United States
Environmental Protection
Agency
Air and Radiation
(66d4J)
402-fi-e3-OSS
September 1993
v>EPA EPA's Map of Radon Zones
VERMONT
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EPA'S MAP OF RADON ZONES
VERMONT
RADON DIVISION
OFFICE OF RADIATION AND INDOOR AIR
U.S. ENVIRONMENTAL PROTECTION AGENCY
SEPTEMBER, 1993
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ACKNOWLEDGEMENTS
This document was prepared by the U.S. Environmental Protection Agency's (EPA's)
Office of Radiation and Indoor Air (ORIA) in conjunction with the U.S. Geological Survey
(USGS). Sharon W. White was the EPA project manager. Numerous other people in ORIA
were instrumental in the development of the Map of Radon Zones, including Lisa Ratcliff,
Kirk Maconaughey, R. Thomas Peake, Dave Rowson, and Steve Page.
EPA would especially like to acknowledge the outstanding effort of the USGS
radon team — Linda Gundersen, Randy Schumann, Jim Otton, Doug Owen, Russell
Dubiel, Ken dell Dickinson, and Sandra Szarzi — in developing the technical base for the
Map of Radon Zones.
ORIA would also like to recognize the efforts of all the EPA Regional Offices in
coordinating the reviews with the State programs and the Association of American State
Geologists (AASG) for providing a liaison with the State geological surveys. In addition,
appreciation is expressed to all of the State radon programs and geological surveys for their
technical input and review of the Map of Radon Zones>.
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TABLE OF CONTENTS
I. OVERVIEW
II. THE USGS/EPA RADON POTENTIAL
ASSESSMENTS:INTRODUCTION
III. REGION 1 GEOLOGIC RADON POTENTIAL
SUMMARY
V. PRELIMINARY GEOLOGIC RADON POTENTIAL
ASSESSMENT OF VERMONT
V. EPA'S MAP OF RADON ZONES -- VERMONT
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OVERVIEW
Sections 307 and 309 of the 1988 Indoor Radon Abatement Act (IRAA) direct EPA to
identify areas of the United States that have the potential to produce elevated levels of radon.
EPA, the U.S. Geological Survey (USGS), and the Association of American State Geologists
(AASG) have worked closely over the past several years to produce a series of maps and
documents which address these directives. The EPA Map of Radon Zones is a compilation of
that work and fulfills the requirements of sections 307 and 309 of IRAA. The Map of Radon
Zones identifies, on a county-by-county basis, areas of the U.S. that have the highest potential
for elevated indoor radon levels (greater than 4 pCi/L).
The Map of Radon Zones is designed to assist national, State and local governments
and organizations to target their radon program activities and resources. It is also intended to
help building code officials determine areas that are the highest priority for adopting radon-
resistant building practices. The Map of Radon Zones should not be used to determine if
individual homes in any given area need to be tested for radon. EPA recommends that all
homes be tested for radon, regardless of geographic location or the zone designation of
the county in which they are located.
This document provides background information concerning the development of the
Map of Radon Zones. It explains the purposes of the map, the approach for developing the
map (including the respective roles of EPA and USGS), the data sources used, the conclusions
and confidence levels developed for the prediction of radon potential, and the review process
that was conducted to finalize this effort. :
BACKGROUND
Radon (Rn222) is a colorless, odorless, radioactive gas. It comes from the natural
decay of uranium that is found in nearly all soils. It typically moves through the ground to
the air above and into homes and other buildings through cracks and openings in the
foundation. Any home, school or workplace may have a radon problem, regardless of
whether it is new or old, well-sealed or drafty, or with or without a basement. Nearly one out
of every 15 homes in the U.S. is estimated to have elevated annual average levels of indoor
radon.
Radon first gained national attention in early 1984, when extremely high levels of
indoor radon were found in areas of Pennsylvania, New Jersey, and New York, along the
Reading Prong-physiographic province. EPA established a Radon Program in 1985 to assist
States and homeowners in reducing their risk of lung cancer from indoor radon.
Since 1985, EPA and USGS have been working together to continually increase our
understanding of radon sources and the migration dynamics that cause elevated indoor radon
levels. Early efforts resulted in the 1987 map entitled "Areas with Potentially High Radon
Levels." This map was based on limited geologic information.only because few indoor radon
measurements were available at the time. The development of EPA's Map of Radon Zones
and its technical foundation, USGS' National Geologic Radon Province Map, has been based
on additional information from six years of the State/EPA Residential Radon Surveys,
independent State residential surveys, and continued expansion of geologic and geophysical
information, particularly the data from the National Uranium Resource Evaluation project.
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Purpose of the Mao 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 precacted 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
rjKJpn potential in the lowest liveable area of a structure. This map is unable to estimate
actual exposures to radon. EPA recommends methods for testing and fixing individual homes
based on an estimate of actual exposure to radon. For more information on testing and fixing
elevated radon levels in homes consult these EPA publications: A Citizen's Guide to Radon,
the Consumer's Guide to Radon Reduction and the Home Buyer's and Seller's Guide to
Radon.
EPA believes that States, local governments and other organizations can achieve
optimal risk reductions by targeting resources and program activities to high radon potential
areas. Emphasizing targeted approaches (technical assistance, information and outreach
efforts, promotion of real estate mandates and policies and building codes, etc.) in such areas
addresses the greatest potential risks first.
EPA also believes that the use of passive radon control systems in the construction of
new homes in Zone 1 counties, and the activation of those systems if necessitated by follow-
up testing, is a cost effective approach to achieving significant radon risk reduction.
The Map of Radon Zones and its supporting documentation establish no regulatory
requirements. Use of this map by State or local radon programs and building code officials is
voluntary. The information presented on the Map of Radon Zones and in the supporting
documentation is not applicable to radon in water.
Development of the Map of Radon Zones
The technical foundation for the Map of Radon Zones is the USGS Geologic Radon
Province Map. In order to examine the radon potential for the United States, the USGS
began by identifying approximately 360 separate geologic provinces for the U.S. The
provinces are shown on the USGS Geologic Radon Province Map (Figure 2). Each of the
geologic provinces was evaluated by examining the available data for that area: indoor radon
measurements, geology, aerial radioactivity, soil parameters, and foundation types. As stated
previously, these five factors are considered to be of basic importance in assessing radon
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Figure 1
EPA Map of Radon Zones
Zone designation for Puerto Rico is under development.
Guam - Preliminary Zone designation. ,— m- ,,,_•.,..„
^- I he purpose of this mop is to assist National, State and local organizations to target tnetr resources and to implement radon—resistant building codes.
This map is not Mended to be used to determine if a home in _a given zone should be tested for radon. Homes with elevated levels of radon have been found
in all three, zones. All homes should be fashd, regardless of geographic location,
MEQBIML. Consult the EPA Mop of Radon Zones document (EPA-402-R-93-Q71) before using this map. This document contains information on radon potential variations within counties.
£PA also recommends that this mop be supplemented with any available local data in order to further understand and predict the radon potential of a specific area.
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Figure 2
GENERALIZED GEOLOGIC RADON POTENTIAL OF THE UNITED STATES
by the U.S. Geological Survey
Continental United States
and Hawaii
500
Geologic Radon
Potential
(Predicted Average
Screening Measurement)
[ [LOW (<2pCI/L)
MODERATE/VARIABLE
(2-4pCI/L)
HIGH (>4pCI/L)
Miles
6/93
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potential and some data are available for each of these factors in every geologic province. The
province boundaries do not coincide with political borders (county and state) but define areas
of general radon potential. The five factors were assigned numerical values based on an
assessment of their respective contribution to radon potential, and a confidence level was
assigned to each contributing variable. The approach used by USGS to estimate the. radon
potential for each province is described in Part II of this document.
EPA subsequently developed the Map of Radon Zones by extrapolating from the
province level to the county level so that all counties in the U.S. were assigned to one of
three radon zones. EPA assigned each county to a given zone based on its provincial radon
potential. For example, if a county is located within a geologic province that has a predicted
average screening level greater than 4 pCi/L, it was assigned to Zone 1. Likewise, counties
located in provinces with predicted average screening levels > 2 pCi/L and < 4 pCi/L, and
less than 2 pCi/L, were assigned to Zones 2 and 3, respectively.
If the boundaries of a county fall in more than one geologic province, the county was
assigned to a zone based on the predicted radon potential of the province in which most of
the area lies. For example, if three different provinces cross through a given county, the
county was assigned to the zone representing the radon potential of the province containing
most of the county's land area. (In this case, it is not technically correct to say that the
predicted average screening level applies to the entire county since the county falls in
multiple provinces with differing radon potentials.)
Figures 3 and 4 demonstrate an example of how EPA extrapolated the county zone
designations for Nebraska from the USGS geologic province map for the State. As figure 3
shows, USGS has identified 5 geologic provinces for Nebraska. Most of the counties are
extrapolated "straight" from their corresponding provinces, but there are counties "partitioned"
by several provinces — for example, Lincoln County. Although Lincoln county falls in
multiple provinces, it was assigned to Zone 3 because most of its area falls in the province
with the lowest radon potential.
It is important to note that EPA's extrapolation from the province level to the
county level may mask significant "highs" and "lows" within specific counties. In other
words, within-county variations in radon potential are not shown on the Map of Radon
Zones. EPA recommends that users who may need to address specific within-county
variations in radon potential (e.g., local government officials considering the
implementation of radon-resistant construction codes) consult USGS* Geologic Radon
Province Map and the State chapters provided with this map for more detailed
information, as well as any locally available data.
Map Validation
The Map of Radon Zones is intended to represent a preliminary assessment of radon
potential for the entire United States. The factors that are used in this effort —indoor radon
data, geology, aerial radioactivity, soils, and foundation type — are basic indicators for radon
potential. It is important to note, however, that the map's county zone designations are not
"statistically valid" predictions due to the nature of the data available for these 5 factors at the
county level. In order to validate the map in light of this lack of statistical confidence, EPA
conducted a number of analyses. These analyses have helped EPA to identify the best
situations in which to apply the map, and its limitations.
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Figure 3
Geologic Radon Potential Provinces for Nebraska
Lincoln Co u a t y
81 gk Uoierite Low
Figure 4
NEBRASKA - EPA Map of Radon Zones
Lincoln County
Zttt I Zone 2 Zone
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One such analysis involved comparing county zone designations to indoor radon
measurements from the State/EPA Residential Radon Surveys (SRRS). Screening averages
for. counties with at least 100 measurements were compared to the counties' predicted radon
potential as indicated by the Map of Radon Zones. EPA found that 72% of the county
screening averages were correctly reflected by the appropriate zone designations on the Map.
In all other cases, they only differed by 1 zone.
Another accuracy analysis used the annual average data from the National Residential
Radon Survey (NRRS). The NRRS indicated that approximately 6 million homes in the
United States have annual averages greater than or equal to 4 pCi/L. By cross checking the
county location of the approximately 5,700 honies which participated in the survey, their
radon measurements, and the zone designations for these counties, EPA found that
approximately 3.8 million homes of the 5.4 million homes with radon levels greater than or
equal to 4 pCi/L will be found in counties designated as Zone 1. A random sampling of an
equal number of counties would have only found approximately 1.8 million homes greater
than 4 pCi/L. In other words, this analysis indicated that the map approach is three times
more efficient at identifying high radon areas than random selection of zone designations.
Together, these analyses show that the approach EPA used to develop the Map of
Radon Zones is a reasonable one. In addition, the Agency's confidence is enhanced by results
of the extensive State review process — the map generally agrees with the States' knowledge
of and experience in their own jurisdictions. However, the accuracy analyses'highlight two
important points: the fact that elevated levels will be found in Zones 2 and 3, and that there
will be significant numbers of homes with lower indoor radon levels in all of the Zones. For
these reasons, users of the Map of Radon Zones need to supplement the Map with locally
available data whenever possible. Although, all known "hot spots", i.e., localized areas of
consistently elevated levels, are discussed in the State-
specific chapters, accurately defining the boundaries of the "hot spots" on this scale of map is
not possible at this time. Also, unknown "hot spots" do exist
The Map of Radon Zones is intended to be a starting point for characterizing radon
potential because our knowledge of radon sources and transport is always growing. Although
this effort represents the best data available at this time, EPA will continue to study these
parameters and others such as house construction, ventilation features and meteorology factors
in order to better characterize the presence of radon in U.S homes, especially in high risk
areas. These efforts will eventually assist EPA in refining and revising the conclusions of the
Map of Radon Zones. And although this map is most appropriately used as a targeting tool
by the aforementioned audiences -- the Agency encourages all residents to test their homes
for radon, regardless of geographic location or the zone designation of the county in
which they live. Similarly, the Map of Radon Zones should not to be used in lieu of
testing during real estate transactions.
Review Process
The Map of Radon Zones has undergone extensive review within EPA and outside the
Agency. The Association of American State Geologists (AASG) played an integral role in
this review process. The AASG individual State geologists have reviewed their State-specific
information, the USGS Geologic Radon Province Map, and other materials for their geologic
content and consistency.
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In addition to each State geologist providing technical comments, the State radon
offices were asked to comment on their respective States' radon potential evaluations. In
particular, the States were asked to evaluate the data used to assign their counties to specific
zones. EPA and USGS worked with the States to resolve any issues concerning county zone
designations. In a few cases, States have requested changes in county zone designations. The
requests were based on additional data from the State on geology, indoor radon
measurements, population, etc. Upon reviewing the data submitted by the States, EPA did
make some changes in zone designations. These changes, which do not strictly follow the
methodology outlined in this document, are discussed in the respective State chapters.
EPA encourages the States and counties to conduct further research and data collection
efforts to refine the Map of Radon Zones. EPA would like to be kept informed of any
changes the States, counties, or others make to the maps. Updates and revisions will be
handled in a similar fashion to the way the map was developed. States should notify EPA of
any proposed changes by forwarding the changes through the Regional EPA offices that are
listed in Part II. Depending on the amount of new information that is presented, EPA will
consider updating this map periodically. The State radon programs should initiate proper
notification of the appropriate State officials when the Map of Radon Zones is released and
when revisions or updates are made by the State or EPA.
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THE USGS/EPA RADON POTENTIAL ASSESSMENTS: AN INTRODUCTION
by
Linda C.S. Gundersen and R. Randall Schumann
U.S. Geological Survey
and
Sharon W. White
U.S. Environmental Protection Agency
BACKGROUND
The Indoor Radon Abatement Act of 1988 (15 U.S.C. 2661-2671) directed the U.S.
Environmental Protection Agency (EPA) to identify areas of the United States that have the
potential to produce harmful levels of indoor radon. These characterizations were to be based
on both geological data and on indoor radon levels in homes and other structures. The EPA
also was directed to develop model standards and techniques for new building construction
that would provide adequate prevention or mitigation of radon entry. As part of an
Interagency Agreement between the EPA and the U.S. Geological Survey (USGS), the USGS
has prepared radon potential estimates for the United States. This report is one of ten
booklets that document this effort. The purpose and intended use of these reports is to help
identify areas where states can target theirradon program resources, to provide guidance in -
selecting the most appropriate building-code options for areas, and to provide general
information on radon and geology for each state for federal, state, and municipal officials
dealing with radon issues. These reports are not intended to be used as a substitute for
indoor radon testing, and they cannot and should not be used to estimate or predict the
indoor radon concentrations of individual homes, building sites, or housing tracts. Elevated
levels of indoor radon have been found in every State, and EPA recommends that all homes
be tested for indoor radon.
Booklets detailing the radon potential assessment for the U.S. have been developed for
each State. USGS geologists are the authors of the geologic radon potential booklets. Each
booklet consists of several components, the first being an overview to the mapping project
(Part I), this introduction to the USGS assessment (Part II), including a general discussion of
radon (occurrence, transport, etc.), and details concerning the types of data used. The third
component is a summary chapter outlining the general geology and geologic radon potential
of the EPA Region (Part III). The fourth component is an individual chapter for each state
(Part IV). Each state chapter discusses the state's specific geographic setting, soils, geologic
setting, geologic radon potential, indoor radon data, and a summary outlining the radon
potential rankings of geologic areas in the state. A variety of maps are presented in each
chapter—geologic, geographic, population, soils, aerial radioactivity, and indoor radon data by
county. Finally, the booklets contain EPA's map of radon zones for each state and an
accompanying description (Part V).
Because of constraints on the scales of maps presented in these reports and because the
smallest units used to present the indoor radon data are counties, some generalizations have
been made in order to estimate the radon potential of each area. Variations in geology, soil
characteristics, climatic factors, homeowner lifestyles, and other factors that influence radon
concentrations can be quite large within any particular geologic area, so these reports cannot
be used to estimate or predict the indoor radon concentrations of individual homes or housing
EE-1 Reprinted from USGS Open-File Report 93-292
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tracts. Within any area of a given geologic radon potential ranking, there are likely to be
areas where the radon potential is lower or higher than that assigned to the area as a whole,
especially in larger areas such as the large counties in some western states.
In each state chapter, references to additional reports related to radon are listed for the
°*at'», and the reader is urged to consult these report? 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 (Z22Rn) is produced from the radioactive decay of radium (25SRa), which is, in turn,
a product of the decay of uranium (M8U) (fig. 1). The half-life of "3Rn 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 rrmch
greater than vertical permeability, and air and moisture infiltration is generally slow. Soils
with prismatic or columnar structure have dominantly vertical permeability. Platy and
prismatic structures form in soils with high clay contents. In soils with shrink-swell clays, air
II-2 Reprinted from USGS Open-File Report 93-292
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...
,BIsmuth-210
P 5.01 dayftlP
lead.206
STABLE
Uranlum-238
.51 billion years
p \ProtacMnium-234
1.17 mln.^4 ii . ...
Uranlum-234
247,000 years
,
J 80,000 years a
Radlum-226 fa
1602 years
Figure 1. The uranium-238 decay series, showing the half-lives of elements and their modes of decay (after Wanty and
Sehoen, 1991). a denotes alpha decay, p denotes beta decay.
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and moisture infiltration rates and depth of wetting may be limited when the cracks in the
surface soil layers swell shut. Clay-rich B horizons, particularly those with massive or plary
structure, can form a capping layer that impedes the escape of soil gas to the surface
(Schumann and others, 1992). However, the shrinkage of clays can act to open or widen
cracks upon drying, thus increasing the soil's permeability to gas flow during drier periods.
Radon transport in soils occurs by two processes: (1) diffusion and (2) flow (Tanner,
1964). Diffusion is the process whereby radon atoms move from areas of higher
concentration to areas of lower concentration in response to a concentration gradient. Flow is
the process by which soil air moves through soil pores in response to differences in pressure
within the soil or between the soil and the atmosphere,, carrying the radon atoms along with it.
Diffusion is the dominant radon transport process in soils of low permeability, whereas flow
tends to dominate in highly permeable soils (Sextro and others, 1987). In low-permeability
soils, much of the radon may decay before it is able to enter a building because its transport
rate is reduced. Conversely, highly permeable soils, even those that are relatively low 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 2xIO"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 pC5/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
11-4 Reprinted from USGS Open-File Report 93-292
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solution cavities in the carbonate rock into houses. As warm air enters solution cavities that
are higher on the hillslope than the homes, it cools and settles, pushing radon-laden air from
lower in the cave or cavity system into structures on the hillslope (Gammage and others,
1993). In contrast, homes built over caves having openings situated below the level of the
home had higher indoor radon levels in the winter, caused by cooler outside air entering the
cave, driving radon-laden air into cracks and solution cavities in the rock and soil, and
ultimately, into homes (Gammage and others, 1993).
RADON ENTRY INTO BUILDINGS
A driving force (reduced atmospheric pressure in the house relative to the soil, producing
a pressure gradient) and entry points must exist for radon to enter a building from the soil.
The negative pressure caused by furnace combustion, ventilation devices, and the stack effect
(the rising and escape of warm air from the upper floors of the building, causing a
temperature and pressure gradient within the structure) during cold winter months are
common driving forces. Cracks and other penetrations through building foundations, sump
holes, and slab-to-foundation wall joints are common entry points.
Radon levels in the basement are generally higher than those on the main floor or upper
floors of most structures. Homes with basements generally provide more entry points for
radon, commonly have a more pronounced stack effect, and typically have lower air pressure
relative to the surrounding soil than nonbasement homes. The term "nonbasemeret" 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, rnetamorphic 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 rnetamorphic and
II-5 Reprinted from USGS Open-File Report 93-292
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igneous rocks, and basalts. Exceptions exist within these general lithologic groups because of
the occurrence of localized uranium deposits, commonly of the hydrothermal type in
crystalline rocks or the "roll-front" type in sedimentary rocks. Uranium and radium are
commonly sited in heavy minerals, iron-oxide coatings on rock and soil grains, and organic
materials in soils and sediments. Less common are uranium associated with phosphate and
carbonate complexes in rocks and soils, and uranium minerals.
Although many cases of elevated indoor radon levels can be traced to high radium and
(or) uranium concentrations in parent rocks, some structural features, most notably faults and
shear zones, have been identified as sites of localized uranium concentrations (Deffeyes and
MacGregor, 1980) and have been associated with some of the highest reported indoor radon
levels (Gundersen, 1991). The two highest known indoor radon occurrences are associated
with sheared fault zones in Boyertown, Pennsylvania (Gundersen and others, 1988a; Smith
and others, 1987), and in Clinton, New Jersey (Henry and others, 1991; Muessig and Bell,
1988).
NUKE AERIAL RADIOMETRIC DATA
Aerial radiometric data are used to quantify the radioactivity of rocks and soils.
Equivalent uranium (eU) data provide an estimate of the surficial concentrations of radon
parent materials (uranium, radium) in rocks and soils. Equivalent uranium is calculated from
thu counts received by a gamma-ray detector from the 1.76 MeV (mega-electron volts)
emission energy corresponding to bismuth-214 (2"Bi), with the assumption that uranium and
its decay products are in secular equilibrium. Equivalent uranium is expressed in units of
parts per million (ppm). Gamma radioactivity also may be expressed in terms of a radium
activity; 3 ppm eU corresponds to approximately 1 picocurie per gram (pCi/g) of radium-226.
Although radon is highly mobile in soil and its concentration is affected by meteorological
conditions (Kovach, 1945; Klusman and Jaacks, 1987; Schery and others, 1984; Schumann
and others, 1992), statistical correlations between average soil-gas radon concentrations and
average eU values for a wide variety of soils have been documented (Gundersen and others,
1988a, 1988b; Schumann and Owen, 1988). Aerial radiometric data can provide an estimate
of radon source strength over a region, but the amount of radon that is able to enter a home
from the soil is dependent on several local factors, including soil structure, grain size
distribution, moisture content, and permeability, as well as type of house construction and its
structural condition.
The aerial radiometric data used for these characterizations were collected as part of the
Department of Energy National Uranium Resource Evaluation (NUKE) program of the 1970s
and early 1980s. The purpose of the NUKE program was to identify and describe areas in the
United States having potential uranium resources (U.S. Department of Energy, 1976). The
NUKE 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 NUKE data in
which smoothing, filtering, recalibrating, and matching of adjacent quadrangle data sets were
performed to compensate for background, altitude, calibration, and other types of errors and
inconsistencies in the original data set (Duval and others, 1989). The data were then gridded
and contoured to produce maps of eU with a pixel size corresponding to approximately 2.5 x
2.5 km (1.6 x 1.6 mi).
II-6 Reprinted from USGS Open-File Report 93-292
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fllCilT 11ME SPACING OF SURE AEKUl SURVEYS
E3
2 KM (1 MILE)
5 KH (3 MILES)
2 i 5 O
10 EM {6 HUES)
5 * 10 IH
NO DATA
Figure 2, Nominal flightline spacings for NUKE aerial gamma-ray surveys covering the
contiguous United States (from Duval and others, 1990). Rectangles represent I°x2° quadrangles.
-------
Figure 2 is an index map of NURE 1° x 2° quadrangles showing the flight-line spacing
for each quadrangle. In general, the more closely spaced the flightlines are, the more area
was covered by the aerial gamma survey, and thus, more detail is available in the data set.
For an altitude of 400 ft above the ground surface and with primary flightline spacing
typically between 3 and 6 miles, less than 10 percant of the ground surface of the United
States was actually measured by the airborne gamma-ray detectors (Duval and others, 1989),
although some areas had better coverage than others due to the differences in flight-line
spacing between areas (fig, 2). This suggests that some localized uranium anomalies may not
have been detected by the aerial surveys, but the good correlations of eU patterns with
geologic outcrop patterns indicate that, at relatively small scales (approximately 1:1,000,000
or smaller) the National eU map (Duval and others, 1989) gives reasonably good estimates of
average surface uranium concentrations and thus can assist in the prediction of radon potential
of rocks and soils, especially when augmented with additional geologic and soil data.
The shallow (20-30 cm) depth of investigation of gamma-ray spectrometers, either
ground-based or airborne (Duval and others, 1971; Durrance, 1986), suggests that gamma-ray
data may sometimes underestimate the radon-source strength in soils in which some of the
radionuclides in the near-surface soil layers have been transported downward through the soil
profile. In such cases the concentration of radioactive minerals in the A horizon would be
lower than in the B horizon, where such minerals are typically concentrated. The
concentration of radionuclides in the C horizon and below may be relatively unaffected by
surface solution proces-es. Under these conditions the surface gamma-ray signal may indicate
a lower radon source concentration than actually exists in the deeper soil layers, which are
most likely to affect radon levels in structures with basements. The redistribution of
radionuclides in soil profiles is dependent on a combination of climatic, geologic, and
geochemical factors. There is reason to believe that correlations of eU with actual soil
radium and uranium concentrations at a depth relevant to radon entry into structures may be
regionally variable (Duval, 1989; Schumann and Gundersen, 1991). Given sufficient
understanding of the factors cited above, these regional differences may be predictable.
SOIL SURVEY DATA
Soil surveys prepared by the U.S. Soil Conservation Service (SCS) provide data on soil
characteristics, including soil-cover thickness, grain-size distribution, permeability, shrink-
swell potential, vegetative cover, generalized groundwater characteristics, and land use. The
reports are available in county formats and State summaries. The county reports typically
contain both generalized and-detailed maps of soils in the area.
Because of time and map-scale constraints, it was impractical to examine county soil
reports for each county in the United States, so more generalized summaries at appropriate
scales were used where available. For State or regional-scale radon characterizations, soil
maps were compared to geologic maps of the area, and the soil descriptions, shrink-swell
potential, drainage characteristics, depth to seasonal high water table, permeability, and other
relevant characteristics of each soil group noted. Technical soil terms used in soil surveys are
generally complex; however, a good summary of soil engineering terms and the national
distribution of technical soil types is the "Soils" sheet of the National Atlas (U.S. Department
of Agriculture, 1987).
II-8 Reprinted from USGS Open-File Report 93-292
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Soil permeability is commonly expressed in SCS soil surveys in terms of the speed, in
inches per hour (in/hr), at which water soaks into the soil, as measured in a soil percolation
test. Although in/hr are not truly units of permeability, these units are in widespread use and
are referred to as "permeability" in SCS soil surveys. The permeabilities listed in the SCS
surveys are for water, but they generally correlate well with gas permeability. Because data
on gas permeability of soils is extremely limited, data on permeability to water is used as a
substitute except in cases in which excessive soil moisture is known to exist. Water in soil
pores inhibits gas transport, so the amount of radon available to a home is effectively reduced
by a high water table. Areas likely to have high water tables include river valleys, coastal
areas, and some areas overlain by deposits of glacial origin (for example, loess).
Soil permeabilities greater than 6.0 in/hr may be considered high, and permeabilities less
than 0.6 in/hr may be considered low in terms of soil-gas transport. Soils with low
permeability may generally be considered to have a lower radon potential than more
permeable soils with similar radium concentrations. Many well-developed soils contain a
clay-rich B horizon that may impede vertical soil gas transport. Radon generated below this
horizon cannot readily escape to the surface, so it would instead tend to move laterally,
especially under the influence of a negative pressure exerted by a building.
Shrink-swell potential is an indicator of the abundance of smectitic (swelling) clays in a
soil. Soils with a high shrink-swell potential may cause building foundations to crack,
creating pathways for radon entry ir.to the structure. During dry periods, desiccation cracks in
shrink-swell soils provide additional pathways for soil-gas transport and effectively increase
the gas permeability of the soil. Soil permeability data and soil profile data thus provide
important information for regional radon assessments.
INDOOR RADON DATA
Two major sources of indoor radon data were used. The first and largest source of data is
from the State/EPA Residential Radon Survey (Ronca-Battista and others, 1988; Dziuban and
others, 1990). Forty-two states completed EPA-sponsored indoor radon surveys between 1986
and 1992 (fig. 3). The State/EPA Residential Radon Surveys were designed to be
comprehensive and statistically significant at the state level, and were subjected to high levels
of quality assurance and control. The surveys collected screening indoor radon measurements,
defined as 2-7 day measurements using charcoal canister radon detectors placed in the lowest
livable area of the home. The target population for the surveys included owner-occupied
single family, detached housing units (White and others, 1989), although attached structures
such as duplexes, townhouses, or condominiums were included in some of the surveys if they
met the other criteria and had contact with the ground surface. Participants were selected
randomly from telephone^directory listings. In total, approximately 60,000 homes were tested
in the State/EPA surveys.
The second source of indoor radon data comes from residential surveys that have been
conducted in a specific state or region of the country (e.g. independent state surveys or utility
company surveys). Several states, including Delaware, Florida, Illinois, New Hampshire, New
Jersey, New York, Oregon, and Utah, have conducted their own surveys of indoor radon. The
quality and design of a state or other independent survey are discussed and referenced where
the data are used
II-9 Reprinted from USGS Open-File Report 93-292
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STATE/EPA RESIDENTIAL RADON
SURVEY SCREENING MEASUREMENTS
Estimated Percent of Houses with Screening Levels Greater than 4 pCi/L
0 5 10 15 20 and>
The Slates of D1U'1*NI r.NJ,NY, and Ill-
have conducted Ihcirown surveys. OR &
.SO declined to participate in the SRRS.
These results arc based on 1-1 day screening
measurements in the lowest livable level anu should not
be used to estimate annual averages or health risks.
Figure 3. Percent of homes tested in the State/EPA Residential Radon Survey with screening indoor radon levels exceeding 4 pCi/L.
-------
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 arf», and the Confidence Index (CI), used to express the level of confidence in the
prediction based on the quantity and quality of the data used to make the determination. This
scheme works best if the areas to be evaluated are delineated by geologically-based
boundaries (geologic provinces) rather than political ones (state/county boundaries) in which
the geology may vary across the area.
Radon Index, Table 1 presents the Radon Index (RI) matrix. The five factors—indoor
radon data, geology, aerial radioactivity, soil parameters, and house foundation type—were
quantitatively ranked (using a point value of 1, 2, or 3) for their respective contribution to
radon potential in a given area. At least some data for the 5 factors are consistently available
for every geologic province. Because each of these main factors encompass a wide variety of
complex and variable components, the geologists performing the evaluation relied heavily on
their professional judgment and experience in assigning point values to each category and in
determining the overall radon potential ranking. Background information on these factors is
discussed in more detail in the preceding sections of this introduction.
Indoor radon was evaluated using unweighted arithmetic means of the indoor radon data
for each geologic area to be assessed. Other expressions of indoor radon levels in an area
also could have been used, such as weighted averages or annual averages, but these types of
data were not consistently available for the entire United States at the time of this writing, or
the schemes were not considered sufficient to provide a means of consistent comparison
across all areas. For this report, charcoal-canister screening measurement data from the
State/EPA Residential Radon Surveys and other carefully selected sources were used, as
described in the preceding section. To maintain consistency, other indoor radon data sets
(vendor, state, or other data) were not considered in scoring the indoor radon factor of the
Radon Index if they were not randomly sampled or could not be statistically combined with
the primary indoor radon data sets. However, these additional radon data sets can provide a
means to further refine correlations between geologic factors and radon potential, so they are
II-11 Reprinted from USGS Open-File Report 93-292
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TABLE 1. RADON INDEX MATRIX, "ppm eU" indicates parts per million of equivalent
uranium, as indicated by NURE aerial radiomettic data. See text discussion for details.
FACTOR
INDOOR RADON (average)
AERIAL RADIOACTIVITY
GEOLOGY*
SOIL PERME ABILITY
ARCHITECTURE TYPE
INCREASING RADON POTENTIAL ^
POINT VALUE
1
<2pCi/L
< 1.5 ppm eU
negative
low
mostly slab
2
2-4pO/L
1.5 - 2.5 ppm eU
variable
moderate
mixed
3
>4pCi/L
> 2.5 ppm eU
positive
high
mostly basement
*GEOLOGIC FIELD EVIDENCE (GFE) POINTS: GFE points are assigned in addition to points
for the "Geology" factor for specific, relevant geologic field studies. See text for details.
Geologic evidence supporting: HIGH radon +2 points
MODERATE +1 point
LOW -2 points
No relevant geologic field studies 0 points
SCORING:
Radon potential category
Probable average screening
Pointrange indoor radon for area
LOW
MODERATE/VARIABLE
HIGH
3-8 points
9-11 points
12-17 points
<2pCi/L
2-4pCi/L
>4pCi/L
POSSIBLE RANGE OF POINTS = 3 to 17
TABLE 2. CONFIDENCE INDEX MATRIX
INCREASING CONFIDENCE
w
FACTOR
INDOOR RADON DATA
AERIAL RADIO ACTIVITY
GEOLOGIC DATA
SOIL PERMEABILITY
POINT VALUE
1
sparse/no data
questionable/no data
questionable
questionable/no data
2
fair coverage/quality
glacial cover
variable
variable
3
jjood coverage/quality
no glacial cover
proven geol. model
reliable, abundant
SCORING:
LOW CONFIDENCE
MODERATE CONFIDENCE
HIGH CONFIDENCE
4-6 points
7-9 points
10 -12 points
POSSIBLE RANGE OF POINTS = 4 to 12
11-12 Reprinted from USGS Open-FUe 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 aru 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 *he 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 diffe* 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 sco*t of 15 points minus 3 points gives a minimum of 12 points for the high category.
Note, however, that if both other factors differ by two points from the "ideal", indicating
considerable variability in the system, the total point score would lie in the adjacent (i.e.,
moderate/variable) category.
Confidence Index. Except for architecture type, the same factors were used to establish a
Confidence Index (CI) for the radon potential prediction for each area (Table 2). Architecture
type was not included in the confidence index because house construction data are readily and
reliably available through surveys taken by agencies and industry groups including the
National Association of Home Builders, U.S. Department of Housing and Urban
Development, and the Federal Housing Administration; thus it was not considered necessary
11-14 Reprinted from USGS Open-File Report 93-292
-------
to question the quality or validity of these data. The other factors were scored on the basis of
the quality and quantity of the data used to complete the RI matrix.
Indoor radon data were evaluated based on the distribution and number of data points and
on whether the data were collected by random sampling (State/EPA Residential Radon Survey
or other state survey data) or volunteered vendor dai
-------
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.
II-16 Reprinted from USGS Open-File Report 93-292
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REFERENCES CITED
Akerblom, G., Anderson, P., and Clavensjo, B., 1984, Soil gas radon—A source for indoor radon
daughters: Radiation Protection Dosimetry, v. 7, p. 49-54.
Deffeyes, K.S., and MacGregor, 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 fee 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.G., and Adams, J.A.S., 1971, Circle of investigation of an airborne
gamma-ray spectrometer: Journal of Geophysical Research, v. 76, p. 8466-8470.
Duval, J.S., Jones, W.J., Riggle, F.R., and Pitkin, J.A., 1989, Equivalent uranium map of
conterminous United States: U.S. Geological Survey Open-File Report 89-478,10 p.
-i
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. JH: Preprints: U.S.
Environmental Protection Agency report EPA/600/9-90/005c, Paper IV-2,17 p.
Gammage, R.B., Wilson, DJL, 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 rke Reading Prong, in Marikos, M. A., and Hansman,
R.H., eds., Geologic causes of natural radionuclide anomalies: Missouri Department of
Natural Resources Special Publication 4, p. 91-102.
Gundersen, L.C.S, Reimer, G.M., Wiggs, C.R., and Rice, C.A., 1988b, Map showing radon
potential of rocks and soils in Montgomery County, Maryland: U.S. Geological Survey
Miscellaneous Field Studies Map MF-2043, scale 1:62,500.
Gundersen, Linda C.S., 1991, Radon in sheared metamorphic and igneous rocks, in Gundersen,
Linda C.S., and Richard B. Wanty, eds., Field studies of radon in rocks, soils, and water:
U.S. Geol. Survey Bulletin no. 1971, p. 39-50,
H-17 Reprinted from USGS Open-File Report 93-292
-------
Henry, Mitchell E., Kaeding, Margret E., and Monteverde, Donald, 1991, Radon in soil gas and
gamma-ray activity of rocks and soils at the Mulligan Quarry, Clinton, New Jersey, in
Gundersen, Linda C.S., and Richard B. Wanty, eds., Field studies of radon in rocks,
soils, and water: U.S. Geol. Survey Bulletin no. 1971, p. 65-75.
Klusman, R. W., and Jaacks, J. A., 1987, Environmental influences upon mercury, radon, and
helium concentrations in soil gases at a site near Denver, Colorado: Journal of
Geochemical Exploration, v. 27, p. 259-280.
Kovach, E.M., 1945, Meteorological influences upon the radon content of soil gas: Transactions,
American Geophysical Union, v. 26, p. 241-248.
Kunz, C.» Laymon, C,A., and Parker, C., 1989, Gravelly soils and indoor radon, 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., afid Alexander, B., 1988,
Radori-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 01 America Abstracts With Programs, v. 23,
no. 1, p. 125.
Schumann, R.R., Peake, R.T., Schmidt, K.M., and Owen, D.E., 1991, Correlations of soil-gas
and indoor radon with geology in glacially derived soils of the northern Great Plains, in
Proceedings of the 1990 International Symposium on Radon and Radon Reduction
Technology, Volume 2, Symposium Oral Papers: U.S. Environmental Protection Agency
report EPA/600/9-91/026b, p. 6-23-6-36.
JJ-18 Reprinted fiom USGS Open-FUe Report 93-292
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Schumann, R.R., Owen, D.E,, and Asher-Bolinder, S., 1992, Effects of weather and soil
characteristics on temporal variations in soil-gas radon concentrations, in Gates, A.E., and
Gundersen, L.C.S., eds., Geologic controls on radon: Geological Society of America
Special Paper 271, p. 65-72.
Sextro, R.G., Moed, B.A., Nazaroff, W.W., Revzan, K.L., and Nero, A.V., 1987,
Investigations of soil as a source of indoor radon, in Hopke, P.K., ed., Radon and its
decay products: American Chemical Society Symposium Series 331, p. 10-29.
Sterling, R., Meixel, G., Shen, L., Labs, K., and Bligh, T., 1985, Assessment of the energy
savings potential of building foundations research: Oak Ridge, Term., U.S. Department of
Energy Report ORNL/SUB/84-0024/1.
Smith, R.C., II, Reilly, M.A., Rose, A.W., Barnes, J.H., and Berkheiser, S.W., Jr., 1987,
Radon: a profound case: Pennsylvania Geology, v. 18, p. 1-7.
Tanner, A.B., 1964, Radon migration in the ground: a review, in-Adams, J.A.S., and Lowder,
W.M., eds., The natural radiation environment: Chicago, ILL, 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.
11-19 Reprinted ftomUSGS Open-Me Report 93-292
-------
APPENDIX A
GEOLOGIC TIME SCALE
Subdivisions (and their symbols)
Eon or
Eonothem
Pfmnerozoic2
Proterozoic
(P\
Archeen
JAl
Era or
E rathe m
Cenozoic 2
(Cz»
Mesozoic 2
(Mi)
Paleozoic
(Pi)
Ulf
FtCtBf 0JB« CZ)
WKJOI*
Pfm#fOI8iC IVI
- *»*»„
Proi»rtHotc IX)
Uw
ArtiMn rwi
Micei*
AxK»innn
fct«Y
*r£M*n IU1
Period, System,
Subperfod, Subsystem
Quaternary
«Q)
Neos*ne 2
SuSDiriod or
Tani.rv Su&SVStem !N)
m Paleogene
111 Subeeriodor
Subsystem (Pi)
Cretaceous
(K)
Jurassic
U)
Triassic
(1)
Permian
IP)
Pennsylvania!!
Carboniferous IP)
Systems
'O Mississippian
(M)
Devonian
(D)
Silurian
iet
ll»l
Ordovicisn
en used wWi these hems are informal divisions of the larger unit: the
fiist l«R«r of the modifier b lowercase.
'Rocks oWer than 570 Ma also called Precambrian (p€), a time term without specific rank.
'informal lim« term without spedfic rank.
USGS Open-File Report 93-292
-------
APPENDIX B
GLOSSARY OF TEEMS
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 (KH^ curies) is equal to about 2.2 disintegrations
of radon atoms per minute. A liter is about 1.06 quarts. The average concentration of radon in
U.S. homes measured to date is between 1 and 2 pCi/L.
Bq/m3 (Becquerels per cubic meter)- a metric unit of radioactivity used to describe radon
concentrations in a volume of air. One becquerel is equal to one radioactive disintegration per
second. One pCi/L is equal to 37 Bq/nA
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 dejmjited 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.
tt-21 Reprinted ftom TJSGS 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 (€63) 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
quajtz. Crystals are not visible to the naked eye, giving the rock a milky, duH 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, sMcate 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 genfle 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(CO3)2), and is commonly white, gray, brown, yellow, or pinkish in color.
drainage The manner in which the waters of an area pass, flow off of, or flow into the soil.
Also refers to the water features of an area, such as lakes and rivers, mat drain it
eolian Pertaining to sediments deposited by the wind.
esker A long, narrow, steep-sided ridge composed of irregular beds of sand and gravel deposited
by streams beneath a glacier and left behind when the ice melted,
evapotranspiration Loss of water from a land area by evaporation from the soil and
transpiration from plants. .
extrusive Said of igneous rocks that have been erupted onto the surface of the Earth.
fault A fracture or zone of fractures in rock or sediment along which there has been movement.
fluvial, fluvial deposit Pertaining to sediment that has been deposited by a river or stream.
foliation A linear feature in a rock defined by both mineralogic and structural characteristics. It
may be formed during deformation or metamorphism.
formation A mappable body of rock having similar characteristics.
glacial deposit Any sediment transported and deposited by a glacier or processes associated
with glaciers, such as glaciofluvial sediments deposited by streams flowing from melting glaciers.
gneiss A rock formed by metamorphism in which bands and lenses of minerals of similar
composition alternate with bands and lenses of different composition, giving the rock a striped or
"foliated" appearance.
granite Broadly applied, any coarsely crystalline, quartz- and feldspar-bearing igneous plutonic
rock. Technically, granites have between 10 and 50% quartz, and alkali feldspar comprises at least
65% of the total feldspar.
gravel An unconsoldated, natural accumulation of rock fragments consisting predominantly of
particles greater than 2 mm in size.
heavy minerals Mineral grains in sediment or sedimentary rock having higher than average
specific gravity. May form layers and lenses because of wind or water sorting by weight and size
n-23 Reprinted from USGS Open-File Report 93-292
-------
and may be referred to as a "placer deposit" Some heavy minerals are magnetite, garnet, zircon,
monazite, and xenotime.
igneous Said of a rock or mineral that solidified from molten or partly molten rock material. It is
one of the three main classes into which rocks are divided, the others being sedimentary and
metamorphic.
intermontane A term mat refers to an area between two mountains or mountain ranges.
intrusion, intrusive The processes of emplacement or injection of molten rock into pre-existing
rock. Also refers to the rock formed by intrusive processes, such as an "intrusive igneous rock".
kame A low mound, knob, hummock, or short irregular ridge formed by a glacial stream at the
margin of a melting glacier; composed of bedded sand and gravel.
karst terrain A type of topography that is formed on limestone, gypsum and other rocks by
dissolution of the rock by water, forming sinkholes and caves.
lignite A brownish-black coal that is intermediate in coalification between peat and
subbituminous coal.
limestone A carbonate sedimentary rock consisting of more than 50% calcium carbonate,
primarily in the form of the mineral calcite (CaCOs).
lithology The description of rocks in hand specimen and in outcrop on the basis of color,
composition, and grain size.
loam A permeable soil composed of a mixture of relatively equal parts clay, silt, and sand, and
usually containing some organic matter.
loess A fine-grained eolian deposit composed of silt-sized particles generally thought to have
been deposited from windblown dust of Pleistocene age.
mafic Term describing an igneous rock containing more than 50% dark-colored minerals.
marine Term describing sediments deposited in the ocean, or precipitated from ocean waters.
metamorphic Any rock derived from pre-existing rocks by mineralogical, chemical, or structural
changes in response to changes in temperature, pressure, stress, and the chemical environment.
PhylHte, schist, amphibolite, and gneiss are metamorphic rocks.
moraine A rnound, 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.
olacer 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, cbmposMonally equivalent to granite.
sandstone A clastic sedimentary rock composed of sand-sized rock and mineral material that is
more or less firmly cemented. Sand particles range from 1/16 to 2 mm in size.
schist A strongly foliated crystalline rock, formed by metamorphism, that can be readily split into
thin flakes or slabs. Contains mica; minerals are typically aligned.
screening level Result of an indoor radon test taken with a charcoal canister or similar device,
for a short period of time, usually less than seven days. May indicate the potential for an indoor
radon problem but does not indicate annual exposure to radon.
sediment Deposits of rock and mineral particles or fragments originating from material that is
transported by air, water or ice, or that accumulate by natural chemical precipitation or secretion of
organisms.
semiarid Refers to a climate that has slightly more precipitation than an arid climate.
shale A fine-grained sedimentary rock formed from solidification (lithification) of clay or mud.
shear zone Refers to a roughly linear zone of rock that has been faulted by ductile or non-ductile
processes in which the rock is sheared and both sides are displaced relative to one another.
shrink-swell clay See clay mineral.
siltstone A fine-grained clastic sedimentary rock composed of silt-sized rock and mineral
material and more or less firmly cemented. Silt particles range from 1/16 to 1/256 mm in size.
sinkhole A roughly circular depression in a karst area measuring meters to tens of meters in
diameter. It is funnel shaped and is formed by collapse of the surface material into an underlying
void created by the dissolution of carbonate rock.
slope An inclined part of the earth's surface.
solution cavity A hole, channel or cave-like cavity formed by dissolution of rock.
stratigraphy The study of rock strata; also refers to the succession of rocks of a particular area.
surficial materials Unconsolidated glacial, wind-, or waterborne deposits occurring on the
earth's surface.
tablelands General term for a broad, elevated region with a nearly level surface of considerable
extent.
11-25 Reprinted from USGS Open-File Report 93-292
-------
terrace gravel Gravel-sized material that caps ridges and terraces, left behind by a stream as it
cuts down to a lower level.
terrain A tract or region of the Earth's surface considered as a physical feature or an ecological
environment
till Unsorted, generally uneonsolidated 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 ftom USGS Open-File Report 93-292
-------
APPENDIX C
EPA REGIONAL OFFICES
Regional Offices
State
EPA Region
EPA Region 1
JFK Federal Building
Boston, MA 02203
(617) 565-4502
EPA Region 2
(2AIR:RAD)
2fi 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 u 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
AJasla
Arizona
Arkansas
California
James McNees
Division of Radiation Control
Alabama Department of Public Health
State Office Building
Montgomery, AL 36130
(205)242-5315
1-800-582-1866 in state
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
John Stewart
Arizona Radiation Regulatory Agency
4814 South 40th SL
Phoenix, AZ 85040
(602)255-4845
LeeGershner
Division of Radiation Control
Department of Health
4815 Markham Street, Slot 30
Little Rock, AR 72205-3867
(501)661-2301
J. David Quinton
Department of Health Services
i*14 P Street, Room 600
Sacramento, CA 94234-7320
(916) 324-2208
1-800-745-7236 in state
Linda Martin
Department of Health
4210 East llth Avenue
Denver, CO 80220
(303) 692-3057
1-800-846-3986 in state
Connecticut Alan J, Siniscalchi
Radon Program
Connecticut Department of Health
Services
150 Washington Street
Hartford, CT 061064474
(203)566-3122
Delaware Marai G. Rejai
Office of Radiation Control
Division of Public Health
P.O. Box 637
Dover, DE 19903
(302)736-3028
1-800-554-4636 In State
District Robert Davis
of Columbia DC Department of Consumer and
Regulatory Affairs
614 H Street NW
Room 1014
Washington, DC 20001
(202) 727-71068
Honda N. Michael Giliey
Office of Radiation Control
Department of Health and
Rehabilitative Services
1317 Winewood Boulevard
Tallahassee, EL 32399-0700
(904)488-1525
1-800-543-8279 in state
Georgia Richard Schreiber
Georgia Department of Human
Resources
878 Peachttee St, Room 100
Atlanta, GA 30309
(404) 894-6644
1-800-745-0037 in state
Hawaji Russell Takata
Environmental Health Services
Division
591 Ala Moana Boulevard
Honolulu, ffl 96813-2498
(808)586-4700
n-28
Reprinted from USGS Open-File Report 93-292
-------
Idaho
Indiana
Iowa
Kentucky
PatMcGavarn
Office of Environmental Health
450 West State Street
Boise, ID 83720
(208) 334-6584
1-800-445-8647 in state
Richaid Allen
Illinois Department of Nuclear Safety
1301 Outer Park Drive
Springfield, IL 62704
(217) 524-5614
1-800-325-1245 in state
Lorand Magyar
Radiological Health Section
Indiana State Department of Health
1330 West Michigan Street
P.O. Box 1964
Indianapolis, IN 46206
(317) 633-8563
1-800-272-9723 In State
Donald A. Hater
Bureau of Radiological Health
Iowa Department of Public Health
Lucas State Office Building
Des Moines, IA 50319-0075
(515)281-3478
1-800-383-5992 In State
Harold Spiker
Radiation Control Program
Kansas Department of Health and
Environment
109 SW 9th Street
6th Floor Mills Building
Topeka, KS 66612
(913)296-1561
JeanaPhelps
Radiation Control Branch
Department of Health Services
Cabinet for Human Resources
275 last Main Street
Frankfort, KY 40601
(502) 564-3700
Louisiana Matt Schlenker
Louisiana Department of
Environmental Quality
P.O. Box 82135
Baton Rouge, LA 70884-2135
(504)925-7042
1-800-256-2494 in state
Maine BobStilwell
Division of Health Engineering
Department of Human Services
State House, Station 10
Augusta, ME 04333
(207) 289-5676
1-800-232-0842 in state
Maryland Leon J. Rachuba
Radiological Health Program
Maryland Department of the
Environment
2500 Broening Highway
Baltimore, MD 21224
(410) 631-3301
— 1-800-872-3666 In State
Massachusetts William J. Bell
Radiation Control Program
Department of Public Health
23 Service Center
Northampton, MA 01060
(413) 586-7525
1-800-445-1255 in state
Michigan Sue Hendershott
Division of Radiological Health
Bureau of Environmental and
Occupational Health
3423 North Logan Street
P.O. Box 30195
Lansing, MI 48909
(517)335-8194
Minnesota Laura Oatmann
Indoor Air Quality Unit
925 Delaware Street, SE
P.O. Box 59040
Minneapolis, MN 55459-0040
(612)627-5480
1-800-798-9050 in state
n-29 Reprinted ftom USGS Open-File Report 93-292
-------
Mississippi Silas Anderson
Division of Radiological Health
Department of Health
3 150 Lawson Street
P.O. Box 1700
Jackson, MS 39215-1700
(601)354-6657
1-800-626-7739 in state
Missouri Kenneth V. Miller
Bureau of Radiological Health
Missouri Department of Health
1730 East Elm
P.O. Box 570
Jefferson City, MO 65102
(314)751-6083
1-800-669-7236 In State
Adrian C. Howe
Occupational Health Bureau
Montana Department of Health and
Environmental Sciences
Cogswell Building A113
Helena, MT 59620
(406)444-3671
Nebraska Joseph Milone
Division of Radiological Health
Nebraska Department of Health
301 Centennial Mall, South
P.O. Box 95007
Lincoln, NE 68509
(402)471-2168
1-800-334-9491 In State
Nevada Stan Marshall
Department of Human Resources
505 East King Street
Room 203
Carson City, NV 89710
(702)687-5394
New Hampshire David Chase
Bureau of Radiological KeJth
Division of Public Health Services
Health and Welfare Building
Six Hazen Drive
Concord, NH 03301
(603)271-4674
1-800-852-3345 x4674
New Jersey Tonalee Carlson Key
Division of Environmental Quality
Department of Environmental
Protection
CN415
Trenton, NJ 08625-0145
(609) 987-6369
1-800-648-0394 in state
NewMexico WilliamM.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
Ohio Marcie Matthews
Radiological Health Program
Department of Health
1224 Kinnear Road - Suite 120
Columbus, OH 43212
(614)644-2727
1-800-523-4439 in state
n-ao
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)734-4631
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) 536-4250
Vermont Paul demons
Occupational and Radiological Health
Division
Vermont Department of Health
10 Baldwin Street
Montpelier, VT 05602
(802) 828-2886
1-800-640-0601 in state
Virgin Islands Contact the U.S. Environmental
Protection Agency, Region II
in New York
(212)264^110
n-3i
Reprinted from USGS Open-File Report 93-292
-------
"Virginia Shelly Ottenbrite
Bureau of Radiological Health
Department of Health
109 Governor Street
Richmond, VA 23219
(804) 786-5932
1-800-468-0138 in state
KateColeman
Department of Health
Office of Radiation Protection
Akdustrial Building 5, LE-13
Olympia,WA 98504
(206)753-4518
1-800-323-9727 In State
Wresiyirginig Seattle L. DeBord
Industrial Hygiene Division
West Virginia Department of Health
151 llth Avenue
South Charleston, WV 25303
(304)558-3526
1-800-922-1255 In State
Conrad WeMfenbach
Radiation Protection Section
Division of Health
Department of Health and Social
Services
P.O. Box 309
Madison, WI 53701-0309
(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
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STATE GEOLOGICAL SURVEYS
May, 1993
Alabama Ernest A, Mancini
Geological Survey of Alabama
P.O. Box 0
420 Hackbeny 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
VardeUe 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
Floridg 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
MorriU Hall, Rm. 332
Moscow, ID 83843
(208) 885-7991
Illinois Morris W. Leighton
Illinois State Geological Survey
Natural Resources Building
615 East Peabody Dr.
Champaign, JL 61820
(217)333-4747
Indiana Norman C. Hester
Indiana Geological Survey
611 North Walnut Grove
Bloomington, IN 47405
(812)855-9350
Donald L. Koch
Iowa Department of Natural Resources
Geological Survey Bureau
109 Trowbridge Hall
Iowa City, JA 52242-1319
(319) 335-1575
Kansas Lee C. Gerhard
Kansas Geological Survey
1930 Constant Ave., West:
University of Kansas
Lawrence, KS 66047
(913)864-3965
,allipUS
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
LQIUSJarja William E. Marsalis
Louisiana Geological Survey
P.O. Box 2827
University Station
Baton Rouge, LA 70821-2827
(504)388-5320
Mane 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
1300 St. Paul Street
Baltimore, MD 21218-5210
(410) 554-5500
Massachusetts Joseph A. Sinnott
Massachusetts Office of
Environmental Affairs
100 Cambridge SL, 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 HaH
University of Nebraska
Luicoln,NE 68588-0517
(402)472-2410
Jonathan G. Price
Nevada Bureau of Mines & Geology
Stop 178
University of Nevada-Reno
Reno, NV 89557-0088
(702)784-6691
New Hampshire Eugene L.Boadette
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
NewMexico Charles E. Chapin
New Mexico But JHI of Mines &
Mineral Resources
Campus Station
Socorro.NM 87801
(505)835-5420
New York Robert H. Fakundiny
New York State Geological Survey
3136 Cultural Education Center
Empire State Plaza
Albany, NY 12230
(518)474-5816
11-34 Reprinted from USGS Open-File Report 93-292
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North Carolina Charles H. Gardner
North Carolina Geological Survey
P.O. Box 27687
Raleigh, NC 27611-7687
(919) 733-3833
North Dakota John P. Bluemle
North Dakota Geological Survey
600 East Blvd.
Bismarck, ND 58505-0840
(701)224-4109
Ohio Thomas M. Berg
Ohio Dept of Natural Resources
Division of Geological Survey
4383 Fountain Square Drive
Columbus, OH 43224-1362
(614)265-6576
Oklahoma Charles J. Mankin
Oklahoma Geological Survey
Room N-131, Energy Center
100E.Boyd
Norman, OK 73019-0628
(405)325-30^1
Oregon Donald A. Hull
Dept of Geology & Mineral Indust.
Suite 965
800 NE Oregon St. #28
Portland, OR 97232-2162
(503)731-4600
Pennsylvania Donald M. Hoskins
Dept. of Environmental Resources
Bureau of Topographic & Geologic
Survey
P.O. Box 2357
Harrisburg, PA 17105-2357
(717)787-2169
Puerto Rico Ram6n M. Alonso
Puerto Rico Geological Survey
Division
Box 5887
Puerta de Tierra Station
San Juan, P.R, 00906
(809)722-2526
Rhode Island J. Allan Cain
Department of Geology
University of Rhode Island
315 Green Hall
Kingston, RI02881
(401)792-2265
Utah
Sooth Carolina Alan-Jon W.Zupan (Acting)
South Carolina Geological Survey
5 Geology Road
Columbia, SC 29210-9998
(803) 737-9440
South Dakota CM. Christensen (Acting)
South Dakota Geological Survey
Science Center
University of South Dakota
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
William L. Fisher
Texas Bureau of Economic Geology
University of Texas
University Station, Box X
Austin, TX 78713-7508
(512)471-7721
M. Lee Allison
Utah Geological & Mineral Survey
2363 S. Foothill Dr.
Salt Lake City, UT 84109-1491
(801)467-7970
Vermont Diane L. Conrad
Vermont Division of Geology and
Mineral Resources
103 Soulh Main St.
Waterbury, VT 05671
(802)244-5164
Virginia Stanley S. Johnson
Virginia Division of Mineral
Resources
P.O. Box 3667
Chartottesville, VA
(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
H-35
Reprinted from USGS Open-File Report 93-292
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West Virginia LanyJD.Woodfork
West Virginia Geological and
Economic Survey
Mont Chateau Research Center
P.O. Box 879
Morgantown.WV 26507-0879
(304) 594-2331
Wisconsin James Robertson
Wisconsin Geological & Natural
History Survey
3817 Mineral Point Road
Madison, WI 53705-5100
(608)263-7384
Wyoming Gary B. Glass
Geological Survey of Wyoming
University of Wyoming
Box 3008, University Station
Laramie, WY 82071-3008
(307)766-2286
IL-36 Reprinted fiom USGS Open-File Report 93-292
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EPA REGION 1 GEOLOGIC RADON POTENTIAL SUMMARY
•• by-
Linda C.S. Gundersen, R. Randall Schumann, and Sandra L. Szarzi
U.S. Geological Survey
EPA Region 1 includes the states of Connecticut, Maine, Massachusetts, New Hampshire,
Rhode Island, and Vermont For each state, geologic radon potential areas were delineated and
ranked on the basis of geology, soil, housing construction, indoor radon, 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 1 is given in the individual
state chapters. The individual chapters describing the geology and radon potential of the states in
Region 1, though much more detailed than this summary, stiE 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/geologic provinces in Region L
The following summary of radon potential in Region 1 is based on these provinces. Figure 1
shows average screening indoor radon levels by county, calculated from the State/EPA Residential
Radon Survey data. Figure 3 shows the geologic radon potential of areas in Region 1, combined
and summarized from the individual state chapters.
CONNECTICUT
The Western Uplands of western Connecticut comprise several terranes underlain by
metamorphosed sedimentary and igneous rocks. Soils developed on the Proterozoic massifs and
overlying till in the Proto-North American Terrane (area 23, fig. 1) have moderate to high
permeability. Equivalent uranium is generally low and indoor radon averaged 2.5 pCi/L over the
massifs. The carbonate shelf rocks of the Proto-North American Terrane (23, fig. 1) are
predominantly marble, schist, and quartzite, all overlain in places by glacial till. Indoor radon
averaged 2.8 pCi/L for homes built on the carbonate shelf rocks. Some homes built on parts of the
Stockbridge Marble have elevated indoor radon levels. The Taconic Allochthons (24,25, fig. 1)
underlie seveial fault-bounded areas in the northeffijpart of the Western Uplands. The dominant
rock type is schist of varying composition. Equivalent uranium is generally moderate and
permeability is low to moderate in this area. Indoor radon in the Taconic Allochthons averaged
2.7 pCi/L. Overall, these terranes have moderate radon potential.
Rocks of the Connecticut Valley Synclinorium (26, fig. 1) underlie most of the Western
Uplands. These rocks are schist, gneiss, granite, and phyllite, predominantly granitic or
aluminous in composition. Equivalent uranium is moderate to high with areas of very high
equivalent uranium over granitic gneisses in the southern portion. The Pinewood Adamellite has
high radioactivity and generates locally elevated indoor radon levels. Other granites and granitic
gneisses associated with elevated indoor radon include the Harrison Gneiss, an Ordovician granite
gneiss, and the Shelton Member of the Trap Falls Formation. These rocks all occur mainly in the
ffl-l Reprinted from USOSOpen-FUe Report 93-292-A
-------
LAKE
CHAMPLAIN
Figure 1. Geologic radon potential areas of EPA Region 1. 1,5-Melange; 2-Seboomook Formation;
3-Metasedimentary rocks, predominantly carbonates; 4-Granite and high-grade metamorphic rocks; 6,7, 8,11-Glacial
lake clay, marine clay; 9,10-Penobscot Formation, granites, and minor metamorphic rocks; 12-Boundary Mountains
Tenane; 13-GanderTerrane; 14-Avalonian Composite Terrane; 15-Northeastern Highlands; 16-Ven.,unt Piedmont;
17-Green Mountains; 18-Champlain Lowland; 19-Vermont Valley; 20,21-Taconic Mountains-Stockbridge Valley;
22-Berkshire Mountains; 23-Proto-North American Terrane; 24,25-Taconic Allochthons; 26-Connecticut Valley
Synclinorium; 27-Westem Connecticut Valley Belt; 28,29-Connecticut Valley (Mesozoic Basins); 30-Gneissic domes
Of the Eastern Connecticut Valley Belt; 31-Bronson Hill Anticlinorium; 32,33-Merrimack Synclinorium; 34,35,37,38,
40-Avalonian Terrane (includes Hope Valley subterrane); 36-Nashoba and Rhode Island Terrenes; 39,44,46-Esmond-
Dedham Terrane; 41-Newbury Basin volcanics; 42-Cape Ann and Peabody plutons; 43-Boston Basin;
45-Narrangansett Basin; 47-Coastal Plain.
-------
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 9.1
1 D Missing Data
100 Miles
Figure 2. Average screening indoor radon levels, by county, for EPA Region 1. Data are from
2-7 day charcoal canister tests. Data from the EPA/State Residential Radon Survey, except for
New Hampshire data, which are from the New Hampshire Division of Public Health Services
radon survey. Histograms in map legend show the number of counties in each category.
-------
GEOLOGIC RADON POTENTIAL
LOW (<2 pCi/L)
MODERATE/VARIABLE (2-4 pCW.)
HIGH (>4 pCi/L)
Figure 3. Geologic radon potential areas of EPA Region 1. For more detail, refer to individual
state radon potential chapters.
-------
southern part of the Connecticut Valley Synclinorium and are associated with the high radioactivity
and with elevated indoor radon. The Nonewaug Granite and the Scranton Member of the Taine
Mountain Formation are also associated with high aeroradioactivity and elevated indoor radon
levels. Graphitic schist and phyllites may be the cause of elevated indoor radon levels associated
with the Wepawaug Schist. Soils are derived from the rocks and overlying tills and have low to
moderate permeability. Indoor radon averages 3.5 pCi/L in the Connecticut Valley Synclinorium.
Because many of the rocks of this terrane have the potential to generate elevated radon levels, this
area is assigned a high geologic radon potential.
The Central Lowlands of Connecticut (29, fig. 1) are underlain by Triassic and Jurassic
sedimentary and volcanic rocks of the Newark Terrane. The average indoor radon in the Central
Lowlands was 1.6 pCi/L. Radioactivity in the Hartford and Pomperaug basins is generally low
and the soils have generally low to moderate permeability or are poorly drained. Overall, the
Central Lowlands have a low radon potential. However, localized uranium occurrences in the
upper New Haven Arkose, the middle Portland Formation, and possibly in the Shuttle Meadow,
East Berlin, and Portland Formations could generate locally elevated indoor radon levels, but they
are not expected to be common or widespread.
Rocks of the Bronson Hill Anticlinorium, in the Eastern Uplands of Connecticut (31,
fig. 1), include felsic and mafic schists and gneisses, quartzite, and granite gneiss. Radioactivity
in the Bronson Hill is moderate to locally high, and equivalent uranium anomalies in the central
part of the area appear to be associated with outcrops of granite gneiss. The soils have low to
moderate permeability with areas of locally high permeability. The Glastonbury granite gneiss and
graphitic schists in the Collins Hill Formation are likely to generate elevated indoor radon levels.
The Monson Gneiss, and schist and granofels of the Middletown Formation, also generate high
average indoor radon levels. Average indoor radon in the Bronson Hill Anticlinorium is
5.6 pCi/L, the highest among the geologic terranes of Connecticut. Overall, this area has a high
radon potential.
The Merrimack Synclinorium, in the central part of the Eastern Uplands (33, fig. 1), is
underlain by gneiss, schist, granofels, and quartzite that are intruded by granite gneiss, diorite, and
gabbro. The area has moderate to high radioactivity. Soils have low to high permeability but most
are in the low to moderate range. Indoor radon in the Merrimack Synclinorium averaged 2,7
pCi/L. The Canterbury granite gneiss, which occurs in several broad outcrop bands in the
northern and central parts of the area, appears to be associated with elevated radioactivity and with
moderate to high indoor radon levels. This area has moderate radon potential overall.
The Avalonian Terrane, along the eastern and southeastern borders of Connecticut (34,35,
fig. 1), is underlain by granite, granite gneiss, mafic gneiss, and amphlbolite. Granitic rocks
known to generate elevated indoor radon levels include the Waterford and Branford Gneisses, and
the Hope Valley Alaskite Gneiss, which also has a high aeroradioactivity signature, as weE as
locally-occurring graphitic scMst and gneiss in the Plainfield Formation. The overall radioactivity
signature of the area is moderate to high. Soils of the Avalonian Terrane have low to high
permeability, with granitic rocks producing sandy, more permeable soils, and mafic and volcanic
rocks producing silty and sandy soils with slowly permeable, clayey substrata. The indoor radon
average for this terrane is 3.3 pCi/L. Overall, this area has high radon potential.
ffl-5 Reprinted from USGS Open-File Report 93-292-A
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MAINE
The rocks, surficial deposits, and geologic structures of Maine that are most likely to cause
high (>4 pCi/L) indoor radon concentrations include: two-mica granite, alkaline and calc-alkalic
granite, and granodiorite; pegmatites, faults and shear zones; and carbonaceous schist, slate, and
phyllite. Deposits and rocks likely to cause moderate (2-4 pQ/L) to high (>4 pCi/L) indoor radon
include soils developed on carbonate rocks, especially the interbedded slates and dolostones in
south-central and northeastern Maine; glacial gravels, especially outwash, kames, and eskers;
melange; granitic gneiss; high- to medium-grade metamorphic rocks, and contact metamorphosed
rocks in the vicinity of plutons. Rocks and deposits with moderate to variable radon potential
include felsic metavolcanic rocks, intermediate composition plutonic rocks, and glacial till. Rocks
likely to cause low indoor radon (< 2 pCi/L) include metamorphosed coarse-grained clastic
sedimentary rocks, mafic metavolcanic rocks, marine clays, and mafic plutonic rocks.
Most of Maine is underlain by Cambrian-Devonian stratified metamorphic rocks of igneous
or sedimentary origin that we have ranked from low to high in radon potential. Uranium
concentration generally increases with metamorphic grade and local uranium concentrations may be
present in fractures and faults. Areas in northern Maine underlain by coarse-grained clastic
metasedimentary rocks and tills derived from these rocks generally have low equivalent uranium
and have soils with low permeability. Many of the rocks in this area belong to the Seboomook
Formation (area 2, fig. 1). In central and southern Maine, indoor radon is low to moderate in areas
underlain by coarse-grained elastic metasedimentary rocks. Formations such as the Vasselboro,
which consists of interbedded carbonate rocks and clastic metasedimentary rocks and tends to be
more calcareous in general, appears to have high indoor radon associated with it in southern
Penobscot County, Central Maine (area 5, fig. 1) is a highly variable area-radon potential varies
from moderate to locally high or low. Locally high areas may be associated with granites, kames,
eskers, carbonate rocks, graphitic or carbonaceous schist, phyllite, and slate. Locally low areas
may be associated with mafic plutonic rocks and clastic metasedimentary rocks. Indoor radon is
highly variable in this area and the type and character of the rocks are variable over short distances.
Soils and glacial deposits derived from interbedded carbonate metasedimentary rocks and
slates in the northeastern portion of the State (3, fig. 1) and in the south-central portion of the State
(5, fig. 1) are associated with moderate and high indoor radon. Equivalent uranium is variable
over these deposits but is higher than the dominantly clastic metasedimentary rocks. Soils, tills,
eskers, and kames derived from these rocks generally have moderate to locally high permeability.
The area underlain by these rock units in the northeastern part of Maine (area 3) has high radon
potential, whereas the rocks in the south-central part (area 5) are assigned a moderate geologic
radon potential.
Most of the carbonaceous or graphitic rock units in Maine have moderate to high equivalent
uranium. Some high indoor radon may be associated with carbonaceous rocks of the Penobscot
Formation in Knox County (area 10, fig. 1). Soils formed on carbonaceous and graphitic rocks in
Maine have low to moderate permeability. Areas underlain by these rock units have high geologic
radon potential.
Plutonic rocks of intermediate to mafic composition generally have low or variable radon
potential. Diorite and mafic intrusives of the New Hampshire series have low equivalent uranium
and comprise two northeast-trending belts along the southern coast and from southern Oxford
County to central Picataquis County. However, two-mica granites, calc-alkaline granites, and
alkalic plutonic rocks in Maine (in areas 4,5,9, fig. 1) have been ranked high in geologic radon
ffl-6 Reprinted from USGS Open-File Report 93-292-A
-------
potential Uranium concentrations in these types of granites are commonly more than 3 ppm and
are as high as several hundred ppm in Maine. Two-mica granites are most abundant in the
southwestern part of the State and include the rocks of the Sebago Pluton. Calc-alkaline to alkaline
granites are more abundant in the southern and central - if the State, particularly in the area
northeast of Penobscot Bay and in the Katadhin pluton in central Maine (the part of area 4 in central
Maine). Indoor radon averages are high in the southwestern counties of Maine, which may be due
to the abundance of igneous plutons and high-grade metamorphic rocks in this area. Most of the
areas underlain by igneous plutonic rocks and associated glacial deposits have moderate to locally
high permeability.
Although there is no obvious anomalous radioactivity associated with major fault and shear
zones in Maine, evidence from other areas of the Appalachians suggests that shear zones can create
isolated occurrences of severe indoor radon, especially when they deform uranium-bearing rocks.
The radon potential of melange, most of which is found in the northwestern part of Maine (area 1
and a small part of area 5, fig, 1), is not well known, but gray to black phyllitic rocks and
deformed zones have the potential to produce at least moderate amounts of radon. We have
tentatively ranked these rocks as moderate or variable in radon potential.
The effect of glacial deposits is difficult to assess in Maine because most till is relatively
locally derived and is composed primarily of clasts of the surrounding bedrock. The areas of
coarse-grained glacial deposits in southwestern Maine and the kame and esker deposits scattered
throughout the State enhance the geologic radon potential doe to their very high permeability; these
units have moderate to high radon potential. The coarser glacial deposits appear to be associated
with the igneous plutonic rocks and belts of calcareous and carbonate rnetasedimentary rocks.
Along the coast, areas of slowly permeable marine and glaciomarine clay (areas 7, 8,11, fig. 1)
probably reduce the radon potential and they are assigned a low geologic radon potential. Glacial
lake sediments with low permeability in Penobscot County (6, fig. 1) appear to be associated with •
low indoor radon. Till with compact, slowly permeable substrata is dominant hi much of central
and northern Maine and the rocks underlying these areas are rnetasedimentary and metavolcanic
rocks that are generally low in uranium.
MASSACHUSETTS
The metamorphic rocks of the Taconic Mountains and carbonate sedimentary and
rnetasedimentary rocks of the Vermont-Stockbridge Valley, in westernmost Massachusetts
(area 21, fig. 1), have been ranked moderate in geologic radon potential. Graphitic phyllites and
schist of the Walloomsac Formation have moderate to high radioactivity associated with them and
may produce locally elevated indoor radon levels. Elevated radon may also be associated with fault
and shear zones, especially in the Taconic Mountains.
The Berkshire Mountains (area 22, fig. 1) have been ranked moderate overall in radon
potential. Granitic to dioritic gneiss and schist have generally low equivalent uranium associated
with them. Shear zones, pegmatites, and local accumulations of monazite in biotite schist and
gneiss may be sources of locally high indoor radon levels. Soil permeability is low to moderate.
Metamorphic rocks of the Connecticut Valley Belt, flanking the Mesozoic basins of west-
central Massachusetts (27,30, fig. 1), have been ranked moderate in radon potential,
Metasedimentary and metavolcanic gneisses and schists have generally low to moderate
radioactivity associated with them. Soils have generally moderate permeability. The Pauchaug and
Glastonbury granite gneisses, which form the cores of the Warwick and Glastonbury domes, as
ffl-7 Reprinted ftomUSGS Open-File Report 93-292-A
-------
well as other locally-occurring granitic rocks in area 30 (fig. 1), may generate locally high indoor
radon levels. Locally high radon levels are likely to be associated with an area of anomalous
radioactivity at the south end of the Warwick dome and may be associated with faults and shears
throughout the area.
Mesozoic sedimentary and igneous rocks of the Connecticut Valley (28, fig. 1) have been
ranked moderate or variable in radon potential. Most of the sedimentary rocks have low radon
potential but locally high indoor radon levels may be associated with Jurassic-age black shales and
localized uranium deposits in fluvial sandstone and conglomerates. Geologic radon potential is
low to moderate in glacial lake-bottom sediments, and moderate to high in glaciofluvial deposits
including outwash, lacustrine delta deposits, and alluvium.
Granitic plutons of the Merrimack Belt, central Massachusetts (32, fig. 1), have been
ranked high in radon potential. The metasedimentary rocks surrounding the plutons are
predominantly phyllites and carbonaceous slates and schists with moderate to high radon potential.
Mafic metamorphic rocks, which are less common in the Merrimack Belt, have generally low to
moderate radon potential. Faults and shear zones may produce locally high radon concentrations.
Granitic plutonic rocks and metamorphic rocks of the Nashoba terrane (36, fig. 1), the
northward extention of the Avalonian terrane (37, fig. 1), and granites of the Cape Ann and
Peabody plutons, in northeastern Massachusetts (42, fig. 1), are ranked high in radon potential.
They are associated with moderate to high radioactivity and the soils developed on these rocks have
moderate to high permeability. Relationships between radon and underlying bedrock in eastern
Massachusetts, particularly in the Merrimack zone and in these areas, are less distinct, probably
due to the influence of glacial deposits that are made up of a mixture of the rock types underlying
eastern Massachusetts and areas to the north. The glacial deposits generally have enhanced
permeability and may have enhanced radon emanation due to the redistribution of rock
components, mixing, and grain-size reduction effects of the glacial processes. Volcanic rocks and
soils of the Newbury basin (41, fig. 1) are ranked moderate in radon potential.
The Esmond-Dedham terrane, southeastern Massachusetts (44,46, fig. 1), is ranked
moderate overall in geologic radon potential. This area includes a number of granite plutons and
fault zones that may generate high radon levels, as well as mafic metasedimentary and metavoleanic
rocks having low to moderate radon potential. Aeroradioactivity is generally low to moderate with
one anomaly associated with granite of the Rattlesnake Hill Pluton. Soils in this area have low to
moderate permeability.
Pennsylvanian sedimentary rocks of the Narragansett basin, southeastern Massachusetts
(45, fig. 1), are associated with low to moderate radioactivity and low to moderate soil
permeability, and have moderate geologic radon potential. The Norfolk basin is similar to the
Narragansett basin and also has moderate radon potential. Proterozoie to Pennsylvanian
sedimentary rocks of the Boston basin (43, fig. 1) have been ranked low in radon potential.
Information on soil characteristics and radioactivity is unavailable for the Boston basin but
radioactivity is assumed to be generally low based on the radioactivity of similar rocks elsewhere in
the State. Soil characteristics are highly variable in urban areas due to human disturbance, and thus
are considered to be variable for this assessment Black shales and conglomerates in the Boston
basin may have locally high radioactivity and may cause locally elevated indoor radon levels.
Sediments of the Coastal Plain are found primarily on Nantucket Island and Martha's
Vineyard (47, fig. 1). Areas underlain by Cretaceous and Tertiary sediments have low radon
potential, but areas underlain by the Martha's Vineyard and Nantucket moraines have moderate to
locally high radon potential caused by their relatively higher permeability and better drainage
IE-8 Reprinted from USGS Open-FUe Report 93-292-A
-------
characteristics compared to surrounding areas, and the crystalline rock source component of the
moraines. This is also true of the Buzzard's Bay and Sandwich moraines on Cape Cod. Areas
underlain by highly permeable glacial outwash may also generate locally elevated indoor radon
levels if the soils are not too we* to preclud~ "oil-gas tr~ ^ort
NEW HAMPSHIRE
The Avalonian Composite Terrane, in southeastern New Hampshire (area 14, fig. 1), is
underlain by the Merrimack Group, Massabesic Gneiss, the Rye Formation and several bodies of
two-mica granites, alkalic plutonic rocks, and mafic plutonic rocks. Soils in this area have
generally low permeability that is locally moderate to high. The Merrimack Group has low to
moderate equivalent uranium, whereas other rocks have generally moderate to high equivalent
uranium, particularly the Massabesic Gneiss, two-mica granites, and the extensive fault zones.
The Merrimack Group and Rye Formation have overall moderate radon potential, with locally low
radon potential. The Massabesic Gneiss, the granite intrusives, and the fault zones have high
radon potential. Average indoor radon for the townships underlain by Avalonian rocks is
predominantly moderate to high. Overall, the Avalonian Composite Terrane has been ranked
moderate to high in radon potential.
About half of New Hampshire is underlain by Cambrian-Devonian stratified metamorphic
rocks of igneous or sedimentary origin of the Gander (area 13, fig. 1) and Boundary Mountains
(area 12) Terranes, These rocks r»ave been ranked moderate in radon potential overaE. The
metasedimentary and metavolcanic rocks have variable uranium content, with increasing uranium
as metamorphic grade increases, and contain local uranium concentrations in fractures and faults.
Graphitic slates, phyllites, and schists are may also be possible sources of high indoor radon.
Where indoor radon data are available, the stratified metamorphic rocks appear to be associated
with low to moderate indoor radon in the western portion of the State and with higher indoor radon
in the eastern portion of the State and in the vicinity of plutonic rocks. Intermediate to mafic
plutonic rocks generally have low or variable radon potential. The Lake Winnipesaukee Quartz
Diorite and the Kinsman Quartz Monzonite appear to have low equivalent uranium and low indoor
radon associated with them, and are ranked low in geologic radon potential.
Several of the Oliverian domes have distinct radiometric highs associated with them except
for the northernmost and largest of the Oliverian rocks in the northern Gander Terrane, which have
low radioactivity. Indoor radon in the townships underlying this area is variable from low to high.
The Oliverian rocks and intermediate composition plutonic rocks are ranked moderate or variable in
geologic radon potential.
Two mica granites, calc-alkaline granites, and alkalic plutonic rocks in New Hampshire
have been ranked high in radon potential. Uranium content of these granites is commonly more
than 3 ppm and ranges to several hundreds of ppm. Two-mica granites occur throughout the
central and eastern portions of New Hampshire. Calc-aUcaline granites occur from east-central to
northwestern New Hampshire. The largest body of calc-alkaline granite underlies the White
Mountains and has very high radioactivity associated with it Indoor radon levels in several
townships in this area are high.
High radon concentrations in domestic water are associated with granites, pegmatites, and
faults in some parts of New Hampshire. The radon in these wells may be high enough to
contribute significantly to the radon content of the indoor air.
m-9 Reprinted from USGS Open-FEe Report 93-292-A
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RHODE ISLAND
The radon potential of Rhode Island appears to be influenced most by the composition of
*Ke underlying bedrock and secondarily affected by glacial deposits. The greatest percentage of
homes with 4 pCi/L or more of radon are concentrated in the southern part of the State over the
Scituate and Narragansett Pier Igneous Suites, and parts of the Esmond Igneous Suite (area 39,
fig, 1), as well as with two areas also noted for high uranium: the northwestern and southwestern
comers of the State, underlain by the Sterling Plutonic group (38,40, fig, 1), and in the East Bay
Area, which is underlain by the granites of Southeastern Rhode Island. Igneous intrusive rocks of
the Scituate Igneous Suite, rocks of the Hope Valley Group, granites of southeastern Rhode
Island, the Narragansett Pier Granite, and alkalic granites of the Cumberland area have significant
uranium concentrations and surface radioactivity. Many of the areas underlain by these rocks also
have locally derived tills, kames and glacial lake deposits that may contribute significantly to the
overall high radon potential. The lowest radon potential appears to be associated with the less-
metamorphosed sediments of the Rhode Island Formation, which is overlain by glacial outwash
deposits in the northern portion of the Narragansett Lowlands (45, fig, 1). Low to moderate radon
appears to be associated with stratified metamorphic rocks of the Blackstone Group, the Harmony
Group, the Plainfield Formation, parts of the Esmond Igneous Suite, and scattered stratified
metamorphic rocks in the Narragansett Lowlands. These areas are ranked moderate or variable in
geologic radon potential overall.
The effect of glacial deposits is complex because most of the materials making up the
glacial deposits are locally derived and primarily reflect a coEection of the surrounding bedrock.
The majority of soils and glacial deposits are moderate to high in permeability and probably
enhance the geologic radon potential. In the southern half of the State, stratified glacial deposits
appear to have lower radioactivity than areas of till over the same bedrock. Stratified glacial
deposits are most common along valley floors and in the Narragansett Basin, and are thicker and
generally coarser than the till. The thickness of the stratified deposits may damp the radioactivity
of the bedrock or indicate an overall lower radioactivity for the glacial deposit. Although the
coarser stratified glacial sediments have higher permeability than some of the tills, their radon
emanation coefficient tends not to be as high as for some tills. Tills commonly have higher radon
emanation because of the higher proportion of finer-grained sediments. This is also true of some
glacial lake deposits. Thick deposits of outwash sand and gravel blanket much of the northern
Narragansett Lowlands and appear to have both low radioactivity and low indoor radon associated
with them; this area is assigned a low geologic radon potential. The southern part of the
Narragansett Lowlands and East Bay Area, however, have a significantly higher percentage of
indoor radon readings exceeding 4 pCi/L. This may be due to the fact that the southern part of the
Narragansett Lowlands and East Bay Area are dominated by thin glacial till containing components
of uraniferous granite and phyllite; this area has a moderate or variable geologic radon potential.
Another example of the influence of glacial deposits may be seen in the area of the Narragansett
Pier Granite, where high percentages of homes have indoor radon levels greater than 4 pCi/L.
The types of glacial deposits in this area include kames, glacial lake deposits, and till, which are
known to have enhanced radon exhalation. These glacial deposits may also have significant source
components in the adjacent Scituate Igneous Suite and Sterling Plutonic Group as well as the
Narragansett Pier granite, all of which have some elevated uranium concentrations.
ffl-10 Reprinted from USGS Open-File Report 93-292-A
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VERMONT ' '
The geologic radon potential of the Champlain Lowlands (area 18, fig. 1) is low, with
areas of locally moderate to high radon potential possible. The Vermont Valley (19, fig. 1) has
generally moderate geologic radon potential. Clay-rich soils with low permeability dominate the
lowlands and include glacial lake and marine clays, which probably reduce the radon potential
significantly. Radioactivity is generally low, with a few scattered high and moderate areas that
appear to be associated with the Clarendon Springs Formation and, possibly, with black shales and
slates in surrounding rock units. Indoor radon levels in the counties underlain by the Champlain
Lowlands are generally less than 4 pCi/L except in Addison County, where out of 26 readings, six
were greater than 4 pCi/L and of these, two were greater than 20 pCi/L.
The Green Mountains (17, fig. 1) have been rated moderate in radon potential; however,
the radon potential is actually highly variable. Areas with locally high radon potential are those
underlain by metamorphic rocks of Proterozoic age, including quartzite; graphite- and pyrite-
bearing schists and slates; migmatitic schist and gneiss; biotite-rich zones in mica schist; and schist
and gneiss with high concentrations of the minerals monazite, allanite, and zircon; the Cheshire
Quartzite; and local deposits of uranium in veins and fault zones. Mafic metamorphic rocks such
as amphibolite, hornblende gneiss, gabbro, and serpentinite, have low geologic radon potential.
Radioactivity is variable—low in the southern portion but containing local high radioactivity areas,
moderate to high radioactivity in the central portion, and low in the north.
The Taconic Mountains (20, fig. 1) have mode/ate geologic radon potential. Radioactivity
is generally moderate to high, and several rock types appear to have elevated levels of uranium,
especially the carbonaceous sedimentary rocks of the Pawlet Formation. Elevated concentrations
of uranium in the black to gray phyllites and slates are probably the principal radon sources in this
area.
The Vermont Piedmont (16, fig. 1) has moderate but variable geologic radon potential.
Much of the area is underlain by mafic rocks with low radon potential. Granites, granitic gneiss
and schist, and carbonaceous or graphitic slate and phyllite have the potential to generate moderate
to high indoor radon levels.
The Northeastern Highlands (15, fig. 1) have moderate radon potential. Plutonic igneous
rocks are abundant in this area and in the northern half of the Vermont Piedmont, but only a few of
the plutons have distinct radiometric anomalies associated with them. Indoor radon for counties
underlain by these rocks is moderate with the exception of Caledonia County, in which 11 of the
51 indoor radon measurements in the State/EPA Residential Radon Survey were greater than
4 pCi/L.
m-11 Reprinted from USGS Open-File Report 93-292-A
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Page Intentionally Blank
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PRELIMINARY GEOLOGIC RADON POTENTIAL ASSESSMENT OF VERMONT
by
Linda C.S. Gundersen and R. Randall Schumann
U.S. Geological Survey
INTRODUCTION
The radon potential of Vermont is generally moderate but can be variable across the State.
Indoor radon data from 710 homes sampled in the State/EPA Residential Radon Survey conducted
in Vermont during the winter of 1988-89 have an average of 2.6 pCi/L. Sixteen percent of the
measurements exceeded 4 pCi/L. Several types of rocks in Vermont have the potential to produce
high radon levels. These include granitic and micaceous metamorphic rocks in parts of the Green
Mountains, Vermont Piedmont, and Northeastern Highlands, granite plutons in the Northeastern
Highlands and Vermont Piedmont, graphitic and carbonaceous phyllites, slates, and schists in
parts of the Taconic Mountains, Green Mountains, and Vermont Piedmont, and some clastic and
carbonate sedimentary rocks in the Green Mountains, Vermont Valley, and Champlain Lowlands,
including the Cheshire quartzite, breccias in the Clarendon Springs and Dunham Dolomite, and
related black shales. Low radon potential is associated with mafic igneous and metamorphic rocks,
including amphibolite, hornblende gneiss, gabbro, and serpentinite found throughout the State,
especially in the Green Mountains, Vermont Piedmont, and Northeastern Highlands.
This is a generalized assessment of geologic radon potential of rocks, soils, and surficial
deposits of Vermont 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 SETTING
The physiography of Vermont (fig. 1) is in part a reflection of the underlying bedrock
geology (fig. 2) and the effects of glaciation in the State. Vermont has six major physiographic
regions: the Champlain Lowlands, the Taconic Mountains, the Vermont Valley, the Green
Mountains, the Vermont Piedmont, and the Northeastern Highlands. Vermont's elevation ranges
from 95 to 4,393 feet, with the highest elevations in the Green Mountains and the lowest elevations
in the Champlain Lowlands. The Champlain Lowland is a structural trough between the
Adirondacks in New York and the Green Mountains. The Lowlands have elevations generally less
than 500 feet and are underlain by Cambrian-Ordovician sedimentary rocks with little or low-grade
metamorphism. The Taconic Mountains lie in the southwestern part of the State and are as rugged
and steep as the Green Mountains, but average elevations range from 1000-2000 feet above sea
level. Cambrian through Ordovician metamorphosed sedimentary rocks form the steep to hilly
topography. The Vermont Valley separates the Taconic and Green Mountains and is a long,
IV-1 Reprinted from USGS Open-File Report 93-292-A
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A S
A C H U SET
Figure 1. Physiographic areas of Vermont (modified from Stewart and MacClintock, 1969),
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n 5 10 15 20 25 MlM
Figure 2. Generalized bedrock geologic map of Vermont (modified from Bennison, 1976).
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Explanation for the Geologic Map of Vermont
Precambrian
Predominately biotite gneiss, chloritic in western areas, and amphibolite-hornblende
gneiss, with minor mica schist, quartzite, calc-silicate granulite,and pegmatitic and gneissic
granite of the Mount Holly Complex. Massive quartzite and micaceous quartzite associated
with marble is important in western Windham and Windsor Counties and eastern Rutland
County. Granitic gneiss of the Stamford gneiss in southernmost Bennington County.
Gneiss, quartzite, and calc-silicate granulite.
Gneissic biotite granite, quartz monzonite, and granodiorite.
Quartz-muscovite schist with minor marble of the Cavendish Formation. Mostly quartz-
plagioclase gneiss in west-central Windham County.
Cambrian
Green, and variegated slate and phyllite of the St. Catherine Formation, black phyllite with
marble interbeds of the Brezee Formation, and carbonaceous black slate of the West
Castleton Formation. Graywacke sandstone of the St. Catherine and calcareous quartzite
of the Hatch Hill Formation comprise about one-third the unit in northwestern Rutland
County.
Schistose graywacke of the Pinnacle Formation with common quartz-cobble and boulder
conglomerate near base comprises most of the rocks north of the Windsor-Rutland County
line. Felspathic quartz schist, that is locally carbonaceous, and schistose quartzite of the
Tyson, Dalton and Hoosac Formations dominate to the south
Albitic greenstone, locally pillowed and vesicular, of theTibbit Hill volcanic member of
the Pinnacle Formation.
Gray-green, quartz-albite schist, in places carbonaceous, of the Underbills, Hazens Notch
and Hoosac Formations, carbonaceous phyllites of the Pine Hollow Formation and the
Plymouth Member of the Hoosac, and quartzites, carbonates, and black phyllites and slates
of the Cheshire and Monkton Quartzites, Dunham Dolomite, Forestdale Marble,
Moosalamoo Phyllite, Hatch Hill and West Castleton Formations, and Parker Slate.
Quartz-plagioclase gneiss (Bull Hill Gneiss) of the Cavendish Formation overlain by
locally carbonaceous, quartz-albite schist of the Hoosac Formation.
predominately dolomites and quartzites of the Winooski, Saxe Brook, Clarendon Springs,
Ticonde-^oa, and Rock River Dolomites and the Rugg Brook, Danby, and Potsdam
Formations. Upper part includes black slates, carbonates, and conglomerates of the
Sweetsburg and Gorge Formations.
Black, carbonaceous phyllite and schist with quartzite interbeds of the Ottauquechee
Formation.
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Ordovician
Quartz-sericite phyllite and schist of the Stowe Formation. Phyllitic graywacke is an
important component north of the Lamoille-Orleans county line.
Greenstone and amphibolite of the Stowe Formation.
Predominately limestone, dolomite, and marble with minor sandstone and quartzite of the
Highgate, Shelboume, Whitehall, and Strites Formations, Cutting Dolomite, Orwell, Isle
La Motte, and Lowville Limestones, and Hortonville, Cumberland Head, Glens
Falls,Bascom, Chipman, and Morses Line Formations.
Predominately quartzite, quartz-plagioclase granulite, and feldspathic quartzite interbedded
with gray green phyllite, slate, and schist of the Missisquoi and Albee Formations. Black
carbonaceous slate and phyllite increase upsection and westward in the Crum Hill Member
of the Missisiquoi, and in the Ordville, Partridge, Mount Hamilton, and Pawlet
Formations.
Biotite and hornblende gneiss and amphibolite of the Barnard Volcanic Member of the
Missisiquoi Formation and the Partridge Formation and biotite gneiss and greenstone of the
Ammonoosuc Volcanics, Ordville Formation ,and the Coburn Hill Volcanic Member of the
Missisiquoi. The Ammonoosuc is composed of rhyolitic tuff, breccia, and flows in the
northeast part of the state. Also includes amphibolite mapped as the Standing Pond
Member of the Waits River Formation and Ordovician diorite gneiss in Windham County.
Black shale, calcareous shale, and carbonaceous slate and phyllite of the Cumberland,
Hortonville, Stony Point, Iberville, and Hathaway Formations.
j^ Granitic rocks of the Highlandcroft plutonic series.
The Pawlet Formation is gray to black, carbonaceous and pyritiferous silty slate
interbedded with rusty weathering thin beds of graywacke.
Silurian-Devonian
Predominately quartzose micaceous limestone interbedded with gray phyllite and schist of
the Waits River Formation, and gray phyllite and schist with micaceous quartzite interbeds
of the Gile Mountain Formation and their metamorphic equivalents. Basal quartzose
limestone and conglomerate of the Shaw Mountain and Clough Formations are overlain by
slate and phyllite of the Northfield, Fitch, and Litfletone Formations, followed by the Waits
River and Gile Mountain Formations. Also includes granitic gneiss of the Bethlehem
Gneiss in Winddm County.
Amphibolite, garnet i mphibolite and schist, hornblende maculite,. and greenstone of the
Standing Pond Volcanic Member of the Waits River Formation.
Granite and granitic gneiss of the New Hampshire plutonic series.
Permian/Jurassic?
Hornblende and biotite granite, diorite gneiss, augite syenites of the White Mountain
plutonic series.
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narrow lowland underlain by Cambrian-age metamorphosed sedimentary rocks. Elevations are
generally 500 to 1000 feet The Green Mountains are ragged, steeply sloping mountains underlain
by Proterozoic to Paleozoic igneous, metamorphic, and sedimentary rocks. Elevation averages
2000 feet and the mountains form a central topographic high trending north to south across the
State. To the east of the Green Mountains Hes the Vermont Piedmont, which is part of the New
England Upland. It is underlain by Paleozoic metavolcanic and metasedimentary rocks that are
intruded by igneous plutonic rocks. This part of the New England Upland is a dissected plateau
with numerous steep-sided valleys and undulating to hilly topography averaging 1000-2000 feet
above sea level. The Northeastern Highlands, in the northeastern corner of the State, are the
western margin of the White Mountains of New Hampshire. The mountains comprise late
Paleozoic to Mesozoic-age igneous rocks intruded into Silurian-Devonian metasedimentary and
metavolcanic rocks. Elevations are generally 1000-2000 feet with several mountains reaching
3000 feet or more.
In 1990, the population of Vermont was 562,758, including 34 percent urban population
(fig. 3). The average population density is approximately 58 persons per square mile. The climate
of Vermont is temperate, with considerable temperature extremes and heavy snowfall in the
mountains. Winter temperatures can drop to -30° F, and summer temperatures are generally less
than 90° F. Average precipitation ranges from 34 to 40 inches per year (fig. 4) and is highest in the
Green Mountains.
GEOLOGIC SETTING
The metamorphic and sedimentary rocks of Vermont form folded and faulted, north-south
trending belts that are intruded by a series of granitic plutons in the eastern part of the State.
Cambrian and Ordovician rocks are bounded by large north-south trending thrust belts in the
western part of the State, most notably in the Taconic Mountains of the southwest. Proterozoic
igneous and metamorphic rocks form the core of a large anticlinorium in the southern Green
Mountains and Devonian metasedimentary and metavolcanic rocks form the core of a large
synclinorium in the northern Vermont Piedmont A detailed lithologic description of the important
rock units is provided below. The geologic descriptions that follow are derived from Doll and
others (1961) and a general geologic map is given for reference in figure 2. It is suggested,
however, that the reader refer to the published Geologic Map of Vermont (Doll and others, 1961)
and other publications available from the State Geological Survey of Vermont.
The Green Mountains
The Green Mountains contain the oldest rocks in the State and are underlain predominantly
by biotite gneiss, amphibolite, and hornblende gneiss of the Mount Holly Complex, thought to be
Proterozoic-Y age. Quaitzite that is locally micaceous, graphitic schist, and marble comprise fold
belts within the Mount Holly Complex, particularly in western Windham and Windsor Counties
and eastern Rutland County. The Stamford Gneiss, a granitic gneiss, underlies a small area in
southernmost Bennington County and a small body of gneissic granite and quartz monzonite is
located in western Windham County. Proterozoic-Z rocks are predominantly quartz-muscovite
schist with minor marble of the Cavendish Formation, which grade northward into quartz-
plagioclase gneiss in west-central Windham County. Slate and phylite in southwestern
Bennington County is also thought to be Proterozoic-Z age.
IV-6 Reprinted from USGS Open-File Report 93-292-A
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POPULATION (1990)
0 to 10000
10001 to 25000
25001 to 50000
50001 to 100000
100001 to 131761
m
Figure 3. Population of counties in Vermont (1990 U.S. Census data).
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28"
w-
10 20 30
' ' """ > Imltos
Figure 4. Average annual precipitation in Vermont (from Facts on File, 1984).
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Cambrian rocks dominate the northern half of the Green Mountains. The belt of late
Proterozoic-early Cambrian rocks that forms the western margin of the Green Mountains is
characterized by schistose graywacke of the Pinnacle Formation, north of the Windsor-Rutland
county line The Pinnacle graywackes intertongue northward with albitic greenstone of the Tibbet
Hill Member in Lamoille County. Locally carbonaceous, gray-green feldspathic quartz schist and
schistose quartzite of the Tyson, Dalton, and Hoosac Formations comprise equivalent age rocks to
the south and dominate the broad belt of Lower Cambrian rocks in the eastern Green Mountains.
This belt also includes the Underbill and Hazens Notch Formations to the north and the Hoosac
Formation to the south. These rocks become more micaceous and phyllitic upsection to the west
and south and include the Pinney Hollow Formation and the dolomitic, carbonaceous Plymouth
Member of the Hoosac Formation. The easternmost edge of the Green Mountains consists of a
narrow band of black, carbonaceous phyllite and schist with quartzite interbeds of the
Ottauquechee Formation. The westernmost portion of the southern Green Mountains is underlain
by the Cheshire and Monkton Quartzites, Dunham Dolomite, Forestdale Marble, and the black,
carbonaceous Moosalamoo Phyllite and Parker Slate. In eastern Windsor and Windham Counties,
a narrow belt of Bull Hill Gneiss, a quartz-plagioclase gneiss, overlies the Mount Holly Complex
and is overlain by narrow belts of the Hoosac and Underbill Formations.
Champlain Lowlands and Vermont Valley
In the Champlain Lowlands, the easternmost bedrock is a belt of Pinnacle Formation
graywackes and albitic greenstones, overlain by Cheshire Quartzite, and bounded on the west by
the Hinesburg thrust fault. West of this fault and south into the Vermont Valley, the Cambrian
rocks consist predominantly of dolomites and quartzites, including the Winooski, Saxe Brook,
Clarendon Springs, Ticonderoga, and Rock River Dolomites, as well as the Cheshire, Monkton,
Rugg Brook, Danby, and Potsdam Formations. The Dunham Dolomite comprises the most
extensive outcrop belt within these units. The upper part of the Cambrian sequence in the
Champlain Lowlands includes black slates, carbonate rocks, and conglomerates of the Sweetsburg
and Gorge Formations. The Sweetsburg forms a prominent unit extending across the Franklin-
Chittenden county line. The Champlain thrust belt is the western boundary of most of the
Cambrian rocks in the Champlain Lowlands.
The lower Ordovician rocks in the Champlain Lowlands and Vermont Valley consist
predominantly of limestone, dolomite, and marble with minor calcareous sandstone and quartzite
of the Highgate, Shelburne, Whitehall, and Suites Formations; Cutting Dolomite; Orwell, Isle La
Motte, and Lowville Limestones; and Hortonville, Cumberland Head, Glens Falls, Bascom,
Chipman, and Morses Line Formations. These units form narrow outcrop belts, except the
Bascom Formation, which forms a broader belt of limestone, marble, nyartzite, and conglomerate
in the Vermont Valley. This sequence is overlain to the west, in the Champlain Lowlands, by a
belt of black shale, calcareous shale, and carbonaceous slate and phyllite of the Cumberland,
Hortonville, Stony Point, Iberville, and Hathaway Formations.
The Taconic Mountains
Cambrian-age rocks in the Taconic Mountains are dominated by green and variegated slate
and phyllite of the St Catherine Formation, black phyllite with marble interbeds of the Brezee
Formation, and carbonaceous black slate of the West Castieton Formation. Graywacke sandstone
of the St. Catherine Formation and calcareous quartzite of the Hatch Hill Formation make up about
one-third of the Cambrian rocks underlying northwestern Rutland County. A narrow, U-shaped
IV-9 Reprinted from USGS Open-File Report 93-292-A
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belt of Qrdovician rocks, consisting of black to variegated shales interbedded with quartzites and
limestones of the Mount Hamilton Formation, overlain by black carbonaceous shale of the Pawlet
Formation, lies along the State's western border.
Vermont Piedmont and Northeastern Highlands
The western Vermont Piedmont is underlain by a belt of quartz-sericite phyllite and schist
of the Stowe Formation thatintertongiies with phyllitie graywacke and volcanic greenstone and
arnphibolite north of the Lamoille-Qrleans county line. These rocks are overlain to the east by a
belt of predominantly quartzite, quartz-plagioclase granulite, and feldspathic quartzite interbedded
with gray-green phyllite, slate, and schist of the Missisquoi Formation. Black carbonaceous slate
and phyllite become more abundant upsection to the east in the Cram Hill and Whetstone Members
of the Missisquoi. South of the Qrange-Windham county line, biotite and hornblende gneiss and
amphibolite of the Barnard Volcanic Member of the Missisquoi Formation forms an eastern belt
to northernmost Orleans County, the Coburn Hill Volcanic Member of the Missisquoi, consisting
of greenstone and hornblende amphibolite, comprises half the width of the outcrop belt. The
sedimentary and volcanic rocks of the Missisquoi extend south along the eastern margin of the
Green Mountains in Windham County.
Along the eastern margin of the Vermont Piedmont and the southern end of the
Northeastern Highlands, quartzites and feldspathic quartzite, interbedded with gray-green slate and
phyllite of the Albee Formation, dominate the Qrdovician sedimentary rocks. South of the
Caledonia-Orange county line, black carbonaceous slate and phyllite of the Partridge and
Orfordville Formations comprise most of the narrow belts. Greenstone, chloritic schist, and
amphibolite of the Post Pond Volcanics in the Orfordville Formation comprise a prominent belt
across the Orange-Windsor county line. The Ammonusac Volcanics, consisting of biotite gneiss
and greenstone in the southern part of the State and rhyolitic tuff, breccia, and flows in the
northeastern part of the State, form small, isolated patches along the belt Other Ordovician rocks
include granitic rocks of the Highlandcroft Plutonic series in eastern Essex County and isolated
patches of biotite-quartz diorite gneiss of the Oliverian Plutonic series.
Most of the Vermont Piedmont and Northeastern Highlands are underlain by the Devonian
Waits River and Gile Mountain Formations. The Waits River forms two broad outcrop belts in the
central and western portions of the Vermont Piedmont that join to the south. It consists of
quartzose micaceous limestone interbedded with gray quartz phyllite and schist. The western belt
is less quartzose and more phyllitic than the central belt In the southern part of the Vermont
Piedmont, amphibolite, garnet amphibolite, schist, and greenstone of the Standing Pond Volcanic
Member of the Waits River Formation forms several narrow belts. The Gile Mountain also forms
two broad belts that join to the south and to the north underlying most of the northern part of the
Highlands. The Gile Mountain Formation consists of gray phyllite and schist with micaceous
quartzite interbeds. A narrow belt of gray slate comprises the easternmost margin of the formation.
Along the western margin of the Vermont Piedmont, a very narrow belt of Silurian quartzites,
conglomerates and limestones of the Shaw Mountain Formation is overlain by a narrow belt of
black slate or phyllite with thin limestone beds of the Northfield Formation. In the eastern portion
of the Northeastern Highlands and the southeastern most part of the Green Mountains, the Silurian
to Devonian transition comprises narrow belts of the Clough Formation conglomerate and
quartzite, the Fitch Formation limestone and dolomite, and gray slate and phyllite of the Littleton
Formation.
IV-10 Reprinted from USGS Open-File Report 93-292-A
-------
Several large granite and granitic gneiss bodies of the New Hampshire plutonic series
intrude the sedimentary rocks of the northern Vermont Piedmont and Northeastern Highlands.
Where these intrude the sedimentary rocks they are commonly altered to more metamorpMc
assemblages. Granite and granitic gneiss of the Bethlehem Gneiss also forms some small intrusive
bodies. In northeastern Essex County, Monadnock Mountain is underlain by hornblende, biotite,
quartz, and augite syenites of the White Mountain plutonic series.
GLACIAL GEOLOGY
Deposits of three Wiscdnsinan (Late Pleistocene) glacial advances in Vermont have been
recognized or inferred from surface or subsurface data. The Bennington Glacial Stade is the first
positively identified glacial advance that left datable deposits in Vermont During this period,
glaciers advanced across the State from the northwest and covered all of Vermont (Stewart and
MacClintock, 1969). The Shelburne Stade followed the Bennington and was marked by a glacial
advance from the northeast that covered all but the extreme southern part of Vermont. The
Burlington Stade marked the final Pleistocene glacial advance, which progressed across Vermont
from the north-northwest, covering the Champlain Lowland, all of the Green Mountains north of
Brandon, and the Memphremagog Basin in northern Vermont (Stewart and MacClintock, 1969).
Between each advance was a period of weathering and erosion called an interstade. Glacial lakes
occupied several valleys during the interstades and following the final retreat of glaciers from
Vermont, which occurred about 12,500 years ago (Stewart and MacClintock, 1969). Major glacial
lakes include Lake Vermont, which occupied the Champlain Lowland; Lake Hitchcock in the
Connecticut Valley; a lake in the Manchester-Bennington area of the southern Vermont Valley; and
lakes that occupied the Memphremagog Basin and the Lamoille, Winooski, Huntington, and Mad
Dog River valleys in north-central Vermont (Stewart and MacClintock, 1969). Glacial lake
deposits in parts of the Champlain Lowland are overlain by marine deposits from a postglacial
incursion of the sea into the lowland about 11,900 years ago (Stone and Borns, 1986) when sea
level rose due to input of water from melting glacial ice. The sea subsequently retreated when the
land surface rose due to postglacial rebound.
Figure 5 is a generalized map of glacial deposits in Vermont. Three main classes of glacial
deposits are shown on the map—tiU, glaciofiuvial deposits, and glacial lake and marine sediments.
Each of these general units is further subdivided into units which reflect the origin of the deposits
in more detail. Except where noted, the following discussion is.condensed from Stewart and
MacClintock (1969,1970).
Till is the most common and widespread type of glacial deposit in Vermont. It is an
unsorted deposit of gravel, sand, silt, and clay, with occasional cobbles and boulders, that was left
by the glacier. Thickness of the tifl ranges from a thin, discontinuous veneer of less than one laeter
to more than 30 meters in some valleys, but it is generally less than 8 m thick. Till is typically
thinner on uplands and thicker in valleys. The composition of the till typically reflects the
underlying bedrock, and sandy till is much more common in Vermont than clayey till. There are
two distinctly different types of till in Vermont. One is a dense, compact till containing rounded,
striated boulders and a relatively high amount of erratics (cobbles and boulders from distant
bedrock sources), called basal till. The clay content of basal till is generally less than 30 percent;
however, basal till usually contains a significant amount of silt, which together with the clay is
responsible for the compactness of the basal till. The other type of till is a loosely packed, very
sandy till containing angular boulders of local bedrock and little or no clay. This type of till is
IV-11 Reprinted from USGS Open-File Report 93-292-A
-------
EXPLANATION
[ I TILL—unstratified mix of gravel, sand, silt, and
I 1 clay
MORAINE—irregular ridge of till formed at the
margins of retreating glaciers
GLAaOELUVIALDEPOSrrS—mainly sand
and gravel deposits of kames, kame terraces,
kame moraines, eskers, outwash, and recent
alluvium
HUD LAKE-BOTTOM SEDIMENTS— stratified sUt
and clay deposited by glacial lakes; may be
varved
COARSE-GRAINED LAKE AND MARINE
SEDIMENTS— sand and gravel deposits of
lacustrine deltas, and marine and lacustrine
terraces and beaches
MARINE CLAY—stratified silt and clay
deposited by postglacial marine incursions
BEDROCK EXPOSURES
Figure 5. Generalized glacial geologic map of Vermont (after Stewart and MacClintock, 1969).
-------
called ablation till. Ablation till is the upper till unit, always overlying either basal till or bedrock.
Often the ablation till and underlying basal till have fabrics (orientations of elongated pebbles and
glacial striations) oriented in different directions, indicating that the two till unite were deposited
during different glacial episodes. These two types of til are found throughout most of New
England and are more commonly referred to simply as the "upper till" and "lower till" (Richmond
and Fullerton, 1991,1992). The two types of till are not differentiated on the surficial geologic
map of Vermont (Stewart and MacClintock, 1970), of which figure 5 is a generalized version.
Glacial landforms typically associated with till include dramlins, kettles, and moraines. Moraines
are accumulations of till deposited at the margins of retreating ice and are not common features to
Vermont Only a few significant moraines occur in three regions in Vermont—the St. Johnsbury
region in northeastern Vermont, the Rutland area in the west-central portion of the State, and the
Manchester-Bennington area of southwestern Vermont (fig. 5).
Glatiofluvial deposits are stratified sediments deposited by glacial meltwater adjacent to, or
in front of, the ice margin. These ice-marginal or ice-contact deposits include karnes, kame
terraces, kame moraines, eskers, and outwash deposits. Characteristic of all types of glaciofluvial
deposits is their coarse texture, being composed primarily of sand and gravel. Kame terraces
formed between the edge of a glacier and a valley wall. They are one of the most common glacial
features in Vermont and constitute a significant source for sand and gravel in the State. Kame
moraines are deposits of gravel that formed in front of the glacier and have topography similar to
that of a till moraine. Eskers are sinuous ridges composed of outwash sand and gravel deposited
by rivers that flowed in tunnels underneath an ice sheet or valley glacier. Eskers in Vermont range
from highly discontinuous to long, sinuous ridges that can be traced for many kilometers; for
example, an esker in the Passumpic Valley extends from West Burke southward beyond St.
Johnsbury, a distance of almost 39 km (Stewart and MacClntock, 1969). Outwash gravel was
deposited in some valleys by rivers that drained the melting glaciers; however, it is a relatively
uncommon type of glacial deposit in Vermont
Lacustrine (lake) and marine sediments are layered silts and clays deposited by large
postglacial lakes and in marine (ocean) environments, respectively. Because the valleys and
lowlands were the sites of final melting of stagnant ice masses, drainage was blocked and many
small lakes developed. Larger lakes, including Lake Vermont, which occupied the Champlain
Lowland, were dammed by glacial ice or by moraines. Lake-bottom sediments consist of silt and
clay, shallow-water sediments are composed primarily of sand, and beach and delta deposits
contain primarily sand and gravel. Marine sediments have characteristics similar to lacustrine
sediments, in that they also are classified into fine-grained bottom deposits, sandy shallow-water
deposits, and sand and gravel beach and deltaic deposits. Marine sediments were deposited in the
Champlain Lowland when sea level rose and the ocean invaded the Champlain Lowland.
SOILS
Soils in Vermont include Inceptisols, mineral soils with horizons of alteration or
accumulation of metal oxides such as iron, aluminum, or manganese; Spodosols, acid soils with
subsurface accumulations of organic matter and compounds of aluminum and iron; Entisols,
mineral soils with no discernible horizons because their parent material is inert (such as quartz
sand) or because the soils are very young; and Alfisols, moist soils with subsurface horizons of
clay accumulation (U.S. Soil Conservation Service, 1987). Figure 6 is a generalized soil map of
Vermont The following discussion is condensed from the general soils map of Vermont (U.S.
IV-13 Reprinted from USGS Open-File Report 93-292-A
-------
Figure 6, Generalized soils map of Vermont (after U.S. Department of Agriculture, 1982)
-------
GENERALIZED SOIL MAP OF VERMONT
EXPLANATION
Soils on Jake plains in the Champlain Valley—silly clays and clays with low permeability
**.*"•] Soils on glacial till uplands in the Champlain and Vermont Valleys--silty, sandy, and gravelly loams
''": '" '' with low to moderate permeability
Soils within the Taconic Mountains and southeastern uplands adjacent to the Connecticut River
Areas dominated by deep, loamy soils—silty and sandy loams with low to moderate permeability
|||i|| Areas dominated by shallow and moderately deep, loamy soils—silty loams with moderate
""•' permeability
Soils within the Green Mountains and associated foothills
Areas dominated by deep, loamy soils—silty loams, fine sandy loams, and gravelly loams with low
to moderate permeability
Areas dominated by shallow and moderately deep, loamy soils—tine sandy loam and gravelly
sandy loams with moderate permeability
Soils at high elevations with cryic soil temperature—silty and fine sandy loams with moderate
permeability
Soils within eastern upland areas—loam, silty loam, and fine sandy loam with moderate permeability
[>•*/!?: Sandy and gravelly soils developed on stream terraces, outwash plains and terraces, karnes,
''•'••'•I eskers, moraines, and deltas—sand, loamy sand, gravelly sand, and gravel with moderate to
permeability
high
Soils on bottomlands—silty and fine sandy loam with moderate permeability
Soils in swamps and marshes—Histosols (muck and peat)
-------
Department of Agricultuie, 1982) and from soil interpretation records ("Soils-5" forms) provided
by the U.S. SoU Conservation Service for each of the soil series in the State (the information on
the soil interpretation records can also be found in county soil surveys). State- and county-scale
soil survey reports should be consulted for more detailed descriptions and information.
Soils developed on glacial lake deposits in the Charnplain Lowland (fig. 6) are deep, poorly
to moderately drained, silty loam, silty clay, and clay. This map unit also includes soils formed on
deposits of small lake plains in northwestern Vermont These soils have low permeability and are
typically wet at least part of the year. Soils of marshes and swamps occupy some low-lying areas
in the Charnplain Lowland (fig. 6). These soils are organic-rich Histosols derived from muck and
peat These soils have low to high permeability but are commonly water-saturated.
Soils formed in glacial till on uplands within the Charnplain and Vermont Valleys consist of
shallow to deep, poorly to well drained, silty, sandy, and gravelly loams and loams. The till
parent materials are derived primarily from limestone and metamorpMe rocks. Soils of this group
with clayey B horizons have low permeability; soils of this group with friable (loosely packed,
easily separated, and permeable) substrata have moderate permeability.
Soils of the Taconic Mountains and soils of the uplands adjacent to the Connecticut River in
southeastern Vermont are represented by two map units (fig. 6). Soils on lower slopes and valley
floors are deep, moderately well to well drained, silty and sandy loams developed in till. Soils of
this type, have firm substrata, low permeability, and are seasonally wet Soils on steeper slopes in
the Taconic Mountains and southeastern Vermont are shallow to moderately deep, excessively
drained silt loams developed in glacial till with moderate permeability. Soils of both units are
developed on glacial tills derived primarily from schist, phyllite, slate, and shale.
Soils of the Green Mountains and associated foothills cover about one-third of the State's
land area (fig. 6). Moderately deep to very deep, poorly drained to moderately well drained, silty,
sandy, and locally gravelly loams developed on compact, loamy till derived from schist and gneiss
occur in the southern Green Mountains and in the foothills in the northern part of the State. Most
of these soils have firm substrata and low permeability, and poorly drained soils of this unit may
be wet at least part of the year. About one-third of the soils in this map area have moderate
permeability. Soils in the northern Green Mountains are shallow to moderately deep, well drained,
silty loams, fine sandy loams, and locally gravelly loams formed on loamy glacial till derived from
schist and other metamorphic rocks. These soils have moderate permeability.
Soils at high elevations with cryic soil temperature (mean annual soil temperature is 0-8°C
at 50 cm depth) are shallow to moderately deep, well drained silty and fine sandy loams developed
on glacial till derived from mica schist. These soils have moderate permeability.
Soils within the eastern upland areas of Vermont are shallow to deep, well drained to
ercessively drained, fine sandy loams and silty loams developed in glacial till that is derived
primarily from schist These soils have moderate permeability and typically have friable substrata.
Soils developed on glacial outwash plains and outwash terraces, kames, eskers, moraines,
lacustrine deltas, and stream terraces are deep, well drained to excessively drained (poorly drained
on some floodplains), sands and loamy sands to gravelly sands and gravels. These soils occur
adjacent to the Connecticut River and in the lower parts of many drainages in the upland areas of
Vermont (fig, 6). These soils have moderately high to high permeability, but have low
permeability to air if they are wet Soils of bottomlands and floodplains are deep, poorly drained
to moderately drained, silty loams and fine sandy loams. These soils have moderate permeability
but they are commonly wet and subject to flooding.
IV-16 Reprinted from USGS Open-File Report 93-292-A
-------
RADIOACTIVITY
An aeroradiometric map of Vermont (fig. 7) compiled from the National Uranium
Resource Evaluation (NURE) flightline data (Duval and others, 1989) shows several areas of high
radioactivity (> 2.5 ppm) associated with rocks of the Mount Holly complex, phyllites and slates in
the western Taconic Mountains (possibly the Pawlet Formation), granite exposed at Ascuteny
Mountain, the Cheshire Quartzite in several parts of the Green Mountains, carbonaceous phyllite
and schist in the Pinney Hollow Formation, graphitic schist and phyllite in several areas of the
Green Mountains and Vermont Piedmont, and several of the granitic bodies in the Vermont
Piedmont and Northeastern Highlands. Uranium deposits in hydrothermal veins account for a
number of the anomalies in these rocks. Low radioactivity (<1.5 ppm eU) is found in
northernmost Vermont, southern Vermont and parts of the Champlain Lowlands and Vermont
Valley, associated most commonly with mafic metavolcanic and igneous rocks, diorite, and several
of the Paleozoic carbonate and clastic rock unite. Moderate radioactivity (1.5-2.5 ppm) covers
most of central Vermont, especially in the Vermont Piedmont and Green Mountains.
There are several reports on radioactivity and uranium occurrences in Vermont Popenoe's
map (1964) of the aerial radioactivity of the southern half of Vermont includes geologic maps and
descriptions describing the data and its association with geology. Several NURE reports present
aerial radioactivity data (compiled in Duval and others, 1989) and stream sediment data for parts of
Vermont (Cook and Roller, 1980; Cook, 198 la, b, c). Ratte and Vanacek (1980) have compiled a
radioactivity map of Vermont derived from Popenoe (1964), NURE, and other available aerial and
ground radioactivity surveys, as well as uranium occurrence data. Olszewski and Boudette (,1986)
have compiled a generalized geologic map of New England with emphasis on uranium endowment
and radon production. Washington (1988) discusses some of the deposits containing the highest
concentrations of uranium in southern Vermont.
In the Champlain Lowlands and Vermont Valley, Ratt6 and Vanacek (1980) have identified
the Clarendon Springs and Dunham Dolomites as possible sources of uranium. Samples from
Milton and Highgate have yielded Mgh uranium concentrations in carbonate breccias of the
Clarendon Springs. The radioactivity map of Duval and others (1989, fig. 7) shows some high to
moderate radioactivity, particularly in Chittenden County associated with the Paleozoic clastic and
carbonate rocks including the dolomites. Olszewski and Boudette (1986) classify these rocks as
variable, with increasing uranium as metamorphic grade increases, and note local uranium
concentrations in fractures and faults.
Rattf and Vanacek's (1980) uranium province map shows all the rocks of the Green
Mountains as possible uranium resources. According to the authors, uranium is concentrated in
veins within quartzite, in tourmaline-bearing pegmatites, in migmatite, in biotite-rich zones in mica
schist, along fracture surfaces, and in shear zones. Uranium is also associated with graphite,
pyrite, garnet, and blue quartz. High concentrations of accessory minerals such as uraniferous
monazite, allanite, and zircon are local sources of high uranium concentrations. These minerals are
common in the schists and gneisses of Vermont and may form placer-type deposits in Pleistocene
to Recent gravels in river and stream sediments. Washington (1988) describes an unusually
abundant occurrence of uraniferous allanite in a extensive hydrothermal deposit at Searsburg
Ridge. Olszewski and Boudette (1986) classified the Green Mountains as variably low to high
with a tendency for enrichment in the higher-grade metamorphic zones of quartzo-feldspathic
(granitic) rocks, in veins, in accessory minerals and along grain boundaries.
IV-17 Reprinted from USGS Open-File Report 93-292-A
-------
Rgure 7. Aerial radiometric map of Vermont (after Duval and others, 1989). Contour lines at 1.5
and 2.5 ppra equivalent uranium (eU). Pixels shaded at 0.5 ppm eU increments; darker pixels
have lower eU values; white indicates no data.
-------
The Taconic Mountains have generally moderate to high radioactivity (fig. 7) but only a
few uranium occurrences are reported from, the northernmost part of the Taconic Mountains in the
St. Catherine Formation (Ratte and Vanacek, 1980). The radioactivity (fig. 7) appears to be
associated with carbonaceous and pyritic phyllites and slates of the Pawlet Formation. Similar
kinds of black and carbonaceous slates also comprise the West Hill and West Castleton
Formations.
Olszewski and Boudette (1986) classified the igneous plutdns of the Vermont Piedmont
and Northeastern Highlands as two-mica granites with moderate to very high uranium enrichment
Uranium in these rocks occurs as primary uranium oxides such as uraninite or in abundant
accessory minerals. They classify the Paleozoic metasedimentary and metavolcanic rocks of these
areas as variable, with increasing uranium as metamorphic grade increases and local uranium
concentrations in fractures and faults. Ratte and Vanacek (1980) designated the igneous plutons
and granites of Ascuteny and Manadonock Mountains as uranium resources. These two mountains
have distinct radiometric highs but the other plutons are variable in their radioactivity. The large
pluton that underlies Knox, Spruce, and Hardwood Mountains along the Caledonia-Washington
county line and the pluton in the vicinity of Lake Willoughby have distinct radiometric highs. The
Giles Mountain and Waits River Formations underlie most of the Vermont Piedmont and several
analyses cited in Ratte and Vanacek (1980) indicate an overall enrichment of uranium but at
relatively lower concentrations, between 3 and 7 ppm of uranium.
INDOOR RADON
Indoor radon data from 710 homes sampled in the State/EPA Residential Radon Survey
conducted in Vermont during the winter of 1989 are shown in figure 8 and listed in Table 1. A
map of counties is included for reference (fig. 9). Indoor radon was measured by charcoal
canister. The maximum value recorded in the survey was 47 pCi/L in Addison County. The
average indoor radon for the State was 2.6 pCi/L and the 16.6 percent of the homes tested had
indoor radon levels exceeding 4 pCi/L. Notable counties include Addison and Caledonia, with
average indoor radon concentrations greater than 4 pCi/L, probably associated with the
metamorphic and igneous rocks of the Green Mountains and Vermont Piedmont and with elevated
uranium concentrations in some of the Paleozoic sedimentary rocks. Low (< 2 pCi/L) county
indoor radon averages in Chittenden, Franklin, and Grand Isle Counties appear to be associated
with the Champlain Lowlands. Generally moderate county indoor radon averages are found
throughout the rest of Vermont.
GEOLOGIC RADON POTENTIAL
The geologic radon potential of the Champlain Lowlands is low, with areas of locally
moderate to high radon potential possible. The Vermont Valley has generally moderate geologic
radon potential. Clay-rich soils with low permeability dominate the lowlands and include glacial
lake and marine clays which probably reduce the radon potential significantly. Radioactivity is
generally low with a few scattered high and moderate areas that appear to be associated with the
Clarendon Springs Formation and possibly with black shales and slates in surrounding rock units.
Indoor radon levels in the counties underlain by the Champlain Lowlands are generally less than 4
pCi/L except in Addison County, where out of 26 readings, six were greater than 4 pCi/L and of
these, two were greater than 20 pCi/L.
IV-19 Reprinted from USGS Open-File Report 93-292-A
-------
Bsmt & 1st Floor Rn
% > 4 pCi/L
OtolO
11 to 20
21 to 30
LXXXXXN
4
lOMfles
Bsmt. & 1st Floor Rn
Average Concentration (pCi/L)
0.0 to 1.9
2.0 to 4.0
4.1 to 5.0
o IXXXXXXXs
2 1^1
Figure 8. Screening indoor radon data from the EPA/State Residential Radon Survey of
Vermont, 1988-89. Data are from 2-7 day charcoal canister tests. Histograms in map legends
show the number of counties in each category. The number of samples in each county (See
Table 1) may not be sufficient to statistically characterize the radon levels of the counties, but
they do suggest general trends. Unequal category intervals were chosen to provide reference to
decision and action levels.
-------
TABLE 1. Screening indoor radon data from the EPA/State Residential Radon Survey of
Vermont conducted during 1988-89, Data represent 2-7 day charcoal canister measurements
from the lowest level of each home tested.
COUNTY
ADDISON
BENNINGTON
CALEDONIA
CHTTTENDEN
ESSEX
FRANKLIN
GRAND ISLE
LAMOILLE
ORANGE
ORLEANS
RUTLAND
WASHINGTON
WINDHAM
WINDSOR
NO. OF
MEAS.
26
58
51
102
14
24
12
29
43
50
70
101
51
79
MEAN
5.0
2.7
4.2
1.4
2.3
1.7
1.7
2.2
3.5
2.2
2.0
2.8
3.0
2.8
GEOM.
MEAN
1.5
1.5
2.2
0.8
• 1.3
0.8
0.7
1.5
2.0
1.3
1.1
1.7
1.8
1.4
MEDIAN
1.1
1.7
2.1
0.8
1.1
0.7
1.0
1.5
2.1
1.3
1.1
1.7
1.8
1.7
STD.
DEV.
10.3
2.8
7.1
1.8
3.6
3.4
2.3
2.0
3.9
2.7
2.7
4.0
3.3
3.8
MAXIMUM
47.0
12.8
41.8
10.6
14.5
15.6
7.5
7.5
17.4
15.1
16.5
35.2
17.9
23.9
%>4pCi/L
23
24
22
8
7
8
17
17
28
8
16
17
18
20
%>20pCi/L
8
0
4
0
0
0
0
0
0
0
0
1
0
1
-------
w-
10 20 30
* * tm
-------
Addison County is also underlain partly by the Green Mountains, which have been ranked
moderate in radon potential; however, the radon potential is actually highly variable. Areas of the
mountains with locally high radon potential are metamorphic rocks of Proterozoic age, including
quartzite, graphite and pyrite-bearing schists and slates, migmatitic schist and gneiss, biotite-rich
zones in mica schist, and schist and gneiss with high concentrations of the minerals monazite,
allanite, and zircon, the Cheshire Quartzite, and local vein and fault deposits of uranium. Mafic
metamorpMc rocks such as amphibolite, hornblende gneiss, gabbro, and serpentinite are low in
geologic radon potential. Permeability of the soils is generally moderate with some low
permeability areas. The glacial deposits are mostly locally-derived tills. Radioactivity is variable-
low in the southern portion with local high (>2.5 ppm eU) radioactivity anomalies, moderate to
high radioactivity in the central portion, and low in the north. Many of the uranium occurrences
seem to be concentrated in the southern and central parts of the Green Mountains.
The Taconic Mountains are also moderate in radon potential. Radioactivity is generally
moderate to high, and several rock types appear to have elevated levels of uranium, especially the
carbonaceous sedimentary rocks of the Pawlet Formation. Elevated concentrations of uranium in
the black to gray phyllites and slates are probably the principal radon sources in this terrain. Soils
generally have moderate to locally low permeability.
The Vermont Piedmont has moderate but variable geologic radon potential. Much of the
area is underlain by mafic rocks, such as amphibolites, with low radon potential. Granites,
granitic gneiss and schist, and carbonaceous or graphitic slate and phyUite have the potential for
moderate to high radon. Radioactivity in the Piedmont is low to moderate with a few highs. Soils
have moderate permeability with some low and high permeabilities. The Northeastern Highlands
have moderate radon potential. Plutonic igneous rocks are abundant in this area and in the northern
half of the Vermont Piedmont, but only a few of the plutons have distinct radiometric anomalies
associated with them. Further, indoor radon for counties underlain by these rocks is moderate
with the exception of Caledonia County. It has one high indoor radon measurement of 41.8 pCi/L.
Eleven of the 51 measurements in the county are greater than 4 pCi/L.
SUMMARY
For the purpose of this assessment, Vermont has been divided into six geologic radon
potential areas and each area assigned a Radon Index (RI) and a Confidence Index (CI) score
(Table 2). The RI is a semi-quantitative measure of radon potential based on geology, soils,
radioactivity, architecture, and indoor radon. The CI is a measure of the relative confidence of the
RI assessment based on the quality and quantity of the data used to assess geologic radon potential
(see the Introduction chapter to this regional booklet for more information).
The radon potential of Vermont is generally moderate but certain rock types appear to be
associated with both high and low radon potential throughout the State. Rocks in Vermont with
locally high geologic radon potential include granitic and micaceous metamorphic rocks in parts of
the Green Mountains, Vermont Piedmont, and Northeastern Highlands, some granite plutons in
the Northeastern Highlands and Vermont Piedmont, carbonaceous and graphitic phyllites, slates,
and schists in parts of the Taconic Mountains, Green Mountains, and Vermont Piedmont and some
clastic and carbonate sedimentary rocks in the Green Mountains, Vermont Valley, and Champlain
Lowlands, including the Cheshire quartzite, Clarendon Springs, Dunham Dolomite, and related
black shales. Low geologic radon potential is associated with mafic igneous and metamorphic
IV-23 Reprinted from USGS Open-File Report 93-292-A
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rocks including amphibolite, hornblende gneiss, gabbro, and serpentinite found throughout the
State, especially in the Green Mountains, Vermont Piedmont, and Northeastern Highlands.
This is a generalized assessment of the geologic radon potential of Vermont 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
rjot 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-24 Reprinted from USGS Open-File Report 93-292-A
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TABLE 2. RI and CI scores for geologic radon potential areas of Vermont
Champlain Lowlands
Taconic Mountains
FACTOR
RI
CI
Mod High
RI
CI
Mod High
Vermont Valley
RI
CI
INDOOR RADON
RADIOACTIVITY
GEOLOGY
SOIL PERM.
ARCHITECTURE
GFE POINTS
TOTAL
1
1
2
1
3
0
8
Low
3
3
2
3
-
-
11
High
Green Mountains
FACTOR
INDOOR RADON
RADIOACTIVITY
GEOLOGY
SOIL PERM.
ARCHITECTURE
GFE POINTS
TOTAL
RI
2
2
2
2
3
0
11
CI
3
3
3
3
-
-
12
2.
2
2
2
3
0
11
Mod
3
3
3
3
-
-
12
High
Piedmont
RI
2
2
2
2
3
0
11
CI
3
3
3
3
-
-
12
2 -
2
2
2
3
0
11
Mod
3
3
3
3
-
-
12
High
ME Highlands
RI
2
2
2
2
3
0
11
CI
3
3
3
3
-
-
12
Mod High
RADON INDEX SCORING:
Radon potential category
Point range
LOW 3-8 points
MODERATE/VARIABLE 9-11 points
HIGH > 11 points
Possible range of points = 3 to 17
CONFIDENCE INDEX SCORING:
Probable screening indoor
radon average for area
LOW CONFIDENCE
MODERATE CONFIDENCE
HIGH CONFIDENCE
4-6 points
7-9 points
10 - 12 points
Possible range of points = 4 to 12
<2pCi/L
2-4pCi/L
> 4 pCi/L
IV-25 Reprinted from USGS Open-File Report 93-292-A
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REFERENCES CITED IN THIS REPORT
AND GENERAL REFERENCES PERTAINING TO RADON IN VERMONT
Bennison, A.P., 1976, Geological Highway Map of the Northeastern Region: American
Association of Petroleum Geologists, U.S. Geological Highway Map Series, Map 10,
scale 1:2,000,000.
Cook, J.R., 1981a, Albany 1° x 2° NTMS area, Connecticut, New Hampshire, Massachusetts,
New York, and Vermont—Data Report—National Uranium Resource Evaluation Program,
Hydrogeoehemical and Stream Sediment Reconnaissance: U.S. Department of Energy
GJBX-107(81), 17 p.
Cook, J.R., 1981b, Glen Falls 1° x 2° NTMS area, New Hampshire, New York, and Vermont-
Data Report—National Uranium Resource Evaluation Program, Hydrogeoehemical and
Stream Sediment Reconnaissance: U.S. Department of Energy GJBX-70(81), 17 p.
Cook, J.R., 198 Ic, Lake Champlain 1° x 2° NTMS area, New York, Vermont, and New
Hampshire—Data Report—National Uranium Resource Evaluation Program,
Hydrogeoehemical and Stream Sediment Reconnaissance: U.S. Department of Energy
GJBX-108(81), 17 p.
Cook, J.R. and Koller, G.R., 1980, Lewiston 1° x 2° NTMS area, Maine, New Hampshire, and
Vermont—Data Report—National Uranium Resource Evaluation Program,
Hydrogeoehemical and Stream Sediment Reconnaissance: U.S. Department of Energy
GJBX-14(81), 17 p.
Doll, C.G., Cady, Thompson Jr., J.B., and Billings, M.P., 1961, Centennial Geologic Map of
Vermont: Vermont Geological Survey, scale 1:250,000.
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.
Facts on File publications, 1984, State Maps on File: New England.
Hall, F.R., Boudette, E.L., and Olszewski, W.J., 1987, Geologic Controls and radon occurrence
in New England, in Graves, Barbara, ed., Radon, Radium, and Other Radioactivity in
Ground Water: Lewis Publishers, p. 15-30,
Olszewski, W.J., Jr., and Boudette, E.L, 1986, Generalized bedrock geologic map of New
England with emphasis on uranium endowment and radon production, Environmental
Protection Agency, Open File Map.
Popenoe, P., 1964, Aeroradioactivity of parts of east-central New York and west-central New
England: U.S. Geological Survey Map GP-358, scale 1:250,000.
Ratt£, C, and Vanacek, D., 1980, Radioactivity Map of Vermont: Vermont Geological Survey,
File No. 1980-1, rev. 3,3 plates with text
IV-26 Reprinted from USGS Open-File Report 93-292-A
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Richmond, G.M., and Fullerton, D.S., eds., 1991, Quaternary geologic map of the Boston 4° x 6°
quadrangle, United States and Canada: U.S. Geological Survey Miscellaneous
Investigations Map 1-1420, sheet NK-19, scale 1:1,000,000.
Richmond, G.M., and Fullerton, D.S., eds., 1992, Quaternary geologic map of the Hudson River
4° x 6° quadrangle, United States and Canada: U.S. Geological Survey Miscellaneous
Investigations Map 1-1420, sheet NK-18, scale 1:1,000,000.
Stewart, D.P., and MacClintock, P., 1969, The surficial geology and Pleistocene history of
Vermont: Vermont Geological Survey Bulletin 31,251 p,
Stewart, D.P., and MacClintock, P., 1970, Surficial geologic map of Vermont: Vermont
Geological Survey, scale 1:250,000.
Stone, B.D., and Borns, H.W., Jr., 1986, Pleistocene glacial and interglacial stratigraphy of New
England, Long Island, and adjacent Georges Bank and Gulf of Maine, in Sibrava, V.,
Bowen, D.Q., and Richmond, G.M., eds., Quaternary Glaciations in the Northern
Hemisphere: Quaternary Science Reviews, v. 5, p. 39-52.
U.S. Department of Agriculture, 1982, Vermont general soil map: Soil Conservation Service,
scale 1:250,000.
U.S. Soil Conservation Service, 1987, Soils: U.S. Geological Survey National Atlas sheet
38077-BE-NA-07M-00, scale 1:7,500,000.
Washington, P.A., 1988, Proper scaling of radon surveys: A perspective based on natural radon
sources in southern Vermont: Northeastern Environmental Science, v. 7, p. 40-44.
IV-27 Reprinted from USGS Open-File Report 93-292-A
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EPA's Map of Radon Zones
The USGS' Geologic Radon Province Map is the technical foundation for EPA's Map
of Radon Zones. The Geologic Radon Province Map defines the radon potential for
approximately 360 geologic provinces. EPA has adapted this information to fit a county
boundary map in order to produce the Map of Radon Zones.
The Map of Radon Zones is based on the same range of predicted screening levels of
indoor radon as USGS' Geologic Radon Province Map. EPA defines the three zones as
follows: Zone One areas have an average predicted indoor radon screening potential greater
than 4 pCi/L. Zone Two areas are predicted to have an average indoor radon screening
potential between 2 pCi/L and 4 pCi/L. Zone Three areas are predicted to have an average
indoor radon screening potential less than 2 pCi/L.
Since the geologic province boundaries cross state and county boundaries, a strict
translation of counties from the Geologic Radon Province Map to the Map of Radon Zones
was not possible. For counties that have variable radon potential (i.e., are located in two or
more provinces of different rankings), the counties were assigned to a zone based on the
predicted radon potential of the province in which most of its area lies. (See Part I for more
details.)
VERMONT MAP OF RADON ZONES
The Vermont Map of Radon Zones and its supporting documentation (Part IV of this
report) have received extensive review by Vermont geologists and radon program experts.
The map for Vermont 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 Vermont" — 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 1 EPA office or the
Vermont radon program for information on testing and fixing homes. Telephone numbers and
addresses can be found in Part II of this report.
V-l
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VERMONT - EPA Map of Radon Zones
The purpose of this map is to assist Nation a!, State and focal oraanfeaflone
to target their resources and to implement radon-resistant building codes.
This map fe not Intended to dttefmkw V a homo in a s*wn w»» should be tested
for radon. Homes wrth elevated levels of radon have been found in aU three
zones. All homes should bo totted, regardless of zone denigration.
GRAND ISLE
Zone 1
Zone 2 Zone 3
IMPORTANT: Consult the publication entWsd 'Preliminary Geologic Radon
Potential Assessment of Vermont" before using this map. This
document contains information on radon potential variations within counties.
EPA also recommends that this map be supplemented with any available
(oca) data in order to further understand and predict the radon potential of a
specific area.
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