United States
Environmental Protection
Agency
Air and Radiation
(6604J)
402-R-93-039
September 1993
vvEPA EPA's Map of Radon Zones
MAINE
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EPA'S MAP OF RADON ZONES
MAINE
RADON DIVISION
OFFICE OF RADIATION AND INDOOR AIR
U.S. ENVIRONMENTAL PROTECTION AGENCY
SEPTEMBER, 1993
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ACKNOWLEDGEMENTS
This document was prepared by the U.S. Environmental Protection Agency's (EPA's)
Office of Radiation and Indoor Air (ORIA) in conjunction with the U.S. Geological Survey
(USGS). Sharon W. White was the EPA project manager. Numerous other people in ORIA
were instrumental in the development of the Map of Radon Zones, including Lisa Ratcliff,
Kirk Maconaughey, R. Thomas Peake, Dave Rowson, and Steve Page.
EPA would especially like to acknowledge the outstanding effort of the USGS
radon team — Linda Gundersen, Randy Schumann, Jim Otton, Doug Owen, Russell
Dubiel, Kendell Dickinson, and Sandra Szarzi — in developing the technical base for the
Map of Radon Zones.
ORIA would also like to recognize the efforts of all the EPA Regional Offices in
coordinating the reviews with the State programs and the Association of American State
Geologists (AASG) for providing a liaison with the State geological surveys. In addition,
appreciation is expressed to all of the State radon programs and geological surveys for their
technical input and review of the Map of Radon Zones.
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TABLE OF CONTENTS
I. OVERVIEW
II. THE USGS/EPA RADON POTENTIAL
ASSESSMENTS:INTRODUCTION
III. REGION 1 GEOLOGIC RADON POTENTIAL
SUMMARY
V. PRELIMINARY GEOLOGIC RADON POTENTIAL
ASSESSMENT OF MAINE
V. EPA'S MAP OF RADON ZONES - MAINE
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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 counry-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, USGS1 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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potential and some data are available for each of these factors in every geologic province. The
province boundaries do not coincide with political borders (county and state) but define areas
of general radon potential. The five factors were assigned numerical values based on an
assessment of their respective contribution to radon potential, and a confidence level was
assigned to each contributing variable. The approach used by USGS to estimate the radon
potential for each province is described in Part II of this document.
EPA subsequently developed the Map of Radon Zones by extrapolating from the
province level to the county level so that all counties in the U.S. were assigned to one of
three radon zones. EPA assigned each county to a given zone based on its provincial radon
potential. For example, if a county is located within a geologic province that has a predicted
average screening level greater than 4 pCi/L, it was assigned to Zone 1. Likewise, counties
located in provinces with predicted average screening levels > 2 pCi/L and < 4 pCi/L, and
less than 2 pCi/L, were assigned to Zones 2 and 3, respectively.
If the boundaries of a county fall in more than one geologic province, the county was
assigned to a zone based on the predicted radon potential of the province in which most of
the area lies. For example, if three different provinces cross through a given county, the
county was assigned to the zone representing the radon potential of the province containing
most of the county's land area. (In this case, it is not technically correct to say that the
predicted average screening level applies to the entire county since the county falls in
multiple provinces with differing radon potentials.)
Figures 3 and 4 demonstrate an example of how EPA extrapolated the county zone
designations for Nebraska from the USGS geologic province map for the State. As figure 3
shows, USGS has identified 5 geologic provinces for Nebraska. Most of the counties are
extrapolated "straight" from their corresponding provinces, but there are counties "partitioned"
by several provinces - for example, Lincoln County. Although Lincoln county falls in
multiple provinces, it was assigned to Zone 3 because most of its area falls in the province
with the lowest radon potential.
It is important to note that EPA's extrapolation from the province level to the
county level may mask significant "highs" and "lows" within specific counties. In other
words, within-county variations in radon potential are not shown on the Map of Radon
Zones. EPA recommends that users who may need to address specific within-county •
variations in radon potential (e.g., local government officials considering the
implementation of radon-resistant construction codes) consult USGS' Geologic Radon
Province Map and the State chapters provided with this map for more detailed
information, as well as any locally available data.
Map Validation
The Map of Radon Zones is intended to represent a preliminary assessment of radon
potential for the entire United States. The factors that are used in this effort —indoor radon
data, geology, aerial radioactivity, soils, and foundation type — are basic indicators for radon
potential. It is important to note, however, that the map's county zone designations are not
"statistically valid" predictions due to the nature of the data available for these 5 factors at the
county level. In order to validate the map in light of this lack of statistical confidence, EPA
conducted a number of analyses. These analyses have helped EPA to identify the best
situations in which to apply the map, and its limitations.
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Figure 3
Geologic Radon Potential Provinces for Nebraska
Lincoln County
Bijl Underlie Lo.
Figure 4
NEBRASKA - EPA Map of Radon Zones
Lincoln County
Zose 1 Zoac 2 Zone 3
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One such analysis involved comparing county zone designations to indoor radon
measurements from the State/EPA Residential Radon Surveys (SRRS). Screening averages
for counties with at least 100 measurements were compared to the counties' predicted radon
potential as indicated by the Map of Radon Zones. EPA found that 72% of the county
screening averages were correctly reflected by the appropriate zone designations on the Map.
In all other cases, they only differed by 1 zone.
Another accuracy analysis used the annual average data from the National Residential
Radon Survey (NRRS). The NRRS indicated that approximately 6 million homes in the
United States have annual averages greater than or equal to 4 pCi/L. By cross checking the
county location of the approximately 5,700 homes which participated in the survey, their
radon measurements, and the zone designations for these counties, EPA found that
approximately 3.8 million homes of the 5.4 million homes with radon levels greater than or
equal to 4 pCi/L will be found in counties designated as Zone 1. A random sampling of an
equal number of counties would have only found approximately 1.8 million homes greater
than 4 pCi/L. In other words, this analysis indicated that the map approach is three times
more efficient at identifying high radon areas than random selection of zone designations.
Together, these analyses show that the approach EPA used to develop the Map of
Radon Zones is a reasonable one. In addition, the Agency's confidence is enhanced by results
of the extensive State review process ~ the map generally agrees with the States' knowledge
of and experience in their own jurisdictions. However, the accuracy analyses highlight two
important points: the fact that elevated levels will be found in Zones 2 and 3, and that there
will be significant numbers of homes with lower indoor radon levels in all of the Zones. For
these reasons, users of the Map of Radon Zones need to supplement the Map with locally
available data whenever possible. Although all known "hot spots", i.e., localized areas of
consistently elevated levels, are discussed in the State-
specific chapters, accurately defining the boundaries of the "hot spots" on this scale of map is
not possible at this time. Also, unknown "hot spots" do exist.
The Map of Radon Zones is intended to be a starting point for characterizing radon
potential because our knowledge of radon sources and transport is always growing. Although
this effort represents the best data available at this time, EPA will continue to study these
parameters and others such as house construction, ventilation features and meteorology factors
in order to better characterize the presence of radon in U.S homes, especially in high risk
areas. These efforts will eventually assist EPA in refining and revising the conclusions of the
Map of Radon Zones. And although this map is most appropriately used as a targeting tool
by the aforementioned audiences ~ the Agency encourages all residents to test their homes
for radon, regardless of geographic location or the zone designation of the county in
which they live. Similarly, the Map of Radon Zones should not to be used in lieu of
testing during real estate transactions.
Review Process
The Map of Radon Zones has undergone extensive review within EPA and outside the
Agency. The Association of American State Geologists (AASG) played an integral role in
this review process. The AASG individual State geologists have reviewed their State-specific
information, the USGS Geologic Radon Province Map, and other materials for their geologic
content and consistency.
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In addition to each State geologist providing technical comments, the State radon
offices were asked to comment on their respective States' radon potential evaluations. In
particular, the States were asked to evaluate the data used to assign their counties to specific
zones. EPA and USGS worked with the States to resolve any issues concerning county zone
designations. In a few cases, States have requested changes in county zone designations. The
requests were based on additional data from the State on geology, indoor radon
measurements, population, etc. Upon reviewing the data submitted by the States, EPA did
make some changes in zone designations. These changes, which do not strictly follow the
methodology outlined in this document, are discussed in the respective State chapters.
EPA encourages the States and counties to conduct further research and data collection
efforts to refine the Map of Radon Zones. EPA would like to be kept informed of any
changes the States, counties, or others make to the maps. Updates and revisions will be
handled in a similar fashion to the way the map was developed. States should notify EPA of
any proposed changes by forwarding the changes through the Regional EPA offices that are
listed in Part 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
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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 repcrts 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 (222Rn) is produced from the radioactive decay of radium (226Ra), which is, in turn,
a product of the decay of uranium (238U) (fig. 1). The half-life of 222Rn is 3.825 days. Other
isotopes of radon occur naturally, but, with the exception of thoron (220Rn), which occurs in
concentrations high enough to be of concern in a few localized areas, they are less important
in terms of indoor radon risk because of their extremely short half-lives and less common
occurrence. In general, the concentration and mobility of radon in soil are dependent on
several factors, the most important of which are the soil's radium content and distribution,
porosity, permeability to gas movement, and moisture content. These characteristics are, in
turn, determined by the soil's parent-material composition, climate, and the soil's age or
maturity. If parent-material composition, climate, vegetation, age of the soil, and topography
are known, the physical and chemical properties of a soil in a given area can be predicted.
As soils form, they develop distinct layers, or horizons, that are cumulatively called the
soil profile. The A horizon is a surface or near-surface horizon containing a relative
abundance of organic matter but dominated by mineral matter. Some soils contain an E
horizon, directly below the A horizon, that is generally characterized by loss of clays, iron, or
aluminum, and has a characteristically lighter color than the A horizon. The B horizon
underlies the A or E horizon. Important characteristics of B horizons include accumulation of
clays, iron oxides, calcium carbonate or other soluble salts, and organic matter complexes. In
drier environments, a horizon may exist within or below the B horizon that is dominated by
calcium carbonate, often called caliche or calcrete. This carbonate-cemented horizon is
designated the K horizon in modern soil classification schemes. The C horizon underlies the
B (or K) and is a zone of weathered parent material that does not exhibit characteristics of A
or B horizons; that is, it is generally not a zone of leaching or accumulation. In soils formed
in place from the underlying bedrock, the C horizon is a zone of unconsolidated, weathered
bedrock overlying the unweathered bedrock.
The shape and orientation of soil particles (soil structure) control permeability and affect
water movement in the soil. Soils with blocky or granular structure have roughly equivalent
permeabilities in the horizontal and vertical directions, and air and water can infiltrate the soil
relatively easily. However, in soils with platy structure, horizontal permeability is much
greater than vertical permeability, and air and moisture infiltration is generally slow. Soils
with prismatic or columnar structure have dominantly vertical permeability. Platy and
prismatic structures form in soils with high clay contents. In soils with shrink-swell clays, air
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and moisture infiltration rates and depth of wetting may be limited when the cracks in the
surface soil layers swell shut. Clay-rich B horizons, particularly those with massive or platy
structure, can form a capping layer that impedes the escape of soil gas to the surface
(Schumann and others, 1992). However, the shrinkage of clays can act to open or widen
cracks upon drying, thus increasing the soil's permeability to gas flow during drier periods.
Radon transport in soils occurs by two processes: (1) diffusion and (2) flow (Tanner,
1964). Diffusion is the process whereby radon atoms move from areas of higher
concentration to areas of lower concentration in response to a concentration gradient. Flow is
the process by which soil air moves through soil pores in response to differences in pressure
within the soil or between the soil and the atmosphere, carrying the radon atoms along with it.
Diffusion is the dominant radon transport process in soils of low permeability, whereas flow
tends to dominate in highly permeable soils (Sextro and others, 1987). In low-permeability
soils, much of the radon may decay before it is able to enter a building because its transport
rate is reduced. Conversely, highly permeable soils, even those that are relatively low in
radium, such as those derived from some types of glacial deposits, have been associated with
high indoor radon levels in Europe and in the northern United States (Akerblom and others,
1984; Kunz and others, 1989; Sextro and others, 1987). In areas of karst topography formed
in carbonate rock (limestone or dolomite) environments, solution cavities and fissures can
increase soil permeability at depth by providing additional pathways for gas flow.
Not all radium contained in soil grains and grain coatings will result in mobile radon
when the radium decays. Depending on where the radium is distributed in the soil, many of
the radon atoms may remain imbedded in the soil grain containing the parent radium atom, or
become imbedded in adjacent soil grains. The portion of radium that releases radon into the
pores and fractures of rocks and soils is called the emanating fraction. When a radium atom
decays to radon, the energy generated is strong enough to send the radon atom a distance of
about 40 nanometers (1 nm = 10'9 meters), or about 2x10'6 inches—this is known as alpha
recoil (Tanner, 1980). Moisture in the soil lessens the chance of a recoiling radon atom
becoming imbedded in an adjacent grain. Because water is more dense than air, a radon atom
will travel a shorter distance in a water-filled pore than in an air-filled pore, thus increasing
the likelihood that the radon atom will remain in the pore space. Intermediate moisture levels
enhance radon emanation but do not significantly affect permeability. However, high
moisture levels, can significantly decrease the gas permeability of the soil and impede radon
movement through the soil.
Concentrations of radon in soils are generally many times higher than those inside of
buildings, ranging from tens of pCi/L to more than 100,000 pCi/L, but typically in the range
of hundreds to low thousands of pCi/L. Soil-gas radon concentrations can vary in response to
variations in climate and weather on hourly, daily, or seasonal time scales. Schumann and
others (1992) and Rose and others (1988) recorded order-of-magnitude variations in soil-gas
radon concentrations between seasons in Colorado and Pennsylvania. The most important
factors appear to be (1) soil moisture conditions, which are controlled in large part by
precipitation; (2) barometric pressure; and (3) temperature. Washington and Rose (1990)
suggest that temperature-controlled partitioning of radon between water and gas in soil pores
also has a significant influence on the amount of mobile radon in soil gas.
Homes in hilly limestone regions of the southern Appalachians were found to have higher
indoor radon concentrations during the summer than in the winter. A suggested cause for this
phenomenon involves temperature/pressure-driven flow of radon-laden air from subsurface
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solution cavities in the carbonate rock into houses. As warm air enters solution cavities that
are higher on the hillslope than the homes, it cools and settles, pushing radon-laden air from
lower in the cave or cavity system into structures on the hillslope (Gammage and others,
1993). In contrast, homes built over caves having openings situated below the level of the
home had higher indoor radon levels in the winter, caused by cooler outside air entering the
cave, driving radon-laden air into cracks and solution cavities in the rock and soil, and
ultimately, into homes (Gammage and others, 1993).
RADON ENTRY INTO BUILDINGS
A driving force (reduced atmospheric pressure in the house relative to the soil, producing
a pressure gradient) and entry points must exist for radon to enter a building from the soil.
The negative pressure caused by furnace combustion, ventilation devices, and the stack effect
(the rising and escape of warm air from the upper floors of the building, causing a
temperature and pressure gradient within the structure) during cold winter months are
common driving forces. Cracks and other penetrations through building foundations, sump
holes, and slab-to-foundation wall joints are common entry points.
Radon levels in the basement are generally higher than those on the main floor or upper
floors of most structures. Homes with basements generally provide more entry points for
radon, commonly have a more pronounced stack effect, and typically have lower air pressure
relative to the surrounding soil than nonbasement homes. The term "nonbasement" applies to
slab-on-grade or crawl space construction.
METHODS AND SOURCES OF DATA
The assessments of radon potential in the booklets that follow this introduction were
made using five main types of data: (1) geologic (lithologic); (2) aerial radiometric; (3) soil
characteristics, including soil moisture, permeability, and drainage characteristics; (4) indoor
radon data; and (5) building architecture (specifically, whether homes in each area are built
slab-on-grade or have a basement or crawl space). These five factors were evaluated and
integrated to produce estimates of radon potential. Field measurements of soil-gas radon or
soil radioactivity were not used except where such data were available in existing, published
reports of local field studies. Where applicable, such field studies are described in the
individual state chapters.
GEOLOGIC DATA
The types and distribution of lithologic units and other geologic features in an
assessment area are of primary importance in determining radon potential. Rock types that
are most likely to cause indoor radon problems include carbonaceous black shales, glauconite-
bearing sandstones, certain kinds of fluvial sandstones and fluvial sediments, phosphorites,
chalk, karst-producing carbonate rocks, certain kinds of glacial deposits, bauxite, uranium-rich
granitic rocks, metamorphic rocks of granitic composition, silica-rich volcanic rocks, many
sheared or faulted rocks, some coals, and certain kinds of contact metamorphosed rocks.
Rock types least likely to cause radon problems include marine quartz sands, non-
carbonaceous shales and siltstones, certain kinds of clays, silica-poor metamorphic and
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igneous rocks, and basalts. Exceptions exist within these general lithologic groups because of
the occurrence of localized uranium deposits, commonly of the hydrothermal type in
crystalline rocks or the "roll-front" type in sedimentary rocks. Uranium and radium are
commonly sited in heavy minerals, iron-oxide coatings on rock and soil grains, and organic
materials in soils.and sediments. Less common are uranium associated with phosphate and
carbonate complexes in rocks and soils, and uranium minerals.
Although many cases of elevated indoor radon levels can be traced to high radium and
(or) uranium concentrations in parent rocks, some structural features, most notably faults and
shear zones, have been identified as sites of localized uranium concentrations (Deffeyes and
MacGregor, 1980) and have been associated with some of the highest reported indoor radon
levels (Gundersen, 1991). The two highest known indoor radon occurrences are associated
with sheared fault zones in Boyertown, Pennsylvania (Gundersen and others, 1988a; Smith
and others, 1987), and in Clinton, New Jersey (Henry and others, 1991; Muessig and Bell,
1988).
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 (2UBi), with the assumption that uranium and
its decay products are in secular equilibrium. Equivalent uranium is expressed in units of
parts per million (ppm). Gamma radioactivity also may be expressed in terms of a radium
activity; 3 ppm eU corresponds to approximately 1 picocurie per gram (pCi/g) of radium-226.
Although radon is highly mobile in soil and its concentration is affected by meteorological
conditions (Kovach, 1945; Klusman and Jaacks, 1987; Schery and others, 1984; Schumann
and others, 1992), statistical correlations between average soil-gas radon concentrations and
average eU values for a wide variety of soils have been documented (Gundersen and others,
1988a, 1988b; Schumann and Owen, 1988). Aerial radiometric data can provide an estimate
of radon source strength over a region, but the amount of radon that is able to enter a home
from the soil is dependent on several local factors, including soil structure, grain size
distribution, moisture content, and permeability, as well as type of house construction and its
structural condition.
The aerial radiometric data used for these characterizations were collected as part of the
Department of Energy National Uranium Resource Evaluation (NURE) program of the 1970s
and early 1980s. The purpose of the NURE program was to identify and describe areas in the
United States having potential uranium resources (U.S. Department of Energy, 1976). The
NURE aerial radiometric data were collected by aircraft in which a gamma-ray spectrometer
was mounted, flying approximately 122 m (400 ft) above the ground surface. The equivalent
uranium maps presented in the state chapters were generated from reprocessed NURE data in
which smoothing, filtering, recalibrating, and matching of adjacent quadrangle data sets were
performed to compensate for background, altitude, calibration, and other types of errors and
inconsistencies in the original data set (Duval and others, 1989). The data were then gridded
and contoured to produce maps of eU with a pixel size corresponding to approximately 2.5 x
2.5 km (1.6 x 1.6 mi).
II-6 Reprinted from USGS Open-File Report 93-292
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FLICUT LINE SPACING OF NUKE AERIAL SURVEYS
2 Kll (1 MILE)
5 KM (3 MILES)
2 i 5 KM
10 KM (6 UILES)
5 t 10 KM
NO DATA
Figure 2. Nominal flightline spacings for NURE aerial gamma-ray surveys covering the
contiguous United States (fromDuval and others, 1990). Rectangles represent I°x2° quadrangles.
-------
Figure 2 is an index map of NURE 1° x 2° quadrangles showing the flight-line spacing
for each quadrangle. In general, the more closely spaced the flightlines are, the more area
was covered by the aerial gamma survey, and thus, more detail is available in the data set.
For an altitude of 400 ft above the ground surface and with primary flightline spacing
typically between 3 and 6 miles, less than 10 percent of the ground surface of the United
States was actually measured by the airborne gamma-ray detectors (Duval and others, 1989),
although some areas had better coverage than others due to the differences in flight-line
spacing between areas (fig. 2). This suggests that some localized uranium anomalies may not
have been detected by the aerial surveys, but the good correlations of eU patterns with
geologic outcrop patterns indicate that, at relatively small scales (approximately 1:1,000,000
or smaller) the National eU map (Duval and others, 1989) gives reasonably good estimates of
average surface uranium concentrations and thus can assist in the prediction of radon potential
of rocks and soils, especially when augmented with additional geologic and soil data.
The shallow (20-30 cm) depth of investigation of gamma-ray spectrometers, either
ground-based or airborne (Duval and others, 1971; Durrance, 1986), suggests that gamma-ray
data may sometimes underestimate the radon-source strength in soils in which some of the
radionuclides in the near-surface soil layers have been transported downward through the soil
profile. In such cases the concentration of radioactive minerals in the A horizon would be
lower than in the B horizon, where such minerals are typically concentrated. The
concentration of radionuclides in the C horizon and below may be relatively unaffected by
surface solution processes. Under these conditions the surface gamma-ray signal may indicate
a lower radon source concentration than actually exists in the deeper soil layers, which are
most likely to affect radon levels in structures with basements. The redistribution of
radionuclides in soil profiles is dependent on a combination of climatic, geologic, and
geochemical factors. There is reason to believe that correlations of eU with actual soil
radium and uranium concentrations at a depth relevant to radon entry into structures may be
regionally variable (Duval, 1989; Schumann and Gundersen, 1991). Given sufficient
understanding of the factors cited above, these regional differences may be predictable.
SOIL SURVEY DATA
Soil surveys prepared by the U.S. Soil Conservation Service (SCS) provide data on soil
characteristics, including soil-cover thickness, grain-size distribution, permeability, shrink-
swell potential, vegetative cover, generalized groundwater characteristics, and land use. The
reports are available in county formats and State summaries. The county reports typically
contain both generalized and detailed maps of soils in the area.
Because of time and map-scale constraints, it was impractical to examine county soil
reports for each county in the United States, so more generalized summaries at appropriate
scales were used where available. For State or regional-scale radon characterizations, soil
maps were compared to geologic maps of the area, and the soil descriptions, shrink-swell
potential, drainage characteristics, depth to seasonal high water table, permeability, and other
relevant characteristics of each soil group noted. Technical soil terms used in soil surveys are
generally complex; however, a good summary of soil engineering terms and the national
distribution of technical soil types is the "Soils" sheet of the National Atlas (U.S. Department
of Agriculture, 1987).
II-8 Reprinted from USGS Open-File Report 93-292
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Soil permeability is commonly expressed in SCS soil surveys in terms of the speed, in
inches per hour (in/hr), at which water soaks into the soil, as measured in a soil percolation
test. Although in/hr are not truly units of permeability, these units are in widespread use and
are referred to as "permeability" in SCS soil surveys. The permeabilities listed in the SCS
surveys are for water, but they generally correlate well with gas permeability. Because data
on gas permeability of soils is extremely limited, data on permeability to water is used as a
substitute except in cases in which excessive soil moisture is known to exist. Water in soil
pores inhibits gas transport, so the amount of radon available to a home is effectively reduced
by a high water table. Areas likely to have high water tables include river valleys, coastal
areas, and some areas overlain by deposits of glacial origin (for example, loess).
Soil permeabilities greater than 6.0 in/hr may be considered high, and permeabilities less
than 0.6 in/hr may be considered low in terms of soil-gas transport. Soils with low
permeability may generally be considered to have a lower radon potential than more
permeable soils with similar radium concentrations. Many well-developed soils contain a
clay-rich B horizon that may impede vertical soil gas transport. Radon generated below this
horizon cannot readily escape to the surface, so it would instead tend to move laterally,
especially under the influence of a negative pressure exerted by.a building.
Shrink-swell potential is an indicator of the abundance of smectitic (swelling) clays in a
soil. Soils with a high shrink-swell potential may cause building foundations to crack,
creating pathways for radon entry into the structure. During dry periods, desiccation cracks in
shrink-swell soils provide additional pathways for soil-gas transport and effectively increase
the gas permeability of the soil. Soil permeability data and soil profile data thus provide
important information for regional radon assessments.
INDOOR RADON DATA
Two major sources of indoor radon data were used. The first and largest source of data is
from the State/EPA Residential Radon Survey (Ronca-Battista and others, 1988; Dziuban and
others, 1990). Forty-two states completed EPA-sponsored indoor radon surveys between 1986
and 1992 (fig. 3). The State/EPA Residential Radon Surveys were designed to be
comprehensive and statistically significant at the state level, and were subjected to high levels
of quality assurance and control. The surveys collected screening indoor radon measurements,
defined as 2-7 day measurements using charcoal canister radon detectors placed in the lowest
livable area of the home. The target population for the surveys included owner-occupied
single family, detached housing units (White and others, 1989), although attached structures
such as duplexes, townhouses, or condominiums were included in some of the surveys if they
met the other criteria and had contact with the ground surface. Participants were selected
randomly from telephone-directory listings. In total, approximately 60,000 homes were tested
in the State/EPA surveys.
The second source of indoor radon data comes from residential surveys that have been
conducted in a specific state or region of the country (e.g. independent state surveys or utility
company surveys). Several states, including Delaware, Florida, Illinois, New Hampshire, New
Jersey, New York, Oregon, and Utah, have conducted their own surveys of indoor radon. The
quality and design of a state or other independent survey are discussed and referenced where
the data are used.
II-9 Reprinted from USGS Open-File Report 93-292
-------
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Data for only those counties with five or more measurements are shown in the indoor
radon maps in the state chapters, although data for all counties with a nonzero number of
measurements are listed in the indoor radon data tables in each state chapter. In total, indoor
radon data from more than 100,000 homes nationwide were used in the compilation of these
assessments. Radon data from State or regional indoor radon surveys, public health
organizations, or other sources are discussed in addition to the primary data sources where
they are available. Nearly all of the data used in these evaluations represent short-term (2-7
day) screening measurements from the lowest livable space of the homes. Specific details
concerning the nature and use of indoor radon data sets other than the State/EPA Residential
Radon Survey are discussed in the individual State chapters.
RADON INDEX AND CONFIDENCE INDEX
Many of the geologic methods used to evaluate an area for radon potential require
subjective opinions based on the professional judgment and experience of the individual
geologist. The evaluations are nevertheless based on established scientific principles that are
universally applicable to any geographic area or geologic setting. This section describes the
methods and conceptual framework used by the U.S. Geological Survey to evaluate areas for
radon potential based on the five factors discussed in the previous sections. The scheme is
divided into two basic parts, a Radon Index (RI), used to rank the general radon potential of
the area, and the Confidence Index (CI), used to express the level of confidence in the
prediction based on the quantity and quality of the data used to make the determination. This
scheme works best if the areas to be evaluated are delineated by geologically-based
boundaries (geologic provinces) rather than political ones (state/county boundaries) in which
the geology may vary across the area.
Radon Index. Table 1 presents the Radon Index (RI) matrix. The five factors—indoor
radon data, geology, aerial radioactivity, soil parameters, and house foundation type—were
quantitatively ranked (using a point value of 1, 2, or 3) for their respective contribution to
radon potential in a given area. At least some data for the 5 factors are consistently available
for every geologic province. Because each of these main factors encompass a wide variety of
complex and variable components, the geologists performing the evaluation relied heavily on
their professional judgment and experience in assigning point values to each category and in
determining the overall radon potential ranking. Background information on these factors is
discussed in more detail in the preceding sections of this introduction.
Indoor radon was evaluated using unweighted arithmetic means of the indoor radon data
for each geologic area to be assessed. Other expressions of indoor radon levels in an area
also could have been used, such as weighted averages or annual averages, but these types of
data were not consistently available for the entire United States at the time of this writing, or
the schemes were not considered sufficient to provide a means of consistent comparison
across all areas. For this report, charcoal-canister screening measurement data from the
State/EPA Residential Radon Surveys and other carefully selected sources were used, as
described in the preceding section. To maintain consistency, other indoor radon data sets
(vendor, state, or other data) were not considered in scoring the indoor radon factor of the
Radon Index if they were not randomly sampled or could not be statistically combined with
the primary indoor radon data sets. However, these additional radon data sets can provide a
means to further refine correlations between geologic factors and radon potential, so they are
II-11 Reprinted from USGS Open-File Report 93-292
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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 PERME ABILITY
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
Point range
Probable average screening
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
4-6 points
7-9 points
10 - 12 points
POSSIBLE RANGE OF POINTS = 4 to 12
II-12 Reprinted from USGS Open-File Report 93-292
-------
included as supplementary information and are discussed in the individual State chapters. If
the average screening indoor radon level for an area was less than 2 pCi/L, the indoor radon
factor was assigned 1 point, if it was between 2 and 4 pCi/L, it was scored 2 points, and if
the average screening indoor radon level for an area was greater than 4 pCi/L, the indoor
radon factor was assigned 3 RI points.
Aerial radioactivity data used in this report are from the equivalent uranium map of the
conterminous United States compiled from NURE aerial gamma-ray surveys (Duval and
others, 1989). These data indicate the gamma radioactivity from approximately the upper 30
cm of rock and soil, expressed in units of ppm equivalent uranium. An approximate average
value of eU was determined visually for each area and point values assigned based on
whether the overall eU for the area falls below 1.5 ppm (1 point), between 1.5 and 2.5 ppm
(2 points), or greater than 2.5 ppm (3 points).
The geology factor is complex and actually incorporates many geologic characteristics. In
the matrix, "positive" and "negative" refer to the presence or absence and distribution of rock
types known to have high uranium contents and to generate elevated radon in soils or indoors.
Examples of "positive" rock types include granites, black shales, phosphatic rocks, and other
rock types described in the preceding "geologic data" section. Examples of "negative" rock
types include marine quartz sands and some clays. The term "variable" indicates that the
geology within the region is variable or that the rock types in the area are known or suspected
to generate elevated radon in some areas but not in others due to compositional differences,
climatic effects, localizeddistribution of uranium, or other factors. Geologic information
indicates not only how much uranium is present in the rocks and soils but also gives clues for
predicting general radon emanation and mobility characteristics through additional factors
such as structure (notably the presence of faults or shears) and geochemical characteristics
(for example, a phosphate-rich sandstone will likely contain more uranium than a sandstone
containing little or no phosphate because the phosphate forms chemical complexes with
uranium); "Negative", "variable", and "positive" geology were assigned 1, 2, and 3 points,-
respectively.
In cases where additional reinforcing or contradictory geologic evidence is available,
Geologic Field Evidence (GFE) points were added to or subtracted from an area's score
(Table 1). Relevant geologic field studies are important to enhancing our understanding of
how geologic processes affect radon distribution. In some cases, geologic models and
supporting field data reinforced an already strong (high or low) score; in others, they provided
important contradictory data. GFE points were applied for geologically-sound evidence that
supports the prediction (but which may contradict one or more factors) on the basis of known
geologic field studies in the area or in areas with geologic and climatic settings similar
enough that they could be applied with full confidence. For example, areas of the Dakotas,
Minnesota, and Iowa that are covered with Wisconsin-age glacial deposits exhibit a low aerial
radiometric signature and score only one RI point in that category. However, data from
geologic field studies in North Dakota and Minnesota (Schumann and others, 1991) suggest
that eU is a poor predictor of geologic radon potential in this area because radionuclides have
11-13 Reprinted from USGS Open-File Report 93-292
-------
been leached from the upper soil layers but are present and possibly even concentrated in
deeper soil horizons, generating significant soil-gas radon. This positive supporting field
evidence adds two GFE points to the score, which helps to counteract the invalid conclusion
suggested by the radiometric data. No GFE points are awarded if there are no documented
field studies for the area.
"Soil permeability" refers to several soil characteristics that influence radon concentration
and mobility, including soil type, grain size, structure, soil moisture, drainage, slope, and
permeability. In the matrix, "low" refers to permeabilities less than about 0.6 in/hr; "high"
corresponds to greater than about 6.0 in/hr, in U.S. Soil Conservation Service (SCS) standard
soil percolation tests. The SCS data are for water permeability, which generally correlates
well with the gas permeability of the soil except when the soil moisture content is very high.
Areas with consistently high water tables were thus considered to have low gas permeability.
"Low, "moderate", and "high" permeability were assigned 1, 2, and 3 points, respectively.
Architecture type refers to whether homes in the area have mostly basements (3 points),
mostly slab-on-grade construction (1 point), or a mixture of the'two. Split-level and crawl
space homes fall into the "mixed" category (2 points). Architecture information is necessary
to properly interpret the indoor radon data and produce geologic radon potential categories
that are consistent with screening indoor radon data.
The overall RI for an area is calculated by adding the individual RI scores for the 5
factors, plus or minus GFE points, if any. The total RI for an area falls in one of three
categories—low, moderate or variable, or high. The point ranges for the three categories were
determined by examining the possible combinations of points for the 5 factors and setting
rules such that a majority (3 of 5 factors) would determine the final score for the low and
high categories, with allowances for possible deviation from an ideal score by the other two
factors. The moderate/variable category lies between these two ranges. A total deviation of 3
points from the "ideal" score was considered reasonable to allow for natural variability of
factors—if two of the five factors are allowed to vary from the "ideal" for a category, they
can differ by a minimum of 2 (1 point different each) and a maximum of 4 points (2 points
different each). With "ideal" scores of 5, 10, and 15 points describing low, moderate, and
high geologic radon potential, respectively, an ideal low score of 5 points plus 3 points for
possible variability allows a maximum of 8 points in the low category. Similarly, an ideal
high score of 15 points minus 3 points gives a minimum of 12 points for the high category.
Note, however, that if both other factors differ by two points from the "ideal", indicating
considerable variability in the system, the total point score would lie in the adjacent (i.e.,
moderate/variable) category.
Confidence Index. Except for architecture type, the same factors were used to establish a
Confidence Index (CI) for the radon potential prediction for each area (Table 2). Architecture
type was not included in the confidence index because house construction data are readily and
reliably available through surveys taken by agencies and industry groups including the
National Association of Home Builders, U.S. Department of Housing and Urban
Development, and the Federal Housing Administration; thus it was not considered necessary
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 eU, geology, and
soil-gas or indoor radon levels were associated with glacial deposits (see the discussion in a
previous section) and typically were assigned a 2-point Confidence Index score. Correlations
among eU, geology, and radon were generally sound in unglaciated areas and were usually
assigned 3 CI points. Again, however, radioactivity data in some unglaciated areas may have
been assigned fewer than 3 points, and in glaciated areas may be assigned only one point, if
the data were considered questionable or if coverage was poor.
To assign Confidence Index scores for the geologic data factor, rock types and geologic
settings for which a physical-chemical, process-based understanding of radon generation and
mobility exists were regarded as having "proven geologic models" (3 points); a high
confidence could be held for predictions in such areas. Rocks for which the processes are
less well known or for which data are contradictory were regarded as "variable" (2 points),
and those about which little is known or for which no apparent correlations have been found
were deemed "questionable" (1 point).
The soil permeability factor was also scored based on quality and amount of data. The
three categories for soil permeability in the Confidence Index are similar in concept, and
scored similarly, to those for the geologic data factor. Soil permeability can be roughly
estimated from grain size and drainage class if data from standard, accepted soil percolation
tests are unavailable; however, the reliability of the data would be lower than if percolation
test figures or other measured permeability data are available, because an estimate of this type
does not encompass all the factors that affect soil permeability and thus may be inaccurate in
some instances. Most published soil permeability data are for water; although this is
generally closely related to the air permeability of the soil, there are some instances when it
may provide an incorrect estimate. Examples of areas in which water permeability data may
not accurately reflect air permeability include areas with consistently high levels of soil
moisture, or clay-rich soils, which would have a low water permeability but may have a
11-15 Reprinted from USGS Open-File Report 93-292
-------
significantly higher air permeability when dry due to shrinkage cracks in the soil. These
additional factors were applied to the soil permeability factor when assigning the RI score, but
may have less certainty in some cases and thus would be assigned a lower CI score.
The Radon Index and Confidence Index give a general indication of the relative
contributions of the interrelated geologic factors influencing radon generation and transport in
rocks and soils, and thus, of the potential for elevated indoor radon levels to occur in a
particular area. However, because these reports are somewhat generalized to cover relatively
large areas of States, it is highly recommended that more detailed studies be performed in
local areas of interest, using the methods and general information in these booklets as a guide.
11-16 Reprinted from USGS Open-File Report 93-292
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and indoor radon with geology in glacially derived soils of the northern Great Plains, in
Proceedings of the 1990 International Symposium on Radon and Radon Reduction
Technology, Volume 2, Symposium Oral Papers: U.S. Environmental Protection Agency
report EPA/600/9-91/026b, p. 6-23-6-36.
IE-18 Reprinted from USGS Open-Ftte Report 93-292
-------
Schumann, R.R., Owen, D.E., and Asher-Bolinder, S., 1992, Effects of weather and soil
characteristics on temporal variations in soil-gas radon concentrations, in Gates, A.E., and
Gundersen, L.C.S., eds., Geologic controls on radon: Geological Society of America
Special Paper 271, p. 65-72.
Sextro, R.G., Moed, B.A., Nazaroff, W.W., Revzan, K.L., and Nero, A.V., 1987,
Investigations of soil as a source of indoor radon, in Hopke, P.K., ed., Radon and its
decay products: American Chemical Society Symposium Series 331, p. 10-29.
Sterling, R., Meixel, G., Shen, L., Labs, K., and Bligh, T., 1985, Assessment of the energy
savings potential of building foundations research: Oak Ridge, Tenn., U.S. Department of
Energy Report ORNL/SUB/84-0024/1.
Smith, R.C., H, Reilly, M.A., Rose, A.W., Barnes, J.H., and Berkheiser, S.W., Jr., 1987,
Radon: a profound case: Pennsylvania Geology, v. 18, p. 1-7.
Tanner, A.B., 1964, Radon migration in the ground: a review, in Adams, J.A.S., and Lowder,
W.M., eds., The natural radiation environment: Chicago, HI., University of Chicago
Press, p. 161-190.
Tanner, A.B., 1980, Radon migration in the ground: a supplementary review, in Gesell, T.F.,
and Lowder, W.M. (eds), Natural radiation environment HI, Symposium proceedings,
Houston, Texas, v. 1, p. 5-56. 5
U.S. Department of Agriculture, 1987, Principal kinds of soils: Orders, suborders, and great
groups: U.S. Geological Survey, National Adas of the United States of America, sheet
38077-BE-NA-07M-00, scale 1:7,500,000.
U.S. Department of Energy, 1976, National Uranium Resource Evaluation preliminary report,
prepared by the U.S. Energy Research and Development Administration, Grand Junction,
Colo.: GJO-11(76).
Wanty, Richard B., and Schoen, Robert, 1991, A review of the chemical processes affecting the
mobility of radionuclides in natural waters, with applications, in Gundersen, Linda C.S.,
and Richard B. Wanty, eds., Field studies of radon in rocks, soils, and water: U.S.
Geological Survey Bulletin no. 1971, p. 183-194.
Washington, J.W., and Rose, A.W., 1990, Regional and temporal relations of radon in soil gas to
soil temperature and moisture: Geophysical Research Letters, v. 17, p. 829-832.
White, S.B., Bergsten, J.W., Alexander, B.V., and Ronca-Battista, M., 1989, Multi-State
surveys of indoor 222Rn: Health Physics, v. 57, p. 891-896.
U-19 Reprinted from USGS Open-FUe Report 93-292
-------
APPENDIX A
GEOLOGIC TIME SCALE
Subdivisions (and their symbols)
Eon or
Eonothem
Phsnerozoic2
Proterozoic
(E)
Archean
IAJ
Era or
. Erathem
Cenoioic 2
(Cz)
Mesozoic2
(Mi)
Paleozoic
(Pi)
1*19
M*Cfl!» _
£»"Y „
LJU
M.OOH
fcanv
Period, System.
Subperiod, Subsystem
Quaternary
(Q)
Neopene 2
Subperiod or
T.^-Y Subsystem (N)
m Paleogene2
"' Suboeriodor
Subsystem (Pi)
Cretaceous
(K)
Jurassic
(J)
Triassic
Hi)
Permian
(P)
Pennsylvanian
Carboniferous IP'
(C) Mississippian
(M)
Devonian
(0)
Silurian
(S)
Ordovician
(Q)
Cambrian
(C)
Epoch or Series
Age estimates
of boundaries
in mega-annum
(Ma)1
Holocene 1 Q010
Pleistocene . .
Pliocene
Miocene
Oligocene
Eocene
Paleocene
Late
Early '
Late
Middle
Early
Late
Middle
Early
Late
Early
Late
Middle
Early
Late
Early
Late
Middle
Early
Late
Middle
Early
Late
Middle
Early
Late
Middle
Early
Upper
Lower
Upper
Middle
Lower
Upper
Middle
Lower
Upper
Lower
Upper
Middle
Lower
Upper
Lower
Uooer
Middle
Lower
Upper
Middle
Lower
Upper
Middle
Lower
Upper
Middle
Lower
None defined
None defined
None defined
None defined
None defined
None defined
E5 (54-561
66 (63-66)
290 (290-305)
360 (360-365)
410 (405-415)
500 (495-510)
.570 3
900
— — 2500
3000
3400
3800?
'Ranow i»n#ct uncertiintiftf of isotopic and btostratioraphic age assignmenl*. Ag« boundaries not closely bracketed by existing
thown by-> Decay conwants and bolopic ratios employed are cited in Steioer and Jloer (1977). Designation m.y. used for an
1 Modifier* '{lower, middle, upper or early, middle, late) when used with these Hems are informal divisions of th« larger unit; the
first totter of th* modifier Is lowercase.
'Rocks older than 570 Ma also called Precambrian (p£). a time term without specific rank.
'Informal time term without specific rank.
USGS Open-File Report 93-292
-------
APPENDIX B
GLOSSARY OF TERMS
Units of measure
pCi/L (picocuries per liter)- a unit of measure of radioactivity used to describe radon
concentrations in a volume of air. One picocurie (10"12 curies) is equal to about 2.2 disintegrations
of radon atoms per minute. A liter is about 1.06 quarts. The average concentration of radon in
U.S. homes measured to date is between 1 and 2 pCS/L.
Bq/m3 (Becquerels per cubic meter)- a metric unit of radioactivity used to describe radon
concentrations in a volume of air. One becquerel is equal to one radioactive disintegration per
second. One pCi/L is equal to 37 Bq/m3.
ppm (parts per million)- a unit of measure of concentration by weight of an element in a
substance, in this case, soil or rock. One ppm of uranium contained in a ton of rock corresponds
to about 0.03 ounces of uranium. The average concentration of uranium in soils in the United
States is between 1 and 2 ppm.
in/hr (inches per hour)- a unit of measure used by soil scientists and engineers to describe the
permeability of a soil to water flowing through it It is measured by digging a hole 1 foot (12
inches) square and one foot deep, filling it with water, and measuring the time it takes for the water
to drain from the hole. The drop in height of the water level in the hole, measured in inches, is
then divided by the time (in hours) to determine the permeability. Soils range in permeability from
less than 0.06 in/hr to greater than 20 in/hr, but most soils in the United States have permeabilities
between these two extremes.
Geologic terms and terms related to the study of radon
aerial radiometric, aeroradiometric survey A survey of radioactivity, usually gamma rays,
taken by an aircraft carrying a gamma-ray spectrometer pointed at the ground surface.
alluvial fan A low, widespread mass of loose rock and soil material, shaped like an open fan
and deposited by a stream at the point where it flows from a narrow mountain valley out onto a
plain or broader valley. May also form at the junction with larger streams or when the gradient of
the stream abruptly decreases.
alluvium, alluvial General terms referring to unconsolidated detrital material deposited by a
stream or other body of running water.
alpha-track detector A passive radon measurement device consisting of a plastic film that is
sensitive to alpha particles. The film is etched with acid in a laboratory after it is exposed. The
etching reveals scratches, or "tracks", left by the alpha particles resulting from radon decay, which
can then be counted to calculate the radon concentration. Useful for long-term (1-12 months)
radon tests.
amphibolite A mafic metamorphic rock consisting mainly of pyroxenes and(or) amphibole and
plagioclase.
II-21 Reprinted from USGS Open-File Report 93-292
-------
argillite, argillaceous Terms referring to a rock derived from clay or shale, or any sedimentary
rock containing an appreciable amount of clay-size material, i.e., argillaceous sandstone.
arid Term describing a climate characterized by dryness, or an evaporation rate that exceeds the
amount of precipitation.
basalt A general term for a dark-colored mafic igneous rocks that may be of extrusive origin,
such as volcanic basalt flows, or intrusive origin, such as basalt dikes.
batholith A mass of plutonic igneous rock that has more than 40 square miles of surface
exposure and no known bottom.
carbonate A sedimentary rock consisting of the carbonate (COs) compounds of calcium,
magnesium, or iron, e.g. limestone and dolomite.
carbonaceous Said of a rock or sediment that is rich in carbon, is coaly, or contains organic
matter.
charcoal canister A passive radon measurement device consisting of a small container of
granulated activated charcoal that is designed to adsorb radon. Useful for short duration (2-7 days)
measurements only. May be referred to as a "screening" test
chert A hard, extremely dense sedimentary rock consisting dominantly of interlocking crystals of
quartz. Crystals are not visible to the naked eye, giving the rock a milky, dull luster. It may be
white or gray but is commonly colored red, black, yellow, blue, pink, brown, or green.
clastic pertaining to a rock or sediment composed of fragments that are derived from preexisting
rocks or minerals. The most common clastic sedimentary rocks are sandstone and shale.
clay A rock containing clay mineral fragments or material of any composition having a diameter
less than 1/256 mm.
clay mineral One of a complex and loosely defined group of finely crystalline minerals made up
of water, silicate and aluminum (and a wide variety of other elements). They are formed chiefly by
alteration or weathering of primary silicate minerals. Certain clay minerals are noted for their small
size and ability to absorb substantial amounts of water, causing them to swell. The change in size
that occurs as these clays change between dry and wet is referred to as their "shrink-swell"
potential.
concretion A hard, compact mass of mineral matter, normally subspherical but commonly
irregular in shape; formed by precipitation from a water solution about a nucleus or center, such as
a leaf, shell, bone, or fossil, within a sedimentary or fractured rock.
conglomerate A coarse-grained, clastic sedimentary rock composed of rock and mineral
fragments larger than 2 mm, set in a finer-grained matrix of clastic material.
cuesta A hill or ridge with a gentle slope on one side and a steep slope on the other. The
formation of a cuesta is controlled by the different weathering properties and the structural dip of
the rocks forming the hill or ridge.
daughter product A nuclide formed by the disintegration of a radioactive precursor or "parent"
atom.
11-22 Reprinted from USGS Open-File Report 93-292
-------
delta, deltaic Referring to a low, flat, alluvial tract of land having a triangular or fan shape,
located at or near the mouth of a river. It results from the accumulation of sediment deposited by a
river at the point at which the river loses its ability to transport the sediment, commonly where a
river meets a larger body of water such as a lake or ocean.
dike A tabular igneous intrusion of rock, younger than the surrounding rock, that commonly cuts
across the bedding or foliation of the rock it intrudes.
diorite A plutonic igneous rock that is medium in color and contains visible dark minerals that
make up less than 50% of the rock. It also contains abundant sodium plagioclase and minor
quartz.
dolomite A carbonate sedimentary rock of which more than 50% consists of the mineral dolomite
(CaMg(CO3)2), and is commonly white, gray, brown, yellow, or pinkish in color.
drainage The manner in which the waters of an area pass, flow off of, or flow into the soil.
Also refers to the water features of an area, such as lakes and rivers, that drain it
eolian Pertaining to sediments deposited by the wind.
esker A long, narrow, steep-sided ridge composed of irregular beds of sand and gravel deposited
by streams beneath a glacier and left behind when the ice melted.
evapotranspiration Loss of water from a land area by evaporation from the soil and
transpiration from plants.
extrusive Said of igneous rocks that have been erupted onto the surface of the Earth.
fault A fracture or zone of fractures in rock or sediment along which there has been movement.
fluvial, fluvial deposit Pertaining to sediment that has been deposited by a river or stream.
foliation A linear feature in a rock defined by both mineralogic and structural characteristics. It
may be formed during deformation or metamorphism.
formation A mappable body of rock having similar characteristics.
glacial deposit Any sediment transported and deposited by a glacier or processes associated
with glaciers, such as glaciofluvial sediments deposited by streams flowing from melting glaciers.
gneiss A rock formed by metamorphism in which bands and lenses of minerals of similar
composition alternate with bands and lenses of different composition, giving the rock a striped or
"foliated" appearance.
granite Broadly applied, any coarsely crystalline, quartz- and feldspar-bearing igneous plutonic
rock. Technically, granites have.between 10 and 50% quartz, and alkali feldspar comprises at least
65% of the total feldspar.
gravel An unconsolidated, natural accumulation of rock fragments consisting predominantly of
particles greater than 2 mm in size.
heavy minerals Mineral grains in sediment or sedimentary rock having higher than average
specific gravity. May form layers and lenses because of wind or water sorting by weight and size
H-23 Reprinted fiom 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 b^mg sedimentary and
metamorphic.
intermontane A term that refers to an area between two mountains or mountain ranges.
intrusion, intrusive The processes of emplacement or injection of molten rock into pre-existing
rock. Also refers to the rock formed by intrusive processes, such as an "intrusive igneous rock".
kame A low mound, knob, hummock, or short irregular ridge formed by a glacial stream at the
margin of a melting glacier; composed of bedded sand and gravel.
karst terrain A type of topography that is formed on limestone, gypsum and other rocks by
dissolution of the rock by water, forming sinkholes and caves.
lignite A brownish-black coal that is intermediate in coalification between peat and
subbituminous coal.
limestone A carbonate sedimentary rock consisting of more than 50% calcium carbonate,
primarily in the form of the mineral calcite (CaCOs).
lithology The description of rocks in hand specimen and in outcrop on the basis of color,
composition, and grain size.
loam A permeable soil composed of a mixture of relatively equal parts clay, silt, and sand, and
usually containing some organic matter.
loess A fine-grained eolian deposit composed of silt-sized particles generally thought to have
been deposited from windblown dust of Pleistocene age.
mafic Term describing an igneous rock containing more than 50% dark-colored minerals.
marine Term describing sediments deposited in the ocean, or precipitated from ocean waters.
metamorphic Any rock derived from pre-existing rocks by mineralogical, chemical, or structural
changes in response to changes in temperature, pressure, stress, and the chemical environment.
Phyllite, schist, amphibolite, and gneiss are metamorphic rocks.
moraine A mound, ridge, or other distinct accumulation of unsorted, unbedded glacial material,
predominantly till, deposited by the action of glacial ice.
outcrop That part of a geologic formation or structure that appears at the surface of the Earth, as
in "rock outcrop".
percolation test A term used in engineering for a test to determine the water permeability of a
son. A hole is dug and filled with water and the rate of water level decline is measured.
permeability The capacity of a rock, sediment, or soil to transmit liquid or gas.
phosphate, phosphatic, phosphorite Any rock or sediment containing a significant amount
of phosphate minerals, i.e., minerals containing PO4.
IE-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, compositionaUy equivalent to granite.
sandstone A clastic sedimentary rock composed of sand-sized rock and mineral material that is
more or less firmly cemented. Sand particles range from 1/16 to 2 mm in size.
schist A strongly foliated crystalline rock, formed by metamorphism, that can be readily split into
thin flakes or slabs. Contains mica; minerals are typically aligned.
screening level Result of an indoor radon test taken with a charcoal canister or similar device,
for a short period of time, usually less than seven days. May indicate the potential for an indoor
radon problem but does not indicate annual exposure to radon.
sediment Deposits of rock and mineral particles or fragments originating from material that is
transported by air, water or ice, or that accumulate by natural chemical precipitation or secretion of
organisms.
semiarid Refers to a climate that has slightly more precipitation than an arid climate.
shale A fine-grained sedimentary rock formed from solidification (lithification) of clay or mud.
shear zone Refers to a roughly linear zone of rock that has been faulted by ductile or non-ductile
processes in which the rock is sheared and both sides are displaced relative to one another.
shrink-swell clay See clay mineral.
siltstone A fine-grained clastic sedimentary rock composed of silt-sized rock and mineral
material and more or less firmly cemented. Silt particles range from 1/16 to 1/256 mm in size.
sinkhole A roughly circular depression in a karst area measuring meters to tens of meters in
diameter. It is funnel shaped and is formed by collapse of the surface material into an underlying
void created by the dissolution of carbonate rock.
slope An inclined part of the earth's surface.
solution cavity A hole, channel or cave-like cavity formed by dissolution of rock.
stratigraphy The study of rock strata; also refers to the succession of rocks of a particular area.
surficial materials Unconsolidated glacial, wind-, or waterborne deposits occurring on the
earth's surface.
tablelands General term for a broad, elevated region with a nearly level surface of considerable
extent.
11-25 Reprinted from USGS Open-File Report 93-292
-------
terrace gravel Gravel-sized material that caps ridges and terraces, left behind by a stream as it
cuts down to a lower level.
terrain A tract or region of the Earth's surface considered as a physical feature or an ecological
environment
till Unsorted, generally unconsolidated and imbedded rock and mineral material deposited directly
adjacent to and underneath a glacier, without reworking by meltwater. Size of grains varies greatly
from clay to boulders.
uraniferous Containing uranium, usually more than 2 ppm.
vendor data Used in this report to refer to indoor radon data collected and measured by
commercial vendors of radon measurement devices and/or services.
volcanic Pertaining to the activities, structures, and extrusive rock types of a volcano.
water table The surface forming the boundary between the zone of saturation and the zone of
aeration; the top surface of a body of unconfined groundwater in rock or soil.
weathering The destructive process by which earth and rock materials, on exposure to
atmospheric elements, are changed in color, texture, composition, firmness, or form with little or
no transport of the material.
11-26 Reprinted from USGS Open-File Report 93-292
-------
APPENDIX C
EPA REGIONAL OFFICES
EPA Regional Offices
State
EPA Region
EPA Region 1
JFK Federal Building
Boston, MA 02203
(617) 565-4502
EPA Region 2
(2AIR:RAD)
26 Federal Plaza
New York, NY 10278
(212) 264-4110
Region 3 (3AH14)
841 Chestnut Street
Philadelphia, PA 19107
(215) 597-8326
EPA Region 4
345 Courtland Street, N.E.
Atlanta, GA 30365
(404) 347-3907
EPA Region 5 (5AR26)
77 West Jackson Blvd.
Chicago, IL 60604-3507
(312) 886-6175
EPA Region 6 (6T-AS)
1445 Ross Avenue
Dallas, TX 75202-2733
(214) 655-7224
EPA Region 7
726 Minnesota Avenue
Kansas City, KS 66101
(913) 551-7604
EPA Region 8
(8HWM-RP)
999 18th Street
One Denver Place, Suite 1300
Denver, CO 80202-2413
(303) 293-1713
EPA Region 9 (A-3)
75 Hawthorne Street
San Francisco, CA 94105
(415) 744-1048
EPA Region 10
1200 Sixth Avenue
Seattle, WA 98101
(202) 442-7660
Alabama 4
Alaska 10
Arizona 9
Arkansas 6
California 9
Colorado 8
Connecticut 1
Delaware 3
District of Columbia 3
Florida 4
Georgia 4
Hawaii 9
Idaho 10
Illinois 5
Indiana 5
Iowa 7
Kansas ; 7
Kentucky 4
Louisiana '. 6
Maine 1
Maryland 3
Massachusetts 1
Michigan , 5
Minnesota 5
Mississippi 4
Missouri 7
Montana 8
Nebraska 7
Nevada 9
New Hampshire 1
New Jersey 2
New Mexico 6
New York 2
North Carolina 4
North Dakota 8
Ohio 5
Oklahoma 6
Oregon 10
Pennsylvania... 3
Rhode Island 1
South Carolina 4
South Dakota 8
Tennessee 4
Texas 6
Utah 8
Vermont 1
Virginia 3
Washington 10
West Virginia 3
Wisconsin 5
Wyoming 8
n-27
Reprinted from USGS Open-File Report 93-292
-------
STATE RADON CONTACTS
May, 1993
Alabama James McNees
Division of Radiation Control
Alabama Department of Public Health
State Office Building
Montgomery, AL 36130
(205)242-5315
1-800-582-1866 in state
Alaskq
Charles Tedford
Department of Health and Social
Services
P.O. Box 110613
Juneau.AK 99811-0613
(907)465-3019
1-800-478-4845 in state
John Stewart
Arizona Radiation Regulatory Agency
4814 South 40th St.
Phoenix, AZ 85040
(602)255-4845
Arkansas LeeGershner
Division of Radiation Control
Department of Health
4815 Markham Street, Slot 30
Little Rock, AR 72205-3867
(501) 661-2301
California J. David Quinton
Department of Health Services
714 P Street, Room 600
Sacramento, CA 94234-7320
(916) 324-2208
1-800-745-7236 in state
Colorado Linda Martin
Department of Health
4210 East llth Avenue
Denver, CO 80220
(303)692-3057
1-800-846-3986 in state
Connecticut Alan J. Siniscalchi
Radon Program
Connecticut Department of Health
Services
150 Washington Street
Hartford, CT 061064474
(203)566-3122
Delaware MaraiG. Rejai
Office of Radiation Control
Division of Public Health
P.O. Box 637
Dover, DE 19903
(302) 736-3028
1-800-554-4636 In State
District Robert Davis
of Columbia DC Department of Consumer and
Regulatory Affairs
614 H Street NW
Room 1014
Washington, DC 20001
(202) 727-71068
Florida N. Michael Gilley
Office of Radiation Control
Department of Health and
Rehabilitative Services
1317 Winewood Boulevard
Tallahassee, FL 32399-0700
(904)488-1525
1-800-543-8279 in state
Richard Schreiber
Georgia Department of Human
Resources
878 Peachtree St, Room 100
Atlanta, GA 30309
(404) 894-6644
1-800-745-0037 in state
Hawaii Russell Takata
Environmental Health Services
Division
591 Ala Moana Boulevard
Honolulu, ffl 96813-2498
(808) 5864700
n-28
Reprinted from USGS Open-File Report 93-292
-------
Idaho
Illinois
Indiana
Iowa
Kentucky
PatMcGavarn
Office of Environmental Health
450 West State Street
Boise, ID 83720
(208) 334-6584
1-800-445-8647 in state
Richard Allen
Illinois Department of Nuclear Safety
1301 Outer Park Drive
Springfield, IL 62704
(217) 524-5614
1-800-325-1245 in state
Lorand Magyar
Radiological Health Section
Indiana State Department of Health
1330 West Michigan Street
P.O. Box 1964
Indianapolis, IN 46206
(317)633-8563
1-800-272-9723 In State
Donald A. Plater
Bureau of Radiological Health
Iowa Department of Public Health
Lucas State Office Building
Des Moines, IA 50319-0075
(515) 281-3478
1-800-383-5992 In State
Harold Spiker
Radiation Control Program
Kansas Department of Health and
Environment
109 SW 9th Street
6th Floor Mills Building
Topeka, KS 66612
(913) 296-1561
JeanaPhelps
Radiation Control Branch
Department of Health Services
Cabinet for Human Resources
275 East Main Street
Frankfort, KY 40601
(502)564-3700-
Louisiana Matt Schlenker
Louisiana Department of
Environmental Quality
P.O. Box 82135
Baton Rouge, LA 70884-2135
(504) 925-7042
1-800-256-2494 in state
Maine BobStilwell
Division of Health Engineering
Department of Human Services
State House, Station 10
Augusta, ME 04333
(207)289-5676
1-800-232-0842 in state
Maryland Leon J. Rachuba
Radiological Health Program
Maryland Department of the
Environment
2500 Broening Highway
Baltimore, MD 21224
(410)631-3301
1-800-872-3666 Di State
Massachusetts William J. Bell
Radiation Control Program
Department of Public Health
23 Service Center
Northampton, MA 01060
(413) 586-7525
1-800-445-1255 in state
Michigan Sue Hendershott
Division of Radiological Health
Bureau of Environmental and
Occupational Health
3423 North Logan Street
P.O. Box 30195
Lansing, MI 48909
(517) 335-8194
Minnesota Laura Oatmann
Indoor Air Quality Unit
925 Delaware Street, SE
P.O. Box 59040
Minneapolis, MN 55459-0040
(612)627-5480
1-800-798-9050 in state
H-29
Reprinted from USGS Open-File Report 93-292
-------
Mississippi
Missouri
Montana
Silas Anderson
Division of Radiological Health
Department of Health
3 150 Lawson Street
P.O. Box 1700
Jackson, MS 39215-1700
(601) 354-6657
1-800-626-7739 in state
Kenneth V. Miller
Bureau of Radiological Health
Missouri Department of Health
1730 East Elm
P.O. Box 570
Jefferson City, MO 65102
(314)751-6083
1-800-669-7236 In State
Adrian C. Howe
Occupational Health Bureau
Montana Department of Health and
Environmental Sciences
Cogswell Building A113
Helena, MT 59620
(406)444-3671
Joseph Milone
Division of Radiological Health
Nebraska Department of Health
301 Centennial Mall, South
P.O. Box 95007
Lincoln, NE 68509
(402)471-2168
1-800-334-9491 In State
Stan Marshall
Department of Human Resources
505 East King Street
Room 203
Carson City, NV 89710
(702)687-5394
New Hampshire David Chase
Bureau of Radiological Health
Division of Public Health Services
Health and Welfare Building
Six Hazen Drive
Concord, NH 03301
(603)271-4674
1-800-852-3345 x4674
Nebraska
New Jersey Tonalee Carlson Key
Division of Environmental Quality
Department of Environmental
Protection
CN415
Trenton, NJ 08625-0145
(609) 987-6369
1-800-648-0394 in state
New Mexico William M. Floyd
Radiation Licensing and Registration
Section
New Mexico Environmental
Improvement Division
1190 St. Francis Drive
Santa Fe,NM 87503
(505) 827-4300
New York William J. Condon
Bureau of Environmental Radiation
Protection
New York State Health Department
Two University Place
Albany, NY 12202
(518)458-6495
1-800-458-1158 in state
North Carolina Dr. Felix Fong
Radiation Protection Division
Department of Environmental Health
and Natural Resources
701 Barbour Drive
Raleigh, NC 27603-2008
(919) 571-4141
1-800-662-7301 (recorded info x4196)
North Dakota Arlen Jacobson
North Dakota Department of Health
1200 Missouri Avenue, Room 304
P.O. Box 5520
Bismarck, ND 58502-5520
(701)221-5188
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 fiom USGS Open-File Report 93-292
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Oklahnmfl
Oregon
Pennsylvania
Puerto Rico
Rhode Island
South Carolina
Gene Smith
Radiation Protection Division
Oklahoma State Department of
Health
P.O. Box 53551
Oklahoma City, OK 73152
(405) 271-5221
George Toombs
Department of Human Resources
Health Division
1400 SW 5th Avenue
Portland, OR 97201
(503)731-4014
Michael Pyles
Pennsylvania Department of
Environmental Resources
Bureau of Radiation Protection
P.O. Box 2063
Harrisburg, PA 17120
(717) 783-3594
1-800-23-RADON In State
David Saldana
Radiological Health Division
G.P.O. Call Box 70184
Rio Piedras, Puerto Rico 00936
(809) 767-3563
Edmund Arcand
Division of Occupational Health and
Radiation
Department of Health
205 Cannon Building
Davis Street
Providence, RI02908
(401) 277-2438
Bureau of Radiological Health
Department of Health and
Environmental Control
2600 Bull Street
Columbia, SC 29201
(803)734-4631
1-800-768-0362
South Dakota MikePochop
Division of Environment Regulation
Department of Water and Natural
Resources
Joe Foss Building, Room 217
523 E. Capitol
Pierre, SD 57501-3181
(605)773-3351
Tennessee Susie Shimek
Division of Air Pollution Control
Bureau of the Environment
Department of Environment and
Conservation
Customs House, 701 Broadway
Nashville, TN 37219-5403
(615)532-0733
1-800-232-1139 in state
Texas Gary Smith
Bureau of Radiation Control
Texas Department of Health
1100 West 49th Street
Austin, TX 78756-3189
(512)834-6688
Utah John Hultquist
Bureau of Radiation Control
Utah State Department of Health
288 North, 1460 West
P.O. Box 16690
Salt Lake City, UT 84116-0690
(801) 536-4250
Vermont Paul demons
Occupational and Radiological Health
Division
Vermont Department of Health
10 Baldwin Street
Montpelier, VT 05602
(802)828-2886
1-800-640-0601 in state
Virgin Islands Contact the U.S. Environmental
Protection Agency, Region n
in New York
(212)264-4110
II-31 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 KaleColeman
Department of Health
Office of Radiation Protection
Airdustrial Building 5, LE-13
Olympia, WA 98504
(206)753-4518
1-800-323-9727 Li State
West Virginia BeattieL.DeBord
Industrial Hygiene Division
West Virginia Department of Health
151 llth Avenue
South Charleston, WV 25303
(304) 558-3526
1-800-922-1255 In State
Wisconsin Conrad Weiffenbach
Radiation Protection Section
Division of Health
Department of Health and Social
Services
P.O. Box 309
Madison, WI53701-0309
(608)267-4796
1-800-798-9050 in state
Wyoming Janet Hough
Wyoming Department of Health and
Social Services
Hathway Building, 4th Floor
Cheyenne, WY 82002-0710
(307)777-6015
1-800-458-5847 in state
II-32 Reprinted from USGS Open-File Report 93-292
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STATE GEOLOGICAL SURVEYS
May, 1993
Alabama Ernest A. Mancini
Geological Survey of Alabama
P.O. Box 0
420 Hackbenry Lane
Tuscaloosa, AL 35486-9780
(205) 349-2852
Alaska Thomas E. Smith
Alaska Division of Geological &
Geophysical Surveys
794 University Ave., Suite 200
Fairbanks, AK 99709-3645
(907)479-7147
Arizona Larry D. Fellows
Arizona Geological Survey
845 North Park Ave., Suite 100
Tucson, AZ 85719
(602) 882-4795
Arkansas Norman F. Williams
Arkansas Geological Commission
Vardelle Parham Geology Center
3815 West Roosevelt Rd.
Little Rock, AR 72204
(501) 324-9165
California James F. Davis
California Division of Mines &
Geology
801 K Street, MS 12-30
Sacramento, CA 95814-3531
(916)445-1923
Colorado Pat Rogers (Acting)
Colorado Geological Survey
1313 Sherman St., Rm 715
Denver, CO 80203
(303)866-2611
Connecticut Richard C. Hyde
Connecticut Geological & Natural
History Survey
165 Capitol Ave., Rm. 553
Hartford, CT 06106
(203) 566-3540
Delaware Robert R. Jordan
Delaware Geological Survey
University of Delaware
101 Penny Hall
Newark, DE 19716-7501
(302) 831-2833
Florida Walter Schmidt
Florida Geological Survey
903 W. Tennessee Su
Tallahassee, FL 32304-7700
(904)488-4191
William H. McLemore
Georgia Geologic Survey
Rm. 400
19 Martin Luther King Jr. Dr. S W
Atlanta, GA 30334
(404) 656-3214
Hawaii Manabu Tagomori
Dept. of Land and Natural Resources
Division of Water & Land Mgt
P.O. Box 373
Honolulu, ffl 96809
(808) 548-7539
Idaho Earl H. Bennett
Idaho Geological Survey
University of Idaho
Morrill Hall, Rm. 332
Moscow, ID 83843
(208) 885-7991
Illinois Morris W. Leighton
Illinois State Geological Survey
Natural Resources Building
615 East Peabody Dr.
Champaign, IL 61820
(217) 333^747
Indiana Norman C. Hester
Indiana Geological Survey
611 North Walnut Grove
Bloomington, IN 47405
(812) 855-9350
Iowa Donald L.Koch
Iowa Department of Natural Resources
Geological Survey Bureau
109 Trowbridge Hall
Iowa City, IA 52242-1319
(319) 335-1575
Kansas Lee C.Gerhard
Kansas Geological Survey
1930 Constant Ave., West Campus
University of Kansas
Lawrence, KS 66047
(913) 864-3965
H-33 Reprinted from USGS Open-File Report 93-292
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Kentucky Donald C. Haney
Kentucky Geological Survey
University of Kentucky
228 Mining & Mineral Resources
Building
Lexington, KY 40506-0107
(606)257-5500
Louisiana William E. Marsalis
Louisiana Geological Survey
P.O. Box 2827
University Station
Baton Rouge, LA 70821-2827
(504)388-5320
Maine Walter A. Anderson
Maine Geological Survey
Department of Conservation
State House, Station 22
Augusta, ME 04333
(207)289-2801
Maryland Emery T. Cleaves
Maryland Geological Survey
2300 St. Paul Street
Baltimore, MD 21218-5210
(410) 554-5500
Massachusetts Joseph A. Sinnott
Massachusetts Office of
Environmental Affairs
100 Cambridge St, Room 2000
Boston, MA 02202
(617)727-9800
Michigan R. Thomas Segall
Michigan Geological Survey Division
Box 30256
Lansing, MI 48909
(517) 334-6923
Minnesota Priscilla C. Grew
Minnesota Geological Survey
2642 University Ave.
SL Paul, MN 55114-1057
(612)627-4780
Mississippi S. Cragin Knox
Mississippi Office of Geology
P.O. Box 20307
Jackson, MS 39289-1307
(601) 961-5500
Missouri James H. Williams
Missouri Division of Geology &
Land Survey
111 Fairgrounds Road
P.O. Box 250
Rolla, MO 65401
(314) 368-2100
Montana Edward T. Ruppel
Montana Bureau of Mines & Geology
Montana College of Mineral Science
and Technology, Main Hall
Butte, MT 59701
(406)496-4180
Nebraska Perry B. Wigley
Nebraska Conservation & Survey
Division
113 Nebraska Hall
University of Nebraska
Lincoln, NE 68588-0517
(402)472-2410
Nevada Jonathan G. Price
Nevada Bureau of Mines & Geology
Stop 178
University of Nevada-Reno
Reno, NV 89557-0088
(702) 784-6691
New Hampshire Eugene L.Boudette
Dept. of Environmental Services
117 James Hall
University of New Hampshire
Durham, NH 03824-3589
(603)862-3160
New Jersey Haig F. Kasabach
New Jersey Geological Survey
P.O. Box 427
Trenton, NJ 08625
(609)292-1185
New Mexico Charles E. Chapin
New Mexico Bureau of Mines &
Mineral Resources
Campus Station
Socorro.NM 87801
(505) 835-5420
New York Robert H. Fakundiny
New York State Geological Survey
3136 Cultural Education Center
Empire State Plaza
Albany, NY 12230
(518)474-5816
11-34 Reprinted from USGS Open-File Report 93-292
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North Carolina Charles H. Gardner
North Carolina Geological Survey
P.O. Box 27687
Raleigh, NC 27611-7687
(919) 733-3833
North Dakota John P. Bluemle
North Dakota Geological Survey
600 East Blvd.
Bismarck, ND 58505-0840
(701)224-4109
Ohio Thomas M. Berg
Ohio DepL of Natural Resources
Division of Geological Survey
4383 Fountain Square Drive
Columbus, OH 43224-1362
(614)265-6576
Oklahoma Charles J. Mankin
Oklahoma Geological Survey
Room N-131, Energy Center
lOOE.Boyd
Norman, OK 73019-0628
(405) 325-3031
Oregon Donald A. Hull
Dept of Geology & Mineral Indust.
Suite 965
800 NE Oregon St. #28
Portland, OR 97232-2162
(503)731-4600
Pennsylvania Donald M. Hoskins
Dept. of Environmental Resources
Bureau of Topographic & Geologic
Survey
P.O. Box 2357
Harrisburg, PA 17105-2357
(717) 787-2169
Puerto Rico Ramon M. Alonso
Puerto Rico Geological Survey
Division
Box 5887
Puerta de Tierra Station
San Juan, P.R. 00906
(809) 722-2526
Rhode Island J. Allan Cain
Department of Geology
University of Rhode Island
315 Green Hall
Kingston, RI02881
(401) 792-2265
South Carolina Alan-Jon W. Zupan (Acting)
South Carolina Geological Survey
5 Geology Road
Columbia, SC 29210-9998
(803) 737-9440
South Dakota CM. Christensen (Acting)
South Dakota Geological Survey
Science Center
University of South Dakota
Vermillion, SD 57069-2390
(605)677-5227
Tennessee Edward T. Luther
Tennessee Division of Geology
13th Floor, L & C Tower
401 Church Street
Nashville, TN 37243-0445
(615) 532-1500
Texas William L. Fisher
Texas Bureau of Economic Geology
University of Texas
University Station, Box X
Austin, TX 78713-7508
(512)471-7721
Utah M. Lee Allison
Utah Geological & Mineral Survey
2363 S. Foothill Dr.
Salt Lake City, UT 84109-1491
(801)467-7970
Vermont Diane L. Conrad
Vermont Division of Geology and
Mineral Resources
103 South Main St.
Waterbury.VT 05671
(802) 244-5164
Virginia Stanley S. Johnson
Virginia Division of Mineral
Resources
P.O. Box 3667
Charlottesville, VA 22903
(804)293-5121
Washington Raymond Lasmanis
Washington Division of Geology &
Earth Resources
Department of Natural Resources
P.O. Box 47007
Olympia, Washington 98504-7007
(206) 902-1450
n-35 Reprinted from USGS Open-File Report 93-292
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Wisconsin
Wyoming
Larry D.Woodfbrk
West Virginia Geological and
Economic Survey
Mont Chateau Research Center
P.O. Box 879
Mqrgantown, WV 26507-0879
(304)594-2331
James Robertson
Wisconsin Geological & Natural
History Survey
3817 Mineral Point Road
Madison, WI 53705-5100
(608)263-7384
Gary B. Glass
Geological Survey of Wyoming
University of Wyoming
Box 3008, University Station
Laramie, WY 82071-3008
(307)766-2286
n-36 Reprinted from USGS Open-File Report 93-292
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EPA REGION 1 GEOLOGIC RADON POTENTIAL SUMMARY
by
Linda C.S. Gundersen, R. Randall Schumann, and Sandra L. Szarzi
U.S. Geological Survey
EPA Region 1 includes the states of Connecticut, Maine, Massachusetts, New Hampshire,
Rhode Island, and Vermont. For each state, geologic radon potential areas were delineated and
ranked on the basis of geology, soil, housing construction, indoor radon, and other factors. Areas
in which the average screening indoor radon level of all homes within the area is estimated to be
greater than 4 pCi/L were ranked high. Areas in which the average screening indoor radon level
of all homes within the area is estimated to be between 2 and 4 pCi/L were ranked
moderate/variable, and areas in which the average screening indoor radon level of all homes within
the area is estimated to be less than 2 pCi/L were ranked low. Information on the data used and on
the radon potential ranking scheme is given in the introduction to this volume. More detailed
information on the geology and radon potential of each state in Region 1 is given in the individual
state chapters. The individual chapters describing the geology and radon potential of the states in
Region 1, though much more detailed than this summary, 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 generally low and indoor radon averaged 2.5 pCi/L over the
massifs. The carbonate shelf rocks of the Proto-North American Terrane (23, fig. 1) are
predominantly marble, schist, and quartzite, all overlain in places by glacial till. Indoor radon
averaged 2.8 pCi/L for homes built on the carbonate shelf rocks. Some homes built on parts of the
Stockbridge Marble have elevated indoor radon levels. The Taconic Allochthons (24,25, fig. 1)
underlie 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
ffl-1 Reprinted from USGS Open-File Report 93-292-A
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LAKE \ /
CHAMPLAINM/
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, IG-Penobscot Formation, granites, and minor metamorphic rocks; 12-Boundary Mountains
Terrane; 13-Gander Terrane; 14-Avalonian Composite Terrane; 15-Northeastem Highlands; 16-Vermont Piedmont;
17-Green Mountains; 18-Champlain Lowland; 19-Vermont Valley; 20,21-Taconic Mountains-Stockbridge VaUey;
22-Berkshire Mountains; 23-Proto-North American Terrane; 24,25-Taconic AUochthons; 26-Connecticut Valley '
Synclinorium; 27-Western Connecticut Valley Belt; 28,29-Connecticut Valley (Mesozoic Basins); 30-Gneissic domes
of the Eastern Connecticut Valley Belt; 31-Bronson Hill Anticlinorium; 32,33-Merrimack Synclinorium; 34,35, 37,38
40-Avalonian Terrane (includes Hope Valley subterrane); 36-Nashoba and Rhode Island Terranes; 39,44,46-Esmo'nd-
Dedham Terrane; 41-Newbury Basin volcanics; 42-Cape Ann and Peabody plutons; 43-Boston Basin;
45-Narrangansett Basin; 47-Coastal Plain.
-------
Bsmt. & 1st Floor Rn
Average Concentration (pCi/L)
0.0 to 1.9
2.0 to 4.0
4.1 to 6.0
6.1 to 9.1
1 D Missing Data
100 Miles
Figure 2. Average screening indoor radon levels, by county, for EPA Region 1. Data are from
2-7 day charcoal canister tests. Data from the EPA/State Residential Radon Survey, except for
New Hampshire data, which are from the New Hampshire Division of Public Health Services
radon survey. Histograms in map legend show the number of counties in each category.
-------
GEOLOGIC RADON POTENTIAL
LOW(<2pCi/L)
MODERATE/VARIABLE (2-4 pCi/L)
HIGH(>4pCi/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 phyUites may be the caua. . levated indoor radon levels associated
with the Wepawaug Schist. Soils are derived from the rocks and overlying tills and have low to
moderate permeability. Indoor radon averages 3.5 pCi/L in the Connecticut Valley Synclinorium.
Because many of the rocks of this terrane have the potential to generate elevated radon levels, this
area is assigned a high geologic radon potential.
The Central Lowlands of Connecticut (29, fig. 1) are underlain by Triassic and Jurassic
sedimentary and volcanic rocks of the Newark Terrane. The average indoor radon in the Central
Lowlands was 1.6 pCi/L. Radioactivity in the Hartford and Pomperaug basins is generally low
and the soils have generally low to moderate permeability or are poorly drained. Overall, the
Central Lowlands have a low radon potential. However, localized uranium occurrences in the
upper New Haven Arkose, the middle Portland Formation, and possibly in the Shuttle Meadow,
East Berlin, and Portland Formations could generate locally elevated indoor radon levels, but they
are not expected to be common or widespread.
Rocks of the Branson Hill Anticlinorium, in the Eastern Uplands of Connecticut (31,
fig. 1), include felsic and mafic schists and gneisses, quartzite, and granite gneiss. Radioactivity
in the Bronson Hill is moderate to locally high, and equivalent uranium anomalies in the central
part of the area appear to be associated with outcrops of granite gneiss. The soils have low to
moderate permeability with areas of locally high permeability. The Glastonbury granite gneiss and
graphitic schists in the Collins Hill Formation are likely to generate elevated indoor radon levels.
The Monson Gneiss, and schist and granofels of the Middletown Formation, also generate high
average indoor radon levels. Average indoor radon in the Bronson Hill Anticlinorium is
5.6 pCi/L, the highest among the geologic terranes of Connecticut. Overall, this area has a high
radon potential.
The Merrimack Synclinorium, in the central part of the Eastern Uplands (33, fig. 1), is
underlain by gneiss, schist, granofels, and quartzite that are intruded by granite gneiss, diorite, and
gabbro. The area has moderate to high radioactivity. Soils have low to high permeability but most
are in the low to moderate range. Indoor radon in the Merrimack Synclinorium averaged 2.7
pCi/L. The Canterbury granite gneiss, which occurs in several broad outcrop bands in the
northern and central parts of the area, appears to be associated with elevated radioactivity and with
moderate to high indoor radon levels. This area has moderate radon potential overall.
The Avalonian Terrane, along the eastern and southeastern borders of Connecticut (34,35,
fig. 1), is underlain by granite, granite gneiss, mafic gneiss, and 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.
ffl-5 Reprinted from USGS Open-File Report 93-292-A.
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MAME
The rocks, surficial deposits, and geologic structures of Maine that are most likely to cause
high (>4pCi/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
m-6 Reprinted from USGS Open-File Report 93-292-A
-------
potential. Uranium concentrations in these types of granites are commonly more than 3 ppm and
are as high as several hundred ppm in Maine. Two-mica granites are most abundant in the
southwestern part of the State and include the rocks of the Sebago Pluton. Calc-alkaline to alkaline
granites are more abundant in th", southern ~d cental" -* of the State, irticularly 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 hi radon
potential. Granitic to dioritic gneiss and schist have generally low equivalent uranium associated
with them. Shear zones, pegmatites, and local accumulations of monazite in biotite schist and
gneiss may be sources of locally high indoor radon levels. Soil permeability is low to moderate.
Metamorphic rocks of the Connecticut Valley Belt, flanking the Mesozoic basins of west-
central Massachusetts (27,30, fig. 1), have been ranked moderate in radon potential.
Metasedimentary and metavolcanic gneisses and schists have generally low to moderate
radioactivity associated with them. Soils have generally moderate permeability. The Pauchaug and
Glastonbury granite gneisses, which form the cores of the Warwick and Glastonbury domes, as
m-7 Reprinted from USGS Open-File Report 93-292-A
-------
well as other locally-occurring granitic rocks in area 30 (fig. 1), may generate locally high indoor
radon levels. Locally high radon levels are likely to be associated with an area of anomalous
radioactivity at the south end of the Warwick dome and may be associated with faults and shears
*'ircughout 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 glaciofiuvial deposits
including outwash, lacustrine delta deposits, and alluvium.
Granitic plutons of the Merrimack Belt, central Massachusetts (32, fig. 1), have been
ranked high in radon potential. The metasedimentary rocks surrounding the plutons are
predominantly phyllites and carbonaceous slates and schists with moderate to high radon potential.
Mafic metamorphic rocks, which are less common in the Merrimack Belt, have generally low to
moderate radon potential. Faults and shear zones may produce locally high radon concentrations.
Granitic plutonic rocks and metamorphic rocks of the Nashoba terrane (36, fig. 1), the
northward extention of the Avalonian terrane (37, fig. 1), and granites of the Cape Ann and
Peabody plutons, in northeastern Massachusetts (42, fig. 1), are ranked high in radon potential.
They are associated with moderate to high radioactivity and the soils developed on these rocks have
moderate to high permeability. Relationships between radon and underlying bedrock in eastern
Massachusetts, particularly in the Merrimack zone and in these areas, are less distinct, probably
due to the influence of glacial deposits that are made up of a mixture of the rock types underlying
eastern Massachusetts and areas to the north. The glacial deposits generally have enhanced
permeability and may have enhanced radon emanation due to the redistribution of rock
components, mixing, and grain-size reduction effects of the glacial processes. Volcanic rocks and
soils of the Newbury basin (41, fig. 1) are ranked moderate in radon potential.
The Esmond-Dedham terrane, southeastern Massachusetts (44,46, fig. 1), is ranked
moderate overall in geologic radon potential. This area includes a number of granite plutons and
fault zones that may generate high radon levels, as well as mafic metasedimentary and 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
ffl-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 Merrimack Group, Massabesic Gneiss, the Rye Formation and several bodies of
two-mica granites, alkalic plutonic rocks, and mafic plutonic rocks. Soils in this area have
generally low permeability that is locally moderate to high. The Merrimack Group has low to
moderate equivalent uranium, whereas other rocks have generally moderate to high equivalent
uranium, particularly the Massabesic Gneiss, two-mica granites, and the extensive fault zones.
The Merrimack Group and Rye Formation have overall moderate radon potential, with locally low
radon potential. The Massabesic Gneiss, the granite intrusives, and the fault zones have high
radon potential. Average indoor radon for the townships underlain by Avalonian rocks is
predominantly moderate to high. Overall, the Avalonian Composite Terrane has been ranked
moderate to high in radon potential.
About half of New Hampshire is underlain by Cambrian-Devonian stratified metamorphic
rocks of igneous or sedimentary origin of the Gander (area 13, fig. 1) and Boundary Mountains
(area 12) Terranes. These rocks 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 Olivcrian 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.
m-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 glacial deposits. The greatest percentage of
homes with 4 pCi/L or more of radon are concentrated in the southern part of the State over the
Scituate and Narragansett Pier Igneous Suites, and parts of the Esmond Igneous Suite (area 39,
fig. 1), as well as with two areas also noted for high uranium: the northwestern and southwestern
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 Pier Granite, and alkalic granites of the Cumberland area have significant
uranium concentrations and surface radioactivity. Many of the areas underlain by these rocks also
have locally derived tills, kames and glacial lake deposits that may contribute significantly to the
overall high radon potential. The lowest radon potential appears to be associated with the less-
metamorphosed sediments of the Rhode Island Formation, which is overlain by glacial outwash
deposits in the northern portion of the Narragansett Lowlands (45, fig. 1). Low to moderate radon
appears to be associated with stratified metamorphic rocks of the Blackstone Group, the Harmony
Group, the Plainfield Formation, parts of the Esmond Igneous Suite, and scattered stratified
metamorphic rocks in the Narragansett Lowlands. These areas are ranked moderate or variable in
geologic radon potential overall.
The effect of glacial deposits is complex because most of the materials making up the
glacial deposits are locally derived and primarily reflect a 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 tills. Tills commonly have higher radon
emanation because of the higher proportion of finer-grained sediments. This is also true of some
glacial lake deposits. Thick deposits of outwash sand and gravel blanket much of the northern
Narragansett Lowlands and appear to have both low radioactivity and low indoor radon associated
with them; this area is assigned a low geologic radon potential. The southern part of the
Narragansett Lowlands and East Bay Area, however, have a significantly higher percentage of
indoor radon readings exceeding 4 pCi/L. This may be due to the fact that the southern part of the
Narragansett Lowlands and East Bay Area are dominated by thin glacial till containing components
of uraniferous granite and phyllite; this area has a moderate or variable geologic radon potential.
Another example of the influence of glacial deposits may be seen in the area of the Narragansett
Pier Granite, where high percentages of homes have indoor radon levels greater than 4 pCi/L.
The types of glacial deposits in this area include kames, glacial lake deposits, and till, which are
known to have enhanced radon exhalation. These glacial deposits may also have significant source
components in the adjacent Scituate Igneous Suite and Sterling Plutonic Group as well as the
Narragansett Pier granite, all of which have some elevated uranium concentrations.
m-10 Reprinted from USGS Open-File Report 93-292-A
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VERMONT
The geologic radon potential of the Champlain Lowlands (area 18, fig. 1) is low, with
areas of locally moderate to high radon potential possible. The Vermont Valley (19, fig. 1) has
generally moderate geologic radon potential. Clay-rich soils with low permeability dominate the
lowlands and include glacial lake and marine clays, which probably reduce the radon potential
significantly. Radioactivity is generally low, with a few scattered high and moderate areas that
appear to be associated with the Clarendon Springs Formation and, possibly, with black shales and
slates in surrounding rock units. Indoor radon levels in the counties underlain by the Champlain
Lowlands are generally less than 4 pCi/L except in Addison County, where out of 26 readings, six
were greater than 4 pCi/L and of these, two were greater than 20 pCi/L.
The Green Mountains (17, fig. 1) have been rated moderate in radon potential; however,
the radon potential is actually highly variable. Areas with locally high radon potential are those
underlain by metamorphic rocks of Proterozoic age, including quartzite; graphite- and pyrite-
bearing schists and slates; migmatitic schist and gneiss; biotite-rich zones in mica schist; and schist
and gneiss with high concentrations of the minerals monazite, allanite, and zircon; the Cheshire
Quartzite; and local deposits of uranium in veins and fault zones. Mafic metamorphic rocks such
as amphibolite, hornblende gneiss, gabbro, and serpentinite, have low geologic radon potential.
Radioactivity is variable—low in the southern portion but containing local high radioactivity areas,
moderate to high radioactivity in the central portion, and low in the north.
The Taconic Mountains (20, fig. 1) have 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.
M-ll Reprinted from USGS Open-File Report 93-292-A
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PRELIMINARY GEOLOGIC RADON POTENTIAL ASSESSMENT OF MAINE
by
Linda C.S. Gundersen andR. Randall Schumann
U.S. Geological Survey
INTRODUCTION
This chapter presents a discussion of the bedrock and glacial geology, soils, and
radioactivity of Maine in the context of indoor radon. A number of studies on radon in Maine's
water supplies (summarized in Norton and others, 1989; Paulsen, 1991; and Clausen, 1990) and
on related health factors (Hess and others, 1983; Lanctot, 1985) have been conducted. During the
winter of 1989-1990, as part of the State/EPA Residential Radon Survey, 839 randomly selected
homes throughout the State were measured for indoor radon. The percentage of homes with
measurements greater than 4 pCi/L was 29.9 and the average indoor radon in the State was
4.0 pCi/L. Examination of these indoor radon data in the context of geology, soil parameters, and
radioactivity suggests that the majority of counties with high (> 4 pCi/L) indoor radon are
underlain by uranium-bearing granites and high-grade metamorphic rocks, particularly in the
southern portion of the State. High indoor radon may also be associated with pegmatites, major
fault zones, and carbonaceous slate, phyllite, and schist Elevated levels of radon in domestic
water are associated with granites, pegmatites, and faults in Maine. The radon in these wells may
be high enough to contribute significantly to the radon content of the indoor air.
This is a generalized assessment of geologic radon potential of rocks, soils, and surficial
deposits of Maine. 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 Maine (fig. 1) is a result of the influence of bedrock geology (fig. 2)
and continental glaciation. Six major physiographic provinces have been delineated in Maine: the
Northern Maine Lowlands, Boundary Mountains Highlands, Lobster Mountain-Moose River
Lowlands, Central Maine Highlands, Central Maine Lowlands, and the Coastal Province (Hanson
and Caldwell, 1989). Elevations in Maine range from sea level, along the coastline in the southern
part of the State, to 5268 ft at Mt Katahdin in north-central Maine.
The Northern Maine Lowlands is the largest province, covering roughly the northern one-
third of Maine. It is underlain primarily by Cambrian through Devonian, low-grade
metasedimentary and volcanic rocks. Elevations range from a few hundred feet in the northern part
to over 2000 ft in the southwestern part (Denny, 1982). Relief is lowest in the broad valleys of the
Upper St John River and its tributaries in the north, and increases toward the gently rolling,
IV-1 Reprinted from USGS Open-File Report 93-292-A
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Northern Maine Lowlands
0 20 40 Miles
I 1*1 I' t ' '
0 20 40 Kilometers.
Figure 1. Physiographic regions of Maine (modified from Hanson and Caldwell, 1989).
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Figure 2. Generalized bedrock geologic map of Maine (after Osberg and others, 1985).
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GENERALIZED GEOLOGIC MAP OF MAINE (FIG. 2)
EXPLANATION
Stratified metamorphic rocks
Clastic and carbonate sedimentary rocks and their metamorohic equivalents (Coastal Proving)
Devonian - Proterozoic
Appleton Ridge Formation (Fm.); Gonic Fm.
Silurian - Proterozoic
Berwick Fm.; Eliot Fm.; and Kittery Fm.
Ordovician - Proterozoic
The quartzite member of the Cape Elizabeth Fm.; Ellsworth Fm.; and Macworth Fm.
Proterozoic
Coombs Limestone; Ogier Point Fm., Rockport Fm.; and Rocks of Islesboro (includes local
outcrops of limestone member).
Mafic to felsic volcanic rocks and their metamornhic equivalents (Coastal Province)
Volcanic member of the Gushing Fm.; mafic to felsic volcanic member of the Cape Elizabeth
Fm.; metasedimentary, metavolcanic, and calc-silicate rocks of the Passagassawakeag block;
and Spring Point Fm. (Includes local outcrops of Spurwink Limestone, limestone member of
the Gushing Fm., and interbedded pelite and quartz sandstone of the Passagassawakeag block.)
jc and carhnnate sedimentary rocks and their metamorphic equivalents
Devonian
Beck Pond Limestone; Carrabassett Fm.; Chapman Sandstone; Edmunds Hill Andesite;
HUdreths Fm.; Hedgehog Fm.; Heald Mountain Rhyolite; Ironbound Mountain Fm.;
Matagamon Sandstone; Perry Fm.; Parker Bog Fm.; Seboomook Fm.; Swanback Fm.;
Tarratine Fm.; Tomhegan Fm.; Traveler Rhyolite; and Trout Valley Fm.
Devonian - Silurian
Allagash Fm.; Bell Brook Fm.; Bar Harbor Fm.; Castine Fm.; Calderwood Fm.; Daggett Ridge
Fm.; Fogelin Hill Fm.; Frost Pond Shale; Fish River Lake Fm.; Madrid Fm.; undifferentiated
sedimentary rocks in areas of extreme migmatization; and undifferentiated sedimentary rocks
of the Spider Lake, Chandler Pond, and Third Lake Fms.
Devonian - Ordovician
Bucksport Fm.; Digdeguash Fm.; and Hume Ridge Fm.
Silurian
Burnt Brook Fm.; undifferentiated pelites, conglomerates, and sandstones in the Allsbury Fm.;
Frenchville Fm.; rocks of the Fivemile Brook Sequence; Greenvale Cove Fm.; Hersey Fm.;
Hardwood Mountain Fm.; Jemtiand Fm.; Maple Mountain Fm.; New Sweden Fm.; Perry
Mountain Fm.; pelites of the Quoddy Fm.; Rangeley Fm.; Ripogenus Fm.; the Anasagunticook
Member and limestone of the Sangerville Fm.; Smyrna Mills Fm.; The Forks Fm.; and
Waterville Fm.
Silurian - Ordovician
Aroostook Fm.; Frontenac Fm. (excluding the Canada Falls Volcanic Member); Lobster Lake
Fm.; Nine Lake Fm.; and Vassalboro Fm.
-------
Ordovician
Benner Hill Fm.; Chase Lake Fm.; Chandler Ridge Fm.; Depot ML Sequence; Dry Wall
Volcanic Rocks; Kamankeag Fm.; andesite and basalt of the Lobster Mt Volcanic Complex-
Madawaska Lake Fm.; Pile Mountain Argillite; Quimby Fm.; and Wassataquoik Chert '
Ordovician - Cambrian
Sulfidic quartz sandstone and lithic sandstone/pelite of the Cookson Fm.; Dead River Fm •
Megunticook Fm.; Sawmill Fm.; and Southeast Cove Fm.
Cambrian
Grand Pitch Fm.
lie - carbonaceous pelites and their metamnrphic equivalents
Devonian " "
Temple Stream Member of the Seboomook Fm.
Devonian - Silurian
Sulfidic pelite of the Rindgemere Fm. and Towow Fm.
Silurian
Sulfidic pelite of the Sangerville Fm., Anasagunticook Member, and Small Falls Fm
Ordovician
Blind Brook Fm.; sulfidic pelite of the Benner Hill Fm.; and pelite of the Kamankeag Fm
Ordovician - Cambrian
Cookson Fm. (excluding sulfidic quartzose sandstone and lithic sandstone/pelite members)
Penobscot Fm. (excluding the basalt member).
Ordovician - Proterozoic
Sulfidic pelite member of the Gushing Fm. and the Scarboro and Diamond Island Fm.s.
Interbedded pelites and limestones and/or dolostones and their metamorphic equivalents
Devonian - Silurian
Rindgemere Fm. (excluding sulfidic pelite member) and Towow Fm.
Silurian
Sangerville Fm. (excluding Anasagunticook Member and sulfidic pelite ) Spragueville Fm
Silurian - Ordovician
Carys Mills Fm.
Melange-deformed and sheared phvllite. slate, and breccia
Ordovician
Kennebec Fm.
Ordovician • Cambrian
Chase Brook Fm.; Hurd Mountain Fm.; and Saint Daniel Fm.
Cambrian
Hurricane Mountain Fm.
Mafic volcanic rocks and their metamornhic equivalents
Silurian
Basalt member of the Dennys Fm. and the basalt member of the Leighton Fm
Silurian - Ordovician
Canada Falls Volcanic Member of the Frontenac Fm.
Ordovician
Bluffer Pond Fm. and Winterville Fm.
Ordovician - Cambrian
Basalt member of the Penobscot Fm.
Cambrian
Caucomgomoc Lake Fm. and Jim Pond Fm.
Proterozoic
North Haven Fm.
-------
Mafic to felsic (and undetermined) volcanic rocks and their metamorphic equivalents
Devonian
Eastport Fm.
Devonian - Ordovician
Undifferentiated mafic to felsic volcanic rocks.
Silurian
Mafic to felsic volcanic rock member of the Dennys Fm.; Edmunds Fm.; and Quoddy Fm.
(excluding the pelite member).
Silurian - Ordovician
Dunn Brook Fm.
Ordovician
Ammonoosuc Volcanics and Lobster Mountain Volcanic Complex.
Ordovician - Cambrian
Mafic to felsic volcanic rocks of the Cookson Fm.
Felsic volcanic rocks and their metamorphic equivalents
Devonian - Silurian
Undifferentiated volcanic rocks of the Spider Lake and Chandler Pond Fm s.
Ordovician
Munsungun Lake Fm. and Shin Brook Fm,
Plutonic igneous rocks
Cretaceous intrusive rocks
Alkali feldspar quartz syenite, quartz monzodiorite, quartz diorite, alkali feldspar syenite,
monzodiorite,and some gabbro-diorite-ultramafic compositions.
~1 Triassic granite
•Lfl
'^H Alkali feldspar granite and granite.
Triassic svenite
Alkali feldspar quartz syenite and alkali feldspar syenite (includes some triassic mafic to felsic
volcanic rocks).
Mesozoic granite
Granite with hornblende locally as an accessory mineral.
Mesozoic svenite
Fold-bearing syenite.
Carboniferous granite
Granite with locally abundant muscovite.
Carboniferous quartz-poor intrusives _____________________________________
Syenite and/or gabbroic-dioritic-ultramafic rocks.
Devonian granite
Granite and alkali feldspar granite, locally porphyritic; hornblende and muscovite are common
accessory minerals.
-------
Devonian granodiorite - syenite __
Granodiorite to syenite, locally porphyritic; may contain hornblende and/or muscovite as
accessory minerals
Devonian quartz-poor intrusive rocks
2 Gabbroic-dioritic-ultrarnafic rocks, locally associated with rocks of quartz diorite composition.
Silurian granite
Granite ~ ' " '
^j Silurian quartz-poor intrusive rocks
Gabbroic-dioritic-ultrarnafic rocks.
Ordovician granite
Granite locally associated with granodiorite.
Ordovician granodiorite/gngrfo monzonite
Granodiorite to quartz monzonite, locally containing hornblende as an accessory mineral.
Ordovician quartz-poor intrusive rocks
Gabbroic-dioritic-ultrarnafic rocks. " " "
Cambrian intrusive rocks
Locally occurring quartz diorite and gabbro, diorite, and ultramafic rocks.
Basement rocks
Gneiss and granofels of the Chain Lakes Massif
-------
rounded hills in the south. The Lobster Mountain-Moose River Lowlands are essentially a
southwestern arm of the Northern Maine Lowlands that extends just beyond the New Hampshire
state line. They are underlain by Devonian and older metasedimentary and volcanic rocks, except
for the southern tip of the lowland, which is underlain by igneous and high-grade metamorphic
rocks. The linear ridges and valleys of this area resemble the Valley and Ridge Province of the
Appalachians, though on a much smaller scale. Elevations range from a few hundred feet on the
valley floors to over 3800 ft at Hurricane Mountain, with elevations of 2000 ft or more common on
theridgetops.
The Boundary Mountain Highlands lie to the north of the Lobster Mountain-Moose River
Lowlands (fig. 1). An irregular topography has developed on the crystalline rocks underlying this
province. The mountainous areas are underlain by more resistant gneiss, granofels, hornfelsic and
volcanic rock, and fine-grained plutonic rocks, whereas the valleys are underlain primarily by
coarse-grained plutonic rocks (Hanson and Caldwell, 1989). Linear hills and small ridges are
common in the northernmost part of the province. Although the terrain is rugged, the relief is less
than in the Central Maine Highlands, and the elevations of the mountain peaks decrease from east
to west. Most of the mountain peaks in this region are less than 4000 ft and have relief of 1200 ft
or less (Hanson and Caldwell, 1989).
The Central Maine Highlands extend from the New Hampshire border to the New
Brunswick border near Houlton and comprise several mountain ranges, including the Mahoosuc
Range, Blue Range, Bigelow Range, Squaw Mountain-Ragged Mountain Range, Onawa Range,
Katahdin and Traveler Ranges, Chase Mountain Range, and Oakfield Hills (Hanson and Caldwell,
1989). The highlands are formed almost entirely on a broad belt of regionally-deformed, Silurian
and Devonian metasedimentary rocks and Devonian plutonic rocks. Topography is strongly
related to the regional structure and to the occurrence of plutons. The average elevation of the
mountains, as well as the relief, decreases toward the northeast Elevations range from about
600 ft in valleys in the northern part to 5268 ft at Mt Katahdin, near the central part of the
province. A number of peaks in the southwestern part of the province are higher than 4000 ft
(Hanson and Caldwell, 1989).
The Central Maine Lowlands are adjacent to and southeast of the Central Maine Highlands.
They are an area of low relief, generally less than 100 ft. Most of the province is underlain by
erosionally-weak slate, phyllite, metasandstone, and limestone. Highlands are local ridges of more
resistant sandstone or irregular hills underlain by contact metamorphic rocks, with altitudes less
than 1500 ft (Hanson and Caldwell, 1989).
The Coastal Province is an area of low uplands developed on metasedimentary,
metavolcanic, and igneous plutonic rocks. Some of the peaks are in areas of contact
metamorphism adjacent to plutonic rocks. Many of the low mountains reach elevations of more
than 1000 ft (Denny, 1982). East of the Penobscot River, streams flow over plutonic rocks and
have strong southward orientations that follow the major trend of joint and fracture systems in the
rocks. West of the Penobscot River, streams in the area flow over metasedimentary rocks and
generally exhibit a southwestward trend, parallel to regional faults and to the structural orientation
of the rocks. North of the Saco River, the coastline is highly indented, and many of the peaks near
the shore are separated by narrow bays. The southern coastline is smoother, most likely due to the
parallel orientation of the shore with regional structure, to less extensive glacial excavation of the
shoreline, and to the presence of thicker deposits of glaciomarine sediments (Hanson and
Caldwell, 1989).
IV-8 Reprinted from USGS Open-File Report 93-292-A
-------
In 1990 the population of Maine was 1,227,928, including 58 percent urban population
(fig. 3). Population density is approximately 36.2 per square mile. There are three climatic
regions in Maine: the southern portion of the State, which is influenced by coastal air masses; the
southern interior region, with a climate between that of the northern and southern areas; and the
northern regions, which have a harsher climate, averaging 100 or more inches of snow per year
Average annual temperatures range from 37° F in the north to 45° F in the south. Annual
precipitation averages 40-46 inches (fig. 4).
GEOLOGIC SETTING
The geology of Maine is complex and the names of rock formations and the way rocks are
grouped have changed with time. It is beyond the scope of this report to resolve the complicated
stratigraphy of the State, therefore this description of the geology tries to convey the major rock
types of Maine, especially as they pertain to the radon problem. Descriptions in this report are
derived from Tucker and Marvinney (1989) and Osberg and others (1985). A general geologic
map is given in figure 2. It is suggested, however, that the reader refer to the most recent State
geologic map (Osberg and others, 1985) as weU as other detailed geologic maps available from the
Maine Geological Survey for more information.
In figure 2, the geology of Maine has been subdivided into general rock groups based on
the origin of the rocks, age, and the dominant rock types. We have also tried to group the rocks
according to their probable radon potential based on radioactivity and known uranium
concentrations (these data are presented in a following section). Maine is underlain by
Precambrian to Paleozoic metamorphosed sedimentary and volcanic rocks that have been
pervasively intruded by Paleozoic mafic to felsic plutons. Metamorphic grade of the rocks
decreases from southwest to northeast (fig. 5a) and metamorpnic grade is locally high near the
plutons. Many of the rocks in the State have been folded and faulted during several major
orogenies. A tectonic map showing some of the major structures in Maine is shown in figure 5b
t™-ThC m°St areaHy extensive grouP of rocks in figure 2 (patterned white) consists of
Cambrian through Devonian metasedimentary rocks that are predominantly clastic but contain
minor amounts of carbonate rock. In the Connecticut Valley-Gaspe Synclinorium, the Aroostook-
Matapedia belt, and the Moose River Synclinorium, these rocks are mostly part of the Seboomook
Formation. The Seboomook Formation is cyclically-layered dark sandstone and slate In the
Northern Boundary Mountains, the feldspathic sandstone, slate, phyllite, schist, greenstone, and
felsic metavolcamcs of the Frontenac and the Lronbound Mountain Formations are the principal
rock units. The Notre Dame anticlinorium is underlain by an unusual rock, termed melange that
consists of sheared and deformed slate, phyllite, and breccia. The Munsungun-WinterviUe
Anticlinonum is underlain by Cambrian-Devonian felsic and mafic metavolcanic rocks and
Cambrian melange. The eastern portion of the Aroostook-Matapedia Belt is underlain by
Ordovician-Devonian sandstone, graywacke, slate, metavolcanic rocks, shale, limestone, and
dolostone. The Ordovician-Silurian shales and carbonate rocks of the Gary Mills and SpragueviUe
Formation have been grouped separately in figure 2.
The Weeksboro-Lunkoos Anticlinorium is underlain mostly by varigated slate and phyllite
with thin quartzite interbeds of the Cambrian Grand Pitch Formation. Ordovician andesites and
basalts bound the southern part of the anticlinorium and the eastern edge of the Devonian Katahdin
pluton, which divides the anticlinorium into two parts. Ordovician diorite plutons intrude both
parts of the anticlinorium. Black phyllite with melange textures of the Hurricane Mountain
IV-9 Reprinted from USGS Open-File Report 93-292-A
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POPULATION (1990)
Q 0 to 10000
D 10001 to 25000
E2 25001 to 50000
H 50001 to 100000
• 100001 to 243135
Figure 3. Population of counties in Maine (1990 U.S. Census).
-------
40"
44'
w-
10
20 30 40 50 miles
Figure 4. Average annual precipitation in Maine (from Facts on File, 1984).
-------
METAMORPHIC GRADE
Ev5l UNMETAMORPHOSED
I I LOW GRADE
EE1 MEDIUM GRADE
E3 HIGH GRADE
IGNEOUS PLUTONS
Figure 5a. Generalized map of metamorphic zones in Maine (modified from C.V. Giodotti, in
Osberg and others, 1985).
-------
NOTRE DAME_
ANTICLINORIUM
MUNSUNGUN - WINTERVILLE
ANTICLINORIUM
BOUNDARY MOUNTAINS
ANTICLINORIUM
CHAIN LAKES
MASSIF
WEEKSBORO - LUNKSOOS
ANTICLINORIUM
MIRAMICHI
ANTICLINORIUM
LOBSTER MOUNTAIN
ANTICLINORIUM
BRONSON HILL
ANTICLINORIUM
COASTAL.
LITHO-TECTONIC
BLOCK
JWERRIMACK
TROUGH
Figure 5b. Tectonic map of Maine (modified from Osberg and others, 1985).
-------
Formation occurs in the western side of the anticlinorium, which is mostly underlain by unnamed
Cambrian-Ordovician metapelite and metagraywacke.
The oldest rocks in Maine are Precambrian rocks exposed in the Chain Lakes Massif and
the Coastal Province. The Chain Lakes Massif, which underlies part of the Boundary Mountains
Highland and forms the core of the Boundary Mountains anticlinorium, consists predominantly of
gneiss and granofels (metamorphic rocks with little or no layering). In the lower unit of the
massif, the granofels and gneiss contain large clasts of quartz, mafic and felsic plutonic and
volcanic rock, and sedimentary rocks. These clasts occur within a matrix of quartz, feldspar,
mica, sillimanite, and chlorite. The granofels and gneiss of the lower unit grade into more layered
gneiss in the upper unit, including quartz-feldspar gneiss and schist, felsic metavolcanic rocks,
quartzite, black schist, and amphibolite. Surrounding the Chain Lakes massif are Cambrian
through Devonian metasedimentary, metavolcanic, and plutonic rocks.
The Bronson Hill and Lobster Mountain Anticlinoria are mosdy underlain by Cambrian and
Ordovician metavolcanic and metasedimentary rocks. Three units dominate the Lobster Mountain
Anticlinorium: greenstone, keratophyric metavolcanics, and metagraywacke of the Cambrian Jim
Pond Formation; the Hurricane Mountain Formation melange; and slate or phyllite with equal
proportions of metavolcanic feldspathic, chlorite-rich arenite of the Cambrian-Ordovician Dead
River Formation. Andesitic and basaltic volcanics of the Ordovician Lobster Mountain Volcanic
Complex occur at the northeastern end of the anticlinorium. The Bronson Hill Anticlinorium is
mostly underlain by the Dead River Formation but also has significant areas underlain by
metapelites of the Cambrian-Ordovician Azicohos Formation, and metagraywacke,
metaconglomerate, and sulfidic metapelite of the Ordovician Quimby Formation. The stratified
rocks of both anticlinoria are intruded by Devonian alkalic and calc-alkalic granite and diorite
plutons.
The Kearsarge-Central Maine Synclinorium occupies a broad belt in south-central Maine
that is mostly underlain by Silurian and Devonian metasedimentary rocks. The Sebago Pluton,
consisting of Carboniferous two-mica granite, dominates the southwestern part of the area, and
Devonian alkalic and calc-alkaline granites and diorites are common along the western, northern,
and southeastern parts of the synclinorium.
Most of the southern boundary of the Kearsarge-Central Maine Synclinorium is occupied
by a broad belt of slightly calcareous graywacke with sulfidic phyllite and mica schist interbeds of
the Silurian Vassalboro Formation. The less pelitic Hutchins Corners Formation is found in the
southwest. Northwest of the Vassalboro-Hutchins Corners belt, phyllite with quartzite and
graywacke interbeds of the Silurian Waterville Formation and graywacke with minor phyllite of the
Sangerville Formation both contain prominent limestone members. These units comprise the
checked pattern on the geologic map (fig. 2) in the west-central part of the synclinorium. The
northern half of the synclinorium is dominated by slightly calcareous quartz graywacke and lesser
phyllite of the Silurian-Devonian Madrid Formation, and north of that, gray pelites with rhythmic
interbeds of graywacke sandstone and siltstone of the Devonian Carabasset Formation. The
eastern margin of the synclinorium is underlain by phyllite with quartzite and graywacke interbeds
and limestone of the Silurian Allsbury Formation and sandstone and phyllite of the Silurian
Smyrna Mills Formation. The southwesternmost corner of the synclinorium is underlain by
metapelite with limestone and dolostone interbeds of the Silurian-Devonian Rindgemere
Formation. Gray metapelite, metagraywacke, and metavolcanics of the Devonian Littleton
Formation underlie a significant area northwest of the Sebago Pluton along the New Hampshire
state line. Black, sulfidic phyllite characterizes the Silurian Small Falls Formation and the
IV-14 Reprinted from USGS Open-File Report 93-292-A
-------
Devonian Towow Formation, which comprise narrow outcrop bands in the northwestern part of
the synclinorium. Black, sulfidic phyllites also occur at the base of the Sangerville Formation and
within the Rindgemere Formation.
The Miramichi Anticlinorium is mostly underlain by red to gray chloritic graywacke
grading up to gray shale, then sulfidic, carbonaceous slate of the Cambrian (?) Baskahegan
Formation. This is overlain by unnamed Qrdovician felsic metavolcanics, then gray to black slate
and graywacke of the Belle Lake Formation. Devonian rocks underlie small areas and include
polymict conglomerate and sandstone of the Daggett Ridge Formation and gray slate with
sandstone, conglomerate, and limestone of the Hartin Formation.
Over 100 plutons intrude the metasedimentary and metavolcanic rocks of the coastal
province. Most of these are Devonian alkalic to calc-alkaline granites or two-mica granites, but
include Devonian diorites in the east, and Carboniferous granites and a small Mesozoic alkaline
granite in the west From Kittery Point to Old Orchard Beach, the rocks of the Coastal Province
are predominately metasiltstones and phyllites of the Kittery and Berwick Formations. A sequence
of Proterozoic to Ordovician rocks dominated by metasedimentary and metavolcanic schist, gneiss,
phyllite, and amphibolite of the Gushing, Cape Elizabeth, and Sebascodegan Formations stretches'
from Old Orchard Beach, throughout most of Casco Bay, north along the Norumbega Fault Zone
to Bangor. Black, sulfidic phyllite and mica schist are minor components of the Gushing and Cape
Elizabeth Formations and comprise the Diamond Island Formation. Li Penobscot Bay, Proterozoic
rocks comprise an older sequence of schist and gneiss with greenstone, unconformably overlain by
quartzite, slate, and limestone. A small area west of Penobscot Bay is underlain by Ordovician
schist and quartzite of the Benner Hill sequence. Across the northern part of Penobscot Bay is
Cambrian-Ordovician quartzite and mica schist of the Megunticook Formation, which is overlain
by black, sulfidic mica schist of the Penobscot Formation. The Penobscot also crops out in fault
blocks that form a northeast-trending belt to St. Croix Bay, where equivalent rocks are called the
Cookson Formation. South of the belt of Penobscot Formation and its equivalents between
Penobscot Bay and Pleasant Bay, Proterozoic to Ordovician rocks are dominated by phyllite and
siliceous siltstone of the Ellsworth Formation and its equivalent schist of the Columbia Falls
Formation. East of Pleasant Bay to Passamaquoddy Bay, Silurian to Devonian mafic and felsic
metavolcanics of the Quoddy, Dennys, and Eastport Formations dominate. The Quoddy
Formation also contains significant intervals of black, sulfidic siltstone and argillite. The
Fredericton Trough is dominated by graywacke sandstone and siltstone and gray phyllite and slate
of the Devonian Digdeguash and Flume Ridge Formations, and to the southwest, by feldspathic
graywacke and gray biotite schist of the Bucksport Formation.
GLACIAL GEOLOGY
Stratigraphic evidence from New England and the Gulf of Maine indicates that there were at
least four, and as many as six, glacial advances in this region during the Pleistocene epoch. Three
Wisconsinan (Late Pleistocene) tin units have been identified in Maine from surface and subsurface
data (Stone and Borns, 1986). The "lower till" is probably early Wisconsinan in age, it is typically
compact, and it has a weathered zone or paleosol at the top (Stone and Borns, 1986). The "middle
till" is middle Wisconsinan or early late Wisconsinan and it is overlain by a layer of laminated sand
and silt that is in turn overlain by the "upper till". The middle till is not found in glacial deposits in
southern New England, suggesting that the glacial advance(s) associated with the middle till did
not reach the southern part of the region (Stone and Borns, 1986). The late Wisconsin till ("upper
IV-15 Reprinted from USGS Open-File Report 93-292-A
-------
till") is a single surface till with a dominantiy silty to sandy matrix. Variations in dominant grain
size, color, and stoniness of the till are closely related to bedrock geology (Stone and Borns,
1986).
Glaciers moved in a generally northwest-southeast direction across Maine. Glacial retreat
is recorded in the Maine coastal zone by a 30-km-wide belt of end moraines aligned roughly
parallel to the coastline and by coarse-grained glaciomarine delta and fan deposits (Borns, 1973).
After glaciers retreated from the area, the sea inundated the Maine coastal zone when sea level rose
due to glacial melting. The sea occupied the area from about 13,800 years BP to about 11,500
years BP, when post-glacial rebound caused the land surface to re-emerge above sea level.
Figure 6 is a generalized map of glacial deposits in Maine. Three main classes of glacial
deposits are shown on the map—till, glaciofluvial deposits, and glaciolacustrine and glaciomarine
sediments. Each of these general units is further subdivided into units which reflect the origin of
the deposits in more detail. Till is the most common and widespread type of glacial deposit in
Maine. It is an unsorted deposit of gravel, sand, silt, and clay, with occasional cobbles and
boulders. Thickness of the till ranges from a thin, discontinuous veneer of less than one meter to
more than 10 meters in some valleys, but it is generally in the range 1.5-4 m thick (Richmond and
FuUerton, 1987). Till is typically thinner on uplands and thicker in valleys. The composition of
the till commonly reflects the local bedrock. There are two main types of till in Maine. Loamy till
(also called basal till) is a calcareous to non-calcareous loam, silt loam, clay loam, or silty clay
loam. Loamy till is locally clayey where it is underlain by shale and locally sandy where it is
underlain by coarse-grained crystalline rocks. It is commonly compact in the lower part. Clast
composition of loamy till varies but commonly includes limestone, shale, siltstone, sandstone,
conglomerate, quartzite, graywacke, slate, argillite, granite, diorite, gabbro, diabase, and volcanic
or metavolcanic rocks (Richmond and Fullerton, 1987). Sandy loamy till (also called ablation till)
is a calcareous to non-calcareous sandy loam, with some loamy sand, loam, and silt loam,
commonly containing pebbles and boulders. Clast composition of sandy loamy till includes
granite, pegmatite, granodiorite, rhyolite, diorite, gabbro, basalt, gneiss, schist, argillite, quartzite,
and tuff (Richmond and Fullerton, 1987). Both types of till are exposed at the surface across most
of Maine as ground moraine deposits. Glacial landforms typically associated with till include
drumlins, kettles, and moraines.
Glaciofluvial deposits are stratified sediments deposited by glacial meltwater adjacent to or
in front of the ice margin. These ice-marginal or ice-contact deposits include kames, kame
terraces, kame moraines, eskers, and outwash deposits. Characteristic of all types of glaciofluvial
deposits is their coarse texture, being composed primarily of sand and gravel. Kame terraces
formed between the edge of a glacier and a valley wall. Kame moraines are deposits of gravel that
formed in front of the glacier and have topography similar to that of a till moraine. Eskers are
sinuous ridges composed of outwash sand and gravel deposited by rivers that flowed in tunnels
underneath an ice sheet or valley glacier. Outwash gravel was deposited by rivers that drained the
melting glaciers. Outwash occurs in relatively narrow valley deposits, in sheets covering large
areas, or in fan-shaped deposits..
Glaciolacustrine (lake) and glaciomarine (ocean) sediments are layered silts, clays, and
sands. Because valleys and lowlands were the sites of final melting of stagnant ice masses,
drainage was blocked and many small lakes developed. Larger lakes were dammed by glacial ice
or by moraines. Lake bottom sediments are composed of silt and clay, shallow-water sediments
are composed primarily of sand, and beach and delta deposits contain primarily sand and gravel.
Marine sediments have characteristics similar to lacustrine sediments, in that they also are classified
IV-16 Reprinted from USGS Open-File Report 93-292-A
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&\' ' \
10 0 10 20 30 40 Mllas
Figure 6. Generalized glacial geologic map of Maine (after Thompson and Borns, 1985).
-------
GENERALIZED GLACIAL
GEOLOGIC MAP OF MAINE
EXPLANATION
TILL—unstratified mix of gravel, sand, silt, and
clay; includes stagnation moraine deposits in
northern Maine
MORAINE—irregular ridge of till formed at the
margins of retreating glaciers; commonly overlain
by marine sediments in southern Maine
IGLACIOFLUVIALDEPOSITS—mainly sand
I and gravel deposits of kames, kame terraces,
kame moraines, eskers, outwash, and recent
alluvium
LAKE-BOTTOM SEDIMENTS— stratified silt
and clay deposited by glacial lakes; may be
varved
COARSE-GRAINED LAKE AND MARINE
SEDIMENTS— sand and gravel deposits of
lacustrine deltas, and marine and lacustrine
terraces and beaches
MARINE CLAY—stratified silt and clay
deposited by postglacial marine incursions
: BEDROCK EXPOSURES
-------
into fine-grained bottom deposits, sandy shallow-water deposits, and sand and gravel beach and
deltaic deposits. Marine sediments were deposited in a relatively wide belt along the coast of
Maine when sea level rose and the ocean invaded the southeastern part of the State.
SOILS
Soils in Maine include, in decreasing order of abundance, Spodosols, mineral soils with
subsurface accumulations of organic matter and compounds of aluminum and iron; Inceptisols,
mineral soils with weakly expressed subsurface horizons of alteration or accumulation of metal
oxides such as iron, aluminum, or manganese; Entisols, mineral soils with little evidence of soil
development because their parent material is inert (such as quartz sand) or because the soils are
very young; and Histosols, wet organic-rich soils (peat and muck) in swamp and marsh
environments (Rourke and others, 1978; U.S. Soil Conservation Service, 1987). Figure 7 is a
generalized soil map of Maine. The following discussion is condensed from Rourke and others
(1978). State- and county-scale soil survey reports should be consulted for more detailed
descriptions and information.
Much of the State is covered by loamy soils developed on glacial till derived from
limestone, shale, and slate. Two units of these till-derived soils are shown on the generalized soil
map of Maine (fig. 7). One unit consists of poorly- to well drained, moderately permeable, silty,
sandy, and gravelly loams. The other unit consists of poorly- to well drained, silty, sandy, and,
locally, gravelly loams, with a firm compact substrata and low permeability. Both types of till
soils are generally shallow in upland areas and deeper in lowlands. These soils tend to be well
drained on steeper slopes and poorly drained in flatter lowland areas.
Soils developed on deposits of glacial outwash, kames, deltas, eskers, and alluvium are
shallow to deep sands and gravels with high permeability. Soils developed on terraces, eskers,
and other upland or steeply-sloping areas are well- to excessively drained. Soils in valley bottoms
and other low-lying areas are poorly drained and are commonly wet at least part of the year.
Included in this map unit are organic soils (Histosols) that formed in kettle holes and adjacent to
eskers, kame terraces, and deltas. Histosols are poorly drained and are wet most of the time.
Soils developed on marine and lacustrine sediments, till, and bedrock include deep, poorly-
to moderately well drained silts and clays developed on marine and lacustrine deposits; and shallow
to deep, moderately well- and well drained, silty and sandy loams developed on bedrock and till.
The soils developed on marine and lacustrine deposits have low permeability and cover the
majority of land area represented by this map unit. Soils developed on bedrock and till have
moderate to locally high permeability. These soils are typically found on coastal upland areas and
moraines, whereas the soils derived from marine and lake-bottom sediments occupy low-lying
coastal areas (fig. 7).
RADIOACTIVITY
An aeroradiometric map of Maine, synthesized from the National Uranium Resource
Evaluation (NURE) flightline data (Duval and others, 1989), is shown in figure 8. High
radioactivity in Maine is predominately associated with uranium-rich two-mica granites, calc-
alkaline granites, and alkalic granites of the Devonian-Carboniferous age. These granites have
typical equivalent uranium (eU) values between 2.5 and 4.5 ppm and in places have eU greater
than 5.5 ppm on the aeroradioactivity map (fig. 8). Two-mica granites are most abundant in the
southwestern part of the State. The Sebago Lake pluton, northwest of Portland, and smaller
IV-19 Reprinted from USGS Open-File Report 93-292-A
-------
0 10 20 30 40 Miles
Figure 7. Generalized soil map of Maine (modified from Rourke and others, 1978).
-------
GENERALIZED SOIL MAP OF MAINE
EXPLANATION
Areas dominated by loamy soils with friable substrata developed on glacial till—
shallow to deep, silty, sandy, and gravelly loams with moderate permeability
Areas dominated by loamy soils with firm, compact substrata developed on
glacial till—shallow to deep, silty, sandy, and gravelly loams with low permeability
Areas dominated by sandy and gravelly soils on glacial outwash plains, deltas
kame terraces, eskers, and Recent alluvium—shallow to deep sands and gravels
with high permeability; also includes wet, organic soils in kettles and other
low-lying areas
Areas dominated by silty and clayey soils developed on lacustrine and marine
sediments—deep clays and silts with low permeability; also includes small areas
of shallow to deep, silty and sandy loams with moderate permeability developed
on till and bedrock
-------
Figure 8. Aerial radiometric map of Maine (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.
-------
bodies to the south and east of Portland have UsOg concentrations between 20 and 100 ppm and
as high as 280 ppm (Chiasma Consultants/Inc., 1982);4 North of the Sebago Lake pluton,
however, the two-mica granites have generally lower uranium concentrations (average less than 5
ppm and upper values of 9-16 ppm as reported by Bendix Field Engineering (1982)). Alkalic
granites are more abundant in the eastern part of the State, particularly in the area northeast of
Penobscot Bay and a large body in east-central Piscataquis County. These granites have typical
uranium concentrations between 10 and 20 ppm (Bendix Field Engineering, 1982). High
radioactivity on the aeroradioactivity map (fig. 8) is also associated with several small areas in the
southeastern part of the State underlain by Conway Granite of the White Mountain plutonic series
and two small syenite sills of the New Hampshire series, one northeast of Waldboro and the other
incorporated in a series of faults in northern Hancock County. Chiasma Consultants, tic (1982)
reports a UsOg concentration of 26 ppm from Conway Granite in Maine and values ranging
3-75 ppm in associated trachyte dikes. Bendix Field Engineering (1982) reports uranium
concentrations of 10 to 35 ppm in the syenite sills. Tonalite and monzonite intrusive rocks of the
New Hampshire series underlie several small areas in the east-central part of the State and a large
area near the northernmost part of Hancock County. These intrusive rocks have moderate eU
(1.5-2.5 ppm) on the aeroradioactivity map (fig. 8). Diorite and mafic intrusive rocks of the New
Hampshire series have low eU (0.5-1.5 ppm) on the aeroradioactivity map and comprise two
northeast-trending belts along the southern coast and from southern Oxford County to central
Picataquis County.
In the southern part of the State, most of the metasedimentary and metavolcanic units have
moderate to high eU (2-4 ppm) on the aeroradioactivity map (fig. 8). The individual units are
difficult to distinguish due to the overprint of adjacent granites. Chiasma Consultants, Inc. (1982)
indicate that some uranium anomalies in the Cambro-Ordovician Gushing Formation and the
Silurian Berwick Formation are related to pegmatite dikes from two-mica granites with UsOs
values typically between 30 and 60 ppm and as high as 394 ppm. An increase in uranium with
metamorphic grade resulting from recrystallization and partial melting at progressively high
pressures and temperatures has been suggested by a number of authors (Hess and others 1980-
Olszewski and Boudette, 1986). A comparison of figure 5a with figure 8 shows a broad
correlation of radioactivity anomalies with either igneous plutons or high metamorphic grade.
Several aeroradioactivity anomalies, however, are directly associated with graphitic and sulfidic
slate and schist of Cambrian to Silurian age that crop out in a zone parallel to the southern coast
These rocks include the Cambro-Ordovician Scarboro, Diamond Island, and Gushing Formations,
the Ordovician Penobscot, Quimby, and Beauceville Formations and the Silurian Berwick
Digdegaush, and Quoddy Formations. Graphitic slates in the vicinity of Portland have U3O8
concentrations of 8 ppm (Chiasma Consultants, Inc., 1982). North of this belt is a belt of
Silurian-Devonian metamorphosed calcareous sandstone and limestone of the Bucksport and
Vassalboro Formations. Bendix Field Engineering (1982) noted several anomalous radioactivity
highs in these units, but the Vassalboro stands out as an area of moderate eU (2.0-2.5 ppm) on the
radiometric map (fig.8).
Another belt of mostly Silurian graphitic and sulfidic slate and schist with moderate to high
eU on the aeroradioactivity map (fig. 8) extends northeast from the northern edge of the Sebago
Lake pluton. This belt includes the Silurian Sangerville, Small Falls, Waterville, and Rangeley
Formations. North of this belt the only metasedimentary rocks that stand out with low to moderate
eU (1-2.5 ppm) on the aeroradioactivity map (fig. 8) are black metapelites of the Devonian
Carrabasset, Seboomook, and Tarratine Formations, and the Cambrian Grand Pitch, Dead River,
IV-23 Reprinted from USGS Open-File Report 93-292-A
-------
and Hurricane Formations. The Carrabasset Formation forms a northeast-trending belt, mostly in
southern Piscataquis County. It intertongues to the northeast with the Devonian Flume Ridge
Formation, a metamorphosed calcareous sandstone in which Bendix Field Engineering (1982)
found a few areas of anomalously high surface radioactivity, and to the southwest into faulted and
folded Seboomook Formation and Silurian metapelites, all of which are heavily intruded by New
Hampshire series igneous rocks. The Cambrian metapelites form a belt of low to moderate eU
(fig. 8) north of the Devonian rocks. They are highly faulted and intruded by Devonian igneous
rocks. North of the belt of Cambrian-age rocks, the metamorphic grade is lower and the
radiometric signature on the aeroradiometric map is low. In this area, the Tarratine Formation has
elevated eU on the aeroradioactivity map (fig.8), as does a small fault-bounded belt of the
Cambrian Hurricane Mountain Formation. Bendix Field Engineering (1982) notes several
radioactivity anomalies in the Seboomook Formation, which they argue may be due to fertilizer use
in that heavily agricultural region. They also note anomalies associated with the Ordovician Carys
Mill Formation gray slate and argillaceous limestone, and the Silurian Allsbury Formation slate and
sandstone, which comprise a north-south trending belt in easternmost Aroostook County, and with
Ordovician quartz monzonite and Precambrian gneiss in northern Franklin and western Somerset
Counties. None of these have corresponding anomalies on the radiometric map (fig. 8), although
they are slightly elevated relative to surrounding rocks.
Most of the Ordovician to Devonian rocks in the northern part of the State have low eU
values (0-1.5 ppm) on the radiometric map (fig.8). The lowest values (0-0.5 ppm eU) are
associated with the Cambro-Ordovician Saint Daniel Formation quartzites in western Aroostook
County, Ordovician mafic volcanics of the Winterville Formation in eastern Aroostook County,
and most of the area underlain by the Seboomook Formation. In the south, the metamorphosed
quartzite and mafic volcanics of the Cambro-Ordovician Gushing and Cape Elizabeth Formations
are notably low in radioactivity (0.5-2.0 ppm) on the aeroradiometric map (fig. 8).
INDOOR RADON/RADON IN WATER
Indoor radon data from 839 homes sampled in the State/EPA Residential Radon Survey
conducted in Maine during the winter of 1988-89 are shown in figure 9 and listed in Table 1. A
map of counties is included for reference (fig. 10). Data is presented by both county and zip code.
Because of the large size of the symbols compared to the small scale of the zip code map, some of
the symbols representing relatively small and(or) irregularly shaped zip code areas that are near to
each other appear to overlap. Indoor radon was measured by charcoal canister and data are shown
only for those counties with 5 or more data values. The maximum value recorded in the survey
was 103.2 pCi/L in Franklin County. The average for the State was 4.0 pCi/L and 29.9 percent of
the homes tested had indoor radon levels exceeding 4 pCi/L. Counties with average indoor radon
values exceeding 4 pCi/L include Aroostook, Cumberland, Franklin, Oxford, and York. The
remaining counties all had average indoor radon levels between 2 and 4 pCi/L. Counties with
average radon levels greater than 4 pCi/L occur in the northern and western parts of the State,
whereas counties in the southern'and central parts of Maine have moderate (2-4 pCi/L) indoor
radon averages. The percent of homes in each county with indoor radon levels exceeding 4 pCi/L
follows the same trend as the average values (fig. 9). In Oxford County, 52 percent of the homes
tested had indoor radon levels exceeding 4 pCi/L. In Aroostook, Cumberland, Hancock,
Kennebec, Piscataquis, and York Counties, between 25 and 50 percent of the homes tested had
indoor radon levels exceeding 4 pCi/L (fig. 9). The highest county average, 6.8 pCi/L for
IV-24 Reprinted from USGS Open-File Report 93-292-A
-------
Bsmt. & 1st Floor Rn
%>4pCi/L
00
OtolO
11 to 20
21 to 40
41 to 60
100 Miles
Bsmt. & 1st Floor Rn
Average Concentration (pCi/L)
oQ
0.0 to 1.9
2.0 to 4.0
4.1 to 6.8
no ScreenmS indoor radon data from the EPA/State Residential Radon Survey of Maine,
1988-89. Data are from 2-7 day charcoal canister tests. Histograms in map legends show the
number of counties in each category. The number of samples in each county (See Table 1) may
not be sufficient to statistically characterize the radon levels of the counties, but they do suggest
general trends. Unequal category intervals were chosen to provide reference to decision and
action levels.
-------
RnAVERAGE
(pCi/L)
O 0.0 to 1.9
if 2.0 to 4.0
+ 4.1 to 26.8
Figure 9 (continued). Average basement and &st-floor radon by ZIP code. Each point located in
center of ZIP code area (centroid).
-------
TABLE 1. Screening indoor radon data from the EPA/State Residential Radon Survey of
Maine conducted during 1988-89. Data represent 2-7 day charcoal canister measurements
from the lowest level of each home tested.
COUNTY
ANDROSCOGGIN
AROOSTOOK
CUMBERLAND
FRANKLIN
HANCOCK
KENNEBEC
KNOX
LINCOLN
OXFORD
PENOBSCOT
PISCATAQUIS
SAGADAHOC
SOMERSET
WALDO
WASHINGTON
YORK
NO. OF
MEAS.
47
102
132
22
53
61
30
18
42
79
42
34
31
27
40
79
MEAN
3.1
4.9
5.6
6.8
3.5
3.5
2.8
2.2
5.6
2.1
3.8
2.2
2.1
3.1
2.5
5.6
GEOM.
MEAN
2.2
3.0
3.2
1.8
1.8
1.9
1.6
1.7
3.2
1.4
2.1
1.4
1.6
2.0
1.5
3.1
MEDIAN
2.4
3.6
3.2
1.7
2.2
2.0
1.6
1.7
4.2
1.7
1.9
1.6
1.6
2.1
1.6
2.9
STD.
DEV.
2.7
5.1
8.5
21.7
3.8
4.2
2.9
1.7
5.9
1.8
4.8
2.1
1.5
3.3
2.7
6.7
MAXIMUM
11.4
25.2
82.7
103.2
19.4
19.4
9.7
6.9
30.2
7.5
22.5
8.0
5.8
13.0
122
33.0
%>4pCi/L
23
41
39
18
28
28
23
11
52
15
26
18
19
22
15
41
%>20 pCi/L
0
5
3
5
0
0
0
0
5
0
2
0
0
0
0
4
-------
w-
0 10 20 30 40 50 mile
Figure 10. Maine counties (from Facts on File, 1984).
-------
22 measurements in Franklin County, may be somewhat misleading because of the influence of the
single 103.2 pCi/L value on the arithmetic mean: With this value excluded, the average for the
remaining 21 measurements in Franklin County is 2.2 pCi/L. However, it is important to keep in
mind that this high value indicates that elevated indoor radon levels can occur locally within
Franklin County.
A study was also made of radon in 13,353 school rooms in 653 schools across the State of
Maine (Grodzins and others, 1991). Indoor radon measurements were made with liquid
scintillation charcoal detectors, in rooms at or below grade, from a Friday afternoon to the
following Monday morning. The results indicated that 32 percent of the schools had at least one
room with a radon concentration exceeding 4 pCi/L. Grodzins and others (1991) also noted a
strong correlation between the geographic distribution of radon levels in the school study and those
of the State/EPA indoor radon survey of homes. Li the school survey, they report that school
buildings in Aroostook, York, Cumberland, Androscoggin, and Oxford Counties have uniformly
high mean radon values; Kennebec, Waldo, Hancock and Washington Counties have moderate
values; and Sagadahoc, Lincoln, and Knox Counties have low radon averages.
Radon contributed from domestic well water may also constitute a significant indoor-air
radon problem in Maine. There is considerable debate over the amount of indoor radon contributed
to the air from water use. Several studies indicate that degassing of radon from water can cause
spikes in indoor air concentrations, especially during peak water-use periods (Hess and others,
1986; Nazaroff and Nero, 1988). The amount of radon that is contributed to indoor air from water
vanes substantially and is related to the volume of air in the house and the volume of water used
over a given period of time. The problem of radon in water in Maine has been studied by a number
of authors and part of these data are summarized in Norton and others (1989). They examined data
from 350 wells in Maine and found that the distribution of radon in ground water is primarily
controlled by bedrock geology. Low-grade metamorphic rocks had mean waterborne radon
concentrations between 1,000 and 5,000 pCi/L. Water from medium- to high-grade metamorphic
rocks yielded average radon concentrations in the 10,000 to 15,000 pCi/L range. Granites
consistently yielded water with the highest radon concentrations, averaging 22,000 pCi/L, with
values commonly exceeding 50,000 pCi/L. Radon values were variable within single granite
bodies. Wells developed in surficial materials had significantly lower waterborne radon
concentrations than wells drilled into bedrock. Using these data and the distribution of rock types
within each county, Norton and others (1989) estimated average waterborne radon concentrations
by county. A map showing the estimated average water radon concentrations for each county is
shown in figure 11.
Clausen (1990) examined water data from Hess and others (1980) and from the Maine
Department of Human Services. Data from his thesis for 1533 wells, grouped by lithology, are
presented in Table 2. Generally, the median value for most wells was below 5000 pCi/L,
excluding granite and the general category of igneous rocks. Average values were much higher
than the medians for all rock categories due to the fact that all categories had at least one well with a
radon concentration greater than. 10,000 pCi/L. Clausen concluded that, for the metamorphic
rocks, there is a weak positive correlation with increasing metamorphic grade, and that ground
water from granites seems to be the most highly variable in radon concentration as well as yielding
the highest radon concentrations overall.
IV-29 Reprinted from USGS Open-File Report 93-292-A
-------
Average radon in water in pCi/l
0 - 3,000
3,000 - 6,000
6.000-9,000
9,000- 12,000
12,000- 15,000
15,000 - 18.000
Figure 11. Map showing average radon in water for Maine counties (from Norton and others,
-------
TABLE 2. RADON ACTIVITIES FQR VARIOUS BEDROCK LITHOLOGIES
(from Clausen,'1990)
Radon activitities fr>Ci I'1)
n mean std. dev. med. max.
13 3,858 4,349 2,300 14,800
3 4,691 4,039 3,838 15,809
62 3,809 11,186 1,800 88,600
62 3,810 11,186 1,800 88,800
22 9,185 14,489 2,677 48,890
34 5,916 7,846 3,750 43,620
196 8,744 16,093 2,714 104,000
132 15,231 116,570 2,363 1,341,800
191 6,380 11,852 2,302 103,700
58 5,072 6,056 2,600 30,400
4 3,338 4,705 1,426 10,300
418 18,430 41,817 5,300 363,320
4 3,228 3,254 2,294 15,900
334 30,231 87.440 12.450 363 320
Lithology
Calcareous
Pelite
Sulfidic
Calcareous
Pelite
Feldspathic
Sandstone
Calcareous
Feldspathic
Sandstone
Calcareous
•Quartz
Sandstone
Limestone
Interbedded
Sandstone and
Shale
Interbedded
Limestone and
Shale
Interbedded
Limestone,
Sandstone and
Shale
Mixed Volcanic
Rocks
Undetermined
Volcanic Rocks
Igneous Rocks
Schist
Granite
-------
GEOLOGIC RADON POTENTIAL
The following discussion examines indoor radon, radioactivity, soil properties, and
geology to assess the geologic radon potential for areas in the State. A numeric ranking is given in
Table 3 and geologic radon potential areas are illustrated in figure 12. Previous studies on the
geologic radon potential of Maine include Olszewski and Boudette (1986), who compiled a
generalized geologic map of New England with emphasis on uranium endowment and radon
production. This analysis corresponds well with their uranium endowment map for the State of
Maine and we have followed some of their groupings for rock units. Because of the variability of
the geology of Maine with respect to the distribution of indoor radon data it is difficult to identify
definitive correlations between the indoor radon data and specific geologic formations.
In figure 2, the rocks of Maine have been subdivided into major lithologic groups. Of
these groups, the rocks, surficial deposits, and geologic structures 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.
Stratified metamorphic rocks of igneous or sedimentary origin
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 geologic radon potential. Olszewski
and Boudette (1986) classified these Paleozoic metasedimentary and metavolcanic rocks as having
variable uranium endowment. Uranium concentration generally increases with metamorphic grade
and local uranium concentrations may be present in fractures and faults. Uranium analyses for
most of the metasedimentary and metavolcanic rocks in central and northern Maine (previously
discussed in the radioactivity section of this report) indicate uranium concentrations of less than
3 ppm in general. Areas in northern Maine underlain by coarse-grained clastic metasedimentary
rocks and tills derived from these rocks generally have low equivalent uranium on the NURE map
(fig. 8) and have soils with low permeability. Many of the rocks in this area belong to the
Seboomook Formation (Area 1, fig. 12). Indoor radon data are sparse for northern Maine except
in the northeast, where most of the underlying rocks and tills are composed of carbonate and slate
or shale (Area 2, fig. 12). 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 has interbedded carbonate and clastic metasedimentary rocks and tends to be more
calcareous in general, appears to be associated with high indoor radon in southern Penobscot
County (Area 3, fig. 12). Area 3 on figure 12 is a highly variable areanradon potential varies from
moderate to locally high or low. Locally high areas may be associated with granites, kames,
eskers, carbonates, 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 geology is variable over short distances.
IV-32 Reprinted from USGS Open-File Report 93-292-A
-------
RADON POTENTIAL
LOW
MODERATE/VARIABLE
3 HIGH
Figure 12. Geologic radon potential areas of Maine. See text for discussion of numbered
areas.
-------
Soils and glacial deposits derived from interbedded carbonates and slates in the
northeastern portion of the State and in the south-central portion of the State (Areas 2 and 3,
fig. 12) are associated with moderate and high indoor radon levels. Equivalent uranium is variable
over these deposits (fig. 8) but is higher than in the dominantly clastic metasedimentary rocks.
Soils, tills, eskers, and kames derived from these rocks generally have moderate to locally high
permeability. Carbonate rocks are usually low in radionuclide elements but the soils developed
from carbonate rocks are often elevated in uranium and radium. Carbonate soils are derived from
the dissolution of the CaCOs that makes up the majority of the rock. When the CaCOs has been
dissolved away, the. soils are enriched in the remaining impurities, predominantly base metals,
including radionuclides.
Graphitic or carbonaceous slates, phyllites, and schists are known to be uranium and radon
sources in several areas of the Appalachians (Ratte and Vanacek, 1980; Gundersen and others,
1988) and this may be the case in Maine. Most of the carbonaceous or graphitic rock units in
Maine have corresponding moderate to high equivalent uranium in figure 8. Some high indoor
radon levels may be associated with carbonaceous rocks of the Penobscot Formation in Knox
County (Area 4, fig. 12). Soils formed on carbonaceous and graphitic rocks in Maine have low to
moderate permeability.
Igneous plutonic rocks
Intermediate to mafic plutonic rocks generally have low or variable radon potential. Diorite
and mafic intrusive rocks of the New Hampshire series have low equivalent uranium (0.5-1.5
ppm) and comprise two northeast-trending belts along the southern coast and from southern
Oxford County to central Picataquis County. Two-mica granites, calc-alkaline granites, and alkalic
plutonic rocks in Maine have been ranked high in radon potential (in Areas 3, 5, 6,7, fig. 12).
Uranium concentrations in these types of granites are commonly more than 3 ppm and are as high
as several hundred ppm in Maine. Uranium occurs as primary uranium oxides such as uraninite or
in abundant accessory minerals. Olszewski and Boudette (1986) classified these rocks as moderate
to high in uranium endowment Two-mica granites are most abundant in the southwestern part of
the State and include the rocks of the Sebago Pluton. Calc-alkaline to alkaline granites are more
abundant in the southern and central part of the State, particularly in the area northeast of
Penobscot Bay and in the Katadhin pluton in central Maine (Area 6, fig. 12). Indoor radon is high
in the southwestern counties of Maine and in many of the zipcode areas, and may correlate with the
abundance of igneous plutons and high grade metamorphic rocks in this area (Area 5, fig. 12).
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 the major fault and
shear zones in Maine, evidence from other areas of the Appalachians (Gundersen, 1991) suggests
that shear zones can create isolated occurrences of severe indoor radon, especially when they
deform uranium-bearing rocks. The radon potential of melange (Area 11 and a small part of
Area 3, fig. 12) is not well known; however, 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.
Glacial deposits
The effect of glacial deposits is difficult to assess in Maine because most till is locally
derived and primarily reflects a collection of clasts of the surrounding bedrock. The areas of
IV-34 Reprinted from USGS Open-File Report 93-292-A
-------
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.
Coarser glacial deposits appear to be associated with igneous plutonic rocks and belts of calcareous
and carbonate metasedimentary rocks. Along the coast, areas of slowly permeable marine clay
probably reduce the radon potential (Areas 8, 9, fig. 12). Glacial lake sediments with low
permeability in Penobscot County (Area 10, fig. 12) appear to be associated with low indoor radon
on the zip code radon map. Sagadahoc, Lincoln, Knox, and Washington Counties have average
indoor radon less than 3 pCi/L and are underlain by extensive marine clay deposits. Equivalent
uranium is low to moderate (fig. 8). Metavolcanic and metasedimentary rocks with probable low
uranium concentrations also underlie these counties. Till with compact, low-permeability 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. As can be seen from
the zip code centroid plot of indoor radon in the State (fig. 9), few towns are present in northern
Maine and indoor radon data are sparse.
SUMMARY
For the purpose of this assessment, Maine has been divided into eleven geologic radon
potential groupings 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 booklet for more information).
The rocks, deposits, and geologic structures most likely to cause high (>4 pCi/L) indoor
radon levels in Maine 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, kames, and eskers; melange; granitic gneiss; medium- to high-
grade metamorphic rocks; and contact-metamorphosed rocks in the vicinity of igneous 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
include metamorphosed, coarse-grained, clastic sedimentary rocks; mafic metavolcanic rocks;
marine and glaciomarine clays; and mafic plutonic rocks. Radon escaping into indoor air from
domestic well water may be a significant factor in the indoor radon concentrations seen in Maine.
High radon concentrations in well water correlate positively with granite plutons, pegmatites,
faults, and high-grade metamorphic rocks.
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
not be made without consulting all available local data. For additional information on radon and
how to test, contact your state radon program or EPA regional office. More detailed information
on state or local geology may be obtained from the state geological survey. Addresses and phone
numbers for these agencies are listed in chapter 1 of this booklet.
IV-35 Reprinted from USGS Open-File Report 93-292-A
-------
TABLE 3. RI and CL scores for geologic radon potential areas of Maine. See figure 12 for
locations of areas.
Areal
Seboomook Fm.
Area2
metasedimentary
predominantly carbonate
FACTOR
INDOOR RADON
RADIOACTIVITY
GEOLOGY
SOIL PERM.
ARCHITECTURE
GFE POINTS
TOTAL
RANKING
RI
1
1
2
1
3
0
8
Low
CI
1
2
2
2
-
-
7
Low
RI
3
2
2
2
3
0
12
High
CI
2
2
2
2
-
-
8
Mod
Areas 3 and 11
Heterogeneous
metamoiphic & igneous rocks
RI
2
2
2
2
3
0
11
Mod
CI
2
2
3
2
.
.
9
Mod
Areas 4 and 7
Penobscot Fm., granites
and minor metamoiphic rocks
FACTOR
INDOOR RADON
RADIOACTIVITY
GEOLOGY
SOIL PERM.
ARCHITECTURE
GFE POINTS
TOTAL
RANKING
RI
2
3
3
2
3
0
13
High
CI
2
2
3
2
-
-
9
Mod
Areas 5 and 6
Granite and
high grade metamorphic
RI
3
3
3
2
3
0
14
High
CI
2
2
2 ,
2
-
.
8
Mod
Areas 8, 9, and 10
glacial lake clay
marine clay
RI
2
1
1
1
3
0
8
Low
CI
2
2.
3
2
-
.
9
Mod
RADON INDEX SCORING:
Radon potential category
Point range
LOW 3-8 points
MODERATE/VARIABLE 9-11 points
HIGH > 11 points
Possible range of points = 3 to 17
CONFIDENCE INDEX SCORING:
Probable screening indoor
radon average for area
<2pCi/L
2-4pCi/L
>4pCi/L
LOW CONFIDENCE
MODERATE CONFIDENCE
HIGH CONFIDENCE
4-6 points
7-9 points
10 -12 points
Possible range of points = 4 to 12
IV-36 Reprinted from USGS Open-File Report 93-292-A
-------
REFERENCES CITED IN THIS REPORT
AND GENERAL REFERENCES PERTAINING TO RADON IN MAINE
Bendix Field Engineering, 1982, National Uranium Resource Evaluation, Glen Falls Quadrangle,
New York, Vermont, and New Hampshire: Prepared for the U.S. Department of Energy,
Report PGJ/F-025(82), 31 p.
Borns, H.W., Jr., 1973, Late Wisconsin fluctuations of the Laurentide ice sheet in southern and
eastern New England, in Black, R.F., Goldthwait, R.P., and Willman, H.B., eds., The
Wisconsonan stage: Geological Society of America Memoir 136, p. 37-45.
Boudette, E.L., 1977, Two-mica granite and uranium potential in the northern Appalachian orogen
of New England, in Cambell, J.A., ed., Short papers of the U.S. Geological Survey
uranium-thorium symposium: U.S. Geological Survey Circular 753.
Brutsaert, W.F., Norton, S.A. and Hess, C.T., 1987, Radon in Maine, geology, hydrology, and
health, in Proceedings, American Water Works Association 1987 annual conference:
Proceedings of American Water Works Association 1987 annual conference Kansas City,
MO, June 14-18, 1987, p. 641-656.
Brutsaert, W.F., Norton, S.A., Hess, C.T. and Williams, J.S., 1981, Geologic and hydrologic
factors controlling radon-222 in ground water in Maine: Ground Water, v. 19,
p. 407-417.
Chiasma Consultants, Inc., 1982, National Uranium Resource Evaluation, Portland Quadrangle,
Maine and New Hampshire: Prepared for the U.S. Department of Energy, Report
PGJ/F-028(82), 28 p.
Clausen, J.L., 1990, The Geochemistry of Ground water in Maine: unpub. Master's Thesis,
University of Maine, Orono.
Denny, C.S., 1982, Geomorphology of New England: U.S. Geological Survey Professional
Paper 1208, 18 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, New England.
Grodzins, L., Bradstreet, T., and Moreau, E., 1991, The State of Maine Schools Radon Project:
Results: in Proceedings of the 1991 EPA International Symposium on Radon and Radon
Reduction Technology, EPA-600/4-91, Volume 3: Preprints, paper VI-6.
Gundersen, L.C.S., 1991, Radon in sheared metamorphic and igneous rocks: in Gundersen,
L.C.S., and Wanty R.B., eds., Geologic and Geochemical Field Studies of Radon in
Rocks, Soils, and Water; U.S. Geological Survey Bulletin 1971, p. 38-49.
IV-37 Reprinted from USGS Open-File Report 93-292-A
-------
Gundersen, L.C.S., Reimer, G.M., Wiggs, C.R., and Rice, C.A., 1988, Radon Potential of
Rocks and Soils in Montgomery County Maryland; U.S. Geological Survey
Miscellaneous Field Studies Map 88-2043, scale 1:62,500.
Hanson, L.S., and Caldwell, D.W., 1989, The lithologic and structural controls on the
geomorphology of the mountainous areas in north-central Maine, in Tucker, R.D., and
Marvinney, R.G., eds., Studies in Maine Geology, Volume 5: Quaternary Geology:
Maine Geological Survey, p. 147-167.
Hess, C.T., Casparius, R.E., Norton, S.A. and Brutsaert, W.F., 1980, Investigations of natural
levels of radon-222 in ground water in Maine for assessment of related health effects, in
Gesell, T.F., and Lowder, W.M., eds., Natural radiation environment IE; Vol. 1:
Proceedings of International symposium on the natural radiation environment Houston,
TX, United States April 23-28,1978, DOE Symposium Series 1, p. 529-546.
Hess, C.T., Norton, S.A., Brutseart, W.F., Casparius, R.E., Coombs, J., E. and Hess, A.L.,
1980, Radon-222 in potable water supplies of New England: Journal of the New England
Waterworks Association, v. 94, p. 113-128.
Hess, C.T., Weiffenbach, C.V. and Norton, S.A., 1983, Environmental radon and cancer
correlations in Maine: Health Physics, v. 45, p. 339-348.
Hess, C.T., Korsah, J.K., and Einloth, C.J., 1986, 222Rn in homes due to 222Rn in potable
water, in Hopke, P.K., ed., Radon and its decay products—Occurrence, properties, and
health effects: American Chemical Society Symposium 331, p. 30-41.
Hess, C.T., Vietti, M.A. and Mage, D.T., 1987, Radon from drinking water, in Hemphill D.D.,
(ed.), Trace substances in environmental health: Proceedings of University of Missouri's
21st annual conference on Trace Substances in Eenvironmental Health, St Louis, MO,
May 25-28, 1987, p. 158-171.
Hess, C.T., Vietti, M.A., and Mage, D.T., 1987, Radon from drinking water; evaluation of
waterborne transfer into house air: Environmental Geochemistry and Health v 9
p. 68-73.
Koch, T.J., Gust, D.A. and Lyons, W.B., 1988, Geochemistry of radon-rich waters from two-
mica granites, in Proceedings of the FOCUS conference on Eastern regional ground water
issues, Stamford, CT, Sept. 27-29,1988, National Water Well Association, p. 587-601.
Lanctot, E.M., 1985, Radon in the domestic environment and its relationship to cancer: An
epidemiological study: Maine Geological Survey Open-file report 85-88,39 p.
Lanctot, E.M., Tolman, A.L. and Loiselle, M., 1985, Hydrogeochemistry of radon in ground
water, in Aller, L., Lehr, J.H., and Butcher, K., eds., Proceedings of the Association of
Ground Water Scientists and Engineers eastern regional ground water conference,
Portland, ME, July 16-18, 1985, p. 66-85.
IV-38 Reprinted from USGS Open-File Report 93-292-A
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Lanctot, E.M., Tolman, A.L. and Loiselle, M., 1986 , Ground-water geochemistry of radon in
Maine: Geological Society of America, Abstracts with Programs, v. 18, p. 28.
Lowry, S.B. and Lowry, J.D., 1988, Aeration for the removal of Rn from small water supplies,
in Proceedings of the FOCUS conference on Eastern regional ground water issues
Stamford, CT, Sept. 27-29, 1988, p. 603-312.
Nazaroff, W.W., and Nero, A.V., Jr., 1988, Radon and its decay products in indoor air: New
York, John Wiley and Sons, 518 p.
Norton, S.A., Brutsaert, W.F., Hess, C.T., and Casparius, R.E., 1978, Geologic controls on
natural levels of Rn-222 in ground water in Maine: Geological Society of America,
Abstracts with Programs, v. 10, p. 78.
Norton, S.A., Hess, C.T., and Brutsaert, W.F., 1989, Radon, geology, and human health in
Maine, in Tucker, R.D., and Marvinney, R.G., eds., Studies in Maine Geology, Volume
5: Quaternary Geology: Maine Geological Survey, p. 169-176.
Olszewski, W.J., Jr., and Boudette, E.L., 1986, Generalized bedrock geologic map of New
England with emphasis on uranium endowment and radon production: U.S.
Environmental Protection Agency Open-File Map.
Osberg, P.H., Hussey, A.M., JH, and Boone, G.M., 1985, Bedrock geologic map of Maine:
Maine Geological Survey, scale 1:500,000.
Paulsen, R.T., 1991, Radionuclides in ground water, rock and soil, and indoor air of the
northeastern United States and southeastern Canada—A literature review and summary of
data, 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. 195-225.
Ratte, C., and Vanacek, D., 1980, Radioactivity Map of Vermont: Vermont Geological Survey
File No. 1980-1, rev. 3, 3 plates with text
Richmond, G.M., and Fullerton, D.S., eds., 1987, Quaternary geologic map of the Quebec 4° x 6°
quadrangle, United States and Canada: U.S. Geological Survey Miscellaneous
Investigations Map 1-1420, sheet NL-19, scale 1:1,000,000.
Richmond, G.M., and Fullerton, D.S., eds., 1991, Quaternary geologic map of the Boston
4° x 6° quadrangle, United States and Canada: U.S. Geological Survey Miscellaneous
Investigations Map 1-1420, sheet NK-19, scale 1:1,000,000.
Rourke, R.V., Ferwerda, J.A., and LaFlamme, K.J., 1978, The soils of Maine: University of
Maine at Orono, Life Sciences and Agriculture Experiment Station Miscellaneous Report
203,37 p.; includes general soil map of Maine, scale 1:750,000.
IV-39 Reprinted from USGS Open-File Report 93-292-A
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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.
Thompson, W.B.i and Borns, H.W., Jr., eds., 1985, Surficial geologic map of Maine: Maine
Geological Survey, scale 1:500,000.
Tucker, R.D, and Marvinney, R.G., eds., ,1989, Studies in Maine Geology: Maine Geological
Survey, Department of Conservation, Volumes 1-6,979 pages total.
U.S. Soil Conservation Service, 1987, Soils: U.S. Geological Survey National Atlas sheet
38077-BE-NA-07M-00, scale 1:7,500,000.
Wathen, J.B. and Hall, F.R., 1986, Factors affecting levels of Rn-222 in wells drilled into two-
mica granites in Maine and New Hampshire, in Aller, L., and Butcher, K., eds.,
Proceedings of the Third annual Eastern regional ground water conference: Springfield,
MA, July 28-30, 1986, p. 650-681.
Wathen, J.B., 1987, The effect of uranium siting in two-mica granites on uranium concentrations
and radon activity in ground water, in Graves, B.,ed., Radon, radium, and other
radioactivity in ground water: Lewis Publishers, p. 31-46.
IV-40 Reprinted from USGS Open-File Report 93-292-A
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EPA's Map of Radon Zones
The USGS1 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 USGS1 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.)
MAINE MAP OF RADON ZONKS
The Maine Map of Radon Zones and its supporting documentation (Part IV of this
report) have received extensive review by Maine geologists and radon program experts. The
map for Maine 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.
Six county designations do not strictly follow this methodology for adapting the
geologic provinces to county boundaries. EPA and the Maine Bureau of Health have decided
to designate Somerset, Franklin, Kennebec, Penobscot, Piscataquis and Lincoln counties as
Zone 1. Portions of these counties lie in high radon potential geologic provinces and indoor
radon data collected by Maine indicate that elevated levels of radon can be found in the
populated areas of these counties.
Although the information provided in Part IV of this report -- the State chapter entitled
"Preliminary Geologic Radon Potential Assessment of Maine" ~ 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
Maine radon program for information on testing and fixing homes. Telephone numbers and
addresses can be found in Part II of this report.
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