United States
Environmental Protection
Agency
Air and Radiation
(6SO4J)
402-R-S3-048
September 1393
4>EPA EPA's Map of Radon Zones
NEVADA
Recycled/Recyclable
Printed on paper that contains
at least 50% recycled fiber
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EPA'S MAP OF RADON ZONES
NEVADA
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 peop.le in ORIA
were instrumental in the development of the Map of Radon Zones, including Lisa Ratcliff,
Kirk Maconaughey, R. Thomas Peake, Dave Rowson, and Steve Page.
EPA would especially like to acknowledge the outstanding effort of the USGS
radon team - Linda Gundersen, Randy Schumann, Jim Otton, Doug Owen, Russell
Dubiel, Kendell Dickinson, and Sandra Szarzi — in developing the technical base for the
Map of Radon Zones.
ORIA would also like to recognize the efforts of all the EPA Regional Offices in
coordinating the reviews with the State programs and the Association of American State
Geologists (AASG) for providing a liaison with the State geological surveys. In addition,
appreciation is expressed to all of the State radon programs and geological surveys for their
technical input and review of the Map of Radon Zones.
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TABLE OF CONTENTS
I. OVERVIEW
II. THE USGS/EPA RADON POTENTIAL
ASSESSMENTSiINTRODUCTION
III. REGION 9 GEOLOGIC RADON POTENTIAL
SUMMARY
V.i PRELIMINARY GEOLOGIC RADON POTENTIAL
ASSESSMENT OF NEVADA
V. EPA'S MAP OF RADON ZONES - NEVADA
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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 (USCS), and the Association of American State Geologists
(AASG) have worked closely over the past several years to produce a series of maps and
documents which address these .directives. The EPA Map of Radon Zones is a compilation of
that work and fulfills the requirements of sections 307 and 309 of IRAA. The Map of Radon
Zones identifies, on a county-by-county basis, areas of the U.S. that have the highest potential
for elevated indoor radon levels (greater than 4 pCi/L).
The Map of Radon Zones is designed to assist national, State and local governments
and organizations to target their radon program activities and resources. It is also intended to
help building code officials determine areas that are the highest priority for adopting radon-
resistant building practices. The Map of Radon Zones should not be used to determine if
individual homes in any given area need to be tested for radon. EPA recommends that all
homes be tested for radon, regardless of geographic location or the zone designation of
the county in which they are located.
This document provides background information concerning the development of the
Map of Radon Zones. It explains the purposes of the map, the approach for developing the
map (including the respective roles of EPA and USGS), the data sources used, the conclusions
and confidence levels developed for the prediction of radon potential, and the review process
that was conducted to finalize this effort.
BACKGROUND
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Radon (Rn222) is a colorless, odorless, radioactive gas. It comes from the natural
decay of uranium that is found in nearly all soils. It typically moves through the ground to
the air above and into homes and other buildings'through cracks and openings in the
foundation'. Any home, school or workplace may have a radon problem, regardless of
whether it is new or old, well-sealed or drafty, or with or without a basement. Nearly one out
of every 15 homes in the U.S. is estimated to have elevated annual average levels of indoor
radon. ' • .
•Radon first gained national attention in early 1984, when extremely high levels of
indoor radon were found in areas of Pennsylvania, New Jersey, and New York, along the
Reading Prong-physiographic province. EPA established a Radon Program in 1985 to assist
States and homeowners in reducing their risk of lung cancer from indoor radon.
Since 1985, EPA and USGS have been working together to continually increase our
understanding of radon sources and the migration dynamics that cause elevated indoor radon
levels. Early efforts resulted in the 1987 map entitled "Areas with Potentially High Radon
Levels." This map was based on limited geologic information only because few indoor radon
measurements were available at the time. The development of EPA's Map of Radon Zones
and its technical foundation, USGS1 National Geologic Radon Province Map, has been based
on additional information from six years of the State/EPA Residential Radon Surveys,
independent State residential surveys, and continued expansion of geologic and geophysical
information, particularly the data from the National Uranium Resource Evaluation project.
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Purpose of the Map of Radon Zones
EPA's Map of Radon'Zones (Figure 1) assigns each of the 3141 counties in the
United States to one of three zones:
o Zone 1 counties have a predicted average indoor screening level > than
4 pCi/L
o Zone 2 counties have a predicted average screening level > 2 pCi/L and
< 4 pCi/L
o Zone 3 counties have a predicted average screening level < 2 pCi/L
The Zone designations were determined by assessing five factors that are known to be
important indicators of radon potential: indoor radon measurements, geology, aerial
radioactivity, soil parameters, arid 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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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 how EPA extrapolated the county zone
designations for Nebraska from the USGS geologic province map for the State. As figure 3
shows, USGS has identified 5 geologic provinces for Nebraska. Most of the counties are
extrapolated "straight" from their corresponding provinces, but there are counties "partitioned"
by several provinces -- for example, Lincoln County. Although Lincoln county falls in
multiple provinces, it was assigned/to Zone 3 because most of its area falls in the province
with the lowest radon potential.
It is important to note that EPA's extrapolation from the province level to the
county level may mask significant "highs" and "lows" within specific counties. In other
words, wifhin-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
Bijl
Kolentc
Figure 4
NEBRASKA - EPA Map of Radon Zones
Lincoln County
Zoae 1 Zone 2 Zone 3
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One such analysis involved comparing county zone designations to indoor radon
measurements from the State/EPA Residential Radon Surveys (SRRS). Screening averages
for" counties with at least 100 measurements were compared to the counties' predicted radon
potential as indicated by the Map of Radon Zones. EPA found that 72% of the county
screening averages were correctly reflected by the appropriate zone designations on the Map.
In all other cases, they only differed by 1 zone.
Another accuracy analysis used the annual average data from the National Residential
Radon Survey (NRRS). The NRRS indicated that approximately 6 million homes in the
United States have annual averages greater than or equal to 4 pCi/L. By cross checking the
county location of the approximately 5,700 homes which participated in the survey, their
radon measurements, and the zone designations for these counties, EPA found that
approximately 3.8 million homes of the 5.4 million homes with radon levels greater than or
equal to 4 pCi/L will be found in counties designated as Zone 1. A random sampling of an
equal number of counties would have only found approximately 1.8 million homes greater
than 4 pCi/L. In other words, this analysis indicated that the map approach is three times
more efficient at identifying high radon areas than random selection of zone designations.
Together, these analyses show that the approach EPA used to develop the Map of
Radon Zones is a reasonable one. In addition, the Agency's confidence is enhanced by results
of the extensive State review process -- the map generally agrees with the States' knowledge
of and experience in their own jurisdictions. However, the accuracy analyses highlight two
important points: the fact that elevated levels will be found in Zones 2 and 3, and that there
will be significant numbers of homes with lower indoor radon levels in all of the Zones. For
these reasons, users of the Map of Radon Zones need to supplement the Map with locally
available data whenever possible. Although all known "hot spots", i.e., localized areas of
consistently elevated levels, are discussed in the State-
specific chapters, accurately defining the boundaries of the "hot spots" on this scale of map is
not possible at this time. Also, unknown "hot spots" do exist.
The Map of Radon Zones is intended to be a starting point for characterizing radon
potential because our knowledge of radon sources and transport is always growing. Although
this effort (represents the best data available at this time, EPA will continue to study these
parameters and others such as house construction, ventilation features and meteorology factors
in order to better characterize the presence of radon in U.S homes, especially in high risk
areas. These efforts will eventually assist EPA in refining and revising the conclusions of the
Map of Radon Zones. And although this map is most appropriately used as a targeting, tool
by the aforementioned audiences -- the Agency encourages all residents to test their homes
for radon, regardless of geographic location or the zone designation of the county in
which they live. Similarly, the Map of Radon Zones should not to be used in lieu of
testing during real estate transactions.
Review Process
The Map of Radon Zones has undergone extensive review within EPA and outside the
Agency. The Association of American State Geologists (AASG) played an integral role in
this review process. The AASG individual State geologists have reviewed their State-specific
information, the USGS Geologic Radon Province Map, and other materials for their geologic
content and consistency.
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In addition to each State geologist providing technical comments, the State radon
offices were asked to comment on their respective States' radon potential evaluations. In
particular, the States were asked to evaluate the data used to assign their counties to specific
zones. EPA and USGS worked with the States to resolve any issues concerning county zone
designations. In a few cases, States have requested changes in county zone designations. The
requests were based on additional data from the State on geology, indoor radon
measurements, population, etc. Upon reviewing the data submitted by the States, EPA did
make some changes in zone designations. These changes, which do not strictly follow the
methodology-outlined in this document, are discussed in the respective State chapters.
EPA encourages the States and counties to conduct further research and data collection
efforts to refine the Map of Radon Zones. EPA would like to be kept informed of any
changes the States, counties, or others make to the maps. Updates and revisions will be
handled in a similar fashion to the way the map was developed. States should notify EPA of
any proposed changes by forwarding the changes through the Regional EPA offices that are
listed in Part II. Depending on the amount of new information that is presented, EPA will
consider updating this map periodically. The State radon programs should initiate proper
notification of the appropriate State officials when the Map of Radon Zones is released and
when revisions or updates are made by the State or EPA.
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~ THE USGS/EPA RADON POTENTIAL ASSESSMENTS: AN INTRODUCTION
by
Linda C.S. Gundersen and R. Randall Schumann
U.S. Geological 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 model standards and techniques for new building construction
that would provide adequate prevention or mitigation of radon entry. As part of an
Interagency Agreement between the EPA and the U.S. Geological Survey (USGS), the USGS
has prepared radon potential estimates for the United States. This report is one of ten
booklets that document this effort. The purpose and intended use of these reports is to help
identify areas where states can target their radon program resources, to provide guidance in
selecting the most appropriate building code options for areas, and to provide general
information on radon and geology for each state for federal, state, and municipal officials
dealing with radon issues. These reports are not intended to be used as a substitute for
indoor radon testing, and they cannot and should not be used to estimate or predict the
indoor radon concentrations of individual homes, building sites, or housing tracts. Elevated
levels of indoor radon have been found in every State, and EPA recommends that all homes
be tested for indoor radon.
Booklets detailing the radon potential assessment for the U.S. have been developed for
each State. USGS geologists are the authors of the geologic radon potential booklets. Each
booklet consists of several components, the first being an overview to the mapping project
(Part I), this introduction to the USGS assessment (Part II), including a general discussion of
radon (occurrence, transport, etc.), and details concerning the types of data used. The third
component is a summary chapter outlining the general geology and geologic radon potential
of the EPA Region (Part III). The fourth component is an individual chapter for each state
(Part IV). Each state chapter discusses the state's specific geographic setting, soils, geologic
setting, geologic radon potential, indoor radon data, and a summary outlining the radon
potential rankings of geologic areas in the state. A variety of maps are presented in each
chapter—geologic, geographic, population, soils, aerial radioactivity, and indoor radon data by
county. Finally, the booklets contain EPA's map of radon zones for each state and an
accompanying description (Part V).
Because of constraints on the scales of maps presented in these reports and because the
smallest units used to present the indoor radon data are counties, some generalizations have
been made in order to estimate the radon potential of each area. Variations in geology, soil
characteristics, climatic factors, homeowner lifestyles, and other factors that influence radon
concentrations can be quite large within any particular geologic area, so these reports cannot
be used to estimate or predict the indoor radon concentrations of individual homes or housing
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tracts. Within any area of a given geologic radon potential ranking, there are likely to be
areas where the radon potential is lower or higher than that assigned to the area as a whole,
especially in larger areas such as the large counties in.some western states.
In each state chapter, references to additional reports related to radon are listed for the
state, and the reader is urged to consult these reports for more detailed information. In most
cases the best sources of information on radon for specific areas are state and local
departments of health, state departments responsible for nuclear safety or environmental
protection, and U.S. EPA regional offices. More detailed information on state or local
geology may be obtained from the state geological surveys. Addresses and telephone
numbers of state radon contacts, geological surveys, and EPA regional offices are listed in
Appendix C at the end of this chapter.
RADON GENERATION AND TRANSPORT IN SOILS
Radon (2"Rn) is produced from the radioactive decay of radium ("6Ra), which is, in turn,
a product of the decay of uranium (238U) (fig. 1). The half-life of 22SRn is 3.825 days. Other
isotopes of radon occur naturally, but, with the exception of thoron (:20Rn), which occurs in
concentrations high enough to be of concern in a few localized areas, they are less important
in terms of indoor radon risk because of their extremely short half-lives and less common
occurrence. In general, the concentration and mobility of radon in soil are dependent on
several factors, the most important of which are the soil's radium content and distribution,
porosity, permeability to gas movement, and moisture content. These characteristics are, in
turn, determined by the soil's parent-material composition, climate, and the soil's age or
maturity. If parent-material composition, climate, vegetation, age of the soil, and topography
are known, the physical and chemical properties of a soil in a given area can be predicted.
As soils form, they develop distinct layers, or horizons, that are cumulatively called the
soil profile. The A horizon is a surface or near-surface horizon containing a relative
abundance, of organic matter but dominated by mineral matter. Some soils contain an E
horizon, directly below the A horizon, that is generally characterized by loss of clays, iron, or
aluminum, and has a characteristically lighter color than the A horizon. The B horizon
underlies the A or E horizon. Important characteristics of B horizons include accumulation of
clays, iron oxides, calcium carbonate or other soluble salts, and organic matter complexes. In
drier'environments, a horizon may exist within or below the B horizon that is dominated by
calcium carbonate, often called caliche or calcrete. This carbonate-cemented horizon is
designated the K horizon in modern soil classification schemes. The C horizon underlies the
B (or K) and is a zone of weathered parent material that does not exhibit characteristics of A
or B horizons; that is, it is generally not a zone of leaching or accumulation. In soils formed
in place from'the underlying bedrock, the C horizon is a zone of unconsolidated, weathered
bedrock overlying the unweathered bedrock.
The shape and orientation of soil particles (soil structure) control permeability and affect
water movement in the soil. Soils with blocky or granular structure have roughly equivalent
permeabilities in the horizontal and vertical directions, and air and water can infiltrate the soil
relatively easily. However, in soils with platy structure, horizontal permeability is much
greater than vertical permeability, and air and moisture infiltration is generally slow. Soils
' with prismatic or columnar structure have dominantly vertical permeability. Platy and
prismatic structures form in soils with high clay contents. In soils with shrink-swell clays, air
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and moisture infiltration rates and depth of wetting may be limited when 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 2xlO'fl inches—this is known as alpha
recoil (Tanner, 1980). Moisture in the soil lessens the chance of a recoiling radon atom
becoming'imbedded in an adjacent grain. Because water is more dense than air, a radon atom
will travel' a shorter distance in a water-filled pore than in an air-filled pore, thus increasing
the likelihood that the radon atom will remain in the pore space. Intermediate moisture levels
enhance radon emanation but do not significantly affect permeability. However, high
moisture levels can significantly decrease the gas permeability of the soil and impede radon
movement through the soil.
Concentrations of radon in soils are generally many times higher than those inside of
buildings, ranging from tens of pCi/L to more than 100,000 pCi/L, but typically in the range
of hundreds to low thousands of pCi/L. Soil-gas radon concentrations can vary in response to
variations in climate and weather on hourly, daily, or seasonal time scales. Schumann and
others (1992) and Rose and others (1988) recorded order-of-magnitude variations in soil-gas
radon concentrations between seasons in Colorado and Pennsylvania. The most important
factors appear to be (1) soil moisture conditions, which are controlled in large part by
precipitation; (2) barometric pressure; and (3) temperature. Washington and Rose (1990)
suggest that temperature-controlled partitioning of radon between water and gas in soil pores
also has a significant influence on the amount of mobile radon in soil gas.
Homes in hilly limestone regions of the southern Appalachians were found to have higher
indoor radon concentrations during the summer than in the winter. A suggested cause for this
phenomenon involves temperature/pressure-driven flow of radon-laden air from subsurface
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solution cavities in the carbonate rock into houses. As warm air enters solution cavities that
are higher on the hillslope than the homes, it cools and settles, pushing radon-laden air from
lower in the cave or cavity system into structures on the hillslope (Gammage and others,
1993). In contrast, homes built over caves having openings situated below the level of the
home had higher indoor radon levels in the winter, caused by cooler outside air entering the
cave, driving radon-laden air into cracks and solution cavities in the rock and soil, and
ultimately, into homes (Gammage and others, 1993).
RADON ENTRY INTO BUILDINGS
A driving force (reduced atmospheric pressure in the house relative to the-soil, producing
a pressure gradient) and entry points must exist for radon to enter a building from the soil.
The negative pressure caused by furnace combustion, ventilation devices, and the" stack effect
(the rising and escape of warm air from the upper floors of the building, causing a
temperature and pressure gradient within the structure) during cold winter months are
common driving forces. Cracks and other penetrations through building foundations, sump
holes, and slab-to-foundation wall joints are common entry points.
Radon levels in the basement are generally higher than those on the main floor or upper
floors of most structures. Homes with basements generally provide more entry points for
radon, commonly have a more pronounced stack effect, and typically have lower air pressure
relative to the surrounding soil than nonbasement homes. The term "nonbasement" applies to
slab-on-grade or crawl space construction.
METHODS AND SOURCES OF DATA
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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
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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 grams, 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, 19S8a; 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 (»
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FLIGHT LINE SPACING OF SURE .A E K 1 A L SURVEYS
2 KU (1 MILE)
5 KM (3 MILES)
2 i 5 KM
E3 10 EM {6 MILES)
5 1- 10 EM
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 I°x2° quadrangles.
-------
~~ Figure 2 is an index map of NUKE 1° x 2° quadrangles showing the flight-line spacing
for each quadrangle. In general, the more closely spaced the flightlines are, the more area
was covered by the aerial gamma survey, and thus, more detail is available in the data set.
For an altitude of 400 ft above the ground surface and with primary flightline spacing
yplcally between 3 and 6 miles, less than 10 percei of the ground surface of he United
States was actually measured by the airborne gamma-ray detectors (Duval and others, 1989),
although some areas had better coverage than others due to the differences in flight-line
spacing between areas (fig. 2). -This suggests that some localized uranium anomalies may not
have been detected by the aerial surveys, but the good correlations of eU patterns with
geologic outcrop patterns indicate that, at relatively small scales (approximately 1:1,000,000
or smaller) the National eU map (Duval and others, 1989) gives reasonably good estimates of
average surface uranium concentrations and thus can assist in the prediction of radon potential
of rocks and soils, especially when augmented with additional geologic and soil data.
The shallow (20-30 cm) depth of investigation of gamma-ray spectrometers, either
ground-based or airborne (Duval and others, 1971; Durrance, 1986), suggests that gamma-ray
data may sometimes underestimate the radon-source strength in soils in which some of the
radionuclides in the near-surface soil layers have been transported downward through the soil
profile. In such cases the concentration of radioactive minerals in the A horizon would be
lower than in the B horizon, where such minerals are typically concentrated. The
concentration of radionuclides in the C horizon and below may be relatively unaffected by
surface solution processes. Under these conditions the surface gamma-ray signal may indicate
a lower radon source concentration than actually exists in the deeper soil layers, which are
most likely to affect radon levels in structures with basements. The redistribution of
radionuclides in soil profiles is dependent on a combination of climatic, geologic, and
geochemical factors. There is reason to believe that correlations of eU with actual soil
radium and uranium concentrations at a depth relevant to radon entry into structures may be
regionally variable (Duval, 1989; Schumann and Gundersen, 1991). Given sufficient
understanding of the factors cited above, these regional differences may be predictable.
t
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, coast.al
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 (Rbnca-Battista and others, 1988; Dziuban and
others, 1990). Forty-two states completed EPA-spohsored indoor radon surveys between 1986
and 1992 (fig. 3). The State/EPA Residential Radon Surveys were designed to be
comprehensive and statistically significant at the state level, and were subjected to high levels
of quality assurance and control. The surveys collected screening indoor radon measurements,
defined as 2-7 day measurements using charcoal canister radon detectors placed in the lowest
livable area of the home. The target population for the surveys included owner-occupied
single family, detached housing units (White and others, 1989), although attached structures
such as duplexes, townhouses, or condominiums were included in some of the surveys if they
met the other criteria and had contact with the ground surface. Participants were selected
randomly from telephone-directory listings. In total, approximately 60,000 homes were tested
in the State/EPA surveys.
The second source of indoor radon data comes from residential surveys that have been
conducted in a specific state or region of the country (e.g. independent state surveys or utility
company surveys). Several states, including Delaware, Florida, Illinois, New Hampshire, New
Jersey, New York, Oregon, and Utah, have conducted their own surveys of indoor radon. The
quality and design of a state or other independent survey are discussed and referenced where
the data are used.
II-9 Reprinted from USGS Open-File Report 93-292
-------
-------
Data for only those counties with -five or more measurements are shown in the indoor
radon maps in the state chapters, although data for all counties with a nonzero number of
measurements are listed in the indoor radon data tables in .each state chapter. In total, indoor
radon data from more than 100,000 homes nationwide were used in the compilation of these
assessments. Radon data from State or regional indoor radon surveys, public health
organizations, or other sources are discussed in addition to the primary data sources where
they are available. Nearly all of the data used in these evaluations represent short-term (2-7
day) screening measurements from the lowest livable space of the homes. Specific details
concerning the nature and use of indoor radon data sets other than the State/EPA Residential
Radon Survey are discussed in the individual State chapters.
RADON INDEX AND CONFIDENCE INDEX
Many of the geologic methods used to evaluate an area for radon potential require
subjective opinions based on the professional judgment and experience of the individual
geologist. The evaluations are nevertheless based on established scientific principles that are
universally applicable to any geographic area or geologic setting. This section describes the
methods and conceptual framework used by the U.S. Geological Survey to evaluate areas for
radon potential based on the five factors discussed in the previous sections. The scheme is
divided into two basic parts, a Radon Index (RI), used to rank the general radon potential of
the area, and the Confidence Index (CI), used to express the level of confidence in the
prediction based on the quantity and quality of the data used to make the determination. This
scheme works best if the areas to be evaluated are delineated by geologically-based
boundaries (geologic provinces) rather than political ones (state/county boundaries) in which
the geology may vary across the area.
Radon Index, Table 1 presents the Radon Index (RI) matrix. The five factors—indoor
radon data geology, aerial radioactivity, soil parameters, and house foundation type—were
quantitatively ranked (using a point value of 1, 2; or 3) for their respective contribution to
radon potential in a given area. At least some data for the 5 factors are consistently available
for every geologic province. Because each of these main factors encompass a wide variety of
complex and variable components, the geologists performing the evaluation relied heavily on
their professional judgment and experience in assigning point values to each category and in
determining the overall radon potential ranking. Background information on these factors is
discussed in more detail in the preceding sections of this introduction.
Indoor radon was evaluated using unweighted arithmetic means of the indoor radon data
for each geologic area to be assessed. Other expressions of indoor radon levels in an area
also could have been used, such as weighted averages or annual averages, but these types of
data were not consistently available for the entire United States at the time of this writing, or
the schemes were not considered sufficient to provide a means of consistent comparison
across all areas. For this report, charcoal-canister screening measurement data from the
State/EPA Residential Radon Surveys and other carefully selected sources were used, as
described in the preceding section. To maintain consistency, other indoor radon data sets
'(vendor, state, or other data) were not considered in scoring the indoor radon factor of the
Radon Index if they were not randomly sampled or could not be statistically combined with
the primary indoor radon data sets. However, these additional radon data sets can provide a
means to further refine correlations between geologic factors and radon potential, so they are
II-11 Reprinted from USGS Open-File Report 93-292
-------
TABLE 1. RADON INDEX MATRIX, "ppm eU" indicates parts per million of equivalent
uranium, as indicated by NURE aerial radiometric data. See text discussion for details.
INCREASING RADON POTENTIAL ^
FACTOR
INDOORRADON (average)
AERIAL RADIOACTIVITY
GEOLOGY*
SOIL PERMEABILITY
ARCHITECTURE TYPE
POINT VALUE
1
<2pCi/L
< 1.5 ppm eU
negative
low
mostly slab
2
2-4pCi/L
1.5 - 2.5 ppm eU
variable
moderate
mixed
3
. >4pCi/L
> 2.5 ppm eU
positive
high
mostly basement
*GEOLOGIC FIELD EVIDENCE (GFE) POINTS: GFE points are assigned in addition to points
for the "Geology" factor for specific, relevant geologic field studies. See text for details.
Geologic evidence supporting:
HIGH radon +2 points
MODERATE +1 point
LOW -2 points
No relevant geologic field studies 0 points
SCORING:
Radon potential category
Probable average screening
Point range indoor radon for area
LOW
.MODERATE/VARIABLE
HIGH
3-8 points
9-11 points
12-17 points
<2pCi/L
2-4pCi/L
>4pCi/L
POSSIBLE RANGE OF POINTS = 3 to 17
TABLE 2. CONFIDENCE INDEX MATRIX
INCREASING CONFIDENCE
FACTOR
INDOOR RADON DATA
AERIAL RADIOACTIVITY
GEOLOGIC DATA
SOIL PERMEABILITY
. w
POINT VALUE
1
sparse/no data
questionable/no data
questionable
questionable/no data
2
fair coverage/quality
glacial cover
variable
variable
3
good coverage/quality
no glacial cover
proven geol. model
reliable, abundant
SCORING:
LOW CONFIDENCE
MODERATE CONFIDENCE
HIGH CONFIDENCE
4-6 points
7-9 points
10 -12 points
POSSIBLE RANGE OF POINTS = 4 to 12
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, and 3 points,
respectively.
In cases where additional reinforcing or contradictory geologic evidence is available,
Geologic Field Evidence (GFE) points were added to or subtracted from an area's score
(Table 1). Relevant geologic field studies are important to enhancing our understanding of
how geologic processes affect radon distribution. In some cases, geologic models and
supporting field data reinforced an already strong (high or low) score; in others, they provided
important contradictory data. GFE points were applied for geologically-sound evidence that
supports the prediction (but which may contradict one or more factors) on the basis of known
geologic field studies in the area or in areas with geologic and climatic settings similar
enough that they could be applied with full confidence. For example, areas of the Dakotas,
Minnesota, and Iowa that are covered with Wisconsin-age glacial deposits exhibit a low aerial
radiometric signature and score only one RI point in that category. However, data from
geologic field studies in North Dakota and Minnesota (Schumann and others, 1991) suggest
that eU is a poor predictor of geologic radon potential in this area because radionuclides have
11-13 Reprinted from USGS Open-File Report 93-292
-------
been leached from the upper soil layers but are present and possibly even concentrated in
deeper soil horizons, generating significant soil-gas radon. This positive supporting field
evidence adds two GFE points to the score, which helps to counteract the invalid conclusion
suggested by the radiometric data. No GFE points are awarded if there are no documented
field studies for the area.
"Soil permeability" refers to several soil characteristics that influence radon concentration
and mobility, including soil type, grain size, structure, soil moisture, drainage, slope, and
permeability. In the matrix, "low" refers to permeabilities less than about 0.6 in/hr; "high"
corresponds to greater than about 6.0 in/hr, in U.S. Soil Conservation Service (SCS) standard
soil percolation tests. The SCS data are for water permeability, which generally correlates
well with the gas permeability of the soil except when the soil moisture content is very high.
Areas with consistently high water tables were thus considered to have low gas permeability.
"Low, "moderate", and "high" permeability were assigned 1, 2, and 3 points, respectively.
Architecture type refers to whether homes in the area have mostly basements (3 points),
mostly slab-on-grade construction (1 point), or a mixture of the'two. Split-level and crawl
space homes fall into the "mixed" category (2 points). Architecture information is necessary
to properly interpret the indoor radon data and produce geologic radon potential categories
that are consistent with screening indoor radon data.
The overall RI for an area is calculated by adding the individual RI scores for the 5
factors, plus or minus GFE points, if any. The total RI for an area falls in one of three
categories—low, moderate or variable, or high. The point ranges for the three categories were
determined by examining the possible combinations of points for the 5 factors and setting
rules such that a majority (3 of 5 factors) would determine the final score for the low and
high categories, with allowances for possible deviation from an ideal score by the other two
factors. The moderate/variable category lies between these two ranges. A total deviation of 3
points from the "ideal" score was considered reasonable to allow for natural variability of
factors—if two of the five factors are allowed to vary from the "ideal" for a category, they
can differ by a minimum of 2 (1 point different each) and a maximum of 4 points (2 points
different each). With "ideal" scores of 5, 10, and 15 points describing low, moderate, and
high geologic radon potential, respectively, an ideal low score of 5 points plus 3 points for
possible variability allows a maximum of 8 points in the low category. Similarly, an ideal
high score of 15 points minus 3 points gives a minimum of 12 points for the high category.
Note, however, that if both other factors differ by two points from the "ideal", indicating
considerable variability in the system, the total point score would lie in the adjacent (i.e.,
moderate/variable) category.
Confidence Index. Except for architecture type, the same factors were used to establish a
Confidence Index (CI) for the radon potential prediction for each area (Table 2). Architecture
type was not included in the confidence index because house construction data are readily and
reliably available through surveys taken by agencies and industry groups including the
.National Association of Home Builders, U.S. Department of Housing and Urban
Development, and the Federal Housing Administration; thus it was not considered necessary
11-14 Reprinted from USGS Open-File Report 93-292
-------
to.question the quality or validity of these data. .The other factors were scored on the basis of
the quality and quantity of the data used to complete the RI matrix.
Indoor radon data were evaluated based on the distribution and number of data points and
on whether the data were collected by random sampling (State/EPA Residential Radon Survey
or other state survey data) or volunteered vendor data ^ikely to be nonrandom and biased
toward population centers and/or high indoor radon levels). The categories listed in the CI
matrix for indoor radon data ("sparse or no data", "fair coverage or quality", and "good
coverage/quality") indicate the sampling density and statistical robustness of an indoor radon
data set. Data from the State/EPA Residential Radon Survey and statistically valid state
surveys were typically assigned 3 Confidence Index points unless the data were poorly
distributed or absent in the area evaluated.
Aerial radioactivity data are available for all but a few areas of the continental United
States and for part of Alaska. An evaluation of the quality of the radioactivity data was based
on whether there appeared to be a good correlation between the radioactivity and the actual
amount of uranium or radium available to generate mobile radon in the rocks and soils of the
area evaluated. In general, the greatest problems with correlations among eU, geology, and
soil-gas or indoor radon levels were associated with glacial deposits (see the discussion in a
previous section) and typically were assigned a 2-point Confidence Index score. Correlations
among eU, geology, and radon were generally sound in unglaciated areas and were usually
assigned 3 CI points. Again, however, radioactivity data in some unglaciated areas may have
been assigned fewer than 3 points, and in glaciated areas may be assigned only one point, if
the data were considered questionable or if coverage was poor.
To assign Confidence Index scores for the geologic data factor, rock types and geologic
settings for which a physical-chemical, process-based understanding of radon generation and
mobility exists were regarded as having "proven geologic models" (3 points); a high
confidence could be held for predictions in such areas. Rocks for which the processes are
less well known or for which data are contradictory were regarded as "variable" (2 points),
and those about which little is known or for which no apparent correlations have been found
were deemed "questionable" (1 point).
The soil permeability factor was also scored based on quality and amount of data. The
three categories for soil permeability in the Confidence Index are similar in concept, and
scored similarly, to those for the geologic data factor. Soil permeability can be roughly
estimated from grain size and drainage class if data from standard, accepted soil percolation
tests are unavailable; however, the reliability of the data would be lower than if percolation
test figures or other measured permeability data are available, because an estimate of this type
does not encompass all the factors that affect soil permeability and thus may be inaccurate in
some instances. Most published soil permeability data are for water; although this is
generally closely related to the air permeability of the soil, there are some instances when it
may provide an incorrect estimate. Examples of areas in which water permeability data may
not accurately reflect air permeability include areas with consistently high levels of soil
moisture, or clay-rich soils, which would have a low water permeability but may have a
II-15 Reprinted from USGS Open-File Report 93-292
-------
significantly higher air permeability when dry due to shrinkage cracks in .the soil. These
additional factors were applied to the soil permeability factor when assigning the RI score, but
may have less certainty in some cases and thus would be assigned a lower CI score.
The Radon Index and Confidence Index give a general indication of the relative
contributions of the interrelated geologic factors influencing radon generation and transport in
rocks and soils, and thus, of the potential for elevated indoor radon levels to occur in a
particular area. However, because these reports are somewhat generalized to cover relatively
large areas of States, it-is highly .recommended, that more detailed studies be performed in
local areas of interest, using the methods and general information in these booklets as a guide.
11-16 Reprinted from USGS Open-File Report 93-292
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Press, p. 161-190.
Tanner, A.B., 1980, Radon migration in the ground: a supplementary review, in Gesell, T.F.,
and Lowder, W.M. (eds), Natural radiation environment HI, Symposium proceedings,
Houston, Texas, v. 1, p. 5-56.
U.S. Department of Agriculture, 1987, Principal kinds of soils: Orders, suborders, and great
groups: U.S. Geological Survey, National Atlas of the United States of America, sheet
38077-BE-NA-07M-00, scale 1:7,500,000.
U.S. Department of Energy, 1976, National Uranium Resource Evaluation preliminary report,
prepared by the U.S. Energy Research and Development Administration, Grand Junction,
Colo.: GJO-11(76).
Wanty, Richard B., and Schoen, Robert, 1991, A review of the chemical processes affecting the
mobility of radionuclides in natural waters, with applications, in Gundersen, Linda C.S.,
and Richard B. Wanty, eds., Field studies of radon in rocks, soils, and water: U.S.
Geological Survey Bulletin no. 1971, p. 183-194.
Washington, J.W., and Rose, A.W., 1990, Regional and temporal relations of radon in soil gas to
soil temperature and moisture: Geophysical Research Letters, v. 17, p. 829-832.
White, S.B., Bergsten, J.W., Alexander, B.V., and Ronca-Battista, M., 1989, Multi-State
surveys of indoor 222Rn: Health Physics, v. 57, p. 891-896.
II-19 Reprinted from USGS Open-File Report 93-292
-------
-------
APPENDIX A
GEOLOGIC TIME SCALE
Age estimates
of boundaries
in mega-annum
(Ma)1
Subdivisions (and their symbols)
Period. System,
Subperiod. Subsystem
Epoch or Series
Era or
E rathe m
0.010
1.6 (1.6-1.9)
(4.9-5.3)
(23-26)
(34-38)
(54-56)
(63-66)
(95-97)
Quaternary
(Q)
Neoeene
Subperiod or
Subsystem (Nl
Paieogene
Subperiod or
Subsystem (Pi)
Cretaceous
(Kl
138 (135-141)
205 (200-215)
290 (290-305!
Pennsylvanian
(P)
Carboniferous
Systems
(C)
Mississippian
'Ml
410 (405-415
435 (435-440
Ordovician
(0)
500 (495-510
-J5S*2W^S-S^^
p~.r. midd,, upper or «*. midd... h* when used ^ ***• H.m, .« inform., dhrfsior, o, ft.
• «m. «rm wHhout specific *.
unit: ft.
'Intormal time term without specific rank.
USGS Open-File Report 93-292
-------
-------
APPENDIX B
GLOSSARY OF TERMS
Units of measure
pCi/L (picocuries per liter)- a unit of measure of radioactivity used to describe radon
concentrations in a volume of air. One picocurie (1(H2 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 pG/L.
Bq/m3 (Becquerels per cubic meter)- a metric unit of radioactivity used to describe radon
concentrations in a volume of air. One becquerel is equal to one radioactive disintegration per
second. One pCi/L is equal to 37 Bq/m3.
ppm (parts per million)- a unit of measure of concentration by weight of an element in a
substance, in this case, soil or rock. One ppm of uranium contained in a ton of rock corresponds
to about 0.03 ounces of uranium. The average concentration of uranium in soils in the United
States is between 1 and 2 ppm.
in/hr (inches per hour)- a unit of measure used by soil scientists and engineers to describe the
permeability of a soil to water flowing through it It is measured by digging a hole 1 foot (12
inches) square and one foot deep, filling it with water, and measuring the time it takes for the water
to drain from the hole. The drop in height of the water level in the hole, measured in inches, is
then divided by the time (in hours) to determine the permeability. Soils range in permeability from
less than 0.06 in/hr to greater than 20 in/hr, but most soils in the United States have permeabilities
between these two extremes.
Geologic terms and terms related to the study of radon
aerial radiometric, aeroradiometric survey A survey of radioactivity, usually gamma rays,
taken by an aircraft carrying a gamma-ray spectrometer pointed at the ground surface.
alluvial fan A low, widespread mass of loose rock and soil material, shaped like an open fan
and deposited by a stream at the point where it flows from a narrow mountain valley out onto a
plain or broader valley. May also form at the junction with larger streams or when the gradient of
the stream abruptly decreases.
alluvium, alluvial General terms referring to unconsolidated detrital material deposited by a
stream or other body of running water.
alpha-track detector A passive radon measurement device consisting of a plastic film that is
sensitive to alpha particles. The film is etched with acid in a laboratory after it is exposed. The
etching reveals scratches, or "tracks", left by the alpha particles resulting from radon decay, which
can then be counted to calculate the radon concentration. Useful for long-term (1-12 months)
radon tests.
amphibolite A mafic metamorphic rock consisting mainly of pyroxenes and(or) amphibole and
plagioclase.
n-21 Reprinted from USGS Open-File Report 93-292
-------
argillite, argillaceous Terms referring to a rock derived from clay or shale, or any sedimentary
rock containing an appreciable amount of clay-size material, i.e., argillaceous sandstone.
arid Term describing a climate characterized by dryness, or an evaporation rate that exceeds the
amount of precipitation.
basalt A general term for a dark-colored mafic igneous rocks that may be of extrusive origin,
such as volcanic basalt flows, or intrusive origin, such as basalt dikes.
batholith A mass of plutonic igneous rock that has more than 40 square miles of surface
exposure and no known bottom.
carbonate A sedimentary rock consisting of the carbonate (COs) compounds of calcium,
magnesium, or iron, e.g. limestone and dolomite.
carbonaceous Said of a rock or sediment that is rich in carbon, is coaly, or contains organic
matter.
charcoal canister A passive radon measurement device consisting of a small container of
granulated activated charcoal that is designed to adsorb radon. Useful for short duration (2-7 days)
measurements only. May be referred to as a "screening" test
chert A hard, extremely dense sedimentary rock consisting dominantly of interlocking crystals of
quartz. Crystals are not visible to the naked eye, giving the rock a milky, dull luster. It may be
white or gray but is commonly colored red, black, yellow, blue, pink, brown, or green.
clastic pertaining to a rock or sediment composed of fragments that are derived from preexisting
rocks or minerals. The most common clastic sedimentary rocks are sandstone and shale.
clay A rock containing clay mineral fragments or material of any composition having a diameter
less than 1/256 mm.
clay mineral One of a complex and loosely defined group of finely crystalline minerals made up
of water, silicate and aluminum (and a wide variety of other elements). They are formed chiefly by
alteration or weathering of primary silicate minerals. Certain clay minerals are noted for their small
size and ability to absorb substantial amounts of water, causing them to swell. The change in size
that occurs as these clays change between dry and wet is referred to as their "shrink-swell"
potential.
concretion A hard, compact mass of mineral matter, normally subspherical but commonly
irregular in shape; formed by precipitation from a water solution about a nucleus or center, such as
a leaf, shell, bone, or fossil, within a sedimentary or fractured rock.
conglomerate A coarse-grained, clastic sedimentary rock composed of rock and mineral
fragments larger than 2 mm, set in a finer-grained matrix of clastic material.
cuesta A hill or ridge with a gentle slope on one side and a steep slope on the other. The
formation of a cuesta is controlled by the different weathering properties and the structural dip of
the rocks forming the hill or ridge.
daughter product A nuclide formed by the disintegration of a radioactive precursor or "parent"
atom.
n-22 Reprinted from USGS Open-Rle Report 93-292
-------
delta, deltaic Referring to a low, flat, alluvial tract of land having a triangular or fan shape,
located at or near the mouth of a river. It results from the accumulation of sediment deposited by a
river at the point at which the river loses its ability to transport the sediment, commonly where a
river meets a larger body of water such as a lake or ocean.
dike A tabular igneous intrusion of rock, younger than the surrounding rock, that commonly cuts
across the bedding or foliation of the rock it intrudes.
diorite A plutonic igneous rock that is medium in color and contains visible dark minerals that
make up less than 50% of the rock, it also contains abundant sodium plagioclase and minor
quartz.
dolomite A carbonate sedimentary rock of which more than 50% consists of the mineral dolomite
(CaMg(CO3)2), and is commonly white, gray, brown, yellow, or pinkish in color.
drainage The manner in which the waters of an area pass, flow off of, or flow into the soil.
Also refers to the water features of an area, such as lakes and rivers, that drain it
eolian Pertaining to sediments deposited by the wind.
esker A long, narrow, steep-sided ridge composed of irregular beds of sand and gravel deposited
by streams beneath a glacier and left behind when the ice melted.
evapotranspiration Loss of water from a land area by evaporation from the soil and
transpiration from plants.
extrusive Said of igneous rocks that have been erupted onto the surface of the Earth.
/
fault A fracture or zone of fractures in rock or sediment along which there has been movement.
fluvial, fluvial deposit Pertaining to sediment that has been deposited by a river or stream.
foliation 'A linear feature in a rock defined by both mineralogic and structural characteristics. It
may be formed during deformation or metamorphism.
formation A mappable body of rock having similar characteristics.
glacial deposit Any sediment transported and deposited by a glacier or processes associated
with glaciers, such as glaciofiuvial sediments deposited by streams flowing from melting glaciers.
gneiss A rock formed by metamorphism in which bands and lenses of minerals of similar
composition alternate with bands and lenses of different composition, giving the rock a striped or
"foliated" appearance.
granite Broadly applied, any coarsely crystalline, quartz- and feldspar-bearing igneous plutonic
rock. Technically, granites have between 10 and 50% quartz, and alkali feldspar comprises at least
65% of the total feldspar.
gravel An unconsolidated, natural accumulation of rock fragments consisting predominantly of
particles greater than 2 mm in size.
heavy minerals Mineral grains in sediment or sedimentary rock having higher than average
specific gravity. May form layers and lenses because of wind or water sorting by weight and size
n-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 (CaCOa).
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.
t
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, imbedded glacial material,
predominantly till, deposited by the action of glacial ice.
outcrop That part of a geologic formation or structure that appears at the surface of the Earth, as
in "rock outcrop".
percolation test A term used in engineering for a test to determine the water permeability of a
soil. A hole is dug and filled with water and the rate of water level decline is measured.
permeability The capacity of a rock, sediment, or soil to transmit liquid or gas.
phosphate, phosphatic, phosphorite Any rock or sediment containing a significant amount
of phosphate minerals, i.e., minerals containing PO4.
H-24 Reprinted from USGS Open-File Report 93-292
-------
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, composmonally equivalent to granite.
sandstone A clastic sedimentary rock composed of sand-sized rockandi mmeral 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 metamorpmsm, that can be readily split into
thin flakes or slabs. Contains mica; minerals are typically aligned.
radon problem but does not indicate annual exposure to radon.
organisms.
semiarid Refers to a climate that has slightly more precipitation than an arid climate.
shale A fine-grained sedimentary rock formed from solidification (Unification) of clay or mud.
~!n«Sr^^^^^^
i
shrink-swell clay See clay mineral.
sat
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. .
H-25 Reprinted from USGS Open-File Report 93-292
-------
terrace gravel Gravel-sized material that caps ridges and terraces, left behind by a stream as it
cuts down to a lower level.
terrain A tract or region of the Earth's surface considered as a physical feature or an ecological
environment.
till Unsorted, generally unconsolidated and imbedded rock and mineral material deposited directly
adjacent to and underneath a glacier, without reworking by meltwater. Size of grains varies greatly
from clay to boulders. .
uraniferous Containing uranium, usually more than 2 ppm.
vendor data Used in this report to refer to indoor radon data collected and measured by
commercial vendors of radon measurement devices and/or services.
volcanic Pertaining to the activities, structures, and extrusive rock types of a volcano.
water table The surface forming the boundary between the zone of saturation and the zone of
aeration; the top surface of a body of unconfined groundwater in rock or soil.
weathering The destructive process by which earth and rock materials, on exposure to
atmospheric elements, are changed in color, texture, composition, firmness, or form with little or
no transport of the material.
11-26 Reprinted from USGS Open-File Report 93-292
-------
APPENDIX C
EPA REGIONAL OFFICES
F.PA Regional Offices
EPA Region 1
JFK Federal Building
Boston, MA 02203
(617) 565-4502
EPA Region 2
(2AIR:RAD)
26 Federal Plaza
New York, NY 10278
(212) 264-4110
Region 3 (3AH14)
841'Chestnut Street
Philadelphia, PA 19107
(215) 597-8326
EPA Region 4
345 Courtland Street, RE.
Atlanta, GA 30365
(404) 347-3907
EPA Region 5 (5AR26)
77 West Jackson Blvd.
Chicago, IL 60604-3507
(312) 886-6175
EPA Region 6 (6T-AS)
1445 Ross Avenue
Dallas, TX 75202-2733
(214) 655-7224
EPA Region 7
726 Minnesota Avenue
Kansas City,1 KS 66101
(913) 551-7604
EPA Region 8
(8HWM-RP)
999 18th Street
One Denver Place, Suite 1300
Denver, CO 80202-2413
(303) 293-1713
EPA Region 9 (A-3)
75 Hawthorne Street
San Francisco, CA 94105
(415) 744-1048
EPA Region 10
1200 Sixth Avenue
Seattle, WA 98101
(202) 442-7660
State
EPA Region
Alabama 4
Alaska » 1°
Arizona... 9
Arkansas 6
California 9
Colorado &•
Connecticut 1
Delaware '• 3
District of Columbia 3
Florida 4
Georgia *
Hawaii '. 9
Idaho - 1°
Illinois '
Indiana 5
Iowa 7
Kansas : 7
Kentucky *
Louisiana 6
Maine 1
Maryland 3
Massachusetts 1
Michigan • 5
Minnesota *
Mississippi 4
Missouri ^
Montana 8
Nebraska ^
Nevada • 9
New Hampshire 1
New Jersey . 2
New Mexico 6
NeW York : 2
North Carolina 4
North Dakota 8
. Ohio 5
Oklahoma: 6
Oregon 10
Pennsylvania • 3
Rhode Island , 1
South Carolina • 4
South Dakota 8
Tennessee 4
Texas 6
Utah 8
Vermont 1
Virginia 3
Washington 1°
West Virginia 3
Wisconsin 5
Wyoming *
n-27 Reprinted from USGS Open-FUe Report 93-292
-------
STATE RADON CONTACTS
May, 1993
Alabama James McNees
Division of Radiation Control
Alabama Department of Public
State Office Building
Montgomery, AL 36130
(205)242-5315
1-800-582-1866 in state
Charles Tedford
Department of Health and Social
Services
P.O. Box 110613
Juneau.AK 99811-0613
(907)465-3019
1-800-478-4845 in state
Arizona John Stewart
Arizona Radiation Regulatory Agency
4814 South 40th St.
Phoenix, AZ 85040
(602)255-4845
Arkansas LeeGershner
Division of Radiation Control
Department of Health /
4815 Markham Street, Slot 30
Little Rock, AR 72205-3867
(501)661-2301
California J. David Quinton
Department of Health Services,
714 P Street, Room 600
Sacramento, CA 94234-7320
(916) 324-2208
1-800-745-7236 in state
Colorado Linda Martin
Department of Health
4210 East llth Avenue
Denver, CO 80220
(303)692-3057
1-800-846-3986 in state
Connecticut Alan J. Siniscalchi
Radon Program
Connecticut Department of Health
Services
150 Washington Street
Hartford, CT 06106^474
(203)566-3122
Delaware MaraiG. Rejai
Office of Radiation Control
Division of Public Health
P.O. Box 637
Dover, DE 19903
(302) 736-3028
1-800-554-4636 In State
District Robert Davis
of Columbia DC Department of Consumer and
Regulatory Affairs
614 H Street NW
Room 1014
Washington, DC 20001
(202) 727-71068
Florida N. Michael Gilley
Office of Radiation Control
Department of Health and
Rehabilitative Services
1317 Winewood Boulevard
Tallahassee, FL 32399-0700
(904)488-1525
1-800-543-8279 in state
Georgia Richard Schreiber
Georgia Department of Human
Resources
878 Peachtree SL, Room 100
Atlanta, GA 30309
(404) 894-6644
1-800-745-0037 in state
Hawaii Russell Takata
Environmental Health Services
Division
591 Ala Moana Boulevard
Honolulu, ffl 96813-2498
(808) 58^4700
n-28
Reprinted firom USGS Open-File Report 93-292
-------
Idato
Illinois
Indiana
Iowa
Kansas
Kentucky
PatMcGavam
Office of Environmental Health
450 West State Street
Boise, ID 83720
(208) 334-6584
1-800-445-8647 in state
Richard Allen
Illinois Department of Nuclear Safety
1301 Outer Park Drive
Springfield, IL 62704
(217) 524-5614
1-800-325-1245 in state
Lorand Magyar
Radiological Health Section
Indiana State Department of Health
1330 West Michigan Street
P.O. Box 1964
Indianapolis, IN 46206
(317)633-8563
1-800-272-9723 In State
Donald A. Plater
Bureau of Radiological Health
Iowa Department of Public Health
Lucas State Office Building
Des Moines, IA 50319-0075
(515)281-3478
1-800-383-5992 In State
Harold Spiker
Radiation Control Program
Kansas Department of Health and
Environment
109 SW 9th Street
6th Floor Mills Building
Topeka, KS 66612
(913)296-1561
JeanaPhelps
Radiation Control Branch
Department of Health Services
Cabinet for Human Resources
275 East Main Street
Frankfort, KY 40601
(502) 564-3700
Louisiana Matt Schlenker
Louisiana Department of
Environmental Quality
P.O. Box 82135
Batoa Rouge, LA 7C "84-2135
(504) 925-7042
1-800-256-2494 in state
-Maine Bob Stilwell
Division of Health Engineering
Department of Human Services
State House, Station 10
Augusta, ME 04333
(207)289-5676
1-800-232-0842 in state
Maryland Leon L Rachuba
Radiological Health Program
Maryland Department of the
Environment
2500 Broening Highway
Baltimore, MD 21224
(410)631-3301
1-800-872-3666 In State
Massachusetts William J. Bell
Radiation Control Program
Department of Public Health
23 Service Center
Northampton, MA 01060
(413) 586-7525
1-800-445-1255 in state
'Michigan Sue Hendershott
Division of Radiological Health
Bureau of Environmental and
Occupational Health
3423 North Logan Street
P.O. Box 30195
Lansing, MI 48909
(517) 335-8194
Minnesota Laura Oatmann
Indoor Air Quality Unit
925 Delaware Street, SE
P.O. Box 59040
Minneapolis, MN 55459-0040
(612) 627-5480
1-800-798-9050 in state
n-29 Reprinted from USGS Open-File Report 93-292
-------
Mississippi Silas Anderson
Division of Radiological Health
Department of Health
3150 Lawson Street
P.O. Box 1700
Jackson, MS 39215-1700
(601)354-6657
1-800-626-7739 in state
Missouri Kenneth V. Miller
Bureau of Radiological Health
Missouri Department of Health
1730 East Elm
P.O. Box 570
Jefferson City, MO 65102
(314)751-6083
1-800-669-7236 In State
Montana Adrian C. Howe
Occupational Health Bureau
Montana Department of Health and
Environmental Sciences
Cogswell Building Al 13
Helena, MT 59620
(406)444-3671
Nebraska Joseph Milone
Division of Radiological Health
Nebraska Department of Health
301 Centennial Mall, South
P.O. Box 95007
Lincoln, NE 68509
(402)471-2168
1-800-334-9491 In State
Nevada Stan Marshall
Department of Human Resources
505 East King Street
Room 203
Carson City, NV 89710
(702)687-5394
New Hampshire David Chase
Bureau of Radiological Health
Division of Public Health Services
Health and Welfare Building
Six Hazen Drive
Concord, NH 03301
(603)271-4674
1-800-852-3345 x4674 .
. New Jersey Tonalee Carlson Key
Division of Environmental Quality
Department of Environmental
Protection
CN415
Trenton, NJ 08625-0145
(609) 987-6369
1-800-648-0394 in state
New Mexico William M. Floyd
Radiation Licensing and Registration
Section
New Mexico Environmental
Improvement Division
1190 St. Francis Drive"
Santa Fe,NM 87503
(505) 827-4300
New York William J. Condon
Bureau of Environmental Radiation
Protection
New York State Health Department
Two University Place
Albany, NY 12202
(518)458-6495
1-800-458-1158 in state
North Carolina Dr. Felix Fong
Radiation Protection Division
Department of Environmental Health
and Natural Resources
701 Barbour Drive
Raleigh, NC 27603-2008
(919) 57M141
1-800-662-7301 (recorded info x4196)
North Dakota Aden Jacobson
North Dakota Department of Health
1200 Missouri Avenue, Room 304
P.O. Box 5520
Bismarck, ND 58502-5520
(701)221-5188
Ohio Marcie Matthews
Radiological Health Program
Department of Health
1224 Kinnear Road - Suite 120
Columbus, OH 43212
(614) 644-2727
1-800-523-4439 in state
IE-30 Reprinted from USGS Open-File Report 93-292
-------
Oklahoma Gene Smith
Radiation Protection Division
Oklahoma State Department of
Health
P.O. Box 53551
Oklahoma City, OK 73152
(405) 271-5221
Oregon George Toombs
Department of Human Resources
Health Division
1400 SW 5th Avenue
Portland, OR 97201
(503)731-4014
Pennsylvania Michael Pyles
Pennsylvania Department of
Environmental Resources
Bureau of Radiation Protection
P.O. Box 2063
Harrisburg, PA 17120
(717) 783-3594
1-800-23-RADON In State
Puerto Rico David Saldana
Radiological Health Division
G.P.O. Call Box 70184 /
Rio Piedras, Puerto Rico 00936
(809) 767-3563
Rhode Island Edmund Arcand
Division of Occupational Health and
Radiation
Department of Health
205 Cannon Building
Davis Street
Providence, RI02908
(401) 277-2438
South Carolina
Bureau of Radiological Health
Department of Health and
Environmental Control
2600 Bull Street
Columbia, SC 29201
(803)7344631
1-800-768-0362
South Dakota MikePochbp
Division of Environment Regulation
Department of Water and Natural
Resources
Joe Foss Building, Room 217
523 E. Capitol
Pierre, SD 57501-3181
(605) 773-3351
Tennessee Susie Shimek
Division of Air Pollution Control
Bureau of the Environment
Department of Environment and
Conservation
Customs House, 701 Broadway
Nashville, TN 37219-5403
(615) 532-0733
1-800-232-1139 in state
Texas Gary Smith
Bureau of Radiation Control
Texas Department of Health
1100 West 49th Street
Austin, TX 78756-3189
(512)834-6688
Utah John Hultquist
Bureau of Radiation Control
Utah State Department of Health
288 North, 1460 West
P.O. Box 16690
Salt Lake City, UT 84116-0690
(801) 536-4250
Vermont Paul demons
Occupational and Radiological Health
Division
Vermont Department of Health
10 Baldwin Street
Montpelier, VT 05602
(802) 828-2886
1-800-640-0601 in state
Virgin Islands Contact the U.S. Environmental
Protection Agency, Region JJ
in New York
(212)2644110
H-31 Reprinted ftom USGS Open-File Report 93-292
-------
Virginia Shelly Ottenbrite
Bureau of Radiological Health
Department of Health
109 Governor Street
Richmond, VA 23219
(804)786-5932
1-800-468-0138 in state
Washington KateColeman
Department of Health
Office of Radiation Protection
Airdustrial Building 5, LE-13
Olympia,WA 98504
(206)753-4518
1-800-323-9727 In State
West Virginia BeattieL. DeBprd
Industrial Hygiene Division
West Virginia Department of Health
151 llth Avenue
South Charleston, WV 25303
(304) 558-3526
1-800-922-1255 In State
Wisconsin Conrad Weiffenbach
Radiation Protection Section
Division of Health
Department of Health and Social
Services
P.O. Box 309
Madison, WI53701-0309
(608) 267^796
1-800-798-9050 in state
Wyoming Janet Hough
1 Wyoming Department of Health and
Social Services
Hathway Building, 4th Floor
Cheyenne, WY 82002-0710
(307)777-6015
1-800-458-5847 in state
11-32 Reprinted firom USGS Open-File Report 93-292
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STATE GEOLOGICAL SURVEYS
May, 1993
Alabama Ernest A. Mancini
Geological Survey of Alabama
P.O. Box 0
420 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
James F. Davis
California Division of Mines &
Geology
801 K Street, MS 12-30
1 Sacramento, CA 95814-3531
(916)445-1923
Colorado Pat Rogers (Acting)
Colorado Geological Survey
1313 Sherman St., Rm 715
Denver, CO 80203
(303)866-2611
Connecticut Richard C. Hyde
Connecticut Geological & Natural
History Survey
165 Capitol Ave., Rm. 553
Hartford, CT 06106
(203) 566-3540
Delaware Robert R. Jordan
Delaware Geological Survey
University of Delaware
101 Penny Hall
Newark, DE19716-7501
(302)831-2833
Florida Walter Schmidt
Florida Geological Survey
903 W. Tennessee St.
Tallahassee, FL 32304-7700
(904)4884191
William H. McLemore
Georgia Geologic Survey
Rm. 400
19 Martin Luther King Jr. Dr. SW
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
Idaho 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
615EastPeabodyDr.
Champaign, IL 61820
(217) 3334747
Indiana Norman C. Hester
Indiana Geological Survey
611 North Walnut Grove
Bloomington, IN 47405
(812) 855-9350
Iowa Donald L. Koch
Iowa Department of Natural Resources
Geological Survey Bureau
109 Trowbridge Hall
Iowa City, IA 52242-1319
(319)335-1575
Kansas LeeC.Gerhard
Kansas Geological Survey
1930 Constant Ave., West Campus
University of Kansas
Lawrence, KS 66047
(913) 864-3965
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
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 PriscUla C. Grew
Minnesota Geological Survey
2642 University Ave.
St. Paul, MN 55114-1057
(612)627^780
Missouri James H. Williams
Missouri Division of Geology &
Land Survey
111 Fairgrounds Road
P.O. Box 250
Rolla, MO 65401
(314) 368-210&
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
Jonathan G. Price
Nevada Bureau of Mines & Geology
Stop 178
University of Nevada-Reno
Reno, NV 89557-0088
(702) 784-6691
Mississippi S. Cragin Knox
Mississippi Office of Geology
P.O. Box 20307
Jackson, MS 39289-1307
(601) 961-5500
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 RFakundiny
New York State Geological Survey
3136 Cultural Education Center
Empire State Plaza
Albany, NY 12230
(518)474-5816
11-34 Reprinted rrom USGS Open-File Report 93-292
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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
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
100E.Boyd
Norman, OK 73019-0628
(405) 325-3031
Oregon Donald A. Hull
DepL of Geology & Mineral Indust.
Suite 965
800 ME Oregon St. #28 /
Portland, OR 97232-2162
(503)7314600
Pennsylvania Donald M. Hoskins
Dept. of Environmental Resources
Bureau of Topographic & Geologic
Survey
P.O. Box 2357
Harrisburg, PA 17105-2357
(717) 787-2169
Puerto Rico Ramdn M. Alonso
Puerto Rico Geological Survey
Division
Box 5887
Puerta de Tierra Station
San Juan, P.R. 00906
(809) 722-2526
Rhode bland J. Allan Cain
Department of Geology
University of Rhode Island
315 Green Hall
Kingston, RI02881
(401) 792-2265
South Carolina Alan-Jon W. Zupan (Acting)
South Carolina Geological Survey
5 Geology Road
Columbia, SC 29210-9998
(803)737-9440
South Dakota CM. Christensen (Acting)
South Dakota Geological Survey
Science Center
University of South Dakota
Vermfflion, 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
11-35 Reprinted from USGS Open-File Report 93-292
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West Virginia Larry D.Woodfoik
West Virginia Geological and
Economic Survey
Mont Chateau Research Center
P.O. Box 879
Morgantown,WV 26507-0879
(304)594-2331
Wisconsin James Robertson
Wisconsin Geological & Natural
History Survey
3817 Mineral Point Road
Madison, WI 53705-5100
(608)263-7384
Wyoming Gary B. Glass
Geological Survey of Wyoming
University of Wyoming
Box 3008, University Station
Laramie, WY 82071-3008
(307) 766-2286
H-36 Reprinted from USGS Open-File Report 93-292
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EPA REGION 9 GEOLOGIC RADON POTENTIAL SUMMARY
by
James K. Otton, Douglass E. Owen, Russell F. Dubiel,
G. Michael Reimer, and Sandra L. Szarzi
U.S. Geological Survey
EPA Region 9 includes the states of Arizona, California, Hawaii, and Nevada. For each
state, geologic radon potential areas were delineated and ranked on the basis of geologic, soils,
housing construction, and other factors. Areas in which the average screening indoor radon level
of all homes within the area is estimated to be greater than 4 pCi/L were ranked high. Areas in
which the average screening indoor radon level of all homes within the area is estimated to be
between 2 and 4 pCi/L were ranked moderate/variable, and areas in which the average screening
indoor radon level of all homes within the area is estimated to be less than 2 pCi/L were ranked
low. Information on the data used and on the radon potential ranking scheme is given in the
introduction to this volume. More detailed information on the geology and radon potential of each
state in Region 9 is given in the individual state chapters. The individual chapters describing the
geology and radon potential of the states in EPA Region 9, 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.
The continental part of Region 9 includes thirteen distinct major geologic provinces: the
Klamath Mountains, the Cascade Range, the Modoc Plateau, the Sierra Nevada, the Great Valley,
the Northern Coast Ranges, the Southern Coast and Transverse Ranges, the Peninsular Ranges,
the Colorado Desert, the Basin and Range, the Mojave-Sonoran Desert, the Transition Zone, and
the Colorado Plateau (fig. 1). Hawaii forms its own distinctive geologic province. The moderate
climate, use of air conditioning, evaporative coolers, or open windows, and the small number of
houses with basements throughout much of Region 9 contribute to generally low indoor radon
levels in spite of the fact that this area has some of the highest surface radioactivity of any area in
the United States.
Maps showing arithmetic means of indoor radon data from State/EPA Residential Radon
Surveys of counties in California, Nevada, Arizona, and Hawaii are shown in figure 2. County
sacreening indoor radon averages range from less than 1 pCi/L to 4.6 pCi/L. Details of the indoor
radon studies are described in the individual state chapters.
Klamath Mountains
The Klamath Mountains (1, fig. 1) are underlain by Paleozoic and Mesozoic metavolcanic
and metasedimentary rocks, Jurassic ultramafic rocks, and Mesozoic granitic intrusive rocks. The
Klamath Mountains overall exhibit the lowest eU values in the continental part of Region 9. Most
areas have less than 0.5 parts per million equivalent uranium (ppm eU). Values range from 0.5 to
1.5 ppm eU in some areas. Only one small area has more than 1.5 ppm eU. The Klamath
Mountains are considered to have low radon potential due to the relatively low eU and the high
rainfall and soil moisture. Some structures sited on steeply-sloped soils, or excessively well-
drained, permeable alluvium may have indoor radon levels exceeding 4 pCi/L.
ffl-1 Reprinted from USGS Open-FUe Report 93-292-1
-------
o
-------
Bsmt & 1st Floor Indoor Radon
Arithmetic Mean (pCi/L)
0.0 to 1.0
1.1 to 1.9
2.0 to 3.0
3.1 to 4.0
4.-1 to 4.6
Missing Data
(< 5 measurements)
100 Miles
Figure 2. Screening indoor radon data from the State/EPA Residential Radon Survey, for
counties with 5 or more measurements in EPA Region 9. 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 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.
-------
Cascade Range
uascaae Kange
The Cascade Range (2, fig. 1) is underlain primarily by Upper Tertiary and Quaternary
extrusive rocks, mainly basalt and lesser andesite and rhyolite. In the Cascade Range eU values
range generally from less than 0.5 ppm to 1.5 ppm, however local eU values of as much as
4 5 ppm are present where silicic volcanic rocks occur.
The Cascade Range is thought to have low radon potential overall in spite of the scattered
areas of moderate eU values. The indoor data are sparse in this lightly populated area. Soils are
drier here than in areas closer to the coast and this could contribute to some locally elevated indoor
radon levels in spite of relatively low eU. Steep topography and excessively well-drained soils
may also contribute to some locally elevated indoor radon levels (for the purposes of this
discussion, "elevated", when used in the context of indoor radon, refers to levels greater than
4pCi/L).
Modoc Plateau . .
The Modoc Plateau (3, fig. 1) is underlain by Tertiary basalt flows, Upper Tertiary to
Quaternary basalt flows, and lesser amounts of andesite and rhyolite. Like the Cascade Range, eU
values in the Modoc Plateau generally range from less than 0.5 ppm to 1.5 ppm eU; however,
locally higher eU values occur near outcrops of silicic volcanic rocks.
The Modoc Plateau has low radon potential overall in spite of the locally moderate eU
signatures. Like the Cascade Range, the indoor data are sparse in this lightly populated area, and
soils are drier here than in areas closer to the coast Steep topography and excessively well-drained
dry soils-may contribute locally to some elevated radon values indoors.
Sierra Nevada / ,,.
The northern part of the Sierra Nevada (4, fig. 1) is underlain by Paleozoic and Mesozoic
metamorphic rocks with lesser Mesozoic granitic rocks, whereas in the southern part, Mesozoic
granitic rocks predominate with lesser outcrop areas of Mesozoic metamorphic rocks. In the
northern part, Tertiary volcanic rocks, including basalt, rhyolite, and the sedimentary rocks denved
from them, crop out along the crests of many ranges. .
The metamorphic rocks and early Mesozoic granites of the northern Sierra Nevada typically
have low eU values ranging from less than 0.5 to 1.5 ppm. However, from Lake Tahoe
southward the rocks show persistently high eU values, with large areas ranging from 3.0 to greater
than 5.5 ppm. Low values occur only where areas of basaltic volcanic rocks, metamorphosed
sedimentary rocks, or ultramafic rocks crop out In the central and southern Sierra Nevada, these
lower eU values are restricted to rocks of the western foothills.
The Sierra Nevada has moderate radon potential overall owing to high eU throughout much
of the province and the predominance of steeply sloped, well-drained soils that are likely to favor
radon transport Small areas with high potential are most likely in areas of elevated eU south of the
latitude of Lake Tahoe.
Great Valley
The Great Valley (5, fig. 1) is underlain by surficial materials composed of Quaternary
alluvium derived largely from the Sierra Nevada to the east and the Coast Ranges to the west
Equivalent uranium values for rocks and soils in the Great Valley are influenced greatly by the
uranium content of material supplied by the nearby mountains. The northernmost part of the Great
Valley has eU values that generally range from 0.5 to 2.5 ppm, except for the Sutler Buttes area
m-4 Reprinted from USGS Open-FUe Report 93-292-1
-------
which has values of as much as 5.5 ppm eTJ. From Sacramento southward, the eU signature of
the alluvium on the east flank of the valley increases, and eU values locally exceed 5.5 ppm.
Alluvial fans derived from less uraniferous rocks in the Sierra foothills locally have lower eU
signatures, some as low as 0.5 ppm. Alluv' ' fans fr DP- •*••* Southern C ast Ranges also vary in
eU values, but overall they are lower than those derived from the Sierra Nevada. An exception to
this occurs in the southernmost Great Valley, where uranium-bearing marine sedimentary rocks of
the Southern Coast Ranges contribute alluvium to the valley floor.
The Great Valley has-low radon potential-overall. The area along the east side of the valley
from Sacramento southward, however, appears more likely to have elevated average indoor radon
levels and a greater percentage of homes over 4 pCi/L than the rest of the Great Valley.
Northern Coast Ranges
The Northern Coast Ranges (6, fig. 1) are underlain principally by the Franciscan
Complex, an assemblage of metamorphosed marine sedimentary rocks and ultramafic rocks.
Cretaceous sedimentary rocks lie along the eastern edge of the Northern Coast Ranges and some
volcanic rocks occur in the southern part of the Coast Ranges. Numerous major strike-slip faults
tend to align the mountain ranges parallel to the Pacific Coast
Equivalent uranium values of 0.5 to 1.5 ppm characterize the Franciscan rocks of most of
the Northern Coast Ranges. Higher eU values are associated with Quaternary and Tertiary
extrusive rocks, especially those found north of the San Francisco Bay area, where eU signatures
of as much as 4.5 ppm were measured.
The Northern Coast Range province has low radon potential overall. Some indoor radon
levels greater than 4 pCi/L are likely to occur in areas of elevated eU along the east side of the
southern half of this province, especially where steep, excessively well-drained, or highly
permeable soils coincide with the elevated eU in soils.
Southern Coast and Transverse Ranges
The Southern Coast Ranges (7, fig. 1) include the Franciscan and Cretaceous rocks
mentioned above, Triassic metamorphic rocks and Mesozoic granitic rocks, and a series of fault-
bounded linear basins in which Tertiary marine and continental sedimentary rocks were deposited.
The San Andreas fault and other parallel faults pass through the Southern Coast Ranges. Mountain
ranges tend to be aligned parallel to these faults.
Equivalent uranium values vary significantly for the Southern Coast Ranges. Values for
Franciscan metamorphic rocks, Triassic metamorphic rocks, and Tertiary sedimentary rocks
derived from them generally range 0.5-2.0 ppm eU. Mesozoic granitic rocks, Tertiary sedimentary
rocks derived from them, and Tertiary marine sedimentary rocks deposited in restricted
environments locally exceed 5.5 ppm eU.
The Transverse Ranges are an east-west trending mountain block bordered and transected
by several faults, including the San Andreas fault. The eastern part of the Transverse Ranges are
underlain by Precambrian metamorphic rocks and Mesozoic granitic rocks, whereas the western
part of the Province is underlain principally by Cretaceous to Pliocene marine sedimentary rocks.
The Los Angeles Basin, considered part of this physiographic province, is underlain by surficial
materials composed primarily of Quaternary alluvium. The Transverse Ranges generally exhibit
low eU (1.0-2.0 ppm) in the eastern part, which is underlain by Precambrian metamorphic rocks
and Mesozoic intrusive rocks, but in the western Transverse Ranges many of the sedimentary units
contain more uranium (as much as 5.5 ppm eU). The western area includes marine sedimentary
ffl-5 Reprinted from USGS Open-File Report 93-292-1
-------
rock deposited in restricted marine environments favorable for uranium accumulation and
continental sedimentary rocks containing uranium occurrences.
connnema^^^ y^^^^TnmsverseRangeshavemoderateradonpotentiai overall;
' >v Sver,muchof the radon potential associated with areas of elevated radioacuv^ from
Monte^ Bay southward in the Coast Range and in the western two-thirds of the Transverse
Sges Houses sited directly on uranium-enriched marine sedimentary rocks in these two areas
S2 the Monterey Formation and the Rincon Shale, are very likely to exceed 4 pO/L, especially
where parts of the home are below grade.
me i-eninsuiar juuig^ A fig- D «* dominated by Mesozoic granitic rocks with lesser
Mesozoic metamoxphic rocks. Tertiary sedimentary rocks lie along the coast Mesozoic intrusive
rocks of the Peninsular Ranges are generally low in uranium, with eU values ranging 1.0-2.5
ppm. Some areas of Tertiary sedimentary rocks and Mesozoic granitic rocks are more uraniferous.
The Peninsular Ranges have low'radon potential as indicated by the low to moderate eU across the
area. Areas of elevated eU and excessively drained soils in the foothills east of the San Diego
metropolitan area may locally yield some elevated radon levels indoors.
° ^ The Colorado Desert (9, fig.l) is underlain by Quaternary alluvium derived from the
adjacent mountains. Equivalent uranium signatures over the Colorado Desert vary significantly.
Some Quaternary alluvium derived from rocks in the adjacent Mojave Desert are elevated in eU
(>2.5 ppm), but other areas range from 1.0-2.5 ppm eU.
The Colorado Desert provinces has a low potential for radon indoors.
Basin ^^ ^ Range (1Q) fig 1} is composed Of Precambrian metamorphic rocks late
Precambrian and Paleozoic metamorphosed and unmetamorphosed sedimentary and less abundant
igneous rodcs, Mesozoic metamoiphosed and unmetamorphosed volcanic and sedimeruary rocks,
Mesozoic and Tertiary intrusive rocks, and Tertiary sedimentary and volcanic rocks. The region is
structurally complex, with the aforementioned rocks forming the mountain ranges and alluvium
derived from the ranges filling the basins. Sedimentary rocks of the mountain ranges include
marine carbonates, shales, cherts, quartzites, and sandstones, as well as fluvial and continental
sandstones, siltstones, and shales. Locally, uranium deposits occur in the sedimentary rocks.
The Basin and Range also shows variation in eU related to mapped rock units.
Precambrian metamorphic rocks, most Mesozoic granitic rocks, and Tertiary silicic volcanic rocks
have elevated eU values. Tertiary sedimentary rocks and Quaternary alluvium derived from the
uraniferous rocks of the ranges and from uraniferous rocks of the Sierra Nevada to the west are
generally also uranium-enriched. All these rocks generally range from 2.5 to greater then 5.5 ppm
eU Late Precambrian and Paleozoic sedimentary and metamorphosed sedimentary rocks,
Mesozoic diorite, early Mesozoic granites, and alluvium derived from them contain less uranium,
typically ranging from 0.5 to 2.5 ppm eU. These latter rocks are widely exposed in the iuca
around Las Vegas and contribute to the low eU signature observed in the mountains and valleys in
Overall the Basin and Range has moderate radon potential. Areas with moderate and
locally high radon potential include the Tertiary volcanic rocks, particularly the Miocene and
ffl-6 Reprinted from USGS Open-File Report 93-292-1
-------
Pliocene age rocks that are found throughout the Basin and Range Province, Precambrian gneiss in
southern Nevada, and the Carson Valley alluvium, which is derived from uraniferous granites in
the Sierra Nevada.
Mojave-Sonoran Desert
The Mojave-Sonoran Desert (11, fig. 1) consists of faulted mountain ranges that are
partially or completely surrounded by late Cenozoic basins. Uplifted rocks in the ranges consist
primarily of Preeambrian metamorphic, igneous, and sedimentary rocks, variably altered and
metamorphosed Paleozoic to Cenozoic sandstone and limestone, and Tertiary plutonic and volcanic
rocks. Mesozoic sedimentary rocks occur in some mountain blocks. The intervening basins are
filled by fluvial, lacustrine, colluvial, and alluvial-fan deposits.
From the central Mojave Desert to Tucson in the eastern Sonoran Desert, most of the rocks
of the mountains and the intervening basins contain more than 2.5 ppm ell, with a broad area of
mountains and adjacent valley alluvium in southeasternmost California and westernmost Arizona
above 5.5 ppm eU. In the western Mojave, much of the area has eU in the 1.0-2.5 ppm range,
except for the area underlain by the Tertiary sedimentary rocks of the Barstow Basin, where values
of as much as 4.5 ppm eU occur. Highly uraniferous Tertiary lacustrine sedimentary rocks are
exposed in many of the basins. Uranium occurrences and deposits are numerous.
The Mojave-Sonoran Desert Province has moderate radon potential overall due to its high
eU signature. Highest indoor radon levels are to be expected where homes are sited on uranium-
bearing rocks, such as Tertiary lacustrine sedimentary rocks or fractured granites.
Transition Zone
The Transition Zone (12, fig./l), running generally southeast to northwest across the
central part of Arizona, contains mountainous areas of uplifted plutonic and metamorphic rocks,
with many intervening valleys rilled with upper Cenozoic alluvium and lacustrine deposits. Many
of the granitic rocks of the mountainous areas are enriched in uranium and have elevated eU values
(3 ppm eU, or more). Some of the lacustrine rocks in the intervening valleys are also uraniferous
and host uranium deposits.
The Transition Zone has moderate radon potential. Elevated to extreme indoor radon levels
may occur if a home is sited on a uranium occurrence, fractured uraniferous granite, or uraniferous
lacustrine rocks.
Colorado Plateau
The Colorado Plateau (13, fig. 1) covers the northeastern third of Arizona. Subhorizontal
to gently folded Paleozoic to Cenozoic sedimentary strata composed mostly of sandstone,
limestone, shale, and coal cover the entire area. In the deepest parts of the Grand Canyon,
Precambrian sedimentary, igneous, and metamorphic rocks are exposed. Locally, Tertiary and
Quaternary volcanic rocks cover the sedimentary strata. Many of the sedimentary rocks are
anomalously uraniferous, notably the Cretaceous and Triassic sandstones and shales. Locally,
these units host substantial sandstone uranium deposits. Breccia pipe uranium deposits occur in
the Grand Canyon area. The areas where these deposits occur is generally sparsely populated.
The Colorado Plateau has moderate radon potential overall. Elevated to extreme indoor
radon levels may occur if a structure is sited on one of the uraniferous shales or sandstones or on a
uranium occurrence.
m-7 Reprinted from USGS Open-FUe Report 93-292-1
-------
The volcanic island chain of Hawaii (14, fig. 1) consists of Tertiary to Recent volcanic
rock predominantly basaltic lavas, ashes, and tuffs, with minor carbonate and clastic marine
sediments, alluvium, colluvium, dune sands, and mudflow deposits. Although some soil gas
contains greater than 500 pCi/L radon, the low uranium content of the rocks throughout the
islands the local architecture, and the lifestyle of the inhabitants contributes tolhe overall very low
potential for indoor radon in the islands. About 0.4 percent of the homes measured in the
State/EPA Residential Radon Survey in Hawaii exceed 4 pCi/L.
m-8 Reprinted from USGS Open-File Report 93-292-1
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- PRELIMINARY GEOLOGIC RADON POTENTIAL ASSESSMENT OF NEVADA
by
Douglass E. Oweri
U.S. Geological Survey
INTRODUCTION
Nevada is an arid western state bordered by Utah and Arizona on the east, California on the
south and west, and by Oregon and Idaho on the north. Most of Nevada receives less than 10
inches (25 cm) of precipitation per year (Manahan, 1990). Nevada is subdivided into 17 counties,
most of which cover vast land areas (fig. 1). Most of Nevada has a sparse population; 8 of the
counties have less than 10,000 inhabitants, and only 2 counties have more than 100,000 people
(fig. 2). The population is concentrated in two clusters, one in the vicinity of Las Vegas and the
other in the Reno/Carson City area (fig. 2).
This is a generalized assessment of geologic radon potential of rocks, soils, and surficial
deposits of Nevada. 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
GEOGRAPHIC SETTING
i
Almost all of Nevada lies within the Basin and Range Province, and most of Nevada is in
the Great Basin Section of this province (fig. 3). The Great Basin Section is characterized by
isolated mountain ranges separated by aggraded desert plains (Peterson, 1981). The southern tip
of Nevada is in the Sonoran Desert Section of the Basin and Range Province (fig. 3), and is
characterized by widely separated mountain ranges in desert plains (Peterson, 1981). The
mountainous western side of Nevada, where the state line turns to the north, lies within the Sierra
Nevada Province. The Owyhee Upland is adjacent to the Snake River Plain and extends into
Nevada along the State's border with Idaho. The Owyhee Upland is an area of low relief and
moderate elevation (Stewart, 1980).
Mountain ranges in Nevada generally rise 1,000 to 5,000 feet (300 to 1,500 m) above the
adjacent valleys and have widths that range from 5 to 15 miles (8 to 24 km) (Stewart, 1980). The
valleys tend to be similar in width to their corresponding mountain ranges. Typically the mountain
ranges are elongate with a north-northeast orientation and many of the ranges extend for more than
50 miles (80 km) (Stewart, 1980). The lowest elevations in the State are found along the Colorado
River in the south. Boundary Peak, the highest point in the State, has an elevation of 13,145 feet
(4,006 m) and is located in the White Mountains near the California-Nevada state line.
IV-1 Reprinted from USGS Open-File Report 93-292-1
-------
Carson Chy
Fig. 1. Counties
-------
* * * * * j * * ***2* ***
*********AM**
POPULATION (1990)
Q 0 to 10000
E3 10001 to 25000
0 25001 to 50000
H 50001 to 100000
• 100001 to 741459
Figure 2. Population of counties in Nevada (1990 U.S.. Census data).
-------
Sierra
Nevada
Mountains
XOwyhee Uplands
***************
Sonoran
^Desert
>£iSection
FigureS. Physiographic provinces of Nevada (after Peterson, 1981). Areas listed as
"sections" are subdivisions of the Basin and Range Province.
-------
GEOLOGIC SETTING
Nevada is a large state with a complex, fault-dominated geology consisting of rocks and
sediments that range in age from Precambrian to Holocene. Stewart (1980) gives the following
summary of the geology and geologic history of Nevada:
"Nevada has had a long and complex geologic history that includes major
episodes of sedimentation, igneous activity, orogenic deformation [mountain
building], and continental rifting. The record of this history starts in the
Precambrian and is well documented throughout the Phanerozoic [Cambrian and
later time].
The oldest rocks in Nevada crop out in the southernmost part of the State
and consist of metamorphic and intrusive rocks of Precambrian age containing
folded granite lenses dated as 1,740 m.y. [million years] old. These rocks are
intruded by porphyritic rapakivi granite [granite that is characterized by alkali
feldspar phenocrysts that are mantled with plagioclase] dated as 1,450 m.y. old.
The next youngest rocks in Nevada are uppermost Precambrian to Upper
Devonian shallow-water subtidal to supratidal terrigenous detrital and carbonate
strata deposited on a broad shelf along the western margin of North America. This
deposition created a prism of sediment (the Cordilleran miogeocline) that thickens
from a few thousand feet in cratonic areas [areas that have obtained stability and
have had little deformation for a long time] in central Utah to nearly 30,000 feet
(10,000 m) in central Nevada. Coeval [same age] rocks in western Nevada are
considered to be mainly deep-water strata and consist predominantly of shale,
radiolarian chert, quartzite, arid mafic pillow lava.
During the Late Devonian and Early Mississippian, wide-spread orogenic
activity of the Antler orogeny affected Nevada and resulted in the emplacement of
the Roberts Mountains allochthon [a mass of rock that has been moved from its
place of origin by tectonic processes], a sheet of oceanic siliceous and volcanic
assemblage rocks thrust eastward as much as 90 miles (145 km) over coeval shelf
carbonate rocks. This orogeny produced the Antler highland, an upland belt
trending north-northeast medially hi Nevada along what was formerly the edge of
the shelf.
During the late Paleozoic, the sedimentary and tectonic provinces in Nevada
were, from east to west, (1) a shallow-water carbonate shelf; (2) a foreland basin
containing coarse detrital material derived from the west as well as more widespread
shallow-water carbonate sediments; (3) the Antler highland, overlapped in
Pennsylvanian and Permian time by thin coarse detrital marine sediments; (4) a
western deep-water basin containing fine to coarse detrital rocks, radiolarian chert,
silty-limestone, and mafic lava; and (5) a Permian magmatic arc terrane, largely of
mafic lava.
During the Late Permian and Early Triassic, Nevada was subjected to
another major orogeny (the Sonoma orogeny) during which ocean-floor sediments
were thrust eastward as part of the Golconda allochthon for perhaps as much as 60
miles (100 km) over shallow-water deposits on the Antler highland.
IV-5 Reprinted from USGS Open-File Report 93-292-1
-------
Mesozoic sedimentary rocks in Nevada are largely of Triassic and Early
Jurassic age and occur in an eastern and a western region. In the eastern region,
strata are the western continuation of shallow-water marine and continental, largely
terrigenous detrital deposits that are extensively exposed to the east in the Colorado
Plateau region of Utah and Arizona. In the western region, shallow-water marine
carbonate and deeper water mudstone give way westward into a complex of
volcanogenic sediments and lavas and fine-grained detrital rocks. Sedimentary
rocks of Cretaceous age occur at scattered localities in Nevada and consist of
continental sediments deposited in local basins.
Jurassic and Cretaceous igneous rocks occur widely in western Nevada and
at scattered localities elsewhere in the State. Those in western Nevada are along the
eastern margin of the Sierra Nevada batholith.
During the Mesozoic, tectonic activity was widespread in Nevada. After the
Sonoma orogeny, folding and thrusting may have started again as early as the Late
Triassic or Early Jurassic.and by the mid-Jurassic, were extensive in western
Nevada. During the remainder of the Mesozoic, tectonic activity probably prevailed
throughout much of the State, culminating in the major tectonic deformation of the
late Mesozoic Sevier orogeny in western Utah and easternmost Nevada.
Rocks of early Cenozoic age are sparse in Nevada, During this time, the
State was probably high and undergoing erosion. During middle Cenozoic time,
volcanic activity was widespread in Nevada, starting about 43 m.y. ago in the
northernmost part of the State and moving gradually southward. Voluminous
siliceous ash-flow tuffs were erupted about 34 to 17 m.y. ago in an east-trending
belt across the central part of the State.
About 17 m.y. ago, a-major change occurred in the tectonic setting of
Nevada with the onset of extensional faulting and the eruption of basalt or bimodal
assemblages of basalt and rhyolite. During the past 17 m.y., the major basins and
ranges that characterize the present-day physiography of the State formed by
extensional block faulting, and continental sediments were trapped in fault-related
basins."
Figure 4 is a small-scale geologic map of Nevada generalized from the geologic map of
Nevada (Stewart and Carlson, 1977). The complex and varied geology of a state like Nevada
cannot be satisfactorily shown on a page size map; see Stewart and Carlson (1977) for a more
detailed geologic map and Stewart (1980) for a more detailed discussion of the geology of Nevada.
SOILS
Most of the soils in the basins of Nevada are arid soils (fig. 5). These soils are usually
light colored, but are often reddish and calcareous. Except where carbonate buildup is heavy, the
soils formed on alluvium and colluvium shed from the mountain ranges are probably at least
moderately permeable. The surficial geology map of Hunt (1979) shows the basin deposits as fan
gravels, an indication that the basin soils typically have high permeabilities. However, many of the
basins or valleys also contain broad areas of lacustrine and playa deposits with lower permeability.
Most of the soils developed on the uplands are shallow or immature (fig. 5). The semiarid soils in
IV-6 Reprinted from USGS Open-File Report 93-292-1
-------
42°
120'
39°-l
| Oa
l.'Qtv
I Kim
|Mzr
EXPLANATION
AlkivW «nd pl. rtiyoiM. Hide Ml. Wnxi ra
roeka (17-43 m.y.): i*ac aid. myedn.
Tuttooou* wttnwilwy i^M (»-" -.
imounu « MI. m»y kx*x). reou rt CXHUmtf/ x*.
Cnou.lv. redo: grmnBc and <*xtfc roan « UMOZO
and porpnyflUo or apnuulc Wn«*»
>nd m««m«plilw.canglonwiu.iaMylliTiMli>ioaiK)lliT»iu»»iKxigUw
cmmon«« TO* In tonuM turn of on *>•«.
j . .
UIM m«»sin « » MM orojxie OK:
quvon. ImMMin. «ndBf««MW>».
OAonm >nd tmn.»lor»l ~ Mmbtag«i (PraonUxten I
In m«
.i^iolc); roou
IHMIWW and limy
XBUM md IMMT »moun» ol ft
...
PT»C»ITWWI Z «nd Lo~r Cimonm (ecu. oxiux « pnyiync
iMOon^ dotanM. suxtttoiM. and quain
M-Mnoipftfc!«-lnu>J«~foc*c.
-------
Immature or Shallow
Alluvial
Sub-Humid, dark
Semi-Arid, moderately dark
Ffg. 5. Soils
-------
Nevada are moderately dark to dark in color and occur primarily in the western and northern parts
of the State (fig. 5).
INDOOR RADON DATA
Figure 6 shows the indoor radon data for the State/EPA Residential Radon Survey of
Nevada. Table 1 shows the number of measurements and other statistics for the data set Two
counties, Douglas and Lincoln, had average radon concentrations greater than 4 pCi/L for the
homes measured (fig. 6). In three counties (Douglas, Lincoln, and Mineral), between 30 and 40
percent of the homes tested had screening indoor radon concentrations greater than 4 pCi/L (fig. 6
and Table 1). [Note: The indoor radon data base for the State continues to grow, and since the
data was provided for figure 6 there have been more measurements made in Pershing County that
would significantly change the results depicted for that county!. Out of 15 measurements, 6 are
above 4 pCi/L with the maximum being 40.7 pCi/L.]
The Nevada Bureau of Mines and Geology (1991) analyzed the 1989 and 1990-1991 radon
survey data for communities that had at least 10 indoor radon measurements (Table 2). In the
following communities, 10 percent or less of the homes tested had screening indoor radon
concentrations greater than 4 pCi/L: Alamo, Battle Mountain, Boulder City, Fallon, Fernley,
Gabbs, Goldfield, Henderson, Las Vegas, Lund, McDermitt, McGill, North Las Vegas,
Parhrump, Paradise Valley, Round Mountain, Sparks, and Tonopah. Eleven to 50 percent of the
homes tested had indoor radon concentrations greater than 4 pCi/L in Austin, Beatty, Caliente,
Carlin, Carson City, Dayton, Elko, Ely, Eureka, Gardnerville, Hawthorne, Minden, Pioche,
Reno, Ruby Valley, Ruth, Wells, Wendover, Winnemucca, and Yerington. Only the following
communities had screening indoor radon levels greater than 4 pCi/L in more than 50 percent of the
homes tested: Lovelock, Orvada, Pariaca, and Zephyr Cove, Li year-long studies conducted in the
Las Vegas area, Nyberg and Bernhart (1983) found that indoor radon levels showed a seasonal
trend with the highest radon levels occurring in the month of October.
During the relatively cold winter of 1989, the Nevada Bureau of Mines and Geology
conducted a survey of indoor radon in 238 Nevada homes, which were widely distributed across
the State, and found that 21 percent of the homes had indoor radon concentrations greater than
4 pCi/L (Rigby, 1989a; Rigby 1989b; Rigby, 1990a). Additional measurements were made, and
with a data base of 1,950 indoor radon measurements the percentage of the homes with greater
than 4 pCi/L was 17.7 percent (Rigby, 1990b). In 1991, with a data base of 2,355 measurements
(Nevada Bureau of Mines and Geology, 1991), the percentage of homes with greater than 4 pCi/L
stood at 19 percent. When weighted to compensate for variability in sampling intensity (giving
more weight to urban areas), the Bureau concluded that about 10 percent of Nevadans live in
houses with radon levels greater than 4 pCi/L (Nevada Bureau of Mines and Geology, 1991).
GEOLOGIC RADON POTENTIAL
High radon potential is generally linked to rocks with relatively high uranium contents and
is not limited to areas around known uranium-mineral occurrences. Nonetheless, areas in the
vicinity of known uranium occurrences have a high radon potential for several reasons other than
the unlikely occurrence that homes would be built over an ore body itself. These reasons are: (1)
noncommercial concentrations of uranium are often also present in an area that contains ore-grade
deposits; (2) even minor mineralization of uranium (primary or secondary) along faults and
IV-9 Reprinted from USGS Open-FUe Report 93-292-1
-------
Bsmt & 1st Floor Rn
% > 4pCi/L
7 IXNXNX1
OtolO
11 to 20
21 to 30
31 to 40"
Missing Data
or < 5 measurements
100 Miles
Bsmt. & 1st Floor Rn
Average Concentration (pCi/L)
0.0 to 1.9
2.0 to 4.0
4.1 to 4.6
Missing Data
or < 5 measurements
in iX\\X\X\>l
100 Miles
Figure 6. Screening indoor radon data from the State/EPA Residential Radon Survey of
Nevada, 1989-90, 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 EPA/State Residential Radon Survey of
Nevada conducted during 1989-90. Data represent 2-7 day charcoal canister measurements
from the lowest level of each home tested.
COUNTY
CARSON CITY
CHURCHILL
CLARK
DOUGLAS
ELKO
ESMERALDA
EUREKA
HUMBOLDT
LANDER
LINCOLN
LYON
MINERAL
NYE
PERSHING
STOREY
WASHOE
WHITE PINE
NO. OF
MEAS.
64
110
188
52
185
11
21
204
40
103
53
54
120
6
3
154
194
MEAN
3.0
2.3
1.1
4.2
2.7
1.3
3.5
•2.3
3.1
4.6
2.3
4.0
1.8
0.8
2.1
2.7
3.3
GEOM.
MEAN
2.1
1.6
0.6
2.2
1.6
1.0
1.6
1.3
1.1
2.0
1.4
2.5
1.1
0.6
2.1
1.2
2.1
MEDIAN
2;5
1.8
0.8
2.1
1.8
1.2
1.4
1.3
1.2
2.7
1.6
3.1
1.2
0.8
2.1
1.3
2.3
STD.
DEV.
2.9
2.8
1.3
4.9
2.7
1.0
6.2
3.9
8.2
6.8
2.0
4.2
2.2
0.6
0.5
4.9
3.2
MAXIMUM
17.5
20.1
11.0
21.9
13.8
3.0
29.1
43.4
46.7
41.8
8.8
23.6
17.5
1.7
2.6
32.0
20.1.
%>4 pCi/L
16
'9
4
35
16
0
19
12
13
32
11
31
7
0
0
16
26
%>20 pCi/L
0
1
0
i
0
0
5
1
5
3
0
2
0
0
0
3
1
-------
-------
TABLE 2. Screening indoor radon data for cities in Nevada with 10 or more
usable indoor radon measurements. Data represent charcoal-canister tests
made between 1989 and 1991,
CITY
Alamo
Austin
Battle Mountain
Beatty
Boulder City
Caliente
Carlin
Carson Citv
Dayton
Elko
Elv
Eureka
Fallen
Femlev
Gabbs
Gardnerville
Goldfield
Hawthorne
Henderson
Las Vegas
Lovelock
Lund
McDermitt
McGffl
Minden
North Las Vegas
Orovada
Pahrump
'anaca
Paradise Valley
Pioche
Reno
lound Mountain
Ruby Valley
Ruth
Sparks
Tonopah
Wells
Wendover
Winnemucca
Yerington
Zephyr Cove.
NO. OF
MEAS.
30
.22
48
14
21
44
25
105
. 17
173
163
30
141
18
• 13
44
17
67
22
193
32
15
10
47
15
10
13
67
29
10
31
311
12
10
15
82
42
23
14
210
23
13
HIGH
pCi/L
7.0
46.7
7.7
10.0
5.3
41.8
11.5
31.6
8.1
17.2
23.7
35.4
20.1
7.0
2.6
21.9
2.8
23.6
3.4
11.0
40.7
4.0
43.4
3.8
8.9
2.9
30.5
17.5
16.8
5.8
39.8
40.6
3.1
18.0
6.6
9.0
7.6
13.3
6.4
20.8
11.0
19.1
LOW
pCi/L
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.3
0.0
0.0
0.0
0.0
0.1
0.0
0.7
0.7
, 0.1
,0.0
0.4
0.6
0.0
0.0
1.0
0.4
0.0
0.0
0.0
0.5
0.3
0.0
0.0
0.0
0.1
0.0
0.5
1.4
AVERAGE
pCi/L
1.3
6.7
1.3
2.3
1.8
5.1
2.9
4.1
1.9
2.6
4.3
5.5
2.2
1.5
1.1
4.2
1.0
4.5
1.1
0.9
7.9
2.1
5.8
1.2
2.8
1.5
6.9
1.8
5.2
1.7
5.4
3.3
1.4
5.0
1.8
1.4
1.5
4.3
2.0
2.0
3.8
7.4
% > 4 pCi/L
10.0
40.9
6.3
14.3
9.5
34.1
24.0
30.5
11.8
17.9
39.3
33.3
8.5
5.6
0.0
34.1
0.0
37.3
0.0
3.1
56.3
6.7
10.0
0.0
26.7
0.0
61.5
7.5
55.2
10.0
38.7
21.2
0.0
40.0
13.3
6.1
7.1
39.1
14.3
11.0
34.8
69.2
-------
-------
fractures is enough to produce a radon hazard in homes built above them; (3) sediments eroded and
transported from rocks with elevated uranium and the soils that develop on them are also likely to
have elevated uranium levels. There are 442 radioactive mineral occurrences in Nevada described
by Garside (1973). The number of radioactive mineral occurrences found in each county is shown
in figure 7. Every county in Nevada has at least one occurrence and most counties have many
(fig. 7). Additional information on radioactive mineral occurrences in Nevada can be found in
Garside (1979).
Figure 8 is an equivalent uranium (eU) map for Nevada. A contour map of eU at a scale of
1:750,000 can be found in Duval (1988). Based on these maps (fig. 8 & Duval, 1988), most of
Nevada has surficial uranium concentrations above 2,0 ppm. Duval (1987) suggested that areas in
Nevada with eU concentrations greater than 2 ppm might have more than 20 percent of the homes
with indoor radon concentrations greater than 4 pQ/L. On a national basis, Peake and Schumann
(1992) concluded that eU concentrations of 2 ppm or greater indicate areas that have the potential to
produce a substantial number of elevated (greater than 4 pCi/L) indoor radon levels (in this report,
eU values of 2.5 ppm or greater are considered to have high potential for generating elevated
radon). Because of the dry climate, evaporative coolers are commonly used during summer
months to cool homes. The use of such coolers blocks or greatly reduces the infiltration of soil-
gas radon into homes by pressurizing the inside of the home. In southern Nevada, the use of
evaporative coolers, less heating because of the warm climate, and the prevalent use of slab-on-
grade construction, in which there is less contact area with the soil than in a basement home, may
significantly reduce the number of homes with radon concentrations greater than 4 pQ/L despite
the presence of ample source material in most Nevada soils.
The Paleozoic rocks, a mixture of carbonate and clastic rocks, found in a band in the
southern corner of the State and scattered approximately through the eastern third of the State, have
a relatively low eU signature (figs. 4/& 8). A band of rocks composed of Tertiary volcanics found
along the border with California in the northwest corner of the State also have a low eU signature
(figs. 4 & 8). Rocks with a lower eU signature should theoretically provide less of a radon risk
because they contain less of the parent material for radon production.
The Precambrian gneiss and Tertiary volcanics in the southern tip of Nevada have elevated
eU signatures (figs. 4 & 8). The Tertiary volcanic rocks (dominanfly Miocene and Pliocene in age)
so prevalent throughout the State have elevated eU signatures, as do the sediments derived from
them (figs. 4 & 8). The Cretaceous granitic rocks found in the Sierra Nevada and adjacent ranges
on the western side of the State also have an elevated eU signature. Elevated levels of radon have
been found in ground water samples from the Carson Valley in west-central Nevada (samples
ranged from <100 pCi/L to 16,000 pCi/L), particularly on the west side (Lico and others, 1989;
Lico and others, 1992). The use of well water in west-central Nevada is likely contributing small
amounts of radon to some homes.
The Nevada Bureau of Mines and Geology (1991) concluded that granitic rocks in west-
central Nevada were producing elevated indoor radon and that granitic rocks around Austin and
Lovelock may also be a source for elevated radon in these communities. They believe that
metamorphic or granitic rocks may be a source of indoor radon for Carson City and Hawthorne.
Silicic volcanic rocks, because they have relatively high uranium contents, have the potential to
generate significant amounts of radon. Elevated radon in homes in Lincoln and Elko Counties and
in the towns of Lovelock, Eureka, and Yerington may be attributed to the silicic volcanic rocks
(Nevada Bureau of Mines and Geology, 1991).
IV-13 Reprinted from USGS Open-File Report 93-292-1
-------
Fig. 7.
Number of radioactive occurrences by county
(statistics from Garside. 1973)
-------
Fig. 8.
Aerial radiometric map of Nevada (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.
-------
Most of Nevada has ample radon source material present in the near surf ace and suitable
soil permeabilities for radon transport to give Nevada at least a moderate geologic radon potential.
Nevada also has a number of uranium occurrences that represent locally high radon potentials. The
common use of evaporative coolers and slab-on-grade construction within the State may have
significantly lowered the total number of homes that have indoor radon concentrations above
4 pCJ/L, especially in the southern half of the State, which also contains the largest percentage of
the State's population.
SUMMARY
The RADON INDEX (RI) and the CONFIDENCE INDEX (CI) discussed in the
introduction to this volume have been used to evaluate the geologic radon potential of the State.
This evaluation is presented in Table 3, and the radon potential areas are shown on figure 9. Area
1, which includes the Sierra Nevada and adjacent ranges (fig. 3), is dominantiy made up of
intrusive and volcanic rocks with high eU. Area 1 falls in the high end of the moderate radon
potential ranking. Area 2 contains many basaltic rocks that have very low eU. Area 2 falls in the
low end of the moderate radon potential ranking. Area 3 is mixture of volcanic, intrusive, and
sedimentary rocks with varying uranium contents. Area 3 has a moderate radon potential. Area 4
is dominated by volcanic rocks with high eU and falls in the high end of the moderate radon
potential ranking. Area 5 contains dominantiy a mixture of Paleozoic carbonate rocks that have
low eU and volcanic and intrusive rocks with higher eU. Area 5 has a moderate radon potential.
Area 6 is dominated by Paleozoic carbonate rocks with low eU and falls in the high end of the low
radon potential ranking. Area 7 contains intrusive, volcanic, and metamorphic rocks with high eU
and also contains numerous uranium occurrences. Area 7 falls in the high end of the moderate
radon potential ranking. /
This assessment of the State's radon potential is part of a nationwide assessment and is
necessarily at a scale that may be too small for use in large counties of Nevada, because the
geology of Nevada is quite complicated and variable. The assessments in this report are weighted
by the available measurements of radon in homes. An area with geologically high potential for
producing radon may not appear to be a problem area because of local building practices, such as
few basements. Officials need to be aware that problems may arise if different building practices
are used in the future. Larger scale mapping of radon potential is being conducted by various State
agencies in Nevada (see list of State contacts in the Introduction chapter) and the reader is also
encouraged to contact them for additional information.
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
HOI 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-16 Reprinted from USGS Open-File Report 93-292-1
-------
TABLE 3. Radon Index (RI) and Confidence Index (GO scores for geologic radon potential areas
of Nevada. See text for discussion of areas and figure 9 for location of areas.
FACTOR
INDOOR RADON
RADIOACTIVITY
GEOLOGY
SOIL PERM.
ARCHTrECTURE
GFE POINTS
TOTAL
RANKING
FACTOR
INDOOR RADON
RADIOACTIVITY
GEOLOGY
SOIL PERM.
ARCHITECTURE
GFE POINTS
TOTAL
RANKING
1
RI
2
3
3
2
1
0
11
MOD
5
RI
2
3
2
2
1
0
10
MOD
CI
3
3
2
2
-
-
10
HIGH
CI
3
3
2
2 /
-
-
10
HIGH
RI
2
2
2
2
1
0
9
MOD
RI
1
2
2
2
1
0
8
LOW
2
CI
3
3
2
2
-
-
10
HIGH
6
CI
3
3
2
2
•-
-
10
HIGH
RI
2
. 3
2
2
1
0
10
MOD
RI
2
3
3
2
1
0
11
MOD
3
a
3
3
2
2
-
-
10
HIGH
7
a
3
3
2
2
-
-
10
HIGH
4
RI
2
3
3
2
1
0
11
MOD
a
3
3
2
' 2
-
-
10
HIGH
RADON INDEX SCORING:
Radon potential category Point range
LOW 3-8 points
MODERATE/VARIABLE 9-11 points
HIGH > 11 points
Possible range of points = 3 to 17
CONFIDENCE INDEX SCORING:
Probable screening indoor
radon average for area
LOW CONFIDENCE
MODERATE CONFIDENCE
HIGH CONFIDENCE
4-6 points
7-9 points
10 - 12 points
Possible range of points = 4 to 12
<2pCi/L
2-4pCi/L
>4pCi/L
IV-17 Reprinted from USGS Open-FUe Report 93-292-1
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119
I
11S
Fig. 9. Radon Potential Areas
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REFERENCES CITED IN THIS REPORT
AND GENERAL REFERENCES PERTAINING TO RADON IN NEVADA
Agricultural Experiment Stations and Soil Conservation Service, 1964, Soils of the Western
United States: U.S. Department of Agriculture, 69 p.
Carmichael, R.S., 1989, Practical Handbook of Physical Properties of Rocks and Minerals: CRC
Press, Inc., 741 p.
Durrance, E.M., 1986, Radioactivity In Geology, Principles and Applications: John Wiley and
Sons, 441 p.
Duval, J.S., 1987, Written communication to Larry J. Garside regarding Nevada gamma-ray
maps: 2 p.
Duval, J.S., 1988, Aerial Gamma-Ray Contour Maps of Regional Surface Concentrations of
Potassium, Uranium, and Thorium in Nevada: U.S. Geological Survey Map GP-982,
scale 1:750,000.
Duval, J.S., 1989, Radioactivity And Some Of Its Applications In Geology in Proceedings of the
Symposium on the Application of Geophysics to Engineering and Environmental
Problems: Society of Engineering and Mineral Exploration Geophysicists, p. 1-61.
Eisenbud, M., 1987, Environmental Radioactivity: Academic Press, Inc., 475 p.
/
Garside, L.J., 1973, Radioactive Mineral Occurrences in Nevada: Nevada Bureau of Mines and
Geology Bulletin 81,121 p.
Garside, L. J., 1979, Radioactive Mineral Occurrences in Nevada—An Update to Nevada Bureau
of Mines and Geology Bulletin 81: Nevada Bureau of Mines and Geology, NBMG 79-2,
28 p.
Hunt, C.B., 1979, Surficial Geology: U.S. Geological Survey National Aflas Sheet NAC-P-204-
75-O, scale 1:7,500,000.
Lico, M.S., Hughes, J.L., and Welch, A.H., 1989, Hydrogeologic Controls on Radon-222 in
Ground Water of West-Central Nevada: GSA Abstracts with Programs v. 21, no. 5,
p. 106.
Lico, M.S. and Rowe, T.G., 1992, Radon in ground water of Carson Valley, West-Central
Nevada in Gundersen, L.C.S. and Wanty, R.B. (eds.) Field Studies of Radon in Rocks,
Soils, and Water: U.S. Geological Survey Bulletin 1971, p. 279-288.
Manahan, S.E., 1990, Environmental Chemistry: Lewis Publishers, 612 p.
IV-19 Reprinted from USGS Open-File Report 93-292-1
-------
Milvy, P. and Cothern, C.R., 1990, Scientific Background for the Development of Regulations
for Radionuclides in Drinking Water in Radon, Radium and Uranium in Drinking Water,
Cothern, C.R. and Rebers, P.A. (eds.): Lewis Publishers, p. 1-16.
Nevada Bureau of Mines and Geology, 1991, Radon in Nevada-A Natural Hazard: Nevada Bureau
of Mines and Geology Education Series No. 18,4 p.
Nevada Bureau of Mines and Geology, 1992, Reducing Radon in Nevada Homes: Nevada Bureau
of Mines and Geology Education Series No. 21,6 p.
Nyberg, P.C. and Bemhardt, D.E., 1983, Measurement of Time-integrated Radon Concentrations
in Residences: Health Physics, v. 45, p. 539-543.
Peake, R.T. and Schumann, R.R., 1992, Regional Radon Characterizations in Gundersen, L.C.S.
and Wanty, R.B. (eds.) Field Studies of Radon in Rocks, Soils, and Water: U.S.
Geological Survey Bulletin 1971, p. 163-175.
Peterson, F.F., 1981, Landforms of the Basin & Range Province Defined for Soil Survey: Nevada
Agricultural Experiment Station, University of Nevada at Reno, Technical Bulletin 28,
52 p.
Rigby, J., 1989a, Radon Hazards in Nevada: Nevada Geology no. 3, p. 2-3.
Rigby, J., 1989b, Radon Hazards in Nevada: Nevada Realtor, Summer 1989, p. 16-17.
/
Rigby, J.G., 1990a, Radon Hazards in Nevada—First Results: GSA Abstracts with Programs,
v. 22, p. 78.
Rigby, J.,i 1990b, Nevada Indoor Radon Survey: Nevada Geology, no. 9, p. 1-3.
Rigby, J.G., Christensen, L.G., and Price, J.G., 1991, Geological Implications of Radon Hazard
Surveys—Experience From Nevada: Geological Society of America 1991 Annual Meeting,
San Diego, California October 21-24,1991, Abstracts with Programs, p. A204.
Stewart, J.H. and Carlson, I.E., 1977, Million Scale Geologic Map of Nevada: Nevada Bureau of
Mines and Geology Map 57.
Stewart, J.H. and Carlson, J.E., 1978, Geologic Map of Nevada: U.S. Geological Survey, scale
1:500,000.
Stewart, J.H., 1980, Geology of Nevada—A Discussion to Accompany the Geologic Map of
Nevada: Nevada Bureau of Mines and Geology Special Publication 4,136 p.
United States Department of Commerce, 1983, County and City Data Book 1983: p. 974.
IV-20 Reprinted from USGS Open-File Report 93-292-1
-------
EPA's Map of Radon Zones
The USGS' Geologic Radon Province Map is the technical foundation for EPA's Map
of Radon Zones. The Geologic Radon Province Map defines the radon potential for
approximately 360 geologic provinces. EPA has adapted this information to fit a county
boundary map in order to produce the Map of Radon Zones.
The Map of Radon Zones is based on the same range of predicted screening levels of
indoor radon as USGS' Geologic Radon Province Map. EPA defines the three zones as
follows: Zone One areas have an average predicted indoor radon screening potential greater
than 4 pCi/L. Zone Two areas are predicted to have an average indoor radon screening
potential between 2 pCi/L and 4 pCi/L. Zone Three areas are predicted to have an average
indoor radon screening potential less than 2 pCi/L.
Since the geologic province boundaries cross state and county boundaries, a strict
translation of counties from the Geologic Radon Province Map to the Map of Radon Zones
was not possible. For counties that have variable radon potential (i.e., are located in two or
more provinces of different rankings), the counties were assigned to a zone based on the
predicted radon potential of the province in which most of its area lies. (See Part I for more
details.)
NEVADA MAP OF RADON ZONES
The Nevada Map of Radon Zones and its supporting documentation (Part IV of this
report) have received extensive review by Nevada geologists and radon program experts. The
map for Nevada 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.
Nine county designations do not strictly foljow the methodology for adapting the
geologic provinces to county boundaries. EPA, the Nevada Department of Human Resources
and the Nevada Bureau of Mines and Geology have decided to designate Lincoln, White Pine,
Eureka, Lander, Pershing, Mineral, Lyon, Douglas and Carson City counties as Zone 1.
Although these areas are rated as having a moderate radon potential on the whole, areas of
variability and high radon potential are known to exist in these counties. Indoor radon data
indicate that population centers of these counties are located in the higher radon potential
areas and therefore warrant Zone 1 designations.
Although the information provided in Part IV of this report - the State chapter entitled
"Preliminary Geologic Radon Potential Assessment of Nevada" — 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 9 EPA office or the
Nevada radon program for information on testing .and fixing homes. Telephone numbers and
addresses can be found in Part II of this report.
V-l
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