United States
Environmental Protection
Agency
Air and Radiation
(6604J)
402-R-93-OA2
September 1993
4>EPA EPA's Map of Radon Zones
MICHIGAN
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EPA'S MAP OF RADON ZONES
MICHIGAN
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 MICHIGAN
V. EPA'S MAP OF RADON ZONES -- MICHIGAN
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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 o.f 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 nf the Map of Radon Zones-
EPA's Map of Radon Zones (Figure 1) assigns each of the 3141 counties in the
United States to one of three zones:
o Zone 1 counties have a predicted average indoor screening level > than
4 pCi/L
o Zone 2 counties have a predicted average screening level > 2 pCi/L and
<, 4 pCi/L
o Zone 3 counties have a predicted average screening level < 2 pCi/L
The Zone designations were determined by assessing five factors that are known to be
important indicators of radon potential: indoor radon measurements, geology, aerial
radioactivity, soil parameters, 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 arid 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 Mao 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
gilt Uoietnc Low
Figure 4
NEBRASKA - EPA Map of Radon Zones
Lincoln Count y
Zest I Zoae 2 Zone 3
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One such analysis involved comparing county zone designations to indoor radon
measurements from the State/EPA Residential Radon Surveys (SRRS). Screening averages
for counties with at least 100 measurements were compared to the counties' predicted radon
potential as indicated by the Map of Radon Zones. EPA found that 72% of the county
screening averages were correctly reflected by the appropriate zone designations on the Map.
In all other cases, they only differed by 1 zone.
Another accuracy analysis used the annual average data from the National Residential
Radon Survey (NRRS). The NRRS indicated that approximately 6 million homes in the
United States have annual averages greater than or equal to 4 pCi/L. By cross checking the
county location of the approximately 5,700 homes which participated in the survey, their
radon measurements, and the zone designations for these counties, EPA found that
approximately 3.8 million homes of the 5.4 million homes with radon levels greater than or
equal to 4 pCi/L will be found in counties designated as Zone 1. A random sampling of an
equal number of counties would have only found approximately 1.8 million homes greater
than 4 pCi/L. In other words, this analysis indicated that the map approach is three times
more efficient at identifying high radon areas than random selection of zone designations.
Together, these analyses show that the approach EPA used to develop the Map of
Radon Zones is a reasonable one. In addition, the Agency's confidence is enhanced by results
of the extensive State review process -- the map generally agrees with the States' knowledge
of and experience in their own jurisdictions. However, the accuracy analyses highlight two
important points: the fact that elevated levels will be found in Zones 2 and 3, and that there
will be significant numbers of homes with lower indoor radon levels in all of the Zones. For
these reasons, users of the Map of Radon Zones need to supplement the Map with locally
available data whenever possible. Although all known "hot spots", i.e., localized areas of
consistently elevated levels, are discussed in the State-
specific chapters, accurately defining the boundaries of the "hot spots" on this scale of map is
not possible at this time. Also, unknown "hot spots" do exist.
The Map of Radon Zones is intended to be a starting point for characterizing radon
potential because our knowledge of radon sources and transport is always growing. Although
this effort represents the best data available at this time, EPA will continue to study these
parameters and others such as house construction, ventilation features and meteorology factors
in order to better characterize the presence of radon in U.S homes, especially in high risk
areas. These efforts will eventually assist EPA in refining and revising the conclusions of the
Map of Radon Zones. And although this map is most appropriately used as a targeting tool
by the aforementioned audiences — the Agency encourages all residents to test their homes
for radon, regardless of geographic location or the zone designation of the county in
which they live. Similarly, the Map of Radon Zones should not to be used in lieu of
testing during real estate transactions.
Review Process
The Map of Radon Zones has undergone extensive review within EPA and outside the
Agency. The Association of American State Geologists (AASG) played an integral role in
this review process. The AASG individual State geologists have reviewed their State-specific
information, the USGS Geologic Radon Province Map, and other materials for their geologic
content and consistency.
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In addition to each State geologist providing technical comments, the State radon
offices were asked to comment on their respective States' radon potential evaluations. In
particular, the States were asked to evaluate the data used to assign their counties to specific
zones. EPA and USGS worked with the States to resolve any issues concerning county zone
designations. In a few cases, States have requested changes in county zone designations. The
requests were based on additional data from the State on geology, indoor radon
measurements, population, etc. Upon reviewing the data submitted by the States, EPA did
make some changes in zone designations. These changes, which do not strictly follow the
methodology outlined in this document, are discussed in the respective State chapters.
EPA encourages the States and counties to .conduct further research and data collection
efforts to refine the Map of Radon Zones. EPA would like to be kept informed of any
changes the States, counties, or others make to the maps. Updates and revisions will be
handled in a similar fashion to the way the map was developed. States should notify EPA of
any proposed changes by forwarding the changes through the Regional EPA offices that are
listed in Part EL 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
.*•>''', ,
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
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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 ("2Rn) is produced from the radioactive decay of radium (22SRa), which is, in turn,
a product of the decay of uranium (M8U) (fig. 1). The half-life of 222Rn is 3.825 days. Other
isotopes of radon occur naturally, but, with the exception of thoron (220Rn), which occurs in
concentrations high enough to be of concern in a few localized areas, they are less important
in terms of indoor radon risk because of their extremely short half-lives and less common
occurrence. In general, the concentration and mobility of radon in soil are dependent on
several factors, the most important of which are the soil's radium content and distribution,,
porosity, permeability to gas movement, and moisture content. These characteristics are, in
turn, determined by the soil's parent-material composition, climate, and the soil's age or
maturity. If parent-material composition, climate, vegetation, age of the soil, and topography
are known, the physical and chemical properties of a soil in a given area can be predicted.
As soils form, they develop distinct layers, or horizons, that are cumulatively called the
soil profile. The A horizon is a surface or near-surface horizon containing a relative
abundance of organic matter but dominated by mineral matter. Some soils contain an E
horizon, directly below the A horizon, that is generally characterized by loss of clays, iron, or
aluminum, and has a characteristically lighter color than the A horizon. The B horizon
underlies the A or E horizon. Important characteristics of B horizons include accumulation of
clays, iron oxides, calcium carbonate or other soluble salts, and organic matter complexes. In
drier environments, a horizon may exist within or below the B horizon that is dominated-by
calcium carbonate, often called caliche or calcrete. This carbonate-cemented horizon is
designated the K horizon in modern soil classification schemes. The C horizon underlies the
B (or K) and is a zone of weathered parent material that does not exhibit characteristics of A
or B horizons; that is, it is generally not a zone of leaching or accumulation. In soils formed
in place from the underlying bedrock, the C horizon is a zone of unconsolidated, weathered
bedrock overlying the unweathered bedrock.
The shape and orientation of soil particles (soil structure) control permeability and affect
water movement in the soil. Soils with blocky or granular structure have roughly equivalent
permeabilities in the horizontal and vertical directions, and air and water can infiltrate the soil
relatively easily. However, in soils with platy structure, horizontal permeability is much
greater than vertical permeability, and air and moisture infiltration is generally slow. Soils
.with prismatic or columnar structure have dominantly vertical permeability. Platy and
prismatic structures form in soils with high clay contents. In soils with shrink-swell clays, air
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and moisture infiltration rates and depth of wetting may be limited when the cracks in the
surface soil layers swell shut. Clay-rich B horizons, particularly those with massive or platy
structure, can form a capping layer that impedes the escape of soil gas to the surface
(Schumann and others, 1992). However, 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 2x10'6 inches—this is known as alpha
recoil (Tanner, 1980). Moisture in the soil lessens the chance of a recoiling radon atom
becoming imbedded in an adjacent grain. Because water is more dense than air, a radon atom
will travel a shorter distance in a water-filled pore than in an air-filled pore, thus increasing
the likelihood that the radon atom will remain in the pore space. Intermediate moisture levels
enhance radon emanation but do not significantly affect permeability. However, high
moisture levels can significantly decrease the gas permeability of the soil and impede radon
movement through the soil.
Concentrations of radon in soils are generally many times higher than those inside of
buildings, ranging from tens of pCi/L to more than 100,000 pCi/L, but typically in the range
of hundreds to low thousands of pCi/L. Soil-gas radon concentrations can vary in response to
variations in climate and weather on hourly, daily, or seasonal time scales. Schumann and
others (1992) and Rose and others (1988) recorded order-of-magnitude variations in soil-gas
radon concentrations between seasons in Colorado and Pennsylvania. The most important
factors appear to be (1) soil moisture conditions, which are controlled in large part by
precipitation; (2) barometric pressure; and (3) temperature. Washington and Rose (1990)
suggest that temperature-controlled partitioning of radon between water and gas in soil pores
also has a significant influence on the amount of mobile radon in soil gas.
Homes in hilly limestone regions of the southern Appalachians were found to have higher
indoor radon concentrations during the summer than in the winter. A suggested cause for this
phenomenon involves temperature/pressure-driven flow of radon-laden air from subsurface
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solution cavities in the carbonate rock into houses. As warm air enters solution cavities that
are higher on the hillslope than the homes, it cools and settles, pushing radon-laden air from
lower in the cave or cavity system into structures on the hillslope (Gammage and' others,
1993). In contrast, homes built over caves having openings situated below the level of the
home had higher indoor radon levels in the winter, caused by cooler outside air entering the
cave, driving radon-laden air into cracks and solution cavities in the rock and soil, and
ultimately, into homes (Gammage and others, 1993).
RADON ENTRY INTO BUILDINGS
A driving force (reduced atmospheric pressure in the house relative to the soil, producing
a pressure gradient) and entry points must exist for radon to enter a building from the soil..
The negative pressure caused by furnace combustion, ventilation devices, and the stack effect
(the rising and escape of warm air from the upper floors of the building, causing a
temperature and pressure gradient within the structure) during cold winter months are
common driving forces. Cracks and other penetrations through building foundations, sump
holes, and slab-to-foundation wall joints are common entry points.
Radon levels in the basement are generally higher than those on the main floor or upper
floors of most structures. Homes with basements generally provide more entry points for
radon, commonly have a more pronounced stack effect, and typically have lower air pressure
relative to the surrounding soil than nonbasement homes. The term "nonbasement" applies to
slab-on-grade or crawl space construction.
METHODS AND SOURCES OF DATA
The assessments of radon potential in the booklets that follow this introduction were
made using five main types of data: (1) geologic (lithologic); (2) aerial radiometric; (3) soil
characteristics, including soil moisture, permeability, and drainage characteristics; (4) indoor
radon data; and (5) building architecture (specifically, whether homes in each area are built
slab-on-grade or have a basement or crawl space). "These five factors were evaluated and
integrated to produce estimates of radon potential. Field measurements of. soil-gas radon or
soil radioactivity were not used except where such data were available in existing, published
reports of local field studies. Where applicable, such field studies are described in the
individual state chapters.
GEOLOGIC DATA
The types and distribution of lithologic units and other geologic features in an
assessment area are of primary importance in determining radon potential. Rock types that
are most likely to cause indoor radon problems include carbonaceous black shales, glauconite-
bearing sandstones, certain'kinds of fluvial sandstones and fluvial sediments, phosphorites,
chalk, karst-producing carbonate rocks, certain kinds of glacial deposits, bauxite, uranium-rich
granitic rocks, metamorphic rocks of granitic composition, silica-rich volcanic rocks, many
sheared or faulted rocks, some coals, and certain kinds of contact metamorphosed rocks.
Rock types least likely to cause radon problems include marine quartz sands, non-
carbonaceous shales and siltstones, certain kinds of clays, silica-poor metamorphic and
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igneous rocks, and basalts. Exceptions exist within these general lithologic groups because of
the occurrence of localized uranium deposits, commonly of the hydrothermal type in
crystalline rocks or the "roll-front" type in sedimentary rocks. Uranium and radium are
commonly sited in heavy minerals, iron-oxide coatings on rock and soil grains, and organic
materials in soils and sediments. Less common are uranium associated with phosphate and
carbonate complexes in rocks and soils, and uranium minerals.
Although many cases of elevated indoor radon levels can be traced to high radium and
(or) uranium concentrations in parent rocks, some structural features, most notably faults and
shear zones, have been identified as sites of localized uranium concentrations (Deffeyes and
MacGregor, 1980) and have been associated with some of the highest reported indoor radon
levels (Gundersen, 1991). The two highest known indoor radon occurrences are associated
with sheared fault zones in Boyertown, Pennsylvania (Gundersen and others, 1988a; Smith
and others, 1987), and in Clinton, New Jersey (Henry and others, 1991; Muessig and Bell,
1988).
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 (2HBi), with the assumption that uranium and
its decay products are in secular equilibrium. Equivalent uranium is expressed in units of
parts per million (ppm). Gamma radioactivity also may be expressed in terms of a radium
activity; 3 ppm eU corresponds to approximately 1 picocurie per gram (pCi/g) of radium-226.
Although radon is highly'mobile in soil and its concentration is affected by meteorological
conditions (Kovach, 1945; Klusman and Jaacks, 1987; Schery and others, 1984; Schumann
and others, 1992), statistical correlations between average soil-gas radon concentrations and
average eU values for a wide variety of soils have been documented (Gundersen and others,
1988a, 1988b; Schumann and Owen, 1988). Aerial radiometric data can provide an estimate
of radon source strength over a region, but the amount of radon that is able to enter a home
from the soil is dependent on several local factors, including soil structure, grain size
distribution, moisture content, and permeability, as well as type of house construction and its
structural condition.
The aerial radiometric data used for these characterizations were collected as part of the
Department of Energy National Uranium Resource Evaluation (NURE) program of the 1970s
and early 1980s. The purpose of the NURE program was to identify and describe areas in the
United States having potential uranium resources (U.S. Department of Energy, 1976). The
NURE aerial radiometric data were collected by aircraft in which a gamma-ray spectrometer
was mounted, flying approximately 122 m (400 ft) above the ground surface. The equivalent
uranium maps presented in the state- chapters were generated from reprocessed NURE data in
which smoothing, filtering, recalibrating, and matching of adjacent quadrangle data sets were
performed to compensate for background, altitude, calibration, and other types of errors and
inconsistencies in the original data set (Duval and others, 1989). The data were then gridded
and contoured to produce maps of eU with a pixel size corresponding to approximately 2.5 x
2.5 km (1.6 x 1.6 mi). - .
II-6 Reprinted from USGS Open-File Report 93-292
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FLIGHT LINE SPICING Of SORE AERIAL SURVEYS
2 I'U (1 HUE)
5 KM (3 MILES)
2 fc 5 O
ES 10 Elf (6 MILES)
5 t 10 IK
NO DATA
Figure 2. Nominal flightline spacings for NURE aerial gamma-ray surveys covering the
contiguous United States (from Duval and others, 1990). Rectangles represent I°x2° quadrangles.
-------
Figure 2 is an index map of 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 United
States was actually measured by the airborne gamma-ray detectors (Duval and others, 1989),
although some areas had better coverage than others due to the differences in flight-line
spacing between areas (fig. 2). This suggests that some localized uranium anomalies may not
have been detected by the aerial surveys, but the good correlations of eU patterns with
geologic outcrop patterns indicate that, at relatively small scales (approximately 1:1,000,000
or smaller) the National eU map (Duval and others, 1989) gives reasonably good estimates of
average surface uranium concentrations and thus can assist in the prediction of radon potential
of rocks and soils, especially when augmented with additional geologic and soil data.
The shallow (20-30 cm) depth of investigation of gamma-ray spectrometers, either
ground-based or airborne (Duval and others, 1971; Durrance, 1986), suggests that gamma-ray
data may sometimes underestimate the radon-source strength in soils in which some of the
radionuclides in the near-surface soil layers have been transported downward through the soil
profile. In such cases the concentration of radioactive minerals in the A horizon would be
lower than in the B horizon, where such minerals are typically concentrated. The
concentration of radionuclides in the C horizon and below may be relatively unaffected by
surface solution processes. Under these conditions the surface gamma-ray signal may indicate
a lower radon source concentration than actually exists in the deeper soil layers, which are
most likely to affect radon levels in structures with basements. The redistribution of
radionuclides in soil profiles is dependent on a combination of climatic, geologic, and
geochemical factors. There is reason to believe that correlations of eU with actual soil
radium and uranium concentrations at a depth relevant to radon entry into structures may be
regionally variable (Duval, 1989; Schumann and Gundersen, 1991). Given sufficient
understanding of the factors cited above, these regional differences may be predictable.
SOIL SURVEY DATA
Soil surveys prepared by the U.S. Soil Conservation Service (SCS) provide data on soil
characteristics, including soil-cover thickness, grain-size distribution, permeability, shrink-
swell potential, vegetative cover, generalized groundwater characteristics, and land use. The
reports are available in county formats and State summaries. The county reports typically
contain both generalized and detailed maps of soils in the area.
Because of time and map-scale constraints, it was impractical to examine county soil
reports for each county in the United States, so more generalized summaries at appropriate
scales were used where available. For State or regional-scale radon characterizations, soil
maps were compared to geologic maps of the area, and the soil descriptions, shrink-swell
potential, drainage characteristics, depth to seasonal high water table, permeability, and other
relevant characteristics of each soil group noted. Technical soil terms used in soil surveys are
generally complex; however, a good summary of soil engineering terms and the national
distribution of technical soil types is the "Soils" sheet of the National Atlas (U.S. Department
,of Agriculture, 1987).
II-8 Reprinted from USGS Open-File Report 93-292
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Soil permeability is commonly expressed in SCS soil surveys in terms of the speed, in
inches per hour (in/hr), at which water soaks into the soil, as measured in a soil percolation
test. Although in/hr are not truly units of permeability, these units are in widespread use and
are referred to as "permeability" in SCS soil surveys. The permeabilities listed in the SCS
surveys are for water, but they generally correlate well with gas permeability. Because data
on gas permeability of soils is extremely limited, data on permeability to water is used as a
substitute except in cases in which excessive soil moisture is known to exist. Water in soil
pores inhibits gas transport, so the amount of radon available to a home is effectively reduced
by a high water table. Areas likely to have high water tables include river valleys, coastal
areas, and some areas overlain by deposits of glacial origin (for example, loess).
Soil permeabilities greater than 6.0 in/hr may be considered high, and permeabilities less
than 0.6 in/hr may be considered low in terms of soil-gas transport. Soils with low
permeability may generally be considered to have a lower radon potential than more .
permeable soils with similar radium concentrations. Many well-developed soils contain a
clay-rich B horizon that may impede vertical soil gas transport. Radon generated below this
horizon cannot readily escape to the surface, so it would instead tend to move laterally,
especially under the influence of a. negative pressure exerted by a building. .
Shrink-swell potential is an indicator of the abundance of smectitic (swelling) clays in a
soil. Soils with a high shrink-swell potential may cause building foundations to crack,
creating pathways for radon entry into the structure. During dry periods, desiccation cracks in
shrink-swell soils provide additional pathways for soil-gas transport and effectively increase
the gas permeability of the soil. Soil permeability data and soil profile data thus provide
important information for regional radon assessments.
INDOOR RADON DATA
Two major sources of indoor radon data were used. The first and largest source of data is
from the State/EPA Residential Radon Survey (Ronca-Battista and others, 1988; Dziuban and
others, 1990). Forty-two states completed EPA-sponsored indoor radon surveys between 1986
and 1992 (fig. 3). The State/EPA Residential Radon Surveys were designed to be
comprehensive and statistically significant at the state level, and were subjected to high levels
of quality assurance and control. The surveys collected screening indoor radon measurements,
defined as 2-7 day measurements using charcoal canister radon detectors placed in the lowest
livable area of the home. The target population for the surveys included owner-occupied
single family, detached housing units (White and others, 1989), although attached structures
such as duplexes, townhouses, or condominiums were included in some of the surveys if they
met the other criteria and had contact with the ground surface. Participants were selected
randomly from telephone-directory listings. In total, approximately 60,000 homes were tested
in the State/EPA surveys.
The second source of indoor radon data comes from residential surveys that have been
conducted in a specific state or region of the country (e.g. independent state surveys or utility
company surveys). Several states, including Delaware, Florida, Illinois, New Hampshire, New
Jersey, New York, Oregon, and Utah, have conducted their own surveys of indoor radon. The
quality and design of a state or other independent survey are discussed and referenced where
.the data are used.
II-9 Reprinted from USGS Open-File Report 93-292
-------
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Data for only those counties with five or more measurements are shown in the indoor
radon maps in the state chapters, although data for all counties with a nonzero number of
measurements are listed in the indoor radon data tables in each state chapter. In 'total, indoor
radon data from more.than 100,000 homes nationwide were used in the compilation of these
assessments. Radon data from State or regional indoor radon surveys, public health
organizations, or other sources are discussed in addition to the primary data sources where
they are available.. Nearly all of the data used in these evaluations represent short-term (2-7
day) screening measurements from the lowest livable space of the homes. Specific details
concerning the -nature and use of indoor radon data sets other than the State/EPA Residential
Radon Survey are discussed in the individual State chapters.
RADON INDEX AND CONFIDENCE INDEX
Many of the geologic methods used to evaluate an area for radon potential require
subjective opinions based on the professional judgment and experience of the individual
geologist. The evaluations are nevertheless based on established scientific principles that are
universally applicable to any geographic area or geologic setting. This section describes the
methods and conceptual framework used by the U.S. Geological Survey to evaluate areas for
radon potential based on the five factors discussed in the previous sections. The scheme is
divided into two basic parts, a Radon Index (RI), used to rank the general radon potential of
the area, and the Confidence Index (CI), used to express the level of confidence in the
prediction based on the quantity and quality of the data used to make the determination. This
scheme works best if the areas to be evaluated are delineated by geologically-based
boundaries (geologic provinces) rather than political ones (state/county boundaries) in which
the geology may vary across the area.
Radon Index. Table 1 presents the Radon Index (RI) matrix. The five factors—indoor
radon data, geology, aerial radioactivity, soil parameters, and house foundation type—were
quantitatively ranked (using a point value of 1, 2, or 3) for their respective contribution to
radon potential in a given area. At least some data for the 5 factors are consistently available
for every geologic province. Because each of these main factors encompass a wide variety of
complex and variable components, the geologists performing the evaluation relied heavily on
their professional judgment and experience in assigning point values to each category and in
determining the overall radon potential ranking. Background information on these factors is
discussed in more detail in the preceding sections of this introduction.
Indoor radon was evaluated using unweighted arithmetic means of the indoor radon data
for each geologic area to be assessed. Other expressions of indoor radon levels in an area
also could have been used, such as weighted averages or annual averages, but these types of
data were not consistently available for the entire United States at the time of this writing, or
the schemes were not considered sufficient to provide a means of consistent comparison
across all areas. For this report, charcoal-canister screening measurement data from the
State/EPA Residential Radon Surveys and other carefully selected sources were used, as
described in the preceding section. To maintain consistency, other indoor radon data sets
(vendor, state, or other data) were not considered in scoring the indoor radon factor of the
Radon Index if they were not randomly sampled or could not be statistically combined with
the primary indoor radon data sets. However, these additional radon data sets can provide a
means to further refine correlations between geologic factors and radon potential, so they are
II-11 Reprinted from USGS Open-File Report 93-292
-------
TABLE 1. RADON INDEX MATRIX, "ppm eU" indicates parts per million of equivalent
uranium, as indicated by NURE aerial radiometric data. See text discussion for details.
FACTOR
INDOOR RADON (average)
AERIAL RADIO ACTIVITY
GEOLOGY*
SOIL PERMEABILITY
ARCHITECTURE TYPE
INCREASING RADON POTENTIAL ^
POINT VALUE
1
<2pCi/L
< 1.5 ppm eU
negative
low
mostly slab
.2
2-4pCi/L
1.5 - 2.5 ppm eU
variable
moderate
mixed
3
>4pCi/L
> 2.5 ppm eU
positive
high
mostly basement
'GEOLOGIC FIELD EVIDENCE (GFE) POINTS: GFE points are assigned in addition to points
for the "Geology" factor for specific, relevant geologic field studies. See text for details.
Geologic evidence supporting: HIGH radon +2 points
MODERATE +1 point
LOW -2 points
No relevant geologic field studies 0 points
SCORING:
Radon potential category
LOW
MODERATE/VARIABLE
HIGH
Probable average screening
Point ranee indoor radon for area
3-8 points
9-11 points
12-17 points
<2pCi/L
2-4pCi/L
>4pCi/L
POSSIBLE RANGE OF POINTS = 3 to 17
TABLE 2. CONFIDENCE INDEX MATRIX
INCREASING CONFIDENCE
FACTOR
INDOOR RADON DATA
AERIAL RADIO ACTIVITY
GEOLOGIC DATA
SOIL PERMEABILITY
POINT VALUE
1
sparse/no data
questionable/no data
questionable
questionable/no data
2
fair coverage/quality
glacial cover
variable
variable
3
good coverage/quality
no glacial cover
proven geol. model
reliable, abundant
SCORING:
LOW CONFIDENCE
MODERATE CONFIDENCE
HIGH CONFIDENCE
4-6 points
7-9 points
10 -12 points
POSSIBLE RANGE OF POINTS = 4 to 12
n-12 Reprinted from USGS Open-File Report 93-292
-------
included as supplementary information and are discussed in the individual State chapters. If
the average screening indoor radon level for an area Was less than 2 pCi/L, the indoor radon
factor was assigned 1 point, if it was between 2 and 4 pCi/L, it was scored 2 points, and if
the average screening indoor radon level for an area was greater than 4 pCi/L, the indoor
radon factor was assigned 3 RI points.
Aerial radioactivity data used in this report are from the equivalent uranium map of the
conterminous United States compiled from NURE aerial gamma-ray surveys (Duval and
others, 1989). These data indicate the gamma radioactivity from approximately the upper 30
cm of rock and soil, expressed in units of ppm equivalent uranium. An approximate average
value of eU was determined visually for each area and point values assigned based on
whether the overall eU for the area falls below 1.5 ppm (1 point), between 1.5 and 2.5 ppm
(2 points), or greater than 2.5 ppm (3 points). ;
The geology factor is complex and actually incorporates many geologic characteristics. In
the matrix, "positive" and "negative" refer to the presence or absence and distribution of rock
types known to have high uranium contents and to generate elevated radon in soils or indoors.
Examples of "positive" rock types include granites, black shales, phosphatic rocks, and other
rock types described in the preceding "geologic data" section. Examples of "negative" rock
types include marine quartz sands and some clays. The term "variable" indicates that the
geology within the region is variable or that the rock types in the area are known or suspected
to generate elevated radon in some areas but not in others due to compositional differences,
climatic effects, localizeddistribution of uranium, or other factors. Geologic information
indicates not only how much uranium is present in the rocks and soils but also gives clues for
predicting general radon emanation and mobility characteristics through additional factors
such as structure (notably the presence of faults or shears) and geochemical characteristics
(for example, a phosphate-rich sandstone will likely contain more uranium than a sandstone
containing little or no phosphate because the phosphate forms chemical complexes with
uranium). "Negative", "variable", and "positive" geology were assigned 1, 2, and 3 points,
respectively.
In cases where additional reinforcing or contradictory geologic evidence is available,
Geologic Field Evidence (GFE) points were added to or subtracted from an area's score
(Table 1). Relevant geologic field studies are important to enhancing our understanding of
how geologic processes affect radon distribution. In some cases, geologic models and
supporting field data reinforced an already strong (high or low) score; in others, they provided
important contradictory data. GFE points were applied for geologically-sound evidence that
supports the prediction (but which may contradict one or more factors) on the basis of known
geologic field studies in the area or in areas with geologic and climatic settings similar
enough that they could be applied with full confidence. For example, areas of the Dakotas,
Minnesota, and Iowa that are covered with Wisconsin-age glacial deposits exhibit a low aerial
radiometric signature and score only one RI point in that category. However, data from
geologic field studies in North Dakota and Minnesota (Schumann and others, 1991) suggest
that eU is a poor predictor of geologic radon potential in this area because radionuclides have
11-13 Reprinted from USGS Open-File Report 93-292
-------
been leached from the upper soil layers but are present and possibly even concentrated in
deeper soil horizons, generating significant soil-gas radon. This positive supporting field
evidence adds two GFE points to the score, which helps to counteract the invalid' conclusion
suggested by the radiometric data. No GFE points are awarded if there are no documented
field studies for the area.
"Soil permeability" refers to several soil characteristics that influence radon concentration
and mobility, including soil type, grain size, structure, soil moisture, drainage, slope, arid
permeability. In the matrix, "low" refers to permeabilities less than about 0.6 in/hr; "high"
corresponds to greater than about 6.0 in/hr, in U.S. Soil Conservation Service (SCS) standard
soil percolation tests. The SCS data are for water permeability, which generally correlates
well with the gas permeability of the soil except when the soil moisture content is very high.
Areas with consistently high water tables were thus considered to have low gas permeability.
"Low, "moderate", and "high" permeability were assigned 1, 2, and 3 points, respectively.
Architecture type refers to whether homes in the area have mostly basements (3 points),
mostly slab-on-grade construction (1 point), or a mixture of the'two. Split-level and crawl
space homes fall into the "mixed" category (2 points). Architecture information is necessary
to properly interpret the indoor radon data and produce geologic radon potential categories
that are consistent with screening indoor radon data.
The overall RI for an area is calculated by adding the individual RI scores for the 5
factors, plus or minus GFE points, if any. The total RI for an area falls in one of three
categories—low, moderate or variable, or high. The point ranges for the three categories were
determined by examining the possible combinations of points for the 5 factors and setting
rules such that a majority (3 of 5 factors) would determine the final score for the low and
high categories, with allowances for possible deviation from an ideal score by the other two
factors. The moderate/variable category lies between these two ranges. A total deviation of 3
points from the "ideal" score was considered reasonable to allow for natural variability of
factors—if two of the five factors are allowed to vary from the "ideal" for a category, they
can differ by a minimum of 2 (1 point different each) and a maximum of 4 points (2 points
different each). With "ideal" scores of 5, 10, and 15 points describing low, moderate, and
high geologic radon potential, respectively, an ideal low score of 5 points plus 3 points for
possible variability allows a maximum of 8 points in the low category. Similarly, an ideal
high score of 15 points minus 3 points gives a minimum of 12 points for the high category.
Note, however, that if both other factors differ by two points from the "ideal", indicating
considerable variability in the system, the total point score would lie in the adjacent (i.e.,
moderate/variable) category.
Confidence Index. Except for architecture type, the same factors were used to establish a
Confidence Index (CI) for the radon potential prediction for each area (Table 2). Architecture
type was not included in the confidence index because house construction data are readily and
reliably available through surveys taken by agencies and industry groups including the
National Association of Home Builders, U.S. Department of Housing and Urban
Development,,and the Federal Housing Administration; thus it was not considered necessary
11-14 Reprinted from USGS Open-File Report 93-292
-------
to question the quality or validity of these data. The other factors were scored on the basis of
the quality and quantity of the data used to complete the RI matrix.
Indoor radon data were evaluated based on the distribution and number of data points and
on whether the data were collected by random sampling (State/EPA Residential Radon Survey
or other state survey data) or volunteered vendor data (likely to be nonrandom and biased
toward population centers and/or high indoor radon levels). The categories listed in the CI
matrix for indoor radon data ("sparse or no data", "fair coverage or quality", 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 rado'n in the rocks and soils of the
area evaluated. In general, the greatest problems with correlations among elJ, 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 ell, geology, and radon were generally sound in unglaciated areas and were usually
assigned 3 CI points. Again, however, radioactivity data in some unglaciated areas may have
been assigned fewer than 3 points, and in glaciated areas may be assigned only one point, if
the data were considered questionable or if coverage was poor.
To assign Confidence Index scores for the geologic data factor, rock types and geologic
settings for which a physical-chemical, process-based understanding of radon generation and
mobility exists were regarded as having "proven geologic models" (3 points); a high
confidence could be held for predictions in such areas. Rocks for which the processes are
less well known or for which data are contradictory were regarded as "variable" (2 points),
and those about which little is known or for which no apparent correlations have been found
were deemed "questionable" (1 point).
The soil permeability factor was also scored based on quality and amount of data. The
three categories for soil permeability in the Confidence Index are similar in concept, and
scored similarly, to those for the geologic data factor. Soil permeability can be roughly
estimated from grain size and drainage class if data from standard, accepted soil percolation
tests are unavailable; however, the reliability of the data would be lower than if percolation
test figures or other measured permeability data are available, because an estimate of this type
does not encompass all the factors that affect soil permeability and thus may be inaccurate in
some instances. Most published soil permeability data are for water; although this is
generally closely related to the air permeability of the soil, there are some instances when it
may provide an incorrect estimate. Examples of areas in which water permeability data may
not accurately reflect air permeability include areas with consistently high levels of soil
moisture, or clay-rich soils, which would have a low water permeability but may have a
11-15 Reprinted from USGS Open-File Report 93-292
-------
significantly higher air permeability when dry due to shrinkage cracks in the soil. These
additional factors were applied to the soil permeability factor when assigning the RI score, but
may have less certainty in some cases and thus would be assigned a lower CI score.
The Radon Index and Confidence Index give a general indication of the relative
contributions of the interrelated geologic factors influencing radon generation and transport in
rocks and soils, and thus, of the potential for elevated indoor radon levels to occur in a
particular area. However, because these reports are somewhat generalized to cover relatively
large areas of States, it is highly recommended that more detailed studies be performed in
local areas of interest, using the methods and general information in these booklets as a guide.
11-16 Reprinted from USGS Open-File Report 93-292
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REFERENCES CITED
Akerblom, G., Anderson, P., and Clavensjo, B., 1984, Soil gas radon--A source for indoor radon
daughters: Radiation Protection Dosimetry, v. 7, p. 49-54.
Deffeyes, K.S., and MacGregor, ID., 1980, World uranium resources: Scientific American,
v. 242, p. 66-76.
Durrance, E.M., 1986, Radioactivity in geology: Principles and applications: New York, N.Y.,
Wiley and Sons, 441 p. .
Duval, J.S., 1989, Radioactivity and some of its applications in geology: Proceedings of the
symposium on the application of geophysics to engineering and environmental problems
(SAGEEP), Golden, Colorado, March 13-16,1989: Society of Engineering and Mineral
Exploration Geophysicists, p. 1-61.
Duval, J.S., Cook, E.G., and Adams, J.A.S., 1971, Circle of investigation of an airborne
gamma-ray spectrometer: Journal of Geophysical Research, v. 76, p. 8466-8470.
Duval, J.S., Jones, W.J., Riggle, F.R., and Pitkhi, J.A., 1989, Equivalent uranium map of
conterminous United States: U.S. Geological Survey Open-File Report 89-478,10 p.
Duval, J.S., Reimer, G.M., Schumann, R.R., Owen, D.E., and Otton, J.K., 1990, Soil-gas
radon compared to aerial and ground gamma-ray measurements at study sites near Greeley
and Fort Collins, Colorado: U.S. Geological Survey Open-File Report 90-648,42 p.
Dziuban, J.A., Clifford, M.A., White, S.B., Bergstein, J.W., and Alexander, B.V., 1990,
Residential radon survey of twenty-three States, in Proceedings of the 1990 International
Symposium on Radon and Radon Reduction Technology, Vol. IJJ: Preprints: U.S.
Environmental Protection Agency report EPA/600/9-90/005c, Paper IV-2,17 p.
Gammage, R.B., Wilson, D.L., Saultz, R.J., and Bauer, B.C., 1993, Subtereanean transport of
radon and elevated indoor radon in hilly karst terranes: Atmospheric Environment
(in press).
Gundersen, L.C.S., Reimer, G.M., and Agard, S.S., 1988a, Correlation between geology, radon
in soil gas, and indoor radon in the Reading Prong, in Marikos, M.A., and Hansman,
R.H., eds., Geologic causes of natural radionuclide anomalies: Missouri Department of
Natural Resources Special Publication 4, p. 91-102.
Gundersen, L.C.S, Reimer, G.M., Wiggs, C.R., and Rice, C.A., 1988b, Map showing radon
potential of rocks and soils in Montgomery County, Maryland: U.S. Geological Survey
Miscellaneous Field Studies Map MF-2043, scale 1:62,500.
Gundersen, Linda C.S., 1991, Radon in sheared metamorphic and igneous rocks, in Gundersen,
Linda C.S., and Richard B. Wanty, eds., Field studies of radon in rocks, soils, and water:
U.S. Geol. Survey Bulletin no. 1971, p. 39-50.
H-17 Reprinted from USGS Open-File Report 93-292
-------
Henry, Mitchell E., Kaeding, Margret E., and Monteverde, Donald, 1991, Radon in soil gas and
gamma-ray activity of rocks and soils at the Mulligan Quarry, Clinton, New Jersey, in
Gundersen, Linda C.S., and Richard B. Wanty, eds., Field studies of radon in rocks,
soils, and water: U.S. Geol. Survey Bulletin no. 1971, p. 65-75.
Klusman, R. W., and Jaacks, J. A., 1987, Environmental influences upon mercury, radon, and
helium concentrations in soil gases at a site near Denver, Colorado: Journal of
Geochemical Exploration, v. 27, p. 259-280.
Kovach, E.M., 1945, Meteorological influences upon the radon content of soil gas: Transactions,
American Geophysical Union, v. 26, p. 241-248.
Kunz, C., Laymon, C.A., and Parker, C., 1989, Gravelly soils and indoor radon, to Osborne,
M.C., and Harrison, J., eds., Proceedings of the 1988 EPA Symposium on Radon and
Radon Reduction Technology, Volume 1: U.S. Environmental Protection Agency Report
EPA/600/9-89/006A, p. 5-75-5-86.
Muessig, K., and Bell, C, 1988, Use of airborne radiometric data to direct testing for elevated
indoor radon: Northeastern Environmental Science, v. 7, no. 1, p. 45-51.
Ronca-Battista, M., Moon, M., Bergsten, J., White, S.B., Holt, N., and Alexander, B., 1988,
Radon-222 concentrations in the United States-Results of sample surveys in five states:
Radiation Protection Dosimetry, v. 24, p. 307-312.
Rose, A.W., Washington, J.W., and Greeman, D.J., 1988, Variability of radon with depth and
season in a central Pennsylvania soil developed on limestone: Northeastern Environmental
Science, v. 7, p. 35-39.
Schery, S.D., Gaeddert, D.H., and Wilkening, M.H., 1984, Factors affecting exhalation of radon
from a gravelly sandy loam: Journal of Geophysical Research, v. 89, p. 7299-7309.
Schumann, R.R., and Owen, D.E., 1988, Relationships between geology, equivalent uranium
concentration, and radon in soil gas, Fairfax County, Virginia: U.S. Geological Survey
Open-File Report 88-18,28 p.
Schumann, R.R., and Gundersen, L.C.S., 1991, Regional differences in radon emanation
coefficients in soils: Geological Society of America Abstracts With Programs, v. 23,
no. 1, p. 125.
Schumann, R.R., Peake, R.T., Schmidt, KM., 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/600/9-9l/026b, p. 6-23-6-36.
11-18 Reprinted from USGS Open-File Report 93-292
-------
Schumann, R.R., Owen, D.E., and Asher-Bolinder, S., 1992, Effects of weather and soil
characteristics on temporal variations in soil-gas radon concentrations, in Gates, A.E., and
Gundersen, L.C.S., eds., Geologic controls on radon: Geological Society of America
Special Paper 271, p. 65-72.
Sextro, R.G., Moed, B.A., Nazaroff, W.W., Revzan, K.L., and Nero, A.V., 1987,
Investigations of soil as a source of indoor radon, in Hopke, P.K., ed., Radon and its
decay products: American Chemical Society Symposium Series 331, p. 10-29.
Sterling, R., Meixel, G., Shen, L., Labs, K., andBligh, T., 1985, Assessment of the energy
savings potential of building foundations research: Oak Ridge, Term., U.S. Department of
Energy Report ORNL/SUB/84-0024/1.
Smith, R.C., 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, in Adams, J.A.S., and Lowder,
W.M., eds., The natural radiation environment: Chicago, HI., University of Chicago
Press, p. 161-190.
Tanner, A.B., 1980, Radon migration in the ground: a supplementary review, m Gesell, T.F.,
and Lowder, W.M. (eds), Natural radiation environment HI, Symposium proceedings,
Houston, Texas, v. 1, p. 5-56.
U.S. Department of Agriculture, 1987, Principal 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.
TI-19 Reprinted from USGS Open-File Report 93-292
-------
APPENDIX A
GEOLOGIC TIME SCALE
Subdivisions (and their symbols)
Eon or
Eonothem
Phanerozoic2
Proterozoic
IB)
Archean
(A)
Era or
Erathem
Cenozoic
(Cz)
Mesozoic2
(Mi)
Paleozoic2
(Pi)
M-OOi*
E»nv
M>oaw
t»ny
Period, System,
Subperiod, Subsystem
Quaternary 2
(Q)
Neogene z
Subperiod or
•p,.-:.^ Subsystem (N)
m Paieogene2
' " Suboeriodor
Subsystem (Pi)
Cretaceous
(K)
Jurassic
(J)
• Triassic
Hi)
Permian
(P)
Pennsylyanian
Carboniferous 'P'
(C) Mississippian
fM)
Devonian
(D)
Silurian
(S)
Ordovician
-------
APPENDIX B
GLOSSARY OF TERMS
Units of measure
pCi/L (picocuries per liter)- a unit of measure of radioactivity used to describe radon
concentrations in a volume of air. One picocurie (10"12 curies) is equal to about 2.2 disintegrations
of radon atoms per minute. A liter is about 1.06 quarts. The average concentration of radon in
U.S. homes measured to date is between 1 and 2 pCi/L.
Bq/m3 (Becquerels per cubic meter)- a metric unit of radioactivity used to describe radon
concentrations in a volume of air. One becquerel is equal to one radioactive disintegration per
second. One pCi/L is equal to 37 Bq/m3.
ppm (parts per million)- a unit of measure of concentration by weight of an element in a
substance, in this case, soil or rock. One ppm of uranium contained in a ton of rock corresponds
to about 0.03 ounces of uranium. The average concentration of uranium in soils in the United
States is between 1 and 2 ppm.
in/hr (inches per hour)- a unit of measure used by soil scientists and engineers to describe the
permeability of a soil to water flowing through it It is measured by digging a hole 1 foot (12
inches) square and one foot deep, filling it with water, and measuring the time it takes for the water
to drain from the hole. The drop in height of the water level in the hole, measured in inches, is
then divided by the time (in hours) to determine the permeability. Soils range in permeability from
less than 0.06 in/hr to greater than 20 in/hr, but most soils in the United States have permeabilities
between these two extremes.
Geologic terms and terms related to the study of radon
aerial radiometric, aeroradiometric survey A survey of radioactivity, usually gamma rays,
taken by an aircraft carrying a gamma-ray spectrometer pointed at the ground surface.
alluvial fan A low, widespread mass of loose rock and soil material, shaped like an open fan
and deposited by a stream at the point where it flows from a narrow mountain valley out onto a
plain or broader valley. May also form at the junction with larger streams or when the gradient of
the stream abruptly decreases.
alluvium, alluvial General terms referring to unconsolidated detrital material deposited by a
stream or other body of running water.
alpha-track detector A passive radon measurement device consisting of a plastic film that is
sensitive to alpha particles. The film is etched with acid in a laboratory after it is exposed. The
etching reveals scratches, or "tracks", left by the alpha particles resulting from radon decay, which
can then be counted to calculate the radon concentration. Useful for long-term (1-12 months)
radon tests.
amphibolite A mafic metamorphic rock consisting mainly of pyroxenes and(or) amphibole and
plagioclase.
n-21 Reprinted from USGS Open-File Report 93-292
-------
argillite, argillaceous Terms referring to a rock derived from clay or shale, or any sedimentary
rock containing an appreciable amount of clay-size material, i.e., argillaceous sandstone.
arid Term describing a climate characterized by dryness, or an evaporation rate that exceeds the
amount of precipitation.
basalt A general term for a dark-colored mafic igneous rocks that may be of extrusive origin,
such as volcanic basalt flows, or intrusive origin, such as basalt dikes.
batholith A mass of plutonic igneous rock that has more than 40 square miles of surface
exposure and no known bottom. •
carbonate A sedimentary rock consisting of the carbonate (COs) compounds of calcium,
magnesium, or iron, e.g. limestone and dolomite.
carbonaceous Said of a rock or sediment that is rich in carbon, is coaly, or contains organic
matter.
charcoal canister A passive radon measurement device consisting of a small container of
granulated activated charcoal that is designed to adsorb radon. Useful for short duration (2-7 days)
measurements only. May be referred to as a "screening" test
chert A hard, extremely dense sedimentary rock consisting dominantly of interlocking crystals of
quartz. Crystals are not visible to the naked eye, giving the rock a milky, dull luster. It may be
white or gray but is commonly colored red, black, yellow, blue, pink, brown, or green.
clastic pertaining to a rock or sediment composed of fragments that are derived from preexisting
rocks or minerals. The most common clastic sedimentary rocks are sandstone and shale.
day 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.
11-22 Reprinted from USGS Open-PHe Report 93-292
-------
delta, deltaic Referring to a low, flat, alluvial tract of larid 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 rocks are divided, the others being sedimentary and
metamorphic.
intermontane A term that refers to an area between two mountains or mountain ranges.
intrusion, intrusive The processes of emplacement or injection of molten rock into pre-existing
rock. Also refers to the rock formed by intrusive processes, such as an "intrusive igneous rock".
kame A low mound, knob, hummock, or short irregular ridge formed by a glacial stream at the
margin of a melting glacier; composed of bedded sand and gravel.
karst terrain A type of topography that is formed on limestone, gypsum and other rocks by
dissolution of the rock by water, forming sinkholes and caves.
lignite A brownish-black coal that is intermediate in coalification between peat and
subbituminous coal.
limestone A carbonate sedimentary rock consisting of more than 50% calcium carbonate,
primarily in the form of the mineral calcite
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 hi temperature, pressure, stress, and the chemical environment
Phyllite, schist, amphibolite, and gneiss are metamorphic rocks.
moraine A mound, ridge, or other distinct accumulation of unsorted, unbedded glacial material,
predominantly till, deposited by the action of glacial ice.
outcrop That part of a geologic formation or structure that appears at the surface of the Earth, as
in "rock outcrop".
percolation test A term used in engineering for a test to determine the water permeability of a
soil. A hole is dug and filled with water and the rate of water level decline is measured.
permeability The capacity of a rock, sediment, or soil to transmit liquid or gas.
phosphate, phosphatic, phosphorite Any rock or sediment containing a significant amount
of phosphate minerals, i.e., minerals containing PO4.
n-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 geomorphic history, and whose topography or landforms differ
significantly from adjacent regions.
placer deposit See heavy minerals
residual Formed by weathering of a material in place.
residuum 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 hi 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 (k'thification) of clay or mud.
shear zone Refers to a roughly linear zone of rock that has been faulted by ductile or non-ductile
processes in which the rock is sheared and both sides are displaced relative to one another.
shrink-swell clay See clay mineral.
siltstone A fine-grained clastic sedimentary rock composed of silt-sized rock and mineral
material and more or less firmly cemented. Silt particles range from 1/16 to 1/256 mm in size:
sinkhole A roughly circular depression in a karst area measuring meters to tens of meters in
diameter. It is funnel shaped and is formed by collapse of the surface material into an underlying
void created by the dissolution of carbonate rock.
slope An inclined part of the earth's surface.
solution cavity A hole, channel or cave-like cavity formed by dissolution of rock.
stratigraphy The study of rock strata; also refers to the succession of rocks of a particular area.
surficial materials Unconsolidated glacial, wind-, or waterborne deposits occurring on the
earth's surface.
tablelands General term for a broad, elevated region with a nearly level surface of considerable
extent.
n-25 Reprinted from TJSGS Open-File Report 93-292
-------
terrace gravel Gravel-sized material that caps ridges and terraces, left behind by a stream as it
cuts down to a lower level.
terrain A tract or region of the Earth's surface considered as a physical feature or an ecological
environment.
till Unsorted, generally unconsolidated and unbedded rock and mineral material deposited directly
adjacent to and underneath a glacier, without reworking by meltwater. Size of grains varies greatly
from clay to boulders.
uraniferous Containing uranium, usually more than 2 ppm.
vendor data Used in this report to refer to indoor radon data collected and measured by
commercial vendors of radon measurement devices and/or services.
volcanic Pertaining to the activities, structures, and extrusive rock types of a volcano.
water table The surface forming the boundary between the zone of saturation and the zone of
aeration; the top surface of a body of unconfined groundwater in rock or soil.
weathering The destructive process by which earth and rock materials, on exposure to
atmospheric elements, are changed in color, texture, composition, firmness, or form with little or
no transport of the material.
H-26
Reprinted from USGS Open-File Report 93-292
-------
APPENDIX C
EPA REGIONAL OFFICES
EPA Regional Offices
State
EPA Region
EPA Region 1
JFK Federal Building
Boston, MA 02203
(617) 565-4502
EPA Region 2
(2AIR:RAD)
26 Federal Plaza
New York, NY 10278
(212) 264-4110
Region 3 (3AH14)
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
niinois 5
Indiana 5
Iowa 7
Kansas .- ...7
Kentucky 4
Louisiana 6
Maine 1
Maryland 3
Massachusetts 1
Michigan 5
Minnesota 5
Mississippi 4
Missouri 7
Montana 8
Nebraska 7
Nevada 9
New Hampshire 1
New Jersey 2
New Mexico 6
New York , 2
North Carolina 4
North Dakota 8
Ohio 5
Oklahoma , 6
Oregon .• 10
Pennsylvania 3
Rhode Island 1
South Carolina 4
South Dakota 8
Tennessee 4
Texas 6
Utah 8
Vermont 1
Virginia 3
Washington 10
West Virginia 3
Wisconsin 5
Wyoming 8
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
State Office Building
Montgomery, AL 36130
(205)242-5315
1-800-582-1866 in state
Charles Tedfoid
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
Connecucut Department of Health
Services
150 Washington Street
Hartford, CT 06106-4474
(203)566-3122
Delaware Marai G. Rejai
Office of Radiation Control
Division of Public Health
P.O. Box 637
Dover, DE 19903
(302) 736-3028
1-800-554-4636 In State
District Robert Davis
of Columbia DC Department of Consumer and
Regulatory Affairs
614 H Street NW
Room 1014
Washington, DC 20001
(202) 727-71068
Florida N. Michael Gilley
Office of Radiation Control
Department of Health and
Rehabilitative Services
1317 Winewood Boulevard
Tallahassee, FL 32399-0700
(904)488-1525
1-800-543-8279 in state
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
11-28 Reprinted from USGS Open-File Report 93-292
-------
Idaho
Indiana
Iowa
Kansas
Kentucky
PatMcGavam
Office of Environmental Health
450 West State Street
Boise, ID 83720
(208) 334-6584
1-800-445-8647 in state
Richard Allen
Illinois Department of Nuclear Safety
1301 Outer Park Drive
Springfield, IL 62704
(217) 524-5614
1-800-325-1245 in state
Lorand Magyar
Radiological Health Section
Indiana State Department of Health
1330 West Michigan Street
P.O. Box 1964
Indianapolis, IN 46206
(317) 633-8563
1-800-272-9723 In State
Donald A. Plater
Bureau of Radiological Health
Iowa Department of Public Health
Lucas State Office Building
Des Moines, IA 50319-0075
(515) 281-3478
1-800-383-5992 In State
Harold Spiker
Radiation Control Program
Kansas Department of Health and
Environment
109 SW 9th Street
6th Floor Mills Building
Topeka, KS 66612
(913) 296-1561
JeanaPhelps
Radiation Control Branch
Department of Health Services
Cabinet for Human Resources
275 East Main Street
Frankfort, KY 40601
(502) 564-3700
Louisiana Matt Schlenker
Louisiana Department of
Environmental Quality
P.O. Box 82135
Baton Rouge, LA 70^84-2135
(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 LeonJ. Rachuba
Radiological Health Program
Maryland Department of the
Environment
2500 Broening Highway
Baltimore, MD 21224
(410) 631-3301
1-800-872-3666 In State
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 SueHendershott
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
H-29
Reprinted from USGS Open-File Report 93-292
-------
Mississippi Silas Anderson
Division of Radiological Health
Department of Health
3150 Lawson Street
P.O. Box 1700
Jackson, MS 39215-1700
(601)354-6657
1-800-626-7739 in state
Missouri Kenneth V. Miller
Bureau of Radiological Health
Missouri Department of Health
1730 East Elm
P.O. Box 570
Jefferson City, MO 65102
(314)751-6083
1-800-669-7236 In State
Montana Adrian C. Howe
Occupational Health Bureau ,
Montana Department of Health and
Environmental Sciences
Cogswell Building A113
Helena, MT 59620
(406)444-3671
Nebraska Joseph Milone
Division of Radiological Health
Nebraska Department of Health
301 Centennial Mall, South
P.O. Box 95007
• Lincoln, NE 68509
(402)471-2168
1-800-334-9491 In State
Neva3a Stan Marshall
Department of Human Resources
505 East King Street
Room 203
Carson City, NV 89710
(702) 687-5394
New Hampshire David Chase
Bureau of Radiological Health
Division of Public Health Services
Health and Welfere Building
Six Hazen Drive
Concord, NH 03301
(603) 271-4674
1-800-852-3345 x4674
New Jersey Tonalee Carlson Key
Division of Environmental Quality
Department of Environmental
Protection
CN415
Trenton, NJ 08625-0145
(609) 987-6369
1-800-648-0394 in state
New Mexico William M. Floyd
Radiation Licensing and Registration
Section
New Mexico Environmental
Improvement Division
1190 St. Francis Drive
Santa Fe,NM 87503
(505)827^300
New York William J. Condon
.Bureau of Environmental Radiation
Protection
New York State Health Department
Two University Place
Albany, NY 12202
(518)458-6495
1-800-458-1158 in state
North Carolina Dr. Felix Fong
Radiation Protection Division
Department of Environmental Health
and Natural Resources
701 Barbour Drive
Raleigh, NC 27603-2008
(919) 571-4141
1-800-662-7301 (recorded info x4196)
North Dakota Arlen Jacobson
North Dakota Department of Health
1200 Missouri Avenue, Room 304
P.O. Box 5520
Bismarck, ND 58502-5520
(701)221-5188
Ohio Marcie Matthews
Radiological Health Program
Department of Health
1224 Kinnear Road - Suite 120
Columbus, OH 43212
(614) 644-2727
1-800-523-4439 in state
n-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-RADONLi 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 demons
Occupational and Radiological Health
Division
Vermont Department of Health
10 Baldwin Street
Montpelier, VT 05602
(802) 828-2886
1-800-640-0601 in state
Virgin Islands Contact the U.S. Environmental
Protection Agency, Region n
in New York
(212) 264-4110
II-31 Reprinted fiom USGS Open-File Report 93-292
-------
Virginia Shelly Ottenbrite
Bureau of Radiological Health
Department of Health
109 Governor Street
Richmond, VA 23219
(804)786-5932
1-800-468-0138 in state
Washington KateColeman
Department of Health
Office of Radiation Protection
Airdustrial Building 5, LE-13
Olympia,WA 98504
(206)753^518
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. Mancini
Geological Survey of Alabama
P.O. Box 0
420 Hackberry Lane
Tuscaloosa, AL 35486-9780
(205) 349-2852
Alaska Thomas E. Smith
Alaska Division of Geological &
Geophysical Surveys
794 University Ave., Suite 200
Fairbanks, AK 99709-3645
(907)479-7147
Arizona Larry D. Fellows
Arizona Geological Survey
845 North Park Ave., Suite 100
Tucson, AZ 85719
(602) 882-4795
Arkansas Norman F. Williams
Arkansas Geological Commission
Vardelle Parham Geology Center
3815 West Roosevelt Rd.
Little Rock, AR 72204
(501) 324-9165
California James F. Davis
California Division of Mines &
Geology
801 K Street, MS 12-30
Sacramento, CA 95814-3531
(916)445-1923
Colorado Pat Rogers (Acting)
Colorado Geological Survey
1313 Sherman St., Rm 715
Denver, CO 80203
(303) 866-2611
Connecticut Richard C. Hyde
Connecticut Geological & Natural
History Survey
165 Capitol Ave., Rm. 553
Hartford, CT 06106
(203) 566-3540
Delaware Robert R. Jordan
Delaware Geological Survey
University of Delaware
101 Penny Hall
Newark, DE 19716-7501
(302)831-2833
Walter Schmidt
Florida Geological Survey
903 W. Tennessee St.
Tallahassee, FL 32304-7700
(904)488^191
Georgia William H. McLemore
Georgia Geologic Survey
Rm. 400
19 Martin Luther King Jr. Dr. SW
Atlanta, GA 30334
(404) 656-3214
Hawaii Manabu Tagomori
Dept. of Land and Natural Resources
Division of Water & Land Mgt
P.O. Box 373
Honolulu, ffl 96809
(808) 548-7539
Idaho Earl H. Bennett
Idaho Geological Survey
University of Idaho
Morrffl 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 LeeC.Gerhard
Kansas Geological Survey
1930 Constant Ave., West Campus
University of Kansas
Lawrence, KS 66047
(913) 864-3965
n-33 Reprinted from USGS Open-File Report 93-292
-------
Kentucky Donald C. Haney
Kentucky Geological Survey
University of Kentucky
228 Mining & Mineral Resources
Building
Lexington, KY 40506-0107
(606)257-5500
Louisiana William E. Marsalis
Louisiana Geological Survey
P.O. Box 2827
University Station
Baton Rouge, LA 70821-2827
(504)388-5320
Maine Walter A. Anderson
Maine Geological Survey
Department of Conservation
State House, Station 22
Augusta, ME 04333
(207)289-2801
Maryland Emery T. Cleaves
Maryland Geological Survey
2300 St Paul Street
Baltimore, MD 21218-5210
(410)554-5500
Massachusetts Joseph A. Sinnott
Massachusetts Office of
Environmental Affairs
100 Cambridge St., Room 2000
Boston, MA 02202
(617)727-9800
Michipan 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, NE 68588-0517
(402)472-2410
Nevada Jonathan G. Price
Nevada Bureau of Mines & Geology
Stop 178
University of Nevada-Reno
Reno, NV 89557-0088
(702)784-6691
New Hampshire Eugene L.Boudette
Dept of Environmental Services
117 James Hall
University of New Hampshire
Durham, NH 03824-3589
(603)862-3160
New Jersey Haig F. Kasabach
New Jersey Geological Survey
P.O. Box 427
Trenton, NJ 08625
(609)292-1185
New Mexico Charles E. Chapin
New Mexico Bureau of Mines &
Mineral Resources
Campus Station
Socorro.NM 87801
(505) 835-5420
New York Robert H. Fakundiny
New York State Geological Survey
3136 Cultural Education Center
Empire State Plaza
Albany, NY 12230
(518)474-5816
H-34
Reprinted from USGS Open-File Report 93-292
-------
North Carolina Charles H. Gardner
North Carolina Geological Survey
P.O. Box 27687
Raleigh, NC 27611-7687
(919)733-3833
North Dakota John P. Bluemle
North Dakota Geological Survey
600 East Blvd.
Bismarck, ND 58505-0840
(701)224-4109
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
Donald A. Hull
DepL of Geology & Mineral Indust.
Suite 965
800 NE Oregon St. #28
Portland, OR 97232-2162
(503)731^4600
Pennsylvania Donald M. Hoskins
Dept. of Environmental Resources
Bureau of Topographic & Geologic
Survey
P.O. Box 2357
Harrisburg, PA 17105-2357
(717) 787-2169
Puerto Rico Ram6n M. Alonso
Puerto Rico Geological Survey
Division
Box 5887
Puerta de 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.Wbodfork
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, niuiana, 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
soil 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
ffl-l 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 aftd 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 !:hanor,u uranium cc. ^entrations 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 "Driftless Area" (fig. 1). It is not covered by
glacial deposits but parts of the area were likely overrun by glaciers at least once. The Driftless
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 fllinoian, 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.
ffl-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
.aLareous, containing pebbles and cobbles of limestc..e, dolomite, und 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
radiometric 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.
ffl-6 Reprinted from USGS Open-File Report 93-292-E
-------
PRELIMINARY GEOLOGIC RADON POTENTIAL ASSESSMENT OF MICHIGAN
by
R. Randall Schwnann
US. Geological Survey
INTRODUCTION
In a survey of 1989 homes conducted during the winters of 1986-88 by the Michigan
Department of Public Health and the U.S. Environmental Protection Agency (EPA), 14 percent of
the homes had indoor radon levels exceeding the EPA's guideline of 4 pCi/L. This chapter
describes the geology and other aspects of Michigan in terms of their potential to generate radon.
This is a generalized assessment of geologic radon potential of rocks, soils, and surficial
deposits of Michigan. The scale of this assessment is such that it is inappropriate for use in
identifying the radon potential of small areas such as neighborhoods, individual building sites, or
housing tracts. Any localized assessment of radon potential must be supplemented with additional
data and information from the locality. Within any area of a given radon potential ranking, there
are likely to be areas with higher or lower radon levels than characterized for the area as a whole.
Indoor radon levels, both high and low, can be quite localized, and there is no substitute for testing
individual homes. Elevated levels of indoor radon have been found in every state, and EPA
recommends that all homes be tested. For more information on radon, the reader is urged to
consult the local or State radon program or EPA regional office. More detailed information on state
or local geology may be obtained from the State geological survey. Addresses and phone numbers
for these agencies are listed in chapter 1 of this booklet
PHYSIOGRAPHIC AND GEOGRAPHIC SETTING
Michigan's geography is unique hi that the State is divided into two parts, an Upper, or
Northern, Peninsula and a Lower, or Southern, Peninsula, separated by Lake Michigan. Most of
Michigan lies in the Central Lowlands province of the north-central United States. The western
part of the Upper Peninsula is part of the Superior Upland province, which is formed on the
crystalline core of the continent known as the North American Shield (or Canadian Shield). The
State can be further subdivided into six main physiographic regions (fig. 1). Politically, Michigan
is divided into 83 counties (fig. 2).
The Hilly Moraines region covers most of the southern half of the Lower Peninsula
(fig. 1). It is characterized by a series of narrow glacial moraines spaced from 10 to 25 miles (16
to 40 km) apart and separated by outwash or till plains (Sommers and others, 1984). Overall, the
area is gently rolling to hilly and contains many lakes and poorly drained areas. This area is the
most densely populated part of the State (fig. 3). Most of the northern half of the Lower Peninsula
is the region known as the High Plains and Moraines. In this region, sandy areas are more
common, the moraines are more massive, and the elevation is generally higher than in the Hilly
Moraines region to the south (Sommers and others, 1984). The area bordering Lake Michigan
along the western edge of the Lower Peninsula is characterized by beaches and dunes that vary
from low and tree-covered to high and bare-sand covered. Many of the sand dunes are
accumulated on glacial moraines.
An area called Eastern Lowlands is found on each of Michigan's two peninsulas. In the
Lower Peninsula, the Eastern Lowlands is an area of very flat topography along the eastern edge of
the peninsula and encompasses a relatively large area surrounding Saginaw Bay. This area was
IV-1 Reprinted from USGS Open-File Report 93-292-E
-------
«£>
CrystallineA
Uplands
G
i Eastern Lowlands
High Plains
and Moraines
0 20 40 60 80 100 mi
till i
Eastern
; Lowlands
Hilly Moraines
1 i i
Figure 1. Physiographic regions of Michigan. K, Keweenaw Peninsula; M,
Marquette Highland; G, Gogebic Upland. After Sommers and others (1984).
-------
Figure 2. Michigan counties.
-------
POPULATION (1990)
C3 0 to 10000
E2 10001 to 50000
E3 50001 to 100000
H 100001 to 500000
• 500001 to 2111687
Figure 3. Population of counties in Michigan (1990 U.S. Census data).
-------
glacial lake floor that was exposed after the ice retreated and the land rose, or rebounded. Much of
the area is underlain by poorly drained soils formed from silt- and clay-rich lake deposits. The
most significant cultural feature of this region is the Detroit metropolitan area in the southeastern
part of the State. The eastern half of the Upper Peninsula is also called Eastern Lowlands, and is
also covered by a veneer of glacial lake deposits, though the deposits are generally thinner than in
the Lower Peninsula and bedrock is exposed at the surface in some places (Sommers and others,
1984). Much of this area is covered by forests, lakes, ponds, and wetlands. The Mackinac
Bridge, built in 1957, spans from St. Ignace on the Northern Peninsula to Mackinaw City on the
Southern Peninsula, connecting the two parts of the State.
The western part of the Upper Peninsula is called the Crystalline Uplands and consists of
glacially-sculpted bedrock mountains and hills and glacial landforms such as moraines and till
plains. The highest point in the State, Mount Arvon, at 1979 feet (603 m), is located in this area
just east of the southern tip of Keweenaw Bay. Subdivisions of the Crystalline Uplands area
include the Gogebic Iron Range, Marquette Highland, and the Keweenaw Peninsula (fig. 1).
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 For more detailed discussions and maps of the geology, the reader is
encouraged to consult Dorr and Eschman (1970), Martin (1936a, 1936b, 1955,1957), Richmond
and Fullerton (1983, 1984,1991), and other reports.
Bedrock geology: Michigan's bedrock geology is characterized by two distinct terranes:
the Michigan Basin, a sedimentary sequence covering all of the Lower Peninsula and the eastern
half of the Upper Peninsula, and the Canadian Shield (also called the North American Shield), an
area of mostly Precambrian igneous and metamorphic rocks in the western part of the Upper
Peninsula. The Michigan Basin covers the entire Lower Peninsula, the eastern part of the Upper
Peninsula, and parts of Wisconsin, Illinois, Indiana, Ohio, Ontario, and much of the Great Lakes.
The basin center lies near the center of the Lower Peninsula. The rocks directly underlying the
glacial deposits in the Michigan Basin include marine limestone, dolomite, sandstone, and shale,
and some continental sandstone, ranging in age from Cambrian to Jurassic (fig. 4). Carbonate
rocks of Silurian and Devonian age and evaporites, including gypsum, anhydrite, and halite, form
karst and other solution features in the northern part of the Lower Peninsula and the adjacent part
of the Upper Peninsula, and in Monroe and Lenawee Counties in the southeastern part of the State
(Western Michigan University, 1981).
The western part of the Upper Peninsula is underlain mostly by rocks of the Canadian
Shield, including granite, gneiss, basalt, quartzite, marble, slate, and schist of Precambrian age.
Precambrian iron-formation is found in Gogebic, Iron, Baraga, Marquette, and Dickinson
Counties. The Keweenaw Peninsula is underlain by Precambrian and Cambrian sandstone and
conglomerate separated by a ridge of Precambrian basalt (fig. 4).
Glacial geology: Glacial deposits of late Wisconsinan age cover nearly all of Michigan. Ice
moved from the northwest, north, and northeast in four major lobes and several large sublobes
(fig. 5). The arrows shown in figure 5 show general directions of ice movement during the last
IV-5 Reprinted from USGS Open-File Report 93-292-E
-------
0 20 40 60 80 100 mi
< i i i i
Figure 4. Generalized bedrock geologic map of Michigan (redrawn from King and Beikman, 1974).
-------
GENERALIZED BEDROCK GEOLOGIC MAP OF MICfflGAN
EXPLANATION OF MAP UNITS
(after Martin, 1936; King and Beikman, 1974; Western Michigan University, 1981).
Jurassic "Red beds" (continental sedimentary rocks)
Pennsylvanian Grand River Fm. (marine sandstones with some shale)
Pennsylvanian Saginaw Fm. (limestone with thin beds of sandstone, shale, coal)
Mississippian Bayport Limestone (limestone and chert); Michigan Fm. (shale, sandstone,
gypsum, limestone, dolomite)
[•••Ji-iXvJ
P-%v£l Mississippian Marshall Sandstone; Coldwater Shale; Sunbury Shale; Berea Sandstone;
Bedford Shale; Ellsworth Shale
Devonian Antrim Shale
Devonian Traverse Group (limestone and shale); Rogers City Limestone;
Dundee Limestone; Detroit River Group (dolomite and sandstone); Sylvania Sandstone;
Bois Blanc Fm. (limestone, dolomite, chert); Macinac Breccia (limestone, limestone breccia)
Silurian Bass Islands Group (dolomite and shale); St. Ignace Dolomite (Northern Peninsula);
Point Aux Chenes Shale (Northern Peninsula)
Silurian Engadine Dolomite; Manistique Group (dolomite and limestone); Burnt Bluff Group
(limestone and dolomite)
Silurian Cataract Group (limestone and shale)
Ordovician Richmond Group (limestone and shale); Collingwood Fm. (shale)
Ordovician Trenton Group (limestone); Black River Group (limestone and dolomite)
Ordovician St Peter Sandstone; Hermansville Fm. (dolomitic sandstone, dolomite)
Cambrian Munising Fm. (sandstone); Mt Simon Sandstone
Precambrian Z Jacobsville Sandstone
Precambrian Y Freda Sandstone; Nonesuch Shale; Copper Harbor Conglomerate
Precambrian Y Porcupine Mountain Fm.; Bergland Hills Rhyolite; Portage Lake Lava
Precambrian X Killarney Granite (Presque Isle Granite); Michigamme Slate; Tyler Slate;
Clarksburg Fm. (mafic volcanic rocks); Siamo Fm. (slate, quartzite, schist); Ajibik Fm.
(quartzite, schist, granite gneiss, granite); Palms Fm. (slate); Wewe, Kona, Mesnard,
Goodrich, and Sunday Fms. (slate, quartzite, graywacke, dolomite, marble, conglomerate)
Precambrian X lion Formation
Precambrian W Granite and granite gneiss
Precambrian W Metamorphosed volcanics and sediments, greenstone
Figure 4 (continued)
-------
0 20 40 60 80 100 mi
' ' ' '
50
100 150 km
EXPLANATION
Glacial lake deposits
. General direction of
ice lobe movement
Figure 5 Map showing names and locations of Wisconsinan glacial lobes, general directions
of ice movement, and glacial lake deposits of Michigan, ^j™™^,^*1^ 1QQn
Where uncertain. After Martin (1955,1957) and Richmond and Fullerton (1983,1984,1991).
-------
advance of each lobe. The Huron lobe advanced from the northwest across the eastern part of the
Upper Peninsula, across the northern part of the Lower Peninsula, and combined with the Erie
lobe in the southeastern part of the State. The latest advance of the Huron lobe deposited red, clay-
rich till from Lake Superior which contrasts with underlying gray to brown sandy till from an
earlier advance in which the Huron lobe entered the area from the northeast (Wayne and Zumberge,
1965). The Saginaw sublobe branched from the main part of the Huron lobe and moved in a
southwest direction, carving Saginaw Bay (fig. 5). The southern part of the area covered by
Saginaw sublobe deposits, in particular, contains many arcuate moraines left by the retreating ice
mass. Huron lobe tills (including the Saginaw sublobe) 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 (Wayne and Zumberge, 1965; Richmond
and Fullerton, 1983,1984,1991). Tills of the Erie and Lake Michigan lobes are derived from
similar source rocks but are more silty and clayey in texture (Wayne and Zumberge, 1965).
The Superior lobe, including the Langlade sublobe, and the Green Bay lobe advanced from
the north and northeast across the western part of the Upper Peninsula (fig. 5), depositing sandy
tills. Green Bay lobe tills are derived from sandstone, limestone, and dolomite, with cobbles and
boulders of igneous and metamorphic rocks. Superior and Langlade tills contain clasts of granite,
metavolcanic rocks, and sandstone (Richmond and Fullerton, 1983,1984,1991). Areas underlain
by significant glacial lake deposits are shaded in figure 5. Glacial lake deposits are typically clays
or silty clays with low permeability; areas underlain by these deposits are commonly poorly
drained and may contain numerous lakes and wetlands.
Uranium geology: Most uranium occurrences in Michigan occur in Precambrian rocks in
the Northern Peninsula (fig. 6). Uranium is associated with mineralized shear and fracture zones
in Precambrian metasedimentary rocks, diabase dikes, and felsites. Granitic gneisses contain
uranium minerals in the granite; in faults, fractures, and shears; and in uranium-bearing pegmatite
dikes. Uranium in metasedimentary rocks occurs mainly in black slates and in iron-formation near
stratigraphic contacts with black slates. Uranium occurrences are also associated with spoil from
iron mines in a number of localities (Johnson, 1976). Uranium occurrences in Precambrian rocks
discussed by Johnson (1976) but not shown on figure 6 include a basal conglomerate in the
Proterozoic-age Ajibik Quartzite, near Negaunee, containing as much as 12.4 ppm equivalent
uranium (eU) and the Proterozoic Mesnard Quartzite in the Palmer area, with 10.7 ppm eU.
Uranium contents of 10-62 ppm were measured in 10 outcrop and glacial boulder samples of the
basal conglomerate of the Proterozoic Goodrich Quartzite in the Palmer area (Parker, 1981). The
uranium, as well as high thorium and rare earth element concentrations, appear to be associated
with a detrital monazite-rich zone in the Goodrich Quartzite that has an outcrop area of about 4 mi2
(Parker, 1981). The Keweenawan (Middle Proterozoic) Nonesuch Shale was found to contain
10-30 ppm eU in the White Pine Mine in Ontonagon County (Johnson, 1976).
In the Southern Peninsula, the Devonian Bell Shale, Devonian and Mississippian Antrim
Shale, and Mississippian Sunbury and Ellsworth Shales contain organic rich (black shale) layers
with higher-than-average amounts of uranium (according to Carmichael (1989), the average crustal
abundance of uranium is 2.5 ppm). 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. Samples of Antrim
Shale in Charlevoix and St. Clair Counties contained from 6 to 36 ppm uranium, and subsurface
gamma-ray logs from a number of wells suggest that these uranium contents may be typical of the
Antrim Shale across the State. The Ellsworth Shale has radioactivity levels in the 6 to 10 ppm eU
IV-9 Reprinted from USGS Open-File Report 93-292-E
-------
^V^^-L e&'s. Kj\ z'>^£zr/X
Upper Precambrian v ^-O^^X^ * v^';?/ <. i' ??§^7
^^jt£££^4$^
KVlirJHlQ Pronnmhrinn ^-5.^ 'i^-'x'H.^ •'^p:H\
Middle Precambrian
Lower Precambrian
Keweenato fault
JMENCMINEe
10
ZO MILES
SCALE
Radioactive occurrences
Bose ond geology from Leith, Lund ond Leith, I93S — Modified after R. C. Vickers, 1956.
Figure 6. Radioactive occurrences in northern Michigan (from Johnson, 1976).
-------
Figure 6 (continued). Radioactive occurrences in northern Michigan. Data from Johnson (1976).
NO., map number, U, highest reported uranium content for each occurrence; -, no data.
NO. NAME COUNTY
1. Erikson Prospect Gogebic
2. Cardiff Mine Iron
3. WausecaMine Iron
4. James Mine Iron
5. Sherwood Mine Iron
6. Zimmerman Mine Iron
7. Buck Mine Iron
8. Book Mine Iron
9. S.MastadonMine Iron
10. TobinMine Iron
11. Anderson-Wiggins Prospect Iron
12. Graphite Quarry Baraga
12. Graphite Quarry Baraga
13. Huron River Baraga
14. Portland Mine Baraga
15. Taxpayer Sample Marquette
16. M&GMine Marquette
16. M&GMine Marquette
16. M&GMine Marquette
17. Float Marquette
18. Greens Creek slate trench Marquette
19. Princeton Mine Marquette
20. Stephenson Mine Marquette
21. Francis Mine Marquette
22. Isham Prospect Dickinson
23. Bergland Prospect Ontonagon
24. Indiana Copper Mine Ontonagon
25. Lavato's Occurrences Iron
26. Float Iron
27. Sargent Prospect Marquette
28. Republic Migmatite Marquette
29. Syenite dike Marquette
30. Voelker Prospect Marquette
31. Greens Creek granite prospect Marquette
32. Goodrich Conglomerate . Marquette
33. Goodrich boulder Marquette
34. Goodrich float Marquette
35. Smith Mine Marquette
36. Leitch and Isham sec. 13 Dickinson
37. Leitch and Isham sec. 12 Dickinson
38. Joe Forsythe Prospect Baraga
39. HaggettDike Baraga
40. Big Eric's Crossing Baraga
41. Taylor Mine Baraga
HOST ROCK
iue Isle Gneiss
U
40ppm
410 ppm
150 ppm
200 ppm
0.513%
140 ppm
100 ppm
100 ppm
140 ppm
20 ppm
0.1%
40 ppm
170 ppm
350 ppm
20 ppm
50 ppm
0.3%
0.87%
0.1%
120 ppm
0.12%
0.11%
200 ppm
418 ppm
30 ppm
14.7 ppm
18 ppm
granite in Pr<
iron formation
iron formation (?)
iron formation (?)
pitchblende, oxidized iron formation
iron formation (?)
pitchblende, slate, iron formation
iron formation (?)
ironformation(?)
iron formation (?)
granite in Margeson Creek Gneiss
metadiabase dike in Michigamme Slate
Michigamme Slate
shears in Michigamme Slate
iron formation
oxidizediron formation
unoxidized iron formation
black slate
ferruginous slate
slate and quartzite in Compeau Creek
Gneiss
iron formation
iron formation
pitchblende, iron formation
fracture zones in granite, granite
altered felsite
felsite
Margeson Creek Gneiss
(shear zone)
Margeson Creek Gneiss
Bell Creek (granite) Gneiss
leucocratic part of migmatite
syenite dike in granite
granite gneiss (shear zone)
pegmatite in granite
base of Goodrich Quartzite
Goodrich Quartzite
Goodrich Quartzite
iron formation
boitite schist in granite gneiss
shear zone in granite
iron formation
diabase dike in granite gneiss
Lower Precambrian granite
brecciated slate in Baraga Group (?)
180 ppm
300 ppm
200 ppm
-------
range in subsurface well logs, and the Sunbury Shale has values similar to that of the Antrim Shale
(J.K. Otton, unpublished report, 1986).
SOILS
Most of the soils in Michigan are either Spodosols, Alfisols, or Inceptosols (U.S.
Department of Agriculture, 1987). Most of the Upper Peninsula and the northern half of the
Lower Peninsula are covered by Haplorthods, a type of Spodosol, and by smaller areas of
Psammaquents (a permanently or seasonally wet type of Entisol), Eutroboralfs, and Glossoboralfs
(generally wet Alfisols). A relatively large area surrounding Saginaw Bay and the "thumb" area is
covered by Haplaquepts, seasonally wet Inceptosols. The southern half of the Lower Peninsula is
covered by Hapludalfs, a moist to seasonally dry form of Alfisol (U.S. Department of Agriculture,
1987). Soils in Michigan are generally moist to wet and contain subsurface accumulations of iron
and aluminum oxides or clay. Many of the soils contain significant accumulations of organic
matter in the upper horizons (Whiteside and others, 1968).
A generalized soil permeability map (fig. 7) suggests that much of the northern part of the
Lower Peninsula is covered by soils with high permeability. However, it is important to point out
that the "permeability" values given in the SCS soil surveys are actually water percolation rates.
These values correspond fairly well to actual permeability to water moving through the soil.
Permeability to gas flow is similar to that for water except that it is also dependent on soil moisture;
water in the soil pores may partially or completely obstruct gas flow in otherwise "highly
permeable" soils, giving these soils a low gas permeability when the soils are wet Because many
of the soils in Michigan are moist to wet at least seasonally, particularly in the northern part of the
State and around Saginaw Bay, their gas permeability is usually lower than that indicated by the
water permeability.
INDOOR RADON DATA
Indoor radon data from 1989 homes tested in the State/EPA Residential Radon Survey
conducted in Michigan during the winters of 1986-88 are listed in Table 1 and shown in figure 8.
Data are shown in figure 8 only for those counties with 5 or more data values. The maximum
value recorded in the survey was 162 pCi/L in Republic Township, southwestern Marquette
County. The statewide average radon value in this survey was 2.4 pCi/L, and 14 percent of the
homes tested had screening indoor radon levels exceeding 4 pCi/L. In this discussion, "elevated"
refers to screening indoor radon levels greater than 4.0 pCi/L.
Counties with average screening indoor radon levels greater than 4.0 pCi/L include
Hillsdale, Kalamazoo, Lenawee, and Washtenaw (fig. 8). More than 50 percent of the homes
tested in Hillsdale and Lenawee Counties had indoor radon levels greater than 4 pCi/L (fig. 8,
Table 1). The highest county screening radon average is 8.2 pCi/L in Lenawee County. Most
areas of Michigan have characteristically low (<2 pCi/L) to moderate (2-4 pCi/L) average indoor
radon values. Areas with significant numbers of elevated indoor radon values are the South-
Central part of the Lower Peninsula, the northern part of the Lower Peninsula (from Antrim to
Alpena County and north), and the Gogebic Iron Range and Marquette Highland (fig. 8).
As part of EPA's cooperative State Indoor Radon Grant program, screening indoor radon
tests were conducted by the Michigan Department of Public Health in about 230 of the 350 homes
in Republic Township, southwestern Marquette County, where the highest indoor radon level in
IV-12 Reprinted from USGS Open-File Report 93-292-E
-------
0 20 40 60 80 100 mi
I L-r-1 ' ' J
50
100
EXPLANATION
LOW (< 0.6 in/hr)
MODERATE (0.6 - 6.0 in/hr)
HIGH (> 6.0 in/hr)
Figure?. Generalized soil permeability map of Michigan. Boundaries are approximate.
Compiled by Kevin M. Schmidt, U.S. Geological Survey, from Martin (1955,1957) and
SCS soil survey data.
-------
Bsmt. & 1st Floor Rn
%24pCi/L
AH K-^VWWI otolO
11 P^J 11 to 20
12 ES^ 21 to 40
3 0 41 to 60
1 H 61 to 80
0 • 81 to 100
13 ' ' Missing Data
(< 5 measurements)
100 Miles
Bsmt. & 1st Floor Rn
Average Concentration (pCi/L)
J 0.0 to 1.9
24 t\\\M 2.0 to 4.0
13
4.1 to 8.2
Missing Data
(< 5 measurements)
100 Miles
Figure 8. Screening indoor radon data from the EPA/State Residential radon Survey of Michigan,
1956-88, 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
Michigan conducted during 1986-88. Data represent 2*7 day charcoal canister measurements
from the lowest level of each home tested.
COUNTY
ALCONA
ALGER
ALLEGAN
ALPENA
ANTRIM
ARENAC
BARAGA
BARRY
BAY
BENZffi
RKRfcTRN
BRANCH
CALHOUN
CHARLEVOIX
CHEBOYGAN
CHIPPEWA
CLARE
CLINTON
CRAWFORD
DELTA
DICKINSON
EATON
EMMET
GENESEE
GLADWIN
GOGEBIC
GRAND TRAVERSE
GRATIOT
Hn,T,SDAT,F,
HOUGHTON
HURON
INGHAM
IONIA
IOSCO
IRON
ISABELLA
JACKSON
KALAMAZOO
KALKASKA
KENT
KEWEENAW
NO. OF
MEAS.
4
11
8
18
8
3
22
14
18
3
44
9
31
12
14
8
3
18
1
41
77
21
4
42
4
11
21
7
12
18
15
42
10
9
38
12
23
55
5
73
6
MEAN
0.6
1.1
1.3
0.8
1.1
0.7
2.4
1.5
1.2
0.9
1.8
3.7
3.8
2.5
1.0
1.0
1.1
3.8
0.3
2.0
3.7
3.4
1.2
1.8
1.4
1.0
1.9
* 1.3
6.7
1.8
1.5
3.3
1.7
0.5
3.8
2.1
3.9
4.5
1.0
1.8
2.1
GEOM.
MEAN
0.4
0.8
1.1
0.7
- 0.7
0.7
1.1
1.0
0.9
0.8
1.3
2.1
2.9
1.9
0.5
0.8
1.0
2.4
0.3
1.2
2.5
2.4
0.6
1.3
1.0
0.7
1.4
1.2
4.3
0.7
0.9
2.4
1.2
0.4
2.3
1.5
3.3
3.2
0.6
1.4
1.4
MEDIAN
0.4
0.6
1.4
0.7
1.0
0.7
1.0
1.4
0.9
0.9
1.4
2.4
2.8
1.7
0.7
0.9
1.3
3.2
0.3
1.1
2.3
2.4
0.8
1.5
1.5
0.5
1.1
1.1
4.9
0.8
0.7
2.2
1.6
0.5
2.0
1.5
3.1
3.5
1.1
1.5
1.0
STD.
DEV.
0.5
1.0
0.6
0.5
1.0
0.1
6.0
1.1
1.0
0.4
1.6
4.5
3.0
1.7
1.3
0.6
0.7
3.2
0.0
3.1
4.0
3.2
1.3
1.4
1.0
0.9
1.5
0.6
8.5
4.1
1.5
4.1
1.2
0.3
4.3
2.4
2.4
3.7
0.9
1.5
2.1
MAXIMUM
1.3
3.3
2.1
L9
2.5
0.7
29.1
3.1
3.5
1.3
8.2
14.9
14.9
4.7
5.1
2.1
1.7
11.9
0.3
16.8
23.9
13.8
2.9
6.3
2.3
3.1
5.1
2.3
32.8
18.1
4.7
26.2
3.6
1.1
14.4
9.4
9.6
18.1
2.3
8.3
5.1
%>4pCi/L
0
0
0
0
0
0
5
0
0
0
9
22
45
33
7
0
0
33
0
7
29
29
0
7
0
0
14
0
67
6
13
17
0
0
24
8
35
44
0
7
33
%>20pCi/L
0
0
0
0
0
0
5
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
8
0
0
2
0
0
0
0
0
0
0
0
0
-------
TABLE 1 (continued). Screening indoor radon data for Michigan.
COUNTY
LAPRRR
T.T-FT.ANAU
LENAWEE
LIVINGSTON
LUCE
MACKINAC
MACOMB
MANISTEE
MAROUETTE
MASON
MECOSTA
MENOMINEE
MIDLAND
MISSAUKEE
MONROE
MONTCALM
MONTMORENCY
MUSKEGON
OAKLAND
OGEMAW
ONTONAGON
OSCEOLA
OSCODA
OTSEGO
OTTAWA
PRESQUEISLE
ROSCOMMON
SAGINAW
SANILAC
SCHOOLCRAFT
SHIAWASSEE
ST.CLAIR
ST. JOSEPH
TUSCOLA
VANBUREN
WASHTENAW
WAYNE
WEXFORD
NO. OF
MEAS.
13
6
37
21
7
6
92
6
139
6
5
22
16
7
20
10
8
34
158
7
24
9
4
15
36
12
9
41
'21
8
18
60
13
17
15
93
177
2
MEAN
2.7
1.6
8.2
3.3
1.0
0.8
1.2
1.7
3.4
1.3
2.2
1.5
0.7
1.9
1.8
1.6
1.5
1.1
. 2.5
1.1
0.9
1.2
0.9
2.3
1.8
3.0
0.9
1.4
2.1
0.6
2.7
1.1
2.7
2.0
0.7
4.8
1.3
1.4
GEOM.
MEAN
1.9
1.3
4.5
2.0
0.8
0.5
0.9
1.2
1.5
0.9
1.8
1.1
0.5
1.7
1.3
1.4
1.2
0.9
1.5
0.9
0.7
1.0
0.7
1.5
1.2
1.8
0.7
1.0
1.3
0.5
2.1
0.7
2.3
1.6
0.5
2.8
1.1
1.4
MEDIAN
1.4
1.5
5,0
2.4
0.7
0.6
1.0
1.0
1.5
0.7
1.6
1.1
0.5
1.9
2.0
1.5
1.2
1.0
1.3
0.9
0.7
1.0
0.8
1.9
1.1
1.7
0.7
1.1
1.4
0.5
1.9
0.9
2.3
1.7
0.5
3.3
1.0
1.4
STD.
DEV.
2.8
1.0
11.7
3.1
0.9
0.9
0.9
1.9
13.9
1.2
1.8
1.3
0.5
0.9
1.1
0.8
1.1
0.7
3.4
0.9
0.5
0.8
0.7
1.8
1.9
3.3
0.8
1.2
3.1
0.5
2.1
1.1
2.0
1.4
0.5
6.7
1.2
0.0
MAXIMUM
10.3
2.7
69.7
13.0
2.7
2.4
5.8
5.5
162.1
3.2
5.2
5.3
1.6
3.1
3.9
2.9
4.0
3.5
29.5
3.1
2.0
2.5
1.9
6.3
9.8
11.9
2.9
5.8
14.9
1.4
9.5
7.2
8.5
5.2
1.7
47.7
10.5
1.4
%>4pCi/L
23
0
51
33
0
0
2
17
12
0
20
5
0
0
0
0
0
0
16
0
0
0
0
13
8
33
0
5
10
0
11
2
15
12
0
37
3
0
%>20 pCi/L
0
0
5
0
0
• o
0
0
1
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
3
0
0
-------
the State/EPA survey was measured. Of the 230 homes tested, 84 percent had screening indoor
radon levels exceeding 4 pCi/L and nearly 20 percentM the homes had screening levels greater
than 20 pCi/L. About 5 percent of the homes tested hail screening indoor radon levels exceeding
100 pCi/L. The highest indoor radon level of those tested was 389 pCi/L in the basement of a
home in the Republic area (R. DeHaan, personal communication, 1992).
GEOLOGIC RADON POTENTIAL
A map of equivalent uranium (eU) concentrations in surficial deposits (fig. 9) derived from
National Uranium Resource Evaluation (NURE) aeroradiometric data (Duval and others, 1989)
suggests that most of Michigan is covered by soils and surficial deposits with low surface
radioactivity. Only one area of the State has a radiometric signature exceeding 2.0 parts per million
(ppm) eU. This area extends from central Sanilac to eastern Hillsdale County along the
southeastern border of the State (fig. 9). This eastern part of this area appears to coincide with the
pattern of bedrock exposure of the Antrim Shale or with glacial deposits derived from it. The
western part of the area, comprising southern Hillsdale, central Lenawee, and southern Washtenaw
Counties, is east of the Antrim Shale outcrop area and also has an eU signature in the 2-3 ppm
range (fig. 9). This area of higher radioactivity may be associated with glacial deposits containing
transported Antrim Shale fragments and(or) Coldwater Shale fragments.
The eU pattern across the State is generally consistent with the geology, although the
radiometric signature of the State as a whole appears lower than expected given the known higher
uranium concentrations in the bedrock sources of the glacial deposits in several areas, and
compared with the radiometric signature of non-glaciated areas on a national scale (see Duval and
others, 1989). Recent studies (for example, Lively and others, 1991; Schumann and others, 1991)
suggest that some 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 in some areas. Glacial crushing and grinding of the rocks exposes more radionuclides
at grain surfaces, enhancing radionuclide mobility and radon emanation. In addition, glacial drift
may in many cases have higher permeability than the bedrock from which it is derived.
Elevated indoor radon levels in Iron, Dickinson, and Marquette Counties are probably
associated with igneous and metamorphic bedrock exposed at the surface or under shallow glacial
drift on this area, particularly granitic intrusive rocks in the Marquette and Gogebic Ranges.
Localized elevated radon levels may occur in homes underlain by mineralized shear and fracture
zones in Precambrian metasedimentary rocks, diabase dikes, felsites, in black slates, and in iron-
formation near stratigraphic contacts with black slates (see the uranium geology section earlier in
this report). Some elevated indoor radon levels in the Republic area, southwestern Marquette
County, may be associated with a northwest-trending, mylonitized (and possibly mineralized)
shear zone. Fault and shear zones are commonly areas of locally elevated radon because these
zones typically have higher permeability than the surrounding rocks, because they are preferred
zones of uranium mineralization, and because they are pathways for potentially uranium-, radium-,
and(or) radon-bearing fluids and gases to migrate (Gundersen, 1991). Rock types in the area that
are likely to cause a radon problem include black slate of the Michigamme Formation, the Ajibik
Quartzite, granitic gneiss of the southern Marquette Complex, and iron-formation. The high radon
levels in the Republic area are likely due to proximity to the shear zone, contact with one or more
IV-17 Reprinted from USGS Open-File Report 93-292-E
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Figure 9. Aerial radiometric map of Michigan (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.
-------
of the rock types lised above, use of iron mine tailings as fill in housing construction, or a
combination of these factors. t
Sedimentary rocks, primarily Ordovlcian carbonate rocks, in Menominee, eastern
Marquette, and Alger Counties, form the northwestern edge of the Michigan Basin and have
moderate radon potential. Precambrian and Cambrian sandstones in this area likely generate lower
radon levels than adjacent carbonate rocks.
The northern part of the Lower Peninsula that is underlain by the Antrim black shale and by
glacial deposits derived from the Antrim Shale has the potential to produce elevated indoor radon
levels. This area includes parts of Manistee, Benzie, Leelanau, Grand Traverse, Antrim, Ostego,
Charlevoix, Cheboygan, Montmorency, and Alpena Counties. Elevated indoor radon levels in
Presque Isle County may be associated with karst or other solution features in the limestone
bedrock or with glacial deposits and soils derived from the carbonate rocks.
The Antrim Shale, and glacial deposits derived from it, also underlie an area in the
southeastern part of the Lower Peninsula from Lenawee to St. Clair County (fig. 4). The Antrim
or Coldwater shales, or glacial deposits containing either or both of these shales as a significant
source component, appear to be the cause of elevated indoor radon levels in Lenawee, Washtenaw,
and Oakland Counties. Wayne, Macomb, and St Clair Counties are covered by glacial lake
deposits with relatively low permeability and poor drainage characteristics, and thus do not appear
to have the potential for significant indoor radon problems, although localized elevated levels are
more likely to be found in the western and northern suburbs of Detroit than in other parts of these
counties.
A significant number of the homes sampled in the south-central part of the Lower Peninsula
also had elevated screening indoor radon levels. This area includes parts or all of the following
counties: Branch, Hillsdale, Lenawee, Kalamazoo, Calhoun, Jackson, Washtenaw, Eaton,
Ingham, Livingston, and Clinton. The elevated radon levels in this area are probably due to
several geologic factors or combinations of factors. The area is underlain primarily by glacial
deposits derived from sandstone, limestone, and shale, but may also contain some black shale
fragments from sources to the east (Antrim Shale). Though they have lower uranium contents than
the Antrim Shale, "gray shales" such as the Coldwater and Ellsworth shales contain sufficient
uranium to generate elevated radon levels in many areas. Southern Michigan also has a higher
concentration of moraines than other parts of the State, and the soils may be relatively drier, and
thus more permeable to gas, on these topographically higher areas than in low-lying areas.
Kalamazoo and St. Joseph Counties contain relatively large amounts of highly permeable glacial
outwash.
Some elevated radon levels in southern Michigan may be related to geologic structural
features, such as faults or fracture systems. The Howell anticline, a structural feature that is likely
associated with faults or fracture zones, underlies parts of Livingston, Shiawassee, and Clinton
Counties and may be a source for high radon in those areas. Faults associated with an oilfield in
Hillsdale county may be a source for elevated radon there. More detailed studies would be needed
to definitively identify the source(s) of elevated radon in southern Michigan; nevertheless, the area
has a moderate to high radon potential overall.
The remainder of the State has a generally low radon potential (although very localized
elevated indoor radon levels could be found almost anywhere in Michigan). Low radon potential is
generally associated with rocks and soils with low radium content, low soil permeability, wet
soils, or some combination of these factors.
IV-19 Reprinted from USGS Open-File Report 93-292-E
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SUMMARY
Discrete areas of Michigan were delineated based on the data discussed in the preceding
sections and designated geologic radon potential areas (fig. 10). For each area, a Radon Index
(RI) and Confidence Index (CI) were determined (Table 2). For additional information on the
methods and data used to derive the RI and CI, refer to the introduction chapter of this booklet.
Area labelled GLA are underlain primarily by glacial lake deposits which typically have low
soil permeability and poor drainage characteristics. In Michigan the source rocks for these lake
deposits do not contain significant amounts of radioactive minerals. Areas labelled GLA have a
low radon potential (RI=7) with a moderate confidence (CI=9) assigned to this ranking. Area
LML, Lake Michigan lobe deposits, is underlain by sandy to clayey glacial deposits and some
glacial lake deposits. This area has a low radon potential (RI=8) with moderate confidence (CI=9).
Area 8MB, the south-central part of the Michigan Basin, is underlain by sandy and silty glacial
deposits derived from sandstones, gray shales, limestones, and dolomites. This area has a
moderate radon potential (RI=10) with a moderate confidence index (CI=9). Area NMB, the
north-central part of the Michigan Basin, is geologically similar to area SMB. Soils in this area
have higher water permeability but are also generally wetter than those to the south, which may
account for their low radon potential (RI=8). There is moderate confidence (CI=8) associated with
this ranking. An area of Paleozoic-age carbonate rocks and sandstones at the outer edge of the
Michigan Basin has been designated OMB. Carbonate (limestone and dolomite) bedrock and
glacial deposits derived from carbonate rocks have moderate radon potential, whereas areas
underlain by sandstones have generally lower radon potential, although locally moderate or high
indoor radon levels are possible anywhere in the area. This area is assigned an overall moderate
(RI=10) radon potential with moderate confidence (CI=9).
Area AS, underlain by the Antrim black shale, has a moderate radon potential (RI=10) and
a moderate associated confidence index (CI=9). Homes in this area may have indoor radon levels
ranging from less than 1 to more than 4 pCi/L depending on their individual settings and
construction characteristics. Area SAS is also underlain in part by the Antrim Shale, but is covered
by glacial lake deposits. This area has moderate radon potential (RI=9) and confidence (CI=9).
Area SLM (Saginaw lobe moraine area) contains counties with high and moderate indoor
radon averages. There are several possible explanations, depending on specific location, for the
elevated radon values in this area (see the preceding geologic radon potential section). This area is
assigned a high radon potential (RI=12) with moderate confidence (CI=9). Area MKG includes
the Marquette Highland, Keweenaw Peninsula, and Gogebic Range in the Northern Peninsula.
Locally elevated radon levels occur in areas underlain by granites, in the vicinity of iron-formation,
and near fault and shear zones. Overall, the area has a moderate geologic radon potential (RI=11)
with moderate confidence in the assessment (CI=9).
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-20 Reprinted from USGS Open-FUe Report 93-292-E
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TABLE 2. Radon Index (RI) and Confidence Index (CI) scores for geologic radon potential areas
of Michigan. See figure 10 for locations and abbreviations of areas.
FACTOR
INDOOR RADON
RADIOACTIVITY"
GEOLOGY
SOIL PERM.
ARCHITECTURE
GFE POINTS
TOTAL
RI
1
1
1
1
3
0
7
GLA
CI
3
2
2
2
9
LML
RI CI
1
1
1
2
3
0
8
3
2
2
2
9
AREA
SMB
RI Q
2
1
2
2
3
0
10
3
2
. 2
2
9
NMB
RI
1
1
2 .
2
2
0
8
CI
2
2
2
2
8
RANKING LOW MOD
LOW MOD
MOD MOD
LOW MOD
FACTOR
INDOOR RADON
RADIOACTIVITY
GEOLOGY
SOIL PERM.
ARCHITECTURE
GFE POINTS
TOTAL
AS
RI CI
2
1
3
2
2
0
10
3
2
2
2
—
—
9
SAS
RI CI
1
2
2
1
3
0
9
3
2
2.
2
—
—
9
SLM
RI CI
3
1
3
2
3
0
12
3
2
2
2
—
—
9
MKG
RI CI
2
1
3
2
3
0
11
3
2
2
2
—
—
9
OMB
RI CI
2
1
2
2
3
0
10
3
2
2
2
—
—
9
RANKING MOD MOD
MOD MOD
HIGH MOD
MOD MOD
MOD MOD
RADON INDEX SCORING:
Radon potential category
LOW
MODERATE/VARIABLE
HIGH
Point range
3-8 points
9-11 points
> 1 1 points
Probable screening indoor
. radon average for area
<2pCi/L
2-4pCi/L
>4pCi/L
Possible range of points = 3 to 17
CONFIDENCE INDEX SCORING:
LOW CONFIDENCE
MODERATE CONFIDENCE
HIGH CONFIDENCE
4-6 points
7-9 points
10 - 12 points
Possible range of points = 4 to 12
IV-21 Reprinted from USGS Open-Kle Report 93-292-E
-------
20 40 60 80 100 mi
GEOLOGIC RADON POTENTIAL
| | LOW (< 2 pCi/L)
| MODERATE or VARIABLE (2 - 4 pCi/L)
I HIGH (> 4 pCi/L)
Figure 10. Geologic radon potential areas of Michigan. Radon levels in parentheses
indicate expected average screening indoor radon levels for all homes, taken as a group, in
the indicated geologic radon potential area. Refer to text for discussion of areas.
-------
REFERENCES CITED IN THIS REPORT
AND GENERAL REFERENCES RELAVENT TO RADON IN MICHIGAN
Carmichael, R.S., 1989, Practical Handbook of physical properties of rocks and minerals: Boca
Raton, Fla., CRC Press, 741 p.
Dorr, J.A., Jr., and Eschman, D.F., 1970, Geology of Michigan: Ann Arbor, Mich., The
University of Michigan Press, 476 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.
Ghahremani, D.T., 1987 , Radon and hydrocarbon prospecting in basins with shallow black shale
deposits: AAPG Bulletin, v. 71, p. 1104.
Grace, J.D., 1985, Radon emanations from basement floors: Geological Society of America,
Abstracts with Programs, v. 17, no. 5, p. 290.
Grace, J.D., 1986, Variations in radon soil gas geochemistry in Southwest Michigan: Geological
Society of America, Abstracts with Programs, v. 18, no. 4, p. 290.
Grace, J.D., 1988, Variation in radon activity from cement basement floors, in Proceedings of
V.M. Goldschmidt Conference, Baltimore, MD, May 11-13,1988, p. 44.
Gundersen, L.C.S., 1991, Radon in sheared metamorphic and igneous rocks, in Gundersen,
L.C.S., and Wanty, R.B. (eds), Field studies of radon hi rocks, soils, and water: U.S.
Geological Survey Bulletin 1971, p. 39-50.
Horrocks, R., 1979, The use of radon for oil and gas exploration, in Hydrocarbon potential, the
Michigan Basin; the way ahead: Proceedings of the Michigan Basin Geological Society
Annual Field Conference, Lansing, Mich., May 17-18,1979, p. 20.
Johnson, Carol, 1976, Modes of occurrence of uranium and thorium in the Precambrian rocks of
the Upper Peninsula of Michigan, in KalliokosM, J., Uranium and thorium occurrences in
Precambrian rocks, Upper Peninsula of Michigan and northern Wisconsin, with thoughts
on other possible settings: Report prepared for the U.S. Energy Research and
Development Administration, Grand Junction , CO, GJBX 48(76), p. 13-159.
King, P.B., and Beikman, Helen M., 1974, Geologic Map of the United States: U.S. Geological
s Survey, scale 1:2,500,000.
Lively, Richard, Steck, Daniel, and Brasaemle, Bruce, 1991, A site study of soil characteristics
and soil gas radon in Rochester, Minnesota: Center for Urban and Regional Affairs report
CURA 91-2, 15 p.
Martin, Helen M., 1936a, The centennial geologic map of the Northern Peninsula of Michigan:
Michigan Department of Conservation, Geological Survey Division Publication 39, scale
. 1:500,000.
IV-23 Reprinted from USGS Open-FUe Report 93-292-E
-------
Martin, Helen M., 1936b, The centennial geologic map of the Southern Peninsula of Michigan:
Michigan Department of Conservation, Geological Survey Division Publication 39, scale
1:500,000.
Martin, Helen M., 1955, Map of the surface formations of the Southern Peninsula of Michigan:
Michigan Department of Conservation, Geological Survey Division Publication 49, scale
1:500,000.
Martin, Helen M., 1957, Map of the surface formations of the Northern Peninsula of Michigan:
Michigan Department of Conservation, Geological Survey Division Publication 49, scale
1:500,000.
Michigan Department of Public Health, 1988, Indoor radon in Michigan, Report to the Governor:
Michigan Department of Public Health report RH-947,116 p.
Moed, B.A., Prichard, H.M., Gesell, T.F. and Adams, J.A.S., 1977, Potential radiometric
impact of technologically mobilized radon-222 and its progeny: Geological Society of
America, Abstracts with Programs, v. 9, no. 7, p. 1097-1098.
Parker, B.K., 1981, Rare earth and related elements in the Goodrich Quartzite, Marquette County,
Michigan: Michigan Department of Natural Resources, Geological Survey Division report,
21 p.
Paull, R.K., and Paull, R.A., 1977, Geology of Wisconsin and upper Michigan including parts of
adjacent states: Dubuque, Iowa, Kendall/Hunt Publishing Company, 232 p.
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 NL-15,
Minneapolis 4°x6° quadrangle, 1983; sheet NL-16, Lake Superior 4°x6° quadrangle, 1984;
sheet NK-15, Des Moines 4°x6° quadrangle, 1991; sheet NK-16, Chicago 4°x6°
quadrangle, 1983; scale 1:1,000,000.
Schumann, R.R., Peake, R.T., Schmidt, K.M., and Owen, D.E., 1991, Correlations of soil-gas
and indoor radon with geology in glacially derived soils of the northern Great Plains, in
Proceedings of the 1990 International Symposium on Radon and Radon Reduction
Technology, Volume 2, Symposium Oral Papers: U.S. Environmental Protection Agency
report EPA/600/9-9 l/026b, p. 6-23-6-36.
Sims, P.K., 1976, Precambrian tectonics and mineral deposits, Lake Superior region: Economic
Geology, v. 71, p. 1092-1127.
Sims, P.K., 1992, Geologic map of Precambrian rocks, southern Lake Superior region,
Wisconsin and northern Michigan: U.S. Geological Survey Miscellaneous Investigations
Map 1-2185, scale 1:500,000.
Sommers, L.M., Darden, J.T., Harman, J.R., and Sommers, L.K., 1984, Michigan: A
geography: Boulder, Colo., Westview Press, 254 p.
IV-24 Reprinted firom USGS Open-File Report 93-292-E
-------
Stock, D.J., 1987 , Geological variation of radon sources and indoor radon concentrations along
the southwestern edge of the Canadian Shield: Health Physics, v. 52, p. S40.
Stock, D.J., 1988, Geological variation of radon sources and indoor radon along the southwestern
edge of the Canadian Shield, in M.A. Marikos and R.H. Hansman (eds), Geologic causes
of natural radionuch'de anomalies: Proceedings of the GEORAD Conference, St Louis,
MO, Missouri Department of Natural Resources Special Publication 4, p. 17-23.
U.S. Department of Agriculture (Soil Conservation Service), 1987, Soils: U.S. Geological
Survey National Adas sheet 38077-BE-NA-07M-00, scale 1:7,500,000.
Wayne, W.J., and Zumberge, J.H., 1965, Pleistocene geology of Indiana and Michigan, in
Wright, H.E., Jr., and Frey, D.G. (eds.), The Quaternary of the United States: Princeton,
NJ, Princeton University Press, p. 63-84.
Western Michigan University, 1981, Hydrogeologic atlas of Michigan: Kalamazoo, Michigan,
Western Michigan University, 35 plates, scale 1:500,000.
Whiteside, E.P., Schneider, I.F., and Cook, R.L., 1968^ Soils of Michigan: Agricultural
Experiment Station, Michigan State University, Extension Bulletin E-630,52 p.
IV-25 Reprinted from USGS Open-File Report 93-292-E
-------
-------
EPA's Map of Radon Zones
The USGS' Geologic Radon Province Map is the technical foundation for EPA's Map
of Radon Zones. The Geologic Radon Province Map defines the radon potential for
approximately 360 geologic provinces. EPA has adapted this information to fit a county
boundary map in order to produce the Map of Radon Zones.
The Map of Radon Zones is based on the same range of predicted screening levels of
indoor radon as USGS' Geologic Radon Province Map. EPA defines the three zones as
follows: Zone One areas have an average predicted indoor radon screening potential greater
than 4 pCi/L. Zone Two areas are predicted to have an average indoor radon screening
potential between 2 pCi/L and 4 pCi/L. Zone Three areas are predicted to have an average
indoor radon screening potential less than 2 pCi/L.
Since the geologic province boundaries cross state and county boundaries, a strict
translation of counties from the Geologic Radon Province Map to the Map of Radon Zones
was not possible. For counties that have variable radon potential (i.e., are located in two or
more provinces of different rankings), the counties were assigned to a zone based on the
predicted radon potential of the province in which most of its area lies. (See Part I for more
details.)
MICHIGAN MAP OF RADON ZONES
The Michigan Map of Radon Zones and its supporting documentation (Part IV of this
report) have received extensive review by Michigan geologists and radon program experts.
The map for Michigan 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. >
Three county designations do not strictly follow the methodology for adapting the
geologic provinces to county boundaries. EPA and the Michigan Department of Public
Health have determined that the most appropriate zone desgination for Wayne, Macomb, and
St. Clair counties is Zone 3. The Zone 3 designation for these counties does not mean that
there is no risk of finding elevated indoor radon levels. However, the indoor radon data for
these counties indicate less radon potential than that indicated by the geology. Elevated
levels have been found in each of these counties, but as a whole the radon potential is lower
than expected.
Although the information provided in Part IV of this report — the State chapter entitled
"Preliminary Geologic Radon Potential Assessment of Michigan" — 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
Michigan 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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