United States
Environmental Protection
Agency
Air and Radiation
(8604J)
402-R-93-061
September 1993
wEPA EPA's Map of Radon Zones
SOUTH DAKOTA
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EPA'S MAP OF RADON ZONES
SOUTH DAKOTA
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)
cof Radiation and Ind°°r Air (ORIA) in «>nJ™cti<« 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
Dnbiel, 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 Stale programs and the Association of American State
Geologists (AASG) for providing a liaison with the State geological surveys In addition
appreciation is expressed to all of the State radon programs and geological surveys for their
technical input and review of the Map of Radon Zones.
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TABLE OF CONTENTS
I. OVERVIEW
II. THE USGS/EPA RADON POTENTIAL
ASSESSMENTS:INTRODUCTION
III. REGION 8 GEOLOGIC RADON POTENTIAL
SUMMARY
V. PRELIMINARY GEOLOGIC RADON POTENTIAL
ASSESSMENT OF SOUTH DAKOTA
V. EPA'S MAP OF RADON ZONES ~ SOUTH DAKOTA
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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 ths Association of American State Geologists
(AASG) have worked closely over the past several years to produce a series of maps and
documents which address these directives. The EPA Map of Radon Zones is a compilation of
that work and fulfills the requirements of sections 307 and 309 of IRAA. The Map of Radon
Zones identifies, on a county-by-counry basis, areas of the U.S. that have the highest potential
for elevated indoor radon levels (greater than 4 pCi/L).
The Map of Radon Zones is designed to assist national, State and local governments
and organizations to target their radon program activities and resources. It is also intended to
help building code officials determine areas that are the highest priority for adopting radon-
resistant building practices. The Map of Radon Zones should not be used to determine if
individual homes in any given area need to be tested for radon. EPA recommends that all
homes be tested for radon, regardless of geographic location or the zone designation of
the county in which they are located.
This document provides background information concerning the development of the
Map of Radon Zones. It explains the purposes of the map, the approach for developing the
map (including the respective roles of EPA and USGS), the data sources used, the conclusions
and confidence levels developed for the prediction of radon potential, and the review process
that was conducted to finalize this effort.
BACKGROUND
Radon (Rn222) is a colorless, odorless, radioactive gas. It comes from the natural
decay of uranium that is found in nearly all soils. It typically moves through the ground to
the air above and into homes and other buildings through cracks and openings in the
foundation. Any home, school or workplace may have a radon problem, regardless of
whether it is new or old, well-sealed or drafty, or with or without a basement. Nearly one out
of every 15 homes in the U.S. is estimated to have elevated annual average levels of indoor
radon.
Radon first gained national attention in early 1984, when extremely high levels of
indoor radon were found in areas of Pennsylvania, New Jersey, and New York, along the
Reading Prong-physiographic province. EPA established a Radon Program in 1985 to assist
States and homeowners in reducing their risk of lung cancer from indoor radon.
Since 1985, EPA and USGS have been working together to continually increase our
understanding of radon sources and the migration dynamics that cause elevated indoor radon
levels. Early efforts resulted in the 1987 map entitled "Areas with Potentially High Radon
Levels." This map was based on limited geologic information only because few indoor radon
measurements were available at the time. The development of EPA's Map of Radon Zones
and its technical foundation, USGS' National Geologic Radon Province Map, has been based
on additional information from six years of the State/EPA Residential Radon Surveys,
independent State residential surveys, and continued expansion of geologic and geophysical
information, particularly the data from the National Uranium Resource Evaluation project.
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Purpose of the Map of Radon Zones
EPA's Map of Radon Zones (Figure 1) assigns each of the 3141 counties in the
United States to one of three zones:
o Zone 1 counties have a predicted average indoor screening level > than
4pCi/L
o Zone 2 counties have a predicted average screening level > 2 pCi/L and
• <4pCi/L
o Zone 3 counties have a predicted average screening level < 2 pCi/L
The Zone designations were determined by assessing five factors that are known to be
important indicators of radon potential: indoor radon measurements, geology, aerial
radioactivity, soil parameters, and foundation types.
The predictions of average screening levels in each of the Zones is an expression of
radon potential in the lowest liveable area of a structure. This map is unable to estimate
actual exposures to radon. EPA recommends methods for testing and fixing individual homes
based on an estimate of actual exposure to radon. For more information on testing and fixing
elevated radon levels in homes consult these EPA publications: A Citizen's Guide to Radon
the Consumer's Guide to Radon Reduction and the Home Buyer's and Seller's Guide to
Radon.
EPA believes that States, local governments and other organizations can achieve
optimal risk reductions by targeting resources and program activities to high radon potential
areas. Emphasizing targeted approaches (technical assistance, information and outreach
efforts, promotion of real estate mandates and policies and building codes, etc ) in such areas
addresses the greatest potential risks first.
EPA also believes that the use of passive radon control systems in the construction of
new homes in Zone 1 counties, and the activation of those systems if necessitated by follow-
up testing, is a cost effective approach to achieving significant radon risk reduction.
The Map of Radon Zones and its supporting documentation establish no regulatory
requirements. Use of this map by State or local radon programs and building code officials is
voluntary. The information presented on the Map of Radon Zones and in the supporting
documentation is not applicable to radon in water.
Development of the Map of Radon Zones
The technical foundation for the Map of Radon Zones is the USGS Geologic Radon
Province Map. In order to examine the radon potential for the United States, the USGS
began by identifying approximately 360 separate geologic provinces for the U.S. The
provinces are shown on the USGS Geologic Radon Province Map (Figure 2). Each of the
geologic provinces was evaluated by examining the available data for that area: indoor radon
measurements, geology, aerial radioactivity, soil parameters, and foundation types. As stated
previously, these five factors are considered to be of basic importance in assessing radon
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potential and some data are available for each of these factors in every geologic province. The
province boundaries do not coincide with political borders (county and state) but define areas
of general radon potential. The five factors were assigned numerical values based on an
assessment of their respective contribution to radon potential, and a confidence level was
assigned to each contributing variable. The approach used by USGS to estimate the radon
potential for each province is described in Part II of this document.
EPA subsequently developed the Map of Radon Zones by extrapolating from the
province level to the county level so that all counties in the U.S. were assigned to one of
three radon zones. EPA assigned each county to a given zone based on its provincial radon
potential. For example, if a county is located within a geologic province that has a predicted
average screening level greater than 4 pCi/L, it was assigned to Zone 1. Likewise, counties
located in provinces with predicted average screening levels > 2 pCi/L and < 4 pc'i/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
Ilfk Ueteriie Loi
Figure 4
NEBRASKA - EPA Map of Radon Zones
Lificoln County
Zest 1 2«*e 2 Zoic 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 zonj.
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
lequests were based on additional data from the State on geology, indoor radon
measurements, population, etc. Upon reviewing the data submitted by the States, EPA did
make some changes in zone designations. These changes, which do not strictly follow the
methodology outlined in this document, are discussed in the respective State chapters.
EPA encourages the States and counties to conduct further research and data collection
efforts to refine the Map of Radon Zones. EPA would like to be kept informed of any
changes the States, counties, or others make to the maps. Updates and revisions will be
handled in a similar fashion to the way the map was developed. States should notify EPA of
any proposed changes by forwarding the changes through the Regional EPA offices that are
listed in Part II. Depending on the amount of new information that is presented, EPA will
consider updating this map periodically. The State radon programs should initiate proper
notification of the appropriate State officials when the Map of Radon Zones is released and
when revisions or updates are made by the State or EPA.
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THE USGS/EPA RADON POTENTIAL ASSESSMENTS: AN INTRODUCTION
by
Linda C.S. Gundersen and R. Randall Schumann
U.S. Geological Survey
and
Sharon W. White
U.S. Environmental Protection Agency
BACKGROUND
The Indoor Radon Abatement Act of 1988 (15 U.S.C. 2661-2671) directed the U.S.
Environmental Protection Agency (EPA) to identify areas of the United States that have the
potential to produce harmful levels of indoor radon. These characterizations were to be based
on both geological data and on indoor radon levels in homes and other structures. The EPA
also was directed to develop model standards and techniques for new building construction
that would provide adequate prevention or mitigation of radon entry. As part of an
Interagency Agreement between the EPA and the U.S. Geological Survey (USGS), the USGS
has prepared radon potential estimates for the United States. This report is one of ten '
booklets that document this effort. The purpose and intended use of these reports is to help
identify areas where states can target their radon program resources, to provide guidance in
selecting the most appropriate building code options for areas, and to provide general
information on radon and geology for each state for federal, state, and municipal officials
dealing with radon issues. These reports are not intended to be used as a substitute for
indoor radon testing, and they cannot and should not be used to estimate or predict the
indoor radon concentrations of individual homes, building sites, or housing tracts. Elevated
levels of indoor radon have been found in every State, and EPA recommends that all homes
be tested for indoor radon.
Booklets detailing the radon potential assessment for the U.S. have been developed for
each State. USGS geologists are the authors of the geologic radon potential booklets. Each
booklet consists of several components, the first being an overview to the mapping project
(Part I), this introduction to the USGS assessment (Part II), including a general discussion of
radon (occurrence, transport, etc.), and details concerning the types of data used. The third
component is a summary chapter outlining the general geology and geologic radon potential
of the EPA Region (Part HI). 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
It-1 Reprinted from USGS Open-File Report 93-292
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tracts. Within any area of a given geologic radon potential ranking, there are likely to be
areas where the radon potential is lower or higher than that assigned to the area as a whole,
especially in larger areas such as the large counties in some western states.
In each state chapter, references to additional reports related to radon are listed for the
state, and the reader is urged to consult these reports for more detailed information. In most
cases the best sources of information on radon for specific areas are state and local
departments of health, state departments responsible for nuclear safety or environmental
, protection, and U.S. EPA regional offices. More detailed information on state or local
geology may be obtained from the state geological surveys. Addresses and telephone
numbers of state radon contacts, geological surveys, and EPA regional offices are listed in
Appendix C at the end of this chapter.
RADON GENERATION AND TRANSPORT IN SOILS
Radon (H1Rn) is produced from the radioactive decay of radium (M6Ra), which is, in turn
a product of the decay of uranium (U8U) (fig. 1). The half-life of ™Rn is 3.825 days'. Other '
isotopes of radon occur naturally, but, with the exception of tho'ron (MORn), 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 are^s of karst topography formed
in carbonate rock (limestone or dolomite) environments, solution cavities and fissures can
increase soil permeability at depth by providing additional pathways for gas flow.
Not all radium contained in soil grains and grain coatings will result in mobile radon
when the radium decays. Depending on where the radium is distributed in the soil, many of
the radon atoms may remain imbedded in the soil grain containing the parent radium atom or
become imbedded in adjacent soil grains. The portion of radium that releases radon into the
pores and fractures of rocks and soils is called the emanating fraction. When a radium atom
decays to radon, the energy generated is strong enough to send the radon atom a distance of
about 40 nanometers (1 nm = 10'9 meters), or about 2x10-* inches—this is known as alpha
recoil (Tanner, 1980). Moisture in the soil lessens the chance of a recoiling radon atom
becoming imbedded in an adjacent grain. Because water is more dense than air, a radon atom
will travel a shorter distance in a water-filled pore than in an air-filled pore, thus increasing
the likelihood that the radon atom will remain in the pore space. Intermediate moisture levels
enhance radon emanation but do not significantly affect permeability. However, high
moisture levels can significantly decrease the gas permeability of the soil and impede radon
movement through the soil.
Concentrations of radon in soils are generally many times higher than those inside of
buildings, ranging from tens of pCi/L to more than 100,000 pCi/L, but typically in the range
of hundreds to low thousands of pCi/L. Soil-gas radon concentrations can vary in response to
variations in climate and weather on hourly, daily, or seasonal time scales. Schumann and
others (1992) and Rose and others (1988) recorded order-of-magnitude variations in soil-gas
radon concentrations between seasons in Colorado and Pennsylvania. The most important
factors appear to be (1) soil moisture conditions, which are controlled in large part by
precipitation; (2) barometric pressure; and (3) temperature. Washington and Rose (1990)
suggest that temperature-controlled partitioning of radon between water and gas in soil pores
also has a significant influence on the amount of mobile radon in soil gas.
Homes in hilly limestone regions of the southern Appalachians were found to have higher
indoor radon concentrations during the summer than in the winter. A suggested cause for this
phenomenon involves temperature/pressure-driven flow of radon-laden air from subsurface
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solution cavities in the carbonate rock into houses. As warm air enters solution cavities that
are higher on the hillslope than the homes, it cools and settles, pushing radon-laden air from
lower in the cave or cavity system into,structures on the hillslope (Gammage and others,
1993). In contrast, homes built over caves having openings situated below the level of the
home had higher indoor radon levels in the winter, caused by cooler outside air entering the
cave, driving radon-laden air into cracks and solution cavities in the rock and soil and
ultimately, into homes (Gammage and others, 1993).
RADON ENTRY INTO BUILDINGS
A driving force (reduced atmospheric pressure in the house relative to the soil producing
a pressure gradient) and entry points must exist for radon to enter a building from the soil
The negative pressure caused by furnace combustion, ventilation devices, and the stack effect
(the rising and escape of warm air from the upper floors of the building, causing a
temperature and pressure gradient within the structure) during cold winter months are
common driving forces. Cracks and other penetrations through building foundations sump
holes, and slab-to-foundation wall joints are common entry points
Radon levels in the basement are generally higher than those on the main floor or upper
floors of most structures. Homes with basements generally provide more entry points for
radon, commonly have a more pronounced stack effect, and typically have lower air pressure
relative to the surrounding soil than nonbasement homes. The term "nonbasement" applies to
slab-on-grade or crawl space construction.
METHODS AND SOURCES OF DATA
The assessments of radon potential in the booklets that follow this introduction were
made using five main types of data: (1) geologic (lithologic); (2) aerial radiometric; (3) soil
characteristics, including soil moisture, permeability, and drainage characteristics; (4) indoor
radon data; and (5) budding 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-
beanng sandstones, certain kinds of fluvial sandstones arid fluvial sediments, phosphorites
chalk, karst-producmg 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 XOKE AEKUL SURVEYS
2 KM (1 MILE)
5 KM (3 MILES)
2 i 5 I'M
10 EM (6 HILES)
5 * 10 KM
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.
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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
yp.cally between 3 and 6 miles, less than 10 percen' of the ground surface of ''ie 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 M 000000
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
radionuchdes 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
radionuchdes 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 nat:?r.al
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 (m/hr), at which water soaks into the soil, as measured in a soil percolation
test. Although m/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 m/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
* fo!me?PA Residential Radon Survgy (Ronca-Battista and others, 1988; Dziuban and
^ooV>?' Il°rty'!wo 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
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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 RADIOACTIVITY
GEOLOGY*
SOIL PERMEABILITY
ARCHITECTURE TYPE
^
POINT VALUE
1
<2pCi/L
< 1.5 ppm eU
negative
low
mostly slab
2
2-4pCi/L
1.5 - 2.5 ppm eU
variable
moderate
mixed
3
>4pCi/L
> 2.5 ppm eU
positive
high
mostly basement
'GEOLOGIC HELD 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
Ppjnt rang? 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
POINT VALUE
INDOOR RADON DATA
sparse/no data
fair coverage/quality
good coverage/quality
AERIAL RADIOAdTVlTY
questionable/no data
glacial cover
no glacial cover
GEOLOGIC DATA
questionable
variable
proven geol. model
SOIL PERMEABILITY
questionable/no data
variable
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
11-12 Reprinted from USGS Open-File Repot 93-292
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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,'l991) suggest
that eU is a poor predictor of geologic radon potential in this area because radionuclides have
11-13 Reprinted from USGS Open-File Report 93-292
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been leached from the upper soil layers but are present and possibly even concentrated in
deeper soil horizons, generating significant soil-gas radon. This positive supporting field
evidence adds two GFE points to the score, which helps to counteract the invalid conclusion
suggested by the radiometric data. No GFE points are awarded if there are no documented
field studies for the area.
"Soil permeability" refers to several soil characteristics that influence radon concentration
and mobility, including soil type, grain size, structure, soil moisture, drainage, slope, and
permeability. In the matrix, "low" refers to permeabilities less than about 0.6 in/hr; "high"
corresponds to greater than about 6.0 in/hr, in U.S. Soil Conservation Service (SCS) standard
soil percolation tests. The SCS data are for water permeability, which generally correlates
well with the gas permeability of the soil except when the soil moisture content is very high.
Areas with consistently high water tables were thus considered to have low gas permeability.
"Low, "moderate", and "high" permeability were assigned 1, 2, and 3 points, respectively.
Architecture type refers to whether homes in the area have mostly basements (3 points),
mostly slab-on-grade construction (1 point), or a mixture of the'two. Split-level and crawl '
space homes fall into the "mixed" category (2 points). Architecture information is necessary
to properly interpret the indoor radon data and produce geologic radon potential categories
that are consistent with screening indoor radon data.
The overall RI for an area is calculated by adding the individual RI scores for the 5
factors, plus or minus GFE points, if any. The total RI for an area falls in one of three
categories—low, moderate or variable, or high. The point ranges for the three categories were
determined by examining the possible combinations of points for the 5 factors and setting
rules such that a majority (3 of 5 factors) would determine the final score for the low and
high categories, with allowances for possible deviation from an ideal score by the other two
factors. The moderate/variable category lies between these two ranges. A total deviation of 3
points from the "ideal" score was considered reasonable to allow for natural variability of
factors—if two of the five factors are allowed to vary from the "ideal" for a category, they
can differ by a minimum of 2 (1 point different each) and a maximum of 4 points (2'points
different each). With "ideal" scores of 5, 10, and 15 points describing low, moderate, and
high geologic radon potential, respectively, an ideal low score of 5 points plus 3 points for
possible variability allows a maximum of 8 points in the low category. Similarly, an ideal
high score of 15 points minus 3 points gives a minimum of 12 points for the high category.
Note, however, that if both other factors differ by two points from the "ideal", indicating
considerable variability in the system, the total point score would lie in the adjacent (i.e.,
moderate/variable) category.
Confidence Index. Except for architecture type, the same factors were used to establish a
Confidence Index (CI) for the radon potential prediction for each area (Table 2). Architecture
type was not included in the confidence index because house construction data are readily and
reliably available through surveys taken by agencies and industry groups including the
National Association of Home Builders, U.S. Department of Housing and Urban
Development, and the Federal Housing Administration; thus it was not considered necessary
II-14 Reprinted from USGS Open-File Report 93-292
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to question the quality or validity of these data. The other factors were scored on the basis of
the quality and quantity of the data used to complete the RI matrix.
Indoor radon data were evaluated based on the distribution and number of data points and
on whether the data were collected by random sampling (State/EPA Residential Radon Survey
or other state survey data) or volunteered vendor data ^likely to be nonrandom and biased
toward population centers and/or high indoor radon levels). The categories listed in the CI
matrix for indoor radon data ("sparse or no data", "fair coverage or quality", and "good
coverage/quality") indicate the sampling density and statistical robustness of an indoor radon
data set. Data from the State/EPA Residential Radon Survey and statistically valid state
surveys were typically assigned 3 Confidence Index points unless the data were poorly
distributed or absent in the area evaluated.
Aerial radioactivity data are available for all but a few areas of the continental United
States and for part of Alaska. An evaluation of the quality of the radioactivity data was based
on whether there appeared to be a good correlation between the radioactivity and the actual
amount of uranium or radium available to generate mobile radon in the rocks and soils of the
area evaluated. In general, the greatest problems with correlations among eU, geology, and
soil-gas or indoor radon levels were associated with glacial deposits (see the discussion in a
previous section) and typically were assigned a 2-point Confidence Index score. Correlations
among eU, geology, and radon were generally sound in unglaciated areas and were usually
assigned 3 CI points. Again, however, radioactivity data in some unglaciated areas may have
been assigned fewer than 3 points, and in glaciated areas may be assigned only one point, if
the data were considered questionable or if coverage was poor.
To assign Confidence Index scores for the geologic data factor, rock types and geologic
settings for which a physical-chemical, process-based understanding of radon generation and
mobility exists were regarded as having "proven geologic models" (3 points); a high
confidence could be held for predictions in such areas. Rocks for which the processes are
less well known or for which data are contradictory were regarded as "variable" (2 points),
and those about which little is known or for which no apparent correlations have been found
were deemed "questionable" (1 point).
The soil permeability factor was also scored based on quality and amount of data. The
three categories for soil permeability in the Confidence Index are similar in concept, and
scored similarly, to those for the geologic data factor. Soil permeability can be roughly
estimated from grain size and drainage class if data from standard, accepted soil percolation
tests are unavailable; however, the reliability of the data would be lower than if percolation
test figures or other measured permeability data are available, because an estimate of this type
does not encompass all the factors that affect soil permeability and thus may be inaccurate in
some instances. Most published soil permeability data are for water; although this is
generally closely related to the air permeability of the soil, there are some instances when it
may provide an incorrect estimate. Examples of areas in which water permeability data may
not accurately reflect air permeability include areas with consistently high levels of soil
moisture, or clay-rich soils, which would have a low water permeability but may have a
11-15 Reprinted from USGS Open-File Report 93-292
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significantly higher air permeability when dry due to shrinkage cracks in the soil. These
additional factors were applied to the soil permeability factor when assigning the RI score, but
may have less certainty in some cases and thus would be assigned a lower CI score.
The Radon Index and Confidence Index give a general indication of the relative
contributions of the interrelated geologic factors influencing radon generation and transport in
rocks and soils, and thus, of the potential for elevated indoor radon levels to occur in a
particular area. However, because these reports are somewhat generalized to cover relatively
large areas of States, it is highly recommended that more detailed studies be performed in
local areas of interest, using the methods and general information in these booklets as a guide.
11-16 Reprinted from USGS Open-File Report 93-292
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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/600y9-91/026b, 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., and Bligh, T., 1985, Assessment of the energy
savings potential of building foundations research: Oak Ridge, Tenn., U.S. Department of
Energy Report ORNL/SUB/84-0024/1.
Smith, R.C., H, Reilly, M.A., Rose, A.W., Barnes, J.H., and Berkheiser, S.W., Jr., 1987,
Radon: a profound case: Pennsylvania Geology, v. 18, p. 1-7.
Tanner, A.B., 1964, Radon migration in the ground: a review, in Adams, J.A.S., and Lowder,
W.M., eds., The natural radiation environment Chicago, HI., University of Chicago
Press, p. 161-190.
Tanner, A.B., 1980, Radon migration in the ground: a supplementary review, in Gesell, T.F.,
and Lowder, W.M. (eds), Natural radiation environment m, 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 Adas 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.
11-19 Reprinted ftom USGS Open-File Report 93-292
-------
-------
APPENDIX A
GEOLOGIC TIME SCALE
Honor
Eonothem
Phanerozoic2
(B)
Era or
Erathem
Cmotoic 2
(Cz)
Mesozoic2
(Mi)
Paleozoic2
(PJ
Pfewroio* Si
M«dlt
*roi*re»ie fV)
An Decay constants and isoiopto ratios employed are died in Steiger and Jiger (1977). Designation m.y. used for an
interval of time.
'Modifier* (lower, middle, upper or early, middle, tote) when used with these Herns are informal divisions of the larger unit; the
first letter of the modifier is lowercase.
'Rocks older than 570 Ma also called Precambrian (pC). a time term without specif* rank.
'informal time tern) without specific rank.
USGS Open-File Report 93-292
-------
-------
APPENDIX B
GLOSSARY OF TERMS
Units of measure
pCi/L (picocuries per liter)- a unit of measure of radioactivity used to describe radon
concentrations in a volume of air. One picocurie (10'12 curies) is equal to about 2.2 disintegrations
of radon atoms per minute. A liter is about 1.06 quarts. The average concentration of radon in
U.S. homes measured to date is between 1 and 2 pQ/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. OnepCi/Lisequalto37Bq/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 thp. 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 surfoce.
alluvial fan A low, widespread mass of loose rock and soil material, shaped like an open fan
and deposited by a stream at the point where it flows from a narrow mountain valley out onto a
plain or broader valley. May also form at the junction with larger streams or when the gradient of
the stream abruptly decreases.
alluvium, alluvial General terms referring to unconsolidated detrital material deposited by a
stream or other body of running water.
alpha-track detector A passive radon measurement device consisting of a plastic film that is
sensitive to alpha particles. The film is etched with acid in a laboratory after it is exposed The
etching reveals scratches, or "tracks", left by the alpha particles resulting from radon decay, which
can then be counted to calculate the radon concentration. Useful for long-term (1-12 months')
radon tests. • '
amphibolite A mafic metamorphic rock consisting mainly of pyroxenes and(or) amphibole and
plagioclase. .
H-21 Reprinted from USGS Open-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, ie., argWeous sam£ie ^
arid Term describing a climate characterized by dryness, or an evaporation rate that exceeds the
amount ot 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. »««»*,
carbonaceous Said of a rock or sediment that is rich in carbon, is coaly, or contains organic
ice consisting of a small container of
chert A hard extremely dense sedimentary rock consisting dominantly of interlocking ovstafe of
SSRn.03*? ?* n0t VJSibJe to *" naked eye' «h*« *"«* a ma&?duu1uSl SyU
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 mid shTg
sition having a diameter
size and ability to absorb substantial amounts of water,
concretion A hard, compact mass of mineral matter, normally subspherical but commonlv
Self ^S US f T^-?7 W*^ from a water solution abo^t a nSdSSSXo
»»u
e - a waer souon aot a ndodi as
a leaf, shell, bone, or fossil, within a sedimentary or fractured rock. »»uvu«»
wi^lomerate 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 hm or ridge with a gentle slope on one side and a steep slope on the other. The
£STf£^^
daughter product A nuclide formed by the disintegration of a radioactive precursor or "parent"
H-22
Reprinted from USGS Open-File Report 93-292
-------
delta, deltaic Referring to a low, flat, alluvial ffact of land having a triangular or fan share
tocaed at or near the mouth of a river. It results from fte accumulation of sedim^t ^posted by a
diorite A plutonic igneous rock that is medium in color and
make up less than 50% of the rock. It also contains abimdan
quartz.
T^ T* sedimenfy ™* of whi°h more than 50% consists of the mineral dolomite
)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.
b
of """" from a land "*" * evaporation from *• s°a —
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.
*
formation A mappable body of rock having similar characteristics.
glacial deposit Any sediment transported and deposited by a glacier or Dro
with glaciers, such as glaciofluvial sediments deposed by LSSSSS
gneiss A rock formed by metamorphism in which bands and lenses of minerals of similar
™d knSeS °f differcnt comP°sition' «**•« ^ rock a striped or
granite Broadly applied, any coarsely crystalline, quartz- and feldspar-bearing igneous plutonic
S» JSS^? s e ***"* 10 ^ 50% <***• ** ^ feldsp^ ^L
10 ^ 50% <***•
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
11-23 Reprinted from USGS Open-File Hepott 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
mctamorphic.
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".
karne A low mound, knob, hummock, or short irregular ridge formed by a glacial stream at the
margin of a melting glacier; composed of bedded sand and gravel.
karst terrain A type of topography that is formed on limestone, gypsum and other rocks by
dissolution of the rock by water, forming sinkholes and caves.
lignite A brownish-black coal that is intermediate in coalification between peat and
subbituminous coal.
limestone A carbonate sedimentary rock consisting of more than 50% calcium carbonate,
primarily in the form of the mineral calcite (CaCOs).
lithology The description of rocks in hand specimen and in outcrop on the basis of color,
composition, and grain size.
loam A permeable soil composed of a mixture of relatively equal parts clay, silt, and sand and
usually containing some organic matter.
loess A fine-grained eolian deposit composed of silt-sized particles generally thought to have
been deposited from windblown dust of Pleistocene age.
mafic Term describing an igneous rock containing more than 50% dark-colored minerals.
marine Term describing sediments deposited in the ocean, or precipitated from ocean waters.
metamorphic Any rock derived from pre-existing rocks by mineralogical, chemical, or structural
changes in response to changes in temperature, pressure, stress, and the chemical environment
Phyllite, schist, ampnibolite, and gneiss are metamorphic rocks.
moraine A mound, ridge, or other distinct accumulation of unsorted, imbedded glacial material
predominantly till, deposited by the action of glacial ice.
outcrop That part of a geologic formation or structure that appears at the surface of the Earth, as
in "rock outcrop".
percolation test A term used in engineering for a test to determine the water permeability of a
soft. 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
-------
WW? S parts "» "'"^ to S"01^ structure and
a^ *"**' "* WhOSe ««-* or landfor™ differ
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.
osure to radon.
semiarid Refers to a climate that has slightly more precipitation than an arid climate.
shale A fine-grained sedimentary rock formed from solidification (Uthification) of clay or mud.
shrink-swell clay See clay mineral.
i A,fme-Srained gastic sedimentary rock composed of silt-sized rock and mineral
material and more or less firmly cemented. Sntparticlesrange from 1/16 to
sinkhole A roughly circular depression in a karst area measuring meters to tens
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.
e^^surfa^18 ^^^^^S^^'^d-.orwaterbome deposits occurring on the
to^Melands General term for a broad, elevated region wife a nearly level surface of considerable
11-25 Reprinted firom USGS Open-File R^ott 93-292
-------
terrace gravel Gravel-sized material that caps ridges and terraces, left behind by a stream as it
cuts down to a lower level.
terrain A tract or region of the Earth's surface considered as a physical feature or an ecological
environment.
till Unsorted, generally unconsolidated and imbedded rock and mineral material deposited directly
adjacent to and underneath a glacier, without reworking by meltwater. Size of grains varies greatly
from clay to boulders.
uraniferous Containing uranium, usually more than 2 ppm.
vendor data Used in this report to refer to indoor radon data collected and measured by
commercial vendors of radon measurement devices and/or services.
volcanic Pertaining to the activities, structures, and extrusive rock types of a volcano.
water table The surface forming the boundary between the zone of saturation and the zone of
aeration; the top surface of a body of unconfined groundwater in rock or soil.
weathering The destructive process by which earth and rock materials, on exposure to
atmospheric elements, are changed in color, texture, composition, firmness, or form with little or
no transport of the material.
11-26 Reprinted from USGS Open-File Repeat 93-292
-------
APPENDIX C
EPA REGIONAL OFFICES
EPA Region 1
JFK Federal Building
Boston, MA 02203
(617) 565-4502
EPA Region 2
(2AIR:RAD)
26 Federal Plaza
New York, NY 10278
(212) 264-4110
Region 3 (3AH14)
841 Chestnut Street
Philadelphia, PA 19107
(215) 597-8326
EPA Region 4
345 Courtland Street, N.E.
Atlanta, GA 30365
(404) 347-3907
EPARegion5(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
State
Alabama
Alaska
Arizona
Arkansas
California
Colorado
Connecticut
Delaware
District of Columbia
Florida
Georgia
Hawaii
Idaho
Illinois
Indiana
Iowa
Kansas •
Kentucky
Louisiana
Maine
Maryland
Massachusetts
Michigan
Minnesota
Mississippi
Missouri
Montana
Nebraska
Nevada
New Hampshire
New Jersey
New Mexico
New York
North Carolina
North Dakota
. Ohio ,
Oklahoma
Oregon
Pennsylvania
Rhode Island
South Carolina
South Dakota ,
Tennessee
Texas
Utah
Vermont
Virginia
Washington
West Virginia
Wisconsin
Wyoming
EPA Ppqinn
4
1 n
6
9
8
1
3
3
, 4
4
5,
5
7
4
6
1
3
1
5
5
4
7
8
7
9
1
2
6
2
4
8
5
6
10
3
, 1
4
8
4
1
3
10
3
5
8
H-27 Reprinted from USGS Open-File Report 93-292
-------
STATE RADON CONTACTS
May, 1993
Alabama James McNees
Division of Radiation Control
Alabama Department of Public Health
State Office Building
Montgomery, AL 36130
(205)242-5315
1-800-582-1866 in state
Afo'ifa Charles Tedf and
Department of Health and Social
Services
P.O. Box 110613
Juneau, AK 99811-0613
(907)465-3019
1-800-478-4845 in state
John Stewart
Arizona Radiation Regulatory Agency
4814 South 40th St.
Phoenix, AZ 85040
(602)255-4845
Arkansas LeeGershner
Division of Radiation Control
Department of Health
4815 Markham Street, Slot 30
Little Rock, AR 72205-3867
(501)661-2301
California J. David Quinton
Department of Health Services
714 P Street, Room 600
Sacramento, CA 94234-7320
(916)324-2208
1-800-745-7236 in state
Colorado Linda Martin
Department of Health
4210 East llth Avenue
Denver, CO 80220
(303)692-3057
1-800-846-3986 in state
Connecticut Alan J. Siniscalchi
Radon Program
Connecticut Department of Health
Services
150 Washington Street
Hartford, CT 061064474
(203)566-3122
Delaware MaraiG. Rejai
Office of Radiation Control
Division of Public Health
P.O. Box 637
Dover, DE 19903
(302)736-3028
1-800-554-4636 In State
Pjsjrjci Robert Davis
of Columbia DC Department of Consumer and
Regulatory Affairs
614 H Street NW
Room 1014
Washington, DC 20001
(202)727-71068
Honda N. Michael GiUey
Office of Radiation Control
Department of Health and
Rehabilitative Services
1317 Winewood Boulevard
Tallahassee, PL 32399-0700
(904)488-1525
1-800-543-8279 in state
Richard Schreiber
Georgia Department of Human
Resources
878 Peachtree St, Room 100
Atlanta, GA 30309
(404)894-6644
1-800-745-0037 in state
Hawaii Russell Takata
Environmental Health Services
Division
591 Ala Moana Boulevard
Honolulu, HI 96813-2498
(808)586-4700
H-28 Reprinted from USGS Open-Fife Report 93-292
-------
lildjana.
Kentuck
PatMcGavarn
Office of Environmental Health
450 West State Street
Boise, ID 83720
(208)334-6584
1-800-445-8647 in slate
Richard Allen
Illinois Department of Nuclear Safely
1301 Outer Park Drive
Springfield, IL 62704
(217)524-5614
1-800-325-1245 in state
Lorand Magyar
Radiological Health Section
Indiana State Department of Health
1330 West Michigan Street
P.O. Box 1964
Indianapolis, IN 46206
(317)633-8563
1-800-272-9723 In State
Donald A. Plater
Bureau of Radiological Health
Iowa Department of Public Health
Lucas State Office Building
Des Moines, IA 50319-0075
(515)281-3478
1-800-383-5992 In State
Harold Spiker
Radiation Control Program
Kansas Department of Health and
Environment
109 SW 9th Street
6th Floor Mills Building
Topeka, KS 66612
(913)296-1561
JeanaPhelps
Radiation Control Branch
Department of Health Services
Cabinet for Human Resources
275 East Main Street
Frankfort, KY 40601
(502)564-3700
Louisiana Matt Schlenker
Louisiana Department of
Environmental Quality
P.O. Box 82135
Baton Rouge, LA 70884-2135
(504)925-7042
1-800-256-2494 in state
Mains BpbStilwell
Division of Health Engineering
Department of Human Services
State House, Station 10
Augusta, ME 04333
(207)289-5676
1-800-232-0842 in state
Maryland Leon J. Rachuba
Radiological Health Program
Maryland Department of the
Environment
2500 Broening Highway
Baltimore, MD 21224
(410)631-3301
1-800-872-3666 In State
Massachusetts William J. Bell
Radiation Control Program
Department of Public Health
23 Service Center
Northampton, MA 01060
(413)586-7525
1-800-445-1255 in state
Michigan 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
11-29 Reprinted from USGS Open-File Report 93-292
-------
Mississii
Missouri
Montana
Silas Anderson
Division of Radiological Health
Department of Health
3150 Lawson Street
P.O. Box 1700
Jackson, MS 39215-1700
(601)354-6657
1-800-626-7739 in state
Kenneth V. Miller
Bureau of Radiological Health
Missouri Department of Health
1730 East Elm
P.O. Box 570
Jefferson City, MO 65102
(314)751-6083
1-800-669-7236 In State
Adrian C. Howe
Occupational Health Bureau
Montana Department of Health and
Environmental Sciences
Cogswell Building A113
Helena, MT 59620
(406)444-3671
Joseph Milone
Division of Radiological Health
Nebraska Department of Health
301 Centennial Mall, South
P.O. Box 95007
Lincoln, NE 68509
(402)471-2168
1-800-334-9491 In State
Stan Marshall
Department of Human Resources
505 East King Street
Room 203
Carson City, NV 89710
(702)687-5394
New Hampshire David Chase
Bureau of Radiological Health
Division of Public Health Services
Health and Welfare Building
Six Hazen Drive
Concord, NH 03301
(603)271-4674
1-800-852-3345 x4674
New Jersey Tonalee Carlson Key
Division of Environmental Quality
Department of Environmental
Protection
CN415
Trenton, NJ 08625-0145
(609)987-6369
1-800-648-0394 in state
New Mexico William M. Floyd
Radiation Licensing and Registration
Section
New Mexico Environmental
Improvement Division
1190 St. Francis Drive
Santa Fe,NM 87503
(505)827-4300
NewYoik William J. Condon
Bureau of Environmental Radiation
Protection
New York Slate 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 Alien Jacobson
North Dakota Department of Health
1200 Missouri Avenue, Room 304
P.O. Box 5520
Bismarck, ND 58502-5520
(701)221-5188
QJup. Marcie Matthews
Radiological Health Program
Department of Health
1224 Kinnear Road - Suite 120
Columbus, OH 43212
(614)644-2727
1-800-523-4439 in state
11-30 Reprinted from USGS Open-File Report 93-292
-------
Oregon
Pennsylvania
Puerto Rico
Rhode Island
South Carolina
Gene Smith
Radiation Protection Division
Oklahoma Slate Department of
Health
P.O. Box 53551
Oklahoma City, OK 73152
(405)271-5221
George Toombs
Department of Human Resources
Health Division
1400 SW 5th Avenue
Portland, OR 97201
(503)73M014
Michael Pyles
Pennsylvania Department of
Environmental Resources
Bureau of Radiation Protection
P.O. Box 2063
Harrisburg, PA 17120
(717)783-3594
1-800-23-RADONIn State
David Saldana
Radiological Health Division
G.P.O. Call Box 70184
Rio Piedras, Puerto Rico 00936
(809)767-3563
Edmund Arcand
Division of Occupational Health and
Radiation
Department of Health
205 Cannon Building
Davis Street
Providence, RI02908
(401)277-2438
Bureau of Radiological Health
Department of Health and
Environmental Control
2600 Bull Street
Columbia, SC 29201
(803)734-4631
1-800-768-0362
South Dakota MikePochop
Division of Environment Regulation
Department of Water and Natural
Resources
JoeFoo 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
Gary Smith
Bureau of Radiation Control
Texas Department of Health
1100 West 49th Street
Austin, TX 78756-3189
(512)834-6688
Utah John Hultquist
Bureau of Radiation Control
Utah State Department of Health
288 North, 1460 West
P.O. Box 16690
Salt Lake City, UT 84116-0690
(801)536-4250
Vermont Paul demons
Occupational and Radiological Health
Division
Vermont Department of Health
10 Baldwin Street
Montpelier, VT 05602
(802) 828-2886
1-800-640-0601 in state
Islands Contact the U.S. Environmental
Protection Agency, Region n
in New York
(212)264^110
n-31 Reprinted from USGS Open-File Report 93-292
-------
Virginia Shelly Ottenbnte
Bureau of Radiological Health
Department of Health
109 Governor Street
Richmond, VA 23219
(804)786-5932
1-800-468-0138 in state
Washington KateColeman
Department of Health
Office of Radiation Protection
Airdustrial Building 5, LE-13
Olympia,WA 98504
(206)753-4518
1-800-323-9727 In State
West Virginia BeattieL. DeBord
Industrial Hygiene Division
West Virginia Department of Health
151 llth Avenue
South Charleston, WV 25303
(304)558-3526
1-800-922-1255 In State
Wisconsin Conrad Weiffenbach
Radiation Protection Section
Division of Health
Department of Health and Social
Services
P.O. Box 309
Madison, WI53701-0309
(608) 267-4796
1-800-798-9050 in state
Wyoming Janet Hough
Wyoming Department of Health and
Social Services
Hallway Building, 4th Floor
Cheyenne, WY 82002-0710
(307)777-<5015
1-800-458-5847 in state
n-32 Reprinted from USGS Open-File Report 93-292
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STATE GEOLOGICAL SURVEYS
May, 1993
Alabama
AJasJ&
Arizona
Arkansas
California
Colorao
Connecticut
Ernest A. Mancini
Geological Survey of Alabama
P.O. Box 0
420 Hackbeny Lane
Tuscaloosa, AL 35486-9780
(205)349-2852
Thomas E. Smith
Alaska Division of Geological &
Geophysical Surveys
794 University Ave., Suite 200
Fairbanks, AK 99709-3645
(907)479-7147
Larry D. Fellows
Arizona Geological Survey
845 North Park Ave., Suite 100
Tucson, AZ 85719
(602) 882-4795
Norman F. Williams
Arkansas Geological Commission
Vardelle Parham Geology Center
3815 West Roosevelt Rd.
Little Rock, AR 72204
(501)324-9165 —
James F. Davis
California Division of Mines &
Geology
801 K Street, MS 12-30
Sacramento, CA 95814-3531
(916)445-1923
Pat Rogers (Acting)
Colorado Geological Survey
1313 Sherman St., Rm 715
Denver, CO 80203
(303)866-2611
Richard C. Hyde
Connecticut Geological & Natural
History Survey
165 Capitol Ave., Rm. 553
Hartford, CT 06106
(203) 566-3540
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)488-4191
William H. McLemore
Georgia Geologic Survey
Rm. 400
19 Martin Luther King Jr. Dr. SW
Atlanta, GA 30334
(404)656-3214
Hawaii Manabu Tagomori
Dept of Land and Natural Resources
Division of Water & Land Mgt
P.O. Box 373
Honolulu, HI 96809
(808)548-7539
Idaho. Earl H. Bennett
Idaho Geological Survey
University of Idaho
Morrfll Hall, Rm. 332
Moscow, ID 83843
(208)885-7991
Illinois Morris W. Leighton
Illinois State Geological Survey
Natural Resources Building
615EastPeabodyDr.
Champaign, IL 61820
(217)333-4747
Indiana Norman C. Hester
Indiana Geological Survey
61 1 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
Lee C. 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.q.'Box2827
University Station
Baton Rouge, LA 70821-2827
(504)388-5320
Mains Walter A. Anderson
Maine Geological Survey
Department of Conservation
State House, Station 22
Augusta, ME 04333
(207)289-2801
Maryland Emery T. Cleaves
Maryland Geological Survey
2300 St. Paul Street
Baltimore, MD 21218-5210
(410)554-5500
Massachusetts Joseph A. Sinnott
Massachusetts Office of
Environmental Affairs
100 Cambridge St., Room 2000
Boston, MA 02202
(617)727-9800
Michigan R. Thomas Segall
Michigan Geological Survey Division
Box 30256
Lansing, MI 48909
(517)334-6923
Minnesota Priscilla C. Grew
Minnesota Geological Survey
2642 University Ave.
St. Paul, MN 55114-1057
(612)627-4780
Mississippi S. Cragin Knox
Mississippi Office of Geology
P.O. Box 20307
Jackson, MS 39289-1307
(601)961-5500
Missouri James H. Williams
Missouri Division of Geology &
Land Survey
111 Fairgrounds Road
P.O. Box 250
Rolla, MO 65401
(314)368-2100
Montana Edward T.Ruppel
Montana Bureau of Mines & Geology
Montana College of Mineral Science
and Technology, Main Hall
Butte.MT 59701
(406)496-4180
Nebraska Perry B.Wigley
Nebraska Conservation & Survey
Division
113 Nebraska Hall
University of Nebraska
Lincoln, NE 68588-0517
(402)472-2410
Jonathan G. Price
Nevada Bureau of Mines & Geology
Stop 178
University of Nevada-Reno
Reno, NV 89557-0088
(702)784^691
New Hampshire Eugene L.Boudette
Dept. of Environmental Services
117 James Hall
University of New Hampshire
Durham, NH 03824-3589
(603)862-3160
New Jersey Haig F. Kasabach
New Jersey Geological Survey
P.O. Box 427
Trenton, NJ 08625
(609)292-1185
New Mexico Charles E. Chapin
New Mexico Bureau of Mines &
Mineral Resources
Campus Station
Socorro.NM 87801
(505)835-5420
New York Robert H. Fakundiny
New York State Geological Survey
3136 Cultural Education Center
Empire State Plaza
Albany, NY 12230
(518)474-5816
11-34 Reprinted from USGS Open-File Report 93-292
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North Carolina Charles H. Gardner
North Carolina Geological Survey
P.O. Box 27687
Raleigh, NC 27611-7687
(919)733-3833
North Dakota John P. Bluemle
North Dakota Geological Survey
600 East Blvd.
Bismarck, ND 58505-0840
(701)224-4109
Ohio Thomas M. Berg
Ohio Dept. of Natural Resources
Division of Geological Survey
4383 Fountain Square Drive
Columbus, OH 43224-1362
(614)265-6576
Oklahoma Charles J. Mankin
Oklahoma Geological Survey
Room N-131, Energy Center
ICOE.Boyd
Norman, OK 73019-0628
(405)325-3031
Ojsgon Donald A. Hull
Dept of Geology & Mineral Indust.
Suite 965
800 NE Oregon SL #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 Ramdn 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 CM. Christensen (Acting)
South Dakota Geological Survey
Science Center
University of South Dakota
Vermfflion, SD 57069-2390
(605)677-5227
Tennessee Edward T. Luther
Tennessee Division of Geology
13th Floor, L & C Tower
401 Church Street
Nashville, TN 37243-0445
(615)532-1500
William L. Fisher
Texas Bureau of Economic Geology
University of Texas
University Station, Box X
Austin, TX 78713-7508
(512)471-7721
IMl M Lee Allison
Utah Geological & Mineral Survey
2363 S. Foothill Dr.
Salt Lake City, UT 84109-1491
(801)467-7970
Diane L. Conrad
Vermont Division of Geology and
Mineral Resources
103 South Main St
Waterbury.VT 05671
(802)244-5164
Virginia Stanley S. Johnson
Virginia Division of Mineral
Resources
P.O. Box 3667
Charlottesville, VA 22903
(804)293-5121
Washington Raymond Lasmanis
Washington Division of Geology &
Earth Resources
Department of Natural Resources
P.O. Box 47007
Olympia, Washington 98504-7007
(206)902-1450
11-35 Reprinted from USGS Open-File Report 93-292
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West Virginia Larry D.Woodfork
West Virginia Geological and
Economic Survey
Mont Chateau Research Center
P.O. Box 879
Morgantown,WV 26507-0879
(304) 594-2331
Wisconsin James Robertson
Wisconsin Geological & Natural
History Survey
3817 Mineral Point Road
Madison, WI 53705-5100
(608)263-7384
Wyoming Gary B. Glass
Geological Survey of Wyoming
University of Wyoming
Box 3008, University Station
Laramw, WY 82071-3008
(307)766-2286
11-36 Reprinted from USGS Open-File Report 93-292
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EPA REGION 8 GEOLOGIC RADON POTENTIAL SUMMARY
by
R. Randall Schumann, Douglass E. Owen, Russell F. Dubiel, and Sandra L. Szarzi
UJS. theological
T T u ?«, Reg!°n 8 indudeS ** States Of Colorad0' Montana, North Dakota, South Dakota
Utah, and Wyoming. For each state, geologic radon potential areas were delineated and ranked on
the basis of geologic, soils, housing construction, and other factors. Areas in which the average
screening indoor radon level of all homes within the area is estimated to be greater than 4 pCil
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 L wSh
die average screening indoor radon level of all homes within the area is estimated to be less than
2 pO/L were ranked low. Information on the data used and on the radon potential ranking scheme
is ; given in the introduction to this volume. More detailed information on tl geology tdfadon
potential of each state in Region 8 is given in the individual state chapters. The individual chanters
deL^Tth, *• ^ ^ ^ P0tential °f the S1X StateS in EPA K^0" 8> ^Sh much more
ho±^±T ^ssummary stdl are generalized assessments and there is no substitute for having a
home tested. Within any radon potential area homes with indoor radon levels both above and
below the predicted average likely will be found.
Figure 1 shows a generalized map of the physiographic provinces in EPA Region 8 The
following summary of radon potential in Region 8 is based on Aese provinces. Figure 2 shows
SSZi^TTE doorradonlevels fey ^unty. The data for South Dakota are from the
EPA/Indian Health Service Residential Radon Survey and from The Radon Project of the
$SSL °f 7"^
-------
-------
~ 8
cw- 1967-
-------
100 Miles
Indoor Radon Screening
Measurements: Average (pCi/L)
16 E3
76 VSSA
106
11
0.0 to 1.9
2.0 to 4.0
4.1 to 9.9
10.0 to 29.2
Missing Data
Rgure2. Average screening indoor radon levels by county for EPA Region 8. Data for
CO, MT, ND, and WY from the EPA/State Residential Radon Survey; data for UT from
the Utah Bureau of Radiation Control indoor radon survey; data for SD from the EPA/MS
Indoor Radon Survey and from The Radon Project Histograms in map legend
indicate the number of counties in each measurement category.
-------
GEOLOGIC
RADON POTENTIAL
HIGH
MODERATE
LOW
Figure 3. Geologic radon potential of EPA Region 8.
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-------
lakes. Many of the glacial deposits are derived from or contain components of the uranium-bearing
Pierre Shale. Although many of the soils derived from glacial deposits in the Dakotas contain
significant amounts of clay, the soils can have permeabilities that are higher than indicated by
standard water percolation tests due to shrinkage cracks when dry. In addition, clays tend to have
high radon emanation coefficients because clay particles have a high surface-area-to-volume ratio
compared to larger and(or) more spherical soil grains. These two factors make areas underlain by
glacial deposits derived from the Pierre Shale, and areas underlain by glacial lake deposits, such as
the Red River Valley, highly susceptible to indoor radon problems. Average indoor radon levels in
this province generally are greater than 4 pCi/L (fig. 2). The Central Lowland in Region 8 has
high radon potential.
The Great Plains Province is an extension of the Central Lowlands that rises from 2,000
feet in the east to 5,000 feet above sea level in the west. In Region 8, it covers the western part of
North and South Dakota and the eastern portions of Montana, Wyoming, and Colorado. The
northern part of the Great Plains has been glaciated (fig. 1) and previous comments about
continental glaciation apply. The Great Plains are largely underlain by Cretaceous and Tertiary
sedimentary rocks. In general, the Cretaceous and Tertiary rocks in the southern part of the Great
Plains in Region 8 have a moderate to high radon potential. The Cretaceous Inyan Kara Group,
which surrounds the Black Hills in southwestern South Dakota and northeastern Wyoming, locally
hosts uranium deposits. There are a number of uranium occurrences in Tertiary sedimentary rocks
in the northern part of the Great Plains, such as in the Powder River Basin. The northwestern part
of the Great Plains contains numerous discontinuous uplifts (mountainous areas) that generally
have high radon potential. A few, such as the Black Hills, have uranium districts associated with
them. Average indoor radon levels in this province are greater than 2 pCi/L, with a significant
number of counties having average indoor radon concentrations exceeding 4 pCi/L (fig. 2).
The Northern Rocky Mountains Province (fig. 1) has high radon potential. Generally, the
igneous and metamorphic rocks of this province have elevated uranium contents. The soils
developed on these rocks typically have moderate or high permeability. Coarse-grained glacial
flood deposits composed of sand, gravel, and boulders, which are found in many of the valleys in
the province, also have high permeability. A number of uranium occurrences are found in granite
and chalcedony in the Boulder Batholith; in veins or pegmatite dikes in igneous and metamorphic
rocks near Clancy in Jefferson County, near Saltese in Mineral County, and in the Bitterroot and
Beartooth Mountains, all in Montana. Uranium also occurs in Tertiary volcanic rocks about 20
miles east of Helena, and in the Mississippian-age Madison Limestone in the Pryor Mountains
County average indoor radon levels generally exceed 4 pCi/L in the province (fig. 2).
The Wyoming Basin Province lies dominantly in Wyoming, but also includes an area of
Tertiary sedimentary rocks in northern Colorado (fig. 1). The Wyoming Basin consists of a
number of elevated semiarid basins separated by small mountain ranges. In general the rocks and
soils have uranium contents greater than 2.5 ppm and host a number of uranium occurrences as
well, particularly in the Tertiary Fort Union and Wasatch Formations. Average indoor radon levels
for homes tested in this area generally are greater than 3 pCi/L (fig. 2). The Wyoming Basin has a
high radon potential.
The Middle Rocky Mountains Province (fig. ]) has both moderate and high radon potential
areas (fig. 3). The southern part of the Middle Rocky Mountains province contains the Wasatch
Range in Utah, which has high radon potential, and the Uinta Mountains and the Overthrust Belt in
Utah and Wyoming, both of which have moderate radon potential. The northern part of the
province contains the Yellowstone Plateau, which is underlain by volcanic rocks containing
m-5 Reprinted from USGS Open-File Report 93-2.92-H
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relatively high uranium concentrations. Mountain ranges such as the Grand Tetons and Big Horn
Mountains, which are underlain by granitic and metamorpnic rocks that generally contain more
than 2.5 ppm uranium, also occur in this province. County average indoor radon levels are mostly
in the 2-4 pCi/L range (fig. 2). The Yellowstone Plateau, Grand Tetons, and Big Horn Mountains
all have high geologic radon potential.
The Southern Rocky Mountains Province lies dominantly in Colorado (fig. 1). Much of
the province is underlain by igneous and metamorpnic rocks with uranium contents generally
exceeding the upper continental crustal average of 2.5 ppm. The Front Range Mineral Belt west of
Denver hosts a number of uranium occurrences and inactive uranium mines. County indoor radon
averages generally are greater than 4 pCi/L, except in the San Juan Mountains in south-central
Colorado, where the county radon averages range from 1 to 4 pCi/L (fig. 3). The Southern Rocky
Mountains generally have high radon potential, with the main exception being the volcanic rocks of
the San Juan volcanic field (located in the southwestern part of the province) which have moderate
radon potential.
The part of the Colorado Plateau Province in Region 8 has a band of high radon potential
and a core of moderate radon potential (figs. 1,3). The band of high radon potential consists
largely of: (1) the Uravan Mineral Belt, a uranium mining district, on the east; (2) the Uinta Basin,
which contains uranium-bearing Tertiary rocks, on the north; and (3) Tertiary volcanic rocks,
which have a high aeroradiometric signature, on the west The moderate radon potential zone in
the interior part of the province is underlain primarily by sedimentary rocks, including sandstone,
limestone, and shale, which have a low aeroradiometric signature. County average screening
indoor radon levels in the Colorado Plateau are mostly greater than 2 pCi/L (fig. 3).
The part of the Basin and Range Province lying in EPA Region 8 has moderate geologic
radon potential. The part of the province which is in Region 8 is actually a part of the Great Basin
Section of the Basin and Range Province. The entire province is laced with numerous faults, and
large displacements along the faults are common. Many of the faulted mountain ranges have high
aeroradiometric signatures, whereas the intervening valleys or basins often have low
aeroradiometric signatures. Because of the numerous faults and igneous intrusions, the geology is
highly variable and complex. Indoor radon levels are similarly variable, with county averages
ranging from less than 1 pCi/L to more than 4 pCi/L (fig. 3).
ffl-6 Reprinted from USGS Open-File Report 93-292-H
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PRELIMINARY GEOLOGIC RADON POTENTIAL ASSESSMENT OF SOUTH DAKOTA
by
R. Randall Schumann
US. Geological Survey
INTRODUCnON
A^-t11?^ *&*?***"***** of geologic radon potential of rocks, soils, and surficial
fdS ?H H P^^ ?f SC3le °f ^ aSS6SSment * such ** * * inappropriate for ^eln
identifying the radon potential of small areas such as neighborhoods, individL building sites or
housrng tracts. Any localized assessment of radon potential must te supplement SSonal
data and mformation from the locality. Within any area of a given radon] potential rarJdngTere
M™ 7 T T^^" OT 10WCT rad°n leVek ^ ch^erized for the areTaTa iS
Moor radon levels both high and low, can be quite localized, and there is no substitute foT te,L
individual homes. Elevated levels of indoor radon have been found in every state and EPA
rsT*± f ^"^ Formore^^ononradon,theTdtis^t
consul the local or State radon program or EPA regional office. More detailed information on state
PHYSIOGRAPHIC AND GEOGRAPHIC SETTING
falls wi^nlD^± ?TS ^ 1° ^^P^^phicprovinces-the eastern part of the State
T^ Sn^^^df if *ZVmC*' ™d *e WeStem Part is k ^ Great H*ns Province.
^veS ^prt^riTvT,^ ^ ^i™^ Y "haraCterized ^ ^^^ Pr^' ^hereas the Great Plains is
SThJ^T ?• yu "^ medlum-Srass prairie. Mean annual precipitation ranges from 24
nches (610 mm) in the southeast corner of the State and in the Black Bilk, to 14 incE (35?mm)
r±TviSH P; °ftheS^(Hogan and others, 1970). Within the State the physfoiaphyT
r subdivided into several areas characterized by specific features (fig 1) Approximatelv half
0'
mnt • ,T«^
matenal. The James River Lowland is a large, shallow, flat-floored trough 50-75
e
e bSSm' dep°SltS Of ^^ L^6 Dakota form a large, flat, mostly
^
that separate it from the James River Lowland to the west and tte£im£o2S? ^
I^ver Lowland to the east The Prairie Coteau rises to elevations of as much as 2000 tet ®O> m)
atuUSO^Sm^^J^eS^^^
aoout 10UO ft (300 m). The hills of this area owe their origin primarily to the action of glaciers
which deposited as much as 400-500 ft (120-150 m) of drift and reworked the sanL Javels and
clays to form ridges and hills (Rothrock, 1943). gravels, and
IV-1 Reprinted from USGS Open-File Report 93-292-H
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-------
The northeastern corner of the State is occupied by the Minnesota-Red River Lowland
cT^l^
contains Big Stone and Traverse Lakes. This steep-sided trench was a spillway for glacM Ske
Agassiz, which drained southward through this channel and the valley of the Minnesota mvTto
The Northern Plateaus, Pierre Hills, and Southern Plateaus regions together make un the
Missouri Plateaus division of the Great Plains Province in western South DaS TrSfa^eTis
K
'
GEOLOGY
The discussion of geology is divided into three sections: bedrock geology uranium
geology, and glacial geology. "Bedrock" refers to non-glacial rock units S^^ed at
^surface west of the Missouri River and are mostly covered by gl«U^SSS
The bedrock geologic map (fig. 4) shows rock units exposed at the surface £ the ungh
and those which would be at the surface if the glacial deposits were absent The gS
are composed of material derived from underlying bedrock and from rock ur^ toSo
deposited on land by the action of rivers, glaciers, or wind. The section on glacM geokL is
summarized from Flint (1955), Hammond (1991), Lemke and others
Bedrock geology: Most of the State is underlain by marine
' °f CretaCe°US age (fiS- 4>' ™« units fa
rw - ' osc
S2 ' , '^ \ F^nalion. Fox Hills Sandstone, Pierre Shale, Colorado Group screek
tos^e Sel ^1°- T ^ ""^ °f " ^ Shale' «d«^ ^to'ne -d^ome
umestone. The Pierre Shale is the most extensive unit and it contains a uranium-bearing black
shale unit known as the Sharon Springs Member. Rocks older than GetaceouTSmarfte
IV-3 Rqp^ted from USGS Open-File Report 93-292-H
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-------
IP
-------
-------
uojun fS
•a
c
I
*•«
§
co
en
60
-------
-------
JM«
in*
i)
>Wr^ tt.u...i i .^, Tailim,
Mtam
EXPLANATION
•«»PM«i.«iljnM>
tkilc. 1
fiwn Dm. P. JJ^ 19T4. moUlCM br 3.3. Norton.
be Upper Cretaceous in age.
-------
-------
f16 °r.W"?fc »" Mesoz°i<= •» tha, are exposed in and around the
«Tf ^ ™*an.o,phic rocks forming the core of the Black Hffls
Kara CtamtThfpH^'' UKUliUm l!?**"8 °CCUr ta sandstt«KS °f ">e Lower Cretaceous Inyar,
sdt tones and carbonaceous shales in the Fort Union Formation in the northwestern Woffte
State, particularly in the Slim Buttes and Cave Hills areas of Harding County (fi^) Cranium
£eS Co? ^VC f ° T f°Und fa ^ ^^ T°ngUe ^ and HeU Cr^k locations r
Perkins County, and may be present in other parts of northwestern South Dakota (Curtiss 1
Locahzed uranium deposits occur in pegmatite zones and in granites in the Blackft^rSa
minerals have also been found in the Deadwood and ^mJSSa^S^^
Paleozoic rocks on figure 4), Spearfish Formation, Newcastle Sandstone the SSS?
S^S^
Oroup, and the Ogallala and Ankaree Formations/in western South Dakota (Curtiss 1955)
deposited under reducing conditions under which uranium i
nn ^ f^V*1* ^SSOUri Rivcr> gladal drift ^ nearly c°ntinuous and averages about 100 feet
(30 m) m fluckness, but some areas, such as the northern part of the Coteau des Prairies are
underiain by as much as 800 feet (250 m) of drift (Tipton, 1975). West of tlS
drift is discontinuous and consists mainly of scattered glacially-rounded boulders
d°Sit" **<** f
ll fl au
shale in the source bedrock is reflected in the high clay content of the tills. Till layers are seoara
by layers of stratified drift and, in some areas, loess (windblown silt) or paleosoXSl ^
IV-7 Reprinted from USGS Open-File Report 93-292-H
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-------
r> - - — — -r*-p.- — -~-<•
EXPLANATION
Major deposits
Minor deposits
Figure 5. Locadons of uranium deposits in western South Dakota (from U.S. Geological Survey,
1975).
-------
1 3
ss i i = i *
8> ra := co
• ^ T °G
J£ to c m ja
5 o. = D. CD
d
•
E
B
o
1
I
_rt
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CO
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t
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representing individual glacial advances separated by non-glacial periods. Late Wisconsin deposits
consist of clay-nch till and fragments of local Cretaceous shale bedrock ^195^-^
Wisconsin glacial deposits contain significantly fewer shale fragments, reflecting their primary
source, Precambnan igneous and metamorphic rocks from northern Minnesota. This indicates that
?nth ? ^T? ^^ adVanC6d fr°m ** northeast rather *» fr<™ the north and
northwest as did the late Wisconsin glaciers (Lemke and others, 1965) -
During the last part of the glacial stage, as the glaciers were melting, two glacial lakes
in boutn Dakota. Glacial Lake Dakota coven-A the nnrth«m «,„* ~f *u» T n-
,
Sw^d ^^ G1fM^eDak0*™^^^
Lowland depositing as much as 40 feet (12 m) of silt with lesser amounts of clay and fine sand
Snh ,\ K LakC AgaSSlZ OCCUpied ^ Red K™ VaUev «* extended from northern
Manitoba to the norfceastern corner of South Dakota. At its maximum extent, Lake Agassk
covered more area than all of the present Great Lakes combined (Flint, 1955). Lake Agassiz
drained eastward into the ancestral Minnesota River system through a deep trench now orcupied by
Lake Traverse and Big Stone Lake. Silt and clay lake bed deposits and beach deposits
with Lake Agassiz are found in the northeastern corner of the State.
SOILS
soik of , Sh°Wn " fi«ire 7A- T^6 ^lude Aridic Borolls-
soils of cool, very dry plains; Aridic Ustolls-soils of warm, very dry plains; Typic BoroUs-Sls
% feToT Usf S7SOUS °f Waim' "* ^ ™< Bc^lls-sofc of cSmo Lt
tnTL^ ^ rS°, S ,°f Waim' m°iSt prairie- SoU textures ranSe from clays and clay
to loams sdty and sandy loams, and sands. Clayey and silty soils are most common aT
^^^
-formed soils or weathered bedrock at the surface
INDOOR RADON DATA
Health £^T rad°nHdata Tsliown "fig™ 8 ^ Panted in Table 1 are from The EPA/Indian
^e Ral7£ RetS^ntial Radon Survey and The Radon Project of the University of Pittsburgh
t?ar ™± ^ *, repreSem 7° SCTeening measur^ents in seven counties from homeowners
that purchased charcoal canister radon detectors from The Radon Project Indoor radon dSwe^
S£S±S m a smvey of 669 homes conducted during 1988-89 ^ EPA «^2S^SST
D^ <£? f°n r^Servatlons^ ^ Great Plains (fig. 9). Of these, 378 homes were in South
Dakom. Data for Brookmgs, Brown, Davison, Hughes, Hutchinson, Minnehaha, and YanSon
"
rann i oan
± P IeV^Hgreater *" 4 PCi/L- Taken « ^ group, the Lower Brule, Pine Ridge, Rapid W
and Rosebud reservations in central and southern South Dakota (fig. 9) had a relatively low
percentage of homes (20 percent) with radon levels greater than 4 pCi/L. The Standing Rock and
IV-10 Reprinted from USGS Open-File Report 93-292-H
-------
-------
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Bsmt. & 1st Floor Rn
%>4pCi/L
3E3
5 E3
8 ESS
OtolO
11 to 25
26 to 50
51 to 75
76 to 100
Missing Data
or < 5 measurements
100 Miles
Bsmt. & 1st Floor Rn
Average Concentration (pCi/L)
8 ESJ
8 ES3
4M
J
0.0 to 1.9
2.0 to 4.0
4.1 to 10.0
10.1 to 29.2
Missing Data
or < 5 measurements
^
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TABLE 1. Screening indoor radon data for South Dakota from the EPA/Indian Health
Service Residential Radon Survey and The Radon Project of the University of Pittsburgh
Da* represent 2-7 day charcoal canister measurements. * indicates county data torn The
Radon Project; data for all other counties are from the EPA/ffiS survey
- indicates no data. '
COUNTY
JBennett
[Brookings*
JBrown*
Buffalo
(Corson
Davison
(Dewey
Hutchinson*
(Jackson
{Lyman
I Marshall
(Mellette
iMinnehaha*
|Mood>
jPennington
(Roberts
l^—
Shannon
Todd
Trir
Yankton*
(Ziebach
D.OF
HAS.
6
••••••^w
18
MEAN
1.6
6.3
GEOM.
MEAN
1.4
ME
3.5
1.6
2.6
12
15
10
29.2
5.6
1.6
17
62
16.2
3.5
STD.
DEV.
0.7
Mix
*
26
37
9
5
7.8
6.9
3.9
11.2
^~
5.0 6.2
4.1 3.8i
10.5 8.8
24.7
6.4|
4.9
3.3
80.2
2.5
73.7
12.3
%>20i
93
62
43
63
40
* J.C
t 1.5
1 ~
i 2.5
3.7
2.0
3.0
1.4
1.7
2.2
o.u
0.7
~
4.5
3.9
5.5
2.2
1.7
0.9
4.1
9.*
3.1
_
12.9
14.4
23.0
8.8
7.1
3.3
16.2
50
47
24
24
14
100
18
331
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n
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Cheyenne River reservations in north-central South Dakota had 25 percent of homes with indoor
radon levels greater than 4 pCi/L. The Crow Creek, Flandreau, Sisseton, and Yankton
reservations together had 57 percent of homes with screening radon levels greater than 4 PCi/L
The Crow Creek and Lower Brule reservations (fig. 9) had the highest maximum indoor radon'
tevels with one reading as high as 316 PCi/L in the Lower Brule reservation in Lyman County
Notable counties include Buffalo County, with an indoor radon average of 23.2 pCi/L and a
S?TJ rfd?? °f T3-7 pCi/L °f 15 ^asurements, and Lyman County, with « average of
29 2: pCi/L for 15 readings (the average is skewed toward the 315.7 pCi/L reading, as indicated
bythegeometncmeanof5.4paa.andthemedianof3.3PCi^forthecounty). Theseven
iT^r^J** ?T ""* Rad°n ***** had avera8e ™doorradon kvels ranging from 3.5 to
10.2 pU/L. Five of the seven counties had average indoor radon levels exceeding 4 pCi/L (the
exceptions are Brown and Davison Counties).
GEOLOGIC RADON POTENTIAL
Aerial radioactivity, shown on an equivalent uranium (eU) map of South Dakota (fig 10)
corre ates fairly weU with exposures of uranium-bearing rocks in the unglaciated western part of
the State. Areas with high eU (defined here as > 2.5 parts per million, or ppm) are associated with
the granite core of the Black Hills and with the Cretaceous Inyan Kara and Colorado Grou^T
surrounding the Black Hills (see figure 4). Although they have high radioactivity, PrecambW
SnriSrp ^^ ™ks "» considered to be primarily moderate to locally high in radon
potential. Rock types of the Black Hills core with high radon potential include conglomeratic
metasedimentary rocks near Nemo and pegmatites (Chadima, 1989). High radioactivity is also
associated with Tertiary sediments in Custer and Pennington Counties and with the Tertiary
™rt rL FortUmon ^"nations and White River Group in the Northern Plateaus. Cretaceous
and Tertiary sandstones host uranium deposits in the northwestern and southwestern parts of the
n^fh rTn hlgher:*an;average Counts of uranium in many areas. These rocks have an
™^ ^h/ad°1n P°tential- Ter*»ry rocks in the Southern Plateaus region have a moderate radon
potential but are likely to generate locally high indoor radon levels
h^ ^r? °^gh el[(about 3 PPm>located ™ the central part of the State just north of Pierre
between Blunt and Gettysburg and west to the Missouri River, appears to be associated with
Wisconsin glacial deposits. With this exception, virtually all of the glaciated part of Sou*
Dakota has an anomalously low eU signature. The glacial drift, which is derived mainly from
Cretaceous shale, contains sufficient uranium to generate radon at levels of concern. However
most of the uranium and radium has probably been leached from the near-surface son layers and
transported downward in the soil profile (Schumann and others, 1991). The glacial deposits likely
contain significantly more uranium than is indicated by the eU map, but the gLma-ray
spectrometer, which obtains most of its signal from the upper 30 cm of soil, cannot detect these
higher levels of uranium and radium in the deeper soil horizons.
*nH • ^.genT?' Soil* d?vd?)cd from &*** deP°sits are rapidly weathered, because crushing
aenfT!S£ r 6 T J f SCia! aCti°n CSn Cnhance "* Speed UP soil ^thering processes
(Jenny, 1935) Grinding of the rocks increases the mobility of uranium and radium and the radon
emanation coefficient in the soils by exposing uranium and radium at grain surfaces. Poorly-sorted
glacial drift may also have somewhat higher permeability than the shale bedrock from which it is
derived due to mixing with coarser materials. In addition, cracking of the clayey glacial soils
during dry periods can create sufficient permeability for radon transport. Desiccation cracking is
IV-16 Reprinted from USGS Open-File Report 93-292-H
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an important factor causing elevated radon levels in areas underlain by clayey glacial deposits
Deposits of glacial Lakes Dakota and Agassiz are likely to generate elevated indoor radon levels.
The lake clays and silts have a relatively high radon emanation coefficient and are known to
generate elevated radon in homes and in soil gas in Manitoba (Grasty, 1989) and North Dakota
(Schumann and others, 1991). Unglaciated areas underlain by shale bedrock have a moderate
radon potential due to their combination of above-average uranium content and low permeability
but locaUy elevated radon levels are likely to occur in areas where weathering of the^ale has
produced fractured, relatively more permeable soils.
SUMMARY
Figure 11 shows radon potential areas of South Dakota delineated in this report and
assigned Radon Index (RI) and Confidence Index (CI) scores in Table 2. Area BH, the Black
HiUs, has a moderate radon potential (RI=11) and moderate confidence (CI=8). The granite core
of the Black Hills has a high radiometric signature and may produce locally elevated indoor radon
levels particularly in areas underlain by pegmatites. Area KS, underlain by sandstones and shales
co^d^eTrT^**/mTOUn? ** Black H*8'has a Wgh radon potential (RI=14) and moderate
confidence (CI=9). Of particular concern in this area is the Inyan Kara Group, which is known to
host uranium deposits, especially in the area between Edgemont and Hot Springs. Area ETS
Early Tertiary sandstones, mostly equivalents of the Fort Union Formation of Paleocene age but
bcaUy including the White River Group and Arikaree Formation, has a high radon potential
Se Slim B^ef ^H
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ofSouA DakoTs^fTa iT? CrfidenCe *** (CI) SC°reS f°r geol°Sic radon P°ten^ areas
otbouth Dakota. See figure 11 for locations and abbreviations of ar^
FACTOR
INDOOR RADON
RADIOACTIVITY
GEOLOGY
SOIL PERM.
ARCHITECTURE
GFE POINTS
TOTAT
RANKING
RI
•••MHMH
2
2
2
2
3
0
MHi^V^HH
BH
CI
—^— •———•«
1
3
2
2
__
o
O
—•— — — —•— — — .
MOD MOD
KS
RI
— — •— •— ««««™
3
3
3
2
3
0
CI
1
3
3
2
^•MMM^KM
14 y
HIGH MOD
RI
3
3
3
2
3
0
ETS
CI
1
i
3
3
9
14 9
HIGH MOD
RI
0
11
^^^••^•^^w
MOD
LTS
CI
__
9
^^^^••^•^•IM
MOD
SH
FACTOR RI
INDOOR RADON 1
RADIOACTIVITY 1
GEOLOGY 1
SOIL PERM. 2
ARCHITECTURE 3
GFE POINTS 0
TOTAL 8
CI
1
3
2
2
__
—
8
RANKING LOW MOD
RADON INDEX SCORING:
Radon potential ratpf
jory
LOW
MODERATE/VARIABLE
HIGH
PH
RI CI
2 1
2 3
2 2
1 2
3
0
10 8
MOD MOD
Point ranpe
3-8 points
9-11 points
> 1 1 points
GC
RI
3
1
3
2
3
+2
14
CI
i
i
3
3
j
_
Q
GL
RI
i
i
•
+2
1/1
ri
n
" J--T ?
HIGH MOD HIGH MOD
Probable screening indoor
< 2 pCi/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-20 Reprinted from USGS Open-File Report 93-292-H
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REFERENCES CITED IN THIS REPORT
AND GENERAL REFERENCES PERTAINING TO RADON IN SOUTH DAKOTA
Carmichael, R.S., 1989, Practical handbook of physical properties of rocks and minerals- Boca
Raton, FL: CRC Press, 741 p.
Chadima, Sarah A., 1989, Generalized potential for radon emission based on estimated uranium
content in geologic rock units, South Dakota: South Dakota Geological Survey Circular 44,
21 p.
Curtiss, R.E., 1955, A preliminary report on uranium in South Dakota: South Dakota Geological
Survey Report of Investigations 79,102 p.
Darton, N.H., 1951, Geologic map of South Dakota: U.S. Geological Survey, scale 1:500,000.
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.
Flint, R.F., 1955, Pleistocene geology of eastern South Dakota: U.S. Geological Survey
Professional Paper 262,173 p.
Grasty, R.L., 1989, The relationship of geology and gamma-ray spectrometry to radon in homes
(abs): EOS, v. 70, p. 496.
Hammond, R.H., 1991, Geology of Lake and Moody Counties, South Dakota: South Dakota
Geological Survey Bulletin 35,49 p.
Hogan, E.P., Opheim, L.A., and Zieske, S.H., 1970, Adas of South Dakota: Dubuqe IA
Kendall/Hunt Publishing Company, 137 p. ' '
Jenny, H., 1935, The clay content of the soil as related to climatic factors, particularly temperature-
Soil Science, v. 40, p. 111-128.
Lemke, R.W., Laird, W.M., Tipton, M.J., and Lindvall, R.M., 1965, Quaternary geology of the
northern Great Plains, in Wright, H.E., Jr., and Frey, D.G. (eds), The Quaternary of the
United States: Princeton, NJ, Princeton University Press, p. 15-27.
Richmond, G.M., Fullerton, D.S., and Christiansen, Ann Coe (eds.), 1991, Quaternary geologic
map of the Des Moines 4°x6° quadrangle, United States: U.S. Geological Survey
Miscellaneous Investigations Map 1-1420, sheet NK-15, scale 1:1,000,000.
Rothrock, E.P., 1943, A geology of South Dakota, part 1. The surface: South Dakota Geological
Survey Bulletin 13, 88 p.
Schnabel, R.W., 1975, Uranium, m Mineral and Water Resources of South Dakota: South Dakota
Geological Survey Bulletin 16, p. 172-176.
IV-21 Reprinted from USGS Open-File Report 93-292-H
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Schumann, R.R., Peake, R.T., Schmidt, K.M., and Owen, D.E., 1991, Correlations of soil-gas
and indoor radon with geology in glacially derived soils of the northern Great Plains, in
Proceedings of the 1990 International Symposium on Radon and Radon Reduction
Technology, Volume 2, Symposium Oral Papers: U.S. Environmental Protection Aeencv
report EPA/600/9-91/026b, p. 6-23-6-36.
South Dakota Agricultural Experiment Station, 1971, Soil associations of South Dakota: Map
prepared in cooperation with the U.S. Department of Agriculture, Soil Conservation
Service, AES Info Series 3, scale 1:500,000.
Tipton, M.J., 1975, Quaternary glacial deposits and alluvium, in Mineral and water resources of
South Dakota: South Dakota Geological Survey Bulletin 16, p. 47-49.
U.S. Department of Agriculture and the Agricultural Experiment Stations of Illinois, Indiana,
Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, South
Dakota, and Wisconsin, 1960, Soils of the north central region of the United States:
University of Wisconsin Agricultural Experiment Station Bulletin 544,192 p.
U.S. Geological Survey, 1975, Mineral and water resources of South Dakota: Report prepared for
the U.S. Senate Committee on Interior and Insular Affairs, reprinted as South Dakota
Geological Survey Bulletin 16,313 p.
Ward, D.C, 1985, Radon-222 and daughter concentrations in conventionally constructed and
energy efficient structures in South Dakota: Report prepared by the South Dakota
Department of Water and Natural Resources, Office of Air Quality and Solid Waste 24 p
IV-22 Reprinted from USGS Open-File Report 93-292-H
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EPA's Map of Radon Zones
USGS'Geologic Radon Province Map is the technical foundation for EPA's Mao
60'0 Rad°n radon POtentS for "
a r
approxmaately 360 geologic provmces. EPA has adapted this information to fit a county
boundary map m order to produce the Map of Radon Zones.
The Map of Radon Zones is based on the same range of predicted screening lewh «f
f±ws zle^08' GeH°IOgiC Rad°n Pr°VinCe MaP" EPA ^££H±?* °f
fhal Tncfr 7 TeaS 6 " aVera§e PfediCted ind°°r radon screeni"g Potential greater
5^L^^^
indoor radon screening potential less than 2 pCi/L. average
Since the geologic province boundaries cross state and county boundaries a strict
^anslation 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
SScTTT °f diff*rfrankinBS)> ^ C°UntieS — assigned lo^'zone based on Z
prated radon potentxal of the province in which most of its area lie, (See Part I for more
SOUTH DAKOTA IUAP r>F
South Dakota radon program for information on testing and fixinj homes. Telephone
numbers and addresses can be found in Part II of this report.
V-l
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