United States
Environmental Protection
Agency
Air and Radiation
(6604J)
402-R-93-028
September 1993
EPA's Map of Radon Zones
DELAWARE
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EPA'S MAP OF RADON ZONES
DELAWARE
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
ASSESSMENTSrINTRODUCTION
III. REGION 3 GEOLOGIC RADON POTENTIAL
SUMMARY
V. PRELIMINARY GEOLOGIC RADON POTENTIAL
ASSESSMENT OF DELAWARE
V. EPA'S MAP OF RADON ZONES - DELAWARE
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OVERVIEW
Sections 307 and 309 of the 1988 Indoor Radon Abatement Act (IRAA) direct EPA to
identify areas of the United States that have the potential to produce elevated levels of radon.
EPA, the U.S. Geological Survey (USGS), and the Association of American State Geologists
(AASG) have worked closely over the past several years to produce a series of maps and
documents which address these directives. The EPA Map of Radon Zones is a compilation of
that work and fulfills the requirements of sections 307 and 309 of IRAA. The Map of Radon
Zones identifies, on a county-by-county basis, areas of the U.'s. that have the highest potential
for elevated indoor radon levels (greater than 4 pCi/L).
The Map of Radon Zones is designed to assist national, State and local governments
and organizations to target their radon program activities and resources. It is also intended to
help building code officials determine areas that are the highest priority for adopting radon-
resistant building practices. The Map of Radon Zones should not be used to determine if
individual homes in any given area need to be tested for radon. EPA recommends that all
homes be tested for radon, regardless of geographic location or the zone designation of
the county in which they are located.
This document provides background information concerning the development of the
Map of Radon Zones. It explains the purposes of the map, the approach for developing the
map (including the respective roles of EPA and USGS), the data sources used, the conclusions
and confidence levels developed for the prediction of radon potential, and the review process
that was conducted to finalize this effort.
BACKGROUND
Radon (Rn222) is a colorless, odorless, radioactive gas. It comes from the natural
decay of uranium that is found in nearly all soils. It typically moves through the ground to
the air above and into homes and other buildings through cracks and openings in the
foundation. Any home, school or workplace may have a radon problem, regardless of
whether it is new or old, well-sealed or drafty, or with or without a basement. Nearly one out
of every 15 homes in the U.S. is estimated to have elevated annual average levels of indoor
radon.
Radon first gained national attention in early 1984, when extremely high levels of
indoor radon were found in areas of Pennsylvania, New Jersey, and New York, along the
Reading Prong-physiographic province. EPA established a Radon Program in 1985 to assist
States and homeo"wners in reducing their risk of lung cancer from indoor radon.
Since 1985, EPA and USGS have been working together to continually increase our
understanding of radon sources and the migration dynamics that cause elevated indoor radon
levels. ^ Early efforts resulted in the 1987 map entitled "Areas with Potentially High Radon
Levels." This map was based on limited geologic information only because few indoor radon
measurements were available at the time. The development of EPA's Map of Radon Zones
and its technical foundation, USGS1 National Geologic Radon Province Map, has been based
on additional information from six years of the State/EPA Residential Radon Surveys,
independent State residential surveys, and continued expansion of geologic and geophysical
information, particularly the data from the National Uranium Resource Evaluation project.
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Purpose of the Map of Radon Zones
EPA's Map of Radon Zones (Figure 1) assigns each of the 3141 counties in the
United States to one of three zones:
o Zone 1 counties have a predicted average indoor screening level > than
4 pCi/L
o Zone 2 counties have a predicted average screening level > 2 pCi/L and
< 4 pCi/L
o Zone 3 counties have a predicted average screening level < 2 pCi/L
The Zone designations were determined by assessing five factors that are known to be
important indicators of radon potential: indoor radon measurements, geology, aerial
radioactivity, soil parameters, and foundation types.
The predictions of average screening levels in each of the Zones is an expression of
radon potential in the lowest liveable area of a structure. This map is unable to estimate
actual exposures to radon. EPA recommends methods for testing and fixing individual homes
based on an estimate of actual exposure to radon. For more information on testing and fixing
elevated radon levels in homes consult these EPA publications: A Citizen's Guide to Radon.
the Consumer's Guide to Radon Reduction and the Home Buyer's and Seller's Guide to
Radon.
EPA believes that States, local governments and other organizations can achieve
optimal risk reductions by targeting resources and program activities to high radon potential
areas. Emphasizing targeted approaches (technical assistance, information and outreach
efforts, promotion of real estate mandates and policies and building codes, etc.) in such areas
addresses the greatest potential risks first.
EPA also believes that the use of passive radon control systems in the construction of
new homes in Zone 1 counties, and the activation of those systems if necessitated by follow-
up testing, is a cost effective approach to achieving significant radon risk reduction.
The Map of Radon Zones and its supporting documentation establish no regulatory
requirements. Use of this map by State or local radon programs and building code officials is
voluntary. The information presented on the Map of Radon Zones and in the supporting
documentation is not applicable to radon in water.
Development of the Map of Radon Zones
The technical foundation for the Map of Radon Zones is the USGS Geologic Radon
Province Map. In order to examine the radon potential for the United States, the USGS
began by identifying approximately 360 separate geologic provinces for the U.S. The
provinces are shown on the USGS Geologic Radon Province Map (Figure 2). Each of the
geologic provinces was evaluated by examining the available data for that area: indoor radon
measurements, geology, aerial radioactivity, soil parameters, and foundation types. As stated
previously, these five factors are considered to be of basic importance in assessing radon
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potential and some data are available for each of these factors in every geologic province. The
province boundaries do not coincide with political borders (county and state) but define areas
of general radon potential. The five factors were assigned numerical values based on an
assessment of their respective contribution to radon potential, and a confidence level was
assigned to each contributing variable. The approach used by USGS to estimate the radon
potential for each province is described in Part II of this document.
EPA subsequently developed the Map of Radon Zones by extrapolating from the
province level to the county level so that all counties in the U.S. were assigned to one of
three radon zones. EPA assigned each county to a given zone based on its provincial radon
potential. For example, if a county is located within a geologic province that has a predicted
average screening level greater than 4 pCi/L, it was assigned to Zone 1. Likewise, counties
located in provinces with predicted average screening levels > 2 pCi/L and < 4 pCi/L, and
less than 2 pCi/L, were assigned to Zones 2 and 3, respectively.
If the boundaries of a county fall in more than one geologic province, the county was
assigned to a zone based on the predicted radon potential of the province in which most of
the area lies. For example, if three different provinces cross through a given county, the
county was assigned to the zone representing the radon potential of the province containing
most of the county's land area. (In this case, it is not technically correct to say that the
predicted average screening level applies to the entire county since the county falls in
multiple provinces with differing radon potentials.)
Figures 3 and 4 demonstrate an example of how EPA extrapolated the county zone
designations for Nebraska from the USGS geologic province map for the State. As figure 3
shows, USGS has identified 5 geologic provinces for Nebraska. Most of the counties are
extrapolated "straight" from their corresponding provinces, but there are counties "partitioned"
by several provinces -- for example, Lincoln County. Although Lincoln county falls in
multiple provinces, it was assigned to Zone 3 because most of its area falls in the province
with the lowest radon potential.
It is important to note that EPA's extrapolation from the province level to the
county level may mask significant "highs" and "lows" within specific counties. In other
words, within-county variations in radon potential are not shown on the Map of Radon
Zones. EPA recommends that users who may need to address specific within-county
variations in radon potential (e.g., local government officials considering the
implementation of radon-resistant construction codes) consult USGS' Geologic Radon
Province Map and the State chapters provided with this map for more detailed
information, as well as any locally available data.
Map Validation
The Map of Radon Zones is intended to represent a preliminary assessment of radon
potential for the entire United States. The factors that are used in this effort --indoor radon
data, geology, aerial radioactivity, soils, and foundation type ~ are basic indicators for radon
potential. It is important to note, however, that the map's county zone designations are not
"statistically valid" predictions due to the nature of the data available for these 5 factors at the
county level. In order to validate the map in light of this lack of statistical confidence, EPA
conducted a number of analyses. These analyses have helped EPA to identify the best'
situations in which to apply the map, and its limitations.
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Figure 3
Geologic Radon Potential Provinces for Nebraska
Lincoln County
Hiji Uoieraie Low
Figure 4
NEBRASKA - EPA Map of Radon Zones
Lincoln County
Zoae I Zone 2 Zone 3
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One such analysis involved comparing county zone designations to indoor radon
measurements from the State/EPA Residential Radon Surveys (SRRS). Screening averages
for counties with at least 100 measurements were compared to the counties' predicted radon
potential as indicated by the Map of Radon Zones. EPA found that 72% of the county
screening averages were correctly reflected by the appropriate zone designations on the Map.
In all other cases, they only differed by 1 zone.
Another accuracy analysis used the annual average data from the National Residential
Radon Survey (NRRS). The NRRS indicated that approximately 6 million homes in the
United States have annual averages greater than or equal to 4 pCi/L. By cross checking the
county location of the approximately 5,700 homes which participated in the survey, their
radon measurements, and the zone designations for these counties, EPA found that
approximately 3.8 million homes of the 5.4 million homes with radon levels greater than or
equal to 4 pCi/L will be found in counties designated as Zone 1. A random sampling of an
equal number of counties would have only found approximately 1.8 million homes greater
than 4 pCi/L. In other words, this analysis indicated that the map approach is three times
more efficient at identifying high radon areas than random selection of zone designations.
Together, these analyses show that the approach EPA used to develop the Map of
Radon Zones is a reasonable one. In addition, the Agency's confidence is enhanced by results
of the extensive State review process ~ the map generally agrees with the States' knowledge
of and experience in their own jurisdictions. However, the accuracy analyses highlight two
important points: the fact that elevated levels will be found in Zones 2 and 3, and that there
will be significant numbers of homes with lower indoor radon levels in all of the Zones. For
these reasons, users of the Map of Radon Zones need to supplement the Map with locally
available data whenever possible. Although all known "hot spots", i.e., localized areas of
consistently elevated levels, are discussed in the State-
specific chapters, accurately defining the boundaries of the "hot spots" on this scale of map is
not possible at this time. Also, unknown "hot spots" do exist.
The Map of Radon Zones is intended to be a starting point for characterizing radon
potential because our knowledge of radon sources and transport is always growing. Although
this effort represents the best data available at this time, EPA will continue to study these
parameters and others such as house construction, ventilation features and meteorology factors
in order to better characterize the presence of radon in U.S homes, especially in high risk
areas. These efforts will eventually assist EPA in refining and revising the conclusions of the
Map of Radon Zones. And although this map is most appropriately used as a targeting tool
by the aforementioned audiences ~ the Agency encourages all residents to test their homes
for radon, regardless of geographic location or the zone designation of the county in
which they live. Similarly, the Map of Radon Zones should not to be used in lieu of
testing during real estate transactions.
Review Process
The Map of Radon Zones has undergone extensive review within EPA and outside the
Agency. The Association of American State Geologists (AASG) played an integral role in
this review process. The AASG individual State geologists have reviewed their State-specific
information, the USGS Geologic Radon Province Map, and other materials for their geologic
content and consistency.
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In addition to each State geologist providing technical comments, the State radon
offices were asked to comment on their respective States' radon potential evaluations. In
particular, the States were asked to evaluate the data used to assign their counties to specific
zones. EPA and USGS worked with the States to resolve any issues concerning county zone
designations. In a few cases, States have requested changes in county zone designations. The
requests were based on additional data from the State on geology, indoor radon
measurements, population, etc. Upon reviewing the data submitted by the States, EPA did
make some changes in zone designations. These changes, which do not strictly follow the
methodology outlined in this document, are discussed in the respective State chapters.
EPA encourages the States and counties to conduct further research and data collection
efforts to refine the Map of Radon Zones. EPA would like to be kept informed of any
changes the States, counties, or others make to the maps. Updates and revisions will be
handled in a similar fashion to the way the map was developed. States should notify EPA of
any proposed changes by forwarding the changes through the Regional EPA offices that are
listed in Part II. Depending on the amount of new information that is presented, EPA will
consider updating this map periodically. The State radon programs should initiate proper
notification of the appropriate State officials when the Map of Radon Zones is released and
when revisions or updates are made by the State or EPA.
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THE USGS/EPA RADON POTENTIAL ASSESSMENTS: AN INTRODUCTION
by
Linda C.S. Gundersen and R. Randall Schumann
U.S. Geological Survey
and
Sharon W. White
U.S. Environmental Protection Agency
BACKGROUND
The Indoor Radon Abatement Act of 1988 (15 U.S.C. 2661-2671) directed the U.S.
Environmental Protection Agency (EPA) to identify areas of the United States that have the
potential to produce harmful levels of indoor radon. These characterizations were to be based
on both geological data and on indoor radon levels in homes and other structures. The EPA
also was directed to develop model standards and techniques for new building construction
that would provide adequate prevention or mitigation of radon entry. As part of an
Interagency Agreement between the EPA and the U.S. Geological Survey (USGS), the USGS
has prepared radon potential estimates for the United States. This report is one of ten
booklets that document this effort. The purpose and intended use of these reports is to help
identify areas where states can target their radon program resources, to provide guidance in
selecting the most appropriate building code options for areas, and to provide general
information on radon and geology for each state for federal, state, and municipal officials
dealing with radon issues. These reports are not intended to be used as a substitute for
indoor radon testing, and they cannot and should not be used to estimate or predict the
indoor radon concentrations of individual homes, building sites, or housing tracts. Elevated
levels of indoor radon have been found in every State, and EPA recommends that all homes
be tested for indoor radon.
Booklets detailing the radon potential assessment for the U.S. have been developed for
each State. USGS geologists are the authors of the geologic radon potential booklets. Each
booklet consists of several components, the first being an overview to the mapping project
(Part I), this introduction to the USGS assessment (Part II), including a general discussion of
radon (occurrence, transport, etc.), and details concerning the types of data used. The third
component is a summary chapter outlining the general geology and geologic radon potential
of the EPA Region (Part III). The fourth component is an individual chapter for each state
(Part IV). Each state chapter discusses the state's specific geographic setting, soils, geologic
setting, geologic radon potential, indoor radon data, and a summary outlining the radon
potential rankings of geologic areas in the state. A variety of maps are presented in each
chapter—geologic, geographic, population, soils, aerial radioactivity, and indoor radon data by
county. Finally, the booklets contain EPA's map of radon zones for each state and an
accompanying description (Part V).
Because of constraints on the scales of maps presented in these reports and because the
smallest units used to present the indoor radon data are counties, some generalizations have
been made in order to estimate the radon potential of each area. Variations in geology, soil
characteristics, climatic factors, homeowner lifestyles, and other factors that influence radon
concentrations can be quite large within any particular geologic area, so these reports cannot
be used to estimate or predict the indoor radon concentrations of individual homes or housing
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 report for more detailed information. In most
cases the best sources of information on radon for specific areas are state and local
departments of health, state departments responsible for nuclear safety or environmental
protection, and U.S. EPA regional offices. More detailed information on state or local
geology may be obtained from the state geological surveys. Addresses and telephone
numbers of state radon contacts, geological surveys, and EPA regional offices are listed in
Appendix C at the end of this chapter.
RADON GENERATION AND TRANSPORT IN SOILS
Radon (2MRn) is produced from the radioactive decay of radium (2MRa), which is, in turn,
a product of the decay of uranium (238U) (fig. 1). The half-life of 222Rn is 3.825 days. Other
isotopes of radon occur naturally, but, with the exception of thoron (220Rn), which occurs in
concentrations high enough to be of concern in a few localized areas, they are less important
in terms of indoor radon risk because of their extremely short half-lives and less common
occurrence. In general, the concentration and mobility of radon in soil are dependent on
several factors, the most important of which are the soil's radium content and distribution,
porosity, permeability to gas movement, and moisture content. These characteristics are, in
turn, determined by the soil's parent-material composition, climate, and the soil's age or
maturity. If parent-material composition, climate, vegetation, age of the soil, and topography
are known, the physical and chemical properties of a soil in a given area can be predicted.
As soils form, they develop distinct layers, or horizons, that are cumulatively called the
soil profile. The A horizon is a surface or near-surface horizon containing a relative
abundance of organic matter but dominated by mineral matter. Some soils contain an E
horizon, directly below the A horizon, that is generally characterized by loss of clays, iron, or
aluminum, and has a characteristically lighter color than the A horizon. The B horizon
underlies the A or E horizon. Important characteristics of B horizons include accumulation of
clays, iron oxides, calcium carbonate or other soluble salts, and organic matter complexes. In
drier environments, a horizon may exist within or below the B horizon that is dominated by
calcium carbonate, often called caliche or calcrete. This carbonate-cemented horizon is
designated the K horizon in modern soil classification schemes. The C horizon underlies the
B (or K) and is a zone of weathered parent material that does not exhibit characteristics of A
or B horizons; that is, it is generally not a zone of leaching or accumulation. In soils formed
in place from the underlying bedrock, the C horizon is a zone of unconsolidated, weathered
bedrock overlying the unweathered bedrock.
The shape and orientation of soil particles (soil structure) control permeability and affect
water movement in the soil. Soils with blocky or granular structure have roughly equivalent
permeabilities in the horizontal and vertical directions, and air and water can infiltrate the soil
relatively easily. However, in soils with platy structure, horizontal permeability is much
greater than vertical permeability, and air and moisture infiltration is generally slow. Soils
with prismatic or columnar structure have dominantly vertical permeability. Platy and
prismatic structures form in soils with high clay contents. In soils with shrink-swell clays, air
II-2 Reprinted from USGS Open-File Report 93-292
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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 area's of karst topography formed
in carbonate rock (limestone or dolomite) environments, solution cavities and fissures can
increase soil permeability at depth by providing additional pathways for gas flow.
Not all radium contained in soil grains and grain coatings will result in mobile radon
when the radium decays. Depending on where the radium is distributed in the soil, many of
the radon atoms may remain imbedded in the soil grain containing the parent radium atom, or
become imbedded in adjacent soil grains. The portion of radium that releases radon into the
pores and fractures of rocks and soils is called the emanating fraction. When a radium atom
decays to radon, the energy generated is strong enough to send the radon atom a distance of
about 40 nanometers (1 nm = 10'9 meters), or about 2x10* 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 cavit.es m 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 surroundmg soil than nonbasement homes. The term "nonbasement" applies to
siab-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 mam types of data: (1) geologic (lithologic); (2) aerial radiometric; (3) soil
characteristics, me udmg 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-
beanng sandstones, certain kinds of fluvial sandstones and fluvial sediments, phosphorites
chalk, karst-producmg carbonate rocks, certain kinds of glacial deposits, bauxite, uranium-rich
granitic rocks, metamorphic rocks of granitic composition, silica-rich volcanic rocks many
sheared or faulted rocks, some coals, and certain kinds of contact metamorphosed rocks
Rock types least likely to cause radon problems include marine quartz sands non-
carbonaceous shales and siltstones, certain kinds of clays, silica-poor metamorphic and
II-5 Reprinted from USGS Open-File Report 93-292
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igneous rocks, and basalts. Exceptions exist within these general lithologic groups because of
the occurrence of localized uranium deposits, commonly of the hydrothermal type in
crystalline rocks or the "roll-front" type in sedimentary rocks. Uranium and radium are
commonly sited in heavy minerals, iron-oxide coatings on rock and soil grains, and organic
materials in soils and sediments. Less common are uranium associated with phosphate and
carbonate complexes in rocks and soils, and uranium minerals.
Although many cases of elevated indoor radon levels can be traced to high radium and
(or) uranium concentrations in parent rocks, some structural features, most notably faults and
shear zones, have been identified as sites of localized uranium concentrations (Deffeyes and
MacGregor, 1980) and have been associated with some of the highest reported indoor radon
levels (Gundersen, 1991). The two highest known indoor radon occurrences are associated
with sheared fault zones in Boyertown, Pennsylvania (Gundersen and others, 1988a; Smith
and others, 1987), and in Clinton, New Jersey (Henry and others, 1991; Muessig and Bell,
1988).
NURE AERIAL RADIOMETRIC DATA
Aerial radiometric data are used to quantify the radioactivity of rocks and soils.
Equivalent uranium (eU) data provide an estimate of the surficial concentrations of radon
parent materials (uranium, radium) in rocks and soils. Equivalent uranium is calculated from
the counts received by a gamma-ray detector from the 1.76 MeV (mega-electron volts)
emission energy corresponding to bismuth-214 (214Bi), 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 fadon source strength over a region, but the amount of radon that is able to enter a home
from the soil is dependent on several local factors, including soil structure, grain size
distribution, moisture content, and permeability, as well as type of house construction and its
structural condition.
The aerial radiometric data used for these characterizations were collected as part of the
Department of Energy National Uranium Resource Evaluation (NURE) program of the 1970s
and early 1980s. The purpose of the NURE program was to identify and describe areas in the
United States having potential uranium resources (U.S. Department of Energy, 1976). The
NURE aerial radiometric data were collected by aircraft in which a gamma-ray spectrometer
was mounted, flying approximately 122 m (400 ft) above the ground surface. The equivalent
uranium maps presented in the state chapters were generated from reprocessed NURE data in
which smoothing, filtering, recalibrating, and matching of adjacent quadrangle data sets were
performed to compensate for background, altitude, calibration, and other types of errors and
inconsistencies in the original data set (Duval and others, 1989). The data were then gridded
and contoured to produce maps of eU with a pixel size corresponding to approximately 2.5 x
2.5 km (1.6 x 1.6 mi).
II-6 Reprinted from USGS Open-File Report 93-292
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FLIGHT LINE SPACING Of SORE AEKlAL SURVEYS
2 KM (1 MILE)
5 EH (3 MILES)
2 i 5 KM
ES 10 IU (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.
-------
Figure 2 is an index map of NUKE 1° x 2° quadrangles showing the flight-line spacing
for each quadrangle. In general, the more closely spaced the flightlines are, the more area
was covered by the aerial gamma survey, and thus, more detail is available in the data set.
For an altitude of 400 ft above the ground surface and with primary flightline spacing
typically between 3 and 6 miles, less than 10 percent of the ground surface of the United
States was actually measured by the airborne gamma-ray detectors (Duval and others, 1989),
although some areas had better coverage than others due to the differences in flight-line
spacing between areas (fig. 2). This suggests that some localized uranium anomalies may not
have been detected by the aerial surveys, but the good correlations of eU patterns with
geologic outcrop patterns indicate that, at relatively small scales (approximately 1:1,000,000
or smaller) the National eU map (Duval and others, 1989) gives reasonably good estimates of
average surface uranium concentrations and thus can assist in the prediction of radon potential
of rocks and soils, especially when augmented with additional geologic and soil data.
The shallow (20-30 cm) depth of investigation of gamma-ray spectrometers, either
ground-based or airborne (Duval and others, 1971; Durrance, 1986), suggests that gamma-ray
data may sometimes underestimate the radon-source strength in soils in which some of the
radionuclides in the near-surface soil layers have been transported downward through the soil
profile. In such cases the concentration of radioactive minerals in the A horizon would be
lower than in the B horizon, where such minerals are typically concentrated. The
concentration of radionuclides in the C horizon and below may be relatively unaffected by
surface solution processes. Under these conditions the surface gamma-ray signal may indicate
a lower radon source concentration than actually exists in the deeper soil layers, which are
most likely to affect radon levels in structures with basements. The redistribution of
radionuclides in soil profiles is dependent on a combination of climatic, geologic, and
geochemical factors. There is reason to believe that correlations of eU with actual soil
radium and uranium concentrations at a depth relevant to radon entry into structures may be
regionally variable (Duval, 1989; Schumann and Gundersen, 1991). Given sufficient
understanding of the factors cited above, these regional differences may be predictable.
SOIL SURVEY DATA
Soil surveys prepared by the U.S. Soil Conservation Service (SCS) provide data on soil
characteristics, including soil-cover thickness, grain-size distribution, permeability, shrink-
swell potential, vegetative cover, generalized groundwater characteristics, and land use. The
reports are available in county formats and State summaries. The county reports typically
contain both generalized and detailed maps of soils in the area.
Because of time and map-scale constraints, it was impractical to examine county soil
reports for each county in the United States, so more generalized summaries at appropriate
scales were used where available. For State or regional-scale radon characterizations, soil
maps were compared to geologic maps of the area, and the soil descriptions, shrink-swell
potential, drainage characteristics, depth to seasonal high water table, permeability, and other
relevant characteristics of each soil group noted. Technical soil terms used in soil surveys are
generally complex; however, a good summary of soil engineering terms and the national
distribution of technical soil types is the "Soils" sheet of the National Atlas (U.S. Department
of Agriculture, 1987).
II-8 Reprinted from USGS Open-File Report 93-292
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Soil permeability is commonly expressed in SCS soil surveys in terms of the speed, in
inches per hour (in/hr), at which water soaks into the soil, as measured in a soil percolation
test. Although in/hr are not truly units of permeability, these units are in widespread use and
are referred to as "permeability" in SCS soil surveys. The permeabilities listed in the SCS
surveys are for water, but they generally correlate well with gas permeability. Because data
on gas permeability of soils is extremely limited, data on permeability to water is used as a
substitute except in cases in which excessive soil moisture is known to exist. Water in soil
pores inhibits gas transport, so the amount of radon available to a home is effectively reduced
by a high water table. Areas likely to have high water tables include river valleys, coastal
areas, and some areas overlain by deposits of glacial origin (for example, loess).
Soil permeabilities greater than 6.0 in/hr may be considered high, and permeabilities less
than 0.6 in/hr may be considered low in terms of soil-gas transport. Soils with low
permeability may generally be considered to have a lower radon potential than more
permeable soils with similar radium concentrations. Many well-developed soils contain a
clay-rich B horizon that may impede vertical soil gas transport. Radon generated below this
horizon cannot readily escape to the surface, so it would instead tend to move laterally,
especially under the influence of a negative pressure exerted by a building.
Shrink-swell potential is an indicator of the abundance of smectitic (swelling) clays in a
soil. Soils with a high shrink-swell potential may cause building foundations to crack,
creating pathways for radon entry into the structure. During dry periods, desiccation cracks in
shrink-swell soils provide additional pathways for soil-gas transport and effectively increase
the gas permeability of the soil. Soil permeability data and soil profile data thus provide
important information for regional radon assessments.
INDOOR RADON DATA
Two major sources of indoor radon data were used. The first and largest source of data is
from the State/EPA Residential Radon Survey (Ronca-Battista and others, 1988; Dziuban and
others, 1990). Forty-two states completed EPA-sponsored indoor radon surveys between 1986
and 1992 (fig. 3). The State/EPA Residential Radon Surveys were designed to be
comprehensive and statistically significant at the state level, and were subjected to high levels
of quality assurance and control. The surveys collected screening indoor radon measurements,
defined as 2-7 day measurements using charcoal canister radon detectors placed in the lowest
livable area of the home. The target population for the surveys included owner-occupied
single family, detached housing units (White and others, 1989), although attached structures
such as duplexes, townhouses, or condominiums were included in some of the surveys if they
met the other criteria and had contact with the ground surface. Participants were selected
randomly from telephone-directory listings. In total, approximately 60,000 homes were tested
in the State/EPA surveys.
The second source of indoor radon data comes from residential surveys that have been
conducted in a specific state or region of the country (e.g. independent state surveys or utility
company surveys). Several states, including Delaware, Florida, Illinois, New Hampshire, New
Jersey, New York, Oregon, and Utah, have conducted their own surveys of indoor radon. The
quality and design of a state or other independent survey are discussed and referenced where
the data are used.
II-9 Reprinted from USGS Open-File Report 93-292
-------
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Data for only those counties with five or more measurements are shown in the indoor
radon maps in the state chapters, although data for all counties with a nonzero number of
measurements are listed in the indoor radon data tables in each state chapter. In total indoor
radon data from more than 100,000 homes nationwide were used in the compilation of these
assessments. Radon data from State or regional indoor radon surveys, public health
organizations, or other sources are discussed in addition to the primary data sources where
they are available. Nearly all of the data used in these evaluations represent short-term (2-7
day) screening measurements from the lowest livable space of the homes. Specific details
concerning the nature and use of indoor radon data sets other than the State/EPA Residential
Radon Survey are discussed in the individual State chapters.
RADON INDEX AND CONFIDENCE INDEX
Many of the geologic methods used to evaluate an area for radon potential require
subjective opinions based on the professional judgment and experience of the individual
geologist. The evaluations are nevertheless based on established scientific principles that are
universally applicable to any geographic area or geologic setting. This section describes the
methods and conceptual framework used by the U.S. Geological Survey to evaluate areas for
radon potential based on the five factors discussed in the previous sections. The scheme is
divided into two basic parts, a Radon Index (RI), used to rank the general radon potential of
the area, and the Confidence Index (CI), used to express the level of confidence in the
prediction based on the quantity and quality of the data used to make the determination. This
scheme works best if the areas to be evaluated are delineated by geologically-based
boundaries (geologic provinces) rather than political ones (state/county boundaries) in which
the geology may vary across the area.
Radon Index, Table 1 presents the Radon Index (RI) matrix. The five factors—indoor
radon data, geology, aerial radioactivity, soil parameters, and house foundation type—were
quantitatively ranked (using a point value of 1, 2, or 3) for their respective contribution to
radon potential in a given area. At least some data for the 5 factors are consistently available
for every geologic province. Because each of these main factors encompass a wide variety of
complex and variable components, the geologists performing the evaluation relied heavily on
their professional judgment and experience in assigning point values to each category and in
determining the overall radon potential ranking. Background information on these factors is
discussed in more detail in the preceding sections of this introduction.
Indoor radon was evaluated using unweighted arithmetic means of the indoor radon data
for each geologic area to be assessed. Other expressions of indoor radon levels in an area
also could have been used, such as weighted averages or annual averages, but these types of
data were not consistently available for the entire United States at the time of this writing, or
the schemes were not considered sufficient to provide a means of consistent comparison *"
across all areas. For this report, charcoal-canister screening measurement data from the
State/EPA Residential Radon Surveys and other carefully selected sources were used, as
described in the preceding section. To maintain consistency, other indoor radon data sets
(vendor, state, or other data) were not considered in scoring the indoor radon factor of the
Radon Index if they were not randomly sampled or could not be statistically combined with
the primary indoor radon data sets. However, these additional radon data sets can provide a
means to further refine correlations between geologic factors and radon potential, so they are
II-11 Reprinted from USGS Open-File Report 93-292
-------
TABLE 1. RADON INDEX MATRIX, "ppm eU" indicates parts per million of equivalent
uranium, as indicated by MURE aerial radiometric data. See text discussion for details.
FACTOR
INDOOR RADON (average)
AERIAL RADIOACTIVITY
GEOLOGY*
SOIL PERMEABILITY
ARCfflTECTURE TYPE
INCREASING RADON POTENTIAL ^
POINT VALUE
1
<2pCi/L
< 1.5 ppm eU
negative
low
mostly slab
2
2-4pCi/L
1.5 - 2.5 ppm eU
variable
moderate
mixed
3
>4pCi/L
> 2.5 ppm eU
positive
high
mostly basement
'GEOLOGIC FIELD EVIDENCE (GFE) POINTS: GFE points are assigned in addition to points
for the "Geology" factor for specific, relevant geologic field studies. See text for details.
Geologic evidence supporting: HIGH radon +2 points
MODERATE +1 point
LOW -2 points
No relevant geologic field studies 0 points
SCORING:
Radon potential category
Point 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 RADIO ACnVlTY
GEOLOGIC DATA
SOIL PERMEABILITY
POINT VALUE
1
sparse/no data
questionable/no data
questionable
questionable/no data
2
fair coverage/quality
glacial cover
variable
variable
3
good coverage/quality
no glacial cover
proven geol. model
reliable, abundant
SCORING:
LOW CONFIDENCE
MODERATE CONFIDENCE
HIGH CONFIDENCE
4-6 points
7-9 points
10 -12 points
POSSIBLE RANGE OF POINTS = 4 to 12
II-12 Reprinted from USGS Open-File Report 93-292
-------
included as supplementary information and are discussed in the individual State chapters. If
the average screening indoor radon level for an area was less than 2 pCi/L, the indoor radon
factor was assigned 1 point, if it was between 2 and 4 pCi/L, it was scored 2 points, and if
the average screening indoor radon level for an area was greater than 4 pCi/L, the indoor
radon factor was assigned 3 RI points.
Aerial radioactivity data used in this report are from the equivalent uranium map of the
conterminous United States compiled from NUKE aerial gamma-ray surveys (Duval and
others, 1989). These data indicate the gamma radioactivity from approximately the upper 30
cm of rock and soil, expressed in units of ppm equivalent uranium. An approximate average
value of eU was determined visually for each area and point values assigned based on
whether the overall eU for the area falls below 1.5 ppm (1 point), between 1.5 and 2.5 ppm
(2 points), or greater than 2.5 ppm (3 points).
The geology factor is complex and actually incorporates many geologic characteristics. In
the matrix, "positive" and "negative" refer to the presence or absence and distribution of rock
types known to have high uranium contents and to generate elevated radon in soils or indoors.
Examples of "positive" rock types include granites, black shales, phosphatic rocks, and other
rock types described in the preceding "geologic data" section. Examples of "negative" rock
types include marine quartz sands and some clays. The term "variable" indicates that the
geology within the region is variable or that the rock types in the area are known or suspected
to generate elevated radon in some areas but not in others due to compositional differences,
climatic effects, localizeddistribution of uranium, or other factors. Geologic information
indicates not only how much uranium is present in the rocks and soils but also gives clues for
predicting general radon emanation and mobility characteristics through additional factors
such as structure (notably the presence of faults or shears) and geochemical characteristics
(for example, a phosphate-rich sandstone will likely contain more uranium than a sandstone
containing little or no phosphate because the phosphate forms chemical complexes with
uranium). "Negative", "variable", and "positive" geology were assigned 1, 2, and 3 points,
respectively.
In cases where additional reinforcing or contradictory geologic evidence is available,
Geologic Field Evidence (GFE) points were added to or subtracted from an area's score
(Table 1). Relevant geologic field studies are important to enhancing our understanding of
how geologic processes affect radon distribution. In some cases, geologic models and
supporting field data reinforced an already strong (high or low) score; in others, they provided
important contradictory data. GFE points were applied for geologically-sound evidence that
supports the prediction (but which may contradict one or more factors) on the basis of known
geologic field studies in the area or in areas with geologic and climatic settings similar
enough that they could be applied with full confidence. For example, areas of the Dakotas,
Minnesota, and Iowa that are covered with Wisconsin-age glacial deposits exhibit a low aerial
radiometric signature and score only one RI point in that category. However, data from
geologic field studies in North Dakota and Minnesota (Schumann and others, 1991) suggest
that eU is a poor predictor of geologic radon potential in this area because radionuclides have
11-13 Reprinted from USGS Open-File Report 93-292
-------
been leached from the upper soil layers but are present and possibly even concentrated in
deeper soil horizons, generating significant soil-gas radon. This positive supporting field
evidence adds two GFE points to the score, which helps to counteract the invalid conclusion
suggested by the radiometric data. No GFE points are awarded if there are no documented
field studies for the area.
"Soil permeability" refers to several soil characteristics that influence radon concentration
and mobility, including soil type, grain size, structure, soil moisture, drainage, slope, and
permeability. In the matrix, "low" refers to permeabilities less than about 0.6 in/hr; "high"
corresponds to greater than about 6.0 in/hr, in U.S. Soil Conservation Service (SCS) standard
soil percolation tests. The SCS data are for water permeability, which generally correlates
well with the gas permeability of the soil except when the soil moisture content is very high.
Areas with consistently high water tables were thus considered to have low gas permeability.
"Low, "moderate", and "high" permeability were assigned 1, 2, and 3 points, respectively.
Architecture type refers to whether homes in the area have mostly basements (3 points),
mostly slab-on-grade construction (1 point), or a mixture of the'two. Split-level and crawl
space homes fall into the "mixed" category (2 points). Architecture information is necessary
to properly interpret the indoor radon data and produce geologic radon potential categories
that are consistent with screening indoor radon data.
The overall RI for an area is calculated by adding the individual RI scores for the 5
factors, plus or minus GFE points, if any. The total RI for an area falls in one of three
categories—low, moderate or variable, or high. The point ranges for the three categories were
determined by examining the possible combinations of points for the 5 factors and setting
rules such that a majority (3 of 5 factors) would determine the final score for the low and
high categories, with allowances for possible deviation from an ideal score by the other two
factors. The moderate/variable category lies between these two ranges. A total deviation of 3
points from the "ideal" score was considered reasonable to allow for natural variability of
factors—if two of the five factors are allowed to vary from the "ideal" for a category, they
can differ by a minimum of 2 (1 point different each) and a maximum of 4 points (2 points
different each). With "ideal" scores of 5, 10, and 15 points describing low, moderate, and
high geologic radon potential, respectively, an ideal low score of 5 points plus 3 points for
possible variability allows a maximum of 8 points in the low category. Similarly, an ideal
high score of 15 points minus 3 points gives a minimum of 12 points for the high category.
Note, however, that if both other factors differ by two points from the "ideal", indicating
considerable variability in the system, the total point score would lie in the adjacent (i.e.,
moderate/variable) category.
Confidence Index. Except for architecture type, the same factors were used to establish a
Confidence Index (CI) for the radon potential prediction for each area (Table 2). Architecture
type was not included in the confidence index because house construction data are readily and
reliably available through surveys taken by agencies and industry groups including the
National Association of Home Builders, U.S. Department of Housing and Urban
Development, and the Federal Housing Administration; thus it was not considered necessary
11-14 Reprinted from USGS Open-File Report 93-292
-------
to question the quality or validity of these data. The other factors were scored on the basis of
the quality and quantity of the data used to complete the RI matrix.
Indoor radon data were evaluated based on the distribution and number of data points and
on whether the data were collected by random sampling (State/EPA Residential Radon Survey
or other state survey data) or volunteered vendor data (likely to be nonrandom and biased
toward population centers and/or high indoor radon levels). The categories listed in the CI
matrix for indoor radon data ("sparse or no data", "fair coverage or quality", and "good
coverage/quality") indicate the sampling density and statistical robustness of an indoor radon
data set. Data from the State/EPA Residential Radon Survey and statistically valid state
surveys were typically assigned 3 Confidence Index points unless the data were poorly
distributed or absent in the area evaluated.
Aerial radioactivity data are available for all but a few areas of the continental United
States and for part of Alaska. An evaluation of the quality of the radioactivity data was based
on whether there appeared to be a good correlation between the radioactivity and the actual
amount of uranium or radium available to generate mobile radon in the rocks and soils of the
area evaluated. In general, the greatest problems with correlations among eU, geology, and
soil-gas or indoor radon levels were associated with glacial deposits (see the discussion in a
previous section) and typically were assigned a 2-point Confidence Index score. Correlations
among eU, geology, and radon were generally sound in unglaciated areas and were usually
assigned 3 CI points. Again, however, radioactivity data in some unglaciated areas may have
been assigned fewer than 3 points, and in glaciated areas may be assigned only one point, if
the data were considered questionable or if coverage was poor.
To assign Confidence Index scores for the geologic data factor, rock types and geologic
settings for which a physical-chemical, process-based understanding of radon generation and
mobility exists were regarded as having "proven geologic models" (3 points); a high
confidence could be held for predictions in such areas. Rocks for which the processes are
less well known or for which data are contradictory were regarded as "variable" (2 points),
and those about which little is known or for which no apparent correlations have been found
were deemed "questionable" (1 point).
The soil permeability factor was also scored based on quality and amount of data. The
three categories for soil permeability in the Confidence Index are similar in concept, and
scored similarly, to those for the geologic data factor. Soil permeability can be roughly
estimated from grain size and drainage class if data from standard, accepted soil percolation
tests are unavailable; however, the reliability of the data would be lower than if percolation
test figures or other measured permeability data are available, because an estimate of this type
does not encompass all the factors that affect soil permeability and thus may be inaccurate in
some instances. Most published soil permeability data are for water; although this is
generally closely related to the air permeability of the soil, there are some instances when it
may provide an incorrect estimate. Examples of areas in which water permeability data may
not accurately reflect air permeability include areas with consistently high levels of soil
moisture, or clay-rich soils, which would have a low water permeability but may have a
11-15 Reprinted from USGS Open-File Report 93-292
-------
significantly higher air permeability when dry due to shrinkage cracks in the soil. These
additional factors were applied to the soil permeability factor when assigning the RI score, but
may have less certainty in some cases and thus would be assigned a lower CI score.
The Radon Index and Confidence Index give a general indication of the relative
contributions of the interrelated geologic factors influencing radon generation and transport in
rocks and soils, and thus, of the potential for elevated indoor radon levels to occur in a
particular area. However, because these reports are somewhat generalized to cover relatively
large areas of States, it is highly recommended that more detailed studies be performed in
local areas of interest, using the methods and general information in these booklets as a guide.
11-16 Reprinted from USGS Open-File Report 93-292
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Akerblom, G., Anderson, P., and Clavensjo, B., 1984, Soil gas radon-A source for indoor radon
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Deffeyes, K.S., and MacGregor, I.D., 1980, World uranium resources: Scientific American
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Durrance, E.M., 1986, Radioactivity in geology: Principles and applications: New York, N.Y.,
Wiley and Sons, 441 p.
Duval, J.S., 1989, Radioactivity and some of its applications in geology: Proceedings of the
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Duval, J.S., Cook, B.G., and Adams, J.A.S., 1971, Circle of investigation of an airborne
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Duval, J.S., Jones, W.J., Riggle, F.R., and Pitkin, J.A., 1989, Equivalent uranium map of
conterminous United States: U.S. Geological Survey Open-File Report 89-478,10 p.
Duval, J.S., Reimer, G.M., Schumann, R.R., Owen, D.E., and Otton, J.K., 1990, Soil-gas
radon compared to aerial and ground gamma-ray measurements at study sites near Greeley
and Fort Collins, Colorado: U.S. Geological Survey Open-File Report 90-648,42 p.
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M.C., and Harrison, J., eds., Proceedings of the 1988 EPA Symposium on Radon and
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EPA/600/9-89/006A, p. 5-75-5-86.
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Ronca-Battista, M., Moon, M., Bergsten, J., White, S.B., Holt, N., and Alexander, B., 1988,
Radon-222 concentrations in the United States-Results of sample surveys in five states:
Radiation Protection Dosimetry, v. 24, p. 307-312.
Rose, A.W., Washington, J.W., and Greeman, D.J., 1988, Variability of radon with depth and
season in a central Pennsylvania soil developed on limestone: Northeastern Environmental
Science, v. 7, p. 35-39.
Schery, S.D., Gaeddert, D.H., and Wilkening, M.H., 1984, Factors affecting exhalation of radon
from a gravelly sandy loam: Journal of Geophysical Research, v. 89, p. 7299-7309.
Schumann, R.R., and Owen, D.E., 1988, Relationships between geology, equivalent uranium
concentration, and radon in soil gas, Fairfax County, Virginia: U.S. Geological Survey
Open-File Report 88-18,28 p.
Schumann, R.R., and Gundersen, L.C.S., 1991, Regional differences in radon emanation
coefficients in soils: Geological Society of America Abstracts With Programs, v. 23,
no. 1, p. 125.
Schumann, R.R., Peake, R.T., Schmidt, K.M., and Owen, D.E., 1991, Correlations of soil-gas
and indoor radon with geology in glacially derived soils of the northern Great Plains, in
Proceedings of the 1990 International Symposium on Radon and Radon Reduction
Technology, Volume 2, Symposium Oral Papers: U.S. Environmental Protection Agency
report EPA/600/9-9 l/026b, p. 6-23-6-36.
II-18 Reprinted from USGS Open-File Report 93-292
-------
Schumann, R.R., Owen, D.E., and Asher-Bolinder, S., 1992, Effects of weather and soil
characteristics on temporal variations in soil-gas radon concentrations, in Gates, A.E., and
Gundersen, L.C.S., eds., Geologic controls on radon: Geological Society of America
Special Paper 271, p. 65-72.
Sextro, R.G., Moed, B.A., Nazaroff, W.W., Revzan, K.L., and Nero, A.V., 1987,
Investigations of soil as a source of indoor radon, in Hopke, P.K., ed., Radon and its
decay products: American Chemical Society Symposium Series 331, p. 10-29.
Sterling, R., Meixel, G., Shen, L., Labs, K., and Bligh, T., 1985, Assessment of the energy
savings potential of building foundations research: Oak Ridge, Term., U.S. Department of
Energy Report ORNL/SUB/84-0024/1.
Smith, R.C., II, Reilly, M.A., Rose, A.W., Barnes, J.H., and Berkheiser, S.W., Jr., 1987,
Radon: a profound case: Pennsylvania Geology, v. 18, p. 1-7.
Tanner, A.B., 1964, Radon migration in the ground: a review, in Adams, J.A.S., and Lowder,
W.M., eds., The natural radiation environment: Chicago, El., University of Chicago
Press, p. 161-190.
Tanner, A.B., 1980, Radon migration in the ground: a supplementary review, in Gesell, T.F.,
and Lowder, W.M. (eds), Natural radiation environment m, Symposium proceedings '
Houston, Texas, v. 1, p. 5-56.
U.S. Department of Agriculture, 1987, Principal kinds of soils: Orders, suborders, and great
groups: U.S. Geological Survey, National Atlas of the United States of America sheet
38077-BE-NA-07M-00, scale 1:7,500,000.
U.S. Department of Energy, 1976, National Uranium Resource Evaluation preliminary report,
prepared by the U.S. Energy Research and Development Administration, Grand Junction
Colo.: GJO-llfa).
Wanty, Richard B., and Schoen, Robert, 1991, A review of the chemical processes affecting the
mobility of radionuclides in natural waters, with applications, in Gundersen, Linda C.S.,
and Richard B. Wanty, eds., Field studies of radon in rocks, soils, and water: U.S.
Geological Survey Bulletin no. 1971, p. 183-194.
Washington, J.W., and Rose, A.W., 1990, Regional and temporal relations of radon in soil gas to
soil temperature and moisture: Geophysical Research Letters, v. 17, p. 829-832.
White, S.B., Bergsten, J.W., Alexander, B.V., and Ronca-Battista, M., 1989, Multi-State
surveys of indoor 222Rn: Health Physics, v. 57, p. 891-896.
11-19 Reprinted from USGS Open-File Report 93-292
-------
APPENDIX A
GEOLOGIC TIME SCALE
Subdivisions (and their symbols)
Eon or
Eonothem
Phanerozoic2
Proterozoic
(P\
Archean
(At
l«J
Era or
Erathem
Cenozoic 2
(Cz)
Mesozoic2
(Mt)
Paleozoic2
(Pa
UW.
rotBror&ic 0'C rf\
£«ny
'rmvroToiC (X)
laia
Arttivan IW1
MlOdM
Afthtan (V)
t»nv
Aretwn (Ul
Per od. System,
Subperiod. Subsystem
Quaternary
(Q)
Neopene J
Subperiod or
T.rrJ.ry Subsystem (N)
m Paleogene2
Suboeriodor
Subsystem (Pi)
Cretaceous
(K)
Jurassic
Triassic
C5)
Permian
(P)
Pennsylvanian
Carboniferous (P)
(O Mississippian
(M)
Devonian
in)
Silurian
IC\
(a)
Ordovician
/Ol
(Ul
Cambrian
K.)
Epoch or Series
Holocene
Pleistocene
Pliocene
Miocene
Oligocene
Eocene
Paleocene
Late
Early
Late
Middle
Early
Late
Middle
Early
Late
Early
Late
Middle
Early
Late
Early
Late
Middle
Early
Late
Middle
Early
Late
Middle
Early
Late
Middle
Early
Upper
Lower
Upper
Middle
Lower
Upper
Middle
Lower
Upper
Lower
Upper
Middle
Lower
Upper
Lower
Uooer
Middle
Lower
Upper
Middle
Lower
Upper
Middle
Lower
Upper
Middle
Lower
None defined
None defined
None defined
None defined
None defined
None defined
pr*-Arch«n (pA) *
Age estimates
of boundaries
in mega-annum
(Ma)1
-570*
1R*nots reflect uncertainties of bolopie and bbstratigraphic agi assignments. Ape boundaries not closely bracketed by existing
data shown by -> Decay constants and bolopic ratios employed are cited in Steiger and Jiger (1977). Designation m.y. used for an
Interval of time.
* Modifiers (tower, middle, upper or early, middle, late) when used with these Hems are Informal divisions of the larger unit; the
tint letter of the modifier is lowercase.
'Rocks older than 570 Ma also called Precambrian (p€). a time term without specific rank.
'informal time term without specific tank.
USGS Open-File Report 93-292
-------
APPENDIX B
GLOSSARY OF TERMS
Units of measure
pCi/L (picocuries per liter)- a unit of measure of radioactivity used to describe radon
concentrations in a volume of air. One picocurie (10'12 curies) is equal to about 2.2 disintegrations
of radon atoms per minute. A liter is about 1.06 quarts. The average concentration of radon in
U.S. homes measured to date is between 1 and 2 pCi/L.
Bq/m3 (Becquerels per cubic meter)- a metric unit of radioactivity used to describe radon
concentrations in a volume of air. One becquerel is equal to one radioactive disintegration per
second. One pCi/L is equal to 37 Bq/m3.
ppm (parts per million)- a unit of measure of concentration by weight of an element in a
substance, in this case, soil or rock. One ppm of uranium contained in a ton of rock corresponds
to about 0.03 ounces of uranium. The average concentration of uranium in soils in the United
States is between 1 and 2 ppm.
in/hr (inches per hour)- a unit of measure used by soil scientists and engineers to describe the
permeability of a soil to water flowing through it It is measured by digging a hole 1 foot (12
inches) square and one foot deep, filling it with water, and measuring the time it takes for the water
to drain from the hole. The drop in height of the water level in the hole, measured in inches, is
then divided by the time (in hours) to determine the permeability. Soils range in permeability from
less than 0.06 in/hr to greater than 20 in/hr, but most sons in the United States have permeabilities
between these two extremes.
Geologic terms and terms related to the study of radnn
aerial radiometric, aeroradiometric survey A survey of radioactivity, usually gamma rays,
taken by an aircraft carrying a gamma-ray spectrometer pointed at the ground surface.
alluvial fan A low, widespread mass of loose rock and soil material, shaped like an open fan
and deposited by a stream at the point where it flows from a narrow mountain valley out onto a
plain or broader valley. May also form at the junction with larger streams or when the gradient of
the stream abruptly decreases.
alluvium, alluvial General terms referring to unconsolidated detrital material deposited by a
stream or other body of running water.
alpha-track detector A passive radon measurement device consisting of a plastic film that is
sensitive to alpha particles. The film is etched with acid in a laboratory after it is exposed The
etching reveals scratches, or "tracks", left by the alpha particles resulting from radon decay, which
can then be counted to calculate the radon concentration. Useful for long-term (1-12 months)
radon tests.
amphibolite A mafic metamorphic rock consisting mainly of pyroxenes and(or) amphibole and
11-21 Reprinted from USGS Open-File Report 93-292
-------
argillite, argillaceous Terms referring to a rock derived from clay or shale, or any sedimentary
rock containing an appreciable amount of clay-size material, i.e., argillaceous sandstone.
arid Term describing a climate characterized by dryness, or an evaporation rate that exceeds the
amount of precipitation.
basalt A general term for a dark-colored mafic igneous rocks that may be of extrusive origin,
such as volcanic basalt flows, or intrusive origin, such as basalt dikes.
batholith A mass of plutonic igneous rock that has more than 40 square miles of surface
exposure and no known bottom.
carbonate A sedimentary rock consisting of the carbonate (COs) compounds of calcium,
magnesium, or iron, e.g. limestone and dolomite.
carbonaceous Said of a rock or sediment that is rich in carbon, is coaly, or contains organic
matter.
charcoal canister A passive radon measurement device consisting of a small container of
granulated activated charcoal that is designed to adsorb radon. Useful for short duration (2-7 days)
measurements only. May be referred to as a "screening" test
chert A hard, extremely dense sedimentary rock consisting dominantly of interlocking crystals of
quajrtz. Crystals are not visible to the naked eye, giving the rock a milky, dull luster. It may be
white or gray but is commonly colored red, black, yellow, blue, pink, brown, or green.
clastic pertaining to a rock or sediment composed of fragments that are derived from preexisting
rocks or minerals. The most common clastic sedimentary rocks are sandstone and shale.
clay A rock containing clay mineral fragments or material of any composition having a diameter
less than 1/256 mm.
clay mineral One of a complex and loosely defined group of finely crystalline minerals made up
of water, silicate and aluminum (and a wide variety of other elements). They are formed chiefly by
alteration or weathering of primary silicate minerals. Certain clay minerals are noted for then- smaU
size and ability to absorb substantial amounts of water, causing them to swell. The change in size
that occurs as these clays change between dry and wet is referred to as their "shrink-swell"
potential.
concretion A hard, compact mass of mineral matter, normally subspherical but commonly
irregular in shape; formed by precipitation from a water solution about a nucleus or center, such as
a leaf, shell, bone, or fossil, within a sedimentary or fractured rock.
conglomerate A coarse-grained, clastic sedimentary rock composed of rock and mineral
fragments larger than 2 mm, set in a finer-grained matrix of clastic material.
cuesta A hill or ridge with a gentle slope on one side and a steep slope on the other. The
formation of a cuesta is controlled by the different weathering properties and the structural dip of
the rocks forming the hill or ridge.
daughter product A nuclide formed by the disintegration of a radioactive precursor or "parent"
atom.
11-22 Reprinted from USGS Open-File Report 93-292
-------
delta, deltaic Referring to a low, flat, alluvial tract of land having a triangular or fan shape
OT * ° '
°f •* *?* *.**** ^ ^ ^cumulation of sediment depo'by a
the smTounding rock' that commoniy
™ 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.
-e sedimer"arv ™.ck of which more than 50% consists of the mineral dolomite
is commonly white, gray, brown, yellow, or pinkish in color. uolormie
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. deposited
of water from a land ~ by evaporation from
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.
™t^^^ *
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 stteaL fl?w^f from Sg gSers.
gneiss A rock formed by metamorphism in which bands and lenses of minerals of similar
SffiS" aea ^ ^ *"** °f ***** comPosition' ^ing the rockTslriped or
" appeae.
COa5Sely crysteMne, quartz- and feldspar-bearing igneous plutonic
65%
of
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 sortil b
or water sortig byweigh size
11-23 Reprinted from USGS Open-File Report 93-292
-------
and may be referred to as a "placer deposit." Some heavy minerals are magnetite, garnet, zircon,
monazite, and xenotime.
igneous Said of a rock or mineral that solidified from molten or partly molten rock material. It is
one of the three main classes into which rocks are divided, the others being sedimentary and
metamorphic.
intermontane A term that refers to an area between two mountains or mountain ranges.
intrusion, intrusive The processes of emplacement or injection of molten rock into pre-existing
rock. Also refers to the rock formed by intrusive processes, such as an "intrusive igneous rock".
kame A low mound, knob, hummock, or short irregular ridge formed by a glacial stream at the
margin of a melting glacier; composed of bedded sand and gravel.
karst terrain A type of topography that is formed on limestone, gypsum and other rocks by
dissolution of the rock by water, forming sinkholes and caves.
lignite A brownish-black coal that is intermediate in coalification between peat and
subbituminous coal.
limestone A carbonate sedimentary rock consisting of more than 50% calcium carbonate,
primarily in the form of the mineral calcite (CaCOa).
lithology The description of rocks in hand specimen and in outcrop on the basis of color,
composition, and grain size.
loam A permeable soil composed of a mixture of relatively equal parts clay, silt, and sand, and
usually containing some organic matter.
loess A fine-grained eolian deposit composed of silt-sized particles generally thought to have
been deposited from windblown dust of Pleistocene age.
mafic Term describing an igneous rock containing more than 50% dark-colored minerals.
marine Term describing sediments deposited in the ocean, or precipitated from ocean waters.
metamorphic Any rock derived from pre-existing rocks by mineralogical, chemical, or structural
changes in response to changes in temperature, pressure, stress, and the chemical environment.
Phyllite, schist, amphibolite, and gneiss are metamorphic rocks.
moraine A mound, ridge, or other distinct accumulation of unsorted, unbedded glacial material,
predominantly till, deposited by the action of glacial ice.
outcrop That part of a geologic formation or structure that appears at the surface of the Earth, as
in "rock outcrop".
percolation test A term used in engineering for a test to determine the water permeability of a
soil. A hole is dug and filled with water and the rate of water level decline is measured.
permeability The capacity of a rock, sediment, or soil to transmit liquid or gas.
phosphate, phosphatic, phosphorite Any rock or sediment containing a significant amount
of phosphate minerals, i.e., minerals containing PO4.
11-24 Reprinted from USGS Open-File Report 93-292
-------
physiographic province A region in which all parts are similar in geologic structure and
climate, which has had a uniform geomorphic history, and whose topography or landforms differ
significantly from adjacent regions.
nlacer deposit See heavy minerals
residual Formed by weathering of a material in place.
residuum Deposit of residual material.
rhyolite An extrusive igneous rock of volcanic origin, compositionally equivalent to granite.
sandstone A clastic sedimentary rock composed of sand-sized rock and mineral material that is
more or less firmly cemented. Sand particles range from 1/16 to 2 mm in size.
schist A strongly foliated crystalline rock, formed by metamorphism, that can be readily split into
thin flakes or slabs. Contains mica; minerals are typically aligned.
screening level Result of an indoor radon test taken with a charcoal canister or similar device
for a short period of time, usually less than seven days. May indicate the potential for an indoor'
radon problem but does not indicate annual exposure to radon.
sediment Deposits of rock and mineral particles or fragments originating from material that is
transported by air, water or ice, or that accumulate by natural chemical precipitation or secretion of
organisms.
semiarid Refers to a climate that has slightly more precipitation than an arid climate.
shale A fine-grained sedimentary rock formed from solidification (lithification) of clay or mud.
shear zone Refers to a roughly linear zone of rock that has been faulted by ductile or non-ductile
processes in which the rock is sheared and both sides are displaced relative to one another.
shrink-swell clay See clay mineral.
siltstone A fine-grained clastic sedimentary rock composed of silt-sized rock and mineral
material and more or less firmly cemented. Silt particles range from 1/16 to 1/256 mm in size.
sinkhole A roughly circular depression in a karst area measuring meters to tens of meters in
diameter. It is funnel shaped and is formed by collapse of the surface material into an underlving
void created by the dissolution of carbonate rock.
slope An inclined part of the earth's surface.
solution cavity A hole, channel or cave-like cavity formed by dissolution of rock.
stratigraphy The study of rock strata; also refers to the succession of rocks of a particular area.
surficial materials Unconsolidated glacial, wind-, or waterborne deposits occurring on the
earth's surface.
tablelands General term for a broad, elevated region with a nearly level surface of considerable
extent.
11-25 Reprinted from USGS Open-File Report 93-292
-------
terrace gravel Gravel-sized material that caps ridges and terraces, left behind by a stream as it
cuts down to a lower level.
terrain A tract or region of the Earth's surface considered as a physical feature or an ecological
environment
till Unsorted, generally unconsolidated and unbedded rock and mineral material deposited directly
adjacent to and underneath a glacier, without reworking by meltwater. Size of grains varies greatly
from clay to boulders.
uraniferous Containing uranium, usually more than 2 ppm.
vendor data Used in this report to refer to indoor radon data collected and measured by
commercial vendors of radon measurement devices and/or services.
volcanic Pertaining to the activities, structures, and extrusive rock types of a volcano.
water table The surface forming the boundary between the zone of saturation and the zone of
aeration; the top surface of a body of unconfined groundwater in rock or soil.
weathering The destructive process by which earth and rock materials, on exposure to
atmospheric elements, are changed in color, texture, composition, firmness, or form with little or
no transport of the material.
n-26 Reprinted from USGS Open-File Report 93-292
-------
APPENDIX C
EPA REGIONAL OFFICES
EPA Regional Offices
State
EPA Region
EPA Region 1
JFK Federal Building
Boston, MA 02203
(617) 565-4502
EPA Region 2
(2AIR:RAD)
26 Federal Plaza
New York, NY 10278
(212) 264-4110
Region 3 (3AH14)
841 Chestnut Street
Philadelphia, PA 19107
(215) 597-8326
EPA Region 4
345 Courtland Street, N.E.
Atlanta, GA 30365
(404) 347-3907
EPA Region 5 (5AR26)
77 West Jackson Blvd.
Chicago, IL 60604-3507
(312) 886-6175
EPA Region 6 (6T-AS)
1445 Ross Avenue
Dallas, TX 75202-2733
(214) 655-7224
EPA Region 7
726 Minnesota Avenue
Kansas City, KS 66101
(913) 551-7604
EPA Region 8
(8HWM-RP)
999 18th Street
One Denver Place, Suite 1300
Denver, CO 80202-2413
(303) 293-1713
EPA Region 9 (A-3)
75 Hawthorne Street
San Francisco, CA 94105
(415) 744-1048
EPA Region 10
1200 Sixth Avenue
Seattle, WA 98101
(202) 442-7660
Alabama 4
Alaska 10
Arizona 9
Arkansas 6
California 9
Colorado 8
Connecticut 1
Delaware 3
District of Columbia 3
Florida 4
Georgia 4
Hawaii 9
Idaho 10
Illinois 5
Indiana 5
Iowa 7
Kansas .• 7
Kentucky 4
Louisiana 6
Maine 1
Maryland 3
Massachusetts 1
Michigan 5
Minnesota 5
Mississippi 4
Missouri 7
Montana 8
Nebraska 7
Nevada 9
New Hampshire 1
New Jersey 2
New Mexico 6
New York 2
North Carolina 4
North Dakota 8
Ohio 5
Oklahoma 6
Oregon 10
Pennsylvania 3
Rhode Island \
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
Alabama James McNees
Division of Radiation Control
Alabama Department of Public Health
State Office Building
Montgomery, AL 36130
(205)242-5315
1-800-582-1866 in state
Alaska Charles Tedford
Department of Health and Social
Services
P.O. Box 110613
Juneau,AK 99811-0613
(907)465-3019
1-800-478-4845 in state
Arizona John Stewart
Arizona Radiation Regulatory Agency
4814 South 40th St.
Phoenix, AZ 85040
(602) 255^845
Arkansas Lee Gershner
Division of Radiation Control
Department of Health
4815 Markham Street, Slot 30
Little Rock, AR 72205-3867
(501) 661-2301
California J. David Quinton
Department of Health Services
714 P Street, Room 600
Sacramento, CA 94234-7320
(916)324-2208
1-800-745-7236 in state
Colorado Linda Martin
Department of Health
4210 East llth Avenue
Denver, CO 80220
(303) 692-3057
1-800-846-3986 in state
Connecticut Alan J. Siniscalchi
Radon Program
Connecticut Department of Health
Services
150 Washington Street
Hartford, CT 06106-4474
(203) 566-3122
Delaware Marai G. Rejai
Office of Radiation Control
Division of Public Health
P.O. Box 637
Dover, DE 19903
(302) 736-3028
1-800-554-4636 In State
Disttict Robert Davis
of Columbia DC Department of Consumer and
Regulatory Affairs
614 H Street NW
Room 1014
Washington, DC 20001
(202) 727-71068
Florida N. Michael Gilley
Office of Radiation Control
Department of Health and
Rehabilitative Services
1317 Winewood Boulevard
Tallahassee, PL 32399-0700
(904)488-1525
1-800-543-8279 in state
Richard Schreiber
Georgia Department of Human
Resources
878 Peachtree St., Room 100
Atlanta, GA 30309
(404) 894-6644
1-800-745-0037 in state
Hawaii Russell Takata
Environmental Health Services
Division
591 Ala Moana Boulevard
Honolulu, ffl 96813-2498
(808) 586-4700
n-28
Reprinted from USGS Open-File Report 93-292
-------
Idaho PatMcGavarn
Office of Environmental Health
450 West State Street
Boise, ID 83720
(208) 334-6584
1-800-445-8647 in state
Illinois Richard Allen
Illinois Department of Nuclear Safety
1301 Outer Park Drive
Springfield, IL 62704
(217) 524-5614
1-800-325-1245 in state
Indiana 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
Iowa 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
Kansas. 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
Kentucky JeanaPhelps
Radiation Control Branch
Department of Health Services
Cabinet for Human Resources
275 East Main Street
Frankfort, KY 40601
(502)564-3700
Louisiana Matt Schlenker
Louisiana Department of
Environmental Quality
P.O. Box 82135
Baton Rouge, LA 70884-2135
(504) 925-7042
1-800-256-2494 in state
Maine Bob Stilwell
Division of Health Engineering
Department of Human Services
State House, Station 10
Augusta, ME 04333
(207)289-5676
1-800-232-0842 in state
Maryland Leon J. Rachuba
Radiological Health Program
Maryland Department of the
Environment
2500 Broening Highway
Baltimore, MD 21224
(410)631-3301
1-800-872-3666 In State
Massachusetts William J. Bell
Radiation Control Program
Department of Public Health
23 Service Center
Northampton, MA 01060
(413) 586-7525
1-800-445-1255 in state
Michigan Sue Hendershott
Division of Radiological Health
Bureau of Environmental and
Occupational Health
3423 North Logan Street
P.O. Box 30195
Lansing, ME 48909
(517)335-8194
Minnesota Laura Oatmann
Indoor Air Quality Unit
925 Delaware Street, SE
P.O. Box 59040
Minneapolis, MN 55459-0040
(612)627-5480
1-800-798-9050 in state
11-29 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 Al 13
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, NJ 08625-0145
(609) 987-6369
1-800-648-0394 in state
New Mexico William M. Floyd
Radiation Licensing and Registration
Section
New Mexico Environmental
Improvement Division
1190 St. Francis Drive
Santa Fe,NM 87503
(505) 827-4300
New York William J. Condon
Bureau of Environmental Radiation
Protection
New York State Health Department
Two University Place
Albany, NY 12202
(518)458-6495
1-800-458-1158 in state
North Carolina Dr. Felix Fong
Radiation Protection Division
Department of Environmental Health
and Natural Resources
701 Barbour Drive
Raleigh, NC 27603-2008
(919) 571-4141
1-800-662-7301 (recorded info x4196)
North Dakota Arlen Jacobson
North Dakota Department of Health
1200 Missouri Avenue, Room 304
P.O. Box 5520
Bismarck, ND 58502-5520
(701) 221-5188
Ohio Marcie Matthews
Radiological Health Program
Department of Health
1224 Kinnear Road - Suite 120
Columbus, OH 43212
(614) 644-2727
1-800-523-4439 in state
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)73W014
Michael Pyles
Pennsylvania Department of
Environmental Resources
Bureau of Radiation Protection
P.O. Box 2063
Harrisburg, PA 17120 -
(717) 783-3594
1-800-23-RADON In State
David Saldana
Radiological Health Division
G.P.O. Call Box 70184
Rio Piedras, Puerto Rico 00936
(809) 767-3563
Edmund Arcand
Division of Occupational Health and
Radiation
Department of Health
205 Cannon Building
Davis Street
Providence, RI02908
(401) 277-2438
Bureau of Radiological Health
Department of Health and
Environmental Control
2600 Bull Street
Columbia, SC 29201
(803)734^*631
1-800-768-0362
South Dakntq 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)536^250
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 JJ
in New York
(212)264-4110
H-31 Reprinted from USGS Open-File Report 93-292
-------
Virginia Shelly Ottenbrite
Bureau of Radiological Health
Department of Health
109 Governor Street
Richmond, VA 23219
(804) 786-5932
1-800-468-0138 in state
Washington Kate Coleman
Department of Health
Office of Radiation Protection
Airdustrial Building 5, LE-13
Olympia, WA 98504
(206)7534518
1-800-323-9727 In State
West Virginia Beattie L. DeBord
Industrial Hygiene Division
West Virginia Department of Health
151 llth Avenue
South Charleston, WV 25303
(304) 558-3526
1-800-922-1255 In State
Wisconsin Conrad Weiffenbach
Radiation Protection Section
Division of Health
Department of Health and Social
Services
P.O. Box 309
Madison, WI53701-0309
(608) 2674796
1-800-798-9050 in state
Wyoming Janet Hough
Wyoming Department of Health and
Social Services
Hathway Building, 4th Floor
Cheyenne, WY 82002-0710
(307) 777-6015
1-800-458-5847 in state
IE-32 Reprinted from USGS Open-File Report 93-292
-------
STATE GEOLOGICAL SURVEYS
May, 1993
Alabama Ernest A. Mancini
Geological Survey of Alabama
P.O. Box 0
420 Hackbeny Lane
Tuscaloosa, AL 35486-9780
(205) 349-2852
Alaska " Thomas E. Smith
Alaska Division of Geological &
Geophysical Surveys
794 University Ave., Suite 200
Fairbanks, AK 99709-3645
(907)479-7147
Arizona Larry D. Fellows
Arizona Geological Survey
845 North Park Ave., Suite 100
Tucson, AZ 85719
(602) 882-4795
Arkansas Norman F. Williams
Arkansas Geological Commission
Vardelle Parham Geology Center
3815 West Roosevelt Rd.
Little Rock, AR 72204
(501) 324-9165
California James F. Davis
California Division of Mines &
Geology
801 K Street, MS 12-30
Sacramento, CA 95814-3531
(916)445-1923
Colorado Pat Rogers (Acting)
Colorado Geological Survey
1313 Sherman St., Rm 715
Denver, CO 80203
(303)866-2611
Connecticut Richard C. Hyde
Connecticut Geological & Natural
History Survey
165 Capitol Ave., Rm. 553
Hartford, CT 06106
(203) 566-3540
Delaware Robert R. Jordan
Delaware Geological Survey
University of Delaware
101 Penny Hall
Newark, DE 19716-7501
(302)831-2833
Florida Walter Schmidt
Florida Geological Survey
903 W. Tennessee St.
Tallahassee, FL 32304-7700
(904)488-4191
William H. McLemore
Georgia Geologic Survey
Rm. 400
19 Martin Luther King Jr. Dr. SW
Atlanta, GA 30334
(404)656-3214
Hawaii Manabu Tagomori
Dept. of Land and Natural Resources
Division of Water & Land Mgt
P.O. Box 373
Honolulu, HI 96809
(808) 548-7539
Idaho Earl H. Bennett
Idaho Geological Survey
University of Idaho
Morrill Hall, Rm. 332
Moscow, ID 83843
(208) 885-7991
Illinois Morris W. Leighton
Illinois State Geological Survey
Natural Resources Building
615EastPeabodyDr.
Champaign, IL 61820
(217)333-4747
Indiana Norman C. Hester
Indiana Geological Survey '
611 North Walnut Grove
Bloomington, IN 47405
(812) 855-9350
Iowa Donald L. Koch
Iowa Department of Natural Resources
Geological Survey Bureau
109 Trowbridge Hall
Iowa City, JA 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
11-33 Reprinted from USGS Open-File Report 93-292
-------
Kentucky Donald C. Haney
Kentucky Geological Survey
University of Kentucky
228 Mining & Mineral Resources
Building
Lexington, KY 40506-0107
(606) 257-5500
Louisiana William E. Marsalis
Louisiana Geological Survey
P.O. Box 2827
University Station
Baton Rouge, LA 70821-2827
(504) 388-5320
Maine Walter A. Anderson
Maine Geological Survey
Department of Conservation
State House, Station 22
Augusta, ME 04333
(207)289-2801
Maryland Emery T. Cleaves
Maryland Geological Survey
2300 St. Paul Street
Baltimore, MD 21218-5210
(410) 554-5500
Massachusetts Joseph A. Sinnott
Massachusetts Office of
Environmental Affairs
100 Cambridge St, Room 2000
Boston, MA 02202
(617)727-9800
Michigan R. Thomas Segall
Michigan Geological Survey Division
Box 30256
Lansing, MI 48909
(517) 334-6923
Minnesota Priscilla C. Grew
Minnesota Geological Survey
2642 University Ave.
St. Paul, MN 55114-1057
(612) 627-4780
Mississippi S. Cragin Knox
Mississippi Office of Geology
P.O. Box 20307
Jackson, MS 39289-1307
(601)961-5500
Missouri James H. Williams
Missouri Division of Geology &
Land Survey
111 Fairgrounds Road
P.O. Box 250
Rolla, MO 65401
(314) 368-2100
Montana Edward T. Ruppel
Montana Bureau of Mines & Geology
Montana College of Mineral Science
and Technology, Main Hall
Butte, MT 59701
(406)4964180
Nebraska Perry B. Wigley
Nebraska Conservation & Survey
Division
113 Nebraska Hall
University of Nebraska
Lincoln, NE 68588-0517
(402)472-2410
Nevada Jonathan G. Price
Nevada Bureau of Mines & Geology
Stop 178
University of Nevada-Reno
Reno, NV 89557-0088
(702)784-6691
New Hampshire Eugene L.Boudette
Dept. of Environmental Services
117 James Hall
University of New Hampshire
Durham, NH 03824-3589
(603)862-3160
New Jersey Haig F. Kasabach
New Jersey Geological Survey
P.O. Box 427
Trenton, NJ 08625
(609)292-1185
New Mexico Charles E. Chapin
New Mexico Bureau of Mines &
Mineral Resources
Campus Station
Socorro.NM 87801
(505) 835-5420
New York Robert H. Fakundiny
New York State Geological Survey
3136 Cultural Education Center
Empire State Plaza
Albany, NY 12230
(518)474-5816
11-34 Reprinted from USGS Open-File Report 93-292
-------
North Carolina Charles H. Gardner
North Carolina Geological Survey
P.O. Box 27687
Raleigh, NC 27611-7687
(919) 733-3833
North Dakota John P. Bluemle
North Dakota Geological Survey
600 East Blvd.
Bismarck, ND 58505-0840
(701)224^109
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
Donald A. Hull
DepL of Geology & Mineral Indust.
Suite 965
800 NE Oregon St. #28
Portland, OR 97232-2162
(503)73W600
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 Ram<5n M. Alonso
Puerto Rico Geological Survey
Division
Box 5887
Puerta de Tierra Station
San Juan, P.R. 00906
(809)722-2526
Rhode Island J. Allan Cain
Department of Geology
University of Rhode Island
315 Green Hall
Kingston, RI02881
(401) 792-2265
South Carolina Alan-Jon W. Zupan (Acting)
South Carolina Geological Survey
5 Geology Road
Columbia, SC 29210-9998
(803) 737-9440
South Dakota C.M. Christensen (Acting)
South Dakota Geological Survey
Science Center
University of South Dakota
Vermillion, SD 57069-2390
(605) 677-5227
Tennessee Edward T. Luther
Tennessee Division of Geology
13th Floor, L & C Tower
401 Church Street
Nashville, TN 37243-0445
(615) 532-1500
Texas William L. Fisher
Texas Bureau of Economic Geology
University of Texas
University Station, Box X
Austin, TX 78713-7508
(512)471-7721
Utah M. Lee Allison
Utah Geological & Mineral Survey
2363 S. Foothill Dr.
Salt Lake City, UT 84109-1491
(801)467-7970
Vermont Diane L. Conrad
Vermont Division of Geology and
Mineral Resources
103 South Main St.
Waterbury, VT 05671
(802)244-5164
Virginia Stanley S. Johnson
Virginia Division of Mineral
Resources
P.O. Box 3667
Charlottesville, VA 22903
(804) 293-5121
Washington Raymond Lasmanis
Washington Division of Geology &
Earth Resources
Department of Natural Resources
P.O. Box 47007
Olympia, Washington 98504-7007
(206)902-1450
H-35
Reprinted from USGS Open-File Report 93-292
-------
West Virginia Lairy D. Woodfoik
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-File Report 93-292
-------
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 iii 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 USGS Open-File 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-Atlantic Coastal Plain; 18-Central
Allegheny Plateau; 19-CumberIand 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 Phyllitc,
25-Culpeper, Gettysburg, and other Mesozoic basins; 26-Mesozoic basins; 27-Eastern Piedmont, schist'and gneiss;
28-Inner Piedmont; 29-Goochland Terrane; 30,31-Coasta! 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
-------
GEOLOGIC
RADON POTENTIAL
j | LOW
HU 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 sediments 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 Castle 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
*nH * ™etWeS'!;rn Su°rl°f Maryland has tee*1 ranked moderate to locally high in radon potential
and the Eastern Shore has been ranked low in radon potential. The Coastal Plain Province is
under am by relatively ^consolidated 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,
LTnlt7 T^ ^ Creta<;eoUS and Tertiary Sediments of P^6 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
glaucoma 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 pCi/L, and the Tertiary-Cretaceous Brightseat
Formation and Monmouth Group had average soil radon of 1300 pCi/L. Soil permeability on the
Western Shore vanes from low to moderate with some high permeability in sandier soils. Well-
?h7t0plp fpy B^°nz1°"S 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 generaUy low to moderate. Moderate to high average indoor radon is found in most of the
Western Shore counties.
inri H- F^S aS*eSSment we have ranked P3* of the Western Shore as high in radon potential,
uicluding 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 pCi/L reported.
Piedmont
Gneisses and schists in the eastern Piedmont, phyllites in the western Piedmont, and
Paleozoic metasedimentary rocks of the Frederick Valley 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 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 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
IH-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 Sn—jy calculated the median uranium
content of 80 samples of Catoctin metabasalt and metadiaoase 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 in 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 nigh in geologic radon potential. Indoor radon measurements are generally moderate to
high in Allegany County. Soil permeabmty 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
m-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
m-8 Reprinted from USGS Open-File Report 93-292-C
-------
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 Ordovician through Pennsylvanian-age black to gray shales and fluvial sandstones, have been
extensively cited in the literature for their uioiiium coni^,. 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 Ordovician 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.
Coastal Plain
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
m-9 Reprinted from USGS Open-FUe Report 93-292-C
-------
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
tne 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
HMO Reprinted from USGS Open-File Report 93-292-C
-------
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.
WEST VIRGINIA
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
-------
Ridge and Valley Province
The southern part of the Appalachian Ridge and Valley Province in West Virginia has
moderate radon potential overall. The eU signature for this province is elevated (> 2.5 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.
m-12 Reprinted from USGS Open-File Report 93-292-C
-------
PRELIMINARY GEOLOGIC RADON POTENTIAL ASSESSMENT OF DELAWARE
by
Linda C. S. Gundersen
U.S. Geological Survey
INTRODUCTION
The Office of Radiation Control in the Delaware Department of Health and Sotial Services
assisted Delaware citizens in testing for indoor radon from 1985-1990 (Eichler and Wright 1991)
Of more tfian 7000 indoor radon measurements performed in the State, 10.5 percent of the homes '
tested had indoor radon levels exceeding the U.S. Environmental Protection Agency's 4 pCi/L
guideline. Statewide radon levels ranged from 0.5 to 164 PCi/L and averaged 2 pCi/L Ninety-
eight percent of the testing was done by means of charcoal canister. The Delaware Geological
s
.
Examination of the indoor radon data in the context of geology, soil permeability, and
radioactivity suggest that some of the metamorphic and igneous rocks of the Piedmont and some
sediments of the northern portion of the Atlantic Coastal Plain have moderate to locally high radon
potential. Much of the Atlantic Coastal Plain in the central and southern portion of the State has
low radon potential.
This is a generalized assessment of geologic radon potential of rocks, soils, and surficial
deposits of Delaware. 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. 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
concentrations, both high and low, can be quite localized, and there is no substitute for testing
individual homes. For more information, the reader is urged to consult the Office of Radiation
Control, Delaware Department of Health and Social Services, or the 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
Delaware lies within parts of two physiographic provinces (fig. 1). The Piedmont is
underlain by igneous and metamorphic rocks with gently rolling, wooded and open uplands
averaging 250 feet in elevation, but with as much as 300 feet of local relief. The rest of Delaware
is within the Atlantic Coastal Plain. The northern portion of the Atlantic Coastal Plain is
characterized by gently rolling hills with minor relief, underlain by fluvial and marine sediments
ine central, southern, and coastal portions of the Atlantic Coastal Plain consist of bottom land
pine woods, and marshes, which are also underlain by fluvial and marine sediments The entire
Mate is well drained, with a central divide postulated to be controlled by tectonic tilt of the
Delmarva Peninsula (Spoljaric, 1980).
In 1990, the population of Delaware was 666,168 (U.S. Census Bureau fig 2) The
majority of its population resides in the northernmost county of New Castle, where technological
marine, and heavy industries support the population centers of Wilmington, Newark, and New '
Castle. The two southern counties of Kent and Sussex are dominantiy agricultural.
IV-l Reprinted from USGS Open-File Report 93-292-C
-------
Piedmont
Figure 1. Physiographic areas of Delaware.
GEOLOGY AND SOILS
The following discussion of bedrock and surficial geology is condensed from Jordan
(1962,1964,1974,1983), Pickett and Spoljaric (1971), Woodruff (1985,1986), Woodruff and
Thompson (1972,1975), Pickett and Benson (1977,1983), Kraft and Carey (1980), Thompson
(1980), Talley (1982,1987), Andres (1986), Benson and Pickett (1986), Ramsey and Schenck
(1990), and Wagner and others (1991). Discussion of soils is based on Richmond and others
(1987) and the Soil Conservation Service county soil surveys (Mathews and Lavoie, 1970;
Mathews and Ireland, 1971; and Ireland and Mathews, 1974). A generalized geologic map of
Delaware is shown in figure 3, cross sections of the Coastal Plain are given in figure 4a and b, and
a generalized surficial geologic map of Delaware is shown in figure 5.
The Piedmont
The Piedmont is underlain by a complex sequence of high-grade metamorphic and igneous
rocks that have been folded and faulted. These crystalline rocks are generally weathered to a depth
of 10 feet or more, and in some cases, depth of weathering may exceed 70 feet. Soils formed on
these rocks are saprolitic and reflect the original composition of the rock. Because the crystalline
rocks are so complex, the soils formed on them are also complex. The descriptions of soils
presented here are generalized and do not reflect site-specific conditions that one would expect to
observe in the field.
The oldest rocks in the Piedmont are Precambrian Grenville gneisses that occur along the
Pennsylvania border in the core of the Mill Creek dome in the northwestern part of the Piedmont.
They have been correlated with the Baltimore Gneiss and consist of quartz-feldspar gneisses,
biotite schist, and minor amphibolite. Saprolite soils developed on the gneiss are sandy to silty
loams and clayey, silty sands. Permeability in the sandy, silty loams ranges from moderate to
moderately rapid. Deeply developed soils and soils from the micaceous schist tend to be more
IV-2 Reprinted from USGS Open-FDe Report 93-292-C
-------
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POPULATION (1990)
C2 100000 to 200000
E3 200001 to'300000
0 300001to400000
H 400001 to 500000
10 Miles
Figure 2. Population of counties in Delaware (1990 U.S. Census data).
-------
Figure 3. Generalized geologic map of Delaware showing rock units ranging in age from
Precambrian to Tertiary (after Pickett, 1976). Quaternary units are shown on the surficial
geologic map (fig. 5).
-------
GENERflLIZED GEOLOGIC MflP OF DELRUJRRE (PRECflMBRIBN-TERTIflRV)
EHPLRNRTION
TERTIRRV
PLIOCENE
Beaverdam Formation - Fairly well sorted medium sand, some gravel.
PLIOCENE?
Bryn Mawr Formation - Red and brown quartz sand with silt, clay and fine gravel
(in Piedmont).
MIOCENE-PLIOCENE(?)
Chesapeake Group - Bluish gray silt with quartz sand and some shell beds.
PflLEOCENE-EOCENE{?)
-.0.«
Vt
Vincentown Formation - Green, gray and reddish-brown fine to coarse, highly
quartzose glauconitic sand with some silt.
CRETflCEOUS-PRLEOCENE
Hornerstown Formation - Green, gray and reddish-brown fine to medium, silty
highly glauconitic sand and sandy silt. '
CRETRCEOUS
.» X
X X
X X
Mount Laurel -Monmouth Formations - Gray, green and red-brown, glauconitic
fine to medium, quartz sand with some silt s*uiwniuc
Matawan Group
ion " Dark greenish-gray, massive, very glauconitic silty,
Englishtown Formation - Light gray and rust brown, well sorted micaceous sand
with thin mterbedded layers of dark gray silty sand; abundant fossil burrows.
micaceous'
itic sandy
I Magothy Formation - White and buff quartz sand with beds of gray and black clayey
Potomac Formation - Variegated silts and clays with beds of quartz sand.
-------
PRECflMBR IBN-PflLEOZO IC
Wissahickon Formation - Gneiss, schist, amphibolite, and minor serpentine.
Setters Formation & Cockeysville Marble of the Lower Glenarm Series - Quartz -
mica schist and dense white crystalline marble.
Baltimore Gneiss - Feldspathic biotite gneiss and minor schist.
Anorthosite - Andesine anorthosite and anorthositic gabbro.
James Run Formation - Amphibolite; hypersthene gneiss and minor pelitic gneiss.
Wilmington Complex - Hypersthene-bearing felsic gneiss, minor amphibolite, with
gabbro, norite, and anorthosite plutons.
-------
A.
1000
LOCATION OF
CROSS-SECTIONS
2000
Qhl - Holocene Deposits
QToml, Qomu - Omar Formation
Qcl - Columbia Formation
Tbd • Beaverdam Formation
Tbt - Bethany Formation
Tma, Tmb - Manokin Formation
Tsm - St. Marys Formation
Teh - Choptank Formation
Tc - Calvert Formation
EXPLANATION
Tna-
Tvt-
TM-
Kml.
Kmt
Ket-
Kmv
Km-
Kpt-
• Nanjemoy Formation
Vincentown Formation
Hornerstown Formation
• Mount Laurel Formation
- Marshalltown Formation
Englishtown Formation
- Merchantville Formation
Magothy Formation
Potomac Formation
B.
NNW
KENT COUNTY
SUSSEX COUNTY
Oomu
SSE
.Tbt
« r »i £g ? , f S^PS10 cross-sections of (A) the Middletown-Odessa area,
-New Castle County (after Pickett and Spoljaric, 1971), and (B) Kent and Sussex
counties, southern Delaware (after Ramsey and Schenck 1990)
-------
10
Figure 5. Generalized surficial geologic map of Delaware (after Richmond and others, 1987, and
Ramsey and Schenck, 1990).
-------
GENERflLIZEO SURFICIflL GEOLOGIC MBP OF DELflUJflRE
EKPLflNHTION
(After Richmond and others, 1987, and Ramsey and Schenck, 1990)
HOLOCENE
Beach, Barrier, and Spit Deposits - White'to gray, fine to coarse sand with scattered gray silty clay beds Well
sorted, laminated, and crossbedded, mostly quartz, includes some organic matter and shells.
Swamp and Saline-Marsh Deposits - Interbedded dark-gray, black, or greenish-gray silty clay to clayey fine
sand and carbonaceous clay; dark-brown to black organic debris, muck, and local peat, mixed with muck
composed of fine sand, silt and kaolinitic clay. Commonly bioturbated; local marl in calcareous clay at depth
PLEISTOCENE
Alluvial and Estuarine Sand and Silt - White to light reddish-brown medium to coarse sand, gravelly sand
gravel, silty clay, and organic-rich silty clay. Sand commonly crossbedded. Fossiliferous in places (Delaware
Jisy deposits}.
Alluvial Gravelly Sand - Gray to brown, fine to medium sand, gravelly sand, clayey silt, and silty clay Both
sand and gravel are chiefly quartz. Deposit is poorly sorted, thin to medium bedded, and locally crossbedded
Capped in places by well-sorted fine sand associated with dunes.(Nanticoke deposits).
IHT] ftoeto coa^Snd6 ^"^ ^ *** -CIay" ™* *° ** to WuiSh ffay ^ ^ Sa"d'dayey ^ **F clay'and
Sandy and Silty Decomposition Residuum - Tan to dark gray silty and clayey sand and sandy silt (Staytonville
Sandy Decomposition Residuum - Orange-red, reddish-brown, tan, light gray, or white sandy loam that grades
downward into medium to coarse feldspathic sand with minor gravel and silt; with reddish-brown or orange
brown iron oxide stains. Residuum is chiefly on broad upland surfaces (Columbia Formation)
QURTERNRRV RND TERTIHRV
Sandy Clay Saprolite and Alluvium - Red, yellowish-red, strong-brown , yellow, light-gray, or greenish-grav
shghtly clayey sand to sandy clay. Clays are mixed smectite and kaolinite if, saproUtf. wS souSSJS
Micaceous Saprolite and Alluvium - Red, reddish-brown, strong-brown, yellowish-red, or gray, micaceous
clayey to shghfly clayey sand to clayey sandy silt. Clay is kaolinite and lesser amounts of gibbsite Mica mostly
weathered to micaceous clay and (or) kaolinite near ground surface y
TERTIHRV
~^ Sand and Sandy Decomposition Residuum - Pale white, buff, or greenish-gray, medium sand with scattered
LHJ beds of coarse sand gravelly sand, and silty clay. Unit fines upwards; contains rare glauconite. Residuum is
chiefly on broad upland surfaces (Beaverdam Formation) «»uuui,,»
-------
clayey and have slow to moderate permeability. Soils derived from amphibolite are clayey loams
to clayey silts and silty, sandy clays that are slowly to moderately permeable.
The Baltimore Gneiss is unconformably overlain by the Setters Formation and
Cockeysville Marble of the Lower Glenarm Series. The Setters Formation comprises thin lenses
of quartzitic mica schist and is very limited in exposure. The Cockeysville Marble is a calcitic to
locally dolomitic, coarse-grained marble that underlies the Hockessin-Yorklyn Valley and Pleasant
Valley near Newark. Where soils are well developed, the marble weathers to form silty clays and
clayey loams of slow permeability. Steeper slopes of the marble tend to have soils that are less
deep and stony soils of moderate permeability that vary from sandy loam to silty clay.
Much of the western part of the Piedmont is underlain by the Wissahickon Formation,
consisting of quartzitic to micaceous, felsic schists and gneisses, amphibolite, and small areas of
serpentinite and granitic pegmatite. Soils developed on the quartzitic schist are sandy to silty loams
and clayey, silty sands with moderate to moderately rapid permeability. Soils developed on the
micaceous schist tend to be more clayey and have slow to moderate permeability. Soils derived
from amphibolite and serpentinite are clayey loams to silty clays with slow permeability. Lying in
an elongate belt between the Wissahickon Formation and the Wilmington Complex is the James
Run (?) Formation (fig. 3). Interpretation and distribution of this rock type is the subject of
debate. The James Run (?) Formation as shown on the map of Pickett (1976) in figure 3 is similar
to the distribution of the James Run (?) Formation in Thompson (1980). On the geologic maps of
Woodruff and Thompson (1972,1975) these rocks are included in the Wilmington Complex.
They are described in the western Piedmont as felsic and mafic gneiss with minor pelitic schist.
The mafic and felsic gneisses may also contain hornblende and hypersthene. In the eastern
Piedmont, they are described as hornblende-plagioclase gneiss interlayered with smaller amounts
of pyroxene-bearing felsic gneiss, amphibolite, and quartz-feldspar gneiss (Woodruff and
Thompson, 1975). Wagner and others (1991) show the James Run Formation only in the
southwesternmost corner of the Piedmont in contact with a small body of granitic gneiss. They
place most of the western felsic and mafic gneisses in the Wissahickon Formation and include the
eastern hornblende- and pyroxene-bearing gneisses in the Wilmington Complex.
The Wilmington Complex underlies much of the eastern third of the Piedmont. It
comprises hypersthene-bearing felsic gneiss, minor amphibolite, and small plutons. Two of the
largest plutons are in the eastern and southeastern portions of the Wilmington Complex. The
Arden Pluton has been described as anorthosite, noritic anorthosite, norite, and minor charnockite
by Woodruff and Thompson (1975), and as a granodiorite-norite-charnockite by Wagner and
others (1991). The other major pluton is the Bringhurst Gabbro, which underlies part of the city
of Wilmington and consists of gabbro and norite. The felsic rocks of the Wilmington Complex
form silty sands ^nd sandy loams of moderate to moderately rapid permeability. The mafic rocks
of the Wilmington Complex (gabbro, amphibolite) form silty clays and clayey loams with slow
permeability.
The Coastal Plain
The Coastal Plain consists of relatively unconsolidated Cretaceous and Tertiary sediments
that are unconformably overlain by Tertiary, Quaternary, and Holocene sediments (fig. 4). At the
surface, the Cretaceous portion of the Coastal Plain consists of the fluvial and marine sediments of
the Potomac and Magothy Formations, Matawan Group, and the Mount Laurel (Monmouth)
Formation. Other units exist in the subsurface and are shown in figure 4. Only surface units are
described in this section.
IV-10 Reprinted from USGS Open-File Report 93-292-C
-------
The Potomac Formation consists of fluvial channel sands with variegated, locally lignitic
silt and clay deposited in an alluvial plain. Iron oxide concretions and cements are common The
Magothy Formation consists of quartz sands and lignitic, gray and black clayey silt of estuarine
and marginal deltaic origin. The Matawan Group is subdivided into the Marshalltown
Englishtown, and Merchantville Formations. Downdip, the lithologies in these three formations
grade into a single unit and the Matawan Group is changed to formation rank. It consists
predominantly of marine silty sands and sandy silt with abundant glauconite. The Mount Laurel
Formation (also known as the Monmouth in the subsurface) is made up of glauconitic silty sands
and silt. Glauconite may locally comprise more than 80 percent of the sediment in the Matawan
Group and Mount Laurel Formation (Spoljaric, 1980). These Cretaceous units are generally
exposed in some of the major river drainages, canals, and estuaries, as well as where the overlying
Quaternary sediments are absent. The fluvial sands of the Potomoc Formation tend to have
moderate to moderately rapid permeability. Marine sands with abundant glauconite or sands that
have abundant iron-oxide content tend to be more clayey and have slow to moderate permeability
Silt and fine sandy sediments are slowly to moderately permeable and the clays (except where drv
and fractured) are slowly permeable.
The oldest part of the Tertiary sequence exposed at the surface is the glauconitic sands and
sandy silts of the Rancocas Group, consisting of the Hornerstown and Vincentown Formations
Soils derived from these formations are sandy to clayey loams with slow to moderate permeability
I he rest of the Tertiary sequence exposed at the surface, the Chesapeake Group, includes the
Calvert and Choptank Formations. The Calvert Formation is predominantly fine sand with shelly
mterbeds. The Choptank Formation consists of several fining-upward sequences varying from
shelly sand to sandy, clayey silt. These deposits generally lack glauconite. Soils formed on the
Chesapeake Group typically have slow to moderately rapid permeability. Other Tertiary units exist
in the subsurface of the Coastal Plain and are shown in figure 4.
Quaternary and late Tertiary sediments, where present, vary from 5 to 100 feet in thickness
and blanket much of the Atlantic Coastal Plain (fig. 5). The Quaternary fluvial deposits in the
northern and central portion of the Atlantic Coastal Plain are called the Columbia Formation and
they unconformably overlie the older Cretaceous and Tertiary sediments. They consist of rusty-
weathering, feldspathic quartz sands with gravel and silt beds that are derived primarily from older
units to the northeast and north. The Staytonville unit is a silty to clayey sand and sandy silt that
overlies the Columbia and is exposed in a limited area in southwestern Kent County near the
county line. The Staytonville unit's relationship to the Columbia Formation is not known The
Columbia Formation overlaps an older fluvial unit in southern Delaware, the Pliocene Beaverdam
Formation. This unit is siltier than the Columbia Formation, is partly unconformable with older
Tertiary units, and crops out only in Sussex County. The Beaverdam Formation is predominantly
sand with some gravelly sand and silty clay layers. The sand has a silt matrix in the upper half of
the unit. In southeastern Delaware, the Tertiary-Quaternary Omar Formation overlies the
Beaverdam Formation. It consists of silty fine sand, clayey silt and silty clay, and fine to coarse
sand. The upper Omar Formation is the principal part of the unit exposed at the surface; the lower
part of the Omar Formation is restricted to a paleovalley cut into the Beaverdam Formation
Permeability of the Quaternary sediments is generally moderate to moderately rapid, but areas of
slow permeability exist in more clay-rich or water-saturated sediments. In the Nanticoke River
Valley, deposits of silty clay, gravelly sand, and fine- to medium-grained sand are termed the
Nanticoke deposits and are Quaternary in age. In Delaware Bay, Quaternary deposits of sand
minor gravel, silty clay, and organic-rich silty clay comprise the Delaware Bay deposits Shoreline
IV-11 Reprinted from USGS Open-FUe Report 93-292-C
-------
deposits of Holocene age dominate in southeasternmost Delaware and along the Atlantic coastline.
These sediments include: organic rich silty clay and sand of marsh and swamp deposits; fine to
coarse, white quartz sand and silty clay beds found in the present day beach, barrier, and spit
deposits; and organic-rich silty clay and clayey silty sand in present day lagoon and estuary
deposits.
RADIOACTIVITY
An aeroradiometric map of Delaware (fig. 6) was compiled from spectral gamma-ray data
acquired during the U.S. Department of Energy's National Uranium Resource Evaluation (NURE)
program (Duval and others, 1989). For the purposes of this assessment, low equivalent uranium
(eU) is defined as less than 1.5 parts per million (ppm) of uranium, moderate eU is defined as
1.5-2.5 ppm, and high eU is defined as greater than 2.5 ppm. Low radioactivity appears to be
associated with most of the Atlantic Coastal Plain sediments. Moderate eU is found in parts of the
central and northern portions of the State associated with the Piedmont and parts of the Coastal
Plain. There are no areas of high radioactivity on the map. The pattern of radioactivity over the
Coastal Plain in figure 6 cannot be readily correlated with any specific geologic units.
A recent study of radon and radioactivity in part of the Coastal Plain by the Delaware
Geological Survey (Woodruff and others, 1992) used portable gamma radiation detectors to survey
the surface areas underlain by glauconitic sediments in southern New Castle County. They found
that, despite the cover of Columbia Formation, ranging from 10 to 70 feet thick, gamma-ray
measurements over subcrops of the glauconite-rich Mount Laurel Formation and Rancocas Group
displayed typically higher radioactivity (72-139 counts per second, cps) than the non-glauconitic
deposits of the Chesapeake Group (60-80 cps) to the south. The highest gamma radiation
measurements were associated with the Hornerstown Formation (130-140 cps). They measured
uranium concentrations ranging from 0.8-114 ppm with an average of 8.2 ppm in samples of the
Mount Laurel Formation and Rancocas Group, and ranging from 0.6-4.9 ppm with an average of
1.89 ppm (J.H. Talley, written commun., 1993) in the Columbia Formation. Soil radon
measurements by Woodruff and others (1992) in the Columbia Formation ranged from 53.9-
419.1 pCi/L in areas underlain by glauconitic sediments and 25.7-259.9 pCi/L hi areas underlain
by non-glauconitic sediments; however, the authors do not feel that the differences in the radon
concentrations are statistically significant. The authors suggested that gamma radiation and,
possibly, radon gas from the glauconitic sediments beneath the Columbia Formation, were
contributing to the natural radioactivity measured at and near the surface.
INDOOR RADON DATA
During the period from November, 1985, to June, 1990, the Office of Radiation Control in
the Delaware Department of Health and Social Services assisted homeowners and others in testing
for indoor radon, and compiled test data to map indoor radon levels in the State. Results of this
study are presented in a report by Eichler and Wright (1991). This data set includes all 150 public
schools in Delaware and more than 30 private schools. Ninety-eight percent of the tests were done
by charcoal canister. The average indoor radon level for the more than 7000 tests in the State
survey was 2 pCi/L. Table 1 summarizes the data by zip code. Figures 7a and b are maps of the
average indoor radon and percent of indoor radon measurements exceeding 4 pCi/L, plotted by zip
code centroid—each point is located hi the center of the zip code area. These zipcode maps show
IV-12 Reprinted from USGS Open-File Report 93-292-C
-------
EQUIVALENT URANIUM
> 1.5 ppm
(==:l 1.0-1.5 ppm
< 1 -0 ppm
| | NO DATA
10
Miles
Figure 6. Aerial radiometric map of Delaware (after Duval and others, 1989).
-------
TABLE 1. Screening indoor radon data complied by the Delaware Department of Public Health
for homes tested during the period 1986-1990. Data represent 2-7 day charcoal canister
measurements. Units for all columns of radon data are pCi/L.
ZIP
CODE
19701
19702
19703
19706
19707
19708
19709
19710
19711
19713
19714
19715
19720
19730
19731
19732
19733
19734
19735
19736
19800
19801
19802
19803
19804
19805
19806
19807
19808
19809
19810
19901
19930
19931
19933
19934
19936
19938
19939
19940
19941
19942
CITY
BEAR
NEWARK
CLAYMONT
DEL. CITY
HOCKESSIN
KIRKWOOD
MEDDLETOWN
MONTCHANIN
NEWARK
NEWARK
NEWARK
NEWARK
NEW CASTLE
ODESSA
PORTPENN
ROCKLAND
ST. GEORGES
TOWNSEND
YORKLYN
YORKLYN
WILMINGTON
WILMINGTON
WILMINGTON
WILMINGTON
WILMINGTON
WILMINGTON
WILMINGTON
WILMINGTON
WILMINGTON
WILMINGTON
WILMINGTON
DOVER
BETHANY
BETHAL
BRTDGEVILLE
CAMDEN
CHESWOLD
CLAYTON
DAGSBORO
DELMAR
ELLENDALE
FARMINGTON
COUNTY
NEW CASTLE
NEWCASTLE
NEWCASTLE
NEW CASTLE
NEW CASTLE
NEWCASTLE
NEWCASTLE
NEWCASTLE
NEWCASTLE
NEWCASTLE
NEWCASTLE
NEWCASTLE
NEWCASTLE
NEW CASTLE
NEW CASTLE
NEW CASTLE
NEWCASTLE
NEW CASTLE
NEW CASTLE
NEW CASTLE
NEW CASTLE
NEWCASTLE
NEWCASTLE
NEWCASTLE
NEW CASTLE
NEW CASTLE
NEWCASTLE
NEWCASTLE
NEW CASTLE
NEWCASTLE
NEWCASTLE
KENT
SUSSEX
SUSSEX
SUSSEX
KENT
KENT
KENT
SUSSEX
SUSSEX
SUSSEX
KENT
NO. OF
MEAS.
140
175
132
33
352
5
240
15
821
197
2
4
269
47
13
6
5
106
1
15
2
39
114
688
171
194
78
178
572
234
691
295
21
3
49
58
5
48
32
24
7
1
AVERAGE
1.8
1.5
1.8
1.0
2.4
0.9
3.0
1.7
2.7
1.5
2.7
1.7
1.7
3.2
1.2
1.7
2.9
1.6
0.8
2.3
0.5
1.5
1.7
2.1
1.9
1.6
1.6
2.2
2.2
2.1
2.6
1.6
0.7
1.0
1.0
1.1
0.9
1.1
1.5
0.8
0.6
0.5
MEDIAN
1.3
1.0
1.3
0.6
1.6
0.5
2.0
1.5
1.5
0.9
2.7
1.8
1.3
2.0
0.5
1.5
2.2
1.0
0.8
1.3
0.5
1.1
1.1
1.6
1.7
1.0
1.1
1.7
1.6
1.5
1.8
1.2
0.5
1.0
0.8
0.9
0.5
0.8
0.5
0.5
0.5
0.5
GM
1.3
1.1
1.3
0.9
1.7
0.8
2.0
1.4
1.5
1.0
2.6
1.6
1.2
2.0
0.9
1.3
2.5
1.1
0.8
1.4
0.4
1.2
1.2
1.5
1.4
1.0
1.2
1.6
1.6
1.5
1.8
1.1
0.6
0.9
0.9
0.9
0.8
0.9
0.8
0.7
0.6
0.5
STD
1.9
1.5
1.5
0.7
2.5
0.6
4.0
1.1
7.5
1.6
0.2
0.6
1.8
3.1
1.4
1.2
1.9
1.8
***
3.3
0.3
1.1
1.6
1.8
1.4
3.0
1.3
1.9
2.3
1.9
2.7
1.4
0.4
0.4
0.5
0.9
0.5
1.0
3.1
0.4
0.4
***
MAX
15.8
13.4
7.5
3.0
17.5
1.7
38.9
4.2
163.9
13.1
2.8
2.4
21.0
13.0
5.4
3.2
6.2
9.6
0.8
13.3
0.7
5.6
10.2
12.3
6.5
37.2
7.4
12.8
26.5
13.0
40.5
9.5
2.0
1.4
3.3
5.5
1.5
6.0
17.1
2.1
1.5
0.5
%>4
pCi/L
11
4
11
0
15
0
19
7
14
5
0
0
7
30
8
0
20
9
0
7
0
3
9
14
8
6
5
13
13
13
19
6
0
0
0
3
0
2
6
0
0
0
%>20
pCi/L
0
0
0
0
0
0
1
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
-------
TABLE 1 (continued). Screening indoor radon data for Delaware.
ZIP
CODE
1994
19944
1994
1994
19947
19950
1995
19952
19953
19954
19955
19956
19958
19960
19961
19962
19963
19964
19966
19968
19969
19970
19971
19973
19975
19977
19979
19980
CITY
FELTON
FENWICKIS.
FRANKFORD
FREDERICA
GEORGETOWN
GREENWOOD
HARBESON
HARRINGTON
HARTLY
HOUSTON
KENTON
LAUREL
LEWES
LINCOLN
LITTLE CREK
MAGNOLIA
MILFORD
MARYDEL
MILLSBORO
MILTON
NASSAU
MDLLVILLE
REHOBOTH
EAFORD
ELBYVILLE
MYRNA
VIOLA
WOODSIDE
COUNTY
KENT
SUSSEX
SUSSEX
KENT
SUSSEX
KENT
SUSSEX
KENT
•CENT
SENT
CENT
SUSSEX
SUSSEX
SUSSEX
CENT
CENT
SUSSEX
KENT
SUSSEX
SUSSEX
USSEX
USSEX
USSEX
USSEX
USSEX
KENT
NEW CASTLE
CENT
NO. OF
MEAS
5
3
2
7
3«
12
38
17
16
52
88
2'
]
2J
81
e
64
55
3
50
63
105
36
99
3
1
AVERAGE
1.
0.
0.
1.
0.
\J-
0.
o.;
0.!
1.
0.5
0.<
1.:
o.<
2.]
1.6
l.f
0.',
0.9
1.0
1.5
0.8
1.2
1.1
0.5
1.6
1.2
0.5
MEDIAN
0.
0.
0.
0.
0.
0.
0.5
0.5
0.5
0.8
0.5
0.5
0.7
0.5
2.]
i.:
1.0
0.7
0.5
0.6
1.C
0.5
0.7
0.8
0.5
1.0
1.5
0.5
GM
0.
0.
o;
l.:
0.'
0.
1)
0.7
0.7
0.9
0.5
0.7
O.J
0.7
2 ]
1.2
1.]
0.7
0.7
0.8
1.3
0.7
0.9
0.9
0.5
1.2
1.0
0.5
STD
1.
0.
0.
1.;
0.
1.7
0.6
0.7
0.6
0.6
***
().!
0.9
O.I
1.^
1.2
0.2
0.6
0.*
1.0
0.5
1.2
1.0
0.2
1.6
0.6
MAX
8.
0.
3.
4.
c
9.3
1.
4.6
2.6
2
0.5
4.7
4.1
2.1
6.3
7.C
1.1
3.0
5.0
27
2.3
8.1
5.2
1.7
11.7
1.5
0.5
%>4
pCi/T
1
0
0
0
0
0
1
0
0
0
2
0
0
3
3
0
6
0
0
%>20
pCi/L
0
0
0
0
0
0
0
o
0
o
o
o
o
o
o
o
o
o
o
o
0
-------
f
N
Bsmt & 1st Floor Rn
Average Concentration (pCi/L)
•fr 0.0 to 1.0
* 1.1 to 2.0
* 2.1 to 3.0
* 3.1 to 4.0
10 Miles
#
#
^ * #
*• ^
^r ^
Figure 7a. Average indoor radon levels of homes sampled in each zip code area, plotted
by zip code centroid. Points are plotted only for those zip code areas containing 5 or
more measurements. Points representing the average indoor radon reading are plotted at
the center of each zip code area. Data compiled by the Delaware Department of Public
Health for homes tested between 1986-1990 (see Table 1).
-------
t
N
Bsmt & 1st Floor Rn
%>4pCi/L
# 0 to 10
* 11 to 20
* 21 to 30
10 Miles
Figure 7b. Percent of homes tested with indoor radon measurements greater than 4 pCi/L
plotted by zip code centroid. Points are plotted only for those zip code areas with 5 or '
more measurements. Points representing the percent of readings greater than 4 pCi/L
are plotted at the center of each zip code area. Data compiled by the Delaware Department
of Public Health for homes tested between 1986-1990 (see Table 1)
-------
data only for those zipcodes with 5 or more indoor radon readings. Figure 8 is a map of counties
for reference. Figure 9 shows the frequency distribution of individual indoor radon measurements
by county. In general, the indoor radon measurements were highest in New Castle County and
lowest in Sussex County. New Castle County had 16 measurements exceeding 20 pCi/L whereas
Kent and Sussex Counties had no readings over 20 pCi/L.
GEOLOGIC RADON POTENTIAL
An examination of aerial radioactivity, geologic, and indoor radon data, and radioactivity
surveys conducted by the Delaware Geological Survey (Woodruff and others, 1992) allows us to
make some observations about the geologic radon potential of the State. It appears that the
Piedmont and northern portion of the Atlantic Coastal Plain have the highest geologic radon
potential. Average indoor radon in the Piedmont varies 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 examination of 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 is predominantly schist.
Soils developed on this schist have generally moderate permeability. This formation is moderate to
locally high in geologic radon potential. Studies of equivalent schists in the Piedmont of Maryland
(Gundersen and others, 1988) indicate that these rocks can have uranium concentrations of 3-5
ppm, especially where faulted. The soils developed on these schists can also have soil-gas radon
concentrations greater than 1000 pCi/L. 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 the elevated radon levels, whereas mafic rocks
such as amphibolite and gabbro, and quartz-poor rocks such as charnockite and diorite, are
probably lower in radon potential. The soils developed on the felsic rocks also tend to have higher
permeability than the soils developed on the mafic rocks. The average indoor radon (fig. 7a) is
distinctly lower in parts of the Wilmington Complex than in surrounding areas, particularly in
zipcode areas underlain by the Bringhurst Gabbro and the Arden pluton. Plotting of individual
indoor radon readings may better delineate specific geologic units; however, given the present
format of the data, this is not possible. .
Studies of radon and uranium in Coastal Plain sediments in New Jersey (Gundersen and
others, 1991) and Maryland (Reimer and others, 1991) suggest that glauconitic marine sediments
equivalent to those in the northern portion of the Delaware Coastal Plain can generate 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 geologic 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 that variable but
generally moderate concentrations of uranium occur, 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 from the State indoor radon survey for New Castle County
indicates that areas underlain by the non-glauconitic Cretaceous fluvial sediments 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
IV-18 Reprinted from USGS Open-File Report 93-292-C
-------
Figure 8. Counties in Delaware.
-------
New Castle
10000
ffl
I
in
TO
OJ
-------
sands, silts, gravels, and clays that have low geologic radon potential. These sediments are low in
radioactivity and generally have a smaU percentage of homes with indoor radon levels greater than
4 pCi/L.
SUMMARY
For the purpose of this assessment, Delaware has been divided into 3 geologic radon
potential areas and each area assigned a Radon Index (RI) and a Confidence Index (CI) score
(Table 2) using the information outlined in the sections above (please see the introduction chapter
to this report for a detailed explanation of the indexes). 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.
New Castle County has generally moderate but variable radon potential. Northern New
Castle County is underlain by the metamorphic and igneous rocks of the Piedmont that have
moderate radon potential, but that may be locally high or low, as discussed in the previous section.
Central New Castle County is underlain in part by glauconitic marine sediments of Cretaceous and
Tertiary age that have moderate to locally high geologic 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 (Woodruff and
others, 1992) of Cretaceous and Tertiary glauconitic marine sediments and fluvial sediments of the
Columbia Formation indicate that moderate concentrations of uranium, generally averaging 1 89
ppm or greater, occur. The permeability of soils in these areas is variable but generally moderate to
high, allowing radon gas to move readily through the soil. Data from the State indoor radon
survey also indicate that these areas of New Castle County have the highest percentage of homes
with elevated indoor radon as well as the highest indoor radon concentrations found in the State
Kent County and all of Sussex County are underlain by quartz-dominated sands, silts, gravels and
clays that have lowgeologic 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.
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-21 Reprinted from USGS Open-FUe Report 93-292-C
-------
TABLE 2. Radon Index and Confidence Index scores for Delaware.
FACTOR
(2) Coastal Plain (3) Coastal Plain
Upper Cretaceous Cretaceous, Tertiary, Quaternary
(1) Piedmont and lower Tertiary quartzitic
glauconitic marine sediments fluvial and marine sediments
RI CI RI CI RI CI
INDOOR RADON
RADIOACTIVITY
GEOLOGY
SOIL PERM.
ARCHITECTURE
GFE POINTS
TOTAL
2
2
2
2
3
0
11
Mod
2
2
2
3
-
-
9
Mod
2
2
2
2
2
0
10
Mod
2
2
2
3
-
.
9
Mod
1
1
1
2
2
0
7
Low
2
2
2
3
-
_
9
Mod
RADON INDEX SCORING:
Radon potential cateeorv
LOW
MODERATE/VARIABLE
HIGH
Point range
3-8 points
9- 11 points
> 1 1 points
Probable screening indoor
radon average for area
<2pCi/L
2-4pCi/L
>4pCi/L
Possible range of points = 3 to 17
CONFIDENCE INDEX SCORING:
LOW CONFIDENCE
MODERATE CONFIDENCE
HIGH CONFIDENCE
4-6 points
7-9 points
10 - 12 points
Possible range of points = 4 to 12
IV-22 Reprinted from USGS Open-File Report 93-292-C
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REFERENCES CITED IN THIS REPORT
AND GENERAL REFERENCES PERTAINING TO RADON IN DELAWARE
Andres, A.S., 1986, Stratigraphy and depositional history of the post-Choptank Chesapeake
Group: Delaware Geological Survey, Report of Investigations No. 42, 39 p.
Benson, R.N., and Pickett, T.E., 1986, Geology of south central Kent County, Delaware:
Delaware Geological Survey, Geologic Map Series No. 7, scale 1:24,000.
Duval, J.S., Jones, W.J., Riggle, F.R., and Pitkin, J.A., 1989, Equivalent uranium map of
conterminous United States: U.S. Geological Survey Open-File Report 89-478,10 p.
Eichler, Thomas P, and Wright, Lester N., 1991, The Delaware Radon Program: Department of
Health and Social Services, Division of Public Health, Authority on Radiation Protection,
29 p.
Elsinger, R.J., 1982, Estuarine geochemistry of 224 Ra, 228 Ra, 226 Ra, and 222 Rn: Doctoral
Thesis, Univ. of South Carolina, Columbia, SC, 95 p.
Gundersen, L. C.S, Peake, R.T., Latske, G.D., Hauser, L.M., and Wiggs,C.R., 1991, A
statistical summary of uranium and radon in soils from the Coastal Plain of Texas,
Alabama, and New Jersey, in Proceedings of the 1990 International Symposium on Radon
and Radon Reduction Technology,Volume 2: Symposium Oral Papers, U.S. EPA report
EPA-600/9-91/026b,p.CVI4-l-13.
Gundersen, L.C.S., Reimer, G.M., Wiggs, C.R. and Rice, C.A., 1988, Radon Potential of
Rocks and Soils in Montgomery County, Maryland: U. S. Geological Survey
Miscellaneous Field Studies Map 88-2043, scale 1:62,000.
Hammond, D., Simpson, H.J., and Mathieu, G., 1976, Distribution of radon-222 in the Delaware
and Hudson estuaries as an indicator of migration rates of dissolved species across the
sediment-water interface: Eos, Transactions of the American Geophysical Union v 57
p. 151. '
Ireland, W., Jr., and Matthews, E.D., 1974, Soil survey of Sussex County, Delaware: U.S.
Department of Agriculture, Soil Conservation Service, 74 p.
Jordan, R.R., 1962, Stratigraphy of the sedimentary rocks of Delaware: Delaware Geological
Survey, Bulletin No. 9, 51 p.
Jordan, R.R., 1964, Columbia (Pleistocene) sediments of Delaware: Delaware Geological Survev
Bulletin No. 12, 61 p. *'
Jordan, R.R., 1974, Pleistocene deposits of Delaware, in Oakes, R.Q., and Dubar, J.R., eds.,
Post-Miocene Stratigraphy, Central and Southern Atlantic Coastal Plain: Logan, Utah,
Utah State University Press, p. 30-52.
IV-23 Reprinted from USGS Open-File Report 93-292-C
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Jordan, R.R., 1983, Stratigraphic nomenclature of nonmarine Cretaceous rocks of inner margin of
Coastal Plain in Delaware and adjacent states: Delaware Geological Survey, Report of
Investigations No. 37,43 p.
Kraft, J.C., and Carey, W., eds., 1980, Selected Papers on the Geology of Delaware: Special
publication of the Delaware Geological Survey, 268 p.
Matthews, E.D., and Lavoie, O.L., 1970, Soil survey of New Castle County, Delaware: U.S.
Department of Agriculture, Soil Conservation Service, 97 p.
Matthews, E.D., and Ireland, W., Jr., 1971, Soil survey of Kent County, Delaware: U.S.
Department of Agriculture, Soil Conservation Service, 66 p.
Pickett, T.E., 1976, Generalized Geologic Map of Delaware: Delaware Geological Survey Special
Publication No. 9, scale approx. 1:576,000.
Pickett, T.E., and Benson, R.N., 1977, Geology of the Smyrna-Clayton area, Delaware:
Delaware Geological Survey, Geologic Map Series No. 6, scale 1:24,000.
Pickett, T.E., and Benson, R.N., 1983, Geology of the Dover area, Delaware: Delaware
Geological Survey, Geologic Map Series No. 7, scale 1:24,000.
Pickett, T.E., and Spoljaric, N., 1971, Geology of the Middletown-Odessa area, Delaware:
Delaware Geological Survey, Geologic Map Series No. 2, scale 1:24,000.
Pierce, A.P., 1956, Radon and helium studies: U.S. Geological Survey Rept TEI-620
p. 305-309.
Ramsey, K.W., and Schenck, W.S., 1990, Geologic map of southern Delaware: Delaware
Geological Survey, Open-File Report No. 32, scale 1:100,000.
Reimer, G.M., Gundersen, L.C.S., Szarzi, S.L., and Been, J.M., 1991, Reconnaissance
approach using geology and soil-gas radon concentrations for rapid and preliminary
estimates of 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.
Richmond, G.M., Fullerton, D.S., and Weide, D.L., compilers, 1987, Quaternary geologic map
of the Chesapeake Bay 4°x6° quadrangle, United States and Canada: U.S. Geological
Survey Miscellaneous Investigations Map 1-1420 (NJ-18), scale 1:1,000,000.
Spoljaric, R, 1980, The geology of the Delaware Coastal Plain, in Kraft, J.C., and Carey, W.,
eds., Selected Papers on the Geology of Delaware: Special publication of the Delaware
Geological Survey, p. 87-114.
Talley, J.H., 1982, Geohydrology of the Milford area, Delaware: Delaware Geological Survey,
Hydrologic Map Series No. 4, scale 1:24,000.
IV-24 Reprinted from USGS Open-File Report 93-292-C
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Talley, J.H., 1987, Geohydrology of the southern coastal area, Delaware: Delaware Geological
Survey, Hydrologic Map Series No. 7,2 sheets, scale 1:24,000.
Thompson, A.M., 1980, A summary of the geology of the Piedmont in Delaware, in Kraft, J.C.,
and Carey, W., eds., Selected Papers on the Geology of Delaware: Special publication of
the Delaware Geological Survey, p. 115-1"''
van Assendelft, A.C.E., 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.
Wagner, Mary Emma, Srogi, LeeAnn, Wiswell, C. Gil, and Alcock, James, 1991, Taconic
collision in the Delaware-Pennsylvania Piedmont and implications for subsequent geologic
history, in Schultz, A., and Compton-Gooding, E., eds., Geologic evolution of the eastern
United States, Field trip guidebook, Geological Society of America, NE-SE section,
p. 91-119.
Woodruff, K.D., 1980, Geohydrology of Delaware, in Kraft, J.C., and Carey, W., eds., Selected
Papers on the Geology of Delaware: Special publication of the Delaware Geological
Survey, p. 135-166. *
Woodruff, K.D., 1985, Geohydrology of the Wilmington area, Delaware: Delaware Geological
Survey, Hydrologic Map Series No. 3,4 sheets, scale 1:24,000.
Woodruff, K.D., 1986, Geohydrology of the Chesapeake and Delaware Canal area, Delaware-
Delaware Geological Survey, Hydrologic Map Series No. 6, 2 sheets, scale 1:24,000.
Woodruff, K.D., and Thompson, A.M., 1972, Geology of the Newark area, Delaware: Delaware
Geological Survey, Geologic Map Series No. 3, scale 1:24,000.
Woodruff, K.D., and Thompson, A.M., 1975, Geology of the Wilmington area, Delaware:
Delaware Geological Survey, Geologic Map Series No. 4, scale 1:24,000.
Woodruff, K.D., Ramsey, K.W., and Talley, J.H., 1992, Radon potential of the glauconitic
sediments in the Coastal Plain of Delaware: Final Report to Delaware Department of Health
and Social Services, Division of Public Health, Health Systems Protection, Radiation
Control, Contract No. 92-105,43 p.
IV-25 Reprinted from USGS Open-FUe 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.)
DELAWARE MAP OF RAnnxr
The Delaware Map of Radon Zones and its supporting documentation (Part IV of this
report) have received extensive review by Delaware geologists and radon program experts
The map for Delaware 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 Delaware" - 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
Delaware radon program for information on testing and fixing homes. Telephone numbers
and addresses can be found in Part II of this report.
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