Air and Radiation
4O2-R-93-O25
(6604J1
September 1993
ERA'S
of Radon Zones
Printed on R&ycled Paper
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EPA'S MAP OF RADON ZONES
CALIFORNIA
RADON DIVISION
OFFICE OF RADIATION AND INDOOR AIR
U.S. ENVIRONMENTAL PROTECTION AGENCY
SEPTEMBER, 1993
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ACKNOWLEDGEMENTS
This document was prepared by the U.S. Environmental Protection Agency's (EPA's)
Office of Radiation and Indoor Air (ORIA) in conjunction with the U.S. Geological Survey
(USGS). Sharon W. White was the EPA project manager. Numerous other people in ORIA
were instrumental in the development of the Map of Radon Zones, including Lisa Ratcliff,
Kirk Maconaughey, R. Thomas Peake, Dave Rowson, and Steve Page.
EPA would especially like to acknowledge the outstanding effort of the USGS
radon team — Linda Gundersen, Randy Schumann, Jim Otton, Doug Owen, Russell
Dubiel, Kendell Dickinson, and Sandra Szarzi — in developing the technical base for the
Map of Radon Zones.
ORIA would also like to recognize the efforts of all the EPA Regional Offices in
coordinating the reviews with the State programs and the Association of American State
Geologists (AASG) for providing a liaison with the State geological surveys. In addition,
appreciation is expressed to all of the State radon programs and geological surveys for their
technical input and review of the Map of Radon Zones.
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TABLE OF CONTENTS
I. OVERVIEW
II. THE USGS/EPA RADON POTENTIAL
ASSESSMENTS:INTRODUCTION
III. REGION 9 GEOLOGIC RADON POTENTIAL
SUMMARY
V. PRELIMINARY GEOLOGIC RADON POTENTIAL
ASSESSMENT OF CALIFORNIA
V. EPA'S MAP OF RADON ZONES - CALIFORNIA
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OVERVIEW
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Sections 307 and 309 of the 1988 Indoor Radon Abatement Act (IRAA) direct EPA to
identify areas of the United States that have the potential to produce elevated levels of radon.
EPA, the U.S. Geological Survey (USGS), and the Association of American State Geologists
(AASG) have worked closely over the past several years to produce a series of maps and
documents which address these directives. The EPA Map of Radon Zones is a compilation of
that work and fulfills the requirements of sections 307 and 309 of IRAA. The Map of Radon
Zones identifies, on a county-by-county basis, areas of the U.S. that have the highest potential
for elevated indoor radon levels (greater than 4 pCi/L).
The Map of Radon Zones is designed to assist national, State and local governments
and organizations to target their radon program activities and resources. It is also intended to
help building code officials determine areas that are the highest priority for adopting radon-
resistant building practices. The Map of Radon Zones should not be used to determine if
individual homes in any given area need to be tested for radon. EPA recommends that all
homes be tested for radon, regardless of geographic location or the zone designation of
the county in which they are located.
This document provides background information concerning the development of the
Map of Radon Zones. It explains the purposes of the map, the approach for developing the
map (including the respective roles of EPA and USGS), the data sources used, the conclusions
and confidence levels developed for the prediction of radon potential, and the review process
that was conducted to finalize this effort.
BACKGROUND
Radon (Rn222) is a colorless, odorless, radioactive gas. It comes from the natural
decay of uranium that is found in nearly all soils. It typically moves through the ground to
the air above and into homes and other buildings through cracks and openings in the
foundation. Any home, school or workplace may have a radon problem, regardless of
whether it is new or old, well-sealed or drafty, or with or without a basement. Nearly one out
of every 15 homes in the U.S. is estimated to have elevated annual average levels of indoor
radon.
Radon first gained national attention in early 1984, when extremely high levels of
indoor radon were found in areas of Pennsylvania, New Jersey, and New York, along the
Reading Prong-physiographic province. EPA established a Radon Program in 1985 to assist
States and homeowners in reducing their risk of lung cancer from indoor radon.
Since 1985, EPA and USGS have been working together to continually increase our
understanding of radon sources and the migration dynamics that cause elevated indoor radon
levels. Early efforts resulted in the 1987 map entitled "Areas with Potentially High Radon
Levels." This map was based on limited geologic information only because few indoor radon
measurements were available at the time. The development of EPA's Map of Radon Zones
and its technical foundation, USGS1 National Geologic Radon Province Map, has been based
on additional information from six years of the State/EPA Residential Radon Surveys,
independent State residential surveys, and continued expansion of geologic and geophysical
information, particularly the data from the National Uranium Resource Evaluation project.
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Purpose of the Map of Radon Zones
•rf*' ,
EPA's Map of Radon Zones (Figure 1) assigns each of the 3141 counties in the
United States to -one of three zones:
o Zone 1 counties have a predicted average indoor screening level > than
4 pCi/L
o Zone 2 counties have a predicted average screening level > 2 pCi/L and
<4 pCi/L
o Zone 3 counties have a predicted average screening level < 2 pCi/L
The Zone designations were determined by assessing five factors that are known to be
important indicators of radon potential: indoor radon .measurements, geology, aerial
radioactivity, soil parameters, and foundation types.
The predictions of average screening levels in each of the Zones is an expression of
radon potential in the lowest liveable area of a structure. This map is unable to estimate
actual exposures to radon. EPA recommends methods for testing and fixing individual homes
based on an estimate of actual exposure to radon. For more information on testing and fixing
elevated radon levels in homes consult these EPA publications: A Citizen's Guide to Radon,
the Consumer's Guide to Radon Reduction and the Home Buyer's and Seller's Guide to
Radon.
EPA believes that States, local governments and other organizations can achieve
optimal risk reductions by targeting resources and program activities to high radon potential
areas. Emphasizing targeted approaches (technical assistance, information and outreach
efforts, promotion of real estate mandates and policies and building codes, etc.) in such areas
addresses the greatest potential risks first.
EPA also believes that the use of passive radon control systems in the construction of
new homes in Zone 1 counties, and the activation of those systems if necessitated by follow-
up testing, is a cost effective approach to achieving significant radon risk reduction.
The Map of Radon Zones and its supporting documentation establish no regulatory
requirements. Use of this map by State or local radon programs and building code officials is
voluntary. The information presented on the Map of Radon Zones and in the supporting
documentation is not applicable to radon in water.
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, within-county variations in radon potential are not shown on the Map of Radon
Zones. EPA recommends that users who may need to address specific within-county
variations in radon potential (e.g., local government officials considering the
implementation of radon-resistant construction codes) consult USGS1 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
Lificola County
Ueierit e Low
Figure 4
NEBRASKA - EPA Map of Radon Zones
Lincoln County
Zeie 1 Zoae 2 Zoic 3
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One such analysis involved comparing county zone designations to indoor radon
measuremenjs 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 n. Depending on the amount of new information that is presented, EPA will
consider updating this map periodically. The State radon programs should initiate proper
notification of the appropriate State officials when the Map of Radon Zones is released and
when revisions or updates are made by the State or EPA.
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THE USGS/EPA RADON POTENTIAL ASSESSMENTS: AN INTRODUCTION
. by
. Linda C.S. Gundersen and R. Randall Schumann
U.S: Geological Survey
and .
Sharon W. White
U.S. Environmental Protection Agency
BACKGROUND .
The Indoor Radon Abatement Act of 1988 (15 U.S.C. 2661-2671) directed the U.S.
Environmental Protection Agency (EPA) to identify areas of the United States that have the
potential to produce harmful levels of indoor radon. These characterizations were to be based
on both geological data and on indoor radon levels in homes and other structures. The EPA
also was directed to develop model standards and techniques for new building construction
that would provide adequate prevention or mitigation of radon entry. As part of an
Interagency Agreement between the EPA and the U.S. Geological Survey (USGS), the USGS
has prepared radon potential estimates for the United States. This report is one of ten
booklets that document this effort. The purpose and intended use of these reports is to help
identify areas where states can target their radon program resources, to provide guidance in
selecting the most appropriate building code options for areas, and to provide general
information on radon and geology for each state for federal, state, and municipal officials
dealing with radon issues. These reports are not intended to be used as a substitute for
indoor radon testing, and they cannot and should not be used to estimate or predict the
indoor radon concentrations of individual homes, building sites, or housing tracts. Elevated
levels of indoor radon have been found in every State, and EPA recommends that all homes
be tested for indoor radon.
Booklets detailing the radon potential assessment for the U.S. have been developed for
each State. USGS geologists are the authors of the geologic radon potential booklets. Each
booklet consists of several components, the first being an overview to the mapping project
(Part I), this introduction to the USGS assessment (Part H), 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 ;eports for more detailed information. In most
cases the best sources of information on radon for specific areas are state and local
departments of health, state departments responsible for nuclear safety or environmental
protection, and U.S.-EPA-regional offices: -More detailed information on state or local
geology may be obtained from the state geological surveys. Addresses and telephone
numbers of state radon contacts, geological surveys, and EPA regional offices are listed in
Appendix C at the end of this chapter.
RADON GENERATION AND TRANSPORT IN SOILS
Radon (^Rn) is produced from the radioactive decay of radium (226Ra), which is, in turn,
a product of the decay of uranium (asU) (fig. 1). The half-life of 222Rn is 3.825 days. Other
isotopes of radon occur naturally, but, with the exception of thoron (220Rn), 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. fhe shrirkf^e of clays can ^ct 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 2x\0'6 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
Lome had higher indoor radon levels in the winter, caused by cooler outside ah entering the
cave, driving radon-laden air into cracks and solution cavities in the rock and soil, and
ultimately, into homes (Gammage and others, 1993).
RADON ENTRY INTO BUILDINGS
A driving force (reduced atmospheric pressure in the house relative to the soil, producing
a pressure gradient) and entry points must exist for radon to enter a building from the soil.
The negative pressure caused by furnace combustion, ventilation devices, and the stack effect
(the rising and escape of warm air from the upper floors of the building, causing a
temperature and pressure gradient within the structure) during cold winter months are
common driving forces. Cracks and other penetrations through building foundations, sump
holes, and slab-to-foundation wall joints are common entry points.
Radon levels in the basement are generally higher than those on the main floor or upper
floors of most structures. Homes with basements generally provide more entry points for
radon, commonly have a more pronounced stack effect, and typically have lower air pressure
relative to the surrounding soil than nonbasement homes. The term "nonbasement" applies to
slab-on-grade or crawl space construction.
METHODS AND SOURCES OF DATA
The assessments of radon potential in the booklets that follow this introduction were
made using five main types of data: (1) geologic (lithologic); (2) aerial radiometric; (3) soil
characteristics, including soil moisture, permeability, and drainage characteristics; (4) indoor
radon data; and (5) building architecture (specifically, whether homes in each area are built
slab-on-grade or have a basement or crawl space). These five factors were evaluated and
integrated to produce estimates of radon potential. Field measurements of soil-gas radon or
soil radioactivity were not used except where such data were available in existing, published
reports of local field studies. Where applicable, such field studies are described in the
individual state chapters.
GEOLOGIC DATA
The types and distribution of lithologic units and other geologic features in an
assessment area are of primary importance in determining radon potential. Rock types that
are most likely to cause indoor radon problems include carbonaceous black shales, glauconite-
bearing sandstones, certain kinds of fluvial sandstones and fluvial sediments, phosphorites,
chalk, karst-producing carbonate rocks, certain kinds of glacial deposits, bauxite, uranium-rich
granitic rocks, metamorphic rocks of granitic composition, silica-rich volcanic rocks, many
sheared or faulted rocks, some coals, and certain kinds of contact metamorphosed rocks.
Rock types least likely to cause radon problems include marine quartz sands, non-
carbonaceous shales and siltstones, certain kinds of clays, silica-poor metamorphic and
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igneous rocks, and basalts. Exceptions exist within these general lithologic groups because of
the occurrence of localized uranium deposits, commonly of the hydrothermal type in
crystalline rocks- or the "roll-front" type in sedimentary rocks. Uranium and radium are
commonly sited in heavy minerals, iron-oxide coatings on rock and soil grains, and organic
materials in soils and sediments. Less common are uranium associated with phosphate and
carbonate complexes in rocks and soils, and uranium minerals.
Although many cases of elevated indoor radon levels can be traced to high radium and
(or) uranium concentrations in parent rocks; some-structural features, most notably faults and
shear zones, have "been identified as sites of localized uranium concentrations (Deffeyes and
MacGregor, 1980) and have been associated with some of the highest reported indoor radon
levels (Gundersen, 1991). The two highest known indoor radon occurrences are associated
with sheared fault zones in Boyertown, Pennsylvania (Gundersen and others, 1988a; Smith
and others, 1987), and in Clinton, New Jersey (Henry and others, 1991; Muessig and Bell,
1988).
MURE AERIAL RADIOMETRIC DATA
Aerial radiometric data are used to quantify the radioactivity of rocks and soils.
Equivalent uranium (ell) 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 1.7£TMeV (mega-electron volts)
emission energy corresponding to bismuth-214 (2HBi), with the assumption that uranium and
its decay products are in secular equilibrium. Equivalent uranium is expressed in units of
parts per million (ppm). Gamma radioactivity also may be expressed in terms of a radium
activity; 3 ppm elJ corresponds to approximately 1 picocurie per gram (pCi/g) of radium-226.
Although radon is highly mobile in soil and its concentration is affected by meteorological
conditions (Kovach, 1945; Klusman and Jaacks, 1987; Schery and others, 1984; Schumann
and others, 1992), statistical correlations between average soil-gas radon concentrations and
average eU values for a wide variety of soils have been documented (Gundersen and others,
1988a, 1988b; Schumann and Owen, 1988). Aerial radiometric data can provide an estimate
of radon source strength over a region, but the amount of radon that is able to enter a home
from the soil is dependent on several local factors, including soil structure, grain size
distribution, moisture content, and permeability, as well as type of house construction and its
structural condition.
The aerial radiometric data used for these characterizations were collected as part of the
Department of Energy National Uranium Resource Evaluation (NURE) program of the 1970s
and early 1980s. The purpose of the NURE program was to identify and describe areas in the
United States having potential uranium resources (U.S. Department of Energy, 1976). The
NURE aerial radiometric data were collected by aircraft in which a gamma-ray spectrometer
was mounted, flying approximately 122 m (400 ft) above the ground surface. The equivalent
uranium maps presented in the state chapters were generated from reprocessed NURE data in
which smoothing, filtering, recalibrating, and matching of adjacent quadrangle data sets were
performed to compensate for background, altitude, calibration, and other types of errors and
inconsistencies in the original data set (Duval and others, 1989). The data were then gridded
and contoured to produce maps of eU with a pixel size corresponding to approximately 2.5 x
2.5 km (1.6 x 1.6 mi).
II-6 Reprinted from USGS Open-File Report 93-292
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F11CHT LIKE SPACING OF NUKE AEKIAL SURVEYS
2 rV (I MILE)
5 KM (3 HUES)
2 * 5 EH
10 Elf (6 HUES)
5 * 10 IH
NO OiTi
Figure 2. Nominal flighfline 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
typically between 3 and 6 miles, less than 10 percent of the ground surface of the United
States was actually measured by the airborne gamma-ray detectors (Duval and others, 1989),
although some areas had better coverage than others due to the differences in flight-line
spacing between areas (fig. 2). This suggests that some localized uranium anomalies may not
have been detected by the aerial surveys, but the good correlations of eU patterns with
geologic outcrop patterns indicate that, at relatively small scales (approximately 1:1,000,000
or smaller) the National eU map (Duval and others, 1989) gives reasonably good estimates of
average surface uranium concentrations and thus can assist in the prediction of radon potential
of rocks and soils, especially when augmented with additional geologic and soil data.
The shallow (20-30 cm) depth of investigation of gamma-ray spectrometers, either
ground-based or airborne (Duval and others, 1971; Durrance, 1986), suggests that gamma-ray
data may sometimes underestimate the radon-source strength in soils in which some of the
radionuclides in the near-surface soil layers have been transported downward through the soil
profile. In such cases the concentration of radioactive minerals in the A horizon would be
lower than in the B horizon, where such minerals are typically concentrated. The
concentration of radionuclides in the C horizon and below may be relatively unaffected by
surface solution processes. Under these conditions the surface gamma-ray signal may indicate
a lower radon source concentration than actually exists in the deeper soil layers, which are
most likely to affect radon levels in structures with basements. The redistribution of
radionuclides in soil profiles is dependent on a combination of climatic, geologic, and
geochemical factors. There is reason to believe that correlations of eU with actual soil
radium and uranium concentrations at a depth relevant to radon entry into structures may be
regionally variable (Duval, 1989; Schumann and Gundersen, 1991). Given sufficient
understanding of the factors cited above, these regional differences may be predictable.
SOIL SURVEY DATA
Soil surveys prepared by the U.S. Soil Conservation Service (SCS) provide data on soil
characteristics, including soil-cover thickness, grain-size distribution, permeability, shrink-
swell potential, vegetative cover, generalized groundwater characteristics, and land use. The
reports are available in county formats and State summaries. The county reports typically
contain both generalized and detailed maps of soils in the area.
Because of time and map-scale constraints, it was impractical to examine county soil
reports for each county in the United States, so more generalized summaries at appropriate
scales were used where available. For State or regional-scale radon characterizations, soil
maps were compared to geologic maps of the area, and the soil descriptions, shrink-swell
potential, drainage characteristics, depth to seasonal high water table, permeability, and other
relevant characteristics of each soil group noted. Technical soil terms used in soil surveys are
generally complex; however, a good summary of soil engineering terms and the national
distribution of technical soil types is the "Soils" sheet of the National Atlas (U.S. Department
of Agriculture, 1987).
II-8 Reprinted from USGS Open-File Report 93-292
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Soil permeability is commonly expressed in SCS soil surveys in terms of the speed, in
inches per hour (in/hr), at which water soaks into the soil, as measured in a soil percolation
test. Although in/hr are not truly units of permeability, these units are in widespread use and
are referred to as "permeability" in SCS soil surveys. The permeabilities listed in the SCS
surveys are for water, but they generally correlate well with gas permeability. Because data
on gas permeability of soils is extremely limited, data on permeability to water is used as a
substitute except in cases in which excessive soil moisture is known to exist. Water in soil .
pores inhibits gas transport;'so the amount of radon available to a home is effectively reduced
by a high water table. Areas likely to have high water tables include river valleys, coastal
areas, and some areas overlain by deposits of glacial origin (for example, loess).
Soil permeabilities greater than 6.0 in/hr may be considered high, and permeabilities less
than 0.6 in/hr may be considered low in terms of soil-gas transport. Soils with low
permeability may generally be considered to have a lower radon potential than more
permeable soils with similar radium concentrations. Many well-developed soils contain a
clay-rich B horizon that may impede vertical soil gas transport. Radon generated below this
horizon cannot readily escape to the surface, so it would instead tend to move laterally,
especially under the influence of a negative pressure exerted by a building.
Shrink-swell potential is an indicator of the abundance of smectitic (swelling) clays in a
soil. Soils with a high shrink-swell potential may cause building foundations to crack,
creating pathways for radon entry into the structure. During dry periods, desiccation cracks in
shrink-swell soils provide additional pathways for soil-gas transport and effectively increase
the gas permeability of the soil. Soil permeability data and soil profile data thus provide
important information for regional radon assessments.
INDOOR RADON DATA
Two major sources of indoor radon data were used. The first and largest source of data is
from the State/EPA Residential Radon Survey (Ronca-Battista and others, 1988; Dziuban and
others, 1990). Forty-two states completed EPA-sponsored indoor radon surveys between 1986
and 1992 (fig. 3). The State/EPA Residential Radon Surveys were designed to be
comprehensive and statistically significant at the state level, and were subjected to high levels
of quality assurance and control. The surveys collected screening indoor radon measurements,
defined as 2-7 day measurements using charcoal canister radon detectors placed in the lowest
livable area of the home. The target population for the surveys included owner-occupied
single family, detached housing units (White and others, 1989), although attached structures
such as duplexes, townhouses, or condominiums were included in some of the surveys if they
met the other criteria and had contact with the ground surface. Participants were selected
randomly from telephone-directory listings. In total, approximately 60,000 homes were tested
in the State/EPA surveys.
The second source of indoor radon data comes from residential surveys that have been
conducted in a specific state or region of the country (e.g. independent state surveys or utility
company surveys). Several states, including Delaware, Florida, Illinois, New Hampshire, New
Jersey, New York, Oregon, and Utah, have conducted their own surveys of indoor radon. The
quality and design of a state or other independent survey are discussed and referenced where
the data are used.
II-9 Reprinted from USGS Open-File Report 93-292
-------
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Data forpnly 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.
Ration 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 'MURE aerial radiometric data. See text discussion for details.
FACTOR
INDOOR RADON (average)
AERIAL RADIOACTIVITY:
GEOLOGY*
SOIL PERMEABILITY
ARCHITECTURE TYPE
INCREASING RADON POTENTIAL ^
POINT VALUE
i
<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 notential catefiorv
LOW
MODERATE/VARIABLE
HIGH
Probable average screening
Point range indoor radon for area
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
FACTOR
INDOOR RADON DATA
AERIAL RADIO ACTIVITY
GEOLOGIC DATA
SOIL PERMEABILITY
UNUKHA51JNU LXWNMLMlJNUH ^
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
II-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 th^re 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 wer.e 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
i
11-14 Reprinted from USGS Open-File Report 93-292
-------
to question the quality or validity of these data. The other factors were scored on the basis of
the quality and quantity of the data used to complete the RI matrix.
Indoor radon data were evaluated based on the distribution and number- of data points and
on whether the data were collected by random sampling (State/EPA Residential Radon Survey
or other state survey data) or volunteered vendor data (likely to be nonrandom and biased
toward population centers and/or high indoor radon levels). The categories listed in the CI
matrix for indoor radon data ("sparse or no data"r"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 ell, geology, and
soil-gas or indbor radon levels were associated with glacial deposits (see the discussion in a
previous section) and typically were assigned a 2-point Confidence Index score. Correlations
among eU, geology, and radon were generally sound in unglaciated areas and were usually
assigned 3 CI points. Again, however, radioactivity data in some unglaciated areas may have
been assigned fewer than 3 points, and in glaciated areas may be assigned only one point, if
the data were considered questionable or if coverage was poor.
To assign Confidence Index scores for the geologic data factor, rock types and geologic
settings for which a physical-chemical, process-based understanding of radon generation and
mobility exists were regarded as having "proven geologic models" (3 points); a high
confidence could be held for predictions in such areas. Rocks for which the processes are
less well known or for which data are contradictory were regarded as "variable" (2 points),
and those about which little is known or for which no apparent correlations have been found
were deemed "questionable" (1 point).
The soil permeability factor was also scored based on quality and amount of data. The
three categories for soil permeability in the Confidence Index are similar in concept, and
scored similarly, to those for the geologic data factor. Soil permeability can be roughly
estimated from grain size and drainage class if data from standard, accepted soil percolation
tests are unavailable; however, the reliability of the data would be lower than if percolation
test figures or other measured permeability data are available, because an estimate of this type
does not encompass all the factors that affect soil permeability and thus may be inaccurate in
some instances. Most published soil permeability data are for water; although this is
generally closely related to the air permeability of the soil, there are some instances when it
may provide an incorrect estimate. Examples of areas in which water permeability data may
not accurately reflect air permeability include areas with consistently high levels of soil
moisture, or clay-rich soils, which would have a low water permeability but may have a
11-15 Reprinted from USGS Open-File Report 93-292
-------
significantly higher air permeability when dry due to shrinkage cracks in the soil. These
additional factors were applied to the soil permeability factor when assigning the RI score, but
may have less certainty in some cases and thus would be assigned a lower CI score.
The Radon Index and Confidence Index give a general indication of the relative
contributions of the interrelated geologic factors influencing radon generation and transport in
rocks and soils, and thus, of the potential for elevated indoor radon levels to occur in a
particular area. However, because these reports are somewhat generalized to cover relatively
large areas of States, it is highly recommended that more detailed studies be performed in
local areas of interest, using the methods and general information in these booklets as a guide.
11-16 Reprinted from USGS Open-File Report 93-292
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*? REFERENCES CITED
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Durrance, E.M., 1986, Radioactivity in geology: Principles and applications: New York, N.Y.,
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Schumann, R.R., and Owen, D.E., 1988, Relationships between geology, equivalent uranium
concentration, and radon in soil gas, Fairfax County, Virginia: U.S. Geological Survey
Open-File Report 88-18,28 p.
Schumann, R.R., and Gundersen, L.C.S., 1991, Regional differences in radon emanation
coefficients in soils: Geological Society of America Abstracts With Programs, v. 23,
no. 1, p. 125.
Schumann, R.R., Peake, R.T., Schmidt, K.M., and Owen, D.E., 1991, Correlations of soil-gas
and indoor radon with geology in glacially derived soils of the northern Great Plains, in
Proceedings of the 1990 International Symposium on Radon and Radon Reduction
Technology, Volume 2, Symposium Oral Papers: U.S. Environmental Protection Agency
report EPA/600/9-91/026b, p. 6-23-6-36.
JI-18 Reprinted from USGS Open-FUe Report 93-292
-------
Schumann, R.R., Owen, D.E., and Asher-Bolinder, S., 1992, Effects of weather and soil
characteristics on temporal variations in soil-gas radon concentrations, in Gates, A.E., and
Gundersen, L.C.S., eds., Geologic controls on radon: Geological Society of America
Special Paper 271, p. 65-72.
Sextro, R.G., Moed, B.A., Nazaroff, W.W., Revzan, K.L., and Nero, A.V., 1987,
Investigations of soil as a source of indoor radon, in Hopke, P.K., ed., Radon and its
decay products: American Chemical Society Symposium Series 331, p. 10-29.
Sterling, R., Meixel, G., Shen, L., Labs, K., and Bligh, T., 1985, Assessment of the energy
savings potential of building foundations research: Oak Ridge, Tenn., U.S. Department of
Energy Report ORNL/SUB/84-0024/1.
Smith, R.C., H, Reilly, M.A., Rose, A.W., Barnes, J.H., and Berkheiser, S.W., Jr., 1987,
Radon: a profound case: Pennsylvania Geology, v. 18, p. 1-7.
Tanner, A.B., 1964, Radon migration in the ground: a review, m Adams, J.A.S., and Lowder,
W.M., eds., The natural radiation environment: Chicago, HI., University of Chicago
Press, p. 161-190.
Tanner, A.B., 1980, Radon migration in the ground: a supplementary review, m 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 lands 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.
- U-19 Reprinted from USGS Open-File Report 93-292
-------
-------
APPENDIX A
GEOLOGIC TIME SCALE
Subdivisions (and their symbols)
Eon or
Eonothem
Phanerozoic2
Proterozoie
(P)
Archean
(A)
Era or
E rathe m
Cenozoic2
-------
-------
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 (lO"12 curies) is equal to about 2.2 disintegrations
of radon atoms per minute. A liter is about 1.06 quarts. The average concentration of radon in
U.S. homes measured to date is between 1 and 2 pCi/L.
Bq/m3 (Becquerels per cubic meter)- a metric unit of radioactivity used to describe radon
concentrations in a volume of air. One becquerel is equal to one radioactive disintegration per
second. One pCi/L is equal to 37 Bq/m3.
ppm (parts per million)- a unit of measure of concentration by weight of an element in a
substance, in this case, soil or rock. One ppm of uranium contained in a ton of rock corresponds
to about 0.03 ounces of uranium. The average concentration of uranium in soils in the United
States is between 1 and 2 ppm.
in/hr (inches per hour)- a unit of measure used by soil scientists and engineers to describe the
permeability of a soil to water flowing through it It is measured by digging a hole 1 foot (12
inches) square and one foot deep, filling it with water, and measuring the time it takes for the water
to drain from the hole. The drop in height of the water level in the hole, measured in inches, is
then divided by the time (in hours) to determine the permeability. Soils range in permeability from
less than 0.06 in/hr to greater than 20 in/hr, but most soils in the United States have permeabilities
between these two extremes.
Geologic terms and terms related to the study of radon
aerial radiometric, aeroradiometric survey A survey of radioactivity, usually gamma rays,
taken by an aircraft carrying a gamma-ray spectrometer pointed at the ground surface.
alluvial fan A low, widespread mass of loose rock and soil material, shaped like an open fan
and deposited by a stream at the point where it flows from a narrow mountain valley out onto a
plain or broader valley. May also form at the junction with larger streams or when the gradient of
the stream abruptly decreases.
alluvium, alluvial General terms referring to unconsolidated detrital material deposited by a
stream or other body of running water.
alpha-track detector A passive radon measurement device consisting of a plastic film that is
sensitive to alpha particles. The film is-etehed 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 metamoiphic rock consisting mainly of pyroxenes and(or) amphibole and
plagioclase.
11-21 Reprinted from USGS Open-File Report 93-292
-------
argillite, argillaceous Terms referring to a rock derived from clay or shale, or any sedimentary
rock containing an appreciable amount of clay-size material, i.e., argillaceous sandstone.
arid Term describing a climate characterized by dryness, or an evaporation rate that exceeds the
amount of precipitation.
basalt A general term for a dark-colored mafic igneous rocks that may be of extrusive origin,
such as volcanic basalt flows, or intrusive origin, such as basalt dikes.
bathoHth 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 ihe 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 fiom USGS Open-File Report 93-292
-------
delta, deltaic Referring to a low, flat, alluvial tract of land having a triangular or fan shape,
located at or near the mouth of a river. It results from the accumulation of sediment deposited by a
river at the point at which the river loses its ability to transport the sediment, commonly where a
river meets a larger body of water such as a lake or ocean.
dike A tabular igneous intrusion of rock, younger than the surrounding rock, that commonly cuts
across the bedding or foliation of the rock it intrudes.
diorite A plutonic igneous rock that is medium in color and contains visible dark minerals that
make up less than 50% of the rock. It also contains abundant sodium plagioclase and minor
quartz. -
dolomite A carbonate sedimentary rock of which more than 50% consists of the mineral dolomite
(CaMg(CO3)2), and is commonly white, gray, brown, yellow, or pinkish in color.
drainage The manner in which the waters of an area pass, flow off of, or flow into the soil.
Also refers to the water features of an area, such as lakes and rivers, that drain it
eolian Pertaining to sediments deposited by the wind.
esker A long, narrow, steep-sided ridge composed of irregular beds of sand and gravel deposited
by streams beneath a glacier and left behind when the ice melted.
evapotranspiration Loss of water from a land area by evaporation from the soil and
transpiration from plants.
extrusive Said of igneous rocks that have been erupted onto the surface of the Earth.
fault A fracture or zone of fractures in rock or sediment along which there has been movement
fluvial, fluvial deposit Pertaining to sediment that has been deposited by a river or stream.
foliation A linear feature in a rock defined by both mineralogic and structural characteristics. It
may be formed during deformation or metamorphism.
formation A mappable body of rock having similar characteristics.
glacial deposit Any sediment transported and deposited by a glacier or processes associated
with glaciers, such as glaciofluvial sediments deposited by streams flowing from melting glaciers.
gneiss A rock formed by metamorphism in which bands and lenses of minerals of similar
composition alternate with bands and lenses of different composition, giving the rock a striped or
"foliated" appearance.
granite Broadly applied, any coarsely crystalline, quartz- and feldspar-bearing igneous plutonic
rock. Technically, granites have between 10 and 50% quartz, and alkali feldspar comprises at least
65% of the total feldspar.
gravel An unconsolidated, natural accumulation of rock fragments consisting predominantly of
particles greater than 2 mm in size.
heavy minerals Mineral grains in sediment or sedimentary rock having higher than average
specific gravity. May form layers and lenses because of wind or water sorting by weight and size
n-23 Reprinted from USGS Open-Ffle 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 (CaCO3).
lithology The description of rocks in hand specimen and in outcrop on the basis of color,
composition, and grain size.
loam A permeable soil composed of a mixture of relatively equal parts clay, silt, and sand, and
usually containing some organic matter.
loess A fine-grained eolian deposit composed of silt-sized particles generally thought to have
been deposited from windblown dust of Pleistocene age.
mafic Term describing an igneous rock containing more than 50% dark-colored minerals.
marine Term describing sediments deposited in the ocean, or precipitated from ocean waters.
metamorphic Any rock derived from pre-existing rocks by mineralogical, chemical, or structural
changes in response to changes in temperature, pressure, stress, and the chemical environment
Phyllite, schist, amphibolite, and gneiss are metamorphic rocks.
moraine A mound, ridge, or other distinct accumulation of unsorted, unbedded glacial material,
predominantly till, deposited by the action of glacial ice.
outcrop That part of a geologic formation or structure that appears at the surface of the Earth, as
in "rock outcrop",
percolation test A term used in engineering for a test to determine the water permeability of a
soil. A hole is dug and filled with water and the rate of water level decline is measured.
permeability The capacity of a rock, sediment, or soil to transmit liquid or gas.
phosphate, phosphatic, phosphorite Any rock or sediment containing a significant amount
of phosphate minerals, i.e., minerals containing PO4.
11-24 Reprinted from USGS Open-PHe Report 93-292
-------
physiographic province A region in which all parts are similar in geologic structure and
climate, which has had a uniform geomorphic history, and whose topography or landforms differ
significantly from adjacent regions.
placer deposit See heavy minerals
residual Formed by weathering of a material in place.
residuum Deposirof residual material.
rhyolite An extrusive igneous rock of volcanic origin, compositionalry equivalent to granite.
sandstone A clastic sedimentary rock composed of sand-sized rock and mineral material that is
more or less firmly cemented. Sand particles range from 1/16 to 2 mm in size.
schist A strongly foliated crystalline rock, formed by metamorphism, that can be readily split into
thin flakes or slabs. Contains mica; minerals are typically aligned.
screening level Result of an indoor radon test taken with a charcoal canister or similar device,
for a short period of time, usually less than seven days. May indicate the potential for an indoor'
radon problem but does not indicate annual exposure to radon.
sediment Deposits of rock and mineral particles or fragments originating from material that is
transported by air, water or ice, or that accumulate by natural chemical precipitation or secretion of
organisms.
semiarid Refers to a climate that has slightly more precipitation than an arid climate.
shale A fine-grained sedimentary rock formed from solidification (lithification) of clay or mud.
shear zone Refers to a roughly linear zone of rock that has been faulted by ductile or non-ductile
processes in which the rock is sheared and both sides are displaced relative to one another.
shrink-swell clay See clay mineral.
siltstone A fine-grained clastic sedimentary rock composed of silt-sized rock and mineral
material and more or less firmly cemented. Silt particles range from 1/16 to 1/256 mm in size.
sinkhole A roughly circular depression in a karst area measuring meters to tens of meters in
diameter. It is funnel shaped and is formed by collapse of the surface material into an underlying
void created by the dissolution of carbonate rock.
slope An inclined part of the earth's surface.
solution cavity A hole, channel or cave-like cavity formed by dissolution of rock.
stratigraphy The study of rock strata; also refers to the succession of rocks of a particular area.
surficial materials Unconsolidated glacial, wind-, or waterborne deposits occurring on the
earth's surface.
tablelands General term for a broad, elevated region with a nearly level surface of considerable
extent.
n-25 Reprinted from USGS Qpen-FUe Report 93-292
-------
terrace gravel Gravel-sized material that caps ridges and terraces, left behind by a stream as it
cuts down to a lower level.
terrain A tract or region of the Earth's surface considered as a physical feature or an ecological
environment
till Unsorted, generally unconsolidated and unbedded rock and mineral material deposited directly
adjacent to and underneath a glacier, without reworking by meltwater. Size of grains varies greatly
from clay to boulders.
uraniferous Containing uranium, usually more than 2 ppm.
vendor data Used in this report to refer to indoor radon data collected and measured by
commercial vendors of radon measurement devices and/or services.
volcanic Pertaining to the activities, structures, and extrusive rock types of a volcano.
water table The surface forming the boundary between the zone of saturation and the zone of
aeration; the top surface of a body of unconfined groundwater in rock or soil.
weathering The destructive process by which earth and rock materials, on exposure to
atmospheric elements, are changed in color, texture, composition, firmness, or form with little or
no transport of the material.
H-26
Reprinted from USGS Open-File Report 93-292
-------
APPENDIX C
EPA REGIONAL OFFICES
EPA Regional Offices
State
•EPA Region
EPA Region 1
JFK Federal Building
Boston, MA 02203
(617) 565-4502
EPA Region 2
(2AIR:RAD)
26 Federal Plaza
New York, NY 10278
(212) 264-4110
Region 3 (3AH14)
S41 Chestnut Street
Philadelphia, PA 19107
(215) 597-8326
EPA Region 4
345 Courtland Street, N.E.
Atlanta, GA 30365
(404) 347-3907
EPA Region 5 (5AR26)
77 West Jackson Blvd.
Chicago, IL 60604-3507
(312) 886-6175
EPA Region 6 (6T-AS)
1445 Ross Avenue
Dallas, TX 75202-2733
(214) 655-7224
EPA Region 7
726 Minnesota Avenue
Kansas City, KS 66101
(913) 551-7604
EPA Region 8
(8HWM-RP)
999 18th Street
One Denver Place, Suite 1300
Denver, CO 80202-2413
(303) 293-1713
EPA Region 9 (A-3)
75 Hawthorne Street
San Francisco, CA 94105
(415) 744-1048
EPA Region 10
1200 Sixth Avenue
Seattle, WA 98101
(202) 442-7660
Alabama ; ; ...4
Alaska 10
Arizona 9
Arkansas 6
-California 9
Colorado , 8
Connecticut 1
Delaware 3
District of Columbia 3
Florida..... 4
Georgia 4
Hawaii 9
Idaho , 10
Illinois 5
Indiana 5
Iowa 7
Kansas t 7
Kentucky 4
Louisiana 6
Maine 1
Maryland 3
Massachusetts 1
Michigan 5
Minnesota 5
Mississippi 4
Missouri 7
Montana 8
Nebraska 7
Nevada 9
New Hampshire 1
New Jersey 2
New Mexico 6
New York ...2
North Carolina 4
North Dakota 8
Ohio 5
Oklahoma 6
Oregon 10
Pennsylvania 3
Rhode Island 1
South Carolina 4
South Dakota 8
Tennessee 4
Texas - 6
Utah 8
Vermont 1
Virginia 3
Washington 10
West Virginia 3
Wisconsin 5
Wyoming 8
n-27
Reprinted from USGS Open-File Report 93-292
-------
STATE RADON CONTACTS
May, 1993
Alabama James McNees
Division of Radiation Control
Alabama Department of Public I.. Jth
State Office Building
Montgomery, AL 36130
(205)242-5315
1-800-582-1866 in state
Alaska Charles Tedfbrd
Department of Health and Social
Services
P.O. Box 110613
Juneau,AK 99811-0613
(907)465-3019
1-800-478-4845 in state
Arizona John Stewart
Arizona Radiation Regulatory Agency
4814 South 40th St
Phoenix, AZ 85040
(602)255^845
Arkansas LeeGershner
Division of Radiation Control
Department of Health
4815 Markham Street, Slot 30
Little Rock, AR 72205-3867
(501) 661-2301
California J. David Quinton
Department of Health Services
714 P Street, Room 600
Sacramento, CA 94234-7320
(916) 324-2208
1-800-745-7236 in state
Colorado Linda Martin
Department of Health
4210 East llth Avenue
Denver, CO 80220
(303) 692-3057
1-800-846-3986 in state
Connecticut Alan J. Siniscalchi
Radon Program
•Connet-cut Department of Health
Services
150 Washington Street
Hartford, CT 06106-4474
(203)566-3122
Delaware MaraiG. Rejai
Office of Radiation Control
Division of Public Health
P.O. Box 637
Dover, DE 19903
(302) 736-3028
1-800-554-4636 In State
District Robert Davis
of Columbia DC Department of Consumer and
Regulatory Affairs
614 H Street NW
Room 1014
Washington, DC 20001
(202)727-71068
Florida N. Michael Gilley
Office of Radiation Control
Department of Health and
Rehabilitative Services
1317 Winewood Boulevard
Tallahassee, EL 32399-0700
(904)488-1525
1-800-543-8279 in state
Richard Schreiber
Georgia Department of Human
Resources
878 Peachtree St, Room 100
Atlanta, GA 30309
(404)894-6644
1-800-745-0037 in state
Hawaii Russell Takata
Environmental Health Services
Division
' 591 Ala Moana Boulevard
Honolulu, HI 96813-2498
(808) 586^700
II-28 Reprinted from USGS Open-File Report 93-292
-------
Idaho
Illinois
Indiana
Iowa
Kansas
Kentucky
PatMcGavam
Office of Environmental Health
450 West State Street
Boise, ID 83720
(208)334-6584
1-800-445-8647 in state
Richard Allen
Illinois Department of Nuclear Safety
1301 Outer Park Drive
Springfield, IL 62704
(217)524-5614
1-800-325-1245 in state
Lorand Magyar
Radiological Health Section
Indiana State Department of Health
1330 West Michigan Street
P.O. Box 1964
Indianapolis, IN 46206
(317)633-8563
1-800-272-9723 In State
Donald A. Plater
Bureau of Radiological Health
Iowa Department of Public Health
Lucas State Office Building
Des Moines, IA 50319-0075
(515)281-3478
1-800-383-5992 In State
Harold Spiker
Radiation Control Program
Kansas Department of Health and
Environment
109 SW 9th Street
6th Floor Mills Building
Topeka, KS 66612
(913)296-1561
JeanaPhelps
Radiation Control Branch
Department of Health Services
Cabinet for Human Resources
275 East Main Street
Frankfort, KY 40601
(502) 564-3700
Louisiana Matt Schlenker
Louisiana Department of
• Environmental Quality
P.O. Box 82135
Baton Rouge, LA 7C: 84-2135
(504)925-7042
1-800-256-2494 in state
ft/fajne 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 LeonJ.Rachuba
Radiological Health Program
Maryland Department of the
Environment
2500 Broening Highway
Baltimore, MD 21224
(410) 631-3301
1-800-872-3666 In State
Massachusetts William J. Bell
Radiation Control Program
Department of Public Health
" 23 Service Center
Northampton, MA 01060
(413) 586-7525
1-800-445-1255 in state
Michigan Sue Hendershott
Division of Radiological Health
Bureau of Environmental and
Occupational Health
3423 North Logan Street
P.O. Box 30195
Lansing, MI 48909
(517) 335-8194
Minnesota LauraOatmann
Indoor Air Quality Unit
925 Delaware Street, SE
P.O. Box 59040
Minneapolis, MN 55459-0040
(612)627-5480
1-800-798-9050 in state
n-29 - Reprinted from USGS Open-File Report 93-292
-------
Mississippi - Silas Anderson
Division of'Radiological Health
Department of Health
3150 Lawson Street
P.O. Box 1700
Jackson, MS 39215-1700
(601)354-6657
1-800-626-7739 in state
Missouri Kenneth V. Miller
Bureau of Radiological Health
Missouri Department of Health
1730 East Elm
P.O. Box 570
Jefferson City, MO 65102
(314)751-6083
1-800-669-7236 In State
Montana Adrian C. Howe
Occupational Health Bureau
Montana Department of Health and
Environmental Sciences
Cogswell Building A113
Helena, MT 59620
(406)444-3671
Nebraska Joseph Milone
Division of Radiological Health
Nebraska Department of Health
301 Centennial Mall, South
P.O. Box 95007
Lincoln, NE 68509
(402)471-2168
1-800-334-9491 In State
Nevada Stan Marshall
Department of Human Resources
505 East King Street
Room 203
Carson City, NV 89710
(702) 687-5394
New Hampshire David Chase
Bureau of Radiological Health
Division of Public Health Services
Health and Welfare Building
Six Hazen Drive
Concord, NH 03301
(603)271^674
1-800-852-3345 x4674
New Jersey Torialee Carlson Key
Division of Environmental Quality
Department of Environmental
Protection
CN415
Trenton, NJ 08625-0145
(609) 987-6369
1-800-648-0394 in state
New Mexico William M. Floyd
Radiation Licensing and Registration
Section
New Mexico Environmental
Improvement Division
1190 St. Francis Drive
Santa Fe,NM 87503
(505) 827-4300
New York William J. Condon
Bureau of Environmental Radiation
Protection
New York State Health Department
Two University Place
Albany, NY 12202
(518)458-6495
1-800-458-1158 in state
North Carolina Dr. Felix Fong
Radiation Protection Division
Department of Environmental Health
and Natural Resources
701 Barbour Drive
Raleigh, NC 27603-2008
(919) 571-4141
1-800-662-7301 (recorded info x4196)
North Dakota Arlen Jacobson
North Dakota Department of Health
1200 Missouri Avenue, Room 304
P.O. Box 5520
Bismarck, ND 58502-5520
(701) 221-5188
Ohio Marcie Matthews
Radiological Health Program
Department of Health
1224 Kinnear Road - Suite 120
Columbus, OH 43212
(614) 644-2727
1-800-523-4439 in state
11-30 Reprinted from USGS Open-File Report 93-292
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Oklahoma
Oregon
Pennsylvania
Puerto Rico
Rhode Island
South Carolina
Gene Smith
Radiation Protection Division
Oklahoma State Department of
Health
P.O. Box 53551
Oklahoma City, OK 73152
(405)271-5221
George Toombs
Department of Human Resources
Health Division
1400 SW 5th Avenue
Portland, OR 97201
(503)73M014
Michael Pyles
Pennsylvania Department of
Environmental Resources
Bureau of Radiation Protection
P.O. Box 2063
Harrisburg, PA 17120
(717) 783-3594
1-800-23-RADON In State
David Saldana
Radiological Health Division
G-P.O. Call Box 70184
Rio Piedras, Puerto Rico 00936
(809)767-3563
Edmund Arcand
Division of Occupational Health and
Radiation
Department of Health
205 Cannon Building
Davis Street
Providence, RI02908
(401)277-2438
Bureau of Radiological Health
Department of Health and
Environmental Control
2600 Bull Street
Columbia, SC 29201
(803)734-4631
1-800-768-0362
South Dakota MikePochop
Division of Environment Regulation
Department of Water and Natural
Resources
Joe Foss Building, Room 217
523 E. Capitol
Pierre, SD 57501-3181
(605)773-3351
Tennessee Susie Shimek
Division of Air Pollution Control
Bureau of Ihe Environment
Department of Environment and
Conservation
Customs House, 701 Broadway
Nashville, IN 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) 53&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)264-4110
Er31 ~ Reprinted from USGS Open-File Report 93-292
-------
Virginia Shelly Ottenbrite
Bureau of Radiological Health
Department of Health
109 Governor Street
Richmond, VA 23219
(804) 786-5932
1-800-468-0138 in state
Washington Kate Coleman
Department of Health
Office of Radiation Protection
Airdustrial Building 5, LE-13
Olympia, WA 98504
(206)753-4518
1-800-323-9727 In State
West Virgim> Beattie L. DeBord
Industrial Hygiene Division
West Virginia Department of Health
151 llth Avenue
South Charleston, WV 25303
(304)558-3526
1-800-922-1255 In State
Wisconsin Conrad Weiffenbach
Radiation Protection Section
Division of Health
Department of Health and Social
Services
P.O. Box 309
Madison, WI53701-0309
(608) 267^796
1-800-798-9050 in state
Wyoming Janet Hough
Wyoming Department of Health and
Social Services
Hathway Building, 4th Floor
Cheyenne, WY 82002-0710
(307)777-6015
1-800-458-5847 in state
11-32 Reprinted from USGS Open-File Report 93-292
-------
STATE GEOLOGICAL SURVEYS
May, 1993
Alabama Ernest A. Mancini
Geological Survey of Alabama
P.O. Box 0
420 Hackberry Lane
Tuscaloosa, AL 35486-9780
(205)349-2852
Alaska Thomas E. Smith
Alaska Division of Geological &
Geophysical Surveys
794 University Ave., Suite 200
Fairbanks, AK 99709-3645
(907)479-7147
Arizona Larry D. Fellows
Arizona Geological Survey
845 North Park Ave., Suite 100
Tucson, AZ 85719
(602) 882-4795
Arkansas Norman F. Williams
Arkansas Geological Commission
Vardelle Parham Geology Center
3815 West Roosevelt Rd.
Little Rock, AR 72204
(501) 324-9165
California James F. Davis
California Division of Mines &
Geology
801 K Street, MS 12-30
Sacramento, CA 95814-3531
(916)445-1923
Colorado Pat Rogers (Acting)
Colorado Geological Survey
1313 Sherman St., Rm 715
Denver, CO 80203
(303)866-2611
•*-
Connecticut Richard C. Hyde
Connecticut Geological & Natural
History Survey
165 Capitol Ave., Rm. 553
Hartford, CT 06106
(203) 566-3540
Delaware Robert R. Jordan
Delaware Geological Survey
University of Delaware
101 Penny Hall
Newark, DE19716-7501
(302)831-2833 -
Florida Walter Schmidt
Florida Geological Survey
903 W. Tennessee St
Tallahassee, FL 32304-7700
(904)488^191
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
615 East Peabody Dr.
Champaign, IL 61820
(217)333^747
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 Lee C.Gerhard
Kansas Geological Survey
1930 Constant Ave., West Campus
University of Kansas
Lawrence, KS 66047
(913)864-3965
11-33 Reprinted fromUSGS Open-File Report 93-292
-------
Kentucky Donald CHaney
Kentucky Geological Survey
University of Kentucky
228 Mining & Mineral Resources
Building
Lexington, KY 40506-0107
(606)257-5500
Louisiana William E. Marsalis
Louisiana Geological Survey
P.O.-Box 2827
University Station
Baton Rouge, LA 70821-2827
(504) 388-5320
Maine Walter A. Anderson
Maine Geological Survey
Department of Conservation
State House, Station 22
Augusta, ME 04333
(207)289-2801
Maryland Emery T. Cleaves
Maryland Geological Survey
2300 St. Paul Street
Baltimore, MD 21218-5210
(410)554-5500
Massachusetts Joseph A. Sinnott
Massachusetts Office of
Environmental Affairs
100 Cambridge St., Room 2000
Boston, MA 02202
(617)727-9800
Michigan R. Thomas Segall
Michigan Geological Survey Division
Box 30256
Lansing, MI 48909
(517)334-6923
Minnesota Priscilla C. Grew
Minnesota Geological Survey
2642 University Ave.
St. Paul, MN 55114-1057
(612)627-4780
Mississippi S. Cragin Knox
Mississippi Office of Geology
P.O. Box 20307
Jackson, MS 39289-1307
(601) 961-5500
Missouri James H. Williams
Missouri Division of Geology &
Land Survey
111 Fairgrounds Road
P.O. Box 250
Rolla, MO 65401
(314) 368-2100
Montana Edward T.Ruppel
Montana Bureau of Mines & Geology
Montana College of Mineral Science
and Technology, Main Hall
Butte, MT 59701
(406)496-4180
Nebraska Perry B. Wigley
.Nebraska Conservation & Survey
Division
113 Nebraska Hall
University of Nebraska
Lincoln, NE 68588-0517
(402)472-2410
Nevada Jonathan G. Price
Nevada Bureau of Mines & Geology
Stop 178
University of Nevada-Reno
Reno, NV 89557-0088
(702) 784-6691
New Hampshire Eugene L. Boudette
Dept. of Environmental Services
117 James Hall
University of New Hampshire
Durham, NH 03824-3589
(603) 862-3160
New Jersey Haig F. Kasabach
New Jersey Geological Survey
P.O. Box 427
Trenton, NJ 08625
(609)292-1185
New Mexico Charles E. Chapin
New Mexico Bureau of Mines &
Mineral Resources
Campus Station
Socorro.NM 87801
(505) 835-5420
New York Robert H. Fakundiny
New York State Geological Survey
3136 Cultural Education Center
Empire State Plaza
Albany, NY 12230
(518)474-5816
11-34 Reprinted from USGS Open-File Report 93-292
-------
North Carolina Charles H. Gardner
North Carolina Geological Survey
P.O. Box 27687
Raleigh, NC 27611-7687
(919)733-3833
North Dakota John P. Bluemle
North Dakota Geological Survey
600 East Blvd.
Bismarck, ND 58505-0840
(701)224-4109
Ohio Thomas M. Berg
Ohio Dept. of Natural Resources
Division of Geological Survey
4383 Fountain Square Drive
Columbus, OH 43224-1362
(614)265-6576
Oklahoma Charles J. Mankin
Oklahoma Geological Survey
Room N-131, Energy Center
100E.Boyd
Norman, OK 73019-0628
(405) 325-3031
Oregon Donald A. Hull
Dept 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 Ram6n M. Alonso
Puerto Rico Geological Survey
Division
Box 5887
Puerta de Tierra Station
San Juan, P.R. 00906
(809)722-2526
Rhode Island J. Allan Cain
Department of Geology
University of Rhode Island
315 Green Hall
Kingston, RI02881
(401)792-2265
South Carolina Alan-Jon W.Zupan (Acting)
South Carolina Geological Survey
5 Geology Road
Columbia, SC 29210-9998
(803)737-9440
South Dakota C.M. Christensen (Acting)
South Dakota Geological Survey
Science Center
University of South Dakota
Vermillion, SD 57069-2390
(605)677-5227
Tennessee Edward T.Luther
Tennessee Division of Geology
13th Floor, L & C Tower
401 Church Street
Nashville, TN 37243-0445
(615)532-1500
Texas William L. Fisher
Texas Bureau of Economic Geology
University of Texas
University Station, Box X
Austin, TX 78713-7508
(512)471-7721
Utah M. Lee Allison
Utah Geological & Mineral Survey
2363 S. Foothill Dr.
Salt Lake City, UT 84109-1491
(801)467-7970
Vermont Diane L. Conrad
Vermont Division of Geology and
Mineral Resources
103 South Main St.
Waterbury,VT 05671
(802)244-5164
Virginia Stanley S.Johnson
Virginia Division of Mineral
Resources
P.O. Box 3667
Charlottesvffle, VA 22903
(804)293-5121
Washington Raymond Lasmanis
Washington Division of Geology &
Earth Resources
Department of Natural Resources
P.O. Box 47007
Olympia, Washington 98504-7007
(206)902-1450
n-35 Reprinted fiomUSGS Open-File Report 93-292
-------
West Virginia Larry D.Woodfoik
West Virginia Geological and
•Economic Survey
Mont Chateau Research Center
P.O. Box 879
Morgantown,WV 26507-0879
(304)594-2331
Wisconsin James Robertson
Wisconsin Geological & Natural
History Survey
3817 Mineral Point Road
Madison, WI 53705-5100
(608)263-7384
Wyoming Gary B. Glass
Geological Survey of Wyoming
University of Wyoming
Box 3008, University Station
Laramie, WY 82071-3008
(307)766-2286
11-36 Reprinted from USGS Open-File Report 93-292
-------
^ EPA REGION 9 GEOLOGIC RADON POTENTIALSUMMARY
by
James K. Otton, Douglass E. Owen, Russell F. Dubiel,
G. Michael Reimer, and Sandra L. Szarzi
UJS. 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 pQ/L were ranked high. Areas in
which the average screening indoor radon level of all homes within the area is estimated to be
between 2 and 4 pQ/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 pCS/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 (K5 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.
HI-l Reprinted firomUSGS Open-File Report 93-292-1
-------
o
Figure 1- Geologic radon provinces of EPA region 9. 1-Klamath Mountains; 2-Cascade Range;
3- Modoc Plateau; 4- Sierra Nevada; 5- Great Valley; 6- Northern Coast Ranges; 7- Southern
Coast and Transverse Ranges; 8- Peninsular Ranges; 9- Colorado Desert; 10- Basin and Range;
11- Mojave-Sonoran Desert; 12- Transition Zone; 13- Colorado Plateau; 14- Hawaii
-------
Bsmt & 1st Floor Indoor Radon
Arithmetic Mean (pCt/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
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
4 pCi/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 derived
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 Sutter Buttes area
m-4 Reprinted from USGS Open-FUe Report 93-2924
-------
which has values of as much as 5.5 ppm ell. 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. Alluvial fans from the Southern Coast 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.
The Southern Coast Range and Transverse Ranges have moderate radon potential overall;
however, much of the radon potential is associated with areas of elevated radioactivity from
Monterey Bay southward in the Coast Range and in the western two-thirds of the Transverse
Ranges. Houses sited directly on uranium-enriched marine sedimentary rocks in these two areas,
such as the Monterey Formation and the Rincon Shale, are very likely to exceed 4 pCS/L, especially
where parts of the home are below grade.
Peninsular Ranges
The Peninsular Ranges (8, fig. 1) are dominated by Mesozoic granitic rocks with lesser
Mesozoic metamorphic 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.
Colorado Desert
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 province has a low potential for radon indoors.
Basin and Range
The Basin and Range (10, fig. 1) is composed of Precambrian metamorphic rocks, late
Precambrian and Paleozoic metamorphosed and unmetamorphosed sedimentary and less abundant
igneous rocks, Mesozoic metamorphosed and unmetamorphosed volcanic and sedimentary 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
iiraniferous 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?aleozoic 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 area
around Las Vegas and contribute to the low eU signature observed in the mountains and valleys in
that area.
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
m-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 Precambrian 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.
Rom 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 eU, with a broad area of
mountains and adjacent valley alluvium in southeastemmost California and westernmost Arizona
above 5.5 ppm eU. Li 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. 1), running generally southeast to northwest across the
central part of Arizona, contains mountainous areas of uplifted plutonic and metamorphic rocks,
with many intervening valleys filled 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 gentiy 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 andTriassic 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
-------
Hawaii
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 to the 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 pQ/L.
m-8 Reprinted from USGS Open-File Report 93-292-1
-------
PRELIMINARY GEOLOGIC RADON POTENTIAL ASSESSMENT OF CALIFORNIA
by
James K, Otton
US. Geological Survey
INTRODUCTION
This assessment of the radon potential of California relies heavily on geologic information
derived from publications of the California Division of Mines and Geology, from publications of
the U.S. Geological Survey, from previous work by personnel at Lawrence Berkeley Laboratory
(Moed and others, 1984), from an analysis of indoor radon data from the State/EPA Indoor Radon
Survey of California conducted during 1989-1990, and from a study of radon potential in
California by the California Air Resources Board (Liu and others, 1990). Much information in the
geographic setting section is derived from The National Atlas of the United States of America and
from the Adas of California (Donley and others, 1979).
This is a generalized assessment of geologic radon potential of rocks, soils, and surficial
deposits of California. 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
California lies at the western edge of North America. Twelve physiographic provinces are
discussed here (slightly modified from the 11 of Donley and others, 1979): the Klamath
Mountains, the Cascade Range, the Modoc Plateau, the Northern Coast Ranges, the Southern
Coast Ranges, the Great Valley, the Sierra Nevada, the Basin and Range, the Mojave Desert, the
Transverse Ranges, the Peninsular Ranges, and the Colorado Desert (fig. 1).
The Klamath Mountains form an area of high mountains where the relief generally ranges
3000-5000 feet except in coastal areas where the relief is 1000-3000 feet Less than 20 percent of
the surface area is gently sloped. The Cascade Range is characterized by open high mountains
where the relief is 3000-5000 feet and 20-50 percent of the land's surface is gently sloped. The
Modoc Plateau is an area of tablelands of moderate relief (300-500 feet) and plains with low
mountains (relief 1000-3000 feet). Gentle slopes occupy 50-80 percent of the land.
The Northern Coast Ranges comprise mostly low mountains with open low mountains in
the southern part. Relief ranges from about 1000-3000 feet The Southern Coast Ranges are
mostly open low mountains, but high mountains lie along the coast south of Monterey Bay and
IV-l Reprinted from USGS Open-File Report 93-292-1
-------
Fig. 1- Physiographic provinces of California. Modified from Donley and others, 1979.
-------
low mountains flank the Great Valley along the eastern side of this province. Relief is 1000-3000
feet except in the high mountains where it is 3000-5000 feet
The Great Valley is an area of flat plains where local relief is less than 100 feet Greater
then 80 percent of the area is gently sloping. Large wetlands occupy the central parts of the
northern and south-central Great Valley. Irregular plains or irregular plains and hills flank the
Great Valley to the north and east and form a transition to adjacent mountains.
The Sierra Nevada is the largest and highest mountain range in the State. High mountains
with relief ranging 3000-5000 feet form the western two-thirds of this range and low mountains
with 1000-3000 feet of relief lie between the higher mountains to the east and the adjacent Great
Valley. The Basin and Range is characterized by plains with high mountains and open high
mountains where relief ranges 3000-5000 feet The Mojave Desert is an area of plains with low
mountains and, in its western parts, plains with hills. Relief is 1000-3000 feet in the east and 300-
500 feet in the west
The Transverse Ranges are composed of high mountains (relief 3000-5000 feet) and open
low mountains (relief 1000-3000 feet). The Peninsular Ranges are characterized by high
mountains to the east (relief 3000-5000 feet), open low mountains in the central part (relief 1000-
3000 feet) and tablelands of moderate relief (300-500 feet) along the coast Plains with high hills
occupy the area around Los Angeles (relief 1000-3000 feet). The Colorado Desert is an area of
smooth plains where relief ranges 100-300 feet The central part of this area is occupied by the
Salton Sea. Large sand dunes occur in the eastern and western part of this province.
Precipitation in the mountains of the Cascade Range, the Klamath Mountains, the Northern
Coast Ranges, and the Sierra Nevada ranges from 20 to more than 80 inches per year with the
higher amounts occurring at the higher elevations. Some of the lower valleys in the eastern
Klamath Mountains and the Cascade Range receive only 10-20 inches of precipitation per year.
The Modoc Plateau receives 10-20 inches of precipitation per year. In the Southern Coast Ranges
the high mountains near the coast receive 20-80 inches per year, but the rest of the area receives
only 4 to 30 inches per year with the driest areas being the western interior valleys.
The Great Valley receives 4-30 inches of precipitation per year with the lower and southern
parts of the valley being the driest The Basin and Range province receives less than 4 to as much
as 30 inches of precipitation per year, but only the mountains receive more than 10 inches. Most
of the Mojave Desert receives less than 4 inches per year.
The Transverse Ranges receive 10 to 60 inches per year with altitude strongly controlling
the amounts received. The Peninsular Ranges receive 4 to as much as 40 inches per year but only
the higher mountains in the east part of the Province receive more than 20 inches per year. The
Colorado Desert generally receives less than 4 inches of precipitation per year.
Most of the population of the State is concentrated in counties in coastal bay and valley
areas and in the Great Valley (fig. 2, see fig. 3 for county names). Most of the desert areas of the
Modoc Plateau, the Basin and Range, and the Mojave Desert, and the mountain areas of the
Klamath Mountains, Cascade Range, Northern Coast Range, and the Sierra Nevada, are very
sparsely populated.
The Klamath Mountains, the Northern Coast Ranges, the Cascade Range, and the Sierra
Nevada are dominated by forest and woodland, some grazed and some ungrazed. Grazed open
woodlands and desert shrublands are present throughout most of the Modoc Plateau. The Great
Valley is one of the heavily developed agricultural areas of the world. Irrigated croplands and
croplands with grazing occur throughout the Great Valley. The Southern Coast Ranges are a mix
of grazed open woodland, ungrazed forest and woodland, and, in the valleys, cropland and
IV-3 Reprinted from USGS Open-File Report 93-292-1
-------
POPULATION (1990)
G 0 to 25000
E3 25000 to 50000
0 50000 to 100000
100001 to 500000
500001 to 8863164
Figure 2. Population of counties of California (1990 U.S. Census data).
-------
Fig. 3- Map showing location and names of counties in California.
-------
grazing land. The Transverse Ranges are dominantly foresdand and woodland and grazed open
woodland. The Basin and Range, the Mojave Desert, and the Colorado Desert are dominated by
ungrazed desert shrubland. However, grazed desert shrubland occurs at the western edge of these
three areas and in the area closest to Las Vegas. A large area of irrigated cropland occurs in the
lower Colorado Desert area. The Peninsular Ranges are mostly open grazed woodland.
Most of the housing in California is slab-on-grade which generally results in lower indoor
radon levels because there is less contact between the structure and the underlying soil. However,
houses on hillslopes commonly have lower floors which are recessed into the hillslope, creating a
lower level partly below grade. Such below-grade floors are more susceptible to elevated indoor
radon levels and measurements of such areas in houses may contribute many of the higher values.
GEOLOGIC SETTING
The geology of California is diverse and geologic provinces are often separated by sharp
structural and geomorphic boundaries (fig. 4). The Klamath Mountains are underlain by Paleozoic
and Mesozoic metavolcanic and metasedimentary rocks, Jurassic ultramafic rocks, and Mesozoic
granitic intrusive rocks. The Cascade Range is underlain primarily by upper Tertiary and
Quaternary extrusive rocks, mainly basalt and lesser andesite and rhyolite. The Modoc Plateau is
underlain by Tertiary basalt flows, upper Tertiary to Quaternary basalt flows, and lesser amounts
of andesite and rhyolite.
The Northern Coast Ranges 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 The Southern Coast Ranges 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.
The Great Valley is underlain by surficial materials composed of Quaternary alluvium,
largely derived from the Sierra Nevada to the east and the Coast Ranges to the west The northern
part of the Sierra Nevada is underlain by Paleozoic and Mesozoic metamorphic rocks with lesser
Mesozoic granitic rocks, whereas in the southern part Mesozoic granitic rocks predominate, with
lesser Mesozoic metamorphic rocks. In the northern part, Tertiary volcanic rocks, including
basalt, rhyolite and sedimentary rocks derived from them, crop out along the crests of many
ranges.
The Basin and Range is tectonically active. It is separated from the Sierra Nevada by
normal faults of large displacement and corresponding mountain fronts of great relief. The ranges
are composed of Precambrian metamorphic rocks, late Precambrian and Paleozoic metamorphosed
and unrnetamorphosed sedimentary rocks, Mesozoic and Tertiary intrusive rocks, and Tertiary
sedimentary and volcanic rocks. The basins are filled with alluvium derived from the adjacent
ranges. Upper Tertiary and Quaternary volcanic rocks occur around Mono Lake. The Mojave
Desert is underlain by rocks similar to those of the Basin and Range except the ranges are smaller
and more deeply eroded and the alluvial valleys are wider.
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
IV-6 Reprinted from USGS Open-File Report 93-292-1
-------
EXPLANATION
Quaternary-tertiary extrusives: mainly
basaft. some andesite and myoSte
Tertiary e«tnjsrves: primarily basatt
Juassic utoabasie Wnisives:
pendotte. some weathered to
.serpentine
Mesezoie intRisives: gnuute (Siena
Nevada bathoBh
Mesozoie extnnmes: basalt and
andesite
Paleozoic (mainly Devonian)
PnOunbrian MnnKW: noMy
granilt
Ft»Cambriannnc«maiphies:som»
dotornw & iinntOM inekjdad
|Q*I QuattmaiyaBuvium
• 1 Eoe«nwplioc«n« wtfmtnis: mainlsr
UU sandstone & congtonwma
Eocen*OIiooein«'s«dim«ms:
1"^ I mainly sandstone 4 eongte-
mant*. some shale
rjn Cmuoous sediments: sandstone.
L—' congtomwite and shale
lie meumoiphic: nxks &
metasedimenu ol Coast Range.
Francisean Fonnation.
EanyMesozoicm«tamon3hies:n>ete
o< the Mojave region
Triassicmetamo>phies:iDd(S&
nwtaseolmenu. some shale &
Smestoo*
Me
oie metavolcanies.
metasedimenisimauinorphieaol
w. slope ol Siena Nevada: slates.
graywackes
Late Paleozoic (maWy Pemian)
meusedimen»4meiavolcanfci
Pale
idimemi*
meumoiphie nxks. In Siemu slate.
pnyKte. gnywacker'fntheKlamitte:
metaseolments A some sehM
Cambrian meusedknems & meta-
morpMc lochs: quanzte & shale
Fig. 4- Generalized geologic map of California. Modified from Donley and others, 1979.
-------
underlain by Erccambrian 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 Peninsular Ranges are dominated by Mesozoic granitic rocks with lesser Mesozoic
metamorphic rocks. Tertiary sedimentary rocks lie along the coast The Colorado Desert (Salton
trough) is underlain by Quaternary alluvium derived from the adjacent mountains.
Aeroradioactivity exhibits considerable variation across the State (fig. 5). For the purposes
of this report, "uraniferous" or "high uranium values" refers to uranium concentrations or
equivalent uranium (eU) concentrations sufficient to generate indoor radon concentrations
exceeding 4 pQ/L, defined here as greater than 2.5 ppm. Equivalent uranium (eU) values range
from less than 0.5 ppm over ultramafic rocks of the Klamath Mountains to greater than 5.5 ppm
over metamorphic and granitic terranes in the eastern Mojave Desert The Klamath Mountains
overall exhibit the lowest eU signatures in the State. Ultramafic rocks and Paleozoic
metasedimentary rocks in the Klamath Mountains typically have less than 0.5 ppm eU. The other
rocks range from 0.5 to 1.5 ppm eU. Only one small granitic pluton in the Klamaths has more
than 1.5 ppm eU.
The Cascade Range and the Modoc Plateau generally range from less than 0.5 ppm to 1.5
ppm eU, however local eU values of as much as 4.5 ppm are interpreted to result from outcrops of
silicic volcanic rocks. 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
values of as much as 4.5 ppm were measured.
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. From Lake Tahoe southward,
however, the granitic rocks and the thin volcanic cover of most of the Sierra Nevada have
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.
Equivalent uranium values for rocks and soils in the Great Valley are strongly influenced
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, reflecting the relatively low
uranium content of rocks in the nearby northern Sierra Nevada and Northern Coast Ranges.
However, Sutler Buttes, prominent hills in the middle of the northern Great Valley that are
underlain mostly by volcanic rocks, exhibits values of as much as 5.5 ppm eU. From Sacramento
southward, the eU signature of the alluvium on the east flank of the valley increases as the
uraniferous granitic and volcanic rocks from the Sierra Nevada have contributed more detritus to
the valley alluvium. eU values locally exceed 5.5 ppm. Alluvial fans derived from less
uraniferous rocks in the SierrafbothlUs locally "have lower eU signatures, some as low as 0.5 ppm.
Alluvial fans from the Southern Coast 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 uraniferous sedimentary rocks of the Southern Coast Ranges contribute
alluvium to the valley floor.
Equivalent uranium values vary significantly for the Southern Coast Ranges. Franciscan
metamorphic rocks, Triassic metamorphic rocks, and Tertiary sedimentary rocks derived from
IV-8 Reprinted from USGS Open-File Report 93-292-1
-------
Figure 5 - Aerial radiometric map of California (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.
-------
them generally range 0.5-2.0 ppmeU. 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 Basin and Range also exhibits variation in eU related to mapped rock units.
Frecambrian metamorphic rocks, most Mesozoic granitic rocks and Tertiary silicic volcanic rocks
have elevated eU. 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. LatePrecambrian 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.
In the Mojave Desert the apparent uranium content of the rocks decreases from east to west
Much of the eastern half of the Mojave Desert has more than 2.5 ppm eU, with a broad area of
mountains and adjacent valley alluvium in southeastemmost California above 5.5 ppm eU. In the
western Mojave much of the area has lower eU (1.0-2.5 ppm) 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.
The Transverse Ranges generally exhibit low eU in the eastern part (1.0-2.0 ppm), which
is underlain by Precambrian metamorphic rocks and Mesozoic intrusive rocks, but in the western
Transverse Ranges many of the sedimentary units are more uraniferous (as much as 5.5 ppm eU).
The western area includes marine sedimentary rock deposited in restricted marine environments
favorable for uranium accumulation and continental sedimentary rocks containing uranium
occurrences.
Mesozoic intrusive rocks of the Peninsular Ranges are generally low in uranium, with eU
values ranging 1.0-2.5 ppm eU. Some areas of Tertiary sedimentary rocks and Mesozoic granitic
rocks are more uraniferous. Equivalent uranium signatures over the Colorado Desert vary
significantly. Some Quaternary alluvium derived from rocks hi the Mojave Desert are elevated in
eU (>2.5 ppm), but other areas range from 1.0-2.5 ppm eU.
Uranium occurrences have been found widely in the southern two-thirds of California and
are generally co-extensive with areas of aeroradioactivity exceeding 2.5 ppm eU. Tertiary silicic
volcanic rocks, Tertiary sedimentary rocks rich in volcanic ash, Tertiary arkosic sandstones with
abundant plant debris, marine gray to black phosphatic shales, and sheared and faulted uraniferous
granites and metamorphic rocks are common hosts for uranium occurrences in California.
Uraniferous Tertiary sedimentary rocks are common in the western Transverse Ranges and the
Southern Coast Ranges.
SOILS
Soils in several areas are likely to be excessively well-drained, very rapidly permeable, or
both. Because of the generally mountainous terrain of much of California, coarse-grained alluvial
soils are common in many areas including most mountain valleys, the margins of valleys in the
Basin and Range and the Mojave Desert, and the margins of larger valleys such as the Great
Valley. High permeability in such soils increases the radon potential of structures built on them.
Steep slopes are also common in much of California. Steep slopes tend to be well-drained and
drier, even in areas of high precipitation, and thus tend to transmit radon more effectively either by
diffusion or flow.
IV-10 Reprinted from USGS Open-File Report 93-292-1
-------
Swelling clay soils are common in parts of California (Donley and others, 1979), including
the north-central part of the Great Valley, the eastern slopes of the northern part of the Southern
Coast Ranges, and the Los Angeles Basin area. Such soils may have enhanced permeability
during dry periods of the year due to cracking.
Ihceptisols or entisols are common throughout California (Donley and others, 1979). Both
Entisols and Inceptisols are poorly developed, lack or have poorly developed genetic horizons, and
often develop on or are composed of transported materials. In poorly developed soils only modest
amounts of uranium or radium have leached from mineral grains in the soil. Thus uranium and
radium are less likely to occur on the surfaces of mineral grains and more likely to be found within
mineral grains. In immature soils the grains have not broken down to smaller sizes so the specific
surface area remains small. Where this occurs, less radon can escape from mineral matter and
reach pore spaces. The radon potential of such soils is lower than for soils of similar radium
content that have been heavily weathered.
The effect of caliche and hardpan soils on radon potential in semiarid to arid areas is not
well understood. In such soils radium tends to accumulate in the calcium-rich caliche and hardpan,
but such material is often highly cemented and radon in these soils may not reach pore spaces
readily unless the parent radium is concentrated in surface coatings. The dryness of many of these
soils may also inhibit radon emanation.
Soil moisture-temperature regimes in California vary systematically with altitude, latitude,
and distance from the coastline (Rose and others, 1990). Soils in most of Ihe Klamath Mountains,
the northern Cascade Range and the crest of the Sierra Nevada are frigid xeric and thus are very
moist in the wintertime (56-96 percent pore space saturation in a sandy loam and 74-99 percent
saturation in a clay loam) and moderately moist in the summertime (44-56 percent saturation in a
sandy loam and 58-74 percent saturation in a clay loam). Soils in the more southerly parts of the
Klamath Mountains and the Cascade Range, the Modoc Plateau, the inland parts of the Northern
Coast Ranges, the western foothills of the Sierra Nevada, and the eastern parts of the Transverse
Ranges and the Peninsular Ranges are mesic xeric. These soils are very moist in the wintertime
(56-96 percent pore space saturation in a sandy loam and 74-99 percent saturation in a clay loam)
and slightly moist in the summertime (24-44 percent pore saturation in a sandy loam and 39-58
percent pore saturation in a clay loam).
The soils of the coastal parts of the Northern Coast Range and the Klamath Mountains are
mesic udic. These soils are very moist in the wintertime (56-96 percent pore space saturation in a
sandy loam and 74-99 percent saturation in a clay loam) and moderately moist in the summertime
(44-56 percent saturation in a sandy loam and 58-74 percent saturation in a clay loam).
Soils of the Great Valley, the Southern Coast Ranges, the western part of the Transverse
Ranges, and the coastal parts of the Peninsular Ranges are thermic xeric. They are moderately
moist in the wintertime (44-56 percent saturation in a sandy loam and 58-74 percent saturation in a
clay loam) and slightly dry in the summertime (4-24 percent saturation in a sandy loam and 6-39
percent saturation in a clay loam). Soils of the Basin and Range are generally thermic aridic except
in lower altitudes nearDeaih Valley where they are hyperthermic aridic. Soils throughout the
Mojave Desert and the Colorado Desert are hyperthermic aridic. Thermic aridic soils are slightly
moist in the wintertime (24-44 percent pore saturation in a sandy loam and 39-58 percent pore
saturation in a clay loam) and slightly dry in the summertime (4-24 percent saturation in a sandy
loam and 6-39 percent saturation in a clay loam). Hyperthermic aridic soils are slightly dry all year
(4-24 percent saturation in a sandy loam and 6-39 percent saturation in a clay loam).
IV-11 Reprinted from USGSOpen-FUe Report 93-292-1
-------
INDOORRADONDATA .
The U.S. Environmental Protection Agency (EPA), in cooperation with the State of
California, completed a random, population-based, screening survey of indoor radon levels in
1885 homes across California during the winter of 1989-1990 (Table 1, fig. 6). All data represent
2-7 day charcoal canister measurements. Colusa, San Benito, Alpine, Sierra, Mono, Liyo, and
Imperial Counties have 5 or fewer indoor radon measurements (fig. 6) and only limited
conclusions should be drawn from these data. Geologic interpretations of population-based data
must be made with caution because the measured houses are typically only from a relatively few
population centers within a given county and do not provide good geographic coverage of the
county's surface area. This has a significant impact in interpreting the radon potential of the Basin
and Range and the Mojave Desert provinces, in which nearly all of the measured houses are in the
populated parts in westernmost Riverside County, southwesternmost San Bemadino County, and
eastern Kern County.
Average indoor radon readings for counties vary from 0.3 pCS/L in Del Norte and
Riverside Counties (8 and 24 measurements, respectively) to 2.7 pCi/L in San Luis Obispo County
(15 measurements). Counties averaging less than 1.0 pCi/L generally occur in the northern Coast
Ranges, the Klamath Mountains, the northern part of the southern Coast Ranges, the San
Francisco Bay area, the Peninsular Ranges, and the Mojave Desert. Counties averaging 1.5 to 2.7
pCi/L occur in the southern part of the Great Valley, the Siena Nevada, the southern part of the
Southern Coast Ranges and the western part of the Transverse Ranges. Houses in the Basin and
Range and Mojave Desert may average 1.5 pQ/L or more, but only limited data are available.
Only Madcra, Nevada, San Joaquin, Merced, and San Luis Obispo Counties average 2.0 pCi/L or
more.
Twenty-four counties had no houses that measured 4 pCS/L or more in the State/EPA
dataset They occur in the Northern Coast Range, the Peninsular Range, the westernmost Mojave
Desert, parts of the Modoc Plateau, parts of the northernmost and central Sierra Nevada, and parts
of the northern Great Valley.
Readings above 4 pCi/L tend to be clustered (fig. 7). Some clustering coincides with high
sampling density, simply because sampling a larger number of homes in a limited area is more
likely to identify those houses whose indoor radon levels fall in the upper part of the distribution of
values. This occurs in the San Francisco Bay area, for example, but not in the Los Angeles or San
Diego areas. However, some clusters are related to geology. Most of the elevated indoor radon
values were measured in the following areas: 1) along the California coast from the western part of
Los Angeles County northward to southwestern San Luis Obispo County; 2) along the
northeastern flank of the Great Valley and along the adjacent Sierra foothills from Tulare County to
Sacramento County; 3) in the southern San Francisco Bay area in the alluvial valley surrounding
San Jose; 4) in the hilly terrane north and south of the Bay area; 5) on the west side of Lake Tahoe
and in mountain communities between Lake Tahoe and the northern Great Valley, and 6) in the
upper Sacramento River Valley in Shasta and Tehama Counties.
Clustering of values over 4 pCi/L seems to be associated with areas of elevated
aeroradioactivity in the central and southern Great Valley, in Santa Barbara and Ventura Counties,
and in some localities north of the Bay area. Perhaps slightly more than half of the elevated values
may be attributed to radium-rich rocks and soils. Elsewhere, highly permeable soils, excessively
well-drained soils on steep slopes, and soils with high radon emanation may be responsible for
many of the other elevated indoor radon levels. For example, four houses in the study around the
IV-12 Reprinted from USGS Open-File Report 93-292-1
-------
xo r ***** A * * A A I
48 i* * * »«.«» > * * >i
30
0§
7 a
Bsmt & 1st Floor Rn
% > 4 pCi/L
Oto.10
11 to'20
21 to 30
Missing Data
or < 5 measurements
100 Miles
BsmL& 1st Floor Rn
Average Concentration (pCi/L)
3
5
7dl
0.0 to 1.9
2.0 to 2.7
Missing Data
or < 5 measurements
100 Mites
Figure 6. Screening indoor radon data from the EPA/State Residential Radon Survey of
California, 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
California conducted during 1989-90. Data represent 2-7 day charcoal canister measurements
from the lowest level of each home tested.
COUNTY
ALAMEDA
AMADOR
BU'lTH
CALAVERAS
COLUSA
CONTRA COSTA
DEL NORTE
ELDORADO
FRESNO
GLENN
HUMBOLDT
IMPERIAL
INYO
KERN
KINGS
LAKE
LASSEN
LOS ANGELES
MADERA
MARIN
MARIPOSA
MENDOCINO
MERCED
MODOC
MONO
MONTEREY
NAPA
NEVADA
ORANGE
PLACER
PLUMAS
RIVERSIDE
SACRAMENTO
SAN BENITO
SAN BERNARDINO
SAN DIEGO
SAN FRANCISCO
SANJOAQUIN
SAN LUIS OBISPO
SAN MATEO
SANTA BARBARA
NO. OF
MEAS.
60
15
44
18
2
60
8
34
106
10
36
2
1
100
12
16
18
69
24
58
9
17
10
5
2
20
29
26
31
82
11
24
55
2
-17
39
20
22
15
38
90
MEAN
0.8
1.5
0.5
1.2
0.6
0.8
0.3
1.3
1.3
0.4
0.4
1.5
1.7
1.4
1.5
1.4
1.1
0.7
2.6
0.8
1.0
0.4
2.1
1.0
1.9
1.0
1.0
2.4
0.7
0.9
1.3
0.3
1.0
0.4
-•0.7
0.6
0.6
2.5
2.7
0.8
1.5
GEOM.
MEAN
0.5
0.8
0.3
0.7
0.3
0.4
0.3
0.7
0.8
0.3
0.2
1.4
1.7
1.0
0.9
0.5
0.8
0.4
1.3
0.4
0.6
0.2
1.3
0.4
1.8
0.2
0.5
0.7
0.5
0.4
0.7
0.3
0.4
0.2
0.5
0.4
0.4
1.3
0.7
0.4
0.7
MEDIAN
0.7
1.3
0.5
1.1
0.6
0.7
0.5
0.9
0.9
0.4
0.1
1.5
1.7
1.3
1.2
0.8
1.0
0.5
1.4
0.4
0.9
0.3
1.7
0.5
1.9
0.2
0.7
1.1
0.6
0.6
1.0
0.5
0.7
0.4
•0.7
0.6
0.6
1.5
0.7
0.5
0.9
STD.
DEV.
l.C
1.3
1.1
1.1
0.6
0.9
0.8
1.6
1.3
0.6
1.6
0.5
0.0
1.2
1.5
2.7
0.9
1.0
5.7
1.3
1.0
0.5
1.8
2.2
0.4
2.2
2.1
5.3
0.7
1.7
1.3
0.8
2.3
0.5
1.0
0.6
0.6
3.8
5.7
1.3
2.6
MAXIMUM
4.0
3.9
3.2
3.2
1.0
4.0
1.1
5.7
9.4
1.8
8.6
1.8
1.7
8.5
5.3
11.1
3.4
5.6
29.1
6.4
3.3
1.3
6.1
4.6
2.1
7.4
9.7
27.3
2.2
9.1
3.7
1.7
15.9
0.7
2.9
2.4
2.1
18.0
22.1
6.6
19.5
%>4pCi/L
0
0
0
0
0
0
0
9
2
0
3
0
0
2
8
6
0
1
4
3
0
0
10
20
0
10
7
12
0
5
0
0
2
0
0
0
0
9
13
3
7
%>20 pCi/L
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
4
0
0
0
0
0
0
0
0
4
0
0
0
0
0
0
0
0
0
0
7
0
0
-------
TABLE 1 (continued). Screening indoor radon data for California.
COUNTY
SANTA CLARA
SANTA CRUZ
SHASTA
SIERRA
SISKIYOU
SOLANO
SONOMA
STANISLAUS
SUTTER
TEHAMA
TRINITY
TULARE
TUOLUMNE
VENTURA
YOLO
YUBA
NO. OF
MEAS.
77
10
79
2
27
43
82
14
15
17
6
63
24
140
14
15
MEAN
1.4
1.2
1.1
1.4
0.9
0.9
0.6
1.8
1.1
0.9
0.4
1.9
1.2
1.2
1.4
1.3
GEOM.
MEAN
0.7
0.5
0.5
1.3
0.5
0.4
0.3
1.2
0.4
0.3
0.2
1.5
0.7
0.8
0.8
0.6
MEDIAN
1.0
0.8
0.6
1.4
0.8
0.5
0.3
1.3
0.4
0.8
0.2
1.5
0.9
0.9
1.2
0.8
STD.
DEV.
1.9
1.4
1.9
0.1
1.5
1.5
0.9
1.5
2.0
1.8
0.8
1.4
1.0
1.3
1.5
2.0
MAXIMUM
9.2
4.8
11.5
1.4
6.8
8:6
4.1
5.9
7.7
7.5
1.7
8.0
3.2
8.2
5.8
8.3
%>4 pCi/L
9
10
4
0
4
5
1
7
7
6
0
5
0
4
7
7
%>20 pCi/L
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
-------
Fig. 7- Approximate location of zipcodes in California with houses measuring greater than
or equal to 4 pG/L in die State/EPA Indoor Radon Survey (the data used in this
figure are from an extended version of the dataset which includes 2321
measurements).
-------
-------
western side of Lake Tahoe had screening indoor radon readings greater than 4 pCi/L. Although
the geologic setting of the individual houses in the study is not known, this area is characterized by
housing on highly permeable alluvial soils and on steep slopes with thin, coarse, sandy soils and
shallow bedrock.
Fourteen readings of 4 pCi/L or more occur in Santa Barbara and Ventura Counties
(fig. 7). Although no precise location information is available for the measured homes in the
State/EPA study, an independent study conducted in Santa Barbara County found that indoor
radon screening readings ranging from 4-50 pCi/L occur in about three-fourths of the homes sited
on the Rincon Shale in Santa Barbara County (D. Carlisle, 1991, written commun.). This unit is
widely scattered across Santa Barbara and Ventura Counties, is probably responsible for the
elevated ell signature in these two counties (see general geologic map, fig. 4), and is likely
responsible for many of the elevated indoor readings in the State/EPA study.
Los Angeles, Orange, and San Diego Counties combined contain only 1 reading above 4
pCi/L in spite of the high population density and the corresponding high sample density. In the
Basin and Range, the Mojave Desert, and the Colorado Desert in southeastern California, no
values over 4 pCi/L were measured. However, the sampling is sparse and all of the sampled
homes in the five counties (Mono, Inyo, San Bemadino, Riverside, and Imperial) come from the
westernmost part of the Basin and Range and the Mojave Desert and many houses are actually in
the adjacent Peninsular and Transverse Ranges Provinces. Only two houses were sampled in the
Colorado Desert (the town of Brawley in Imperial County). No houses were measured in the
eastern Mojave Desert where substantial parts of the area have high eU values.
The California Air Resources Board (CARB) conducted a study of outdoor radon, soil
radon, and indoor radon across the state (Liu and others, 1990). Thirty-eight houses were
sampled in a pretest in the Salinas/Santa Cruz area (Santa Cruz and Monterey Counties); 310
houses were sampled across the entire state in the main study, and 37 residences were sampled in
the Sierra Nevada foothills (Fresno, Mono, and Tulare Counties) in a followup study. Residences
were selected randomly for participation from Department of Motor Vehicles registration lists.
Annual average values in the pretest area had geometric means of about 0.9 pCi/L in living areas
with the highest value at 5.9 pCi/L. Statewide, the "whole house" geometric mean was about
0.85 pCi/L with the highest measured value being 16 pCi/L. The geometric mean of 27 basements
measured in the statewide study was 2.17 pCi/L. In the Sierra Nevada foothills, the whole house
annual average geometric mean was 1.28 pCi/L and the highest value was 8.8 pCi/L. The authors
of the CARB study concluded that the Sierra Nevada foothills and Ventura County were areas of
elevated indoor radon.
Analysis of these indoor radon data sets suggests that elevated indoor readings in California
are the result of elevated radium content in soils on which homes are located, locally highly
permeable soils, local steep slopes, and unusual housing circumstances. Basement measurements
in the various studies average 2 to 3 times that of first floor or "whole house" measurements. This
suggests that homes with basements or parts of the structure below grade are more likely to have
elevated indoor radon levels than homes tmilt above grade.
GEOLOGIC RADON POTENTIAL
The geologic radon potential of the state seems to be lowered overall by the relatively mild
climate, especially in the most populous areas, and the predominance of above grade, slab
housing. In the two indoor radon studies discussed here, only a few values exceed 20 pCi/L and a
IV-17 Reprinted from USGS Open-File Report 93-292-1
-------
relatively small percentage exceed 4 pCi/L. However, no area in California appears to be
completely free from indoor radon levels above 4 pCi/L.
Elevated, indoor radon can be expected in several geologic settings in California.
Uraniferous granites, uraniferous Tertiary silicic volcanic and sedimentary rocks, uraniferous dark
marine shales, and residual soils and alluvium derived from these units are likely to have
significant percentages of homes with indoor radon levels exceeding 4 pCi/L. The most likely
areas for such rock formations to occur are those where elevated ell values occur in the
acroradiometric data (fig. 5). Where structures are sited on excessively drained soils or steep
slopes, the radon potential is higher. Extreme indoor radon levels (greater than 100 pCi/L) may be
expected where structures are inadvertently sited on uranium occurrences. In those areas where the
eU values are moderate to low, excessively well-drained soils or soils with unusually high
emanating power may locally cause some indoor radon levels to exceed 4 pCi/L. The presence of
steep slopes may also influence radon potential because, in many cases, the structure is built partly
below grade. The below-grade parts of the house are more likely to draw soil-gas radon indoors.
Where the slope is accommodated by placing the structure on stilts rather than cutting into the
hillslope, the radon potential of the structure is low.
Areas of the State along the northern coast, where precipitation and soil moisture are high
and where eU values are low, are expected to have low radon potential. Only those localities
where soils are excessively well drained are likely to yield a few homes over 4 pCi/L. The eastern
part of the Transverse Ranges and all of the Peninsular Ranges (including the Los Angeles Basin in
the northern part of the Peninsular Ranges) have relatively low eU which, coupled with the mild
climate and predominance of slab-on-grade housing, also suggests low radon potential. Those
parts of the eastern Mojave Desert and various areas of the Basin and Range where eU values are
unusually high may have increased indoor radon potential, but the effects of highly cemented,
often immature, soils on radon potential in these areas are uncertain and houses there have not been
adequately sampled.
SUMMARY
California was divided into twelve geologic provinces for which geologic radon potential
may be evaluated. A relative index of radon potential (RI) and an index of the level of confidence
in the available data (CT) (see discussion in chapter 1, the introductory section of this volume) have
been applied to each of these areas (Table 2).
The Cascade Range and Modoc Plateau are thought to have low geologic radon potential
overall in spite of the locally moderate eU signature across these two provinces. The indoor data
are sparse in this lightly populated area and litfle is known about the processes that control radon
emanation and migration in soils derived from volcanic rocks. In Susanville (8 measurements),
Lassen County, the average of all measurements was 1.8 pCi/L. In Modoc County, the average of
all measurements (6) was 2.1 pCS/L and two readings were above 4.0 pCi/L. Soils are drier here
than in areas closer to the coast and this may contribute to the apparent locally elevated indoor
radon levels in spite of relatively low eU. Steep topography and excessively well-drained soils
may also contribute to the locally moderate to elevated values.
The Northern Coast Range province has low geologic radon potential overall; however,
missing aeroradiometric data for the central part of this province lowers the confidence in this
evaluation slightly. Areas of elevated eU occur along the east side of the southern half of this
province and these are areas where some indoor radon levels exceeding 4 pCi/L are nicely to occur,
IV-18 Reprinted from USGS Open-File Report 93-292-1
-------
especially where steep, excessively well-drained, or highly permeable soils coincide with the
elevated eU in soils.
The Southern Coast Range has moderate geologic radon potential overall; however, much
of the radon potential is associated with areas of elevated radioactivity inland from the coast, from
Monterey Bay southward, and this area is less populated than areas elsewhere in this province.
Houses sited directly on radium-rich marine sedimentary rocks in this province, such as the
Monterey Formation, are very likely to exceed 4 pCi/L.
The Great Valley has low geologic radon potential overall; however, the area along the east
side of the valley from Sacramento southward seems more likely to have elevated average indoor
radon levels and a greater percentage of homes over 4 pCi/L, as indicated by higher eU values,
than the rest of the Great Valley. The Sierra Nevada has moderate radon potential overall owing to
high eU throughout much of the province and the predominance of soils that are likely to favor
radon transport Indoor radon data are sparse in this province because of the low population
density, thus the confidence in this assessmentis lower than elsewhere. The Basin and Range has
moderate radon potential overall, but the paucity of indoor radon data lowers the confidence in this
assessment
The Transverse Ranges have moderate geologic radon potential overall. The potential is
higher in the western two-thirds of the province as indicated by higher eU and the presence of
radium-rich marine sedimentary rocks such as the Rincon Shale. Indoor radon levels in houses
sited on these marine sedimentary rocks are very likely to exceed 4 pCi/L, especially where homes
are sited on steep slopes and parts of the home are below grade. The Mojave Desert also has
moderate radon potential but, like the Basin and Range, the paucity of indoor radon data lowers the
confidence in this assessment Of particular concern are the eU values exceeding 5.5 ppm in the
mountains and alluvial valleys near Blythe. Although this area is very sparsely populated, any
structures in this area may have elevated indoor radon levels.
The Peninsular Ranges have low geologic 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 indoor radon. The Los
Angeles metropolitan area at the north end of the Peninsular Ranges has low radon potential. The
Colorado Desert province has low geologic radon potential but, similarly to the Basin and Range
and the Mojave Desert, lack of indoor radon data lowers the confidence in this assessment
This is a generalized assessment of the State's geologic radon potential and there is no
substitute for having a home tested. The conclusions about radon potential presented in this report
cannot be applied to individual homes or building sites. Indoor radon levels, both high and low,
can be quite localized, and within any radon potential area there will likely be areas with higher or
lower radon potential that assigned to the area as a whole. Any local decisions about radon should
not be made without consulting all available local data. For additional information on radon and
how to test, contact your State radon program or EPA regional office. More detailed information
on state or local geology may be obtained from the State geological survey. Addresses and phone
numbers for these agencies are listed in chapter 1 of this booklet
IV-19 Reprinted fiom USGS Open-File Report 93-292-1
-------
TABLE 2. Radon Index (RI) and Confidence Index (CI) for geologic radon potential areas
of California, See figure 1 for locations of areas. See the introductory chapter for discussion of
RlandCL •
FACTOR
INDOOR RADON
RADIOACTIVITY
GEOLOGY
SOIL PERMEABILITY
ARCHITECTURE
GFE POINTS
TOTAL
RANKING
FACTOR
INDOORRADON
RADIOACTIVITY
GEOLOGY
SOIL PERMEABILITY
ARCHITECTURE
GFE POINTS
TOTAL
RANKING
Klamath
Mountains
RI CI
1 3
1 3
1 2
2 3
1
0
6 11
Low High
Southern
Coast
Range
RI O
1 3
2 3
2 2
2 3
1
+1
9 11
Mod High
Cascade
Range
RI CI
2? 1
1 3
2 2
2 2
1 -
0 -
8? 8
Low Mod
Great
Valley
RI a
1 3
2 3
2 2
2 3
1 -
0 -
8 11
Low High
Modoc
Plateau
RI CI
2? 1
1 3
2 2
2 2
1
0
8? 8
Low Mod
Sierra
Nevada
RI CI
1 1
3 3
2 2
2 2
1
0
9 8
Mod Mod
Northern
Coast
Range
RI CI
1 3
1 2
1 2
2 3
1 -
0 -
6 10
Low High
Basin &
Range
RI a
2 1
2 3
2 1
2 2
1 -
0 -
9 7
Mod Mod
IV-20 Reprinted from USGS Open-File Report 93-292-1
-------
TABLE 2 (continued).
FACTOR
INDOOR RADON
RADIOACTIVITY
GEOLOGY
SOIL PERMEABILITY
ARCHITECTURE
GFE POINTS
TOTAL
RANKING
Transverse
Ranges
RI CI
1
2
2
2
1
+1
9
Mod
3
3
2
3
11
High
Mojave
Desert
RI CT
2
3
2
2
1
0
10
Mod
1
3
1
2
7
Mod
Peninsular
Ranges
RI CI
1
1
2
2
1
0
7
Low
3
3
2
3
11
High
Colorado
Desert
RI CI
1
2
2
2
1
0
8
Lov
1
3
1
2
7
rMod
- Not used in CI.
RADON INDEX SCORING:
Radon potential category
LOW 3-8 points
MODERATE/VARIABLE 9-11 points
HIGH > 11 points
Possible range of points = 3 to 17
Probable screening indoor
Point range radon average for area
<2pCi/L
2-4pCi/L
>4pCi/L
CONFIDENCE INDEX SCORING:
LOW CONFIDENCE
MODERATE CONFIDENCE
HIGH CONFIDENCE
4-6 points
7-9 points
10-12 points
Possible range of points = 4 to 12
IV-21 Reprinted from USGS Open-File Report 93-292-1
-------
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IV-22 Reprinted from USGS Open-FHe Report 93-292-1
-------
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IV'23 Reprinted from USOSOpen-FUe Report 93-292-1
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~rado~n-222 concentrations in U.S. homes: Science, v. 234, p. 992-997.
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variations in soil moisture and temperature on soil gas radon, in The 1990 International
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alluvial aquifer in the Santa Clara Valley, California, in Graves, Barbara, ed., Radon,
radium, and other radioactivity in ground water, NWWA conference, Somerset, NJ,
Apr. 7-9, 1987, Lewis Publishers, p. 205-218.
Shapiro, M.H., Melvin, J.D., Mendenhall, M.H., Rice, A., and Tombrello, T.A., 1982, Recent
changes in southern California radon and geochemical data: EOS, v. 63, no. 45, p. 1043.
Wiegand, Jeffery, Yamamoto, Gary and Gaston, Will, 1987, Elevated levels of radioactivity in
water wells in Los Angeles and Orange counties, California, in Graves, Barbara, ed.,
Radon, radium, and other radioactivity in ground water, NWWA conference, Somerset,
NJ, Apr. 7-9,1987, Lewis Publishers, p. 71-72.
Wollenburg, H.A., and Rezvan, K.L., 1990, Radium regionalization in California: Geophysical
Research Letters, v. 17, no. 6, p. 805-808.
ZuMn, Jeffrey G., Hammond, Douglas E., Ku, Teh-Lung and Elders, Wilfred A., 1987,
Uranium-thorium series radionuclides in brines and reservoir rocks from two deep
geothermal boreholes in the Salton Sea geothermal field, southeastern California:
Geochimica et Cosmochimica Acta, v. 51, no. 10, p. 2719-2731.
IV-24 Reprinted from USGS Open-FUe Report 93-292-1
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EPA's Map of Radon Zones
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