United States
Environmental Protection
Agency
Air and Radiation
(6604J)
402-R-93-027
September 1993
v>EPA EPA's Map of Radon Zones
CONNECTICUT
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EPA'S MAP OF RADON ZONES
CONNECTICUT
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 RatcIifF,
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:INTRODUCnON
III. REGION 1 GEOLOGIC RADON POTENTIAL
SUMMARY
V. PRELIMINARY GEOLOGIC RADON POTENTIAL
ASSESSMENT OF CONNECTICUT
V. EPA'S MAP OF RADON ZONES - CONNECTICUT
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OVERVIEW
Sections 307 and 309 of the 1988 Indoor Radon Abatement Act (IRAA) direct EPA to
identify areas of the United States that have the potential to produce elevated levels of radon.
EPA, the U.S. Geological Survey (USGS), and the Association of American State Geologists
(AASG) have worked closely over the past several years to produce a series of maps and
documents which address these directives. The EPA Map of Radon Zones is a compilation of
that work and fulfills the requirements of sections 307 and 309 of IRAA. The Map of Radon
Zones identifies, on a county-by-county basis, areas of the U.S. that have the highest potential
for elevated indoor radon levels (greater than 4 pCi/L).
The Map of Radon Zones is designed to assist national, State and local governments
and organizations to target their radon program activities and resources. It is also intended to
help building code officials determine areas that are the highest priority for adopting radon-
resistant building practices. The Map of Radon Zones should not be used to determine if
individual homes in any given area need to be tested for radon. EPA recommends that all
homes be tested for radon, regardless of geographic location or the zone designation of
the county in which they are located.
This document provides background information concerning the development of the
Map of Radon Zones. It explains the purposes of the map, the approach for developing the
map (including the respective roles of EPA and USGS), the data sources used, the conclusions
and confidence levels developed for the prediction of radon potential, and the review, process
that was conducted to finalize this effort.
BACKGROUND
Radon (Rn222) is a colorless, odorless, radioactive gas. It comes from the natural
decay of uranium that is found in nearly all soils. It typically moves through the ground to
the air above and into homes and other buildings through cracks and openings in the
foundation. Any home, school or workplace may have a radon problem, regardless of
whether it is new or old, well-sealed or drafty, or with or without a basement. Nearly one out
of every 15 homes in the U.S. is estimated to have elevated annual average levels of indoor
radon.
Radon first gained national attention in early 1984, when extremely high levels of
indoor radon were found in areas of Pennsylvania, New Jersey, and New York, along the
Reading Prong-physiographic province. EPA established a Radon Program in 1985 to assist
States and homeowners in reducing their risk of lung cancer from indoor radon.
Since 1985, EPA and USGS have been working together to continually increase our
understanding of radon sources and the migration dynamics that cause elevated indoor radon
levels. Early efforts resulted in the 1987 map entitled "Areas with Potentially High Radon
Levels." This map was based on limited geologic information only because few indoor radon
measurements were available at the time. The development of EPA's Map of Radon Zones
and its technical foundation, USGS' National Geologic Radon Province Map, has been based
on additional information from six years of the State/EPA Residential Radon Surveys,
independent State residential surveys, and continued expansion of geologic and geophysical
information, particularly the data from the National Uranium Resource Evaluation project.
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Purpose of the Map of Radon Zones
EPA's Map of Radon Zones (Figure 1) assigns each of the 3141 counties in the
United States to one of three zones:
o Zone 1 counties have a predicted average indoor screening level > than
4 pCi/L
o Zone 2 counties have a predicted average screening level > 2 pCi/L and
< 4 pCi/L
o Zone 3 counties have a predicted average screening level < 2 pCi/L
The Zone designations were determined by assessing five factors that are known to be
important indicators of radon potential: indoor radon measurements, geology, aerial
radioactivity, soil parameters, and foundation types.
The predictions of average screening levels in each of the Zones is an expression of
radon potential in the lowest liveable area of a structure. This map is unable to estimate
actual exposures to radon. EPA recommends methods for testing and fixing individual homes
based on an estimate of actual exposure to radon. For more information on testing and fixing
elevated radon levels in homes consult these EPA publications: A Citizen's Guide to Radon,
the Consumer's Guide to Radon Reduction and the Home Buyer's and Seller's Guide to
Radon.
EPA believes that States, local governments and other organizations can achieve
optimal risk reductions by targeting resources and program activities to high radon potential
areas. Emphasizing targeted approaches (technical assistance, information and outreach
efforts, promotion of real estate mandates and policies and building codes, etc.) in such areas
addresses the greatest potential risks first
EPA also believes that the use of passive radon control systems in the construction of
new homes in Zone 1 counties, and the activation of those systems if necessitated by follow-
up testing, is a cost effective approach to achieving significant radon risk reduction.
, The Map of Radon Zones and its supporting documentation establish no regulatory
requirements. Use of this map by State or local radon programs and building code officials is
voluntary. The information presented on the Map of Radon Zones and in the supporting
documentation is not applicable to radon in water.
Development of the Map of Radon Zones
The technical foundation for the Map of Radon Zones is the USGS Geologic Radon
Province Map. In order to examine the radon potential for the United States, the USGS
began by identifying approximately 360 separate geologic provinces for the U.S. The
provinces are shown on the USGS Geologic Radon Province Map (Figure 2). Each of the
geologic provinces was evaluated by examining the available data for that area: indoor radon
measurements, geology, aerial radioactivity, soil parameters, and foundation types. As stated
previously, these five factors are considered to be of basic importance in assessing radon
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Figure 1
EPA Map of Radon Zones
Zone designation for Puerto Rico is under development
Guam — Preliminary Zone designation.
The purpose of this mop Is to assist Notional, State and local organizations to target their resources and to implement radon-resistant building codes.
This mop is not Mended to be used to determine if o home in a given zone should be tested for radon. Homes with elevated levels of radon have been foun,
in oil three zones. All homes should bs tested, regardless of geographic location.
Consult the EPA Mop of Radon Zones document (EPA-402-R-93-071) before using this mop. This document contains information on radon potential variations within counties.
EPA also recommends that th,s map be supplemented with any available local data in order to further understand and predict the radon potential of o specific area.
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ligure 2
GENERALIZED GEOLOGIC RADON POTENTIAL OF THE UNITED STATES
by the U.S. Geological Survey
500
Geologic Radon
Potential
(Predicted Average
Screening Measurement)
LOW (<2pCi/L)
mm MODERATE/VARIABLE
iHl{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: 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, whhin-county variations in radon potential are not shown on the Map of Radon
Zones. EPA recommends that users who may need to address specific within-county
variations in radon potential (e.g., local government officials considering the
implementation of radon-resistant construction codes) consult USGS' Geologic Radon
Province Map and the State chapters provided with this map for more detailed
information, as well as any locally available data.
Map Validation
The Map of Radon Zones is intended to represent a preliminary assessment of radon
potential for the entire United States. The factors that are used in this effort —indoor radon
data, geology, aerial radioactivity, soils, and foundation type ~ are basic indicators for radon
potential. It is important to note, however, that the map's county zone designations are not
"statistically valid" predictions due to the nature of the data available for these 5 factors at the
county level. In order to validate the map in light of this lack of statistical confidence, EPA
conducted a number of analyses. These analyses have helped EPA to identify the best
situations in which to apply the map, and its limitations.
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Figure 3
Geologic Radon Potential Provinces for Nebraska
Lincoln County
Sift
Underi! :
Figure 4
NEBRASKA - EPA Map of Radon Zones
Lincoln County
Zoie l last I
lane 3
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One such analysis involved comparing county zone designations to indoor radon
measurements from the State/EPA Residential Radon Surveys (SRRS). Screening averages
for counties with at least 100 measurements were compared to the counties' predicted radon
potential as indicated by the Map of Radon Zones. EPA found that 72% of the county
screening averages were correctly reflected by the appropriate zone designations on the Map.
In all other cases, they only differed by 1 zone.
Another accuracy analysis used the annual average data from the National Residential
Radon Survey (NRRS). The NRRS indicated that approximately 6 million homes in the
United States have annual averages greater than or equal to 4 pCi/L. By cross checking the
county location of the approximately 5,700 homes which participated in the survey, their
radon measurements, and the zone designations for these counties, EPA found that
approximately 3.8 million homes of the 5.4 million homes with radon levels greater than or
equal to 4 pCi/L will be found in counties designated as Zone 1. A random sampling of an
equal number of counties would have only found approximately 1.8 million homes greater
than 4 pCi/L. In other words, this analysis indicated that the map approach is three times
more efficient at identifying high radon areas than random selection of zone designations.
Together, these analyses show that the approach EPA used to develop the Map of
Radon Zones is a reasonable one. In addition, the Agency's confidence is enhanced by results
of the extensive State review process — the map generally agrees with the States' knowledge
of and experience in their own jurisdictions. However, the accuracy analyses highlight two
important points: the fact that elevated levels will be found in Zones 2 and 3, and that there
will be significant numbers of homes with lower indoor radon levels in all of the Zones. For
these reasons, users of the Map of Radon Zones need to supplement the Map with locally
available data whenever possible. Although all known "hot spots", i.e., localized areas of
consistently elevated levels, are discussed in the State-
specific chapters, accurately defining the boundaries of the "hot spots" on this scale of map is
not possible at this time. Also, unknown "hot spots" do exist.
The Map of Radon Zones is intended to be a starting point for characterizing radon
potential because our knowledge of radon sources and transport is always growing. Although
this effort represents the best data available at this time, EPA will continue to study these
parameters and others such as house construction, ventilation features and meteorology factors
in order to better characterize the presence of radon in U.S homes, especially in high risk .
areas. These efforts will eventually assist EPA in refining and revising the conclusions of the
Map of Radon Zones And although this map is most appropriately used as a targeting tool
by the aforementioned audiences — the Agency encourages all residents to test their homes
for radon, regardless of geographic location or the zone designation of the county in
which they live. Similarly, the Map of Radon Zones should not to be used in lieu of
testing during real estate transactions.
Review Process
The Map of Radon Zones has undergone extensive review within EPA and outside the
Agency. The Association of American State Geologists (AASG) played an integral role in
this review process. The AASG individual State geologists have reviewed their State-specific
information, the USGS Geologic Radon Province Map, and other materials for their geologic
content and consistency.
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In addition to each State geologist providing technical comments, the State radon
offices were asked to comment on their respective States' radon potential evaluations. In
particular, the States were asked to evaluate the data used to assign their counties to specific
zones. EPA and USGS worked with the States to resolve any issues concerning county zone
designations. In a few cases, States have requested changes in county zone designations. The
requests were based on additional data from the State on geology, indoor radon
measurements, population, etc. Upon reviewing the data submitted by the States, EPA did
make some changes in zone designations. These changes, which do not strictly follow the
methodology outlined in this document, are discussed in the respective State chapters.
EPA encourages the States and counties to conduct further research and data collection
efforts to refine the Map of Radon Zones. EPA would like to be kept informed of any
changes the States, counties, or others make to the maps. Updates and revisions will be
handled in a similar fashion to the way the map was developed. States should notify EPA of
any proposed changes by forwarding the changes through the Regional EPA offices that are
listed in Part II. Depending on the amount of new information that is presented, EPA will
consider updating this map periodically. The State radon programs should initiate proper
notification of the appropriate State officials when the Map of Radon Zones is released and
when revisions or updates are made by the State or EPA.
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THE USGS/EPA RADON POTENTIAL ASSESSMENTS: AN INTRODUCTION
by
Linda C.S. Gundersen and R. Randall Schumann
U.S. Geological Survey
and
Sharon W. White
U.S. Environmental Protection Agency
BACKGROUND
The Indoor Radon Abatement Act of 1988 (15 U.S.C. 2661-2671) directed the U.S.
Environmental Protection Agency (EPA) to identify areas of the United States that have the
potential to produce harmful levels of indoor radon. These characterizations were to be based
on both geological data and on indoor radon levels in homes and other structures. The EPA
also was directed to develop model standards and techniques for new building construction
that would provide adequate prevention or mitigation of radon entry. As part of an
Interagency Agreement between the EPA and the U.S. Geological Survey (USGS), the USGS
has prepared radon potential estimates for the United States. This report is one of ten
booklets that document this effort. The purpose and intended use of these reports is to help
identify areas where states can target their radon program resources, to provide guidance in
selecting the most appropriate building code options for areas, and to provide general
information on radon and geology for each state for federal, state, and municipal officials
dealing with radon issues. These reports are not intended to be used as a substitute for
indoor radon testing, and they cannot and should not be used to estimate or predict the
indoor radon concentrations of individual homes, building sites, or housing tracts. Elevated
levels of indoor radon have been found in every State, and EPA recommends that all homes
be tested for indoor radon.
Booklets detailing the radon potential assessment for the U.S. have been developed for
each State. USGS geologists are the authors of the geologic radon potential booklets. Each
booklet consists of several components, the first being an overview to the mapping project
(Part I), this introduction to the USGS assessment (Part II), including a general discussion of
radon (occurrence, transport, etc.), and details concerning the types of data used. The third
component is a summary chapter outlining the general geology and geologic radon potential
of the EPA Region (Part III). The fourth component is an individual chapter for each state
(Part IV). Each state chapter discusses the state's specific geographic setting, soils, geologic
setting, geologic radon potential, indoor radon data, and a summary outlining the radon
potential rankings of geologic areas in the state. A variety of maps are presented in each
chapter—geologic, geographic, population, soils, aerial radioactivity, and indoor radon data by
county. Finally, the booklets contain EPA's map of radon zones for each state and an
accompanying description (Part V).
Because of constraints on the scales of maps presented in these reports and because the
smallest units used to present the indoor radon data are counties, some generalizations have
been made in order to estimate the radon potential of each area. Variations in geology, soil
characteristics, climatic factors, homeowner lifestyles, and other factors that influence radon
concentrations can be quite large within any particular geologic area, so these reports cannot
be used to estimate or predict the indoor radon concentrations of individual homes or housing
II-l Reprinted from USGS Open-File Report 93-292
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tracts. Within any area of a given geologic radon potential ranking, there are likely to be
areas where the radon potential is lower or higher than that assigned to the area as a whole,
especially in larger areas such as the large counties in some western states.
In each state chapter, references to additional reports related to radon are listed for the
state, and the reader is urged to consult these reports for more detailed information. In most
cases the best sources of information on radon for specific areas are state and local
departments of health, state departments responsible for nuclear safety or environmental
protection, and U.S. EPA regional offices. More detailed information on state or local
geology may be obtained from the state geological surveys. Addresses and telephone
numbers of state radon contacts, geological surveys, and EPA regional offices are listed in
Appendix C at the end of this chapter.
RADON GENERATION AND TRANSPORT IN SOILS
Radon (235Rn) is produced from the radioactive decay of radium (SKRa), which is, in turn,
a product of the decay of uranium (M8U) (fig. 1). The half-life of 222Rn is 3.825 days. Other
isotopes of radon occur naturally, but, with the exception of thoron (230Rn), which occurs in
concentrations high enough to be of concern in a few localized areas, they are less important
in terms of indoor radon risk because of their extremely short half-lives and less common
occurrence. In general, the concentration and mobility of radon in soil are dependent on
several factors, the most important of which are the soil's radium content and distribution,
porosity, permeability to gas movement, and moisture content. These characteristics are, in
turn, determined by the soil's parent-material composition, climate, and the soil's age or
maturity. If parent-material composition, climate, vegetation, age of the soil, and topography
are known, the physical and chemical properties of a soil in a given area can be predicted.
As soils form, they develop distinct layers, or horizons, that are cumulatively called the
soil profile. The A horizon is a surface or near-surface horizon containing a relative
abundance of organic matter but dominated by mineral matter. Some soils contain an E
horizon, directly below the A horizon, that is generally characterized by loss of clays, iron, or
aluminum, and has a characteristically lighter color than the A horizon. The B horizon
underlies the A or E horizon. Important characteristics of B horizons include accumulation of
clays, iron oxides, calcium carbonate or other soluble salts, and organic matter complexes. In
drier environments, a horizon may exist within or below the B horizon that is dominated by
calcium carbonate, often called caliche or calcrete. This carbonate-cemented horizon is
designated the K horizon in modern soil classification schemes. The C horizon underlies the
B (or K) and is a zone of weathered parent material that does not exhibit characteristics of A
or B horizons; that is, it is generally not a zone of leaching or accumulation. In soils formed
in place from the underlying bedrock, the C horizon is a zone of unconsolidated, weathered
bedrock overlying the unweathered bedrock.
The shape and orientation of soil particles (soil structure) control permeability and affect
water movement in the soil. Soils with blocky or granular structure have .-roughly equivalent
permeabilities in the horizontal and vertical directions, and air and water can infiltrate the soil
relatively easily. However, in soils with platy structure, horizontal permeability is much
greater than vertical permeability, and air and moisture infiltration is generally slow. Soils
with prismatic or columnar structure have dominantly vertical permeability. Platy and
prismatic structures form in soils with high clay contents. In soils with shrink-swell clays, air
U-2 Reprinted from USGS Open-File Report 93-292
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Lead-206
STABLE
138.4 days
Uranlum-238
4.51 billion years
Protactlnlum-234
Uranlum-234
247,000 years
'80,000 years
Radlum-226 fa
f
Figure 1. The oranium-238 decay series, showing the half-lives of elements and their modes of decay (after Wanty and
Schoen, 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 platy
structure, can form a capping layer that impedes the escape of soil gas to the surface
(Schumann and others, 1992). However, the shrinkage of clays can act to open or widen
cracks upon drying, thus increasing the soil's permeability to gas flow during drier periods.
Radon transport in soils occurs by two processes: (1) diffusion and (2) flow (Tanner,
1964). Diffusion is the process whereby radon atoms move from areas of higher
concentration to areas of lower concentration in response to a concentration gradient. Flow is
the process by which soil air moves through soil pores in response to differences in pressure
within the soil or between the soil and the atmosphere, carrying the radon atoms along with it.
Diffusion is the dominant radon transport process in soils of low permeability, whereas flow
tends to dominate in highly permeable soils (Sextro and others, 1987). In low-permeability
soils, much of the radon may decay before it is able to enter a building because its transport
rate is reduced. Conversely, highly permeable soils, even those that are relatively low in
radium, such as those derived from some types of glacial deposits, have been associated with
high indoor radon levels in Europe and in the northern United States (Akerblom and others,
1984; Kunz and others, 1989; Sextro and others, 1987). In areas of karst topography formed
in carbonate rock (limestone or dolomite) environments, solution cavities and fissures can
increase soil permeability at depth by providing additional pathways for gas flow.
Not all radium contained in soil grains and grain coatings will result in mobile radon
when the radium decays. Depending on where the radium is distributed in the soil, many of
the radon atoms may remain imbedded in the soil grain containing the parent radium atom, or
become imbedded in adjacent soil grains. The portion of radium that releases radon into the
pores and fractures of rocks and soils is called the emanating fraction. When a radium atom
decays to radon, the energy generated is strong enough to send the radon atom a distance of
about 40 nanometers (1 nm = 10"9 meters), or about 2x10'6 inches—this is known as alpha
recoil (Tanner, 1980). Moisture in the soil lessens the chance of a recoiling radon atom
becoming imbedded in an adjacent grain. Because water is more dense than air, a radon atom
will travel a shorter distance in a water-filled pore than in an air-filled pore, thus increasing
the likelihood that the radon atom will remain in the pore space. Intermediate moisture levels
enhance radon emanation but do not significantly affect permeability. However, high
moisture levels can significantly decrease the gas permeability of the soil and impede radon
movement through the soil.
Concentrations of radon in soils are generally many times higher than those inside of
buildings, ranging from tens of pCi/L to more than 100,000 pCi/L, but typically in the range
of hundreds to low thousands of pCi/L. Soil-gas radon concentrations can vary in response to
variations in climate and weather on hourly, daily, or seasonal time scales. Schumann and
others (1992) and Rose and others (1988) recorded order-of-magnitude variations in soil-gas
radon concentrations between seasons in Colorado and Pennsylvania, The most important
factors appear to be (1) soil moisture conditions, which are controlled in large part by
precipitation; (2) barometric pressure; and (3) temperature. Washington and Rose (1990)
suggest that temperature-controlled partitioning of radon between water and gas in soil pores
also has a significant influence on the amount of mobile radon in soil gas.
Homes in hilly limestone regions of the southern Appalachians were found to have higher
indoor radon concentrations during the summer than in the winter. A suggested cause for this
phenomenon involves temperature/pressure-driven flow of radon-laden air from subsurface
II-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 otherpenetrations through building foundations, sump
holes, and slab-to-foundation wall joints are common entry points.
Radon levels in the basement are generally higher than those on the main floor or upper
floors of most structures. Homes with basements generally provide more entry points for
radon, commonly have a more pronounced stack effect, and typically have lower air pressure
relative to the surrounding soil than nonbasement homes. The term "nonbasement" applies to
slab-on-grade or crawl space construction.
METHODS AND SOURCES OF DATA
The assessments of radon potential in the booklets that follow this introduction were
made using five main types of data: (1) geologic (lithologic); (2) aerial radiometric; (3) soil
characteristics, including soil moisture, permeability, and drainage characteristics; (4) indoor
radon data; and (5) building architecture (specifically, whether homes in each area are built
slab-on-grade or have a basement or crawl space). These five factors were evaluated and
integrated to'produce estimates of radon potential. Field measurements of soil-gas radon or
soil radioactivity were not used except where such data were available in existing, published
reports of local field studies. Where applicable, such field studies are described in the
individual state chapters.
GEOLOGIC DATA
The types and distribution of lithologic units and other geologic features in an
assessment area are of primary importance in determining radon potential. Rock types that
are most likely to cause indoor radon problems include carbonaceous black shales, glauconite-
bearing sandstones, certain kinds of fluvial sandstones and fluvial sediments, phosphorites,
chalk, karst-producing carbonate rocks, certain kinds of glacial deposits, bauxite, uranium-rich
granitic rocks, metamorphic rocks of granitic composition, silica-rich volcanic rocks, many
sheared or faulted rocks, some coals, and certain kinds of contact metamorphosed rocks.
Rock types least likely to cause radon problems include marine quartz sands, non-
carbonaceous shales and siltstones, certain kinds of clays, silica-poor metamorphic and
II-5 Reprinted from USGS Open-File Report 93-292
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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).
NURE AERIAL RADIOMETRIC DATA
Aerial radiometric data are used to quantify the radioactivity of rocks and soils.
Equivalent uranium (eU) data provide an estimate of the surficial concentrations of radon
parent materials (uranium, radium) in rocks and soils. Equivalent uranium is calculated from
the counts received by a gamma-ray detector from the 1.76 MeV (mega-electron volts)
emission energy corresponding to bismuth-214 (2HBi), with the assumption that uranium and
its decay products are in secular equilibrium. Equivalent uranium is expressed in units of
parts per million (ppm). Gamma radioactivity also may be expressed in terms of a radium
activity; 3 ppm eU corresponds to approximately 1 picocurie per gram (pCi/g) of radium-226.
Although radon is highly mobile in soil and its concentration is affected by meteorological
conditions (Kovach, 1945, Kiusman and Jaacks, 1987; Schery and others, 1984; Schumann
and others, 1992), statistical correlations between average soil-gas radon concentrations and
average eU values for a wide variety of soils have been documented (Gundersen and others,
1988a, 1988b; Schumann and Owen, 1988). Aerial radiometric data can provide an estimate
of radon source strength over a region, but the amount of radon that is able to enter a home
from the soil is dependent on several local factors, including soil structure, grain size
distribution, moisture content, and permeability, as well as type of house construction and its
structural condition.
The aerial radiometric data used for these characterizations were collected as part of the
Department of Energy National Uranium Resource Evaluation (NURE) program of the 1970s
and early 1980s. The purpose of the NURE program was to identify and describe areas in the
United States having potential uranium resources (U.S. Department of Energy, 1976). The
NURE aerial radiometric data were collected by aircraft in which a gamma-ray spectrometer
was mounted, flying approximately 122 m (400 ft) above the ground surface. The equivalent
uranium maps presented in the state chapters were generated from reprocessed NURE data in
which smoothing, filtering, recalibrating, and matching of adjacent quadrangle data sets were
performed to compensate for background, altitude, calibration, and other types of errors and
inconsistencies in the original data set (Duval and others, 1989). The data were then gridded
and contoured to produce maps of eU with a pixel size corresponding to approximately 2.5 x
2.5 km (1.6 x 1.6 mi).
II-6 Reprinted from USGS Open-File Report 93-292
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FLIGHT LINE SPACING OF SURE AEKUL SURVEYS
2 I'M (1 KILE)
5 KJ[ (3 HUES)
2 i 5 KU
10 EU (6 IIILES)
5 fr 10 IK
NO DATA
Figure 2. Nominal flightline spacings for NURE aerial gamma-ray surveys covering the
contiguous United States (from Duval and others, 1990). Rectangles represent I°x2° quadrangles.
-------
Figure 2 is an index map of NUKE 1° x 2° quadrangles showing the flight-line spacing
for each quadrangle. In general, the more closely spaced the flightlines are, the more area
was covered by the aerial gamma survey, and thus, more detail is available in the data set.
For an altitude of 400 ft above the ground surface and with primary flightline spacing
typically between. 3 and 6 miles, less than 10 percent of the ground surface of the United
States was actually measured by the airborne gamma-ray detectors (Duval and others, 1989),
although some areas had better coverage than others due to the differences in flight-line
spacing between areas (fig. 2). This suggests that some localized uranium anomalies may not
have been detected by the aerial surveys, but the good correlations of eU patterns with
geologic outcrop patterns indicate that, at relatively small scales (approximately 1:1,000,000
or smaller) the National eU map (Duval and others, 1989) gives reasonably good estimates of
average surface uranium concentrations and thus can assist in the prediction of radon potential
of rocks and soils, especially when augmented with additional geologic and soil data.
The shallow (20-30 cm) depth of investigation of gamma-ray spectrometers, either
ground-based or airborne (Duval and others, 1971; Durrance, 1986), suggests that gamma-ray
data may sometimes underestimate the radon-source strength in soils in which some of the
radionuclides in the near-surface soil layers have been transported downward through the soil
profile. In such cases the concentration of radioactive minerals in the A horizon wouid be
lower than in the B horizon, where such minerals are typically concentrated. The
concentration of radionuclides in the C horizon and below may be relatively unaffected by
surface solution processes. Under these conditions the surface gamma-ray signal may indicate
a lower radon source concentration than actually exists in the deeper soil layers, which are
most likely to affect radon levels in structures with basements. The redistribution of
radionuclides in soil profiles is dependent on a combination of climatic, geologic, and
geochemical factors. There is reason to believe that correlations of eU with actual soil
radium and uranium concentrations at a depth relevant to radon entry into structures may be
regionally variable (Duval, 1989; Schumann and Gundersen, 1991). Given sufficient
understanding of the factors cited above, these regional differences may be predictable.
SOIL SURVEY DATA
Soil surveys prepared by the U.S. Soil Conservation Service (SCS) provide data on soil
characteristics, including soil-cover thickness, grain-size distribution, permeability, shrink-
swell potential, vegetative cover, generalized groundwater characteristics, and land use. The
reports are available in county formats and State summaries. The county reports typically
contain both generalized and detailed maps of soils in the area.
Because of time and map-scale constraints, it was impractical to examine county soil
reports for each county in the United States, so more generalized summaries at appropriate
scales were used where available. For State or regional-scale radon characterizations, soil
maps were compared to geologic maps of the area, and the soil descriptions, shrink-swell
potential, drainage characteristics, depth to seasonal high water table, permeability, and other
relevant characteristics of each soil group noted. Technical soil terms used in soil surveys are
generally complex; however, a good summary of soil engineering terms and the national
distribution of technical soil types is the "Soils" sheet of the National Atlas (U.S. Department
of Agriculture, 1987),
II-8 Reprinted from USGS Open-File Report 93-292
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Soil permeability is commonly expressed in SCS soil surveys in terms of the speed, in
inches per hour (in/hr), at which water soaks into the soil, as measured in a soil percolation
test. Although in/hr are not truly units of permeability, these units are in widespread use and
are referred to as "permeability" in SCS soil surveys. The permeabilities listed in the SCS
surveys are for water, but they generally correlate well with gas permeability. Because data
on gas permeability of soils is extremely limited, data on permeability to water is used as a
substitute except in cases in which excessive soil moisture is known to exist. Water in soil
pores inhibits gas transport, so the amount of radon available to a home is effectively reduced
by a high water table. Areas likely to have high water tables include river valleys, coastal
areas, and some areas overlain by deposits of glacial origin (for example, loess).
Soil permeabilities greater than 6.0 in/hr may be considered high, and permeabilities less
than 0.6 in/hr may be considered low in terms of soil-gas transport. Soils with low
permeability may generally be considered to have a lower radon potential than more
permeable soils with similar radium concentrations. Many well-developed soils contain a
clay-rich B horizon that may impede vertical soil gas transport. Radon generated below this
horizon cannot readily escape to the surface, so it would instead tend to move laterally,
especially under the influence of a negative pressure exerted by.a building.
Shrink-swell potential is an indicator of the abundance of smectitic (swelling) clays in a
soil. Soils with a high shrink-swell potential may cause building foundations to crack,
creating pathways for radon entry into the structure. During dry periods, desiccation cracks in
shrink-swell soils provide additional pathways for soil-gas transport and effectively increase
the gas permeability of the soil. Soil permeability data and soil profile data thus provide
important information for regional radon assessments.
INDOOR RADON DATA
Two major sources of indoor radon data were used. The first and largest source of data is
from the State/EPA Residential Radon Survey (Ronca-Battista and others, 1988; Dziuban and
others, 1990). Forty-two states completed EPA-sponsored indoor radon surveys between 1986
and 1992 (fig. 3). The State/EPA Residential Radon Surveys were designed to be
comprehensive and statistically significant at the state level, and were subjected to high levels
of quality assurance and control. The surveys collected screening indoor radon measurements,
defined as 2-7 day measurements using charcoal canister radon detectors placed in the lowest
livable area of the home. The target population for the surveys included owner-occupied
single family, detached housing units (White and others, 1989), although attached structures
such as duplexes, townhouses, or condominiums were included in some of the surveys if they
met the other criteria and had contact with the ground surface. Participants were selected
randomly from telephone-directory listings. In total, approximately 60,000 homes were tested
in the State/EPA surveys.
The second source of indoor radon data comes from residential surveys that have been
conducted in a specific state or region of the country (e.g. independent state surveys or utility
company surveys). Several states, including Delaware, Florida, Illinois, New Hampshire, New
Jersey, New York, Oregon, and Utah, have conducted their own surveys of indoor radon. The
quality and design of a state or other independent survey are discussed and referenced where
the data are used.
II-9 Reprinted from USGS Open-File Report 93-292
-------
The States of DE.W J^H,NJ,NY,and UT
have conducted incir own surveys, OR &
SD declined to participate in Ihc SRRS.
STATE/EPA RESIDENTIAL RADON
SURVEY SCREENING MEASUREMENTS
0
Estimated Percent of Houses with Screening Levels Greater than 4 pCi/L
20 and >
These results arc based on 2-7 day screening
measurements in the lowest livable level and 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 area, and the Confidence Index (CI), used to express the level of confidence in the
prediction based on the quantity and quality of the data used to make the determination. This
scheme works best if the areas to be evaluated are delineated by geologically-based
boundaries (geologic provinces) rather than political ones (state/county boundaries) in which
the geology may vary across the area.
Radon Index. Table 1 presents the Radon Index (RI) matrix. The five factors—indoor
radon data, geology, aerial radioactivity, soil parameters, and house foundation type—were
quantitatively ranked (using a point value of 1, 2, or 3) for their respective contribution to
radon potential in a.given area. At least some data for the 5 factors are consistently available
for every geologic province. Because each of these main factors encompass a wide variety of
complex and variable components, the geologists performing the evaluation relied heavily on
their professional judgment and experience in assigning point values to each category and in
determining the overall radon potential ranking. Background information on these factors is
discussed in more detail in the preceding sections of this introduction.
Indoor radon was evaluated using unweighted arithmetic means of the indoor radon data
for each geologic area to be assessed. Other expressions of indoor radon levels in an area
also could have been used, such as weighted averages or annual averages, but these types of
data were not consistently available for the entire United States at the time of this writing, or
the schemes were not considered sufficient to provide a means of consistent comparison
across all areas. For this report, charcoal-canister screening measurement data from the
State/EPA Residential Radon Surveys and other carefully selected sources were used, as
described in the preceding section. To maintain consistency, other indoor radon data sets
(vendor, state, or other data) were not considered in scoring the indoor radon factor of the
Radon Index if they were not randomly sampled or could not be statistically combined with
the primary indoor radon data sets. However, these additional radon data sets can provide a
means to further refine correlations between geologic factors and radon potential, so they are
*».
II-11 Reprinted from USGS Open-File Report 93-292
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TABLE 1. RADON INDEX MATRIX, "ppm eU" indicates parts per million of equivalent
uranium, as indicated by NURE aerial radiometric data. See text discussion for details.
FACTOR
INDOOR RADON (average)
AERIAL RADIOACTIVITY
GEOLOGY*
SOIL PERMEABILITY
ARCHITECTURE TYPE
INCREASING RADON POTENTIAL ^
POINT VALUE
1
<2pCi/L
< 1.5 ppm eU
negative
low
mostly slab
2
2-4pCi/L
1.5 - 2.5 ppm eU
variable
moderate
mixed
3
>4pCi/L
> 2.5 ppm eU
positive
high
mostly basement
*GEOLOGIC FIELD EVIDENCE (GFE) POINTS: GFE points are assigned in addition to points
for the "Geology" factor for specific, relevant geologic field studies. See text for details.
Geologic evidence supporting: HIGH radon +2 points
MODERATE +1 point
LOW -2 points
No relevant geologic field studies 0 points
SCORING:
Radon potential category
Probable average screening
Point range 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
FACTOR
INDOOR RADON DATA
AERIAL RADIOACTIVITY
GEOLOGIC DATA
SOIL PERMEABILITY
POINT VALUE
1
sparse/no data
questionable/no data
questionable
questionable/no data
2
fair coverage/quality
glacial cover
variable
variable
3
good coverage/quality
no glacial cover
proven geol. model
reliable, abundant
SCORING:
LOW CONFIDENCE
MODERATE CONFIDENCE
HIGH CONFIDENCE
POSSIBLE RANGE OF POINTS = 4 to 12
f
4-6 points
7-9 points
10 -12 points
n-12
Reprinted from USGS Open-File Report 93-292
-------
included as supplementary information and are discussed in the individual State chapters. If
the average screening indoor radon level for an area was less than 2 pCi/L, the indoor radon
factor was assigned 1 point, if it was between 2 and 4 pCi/L, it was scored 2 points, and if
the average screening indoor radon level for an area was greater than 4 pCi/L, the indoor
radon factor was 'assigned 3 RI points.
Aerial radioactivity data used in this report are from the equivalent uranium map of the
conterminous United States compiled from NURE aerial gamma-ray surveys (Duval and
others, 1989). These data indicate the gamma radioactivity from approximately the upper 30
cm of rock and soil, expressed in units of ppm equivalent uranium. An approximate average
value of eU was determined visually for each area and point values assigned based on
whether the overall eU for the area falls below 1.5 ppm (1 point), between 1.5 and 2.5 ppm
(2 points), or greater than 2.5 ppm (3 points).
The geology factor is complex and actually incorporates many geologic characteristics. In
the matrix, "positive" and "negative" refer to the presence or absence and distribution of rock
types known to have high uranium contents and to generate elevated radon in soils or indoors.
Examples of "positive" rock types include granites, black shales, phosphatic rocks, and other
rock types described in the preceding "geologic data" section. Examples of "negative" rock
types include marine quartz sands and some clays. The term "variable" indicates that the
geology within the region is variable or that the rock types in the area are known or suspected
to generate elevated radon in some areas but not in others due to compositional differences,
climatic effects, localizeddistribution of uranium, or other factors. Geologic information
indicates not only how much uranium is present in the rocks and soils but also gives clues for
predicting general radon emanation and mobility characteristics through additional factors
such as structure (notably the presence of faults or shears) and geochemical characteristics
(for example, a phosphate-rich sandstone will likely contain more uranium than a sandstone
containing little or no phosphate because the phosphate forms chemical complexes with
uranium). "Negative", "variable", and "positive" geology were assigned 1, 2, and 3 points,
respectively.
In cases where additional reinforcing or contradictory geologic evidence is available,
Geologic Field Evidence (GFE) points were added to or subtracted from an area's score
(Table 1), Relevant geologic field studies are important to enhancing our understanding of
how geologic processes affect radon distribution. In some cases, geologic models and
supporting field data reinforced an already strong (high or low) score; in others, they provided
important contradictory data. GFE points were applied for geologically-sound evidence that
supports the prediction (but which may contradict one or more factors) on the basis of known
geologic field studies in the area or in areas with geologic and climatic settings similar
enough that they could be applied with full confidence. For example, areas of the Dakotas,
Minnesota, and Iowa that are covered with Wisconsin-age glacial deposits exhibit a low aerial
radiometric signature and score only one RI point in that category. However, data from
geologic field studies in North Dakota and Minnesota (Schumann and others, 1991) suggest
that eTJ is a poor predictor of geologic radon potential in this area because radionuclides have
11-13 Reprinted from USGS Open-File Report 93-292
-------
been leached from the upper soil layers but are present and possibly even concentrated in
deeper soil horizons, generating significant soil-gas radon. This positive supporting field
evidence adds two GFE points to the score, which helps to counteract the invalid conclusion
suggested by the radiometric data. No GFE points are awarded if there are no documented
field studies for the area.
"Soil permeability" refers to several soil characteristics that influence radon concentration
and mobility, including soil type, grain size, structure, soil moisture, drainage, slope, and
permeability. In the matrix, "low" refers to permeabilities less than about 0.6 in/hr; "high"
corresponds to greater than about 6.0 in/hr, in U.S. Soil Conservation Service (SCS) standard
soil percolation tests. The SCS data are for water permeability, which generally correlates
well with the gas permeability of the soil except when the soil moisture content is very high.
Areas with consistently high water tables were thus considered to have low gas permeability.
"Low, "moderate", and "high" permeability were assigned 1, 2, and 3 points, respectively.
Architecture type refers to whether homes in the area have mostly basements (3 points),
mostly slab-on-grade construction (1 point), or a mixture of the'two. Split-level and crawl
space homes fall into the "mixed" category (2 points). Architecture information is necessary
to properly interpret the indoor radon data and produce geologic radon potential categories
that are consistent with screening indoor radon data.
The overall RI for an area is calculated by adding the individual RI scores for the 5
factors, plus or minus GFE points, if any. The total RI for an area falls in one of three
categories—low, moderate or variable, or high. The point ranges for the three categories were
determined by examining the possible combinations of points for the 5 factors and setting
rules such that a majority (3 of 5 factors) would determine the final score for the low and
high categories, with allowances for possible deviation from an ideal score by the other two
factors. The moderate/variable category lies between these two ranges. A total deviation of 3
points from the "ideal" score was considered reasonable to allow for natural variability of
factors—if two of the five factors are allowed to vary from the "ideal" for a category, they.
can differ by a minimum of 2 (1 point different each) and a maximum of 4 points (2 points
different each). With "ideal" scores of 5, 10, and 15 points describing low, moderate, and
high geologic radon potential, respectively, an ideal low score of 5 points plus 3 points for
possible variability allows a maximum of 8 points in the low category. Similarly, an ideal
high score of 15 points minus 3 points gives a minimum of 12 points for the high category.
Note, however, that if both other factors differ by two points from the "ideal", indicating
considerable variability in the system, the total point score would He in the adjacent (i.e.,
moderate/variable) category.
Confidence Index. Except for architecture type, the same factors were used to establish a
Confidence Index (CI) for the radon potential prediction for each area (Table 2). Architecture
type was not included in the confidence index because house construction data are readily and
reliably available through surveys taken by agencies and industry groups including the
National Association of Home Builders, U.S. Department of Housing and Urban
Development, and the Federal Housing Administration; thus it was not considered necessary
11-14 Reprinted from USGS Open-File Report .93-292
-------
to question the quality or validity of these data. The other factors were scored on the basis of
the quality and quantity of the data used to complete the RI matrix.
Indoor radon data were evaluated based on the distribution and number of data points and
on whether the data were collected by random sampling (State/EPA Residential Radon Survey
or other state survey data) or volunteered vendor data (likely to be nonrandom and biased
toward population centers and/or high indoor radon levels). The categories listed in the CI
matrix for indoor radon data ("sparse or no data", "fair coverage or quality", and "good
coverage/quality") indicate the sampling density and statistical robustness of an indoor radon
data set. Data from the State/EPA Residential Radon Survey and statistically valid state
surveys were typically assigned 3 Confidence Index points unless the data were poorly
distributed or absent in the area evaluated.
Aerial radioactivity data are available for all but a few areas of the continental United
States and for part of Alaska. An evaluation of the quality of the radioactivity data was based
on whether there appeared to be a good correlation between the radioactivity and the actual
amount of uranium or radium available to generate mobile radon in the rocks and soils of the
area evaluated. In general, the greatest problems with correlations among etJ, geology, and
soil-gas or indoor radon levels were associated with glacial deposits (see the discussion in a
previous section) and typically were assigned a 2-point Confidence Index score. Correlations
among eU, geology, and radon were generally sound in unglaciated areas and were usually
assigned 3 CI points. Again, however, radioactivity data in some unglaciated areas may have
been assigned fewer than 3 points, and in glaciated areas may be assigned only one point, if
the data were considered questionable or if coverage was poor.
To assign Confidence Index scores for the geologic data factor, rock types and geologic
settings for which a physical-chemical, process-based understanding of radon generation and
mobility exists were regarded as having "proven geologic models" (3 points); a high
confidence could be held for predictions in such areas. Rocks for which the processes are
less well known or for which data are contradictory were regarded as "variable" (2 points),
and those about which little is known or for which no apparent correlations have been found
were deemed "questionable" (1 point).
The soil permeability factor was also scored based on quality and amount of data. The
three categories for soil permeability in the Confidence Index are similar in concept, and
scored similarly, to those for the geologic data factor. Soil permeability can be roughly
estimated from grain size and drainage class if data from standard, accepted soil percolation
tests are unavailable; however, the reliability of the data would be lower than if percolation
test figures or other measured permeability data are available, because an estimate of this type
does not encompass all the factors that affect soil permeability and thus may be inaccurate in
some instances. Most published soil permeability data are for water; although this is
generally closely related to the air permeability of the soil, there are some instances when it
may provide an incorrect estimate. Examples of areas in which water permeability data may
not accurately reflect air permeability include areas with consistently high levels of soil
moisture, or clay-rich soils, which would have a low water permeability but may have a
11-15 Reprinted from USGS Open-File Report 93-292
-------
significantly higher air permeability when dry due to shrinkage cracks in the soil. These
additional factors were applied to the soil permeability factor when assigning the RI score, but
may have less certainty in some cases and thus would be assigned a lower CI score.
The Radon Index and Confidence Index give a general indication of the relative
contributions of the interrelated geologic factors influencing radon generation and transport in
rocks and soils, and thus, of the potential for elevated indoor radon levels to occur in a
particular area. However, because these reports are somewhat generalized to cover relatively
large areas of States, it is highly recommended that more detailed studies be performed in
local areas of interest, using the methods and general information in these booklets as a guide.
11-16 Reprinted from USGS Open-File Report 93-292
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Durrance, E.M., 1986, Radioactivity in geology: Principles and applications: New York, N.Y.,
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Duval, J.S., 1989, Radioactivity and some of its applications in geology: Proceedings of the
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Duval, J.S., Reimer, G,M., Schumann, R.R., Owen, D.E., and Otton, J.K., 1990, Soil-gas
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Radon Reduction Technology, Volume 1: U.S. Environmental Protection Agency Report
EPA/600/9-89/006A, p. 5-75-5-86.
Muessig, K., and Bell, C., 1988, Use of airborne radiometric data to direct testing for elevated
indoor radon: Northeastern Environmental Science, v. 7, no. 1, p. 45-51.
Ronca-Battista, M., Moon, M., Bergsten, J., White, S.B., Holt, N., and Alexander, B., 1988,
Radon-222 concentrations in the United States—Results of sample surveys in five states:
Radiation Protection Dosimetry, v. 24, p. 307-312.
Rose, A.W., Washington, J.W., and Greeman, D.J., 1988, Variability of radon with depth and
season in a central Pennsylvania soil developed on limestone: Northeastern Environmental
Science, v. 7, p. 35-39.
Schery, S.D., Gaeddert, D.H., and Wilkening, M.H., 1984, Factors affecting exhalation of radon
from a gravelly sandy loam: Journal of Geophysical Research, v. 89, p. 7299-7309.
Schumann, R.R., and Owen, D.E., 1988, Relationships between geology, equivalent uranium
concentration, and radon in soil gas, Fairfax County, Virginia: U.S. Geological Survey
Open-File Report 88-18,28 p.
Schumann, R.R., and Gundersen, L.C.S., 1991, Regional differences in radon emanation
coefficients in soils: Geological Society of America Abstracts With Programs, v. 23,
no. 1, p. 125.
Schumann, R.R., Peak®, R.T., Schmidt, K.M., and Owen, D.E., 1991, Correlations of soil-gas
and indoor radon with geology in glacially derived soils of the northern Great Plains, in
Proceedings of the 1990 International Symposium on Radon and Radon Reduction
Technology, Volume 2, Symposium Oral Papers: U.S. Environmental Protection Agency
report EPA/600/9-9 l/026b, p. 6-23-6-36.
II-18 Reprinted from USGS Open-File Report 93-292
-------
Schumann, R.R., Owen, D.E., and Asher-Bolinder, S., 1992, Effects of weather and soil
characteristics on temporal variations in soil-gas radon concentrations, in Gates, A.E., and
Gundersen, L.C.S., eds., Geologic controls on radon: Geological Society of America
Special Paper 271, p. 65-72.
Sextro, R.G., Moed, B.A., Nazaroff, W.W., Revzan, K.L., and Nero, A.V., 1987,
Investigations of soil as a source of indoor radon, in Hopke, P.K., ed., Radon and its
decay products: American Chemical Society Symposium Series 331, p. 10-29.
Sterling, R., Meixel, G., Shen, L., Labs, K», and Bligh, T., 1985, Assessment of the energy
savings potential of building foundations research: Oak Ridge, Tenn., U.S. Department of
Energy Report ORNL/SUB/84-0024/1.
Smith, R.C., 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, HI., University of Chicago
Press, p. 161-190.
Tanner, A.B., 1980, Radon migration in the ground: a supplementary review, in Gesell, T.F.,
and Lowder, W.M. (eds), Natural radiation environment M, Symposium proceedings,
Houston, Texas, v. 1, p. 5-56.
U.S. Department of Agriculture, 1987, Principal kinds of soils: Orders, suborders, and great
groups: U.S. Geological Survey, National 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 from TJSGS Open-File Report 93-292
-------
APPENDIX A
GEOLOGIC TIME SCALE
Subdivisions (and their symbols)
Eon or
Eonothem
Phanerozoie2
Proteroioie
(PI
Archean
i&t
Era or
. Erathem
Cenoioic *
(Cil
Mesozoic2
(Md
PtttOZOiC2
(Pi)
UI» _.
Prm«*o*o<< Gn
M<08I*
PrcuroiOfC fVl
. £ Decay constants and botopic ratios employed *re died in Swiger and Jiger (19775. Designation m.y. used lor an
bittrva! of tint*.
*Modif>*ri (lower, middle, upper or early, middle, late} when used with these Hems w* informal division! of the larger unit: the
first lentr of the modifier Is lowercase.
'Rockj older than 570 Ma also called Precambrian (p-G), a lime term without specific rank,
'informal time term without sp«ofic rank.
USGS Open-File Report 93-292
-------
APPENDIX B
GLOSSARY OF TERMS
Units of measure
pCI/L (picocuries per liter)- a unit of measure of radioactivity used to describe radon
concentrations in a volume of air. One pieoeurie (1(H2 curies) is equal to about 2.2 disintegrations
of radon atoms per minute. A liter is about 1.06 quarts. The average concentration of radon in
U.S. homes measured to date is between 1 and 2 pQ/L.
Bq/m3 (Becquerels per cubic meter)- a metric unit of radioactivity used to describe radon
concentrations in a volume of air. One becquerel is equal to one radioactive disintegration per
second. 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 deposited by a
stream or other body of running water.
alpha-track detector A passive radon measurement device consisting of a plastic film that is
sensitive to alpha particles. The film is etched with acid in a laboratory after it is exposed. The
etching reveals scratches, or "tracks", left by the alpha particles resulting from radon decay, which
can then be counted to calculate the radon concentration. Useful for long-term (1-12 months)
radon tests.
amphibolite A mafic metamorphic rock consisting mainly of pyroxenes and(or) amphibole and
plagioclase.
11-21 Reprinted from USGS Open-File Report 93-292
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argillite, argillaceous Terms referring to a rock derived from clay or shale, or any sedimentary
rock containing an appreciable amount of clay-size material, ie., argillaceous sandstone.
arid Term describing a climate characterized by dryness, or an evaporation rate that exceeds the
amount of precipitation.
basalt A general term for a dark-colored mafic igneous rocks that may be of extrusive origin,
such as volcanic basalt flows, or intrusive origin, such as basalt dikes.
batholith A mass of plutonic igneous rock that has more than 40 square miles of surface
exposure and no known bottom.
carbonate A sedimentary rock consisting of the carbonate (COs) compounds of calcium,
magnesium, or iron, e.g. limestone and dolomite.
carbonaceous Said of a rock or sediment that is rich in carbon, is coaly, or contains organic
matter.
charcoal canister A passive radon measurement device consisting of a small container of
granulated activated charcoal that is designed to adsorb radon. Useful for short duration (2-7 days)
measurements only. May be referred to as a "screening" test
chert A hard, extremely dense sedimentary rock consisting dominantly of interlocking crystals of
quartz. Crystals are not visible to the naked eye, giving the rock a milky, dull luster. It may be
white or gray but is commonly colored red, black, yellow, blue, pink, brown, or green.
clastic pertaining to a rock or sediment composed of fragments that are derived from preexisting
rocks or minerals. The most common clastic sedimentary rocks are sandstone and shale.
clay A rock containing clay mineral fragments or material of any composition having a diameter
less than 1/256 mm.
clay mineral One of a complex and loosely defined group of finely crystalline minerals made up
of water, silicate and aluminum (and a wide variety of other elements). They are formed chiefly by
alteration or weathering of primary silicate minerals. Certain clay minerals are noted for their small
size and ability to absorb substantial amounts of water, causing them to swell. The change in size
that occurs as these clays change between dry and wet is referred to as their "shrink-swell"
potential.
concretion A hard, compact mass of mineral matter, normally subspherical but commonly
irregular in shape; formed by precipitation from a water solution about a nucleus or center, such as
a leaf, shell, bone, or fossil, within a sedimentary or fractured rock.
conglomerate A coarse-grained, clastic sedimentary rock composed of rock and mineral
fragments larger than 2 mm, set in a finer-grained matrix of clastic material.
cuesta A hill or ridge with a gentle slope on one side and a steep slope on the other. The
formation of a cuesta is controlled by the different weathering properties and the structural dip of
the rocks forming the hill or ridge.
daughter product A nuclide formed by the disintegration of a radioactive precursor or "parent"
atom.
11-22 Reprinted from USGS Open-File Report 93-292
-------
delta, deltaic Referring to a low, flat, alluvial tract of land having a triangular or fan shape,
located at or near the mouth of a river. It results from the accumulation of sediment deposited by a
river at the point at which the river loses its ability to transport the sediment, commonly where a
river meets a larger body of water such as a lake or ocean.
dike A tabular igneous intrusion of rock, younger than the surrounding rock, that commonly cuts
across the bedding or foliation of the rock it intrudes.
diorite A plutonic igneous rock that is medium in color and contains visible dark minerals that
make up less than 50% of the rock. It also contains abundant sodium plagioclase and minor
quartz.
dolomite A carbonate sedimentary rock of which more than 50% consists of the mineral dolomite
(CaMg(CO3)2), and is commonly white, gray, brown, yellow, or pinkish in color.
drainage The manner in which the waters of an area pass, flow off of, or flow into the soil.
Also refers to the water features of an area, such as lakes and rivers, that drain it.
eolian Pertaining to sediments deposited by the wind.
esker A long, narrow, steep-sided ridge composed of irregular beds of sand and gravel deposited
by streams beneath a glacier and left behind when the ice melted.
evapotranspiration Loss of water from a land area by evaporation from the soil and
transpiration from plants.
extrusive Said of igneous rocks that have been erupted onto the surface of the Earth.
fault A fracture or zone of fractures in rock or sediment along which there has been movement.
fluvial, fluvial deposit Pertaining to sediment that has been deposited by a river or stream.
foliation A linear feature in a rock defined by both mineralogic and structural characteristics. It
may be formed during deformation or metamorphism.
formation A mappable body of rock having similar characteristics.
glacial deposit Any sediment transported and deposited by a glacier or processes associated
with glaciers, such as glaciofluvial sediments deposited by streams flowing from melting glaciers.
gneiss A rock formed by metamorphism in which bands and lenses of minerals of similar
composition alternate with bands and lenses of different composition, giving the rock a striped or
"foliated" appearance. c,
granite Broadly applied, any coarsely crystalline, quartz- and feldspar-bearing igneous plutonic
rock. Technically, granites have between 10 and 50% quartz, and alkali feldspar comprises at least
65% of the total feldspar.
gravel An unconsolidated, natural accumulation of rock fragments consisting predominantly of
particles greater than 2 mm in size.
heavy minerals Mineral grains in sediment or sedimentary rock having higher than average
specific gravity. May form layers and lenses because of wind or water sorting by weight and size
H-23 Reprinted from USGS Open-File Report 93-292
-------
and may be referred to as a "placer deposit" Some heavy minerals are magnetite, garnet, zircon,
monazite, and xenotime.
igneous Said of a rock or mineral that solidified from molten or partly molten rock material. It is
one of the three main classes into which rocks are divided, the others being sedimentary and
metamorphic.
intermontane A term that refers to an area between two mountains or mountain ranges.
intrusion, intrusive The processes of emplacement or injection of molten rock into pre-existing
rock. Also refers to the rock formed by intrusive processes, such as an "intrusive igneous rock".
kame A low mound, knob, hummock, or short irregular ridge formed by a glacial stream at the
margin of a melting glacier; composed of bedded sand and gravel.
karst terrain A type of topography that is formed on limestone, gypsum and other rocks by
dissolution of the rock by water, forming sinkholes and caves.
lignite A brownish-black coal that is intermediate in coalification between peat and
subbituminous coal.
limestone A carbonate sedimentary rock consisting of more than 50% calcium carbonate,
primarily in the form of the mineral calcite (CaCO3>.
lithology The description of rocks in hand specimen and in outcrop on the basis of color,
composition, and grain size.
loam A permeable soil composed of a mixture of relatively equal parts clay, silt, and sand, and
usually containing some organic matter.
loess A fine-grained eolian deposit composed of silt-sized particles generally thought to have
been deposited from windblown dust of Pleistocene age.
mafic Term describing an igneous rock containing more than 50% dark-colored minerals.
marine Term describing sediments deposited in the ocean, or precipitated from ocean waters.
metamorphic Any rock derived from pre-existing rocks by mineralogical, chemical, or structural
changes in response to changes in temperature, pressure, stress, and the chemical environment.
Phyllite, schist, amphibolite, and gneiss are metamorphic rocks.
moraine A mound, ridge, or other distinct accumulation of unsorted, unbedded glacial material,
predominantly till, deposited by the action of glacial ice.
outcrop That part of a geologic formation or structure that appears at the surface of the Earth, as
in "rock outcrop".
percolation test A term used in engineering for a test to determine the water permeability of a
soil. A hole is dug and filled with water and the rate of water level decline is measured.
permeability The capacity of a rock, sediment, or soil to transmit liquid or gas.
phosphate, phpsphatic, phosphorite Any rock or sediment containing a significant amount
of phosphate minerals, i.e., minerals containing PO4.
11-24 Reprinted from USGS Open-File Report 93-292
-------
physiographic province A region in which all parts are similar in geologic structure and
climate, which has had a uniform 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, composMonally 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 TJnsorted, generally unconsoMdated and unbedded rock and mineral material deposited directly
adjacent to and underneath a glacier, without reworking by meltwater. Size of grains varies greatly
from clay to boulders.
uraniferous Containing uranium, usually more than 2 ppm.
vendor data Used in this report to refer to indoor radon data collected and measured by
commercial vendors of radon measurement devices and/or services,
volcanic Pertaining to the activities, structures, and extrusive rock types of a volcano.
water table The surface forming the boundary between the zone of saturation and the zone of
aeration; the top surface of a body of unconfined groundwater in rock or soil.
weathering The destructive process by which earth and rock materials, on exposure to
atmospheric elements, are changed in color, texture, composition, firmness, or form with little or
no transport of the material.
11-26 Reprinted from USGS Open-File Report 93-292
-------
APPENDIX C
EPA REGIONAL OFFICES
ERA Regional Offices
State
EEA Region
EPA Region 1
JFK Federal Building
Boston, MA 02203
(617) 565-4502
EPA Region 2
(2AM:RAD)
26 Federal Plaza
New York, NY 10278
(212) 264-4110
Region 3 (3AH14)
841 Chestnut Street
Philadelphia, PA 19107
(215) 597-8326
EPA Region 4
345 Courtland Street, N.E.
Atlanta, GA 30365
(404) 347-3907
EPA Region 5 (5AR26)
77 West Jackson Blvd.
Chicago, IL 60604-3507
(312) 886-6175
EPA Region 6 (6T-AS)
1445 Ross Avenue
Dallas, TX 75202-2733
(214) 655-7224
EPA Region 7
726 Minnesota Avenue
Kansas City, KS 66101
(913) 551-7604
EPA Region 8
(8HWM-RP)
999 18th Street
One Denver Place, Suite 1300
Denver, CO 80202-2413
(303) 293-1713
EPA Region 9 (A-3)
75 Hawthorne Street
San Francisco, CA 94105
(415) 744.1048
EPA Region 10
1200 Sixth Avenue
Seattle, WA 98101
(202) 442-7660
Alabama 4
Alaska 10
Arizona 9
Arkansas 6
California 9
Colorado,..,..,..... 8
Connecticut ....1
Delaware. 3
District of Columbia 3
Florida 4
Georgia 4
Hawaii 9
Idaho 10
Illinois 5
Indiana 5
Iowa 7
Kansas „• 7
Kentucky..,., 4
Louisiana .....6
Maine 1
Maryland........ 3
Massachusetts .1
Michigan 5
Minnesota 5
Mississippi 4
Missouri 7
Montana 8
Nebraska 7
Nevada 9
NewHampshke 1
New Jersey 2
New Mexico 6
New York. 2
North Carolina.. 4
North Dakota.. 8
Ohio 5
Oklahoma 6
Oregon 10
Pennsylvania 3
Rhode Island 1
South Carolina 4
South Dakota 8
Tennessee , 4
Texas ..6
Utah 8
Vermont 1
Virginia , 3
Washington........ 10
West Virginia 3
Wisconsin 5
Wyoming 8
n-27
Reprinted from USGS Open-File Report 93-292
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STATE RADON CONTACTS
May, 1993
Alabama James McNees
Division of Radiation Control
Alabama Department of Public Health
State Office Building
Montgomery, AL 36130
(205)242-5315
1-800-582-1866 in state
Alaska Charles Tedford
Department of Health and Social
Services
P.O. Box 110613
Juneau,AK 99811-0613
(907)465-3019
1-800-478-4845 in state
Arizona John Stewart
Arizona Radiation Regulatory Agency
4814 South 40th St
Phoenix, AZ 85040
(602)255-4845
Arkansas Lee Gershner
Division of Radiation Control
Department of Health
4815 Marfcham Street, Slot 30
Little Rock, AR 72205-3867
(501) 661-2301
California J, David Quinton
Department of Health Services
714 P Street, Room 600
Sacramento, CA 94234-7320
(916) 324-2208
1-800-745-7236 in state
Colorado Linda Martin
Department of Health
4210 East llth Avenue
Denver, CO 80220
(303) 692-3057
1-800-846-3986 in state
Connecticut Alan J. Siniscalchi
Radon Program
Connecticut Department of Health
Services
150 Washington Street
Hartford, CT 06106-4474
(203) 566-3122
Delaware Marai G, Rejai
Office of Radiation Control
Division of Public Health
P.O. Box 637
Dover, DE 19903
(302) 736-3028
1-800-554-4636 In State
District Robert Davis
of Columbia DC Department of Consumer and
Regulatory Affairs
614 H Street NW
Room 1014
Washington, DC 20001
(202) 727-71068
Florida N. Michael Gilley
Office of Radiation Control
Department of Health and
Rehabilitative Services
1317 Winewood Boulevard
Tallahassee, EL 32399-0700
(904)488-1525
1-800-543-8279 in state
Richard Schreiber
Georgia Department of Human
Resources
878 Peachtree St, Room 100
Atlanta, GA 30309
(404) 894-6644
1-800-745-0037 in state
Hawaii Russell Takata
Environmental Health Services
Division
591 Ala Moana Boulevard
Honolulu, HI 96813-2498
(808) 5864700
n-28
Reprinted from USGS Open-File Report 93-292
-------
Idaho
Illinois
Indiana
Iowa
Kansas
Kentucky
PatMcGavarn
Office of Environmental Health
450 West State Street
Boise, ID 83720
(208) 334-6584
1-800-445-8647 in state
Richard Allen
Illinois Department of Nuclear Safely
1301 Outer Park Drive
Springfield, IL 62704
(217) 524-5614
1-800-325-1245 in state
Lorand Magyar
Radiological Health Section
Indiana State Department of Health
1330 West Michigan Street
P.O. Box 1964
Indianapolis, IN 46206
(317)633-8563
1-800-272-9723 In State
Donald A. Plater
Bureau of Radiological Health
Iowa Department of Public Health
Lucas State Office Building
Des Moines, IA 50319-0075
(515) 281-3478
1-800-383-5992 In State
Harold Spiker
Radiation Control Program
Kansas Department of Health and
Environment
109 SW 9th Street
6th Floor Mills Building
Topeka, KS 66612
(913)296-1561
JeanaPhelps
Radiation Control Branch
Department of Health Services
Cabinet for Human Resources
275 East Main Street
Frankfort, KY 40601
(502) 564-3700
Louisiana Matt Sehlenker
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 SueHendershott
Division of Radiological Health
Bureau of Environmental and
Occupational Health
3423 North Logan S treet
P.O. Box 30195
Lansing, MI 48909
(517) 335-8194
Minnesota LauraOatmann
Indoor Air Quality Unit
925 Delaware Street, SB
P.O. Box 59040
Minneapolis, MN 55459-0040
(612) 627-5480
1-800-798-9050 in state
H-29
Reprinted from USGS Open-File Report 93-292
-------
Mississippi Silas Anderson
Division of Radiological Health
Department of Health
3150 Lawson Street
P.O. Box 1700
Jackson, MS 39215-1700
(601) 354-6657
1-800-626-7739 in state
Missouri Kenneth V. Miller
Bureau of Radiological Health
Missouri Department of Health
1730 East Elm
P.O. Box 570
Jefferson City, MO 65102
(314) 751-6083
1-800-669-7236 In State
Montana Adrian C. Howe
Occupational Health Bureau
Montana Department of Health and
Environmental Sciences
Cogswell Building A113
Helena, MT 59620
(406)444-3671
Ncbraskq 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 Health
Division of Public Health Services
Health and Welfare Building
Six Hazen Drive
Concord, NH 03301
(603)271-4674
1-800-852-3345 x4674
New Jersey Tonalee Carlson Key
Division of Environmental Quality
Department of Environmental
Protection
CN415
Trenton, NJ 08625-0145
(609) 987-6369
1-800-648-0394 in state
New Mexico William M. Floyd
Radiation Licensing and Registration
Section
New Mexico Environmental
Improvement Division
1190 St. Francis Drive
Santa Fe.NM 87503
(505) 827-4300
New York William J. Condon
Bureau of Environmental Radiation
Protection
New York State Health Department
Two University Place
Albany, NY 12202
(518)458-6495
1-800-458-1158 in state
North Carolina Dr. Felix Fong
Radiation Protection Division
Department of Environmental Health
and Natural Resources
701 Barbour Drive
Raleigh, NC 27603-2008
(919) 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
11-30 Reprinted from USGS Open-File Report 93-292
-------
Oklahoma
Oregon
Pennsylvania
Puerto Rico
Rhode Island
South Carolina
Gene Smith
Radiation Protection Division
Oklahoma State Department of
Health
P.O. Box 53551
Oklahoma City, OK 73152
(405)271-5221
George Toombs
Department of Human Resources
Health Division
1400 SW 5th Avenue
Portland, OR 97201
(503)7314014
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 Mike Pochop
Division of Environment Regulation
Department of Water and Natural
Resources
Joe Foss Building, Room 217
523 E. Capitol
Kerre, SD 57501-3181
(605)773-3351
Tennessee Susie SMmek
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
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 n
in New York
(212)2644110
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
Washington KateColeman
Department of Health
Office of Radiation Protection
Airdustrial Building 5, LE-13
Olympia,WA 98504
(206)753-4518
1-800-323-9727 In State
BeattieL.DeBord
Industrial Hygiene Division
West Virginia Department of Health
151 llth Avenue
South Charleston, WV 25303
(304) 558-3526
1-800-922-1255 In State
Conrad Weiffenbach
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 Hoot
Cheyenne, WY 82002-0710
(307)777-6015
1-800-458-5847 in state
n-32
Reprinted ftom USGS Open-File Report 93-292
-------
STATE GEOLOGICAL SURVEYS
May, 1993
Alabama Ernest A, Mancini
Geological Survey of Alabama
P.O. Box 0
420 Hackberry Lane
Tuscaloosa, AL 35486-9780
(205) 349-2852
Thomas E. Smith
Alaska Division of Geological &
Geophysical Surveys
794 University Ave., Suite 200
Fairbanks, AK 99709-3645
(907)479-7147
Arizona Larry D. Fellows
Arizona Geological Survey
845 North Park Ave., Suite 100
Tucson, AZ 85719
(602) 882-4795
Arkansas Norman F. Williams
Arkansas Geological Commission
Vardelle Parham Geology Center
3815 West Roosevelt Rd.
Little Rock, AR 72204
(501) 324-9165
California James F, Davis
California Division of Mines &
Geology
801 K Street, MS 12-30
Sacramento, CA 95814-3531
(916)445-1923
Colorado Pat Rogers (Acting)
Colorado Geological Survey
1313 Sherman St., Rm 715
Denver, CO 80203
(303)866-2611
Connecticut Richard C. Hyde
Connecticut Geological & Natural
History Survey
165 Capitol Ave., Rm. 553
Hartford, CT 06106
(203) 566-3540
Delaware Robert R. Jordan
Delaware Geological Survey
University of Delaware
101 Penny Hall
Newark, DE19716-7501
(302)831-2833
Florida Walter Schmidt
Florida Geological Survey
903 W. Tennessee S..
Tallahassee, EL 32304-7700
(904)4884191
(georjga WMarn H. McLemore
Georgia Geologic Survey
Rm. 400
19 Martin Luther King Jr. Dr. SW
Atlanta, GA 30334
(404) 656-3214
Hawaii Manabu Tagomori
DepL of Land and Natural Resources
Division of Water & Land Mgt
P.O. Box 373
Honolulu, ffl
(808) 548-7539
Idaho Earl H. Bennett
Idaho Geological Survey
University of Idaho
Morrill Hall, Rm. 332
Moscow, ID 83843
(208) 885-7991
Illinois Morris W. Leighton
Illinois State Geological Survey
Natural Resources Building
615 East Peabody Dr.
Champaign, IL 61820
(217) 333-4747
Indiana Norman C. Hester
Indiana Geological Survey
611 North Walnut Grove
Bloomington, IN 47405
(812) 855-9350
Iowa
Donald L. Koch
Iowa Department of Natural Resources
Geological Survey Bureau
109TrowbridgeHal
Iowa City, IA 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
-dJIlpUS
n-33
Reprinted from USGS Open-File Report 93-292
-------
Kentucky Donald C. Haney
Kentucky Geological Survey
University of Kentucky
228 Mining & Mineral Resources
Building
Lexington, KY 40506-0107
(606)257-5500
Louisiana William E. Marsalis
Louisiana Geological Survey
P.O. Box 2827
University Station
Baton Rouge, LA 70821-2827
(504)388-5320
Maine Walter A. Anderson
Maine Geological Survey
Department of Conservation
State House, Station 22
Augusta, ME 04333
(207)289-2801
Maryland Emery T. Cleaves
Maryland Geological Survey
2300 St. Paul Street
Baltimore, MD 21218-5210
(410)554-5500
Massachusetts Joseph A. Sinnott
Massachusetts Office of
Environmental Affairs
100 Cambridge St. Room 2000
Boston. MA 02202
(617)727-9800
Michigan R. Thomas Scgall
Michigan Geological Survey Division
Box 30256
Lansing, MI 48909
(517) 334-6923
Minnesota Priscilla C. Grew
Minnesota Geological Survey
2642 University Ave.
St. Paul, MN 55114-1057
(612)627-4780
Mississippi S. Cragin Knox
Mississippi Office of Geology
P.O. Box 20307
Jackson, MS 39289-1307
(601) 961-5500
Missouri James H. Williams
Missouri Division of Geology &
Land Survey
111 Fairgrounds Road
P.O. Box 250
Rolla, MO 65401
(314) 368-2100
Montana Edward T.Ruppel
Montana Bureau of Mines & Geology
Montana College of Mineral Science
and Technology, Main Hall
Butte,MT 59701
(406)496-4180
Nebraska Perry B. Wigley
Nebraska Conservation & Survey
Division
113 Nebraska Hall
University of Nebraska
Lincoln, NE 68588-0517
(402)472-2410
Nevada Jonathan G. Price
Nevada Bureau of Mines & Geology
Stop 178
University of Nevada-Reno
Reno, NV 89557-0088
(702) 784-6691
New Hampshire Eugene L. Bondette
Dept. of Environmental Services
117 James Hall
University of New Hampshire
Durham, NH 03824-3589
(603) 862-3160
New Jersey Haig F. Kasabach
New Jersey Geological Survey
P.O. Box 427
Trenton, NJ 08625
(609)292-1185
New Mexico Charles E. Chapin
New Mexico Bureau of Mines &
Mineral Resources
Campus Station
Socorro.NM 87801
(505)835-5420
New York Robert H. Fakundiny
New York State Geological Survey
3136 Cultural Education Center
Empire State Plaza
Albany, NY 12230
(518)474-5816
11-34 Reprinted from USGS Open-File Report 93-292
-------
North Carolina Charles H. Gardner •
North Carolina Geological Survey
P.O. Box 27687
Raleigh, NC 27611-7687
(919) 733-3833
North Dakota John P. Bluemle
North Dakota Geological Survey
600 East Blvd.
Bismarck, ND 58505-0840
(701)224-4109
ihio 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
lOORBoyd
Norman, OK 73019-0628
(405)325-3031
Oregon Donald A. Hull
DepL of Geology & Mineral Indust.
Suite 965
800 NE Oregon St. f 28
Portland, OR 97232-2162
(503)731-4600
Pennsylvania Donald M. HosMns
Dept. of Environmental Resources
Bureau of Topographic & Geologic
Survey
P.O. Box 2357
Hanisburg, PA 17105-2357
(717) 787-2169
Puerto Rico Ram6n M. Alonso
Puerto Rico Geological Survey
Division
Box 5887
Puerta de Tierra Station
San Juan, P.R. 00906
(809) 722-2526
Rhode Island J. Allan Cain
Department of Geology
University of Rhode Island
315 Green Hall
Kingston, RI02881
(401)792-2265
South Carolina Alan-Jon W. Zupan (Acting)
South Carolina Geological Survey
5 Geology Road
Columbia, SC 29210-9998
(803) 737-9440
SouthPakpfa 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
Texas William L. Fisher
Texas Bureau of Economic Geology
University of Texas
University Station, Box X
Austin, TX 78713-7508
(512)471-7721
Utah M. Lee Allison
Utah Geological & Mineral Survey
2363 S. Foothill Dr.
Salt Lake City, UT 84109-1491
(801)467-7970
Vermont Diane L. Conrad
Vermont Division of Geology and
Mineral Resources
103 South Main St.
Waterbury.VT 05671
(802)244-5164
Stanley S. Johnson
Virginia Division of Mineral
Resources
P.O. Box 3667
Chartottesville, VA 22903
(804) 293-5121
Washington Raymond Lasmanis
Washington Division of Geology &
Earth Resources
Department of Natural Resources
P.O. Box 47007
Olympia, Washington 98504-7007
(206)902-1450
n-35
Reprinted from USGS Open-File Report 93-292
-------
West Virginia Larry D. Woodfork
West Virginia Geological and
Economic Survey
Mont Chateau Research Center
P.O. Box 879
Morgantown, WV 26507-0879
(304) 594-2331
Wisconsin James Robertson
Wisconsin Geological & Natural
History Survey
3817 Mineral Point Road
Madison, WI 53705-5100
(608) 263-7384
Wyoming Gary B. Glass
Geological Survey of Wyoming
University of Wyoming
Box 3008, University Station
Laramie, WY 82071-3008
(307)766-2286
tt-36
Reprinted from USGS Open-File Report 93-292
-------
EPA REGION 1 GEOLOGIC RADON POTENTIAL SUMMARY
by
Linda C.S. Gundersen, R. Randall Schumann, and Sandra L. Szarzi
US. 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, still are generalized assessments and
there is no substitute for having a home tested. Within any radon potential area homes with indoor
radon levels both above and below the predicted average likely will be found.
Figure 1 shows a generalized map of the physiographic/geologic provinces in Region 1.
The following summary of radon potential in Region 1 is based on these provinces. Figure 2
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 generaEy 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 several fault-bounded areas in the northern part 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
fll-l Reprinted from USGS Open-File Report 93-292-A
-------
LAKE
CHAMPLAIN
23'
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
Terrane; 13-GanderTerrane; 14-Avalonian Composite Terrane; 15-Northeastern Highlands; 16-Vermont Piedmont;
17-Gresn Mountains; 18-Champlain Lowland; 19-Vermont Valley; 20,21-Taconic Mouniains-Stockbridge Valley;
22-Berkshire Mountains; 23-Proto-North American Terrane; 24,25-Taconie Allochthons; 26-Connecticut Valley
Synclinorium; 27-Western Connecticut Valley Belt; 28,29-Connecticut Valley (Mesozoic Basins); 30-Gneissic domes
of the Eastern Connecticut VaHey 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 Terranes; 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
3 B3 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
f~1 LOW (<2 pCt/L)
EU MODERATE/VARIABLE (2-4 pCi/L)
HI 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 wf elevated indoor radon lev Js 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 SyncHnorium 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 amphibolite. 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 well as
locally-occurring graphitic schist 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.
m-5 Reprinted from USGS Open-File Report 93-292-A.
-------
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 pCi/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 clastic 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. Gale-alkaline to alkaline
granites are more abundant in the southern and central part of 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 due 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 metasedimentary 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 in much of central
and northern Maine and the rocks underlying these areas are metasedimentary and metavolcanic
rocks that are generally low in uranium.
MASSACHUSETTS
The metamorphic rocks of the Taconic Mountains and carbonate sedimentary and
metasedimentary 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 permeabiEty. The Pauchaug and
Glastonbury granite gneisses, which form the cores of the Warwick and Glastonbury domes, as
ffl-7 Reprinted from USGS Open-File Report 93-292-A
-------
well as other locaUy-oecurring 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 metamorphie 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 metavolcanic
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. Proterozoic 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
IH-8 Reprinted from USGS Open-File 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 wet to preclude soil-gas transport
NEW HAMPSHIRE
The Avalonian Composite Terrane, in southeastern New Hampshire (area 14, fig, 1), is
underlain by the Merriniack Group, Massabesic Gneiss, the Rye Formation and several bodies of
two-mica granites, alkalic plutonic rocks, and mafic plutonie 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 metamorpMc
rocks of igneous or sedimentary origin of the Gander (area 13, fig. 1) and Boundary Mountains
(area 12) Terranes. These rocks have been ranked moderate in radon potential overall. 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-alkaline 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.
ffl-9 Reprinted from USGS Open-File 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
the underlying bedrock and secondarily affected by "I"1"*'' * 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. I), as well as with two areas also noted for high uranium: the northwestern and southwestern
corners 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 Her 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 collection 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 tils. Tills commonly have Mgher 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, aU of which have some elevated uranium concentrations.
DI-IO 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 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 moderate 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.
-l 1 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 CONNECTICUT
by
Linda C,S, Gundersen andR. Randall Schumann
U.S. Geological Survey
INTRODUCTION
Radon potential in Connecticut varies from low to high. In measurements of 4798 homes
sampled in the State/EPA Residential Radon Survey and the Connecticut Household Testing
Program during 1986-88, the average for the state was 3.1 pCi/L and 20.3 percent of the homes
tested had indoor radon levels exceeding 4 pCi/L, Of the eight counties in Connecticut, only New
Haven County had an indoor radon average greater than 4 pCi/L. Averages for the rest of the
counties were between 2 and 4 pCi/L. Most sedimentary rocks of the Hartford and Pomperaug
basins have low geologic radon potential, whereas granites, granitic gneisses, and some graphitic
schists and phyllites tend to generate elevated indoor radon levels and thus are assigned high radon
potential. TMs chapter presents a discussion of the bedrock and glacial geology, soils, and
radioactivity of Connecticut in the context of indoor radon.
This is a generalized assessment of geologic radon potential of rocks, soils, and surficial
deposits of Connecticut. The scale of this assessment is such that it is inappropriate for use in
identifying the radon potential of small areas such as neighborhoods, individual building sites, or
housing tracts. Any localized assessment of radon potential must be supplemented with additional
data and information from the locality. Within any area of a given radon potential ranking, there
are likely to be areas with higher or lower radon levels than characterized for the area as a whole.
Indoor radon levels, both high and low, can be quite localized, and there is no substitute for testing
individual homes. Elevated levels of indoor radon have been found in every State, and EPA
recommends that all homes be tested. For more information on radon, the reader is urged to
consult the local or State radon program or EPA regional office. More detailed information on state
or local geology may be obtained from the state geological survey. Addresses and phone numbers
for these agencies are listed in chapter 1 of this booklet
PHYSIOGRAPHIC AND GEOGRAPHIC SETTING
The physiography of Connecticut (fig. 1) is in part a reflection of the underlying bedrock
geology (fig. 2), and each major physiographic region is underlain by distinct geologic terranes
(fig. 1). The surface of the land has also been shaped extensively by glaciers. There are three
major physiographic regions in Connecticut: the Western Uplands, the Central Lowlands, and the
Eastern Uplands. Elevation ranges from sea level along the Atlantic coast in the southern part of
the State to 2,380 ft at Mt Frissell in the Western Uplands.
The Western Uplands consists of rolling hills and mountains underlain by deformed
sedimentary, igneous, and metamorphic rocks. In the northwestern portion of the Western
Uplands, valleys, such as the Marble Valley, are underlain by carbonate rocks, whereas the
mountains are formed from schist, gneiss, and granite. To the southwest, the terrain is gentler,
more rolling Mils underlain by schist The northern part of the Western Uplands includes the
southern extension of the Berkshire Mountains, and the Taconic Mountains, Housatonic
Highlands, and Hudson Highlands form mountains along the State's western border.
IV-1 Reprinted from USGS Open-File Report 93-292-A
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WESTERN UPLAMDS
» 4_GENTRAL LOWLANDS -M
EASTERN UPLANDS
GEOLOGIC TERRANES Of
CONNECTICUT
I. Newark (Rift Valley) Tenane
a, Hartford Basin
b. Poinperaug Basin
2.1'roto-Norlh American (Continental) Terrene
a. Carbonate shelf
b. Proterozoic massifs "Orcnviile"
3. Inpetos (Oceanic) Terrane
a, Connecticut Valley Synclinorium
b. Bronson Hill Anticlinorium
c. Merrimack Synclinotium
d. Taconic AUochthons
4. Avaioniart (Continental) Terrane
Figure 1. Physiographic provinces and geologic terranes of Connecticut (after Rodgers, 1985).
-------
Figure 2.
Generalized bedrock geologic map of
Connecticut (modified from Benmson,
1976, using Rodgers, 1985),
-------
GENERALIZED GEOLOGIC MAP OF CONNECTICUT
EXPLANATION
QUATERNARY
Undifierentiated alluvium and glacial deposits
TACONIC ALLOCHTHONS (DISPLACED IAPETOS TERRANE)
CAMBRIAN
Everett Schist: Schist and phyllite, composed of quartz, albite or oligoclase, muscovite, garnet, staurolite
or chloritoid, and generally chlorite
Manhattan Schist: Gneiss and schistose gneiss, composed of quartz, oligoclase, microcline, Motile, and
muscovite, and generally sillimanite and garnet Amphibolite layers locally, especially near base.
Canaan Mountain Schist: Schist and schistose gneiss, composed of quartz, plagioclase, biotite,
muscovite, and generally garnet and sillimanite; also layers of amphibolite and quartzite
Hoosac Schist; Schistose gneiss composed of quartz, biotite, plagioclase, muscovite, and generally garnet
and sillimanite or kyanite.
Waterbury Gneiss: Schist and schistose gneiss, composed of biotite, quartz, oligoclase, kyanite (or
sillimanite), and garnet, also locally microcline, irregularly mixed with granitoid gneiss, composed of
oligoclase or andesine, quartz, biotite, and commonly microcline and muscovite (in Connecticut Valley
Synclinorium)
ORDOVICIAN AND CAMBRIAN SHELF SEQUENCE
ORDOVICIAN
Walloomsac Schist: Schist or phyllite, composed of quartz, albite, and commonly garnet and staurolite or
sillimanite (locally strongly retrograded to chlorite and muscovite). Locally feldspathic or calcareous near
the base
Stockbridge Marble (including Inwood Marble) (LOWER ORDOVICIAN AND CAMBRIAN):
Massive to layered marble, generally dolomitic but containing calcite marble in upper part, locally
interlayered with schist or phyllite and with calcareous siltstone, sandstone, and quartzite
CAMBRIAN
Cheshire Quartzite: Mainly pure, white, glassy, tough quartzite
Dalton Formation (including Poughquag Quartzite and Lowerre Formation): Gneiss or feldspathic
quartzite, composed of quartz, microcline, plagioclase, muscovite, biotite, and generally tourmaline; some
schistose micaceous layers have sillimanite, commonly as quartz-sillimanite nodules rimmed with
muscovite. Layers of purer quartzite in many areas, especially near the top or where the formation is thin
PROTEROZOIC MASSIFS - "GRENVILLE"
PROTEROZOIC
Pink granitic gneiss composed of quartz, microcline, oligoclase, and either biotite or muscovite or both,
also locally amphibole or
Augen gneiss (including local term "Danbury Gneiss;"Granitic gneiss, composed of microcline (largely as
megacrysts or augen up to 10 cm long), quartz, albite, or oligoclase, biotite and minor hornblende
Layered gneiss composed of quartz and plagioclase, with microcline locally in the light layers and abundant
biotite and common hornblende in the dark layers; garnet or epidote locally. Layers and lenses of calc-
silicate rock and amphibolite in some areas
Hornblende gneiss and amphibolite composed of hornblende and plagioclase, also commonly biotite and
minor quartz; commonly interlayered with banded felsic gneiss. Locally contains calc-silicate rock or
diopsidic calcite marble
Rusty mica schist and gneiss composed of quartz, plagioclase, biotite, muscovite, sillimanite, and locally
garnet; some layers of feldspathic quartzite and garnetiferous amphibolite
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GEOLOGIC MAP OF CONNECTICUT EXPLANATION PG 2
NEWARK TERRANE
HARTFORD AND POMPERAUG MESOZOIC BASINS
JURASSIC
Buttress Dolerite: Basalt near contacts to fine-grained gabbro in the interior, composed of plagioclase and
pyroxene with accessory opaques and locally devitrified glass, quartz or olivine
West Rock Dolerite: Basalt near contacts to fine-grained gabbro in the interior, generally massive with
well-developed columnar jointing, composed of plagioclase and pyroxene with accessory opaques and
locally devitrified glass, quartz, or olivine
Newark Supergroup
Portland Arkose: Arkose, siltstone and red to black fissile silty shale. Grades eastward into coarse
conglomerate (fanglomerate)
Hampden Basalt (Lower Jurassic): Greenish-gray to black (weathers bright orange to brown), fine- to
medium-grained, grading from basalt near contacts to fine-grained gabbro in the interior, composed of
pyroxene and plagioclase with accessory opaques and locally olivine or devitrified glass
Holyoke Basalt: Basalt near contacts to gabbro in the interior, composed of pyroxene and plagioclase with
accessory opaques and locally olivine or devitrified glass
Shuttle Meadow Formation: Siltstone, and fine-grained silty sandstone, generally well and thinly
laminated. In the southern part of the State includes a layer, up to 5 m thick, of blue, commonly sandy,
fine-grained limestone or dolomitic limestone, grading laterally into calcareous siltstone. Coarser and more
arkosic to east and south, grading into conglomerate near the eastern border fault
Talcott Basalt: Basalt near contacts to fine-grained gabbro in the interior, composed of pyroxene and
plagioclase with accessory opaques and locally olivine or devitrified glass. Pillows in many places;
volcanic breccia with fragmentary pillows in others
East Berlin Formation: Siltstone, silty and sandy shale, and fine-grained silty sandstone, generally well
laminated and commonly well indurated, alternating with dark fissile shale; dolomitic carbonate common in
cement, concretions, and thin argillaceous laminae. Local arkose; grades eastward into coarse
conglomerate close to eastern border fault
UPPER TRIASSIC TO LOWER JURASSIC
New Haven Arkose: Arkose, interbedded with brick-red micaceous, locally shaly siltstone and fine-
grained feldspathic clayey sandstone
IAPETOS (OCEANIC) TERRANE
CONNECTICUT VALLEY SYNCLINORIUM
DEVONIAN
Nonewaug Granite: Massive to layered granite composed of albite, microcline, quartz, and museovite,
with minor biotite and garnet.
ORDOVICIAN (?)
Granitic gneiss composed of sodic plagioclase, quartz, microcline, museovite, and biotite, and locally
garnet or sulimanite. Commonly contains numerous inclusions or layers of mica schist and gneiss
ORDOVICIAN
Litchfield Norite: Massive mafic rock (olivine norite, quartz norite, hypersthene pyroxenite), composed of
labradorite, hypersthene, augite, and olivine in varying proportions, also hornblende and biotite (and minor
quartz in quartz norite). Associated with small mineral deposits of pyrrhotite, penflandite, and chalcopyrite
Brookfield Gneiss Speckled or banded, medium- to coarse-grained, massive to poorly foliated gneiss,
composed of plagioclase, biotite, and hornblende, generally with quartz and K-feldspar, the latter
commonly as megacrysts 1 to 3 cm across (also plagioclase megacrysts in darker rocks), locally associated
with hornblende schist
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GEOLOGIC MAP OF CONNECTICUT EXPLANATION PG 3
Hartland Belt
DEVONIAN-SILURIAN
The Straits Schist: Schist composed of quartz, muscovite, biotite, oHgoelase, garnet, and commonly
staurolite and kyanite or sillimanite; graphitic almost throughout
Southington Mountain Member of Straits Schist: Massive adamellite, composed of microcline,
albite; quartz, and muscovite with accessory fluorite. High radioactivity
Basal member of the Straits Schist; Layers of amphibolitc, marble, calc-silicate rock, and quartzitc
within more uniform schist like that on either side. Minor, unevenly distributed mineralization in W,
Bi, Cu, Ni, and other metals
Wepawaug Schist (Orange-Milford Belt): Schist or phyllite and metasiltstone, composed of quartz,
muscovite or sericite, plagioclase, biotite, and in appropriate metamorphic zones chlorite, garnet, stauroHte,
and kyanite. Schist or phyllite generally graphitic
ORDOVICIAN
Trap Falls Formation (may be equivalent in part of Golden Hill Schist) Well layered schist, composed of
quartz, sodic plagioclase, biotite, muscovite, and garnet, locally with sillimanite or kyanite, interlayered
with two-mica gneiss and granulite and with amphiboHte
Carringtons Pond Member: Schist and light-gray, fine- to medium-grained gneiss, composed of
interlayered medium- to dark-gray, rusty-weathering, medium-grained schist and light-gray, fine- to
medium-grained gneiss, composed of quartz sodic plagioclase, biotite, muscovite, and garnet, schist
locally contains sillimanite or kyanite; gneiss locally contains K-feldspar; amphibolite layers common
Schist and granulite member: Schist and fine-grained granofels, composed of quartz, sodic
plagioclase, biotite, and muscovite; garnet common in schist
Cobble Mountain Formation: Schist and granofels, composed of quartz, oligoclase, muscovite, biotite,
and garnet, and locally kyanite and staurolite or sillimanite, some amphibolite layers
Harrison Gneiss: (including Prospect Gneiss) Gneiss, composed of andesine, quartz, hornblende, and
biotite (also locally K-feldspar as megacrysts 1 to 5 cm long). Thought to be metavolcanic equivalent of
Brookfield Gneiss
Pumpkin Ground Member: Gneiss, composed of oligoclase, microcline, quartz, and biotite; some
layers have numerous microcline megacrysts 1 to 5 cm across; others have hornblende. Minor layers
of garnetiferous schist and gneiss
Beardsley Member: Gneiss, composed of plagioclase, quartz, microcline, hornblende, biotite, and
epidote. Microcline may occur as megacrysts 1 to 3 cm across. Minor layers of gametiferous schist
and rarely of calc-silicate rock or marble
Nodular member: Harrison Gneiss containing prominent quartz-sillimanite nodules
Golden Hill Schist (may be equivalent to part of Trap Falls Formation) Schist and granofels, composed of
quartz, muscovite, biotite, plagioclase, and garnet
Eatlum Mountain Schist Interlayered schist and granofels, composed of quartz, oligoclase, muscovite (in
the schist), Biotite, and garnet, also Gray, medium-grained, interlayered schist and granofels, composed of
quartz, oligoclase, muscovite (in the schist), biotite, and garnet, also staurolite and kyanite in the schist.
Numerous layers and lenses of amphibolite; also some of quartz-spessartine (coticule) and Gale-silicate
rock. Includes an amphibolite unit composed of massive amphibolite and hornblende gneiss, composed of
hornblende and andesine, commonly with minor quartz and magnetite, and locally with garnet, biotite, and
epidote
Rowe Schist (ORDOVICIAN TO CAMBRIAN): Schist, composed of quartz, muscovite, biotite,
oligoclase, and generally garnet, stauroHte, and kyanite or sillimanite. Layers of granofels common; also
some layers of amphibolite, quartz-spessartine rock (coticule), and calc-silicate rock. Includes an
amphibolite unit comprising generally massive amphibolite and hornblende gneiss, composed of
hornblende and andesine
Taine Mountain Formation: Gneissic or schistose granofels, composed of quartz, oligoclase, biotite,
muscovite, and garnet, and locally staurolite and kyanite or sillimanite
Whigville Member: Gneissic or schistose granofels, composed of quartz, oligoclase, biotite,
muscovite, and garnet, and locally stauroHte and kyanite or silHmanite
Scranton Mountain Member: Schist, composed of quartz, muscovite, biotite, plagioclase, garnet,
and generally kyanite
Wildcat Member: Gneissic or schistose granofels, composed of quartz, oHgoclase, biotite, muscovite,
and garnet, and locally stauroHte and kyanite or silHmanite
Basal member around Waterbury dome: Differs from rest of Taine Mountain Formation in being
especially well layered and generally less micaceous and schistose
-------
GEOLOGIC MAP OF CONNECTICUT EXPLANATION PG 4
ORDOVICIAN ' „.
INCLUDED IN THIS MAP UNIT (outcrops too small to be shown separately):
Pmewood Adamellite(PERMIAN): Massive adamellite, composed of microcline, albite, quartz, and
muscovite with accessory fluorite. High radioactivity
Lamprophyre (DEVONIAN?): Badly altered dike rock, composed of biotite, augite, K-feldspar, and
accessory apatite and sphene, plus secondary minerals
Ultramaftc rock (ORDOVICIAN OR OLDER), originally composed of olivine and pyroxene, now
generally altered to tremolite, talc, chlorite, or serpentine
Shelton Member of Trap Falls Formation: Granitic gneiss, composed of sodic plagioclase, quartz,
microcline, muscovite, and garnet (in tiny almost ubiquitous grains), also commonly minor biotite;
generally interlayered with mica schist, biotite gneiss, and calc-silicate rock.
Hawley Formation (carbonaceous schist fades); Schist and granofels, composed of quartz, oligoclase,
and biotite; some muscovite and graphite, rare garnet and kyanite or sillimanite. Layers of quartz-
spessartine rock (coticule) common
Collinsville Formation (undivided): Mixture of schist, composed of quartz, oligoclase, biotite, muscovite,
and garnet, and in place kyanite or sfflimanite (Sweetheart Mountain Member), with hornblende gneiss
described below; in many areas felsic and mafic striped metavolcanic rocks predominate
INCLUDED IN THIS MAP UNIT (outcrops too small to be shown separately):
Porphyry (dacite or rhyolite) (PERMIAN): Massive porphyry with phenocrysts of quartz, feldspar, and
biotite; muscovite and accessory fluorite in ground mass
Syenite (PEEMIAN): Massive syenite, composed of microcline, amphibole and biotite with accessory
apatite and sphene
Hornblende gneiss member of Collinsville Fin.: Well-layered amphibolite and hornblende gneiss,
composed of hornblende and plagioclase, commonly with biotite, garnet, or epidote, interlayered with
light-gray felsic gneiss and pink quartz-spessartine rock (coticule). Grades into Bristol Gneiss; includes
minor amounts of the Sweetheart Mountain Member of Collinsville Fm.
Bristol Gneiss: Gneiss, composed of plagioclase, quartz, and biotite, also muscovite and garnet in many
layers, interlayered in places with dark amphibolite
Orange-Milford Belt
ORDOVICIAN
Maltby Lakes Metavolcanics: Greenstone, greenschist, and schist; also dark amphibolite to west and
southwest. Upper pare Greenstone and greenschist, composed of epidote, albite, actinolite, and chlorite,
and locally minor quartz, sericite, garnet, pyrite, or calcite. Mainly metavolcanic. Lower part:
Greenschist, greenstone, and schist or phyllite, composed of albite and chlorite, plus quartz and sericite or
epidote and actinolite. Mixed metavolcanic and metasedimentary rocks
Allingtown Metavolcanics: Greenstone, composed of epidote, actinolite, albite, and chlorite, commonly
with abundant megacrysts of saussurite, interlayered with minor green phyllite, generally containing quartz
and sericite. Dark amphibole in western outcrops
Oronoque Schist: Schist and granofels, composed of quartz, oligoclase or albite, muscovite or sericite,
biotite or chlorite, and in western belt local garnet, staurolite, and kyanite. Small lenses of amphibolite or
greenstone
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GEOIXJGIC MAP OF CONNECTICUT EXFLANA-ilONPO 5
BRONSON HILL ANTICLINORIUM
DEVONIAN(?)
Maromas Granite Gneiss: Granitic gneiss, composed of quartz and microcline with minor plagioclase
and biotite. Central body is massive, but outlying strips are foliated and have accessory hornblende or
garnet Massive parts may be young anatectic intrusive rocks; foliated parts may include older felsic
metavolcanic rocks belonging to the metavolcanic member of the Collins Hill Formation, Pegmatite bodies
are common in the vicinity
DEVONIAN
Erving Formation: Granofels and schist, composed of quartz, plagioclase, and biotite, also muscovite in
schist, and accessory garnet and kyanite
Littleton Formation: Alternating schist and micaceous quartzite, composed of quartz, muscovite, biotite,
garnet, and oligoclase, also staurolite, graphite, and ilmenite, and in certain areas kyanite or sillimanite in
schist
Mount Pisgah Member of Littleton Formation: Granofels or micaceous quartzite with some schist,
composed of quartz, oligoclase, biotite, garnet, and sillimanite
SILURIAN
Fitch Formation: Cale-silicate rock, composed of quartz, biotite, calcite, aetinolite, diopside, microcline,
and locally garnet, scapolite, or epidote, interlayered with two-mica schist
Clough Quartzite: Quartzite and muscovitic quartzite, locally with garnet; conglomeratic (commonly with
tourmaline) in lower part
ORDOVICIAN
Glastonbury Gneiss: Granitoid gneiss composed of oligoclase, quartz, microcline, and biotite (as
patches), also epidote and hornblende in many areas, commonly associated with layers of amphibolite; else
where minor muscovite and garnet
Collins Hill Formation: Schist, composed of quartz, oligoclase, muscovite, biotite, and garnet, and
commonly staurolite, kyanite, or sillimanite, generally graphitic, interlayered with fine-grained two-mica
gneiss, especially to ihe west, and with calc-silicate and amphibolite layers, also rare quartz-spessartine
(coticule) layers
Metavolcanic member of Collins Hill Formation: Ranges from mafic to felsic, from dark layered
amphibolite and hornblende schist, locally with garnet or epidote, to light-gray (in places purplish),
laminated gneiss, composed of quartz, oligoclase, and biotite, in which some layers contain garnet
(generally manganifcrous) and hornblende or cummingtonite
Middletown Formation: Gneiss and granofels, ranging from quartz-biotite gneiss through felsic
amphibole gneiss to amphibolite and characteristically containing anthophyllite or cummingtonite with or
without hornblende. Also layers of calc-silicate rock and of biotite gneiss with quartz-silfimanite nodules
Upper member: Gneiss and granofels, composed of oligoclase, quartz, biotite, and amphibole
(cummingtonite, anthophyllite, gedrite, or hornblende, or several of these), also garnet and chlorite.
Many layers of amphibolite and biotite gneiss throughout
Lower member: Amphibolite and hornblende gneiss, commonly with garnet, diopside, or epidote,
interlayered with light-gray gneiss composed of oligoclase, quartz, biotite, and generally one or more
amphiboles, also garnet
Massive mafic rock (in Middletown Fm.): Massive amphibolite and metagabbro, composed of
hornblende and plagioclase; in places with quartz and epidote, in others with patches of actinolite or
anthophyllite, chlorite, and epidote or garnet. May be intrusive
Ultramafic rock: Ultramafic rock, originally composed of olivine and pyroxene, now generally altered to
tremolite, talc, chlorite, or serpentine
Monson Gneiss: Gneiss and amphibolite; gneiss composed of plagioclase, quartz, and biotite, with
hornblende in some layers and microcline in others; traces of garnet, epidote, and magnetite; map unit
includes small outcrops of the Proterozoic Waterford Group
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GEOLOGIC MAP OF CONNECTICUT EXPLANATION PO 6
MERRIMACK SYNCLINORIUM
DEVONIAN OR SILURIAN
Scotland Schist: Schist, composed of quartz, muscovite, biotite, staurolite, and oligoclase, locally with
kyanite or sillimanite; interlayered, especially below and to the west, with quartz-oligoclase-biofite schist
and granofels and locally with quartzite; includes a quartzite unit: Quartzite, generally micaceous,
interlayered with mica schist
SILURIAN-ORDOVICIAN
Bigelow Brook Formation
Upper, member: Schist, composed of plagioclase, quartz, biotite, garnet, and sillimanite, locally with
K-feldspar or cordierite, fissile layers commonly with graphite and pyrrhotite, interlayered with
quartzose granofels with less biotite but with calc-silicate minerals
Middle member: Calc-silicate rock, composed of plagioclase, quartz, and diopside (locally
hornblende and scapolite), interbedded with schist and granofels composed of plagioclase, quartz,
biotite, and commonly garnet and sillimanite
Lower member: Granofels, composed of quartz, oligoclase, and biotite, commonly with garnet and
sillimanite, interlayered with thinly fissile sffimanitic, graphitic, pyrrhotMc biotite schist and with
calc-silicate rock
Southbridge Formation: Interlayered granofels and schist, composed of quartz, plagioclase, and biotite,
with muscovite in schist, and amphibole, calc-silicate minerals or K-feldspar in certain layers; also locally
mappable units and thinner layers of calc-silicate rock ampMbolite, and sillimanite-gamet and sillimanite-
graphite-pyrrhotite schist.
Hebron Gneiss: Schist, composed of andesine, quartz, biotite, and local K-feldspar, and greenish-gray,
fine- to medium-grained calc-silicate rock, composed of labradorite, quartz, biotite, actinolite, hornblende,
and diopside, and locally saprolite. Local lenses of graphitic two-mica schist
_ Porphyritic member of Southbridge Formation: Massive to layered gneiss, composed of quartz,
oligoclase, microcline, and biotite, with megacrysts 1 to 2 cm long of microcline
ORDOVICIAN
Brimfield Schist: Interlayered schist and gneiss, composed of oligoclase, quartz, K-feldspar, and biotite,
and commonly garnet, siffimanite, graphite, and pyrrhotite. K-feldspar partly as augen 1 to 3 cm across.
Minor layers and lenses of hornblende- and pyroxene-bearing gneiss, ampMbolite, and calc-silicate rock
Hornblende norite (DEVONIAN?): Massive rock, composed of bytownite, hornblende, and hypersthene
Foliated quartz diorite (DEVONIAN in part, ORDOVICIAN in part): Gneiss (locally strongly
sheared, especially near contacts), composed of plagioclase, quartz, biotite, and hornblende, locally also
pyroxene
Gneiss (metavolcanic) member of Brimfield Schist: Layered gneiss and schist, composed of oligoclase,
quartz, and biotite; some gneiss and most schist layers contain garnet and sillimanite; some gneiss layers
contain garnet, hornblende, or pyroxene or grade into amphibolite or calc-siHeate rock. Probably includes
metavolcanic rocks
Tataic HOI Formation; Gneiss or schist composed of quartz, andesine, biotite, garnet, and sillimanite,
locally kyanite, muscovite, or K-feldspar, interlayered with locally mappable units and thinner layers of
rusty-weathering graphitic pyrrhotitie two-mica schist, amphibolite, and calc-sflicate rock
Yantic Member: Schist, composed of quartz, oligoclase, biotite, and muscovite, some layers with
garnet, stauroHte, and kyanite or garnet and sillimanite, local epidote or K-feldspar; some layers of
rusty-weathering graphitic, pyrrhotitie, two-mica schist
Fly Pond Member: Massive calc-silicate gneiss, composed of andesine, quartz, hornblende or
actinolite, epidote, and commonly diopside, biotite, and scapolite; some layers are calcitic
Quinebaug Formation: Gneiss, composed of hornblende, andesine, biotite, and epidote, commonly with
quartz or garnet, interlayered with amphibolite
Felsic gneiss member: Gneiss, composed of pkgioclase, quartz, biotite, and muscovite, commonly
with K-feldspar
Black Hill Member: Schist and granofels, composed of oligoclase, quartz, and biotite, commonly
with hornblende or muscovite, and locally with calcite, garnet of epidote
-------
GEOLOGIC MAP OF CONNECTICUT EXPLANATION PG 7
DEVONIAN?
Foliated granitic gneiss: Gneiss, composed of phenocrysts of K-feldspar in a groundmass of plagioclase,
quartz, K-feldspar, and biotite, with accessory sillimanite and garnet
DEVONIAN
Canterbury Gneiss: Gneiss, composed of quartz, oligoclase, microcline, and biotite, locally also
muscovite or epidote, and generally with megacrysts 1 to 2 cm long of either or both feldspars
"Eastford gneiss phase": Gneiss, composed of quartz, microcline, oligoclase or albite, biotite, and
muscovite
Lebanon Gabbro: Locally sheared gabbro, composed of hornblende, labradorite, and opaques. Some
bodies contain biotite and quartz; some smaller ones are nearly pure hornblende with local augite,
Dioritic phase: Foliated or sheared gneiss, composed of plagioclase, biotite, quartz, and generally
hornblende
Preston Gabbro (MIDDLE ORDOVICIAN OR OLDER): Massive gabbro, composed of labradorite,
augite, and opaques, generally with hornblende, locally hypersthene or olivine or both
Dioritic phase: Medium-grained diorite and quartz diorite, gneissic where sheared near contact,
composed of plagioclase, hornblende, and biotite, and locally quartz and relic pyroxene
AVALONIAN (CONTINENTAL) TERRANE
AVALONIAN ANTICLINORIUM
PERMIAN
Narragansett Pier Granite: Granite, composed of microcline, oligoclase, quartz, and biotite and
accessory muscovite and magnetite. Considerable associated pegmatite
Mafic phase: Massive granite, like the Narragansett Pier Granite but with more biotite and locally
hornblende
PROTEROZOIC Z?
Sterling Plutonic Group
Hope Valley Alaskite Gneiss: AlasMtic gneiss, composed of microcline, quartz, albite or oligoclase, and
minor magnetite, and locally biotite and muscovite. Lineation formed by rods of quartz. Locally contains
quartz-siUimanite nodules
Potter Hill Granite Gneiss: Granitic gneiss, composed of microcline, quartz, oligoclase (or albite), biotite,
and magnetite, minor muscovite, and local garnet
"Scituate" Granite Gneiss (probably not equivalent to type Scituate in Rhode Island, which is probably
Devonian): Granitic gneiss, composed of microcline, quartz, albite or orthoclase, biotite, hornblende, and
magnetite. Megacrysts of microcline up to 3 cm long; lineation formed by splotches of biotite or by rods of
quartz
Porpbyritic phase of Potter Hill Granite Gneiss: Granitic gneiss, composed of microcline (much of it as
megacrysts up to 4 cm long), quartz, oligoclase, biotite, and magnetite
Ponaganset Gneiss: Gneiss, composed of oligoclase, quartz, microcline (mostly as megacrysts to to 8 cm
long), biotite, magnetite, and generally hornblende; also garnet and muscovite where hornblende is absent
Light House Gneiss: Granitic gneiss, composed of K-feldspar, oHgoclase, quartz, biotite, and magnetite,
with local muscovite but no garnet
Branford Gneiss: Granitic gneiss, composed of oligoclase, K-feldspar, quartz, biotite, garnet, magnetite,
and muscovite
Stony Creek Granite Gneiss: Granite or granite gneiss, composed of oligoclase, K-feldspar, and quartz
with minor biotite and magnetite, sporadic garnet (in foliated varieties), and local muscovite. Commonly
contains granite and pegmatite of Narragansett Her type (and probably age). In much of area both granites
occur as innumerable veins penetrating other units or as larger bodies Ml of inclusions of those units,
which can be mapped through the bodies of granite
-------
GEOIXJ0IC MAP OF CONNECIICOTEXKANATION PG S
PROTEROZOIC Z?
Waterford Group: Gneiss, composed ofplagioclase; Quartz, and biotite, with hornblende in some layers
and mierocline in others. Some layers of amphibolite
Rope Ferry Gneiss: Gneiss, composed ofplagioclase, quartz, and biotite, with hornblende in some layers
and mierocline in others. Some layers of amphibolite
Mamacoke Formation: Gneiss, composed ofplagioclase, quartz, and biotite, sillimanite, garnet,
hornblende or mierocline in certain layers; in upper part locally contains quartz-sillimanite nodules or thin
layers of quartzite, amphibolite, or calc-silicate rock
Westerly Granite (PERMIAN): Granite, composed of oligoclase or albite, quartz, and K-feldspar, with
minor biotite and accessory muscovite, magnetite, allanite, and sphene
New London Gneiss: Granodioritic gneiss, also interlayered light-gray gneiss and dark-gray amphibolite;
gneiss generally medium grained; composed of oligoclase, quartz, biotite, and magnetite, also mierocline in
massive gneiss
Joshua Rock Member: Gneiss composed of microperthite, quartz, albite, aegerine-augite, and
magnetite; rare riebeckite
Plainfield Formation: Interlayered quarteite, phyUite, (locally graphitic) and gneiss composed of quartz,
oligoclase, and biotite (rarely mierocline), medium- to dark-gray schist composed of quartz oligoclase,
biotite, sillimanite, and garnet, dark-gray or green gneiss composed ofplagioclase, quartz, biotite, and
hornblende (commonly with diopside), amphibolite, diopside-bearing quartzite, and calc-silicate rock. In
places contains quartz-sillimanite nodules
Quartzite unit: Quartzite, also feldspathic and micaceous quartzite containing quartz-sillimanite
nodules
FAULT-RELATED ROCKS
Silicified rock and mylonite along Mesozoic faults (PROBABLY JURASSIC): Close network of quartz
veins and veinlets cutting each other and older rock. In places, incompletely replaced rock shows strongly
mylonitic texture
Mylonite along Paleozoic faults (PALEOZOIC): Intensely granulated quartz, plagioclase, biotite, and
epidote, in places with hornblende and microeline and commonly with secondary minerals. In places has
been silicified
-------
The Central Lowlands, also called the Connecticut Valley, is a downfaulted block of land
underlain by sedimentary and igneous rocks. The terrain is level to flat with few areas of Mils and
ridges; elevations range from sea level to about 300 ft. The Central Valley is divided by a ridge of
volcanic rock called the Metacomet Ridge, which runs almost the entire length of the valley in both
Connecticut and Massachusetts.
The Eastern Uplands are underlain by rolling hills of schist, gneiss, and granite.
Elevations reach over 1000 ft in the northern hills and decrease to less than 700 ft towards the
south. Elevation is at sea level at the Atlantic coast Along the western edge of the Eastern
Uplands, a group of long ridges, including the prominent Bolton Ridge, which runs from the
Massachusetts state line southward to Portland, Connecticut, have the most rugged topography of
the region. Another less prominent group of ridges runs along the Rhode Island-Connecticut
border south to North Stonington, where the ridges change to a generally east-west trend, ending
at the Connecticut River in Lyme (Bell, 1985). The central part of the Eastern Uplands consists
mainly of rounded, rolling hills.
The population of Connecticut was approximately 3,287,116 in 1990, including 79 percent
urban population (fig. 3). The climate is moderate, with winter temperatures averaging 32 °F and
winter snowfall averaging 3-5 ft; summers average between 70 °F and 75 °F. Average annual
precipitation ranges from 44 to 52 inches (fig. 4).
BEDROCK GEOLOGY
The following discussion of bedrock geology is derived from the Bedrock Geological Map
of Connecticut by Rodgers (1985). A general geologic map is given for reference in figure 2. It
is suggested, however, that the reader refer to the detailed State Geologic Map of Connecticut and
to other detailed geologic maps and information available from the Connecticut Department of
Environmental Protection's Natural Resources Center (Levere, 1991). The geology of Connecticut
has been divided into several terranes and sub-terranes (fig. 1). These terranes reflect the geologic
processes (plate tectonics) that produced the rocks seen today. The Avalonian terrane was thrust
against the continent of Proto-North America approximately 450-250 million years ago. This
collision closed the intervening lapetos Ocean and deformed the two terranes and the sediments of
the lapetos Ocean floor, forming the schists, gneisses and granites that underlie the Western and
Eastern Uplands. About 235 million years ago, the terranes began breaking apart, forming a rift
basin. The Newark Terrane is the erosional remnant of that rift basin.
The Western Uplands
The Western Uplands contain the Proto-North American Terrane and part of the lapetos
Terrane. Carbonate shelf rocks and Proterozoic-age massifs comprise the Proto-North American
Terrane, whereas schist of the Connecticut Valley Synclinorium and the Taconic Allochthons
comprise the lapetos Terrane. The oldest rocks of the Western Uplands are the complexly folded
and faulted crystalline rocks of the Proterozoic massifs. These rocks underlie much of the northern
and western portions of the province and are infolded with younger metasedimentary rocks of
Paleozoic age. Layered gneiss, hornblende gneiss and amphiboEte, micaceous schist and quartz-
feldspar gneiss are the principal rock types. Pink granitic gneiss forms irregular masses
throughout the sequence and augen gneiss occurs locally. The layered gneiss contains alternating
bands of light and dark minerals with minor layers and lenses of Gale-silicate rock and amphibolite.
Hornblende gneiss and amphibolite is composed of hornblende and feldspar with biotite and minor
IV-12 Reprinted from USGS Open-File Report 93-292-A
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POPULATION (1990)
Q 0 to 25000
Q 25001 to 50000
0 50001 to 100000
B 100001 to 500000
• 500001 to 851783
Figure 3. Population of counties in Connecticut (1990 U.S. Census data).
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46- 4f SO" 52- 5J"S0*4«"46*
Figure 4. Average annual precipitation in Connecticut (modified from Smith, 1974).
-------
quartz. These are commonly interlayered with banded felsic gneiss and locally contain calc-silicate
rock or diopsidic caltite marble. Much of the schist and gneiss has a distinct iron staining referred
to as rusty weathering.
Ordovician and Cambrian metasedimentary rocks comprise the carbonate shelf sequence
found in the western portion of the province. Cambrian-age clastic rocks appear to be the oldest
rocks of the sequence and consist of highly variable, locally schistose quartzite of the Dalton
Formation. This is overlain by a thick sequence of carbonate rocks called the Stockbridge Marble,
a calcic to dolomitic massive marble with layers of calcareous siltstone, sandstone, quartzite,
phyUite, and schist Unconformably overlying the Stockbridge Marble is the Qrdovician-age
Wallobmsac Schist, consisting of quartzose schist and phyllite locally with garnet, staurolite, or
sillimanite.
The Taconic Allochthons are fault-bounded rock bodies thrust over the above-described
units. The Taconic Allochthons contain Cambrian-age metamorphic rocks of the Everett Schist,
Canaan Mountain Schist, Hoosac Schist, and Manhattan Schist. The Everett, Cannan Mountain,
and Hoosac Schists are found in the northernmost bodies of the Allochthon. The Everett Schist is
comprised of aluminous schist and phyllite. The Cannan Mountain Schist is well-layered mica
schist and schistose gneiss with layers of amphibolite and quartzite. The Hoosac Schist is
aluminous schist and poorly-layered schistose gneiss. The southern exposures of the Taconic
AEoehthons are made up of the Manhattan Schist, a rusty-weathering, biotite gneiss and schistose
gneiss with minor amphibolite.
More than half of the Western Uplands is underlain by the schist, gneiss, and phyllite of
the Connecticut Valley Synclinorium. The northwestern portion of the synclinorium is underlain
predominantly by aluminous schist, with minor amphibolite and calc-silicate rock of the Rowe
Schist and the Ratlum Mountain Schist Qrdovician-age granite gneiss and the Qrdovician
Brookfield Gneiss, consisting of granodioritic and dioritic gneiss, lie to the south of the schists and
in smaller areas to the north, where the exposures also include the Litchfield Norite. The Harrison
Gneiss, a light- to dark gray mafic gneiss, is exposed in the southwestern part of the State, and
outcrops of the Harrison extend northward along the eastern edge of the Western Uplands to the
southwest corner of Hartford County. The Trap Falls Formation overlies the Harrison Gneiss and
is exposed in the southern part of the Western Uplands. It consists of gray to silvery, rusty-
weathering schist and lighted-colored gneiss. The Golden Hill Schist, exposed in eastern Fairfield
County near the Long Island Sound, may be equivalent to part of the Trap Falls Formation.
The eastern part of the Connecticut Valley Synclinorium is underlain by schist, gneiss, and
phyllite. The oldest rocks in this area are those of the Cambrian Waterbury Gneiss, a gneiss and
schistose gneiss irregularly mixed with granite gneiss, forming the Waterbury Dome in the vicinity
of Waterbury in north-central New Haven County. The Ordovician Taine Mountain Formation,
consisting of "pin stripe" gneissic and schistose granofels, and the Collinsville Formation,
comprising felsic and mafic schist and gneiss, are exposed throughout the eastern Connecticut
Valley Synclinorium. The Bristol Gneiss, a felsic gneiss interlayered in places with amphibolite, is
exposed in the vicinity of Bristol in southwestern Hartford County, with a smaller outcrop near
Collinsville in west-central Hartford County. The Hawley Formation, a gray, rusty-weathering,
carbonaceous schist, is exposed in thin bands in the northeastern part of the area. The Cobble
Mountain Formation, consisting of gray to silvery schist and granofels, underlies an area just east
of Barkhamsted Reservoir near the Massachusetts border. The Silurian-Devonian Straits Schist is
exposed in wide bands along the eastern edge of the Western Uplands from the Massachusetts
border almost to the Atlantic coastline. It is a silvery to gray, coarse-grained schist that is graphitic
IV-15 Reprinted from USGS Open-File Report 93-292-A
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almost throughout The Devonian Nonewaug Granite intrudes the Rowe and Ratlum Mountain
Schists in the northern and central part of the area, and the Permian-age Pinewood Adamellite, a
light gray granite, intrudes the Trap Falls Formation in the vicinity of Pinewood Lake in
southeastern Fairfield County. Intrusive rocks ranging in age from Devonian to Jurassic are
found, primarily as dikes, throughout the area.
The southeasternmostpart of the Connecticut Valley Synclinorium is an area referred to as
the Qrange-Milford Belt, separated from the rest of the area by the East Derby Fault It is underlain
by rocks of Ordovician to Devonian age, including the Oronoque Schist, a light colored schist and
granofels; the Allingtown and Maltby Lakes Metavolcanics, comprising greenstone, schist, and
phyllite; and the Wepawaug Schist, comprising graphitic schist and phyllite, and metasiltstone.
The Central Lowlands (Newark Terrane, including the Hartford and Pomperaug Basins)
Late Triassic-early Jurassic continental sedimentary and igneous rocks of the Newark
Supergroup (Froelich and Olsen, 1984) occur in two half-graben basins extending from north to
south in the central part of the State. Each basin is underlain by eastward-dipping strata that are
folded into broad synclines along the faulted eastern margin. The Hartford basin is the largest of
the Mesozoic basins, occupying the Central Lowlands and extending northward into
Massachusetts. The basal Triassic New Haven Arkose consists of fluvial arkosic sandstone,
conglomerate, and siltstone, forming a wide band on the western side of the basin. It is more
conglomeratic along its basal contact with older rocks to the west The New Haven Arkose is
overlain by a narrow belt of complexly-faulted Jurassic volcanic and sedimentary rocks that include
the Talcott Basalt, Shuttle Meadow Formation, Holyoke Basalt, East Berlin Formation, and the
Hampden Basalt The Shuttle Meadow and East Berlin Formations comprise a mixture of
sandstone and conglomerate and red and black lacustrine shales. The Talcott, Holyoke, and
Hampden Basalts are tholeiitic basalt flows. The eastern part of the Hartford basin is a wide belt of
sedimentary rocks of the Jurassic Portland Formation. The lower part of the Portland consists of
lacustrine black shales and red siltstones and the upper part consists of fluvial sandstones and
conglomerates. Along the eastern margin of the basin, all of the formations intertongue with
alluvial fan conglomerates composed of the older rocks immediately outside of the basin.
The Pomperaug basin is a tiny half graben west of the Hartford basin, near the center of the
Western Uplands. It has the same stratigraphic sequence as the Hartford basin, but all of the units
are proportionally thinner within the basin. Jurassic diabase dikes and sills intrude the sedimentary
rocks of both basins.
The Eastern Uplands
The Eastern Uplands consist of the Bronson Hill Anticlinorium and the Merrimack
Synclinorium of the lapetos Terrane, and the Avalonian Terrane. The Ordovician Monson Gneiss,
an interlayered gneiss and amphibolite, is the oldest rock unit in the Bronson Hill Anticlinorium. It
covers much of the southern part of the area and forms a relatively narrow outcrop band along the
eastern side of the Anticlinorium. It is overlain by the Middletown Formation, consisting of
gneiss, granofels, hornblende gneiss, amphibolite, and metagabbro, which is equivalent to the
Ammonoosuc Volcanics of New Hampshire. These are overlain by the Collins Hill Formation,
containing rusty-weathering, graphitic schist interlayered with two-mica gneiss, and mafic to felsic
metavolcanic rocks; the Clough Quartzite; the Fitch Formation, consisting of calc-silicate rock and
two-mica schist; the Littleton Formation, consisting of schist, micaceous quartzite, and granofels;
and the Erving Formation, comprising granofels and schist. Intrusive rocks include the Ordovician
IV-16 Reprinted from USGS Open-File Report 93-292-A
-------
Glastonbury Gneiss, which forms a wide band in the northern and central part of the area, and the
Devonian Maromas Granite Gneiss, which is exposed ill thin bands adjacent to the Monson and
Glastonbury Gneisses. Massive mafic and ultramafic rocks, thought to be intrusive, are found
within exposures of the Middletown Formation,
The Merrimack Synclinorium lies east of the Bronson Hill Anticlinorium and underlies the
central part of the Eastern Uplands (fig. 1). The Ordovician-age Quinebaug Formation, consisting
of mafic gneiss, amphibolite, schist, and granofels, and the Preston Gabbro, are the oldest rocks in
the Synclinorium, and they underlie the easternmost part. These are overlain by the Tatnic Hill
Formation, consisting of gneiss and schist with thin layers of graphitic pyrrotitic schist,
amphibolite, and calc-silicate rock; the Brimfield Schist, a gray, rusty-weathering, interlayered
schist and gneiss; and the Hebron Gneiss, consisting of interlayered dark gray schist and calc-
silicate rock with local lenses of graphitic two-mica schist The Southbridge Formation,
comprising interlayered granofels and schist, and porphyritic gneiss, is exposed mainly in the
northern part of the area. It is overlain by the Bigelow Brook Formation, consisting of fissile
schist with graphite and pyrrhotite and interlayered schist and granofels. The Scotland Schist
underlies a large part of the central Merrimack Synclinorium. It is composed of schist and
granofels that is interlayered locally with quartzite. Intrusive rocks include the Lebanon Gabbro
and Canterbury (granitic) Gneiss, which intrude metamorphic rocks in the central part of the area,
and smaller intrusions of hornblende norite and foliated quartz diorite and granitic gneiss, all of
Devonian age.
The Avalonian Terrane occupies the eastern and southern parts of the Eastern Uplands,
separated from the Merrimack Synclinorium by the Lake Char Fault (fig. 1). Relatively small
windows of Avalonian Terrane rocks are also found in the central part of the Merrimack
Synclinorium near Wiffimantic in southwestern Windham County. Most of the rocks of the
Avalonian Terrane are Proterozoic in age. The Plainfield Formation consists of interlayered
quartzite, locally graphitic phyllite, gneiss, amphibolite, and calc-silicate rock. It is overlain by the
Waterford Group, consisting of the Rope Ferry Gneiss, New London Gneiss, and Mamacoke
Formation gneiss. These are intruded by a number of granitic gneisses, including the Light House
Gneiss; Branford Gneiss; Stony Creek Granite Gneiss; the Sterling Plutonic Group, consisting of
the Hope Valley Alaskite Gneiss, Potter HE1 Granite Gneiss, Ponaganset Gneiss, and "Scituate"
Granite Gneiss, which is probably not equivalent to the Scituate Granite Gneiss in Rhode Island
(Rodgers, 1985); and the Permian-age Narragansett Pier and Westerly Granites. The Narragansett
Pier Granite also has a mafic phase, containing biotite and hornblende, which underlies a small
area in the southeasternmost part of the State.
GLACIAL GEOLOGY
Deposits of five or possibly six Pleistocene glacial advances in New England have been
recognized or inferred from surface or subsurface data (Stone and Barns, 1986); however, only
two tiH units are identified in Connecticut by Stone and others (1992). Glacial deposits exposed at
the surface in Connecticut are of Late Wisconsin age. Glaciers moved in a dominantly N-S or
NNW-SSE direction across the State, terminating on Long Island at their maximum extent. la Late
Wisconsin time, two main glacial lobes advanced across Connecticut The Hudson-Champlain
Lobe advanced across New York and western Connecticut, The Connecticut Valley Lobe covered
the remainder of the State and carved the Connecticut River Valley. Glacial Lake Hitchcock
occupied the northern part of the Connecticut Valley from approximately 16,500 years ago until
IV-17 Reprinted from USGS Open-File Report 93-292-A
-------
about 13,500 years ago (Stone and Borns, 1986), Silt and clay glacial lake deposits occupy the
floor of the Connecticut Valley from the northern border of the State to just south of Berlin in
south-central Hartford County (fig. 5). The final retreat of Wisconsinan glaciers from Connecticut
occurred about 12,000 years ago (Stone and Borns, 1986).
Glacial deposits in Connecticut range from a few feet to several hundred feet in thickness
(Stone and others; 1992). Figure 5 is a generalized map of glacial deposits in Connecticut Till,
sometimes also referred to as drift or ground moraine, is the most widespread glacial deposit
(fig. 5). Till was deposited directly by glacier ice and it is composed of a poorly sorted matrix of
sand, silt, and clay containing variable amounts of rounded cobbles and boulders. Glacial
landforms typically associated with till include drumlns, ketfles, and moraines. Stratified glacial
deposits were laid down by glacial meltwater in streams and lakes in front of the retreating ice
margin. They are characterized by layers of poorly-sorted to weE-sorted gravel, sand, silt, and
clay (Stone and others, 1992). Ice-contact stratified drift (referred to as stratified glacial deposits
on fig. 5) includes deposits of kames, eskers, lacustrine deltas, and karne moraines. These coarse-
grained deposits range from poorly sorted to well sorted and consist of sand, gravel, cobbles, and
boulders, with varying amounts of silt and clay, though they generally contain considerably less
fine-grained material than till. Outwash consists of layers of sand and gravel deposited by glacial
meltwater streams. Outwash is generally the coarsest-grained class of glacial deposits because
most of the silt and clay was removed by the rapidly-moving water. Glacial lake-bottom deposits
consist primarily of finely bedded silt and clay.
In the upland areas of the State, till is the most common type of glacial deposit, occurring
as a discontinuous layer that is thickest in drumlins and on the northwest slopes of hills. The
matrix of most tills is composed dominantly of sand and silt, but clayey tills occur in areas in
which a fine-grained bedrock source is present. Stratified glacial deposits averaging 10-40 feet
thick, but locally as much as 200 feet thick, overlie till in small upland valleys and north-sloping
pockets between bedrock hills (Stone and others, 1992). In the Central Lowlands, stratified glacial
deposits are the predominant surficial deposit type. They generally overlie till and average 50-100
feet in thickness. Glacial lake deposits cover most of the northern part of the Connecticut Valley
(fig. 5).
The color and lithology of the tills vary across the State and reflect the characteristics of the
local bedrock from which the till is derived. The sedimentary rocks of the Central Lowlands
produce tills that are brown to red-brown in color; siltstones contribute a significant amount of
fine-grained material. Fragments of basalt and dolerite that occur adjacent to the sedimentary rocks
are commonly found in the reddish-brown tills of the Central Lowlands. Deposits derived from
quartzite tend to be sandy, containing abundant quartz sand grains and quartzite fragments.
Marbles produce fine-grained, light-colored, calcareous (calcium carbonate rich) glacial deposits.
Dark-colored schists and phyffites produce fine-grained, dark-colored tills. Muscovite schists
produce lighter-colored tills containing abundant mica flakes. Schists and gneisses containing
abundant iron sulfides produce reddish-brown tills, commonly with iron cements. Glacial deposits
derived from granitic rocks are generally light-colored and sandy. Mafic rocks such as amphibolite
and hornblende gneiss produce dark-colored glacial deposits containing abundant iron minerals.
Light- to medium-gray schists and gneisses underlie more than half of Connecticut and produce
gray to yellowish-gray, silty and sandy tills (Stone and others, 1992).
IV-18 Reprinted from USGS Open-File Report 93-292-A
-------
EXPLANATION
H I TILL — pootlyiortcd,uiutr«tifie4nmK of gravel, sand,
tflt, »ad city; 8»trU domJsiwfly Sue stud tad sOt
S1RATIF1BD GLACIAL DBPOSITS-iai, und,u»d
gravel dcpoiila of lacoatikc deitu, lacustrine terraces,
, fc«ae tcprtces, «nd eikers
OUTWASH AND ALLUVIUM— msiirfysiuad and
gravel dcpotited by gl*cul mcttwiter stretmi *nd
modem riveis
GLACIAL LAKH-BOTTOM SEDIMENTS—
»tri lifted sflt tnd cj»y deposited by gltcitl liVca; may
bevtrved
Figure 5. Generalized map of glacial deposits in Connecticut (after Flint and others, 1959, and Stone and others, 1992).
-------
SOILS
Soils in Connecticut include, in order of abundance, Inceptisols, mineral soils with
horizons of alteration or accumulation of metal oxides such as iron, aluminum, or manganese;
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 Histosols, organic soils such as peats or
mucks which occur along coastlines or in river valleys (Hill and others, 1980). A generalized soil
map of Connecticut (fig. 6) and the following descriptions of soils in the State are condensed from
Gonick (1978) and Hill and others (1980).
Soils formed in glacial till derived from gneiss, schist, and granite occur in the Eastern and
Western Uplands. These soils are typically described as shallow, moderately well-drained to
excessively drained, stony, silty and sandy loams. Many of these soils have a firm, clayey
subsurface horizon. Permeability of these soils ranges from low to high, but most soils in this area
have low to moderate permeability (fig. 6). Soils formed on stratified deposits (outwash, ice-
contact deposits, and alluvium) derived from gneiss, schist, and granite in the Eastern and Western
Uplands are deep, poorly-drained to well-drained, gravelly, silty and sandy loams with moderate
to high permeability. These soils are generally formed on terraces (Gonick, 1978) and are
underlain by sand and gravel deposits.
Soils formed on glacial till derived from limestone, dolomite, and marble, and soils formed
on stratified deposits derived from limestone and marble occur in the Western Uplands along the
Connecticut-New York border. These soils are deep, moderately well-drained to excessively
drained, calcareous, gravelly, sandy and silty loams. Soils developed on glacial till are generally
found in upland areas and have low to moderate permeability, whereas soils developed on stratified
deposits typically occur on terraces and have high permeability (Hill and others, 1980).
Soils of the Central Lowlands include gravelly, silty and sandy loams developed on glacial
till derived from sandstone, shale, conglomerate, and basalt; and silty and sandy loams developed
on stratified deposits derived from sandstone, shale, conglomerate, and basalt (fig. 6). These soils
have a distinctive red color acquired from the underlying red sandstone bedrock (Hill and others,
1980). The soils developed on glacial till are generally sited on uplands whereas those developed
on stratified deposits are typically found on terraces (Gonick, 1978). Soils developed on glacial
deposits in the Central Lowlands are typically well-drained to excessively drained but have low to
moderate permeability. Soils developed on stratified deposits in the Central Lowlands have
moderate to high permeability but drainage characteristics range from poorly drained to well
drained. Soils in the northern part of the Central Valley west of the Connecticut River are formed
on silt and clay glacial lake deposits with low permeability (Hill and others, 1980). Several of the
soil units in this area are classified as wet, particularly those developed on glacial lake deposits,
floodplains, and low-lying terraces (fig. 6). Some of the soils along the coast and locally in the
Connecticut River Valley are organic soils with silty substrata developed on low-lying wetlands
that are commonly flooded (fig. 6).
Descriptions of these soils as silty or sandy loams generally apply to the uppermost soil
layer. Many of the soils have a subsurface horizon in which iron and aluminum oxides and(or)
clays have accumulated. Soils with clayey B horizons, including many of the soils developed on
glacial deposits, can inhibit radon transport to the surface but may have sufficient permeability
below the B horizon to allow significant lateral radon transport, allowing radon to enter a
building's foundation if the basement extends below the depth of the B horizon.
IV-20 Reprinted from USGS Open-File Report 93-292-A
-------
Figure 6. Generalized soil map of Connecticut (modified from Hill and others, 1980).
-------
GENERALIZED SOIL MAP OF CONNECTICUT
EXPLANATION
SOILS OFTHEEASTERN AND WESTERN HIGHLANDS FORMED IN GLACIAL TILL DERIVED
FROM GNEISS, SCHIST, AND GRANITE
stony, silty and sandy loams—moderate permeability
silty and loamy soils with firm substrata—low permeability
silty soils with friable substrata—moderate to high permeability
SOILS OFTHEEASTERN ANDWESTERN HIGHLANDS FORMED IN STRATIFIED DEPOSITS
DERIVED FROM GNEISS, SCHIST, AND GRANITE
sandy and gravelly soils—high permeability
SOILS OF THE WESTERN HIGHLANDS FORMED IN GLACIAL TILL DERIVED FROM LIMESTONE
AND SCHIST
calcareous sandy and silty loams—low to moderate permeability
SOILS OFTHEWESTERN HIGHLANDS FORMED IN STRATIFIED DEPOSITS DERIVED FROM
LIMESTONE AND SCHIST
calcareous, gravelly, sandy and silty loams—high permeability
SOILS OF THE CENTRAL LOWLANDS OF THBDONNECTICUT RlVER VALLEY FORMED IN
GLACIAL TILL DERIVED FROM SANDSTON^ SHALE, CONGLOMERATE, AND BASALT
gravelly, silty and sandy loams—low to moderate permeability
silty and sandy loams with firm substrata—low permeability
SOILS OF THE CENTRAL LOWLANDS OF THECONNECTICUT RlVER VALLEY FORMED IN
STRATIFIED DEPOSITS DERIVED FROM SANDSTONE, SHALE, CONGLOMERATE, AND BASALT
gravelly and sandy soils—high permeability
silts and clays formed on glacial lake deposits—low permeability
silty and sandy alluvial soils—moderate permeability
Ss?
SOILS OF COASTAL LOWLANDS AFFECTED BY TIDAL WATER
organic soils with silty substrata—moderate permeability, wet
-------
RADIOACTIVITY
An aeroradiometric map of Connecticut (fig. 7a) compiled from NUKE flightiine data
(Duval and others, 1989) shows radioactivity of surficial materials in the State. Low radioactivity
(<1.5 ppm elJ) is found in the northernmost Western Uplands associated with Proterozoic gneiss
of the Berkshire Mountains, in several parts of the Central Lowlands associated with Jurassic
igneous rocks, and along the eastern border of the State in the Eastern Uplands associated with
Proterozoic schist Moderate radioactivity (1.5-2.5 ppm) covers most of Connecticut, including
the northern half of the Western Uplands, most of the Central Lowlands and northern portions of
the Eastern Uplands. High radioactivity (>2.5 ppm) is associated with rocks of the Connecticut
Valley Synclinorium, especially Qrdovician-age granitic gneiss in the southern half of the
syncMnorium. High radioactivity is also prevalent in Bronson Hill Anticlinorium and is associated
with granitic rocks in parts of the Avalonian Terrane and Memmack Synclinorium. A moderate to
high radioactivity anomaly clearly follows the path of the Connecticut River and may reflect the
radioactivity of bedrock exposed by river erosion relative to the generally lower radioactivity of
surrounding till.
The Connecticut Geological Survey has also compiled a map using total gamma
radioactivity (compiled from Popenoe, 1964,1966) and percent of indoor radon greater than
4 pCi/L in the State/EPA Residential Radon Survey of Connecticut. This map is shown in figure
7b. Areas of highest radioactivity are the southern Connecticut Valley Syncfinorium and the
Avalonian Terrane. In both of these areas, high radioactivity appears to be most closely associated
with granites and granitic gneisses. Scattered high radioactivity areas in the Merrimack
Synclinorium and in the northern and central parts of the Connecticut Valley Synclinorium also
appear to be associated with granitic rocks and locally with graphitic schist, particularly the Straits
Schist. Towns located in areas of high radioactivity (700-900 counts per second total gamma
radioactivity) also had the highest percentage of homes with indoor radon levels exceeding 4 pCi/L
(fig. 7b).
A carborne gamma radioactivity conducted by the Connecticut Geological Survey (Thomas,
1987) also confirms these correlations. Total-count gamma radioactivity was measured in
traverses covering 1367 miles in all parts of the State. When analyzed by geologic terrane, it was
found that the Merrimack Synclinorium and Avalonian Terrane had the highest radioactivity, and
that radioactivity was lowest over the Newark Terrane.
INDOORRADON
The State of Connecticut has conducted extensive indoor radon testing and data analysis.
The Connecticut Department of Health Services conducted a Household Testing Program (HTP) in
which short-term charcoal canister tests were made in 3378 homes during 1987-88, These data
were combined with indoor radon measurements from the Connecticut Radon Survey, in which
202 homes were tested using three-month alpha-track tests, and with data from the State/EPA
Residential Radon Survey, representing a total of 5036 homes, or about one percent of single
family homes in Connecticut (Siniscalchi and others, 1991). Of the 169 towns in Connecticut, 20
have average indoor radon levels exceeding 4 pCi/L. The averages range from 4.03 to 8.33 pCi/L,
and the towns, in order from highest to lowest, are Guilford, Sprague, Woodstock, Ansonia,
Branford, Morris, Bethany, Voluntown, Weston, Westport, Hampton, Madison, Haddam,
Canterbury, Scotland, Oxford, Putnam, Woodbridge, Glastonbury, and Thompson.
IV-23 Reprinted from USGS Open-File Report 93-292-A
-------
Figure 7a. Aerial radiometric map of Connecticut (after Duval and others, 1989). Contour lines at 1,5 and 2.5 ppm equivalent uranium
(eU). Pixels shaded at 0.5 ppm eU increments; darker pixels have lower eU values; white indicates no data.
-------
GENERALIZED AERORADIOACTIVITY MAP OF CONNECTICUT
WITH RADON POTENTIAL ASSESSMENTS
i M IS ?£ 35 HlltS
Produced by the Connecticut Department of Environmental Protection,
Geographic Information System. Base information from U.S.G.S.
publicarioni GP-358 0964) and GP-3S9 (1966) by Peter Popcnoc.
Generalized mapping units represent the designated range ±50
cps gamma.
40
Basement Air Radon vs. Aeroradioactivity
< 300 300-500 SOO-700
Aeroradioactivity (cps gamma]
700-900
Legend
Aeroradioactivity Frequency
+50 cps gamma % >4 pCi/1
I I <300 0
&2 300-500 133
S3 500-700 22.6
13 700-900 35.7
•• >9QO —
XV
Radioactivity unit boundary:
inferred, well defined, or
gradationaL
JGISJ
Figure 7b. Total-count aeroradioactivity map of Connecticut and comparison of aeroradioactivity
with screening indoor radon levels (from Thomas, 1990).
-------
Data from the HTP were analyzed by geologic terrane by the Connecticut Geological
Survey (M.A, Thomas, personal communication, 1991). The values represent winter basement
charcoal canister tests in a total of 4798 homes from two surveys: the 1986-1987 State/EPA
Residential Radon Survey and the 1987-88 Connecticut Household Testing Program, These data
are summarized in Table 1 by geologic terrane and Table 2 by county. They are also shown by
county in figure 8. A map of counties is included for reference (fig. 9). In this grouping the
highest arithmetic mean, and the only one exceeding 4 pQ/L, was 5.56 pCi/L for 493 homes tested
in the Bronson Hill Anticlinorium (Table 1). The indoor radon readings were also grouped by
individual rock unit as shown on the bedrock geological map of Connecticut (Rodgers, 1985),
Rock units generating indoor radon averages exceeding 4 pCi/L are dominantly granitic rocks in
the Connecticut Valley Synclinorium, Bronson Hill Anticlinorium, and the Avalonian Terrane,
and, locally, volcanic rocks in the Newark Terrane (M.A. Thomas, personal communication,
1991).
TABLE 1. Connecticut indoor radon summary by geologic terrane.
Numbers refer to map of geologic terranes (fig. 1). Data from the Connecticut Geological Survey
(M.A. Thomas, personal communication, 1991).
Geologic Terrane # of Homes Geometric Mean Arithmetic Mean
Newark Terrane (1)
Proto-NA Terrane
Carbonate Shelf (2a)
Proterozoic Massifs (2b)
lapetos Terrane
Ct Valley Syn. (3a)
Bronson Hill Ant. (3b)
Merrimack Syn. (3c)
Taconic Allocth. (3d)
Avalonian Terrane (4)
Lake Char Fault
589
116
88
1568
493
802
208
907
4
1.18
1.83
1.73
2.19
2.68
1.84
1.58
1.9
1.24
1.55
2.8
2.47
3.46
5.56
2.69
2.7
3.32
1.1
TABLE 2. Connecticut indoor radon summary by county.
Data represent 2-7 day charcoal canister measurements. Data from M. A. Thomas (1990 and
personal communication).
Number of Geometric Arithmetic
County Homes Mean Mean Maximum %>4 pCi/L
Fairfield
Hartford
Litchfield
Middlesex
New Haven
New London
ToUand
Windham
865
375
805
496
701
842
307
407
2.09
1.48
1.95
1.82
2.24
1.70
1.70
2.09
3.16
2.49
3.10
2.91
5.04
2.75
2.29
3.04
98.4
80.9
75.0
47.2
485.0
72.6
18.9
45.4
21
14
21
20
29
17
14
21
IV-26 Reprinted from USGS Open-File Report 93-292-A
-------
Bsmt. & 1st Floor Rn
%>4pCi/L
o D
otoio
1 1 to 20
21 to 30
Bsmt. & 1st Floor Rn
Average Concentration (pCi/L)
0_0 0.0 to 1.9
2.0 to 4.0
4.1 to 4.5
25 Miles
Figure 8. Screening indoor radon data from the 1986-1987 EPA/State Residential Radon Survey
and the Connecticut 1987-88 Household Testing Program. Data are from 2-7 day charcoal
canister tests. Histograms in map legends show the number of counties in each category.
Unequal category intervals were chosen to provide reference to decision and action levels.
-------
Figure 9. Connecticut counties.
-------
GEOLOGIC RADON POTENTIAL
Western Uplands
The Western Uplands 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 have moderate to high permeability. Equivalent uranium (fig. 7a) is
generally low and indoor radon averaged 2.47 pCi/L over the massifs. The carbonate shelf rocks
of the Proto-North American Terrane are predominantly marble, schist, and quartzite, overlain by
glacial till. Equivalent uranium over this area is generally low and the soils have low to moderate
permeability. Indoor radon averages 2.8 pQ/L for homes built on the carbonate shelf rocks.
Some homes built on units a and c of the Stockbridge Marble have elevated indoor radon levels in
the summary of indoor radon levels by underlying rock type (here designated SRRT for
convenience) compiled by the Connecticut Geological Survey (M.A. Thomas, personal
communication, 1991). Overall, this terrane has moderate radon potential.
The Taconic Allochthons underlie several fault-bounded areas in the northern part 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. This area has an overall moderate radon potential.
Rocks of the Connecticut Valley Synclinorium 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 produces a distinct high radioactivity
anomaly on the equivalent uranium map (fig. 7a) 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 (map unit Og on the bedrock geologic map of
Connecticut (Rodgers, 1985)), and the Shelton Member of the Trap Falls Formation. These rocks
all occur mainly in the southern part of the Connecticut Valley Synclinorium and are associated
with the high radioactivity on figure 7a and with elevated indoor radon levels in the SRRT. The
Nonewaug Granite and the Scranton Member of the Taine Mountain Formation underlie areas in
the northern and central part of the area and are also associated with high aeroradioactivity and
elevated indoor radon levels. Graphitic schists and phyllites commonly contains elevated
concentrations of uranium, and is known to be associated with elevated indoor radon levels in
other parts of New England and other areas (Gundersen and others, 1988; Ratt6 and Vanecek,
1980). 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 3.46 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.
Central Lowlands
The Central Lowlands are underlain by Triassic and Jurassic sedimentary and volcanic rocks.
The average indoor radon in the Newark Terrane was 1.55 pCi/L. Outcrops of the Jurassic Talcott
Basalt and Buttress Dolerite are associated with indoor radon averages exceeding 4 pCi/L in a
sample of 10 homes in the SRRT. 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 Newark Terrane has a low radon potential. However, uranium occurrences have been
IV-29 Reprinted from USGS Open-File Report 93-292-A
-------
reported associated with copper in the upper New Haven Arkose, and in the middle Portland
Formation associated with carbonaceous debris in fluvial erossbeds, in the Hartford basin
(Robinson and Sears, 1988). Similar copper deposits that are also probably uranium-rich are
known from many locales within these units and in the same units within the Pomperaug basin.
Although no occurrences have been reported, black shales and gray sandstones in the Shuttle
Meadow, East BerHn, and Portland Formations in both basins also may have some elevated
uranium. These uranium occurrences may cause localized indoor radon problems but are not
expected to be common or widespread. The basalts and diabase, lower New Haven Arkose, and
upper Portland Formation are not likely to have significant uranium concentrations, except possibly
along fractures, and are generally low in radon potential.
Eastern Uplands
Rocks of the Bronson Hill AnticUnorium include felsic and mafic schists and gneisses,
quartzate, and granite gneiss. Radioactivity in the Bronson Hill is moderate to locally high, and
equivalent uranium anomalies in the central part of the area (fig. 7a) 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 average indoor radon levels between 4.3 and 10.1 in
the SRRT. Average indoor radon in the Bronson Hill Anticlinorium is 5.56 pQ/L, the highest
among the geologic terranes of Connecticut (Table 1). Overall, this area has a high radon potential.
The Merrimack Synclinorium is underlain by gneiss, schist, granofels, and quartette that are
intruded by granite gneiss, diorite, and gabbro. The area has moderate to high radioactivity on the
NURE map (fig. 7a) and had the highest radioactivity in the Connecticut Geological Survey's
carborne survey (Thomas, 1987). Soils have low to high permeability but most are in the low to
moderate range. Indoor radon in the Merrimack Synclinorium averaged 2.69 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 (fig. 7a) and with elevated
indoor radon levels (average of 4.1 pCi/L for 39 homes tested in the SRRT). This area has
moderate radon potential overall.
The Avalonian Terrane is underlain by granite, granite gneiss, mafic gneiss, and amphibolite.
Granitic rocks known to generate elevated indoor radon levels (averages greater than 4 pCi/L in the
SRRT) include the Waterford and Branford Gneisses, and the Hope Valley AlasMte Gneiss, which
also has a high aeroradioactivity signature (fig. 7a), as well as locally-occurring graphitic schist
and gneiss in the Plainfield Formation. Overall, the 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 3.32
pCi/L, Overall, this area has high radon potential.
IV-30 Reprinted from USGS Open-File Report 93-292-A
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SUMMARY
ti
For the purpose of this assessment, Connecticut has been divided into eight geologic radon
potential areas (fig. 10) and each area assigned a Radon Index (RI) and a Confidence Index (CI)
score (Table 3). 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 Newark Terrane, consisting of the Hartford and Pomperaug basins, is the only area of
Connecticut ranked as having low radon potential. Areas with moderate or variable geologic radon
potential include the Proterozoic massifs, carbonate shelf, and Taconic Allochthons, and the
Merrimack Synclinorium in the eastern part of the State. Areas with high radon potential include
the Connecticut Valley Synclinorium, Bronson Hill Anticlinorium, and Avalonian Terrane,
particularly those parts underlain by granitic rocks and by tills with granites, granite gneisses, or
other uraniferous rocks, such as graphitic schists and phyllites, as a major source component.
Faults and shear zones in many parts of the State have the potential to generate locally high indoor
radon.
This is a generalized assessment of the State's geologic radon potential and there is no
substitute for having a home tested. The conclusions about radon potential presented in this report
cannot be applied to individual homes or building sites. Indoor radon levels, both high and low,
can be quite localized, and within any radon potential area there will likely be areas with higher or
lower radon potential than assigned to the area as a whole. Any local decisions about radon should
UOt 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-31 Reprinted from USGS Open-File Report 93-292-A
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TABLE 3. RI and CI scores for geologic radon potential areas of Connecticut.
FACTOR
INDOOR RADON
RADIOACTIVITY
GEOLOGY
SOIL PERM.
ARCHTraCTURE
GFE POINTS
TOTAL
FACTOR
INDOOR RADON
RADIOACTIVITY
GEOLOGY
SOIL PERM.
ARCHITECTURE
GFE POINTS
TOTAL
FACTOR
INDOOR RADON
RADIOACnVirY
GEOLOGY
SOIL PERM.
ARCHITECTURE
GFE POINTS
TOTAL
Newark
Tenrane
RI CI
1
1
2
1
3
0
8
3
2
3
3
11
Low High
Connecticut Valley
Synclinorium
RI CI
2
2
3
2
3
0
12
3
2
3
3
11
High High
Taconic
Allochthons
RI CI
2
2
2
2
3
0
11
Mod
3
2
3
3
11
High
Carbonate
Shelf
RI CI
2
1
1
2
3
0
9
3
2
3
3
11
Mod High
Bionson Hill
Anticlinorium
RI CI
3
2
2
2
3
0
12
3
2
3
3
11
High High
Avalonian
Terrane
RI CI
2
2
3
2
3
0
12
High
3
2
3
3
11
High
Proterozoic
massifs
RI CI
2
1
2
2
3
0
10
3
2
3
3
11
Mod High
Meirimack
Synclinorium
RI CI
2
2
2
2
3
0
11
Mod
3
2
3
3
11
High
RADON INDEX SCORING:
Radon potential category
Point range
LOW 3-8 points
MODERATE/VARIABLE 9-11 points
HIGH > 11 points
Probable screening indoor
radon average for area
<2pCi/L
2-4pCi/L
>4pCi/L
Possible range of points = 3 to 17
CONFIDENCE INDEX SCORING:
LOW CONFIDENCE
MODERATE CONFIDENCE
HIGH CONFIDENCE
4-6 points
7-9 points
10 -12 points
Possible range of points = 4 to 12
IV-32 Reprinted from USGS Open-File Report 93-292-A
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X
GEOLOGIC RADON POTENTIAL: d|LOW E3 MODERATE/VARIABLE f=| HIGH
Figure 10. Geologic radon potential areas of Connecticut. Numbers on map refer to geologic terranes (see figure 1 for names).
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REFERENCES CITED IN THIS REPORT
AND GENERAL REFERENCES RELEVANT TO RADON IN CONNECTICUT
Bell, M., 1985, The face of Connecticut: People, geology, and the land: Connecticut Geological
and Natural History Survey Bulletin 110,196 p.
Bennison, A.P. (compiler), 1976, Geological highway map of the northeastern region: American
Association of Petroleum Geologists, United States Geological Highway Map no. 10, scale
1:2,000,000.
Cohen, B.L., 1988, A possible association between lung cancer and a geological outcrop,
discussion and reply: Health Physics, v. 54, p. 224-226.
Cooper, M., 1958, Bibliography and index of literature on uranium and thorium and radioactive
occurrences in the United States, Part 5: Connecticut, Delaware, Illinois, Indiana, Maine,
Maryland, Massachusetts, Michigan, New Hampshire, New Jersey, New York, Ohio,
Pennsylvania, Rhode Island, Vermont, and Wisconsin: Special Paper 67, Geological
Society of America, 472 p.
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, 1984, State Maps on File.
Fleischer, R.L., 1986, A possible association between lung cancer and a geological outcrop:
Health Physics, v. 50, p. 823-827.
Flint, R.F, Colton, R.B., Goldthwait, R.P., and Willman, H.B. (compilers), 1959, Glacial map
of the United States east of the Rocky Mountians: Geological Society of America Map and
Chart series mc-1, scale 1:750,000.
Froelich, A.J., and Olsen, P.E., 1984, Newark Supergroup, a revision of the Newark Group in
eastern North America: Stratigraphic Notes 1983, U.S. Geological Survey Bulletin
1537-A, p. A55-A58.
Gonick, W.N., 1978, General soil map of Connecticut: U.S. Department of Agriculture, Soil
Conservation Service map 1-13226, scale 1:250,000.
Graustein, W.C., Krishnaswami, S., Turekian, K.K. and Dowd, J.F., 1982, Measurement of
retardation factors using uranium and thorium decay series nuclides: Eos, Transactions,
American Geophysical Union, v. 63, p. 324-325.
Gundersen, L.C.S, Reimer, G.M., Wiggs, C.R., and Rice, C.A., 1988, 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.
IV-34 Reprinted from USGS Open-File Report 93-292-A
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Gundersen, L.C.S., 1991, Radon in sheared metamorphic and igneous rocks, in Gundersen,
L.C.S., and Wanty, R.B., eds, Field studies of radon in rocks, soils, and water: U.S.
Geological Survey Bulletin 1971, p. 39-50.
Hill, D.E., Sautter, E.H,, and Gonick, W.N., 1980, Soils of Connecticut: Connecticut
Agricultural Experiment Station Bulletin 787,36 p.
Krishnaswami, S., Graustein, W.C., Turekian, K.K. and Dowd, J.F., 1981, Chronometric
applications of radium isotopes and radon in groundwater: Abstracts with Programs,
Geological Society of America, v. 13, p. 491-492.
Rrishnaswami, S., Graustein, W.C., Turekian, K.K. and Dowd, J.F., 1982, Radium, thorium
and radioactive lead isotopes in groundwaters; application to the in situ determination of
adsorption-desorption rate constants and retardation factors: Water Resources Research,
v. 18, p. 1633-1675.
Levere, A. M.3 1991, Natural Resources Information Directory and List of Publications:
Department of Environmental Protection, Natural Resources Center, 39 p. and appendix.
Olsewski, W., Jr., and Boudette, E.L., 1986, Generalized bedrock map of New England: New
Hampshire Water Supply and Pollution Control Commission and U.S. Environmental
Protection Agency Region 1.
Paulsen, R.T., 1988, Radionuclides in groundwaters of the northeastern United States and
southern Canada; a literature review and summary: Northeastern Environmental Science,
v. 7, p. 8.
Popenoe, P., 1964, Aeroradioactivity of parts of east-central New York and west-central New
England: U.S. Geological Survey Geophysical Investigations Map GP-358, scale
1:250,000.
Popenoe, P., 1966, Aeroradioactivity and generalized geologic map of parts of New York,
Connecticut, Rhode Island, and Massachusetts: U.S. Geological Survey Geophysical
Investigations Map GP-359, scale 1:250,000.
Ratt6, C, and Vanacek, D., 1980, Radioactivity Map of Vermont: Vermont Geological Survey,
File No., 1980-1, rev. 3, 3 plates with text.
Robinson, G.R., Jr., and Sears, C.M., 1988, Inventory of metal mines and occurrences
associated with the early Mesozoic basins of the eastern United States - Summary tables: in
A.J, Froelich and G.R. Robinson, Jr., eds., Studies of the early Mesozoic basins of the
eastern United States, U.S. Geological Survey Bulletin 1776, p. 265-303.
Rodgers, J., 1985, Bedrock geological map of Connecticut: Connecticut Geological and Natural
History Survey, scale 1:125,000.
IV-35 Reprinted from USGS Open-File Report 93-292-A
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Sanders, I.E., 1988, Late Pleistocene geologic history of SE New York; one Wisconsinan glacier
from the NNE? Or several, including two from the NNW?: Northeastern Environmental
Science, v. 7, p. 9.
Siniscalchi, A.J., Rothney, L.M., Toal, B.F., Thomas, M.A., Brown, D.R., van der Werff,
M.C., and Dupuy, C.J., 1991, Radon exposure in Connecticut: Analysis of three
statewide surveys of nearly one percent of single family homes, in Proceedings of the 1990
EPA International Symposium on Radon and Radon Reduction Technology, Proceedings,
Vol. 1: Symposium Oral Papers: Research Triangle Park, N.C., U.S. Environmental
Protection Agency Rept. EPA600/9-91-026a, p. 4-1--4-14.
Smith, A.R., 1974, Connecticut: a thematic atlas: Berlin, Conn.: Atlas Publishing Inc., 90 p.
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.
Stone, J.R., Schafer, J.P., London, E.H., and Thompson, W.B., 1992, Surficial materials map
of Connecticut U.S. Geological Survey, scale 1:125,000, 2 sheets.
Thomas, M., and Scull, J., 1988, A geographic information system approach to managing
Connecticut's radon program: Abstracts with Programs, Geological Society of America,
v. 20, p. 75.
Thomas, M.A., 1987, A Connecticut radon study; using limited water sampling and a statewide
ground gamma radiation survey to help guide an indoor air testing program; a progress
report, in Graves, B., ed., Radon, radium, and other radioactivity in ground water: Lewis
Publushers, p. 347-362.
Thomas, M.A., 1990, Proceedings of the New England Environmental Expo, April 10-12,
Boston, MA, p. 273.
Thomas, M.A., Hollis, J.N., Rothney, L.M., Toal, B.F., and Dupuy, C.J., 1988, Correlating
radon distribution with geology and area! radioactivity in Connecticut: Northeastern
Environmental Science, v. 7, p. 10.
U.S. Soil Conservation Service, 1987, Soils: U.S. Geological Survey National Atlas sheet
38077-BE-NA-07M-00, scale 1:7,500,000.
IV-36 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.)
CONNECTICUT MAP OF RADON ZONES
The Connecticut Map of Radon Zones and its supporting documentation (Part IV of
this report) have received extensive review by Connecticut geologists and radon program
experts. The map for Connecticut 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 Connecticut" — 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
Connecticut 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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CONNECTICUT - EPA Map of Radon Zones
The purpose of Ws map Is to assist National, State and local organizations
to target their resources and to frnptement radon-resistant building codes.
TWs map Is not Intended to determine rf a homo in a given zone should be tested
for radon. Homes with elevated levels of radon have been found in d I three
zones. All homos should bo testod, regard/oss ofrono designation.
Zone 1
Zone 2
ZoneS
IMPORTANT: Consult the publication entitled "Preliminary Geologic Radon
Potential Assessment of Connecticut1 before using this map. This
document contains information on radon potential variations within counties.
EPA also recommends that this map be supplemented w'rth any available
local data in order to further understand and predict the radon potential of a
specific area.
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