United States
          Environmental Protection
          Agency
Air and Radiation
(6604J)
402-R-93-046
September 1993
<&EPA   EPA's Map of Radon Zones
          MONTANA

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       EPA'S MAP OF RADON ZONES
                MONTANA
             RADON DIVISION
  OFFICE OF RADIATION AND INDOOR AIR
U.S. ENVIRONMENTAL PROTECTION AGENCY
             SEPTEMBER, 1993

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                              ACKNOWLEDGEMENTS
       This document was prepared by the U.S. Environmental Protection Agency's (EPA's)
 Office of Radiation and Indoor Air (ORIA) in conjunction with the U.S. Geological Survey
 (USGS). Sharon W.  White was the EPA project manager.  Numerous other people in ORIA
 were instrumental in the development of the Map of Radon Zones, including Lisa Ratcliff
 Kirk Maconaughey, R. Thomas Peake, Dave Rowson, and Steve Page.

       EPA would especially like to acknowledge the outstanding effort of the USGS
 radon  team » Linda Gundersen, Randy Schumann,  Jim Otton, Doug Owen, Russell
 Dubiel, Kendell Dickinson, and Sandra Szarzi - in developing the technical base for the
 Map of Radon Zones.

       ORIA would also like to  recognize the efforts of all the EPA Regional Offices in
 coordinating the reviews with the State programs and the Association of American State
 Geologists (AASG) for providing a liaison with the State geological surveys. In addition,
appreciation is expressed to all of the State radon programs and geological surveys for their
technical input and review of the Map of Radon Zones.

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            TABLE OF CONTENTS
               I. OVERVIEW
     II. THE USGS/EPA RADON POTENTIAL
        ASSESSMENTSrINTRODUCTION
  III. REGION 8 GEOLOGIC RADON POTENTIAL
                SUMMARY
V. PRELIMINARY GEOLOGIC RADON POTENTIAL
         ASSESSMENT OF MONTANA
 V. EPA'S MAP OF RADON ZONES - MONTANA

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                                      OVERVIEW


        Sections 307 and 309 of the 1988  Indoor Radon Abatement Act (IRAA) direct EPA to
 identify areas of the United States that have the potential to produce elevated levels of radon,
 EPA, the U.S. Geological Survey (USGS), and the Association of American State Geologists
 (AASG) have worked closely over the past several years to produce a series of maps and
 documents which address these directives.  The EPA Map of Radon Zones is a compilation of
 that work  and fulfills the requirements of sections 307 and 309 of IRAA.  The Map of Radon
 Zones identifies, on a county-by-counry basis, areas of the U.S. that have the highest potential
 for elevated indoor radon levels (greater than 4 pCi/L).
        The Map of Radon Zones is designed to assist national, State and  local governments
 and organizations to target their radon program activities and resources.  It is also intended to
 help  building code officials determine areas that are the highest priority for adopting radon-
 resistant building practices.  The Map of Radon Zones should not be used to determine if
 individual  homes in any given area need to be tested for radon.  EPA  recommends that all
 homes be  tested for radon, regardless of geographic location or the zone designation of
 the county in which they  are located.
       This document provides background information concerning the development of the
 Map  of  Radon Zones.  It explains the purposes of the map, the approach for developing the
 map (including the respective roles of EPA and USGS), the data  sources used, the conclusions
 and confidence levels developed for the prediction of radon potential, and the review process
 that was conducted to finalize this effort.

 BACKGROUND

       Radon (Rn222) is a colorless, odorless, radioactive gas.  It comes from the natural
 decay of uranium that is found in nearly all soils.  It  typically moves through the ground to
 the air above and into homes and other buildings through cracks and openings in the
 foundation. Any home, school or workplace may have a radon problem, regardless of
 whether  it  is new or old, well-sealed or drafty, or with or without a basement. Nearly one-out
 of every 15 homes in the U.S. is estimated to have elevated annual average levels of indoor
 radon.
       Radon first gained national  attention in early  1984, when extremely high levels of
 indoor radon were found in areas of Pennsylvania, New Jersey, and New York, along the
 Reading  Prong-physiographic province.  EPA established a Radon Program in 1985 to assist
 States and  homeowners  in reducing their risk of lung cancer from indoor radon.
       Since 1985, EPA and USGS have been working together to continually increase our
 understanding of radon sources and the migration dynamics that cause elevated indoor radon
 levels. Early efforts resulted in the 1987 map entitled "Areas with Potentially High Radon
Levels."  This map was  based on limited geologic information only  because few indoor radon
measurements were available at the time. The development of EPA's Map of Radon Zones
and its technical foundation, USGS1 National Geologic Radon Province Map, has been based
on additional information from six years of the State/EPA Residential Radon Surveys,
independent State residential surveys, and continued expansion of geologic and geophysical
information, particularly the data from the  National Uranium Resource  Evaluation project.
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 Purpose of the Map of Radon Zones

        EPA's Map of Radon Zones (Figure 1) assigns each of the 3141  counties in. the
 United States to one of three zones:

               o     Zone 1  counties have a predicted average indoor screening level > than
                     4 pCi/L

               o      Zone 2  counties have a predicted average screening level > 2  pCi/L and
                     < 4 pCi/L

               o      Zone 3 counties have a predicted average screening level < 2  pCi/L

        The Zone designations were determined by assessing five factors that are known to be
 important indicators of radon potential: indoor radon measurements, geology, aerial
 radioactivity, soil parameters, and foundation types.
        The predictions of average screening levels in each of the Zones is an expression of
 radon potential in the lowest liveable area of a structure.  This map is unable to estimate
 actual exposures to radon.  EPA recommends methods for testing and fixing individual homes
 based on an  estimate of actual exposure to radon.  For more information  on testing and fixing
 elevated radon levels in homes consult these EPA publications: A  Citizen's Guide to Radon.
 the Consumer's Guide to Radon Reduction and the Home Buyer's and Seller's Guide to
 Radon.
       EPA  believes that States, local governments and other organizations can achieve
 optimal risk  reductions by  targeting resources and program activities to high radon potential
 areas. Emphasizing targeted approaches (technical assistance, information and outreach
 efforts, promotion of real estate mandates and policies and building  codes, etc.) in such areas
 addresses the greatest potential risks first.
       EPA also believes that the  use of passive radon control systems in the construction of
 new homes in Zone 1 counties, and the activation of those systems if necessitated by follow-
 up testing, is a cost effective approach to achieving significant radon risk reduction.
       The Map of Radon  Zones and its supporting documentation establish no regulatory
 requirements. Use of this map by State or local  radon programs and building code officials is
 voluntary.  The information presented on the Map of Radon Zones and in the supporting
 documentation  is not applicable to radon in water.

Development of the Map of Radon Zones

       The technical foundation  for the Map of Radon Zones is the USGS Geologic Radon
Province Map.  In order to examine the radon potential for the United States, the USGS
began by identifying approximately 360 separate geologic provinces for the U.S. The
provinces are shown on the USGS Geologic Radon  Province Map (Figure 2).   Each  of the
geologic provinces was evaluated by examining the available data for that area: indoor radon
measurements, geology, aerial radioactivity, soil parameters, and foundation types. As stated
previously, these  five factors are considered to be of basic importance in assessing radon
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  potential and some data are available for each of these factors in every geologic province The
  province boundaries do not coincide with political borders (county and state) but define areas
  of general radon potential.  The five factors were assigned numerical values based on an
  assessment of their respective contribution to radon potential, and a confidence level was
  assigned to each contributing variable. The approach used by USGS to estimate the radon
  potential for each province is described in Part II of this document.
         EPA subsequently  developed the Map of Radon Zones by extrapolating from the
  province level to the county level so that all counties in the U.S. were assigned to one of
  three radon zones.   EPA assigned each county to a given  zone based on its provincial radon
  potential.  For example, if a county is located within a geologic province that has a predicted
  average screening level greater than 4 pCi/L, it was assigned to Zone 1. Likewise, counties
  located in provinces with predicted average screening levels > 2 pCi/L and < 4 pCi/L and
  less than 2 pCi/L, were assigned to Zones 2  and  3, respectively.
        If the boundaries of a county fall in more than one geologic province  the county was
  assigned to a zone  based on the predicted radon potential of the province in which most of
  the area lies.  For example, if three different provinces cross through  a given county  the
  county was assigned to the zone  representing the radon potential of the  province containing
  most of the county's land area.  (In this case, it is not technically correct to say that the
  predicted average screening level applies to the entire county since  the county falls in
  multiple provinces with differing radon potentials.)
        Figures 3 and 4 demonstrate an example of how EPA extrapolated the county zone
  designations for Nebraska from the USGS geologic province map for the State  As figure 3
 shows, USGS has identified 5 geologic provinces for Nebraska.  Most of the counties are
 extrapolated "straight" from their corresponding provinces, but there are counties "partitioned"
 by several provinces - for  example, Lincoln  County.  Although Lincoln county falls in
 multiple provinces,  it was assigned to Zone 3 because most of its area falls in the province
 with the lowest radon potential.
       It is important to note that  EPA's extrapolation  from the province level to the
 county level may mask significant "highs" and "lows" within specific counties.  In other
 words, withm-county variations in  radon potential are not shown on the Map of Radon
 Zones.  EPA recommends that users who may need to address specific within-county
 variations in radon potential (e.g., local government officials considering the
 implementation of radon-resistant construction codes) consult USGS' Geologic Radon
 Province Map and the State chapters provided with this map for more detailed
 information, as well as any locally available data.

 Map Validation

       The Map of Radon Zones is intended to represent a preliminary assessment of radon
potential for the entire United States.  The  factors that are used in this effort --indoor radon
data, geology, aerial radioactivity, soils, and foundation type -  are basic  indicators for radon
potential.  It is important to note, however, that the map's county zone designations are not
"statistically valid" predictions due to the nature of the data available for these 5 factors at the
county level. In order to validate  the map in light of this lack of statistical confidence EPA
conducted a number of analyses.  These analyses have helped EPA to identify the best'
situations in which to apply  the map,  and its limitations.
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 Figure 3
                 Geologic Radon  Potential  Provinces for  Nebraska
         Lincoln  County
           Dijk      Uoierile      Loi
Figure 4
         NEBRASKA  -  EPA  Map  of Radon  Zones
        Lincoln  County
         Zone 1    Zone 2     Zone 3
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        One such analysis involved comparing county zone designations to indoor radon
 measurements from the State/EPA Residential Radon Surveys (SRRS). Screening  averages
 for counties with at least 100 measurements were compared to the counties' predicted radon
 potential as indicated by the Map of Radon Zones.  EPA found that 72% of the county
 screening averages were correctly  reflected by the appropriate zone designations on tiie 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  ail residents to test their homes
 for radon, regardless of geographic location or the zone designation of the county in
which they live. Similarly, the Map of Radon Zones should not to be used in lieu of
 testing  during real estate transactions.

Review Process

      The Map of Radon Zones has undergone extensive review within EPA and outside the
Agency. The Association of American State Geologists (AASG) played an integral role in
this review process. The AASG individual State geologists have reviewed their State-specific
information, the USGS Geologic Radon Province Map, and other materials for their geologic
content  and consistency.
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       In addition to each State geologist providing technical comments, the State radon
 offices were asked to comment on their respective States' radon potential evaluations.  In
 particular, the States were asked to evaluate the data used to assign their counties to specific
 zones. EPA and USGS worked with the States to resolve any issues concerning county zone
 designations.  In a few cases, States have requested changes in county zone designations.  The
 requests  were based on additional data from the State on geology, indoor radon
 measurements, population, etc.  Upon reviewing the data submitted by the States, EPA did
 make some  changes in zone designations.  These changes, which do not strictly follow the
 methodology outlined in  this document, are discussed in the respective State chapters.
       EPA encourages the States and  counties to  conduct further research and data collection
 efforts to refine the Map of Radon Zones. EPA would like to be kept informed of any
 changes the States, counties, or others make to the maps. Updates  and revisions will be
 handled in a similar fashion to the way the map was developed.  States should notify EPA of
 any proposed changes by forwarding the changes through the Regional EPA offices that are
 listed in Part II.  Depending on the  amount of new information that is presented, EPA  will
 consider  updating this map periodically. The State radon programs should initiate proper
notification of the appropriate State officials when  the Map of Radon Zones is released and
when revisions or updates are made by the State or EPA.
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     THE USGS/EPA RADON POTENTIAL ASSESSMENTS: AN INTRODUCTION
                                            by
                      Linda C.S. Gundersen and R. Randall Schumann
                                  U.S. Geological Sun>ey
                                           and
                                     Sharon W. White
                           U.S. Environmental Protection Agency

 BACKGROUND

     The Indoor Radon Abatement Act of 1988 (15  U.S.C.  2661-2671) directed the U.S.
 Environmental Protection Agency (EPA) to identify areas of the United States that have the
 potential  to produce harmful levels of indoor radon. These characterizations were to be based
 on both geological data and on indoor radon levels in homes and other structures. The EPA
 also was  directed to develop model standards and techniques for new building construction
 that would provide adequate prevention or mitigation of radon entry.  As part of an
 Interagency Agreement between the EPA and the U.S.  Geological  Survey (USGS), the USGS
 has prepared radon potential estimates for the United States.  This report is one of ten
 booklets that document this effort.  The purpose and intended use of these reports is to help
 identify areas where states can target  their radon  program resources, to provide guidance in
 selecting  the most appropriate building code  options for areas, and to  provide general
 information on radon and geology for each state  for federal, state,  and municipal  officials
 dealing with radon issues.  These reports are not intended to be used  as a substitute for
 indoor radon testing, and they cannot and should not be used to estimate or predict the
 indoor radon concentrations of individual homes, building sites, or housing tracts. Elevated
 levels of indoor radon have been found in every State, and EPA recommends that all homes
 be tested for indoor radon.
    Booklets detailing the radon potential assessment for the U.S. have been developed for
 each State.  USGS  geologists are the  authors of the geologic radon potential booklets.  Each
 booklet consists of several components, the first being an overview to the mapping project
 (Part I), this introduction to the USGS assessment (Part II), including  a general discussion of
 radon (occurrence, transport, etc.), and details concerning the types of data used.  The third
 component is a summary chapter outlining the general geology and geologic radon potential
 of the EPA Region (Part III). The fourth component is an individual  chapter for each state
 (Part IV).  Each state chapter discusses the state's specific geographic  setting, soils, geologic
 setting,  geologic radon potential, indoor radon data, and a summary outlining the radon
 potential rankings of geologic areas in the state.   A variety of maps are presented in each
 chapter—geologic, geographic, population, soils, aerial  radioactivity, and indoor radon data by
 county.  Finally, the booklets contain  EPA's map of radon zones for each state and an
 accompanying description (Part V).
    Because of constraints on the scales of maps  presented in these reports and because the
 smallest units used  to present the indoor radon data are counties, some generalizations have
 been  made in order to estimate the radon potential  of each area.  Variations in geology, soil
characteristics, climatic factors, homeowner lifestyles, and other factors that influence radon
concentrations can be quite large within any particular geologic area, so these reports cannot
be used to estimate or predict the indoor radon concentrations of individual homes or housing


                                           II-l    Reprinted from USGS Open-File Report 93-292

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 tracts. Within any area of a given geologic radon potential ranking, there are likely to be
 areas where the radon potential is lower or higher than that assigned to the area as a whole,
 especially in larger areas such  as the large counties in some western states.
     In each state chapter, references to additional reports related to radon are listed for the
 state, and the reader is urged to consult these 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 (2"Rn) is produced from the radioactive  decay of radium (226Ra), which is, in  turn,
 a product of the decay of uranium (238U) (fig.  1). The half-life of 222Rn is 3.825 days.  Other
 isotopes of radon occur naturally, but, with the exception  of thoron (220Rn), which  occurs in
 concentrations high enough  to be of concern  in a few localized areas, they are less important
 in terms of indoor radon risk because of their extremely short half-lives and less common
 occurrence.  In general, the  concentration and mobility of radon in soil are dependent on
 several factors, the most important of which are the soil's radium content and distribution,
 porosity, permeability to gas movement, and moisture content.  These characteristics are, in
 turn, determined by the soil's parent-material  composition, climate, and the soil's age or
 maturity.  If parent-material composition,  climate, vegetation, age of the soil, and topography
 are known, the physical and chemical properties of a soil in a given area can be predicted.
     As soils form, they develop distinct layers, or horizons, that are cumulatively called the
 soil  profile.  The A horizon  is a surface or near-surface horizon containing a relative
 abundance of organic matter but dominated by mineral matter.  Some soils contain an E
 horizon, directly below the A horizon, that is generally characterized by loss of clays,  iron, or
 aluminum, and has a characteristically lighter color than the A horizon. The B horizon
 underlies the A or E horizon.  Important characteristics of B horizons include accumulation of
 clays, iron oxides, calcium carbonate or other  soluble salts, and organic matter complexes.   In
 drier environments, a horizon may exist within or below the B horizon that is dominated by
 calcium carbonate, often called caliche or calcrete.  This carbonate-cemented horizon is
 designated the K horizon in  modern soil classification schemes.  The C horizon  underlies the
 B (or K) and  is a zone of weathered parent material that does not exhibit characteristics of A
 or B horizons; that is, it is generally not a zone of leaching or accumulation. In soils formed
 in place from the underlying bedrock, the C horizon is a zone of unconsolidated, weathered
 bedrock overlying the unweathered bedrock.
    The shape and orientation of soil particles (soil  structure) control permeability and affect
 water movement in the soil.  Soils with blocky or granular structure have roughly  equivalent
 permeabilities in the horizontal  and vertical directions, and air and water can infiltrate the soil
 relatively easily. However, in soils with platy structure, horizontal permeability is much
greater than vertical permeability, and air  and  moisture infiltration is generally slow.  Soils
with prismatic or columnar structure have dominantly vertical permeability.  Platy and
prismatic structures form in soils with high clay contents.  In soils with shrink-swell clays, air


                                           II-2     Reprinted from USGS Open-File  Report 93-292

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 and moisture infiltration rates and depth of wetting may be limited when the cracks in the
 surface soil layers swell shut. Clay-rich B horizons, particularly those with  massive or platy
 structure, can form a capping layer that impedes the escape of soil gas to the surface
 (Schumann and others, 1992).  However the shrink?«e of clays can act to open or widen
 cracks upon drying, thus increasing the soil's permeaoility 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 2xlO'6 inches—this  is known as alpha
 recoil (Tanner, 1980).  Moisture in the soil lessens the chance of a recoiling  radon  atom
 becoming imbedded in an adjacent grain.  Because water is more dense than air,  a  radon atom
 will travel a shorter distance in a water-filled pore than in an air-filled pore,  thus increasing
 the likelihood that the radon atom will remain in the pore space. Intermediate moisture levels
 enhance radon  emanation but do not.significantly affect permeability.  However,  high
 moisture levels can significantly decrease the gas permeability of the soil and impede  radon
 movement through  the soil.
    Concentrations  of radon in soils  are generally many times higher than those inside of
 buildings, ranging from tens of pCi/L to more than  100,000 pCi/L, but typically in  the range
of hundreds to low thousands of pCi/L. Soil-gas radon concentrations can vary in response to
variations in climate and weather on hourly, daily, or seasonal time scales.  Schumann and
others (1992) and Rose and others (1988) recorded order-of-magnitude variations in soil-gas
 radon concentrations between seasons in Colorado and Pennsylvania.  The most important
factors appear to be (1) soil moisture conditions, which are controlled in large part by
precipitation; (2) barometric pressure; and (3) temperature.  Washington and Rose (1990)
suggest that temperature-controlled partitioning of radon between water  and gas in soil pores
 also has a significant influence on the amount of mobile radon in  soil gas.
    Homes in hilly  limestone regions of the southern Appalachians were found to have higher
 indoor radon concentrations during the summer than in the winter.  A suggested cause for this
phenomenon involves temperature/pressure-driven flow of radon-laden air from subsurface


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solution cavities in the carbonate rock into houses.  As warm air enters solution cavities that
are higher on the hillslope than  the homes, it cools and settles, pushing radon-laden air from
lower in the cave or cavity system into structures on the hillslope (Gammage and others,
1993).  In contrast, homes built over caves having openings situated below the level of the
home had higher indoor radon levels in the winter, caused by cooler outside air entering the
cave, driving radon-laden air into  cracks and solution cavities in the rock and soil, and
ultimately, into homes (Gammage and others, 1993).

RADON ENTRY INTO BUILDINGS

    A driving force (reduced atmospheric pressure in the house relative to the soil, producing
a pressure gradient) and entry points  must exist for radon to  enter a building from the soil.
The negative pressure caused by furnace combustion, ventilation devices, and the  stack effect
(the rising and escape of warm air from the upper floors of the building,  causing a
temperature and pressure gradient  within the structure) during cold winter months are
common driving forces.  Cracks and other penetrations through .building foundations, sump
holes, and slab-to-foundation wall  joints are common entry points.
    Radon levels in the basement  are generally higher than those on the main floor or upper
floors of most structures. Homes  with basements generally provide more entry points for
radon, commonly have a more pronounced stack  effect, and typically have lower air pressure
relative  to the surrounding soil than nonbasement homes.  The term "nonbasement" applies to
slab-on-grade or crawl space construction.

METHODS AND  SOURCES  OF  DATA

    The assessments of radon potential in the booklets that follow this introduction were
made using five main types of data:  (1) geologic (lithologic); (2) aerial radiometric; (3) soil
characteristics, including soil moisture, permeability, and drainage characteristics; (4) indoor
radon data;  and (5) building architecture (specifically, whether homes, in each area are built
slab-on-grade or have a basement  or crawl space). These five factors were evaluated and
integrated to produce estimates of radon potential. Field measurements of soil-gas radon or
soil radioactivity were not used  except where such data were available in existing, published
reports of local field studies.  Where  applicable, such field studies are described in the
individual state chapters.

GEOLOGIC DATA

    The types and distribution of lithologic units and other  geologic  features in an
assessment area are of primary importance in determining radon potential. Rock types that
are most likely to  cause  indoor radon problems include carbonaceous black shales, glauconite-
bearing  sandstones, certain kinds of fluvial sandstones and fluvial  sediments, phosphorites,
chalk, karst-producing carbonate rocks, certain  kinds of glacial deposits, bauxite, uranium-rich
granitic rocks, metamorphic rocks of granitic composition, silica-rich  volcanic rocks, many
sheared  or faulted rocks, some coals, and certain  kinds of contact metamorphosed rocks.
Rock types least likely to cause radon problems include marine quartz sands,  non-
carbonaceous shales and siltstones, certain kinds of clays, silica-poor metamorphic and


                                           H-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 sued 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).

  NUKE 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 (-Bi), 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
 activuy; 3 ppm eU  corresponds to  approximately 1 picocurie per gram (pCi/g) of radium-226
 Although radon is highly mobile in soil and  its concentration is affected by meteorological
 conditions (Kovach, 1945; Klusman and Jaacks, 1987; Schery and others, 1984- Schumann
 and others, 1992), statistical correlations between average soil-gas radon concentrations and
 ^cc^oYor1^! f°r 3 Wide V3riety °f S°ils 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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                  FLIGHT LINE  SPICING OF SURE AERIAL  SURVEYS
                     2 L'l!  (1  VILE)
                     5 I'M  (3  MILES)
                     2 k 5  Kll
                 E3 10 Eli  (6 HUES)
                     5 k 10  IK
                     NO DATA
Figure 2. Nominal flighfline spacings for NURE aerial gamma-ray surveys covering the
contiguous United States (from Duval and others, 1990). Rectangles represent I°x2° quadrangles.

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     Figure 2 is an index map of NURE 1° x 2° quadrangles showing the flight-line spacing
 for each quadrangle.  In general, the more closely spaced the flightlines are, the more area
 was covered by the aerial gamma survey, and thus, more detail is available in the data set.
 For an altitude of 400 ft above the ground surface and with primary flightline spacing
 typically between 3 and 6 miles, less than 10 percent of the ground surface of the United
 States was actually measured by  the airborne gamma-ray detectors (Duval  and others, 1989),
 although some areas had better coverage than others due to the differences in flight-line
 spacing between  areas (fig.  2). This suggests that some localized uranium anomalies may not
 have been detected by the aerial  surveys, but the good correlations of eU patterns with
 geologic outcrop patterns indicate that, at relatively small scales (approximately  1:1,000,000
 or smaller) the National eU map  (Duval and others,  1989) gives reasonably good estimates of
 average surface uranium concentrations and thus can assist in the prediction of radon potential
 of rocks and soils, especially when augmented with additional geologic and soil data.
     The shallow (20-30 cm) depth of investigation of gamma-ray spectrometers, either
 ground-based or airborne (Duval  and others,  1971; Durrance,  1986), suggests that gamma-ray
 data may sometimes underestimate the radon-source strength in soils in which some of the
 radionuclides in the near-surface  soil layers have been  transported downward through the soil
 profile.  In such cases the concentration of radioactive  minerals in the A horizon  would be
 lower than in the B horizon, where such minerals are typically concentrated.  The
 concentration of radionuclides in  the C horizon and below may be relatively unaffected by
 surface solution processes.  Under these conditions the surface gamma-ray  signal  may indicate
 a lower radon source concentration than actually  exists in the deeper soil layers, which are
 most likely to affect radon levels  in structures with basements.  The redistribution of
 radionuclides in soil profiles is dependent on a combination of climatic, geologic, and
 geochemical factors.  There  is reason to believe that correlations of eU with actual soil
 radium and uranium concentrations at a depth relevant  to radon entry  into structures may be
 regionally variable (Duval,  1989;  Schumann and Gundersen, 1991). Given sufficient
 understanding of the factors cited above, these regional differences may be predictable.

 SOIL SURVEY DATA

    Soil surveys prepared by the U.S. Soil Conservation Service (SCS) provide data on soil
 characteristics, including soil-cover thickness, grain-size distribution, permeability, shrink-
 swell potential,  vegetative cover, generalized groundwater characteristics, and land use. The
 reports are available in county formats and State summaries.  The county reports typically
 contain both generalized and detailed maps of soils in the area.
    Because of  time and map-scale constraints, it was impractical to examine county soil
 reports for each county in the United States, so  more generalized summaries at appropriate
scales were used where available.  For State or regional-scale radon characterizations, soil
maps were compared to geologic  maps of the area, and the soil descriptions, shrink-swell
potential, drainage characteristics,  depth to seasonal high water table, permeability, and other
relevant characteristics of each soil group noted.   Technical soil terms used in soil' surveys are
generally complex; however, a good summary of soil engineering terms and the national
distribution of technical  soil  types is the "Soils" sheet of the National Atlas (U.S.  Department
of Agriculture, 1987).
                                           II-8     Reprinted from USGS Open-File Report 93-292

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     Soil permeability is commonly expressed in SCS soil surveys in terms of the speed, in
 inches per hour (in/hr), at which water soaks into the soil, as measured in a soil percolation
 test. Although in/hr are not truly units of permeability, these units are in  widespread use and
 are referred to as "permeability" in SCS soil surveys. The permeabilities listed in the SCS
 surveys are for water, but they generally correlate well with gas permeability. Because data
 on gas permeability of soils is extremely limited, data on permeability to water is used as  a
 substitute  except in cases in which excessive soil moisture is known to exist. Water in soil
 pores inhibits gas transport, so the amount of radon available to a home is effectively reduced
 by a high  water table.  Areas likely to have high water tables include river valleys, coastal
 areas, and some areas overlain by deposits of glacial origin (for example, loess).
     Soil permeabilities greater than 6.0 in/hr may be considered high, and permeabilities less
 than 0.6 in/hr may be considered low in terms of soil-gas transport.  Soils with low
 permeability may generally be considered to have a lower radon potential  than more
 permeable soils with similar radium concentrations.   Many well-developed soils contain a
 clay-rich B horizon that may  impede vertical soil gas transport.  Radon generated below this
 horizon cannot readily  escape to the surface, so it would instead tend to move laterally,
 especially  under the influence of a negative pressure exerted by'a building.
     Shrink-swell potential is an indicator of the abundance of smectitic (swelling) clays in a
 soil.  Soils with a high shrink-swell potential may cause building foundations to crack,
 creating pathways for radon entry into the structure.  During dry periods, desiccation  cracks in
 shrink-swell soils provide additional pathways for soil-gas transport and effectively increase
 the gas permeability of the soil. Soil  permeability data and soil profile data thus provide
 important information for regional  radon assessments.

 INDOOR RADON DATA

    Two major sources of indoor radon data were used.  The first and largest source of data is
 from the State/EPA Residential Radon Survey (Ronca-Battista and others, 1988; Dziuban and
 others,  1990). Forty-two states completed EPA-sponsored indoor radon surveys between 1986
 and  1992 (fig. 3).   The State/EPA Residential Radon Surveys were  designed to be
 comprehensive and statistically significant at the  state level, and were subjected to high levels
 of quality assurance and control. The surveys collected screening indoor radon measurements,
 defined as  2-7 day  measurements using charcoal  canister radon detectors placed in the lowest'
 livable  area of the home.  The target population for  the surveys included owner-occupied
 single family, detached housing units (White and others, 1989),  although attached structures
 such as duplexes, townhouses, or condominiums  were included in some of the surveys if they
 met the other criteria and had contact  with the ground surface.   Participants were selected
 randomly from telephone-directory listings.  In total, approximately 60,000 homes were tested
 in the State/EPA surveys.
    The second source of indoor radon data comes from residential surveys that have been
 conducted in a specific  state or region of the country (e.g. independent state surveys or utility
 company surveys).  Several states, including Delaware, Florida,  Illinois, New Hampshire, New
 Jersey, New York,  Oregon, and Utah,  have conducted their own surveys of indoor radon.  The
 quality and design of a  state or other independent survey are discussed and referenced where
the data are used.
                                           II-9     Reprinted from USGS Open-File Report 93-292

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     Data for only those counties with five or more measurements are shown in the indoor
 radon maps in the state chapters,  although data for all counties with a nonzero number of
 measurements are listed in the indoor radon data tables in each state chapter.  In total, indoor
 radon data from more than 100,000 homes nationwide were used in the compilation of these
 assessments.  Radon data from State or regional indoor radon surveys, public health
 organizations, or other sources are discussed in addition to the primary data sources where
 they are available. Nearly all of the data used in these evaluations represent short-term (2-7
 day) screening measurements from the lowest livable space of the homes.  Specific details
 concerning the nature  and use of indoor radon data sets other than the State/EPA Residential
 Radon Survey are discussed in the individual State chapters.

 RADON INDEX AND CONFIDENCE INDEX

     Many of the geologic methods used to evaluate an area for radon potential require
 subjective opinions based on the professional judgment and experience  of the individual
 geologist.  The evaluations are nevertheless based on established  scientific principles that are
 universally applicable  to any geographic area or geologic setting.  This section describes the
 methods and conceptual framework used by the U.S. Geological  Survey to evaluate areas for
 radon potential based on the five factors discussed in the previous sections. The scheme is
 divided into two basic parts, a Radon Index (RI), used to rank the general  radon potential of
 the area, and the Confidence Index (CI), used to express the level of confidence in the
 prediction based on the quantity and quality of the data used to make the determination. This
 scheme works best if the areas to  be evaluated are delineated by  geologically-based
 boundaries (geologic provinces) rather than political ones (state/county boundaries) in which
 the geology may vary  across the area.
    Radon Index. Table 1  presents the Radon Index (RI) matrix. The five factors—indoor
 radon data, geology, aerial radioactivity, soil parameters, and house foundation type—were
 quantitatively  ranked (using a point value of 1, 2, or 3) for their  respective contribution to
 radon potential in  a given area.  At least some data for the 5 factors are consistently available
 for every geologic province. Because each of these main factors encompass a wide variety  of
 complex and variable components, the geologists performing the  evaluation relied heavily on
 their professional judgment and experience in assigning point values to  each category and in
 determining the overall radon potential ranking. Background information on these factors is
 discussed in more detail in the preceding sections of this introduction.
    Indoor radon was evaluated using unweighted arithmetic means of the indoor radon data
 for each  geologic area to be  assessed. Other expressions of indoor radon levels in an area
 also could have been used, such as weighted averages or annual averages, but these types of
 data were not consistently available for the entire United States at the time of this writing, or
 the schemes were not considered sufficient to provide a means of consistent comparison
 across all areas. For this report, charcoal-canister screening measurement data from the
 State/EPA Residential  Radon Surveys and other carefully selected sources were used, as
 described in the preceding section. To maintain consistency, other indoor radon data sets
 (vendor,  state, or other data) were not considered in scoring the indoor radon factor of the
Radon Index if they were not randomly sampled or could not be  statistically combined with
the primary indoor radon data sets.  However, these additional  radon data sets can provide a
means to further refine correlations between geologic factors and radon potential, so they are


                                           II-11     Reprinted from USGS Open-File Report 93-292

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 TABLE 1. RADON INDEX MATRIX,  "ppm ell" indicates parts per million of equivalent
 uranium, as indicated by NURE aerial radiometric data. See text discussion for details.
                                  INCREASING RADON POTENTIAL
FACTOR
INDOOR RADON (average)
AERIAL RADIOACTIVITY
GEOLOGY*
SOIL PERMEABILITY
ARCHITECTURE TYPE
POINT VALUE
1
<2pCi/L
< 1.5 ppm eU
negative
low
mostly slab
2
2-4pCi/L
1.5 - 2.5 ppm eU
variable
moderate
mixed
3
>4pCi/L
> 2.5 ppm eU
positive
high
mostly basement
*GEOLOGIC FIELD EVIDENCE (GFE) POINTS: GFE points are assigned in addition to points
   for the "Geology" factor for specific, relevant geologic field studies. See text for details.
   Geologic evidence supporting:   HIGH radon       +2 points
                              MODERATE       +1 point
                              LOW              -2 points
                  No relevant geologic field studies    0 points
SCORING:
            Radon potential category
            LOW
            MODERATE/VARIABLE
            HIGH
                                   Probable average screening
                      Point ranpe      indoor radon for area
                      3-8 points
                      9-11 points
                     12-17 points
            <2pCi/L
            2-4pCi/L
            >4pCi/L
                     POSSIBLE RANGE OF POINTS = 3 to 17
TABLE 2.  CONFIDENCE INDEX MATRIX
FACTOR
INDOOR RADON DATA
AERIAL 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
                                    11-12     Reprinted from USGS Open-File Report 93-292

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 included as supplementary information and are discussed in the individual State chapters.  If
 the average screening indoor radon level for an area was less than 2 pCi/L, the indoor radon
 factor was assigned 1 point, if it was between 2 and 4 pCi/L, it was scored 2 points, and if
 the average screening indoor radon level for an area was greater than 4 pCi/L, the indoor
 radon factor was assigned 3 RI points.
     Aerial radioactivity data used in this report are from the equivalent uranium map of the
 conterminous United States compiled from NURE aerial gamma-ray surveys (Duval  and
 others, 1989).  These data indicate the gamma radioactivity  from approximately  the upper 30
 cm of rock and soil, expressed in units of ppm equivalent uranium.  An approximate average
 value of eU was determined visually for each area and point values assigned based on
 whether the overall eU for the area falls below 1.5 ppm (1  point),  between 1.5 and 2.5 ppm
 (2 points), or greater than 2.5  ppm (3 points).
     The geology factor is complex and actually incorporates many geologic characteristics.  In
 the matrix, "positive1.1 and "negative" refer to the presence or absence and distribution of rock
 types known to have high uranium contents and to generate elevated radon in soils or indoors.
 Examples  of "positive" rock types include granites, black shales, phosphatic rocks, and other
 rock types described in the preceding "geologic data" section.  Examples of "negative" rock
 types include marine quartz sands and some clays. The term "variable" indicates that the
 geology within the region is variable or  that the rock types  in the area  are known or  suspected
 to generate elevated radon in some areas but not in others due  to compositional differences,
 climatic effects, localizeddistribution of uranium, or other factors.   Geologic information
 indicates not only how much uranium is present in the rocks and soils but also gives clues for
 predicting  general radon emanation and mobility characteristics through additional factors
 such as structure (notably the presence of faults or shears) and  geochemical characteristics
 (for example, a phosphate-rich sandstone will  likely contain  more uranium than a sandstone
 containing little or  no phosphate because the phosphate forms chemical complexes with
 uranium).  "Negative", "variable",  and "positive" geology were  assigned 1, 2, and 3 points,
 respectively.
    In cases where additional reinforcing or contradictory geologic evidence is available,
 Geologic Field Evidence (GFE) points were added to or subtracted from an area's score
 (Table 1).  Relevant geologic field studies are important to enhancing our understanding of
 how geologic processes affect radon distribution.  In some cases, geologic models and
 supporting field data reinforced an already strong  (high or low) score; in others, they provided
 important contradictory data.  GFE points were applied for geologically-sound evidence that
 supports the prediction (but which may contradict one or more factors) on  the basis of known
 geologic field studies in the area or in areas with geologic and  climatic settings similar
 enough  that they could  be applied with full confidence.  For example, areas of the Dakotas,
 Minnesota, and Iowa that are covered with Wisconsin-age glacial deposits exhibit a low aerial
 radiometric signature and score only one RI point in that category.  However, data from
geologic field studies in North Dakota and Minnesota (Schumann and others, 1991) suggest
that eU is a poor predictor of geologic radon potential in this area because radionuclides have

                                         /11-13     Reprinted  from USGS Open-File Report 93-292

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 been leached from the upper soil layers but are present and possibly even concentrated in
 deeper soil horizons, generating significant soil-gas radon.  This positive supporting field
 evidence adds two GFE points to the score, which helps to counteract the invalid conclusion
 suggested by the radiometric data.  No GFE points are awarded if there are no documented
 field studies for the area.
      "Soil permeability" refers to several soil characteristics that influence radon concentration
 and  mobility, including soil type, grain size, structure, soil moisture, drainage, slope, and
 permeability.  In the matrix, "low"  refers to permeabilities less than about 0.6 in/hr; "high"
 corresponds to greater than about 6.0 in/hr, in U.S. Soil Conservation Service (SCS) standard
 soil percolation tests. The SCS data are for water permeability,  which generally correlates
 well with the gas permeability  of the soil except when the soil moisture content is very high.
 Areas with consistently high water  tables were thus considered to have low gas permeability.
 "Low, "moderate", and "high" permeability were assigned 1, 2, and 3 points, respectively.
     Architecture type refers to  whether homes in the area have mostly basements  (3 points),
 mostly slab-on-grade construction (1 point), or a mixture of the.two. Split-level and crawl
 space homes fall into the "mixed" category (2 points). Architecture information is necessary
 to properly interpret the  indoor radon data and produce geologic radon potential categories
 that are consistent with screening indoor radon data.
      The overall RI for an  area is calculated by  adding the individual RI scores for the 5
 factors, plus or minus GFE points, if any.  The total RI for an area falls in one of three
 categories—low, moderate or variable, or high.  The point ranges for the three categories were
 determined by examining the possible combinations of points for the 5 factors and setting
 rules such  that a majority (3 of 5  factors) would determine the final  score for the low and
 high  categories, with allowances for possible deviation from an ideal  score by the  other two
 factors.  The moderate/variable category lies between these two  ranges.  A total deviation of 3
 points from the "ideal" score was considered  reasonable to allow for natural variability of
 factors—if two of the five factors are allowed to vary from the "ideal" for a category, they
 can differ by a minimum of 2  (1 point different each) and a maximum of 4 points (2 points
 different each).  With "ideal" scores of 5, 10, and  15 points describing low, moderate, and
 high geologic radon potential, respectively, an ideal low score of 5 points plus 3 points for
 possible variability allows a maximum of 8 points in the low category.  Similarly, an ideal
 high score of 15  points minus 3 points gives a minimum of 12 points for the high category.
 Note, however, that if both other factors differ by  two points from the "ideal", indicating
 considerable variability in the system, the total point score would lie in the adjacent (i.e.,
 moderate/variable) category.
    Confidence Index. Except for architecture type, the same factors were used to establish a
 Confidence Index (CI) for the radon potential prediction for each area (Table 2).  Architecture
type was not included in  the confidence index because house construction data are readily and
reliably available through surveys taken by agencies and industry groups including the
National Association of Home Builders, U.S. Department of Housing  and  Urban
Development, and the Federal Housing Administration; thus it was not considered necessary

                                          11-14     Reprinted from USGS Open-File Report 93-292

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 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 iandom sampling (State/EPA  Residential Radon Survey
 or other state survey data) or volunteered vendor data (likely to be nonrandom and biased ,
 toward population centers and/or high indoor radon levels).  The categories listed in the CI
 matrix for indoor radon data ("sparse or no data",  "fair  coverage or quality", and "good
 coverage/quality") indicate the sampling density and statistical robustness  of an indoor radon
 data set.  Data from the State/EPA Residential Radon Survey and statistically valid state
 surveys were typically assigned 3 Confidence Index points unless the data were poorly
 distributed or absent in the area evaluated.
     Aerial radioactivity data are available for all but a few areas of the continental United
 States and for part of Alaska.  An  evaluation of the quality of the radioactivity data was based
 on whether there appeared to be a  good correlation between the radioactivity and the  actual
 amount of uranium or  radium available  to generate mobile radon in the rocks and soils of the
 area evaluated.  In general, the greatest  problems with correlations among eU, geology, and
 soil-gas or indoor radon levels were associated with glacial deposits (see the discussion in a
 previous section) and typically were assigned a 2-point Confidence Index  score.  Correlations
 among eU, geology, and radon were generally sound in unglaciated areas  and were usually
 assigned 3 CI points.  Again, however, radioactivity data in some unglaciated  areas may have
 been assigned fewer than 3 points,  and in  glaciated areas may be assigned only one point, if
 the data were considered  questionable or if coverage was poor.
    To assign Confidence Index scores for the geologic data factor, rock types and geologic
 settings for which a physical-chemical, process-based  understanding of radon generation and
 mobility exists were regarded as having "proven geologic models" (3 points); a high
 confidence could be held for predictions in such areas.  Rocks for which the processes are
 less well known or for which data are contradictory were regarded as "variable" (2 points),
 and those about which  little is known or for which no apparent correlations  have been found
 were deemed  "questionable" (1 point).
    The soil permeability factor was also scored based on  quality and amount of data.  The
 three categories for soil permeability in  the Confidence Index are similar in  concept, and
 scored similarly, to those for the geologic  data factor. Soil permeability can be roughly
 estimated from grain size and drainage class if data from standard, accepted  soil percolation
tests are unavailable; however, the reliability of the data would be lower than if percolation
test figures or other measured permeability data are available, because an estimate of this type
does not encompass all the factors that affect soil permeability and thus may be inaccurate in
some instances.  Most published soil permeability data are for water; although this is
generally closely related to the air permeability of the soil, there are some instances when it
may provide an  incorrect  estimate.  Examples of areas in which water permeability data may
not accurately reflect air permeability include areas with consistently  high  levels of soil
moisture, or clay-rich soils, which would have a low water permeability but  may have a

                                           11-15     Reprinted from USGS Open-File Report 93-292

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significantly higher air permeability when dry due to shrinkage cracks in the soil.  These
additional factors were applied to the soil permeability factor when assigning the RI score, but
may have less certainty in some  cases and thus would be assigned a lower CI score.
    The Radon Index and Confidence Index give a general indication of the relative
contributions of the interrelated geologic factors influencing radon generation and transport in
rocks and soils,  and thus, of the potential for elevated indoor radon levels to occur in a
particular area.  However, because these reports are somewhat generalized to cover relatively
large areas of States, it is highly  recommended that more detailed studies be performed in
local areas of interest,  using the methods and general information in these booklets as a guide.
                                         11-16    Reprinted from USGS Open-File Report 93-292

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                                 REFERENCES CITED

 Akerblom, G., Anderson, P., and dave:.;.»jo, B., 1984, Soil gas radon~A source for indoor radon
       daughters: Radiation Protection Dosimetry, v. 7, p. 49-54.

 Deffeyes, K.S., and MacGregor, I.D., 1980, World uranium resources: Scientific American,
       v. 242, p. 66-76.

 Durrance, E.M., 1986, Radioactivity in geology: Principles and applications:  New York, N.Y.,
       Wiley and Sons, 441 p.

 Duval, J.S., 1989, Radioactivity and some of its applications in geology: Proceedings of the
       symposium on the application of geophysics to engineering and environmental problems
       (SAGEEP), Golden, Colorado, March 13-16,1989:  Society of Engineering and Mineral
       Exploration Geophysicists, p. 1-61.

 Duval, J.S., Cook, B.G., and Adams, J.A.S., 1971, Circle of investigation of an airborne
       gamma-ray spectrometer: Journal of Geophysical Research, v. 76, p. 8466-8470.

 Duval, J.S., Jones, W.J., Riggle, F.R., and Pitkin, J.A., 1989, Equivalent uranium map of
       conterminous United States: U.S. Geological Survey Open-File Report 89-478,10 p.

 Duval, J.S., Reimer, G.M., Schumann, R.R., Owen, D.E., and Otton, J.K., 1990, Soil-gas
       radon compared to aerial and ground gamma-ray measurements at study sites near Greeley
       and Fort Collins, Colorado:  U.S. Geological Survey Open-File Report 90-648,42 p.

 Dziuban, J.A., Clifford, M.A., White,  S.B., Bergstein, J.W.,  and Alexander, B.V., 1990,
       Residential radon survey of twenty-three States, in Proceedings of the 1990 International
       Symposium on Radon and Radon Reduction Technology, Vol. TJI: Preprints: U.S.
       Environmental Protection Agency report EPA/600/9-90/005c, Paper IV-2,17 p.

 Gammage, R.B., Wilson, D.L., Saultz, R.J., and Bauer, B.C., 1993, Subtereanean transport of
       radon and elevated indoor radon in hilly karst terranes: Atmospheric Environment
       (in press).

 Gundersen, L.C.S., Reimer, G.M., and Agard, S.S.,  1988a, Correlation between geology, radon
       in soil gas, and indoor radon in  the Reading Prong, in Marikos, M. A., and Hansman,
       R.H., eds., Geologic causes of natural radionuclide anomalies: Missouri Department of
       Natural Resources Special Publication 4, p. 91-102.

Gundersen, L.C.S, Reimer, G.M., Wiggs, C.R., and Rice, C.A., 1988b, Map showing radon
       potential of rocks and soils in Montgomery County, Maryland: U.S. Geological Survey
       Miscellaneous Field Studies Map MF-2043, scale 1:62,500.

Gundersen, Linda C.S., 1991, Radon in sheared metamorphic and igneous rocks, in Gundersen,
       Linda C.S., and Richard B. Wanty, eds., Field studies of radon in rocks, soils, and water:
       U.S. Geol. Survey Bulletin no. 1971, p. 39-50.
                                        U-17     Reprinted from USGS Open-File Report 93-292

-------
 Henry, Mitchell E., Kaeding, Margret E., and Monteverde, Donald, 1991, Radon in soil gas and
       gamma-ray activity of rocks and soils at the Mulligan Quarry, Clinton, New Jersey, in
       Gundersen, Linda C.S., and Richard B. Wanty, eds., Field studies of radon in rocks,
       soils, and water: U.S. Geol. Survey Bulletin no. 1971, p. 65-75.

 Klusman, R. W., and Jaacks, J. A., 1987, Environmental influences upon mercury, radon, and
       helium concentrations in soil gases at a site near Denver, Colorado: Journal of
       Geochemical Exploration, v. 27, p. 259-280.

 Kovach, E.M., 1945, Meteorological influences upon the radon content of soil gas: Transactions,
       American Geophysical Union, v. 26, p. 241-248.

 Kunz, Q, Laymon, C.A., and Parker, C, 1989, Gravelly soils and indoor radon,  in Osborne,
       M.C., and Harrison, J., eds., Proceedings of the 1988 EPA Symposium on Radon and
       Radon Reduction Technology, Volume 1:  U.S. Environmental Protection Agency Report
       EPA/600/9-89/006A, p. 5-75-5-86.

 Muessig, K., and Bell, C., 1988, Use of airborne radiometric data to direct testing for elevated
       indoor radon: Northeastern Environmental Science, v. 7, no. 1, p. 45-51.

 Ronca-Battista, M., Moon, M., Bergsten, J., White, S.B., Holt, N., and Alexander, B., 1988,
       Radon-222 concentrations in the United States-Results of sample surveys in five states:
       Radiation Protection Dosimetry, v. 24, p. 307-312.

 Rose, A.W., Washington, J.W., and Greeman, D.J., 1988, Variability of radon with depth and
       season in a central Pennsylvania soil developed on limestone: Northeastern Environmental
       Science, v. 7, p. 35-39.

 Schery, S.D., Gaeddert, D.H., and Wilkening, M.H., 1984, Factors affecting exhalation of radon
       from a gravelly sandy loam: Journal of Geophysical Research, v. 89, p. 7299-7309.

 Schumann, R.R., and Owen, D.E., 1988, Relationships between geology, equivalent uranium
       concentration, and radon in soil gas, Fairfax County, Virginia: U.S. Geological Survey
       Open-File Report 88-18,28 p.

Schumann, R.R., and Gundersen, L.C.S., 1991, Regional differences in radon emanation
       coefficients in soils: Geological Society of America Abstracts With Programs, v. 23,
       no. 1, p. 125.

Schumann, R.R., Peake, R.T., Schmidt, K.M., and Owen, D.E., 1991, Correlations of soil-gas
       and indoor radon with geology in glacially derived soils of the northern Great Plains, in
       Proceedings of the 1990 International Symposium on Radon and Radon Reduction
       Technology, Volume 2, Symposium Oral Papers:  U.S. Environmental Protection Agency
       report EPA/600/9-9l/026b, p. 6-23-6-36.
                                         H-18     Reprinted from USGS Open-File Report 93-292

-------
 Schumann, R.R., Owen, D.E., and Asher-Bolinder, S., 1992, Effects of weather and soil
       characteristics on temporal variations in soil-gas radon concentrations, in Gates, A.E., and
       Gundersen, L.C.S., eds., Geologic controls on radon: Geological Society of America
       Special Paper 271, p. 65-72.

 Sextro, R.G., Moed, B.A., Nazaroff, W.W., Revzan, K.L., and Nero, A.V., 1987,
       Investigations of soil as a source of indoor radon, in Hppke, P.K., ed., Radon and its
       decay products: American Chemical Society Symposium Series 331, p. 10-29.

 Sterling, R., Meixel, G., Shen, L., Labs, K., and Bligh, T., 1985, Assessment of the energy
       savings potential of building foundations research: Oak Ridge, Term., U.S. Department of
       Energy Report ORNL/SUB/84-0024/1.

 Smith, R.C., H, Reilly, M.A., Rose, A.W., Barnes, J.H., and Berkheiser, S.W., Jr., 1987,
       Radon: a profound case: Pennsylvania Geology, v. 18, p. 1-7.

 Tanner, A.B., 1964, Radon migration in the ground: a review, in Adams, J.A.S., and Lowder,
       W.M., eds., The natural radiation environment:  Chicago, HI., University of Chicago
       Press, p.  161-190.

 Tanner, A.B., 1980, Radon migration in the ground: a supplementary review, in Gesell, T.F.,
       and Lowder, W.M. (eds), Natural radiation environment HI, Symposium proceedings,
       Houston, Texas, v. 1, p. 5-56.

 U.S. Department of Agriculture, 1987, Principal kinds of soils: Orders, suborders, and great
       groups: U.S. Geological Survey, National Atlas of the United States of America, sheet
       38077-BE-NA-07M-00, scale 1:7,500,000.

 U.S. Department of Energy, 1976, National Uranium Resource Evaluation preliminary report,
       prepared by the U.S. Energy Research and Development Administration, Grand Junction,
       Colo.: GJO-11(76).

Wanty, Richard B., and Schoen, Robert, 1991, A review of the chemical processes affecting the
       mobility of radionuclides in natural waters, with applications, in Gundersen, Linda C.S.,
       and Richard B. Wanty, eds., Field studies of radon in rocks, soils, and water: U.S.
       Geological Survey Bulletin no. 1971, p. 183-194.

Washington, J.W., and Rose, A.W., 1990, Regional and temporal relations of radon in soil gas to
       soil temperature and moisture: Geophysical Research Letters, v. 17, p. 829-832.

White, S.B., Bergsten, J.W., Alexander, B.V., and Ronca-Battista, M.,  1989, Multi-State
       surveys of indoor 222Rn: Health Physics,  v. 57, p. 891-896.
                                        H-19     Reprinted from USGS Open-File Report 93-292

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                                               APPENDIX  A
                                       GEOLOGIC TIME SCALE
Subdivisions (and their symbols)
Eon or
Eonothem
Phsnerozoic2

Proterozoic
IP)


Archean
(Al

Era or
Erathem
Cenozoic 2
(Cz)
Mesozoic2
(Mi)

Paleozoic2
(Pi)


Prow oio*e (2)
M»00I*
Protvro?O'C fYl
Pretvoioie IX)
Ult
Arcftaan (W)
MiadW
ArttMtn (VI
£»rty
AreftMn IU1
Period, System,
Subperiod, Subsystem
Quaternary
(Q)
Neocene *
Subperiod or
T.rriarv Subsystem (N)
f-r, PaleoQene
Suooeriod or
Subsystem (Pi)
Cretaceous
(K)
Jurassic
(J)
Triassic
C5)
Permian
)

Ordovician
m\
•y

Cambrian
tC)
Epoch or Series
Holocene
Age estimates
of boundaries
in mega-annum
(Ma)1

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
pr*-A/chMn 
-------
                                     APPENDIX  B
                                GLOSSARY OF TERMS


 Units of measure

 pCi/L (picocuries per liter)- a unit of measure of radioactivity used to describe radon
 concentrations in a volume of air.  One picocurie (1(H2 curies) is equal to about 2.2 disintegrations
 of radon atoms per minute. A liter is about 1.06 quarts. The average concentration of radon in
 U.S. homes measured to date is between 1 and 2 pCi/L.

 Bq/m3 (Becquerels per cubic meter)- a metric unit of radioactivity used to describe radon
 concentrations in a volume of air. One becquerel is equal to one radioactive disintegration per
 second.  One pCi/L is equal to 37 Bq/m3.

 ppm (parts per million)- a unit of measure of concentration by weight of an element in a
 substance, in this case, soil or rock. One ppm of uranium contained in a ton of rock corresponds
 to about 0.03 ounces of uranium.  The average concentration of uranium in soils in the United
 States is between 1 and 2 ppm.

 in/hr (inches per hour)-  a unit of measure used by soil scientists and engineers to describe the
 permeability of a soil to water flowing through it It is measured by digging a hole 1 foot (12
 inches) square and one foot deep, filling it with water, and measuring the time it takes for the water
 to drain from the hole. The drop in height of the water level in the hole, measured in inches, is
 then divided by the time (in hours) to determine the permeability.  Soils range in permeability from
 less than 0.06 in/hr to greater than 20 in/hr, but most soils in the United States have permeabilities
 between these two extremes.
Geologic terms and terms related to the study of radon

aerial radiometric, aeroradiometric survey A survey of radioactivity, usually gamma rays,
taken by an aircraft carrying a gamma-ray spectrometer pointed at the ground surface.

alluvial fan A low, widespread mass of loose rock and soil material, shaped like an open fan
and deposited by a stream at the point where it flows from a narrow mountain valley out onto a
plain or broader valley. May also form at the junction with larger streams or when the gradient of
the stream abruptly decreases.

alluvium, alluvial General terms referring to unconsolidated detrital material deposited by a
stream or other body of running water.

alpha-track detector A passive radon measurement device consisting of a plastic film that is
sensitive to alpha particles.  The film is etched with acid in a laboratory after it is exposed. The
etching reveals scratches, or "tracks", left by the alpha particles resulting from radon decay, which
can then be counted to calculate the radon concentration. Useful for long-term (1-12 months)
radon tests.

amphibolite A mafic metamorphic rock consisting mainly of pyroxenes and(or) amphibole and
plagioclase.
                                         11-21     Reprinted from USGS Open-File Report 93-292

-------
 argillite, argillaceous  Terms referring to a rock derived from clay or shale, or any sedimentary
 rock containing an appreciable amount of clay-size material, i.e., argillaceous sandstone.

 arid Term describing a climate characterized by dryness, or an evaporation rate that exceeds the
 amount of precipitation.

 basalt A general term for a dark-colored mafic igneous rocks that may be of extrusive origin,
 such as volcanic basalt flows, or intrusive origin, such as basalt dikes.

 batholith A mass of plutonic igneous rock that has more than 40 square miles of surface
 exposure and no known bottom.

 carbonate A sedimentary rock consisting of the carbonate (COs) compounds of calcium,
 magnesium, or iron, e.g. limestone and dolomite.

 carbonaceous  Said of a rock or sediment that is rich in carbon, is coaly, or contains organic
 matter.

 charcoal canister A passive radon measurement device consisting of a small container of
 granulated activated charcoal that is designed to adsorb radon.  Useful for short duration (2-7 days)
 measurements only. May be referred to as a "screening" test

 chert  A hard, extremely dense sedimentary rock consisting dominantly of interlocking crystals of
 quartz. Crystals are not visible to the naked eye, giving the rock a milky, dull luster. It may be
 white or gray but is commonly colored red, black, yellow, blue, pink, brown, or green.

 clastic pertaining to a rock or sediment composed of fragments that are derived from preexisting
 rocks or minerals. The most common clastic sedimentary rocks are sandstone and shale.

 clay A rock containing clay mineral fragments or material of any composition having a diameter
 less than 1/256 mm.

 clay mineral One of a complex and loosely defined group of finely crystalline minerals made up
 of water, silicate and aluminum (and a wide variety of other elements).  They are formed chiefly by
 alteration or weathering of primary silicate minerals. Certain clay minerals are noted for their small
 size and ability to absorb substantial amounts of water, causing them to swell.  The change in size
 that occurs as these clays change between dry and wet is referred to as their "shrink-swell"
potential.

 concretion A hard, compact mass of mineral matter, normally subspherical but commonly
irregular in shape; formed by precipitation from a water solution about a nucleus or center, such as
a leaf,  shell, bone, or fossil, within a sedimentary or fractured rock.

conglomerate A coarse-grained, clastic sedimentary rock composed of rock and mineral
fragments larger than 2 mm, set in a finer-grained matrix of clastic material.

cuesta A hill or ridge with a gentle slope on one side and a steep slope on the other. The
formation of a cuesta is controlled by the different weathering properties and the structural dip of
the rocks forming the hill or ridge.

daughter product A nuclide formed by the disintegration of a radioactive precursor or "parent"
atom.
                                         11-22     Reprinted from USGS Open-File Report 93-292

-------
 delta, deltaic Referring to a low, flat, alluvial tract of land having a triangular or fan shape,
 located at or near the mouth of a river. It results from the accumulation of sediment deposited by a
 river at the point at which the river loses its ability to transport the sediment, commonly where a
 river meets a larger body of water such as a lake or ocean.

 dike  A tabular igneous intrusion of rock, younger than the surrounding rock, that commonly cuts
 across the bedding or foliation of the rock it intrudes.

 diorite A plutonic igneous rock that is medium in color and contains visible dark minerals that
 make up less than 50% of the rock. It also contains abundant sodium plagioclase and minor
 quartz.

 dolomite A carbonate sedimentary rock of which more than 50% consists of the mineral dolomite
 (CaMg(COs)2), and is commonly white, gray, brown, yellow, or pinkish in color.

 drainage The manner in which the waters of an area pass, flow off of, or flow into the soil.
 Also refers to the water features of an area, such as lakes and rivers, that drain it.

 eolian Pertaining to sediments deposited by the wind.

 esker A long, narrow, steep-sided ridge composed of irregular beds of sand and gravel deposited
 by streams beneath a glacier and left behind when the ice melted.

 evapotranspiration Loss of water from a land area by evaporation from the soil and
 transpiration from plants.

 extrusive Said of igneous rocks that have been erupted onto the surface of the Earth.

 fault A fracture or zone of fractures in rock or sediment along which there has been movement.

 fluvial, fluvial deposit Pertaining to sediment that has been deposited by a river or stream.

 foliation A linear feature hi a rock defined by both mineralogic and structural characteristics. It
 may be formed during deformation or metamorphism.

 formation A mappable body of rock having similar characteristics.

 glacial deposit Any sediment transported and deposited by a glacier or processes associated
 with glaciers, such as glaciofluvial sediments deposited by streams flowing from melting glaciers.

 gneiss A rock formed by metamorphism in which bands and lenses of minerals of similar
 composition alternate with bands and lenses of different composition, giving the rock a striped or
 "foliated" appearance.

 granite Broadly applied, any coarsely crystalline, quartz- and feldspar-bearing igneous plutonic
 rock. Technically, granites have between 10 and 50% quartz, and alkali feldspar comprises at least
 65% of the total feldspar.

 gravel An unconsolidated, natural accumulation of rock fragments consisting predominantly of
particles greater than 2 mm in size.

 heavy minerals Mineral grains in sediment or sedimentary rock having higher than average
 specific gravity. May form layers and lenses because of wind or water sorting by weight and size
                                          H-23      Reprinted from USGS Open-File Report 93-292

-------
  and may be referred to as a "placer deposit"  Some heavy minerals are magnetite, garnet, zircon,
  monazite, and xenotime.
  igneous Said of a rock or mineral that solidified from molten or partly molten rock material. It is
  one of the three main classes into which rocks are divided, the others being sedimentary and
  metamorphic.
  intermontane A term that refers to an area between two mountains or mountain ranges.
  intrusion, intrusive The processes of emplacement or injection of molten rock into pre-existing
  rock.  Also refers to the rock formed by intrusive processes, such as an "intrusive igneous rock".
  kame A low mound, knob, hummock, or short irregular ridge formed by a glacial stream at the
  margin of a melting glacier; composed of bedded sand and gravel.
 karst terrain A type of topography that is formed on limestone, gypsum and other rocks by
 dissolution of the rock by water, forming sinkholes and caves.
 lignite A brownish-black coal that is intermediate in coalification between peat and
 subbiturninous coal.
 limestone A carbonate sedimentary rock consisting of more than 50% calcium carbonate,
 primarily in the form of the mineral calcite (CaCOs).
 lithology The description of rocks in hand specimen and in outcrop on the basis of color
 composition, and grain size.
 loam A permeable soil composed of a mixture of relatively equal parts clay, silt, and sand, and
 usually containing some organic matter.
 loess A fine-grained eolian deposit composed of silt-sized particles generally thought to have
 been deposited from windblown dust of Pleistocene age.
 mafic  Term describing an igneous rock containing more than 50% dark-colored minerals.
 marine Term describing sediments deposited in the ocean, or precipitated from ocean waters.
 metamorphic Any rock derived from pre-existing rocks by mineralogical, chemical, or structural
 changes in response to changes in temperature, pressure, stress, and the chemical environment.
 Phyllite, schist, amphibolite, and gneiss are metamorphic rocks.
 moraine A mound, ridge, or other distinct accumulation of unsorted, imbedded glacial material,
predominantly till, deposited by the action of glacial ice.
outcrop  That part of a geologic formation or structure that appears at the surface of the Earth as
in "rock outcrop".
percolation test A term used in engineering for a test to determine the water permeability of a
soil. A hole is dug and filled with water and the rate of water level decline is measured.
permeability  The capacity of a rock, sediment, or soil to transmit liquid or gas.
phosphate, phosphatic, phosphorite Any rock or sediment containing a significant amount
of phosphate minerals, i.e., minerals containing PO4.

                                          n-24      Reprinted from USGS Open-File Report 93-292

-------
physiographic province A region in which all parts are similar in geologic structure and
climate, which has had a uniform geomorphic history, and whose topography or landforms differ
significantly from adjacent regions.
placer deposit See heavy minerals
residual Formed by weathering of a material in place.
residuum  Deposit of residual material.
rhyolite An extrusive igneous rock of volcanic origin, compositionally equivalent to granite.
sandstone A clastic sedimentary rock composed of sand-sized rock and mineral material that is
more or less firmly cemented. Sand particles range from 1/16 to 2 mm in size.
schist  A strongly foliated crystalline rock, formed by metamorphism, that can be readily split into
thin flakes or slabs.  Contains mica; minerals are typically aligned.
screening level  Result of an indoor radon test taken with a charcoal canister or similar device,
for a short period of time, usually less than seven days. May indicate the potential for an indoor
radon problem but does not indicate annual exposure to radon.
sediment Deposits of rock and mineral particles or fragments originating from material that is
transported by air, water or ice, or that accumulate by natural chemical precipitation or secretion of
organisms.
semiarid Refers to a climate that has slightly more precipitation than an arid climate.
shale A fine-grained sedimentary rock formed from solidification (lithification) of clay or mud.
shear zone Refers to a roughly linear zone of rock that has been faulted by ductile or non-ductile
processes in which the rock is sheared and both sides are displaced relative to one another.
shrink-swell  clay  See clay mineral.
siltstone A fine-grained clastic sedimentary rock composed of silt-sized rock and mineral
material and more or less firmly cemented. Silt particles range from 1/16 to 1/256 mm in size.
sinkhole A roughly circular depression in a karst area measuring meters to tens of meters in
diameter. It is funnel shaped and is formed by collapse of the surface material into an underlying
void created by the dissolution of carbonate rock.
slope An inclined part of the earth's surface.
solution cavity  A hole, channel or cave-like cavity formed by dissolution of rock.
stratigraphy  The study of rock strata;  also refers to the succession of rocks of a particular area.
surficial materials Unconsolidated glacial, wind-, or waterborne deposits occurring on the
earth's surface,
tablelands General term for a broad, elevated region with a nearly level surface of considerable
extent
                                          11-25     Reprinted from USGS Open-File Report 93-292

-------
 terrace gravel Gravel-sized material that caps ridges and terraces, left behind by a stream as it
 cuts down to a lower level.


 terrain A tract or region of the Earth's surface considered as a physical feature or an ecological
 environment


 till Unsorted, generally unconsolidated and unbedded rock and mineral material deposited directly
 adjacent to and underneath a glacier, without reworking by meltwater.  Size of grains varies greatly
 from clay to boulders.

 uraniferous Containing uranium, usually more than 2 ppm.

 vendor data Used in this report to refer to indoor radon data collected and measured by
 commercial vendors of radon measurement devices and/or services.

 volcanic Pertaining to the activities, structures, and extrusive rock types of a volcano.

 water table The surface forming the boundary between the zone of saturation and the zone of
 aeration; the top surface of a body of unconfined groundwater in rock or soil.

 weathering  The destructive process by which earth and rock materials, on  exposure to
 atmospheric elements, are changed in color, texture, composition, firmness, or form with little or
no transport of the material.
                                         11-26     Reprinted from USGS Open-File Report 93-292

-------
                                          APPENDIX C
                                  EPA REGIONAL OFFICES
EPA   Regional  Offices
State
                                                                                  EPA Repinn
EPA Region 1
JFK Federal Building
Boston, MA 02203
(617)  565-4502

EPA Region 2
(2AIR:RAD)
26 Federal Plaza
New York, NY 10278
(212)  264-4110

Region 3 (3AH14)
841 Chestnut Street
Philadelphia, PA 19107
(215)  597-8326

EPA Region 4
345 Courtland Street, N.E.
Atlanta, GA 30365
(404)  347-3907

EPA Region 5 (5AR26)
77 West Jackson Blvd.
Chicago, XL 60604-3507
(312)  886-6175

EPA Region 6 (6T-AS)
1445 Ross Avenue
Dallas, TX 75202-2733
(214)  655-7224

EPA Region 7
726 Minnesota Avenue
Kansas City, KS 66101
(913)  551-7604

EPA Region 8
(8HWM-RP)
999 18th Street
One Denver Place, Suite 1300
Denver, CO 80202-2413
(303)  293-1713

EPA Region 9 (A-3)
75 Hawthorne Street
San Francisco, CA 94105
(415)  744-1048

EPA Region 10
1200 Sixth Avenue
Seattle, WA 98101
(202)  442-7660
Alabama.	4
Alaska	10
Arizona	9
Arkansas	6
California	9
Colorado	8
Connecticut	1
Delaware	3
District of Columbia	3
Florida	4
Georgia	4
Hawaii	9
Idaho	10
Illinois	5
Indiana	5
Iowa	7
Kansas	:	.7
Kentucky	4
Louisiana	6
Maine	1
Maryland	3
Massachusetts	1
Michigan	5
Minnesota	5
Mississippi	4
Missouri	7
Montana	8
Nebraska	7
Nevada	9
New Hampshire	1
New  Jersey	2
New Mexico	6
New York	2
North  Carolina	4
North  Dakota	8
Ohio	5
Oklahoma	6
Oregon	10
Pennsylvania	3
Rhode Island	1
South  Carolina	4
South  Dakota	8
Tennessee	4
Texas	6
Utah	8
Vermont	1
Virginia	3
Washington	10
West Virginia	.....3
Wisconsin	5
Wyoming	8
                                                n-27      Reprinted from USGS Open-File Report 93-292

-------
                                  STATE RADON CONTACTS
                                              May, 1993
 Alabama       James McNees
                Division of Radiation Control
                Alabama Department of Public ^calth
                State Office Building
                Montgomery, AL 36130
                (205)242-5315
                1-800-582-1866 in state

 Alaska         Charles Tedford
                Department of Health and Social
                  Services
                P.O. Box 110613
                Juneau.AK 99811-0613
                (907)465-3019
                1-800-478-4845 in state

 Arizona         John Stewart
                Arizona Radiation Regulatory Agency
                4814 South 40th St.
                Phoenix, AZ 85040
                (602)255-4845
Arkansas       LeeGershner
               Division of Radiation Control
               Department of Health
               4815 Markham Street, Slot 30
               Little Rock, AR 72205-3867
               (501) 661-2301
California^      J. David Quinton
               Department of Health Services
               714 P Street, Room 600
               Sacramento, CA 94234-7320
               (916) 324-2208
               1-800-745-7236 in state
Colorado       Linda Martin
               Department of Health
               4210 East llth Avenue
               Denver, CO 80220
               (303)692-3057
               1-800-846-3986 in state
 Connecticut  Alan J. Siniscalchi
             Radon Program
             Connecticut Department of Health
               Services
             150 Washington Street
             Hartford, CT 06106^4474
             (203) 566-3122

   Delaware  MaraiG. Rejai
             Office of Radiation Control
             Division of Public Health
             P.O. Box 637
             Dover, DE 19903
             (302) 736-3028
             1-800-554-4636 Instate

    District  Robert Davis
of Columbia  DC Department of Consumer and
              Regulatory Affairs
             614 H Street NW
             Room 1014
             Washington, DC 20001
             (202) 727-71068

    Florida N. Michael GUley
            Office of Radiation Control
            Department of Health and
              Rehabilitative Services
             1317 Winewood Boulevard
            Tallahassee, EL 32399-0700
            (904)488-1525
             1-800-543-8279 in state
            Richard Schreiber
            Georgia Department of Human
              Resources
            878 Peachtree St., Room 100
            Atlanta, GA 30309
            (404) 894-6644
            1-800-745-0037 in state
    Hawaii  Russell Takata
            Environmental Health Services
              Division
            591 Ala Moana Boulevard
            Honolulu, HI 96813-2498
            (808)586-4700
                                              11-28      Reprinted from USGS Open-File Report 93-292

-------
 Idaho
 Illinois
 Indiana
Iowa
Kansas
Kentucky
 PalMcGavarn
 Office of Environmental Health
 450 West State Street
 Boise, ID 83720
 (208) 334-6584
 1-800-445-8647 in state
 Richard Allen
 Illinois Department of Nuclear Safety
 1301 Outer Park Drive
 Springfield, IL 62704
 (217) 524-5614
 1-800-325-1245 in state
 Lorand Magyar
 Radiological Health Section
 Indiana State Department of Health
 1330 West Michigan Street
 P.O. Box 1964
 Indianapolis, IN 46206
 (317) 633-8563
 1-800-272-9723 In State

 Donald A. Plater
 Bureau of Radiological Health
 Iowa Department of Public Health
 Lucas State Office Building
 Des Moines, IA 50319-0075
 (515)281-3478
 1-800-383-5992 In State

 Harold Spiker
 Radiation Control Program
 Kansas Department of Health and
  Environment
 109 SW 9th Street
 6th Floor Mills Building
 Topeka, KS 66612
 (913)296-1561

JeanaPhelps
Radiation Control Branch
 Department of Health Services
 Cabinet for Human Resources
 275 East Main Street
Frankfort, KY 40601
 (502)564-3700
    Louisiana Matt Schlenker
              Louisiana Department of
                Environmental Quality
              P.O. Box 82135
              Baton Rouge, LA 7Co84-2135
              (504)925-7042
              1-800-256-2494 in state

       Mains Bob Stilwell
              Division of Health Engineering
              Department of Human Services
              State House, Station 10
              Augusta, ME 04333
              (207)289-5676
              1-800-232-0842 in state

    Maryland Leon J. Rachuba
              Radiological Health Program
              Maryland Department of the
                Environment
              2500 Broening Highway
              Baltimore, MD 21224
              (410)631-3301
              1-800-872-3666 In State

Massachusetts  William J. Bell
              Radiation Control Program
              Department of Public Health
              23 Service Center
              Northampton, MA 01060
              (413)586-7525
              1-800-445-1255 in state

    Michigan  SueHendershott
              Division of Radiological Health
              Bureau of Environmental and
                Occupational Health
              3423 North Logan Street
              P.O. Box 30195
              Lansing, MI 48909
              (517) 335-8194

   Minnesota  Laura Oatmann
              Indoor Air Quality Unit
              925 Delaware Street, SE
              P.O. Box 59040
              Minneapolis, MN 55459-0040
              (612)627-5480
              1-800-798-9050 in state
                                               11-29      Reprinted from USGS Open-File Report 93-292

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Mississii
Missouri
Montana
                Silas Anderson
                Division of Radiological Health
                Department of Health
                3 150 Lawson Street
                P.O. Box 1700
                Jackson, MS 39215-1700
                (601) 354-6657
                1-800-626-7739 in state

                Kenneth V. Miller
                Bureau of Radiological Health
                Missouri Department of Health
                1730 East Elm
                P.O. Box 570
                Jefferson City, MO 65102
                (314) 751-6083
                1-800-669-7236 In State

                Adrian C. Howe
                Occupational Health Bureau
                Montana Department of Health and
                 Environmental Sciences
                Cogswell Building A113
                Helena, MT 59620
                (406)444-3671
               Joseph Milone
               Division of Radiological Health
               Nebraska Department of Health
               301 Centennial Mall, South
               P.O. Box 95007
               Lincoln, NE 68509
               (402)471-2168
               1-800-334-9491 In State

               Stan Marshall
               Department of Human Resources
               505 East King Street
               Room 203
               Carson City, NV 89710
               (702) 687-5394
New Hampshire  David Chase
                Bureau of Radiological Health
                Division of Public Health Services
                Health and Welfare Building
                Six Hazen Drive
                Concord, NH 03301
                (603)271-4674
                1-800-852-3345 x4674
Nebraska
    New Jersey  Tonalee Carlson Key
               Division of Environmental Quality
               Department of Environmental
                 Protection
               CN415
               Trenton, NJ 08625-0145
               (609)987-6369
               1-800-648-0394 in state

  New Mexico  William M. Floyd
               Radiation Licensing and Registration
                 Section
               New Mexico Environmental
                 Improvement Division
               1190 St. Francis Drive
               Santa Fe,NM 87503
               (505) 827-4300

    New York  William J. Condon
               Bureau of Environmental Radiation
                 Protection
               New York State Health Department
               Two University Place
               Albany, NY 12202
               (518)458-6495
               1-800-458-1158 in state

North Carolina  Dr. Felix Fong
               Radiation Protection Division
               Department of Environmental Health
                 and Natural Resources
               701 Barbour Drive
               Raleigh, NC 27603-2008
               (919) 571-4141
               1-800-662-7301 (recorded info x4196)

 North Dakota  Alien Jacobson
               North Dakota Department of Health
               1200 Missouri Avenue, Room 304
               P.O. Box 5520
               Bismarck, ND 58502-5520
               (701)221-5188

        Ohio  Marcie Matthews
               Radiological Health Program
               Department of Health
               1224 Kinnear Road - Suite 120
               Columbus, OH 43212
               (614) 644-2727
               1-800-523-4439 in state
                                               n-30
                                                          Reprinted from USGS Open-File Report 93-292

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 Oklahoma
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-RADONIn State

David Saldana
Radiological Health Division
G.P.O. Call Box 70184
Rio Piedras, Puerto Rico 00936
(809)767-3563
Edmund Arcand
Division of Occupational Health and
  Radiation
Department of Health
205 Cannon Building
Davis Street
Providence, RI02908
(401) 277-2438
               Bureau of Radiological Health
               Department of Health and
                 Environmental Control
               2600 Bull Street
               Columbia, SC 29201
               (803)734-4631
               1-800-768-0362
 South Dakota  Mike Pochop
              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)53fr4250

    Vermont Paul demons
             Occupational and Radiological Health
               Division
             Vermont Department of Health
             10 Baldwin Street
             Montpelier, VT 05602
             (802) 828-2886
             1-800-640-0601 in state

Virgin Islands Contact the U.S. Environmental
             Protection Agency, Region n
             in New York
             (212)264-4110
                                               n-3i
                                           Reprinted from USGS Open-File Report 93-292

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 Virginia        Shelly Ottenbrite
                Bureau of Radiological Health
                Department of Health
                109 Governor Street
                Richmond, VA 23219
                (804) 786-5932
                1-800-468-0138 in state

 Washington     Kate Coleman
                Department of Health
                Office of Radiation Protection
                Airdustrial Building 5, LE-13
                Olympia, WA 98504
                (206) 753^518
                1-800-323-9727 In State

 West Virginia    Beanie L. DeBord
                Industrial Hygiene Division
                West Virginia Department of Health
                151 llth Avenue
                South Charleston, WV 25303
                (304) 558-3526
                1-800-922-1255 In State

 Wisconsin       Conrad Weiffenbach
                Radiation Protection Section
                Division of Health
                Department of Health and Social
                 Services
                P.O. Box 309
                Madison, WI53701-0309
                (608)267-4796
                1-800-798-9050 in state

Wyoming       Janet Hough
                Wyoming Department of Health and
                 Social Services
                Hathway Building, 4th Floor
                Cheyenne, WY 82002-0710
                (307)777-6015
                1-800-458-5847 in state
                                                H-32      Reprinted from USGS Open-File Report 93-292

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                             STATE  GEOLOGICAL  SURVEYS
                                             May, 1993
 Alabama        Ernest A. Mancini
                Geological Survey of Alabama
                P.O. Box 0
                420 Hackbeny Lane
                Tuscaloosa, AL 35486-9780
                (205)349-2852
                Thomas E. Smith
                Alaska Division of Geological &
                  Geophysical Surveys
                794 University Ave., Suite 200
                Fairbanks, AK 99709-3645
                (907)479-7147
 Arizona        Larry D. Fellows
               Arizona Geological Survey
               845 North Park Ave., Suite 100
               Tucson, AZ 85719
               (602) 882-4795
 Arkansas       Norman F. Williams
               Arkansas Geological Commission
               Vardelle Parham Geology Center
               3815 West Roosevelt Rd.
               Little Rock, AR 72204
               (501)324-9165

 California      James F. Davis
               California Division of Mines &
                 Geology
               801 K Street, MS 12-30
               Sacramento, CA 95814-3531
               (916)445-1923

 Colorado       Pat Rogers (Acting)
               Colorado Geological Survey
               1313 Sherman St, Rm 715
               Denver, CO 80203
               .(303)866-2611

Connecticut     Richard C. Hyde
               Connecticut Geological & Natural
                 History Survey
               165 Capitol Ave., Rm. 553
               Hartford, CT 06106
               (203)566-3540

Delaware       Robert R. Jordan
               Delaware Geological Survey
               University of Delaware
               101 Penny Hall
               Newark, DE 19716-7501
               (302) 831-2833
 Florida Walter Schmidt
        Florida Geological Survey
        903 W. Tennessee St.
        Tallahassee, FL 32304-7700
        (904)488-4191
        William H. McLemore
        Georgia Geologic Survey
        Rm. 400
        19 Martin Luther King Jr. Dr. SW
        Atlanta, GA 30334
        (404) 656-3214
Hawaii  Manabu Tagomori
        Dept. of Land and Natural Resources
        Division of Water & Land Mgt
        P.O. Box 373
        Honolulu, ffl 96809
        (808) 548-7539
        Earl H. Bennett
        Idaho Geological Survey
        University of Idaho
        Morrill Hall, Rm.  332
        Moscow, ID 83843
        (208) 885-7991
Illinois  Morris W. Leighton
        Illinois State Geological Survey
        Natural Resources Building
        615EastPeabodyDr.
        Champaign, IL 61820
        (217) 333-4747

Indiana  Norman C. Hester
        Indiana Geological Survey
        611 North Walnut Grove
        Bloomington, IN 47405
        (812)855-9350

  Iowa  Donald L. Koch
        Iowa Department of Natural Resources
        Geological Survey Bureau
        109 Trowbridge Hall
        Iowa City, IA 52242-1319
        (319) 335-1575

        Lee C.Gerhard
        Kansas Geological Survey
        1930 Constant Ave., West Campus
        University of Kansas
        Lawrence, KS 66047
        (913)864-3965
                                              11-33      Reprinted from USGS Open-File Report 93-292

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 Kentucky       Donald C. Haney
                Kentucky Geological Survey
                University of Kentucky
                228 Mining & Mineral Resources
                  Building
                Lexington, KY 40506-0107
                (606)257-5500

 Louisiana       William E. Marsalis
                Louisiana Geological Survey
                P.O. Box 2827
                University Station
                Baton Rouge, LA 70821-2827
                (504) 388-5320

 Maine          Walter A. Anderson
                Maine Geological Survey
                Department of Conservation
                State House, Station 22
                Augusta, ME 04333
                (207) 289-2801
Maryland       Emery T. Cleaves
               Maryland Geological Survey
               2300 SL Paul Street
               Baltimore, MD 21218-5210
               (410) 554-5500
Massachusetts   Joseph A. Sinnott
               Massachusetts Office of
                 Environmental Affairs
               100 Cambridge SL, Room 2000
               Boston, MA 02202
               (617)727-9800

Michigan       R. Thomas Segall
               Michigan Geological Survey Division
               Box 30256
               Lansing, MI 48909
               (517)334-6923

Minnesota      Priscilla C. Grew
               Minnesota Geological Survey
               2642 University Ave.
               St. Paul, MN 55114-1057
               (612)627-4780
Mississippi     S. Cragin Knox
               Mississippi Office of Geology
               P.O. Box 20307
               Jackson, MS 39289-1307
               (601)961-5500
      Missouri  James H. Williams
                Missouri Division of Geology &
                 Land Survey
                111 Fairgrounds Road
                P.O. Box 250
                Rolla, MO 65401
                (314)368-2100

      Montana  Edward T.Ruppel
                Montana Bureau of Mines & Geology
                Montana College of Mineral Science
                 and Technology, Main Hall
                Butte,MT 59701
                (406)4964180

      Nebraska  Perry B. Wigley
                Nebraska Conservation & Survey
                 Division
                113 Nebraska Hall
                University of Nebraska
                Lincoln, NE 68588-0517
                (402)472-2410

        Nevada  Jonathan G. Price
                Nevada Bureau of Mines & Geology
                Stop 178
               University of Nevada-Reno
               Reno, NV 89557-0088
                (702) 784-6691

New Hampshire Eugene L.Boudette
               Dept. of Environmental Services
                117 James Hall
               University of New Hampshire
               Durham, NH 03824-3589
               (603)862-3160

    New Jersey Haig F. Kasabach
               New Jersey Geological Survey
               P.O. Box 427
               Trenton, NJ 08625
               (609)292-1185

   New Mexico Charles E. Chapin
               New Mexico Bureau of Mines &
                 Mineral Resources
               Campus Station
               Socorro.NM 87801
               (505) 835-5420

    New York Robert H. Fakundiny
               New York State Geological Survey
               3136 Cultural Education Center
               Empire State Plaza
               Albany, NY 12230
               (518)474-5816
                                               n-34      Reprinted from USGS Open-File Report 93-292

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  North Carolina Charles H. Gardner
                North Carolina Geological Survey
                P.O. Box 27687
                Raleigh, NC 27611-7687
                (919)733-3833

 North Dakota   John P. Bluemle
                North Dakota Geological Survey
                600 East Blvd.
                Bismarck, ND 58505-0840
                (701) 224-4109
 Ohio           Thomas M. Berg
                Ohio Dept. of Natural Resources
                Division of Geological Survey
                4383 Fountain Square Drive
                Columbus, OH 43224-1362
                (614)265-6576

 Oklahoma       Charles J. Mankin
                Oklahoma Geological Survey
                Room N-131, Energy Center
                100E.Boyd
                Norman, OK 73019-0628
                (405)325-3031

 Oregon         Donald A. Hull
                DepL of Geology & Mineral Indust.
                Suite 965
                800 NE Oregon St. #28
                Portland, OR 97232-2162
                (503) 731-4600

 Pennsylvania     Donald M. Hoskins
                Dept. of Environmental Resources
                Bureau of Topographic & Geologic
                 Survey
                P.O. Box 2357
                Harrisburg, PA 17105-2357
                (717)787-2169

Puerto Rico      Ramdn M. Alonso
                Puerto Rico Geological Survey
                 Division
                Box 5887
                Puerto de Tierra Station
                San Juan, PJL 00906
                (809) 722-2526

Rhode Island     J. Allan Cain
                Department of Geology
                University of Rhode Island
                315 Green Hall
                Kingston, RI02881
                (401)792-2265
South Carolina Alan-Jon W. Zupan (Acting)
              South Carolina Geological Survey
              5 Geology Road
              Columbia, SC 29210-9998
              (803)737-9440

 South Dakota CM. Christensen (Acting)
              South Dakota Geological Survey
              Science Center
              University of South Dakota
              Vermfflion, SD 57069-2390
              (605)677-5227

    Tennessee Edward T.Luther
              Tennessee Division of Geology
              13th Floor,L&C Tower
              401 Church Street
              Nashville, TN 37243-0445
              (615) 532-1500

       Texas  William L. Fisher
              Texas Bureau of Economic Geology
              University of Texas
              University Station, Box X
              Austin, TX  78713-7508
              (512)471-7721

        Utah  M. Lee Allison
              Utah Geological & Mineral Survey
              2363 S. Foothill Dr.
              Salt Lake City, UT 84109-1491
              (801)467-7970
     Vermont Diane L. Conrad
             Vermont Division of Geology and
               Mineral Resources
             103 South Main St.
             Waterbury.VT 05671
             (802)244-5164
     Virginia Stanley S. Johnson
             Virginia Division of Mineral
               Resources
             P.O. Box 3667
             CharlottesviUe, 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 fiomUSGS Open-File Report 93-292

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  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
                                             11-36      Reprinted from USGS Open-File Report 93-292

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                EPA REGION 8 GEOLOGIC RADON POTENTIAL SUMMARY
                                            by
        R. Randall Schumann, Douglass E. Owen, Russell F. Dubiel, and Sandra L. Szarzi
                                   U.S. Geological Survey

        EPA Region 8 includes the states of Colorado, Montana, North Dakota, South Dakota,
  Utah, and Wyoming. For each state, geologic radon potential areas were delineated and ranked on
  the basis of geologic, soils, housing construction, and other factors. Areas in which the average
  screening indoor radon level of all homes within the area is estimated to be greater than 4 pCi/L
  were ranked high.  Areas in which the average screening indoor radon level of all homes within the
  area is estimated to be between 2 and 4 pCi/L were ranked moderate/variable, and areas in which
  the average screening indoor radon level of all homes within the area is estimated to be less than
  2 pCi/L were ranked low. Information on the data used and on the radon potential ranking scheme
  is given in the introduction to this volume. More detailed information on the geology and radon
 potential of each state in Region 8 is given in the individual state chapters. The individual chapters
 describing the geology and radon potential of the six states in EPA Region 8, 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 provinces in EPA Region 8  The
 following summary of radon potential in Region 8 is based on these provinces. Figure 2 shows
 average screening indoor radon levels by county. The data for South Dakota are from the
 EPA/Indian Health Service Residential Radon Survey and from The Radon Project of the
 University of Pittsburgh; data for Utah are from an indoor radon survey conducted in 1988 by the
 Utah Bureau of Radiation Control; data for Colorado, Montana, North Dakota, and Wyoming are
 from the State/EPA Residential Radon Survey. Figure 3 shows the geologic radon potential areas
 in Region 8, combined and summarized from the individual state chapters. Rocks and soils in
 EPA Region 8 contain ample radon source material (uranium and radium) and have soil
 permeabilities sufficient to produce moderate or high radon levels in homes. At the scale of this
 evaluation, all areas in EPA Region 8 have either moderate or high geologic radon potential, except
 for an area in southern South Dakota corresponding to the northern part of the Nebraska Sand
 Hills, which has low radon potential.
       The limit of continental glaciation is of great significance in Montana, North Dakota and
 South Dakota (fig.  1).  The glaciated  portions of the Great Plains and the Central Lowland '
 generally have a higher radon potential than their counterparts to the south because glacial action
 crushes and grinds up rocks as it forms till and other glacial deposits.  This crushing and grinding
 enhances weathering and increases the surface area from which radon may emanate; further it
 exposes more uranium and radium at grain surfaces where they are more easily leached  Leached
 uranium and radium may be transported downward in the soil below the depth at which it may be
 detected by a gamma-ray spectrometer (approximately 30 cm), giving these areas a relatively low
 surface or aerial radiometric signature. However, the uranium and radium still are present at
 depths shallow enough to allow generated radon to migrate into a home.
       The Central Lowland Province is a vast plain that lies between 500 and 2,000 feet above
 sea level and forms the agricultural heart of the United States.  In Region 8, it covers the eastern
part of North Dakota and South  Dakota. The Central Lowland in Region 8 has experienced the
effects of continental glaciation and also contains silt and clay deposits from a number of glacial


                                          m-l    Reprinted from USGS Open-File Report 93-292-H

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Figure 1. Physiographic provinces in EPA Region 8 (after Hunt, C.W., 1967, Physiography of
the United States: Freeman and Co., p. 8-9.)

-------
                                 100 Miles
                             Indoor Radon Screening
                          Measurements: Average (pCi/L)

                           160  0.0 to 1.9
                       76IZZZ2  2.0 to 4.0

                           11 M  10.0 to 29.2
                       82 I      I  Missing Data
Figure 2. Average screening indoor radon levels by county for EPA Region 8.  Data for
CO, MT, ND, and WY from the EPA/State Residential Radon Survey; data for UT from
the Utah Bureau of Radiation Control indoor radon survey; data for SD from the EPA/LHS
Indoor Radon Survey and from The Radon Project. Histograms in map legend
indicate the number of counties in each measurement category.

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                                             GEOLOGIC
                                         RADON POTENTIAL

                                         E3 HIGH
                                             MODERATE
                                           ] LOW
Figure 3. Geologic radon potential of EPA Region 8.

-------
  lakes. Many of the glacial deposits are derived from or contain components of the uranium-bearing
  Pierre Shale. Although many of the soils derived from glacial deposits in the Dakotas contain
  significant amounts of clay, the soils can have permeabilities that are higher than indicated by
  standard water percolation tests due to shrinkage cracks when dry.  In addition, clays tend to have
  high radon emanation coefficients because clay particles have a high surface-area-to-volume ratio
  compared to larger and(or) more spherical soil grains. These two factors make areas underlain by
  glacial deposits derived from the Pierre Shale, and areas underlain by glacial lake deposits, such as
  the Red River Valley, highly susceptible to indoor radon problems.  Average indoor radon levels in
  this province generally are greater than 4 pCi/L (fig. 2). The Central Lowland in Region 8 has
  high radon potential.
        The Great Plains Province is an extension of the Central Lowlands that rises from 2,000
  feet in the east to 5,000 feet above sea level in the west. In Region 8, it covers the western part of
  North and South Dakota and the eastern portions of Montana, Wyoming, and Colorado. The
  northern part of the Great Plains has been glaciated (fig. 1) and previous comments about
  continental glaciation apply. The Great Plains are largely underlain by Cretaceous and Tertiary
  sedimentary rocks. In general, the Cretaceous and Tertiary rocks in the southern part of the Great
  Plains in Region 8 have a moderate to high radon potential.  The Cretaceous Inyan Kara Group
  which surrounds the Black Hills in southwestern South Dakota and northeastern Wyoming, locally
  hosts uranium deposits.  There are a number of uranium occurrences in Tertiary sedimentary rocks
  in the northern part of the Great Plains, such as in the Powder River Basin. The northwestern part
  of the Great Plains contains numerous discontinuous uplifts (mountainous areas) that generally
  have high radon potential.  A few, such as the Black Hills, have uranium districts associated with
 them. Average indoor radon levels in this province are greater than 2 pCi/L, with a significant
 number of counties having average indoor radon concentrations exceeding 4 pCi/L (fig. 2).
        The Northern Rocky Mountains Province (fig. 1) has high radon potential.  Generally, the
 igneous and metamorphic rocks of this province have elevated uranium contents. The soils
 developed on  these rocks typically have moderate or high permeability. Coarse-grained glacial
 flood deposits composed of sand, gravel, and boulders, which are found in many of the valleys in
 the province, also have high permeability. A number of uranium occurrences are found in granite
 and chalcedony in the Boulder Batholith; in veins or pegmatite dikes in igneous and metamorphic
 rocks near Clancy in Jefferson County, near Saltese in Mineral County, and in the Bitterroot and
 Beartooth Mountains, all in Montana. Uranium also occurs in Tertiary volcanic rocks about 20
 miles east of Helena, and in the Mississippian-age Madison Limestone in the Pryor Mountains.
 County average indoor radon levels generally exceed 4 pCi/L in the province (fig. 2).
       The Wyoming Basin Province lies dominantly in Wyoming, but also includes an area of
 Tertiary sedimentary rocks in northern Colorado (fig. 1). The Wyoming Basin consists of a
 number of elevated semiarid basins separated by small mountain ranges. In general the rocks and
 soils have uranium contents greater than 2.5 ppm and host a number of uranium occurrences as
 well, particularly in the Tertiary Fort Union and Wasatch Formations. Average indoor radon levels
 for homes tested in this area generally are greater than 3 pCi/L (fig. 2). The Wyoming Basin has a
 high radon potential.
       The Middle Rocky Mountains Province (fig. 1) has both moderate and high radon potential
 areas (fig. 3). The southern part of the Middle Rocky Mountains province contains the Wasatch
 Range in Utah, which has high radon potential, and the Uinta Mountains and the Overthrust Belt in
 Utah and Wyoming, both of which have moderate radon potential. The northern part of the
province contains the Yellowstone Plateau, which is underlain by volcanic rocks containing


                                           m-5    Reprinted from  USGS Open-File Report 93-292-H

-------
 relatively high uranium concentrations. Mountain ranges such as the Grand Tetons and Big Horn
 Mountains, which are underlain by granitic and metamorphic rocks that generally contain more
 than 2.5 ppm uranium, also occur in this province. County average indoor radon levels are mostly
 in the 2-4 pCi/L range (fig. 2). The Yellov^one Plate"-1 Grand Teton<- and Big Horn Mountains
 all have high geologic radon potential.
        The Southern Rocky Mountains Province lies dominantly in Colorado (fig.  1).  Much of
 the province is underlain by igneous and metamorphic rocks with uranium contents  generally
 exceeding the upper continental crustal average of 2.5 ppm. The Front Range Mineral Belt west of
 Denver hosts a number of uranium occurrences and inactive uranium mines.  County indoor radon
 averages generally are greater than 4 pCi/L, except in the San Juan Mountains in south-central
 Colorado, where the county radon averages range from 1 to 4 pCi/L (fig. 3). The Southern Rocky
 Mountains generally have high radon potential, with the main exception being the volcanic rocks of
 the San Juan volcanic field (located in the southwestern part of the province) which have moderate
 radon potential.
        The part of the Colorado Plateau Province in Region 8 has a band of high radon potential
 and a core of moderate'radon potential (figs. 1,3).  The band of high radon potential consists
 largely of: (1) the Uravan Mineral Belt, a uranium mining district, on the east; (2) the Uinta Basin,
 which contains uranium-bearing Tertiary rocks, on the north; and (3) Tertiary volcanic rocks,
 which have a high aeroradiometric signature, on the west The moderate radon potential zone in
 the interior part of the province is underlain primarily by sedimentary rocks, including sandstone,
 limestone, and shale, which have a low aeroradiometric signature. County average screening
 indoor radon levels in the Colorado Plateau are mostly greater than 2 pCi/L (fig. 3).
       The part of the Basin and Range Province lying in EPA Region 8 has moderate geologic
radon potential. The part of the province which is in Region 8 is actually a part of the Great Basin
 Section of the Basin and Range Province. The entire province is laced with numerous faults, and
large displacements along the faults are common. Many of the faulted mountain ranges  have high
aeroradiometric signatures, whereas the intervening valleys or basins often have low
aeroradiometric signatures.  Because of the numerous faults and igneous intrusions, the geology is
highly variable and complex. Indoor radon levels are similarly variable, with county averages
ranging from less than 1 pCi/L to more than 4 pCi/L (fig. 3).
                                           ffl-6    Reprinted from USGS Open-File Report 93-292-H

-------
       PRELIMINARY GEOLOGIC RADON POTENTIAL ASSESSMENT OF MONTANA
                                            by
                                     Douglass E. Owen
                                   U.S. Geological Survey

  INTRODUCTION

        Montana lies along the border with Canada in the continental interior of the United States
  between 45 and 49 degrees north latitude and 104 and 116 degrees west longitude.  It covers an
  area of 147,138 square miles and is the fourth largest state in the union; only Alaska, Texas, and
  California are larger. Montana is divided into a number of counties shown on figure 1. It is a rural
  state and agriculture, ranching, forestry, and mining are major economic activities. Most of the
  counties in Montana have less than 10,000 inhabitants. Yellowstone County, which contains the
  city of Billings, is the only county  that has a population of greater than 100,000 people (figs. 1,2).
        This is a generalized assessment of the geologic radon potential of rocks, soils, and
  surficial deposits of Montana. The scale of this assessment is such that it is inappropriate for use
  in identifying the radon potential of small areas such as neighborhoods, individual building sites,
  or housing tracts. Any localized assessment of radon potential must be supplemented with
  additional data and information from the locality. Within any area of a given radon potential
 ranking, there are likely to be areas with higher or lower radon levels than characterized for the area
 as a whole. Indoor radon levels, both high and low, can be quite localized, and there is no
 substitute for testing individual homes.  Elevated levels of indoor radon have been found in every
 state, and EPA recommends that all homes be tested. For more information on radon, the reader is
 urged to consult the local or State radon program or EPA regional office. More detailed
 information on state or local geology may be obtained from the Montana Bureau of Mines and
 Geology. Addresses and phone numbers for these agencies are listed in chapter 1 of this booklet.

 GEOGRAPHIC SETTING

       Montana can be divided into three physiographic divisions (fig. 3). Each division covers
 approximately one third of the State and forms a diagonal (NW-SE) band. The westernmost
 physiographic division is the Rocky Mountains. This division is made up of 42 named mountain
 areas (Perry, 1962). The major mountain ranges are shown on figure 4. These mountain ranges
 are separated by large valleys  5 to 25 miles wide and up to 50 or more miles long (Perry, 1962).
       The middle physiographic division, Plains and Mountains, is a continuation of the Great
 Plains that is broken by isolated island-like mountains ranges (figs. 3,4). The easternmost
 physiographic division in Montana (fig. 3) is a part of the Great Plains Province. The glaciated
 parts of the Great Plains in Montana (delineated on figure 5) are topographically smoother and less
 dissected than the unglaciated  parts found in the south.
       The Missouri and Yellowstone Rivers with their tributaries form the major drainage
 systems in Montana (fig. 4). Topographic elevations in Montana range from about 2,000 feet in
 the east, where the Missouri and Yellowstone Rivers exit the State, to more than 12,000 feet in the
mountains of the west Most of the major mountain areas receive 40 or more inches of
precipitation per year, and some of the mountain areas in the northwestern part of the State receive
over 100 inches. Yearly precipitation in the intermontane valleys in the southwestern part of the
state is 12 inches or less, whereas the intermontane valleys in the northwestern part of the state
                                          IV-1    Reprinted from USGS Open-File Report 93-292-H

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 receive about 16 inches.  Areas within the Great Plains generally receive 12 or less inches of
 precipitation per year, with more than half of the annual precipitation falling during the growing
 season (Taylor and others, 1974).

 GEOLOGIC SETTING

        Geologic formations found in Montana range in age from Precambrian to Holocene.
 (Note~A geologic time scale is provided for reference in the introduction to this volume.) A
 simplified geologic map of the State is shown in figure 6. Precambrian rocks are only exposed in
 the western part of the State and are dominantly metamorphic rocks. The oldest Precambrian rocks
 are found in the southwestern part of the state and consist of gneiss, schist, quartzite, and marble.
 The younger Precambrian rocks, known as the Belt Supergroup, dominate the northwestern part of
 Montana, but are also present in southwestern corner of the State. The Belt Supergroup is made
 up largely of quartzites, argillites, impure limestones, and conglomerates.
        Paleozoic rocks do not have an extensive outcrop pattern in the State, but are found in some
 of the mountain areas (fig. 6). The Paleozoic rocks are dominantly limestones and dolomites, but
 some sandstones and shales are present. Mesozoic rocks are present in the eastern two thirds of
 the State  (fig. 6) and consist of sandstones, shales, conglomerates, limestones, and some gypsum-
 bearing rocks. Cenozoic rocks consist of massive sandstones, shales, coals, clinker, volcanic ash,
 glacial deposits, and lacustrine deposits.
        Figure 5 shows the extent of Pleistocene glaciation in Montana. The continental glaciers
 smoothed out the northern part of the Great Plains in Montana by filling previously existing valleys
 with glacial deposits. The ice blocked many rivers, which previously flowed north, and formed
 huge glacial lakes. Water depth in some of these lakes reached 2,000 feet, which was the
 thickness  of the ice. Some of these ice-dammed lakes were over 100 miles long and covered
 hundreds  to thousands of square miles.  Tremendous floods, which produced extensive, very
 coarse-grained deposits (abundant cobbles and boulders), occurred when the ice dams were
 breached. Valley deposits that formed in the lakes or that were deposited during the floods are
 shown in  figure 7.

 SOILS

       Montana has 8 major soil types (fig. 8) that can be practically shown at the scale of this
 report.  Highly permeable soils allow convective transport of radon (Sextro and others, 1987).
 Alluvial soils (fig. 8) are commonly highly permeable because the fines have been winnowed by
 the moving water. The alluvial soils that formed on the great glacial flood deposits found in the
 southwestern part of the State are probably highly permeable. Soil permeabilities greater than 6
 inches per hour (water percolation rate listed in soil surveys) are considered highly permeable.
 Duval, Otton, and Jones (1989), in a study for the Bonneville Power Administration, examined
 some of the soil surveys for the western two-thirds of Montana.  They found soils  or intervals
 within soils that were described in the soil reports as having permeabilities greater than 6 inches per
hour for the following counties: Bighorn, Blaine, Broadwater, Carbon, Cascade, Judith Basin,
Lewis and Clark, Missoula, Phillips, Ravalli, and Stillwater.
       Fine-textured shallow to moderately deep soils over shale (fig. 8) are expected to have low
to moderate permeabilities and may inhibit radon transport  Soils above timberline (fig. 8) and
soils on forested mountain slopes in Montana receive 40 to, in some cases, more than 100 inches
                                          IV-7    Reprinted from USGS Open-File Report 93-292-H

-------
                       112
                                                 108
                                                (modified from Wltklnd and Grose. 1972).
EXPLANATION
n
  • *.
  • • •
Quaternary rocks and sediments


Tertiary sedimentary rocks


Mostly Cretaceous sedimentary rocks
 -_-'( Mixed Paleozoic, Triassic, and Jurassic rocks
       Precambrian sedimentary rocks
       Igneous and metamorphic rocks undifferentiated
  Fig  6.  Geologic Map of Montana

-------
                                                 SO1*0
                                     (modified from Perry, 1962)
Fig. 7. Valley Deposits

-------
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 of precipitation per year. Not many homes have been constructed above timberline, but many are
 found on forested mountain sides where high precipitation occurs. The resulting high soil
 moisture content in these areas can retard radon transport through soil pore spaces.

 INDOOR RADON DATA

        Figure 9 shows graphically the State/EPA Residential Radon Survey data used in this
 report The average measured indoor radon concentration was 4.1 pCi/L or greater for the
 following counties with 5 or more measurements: Beaverhead, Chouteau, Deer Lodge, Flathead,
 Gallatin, Garfield, Golden Valley, Jefferson, Judith Basin, Lewis and Clark, McCone, Meagher,
 Missoula, Park, Phillips, Pondera, Powder River, Powell, Prairie, Ravalli, Richland, Sanders,
 Sheridan, Silver Bow, Sweer Grass, Wheatland, and Wibaux (fig. 9). Table 1 presents a
 summary of the State/EPA Residential Radon Survey data. Two counties had maximum screening
 indoor radon concentrations over 100 pCi/L, Flathead County and Lewis and Clark County (Table
 1). With 833 measurements made in the State the average radon concentration for the State was
 5.9 pCi/L and the percent of homes measured with screening indoor radon concentrations equal to
 or greater than 4 pCi/L was 43.6 percent.

 GEOLOGIC RADON POTENTIAL

       Areas in the vicinity of known uranium occurrences have a high radon potential for several
 reasons other than the unlikely occurrence that homes would be built over an ore body itself: (1)
 Noncommercial concentrations of uranium are often also present in an area that contains ore-grade
 deposits; (2) Even minor mineralization (primary or secondary) of uranium along faults and
 fractures is enough to produce a radon hazard in homes built above them; (3) Sediments eroded
 and transported from rocks with elevated uranium and soils that develop on them are also likely to
 have elevated uranium levels.  Figures 10A and 10B show known uranium occurrences in
 Montana. Most of these occurrences are concentrated within the Rocky Mountains physiographic
 division (fig. 3), where, coincidentally, a large proportion of the population of Montana resides.
       Figure 11 is an equivalent uranium (eU) map for Montana. By comparing figure 6 with
 figure 11 it can be seen that most of the areas with more than 2.5 ppm eU in the western part of the
 state correspond to igneous and metamorphic rocks. As mentioned in the introduction to this
 volume, igneous and metamorphic rocks tend to be good sources of radon. Likewise, marine
 black shales tend to be good sources of radon because they are frequently uranium-bearing (Fix,
 1958). The Cretaceous sedimentary rocks (fig.  6) include the Pierre Shale, parts of which are
 known to be uranium-bearing (Tourtelot, 1956). The surficial materials in the eastern half of the
 State dominantly have eU signatures between 1.5 and 2.5 ppm, although some areas with eU
 signatures above and below this range exist (fig. 11).
       The glaciated portions of both the Great Plains and the Plains and Mountains physiographic
 divisions have a higher radon potential than their counterparts to the south because glacial action
 crushes and grinds up rocks. This crushing and grinding enhances weathering and increases the
 surface area from which radon may emanate and also exposes more uranium and radium at grain
 surfaces where they are more easily leached. Leached uranium and radium may be carried to a soil
 depth below the detection limit of surface gamma-ray surveys (approximately 30 cm), but still are
present at depths shallow enough to allow generated radon to migrate into a home.
                                         IV-l 1   Reprinted from USGS Open-File Report 93-292-H

-------
  Bsmt & 1st Floor Rn
      %>4pCi/L

         OtolO
         11 to 25
         26 to 50
         51 to 75
         76 to 100
         Missing Data
         or < 5 measurements
20
    BsmL & 1st Floor Rn
Average Concentration (pCi/L)
         0.0 to 1.9
         2.0 to 4.0
         4.1 to 10.0
         10.1 to 26.3
         Missing Data
         or < 5 measurements
                                                            100 Miles
Figure 9. Screening indoor radon data from the State/EPA Residential Radon Survey of
Montana, 1991-92, for counties with 5 or more measurements.  Data are from 2-7 day
charcoal canister tests.  Histograms in map legends show the number of counties in each
category. The number of samples in each county (See Table 1) may not be sufficient to
statistically characterize the radon levels of the counties, but they do suggest general trends
Unequal category intervals were chosen to provide reference to decision and action levels

-------
TABLE 1.  Screening indoor radon data from the EPA/State Residential Radon Survey of
Montana conducted during 1991-92. Data represent 2-7 day charcoal canister measurements
from the lowest level of each home tested.
COUNTY
BEAVERHEAD
BIG HORN
ELAINE
BROADWATER
CARBON
CARTER
[CASCADE
CHOUTEAU
CUSTER
DANIELS
DAWSON
DEER LODGE
FALLON
FERGUS
FLATHEAD
GALLATIN
GARFffiLD
GLACIER
GOLDEN VALLEY
GRANITE
HILL
JEFFERSON
JUDITH BASIN
LAKE
LEWIS AND CLARK 1
LIBERTY
LINCOLN
MADISON
MCCONE
MEAGHER
MINERAL
MISSOULA
MUSSELSHELL
PARK
PETROLEUM
PHILLIPS
PONDERA
POWDER RIVER
POWELL
PRAIRIE
RAVALLI
NO. OF
MEAS.
15
9
10
4
9
. 70
	 	
	 ~
5
10
	 9.
5
12
43
49
5
6
4
9
6
7
9
58
4
20
8
8
6
»
60
	 4
14
3
11
6
12
6
6
30
MEAh
6.3
2.5
2.8
8.3
•a o
3.8
3.8
4.3
3.1
1.8
r 1.8
7.2
3.7
3.9
8.9
6.1
60
2.3
4.9
5.0
2.9
9.2
6.7
3.0
10.7
8.5
3.9
2.7
4.4
4.9
_«
66 1
2.7
10.4
5.0
6.4
5.9
4.3
6.0
6.9
9.3
GEOM.
f MEAN
3.5
2.0
2.4
2.0
1 A
4.A
3.2
2.5
3.6
2.4
. 1-5
J— ~
5.0
3.1
2.9
3.3
4.2
49
1.8
4.5
4.5
2.3
4.4
5.4
1.6
5.0
6.7
1.9
2.2
3.7
4.2
1.5
Af.
2.6
3.3
3.7
4.4
5.1
3.2
4.7
5.2
4.9
MEDIAN
2.8
1.9
2.6
2.2
[ 2.5
3.3
2.0
4.1
2.5
1.2
1.3
4.1
4.0
3.6
2.6
5.3
A A
1A
2.1
4.6
4.2
2.7
6.9
6.7
1.4
4.0
8.7
1.8
2.1
3.9
3.8
2.5
A fi
1.O
2.4
4.5
4.3
6.4
5.1
3.9
3.8
7.2
3.4
STD.
DEV.
10.0
2.1
1.7
13.6
2.3
1.9
4.2
2.7
2.8
1.4
2.1
6.7
2.2
2.7
22.5
4.9
C f\
5.0
1.6
2.2
2.8
1.8
9.6
4.3
4.3
17.8
6.0
6.8
2.0
2.5
3.1
1.9
< C
DO
1.2
17.1
4.0
5.3
3.6
3.4
4.5
3.4
12.4
MAXIMUM
40.7
7.7
6.8
28.5
6.7
6.5
19.7
11.8
12.0
4.2
21.6
6.4
8.9
133.6
20.2
13.8
4.4
8.9
9.1
6.0
26.9
14.7
13.9
115.1
13.9
31.7
7.3
9.3
10.6
4.4
42.2
4.4
63.4
9.3
17.0
12.2
13.1
12.8
10.5
51.6
%>4pCi/L
33
11
10
25
45
44
26
50
21
20
10
56
40
42
30
57
60
20
67
50
22
67
71
22
48
. 50
30
13
50
50
40
58
25
64
67
55
83
42
33
83
47
%>20 nPi/T
7
25~]
0
0
0
0
0
0
0
»
— II-
5
2
0
0
o
— g-
17
0
0
16
0
5
0
	 	 ^
0
0
3
0
14
0
0
0
0
0
13

-------
TABLE 1 (continued). Screening indoor radon data for Montana.
COUNTY
HIGHLAND
ROOSEVELT
ROSEBUD
SANDERS
SHERIDAN
SILVER BOW
STILLWATER
SWEET GRASS
TETON
TOOLE
TREASURE
VALLEY
WHEATLAND
WIBAUX
YELLOWSTONE
NO. OF
MEAS.
11
4
11
14
9
35
9
10
5
2
6
7
5
5
101
MEAN
4.8
3.6
3.0
9.9
9.3
9.5
4.0
5.3
4.0
2.4
2.6
3.8
7.8
26.3
3.7
GEOM.
MEAN
4.4
3.4
2.4
2.7
7.1
6.1
3.2
3.6
2.0
2.3
2.0
3.6
5.1
24.7
2.9
MEDIAN
5.4
4.0
3.3
1.8
6.7
6.7
4.9
4.3
2.3
2.4
2.1
3.0
5.0
22.1
3.2
STD.
DEV.
1.9
1.1
1.7
20.2
7.6
9.3
2.3
4.3
4.9
1.1
1.8
1.4
8.6
11.5
2.7
MAXIMUM
7.7
4.5
5.6
69.1
27.1
44.3
6.8
12.5
12.2
3.2
5.8
5.6
22.8
46.0
14.6
%>4pCi/L
64
25
27
21
89
69
56
50
40
0
17
43
80
100
32
%>20 pCi/L
0
0
0
14
11
11
0
0
0
0
0
0
20
80
0

-------
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EXPLANATION
URANIUM OCCURRENCES •
tfattljncoui XM>m* vccwrMa
• 81. Momto B»r «a
¥«« t»t «Mki KnneKa J. 0. C. dims
481 ji PW mw '
3. 8««tH H*m~t A
4. Crescent mine UwMinvbHrMf thftftle
5. &mki«t MM 1 1. Jnwer rtik rei( piicers
"" t C 1. In Crttk
Ur»"«nii*eiiin| plxen 2. Cuoirlwrj YiHtj tru
6 1. Sllfllri bnn 3. Ukew Fbls
2. Bar vnie, 4. (Wey^jirliiM «i
3. Wh.lt Hiwk bis.
4. Elk Cirr KU
5. DarulSirMip
A
C 1. Pnm likt grespeet
2. MiaMOBnUM




              -Index map .howtog the location of nranlum- and thorinm-bearins deposit, and occurrence, in Idabo and M,
Fig.  10A. Uranium Occurrences
'ontana.
                                 *          *      **
                                                         (modified from Jarrcrd. 1857)
    10B. Uranium  Occurrences

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        Considering the geology, the known uranium occurrences, and the alluvial soils with high
 permeability, the Rocky Mountain physiographic'division has a high geologic radon potential.
 Other mountain areas in the Mountains and Plains physiographic division have rocks with similar
 lithologies and eU to those found in the Rocky Mountains.  In addition, some also contain known
 uranium occurrences. Consequently, they have been grouped with the Rocky Mountains as having
 a high geologic radon potential. Lloyd (1983) found that the average radon concentrations in
 outside air at a monitoring station on Hornet street in Butte were between 3 and 6 pCi/L from May
 through October. When outside air concentrations are above 4 pCi/L, air inside homes is also
 expected to be above 4 pCi/L. Other areas in Butte tested at this time were not nearly as extreme,
 but this stresses the importance of ambient radon concentration in outside air. Temperature
 inversions occur in the intermontane valleys of the Rocky Mountain physiographic division during
 the winter months and may trap radon and other air pollutants and exacerbate radon mitigation
 attempts. Because of the construction techniques employed in the mountain regions of Montana,
 mitigation using sub-slab suction has been very effective and can frequently be done with less than
 $300 worth of materials (Personal communication with Adrian Howe, Montana Department of
 Health and Environmental Science, 1992).

 SUMMARY

       Geologic radon potential areas for Montana are shown in figure 12. These areas have been
 evaluated using the RADON INDEX MATRIX (RI) and the CONFIDENCE INDEX MATRIX
 (CI) discussed in the introduction to this volume. This evaluation is presented in Table 2. Area 1
 consists of the Rocky Mountains and other mountain areas and has a high radon potential at a high
 confidence level.  Area 2, which is the glaciated portion of the Great Plains, has a high  geologic
 radon potential at a moderate confidence level. This area was assigned 2 GFE points despite a
 number of the counties having indoor radon averages below 4 pCi/L (fig. 9) because similar
 lithologic units in the glaciated area of North Dakota have showed a high incidence of homes with
 greater than 4 pCi/L (Schumann and others, 1991). Area 3, underlain primarily by Cretaceous and
 Tertiary sedimentary rocks, is ranked in geologic radon potential at a moderate confidence level.
 Area 4, which is made up of Tertiary sedimentary rocks that are known uranium producers in the
 Powder River Basin in Wyoming, has a high radon potential at a moderate confidence level.  Area
 5, mostly Cretaceous sedimentary rocks, ranked in the high end of the moderate range at a
 moderate confidence level.
       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
 noj be made without consulting all available local data. For additional information on radon and
how to test, contact your State radon program or EPA regional office. More detailed information
 on state or local geology may be obtained from the State geological survey. Addresses  and phone
numbers for these agencies  are listed in chapter 1 of this booklet
                                         IV-17    Reprinted from USGS Open-FUe Report 93-292-H

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 TABLE 2. Radon Index (RI) and Confidence Index (CI) scores for geologic radon potential
 areas of Montana.
FACTOR
INDOOR RADON
RADIOACTIVITY
GEOLOGY
SOIL PERM.
ARCHITECTURE
GFE POINTS
TOTAL
Areal
RI CI
3
3
3
2
2
0
13
3
3
2
2
-
-
10
Area 2
RI CI
2
2
3
2
2
2
13
3
2
2
2
-
-
9
Area 3
RI CI
2
2
2
2
2
0
10
3
2
2
2
_
_
9
        RANKING HIGH  HIGH
       RANKING HIGH  MOD
HIGH  MOD
FACTOR
INDOOR RADON
RADIOACTIVITY
GEOLOGY
SOIL PERM.
ARCHITECTURE
GFE POINTS
TOTAL
Area 4
RI CI
3
2
3
2
2
0
12
3
2
2
2
-
-
9
Area 5
RI CI
3
2
2
2
2
0
11
3
2
2
2
_
_
9
MOD  MOD
MOD  MOD
Radon potential cateporv
LOW
MODERATE/VARIABLE
HIGH
Point ranse
3-8 points
9- 11 points
> 1 1 points
Probable screening indoor
radon average for area
<2pCi/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-18   Reprinted from USGS Open-File Report 93-292-H

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                        REFERENCES CITED IN THIS REPORT
          AND GENERAL REFERENCES RELAVENT TO RADON IN MONTANA

 Alt, D. and Hyndman, D.W., 1986, Roadside Geology of Montana: Mountain Press Publishing
       Company, 427 p.

 AAPG, 1972, Geologic Highway Map-NORTHERN ROCKY MOUNTAIN REGION-Idaho,
       Montana, Wyoming: AAPG, Tulsa, Oklahoma.

 Anderson, J.A., Feldmann, R.M., and Palmer, D.F., 1975, A Summary of Reserve and Resource
       Data on Coal, Uranium, and Oil Shale in the States of Michigan, Ohio, Kentucky,
       Tennessee, West Virginia, North Dakota, South Dakota, Montana, Wyoming, Colorado,
       and Utah: American Petroleum Institute, p. 41-44.

 Anderson, J.J., Palmer, D.F., and Feldman, R.M., 1975, Reserve and Resource Data on Coal,
       Uranium, and Oil Shale in the States of North Dakota, South Dakota, Montana, Wyoming,
       Colorado, Utah, Michigan, Ohio, Kentucky, Tennessee, and West Virginia: American
       Petroleum Institute, p. 13-21.

 Becraft, G.E., 1958, Uranium in Carbonaceous Rocks in the Townsend and Helena Valleys
       Montana: U.S. Geological Survey Bulletin 1046-G, 15 p.

 Blaster, C.A., 1980, Stratigraphic Nomenclature Chart for Montana and Adjacent Areas: Montana
       Bureau of Mines and Geology Geologic Map 8.

 Carmichael, R.S., 1989, Practical Handbook of Physical Properties of Rocks and Minerals: CRC
       Press, Inc., 741 p.

 Durance, E.M., 1986, Radioactivity In Geology, Principles and Applications: John Wiley & Sons,
       441 p.

 Duval, J.S., 1989, Radioactivity And Some Of Its Applications In Geology, in Proceedings on the
       Application of Geophysics to Engineering and Environmental Problems: Society of
       Engineering and Mineral Exploration Geophysicists, p. 1-61.

 Duval, J.S., Otton, J.K., and Jones, W.J., 1989, Estimation of Radon Potential in the Pacific
       Northwest Using Geological Data: U.S. Department of Energy, Bonneville Power
       Administration, 146 p.

Duval, J.S., Jones, W.J., Riggle, F.R., and Pitkin, J.A., 1989, Equivalent uranium map of the ,
       conterminous United States: U.S. Geological Survey Open-File Report 89-478,10 p.

Eisenbud, M., 1987, Environmental Radioactivity From Natural, Industrial, and Military Sources:
       Academic Press, Inc., 475 p.

Fix, C.E., 1958, Selected annotated bibliography of the geology and occurrence of uranium-
       bearing marine black shales in the United States: U.S. Geological Survey Bulletin 1059-F
       65 p.
                                       IV-20    Reprinted from USGS Open-File Report 93-292-H

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  Greenwood, W.R., Ludington, S., Miller, W.R., Hanna, W.F., Wenrich, K.J., Suits, V.J., and
         McHugh, J.B., 1990, Mineral Resources of the Elkhorn Wilderness Study Area,
         Broadwater and Jefferson Counties, Montana: U.S. Geological Survey Bulletin 1805,
         37 p.

  Habashi, R, 1970, Uranium in Phosphate Rock: Montana Bureau of Mines and Geology Special
         Publication 52,33 p.

  Jarrard, L.D., 1957, Some Occurrences of Uranium and Thorium in Montana: Montana Bureau of
        Mines and Geology Miscellaneous Contribution No. 15, 90 p.

  Lloyd, L.L., 1983, Evaluation of Radon Sources and Phosphate Slag in Butte, Montana- EPA
        520/6-83-026, 75 p.

  Perry, E.S., 1962, Montana in the Geologic Past: Montana Bureau of Mines and Geology Bulletin
        ^o, /y p.

  Raines, G.L. and Marrs, R!W., 1983, Lithofacies Map, Cross Section, and Favorable Areas for
        Uranium Deposits, Powder River Basin, Wyoming and Montana: U.S. Geological Survey
        Map 1-1501.                                                                 *

  Sahinen, U.M., 1956, Prospecting for uranium in Montana: Montana Bureau of Mines and
        Geology Information Circular No. 6,13 p.

 Schumann, R.R., Peake, R.T., Schmidt, K.M., and Owen, D.E., 1991, Correlations of soil-gas
        and indoor radon with geology in glacially derived soils of the Northern Great Plains, in
        Proceedings of the 1990 International Symposium on Radon and Radon Technology U S
        Environmental Protection Agency EPA600/9-91-026b, v. 2, p. 6-23 to 6-36.

 Sextro, R.G., Moed, B.A., Nazaroff, W.W., Revzan,  K.L., and Nero, A.V., 1987,
       Investigations of soil as a source of indoor radon, in Hopke, P.K., (ed), Radon and its
       decay products-Occurrence, properties, and health effects: Washington, D.C., American
       Chemical Society Symposium Series 331, p. 10-29.

 Sharp, W.N. and Cavender, W.S., 1962, Geology and Thorium-Bearing Deposits of the Lemhi
       Pass Area Lemhi County, Idaho, and Beaverhead County, Montana: U.S. Geological
       Survey Bulletin 1126,76  p.

 Sonderegger, J.L., 1987, Discussion of "Radon and Radium Emanations from Fractured
       Crystalline Rocks~A Conceptual Hydrogeological Model," by Harry E. LeGrand
       January-February 1987 issue, v.  25, no. 1, pp. 56-69: Ground Water, v. 25, no. 3,
       p. 346.

Taylor, R.L., Edie, M.J., and Gritzner, C.F., 1974, Montana in Maps: Big Sky Books, Montana
       State University, Bozeman, Montana, 75 p.

Tpurtelot, H.A., 1956, Radioactivity and uranium content of some Cretaceous Shales Central
       Great Plains:  AAPG Bulletin, v. 40, p. 62-83.
                                        IV-21    Reprinted from USGS Open-File Report 93-292-H

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Trites, A.F. and Tooker, E.W., 1953, Uranium and Thorium Deposits in East-Central Idaho,
       Southwestern Montana: U.S. Geological Survey Bulletin 988-H, 52 p.

Weis, P.L., Armstrong, F.C., and Rosenblum, S., 1958, Reconnaissance for Radioactive
       Minerals in Washington, Idaho, and Western Montana 1952-1955: U.S. Geological
       Survey Bulletin 1074-B, 48 p.
                                        IV-22    Reprinted from USGS Open-File Report 93-292-H

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                             EPA's Map of Radon Zones


        The USGS1 Geologic Radon Province Map is the technical foundation for EPA's Map
  of Radon Zones.  The Geologic Radon Province Map defines the radon potential for
  approximately 360 geologic provinces.  EPA has adapted this information to fit a county
  boundary map in order to produce the Map of Radon Zones.
        The Map of Radon Zones is based on the same range of predicted screening levels of
  indoor radon as USGS1 Geologic Radon Province  Map. EPA defines the three zones as
  follows:  Zone One areas have an average predicted indoor radon screening potential greater
  than 4 pdfL.  Zone Two areas are predicted to have an average indoor radon screening
  potential between 2 pCi/L and 4 pCi/L.  Zone Three  areas  are predicted to have an average
  indoor radon screening potential less than 2 pCi/L.
        Since the geologic province boundaries cross state and county boundaries, a strict
 translation of counties from the Geologic Radon Province Map  to the Map of Radon Zones
 was not possible.  For counties that have variable  radon potential (i.e., are located in two or
 more provinces of different rankings), the counties were assigned to a zone based on the
 predicted radon potential of the province in which most of its area lies   (See Part I  for more
 details.)
 MONTANA MAP OF RAnrw
       The Montana Map of Radon Zones and its supporting documentation (Part IV of this
 report) have received extensive review by Montana geologists and radon program experts
 The map for Montana generally reflects current State knowledge about radon for its counties.
 Some States have been able to conduct radon investigations in areas smaller than geologic
 provinces and counties, so it is important to consult locally available data.
       Four county designations do not strictly follow the methodology for adapting the
 geologic provinces to county boundaries. EPA and the Montana Department of Health and
 Environmental Sciences have decided to  include Park, Fergus, Stillwater and Carter as Zone  1
 counties.  These designations have been made based on the Montana State radon survey
 results and on the past experiences  of the Occupational and Radiological Health Bureau that
 indicate consistently elevated levels of radon have been found in these areas.
       Although the information provided in Part IV of this report -- the State chapter  entitled
 "Preliminary Geologic Radon Potential Assessment of Montana" -- may  appear to be quite
 specific, it cannot be applied to determine the radon levels of a neighborhood housing tract
 individual house, etc   THE ONLY WAY TO DETERMINE IF A HOUSE' HAS
 ELEVATED INDOOR RADON IS TO TEST.  Contact the Region 8 EPA office or the
Montana radon program for information on testing and fixing homes.  Telephone numbers and
addresses can be found in Part II of this report.
                                         V-l

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