United States
Environmental Protection
Agency
Air and Radiation
(6604J)
4O2-R-93-O33
September 1993
v>EPA EPA's Map of Radon Zones
ILLINOIS
Recycled/Recyclable
Printed on paper that contains
at least 50% recycled fiber
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EPA'S MAP OF RADON ZONES
ILLINOIS
RADON DIVISION
OFFICE OF RADIATION AND INDOOR AIR
U.S. ENVIRONMENTAL PROTECTION AGENCY
SEPTEMBER, 1993
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ACKNOWLEDGEMENTS
This document was prepared by the U.S. Environmental Protection Agency's (EPA's)
Office of Radiation and Indoor Air (ORIA) in conjunction with the U.S. Geological Survey
(USGS). Sharon W. White was the EPA project manager. Numerous other people in ORIA
were instrumental in the development of the Map of Radon Zones, including Lisa Ratcliff,
Kirk Maconaughey, R. Thomas Peake, Dave Rowson, and Steve Page.
EPA would especially like to acknowledge the outstanding effort of the USGS
radon team — Linda Gundersen, Randy Schumann, Jim Otton, Doug Owen, Russell
Dubiel, Kendell Dickinson, and Sandra Szarzi - in developing the technical base for the
Map of Radon Zones.
ORIA would also like to recognize the efforts of all the EPA Regional Offices in
coordinating the reviews with the State programs and the Association of American State
Geologists (AASG) for providing a liaison with the State geological surveys. In addition,
appreciation is expressed to all of the State radon programs and geological surveys for their
technical input and review of the Map of Radon Zones.
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TABLE OF CONTENTS
I. OVERVIEW
II. THE USGS/EPA RADON POTENTIAL
ASSESSMENTSiINTRODUCTION
III. REGION 5 GEOLOGIC RADON POTENTIAL
SUMMARY
V. PRELIMINARY GEOLOGIC RADON POTENTIAL
ASSESSMENT OF ILLINOIS
V. EPA'S MAP OF RADON ZONES -- ILLINOIS
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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
EPA's Map of Radon Zones (Figure 1) assigns each of the 3 141 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
Lincoln County
Underlie Low
Figure 4
NEBRASKA - EPA Map of Radon Zones
Liacola County
Zest 1 Zoae 2
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One such analysis involved comparing county zone designations to indoor radon
measurements from the State/EPA Residential Radon Surveys (SRRS). Screening averages
for counties with at least-100 measurements were compared to the counties' predicted radon
potential as indicated by the Map of Radon Zones. EPA found that 72% of the county
screening averages were correctly reflected by the appropriate zone designations on the Map.
In all other cases, they only differed by 1 zone.
Another accuracy analysis used the annual average data from the National Residential
Radon Survey (NRRS). The NRRS indicated that approximately 6 million homes in the
United States have annual averages greater than or equal to 4 pCi/L. By cross checking the
county location of the approximately 5,700 homes which participated in the survey, their
radon measurements, and the zone designations for these counties, EPA found that
approximately 3.8 million homes of the 5.4 million homes with radon levels greater than or
equal to 4 pCi/L will be found in counties designated as Zone 1. A random sampling of an
equal number of counties would have only found approximately 1.8 million homes greater
than 4 pCi/L. In other words, this analysis indicated that the map approach is three times
more efficient at identifying high radon areas than random selection of zone designations.
Together, these analyses show that the approach EPA used to develop the Map of
Radon Zones is a reasonable one. In addition, the Agency's confidence is enhanced by results
of the extensive State review process — the map generally agrees with the States' knowledge
of and experience in their own jurisdictions. However, the accuracy analyses highlight two
important points: the fact that elevated levels will be found in Zones 2 and 3, and that there
will be significant numbers of homes with lower indoor radon levels in all of the Zones. For
these reasons, users of the Map of Radon Zones need to supplement the Map with locally
available data whenever possible. Although all known "hot spots", i.e., localized areas of
consistently elevated levels, are discussed in the State-
specific chapters, accurately defining the boundaries of the "hot spots" on this scale of map is
not possible at this time. Also, unknown "hot spots" do exist.
The Map of Radon Zones is intended to be a starting point for characterizing radon
potential because our knowledge of radon sources and transport is always growing. Although
this effort represents the best data available at this time, EPA will continue to study these
parameters and others such as house construction, ventilation features and meteorology factors
in order to better characterize the presence of radon in U.S homes, especially in high risk
areas. These efforts will eventually assist EPA in refining and revising the conclusions of the
Map of Radon Zones. And although this map is most appropriately used as a targeting tool
by the aforementioned audiences ~ the Agency encourages all residents to test their homes
for radon, regardless of geographic location or the zone designation of the county in
which they live. Similarly, the Map of Radon Zones should not to be used in lieu of
testing during real estate transactions.
Review Process
The Map of Radon Zones has undergone extensive review within EPA and outside the
Agency. The Association of American State Geologists (AASG) played an integral role in
this review process. The AASG individual State geologists have reviewed their State-specific
information, the USGS Geologic Radon Province Map, and other materials for their geologic
content and consistency.
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In addition to each State geologist providing technical comments, the State radon
offices were asked to comment on their respective States' radon potential evaluations. In
particular, the States were asked to evaluate the data used to assign their counties to specific
zones, EPA and USGS worked with the States to resolve any issues concerning county zone
designations. In a few cases, States have requested changes in county zone designations. The
requests were based on additional data from the State on geology, indoor radon
measurements, population, etc. Upon reviewing the data submitted by the States, EPA did
make some changes in zone designations. These changes, which do not strictly follow the
methodology outlined in this document, are discussed in the respective State chapters.
EPA encourages the States and counties to conduct further research and data collection
efforts to refine the Map of Radon Zones. EPA would like to be kept informed of any
changes the States, counties, or others make to the maps. Updates and revisions will be
handled in a similar fashion to the way the map was developed. States should notify EPA of
any proposed changes by forwarding the changes through the Regional EPA offices that are
listed in Part II. Depending on the amount of new information that is presented, EPA will
consider updating this map periodically. The State radon programs should initiate proper
notification of the appropriate State officials when the Map of Radon Zones is released and
when revisions or updates are made by the State or EPA.
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THE USGS/EPA RADON POTENTIAL ASSESSMENTS: AN INTRODUCTION
by
Linda C.S. Gundersen and R. Randall Schumann
U.S. Geological 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 local
departments of health, state departments responsible for nuclear safety or environmental
protection, and U.S. EPA regional offices. More detailed information on state or local
geology may be obtained from the state geological surveys. Addresses and telephone
numbers of state radon contacts, geological surveys, and EPA regional offices are listed in
Appendix C at the end of this chapter.
RADON GENERATION AND TRANSPORT IN SOILS
Radon (z"Rn) is produced from the radioactive decay of radium (226Ra), which is, in turn,
a product of the decay of uranium (U8U) (fig. 1). The half-life of :22Rn 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
II-2 Reprinted from USGS Open-File Report 93-292
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and moisture infiltration rates and depth of wetting may be limited when the cracks in the
surface soil layers swell shut. Clay-rich B horizons, particularly those with massive or platy
structure, can form a capping layer that impedes the escape of soil gas to the surface
(Schumann and others, 1992). However, the shrinkage of clays can act to open or widen
cracks upon drying, thus increasing the soil's permeability to gas flow during drier periods.
Radon transport in soils occurs by two processes: (1) diffusion and (2) flow (Tanner,
1964). Diffusion is the process whereby radon atoms move from areas of higher
concentration to areas of lower concentration in response to a concentration gradient. Flow is
the process by which soil air moves through soil pores in response to differences in pressure
within the soil or between the soil and the atmosphere, carrying the radon atoms along with it.
Diffusion is the dominant radon transport process in soils of low permeability, whereas flow
tends to dominate in highly permeable soils (Sextro and others, 1987). In low-permeability
soils, much of the radon may decay before it is able to enter a building because its transport
rate is reduced. Conversely, highly permeable soils, even those that are relatively low in
radium, such as those derived from some types of glacial deposits, have been associated with
high indoor radon levels in Europe and in the northern United States (Akerblom and others,
1984; Kunz and others, 1989; Sextro and others, 1987). In areas of karst topography formed
in carbonate rock (limestone or dolomite) environments, solution cavities and fissures can
increase soil permeability at depth by providing additional pathways for gas flow.
Not all radium contained in soil grains and grain coatings will result in mobile radon
when the radium decays. Depending on where the radium is distributed in the soil, many of
the radon atoms may remain imbedded in the soil grain containing the parent radium atom, or
become imbedded in adjacent soil grains. The portion of radium that releases radon into the
pores and fractures of rocks and soils is called the emanating fraction. When a radium atom
decays to radon, the energy generated is strong enough to send the radon atom a distance of
about 40 nanometers (1 nm = 10'9 meters), or about 2x10"* inches—this is known as alpha
recoil (Tanner, 1980). Moisture in the soil lessens the chance of a recoiling radon atom
becoming imbedded in an adjacent grain. Because water is more dense than air, a radon atom
will travel a shorter distance in a water-filled pore than in an air-filled pore, thus increasing
the likelihood that the radon atom will remain in the pore space. Intermediate moisture levels
enhance radon emanation but do not significantly affect permeability. However, high
moisture levels can significantly decrease the gas permeability of the soil and impede radon
movement through the soil.
Concentrations of radon in soils are generally many times higher than those inside of
buildings, ranging from tens of pCi/L to more than 100,000 pCi/L, but typically in the range
of hundreds to low thousands of pCi/L. Soil-gas radon concentrations can vary in response to
variations in climate and weather on hourly, daily, or seasonal time scales. Schumann and
others (1992) and Rose and others (1988) recorded order-of-magnitude variations in soil-gas
radon concentrations between seasons in Colorado and Pennsylvania. The most important
factors appear to be (1) soil moisture conditions, which are controlled in large part by
precipitation; (2) barometric pressure; and (3) temperature. Washington and Rose (1990)
suggest that temperature-controlled partitioning of radon between water and gas in soil pores
also has a significant influence on the amount of mobile radon in soil gas.
Homes in hilly limestone regions of the southern Appalachians were found to have higher
indoor radon concentrations during the summer than in the winter. A suggested cause for this
phenomenon involves temperature/pressure-driven flow of radon-laden air from subsurface
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solution cavities in the carbonate rock into houses. As warm air enters solution cavities that
are higher on the hillslope than the homes, it cools and settles, pushing radon-laden air from
lower in the cave or cavity system into structures on the hillslope (Gammage and others,
1993). In contrast, homes built over caves having openings situated below the level of the
home had higher indoor radon levels in the winter, caused by cooler outside air entering the
cave, driving radon-laden air into cracks and solution cavities in the rock and soil, and
ultimately, into homes (Gammage and others, 1993).
RADON ENTRY INTO BUILDINGS
A driving force (reduced atmospheric pressure in the house relative to the soil, producing
a pressure gradient) and entry points must exist for radon to enter a building from the soil.
The negative pressure caused by furnace combustion, ventilation devices, and the stack effect
(the rising and escape of warm air from the upper floors of the building, causing a
temperature and pressure gradient within the structure) during cold winter months are
common driving forces. Cracks and other penetrations through building foundations, sump
holes, and slab-to-foundation wall joints are common entry points.
Radon levels in the basement are generally higher than those on the main floor or upper
floors of most structures. Homes with basements generally provide more entry points for
radon, commonly have a more pronounced stack effect, and typically have lower air pressure
relative to the surrounding soil than nonbasement homes. The term "nonbasement" applies to
slab-on-grade or crawl space construction.
METHODS AND SOURCES OF DATA
The assessments of radon potential in the booklets that follow this introduction were
made using five main types of data: (1) geologic (lithologic); (2) aerial radiometric; (3) soil
characteristics, including soil moisture, permeability, and drainage characteristics; (4) indoor
radon data; and (5) building architecture (specifically, whether homes in each area are built
slab-on-grade or have a basement or crawl space). These five factors were evaluated and
integrated to produce estimates of radon potential. Field measurements of soil-gas radon or
soil radioactivity were not used except where such data were available in existing, published
reports of local field studies. Where applicable, such field studies are described in the
individual state chapters.
GEOLOGIC DATA
The types and distribution of lithologic units and other geologic features in an
assessment area are of primary importance in determining radon potential. Rock types that
are most likely to cause indoor radon problems include carbonaceous black shales, glauconite-
bearing sandstones, certain kinds of fluvial sandstones and fluvial sediments, phosphorites,
chalk, karst-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
H-5 Reprinted from USGS Open-File Report 93-292
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igneous rocks, and basalts. Exceptions exist within these general-lithologic groups because of
the occurrence of localized uranium deposits, commonly of the hydrothermal type in
crystalline rocks or the "roll-front" type in sedimentary rocks. Uranium and radium are
commonly sited in heavy minerals, iron-oxide coatings on rock and soil grains, and organic
materials in soils and sediments. Less common are uranium associated with phosphate and
carbonate complexes in rocks and soils, and uranium minerals.
Although many cases of elevated indoor radon levels can be traced to high radium and
(or) uranium concentrations in parent rocks, some structural features, most notably faults and
shear zones, have been identified as sites of localized uranium concentrations (Deffeyes and
MacGregor, 1980) and have been associated with some of the highest reported indoor radon
levels (Gundersen, 1991). The two highest known indoor radon occurrences are associated
with sheared fault zones in Boyertown, Pennsylvania (Gundersen and others, 1988a; Smith
and others, 1987), and in Clinton, New Jersey (Henry and others, 1991; Muessig and Bell,
1988).
NUKE 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 C^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 SPACING OF SURE AERIAL SURVEYS
2 I'll (1 KILE)
5 KU (3 MILES)
2 t 5 Kit
10 III (6 MILES)
5 t 10 EM
NO DATA
Figure 2. Nominal flightline spacings for NURE aerial gamma-ray surveys covering die
contiguous United States (fromDuval 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
was covered by the aerial gamma survey, and thus, more detail is available in the data set.
For an altitude of 400 ft above the ground surface and with primary flightline spacing
typically between 3 and 6 miles, less than 10 percent of the ground surface of the Unrted
States was actually measured by the airborne gamma-ray detectors (Duval and others, 1989),
although some areas had better coverage than others due to the differences in flight-line
spacing between areas (fig. 2). This suggests that some localized uranium anomalies may not
have been detected by the aerial surveys, but the good correlations of eU patterns with
geologic outcrop patterns indicate that, at relatively small scales (approximately 1:1,000,000
or smaller) the National eU map (Duval and others, 1989) gives reasonably good estimates of
average surface uranium concentrations and thus can assist in the prediction of radon potential
of rocks and soils, especially when augmented with additional geologic and soil data.
The shallow (20-30 cm) depth of investigation of gamma-ray spectrometers, either
ground-based or airborne (Duval and others, 1971; Durrance, 1986), suggests that gamma-ray
data may sometimes underestimate the radon-source strength in soils in which some of the
radionuclides in the near-surface soil layers have been transported downward through the soil
profile. In such cases the concentration of radioactive minerals in the A horizon would be
lower than in the B horizon, where such minerals are typically concentrated. The
concentration of radionuclides in the C horizon and below may be relatively unaffected by
surface solution processes. Under these conditions the surface gamma-ray signal may indicate
a lower radon source concentration than actually exists in the deeper soil layers, which are
most likely to affect radon levels in structures with basements. The redistribution of
radionuclides in soil profiles is dependent on a combination of climatic, geologic, and
geochemical factors. There is reason to believe that correlations of eU with actual soil
radium and uranium concentrations at a depth relevant to radon entry into structures may be
regionally variable (Duval, 1989; Schumann and Gundersen, 1991). Given sufficient
understanding of the factors cited above, these regional differences may be predictable.
SOIL SURVEY DATA
Soil surveys prepared by the U.S. Soil Conservation Service (SCS) provide data on soil
characteristics, including soil-cover thickness, grain-size distribution, permeability, shrmk-
swell potential, vegetative cover, generalized groundwater characteristics, and land use. The
reports are available in county formats and State summaries. The county reports typically
contain both generalized and detailed maps of soils in the area.
Because of time and map-scale constraints, it was impractical to examine county soil
reports for each county in the United States, so more generalized summaries at appropriate
scales were used where available. For State or regional-scale radon characterizations, soil
maps were compared to geologic maps of the area, and the soil descriptions, shrmk-swell
potential drainage characteristics, depth to seasonal high water table, permeability, and other
relevant characteristics of each soil group noted. Technical soil terms used in soil surveys are
generally complex; however, a good summary of soil engineering terms and the national
distribution of technical soil types is the "Soils" sheet of the National Atlas (U.S. Department
of Agriculture, 1987).
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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 hot truly units;of''permeability, trlese units are in widespread use and
are referred to as "permeability" in SCS soil surveys. The permeabilities listed in the SCS
surveys are for water, but they generally correlate well with gas permeability. Because data
on gas permeability of soils is extremely limited, data on permeability to water is used as a
substitute except in cases in which excessive soil moisture is known to exist. Water in soil
pores inhibits gas transport, so the amount of radon available to a home is effectively reduced
by a high water table. Areas likely to have high water tables include river valleys, coastal
areas, and some areas overlain by deposits of glacial origin (for example, loess).
Soil permeabilities greater than 6.0 in/hr may be considered high, and permeabilities less
than 0.6 in/hr may be considered low in terms of soil-gas transport. Soils with low
permeability may generally be considered to have a lower radon potential than more
permeable soils with similar radium concentrations. Many well-developed soils contain a
clay-rich B horizon that may impede vertical soil gas transport. Radon generated below this
horizon cannot readily escape to the surface, so it would instead tend to move laterally,
especially under the influence of a negative pressure exerted by.a building.
Shrink-swell potential is an indicator of the abundance of smectitic (swelling) clays in a
soil. Soils with a high shrink-swell potential may cause building foundations to crack,
creating pathways for radon entry into the structure. During dry periods, desiccation cracks in
shrink-swell soils provide additional pathways for soil-gas transport and effectively increase
the gas permeability of the soil. Soil permeability data and soil profile data thus provide
important information for regional radon assessments.
INDOOR RADON DATA
Two major sources of indoor radon data were used. The first and largest source of data is
from the State/EPA Residential Radon Survey (Ronca-Battista and others, 1988; Dziuban and
others, 1990). Forty-two states completed EPA-sponsored indoor radon surveys between 1986
and 1992 (fig. 3). The State/EPA Residential Radon Surveys were designed to be
comprehensive and statistically significant at the state level, and were subjected to high levels
of quality assurance and control. The surveys collected screening indoor radon measurements,
defined as 2-7 day measurements using charcoal canister radon detectors placed in the lowest
livable area of the home. The target population for the surveys included owner-occupied
single family, detached housing units (White and others, 1989), although attached structures
such as duplexes, townhouses, or condominiums were included in some of the surveys if they
met the other criteria and had contact with the ground surface. Participants were selected
randomly from telephone-directory listings. In total, approximately 60,000 homes were tested
in the State/EPA surveys.
The second source of indoor radon data comes from residential surveys that have been
conducted in a specific state or region of the country (e.g. independent state surveys or utility
company surveys). Several states, including Delaware, Florida, Illinois, New Hampshire, New
Jersey, New York, Oregon, and Utah, have conducted their own surveys of indoor radon. The
quality and design of a state or other independent survey are discussed and referenced where
the data are used.
II-9 Reprinted from USGS Open-File Report 93-292
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-------
Data 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 at! of the data used in these evaluations represent short-term (2-7
day) screening measurements from the lowest livable space of the homes. Specific details
concerning the nature and use of indoor radon data sets other than the State/EPA Residential
Radon Survey are discussed in the individual State chapters.
RADON INDEX AND CONFIDENCE INDEX
Many of the geologic methods used to evaluate an area for radon potential require
subjective opinions based on the professional judgment and experience of the individual
geologist. The evaluations are nevertheless based on established scientific principles that are
universally applicable to any geographic area or geologic setting. This section describes the
methods and conceptual framework used by the U.S. Geological Survey to evaluate areas for
radon potential based on the five factors discussed in the previous sections. The scheme is
divided into two basic parts, a Radon Index (RI), used to rank the general radon potential of
the area, and the Confidence Index (CI), used to express the level of confidence in the
prediction based on the quantity and quality of the data used to make the determination. This
scheme works best if the areas to be evaluated are delineated by geologically-based
boundaries (geologic provinces) rather than political ones (state/county boundaries) in which
the geology may vary across the area.
Ration Index. Table 1 presents the Radon Index (RI) matrix. The five factors—indoor
radon data, geology, aerial radioactivity, soil parameters, and house foundation type—were
quantitatively ranked (using a point value of 1, 2, or 3) for their respective contribution to
radon potential in a given area. At least some data for the 5 factors are consistently available
for every geologic province. Because each of these main factors encompass a wide variety of
complex and variable components, the geologists performing the evaluation relied heavily on
their professional judgment and experience in assigning point values to each category and in
determining the overall radon potential ranking. Background information on these factors is
discussed in more detail in the preceding sections of this introduction.
Indoor radon was evaluated using unweighted arithmetic means of the indoor radon data
for each geologic area to be assessed. Other expressions of indoor radon levels in an area
also could have been used, such as weighted averages or annual averages, but these types of
data were not consistently available for the entire United States at the time of this writing, or
the schemes were not considered sufficient to provide a means of consistent comparison
across all areas. For this report, charcoal-canister screening measurement data from the
State/EPA Residential Radon Surveys and other carefully selected sources were used, as
described in the preceding section. To maintain consistency, other indoor radon data sets
(vendor, state, or other data) were not considered in scoring the indoor radon factor of the
Radon Index if they were not randomly sampled or could not be statistically combined with
the primary indoor radon data sets. However, these additional radon data sets can provide a
means to further refine correlations between geologic factors and radon potential, so they are
II-11 Reprinted from USGS Open-File Report 93-292
-------
-------
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.
i
Aerial radioactivity data used in this report are from the equivalent uranium map of the
conterminous United States compiled from NUKE 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
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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
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to question the quality or validity of these data. The other factors were scored on the basis of
the quality and quantity of the data used to complete the RI matrix.
Indoor radon data were evaluated based on the distribution and number of data points and
on whether the data were collected by random sampling (State/EPA Residential Radon Survey
or other state survey data) or volunteered vendor data (likely to be nonrandom and biased
toward population centers and/or high indoor radon levels). The categories listed in the CI
matrix for indoor radon data ("sparse or no data", "fair coverage or quality", and "good
coverage/quality") indicate the sampling density and statistical robustness of an indoor radon
data set. Data from the State/EPA Residential Radon Survey and statistically valid state
surveys were typically assigned 3 Confidence Index points unless the data were poorly
distributed or absent in the area evaluated.
Aerial radioactivity data are available for all but a few areas of the continental United
States and for part of Alaska, An evaluation of the quality of the radioactivity data was based
on whether there appeared to be a good correlation between the radioactivity and the actual
amount of uranium or radium available to generate mobile radon in the rocks and soils of the
area evaluated. In general, the greatest problems with correlations among eU, geology, and
soil-gas or indoor radon levels were associated with glacial deposits (see the discussion in a
previous section) and typically were assigned a 2-point Confidence Index score. Correlations
among eU, geology, and radon were generally sound in unglaciated areas and were usually
assigned 3 CI points. Again, however, radioactivity data in some unglaciated areas may have
been assigned fewer than 3 points, and in glaciated areas may be assigned only one point, if
the data were considered questionable or if coverage was poor.
To assign Confidence Index scores for the geologic data factor, rock types and geologic
settings for which a physical-chemical, process-based understanding of radon generation and
mobility exists were regarded as having "proven geologic models" (3 points); a high
confidence.could be held for predictions in such areas. Rocks for which the processes are
less-well known or for which data are contradictory were regarded as "variable" (2 points),
and those about which little is known or for which no apparent correlations have been found
were deemed "questionable" (1 point).
The soil permeability factor was also scored based on quality and amount of data. The
three categories for soil permeability in the Confidence Index are similar in concept, and
scored similarly, to those for the geologic data factor. Soil permeability can be roughly
estimated from grain size and drainage class if data from standard, accepted soil percolation
tests are unavailable; however, the reliability of the data would be lower than if percolation
test figures or other measured permeability data are available, because an estimate of this type
does not encompass all the factors that affect soil permeability and thus may be inaccurate in
some instances. Most published soil permeability data are for water; although this is
generally closely related to the air permeability of the soil, there are some instances when it
may provide an incorrect estimate. Examples of areas in which water permeability data may
not accurately reflect air permeability include areas with consistently high levels of soil
moisture, or clay-rich soils, which would have a low water permeability but may have a
11-15 Reprinted from USGS Open-File Report 93-292
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significantly higher air permeability when dry due to shrinkage cracks in the soil. These
additional factors were applied to the soil permeability factor when assigning the RI score, but
may have less certainty in some cases and thus would be assigned a lower CI score.
The Radon Index and Confidence Index give a general indication of the relative
contributions of the interrelated geologic factors influencing radon generation and transport in
rocks and soils, and thus, of the potential for elevated indoor radon levels to occur in a
particular area. However, because these reports are somewhat generalized to cover relatively
large areas of States, it is highly recommended that more detailed studies be performed in
local areas of interest, using the methods and general information in these booklets as a guide.
11-16 Reprinted from USGS Open-File Report 93-292 .
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savings potential of building foundations research: Oak Ridge, Term., U.S. Department of
Energy Report ORNL/SUB/84-0024/1.
Smith, R.C., H, Reilly, M.A., Rose, A.W., Barnes, J.H., and Berkheiser, S.W., Jr., 1987,
Radon: a profound case: Pennsylvania Geology, v. 18, p. 1-7.
Tanner, A.B., 1964, Radon migration in the ground: a review, w-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.
JJ-19 Reprinted from USGS Open-File Report 93-292
-------
-------
APPENDIX A
GEOLOGIC TIME SCALE
Subdivisions (and their symbols)
Eon or
Eonothem
Phanerozoic2
Proterozoic
/at
(CI
Archean
f At
\AJ
Era or
Erathem
Cenozoic 2
-ICz)
Mesozoic2
(Md
Paleozoic2
(Pd
LM« _
MiOfll*
Pmmrotoic TV)
Eafty
L*i«
Miodn
fctrtv
Period, System,
Subper od. Subsystem
Quaternary
(Q)
Neogene 2
Subperiod or
T.frf«Y Subsystem (N)
m Paieogene
11 Subperiod or
Subsystem (Pi)
Cretaceous
(K)
Jurassic
(J)
Triassic
CR)
Permian
(P)
Pennsylvanian
Carboniferous (P'
(C) Mississippian
(M)
Devonian
ID)
Silurian
fC\
(a)
Ordovician
to)
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
Uooer
Middle
Lower
Upper
Middle
Lower
Upper
Middle
Lower
Upper
Middle
Lower
None defined
None defined
None defined
None defined
None defined
None defined
pr*-Arch**n (pAI '
Age estimates
"f boundaries
in mega-annum
(Ma)1
5/4 Q— R ^
-570 3
1 Ranges reflect uneenaimiw of isolopic and btestrsfioraphie age assignment*. Aoe boundaries not closely bracketed by existing
data shown by * Decay constants and isotopic ratios employed are cited in Steiger mnd Jiger (1977). Designation m.y. used for an
interval of time.
* Modifiers (tower, middle, upper or earty. middle, late) when used with these Hems are informal division* of the larger unit; the
first letter of the modifier is lowercase.
'Rocks older than 570 Ma also called Precambrian (c-C). a time term without specific rank.
'informal time term without specific rank.
USGS Open-File Report 93-292,
-------
-------
APPENDIX B
GLOSSARY OF fEtfMS
Units of measure
pCi/L (picocuries per liter)- a unit of measure of radioactivity used to describe radon
concentrations in a volume of air. One picocurie (10'12 curies) is equal to about 2.2 disintegrations
of radon atoms per minute. A liter is about 1.06 quarts. The average concentration of radon in
U.S. homes measured to date is between 1 and 2 pCi/L.
Bq/m3 (Becquerels per cubic meter)- a metric unit of radioactivity used to describe radon
concentrations in a volume of air. One becquerel is equal to one radioactive disintegration per
second. One pCi/L is equal to 37 Bq/m3.
ppm (parts per million)- a unit of measure of concentration by weight of an element in a
substance, in this case, soil or rock. One ppm of uranium contained in a ton of rock corresponds
to about 0.03 ounces of uranium. The average concentration of uranium in soils in the United
States is between 1 and 2 ppm.
in/hr (inches per hour)- a unit of measure used by soil scientists and engineers to describe the
permeability of a soil to water flowing through it It is measured by digging a hole 1 foot (12
inches) square and one foot deep, filling it with water, and measuring the time it takes for the water
to drain from the hole. The drop in height of the water level in the hole, measured in inches, is
then divided by the time (in hours) to determine the permeability. Soils range in permeability from
less than 0.06 in/hr to greater than 20 in/hr, but most soils in the United States have permeabilities
between these two extremes.
Geologic terms and terms related to the study of radon
aerial radiometric, aeroradiometric survey A survey of radioactivity, usually gamma rays,
taken by an aircraft carrying a gamma-ray spectrometer pointed at the ground surface.
alluvial fan A low, widespread mass of loose rock and soil material, shaped like an open fan
and deposited by a stream at the point where it flows from a narrow mountain valley out onto a
plain or broader valley. May also form at the junction with larger streams or when the gradient of
the stream abruptly decreases.
alluvium, alluvial General terms referring to unconsolidated detrital material deposited by a
stream or other body of running water.
alpha-track detector A passive radon measurement device consisting of a plastic film that is
sensitive to alpha particles. The film is etched with acid in a 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.
H-21 Reprinted from USGS Open-FUe Report 93-292
-------
argiilite, 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 (CQs) 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.
H-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-File Report 93-292
-------
and may be referred to as a "placer deposit." Some heavy minerals are magnetite, garnet, zircon,
monazite, and xenotime.
igneous Said of a rock or mineral that solidified from molten or partly molten rock material. It is
one of the three main classes into which roc^ are di\ id _, Jie others be^ig 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 (CaCOs).
lithology The description of rocks in hand specimen and in outcrop on the basis of color,
composition, and grain size.
loam A permeable soil composed of a mixture of relatively equal parts clay, silt, and sand, and
usually containing some organic matter.
loess A fine-grained eolian deposit composed of silt-sized particles generally thought to have
been deposited from windblown dust of Pleistocene age.
mafic Term describing an igneous rock containing more 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
PhylHte, schist, amphibolite, and gneiss are metamorphic rocks.
moraine A mound, ridge, or other distinct accumulation of unsorted, imbedded glacial material,
predominantly till, deposited by the action of glacial ice.
outcrop That part of a geologic formation or structure that appears at the surface of the Earth, as
in "rock outcrop".
percolation test A term used in engineering for a test to determine the water permeability of a
soil. A hole is dug and filled with water and the rate of water level decline is measured.
permeability The capacity of a rock, sediment, or soil to transmit liquid or gas.
phosphate, phpsphatic, phosphorite Any rock or sediment containing a significant amount
of phosphate minerals, i.e., minerals containing PO4.
11-24 Reprinted from USGS Open-File Report 93-292
-------
physiographic province A region in which all parts are similar in geologic structure and
climate, which has had a uniform geomdrphic history, arid whose topography or landforms differ
significantly from adjacent regions.
piacer 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 uu the
earth's surface.
tablelands General term for a broad, elevated region with a nearly level surface of considerable
extent.
H-25 Reprinted from USGS Open-File Report 93-292
-------
terrace gravel Gravel-sized material that caps ridges and terraces, left behind by a stream as it
cuts down to a lower level.
terrain A tract or region of the Earth's surface considered as a physical feature or an ecological
environment
till Unsorted generally unconsolidated and unbedded rock and mineral material deposited directly
adjacent to and underneath a glacier, without reworking by meltwater. Size of grains vanes greatly
from clay to boulders.
uraniferous Containing uranium, usually more than 2 ppm.
vendor data Used in this report to refer to indoor radon data collected and measured by
commercial vendors of radon measurement devices and/or services.
volcanic Pertaining to the activities, structures, and extrusive rock types of a volcano.
water table The surface forming the boundary between the zone of saturation and the zone of
aeration; the top surface of a body of unconfined groundwater in rock or soil.
weathering The destructive process by which earth and rock materials, on exposure to
atmospheric elements, are changed in color, texture, composition, firmness, or form with little or
no transport of the material.
H-26 Reprinted from USGS Open-Ftfe 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, IL 60604-3507
(312) 886-6175
EPA Region 6 (6T-AS)
1445 Ross Avenue
Dallas, TX 75202-2733
(214) 655-7224
EPA Region 7
726 Minnesota Avenue
Kansas City, KS 66101
(913) 551-7604
EPA Region 8
(8HWM-RP)
999 18th Street
One Denver Place, Suite 1300
Denver, CO 80202-2413
(303) 293-1713
EPA Region 9 (A-3)
75 Hawthorne Street
San Francisco, CA 94105
(415) 744-1048
EPA Region 10
1200 Sixth Avenue
Seattle, WA 98101
(202) 442-7660
Alabama 4
Alaska 10
Arizona 9
Arkansas 6
California 9
Colorado 8
Connecticut 1
Delaware 3
District of Columbia 3
Florida 4
Georgia 4
Hawaii .9
Idaho 10
Illinois 5
Indiana 5
Iowa 7
Kansas t 7
Kentucky 4
Louisiana 6
Maine 1
Maryland.... 3
Massachusetts 1
Michigan 5
Minnesota 5*
Mississippi 4
Missouri 7
Montana 8
Nebraska 7
Nevada 9
New Hampshire 1
New Jersey... 2
New Mexico 6
New York 2
North Carolina 4
North Dakota 8
Ohio 5
Oklahoma 6
Oregon 10
Pennsylvania 3
Rhode Island 1
South Carolina .4
South Dakota 8
Tennessee 4
Texas 6
Utah 8
Vermont 1
Virginia 3
Washington 10
West Virginia 3
Wisconsin 5
Wyoming .....8
11-27 Reprinted from USGS Open-File Report 93-292
-------
STATE RADON CONTACTS
May, 1993
Alabama James McNees
Division of Radiation Control
Alabama Department of Public Health
State Office Building
Montgomery, AL 36130
(205)242-5315
1-800-582-1866 in state
Ajaslsa 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
LeeGershner
Division of Radiation Control
Department of Health
4815 Markham Street, Slot 30
Little Rock, AR 72205-3867
(501) 661-2301
California J. David Quinton
Department of Health Services
714 P Street, Room 600
Sacramento, CA 94234-7320
(916) 324-2208
1-800-745-7236 in state
Colorado Linda Martin
Department of Health
4210 East llth Avenue
Denver, CO 80220
(303) 692-3057
1-800-846-3986 in state
Connecticut Alan J. Siniscalchi
Radon Program
Connecticut Department of Health
Services
150 Washington Street
Hartford, CT 06106-4474
(203) 566-3122
Delaware MaraiG. Rejai
Office of Radiation Control
Division of Public Health
P.O. Box 637
Dover, DE 19903
(302) 736-3028
1-800-554-4636 In State
District
of Columbia
Robert Davis
DC Department of Consumer and
Regulatory Affairs
614 H Street NW
Room 1014
Washington, DC 20001
(202) 727-71068
N. Michael Gilley
Office of Radiation Control
Department of Health and
Rehabilitative Services
1317 Winewood Boulevard
Tallahassee, FL 32399-0700
(904)488-1525
1-800-543-8279 in state
Georgia Richard Schreiber
Georgia Department of Human
Resources
878 Peachtree St., Room 100
Atlanta, GA 30309
(404) 894-6644
1-800-745-0037 in state
Hawaii Russell Takata
Environmental Health Services
Division
591 Ala Moana Boulevard
Honolulu, ffl 96813-2498
(808) 586-4700
n-28 Reprinted from USGS Open-File Report 93-292
-------
Idaho
Illinois
Indiana
Iowa
Kansas
Kentucky
PatMcGavam
Office of Environmental Health
450 West State Street
Boise, ID 83720
(208) 334-6584
1-800-445-8647 in state
Richard Allen
Illinois Department of Nuclear Safety
1301 Outer Park Drive
Springfield, IL 62704
(217) 524-5614
1-800-325-1245 in state
Lorand Magyar
Radiological Health Section
Indiana State Department of Health
1330 West Michigan Street
P.O. Box 1964
Indianapolis, IN 46206
(317)633-8563
1-800-272-9723 In State
Donald A. Hater
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) 296rl561
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 BobStilwell
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 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
Montana Adrian C. Howe
Occupational Health Bureau
Montana Department of Health and
Environmental Sciences
Cogswell Building A113
Helena, MT 59620
(406)444-3671
Nebraska Joseph Milone
Division of Radiological Health
Nebraska Department of Health
301 Centennial Mall, South
P.O. Box 95007
Lincoln, NE 68509
(402)471-2168
1-800-334-9491 In State
Nevada Stan Marshall
Department of Human Resources
505 East King Street
Room 203
Carson City, NV 89710
(702) 687-5394
ffew. Hampshire David Chase
Bureau of Radiological Health
Division of Public Health Services
Health and Welfare Building
Six Hazen Drive
Concord, NH 03301
(603)271-4674
1-800-852-3345 x4674
New Jersey Tonalee Carlson Key
Division of Environmental Quality
Department of Environmental
Protection
CN415
Trenton, NJ 08625-0145
(609) 987-6369
1-800-648-0394 in state
New Mexico William M. Floyd
Radiation Licensing and Registration
Section
New Mexico Environmental
Improvement Division
1190 St. Francis Drive
Santa Fe,NM 87503
(505) 827-4300
New York William J. Condon
Bureau of Environmental Radiation
Protection
New York State Health Department
Two University Place
Albany, NY 12202
(518)458-6495
1-800-458-1158 in state
North Carolina Dr. Felix Fong
Radiation Protection Division
Department of Environmental Health
and Natural Resources
701 Barbour Drive
Raleigh, NC 27603-2008
(919) 57 W141
. 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
Oregon
Pennsylvania
Puerto Rico
Rhode Island
South Carolina
Gene Smith
Radiation Protection Division
Oklahoma State Department of
Health
P.O. Box 53551
Oklahoma City, OK 73152
(405)271-5221
George Toombs
Department of Human Resources
Health Division
1400 SW 5th Avenue
Portland, OR 97201
(503) 731-4014
Michael Pyles
Pennsylvania Department of
Environmental Resources
Bureau of Radiation Protection
P.O. Box 2063
Harrisburg, PA 17120
(717) 783-3594
1-800-23-RADON In State
David Saldana
Radiological Health Division
G.P.O. Call Box 70184
Rio Piedras, Puerto Rico 00936
(809)767-3563
Edmund Arcand
Division of Occupational Health and
Radiation
Department of Health
205 Cannon Building
Davis Street
Providence, RI02908
(401) 277-2438
Bureau of Radiological Health
Department of Health and
Environmental Control
2600 Bull Street
Columbia, SC 29201
(803)734^631
1-800-768-0362
South Dakota Mike Pochop
Division of Environment Regulation
Department of Water and Natural
Resources
Joe Foss Building, Room 217
523 E. Capitol
Pierre, SD 57501-3181
(605) 773-3351
Tennessee Susie Shimek
Division of Air Pollution Control
Bureau of the Environment
Department of Environment and
Conservation
Customs House, 701 Broadway
Nashville, TN 37219-5403
(615) 532-0733
1-800-232-1139 in state
Texas Gary Smith
Bureau of Radiation Control
Texas Department of Health
1100 West 49th Street -
Austin, TX 78756-3189
(512) 834-6688
Utah John Hultquist
Bureau of Radiation Control
Utah State Department of Health
288 North, 1460 West
P.O. Box 16690
Salt Lake City, UT 84116-0690
(801) 53&4250
Vermont Paul Clemens
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
n-3i
Reprinted from USGS Open-File Report 93-292
-------
Virginia Shelly Ottenbrite
Bureau of Radiological Health
Department of Health
109 Governor Street
Richmond, VA 23^ 19
(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)753^518
1-800-323-9727 In State
West Virginia BeattieL.DeBprd
Industrial Hygiene Division
West Virginia Department of Health
151 llth Avenue
South Charleston, WV 25303
(304)558-3526
1-800-922-1255 In State
Wisconsin Conrad Weiffenbach
Radiation Protection Section
Division of Health
Department of Health and Social
Services
P.O. Box 309
Madison, WI53701-0309
(608)267-4796
1-800-798-9050 in state
Wyoming Janet Hough
Wyoming Department of Health and
Social Services
Hathway Building, 4th Floor
Cheyenne, WY 82002-0710
(307) 777-6015
1-800-458-5847 in state
11-32 Reprinted from USGS Open-File Report 93-292
-------
STATE GEOLOGICAL SURVEYS
May, 1993
Alabama Ernest A. Manclni
Geological Survey of Alabama
P.O. Box 0
420 Hackberry Lane
Tuscaloosa, AL 35486-9780
(205)349-2852
Alaska Thomas E. Smith
Alaska Division of Geological &
Geophysical Surveys
794 University Ave., Suite 200
Fairbanks, AK 99709-3645
(907)479-7147
Arizona Larry D. Fellows
Arizona Geological Survey
845 North Park Ave., Suite 100
Tucson, AZ 85719
(602) 882-4795
Arkansas Norman F. Williams
Arkansas Geological Commission
Vardelle Parham Geology Center
3815 West Roosevelt Rd.
Little Rock, AR 72204
(501) 324-9165
California James F. Davis
California Division of Mines &
Geology
801 K Street, MS 12-30
Sacramento, CA 95814-3531
(916)445-1923
Colorado Pat Rogers (Acting)
Colorado Geological Survey
1313 Sherman St., Rm 715
Denver, CO 80203
(303)866-2611
Connecticut Richard C. Hyde
Connecticut Geological & Natural
History Survey
165 Capitol Ave., Rm. 553
Hartford, CT 06106
(203)566-3540
Delaware Robert R. Jordan
Delaware Geological Survey
University of Delaware
101 Penny Hall
Newark, DE19716-7501
(302) 831-2833
Florida Walter Schmidt
Florida Geological S Tvey
903 W. Tennessee St.
Tallahassee, FL 32304-7700
(904)488-4191
William H. McLemore
Georgia Geologic Survey
Rm. 400
19 Martin Luther King Jr. Dr. SW
Atlanta, GA 30334
(404) 656-3214
Hawaii Manabu Tagomori
Dept. of Land and Natural Resources
Division of Water & Land Mgt
P.O. Box 373
Honolulu, ffl 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, JL 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
H-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
Mains 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)496-4180
Nebraska Perry B. Wigley
Nebraska Conservation & Survey
Division
113 Nebraska Hall
University of Nebraska
Lincoln, ME 68588-0517
.(402)472-2410
Nevada Jonathan G. Price
Nevada Bureau of Mines & Geology
Stop 178
University of Nevada-Reno
Reno, NV 89557-0088
(702) 784-6691
New Hampshire Eugene L.Boudette
Dept. of Environmental Services
117 James Hall
University of New Hampshire
Durham, NH 03824-3589
(603) 862-3160
New Jersey Haig F. Kasabach
New Jersey Geological Survey
P.O. Box 427
Trenton, NJ 08625
(609)292-1185
New Mexico Charles E. Chapin
New Mexico Bureau of Mines &
Mineral Resources
Campus Station
Socorro.NM 87801
(505) 835-5420
New York Robert H. Fakundiny
New York State Geological Survey
3136 Cultural Education Center
Empire State Plaza
Albany, NY 12230
(518)474-5816
11-34 Reprinted from USGS Open-File Report 93-292
-------
North Carolina Charles H. Gardner
North Carolina Geological Survey
P.O. Box 27687
Raleigh, NC 27611-7687
(919) 733-3833
North Dakota John P. Bluemle
North Dakota Geological Survey
600 East Blvd.
Bismarck, ND 58505-0840
(701) 224-4109
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 ME Oregon St. #28
Portland, OR 97232-2162
(503)73M600
Pennsylvania Donald M. Hoskins '
Dept. of Environmental Resources
Bureau of Topographic & Geologic
Survey
P.O. Box 2357
Harrisburg, PA 17105-2357
(717) 787-2169
Puerto Rico Ramon M. Alonso
Puerto Rico Geological Survey
Division '
Box 5887
Puerta de Tierra Station
San Juan, P.R. 00906
(809) 722-2526
Rhode Island J. Allan Cain
Department of Geology
University of Rhode Island
315 Green Hall
Kingston, RI02881
(401) 792-2265
South Carolina Alan-Jon W. Zupan (Acting)
South Carolina Geological Survey
5 Geology Road
Columbia, SC 29210-9998
(803) 737-9440
South Dakota C.M. Christensen (Acting)
South Dakota Geological Survey
Science Center
University of South Dakota
Vermillion, SD 57069-2390
(605)677-5227
Tennessee Edward T.Luther
Tennessee Division of Geology
13th Floor, L & C Tower
401 Church Street
Nashville, TN 37243-0445
(615) 532-1500
Texas William L. Fisher
Texas Bureau of Economic Geology
University of Texas
University Station, Box X
Austin, TX 78713-7508
(512)471-7721
Utah M. Lee Allison
Utah Geological & Mineral Survey
2363 S. Foothill Dr.
Salt Lake City, UT 84109-1491
(801)467-7970
Vermont Diane L. Conrad
Vermont Division of Geology and
Mineral Resources
103 South Main St.
Waterbury,VT 05671
(802)244-5164
Virginia Stanley S. Johnson
Virginia Division of Mineral
Resources
P.O. Box 3667
Charlottesville, VA 22903
(804)293-5121
Washington Raymond Lasmanis
Washington Division of Geology &
Earth Resources
Department of Natural Resources
P.O. Box 47007
Olympia, Washington 98504-7007
(206) 902-1450
11-35 Reprinted from USGS Open-File Report 93-292
-------
West Virginia Larry D. Woodfoifc
West Virginia Geological and
Economic Survey
Mont Chateau Research Center
P.O. Box 879
Morgantown.WV 26507-0879
(304)594-2331
Wisconsin James Robertson
Wisconsin Geological & Natural
History Survey
3817 Mineral Point Road
Madison, WI 53705-5100
(608)263-7384
Wyoming Gary B. Glass
Geological Survey of Wyoming
University of Wyoming
Box 3008, University Station
Laramie,WY 82071-3008
(307) 766-2286
11-36 Reprinted from USGS Open-File Report 93-292
-------
EPA REGION 5 GEOLOGIC RADON POTENTIAL SUMMARY
by
R, Randall Schumann, Douglass E. Owen, and Sandra L. Szarzi
U.S. Geological Survey
EPA Region 5 comprises the states of Illinois, Indiana, Michigan, Minnesota, Ohio, and
Wisconsin. For each state, geologic radon potential areas were delineated and ranked on the
basis of geologic, soil, housing construction, and other factors. Areas in which the average
screening indoor radon level of all homes within the area is estimated to be greater than 4 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 chapter. More detailed information on the geology
and radon potential of each state in Region 5 is given in the individual state chapters. The
individual chapters describing the geology and radon potential of the six states in EPA Region 5,
though much more detailed than this summary, still are generalized assessments and there is no '
substitute for having a home tested. Radon levels, both high and low, can be quite localized, and
within any radon potential area homes with indoor radon levels both above and below the
predicted average will likely be found.
Radon potential in EPA Region 5 is controlled by three primary factors. Bedrock
geology provides the source material for the overlying glacial deposits, and in areas with no
glacial cover, directly provides the parent material for the soils. Glacial geology (fig. 1) is an
important factor because glaciers redistributed the bedrock and glacially-derived soils have
different soil characteristics from soils developed on bedrock. Climate, particularly precipitation
and temperature, in concert with the soil's parent material, controls soil moisture, the extent of
soU development and weathering, and the types of weathering products that form in the soils.
The following is a brief, generalized discussion of the bedrock and glacial geology of EPA
Region 5 as they pertain to indoor radon. More detailed discussions may be found in the
individual state geologic radon potential chapters.
Western and southern Minnesota are underlain by deposits of the Des Moines and Red
River glacial lobes. Des Moines lobe tills are silty clays and clays derived from Upper
Cretaceous sandstones and shales, which have relatively high concentrations of uranium and high
radon emanating power. Deposits of the Red River lobe are similar to those of the Des Moines
lobe, but also contain silt and clay deposits of glacial Lake Agassiz, a large glacial lake that
occupied the Red River Valley along the Minnesota-North Dakota border. The Upper
Cretaceous Pierre Shale provides good radon source material because, as a whole, it contains
higher-than-average amounts of uranium (average crustal abundance of uranium is about 2.5
parts per million). Glacial deposits of the Red River and Des Moines lobes generate high
(> 4 pCi/L) average indoor radon concentrations (fig. 2) and have high geologic radon potential
(fig. 3). Northern Wisconsin, the western part of the Upper Peninsula of Michigan, and part of
northern Minnesota are underlain by glacial deposits of the Lake Superior lobe. Parts of northern
Minnesota are also underlain by deposits of the Rainy and Wadena lobes (fig. 1). The
underlying source rocks for these tills are Precambrian volcanic rocks, metasedimentary and
metavolcanic rocks, and granitic plutonic rocks of the Canadian Shield. The volcanic,
metasedimentary, and metavolcanic rocks have relatively low uranium contents, and the granitic
rocks have variable, mostly moderate to high, uranium contents. The sandy tills derived from the
HI-1 Reprinted from USGS Open-File Report 93-292-E
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volcanic, metasedimentary, and metavolcanic rocks have relatively high permeability, but
because of their lower uranium content of and lower emanating power, they have mostly
moderate to locally high radon potential (fig. 3). Sandy, granite-rich tills in northern Minnesota
generally have high radon potential. Granites and granite gneisses, black slates and graphitic
schists, and iron-formation are associated with anomalous uranium concentrations and locally
high radon in northern Wisconsin and adjacent northwestern Michigan. In central Wisconsin,
uraniferous granites of the Middle Proterozoic Wolf River and Wausau plutons are exposed at
the surface or covered by a thin layer of glacial deposits and cause some of the highest indoor
radon concentrations in the State. An area in southwestern Wisconsin and adjacent smaller parts
of Minnesota, Iowa, and Illinois, is called the "Driftiess Area" (fig. 1). It is not covered by
glacial deposits but parts of the area were likely overrun by glaciers at least once. The Driftiess
Area is underlain by Cambrian and Ordovician limestone, dolomite, and sandstone with
moderate to high radon potential.
Glacial deposits in southern Wisconsin, northern and central Illinois, and western Indiana
are primarily from the Green Bay and Lake Michigan lobes. The Green Bay and Lake Michigan
lobes advanced from their source in the Hudson Bay region of Canada and moved southward,
terminating in Illinois and Iowa. These tills range from sandy to clayey and are derived
primarily from shales, sandstones, and carbonate rocks of southern Wisconsin, the western
Michigan Basin, and the northern Illinois Basin. A small part of eastern Illinois and much of
western Indiana are covered by deposits of the Huron-Erie lobe, and west-central Illinois is
covered by glacial deposits of pre-Wisconsinan, mostly Illinoian, age. The Huron-Erie lobe
entered Illinois from the east and moved westward and southwestward into the State. Huron-Erie
lobe and pre-Wisconsinan glacial deposits are derived from Paleozoic shale, sandstone, siltstone,
carbonate rocks, and coal of the Illinois Basin, and they are commonly calcareous due to the
addition of limestones and dolomites of northern Indiana and Ohio and southern Ontario. In
contrast, Lake Michigan lobe deposits contain significant amounts of dark gray to black
Devonian and Mississippian shales of the Michigan Basin, accounting for the high clay content
of Lake Michigan lobe tills. Unglaciated southernmost Illinois is part of the Mississippi
Embayment of the Coastal Plain and has low geologic radon potential.
Wisconsin-age glacial deposits in Indiana were deposited by three main glacial lobes—
the Lake Michigan lobe, which advanced southward as far as central Indiana; the Huron-Erie
lobe; and the Saginaw sublobe of the Huron lobe (labeled Huron lobe on fig. 1), which advanced
from the northeast across northern Ohio and southern Michigan, respectively. Michigan lobe
deposits are clayey near Lake Michigan, sandy and gravelly in an outwash and morainal area in
northwestern Indiana, and clayey to loamy in west-central Indiana. Saginaw sublobe deposits are
loamy and calcareous and are derived primarily from carbonate rocks and shale. The Huron-Erie
lobe advanced from the northeast and covered much of northern and central Indiana at its
maximum extent Eastern Indiana and western Ohio are underlain by tills of the Huron-Erie lobe
that are derived in part from black shales of the Devonian Ohio Shale and Devonian-
Mississippian New Albany Shale, but also include Paleozoic limestone, dolomite, sandstone,
siltstone, and gray shale. Black shales and carbonates underlie and provide source material for
glacial deposits in a roughly north-south pattern through central Ohio, including the Columbus
area, and extend south of the glacial limit, where the black shales form a prominant arcuate
pattern in northern Kentucky that curves northward into southern Indiana and underlies glacial
deposits in east-central Indiana. The overall radon potential of this area is high. Eastern Ohio is
underlain by Devonian to Permian shales and limestones with moderate to high radon potential.
m-5 Reprinted from USGS Open-File Report 93-292-E
-------
The Michigan Basin covers all of the Southern Peninsula and the eastern half of the
Northern Peninsula of Michigan, as well as parts of eastern Wisconsin and northeastern Illinois,
northern Indiana, and northwestern Ohio. Glacial deposits include silty and clayey tills of the
Lake Michigan, Huron, and Huron-Erie lobes (fig. 1). Huron lobe tills are sandy to gravelly and
calcareous, containing pebbles and cobbles of limestone, dolomite, and some sandstone and
shale, with boulders of igneous and metamorphic rocks and quartzite. Tills of the Huron-Erie
and Lake Michigan lobes are derived from similar source rocks but are more silty and clayey in
texture. Source rocks for these tills are sandstones, gray shales, and carbonate rocks of the
Michigan Basin, which are generally poor radon sources. In the Southern Peninsula, the
Devonian Bell, Antrim, and Ellsworth Shales, and Mississippian Sunbury Shale locally-contain
organic-rich black shale layers with higher-than-average amounts of uranium, except for the
Antrim Shale, which is organic rich throughout. These shales underlie and constitute source rock
for glacial deposits in the northern, southeastern, and southwestern parts of the Southern
Peninsula, and are locally exposed at the surface in the northern part of the Southern Peninsula.
Because of generally moist soils, soils developed on tills derived from black shales in Michigan
generate moderate to locally high radon, with higher values more common in the southern part of
the State (fig. 2).
Glaciated areas present special problems for radon-potential assessment because bedrock
material in the central United States was commonly transported hundreds of km from its source.
Glaciers are quite effective in redistributing uranium-rich rocks; for example, in Ohio, uranium-
bearing black shales have been disseminated over much of western Ohio and eastern Indiana,
now covering a much larger area than their original outcrop pattern, and display a prominent
radiornetric high. The physical, chemical, and drainage characteristics of soils formed from
glacial deposits vary according to source bedrock type and the glacial features on which they are
formed. For example, soils formed from ground moraine deposits tend to be more poorly
drained and contain more fine-grained material than soils formed on kames, moraines, or eskers,
which are generally coarser and well-drained. In general, soils developed from coarser-grained
tills are poorly structured, poorly sorted, and poorly developed, but are generally more highly
permeable than the bedrock from which they are derived.
Clayey tills, such as those underlying parts of western and southern Minnesota, have
relatively high emanation coefficients and usually have low to moderate permeability, depending
on the degree to which the clays are mixed with coarser sediments. Tills consisting of mostly
coarse material tend to emanate less radon because larger grains have lower surface area-to-
volume ratios, but because these soils have generally high permeabilities, radon transport
distances are generally longer. Structures built in these materials are thus able to draw soil air
from a larger source volume, so moderately to highly elevated indoor radon concentrations may
be achieved from comparatively lower-radioactivity soils. In till soils with extremely high
permeability, atmospheric dilution may become significant, and if the soils have low to moderate
radium contents, elevated indoor radon levels would be less likely to occur. Soil moisture has a
significant effect on radon generation and transport and high levels of soil moisture generally
lower the radon potential of an area. The main effect of soil moisture is its tendency to occlude
soil pores and thus inhibit soil-gas transport. Soils in wetter climates from northern Minnesota to
northern Michigan generally have lower radon potential than soils derived from similar tills in
the southern parts of those states or in Indiana and Illinois, in part because of higher soil moisture
conditions to the north.
ni-6 Reprinted from USGS Open-File Report 93-292-E
-------
PRELIMINARY GEOLOGIC RADON POTENTIAL ASSESSMENT OF ILLINOIS
by
R. Randall Schvunann
U.S. Geological Survey
INTRODUCTION
Many of the rocks and soils in Illinois have the potential to generate levels of indoor radon
exceeding the U.S. Environmental Protection Agency's guideline of 4 pCi/L. In a survey of 1450
homes conducted during the winter of 1990-91 by the Illinois Department of Nulcear Safety
(IDNS) and the EPA, 22 percent of the homes had screening indoor radon levels exceeding this
value. Only one percent of the homes tested had screening indoor radon levels exceeding
20 pCi/L. Similar results were reported from statewide survey of indoor radon levels in 4140
homes conducted by the IDNS. Thirty-two percent of the homes tested in the IDNS study had
indoor radon levels exceeding 4 pCi/L, and about one percent of the homes had radon levels
exceeding 20 pCi/L. While no level of radon can be considered absolutely safe, the Illinois
Department of Nulcear Safety predicts, based on these surveys, that there are very few homes in
Illinois (less than one percent) in which radon could be considered a severe problem (i.e.,
exceeding 20 pCi/L).
This is a generalized assessment of geologic radon potential of rocks, soils, and surficial
deposits of Illinois. 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 (Illinois Department of Nulcear Safety) or EPA regional
office. More detailed information on state or local geology may be obtained from the State
geological survey. Addresses and phone numbers for these agencies are listed in chapter 1 of this
booklet.
PHYSIOGRAPHIC AND GEOGRAPHIC SETTING
Illinois1 landscape stretches from the Great Lakes to the Coastal Plain. The State contains
part of four major physiographic provinces—the Central Lowland, Interior Low Plateaus, Ozark
Plateaus, and the Coastal Plain—with a number of subdivisions (fig. 1). More than three-quarters
of Illinois is in the Till Plains section of the Central Lowlands Province. The Till Plains section is
subdivided into seven physiographic areas in Illinois (fig. 1). The Rock River Hill Country,
Galesburg Plain, Springfield Plain, and Mt. Vernon Hill Country are covered by Pre-Wisconsinan
glacial deposits, but their topography is defined more by the topography of the pre-glacial surface
than by glacial features which only locally form prominent features in these areas (Willman and
others, 1975). The Green River Lowland and Kankakee Plain are lowlands that are partially
covered by sand dunes. The Bloomington Ridged Plain occupies much of northeastern Illinois and
displays marked glacial topography including morainal ridges, drift plains, and outwash plains.
The Wheaton Morainal Country, with topography similar to that of the Bloomington Ridged Plain,
IV-1 Reprinted from USGS Open-File Report 93-292-E
-------
/TILL PLAINS SECTION *
GREAT LAKE
[SECTION
j 5 Hill Country
I i I
fr]'-.'I Ozork Plateaus Province
{%%j Interior Low Plateaus Province
| | Central Lowland Province
BS889 Coastal Plain Province
Figure 1. Physiographic regions of Illinois (modified from Willman and others, 1975).
-------
and the Chicago Lake Plain, which was covered by glacial Lake Chicago, belong to the Great Lake
Section of the Central Lowland Province. The presumably unglaciated and deeply dissected
Wisconsin Driftless Section and a small part of the Dissected Till Plains Section, both in
northwestern Illinois, also belong to the Central Lowland Province (Willman and others, 1975).
The Lincoln Hills and Salem Plateau Sections, small parts of subdivisions of the Ozark
Plateaus Province, extend into Illinois along the Mississippi River (fig. 1). The Lincoln Hills
contains dissected flat-lying rocks, whereas the strata in the Salem Plateau Section are mildly
folded and faulted (Willman and others, 1975). The Shawnee Hills Section of the Interior Low
Plateaus Province is an unglaciated area containing hills of relatively high relief. The southern tip
of Illinois is an area of low, rounded hills which is part of the Coastal Plain Province (fig. 1).
Illinois is divided into 102 counties (fig. 2). Most of the State's population is clustered
around urban centers, with the counties in the Chicago area having the highest populations. The
southern and western parts of Illinois are largely rural and have lower county populations (fig. 3).
GEOLOGY
The discussion of geology is divided into three sections: bedrock geology, glacial geology,
and a discussion of uranium in rocks and soils. "Bedrock" refers to pre-glacial rock units, which
are covered by glacial deposits in most parts of the State. A bedrock geologic map (fig. 4) shows
rock units that underlie glacial deposits or are exposed at the surface in some areas. The glacial
deposits are composed of material derived from underlying bedrock and from rock units to the
north and northeast. The discussion of bedrock geology is summarized from Willman and others
(1975). The section on glacial geology is summarized from Willman and Frye (1970), Frye and
others (1965), and Richmond and Fullerton (1983,1991). For more detailed discussions and
maps of the geology, the reader is encouraged to consult these and other reports (see the reference
list at the end of this chapter for additional suggested references).
Bedrock geology: The bedrock geologic setting of Illinois is dominated by the Illinois
Basin, a structural and sedimentary basin occupying most of the State. It is bounded on the north
by the Kankakee and Wisconsin arches which extend into northern Illinois; on the west by the
Mississippi River Arch in Iowa and Missouri; and on the southwest by the Ozark Uplift in
Missouri. The Illinois Basin extends into Indiana to the east and into Kentucky and Tennessee to
the southeast With the exception of Pliocene continental sedimentary rocks, all of the pre-glacial
bedrock underlying Illinois consists of marine or marginal-marine sedimentary rocks, including
limestone, dolomite, sandstone, siltstone, shale, and coal (fig. 4). Most of the rocks are from
Cambrian through Pennsylvanian in age. Cretaceous and Tertiary rocks are exposed in a relatively
small area in southern Illinois; a small subcrop of Cretaceous rocks underlies glacial drift in
western Illinois (fig. 4).
Glacial geology: Glaciers advanced into Illinois from three directions during the
Pleistocene Epoch. The earliest glaciers (Pre-Illinoian, formerly called Nebraskan and Kansan)
advanced from the northwest into western Illinois, and from the north into eastern Illinois. Pre-
niinoian glacial deposits are exposed in Illinois only in a small area in the western part of the State
(fig. 5), but they underlie younger deposits throughout much of southern Illinois. Later glaciers
(Dlinoian and Wisconsinan) advanced from the north and northeast. The Green Bay and Lake
Michigan lobes advanced from their source in the Hudson Bay region and moved southward into
Illinois. The Erie Lobe (and possibly the Saginaw Lobe) advanced from the Labradorean center,
entering Illinois from the northeast (Willman and Frye, 1970). About two-thirds of Illinois is
IV-3 Reprinted from USGS Open-File Report 93-292-E
-------
Figure 2. Illinois counties.
-------
POPULATION (1990)
C3 0 to 25000
Q 25001 to 50000
£3 50001 to 100000
H 100001 to 500000
• 500001 to 5105067
Figure 3. Population of counties in Illinois (1990 U.S. Census data).
-------
Pleistocene and
Pliocene not shown
TERTIARY
CRETACEOUS
PENNSYLVANIAN
Bond and Malloon Formations
Includes narrow belts of
older formations along
LoSalle Anticline
PENNSYLVANIAN
Carbondale and Modesto Formations
PENNSYLVANIAN
Caseyville, Abbott, and Spoon
Formations
MISSISSIPPIAN
Includes Devonian in
Hardin County
DEVONIAN
Includes Silurian in Douglas,
Champaign, and western
Rock Island Counties
SILURIAN
Includes Ordovician and Devonian in Calhoun
Greenland Jersey Counties
ORDOVICIAN
CAMBRIAN
Des Plaines Complex - Ordovician to Pennsylvanian
Fault
Figure 4. Generalized bedrock geologic map of Illinois (modified from Willman and others, 1975).
-------
GENERALIZED STRATIGRAPHIC CHART FOR ILLINOIS
EUA.
EKATHEM
CENOZOIC
MESOZOIC
PALEOZOIC
PtECAMIUAN
PHIOD.
SYSTEM
OUATE*NA*Y
TEHTIAIY
CRETACEOUS
PENNSYWANIAN
MISSISSIPPI
DEVONIAN
SIUIUAN
OCDOVIC1AN
CAMSHIAN
, KOCH.
SEKIES
PLEISTOCENE
PUOCENE
EOCENE
PAIEOCENE
CUIFUN
VMGIUAN
MISSOUUAN
OESMOINESIAN
ATOKAN
MOMOWAN
CHCSTERIAN
VAIMETEtAN
KINDEJWXXIAN
UPfK
MIODIE
lOWEt
CAYUCAN
NIACARAN
AlEXANDIIAN
CINONNATIAN
CHAM PLUN IAN
CANADIAN
OtOIXAN
ditolN AND CHAIACTEt
Conrmentol^glecial, river and
stream, wind. lakt. swamp,
end collwvial dcpaiiti and
sals
Continental — river depoiiri,
••airly gravel, some sand
Dertolc — motriy land, some
silt
Marine — Mostly day, tome
sand
DettoiC' and neorshore marine
— sand, some sin end day,
locally lignWc
Major unconformifr _^^-^^__
Marine, deltoic, continental^ '
cvdke! deposits, manly shak.
sandstone, and siflstont with
some Bmestone. coal, day,
btacit sheety shale; sandstone
dominant in lower part, shale
above; coal moit prominent
in middle pert, limestone in
•pperpart
Marine, dekoic — cyclical de-
posits ef Kmeitone, sand-
stone, shale
Marine, deltaic — limestone.
sinstone, shote, chert, sand-
stone
Marine — shale, limestone, silt-
stone
Marine— shale, limestone
Marine — larger/ Smestone,
seme shale
Marine — cherty limestone.
chert
Marine — shale, sibftone. lime-
stone
Marine — dolemite. limestone.
shale, local reefs
Marine — dolomite, limestone,
shale
Marine — shale. Hmestene, sill-
stone, dolomite
Marine — limestone, dolomite,
sandstone .
Marine — dolomite, sandstone
Marine — sandstone, dolomite,
shale
Intrusive igneous recks— metHy
granite
GREATEST
THICKNESS
(ftl1
400
50
300
150
500
3000
1400
2000
150
300
450
1300
100
WOO
150
300
MOO
1000
4000
AGE
{millions
e« years?
IS
7
«4-«5
I3e
315
345
305
430-440
500
(525'
I (tM4] •»*, •*•.
(MM ckM h- VM Eyttec* [IfTJIJ
Figure 4 (continued) (modified from Willman and others, 1975).
-------
PRE-ILLINOIAN
Till plain
HOLOCENE AND WISCONSINAN
v -
'
Alluvium, sand dunes,
and grovel terraces
WISCONSINAN
Lake deposits
Moraine
Front of morainic system
I, : I Groundmoraine
Till plain
1LLINOIAN
Moraine and ridged drift
Groundmoraine
Figure 5. Glacial map of Illinois (modified from Willman and Frye, 1970).
-------
covered by Ulinoian-age deposits, about one-third of the State (the northeastern part) is covered by
Wisconsinan deposits, and small areas in the northwestern corner, along the western edge, and the
southern tip of Illinois are unglaciated (fig.^). Glacierf from all four northern and northeastern
lobes probably advanced into the State during Dlinoian time, and the Llinoian deposits are not
specifically differentiated by source lobe. During the Wisconsinan Stage, the Lake Michigan and
Erie lobes re-entered northeastern Illinois (fig. 6). Glaciers made at least three separate advances
into Illinois during Dlinoian time and three advances during Wisconsinan time (Willman and Frye,
1970). During Late Wisconsinan time, many lakes were formed in the low areas behind moraines
or behind dams of glacial ice. Areas now underlain by glacial lake deposits are shown in figure 7.
Lakes Watseka, Wauponsee, Pontiac, and Ottowa (fig. 7) resulted from the Kankakee Flood and
their deposits range in texture from silt to boulders. Most of the lakes in southern Illinois are
slackwater lakes that left mainly silt deposits derived from windblown silt (loess) and glacial
outwash. Lake Chicago (fig. 7) was the glacial predecessor of modern Lake Michigan. Lake
Chicago deposits underlie most of the Chicago metropolitan area and consist primarily of silt and
clay.
The major bedrock units of Illinois that contributed material to glacial deposits in the State
include: (1) Silurian dolomite in the northeast and in a small part of the glaciated area in the
northwest; (2) Ordovician dolomite in the north-central part of the State; (3) Ordovician shale
(northern Illinois); (4) Mississippian limestones with minor amounts of shale and sandstone in
western Illinois; (5) Pennsylvanian rocks throughout the central and southern part of the State,
which consist of shale (50 percent), sandstone and siltstone (40 percent), limestone, coal, and
other minor constituents (10 percent) (Willman and Frye, 1970). Precambrian igneous and
metamorphic rocks from the Canadian Shield in Canada and the Lake Superior region also
constitute a significant part of most tills in the State. Major additions to Erie Lobe deposits came
from Ordovician, Silurian, and Devonian limestones of northern Indiana and Ohio and southern
Ontario, making Erie Lobe deposits more calcareous (calcium carbonate-rich) than Lake Michigan
Lobe deposits. Pre-Illinoian glacial deposits from northwestern sources are also notably
calcareous. In contrast, Lake Michigan lobe deposits contain significant amounts of dark gray to
black Devonian and Mississippian shales of the Michigan Basin, accounting for the high illite (non-
expanding clay) content of Lake Michigan Lobe tills. Smectite (swelling clay) in Cretaceous shales
is the dominant clay mineral in glacial deposits from northwestern sources (Willman and Frye,
1970).
Loess (windblown silt) was formed as rivers separated the various size fractions (gravel,
sand, silt, clay) from glacial drift, and the silt fraction was picked up and transported by wind.
Loess deposits from less than one to more than 30 meters thick cover most of Illinois, averaging
about 1.5 meters.thick over about 90 percent of the State (Willman and Frye, 1970).
Uranium geology: Because no comprehensive studies of uranium contents of glacial
deposits and loess in Illinois are known to exist, and because these deposits have underlying
bedrock as a major source component (in addition to material derived from the north and
northeast), a brief discussion of known concentrations of uranium in rocks and soils of Illinois is
presented here in order to provide clues to the sources of radon parent materials (uranium and(or)
radium) in surficial deposits. Many rocks throughout the State contain higher-than-average
amounts of uranium [average crustal abundance of uranium is approximately 2.5 parts per million
(ppm) (Carmichael, 1989)]. Gilkeson and others (1988) list the following typical uranium
concentrations for rocks in Illinois: shales, 5-31 ppm; lacustrine sediments of Lake Michigan, 2.3
ppm; limestones, 4.5 ppm; sandstones, 1.5 ppm.
IV-9 Reprinted from USGS Open-File Report 93-292-E
-------
Hgure 6. Late Wisconsinan glacial lobes and sublobes in Illinois (modified from Willman and
Frye, 1970).
-------
Figure 7. Glacial lake deposits in Illinois (modified from Willman and Frye, 1970).
-------
Black shales, which are fairly common in some parts of the bedrock succession of Illinois,
are well-known concentrators of uranium and are known causes of radon problems in a number of
areas in the United States. Ostrom and others (1955) collected and analyzed 175 samples of black
shales and gray shales from scattered exposures in streams, roadcuts, and open-pit mines in 44
counties covering the lower four-fifths of Illinois. Black shales of Pennsylvanian, Mississippian,
and Devonian-Mississippian age had uranium concentrations ranging from near zero to 170 ppm.
Uranium is concentrated with organic matter in the shale or in phosphate layers within the shales
(Ostrom and others, 1955). Ordovician gray shales contained between 10 and 20 ppm equivalent
uranium (Ostrom and others, 1955). Frost and others (1985) found 3-75 ppm uranium in 392
subsurface drillhole samples of the Devonian-Mississippian New Albany Shale Group in Illinois.
Many soils in Illinois contain sufficient uranium to generate indoor radon levels exceeding
4 pCi/L under the proper soil permeability and building construction/ventilation conditions. Out of
153 samples from surface horizons of upland soils across Illinois collected and analyzed by Jones
(1991), the average uranium concentration was 3.4 ppm,.with a range of 1.2 to 7.7 ppm. There
appeared to be no particular correlation of uranium content with soil order, moisture regime, or
degree of weathering (Jones, 1991).
SOILS
Major soil orders in Illinois are shown in figure 8. Mollisols are dark-colored soils formed
under grass. They contain a thick (> 25 cm), dark, organic-rich layer at the surface and calcium
carbonate (CaCOs) accumulations in the B horizon (Feherenbacher and others, 1984). Mollisols
are most extensive in northern and central Illinois (fig. 8). Alfisols in Illinois are generally light-
colored soils formed under forest vegetation. The surface layer may be light or dark in color, but it
has a low organic matter content Alfisols have a recognizable B horizon of clay accumulation.
Alfisols are most common in southern Illinois, although they are found in most areas of the State
(fig. 8). Entisols are generally light-colored, young soils formed mostly in recent alluvium. These
soils occur along streams in the southern and western parts of the State and in other very sandy
areas such as the dunefields in the northern and central parts of the State (fig. 8). Because they are
relatively young, these soils usually have not yet formed distinct horizons. Some of the Entisols in
central and northern Illinois and in the Wabash River valley are light-colored, sandy soils with
sufficient quantities of weatherable minerals to have formed recognizable horizons (Fehrenbacher
and others, 1984). Inceptisols, soils with weakly developed horizons, and Histosols, organic
soils (peats and mucks), also occur in Illinois but their areas are too small to be shown on figure 8.
A generalized soil permeability map of Illinois (fig. 9) was compiled from a soil survey
report containing maps of soil-units and information on soil characteristics, including permeability
(Fehrenbacher and others, 1984). The available data, which are shown in figure 9, are for
permeability of the soils to water. Permeability to air, which is more relevant to soil-gas radon
transport, generally follows that of water permeability except in soils with high soil moisture
contents, in which case the water in the soil pores restricts or prevents soil-gas movement. Most
of the soils in the southern part of Illinois and some of the soils derived from glacial lake deposits
in northeastern Illinois have low permeability. Soils with high permeability occur in the
northeastern and central parts of the State (fig. 9). About two-thirds of the soils in Illinois have
moderate permeability. More detailed information on permeability of shallow surficial soil and
rock units may be found in Keefer and Berg (1990), Berg and Kempton (1988), and Berg and
others (1984).
IV-12 Reprinted from USGS Open-File Report 93-292-E
-------
SOIL ORDER
| | Mollisols
Alfisols
Entisols
Figure 8. Major soil orders of Illinois (modified from Feherenbacher and others, 1984).
-------
SOIL PERMEABILITY
HI LOW
j \ MODERATE
HIGH
Hgure 9. Generalized soil permeability map of Illinois. Data from Feherenbacher and others
(1984).
-------
INDOOR RADON DATA
Screening indoor radon data from 1H50 homesiampled in the State/EPA Residential Radon
Survey conducted in Illinois during the winter of 1990-91 are listed in Table 1 and shown in figure
10. This survey employed short-term (2-7 day) charcoal canister indoor radon tests. The
maximum value recorded in the survey was 92 pCi/L in Madison County. The statewide indoor
radon average in this survey was 3.2 pCi/L. A number of counties with average indoor radon
levels exceeding 4 pCi/L are found in the northern two-thirds of the State (fig. 10). Counties in
which more than 50 percent of the homes tested had screening indoor radon values exceeding
4 pCi/L are restricted to the northern half of the State (fig. 10). Lake and Cook counties,
bordering Lake Michigan and including most of the Chicago metropolitan area, have low average
indoor radon values (fig. 10). The southern one-third of the State generally has low to moderate
average indoor radon values (fig. 10).
The Illinois State Department of Nuclear Safety (TONS) also conducted statewide indoor
radon sampling in 4140 randomly-selected homes during 1987-1991 (Allen and Hamel-Caspary,
1991). This study employed alpha-track detectors placed in the home for a period of 2 weeks to 3
months. The statewide average indoor radon concentration in this study was 3.9 pCi/L, and 32
percent of the homes sampled had indoor radon values exceeding 4 pCi/L (fig. 11 and Table 2).
About one percent of the homes tested had indoor radon levels exceeding 20 pCi/L. The data from
this survey correspond fairly well with the State/EPA Residential Radon Survey data, although the
average values and percent of homes greater than 4 pCi/L are generally somewhat higher for most
counties in the IDNS survey than in the State/EPA survey. The pattern of higher radon values in
the northern two-thirds of Illinois, generally lower values in the southern one-third of the State,
and low to moderate indoor radon levels in the area adjacent to Lake Michigan, is similar for both
data sets.
GEOLOGIC RADON POTENTIAL
An aeroradiometric map of Illinois (fig. 12) compiled from filtered, smoothed, and
contoured MURE flightline data (Duval and others, 1989) shows no extremely high or low
radioactivity areas within the State. Lower equivalent uranium (elJ) areas are associated with
alluvium and sand deposits along the drainages of the Illinois, Rock, and Kaskaskia Rivers, and
with windblown sand deposits in northeastern Illinois (fig. 7). Areas with eU signatures greater
than 2.5 ppm are scattered throughout the northern one-third of the State, and larger areas occur in
east-central and southern Illinois which could not be directly correlated with surface features. The
pattern of anomalies suggests a possible correlation with glacial lake deposits or areas of thin loess
cover or bedrock exposure, but the relatively higher eU values in the southern part of the State are
not associated with high radon values; in fact, indoor radon concentrations in the southern one-
third of Illinois are generally less than 4 pCi/L.
Most of the State has an eU signature between 1.0 and 2.5 ppm. The radiometric signature
of Illinois as a whole appears lower than expected compared to indoor radon, and compared with
the radiometric signature of unglaciated areas on a national scale (see Duval and others, 1989).
Recent studies (for example, Lively and others, 1991; Schumann and others, 1991) suggest that
much of the radium in the near-surface horizons of glacially-derived soils may have been leached
and transported downward in the soil profile, giving a low surface radiometric signature while
generating significant radon at depth (1-2 m or greater) to produce elevated indoor radon levels.
IV-15 Reprinted from USGS Open-File Repent 93-292-E
-------
Bsmt. & 1st Floor Rn
35
10
22
15
OtolO
11to20
21to40
41 to 60
61 to 80
0 i 81 to 100
15 dZH Missing Data (< 5 measurements)
100 Miles
Bsmt. & 1st Floor Rn
Average Concentration (pCi/L)
31 iwwi o.O to 1.9
35 NWVM 2.0 to 4.0
20 4.1 to 10.0
1 • 10.1 to 23.0
15 [HZ! Missing Data (< 5 measurements)
100 Miles
Figure 10. Screening indoor radon data from the EPA/State Residential Radon Survey of Illinois,
1990-91, for counties with 5 or more measurements. Data are from 2-7 day charcoal canister tests.
Histograms in map legends show the number of counties in each category. The number of samples
in each county (see Table 1) may not be sufficient to statistically characterize the radon levels of the
counties, but they do suggest general trends. Unequal category intervals were chosen to provide
reference to decision and action levels.
-------
TABLE 1. Screening indoor radon data from the EPA/State Residential Radon Survey of
Illinois conducted during 1990-91. Data represent 2-7 day charcoal canister measurements
from the lowest level of each home tested.
COUNTY
ADAMS
ALEXANDER
BOND
BOONE
BROWN
BUREAU
CALHOUN
CARROLL
CASS
CHAMPAIGN
CHRISTIAN
CLARK
CLAY
CLINTON
COLES
COOK
CRAWFORD
CUMBERLAND
DEWTTT
DOUGLAS
DUPAGE
EDGAR .
EDWARDS
EFFINGHAM
FAYETTE
FORD
FRANKLIN
FULTON
GALLATIN
GREENE
GRUNDY
HAMILTON
HANCOCK
HENDERSON
HENRY
IROQUOIS
JACKSON
JASPER
JEFFERSON
JERSEY
JODAVJJ3SS
NO. OF
MEAS.
22
7
2
3
1
5
3
3
2
33
13
6
6
14
10
121
15
5
11
2
80
7
3
17
9
5
19
14
3
4
2
4
6
4
14
3
16
4
13
5
1
MEAN
8.4
0.9
1.7
2.3
12.8
3.1
2.1
2.0
10.4
3.6
3.3
1.1
0.7
1.1
3.4
1.6
1.8
0.8
6.4
6.2
3.0
2.0
1.4
1.1
2.3
2.6
0.9
6.7
0.7
4.0
5.1
0.9
3.5
23.0
6.5
2.4
1.2
0.6
0.9
3.0
5.3
GEOM.
MEAN
4.0
0.7
1.1
2.3
12.8
2.8
1.6
1.9
8.4
2.1
2.0
0.8
0.4
0.6
2.0
0.9
0.9
0.5
3.5
1.1
1.8
1.1
1.3
0.8
1.4
1.7
0.6
3.4
0.3
3.2
5.0
0.6
0.9
5.4
5.0
1.9
0.8
0.4
0.5
1.6
5.3
MEDIAN
5.0
0.8
1.7
2.4
12.8
2.5
1.2
1.9
10.4
2.2
3.2
1.0
0.8
0.8
1.8
1.2
0.9
0.6
2.6
6.2
1.8
1.7
1.5
0.6
1.8
1.4
0.8
3.7
0.6
4.3
5.1
0.5
1.4
2.8
5.3
2.7
1.0
0.6
0.7
2.2
5.3
STD.
DEV.
15.3
0.6
1.8
0.6
0.0
1.5
2.0
0.4
8.6
4.5
2.7
0.7
0.6
1.1
3.7
2.0
3.1
0.9
9.3
8.6
3.6
2.2
0.5
1.1
2.4
2.5
1.0
9.0
0.7
2.6
0.8
1.0
6.1
41.4
5.5
1.6
0.9
0.5
0.9
2.4
0.0
MAXIMUM
74.6
1.9
3.0
2.8
12.8
5.1
4.4
2.4
16.4
23.4
9.8
2.3
1.3
3.4
10.8
16.0
12.6
2.3
31.2
12.3
22.9
6.6
1.8
4.4
8.1
6.1
4.4
31.6
1.4
6.4
5.6
2.3
15.8
85.1
21.0
3.9
3.2
1.1
2.8
5.5
5.3
%>4pCi/L
59
0
0
0
100
40
33
0
100
24
31
0
0
0
30
6
7
0
36
50
18
14
0
6
11
40
5
43
0
50
100
0
17
25
71
0
0
0
0
40
100
%>20pCi/L
5
0
0
0
0
0
0
0
0
3
0
0
0
0
0
0
0
0
9
0
1
0
0
0
0
0
0
14
0
0
0
0
0
25
7
0
0
0
0
0
0
-------
-------
TABLE 1 (continued). Screening indoor radon data for Illinois.
COUNTY
JOHNSON
KANE
KANKAKEE
KENDALL
KNOX
LASALLE
LAKE
LAWRENCE
LEE
LIVINGSTON
LOGAN
MACON
MACOUPIN
MADISON
MARION
MARSHALL
MASON
MASSAC
MCDONOUGH
MCHENRY
MCLEAN
MENARD
MERCER
MONROE
MONTGOMERY
MORGAN
MOULTRIE
OGLE
PEORIA
PERRY
PIATT
PIKE
POPE
PULASKI
RANDOLPH
RICHLAND
ROCK ISLAND
SALINE
SANGAMON
SCHUYLER
SCOTT
STIFF .WV
ST.CLAIR
NO. OF
MEAS.
2
24
10
4
22
11
29
2
2
5
5
30
20
110
12
4
4
7
13
23
26
5
8
16
10
12
7
7
55
9
4
6
1
5
20
9
43
14
42
1
4
6
7J
MEAN
0.9
4.0
1.8
4.7
5.1
4.0
1.6
0.4
1.3
8.6
4.6
23
1.7
3.2
1.4
4.4
4.0
1.1
5.4
3.4
3.5
3.6
6.9
2.5
2.9
4.8
5.6
4.1
3.5
1.C
2.6
2.9
0.5
O.S
1.5
1.2
5.7
0.*
3/
1.:
2.:
2;
2.1
SEOM.
MEAN
0.3
3.1
1.0
4.6
3.5
3.0
0.8
0.4
1.2
7.5
3.5
2.0
0.7
1.7
0.7
3.2
2.7
0.8
3.3
2.4
2.2
2.9
5.4
2.1
22
3.9
32
3.5
2.5
0.6
1.3
2.6
0.5
0.3
1.C
0.6
3.S
0.5
2.2
1.:
1.1
1.6
1.!
MEDIAN
0.9
3.4
1.1
4.8
3.6
2.6
0.9
0.4
1.3
8.5
2.2
2.2
0.8
1.9
0.9
2.8
3.1
1.0
2.6
2.3
2.9
4.5
5.8
1.8
2.1
3.9
3.1
3.6
2.5
0.8
0.8
2.5
0.5
0.3
1.C
1.2
3.S
O.S
2.7
1.:
2.7
1.;
2.2
TD.
DEV.
1.3
3.1
2.0
1.3
4.3
4.5
IS
0.0
0.6
5.0
3.7
2.7
3.0
8.8
1.8
4.1
3.7
0.7
6.9
2.8
2.6
2.0
5.4
1.7
2.2
3.5
5.9
2.4
3.6
0.9
3.8
1.5
O.C
1.7
1.9
1.1
5.2
0.7
3.2
0.(
1.2
2.9
2.6
MAXIMUM
1.8
14.6
6.9
6.2
17.3
17.3
9.4
0.4
1.7
16.4
9.6
13.2
13.8
91.6
6.4
10.3
9.0
2.0
22.1
10.2
10.0
5.4
18.8
5.7
7.8
14.2
16.9
7.8
23.6
3.1
8.3
5.8
0.5
3.8
8.8
3.0
22.5
2.5
20.0
1.3
3.3
7.9
19.5
9fc>4pCi/L
0
42
10
75
36
27
7
0
0
80
40
17
5
15
8
25
50
0
23
35
35
60
63
19
30
42
43
43
24
0
25
17
0
0
5
0
49
0
26
0
0
33
18
%>20pCi/L
0
0
0
0
0
0
0
0
0
0
0
0
0
. 1
0
0
0
0
8
0
0
0
0
0
0
0
0
0
2
0
0
0
0
0
0
0
2
0
0
0
0
0
0
-------
TABLE 1 (continued). Screening indoor radon data for Illinois.
COUNTY
STARK
STEPHENSON
TAZEWFT.T,
UNION
VERMILION
WABASH
WARREN
WASHINGTON
WAYNE
WHITE
WHTIESIDE
WILL
WILLIAMSON
WINNEBAGO
WOODFORD
NO. OF
MEAS.
1
5
41
9
35
6
7
11
7
9
8
21
20
19
7
MEAN
6.9
8.8
5.8
1.4
2.2
0.6
7.8
0.9
1.0
1.2
3.1
4.9
1.0
2.8
8.6
GEOM.
MEAN
6.9
2.9
4.4
1.1
1.5
0.5
5.7
0.6
0.7
0.7
1.6
2.5
0.7
2.5
5.6
MEDIAN
6.9
5.5
4.2
1.1
2.0
0.5
4.5
0.7
1.2
1.1
2.5
2.6
0.8
2.5
6.0
STD.
DEV.
0.0
11.4
4.1
1.0
1.7
0.3
6.6
0.9
0.7
1.1
2.9
7.4
1.2
1.6
9.2
MAXIMUM
6.9
28.7
17.3
3.3
7.0
1.1
18.9
3.1
2.2
3.4
9.1
34.9
5.5
6.7
28.3
%>4pCi/L
100
60
51
0
20
0
57
0
0
0
25
~~43~1
5
16
71
%>20pCi/L
0
20
0
0
0
0
0
0
0
0
0
5
0
0
14
-------
Bsmt. & 1st Floor Radon
%>4pCi/L
17 E"^ OtolO
21
32
21
11 to 20
21 to 40
41 to 60
61 to 80
81 to 100
100 Miles
Bsmt. & 1st Floor Radon
Average concentration (pCi/L)
12
0.0 to 1.9
2.0 to 4.0
4.-) to 10.0
10.1 to 11.4
100 Miles
Figure 11. Screening indoor radon data from the Illinois Department of Nuclear Safety indoor
radon survey conducted during 1987-1991. Data represent 2-week to 3-month alpha-track
detector tests. Histograms in map legends show the number of counties in each category. See
Table 2 for additional information from this survey.
-------
TABLE 2. Screening indoor radon data from the IDNS statewide radon survey conducted
in Illinois during 1987-9.1. Data represent 2-week to 3-month alpha-track measurements from
the lowest level of each home tested.
COUNTY
Adams
Alexander
Bond
Boone
Brown
Bureau
Calhoun
Carroll
Cass
Champaign
Christian
Clark
Clay
Clinton
Coles
Cook
Crawford
Cumberland
DeKalb
DeWitt
Douglas
DuPage
Edgar
Edwards
Effingham
Fayette
Ford
Franklin
Fulton
Gallatin
Greene
Grundy
Hamilton
Hancock
Hardin
Henderson
Henry
Iroquois
Jackson
Jasper
Jefferson
Jersey
Jo Daviess
NO. OF
MEAS.
65
25
27
55
35
24
25
28
28
33
50
,26
24
15
36
261
30
35
56
27
22
167
31
29
36
40
28
34
34
30
13
10
30
17
29
28
36
30
35
30
33
10
21
MEAN
2.8
3.0
2.2
5.0
3.9
3.0
3.9
5.1
5.2
5.0
4.7
2.6
2.3
2.7
3.7
2.8
1.5
1.8
4.3
7.5
4.5
4.4
3.0
2.3
3.5
2.9
3.3
2.0
3.7
2.4
3.8
2.2
2.7
2.1
4.4
1.7
7.7
2.9
1.6
1.5
1.7
3.0
7.1
GEOM.
MEAN
1.9
2.7
1.5
4.4
2.0
2.6
3.4
3.5
4.6
4.0
3.8
1.5
1.7
2.0
2.6
2.3
1.1
1.5
3.7
4.2
2.3
3.2
2.3
1.4
2.2
2.5
2.5
1.5
2.7
2.1
2.4
1.6
2.1
1.4
3.7
1.4
6.2
1.9
1.1
1.1
1.3
2.2
3.6
MEDIAN
2.1
3.1
1.5
4.7
2.0
3.1
3.1
3.4
4.7
3.9
3.7
1.0
1.8
1.7
2.7
2.2
0.8
1.6
3.9
4.9
2.8
3.1
2.0
1.0
1.6
2.5
3.3
1.1
2.9
2.2
2.5
1.7
2.3
1.1
3.2
1.0
6.9
1.7
0.9
1.0
1.1
2.7
2.8
STD.
DEV.
2.7
1.3
1.8
2.5
9.1
1.6
2.3
5.5
2.5
3.6
3.2
3.3
1.8
2.3
3.7
1.8
1.7
1.0
2.7
13.9
.8.5
6.0
2.7
3.5
4.1
1.7
2.2
1.6
3.9
1.3
4.3
1.8
1.9
2.3
3.3
1.2
5.5
3.3
1.5
1.4
1.6
2.0
9.5
MAXIMUM
13.6
5.6
6.2
13.3
55.1
7.0
10.8
25.4
11.3
17.6
15.5
14.2
5.7
8.2
18.5
11.6
9.7
4.8
18.9
75.6
41.6
64.5
14.3
17.8
19.3
8.4
9.1
5.7
18.1
6.0
16.3
5.6
8.2
8.8
13.5
4.6
25.4
16.9
6.6
7.0
7.4
8.1
37.5
%>4 pCi/L
23
24
19
62
23
21
32
43
68
48
48
19
25
20
33
19
3
3
43
56
23
31
26
10
28
20
36
21
29
13
31
20
23
18
38
7
81
20
6
7
9
10
43
%>20pCi/L
0
0
0
0
3
0
0
4
0
0
0
0
0
0
0
0
0
0
0
4
5
2
0
0
0
0
0
0
0
0
0
0
0
0
0
0
6
0
0
0
0
0
10
-------
TABLE 2 (continued). Indoor radon data from the IDNS statewide radon survey of Illinois.
COUNTY
Johnson
Kane
Kankakee
Kendall
Knox
Lake
LaSalle
Lawrence
Lee
Livingston
Logan
Macon
Macoupin
Madison
Marion
Marshall
Mason
Massac
McDonough
McHenry
McLean
Menard
Mercer
Monroe
Montgomery
Morgan
Moultrie
Ogle
Peoria
Perry
Piatt
Pike
Pope
Pulaski
Putnam
Randolph
Richland
Rock Island
Saline
Sangamon
Schuyler
Scott
Shelby
St. Clair
Stark
NO. OF
MEAS.
28
70
35
27
57
90
86
29
34
26
57
72
30
66
30
26
29
26
66
77
52
30
28
26
32
59
26
29
55
35
35
27
30
27
26
36
29
66
26
103
28
30
28
48
28
MEAN
2.2
5.5
2.7
6.0
5.9
2.3
4.6
1.1
3.4
7.7
5.0
3.0
2.3
2.6
1.5
6.0
5.9
4.5
4.5
4.3
6.3
4.9
8.5
5.5
3.5
6.8
3.0
3.9
5.0
1.8
3.2
5.5
3.8
2.3
4.5
1.8
2.0
6.0
2.1
3.9
5.5
5.1
3.0
2.7
6.7
GEOM.
MEAN
1.9
4.0
1.8
4.8
4.7
1.6
3.7
1.0
2.4
5.9
3.9
2.0
1.7
1.6
1.1
3.5
4.8
3.2
3.0
3.4
4.8
3.0
6.5
4.5
2.4
5.6
2.2
2.8
3.5
1.5
2.5
4.2
3.1
2.2
2.4
1.4
1.7
4.1
1.8
3.0
4.2
4.4
2.2
2.1
4.9
MEDIAN
1.9
4.0
1.7
4.9
5.5
1.6
3.8
0.9
2.1
6.0
3.9
2.0
1.5
1.6
1.0
3.3
5.0
2.9
3.4
3.2
5.7
3.1
7.8
4.0
2.5
5.9
2.2
2.9
3.6
1.3
2.6
4.4
2.6
2.1
2.5
1.1
1.5
4.7
1.7
2.7
4.0
4.4
2.1
2.3
4.4
1 STD.
" DEV.
1.3
5.2
3.0
4.4
4.1
2.0
3.1
0.9
3.2
7.4
3.7
3.3
1.9
4.3
1.2
6.9
4.0
5.7
4.1
3.7
4.7
4.9
6.1
3.8
3.3
4.3
2.7
3.4
4.5
1.0
3.0
3.9
3.2
0.7
8.4
1.4
1.4
6.5
1.2
3.8
4.2
2.7
2.5
2.0
5.4
MAXIMUM
5.6
34.4
16.8
19.1
21.1
9.6
15.5
5.1
15.0
39.8
19.2
15.7
7.5
34.2
4.6
23.4
20.8
28.1
17.8
23.6
23.2
20.0
23.1
15.4
16.9
19.2
11.0
16.8
22.4
4.2
17.9
15.9
17.6
4.0
43.8
4.8
5.3
46.2
4.9
23.2
19.0
10.9
10.2
12.3
21.3
%>4 pCi/L
14
51
26
59
65
14
47
3
24
81
46
21
20
11
10
35
62
23
41
30
62
43
64
54
31
68
23
34
42
6
23
52
30
4
27
14
10
53
8
29
50
57
21
17
61
%>20 pCi/L
0
3
0
0
2
0
0
0
0
4
0
0
0
2
0
12
3
4
0
1
4
3
11
0
0
0
0
0
2
0
0
0
0
0
4
0
0
3
0
2
0
0
0
0
4
-------
TABLE 2 (continued). Indoor radon data from the IDNS statewide radon survey of Illinois.
COUNTY
Stephenson
Tazwell
Union
Vermillion
Wabash
Warren
Washington
Wayne
White
Whiteside
Will
Waiiamson
Winnebago
Woodford
NO. OF
MEAS.
56
59
30
36
32
50
36
20
32
36
58
35
55
27
MEAN
4.6
5.5
3.1
3.9
1.6
11.4
2.4
1.0
2.0
2.8
3.6
2.2
4.1
9.7
GEOM.
MEAN
3.7
4.6
2.8
2.9
1.3
8.5
1.8
0.8
1.6
2.3
2.6
1.4
3.4
7.3
MEDIAN
4.3
4.8
2.9
2.5
1.2
8.6
1.9
0.9
1.7
2.5
3.0
0.9
3.3
8.3
STD.
DEV.
2.9
3.2
1.4
3.1
1.0
10.3
1.7
0.7
1.5
1.8
3.3
2.9
2.9
7.7
MAXIMUM
14.9
14.3
5.9
12.8
5.5
59.5
7.2
3.1
6.4
8.1
16.8
11.7
19.0
33.7
%>4 pCi/L
52
64
27
36
3
84
14
0
13
19
29
9
38
78
%>20 pCi/L
0
0
0
0
0
16
0
0
0
0
0
0
0
11
-------
Figure 12. Aerial radiometric map of Illinois (after Duval and others, 1989). .Contour lines at 1.5
and 2.5 ppm equivalent uranium (eU). Pixels shaded from 0 to 6.0 ppm eU at 0.5 ppm eU
increments; darker pixels have lower eU values; white indicates no data.
-------
-------
In addition, poorly-sorted glacial drift may in many cases have higher permeability than the
bedrock from which it is .derived. Cracking of clayey soils during dry periods can create sufficient
permeability for convective radon transport to occur. This may be an important factor causing
elevated radon levels in areas underlain by clay-rich glacial deposits. •
Areas underlain by glacial deposits have generally high radon potential, with the exception
of windblown sand deposits, such as in part of the Kankakee Plain and major river valleys such as
the Illinois and Rock River valleys, and some areas underlain by glacial lake deposits or saturated
soils, such as the Chicago Lake Plain and most of the Wheaton Morainal Country (fig. 1). Areas
of low soil permeability have generally lower radon potential, a good example of which is the soils
developed on Dlinoian glacial deposits in the southern one-third of the State (fig. 9), which are
deemed to have low to moderate radon potential rather than high, due in part to their low soil
permeability. Areas in which black shale constitutes a significant source component to the glacial
deposits have high radon potential, but because of the thin subcrop pattern of most of the black
shale units underlying Illinois, such areas are expected to be relatively small or localized.
Areas underlain by weathered limestone, such as the Driftiess Area in the northwestern
corner of the State, or in which carbonate rocks constitute a significant source component to the
glacial deposits, have moderate to high radon potential. Although the carbonate rocks themselves
are low in uranium and radium, soils and residual deposits developed from these rocks are derived
from the dissolution of the calcium carbonate (CaCOs) that makes up the majority of the rock. As
the CaCOs is dissolved away, the soils become relatively enriched in the remaining impurities—
predominantly base metals, including uranium. Rinds containing relatively high concentrations of
uranium and uranium minerals can be formed on the surfaces of rocks involved with CaCOs
dissolution.
Unglaciated areas in the southern and southwestern parts of Illinois are underlain by
sedimentary rocks of Devonian through Pennsylvanian age that have a generally moderate radon
potential, except for areas underlain by carbonate rocks or black shales, which have a locally high
radon potential. The southern tip of Illinois belonging to the Coastal Plain Province has a low
geologic radon potential.
SUMMARY
For the purposes of this assessment, Illinois is divided into eight geologic radon potential
areas (fig. 13) and each assigned Radon Index (RI) and Confidence Index (CI) scores (Table 3).
The Radon Index is a semiquantitative measure of radon potential based on geologic, soil, and
indoor radon factors, and the Confidence Index is a measure of the relative confidence of the RI
assessment based on the quality and quantity of data used to make the predictions (see the
Introduction chapter to this regional booklet for more information on the methods and data used).
Area 1 (fig. 13) is the Driftiess Area underlain primarily by carbonate rocks. This area has
high geologic radon potential (RI=12) with high confidence (CI=10). Area 2 is underlain by
niinoian glacial deposits and loess with generally moderate permeability. This area also includes
small areas of Pre-Hlinoian glacial deposits and small unglaciated areas along the State's western
border (fig. 5). Area 2 has high geologic radon potential (RI=13) with high confidence (CI=10).
Area 3 is underlain by Wisconsinan glacial deposits and loess with generally moderate
permeability. Local areas underlain by soils with low permeability (fig. 9) may generate moderate
radon levels (averaging 2-4 pCi/L). As a whole, Area 3 has generally high geologic radon
potential (RI=13) with high confidence (CI=10). Area 4 is underlain by glacial lake deposits and
IV-25 Reprinted from USGS Open-File Report 93-292-E
-------
0
1
1
0
20 40
i i
50
60 miles
1
100km
GEOLOGIC
RADON POTENTIAL
| | Low
fcXXl Moderate or Variable
Figure 13. Geologic radon potential areas of Illinois. See Table 3 for Radon Index
and Confidence Index rankings of areas.
-------
clay-rich glacial deposits with generally low permeability. Approximately half of this area has no
NURE radioactivity data due to restrictions on low-level aircraft flights over the Chicago area. The
radioactivity score of 2 points for the area was determitied by noting the radioactivity north and
south of the Chicago area and assuming that the radioactivity in the Chicago area is similar. The
estimate is assigned only one confidence index point due to the lack of data for approximately half
of Area 4. This area has moderate geologic radon potential (RI=11) with a moderate confidence
index score (CI=8).
Area 5 is underlain by windblown sand deposits with high permeability but low
radioactivity because the sand contains mostly quartz with very low concentrations of heavy
minerals (including uranium). Areas in which the sand layer is thinner may have moderate to
locally high indoor radon levels. Area 5 has moderate geologic radon potential (RI=11) with
moderate confidence (CI=9). Homes on windblown sand deposits in Areas 2 and 3 are also likely
to have locally low to moderate indoor radon levels. Area 6 is underlain by Dlinoian glacial
deposits with generally low permeability. The bedrock source material for these deposits contains
more sandstone and gray shale, and relatively less black shale and carbonate rock, than in Areas 2
and 3. Areas underlain by glacial lake deposits are likely to have low to moderate indoor radon
levels. This area has overall moderate radon potential (RI=9) with moderate confidence (CI=9).
Area 7 is unglaciated and is underlain by limestones, sandstones, and shales of Ordovician to
Pennsylvanian age (fig. 4). This area has a moderate geologic radon potential (RI=10) with high
confidence (CI=10). Area 8 is underlain by alluvium, sand, and loess of the Coastal Plain
Province. Area 8 has a low geologic radon potential (RI=8) with high confidence (CI=10). Some
areas within Area 8, especially those underlain by thick loess, may have moderate to locally high
indoor radon levels.
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-27 Reprinted from USGS Open-File Report 93-292-E
-------
TABLE 3. Radon Index (RI) and Confidence Index (CI) scores for geologic radon potential areas
of Illinois. See figure 13 for locations and abbreviations of areas.
TOTAL 12
10
RANKING HIGH HIGH
FACTOR
INDOOR RADON
RADIOACTIVITY
GEOLOGY
SOIL PERM.
ARCHITECTURE
GEE POINTS
1
RI
2
2
3
2
3
0
CI
3
2
3
2
--
—
2
RI
3
2
3
2
3
0
CI
3
2
3
2
—
—
3
RI
3
2
3
2
3
0
CI
3
2
3
2
—
—
4
RI
2
2
2
2
3
0
CI
3
1
2
2
—
--
13 10
HIGH HIGH
13 10
HIGH HIGH
11
8
MOD MOD
FACTOR
INDOOR RADON
RADIOACTIVITY
GEOLOGY
SOIL PERM.
ARafflTECTURE
GFE POINTS
TOTAL
5
RI
2
1
2
3
3
0
11
CI
3
2
2
2
~
—
9
RI
2
2
2
1
2
0
9
6
CI
3
2
2
2
—
—
9
.7
RI
2
2
2
2
2
0
10
CI
3
3
2
2
—
—
10
8
RI
1
2
1
2
2
0
8
CI
3
3
2
2
—
—
10
RANKING MOD MOD
MOD MOD
MOD HIGH
LOW HIGH
RADON INDEX SCORING:
Radon potential category
LOW " " " .3-8 points
MODERATE/VARIABLE 9-11 points
HIGH > 11 points
Possible range of points = 3 to 17
CONFIDENCE INDEX SCORING:
Probable screening indoor
Point range radon average for area
LOW CONFIDENCE
MODERATE CONFIDENCE
HIGH CONFIDENCE
4-6 points
7-9 points
10 -12 points
Possible range of points = 4 to 12
<2pCi/L
2-4pCi/L
>4pCi/L
IV-28 Reprinted from USGS Open-File Report 93-292-E
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REFERENCES USED IN THIS REPORT
AND GENERAL REFERENCES RELATED TO RADON IN ILLINOIS
Allen, R., and Hamel-Caspary, M., 1991, Radon in Illinois: A status report, in Proceedings of the
1991 International Symposium on Radon and Radon Reduction Technology, Volume 4,
Symposium Poster Papers: U.S. Environmental Protection Agency report
EPA/600/9-91/037D, p. P7-15--P7-33.
Assaf, G., 1971, Comments on "Aircraft measurements of the vertical distribution of radon in the
lower atmosphere" by W. E. Bradley and J. E. Pearson: Journal of Geophysical Research,
v. 76, p. 2897.
Berg, R.C., and Kempton, J.P., 1988, Stack-unit mapping of geologic materials in Illinois to a
depth of 15 meters: Illinois State Geological Survey Circular 542,23 p., 4 plates.
Berg, R.C., Kempton, J.P., and Cartwright, K., 1984, Potential for contamination of shallow
aquifers in Illinois: Illinois State Geological Survey Circular 532,30 p., 2 plates.
Bradbury, J.C., Ostrom, M.E., and McVicker, L.D., 1955, Preliminary report on uranium in
Hardin County, Illinois: Illinois State Geological Survey Circular 200,21 p.
Cahill, R.A., and Coleman, D.D., 1989, An overview of the significance of radon in natural gas,
in Proceedings of Conference on Gas Quality and Energy Measurements, sponsored by the
Institute of Gas Technology, Rosemont, Illinois, June 12-13,1989,19 p.
Cahill, R.A., and Coleman, D.D., 1990, An overview of the significance of radon in natural gas:
An update, in Proceedings of Conference on Gas Quality and Energy Measurements,
sponsored by the Institute of Gas Technology, Chicago, Illinois, July 16-18,1990,18 p.
Carmichael, R.S., 1989, Practical Handbook of physical properties of rocks and minerals: Boca
Raton, Ha., CRC Press, 741 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.
Feherenbacher, J.B., Alexander, J.D., Jansen, I.J., Darmody, R.G., Pope, R.A., Flock, M.A.,
Voss, E.E., Scott, J.W., Andrews, W.F., and Bushue, L.J., 1984, Soils of Illinois:
Illinois Agricultural Experiment Station Bulletin 778, 85 p.
Frost, Joyce K., Zierath, D.L., and Shimp, N.F., 1985, Chemical composition and geochemistry
of the New Albany Shale Group (Devonian-Mississippian) in Illinois: Illinois State
Geological Survey Contract/Grant Report 1985-4,134 p.
Frye, J.C., Willman, H.B., and Black, R.F., 1965, Outline of glacial geology of Illinois and
Wisconsin, in Wright, H.E., Jr., and Frye, D.G. (eds.), The Quaternary of the United
States: Princeton, NJ, Princeton University Press, p. 29-41.
IV-29 Reprinted from USGS Open-File Report 93-292-E
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Ghahremani, D.T., 1987, Radon and hydrocarbon prospecting in basins with shallow black shale
deposits: AAPG. Bulletin, v. 71, p. 1104.
Gilkeson, R.H., Cartwright,.K., Cowart, J.B. and Holtzman, R.B., 1983, Hydrogeologic and
geochemical studies of selected natural radioisotopes and barium in groundwater in Illinois:
University of Illinois Water Resources Center Research Report 180, p. 93 p.
Gilkeson,'R.H., Perry, E.G., Jr., Cowart, J.B. and Holtzman, R.B., 1984, Isotopic studies of
the natural sources of radium in groundwater in Illinois: University of Illinois Water
Resources Center Research Report 187, 50 p.
Gilkeson, R.H. and Cowart, J.B., 1987, Radium, radon and uranium isotopes in ground water
from Cambrian-Ordovician sandstone aquifers in Illinois, in B. Graves (ed), Radon,
radium, and other radioactivity in ground water: Lewis Publishers, p. 403-422.
Gilkeson, R.H., CahiU, R.A., and Gendron, C.R., 1988, Natural background radiation in the
proposed Illinois SSC siting area: Illinois State Geological Survey Environmental Geology
Notes 127,47 p.
Hudson, T.B. and Nelson, R.S., 1989, Analysis of radon concentrations in Pleistocene deposits
in Illinois: Transactions of the Illinois State Academy of Science, Suppl., v. 82, p. 49.
Jones, R.L., 1991, Uranium in Illinois surface soils: Soil Science Society of America Journal,
v. 55, p. 549-550.
Keefer, D.A., and Berg, R.C., 1990, Potential for aquifer recharge in Illinois: Illinois State
Geological Survey map, scale 1:1,000,000.
Lineback, Jerry A., 1979, Quaternary deposits of Illinois: Illinois State Geological Survey, scale
1:500,000.
Lively, Richard, Steck, Daniel, and Brasaemle, Bruce, 1991, A site study of soil characteristics
and soil gas radon in Rochester, Minnesota:' Minnesota Center for Urban and Regional
Affairs report CURA 91-2,15 p.
Ostrom, M.E., Hopkins, M.E., White, W.A., and McVicker, L.D., 1955, Uranium in Illinois
black shales: Illinois State Geological Survey Circular 203,15 p.
Pearson, J.E. and Jones, G.E., 1965, Emanation of radon 222 from soils and its use as a tracer:
Journal of Geophysical Research, v. 70, p. 5279-5290.
Pearson, J.E. and Jones, G.E., 1966, Soil concentrations of "emanating radium-226" and the
emanation of radon-222 from soils and plants: Tellus, v. 18, p. 655-662.
Richmond, G.R., and Fullerton, D.S. (eds.), Quaternary Geologic Atlas of the United States:
U.S. Geological Survey Miscellaneous Investigations Map 1-1420, sheet NK-16, Chicago
4°x6° quadrangle, 1983; sheet NK-15, Des Moines 4°x6° quadrangle, 1991; sheet NJ-16,
Louisville 4°x6° quadrangle, 1991; scale 1:1,000,000.
IV-30 Reprinted from USGS Open-File Report 93-292-E
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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.
Striegl, R.G., 1985, Distribution of gases in the unsaturated zone near buried low-level radioactive
waste, in N.R. Tilford (ed), Site selection, characterization, and design exploration:
Proceedings of Association of Engineering Geologists 28th annual meeting; Site selection,
characterization, and design exploration; in conjunction with International Symposium on
Management of hazardous chemical waste sites, Winston-Salem,. NC, Oct. 7-11,1985,
p. 96.
Striegl, R.G., 1988, Distribution of gases in the unsaturated zone at a low-level radioactive-waste
disposal site near Sheffield, Illinois: U.S. Geological Survey Water Resources
. Investigations 88-4025, 69 p.
Willman, H.B., and Frye, J.C., 1970, Pleistocene stratigraphy of Illinois: Illinois State
Geological Survey Bulletin 94,204 p.
Willman, H.B., and others, 1967, Geologic map of Illinois: Illinois State Geological Survey, scale
1:500,000.
Willman, H.B., Atherton, E., Buschbach, T.C., Collinson, C., Frye, J.C., Hopkins, M.E.,
Lineback, J.A., and Simon, J.A., 1975, Handbook of Illinois stratigraphy: Illinois State
Geological Survey Bulletin 95,251 p.
IV-31 Reprinted from USGS Open-File Report 93-292-E
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EPA's Map of Radon Zones
The USGS1 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 USGS1 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.)
ILLINOIS MAP OF RADON ZONES
The Illinois Map of Radon Zones and its supporting documentation (Part IV of this
report) have received extensive review by Illinois geologists and radon program experts. The
map for Illinois generally reflects current State knowledge about radon for its counties. Some
States have been able to conduct radon investigations in areas smaller than geologic provinces
and counties, so it is important to consult locally available data.
Although the information provided in Part IV of this report ~ the State chapter entitled
"Preliminary Geologic Radon Potential Assessment of Illinois" ~ 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 5 EPA office or the
Illinois 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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