure 1 shows a generalized map of the physiographic/geologic provinces in Region 6.
The following summary of radon potential in Region 6 is based on these provinces. Figure 2
shows average screening indoor radon levels by county calculated from the State/EPA Residential
Radon Survey. Figure 3 shows the geologic radon potential areas in Region 6, combined and
summarized from the individual state chapters,
ARKANSAS
The geologic radon potential of Arkansas is generally low to moderate. Paleozoic marine
limestones, dolomites, and uraniferous black shales appear to be associated with most of the
indoor radon levels greater than 4 pCi/L in the State."
Ordovician through Mississippian-age sedimentary rocks, including limestone, dolomite,
shale, and sandstone, underlie most of the Springfield and Salem Plateaus. Black shales and
residual soils developed from carbonate rocks in the Springfield and Salem Plateaus are moderate
to locally high in geologic radon potential. The Ordovician limestones, dolomites, black shales,
and sandstones have moderate (1.5-2.5 ppm) to high (>2.5 ppm) equivalent uranium (eU, from
aeroradioactivity surveys) and some of the highest indoor radon in the State is associated with
them. The Mississippian limestones and shales, however, have low (<1.5 ppm) equivalent
uranium with very localized areas of high eU, but also-have moderate to high levels of indoor
radon associated with them. Black shales and carbonaceous sandstones within the Mississippian,
Devonian, and Ordovician units of the plateaus are the likely cause of the local areas of high eU.
The Chattanooga Shale and shale units within the Mississippian limestones may be responsible for
some of the high indoor radon levels found in Benton County. Limestones are usually low in
radionuclide elements but residual soils developed from limestones may be elevated in uranium and
radium. Karst and cave features are also thought to* accumulate radon.
The Boston Mountains, Arkansas Valley, Fourche Mountains, and Athens Plateau are
underlain predominantly by Mississippian and Pennsylvanian sandstones and shales with low to
m-1 Reprinted from USGS Open-File Report 93-292-F
-------
30
J-
i\
1i_ _
J _¦
4-
ji
13
- J10
.1 .a
_ i
>v?£ c *
»_ _i _
n
r~
:22>.
miles
Figure 1. Geologic radon potential areas of EPA Region 6. 1,4,7-Cretaceous marine rocks; 2-Jemez Mountains; 3,11-Southern Rocky Mountains; 5, 15-
Tertiary Ogallala Formation (High Plains);-6-Grants uranium belt; 8,9-Plains and Plateaus (Triassic, Cretaceous and Quaternary deposits; 10-DatiI-MogolIon
volcanic field; 12-Tertiary volcanic and Cretaceous sedimentary rocks; 13-Late Paleozoic marine limestones; 14-Eastward extension .of the Basin and Range
Province; 16-Ccntral Oklahoma and Texas (Paleozoic marine sediments); 17-Wichita Mountains; 18,19-Cretaceous Central Texas juid Llano Uplift; 20-
Northern Coastal Plains (Old Uplands (LA)); 21-Southern Texas Plain; 22-Coastal Plain (TX)/01d Uplands (LA); 23-Ozark Plateau: 24-Lower Arkansas River
Valley; 25-Ouachita Mountains; 26,29-Saletn Plateau; 27-Springfield Plateau; 28-Boston Mountains; 30-Crowley's Ridge; 31-Fourdie Mountains; 32-Athens
Plateau; 33-Central Ouchita Mountains; 34Mississippi Alluvial Plain; 35,37-Terraces; 36rPrairies.
-------
Indoor Radon Screening
Measurements: Average {pCi/L)
0.0 to 1.9
2.0 to 4.0
4.1 to 7.5
Missing Data or < 5 Measurements
Figure 2. Screening indoor radon average for counties with 5 or more measurements in EPA Region 6. Data are from 2-7 day
charcoal canister tests.. Data for all states are from the EPA/State Residential Radon Survey. Histograms in map legends show the
number of counties in each category.
-------
Ml IBS
GEOLOGIC RADON POTENTIAL
I I LOW (<2 pCi/l)
FTvVl MODERATE/VARIABLE (2-4 pCi/L)
H HIGH (>4 pCi/L)
Figure 3. Geologic radon potential areas of EPA Region 6. For more detail, refer to individual state radon potential chapters.
-------
moderate radon potential. Although the indoor rad2.5 ppm) eU associated with ihem. Uranium also occurs in the Jackfork
Sandstone in Montgomery County and in the Atoka Formation in Crawford County. These rocks
are the most likely sources for the indoor radon levels. Radon from a hydrocarbon source in these
rocks should not be ruled out. The presence of radon and uranium in some natural gas, petroleum,
and asphaltite is well known and could contribute radon to indoor air in some locations.
The Central Ouachita Mountains are underlain by intensely-deformed Ordovician and
Silurian shales and sandstones with minor chert and limestone. These rocks generally have low to
moderate radon potential. A'eroradiometric signatures of 2.5 ppm eU or more are associated with
the Ordovician black shales and possibly with some syenite intrusions. Indoor radon in the Central
Ouachita Mountains is low to moderate and permeability of the soils is low to moderate.
The West Gulf Coastal Plain is generally low in radon potential. Some of the Cretaceous
and Tertiary sediments have moderate eU (1.5-2.5 ppm). Recent studies in the Coastal Plain of
Texas, Alabama, and New Jersey show that glauconite and phosphate in sandstones, chalks,
marls, and limestones, as well as black organic clays, shales, and muds, are often associated with
high concentrations of uranium and radon in the sediments, and could be sources for elevated
indoor radon levels. Several formations within the Gulf Coastal Plain of Arkansas contain these
types of sediments, especially parts of the upper Cretaceous'and lower Tertiary section, but
average indoor radon levels in this area are not elevated. The Quaternary sediments of the Coastal
Plain have low eU and the indoor radon average is low for the Gulf Coastal Plain overall.
The Mississippi Alluvial Plain and Crowley's Ridge have low to locally moderate radon
potential. The southern half of the Mississippi Alluvial Plain is made up predominantly of
quartzose sediments, has generally low eU, and has low indoor radon. The northern half of the
alluvial plain, however, includes the loess of Crowley's Ridge, which appears to have high
equivalent uranium associated with it, and possibly a high loess content in the surrounding
sediments in general. The northeastern corner of Arkansas appears to be crossed by the large belt
of loess that continues into Kentucky and Tennessee and shows as a distinct area of high eU on the
aeroradiometric map of the United States. Some areas of high eU may also be due to uranium in
phosphate-rich fertilizers used in agricultural areas., Several of the counties in the northern part of
the alluvial plain have maximum indoor radon values greater than 4 pCi/L and indoor radon
averages between 1 and 2 pCi/L, which are generally higher than those in surrounding counties.
LOUISIANA
The geology of Louisiana is dominated by ancient marine sediments of the Gulf Coastal
Plain and modern river deposits from the Mississippi River and its tributaries. Louisiana is
generally an area of low geologic radon potential. The climate, soil, and lifestyle-of the inhabitants
of Louisiana have influenced building construction styles and building ventilation which, in
general, do not allow high concentrations of radon to accumulate. Many homes in Louisiana are
built on piers or are slab-on-grade. Overall indoor radon is low; however, several parishes had
individual homes with radon levels greater than 4 pCi/L. Parishes with indoor radon levels greater
than 4 pCi/L are found in different parts of the State, in parishes underlain by coastal plain .
sediments, terrace deposits, and loess.
ffl-5 Reprinted from USGS Open-File Report 93-292-F
-------
In the Coastal Plain of Louisiana the glauconitic, carbonaceous, and phosphatic sediments
have some geologic potential to produce radon, particularly the Cretaceous and lower Tertiary-age
geologic units located in the northern portion (Old Uplands) of the State.. Soils from clays, shales,
and marls in the Coastal Plain commonly have low permeability, so even though these sediments
may be a possible source of radon, low permeability probably inhibits radon availability. Some of
the glauconitic sands and silts with moderate permeability may be the source of locally high indoor
radon. Moderate levels of radioactivity (1.5-2.5 ppm eU) are associated with areas underlain by
the Eocene through lower Oligocene-age Coastal Plain sediments, but do not follow formation
boundaries or strike belts in a systematic manner. The pattern of moderate radioactivity in this area
does appear to follow river drainages and the aeroradioactivity pattern may be associated with
northwest- and northeast-trending joints and or faults which, in turn, may control drainage
patterns. Part of the pattern of low aeroradioactivity in the Coastal Plain may be influenced by
ground saturation with water. This area receives high precipitation and contains an extensive
system of bayous and rivers. Besides damping gamma radioactivity, ground saturation can also
inhibit radon movement.
The youngest Coastal Plain sediments, particularly Oligocene and younger, have
decreasing amounts of glauconite and phosphate and become increasingly siliceous (silica-rich),
and thus, are less likely to be significant sources of radon. However, the possibility of roll-front
uranium deposits in sedimentary rocks and sediments of Oligocene-Miocene age, analogous to the
roll-front uranium deposits in Texas, has been proposed. Anomalous gamma-ray activity has been
measured in the lower Catahoula sandstone, but no uranium deposits have yet been identified.
The fluvial and deltaic sediments in the Mississippi Alluvial Plain are low in geologic radon
potential. They are not likely to have elevated amounts of uranium and the saturated to seasonally
wet conditions of the soils, as well as the high water tables, do not facilitate radon availability.
Coarse gravels in the terraces of the Mississippi Alluvial Plain have locally very high permeability
and may be a source of radon.
Loess units in the northern portion of the Mississippi floodplain can easily be identified by
their radiometric signature on the aeroradioactivity map of Louisiana. Loess is associated with
high radiometric anomalies throughout the United States. Radiometric anomalies also seem to be
associated with exposures of loess in Iberia, Lafayette, eastern Acadia, and northern Vermilion
Parishes, in the southeastern part of the Prairies. Loess tends to have low permeability, so even
though these sediments may be a possible source of high radon, the lack of permeability,
particularly in wet soils, may inhibit radon availability.
NEW MEXICO
An overriding factor in the geologic evaluation of New Mexico is the abundance and
widespread outcrops in local areas of known uranium-producing and uranium-bearing rocks in the
State. Rocks known to contain significant uranium deposits, occurrences, or reserves, and rocks
such as marine shales or phosphatic limestones that are known to contain low but uniform
concentrations of uraniufri, all have the potential to contribute to elevated levels of indoor radon. In
New Mexico, these rocks include Precambrian granites, pegmatites, and small hydrothermal veins;
the Pennsylvanian and Permian Cutler Formation, Sangre de Cristo Formation, and San Andres
Limestone; the Triassic Chinle Formation; the Jurassic Morrison Formation and Todilto Limestone
Member (Wanakah Formation); the Cretaceous Dakota Sandstone, Kirtland Shale, Fruitland
Formation, and Crevasse Canyon Formation; the Cretaceous and Tertiary Ojo Alamo Sandstone;
m-6 Reprinted from USGS Open-File Report 93-292-F
-------
Tertiary Ogallala Formation and Popotosa Formation (Santa Fe Group); Tertiary alkalic intrusive
rocks and rhyolitic and andesitic volcanic rocks such as the Alum Mountain andesite; and the
Quaternary Bandelier Tuff and Valles Rhyolite.
Several areas in New Mexico contain outcrops of one or more of these rock units that may
contribute to elevated radon levels. The southern tern rims of the San Juan Basin expose a
Paleozoic to Tertiary sedimentary section that contains the Jurassic, Cretaceous, and Tertiary-
sedimentary rocks having a high radiometric signature and that are known to host uranium deposits
in the Grants uranium district, as well as in the Chuska and Carrizo Mountains. In north-central
New Mexico, the Jemez Mountains are formed in part by volcanic rocks that include the Bandelier
Tuff and the Valles Rhyolite; this area also has an associated high radiometric signature. In
northeastern New Mexico, Precambrian crystalline rocks and Paleozoic sedimentary rocks of the
southern Rocky Mountains and Tertiary volcanic rocks and Cretaceous sedimentary rocks are
associated with radiometric highs. In southwestern New Mexico, middle Tertiary volcanic rocks
of the.Datil-Mogollon region are also associated with high radiometric signatures. Remaining areas
of the Colorado Plateau, the Basin and Range, and the Great Plains are associated with only
moderate to low radiometric signatures on the aeroradiometric map; these areas generally contain
Paleozoic to Mesozoic sedimentary rocks, scattered Tertiary and Quaternary volcanic rocks, and
locally, Tertiary sedimentary rocks.
The southern extension of the Rocky Mountains and uplifted Paleozoic sedimentary rocks in
central New Mexico; Upper Cretaceous marine shales and uranium-bearing Jurassic fluvial
sandstones of the Grants uranium belt in the northeastern part of the State; and Tertiary volcanic
rocks in the Jemez Mountains, just west of the southern Rocky Mountains, have high radon
potential. Average screening indoor radon levels are greater than 4 pCi/L and aeroradioactivity.
signatures are generally greater than 2.5 ppm eU. Rocks such as Precambrian granites and uplifted
Paleozoic strata, Jurassic sandstones and limestones, or Cretaceous to Tertiary shales and volcanic
rocks that are known to contain or produce uranium are the most likely sources of elevated indoor
radon levels in these areas. The remainder of the State has generally moderate radioactivity,
average screening indoor radon levels less than 4 pCi/L, and overall moderate geologic radon
potential.
OKLAHOMA
«
The geology of Oklahoma is dominated by sedimentary rocks and unconsolidated
sediments that vary in age from Cambrian to Holocene. Precambrian and Cambrian igneous rocks
are exposed in the,;core of the Arbuckle arid Wichita Mountains and crop out in about 1 percent of
the State. The western, northern, and central part of the State is underlain by very gently west-
dipping sedimentary focks of the northern shelf areas. A series of uplifts and basins flank the
central shelf area. The Gulf Coastal Plain forms the southeastern edge of the State.
Most of the rocks that crop out in the central and eastern part of the State are marine in
origin; they include limestone, dolomite, shale, sandstone, chert, and coal of Cambrian through
Permian age. Nonmarine rocks of Permian and Tertiary age, including shale, sandstone, and
conglomerate, are present in the western part of the central Oklahoma Hills and Plains area; sand,
clay, gravel, and caliche dominate in the High Plains in the western part of the State. The Gulf
Coastal Plain is underlain by Cretaceous nonmarine sand and clay and marine limestone and clay.
Some of these units locally are moderately uranium-bearing.
m-7 Reprinted from USGS Open-File Report 93-292-F
-------
Surface radioactivity across the State varies from less than 0.5 ppm to 5.0 ppm eU. Higher
levels of equivalent uranium (>2.5 ppm) are consistently associated with black shales-in the
southeastern and westernmost Ouachita Mountains, the Arbuckle Mountains, and the Ozark
Plateau; with Permian shale in Roger Mills, Custer, Washita, and Beckham Counties; with granites
and related rocks in the Wichita Mountains; and with Cretaceous shale and associated limestone in
the Coastal Plain. Low eU values (<1.5 ppm) are associated with large areas of dune sand
adjacent to rivers in western Oklahoma; with eolian sands in the High Plains in Cimarron and Ellis
Counties; and with Mississippian and Pennsylvanian rocks in the Ouachita Mountains, the Ozark
Plateau, and the eastern part of the central Oklahoma plains and hills. .
Areas of Oklahoma ranked as locally moderate to high are underlain by black, phosphatic
shales and associated limestones in the northeastern part of the State and near the Arbuckle
Mountains; the Upper Permian Rush Springs Formation in Caddo County; and granites, rhyolites,
and related dikes in the Wichita Mountains in the southwestern part of the State. Area's ranked as
generally low are underlain by Paleozoic marine sedimentary rocks in central and northwestern
Oklahoma and by Tertiary continental sedimentary rocks on the High Plains.
Well-drained alluvial terraces along some rivers (for example, along the Arkansas River
west of Tulsa); steep, thin, sandy to gravelly soils developed on sandstone on river bluffs (for
example, bluffs in the southeastern suburbs of Tulsa); and clayey loams on uraniferous shales (in
the northeastern corner of the State) are responsible for a significant percentage of elevated indoor
radon levels in those areas. Thus, in addition to soils derived from rocks with elevated uranium
content, soils in selected parts of counties where river terraces and sandstone bluffs occur might
also have elevated radon potential.
Soil moisture may have an additional effect on radon potential across the State. Indoor
radon values tend to be higher west of Oklahoma City where rainfall is less than 32 inches per year
and lowest in the southeastern corner of the State, where rainfall ranges from 32 to 64 inches per
year. Indoor radon values in northeastern Oklahoma, where rainfall is also high, include many
readings greater than 4 pCi/L, but the effects of uraniferous black shales and weathered limestone
soils on indoor radon may increase the levels overall and counter the effects of regional variation in
soil moisture. High permeability, dry soils, and moderate uranium content may be responsible for
elevated indoor radon readings in Beaver County.
TEXAS
The geologic radon potential of Texas is relatively low to moderate overall. The relatively
mild climate throughout much of the State, especially in the most populous areas, and the
predominance'of slab-on-grade housing seems to have influenced the overall potential. Significant
percentages of houses with radon levels exceeding 4 pCi/L are restricted primarily to the High
Plains and the Western Mountains and Basins provinces. However, no physiographic province in
Texas is completely free from indoor radon levels greater than 4 pCi/L.
Elevated indoor radon can be expected in several geologic settings in Texas. Granites and
metamorphic rocks in central Texas, Tertiary silicic volcanic and tuffaceous sedimentary rocks in
western Texas, dark marine shales in east-central Texas and the Big Bend area, sand and caliche
associated with the Ogallala Formation and overlying units in the High Plains of Texas, sediments
of Late Cretaceous age along the eastern edge of central Texas, and residual soils and alluvium
derived from these units are likely to have significant percentages of homes over 4 pCi/L. Except
for the High Plains and the Western Mountains and Basins Provinces, these rocks generally make
ni-8
Reprinted from USGS Open-File Report 93-292-F
-------
up only a relatively small percentage of the surface area of the various physiographic provinces.
However, the outcrop belt of Upper Cretaceous sedimentary rocks of the East Texas Province
passes near some substantial population centers. Extreme indoor radon levels (greater than 100
pCi/L) may be expected where structures are inadvertently sited on uranium occurrences. This is
more likely to occur in more populated are- along the .rop belt of L. j Ogallala Formation at the
edge of the Llano Estacada in the northern and central parts of the High Plains and Plateaus
Province. In this outcrop area, sedimentary rocks with more than 10 ppm uranium are relatively
common.
The northern part of the High Plains and Plateau Province has moderate radon potential.
Uranium occurrences, uranium-bearing calcrete and silcrete, and uranium-bearing lacustrine rocks
along the outcrop belt of the Ogallala Formation and in small upper Tertiary lacustrine basins
within the northern High Plains may locally cause very high indoor radon levels. Indoor radon
data are elevated in many counties in this area. Equivalent uranium values in this area range from
1.0 to 4.0 ppm. An area of elevated eU along the Rio Grande River is included in this radon
potential province. The southern part of the High Plains and Plateaus Province has low radon
potential overall as suggested by generally low eU values and low indoor radon. This area is
sparsely populated and existing indoor radon measurements may not adequately reflect the geologic
radon potential. An area of low eU covered by the sandy fades of the Blackwater Draw
Formation in the northeastern corner of the Western Mountains and Basins Province is included in
this radon potential area. Some parts of this province that may have locally elevated indoor radon
levels include areas of thin soils over limestone and dolomite in the Edwards Plateau of the
southern part of this province, and areas of carbonaceous sediments in the southeastern part of this
province.
The Western Mountains and Basins Province has moderate indoor radon potential overall.
Although average indoor radon levels are mixed (low in El Paso County, but high in three southern
counties), areas of elevated eU are widespread. Uranium-bearing Precambrian rocks, silicic
volcanic rocks, and alluvium derived from them may locally cause average indoor radon levels in
some communities to exceed 4 pCi/L. Some indoor radon levels exceeding 20 pCi/L may also be
expected. Exceptionally dry soils in this province may tend to lower radon potential. In very dry
soils, the emanating fraction of radon from mineral matter is lowered somewhat
The Central Texas Province has low radon potential overall; however, areas along the
outcrop belt of the Woodbine and Eagle Ford Formations and the Austin Chalk along the east edge
of this province,- and areas of Precambrian metamorphic and undifferentiated igneous rocks in the
Llano Uplift in the southern part of this province have moderate geologic radon potential.
Structures sited on uranium occurrences in the Triassic Dockum Group in the western part of this
province may locally have very high indoor radon levels.
The East Texas Province has low radon potential overall. Soil moisture levels are typically
high; soil permeability is typically low to moderate; and eU levels are low to moderate. A few
areas of well-drained soils and elevated eU may be associated with locai areas of moderately
elevated indoor radon levels.
The South Texas Plain has low radon potential due to generally low eU and low to
moderate soil permeability. Some structures sited on soils with slightly elevated uranium contents
in this province may locally have elevated indoor radon levels, but such soils are generally also
clay rich and this may mitigate radon movement. The Texas Coastal Plain has low radon potential.
Low aeroradioactivity, low to moderate soil permeability, and locally high water tables contribute
to the low radon potential of the region.
m-9 Reprinted from USGS Open-File Report 93-292-F
-------
Page Intentionally Blank
-------
PRELIMINARY GEOLOGIC RADON POTENTIAL ASSESSMENT OF TEXAS
by
James K. Otton and Linda C.S. Gundersen
U.S. Geological Survey
INTRODUCTION
This assessment of the radon potential of Texas is based upon geologic information derived
from publications of the Texas Bureau of Economic Geology, from publications of the U.S.
Geological Survey, and from an analysis of indoor radon data gathered by the State of Texas and
the US Environmental Protection Agency (EPA) during the winter of 1990-91 Much information
on the geographic setting is derived from The National Atlas of the United States of America.
This is a generalized assessment of geologic radon potential of rocks, soils, and surficial
deposits of Texas. The scale of this assessment is such that it is inappropriate for use in
identifying the radon potential of small areas such as neighborhoods, individual building sites, or
housing tracts. Any localized assessment of radon potential must be supplemented with additional
data and information from the locality. Within any area of a given radon potential ranking, there
are likely to be areas with higher or lower radon levels than characterized for the area as a whole.
Indoor radon levels, both high and low, can be quite localized, and there is no substitute for testing
individual homes. Elevated levels of indoor radon have been found in every State, and EPA
recommends that all homes be tested. For more information on radon, the reader is urged to
consult the local or State radon program or EPA regional office. More detailed information on state
or local geology may be obtained from the state geological survey. Addresses and phone numbers
for these agencies are listed in chapter 1 of this booklet
PHYSIOGRAPHIC SETTING
Texas is a large state that extends from the Gulf Coast westward to the southern limits of
the Rocky Mountains and northward to the continental interior of the United States. For the
purposes of this report, six physiographic subdivisions have been defined (fig. 1). The Western
Mountains and Basins province is characterized by plains with intervening mountains and hills. In
the western part of this province, high mountains with 3000-5000 feet of relief occur. In the
eastern part, relief decreases to 500-1000 feet.
The High Plains and Plateaus Province comprises broad, smooth plains with 100-300 feet
of relief in the northern portion, and areas of tablelands, high hills, and plains with moderate relief
(300-1000 feet) in the southern portion. The Central Texas Province is an extension of the Great
Plains. It is characterized by tablelands and plains with hills of low to moderate relief (100-500
feet) in the west and irregular plains and hills (relief 100-500 feet) to the east The East Texas
Province is an area composed mostly of irregular plains (100-300 feet of relief), except for an area
of plains with hills (300-500 feet of relief) in the east-central part The Coastal Plain Province is an
area of smooth plains of low relief (0-100 feet). The South Texas Plain Province includes a large
area of irregular plains to the northwest (relief 100-300 feet) and an area of-flat plains along the
coast (0-100 feet of relief).
Annual precipitation (fig. 2) increases eastward across Texas from less than 10 inches per
year to 55-60 inches per year in the southeast corner of the State near the Texas-Louisiana border.
In hilly to mountainous areas, precipitation increases with altitude.
IV-1 Repnnted from USCJS Open-File Report 93-292-F
-------
CENTRA
TEXAS
WESTERN
MOUNTAINS
& BASINS
--f-V'-'i HIGH PLAINS'.-
VV-VV & PLATEAU '
COASTAL
PLAIN
SOUTH
TEXAS
PLAIN
100mi
Fig. 1- Map showing physiographic provinces of Texas.
From Facts on File, 1984.
-------
Amarillo
Lubbock*
Dallas#
Abilene
San Angel
Ft. Stockton
Austii
Port
j Arthur
'Houston'
100mi
;orpus Christi
(Brownsville
Fig. 2- Map showing annual precipitation in Texas.
From Facts on File, 1984.
-------
About 80 percent of the population of Texas (fig. 3) is concentrated in urban areas of the
central and southeast parts of the State. Dallas-Ft. Worth, Houston, and San Antonio are the major
urban centers. Rural areas in the Western Mountains and Basins and South Texas Plain Provinces
are sparsely populated, whereas rural areas in the East Texas Province and the western part of the
Central Texas Province are more heavily populated.
Vegetation and land use vary considerably across the State. Most of the High Plains and
Plateaus Province is used principally for dryland and irrigated crops, although in many areas
semiarid grasslands are used for grazing. In the southeast part of this province, grazed forest and
woodlands predominate. In the Western Mountains and Basins Province, grazed desert
shrublands, grasslands, and open woodlands are found. In the Central Texas Province, croplands
dominate, with some pasture, woodland, and forest. Grazed grasslands lie at the western edge of
this province. The East Texas Province is largely covered by-woodland and forest, with lesser
cropland and pasture. In the Coastal Plain Province, there is a mixture of cropland, pasture, and
grazed forest and woodlands. Extensive marshlands occur along the coast In the South Texas
Plain Province, grazed grassland, open woodland, and desert shrubland occur, plus some areas of
dry and irrigated cropland.
GEOLOGIC SETTING
Texas is underlain mostly by sedimentary rocks and unconsolidated sediments that vary in
age from Cambrian to Holocene. Precambrian metamorphic and igneous rocks are exposed in the
core of the Llano (southern Central Texas Province) and Van Horn uplifts (Western Mountains and
Basins Province) (figs. 4 and 5), but they are exposed in less than 1 percent of the State. Tertiary,
volcanic rocks and related Tertiary volcaniclastic sedimentary rocks occur in volcanic centers and
associated small basins in the Western Mountains and Basins Province.
Structurally, the northern, western, and central part of the State is characterized by series of
uplifts and basins of pre-Cretaceous age (Figs. 4 and 5). Cretaceous and younger sedimentary
rocks of the southeastern 40 percent of the State dip into the Gulf of Mexico basin. Tertiary
volcanism and subsequent extension affected the westernmost part of the State, resulting in the
formation of extensional basins, intervening mountain ranges, and volcanic centers. During the
Miocene, a broad sheet of alluvial fan and related sedimentary rocks (the Og'allalla Formation and
overlying units) were deposited on the flank of a broad north-trending uplift in central New
Mexico. The erosional remnants of this sheet form the Texas High Plains (the northern part of the
High Plains and Plateaus Province).
The sedimentary rocks that crop out in the Western Mountains and Basins, southern High
Plains and Plateaus, and most of the East Texas Provinces are marine in origin; they include
limestone, dolomite, shale, evaporite deposits, and sandstone of Cambrian through Cretaceous age
(fig. 5). Nonmarine rocks of Triassic age, including shale, sandstone, and conglomerate, are
present in limited areas in the western part of the Central Texas Province and along the Canadian
River valley in the northern part of the High Plains and Plateaus Province. Nonmarine gravel,
sand, clay, and caliche (also called calcrete) dominate the northern 60 percent of the High Plains
and Plateaus Province. The East Texas, Coastal Plain, South Texas Plain, and the east edge of the
Central Texas Provinces are underlain by Cretaceous through Quaternary marine sandstone, shale,
chalk, limestone, siltstone, clay, and lignite. Some of the sandstones and shales in this latter area
arc tuffaceous and some of the shales are carbonaceous.
rv-4
Reprinted from USGS Open-File Report 93-292-F
-------
3
.era'
u>
i
TJ-
o
e,
¦ ef.
o
3
O
>-h
O
O
e
3
St.
a>
en
5*
S
cn .
vo
vo'
O
G
in
O
CT
3
vx
C
V)
a.
p
.P.
tfl -* 01 M O
o o o cn m.
o o o o o
o o o O iv,
o o - -» {)>
o
o
-*¦ cn o
M Ol O O
00 o o o
-* o o o
00 o o o
o o
-------
Fig. 4- Major geologic structures in Texas. From Renfro and others, 1973.
-------
Quaternary
Pliocene, Miocene,
& Oligocene
£«a&v.
&MM Eocene
Cretaceous
(Gulfian Series)
Cretaceous
(Comanchian Series)
a
EXPLANATION
Jurassic & Triassic
Permian
Pennsylvanian & Mississippian
Devonian, Silurian, Ordovician,
& Cambrian
Precambrian (schist & gneiss)
Tertiary and Precambrian (igneous)
80 mi
Fig. 5- Generalized geologic map of Texas. From Arbingast (1976).
-------
An aeroradiometric map of Texas (fig. 6) shows that the average equivalent uranium (eU)
content of rocks and soils at the surface is about 1.5 ppm. Rocks and soils across the State vary
from less than 0.5 ppm to greater than 5.5 ppm eU. Levels of eU less than 1.0 ppm are associated
with eolian deposits (especially the sand-rich facies of the Pleistocene Blackwater Draw Formation)
of western Texas and with Quaternary marine deposits of the Gulf Coastal area. Higher levels of
uranium (>2.5 ppm) are associated with 1) Precambrian metamorphic and igneous rocks in the
Llano and Van Horn uplifts, and alluvium derived from them; 2) Tertiary rhyolitic and alkaline
volcanic rocks in westernmost Texas; 3) the Miocene Ogallalla Formation and overlying sediments
in the Panhandle of Texas (northernmost part of the High Plains and Plateaus Province); 4)
Triassic nonmarine sedimentary rocks of the Dockum Group in northwestern Texas; 5) Upper
Cretaceous carbonaceous rocks in east-central Texas (the Woodbine and Eagle Ford Formations
between the Dallas-Ft Worth and Austin areas) and in the Big Bend area; and 6) part of the
northeast-trending outcrop belt of Tertiary tuffaceous fluvial and marine sedimentary rocks in the
northern part of the South Texas Plain and southwest part of the Coastal Plain Provinces. Two
small areas-of greater than 5.5 ppm eU occur in this latter area; these represent places where the
aircraft flew over open-pit uranium mines. .
Studies of soil-gas radon and radioactivity along transects crossing Cretaceous and younger
rocks from the Central Texas Province to the Coastal Plain Province (Gundersen and others, 1991)
show that elevated soil-gas radon (as much as 6500 picocuries per liter, pCi/L) is associated with
some Upper Cretaceous sedimentary rocks, principally carbonaceous shale and mudstone of the
Woodbine and Eagle Ford Formations and the Austin Chalk, but that most of the Cretaceous,
Tertiary and Quaternary units were low to moderate in soil-gas radon and radioactivity.
Uranium occurrences and deposits are found in several areas of Texas. A major uranium
mining district is hosted by Tertiary sandstones in South Texas. Small uranium deposits occur in
sandstones of the Triassic Dockum Group in the western part of central Texas. Uranium-rich
calcrete and silcrete occurs in sandstones and mudstones of the Ogallalla Formation and in
overlying Pliocene and Pleistocene sandstones and lacustrine sedimentary rocks in the northern
part of the High Plains and Plateaus Province. Uranium occurs in volcanic rocks and
volcaniclastic sedimentary rocks near volcanic centers in the Western Mountains and Basins
Province.
SOILS
Extensive areas of highly permeable soils (>6 in/hr in a percolation test) are generally not
found in Texas, although sandy soils with permeabilities near or locally exceeding this value occur
in several areas. In the central part of the High Plains and Plateaus Province, near the southeastern
corner of New Mexico, sandy loams and fine sandy loams dominate. These soils may have
sufficient permeability to influence indoor radon levels. Substantial areas of sandy soils occur in
the central parts of the South Texas Plain Province and the southwestern part of the Coastal Plain
Province; however, these often have highly cemented zones of caliche at depth that may hinder the
ability of radon to migrate. Alluvial fan deposits in the Western Mountains and Basins Province
may also locally be highly permeable, but these are also commonly highly cemented.
Thin soils with bedrock at shallow depths occur over the limestone and dolomite in the
southern part of the High Plains and Plateau Province (Edwards Plateau) and thin, sandy soils
occur over granitic rocks in the Llano uplift area. Shallow bedrock in these areas typically contains
abundant fracture zones that enhance radon migration.
IV-8 Reprinted from USGS Open-File Report 93-292-F
-------
Fig. 6- Aerial radiometric map of Texas (after Duval and others, 1989). Contour lines at 1.5
and 2.5 ppm equivalent uranium (eU). Pixels shaded from 0 to 6.0 ppm eU at 0.5 ppm eU
increments; darker pixels have lower eU values; white indicates no data.
-------
Soil temperature and soil moisture vary widely across Texas, with steady increases in soil
temperature from north to south and steady increases in soil moisture from west to east (Rose and
others, 1991). Soils of the northern 10 percent of the High Plains and Plateaus Province are mesic
ustic and thus are moderately moist in the wintertime (44-56 percent pore saturation in sandy
loams, and 58-74 percent in a silty clay loam) and slightly moist in the summertime (24-44 percent
pore saturation in sandy loams, and 39-58 percent pore saturation in silty clay loams). The soils of
the Western Mountains and Basins Province are thermic aridic-slightly moist in the wintertime
(24-44 percent pore saturation in sandy loams, and 39-58 percent pore saturation in silty clay
loams) and slightly dry in the summertime (4-24 percent pore saturation in sandy loams and 6-39
percent pore saturation in silty clay loam). Soils of the rest of the High Plains and Plateaus '
Province and all of the central Texas Province are thermic ustic-moderately moist in the wintertime
(44-56 percent saturation in sandy loams, and 58-74 percent in a silty clay loam) and slightly moist
in the summertime (24-44 percent pore saturation in sandy loams, and-39-58 percent pore
saturation in silty clay loams). The soils of the East Texas Province and the eastern part of the
Coastal Plain Province are thermic udic and are very moist in the wintertime (56-96 percent pore
saturation in sandy loams, and 74-99 percent saturation in a silty clay loam) and slightly moist in
the summertime (24-44 percent pore saturation in sandy loams, and 39-58 percent pore saturation
in silty clay loams). The South Texas Plain and the western part of the Coastal Plain range from
hyperthermic aridic along the Rio Grande River to hyperthermic ustic elsewhere. Hyperthermic
aridic soils are slightly dry all year long and hyperthermic ustic soils are slightly moist all year
long.
The low soil moisture levels in the dry soils of western and southern Texas may decrease
the radon emanation coefficient somewhat, especially during the drier periods of the year. The wet
winter soils in the East Texas Province may slow radon migration because pore spaces are filled
with water.
INDOOR RADON DATA
The U.S. Environmental Protection Agency (EPA), in cooperation with the Texas
Department of Health, completed a random, stratified (geology and population) survey of indoor
radon levels in homes across Texas during the winter of 1990-1991 (Table 1, fig. 7). A map of
counties is included for reference (fig. 8). About 5 percent of measurements in the State/EPA
Residential Radon Survey dataset are equal to or greater than 4 pCi/L. Average measurements for
3 counties in the northern High Plains and Plateaus Province average greater than 4 pCi/L. Hale
County averages 7.5 pCi^L. Average measurements range from 2-4 pCi/L for three counties in the
Big Bend area of the Western Mountains and Basins Province, for several counties in the northern
and central High Plains and Plateaus Province, and for Brown County in the Central Texas
Province (fig. 7). Values exceeding 20 pCi/L are restricted to the High Plains and Plateaus
Province and the Western Mountains and Basins Province. Indoor radon levels are low in counties
in the uranium mining area in south Texas, however only 50 houses were measured in 12 counties
where uranium mining occurs and this sampling may not have been sufficient to identify areas of
possible elevated indoor radon levels asssociated with uranium deposits in the subsurface.
IV-10
Reprinted from USGS Open-File Report 93-292-F
-------
Bsmt & 1st Floor Indoor Rn
% & 4 pCi/L
103
132
132
Oto 10
11 ~ 11 to 20
7 E3 21 to 40
1 0 41 to 60
0 i 61 to 80
I Missing Data
(< 5 measurements)
Bsmt & 1 st Floor Indoor Rn
Average Concentration (pCi/L)
107 IZZZZZU 0.0 to 1.9
12 Q 2.0 to 4.0
3 1 4.1 to 7.5
Missing Data
(< 5 measurements)
HJ
100 Miles
Fig. 7- Screening indoor radon data from the EPA/State Residential Radon Survey of Texas,
1990-91, 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.
-------
TABLE 1. Screening indoor radon data from the State/EPA Residential Radon Survey of
Texas conducted during 1990-91. Data represent 2-7 day charcoal canister measurements
from the lowest level of each home tested.
COUNTY
NO. OF
MEAS.
AVERAGE
MEDIAN
GEOM.
MEAN
MAX
%>4 pCi/L
%>20 pCi/L
ANDERSON
3
0.0
0.1
0.4
1.4
0
0
ANDREWS
2
1.0
1.0
0.9
1.1
0
0
ANGELINA
12
0.3
0.3
0.3
1.3
0
0
ARANSAS
2
0.0
0.0
0.0
0.0
0
0
ARCHER
2
0.7
0.7
0.5
1.2
0
0
ARMSTRONG
3
2.9
1.5
2.4 .
5.8
33
0
ATASCOSA
11
0.5
0.5
0.5
1.7
0
0
AUSTIN '
8
0.5
0.3
0.4
2.2
0
0
BAILEY
3
3.6
1.6
2.0
8.6
33
0
BANDERA
5
0.6
0.4
0.5
1.0
0
0
BASTROP
9
1.6
0.5
0.9
9.8
11
0
BAYLOR
2
1.0
1.0
0.9
1.4
0
¦ 0
BEE
5
0.4
0.3
0.5
0.9
0
0
BELL
18
1.2
1.1
0.9
3.9
0
0
BEXAR
57
1.1
0.8
0.8
6.7
4
0
BLANCO
3
2.0
2.3
1.9
2.7
0
0
BORDEN
2
0.7
0.7
0.6
L0
0
0
BOSQUE
4
1.2
1.4
1.2
1.5
0
0
BOWIE
22
0.5
0.4
0.5
1.8
0
0
BRAZORIA
25
0.3
0.2
0.4
1.2
0
0
BRAZOS
19
0.8
0.5
0.5
4.2
5
0
BREWSTER
57
2.5
2.3
2.0
8.4
18
0
BRISCOE
2
3.3
3.3
2.8
5.0
50
0
BROWN
6
2.6
0.9
1.3
7.8
33
0
BURNET
97
1.3
1.0
0.9
13.9
5
0
CALDWELL
7
0.2
0.2
0.4
2.2
0
0
CALHOUN
1
1.2
1.2
1.2
1.2
0
0
CALLAHAN
5
0.6
0.6
0.7
1.4
0
0
CAMERON
9
0.5
0.4
0.4
1.4
0
0
CAMP
2
0.8
0.8
0.7
1.0
0
0
CARSON
4
8.8 .
2.0
3.3
30.1
25
25
CASS
9
0.6
0.8
0.6
1.1
0
.0
CASTRO
3
1.6
1.3
1.4
2.7
0
0
CHEROKEE
7
1.0
0.9
0.9
1.6
0
0
CLAY
2
1.4
1.4
1.3
1.4
0
0
COCHRAN
1
1.5
1.5
1.5
1.5
0
0
COKE
1
0.0
0.0
0.0
0.0
0
0
COLEMAN
2
0.6
0.6
0.5
0.9
0
0
COLLIN
36
1.0
0.8
0.8
5.2
3
0
COLORADO
6
0.3
0.4
0.3
0.4
0
0
COMAL
18
1.1
0.8 .
0.8
3.7
0
0
COMANCHE
4
0.7
0.6
0.6
1.0
0
0
CONCHO
2
0.2
0.2
0.3
0.3
0
0
-------
TABLE 1 (continued). Screening indoor radon data for Texas.
COUNTY
NO. OF
MEAS.
AVERAGE
MEDIAN
GEOM.
MEAN
MAX
%>4 pCi/L
%>20 pCi/L
COOKE
7
1.0
0.9
1.0
1.8
0
0
CORYELL
6
0.9
0.8
0.6
2.2
0
0
CRANE
1
0.1
0.1
0.1
0.1
0
0
CROCKETT
2
1.1
1.1
1.1
1.2
0
0
CROSBY
3
1.2
r.2
1.1
1.8
0
0
DALLAM
1
0.1
0.1
0.1
0.1
0
0
DALLAS
85
1.2
1.0
0.9
6.8
4
0
DAWSON
3
1.8
1.5
1.6
2.7
0
0
DEAF SMITH
6
3.2
3.2
2.3
7.7
17
0
DELTA
1
0.6
0.6
0.6
0.6
0
0
DENTON
30
1.0
0.9
0.8
3.0
0
0
DE WITT
4
0.4
0.4
0.4
0.7
0
0
DICKENS
1
3.1
3.1
3.1
3.1
0
0
DIMMIT
2
0.5
0.5
0.5
0.5
0
0
DONLEY
1
3.2
3.2
3.2
3.2
0
0
DUVAL
3
0.7
0.4
0.9
2.1
0
0
EASTLAND
5
0.6
0.6
0.6
1.2
0
0
ECTOR
39
0.9
0.8 .
0.7
7.3
3
0
ELLIS
13
0.8
0.7
0.6
2.3
0
0
EL PASO
96
1.0
0.6
0.6
21.6
2
1
ERATH
'6
0.4
0.4
0.4
0.7
0
0
FALLS
2
0.4
0.4
0.3
0.7
0
0
FANNIN
2
1.0
1.0
0.4
1.8
0
0
FAYETTE
13
1.1
0.9
0.8
3.2
0
0
FISHER
1
0.0
0.0
0.0
0.0
0
0
FLOYD
2
0.5
0.5
0.4
0.5
0
0
FORT BEND
23
0.3
0.2
0,3
2.2
0
0
FRANKLIN
2
0.2
0.2
0.5
0.5
0
o-
FREESTONE
3
0.2
0.2
0.2
0.4
0
0
FRIO
3
0.7
1.0
0.6
. 1.0
0
0
GAINES
2
0.8
0.8
0.8
1J0
0 »
0
GALVESTON
35
0.2
0.1
0.3
0.9
0
0
GARZA
20
2.1
1.9
1.7
6.9
10
0
GILLESPIE
12
1.3
0.9
0.8
4.7
8
0
GLASSCOCK
2
1.3
1.3 .
1.2
1.4
0
0
GOLIAD
4
0.4
0.4
0.3
0.7
0
0
GONZALES
5
1.3
0.6
0.8
3.4
0
0
GRAY
9
1.7
1.7
1.6
2.6
0
0
GRAYSON
14
1.2
0.7
0.7
5.3
7
0
GREGG
21
0.9
0.5
0.6
7.1
' 5
0
GRIMES
3
0.5
0.1
0.4
1.4
0
0
GUADALUPE
15
1.0
0.9
0.8
3.1
0
0
HALE
15
7.5
3.0
4.2
41.3
47
13
HALL
1
0.4
0.4
0.4
0.4
0
0
-------
TABLE 1 (continued). Screening indoor radon data for Texas.
COUNTY
NO. OF
MEAS.
AVERAGE
MEDIAN
GEOM.
MEAN
MAX
%>4 pCi/L
%>20 pCi/L
HAMILTON
1
0.4
0.4
0.4
0.4
0
0
HANSFORD
3
3.7
3.7
2.5
6.8
33
0
HARDIN
5
0.7
0.8
0.7
1.2
0
0
HARRIS
116
0.4
0.3
0.3
3:8
0
0
HARRISON
21
0.5
0.5
0.5
1.2
0
0
HARTLEY
1
0.6
0.6
0.6
0.6
0
0
HASKELL
1
0.8
0.8
0.8
0.8
0
0
HAYS
15
1.1
0.9
0.9
2.6
0
0
HEMPHILL
1
1.6
1.6
1.6
1.6
0
0
HENDERSON
14
0.7
.0.3
0.4
5.1
7
0
HIDALGO
20
0.5
0.4
0.4
1.9
0
0
HILL
2
0.5
0.5
0.5
0.7
0
0
HOCKLEY
7
2.8
1.0
1.8
13.5
14
0
HOOD
7
1.2
1.0
1.0
3.0
0
0
HOPKINS
6
0.3
0.3
0.4
0.6
0
0
HOUSTON
7
0.4
0.2
0.4
1.3
0
0
HOWARD
114
1.7
0.9
0.9
65.9
4
1
HUDSPETH
2
0.6
0.6
0.6
0.8
0
0
HUNT
9
0.6
0.4
0.5
1.8
0
0
HUTCHINSON
14
1.5
1.2
1.3
6.3
7
0
JACK
1
0.3
0.3
0.3
0.3
0
0
JASPER
11
0.5
0.2
0.3
3.1
0
0
JEFF DAVIS
16
3.7
1.7
1.9
13.6
19
.0
JEFFERSON
25
0.3
0.2
0.3
0.9
0
.0
JIM HOGG
1
1.1
1.1
1.1
1.1
0
0
JOHNSON
7
0.7
0.7
0.7
2.1
0
0
JONES
5
1.0
0.7
0.9
2.8
0
0
KARNES
3
1.7
0.7
0.7
4.4
33
0
KAUFMAN
5
1.1
1.5
0.8
1.6
0
0
KENDALL
5
1.0
1.0
. 0.9
1.9
0
0
KERR
20
1.4
1.4
1.0
6.0
5
0
KINNEY
3
0.1
0.1
0.2
0.3
0
0
KLEBERG
1
0.5
0.5
0.5
0.5
0
0
KNOX
1
0.9
0.9
0.9
0.9
0
0
LAMAR
5
0.2
0.3
0.4
0.5
0
0
LAMB
10
2.9
2.1
2.2
6.9
30
0
LAMPASAS
2
1.9
1.9
0.8
3.5
0
0
LA SALLE
1
0.1
0.1
0.1
0.1
0
0
LAVACA
10
1.2
0.4
0.7
7.5
10
0
LEE
3
1.2
0.6
0.7
2.9
0
0
LEON
3
0.2
0.2
0.3
0.4
0
0
LIBERTY
2
0.0
0.0
0.0
0.0
0
0
LIMESTONE
4
0.0
0.0
0.2
0.3
0
0
LIPSCOMB
2
1.6
1.6
1.5
1:9
0
0
-------
TABLE 1-(continued). Screening indoor radon data for Texas.
COUNTY
NO. OF
MEAS.
AVERAGE
MEDIAN
GEOM.
MEAN
MAX
%>4 pCi/L
%>20 pCi/L
LIVE OAK
4
0.8
0.4
0.7
2.5
0
0
LLANO
47
1.7
1.3
1.3
5.4
15
0
LUBBOCK
68
2.8
1.9
1.9
23.9
18
1
LYNN
1
1.5
1.5
1.5
1.5
0
. 0
MCCULLOCH
26
1.2
0.8
0.7
12.5
4
0
MCLENNAN
29
1.2
0.8
0.7
5.9
3
0
MCMULLEN
1
1.5
1.5
1.5
1.5
0
0
MADISON
2
0.4
0.4
0.7
0.7
0
0
MARION
3
0.8
1.0
1.1
1.3
0
0
MARTIN
3
1.8
1.2
1.3
3.8
0
0
MASON
21
1.3
0.9
0.9
7.0
10
0
MATAGORDA
8
0.7
0.5
0.7
2.9
0
0
MAVERICK
3
1.5
1.5
1.4
2.2
0
0
MEDINA
9
0.5
0.4
.0.4
1.1
0
0
MENARD
3
1.0
1.1
1.0
1.4
o -
0
MIDLAND
48
1.1
1.0
. 0.9
3.4
0
0
MILAM
7
0.6
0.5
0.7
1.7
. 0
0
MITCHELL
34
1.4
0.9
0.9
14.0
6
0
MONTAGUE
. 3
0.7
0.5
0.6
1.3
0
0
MONTGOMERY
27
0.3
0.2
0.4
2.1
0
0
MOORE
6
3.4
3.1
3.3
5.2
33
0
MORRIS
7
0.7
0.9
0.8
1.1
O
0
NACOGDOCHES
9
0.6
0.3
0.5
1.4
0
0
NAVARRO
3
0.1
0.0
0.5
0.5
0
0
NEWTON
2
0.1
0.1
0.3
0.3
0
0
NOLAN
5 '
0.9
1.1
0.9
1.8
0
0
NUECES
17
0.7
0.5
0.7
2.1
0
0
OCHILTREE
5
3.6
3.1
3.4
5.5
40
0
ORANGE
13
' 0.5
0.4
0.4
1.2
0
0
PALO PINTO
6
0.7
0.6
0.6
1.9
0
0
PANOLA
9
0.3 '
0.2
0.3
0.7
0
0
PARKER
5
0.3
0.1
0.3
0.8
0
0
PARMER
4
3.2
3.1
2.1
6.2
50
0
PECOS
6
0.4
0.4
0.3
0.8
0
0
POLK
7
0.5
0.4
0.7
1.3
0
0
POTTER
29
3.4 ¦
3.3
2.6
11.1
34
0
PRESIDIO
43
2.6
2.3
2.0
7.2
19
0
RAINS
3
0.3
0.3
0.3
0.3
0
0
RANDALL
20
5.6
3.4
3.3
33.1
35
5
REAL
2
0.2
0.2
0.4
0.4
0
0
RED RIVER
1
0.0
0.0
0.0
0.0
0
0
REEVES
9
1.2
1.2
0.8
2.8
0
0
REFUGIO
1
0.2
0.2
0.2
0.2
0
0
ROBERTSON
5
0.6
0.5
0.4
1.1
0
0
-------
TABLE 1 (continued). Screening indoor radon data for Texas.
COUNTY
NO. OF
MEAS.
AVERAGE
MEDIAN
GEOM.
MEAN
MAX
%£4 pCi/L
%>20 pCi/L
ROCKWALL
3
0.3
0.4
0.4
0.5
0
0
RUNNELS
4
0.8
0.7
0.8
1.1
0
0
RUSK
10
0.2
0.3
0.3
0.7
0
0
SABINE
3
0.5
0.5
0.5
0.8
0
0
SAN AUGUSTINE
5
0.7
0.4
0.7
1.5
0
0
SAN JACINTO
5
0.3
0.3
0.4
0.5
0
0
SAN PATRICIO
7
0.6
0.2
0.3
3.1
0
0
SAN SABA
30
1.2
0.7
0.8
9.6
3
0
SCHLEICHER
I
0.3
0.3
0.3
0.3
0
0
SCURRY
75
1.4
1.1
1.0
7.6
3
0
SHACKELFORD
2
0.4
0.4
0.3
0.4
0
0
SHELBY
3
0.0
0.0
0.4
0.4
0
0
SHERMAN
3
11.7
15.3
10.1
15.6
67
0
SMITH
46
0.5
0.4
0.4
3.7
0
0
STARR
1
0.8
0.8
0.8
0.8
0
0
STEPHENS
3
2.3
2.1
2.2
3.4
0
0
STERLING
1
3.6
3.6
3.6
3.6
0
0
STONEWALL
1
0.7
0.7
0.7
0.7
0
0
SUTTON
1
0.4
0.4
0.4
0.4
0
0
SWISHER
5
6.3
1.9
2.8
15.4
40
0
TARRANT
84
1.1
0.7
0.8
7.4
4
0
TAYLOR
26
1.4
0.9
1.0
5.7
12
0
TERRY
5
1.6
1,5
1.1
3.3
0
0
THROCKMORTON
1
2.0
2.0
2.0
2.0
0
0
TITUS
7
0.4
0.4
0.5
1.0
0
0
TOM GREEN
15
0.9
0.7
0.7
3.3
0
0
TRAVIS
53
1.4
0.8
0.9
7.0
8
0
TRINITY
1
0.6
0.6
0.6
0.6
0
0
TYLER
4
0.5
0.6
0.7
1.0
0
0
UPSHUR
9
0.4
0.1
0.4
1.1
0
0
UPTON
I
2.0
2.0
2.0
2.0
0
0
UVALDE
6
0.8
0.6
0.8
1.9
0
0
VAL VERDE
8
0.5
0.4
0.4
1.0
0
0
VANZANDT
8
0.3
0.3
0.3
0.7
0
0
VICTORIA
9
1.4
0.4
0.7
9.5
11
0
WALKER
12
0.6
0.2
0.5
2.8
0
0
WALLER
6
0.2
0.3
0.4
0.6
0
0
WARD
6
0.5
0.7
0.7
1.0
0
0
WASHINGTON
5
0.4
0.3
0.5
1.1
0
0
WEBB
19
0.4
0.4
0.4
1.5
0
0
WHARTON
3
0.6
0.0
1.9
1.9
0
0
WHEELER
4
1.8
2.0
1.2
3.2
0
0
WICHITA
13
1.5
1.3
1.2
4.3
8
0
WILLACY
2
0.5
0.5
0.5
0.6
0
0
-------
TABLE 1 (continued). Screening indoor radon data for Texas.
COUNTY
NO. OF
ME AS.
AVERAGE
MEDIAN
GEOM.
MEAN
MAX
%>4 pCi/L
%>20 oCi/L
WILLIAMSON
38
1.4
1.1
1.0
6.4
3
0
WILSON
6
0.2
0.1
0.3
1.0
0
0
WINKLER
3
0.2
0.0
1.0
1.0
0
0
WISE
3
0.6
0.6
0.9
1.5
0
0
WOOD
16
0.3
0.3
0.3
0.8
0
0
YOAKUM
4
3.2
2.7
1.8
7.3
25
0
YOUNG
2
0.9
0.9
0.9
1.1
0
0
ZAVALA
4
0.6
0.6
0.6
1.1
0
0
-------
Fig. 8- Map showing counties'and county names in Texas.
-------
GEOLOGIC RADON POTENTIAL
The geologic radon potential of Texas is generally low overall. The relatively mild climate
throughout much of the State, especially in the most populous areas, and the predominance of slab-
on-grade housing seems to have influenced the overall potential. Significant percentages of houses
with indoor radon levels exceeding 4 pCi/L are restricted to the High Plains and the Western
Mountains and Basins Provinces. However, no physiographic province in Texas is completely
free from indoor radon levels above 4 pCi/L.
Elevated indoor radon can be expected in several geologic settings in Texas. Uranium-rich
(>2.5 ppm for the purposes of this report) granites and metamorphic rocks in central Texas,
uranium-rich Tertiary silicic .volcanic and tuffaceous sedimentary rocks in western Texas, uranium-
rich dark marine shales in east-central Texas and the Big Bend area, uranium-rich sand and caliche
associated with the Ogallalla Formation and overlying units in the High Plains of Texas, uranium-
rich sediments of Late Cretaceous age along the eastern edge of central Texas, and residual soils
and alluvium derived from these units are likely to have significant percentages of homes with
indoor radon levels exceeding 4 pCi/L. Except for the High Plains and the Western Mountains
and Basins Provinces, these rocks generally make up only a small percentage of the surface area of
the various physiographic provinces. However, the outcrop belt of Upper Cretaceous sedimentary
rocks of the East Texas Province passes near substantia] population centers. The most likely areas
for elevated indoor radon levels to occur are those in which elevated eU values occur in the
aeroradiometric data (fig. 6). An exception may be the uranium mining district in south Texas.
There, the uranium deposits occur at depth, often below the water table, and the influence of such
deposits on the near surface soil-gas radon levels may be subdued.
Extreme indoor radon levels (greater than 100 pCi/L) may be expected where structures are
inadvertently sited on uranium occurrences. This is more likely to occur in more populated areas
along the outcrop belt of the Ogallalla Formation at the edge of the Llano Estacada in the northern,
and central parts of the High Plains and Plateaus Province. In this outcrop area, sedimentary-rocks
with more than 10 ppm uranium are common.
SUMMARY
Eight areas of Texas for which geologic radon potential may be evaluated were delineated
(fig. 9). These areas generally follow the physiographic provinces of figure 1 with some
modifications based on internal differences in geology, soils, and aeroradiometric signature. A
relative index of radon potential (RI) and an index of the level of confidence in the available data
(CI) have been established (see discussion in the introductory section of this volume). The areas
are evaluated in Table 2.
The northern part of the High Plains and Plateau Province (N, fig. 9) has moderate radon
potential. Uranium occurrences, anomalously uranium-rich calcrete and silcrete, and uranium-rich
lacustrine rocks along the outcrop belt of the Ogallalla Formation and in small upper Tertiary
lacustrine basins within the northern High Plains may locally cause very high indoor radon levels.
Indoor radon data are elevated in many counties in this area. Equivalent utanium values in this
area rangefrom 1.0-4.0 ppm. An area of elevated eU along the Rio Grande River (also labeled
"N" in fig. 9) is included in this radon potential province..
/
IV-19 Reprinted from USGS Open-File Report 93-292-F
-------
CP
100 mi
ST
Fig. 9- Map showing radon potential areas of Texas. W- Western mountains and basins;
N- Northern High Plains and Plateaus; S- Southern High Plains and Plateaus; C- Central
Texas; K- Cretaceous Central Texas and Llano Uplift;; E- East Texas; ST- Southern Texas
Plain; CP- Coastal Plain. Cross-hatched areas have moderate potential. The other areas are
low.
-------
The southern part of the High Plains and Plateaus Province has low radon potential overall
as suggested by generally low eU values and low indoor radon. This area is sparsely populated
and indoor radon measurements may not adequately reflect the geologic radon potential. An area
of low eU covered by the sandy facies of the Blackwater Draw Formation in the northeast corner
of the Western Mountains and Basins Province is included in this radon potential province. Some
local areas within this province with potentially high indoor radon levels include areas covered by
thin soils over limestone and dolomite in the Edwards Plateau of the southern part of this province
and areas underlain by carbonaceous sediments in the southeastern part of this province.
The Western Mountains and Basins Province has moderate indoor radon potential overall.
Although average indoor radon levels are mixed (low in El Paso County, but high in three southern
counties), areas of elevated eU are widespread (fig. 6). Uranium-rich Precambrian rocks and
uranium-rich silicic volcanic rocks and alluvium derived from them may locally cause average
indoor radon levels in spme communities to exceed 4 pCi/L. Values exceeding 20 pCi/L may also
be expected locally. Exceptionally dry soils in this province may tend to lower radon potential. In
very dry soils, the emanating fraction of radon from mineral matter is lowered.
The Central Texas Province has low radon potential overall; however, areas along the
outcrop belt of the Woodbine and Eagle Ford Formations and the Austin Chalk (part of the Upper
Cretaceous Gulfian Series, fig. 5) along the eastern edge of this province and areas of Precambrian
metamorphic and.undifferentiated igneous rocks in the Llano Uplift (fig. 5) in the southern part of
this province have moderate geologic radon potential and are separated out as a distinctive radon
potential area. Structures sited on uranium occurrences in the Triassic Dockum Group in the
western part of this province may locally have very high indoor radon levels.
The East Texas Province has low radon potential overall. Soil moistures are typically high;
soil permeability is typically low to moderate; and eU levels are low to moderate. A few areas of
well-drained soils and elevated eU (fig. 6) may be localized areas of moderate radon potential.
The Texas Coastal Plain has low geologic radon potential. Low aeroradioactivity, low to
moderate soil permeability, and locally high water tables contribute to low radon potential.
The South Texas Plain has low radon potential due to generally low eU and low to
moderate soil permeability. Some structures sited on the more uranium-rich soils in this province
(fig. 6) may locally have elevated indoor radon levels, but such soils are generally also clay-rich
and this may mitigate against radon movement.
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 that assigned to the area as a whole. Any local decisions about radon should
not be made without consulting all available local data. For additional information on radon and
how to test, contact your State radon program or EPA.regional office. More detailed information
on state or local geology may be obtained from the state geological survey. Addresses and phone
numbers for these agencies are listed in chapter 1 of this booklet.
IV-21
Reprinted from USGS Open-File Report 93-292-F
-------
TABLE 2. Radon Index (RI) and Confidence Index (CI) scores for geologic radon potential areas
of Texas. See figure 9 for locations of areas.
Northern
Southern
Western
Central
High P/P
High P/P
Mtns/Basins
Texas
FACTOR
RI
CI
RI
CI
RI
CI
RI
CI
INDOOR RADON
2
2
1?
1
2?
1
1
2
RADIOACTIVITY
2
2
1
2
2
3
1
3
GEOLOGY
2
2
2
2
2
2
2
2
SOIL PERM.
2
3
2
3
2
3
2
' 3
ARCHITECTURE
2
-
1
-
1
-
1
-
GFE POINTS
0
-
0
-
0
-
0
-
TOTAL
10
9
7
8
9
9
7
10
RANKING
MOD
MOD
LOW
MOD
MOD
MOD
LOW
HIGH
Cretaceous
East
Coastal
South Texas
Cent. Texas
Texas
Plain
Plain
FACTOR
RI
CI
RI
CI
RI
CI
RI
CI
INDOORRADON
2?
1
1
2
1
2
1?
1
RADIOACTIVITY
2
2
1
3
1
3
1
3
GEOLOGY
2
2
2
2
'2
2
2
2 '
SOIL PERM.
2
3
1
.3
2
3
2
3
ARCHITECTURE
1
-
1
-
1
-
1
. -
GFE POINTS
1
-
0
-
0
-
0
-
TOTAL
10
8
6
10
7
10
7
9
RANKING
MOD
MOD
LOW
HIGH
LOW
HIGH .
LOW
MOD
- Not used in CI.
RADON INDEX SCORING:
Probable screening indoor
Radon potential category Point range radon average for area
LOW 3-8 points < 2 pCi/L
MODERATE/VARIABLE 9-11 points 2-4 pCi/L
HIGH >11 points >4 pCi/L
Possible range of points = 3 to 17
CONFIDENCE INDEX SCORING:
LOW CONFIDENCE 4 - 6 points
MODERATE CONFIDENCE 7-9 points
HIGH CONFIDENCE 10 - 12 points
Possible range of points = 4 to 12
IV-22
Reprinted from USGS Open-File Report 93-292-F
-------
REFERENCES CITED IN THIS REPORT
AND GENERAL REFERENCES PERTAINING TO RADON IN TEXAS
Aiken, M. J., 1981, Mineralogy and geochemistry of a lacustrine uranium occurrence, Andersen
Ranch, Brewster County, Texas: Master's thesis, Univ. of Texas, El Paso, unknown p.
Arbingast, S., 1976, Atlas of Texas: Austin, University of Texas.
Bomber, B. J., Ledger, E. B., and Tieh, T. T., 1986, Ore petrography of a sedimentary uranium
deposit, Live Oak County, Texas: Economic Geology, v. 81,n. 1, p. 131-142.
Cech, I., 1986, Radium and radon in Harris County: Houston Geological Society Bulletin v.29,
no. 4, 11 p.
Cech, I., Prichard, H. M., Mayerson, A. and Lemma, M., 1987, Pattern of distribution of radium
226 in drinking water of Texas: Water Resources Research, v. 23, n.' 10, p. 1987-1995.
Cech, I., Kreitler, C. W., Prichard, H., Holguin, A., and Lemma, M., 1988, Radon distribution
in domestic water of Texas: Ground Water, v. 26, n.5, p. 561-569.
Cech, I. Lemma, M., Prichard, H., and Kreitler, C. W., 1987, Radium-222 and radon-222 in
domestic water of Houston-Harris County, Texas: in Graves, Barbara, ed., Radon,
radium, and other radioactivity in ground water: Lewis Publishers, p. 377-402.
Chatham, J. R., 1981, The applications of solution-mineral equilibria concepts in prospecting for
sandstone-type uranium deposits: Colorado School of Mines, Golden, CO, USA Doctoral
thesis, 177 p.
Cook, L. M., 1980, The uranium district of the Texas Gulf Coastal Plain, in Gesell, T. F. and
Lowder, W. M., eds., International symposium on the natural radiation environment,
Houston, TX, United States, April 23-28, 1978: Natural radiation environment HI, DOE
Symposium Series CONF-780422, v. 2, p. 1602-1622.
Dahl, H. M. and Callender, C. A., 1985, Mineralogy and geology of Texaco's Hobson uranium
deposit, Karnes County, Texas, in Hausen, D. M. and Kopp, O. C., eds., Mineralogy;
applications to the minerals industry; proceedings of the Paul F. Kerr memorial
symposium, New York, NY, Feb. 28,1985: American Institute Mining, Metallurgy and
Petroleum Engineering, Society Mining Engineering, p. 89-102.
Dickinson, K. A., 1976, Uranium potential of the Texas coastal plain: U. S. Geological Survey
Open-File Report 76-0879, 21 p.
Dickinson, K. A., 1978, Stratigraphy and depositional environments of uranium host rocks in
western Karnes County, Texas: U.S. Geological Survey Map MF-1029, scale 1:24,000.
Duex, T.W., and Henry, C. D., 1981, Calderas and mineralization: volcanic geology and
mineralization in the Chinati caldera complex, Trans-Pecos Texas: Austin, Texas : Bureau
of Economic Geology Geological Circular 81-2 ,14 p.
IV-23
Reprinted from USGS Open-File Report 93-292-F
-------
Duval, J. S., Jones, W. J., Riggle, F. R., and Pitkin, J. A., 1989, Equivalent uranium map of the
conterminous United States: U.S. Geological Survey Open-File Report 89-478,10 p.
Ece, O., 1978, Uranium mineralization in Northwest Bee County, Oakville Formation, Texas
coastal region: Master's thesis, Univ. of Texas, Austin, unknown p.
Facts on File, Inc. 1984, State maps on file.
Finch, W. I. and Wright, J. C., 1983, Measured stratigraphic sections of uranium-bearing Upper
Triassic rocks of the Dockum Basin, eastern New Mexico, West Texas, and the Oklahoma
Panhandle, with brief discussion of stratigraphic problems: United States Geological
Survey Open-File Report 83-0701,123 p.
Finch, W. I., 1975, Uranium in West Texas: United States Geological Survey Open-File Report
75-0356, 20 p.
Finch, W. I., Wright, J. C., and Sullivan, M. W., 1975, Selected bibliography pertaining to
uranium occurrence in eastern New Mexico and West Texas and nearby parts of Colorado,
Oklahoma, and Kansas: Report No. PB-241 629/AS (NTIS), 99 p.
Fouch-Flores, D. L., 1982, Regional uranium resource evaluation using Landsat imagery and
NURE. geochemical data, southern Trans-Pecos, Texas: Texas Christian Univ.Master's
thesis, 69 p.
Galloway, W. E., 1985, The depositional and hydrogeologic environment of Tertiary uranium
deposits, South Texas uranium province, in Finch, W. Land Davis, J. F., eds., Geological
environments of sandstone-type uranium deposits, International Atomic Energy Agency
TECDOC-328, p. 215-227.
Galloway, W. E., Finley, R. J., and Henry, C. D., 1979, South Texas uranium province-
geologic perspective: Austin, Texas, Bureau of Economic Geology Guidebook 18, 81 p.
Galloway, W. E., Henry, C. D., and Smith, G. E., 1982, Depositional framework,
hydrostratigraphy, and uranium mineralization of the Oakville Sandstone (Miocene), Texas
Coastal Plain: Austin, Texas, Bureau of Economic Geology, Report of Investigations no.
113, 51 p.
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. 6-356-47.
Henry, C. D. and Kapadia, R. R., 1980, Trace elements in soils of the south Texas uranium
district: concentrations, origin, and environmental significance: Austin, Texas, Bureau of
Economic Geology Report of Investigations no. 101, 52 p.
Henry, C. D. and Walton, A.W., 1978, Formation of uranium ores by diagenesis of volcanic
sediments: final report: United States Dept. of Energy Report GJBX-22 (79), 421 p.
rv-24
Reprinted from USGS Open-File Report 93-292-F
-------
Ilger, J. D., Ilger, W. A., Zingaro, R. A. and Mohan, M. S., 1987, Modes of occurrence of
uranium in carbonaceous uranium deposits; characterization of uranium in a South Texas
(U.S.A.) lignite: Chemical Geology, v. 63, n. 3-4, p. 197-216.
Kaback, D. S., 1984, Regional hydrogeochemical exploration for sandstone uranium deposits in
South Texas; the solution-mineral equilibria approach: American Association Petroleum
Geologists Bulletin, v. 68, n. 4, p. 494.
Kaback, D. S., 1986, Groundwater geochemistry as a uranium exploration tool; the solution-
» mineral equilibria approach, Carrizo Formation, Atascosa County, Texas: in Stapp,
Wilford Lee, Dutton, Laurie A., Weise, Bonnie R., Jones, Leslie P. and Fergeson, W.
Grant, eds., Contributions to the geology of South Texas 1986: South Texas Geological
Society, p. 171-193. ¦ .
Kraemer, T. F., 1986, Radon in unconventional natural gas from Gulf Coast geopressured-
geothermal reservoirs: Environmental Science & Technology, vl 20, p. 939-942.
Laul, J. C. and Smith, M. R., 1988, Disequilibrium study of natural radionuclides of uranium and
thorium series in cores and briny groundwaters from Palo Duro Basin, Texas: Radioactive
Waste Management and the Nuclear Fuel Cycle, v. 11, p. 169-225.
Ledger, E. B. and Tieh, T. T., 1983, Catahoula Formation as a source of sedimentary uranium
deposits in East Texas: American Association of Petroleum Geologists Bulletin, v. 67,
p. 500.
Ledger, E. B., Tieh, T. T., and Rowe, M. W., 1984, An evaluation of the Catahoula Formation
as a uranium source rock in East Texas, in White, B. R. and Kier, R., eds., Transactions
of the 34th annual meeting, Gulf Coast Association of Geological Societies and thirty-first
annual meeting of the Gulf Coast Section of SEPM, Shreveport, LA, United States, Oct.*
24-26, 1984: Transactions- Gulf Coast Association of Geological Societies, v. 34, '
p. 99-108.
Ledger, E. B Tieh, T. T., Crocker, M. C., and Rowe, M. W., 1986, Uranium occurrence and
trace element geochemistry of sheep pasture tuffs, Trans-Pecos volcanic province, Texas:
The Texas Journal of Science, v. 38, p. 219-225.
McCulloh, Richard P. and Roberts, Charles, 1986, Geology of the Nuhn uranium ore body,
Jackson Group, South Texas uranium district: in Stapp, Wilford Lee, Dutton, Laurie A.,
Weise, Bonnie R., Jones, Leslie P. and Fergeson, W. Grant, eds., Contributions to the
geology of South Texas 1986: South Texas Geological Society., p. 109-125.
NUS Corporation, 1987, Determination of background radiological characteristics within the Palo
Duro Basin, Texas, USA: Technical Report 638, 81 p.
Otton, J. K., 1984, Surficial uranium deposits in the United States of America, in Toens,
P.D.(leader), Surficial uranium deposits: International Atomic Energy Agency TECDOC-
322, p. 237-242.
IV-25 Reprinted from USGS Open-File Report 93-292-F
-------
Pingitore, N. E., Schmidt, J. S., and Keller, G. R., 1984, Radiometric traps of the Permian
Basin; surface uranium and potassium activity derived from NURE Program, in Mazzullo,
S. J.(chairperson), Symposium on the geological evolution of the Permian Basin, Midland,
TX, United States, April 25-26, 1984: SEPM, Permian Basin Section., p. 39-40.
Podsednik, M., 1990, Geologic assessment of radon-222 in Mclennan County, Texas: Baylor
Geological Studies Bulletin, no. 50, p. 42.
Prasse, Eric Martin, 1978, Uranium and its relationship to host rock mineralogy in an unoxidized
roll front in the Jackson Group, south Texas: Master's thesis, Texas A&M Univ.,
unknown p.
Reimer, G. M., 1985, Gaseous emanations associated with sandstone-type uranium deposits, in
Finch, W. I.and Davis, J. F., eds., Geological environments of sandstone-type uranium
deposits, International Atomic Energy Agency TECDOC-328, p. 335-346.
«
Renfro, H.B., Feray, D.E., and King, P.B., 1973, Geological Highway Map of Texas: Tulsa,
Oklahoma, American Association of Petroleum Geologists United States Geological
Highway Map Series No. 7,1 sheet.
Rose, A.W., Ciolkosz, E.J., and Washington, J.W., 1991, Effects of regional and seasonal
variations in soil moisture and temperature on soil gas radon, in The 1990 International
Symposium on Radon and Radon Reduction Technology, Proceedings, Vol. 3:
Symposium Poster Papers: Research Triangle Park, N.C., U.S. Environmental Protection
Agency Rept. EPA600/9-91-026c, p. 6-49-6-60.
Schaftenaar, W. E. and Tieh, T. T., 1983, Uranium in igneous rocks of central Davis Mountains,
West Texas: American Association of Petroleum Geologists Bulletin, v. 67, p. 545.
Tewalt, S. J. and Jones, C. M., 1986, Chemical and petrologic characteristics of deep-subsurface
Wilcox lignites (Eocene) from east and east-central Texas, in Garbini, S. and
Schweinfurth, S. P., eds., Symposium proceedings; A national agenda for coal-quality
research, Reston, VA, April 9-11, 1985: U.S. Geological Survey Circular 979, p. 257.
Thomann, W. F., Pyron, A. J. and Ray, D. R., 1985, Distribution of uranium, thorium and
potassium in Proterozoic igneous rocks, Franklin Mountains, West Texas, in Sibbald, T. I.
I.and Petruk, W., eds., Geology of uranium deposits, Canadian Institute of Mining and
Metallurgy Special Volume 32, p. 195-201.
Travis, Steven L., 1981, Uranium mineralization in Jim Wells County, Texas: Master's thesis,
Wichita State University., 50 p.
Wanty, R. B.and Gundersen, L.C.S.,1987, Factors affecting radon concentrations in ground
water; evidence from sandstone and crystalline aquifers: Geological Society of America,
Abstracts with Programs, v. 19, no. 2, p. 135.
Woodrome, Larry S., 1980, Uranium; Trans-Pecos, Texas Tertiary intrusive and groundwater '
anomalies: Master's thesis, University of Texas, El Paso, unknown p.
IV-26
Reprinted from USGS Open-File Report 93-292-F
-------
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
bouhdary 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.)
TEXAS MAP OF RADON ZONES
The Texas Map of Radon Zones and its supporting documentation (Part IV of this-
report) have received extensive review by Texas geologists and radon program experts' The
map for Texas 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.
A few county designations do not strictly follow this methodology for adapting the
geologic provinces to county boundaries. EPA and the Texas Department of Health have
decided to designate Reagan, Upion, Glasscock, Borden, Howard, Scurry, Mitchell, Sterling,
Grayson, Fannin", Collin, and-El Paso as Zone 3 counties. Although the indoor radon data for
these counties are limited, they indicate low indoor radon averages. However, these counties
contain much variability in geology and aerial radioacivity, and some elevated levels will be
found in these counties.
Although the information provided in Part IV of this report the State chapter entitled
"Preliminary Geologic Radon Potential Assessment of Texas" 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 6 EPA office or the
Texas radon program for information on testing and fixing-homes. Telephone numbers and
addresses can be found in Part II of this report.
V-l
-------
TEXAS - EPA Map of Radon Zones
The purpose of this map is to assist National, State and local organizations
to tasget their resources and to implement rodon-resistant building codes.
This map is not Mended 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 homes should bo tasted, regardless of zona designation.
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