United Steles
Environmental Protection
Agency
Air and Radiation
(6604J)
A02-R-93-059
September 1993
&EPA EPA's Map of Radon Zones
RHODE ISLAND
-------
-------
EPA'S MAP OF RADON ZONES
RHODE ISLAND
RADON DIVISION
OFFICE OF RADIATION AND INDOOR AIR
U.S. ENVIRONMENTAL PROTECTION AGENCY
SEPTEMBER, 1993
-------
-------
ACKNOWLEDGEMENTS
This document was prepared by the U.S. Environmental Protection Agency's (EPA's)
Office of Radiation and Indoor Air (ORIA) in conjunction with the U.S. Geological Survey
(USGS). Sharon W. White was the EPA project manager. Numerous other people in ORIA
were instrumental in the development of the Map of Radon Zones, including Lisa Ratcliff,
Kirk Maconaughey, R. Thomas Peake, Dave Rowson, and Steve Page.
EPA would especially like to acknowledge the outstanding effort of the USGS
radon team — Linda Gundersen, Randy Schumann, Jim Otton, Doug Owen, Russell
Dubiel, Kendell Dickinson, and Sandra Szarzi — in developing the technical base for the
Map of Radon Zones.
ORIA would also like to recognize the efforts of all the EPA Regional Offices in
coordinating the reviews with the State programs and the Association of American State
Geologists (AASG) for providing a liaison with the State geological surveys. In addition,
appreciation is expressed to all of the State radon programs and geological surveys for their
technical input and review of the Map of Radon Zones.
-------
-------
TABLE OF CONTENTS
I. OVERVIEW
II. THE USGS/EPA RADON POTENTIAL
ASSESSMENTSiINTRODUCTION
III. REGION 1 GEOLOGIC RADON POTENTIAL
SUMMARY
V. PRELIMINARY GEOLOGIC RADON POTENTIAL
ASSESSMENT OF RHODE ISLAND
V. EPA'S MAP OF RADON ZONES -- RHODE ISLAND
-------
-------
OVERVIEW
Sections 307 and 309 of the 1988 Indoor Radon Abatement Act (IRAA) direct EPA to
identify areas of the United States that have the potential to produce elevated levels of radon.
EPA, the U.S. Geological Survey (USGS), and the Association of American State Geologists
(AASG) have worked closely over the past several years to produce a series of maps and
documents which address these directives. The EPA Map of Radon Zones is a compilation of
that work and fulfills the requirements of sections 307 and 309 of IRAA. The Map of Radon
Zones identifies, on a county-by-county basis, areas of the U.S. that have the highest potential
for elevated indoor radon levels (greater than 4 pCi/L).
The Map of Radon Zones is designed to assist national, State and local governments
and organizations to target their radon program activities and resources. It is also intended to
help building code officials determine areas that are the highest priority for adopting radon-
resistant building practices. The Map of Radon Zones should not be used to determine if
individual homes in any given area need to be tested for radon. EPA recommends that all
homes be tested for radon, regardless of geographic location or the zone designation of
the county in which they are located.
This document provides background information concerning the development of the
Map of Radon Zones. It explains the purposes of the map, the approach for developing the
map (including the respective roles of EPA and USGS), the data sources used, the conclusions
and confidence levels developed for the prediction of radon potential, and the review process
that was conducted to finalize this effort.
BACKGROUND
Radon (Rn222) is a colorless, odorless, radioactive gas. It comes from the natural
decay of uranium that is found in nearly all soils. It typically moves through the ground to
the air above and into homes and other buildings through cracks and openings in the
foundation. Any home, school or workplace may have a radon problem, regardless of
whether it is new or old, well-sealed or drafty, or with or without a basement. Nearly one out
of every 15 homes in the U.S. is estimated to have elevated annual average levels of indoor
radon.
Radon first gained national attention in early 1984, when extremely high levels of
indoor radon were found in areas of Pennsylvania, New Jersey, and New York, along the
Reading Prong-physiographic province. EPA established a Radon Program in 1985 to assist
States and homeowners in reducing their risk of lung cancer from indoor radon.
Since 1985, EPA and USGS have been working together to continually increase our
understanding of radon sources and the migration dynamics that cause elevated indoor radon
levels. Early efforts resulted in the 1987 map entitled "Areas with Potentially High Radon
Levels." This map was based on limited geologic information only because few indoor radon
measurements were available at the time. The development of EPA's Map of Radon Zones
and its technical foundation, USGS' National Geologic Radon Province Map, has been based
on additional information from six years of the State/EPA Residential Radon Surveys,
independent State residential surveys, and continued expansion of geologic and geophysical
information, particularly the data from the National Uranium Resource Evaluation project.
1-1
-------
Purpose of the Map of Radon Zones
EPA's Map of Radon Zones (Figure I) assigns each of the 3141 Counties in the
United States to one of three zones:
o Zone 1 counties have a predicted average indoor screening level > than
4 PCi/L
o Zone 2 counties have a predicted average screening level > 2 pCi/L and
< 4 pCi/L
o Zone 3 counties have a predicted average screening level < 2 pCi/L
The Zone designations were determined by assessing five factors that are known to be
important indicators of radon potential: indoor radon measurements, geology, aerial
radioactivity, soil parameters, and foundation types.
The predictions of average screening levels in each of the Zones is an expression of
radon potential in the lowest liveable area of a structure. This map is unable to estimate
actual exposures to radon. EPA recommends methods for testing and fixing individual homes
based on an estimate of actual exposure to radon. For more information on testing and fixing
elevated radon levels in homes consult these EPA publications: A Citizen's Guide to Radon.
the Consumer's Guide to Radon Reduction and the Home Buyer's and Seller's Guide to
Radon.
EPA believes that States, local governments and other organizations can achieve
optimal risk reductions by targeting resources and program activities to high radon potential
areas. Emphasizing targeted approaches (technical assistance, information and outreach
efforts, promotion of real estate mandates and policies and building codes, etc.) in such areas
addresses the greatest potential risks first.
EPA also believes that the use of passive radon control systems in the construction of
new homes in Zone 1 counties, and the activation of those systems if necessitated by follow-
up testing, is a cost effective approach to achieving significant radon risk reduction.
The Map of Radon Zones and its supporting documentation establish no regulatory
requirements. Use of this map by State or local radon programs and building code officials is
voluntary. The information presented on the Map of Radon Zones and in the supporting
documentation is not applicable to radon in water.
Development of the Map of Radon Zones
The technical foundation .for the Map of Radon Zones is the USGS Geologic Radon
Province Map. In order to examine the radon potential for the United States, the USGS
began by identifying approximately 360 separate geologic provinces for the U.S. The
provinces are shown on the USGS Geologic Radon Province Map (Figure 2). Each of the
geologic provinces was evaluated by examining the available data for that area: indoor radon
measurements, geology, aerial radioactivity, soil parameters, and foundation types. As stated
previously, these five factors are considered to be of basic importance in assessing radon
1-2
-------
Q
d
O
S3
O
3
ed
O
C
cd
5 o
oo
-------
CO
S?
CD
-------
potential and some data are available for each of these factors in every geologic province. The
province boundaries do not coincide with political borders (county and state) but define areas
of general radon potential. The five factors were assigned numerical values based on an
assessment of their respective contribution to radon potential, and a confidence level was
assigned to each contributing variable. The approach used by USGS to estimate the radon
~>c*ential for each province is described in Part II or 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 confide" -e, EPA
conducted a number of analyses. These analyses have helped EPA to identify the best
situations in which to apply the map, and its limitations.
1-5
-------
Figure 3
Geologic Radon Potential Provinces for Nebraska
Lincoln County
Higk Moderate Low
Figure 4
NEBRASKA - EPA Map of Radon Zones
Lincoln County
Zone 1 Zone 2 Zone 3
1-6
-------
One such analysis involved comparing county zone designations to indoor radon
measurements from the State/EPA Residential Radon Surveys (SRRS). Screening averages
for counties with at least 100 measurements were compared to the counties' predicted radon
potential as indicated by the Map of Radon Zones. EPA found that 72% of the counts'
screening averages were correctly reflected by the appropriate zone designations on the Map.
In all other cases, they only differed by 1 zone.
Another accuracy analysis used the annual average data from the National Residential
Radon Survey (NRRS). The NRRS indicated that approximately 6 million homes in the
United States have annual averages greater than or equal to 4 pCi/L. By cross checking the
county location of the approximately 5,700 homes which participated in the survey, their
radon measurements, and the zone designations for these counties, EPA found that
approximately 3.8 million homes of the 5.4 million homes with radon levels greater than or
equal to 4 pCi/L will be found in counties designated as Zone 1. A random sampling of an
equal number of counties would have only found approximately 1.8 million homes greater
than 4 pCi/L. In other words, this analysis indicated that the map approach is three times
more efficient at identifying high radon areas than random selection of zone designations.
Together, these analyses show that the approach EPA used to develop the Map of
Radon Zones is a reasonable one. In addition, the Agency's confidence is enhanced by results
of the extensive State review process — the map generally agrees with the States' knowledge
of and experience in their own jurisdictions. However, the accuracy analyses highlight two
important points: the fact that elevated levels will be found in Zones 2 and 3, and that there
will be significant numbers of homes with lower indoor radon levels in all of the Zones. For
these reasons, users of the Map of Radon Zones need to supplement the Map with locally
available data whenever possible. Although all known "hot spots", i.e., localized areas of
consistently elevated levels, are discussed in the State-
specific chapters, accurately defining the boundaries of the "hot spots" on this scale of map is
not possible at this time. Also, unknown "hot spots" do exist.
The Map of Radon Zones is intended to be a starting point for characterizing radon
potential because our knowledge of radon sources and transport is always growing. Although
this effort represents the best data available at this time, EPA will continue to study these
parameters and others such as house construction, ventilation features and meteorology factors
in order to better characterize the presence of radon in U.S homes, especially in high risk
areas. These efforts will eventually assist EPA in refining and revising the conclusions of the
Map of Radon Zones. And although this map is most appropriately used as a targeting tool
by the aforementioned audiences — the Agency encourages all residents to test their homes
for radon, regardless of geographic location or the zone designation of the county in
which they live. Similarly, the Map of Radon Zones should not to be used in lieu of
testing during real estate transactions.
Review Process
The Map of Radon Zones has undergone extensive review within EPA and outside the
Agency. The Association of American State Geologists (AASG) played an integral role in
this review process. The AASG individual State geologists have reviewed their State-specific
information, the USGS Geologic Radon Province Map, and other materials for their geologic
content and consistency.
1-7
-------
In addition to each State geologist providing technical comments, the State radon
offices were asked to comment on their respective States' radon potential -evaluations. In
particular, the States were asked to evaluate the data used to assign their counties to specific
zones. EPA and USGS worked with the States to resolve any issues concerning county zone
designations. In a few cases, States have requested changes in county zone designations. The
requests were based on additional data from,the 3tate on geology, indoor radon
measurements, population, etc. Upon reviewing the data submitted by the States, EPA did
make some changes in zone designations. These changes, which do not strictly follow the
methodology outlined in this document, are discussed in the respective State chapters.
EPA encourages the States and counties to conduct further research and data collection
efforts to refine the Map of Radon Zones. EPA would like to be kept informed of any
changes the States, counties, or others make to the maps. Updates and revisions will be
handled in a similar fashion to the way the map was developed. States should notify EPA of
any proposed changes by forwarding the changes through the Regional EPA offices that are
listed in Part II. Depending on the amount of new information that is presented, EPA will
consider updating this map periodically. The State radon programs should initiate proper
notification of the appropriate State officials when the Map of Radon Zones is released and
when revisions or updates are made by the State or EPA.
1-8
-------
THE USGS/EPA RADON POTENTIAL ASSESSMENTS: AN INTRODUCTION
by
Linda C.S. Gundersen and R. Randall Schumann
U.S. Geological Survey
-and
Sharon W. White
U.S. Environmental Protection Agency
BACKGROUND
The Indoor Radon Abatement Act of 1988 (15 U.S.C. 2661-2671) directed the U.S.
Environmental Protection Agency (EPA) to identify areas of the United States that have the
potential to produce harmful levels of indoor radon. These characterizations were to be based
on both geological data and on indoor radon levels in homes and other structures. The EPA
also was directed to develop model standards and techniques for new building construction
that would provide adequate prevention or mitigation of radon entry. As part of an
Interagency Agreement between the EPA and the U.S. Geological Survey (USGS), the USGS
has prepared radon potential estimates for the United States. This report is one of ten
booklets that document this effort. The purpose and intended use of these reports is to help
identify areas where states can target their radon program resources, to provide guidance in
selecting the most appropriate building code options for areas, and to provide general
information on radon and geology for each state for federal, state, and municipal officials
dealing with radon issues. These reports are no! 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 evety State, and EPA recommends that all homes
be tested for indoor radon.
Booklets detailing the radon potential assessment for the U.S. have been developed for
each State. USGS geologists are the authors of the geologic radon potential booklets. Each
booklet consists of several components, the first being an overview to the mapping project
(Part I), this introduction to the USGS assessment (Part II), including a general discussion of
radon (occurrence, transport, etc.), and details concerning the types of data used. The third
component is a summary chapter outlining the general geology and geologic radon potential
of the EPA Region (Part III). The fourth component is an individual chapter for each state
(Part IV). Each state chapter discusses the state's specific geographic setting, soils, geologic
setting, geologic radon potential, indoor radon data, and a summary outlining the radon
potential rankings of geologic areas in the state. A variety of maps are presented in each
chapter—geologic, geographic, population, soils, aerial radioactivity, and indoor radon data by
county. Finally, the booklets contain EPA's map of radon zones for each state and an
accompanying description (Part V).
Because of constraints on the scales of maps presented in these reports and because the
smallest units used to present the indoor radon data are counties, some generalizations have
been made in order to estimate the radon potential of each area. Variations in geology, soil
characteristics, climatic factors, homeowner lifestyles, and other factors that influence radon
concentrations can be quite large within any particular geologic area, so these reports cannot
be used to estimate or predict the indoor radon concentrations of individual homes or housing
. ' II-1 Reprinted from USGS Open-File Report 93-292
-------
tracts. Within any area of a given geologic radon potential ranking, there are likely to be
areas where the radon potential is lower or higher than that assigned to the area as a whole,
especially in larger areas such as the large counties in some western states.
In each state chapter, references to additional reports related to radon are listed for the
state, and the reader is urged to consult these reports for more detailed information. In most
cases the best sources of information on radon for specific areas are state and local
departments of health, state departments responsible for nuclear safety or environmental
protection, and U.S. EPA regional offices. More detailed information on state or local
geology may be obtained from the state geological surveys. Addresses and telephone
numbers of state radon contacts, geological surveys, and EPA regional offices are listed in
Appendix C at the end of this chapter.
RADON GENERATION AND TRANSPORT IN SOILS
Radon (222Rn) is produced from the radioactive decay of radium (226Ra), which is, in turn,
a product of the decay of uranium (23SU) (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
11-2 Reprinted from USGS Open-File Report 93-292
-------
T3
03
8
•o
o
ID
C3
en
•*-•
I
13
<*-,
o
S3 S
03 0)
±: u
00 -°
C M
.~ •<-5
s °
o c
JS D
to -o
(U -
Cf)
•a _a,
oo "«
SQ S
Eg
s S
CT3
2 s
•S .
4) ^>
-------
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
».ra^ks upon drying, thus increasing the soil's1 permeability to gas flow during c ier 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 o-f 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'* meters), or about 2x10'" inches—this is known as alpha
recoil (Tanner, 1980). Moisture in the soil lessens the chance of a recoiling radon atom
becoming imbedded in an adjacent grain. Because water is more dense than air, a radon atom
will travel a shorter distance in a water-filled pore than in an air-filled pore, thus increasing
the likelihood that the radon atom will remain in the pore space. Intermediate moisture levels
enhance radon emanation but do not significantly affect permeability. However, high
moisture levels can significantly decrease the gas permeability of the soil and impede radon
movement through the soil.
Concentrations of radon in soils are generally many times higher than those inside of
buildings, ranging from tens of pCi/L to more than 100,000 pCi/L, but typically in the range
of hundreds to low thousands of pCi/L. Soil-gas radon concentrations can vary in response to
variations in climate and weather on hourly, daily, or seasonal time scales. Schumann and
others (1992) and Rose and others (1988) recorded order-of-magnitude variations in soil-gas
radon concentrations between seasons in Colorado and Pennsylvania. The most important
factors appear to be (1) soil moisture conditions, which are controlled in large part by
precipitation; (2) barometric pressure; and (3) temperature. Washington and Rose (1990)
suggest that temperature-controlled partitioning of radon between water and gas in soil pores
also has a significant influence on the amount of mobile radon in soil gas.
Homes in hilly limestone regions of the southern Appalachians were found to have higher
indoor radon concentrations during the summer than in the winter. A suggested cause for this
phenomenon involves temperature/pressure-driven flow of radon-laden air from subsurface
II-4 Reprinted from USGS Open-File Report 93-292
-------
solution cavities in the carbonate rock into houses. As warm air enters solution cavities that
are higher on the hillslope than the homes, it cools and settles, pushing radon-laden air from
lower in the cave or cavity system into structures on the hillslope (Gammage and others,
1993). In contrast, homes built over caves having openings situated below the level of the
home had higher indoor radon levels in the winter, caused by cooler outside air entering the
cave, driving radon-laden air into cracks and solution cavities in the rock and soil, and
ultimately, into homes (Gammage and others, 1993).
RADON ENTRY INTO BUILDINGS
A driving force (reduced atmospheric pressure in the house relative to the soil, producing
a pressure gradient) and entry points must exist for radon to enter a building from the soil.
The negative pressure caused by furnace combustion, ventilation devices, and the stack effect
(the rising and escape of warm air from the upper floors of the building, causing a
temperature and pressure gradient within the structure) during cold winter months are
common driving forces. Cracks and other penetrations through building foundations, sump
holes, and slab-to-foundation wall joints are common entry points.
Radon levels in the basement are generally higher than those on the main floor or upper
floors of most structures. Homes with basements generally provide more entry points for
radon, commonly have a more pronounced stack effect, and typically have lower air pressure
relative to the surrounding soil than nonbasement homes. The term "nonbasement" applies to
slab-on-grade or crawl space construction.
METHODS AND SOURCES OF DATA
The assessments of radon potential in the booklets that follow this introduction were
made using five main types of data: (1) geologic (lithologic); (2) aerial radiometric; (3) soil
characteristics, including soil moisture, permeability, and drainage characteristics; (4) indoor
radon data; and (5) building architecture (specifically, whether homes in each area are built
slab-on-grade or have a basement or crawl space). These five factors were evaluated and
integrated to produce estimates of radon potential. Field measurements of soil-gas radon or
soil radioactivity were not used except where such data were available in existing, published
reports of local field studies. Where applicable, such field studies are described in the
individual state chapters.
GEOLOGIC DATA
The types and distribution of lithologic units and other geologic features in an
assessment area are of primary importance in determining radon potential. Rock types that
are most likely to cause indoor radon problems include carbonaceous black shales, glaucomte-
bearing sandstones, certain kinds of fluvial sandstones and fluvial sediments, phosphorites,
chalk, karst-producing carbonate rocks, certain kinds of glacial deposits, bauxite, uranium-rich
granitic rocks, metamorphic rocks of granitic composition, silica-rich volcanic rocks, many
sheared or faulted rocks, some coals, and certain kinds of contact metamorphosed rocks.
Rock types least likely to cause radon problems include marine quartz sands, non-
carbonaceous shales and siltstones, certain kinds of clays, silica-poor metamorphic and
II-5 Reprinted from USGS Open-File Report 93-292
-------
igneous rocks, and basalts. Exceptions exist within these general lithologic groups because of
the occurrence of localized uranium deposits, commonly of the hydrothermal type in
crystalline rocks or the "roll-front" type in sedimentary rocks. Uranium and radium are
commonly sited in heavy minerals, iron-oxide coatings on rock and soil grains, and organic
materials in soils and sediments. Less common a/e uranium associated with phosphate and
carbonate complexes in rocks and soils, and uranium minerals.
Although many cases of elevated indoor radon levels can be traced to high radium and
(or) uranium concentrations in parent rocks, some structural features, most notably faults and
shear zones, have been identified as sites of localized uranium concentrations (Deffeyes and
MacGregor, 1980) and have been associated with some of the highest reported indoor radon
levels (Gundersen, 1991). The two highest known indoor radon occurrences are associated
with sheared fault zones in Boyertown, Pennsylvania (Gundersen and others, 1988a; Smith
and others, 1987), and in Clinton, New Jersey (Henry and others, 1991; Muessig and Bell,
1988).
NURE AERIAL RADIOMETRIC DATA
Aerial radiometric data are used to quantify the radioactivity of rocks and soils.
Equivalent uranium (eU) data provide an estimate of the surficial concentrations of radon
parent materials (uranium, radium) in rocks and soils. Equivalent uranium is calculated from
the counts received by a gamma-ray detector from the 1.76 MeV (mega-electron volts)
emission energy corresponding to bismuth-214 (2HBi), with the assumption that uranium and
its decay products are in secular equilibrium. Equivalent uranium is expressed in units of
parts per million (ppm). Gamma radioactivity also may be expressed in terms of a radium
activity; 3 ppm eU corresponds to approximately 1 picocurie per gram (pCi/g) of radium-226.
Although radon is highly mobile in soil and its concentration is affected by meteorological
conditions (Kovach, 1945; 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
-------
FLICUT LINE SPACING OF NUKE AEKIAL SURVEYS
2 K« (1 i(ILE)
5 KU (3 MILES)
2 i- 5 KM
E3 10 111 (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 elJ 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
-------
Soil permeability is commonly expressed in SCS soil surveys in terms of the speed, in
inches per hour (in/hr), at which water soaks into the soil, as measured in-'a soil percolation
test. Although in/hr are not truly units of permeability, these units are in widespread use and
are referred to as "permeability" in SCS soil surveys. The permeabilities listed in the SCS
surveys are for water, but they generally correlate well with gas permeability. Because data
on gas permeability of soils is extremely limited, data on permeability to water is used as a
substitute except in cases in which excessive soil moisture is known to exist. Water in soil
pores inhibits gas transport, so the amount of radon available to a home is effectively reduced
by a high water table. Areas likely to have high water tables include river valleys, coastal
areas, and some areas overlain by deposits of glacial origin (for example, loess).
Soil permeabilities greater than 6.0 in/hr may be considered high, and permeabilities less
than 0.6 in/hr may be considered low in terms of soil-gas transport. Soils with low
permeability may generally be considered to have a lower radon potential than more
permeable soils with similar radium concentrations. Many well-developed soils contain a
clay-rich B horizon that may impede vertical soil gas transport. Radon generated below this
horizon cannot readily escape to the surface, so it would instead tend to move laterally,
especially under the influence of a negative pressure exerted by.a building.
Shrink-swell potential is an indicator of the abundance of smectitic (swelling) clays in a
soil. Soils with a high shrink-swell potential may cause building foundations to crack,
creating pathways for radon entry into the structure. During dry periods, desiccation cracks in
shrink-swell soils provide additional pathways for soil-gas transport and effectively increase
the gas permeability of the soil. Soil permeability data and soil profile data thus provide
important information for regional radon assessments.
INDOOR RADON DATA
Two major sources of indoor radon data were used. The first and largest source of data is
from the State/EPA Residential Radon Survey (Ronca-Battista and others, 1988; Dziuban and
others, 1990). Forty-two states completed EPA-sponsored indoor radon surveys between 1986
and 1992 (fig. 3). The State/EPA Residential Radon Surveys were designed to be
comprehensive and statistically significant at the state level, and were subjected to high levels
of quality assurance and control. The surveys collected screening indoor radon measurements,
defined as 2-7 day measurements using charcoal canister radon detectors placed in the lowest
livable area of the home. The target population for the surveys included owner-occupied
single family, detached housing units (White and others, 1989), although attached structures
such as duplexes, townhouses, or condominiums were included in some of the surveys if they
met the other criteria and had contact with the ground surface. Participants were selected
randomly from telephone-directory listings. In total, approximately 60,000 homes were tested
in the State/EPA surveys.
The second source of indoor radon data comes from residential surveys that have been
conducted in a specific state or region of the country (e.g. independent state surveys or utility
company surveys). Several states, including Delaware, Florida, Illinois, New Hampshire, New
Jersey, New York, Oregon, and Utah, have conducted their own surveys of indoor radon. The
quality and design of a state or other independent survey are discussed and referenced where
the data are used.
II-9 Reprinted from USGS Open-File Report 93-292
-------
u
ex
co
u
c
o
T3
w<
O
o
•c
c
-------
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
-------
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.
INCREASING RADON POTENTIAL
FACTOR
INDOOR RADON (average)
AERIAL RADIOACTIVITY
GEOLOGY*
SOIL PERMEABILITY
ARCHITECTURE TYPE
POINT VALUE
1
<2pCi/L
< 1.5 ppmeU
negative
low
mostly slab
2
2 - 4 pCi/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
FACTOR
INDOOR RADON DATA
AERIAL RADIOACTIVITY
GEOLOGIC DATA
SOIL PERMEABILITY
POINT VALUE
1
naKMBaBBCSHBBSKSSS
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
-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
Held 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
-------
REFERENCES CITED
Akerblom, G., Anderson, P., and Clavensjo, B., 1984, Soil gas radon-A source for indoor radon
daughters: Radiation Protection Dosimetry, v. 7, p. 49-54.
Deffeyes, K.S., and MacGregor, I.D., 1980, World uranium resources: Scientific American,
v. 242, p. 66-76.
Durrance, E.M., 1986, Radioactivity in geology: Principles and applications: New York, N.Y.,
Wiley and Sons, 441 p.
Duval, J.S., 1989, Radioactivity and some of its applications in geology: Proceedings of the
symposium on the application of geophysics to engineering and environmental problems
(SAGEEP), Golden, Colorado, March 13-16, 1989: Society of Engineering and Mineral
Exploration Geophysicists, p. 1-61.
Duval, J.S., Cook, E.G., and Adams, J.A.S., 1971, Circle of investigation of an airborne
gamma-ray spectrometer: Journal of Geophysical Research, v. 76, p. 8466-8470.
Duval, J.S., Jones, W.J., Riggle, F.R., and Pitkin, J.A., 1989, Equivalent uranium map of
conterminous United States: U.S. Geological Survey Open-File Report 89-478,10 p.
Duval, J.S., Reimer, G.M., Schumann, R.R., Owen, D.E., and Otton, J.K., 1990, Soil-gas
radon compared to aerial and ground gamma-ray measurements at study sites near Greeley
and Fort Collins, Colorado: U.S. Geological Survey Open-File Report 90-648,42 p.
Dziuban, J.A., Clifford, M.A., White, S.B., Bergstein, J.W., and Alexander, B.V., 1990,
Residential radon survey of twenty-three States, in Proceedings of the 1990 International
Symposium on Radon and Radon Reduction Technology, Vol. JH: Preprints: U.S.
Environmental Protection Agency report EPA/600/9-90/005c, Paper IV-2,17 p.
Gammage, R.B., Wilson, D.L., Saultz, R.J., and Bauer, B.C., 1993, Subtereanean transport of
radon and elevated indoor radon in hilly karst terranes: Atmospheric Environment
(in press).
Gundersen, L.C.S., Reimer, G.M., and Agard, S.S., 1988a, Correlation between geology, radon
in soil gas, and indoor radon in the Reading Prong, in Marikos, M. A., and Hansman,
R.H., eds., Geologic causes of natural radionuclide anomalies: Missouri Department of
Natural Resources Special Publication 4, p. 91-102.
Gundersen, L.C.S, Reimer, G.M., Wiggs, C.R., and Rice, C.A., 1988b, Map showing radon
potential of rocks and soils in Montgomery County, Maryland: U.S. Geological Survey
Miscellaneous Field Studies Map MF-2043, scale 1:62,500.
Gundersen, Linda C.S., 1991, Radon in sheared metamorphic and igneous rocks, in Gundersen,
Linda C.S., and Richard B. Wanty, eds., Field studies of radon in rocks, soils, and water:
U.S. Geol. Survey Bulletin no. 1971, p. 39-50.
JJ-17 Reprinted from USGS Open-File Report 93-292
-------
Henry, Mitchell E., Kaeding, Margret E., and Monteverde, Donald, 1991, Radon in soil gas and
gamma-ray activity of rocks and soils at the Mulligan Quarry, Clinton, New Jersey, in
Gundersen, Linda C.S., and Richard B. Wanty, eds., Field studies of radon in rocks,
soils, and water: U.S. Geol. Sur-ey Bulletin no. 1971, p. 65-75.
Klusman, R. W., and Jaacks, J. A., 1987, Environmental influences upon mercury, radon, and
helium concentrations in soil gases at a site near Denver, Colorado: Journal of
Geochemical Exploration, v. 27, p. 259-280.
Kovach, E.M., 1945, Meteorological influences upon the radon content of soil gas: Transactions,
American Geophysical Union, v. 26, p. 241-248.
Kunz, C., Laymon, C.A., and Parker, C, 1989, Gravelly soils and indoor radon, in Osborne,
M.C., and Harrison, J., eds., Proceedings of the 1988 EPA Symposium on Radon and
Radon Reduction Technology, Volume 1: U.S. Environmental Protection Agency Report
EPA/600/9-89/006A, p. 5-75-5-86.
Muessig, K., and Bell, C., 1988, Use of airborne radiometric data to direct testing for elevated
indoor radon: Northeastern Environmental Science, v. 7, no. 1, p. 45-51.
Ronca-Battista, M., Moon, M., Bergsten, J., White, S.B., Holt, N., and Alexander, B., 1988,
Radon-222 concentrations in the United States-Results of sample surveys in five states:
Radiation Protection Dosimetry, v. 24, p. 307-312.
Rose, A.W., Washington, J.W., and Greeman, D.J., 1988, Variability of radon with depth and
season in a central Pennsylvania soil developed on limestone: Northeastern Environmental
Science, v. 7, p. 35-39.
Schery, S.D., Gaeddert, D.H., and Wilkening, M.H., 1984, Factors affecting exhalation of radon
from a gravelly sandy loam: Journal of Geophysical Research, v. 89, p. 7299-7309.
Schumann, R.R., and Owen, D.E., 1988, Relationships between geology, equivalent uranium
concentration, and radon in soil gas, Fairfax County, Virginia: U.S. Geological Survey
Open-File Report 88-18,28 p.
Schumann, R.R., and Gundersen, L.C.S., 1991, Regional differences in radon emanation
coefficients in soils: Geological Society of America Abstracts With Programs, v. 23,
no. 1, p. 125.
Schumann, R.R., Peake, R.T., Schmidt, K.M., and Owen, D.E., 1991, Correlations of soil-gas
and indoor radon with geology in glacially derived soils of the northern Great Plains, in
Proceedings of the 1990 International Symposium on Radon and Radon Reduction
Technology, Volume 2, Symposium Oral Papers: U.S. Environmental Protection Agency
report EPA/600/9-9 l/026b, p. 6-23-6-36.
n-18 Reprinted from USGS Open-File Report 93-292
-------
Schumann, R.R., Owen, D.E., and Asher-Bolinder, S., 1992, Effects of weather and soil
characteristics on temporal variations in soil-gas radon concentrations, in Gates, A.E., and
Gundersen, L.C.S., eds., Geologic controls on radon: Geological Society of America
Special Paper 271, p. 65-72.
Sextro, R.G., Moed, B.A., Nazaroff, .W.W., Revzan, K.L., and Nero, A.V., 1987,
Investigations of soil as a source of indoor radon, in Hopke, P.K., ed., Radon and its
decay products: American Chemical Society Symposium Series 331, p. 10-29.
Sterling, R., Meixel, G., Shen, L., Labs, K., and Bligh, T., 1985, Assessment of the energy
savings potential of building foundations research: Oak Ridge, Tenn., U.S. Department of
Energy Report ORNL/SUB/84-0024/1.
Smith, R.C., II, Reilly, M.A., Rose, A.W., Barnes, J.H., and Berkheiser, S.W., Jr., 1987,
Radon: a profound case: Pennsylvania Geology, v. 18, p. 1-7.
Tanner, A.B., 1964, Radon migration in the ground: a review, in Adams, J. A.S., and Lowder,
W.M., eds., The natural radiation environment: Chicago, HI., University of Chicago
Press, p. 161-190.
Tanner, A.B., 1980, Radon migration in the ground: a supplementary review, in Gesell, T.F.,
and Lowder, W.M. (eds), Natural radiation environment HI, Symposium proceedings,
Houston, Texas, v. 1, p. 5-56.
U.S. Department of Agriculture, 1987, Principal kinds of soils: Orders, suborders, and great
groups: U.S. Geological Survey, National Atlas of the United States of America, sheet
38077-BE-NA-07M-00, scale 1:7,500,000.
U.S. Department of Energy, 1976, National Uranium Resource Evaluation preliminary report,
prepared by the U.S. Energy Research and Development Administration, Grand Junction,
Colo.: GJO-11(76).
Wanty, Richard B., and Schoen, Robert, 1991, A review of the chemical processes affecting the
mobility of radionuclides in natural waters, with applications, in Gundersen, Linda C.S.,
and Richard B. Wanty, eds., Field studies of radon in rocks, soils, and water: U.S.
Geological Survey Bulletin no. 1971, p. 183-194.
Washington, J.W., and Rose, A.W., 1990, Regional and temporal relations of radon in soil gas to
soil temperature and moisture: Geophysical Research Letters, v. 17, p. 829-832.
White, S.B., Bergsten, J.W., Alexander, B.V., and Ronca-Battista, M., 1989, Multi-State
surveys of indoor 222Rn: Health Physics, v. 57, p. 891-896.
H-19 Reprinted from 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 pCi/L.
Bq/m3 (Becquerels per cubic meter)- a metric unit of radioactivity used to describe radon
concentrations in a volume of air. One becquerel is equal to one radioactive disintegration per
second. One pCi/L is equal to 37 Bq/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 tn 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 metamornhic rock consisting mainly of pyroxenes and(or) amphibole and
plagioclase.
H-21 Reprinted from USGS Open-File Report 93-292
-------
argillite, argillaceous Terms referring to a rock derived from clay or shale, or any sedimentary
rock containing an appreciable amount of clay-size material, 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 fitom USGS Open-FUe 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
n-23 Reprinted ftom 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 diviued, the others oeing sedimentary and
metamorphic.
inter-montane 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
subbiruminous coal.
limestone A carbonate sedimentary rock consisting of more than 50% calcium carbonate,
primarily in the form of the mineral calcite (CaCOs).
lithology The description of rocks in hand specimen and in outcrop on the basis of color,
composition, and grain size.
loam A permeable soil composed of a mixture of relatively equal parts clay, silt, and sand, and
usually containing some organic matter.
loess A fine-grained eolian deposit composed of silt-sized particles generally thought to have
been deposited from windblown dust of Pleistocene age.
mafic Term describing an igneous rock containing more than 50% dark-colored minerals.
marine Term describing sediments deposited in the ocean, or precipitated from ocean waters.
metamorphic Any rock derived from pre-existing rocks by mineralogical, chemical, or structural
changes in response to changes in temperature, pressure, stress, and the chemical environment.
Phyllite, schist, amphibolite, and gneiss are metamorphic rocks.
moraine A mound, ridge, or other distinct accumulation of unsorted, unbedded glacial material,
predominantly till, deposited by the action of glacial ice.
outcrop That part of a geologic formation or structure that appears at the surface of the Earth, as
in "rock outcrop".
percolation test A term used in engineering for a test to determine the water permeability of a
soil. A hole is dug and filled with water and the rate of water level decline is measured.
permeability The capacity of a rock, sediment, or soil to transmit liquid or gas.
phosphate, phosphatic, phosphorite Arty rock or sediment containing a significant amount
of phosphate minerals, i.e., minerals containing PCU.
n-24 Reprinted from USGS Open-File Report 93-292
-------
physiographic province A region in which all parts are similar in geologic structure and
climate, which has had a uniform geomorphic history, and whose topography or landforms differ
significantly from adjacent regions.
placer deposit See heavy minerals
residual Formed by weathering of a material in place.
residuum Deposit of residual material.
rhyolite An extrusive igneous rock of volcanic origin, compositionally equivalent to granite.
sandstone A clastic sedimentary rock composed of sand-sized rock and mineral material that is
more or less firmly cemented. Sand particles range from 1/16 to 2 mm in size.
schist A strongly foliated crystalline rock, formed by 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.
H-25 Reprinted from USGS Open-File Report 93-292
-------
terrace gravel Gravel-sized material that caps ridges and terraces, left behifid by a stream as it
cuts down to a lower level.
terrain A tract or region of the Earth's surface considered as a physical feature or an ecological
environment.
till Unsorted, generally unconsolidated and unbedded rock and mineral material deposited directly
adjacent to and underneath a glacier, without reworking by meltwater. Size of grains varies greatly
from clay to boulders.
uraniferous Containing uranium, usually more than 2 ppm.
vendor data Used in this report to refer to indoor radon data collected and measured by
commercial vendors of radon measurement devices and/or services.
volcanic Pertaining to the activities, structures, and extrusive rock types of a volcano.
water table The surface forming the boundary between the zone of saturation and the zone of
aeration; the top surface of a body of unconfined groundwater in rock or soil.
weathering The destructive process by which earth and rock materials, on exposure to
atmospheric elements, are changed in color, texture, composition, firmness, or form with little or
no transport of the material.
H-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
11-27 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
Alaska Charles Tedford
Department of Health and Social
Services
P.O. Box 110613
Juneau.AK 99811-0613
(907)465-3019
1-800-478-4845 in state
Arizona John Stewart
Arizona Radiation Regulatory Agency
4814 South 40th St.
Phoenix, AZ 85040
(602)255-4845
Arkansas Lee Gershner
Division of Radiation Control
Department of Health
4815 Markham Street, Slot 30
Little Rock, AR 72205-3867
(501) 661-2301
California J. David Quinton
Department of Health Services
714 P Street, Room 600
Sacramento, CA 94234-7320
(916) 324-2208
1-800-745-7236 in state
Colorado Linda Martin
Department of Health
4210 East llth Avenue
Denver, CO 80220
(303) 692-3057
1-800-846-3986 in state
Connecticut Alan J. Siniscalchi
Radon Program
Connecticut Department of Health
Services
150 Washington Street
Hartford, CT 06106-4474
(203)566-3122
Delaware Marai G. Rejai
Office of Radiation Control
Division of Public Health
P.O. Box 637
Dover, DE 19903
(302) 736-3028
1-800-554-4636 In State
District Robert Davis
of Columbia DC Department of Consumer and
Regulatory Affairs
614 H Street NW
Room 1014
Washington, DC 20001
(202) 727-71068
Florida N. Michael Gilley
Office of Radiation Control
Department of Health and
Rehabilitative Services
1317 Winewood Boulevard
Tallahassee, 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
Kansas
Kentucky
Pat McGavarn
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. Hater
Bureau of Radiological Health
Iowa Department of Public Health
Lucas State Office Building
Des Moines, IA 50319-0075
(515) 281-3478
1-800-383-5992 In State
Harold Spiker
Radiation Control Program
Kansas Department of Health and
Environment
109 SW 9th Street
6th Floor Mills Building
Topeka, KS 66612
(913) 296-1561
JeanaPhelps
Radiation Control Branch
Department of Health Services
Cabinet for Human Resources
275 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 Bob Stilwell
Division of Health Engineering
Department of Human Services
State House, Station 10
Augusta, ME 04333
(207)289-5676
1-800-232-0842 in state
Maryland Leon J. Rachuba
Radiological Health Program
Maryland Department of the
Environment
2500 Broening Highway
Baltimore, MD 21224
(410) 631-3301
1-800-872-3666 In State
Massachusetts William J. Bell
Radiation Control Program
Department of Public Health
23 Service Center
Northampton, MA 01060
(413) 586-7525
1-800-445-1255 in state
Michigan Sue Hendershott
Division of Radiological Health
Bureau of Environmental and
Occupational Health
3423 North Logan Street
P.O. Box 30195
Lansing, MI 48909
(517) 335-8194
Minnesota Laura Oatmann
Indoor Air Quality Unit
925 Delaware Street, SE
P.O. Box 59040
Minneapolis, MN 55459-0040
(612) 627-5480
1-800-798-9050 in state
n-29 Reprinted from USGS Open-File Report 93-292
-------
Mississippi Silas Anderson
Division of Radiological Health
Department of Health
3150 Lawson Street
P.O. Box 1700
Jackson, MS 39215-1700
(601) 354-6657
1-800-626-7739 in state
Missouri Kenneth V. Miller
Bureau of Radiological Health
Missouri Department of Health
1730 East Elm
P.O. Box 570
Jefferson City, MO 65102
(314)751-6083
1-800-669-7236 In State
Montana Adrian C. Howe
Occupational Health Bureau
Montana Department of Health and
Environmental Sciences
Cogswell Building A113
Helena, MT 59620
(406)444-3671
Nebraska Joseph Milone
Division of Radiological Health
Nebraska Department of Health
301 Centennial Mall, South
P.O. Box 95007
Lincoln, NE 68509
(402)471-2168
1-800-334-9491 In State
Nevada Stan Marshall
Department of Human Resources
505 East King Street
Room 203
Carson City, NV 89710
(702) 687-5394
New Hampshire David Chase
Bureau of Radiological Health
Division of Public Health Services
Health and Welfare Building
SixHazen Drive
Concord, NH 03301
(603)271-4674
1-800-852-3345 x4674
New Jersey Tonalee Carlson Key
Division of Environmental Quality
Department of Environmental
Protection
CN415
Trenton, NJ 08625-0145
(609) 987-6369
1-800-648-0394 in state
New Mexico William M. Floyd
Radiation Licensing and Registration
Section
New Mexico Environmental
Improvement Division
1190 St. Francis Drive
Santa Fe,NM 87503
(505) 827-4300
New York William J. Condon
Bureau of Environmental Radiation
Protection
New York State Health Department
Two University Place
Albany, NY 12202
(518)458-6495
1-800-458-1158 in state
North Carolina Dr. Felix Fong
Radiation Protection Division
Department of Environmental Health
and Natural Resources
701 Barbour Drive
Raleigh, NC 27603-2008
(919) 57W141
1-800-662-7301 (recorded info x4196)
North Dakota Arlen Jacobson
North Dakota Department of Health
1200 Missouri Avenue, Room 304
P.O. Box 5520
Bismarck, ND 58502-5520
(701)221-5188
Ohio Marcie Matthews
Radiological Health Program
Department of Health
1224 Kinnear Road - Suite 120
Columbus, OH 43212
(614) 644-2727
1-800-523-4439 in state
11-30 Reprinted from USGS Open-File Report 93-292
-------
Oklahoma Gene Smith
Radiation Protection Division
Oklahoma State Department of
Health
P.O. Box 53551
Oklahoma City, OK 73152
(405) 271-5221
Oregon George Toombs
Department of Human Resources
Health Division
1400 SW 5th Avenue
Portland, OR 97201
(503) 731-4014
Pennsylvania 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
Puerto Rico David Saldana
Radiological Health Division
G.P.O. Call Box 70184
Rio Piedras, Puerto Rico 00936
(809) 767-3563
Rhqde Island Edmund Arcand
Division of Occupational Health and
Radiation
Department of Health
205 Cannon Building
Davis Street
Providence, RI02908
(401)277-2438
South Carolina
Bureau of Radiological Health
Department of Health and
Environmental Control
2600 Bull Street
Columbia, SC 29201
(803)734^631
1-800-768-0362
South Dakota MikePochop •
Division of Environment Regulation
Department of Water and Natural
Resources
Joe Fo; 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 andRadiological Health
Division
Vermont Department of Health
10 Baldwin Street
Montpelier, VT 05602
(802) 828-2886
1-800-640-0601 in state
Virgin Islands Contact the U.S. Environmental
Protection Agency, Region n
in New York
(212)264-4110
n-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 KateColeman
Department of Health
Office of Radiation Protection
Airdustrial Building 5, LE-13
Olympic WA 98504
(206)753-4518
1-800-323-9727 In State
West Virginia Beattie L. DeBord
Industrial Hygiene Division
West Virginia Department of Health
151 llth Avenue
South Charleston, WV 25303
(304) 558-3526
1-800-922-1255 In State
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
H-32 Reprinted from USGS Open-FUe Report 93-292
-------
STATE GEOLOGICAL SURVEYS
May, 1993
Alabama Ernest A. Mancini
Geological Survey of Alabama
P.O. Box 0
420 Hackberry Lane
Tuscaloosa, AL 35486-9780
(205) 349-2852
Alaska Thomas E. Smith
Alaska Division of Geological &
Geophysical Surveys
794 University Ave., Suite 200
Fairbanks, AK 99709-3645
(907)479-7147
Arizona . Larry D. Fellows
Arizona Geological Survey
845 North Park Ave., Suite 100
Tucson, AZ 85719
(602) 882-4795
Arkansas Norman F. Williams
Arkansas Geological Commission
Vardelle Parham Geology Center
3815 West Roosevelt Rd.
Little Rock, AR 72204
(501) 324-9165
California James F. Davis
California Division of Mines &
Geology
801 K Street, MS 12-30
Sacramento, CA 95814-3531
(916)445-1923
Colorado Pat Rogers (Acting)
Colorado Geological Survey
1313 Sherman St., Rm 715
Denver, CO 80203
(303)866-2611
Connecticut Richard C. Hyde
Connecticut Geological & Natural
History Survey
165 Capitol Ave., Rm. 553
Hartford, CT 06106
(203) 566-3540
Delaware Robert R. Jordan
Delaware Geological Survey
University of Delaware
101 Penny Hall
Newark, DE 19716-7501
(302) 331-2833
Florida Walter Schmidt
Florida Geological Survey
903 W. Tennessee St.
Tallahassee, FL 32304-7700
(904)488-4191
William H. McLemore
Georgia Geologic Survey
Rm. 400
19 Martin Luther King Jr. Dr. SW
Atlanta, GA 30334
(404) 656-3214
Hawaii Manabu Tagomori
Dept. of Land and Natural Resources
Division of Water & Land Mgt
P.O. Box 373
Honolulu, ffl 96809
(808) 548-7539
Idaho Earl H. Bennett
Idaho Geological Survey
University of Idaho
Morrill Hall, Rm. 332
Moscow, ID 83843
(208) 885-7991
Illinois Morris W. Leighton
Illinois State Geological Survey
Natural Resources Building
615 East Peabody Dr.
Champaign, EL 61820
(217) 333-4747
Indiana Norman C. Hester
Indiana Geological Survey
611 North Walnut Grove
Bloomington, IN 47405
(812) 855-9350
Iowa Donald L.Koch
Iowa Department of Natural Resources
Geological Survey Bureau
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
n-33 Reprinted from USGS Open-File Report 93-292
-------
Kentucky Donald C. Haney
Kentucky Geological Survey
University of Kentucky
228 Mining & Mineral Resources
Building
Lexington, KY 40506-0107
(606) 257-5500
Louisiana William E. Marsalis
Louisiana Geological Survey
P.O. Box 2827
University Station
Baton Rouge, LA 70821-2827
(504) 388-5320
Maine Walter A. Anderson
Maine Geological Survey
Department of Conservation
State House, Station 22
Augusta, ME 04333
(207)289-2801
Maryland Emery T. Cleaves
Maryland Geological Survey
2300 St. Paul Street
Baltimore, MD 21218-5210
(410) 554-5500
Massachusetts Joseph A. Sinnott
Massachusetts Office of
Environmental Affairs
100 Cambridge St., Room 2000
Boston, MA 02202
(617) 727-9800
Michigan R. Thomas Segall
Michigan Geological Survey Division
Box 30256
Lansing, MI 48909
(517)334-6923
Minnesota Priscilla C. Grew
Minnesota Geological Survey
2642 University Ave.
St. Paul, MN 55114-1057
(612) 627-4780
Mississippi S. Cragin Knox
Mississippi Office of Geology
P.O. Box 20307
Jackson, MS 39289-1307
(601) 961-5500
Missouri James H. Williams
Missouri Division of Geology &
Land Survey
111 Fairgrounds Road
P.O. Box 250
Rolla, MO 65401
(314) 368-2100
Montana Edward T. Ruppel
Montana Bureau of Mines & Geology
Montana College of Mineral Science
and Technology, Main Hall
Butte, MT 59701
(406)496-4180
Nebraska Perry B. Wigley
Nebraska Conservation & Survey
Division
113 Nebraska Hall
University of Nebraska
Lincoln, NE 68588-0517
(402)472-2410
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
-------
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
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
DepL 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 Ramdn M. Alonso
Puerto Rico Geological Survey
Division
Box 5887
Puerta de Tierra Station
San Juan, P.R. 00906
(809) 722-2526
Rhode Island J. Allan Cain
Department of Geology
University of Rhode Island
315 Green Hall
Kingston, RI02881
(401) 792-2265
South Carolina Alan-Jon W. Zupan (Acting)
» South Carolina Geological Survey
5 Geology Road
Columbia, SC 29210-9998
(803) 737-9440
South Dakota C.M. Christensen (Acting)
South Dakota Geological Survey
Science Center
University of South Dakota
Vermillion, SD 57069-2390
(605) 677-5227
Tennessee Edward T.Luther
Tennessee Division of Geology
13th Floor, L & C Tower
401 Church Street
Nashville, TN 37243-0445
(615) 532-1500
Texas William L. Fisher
Texas Bureau of Economic Geology
University of Texas
University Station, Box X
Austin, TX 78713-7508
(512)471-7721
Utah M. Lee Allison
Utah Geological & Mineral Survey
2363 S. Foothill Dr.
Salt Lake City, UT 84109-1491
(801)467-7970
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
-------
West Virginia Larry D. Wopdfoik
West Virginia Geological and
Economic Survey
Mont Chateau Research Center
P.O. Box 879
Morgantown,WV 26507-0879
(304)594-2331
Wisconsin James Robertson
Wisconsin Geological & Natural
History Survey
3817 Mineral Point Road
Madison, WI 53705-5100
(608) 263-7384
Wyoming Gary B. Glass
Geological Survey of Wyoming
University of Wyoming
Box 3008, University Station
Laramie, WY 82071-3008
(307)766-2286
H-36 Reprinted fiom USGS Open-File Report 93-292
-------
EPA REGION 1 GEOLOGIC RADON POTENTIAL SUMMARY
by
Linda C.S. Gundersen, R. Randall Schumann, and Sandra L. Szarzi
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
-------
LAKE
CHAMPLAIN
23'
Figure 1. Geologic radon potential areas of EPA Region 1. 1.5-Melange; 2-Seboomook Formation;
3-Metasedimentary rocks, predominantly carbonates; 4-Granite and high-grade metamorphic rocks; 6,7, 8,11-Glacial
lake clay, marine clay; 9,10-Penobscot Formation, granites, and minor metamorphic rocks; 12-Boundary Mountains
Terrane; 13-Gander Terrane; 14-Avalonian Composite Terrane; 15-Northeastern Highlands; 16-Vermont Piedmont;
17-Green Mountains; 18-Champlain Lowland; 19-Vermont Valley; 20,21-Taconic Mountains-Stockbridge Valley;
22-Berkshire Mountains; 23-Proto-North American Terrane; 24,25-Taconic Allochthons; 26-Connecticut Valley
Synclinorium; 27—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-Esmond-
Dedham Terrane; 41-Newbury Basin volcanics; 42-Cape Ann and Peabody plutons; 43-Boston Basin;
45-Narrangansett Basin; 47-Coastal Plain.
-------
Bsmt. & 1st Floor Rn
Average Concentration (pCi/L)
0.0 to 1.9
2.0 to 4.0
4.1 to 6.0
3 B3 6.1 to 9.1
1 D Missing Data
100 Miles
Figure 2. Average screening indoor radon levels, by county, for EPA Region 1. Data are from
2-7 day charcoal canister tests. Data from the EPA/State Residential Radon Survey, except for
New Hampshire data, which are from the New Hampshire Division of Public Health Services
radon survey. Histograms in map legend show the number of counties in each category.
-------
GEOLOGIC RADON POTENTIAL
I | LOW(<2pCi/L)
E51 MODERATE/VARIABLE (2-4 pCi/L)
HIGH (>4 pCi/L)
Figure 3. Geologic radon potential areas of EPA Region 1. For more detail, refer to individual
state radon potential chapters.
-------
southern part of the Connecticut Valley Synclinorium and are associated with the high radioactivity
and with elevated indoor radon. The Nondwaug Granite and the Scranton Member of the Taine
Mountain Formation are also associated with high aeroradioactivity and elevated indoor radon
levels. Graphitic schist and ph) llites may I .he cause " levated indc': radon levels associated
with the Wepawaug Schist. Soils are derived from the rocks and overlying tills and have low to
moderate permeability. Indoor radon averages 3.5 pCi/L in the Connecticut Valley Synclinorium.
Because many of the rocks of this terrane have the potential to generate elevated radon levels, this
area is assigned a high geologic radon potential.
The Central Lowlands of Connecticut (29, fig. 1) are underlain by Triassic and Jurassic
sedimentary and volcanic rocks of the Newark Terrane. The average indoor radon in the Central
Lowlands was 1.6 pCi/L. Radioactivity in the Hartford and Pomperaug basins is generally low
and the soils have generally low to moderate permeability or are poorly drained. Overall, the
Central Lowlands have a low radon potential. However, localized uranium occurrences in the
upper New Haven Arkose, the middle Portland Formation, and possibly in the Shuttle Meadow,
East Berlin, and Portland Formations could generate locally elevated indoor radon levels, but they
are not expected to be common or widespread.
Rocks of the Bronson Hill Anticlinorium, in the Eastern Uplands of Connecticut (31,
fig. 1), include felsic and mafic schists and gneisses, quartzite, and granite gneiss. Radioactivity
in the Bronson Hill is moderate to locally high, and equivalent uranium anomalies in the central
part of the area appear to be associated with outcrops of granite gneiss. The soils have low to
moderate permeability with areas of locally high permeability. The Glastonbury granite gneiss and
graphitic schists in the Collins Hill Formation are likely to generate elevated indoor radon levels.
The Monson Gneiss, and schist and granofels of the Middletown Formation, also generate high
average indoor radon levels. Average indoor radon in the Bronson Hill Anticlinorium is
5.6 pCi/L, the highest among the geologic terranes of Connecticut. Overall, this area has a high
radon potential.
The Merrimack Synclinorium, in the central part of the Eastern Uplands (33, fig. 1), is
underlain by gneiss, schist, granofels, and quartzite that are intruded by granite gneiss, diorite, and
gabbro. The area has moderate to high radioactivity. Soils have low to high permeability but most
are in the low to moderate range. Indoor radon in the Merrimack Synclinorium averaged 2.7
pCi/L. The Canterbury granite gneiss, which occurs in several broad outcrop bands in the
northern and central parts of the area, appears to be associated with elevated radioactivity and with
moderate to high indoor radon levels. This area has moderate radon potential overall.
The Avalonian Terrane, along the eastern and southeastern borders of Connecticut (34, 35,
fig. 1), is underlain by granite, granite gneiss, mafic gneiss, and amphibolite. Granitic rocks
known to generate elevated indoor radon levels include the Waterford and Branford Gneisses, and
the Hope Valley Alaskite Gneiss, which also has a high aeroradioactivity signature, as well as
locally-occurring graphitic schist and gneiss in the Plainfield Formation. The overall radioactivity
signature of the area is moderate to high. Soils of the Avalonian Terrane have low to high
permeability, with granitic rocks producing sandy, more permeable soils, and mafic and volcanic
rocks producing silty and sandy soils with slowly permeable, clayey substrata. The indoor radon
average for this terrane is 3.3 pCi/L. Overall, this area has high radon potential.
m-5 Reprinted from USGS Open-File Report 93-292-A.
-------
MAINE
The rocks, surficial deposits, and geologic structures of Maine that are most likely to cause
Mg^ (>4 pCi/L) indoor radon concentrations include: r-o-mica granite alkaline anH 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-rriiea 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 (the part of area 4 in central
Maine). Indoor radon averages are high in the southwestern counties of Maine, which may be due
to the abundance of igneous plutons and high-grade metamorphic rocks in this area. Most of the
areas underlain by igneous plutonic rocks and associated glacial deposits have moderate to locally
high permeability.
Although there is no obvious anomalous radioactivity associated with major fault and shear
zones in Maine, evidence from other areas of the Appalachians suggests that shear zones can create
isolated occurrences of severe indoor radon, especially when they deform uranium-bearing rocks.
The radon potential of melange, most of which is found in the northwestern part of Maine (area 1
and a small part of area 5, fig. 1), is not well known, but gray to black phyllitic rocks and
deformed zones have the potential to produce at least moderate amounts of radon. We have
tentatively ranked these rocks as moderate or variable in radon potential.
The effect of glacial deposits is difficult to assess in Maine because most till is relatively
locally derived and is composed primarily of clasts of the surrounding bedrock. The areas of
coarse-grained glacial deposits in southwestern Maine and the kame and esker deposits scattered
throughout the State enhance the geologic radon potential due to their very high permeability; these
units have moderate to high radon potential. The coarser glacial deposits appear to be associated
with the igneous plutonic rocks and belts of calcareous and carbonate metasedimentary rocks.
Along the coast, areas of slowly permeable marine and glaciomarine clay (areas 7,8,11, fig. 1)
probably reduce the radon potential and they are assigned a low geologic radon potential. Glacial
lake sediments with low permeability in Penobscot County (6, fig. 1) appear to be associated with
low indoor radon. Till with compact, slowly permeable substrata is dominant in much of central
and northern Maine and the rocks underlying these areas are metasedimentary and metavolcanic
rocks that are generally low in uranium.
MASSACHUSETTS
The metamorphic rocks of the Taconic Mountains and carbonate sedimentary and
metasedimentary rocks of the Vermont-Stockbridge Valley, in westernmost Massachusetts
(area 21, fig. 1), have been ranked moderate in geologic radon potential. Graphitic phyllites and
schist of the Walloomsac Formation have moderate to high radioactivity associated with them and
may produce locally elevated indoor radon levels. Elevated radon may also be associated with fault
and shear zones, especially in the Taconic Mountains.
The Berkshire Mountains (area 22, fig. 1) have been ranked moderate overall in radon
potential. Granitic to dioritic gneiss and schist have generally low equivalent uranium associated
with them. Shear zones, pegmatites, and local accumulations of monazite in biotite schist and
gneiss may be sources of locally high indoor radon levels. Soil permeability is low to moderate.
Metamorphic rocks of the Connecticut Valley Belt, flanking the Mesozoic basins of west-
central Massachusetts (27,30, fig. 1), have been ranked moderate in radon potential.
Metasedimentary and metavolcanic gneisses and schists have generally low to moderate
radioactivity associated with them. Soils have generally moderate 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
throughout the area.
Mesozoic sedimentary and igneous rocks of the Connecticut Valley (28, fig. 1) have been
ranked moderate or variable in radon potential. Most of the sedimentary rocks have low radon
potential but locally high indoor radon levels may be associated with Jurassic-age black shales and
localized uranium deposits in fluvial sandstone and conglomerates. Geologic radon potential is
low to moderate in glacial lake-bottom sediments, and moderate to high in glaciofluvial deposits
including outwash, lacustrine delta deposits, and alluvium.
Granitic plutons of the Merrimack Belt, central Massachusetts (32, fig. 1), have been
ranked high in radon potential. The metasedimentary rocks surrounding the plutons are
predominantly phyllites and carbonaceous slates and schists with moderate to high radon potential.
Mafic metamorphic rocks, which are less common in the Merrimack Belt, have generally low to
moderate radon potential. Faults and shear zones may produce locally high radon concentrations.
Granitic plutonic rocks and metamorphic rocks of the Nashoba terrane (36, fig. 1), the
northward extention of the Avalonian terrane (37, fig. 1), and granites of the Cape Ann and
Peabody plutons, in northeastern Massachusetts (42, fig. 1), are ranked high in radon potential.
They are associated with moderate to high radioactivity and the soils developed on these rocks have
moderate to high permeability. Relationships between radon and underlying bedrock in eastern
Massachusetts, particularly in the Merrimack zone and in these areas, are less distinct, probably
due to the influence of glacial deposits that are made up of a mixture of the rock types underlying
eastern Massachusetts and areas to the north. The glacial deposits generally have enhanced
permeability and may have enhanced radon emanation due to the redistribution of rock
components, mixing, and grain-size reduction effects of the glacial processes. Volcanic rocks and
soils of the Newbury basin (41, fig. 1) are ranked moderate in radon potential.
The Esmond-Dedham terrane, southeastern Massachusetts (44,46, fig. 1), is ranked
moderate overall in geologic radon potential. This area includes a number of granite plutons and
fault zones that may generate high radon levels, as well as mafic metasedimentary and metavolcanic
rocks having low to moderate radon potential. Aeroradioactiviry 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 Oliverian domes have distinct radiometric highs associated with them except
for the northernmost and largest of the Oliverian rocks in the northern Gander Terrane, which have
low radioactivity. Indoor radon in the townships underlying this area is variable from low to high.
The Oliverian rocks and intermediate composition plutonic rocks are ranked moderate or variable in
geologic radon potential.
Two mica granites, calc-alkaline granites, and alkalic plutonic rocks in New Hampshire
have been ranked high in radon potential. Uranium content of these granites is commonly more
than 3 ppm and ranges to several hundreds of ppm. Two-mica granites occur throughout the
central and eastern portions of New Hampshire. Calc-alkaline granites occur from east-central to
northwestern New Hampshire. The largest body of calc-alkaline granite underlies the White
Mountains and has very high radioactivity associated with it. Indoor radon levels in several
townships in this area are high.
High radon concentrations in domestic water are associated with granites, pegmatites, and
faults in some parts of New Hampshire. The radon in these wells may be high enough to
contribute significantly to the radon content of the indoor air.
ffl-9 Reprinted from USGS Open-File Report 93-292-A
-------
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 4pCi/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
-------
VERMONT
The geologic radon potential of the Champlain Lowlands (area 18, fig. 1) is low, with
areas of locally moderate to high radon potential pc5^1 - 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-11 Reprinted from USGS Open-File Report 93-292-A
-------
-------
PRELIMINARY GEOLOGIC RADON POTENTIAL ASSESSMENT OF RHODE ISLAND
by
Linda C.S. Gund&rsen and R. Randall Schumann
U.S. Geological Survey
INTRODUCTION
This is a generalized assessment of geologic radon potential of rocks, soils, and surficial
deposits of Rhode Island. 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 Rhode Island (fig. 1) is in part a reflection of the underlying bedrock
(fig. 2) and surficial geology. All regions of Rhode Island were greatly altered by glaciation. The
western portion of the State has rolling hills with an elevation as high as 800 feet above sea level.
The remainder of the State is gently hilly to level. Rhode Island has four major physiographic
regions: the East Bay Coastal Area; the Narragansett Lowlands; the West Bay Coastal Area; and the
Western Rocky Upland. The Western Rocky Upland is underlain by igneous and metamorphic
rocks forming hills with elevations from 300 to 800 feet above sea level and local relief of several
hundred feet. Many of the hills are capped by glacial till. The West Bay Coastal Area includes
areas with elevations up to 200 feet above sea level, but is generally undulating to flat terrain
underlain by alluvial valley fill, stratified glacial deposits, and till. The Narragansett Lowlands
includes the till-covered islands of Narragansett Bay, with elevations up to 200 feet above sea
level. The East Bay Coastal Area is flat lying, with till cover and significant marshland.
In 1990, Rhode Island's population was 1,003,464, with 87 percent of the population
living in urban areas (fig. 3). The population density is approximately 819 per square mile. The
climate of Rhode Island is moderate, with an annual average temperature of 50° F and annual
precipitation of about 37 inches (fig. 4).
GEOLOGIC SETTING
Rhode Island is underlain by Proterozoic through Paleozoic igneous plutonic,
metasedimentary, and metavolcanic rocks (fig. 2). Geologic descriptions presented in the
following section are derived from Quinn (1971) and Hermes and others (in press) who have
recently remapped the bedrock geology of the State. The terminology used is from Hermes and
others (in press), however, much of the previous literature concerning radioactivity and uranium
IV-1 Reprinted from USGS Open-File Report 93-292-A
-------
Blackslone Valley &
Woonsockel Lowland
WOONASQUATUCKET
VALLEY
W-
Figure 1. Physiographic regions of Rhode Island (from Facts on File, 1984).
-------
Figure 2. Generalized bedrock geologic map of Rhode Island (from Hermes and others, in press).
-------
JURASSIC
TRJASSIC
GENERALIZED GEOLOGIC MAP OF RHODE ISLAND
EXPLANATION
AVALON TERRANE
CRETACEOUS |KrvJ Raritan Formation
monchiquite dike
diabase dike
s^ vein quartz
PERMIAN \~_
PENNSYLVANIAN NARRAGANSETT BAY GROUP (Narragansett Bay Region)
Narragansett Pier Plutonic Suite—fine grained to porhyritic granite, granite,
leucogranite
\\\\
\ \ \ \
MISSISSJPPIAN-
DEVONIAN
Dighton Conglomerate
Purgatory Conglomerate
Rhode Isalnd Formation
Wamsutta Formation
Sachuest Arkose
Pondville Conglomerate
metaclastic rocks undifferentiated
Alkali-feldspar granite of Cumberland
DEVONIAN ScrruATElGNEous SUITE (West-Central Rhode Island)
volcaniclastic rock
rhyolite
Scituate and associated granites
fine grained granite, alkali-feldspar granite, and granite
monzonite/monzodiorite
diorite/gabbro
ORDOVICIAN-
CAMBRIAN CoNANicurGROUP (Southern Narragansett Bay Region)
Dutch Island Harbor Formation
Fort Burnside and Jamestown Formations (includes small outcrop of
Cambrian Pirate Cove Formation in East Bay Area)
undifferentiated rock
*\j minettedike
-------
Generalized Geologic Map of Rhode Island-Continued
LATE HOPE VALUEYSUBTERRANE (Southwestern and northwestern Rhode Island)
PROTEROZOIC waterford Group
Ropes Ferry Gneiss
Mamacoke Formation
Plainfield Formation
Sterling Plutonic Series
[£r|£sM granite gneiss and alaskite gneiss
|^^ mafic/intermediate gneiss
ESMOND-DEDHAM SUBTERRANE-WESTfiAY AKEA
Cumberlandite
gabbro-diorite
ESMOND IGNEOUS SUITE
felsic volcaniclastic rocks
Esmond Granite, including fine-grained granite, granite, granodiorite,
augen granite gneiss, and granite gneiss
mafic/intermediate rock
Harmony Group (North-Central Rhode Island)
Woonasquatucket Fm.
Hznzj AbsalonaFm.
Nipsachuck Fm.
Blackstone Group
|QOOOO°| quartzite
^^H epidote and biotite schist
4 I greenstone, amphibolite, and serpentenite
undifferentiated rock
ESMOND-DEDHAM SUBTERRANE-EAST BAY AREA
Newport Group
Fort Adams Fromation
Newport Neck Formation (includes small outcrop of Cambro-Ordovician
East Passage Formation in East Bay Area)
Price Neck Formation
P ; '[ mica schist
DC^^^sa^s
Granites of Southeastern Rhode Island
granite
porphyritic granite
-------
POPULATION (1990)
0 to 50000
50001 to 100000
100001 to 250000
250001 to 500000
500001 to 596270
Figure 3. Population of counties in Rhode Island (1990 U.S. Census data).
-------
50"
w-
10
Figure 4. Average annual precipitation in Rhode Island (from Facts on File, 1984).
-------
occurrences in the State uses the terminology of Quinn (1971). An effort has been made to make
reference to the older terminology where appropriate.
The complicated igneous and metamorphic geology of Rhode Island falls within the Avalon
Terrane and is divided into the Hope Valley Subterrane and the Esmond-Dedham Subterrane.
These terrane designations will be referred to throughout the text.
The Hope Vallev Subterrane
The Hope Valley Subterrane includes the southwestern and northwestern corners of the
State. It is separated from the Esmond-Dedham Subterrane by the Hope Valley Shear Zone.
Rocks of the Hope Valley Subterrane include deformed and recrystallized rocks of the Late
Proterozoic-age Sterling Plutonic Group and stratified metamorphic rocks of Late Proterozoic or
older age. The Sterling Plutonic Group [formerly the Hope Valley Alaskite Gneiss of Quinn
(1971)] consists of light colored, quartz-feldspar alaskite gneiss with a strong lineation produced
by the alignment of minerals. Pink microcline-quartz gneiss crops out southwest of the main body
of alaskite and forms small bodies in northern parts of the alaskite outcrop area. Intermediate to
mafic layered gneiss occurs in the central part of the alaskite outcrop area. The stratified rocks to
the southwest of the main body of alaskite belong to the Waterford Group and consist of the Rope
Ferry Gneiss, a layered felsic gneiss; the Mamacoke Formation, a layered and foliated hornblende
amphibolite; and the Plainfield Formation, comprised of feldspar-quartz-biotite gneiss, schistose
gneiss, quartzite, mica schist, and calc-silicate rock. The Westerly Granite of Quinn (1971) and
Narragansett Pier Granite intrude the above units and occur as small intrusive dikes and irregular
bodies.
Esmond-Dedham Subterrane-West Bav Area
This terrane comprises a Late Proterozoic-age suite of granitic rocks that intrude older
metasedimentary and mafic metavolcanic rocks. Younger metasedimentary rocks overlie the entire
sequence.
Stratified metamorphic rocks of the Blackstone Group crop out in several parts of northern
Rhode Island. They are characterized by interlayered quartzite, epidote and biotite schist,
greenstone, amphibolite, and serpentinite. The Harmony Group crops out in north-central Rhode
Island and comprises the Absalona, the Woonasquatucket, and the Nipsachuck Formations. The
Absalona is a schistose, dark-colored, biotite gneiss and is the most extensive formation of the
Harmony Group. It is composed of several kinds of feldspar, quartz, biotite, and minor amounts
of muscovite, epidote, and hornblende. The Woonasquatucket Formation is chiefly light-colored
schist and gneiss with feldspar, quartz, muscovite, and biotite. It is not well foliated or layered.
The Nipsachuck Formation consists of light-colored, medium-grained gneiss with prominent
biotite streaks and foliation. It is made up of feldspar, quartz, biotite, and muscovite.
The Esmond Igneous Suite lies to the east of the Hope Valley Shear Zone and to the north
and south of the Scituate Igneous Suite. It is characterized by various calc-alkaline granites and
granitic gneiss, predominantly augen granite gneiss with lesser amounts of -granodiorite, granite
gneiss, fine grained granite, and intermediate to mafic rocks. Felsic volcaniclastic rocks also
occur. The Esmond Igneous Suite includes the Esmond and Dedham Granite, and the formerly
named Ponaganset Gneiss, the Grant Mills Granodiorite, the Tenrod Granite (Quinn, 1971) and
unnamed diorite, felsic gneiss, and gabbro.
The Scituate Igneous Suite underlies much of west-central Rhode Island. It comprises
several granites and alkaline granites of Devonian age that intrude the above-mentioned rock units.
' ' IV-8 Reprinted from USGS Open-File Report 93-292-A
-------
The Scituate Igneous Suite is predominantly a light-colored, medium- to coarse-grained granite
gneiss composed of feldspar, quartz, biotite, and minor hornblende and magnetite. Biotite occurs
in splotches with sphene, magnetite, zircon, allanite, ipidote, and apatite, which define a lineation
common to the granite. The formerly named Gowesett Granite (Quinn, 1971) crops out on the
eastern flank of the main body of Scituate and consists of pink, medium to coarse-grained granite.
A small body of felsic volcanic rocks, formerly named the Spencer Hill Volcanics (Quinn, 1971)
also crops out in this area. Mississippian alkali granite of the Cumberland, also known in part as
the Rhode Island Quincy Plutonic Suite of Quinn (1971) occurs as a small body of granite in the
northeastern corner of the State.
The Narragansett Bay Group underlies most of the Narragansett Lowlands and extends
north into Massachusetts. It is a complex, deformed sequence of Pennsylvanian sedimentary rocks
that form a series of basins known as the Narragansett (which underlies most of the Narragansett
Lowlands), the Woonsocket (in north-central Rhode Island near Woonsocket), and the North
Scituate basins. Rock units include the Dighton Conglomerate, Purgatory Conglomerate, Rhode
Island Formation, Wamsutta Formation, Sachuest Arkose, and the Pondville Conglomerate. The
Rhode Island Formation is the most extensive of these rock units and comprises fine- to coarse-
grained sandstone and lithic graywacke, black shale, conglomerate, minor meta-anthracite in the
Narragansett basin, and is metamorphosed and characterized by aluminosilicate schists and
conglomeratic schists in the other two basins. The Wamsutta Formation occurs in limited exposure
in the northeastern part of Rhode Island and it is characterized by red sandstone, lithic graywacke,
conglomerate, and shale. The Purgatory and Dighton Conglomerates have a scattered outcrop
pattern, occurring principally in the East Bay area. The Pondville Conglomerate crops out along
the western margin of the basin and to the north in Massachusetts.
The Narragansett Pier Granite is Permian in age and intrudes Pennsylvanian and older
rocks, including both principal subterranes of the Avalon Terrane. It crops out along the length of
the southwestern coast of Rhode Island. It is a light colored, medium grained, locally porphyritic,
massive to weakly foliated quartz monzonite to granodiorite. It is composed of feldspar, quartz,
biotite, and minor muscovite with accessory apatite, monazite, zircon, allanite, garnet, and rutile.
The East Bay Area
The East Bay area includes some of the sedimentary rocks of the Narragansett Group but
also includes a variety of stratified metasedimentary and metavolcanic rocks of the Newport
Group. These include the slate, quartzite, volcanic tuff, and mica schists of the Fort Adams
Formation, Newport Neck Formation, and Price Neck Formation.
Several areas of the East Bay, including Conanicut Island, Newport Neck, Bristol Neck,
and the East Bay Coastal Area, are also underlain by various granites and granite gneiss called the
Granites of Southeastern Rhode Island.
Minor metasedimentary rocks (sandstones, phyllites, and quartzites) that are thought to be
Cambrian through Ordovician in age underlie the Islands of the East Bay area. These include the
Cambrian Pirate Cove Formation and the Cambrian through Ordovician metasedimentary rocks of
the Conanicut Group, comnsisting of the Dutch Island Harbor Formation, Fort Burnside
Formation, Jamestown Formation, and East Passage Formation.
IV-9 Reprinted from USGS Open-File Report 93-292-A
-------
GLACIAL GEOLOGY
Deposits of five or possibly six Pleistocene glacial advances in New England have been
recognized or inferred from surface or subsurface data (Stone and Borns, 1986); however, two
main till units are mapped throughout much of southern New England (Richmond and Fullerton,
1991). Glacial deposits exposed at the surface' in Rhode Island are of Late Wisconsin age.
Glaciers moved in a dominantly N-S or NW-SE direction across the State, terminating on Long
Island and Martha's Vineyard at their maximum extent. In Late Wisconsin time, parts of three
glacial lobes advanced across Rhode Island. The Connecticut Valley Lobe covered the western
part of the State and the Narragansett Bay-Buzzard's Bay Lobe covered most of the eastern hah0.
The Charles-Merrimack Lobe entered the northern part of Rhode Island (fig. 5). The final retreat
of Wisconsinan glaciers from the State occurred about 12,000 years ago (Stone and Borns, 1986).
Glacial deposits in Rhode Island range from a few meters to about 40 meters in thickness.
Figure 6 is a generalized map of glacial deposits in Rhode Island. The glacial deposits are divided
into two main categories, till and stratified glacial deposits. Till, sometimes referred to as glacial
drift or ground moraine, is the most widespread glacial deposit (fig. 6). Till was deposited directly
by glacier ice and it is composed of a poorly sorted matrix of sand, silt, and clay containing
variable amounts of rounded cobbles and boulders. Till composition generally reflects the local
bedrock. The "upper till", which covers most of the surface mapped as till on figure 6, is sandy to
gravelly and locally calcareous. It typically overlies a "lower till" which is more clayey, more
compact, and less bouldery than the upper till (Richmond and Fullerton, 1991). Till thickness is
generally 1.5-4 m, and is rarely more than 10 m (Richmond and Fullerton, 1991). Areas largely
underlain by till include the Upland Till Plains and the Narragansett Till Plains. The Upland Till
Plains covers most of the western half of Rhode Island. In this area the till is derived primarily
from gneiss, schist, and granite. Stones and boulders are scattered across the surface of the till,
and bedrock outcrops occur locally (Re.ctor, 1981). The Narragansett Till Plains occupy the
Narragansett Lowlands. This area is covered by till derived primarily from sandstone, shale,
conglomerate, and locally, coal. Bedrock is generally poorly exposed in this area. Glacial
landforms associated with till include drumlins, kettles, and moraines.
Several glacial end moraines are found in Rhode Island; the largest and most important of
these are the Charlestown and Block Island moraines. The Charlestown Moraine, which roughly
follows the coastline from Wakefield to Watch Hill in southwestern Rhode Island (fig. 6), is dated
at approximately 18,000 years B.P. (Stone and Borns, 1986). The Charlestown moraine blocks
normally southward-flowing drainages, diverting them to the east and west. The Block Island
Moraine, which covers all of Block Island, is part of a larger end moraine complex that stretches
from Long Island to Martha's Vineyard. The Block Island Moraine was deposited approximately
21,000 years ago (Stone and Borns, 1986).
Stratified glacial deposits were laid down by glacial meltwater in streams and lakes in front
of the retreating ice margin. They are characterized by layers of poorly-sorted to well-sorted gravel
and sand with minor beds of silt and clay. Stratified glacial deposits are further subdivided into
two categories on figure 6. Outwash consists of layers of sand and gravel deposited by glacial
meltwater streams. Outwash is generally the coarsest-grained class of glacial deposits because
most of the silt and clay was removed by the rapidly-moving water. Ice-contact stratified drift
includes deposits of kames, eskers, kame terraces, and collapsed stratified drift. These coarse-
grained deposits range from poorly sorted to well sorted and consist of sand, gravel, cobbles, and
IV-10 Reprinted from USGS Open-File Report 93-292-A
-------
73°
Ti-
67'
47°
45°
y #
«/ u
x^^^ i-c
cS 7/'^
x pi> ,-' i\
\ c^ C ( -
; t ^__Xc^NADA\ A I ^V Y
M^ UNIJED STATES J \ \/ ^/*•;
43
41
".* /
:' ' \u-'
' \ xT^-
-------
Figure 6. Generalized glacial geologic map of Rhode Island (modified from Richmond and
Fullerton, 1991).
-------
GENERALIZED GLACIAL GEOLOGIC MAP OF RHODE ISLAND
EXPLANATION
HOLOCENE
BEACH AND DUNE SAND-Beach sand is well spited, medium to coarse; commonly contains
scattered shell fragments, seaweed, and., locally, organic and inorganic debris. Associated dune sand is
commonly present as narrow strips adjacent to and immediately inland from beach sand. Thickness of
beach sand 1-3 m, dune sand 1-5 m
HOLOCENE AND LATE WISCONSIN
||l|&| SWAMP DEPOSrr~Muck, mucky peat, peat, and organic residues mixed with fine-grained
mineral sediment. Occurs in ice-block depressions, abandoned glacial meltwater channels, and in
basins dammed by glacial deposits. Thickness generally 1-3 m, rarely more than 5 m
LATE WISCONSIN
LAKE SILT AND CLAY-Stratified silt and clay. Local thin beds of fine sand. Predominantly thinly
laminated; locally varved. Most deposits underlie flat, low areas or valley floors formerly occupied by
glacial lakes. Thickness generally 1-10 m; rarely more than 25 m
OUTWASH SAND AND GRAVEL-Fine to coarse sand or pebbly sand alternating with layers of
granule- to cobble-gravel and minor beds of silt; locally bouldery. Underlies terraces, outwash plains,
valley trains, fans, and meltwater-channel fills. Thickness generally 1-10 m; rarely as much as 60 m
OUTWASH SAND AND UNDERLYING LAKE DEPOSITS-Medium to coarse sand with sparse
scattered pebbles and local lenses of gravel. Underlying lake deposits chiefly flat bedded, lenticularly
crossbedded, or ripple-bedded medium to fine sand and laminated or varved silt and clay. Thickness of
outwash sand 5-10 m; underlying lake deposits 5-30 m
ICE-CONTACT SAND AND GRAVEL-Fine to coarse sand and gravel containing minor beds of silt
and clay and local lenses or masses of till or flowtill. Underlies kame terraces and forms complexes of
crevasse fillings, eskers, mounds, and hummocks in valleys. Inferred to have been deposited against
irregular remnants of stagnant ice. Surface locally pitted with ice-block depressions, and in places
strewn with boulders. Thickness 5-20 m
ICE-CONTACT DELTA SAND AND GRAVEL-Sand and pebble- or cobble-gravel. Most ice-
contact deposits are in valleys, but some are perched on terrain above the valley floor. They are
inferred to have been deposited at successive ice marginal positions by streams flowing from stagnant
ice into ice-marginal lakes or ponds. Thickness 5-15 m; locally as much as 40 m
SANDY TILL—Texture highly variable, stony sand to stony sandy loam; locally dense, fissile silty clay
with boulders. Commonly gravelly, cobbly, bouldery, or rubbly. Locally weakly calcareous to
noncalcareous, reflecting composition of source materials. Generally friable; loose to moderately
compact. Rock types reflect local bedrock, which changes markedly over relatively short distances.
The sandy till at the surface, or "upper till," locally overlies a "lower till," not separately mapped, which
is dark gray brown or dark gray and more clayey, more compact, and less bouldery than the "upper
till". The "upper till" forms ground moraine, which varies greatly in thickness but is rarely very thick,
and attenuated drift, which is very thin and discontinuous with intervening areas of glaciated bedrock.
Thickness generally 1.5-4 m; rarely more than 10 m
H^H KAME MORAINE—Loose sandy till several meters thick underlain by sand and gravel that locally
includes masses of lake silt and clay or sandy loamy till. Forms end moraine ridge as long as 20 km
and as high as 10-20 m in southern Rhode Island. Thickness 5-80 m
LATE WISCONSIN AND EARLY WISCONSIN
SANDY TO CLAYEY TELL-Complex deposit of late Wisconsin sandy to clayey till and early
Wisconsin clayey till (Montauk Till) on Block Island. Early Wisconsin till exposed only in coastal
bluffs. Both tills discontinuous. Thickness 3-5 m; locally more than 10 m
PLIOCENE AND OLDER CENOZOIC
[$$$$ GLACIATED GRANITIC GRUS-Coarse granitic grus; overlain locally by patches of thin sandy
till, sand, and widely scattered glacial pebbles, cobbles, and boulders from local and distant
sources. Grus is developed in coarse mafic rocks as well as in granite in Rhode Island. Remnant
thickness 0.5-3 m
-------
boulders, with varying amounts of silt and clay, though they generally contain, considerably less
fine-grained material than till.
SOILS
Most of the soils in Rhode Island are classified as Inceptisols, soils with weakly developed
horizons in which materials have been altered or removed but in which little accumulation has
occurred. These soils are typically developed on glacial till or bedrock. Inceptisols cover about 85
percent of Rhode Island's land surface. Some of the soils developed on outwash and alluvium are
classified as Entisols, relatively young soils with no pedogenic horizons. Entisols occupy about
10 percent of the State's land surface area. Soils in low-lying inland areas that contain an
abundance of organic matter (peat and muck) are classified as Histosols. Histosols occupy about 5
percent of the State's land surface area (Rector, 1981).
Figure 7 is a generalized soil map of Rhode Island. Soils of the glaciated uplands having a
friable (loosely packed, easily separated, and permeable) substratum occur primarily in the western
part of the State. These soils are deep, moderately well to excessively drained, and have a loamy,
silty, or sandy texture. The soils are formed on glacial till derived from schist, gneiss, granite, and
phyllite, and locally on bedrock. These soils have moderate permeability except for one unit,
shown separately on figure 7, which is formed on till, moraines, and outwash, and has high
permeability. This unit is the dominant soil type on the Charlestown Moraine (fig. 6, 7).
Soils of the glaciated uplands having a firm (clayey) substratum occur across the State
(fig. 7). They are described as deep, poorly drained to well drained, coarse-loamy soils with a
clayey subsurface horizon. The soils are developed on till derived from dark-colored sandstone
and phyllite, argillite, conglomerate, shale, slate, schist, gneiss, and granite. They are commonly
found on till-covered slopes and uplands, and on the slopes and tops of drumlins. These soils
have moderate permeability in the surface horizons and low permeability below 0.5-0.75 m depth
(Rector, 1981).
Soils developed on outwash plains and terraces, kames, eskers, and recent alluvium are
scattered across the State and are described as deep, poorly to excessively drained, coarse-loamy
and sandy soils with sandy and gravelly substrata (Soil Conservation Service, 1978). The soils
are formed on outwash, glaciofluvial deposits, and alluvium derived from schist, gneiss, phyllite,
and granite. Soils on outwash plains and terraces are generally well- to excessively drained,
whereas those in depressions and on floodplains are poorly drained. These soils have moderate
permeability in the surface horizons and high permeability at depth (Rector, 1981).
Organic soils form in swamps and marshes in depressions and small drainages of upland
tills, outwash plains, and moraines (fig. 7). These soils have a thin to thick surface layer of peat or
organic muck overlying a sandy substratum (Rector, 1981). Although these soils have moderate to
high permeability, they are poorly drained and tend to be wet
Soils of beaches and coastal lowlands are sandy and have high permeability. Soils of
coastal marshes have a surface layer of organic material and are poorly drained, whereas beach
soils are sandy throughout the profile and are excessively drained (Rector, 1981).
RADIOACTIVITY
An aeroradiometric map of Rhode Island (fig. 8) was compiled from spectral gamma-ray
data acquired during the U.S. Department of Energy's National Uranium Resource Evaluation
(NURE) program (Duval and others, 1989). For the purposes of this report, low equivalent
' ' IV-14 Reprinted from USGS Open-File Report 93-292-A
-------
SCALE
10123 * 5 Miles
Figure 7. Generalized soil map of Rhode Island (modified from Rector, 1981).
-------
GENERALIZED SOIL MAP OF RHODE ISLAND
EXPLANATION
AREAS OF GLACIATED UPLANDS DOMINATED BY DEEP SOILS WITH A FRIABLE
SUBSTRATUM (INCEPTISOLS)—moderately well and well drained, silty and loamy soils
developed on till derived from schist, gneiss, phyllite, and granite; moderate to locally high
permeability
AREAS OF GLACIATED UPLANDS DOMINATED BY DEEP, SANDY SOILS
(INCEPTISOLS AND ENTISOLS)—somewhat excessively drained and excessively drained
soils formed in mixed sandy till and stratified glacial deposits derived from schist, gneiss,
and granite; high permeability
AREAS OF GLACIATED UPLANDS DOMINATED BY DEEP SOILS WITH A FIRM
SUBSTRATUM DERIVED FROM MAFIC ROCKS (INCEPTISOLS)—very poorly
drained to well drained, silty and loamy soils developed on till derived from phyllite,
argillite, slate, schist, shale, and sandstone; low permeability
AREAS OF GLACIATED UPLANDS DOMINATED BY DEEP SOILS WITH
A FIRM SUBSTRATUM DERIVED FROM CRYSTALLINE ROCKS (INCEPTISOLS)—poorly
drained to well drained loamy soils developed on till derived from schist, gneiss, and granite;
low permeability
AREAS OF OUTWASH PLAINS, TERRACES, KAMES, AND ESKERS DOMINATED BY
DEEP SOILS {INCEPTISOLS AND SOME ENTISOLS)—poorly to excessively drained,
silty and sandy soils with high permeability; derived mostly from schist, gneiss, and phyllite
AREAS OF INLAND DEPRESSIONS AND LOW-LYING POSITIONS DOMINATED BY
ORGANIC SOILS (HISTOSOLS)—very poorly drained soils formed in organic deposits
derived from plant materials; moderate to high permeability, commonly wet
AREAS OF COASTAL LOWLANDS AFFECTED BY TIDAL WATER AND DOMINATED BY
SOILS FORMED IN SANDY SEDIMENTS (ENTISOLS)—very poorly drained and excessively
drained sandy soils of tidal marshes, dune areas, and beaches; high permeability
-------
Figure 8. Aerial radiometric map of Rhode Island and surrounding areas (after Duval and others,
19.89). Contour lines at 1.5 and 2.5 ppm equivalent uranium (eU). Pixels shaded from 0 to 6.0
ppm eU at 0.5 ppm eU increments; darker pixels have lower eU values; white indicates no data.
-------
TABLE 1. Uranium concentrations in major rock types of Rhode Island (from Nevins, 1991).
no. of U (ppm)
Rock types samples range mean
Hope Valley Group
Alaskite gneiss 7 1.7-5.8 3.3
Other Precantbrian Igneous Rocks
Felsite 2 2.0-2.1 2.1
Blackstone Series
Greenstone 3 0.1-0.7 0.4
Esmond Plutonic Suite
Tonalite
Granodiorite
Ene-gr. granite
Granite
Augen gneiss
Granite gneiss
Scituate Igneous
Felsite
Granite
Alkali-feld. gr.
2
2
1
4
5
1
Suite
4
16
9
1.5-1.7
1.5-2.5
0.9-2.8
1.5-2.3
2.2-9.8
2.2-13.2
2.2-22.1
1.6
2.0
4.0
1.9
1.9
2.8
7.3
4.1
7.9
RT Quincy Plutonic Suite
AlkaU-feld.gr. 2 11.4-16.5 14.0
Narragansett Pier-Westerly Plutonic Suite
Fine-gr. granite 3 2.1-3.4 3
Granite 6 2.7-13.8 5.9
Leucooratic gr. 3 5.0-13.1 9.7
Narragansett Bay Group
Sandstone 2 3.2-3.9 3.6
Carb. shale 2 1.8-3.3 2.6
Carb. slate 2 4.9-5.1 5.0
Siltstone 1 7-°
alkali-feld. gr. = alkali-feldspar granite, fine-gr.granite = fine-grained granite,
carb. shale = carbonaceous shale
-------
uranium (eU) on the map is defined as less than 1.5 parts per million (ppm), moderate eU is
defined as 1.5-2.5 ppm, and high eU is defined as greater than 2.5 ppm. In figure 8, the three
highest areas of eU appear to be associated with the Scituate Igneous Suite, its intrusive contact
with the Blackstone Series, and the alkalic granite of the Cumberland. Low eU is found in the
northwest and central parts of the State and appears to be associated with the Woonsocket Basin,
the Harmony Group, and the northwestern outcrops of the Esmond Igneous Suite and Blackstone
Group. Moderate eU covers much of the rest of the State. The total gamma radioactivity map of
Popenoe (1966) covers the entire State and shows similar patterns of radioactivity. Anomalously
high areas of radioactivity include a small outcrop of alkalic granite near Cumberland; most of the
area underlain by the Scituate Igneous Suite (including a particularly high area where the granite
intrudes the Blackstone Group); the Narragansett Pier Plutonic Suite, parts of the Sterling Plutonic
Group in both the southwest and northwest corners of the State; and the granites of southeastern
Rhode Island in the East Bay Area. The NURE report for the Providence Quadrangle (Zollinger
and others, 1982) gives a maximum of 33 ppm uranium for alkalic granite of Cumberland; 24 ppm
uranium for Scituate granite where it intrudes the Blackstone Group; and 7 ppm uranium in the
Narragansett Pier Plutonic Suite. Uranium chemistry of the major rock units in Rhode Island was
also investigated by Nevins (1991) and her data are presented in Table 1. Rock units with uranium
concentrations greater than 2 ppm include alaskite gneiss of the Sterling Plutonic Group (Hope
Valley Group), Precambrian-age felsite, granitic rocks of the Esmond Plutonic Suite, alkali granitic
rocks of the Scituate Igneous Suite, the Rhode Island Quincy Plutonic Suite, the Narragansett Pier
and Westerly Granites, and carbonaceous sediments of the Narragansett Bay Group. The data in
Table 1 suggests that many of the principal rock units in Rhode Island, especially the igneous
suites, are uraniferous and may provide an significant source of radon to homes.
INDOOR RADON DATA
Indoor radon data from 376 homes sampled in the State/EPA Residential Radon Survey
conducted in Rhode Island during the winter of 1987 are shown in figure 9 and listed in Table 2.
A map of counties is included for reference (fig. 10). Indoor radon was measured by charcoal
canister. The maximum value recorded in the survey was 64.1 pCi/L in Kent County. The
average for the State was 3.3 pCi/L and 20.7 percent of the homes tested had indoor radon levels
exceeding 4 pCi/L. Kent and Washington Counties have indoor radon averages greater than
4 pCi/L. Bristol County has the lowest average indoor radon and Newport and Providence
Counties have indoor radon averages between 2-3 pCi/L.
TABLE 2. Screening indoor radon data from the State/EPA Residential Radon Survey of Rhode
Island conducted during 1987. Data represent 2-7 day charcoal canister measurements from the
lowest level of each home tested.
COUNTY
BRISTOL
KENT
NEWPORT
PROVIDENCE
WASHINGTON
NO. OF
ME AS.
22
80
37
185
52
AVERAGE
1.8
4.7
2.9
2.6
4.1
GEOM.
MEAN
1.4
2.2
1.5
1.8
2.7
MEDIAN
1.6
2.0
1.3
1.7
2.3
STD.
DEV.
1.5
9.0
5.3
2.9
4.4
MAXIMUM
7.7
64.1
29.5
27.8
23.5
%>4 pCi/L
5
25
16
17
37
%>20 pCi/L
0
4
3
1
4
IV-19 Reprinted from USGS Open-File Report 93-292-A
-------
Bsmt. & 1st Floor Rn
% > 4 pCi/L
1 N*..*^1 0 to 10
2 K\\\VM 11 to 20
1 ggg 21 to 30
Bsmt. & 1st Floor Rn
Average Concentration (pCi/L)
1 ivv*.1 o.O to 1.9
2 K\\\\N 2.0 to 4.0
4.1 to 4.7
20 Miles
Figure 9. Screening indoor radon data from the EPA/State Residential Radon Survey of Rhode
Island, 1986-87. 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 2)
may not be sufficient to statistically characterize the radon levels of the counties, but they dp
suggest general trends. Unequal category intervals were chosen to provide reference to decision
and action levels.
-------
w-
10
Figure 10. Rhode Island counties (from Facts on File, 1984).
-------
GEOLOGIC RADON POTENTIAL
The geologic radon potential of Rhode Island has been investigated by Nevins (1991). Her
analysis includes data on uranium concentrations in all the major rock types (Table 1), radon in
water, and correlations with non-random indoor radon data collected through the Rhode Islanders
Saving Energy (RISE) Program. Data from RISE (fig. 11) show that 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, Narragansett Pier, and parts of the Esmond Igneous Suite, as well as with two areas also
noted for high uranium: the northwestern corner of the State, which has anomalously high
radioactivity on Popenoe's (1966) map and is underlain by the Sterling Plutonic Group, and in the
East Bay Area over the granites of Southeastern Rhode Island. Frohlich and Pearson (1988) also
suggested, from examining Popenoe's (1966) map, that the Scituate Granite and the Rhode Island
Quincy Granite constitute significant geologic radon potential. The northern half of the
Narragansett basin (where the Pennsylvanian-age sediments are less metamorphosed and thick
glacial outwash is present) and the northernmost township of Woonsocket (corresponding to the
Woonsocket Basin) have the lowest percentage of indoor radon readings exceeding 4 pCi/L.
Non-random data are expected to have higher readings than random data overall (White and
others, 1989); however, the State/EPA data set and the RISE data do appear to agree in that both
show that the southwestern half of the State has the greatest number of readings over 4 pCi/L.
Nevins (1991) concluded that the lowest indoor radon is geographically associated with the
Narragansett Bay Group whereas the higher percentages of indoor radon over 4 pCi/L are
associated with the Scituate Igneous Suite, the alaskite gneiss in the Hope Valley Subterrane, and
the Narragansett Pier granite.
The effect of glacial deposits is difficult to assess in Rhode Island since 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 most probably enhance the geologic radon potential. Popenoe's (1966) map may
reveal a secondary influence of the glacial deposits on surface radioactivity. 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 grained 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 emanating power because of the higher proportion
of finer-grained sediments. This is also true of some glacial lake deposits. Radon emanation is
enhanced by the higher specific surface area of the fine-grained fraction (Schumann and others,
1991). 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.
The southern part of the Narragansett Lowlands and East Bay Area, however, have a significantly
higher percentage of indoor radon readings greater than 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
with components of uraniferous granite and phyllite. Another example of glacial deposit influence
may be seen in the area of the Narragansett Pier Granite, where high percentages of homes with
indoor radon over 4 pCi/L exist. The types of glacial deposits there include kames, glacial lake
deposits, and till, which are known to have enhanced radon emanation coefficients. These glacial
IV-22 Reprinted from USGS Open-File Report 93-292-A
-------
Percent of homes tested
exceeding 4pCi/l Radon-222
Harrington
Bristol
Burrillville
Central Falls
Charlestown
Coventry
Cranston
Cumberland
East Greenwich
East Providence
Exeter
Forster
Glocester
Hopkinton
Jamestown
Johnston
Lincoln
Little Compton
Middletown
Narragansett
Newport
North Kingstown
North Providence
North Smithfield
Pawtucket
Providence
Portsmouth
Richmond
Scituate
South Kingstown
Smithfield
Tiverton
Warren
Warwick
West Greenwich
West Warwick
Westerly
Woonsocket
122
42
26
9
64
120
300
68
200
135
36
24
35
17
28
75
59
13
0
66
106
176
42
5
126
433
47
24
60
102
94
92
25
325
1
92
48
62
Figure 11. Screening indoor radon data by township from the RISE survey (from Nevins, 1991).
-------
deposits may also have significant source components in the adjacent Scituate-Igneous Suite and
Sterling Plutonic Group as well as the Narragansett Pier granite, which all have some high uranium
concentrations (fig. 5).
Although there are no obvious radioactivity anomalies associated with the major shear
zones in Rhode Island, evidence from many other shear zones (Gundersen, 1991) suggests that
shear zones can create isolated incidences of severe indoor radon, especially when they deform
uraniferous rocks. The Hope Valley Shear zone that separates the two subterranes does have
anomalous radioactivity associated with it in parts of Connecticut and may be a source of high
radon in Rhode Island.
SUMMARY
For the purpose of this assessment, Rhode Island has been divided into six geologic radon
potential areas and each area assigned a Radon Index (RI) and a Confidence Index (CI) score
(Table 3). These areas are shown in figure 12. The RI is a semi-quantitative measure of radon
potential based on geology, soils, radioactivity, architecture, and indoor radon. The CI is a
measure of the relative confidence of the RI assessment based on the quality and quantity of the
data used to assess geologic radon potential (see the Introduction chapter to this regional booklet
for more information).
The radon potential of Rhode Island appears to be influenced most by the composition of
the underlying bedrock and secondarily affected by glacial deposits. 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 and the greatest potential for creating indoor radon
problems. 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 that are overlain by glacial outwash deposits in the northern portion of the
Narragansett Lowlands. Low to moderate radon potential 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.
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-24 Reprinted from USGS Open-File Report 93-292-A
-------
REFERENCES XHTED IN THIS REPORT
AND OTHER REFERENCES RELEVANT TO RADON IN RHODE ISLAND
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: Facts on File publications.
Frohlich, R.K., and Pearson, C.A., 1988, Potential radon hazard in Rhode Island estimated from
geophysical and geological surveys: Northeastern Environmental Science, v. 7, p. 30-34.
Gundersen, L.C.S., 1991, Radon in sheared metamorphic and igneous rocks: in Gundersen,
L.C.S., and Wanty, R.B., eds., Field Studies of Radon in Rocks, Soils, and Water; U.S.
Geological Survey Bulletin 1971, p. 38-49.
Hermes, O.D., Gromet, L.P., and Murray, D.P., (in press), Bedrock Geologic Map of Rhode
Island: Office of the Rhode Island State Geologist, University of Rhode Island, Kingston,
4 plates, Scale: 1:100,000 and 1, 250,000.
Matyas, B.T., and Dundulis, W.P., Jr., 1991(7), Residential indoor air radon levels in Rhode
Island: Summary of state experience to date: 6 p.
Nevins, Nancy, 1991, uranium in Rhode Island Bedrock: A primary source of radon in indoor air
and groundwater (M.S. Thesis): University of Rhode Island, Kingston, Rhode Island,
146 p. •
Popenoe, P., 1966, Aeroradioactivity and generalized geologic maps of parts of New York,
Connecticut, Rhode Island and Massachusetts: U.S. Geological Survey Map GP-359,
scale 1:250,000.
Quinn, A.W., 1971, Bedrock geology of Rhode Island: U.S. Geological Survey Bulletin 1295,
68 p.
Rector, D.D., 1981, Soil survey of Rhode Island: U.S. Department of Agriculture, Soil
Conservation Service, 200 p.
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.
Schumann, R.R., Peake, R.T., Schmidt, K.M., and Owen, D.E., 1991, Correlations of soil-gas
and indoor radon with geology in glacially derived soils of the northern Great Plains, in
Proceedings of the 1990 International Symposium on Radon and Radon Reduction
Technology, Volume 2, Symposium Oral Papers: U.S. Environmental Protection Agency
report EPA/600/9-91/026b, p. 6-23-6-36.
IV-27 Reprinted from USGS Open-File Report 93-292-A
-------
Soil Conservation Service, 1978, General soil map of Rhode Island: U.S. Department of
Agriculture, scale 1:72,000.
Stone, B.D., and Boms, 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.
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.
Zollinger, R.C., Blauvelt, R.P., and Chew, R.T., 1982 National Uranium Resource Evaluation,
Providence Quadrangle Connecticut, Rhode Island, and Massachusetts: U.S. Department
of Energy Report PGJ/F-101(82), 40 p.
IV-28 Reprinted from USGS Open-File Report 93-292-A
-------
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 USGS' Geologic Radon Province Map. EPA defines the three zones as
follows: Zone One areas have an average predicted indoor radon screening potential greater
than 4 pCi/L. Zone Two areas are predicted to have an average indoor radon screening
potential between 2 pCi/L and 4 pCi/L. Zone Three areas are predicted to have an average
indoor radon screening potential less than 2 pCi/L.
Since the geologic province boundaries cross state and county boundaries, a strict
translation of counties from the Geologic Radon Province Map to the Map of Radon Zones
was not possible. For counties that have variable radon potential (i.e., are located in two or
more provinces of different rankings), the counties were assigned to a zone based on the
predicted radon potential of the province in which most of its area lies. (See Part I for more
details.)
RHODE ISLAND MAP OF RADON ZONES
The Rhode Island Map of Radon Zones and its supporting documentation (Part IV of
this report) have received extensive review by Rhode Island geologists and radon program
experts. The map for Rhode Island generally reflects current State knowledge about radon for
its counties. Some States have been able to conduct radon investigations in areas smaller than
geologic provinces and counties, so it is important to consult locally available data.
Although the information provided in Part IV of this report — the State chapter entitled
"Preliminary Geologic Radon Potential Assessment of Rhode Island" — 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
Rhode Island radon program for information on testing and fixing homes. Telephone numbers
and addresses can be found in Part II of this report.
V-l
-------
------- |