United States
Environmental Protection
Agency
Air and Radiation
(6604J)
402-H-93-054
September 1993
EPA's Map of Radon Zones
NORTH DAKOTA
-------
-------
EPA'S MAP OF RADON ZONES
NORTH DAKOTA
RADON DIVISION
OFFICE OF RADIATION AND INDOOR AIR
U.S. ENVIRONMENTAL PROTECTION AGENCY
SEPTEMBER, 1993
-------
-------
ACKNOWLEDGEMENTS
This document was prepared by the U.S. Environmental Protection Agency's (EPA's)
Office of Radiation and Indoor Air (ORIA) in conjunction with the U.S. Geological Survey
(USGS). Sharon W. White was the EPA project manager. Numerous other people in ORIA
were instrumental in the development of the Map of Radon Zones, including Lisa Ratcliff,
Kirk Maconaughey, R. Thomas Peake, Dave Rowson, and Steve Page.
EPA would especially like to acknowledge the outstanding effort of the USGS
radon team — Linda Gundersen, Randy Schumann, Jim Otton, Doug Owen, Russell
Dubiel, Kendell Dickinson, and Sandra Szarzi — in developing the technical base for the
Map of Radon Zones.
ORIA would also like to recognize the efforts of all the EPA Regional Offices in
coordinating the reviews with the State programs and the Association of American State
Geologists (AASG) for providing a liaison with the State geological surveys. In addition,
appreciation is expressed to all of the State radon programs and geological surveys for their
technical input and review of the Map of Radon Zones.
-------
-------
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 NORTH DAKOTA
V. EPA'S MAP OF RADON ZONES -- NORTH DAKOTA
-------
-------
OVERVIEW
Sections 307 and 309 of the 1988 Indoor Radon Abatement Act (IRAA) direct EPA to
identify areas of the United States that have the potential to produce elevated levels of radon.
EPA, the U.S. Geological Survey (USGS), and the Association of American State Geologists
(AASG) have worked closely over the past several . . to produce a series of maps and
documents which address these directives. The EPA Map of Radon Zones is a compilation of
that work and fulfills the requirements of sections 307 and 309 of IRAA. The Map of Radon
Zones identifies, on a county-by-county basis, areas of the U.S. that have the highest potential
for elevated indoor radon .levels (greater than 4 pCi/L).
The Map of Radon Zones is designed to assist national, State and local governments
and organizations to target their radon program activities and resources. It is also intended to
help building code officials determine areas that are the highest priority for adopting radon-
resistant building practices. The Map of Radon Zones should not be used to determine if
individual homes in any given area need to be tested for radon. EPA recommends that all
homes be tested for radon, regardless of geographic location or the zone designation of
the county in which they are located.
This document provides, background information concerning the development of the
Map of Radon Zones. It explains the purposes of the map, the approach for developing the
map (including the respective roles of EPA and USGS), the data sources used, the conclusions
and confidence levels developed for the prediction of radon potential, and the review process
that was conducted to finalize this effort.
BACKGROUND
Radon (Rn222) is a colorless, odorless, radioactive gas. It comes from the natural
decay of uranium that is found in nearly all soils. It typically moves through the ground to
the air above and into homes and other buildings through cracks and openings in the
foundation. Any home, school or workplace may have a radon problem, regardless of
whether it is new or old, well-sealed or drafty, or with or without a basement. Nearly one out
of every 15 homes in the U.S. is estimated to have elevated annual average levels of indoor
radon.
Radon first gained national attention in early 1984, when extremely high levels of
indoor radon were found in areas of Pennsylvania, New Jersey, and New York, along the
Reading Prong-physiographic province. EPA established a Radon Program in 1985 to assist
States and homeowners in reducing their risk of lung cancer from indoor radon.
Since 1985, EPA and USGS have been working together to continually increase our
understanding of radon sources and the migration dynamics that cause elevated indoor radon
levels. Early efforts resulted in the 1987 map entitled "Areas with Potentially High Radon
Levels." This map was based on limited geologic information only because few indoor radon
measurements were available at the time. The development of EPA's Map of Radon Zones
and its technical foundation, USGS' National Geologic Radon Province Map, has been based
on additional information from six years of the State/EPA Residential Radon Surveys,
independent State residential surveys, and continued expansion of geologic and geophysical
information, particularly the data from the National Uranium Resource Evaluation project.
1-1
-------
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
4 pCi/L
o Zone 2 counties have a predicted average screening level > 2 pCi/L and
< 4 pCi/L
o Zone 3 counties have a predicted average screening level < 2 pCi/L
The Zone designations were determined by assessing five factors that are known to be
important indicators of radon potential: indoor radon measurements, geology, aerial
radioactivity, soil parameters, and foundation types.
The predictions of average screening levels in each of the Zones is an expression of
radon potential in the lowest liveable area of a structure. This map is unable to estimate
actual exposures to radon. EPA recommends methods for testing and fixing individual homes
based on an estimate of actual exposure to radon. For more information on testing and fixing
elevated radon levels in homes consult these EPA publications: A Citizen's Guide to Radon,
the Consumer's Guide to Radon Reduction and the Home Buyer's and Seller's Guide to
Radon.
EPA believes that States, local governments and other organizations can achieve
optimal risk reductions by targeting resources and program activities to high radon potential
areas. Emphasizing targeted approaches (technical assistance, information and outreach
efforts, promotion of real estate mandates and policies and building codes, etc.) in such areas
addresses the greatest potential risks first.
EPA also believes that the use of passive radon control systems in the construction of
new homes in Zone 1 counties, and the activation of those systems if necessitated by follow-
up testing, is a cost effective approach to achieving significant radon risk reduction.
The Map of Radon Zones and its supporting documentation establish no regulatory
requirements. Use of this map by State or local radon programs and building code officials is
voluntary. The information presented on the Map of Radon Zones and in the supporting
documentation is not applicable to radon in water.
Development of the Map of Radon Zones
The technical foundation for the Map of Radon Zones is the USGS Geologic Radon
Province Map. In order to examine the radon potential for the United States, the USGS
began by identifying approximately 360 separate geologic provinces for the U.S. The
provinces are shown on the USGS Geologic Radon Province Map (Figure 2), Each of the
geologic provinces was evaluated by examining the available data for that area: indoor radon
measurements, geology, aerial radioactivity, soil parameters, and foundation types. As stated
previously, these five factors are considered to be of basic importance in assessing radon
1-2
-------
O
S3
c
-d
A
f*
«W
O
00
-------
CM
CO
C7>
CD
-------
potential and some data are available for each of these factors in every geologic province. The
province boundaries do not coincide with political borders (county and state) but define areas
of general radon potential. The five factors were assigned numerical values based on an
assessment of their respective contribution to radon potential, and a confidence level was
assigned to each contributing variable. The approach used by USGS to estimate the radon
potential for each province is described in Part II of this document.
EPA subsequently developed the Map of Radon Zones by extrapolating from the
province level to the county level so that all counties in the U.S. were assigned to one of
three radon zones. EPA assigned each county to a given zone based on its provincial radon
potential. For example, if a county is located within a geologic province that has a predicted
average screening level greater than 4 pCi/L, it was assigned to Zone 1. Likewise, counties
located in provinces with predicted average screening levels > 2 pCi/L and < 4 pCi/L, and
less than 2 pCi/L, were assigned to Zones 2 and 3, respectively.
If the boundaries of a county fall in more than one geologic province, the county was
assigned to a zone based on the predicted radon potential of the province in which most of
the area lies. For example, if three different provinces cross through a given county, the
county was assigned to the zone representing the radon potential of the province containing
most of the county's land area. (In this case, it is not technically correct to say that the
predicted average screening level applies to the entire county since the county falls in
multiple provinces with differing radon potentials.)
Figures 3 and 4 demonstrate an example of how EPA extrapolated the county zone
designations for Nebraska from the USGS geologic province map for the State. As figure 3
shows, USGS has identified 5 geologic provinces for Nebraska. Most of the counties are
extrapolated "straight" from their corresponding provinces, but there are counties "partitioned"
by several provinces - for example, Lincoln County. Although Lincoln county falls in
multiple provinces, it was assigned to Zone 3 because most of its area falls in the province
with the lowest radon potential.
It is important to note that EPA's extrapolation from the province level to the
county level may mask significant "highs" and "lows" within specific counties. In other
words, within-county variations in radon potential are not shown on the Map of Radon
Zones. EPA recommends that users who may need to address specific within-county
variations in radon potential (e.g., local government officials considering the
implementation of radon-resistant construction codes) consult USGS' Geologic Radon
Province Map and the State chapters provided with this map for more detailed
information, as well as any locally available data.
Map Validation
The Map of Radon Zones is intended to represent a preliminary assessment of radon
potential for the entire United States. The factors that are used in this effort -indoor radon
data, geology, aerial radioactivity, soils, and foundation type ~ are basic indicators for radon
potential. It is important to note, however, that the map's county zone designations are not
"statistically valid" predictions due to the nature of the data available for these 5 factors at the
county level. In order to validate the map in light of this lack of statistical confidence, EPA
conducted a number of analyses. These analyses have helped EPA to identify the best'
situations in which to apply the map, and its limitations.
1-5
-------
Figure 3
Geologic Radoo Potential Provinces for Nebraska
Lincoln County
Hilt
Uo 4 c r 11 s
Low
Figure 4
NEBRASKA - EPA Map of Radon Zones
Lincoln County
Zoat 1 Zone 2 Zone 3
1-6
-------
One such analysis involved comparing county zone designations to indoor radon
measurements from the State/EPA Residential Radon Surveys (SRRS). Screening averages
for counties with at least 100 measurements were compared to the counties' predicted radon
potential as indicated by the Map of Radon Zones. EPA found that 72% of the county
screening averages were correctly reflected by the appropriate zone designations on the Map.
In all other cases, they only differed by 1 zone.
Another accuracy analysis used the annual average data from the National Residential
Radon Survey (NRRS). The NRRS indicated that approximately 6 million homes in the
United States have annual averages greater than or. equal to 4 pCi/L. By cross checking the
county location of the approximately 5,700 homes which participated in the survey, their
radon measurements, and the zone designations for these counties* EPA found that
approximately 3.8 million homes of the 5.4 million homes with radon levels greater than or
equal to 4 pCi/L will be found in counties designated as Zone 1. A random sampling of an
equal number of counties would have only found approximately 1.8 million homes greater
than 4 pCi/L. In other words, this analysis indicated that the map approach is three times
more efficient at identifying high radon areas than random selection of zone designations.
Together, these analyses show that the approach EPA used to develop the Map of
Radon Zones is a reasonable one. In addition, the Agency's confidence is enhanced by results
of the extensive State review process -- the map generally agrees with the States' knowledge
of and experience in their own jurisdictions. However, the accuracy analyses highlight two
important points: the fact that elevated levels will be found in Zones 2 and 3, and that there
will be significant numbers of homes with lower indoor radon levels in all of the Zones. For
these reasons, users of the Map of Radon Zones need to supplement the Map with locally
available data whenever possible. Although all known "hot spots", i.e., localized areas of
consistently elevated levels, are discussed in the State-
specific chapters, accurately defining the boundaries of the "hot spots" on this scale of map is
not possible at this time. Also, unknown "hot spots" do exist.
The Map of Radon Zones is intended to be a starting point for characterizing radon
potential because our knowledge of radon sources and transport is always growing. Although
this effort represents the best data available at this time, EPA will continue to study these
parameters and others such as house construction, ventilation features and meteorology factors
in order to better characterize the presence of radon in U.S homes, especially in high risk
areas. These efforts will eventually assist EPA in refining and revising the conclusions of the
Map of Radon Zones. And although this map is most appropriately used as a targeting tool
by the aforementioned audiences -- the Agency encourages all residents to test their homes
for radon, regardless of geographic location or the zone designation of the county in
which they live. Similarly, the Map of Radon Zones should not to be used in lieu of
testing during real estate transactions.
Review Process
The Map of Radon Zones has undergone extensive review within EPA and outside the
Agency. The Association of American State Geologists (AASG) played an integral role in
this review process. The AASG individual State geologists have reviewed their State-specific
information, the USGS Geologic Radon Province Map, and other materials for their geologic
content and consistency.
1-7
-------
In addition to each State geologist providing technical comments, the State radon
offices were asked to comment on their respective States' radon potential evaluations. In
particular, the States were asked to evaluate the data used to assign their counties to specific
zones. EPA and USGS worked with the States to resolve any issues concerning county zone
designations. In a few cases, States have requested changes in county zone designations. The
requests were based on additional data from the State on geology, indoor radon
measurements, population, etc. Upon reviewing the data submitted by the States, EPA did
make some changes in zone designations. These changes, which do not strictly follow the
methodology outlined in this document, are discussed in the respective State chapters.
EPA encourages the States and counties to conduct further research and data collection
efforts to refine the Map of Radon Zones. EPA would like to be kept informed of any
changes the States, counties, or others make to the maps. Updates and revisions will be
handled in a similar fashion to the way the map was developed. States should notify EPA of
any proposed changes by forwarding the changes through the Regional EPA offices that are
listed in Part II. Depending on the amount of new information that is presented, EPA will
consider updating this map periodically. The State radon programs should initiate proper
notification of the appropriate State officials when the Map of Radon Zones is released and
when revisions or updates are made by the State or EPA.
1-8
-------
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 (he
indoor radon concentrations of individual homes, building sites, or housing tracts. Elevated
levels of indoor radon have been found in every State, and EPA recommends that all homes
be tested for indoor radon.
Booklets detailing the radon potential assessment for the U.S. have been developed for
each State. USGS geologists are the authors of the geologic radon potential booklets. Each
booklet consists of several components, the first being an overview to the mapping project
(Part I), this introduction to the USGS assessment (Part II), including a general discussion of'
radon (occurrence, transport, etc.), and details concerning the types of data used. The third
component is a summary chapter outlining the general geology and geologic radon potential
of the EPA Region (Part III). The fourth component is an individual chapter for each state
(Part IV). Each state chapter discusses the state's specific geographic setting, soils, geologic
setting, geologic radon potential, indoor radon data, and a summary outlining the radon
potential rankings of geologic areas in the state. A variety of maps are presented in each
chapter—geologic, geographic, population, soils, aerial radioactivity, and indoor radon data by
county. Finally, the booklets contain EPA's map of radon zones for each state and an
accompanying description (Part V).
Because of constraints on the scales of maps presented in these reports and because the
smallest units used to present the indoor radon data are counties, some generalizations have
been made in order to estimate the radon potential of each area. Variations in geology, soil
characteristics, climatic factors, homeowner lifestyles, and other factors that influence radon
concentrations can be quite large within any particular geologic area, so these reports cannot
be used to estimate or predict the indoor radon concentrations of individual homes or housing
II-1 Reprinted from USGS Open-File Report 93-292
-------
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 (::;Rn) is produced from the radioactive decay of radium ("*Ra), which is, in turn,
a product of the decay of uranium (238U) (fig. 1). The half-life of :"Rn is 3.825 days. Other
isotopes of radon occur naturally, but, with the exception of thoron (220Rn), which occurs in
concentrations high enough to be of concern in a few localized areas, they are less important
in terms of indoor radon risk because of their extremely short half-lives and less common
occurrence. In general, the concentration and mobility of radon in soil are dependent on
several factors, the most important of which are the soil's radium content and distribution,
porosity, permeability to gas movement, and moisture content. These characteristics are, in
turn, determined by the soil's parent-material composition, climate, and the soil's age or
maturity. If parent-material composition, climate, vegetation, age of the soil, and topography
are known, the physical and chemical properties of a soil in a given area can be predicted.
As soils form, they develop distinct layers, or horizons, that are cumulatively called the
soil profile. The A horizon is a surface or near-surface horizon containing a relative
abundance of organic matter but dominated by mineral matter. Some soils contain an E
horizon, directly below the A horizon, that is generally characterized by loss of clays, iron, or
aluminum, and has a characteristically lighter color than the A horizon. The B horizon
underlies the A or E horizon. Important characteristics of B horizons include accumulation of
clays, iron oxides, calcium carbonate or other soluble salts, and organic matter complexes. In
drier environments, a horizon may exist within or below the B horizon that is dominated by
calcium carbonate, often called caliche or calcrete. This carbonate-cemented horizon is
designated the K horizon in modern soil classification schemes. The C horizon underlies the
B (or K) and is a zone of weathered parent material that does not exhibit characteristics of A
or B horizons; that is, it is generally not a zone of leaching or accumulation. In soils formed
in place from the underlying bedrock, the C horizon is a zone of unconsolidated, weathered
bedrock overlying the unweathered bedrock.
The shape and orientation of soil particles (soil structure) control permeability and affect
water movement in the soil. Soils with blocky or granular structure have roughly equivalent
permeabilities in the horizontal and vertical directions, and air and water can infiltrate the soil
relatively easily. However, in soils with platy structure, horizontal permeability is much
greater than vertical permeability, and air and moisture infiltration is generally slow. Soils
with prismatic or columnar structure have dominantly vertical permeability. Platy and
prismatic structures form in soils with high clay contents. In soils with shrink-swell clays, air
II-2 Reprinted from USGS Open-File Report 93-292
-------
C3
I
fr
en
U
•a
o
•S3
•§
eo
o
CO
C3
O
aj
o «
-------
and moisture infiltration rates and depth of wetting may be limited when the cracks in the
surface soil layers swell shut. Clay-rich B horizons, particularly those with massive or platy
structure, can form a capping layer that impedes the escape of soil gas to the surface
(Schumann and others, 1992). However, the shrinkage of clays can act to open or widen
cracks upon drying, thus increasing the soil's permeability to gas flow during drier periods.
Radon transport in soils occurs by two processes: (1) diffusion and (2) flow (Tanner,
1964). Diffusion is'the process whereby radon atoms move from areas of higher
concentration to areas of lower concentration in response to a concentration gradient. Flow is
the process by which soil air moves through soil pores in response to differences in pressure
within the soil or between the soil and the atmosphere, carrying the radon atoms along with it.
Diffusion is the dominant radon transport process in soils of low permeability, whereas flow
tends to dominate in highly permeable soils (Sextro and others, 1987). In low-permeability
soils, much of the radon may decay before it is able to enter a building because its transport
rate is reduced. Conversely, highly permeable soils, even those that are relatively low in
radium, such as those derived from some types of glacial deposits, have been associated with
high indoor radon levels in Europe and in the northern United States (Akerblom and others,
1984; Kunz and others, 1989; Sextro and others, 1987). In areas of karst topography formed
in carbonate rock (limestone or dolomite) environments, solution cavities and fissures can
increase soil permeability at depth by providing additional pathways for gas flow.
Not all radium contained in soil grains and grain coatings will result in mobile radon
when the radium decays. Depending on where the radium is distributed in the soil, many of
the radon atoms may remain imbedded in the soil grain containing the parent radium atom, or
become imbedded in adjacent soil grains. The portion of radium that releases radon into the
pores and fractures of rocks and soils is called the emanating fraction. When a radium atom
decays to radon, the energy generated is strong enough to send the radon atom a distance of
about 40 nanometers (1 nm = 10'9 meters), or about 2xlO'6 inches—this is known as alpha
recoil (Tanner, 1980). Moisture in the soil lessens the chance of a recoiling radon atom
becoming imbedded in an adjacent grain. Because water is more dense than air, a radon atom
will travel a shorter distance in a water-filled pore than in an air-filled pore, thus increasing
the likelihood that the radon atom will remain in the pore space. Intermediate moisture levels
enhance radon emanation but do not significantly affect permeability. However, high
moisture levels can significantly decrease the gas permeability of the soil and impede radon
movement through the soil.
Concentrations of radon in soils are generally many times higher than those inside of
buildings, ranging from tens of pCi/L to more than 100,000 pCi/L, but typically in the range
of hundreds to low thousands of pCi/L. Soil-gas radon concentrations can vary in response to
variations in climate and weather on hourly, daily, or seasonal time scales. Schumann and
others (1992) and Rose and others (1988) recorded order-of-magnitude variations in soil-gas
radon concentrations between seasons in Colorado and Pennsylvania. The most important
factors appear to be (1) soil moisture conditions, which are controlled in large part by
precipitation; (2) barometric pressure; and (3) temperature. Washington and Rose (1990)
suggest that temperature-controlled partitioning of radon between water and gas in soil pores
also has a significant influence on the amount of mobile radon in soil gas.
Homes in hilly limestone regions of the southern Appalachians were found to have higher
indoor radon concentrations during the summer than in the winter. A suggested cause for this
phenomenon involves temperature/pressure-driven .flow of radon-laden air from subsurface
II-4 Reprinted from USGS Open-File Report 93-292
-------
solution cavities in the carbonate rock into houses. As warm air enters solution cavities that
are higher on the hillslope than the homes, it cools and settles, pushing radon-laden air from
lower in the cave or cavity system into structures on the hillslope (Gammage and others,
1993). In contrast, homes built over caves having openings situated below the level of the
home had higher indoor radon levels in the winter, caused by cooler outside air entering the
cave, driving radon-laden air into cracks and solution cavities in the rock and soil, and
ultimately, into homes (Gammage and others, 1993).
RADON ENTRY INTO BUILDINGS
A driving force (reduced atmospheric pressure in the house relative to the soil, producing
a pressure gradient) and entry points must exist for radon to enter a building from the soil.
The negative pressure caused by furnace combustion, ventilation devices, and the stack effect
(the rising and escape of warm air from the upper floors of the building, causing a
temperature and pressure gradient within the structure) during cold winter months are
common driving forces. Cracks and other penetrations through building foundations, sump
holes, and slab-to-foundation wall joints are common entry points.
Radon levels in the basement are generally higher than those on the main floor or upper
floors of most structures. Homes with basements generally provide more entry points for
radon, commonly have a more pronounced stack effect, and typically have lower air pressure
relative to the surrounding soil than nonbasement homes. The term "nonbasement" applies to
slab-on-grade or crawl space construction.
METHODS AND SOURCES OF DATA
The assessments of radon potential in the booklets that follow this introduction were
made using five main types of data: (1) geologic (lithologic); (2) aerial radiometric; (3) soil
characteristics, including soil moisture, permeability, and drainage characteristics; (4) indoor
radon data; and (5) building architecture (specifically, whether homes in each area are built
slab-on-grade or have a basement or crawl space). These five factors were evaluated and
integrated to produce estimates of radon potential. Field measurements of soil-gas radon or
soil radioactivity were not used except where such data were available in existing, published
reports of local field studies. Where applicable, such field studies are described in the
individual state chapters.
GEOLOGIC DATA
The types and distribution of lithologic units and other geologic features in an
assessment area are of primary importance in determining radon potential. Rock types that
are most likely to cause indoor radon problems include carbonaceous black shales, glauconite-
bearing sandstones, certain kinds of fluvial sandstones and fluvial sediments, phosphorites,
chalk, karst-producing carbonate rocks, certain kinds of glacial deposits, bauxite, uranium-rich
granitic rocks, metamorphic rocks of granitic composition, silica-rich volcanic rocks, many
sheared or faulted rocks, some coals, and certain kinds of contact metamorphosed rocks.
Rock types least likely to cause radon problems include marine quartz sands, non-
carbonaceous shales and siltstones, certain kinds of clays, silica-poor metamorphic and
II-5 Reprinted from USGS Open-File Report 93-292
-------
igneous rocks, and basalts. Exceptions exist within these general lithologic groups because of
the occurrence of localized uranium deposits, commonly of the hydrothermal type in
crystalline rocks or the "roll-front" type in sedimentary rocks. Uranium and radium are
commonly sited in heavy minerals, iron-oxide coatings on rock and soil grains, and organic
materials in soils and sediments. Less common are uranium associated with phosphate and
carbonate complexes in rocks and soils, and uranium minerals.
Although many cases of elevated indoor radon levels can be traced to high radium and
(or) uranium concentrations in parent rocks, some structural features, most notably faults and
shear zones, have been identified as sites of localized .uranium concentrations (Deffeyes and
MacGregor, 1980) and have been associated with some of the highest reported indoor radon
levels (Gundersen, 1991). The two highest known indoor radon occurrences are associated
with sheared fault zones in Boyertown, Pennsylvania (Gundersen and others, 1988a; Smith
and others, 1987), and in Clinton, New Jersey (Henry and others, 1991; Muessig and Bell,
1988).
NURE AERIAL RADIOMETRIC DATA
Aerial radiometric data are used to quantify the radioactivity of rocks and soils.
Equivalent uranium (eU) data provide an estimate of the surficial concentrations of radon
parent materials (uranium, radium) in rocks and soils. Equivalent uranium is calculated from
the counts received by a gamma-ray detector from the 1.76 MeV (mega-electron volts)
emission energy corresponding to bismuth-214 (:HBi), 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
-------
FLIGHT LINE SPACING Of NUKE AERIAL SURVEYS
2 L'U (1 VILE)
5 EU (3 HUES)
2 fc 5 KM
10 KM (6 MILES)
5 & 10 EH
NO DATA
Figure 2. Nominal flightline spacings for NURE aerial gamma-ray surveys covering the
contiguous United States (from Duval and others, 1990). Rectangles represent I°x2° quadrangles.
-------
Figure 2 is an index map of NURE 1° x 2° quadrangles showing the flight-line spacing
for each quadrangle. In general, the more closely spaced the flightlines are, the more area
was covered by the aerial gamma survey, and thus, more detail is available in the data set.
For an altitude of 400 ft above the ground su.face and with primary flightline spacing
typically between 3 and 6 miles, less than 10 percent of the ground surface of the United
States was actually measured by the airborne gamma-ray detectors (Duval and others, 1989),
although some areas had better coverage than others due to the differences in flight-line
spacing between areas (fig. 2). This suggests that some localized uranium anomalies may not
have been detected by the aerial surveys, but the good correlations of elJ patterns with
geologic outcrop patterns'indicate that, at relatively small scales (approximately 1:1,000,000
or smaller) the National elJ map (Duval and others, 1989) gives reasonably good estimates of
average surface uranium concentrations and thus can assist in the prediction of radon potential
of rocks and soils, especially when augmented with additional geologic and soil data.
The shallow (20-30 cm) depth of investigation of gamma-ray spectrometers, either
ground-based or airborne (Duval and others, 1971; Durrance, 1986), suggests that gamma-ray
data may sometimes underestimate the radon-source strength in soils in which some of the
radionuclides in the near-surface soil layers have been transported downward through the soil
profile. In such cases the concentration of radioactive minerals in the A horizon would be
lower than in the B horizon, where such minerals are typically concentrated. The
concentration of radionuclides in the C horizon and below may be relatively unaffected by
surface solution processes. Under these conditions the surface gamma-ray signal may indicate
a lower radon source concentration than actually exists in the deeper soil layers, which are
most likely to affect radon levels in structures with basements. The redistribution of
radionuclides in soil profiles is dependent on a combination of climatic, geologic, and
geochemical factors. There is reason to believe that correlations of eU with actual soil
radium and uranium concentrations at a depth relevant to radon entry into structures may be
regionally variable (Duval, 1989; Schumann and Gundersen, 1991). Given sufficient
understanding of the factors cited above, these regional differences may be predictable.
SOIL SURVEY DATA
Soil surveys prepared by the U.S. Soil Conservation Service (SCS) provide data on soil.
characteristics, including soil-cover thickness, grain-size distribution, permeability, shrink-
swell potential, vegetative cover, generalized groundwater characteristics, and land use. The
reports are available in county formats and State summaries. The county reports typically
contain both generalized and detailed maps of soils in the area.
Because of time and map-scale constraints, it was impractical to examine county soil
reports for each county in the United States, so more generalized summaries at appropriate
scales were used where available. For State or regional-scale radon characterizations, soil
maps were compared to geologic maps of the area, and the soil descriptions, shrink-swell
potential, drainage characteristics, depth to seasonal high water table, permeability, and other
relevant characteristics of each soil group noted. Technical soil terms used in soil surveys are
generally complex; however, a good summary of soil engineering terms and the national
distribution of technical soil types is the "Soils" sheet of the National Atlas (U.S. Department
of Agriculture, 1987).
II-8 Reprinted from USGS Open-File Report 93-292
-------
Soil permeability is commonly expressed in SCS soil surveys in terms of the speed, in
inches per hour (in/hr), at which water soaks into the soil, as measured in a soil percolation
test. Although in/hr are not truly units of permeability, these units are in widespread use and
are referred to as "permeability" in SCS soil surveys. The permeabilities listed in the SCS
surveys are for water, but they generally correlate well with gas permeability. Because data
on gas permeability of soils is extremely limited, data on permeability to water is used as a
substitute except in cases in which excessive soil moisture is known to exist. Water in soil
pores inhibits gas transport, so the amount of radon available to a home is effectively reduced
by a high water table. Areas likely to have high water tables include river valleys, coastal
areas, and some areas overlain by deposits of glacial origin (for example, loess).
Soil permeabilities greater than 6.0 in/hr may be considered high, and permeabilities less
than 0.6 in/hr may be considered low in terms of soil-gas transport. Soils with low
permeability may generally be considered to have a lower radon potential than more
permeable soils with similar radium concentrations. Many well-developed soils contain a
clay-rich B horizon that may impede vertical soil gas transport. Radon generated below this
horizon cannot readily escape to the surface, so it would instead tend to move laterally,
especially under the influence of a negative pressure exerted by.a building.
Shrink-swell potential is an indicator of the abundance of smectitic (swelling) clays in a
soil. Soils with a high shrink-swell potential may cause building foundations to crack,
creating pathways for radon entry into the structure. During dry periods, desiccation cracks in
shrink-swell soils provide additional pathways for soil-gas transport and effectively increase
the gas permeability of the soil. Soil permeability data and soil profile data thus provide
important information for regional radon assessments.
INDOOR RADON DATA
Two major sources of indoor radon data were used. The first and largest source of data is
from the State/EPA Residential Radon Survey (Ronca-Battista and others, 1988; Dziuban and
others, 1990). Forty-two states completed EPA-sponsored indoor radon surveys between 1986
and 1992 (fig. 3). The State/EPA Residential Radon Surveys were designed to be
comprehensive and statistically significant at the state level, and were subjected to high levels
of quality assurance and control. The surveys collected screening indoor radon measurements,
defined as 2-7 day measurements using charcoal canister radon detectors placed in the lowest
livable area of the home. The target population for the surveys included owner-occupied
single family, detached housing units (White and others, 1989), although attached structures
such as duplexes, townhouses, or condominiums were included in some of the surveys if they
met the other criteria and had contact with the ground surface. Participants were selected
randomly from telephone-directory listings. In total, approximately 60,000 homes were tested
in the State/EPA surveys.
The second source of indoor radon data comes from residential surveys that have been
conducted in a specific state or region of the country (e.g. independent state surveys or utility
company surveys). Several states, including Delaware, Florida, Illinois, New Hampshire, New
Jersey, New York, Oregon, and Utah, have conducted their own surveys of indoor radon. The
quality and design of a state or other independent survey are discussed and referenced where
the data are used.
II-9 Reprinted from USGS Open-File Report 93-292
-------
u
a.
CD
c
s
J3
o
•§
o
o
"O
CO
C/D
O
1
01
*2
*•_*
C
•8
2
oo
1
s
1
o
<4->
o
€
I
CO
I
to
E
-------
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-
11-11 Reprinted from USGS Open-File Report 93-292
-------
TABLE 1. RADON INDEX MATRIX, "ppm eU" indicates parts per million of equivalent
uranium, as indicated by NURE aerial radiometric data. See text discussion for details.
TNCRHASING RADON POTENTIAL
POINT VALUE
FACTOR
. >4pCi/L
INDOOR RADON (average)
> 2.5 ppm eU
1.5 - 2.5 ppm eU
AERIAL RADIOACTIVITY
<1.5ppmeU
GEOLOGY*
mostly basement
mostly slab
SOIL PERMEABILITY
^«"^^"•^^••••^^••^
ARCHITECTURE TYPE
'GEOLOGIC FIELD EVIDENCE (GFE) POINTS: GFE points arp assi
for the "Geology" factor for specific, relevant geologic field studies, bee text
Geologicevidencesupporting: gggn*. ^points
LOW -2 points
No relevant geologic field studies 0 points
SCORING:
Probable average screening
Point range ind""*" radon for area
LOW
MODERATE/VARIABLE
HIGH
3-8 points
9-11 points
12-17 points
<2pCi/L
2-4pCi/L
>4pCi/L
POSSIBLE RANGE OF POINTS = 3 to 17
TABLE 2. CONFIDENCE INDEX MATRIX
TMrRF.ASTNG CONFIDENCE
FACTOR
INDOOR RADON DATA
AERIAL RADIOACTIVITY
GEOLOGIC DATA
SOIL PERMEABILITY
POINT VALUE
good coverage/qualit
fair coverage/quality
questionable/no data
questionable
variable
questionable/no data
proven geol. model
C«ii^i^—«^^—«^^^~^
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
H-12 Reprinted from USGS Open-File Report 93-292
-------
included as supplementary information and are discussed in the individual State chapters. If
the average screening indoor radon level for an area was less than 2 pCi/L, the indoor radon
factor was assigned 1 point, if it was between 2 and 4 pCi/L, it was scored 2 points, and if
the average screening indoor radon level for an area was greater than 4 pCi/L, the indoor
radon factor was assigned 3 RI points.
Aerial radioactivity data used in this report are from the. equivalent uranium map of the
conterminous United States compiled from NUKE aerial gamma-ray surveys (Duval and
others, 1989). These data indicate the gamma radioactivity from approximately -the upper 30
cm of rock and soil, expressed in units of ppm equivalent uranium. An approximate average
value of eU was determined visually for each area and point values assigned based on
whether the overall eU for the area falls below 1.5 ppm (1 point), between 1.5 and 2.5 ppm
(2 points), or greater than 2.5 ppm (3 points).
The geology factor is complex and actually incorporates many geologic characteristics. In
the matrix, "positive" and "negative" refer to the presence or absence and distribution of rock
types known to have high uranium contents and to generate elevated radon in soils or indoors.
Examples of "positive" rock types include granites, black shales, phosphatic rocks, and other
rock types described in the preceding "geologic data" section. Examples of "negative" rock
types include marine quartz sands and some clays. The term "variable" indicates that the
geology within the region is variable or that the rock types in the area are known or suspected
to generate elevated radon in some areas but not in others due to compositional differences,
climatic effects, localizeddistribution of uranium, or other factors. Geologic information
indicates not only how much uranium is present in the rocks and soils but also gives clues for
predicting general radon emanation and mobility characteristics through additional factors
such as structure (notably the presence of faults or shears) and geochemical characteristics
(for example, a phosphate-rich sandstone will likely contain more uranium than a sandstone
containing little or no phosphate because the phosphate forms chemical complexes with
uranium). "Negative", "variable", and "positive" geology were assigned 1, 2, and 3 points,
respectively.
In cases where additional reinforcing or contradictory geologic evidence is available,
Geologic Field Evidence (GFE) points were added to or subtracted from an area's score
(Table 1). Relevant geologic field studies are important to enhancing our understanding of
how geologic processes affect radon distribution. In some cases, geologic models and
supporting field data reinforced an already strong (high or low) score; in others, they provided
important contradictory data. GFE points were applied for geologically-sound evidence that
supports the prediction (but which may contradict one or more factors) on the basis of known
geologic field studies in the area or in areas with geologic and climatic settings similar
enough that they could be applied with full confidence. For example, areas of the Dakotas,
Minnesota, and Iowa that are covered with Wisconsin-age glacial deposits exhibit a low aerial
radiometric signature and score only one RI point in that category. However, data from
geologic field studies in North Dakota and Minnesota (Schumann and others, 1991) suggest
that eU is a poor predictor of geologic radon potential in this area because radionuclides have
11-13 Reprinted from USGS Open-File Report 93-292
-------
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
-------
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 RJ 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
-------
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
-------
REFERENCES CITED
Akerblom, G., Anderson, P., and Clavensjo, B., 1984, Soil gas radon--A source for indoor radon
daughters: Radiation Protection Dosimetry, v. 7, p. 49-54.
Deffeyes, K.S., and MacGregor, I.D., 1980, World uranium resources: Scientific American,
v. 242, p. 66-76.
Durrance, E.M., 1986, Radioactivity in geology: Principles and applications: New York, N.Y.,
Wiley and Sons, 441 p.
Duval, J.S., 1989, Radioactivity and some of its applications in geology: Proceedings of the
symposium on the application of geophysics to engineering and environmental problems
(SAGEEP), Golden, Colorado, March 13-16,1989: Society of Engineering and Mineral
Exploration Geophysicists, p. 1-61.
Duval, J.S., Cook, B.C., and Adams, J.A.S., 1971, Circle of investigation of an airborne
gamma-ray spectrometer: Journal of Geophysical Research, v. 76, p. 8466-8470.
Duval, J.S., Jones, W.J., Riggle, F.R., and Pitkin, J.A., 1989, Equivalent uranium map of
conterminous United States: U.S. Geological Survey Open-File Report 89-478,10 p.
Duval, J.S., Reimer, G.M., Schumann, R.R., Owen, D.E., and Otton, J.K., 1990, Soil-gas
radon compared to aerial and ground gamma-ray measurements at study sites near Greeley
and Fort Collins, Colorado: U.S. Geological Survey Open-File Report 90-648,42 p.
Dziuban, J.A., Clifford, M.A., White, S.B., Bergstein, J.W., and Alexander, B.V., 1990,
Residential radon survey of twenty-three States, in Proceedings of the 1990 International
Symposium on Radon and Radon Reduction Technology, Vol. ffl: Preprints: U.S.
Environmental Protection Agency report EPA/600/9-90/005c, Paper IV-2,17 p.
Gammage, R.B., Wilson, D.L., Saultz, R.J., and Bauer, B.C., 1993, Subtereanean transport of
radon and elevated indoor radon in hilly karst terranes: Atmospheric Environment
(in press).
Gundersen, L.C.S., Reimer, G.M., and Agard, S.S., 1988a, Correlation between geology, radon
in soil gas, and indoor radon in the Reading Prong, in Marikos, M.A., and Hansman,
R.H., eds., Geologic causes of natural radionuclide anomalies: Missouri Department of
Natural Resources Special Publication 4, p. 91-102.
Gundersen, L.C.S, Reimer, G.M., Wiggs, C.R., and Rice, C.A., 1988b, Map showing radon
potential of rocks and soils in Montgomery County, Maryland: U.S. Geological Survey
Miscellaneous Field Studies Map MF-2043, scale 1:62,500.
Gundersen, Linda C.S., 1991, Radon in sheared metamorphic and igneous rocks, in Gundersen,
Linda C.S., and Richard B. Wanty, eds., Field studies of radon in rocks, soils, and water:
U.S. Geol. Survey Bulletin no. 1971, p. 39-50.
JJ-17 Reprinted from USGS Open-FUe Report 93-292
-------
Henry, Mitchell E., Kaeding, Margret E., and Monteverde, Donald, 1991, Radon in soil gas and
gamma-ray activity of rocks and soils at the Mulligan Quarry, Clinton, New Jersey, in
Gundersen, Linda C.S., and Richard B. Wanty, eds., Field studies of radon in rocks,
soils, and water: U.S. Geol. Survey Bulletin no. 1971, p. 65-75.
Kinsman, R. W., and Jaacks, J. A., 1987, Environmental influences upon mercury, radon, and
helium concentrations in soil gases at a site near Denver, Colorado: Journal of
Geochemical Exploration, v. 27, p. 259-280.
Kovach, E.M., 1945, Meteorological influences upon the radon content of soil gas: Transactions,
American Geophysical Union, v. 26, p. 241-248.
Kunz, C, Laymon, C.A., and Parker, C, 1989, Gravelly soils and indoor radon, in Osborne,
M.C., and Harrison, J., eds., Proceedings of the 1988 EPA Symposium on Radon and
Radon Reduction Technology, Volume 1: U.S. Environmental Protection Agency Report
EPA/600/9-89/006A, p. 5-75-5-86.
Muessig, K., and Bell, C., 1988, Use of airborne radiometric data to direct testing for elevated
indoor radon: Northeastern Environmental Science, v. 7, no. 1, p. 45-51.
Ronca-Battista, M., Moon, M., Bergsten, J., White, S.B., Holt, N., and Alexander, B., 1988,
Radon-222 concentrations in the United States-Results of sample surveys in five states:
Radiation Protection Dosimetry, v. 24, p. 307-312.
Rose, A.W., Washington, J.W., and Greeman, D.J., 1988, Variability of radon with depth and
season in a central Pennsylvania soil developed on limestone: Northeastern Environmental
Science, v. 7, p. 35-39.
Schery, S.D., Gaeddert, D.H., and Wilkening, M.H., 1984, Factors affecting exhalation of radon
from a gravelly sandy loam: Journal of Geophysical Research, v. 89, p. 7299-7309.
Schumann, R.R., and Owen, D.E., 1988, Relationships between geology, equivalent uranium
concentration, and radon in soil gas, Fairfax County, Virginia: U.S. Geological Survey
Open-File Report 88-18,28 p.
Schumann, R.R., and Gundersen, L.C.S., 1991, Regional differences in radon emanation
coefficients in soils: Geological Society of America Abstracts With Programs, v. 23,
no. 1, p. 125.
Schumann, R.R., Peake, R.T., Schmidt, K.M., and Owen, D.E., 1991, Correlations of soil-gas
and indoor radon with geology in glacially derived soils of the northern Great Plains, in
Proceedings of the 1990 International Symposium on Radon and Radon Reduction
Technology, Volume 2, Symposium Oral Papers: U.S. Environmental Protection Agency
report EPA/600/9-9l/026b, p. 6-23-6-36.
H-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, Term., U.S. Department of
Energy Report ORNL/SUB/84-0024/1.
Smith, R.C., U, Reilly, M.A., Rose, A.W., Barnes, J.H., and Berkheiser, S.W., Jr., 1987,
Radon: a profound case: Pennsylvania Geology, v. 18, p. 1-7.
Tanner, A.B., 1964, Radon migration in the ground: a review, in Adams, J.A.S., and Lowder,
W.M., eds., The natural radiation environment: Chicago, HI., University of Chicago
Press, p. 161-190.
Tanner, A.B., 1980, Radon migration in the ground: a supplementary review, in Gesell, T.F.,
and Lowder, W.M. (eds), Natural radiation environment HI, Symposium proceedings,
Houston, Texas, v. 1, p. 5-56.
U.S. Department of Agriculture, 1987, Principal kinds of soils: Orders, suborders, and great
groups: U.S. Geological Survey, National Atlas of the United States of America, sheet
38077-BE-NA-07M-00, scale 1:7,500,000.
U.S. Department of Energy, 1976, National Uranium Resource Evaluation preliminary report,
prepared by the U.S. Energy Research and Development Administration, Grand Junction,
Colo.: GJO-11(76).
Wanty, Richard B., and Schoen, Robert, 1991, A review of the chemical processes affecting the
mobility of radionuclides in natural waters, with applications, in Gundersen, Linda C.S.,
and Richard B. Wanty, eds., Field studies of radon in rocks, soils, and water: U.S.
Geological Survey Bulletin no. 1971, p. 183-194.
Washington, J.W., and Rose, A.W., 1990, Regional and temporal relations of radon in soil gas to
soil temperature and moisture: Geophysical Research Letters, v. 17, p. 829-832.
White, S.B., Bergsten, J.W., Alexander, B.V., and Ronca-Battista, M., 1989, Multi-State
surveys of indoor 222Rn: Health Physics, v. 57, p. 891-896.
II-19 Reprinted from USGS Open-File Report 93-292
-------
APPENDIX A
GEOLOGIC TIME SCALE
Subdivisions (and their symbols)
Eon or
Eonothem
Phanerozoic2
Proterozoic
(B)
Archean
(A)
Era or
Erathem
Cenozoic
(CD
Mesozoic2
(Mz)
Paleozoic2
(Pi)
P.ot."&« IZ1
M,C8I»
Etny
Uii
MiCOM
fc«nv
pr.-Arch.in (p
Period, Sys.em,
Subperiod, Subsystem
Quaternary
(Q)
NeOB«ne 2
Subperiod or
•r^.-y Subsystem (Nil
m Paleogene
11 Subperiod or
Subsystem (Pi)
Cretaceous
(K)
Jurassic
(J)
Triassic
CR)
Permian
(P)
Pennsylvanian
Carboniferous 'P'
(C) Mississippian
(M)
Devonian
-------
APPENDIX B
GLOSSARY OF TERMS
Units of measure
pCi/L (picocuries per liter)- a unit of measure of radioactivity used to describe radon
concentrations in a volume of air. One picocurie (10~12 curies) is equal to about 2.2 disintegrations
of radon atoms per minute. A liter is about 1.06 quarts. The average concentration of radon in
U.S. homes measured to date is between 1 and 2 pCi/L.
Bq/m3 (Becquerels per cubic meter)- a metric unit of radioactivity used to describe radon
concentrations in a volume of air. One becquerel is equal to one radioactive disintegration per
second. One pQ/L is equal to 37 Bq/m3.
ppm (parts per million)- a unit of measure of concentration by weight of an element in a
substance, in this case, soil or rock. One ppm of uranium contained in a ton of rock corresponds
to about 0.03 ounces of uranium. The average concentration of uranium in soils in the United
States is between 1 and 2 ppm.
in/hr (inches per hour)- a unit of measure used by soil scientists and engineers to describe the
permeability of a soil to water flowing through it It is measured by digging a hole 1 foot (12
inches) square and one foot deep, filling it with water, and measuring the time it takes for the water
to drain from the hole. The drop in height of the water level in the hole, measured in inches, is
then divided by the time (in hours) to determine the permeability. Soils range in permeability from
less than 0.06 in/hr to greater than 20 in/hr, but most soils in the United States have permeabilities
between these two extremes.
Geologic terms and terms related to the study of radon
aerial radiometric, aeroradiometric survey A survey of radioactivity, usually gamma rays,
taken by an aircraft carrying a gamma-ray spectrometer pointed at the ground surface.
alluvial fan A low, widespread mass of loose rock and soil material, shaped like an open fan
and deposited by a stream at the point where it flows from a narrow mountain valley out onto a
plain or broader valley. May also form at the junction with larger streams or when the gradient of
the stream abruptly decreases.
alluvium, alluvial General terms referring to unconsolidated detrital material deposited by a
stream or other body of running water.
alpha-track detector A passive radon measurement device consisting of a plastic film that is
sensitive to alpha particles. The film is etched with acid in a laboratory after it is exposed. The
etching reveals scratches, or "tracks", left by the alpha particles resulting from radon decay, which
can then be counted to calculate the radon concentration. Useful for long-term (1-12 months)
radon tests.
amphibolite A mafic metamorphic rock consisting mainly of pyroxenes and(or) amphibole and
plagioclase.
11-21 Reprinted from USGS Open-File Report 93-292
-------
argillite, argillaceous Terms referring to a rock derived from clay or shale, or any sedimentary
rock containing an appreciable amount of clay-size material, i.e., argillaceous sandstone.
arid Term describing a climate characterized by dryness, or an evaporation rate that exceeds the
amount of precipitation.
basalt A general term for a dark-colored mafic igneous rocks that may be of extrusive origin,
such as volcanic basalt flows, or intrusive origin, such as basalt dikes.
batholith A mass of plutonic igneous rock that has more than 40 square miles of surface
exposure and no known bottom.
carbonate A sedimentary rock consisting of the carbonate (COs) compounds of calcium,
magnesium, or iron, e.g. limestone and dolomite.
carbonaceous Said of a rock or sediment that is rich in carbon, is coaly, or contains organic
matter.
charcoal canister A passive radon measurement device consisting of a small container of
granulated activated charcoal that is designed to adsorb radon. Useful for short duration (2-7 days)
measurements only. May be referred to as a "screening" test
chert A hard, extremely dense sedimentary rock consisting dominantly of interlocking crystals of
quartz. Crystals are not visible to the naked eye, giving the rock a milky, dull luster. It may be
white or gray but is commonly colored red, black, yellow, blue, pink, brown, or green.
clastic pertaining to a rock or sediment composed of fragments that are derived from preexisting
rocks or minerals. The most common clastic sedimentary rocks are sandstone and shale.
clay A rock containing clay mineral fragments or material of any composition having a diameter
less than 1/256 mm.
clay mineral One of a complex and loosely defined group of finely crystalline minerals made up
of water, silicate and aluminum (and a wide variety of other elements). They are formed chiefly by
alteration or weathering of primary silicate minerals. Certain clay minerals are noted for their small
size and ability to absorb substantial amounts of water, causing them to swell. The change in size
that occurs as these clays change between dry and wet is referred to as their "shrink-swell"
potential.
concretion A hard, compact mass of mineral matter, normally subspherical but commonly
irregular in shape; formed by precipitation from a water solution about a nucleus or center, such as
a leaf, shell, bone, or fossil, within a sedimentary or fractured rock.
conglomerate A coarse-grained, clastic sedimentary rock composed of rock and mineral
fragments larger than 2 mm, set in a finer-grained matrix of clastic material.
cuesta A hill or ridge with a gentle slope on one side and a steep slope on the other. The
formation of a cuesta is controlled by the different weathering properties and the structural dip of
the rocks forming the hill or ridge.
daughter product A nuclide formed by the disintegration of a radioactive precursor or "parent"
atom.
11-22 Reprinted from USGS Open-File Report 93-292
-------
delta, deltaic Referring to a low, flat, alluvial tract of land having a triangular or fan shape,
located at or near the mouth of a river. It results from the accumulation of sediment deposited by a
river at the point at which the river loses its ability to transport the sediment, commonly where a
river meets a larger body of water such as a lake or ocean.
dike A tabular igneous intrusion of rock, younger than the surrounding rock, that commonly cuts
across the bedding or foliation of the rock it intrudes.
diorite A plutonic igneous rock that is medium in color and contains visible dark minerals that
make up less than 50% of the rock. It also contains abundant sodium plagioclase and minor
quartz.
dolomite A carbonate sedimentary rock of which more than 50% consists of the mineral dolomite
(CaMg(COs)2), and is commonly white, gray, brown, yellow, or pinkish in color.
drainage The manner in which the waters of an area pass, flow off of, or flow into the soil.
Also refers to the water features of an area, such as lakes and rivers, that drain it
eolian Pertaining to sediments deposited by the wind.
esker A long, narrow, steep-sided ridge composed of irregular beds of sand and gravel deposited
by streams beneath a glacier and left behind when the ice melted.
evapotranspiration Loss of water from a land area by evaporation from the soil and
transpiration from plants.
extrusive Said of igneous rocks that have been erupted onto the surface of the Earth.
fault A fracture or zone of fractures in rock or sediment along which there has been movement.
fluvial, fluvial deposit Pertaining to sediment that has been deposited by a river or stream.
foliation A linear feature in a rock defined by both mineralogic and structural characteristics. It
may be formed during deformation or metamorphism.
formation A mappable body of rock having similar characteristics.
glacial deposit Any sediment transported and deposited by a glacier or processes associated
with glaciers, such as glaciofiuvial sediments deposited by streams flowing from melting glaciers.
gneiss A rock formed by metamorphism in which bands and lenses of minerals of similar
composition alternate with bands and lenses of different composition, giving the rock a striped or
"foliated" appearance.
granite Broadly applied, any coarsely crystalline, quartz- and feldspar-bearing igneous plutonic
rock. Technically, granites have between 10 and 50% quartz, and alkali feldspar comprises at least
65% of the total feldspar.
gravel An unconsolidated, natural accumulation of rock fragments consisting predominantly of
particles greater than 2 mm in size.
heavy minerals Mineral grains in sediment or sedimentary rock having higher than average
specific gravity. May form layers and lenses because of wind or water sorting by weight and size
11-23 Reprinted from USGS Open-File Report 93-292
-------
and may be referred to as a "placer deposit" Some heavy minerals are magnetite, garnet, zircon,
monazite, and xenotime.
igneous Said of a rock or mineral that solidified from molten or partly molten rock material. It is
one of the three main classes into which rocks are divided, the others being sedimentary and
metamorphic.
intermontane A term that refers to an area between two mountains or mountain ranges.
Intrusion, intrusive The processes of emplacement or injection of molten rock into pre-existing
rock. Also refers to the rock formed by intrusive processes, such as an "intrusive igneous rock".
kame A low mound, knob, hummock, or short irregular ridge formed by a glacial stream at the
margin of a melting glacier; composed of bedded sand and gravel.
karst terrain A type of topography that is formed on limestone, gypsum and other rocks by
dissolution of the rock by water, forming sinkholes and caves.
lignite A brownish-black coal that is intermediate in coalification between peat and
subbituminous coal.
limestone A carbonate sedimentary rock consisting of more than 50% calcium carbonate,
primarily in the form of the mineral calcite (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, amphibolite, and gneiss are metamorphic rocks.
moraine A mound, ridge, or other distinct accumulation of unsorted, unbedded glacial material,
predominantly till, deposited by the action of glacial ice.
outcrop That part of a geologic formation or structure that appears at the surface of the Earth, as
in "rock outcrop".
percolation test A term used in engineering for a test to determine the water permeability of a
soil. A hole is dug and filled with water and the rate of water level decline is measured.
permeability The capacity of a rock, sediment, or soil to transmit liquid or gas.
phosphate, phosphatic, phosphorite Any rock or sediment containing a significant amount
of phosphate minerals, i.e., minerals containing PO4.
11-24 Reprinted from USGS Open-File Report 93-292
-------
physiographic province A region in which all parts are similar in geologic structure and
climate, which has had a uniform geomorphic history, and whose topography or landforms differ
significantly from adjacent regions.
placer deposit See heavy minerals
residual Formed by weathering of a material in place.
residuum Deposit of residual material.
rhyolite An extrusive igneous rock of volcanic origin, compositionally equivalent to granite.
sandstone A clastic sedimentary rock composed of sand-sized rock and mineral material that is
more or less firmly cemented. Sand particles range from 1/16 to 2 mm in size.
schist A strongly foliated crystalline rock, formed by metarnorphism, that can be readily split into
thin flakes or slabs. Contains mica; minerals are typically aligned.
screening level Result of an indoor radon test taken with a charcoal canister or similar device,
for a short period of time, usually less than seven days. May indicate the potential for an indoor
radon problem but does not indicate annual exposure to radon.
sediment Deposits of rock and mineral particles or fragments originating from material that is
transported by air, water or ice, or that accumulate by natural chemical precipitation or secretion of
organisms.
semiarid Refers to a climate that has slightly more precipitation than an arid climate.
shale A fine-grained sedimentary rock formed from solidification (lithification) of clay or mud.
shear zone Refers to a roughly linear zone of rock that has been faulted by ductile or non-ductile
processes in which the rock is sheared and both sides are displaced relative to one another.
shrink-swell clay See clay mineral.
siltstone A fine-grained clastic sedimentary rock composed of silt-sized rock and mineral
material and more or less firmly cemented. Silt particles range from 1/16 to 1/256 mm in size.
sinkhole A roughly circular depression in a karst area measuring meters to tens of meters in
diameter. It is funnel shaped and is formed by collapse of the surface material into an underlying
void created by the dissolution of carbonate rock.
slope An inclined part of the earth's surface.
solution cavity A hole, channel or cave-like cavity formed by dissolution of rock.
stratigraphy The study of rock strata; also refers to the succession of rocks of a particular area.
surficial materials Unconsolidated glacial, wind-, or waterborne deposits occurring on the
earth's surface.
tablelands General term for a broad, elevated region with a nearly level surface of considerable
extent
11-25 Reprinted from USGS Open-File Report 93-292
-------
terrace gravel Gravel-sized material that caps ridges and terraces, left behind by a stream as it
cuts down to a lower level.
terrain A tract or region of the Earth's surface considered as a physical feature or an ecological
environment
till Unsorted, generally unconsolidated and unbedded rock and mineral material deposited directly
adjacent to and underneath a glacier, without reworking by meltwater. Size of grains varies greatly
from clay to boulders.
uraniferous Containing uranium, usually more than 2 ppm.
vendor data Used in this report to refer to indoor radon data collected and measured by
commercial vendors of radon measurement devices and/or services.
volcanic Pertaining to the activities, structures, and extrusive rock types of a volcano.
water table The surface forming the boundary between the zone of saturation and the zone of
aeration; the top surface of a body of unconfined groundwater in rock or soil.
weathering The destructive process by which earth and rock materials, on exposure to
atmospheric elements, are changed in color, texture, composition, firmness, or form with little or
no transport of the material.
11-26 Reprinted from USGS Open-File Report 93-292
-------
APPENDIX C
EPA REGIONAL OFFICES
EPA Regional Offices
State
EPA Resion
EPA Region 1
JFK Federal Building
Boston, MA 02203
(617) 565-4502
EPA Region 2
(2AIR:RAD)
26 Federal Plaza
New York, NY 10278
(212) 264-4110
Region 3 (3AH14)
841 Chestnut Street
Philadelphia, PA 19107
(215) 597-8326
EPA Region 4
345 Courtland Street, N.E.
Atlanta, GA 30365
(404) 347-3907
EPA Region 5 (5AR26)
77 West Jackson Blvd.
Chicago, IL 60604-3507
(312) 886-6175
EPA Region 6 (6T-AS)
1445 Ross Avenue
Dallas, TX 75202-2733
(214) 655-7224
EPA Region 7
726 Minnesota Avenue
Kansas City, KS 66101
(913) 551-7604
EPA Region 8
(8HWM-RP)
999 18th Street
One Denver Place, Suite 1300
Denver, CO 80202-2413
(303) 293-1713
EPA Region 9 (A-3)
75 Hawthorne Street
San Francisco, CA 94105
(415) 744-1048
EPA Region 10
1200 Sixth Avenue
Seattle, WA 98101
(202) 442-7660
Alabama 4
Alaska 10
Arizona 9
Arkansas ...6
California 9
Colorado '. 8
Connecticut 1
Delaware 3
District of Columbia 3
Florida 4
Georgia 4
Hawaii 9
Idaho 10
Illinois 5
Indiana 5
Iowa 7
Kansas : 7
Kentucky 4
Louisiana 6
Maine 1
Maryland 3
Massachusetts 1
Michigan 5
Minnesota 5
Mississippi 4
Missouri 7
Montana 8
Nebraska 7
Nevada 9
New Hampshire 1
New Jersey 2
New Mexico 6
New York 2
North Carolina ...4
North Dakota 8
Ohio 5
Oklahoma 6
Oregon 10
Pennsylvania 3
Rhode Island 1
South Carolina 4
South Dakota 8
Tennessee 4
Texas 6
Utah 8
Vermont 1
Virginia 3
Washington 10
West Virginia 3
Wisconsin 5
Wyoming 8
n-27 Reprinted from USGS Open-File Report 93-292
-------
STATE RADON CONTACTS
May, 1993
Alabama James McNees
Division of Radiation Control
Alabama Department of Public iiealth
State Office Building
Montgomery, AL 36130
(205) 242-5315
1-800-582-1866 in state
Charles Tedford
Department of Health and Social
Services
P.O. Box 110613
Juneau,AK 99811-0613
(907)465-3019
1-800-478-4845 in state
Arizona John Stewart
Arizona Radiation Regulatory Agency
4814 South 40th St.
Phoenix, AZ 85040
(602)255-4845
Arkansas LeeGershner
Division of Radiation Control
Department of Health
4815 Markham Street, Slot 30
• Little Rock,'AR 72205-3867
(501) 661-2301
California J. David Quinton
Department of Health Services
714 P Street, Room 600
Sacramento, CA 94234-7320
(916) 324-2208
1-800-745-7236 in state
Colorado Linda Martin
Department of Health
4210 East llth Avenue
Denver, CO 80220
(303)692-3057
1-800-846-3986 in state
Connecticut Alan J. Siniscalchi
Radon Program
Connecticut Department of Health
Services
150 Washington Street
Hartford, CT 06106-4474
(203)566-3122 .
Delaware MaraiG. Rejai
Office of Radiation Control
Division of Public Health
P.O. Box 637
Dover, DE 19903
(302)736-3028
1-800-554-4636 In State
District Robert Davis
of Columbia DC Department of Consumer and
Regulatory Affairs
614 H Street NW
Room 1014
Washington, DC 20001
(202) 727-71068
Florida N. Michael Gilley
Office of Radiation Control
Department of Health and
Rehabilitative Services
1317 Winewood Boulevard
Tallahassee, FL 32399-0700
(904)488-1525
1-800-543-8279 in state
Richard Schreiber
Georgia Department of Human
Resources
878 Peachtree St, Room 100
Atlanta, GA 30309
(404) 894-6644
1-800-745-0037 in state
Hawaii Russell Takata
Environmental Health Services
Division
591 Ala Moana Boulevard
Honolulu, ffl 96813-2498
(808) 5864700
11-28 Reprinted from USGS Open-File Report 93-292
-------
Idaho
Indiana
Iowa
Kansas
Kentucky
PatMcGavarn
Office of Environmental Health
450 West State Street
Boise, ID 83720
(208) 334-6584
1-800-445-8647 in state
Richard Allen
Illinois Department of Nuclear Safety
1301 Outer Park Drive
Springfield, IL 62704
(217) 524-5614
1-800-325-1245 in state
Lorand Magyar
Radiological Health Section
Indiana State Department of Health
1330 West Michigan Street
P.O. Box 1964
Indianapolis, IN 46206
(317) 633-8563
1-800-272-9723 In State
Donald A. Plater
Bureau of Radiological Health
Iowa Department of Public Health
Lucas State Office Building
Des Moines, IA 50319-0075
(515)281-3478
1-800-383-5992 In State
Harold Spiker
Radiation Control Program
Kansas Department of Health and
Environment
109 SW 9th Street
6th Floor Mills Building
Topeka, KS 66612
(913)296-1561
JeanaPhelps
Radiation Control Branch
Department of Health Services
Cabinet for Human Resources
275 East Main Street
Frankfort, KY 40601
(502) 564-3700
Louisiana Matt Schlenker
Louisiana Department of
Environmental Quality
P.O. Box 82135
Baton Rouge, LA 70884-2135
(504) 925-7042
1-800-256-2494 in state
Maine BobStilwell
Division of Health Engineering
Department of Human Services
State House, Station 10
Augusta, ME 04333
(207)289-5676
1-800-232-0842 in state
Maryland Leon J. Rachuba
Radiological Health Program
Maryland Department of the
Environment
2500 Broening Highway
Baltimore, MD 21224
(410) 631-3301
1-800-872-3666 In State
Massachusetts William J. Bell
Radiation Control Program
Department of Public Health
23 Service Center
Northampton, MA 01060
(413) 586-7525
1-800-445-1255 in state
Michigan Sue Hendershott
Division of Radiological Health
Bureau of Environmental and
Occupational Health
3423 North Logan Street
P.O. Box 30195
Lansing, MI 48909
(517) 335-8194
Minnesota Laura Oatmann
Indoor Air Quality Unit
925 Delaware Street, SE
P.O. Box 59040
Minneapolis, MN 55459-0040
(612) 627-5480
1-800-798-9050 in state
11-29 Reprinted from USGS Open-File Report 93-292
-------
Mississippi
Missouri
Montana
Silas Anderson
Division of Radiological Health
Department of Health
3150 Lawson Street
P.O. Box 1700
Jackson, MS 39215-1700
(601) 354-6657
1-800-626-7739 in state
Kenneth V. Miller
Bureau of Radiological Health
Missouri Department of Health
1730 East Elm
P.O. Box 570
Jefferson City, MO 65102
(314) 751-6083
1-800-669-7236 In State
Adrian C. Howe
Occupational Health Bureau
Montana Department of Health and
Environmental Sciences
Cogswell Building A113
Helena, MT 59620
(406)444-3671
Joseph Milone
Division of Radiological Health
Nebraska Department of Health
301 Centennial Mall, South
P.O. Box 95007
Lincoln, NE 68509
(402)471-2168
1-800-334-9491 In State
Stan Marshall
Department of Human Resources
505 East King Street
Room 203
Carson City, NV 89710
(702) 687-5394
New Hampshire David Chase
Bureau of Radiological Health
Division of Public Health Services
Health and Welfare Building
Six Hazen Drive
Concord, NH 03301
(603) 271-4674
1-800-852-3345 x4674
Nebraska
New Jersey Tonalee Carlson Key
Division of Environmental Quality
Department of Environmental
Protection
CN415
Trenton, NJ 08625-0145
(609) 987-6369
1-800-648-0394 in state
New Mexico William M. Floyd
Radiation Licensing and Registration
Section
New Mexico Environmental
Improvement Division
1190 St. Francis Drive
Santa Fe,NM 87503
(505) 827-4300
New York William J. Condon
Bureau of Environmental Radiation
Protection
New York State Health Department
Two University Place
Albany, NY 12202
(518)458-6495
1-800-458-1158 in state
North Carolina Dr. Felix Fong
Radiation Protection Division
Department of Environmental Health
and Natural Resources
701 Barbour Drive
Raleigh, NC 27603-2008
(919) 571-4141
1-800-662-7301 (recorded info x4196)
North Dakota Arlen Jacobson
North Dakota Department of Health
1200 Missouri Avenue, Room 304
P.O. Box 5520
Bismarck, ND 58502-5520
(701)221-5188
hio Marcie Matthews
Radiological Health Program
Department of Health
1224 Kinnear Road - Suite 120
Columbus, OH 43212
(614) 644-2727
1-800-523-4439 in state
n-so
Reprinted from USGS Open-File Report 93-292
-------
Oklahoma
Oregon
Pennsylvania
Puerto Rico
Rhode Island
South Carolina
Gene Smith
Radiation Protection Division
Oklahoma State Department of
Health
P.O. Box 53551
Oklahoma City, OK 73152
(405) 271-5221
George Toombs
Department of Human Resources
Health Division
1400 SW 5th Avenue
Portland, OR 97201
(503)731-4014
Michael Pyles
Pennsylvania Department of
Environmental Resources
Bureau of Radiation Protection
P.O. Box 2063
Harrisburg, PA 17120
(717) 783-3594
1-800-23-RADON In State
David Saldana
Radiological Health Division
G.P.O. Call Box 70184
Rio Piedras, Puerto Rico 00936
(809) 767-3563
Edmund Arcand
Division of Occupational Health and
Radiation
Department of Health
205 Cannon Building
Davis Street
Providence, RI02908
(401) 277-2438
Bureau of Radiological Health
Department of Health and
Environmental Control
2600 Bull Street
Columbia, SC 29201
(803)734^631
1-800-768-0362
South Dakota MikePochop
Division of Environment Regulation
Department of Water and Natural
Resources
Joe Foss Building, Room 217
523 E. Capitol
Pierre, SD 57501-3181
. (605)773-3351
Tennessee Susie Shimek
Division of Air Pollution Control
Bureau of the Environment
Department of Environment and
Conservation
Customs House, 701 Broadway
Nashville, TN 37219-5403
(615) 532-0733
1-800-232-1139 in state
Texas Gary Smith
Bureau of Radiation Control
Texas Department of Health
1100 West 49th Street
Austin, TX 78756-3189
(512) 834-6688
Utah John Hultquist
Bureau of Radiation Control
Utah State Department of Health
288 North, 1460 West
P.O. Box 16690
Salt Lake City, UT 84116-0690
(801) 536^250
Vermont Paul demons
Occupational and Radiological Health
Division
Vermont Department of Health
10 Baldwin Street
Montpelier, VT 05602
(802) 828-2886
1-800-640-0601 in state
Virgin Islands Contact the U.S. Environmental
Protection Agency, Region n
in New York
(212)264-4110
n-si
Reprinted from USGS Open-Fife Report 93-292
-------
Virginia Shelly Ottenbrite
Bureau of Radiological Health
Department of Health
109 Governor Street
Richmond, VA 23219
(804) 786-5932
1-800-468-0138 in state
Washington KateColeman
Department of Health
'Office of Radiation Protection
Airdustrial Building 5, LE-13
Olympia,WA 98504
(206) 753-4518
1-800-323-9727 In State
West Virginia 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
Hathway Building, 4th Floor
Cheyenne, WY 82002-0710
(307) 777-6015
1-800-458-5847 in state
n-32 Reprinted from USGS Open-File Report 93-292
-------
STATE GEOLOGICAL SURVEYS
May, 1993
Alabama Ernest A. Mancini
Geological Survey of Alabama
P.O. Box 0
420 Hackberry Lane
Tuscaloosa, AL 35486-9780
(205) 349-2852
Alaska Thomas E. Smith
Alaska Division of Geological &
Geophysical Surveys
794 University Ave., Suite 200
Fairbanks, AK 99709-3645
(907)479-7147
'Arizona Larry D. Fellows
Arizona Geological Survey
845 North Park Ave., Suite 100
Tucson, AZ 85719
(602) 882-4795
Arkansas Norman F. Williams
Arkansas Geological Commission
Vardelle Parham Geology Center
3815 West Roosevelt Rd.
Little Rock, AR 72204
(501) 324-9165
California James F. Davis
California Division of Mines &
Geology
801 K Street, MS 12-30
Sacramento, CA 95814-3531
(916)445-1923
Colorado Pat Rogers (Acting)
Colorado Geological Survey
1313 Sherman St., Rm 715
Denver, CO 80203
(303) 866-2611
Connecticut Richard C. Hyde
Connecticut Geological & Natural
History Survey
165 Capitol Ave., Rm. 553
Hartford, CT 06106
(203) 566-3540
Delaware Robert R. Jordan
Delaware Geological Survey
University of Delaware
101 Penny Hall
Newark, DE 19716-7501
(302) 831-2833
Florii
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, ffl 96809
(808) 548-7539
Idaho Earl H. Bennett
Idaho Geological Survey
University of Idaho
Morrill Hall, Rm. 332
Moscow, ID 83843
(208) 885-7991
Illinois Morris W. Leighton
Illinois State Geological Survey
Natural Resources Building
615 East Peabody Dr.
Champaign, IL 61820
(217)333^747
Indian^ Norman C. Hester
Indiana Geological Survey
611 North Walnut Grove
Bloomington, IN 47405
(812) 855-9350
Iowa Donald L. Koch
Iowa Department of Natural Resources
Geological Survey Bureau
109 Trowbridge Hall
Iowa City, IA 52242-1319
(319)335-1575
Kansas Lee C.Gerhard
Kansas Geological Survey
1930 Constant Ave., West Campus
University of Kansas
Lawrence, KS 66047
(913) 864-3965
11-33 Reprinted from USGS Open-File Report 93-292
-------
Kentucky Donald C. Haney
Kentucky Geological Survey
University of Kentucky
228 Mining & Mineral Resources
Building
Lexington, KY 40506-0107
(606)257-5500
Louisiana William E. Marsalis
Louisiana Geological Survey
P.O. Box 2827
University Station
Baton Rouge, LA 70821-2827
(504) 388-5320
Maine Walter A. Anderson
Maine Geological Survey
, Department of Conservation
State House, Station 22
Augusta, ME 04333
(207) 289-2801
Maryland Emery T. Cleaves
Maryland Geological Survey
2300 St. Paul Street
Baltimore, MD 21218-5210
(410) 554-5500
Massachusetts Joseph A. Sinnott
. Massachusetts Office of
Environmental Affairs
100 Cambridge St., Room 2000
Boston, MA 02202
(617) 727-9800
Michigan R. Thomas Segall
Michigan Geological Survey Division
Box 30256
Lansing, MI 48909
(517)334-6923
Minnesota Priscilla C. Grew
Minnesota Geological Survey
2642 University Ave.
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)4964180
Nebraska Perry B. Wigley
Nebraska Conservation & Survey
Division
113 Nebraska Hall
University of Nebraska
Lincoln, NE 68588-0517
(402)472-2410
Nevada Jonathan G. Price
Nevada Bureau of Mines & Geology
Stop 178
University of Nevada-Reno
Reno, NV 89557-0088
(702) 784-6691
NewJHampshite Eugene L.Boudette
Dept. of Environmental Services
117 James Hall
University of New Hampshire
Durham, NH 03824-3589
(603) 862-3160
New Jersey Haig F. Kasabach
New Jersey Geological Survey
P.O. Box 427
Trenton, NJ 08625
(609)292-1185
New Mexico Charles E. Chapin
New Mexico Bureau of Mines &
Mineral Resources
Campus Station
Socorro.NM 87801
(505) 835-5420
New York Robert H. Fakundiny
New York State Geological Survey
3136 Cultural Education Center
Empire State Plaza
Albany, NY 12230
(518)474-5816
11-34 Reprinted from USGS Open-File Report 93-292
-------
North Carolina Charles H. Gardner
North Carolina Geological Survey
P.O. Box 27687
Raleigh, NC 27611-7687
(919) 733-3833
North Dakota John P. Bluemle
North Dakota Geological Survey
600 East Blvd.
Bismarck, ND 58505-0840
(701) 224-4109
Ohio
Thomas M. Berg
Ohio DepL of Natural Resources
Division of Geological Survey
4383 Fountain Square Drive
Columbus, OH 43224-1362
(614)265-6576
Charles J. Mankin
Oklahoma Geological Survey
Room N-131, Energy Center
lOOE.Boyd
Norman, OK 73019-0628
(405)325-3031
Oregon Donald A. Hull
DepL of Geology & Mineral Indust.
Suite 965
800 NE Oregon St. #28
Portland, OR 97232-2162
(503)731-4600
Pennsylvania Donald M. HosMns
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
3 15 Green Hall
Kingston, RI 02881
(401)792-2265
South Carolina Alan-Jon W. Zupan (Acting)
South Carolina Geological Survey
5 Geology Road
Columbia, SC 29210-9998
(803) 737-9440
South Dakota C.M. Christensen (Acting)
South Dakota Geological Survey
Science Center
University of South Dakota
Vermillion, SD 57069-2390
(605) 677-5227
Tennessee Edward T.Luther
Tennessee Division of Geology
13th Floor, L & C Tower
401 Church Street
Nashville, TN 37243-0445
(615) 532-1500
Texas William L. Fisher
Texas Bureau of Economic Geology
University of Texas
University Station, Box X
Austin, TX 78713-7508
(512)471-7721
Utah M. Lee Allison
Utah Geological & Mineral Survey
2363 S. Foothill Dr.
Salt Lake City, UT 84109-1491
(801)467-7970
ont Diane L. Conrad
Vermont Division of Geology and
Mineral Resources
103 South Main St.
Waterbury.VT 05671
(802)244-5164
Virginia Stanley S. Johnson
Virginia Division of Mineral
Resources
P.O. Box 3667
Charlottesville, VA 22903
(804)293-5121
Washington Raymond Lasmanis
Washington Division of Geology &
Earth Resources
Department of Natural Resources
P.O. Box 47007
Olympia, Washington 98504-7007
(206) 902-1450
11-35 Reprinted from USGS Open-File Report 93-292
-------
West Virginia LanyD. Woodfoifc
West Virginia Geological and
Economic Survey
Mont Chateau Research Center
P.O. Box 879
Morgantown.WV 26507-0879
(304) 594-2331
Wisconsin James Robertson
Wisconsin Geological & Natural
History Survey
3817 Mineral Point Road
Madison, WI 53705-5100
(608)263-7384
Wyoming Gary B. Glass
Geological Survey of Wyoming
University of Wyoming
Box 3008, University Station
Laramie, WY 82071-3008
(307) 766-2286
11-36 Reprinted from USGS Open-File Report 93-292
-------
EPA REGION 8 GEOLOGIC RADON POTENTIAL SUMMARY
by
R. Randall Schumann, Douglass E. Owen, Russell F. Dubiel, and Sandra L. Szarzi
U.S. Geological ^urvey
EPA Region 8 includes the states of Colorado, 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 pCi/L
were ranked high. Areas in which the average screening indoor radon level of all homes within the
area is estimated to be between 2 and 4 pCi/L were ranked moderate/variable, and areas in which
the average screening indoor radon level of all homes within the area is estimated to be less than
2 pCi/L were ranked low. Information on the data used and on the radon potential ranking scheme
is given in the introduction to this volume. More detailed information on the geology and radon
potential of each state in Region 8 is given in the individual state chapters. The individual chapters
describing the geology and radon potential of the six states in EPA Region 8, though much more
detailed than this summary, still are generalized assessments and there is no substitute for having a
home tested. Within any radon potential area homes with indoor radon levels both above and
below the predicted average likely will be found.
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 these provinces. Figure 2 shows
average screening indoor radon levels by county. The data for South Dakota are from the
EPA/Indian Health Service Residential Radon Survey and from The Radon Project of the
University of Pittsburgh; data for Utah are from an indoor radon survey conducted in 1988 by the
Utah Bureau of Radiation Control; data for Colorado, Montana, North Dakota, and Wyoming are
from the State/EPA Residential Radon Survey. Figure 3 shows the geologic radon potential areas
in Region 8, combined and summarized from the individual state chapters. Rocks and soils in
EPA Region 8 contain ample radon source material (uranium and radium) and have soil
permeabilities sufficient to produce moderate or high radon levels in homes. At the scale of this
evaluation, all areas in EPA Region 8 have either moderate or high geologic radon potential, except.
for an area in southern South Dakota corresponding to the northern part of the Nebraska Sand
Hills, which has low radon potential.
The limit of continental glaciation is of great significance in Montana, North Dakota, and
South Dakota (fig. 1). The glaciated portions of the Great Plains and the Central Lowland
generally have a higher radon potential than their counterparts to the south because glacial action
crushes and grinds up rocks as it forms till and other glacial deposits. This crushing and grinding
enhances weathering and increases the surface area from which radon may emanate; further, it
exposes more uranium and radium at grain surfaces where they are more easily leached. Leached
uranium and radium may be transported downward in the soil below the depth at which it may be
detected by a gamma-ray spectrometer (approximately 30 cm), giving these areas a relatively low
surface or aerial radiometric signature. However, the uranium and radium still are present at
depths shallow enough to allow generated radon to migrate into a home.
The Central Lowland Province is a vast plain that lies between 500 and 2,000 feet above
sea level and forms the agricultural heart of the United States. In Region 8, it covers the eastern
part of North Dakota and South Dakota. The Central Lowland in Region 8 has experienced the
effects of continental glaciation and also contains silt and clay deposits from a number of glacial
ffl-1 Reprinted from USGS Open-File Report 93-292-H
-------
Figure 1. Physiographic provinces in EPA Region 8 (after Hunt, C.W., 1967, Physiography of
the United States: Freeman and Co., p. 8-9.)
-------
100 Miles
106
Indoor Radon Screening
Measurements: Average (pCi/L)
0.0 to 1.9
2.0 to 4.0
4.1 to 9.9
10.0 to 29.2
Missing Data
Figure 2. 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/IHS
Indoor Radon Survey and from The Radon Project. Histograms in map legend
indicate the number of counties in each measurement category.
-------
GEOLOGIC
RADON POTENTIAL
ESS HIGH
MODERATE
LOW
Figure 3. Geologic radon potential of EPA Region 8.
-------
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. 1) 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
ffl-5 Reprinted from USGS Open-File Report 93-292-H
-------
relatively high uranium concentrations. Mountain ranges such as the Grand Tetons and Big Horn
Mountains, which are underlain by granitic and metamorphic 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 Pbt<~- 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 metamorphic 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 generaUy 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).
m-6 Reprinted from USGS Open-File Report 93-292-H
-------
PRELIMINARY GEOLOGIC RADON POTENTIAL ASSESSMENT OF NORTH DAKOTA
by
R. Randall Schumann
U.S. Geological Survey
INTRODUCTION
Many of the rocks and soils in North Dakota have the potential to generate levels of indoor
radon exceeding the U.S. Environmental Protection Agency's guideline of 4 pCi/L. In a survey of
about 1600 homes conducted during the winter of 1987-88 by the North Dakota State Department
of Health and the EPA, 63 percent of the homes tested had indoor radon levels exceeding this
value. Every county sampled had one or more homes exceeding 4 pCi/L, although some areas had
more than others.
This is a generalized assessment of geologic radon potential of rocks, soils, and surficial
deposits of North Dakota. The scale of this assessment is such that it is inappropriate for use in
identifying the radon potential of small areas such as neighborhoods, individual building sites, or
housing tracts. Any localized assessment of radon potential must be supplemented with additional
data and information from the locality. Within any area of a given radon potential ranking, there
are likely to be areas with higher or lower radon levels than characterized for the area as a whole.
Indoor radon levels, both high and low, can be quite localized, and there is no substitute for testing
individual homes. Elevated levels of indoor radon have been found in every state, and EPA
recommends that all homes be tested. For more information on radon, the reader is urged to
consult the local or State radon program or EPA regional office. More detailed information on state
or local geology may be obtained from the State geological survey. Addresses and phone numbers
for these agencies are listed in chapter 1 of this booklet
PHYSIOGRAPHIC AND GEOGRAPHIC SETTING
North Dakota lies within the Interior Plains physiographic division, with the northeastern
part of the State falling in the Central Lowlands Province and the southwestern part in the Great
Plains Province. The Central Lowlands were generally characterized by tall-grass prairie prior to
human settlement, whereas the Great Plains were covered primarily by short- and medium-grass
prairie. Within the State the physiography is further subdivided into several areas characterized by
specific features (fig. 1). Much of the topography of North Dakota is subdued and gently rolling
due to the influence of glaciers, which covered about three-quarters of the State with Pleistocene-
age glacial drift and lake deposits. One of the most prominent features is the Red River Valley
along the eastern border of the State, which is underlain mostly by silt and clay deposits of glacial
Lake Agassiz. The part of the Red River Valley that lies within North Dakota is 30-40 miles wide
and narrows to about 10 miles at the southern end. An escarpment of varying height (the Pembina
Escarpment) separates the valley from the Drift Prairie region to its west. The Drift Prairie (or
Glaciated Plains) is a region of gentry undulating to hilly plains underlain by glacial deposits.
Moraines and eskers form low hills, and the many small lakes and marshes indicate the generally
poor drainage characteristics of this area (Hainer, 1956). Areas of plains formed on glacial lake
deposits include the Souris Lake Plain and the area around Devil's Lake (fig. 2). The Turtle
Mountains are an area of drift-mantled hills rising 400 to 800 feet above the surrounding landscape
and located in the north-central part of the State along the Canadian border. Beneath the glacial
deposits, the Turtle Mountains are capped by resistant Tertiary sandstones and shales.
:i'iv!r Reprinted from USGS Open-File Report 93-292-H
-------
E
o
o,
V
o.
-------
£
00
ON
1
D
i
Q
I
5
I
ffi
-------
The Drift Prairie is separated from the Missouri Plateau to the west by an escarpment called
the Missouri Coteau, or "hills of the Missouri". The escarpment is a line of terminal moraines
rising 300 to 500 feet above the Drift Prairie and trending northwest to southeast The Missouri
Plateau, in the western half of the State, is different in character east and west of the Missouri
River. In general, areas north and east of the Missouri River are covered by ground moraine and
outwash, whereas areas to the south and west of the river have thin, discontinuous glacial deposits
with only scattered boulders in the vicinity of the glacial limit (Hainer, 1956). The area northeast
of the river exhibits typical subdued glacial topography, in contrast to the mostly unglaciated area
southwest of the river, where the topography ranges from dissected, gently sloping plains to buttes
and badlands (fig. 1).
Much of North Dakota's industry and land use is devoted to agriculture and livestock
production. Mining and production of energy resources (oil, gas, and coal) are also important in
the western part of the State. Much of the population of the North Dakota is concentrated near
population centers including Bismarck, Minot, Grand Forks, and Fargo (fig. 3).
GEOLOGY
Bedrock geology. Only Upper Cretaceous and younger rocks are exposed at the surface in
North Dakota. Older rocks directly underlie the glacial deposits in parts of the State but they are
not exposed at the surface. A brief discussion of pre-glacial bedrock geology is important because
in most cases the mineralogical constituents of the glacial sediments are derived from nearby
underlying bedrock. Figure 4 is a generalized bedrock geologic map of North Dakota showing the
units that are exposed at the surface in unglaciated areas, and units that directly underlie the glacial
deposits in glaciated areas; that is, units which would be exposed at the surface if glacial deposits
were not present. The information in this section is derived mainly from Bluemle (1977), Clayton
and others (1980a), and Hainer (1956).
Precarnbrian igneous and metamorphic rocks directly underlie glacial deposits in the Red
River Valley in the southeastern part of the State. These rocks form a basement beneath younger
sedimentary rocks in the remainder of the State. The Upper Cretaceous Carlile and Niobrara
Formations are exposed only in river valleys and in outcrops along the Pembina Escarpment in the
eastern part of the State. The Upper Cretaceous Pierre Shale is exposed primarily along the Little
Missouri and Missouri River valleys in the south-central and southwestern parts of the State. All
three units are dark to light gray shales deposited in offshore marine environments. The Upper
Cretaceous Fox Hills and Hell Creek Formations are brown to gray sandstones and shales of
coastal marine and continental origin. These units are exposed mainly in the south-central and
southwestern parts of the State. Tertiary sedimentary rocks, including the Ludlow, Cannonball,
Slope, Bullion Creek (formerly called the Tongue River Member of the Fort Union Formation
[Clayton and others, 1980a], or the Tongue River Formation [Jacob, 1976]), Sentinel Butte, and
Golden Valley Formations, and the White River Group (fig. 4) consist of sandstone, siltstone,
clay, shale, and some freshwater limestone deposited primarily in river, delta, lake, and wetland
environments. Coal occurs in most of the Tertiary units but is most abundant in the Bullion Creek
and Sentinel Butte Formations. Coal beds in the Bullion Creek Formation are as much as .13 m
thick (Leonard and others, 1925).
Glacial Geology: Ice advanced from the north and northwest in as many as 15 separate
glacial advances before and during Wisconsin time, leaving as much as 200 m of glacial deposits
(Clayton and others, 1980a). The Wisconsinan-age deposits shown in white on figure 5 were
IV-4 Reprinted from USGS Open-File Report 93-292-H
-------
I
•o
on
I
•
CO
o
I
O
Q.
O O 00
O O O CM
O O O O
O O IO i-
_ „_
o CM in T- in
2 QGSI
I
Q
.a
I
§
o
en
I
-------
00
oo
i
I
PQ
I
1
10
1
Q
s !
'So
'o
oo
•a
I
i
g
-------
BEDROCK GEOLOGIC MAP OF NORTH DAKOTA
EXPLANATION
Tertiary Rocks ^ -.-£••
|*XX| White River Group - sandstone, siltstone, and shale
Golden Valley Formation - sandstone, siltstone, and shale
Sentinel Butte Formation - sandstone, siltstone, and shale
Bullion Creek Formation - sandstone, siltstone, and shale
Slope Formation - sandstone, siltstone, and shale
'•*;*»«j Cannonball Formation - sandstone and shale
Ludlow Formation - sandstone, siltstone, and shale
Cretaceous Rocks
Hell Creek Formation - sandstone, siltstone, and shale
Fox Hills Formation - sandstone and shale
Pierre Formation - gray shale
Niobrara Formation - shale
Belle Fourche, Mowry, Newcastle, and Skull Creek
Formations - sandstone and shale
Inyan Kara Formation - sandstone and shale
Jurassic Rocks
Mostly shale with some limestone (beneath glacial cover)
Ordovician Rocks
Limestone and dolomite (beneath glacial cover)
Precambrian Rocks
Metamorphic and igneous rocks (beneath glacial cover)
-------
probably all deposited during the period of about 20,000-11,600 years before present (B.P.).
Lake Agassiz existed between about 12,000 and 8,500 B.P. (Clayton and others, 1980a).
Wisconsinan-age glacial deposits were emplaced by three main glacial lobes (fig. 5). The
Red River lobe covered northeastern North Dakota and northwestern Minnesota and was mostly
confined to the area of the Red River Valley. The Des Moines and James lobes covered eastern
North Dakota, western and southern Minnesota, and extended into eastern South Dakota and
central Iowa (Clayton and others, 1980a). The tills of all the ice advances are lithologicaUy
generally similar and were derived primarily from Upper Cretaceous and Tertiary shales,
siltstones, and sandstones that comprise the underlying bedrock in North Dakota and southern
Manitoba and Saskatchewan. Some of the deposits in the northeastern part of the State also
include carbonate-rich till derived from Paleozoic limestone and dolomite in southern Manitoba
(Moran and others, 1976) and granite, gneiss, and basalt from the Canadian Shield (Clayton and
others, 1980a). Tills in the northwestern part of the State contain a larger component of Tertiary
sandstones and shales. Virtually all of the tills have Pierre Shale as a source component; it is a
dominant component of the tills in the central and eastern parts of the State. Most of the tills
consist of nearly equal parts sand, silt, and clay (Lemke, 1960; Winters, 1963). Lacustrine
deposits of glacial lakes Agassiz, Souris, Dakota, and Devil's Lake (fig. 2) are composed primarily
of silty clays and clays, and are commonly interbedded with tills. The unoxidized tills are typically
dark olive gray to bluish gray. Iron oxidation and accumulation of calcium carbonate (CaCOa) are
common weathering effects (Lemke and others, 1965).
Uranium geology: Uranium occurrences of economic interest have been found primarily in
coals and carbonaceous shales, mostly in the Bullion Creek (Tongue River) Formation. The
Ludlow Formation also contains uraniferous lignites in the Cave Hills and Slim Buttes areas
(Jacob, 1976). The source of uranium in the coals is generally believed to be nearby volcanic
rocks (Denson and Gill, 1965; Hansen, 1964; Jacob, 1976). Uranium also occurs in some of the
sandstones of the Bullion Creek and in some ash clay beds of the White River Group (Bergstrpm,
1956). Uranium probably occurs in higher-than-average amounts (average crustal abundance is
2.5 parts per million [Carmichael, 1989]) in much of the Upper Cretaceous sandstone and shale
underlying the glacial deposits, especially the carbonaceous units of the Pierre Shale. In general,
the Pierre Shale as a whole contains higher-than-average amounts of uranium, in part because it
was deposited under reducing conditions under which uranium is relatively immobile and thus
more likely to concentrate at the site of deposition, and because it contains an abundance of clay
minerals that form weak bonds with metals, including uranium.
SOILS
The dominant soil types in North Dakota are MoUisols (formerly called Chernozems and
Chestnut soils) (fig. 6) that cover more than 60 percent of the State (U.S. Soil Conservation
Service, 1977; Omodt and others, 1968). Most of the soils are of low to moderate permeability
(fig. 7) and contain swelling clays. The soils with the lowest permeability are generally associated
with glacial lake deposits and with collapsed glacial sediments in the Missouri Coteau (fig. 7).
Many soils contain significant accumulations of CaCOs at depth, especially in the eastern part of
the State. Soils derived from tills are generally younger than those developed on bedrock, but the
rate of soil development in tills is probably accelerated by glacial crushing and mixing, which made
the potentially mobile chemical constituents of the mineral matter in the tills more accessible to
weathering agents such as percolating water (Jenny, 1935; Schumann and others, 1991).
IV-8 Reprinted from USGS Open-File Report 93-292-H
-------
EXPLANATION
GLACIAL LAKE DEPOSITS
WISCONSINAN GLACIAL LOBES
PRE-WISCONSINAN DEPOSITS
UNGLACIATED
MAJOR DIRECTION OF ICE MOVEMENT
Figure 5. Generalized map showing limits of advances and directions of ice movement
for the James, Red River, and Des Moines lobes in North and South Dakota,
Minnesota, and Iowa. Modified from Hallberg and Kemmis (1986) and G.M.
Richmond, personal communication (1992).
-------
-------
GENERALIZED SOIL MAP OF NORTH DAKOTA
EXPLANATION
Mollisols & Alfisols-deep, fine-loamy and clayey soils developed in
glacial till
Mollisols-deep, clayey and silty, calcic soils developed in glacial
lake sediments
Mollisols & Entisols-deep, coarse loamy and sandy soils
developed on outwash and glacial lake plains
Mollisols-deep, fine-loamy to clayey, calcic soils developed on
glacial till
Mollsiols-deep, fine-loamy soils developed on glacial till
D Mollisols & Entisols-deep, clayey to coarse-loamy, calcic soils
developed on glacial till
Mollisols-deep, clayey and fine-loamy, saline soils developed on
glacial till
Mollisols & Entisols-deep, clayey and fine loamy soils developed
on glacial till
Mollisols & Entisols-shallow to moderately deep, clayey and loamy
soils developed on residuum
Mollisols & Entisols-shallow to moderately deep, loamy and sandy
soils developed on residuum and till
n Mollisols, Entisols, and Inceptisols-shallow to deep, fine-silty to
fine-loamy soils developed on residuum and till
Entisols and Mollisols-shallow to moderately deep, loamy soils
developed on residuum
Entisols, Aridisols, and Mollsiols-shallow to deep, clayey and
loamy soils developed on residuum
-------
o
-------
INDOOR RADON DATA
Indoor radon data from the 1987-88 State/EPA Residential Radon Survey of North Dakota
are presented in figure 8 and Table 1. Only data from counties with five or more measurements are
shown on figure 8. Most of the data are from basements because most of the homes in North
Dakota (about 80 percent) have basements. Figure 9 is a map showing county names and locations
for reference. Of 1596 homes tested in North Dakota in the State/EPA Residential Radon Survey,
63 percent had screening indoor radon measurements exceeding the EPA's guideline level of
4 pCi/L. The highest indoor radon concentration measured in North Dakota in the State/EPA
survey was 184 pCi/L, although measurements higher than 200 pCi/L have been reported by other
sources (U.S. Senate, 1987). Three areas of the State have a relatively large proportion of homes
with high indoor radon concentrations, as indicated by the percent of homes sampled in each
county with screening indoor radon levels greater than 4 pCi/L: The Red River Valley, along the
State's eastern border, the southeastern quarter of the State, and the southwestern part of the State
(fig. 8). Average screening indoor radon levels are greater than 4 pCi/L across most of the State
(fig. 8). Homes with screening indoor radon concentrations between 50 and 100 pCi/L were
found in Bottineau, Cass, Grand Forks, Mercer, and Walsh Counties, and homes with screening
indoor radon levels exceeding 100 pCi/L were found in Bowman, Stark, and Stutsman Counties
(Table 1). In all but two of the counties for which data are presented in figure 8, more than 25
percent of the homes sampled in each county had basement radon levels greater than 4 pCi/L,
indicating that elevated radon levels are widespread across the State.
The data indicate that all areas of North Dakota may have a significant number of homes
with indoor radon levels exceeding 4 pCi/L. The areas with the highest maximum levels as well as
the greatest proportion of homes with elevated radon levels are the Red River Valley and the
southwestern quarter of the State. The geologic reasons for this distribution are discussed below.
GEOLOGIC RADON POTENTIAL
Correlations of aerial radioactivity data (fig. 10) with geology and indoor radon data are
inconsistent in those areas underlain by glacial deposits. Except for the Lake Agassiz deposits in
the Red River Valley, glacial deposits have a surface radioactivity signature that is lower than
expected (fig. 10), especially in light of the measured indoor radon levels. Schumann and others
(1991) conducted field sampling of soils, soil-gas radon, and surface radioactivity in central and
eastern North Dakota and measured surface radioactivities that were consistent with the NURE
aerial radiometric data, indicating that the anomalously low surface radioactivity was not due to
measurement error. Although the soils exhibit low radioactivity in the upper 30 cm of soil (the
typical depth of investigation of the gamma spectrometers), there is obviously sufficient radon
parent material (uranium and radium) deeper than 30 cm in the soil, but shallow enough to generate
elevated levels of indoor radon in many areas.
In general, soils developed from glacial deposits are rapidly weathered, because crushing
and grinding of the rocks by glacial action can enhance and speed up soil weathering processes
(Jenny, 1935). Grinding of the rocks increases the mobility of uranium and radium in the soils by
exposing them at grain surfaces, where they are more easily leached and moved downward
through the soil profile with other mobile ions. Calcium carbonate and iron oxides form soil-grain
coatings or concretions that sorb or associate with uranium (Hansen and Stout, 1968; Nash and
IV-13 Reprinted from USGS Open-File Report 93-292-H
-------
Bsmt. & 1st Floor Rn
%>4pCi/L
OtolO
11 to 20
21 to 40
41 to 60
61 to 80
81 to 100
Missing Data
or < 5 measurements
100 Miles
oD
8E3
Bsmt & 1st Floor Rn
Average Concentration (pCi/L)
0.0 to 1.9
2.0 to 4.0
4.1 to 6.0
6.1 to 11.7
Missing Data
or < 5 measurements
100 Miles
Figure 8. Screening indoor radon data from the EPA/State Residential Radon Survey of North
Dakota, 1987-88, for counties with 5 or more measurements. Data are from 2-7 day charcoal
canister tests. Histograms in map legends show the number of counties in each category. 1 he
number of samples in each county (see Table 1) may not be sufficient to statistically characterize
the radon levels of the counties, but they do suggest general trends. Unequal category intervals
were chosen to provide reference to decision and action levels.
-------
TABLE 1. Screening indoor radon data from the EPA/State Residential Radon Survey of
North Dakota conducted during 1987-88. Data represent 2-7 day charcoal canister measurements
from the lowest level of each home tested.
COUNTY
ADAMS
BARNES
BENSON
BILLINGS
BOTTINEAU
BOWMAN
BURKE
BURLEIGH
CASS
CAVALIER
DICKEY
DIVIDE
DUNN
EDDY
EMMONS
FOSTER
GOLDEN VALLEY
GRAND FORKS
GRANT
GRIGGS
HETTINGER
KIDDER
LAMOURE
LOGAN
MCHENRY
MCINTOSH
MCKENZIE
MCLEAN
MERCER
MORTON
MOUNTRAEL
NELSON
OLIVER
PEMBINA
PIERCE
RAMSEY
RANSOM
RENVILLE
RICHLAND
ROLETTE
SARGENT
NO. OF
MEAS.
23
38
8
9
33
31
4
101
171
14
11
4
28
4
15
7
7
172
23
10
31
8
5
13
30
9
6
17
46
99
20
26
19
59
17
18
7
9
46
20
10
MEAN
9.3
8.0
7.2
8.7
6.0
10.7
2.6
4.9
7.9
3.7
5.5
8.8
8.7
4.6
6.6
3.7
4.0
11.7
8.1
3.3
7.2
4.0
5.2
5.7
3.6
7.1
3.5
5.0
8.1
5.6
7.5
5.3
6.4
9.4
3.8
6.6
8.4
5.1
7.0
5.5
5.5
GEOM.
MEAN
7.4
5.6
4.0
6.3
4.0
5.5
2.4
4.0
5.6
1.7
4.7
7.5
6.4
2.3
4.8
2.9
3.6
9:3
5.8
2.8
5.4
3.3
5.0
5.0
2.8
2.9
3.0
4.6
6.1
4.2
5.1
4.6
5.9
6.4
3.4
5.2
5.9
4:8
4.5
3.6
4.9
MEDIAN
7.3
5.8
4.2
9.2
4.2
6.6
2.7
3.8
5.4
3.1
5.2
8.7
6.7
3.6
4.1
4.0
2.7
9.5
6.1
3.0
5.7
4.0
5.6
4.8
2.9
3.6
3.3
4.4
6.3
4.4
5.3
4.7
6.1
7.1
3.0
5.2
10.5
4.3
4.8
3.8
5.7
STD.
DEV.
7.1
8.0
10.5
6.1
8.7
22.2
0.9
4.0
9.3
3.6
2.7
5.3
6.6
4.8
6.1
2.3
2.1
9.3
7.6
2.0
5.7
2.5
1.7
3.3
2.7
11.1
2.1
2.3
8.1
5.0
8.5
3.0
2.9
7.8
2.3
4.7
6.0
2.4
8.0
4.6
2.5
MAXIMUM
27.8
44.1
32.7
20.6
52.6
126.6
3.5
32.1
85.6
14.4
10.1
13.8
25.3
10.7
25.0
7.4
7.2
77.7
34.9
8.0
25.4
9.0
7.1
14.6
12.6
35.7
6.1
10.6
50.8
32.6
38.1
13.9
14.4
35.0
11.4
16.7
17.4
11.4
48.7
14.5
9.8
%>4pCi/L
78
74
50
78
52
71
0
47
66
36
82
100
75
50
53
43
43
90
61
20
61
50
60
69
33
44
50
71
72
53
60
62
84
73
24
78
57
56
57
50
70
%>20 pCi/L
13
8
13
11
3
6
0
1
6
0
0
0
11
0
7
0
0
10
4
0
6
0
0
0
0
11
0
0
7
3
10
0
0
14
0
0
0
0
4
0
0
-------
TABLE 1 (continued). Screening indoor radon data for North Dakota.
COUNTY
SHERIDAN
SIOUX
SLOPE
STARK
STHPT.F.
STUTSMAN
TOWNER
TRAILL
WALSH
WARD
WELLS
WILLIAMS
NO. OF
MEAS.
5
2
7
122
7
40
10
26
49
66
11
23
MEAN
5.0
4.9
7.0
8.0
5.2
7.8
8.1
6.8
10.5
4.2
5.6
4.6
GEOM.
MEAN
4.8
2.7
4.3
5.1
3.7
4.1
5.2
4.4
7.3
3.2
2.4
3.9
MEDIAN
5.0
4.9
3.3
4.8
3.3
4.6
4.8
5.3
8.0
3.6
2.8
3.8
STD.
DEV.
1.3
5.8
6.3
17.0
5.7
20.7
10.5
7.2
9.2
3.2
7.8
3.0
MAXIMUM
6.6
9.0
15.6
184.2
17.8
134.4
36.8
38.2
50.6
20.6
22.4
13.3
%>4pCi/L
60
50
43
59
43
63
50
65
76
45
27
48
%>20 pCi/L
0
0
0
4
0
3
10
4
10
2
9
0
-------
I
9
O
u
-------
c <»
II
l
in ...
• GO
-------
others, 1981), providing a possible mechanism for uranium accumulation and enhanced radon
emanation in deeper soil horizons. The low. surface radioactivity and comparatively high soil radon
concentrations of the glacial soils suggest that radionuclides have been removed from the upper soil
layers and are concentrated in deeper horizons, providing a possible explanation for the relatively
low measured soil radioactivity and high indoor radon levels in the glaciated areas.
Although many of the soils derived from glacial deposits in North Dakota, including the
Lake Agassiz deposits, contain significant amounts of clay, the soils can have permeabilities that
are higher than indicated by standard water percolation tests due to gas flow through shrinkage
cracks when the soils are dry. In addition, clays tend to have high radon emanation coefficients
because clay particles have a high surface-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 and other areas
shown in figure 5, highly susceptible to indoor radon problems. Because two of the State's largest
population centers, Grand Forks and Fargo, lie within the Red River Valley, a large number of
homes could be affected.
The southwestern quarter of the State, generally including the area southwest of the
Missouri River, is underlain primarily by sedimentary rocks of Late Cretaceous and younger age.
Tertiary-age rock units including the Cannonball, Slope, Bullion Creek, Sentinel Butte, and
Golden Valley Formations, and the White River Group (fig. 4), generally contain higher-than-
average amounts of uranium and are known or likely to cause indoor radon problems in some
homes built on these units. Buildings constructed using fill from mine spoil are also likely to have
elevated indoor radon levels; this is known to have been used in the construction of some homes in
the Belfield area (U.S. Senate, 1987). Finally, although it is not known to be a widespread
problem in North Dakota, it should be mentioned that water from private wells in virtually any area
of the State could contain significant amounts of dissolved radon that could contribute to radon in
indoor air when the water is degassed through use in the home.
SUMMARY
Figure 11 shows radon potential areas of North Dakota delineated in this report and
assigned Radon Index (RI) and Confidence Index (CI) scores in Table 2. For the purposes of
assessing radon potential the State was divided into three areas: the area underlain by bedrock and
not covered by glacial deposits, designated the Unglaciated Area; an area underlain by glacial
deposits, designated the Glaciated Area; and areas underlain by glacial lake deposits, designated
Glacial Lakes (note that each lake is identified individually on figure 11).
The Unglaciated Area has a high radon potential (RI=13) with high confidence (CI=11).
Tertiary and Upper Cretaceous sandstones, shales, and locally, coal-bearing units, are potential
sources of high radon levels in this area. The Glaciated Area, which covers more than half of the
State, has a high radon potential (RI=13) with high confidence (CI=10). Glacial deposits in this
area are largely derived from Cretaceous shales containing higher-than-average amounts of
uranium. Then- low surface radioactivity is misleading because radionuch'des are likely
concentrated in deeper soil horizons, and many of the soils have higher permeability than indicated
by their high clay content because the soils crack when dry. The Glacial Lakes have basically the
same source rocks as the other glacial deposits, but have higher surface radioactivity and may have
even higher radon emanation coefficients and higher permeability than glacial drift, perhaps due to
the better sorting of the silt and clay lake deposits. Some of the highest indoor radon levels in the
IV-19 Reprinted from USGS Open-File Report 93-292-H
-------
_aj
1
o
O—i
o_
^
o_
-------
State have been measured in homes situated on deposits of Lake Agassiz. The Glacial Lakes areas
have a high radon potential (RI=14) and high confidence (CI=10).
This is a generalized assessment of the State's geologic radon potential and there is no
substitute for having a home tested. The conclusions about radon potential presented in this report
cannot be applied to individual homes or building sites. Indoor radon levels, both high and low,
can be quite localized, and within any radon potential area there will likely be areas with higher or
lower radon potential that assigned to the area as a whole. Any local decisions about radon should
not be made without consulting all available local data. For additional information on radon and
how to test, contact your State radon program or EPA regional office. More detailed information
on state or local geology may be obtained from the State geological survey. Addresses and phone
numbers for these agencies are listed in chapter 1 of this booklet.
IV-21 Reprinted from USGS Open-File Report 93-292-H
-------
TABLE 2. Radon Index (RI) and Confidence Index (CI) scores for geologic radon potential areas
of North Dakota. See figure 11 for locations of areas.
FACTOR .
INDOOR RADON
RADIOACTIVITY
GEOLOGY
SOIL PERM.
ARCHITECTURE
GFE POINTS
TOTAL
Unglaciated
Area
RI CI
3
2
3
2
3
0
13
3
3
3
2
11
Glaciated
Area
RI CI
3
1
3
1
3
2
13
3
2
3
2
10
Glacial
Lakes
RI CI
3
2
3
1
3
2
14
3
2.
3
2
10
RANKING HIGH HIGH
HIGH HIGH
HIGH HIGH
sIDEX SCORING:
Radon potential category
LOW
MODERATE/VARIABLE
HIGH
Point range
3-8 points
9- 11 points
> 1 1 points
Probable screening indoor
radon average for area
< 2 pCi/L
2 - 4 pCi/L
> 4 pCi/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-22 Reprinted from USGS Open-File Report 93-292-H
-------
REFERENCES USED IN THIS REPORT
AND GENERAL REFERENCES PERTAINING TO RADON IN NORTH DAKOTA
Bergstrom, J.R., 1956, The general geology of uranium in southwestern North Dakota: North
Dakota Geological Survey Report of Investigations No. 23,1 sheet.
Bluemle, J.P., 1977, The face of North Dakota: The geologic story: North Dakota Geological
Survey Educational Series 11, 73 p.
Bluemle, J.P., 1988, Generalized bedrock geologic map of North Dakota: North Dakota
Geological Survey Miscellaneous Map 28, scale 1:2,500,000.
Carmichael, R.S., 1989, Practical handbook of physical properties of rocks and minerals: Boca
Raton, FL: CRC Press, 741 p.
Clayton, Lee, Moran, S.R., and Bluemle, J.P., 1980a, Explanatory text to accompany the
geologic map of North Dakota: North Dakota Geological Survey Report of Investigation
No. 69, 93 p.
Clayton, Lee, Moran, S.R., Bluemle, J.P., and Carlson, C.G., 1980b, Geologic map of North
Dakota: U.S. Geological Survey, scale 1:500,000.
Cvancara, A.M., 1976, Geology of the Cannonball Formation (Paleocene) in the Williston Basin,
with reference to uranium potential: North Dakota Geological Survey Report of
Investigation No. 57, 22 p.
Cvancara, A.M., 1976, Geology of the Fox Hills Formation (Late Cretaceous) in the Williston
Basin of North Dakota, with reference to uranium potential: North Dakota Geological
Survey Report of Investigation No. 55, 16 p.
Denson, KM., and Gill, J.R., 1965, Uranium-bearing lignite and carbonaceous shale in the
southwestern part of the Williston Basin—a regional study: U.S. Geological Survey
Professional Paper 463, 75 p.
Duval, J.S., Jones, W.J., Riggle, F.R., and Pitkin, J.A., 1989, Equivalent uranium map of the
conterminous United States: U.S. Geological Survey Open-File Report 89-478,10 p.
Grasty, R.L., 1989, The relationship of geology and gamma-ray spectrometry to radon in homes
(abs): EOS, v. 70, p. 496.
Hallberg, G.R., and Kemmis, T.J., 1986, Stratigraphy and correlation of the glacial deposits of
the Des Moines and James lobes and adjacent areas in North Dakota, South Dakota,
Minnesota, and Iowa, in Sibrava, V., Bowen, D.Q., and Richmond, G.M. (eds.),
Quaternary glaciations in the Northern Hemisphere: Quaternary Science Reviews, v. 5,
p. 65-68.
IV-23 Reprinted from USGS Open-File Report 93-292-H
-------
Hansen, D.E., 1964, Uranium of North Dakota, in Tufte, O. (ed), The mineral resources of North
Dakota: Grand Forks, North Dakota, The General Extension Division, University of
North Dakota, p. 109-127.
Hansen, R.O., and Stout, P.R., 1968, Isotopic distributions of uranium and thorium in soils: Soil
Science, v. 105, p. 44-50.
Hainer, J.L., 1956, The geology of North Dakota: North Dakota Geological Survey Bulletin 31,
46 p.
Jacob, A.F., 1976, Geology of the upper part of the Fort Union Group (Paleocene), Williston
Basin, with reference to uranium: North Dakota Geological Survey Report of Investigation
No. 58, 49 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., 1960, Geology of the Souris River area, North Dakota: U.S. Geological Survey
Professional Paper 325, 138 p.
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.
Leonard, A.G., Babcock, E.J., and Dove, L.P., 1925, The lignite deposits of North Dakota:
North Dakota Geological Survey Bulletin 4, 240 p.
Moran, S.R., Arndt, M., Bluemle, J.P., Camara, M., Clayton, L., Fenton, M.M., Harris, K.L.,
Hobbs, H.C., Keatinge, R., Sackreiter, D.K., Salomon, N.L., and Teller, J., 1976,
Quaternary stratigraphy and history of North Dakota, southern Manitoba, and northwestern
Minnesota, in Mahaney, W.C. (ed.), Quaternary stratigraphy of North America:
Stroudsburg, Pennsylvania, Dowden, Huchinson, and Ross, p. 133-158.
Nash, J.T., Granger, H.C., and Adams, S.S., 1981, Geology and concepts of genesis of
important types of uranium deposits: Economic Geology, 75th Anniversary volume,
p. 63-116.
Omodt, H.W., Johnsgard, G.A., Patterson, D.D., and Olson, O.P., 1968, The major soils of
North Dakota: North Dakota Agricultural Experiment Station Bulletin 472, 60 p.
Schumann, R.R., Peake, R.T., Schmidt, K.M., and Owen, D.E., 1991, Correlations of soil-gas
and indoor radon with geology in glacially derived soils of the northern Great Plains, in
Proceedings of the 1990 International Symposium on Radon and Radon Reduction
Technology, Volume 2, Symposium Oral Papers: U.S. Environmental Protection Agency
report EPA/600/9-9 l/026b, p. 6-23-6-36.
IV-24 Reprinted from USGS Open-File Report 93-292-H
-------
U. S. Senate, 1987, Radon contamination problems in North Dakota: Senate hearing 100-285;
100th Congress, first session, held Aug. 20, 1987, Fargo, N.D.: U.S. Government
Printing Office, Washington, D.C., Congressional document 79-382, 64 p.
U.S. Soil Conservation Service, 1977, Soils of North Dakota: U.S. Department of Agriculture,
U.S. Soil Conservation Service, scale 1:2,150,000.
Winters, H.A., 1963, Geology and ground water resources of Stutsman County, North Dakota,
Part I: Geology: North Dakota Geological Survey Bulletin 41, 84 p.
IV-25 Reprinted from USGS Open-File Report 93-292-H
-------
-------
EPA's Map of Radon Zones
The USGS' Geologic Radon Province Map is the technical foundation for EPA's Map
of Radon Zones. The Geologic Radon Province Map defines the radon potential for
approximately 360 geologic provinces. EPA has adapted this information to fit a county
boundary map in order to produce the Map of Radon Zones.
The Map of Radon Zones is based on the same range of predicted screening levels of
indoor radon as USGS' Geologic Radon Province Map. EPA defines the three zones as
follows: Zone One areas have an average predicted indoor radon screening potential greater
than 4 pCi/L. Zone Two areas are predicted to have an average indoor radon screening
potential between 2 pCi/L and 4 pCi/L. Zone Three areas are predicted to have an average
indoor radon screening potential less than 2 pCi/L.
Since the geologic province boundaries cross state and county boundaries, a strict
translation of counties from the Geologic Radon Province Map to the Map of Radon Zones
was not possible. For counties that have variable radon potential (i.e., are located in two or
more provinces of different rankings), the counties were assigned to a zone based on the
predicted radon potential of the province in which most of its area lies. (See Part I for more
details.)
NORTH DAKOTA MAP OF RADON ZONKS
The North Dakota Map of Radon Zones and its supporting documentation (Part IV of
this report) have received extensive review by North Dakota geologists and radon program
experts. The map for North Dakota generally reflects current State knowledge about radon
for its counties. Some States have been able to conduct radon investigations in areas smaller
than geologic provinces and counties, so it is important to consult locally available data.
Although the information provided in Part IV of this report -- the State chapter entitled
"Preliminary Geologic Radon Potential Assessment of North Dakota" -- may appear to be
quite specific, it cannot be applied to determine the radon levels of a neighborhood, housing
tract, individual house, etc. THE ONLY WAY TO DETERMINE IF A HOUSE HAS
ELEVATED INDOOR RADON IS TO TEST. Contact the Region 8 EPA office or the
North Dakota radon program for information on testing and fixing homes. Telephone
numbers and addresses can be found in Part II of this report.
V-l
-------
------- |