United States
Environmental Protection
Agency
Air and Radiation
(6604 J)
402-R-93-067
September 1993
oEPA EPA's Map of Radon Zones
WASHINGTON
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EPA'S MAP OF RADON ZONES
WASHINGTON
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-instrumerital 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 10 GEOLOGIC RADON POTENTIAL
SUMMARY
V. PRELIMINARY GEOLOGIC RADON POTENTIAL
ASSESSMENT OF WASHINGTON
V. EPA'S MAP OF RADON ZONES -- WASHINGTON
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OVERVIEW
Sections 307 and 309 of the 1988 Indoor Radon Abatement Act (IRAA) direct EPA to
identify areas of the United States that have the potential to produce elevated levels of radon.
EPA, the U.S. Geological Survey (USGS), and the Association of American State Geologists
(AASG) have worked closely over the past several years to produce a series of maps and
documents which address these directives. The EPA Map of Radon Zones is a compilation of
that work and fulfills the requirements of sections 307 and 309 of IRAA. The Map of Radon
Zones identifies,- on a county-by-county basis, areas of the U.S. that have the highest potential
for elevated indoor radon levels (greater than 4 pCi/L). •
The Map of Radon Zones is designed to assist national, State and local governments
and organizations to target their radon program activities and resources. It is also intended.to
help building code officials determine areas that are the highest priority for adopting radon-
resistant building practices. The Map of Radon Zones should not be used to determine if
individual homes in any given area need to be tested for radon. EPA recommends that all
homes be tested for radon, regardless of geographic location or the zone designation of
the county in which they are located.
This document provides background information concerning the development of the
Map of Radon Zones. It explains the purposes of the map, the approach for developing the
map (including the respective roles of EPA and USGS), the data sources used, the conclusions
and confidence levels developed for the prediction of radon potential, and the review process
that was conducted to finalize this effort.
BACKGROUND
Radon (Rn222) is a colorless, odorless, radioactive gas. It comes from the natural
decay of uranium that is found in nearly all soils. It typically moves through the ground to
the air above and into homes and other buildings through cracks and openings in the
foundation. Any home, school or workplace may have a radon problem, regardless of
whether it is new or old, well-sealed or drafty, or with or without a basement. Nearly one out
of every 15 homes in the U.S. is estimated to have elevated annual average levels of indoor
radon. .
Radon first gained national attention in early 1984, when extremely high levels of
indoor radon were found in areas of Pennsylvania, New Jersey, and New York, along the
Reading Prong-physiographic province. EPA established a Radon Program in 1985 to assist
States and homeowners in reducing their risk of lung cancer from indoor radon.
Since 1985, EPA and USGS have been working together to continually increase our
understanding of radon sources and the migration dynamics that cause elevated indoor radon
levels. Early efforts resulted in the 1987 map entitled "Areas with Potentially High Radon
Levels." This map was based on limited geologic information only because few indoor radon
measurements were available at the time. The development of EPA's Map of Radon Zones
and its technical foundation, USGS' National Geologic Radon Province Map, has been based
on additional information from six years of the State/EPA Residential Radon Surveys,
independent State residential surveys, and continued expansion of geologic and geophysical
information, particularly the data from the National Uranium Resource Evaluation project.
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Purpose of the Map of Radon Zones
f
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 USGS' Geologic Radon
Province Map and the State chapters provided with this map for more detailed
information, as well as any locally available data.
Map Validation
The Map of Radon Zones is intended to represent a preliminary assessment of radon
potential for the entire United States. The factors that are used in this effort -indoor radon
data, geology, aerial radioactivity, soils, and foundation type - are basic indicators for radon
potential. It is important to note, however, that the map's county zone designations are not
"statistically valid" predictions due to the nature of the data available for these 5 factors at the
county level. In order to validate the map in light of this lack of statistical confidence, EPA
conducted a number of analyses. These analyses have helped EPA to identify the best
situations in which to apply the map, and its limitations.
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Figure 3
Geologic Radon Potential Provinces for Nebraska
Liscoln County
Uoieriit I m
Figure 4
NEBRASKA - EPA Map of Radon Zones
Liacol a County
Zest I Zoae 2 Zoae 3
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One such analysis involved comparing county zone designations to indoor radon
measurements from the State/EPA Residential Radon Surveys (SRRS). Screening averages
for counties with at least 100 measurements were compared to the counties' predicted radon
potential as indicated by the Map of Radon Zones. EPA found that 72% of the county
screening averages were correctly reflected by the appropriate zone designations on the Map.
In all other cases, they only differed by 1 zone.
Another accuracy analysis used the annual average data from the National Residential
Radon Survey (NRRS). The NRRS indicated that approximately 6 million homes in the
United States have annual averages greater than or equal to 4 pCi/L. By cross checking the
county location of the approximately 5,700 homes which participated in the survey, their
radon measurements, and the zone designations for these counties, EPA found that
approximately 3.8 million homes of the 5.4 million homes with radon levels greater than or
equal to 4 pCi/L will be found in counties designated as Zone 1. A random sampling of an
equal number of counties would have only found approximately 1.8 million homes greater
than 4 pCi/L. In other words, this analysis indicated that the map approach is three times
more efficient at identifying high radon areas than random selection of zone designations.
Together, these analyses show that the approach EPA used to develop the Map of
Radon Zones is a reasonable one. In addition, the Agency's confidence is enhanced by results
of the extensive State review process — the map generally agrees with the States' knowledge
of and experience in their own jurisdictions. However, the accuracy analyses highlight two
important points: the fact that elevated levels will be found in Zones 2 and 3, and that there
will be significant numbers of homes with lower indoor radon levels in all of the Zones. For
these reasons, users of the Map of Radon Zones need to supplement the Map with locally
available data whenever possible. Although all known "hot spots", i.e., localized areas of
consistently elevated levels, are discussed in the State-
specific chapters, accurately defining the boundaries of the "hot spots" on this scale of map is
not possible at this time. Also, unknown "hot spots" do exist.
The Map of Radon Zones is intended to be a starting point for characterizing radon
potential because our knowledge of radon sources and transport is always growing. Although
this effort represents the best data available at this time, EPA will continue to study these
parameters and others such as house construction, ventilation features and meteorology factors
in order to better characterize the presence of radon in U.S homes, especially in high risk
areas. These efforts will eventually assist EPA in refining and revising the conclusions of the
Map of Radon Zones. And although this map is most appropriately used as a targeting tool
by the aforementioned audiences — the Agency encourages all residents to test their homes
for radon, regardless of geographic location or the zone designation of the county in
which they live. Similarly, the Map of Radon Zones should not to be used in lieu of
testing during real estate transactions.
Review Process
The Map of Radon Zones has undergone extensive review within EPA and outside the
Agency. The Association of American State Geologists (AASG) played an integral role in
this review process. The AASG individual State geologists have reviewed their State-specific
information, the USGS Geologic Radon Province Map, and other materials for their geologic
content and consistency.
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In addition to each State geologist.providing technical comments, the State radon
offices were asked to comment on their respective States' radon potential evaluations. In
particular, the States were asked to evaluate the data used to assign their counties to specific
zones. EPA and USGS worked with the States to resolve any issues concerning county zone
designations. In a few cases, States have requested changes in county zone designations. The
requests were based on additional data from the State on geology, indoor radon
measurements, population, etc. Upon reviewing the data submitted by the States, EPA did
make some changes in zone designations. These changes, which do not strictly follow the
methodology outlined in this document, are discussed in the respective State chapters.
EPA encourages the States and counties to conduct further research and data collection
efforts to refine the Map of Radon Zones. EPA would like to be kept informed of any
changes the States, counties, or others make to the maps. Updates and revisions will be
handled in a similar fashion to the way the map was developed. States should notify EPA of
any proposed changes by forwarding the changes through the Regional EPA offices that.are
listed in Part II. Depending on the amount of new information that is presented, EPA will
consider updating this map periodically. The State radon programs should initiate proper
notification of the appropriate State officials when the Map of Radon Zones is released and
when revisions or updates are made by the State or EPA.
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THE USGS/EPA RADON POTENTIAL ASSESSMENTS: AN INTRODUCTION
by
Linda C.S. Gundersen and R. Randall Schumann
U.S. Geologic il Survey
and
Sharon W. White
U.S. Environmental Protection Agency
BACKGROUND
The Indoor Radon Abatement Act of 1988 (15 U.S.C. 2661-2671) directed the U.S.
Environmental Protection Agency (EPA) to identify areas of the United States that have the
potential to produce harmful levels of indoor radon. These characterizations were to be based
on both geological data and on indoor radon levels in homes and other structures. The EPA
also was directed to develop model standards and techniques for new building construction
that would provide adequate prevention or mitigation of radon entry. As part of an
Interagency Agreement between the EPA and the U.S. Geological Survey (USGS), the USGS
has prepared radon potential estimates for the United States. This report is one of ten
booklets that document this effort. The purpose and intended use of these reports is to help
identify areas where states can target their radon program resources, to provide guidance in
selecting the most appropriate building code options for areas, and to provide general
information on radon and geology for each state for federal, state, and municipal officials
dealing with radon issues. These reports are not intended to be used as a substitute for
indoor radon testing, and they cannot and should not be used to estimate or predict the
indoor radon concentrations of individual homes, building sites, or housing tracts. Elevated
levels of indoor radon have been found in every State, and EPA recommends that all homes
be tested for indoor radon.
Booklets detailing the radon potential assessment for the U.S. have been developed for
each State. USGS geologists are the authors of the geologic radon potential booklets. Each
booklet consists of several components, the first being an overview to the mapping project
(Part I), this introduction to the USGS assessment (Part II), including a general discussion of
radon (occurrence, transport, etc.), and details concerning the types of data used. The third
component is a summary chapter outlining the general geology and geologic radon potential
of the EPA Region (Part III). The fourth component is an individual chapter for each state
(Part IV). Each state chapter discusses the state's specific geographic setting, soils, geologic
setting, geologic radon potential, indoor radon data, and a summary outlining the radon
potential rankings of geologic areas in the state. A variety of maps are presented in each
chapter—geologic, geographic, population, soils, aerial radioactivity, and indoor radon data by
county. Finally, the booklets contain EPA's map of radon zones for each state and an
accompanying description (Part V).
Because of constraints on the scales of maps presented in these reports and because the
smallest units used to present the indoor radon data are counties, some generalizations have
been made in order to estimate the radon potential of each area. Variations in geology, soil
characteristics, climatic factors, homeowner lifestyles, and other factors that influence radon
concentrations can be quite large within any particular geologic area, so these reports cannot
be used to estimate or predict the indoor radon concentrations of individual homes or housing
II-l Reprinted from USGS Open-File Report 93-292
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tracts. Within any area of a given geologic radon potential ranking, there are likely to be
areas where the radon potential is lower or higher than that assigned to the area as a whole,
especially in larger areas such as the large counties in some western states.
In each state chapter, references to additional reports related to radon are listed for the
state, and the reader is urged to consult these reports for more detailed information. In most
cases the best sources of information on radon for specific areas are state and focal
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 (22SRa), which is, in turn,
a product of the decay of uranium («U) (fig. 1). The half-life pf 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 plary
structure, can form a capping layer that impedes the escape of soil gas to the surface
(Schumann and others, 1992). However, the shrinkage of clays can act to open or widen
cracks upon drying, thus increasing the soil's permeability to gas flow during drier periods.
Radon transport in soils occurs by two processes: (1) diffusion and (2) flow (Tanner,
1964). Diffusion is the process whereby radon atoms move from areas of higher
concentration to areas of lower concentration in response to a concentration gradient. Flow is
the process by which soil air moves through soil pores in response to differences in pressure
within the soil or between the soil and the atmosphere, carrying the radon atoms along with it.
Diffusion is the dominant radon transport process in soils of low permeability, whereas flow
tends to dominate in highly permeable soils (Sextro and others, 1987). In low-permeability
soils much of the radon may decay before it is able to enter a building because its transport
rate is reduced. Conversely, highly permeable soils, even those that are relatively low m
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 = 1(T meters), or about 2x10-* inches—this is known as alpha
recoil (Tanner, 1980). Moisture in the soil lessens the chance of a recoiling radon atom
becoming imbedded in an adjacent grain. Because water is more dense than air, a radon atom
will travel a shorter distance in a water-filled pore than in an air-filled pore, thus increasing
the likelihood that the radon atom will remain in the pore space. Intermediate moisture levels
enhance radon emanation but do not significantly affect permeability. However, high
moisture levels can significantly decrease the gas permeability of the soil and impede radon
movement through the soil. .
Concentrations of radon in soils are generally many times higher than those inside ot
buildings, ranging from tens of pCi/L to more than 100,000 PCi/L, but typically in the range
of hundreds to low thousands of pCi/L. Soil-gas radon concentrations can vary in response to
variations in climate and weather on hourly, daily, or seasonal time scales. Schumann and
others (1992) and Rose and others (1988) recorded order-of-magnitude variations in soil-gas
radon concentrations between seasons in Colorado and Pennsylvania. The most important
factors appear to be (1) soil moisture conditions, which are controlled in large part by
precipitation; (2) barometric pressure; and (3) temperature. Washington and Rose (1990)
suggest that temperature-controlled partitioning of radon between water and gas in soil pores
also has a significant influence on the amount of mobile radon in soil gas.
Homes in hilly limestone regions of the southern Appalachians were found to have higher
indoor radon concentrations during the summer than in the winter. A suggested cause for this
phenomenon involves temperature/pressure-driven flow of radon-laden air from subsurface
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solution cavities in the carbonate rock into houses. As warm air enters solution cavities that
are higher on the hillslope than the homes, it cools and settles, pushing radon-laden air from
lower in the cave or cavity system into structures on the hillslope (Gammage and'others,
1993). In contrast, homes built over caves having openings situated below the level of the
home had higher indoor radon levels in the winter, caused by cooler outside air entering the
cave, driving radon-laden air into cracks and solution cavities in the rock and soil, and
ultimately, into homes (Gammage and others, 1993).
RADON ENTRY INTO BUILDINGS
A driving force (reduced atmospheric pressure in the house relative to the soil, producing
a pressure gradient) and entry points must exist for radon to enter a building from the soil.
The negative pressure caused by furnace combustion, ventilation devices, and the stack effect
(the rising and escape of warm air from the upper floors of the building, causing a
temperature and pressure gradient within the structure) during cold winter months are
common driving forces. Cracks and other penetrations through building foundations, sump
holes, and slab-to-foundation wall joints are common entry points.
Radon levels in the basement are generally higher than those on the main floor or upper
floors of most structures. Homes with basements generally provide more entry points for
radon, commonly have a more pronounced stack effect, and typically have lower air pressure
relative to the surrounding soil than nonbasement homes. The term "nonbasement" applies to
slab-on-grade or crawl space construction.
METHODS AND SOURCES OF DATA
The assessments of radon potential in the booklets that follow this introduction were
made using five main types of data: (1) geologic (lithologic); (2) aerial radiometric; (3) soil
characteristics, including soil moisture, permeability, and drainage characteristics; (4) indoor
radon data; and (5) building architecture (specifically, whether homes in each area are built
slab-on-grade or have a basement or crawl space). These five factors were evaluated and
integrated to produce estimates of radon potential. Field measurements of soil-gas radon or
soil radioactivity were not used except where such data were available in existing, published
reports of local field studies. Where applicable, such field studies are described in the
individual state chapters.
GEOLOGIC DATA
The types and distribution of lithologic units and other geologic features in an
assessment area are of primary importance in determining radon potential. Rock types that
are most likely to cause indoor radon problems include carbonaceous black shales, glauconite-
bearing sandstones, certain kinds of fluvial sandstones and fluvial sediments, phosphorites,
chalk, karst-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).
NURE AERIAL RADIOMETRIC DATA
Aerial radiometric data are used to quantify the radioactivity of rocks and soils.
Equivalent uranium (eU) data provide an estimate of the surficial concentrations of radon
parent materials (uranium, radium) in rocks and soils. Equivalent uranium is calculated from
the counts received by a gamma-ray detector from the 1.76 MeV (mega-electron volts)
emission energy corresponding to bismuth-214 (2"Bi), with the assumption that uranium and
its decay products are in secular equilibrium. Equivalent uranium is expressed in units of
parts per million (ppm). Gamma radioactivity also may be expressed in terms of a radium
activity; 3 ppm eU corresponds to approximately 1 picocurie per gram (pCi/g) of radium-226.
Although radon is highly mobile in soil and its concentration is affected by meteorological
conditions (Kovach, 1945; Klusman and Jaacks, 1987; Schery and others, 1984; Schumann
and others, 1992), statistical correlations between average soil-gas radon concentrations and
average eU values for a wide variety of soils have been documented (Gundersen and others,
1988a, 1988b; Schumann and Owen, 1988). Aerial radiometric data can provide an estimate
of radon source strength over a region, but the amount of radon that is able to enter a home
from the soil is dependent on several local factors, including soil structure, grain size
distribution, moisture content, and permeability, as well as type of house construction and its
structural condition.
The aerial radiometric data used for these characterizations were collected as part of the
Department of Energy National Uranium Resource Evaluation (NURE) program of the 1970s
and early 1980s. The purpose of the NURE program was to identify and describe areas in the
United States having potential uranium resources (U.S. Department of Energy, 1976). The
NURE aerial radiometric data were collected by aircraft in which a gamma-ray spectrometer
was mounted, flying approximately 122 m (400 ft) above the ground surface. The equivalent
uranium maps presented in the state chapters were generated from reprocessed NURE data in
which smoothing, filtering, recalibrating, and matching of adjacent quadrangle data sets were
performed to compensate for background, altitude, calibration, and other types of errors and
inconsistencies in the original data set (Duval and others, 1989). The data were then gridded
.and contoured to produce maps of eU. with a pixel size corresponding to approximately 2.5 x
2.5 km (1.6 x 1.6 mi).
II-6 Reprinted from USGS Open-File Report 93-292
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FLIGHT LINE SPICING OF NUKE AERIAL SURVEYS
2 i'U (1 MILE)
5 IM (3 MILES)
2 t 5 KM
10 III (6 U1LES)
5 t 10 IK
NO DATA
Hgure 2. Nominal flightline spacings for NURE aerial gamma-ray surveys covering the
contiguous United States (from Duval and others, 1990). Rectangles represent I°x2° quadrangles.
-------
Figure 2 is an index map of NURE 1° x 2° quadrangles showing the flight-line spacing
for each quadrangle. In general, the more closely spaced the flightlines are the more area
JSLtuESjAe aerial gamma survey, and thus, more detail is available m the'data set.
For an altitude of 400 ft above the ground surface and with primary flightime< W
typically between 3 and 6 miles, less than 10 percent of the ground surface of the United
la es was actually measured by the airborne gamma-ray detectors (Duval and other 1989),
although some areas had better coverage than others due to the differences in flight-line
tcingbetween areas (fig. 2). This suggests that some localized uranium anomaly 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
TsmaHer) the National eU map (Duval and others, 1989) gives reasonably good estima^s 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 da a.
The shallow (20-30 cm) depth of investigation of gamma-ray spectrometers, either
grounded or Lome (Duval and others, 1971; Durrance, 1986), ^*«£^
data may sometimes underestimate the radon-source strength m soils in which som 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
sSfsdution processes. Under these conditions the surface gamma-ray signal "jay 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
eeochemical factors. There is reason to believe that correlations of eU with actual soil
fadTum 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 shrmk-
swell potential, vegetative cover, generalized groundwater characteristics, and land1 use. The
Sports 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 summanes 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, ;*rmk-swell
potential drainage characteristics, depth to seasonal high water table, permeability and other
?elevlnt'characteristics of each soil group noted. Technical soil terms used m soil surveys are
generally complex; however, a good summary of soil engineering terms and the>™«™*
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. .
H-9 Reprinted from USGS Open-File Report 93-292
-------
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Data for only those counties with five or more measurements are shown in the indoor
radon maps in the state chapters, although data for all counties with a nonzero number of
measurements are listed in the indoor radon data tables in each state chapter. In total, indoor
radon data from more than 100,000 homes nationwide were used in the compilation of these
assessments. Radon data from State or regional indoor radon surveys, public health
organizations, or other sources are discussed in addition to the primary data sources where
they are available. .Nearly all of the data used in these evaluations represent short-term (2-7
day) screening measurements from the lowest livable space of the homes. Specific details
concerning the nature and use of indoor radon data sets other than the State/EPA Residential
Radon Survey are discussed in the individual State chapters.
RADON INDEX AND CONFIDENCE INDEX
Many of the geologic methods used to evaluate an area for radon potential require
subjective opinions based on the professional judgment and experience of the individual
geologist. The evaluations are nevertheless based on established scientific principles that are
universally applicable to any geographic area or geologic setting. This section describes the
methods and conceptual framework used by the U.S. Geological Survey to evaluate areas for
radon potential based on the five factors discussed iri the previous sections. The scheme is
divided into two basic parts, a Radon Index (RI), used to rank the general radon potential of
the area, and the Confidence Index (CI), used to express the level of confidence in the
prediction based on the quantity and quality of the data used to make the determination. This
scheme works best if the areas to be evaluated are delineated by geologically-based
boundaries (geologic provinces) rather than political ones (state/county boundaries) in which
the geology may vary across the area.
Radon Index. Table 1 presents the Radon Index (RI) matrix. The five factors—indoor
radon data, geology, aerial radioactivity, soil parameters, and house foundation type—were
quantitatively ranked (using a point value of 1, 2, or 3) for their respective contribution to
radon potential in a given area. At least some data for the 5 factors are consistently available
for every geologic province. Because each of these main factors encompass a wide variety of
complex and variable components, the geologists performing the evaluation relied heavily on
their professional judgment and experience in assigning point values to each category and in
determining the overall radon potential ranking. Background information on these factors is
discussed in more detail in the preceding sections of this introduction.
Indoor radon was evaluated using unweighted arithmetic means of the indoor radon data
for each geologic area to be assessed. Other expressions of indoor radon levels in an area
also could have been used, such as weighted averages or annual averages, but these types of
data were not consistently available for the entire United States at the time of this writing, or
the schemes were not considered sufficient to provide a means of consistent comparison
across all areas. For this report, charcoal-canister screening measurement data from the
State/EPA Residential Radon Surveys and other carefully selected sources were used, as
described in the preceding section. To maintain consistency, other indoor radon data sets
(vendor, state, or other data) were not considered in scoring the indoor radon factor of the
Radon Index if they were not randomly sampled or could not be statistically combined with
the primary indoor radon data sets. However, these additional radon data sets can provide a
means to further refine correlations between geologic factors and radon potential, so they are
II-11 Reprinted from USGS Open-File Report 93-292
-------
TABLE 1. RADON INDEX MATRIX, "ppm elJ" indicates parts per million of equivalent
uranium, as indicated by NURE aerial radiometric data. See text discussion for details.
INCREASING RADON POTENTIAL ^
FACTOR
INDOOR RADON (average)
AERIAL RADIOACTIVITY
GEOLOGY*
SOIL PERMEABILITY
ARCHITECTURE TYPE
POINT VALUE
1
<2pCi/L
< 1.5 ppm eU
negative
low
mostly slab
2
2 - 4 pCi/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
MODERATE
LOW
No relevant geologic field studies
+2 points
+1 point
-2 points
0 points
SCORING:
Radon potential category
Probable average screening
Point range indoor radon for area
LOW
MODERATE/VARIABLE
HIGH
3-8 points
9-11 points
12-17 points
<2pCi/L
2-4pCi/L
>4pCi/L
POSSIBLE RANGE OF POINTS = 3 to 17
TABLE 2. CONFDDENCE INDEX MATRIX
INCREASING CONFIDENCE
FACTOR
INDOOR RADON DATA
AERIAL RADIO ACTIVITY
GEOLOGIC DATA
SOIL PERMEABILITY
POINT VALUE
1
sparse/no data
questionable/no data
questionable
questionable/no data
2
fair coverage/quality
glacial cover
variable
variable
3
good coverage/quality
no glacial cover
proven geol. model
reliable, abundant
SCORING:
LOW CONFIDENCE
MODERATE CONFIDENCE
HIGH CONFIDENCE
4-6 points
7-9 points
10 - 12 points
POSSIBLE RANGE OF POINTS = 4 to 12
II-12 Reprinted firom USGS Open-File Report 93-292
-------
included as supplementary information and are discussed in the individual State chapters. If
the average screening indoor radon level for an area was less than 2 pCi/L, the indoor radon
factor was assigned 1 point, if it was between 2 and 4 pCi/L, it was scored 2 points, and if
the average screening indoor radon level for an area was greater than 4 pCi/L, the indoor
radon factor was assigned 3 RI points.
Aerial radioactivity data used in this report are from the equivalent uranium map of the
conterminous United States compiled from NURE aerial gamma-ray surveys (Duval and
others, 1989). These data indicate the gamma radioactivity from approximately the upper 30
cm of rock and soil, expressed in units of ppm equivalent uranium. An approximate average
value of eU was determined visually for each area and point values assigned based on
whether the overall eU for the area falls below 1.5 ppm (1 point), between 1.5 and 2.5 ppm
(2 points), or greater than 2.5 ppm (3 points).
The geology factor is complex and actually incorporates many geologic characteristics. In
the matrix, "positive" and "negative" refer to the presence or absence and distribution of rock
types known to have high uranium contents and to generate elevated radon in soils or indoors.
Examples of "positive" rock types include granites, black shales, phosphatic rocks, and other
rock types described in the preceding "geologic data" section. Examples of "negative" rock
types include marine quartz sands and some clays. The term "variable" indicates that the
geology within the region is variable or that the rock types in the area are known or suspected
to generate elevated radon in some areas but not in others due to compositional differences,
climatic effects, localizeddistribution of uranium, or other factors. Geologic information
indicates not only how much uranium is present in the rocks and soils but also gives clues for
predicting general radon emanation and mobility characteristics through additional factors
such as structure (notably the presence of faults or shears) and geochemical characteristics
(for example, a phosphate-rich sandstone will likely contain more uranium than a sandstone
containing little or no phosphate because the phosphate forms chemical complexes with
uranium). "Negative", "variable", and "positive" geology were assigned 1, 2, and 3 points,
respectively. .
In cases where additional reinforcing or contradictory geologic evidence is available,
Geologic Field Evidence (GFE) points were added to or subtracted from an area's score
(Table 1). Relevant geologic field studies are important to enhancing our understanding of
how geologic processes affect radon distribution. In some cases, geologic models and
supporting field data reinforced an already strong (high or low) score; in others, they provided
important contradictory data. GFE points were applied for geologically-sound evidence that
supports the prediction (but which may contradict one or more factors) on the basis of known
geologic field studies in the area or in areas with geologic and climatic settings similar
enough that they could be applied with full confidence. For example, areas of the Dakotas,
Minnesota, and Iowa that are covered with Wisconsin-age glacial deposits exhibit a low aerial
radiometric signature and score only one RI point in that category. However, data from
geologic field studies in North Dakota and Minnesota (Schumann and others, 1991) suggest
that eU is a poor predictor of geologic radon potential in this area because radionuclides have
11-13 Reprinted from USGS Open-File Report 93-292
-------
been leached from the upper soil layers but are present and possibly even concentrated in
deeper soil horizons, generating significant soil-gas radon. This positive supporting field
evidence adds two GFE points to the score, which helps to counteract the invalid'conclusion
suggested by the radiometric data. No GFE points are awarded if there are no documented
field studies for the area.
"Soil permeability" refers to several soil characteristics that influence radon concentration
and mobility, including soil type, grain size, structure, soil moisture, drainage, slope, and
permeability. In the matrix, "low" refers to permeabilities less than about 0.6 in/hr; "high"
corresponds to greater than about 6.0 in/hr, in U.S. Soil Conservation Service (SCS) standard
soil percolation tests. The SCS data are for water permeability, which generally correlates
well with the gas permeability of the soil except when the soil moisture content is very high.
Areas with consistently high water tables were thus considered to have low gas permeability.
"Low, "moderate", and "high" permeability were assigned 1, 2, and 3 points, respectively.
Architecture type refers to whether homes in the area have mostly basements (3 points),
mostly slab-on-grade construction (1 point), or a mixture of the'two. Split-level and crawl
space homes fall into the "mixed" category (2 points). Architecture information is necessary
to properly interpret the indoor radon data and produce geologic radon potential categories
that are consistent with screening indoor radon data.
The overall RI for an area is calculated by adding the individual RI scores for the 5
factors, plus or minus GFE points, if any. The total RI for an area falls in one of three
categories—low, moderate or variable, or high. The point ranges for the three categories were
determined by examining the possible combinations of points for the 5 factors and setting
rules such that a majority (3 of 5 factors) would determine the final score for the low and
high categories, with allowances for possible deviation from an ideal score by the other two
factors. The moderate/variable category lies between these two ranges. A total deviation of 3
points from the "ideal" score was considered reasonable to allow for natural variability of
factors—if two of the five factors are allowed to vary from the "ideal" for a category, they
can differ by a minimum of 2 (1 point different each) and a maximum of 4 points (2 points
different each). With "ideal" scores of 5, 10, and 15 points describing low, moderate, and
high geologic radon potential, respectively, an ideal low score of 5 points plus 3 points for
possible variability allows a maximum of 8 points in the low category. Similarly, an ideal
high score of 15 points minus 3 points gives a minimum of 12 points for the high category.
Note, however, that if both other factors differ by two points from the "ideal", indicating
considerable variability in the system, the total point score would lie in the adjacent (i.e.,
moderate/variable) category.
Confidence Index. Except for architecture type, the same factors were used to establish a
Confidence Index (CI) for the radon potential prediction for each area (Table 2). Architecture
type was not included in the confidence index because house construction data are readily and
reliably available through surveys taken by agencies and industry groups including the
National Association of Home Builders, U.S. Department of Housing and Urban
Development, and the Federal Housing Administration; thus it was not considered necessary
11-14 Reprinted from USGS Open-File Report 93-292
-------
to question the quality or validity of these data. The other factors were scored on the basis of
the quality and quantity of the data used to complete the RI matrix.
Indoor radon data were evaluated based on the distribution and number of data points and
on whether the "data were collected by random sampling (State/EPA Residential Radon Survey
or other state survey data) or volunteered vendor data (likely to be nonrandom and biased
toward population centers and/or high indoor radon levels). The categories listed in the CI
matrix for indoor radon data ("sparse or no data", "fair coverage or quality", arid "good
coverage/quality") indicate the sampling density and statistical robustness of an indoor radon
data set. Data from the State/EPA Residential Radon.Survey and statistically valid state.
surveys were typically assigned 3 Confidence Index points unless the data were poorly
distributed or absent in the area evaluated.
Aerial radioactivity data are available for all but a few areas of the continental United
States and for part of Alaska. An evaluation of the quality of the radioactivity data was based
on whether there appeared to be a good correlation between the radioactivity and the actual
amount of uranium or radium available to generate mobile radon in the rocks and soils of the
area evaluated. In general, the, greatest problems with correlations among eU, geology, and
soil-gas or indoor radon levels were associated with glacial deposits (see the discussion in a
previous section) and typically were assigned a 2-point Confidence Index score. Correlations
among eU, geology, and radon were generally sound in unglaciated areas and were usually
assigned 3 CI points. Again, however, radioactivity data in some unglaciated areas may have
been assigned fewer than 3 points, and in glaciated areas may be assigned only one point, if
the data were considered questionable or if coverage was poor.
To assign Confidence Index scores for the geologic data factor, rock types and geologic
settings for which a physical-chemical, process-based understanding of radon generation and
mobility exists were regarded as having "proven geologic models" (3 points); a high
confidence could be held for predictions in such areas. Rocks for which the processes are
less well known or for which data are contradictory were regarded as "variable" (2 points),
and those about which little is known or for which no apparent correlations have been found
were deemed "questionable" (1 point).
The soil permeability factor was also scored based on quality and amount of data. The
three categories for soil permeability in the Confidence Index are similar in concept, and
scored similarly, to those for the geologic data factor. Soil permeability can be roughly
estimated from grain size and drainage class if data from standard, accepted soil percolation
tests are unavailable; however, the reliability of the data would be lower than if percolation
test figures or other measured permeability data are available, because an estimate of this type
does not encompass all the factors that affect soil permeability and thus may be inaccurate in
some instances. Most published soil permeability data are for water; although this is
generally closely related to the air permeability of the soil, there are some instances when it
may provide an incorrect estimate. Examples of areas in which water permeability data may
not accurately reflect air permeability include areas with consistently high levels of soil
moisture, or clay-rich soils, which would have a low water permeability but may have a
11-15 Reprinted from USGS Open-File Report 93-292
-------
significantly higher air permeability when dry due to shrinkage cracks in the soil. These
additional Lors were applied to the soil permeability factor when ass.gmng the W score, tat
may have less certainty in some cases and thus would be ass,gned a lower CI score.
L Radon Index and Confidence Index give a general ,nd,ca,,on of the relanve _
contributions of the interrelated geologic factors influencing radon generate and transport m
ocks am! soils and thus, of the potential for elevated indoor radon levels to occur ma
p±uTa " However, because these reports are somewhat generalized to cover relanvely
S Teas of States, i, is highiy recommended tha, more detailed stud.es be performed m
^ areas of interest, using the methods and general information m these booklets as a gu,de.
II-16 Reprinted from USGS Open-File Report 93-292
-------
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Deffeyes, K.S., and MacGregor, I.D., 1980, World uranium resources: Scientific American,
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Durrance, E.M.,. 1986, Radioactivity in geology: Principles and applications: New York, N.Y.,
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Duval, J.S., 1989, Radioactivity and some of its applications in geology: Proceedings of the
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Duval, J.S., Jones, W.J., Riggle, F.R., and Pitkin, J.A., 1989, Equivalent uranium map of
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Duval, J.S., Reimer, G.M., Schumann, R.R., Owen, D.E., and Otton, J.K., 1990, Soil-gas
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Klusman, R. W., and Jaacks, J. A., 1987, Environmental influences upon mercury, radon, and
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Kovach, E.M., 1945, Meteorological influences upon the radon content of soil gas: Transactions,
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Kunz, C., Laymon, C.A., and Parker, C., 1989, Gravelly soils and indoor radon, in Osborne,
M.C., and Harrison, J., eds., Proceedings of the 1988 EPA Symposium on Radon and
Radon Reduction Technology, Volume 1: U.S. Environmental Protection Agency Report
EPA/600/9-89/006A, p. 5-75-5-86.
Muessig, K., and Bell, C., 1988, Use of airborne radiometric data to direct testing for elevated
indoor radon: Northeastern Environmental Science, v. 7, no. 1, p. 45-51.
Ronca-Battista, M., Moon, M., Bergsten, J., White, S.B., Holt, N., and Alexander, B., 1988,
Radon-222 concentrations in the United States-Results of sample surveys in five states:
Radiation Protection Dosimetry, v. 24, p. 307-312.
Rose, A.W., Washington, J.W., and Greeman, D.J., 1988, Variability of radon with depth and
season in a central Pennsylvania soil developed on limestone: Northeastern Environmental
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Schery, S.D., Gaeddert, D.H., and Wilkening, M.H., 1984, Factors affecting exhalation of radon
from a gravelly sandy loam: Journal of Geophysical Research, v. 89, p. 7299-7309.
Schumann, R.R., and Owen, D.E., 1988, Relationships between geology, equivalent uranium
concentration, and radon in soil gas, Fairfax County, Virginia: U.S. Geological Survey
Open-File Report 88-18,28 p.
Schumann, R.R., and Gundersen, L.C.S., 1991, Regional differences in radon emanation
coefficients in soils: Geological Society of America Abstracts With Programs, v. 23,
no. 1, p. 125.
Schumann, R.R., Peake, R.T., Schmidt, K.M., and Owen, D.E., 1991, Correlations of soil-gas
and indoor radon with geology in glacially derived soils of the northern Great Plains, in
Proceedings of the 1990 International Symposium on Radon and Radon Reduction
Technology, Volume 2, Symposium Oral Papers: U.S. Environmental Protection Agency
report EPA/600/9-91/026b, p. 6-23-6-36.
JJ-18 Reprinted from USGS Open-Ftte 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, Term., U.S. Department of
Energy Report ORNL/SUB/84-0024/1.
Smith, R.C., II, Reilly, M.A., Rose, A.W., Barnes, J.H., and Berkheiser, S/W., Jr., 1987,
Radon: a profound case: Pennsylvania Geology, v. 18, p. 1-7.
Tanner, A.B., 1964, Radon migration in the ground: a review, in Adams, J.A.S., and Lowder,
W.M., eds., The natural radiation environment: Chicago, HI., University of Chicago
Press, p. 161-190.
Tanner, A.B., 1980, Radon migration in the ground: a supplementary review, in Gesell, T.F.,
and Lowder, W.M. (eds), Natural radiation environment HI, Symposium proceedings,
Houston, Texas, v. 1, p. 5-56.
U.S. Department of Agriculture, 1987, Principal kinds of soils: Orders, suborders, and great
groups: U.S. Geological Survey, National Atlas of the United States of America, sheet
38077-BE-NA-07M-00, scale 1:7,500,000.
U.S. Department of Energy, 1976, National Uranium Resource Evaluation preliminary report,
prepared by the U.S. Energy Research and Development Administration, Grand Junction,
Colo.: GJO-11(76).
Wanty, Richard B., and Schoen, Robert, 1991, A review of the chemical processes affecting the
mobility of radionuclides in natural waters, with applications, in Gundersen, Linda C.S.,
and Richard B. Wanty, eds., Field studies of radon in rocks, soils, and water: U.S.
Geological Survey Bulletin no. 1971, p. 183-194.
Washington, J.W., and Rose, A.W., 1990, Regional and temporal relations of radon in soil gas to
soil temperature and moisture: Geophysical Research Letters, v. 17, p. 829-832.
White, S.B., Bergsten, J.W., Alexander, B.V., and Ronca-Battista, M., 1989, Multi-State
surveys of indoor 222Rn: Health Physics, v. 57, p. 891-896.
U-19 Reprinted from USGS Open-File Report 93-292
-------
APPENDIX A
GEOLOGIC TIME SCALE
Subdivisions (and their symbols)
Eon or
Eonothem
Phanerozoic2
Proterozoic
(c)
Archean
(A)
Era or
Erathem
Cenozoic
(CD
Mesozoic2
(Mi)
Paleozoic
(Pi)
UM
MKJOI*
£•"¥ „
LJ1§
Miaow
tarty
Period, System,
Subperiod, Subsystem
Quaternary
(Q)
Nieo'oene 2
Su&period or
T.n;,,Y Subsystem IN)
m Paleogene
Suboeriod or
Subsystem (Pi)
Cretaceous
(K)
Jurassic
(J)
Triassic
CR)
Permian
(P)
Pennsylvanian
Carboniferous 'P'
(C) Mississippian
(M)
Devonian
mi
Silurian
(S)
Ordovician
• (O)
Cambrian
fC)
Epoch or Series'
Holocene
Pleistocene
.Pliocene
Miocene
Oligocene .
Eocene
Paleocene
Late
Early
Late
Middle
Early
Late
Middle
Early
Late
Early
Late
Middle
Early
Late
Early
Late
Middle
Early
Late
Middle
Early
Late
Middle
Early
Late
Middle
Early
Upper
Lower
Upper
Middle
Lower
Upper
Middle
Lower
Upper
Lower
Upper
Middle
Lower
Upper
Lower
Upper
Middle
Lower
Upper
Middle
Lower
Upper
.Middle
Lower
Upper
Middle
Lower
None defined
None defined
None defined
None defined
None defined
None defined
Age estimates
••* boundaries
in mega-annum
(Ma)1
5 a ci— 5 •?!
410 (405-415)
500 (495-510)
-5703
900
— 2500
3000
3800?
reflect uncertainties of bolopie and btostratigraphie age assignment!. Ag« boundaries not clo»«ly bracketed by existing
data shown by •» Decay constants and Isotopic ratios employed are ched in Steiger and Jlg«r (1877). Designation m.y. used for an
bnervsJ of time.
1 Modifiers (lower, middle, upper or early, middle, late) wtwn used with these Hems are informal divisions of the larger unit: the
first totter of th* modifier b lowercase.
3 Rocks older than 570 Ma also called Precambrian (p€). a time term without specific rank.
'informal time term without specific rank.
USGS Open-File Report 93-292
-------
APPENDIX B
GLOSSARY OF TERMS
Units of measure
pCi/L (picocuries per liter)- a unit of measure of radioactivity used to describe radon
concentrations in a volume of air. One picocurie (10~12 curies) is equal to about 2.2 disintegrations
of radon atoms per minute. A liter is about 1.06 quarts. The average concentration of radon in
U.S. homes measured to date is between land 2 pCi/L.
Bq/m3 (Becquerels per cubic meter)- a metric unit of radioactivity used to describe radon
concentrations in a volume of air. One becquerel is equal to one radioactive disintegration per
second. One pCi/L is equal to 37 Bq/m3.
ppm (parts per million)- a unit of measure of concentration by weight of an element in a
substance, in this case, soil or rock. One ppm of uranium contained in a ton of rock corresponds
to about 0.03 ounces of uranium. The average concentration of uranium in soils in the United
States is between 1 and 2 ppm.
in/hr (inches per hour)- a unit of measure used by soil scientists and engineers to describe the
permeability of a soil to water flowing through it It is measured by digging a hole 1 foot (12
inches) square and one foot deep, filling it with water, and measuring the time it takes for the water
to drain from the hole. The drop in height of the water level in the hole, measured in inches, is
then divided by the time (in hours) to determine the permeability. Soils range in permeability from
less than 0.06 in/hr to greater than 20 in/hr, but most soils in the United States have permeabilities
between these two extremes.
Geologic terms and terms related to the study of radon
aerial radiometric, aeroradiometric survey A survey of radioactivity, usually gamma rays,
taken by an aircraft carrying a gamma-ray spectrometer pointed at the ground surface.
alluvial fan A low, widespread mass of loose rock and soil material, shaped like an open fan
and deposited by a stream at the point where it flows from a narrow mountain valley out onto a
plain or broader valley. May also form at the junction with larger streams or when the gradient of
the stream abruptly decreases.
alluvium, alluvial General terms referring to unconsolidated detrital material deposited by a
stream or other body of running water.
alpha-track detector A passive radon measurement device consisting of a plastic film that is
sensitive to alpha particles. The film is etched with acid in a laboratory after it is exposed. The
etching reveals scratches, or "tracks", left by the alpha particles resulting from radon decay , which
can then be counted to calculate the radon concentration. Useful for long-term (1-12 months)
radon tests.
amphibolite A mafic metamorphic rock consisting mainly of pyroxenes and(or) amphibole and
plagioclase.
n-21 Reprinted from USGS Open-File Report 93-292
-------
argillite, argillaceous Terms referring to a rock derived from clay or shale, or any sedimentary
rock containing an appreciable amount of clay-size material, Le., argillaceous sandstone.
arid Term describing a climate characterized by dryness, or an evaporation rate that exceeds the
amount of precipitation.
basalt A general term for a dark-colored mafic igneous rocks that may be of extrusive origin,
such as volcanic basalt flows, or intrusive origin, such as basalt dikes.
batholith A mass of plutonic igneous rock that has more than 40 square miles of surface
exposure and no known bottom.
carbonate A sedimentary rock consisting of the carbonate (COs) compounds of calcium,
magnesium, or iron, e.g. limestone and dolomite.
carbonaceous Said of a rock or sediment that is rich in carbon, is coaly, or contains organic
matter.
charcoal canister A passive radon measurement device consisting of a small container of
granulated activated charcoal that is designed to adsorb radon. Useful for short duration (2-7 days)
measurements only. May be referred to as a "screening" test
chert A hard, extremely dense sedimentary rock consisting dominantly of interlocking crystals of
quartz. Crystals are not visible to the naked eye, giving the rock a milky, dull luster. It may be
white or gray but is commonly colored red, black, yellow, blue, pink, brown, or green.
clastic pertaining to a rock or sediment composed of fragments that are derived from preexisting
rocks or minerals. The most common clastic sedimentary rocks are sandstone and shale.
clay A rock containing clay mineral fragments or material of any composition having a diameter
less than 1/256 mm.
clay mineral One of a complex and loosely defined group of finely crystalline minerals made up
of water, silicate and aluminum (and a wide variety of other elements). They are formed chiefly by
alteration or weathering of primary silicate minerals: Certain clay minerals are noted for their small
size and ability to absorb substantial amounts of water, causing them to swell. The change in size
that occurs as these clays change between dry and wet is referred to as their "shrink-swell"
potential.
concretion A hard, compact mass of mineral matter, normally subspherical but commonly
irregular in shape; formed by precipitation from a water solution about a nucleus or center, such as
a leaf, shell, bone, or fossil, within a sedimentary or fractured rock.
conglomerate A coarse-grained, clastic sedimentary rock composed of rock and mineral
fragments larger than 2 mm, set in a finer-grained matrix of clastic material.
cuesta A hill or ridge with a gentle slope on one side and a steep slope on the other. The
formation of a cuesta is controlled by the different weathering properties and the structural dip of
the rocks forming the hill or ridge.
daughter product A nuclide formed by the disintegration of a radioactive precursor or "parent"
atom.
n-22 Reprinted from USGS Open-File Report 93-292
-------
delta, deltaic Referring to a low, flat, alluvial tract of land having a triangular or fan shape,
located at or near the mouth of a river. It results from the accumulation of sediment deposited by a
river at the point at which the river loses its ability to transport the sediment, commonly where a
river meets a larger body of water such as a lake or ocean.
dike A tabular igneous intrusion of rock, younger than the surrounding rock, that commonly cuts
across the bedding or foliation of the rock it intrudes.
diorite A plutonic igneous rock that is medium in color and contains visible dark minerals that
make up less than 50% of the rock. It also contains abundant sodium plagioclase and minor
quartz.
dolomite A carbonate sedimentary rock of which more than 50% consists of the mineral dolomite
(CaMg(CO3)2), and is commonly white, gray, brown, yellow, or pinkish in color.
drainage The manner in which the waters of an area pass, flow off of, or flow into the soil.
Also refers to the water features of an area, such as lakes and rivers, that drain it
eolian Pertaining to sediments deposited by the wind.
esker A long, narrow, steep-sided ridge composed of irregular beds of sand and gravel deposited
by streams beneath a glacier and left behind when the ice melted.
evapotranspiration Loss of water from a land area by evaporation from the soil and
transpiration from plants.
extrusive Said of igneous rocks that have been erupted onto the surface of the Earth.
fault A fracture or zone of fractures in rock or sediment along which there has been movement
fluvial, fluvial deposit Pertaining to sediment that has been deposited by a river or stream.
foliation A linear feature in a rock defined by both mineralogic and structural characteristics. It
may be formed during deformation or metamorphism.
formation A mappable body of rock having similar characteristics.
glacial deposit Any sediment transported and deposited by a glacier or processes associated
with glaciers, such as glaciofluvial sediments deposited by streams flowing from melting glaciers.
gneiss A rock formed by metamorphism in which bands and lenses of minerals of similar
composition alternate with bands and lenses of different composition, giving the rock a striped or
"foliated" appearance.
granite Broadly applied, any coarsely crystalline, quartz- and feldspar-bearing igneous plutonic
rock. Technically, granites have between 10 and 50% quartz, and alkali feldspar comprises at least
65% of the total feldspar.
gravel An unconsolidated, natural accumulation of rock fragments consisting predominantly of
particles greater than 2 mm in size.
heavy minerals Mineral grains in sediment or sedimentary rock having higher than average
specific gravity. May form layers and lenses because of wind or water sorting by weight and size
n-23 Reprinted from USGS Open-FUe 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 rc^ks are drvi^d, the others lying sedimentary and
metamorphic.
intermontane A term that refers to an area between two mountains or mountain ranges.
intrusion, intrusive The processes of emplacement or injection of molten rock into pre-existing
rock. -Also refers to the rock formed by intrusive processes, such as an "intrusive igneous rock".
kame A low mound, knob, hummock, or short irregular ridge formed by a glacial stream at the
margin of a melting glacier; composed of bedded sand and gravel.
karst terrain A type of topography that is formed on limestone, gypsum and other rocks by
dissolution of the rock by water, forming sinkholes and caves.
lignite A brownish-black coal that is intermediate in coalification between peat and
subbituminous coal.
limestone A carbonate sedimentary rock consisting of more than 50% calcium carbonate,
primarily in the form of the mineral calcite (CaCOa).
lithology The description of rocks in hand specimen and in outcrop on the basis of color,
composition, and grain size.
loam A permeable soil composed of a mixture of relatively equal parts clay, silt, and sand, and
usually containing some organic matter.
loess A fine-grained eolian deposit composed of silt-sized particles generally thought to have
been deposited from windblown dust of Pleistocene age.
maflc 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, phpsphatic, phosphorite Any rock or sediment containing a significant amount
of phosphate minerals, i.e., minerals containing PO4.
H-24 Reprinted from USGS Open-FUe 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. . " ' •
ntecer deposit See heavy minerals
residual Formed by weathering of a material in place.
residuum Deposit of residual material.
rhyolite An extrusive igneous rock of volcanic origin, compositionally equivalent to granite.
sandstone A clastic sedimentary rock composed of sand-sized rock and mineral material that is
more or less firmly cemented. Sand particles range from 1/16 to 2 mm in size.
schist A strongly foliated crystalline rock, formed by metamorphism, that can be readily split into
thin flakes or slabs. Contains mica; minerals are typically aligned.
screening level Result of an indoor radon test taken with a charcoal canister or similar device,
for a short period of time, usually less than seven days. May indicate the potential for an indoor
radon problem but does not indicate annual exposure to radon.
sediment Deposits of rock and mineral particles or fragments originating from material that is
transported by air, water or ice, or that accumulate by natural chemical precipitation or secretion of
organisms.
semiarid Refers to a climate that has slightly more precipitation than an arid climate.
shale A fine-grained sedimentary rock formed from solidification (lithification) of clay or mud.
shear zone Refers to a roughly linear zone of rock that has been faulted by ductile or non-ductile
processes in which the rock is sheared and both sides are displaced relative to one another.
shrink-swell clay See clay mineral.
siltstone A fine-grained clastic sedimentary rock composed of silt-sized rock and mineral
material and more or less firmly cemented. Silt particles range from 1/16 to 1/256 mm in size.
sinkhole A roughly circular depression in a karst area measuring meters to tens of meters in
diameter. It is funnel shaped and is formed by collapse of the surface material into an underlying
void created by the dissolution of carbonate rock.
slope An inclined part of the earth's surface.
solution cavity A hole, channel or cave-like cavity formed by dissolution of rock.
stratigraphy The study of rock strata; also refers to the succession of rocks of a particular area.
surficial materials Unconsolidated glacial, wind-, or waterborne deposits occurring on the
earth's surface.
tablelands General term for a broad, elevated region with a nearly level surface of considerable
extent.
11-25 Reprinted from USGS Open-File Report 93-292
-------
terrace gravel Gravel-sized material that caps ridges and terraces, left behind by a stream as it
cuts down to a lower level.
terrain A tract or region of the Earth's surface considered as a physical feature or an ecological
environment.
till Unsorted, generally unconsolidated and 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.
11-26 Reprinted from USGS Open-File Report 93-292
-------
APPENDIX C
EPA REGIONAL OFFICES
EPA Regional Offices
State
EPA Region
EPA Region 1
JFK Federal Building
Boston, MA 02203
(617) 565-4502
EPA Region 2
(2AIR:RAD)
26 Federal Plaza
New York, NY 10278
(212) 264-4110
Region 3 (3AH14)
841 Chestnut Street
Philadelphia, PA 19107
(215) 597-8326
EPA Region 4
345 Courtland Street, N.E.
Atlanta, GA 30365
(404) 347-3907
EPA Region 5 (5AR26)
77 West Jackson Blvd.
Chicago, JJL 60604-3507
(312) 886-6175
EPA Region 6 (6T-AS)
1445 Ross Avenue
Dallas, TX 75202-2733
(214) 655-7224
EPA Region 7
726 Minnesota Avenue
Kansas City, KS 66101
(913) 551-7604
EPA Region 8
(8HWM-RP)
999 18th Street
One Denver Place, Suite 1300
Denver, CO 80202-2413
(303) 293-1713
EPA Region 9 (A-3)
75 Hawthorne Street
San Francisco, CA 94105
(415) 744-1048
EPA Region 10
1200 Sixth Avenue
Seattle, WA 98101
(202) 442-7660
Alabama 4
Alaska 10
Arizona 9
Arkansas 6
California 9
Colorado ~8
Connecticut 1
Delaware 3
District of Columbia 3
Florida 4
Georgia 4
Hawaii 9
Idaho 10
Illinois 5
Indiana 5
Iowa 7
Kansas.... , 7
Kentucky •• 4
Louisiana 6
Maine 1
Maryland 3
Massachusetts 1
Michigan 5
Minnesota 5 ,
Mississippi 4
Missouri 7
Montana • 8
Nebraska 7
Nevada 9
New Hampshire.. 1
New Jersey 2
New Mexico 6
New York > 2
North Carolina 4
North Dakota 8
Ohio 5
Oklahoma 6
Oregon ' 10
Pennsylvania 3
Rhode Island 1
South Carolina 4
South Dakota 8
Tennessee 4
Texas 6
Utah 8
Vermont 1
Virginia 3
Washington 10
West Virginia 3
Wisconsin 5
Wyoming 8
H-27 Reprinted from USGS Open-FUe Report 93-292
-------
STATE RADON CONTACTS
May, 1993
Alabama James McNees
Division of Radiation Control'
Alabama Department of Public Health
State Office Building
Montgomery, AL 36130
(205)242-5315
1-800-582-1866 in state
AJaslja Charles Tedford
Department of Health and Social
Services
P.O. Box 110613
Juneau,AK 99811-0613
(907)465-3019
1-800-478-4845 in state
Arizona John Stewart
Arizona Radiation Regulatory Agency
4814 South 40th St.
Phoenix, AZ 85040
(602)255-4845
Arkansas Lee Gershner
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
Cplorado Linda Martin
Department of Health
4210 East llth Avenue
Denver, CO 80220
(303) 692-3057
1-800-846-3986 in state
Connecticut Alan J. Siniscalchi
Radon Program
Connecticut Department of Health
Services
150 Washington Street
Hartford, CT 061064474
(203)566-3122
Delaware Marai G. Rejai
Office of Radiation Control
Division of Public Health
P.O. Box 637
Dover, DE 19903
(302) 736-3028
1-800-554-4636 In State
District Robert Davis
of Columbia DC Department of Consumer and
Regulatory Affairs
614 H Street NW
Room 1014
Washington, DC 20001
(202)727-71068
Florida N. Michael Gilley
Office of Radiation Control
Department of Health and
Rehabilitative Services
1317 Winewood Boulevard
Tallahassee, FL 32399-0700
(904)488-1525
1-800-543-8279 in state
Richard Schreiber
Georgia Department of Human
Resources
878 Peachtree St, Room 100
Atlanta, GA 30309
(404) 894-6644
1-800-745-0037 in state
Hawaii Russell Takata
Environmental Health Services
Division
591 Ala Moana Boulevard
Honolulu, ffl 96813-2498
(808) 5864700
11-28 Reprinted from USGS Open-File Report 93-292
-------
Idaho
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 70884-2135
(504)925-7042
1-800-256-2494 in state
Maine Bob Stilwell
Division of Health Engineering
Department of Human Services
State House, Station 10
Augusta, ME 04333
(207)289-5676
1-800-232-0842 in state
Maryland Leon J. Rachuba
Radiological Health Program
Maryland Department of the
Environment
2500 Broening Highway
Baltimore, MD 21224
(410)631-3301
1-800-872-3666 In State
Massachusetts William J. Bell
Radiation Control Program
Department of Public Health
23 Service Center
Northampton, MA 01060
(413) 586-7525
1-800-445-1255 in state
Michigan Sue Hendershott
Division of Radiological Health
Bureau of Environmental and
Occupational Health
3423 North Logan Street
P.O. Box 30195
Lansing, MI 48909
(517) 335-8194
Minnesota Laura Oatmann
Indoor Air Quality Unit
925 Delaware Street, SE
P.O. Box 59040
Minneapolis, MN 55459-0040
(612) 627-5480
1-800-798-9050 in state
n-29
Reprinted from USGS Open-File Report 93-292
-------
Mississippi
Missouri
Montana
Silas Anderson
Division of Radiological Health
Department of Health
3150 Lawson Street
P.O. Box 1700
Jackson, MS 39215-1700
(601) 354-6657
1-800-626-7739 in state
Kenneth V. Miller
Bureau of Radiological Health
Missouri Department of Health
1730 East Elm
P.O. Box 570
Jefferson City, MO 65102
(314)751-6083
1-800-669-7236 In State
Adrian C. Howe
Occupational Health Bureau
Montana Department of Health and
Environmental Sciences
Cogswell Building A113
Helena, MT 59620
(406)444-3671
Joseph Milone
Division of Radiological Health
Nebraska Department of Health
301 Centennial Mall, South
P.O. Box 95007
Lincoln, NE 68509
(402)471-2168
1-800-334-9491 In State
Stan Marshall
Department of Human Resources
505 East King Street
Room 203
Carson City, NV 89710
(702) 687-5394
New Hampshire David Chase
Bureau of Radiological Health
Division of Public Health Services
Health and Welfare Building
Six Hazen Drive
Concord, NH 03301
(603)271-4674
1-800-852-3345 x4674
New Jersey Tonalee Carlson Key
Division of Environmental Quality
Department of Environmental
Protection
CN415
Trenton, NJ 08625-0145
(609) 987-6369
1-800-648-0394 in state
New Mexico William M. Floyd
Radiation Licensing and Registration
Section
New Mexico Environmental
Improvement Division
1190 St. Francis Drive
Santa Fe,NM 87503
(505)827^300
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
-------
Oklahoma Gene Smith
Radiation Protection Division
Oklahoma State Department of
Health
P.O. Box 53551
Oklahoma City, OK 73152
(405) 271-5221
Oregon George Toombs
Department of Human Resources
Health Division
1400 SW 5th Avenue
Portland, OR 97201
(503)731-4014
Pennsylvania Michael Pyles
Pennsylvania Department of
Environmental Resources
Bureau of Radiation Protection
P.O. Box 2063
Harrisburg, PA 17120
(717) 783-3594
1-800-23-RADON Li State
Puerto Rico David Saldana
Radiological Health Division
G.P.O. Call Box 70184
Rio Piedras, Puerto Rico 00936
(809) 767-3563
Rhode Island Edmund Arcand
Division of Occupational Health and
Radiation
Department of Health
205 Cannon Building
Davis Street
Providence, RI02908
(401) 277-2438
South Carolina
Bureau of Radiological Health
Department of Health and
Environmental Control
2600 Bull Street
Columbia, SC 29201
(803)734^631
1-800-768-0362
South Dakota MikePochop
Division of Environment Regulation
Department of Water and Natural
Resources
Joe Foss Building, Room 217
523 E. Capitol
Pierre, SD 57501-3181
(605)773-3351
Tennessee Susie Shimek
Division of Air Pollution Control
Bureau of the Environment
Department of Environment and
Conservation
Customs House, 701 Broadway
Nashville, IN 37219-5403
(615) 532-0733
1-800-232-1139 in state
Texas Gary Smith
Bureau of Radiation Control
Texas Department of Health
1100 West 49th Street
Austin, TX 78756-3189
(512) 834-6688
Utah John Hultquist
Bureau of Radiation Control
Utah State Department of Health
288 North, 1460 West
P.O. Box 16690
Salt Lake City, UT 84116-0690
(801) 536^250
Vermont Paul demons
Occupational and Radiological Health
Division
Vermont Department of Health
10 Baldwin Street
Montpelier, VT 05602
(802) 828-2886
1-800-640-0601 in state
Virgin Islands Contact the U.S. Environmental
Protection Agency, Region n
in New York
(212)264-4110
II-31 Reprinted ftom USGS Open-File Report 93-292
-------
Virginia Shelly Ottenbrite
Bureau of Radiological Health
Department of Health
109 Governor Street
Richmond, VA 23219
(804) 786-5932
1-800-468-0138 in state
Washington KateColeman
Department of Health
Office of Radiation Protection
Airdustrial Building 5, LE-13
Olympia,WA 98504
(206)753-4518
1-800-323-9727 In State
West Virginia 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
n-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, DE 19716-7501
(302)831-2833
Florida Walter Schmidt
Florida Geological Survey
903 W. Tennessee Su
Tallahassee, FL 32304-7700
(904)488-4191
Georgia William H. McLemore
Georgia Geologic Survey
Rm. 400
19 Martin Luther King Jr. Dr. SW
Atlanta, GA 30334
(404)656-3214
Hawaii Manabu Tagomori
Dept. of Land and Natural Resources
Division of Water & Land Mgt
P.O. Box 373
Honolulu, HI 96809
(808) 548-7539
Idaho Earl H. Bennett
Idaho Geological Survey
University of Idaho
Morrill Hall, Rm. 332
Moscow, ID 83843
(208) 885-7991
Illinois Morris W. Leighton
Illinois State Geological Survey
Natural Resources Building
615 East Peabody Dr.
Champaign, EL 61820
(217) 333-4747
Indiana Norman C. Hester
Indiana Geological Survey
611 North Walnut Grove
Bloomington, IN 47405
(812) 855-9350
Iowa Donald L.Koch
Iowa Department of Natural Resources
Geological Survey Bureau
109 Trowbridge Hall
Iowa City, IA 52242-1319
(319) 335-1575
Kansas Lee C. Gerhard
Kansas Geological Survey
1930 Constant Ave., West Campus
University of Kansas
Lawrence, KS 66047
(913) 864-3965
E-33
Reprinted from USGS Open-File Report 93-292
-------
Kentucky. Donald C. Haney
Kentucky Geological Survey
University of Kentucky
228 Mining & Mineral Resources
Building
Lexington, KY 40506-0107
(606) 257-5500
Louisiana William E. Marsalis
Louisiana Geological Survey
P.O. Box 2827
University Station
Baton Rouge, LA 70821-2827
(504) 388-5320
Maine Walter A. Anderson
Maine Geological Survey
Department of Conservation
State House, Station 22
Augusta, ME 04333
(207) 289-2801
Maryland Emery T. Cleaves
Maryland Geological Survey
2300 St. Paul Street
Baltimore, MD 21218-5210
(410) 554-5500
Massachusetts Joseph A. Sinnott
Massachusetts Office of
Environmental Affairs
100 Cambridge St, Room 2000
Boston, MA 02202
(617) 727-9800
Michigan R. Thomas Segall
Michigan Geological Survey Division
Box 30256
Lansing, MI 48909
(517) 334-6923
Minnesota Priscilla C. Grew
Minnesota Geological Survey
2642 University Ave.
SL Paul, MN 55114-1057
(612) 627-4780
Mississippi S. Cragin Knox
Mississippi Office of Geology
P.O. Box 20307
Jackson, MS 39289-1307
(601)961-5500
Missouri James H. Williams
Missouri Division of Geology &
Land Survey
111 Fairgrounds Road
P.O. Box 250
Rolla, MO 65401
(314) 368-2100
Montana Edward T.Ruppel
Montana Bureau of Mines & Geology
Montana College of Mineral Science
and Technology, Main Hall
Butte, MT 59701
(406)496^180
Nebraska Perry B. Wigley
Nebraska Conservation & Survey
Division
113 Nebraska Hall
University of Nebraska
Lincoln, ME 68588-0517
(402)472-2410
Jonathan G. Price
Nevada Bureau of Mines & Geology
Stop 178
University of Nevada-Reno
Reno, NV 89557-0088
(702) 784-6691
New Hampshire Eugene L. 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
n-34 Reprinted from USGS Open-File Report 93-292
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North Carolina Charles H. Gardner
North Carolina Geological Survey
P.O. Box 27687
Raleigh, NC 27611-7687
(919) 733-3833
North Dakota John P. Bluemle
North Dakota Geological Survey
600 East Blvd.
Bismarck, ND 58505-0840
(701) 22A-4109
Ohio Thomas M. Berg
Ohio DepL of Natural Resources
Division of Geological Survey
4383 Fountain Square Drive
Columbus, OH 43224-1362
(614) 265-6576
Oklahoma Charles J. Mankin
Oklahoma Geological Survey
Room N-131, Energy Center
100E.Boyd
Norman, OK 73019-0628
(405) 325-3031
Oregon . Donald A. Hull
DepL of Geology & Mineral Indust.
Suite 965
800 NE Oregon St. #28
Portland, OR 97232-2162
(503)731^600
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
Vermfflion, SD 57069-2390
(605) 677-5227
Tennessee Edward T. Luther
Tennessee Division of Geology
13th Floor, L & C Tower
401 Church Street
Nashville, TN 37243-0445
(615) 532-1500
Texas William L. Fisher
Texas Bureau of Economic Geology
University of Texas
University Station, Box X
Austin, TX 78713-7508
(512)471-7721
Utah M. Lee Allison
Utah Geological & Mineral Survey
2363 S. Foothill Dr.
Salt Lake City, UT 84109-1491
(801)467-7970
Vermont Diane L. Conrad
Vermont Division of Geology and
Mineral Resources
103 South Main St.
Waterbury.VT 05671
(802) 244-5164
Virginia Stanley S. Johnson
Virginia Division of Mineral
Resources
P.O. Box 3667
Charlottesville, VA 22903
(804)293-5121
Washington Raymond Lasmanis
Washington Division of Geology &
Earth Resources
Department of Natural Resources
P.O. Box 47007
Olympia, Washington 98504-7007
(206) 902-1450
n-35
Reprinted from USGS Open-File Report 93-292
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West Virginia Larry D. Woodfork
West Virginia Geological and
Economic Survey
Mont Chateau Research Center
P.O. Box 879
Morgantown,WV 26507-0879
(304)594-2331
Wisconsin James Robertson
Wisconsin Geological & Natural
History Survey
3817 Mineral Point Road
Madison, WI 53705-5100
(608)263-7384
Wyoming Gary B. Glass
Geological Survey of Wyoming
University of Wyoming
Box 3008, University Station
Laramie, WY 82071-3008
(307)766-2286
11-36 Reprinted from USGS Open-File Report 93-292
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EPA REGION 10 GEOLOGIC RADON POTENTIAL SUMMARY
by
James K. Otton, Kendall A. Dickinson, Douglass E. Owen, and Sandra L. Szarzi
U.S. Geological Survey
EPA Region 10 includes the states of Alaska, Idaho, Oregon, and Washington. For each
state, geologic radon potential areas were delineated and ranked on the basis of geologic, soils,
housing construction, and other factors. Areas in which the average screening indoor radon level
of all homes within the area is estimated to be greater than 4 pCi/L were ranked high. Areas in
which the average screening indoor radon level of all homes within the area is estimated to be
between 2 and 4 pCi/L were ranked moderate/variable, and areas in which the average screening
indoor radon level of all homes within the area is estimated to be less than 2 pCi/L were ranked
low. Information on the data used and on the radon potential ranking scheme is given in the
introduction to this volume. More detailed information on the geology and radon potential of each
state in Region 10 is given in the individual state chapters. The individual chapters describing the
geology and radon potential of the states in EPA Region 10, 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 geology and radon potential of the Pacific Northwest (fig. 1) and Alaska (fig. 2) is
diverse; thus the two areas will be considered separately. The Pacific Northwest includes eight
distinct major radon geologic provinces: the Coastal Range-Klamath Mountains, the Puget
Lowland-Willamette River Valley, the Cascade Range, the Columbia Plateau-High Lava Plains-
Blue Mountains, the northern Rocky Mountains, the Snake River plain, the middle Rocky
Mountains, and the northern Basin and Range-Owyhee Plateau (fig. 1). Maps showing indoor
radon averages for counties in the Pacific Northwest and boroughs in Alaska are shown in figures
3a and 3b. Averages range from less than 1.0 pCi/L to 14.9 pCi/L. Details of the indoor radon
studies are described in the individual state chapters.
PACIFIC NORTHWEST
Coastal Range-Klamath Mountains
The Coastal Range Province (1, fig. 1) extends from the Olympic Peninsula of Washington
south to the coastal parts of the Klamath Mountains in southwestern Oregon. In Washington, the
Coast Ranges are underlain principally by Cretaceous and Tertiary continental and marine
sedimentary rocks and pre-Miocene volcanic rocks. In Oregon, the northern part of the Coastal
Ranges is underlain principally by marine sedimentary rocks and mafic volcanic rocks of Tertiary
age. The southern part of the Coast Range is underlain by Tertiary estuarine and marine
sedimentary rocks, much of them feldspathic and micaceous. The Klamath Mountains (2, fig. 1)
are dominated by Triassic to Jurassic metamorphic, volcanic, and sedimentary rocks, with some
Cretaceous intrusive rocks. These metamorphic and volcanic rocks are largely of mafic
composition. Large masses of ultramafic rocks occur throughout the Klamath area. Sand dunes
and marine terraces are common along the coastal areas of this province.
The radon potential of the Coastal Range Province is low overall. Most of the area has
high rainfall and, as a consequence, high soil moisture. Uranium in the soils is typically low,
although soils of the Oregon part of the Coast Ranges tend to be higher in uranium than do soils of
IE-1 Reprinted from USGS Open-FUe Report 93-292-J
-------
Figure 1- Radon geologic provinces of the Pacific Northwest (generalized from state
chapters included in this report). 1- Coast Ranges; 2- Klamath Mountains; 3- Puget
Lowland; 4- Willamette River Valley; 5- Cascade Range; 6- Northern Rocky
Mountains; 7- Columbia Plateau; 8- Blue Mountains; 9- High Lava Plains; 10-
Basin and Range; 11- Owyhee Plateau; 12- Snake River Plain; and 13- Middle
Rocky Mountains.
-------
the Washington part. A few communities along the river valleys near the coast of Oregon may
have locally elevated indoor radon where highly permeable, excessively well-drained soils occur
on river alluvium with a modestly elevated uranium content The northeastern corner, of the
Olympic Peninsula has lower rainfall and lower soil moisture than does the rest of the Coastal
Range Province. Here, highly permeable, excessively well-drained soils may cause locally
elevated indoor radon levels.
Puget Lowland-Willamette River Valley
The Puget Lowland (3, fig. 1) is underlain almost entirely by glacial deposits and Holocene
alluvium. Most of the glacial and alluvial material of the Puget Lowland is derived from the .
Cascades to the east, and from the mountains of the Olympic peninsula to the west River alluvium
and river terraces underlie most of the Willamette River valley (4, fig. 1). However, many of the
hills that rise above the plains of the Lowland are underlain by Tertiary basalts and marine
sediments.
The Puget Lowland overall has very low radon potential because of low uranium content of
soils and because high rainfall produces high soil moisture, which slows radon movement
Houses in most townships in the Bonneville Power Administration study from Tacoma northward
average less than 1 pCi/L radon. Structures built on locally very steep or well-drained soils,
especially on the east side of the lowland area, may be among the few likely to have elevated
indoor radon levels. The geologic radon potential is moderate only in the southern part of the
Puget Lowland, south of Tacoma, where excessively drained soils and somewhat elevated uranium
in soils occur.
The Willamette River Valley has moderate radon potential overall. Much of the area has
somewhat elevated uranium in soils, and many areas have excessively drained soils and soils with
high emanating power. Studies by the Oregon Department of Health and the Bonneville Power
Administration indicate that houses in many counties and townships in the valley average between
2 and 4 pCi/L radon.
Cascade Range
The Cascade Range (5, fig. 1) can be divided into two geologic terranes: a northern terrane
composed principally of Mesozoic metamorphic rocks intruded by Mesozoic and Tertiary granitic
rocks, and a southern terrane composed of Tertiary and Holocene volcanic rocks. The Holocene
volcanic centers are responsible for locally thick volcanic-ash deposits east of the Cascade
Mountains. Within the southern terrane, the western Cascades are dominated by Tertiary andesite
flows, basalt flows, and pyroclastic rocks, whereas the eastern Cascades have many recently active
volcanoes and are underlain by late Tertiary to Quaternary basaltic and andesitic volcanic rocks.
Overall, the sparsely populated Cascade Range Province has low radon potential because of
the low uranium and high moisture contents of the soils. Areas that are exceptions to this include
the Columbia River Gorge, where highly permeable, excessively well drained soils underlie many
of the communities, and thus the radon potential is moderate. Much of the alluvium in the Gorge is
also derived from the upper Columbia River valley, where the uranium content of the geologic
materials is higher than the rocks within the Cascade Mountain Province itself. Studies by the
Oregon Department of Health and the Bonneville Power Administration show that indoor radon
levels in homes in population centers along the Columbia River average 2 to 4 pCi/L.
ffl-3 Reprinted from USGS Open-File Report 93-292-J
-------
Columbia Plateau, High Lava Plains, and Blue Mountains
The Columbia Plateau (7, fig. 1) is underlain principally by Miocene basaltic and andesitic
volcanic rocks, tuffaceous sedimentary rocks and tuff. An extensive veneer of Pleistocene
glaciofluvial outwash, eolian, and lacustrine deposits covers these volcanic rocks. The High Lava
Plains (9, fig. 1) are underlain by Miocene basaltic and volcanic rocks like those of the Columbia
Plateau without the veneer of younger sedimentary rocks. The Blue Mountains (8, fig. 1) have
similar basaltic and andesitic rocks and also include significant outcrop areas of Triassic and
Jurassic sedimentary and volcanic rocks, weakly metamorphosed in many areas, and younger
intrusive rocks.
The Columbia Plateau, with its areas of extensive Pleistocene glacio-fluvial outwash,
eolian, and lacustrine deposits, contains locally highly permeable soils, soils with high emanating
coefficients, and elevated soil uranium levels. This area has generally moderate radon potential.
Although the Blue Mountains have relatively low uranium in soils, average indoor radon levels are
in the 2-4 pCi/L range, probably because most population centers occur in alluviated valleys with
highly permeable soils. This area has moderate radon potential. In contrast, the High Lava Plains,
with much lower uranium in soils and only local areas of highly permeable soils, have low overall
radon potential.
Northern Rocky Mountains
The Northern Rocky Mountains (6, fig. 1) comprise the mountainous terrane of the
northeast and north-central parts of Washington and northern and central Idaho. This area is
underlain by Precambrian and Paleozoic sedimentary rocks, and by Mesozoic metamorphic rocks;
all are intruded by Mesozoic and Tertiary granitic rocks. The largest intrusive mass, the Idaho
Batholith, is a complex of granitic rock units that range from diorite to granite. Highly
uranifcrous, Late Cretaceous to early Tertiary granites crop out throughout the Northern Rocky
Mountains. An extensive, though dissected, veneer of Tertiary volcanic rocks crops out over
much of the central Idaho portion of the Northern Rocky Mountains.
The Northern Rocky Mountains Province has high radon potential. Excessively well
drained glaciofluvial outwash or coarse gravels hi alluvial fans underlie many of the valleys
throughout the area. The granitic material in much of the outwash contains moderate to locally
high concentrations of uranium. Areas where uranium occurrences are found, such as in the
granitic and metamorphic terranes in the mountains north of Spokane, may have structures with
extreme levels of indoor radon. Buildings in most of the alluvial valleys in Washington and Idaho
north, northwest, and east of Spokane may be expected to have average indoor radon screening
measurements above 4 pCi/L.
Snake River Plain
The Snake River Plain (12, fig. 1) forms an arcuate depression in southern Idaho that is
underlain principally by basaltic volcanic rocks of generally low eU (1 ppm or less). However,
alluvium from neighboring mountains and silicic tuffaceous sedimentary rocks covers much of the
upper Snake River Valley near Wyoming and the western end of the Snake River Plain near Boise
and south of Mountain Home. These materials have eU values that range from 1.5-5.0 ppm.
Those areas underlain by basalt have low to locally moderate radon potential. However, those
areas where basalt is overlain by silicic tuffaceous sedimentary rocks and alluvium along the Snake
River Valley have high overall radon potential. Most populous areas are in the latter category.
m-4 Reprinted from USGS Open-File Report 93-292-J
-------
Middle Rocky Mountains
The Middle Rocky Mountains Province (13, fig. 1) forms a strip along the border between
Wyoming and Idaho and comprises two arels. The northern area is the Yellowstone Plateau, a
high-standing plateau area underlain mostly by rhyolites containing moderate amounts of uranium.
To the south are complexly faulted and folded mountain ranges of Paleozoic and Mesozoic
sedimentary rocks, including uranium-bearing phosphatic rocks.
The high average uranium content of the volcanic rocks of the Yellowstone area and the
coarse alluvium in the valleys of the southern mountain areas suggest that this province has high
geologic radon potential.
Basin and Range Province, Owyhee Plateau
The very sparsely populated northern part of the Basin and Range Province (10, fig. 1) lies
along the southern and southeastern edge of Region 10. It is composed of tectonically extended
areas where linear mountain ranges alternate with valleys and less extended plateau areas. It is
underlain mainly by basaltic to andesitic volcanic rocks, silicic ash-flow tuffs, including some
welded tuffs, and sediments derived from these units. Several playa basins occupy the centers of
the valleys. The Owyhee Plateau of southwestern Idaho (11, fig. 1) consists of Tertiary and
Quaternary basalt, andesite, and rhyolite, and sediments derived from these units. A few caldera
complexes, some of them with associated uranium mineralization, occur within the Owyhee
Plateau. Some mountain ranges in the eastern part of this province are underlain mainly by
Paleozoic and Mesozoic sedimentary rocks. Based on the high aeroradiometric signature of most
of the exposed rock units and the presence of many highly permeable soil units, the radon potential
of this area is generally high.
ALASKA
Alaska can be divided from north to south into eight geologic radon provinces: the Arctic
Coastal Plain, the Arctic Foothills, the Arctic Mountains, Central Alaska, the Northern Plateaus (a
subprovince of Central Alaska), the Alaska-Aleutian Ranges, the Coastal Trough, and the Border
Ranges Provinces (fig. 2).
Arctic Coastal Plain
The Arctic Coastal Plain Province (North Slope, 1, fig. 2) consists primarily of Quaternary
sediment, most of of which is composed of alluvium, glacial debris, and eolian sand and silt A
belt of Tertiary sedimentary rocks along the eastern third of the area separates the coastal plains
from the foothills to the south.
This area has low radon potential. No significant uranium occurrences are known in this
area, and the number of gamma-ray anomalies is low when compared with other parts of Alaska.
The coastal plain is unglaciated and contains tundra soils and permafrost. These soils probably
have low gas transmissivity because of water or ice saturation.
Arctic Foothills
The Arctic Foothills Province (2, fig. 2) is largely composed of marine and nonmarine
Cretaceous sandstone and shale. The Cretaceous beds are folded into west-trending anticlines and
synclines. Part of the area was covered by glaciers.
ffl-5 Reprinted from USGS Open-Ftte Report 93-292-J
-------
Figure 2- Physiographic provinces of Alaska (from the state chapter included in this
report). 1- Arctic Coastal Plain; 2- Arctic Foothills; 3- Arctic Mountains; 4- Central
Province, 4a- Seward Peninsula, 4b- Bering Shelf, 4c- Ahklun Mountains, 4d-
Westem Alaska, 4e- Northern Plateaus; 5- Alaska-Aleutian Province; 6- Coastal
Trough; 7- Pacific Border Ranges; and 8- Coast Mountains.
-------
This area has low radon potential overall. The Cretaceous sandstone and shale that makes
lip the foothills could produce relatively large amounts of radon but no evidence that they do is on
hand. The area contains no known uranium occurrences or deposits, and the part of the area where
airborne gamma-ray measurements were made shows a low number of anomalies. The tundra
soils have permafrost and apparent low gas transmissivity.
Arctic Mountains
The Arctic Mountains Province (3, fig. 2) is composed largely of upper Precambrian and
Paleozoic marine sedimentary rocks. They are cut by west-trending thrust faults with upthrown
sides to the south.
This area has moderate radon potential. The Precambrian and Paleozoic marine
sedimentary rocks that make up the Arctic Mountains probably are not producers of high levels of
radon as there is little or no phosphate rock or black shale in these sequences. There are no known
significant uranium occurrences in this area. However, stream sediments in this province contain
moderately high levels of uraniferous resistate minerals. The area has been glaciated, but much of
the terrane is bare rock without surficial glacial material. The soils are classified as rock land,
which includes glacial ice.
Central Province (exclusive of the Northern Plateaus subprovince)
The Central Province, an area of plains, plateaus, and rounded mountains, is geologically
complex. The Central Province is divided into five subprovinces: Western Alaska, Seward
Peninsula, Aklun Mountains, the Bering Shelf (4a-d, fig. 2) and the Northern Plateaus (5, fig. 2).
The Northern Plateaus are considered separately below.
Western Alaska is underlain mostly by Cretaceous marine sedimentary rocks and lower
Paleozoic sedimentary and metamorphic rocks. A large area of Cretaceous and Tertiary volcanic
rock is present in the western part of this subprovince. The Seward Peninsula consists mostly of
Precambrian and Paleozoic metamorphic rocks, with lesser amounts of Precambrian and Paleozoic
sedimentary rocks, Quaternary sediments, and Tertiary and Quaternary mafic volcanic rocks. The
Aklun Mountains are composed mostly of marine sedimentary rocks and small intrusive masses of
Jurassic and Tertiary age. The Bering Shelf is covered almost entirely by Quaternary surficial
sediments, with minor areas of Tertiary volcanic rocks.
Overall the Central Province has moderate radon potential as many radon-producing rocks .
occur there. There are, for instance, several areas of uraniferous granites together with felsic
intrusive and volcanic rocks. In addition, the area contains a few uranium deposits of potentially
commercial size at Death Valley on the Seward Peninsula and in the Healy Creek coal basin. The
area also contains a significant number of gamma-ray anomalies. Nearly all of the area falls within
a belt of uraniferous stream sediments. The schist that produces high indoor radon near Fairbanks
is in this area. Little of the province has been glaciated. The soils are mostly of the Tundra type
with variable permafrost Significant areas of rockland and subarctic brown forest soils occur.
The latter soils may have high gas transmissivity.
Northern Plateaus
The Northern Plateaus subprovince (5, fig. 2) is covered by flat-lying Tertiary basin-fill
(nonmarine clastic rocks), Quaternary surficial deposits, Precambrian through Cretaceous mostly
marine sedimentary rocks, Paleozoic and Precambrian metamorphic rocks, and Mesozoic intrusive
and volcanic rocks. The metamorphic rocks include metamorphosed granites and amphibolite.
ffl-7 Reprinted firom USGS Open-Hie Report 93-292-J
-------
The mesozoic intnisives are msofly gabbro and diabase. The Tintina and Denali fault zones cross
this subprovince.
The Northern Plateaus subprovince has a moderate radon potential overall. A moderate
number of aeroradiometric anomalies occurs in the subprovince. Although indoor radon data are
sparse, indoor radon in parts of the Fairbanks and Fairbanks Northstar Boroughs is high. Felsic
intrusives are scattered in two belts, one intruding Paleozoic and Precambrian metamorphic rocks
in the southeast one-third of the subprovince and one intruding Lower Paleozoic and (or)
Precambrian sedimentary rocks along the northwest margin of the subprovince. The area contains
one known significant uranium and thorium deposit at Mount Prindle. Uranium is high in stream
sediments in the south-central part and along the northwest border of the subprovince.
Alaska-Aleutian Ranges and Coastal Mountains
The Alaska-Aleutian Ranges and Coastal Mountains Province (6, fig. 2) includes the
Aleutian Peninsula, a northeast-trending mountain belt in south-central Alaska that includes Mt
McKinley, a southeast-trending mountain belt that extends from the Mt McKinley area
southeastward to Canada, and the Coast Mountains in the southeast. On the Aleutian Peninsula
from Unimak Pass westward, the bedrock consists mostly of Quaternary and Tertiary volcanic
rocks and Tertiary sedimentary rocks. Tertiary and Quaternary volcanic rocks are also common
northeast of the Pass, but other rocks, including Jurassic and Cretaceous sedimentary rocks and
Jurassic intrusive rocks of intermediate and felsic composition, are also common in this area. In
addition, large masses of Tertiary mafic volcanic rocks and Jurassic or Cretaceous intermediate
intrusives are found in the area west of Cook Inlet and southwest of Mount McKinley. A varied
assortment of Phanerozoic rocks are present in the Talkeetna Mountains and southeastward to the
Canadian border. These include Paleozoic mafic volcanic rocks together with their sedimentary
and metamorphic derivatives; Mesozoic mafic volcanic flows and tuffs, together with various units
of shale, conglomerate, graywacke, and slate; and Tertiary and Quaternary intermediate volcanic
rocks, Tertiary felsic intrusives, and Quaternary glacial deposits including eolian sand and silt
The Coastal Mountains are composed mostly of ultramafic, intermediate, and silicic volcanic
intrusive rocks of varying ages, and Paleozoic through Mesozoic sedimentary rocks. These rocks
are highly deformed and variably metamorphosed.
This area has moderate radon potential overall, although the uncertainty is high. The
Aleutian-Alaska Range contains felsic intrusives and other rocks that are likely to be uranium-rich,
although no significant uranium occurrences are known in this area. However, the area has a
moderate to substantial number of anomalously uranium-rich stream sediment samples. Most of
the area is or was covered by glaciers and glacial outwash may be highly permeable in many areas.
Soils are mostly classified as rockland or tundra.
Coastal Trough
The Coastal Trough Province (7, fig. 2) includes a series of Cenozoic depositional basins
containing thick sequences of Tertiary continental clastic and volcanic rocks that generally overlie
Cretaceous or older sedimentary rocks penetrated by Tertiary intrusive rocks. Mesozoic
sedimentary rocks and Pleistocene, mostly glacial, deposits, occur in some areas.
The radon potential of this area is moderate overall, but locally high indoor radon levels
could occur near uranium occurrences. The Coastal Trough Province contains Tertiary continental
clastic rocks similar to units that produce uranium in the western conterminous United States. The
overall uranium content of these rocks is not high, but small uranium occurrences are found in the
UI-8 Reprinted from USGS Open-File Report 93-292-J
-------
Susitna Lowlands and in the Admiralty trough in southeastern Alaska. Soils are mostly brown and
gray-brown podzolic forest soils, which could have high gas transmissivity. Heavy rainfall and
saturated soils in southeast Alaska likely retards soil gas migration.
Pacific Border Ranges
The Border Ranges Province (8, fig. 2) is generally south and west of the Coastal Trough
Province. Jurassic and Cretaceous sedimentary and metamorphic rocks with interbedded mafic
volcanic rocks and some gabbro make up most of the Border Ranges rocks. A fairly large area of
early Tertiary sedimentary, volcanogenic sedimentary rocks, and volcanic rocks is found in the
Prince William Sound area.
The Border Ranges Province generally has low radon potential, although some uranium-
bearing rocks and uranium occurrences are likely to be present The uranium deposit at Bokan
Mountain is associated with a uranium-rich peralkaline granite. The uranium content of stream
sediments in the Border Ranges is intermediate for Alaska, although data are absent from many
areas. Podzolic brown and gray-brown forest soils are common in the Border Ranges, and they
could have high gas permeability. However, in this part of Alaska annual rainfall is about 14 feet,
and water saturation likely retards gas flow in soils on all but the steepest slopes.
ffl-9 Reprinted from USGS Open-File Report 93-292-J
-------
Bsmt & 1 st Floor Radon
Average Concentration (pCi/L)
0.0 to 1.0
1.1 to 1.9
2.0 to 3.0
3.1 to 4.0
4.1 to 14.9
Missing Data
(< 5 measurements)
Screening indoor radon data from the State/EPA Residential Radon Survey and the
o?Pto£S, fo-counties with 5 or more measurements in the conterminous part of
™UliKaSSIfo map legends show the number of counties in each category. The
chosen to provide reference to decision and action levels.
-------
11 L
Bsmt & 1st Floor Indoor Radon
Average Concentration (pCi/L)
0.0 to 1.0
1.1 to 1.9
2.0 to 3.0
3.1 to 4.0
4.1 to 6.4
Missing Data
(< 5 measurements)
Figure 3B. Screening indoor radon data from the State/EPA Residential Radon Survey of
Alaska, 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 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.
-------
-------
PRELIMINARY GEOLOGIC RADON POTENTIAL ASSESSMENT OF WASHINGTON
by
James K, Otton
U.S. Geological Survey
INTRODUCTION
Washington is a State of varied geologic and climatic settings and varied radon potential.
This assessment of the radon potential of the State is based largely on data provided by a study of
indoor radon by the State/EPA Indoor Radon Survey of Washington and the Bonneville Power
Administration (BPA), previous work by Duval and others (1989) and Otton and Duval (1990),
and geologic information derived from publications of the Washington Department of Natural
Resources, Division of Geology and Earth Resources. Much of the information in the geographic
setting section is derived from the National Atlas of the United States of America.
This is a generalized assessment of geologic radon potential of rocks, soils, and surficial
deposits of Washington. 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
Washington is divided into several distinctive physiographic provinces (fig. 1). The
Okanogan Highlands area in northeastern and northrcentral Washington is part of the northern
Rocky Mountains. This highland area is dissected by a few north-trending river valleys including
the Columbia River valley. This highland is characterized mostly by low mountains where less
than 20 percent of the area is gently sloping and the local relief is 1000-3000 feet High mountains
with greater relief occur in the northeastern corner of this highland area and low open mountains
occur in the highland area close to Spokane.
The Columbia Basin is in the southeastern part of the State. This terrain is bounded to the
north by the Columbia and Spokane Rivers and to the west by the foothills of the Cascade Range.
It is characterized by irregular plains of low relief (100-300 feet), tablelands of moderate to high
relief (300-3000 feet), and open hills and open low mountains of moderate to high relief (300-3000
feet). The percentage of area underlain by gentle slopes ranges from 50 to 80 percent in the plains
and 20-50 percent in the open hills and open low mountains.
The Blue Mountains area lies in the southeasternmost corner of the State. This area is
characterized by open low mountains with 1000-3000 feet of relief, and 20-50 percent of the area
is gently sloping.
IV-1 Reprinted from USGS Open-FUe Report 93-292-J
-------
Okanogan Highlands
Cascade Mountains
Coastal
Mountains ) Puget
Blue Mountains
Columbia River Gorge
Figure 1- Physiographic divisions of Washington. (Modified from Lasmanis, 1991).
-------
The Cascade Mountains separate these eastern areas from the western part of the State. The
Cascades are high mountains and open high mountains where relief exceeds 3000 feet The
Columbia River has cut a gorge through these mountains along the border between Washington
and Oregon.
Immediately west of the Cascades are the Puget Lowlands, which extend from the
Canadian border southward nearly to the Columbia River. This area is marked by tablelands of
moderate relief (300-500 feet) in the area around Seattle; by plains with low mountains (local relief
of 1000-3000 feet) in the areas near the Canadian border, and by open hills (local relief 300-500
feet) from southern Tacoma southward to the Columbia River. Fifty to eighty percent of the land
is gently sloping in the first two areas whereas 20-50 percent of the latter area is gently sloping.
The Portland Basin, a small physiographic area near Vancouver, is a northward extension
of the Willamette River Valley. This area resembles the southern part of the Puget Lowlands
physiographically.
Westernmost Washington is dominated by the Coastal Mountains and Coastal Hills. The
Coastal Mountains are high mountains (relief greater than 3000 feet) in the eastern half and lower
mountains (relief 100-3000 feet) in the western, coastal part An area of open hills separates the
Coastal Mountains from the Coastal Hills, which are low mountains of 1000-3000 feet local relief.
The western Coastal Mountains, the Coastal Hills, and the Cascades are areas of heavy
rainfall, with amounts ranging from 40 to 200 inches per year. Only the northeasternmost part of
the Coastal Mountains are relatively dry. There, precipitation ranges from 20 to 30 inches per
year. Rainfall in the Puget Lowlands and the Portland Basin generally ranges from 30 to 50 inches
per year. In Seattle, the wettest months are the winter months and summer is somewhat drier, but
even in summer 2 to 3 inches of rain may fall per month.
East of the Cascade Mountains, rainfall is typically in the range of 9 to 15 inches per year,
with the exception of the Okanogan Highlands, which receive as much as 30 to 40 inches per year.
In Spokane, rainfall is fairly evenly distributed through the year, except for July and August,
which are the driest months.
Most of the population of the State is located in the Puget Lowlands and the Portland area at
the west end of the Columbia River Gorge (fig. 2). A lengthy urban corridor in the Puget
Lowlands extends from Bellingham near the Canadian border to the Tacoma/Olympia area at the
south end of Puget Sound. Other scattered population centers occur east of the Cascades,
including Spokane and adjacent areas, the lower Yakima River Valley, and Walla Walla. Most of
the populated areas east of the Cascades lie along the river valleys.
Mountainous areas of the State are used principally for timber or timber and grazing. The
Puget Lowlands outside of the urban areas is used for cropland, with lesser grazing and timber.
The Columbia Basin is dominated by dryland farming and grazing. Some irrigated cropland is
found along the Columbia River valley in the western part of the Columbia Basin.
GEOLOGIC SETTING
The coastal mountains and hills of Washington are underlain principally by Cretaceous and
Tertiary continental and marine sedimentary rocks and pre-Miocene volcanic rocks (fig. 3). The
Puget Lowlands is underlain almost entirely by glacial deposits and Holocene alluvium. Most of
the glacial and alluvial material of the Puget Lowlands is derived from the Cascades to the east and
the mountains of the Olympic Peninsula to the west The Portland Basin is underlain primarily by
alluvial material. The Cascade Mountains can be divided into two geologic terranes: a northerly
IV-3 Reprinted from USGS Open-FUe Report 93-292-3
-------
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terrane composed principally of Mesozoic metamorphic rocks intruded by Mesozoic and Tertiary
granitic rocks, and a southerly terrane composed of Tertiary and Holocene volcanic rocks. The
Holocene volcanic centers are responsible for locally thick volcanic ash deposits east of the
Cascade Mountains. The Columbia Basin is underlain principally by Miocene basaltic volcanic
rocks overlain by extensive veneer of glaciofluvial outwash and eolian and lacustrine deposits.
The mountainous terrain of the northeast and north-central part of the State is underlain by
Precambrian sedimentary rocks, Paleozoic sedimentary rocks, and Mesozoic metamorphic rocks,
all intruded by Mesozoic and Tertiary granites.
During the late Pleistocene, most of the Cascades, the Olympic Peninsula, and the Rocky
Mountains north and northwest of Spokane were glaciated. Extensive glacial deposits now cover
most of the Puget Lowlands. As ice receded from northeastern Washington, large lakes formed
behind ice dams along the ancestral Columbia River valley. When these dams broke, massive
floods poured down many of the river valleys across the Columbia Basin. These floods carried
substantial quantities of alluvium which was deposited along the entire river drainages. In some
places, valleys were scoured clean of surficial sediments down to the underlying basaltic bedrock.
Subsequent westerly winds blew much of the finer-grained river alluvium from river bottoms and
deposited this sand and silt across many of the adjacent valley floors.
Aerial radiometric data for the State of Washington (fig. 4) show that surficial materials
within the Puget Lowlands and the coastal areas to the west contain entirely less than 1.5 ppm
equivalent uranium (eU). Within the Cascades, the rocks have mostly less than 1.5 ppm eU;
however, some of the Holocene volcanic centers in the southern Cascades include volcanic rocks
containing as much as 2.5 ppm eU. In addition, some of the Tertiary granitic plutons in the central
and northern Cascades are significantly enriched in uranium, as much as 5.5 ppm eU. In the
westernmost part of the Okanogan Highlands, Mesozoic and early Tertiary granites have unusually
low eU signatures (as low as 0.5 ppm eU), whereas to the east, many of the granites and some of
the metamorphic rocks have significantly elevated eU signatures (as much as 5 ppm eU).
Although much of the Columbia Basin is underlain by basaltic rocks that are generally low
in uranium content, most of this area has eU signatures of 2.0 to 3.0 ppm because of the extensive
surficial cover of Quaternary and Holocene glaciofluvial, lacustrine, and eolian deposits. This
surficial cover has been derived in large part from more uraniferous rocks in northeastern
Washington and northern Idaho. The larger areas of 0.5 to 1.5 ppm eU within the Columbia Basin
represent areas on the east flank of the southern Cascades and the Blue Mountains where this
surficial cover was not deposited or areas within the Columbia basin where cover was stripped by
late Pleistocene floods.
Uranium occurrences and deposits in Washington, a potential source of elevated radon
levels, are largely associated with granitic and metamorphic rocks in the Okanogan Highland area
north and northwest of Spokane and with Tertiary sedimentary rocks derived from these crystalline
rocks, although some uranium occurrences are located in the central Cascade Mountains. Granitic
rocks in the hills immediately north of Spokane host numerous uranium occurrences.
Organic-rich Holocene and late Pleistocene alluvium along stream valleys in many of the
granitic terranes in the Okanogan Highland area is host to surficial uranium deposits (Johnson and
others, 1987). Because of their relative youth, these Holocene uranium deposits are typically low
in radioactivity (and radioactive decay products such as radon) in spite of average grades that range
from 100 to 800 ppm uranium (Zielinski and others, 1986). Fortunately, most of these deposits
are on the flopdplains of streams or are in wetlands, and thus are not suitable for construction.
IV-7 Reprinted from USGS Open-FUe Report 93-292-J
-------
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SOILS
As part of an earlier study for the BllA, Duval arid others (1989) evaluated permeability
data in the county soil surveys for 30 of the 37 counties in the State (fig. 5). They compiled a map
of the highly permeable soil associations (those soil associations dominated by soils with
permeabilities greater than 6 in/hr in percolation tests) in those 30 counties (fig. 6).
The low coastal areas and coastal mountains and hills of western Washington and the
Cascades of west-central Washington are characterized by very moist soils in the winter (56-96
percent pore saturation in sandy loams, and 74-99 percent saturation in a silty clay loam) and
moderately moist soils in the summer (44-56 percent saturation in sandy loams, and 58-74 percent
in a silty clay loam) (Rose and others, 1990). The Puget Lowlands and the northern and western
edges of the Columbia Basin and the Blue Mountains are characterized by very moist soils in the
winter (56-96 percent pore saturation in sandy loams, and 74-99 percent pore saturation in a silty
clay loam) and slightly moist soils in the summer (24-44 percent pore saturation in sandy loams,
and 39-58 percent pore saturation in silty clay loams). Soils in the rest of the Columbia Basin are
slightly moist in the winter and slightly dry in the summer (4-24 percent pore saturation in sandy
loams and 6-39 percent pore saturation in silty clay loams). Soils in the Okanogan Highlands are
characterized by very moist soils in the wintere and moderately moist soils in the summer.
INDOOR RADON DATA
The EPA and the State of Washington completed a population-weighted survey of indoor
radon levels in Washington during the winter of 1990-1991 (fig. 7; table 1). Sampled houses were
randomly selected from existing housing stock, which means that homes sampled tend to cluster in
the more populated areas. Interpretations of population-weighted 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 geographic coverage of the county's surface area.
Highest indoor radon readings occur in the northeastern part of the State, with three
counties in that area averaging greater than 4 pQ/L. Much of the east and north-central part of the
State has indoor radon averages between 2 and 4 pCi/L. All counties west of the Cascade Rnage
have very low indoor radon averages, generally less than 1 pCi/L. A few readings exceed 4 pCi/L
in three counties in the southern part of the Puget Lowland.
Another source for indoor radon data in the State of Washington is a long-term study
conducted by the BPA. Indoor radon tests were offered as part of BPA's weatherization program,
extended to homeowners across its service area (parts of the states of Washington, Oregon, Idaho,
Montana, and Wyoming). Three month, wintertime alpha-track measurements were made in
participants' homes starting in the fall of 1985. The resulting data were plotted on a township
location system and are presented in figure 8. In this figure all those townships with less than 5
measurements are shown but no data are given. For those townships with at least 5 measured
houses, the percentage of those homes greater than 5 pCi/L is represented (this number was used
as an index by BPA under the assumption that a 5 pCi/L wintertime measurement would
approximately equal a 4 pCi/L year-long measurement). The coverage of the State is less complete
than for the State/EPA data set, however because a smaller geographic area was sampled, more
detailed correlations with geology and soils is possible.
IV-9 Reprinted from USGS Open-File Report 93-292-J
-------
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Bsmt. & 1st Floor Rn
%>4pCi/L
22 t*
Oto10
6I3S] 11 to 20
7 ^^ 21 to 40
2 IH 41 to 60
2 CD Missing Data
or < 5 measurements
Bsmt. & 1st Floor Rn
Avg. Concentration (pCi/L)
23 ^ •>
* -.«.«. •".-.I 0.0 to 1 .9
10 rv\\^ 2.0 to 4.0
4 ES3 4.1 to 10.1
2 C] Missing Data
or < 5 measurements
100 Miles
Figure 7. Screening indoor radon data from the EPA/State Residential Radon Survey of
Washington, 1991-92, for counties with 5 or more measurements. Data are from 2-7 day
charcoal canister tests. Histograms in map legends show the number of counties in each
category. The number of samples in each county (See Table 1) may not be sufficient to
statistically characterize the radon levels of the counties, but they do suggest general trends.
Unequal category intervals were chosen to provide reference to decision and action levels.
-------
TABLE 1. Screening indoor radon data from the EPA/State Residential Radon Survey of
Washington conducted during 1991-92. Data represent 2-7 day charcoal canister measurements
from the lowest level of each home tested.
COUNTY
ADAMS
ASOTIN
BENTON
rWRT.AN
CLALLAM
CLARK
COLUMBIA
COWLITZ
DOUGLAS
FERRY
FRANKLIN
GARFELD
GRANT
GRAYS HARBOR
ISLAND
JEFFERSON
KING
KITSAP
KnTITAS
KLICKITAT
LEWIS
LINCOLN
MASON
OKANOGAN
PACIFIC
PENDOREILLE
PIERCE
SKAGIT
SKAMANIA
SNOHOMISH
SPOKANE
STEVENS
THURSTON
WAHKIAKUM
WALLA WALLA
WHATCOM
WHITMAN
YAKIMA
NO. OF
MEAS.
11
18
106
9
22
69
5
35
17
28
26
5
54
29
10
11
215
34
4
22
"24
15
18
43
11
55
132
9
35
63
449
47
45
21
56
17
31
134
MEAN
3.5
2.9
1.8
2.2
0.3
2.4
3.4
0.5
1.6
3.2
1.6
0.8
1.9
0.7
0.1
0.3
0.4
0.4
1.2
1.7
0.7
2.2
0.6
2.8
0.2
7.2
0.8
0.4
8.3
0.2
9.9
5.1
0.8
1.0
2.6
0.4
5.9
1.8
GEOM.
MEAN
2.3
1.5
1.0
1.4
0.1
1.1
3.0
0.2
1.0
1.5
1.1
0.5
0.9
0.2
0.1
0.2
0.2
0.3
0.9
1.1
0.4
1.7
0.3
1.5
0.1
22
0.3
0.2
1.9
0.1
5.1
2.1
0.3
0.4
1.7
0.3
2.2
1.1
MEDIAN
2.0
1.3
1.1
1.8
0.2
1.3
4.0
0.2
1.2
1.3
1.2
0.6
1.0
0.2
0.2
0.2
0.3
0.3
1.4
0.8
0.5
1.8
0.3
1.3
0.1
2.0
0.4
0.0
1.4
0.1
4.9
1.7
0.3
0.4
1.9
0.3
2.3
1.1
STD.
DEV.
4.4
6.3
3.5
2.2
0.4
3.5
1.7
1.4
1.3
3.9
1.4
0.7
2.9
1.4
0.2
0.4
0.8
0.5
0.7
2.3
0.7
1.6
0.7
3.7
0.2
19.1
1.7
0.6
17.4
0.3
14.2
11.3
1.8
1.8
2.3
0.3
14.0
2.5
MAXIMUM
15.9
27.8
28.1
7.4
1.6
23.0
5.4
8.2
4.0
10.8
5.1
1.9
17.7
6.8
0.4
1.1
6.2
1.8
1.9
10.1
2.8
5.7
2.5
18.7
0.6
136.9
13.6
1.3
79.5
1.4
152.2
73.7
9.1
6.7
9.4
1.3
79.2
17.8
%>4pCi/L
18
6
7
11
0
12
40
3
0
12
0
9
3
0
0
2
0
0
14
0
7
0
21
0
31
0
34
0
59
32
4
10
23
0
39
6
%>20pCi/L
0
6
^
0
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
5
. 0
0
11
0
13
4
0
0
0
0
3
0
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Within the Puget Lowlands, townships extending from the northwestern corner of
Snohomish County southward to northernmost Pierce County show that either 0 percent or 1-5
percent of measured homes are over 5 pO/£ (see fig. 9 for a map of the counties in the State).
This highly populated area has the lowest average indoor radon levels in the entire study. In one
township in Seattle, the highest reading in more than 1000 measurements was about 2.8 pCi/L.
Townships in which 10 percent or more of homes exceed 5 pCi/L (fig. 8) include the
southern suburbs of Tacoma, where they appear to be associated with the highly permeable
Spanaway soils; the Sequim area in western Clallam County, where the soils are relatively dry and
locally highly permeable; the Columbia River gorge in southern Skamania County, where they are
associated with highly permeable, steeply sloped soils; west-central Bentpn County where highly
permeable river alluvium and dune sands occur, the Wenatchee area in southern Chelan County,
where highly permeable river terrace deposits occur, the city of Spokane and its eastern suburbs,
which are built on highly permeable glacial outwash; and the Curlew area in northern Ferry
County, where soils have formed on highly permeable glacial outwash, river terraces, and fans.
The highly permeable soils that cause elevated indoor radon levels in the eastern Spokane suburbs
are widespread throughout the Spokane metropolitan area. In some townships near Spokane as
many as 70 percent of the homes are over 4 pCi/L and indoor radon levels are locally as high as
200pCi/L.
Townships in which 5 to 10 percent of the measured homes are over 5 pCi/L occur in west-
central Lewis County where they seem to be associated with highly permeable soils on glacial
outwash plains and high terraces, and in the Ellensburg area in Kittitas County where they likely
are associated with river alluvium and glacial outwash.
This analysis suggests that the northeastern corner of the State has the highest overall radon
potential, and specific areas elsewhere in the State, generally small parts of counties where unusual
soils are found, may also have significant geologic radon potential.
GEOLOGIC RADON POTENTIAL
The State of Washington can be subdivided into three areas of varying overall geologic
radon potential. Areas within and west of the Cascade Mountains are generally characterized by
very low uranium in soils (less than 1.5 ppm elJ) and high soil moisture due to the high annual
rainfall. Under these conditions only modest levels of radon are generated by the soil and radon
migrates slowly through the soil. Only in local areas where the soils are extremely permeable
(» 20 in/hr) or where the topography is steeply sloped are indoor radon levels likely to be
significant Such areas might include the easternmost and southernmost parts of the Puget
Lowlands, where the combination of steep slopes and extremely permeable glacial outwash occur
locally, or areas in the Portland Basin near Vancouver or along the Columbia River gorge where
highly permeable river or lacustrine delta deposits, volcanic debris flows, and steep slopes locally
occur.
Li the Columbia Basin area east of the Cascade Mountains, most soils are drier (rainfall is
typically in the range of 9 to 15 inches per year), the uranium content of soils is moderately
elevated (most areas range from 1.5 to 2.5 ppm eU), and many river valleys contain soils that are
rapidly (6-20 in/hr) or very rapidly (>20 in/hr) permeable because they have developed on sand,
river alluvium, or glacial outwash (fig. 6). Lacustrine deposits are present in many areas and soils
IV-15 Reprinted from USGS Open-File Report 93-292-J
-------
Figure 9. County boundaries and names in Washington.
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developed on these units often have high porosity and emanating power, and show development of
secondary permeability by soil cracking. Many of these areas have significant potential for
producing elevated indoor radon levels.
In the Okanogan Highland, soils in the valley areas have formed on highly permeable,
coarse glacial outwash, fluvial terraces, and similar materials. Although these soils are generally
wetter than soils in the Columbia Basin to the south, the very high permeability (>20 in/hr) of the
majority of the soils permits rapid drainage of soil water and radon transport by diffusion and
convective flow is significant These areas have significant geolpgic potential for elevated indoor
radon levels.
Of special interest are buildings that may be inadvertently sited on uranium concentrations
in the hills north of Spokane. Very high indoor radon levels are likely in these buildings. Such
uranium occurrences are likely in the granitic rocks that underlie much of the area. Many of these
uranium occurrences are described in the National Uranium Resource Evaluation literature for the
area.
SUMMARY
There are six distinct geologic provinces in Washington for which radon potential may be
evaluated (Table 2): the Coastal mountains and hills, the Puget Lowlands, the Cascade Mountains,
the Okanogan Highlands, the Columbia Basin, and the Blue Mountains. A separate area of
moderate radon potential, the Columbia River Gorge, is also evaluated in Table 2. A relative index
of radon potential (RI) and an index of the level of confidence in the available data (CI) have been
established (see discussion in chapter 1 of this volume).
Low uranium in soils and very high rainfall throughout most of the area contribute to low
radon potential overall in the coastal mountains and hills of western Washington. The
northeastern corner of the Olympic Peninsula has lower rainfall and lower soil moisture than the
rest of the Coastal Range Province. Highly permeable, excessively well drained soils may cause
locally elevated indoor radon levels here.
The Puget lowland overall has very low radon potential because of high rainfall and
consequently high soil moisture, and low uranium content of soils. Most townships from Tacoma
northward average less than 1 pCi/L radon in the BPA study. Structures built on local very steep
or excessively well-drained soils, especially on the east side of the lowland area, may be among the
few likely to have elevated indoor radon levels. Only in the southern part of the Puget lowland
south of Tacoma where excessively drained soils and somewhat elevated uranium in soils occurs is
the potential moderate.
Overall, the sparsely populated Cascade Mountain Province has low radon potential
because of the low uranium content and high soil moisture of the soils. A major exception to this
is the Columbia River Gorge area where highly permeable, excessively well drained soils underlie
many of the communities and the radon potential is moderate. Moreover, much of the alluvium in
the Gorge is derived from the upper Columbia River valley where the uranium content of the
geologic materials is higher than within the Cascade Mountain Province itself. In the State/EPA
survey 85 percent of the basements in homes in Skamania County exceeded 4 pCi/L. Indoor radon
levels in townships along the Columbia River average 2 to 5 pCi/L in the BPA study.
IV-17 Reprinted from USGS Open-File Report 93-292-J
-------
In spite of the fact that bedrock across the Columbia Basin is often composed of low-
uranium basaltic rocks, surficial deposits include extensive Pleistocene glaciofluvial outwash,
eolian, and lacustrine deposits, which locally have highly permeable soils, soils with high
emanating coefficients, and higher soil uranium levels. This area has moderate to locally high
radon potential.
The Okanogan Highlands has high radon potential. This assessment is supported by
several studies (Otton and Duval, 1990; Moed and others, 1984; R. Sextro, written commun.,
1985; Otton and Reimer, unpub. data, 1986). Excessively well drained glaciofluvial outwash
underlies most of the valleys throughout the area. The granitic material in much of the outwash is
highly uraniferous. Areas where uranium occurrences are found, such as. the granitic and
metamorphic terranes in the mountains north and northwest of Spokane, may have buildings with
extreme levels of indoor radon. Homes in most of the alluvial valleys in Washington north and
northwest of Spokane may be expected to have average indoor radon above 4 pCi/L.
The Blue Mountains probably have moderate radon potential in spite of the low soil
uranium content; however, little indoor radon data or soil information is available. Indoor radon
data for the counties in this province mostly come from the populated parts of those counties in the
adjacent Columbia Basin. However, populated areas of this geologic province in nearby counties
in Oregon have indoor radon values averaging 2-4 pCi/L. In those Oregon counties, most housing
is on river valley alluvium and it is likely that soil permeabilities in these areas are high, which
contributes to modestly elevated indoor radon levels in spite of low soil uranium values.
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-18 Reprinted from USGS Open-File Report 93-292-J
-------
TABLE 2. Radon Index (RI) and Confidence Index (CI) for geologic radon potential areas of
Washington. See figure 1 for locations of areas. See chapter 1 for discussion of RI and CI.
FACTOR
Indoor radon
Radioactivity
Geology
Soil permeability
Architecture
GFE points
Total
Ranking
FACTOR
Indoor radon
Radioactivity
Geology
Soil permeability
Architecture
GFE points
Total
Ranking
Coastal
mountains
and hills
RI CI
1 3
1 3
1 2
2 3.
1
0
6 10
Low High
Okanogan
Highland
RI d
3 3
2 2
3 3
3 3
3 -
+2 -
16 11
High High
Puget Cascade
Lowlands Range
RI CI RI CI
1
1
1
2
1
0
6
Low
3 1 3
312
212
32 2
1
0
10 6 8
High Low Mod
Columbia
Basin
RI CI
2 3
2 3
2 2
2 3
2
0
10 11
Mod High
Columbia
River
Gorge
RI CI
23
1 3
• 2 2
3 2
1
0 -
9 10
Mod High
Blue
Mountains
RI CI
2? 1
1 3
2 1
2 1
2
0
9? 6
Mod Low
- Not used in CI.
RADON INDEX SCORING:
Radon potential category
LOW
MODERATE/VARIABLE
HIGH
Point range
3-8 points
9- 11 points
> 1 1 points
Probable screening indoor
radon average for area
<2pCi/L
2-4pCi/L
>4pCi/L
Possible range of points = 3 to 17
CONFIDENCE INDEX SCORING:
LOW CONFIDENCE
MODERATE CONFIDENCE
HIGH CONFIDENCE
4-6 points
7-9 points
10 - 12 points
Possible range of points = 4 to 12
IV-19 Reprinted from USGS Open-File Report 93-292-J
-------
REFERENCES CITED IN TfflS REPORT
AND OTHER REFERENCES RELAVENT TO RADON IN WASHINGTON
Asmerom, Yemane, 1981, Geochemistry of bibtite from a part of the Loon Lake Batholith and its
relationship to uranium mineralization at the Midnite uranium mine, Stevens County,
Washington: Master's thesis, Eastern Washington University, Cheney, WA, 110 p.
Beyer, W. C, 1981, Petrology and genesis of a uranium-bearing system of pegmatite dikes,
Nancy Creek area, northeastern Washington: Master's thesis, University of Montana,
Missoula, MT, 82 p., 1 plate.
Cady, J. W. and Fox, K. R, Jr., 1984, Geophysical interpretation of the gneiss terrane of
northern Washington and southern British Columbia, and its implications for uranium
exploration: U.S. Geological Survey Professional Paper 1260,29 p., 1 plate.
Castor, S. B., Berry, M. A. and Robins, J. W., 1977, Uranium and thorium content of intrusive
rocks in northeastern Washington and northern Idaho, in Bendix Field Engineering
Corporation, 1977 MURE uranium geology symposium; abstracts and visual presentations,
Grand Junction, CO, Dec. 7-8,1977: U.S. Department of Energy Report No. GJBX-
12(78), p. 167-172.
Chou, Gin, 1983, Geochemistry of the Togo metapelites from the Midnite uranium mine,
northeastern Washington: Master's thesis, Eastern Washington University, Cheney, WA,
94 p.
Duval, J. S., Jones, W. J., Riggle, F. R., and Pitkin, J. A., 1989, Equivalent uranium map of the
conterminous United States: U.S. Geological Survey Open-File Report 89-478,10 p.
Duval, J. S., Otton, J. K. and Jones, W. J., 1989, Radium distribution map and radon potential in
the Bonneville Power Administration service area: U. S. Geological Survey Open-File
Report 89-0340,125 p.
Flanigan, V. J., 1976, Geophysical survey of uranium mineralization in alaskitic rocks, eastern
Washington: U. S. Geological Survey Open-File Report 76-0679,25 p.
Gay, S. P., Jr., 1981, Spokane Mountain Deposit, NW U.S.A.; a uranium discovery resulting
from aeromagnetic lineaments analysis in a Precambrian metamorphic terrane: in
Gabrielson, R. H., Ramberg, I. B., Roberts, D. and Steinlein, O. A., eds., Proceedings
of the International Conference on Basement Tectonics, n. 4, p. 145-156.
Johnson, S. Y., Otton, J. K. and Macke, D. L., 1987, Geology of the Holocene surficial uranium
deposit of the north fork of Flodelle Creek, northeastern Washington: Geological Society
of America Bulletin, v. 98, n. 1, p. 77-85.
IV-20 Reprinted from USGS Open-File Report 93-292-J
-------
Kinart, K. P. and Ikramuddin, Mohammed j 1980, Geochemistry of part of the Loon Lake
batholith and its relationship to uranium mineralization at the Midnite mine, northeastern
Washington: Geological Society of America Abstracts with Programs, v. 12, n. 7, p. 463.
Lasmanis, Raymond, 1991, Geology of Washington: Rocks and Minerals Magazine, v. 66, n. 4,
p.262-277.
Lott, Thomas L., Jr., 1982, Petrography, major element chemistry, and geology of uraniferous
igneous rocks in the Turtle Lake Quadrangle, Washington: Master's thesis, University of
Georgia, Athens, GA, 107 p. .
Milne, P. C, 1980, Uranium in Washington: Washington Geologic Newsletter, v. 8, n. 2, p. 1-5
Mitchell, T. E., 1981, Uranium mineralization of the metamorphic aureole of the Spirit pluton,
Stevens County, Washington: Master's thesis, Oregon State University, Corvallis, OR,
109 p., 2 plates.
Moed, B.A., Nazaroff, A.V., Nero, M.B., Schwehr, M.B., and Van Heuvelen, A., 1984,
Identifying areas with potential for high indoor radon levels: analysis of the National
Airborne Radiometric Reconnaissance data for California and the Pacific Northwest:
Berkeley, California, Lawrence Berkeley Laboratory Report No. LBL-16955,70 p.
Nash, J. T. and Lehrman, N. J., 1975, Geology of the Midnite uranium mine, Stevens County,
Washington; a prelirninary report: U. S. Geological Survey Open-File Report 75-0402,36
P-
Nash, J. T. and Lehrman, N., 1975, The Midnite uranium mine, Stevens County, Washington: U.
S. Geological Survey Professional Paper 975, 29 p.
Nash, J. T. and Lehrman, N. J., 1976, Secondary enrichment of uranium, Midnite Mine: U. S.
Geological Survey Professional Paper 1000,38 p.
Nero, A.V., Schwehr, M.B., Nazaroff, W.W., and Revzan, K.L., 1986, Distribution of airborne
radon-222 concentrations in U.S. homes: Science, v. 234, p.992-997.
Otton, James K., 1987, Indoor radon; geologic controls in Pacific Northwest: Geological Society
of America Abstracts with Programs, v.19, n.2, p. 122.
Otton, J.K. and Duval, J.S., 1990, Geologic controls on indoor radon in the Pacific Northwest, in
U.S. Environmental Protection Agency, The 1990 international symposium on radon and
radon reduction technology: Volume HI. Preprints, unpaginated.
Pitkin, J. A., 1975, Truckborne gamma-ray spectrometry in northeastern Washington: in Craig, L.
C., Brooks, R. A. and Patton, P. C., eds., Abstracts of the 1975 Uranium and Thorium
Research and Resources Conference: U.S. Geological Survey Open-File Report 75-595,
p. 35.
IV-21 Reprinted from USGS Open-Ffle Report 93-292-J
-------
Rose, A.W., dolkosz, E.J., and Washington, J.W., 1990, Effects of regional and seasonal
variations in soil moisture and temperature on soil gas radon, in U.S. Environmental
Protection Agency, The 1990 international symposium on radon and radon reduction
technology: Volume in. Preprints, unpaginated.
Schuster, E.J., 1990, Geologic map of Washington: Washington Division of Geology and Earth
Resources, Olympia, 1 plate.
U.S. Geological Survey, 1978, Geology of Washington: Washington Division of Geology and
Earth Resources Reprint 12, p. 13-51,1 plate.
Wicldund, M. A., 1984, Geology and genesis of the rocks of the Graeber uranium area, Stevens
County, Washington: Master's thesis, Eastern Washington University, Cheney, WA,
160 p., 2 plates.
Zielinski, R. A., Bush, C. A. and Rosholt, J. N., 1986, Uranium series disequilibrium in a young
surficial uranium deposit, northeastern Washington, U.S.A.: Applied Geochemistry, v. 1,
n. 4, p. 503-511.
IV-22 Reprinted from USGS Open-File Report 93-292-J
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EPA's Map of Radon Zones
The USGS' Geologic Radon Province Map is the technical foundation for EPA's Map
of Radon Zones. The Geologic Radon Province Map defines the radon potential for
approximately 360 geologic provinces. EPA has adapted this information to fit a county
boundary map in order to produce the Map of Radon Zones.
The Map of Radon Zones is based on the same range of predicted screening levels of
indoor radon as USGS' Geologic Radon Province Map. EPA defines the three zones as
follows: Zone One areas have an average predicted indoor radon screening potential greater
than 4 pCi/L. Zone Two areas are predicted to have an average indoor radon screening
potential between 2 pCi/L and 4 pCi/L. Zone Three areas are predicted to have an average
indoor radon screening potential less than 2 pCi/L.
Since the geologic province boundaries cross state and county boundaries, a strict
.translation of counties from the Geologic Radon Province Map to the Map of Radon Zones
was not possible. For counties that have variable radon potential (i.e., are located in two or
more provinces of different rankings), the counties were assigned to a zone based on the
predicted radon potential of the province in which most of its area lies. (See Part I for more
details.)
WASHINGTON MAP OF RADON ZONES
The Washington Map of Radon Zones and its supporting documentation (Part IV of
this report) have received extensive review by Washington geologists and radon program
experts. The map for Washington generally reflects current State knowledge about radon for
its counties. Some States have been able to conduct radon investigations in areas smaller than
geologic provinces and counties, so it is important to consult locally available data.
Two county designations do not strictly follow the methodology for adapting the
geologic provinces to county boundaries. EPA and the State of Washington Department of
Health have decided to designate Skamania and Clark counties as Zone 1. Portions of these
counties lie in the Columbia River Gorge geologic province. Some very elevated levels of
indoor radon have been attributed to the geology in this province. Although this type of
geology does not cover the majority of these counties, the majority of the counties'
populations reside in this geologic area.
Although the information provided in Part IV of this report — the State chapter entitled
"Preliminary Geologic Radon Potential Assessment of Washington" -- may appear to be quite
specific, it cannot be applied to determine the radon levels of a neighborhood, housing tract,
individual house, etc. THE ONLY WAY TO DETERMINE IF A HOUSE HAS
ELEVATED INDOOR RADON IS TO TEST. Contact the Region 10 EPA office or the
Washington radon program for information on testing and fixing homes. Telephone numbers
and addresses can be found in Part II of this report.
V-l
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