IMItecl States
EnvironrMnt&l Protection
Agency
Air and Radiation
(6804J)
402-FW3-040
September 1M3
vvEPA EPA's Map of Radon Zones
MARYLAND
Printed on Recycled Paper
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EPAfS MAP OF RADON ZONES
MARYLAND
RADON DIVISION
OFFICE OF RADIATION AND INDOOR AIR
U.S. ENVIRONMENTAL PROTECTION AGENCY
SEPTEMBER, 1993
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ACKNOWLEDGEMENTS
This document was prepared by the U.S. Environmental Protection Agency's (EPA's)
Office of Radiation and Indoor Air (ORIA) in conjunction with the U.S. Geological Survey
(USGS). Sharon W. White was the EPA project manager. Numerous other people in ORIA
were instrumental in the development of the Map of Radon Zones, including Lisa Ratcliff,
Kirk Maconaughey, R. Thomas Peake, Dave Rowson, and Steve Page.
EPA would especially like to acknowledge the outstanding effort of the USGS
radon team — Linda Gundersen, Randy Schumann, Jim Otton, Doug Owen, Russell
Dubiel, Kendell Dickinson, and Sandra Szarzi — in developing the technical base for the
Map of Radon Zones.
ORIA would also like to recognize the efforts of all the EPA Regional Offices in
coordinating the reviews with the State programs and the Association of American State
Geologists (AASG) for providing a liaison with the State geological surveys. In addition,
appreciation is expressed to all of the State radon programs and geological surveys for their
technical input and review of the Map of Radon Zones.
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TABLE OF CONTENTS
I. OVERVIEW
II. THE USGS/EPA RADON POTENTIAL
ASSESSMENTS:INTRODUCnON
III. REGION 3 GEOLOGIC RADON POTENTIAL
SUMMARY
V. PRELIMINARY GEOLOGIC RADON POTENTIAL
ASSESSMENT OF MARYLAND
V. EPA'S MAP OF RADON ZONES - MARYLAND
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OVERVIEW
Sections 307 and 309 of the 1988 Indoor Radon Abatement Act (IRAA) direct EPA to
identify areas of the United States that have the potential to produce elevated levels of radon.
EPA, the U.S. Geological Survey (USGS), and the Association of American State Geologists
(AASG) have worked closely over the past several years to produce a series of maps and
documents which address these directives. The EPA Map of Radon Zones is a compilation of
that work and fulfills the requirements of sections 307 and 309 of IRAA. The Map of Radon
Zones identifies, on a county-by-county basis, areas of the U.S. that have the highest potential
for elevated indoor radon levels (greater than 4 pCi/L).
The Map of Radon Zones is designed to assist national, State and local governments
and organizations to target their radon program activities and resources. It is also intended to
help building code officials determine areas that are the highest priority for adopting radon-
resistant building practices. The Map of Radon Zones should not be used to determine if
individual homes in any given area need to be tested for radon. EPA recommends that all
homes be tested for radon, regardless of geographic location or the zone designation of
the county in which they are located.
This document provides background information concerning the development of the
Map of Radon Zones. It explains the purposes of the map, the approach for developing the
map (including the respective roles of EPA and USGS), the data sources used, the conclusions
and confidence levels developed for the prediction of radon potential, and the review process
that was conducted to finalize this effort.
BACKGROUND
Radon (Rn222) is a colorless, odorless, radioactive gas. It comes from the natural
decay of uranium that is found in nearly all soils. It typically moves through the ground to
the air above and into homes and other buildings through cracks and openings in the
foundation. Any home, school or workplace may have a radon problem, regardless of
whether it is new or old, well-sealed or drafry, or with or without a basement. Nearly one out
of every 15 homes in the U.S. is estimated to.have elevated annual average levels of indoor
radon.
Radon first gained national attention in early 1984, when extremely high levels of
indoor radon were found in areas of Pennsylvania, New Jersey, and New York, along the
Reading Prong-physiographic province. EPA established a Radon Program in 1985 to assist
States and homeowners in reducing their risk of lung cancer from indoor radon.
Since 1985, EPA and USGS have been working together to continually increase our
understanding of radon sources and the migration dynamics that cause elevated indoor radon
levels. Early efforts resulted in the 1987 map entitled "Areas with Potentially High Radon
Levels." This map was based on limited geologic information only because few indoor radon
measurements were available at the time. The development of EPA's Map of Radon Zones
and its technical foundation, USGS' National Geologic Radon Province Map, has been based
on additional information from six years of the State/EPA Residential Radon Surveys,
independent State residential surveys, and continued expansion of geologic and geophysical
information, particularly the data from the National Uranium Resource Evaluation project.
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Purpose of the Map of Radon Zones ,.c ^
'am;
EPA's Map of Radon Zones (Figure 1) assigns each of the 3141 counties in the
United States to one of three zones:
o Zone 1 counties have a predicted average indoor screening level > than
4 pdfL
o Zone 2 counties have a predicted average screening level > 2 pCi/L and
< 4 pCi/L
o Zone 3 counties have a predicted average screening level < 2 pCi/L
The Zone designations were determined by assessing five factors that are known to be
important indicators of radon potential: indoor radon measurements, geology, aerial
radioactivity, soil parameters, and foundation types.
The predictions of average 'screening levels in each of the Zones is an expression of
radon potential in the lowest liveable area of a structure.. This map is unable to estimate
actual exposures to radon. EPA recommends methods for testing and fixing individual homes
based on an estimate of actual exposure to radon. For more information on testing and fixing
elevated radon levels in homes consult these EPA publications: A Citizen's Guide to Radon.
the Consumer's Guide to Radon Reduction and the Home Buyer's and Seller's Guide to
Radon.
EPA believes that States, local governments and other organizations can achieve
optimal risk reductions by targeting resources and program activities to high radon potential
areas. Emphasizing targeted approaches (technical assistance, information and outreach
efforts, promotion of real estate mandates and policies and building codes, etc.) in such areas
addresses the greatest potential risks first.
EPA also believes that the use of passive radon control systems in the construction of
new homes in Zone 1 counties, and the activation of those systems if necessitated by follow-
up testing, is a cost effective approach to achieving significant radon risk reduction.
The Map of Radon Zones and its supporting documentation establish no regulatory
requirements. Use of this map by State or local radon programs and building code officials is
voluntary. The information presented on the Map of Radon Zones and in the supporting
documentation is not applicable to radon in water.
Development of the Map of Radon Zones
*
The technical foundation for the Map of Radon Zones is the USGS Geologic Radon
Province Map. In order to examine the radon potential for the United States, the USGS
began by identifying approximately 360 separate geologic provinces for the U.S. The
provinces are shown on the USGS Geologic Radon Province Map (Figure 2). Each of the
geologic provinces was evaluated by examining the available data for that area: indoor radon
measurements, geology, aerial radioactivity, soil parameters, and foundation types. As stated
previously, these five factors are considered to be of basic importance in assessing radon
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potential and some data are available for each of these factors in every geologic province. The
province boundaries do not coincide with political borders (county and state) but define areas
of general radon potential. The five factors were assigned numerical values based on an
assessment of their respective contribution to radon potential, and a confidence level was
assigned to each contributing variable. The approach used by USGS to estimate :the radon
potential for each province is described in Part II of this document.
EPA subsequently developed the Map of Radon Zones by extrapolating from the
province level to the county level so that all counties in the U.S. were assigned to one of
three radon zones. EPA assigned each county to a given zone based on its provincial radon
potential. For example, if a county is located within a geologic province that has a predicted
average screening level, greater than 4 pCi/L, it was assigned to Zone 1. Likewise, counties
located in provinces with predicted average screening levels > 2 pCi/L and < 4 pCi/L, and
less than 2 pCi/L, were assigned to Zones 2 and 3, respectively.
If the boundaries of a county fall in more than one geologic province, the county was
assigned to a zone based on the .predicted radon potential of the province in which most of
the area lies. For example, if three different provinces cross through a given county, the
county was assigned to the zone representing the radon potential of the province containing
most of the county's land area. (In this case, it is not technically correct to say that the
predicted average screening level applies to the entire county since the county falls in
multiple provinces with differing radon potentials.)
Figures 3 and 4 demonstrate an example of how EPA extrapolated the county zone
designations for Nebraska from the USGS geologic province map for the State. As figure 3
shows, USGS has identified 5 geologic provinces for Nebraska. Most of the counties are
extrapolated "straight" from their corresponding provinces, but there are counties "partitioned"
by several provinces — for example, Lincoln County. Although Lincoln county falls in
multiple provinces, it was assigned to Zone 3 because most of its area falls in the province
with the lowest radon potential.
It is important to note that EPA's extrapolation from the province level to the
county level may mask significant "highs" and "lows" within specific counties. In other
words, within-county variations in radon potential are not shown on the Map of Radon
Zones. EPA recommends that users who may need to address specific within-county
variations in radon potential (e.g., local government officials considering the
implementation of radon-resistant construction codes) consult USGS' Geologic Radon
Province Map and the State chapters provided with this map for more detailed
information, as well as any locally available data.
Map Validation
The Map of Radon Zones is intended to represent a preliminary assessment of radon
potential for the entire United States. The factors that are used in this effort —indoor radon
data, geology, aerial radioactivity, soils, and foundation type — are basic indicators for radon
potential. It is important to note, however, that the map's county zone designations are not
"statistically valid" predictions due to the nature of the data available for these 5 factors at the
county level. In order to validate the map in light of this lack of statistical confidence, EPA
conducted a number of analyses. These analyses have helped EPA to identify the best
situations in which to apply the map, and its limitations.
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Figure 3
Geologic Radon Potential Provinces for Nebraska
Liocolfi Couaty
lift Uolettte Lev
Figure 4
NEBRASKA - EPA Map of Radon Zones
Liacola County
Zeit 1 Zeae 2 Zoat 3
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One such analysis involved comparing county zone designations to indoor radon
measurements from the State/EPA Residential Radon Surveys (SRRS). Screening averages
for counties with at least 100 measurements were compared to the counties' predicted radon
potential as indicated by the Map of Radon Zones. EPA found that 72% of the county
screening averages were correctly reflected by the appropriate zone designations on the Map.
in all other cases, they only differed by 1 zone.
Another accuracy analysis used the annual average data from the National Residential
Radon Survey (NRRS). The NRRS indicated that approximately 6 million homes in the
United States have annual averages greater than or equal to 4 pCi/L. By cross checking the
county location of the approximately 5,700 homes which participated in the survey, their
radon measurements, and the zone designations for these counties, EPA found that
approximately 3.8 million homes of the 5.4 million homes with radon levels greater than or
equal to 4 pCi/L will be found in counties designated as Zone 1. A random sampling of an
equal number of counties would have only found approximately 1.8 million homes greater
than 4 pCi/L. In other words, this analysis indicated that the map approach is three times
more efficient at identifying high radon areas than random selection of zone designations.
Together, these analyses show that the approach EPA used to develop the Map of
Radon Zones is a reasonable one. In addition, the Agency's confidence is enhanced by results
of the extensive State review process — the map generally agrees with the States' knowledge
of and experience in their own jurisdictions. However, the accuracy analyses highlight two
important points: the fact that elevated levels will be found in Zones 2 and 3, and that there
will be significant numbers of homes with lower indoor radon levels in all of the Zones. For
these reasons, users of the Map of Radon Zones need to supplement the Map with locally
available data whenever possible. Although all known "hot spots", i.e., localized areas of
consistently elevated levels, are discussed in the State-
specific chapters, accurately defining the boundaries of the "hot spots" on this scale of map is
not possible at this time. Also, unknown "hot spots" do exist.
The Map of Radon Zones is intended to be a starting point for characterizing radon
potential because our knowledge of radon sources and transport is always growing. Although
this effort represents the best data available at this time, EPA will continue to study these
parameters and others such as house construction, ventilation features and meteorology factors
in order to better characterize the presence of radon in U.S homes, especially in high risk
areas. These efforts will eventually assist EPA in refining and revising the conclusions of the
Map of Radon Zones. And although this map is most appropriately used as a targeting tool
by the aforementioned audiences — the Agency encourages all residents to test their homes
for radon, regardless of geographic location or the zone designation of the county in
which they live. Similarly, the Map of Radon Zones should not to be used in lieu of
testing during real estate transactions.
Review Process
The Map of Radon Zones has undergone extensive review within EPA and outside the
Agency. The Association of American State Geologists (AASG) played an integral role in
this review process. The AASG individual State geologists have reviewed their State-specific
information, the USGS Geologic Radon Province Map, and other materials for their geologic
content and consistency.
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In addition to each State geologist providing technical comments, the State radon
offices were asked to comment on their respective States' radon potential evaluations.; In
particular, the States were asked to evaluate the data used to assign their counties to specific
zones. EPA and USGS worked with the States to resolve any issues concerning -'county zone
designations. In a few cases, States have requested changes in county zone designations. The
requests were based on additional data from the State on geology, indoor radon
measurements, population, etc. Upon reviewing the data submitted by the States, EPA did
make some changes in zone designations. These changes, which do not strictly follow the
methodology outlined in this document, are discussed in the respective State chapters.
EPA encourages-the States and counties to conduct further research and data collection
efforts to refine the Map of Radon Zones. EPA would like to be kept informed of any
changes the States, counties, or others make to the maps. Updates and revisions will be
handled in a similar fashion to the way the map was developed. States should notify EPA of
any proposed changes by forwarding the changes through the Regional EPA offices that are
listed in Part II. Depending on the amount of new information that is presented, EPA will
consider updating this map periodically. The State radon programs should initiate proper
notification of the appropriate State officials when the Map of Radon Zones is released and
when revisions or updates are made by the State or EPA.
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THE USGS/EPA RADON POTENTIAL ASSESSMENTS: AN INTRODUCTION
by-
Linda C.S. Gundersen and R. Randall Schumann
U.S. Geological Survey
and
Sharon W. White
U.S. Environmental Protection Agency
BACKGROUND
The Indoor Radon Abatement Acf of 1988 (15 U.S.C. 2661-2671) directed the U.S.
Environmental Protection Agency (EPA) to identify areas of the United States that have the
potential to produce harmful levels of indoor radon. These characterizations were to be based
on both geological data and on indoor radon levels in homes and other structures. The EPA
also was directed to develop model standards and techniques for new building construction
that would provide adequate prevention or mitigation of radon entry. As part of an
Interagency Agreement between the EPA and the U.S. Geological Survey (USGS), the USGS
has prepared radon potential estimates for the United States. This report is one of ten
booklets that document this effort. The purpose and intended use of these reports is to help
identify areas where states can target their radon program resources, to provide guidance in
selecting the most appropriate building code options for areas, and to provide general
information on radon and geology for each state for federal, state, and municipal officials
dealing with radon issues. These reports are not intended to be used as a substitute for
indoor radon testing, and they cannot and should not be used to estimate or predict the
indoor radon concentrations of individual homes, building sites, or housing tracts. Elevated
levels of indoor radon have been found in every State, and EPA recommends that all homes
be tested for indoor radon.
Booklets detailing the radon potential assessment for the U.S. have been developed for
each State. USGS geologists are the authors of the geologic radon potential booklets. Each
booklet consists of several components, the first being an overview to the mapping project
(Part I), this introduction to the USGS assessment (Part II), including a general discussion of
radon (occurrence, transport, etc.), and details concerning the types of data used. The third
component is a summary chapter outlining the general geology and geologic radon potential
of the EPA Region (Part III). The fourth component is an individual chapter for each state
(Part IV). Each state chapter discusses the state's specific geographic setting, soils, geologic
setting, geologic radon potential, indoor radon data, and a summary outlining the radon
potential rankings of geologic areas in the state. A variety of maps are presented in each
chapter—geologic, geographic, population, soils, aerial radioactivity, and indoor radon data by
county. Finally, the booklets contain EPA's map of radon zones for each state and an
accompanying description (Part V).
Because of constraints on the scales of maps presented in these reports and because the
smallest units used to present the indoor radon data are counties, some generalizations have
been made in order to estimate the radon potential of each area. Variations in geology, soil
characteristics, climatic factors, homeowner lifestyles, and other factors that influence radon
concentrations can be quite large within any particular geologic area, so these reports cannot
be used to estimate or predict the indoor radon concentrations of individual homes or housing
II-l Reprinted from USGS Open-File Report 93-292
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tracts. Within any area of a given geologic radon potential ranking, there are likely to be
areas where the radon potential is lower or higher than that assigned to the area as a whole,
especially in larger areas such as the large counties in some western states.
In each state chapter, references to additional reports related to radon are listed for the
state, and the reader is urged to consult these reports for more detailed information. In most
cases the best sources of information on radon for specific areas are state and local
departments of health, state departments responsible for nuclear safety or environmental
protection, and U.S. EPA regional offices. More detailed information on state or local
geology may be obtained from the state geological surveys. Addresses and telephone
numbers of state radon contacts, geological surveys, and EPA regional offices are listed in
Appendix C at the end of this chapter.
RADON GENERATION AND TRANSPORT IN SOILS
Radon (^Rn) is produced from the radioactive decay of radium (226Ra), which is, in turn,
a product of the decay of uranium (n*U) (fig. 1). The half-life of 222Rn is 3.825 days. Other
isotopes of radon occur naturally, but, with the exception of thoron (~°Rn), which occurs in
concentrations high enough to be of concern in a few localized areas, they are less important
in terms of indoor radon risk because of their extremely short half-lives and less common
occurrence. In general, the concentration and mobility of radon in soil are dependent on
several factors, the most important of which are the soil's radium content and distribution,
porosity, permeability to gas movement, and moisture content. These characteristics are, in
turn, determined by the soil's parent-material composition, climate, and the soil's age or
maturity. If parent-material composition, climate, vegetation, age of the soil, and topography
are known, the physical and chemical properties of a soil in a given area can be predicted.
As soils form, they develop distinct layers, or horizons, that are cumulatively called the
soil profile. The A horizon is a surface or near-surface horizon containing a relative
abundance of organic matter but dominated by mineral matter. Some soils contain an E
horizon, directly below the A horizon, that is generally characterized by loss of clays, iron, or
aluminum, and has a characteristically lighter color than the A horizon. The B horizon
underlies the A or E horizon. Important characteristics of B horizons include accumulation of
clays, iron oxides, calcium carbonate or other soluble salts, and organic matter complexes. In
drier environments, a horizon may exist within or below the B horizon that is dominated by
calcium carbonate, often called caliche or calcrete. This carbonate-cemented horizon is
designated the K horizon in modern soil classification schemes. The C horizon underlies the
B (or K) and is a zone of weathered parent material that does not exhibit characteristics of A
or B horizons; that is, it is generally not a zone of leaching or accumulation. In soils formed
in place from the underlying bedrock, the C horizon is a zone of unconsolidated, weathered
bedrock overlying the unweathered bedrock.
The shape and orientation of soil particles (soil structure) control permeability and affect
water movement in the soil. Soils with blocky or granular structure have roughly equivalent
permeabilities in the horizontal and vertical directions, and air and water can infiltrate the soil
relatively easily. However, in soils with platy structure, horizontal permeability is much
greater than vertical permeability, and air and moisture infiltration is generally slow. Soils
with prismatic or columnar structure have dominantly vertical permeability. Platy and
prismatic structures form in soils with high clay contents. In soils with shrink-swell clays, air
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and moisture infiltration rates and depth of wetting may be limited when the cracks in the
surface soil layers swell shut. Clay-rich B horizons, particularly those with massive or platy
structure, can form a capping layer that impedes the escape of soil gas to the surface
(Schumann and others, 1992). However, the shrinkage of clays can act to open or widen
cracks upon drying, thus increasing the soil's permeability to gas flow during drier periods.
Radon transport in soils occurs by two processes: (1) diffusion and (2) flow (Tanner,
1964). Diffusion is the process whereby radon atoms move from areas of higher
concentration to areas of lower concentration in response to a concentration gradient. Flow is
the process by which soil air moves through soil pores in response to differences in pressure
within the soil or between the soil and the atmosphere, carrying the radon atoms along with it.
Diffusion is the dominant radon transport process in soils of low permeability, whereas flow
tends to dominate in highly permeable soils (Sextro and others, 1987). In low-permeability
soils, much of the radon may decay before it is able to enter a building because its transport
rate is reduced. Conversely, highly permeable soils, even those that are relatively low in
radium, such as those derived from some types of glacial deposits, have been associated with
high indoor radon levels in Europe and in the northern United States (Akerblom and others,
1984; Kunz and others, 1989; Sextro and others, 1987). In areas of karst topography formed
in carbonate rock (limestone or dolomite) environments, solution cavities and fissures can
increase soil permeability at depth by providing additional pathways for gas flow.
Not all radium contained in soil grains and grain coatings will result in mobile radon
when the radium decays. Depending on where the radium is distributed in the soil, many of
the radon atoms may remain imbedded in the soil grain containing the parent radium atom, or
become imbedded in adjacent soil grains. The portion of radium that releases radon into the
pores and fractures of rocks and soils is called the emanating fraction. When a radium atom
decays to radon, the energy generated is strong enough to send the radon atom a distance of
about 40 nanometers (1 nm = 10"' 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
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solution cavities in the carbonate rock into houses. As warm air enters solution cavities that
are higher on the hillslope than the homes, it cools and settles, pushing radon-laden air from
lower in the cave or cavity system into structures on the hillslope (Gammage and others,
1993). In contrast, homes built over caves having openings situated below the level of the
home had higher indoor radon levels in the winter, caused by cooler outside air entering the
cave, driving radon-laden air into cracks and solution cavities in the rock and soil, and
ultimately, into homes (Gammage and others, 1993).
RADON ENTRY INTO BUILDINGS
A driving force (reduced atmospheric pressure in the house relative to the soil, producing
a pressure gradient) and entry points'must exist for radon to enter a building from the soil.
The negative pressure caused by furnace combustion, ventilation devices, and the stack effect
(the rising and escape of warm air from the upper floors, of the building, causing a
temperature and pressure gradient within the structure) during cold winter months are
common driving forces. Cracks and other penetrations through building foundations, sump
holes, and slab-to-foundation wall joints are common entry points.
Radon levels in the basement are generally higher than those on the main floor or upper
floors of most structures. Homes with basements generally provide more entry points for
radon, commonly have a more pronounced stack effect, and typically have lower air pressure
relative to the surrounding soil than nonbasement homes. The term "nonbasement" applies to
slab-on-grade or crawl space construction. .
METHODS AND SOURCES OF DATA
The assessments of radon potential in the booklets that follow this introduction were
made using five main types of data: (1) geologic (lithologic); (2) aerial radiometric; (3) soil
characteristics, including soil moisture, permeability, and drainage characteristics; (4) indoor
radon data; and (5) building architecture (specifically, whether homes in each area are built
slab-on-grade or have a basement or crawl space). These five factors were evaluated and
integrated to produce estimates of radon potential. Field measurements of soil-gas radon or
soil radioactivity were not used except where such data were available in existing, published
reports of local field studies. Where applicable, such field studies are described in the
individual state chapters.
GEOLOGIC DATA
The types and distribution of lithologic units and other geologic features in an
assessment area are of primary importance in determining radon potential. Rock types that
are most likely to cause indoor radon problems include carbonaceous black shales, glauconite-
bearing sandstones, certain kinds of fluvial sandstones and fluvial sediments, phosphorites,
chalk, karst-producing carbonate rocks, certain kinds of glacial deposits, bauxite, uranium-rich
granitic rocks, metamorphic rocks of granitic composition, silica-rich volcanic rocks, many
sheared or faulted rocks, some coals, and certain kinds of contact metamorphosed rocks.
Rock types least likely to cause radon problems include marine quartz sands, non-
carbonaceous shales and siltstones, certain kinds of clays, silica-poor metamorphic and
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igneous rocks, and basalts. Exceptions exist within these general lithologic groups because of
the occurrence of localized uranium deposits, commonly of the hydrothermal type in
crystalline rocks or the "roll-front" type in sedimentary rocks. Uranium and radium are
commonly sited in heavy minerals, iron-oxide coatings on rock and soil grains, and organic
uiaterials in soils and sediments. Less common are ..ranium associated with ph jsphate 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 (2MBi), 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 en^iS and
inconsistencies in the original data set (Duval and others, 1989). The data were then gridded
and contoured to produce maps of eU with a pixel size corresponding to approximately 2.5 x
2.5 km (1.6 x 1.6 mi).
II-6 Reprinted from USGS Open-File Report 93-292
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FLIGHT LINE SPACING OF NUkC AERIAL SURVEYS
2 KU (t MILE)
5 IM (3 MILES)
2 t 5 IH
10 Eli (6 MILES)
5 t 10 KM
NO DATA
Figure 2. Nominal flightline spacings for NURE aerial gamma-ray surveys covering the
contiguous United States (from Duval and others, 1990). Rectangles represent I°x2° quadrangles.
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Figure 2 is an index map of NUKE 1° x 2° quadrangles showing the flight-line spacing
for each quadrangle. In general, the more closely spaced the flightlines are, the more area
was covered by the aerial gamma survey, and thus, more detail is available in the data set.
For an altitude of 400 ft above the ground surface and with primary fiightline spacing
typically between 3 and 6 miles, less than 10 percent of the ground surface of the United
States was actually measured by the airborne gamma-ray detectors (Duval and others, 1989),
although some areas had better coverage than others due to the differences in flight-line
spacing between areas (fig. 2). This suggests that some localized uranium anomalies may not
have been detected by the aerial surveys, but the good correlations of eU patterns with
geologic outcrop patterns indicate that, at relatively small scales (approximately 1:1,000,000
or smaller) the National eU map (Duval and others, 1989) gives reasonably good estimates of
average surface uranium concentrations and thus can assist in the prediction of radon potential
of rocks and soils, especially when augmented with additional geologic and soil data.
The shallow (20-30 cm) depth of investigation of gamma-ray spectrometers, either
ground-based or airborne (Duval and others, 1971; Durrance, 1986), suggests that gamma-ray
data may sometimes underestimate the radon-source strength in soils in which some of the
radionuclides in the near-surface soil layers have been transported downward through the soil
profile. In such cases the concentration of radioactive minerals in the A horizon would be
lower than in the B horizon, where such minerals are typically concentrated. The
concentration of radionuclides in the C horizon and below may be relatively unaffected by
surface solution processes. Under these conditions the surface gamma-ray signal may indicate
a lower radon source concentration than actually exists in the deeper soil layers, which are
most likely to affect radon levels in structures with basements. The redistribution of
radionuclides in soil profiles is dependent on a combination of climatic, geologic, and
geochemical factors. There is reason to believe that correlations of eU with actual soil
radium and uranium concentrations at a depth relevant to radon entry into structures may be
regionally variable (Duval, 1989; Schumann and Gundersen, 1991). Given sufficient
understanding of the factors cited above, these regional differences may be predictable.
SOIL SURVEY DATA
Soil surveys prepared by the U.S. Soil Conservation Service (SCS) provide data on soil
characteristics, including soil-cover thickness, grain-size distribution, permeability, shrink-
swell potential, vegetative cover, generalized groundwater characteristics, and land use. The
reports are available in county formats and State summaries. The county reports typically
contain both generalized and detailed maps of soils in the area.
Because of time and map-scale constraints, it was impractical to examine county soil
reports for each county in the United States, so more generalized summaries at appropriate
scales were used where available. For State or regional-scale radon characterizations, soil
maps were compared to geologic maps of the area, and the soil descriptions, shrink-swell
potential, drainage characteristics, depth to seasonal high water table, permeability, and other
relevant characteristics of each soil group noted. Technical soil terms used in soil surveys are
generally complex; however, a good summary of soil engineering terms and the national
distribution of technical soil types is the "Soils" sheet of the National Atlas (U.S. Department
of Agriculture, 1987).
II-8 Reprinted from USGS Open-File Report 93-292
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Soil permeability is commonly expressed in SCS soil surveys in terms of the speed, in
inches per hour (in/hr), at which water soaks into the soil, as measured in a soil percolation
test. Although in/hr are not truly units of permeability, these units are in widespread use and
are referred to as "permeability" in SCS soil surveys. The permeabilities listed in the SCS
surveys are for water, but they generally correlate well with gas permeability. Because data
on gas permeability of soils is extremely limited, data on permeability to water is used as a
substitute except in cases in which excessive soil moisture is known to exist. Water in soil
pores inhibits gas transport, so the amount of radon available to a home is effectively reduced
by a high water table. .Areas likely to have high water tables include river valleys, coastal
areas, and some areas overlain by deposits of glacial origin (for example, loess).
Soil permeabilities greater than 6.0 in/hr may be considered high, and permeabilities less
than 0.6 in/hr may be considered low in terms of soil-gas transport. Soils with low
permeability may generally be considered to have a lower radon potential than more
permeable soils with similar radium concentrations. Many well-developed soils contain a
clay-rich B horizon that may impede vertical soil gas transport. Radon generated below this
horizon cannot readily escape to the surface, so it would instead tend to move laterally,
especially under the influence of a negative pressure exerted by a building.
Shrink-swell potential is an indicator of the abundance of smectitic (swelling) clays in a
soil. Soils with a high shrink-swell potential may cause building foundations to crack,
creating pathways for radon entry into the structure. During dry periods, desiccation cracks in
shrink-swell soils provide additional pathways for soil-gas transport and effectively increase
the gas permeability of the soil. Soil permeability data and soil profile data thus provide
important information for regional radon assessments.
INDOOR RADON DATA
Two major sources of indoor radon data were used. The first and largest source of data is
from the State/EPA Residential Radon Survey (Ronca-Battista and others, 1988; Dziuban and
others, 1990). Forty-two states completed EPA-sponsored indoor radon surveys between 1986
and 1992 (fig. 3). The State/EPA Residential Radon Surveys were designed to be
comprehensive and statistically significant at the state level, and were subjected to high levels
of quality assurance and control. The surveys collected screening indoor radon measurements,
defined as 2-7 day measurements using charcoal canister radon detectors placed in the lowest
livable area of the home. The target population for the surveys included owner-occupied
single family, detached housing units (White and others, 1989), although attached structures
such as duplexes, townhouses, or condominiums were included in some of the surveys if they
met the other criteria and had contact with the ground surface. Participants were selected
randomly from telephone-directory listings. In total, approximately 60,000 homes were tested
in the State/EPA surveys.
The second source of indoor radon data comes from residential surveys that have been
conducted in a specific state or region of the country (e.g. independent state surveys or utility
company surveys). Several states, including Delaware, Florida, Illinois, New Hampshire, New
Jersey, New York, Oregon, and Utah, have conducted their own surveys of indoor radon. The
quality and design of a state or other independent survey are discussed and referenced where
the data are used.
II-9 Reprinted from USGS Open-File Report 93-292
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Data for only those counties with five or more measurements are shown in the indoor
radon maps in the state chapters, although data for all counties with a nonzero number of
measurements are listed in the indoor radon data tables in each state chapter. Iivtotal, indoor
radon data from more than 100,000 homes nationwide were used in the compilation of these
assessments. Radon data from State or regional indoor radon surveys, public health
organizations, or other sources are discussed in addition to the primary data sources where
they are available. Nearly all of the data used in these evaluations represent short-term (2-7
day) screening measurements from the lowest livable space of the homes. Specific details
concerning the nature and use of indoor radon data sets other than the State/EPA Residential
Radon Survey are discussed in the individual State chapters.
RADON INDEX AND CONFIDENCE INDEX
Many of the geologic methods used to evaluate an area for radon potential require
subjective opinions based on the professional judgment and experience of the individual
geologist. The evaluations are nevertheless based on established scientific principles that are
universally applicable to any geographic area or geologic setting. This section describes the
methods and conceptual framework used by the U.S. Geological Survey to evaluate areas for
radon potential based on the five factors discussed in the previous sections. The scheme is
divided into two basic parts, a Radon Index (RI), used to rank the general radon potential of
the area, and the Confidence Index (CI), used to express the level of confidence in the
prediction based on the quantity and quality of the data used to make the determination. This
scheme works best if the areas to be evaluated are delineated by geologically-based
boundaries (geologic provinces) rather than political ones (state/county boundaries) in which
the geology may vary across the area.
Radon Index. Table 1 presents the Radon Index (RI) matrix. The five factors—indoor
radon data, geology, aerial radioactivity, soil parameters, and house foundation type—were
quantitatively ranked (using a point value of 1, 2, or 3) for their respective contribution to
radon potential in a given area. At least some data for the 5 factors are consistently available
for every geologic province. Because each of these main factors encompass a wide variety of
complex and variable components, the geologists performing the evaluation relied heavily on
their professional judgment and experience in assigning point values to each category and in
determining the overall radon potential ranking. Background information on these factors is
discussed in more detail in the preceding sections of this introduction.
Indoor radon was evaluated using unweighted arithmetic means of the indoor radon data
for each geologic area to be assessed. Other expressions of indoor radon levels in an area
also could have been used, such as weighted averages or annual averages, but these types of
data were not consistently available for the entire United States at the time of this writing, or
the schemes were not considered sufficient to provide a means of consistent comparison
across all areas. For this report, charcoal-canister screening measurement data from the
State/EPA Residential Radon Surveys and other carefully selected sources were used, as
described in the preceding section. To maintain consistency, other indoor radon data sets
(vendor, state, or other data) were not considered in scoring the indoor radon factor of the
Radon Index if they were not randomly sampled or could not be statistically combined with
the primary indoor radon data sets. However, these additional radon data sets can provide a
means to further refine correlations between geologic factors and radon potential, so they are
11-11 Reprinted from USGS Open-File Report 93-292
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TABLE 1. RADON INDEX MATRIX, "ppm eU" indicates parts per million of equivalent
uranium, as indicated by NURE aerial radiometric data. See text discussion for details.
FACTOR
INDOOR RADON (average)
AERIAL RADIOACTIVITY
GEOLOGY*
SOIL PERMEABILITY
ARCHrrECTURE TYPE
INCREASING RADON POTENTIAL ^
POINT VALUE
1
<2pCi/L
< 1.5 ppm eU
negative
low
mostly slab
2
2-4pCi/L
1.5 - 2.5 ppm eU
variable
moderate
mixed
3
>4pCi/L
>2.5ppmeU
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 uotential cateeorv
Point ranee
Probable average screening
indoor radon for area
LOW
MODERATE/VARIABLE
HIGH
3-8 points
9-11 points
12-17 points
<2pCi/L
2-4pCi/L
>4pCi/L
POSSIBLE RANGE OF POINTS = 3 to 17
TABLE 2.
CONFIDENCE INDEX MATRIX
INCREASING CONFIDENCE
FACTOR
INDOOR RADON DATA
AERIAL RADIOACTIVITY
GEOLOGIC DATA
SOIL PERMEABILITY
POINT VALUE
1
sparse/no data
questionable/no data
questionable
questionable/no data
2
fair coverage/quality
glacial cover
variable
variable
3
good coverage/quality
no glacial cover
proven geol. model
reliable, abundant
SCORING:
LOW CONFIDENCE
MODERATE CONFIDENCE
HIGH CONFIDENCE
4-6 points
7-9 points
10 -12 points
POSSIBLE RANGE OF POINTS = 4 to 12
11-12 Reprinted from USGS Open-File Report 93-292
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included as supplementary information and are discussed in the individual State chapters. If
the average screening indoor radon level for an area was less than 2 pCi/L, the indoor radon
factor was assigned 1 point, if it was between 2 and 4 pCi/L, it was scored 2 points, and if
the average screening indoor radon level for an area was greater than 4 pCi/L, the indoor
radon factor was assigned 3 RI points.
Aerial radioactivity data used in this report are from the equivalent uranium map of the
conterminous United States compiled from NURE aerial gamma-ray surveys (Duval and
others, 1989). These data indicate the gamma radioactivity from approximately the upper 30
cm of rock and soil, expressed in units of ppm equivalent uranium. An approximate average
value of eU was determined visually for each area and point values assigned based on
whether the overall eU for the area falls below 1.5 ppm (1 point), between 1.5 and 2.5 ppm
(2 points), or greater than 2.5 ppm .(3 points)
The geology factor is complex and actually incorporates many geologic characteristics. In
the matrix, "positive" and "negative" refer to the presence or absence and distribution of rock
types known to have high uranium contents and to generate elevated radon in soils or indoors.
Examples of "positive" rock types include granites, black shales, phosphatic rocks, and other
rock types described in the preceding "geologic data" section. Examples of "negative" rock
types include marine quartz sands and some clays. The term "variable" indicates that the
.geology within the region is variable or that the rock types in the area are known or suspected
to generate elevated radon in some areas but not in others due to compositional differences,
climatic effects, localizeddistribution of uranium, or other factors. Geologic information
indicates not only how much uranium is present in the rocks and soils but also gives clues for
predicting general radon emanation and mobility characteristics through additional factors
such as structure (notably the presence of faults or shears) and geochemical characteristics
(for example, a phosphate-rich sandstone will likely contain more uranium than a sandstone
containing little or no phosphate because the phosphate forms chemical complexes with
uranium). "Negative", "variable", and "positive" geology were assigned 1, 2, and 3 points,
respectively.
In cases where additional reinforcing or contradictory geologic evidence is available,
Geologic Field Evidence (GFE) points were added to or subtracted from an area's score
(Table 1). Relevant geologic field studies are important to enhancing our understanding of
how geologic processes affect radon distribution. In some cases, geologic models and
supporting field data reinforced an already strong (high or low) score; in others, they provided
important contradictory data. GFE points were applied for geologically-sound evidence that
supports the prediction (but which may contradict one or more factors) on the basis of known
geologic field studies in the area or in areas with geologic and climatic settings similar
enough that they could be applied with full confidence. For example, areas of the Dakotas,
Minnesota, and Iowa that are covered with Wisconsin-age glacial deposits exhibit a low aerial
radiometric signature and score only one RI point in that category. However, data from
geologic field studies in North Dakota and Minnesota (Schumann and others, 1991) suggest
that eU is a poor predictor of geologic radon potential in this area because radionuclides have
11-13 Reprinted from USGS Open-File Report 93-292
-------
been leached from the upper soil layers but are present and possibly even concentrated in
deeper soil horizons, generating significant soil-gas radon. This positive supporting field
evidence adds two GFE points to the score, which helps to counteract the invalid conclusion
suggested by the radiometric data. No GFE points are awarded if there are no documented
field studies for the area.
"Soil permeability" refers to several soil characteristics that influence radon concentration
and mobility, including soil type, grain size, structure, soil moisture, drainage, slope, and
permeability. In the matrix, "low" refers to permeabilities less than about 0.6 in/hr; "high"
corresponds to greater than about 6.0 in/hr, in U.S. Soil Conservation Service (SCS) standard
soil percolation tests. The SCS data-are for water permeability, which generally correlates
well with the gas permeability of the soil except when the soil moisture content is very high.
Areas with consistently high water tables were thus considered-to have low gas permeability.
"Low, "moderate", and "high" permeability were assigned 1, 2, and 3 points, respectively.
Architecture type refers to whether homes in the area have mostly basements (3 points),
mostly slab-on-grade construction (1 point), or a mixture of the'two. Split-level and crawl
space homes fall into the "mixed" category (2 points). Architecture information is necessary
to properly interpret the indoor radon data and produce geologic radon potential categories
that are consistent with screening indoor radon data.
The overall RI for an area is calculated by adding the individual RI scores for the 5
factors, plus or minus GFE points, if any. The total RI for an area falls in one of three
categories—low, moderate or variable, or high. The point ranges for the three categories were
determined by examining the possible combinations of points for the 5 factors and setting
rules such that a majority (3 of 5 factors) would determine the final score for the low and
high categories, with allowances for possible deviation from an ideal score by the other two
factors. The moderate/variable category lies between these two ranges. A total deviation of 3
points from the "ideal" score was considered reasonable to allow for natural variability of
factors—if two of the five factors are allowed to vary from the "ideal" for a category, they
can differ by a minimum of 2 (1 point different each) and a maximum of 4 points (2 points
different each). With "ideal" scores of 5, 10, and 15 points describing low, moderate, and
high geologic radon potential, respectively, an ideal low score of 5 points plus 3 points for
possible variability allows a maximum of 8 points in the low category. Similarly, an ideal
high score of 15 points minus 3 points gives a minimum of 12 points for the high category.
Note, however, that if both other factors differ by two points from the "ideal", indicating
considerable variability in the system, the total point score would lie in the adjacent (i.e.,
1 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 dam ^ukely 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
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significantly higher air permeability when dry due to shrinkage cracks in the soil. These
additional factors were applied to the soil permeability factor when assigning the RI score, but
may have less certainty in some cases and thus would be assigned a lower CI score.
The Radon Index and Confidence Index give a general indication of the relative
contributions of the interrelated geologic factors influencing radon generation and transport in
rocks and soils, and thus, of the potential for elevated indoor radon levels to occur in a
particular area. However, because these reports are somewhat generalized to cover relatively
large areas of States, it is highly recommended that more detailed studies be performed in
local areas of interest, using the methods and general information in these booklets as a guide.
11-16 Reprinted from USGS Open-File Report 93-292
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and indoor radon with geology in glacially derived soils of the northern Great Plains, in
Proceedings of the 1990 International Symposium on Radon and Radon Reduction
Technology, Volume 2, Symposium Oral Papers: U.S. Environmental Protection Agency
report EPA/600/9-91/026b, p. 6-23-6-36.
11-18 Reprinted from USGS Open-Hie Report 93-292
-------
Schumann, R.R., Owen, D.E., and Asher-Bolinder, S., 1992, Effects of weather and soil
characteristics on temporal variations in soil-gas radon concentrations, in Gates, A.E., and
Gundersen, L.C.S., eds., Geologic controls on radon: Geological Society of: America
Special Paper 271, p. 65-72.
Sextro, R.G., Moed, B.A., Nazaroff, W.W., Revzan, K.L., and Nero, A.V., 1987,
Investigations of soil as a source of indoor radon, in Hopke, P.K., ed., Radon and its
decay products: American Chemical Society Symposium Series 331, p. 10-29.
Sterling, R., Meixel, G., Shen, L., Labs, K., and Bligh, T., 1985, Assessment of the energy
savings potential of building foundations research: Oak Ridge, Term., U.S. Department of
Energy Report ORNL/SUB/84-0024/1.
Smith, R.C., n, Reilly, M.A., Rose, A.W., Barnes, J.H., and Berkheiser, S.W., Jr., 1987,
Radon: a profound case: Pennsylvania Geology, v. 18, p. 1-7.
Tanner, A.B., 1964, Radon migration in the ground: a review, in Adams, J.A.S., and Lowder,
W.M., eds., The natural radiation environment: Chicago, HI., University of Chicago
Press, p. 161-190.
Tanner, A.B., 1980, Radon migration in the ground: a supplementary review, in Gesell, T.F.,
and Lowder, W.M. (eds), Natural radiation environment HI, Symposium proceedings,
Houston, Texas, v. 1, p. 5-56.
U.S. Department of Agriculture, 1987, Principal kinds of soils: Orders, suborders, and great
groups: U.S. Geological Survey, National Atlas of the United States of America, sheet
38077-BE-NA-07M-00, scale 1:7,500,000.
U.S. Department of Energy, 1976, National Uranium Resource Evaluation preliminary report,
prepared by the U.S. Energy Research and Development Administration, Grand Junction,
Colo.: GJO-11(76).
Wanty, Richard B., and Schoen, Robert, 1991, A review of the chemical processes affecting the
mobility of radionuclides in natural waters, with applications, in Gundersen, Linda C.S.,
and Richard B. Wanty, eds., Field studies of radon in rocks, soils, and water: U.S.
Geological Survey Bulletin no. 1971, p. 183-194.
Washington, J.W., and Rose, A.W., 1990, Regional and temporal relations of radon in soil gas to
soil temperature and moisture: Geophysical Research Letters, v. 17, p. 829-832.
White, S.B., Bergsten, J.W., Alexander, B.V., and Ronca-Battista, M., 1989, Multi-State
surveys of indoor 222Rn: Health Physics, v. 57, p. 891-896.
II-19 Reprinted from USGS Open-File Report 93-292
-------
-------
APPENDIX A
GEOLOGIC TIME SCALE
Subdivisions (and their symbols)
Honor
Eonothem
Phanerozoic2
Proteroroic
tc)
Archean
(A)
Era or
Erathem
Cenozoic
(Cz)
Mesozoic2
(Mi)
Paleozoic2
(Pd
fresco*
pJSS&m
»J£&no
An^ilfW.
Miodw
fcarty
Period, System,
Subperiod. Subsystem
Quaternary 2
(Q)
Neocene 2
Subperiod or
T.^;,^ Subsystem IN)
m Ptieogene
Suboeriod or
Subsystem (Pi)
Cretaceous
(K)
Jurassic
(J)
Triassic
CR)
Permian
Pennsylvanian
Carboniferous
-------
-------
APPENDIX B
GLOSSARY OF TERMS
TTr»ts 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 to the study of radon
aerial radiometric, aeroradiometric survey A survey of radioactivity, usually gamma rays,
taken by an aircraft carrying a gamma-ray spectrometer pointed at the ground surface.
alluvial fan A low, widespread mass of loose rock and soil material, shaped like an open fan
and deposited by a stream at the point where it flows from a narrow mountain valley out onto a
plain or broader valley. May also form at the junction with larger streams or when the gradient of
the stream abruptly decreases.
alluvium, alluvial General terms referring to unconsolidated detrital material deposited by a
stream or other body of running water.
alpha-track detector A passive radon measurement device consisting of a plastic film that is
sensitive to alpha particles. The film is etched with acid in a laboratory after it is exposed. The
etching reveals scratches, or "tracks", left by the alpha particles resulting from radon decay, which
can then be counted to calculate the radon concentration. Useful for long-term (1-12 months)
radon tests.
ampnibolite A mafic metamorphic rock consisting mainly of pyroxenes and(or) amphibole and
plagioclase.
11-21 Rqmnted 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 die
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 man 1/256 mm.
day 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 genfle slope on one side and a steep slope on the other. The
formation of a cuesta is controlled by the different weathering properties and the structural dip of
the rocks forming the hill or ridge.
daughter product A nuclide formed by the disintegration of a radioactive precursor or "parent"
atom.
n-22 Reprinted from USGS Open-File Report 93-292
-------
delta, deltaic Referring to a low, flat, alluvial tract of land having a triangular or fan shape,
located at or near the mouth of a river. It results from the accumulation of sediment deposited by a
river at the point at which the river loses its ability to transport the sediment, commonly where a
river meets a larger body of water such as a lake or ocean.
dike A tabular igneous intrusion of rock, younger than the surrounding rock, that commonly cuts
across the bedding or foliation of the rock it intrudes.
diorite A plutonic igneous rock that is medium in color and contains visible dark minerals that
make up less than 50% of the rock. It also contains abundant sodium plagioclase and minor
quartz.
dolomite A carbonate sedimentary rock of which more than 50% consists of the mineral dolomite
(CaMg(CO3)2), and is commonly white, gray, brown, yellow, or pinkish in color.
drainage The manner in which the waters of an area pass, flow off of, or flow into the soil.
Also refers to the water features of an area, such as lakes and rivers, that drain it
eolian Pertaining to sediments deposited by the wind.
esker A long, narrow, steep-sided ridge composed of irregular beds of sand and gravel deposited
by streams beneath a glacier and left behind when the ice melted.
evapotranspiration Loss of water from a land area by evaporation from the soil and
transpiration from plants.
extrusive Said of igneous rocks that have been erupted onto the surface of the Earth.
fault A fracture or zone of fractures in rock or sediment along which there has been movement
fluvial, fluvial deposit Pertaining to sediment that has been deposited by a river or stream.
foliation A linear feature in a rock defined by both mineralogic and structural characteristics. It
may be formed during deformation or metamorphism.
formation A mappable body of rock having similar characteristics.
glacial deposit Any sediment transported and deposited by a glacier or processes associated
with glaciers, such as glaciofluvial sediments deposited by streams flowing from melting glaciers.
gneiss A rock formed by metamorphism in which bands and lenses of minerals of similar
composition alternate with bands and lenses of different composition, giving the rock a striped or
"foliated" appearance.
granite Broadly applied, any coarsely crystalline, quartz- and feldspar-bearing igneous plutonic
rock. Technically, granites have between 10 and 50% quartz, and alkali feldspar comprises at least
65% of the total feldspar.
gravel An unconsolidated, natural accumulation of rock fragments consisting predominantly of
particles greater than 2 mm in size.
heavy minerals Mineral grains in sediment or sedimentary rock having higher than average
specific gravity. May form layers and lenses because of wind or water sorting by weight and size
n-23 Reprinted from USGS Open-File Report 93-292
-------
and may be refened to as a "placer deposit" Some heavy minerals are magnetite, garnet, zircon,
monazite, and xenotime.
Igneous Said of a rock or mineral that solidified from molten or partly molten rock material. It is
one of the three main classes into which rocks are divided, the others being sedimentary and
metamorphic.
intermontane A term that refers to an area between two mountains or mountain ranges.
intrusion, intrusive The processes of emplacement or injection of molten rock into pre-existing
rock. Also refers to the rock formed by intrusive processes, such as an "intrusive igneous rock".
kame A low mound, knob, hummock, or short irregular ridge formed by a glacial stream at the
margin of a melting glacier; composed of bedded sand and gravel.
karst terrain A type of topography that is formed on limestone, gypsum and other rocks by
dissolution of the rock by water, forming sinkholes and caves.
lignite A brownish-black coal that is intermediate in coalification between peat and
subbituminous coal.
limestone A carbonate sedimentary rock consisting of more than 50% calcium carbonate,
primarily in the form of the mineral calcite (CaCOs).
lithology The description of rocks in hand specimen and in outcrop on the basis of color,
composition, and grain size.
loam A permeable soil composed of a mixture of relatively equal parts clay, silt, and sand, and
usually containing some organic matter.
loess A fine-grained eolian deposit composed of silt-sized particles generally thought to have
been deposited from windblown dust of Pleistocene age.
mafic Term describing an igneous rock containing more than 50% dark-colored minerals.
marine Term describing sediments deposited in the ocean, or precipitated from ocean waters.
metamorphic Any rock derived from pre-existing rocks by mineralogical, chemical, or structural
changes in response to changes in temperature, pressure, stress, and the chemical environment
PhylUte, schist, amphibolite, and gneiss are metamorphic rocks.
moraine A mound, ridge, or other distinct accumulation of unsorted, imbedded glacial material,
predominantly tiB, deposited by the action of glacial ice.
outcrop That part of a geologic formation or structure that appears at the surface of the Earth, as
in "rock outcrop".
percolation test A term used in engineering for a test to determine the water permeability of a
soil. A hole is dug and filled with water and the rate of water level decline is measured.
permeability The capacity of a rock, sediment, or soil to transmit liquid or gas.
phosphate, phosphatic, phosphorite Any rock or sediment containing a significant amount
of phosphate minerals, Le., minerals containing PO4.
TI-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 (Uthification) 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 behind by a stream as it
cuts down to a lower level. • .
terrain A tract or region of the Earth's surface considered as a physical feature or ah ecological
environment
till Unsortcd, generally unconsolidated and imbedded rock and mineral material deposited directly
adjacent to and underneath a glacier, without reworking by meltwater. Size of grains varies greatly
from clay to boulders.
uraniferous Containing uranium, usually more than 2 ppm.
vendor data Used in this report to refer to indoor radon data collected and measured by
commercial vendors of radon measurement devices and/or services.
volcanic Pertaining to the activities, structures, and extrusive rock types of a volcano.
water table The surface forming the boundary between the zone of saturation and the zone of
aeration; the top surface of a body of unconfined groundwater in rock or soil.
weathering The destructive process by which earth and rock materials, on exposure to
atmospheric elements, are changed in color, texture, composition, firmness, or form with little or
no transport of the material.
11-26 Reprinted from USGS Open-Hie 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, JJ, 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
H-27 Reprinted from USGS Open-File Report 93-292
-------
STATE RADON CONTACTS
. May, 1993
Arizona
Clifornia
Colorado
JamesMcNees
Division of Radiation Control
Alabama Department of Public .health
Stale Office Building
Montgomery, AL 36130
(205)242-5315
1-800-582-1866 in state
Charles Tedford
Department of Health and Social
Services
P.O. Box 110613
Juneau,AK 99811-0613
(907)465-3019
1-800-478-4845 in state
John Stewart
Arizona Radiation Regulatory Agency
4814 South 40th St
Phoenix, AZ 85040
(602)255-4845
LeeGershner
Division of Radiation Control
Department of Health
4815 Markham Street, Slot 30
Little Rock, AR 72205-3867
(501)661-2301
J. David Quinton
Department of Health Services
714 P Street, Room 600
Sacramento, CA 94234-7320
(916)324-2208
1-800-745-7236 in state
Linda Martin
Department of Health
4210 East llth Avenue
Denver, CO 80220
(303)692-3057
1-800-846-3986 in state
Connecticut Alan J. Siniscalchi
Radon Program
Connecticut Department of Health
Services
150 Washington Street
Hartford, CT 06106-4474
(203) 566-3122
Delaware MaraiG.Rejai
Office of Radiation Control
Division of Public Health
P.O. Box 637
Dover, DE 19903
(302)736-3028
1-800-554-4636 Li 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 GiUey
Office of Radiation Control
Department of Health and
Rehabilitative Services
1317 Winewood Boulevard
Tallahassee, EL 32399-0700
(904)488-1525
1-800-543-8279 in state
Georgia Richard Schreiber
Georgia Department of Human
Resources
878 Peachtree St. Room 100
Atlanta, GA 30309
(404)894-6644
1-800-745-0037 in state
Hawaii Russell Takata
Environmental Health Services
Division
591 Ala Moana Boulevard
Honolulu, HI 96813-2498
(808)586-4700
n-28 Reprinted from USGS Open-File Report 93-292
-------
Idaho
Illinois
Indiana
Iowa
Kansas
Kentucky
PatMcGavam
Office of Environmental Health
450 West State Street
Boise, ID 83720
(208)334-6584
1-800-445-8647 in state
Richard Allen
Illinois Department of Nuclear Safety
1301 Outer Park Drive
Springfield, IL 62704
(217)524-5614
1-800-325-1245 in state
Lorand Magyar
Radiological Health Section
Indiana State Department of Health
1330 West Michigan Street
P.O. Box 1964
Indianapolis, IN 46206
(317)633-8563
1-800-272-9723 In State
Donald A. Plater
Bureau of Radiological Health
Iowa Department of Public Health
Lucas State Office Building
Des Moines, IA 50319-0075
(515)281-3478
1-800-383-5992 In State
Harold Spiker
Radiation Control Program
Kansas Department of Health and
Environment
109 SW 9th Street
6th Floor Mills Building
Topeka, KS 66612
(913)296-1561
JeanaPhelps
Radiation Control Branch
Department of Health Services
Cabinet for Human Resources
275 East Main Street
Frankfort, KY 40601
(502)564-3700
Louisiana Matt Schlenker
Louisiana Department of
Environmental Quality
P.O. Box 82135
Baton Rouge, LA 70o84-2135
(504)925-7042
1-800-256-2494 in state
Maine. BpbStilwell
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 LeonJ.Rachuba
Radiological Health Program
Maryland Department of the
Environment
2500 Broening Highway
Baltimore, MD 21224
(410)631-3301
1-800-872-3666 In State
Massachusetts William J. Bell
Radiation Control Program
Department of Public Health
23 Service Center
Northampton, MA 01060
(413) 586-7525
1-800-445-1255 in state
Michigan SueHendershott
Division of Radiological Health
Bureau of Environmental and
Occupational Health
3423 North Logan Street
P.O. Box 30195
Lansing, MI 48909
(517)335-8194
Minnesota LauraOatmann
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
Six Hazen Drive
Concord, NH 03301
(603)271-4674
1-800-852-3345 x4674
New Jersey Tonalee Carlson Key
Division of Environmental Quality
Department of Environmental
Protection
CN415
Trenton, NT 08625-0145
(609)987-6369
1-800-648-0394 in state
New Mexico William M. Floyd
Radiation Licensing and Registration
Section
New Mexico Environmental
Improvement Division
1190 St. Francis Drive
Santa Fe,NM 87503
(505) 827-4300
New York William J. Condon
Bureau of Environmental Radiation
Protection
New York State Health Department
Two University Place
Albany, NY 12202
(518)458-6495
1-800-458-1158 in state
North Carolina Dr. Felix Fong
Radiation Protection Division
Department of Environmental Health
and Natural Resources
701 Barbour Drive
Raleigh, NC 27603-2008
(919)571-4141
1-800-662-7301 (recorded info x4196)
North Dakota Alien Jacobson
North Dakota Department of Health
1200 Missouri Avenue, Room 304
P.O. Box 5520
Bismarck, ND 58502-5520
(701)221-5188
Ohio Marcie Matthews
Radiological Health Program
Department of Health
1224 Kinnear Road - Suite 120
Columbus, OH 43212
(614)644-2727
1-800-523-4439 in state
n-30 Reprinted from USGS Open-File Report 93-292
-------
Oklahoma
Oregon
Pennsylvania
Puerto Rico
Rhode Island
South Carolina
Gene Smith
Radiation Protection Division
Oklahoma State Department of
Health
P.O. Box 53551
Oklahoma City, OK 73152
(405)271-5221
George Toombs
Department of Human Resources
Health Division
1400 SW 5th Avenue
Portland, OR 97201
(503)73M014
Michael Pyles
Pennsylvania Department of
Environmental Resources
Bureau of Radiation Protection
P.O. Box 2063
Harrisburg, PA 17120
(717)783-3594
1-800-23-RADON In State
David SaMana
Radiological Health Division
G J».O. Call Box 70184
Rio Piedras, Puerto Rico 00936
(809)767-3563
Edmund Arcand
Division of Occupational Health and
Radiation
Department of Health
205 Cannon Building
Davis Street
Providence, RI02908
(401)277-2438
Bureau of Radiological Health
Department of Health and
Environmental Control
2600 Bull Street
Columbia, SC 29201
(803)734-4631
l-SOO-768-0362
South Dakota MikePochop
Division of Environment Regulation
Department of Water and Natural
Resources
Joe Foss Building, Room 217
523 E. Capitol
Pierre, SD 57501-3181
(605)773-3351
Tennessee Susie Shimek
Division of Air Pollution Control
Bureau of the Environment
Department of Environment and
Conservation
Customs House, 701 Broadway
Nashville, TN 37219-5403
(615)532-0733
1-800-232-1139 in state
Texas Gary Smith
Bureau of Radiation Control
Texas Department of Health
1100 West 49th Street
Austin, TX 78756-3189
(512) 834-6688
Utah John Hultquist
Bureau of Radiation Control
Utah State Department of Health
288 North, 1460 West
P.O. Box 16690
Salt Lake City, UT 84116-0690
(801)536-4250
Vermont Paul demons
Occupational and Radiological Health
Division
Vermont Department of Health
10 Baldwin Street
Montpelier, VT 05602
(802) 828-2886
1-800-640-0601 in state
Virgin Islands Contact the U.S. Environmental
Protection Agency, Region n
in New York
(212)264-4110
n-3i
Reprinted from USGS Open-File Report 93-292
-------
Washington
West Virginia
Wisconsin
Womin
Shelly Ottenbrite
Bureau of Radiological Health
Department of Health
109 Governor Street
Richmond, VA 23219
(804) 786-5932
1-800-468-0138 in state
KateColeman
Department of Health
Office of Radiation Protection
Airdustrial Building 5, LE-13
01ympia,WA 98504
(206)753^*518
1-800-323-972711 State
BeattieL.DeBpid
Industrial Hygiene Division
West Virginia Department of Health
151 llth Avenue
South Charleston, WV 25303
(304)558-3526
1-800-922-1255 In State
ConradWeiffenbach
Radiation Protection Section
Division of Health
Department of Health and Social
Services
P.O. Box 309
Madison, WI 53701-0309
(608)267-4796
1-800-798-9050 in state
Janet Hough
Wyoming Department of Health and
Social Services
Hathway Building, 4th Floor
Cheyenne, WY 82002-0710
(307)777-6015
1-800-458-5847 in state
n-32 Reprinted from USGS Open-Hie 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
CflJiffl"ii? James F. Davis
California Division of Mines &
Geology
801K Street, MS 12-30
Sacramento, CA 95814-3531
(916)445-1923
Colorado Pat Rogers (Acting)
Colorado Geological Survey
1313 Sherman St., Rm 715
Denver, CO 80203
(303)866-2611
Connecticut Richard C. Hyde
Connecticut Geological & Natural
History Survey
165 Capitol Ave., Rm. 553
Hartford, CT 06106
(203)566-3540
Delaware Robert R. Jordan
Delaware Geological Survey
University of Delaware
101 Penny Hall
Newark, DE19716-7501
(302)831-2833
Florida Walter Schmidt
Florida Geological Survey
903 W. Tennessee St.
Tallahassee, FL 32304-7700
(904)488^191
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, HI 96809
(808)548-7539
Idaho Earl H. Bennett
Idaho Geological Survey
University of Idaho
Merrill Hall, Rm. 332
Moscow, ID 83843
(208)885-7991
Illinois Morris W. Leighton
Illinois State Geological Survey
Natural Resources Building
615 East Peabody Dr.
Champaign, IL 61820
(217)333-4747
Indiana Norman C. Hester
Indiana Geological Survey
611 North Walnut Grove
Bloomington, IN 47405
(812)855-9350
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 CHaney
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
Mayland 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 PriscilJa C. Grew
Minnesota Geological Survey
2642 University Ave.
SL Paul, MN 55114-1057
(612)627-4780
Mississippi S. CraginKnox
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
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 HLFakundiny
New York State Geological Survey
3136 Cultural Education Center
Empire State Plaza
Albany, NY 12230
(518)474-5816
U-34 Reprinted from USGS Open-File Report 93-292
-------
North Carolina Charles H. Gardner
North Carolina Geological Survey
P.O. Box 27687
Raleigh, NC 27611-7687
(919)733-3833
North Dakota John P. Bluemle
North Dakota Geological Survey
600 East Blvd.
Bismarck, ND 58505-0840
(701)224-4109
Ohio Thomas M. Berg
Ohio DepL of Natural Resources
Division of Geological Survey
4383 Fountain Square Drive
Columbus, OH 43224-1362
(614)265-6576
Oklahoma Charles J. Mankin
Oklahoma Geological Survey
Room N-131, Energy Center
lOOE.Boyd
Norman, OK 73019-0628
(405)325-3031
Oregon Donald A. Hull
Dept of Geology & Mineral Indust.
Suite 965
800 ME Oregon SL #28
Portland, OR 97232-2162
(503)731-4600
Pennsylvania Donald M. Hoskins
Dept of Environmental Resources
Bureau of Topographic & Geologic
Survey
P.O. Box 2357
Harrisburg, PA 17105-2357
(717)787-2169
Puerto Rico Ramon M. Alonso
Puerto Rico Geological Survey
Division
Box 5887
Puerta de Tierra Station
San Juan, PJL 00906
(809)722-2526
Rhode Island J. Allan Cain
Department of Geology
University of Rhode Island
315 Green Hall
Kingston, RI02881
(401)792-2265
South Carolina Alan-Jon W.Zupan (Acting)
South Carolina Geological Survey
5 Geology Road
Columbia, SC 29210-9998
(803)737-9440
South Dakota CM. Christensen (Acting)
South Dakota Geological Survey
Science Center
University of South Dakota
Vermillion, SD 57069-2390
(605)677-5227
Tennessee Edward T.Luther
Tennessee Division of Geology
13th Floor, L & C Tower
401 Church Street
Nashville, TN 37243-0445
(615)532-1500
Texas William L. Fisher
Texas Bureau of Economic Geology
University of Texas
University Station, Box X
Austin, TX 78713-7508
(512)471-7721
Utah M. Lee Allison
Utah Geological & Mineral Survey
2363 S. Foothill Dr.
Salt Lake City, UT 84109-1491
(801)467-7970
Vermont Diane L. Conrad
Vermont Division of Geology and
Mineral Resources
103 South Main St
Waterbury.VT 05671
(802)244-5164
Virginia Stanley S. Johnson
Virginia Division of Mineral
Resources
P.O. Box 3667
Charlottesville, VA 22903
(804)293-5121
Washington Raymond Lasmanis
Washington Division of Geology &
Earth Resources
Department of Natural Resources
P.O. Box 47007
Olympia, Washington 98504-7007
(206)902-1450
11-35 Reprinted ftomUSGS Open-File Report 93-292
-------
West Virginia LanyD.Woodfrak
West Virginia Geological and .
Economic Survey
Mont Chateau Research Center
P.O. Box 879
Morgantown,WV 26507-0879
(304)594-2331
Wisconsin James Robertson
Wisconsin Geological & Natural
History Survey
3817 Mineral Point Road
Madison, WI 53705-5100
(608)263-7384
Wyoming Gary B. Glass
Geological Survey of Wyoming
University of Wyoming
Box 3008, University Station
Laramie, WY 82071-3008
(307)766-2286
11-36 Reprinted from USGS Open-Hie Report 93-292
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EPA REGION 3 GEOLOGIC RADON POTENTIAL SUMMARY
by
Linda C.S. Gundersen, James K. Otton, and Sandra L. Szarzi
U.S. Geological Survey
EPA Region 3 includes the states of Delaware, Maryland, Pennsylvania, Virginia, and
West Virginia.. For each state, geologic radon potential areas were delineated and ranked on the
basis of geologic, soil, housing construction, and other factors. Areas in which the average
screening indoor radon level of all homes within the area is estimated to be greater than 4 pCi/L
were ranked high. Areas in which the average screening indoor radon level of all homes within the
area is estimated to be between 2 and 4 pCi/L were ranked moderate/variable, and areas in which
the average screening indoor radon level of all homes within the area is estimated to be less than
2 pCi/L were ranked low. Information on the data used and on the radon potential ranking scheme
is given in the introduction to this volume. More detailed information on the geology and radon
potential of each state in Region 3 is given in the individual state chapters. The individual chapters
describing the geology and radon potential of the states in EPA Region 3, 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 will likely be found.
Figure 1 shows a generalized map of the major physiographic/geologic provinces in EPA
Region 3. The summary of radon potential in Region 3 that follows refers to these provinces.
Figure 2 shows average screening indoor radon levels by county. The data for Maryland,
Pennsylvania, Virginia, and West Virginia are from the State/EPA Residential Radon Survey. Data
for Delaware were compiled by the Delaware Department of Health and Social Services. Figure 3
shows the geologic radon potential areas in Region 3, combined and summarized from the
individual state chapters in this booklet.
DELAWARE
Piedmont
The Piedmont in Delaware has been ranked moderate in geologic radon potential. Average
measured indoor radon levels in the Piedmont vary from low (<2 pCi/L) to moderate (2-4 pCi/L).
Individual readings within the Piedmont can be locally very high (> 20 pCi/L). This is not
unexpected when a regional-scale look at the Atlantic coastal states shows that the Piedmont is
consistently an area of moderate to high radon potential. Much of the western Piedmont in
Delaware is underlain by the Wissahickon Formation, which consists predominantly of schist
This formation has moderate to locally high geologic radon potential. Equivalent schists in the
Piedmont of Maryland can have uranium concentrations of 3-5 ppm, especially where faulted.
The Wilmington Complex and James Run Formation, in the central and eastern portions of the
Delaware Piedmont, are variable in radon potential. In these units, the felsic gneiss and schist may
contribute to elevated radon levels, whereas mafic rocks such as amphibolite and gabbro, and
relatively quartz-poor granitic rocks such as charnockite and diorite are probably lower in radon
potential. The average indoor radon is distinctly lower in parts of the Wilmington Complex than in
surrounding areas, particularly in areas underlain by the Bringhurst Gabbro and the Arden pluton.
The permeability of soils in the Piedmont is variable and dependent on the composition of the rocks
from which the soils are derived. Most soils are moderately permeable, with local areas of slow to
m-1 Reprinted from USOSOpen-FUe Report 93-292-C
-------
-------
100
miles
Figure 1. Geologic radon potential areas of EPA Region 3. 1-Central Lowland; 2-Glaciated Pittsburgh Plateau;
3-Pennsylvanian rocks of the Pittsburgh Low Plateau; 4-Permian rocks of the Pittsburgh Low Plateau; 5-High Plateau
Section; 6-Mountainous High Plateau; 7-Allegheny Plateau and Mountains; 8-Appalachian Mountains; 9-Glaciated
Low Plateau, Western Portion; 10-Glaciated Pocono Plateau; 11-Glaciated Low Plateau, Eastern Portion;
12-Reading Prong; 13-Great Valley/Frederick Valley carbonates and elastics; 14-Blue Ridge Province;
15-Gettysburg-Newark Lowland Section (Newark basin) 16,34-Piedmont; 17-Allan tic Coastal Plain; ig-Central
Allegheny Plateau; 19-Cumberland Plateau and Mountains; 20-Appalachian Plateau; 21-Silurian and Devonian rocks
in Valley and Ridge; 22,23-Valley and Ridge (Appalachian Mountains); 24-Western Piedmont Phyllite;
25-Culpeper, Gettysburg, and other Mesozoic basins; 26-Mesozoic basins; 27-Eastern Piedmont, schist and gneiss;
28-Inner Piedmont; 29-Goochland Terrane; 30,31-Coastal Plain (Cretaceous, Quaternary, minor Tertiary sediments)-
32-Carolina terrane; 33-Coastal Plain (Tertiary sediments); 35,37,38-Coastal Plain (quartz-rich Quaternary
sediments); 36-Glauconitic Coastal Plain sediments.
-------
100 Miles
Indoor Radon Screening
Measurements: Average (pCi/L)
0.0 to 1.9
2.0 to 4.0
4.1 to 10.0
10.1 to 32.6
Missing Data
or < 5 measurements
Figure 2. Screening indoor radon averages for counties with 5 or more measurements in EPA
Region 3. Data for Maryland, Pennsylvania, Virginia, and West Virginia are from the State/EPA
Residential Radon Survey. Data for Delaware were compiled by the Delaware Department of
Health and Social Services. Histograms in map legend show the number of counties in each
category.
-------
GEOLOGIC
RADON POTENTIAL
| | LOW
Up MODERATE/VARIABLE
HIGH
100
mile»
Figure 3. Geologic radon potential of EPA Region 3. For more detail, refer to individual state
radon potential chapters.
-------
-------
rapid permeability. Limited aereal radioactivity data for the Delaware Piedmont indicates that
equivalent uranium is generally moderate (1.5-2.5 ppm).
Coastal Plain
Studies of radon and uranium in Coastal Plain aeaiments in New Jersey and Maryland
suggest that glauconitic marine sediments equivalent to those in the northern portion of the
Delaware Coastal Plain can cause elevated levels of indoor radon. Central New Castle County is
underlain by glauconitic marine sediments of Cretaceous and Tertiary age that have moderate to
locally high radon potential. Aerial radiometric data indicate that moderate concentrations of
uranium occur in rocks and soils associated with the Piedmont and parts of the Coastal Plain of
northern Delaware. Chemical analyses of Cretaceous and Tertiary glauconitic marine sediments
and fluvial sediments of the Columbia Formation performed by the Delaware geological survey
indicate variable but generally moderate concentrations of uranium, averaging 1.89 ppm or greater.
The permeability of soils in these areas is variable but generally moderate to high, allowing radon
gas to move readily through the soil. Data for New Castie County from the State indoor radon
survey shows that areas underlain by the Cretaceous fluvial sediments (not glauconitic) have lower
average indoor radon levels than the glauconitic parts of the upper Cretaceous and lower Tertiary
sequence to the south. Kent County and all of Sussex County are underlain by quartz-dominated
sands, silts, gravels, and clays with low radon potential. These sediments are low in radioactivity
and generally have a low percentage of homes with indoor radon levels greater than 4 pCi/L.
MARYLAND
Coastal Plain
The Western Shore of Maryland has been ranked moderate to locally high in radon potential
and the Eastern Shore has been ranked low in radon potential. The Coastal Plain Province is
underlain by relatively unconsolidated fluvial and marine sediments that are variably phosphatic
and glauconitic on the Western Shore, and dominated by quartz in the Eastern Shore.
Radioactivity in the Coastal Plain is moderate over parts of the Western Shore sediments,
particularly in the Upper Cretaceous and Tertiary sediments of Prince George's, Anne Arundel,
and northern Calvert counties. Moderate radioactivity also appears to be associated with the
Cretaceous and Tertiary sediments of the Eastern Shore where these sediments are exposed in
major drainages in Kent, Queen Anne's, and Talbot counties. Soil-gas radon studies in Prince
George's County indicate that soils formed from the locally phosphatic, carbonaceous, or
glauconitic sediments of the Calvert, Aquia, and Nanjemoy Formations can produce significantly
high radon (average soil radon > 1500 pCi/L). The Cretaceous Potomac Group had more
moderate levels of soil radon, averaging 800-900 pCS/L, and the Tertiary-Cretaceous Brightseat
Formation and Monmouth Group had average soil radon of 1300 pCi/L. Soil permeability on the
Western Shore varies from low to moderate with some high permeability in sandier soils. Well-
developed clayey B horizons with low permeability are common. Indoor radon levels measured in
the State/EPA Residential Radon Survey are variable among the counties of the Western Shore but
are generally low to moderate. Moderate to high average indoor radon is found in most of the
Western Shore counties.
For this assessment we have ranked part of the Western Shore as high in radon potential,
including Calvert County, southern Anne Arundel County, and eastern Prince George's County.
This area has the highest radioactivity, high indoor radon, and significant exposure of Tertiary rock
ffl-5 Reprinted from USGS Open-File Report 93-292-C
-------
units. The part of the Western Shore ranked moderate consists of Quaternary sediments with low
radon potential, Cretaceous sediments with moderate radon potential, and lesser amounts of
Tertiary sediments with high radon potential. The Quaternary sediments of the Eastern Shore have
low radioactivity associated with them and are generally quartzose and thus low in uranium.
Heavy-mineral concentrations within these sediments may be very local sources of uranium.
Indoor radon appears to be generally low on the Eastern Shore with only a few measurements over
4 pG/L reported.
Piedmont
Gneisses and schists in the eastern Piedmont, phyllites in the western Piedmont, and
Paleozoic metasedimentary rocks of the Frederick V alley are ranked high in radon potential.
Sedimentary and igneous rocks of the Mesozoic basins have been ranked moderate in radon
potential. Radioactivity in the Piedmont is generally moderate to high. Indoor radon is moderate
to high in the eastern Piedmont and nearly uniformly high in the western Piedmont. Permeability
is low to moderate in soils developed on the mica schists and gneisses of the eastern Piedmont,
Paleozoic sedimentary rocks of the Frederick Valley, and igneous and sedimentary rocks of the
Mesozoic Basins. Permeability is moderate to high in the soils developed on the phyllites of the
western Piedmont The Maryland Geological Survey has compared the geology of Maryland with
the Maryland indoor radon data. They report that most of the Piedmont rocks, with the exception
of ultramafic rocks, can contribute to indoor radon readings exceeding 4 pCi/L. Their data indicate
that the phyllites of the western Piedmont have much higher radon potential than the schists in the
east. Ninety-five percent of the homes built on phyllites of the Gillis Formation had indoor radon
measurements greater than 4 pCi/L, and 47 percent of the measurements were greater than 20
pCi/L. In comparison, 80 percent of the homes built on the schists and gneiss of the Loch Raven
and Oella Formations had indoor radon readings greater than 4 pCi/L, but only 9 percent were
greater than 20 pCi/L.
Studies of the phyllites in Frederick County show high average soil-gas radon (>1000
pCi/L) when compared to other rock types in the county. Limestone and shale soils of the
Frederick Valley and some of the Triassic sedimentary rocks may be significant sources of radon
(500-2000 pCi/L in soil gas). Because of the highly variable nature of the Triassic sediments and
the amount of area that the rocks cover with respect to the county boundaries, it is difficult to say
with confidence whether the high indoor radon in Montgomery, Frederick, and Carroll counties is
partly attributable to the Triassic sediments. In Montgomery County, high uranium concentrations
in fluvial crossbeds of the upper Manassas Sandstone containing gray carbonaceous clay intraclasts
and drapes have been documented. Similar lithologic associations are common in the upper New
Oxford Formation. Black shales and gray sandstones of the Heidlersburg Member are similar to
uranium-bearing strata in the Culpeper basin in Virginia and may be a source of radon. Black
shales in me overlying Gettysburg Formation may also be locally uranium rich. The lower New
Oxford Formation, the lower Manassas Sandstone, the lower Gettysburg Formation, and the Balls
Bluff Siltstone in Maryland are not likely to have concentrations of uranium except where altered
by diabase intrusives and/or faulted. The diabase bodies are low in radon potential.
Appalachian Mountains
The Appalachian Province is divided into the Blue Ridge, Great Valley, Valley and Ridge,
and Allegheny Plateau. Each of these areas is underlain by a distinct suite of rocks with a
particular geologic radon potential. The Blue Ridge is ranked low in radon potential but may be
ffl-6 Reprinted from USGS Open-File Report 93-292-C
-------
locally moderate to high. The Catoctin volcanic rocks that underlie a significant portion of the Blue
Ridge have low radioactivity, yield low soil radon and have low soil permeability. The quartzite
and conglomerates overlying the Catoctin also have low radioactivity and low soil-gas radon.
Further, the Pennsylvania Topographic and Geologic Survey calculated the median uranium
content of 80 samples of Catoctin metabasalt and metadiabase to be less than 0.5 ppm. The
Harpers Formation phyllite bordering the Catoctin volcanic rocks yields high soil-gas radon
(>1000 pCi/L), has greater surface radioactivity than the surrounding rocks and is a potential
source of radon. The Precambrian gneiss that crops out in the Middletown Valley of the southern
Blue Ridge appears to have moderate radioactivity associated with it and yielded some high radon
in soil gas. It is difficult, given the constraints of the indoor radon data, to associate the high
average indoor radon in the part of Frederick County underlain by parts of this province with the
actual rocks. The Blue Ridge is provisionally ranked low hi geologic radon potential, but this
cannot be verified with the presently existing indoor radon data.
Carbonates and black shales in the Great Valley in Maryland have been ranked high in
radon potential. Radioactivity is moderate to high over the Great Valley in Washington County.
Washington County has more than 100 indoor radon measurements, has an average indoor radon
concentration of 8.1 pCi/L in the State/EPA Survey, with over half of the readings greater than
4 pCi/L. To the north in Pennsylvania, carbonate rocks of the Great Valley and Appalachian
Mountain section have been the focus of several studies and the carbonate rocks in these areas
produce soils with high uranium and radium contents that generate high radon concentrations. In
general, indoor radon in these areas is higher than 4 pCi/L. Studies in the carbonates of the Great
Valley in West Virginia suggest that the deepest, most mature soils have the highest radium and
radon concentrations and generate moderate to high indoor radon. High radon in soils and high
indoor radon in homes over the black shales of the Martinsburg Formation of the Great Valley
were also measured in West Virginia.
The Silurian and Devonian rocks of the Valley and Ridge have been ranked moderate to
locally high in geologic radon potential. Indoor radon measurements are generally moderate to
high in Allegany County. Soil permeability is variable but is generally moderate. Radioactivity in
this part of the Valley and Ridge is moderate to locally high. The Tonoloway, Keyser, and Wills
Creek Formations, and Clinton and Hamilton Groups have high equivalent uranium associated
with them and the shales, limestone soils, and hematitic sands are possible sources of the high
readings over these units.
The Devonian through Permian rocks of the Allegheny Plateau are ranked moderate in
geologic radon potential. Indoor radon measurements are generally moderate to high.
Radioactivity in the Allegheny Plateau is low to moderate with locally high equivalent uranium
associated with the Pocono Group and Mauch Chunk Formation. Soil permeability is variable but
generally moderate.
PENNSYLVANIA
New England Province
The New England Province is ranked high in geologic radon potential. A number of
studies on the correlation of indoor radon with geology in Pennsylvania have been done. The
Reading Prong area in the New England Province is the most notable example because of the
national publicity surrounding a particularly severe case of indoor radon. These studies found that
shear zones within the Reading Prong rocks enhanced the radon potential of the rocks and created
ffl-7 Reprinted from USGS Open-File Report 93-292-C
-------
local occurrences of very high uranium and indoor radon. Several of the rock types in the Reading
Prong were found to be highly uraniferous in general and they are the source for high radon levels
throughout much of the province.
Piedmont
The Piedmont is underlain by metamorphic, igneous, and sedimentary rocks of
Precambrian to Mesozoic age that have generally moderate to high radon potential. Rock types in
the metamorphic crystalline portion of the Piedmont that have naturally elevated uranium
concentrations include granitic gneiss, biotite schist, and gray phyllite. Rocks that are known
sources of radon and have high indoor radon associated with them include phyllites and schists,
such as the Wissahickon Formation and Peters Creek Schist, shear zones in these rocks, and the
faults surrounding mafic bodies within these rocks.
Studies in the Newark Basin of New Jersey indicate that the black shales of the Lockatong
and Passaic Formations and fluvial sandstones of the Stockton Formation are a significant source
of radon in indoor air and in water. Where these rock units occur in Pennsylvania, they may be the
source of high indoor radon as well. Black shales of the Heidlersburg Member and fluvial
sandstones of the New Oxford Formation may also be sources of locally moderate to high indoor
radon in the Gettysburg Basin. Diabase sheets and dikes within the basins have low eU. The
Mesozoic basins as a whole, however, are variable in their geologic radon potential. The Narrow
Neck area is distinctly low in radioactivity and Montgomery County, which is underlain almost
entirely by Mesozoic basin rocks, has an indoor radon average less than 4 pCi/L. Other counties
underlain partly by the Mesozoic basin rocks, however, have average indoor radon greater than
4 pCi/L. The Newark basin is high in radon potential whereas the Gettysburg basin is low to
locally moderate. For the purposes of this report the basins have been subdivided along the
Lancaster-Berks county boundary. The Newark basin comprises the Mesozoic rocks east of this
county line.
Blue Ridge
The Blue Ridge Province is underlain by metasedimentary and metavolcanic rocks and is
generally an area of low radon potential. A distinct low area of radioactivity is associated with the
province on the map, although phyllite of the Harpers Formation may be uraniferous. Soils
generally have variable permeability. The metavolcanic rocks in this province have very low
uranium concentrations. It is difficult, given the constraints of the indoor radon data, to associate
the high average indoor radon in counties underlain by parts of this province with specific rock
units. When the indoor radon data are examined at the zip code level, it appears that most of the
high indoor radon is attributable to the Valley and Ridge soils and rocks. The conclusion is that the
Blue Ridge is provisionally ranked low in geologic radon potential although this cannot be verified
with the presently available indoor radon data.
Ridge and Valley and Appalachian Plateaus
Carbonate rocks of the Great Valley and Appalachian Mountain section have been the focus
of several studies and the carbonates in these areas produce soils with high uranium and radium
contents and soil radon concentrations. In general, indoor radon in these areas is higher than
4 pCi/L and the geologic radon potential of the area is high, especially in the Great Valley where
indoor radon is distinctly higher on the average than in surrounding areas. Soils developed on
ffl-8 Reprinted firom USGS Open-FUe Report 93-292-C
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limestone and dolomite rock at the surface in the Great Valley, Appalachian Mountains, and
Piedmont are probably sources of high indoor radon.
The clastic rocks of the Ridge and Valley and Appalachian Plateaus province,-particularly
the Qrdovician through Pennsylvanian-age black to gray shales and fluvial sandstones, have been
extensively cited in the literature for their uranium content as well as their general uranium
potential. It appears from the uranium and radioactivity data and comparison with the indoor radon
data that the black shales of the Qrdovician Martinsburg Formation, the lower Devonian black
shales, Pennsylvanian black shales of the Allegheny Group, Conemaugh Group, and Monogahela
Group, and the fluvial sandstones of the Devonian Catskill and Mississippian Mauch Chunk
Formation may be the source of most moderate to high indoor radon levels in the Appalachian
Plateau and parts of the Appalachian Mountains section.
Only a few areas in these provinces appear to have geologically low to moderate radon
potential. The Greene Formation in Greene County appears to correlate with distinctly low
radioactivity. The indoor radon for Greene County averages less than 4 pCi/L for the few
measurements available in the State/EPA survey.
Somerset and Cambria Counties in the Allegheny Mountain section have indoor radon
averages less than 4 pCi/L, and it appears that low radioactivity and slow permeability of soils may
be factors in the moderate geologic radon potential of this area. These two counties and most of
the Allegheny Mountain section are underlain by Pennsylvanian-age sedimentary rocks. The
radioactivity map shows low to moderate radioactivity for the Pennsylvanian-age rocks in the
Allegheny Mountain section and much higher radioactivity in the Pittsburgh Low Plateau section.
Most of the reported uranium occurrences in these rocks appear to be restricted to the north and
west of the Allegheny Mountain section. Approximately half of the soils developed on these
sediments have slow permeability and seasonally high water tables.
CoastalPlain
Philadelphia and Delaware Counties, in the southeastern corner of Pennsylvania, have
average indoor radon less than 4 pCi/L and have low radioactivity. Part of Delaware County and
most of Philadelphia County are underlain by Coastal Plain sediments with low uranium
concentrations. Soils developed on these sediments are variable, but a significant portion are
clayey with slow permeability.
Glaciated Areas of Pennsylvania
Radiometric lows and relatively lower indoor radon levels appear to be associated with the
glaciated areas of the State, particularly the eastern portion of the Glaciated Low Plateau and
Pocono Plateau in Wayne, Pike, Monroe, and Lackawanna Counties. Glacial deposits are
problematic to assess for radon. In some areas of the glaciated portion of the United States, glacial
deposits enhance radon potential, especially where the deposits have high permeability and are
derived from uraniferous source rocks. In other portions of the glaciated United States, glacial
deposits blanket more uraniferous rock or have low permeability and corresponding low radon
potential. The northeastern corner of Pennsylvania is covered by the Olean Till, made up of 80-90
percent sandstone and siltstone clasts with minor shale, conglomerate, limestone, and crystalline
clasts. A large proportion of the soils developed on this till have seasonally high water tables and
poor drainage, but some parts of the till soils are stony and have good drainage and high
permeability. Low to moderate indoor radon levels and radioactivity in this area may be due to the
seasonally saturated ground and to the tills being made up predominantly of sandstones and
ffl-9 Reprinted from USGS Open-File Report 93-292-C
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siltstones with low uranium contents. A similar situation exists in the northwestern part of the
State, which is covered by a wide variety of tills, predominantly the Kent Till, which contains
mostly sandstone, siltstone, and shale clasts. Many of the soils in this area also have-low
permeabilities and seasonally high water tables. Where the tills are thinner, the western portion of
the Glaciated Low Plateau has higher indoor radon and high radioactivity.
VIRGINIA
Coastal Plain
The Coastal Plain of Virginia is ranked low in geologic radon potential. Indoor radon is
generally low; however, moderate to high indoor -radon can occur locally and may be associated
with phosphatic, glauconitic, or heavy mineral-bearing sediments. Equivalent uranium over the
Tertiary units of the Coastal Plain is generally moderate. Soils developed on the Cretaceous and
Tertiary units are slowly to moderately permeable. Studies of uranium and radon in soils indicate
that the Yorktown Formation could be a source for elevated levels of indoor radon. The
Quaternary sediments generally have low eU associated with them. Heavy mineral deposits of
monazite found locally within the Quaternary sediments of the Coastal Plain may have the potential
to generate locally moderate to high indoor radon.
Piedmont
The Goochland terrane and Inner Piedmont have been ranked high in radon potential.
Rocks of the Goochland terrane and Inner Piedmont have numerous well-documented uranium and
radon occurrences associated with granites; pegmatites; granitic gneiss; monazite-bearing
metasedimentary schist and gneiss; graphitic and carbonaceous slate, phyllite, and schist; and shear
zones. Indoor radon is generally moderate but significant very high radon levels occur in several
areas. Equivalent uranium over the Goochland terrane and Inner Piedmont is predominantly high
to moderate with areas of high eU more numerous in the southern part. Permeability of soils
developed over the granitic igneous and metamorphic rocks of the Piedmont is generally moderate.
Within the Goochland terrane and Inner Piedmont, local areas of low to moderate radon potential
will probably be found over mafic rocks (such as gabbro and amphibolite), quartzite, and some
quartzitic schists. Mafic rocks have generally low uranium concentrations and slow to moderate
permeability in the soils they form.
The Carolina terrane is variable in radon potential but is generally moderate. Metavolcanic
rocks have low eU but the granites and granitic gneisses have moderate to locally high eU. Soils
developed over the volcanic rocks are slowly to moderately permeable. Granite and gneiss soils
have moderate permeability.
The Mesozoic basins have moderate to locally high radon potential. It is not possible to make
any general associations between county indoor radon averages and the Mesozoic basins as a
whole because of the limited extent of many the basins. However, sandstones and siltstones of the
Culpeper basin, which have been lightly metamorphosed and altered by diabase intrusion, are
mineralized with uranium and cause documented moderate to high indoor radon levels in northern
Virginia. Lacustrine black shales and some of the coarse-grained gray sandstones also have
significant uranium mineralization, often associated with green clay clasts and copper. Equivalent
uranium over the Mesozoic basins varies among the basins. The Danville basin has very high eU
associated with it whereas the other basins have generally moderate eU. This radioactivity may be
related to extensive uranium mineralization along the Chatham fault on the west side of the Danville
ffl-10 Reprinted from USGS Open-FUe Report 93-292-C
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basin. Localized high eU also occurs over the western border fault of the Culpeper basin. Soils
are generally slowly to moderately permeable over the sedimentary and intrusive rocks of the
basins.
Valley and Ridge
The Valley and Ridge has been ranked high in geologic radon potential but some areas have
locally low to moderate radon potential. The Valley and Ridge is underlain by Cambrian dolomite,
limestone, shale, and sandstone; Silurian-Ordovician limestone, dolomite, shale, and sandstone;
and Mississippian-Devonian sandstone, shale, limestone, gypsum, and coal. Soils derived from
carbonate rocks and black shales, and black shale bedrock may be sources of the moderate to high
levels of indoor radon in this province. -Equivalent uranium over the Valley and Ridge is generally
low to moderate with isolated areas of high radioactivity. Soils are moderately to highly
permeable. Studies of radon in soil gas and indoor radon over the carbonates and shales of the
Great Valley in West Virginia and Pennsylvania indicate that the rocks and soils of this province
constitute a significant source of indoor radon. Sandstones and red siltstones and shales are
probably low to moderate in radon potential. Some local uranium accumulations are contained in
these rocks.
Appalachian Plateaus
The Appalachian Plateaus Province has been ranked moderate in geologic radon potential.
The plateaus are underlain by Pennsylvanian-age sandstone, shale, and coal. Black shales,
especially those associated with coal seams, are generally elevated in uranium and may be the
source for moderate to high radon levels. The coals themselves may also be locally elevated in
uranium. The sandstones are generally low to moderate in radon potential but have higher soil
permeability than the black shales. Equivalent uranium of the province is low to moderate and
indoor radon is variable from low to high, but indoor radon data are limited in number.
WESTVIRGINIA
Allegheny Plateau
The Central Allegheny Plateau Province has moderate geologic radon potential overall, due
to persistently moderate eU values and the occurrence of steep, well-drained soils. However,
Brooke and Hancock counties, in the northernmost part of this province, have average indoor
radon levels exceeding 4 pCi/L. This appears to be related to underlying Conemaugh and
Monongahela Group sedimentary rocks which have elevated eU values in this area and in adjacent
areas of western Pennsylvania.
The Cumberland Plateau and Mountains Province has low radon potential. The eU values
for the province are low except in areas of heavy coal mining, where exposed shale-rich mine
waste tends to increase values. Indoor radon levels average less than 2 pCi/L in most counties.
The Eastern Allegheny Plateau and Mountains Province has moderate radon potential
overall. Locally high indoor radon levels are likely in homes on dark gray shales of Devonian age
and colluvium derived from them in Randolph County. The southern part of this province has
somewhat lower eU values and indoor radon averages.
ffl-11 Reprinted from USGS Open-File Report 93-292-C
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Ridge and Valley Province
The southern part of the Appalachian Ridge and Valley Province in West Virginia has
moderate radon potential overall. The elJ signature for this province is elevated (> 215 ppm eU).
Locally high radon potential occurs in areas of deep residual soils developed on limestones of the
Mississippian Greenbrier Group, especially in central Greenbrier County, where eU values are
high. Elevated levels of radon may be expected in soils developed on dark shales in this province
or in colluvium derived from them.
The northern part of the Appalachian Ridge and Valley Province in West Virginia has high
geologic radon potential. The soils in this area have an elevated eU signature. Soils developed on
the Martinsburg Formation and on limestones and dolomites throughout the Province contain
elevated levels of radon and a very high percentage of homes have indoor radon levels exceeding
4 pCi/L in this province. Karst topography and associated locally high permeability in soils
increases the radon potential. Structures sited on uraniferous black shales may have very high
indoor radon levels. Steep, well-drained soils developed on phyllites and quartzites of the Harpers
Formation in Jefferson County also produce high average indoor radon levels.
ID-12 Reprinted from USGS Open-File Report 93-292-C
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PRELIMINARY GEOLOGIC RADON POTENTIAL ASSESSMENT OF MARYLAND
by
Linda C.S. Gundersen
U.S. Geological Survey '
INTRODUCTION
A random sampling of indoor radon in 1126 homes in Maryland was conducted for the
State/EPA Residential Radon Survey during the winter of 1991. Indoor radon was measured by
charcoal canister and the average for the State was 3.1 pCi/L. Twenty percent of these indoor
radon measurements exceeded the EPA guideline of 4 pCi/L. The Maryland State Department of
the Environment has also collected more than 37,000 indoor radon measurements from Maryland
residents and commercial vendors since 1986. Examination of these data in the context of
geology, soil parameters, and radioactivity suggest that many of the soils and rocks of the
Piedmont and Great Valley have the potential to produce high levels of indoor radon (> 4 pCi/L).
Soils and rocks of the Allegheny Plateau, Valley and Ridge, and the western shore of the Coastal
Plain have moderate to locally high radon potential. Soils and rocks of the Blue Ridge and Eastern
Shore of the Coastal Plain have relatively low geologic radon potential.
This is a generalized assessment of geologic radon potential of rocks, soils, and surficial
deposits of Maryland. 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, the reader is urged to consult the
local or State (1-800-872-3666) 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 Maryland (fig. 1) is in part a reflection of the underlying bedrock
geology (fig. 2a, 2b). Maryland has three major physiographic regions: the Appalachian
Province, the Piedmont Province, and the Coastal Plain Province. Each of these provinces is
subdivided into several smaller regions (fig. 1). The Coastal Plain Province covers approximately
one half of Maryland and is subdivided into the dissected rolling plain of the Western Shore and
the nearly flat Eastern Shore. Elevations range from sea level to 400 feet at the Fall Line. The Fall
Line is actually a zone where the sediments of the Coastal Plain are thinnest and overlap onto the
crystalline rocks of the Piedmont Province. Across this zone, there is a striking change in the
water velocity of rivers and streams; falls and rapids characterize the streams of the Piedmont.
West of the Fall Line lies the rolling hills of the Piedmont, which is divided into lowlands and
uplands. The Piedmont uplands is underlain by crystalline igneous and metamorphic rocks, and
the Piedmont lowlands are underlain by sedimentary and igneous rocks of the Frederick Valley and
Mesozoic basins. The Appalachian Province lies to the west of the Piedmont It is subdivided into
four distinct subdivisions, and it is underlain by folded and faulted sedimentary and igneous rocks.
IV-1 Reprinted from USGS Open-FUe Report 93-292-C
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GENERALIZED GEOLOGIC MAP OF MARYLAND
EXPLANATION
QUATERNARY—sand, silt, gravel, clay, and peat
TERTIARY—sand, clay, silt, greensand, and diotomaceous earth
CRETACEOUS—sand, gravel, sitt, and clay
TRIASSIC—red shale, re'd sandstone, and conglomerate, intruded
by diabase dikes and sills (indicated by T)
PERMIAN & PENNSYLVANIAN—clyclic sequences of shale, siltstone,
sandstone, clay, limestone, and coal
MISSISSIPPIAN—red beds, shale, siltstone, sandstone, and limestone
DEVONIAN—shale, siltstone, sandstone, limestone, and chert
SILURIAN—shale, mudstone, sandstone, and limestone
ORDOVICIAN—limestone, dolomite, shale, siltstone, and red beds. Slate and
conglomerate in northern Hartford County
1*00*01 CAMBRIAN—limestone, dolomite, shale, and sandstone
PALEOZOIC GRANITIC ROCKS—quartz diorite to granite intrusive rocks and
diamictite
PALEOZOIC BASIC IGNEOUS ROCKS—intrusive rocks; gabbro, serpentine
CAMBRIAN TO PRECAMBRIAN (?)—(South Mountain area) quartzite,
sandstone, shale, and phyllite
PRECAMBRIAN (?)—(South Mountain area and western Piedmont)
metabasalt, metarhyoffle, marble, and phyllite
F|pg PRECAMBRIAN (?)—(Western Piedmont) tuffaceous and non-tuffaceous
1 -1 phyllite, slate, and quartzite
PRECAMBRIAN-PALEOZOIC (?)—(Eastern Piedmont) schist, metagraywacke,
quartzite, diamictite, marble, and metavolcanic rocks
n^n PRECAMBRIAN BASEMENT COMPLEX—gneiss, migmatite, and augen
'• '/;v;"1 gneiss
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The Blue Ridge has rugged topography, with ridges made of resistant quartzite and valley floors
underlain by metavolcanic rocks. West of the Blue Ridge lies the Great Valley, which is underlain
by limestones and shales and has a rolling to nearly level topography. The Valley and Ridge
bounds the western side of the Great Valley and has steep ridges of resistant sandstone and deep
valleys underlain by limestone and shale. The westernmost part of Maryland is in the Allegheny
Plateau, a broad upland crossed by mountain ranges. The highest elevation in Maryland, 3360 feet
above sea level, is in this province. Sedimentary rocks, which include several coal deposits,
underlie the Allegheny Plateau.
Maryland's climate is continental in the western regions to humid subtropical in the east
Average annual precipitation is similar throughout the State, averaging about 44 inches (fig. 3). In
1990 Maryland's population was 4,781,468, with 80 percent of the population living in urban
centers (fig. 4). Population density is approximately 442 per square mile.
GEOLOGIC SETTING
The geology of Maryland is complex, ranging from unconsolidated sands and clays to
granites, marbles, limestones, and volcanic rocks. Names of rock formations and the way rocks
are grouped have changed with time. This description of the geology tries to convey the major
rock types of an area, especially as they pertain to the radon problem. Descriptions in this report
are derived from the following references: Hopson (1964), Cleaves and others (1968), Reinhardt
(1974), Edwards (1986,1988), Hansen and Edwards (1986), Higgins and Conant (1990), and
Smoot (1991). A general geologic map is given in figure 2a and general geologic areas and
terminology are defined in figure 2b. This terminology will be used throughout this report It is
suggested mat the reader refer to the more detailed state geologic map (Cleaves and others, 1968)
as well as the numerous detailed geologic maps available from the Maryland Geological Survey
(1992).
The Coastal Plain
The Coastal Plain Province is underlain by relatively unconsolidated fluvial and marine
sediments forming a wedge of strata that thickens to the east The Coastal Plain is divided into an
inner belt of Cretaceous- and early Tertiary-age sediments and an outer belt of younger Tertiary-
and Quaternary-age units The Lower Cretaceous units are composed of fluvial sediments
including quartz sand, gravel, and clay, whereas the Upper Cretaceous through Quaternary
sediments are largely marine in origin and include calcareous clays and silts, glauconitic clays,
silts, and sands, micaceous clays, silts, and fine sands, and finally, the young coastal deposits of
beach, lagoon, and marsh environments that dominate the shoreline.
The oldest and most extensive Cretaceous-age rocks are the Potomac Group, composed of
interbedded quartz gravels, quartzitic argillaceous sands, and variegated silts and clays. The
younger Cretaceous sediments crop out in narrow belts from north and west of Annapolis to
Washington, D.C., and along drainages in the northern part of the Eastern Shore. Overlying the
Potomac Group is the Magothy Formation, consisting of white, cross-bedded, lignitic sands, gray
silty clays, and ferruginous quartz gravels. The Matawan Formation overlies the Magothy
Formation and is characterized by fine-grained, glauconitic, micaceous sand and silt The Severn
Formation forms the top of the Cretaceous section and consists of fine- to coarse-grained,
glauconitic, micaceous sand with a basal gravel.
IV-6 Reprinted fromUSGS Open-File Report 93-292-C
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Tertiary-age rocks of the Coastal Plain crop out for the most part on the Western Shore and
along major drainages in the central and northern parts of the Eastern Shore. The base of the
Tertiary section is the Pamunkey Group, consisting of the Brightseat, Aquia, Marlboro, and
Nanjemoy Formations. These sediments form a wide band from Washington, D.C. to Annapolis.
The Brightseat consists of fine- to coarse-grained, micaceous and locally glauconitic sand with
locally indurated calcareous beds and phosphatic pebbles and fossils. The glauconitic,
fossiliferous sands of the Aquia Formation overlie the Brightseat Formation. These sands contain
as much as 70 percent glauconite. The Marlboro Clay consists of pink to gray clay with lenses of
fine white sand. The Nanjemoy Formation is characterized by fine- to medium-grained,
argillaceous, glauconitic sands with minor clay. Overlying the Pamunkey Group is the
Chesapeake Group, consisting of the Calvert, Choptank, and St Marys Formations. The Calvert
Formation crops out extensively in the central portion of the Western Shore. The base of the
Calvert is a diatomaceous clay with fine argillaceous sand overlain by interbedded fine grained
argillaceous sand, shelly sand, carbonaceous clay, and sandy clay. Sand is locally cemented to
form sandstone. The Calvert is succeeded by the quartzose, fine-grained sand, silt, shelly sand,
and sandstone of the Choptank Formation. The St Marys Formation is a sandy clay and fine-
grained sand that crops out predominantly in the southern part of the Western Shore.
The youngest Tertiary rocks in Maryland occur in the subsurface or are of questionable
age. The end of Tertiary time and beginning of Quaternary time was a period of deposition and
erosion, including the deposition of very coarse-grained sand and gravel that formed upland
deposits of the Western Shore (McCarten, 1990). Quartzose, cross-bedded sand and gravel, and
minor silt and clay of Tertiary age form upland deposits on the Eastern Shore. Quaternary deposits
occurring in lowlands and along shorelines include quartzose gravel, sand, silt and clay, peat,
marsh muds, and shell-bearing clays and sands.
The Piedmont
For the purposes of this assessment, the Piedmont of Maryland is subdivided into an
eastern and western part (fig. 2b), each underlain by a distinctive sequence of rocks. The
Precambrian-Cambrian (?) crystalline rocks of the western Piedmont consist of phyllite and schist
with thin interbeds of quartzite, and a major belt of metabasalt with minor marble and volcanic
phyllite. To the west of these rocks lie the Paleozoic carbonates, shales, and fine sandstones of
Frederick Valley and the sandstones, siltstones, shales, conglomerates, and diabase dikes of the
Mesozoic Basins. Rocks of the eastern Piedmont are exposed in a large structure called the
Baltimore-Washington anticlinorium. In the core of the anticlinorium is the Precambrian Baltimore
Gneiss, surrounded by younger, Paleozoic metasedimentary schist and marble of the Glenarm
Supergroup. The anticlinorium is flanked by mafic and ultramafic rocks of the Baltimore Mafic
Complex, metavolcanic rocks of the James Run Formation, and various bodies of diamictite,
granitic plutons, and metagraywacke. A more detailed description of the Piedmont from east to
west is given in the following paragraphs.
Metamorphosed volcanic rocks, including greenstone, greenschist, amphibolite, and felsite
of the James Run Formation, crop out in several large irregular areas along the Fall Line, especially
north of the Susquehanna River. Numerous isolated bodies of granitic gneiss and granite plutons
also crop out along the eastern edge of the Piedmont The Aberdeen metagabbro, consisting of
metagabbro and amphibolite, underlies a large area of eastern Harford County, in the area of Havre
de Grace. To the west of these mafic rocks is a wide band of generally granitic rocks, including
granitic gneiss, granofels, schist, felsite, and metagraywacke of the Port Deposit Gneiss, James
IV-9 Reprinted fromUSGS Open-File Report 93-292-C
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Run Formation, the Conowingo Diamictite, and several unnamed rock units that extend from the
northeast corner of the State south to Baltimore. The Port Deposit Gneiss is a deformed complex
of extrusive and shallow intrusive rocks, predominantly biotite-diorite in composition, that is
locally sheared. The James Run Formation is a complicated sequence of metavolcanic rocks
ranging in composition from mafic to felsic as described above. The Conowingo Diamictite is a
mctasedimentary rock with abundant grains and pebbles of quartz, as well as clasts, blocks, and
slabs of other rock types including quartzite, gneiss, schist, graywacke, and amphibolite. The
Baltimore Mafic Complex lies west of the Conowingo Diamictite and east of the Baltimore Gneiss
domes and the Glenarm Supergroup, cropping out from northern Cecil County to southwest of
Baltimore and the Patuxent River. The Baltimore Mafic Complex is composed of gabbro,
serpentinite, amphibolite, and talc schist The Precambrian Baltimore Gneiss is exposed in several
large domes through Baltimore and Howard Counties and comprises biotite-quartz-feldspar gneiss,
biotite hornblende gneiss, and amphibolite. Paleozoic rocks of the lower Glenarm Supergroup
unconformably overlie the Baltimore Gneiss and consist ofthe Setters Formation, a quartzite
interbedded with mica schist, and the Cockeysville Marble, which overlies the Setters Formation
and consists of metadolomite, calc-silicate schist and marble, and calcite marble. The Cockeysville
Marble is overlain by the areally extensive politic schist of the Loch Raven Schist and the Oella
Formation that comprise the upper Glenarm Supergroup (formerly termed the lower politic schist
of the Wissahickon Formation). To the west of the gneiss domes and the Glenarm Supergroup is
the diamictite ofthe Sykesville Formation, and extensive areas of metagraywacke and schist
(formerly mapped as Wissahickon) with isolated bodies of mafic rocks and granitic plutons.
The crystalline rocks of the western Piedmont are distinctly different from the rocks of the
eastern Piedmont The western Piedmont crystalline rocks are dominated by schist and phyllite of
the Gillis, Marburg, Urbana, and Ijamsville Formations, and metavolcanic rocks of the Sams
Creek Formation. The Gillis crops out in a wide band from southwestern Montgomery County
north to Mt Airy and to the west and north through eastern Frederick County into southern Carroll
County. It is composed of interbedded green chloritic phyllite, gray graphitic phyllite,
metasiltstone, and metagraywacke with white vein quartz. The Marburg Schist crops out to the
north of the Gillis and is a fine-grained muscovite-chlorite schist interbedded with quartzite.
Around Linwood is a small mass of crystalline, schistose limestone and calcareous slate called the
Silver Run Limestone Member ofthe Marburg Schist The Urbana Formation crops out west of
the Gillis and extends north to New London. It is composed of gray to green chloritic phyllite
interbedded with siltstone, quartzite, and marble. The Sams Creek Formation crops out in sinuous
bands within the phyllites and schists from Hyattstown northeast to the state line. The Sams Creek
Formation consists of massive to schistose metabasalt with minor phyllite and quartzite. The
Wakefield Marble Member of the Sams Creek Formation forms thin bands in association with the
metabasalt
The crystalline rocks of the Piedmont are bounded on the west by the Gettysburg and
Culpeper basins and by carbonate and clastic rocks of the Frederick Valley. The Frederick Valley
is underlain by locally deformed and metamorphosed Cambrian-Ordovician clastic and carbonate
rocks. The base of the Cambrian sequence is the Araby Formation, consisting of locally phyllitic
siltstone, silty shale, and argillaceous sandstone. It forms a narrow ridge on the east side of the
valley. At the top ofthe Araby is the highly deformed Cash Smith Formation, a gray to black
phyllitic shale and calcareous shale with limestone nodules. The Frederick Formation overlies the
Cash Smith Formation and is the most areally extensive unit of the Frederick Valley. It consists of
three members: the thin bedded, locally sandy, limestone, dolomite, and minor shale of the Rocky
IV-10 Reprinted from USGS Open-File Report 93-292-C
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Springs Station Member; the laminated limestone of the Adamstown Member, and the
fossiliferous, laminated, locally silty and sandy, limestone and dolomite of the Lime Kiln Member.
The Qrdovician Grove Formation overlies the Frederick Formation and consists of fossiliferous
limestone and dolomite with minor sandstone.
Late Triassic-early Jurassic continental sedimentary and igneous rocks of the Newark
Supergroup occur in parts of two half-graben basins (Mesozoic basins) that form a north-south belt
across the central part of the State. The southern corner of the Gettysburg basin extends south
from Pennsylvania. The strata dip westward to the border fault and are folded into broad synclines
separated by faults. The basal Triassic New Oxford Formation forms a belt that thins to the south
along the southeastern margin of the basin. The New Oxford Formation consists of fluvial arkosic
sandstone, siltstone, and conglomerate. It is more conglomeratic along its basal contact with older
rocks on the southeastern margin of the basin. The New Oxford in Maryland is overlain by
Triassic Gettysburg Formation, which comprises the rest of the basin fill. The lower part of the
Gettysburg Formation consists of fluvial red siltstones with thin arkosic sandstones. The upper
part of the Gettysburg Formation consists of lacustrine red and black shales and siltstones. The
lower part of this portion of the Gettysburg Formation contains more frequent occurrences of black
shale and is called the Heidlerburg Member.
South of the Gettysburg basin, the northernmost part of the Culpeper basin extends into
Virginia. The Culpeper strata also dip westward toward the border fault and are part of a broad
syncline that extends into Virginia, but they are cut by numerous north-northeast trending faults.
The basal Manassas Sandstone is a fluvial arkosic sandstone, siltstone, and conglomerate. The
Manassas Sandstone is overlain by the Balls Bluff Siltstone, which in Maryland consists of fluvial
siltstones and thin arkosic sandstones similar to the lower Gettysburg Formation. Along the
western faulted margin of both basins, all of the formations intertongue with conglomerates
containing clasts of the older rocks immediately outside of the basin. In the Culpeper basin, the
conglomerates derived from Paleozoic limestones adjacent to the border are called the Leesburg
Conglomerate Member of the Balls Bluff Siltstone. The sedimentary rocks in both basins are
intruded by Jurassic diabase dikes and sheets.
The Appalachian Province
The Appalachian Province is bounded on the east by Precambrian to Cambrian
metamorphic rocks of the Blue Ridge. The Great Valley, Valley and Ridge, and Allegheny Plateau
comprise a sequence of marine and fluvial sedimentary rocks folded into distinct ridges and
valleys. The rocks range from Cambrian to Permian in age, with limestone and shale forming the
valleys and more resistant sandstones forming the prominent ridges.
The South Mountain Anticlinorium dominates the Blue Ridge and forms prominent
mountains just west of the Mesozoic basins. It is cored by Precambrian granodiorite and biotite
granite gneiss that crop out in the Middletown Valley, which lies between South Mountain and
Catoctin Mountain in the southern part of the area. Overlying the Precambrian basement is a thin
discontinuous unit named the Swift Run Formation, a coarse-grained quartzite interbedded with
phyllite, tuffaceous slate, and minor marble. This in turn is overlain by the Precambrian-Cambrian
Catoctin Metabasalt, which underlies most of the area. It is composed of metabasalt layers with
minor metarhyolite, meta-andesite, and tuffaceous phyllite. Epidote alteration is common. In the
north, the metabasalt is overlain by metarhyolite and associated pyroclastic sediments. A thick
sequence of Cambrian-Ordovician clastic and carbonate sediments overlies the volcanic sequence
and includes thin conglomerate of the Loudoun Formation, which is overlain by a thick layer of the
IV-11 Reprinted from USGS Open-File Report 93-292-C
-------
ridge-forming quartzite of the Weverton Fonnation and followed by phyllite of the Harpers
Formation. This sequence is repeated on both the east and west sides of the anticlinorium; On the
west side of South Mountain, the sequence continues with the Antietam Formation overlying the
Harpers. This unit is succeeded by the Tomstown Dolomite as the section passes into the Great
Valley.
West of South Mountain, the Tomstown Dolomite is succeeded by the thin-bedded
siltstone, shale, sandstone, and dolomite of the Waynesboro Formation. A sequence of Cambrian
through Ordovician limestones and shales follows and underlies most of eastern Washington
County and the Great Valley. This sequence includes the argillaceous limestone, shale, and
dolomite of the Elbrook Limestone, the argillaceous limestone, minor conglomerate, shale, and
sandstone of the Conococheague Limestone, the dolomite, limestone, and conglomerate of the
Stonehenge Limestone, the thick cherty dolomite and limestone of the Rockdale Run Formation,
and the cherty dolomite of the Pinesburg Station Dolomite. These last three units are gathered into
the Beekmantown Group. The Beekmantown Group is followed by Ordovician limestones of the
St Paul Group, including the Row Park Limestone and the New Market Limestone. The St Paul
Group is overlain by the Chambersburg Limestone at the top of the Ordovician carbonate
sequence. West of Hagerstown, a fault separates the carbonate sequence form a wide band of
Ordovician shales, siltstones, and graywackes known as the Martinsburg Formation. West of this
wide band of Martinsburg, the carbonate units and Martinsburg Formation are tightly folded into
thin bands and faulted. Just west of dear Spring, the North Mountain Fault separates the Great
Valley from younger sedimentary rocks of Silurian and Devonian age. Folded Silurian and
Devonian sedimentary rocks underlie most of Allegany County and western Washington County
and comprise the Valley and Ridge in Maryland. Silurian rocks are exposed in several major folds
in central Washington County and eastern and western Allegany County. At the base of the
Silurian section is the Tuscarora Sandstone, which consists of thin to thick-bedded orthoquartzite
that crops out most extensively in western Allegany County. The Tuscarora is overlain by the
Clinton Group, including the interbedded gray shales and sandstones of the Rose Hill Formation,
the quartzite and calcareous quartzite of the Keefer Sandstone, and the calcareous, gray Rochester
Shale. The Clinton Group is overlain by the McKenzie Formation, consisting of gray shales and
argillaceous limestone which grade into interbedded red shales and sandstones to the west The
interbedded red siltstone, shale, and sandstone of the Bloomsburg Formation and limestone,
dolomite, and shale of the Wills Creek Formation occur extensively in the synclines. They are
overlain by the thick limestone, dolomitic limestone, calcareous shale, and sandstone of the
Tonoloway Limestone.
At the top of the Silurian section and base of the Devonian section are the Key ser
Limestone, comprising calcarenite, limestone, and shale, and the Helderberg Formation, consisting
of limestone with minor shale and sandstone. These rocks underlie only small areas in this
province. The Devonian Oriskany Group overlies, and, in places, intertongues with the
Helderberg Formation and crops out in wide bands in western Washington and Allegany Counties.
The Oriskany Group comprises the black shales and bedded cherts of the Shriver Chert and
calcareous quartzite and limestone of the Oriskany Sandstone. The Devonian Needmore Shale
Overlies the Oriskany and crops out extensively in southern Allegheny County and central and
western Washington County. It consists of black shale and argillaceous limestone which is
succeeded by the black carbonaceous and pyritic Marcellus Shale, and the dark gray shale,
siltstone, and fine sandstone of the Mahantango Fonnation. Overlying the Mahantango is the thin,
gray, laminated Harrell Shale, the thick gray shale and siltstone of the Brallier Formation, the
IV-12 Reprinted fitom USGS Open-File Report 93-292-C
-------
sandy shale, graywacke, and conglomeratic sandstones of the Scheir and Foreknobs Formations.
Broad bands of Devonian Hampshire Formation crop out in Allegany and Garrett Counties. It
consists of interbedded red and green mudstone, siltstone, sandstone, and shale. In western
Allegany County, it is followed by thin bands of Mississippian sedimentary rocks and marks the
beginning of the Allegheny Plateau. The Allegheny Plateau is underlain by folded Devonian to
Permian sedimentary rocks. At the base of the Mississippian is the Rockwell Formation,
consisting of cross-bedded sandstone and conglomerate interbedded with gray and red shale,
mudstone, and siltstone. It also includes arkosic sandstone, conglomerate, shale, and thin coal
beds. Sandstone, conglomerate, shale, and coal comprise the overlying Purslane Sandstone. The
Greenbrier Formation consists of narrow belts of red calcareous shale and sandstone interbedded
with argillaceous limestone. It is overlain by the red and green shale, mudstone, and crossbedded
sandstone of the Mauch Chunk Formation, which also forms relatively narrow belts. Overlying
the Mauch Chunk are the Pennsylvanian Pottsville and Allegheny Formations, consisting of a
cyclic sequence of interbedded sandstone, siltstone, mudstone, shale and coal beds with a
conglomeratic quartz sandstone at the base. These two formations crop out extensively in wide
belts throughout the Allegheny Plateau. Overlying the Allegheny Formation is the Conemaugh
Formation, which is composed of gray and brown mudstone, shale, siltstone, and sandstone with
several coal beds. Broad bands of Conemaugh Formation underlie approximately a third of the
Allegheny Plateau. The Monongahela Formation overlies the Conemaugh and comprises
interbedded mudstone, argillaceous limestone, shale, sandstone, and coal beds. The Permian
Dunkard Group overlies the Monongahela and consists of red and green shale, siltstone and
sandstone with thin lenticular beds of argillaceous limestone and coal.
SOILS
Soils in Maryland include Ultisols, Alfisols, Inceptisols, and Histosols (U.S. Soil
Conservation Service, 1987). Ultisols are mineral soils with a horizon containing an appreciable
amount of translocated clay (but they do not contain fragipans) and they often have a moist or wet
substratum. Ultisols occur mainly in the Coastal Plain and Piedmont Alfisols are mineral soils
with clayey subsurface horizons or rragipans, and may contain plinthite (iron-rich horizons) or
calcic horizons in the subsurface. Alfisols cover large parts of the Piedmont and the Blue Ridge.
Inceptisols are described as soils with weakly developed horizons in which materials have been
altered or removed and they may contain horizons of accumulated silica, iron, or bases, but they
generally do not have clayey subsurface horizons. These soils cover most of the Appalachian
Province. Histosols are organic soils such as peats or mucks which occur locally along coastlines
or in river valleys (Soil Survey Staff, 1975). Figure 5 is a generalized soil map of Maryland. The
reader is urged to consult State soil maps and reports and U.S. Soil Conservation Service county
soil surveys for more detailed information.
Coastal Plain Soils
The Coastal Plain is covered by poorly drained to somewhat well-drained soils on the more
dissected and rolling western shore, and mostly poorly drained soils on the nearly flat Eastern
Shore (Miller, 1967). Deep, poorly to well-drained, fine and very fine sand with minor amounts
of glauconite occur on rolling uplands in the southern part of the western shore (fig. 5). These
soils are weakly to moderately well developed and have slightly to moderately clayey subsoils.
Shallow to moderately deep, poorly drained to moderately well drained, sandy and silty soils with
IV-13 Reprinted from USGS Open-File Report 93-292-C
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i
9-
o
CO
"8
•^•4
"S
I
00
E
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EXPLANATION FOR THE GENERALIZED SOILS MAP OF MARYLAND
SOILS FORMED FROM SEDIMENTARY ROCKS
Shallow to moderately deep, moderately well drained to excessively drained, sandy loam, silt
loam, and silty clay loam formed in residuum from gray acid shale, sandstone, and alluvium;
mostly moderate permeability, clayey soils developed on shales have lower permeability
Shallow to moderately deep, well drained to excessively drained, stony, silty and sandy soils
formed in residuum from red and gray acid shale, siltstone, and sandstone; moderate to locally
high permeability.
Shallow to deep, poorly to moderately drained, clayey, silty, and sandy soils developed on red
shale, siltstone, and sandstone; low to moderate permeability
In valleys, deep, well drained, silt loams, some with with clayey substrata, formed in residuum
from limestones, calcareous shale, and interbedded limestone and shale; low to moderate
permeability. Along valley slopes, includes soils developed on colluvium from sandstone and
shale; mostly moderate permeability
SOILS FORMED FROM IGNEOUS AND METAMORPHIC ROCKS
Deep, somewhat poorly drained to well drained, silty soils with clayey substrata or fragipans,
formed on residuum from metabasalt (greenstone), schist, gneiss, diabase, and locally, quartrite;
low permeability
In die western part, shallow, well to excessively drained, skeletal, silt loams formed on
residuum from hard schist and phyllite; moderate to high permeability.
In the eastern part, shallow to moderately deep, poorly to well drained, clayey sandy soils with
clayey substrata developed from soft mica schist; low to locally moderate permeability
Deep, well drained, gravelly to stony soils formed on colluvium of crystalline rocks;
high permeability
Deep, well drained silty to gravelly soils formed on colluvium of schist and limestone;
moderate to high permeability
SOILS FORMED FROM UNCONSOLIDATED COASTAL PLAIN SEDIMENTS
Very deep, poorly drained to excessively drained, sandy, silty, and clayey soils formed on
sandy and silty deposits (contains moderate amounts of glauconite on Western Shore);
moderate to high permeability
•0;#| Verv deeP» sandy, excessively drained to locally poorly drained soils formed on nearly level to
I'- **•' steep uplands of the Coastal Plain; locally moderate to mostly high permeability
Deep, well drained, fine and very fine sand with minor amounts of glauconite;
moderate permeability
Shallow to moderately deep, poorly drained to moderately well drained, sandy and silty soils
with fragipans and clayey subsoils, overlying older gravelly and sandy sediments;
low to moderate permeability
Deep, generally poorly drained, silt loams and clay loams with clayey B horizons and
commonly high water tables; low permeability
Deep, very poorly drained, silty soils in low-lying areas; moderate permeability, typically wet
Deep, well drained, clayey soils on higher uplands of the Coastal Plain; low permeability
Organic-rich soils of tidal marshes; commonly flooded
•
SOILS FORMED FROM ALLUVIAL MATERIALS
Deep, clayey, silty, sandy, and gravelly soils developed on alluvial sediments; upland alluvial
soils and soils of old, high terraces of the Potomac River are generally moderately well to well
drained; alluvial soils of the Coastal Plain are more poorly drained; permeability is variable
depending on parent lithology
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fragipans and clayey subsoils that overlie older gravelly and sandy sediments cover the southern
and western Coastal Plain. These soils are slowly permeable and are subject to seasonally high
water tables due to clay fragipans that form at 15-25 inches depth. Deep, well-drained, clayey, red
soils cover higher uplands of the Coastal Plain. The subsoil clay separates into distinct blocks,'
giving these soils low to locally moderate permeability. Some of the soils in this map unit contain
considerable amounts of sand, although the matrix of the soil is dominanfly clay.
Very deep, poorly drained to excessively drained, sandy and silty soils cover much of the
Eastern Shore of the Coastal Plain (fig. 5). These yellow and brown soils are common to much of
the Coastal Plain region of the Mid-Atlantic States (Miller, 1967). Where these soils are formed on
rolling topography, they are moderately to weU-drained; however, they tend to have high water
tables in flatter areas. Soils of this map unit on the Western Shore are silty and clayey soils
containing moderate amounts of glauconite. Deep, generally poorly drained silt loams and clay
loams with slowly permeable B horizons and commonly high water tables are extensive on the
Eastern Shore (fig. 5). Some of these soils have distinctive mottling, indicating that they remain
wet for considerable periods of time during the year. Soils in the southern part of the Coastal Plain
are deep, very poorly drained, silty soils in low-lying areas, and organic-rich soils of tidal
marshes. The silty soils overlie moderately to highly permeable sands and silts, but because they
are low-lying, these and the adjacent tidal marshes are typically wet throughout the year.
Piedmont Soils
Soils of the Piedmont are formed primarily on igneous and metamorphic rocks, except for
the sedimentary rocks that underlie the Frederick Valley. Shallow to moderately deep, well-
drained to excessively drained, silty and sandy soils form in residuum of red Triassic shale,
siltstone, and sandstone. The red soils have a distinct, red clayey B horizon and they are generally
more poorly drained than the gray soils in this area (Miller, 1967). Shallow to moderately deep,
well-drained, silt loams formed on residuum from mica schist, phyllite, quartzose schist, and
quartzite cover most of the Piedmont province (fig. 5). Soils formed on relatively soft mica schist
saprolites in the eastern half of the province are well developed and contain 20-25 percent clay in
the subsoil (Miller, 1967). Soils in the western Piedmont are formed on more resistant schist and
phyllite and are generally shallow, skeletal, poorly developed, silty or loamy throughout the
profile, and generally well- to excessively drained. Deep, well-drained, gravelly to stony soils
formed on colluvium of quartzite, quartzitic schist, and phyllite occur on the eastern and western
slopes of Catoctin Mountain. These soils are gravelly to stony, poorly developed, excessively
drained, and highly permeable. Colluvial soils formed mainly from schist are found in the eastern
Piedmont just north of Baltimore. These deep, wen-drained, silty to gravelly soils occur at the
base of slopes, and they locally contain fragments of limestone parent material.
Appalachian Province Soils
Soils of the Appalachian province are shallow to moderately deep, moderately well drained
to excessively drained, sandy loam, silt loam, and silty clay loam formed in residuum from gray
acid shale, sandstone, and siltstone. These soils have generally low to moderate permeability and
are common in the Allegheny Plateau and Valley and Ridge provinces. Deep, well-drained, silt
loams, some with clayey substrata, formed in residuum from limestones,, calcareous shale, and
interbedded limestone and shale cover most of the Great Valley, Frederick Valley, and areas
underlain by cherty limestones in the western Valley and Ridge (fig. 5). These soils have a slowly
permeable, plastic clay subsoil and are acidic because most of the carbonates have been leached
IV-16 Reprinted from USGS Open-File Report 93-292-C
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from the soil profile (Miller, 1967). In the Valley and Ridge, these soils are typically well drained
because they occur on steep slopes and limestone-capped ridgetops. Deep, somewhat poorly
drained to well drained, silty soils with slowly permeable, clayey substrata, formed on residuum
from metabasalt, schist, gneiss, diabase, and quartzite, are found in the Blue Ridge province.
RADIOACTIVITY
An aeroradiometric map of Maryland (fig. 6) was compiled from spectral gamma-ray data
acquired during the Department of Energy's National Uranium Resource Evaluation (NURE)
program (Duval and others, 1989). For the purposes of this report, low equivalent uranium (eU)
on the map is defined as less than 1.5 parts per million (ppm), moderate equivalent uranium is
defined as 1.5-2.5 ppm, and high equivalent uranium is defined as greater than 2.5 ppm. Low eU
appears to be associated with the Blue Ridge metavolcanic and metasedimentary rocks, Jurassic
diabase in the western Piedmont, and the Quaternary sediments of the Eastern Shore. Low to
moderate eU covers much of the Allegheny Plateau, the Tertiary and Cretaceous sediments of the
Coastal Plain, and parts of the Valley and Ridge. High eU areas in the State appear to be
associated with Cambrian and Ordovician sediments of the Great Valley; Precambrian, Cambrian,
and Triassic igneous, metamorphic, and sedimentary rocks of the western Piedmont; and
metamorphic and igneous rocks of the eastern Piedmont
The NURE reports for the Harrisburg Quadrangle (LKB Resources, 1978), the Baltimore
Quadrangle (Texas Instruments Incorporated, 1978a), the Cumberland Quadrangle (Texas
Instruments Incorporated, 1980), and the Washington Quadrangle (Texas Instruments
Incorporated, 1978b) indicate that high to moderate eU is associated with particular geologic units
along the flightiines of the aerial radiometric survey. Rock units with high eU include:
Precambrian schists and Baltimore Gneiss of the Piedmont; the Precambrian-Cambrian Harpers
Formation; the Cambrian Elbrook Limestone, Waynesboro Formation, Kinzers Formation,
Tomstown, and Weverton Formations; the Ordovician Chambersburg Limestone, Martinsburg
Formation, and Rockdale Run Formation; the Silurian Tonoloway, Keyser, and Wills Creek
Formations and the Clinton Group; the Devonian Hampshire Formation and Hamilton Group; the
Pennsylvanian Monongahela Formation; and the Tertiary Calvert Formation.
INDOORRADON
Indoor radon data from 1126 homes sampled in the State/EPA Residential Radon Survey
conducted in Maryland during the winter of 1991 are shown in map format in figure 7 and
statistically in Table 1. A map with county names is also included for reference (fig. 8). Indoor
radon was measured by charcoal canister. The maximum value recorded in the survey was 139.6
pO/L in Carroll County. The average for the State was 3.1 pCi/L and 19.9 percent of the homes
tested had indoor radon levels exceeding 4 pCi/L. Notable counties include Calvert, Carroll,
Frederick, Howard, and Washington Counties, in which the average indoor radon for the county
was > 4 pCi/L. The State of Maryland compiled data from volunteers, the University of Pittsburgh
Radon Project (Cohen, 1990), and commercial vendors to produce a non-random data set of more
than 37,000 data points (State of Maryland, 1989). These data are presented in Table 2 for
comparison with the StateEPA/ data. Non-random (volunteer) indoor radon data tend to be biased
toward higher values compared to randomly sampled surveys because it is more likely that many of
the data points are from homeowners that tested their homes after receiving word of a nearby high
value. Four percent of the homes in this dataset had indoor radon levels exceeding 20 pCS/L and
IV-17 Reprinted from USGS Open-File Repent 93-292-C
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11
Bsmt & 1st Floor Rn
% > 4 pCi/L
OtolO
11 to 20
21 to 40
41 to60
Bsmt & 1st Floor Rn
Average Concentration (pCi/L)
0.0 to 1.9
2.0 to 4.0.
4.1 to 10.0
10.1 to 16.3
M^land Sl°9Sot!8^d00r ^ ^from te EPA/State Residential Radon Survey of
Maryland, 1990-91, for counties wth 5 or more measurements. Data are from 2-7 dav charcoal
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TABLE 1. Screening indoor radon data from the EPA/State Residential Radon Survey of
Maryland conducted during 1990-91. Data represent 2-7 day charcoal canister measurements
from the lowest level of each home tested.
COUNTY
ALLEGANY
ANNEARUNDEL
BALTIMORE
BALTIMORE CITY
CALVERT
CAROLINE
CARROLL
CECIL
CHARLES
DORCHESTER
FREDERICK
GARRETT
HARFORD
HOWARD
KENT
MONTGOMERY
PRINCE GEORGE'S
QUEEN ANNE'S
SOMERSET
ST. MARY'S
TALBOT
WASHINGTON
WICOMICO
WORCESTER
NO. OF
MEAS.
74
86
40
79
16
23
16
61
19
18
96
31
27
30
16
101
126
19
17
15
25
115
50
26
MEAN
2.7
1.6
2.3
2.1
4.9
0.4
16.3
2.1
2.6
0.2
5.3
3.6
1.7
5.4
1.1
3.1
2.0
0.4
0.2
1.1
0.4
8.1
0.2
0.1
GEOM.
MEAN
1.3
0.8
1.0
- 0.5
1.4
0.2
5.5
1.1
0.6
0.1
2.7
1.2
1.0
3.3
0.3
1.7
1.0
0.2
0.1
0.6
0.2
4.9
0.2
0.1
MEDIAN
1.3
1.0
1.0
0.4
1.1
0.2
6.3
1.3
0.4
0.1
2.7
1.4
0.9
3.4
0.2
1.8
1.1
0.2
0.1
0.9
0.1
5.3
0.1
0.0
STD.
DEV.
5.8
2.2
2.8
7.4
9.4
0.6
33.7
2.4
7.3
0.4
6.8
7.5
2.0
4.8
2.0
3.9
2.7
0.9
0.7
1.1
0.6
8.4
0.4
0.3
MAXIMUM
46.0
13.2
10.8
63.2
37.9
2.8
139.6
11.2
32.1
1.5
35.8
40.4
8.4
18.0
6.5
26.1
18.7
4.0
2.8
4.0
2.5
63.7
1.3
1.1
%>4pCi/L
12
6
23
8
31
0
50
15
16
0
40
19
7
43
13
24
13
0
0
0
0
59
0
0
%>20pCi/L
1
0
0
1
6
0
13
0
5
0
4
3
0
0
0
1
0
0
0
0
0
6
0
0
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Table 2. Maryland Radon Data Summary. The minimum, maximum,
and average radon levels in pCi/1 are presented for.each county
with at least 100 data points. An asterisk (*) highlights
those jurisdictions with less than 100 data points, indicating
insufficient data to characterize the radon situation in those
jurisdictions. Compare the county average with the State
average of 5.32 pCi/1.
(from State of Maryland, 1989)
Code County # Tests Minimum
pCi/1
01 Allegany 152 .05
03 Anne Arundel 1599 .05
05 Baltimore 594 .05
07* Balto. City 70 .05
09 Calvert 317 .05
11* Caroline 6 . .30
13 Carroll 1140 .05
15* Cecil 52 .05
17 Charles 577 .05
19* Dorchester 7 .05
21 Frederick 1978 .05
23* Garrett 45 .60
25 Harford 230 .05
27 Howard 2512 .05
29* Kent 2 .05
31 Montgomery 20356 .05
33 Prince Georges 6516 .05
35* Queen Anne's 28 .10
37 Saint Marys 260 .05
39* Somerset 1 6.70
41* Talbot 38 .20
43 Washington 612 .05
45* Wicomico 5 .40
47* Worcester 2 .40
Maximum
pCi/1
48.00
313.00
270.30
13.00
52.00
5.80
482.90
49.00
76.00
5.00
491.00
36.10
87.30
895.30
2.50
376.90
209.00
11.00
22.00
6.70
6.70
679.80
2.10
.90
Avg
pCi/1
5.23
4.10
7.62
5.40
15.06
2.72
11.20
7.24
8.61
4.67
2.41
2.03
12.64
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oo
ON
§
CO
o
T3
CO
00
E
o.
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29 percent of the homes tested had indoor radon levels between 4 and 20 pCi/L. Carroll,
Frederick, and Washington Counties had indoor radon averages greater than 10 pCi/L. Charles,
Prince George's, and Saint Mary's Counties, all located in the Coastal Plain, had indoor radon
averages less than 4 pCS/L.
GEOLOGIC RADON POTENTIAL
Coastal Plain Province
The Western Shore has been ranked moderate to locally high in geologic radon potential
and the Eastern Shore has been ranked low in radon potential. The Coastal Plain Province is
underlain by relatively unconsolidated fluvial and marine sediments that are variably phosphatic
and glauconitic on the Western Shore and dominated by quartz in the Eastern Shore. Radioactivity
in the Coastal Plain is moderate over parts of the Western Shore sediments, particularly in the
Upper Cretaceous and Tertiary sediments of Prince George's, Anne Arundel, and northern Calvert
Counties. Moderate radioactivity also appears to be associated with the Cretaceous and Tertiary
sediments of the Eastern Shore where these sediments are exposed in major drainages in Kent,
Queen Anne's, and Talbot Counties. Soil radon studies in Prince George's County (Otton, 1992;
Reimer, 1988; Reimer and others, 1991) indicate that soils formed from the locally phosphatic,
carbonaceous, or glauconitic sediments of the Calvert, Aquia, and Nanjemoy Formations can
produce significantly high radon (average soil radon > 1500 pCi/L). Otton (1992) indicates that
the Cretaceous Potomac Group had generally moderate levels of soil radon, averaging 800-900
pCi/L, and the Tertiary-Cretaceous Brightseat Formation and Monmouth Group had average soil
radon of 1300 pCi/L. Permeability in the Western Shore is variably low to moderate with some
high permeability in sandier soils. Well-developed clayey B horizons with low permeability are
common. Indoor radon from the State/EPA Residential Radon Survey is variable among the
counties of the Western Shore and indoor radon levels are generally low to moderate, with Calvert
County having a high average (4.9 pCi/L, but only 16 measurements in the county). The
Maryland radon data summary (Table 2) indicates moderate to high average indoor radon for most
of the Western Shore counties. For this assessment we have ranked part of the Western Shore as
high in radon potential, including Calvert County, southern Anne Arundel County, and eastern
Prince George's County. This area has the highest radioactivity, high indoor radon, and
significant exposure of Tertiary rock units. The part of the Western Shore ranked moderate
consists of Quaternary sediments with low radon potential, Cretaceous sediments with moderate
radon potential, and lesser amounts of Tertiary sediments with high radon potential. The
Quaternary sediments of the Eastern Shore have low radioactivity associated with them and are
generally quartzose and thus low in uranium. Heavy-mineral concentrations within these
sediments may be very local sources of uranium. Indoor radon appears to be generally low on the
Eastern Shore with only a few measurements over 4 pCi/L reported.
Piedmont Province
Gneisses and schists in the eastern Piedmont, phyllites in the western Piedmont, and
Paleozoic metasedimentary rocks of the Frederick Valley have been ranked high in geologic radon
potential. Sedimentary and igneous rocks of the Mesozoic basins have been ranked moderate in
radon potential. Radioactivity in the Piedmont is generally moderate to high. Indoor radon is
moderate to high in the eastern Piedmont and nearly uniformly high in the western Piedmont
Permeability is low to moderate in soils developed in the mica schists and gneisses of the eastern
IV-23 Reprinted from USGS Open-Ftfe Report 93-292-C
-------
Piedmont, Paleozoic sedimentary rocks of the Frederick Valley, and igneous and sedimentary
rocks of the Mesozoic Basins. Permeability is moderate to high in the soils developed on the
phyllites of the western Piedmont The Maryland Geological Survey has conducted a comparison
of the geology of Maryland with the Maryland radon data summary in Table 2. They report (State
of Maryland, 1989) that most of the Piedmont rocks, with the exception of ultramafics, can
generate indoor radon readings exceeding 4 pCi/L. Then1 data indicate that the phyllites of the
western Piedmont have much higher radon potential than the schists in the east Ninety-five
percent of the homes built on phyllites of the Gillis Formation had indoor radon measurements
greater than 4 pCi/L, and 47 percent of the measurements were greater than 20 pCi/L. In
comparison, 80 percent of the homes built on the schists and gneiss of the Loch Raven and Delia
Formations had indoor radon readings greater than 4 pCi/L, but only 9 percent were greater than
20 pCi/L. Studies by Gundersen and others (1988), Mose and others (1988a, b), and Mose and
Mushrush (1988a, b, c) support this conclusion.
Szarzi and others (1990) have also shown that the phyllites in Frederick County yield the
highest average soil-gas radon when compared to the other rock types, and that soils derived from
limestone and shale, and some of the Triassic sedimentary rocks, in the Frederick Valley may be
significant sources of radon (500-2000 pCi/L in soils). In Maryland, Gundersen and others
(1988) noted high uranium concentrations in fluvial crossbeds of the upper Manassas Sandstone
containing gray carbonaceous clay intraclasts and drapes. Similar lithologic associations are
common in the upper New Oxford Formation. Black shales and gray sandstones of the
Heidlersburg Member are similar to uranium-bearing strata in the Culpeper basin in Virginia.
Black shales in the overlying Gettysburg Formation may also be locally uranium rich. The lower
New Oxford Formation, the lower Manassas Sandstone, the lower Gettysburg Formation, and the
Balls Bluff Siltstone in Maryland are not likely to have significant concentrations of uranium except
where altered by diabase intrusives and/or faulted. The diabase bodies are low in radon potential.
Because of the highly variable nature of the Triassic sediments and the amount of area the rocks
cover with respect to the county boundaries, it is difficult to say with confidence whether the high
indoor radon in Montgomery, Frederick, and Carroll Counties is pardy attributable to the Triassic
sediments.
Appalachian Province
The Appalachian Province is divided into the Blue Ridge, Great Valley, Valley and Ridge,
and Allegheny Plateau. Each of these areas is underlain by a distinct suite of rocks with a
particular radon potential. The Blue Ridge is ranked low in radon potential but may be locally
moderate to high. The Catoctin volcanic rocks that underlie a significant portion of the Blue Ridge
have low radioactivity, yield low soil radon (Szarzi and others, 1990) and have low soil
permeability. The quartzite and conglomerates overlying the Catoctin also have low radioactivity
and low soil radon (Szarzi and others, 1990). Further, the Pennsylvania Topographic and
Geologic Survey (J. Barnes and R. Smith, upub. data) calculated the median uranium content of
80 samples of Catoctin metabasalt and metadiabase (measured by delayed neutron activation) and
found it to be less than 0.5 ppm. The Harpers Formation phyllite yields high soil radon (1000
pCi/L), has higher surface radioactivity than the surrounding rocks (Szarzi and others, 1990), and
is a potential source of radon. The Precambrian gneiss that crops out in the Middletown Valley of
the southern Blue Ridge appears to have moderate radioactivity associated with it and yielded some
high soil-gas radon in Szarzi and others' (1990) study. It is difficult, given the constraints of the
indoor radon data, to associate the high average indoor radon in the part of Frederick County
IV-24 Reprinted from USGS Open-FUe Report 93-292-C
-------
underlain by parts of this province with the actual rocks. The Blue Ridge is provisionally ranked
low in geologic radon potential, but this cannot be verified with the present indoor radon data.
Carbonates and black shales in the Great Valley in Maryland have been ranked high in
radon potential. Radioactivity is moderate to high over the Great Valley in Washington County.
Washington County has more than a hundred indoor radon measurements, has an average indoor
radon of 8.1 pQ/L in the State/EPA Survey, and more than half of the readings are greater than
4 pCi/L. To the north in Pennsylvania, carbonate rocks of the Great Valley and Appalachian
Mountain section have been the focus of several studies (van Assendelft and Sachs, 1982; Gross
and Sachs, 1982; Greeman and Rose, 1990; Luetzelschwab and others, 1989), and the carbonates
in these areas produce soils with high uranium and radium contents that generate high radon
concentrations. Li general, indoor radon levels in these areas are more than 4 pCi/L. Soils
developed from carbonate rocks are often elevated in uranium and radium. Carbonate soils are
derived from the dissolution of the CaCOs that makes up the majority of the carbonate rock. When
the CaCOs has been dissolved away, the soils are enriched in the remaining impurities,
predominantly base metals, including radionuclides. Studies in the carbonates of the Great Valley
in West Virginia suggest that the deepest, most mature soils have the highest radium and radon
concentrations (Schultz and others, 1992). Rinds containing high concentrations of uranium and
uranium-bearing minerals can be formed on the surfaces of rocks affected by CaCOs dissolution
and karstification. Karst and cave morphology is also thought to promote the flow and
accumulation of radon. Schultz and others (1992) also measured high radon in soils and high
indoor radon in homes over the black shales of the Martinsburg Formation.
The Silurian and Devonian rocks of the Valley and Ridge have been ranked moderate to
locally high in geologic radon potential. Indoor radon measurements from the State/EPA
Residential Radon Survey in Allegany County have an average of 2.7 pCi/L and 12 percent of the
74 measurements were greater than 4 pCi/L. In the Maryland radon data summary (Table 2) the
average for Allegeny County was 5.23 pCi/L and 30 percent of the 152 measurements were greater
than 4 pCi/L. Bedford County, Pennsylvania, which is adjacent to Allegeny County and is
underlain by the same rock types, has a high indoor radon average in the State/EPA survey. Soil
permeability is variable but is generally moderate. Radioactivity in the Valley and Ridge is
moderate to locally high. The Tonoloway, Keyser, and Wills Creek Formations and Clinton and
Hamilton Groups have high equivalent uranium associated with them in the NURE aeroradiometric
data. The shales, limestone soils, and hematitic sands are possible sources of these high readings.
The Devonian through Permian rocks of the Allegheny Plateau have been ranked moderate
in geologic radon potential. Indoor radon measurements from the State/EPA survey for Garrett
County have an average of 3.5 pCi/L for the 31 measurements taken in the county. Radioactivity
in the Allegheny Plateau is low to moderate. Soil permeability is variable but is generally
moderate. The NURE report for the Harrisburg Quadrangle (LKB Resources, 1978) reports high
equivalent uranium associated with the Pocono Group and Mauch Chunk Formation.
Van Assendelft and Sachs (1982) list an extensive table of indoor radon and associated
geologic units in Pennsylvania that may be applicable to equivalent units in Maryland. It appears
from the uranium and radioactivity data and comparison with the indoor radon data that the
Cambrian-Ordovician limestone soils, the black shales of the Ordovician Martinsburg Formation,
the early Devonian black shales, Pennsylvanian black shales of the Allegheny Group, Conemaugh
Group, and Monongahela Group, and the fluvial sandstones of the Devonian Hampshire and
Mississippian Mauch Chunk Formations may be sources of moderate to high indoor radon levels
in the Appalachian Province.
IV-25 Reprinted from USGS Open-File Report 93-292-C
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SUMMARY
For the purpose of this assessment, Maryland has been divided into ten geologic radon
potential areas and each area assigned a Radon Index (RI) and a Confidence Index (CI) score using
the information outlined in the sections above (Table 3). The RI is a relative measure of radon
potential based on geology, soils, radioactivity, architecture, and indoor radon. The CI is a
measure of the confidence of the RI assessment based on the quality and quantity of the data used
to assess geologic radon potential (please see the introduction chapter to this regional booklet for a
detailed explanation of the RI and CI). The geologic radon potential areas are shown in figure 9.
Geology, soil permeability, indoor radon, and radioactivity data for Maryland suggest that
many of the soils and rocks of the Piedmont and Great Valley have the potential to produce
moderate (2-4 pCi/L) to high (> 4 pQ/L) levels of indoor radon. Soils and rocks of the Allegheny
Plateau, Valley and Ridge, and the Western Shore of the Coastal Plain are generally moderate in
radon potential but can be locally high in geologic radon potential. Soils and rocks of the Blue
Ridge and Eastern Shore of the Coastal Plain are relatively low in radon potential.
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-26 Reprinted from USGS Open-FUe Report 93-292-C
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o
8
o
o
1
3
&
en
4>
&
I
<4-l
O
C/5
•a
I
o.
§
••a
^o
*o
-------
-------
TABLE 3. RI and CI scores for geologic radon potential areas of Maryland. See figure 9 for
locations of areas.
(2b) Western Shore, Cretaceous
Quaternary, minor Tertiary
FACTOR RI CI
(1) Eastern Shore
Quaternary
RI
(3) Eastern Piedmont
schist and gneiss
(2a) Western Shore
Tertiary
INDOOR RADON
RADIOACTIVITY
GEOLOGY
SOIL PERM.
ARCHITECTURE
GFE POINTS
TOTAL
RANKING
2
2
2
2
2
0
10
Mod
2
2
3
3
-
10
High
1
1
1
2
2
0
7
Low
2
2
3
3
-
10
High
3
2
2
2
3
0
12
High
3
3
3
3
_
12
High
3
2
3
2
2
0
12
High
3
3
3
3
12
High
FACTOR
(4) Western Piedmont
Phyllite
RI CI
(7)BlueRidge (8)Great Valley/(5) Frederick Valley
igneous and sedimentary carbonates and elastics
RI
INDOOR RADON
RADIOACTIVITY
GEOLOGY
SOIL PERM.
ARCHITECTURE
GFE POINTS
TOTAL
RANKING
3
2
2
3
3
2
15
High
3
3
3
3
.
-
12
High
1?
1
1
2
3
0
8
Low
1?
3
2
3
_
9
Mod
3
2
3
2
3
0
13
High
3
3
3
3
12
High
FACTOR
(9)Valley and Ridge
Silurian and Devonian
RI CI
(10) Allegheny Plateau (6) Mesozoic Basins
Culpeper/Gettysburg basins
RI CI
INDOOR RADON
RADIOACTIVITY
GEOLOGY
SOIL PERM.
ARCHITECTURE
GFE POINTS
TOTAL
RANKING
2
2
2
2
3
0
11
Mod
2
3
2
3
.
-
10
High
2
2
2
2
3
0
11
Mod
3
3
3
3
_
12
High
2?
2
2
2
3
0
11
Mod
1
3
3
3
10
High
RADON INDEX SCORING:
Radon potential category
Probable screening indoor
LOW
MODERATE/VARIABLE
HIGH
3-8 points
9-11 points
> 11 points
<2pCi/L
2-4pCi/L
>4pCi/L
Possible range of points = 3 to 17
CONFIDENCE INDEX SCORING:
LOW CONFIDENCE
MODERATE CONFIDENCE
HIGH CONFIDENCE
4-6 points
7-9 points
10 - 12 points
Possible range of points = 4 to 12
IV-28 Reprinted from USGS Open-File Report 93-292-C
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-------
REFERENCES USED IN THIS REPORT
! RELEVANT TO RADON IN MARYLAND
Bailey, J.P., Mose, D.G., and Mushrush, G.W., 1989, Soil to indoor radon ratios and the
prediction of indoor radon: Geological Society of America, Abstracts with Programs,
v. 21, p. 3.
Brooks, J.R., 1988, Radon and your home: Maryland Geological Survey, 3 p.
Candela, P. A., and Wylie, A.G., 1987, The geology of radon in the Maryland Piedmont; the
development of a research plan: Geological Society of America, Abstracts with Programs,
v. 19, p. 78.
Cleaves, E.T., Edwards, J., Jr., and Glaser, J.D., 1968, Geologic map of Maryland: Maryland
Geological Survey, scale 1:250,000.
Cohen, B.L., 1990, Surveys of radon levels in homes by the University of Pittsburgh Radon
Project, in Proceedings of the 1990 International Symposium on Radon and Radon
Reduction Technology, Vol. HE: Preprints: U.S. Environmental Protection Agency report
EPA/600/9-90/005c, Paper IV-3,17 p.
Duval, J.S., Jones, W.J., Riggle, F.R., and Pitkin, J.A., 1989, Equivalent uranium map of
conterminous United States: U.S. Geological Survey Open-File Report 89-478,10 p.
Edwards, J., Jr., 1986, Geologic map of the Union Bridge quadrangle, Carroll and Frederick
Counties, Maryland: Maryland Geological Survey, scale 1:24,000.
Edwards, J., Jr., 1988, Geologic map of the Woodsboro quadrangle, Carroll and Frederick
Counties, Maryland: Maryland Geological Survey, scale 1:24,000.
Facts on File, 1984, State Maps on File: Facts on File Publications.
Greeman, D.J., and Rose, A.W., 1990, Form and behavior of radium, uranium, and thorium in
central Pennsylvania soils derived from dolomite: Geophysical Research Letters, v. 17
p. 833-836.
Gross, S., and Sachs, H.M., 1982, Regional (location) and building factors as determinants of
indoor radon concentrations in eastern Pennsylvania: Princeton University, Center for
Energy and Environmental Studies Report 146,117 p.
Gundersen, L.C.S., 1988, Radon production in shear zones of the Eastern United States:
Northeastern Environmental Science, v. 7, p. 6.
Gundersen, L.C.S., Reimer, G.M., Wiggs, C.R. and Rice, C.A., 1988, Map showing radon
potential of rocks and soils in Montgomery County, Maryland: U.S. Geological Survey
Miscellaneous Field Studies Map MF-2043, scale 1:62,500.
IV-29 Reprinted from USGS Open-File Report 93-292-C
-------
Hanson, H.J., and Edwards, J., Jr., 1986, The lithology and distribution of pre-Cretaceous
basement rocks beneath the Maryland Coastal Plain: Maryland Geological Survey Report
of Investigations no. 44,27 p.
Higgins, M.W., and Conant, L.B., 1990, Geology of Cecil County, Maryland: Maryland
Geological Survey Bulletin 37,183 p. .
Hopson, C.A., 1964, The crystalline rocks of Howard and Montgomery Counties, in The geology
of Howard and Montgomery Counties: Maryland Geological Survey, p. 27-215.
LKB Resources, Inc., 1978, NURE aerial gamma-ray and magnetic reconnaissance survey,
Harrisburg quadrangle: U.S. Department of Energy NURE Report GJBX-33 (78), 128 p.
Luetzelschwab, J.W., Helwick, K.L., and Hurst, K.A., 1989, Radon concentrations in five
Pennsylvania soils: Health Physics, v. 56, p. 181-188.
Maryland Geological Survey, 1967, Generalized Geologic Map of Maryland: Maryland Geological
Survey, scale approximately 1:1,500,000.
Maryland Geological Survey, 1992, List of publications: Maryland Geological Survey, 36 p.
McCarten, L., 1990, Geologic Map of the Coastal Plain and Upland Deposits, Washington West
quadrangle, Washington, D.C., Maryland and Virginia: U.S. Geological Survey Open-File
Report 90-654,16 p., 1 plate, scale 1:24,000.
Miller, RP., 1967, Maryland soils: University of Maryland Cooperative Extension Service
Bulletin 212,42 p.
Mosc, D.G., and Hall, S.T., 1987, Indoor radon survey; citizen response and preliminary
observations in Virginia and Maryland: Geological Society of America, Abstracts with
Programs, v. 19, p. 119.
Mose, D.G., and Hall, S.T., 1988, Effect of home construction and mitigation methods on indoor
radon; Virginia and Maryland homes during the winter of 1986-1987: Geological Society
of America, Abstracts with Programs, v. 20, p. 282.
Mose, D.G., and Mushrush, G.W., 1987, Correlation between indoor radon and geology in VA
& MD: Geological Society of America, Abstracts with Programs, v. 19, p. 779.
Mose, D.G., and Mushrush, G.W., 1988a, Factors that determined indoor radon concentration in
Virginia and Maryland in 1987: EOS, Transactions, American Geophysical Union, v. 69,
p. 317.
Mose, D.G., and Mushrush, G.W., 1988b, Comparison between activated charcoal and alpha-
track measurement of indoor radon in homes in Virginia and Maryland; 1986-1987:
Geological Society of America, Abstracts with Programs, v. 20, p. 282.
IV-30 Reprinted from USGS Open-File Report 93-292-C
-------
Mose, D.G., and Mushrush, G.W., 1988c, Regional levels of indoor radon in Virginia and
Maryland: Environmental Geology and Water Sciences, v. 12, p. 197-201.
Mose, D.G., Mushrush, G.W., and Kline, S.W., 1988a, Geology and time dependent indoor
radon variations in VA and MD: Geological Society of America, Abstracts with Programs,
v. 20, p. 56-57.
Mose, D.G., Mushrush, G.W., and Kline, S.W., 1988b, The interaction of geology, weather and
home construction on indoor radon in northern Virginia and southern Maryland:
Northeastern Environmental Science, v. 7, p. 15-29.
Mose, D.G., Chrosniak, C.E., Mushrush, G.W., and Vitz, E., 1989, Cancer associated with
drinking radon enriched water: Geological Society of America, Abstracts with Programs,
v. 21, p. 51.
Muller, P.D., and Edwards, J., Jr., 1985, Tectono-stratigraphic relationships in the central
Maryland Piedmont: Geological Society of America, Abstracts with Programs, v. 17,
no. 1, p. 55.
Otton, J.K., and Gundersen, L.C.S., 1988 , Geologic assessments of radon potential at county
scales: Northeastern Environmental Science, v. 7, p. 7-8.
Otton, J.K., 1992, Radon in soil gas and soil radioactivity in Prince George's County, Maryland:
U.S. Geological Survey Open-File Report 92- 11,18 p.
Powell, J.A., and Schutz, D.F., 1987, Pre-construction site qualification for susceptibility to
radon emanation: Geological Society of America, Abstracts with Programs, v. 19, p. 124.
Reimer, G.M., 1988, Radon soil-gas survey in Prince George's County, Maryland: U.S.
Geological Survey Open-File Report 88-52,12 p.
Reimer, G.M., Gundersen, L.C.S., Szarzi, S.L., and Been, J.M., 1991, Reconnaisannce
approach to using geology and soil-gas radon concentrations for making rapid and
preliminary estimates of indoor radon potential, 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. 177-181.
Reinhardt, J.A., 1974, Stratigraphy, sedimentology, and Cambro-Ordovician paleogeography of
the Frederick Valley, Maryland: Maryland Geological Survey Report of Investigations
no. 23, 74 p.
Sachs, H.M., Hernandez, T.L., and Ring, J.W., 1982, Regional geology and radon variability in
buildings: Environment International, v. 8, p. 97-103.
Schultz, A.P., and Wiggs, C.R., 1989, Preliminary results of a radon study across the Great
Valley of West Virginia: Geological Society of America, Abstracts with Programs, v. 21,
no. 2, p. 65. -
IV-31 Reprinted from USGS Open-FUe Report 93-292-C
-------
Schultz, A.P., Wiggs, C.R., and Brower, S.D., 1992, Geologic and environmental implications
of high soil-gas radon concentrations in the Great Valley, Jefferson and Berkeley Counties,
West Virginia, in Gates, A.E., and Gundersen, L.C.S., eds, Geologic controls on radon:
Geological Society of America Special Paper 271, p. 29-44.
Smoot, IP., 1991, Sedimentary facies and depostional environments of early Mesozoic Newark
Supergroup basins, eastern North America: Palaeogeography, Palaeoclimatology,
Palaeoecology, v. 84, p. 369-423.
Soil Survey Staff, 1975, Soil taxonomy: U.S. Department of Agriculture, Soil Conservation
• Service Agriculture Handbook 436,754 p.
State of Maryland, 1989, State of Maryland Radon Task Force Final Report to the Governor and
General Assembly: State of Maryland, February 1989, 89 p.
Szarzi, S.L., Reimer, G.M., and Been, J.M., 1990, Soil-gas and indoor radon distribution related
to geology in Frederick County, Maryland (abs): Final Program for the Twenty-ninth
Hanford Symposium on Health and the Environment — Indoor Radon and Lung Cancer:
Reality or Myth?, October 15-19,1990, Richland, Washington, p. 95-96.
Texas Instruments Incorporated, 1978a, Aerial radiometric and magnetic reconnaissance survey of
the Baltimore Quadrangle, Volume 2A, U.S. Department of Energy Report GJBX-133-78.
Texas Instruments Incorporated, 1978b, Aerial radiometric and magnetic reconnaissance survey of
the Washington Quadrangle, Volume 2B, U.S. Department of Energy Report GJBX-133-
78.
Texas Instruments Incorporated, 1980, Aerial radiometric and magnetic reconnaissance survey of
the Cumberland Quadrangle, Volume 2C, U.S. Department of Energy Report GJBX-92-
80.
Thornbury, W.D., 1965, Regional geomorphology of the United States: New York, John Wiley
and Sons, Inc., 609 p.
U.S. Soil Conservation Service, 1987, Soils: U.S. Geological Survey National Atlas sheet
38077-BE-NA-07M-00, scale 1:7,500,000.
van Assendelft, A.CJE., and Sachs, H.M., 1982, Soil and regional uranium as controlling factors
of indoor radon in eastern Pennsylvania: Princeton University, Center for Energy and
Environmental Studies Report 145,68 p.
Vokes, H.E., 1957 (revised 1968,1974), Geography and Geology of Maryland: Maryland
Geological Survey Bulletin 19,242 p.
Wanty, R.B., Johnson, S.L., Briggs, P.H., and Gundersen, L.C.S., 1989, Geochemical
constraints on radionuclide mobility in ground water from crystalline aquifers in
Montgomery County, MD: Geological Society of America, Abstracts with Programs,
v. 21, p. 156.
IV-32 Reprinted from USGS Open-File Report 93-292-C
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EPA's Map of Radon Zones
The USGS' Geologic Radon Province Map is the technical foundation for EPA's Map
of Radon Zones. The Geologic Radon Province Map defines the radon potential for
approximately 360 geologic provinces. EPA has adapted this information to fit a county
boundary map in order to produce the Map of Radon Zones.
The Map of Radon Zones is based on the same range of predicted screening levels of
indoor radon as USGS' Geologic Radon Province Map. EPA defines the three zones as
follows: Zone One areas have an average predicted indoor radon screening potential greater
than 4 pCi/L. Zone Two areas are predicted to have an average indoor radon screening
potential between 2 pCi/L and 4 pCi/L. Zone Three areas are predicted to have an average
indoor radon screening potential less than 2 pCi/L. .
Since the geologic province boundaries cross state and county boundaries, a strict
translation of counties from the Geologic Radon Province Map to the Map of Radon Zones
was not possible. For counties that have variable radon potential (i.e., are located in two or
more provinces of different rankings), the counties were assigned to a zone based on the
predicted radon potential of the province in which most of its area lies. (See Part I for more
details.)
MARYLAND MAP OF RADON ZONES
The Maryland Map of Radon Zones and its supporting documentation (Part IV of this
report) have received extensive review by Maryland geologists and radon program experts.
The map for Maryland 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 Maryland" ~ 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 3 EPA office or the
Maryland radon program for information on testing and fixing homes. Telephone numbers
and addresses can be found in Part n of this report.
V-l
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