United States
Environmental Protection
Agency
Air and Radiation
(6604J)
402-R-93-051
September 1993
v>EPA EPA's Map of Radon Zones
NEW MEXICO
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EPA'S MAP OF RADON ZONES
NEW MEXICO
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 (OKIA) in conjunction with the U.S. Geological Survey
(USGS). Sharon W. White was the EPA project manager. Numerous other people in ORIA
were instrumental in the development of the Map of Radon Zones, including Lisa Ratcliff,
Kirk Maconaughey, R. Thomas Peake, Dave Rowson, and Steve Page.
\ ' - '
EPA would especially like to acknowledge the outstanding effort of the USGS
radon team — Linda Gundersen, Randy Schumann, Jim Otton, Doug Owen, Russell
Dubiel, Kendell Dickinson, and Sandra Szarzi ~ in developing the technical base for the
Map of Radon Zones.
ORIA would also like to recognize the efforts of all the EPA Regional Offices in
coordinating the reviews with the State, programs and the Association-of American State
Geologists (AASG) for providing a liaison with the State geological surveys. In addition,
appreciation is expressed to all of the State radon programs and geological surveys for their
technical input and review of the Map of Radon Zones.
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TABLE OF CONTENTS
I. OVERVIEW
II. THE USGS/EPA RADON POTENTIAL
ASSESSMENTS:INTRODUCTION
III. REGION 6 GEOLOGIC RADON POTENTIAL
SUMMARY
V. PRELIMINARY GEOLOGIC RADON POTENTIAL
ASSESSMENT OF NEW MEXICO
V. EPA'S MAP OF RADON ZONES .-- NEW MEXICO
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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), anJ 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 requirements1 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 te.sted 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 arid homeowners in reducing their risk of lung cancer from indoor radon.
Since 1985, EPA and USGS have been working together to continually increase our
understanding of radon sources and the migration dynamics that cause elevated indoor radon.
levels. Early efforts resulted in the 1987 map entitled "Areas with Potentially High Radon
Levels." This map was based on limited geologic information only because few indoor radon
measurements were available at the time. The development of EPA's Map of Radon Zones
and its technical foundation, USGS' National Geologic Radon Province Map, has been based
on additional information from six years of the State/EPA Residential Radon Surveys,
independent State residential surveys, and continued expansion of geologic and geophysical
information, particularly the data from the National Uranium Resource Evaluation project.
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Purpose of the Map of Radon Zones
EPA's Map of Radon Zones (Figure 1) assigns each of the 3141 counties in the
United States to one of three zones:
o Zone 1 counties have a gredictpd 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 I 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
notentialfor-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 assigne'd 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 bas"ed 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.1 ,
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 A. • ,' . ' • -
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 Nebrask;
Lincoln County
Bill Uoittite Lot
Figure 4
NEBRASKA - EPA Map of Radon Zones
Lincoln County
1 Zoat 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 e'state 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
••'"' ' .• v'.' '• : 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.$. 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 statesman 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.
Bpbklets detailing the radon potential assessment for the U.S. have been developed for
each State. USGS geologists are the authors of the geologic radon p'otential 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 of predict the indoor radon concentrations of individual homes or housing
H-l Reprinted from USGS Open-File Report 93-292
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tracts. Within any.area of a given geologic radon potential ranking, there are likely to be
areas where the radon potential is lower or higher than that assigned to the area as a whole,
especially in larger areas such as the large counties in some western states.
In each state chapter, references to additional reports related to radon are listed for the
state, and the reader is urged to consult these reports for more detailed information. In most
cases the best sources of information on radon for specific areas are state and local
departments of health, state departments responsible for nuclear safety or environmental
protection, and U.S. EPA regional offices. More detailed information on state or local
geology may be obtained from the state geological surveys. Addresses and telephone
numbers of state radon contacts, geological surveys, and EPA regional offices are listed in
Appendix C at the end of this chapter.
RADON GENERATION AND TRANSPORT IN SOILS
Radon <222Rn) is produced from the radioactive decay of radium (22
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and moisture infiltration rates and depth of wetting may be limited when the cracks in the
surface soil layers swell shut. Clay-rich B horizons, particularly those with massive or platy
structure, can form a capping layer that impedes the escape of soil gas to the surface
(Schumann and others, 1992). However, the shrinkage of clays can act to open or widen
cracks upon drying, thus increasing the soil's permeability to gas flow during drier periods.
Radon transport in soils occurs by two processes: (1) diffusion and (2) flow (Tanner,
1964). Diffusion is the process whereby radon atoms move from areas of higher
concentration to areas of lower concentration in response to a concentration gradient. Flow is
the process by which soil air moves through soil pores in response.to differences in pressure
within the soil or between the soil and the atmosphere, carrying the radon atoms 'along with it.
Diffusion is the dominant radon transport process in soils of low permeability, whereas flow
tends to dominate in highly permeable soils (Sextro and others, 1987). "In low-permeability
soils, much of the radon may decay before it is able to enter a building because its transport
rate is reduced. Conversely, highly permeable soils, even those that are relatively low in
radium, such as those derived from some types of glacial deposits, have been associated with
high indoor radon levels in Europe and in the northern United States (Akerblom and others,
1984; Kunz and others, 1989; Sextro and others, 1987). In areas of karst topography formed
in carbonate rock (limestone or dolomite) environments, solution cavities and fissures can
increase soil permeability at depth by providing additional pathways for gas flow.
Not all radium contained in soil grains and grain coatings will result in mobile radon
when the radium decays. Depending on where the radium is distributed in the soil, many of
the radon atoms may remain imbedded in the soil grain containing the parent radium atom, or
become imbedded in adjacent soil grains. The portion of radium that releases radon into the
pores and fractures of rocks and soils is called the emanating fraction. When a radium atom
decays to radon, the energy generated is strong enough to send the radon atom a distance of
about 40 nanometers (1 nm = 10"9 meters), or about 2x10;* inches—this is known as alpha
recoil (Tanner, 1980). Moisture in the soil lessens the chance of a recoiling radon atom
becoming imbedded in an adjacent grain. Because water is more dense than air, a radon atom
will travel a shorter distance in a water-filled pore than in an air-filled pore, thus increasing
the likelihood that the radon atom will remain in the pore space. Intermediate moisture levels
enhance radon emanation but do not significantly affect permeability. However, high
moisture levels can significantly decrease the gas permeability of the soil and impede radon
movement through the soil.
Concentrations of radon in soils are generally many times higher than those inside of
buildings, ranging from tens of pCi/L to more than -100,000 pCi/L, but typically in the range
of hundreds to low thousands of pCi/L. Soil-gas radon concentrations can vary in response to
variations in climate and weather on hourly, daily, or seasonal time scales. Schumann and
others (1992) and Rose and others (1988) recorded order-of-magnitude variations'in soil-gas
radon concentrations between seasons in Colorado and Pennsylvania. The most important
factors appear to be (1) soil moisture conditions, which are controlled in large part by
precipitation; (2) barometric pressure; and (3) temperature. Washington and Rose (1990)
suggest that temperature-controlled partitioning of radon between water and gas in soil pores
also has a significant influence on the amount of mobile radon in soil gas.
Homes in hilly limestone regions of the southern Appalachians were found to have higher
indoor radon concentrations during the summer than in the winter. A suggested cause for this
phenomenon involves temperature/pressure-driven flow of radon-laden air from subsurface
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solution cavities in the, carbonate rock into houses. As warm air enters solution cavities that
are higher on the hillslope,than the homes, it cools and settles, pushing radon-laden air from .
lower in the cave or cavity system into structures on the hillslope (Gammage and others,
1993). In contrast, homes built over caves having openings situated below the level of the
home had higher indoor radon levels in the w.nter, 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 trie surrounding soil than nonbasement homes. .The term "nonbasement" applies to •
slab-on-grade or crawl space construction.
METHODS AND SOURCES OF DATA
The assessments of radon potential- in the booklets that follow this introduction were
made using five main types of data: (1) geologic (lithologic); (2) aerial radiometric; (3) soil
characteristics, including soil moisture, permeability, and drainage characteristics; (4) indoor
radon data; and (5) building architecture (specifically, whether homes in each area are built ,
slab-on-grade or have a basement or crawl space). These five factors were evaluated and
integrated to produce estimates of radon potential. Field measurements of soil-gas radon or
soil radioactivity were not used except where such data were available in .existing, published
reports of local .field studies. Where applicable, such field studies are described in the
individual state chapters. ^ • . ".'•..
GEOLOGIC DATA . - . ' > ; ::,
The types and distribution of lithologic units and other geologic features in an
assessment area are of primary importance in determining radon potential. Rock types that
are most likely to cause indoor radon problems include carbonaceous black shales, glauconite-
bearing sandstones, certain kinds of fluvial sandstones and fluvial sediments, phosphorites,
chalk, karst-producing carbonate rocks, certain kinds of glacial deposits, 'bauxite, uranium-rich
granitic rocks, metamorphic rocks of granitic composition, silica-rich volcanic rocks,-many
sheared or faulted rocks, some coals, and certain kinds of contact metamorphosed rocks.
Rock types least likely to cause radon problems include marine quartz sands, non-
• carbonaceous shales and siltstones, certain kinds of clays, silica-poor metamorphic and
II-5 Reprinted from USGS Open-File Report 93-292
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igneous rocks, and basalts. Exceptions exist within these general lithologic groups because of
the occurrence of localized uranium deposits, commonly of the hydrothermal type in
crystalline rocks or the "roll-front" type in sedimentary rocks. Uranium and radium are
commonly sited in heavy minerals, iron-oxide coatings on rock and soil grains, and organic
materials in soils and sediments. Less common, are uranium associated with phosphate and
carbonate complexes in rocks and soils, and uranium minerals.
Although many cases of elevated indoor radon levels can be traced to high radium and
(or) uranium concentrations in parent rocks, some structural features, most notably faults and
shear zones, have been identified as sites of localized uranium concentrations (Deffeyes and
MacGregor, 1980) and have been associated with some of the highest reported indoor radon
levels (Gundersen, 1991). The two highest known indoor radon occurrences are associated
with sheared fault zones in Boyertown, Pennsylvania (Gundersen and others, 1988a; Smith
and others, 1987), and in Clinton, New Jersey (Henry and others, 1991; Muessig and Bell
1988). .
NURE AERIAL RADIOMETRIC DATA . .
Aerial radiometric data are used to quantify the radioactivity of rocks and soils.
Equivalent uranium (eU) data provide an estimate of the surficial concentrations of radon
parent materials (uranium, radium) in rocks and soils. Equivalent uranium is calculated from
the counts received by a gamma-ray detector from the 1.76 MeV (mega-electron volts)
emission energy corresponding to bismuth-214 (314Bi), 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 soiUgas radon concentrations and
average eU values for a wide variety of soils have been documented (Gundersen and others,
1988a, 1988b; Schumann and Owen, 1988)'. Aerial,radiometric data can provide an estimate
of radon source strength over a region, but the amount of radon that is able to enter a home
from the soil is dependent on several local factors, including soil structure, grain size
distribution, moisture content, and permeability, as well as type of house construction and its
structural condition.
The aerial radiometric data used for these characterizations were collected as part of the
Department of Energy National Uranium Resource Evaluation (NURE) program of the 1970s
and early 1980s. The purpose of the NURE- program was to identify and describe areas in the
United States having potential'uranium resources (U.S. Department of Energy, 1976). The
NURE aerial radiometric data were collected by aircraft in which a gamma-ray spectrometer
was mounted, flying approximately 122 m (400 ft) above the ground surface. The. equivalent
uranium maps presented in the state chapters were generated from reprocessed NURE data in
which smoothing, filtering, recalibrating, and matching of adjacent quadrangle data sets were
performed to compensate for background, altitude, calibration, and other types of errors and
inconsistencies in the original data set (Duval and others, 1989). The data were then gridded
and contoured to produce maps of eU with a pixel size corresponding to approximately 2 5 x
2,5 km (1.6 x 1.6 mi). . .
II-6 Reprinted from USGS Open-File Report 93-292
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FLJCUT LINE SPACING OF SORE AERIAL SURVEYS
2 I'M ( 1 MILE)
5 EH (3 MILES)
2 i 5 k li
10 III (6 HUES)
5 k 10 KM
NO DATA
Figure 2. Nominal flightline spacings for NUKE 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 NURE 1° x 2° quadrangles showing the flight-line spacing
for each quadrangle. In general, the more closely spaced the flightlines are, the more area
was covered by the aerial gamma survey, and thus, more detail is available in the data set.
For an altitude of 400 ft above the ground surface and with primary flightline spacing
typically between 3 and 6 miles, less than 10 percent of the ground surface of the United
States was actually measured by the airborne gamma-ray detectors (Duval and others, 1989),
although some areas had better coverage than others due to the differences in flight-line
spacing between areas (fig. 2). This suggests that some localized uranium anomalies may not
have been detected by the aerial surveys, but the good correlations of eU patterns with
geologic outcrop patterns indicate that, at relatively small scales (approximately 1:1,000,000
or smaller) the National eU map (Duval and others, 1989) gives reasonably -good estimates of
average surface uranium concentrations and thus can assist in the prediction of radon potential
of rocks and soils, especially when augmented with additional geologic and soil data.
The shallow (20-30 cm) depth of investigation of gamma-ray spectrometers, either
ground-based or airborne (Duval and others, 1971; Durrance, 1986), suggests that gamma-ray
data may sometimes underestimate the radon-source strength in soils in which some of the
radionuclides in the near-surface soil layers have been transported downward through the soil
profile. In such cases the concentration of radioactive minerals in the A horizon would be
lower than in the B horizon, where such minerals are typically concentrated. The
concentration of radionuclides in the C horizon and below may be relatively unaffected by
surface solution processes. Under these conditions the surface gamma-ray signal may indicate
a lower radon source concentration than actually exists in the deeper soil layers, which are
most likely to affect radon levels in structures with basements. The redistribution of
radionuclides in soil profiles is dependent on a combination of climatic, geologic, and -
geochemical factors. There is reason to believe that correlations of eU with actual soil
radium and uranium concentrations at a depth relevant to radon entry into structures may be
regionally variable (Duval, 1989; Schumann and Gundersen, 1991). Given sufficient
understanding of the factors cited above, these regional differences may be predictable,
SOIL SURVEY DATA
Soil surveys prepared by the U.S. Soil Conservation Service (SCS) provide data on soil
characteristics, including soil-cover thickness, grain-size distribution, permeability, shrink-
swell potential, vegetative cover, generalized grouhdwater characteristics, and land use. The
reports are available in county formats and State summaries. The county reports typically
contain both generalized and detailed maps of soils in the area.
Because of time and map-scale constraints, it was impractical to examine county soil
reports for each county in the United States, so more generalized summaries at appropriate
scales were used where available. For State or regional-scale radon characterizations, soil
maps were compared to geologic maps of the area, and the soil descriptions, shrink-swell
potential, drainage characteristics, depth to seasonal high water table, permeability, and other
relevant characteristics of each soil group noted. Technical soil terms used in soil surveys are
generally complex; however, a good summary of soil engineering terms and the national
distribution of technical soil types is the "Soils" sheet of the National Atlas (U.S. Department
of Agriculture, 1987).
II-8 Reprinted from USGS Open-File Report 93-292
-------
Soil permeability is commonly expressed in SCS soil surveys in terms of the speed, in
inches per hour (in/hr), at which water soaks into the soil, as measured in a soil percolation
test. Although in/hr are not truly units of permeability, these units are in widespread use and
are referred to as "permeability" in SCS soil surveys. The permeabilities listed in the SCS
surveys are for water, but they generall> 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, arid 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' terrns 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
Bothers, 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 US.GS 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 indoqr 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-li Reprinted from USGS Open-File Report 93-292
-------
TABLE 1. RADON INDEX MATRIX, "ppm eU" indicates parts per million of equivalent
uranium, as indicated by NURE aerial radiometric data. See text discussion for details.
FACTOR
INDOOR RADON (average)
AERIAL RADIOACTIVITY
GEOLOGY*
SOIL PERMEABILITY
ARCHnECTURE TYPE
INCREASING RADON POTENTIAL ^
POINT VALUE
1
<2pCi/L
< 1.5 ppm eU
negative
low
mostly slab
2
2 - 4 pCi/L
1.5 - 2.5 ppm eU
• variable
moderate
mixed
3
>4pCi/L
> 2.5 ppm eU
positive
high
mostly basement
'GEOLOGIC FIELD EVIDENCE (GFE) POINTS: GFE points are assigned in addition to points
for the "Geology" factor for specific, relevant geologic field studies. See text for details.
Geologic evidence supporting: HIGH radon +2 points
MODERATE +1 point
LOW -2 points
No relevant geologic field studies 0 points
SCORING:
Radon potential cateeorv
Point range
Probable average screening
indoor radon for area
LOW
MODERATE/VARIABLE
HIGH
3-8 points
9-11 points
12-17 points
<2pCi/L
2-4pCi/L
>4pCi/L
POSSIBLE RANGE OF POINTS = 3 to 17
TABLE 2. CONFIDENCE INDEX MATRIX
INCREASING CONFIDENCE
^
FACTOR
INDOOR RADON DATA
AERIAL RADIO ACTIVITY
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
H-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 RJ points.
Aerial radioactivity data used in this report are from the equivalent uranium map of the
conterminous United States compiled from NURE aerial gamma-ray surveys (Duval and
others, 1989). These data,indicate the gamma radioactivity from approximately the upper 30
cm of rock and soil, expressed in units of ppm equivalent uranium. An approximate average
value of eU was determined visually for each area and point values assigned based on
whether the overall eU for the area falls below 1.5 ppm (1 point), between 1.5 and 2.5 ppm
' (2 points), or greater than 2.5 ppm (3 points). ,
The geology factor is complex and actually incorporates many geologic characteristics. In
the matrix, "positive" and "negative" refer to the presence or absence and distribution of rock
types known to have high uranium contents and to generate elevated radon in soils or indoors.
Examples of "positive" rock types include granites, black shales, phosphatic rocks, and other
rock types described in the preceding "geologic data" secti'on. 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, locallzeddistribution 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, arid 3 points,
respectively. ' . .
' In cases where additional reinforcing or contradictory geologic evidence isiavailable,
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 »" 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 GI
matrix for indoor radon data ("sparse or ho 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 percolatio'n
test figures or other measured permeability data are available, because ah 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 US.GS 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 tp 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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. "*•
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Investigations of soil as a source of indoor radon, in Hopke, P.K., ed., Radon and its
decay products: American Chemical Society Symposium Series 331, p. 10^29.
Sterling, R., Meixel, G., Shen, L., Labs, K., and Bligh, T., 1985, Assessment of the energy
savings potential of building foundations research: Oak Ridge, . Tenn,> U.S. Department of
Energy Report ORNL/SUB/84-0024/1.
Smith, R.C., II, Reilly, M.A., Rose, A.W., Barnes, JJL, and Berkheiser, S.W., Jr., 1987,
Radon: a profound case: Pennsylvania Geology, v. 18, p. 1-7.
Tanner, A.B., 1964, Radon migration in the ground: a review, in- Adams, J.A.S., and Lowder,
W.M., eds., The natural radiation environment: Chicago, HI., University of Chicago
Press, p. 161-190.
Tanner, A.B., 1980, Radon migration in the ground: a supplementary review, in Gesell, T.F.,
and Lowder, W.M. (eds), Natural radiation environment ffl, Symposium proceedings,
Houston, Texas, v. 1, p. 5-56.
U.S. Department of Agriculture, 1987, Principal kinds of soils: Orders, suborders, and great
groups: U.S. Geological Survey, National Atlas of the United States of America, sheet •
38077-BE-NA-07M-00, scale 1:7,500,000.
U.S. Department of Energy, 1976, National Uranium Resource Evaluation preliminary report,
prepared by the U.S. Energy Research and Development Administration, Grand Junction,
Colo.: GJO-11(76).
Wanty, Richard B., and Schoen, Robert, 1991, A review of the chemical processes affecting the
mobility of radionuclides in natural waters, with applications, in Gundersen, Linda C.S.,
and Richard B. Wanty, eds., Field studies of radon in rocks, soils, and water: U.S.
• Geological Survey Bulletin no. 1971, p. 183-194. '
Washington, J.W., and Rose, A.W., 1990, Regional and temporal relations of radon hi 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 Rorica-Battista, M., 1989, Multi-State
-•'' surveys of indoor 222Rn: Health Physics, v. 57, p. 891-896. .
II-19 .Reprinted from USGS Open-File Report 93-292
-------
APPENDIX A
GEOLOGIC TIME SCALE
Subdivisions (and their symbols)
Eon or
Eonothem
Phaneroioic2
Proterozoic
Archean
(A)
Era or
Erathem
Cenozoic J
(CD
Mesozoic2
(M»)
Paleozoic2
*«.££* Si
*feitof£fYI
>t«»»o»e!e IX)
Aretwinrwi
Miodl*
Arcrv«n(V1
ArcOMnlUI
Per od. System.
Subperiod, Subsystem
Quaternary
(Q)
Neopene 2
SuBperiod or
Teniarv Subsystem (N)
rn Paleooene
Suboenodor
Subsystem (Pi)
Cretaceous
(K)
Jurassic
(J)
Triassic
CR)
Permian
"(P)
Pennsylvanian
(C' Mississippian
(M)
Devonian
(D)
Silurian
1C)
Ordovician
(O)
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
Upper
Middle
Lower
Upper
Middle
Lower
Upper
Middle
Lower
Upper
Middle
Lower •
None defined
None defined
None defined
None defined
None defined
None defined
p«*-Arch**n Decay constants and bolopic ratios employed are died in Steiger and Jager (1977). Designation m.y. used for an
Interval oC time. • '
'Modifier* (lower, middle, upper or eariy, middle, late) when used with these Hems are informal divisions of the larger unit; the
first letter of the modifier b lowercase.
'Rocks older Jhan 570 Ma «lso caDed Precambrian (p€),a time term without specific rank.
'informal time term without specific rank. •
USGS Open-File Report 93-292
-------
APPENDIX B
GLOSSARY OF TERMS
I'ni^s 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.
-------
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.
f ,
carbonaceous Said of a rock or sediment that is rich in carbon, is coaly, or contains organic
matter.
charcoal canister A passive radon measurement device consisting of a small container of
granulated activated charcoal that is designed to adsorb radon. Useful for short duration (2-7 days)
measurements only. May be referred to as a "screening" test
chert A hard, extremely dense sedimentary rock consisting dominantly of interlocking crystals of
quartz. Crystals are not visible to the naked eye, giving the rock a milky, dull luster. It may be
white or gray but is commonly colored red, black, yellow, blue, pink, brown, or green.
clastic pertaining to a rock or sediment composed of fragments that are derived from preexisting
rocks or minerals. The most common clastic sedimentary rocks are sandstone and shale.
clay A rock containing clay mineral fragments or material of any composition having a diameter
less than 1/256 mm. .
clay mineral One of a complex and loosely defined group of finely crystalline minerals made up
of water, silicate and aluminum (and a wide variety of other elements). They are formed chiefly by
alteration or weathering of primary silicate minerals. Certain clay minerals are noted for their small
size and ability to absorb substantial amounts of water, causing them to swell. The change in size
that occurs as these clays change between dry and wet is referred to as their "shrink-swell"
potential.
concretion A hard, compact mass of mineral matter, normally subspherical but commonly
irregular in shape; formed by precipitation from a water solution about a nucleus or center, such as
a leaf, shell, bone, or fossil, within a sedimentary or fractured rock.
conglomerate A coarse-grained, clastic sedimentary rock composed of rock and mineral
fragments larger man 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 Qpen-FUe Report 93-292
-------
I , . ' , -.;;-> -. . t ,
delta, deltaic Referring to a low, flat, alluvial tract of land having a triangular or fan shape
located at or near the mouth of a river. It results from the accumulation of sediment deposited bv a
river at the point at which the river loses its ability to transport the sediment, commonly where a
river meets a larger body of water such as a lake or ocean. . '
dike A tabular igneous intrusion of rock, younger than the surrounding rock, that commonly cuts
across the bedding or fohanon of the rock it intrudes. ' • y
diorite A plutonic igneous rock that is medium in color and contains visible dark minerals that
make up less than "50% of the rock. It also contains abundant sodium plagioclase and minor
quartz. .
n^f b°",a-e s^™611^ r°<* of which more than 50% consists of the mineral dolomite
(CaMg(CO3)2), and is commonly white, gray, brown, yellow, or pinkish in color.
drainage The manner in which the waters of an area pass, flow off of, or flow into the soil.
Also refers to the water features of an area, such as lakes and rivers, that drain it.
eolian Pertaining to sediments deposited by the wind.
esker A long, narrow steep-sided ridge composed of irregular beds of sand and gravel deposited
by streams beneath a glacier and left behind when the ice melted. • - , uc^'lca
evapotranspiration Loss of water from a land area by evaporation from the soil and
transpiration from plants. .
extrusive Said of igneous rocks that have been erupted onto the surface of the Earth.
fault A fracture or zone of fractures in rock or sediment along which there has been movement.
fluvial, fluvial, deposit Pertaining to sediment that has been deposited by a river or stream.
foliation A linear feature in a rock defined by both mineralogic and structural characteristics It
may be formed during deformation or metarnorphism.
formation A mappable body of rock having similar characteristics.
glacial deposit Any sediment transported and deposited by a glacier or processes associated
with glaciers, such as glaciofluvial sediments deposited by streams flowing from melting glaciers.
gneiss A rock formed by-metamorphism in which bands and lenses of minerals of similar
on alternate with bands and lenses of different composition, giving the rock a striped or
appearance. '
granite Broadly applied, any coarsely crystalline, quartz- and feldspar-bearing igneous plutonic
rock. Technically granites have between 10 and 50% quartz, and alkali feldspar comprises at least
65% of the total feldspar.
gravel An unconsolidated, natural accumulation of rock fragments consisting predominantly of
particles greater than 2 mm in size. .
heavy minerals Mineral grains in sediment or sedimentary rock having higher than average
specific .gravity. May form layers and lenses because of wind or water sorting by weight and size
H-23 Reprinted from USGS Open-File Report 93-292
-------
a "placer deposit/1 Some heavy mtoli TO magnetite'
^ °f a ™°k, °r mi?eral Aat solidified from molten or partly molten rock material It is
mam kto which rocks •* divided' ^ °thers s
intermontane A term that refers to an area between two mountains
or mountain ranges.
^^
ote
°Ml ** " totemediaK to ooaliflcation between peat and
SPeCimen Md ta o""0" on *e bads of color,
mafic Term describing an igneous rock containing more than 50% dark-colored minerals.
marine Term describing sediments deposited hi the ocean, or precipitated from ocean waters
scmst, ampftiDolite, and gneiss are metamorphic rocks.
?""! ™k otoT °f " Se°10giC f ormadon ""taicture *« appears at the surface of the Earth, as
^^^^^
permeability The capacity of a rock, sediment, or soil to transmit liquid or gas.
"*« -^S a significant amount
n-24 Reprinted from USGS Open-FUe 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 land'forms differ
significantly from adjacent regions.
placer deposit See heavy minerals
residual Formed by weathering of a material in place.
residuum Deposit of residual material. . V,
rhyolite An extrusive igneous rock of volcanic origin, compositionally equivalent to granite.
\ ' • - - • '
sandstone A clastic sedimentary rock composed of sand-sized rock and mineral'rnaterial that is
more or less firmly cemented. Sand particles range from 1/16 to 2 mm in size.
* i ' ' ' '
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 finetgrained 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 funneLshaped and is formed by collapse of the surface material into an underlying
void created by the dissblution of carbonate rock. •••-..'
slope An inclined part of the earth's surface.
solution cavity A hole, channel or caveTlike cavity formed by dissolution of rock.
stratigraphy The study of rock strata; also refers to the succession of rocks of a particular area.
surficial materials Unconsolidated glacial, wind-, or waterborne deposits occurring on the
earth's surface.
tablelands General term for a broad, elevated region with a nearly level surface of considerable
' extent.
H-25 . Reprinted from USGS Open-File Report 93-292
-------
material that caps ridges and terraces' left "^ by a stream as *
considered as a Physical feature or an ecological
™collsolidated. and unbedded rock and mineral material deposited directly
from day 10 * § ' "*""* ^^ by meltWater- Size °f ^ varies
uraniferous Containing uranium, usually more than 2 ppm.
vendor data Used in this report to refer to indoor radon data coUected and measured bv
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
* C' C0mposition' fraiiness> OT fQim wi* little or
n-26 Reprinted from USGS Open-FUe 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
(4Q4) 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 >s
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..... , .1 10
Illinois.. ,....5"
Indiana .5
Iowa .' ...'......;..7
Kansas '...'....I 7
Kentucky ...4
Louisiana.. .'...6
Maine. 1,
Maryland. ...3
Massachusetts ...1
Michigan..... ...........5
Minnesota -..-. .........:.5
Mississippi ............................4
Missouri I... 7
Montana... < 8
Nebraska...... ..7
Nevada .......9
New Hampshire ..1
New Jersey. 2
New Mexico : 6
New York.... 2,
North Carolinal 4
Nprth Dakota '...8
Ohio.... 5
Oklahoma. 6
Oregon -. 10
Pennsylvania.. .' 3
Rhode Island ....1
South Carolina..*. 4
South Dakota ...8
Tennessee.......' .......4
Texas „ -., 6
Utah........:... , ...8
Vermont 1
Virginia :..; 3^
Washington — 1 ....: 10
West Virginia .....3
Wisconsin.... 5
Wyoming.. 8
n-27 Reprinted from USGS Open-FUe Report 93-292
-------
STATE RADON CONTACTS
May, 1993 '
Alabama James McNees
Division of Radiation Control
Alabama Department of Public Health
State Office Building
Montgomery, AL 36130
(205)242-5315
1-800-582-1866 in state
Alaska Charles Tedford
Department of Health and Social
Services
P.O. Box 110613
Juneau.AK 99811-0613
(907)465-3019
1-800-478-4845 in state
Arizona John Stewart
Arizona Radiation Regulatory Agency
4814 South 40th St.
Phoenix, AZ 85040
(602) 255-4845
LeeGershner
Division of Radiation Control
Department of Health
4815 Markham Street, Slot 30
Little Rock, AR 72205-3867
(501) 661-2301
California J. David Quinton
Department of Health Services
714 P Street, Room 600
Sacramento, CA 94234-7320
(916) 324-2208
1-800-745-7236 in state
Colorado Linda Martin
Department of Health
4210 East llth Avenue
Denver, CO 80220
(303)692-3057
1-800-846-3986 in state
Connecticut Alan J. Siniscalchi
Radon F igram
Connecticut Department of Health
Services
150 Washington Street
Hartford, CT 06106-4474
(203)566-3122
Delaware Marai G. Rejai
Office of Radiation Control
Division of .Public Health
P.O. Box 637
Dover, DE 19903
(302)736-3028
1-800-554-4636 In State
District Robert Davis
of Columbia DC Department of Consumer and
Regulatory Affairs
614HStreetNW
. Room 1014
Washington, DC 20001
(202)727-71068
Florida N. Michael Gffley
Office of Radiation Control
Department of Health and
. Rehabilitative Services
1317 Winewood Boulevard
Tallahassee, FL 32399-0700
(904)488-1525
1-800-543-8279 in state
Richard Schreiber
Georgia Department of Human
Resources
878 Peachtree St., Room 100
Atlanta, GA 30309
(404)894-6644
1-800-745-0037 in state
Hawaii Russell Takata
Environmental Health Services
Division
591 Ala Moana Boulevard
Honolulu, ffl 96813-2498
(808) 586^700
11-28 Reprinted from USGS Open-File Report 93-292
-------
Idaho
Illinois
Indiana
Iowa
Kentucky
PatMcGavarn
Office of Environmental Health
.450 West State Street
Boise, ID 83720
(208)334-6584
1-800-445-8647 in state
Richard Allen
Illinois Department of Nuclear Safety
1301 Outer Park Drive
Springfield, IL 62704
(217)524-5614 , .
1-800-325-1245 in state
Lorand Magyar
Radiological Health Section
Indiana State Department of Health
1330 West Michigan Street
P.O. Box 1964
Indianapolis, IN 46206
(317)633-8563
1-800-272-9723 In State
Donald A. Plater .
Bureau of Radiological Health
Iowa Department of Public Health
Lucas Stale Office Building
Des Moines. IA 50319-0075
(515)281-3478
1-800-383-5992 In State . " •
Harold Spiker
Radiation Control Program
Kansas Department of Health and
Environment
109 SW 9th Street
6th Floor Mills Building
Topeka, KS 66612
(913) 296-1561
JeanaPhelps
Radiation Control Branch
Department of Health Services
Cabinet for Human Resources
275 East Main Street
Frankfort, KY 40601
(502)564-3700
Louisiana Matt Schlenker
Louisiana Department of
Environmental Quality
P.O. Box 82135
Baton Rouge, LA 70884-2135
(504)925-7042
1-800-256-2494 in state
Maine BobStilwell
Division of Health Engineering
Department of Human Services
, State House, Station 10
Augusta, ME 04333
(207)289-5676 ,
1-800-232-0842 in state
Maryland Leon J. Rachuba
Radiological Health Program
, Maryland Department of the
Environment
2500 Broening Highway
Baltimore, MD 21224
(410) 631-3301
1 1-800-872-3666 In State
Massachusetts William J. Bell
Radiation Control Program
Department of Public Health
23 Service Center
Northampton, MA 01060 ,
(413) 586-7525
1-800-445-1255 in state
Michigan Sue Hendershott
Division of Radiological Health
Bureau of Environmental and
Occupational Health
3423 North Logan Street
P.O. Box 30195
Lansing, MI 48909
(517)335-8194
Minnesota LauraOatmann
Indoor Air Quality Unit
925 Delaware Street, SE
P.O. Box 59040
Minneapolis, MN 55459-0040
(612)627-5480
1-800-798-9050 in state
n-29 Reprinted from USGS Open-File Report 93-292
-------
Mississippi Silas Anderson
Division of Radiological Health
Department of Health
3150 Lawson Street
P.O. Box 1700
Jackson, MS 39215-1700
(601) 354-6657
1-800-626-7739 in state
Missouri Kenneth V. Miller
Bureau of Radiological Health
Missouri Department of Health
1730 East Elm
P.O. Box 570
Jefferson City, MO 65102
(314)751-6083
1-800-669-7236 In State
Montana Adrian C. Howe
Occupational Health Bureau
Montana Department of Health and
Environmental Sciences
Cogswell Building A113
Helena, MT 59620
(406)444-3671
Nebraska Joseph Milone
Division of Radiological Health
Nebraska Department of Health
301 Centennial Mall, South
P.O. Box 95007
Lincoln, NE 68509
(402)471-2168
1-800-334-9491 In State
Nevada Stan Marshall
Department of Human Resources
505 East King Street
Room 203
Carson City, NV 89710
(702) 687-5394
New Hampshire David Chase
Bureau of Radiological Health
Division of Public Health Services
Health and WelfareBuilding
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 Fpng
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)731-4014
Michael Pyles
Pennsylvania Department of
Environmental Resources
Bureau of Radiation Protection
P.O. Box 2063
Harrisburg, PA 17120
(717) 783-3594
1-800-23-RADONJji State
David Saldana
Radiological Health Division
G.P.O. Call Box 70184
Rip 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) 7344631
1-800-768-0362
South Dakota MikePochop
Division of Environment Regulation
, Department of Water and Natural
Resources
Joe Foss Building, Room 217
• •' ' 523 E. Capitol
Pierre, SD 57501-3181
(605)773-3351
Tennessee Susie Shimek
Division of Air Pollution Control
Bureau of the Environment
Department of Environment and
Conservation •
Customs House, 701 Broadway
Nashville, TN 37219-5403
(615)532-0733
1-800-232-1139 in state .
Texas Gary Smith
Bureau of Radiation Control
Texas Department of Health
1100 West 49th Street
Austin, TX 78756-3189
(512)834-6688
Utah John Hultquist
Bureau of Radiation Control
Utah State Department of Health
288 North, 1460 West ,
P.O. Box 16690 .
Salt Lake City, UT 84116-0690
(801)536-4250
Vermont PaulQemons
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 H
in New York
(212)2644110
II-31 Reprinted from USGS Open-File Report 93-292
-------
Virginia ShelTy Ottenbrite
Bureau of Radiological Health
Department of Health
109 Governor Street
Richmond, VA 23219
(804) 786-5932
1-800-468-0138 in state
»'
Washington KateColeman
Department of Health
Office of Radiation Protection
Airdustrial Building 5, LE-13
Olympia, WA 98504
(206) 753-4518
1-800-323-9727 In State
West Virginia BeattieL.DeBord
Industrial Hygiene Division
West Virginia Department of Health
151 llth Avenue
South Charleston, WV 25303
(304) 558-3526
1-800-922-1255 In State
Wisconsin Conrad Weiffenbach
Radiation Protection Section
Division of Health
Department of Health and Social
Services
P.O. Box 309
Madison, WI53701-0309
(608) 267-4796
1-800-798-9050 in state
Wyoming Janet Hough
Wyoming Department of Health and
Social Services
Hathway Building, 4th Floor
Cheyenne, WY 82002-0710
(307) 777-6015
1-800-458-5847 in state
11-32 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 Hackbeiry Lane
fuscaloosa, 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)4.
Colorado Geological Survey
1313 Sherman St., Rm 715
Denver, CO 80203
(303)866-2611
* - 9* ' ' . ' •
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)488^191
Georgia 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 Met
P.O. Box 373
Honolulu, ffl 96809
(808) 548-7539
Idaho Earl H. Bennett
Idaho Geological Survey
University of Idaho '
Morrill Hall, Rm. 332
Moscow, ID 83843
(208) 885-7991
Illinois Morris W. Leighton
Illinois State Geological Survey
Natural Resources Building
615 East Peabody Dr.
Champaign, JL 61820
(217)333-4747
Indiana Norman C. Hester /
Indiana Geological Survey
611 North Walnut Grove
Bloomington, IN 47405
(812)855-9350
Donald L Koch
Iowa Department of Natural Resources
Geological Survey Bureau
109 Trowbridge Hall
Iowa City, IA 52242-1319
(319)335-1575
Kansas LeeC.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
Mains 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. Crew
. Minnesota Geological Survey
2642 University Ave.
St. Paul, MN 55114-1057
(612) 627-4780
Mississippi S. Cragin Knox
Mississippi Office of Geology
P.O. Box 20307
Jackson, MS 39289-1307
(601)961-5500
Missouri James H. Williams
Missouri Division of Geology &
Land Survey
111 Fairgrounds Road
P.O. Box 250
Rolla, MO 65401
(314)368-2100
Montana Edward T. Ruppel
Montana Bureau of Mines & Geology
Montana College of Mineral Science
and Technology, Main Hall '
Butte, MT 59701
(406)496^180
Nebraska Perry B. Wigley
Nebraska Conservation & Survey
Division
113 Nebraska Hall
University of Nebraska
Lincoln, ME 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 Dakota
Ohio
Oregon
Pennsylvania
Puerto' Rico
Rhode Island
Charles H. Gardner
North Carolina Geological Survey
P.O. Box 27687
Raleigh, NC 27611-7687
(919)733-3833
John P. Bluemle
North Dakota Geological Survey
600EastBlvd. '
Bismarck, ND 58505-0840
(701)224-4109
Thomas M. Berg
Ohio DepL of Natural Resources
Division of Geological Survey
4383 Fountain Square Drive
Columbus, OH 43224-1362
(614)265-6576
Charles J. Mankin
Oklahoma Geological Survey
Room N-131, Energy Center
lOOE.Boyd
Norman, OK 73019-0628
(405)325-3031
, .- • - "
Donald A. Hull
Dept. of Geology & Mineral Indust.
Suite 965
800 NE Oregon St. #28
Portland, OR 97232-2162
(503)731-4600
Donald M. Hoskins
Dept. of Environmental Resources
Bureau of Topographic & Geologic
Survey
P.O. Box 2357
Harrisburg, PA 17105-2357
(717)787-2169
Ram6n M. Alonso
Puerto Rico Geological Survey
i Division
Box 5887 :
Puerta de Tierra Station
San Juan, P.R. 00906
(809) 722-2526
J. Allan Cain
Department of Geology
University of Rhode Island
315 Green Hall
Kingston, RI 02881
(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
Vermiffion, 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
-
M. Lee Allison
Utah Geological & Mineral Survey
2363 S. Foothill Dr.
Salt Lake City, UT 84109-1491
(801)467-7970
Vermont Diane L. Conrad
Vermont Division of Geology and
Mineral Resources
103 South Main St.
Waterbury.VT 05671
-, (802)244-5164
Virginia Stanley S. Johnson
Virginia Division of Mineral
, Resources
P.O. Box 3667 .
Charlottesville, VA 22903
(804)293-5121
Washington Raymond Lasmanis
Washington Division of Geology &
Earth Resources ,
Department of Natural Resources'
P.O.,Box 47007
Olympia, Washington 98504-7007
(206)902-1450
11-35 Reprinted from USGS Open-Fife Report 93-292
-------
West Virginia Larry 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
H-36
Reprinted from USGS Open-File Report 93-292
-------
EPA REGION 6 GEOLOGIC RADON POTENTIAL SUMMARY
. •- -:-•'•' -.; ' by : '
Linda C.S.Gundersen, James K. Otton, Russell F. Dubiel, and Sandra L. Szarzi
U.S. Geological Survey
''I " . •''.". • ' ' " " :
EPA Region 6 includes the states Arkansas, Louisiana, New Mexico, Oklahoma, and
Texas. For each state, geologic radon potential areas were delineated and ranked on the basis of
geology, soils, housing construction, indoor radon, and other factors. Areas in which the average
screening indoor radon level of all homes within the area is estimated to be greater than 4 pCi/L
were ranked high. Areas in which the average screening indoor radon level of all homes within the
area is estimated to be between 2 and 4 pCi/L were ranked moderate/variable, and areas in which
the average screening indoor radon level of all homes within the area is estimated to be less than
2 pCi/L were ranked low, Information on the data used and on the radon potential ranking scheme
is given in the introduction to this volume. More detailed information on the geology arid radon ;
potential of each state in Region 6 is given in the individual state chapters. The individual chapters
describing the geology and radon potential of the states in Region 6, though much more detailed
than this summary, still are generalized assessments and there is no substitute for having a home
tested. Within any radon potential area homes with indoor radon levels both above and below the
predicted average likely will be found.
Figure 1 shows a generalized map of the physiographic/geologic provinces in Region 6.
The following summary of radon potential in Region 6 is based on these provinces. Figure 2 .
shows average screening indoor radon levels by county calculated from the State/EPA Residential
Radon Survey. Figure 3 shows the geologic radon potential areas in Region 6, combined and
summarized from the individual state chapters, •
ARKANSAS
The geologic radon potential of Arkansas is generally low to moderate. Paleozoic marine
limestones, dolomites, and uraniferous black shales appear to be associated with most of the
indoor radon levels greater than 4 pCi/L in the Stated ;
Ordovician through Mississippian-age sedimentary rocks, including limestone, dolomite,
shale, and sandstone, underlie most of the Springfield and Salem Plateaus. Black shales and
residual soils developed from carbonate rocks in the Springfield and Salem Plateaus are moderate
to locally high in geologic radon potential. The Ordovician limestones, dolomites, black shales,
arid sandstones have moderate (1.5-2.5 ppm) to high (>2.5;ppm) equivalent uranium (eU, from
aeroradioactivity surveys) and some of the highest indoor radon in the State is associated with
them. The Mississippiari limestones and shales, however, have low (<1.5 ppm) equivalent
uranium with very localized areas of high eU, but also have moderate to high levels of indoor
radon associated with them. Black shales and carbonaceous sandstones within the Mississippian,
Devonian, and Ordovician units of the plateaus are the likely cause of the local areas of high eU.
The Chattanooga Shale and shale units within the Mississippian limestones may be responsible for
some of the high indoor radon levels found in Benton County. Limestones are usually low in
radionuclide elements but residual soils developed from limestones may be elevated in uranium and
radium. Karst and cave features are also thought to accumulate radon.
The Boston Mountains, Arkansas Valley, Fourche Mountains, arid Athens Plateau are
underlain predominantly by Mississippian and Pennsylvanian sandstones and shales with low to
m-1 Reprinted from USGS Open-File Report 93-292-F
-------
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moderate radon potential. Although the indoor radon average for these provinces is low, there are
a number of counties in these provinces with screening indoor radon averages slightly higher than
1 pCi/L and maximum readings greater than 4 pCi/L. The marine black shales are probably
uranium-bearing. Further, carbonaceous sandstones of the Upper Atoka Formation and Savanna
Formation have high (>2.5 ppm) eU associated with them. Uranium also occurs in the Jackfork
Sandstone in Montgomery County and in the Atoka Formation in Crawford County. These rocks
are the most likely sources for the indoor radon levels. Radon from a hydrocarbon source in these
rocks should not be ruled out. The presence of radon and uranium in some natural gas, petroleum,
and asphaltite is well known and could contribute radon to indoor air in some locations.
The Central Ouachita Mountains are underlain by intensely-deformed Qrdovician and
Silurian shales and sandstones with minor chert and limestone. These rocks generally have low to
moderate radon potential. Aeroradiometric signatures of 2.5 ppm eU or more are associated with
the Qrdovician black shales and possibly with some syenite intrusions. Indoor radon in the Central
Ouachita Mountains is low to moderate and permeability of the soils is low to moderate.
The West Gulf Coastal Plain is generally low in radon potential. Some of the Cretaceous
and Tertiary sediments have moderate eU (1.5-2.5 ppm). Recent studies in the Coastal Plain of
Texas, Alabama, and New Jersey show that glauconite and phosphate in sandstones, chalks,
marls, and limestones, as well as black organic clays, shales, and muds, are often associated with
high concentrations of uranium and radon in the sediments, and could be sources for elevated
indoor radon levels. Several formations within the Gulf Coastal Plain of Arkansas contain these
types of sediments, especially parts of the upper. Cretaceous and lower Tertiary section, but
average indoor radon levels in this area are not elevated. The Quaternary sediments of the Coastal
Plain have low eU and the indoor radon average is low for the Gulf Coastal Plain overall.
The Mississippi Alluvial Plain and Crowley's Ridge have low to locally moderate radon
potential. The southern half of the Mississippi Alluvial Plain is made up predominantly of
quartzose sediments, Ms generally low eU, and has low indoor radon. The northern half of the
alluvial plain, however, includes the loess of Crowley's Ridge, which appears to have high
equivalent uranium associated with it, and possibly a high loess content in the surrounding
sediments in general. The northeastern corner of Arkansas appears to be crossed by the large belt
of loess that continues into Kentucky and Tennessee and shows as a distinct area of high eU on the
aeroradiometric map of the United States. Some areas of high eU may also be due to uranium in
phosphate-nch fertilizers used in agricultural areas. Several of the counties in the northern part of
the alluvial plain have maximum indoor radon values greater than 4 pCi/L and:indoor radon
averages between-1 and 2 pCi/L, which are generally higher than those in surrounding counties.
LOUISIANA .
The geology of Louisiana is dominated by ancient marine sediments of the Gulf Coastal
Plain and modern river deposits from the Mississippi River and its tributaries. Louisiana is
generally an area of low geologic radon potential. The climate, soil, and lifestyle of the inhabitants
of Louisiana have influenced building construction styles and building ventilation which, in
general, do not allow high concentrations of radon to accumulate. Many homes in Louisiana are
built on piers or are slab-on-grade. Overall indoor radon is low; however, several parishes had
mdividuaniomes with radon levels greater than 4 pCi/L. Parishes with indoor radon levels greater
than 4 pCi/L are found in different parts of the State, in parishes underlain by coastal plain
sediments, terrace deposits, and loess.
ffl-5 . .Reprinted from USGS Open-File Report 93-292-F
''
-------
l ?^ of Louisiana the glauconitic, carbonaceous, and phosphatic sediments
nf ^°°Sic potential to produce radon, particularly the Cretaceous and lower Tertiary-age
f S Zl ?H n T™ 6 n0rthem P0rti°n (°ld Uplands) °f "* State' Soils from clays!7hales,
m^r^±! ^ rT^ ^ lowPeimeabai^ so even though these segments
S^n ? r*^ °i °u' 10W Permeabmty Probably i^bits radon availability. Some of
fte glaucoma: sands and silts with moderate peimeability may be the source of locally high indoor
Se E0±tf h T °f *adi°aCtivity (1'5-2-5 Ppm eU) « associated ^ areas Jderlai'by
SS^ ±3? in61- 01lg0cene-aSe Coastal Plain sediments, but do not follow formation
d^SS T ^ "/ SyStematlC manner' ""* pattem of moderate radioactivity in this area
does appear to follow nver drainages and the aeroradioactivity pattern may be associated with
northwest- and northeast-trending joints and or faults which, in turn, may control drainage
patterns. Part of the pattern of low aeroradioactivity in the'Coastal Plain may be influenced by
*011 ™ ^^ "8 ""* IeCeiveS ^itation
J"8 ""* IeCeiveS ^ P^Pitation and contains an extensive
Duration can also
The youngest Coastal Plain sediments, particularly Oligocene and younger have
anH ,h Tg am°un.t.s °f glauconite and phosphate and become increasingly siliceous (silica-rich)
and thus are less likely to be significant sources of radon., However, Ae possibility of roU-front
uranium deposits in sedimentary rocks and sediments of Oligocene-Miocene age, analogous to the
roll-front uranium deposits in Texas, has been proposed. Anomalous gamma-rU activky has beeL
measured in the lower Catahoula sandstone, butno uranium deposits have yetSSntifiS
otentia]1 Th d-eMC Sediments "*±G Mississippi Alluvial Plain are low in geologic radon
wet conditions of the soils, as well as the high water tables, do ^fTcm^^onav^^ty^ •
£r:yTf^
lorthern portion of the Mississippi floodplain can easily be identified by
on the aeroradioactivity map of Louisiana. Loess is associated with
; throughout the United States. Radiometric anomalies also seem to be
—_ „ —w of loess.in Iberia, Lafayette, eastern Acadia, and northern Vermilion
A in the southeastern part of the Prairies. Loess tends to have low permeability, so even
nmtv i sedimenits mav be a Possible source of high radon, the lack of permeability,
particularly in wet soils, may inhibit radon availability. y>
NEW MEXICO
An overriding factor in the geologic evaluation of New Mexico is the abundance and
widespread outcrops in local areas of known uranium-producing and uranium-bearing rocks in the
su?hea«; r^rin^hT * T^l s«lfcant ™ardum dePosits> occurrences, or reserves, and rocks
such as marine shales or phosphatic limestones that are known to contain low but uniform
concentrations of uranium, all have the potential to contribute to elevated levels of indoor radon In
New Mexico, these rocks include Precambrian granites, pegmatites, and small hydrothermal vein?
the Pennsylvania! and Permian Cutler Formation, Sangre de Cristo Formation and San Andres '
Limestone; the Tnassic Chinle Formation; the Jurassic Morrison Formation and Todilto Limestone
Member (Wanakah Formation); the Cretaceous Dakota Sandstone, Kirdand Shale FruWanT
rormation, and CrevasseCanvon Fnimatinn-thp rv<»ta^»™,o o^^-r™^ /-.- *,.' „ .
oa anstone, rand Shale, Fr
Formation, and Crevasse Canyon Formation; the Cretaceous and Tertiary Ojo Alamo Sandstone;
m-6 Reprinted from USGS Open-File Report 93-292-F
-------
Tertiary Ogallala Formation and Popotosa Formation (Santa Fe Group); Tertiary alkalic intrusive
rocks and rhyolitic and andesitic volcanic rocks such as the Alum Mountain andesite; and the
Quaternary Bandelier Tuff and Valles Rhyolite.
Several areas in New Mexico contain outcrops of one or more of these rock units that may
contribute to elevated radon levels. The southern and western rims of the San Juan Basin expose a
Paleozoic to Tertiary sedimentary section that contains the Jurassic, Cretaceous, and Tertiary
sedimentary rocks having a high radiometric signature and that are known to host uranium deposits
in the Grants uranium district, as well as in the Chuska and Carrizo Mountain$. In north-central
New Mexico, the Jemez Mountains are formed in part by volcanic rocks that include the Bandelier
Tuff and the Valles Rhyolite; this area also has an associated high radiometric signature. In
northeastern New Mexico, Precambrian crystalline rocks and Paleozoic sedimentary rocks of the
southern Rocky Mountains and Tertiary volcanic rocks and Cretaceous sedimentary rocks are
associated with radiometric highs. In southwestern New Mexico, middle Tertiary volcanic rocks
• of the Datil-Mogollon region are also associated with high radiometric signatures. Remaining areas
of the Colorado Plateau, the Basin and Range, and the Great Plains are associated with only
moderate to low radiometric signatures on the aeroradiometric map; these areas generally contain
Paleozoic to Mesozoic sedimentary rocks, scattered Tertiary and Quaternary volcanic rocks, and
locally, Tertiary sedimentary rocks.
The southern extension of the Rocky Mountains and uplifted Paleozoic sedimentary rocks in
central New Mexico; Upper Cretaceous marine shales and uranium-bearing Jurassic fluvial
sandstones of the Grants uranium belt in the northeastern part of the State; and Tertiary volcanic
rocks in the Jemez Mountains, just west of the southern Rocky Mountains, have high radon
potential. Average screening indoor radon levels are greater than 4 pCi/L and aeroradioactivity
signatures are generally greater than 2.5 ppm ell. Rocks such as Precambrian granites and uplifted
Paleozoic strata, Jurassic sandstones and limestones, or Cretaceous to Tertiary shales and volcanic
rocks that are known to contain or produce uranium are the most likely sources of elevated indoor
radon levels in these areas. The remainder of the State has generally moderate radioactivity,
average screening indoor radon levels less than 4 pCi/L, and overall moderate geologic radon
potential. •
OKLAHOMA '
The geology of Oklahoma is dominated by sedimentary rocks and unconsolidated
sediments that vary in age from Cambrian to Holocene. Precambrian and Cambrian igneous rocks
are exposed in the core of the Arbuckle and Wichita Mountains and crop out in about 1 percent of
the State. The western, .northern, and central part of the State is underlain by very gently west-
dipping sedimentary rocks of the northern shelf areas. A series of uplifts and basins flank the
central shelf area. The Gulf Coastal Plain forms the southeastern edge of the State.
Most of the rocks that crop out in the central and eastern part of the State are marine in
origin; they include, limestone, dolomite, shale, sandstone, chert, and coal of Cambrian through
Permian age. Nonmarine rocks of Permian and Tertiary age, including shale, sandstone, and
conglomerate, are present in the western part of the central Oklahoma Hills and Plains area; sand,
clay, gravel, and caliche dominate in the High Plains in the western part of .the State. The Gulf
Coastal Plain is underlain by Cretaceous nonmarine sand and clay and marine limestone and clay.
Some of these units locally are moderately uranium-bearing.
ffl-7 Reprinted from USGS Open-File Report 93-292-F
-------
Surface radioactivity across the State varies from less than 0.5 ppm to 5.0 ppm eU. Higher
levels of equivalent uranium (>2.5 ppm) are consistently associated with black shales in the
southeastern and westernmost Ouachita Mountains, the Arbuckle Mountains, and the Ozark
Plateau; with Permian shale in Roger Mills, Custer, Washita, and Beckham Counties; with granites
and related rocks in the Wichita Mountains; and with Cretaceous shale and associated limestone in
the Coastal Plain. Low eU values (<1.5 ppm) are associated with large areas of dune sand
adjacent to rivers in western Oklahoma; with eolian sands in the High Plains in Cirharron and Ellis
Counties; and with Mississippian and Pennsylvanian rocks in the Ouachita Mountains, the Ozark
Plateau, and the eastern part of the central Oklahoma plains and hills.
Areas of Oklahoma ranked as locally moderate to high are underlain by black, phosphatic
shales and associated limestones in the northeastern part of the State and near the Arbuckle
Mountains; the Upper Permian Rush Springs Formation in Caddo County; and granites, rhyolites,
and related dikes in the Wichita Mountains in the southwestern part of the State. Areas ranked as '
generally low are underlain by Paleozoic marine sedimentary rocks in central and northwestern
Oklahoma and by Tertiary continental sedimentary rocks on the High Plains.
Well-drained alluvial terraces along some rivers (for example, along the Arkansas River
west of Tulsa); steep, thin, sandy to gravelly soils developed on sandstone on river bluffs (for
example, bluffs in the southeastern suburbs of Tulsa); and clayey loams on uraniferous shales (in
the northeastern corner of the State) are responsible for a significant percentage of elevated indoor
radon levels in those areas. Thus, in addition to soils derived from rocks with elevated uranium
content, soils in selected parts of counties where river terraces and sandstone bluffs occur'might
also have elevated radon potential.
Soil moisture may have an additional effect on radon potential across the State. Indoor
radon values tend to be higher west of Oklahoma City where rainfall is less than 32 inches pet year'
and lowest in the southeastern corner of the State, where rainfall ranges from 32 to 64 inches per
year. Indoor radon values in northeastern Oklahoma, where rainfall is also high, include many
readings greater than 4 pCi/L, but the effects of uraniferous black shales and weathered limestone
soils on indoor radon may increase the levels overall and counter the effects of regional variation in
soil moisture. High permeability, dry soils, and moderate uranium content may be responsible for
elevated indoor radon readings in Beaver County.
TEXAS
The geologic radon potential of Texas is relatively low to moderate overall. The relatively
mild climate throughout much of the State, especially in the most populous areas, and the
predominance of slab-on-grade housing seems to have influenced the overall potential. Significant
percentages of houses with radon levels exceeding 4 pCi/L are restricted primarily to the High
Plains and the Western Mountains and Basins provinces. However, no physiographic province in
Texas is completely free from indoor radon levels greater than 4 pCi/L.
Elevated indoor radon can be expected in several geologic settings in Texas. Granites and
metamorphic rocks in central Texas, Tertiary silicic volcanic and tuffaceous sedimentary rocks in
western Texas, dark marine shales in east-central Texas and the Big Bend area, sand and caliche
associated with the Ogallala Formation and overlying units in the High Plains of Texas, sediments
of Late Cretaceous age along the eastern edge of central Texas, and residual soils and alluvium
derived from these units are likely to have significant percentages of homes over 4 pCi/L. Except
for the High Plains and the Western Mountains and Basins Provinces, these rocks generally make
m-8 Reprinted from USGS Open-File Report 93-292-F
-------
up only a relatively small percentage of the surface area of the various physiographic provinces.
However, the outcrop belt of Upper Cretaceous sedimentary rocks of the East Texas Province
passes near some substantial population centers. Extreme indoor radon levels (greater than 100
pQ/L) may be expected where structures are inadvertently sited on uranium occurrences. This is
more likely to occur in more populated areas along the outcrop belt of the Ogallala Formation at the
edge of the Llano Estacada in the northern and central parts of the High Plains and Plateaus
Province. In this outcrop area, sedimentary rocks with more than 10 ppm uranium, are relatively
common.
The northern part of the High Plains and Plateau Province has moderate radon potential.
Uranium occurrences, uranium-bearing calcrete and silcrete, and uranium-bearing lacustrine rocks
along the outcrop belt of the Ogallala Formation and in small upper Tertiary lacustrine basins
within the northern High Plains may locally cause very high indoor radon levels. Indoor radon
data are elevated in many counties in this area. Equivalent uranium values in this area range from
1.0 to 4.0 ppm. An arda of elevated elJ along the Rio Grande River is included in this radon
potential province; The southern part of the High Plains and Plateaus Province has low radon
potential overall as suggested by generally low elJ .values and low indoor radon. This area is
sparsely populated and existing indoor radon measurements may not adequately reflect the geologic
radon potential. An area of low eU covered by the sandy fades of the Blackwater Draw
Formation in the northeastern comer of the Western Mountains and Basins Province is included in
this radon potential area. Some parts of this province that may have locally elevated indoor radon
levels include areas of thin soils over limestone and dolomite in the Edwards Plateau of the
southern part of this province, and areas of carbonaceous sediments in the southeastern part of this
province.
The Western Mountains and Basins Province has moderate indoor radon potential overall.
Although average indoor radon levels are mixed (low in El Paso County, but high in three southern
counties), areas of elevated eU are widespread. Uranium-bearing Precambrian rocks, silicic
volcanic rocks, and alluvium derived from them may locally cause average indoor, radon levels in
some communities to exceed 4 pCi/L. Some indoor radon levels exceeding 20 pCi/L may also be
expected. Exceptionally dry soils in this province may tend to lower radon potential. In very dry
soils, the emanating fraction of radon from mineral matter is lowered somewhat .
The Central Texas Province has low radon potential overall; however, areas along the
outcrop belt of the Woodbine and Eagle Ford Formations and the Austin Chalk along the east edge
of this province, and areas of Precambrian metamorphic and undifferentiated igneous rocks in the
Llano Uplift in the southern part of this province have moderate geologic radon potential.
Structures sited on uranium occurrences in the-Triassic Dockurh Group in the western part of this
province may locally have very high indoor radon levels. • .
The East Texas Province has low radon potential overall. Soil moisture levels are typically
high; soil permeability is typically low to moderate; and eU levels are low to moderate. A few
areas of well-drained soils and elevated eU may be associated with local areas of moderately
elevated indoor radon levels.
The South Texas Plain has low radon potential due to generally low eU and low to
moderate soil permeability. Some structures sited on soils with slightly elevated uranium contents
in this province may locally have elevated indoor radon levels, but such soils are generally also
clay rich and this may mitigate radon movement The Texas Coastal Plain has low radon potential.
Low aeroradioactivity, low to moderate soil permeability, and locally high water tables contribute-.,
to the low radon potential of the region.
m-9 Reprinted .from USQS Open-File Report 93-292-F
-------
-------
PRELIMINARY GEOLOGIC RADON POTENTIAL ASSESSMENT OF NEW MEXICO
'•" ", . • ., by " ' ' '. "•'
Russell F.Dubiel
U.S. Geological Survey
INTRODUCTION
Several areas of New Mexico have the potential to generate and transport radon in sufficient
concentrations to be of concern in indoor air, because radon is a radioactive decay product of
uranium, and because the uranium- and radium-bearing bedrock and the soils and alluvium derived
from those rocks are locally abundant in the State. Uranium deposits in. New Mexico occur in
numerous rock units of varying age and lithology, and New Mexico has ranked first in domestic
uranium production since 1956 (McLemore, 1983; McLemore and Chenoweth, 1989). In addition
to uranium-bearing bedrock, other factors such as shears and fractures iii bedrock, soil
permeability, and the nature and occurrence of groundwater and geothermal areas have the, potential
to affect the generation of radon in local areas.
This is a generalized assessment of geologic radon potential of rocks, soils, and surficial
deposits of New Mexico, 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. My localized assessment of radon potential must be supplemented with additional
data and information from the locality. Within any area of a given radon potential ranking, there
are likely to be areas with higher or lower radon levels than characterized for the area as a whole.
Indoor radon levels, both high and low, can .be quite localized, and there is no substitute for testing
individual homes. Elevated levels of indoor radon have been found in every state, and EPA
recommends that all homes be tested. For more information on radon, the reader is urged to
consult the local or State radon program pr 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
Four major physiographic provinces (fig. 1 A) extend into New Mexico: the Southern
Rocky Mountains, the Colorado Plateau, the Basin and Range, and the Great. Plains (Mallory,
1972). The Southern Rocky Mountains extend only into the north-central part of New Mexico,
Whereas the Colorado Plateau covers the northwestern quarter of the State. The Basin and Range
accounts for one third in-southwestern and central New Mexico, and the Great Plains cover about
the eastern third of the'State.
Each of the major physiographic provinces in New Mexico can be subdivided into several
smaller sections and subsections (fig. IB; Hawley, 1986). The Southern Rocky Mountains extend
south from Colorado into the north-central part of New Mexico. The province consists of two
north-south trending ranges separated by the San Luis Valley, a deep structural basin of the
northern part of the Rio Grande rift. The valley grades southward into the Espanola Valley of the
Basin and Range Province. Numerous glaciated peaks and valleys are present in the mountain
ranges, including Wheeler Peak, which at 13,161 ft is the highest point in New Mexico.
IV-1 . Reprinted from USGS Open-File Report 93-292-F
-------
Figure 1 A. Major physiographic provinces of the western United States (modified from Mallory,
1 y / £tjt . '
-------
^^^p^:^f^i.,/|
4r~/ >: •;'*.•"> !')\V^;'*~.' > -v>4^V^f "•» ft
%&&:•• ' t ^> '/:y'-^^--. > • /> s-"ist&\ \? .'»?•
Itf.Jff-: v-f>4~*\- ., --^ R.' • /Ji^: fe Sr * ^5=
A - Southern Rocky Mountain Province
B -^Colorado Plateau Province
Bl-Navajo Section . '
B2 - Acoma-Zuni Section
C - Datil-Mogbllon Section
D - Basin and Range Province
Dl - Mexican Highland Section
D2 - Sacramento Section •
E - Great Plains Province
El - Raton Section ,
E2 - Pecos Valley Section
E3 - High Plains
Figure IB. Physiographic provinces in New Mexico (modified from Hawley, 1986).
-------
The Col°ra4o Plateau, a roughly circular area centered about the Four Corners region of
Utah, Colorado,, Arizona, and New Mexico, covers about the northwestern quarter of New
Mexico. The Colorado Plateau consists of highly dissected plateaus and mesas ranging in
elevation from about 5,000 ft to over 11,000 ft. The summit of Mount Taylor at 11,301 ft is the
highest point on the Colorado Plateau in New Mexico. The Navajo section of the Colorado Plateau
is dominated by two large structural basins: the San Juan Basin and the GaUup-Zuni basin The
Acoma-Zuni section of the Colorado Plateau, a newly defined physiographic unit (Hawley, 1986),
is characterized by volcanic rocks and basalt flows and is dominated by Mount Taylor an ancient'
volcano. , •
The Basin and Range Province covers about one third of southwestern and central New
Mexico and is characterized by block-faulted, generally north-south trending mountain ranges and
flat-floored basins. The Basin and Range includes several subsections. The Datil-MogoUon
section, a newly defined physiographic subdivision that is transitional between the Basin and
Range and the Colorado Plateau, includes structural basins and block-faulted mountain ranges
along with large volcanic calderas and volcanoes. The Mexican Highland section in the western
part of the Basin and Range Province of New Mexico includes two large areas of Basin and Range
structures and the broad valley of the Rio Grande. The Sacramento section in the eastern part
contains high mesas and rolling plains interspersed with broad basins.
The Great Plains Province in the eastern third of New Mexico includes parts of three
sections: the Raton, Pecos Valley, and High Plains sections. The Raton section is characterized
by high piedmont plains, basalt flows, and deep canyons eroded by the Canadian and Cimarron
Rivers. The Pecos Valley section includes piedmont plains and the valleys of the Canadian and
Pecos Rivers. The High Plains section occurs as three separate areas extending west into New
Mexico from the Panhandle region of Texas and Oklahoma. The High Plains are characterized by
a flat to undulating surface with elevations ranging from about 3,500 ft to 5,000 ft.
Population density and distribution (fig. 2A, B) and land use in New Mexico reflect the
geology, topography, climate, and early exploration and settlement in the State. New Mexico is a
sparsely populated state, having a statewide population density of slightly over 10 persons per
square mile (fig. 2A; Williams, 1986) with much of the population concentrated in a few urban
areas and along rivers and groundwater sources or major transportation routes (fig. 2B). Minor
concentrations of people are localized by proximity to recent economic development related to '
energy and mineral resources.
Major industries in New Mexico include grazing, agriculture, manufacturing, forestry;
military installations, mining, and recreation. Ranchland is the most widespread land use in the
State. Agricultural activities include irrigated and non-irrigated cropland and rangeland. Military
installations provide a small and local contribution to the State's economy. Manufacturing is
restricted to small urban areas, and forestry is locally concentrated in mountainous regions
Mineral and energy resource production have a diverse history in New Mexico, and they are
significant industries in the State. New Mexico has been a leading producer of uranium, potash
and perlite in the United States and is a major producer of many other base and precious metals '
Recreation is a major industry in New Mexico and is shared by both winter activities at ski areas
and by summer recreation and tourism.
IV-4 Reprinted from USGS Open-File Report 93-292-F
-------
0 to 10000
0 10001 to 25000
E2 25001 to 50000
H 50001 to 100000
• 100001 to 480577
Figure 2A. Population of counties in New Mexico (1990 U.S. Census data).
-------
I I Less than 5 people/square mile
| , j 5-20 people/square mile
21-100 people/square mile
Greater than 100 people/square mile
Figure 2B. Map showing population distribution in New Mexico in 1986 (modified from
Williams, 1986).
-------
GEOLOGY
New Mexico's geology is complex and a wide variety of bedrock geology (fig 3} is
exposed m each of the major physiographic provinces. The following discuS otle ^eologv of
New Mexico is condensed from Dane and Bachman (1965), Mallory (1972) I^w Mexico
Geological Sodety (1982), and- Kues and Callender (1986). AdetSedgeo ogicm^TfNew
Mexico is presented by Dane and Bachman (1965); the reader is urged t [«JdtS
-------
EXPLANATION
(Surface Geology)
Precambrian igneous and I 1 Cenozoic sedimentary rocks •
metamorphic rocks '
Late Tertiary-Quaternary
volcanic rocks .
Paleozoic sedimentary rocks
Mesozofe sedimentary rocks
Cretaceous through mid-Tertiary
volcanic and volcaniclaslto rocks
Figure 3. Map showing generalized geology of New Mexico (modified from Kues and Calender,
1986).
-------
the Chama BasinLr Sfin^S? > Lower0Cretaceo^ Burro Canyon Formation in
IV-9 Reprinted from USGS Open-File Report 93-292-F
-------
O 10 20 3O 4O SO
I I I I I
MILES
EXPLANATION
Uranium deposit
X Uranium occurrence
Note: A single symbol may include more than
one deposit and/or occurrence
Figure 4A. Map showing uranium deposits and occurrences in New Mexico (modified from
Chenoweth, 1976).
-------
109*
108-
107*
105*
104*
IO3*
- "Sonta Roto
A 6 A LU P'E , ' .
l 1 !
.-. ,
| 1 j |t-0« Lgnci |
I V A L E N C I A ! E'1"000 !
l G R_A « ,fr. (
> . H—: ^^ .. ' ^
Areas containing economic reserves'and
reasonably assured resources '
Areas containing undiscovered or
potential resources
Areas that may contain speculative
resources
Figure 4B. Map showing areas of uranium resources and resource potential''in New Mexico
(modified from McLemore and Chenoweth, 1989).
-------
Additional significant uranium deposits in New Mexico occur in rocks other than
sandstone. Important uranium deposits occur in limestones of the Middle Jurassic Tbdilto
Limestone Member of the Wanakah Formation in the Grants uranium district along the southern
San Juan Basin, and minor uranium occurrences are known from the Permian Yates, Seven
Rivers, and Queen Formations in Eddy County near Carlsbad. Significant uranium has been
produced from vein-type deposits within the conglomerates of the Santa Fe Group and
Precambrian granite in the Ladron Mountains, and other minor vein-type occurrences are along the
Rio Grande valley in Socorro and Sierra Counties and at the La Bajada deposit in the Oligocene
Espinaso Volcanics. Mineralized collapse-breccia pipes constitute minor uranium occurrences in
the southern San Juan Basin and in the Black Mesa area. . ' .
Igneous and metamorphic rocks are known to contain small and scattered uranium deposits
or occurrences in New Mexico (McLemore and Chenoweth, 1989). Many.scattered localities
contain small uraniferous epithermal veins, but they are .generally thin and discontinuous or have
sporadically distributed uranium minerals. Minor uranium ore and small uranium occurrences have
been noted as disseminated uranium minerals from igneous and metamorphic rocks, including
pegmatites, alkalic rocks, granites, carbonatite dikes, diatremes, volcanogenic strata, and contact
metamorphosed rocks. Uranium is locally found in volcanogenic deposits near Tertiary calderas,
such as in Socorro and Sierra Counties. '
Groundwater in northeastern and east-central New Mexico may contain uranium
(McLemore and Chenoweth, 1989) and thus may contribute to elevated levels of indoor radon
when the radon dissolved in the water degasses into the indoor air. Anomalous concentrations of
uranium in groundwater occur north of the outcrop of the Morrison Formation in southern Union
County and eastern Harding County (McLemore and North, 1985). The Miocene Ogallala
Formation in southeastern New Mexico may contain small surficial uranium deposits in calcrete
and may contribute to anomalous uranium in groundwater where the Ogallala serves as an aquifer.
SOILS
A generalized soil map of New Mexico (fig. 5) compiled from Maker and Daugherty
(1986) shows that the southern half of New Mexico is dominated by Aridisols, and to a lesser
extent by Mollisols. with minor areas of Alfisols, Entisols, and small areas of gypsum sands and
basaltic lavas. In the northern half of New Mexico, the northwestern quarter of the State is
dominated by Entisols. The remaining part contains primarily Aridisols and Mollisols, with minor
regions of Alfisols and basaltic lavas. Data on soil permeability and clay content was not readily
available at the scale of the map used in figure 5, and for the purposes of estimating the radon
potential of areas in the State later in this report, each area was considered to have moderate soil
permeability. County and district soil surveys (U.S. Soil Conservation Service and U.S. Forest
Service) are available for most of the State. They should be consulted for more detailed
information on soil texture, structure, permeability, and seasonal moisture content for specific
localities.
IV-12 Reprinted from USGS Open-File Report 93-292-F
-------
Other Materials
S I Gypsum Sands
• Lava Rocklands
Soil Orders
[ [ Aridisote ' [^ AHisds
•FT] Entisols |^ Mpllisols
Efjj Inceplisols
0 1C 20 80 40 SO Miles
Figure 5. Map showing generalized soils of New Mexico (modified slightly from Maker and
Daugherty, 1986). < .
-------
INDOOR RADON DATA
Screening indoor radon data for New Mexico from the State/EPA Residential Radon
Survey (fig. 6, Table 1) was collected during the winter of 1988-89. Data is shown in figure 6
only for those counties in which five or more measurements were made. A map showing the
counties in New Mexico (fig. 7) is provided to facilitate discussion of correlations among indoor
radon data (fig. 6), geology (fig. 3), aerial radiometric data (fig. 8), and soils (fig. 5) In this
discussion, "elevated" indoor radon levels refers to average indoor radon levels greater than 4 0
pU/L. Seven counties—Colfax, McKinley, Mora, San Miguel, Sandoval, Santa Fe, and Taos—
had screening indoor radon averages greater than 4 pCi/L. The other counties had screening
indoor radon averages less than 4 pCi/L. Eighteen counties throughout the State (fig 6 Table 1)
had screening indoor radon averages between 2 and 4 PCi^, and the remaining 8 counties had
indoor radon averages less than 2 pCi/L (fig. 6; Table 1).
Elevated indoor radon levels appear to correlate with the geology and physiography of
several areas. Counties with the highest indoor radon averages coincide with outcrops of Jurassic
to Cretaceous fluvial sandstones and marine shales along the western and southern margins of the
San JuanBasin in northwestern New Mexico; with the Tertiary and Quaternary volcanic rocks of
the Jemez Mountains in north-central New Mexico; and with Precambrian gneiss, Cretaceous and
Tertiary marine shale, and Tertiary and Quaternary volcanic and intrusive rocks in northeastern
New Mexico. Each of these areas has a corresponding high radiometric signature on the aerial
radiometnc map (fig. 8).
GEOLOGIC RADON POTENTIAL
ft- a A Comparis°n °f Seol°gy (% 3) with aerial radiometric data (fig. 8) and indoor radon data
(fig. 6) provides preliminary indications of rock types and geologic features suspected of
producing elevated indoor radon levels. This evaluation parallels the study of radon availability in
New Mexico by McLemore and Hawley (1988), but the present study identifies areas based on
geologic terrenes and does not identify specific counties with potential radon availability as ihey
did. As pointed out by McLemore and Hawley (1988), counties in New Mexico are very large
and major geologic features cut across county boundaries, thus creating problems in ranking '
counties for radon availability. They also point out that New Mexico's population is sparse and is
concentrated in cities and towns. This population distribution must also be considered in
evaluating the indoor radon data (fig. 6), which are grouped by county.
An overriding factor in the geologic evaluation is the abundance and widespread outcrops
in local areas of known uranium-producing and uranium-bearing rocks in the State (fig 3;
McLemore, 1983). Rocks known to contain significant uranium deposits, occurrences or
reserves (McLemore, 1983,1988; McLemore and Chenoweth, 1989), and rocks such a's marine
shales or phosphatic limestones that are known to typically contain low but uniform concentrations
of uranium, all have the potential to contribute to elevated levels of indoor radon. In New Mexico
these rocks include Precambrian granites, pegmatites, and small hydrothermal veins- the
Pennsylvsanian and Permian Cutler Formation, Sangre de Cristo Formation, and San Andres
Limestone; the Triassic Chinle Formation; the Jurassic Morrison Formation and Todilto Limestone
Member (Wanakah Formation); the Cretaceous Dakota Sandstone, Kirtland Shale Fruitland
Formation, and Crevasse Canyon Formation; the Cretaceous and Tertiary Ojo Alamo Sandstone-
Tertiary Ogallala Formation and Popotosa Formation (Santa Fe Group); Tertiary alkalic intrusives
IV-14 Reprinted from USGS Open-File Report 93-292-F
-------
Bsmt. & 1st Floor Rn
%>4pCi/L
9-'"*'•'*"'"•<• OtolO
10 l\\\\l 11 to 20
8 »^^ 21 to 40
6 I^Hi 41 to 60
0 I 61 to 80
100 Miles
Bsmt. & 1st Floor Rn,
Average Concentration (pCi/L)'
8
0.0 to 1.9
2.0 to 4.0
4.1 to 6.3
100 Miles
Figure 6. Screening indoor radon data from the EPA/State Residential Radon Survey of New
Mexico, 1988-89, for counties with 5 or more measurements. Data are from 2-7 day charcoal
canister tests. Histogramsin map legends show the number of counties in each category. The
number of samples in each county (See Table 1) may not be sufficient to statistically characterize
the radon levels of the counties, but they do suggest general trends. Unequal category intervals
were chosen to provide reference to decision and action levels.
-------
TABLE 1. Screening indoor radon data from the EPA/State Residential Radon Survey of
New Mexico conducted during 1988-89. Data represent 2-7 day charcoal canister measurements
from the lowest level of each home tested.
COUNTY
BERNALELLO
CATRON
CHAVES
CIBOLA
COLFAX
CURRY
DE BACA
DONA ANA
EDDY
GRANT
GUADALUPE
HARDING
HIDALGO
LEA
LINCOLN
LOS ALAMOS
LUNA
MCKJNLEY
MORA
OTERO
QUAY
RIO ARRIBA
ROOSEVELT
SAN JUAN
SAN MIGUEL
SANDOVAL
SANTA FE
SIERRA
SOCORRO
TAOS
TORRANCE
UNION-
VALENCIA
NO. OF
MEAS.
406
16
52
6
91
47
12
86
51
60
8
12
18
50
18
42
49
53
17
46
10
72
44
196
78
76
73
41
41
47
10
32
25
MEAN
3.7
1.4
2.7
2.3
6.0
2.6
1.3
1.8
2.0
2.1
1.3
1.9
3.7
1.6
2.6
3.0
3.8
6.0
4.6
2.7
3.2
3.4
2.2
2.4
4.9
4.6
4.6
1.3
2.5
6.3
3.9
3.4
1.9
GEOM.
MEAN
2.7
1.0
2.2
1.8
3.8
1.9
1.1
1.4
1.2
1.3
1.0
1.2
2.8
1.1
1.9
2.4
2.5
2.8
3.5
1.6
2.7
2.3
1.7
2.0
3.1
2.3
3.2
1.0
1.9
3.8
2.4
2.5
1.8
MEDIAN
• 2.6
1.0
2.3
2.3
3.9
2.1
1.0
1.3
1.3
1.5
1.1
1.1
3.4
1.1
1.7
2.7
2.4
3.2
3.9
1.9
2.6
2.2
1.7
1.9
3.2
2.0
3.5
1.0
2.0
4.7
2.8
2.1
1.7
STD.
DEV.
3.5
1.2
1.7
1.5
11.5
2.1
1.0
1.4
1.9
2.1
0.8
1.9
2.8
1.4
2.5
2.2
4.6
13.0
3.2
3.4
1.8
4.0
1.7
2.2
5.9
10.2
3.8
0.9
1.7
6.6
3.6
3.1
0.8
MAXIMUM
27.0
4.2
6.6
4.7
105.4
11.3
4.2
9.0
7.5
13.4
2.7
6.9
12.5
7.6
10.1
13.0
27.7
87.3
11.5
21.6
6.0
24.7
7.4
24.8
36.2
76.7
21.6
3.9
7.2
31.4
9.4
15.1
3.6
%>4pCi/L
.28
6
17
17
' 49
13
8
7
16
10
0
8
39
6
11
24
22
34
41
17
30
21
11
11
45
20
41
0
17
57
50
31
0
%>20pCi/L
1
0
0
0
3
0
0
0
0
0
0
0
0
. 0
0
0
2
6
0
2
0
1
0
1
4
3
1
0
0
4
0'
0
0
-------
Figure 7. Map showing counties in New Mexico.
-------
Figure 8. Aerial radiometric map of New Mexico (after Duval and others, 1989). Contour lines at
1.5 and 2.5 ppm equivalent uranium (eU). Pixels shaded from 0 to 6.0 ppm eU at 0.5 ppm eU
increments; darker pixels have lower elJ values; white indicates no data.
-------
and rhyolitit and andesitic volcanic rocks such as the Alum Mountain andesite; and the Quaternary
Bandelier Tuff and Valles Rhyolite. i sv
Several areas in New Mexico contain outcrops of one or more of these rock units (fig. 4)
that may contribute to elevated radon levels. The southern and western rims of the San Juan Basin
expose a Paleozoic to Tertiary sedimentary section that contains the Jurassic, Cretaceous, and
Tertiary sedimentary rocks that have a high radiometric signature (fig. 8) and that are known to
host uranium deposits in the Grants uranium district, as well as in the Chuska and Carrizo
Mountains. In north-central New Mexico, the Jerriez Mountains are formed in part by volcanic
rocks that include the Bandelier Tuff and the Valles Rhyolite; this area also has an associated high
radiometric signature. In northeastern New Mexico, Precambrian crystalline rocks and Paleozoic
sedimentary rocks of the southern Rocky Mountains and Tertiary volcanic rocks and Cretaceous
sedimentary rocks are associated with radiometric highs. In southwestern New Mexico, middle
Tertiary volcanic rocks of the Datil-Mogollon region are also associated with high radiometric
signatures. Remaining areas of the Colorado Plateau, the Basin and Range, and the Great Plains
are associated with only moderate to low radiometric signatures oh the aerial radiometric map; these
areas generally contain Paleozoic to Mesozoic sedimentary rocks, scattered Tertiary and Quaternary
volcanic rocks, and locally Tertiary sedimentary rocks.
SUMMARY
- For purposes of assessing the geologic radon potential of the State, New Mexico can be ,
divided into 10 general areas (termed Area 1 through Area 10; fig. 9 and Table 2) and scored with a
Radon Index (El), a semi-quantitative measure of radon potential, and an associated Confidence
Index (CI), a measure of the relative confidence of the assessment based on the quality and
quantity of data used to make the evaluations. For further details on the ranking schemes and the
factors used in the evaluations, refer to the Introduction chapter to this regional booklet. Note that
in any specified area, smaller areas of either higher or lower radon potential than that assigned to
the entire area may exist because of local factors influencing the generation and transport of radon.
Areas 1,2, and 3 each have high radon potential (RI=12) associated with a, high confidence
index (CI=10) on the basis of high indoor radon measurements, high surface radioactivity as
evidenced by the aerial radiometric data, and the presence of rocks such as Precambrian granites
and uplifted Paleozoic strata, Jurassic sandstones and limestones, or Cretaceous to Tertiary shales
and volcanic rocks that are known to contain or produce uranium. Area 1 includes the southern
extension of the-Rocky Mountains and uplifted Paleozoic sedimentary rocks; Area 2 includes
Upper Cretaceous marine shales and uranium-bearing Jurassic fluvial sandstones of the Grants
. uranium belt; and Area 3 includes Tertiary volcanic rocks in the Jemez Mountains. Areas 4
through 10 each have moderate or variable geologic radon potential (RI=11 to 9) associated with a
moderate confidence index (CI=9). These areas exhibit moderate indoor radon measurements,
have moderate surface radioactivity, and contain rocks that are known to contain minor amounts of ;
uranium or scattered uranium anomalies and occurrences. Area 4 includes Tertiary volcanic rocks
of the Datil-Mogbllon volcanic field. Area 5 is an eastward extension of the Basin and Range
Province. Area 6 contains extensive outcrops of Late Paleozoic marine limestones. Area 7
includes three parts of New Mexico that have variable geology but that are primarily underlain by
Cretaceous marine rocks. Area 8 encompasses Tertiary volcanic and Cretaceous sedimentary
rocks. Area 9 is predominantly underlain by sedimentary rocks of the Tertiary Ogallala Formation.
Area 10 is underlain primarily by Triassic and Quaternary deposits. '
TV-19 . Reprinted from USGS Open-File Report 93-292-F
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Figure 9. Map showing radon potential areas in New Mexico.
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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 that 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.
riumbers for these agencies are listed in chapter 1 of this booklet. -
IV-21 Reprinted fromUSGS Open-File Report 93-292-F
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TABLE 2. Radon Index (RI) and Confidence Index (CI) scores for geologic radon potential areas
of New Mexico. See figure 9 for locations of areas.
FACTOR
INDOOR RADON
RADIOACTIVITY
GEOLOGY
SOIL PERM.
ARCHITECTURE
GFE POINTS
TOTAL
RANKING
Area
RI
3
3
3
2
1
0
HIGH
1
CI
3
3
3
1
10
HIGH
Area 2
RI CI
3
3
' 3
2
1
0
12
HIGH
3
3
3
1
10
HIGH
Area
RI
3>
3
3
2
. 1
0
12
HIGH
3
CI
3
3
3
.1
10
HIGH •
Area 4
RI CI
2
3
3
. 2
1
0
11
MOD
3
3
2
1
9
MOD
FACTOR
INDOOR RADON
RADIOACTIVITY
GEOLOGY
SOIL PERM.
ARCHITECTURE
GFE POINTS
TOTAL
RANKING
FACTOR
INDOOR RADON
RADIOACTIVITY
GEOLOGY
SOIL PERM.
ARCHITECTURE
GFE POINTS
TOTAL
RANKING
Area 5
RI CI
2
3'
3
2
1
0
11
3
3
2
1
9
MOD MOD '
Area 9
RI CI
2
2
2
2
1
0
9
MOD
3
3
2
1
9
MOD
Area 6
RI CI
2
2
3
2
1
0
10
3
3
2
1
9
MOD MOD
Area 10
RI CI
3
1
2
2
1
0
9
MOD
3
3 .
2
1
9
MOD
Area?
RI CI
3
2
2
2
1
0
10
MOD
3
3
2
1
9
MOD
AreaS
RI CI
2
3
2
2
1
0
10
MOD
3
3
2
1
9
MOD
RADON INDEX SCORING:
Radon potential category
LOW
MODERATE/VARIABLE
HIGH
Point range
3-8 points
9-11 points
> 11 points
Probable screening indoor
radon average for area
^- o r*n; n
pCi/L
2-4pCi/L
> 4 pCi/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-F
-------
.
Programs, v. 21 p AL4< ™eiacoarea' Geol°8'cal Society of America, Abaracts with
of ^w Mexico: U.
um^pof
. U.S. Geological Survey Open-File Report 89-478 10 p
p. 7553-7556. ^"^sicai Kesearch, C. Oceans and Atmospheres, v. 85,
Fleischer, R.L., Hart, H.R., Jr. and Mogro-eamoero A IQSn p A •
orebody; search for long-iistanStn^^er ] 1980' Radon e™MaBon over an
mineral technolo of r B tma"' CA" ed- ^'W and
^
^^
IV-23 Reprinted from IJSGS Open-File Report 93-292-F
-------
Hans, J.M Jr Horton, T.R. and Prochaska, D., 1978, Estimated average annual radon-222
concentrator around the former uranium mill site in Shiprock, New Meriwti S
' Mto of Radiaaon ^ '
Hawley J W., 1986, Physiographic provinces, m WUliams, J.L., ed., New Mexico in mans-
Albuquerque, University of New Mexico Press, p. 23-27. P
- Mexico: U.S. Geological Survey
£5 mT-'nO56' N°rthWeSt NeW Mexi- U.S. Geological Survey Report
n5 K°ng> EJ'C "^ Lln' LRH" 1987' Radon emissions during mill tailings backfill
opoations m a uramum mine: Environmental Geology and Water Sciences vio! P S
trli?11611^1' JVF" 1986' Ge0l°gic hist°ry' in Williams, J.L., ed., New Mexico in
maps: Albuquerque, University of New Mexico Press, p. 2-4;
P — ISGE ^sactions and
Ss^ -' ^ Mexico in maps:'
McLemore V.T., 1983, Uranium and thorium occurrences in New Mexico: Distribution -
geology^production, and resources, with selected bibliography: New Mexico bureau of
Mines and Mineral Resources, Open-file Report OF-183, 180 p.
McLemore V.T \,and Chenoweth, W.L., 1989, Uranium resources in New Mexico- New
' ' ' n
345, 31 p.
xico Nx ft raon ava
Mexico. New Mexico Bureau of Mines and Mineral Resources,Open-File Report
IV-24 Reprinted from USGS Open-File Report 93-292-F
-------
McLemore, V.T., and North, R.M., 1985, Copper and uranium mineralization in east-central New
Mexico, in Lucas, ed., Santa Rosa-Tucumcari region: New Mexico Geological Society,
36th Annual Field Conference Guidebook, p. 289-299.
New Mexico Geological Society, 1982, New Mexico highway geologic map: Albuquerque, New
Mexico, New Mexico Geological Society, scale 1:1,000,000.
" Pierce, A.P., 1954, Radon and helium studies: U.S. Geological Survey Report TEI-490,
. p. 274-276. • . , ';.
Pierce, A.P., 1956, Radon and helium studies: U.S. Geological Survey Report TEI-620,
p. 305-309.
. Rautman, C.A:, compiler, 1980, Geology and mineral technology of the Grants uranium region,
1979: New Mexico Bureau of Mines and Mineral Resources, Memoir 38,400 p.
Rogers, A.S., 1955, Physical behavior of radon: U.S. Geological Survey Report TEI-590,
p. 337-343.
- " • - v
Rust, W.D., 1969, Radon concentration in a mountain canyon environment: Colorado-Wyoming
, Academy of Science, v. 6, 30 p.
Schery, S.D., Gaeddert, D.H., and Wilkening, M.H., 1982, Transport of radon from fractured
rock: Journal of Geophysical Research, v. 87, p. 2969-2976.
Schery, S.D., Wilkening, M.H., and Gaeddert, D.H., 1981, Radon transport through fractured
rock; a case study: Eos, Transactions of the American Geophysical Union, v. 62, p. 1033.
Tanner^ A.B., 1959, Meteorological influence on radon concentration in drillholes: Mining and
Engineering, v. 11, p. 706-708.
Tanner, A.B., 1960, Meteorological influence on radon concentration in drillholes: American
Institute of Mining, Metallurgical, and Petroleum Engineers, v. 214, p. 706-708. ,
Van Cleave, P.F., 1976, Radon in Carlsbad Caverns and caves of the surrounding area: National
cave management symposium proceedings, 120 p.
, Wilkening, M., and Romero, V., 1981,222 Rn and atmospheric electrical parameters in the
Carlsbad Caverns: Journal of Geophysical Research, C. Oceans and Atmospheres, v. 86,
p. 9911-9916. ;.'•'-'-.
Wilkening, M.H., and Hand, J.E., 1960, Radon flux at the earth-air interface: Journal of
*' Geophysical Research, v. 65, p. 3367-3370.
• ,.',.'' ' ; ' I, . ^. ' !
Wilkening, M.H., Stanley, D., and Clements, W.E., 1972, Radon-222 flux measurements in
widely separated regions: Rice University, Department of Geology, Annual Report, U.S.
Army Engineers Water Experiment Station 1972, (unpaginated).
IV-25 Reprinted from USGS Open-File Report 93-292-F
-------
Williams, J.L.; 1986, Population distribution, in Williams, J.L., ed., New Mexico in maps: ,
Albuquerque, University of New Mexico Press, p. 150-152.
Williams, J.L., ed., 1986, New Mexico in Maps: Albuquerque, University of New Mexico Press,
409 p.
Williams, J.L., and McAllister, P.E., eds., 1979, New Mexico in maps: Albuquerque,
Technology Application Center, Institute for Applied Research Services, University of
New Mexico, 177 p.
Yarborough, K.A., 1980, Radon- and thoron-produced radiation in National Park Service caves,
in .Gesell, T.F., and Lowder, W.M., eds., Natural radiation environment m, Vol. 2:
Proceedings of international symposium on the natural radiation environment, Houston,
TX, April 23-28,1978, DDE Symposium Series 2, p. 1371-1395.
IV-26 Reprinted from USGS Open-File Report 93-292-F
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EPA's Map of Radon Zones
t™ l ,SmCVhe ge0l°fiC Province boundaries cross state and county boundaries a strict
NEW MEXICO MAP OF RADON
v-i
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