United States
             Environmental Protection
                  Air and Radiation
September 1993
EPA's Map of Radon Zones


             RADON DIVISION
             SEPTEMBER, 1993


       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.


               I. OVERVIEW


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


        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 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
_Leygls_."_ This map was based on Ijmited geologic information only because few indoor radon
 measurements were available at the time.  The development of EPA's Map of Radon  Zones
 and its technical foundation, USGS' National Geologic Radon Province Map, has been based
 on additional information from six years of the State/EPA Residential  Radon Surveys,
 independent  State residential surveys, and continued  expansion of geologic and geophysical
 information,  particularly the data from the National  Uranium Resource Evaluation project.

 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 (o Radon Reduction and the Home Buyer's and Seller's Guide to
       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  prderjp e_xmineJhejadjan,j)jol^^                 Sjates^thjLUSGS	
 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





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

 Map Validation

       The Map of Radon  Zones is intended to represent a preliminary assessment of radon
 potential for  the entire United States.  The factors that  are used in  this effort -indoor radon
 data, geology, aerial radioactivity, soils, and foundation type — are basic indicators for radon
 potential.  It  is important to note, however, that the map's county zone designations are not
 "statistically valid" predictions due to  the nature of the data available  for these 5 factors at the
 county level. In order to validate the map in light of this lack of statistical confidence, EPA
 conducted a number of analyses.  These analyses have  helped EPA to identify  the best
situations in which to apply the map, and its limitations.

Figure 3
                Geologic  Radon  Potential  Provinces for  Nebraska
                   Ut> 4 e r 11 e
Figure 4
         NEBRASKA -  EPA Map of  Radon Zones
         Li tea I a J3p u n t y  -^
         Zoae 1    Zone 2    Zone 3

       One such analysis involved comparing county zone designations to indoor radon
 measurements from the State/EPA Residential Radon Surveys (SRRS). Screening  averages
 for counties with at least 100 measurements were compared  to the counties' predicted radon
 potential as indicated by the Map of Radon Zones.  EPA found that 72% of the county
 screening averages were correctly reflected by the appropriate zone designations on the Map.
 In all other cases, they only differed by 1 zone.
       Another accuracy analysis used the annual average data from the National  Residential
 Radon Survey (NRRS).  The NRRS  indicated that approximately 6 million homes in the
 United States have annual averages greater than or equal to 4 pCi/L.  By cross checking the
 county location of the approximately 5,700 homes which participated in the survey, their
 radon measurements,  and the zone designations for these counties,  EPA found that
 approximately 3.8 million homes of the 5.4 million homes with radon levels greater than or
 equal to 4  pCi/L will be found in counties designated as Zone 1.  A random sampling of an
 equal number of counties would have only found approximately 1.8 million homes greater
 than 4 pCi/L. In other words, this analysis indicated that the map approach is three times
 more efficient at identifying high radon areas than random selection of zone designations.
       Together, these analyses show that the approach EPA used to develop  the Map of
 Radon Zones is a reasonable one.  In addition, the Agency's  confidence is enhanced by results
 of the extensive State review process -- the map  generally agrees with the States' knowledge
 of and experience in their own jurisdictions. However, the accuracy analyses highlight two
 important points:  the fact that elevated levels  will be found  in Zones 2 and 3, and that there
 will  be significant numbers of homes with lower indoor radon levels in all of the Zones. For
 these reasons, users of the Map of Radon Zones need to supplement the Map with locally
 available data whenever possible. Although all known  "hot spots", i.e., localized areas of
 consistently elevated levels,  are discussed in the State-
 specific chapters, accurately defining the boundaries of the "hot  spots" on this scale of map is
 not possible at this time.  Also, unknown "hot spots" do exist.
       The Map of Radon Zones is intended to be a starting  point for  characterizing radon
 potential  because our  knowledge of radon  sources and transport  is always growing. Although
 this effort represents the  best data available at this time, EPA will continue to study these
 parameters and others such as house construction, ventilation features and meteorology factors
 in order to better characterize the presence of radon in U.S homes, especially in high risk
 areas.  These efforts will eventually assist  EPA in refining and revising the conclusions of the
 Map of Radon Zones. And  although this map is most appropriately used as a targeting tool
 by the aforementioned audiences - the Agency encourages all  residents to test their homes
 for radon, regardless of geographic location or the zone designation of the county in
which they live. Similarly, the Map of Radon Zones should not to be used in lieu of
 testing during  real estate transactions.

 Review Process
       The Map of Radon Zones has undergone extensive review within EPA and outside the
Agency.  The Association of American State Geologists (AASG) played an integral role in
this review process.  The AASG individual State geologists have reviewed their State-specific
information, the USGS Geologic Radon Province Map, and other materials for their geologic
content and consistency.

       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.

                      Linda C.S. Gundersen and R. Randall Schumann
                                   U.S. Geological Survey
                                     Sharon W. White
                            U.S. Environmental Protection Agency


     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 nor 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
~cWnty7 "Fin'allyVlhe'b^ok^^
 accompanying description (Part V).
     Because of constraints  on the scales of maps presented in these reports and  because the
 smallest units used to present the indoor radon data are counties, some generalizations have
 been  made in order to estimate the radon potential of each area.  Variations in  geology, soil
 characteristics, climatic factors, homeowner lifestyles, and other factors that influence radon
 concentrations can be quite large within any particular geologic area, so these reports cannot
 be used to estimate or predict the indoor radon concentrations of individual homes or housing

                                            II-1     Reprinted from USGS Open-File Report 93-292

 tracts.  Within any area of a given geologic radon potential ranking, there are likely to be
 areas where the radon potential is lower or higher than that assigned to the area as a whole,
 especially in larger areas such as the large counties in some western states.
     In each state chapter,  references to additional reports related to radon are listed for the
 state, and the reader  is urged to consult these reports for more detailed information.  In most
 cases the best sources of information on radon for specific areas are state and local
 departments of health, state departments responsible for nuclear safety or environmental
 protection, and U.S. EPA  regional offices.  More detailed information on state or local
 geology may be obtained  from the state geological  surveys. Addresses and telephone
 numbers of state radon contacts, geological surveys, and EPA regional offices are  listed in
 Appendix C at the end of this chapter.


     Radon (2"Rn) is produced from  the  radioactive  decay of radium (226Ra), which is, in turn,
 a product of the decay of uranium (23SU) (fig. 1).  The half-life of 222Rn is 3.825 days. Other
 isotopes of radon occur naturally, but; with the exception of th&ron (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


and moisture infiltration rates and depth of wetting may be limited when the cracks in the
surface soil layers swell shut.  Clay-rich B horizons, particularly those with massive or platy
structure, can form a capping layer that impedes the escape of soil gas to the surface
(Schumann and others, 1992).  However, the shrinkage of clays can act to open or widen
cracks upon drying, thus increasing the soil's permeability to gas flow during drier periods.
       Radon transport in soils occurs by two  processes: (1) diffusion and (2) flow (Tanner,
1964). Diffusion is the process whereby radon atoms move from areas of higher
concentration to areas of lower concentration in response to a concentration gradient.  Flow is
the process by which soil air moves through soil pores in response to differences in pressure
within the soil or between the soil and the atmosphere, carrying the radon atoms along with it.
Diffusion is the dominant radon transport process in soils of low permeability, whereas flow
tends to dominate in highly permeable soils (Sextro and others, 1987).  In low-permeability
soils, much of the radon may decay before it is able to enter a building because its transport
rate is reduced.  Conversely, highly permeable soils, even those that are relatively low in
radium, such as those derived from some types of glacial deposits, have been  associated with
high indoor radon levels in Europe and in the  northern United States (Akerblom and others,
1984; Kunz and others, 1989; Sextro and others, 1987).  In area's of karst topography formed
in carbonate rock (limestone or dolomite) environments, solution cavities and  fissures can
increase soil permeability at depth by providing additional pathways for gas flow.
    Not all radium contained in soil grains and grain coatings will result in mobile radon
when the radium decays.  Depending on where the radium is distributed in the soil, many of
the radon atoms may remain imbedded in the soil grain containing the parent  radium atom, or
become imbedded in adjacent soil grains.  The portion of radium that releases radon into the
pores and fractures of rocks and soils is called the emanating fraction.  When a radium atom
decays to radon, the energy generated is strong enough to send the radon atom a distance of
about 40 nanometers (1 nm =  10'9 meters),  or about 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-Pennsylvaniar The most-important	
factors appear to be (1) soil moisture conditions, which are controlled in large part by
precipitation; (2) barometric pressure;  and (3)  temperature. Washington  and Rose (1990)
suggest that temperature-controlled partitioning of radon between water and gas in soil pores
also has a significant influence on  the amount of mobile radon  in soil gas.
    Homes in hilly limestone regions of the southern Appalachians were found to  have  higher
indoor radon concentrations during the summer than in the winter.  A suggested cause for this
phenomenon involves temperature/pressure-driven flow of radon-laden air from subsurface

                                           II-4    Reprinted from USGS Open-File Report 93-292

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


    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.


    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.


    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 mosriikely^o^aure indoon-a^
 bearing sandstones, certain kinds of fluvial sandstones and fluvial sediments, phosphorites,
 chalk, karst-producing carbonate  rocks,  certain kinds  of glacial  deposits, bauxite, uranium-rich
 granitic rocks, metamorphic rocks of granitic composition, silica-rich volcanic rocks, many
 sheared or faulted rocks, some coals, and certain  kinds of contact metamorphosed  rocks.
 Rock types least likely to cause radon problems include marine quartz sands, non-
 carbonaceous shales and siltstones, certain  kinds of clays,  silica-poor metamorphic and

                                           II-5      Reprinted from USGS Open-File  Report 93-292

igneous rocks, and basalts.  Exceptions exist within these general lithologic groups because of
the occurrence of localized uranium deposits, commonly of the hydrothermal type in
crystalline rocks or the "roll-front" type in sedimentary rocks. Uranium and radium are
commonly sited in heavy minerals, iron-oxide coatings on rock and soil grains, and organic
materials in soils and sediments.  Less common are uranium associated with phusphate 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,


    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 (2UBi), with the assumption  that uranium and
its decay products are in secular equilibrium. Equivalent uranium is expressed in units of
parts per million (ppm).  Gamma radioactivity also may be expressed in terms of a radium
activity; 3 ppm eU corresponds to approximately 1 picocurie per gram (pCi/g) of radium-226.
Although radon is highly mobile  in soil and its concentration  is  affected by meteorological
conditions (Kovach,  1945; Klusman and Jaacks, 1987; Schery and others, 1984; Schumann
and others, 1992), statistical correlations between average soil-gas radon concentrations and
average eU values for a wide variety of soils have  been documented (Gundersen and others,
1988a, 1988b; Schumann and Owen, 1988).  Aerial radiometric  data can provide an estimate
of radon source strength over a region, but the amount of radon that is able to enter a home
from the soil is dependent on several local factors, including soil structure, grain size
distribution, moisture content, and permeability, as well as type of house construction and its
structural condition.
    The aerial radiometric data used for these characterizations were collected as part of the
Department  of Energy National Uranium Resource Evaluation (NURE) program of the 1970s
and early  1980s.  The purpose of the NURE program was to identify and describe areas  in the
United States having potential  uranium resources (U.S. Department of Energy, 1976). The
NURE aerial radiometric data were -collected-by^aircraft in~whirh^a"
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

                     2 KM  (1  MILE)
                     5 KM  (3  MILES)
                     2 & 5  KM
                     10 KM  (6 MILES)
                     5 t 10  KM
                     NO DATA
Figure 2. Nominal flightline spacings for NURE aerial gamma-ray surveys covering the
contiguous United States (from Duval and others, 1990). Rectangles represent I°x2° quadrangles.

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


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

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


    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 (figi 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

    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.


    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-eomparison—	
 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-l 1     Reprinted from USGS Open-File Report 93-292

TABLE 1. RADON INDEX MATRIX, "ppm eU" indicates parts per million of equivalent
uranium, as indicated by NURE aerial radiometric data. See text discussion for details.

                                  INCREASING RADON POTENTIAL
INDOOR RADON (average)
< 1.5 ppm eU
mostly slab
2 - 4 pCi/L
1.5 - 2.5 ppm eU
> 2.5 ppm eU
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
            Radon potential category
                                   Probable average screening
                      Point range	indoor radon for area
                      3-8 points
                      9-11 points
                     12-17 points
           < 2 pCi/L
                     POSSIBLE RANGE OF POINTS = 3 to 17
                                    INCREASING CONFIDENCE
sparse/no data
.questionable/no data
questionable/no data
fair coverage/quality
glacial cover
good coverage/quality
no glacial cover
proven geol. model
reliable, abundant
 4-6  points
 7-9  points
10 -12 points
                     POSSIBLE RANGE OF POINTS = 4 to 12
                                    II-12     Reprinted from USGS Open-File Report 93-292

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

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

 been leached from the upper soil layers but are present and possibly even concentrated in
 deeper soil horizons, generating significant soil-gas radon.  This positive supporting field
 evidence adds two GFE points to the score, which helps to counteract the invalid conclusion
 suggested by the radiometric data. No GFE points are awarded if there are no documented
 field studies for the area.
     "Soil permeability" refers to several soil characteristics that influence radon concentration
 and mobility, including soil type, grain size, structure, soil  moisture, drainage, slope, and
 permeability.  In the matrix, "low" refers to permeabilities  less than about 0.6 in/hr; "high"
 corresponds to greater than about 6.0 in/hr, in U.S. Soil Conservation Service (SCS) standard
 soil percolation tests.  The  SCS data are for water permeability, which generally correlates
 well with the gas permeability of the soil except when the  soil moisture content is very high.
 Areas with consistently high water tables were thus considered to have low gas permeability.
 "Low, "moderate",  and "high" permeability were assigned  1, 2, and 3 points, respectively.
     Architecture type refers to whether homes in the area have mostly  basements (3 points),
 mostly slab-on-grade construction (1  point), or a mixture of the'two. Split-level and crawl
 space homes fall into  the "mixed" category (2 points).  Architecture information is necessary
 to properly interpret the indoor radon data and produce geologic radon potential categories
 that are consistent with screening indoor radon data.
     The overall RI for an area is calculated by adding the individual RI scores for the 5
 factors, plus or minus GFE points, if any.  The total RI for an area falls in one of three
 categories—low, moderate or variable, or high. The point ranges for the three categories were
 determined by examining the possible combinations of points for the 5  factors and setting
 rules such that a majority (3 of 5 factors) would determine the final score for the low and
 high categories, with allowances for possible deviation  from an ideal score by the other two
 factors. The moderate/variable category lies between these two ranges.  A total deviation of 3
 points from the "ideal" score was considered reasonable to  allow for natural variability of
 factors—if two of the five factors are allowed to vary from the "ideal"  for a category,  they
 can  differ by a minimum of 2 (1 point different each) and a maximum of 4 points (2 points
 different each). With "ideal" scores of 5, 10, and 15 points describing  low, moderate, and
 high geologic radon potential, respectively,  an ideal low score of 5 points plus 3 points for
 possible variability  allows a maximum of 8 points  in the low category.   Similarly, an ideal
 high score of 15 points minus 3 points gives a minimum of 12 points for the high category.
 Note, however, that if both  other factors differ by two points from the  "ideal", indicating
 considerable variability in the system, the total point score would lie in the adjacent (i.e.,
 moderate7vanablej category.                                                              ""
     Confidence Index. Except for architecture type, the same factors were used to establish a
 Confidence Index (CI) for the radon  potential prediction for each area (Table 2).  Architecture
 type was not included in the confidence index because house  construction data are readily and
 reliably available through surveys taken by  agencies and industry groups including the
National Association of Home Builders, U.S. Department of Housing and Urban
Development, and the Federal Housing Administration; thus it was not  considered necessary

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

to question the quality or validity of these data.  The other factors were scored on the basis of
the quality and quantity of the data used to complete the RI  matrix.
    Indoor radon data were evaluated based on the distribution and  number of data points and
on whether the data were collected by random sampling (State/EPA Residential Radon Survey
or other state survey data) or volunteered vendor data (likely to be nonrandom and biased
toward  population centers and/or high indoor radon levels).  The categories listed in the CI
matrix for indoor radon data ("sparse or no data", "fair coverage or  quality", and  "good
coverage/quality") indicate the sampling density and statistical robustness of an indoor radon
data set.  Data from the State/EPA Residential Radon Survey and statistically valid state
surveys were typically assigned 3 Confidence Index points unless the data were poorly
distributed or absent in the area evaluated.
    Aerial radioactivity data are  available for all but a few areas of the continental United
States and for part of Alaska.   An evaluation  of the quality of the radioactivity data was based
on whether there appeared to be a good correlation  between  the radioactivity and the actual
amount of uranium or radium available to generate  mobile radon in the rocks  and soils of the
area evaluated.  In general, the greatest problems with correlations among eU, geology, and
soil-gas or indoor radon  levels were associated with glacial deposits (see the discussion in a
previous section) and typically were assigned a 2-point Confidence Index score.   Correlations
among  eU, geology, and radon were generally sound in  unglaciated areas and  were usually
assigned 3 CI points.  Again, however, radioactivity data in  some unglaciated  areas may have
been  assigned fewer than 3 points,  and in glaciated  areas may be assigned only one point, if
the data were  considered questionable or if coverage was poor.
    To  assign Confidence Index  scores for  the geologic  data factor, rock types and geologic
settings for which a physical-chemical, process-based understanding of radon generation and
mobility exists were regarded as having "proven geologic  models" (3 points); a high
confidence could be held for predictions in such areas.  Rocks for which the processes are
less well  known or for which data are contradictory were  regarded as "variable" (2 points),
and those about which little is known or for which  no apparent correlations have been found
were deemed "questionable" (1 point).
    The soil permeability factor  was also scored based on quality and amount of data.  The
three categories for soil permeability in  the Confidence  Index are similar in concept, and
scored similarly, to those for the geologic data factor. Soil  permeability can be roughly
estimated from grain size and drainage class if data from standard, accepted soil percolation
tests  are unavailable; however, the  reliability  of the data would be lower than  if percolation
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

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

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

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Akerblom, G., Anderson, P., and Clavensjo, B., 1984, Soil gas radon—A source for indoor radon
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Deffeyes, K.S., and MacGregor, I.D., 1980, World uranium resources: Scientific American,
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Durrance, E.M., 1986, Radioactivity in geology: Principles and applications: New York, N.Y.,
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Duval, J.S., 1989, Radioactivity and some of its applications in geology:  Proceedings of the
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Duval, J.S., Cook, E.G., and Adams, J.A.S.,  1971, Circle of investigation of an airborne
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                                         II-17      Reprinted from USGS Open-File Report 93-292

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Kunz, C., Laymon, C.A., and  Parker, C., 1989, Gravelly soils and indoor radon, in Osborne,
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Muessig, K., and Bell, C, 1988, Use of airborne radiometric data to direct testing for elevated
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Schery, S.D., Gaeddert, D.H.,  and Wilkening, M.H., 1984, Factors affecting exhalation of radon
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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,j SchmidtrKM^, and-Owen,-B.E7r 1991,- Correlations of sothgas	
       and indoor radon with geology in glacially derived soils of the northern Great Plains, in
       Proceedings of the 1990 International Symposium on Radon and Radon Reduction
       Technology, Volume 2, Symposium Oral Papers:  U.S. Environmental Protection Agency
       report EPA/600/9-9 l/026b, p. 6-23-6-36.
                                         II-18     Reprinted from USGS Open-File Report 93-292

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

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

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

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

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

Tanner, A.B., 1980, Radon migration in the ground: a supplementary review, in Gesell, T.F.,
       and Lowder, W.M. (eds), Natural radiation environment IE, 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.
                                         JJ-19     Reprinted from USGS Open-File Report 93-292

                                               APPENDIX A
                                      GEOLOGIC TIME SCALE
Subdivisions {and their symbols)
Eon or


Era or
Cenozoic 2

Afchftin (V)
Period, System,
Subperiod, Subsystem
Neogene 2
Subperiod or
T.nfery Subsystem IN)
rn Paleogene
Suboeriod or
Subsystem (ft)
Carboniferous IP)
(C) Mississippian


Epoch or Series
Age estimates
of boundaries
in mega-annum

.0 ll.o-i.9J

,.„„ ee ffi'X-fifil

96 195-97}
j UO |Iftn f^cin^n^l

-• — •* Tlfl

-570 3

    1 Ranges reflect uncertainties of isotopic and biostrmtigraphic age assignments. Age boundaries not closely bracketed by existing
d»ta shown by ^ Decay constants and isoiopic ratios employed are cited in Steiger and JSger (1977). Designation m.y. used for an
Interval of lime.
    'Modifier* (lower, middle, upper or early, middle, late) when used with these hems are informal divisions of the larger unit: th«
first letltr ol th» modifier is lowercase.
    3 Rocks older than S70 Ma also ealted Precambrian (pC). a time term without specific rank.
    'informal time term without specific rank.
                                       USGS Open-File Report 93-292

                                     APPENDIX B
                               GLOSSARY OF TERMS
Units of measure

pCi/L (picdcuries per liter)- a unit of measure of radioactivity used to describe radon
concentrations in a volume of air. One picocurie (10~12 curies) is equal to about 2.2 disintegrations
of radon atoms per minute. A liter is about 1.06 quarts. The average concentration of radon in
U.S. homes measured to date is between 1 and 2 pCi/L.

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

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

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

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

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

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

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"

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, setm~aiiner-~grained~fnalrix 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"
                                          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

dolomite  A carbonate sedimentary rock of which more than 50% consists of the mineral dolomite
(CaMg(CO3)2), and is commonly white, gray, brown, yellow, or pinkish in color.

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

eolian  Pertaining to sediments deposited by the wind.

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

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

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

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

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

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

formation A mappable body of rock having similar characteristics.

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

gneiss A rock formed by metamorphism in which bands and lenses of minerals of similar
composition alternate with bands and lenses of different composition, giving the rock a striped or
"foliated" appearance.
granite-Broadly-appUed,-any coarsely crystdtin^^^                                       —
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
                                          IE-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

intermontane A term that refers to an area between two mountains or mountain ranges.

intrusion, intrusive The processes of emplacement or injection of molten rock into pre-existing
rock. Also refers to the rock formed by intrusive processes, such as an "intrusive igneous rock".

kame A low mound, knob, hummock, or short irregular ridge formed by a glacial stream at the
margin of a melting glacier; composed of bedded sand and gravel.

karst terrain A type of topography that is formed on limestone, gypsum and other rocks by
dissolution of the rock by water, forming sinkholes and caves.

lignite A brownish-black coal that is intermediate in coalification between peat and
subbituminous coal.

limestone A carbonate sedimentary rock consisting of more than 50% calcium carbonate,
primarily in the form of the mineral calcite (CaCOs).

lithology The description of rocks in hand specimen and in outcrop on the basis of color,
composition, and grain size.

loam A permeable soil composed of a mixture of relatively equal parts clay, silt, and sand, and
usually containing some organic matter.

loess A fine-grained eolian deposit composed of silt-sized particles generally thought to have
been deposited from windblown dust of Pleistocene age.

mafic Term describing an igneous rock containing more than 50% dark-colored minerals.

marine Term describing sediments deposited in the ocean, or precipitated from ocean waters.

metamorphic Any rock derived from pre-existing rocks by mineralogical, chemical, or structural
changes in response to changes in temperature, pressure, stress, and the chemical envkonment.
Phyllite, schist, amphibolite, and  gneiss are metamorphic rocks.

moraine A mound, ridge, or other distinct accumulation of unsorted, unbedded glacial material,
predominantly till, deposited by the action of glacial ice.

outcrop That part of a geologic formation-orstructurethalrappears at the surf ace of ^heEarthras
in "rock outcrop".

percolation test A term used in  engineering for a test to determine the water permeability of a
soil. A hole is dug and filled with water and the rate of water level decline is measured.

permeability The capacity of a rock, sediment, or soil to transmit liquid or gas.

phosphate,  phosphatic, phosphorite Any rock or sediment containing a significant amount
of phosphate minerals, i.e., minerals containing PO4.

                                          11-24     Reprinted from USGS Open-File Report 93-292

 physiographic province A region in which all parts are similar in geologic structure and
 climate, which has had a uniform geomorphic history, and whose topography or landforms differ
 significantly from adjacent regions.

 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

 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-holerehannel-or-eave-Hke-cavity-formed-by-dissolutiorrof-rockr	—

 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
                                            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

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

uraniferous Containing uranium, usually more than 2 ppm.

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

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

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

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

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

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

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

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

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

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

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

EPA Region 8
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 ..-,•... .•.•«..„»„.,.-..,-.,.,. .-,m-..-l-0-
  West Virginia	3
  Wisconsin	5
  Wyoming	8
         Reprinted from USGS Open-File Report 93-292

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

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

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

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

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

     Florida N. Michael Gilley
            Office of Radiation Control
            Department of Health and
              Rehabilitative Services
            1317 Winewood Boulevard
            Tallahassee, FL 32399-0700
            1-800-543-8279 in state

    Georgia Richard Schreiber
            Georgia Department of Human
            878 Peachtree St., Room 100
            Atlanta, GA 30309
            (404) 894-6644
            1-800-745-0037 in state
     Hawaii Russell Takata
            Environmental Health Services
            591 Ala Moana Boulevard
    	 — Honolulu, ffl 96813-2498	
            (808) 5864700
                                               E-28      Reprinted from USGS Open-File Report 93-292

 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
 1-800-383-5992 In State

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

 Jeana Phelps
 Radiation Control Branch
 Department of Health Services
 Cabinet for Human Resources
 275 East Main Street
 (502) 564-3700
    Louisiana  Matt Schlenker
              Louisiana Department of
                Environmental Quality
              P.O. Box 82135
              Baton Rouge, LA 70£ 34-2135
              1-800-256-2494 in state

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

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

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

    Michigan  Sue Hendershott
              Division of Radiological Health
              Bureau of Environmental and
                Occupational Health
              3423 North Logan Street
              P.O. Box 30195
              Lansing, MI 48909
              (517) 335-8194
   Minnesota  Laura Oatmann
              Indoor Air Quality Unit
              925 Delaware Street, SE
              P.O. Box 59040
              Minneapolis, MN 55459-0040
                                                                  1-800-798-9050 in state
                                             Reprinted from USGS Open-File Report 93-292

Mississippi     Silas Anderson
               Division of Radiological Health
               Department of Health
               3150 Lawson Street
               P.O. Box 1700
               Jackson, MS 39215-1700
               (601) 354-6657
               1-800-626-7739 in state

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

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

Nevada         Stan Marshall
               Department of Human Resources
               505 East King Street
               Room 203
               Carson City, NV 89710
               (702) 687-5394

New Hampshire David Chase
               Bureau of Radiological Health
               Division of Public Health Services
               Health and Welfare Building
               Six Hazen Drive
         -   - Concord, NH 03301	—	
               1-800-852-3345  x4674
   New Jersey Tonalee Carlson Key
              Division of Environmental Quality
              Department of Environmental
              Trenton, NJ 08625-0145
              (609) 987-6369
              1-800-648-0394 in state

  New Mexico William M. Floyd
              Radiation Licensing and Registration
              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
              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
              70 IBarbour Drive
              Raleigh, NC 27603-2008
              (919) 571-4141
              1-800-662-7301 (recorded info x4196)

 North Dakota Arlen Jacobson
              North Dakota Department of Health
              1200 Missouri Avenue, Room 304
              P.O. Box 5520
              Bismarck, ND 58502-5520
               Marcie Matthews
               Radiological Health Program
               Department of Health
               1224 Kinnear Road - Suite 120
               Columbus, OH 43212
                    644-2727 ----------
               1-800-523-4439 in state
        Reprinted from USGS Open-File Report 93-292

Puerto Rico
Rhode Island
South Carolina
 Gene Smith
 Radiation Protection Division
 Oklahoma State Department of
 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
Michael Pyles
Pennsylvania Department of
  Environmental Resources
Bureau of Radiation Protection
P.O. Box 2063
Harrisburg, PA 17120
(717) 783-3594
1-800-23-RADON In State

David Saldana
Radiological Health Division
G.P.O. Call Box 70184
Rio Piedras, Puerto Rico 00936
(809) 767-3563
Edmund Arcand
Division of Occupational Health and
Department of Health
205 Cannon Building
Davis Street
Providence, RI02908
               Bureau of Radiological Health
               Department of Health and
               2600 Bull Street
               Columbia, SC 29201
 South Dakota MikePochop
              Division of Environment Regulation
              Department of Water and Natural
              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
              Customs House, 701 Broadway
              Nashville, TN 37219-5403
              (615) 532-0733
              1-800-232-1139 in state

       Texas  Gary Smith
              Bureau of Radiation Control
              Texas Department of Health
              1100 West 49th Street
              Austin, TX 78756-3189
              (512) 834-6688
        Utah  John Hultquist
              Bureau of Radiation Control
              Utah State Department of Health
              288 North, 1460 West
              P.O. Box 16690
              Salt Lake City, UT 84116-0690
              (801) 536-4250

              Paul demons
              Occupational and Radiological Health
              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 II
              in New York
                                               II-31      Reprinted from USGS Open-File Report 93-292

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

Washington     KateColeman
               Department of Health
               Office of Radiation Protection
               Airdustrial Building 5, LE-13
               Olympia, WA 98504
               (206) 753-4518
                1-800-323-9727 In State

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

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

Wyoming       Janet Hough
                Wyoming Department of Health and
                  Social Services
                Hathway Building, 4th Floor
                Cheyenne, WY 82002-0710
                (307) 777-6015
                1-800-458-5847 in state
                                                 11-32      Reprinted from USGS Open-File Report 93-292

                              STATE  GEOLOGICAL  SURVEYS
                                              May, 1993
                Ernest A. Mancini
                Geological Survey of Alabama
                P.O. Box 0
                420 Hackberry Lane'
                Tuscaloosa, AL 35486-9780
                (205) 349-2852

 Alaska         Thomas E. Smith
                Alaska Division of Geological &
                  Geophysical Surveys
                794 University Ave., Suite 200
                Fairbanks, AK 99709-3645
                (907) 479-7147

 Arizona        Larry D. Fellows
                Arizona Geological Survey
                845 North Park Ave., Suite 100
                Tucson, AZ 85719
                (602) 882-4795
 Arkansas        Norman F. Williams
                Arkansas Geological Commission
                Vardelle Parham Geology Center
                3815 West Roosevelt Rd.
                Little Rock, AR 72204
                (501) 324-9165

 California       James F. Davis
                California Division of Mines &
                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
	HartfordrCT 06106	
                (203) 566-3540

 Delaware        Robert R. Jordan
                Delaware Geological Survey
                University of Delaware
                101 Penny Hall
                Newark, DE 19716-7501
                (302) 831-2833
         Walter Schmidt
         Florida Geological Survey
         903 W. Tennessee St.
         Tallahassee, FL 32304-7700
 Georgia  William H. McLemore
         Georgia Geologic Survey
         Rm. 400
         19 Martin Luther King Jr. Dr. SW
         Atlanta, GA 30334
         (404) 656-3214

 Hawaii  Manabu Tagomori
         Dept. of Land and Natural Resources
         Division of Water & Land Mgt
         P.O. Box 373
         Honolulu, HI 96809
         (808) 548-7539

   Idaho  Earl H. Bennett
         Idaho Geological Survey
         University of Idaho
         Morrill Hall, Rm. 332
         Moscow, ID 83843
         (208) 885-7991

 Illinois  Morris W. Leighton
         Illinois State Geological Survey
         Natural Resources Building
         Champaign, EL 61820
         (217) 333-4747

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

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

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

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

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

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

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

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

       Montana  Edward T. Ruppel
                Montana Bureau of Mines & Geology
                Montana College of Mineral Science
                  and Technology, Main Hall
                Butte, MT 59701
                (406) 496-4180

       Nebraska  Perry B. Wigley
                Nebraska Conservation & Survey
                113 Nebraska Hall
                University of Nebraska
                Lincoln, NE 68588-0517

        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

    New Mexico  Charles E. Chapin
                New Mexico Bureau of Mines &
                  Mineral Resources
                Campus Station
                Socoiro.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
                                                11-34      Reprinted from USGS Open-File Report 93-292

 North Carolina Charles H. Gardner
               North Carolina Geological Survey
               P.O. Box 27687
               Raleigh, NC 27611-7687
               (919) 733-3833
North Dakota
Puerto Rico
Rhode Island
 John P. Bluemle
 North Dakota Geological Survey
 600 East Blvd.
 Bismarck, ND 58505-0840
 (701) 224-4109
 Thomas M. Berg
 Ohio Dept. of Natural Resources
 Division of Geological Survey
 4383 Fountain Square Drive
 Columbus, OH 43224-1362
 (614) 265-6576

 Charles J. Mankin
 Oklahoma Geological Survey
 Room N-131, Energy Center
 Norman, OK 73019-0628

 Donald A. Hull
 Dept. of Geology  & Mineral Indust.
 Suite 965
 800 NE Oregon St. #28
 Portland, OR 97232-2162

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

 Ramdn M. Alonso
 Puerto Rico Geological Survey
 Box 5887
 Puerta de Tierra Station
 San Juan, P.R. 00906
South Carolina Alan-Jon W. Zupan (Acting)
              South Carolina Geological Survey
              5 Geology Road
              Columbia, SC 29210-9998

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

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

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

        Utah M. Lee Allison
              Utah Geological & Mineral Survey
              2363 S. Foothill Dr.
              Salt Lake City, UT 84109-1491
              (801) 467-7970
     Vermont Diane L.Conrad
              Vermont Division of Geology and
                Mineral Resources
              103 South Main St.
              Waterbury,VT 05671
              Stanley S. Johnson
              Virginia Division of Mineral
              P.O. Box 3667
              Charlottesville, VA 22903
 J. Allan Cain
 Department of Geology
 University of Rhode Island
 315 Green Hall
 Kingston, RI02881
 (401) 792-2265
  Washington Raymond Lasmanis
              Washington Division of Geology &
                Earth Resources
              Department of Natural Resources
              P.O. Box 47007
              Olympia, Washington 98504-7007
              (206) 902-1450
                                               11-35      Reprinted from USGS Open-File Report 93-292

  West Virginia Larry D. Woodfoik
               West Virginia Geological and
                 Economic Survey
               Mont Chateau Research Center
               P.O. Box 879
               Morgantown, WV  16507-0879

Wisconsin      James Robertson
               Wisconsin Geological & Natural
                 History Survey
               3817 Mineral Point Road
               Madison, WI 53705-5100

Wyoming      Gary B. Glass
               Geological Survey of Wyoming
               University of Wyoming
               Box 3008, University Station
               Laramie, WY 82071-3008
               (307) 766-2286
                                               E-36      Reprinted from USGS Open-File Report 93-292

        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
___ uraniujTijnd jadjum jnay_be^ansported dpjyn^^djn 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
                                            ffl-1    Reprinted from USGS Open-File Report 93-292-H

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)

                           16 EZj  0.0 to 1.9
                       76I///V1  2.0 to 4.0
                                 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/EHS
Indoor Radon Survey and from The Radon Project. Histograms in map legend
indicate the number of counties in each measurement category.

                                         RADON POTENTIAL
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
                                  ~         than^^i/L7figTT)7~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
                                          ffl-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 Yellowstone Plateau, Grand Tetons, and Big Horn Mountains
all have high geologic radon potential.
       The Southern Rocky Mountains Province lies dominantry 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
aeroracHometric 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).
                                           m-6    Reprinted from USGS Open-File Report 93-292-H

                                     Russell F. Dubiel
                                  U.S. Geological Survey


        Colorado is the birthplace of the uranium mining industry in the United States, which
 began with the discovery of pitchblende in 1871 in the mine tailings of the Wood mine in the
 Central City district of Gilpin County (Chenoweth, 1980). The subsequent development of the
 uranium mining industry in Colorado reflects the relative importance and abundance of three
 metals: radium, vanadium, and uranium.  In 1980 Colorado'ranked fourth in domestic uranium
 production behind New Mexico, Wyoming, and Utah (Chenoweth, 1980). Although uranium
 mining is not presently economically viable, uranium deposits occur in rocks  of many geologic
 ages and lithologies in Colorado. Because the uranium- and radium-bearing bedrock and the soils
 and alluvium developed from those rocks are widespread in Colorado, and because radon is a
 daughter product of uranium decay, many areas in the state have the potential to generate and
 transport radon in sufficient concentrations to be of concern in indoor air.
        This is a generalized assessment of geologic radon potential of rocks, soils, and surficial
 deposits of Colorado. The scale of this assessment is such that it is inappropriate for use in
 identifying the radon potential of small areas such as neighborhoods, individual building sites, or
 housing tracts. Any localized assessment of radon potential must be supplemented with additional
 data and information from the locality. Within any area of a given radon potential ranking, there
 are likely to be areas with higher or lower radon levels than characterized for the area as a whole.
 Indoor radon levels, both high and low, can be quite localized, and there is no substitute for testing
 individual homes. Elevated levels of indoor radon have been  found in every state, and EPA
 recommends that all homes be tested. For more information on radon, the reader is urged to
 consult the local or State radon program or EPA regional office.  More detailed information on state
 or local geology may be obtained from the State geological survey. Addresses and phone numbers
 for these agencies are listed in chapter 1 of this booklet.


        The physiography of Colorado (fig. 1) is in part a reflection of the underlying bedrock
 geology (fig. 2) (Mallory,  1972). The southern Rocky Mountains form a distinct physiographic
 province that extends in a broad north-south  belt through Colorado from southeastern Wyoming to
 north-central New Mexico. The Rockies rise to more than 14,000 ft, and many of the ranges are
 anticlinal, with Precambrian igneous cores flanked by steeply  dipping hogbacks of Paleozoic and
 Mesozoic sedimentary strata. Large intermontane basins,  or parks, separate many of the ranges.
'ThTfrilenh^n'fane'Basinsaregener^lyTiHe^"b~y"TertiaryMia^"Quaternarydeposits. Tnextreme
 northern Colorado, the Wyoming Basin province is transitional to the southern Rocky Mountains.
 The southern Rocky Mountains separate the Great Plains province in the eastern half of the state
 from the part of the Colorado Plateau province that occupies the southwestern corner of the state.
 The Great Plains in Colorado are generally underlain by Mesozoic and Cenozoic sedimentary rocks
 and rise to about 5,500 ft adjacent to the Rocky Mountains. That part of the Great Plains adjacent
 to the Front Range is known as the Colorado Piedmont or the  High Plains.  The Colorado Plateau
                                           IV-1    Reprinted from USGS Open-File Report 93-292-H

Hgure 1. Major physiographic provinces of the western United States (modified from Mallory,

                                 100 miles
                    Quaternary sedimentary
                      and Igneous rocks
                    Tertiary sedimentary rocks
                    Tertiary volcanic rocks
     sedimentary rocks
    Jurassic, Triassic.
    and Paleozoic rocks
p I Precambrlan
    sedimentary rocks
                    Tertiary intrusive rocks
    Precambrlan igneous
    and metamorphic rocks
Figure 2. Map showing generalized geology of Colorado (modified from Mallory, 1972).

is a roughly circular area centered about the Four Corners region of Colorado, Utah, Arizona, and
New Mexico, and it extends into southwestern Colorado. The Colorado Plateau consists of highly
dissected plateaus and mesas ranging in elevation from about 5,000 to 11,000 ft, except in the
deepest river canyons. The San Juan Mountains in southwestern Colorado form an isolated range
at the transition between the Colorado Plateau and the southern Rocky Mountains and are
composed primarily of Tertiary volcanic rocks.
       Population distribution (fig. 3A, B) and land use in Colorado reflect in part the geology,
topography, and climate of the state (Erickson and Smith, 1985). In 1990, the census indicated
approximately 3.3 million persons residing within Colorado's 103,766 square miles. Thus, the
population density (fig. 3A) is approximately 31 persons per square mile, substantially below the
national average of 65 persons per square mile. Within Colorado, the population is very unevenly
distributed (fig. 3B): some mountainous tracts have virtually no residents, and only a few
ranching and farming families can be found over large areas of both the Great Plains and the
Colorado Plateau provinces. Urban areas are concentrated along the Front Range on the eastern
edge of the Rocky Mountains, extending from Pueblo on the south through Colorado Springs and
Denver to Fort Collins on the north.  This distribution reflects Colorado's early history and the rich
mineral deposits of the Rocky Mountains.  Mineral wealth provided the major impetus for
settlement in Colorado (Erickson and Smith, 1985), and Denver, Colorado Springs, Golden,
Boulder, and other towns along the Front Range were established at the mountain front as supply,
transportation, and smelting centers for the mining industry in the Rocky Mountains. Other cities
such as Grand Junction, Durango, and many smaUer towns are situated along major rivers that
drain the eastern and western slopes of the Continental Divide. These early transportation
corridors provided access to the mineral districts and continue today as the routes followed by
modern highways. Despite the general decline in the minerals industry in the last decade, many
former mining towns in scenic high-country locations have been rejuvenated and have grown in
population in recent years in response to the outdoor recreation and ski industries.
       East of the Rockies on the Great Plains, agricultural activities on irrigated and non-irrigated
cropland, rangeland, or non-irrigated pastureland are the predominate industries; grazing is the
dominant land use in the state (Erickson and Smith, 1985).  Along rivers and on high mesas west
of the mountains on the Colorado Plateau, agriculture as a whole is limited, but fruit orchards
 sustain a major local industry. Grazing is the dominant land use on the western slope of the
 Rockies and on the Colorado Plateau in the southwestern part of the state. The forested Rocky
 Mountains and the high mesas of the Colorado Plateau are used extensively both for forest
 production and for winter and summer recreation (Erikson and Smith, 1985).


        Colorado's geology is complex and varies widely from place to place, but in general the
 bedrocfc geology i^aracteris^	
 addition, many of the radiorrietric anomalies noted on the aerial radiometric map (fig. 4; Duval and
 others, 1989) can be associated with specific bedrock formations.  The following discussion of
 geology and soils of Colorado is condensed from Chronic and Chronic (1972), Mallory (1972),
 Heil and others (1977), Tweto (1979), several topical papers in Kent and Porter (1980), and Beach
 and others (1985).
        The Great Plains east of the Rocky Mountains are characterized by relatively undeformed
 sedimentary rocks consisting primarily of sandstone, siltstone, and mudstone.  The eastern half of

                                            IV-4    Reprinted from USGS Open-File Report 93-292-H

                          POPULATION (1990)

                         E3 0 to 10000
                         E3 10001 to 25000
                         E3 25001 to 50000
                         H 50001 to 100000
                         • 100001 to 467610
Figure 3A. Population of counties in Colorado (1990 U.S. Census data).

 Urban Populition in Thousands of Persons     One dot represents 1,000 persons

                                                       Savin: U.S. CKIKO a Poouuun. 1MO
Figure 3B. Map showing population distribution of Colorado in 1980 (modified from Erickson
           and Smith, 1985).

Figure 4. Aerial radiometric map of Colorado (after Duval and others, 1989). Contourlines at 1.5
   and 2.5 ppm equivalent uranium (eU). Pixels shaded from 0 to 6.0 ppm eU at 0.5 ppm ell
   increments; darker pixels have lower eU values; white indicates no data.

the Great Plains in Colorado and a large area of the plains adjacent to the mountain front from
Colorado Springs to north of Denver are underlain by Tertiary and Quaternary sedimentary rocks,
whereas the remaining western part of the province is underlain by Cretaceous sandstones, shales,
and limestones. In the southeastern part of Colorado, sedimentary strata consisting of Permian,
Triassic, and Jurassic sandstones, mudstones, and minor limestones are exposed in the drainages
of thePurgatoire and Cimarron Rivers.
       The Rocky  Mountains, including the southern Rocky Mountains and the Wyoming Basin,
were formed during the Laramide orogeny, a Late Cretaceous to Eocene structural event that
emplaced Precambrian and Cambrian igneous and metamorphic crystalline rocks and minor
Cenozoic volcanic rocks adjacent to Paleozoic and Mesozoic sedimentary strata. The Paleozoic and
Mesozoic sedimentary rocks consist of conglomerate, sandstone, shale, and limestone. The oldest
rocks in Colorado are Precambrian granite intrusive rocks, Precambrian metamorphic gneiss,
schist, and pegmatite, and sedimentary quartzite, slate, and phyllite exposed in the Rocky
Mountains  and locally on uplifts in the San Juan Mountains in southwestern Colorado. Paleozoic
and Mesozoic sedimentary strata are steeply dipping where they have been uplifted by the igneous
intrusions and along basement faults reactivated by Laramide structural uplift. Cambrian quartzite,
and Ordovician, Devonian, and Mississippian limestone, dolomite, and minor sandstone are
exposed along the western flank of the Rocky Mountains and in scattered outcrops around the
White River uplift in west-central Colorado. Pennsylvanian, Permian, Triassic, Jurassic, and
Cretaceous conglomerate, sandstone, shale, and minor limestone also are locally uplifted and
exposed along the mountain fronts.
       The Colorado Plateau and the Wyoming Basin provinces are underlain by uplifted,
primarily flat-lying, locally folded, deeply eroded sedimentary rocks ranging in age from
Pennsylvanian to Tertiary. Pennsylvanian and Permian rocks are predominantly arkosic
conglomerate, fluvial and eolian sandstone, and minor marine limestone.  Triassic strata comprise
marginal-marine sandstone and shale and extensive continental fluvial and lacustrine sandstone,
mudstone, and limestone.  Jurassic rocks consist of widely exposed eolian sandstone, marine
limestone and shale, and continental lacustrine and fluvial sandstone and mudstone. Cretaceous
rocks form a thick sedimentary section in Colorado and consist of marine shale, sandstone, and
limestone interfingered with nonmarine fluvial sandstone and shale. Tertiary sedimentary strata are
dominandy lacustrine carbonate and mudstone and minor fluvial sandstone. Tertiary volcanic
rocks of extrusive lava, tuff, breccia, and conglomerate and  minor rhyolitic intrusive rocks
compose the San Juan Mountains in southwestern Colorado and are also found in minor exposures
throughout the state.
       Uranium deposits (fig. 5A) and production (fig. 5B) in Colorado occur in rocks of many
geologic ages and lithologies.  A comprehensive report on the uranium deposits in Colorado, from
which the following discussion is summarized, can be found in Chenoweth (1980).  Sedimentary-
hosted uranium deposits are the most common type of uranium occurrence in the State. Uranium-
vanadium deposits in fluvialsandstones of the Salt Wash Member of the Upper Jurassic j^orrisgn	
Formation occur in the Uravan mineraTbeft in western Colorado.  The Uravan mineral belt is an
arcuate area in Mesa, Montrose, and San Miguel Counties containing an abundance of closely
spaced, high-grade ore deposits. Uranium-vanadium deposits also occur in the Salt Wash east of
Meeker on Coal Creek anticline in Rio Blanco County.  Uranium-vanadium deposits in eolian
strata of the Middle Jurassic Entrada Sandstone are known northeast of Rifle in Garfield County,
near Placerville in San Miguel County, and north of Durango at Barlow Creek-Graysill in  San Juan
and Dolores Counties. The Oligocene and Miocene Browns Park Formation is a fluvial, arkosic,
                                           IV-8    Reprinted from USGS Open-File Report 93-292-H

                                                RALSTON CREEK-GOLDEN GATE    vwSMwSTOK
                      COCHETOP~    MARSHALL PASS
Figure 5 A. Map showing major uranium mines, significant uranium ore deposits, and uranium
            production (modified from Chenoweth, 1980).

    Precambrian crystalline rocks exposed


 Size (production plus reserves) of deposits that
      contains at least 0.1 percent  "-"-

More than

1.000 to



Age of
host rock
and Jurassic

    Deposits peneconcotdantwilh sedimentary features
                of enclosing rocks
    Symbol with a vertical stem indicates deposit is in
             coaly carbonaceous rock
                                                             Veins, breccia zones, and related types of deposits
             COaiy caroonatruuiluin

Figure 5B. Map showing major uranium mines and deposits, with known production (modified
              from Mallory, 1972).

 locally tuffaceous sandstone that hosts uranium deposits near Maybell in Moffat County. The
 Tallahassee Creek area on the southeastern flank of the Thirty-nine Mile volcanic field in north-
 central Fremont County contains tabular uranium deposits in the Eocene Echo Park Alluvium,
 which contains arkosic sandstone and conglomerate, and the Oligocene Tallahassee Creek
 Conglomerate, which consists of volcaniclastic conglomerate and tuffaceous sandstone.  The
 Upper Cretaceous Fox Hills Sandstone and Laramie Formation of the Denver Basin in Weld
 County contain roll front-type uranium deposits in fluvial sandstones.  The Upper Cretaceous
 Dakota Sandstone has produced small amounts of uranium ore near Rabbit Ears Pass in Grand
 County, near Badito Cone in Huerfano County, and on the east flank of the Turkey Creek anticline
 in the northwest corner of Pueblo County. The Paleocene and Eocene Coalmont Formation has
 produced uranium ore near Hot Sulfur Springs in Grand County, and ore has been produced from
 the Oligocene Antero Formation near Hartsel in Park County.  Minor amounts of uranium ore have
 been produced from fracture-controlled, sedimentary-hosted deposits in the Middle Pennsylvanian
 to Lower Permian Weber Sandstone and Maroon Formation in Moffat and Park Counties, the
 Middle Jurassic Curtis Formation in Moffat County, the Upper Jurassic Morrison Formation in
 El Paso County, and the Upper Cretaceous Dakota Sandstone and Laramie Formation in Jefferson
        Production from vein-type uranium occurrences in Colorado is subordinate to sedimentary-
 hosted deposits, but significant ore bodies occur in the Front Range west of Denver in Precambrian
 rocks in Larimer, Boulder, Jefferson, Gilpin, Clear Creek, and Park Counties.  Uranium has been
 known in the Central City district of Gilpin County since 1871, where pitchblende was first
 discovered in the United States on the tailings pile of the Wood mine. Since that time, important
 deposits have been found near Jamestown, Ralston Creek, Golden Gate Canyon, and Ideldale.
 These deposits, located near the Central City district, are hosted in the Precambrian (Early
 Proterozoic)  metamorphic complex of the Idaho Springs Formation, which also hosts the
 Schwartzwalder uranium mine, the largest uranium mine in Colorado. Other Precambrian rocks
 along the Front Range locally have produced ore. Complicated fault-vein relationships produce
 uranium in the Marshall Pass area in northern Saguache and southeastern Gunnison Counties.
 Uranium also occurs along high-angle normal faults within the Middle and Upper Jurassic Junction
 Creek Sandstone and Upper Jurassic Morrison  Formation of the Cochetopa area on the northern
 margin of the San Juan Mountains in northwestern Saguache County. Minor amounts of uranium
 ore have been produced from vein deposits in a variety of host rocks in the Park, Sawatch, and
 Sangre de Cristos Ranges and the San Juan and La Plata Mountains.
        In addition to the known deposits in Colorado where uranium has been concentrated as ore,
 uranium also occurs in several rock formations at concentrations too low to be considered
 economic but that may still generate radon at levels considered to be a problem in indoor air. For
 example, the Upper Cretaceous Sharon Springs Member of the Pierre Shale, the Upper Cretaceous
 Mancos Shale, and the Miocene and Pliocene Ogallala Formation all contain low-level but
 consistent concentrations of uranium. Precambrian rocks such as the Middle Proterozic Pikes Peak
"Gramte~nave consistent"ufaHium concentrations and locally Mghe7cbncenSations~along fractures'
 faults, and shear zones (Schumann, Gundersen, and others, 1989). Tertiary volcanic rocks and
 ash-flow tuffs around calderas in the San Juan Mountains have low-level uranium concentrations.
 Many alluvial deposits and soils reworked from uranium-bearing igneous and sedimentary parent
 rocks, particularly along the Front Range, have significant potential to generate radon.
                                          IV-11    Reprinted from USGS Open-File Report 93-292-H


       A generalized soil map of Colorado (fig. 6) compiled from Heil and others (1977) and
Erickson and Smith (1985) indicates that soils in Colorado consist of Mollisols and Aridisols on
the Great Plains; Alfisols, Aridisols, and Inceptisols in the Rocky Mountains; and Entisols, with
minor Alfisols, Mollisols, and Aridisols on the Colorado Plateau. Natrargids (sodium-rich
Aridisols) are the major soil order in the Wyoming Basin in northwestern Colorado. It should be
noted that many of the areas within these generalized soil orders, especially in the Rocky
Mountains and on the Colorado Plateau, consist of bare bedrock with incipient to nonexistent soil
development  In general, most soils in Colorado are moderately permeable; however, each soil
order contains individual soil associations that range from slow to rapid permeability. Although
the data in Heil and others (1977) refers most commonly to depth to bedrock in soil associations,
which generally can vary from less than 20 inches to more than 60 inches, a few associations do
indicate depth to seasonal high water table. For the Aridisols and Natrargids, several soil
associations have depth to seasonal high water table from 2 to more than 6 feet. The Entisols and
Mollisols include a few soil associations that have depth to seasonal high water table from 0 to 2
feet. The shrink-swell potential of many of Colorado's soils can affect radon concentrations in
those soils (Schumann and others, 1989).  Soils with high shrink-swell potential may cause
building foundations to crack and thus allow radon to enter the structure. Swelling soils, which
often crack as  they dry, can have effectively increased soil permeability due to cracks. Several
areas of Colorado have soils with high shrink-swell potential and include areas underlain by
bentonitic Upper Cretaceous marine shales (Benton Formation)  and Cretaceous to Tertiary rocks
(Arapahoe and Denver Formations) in the Great Plains, in the Grand Valley on the Colorado
Plateau, and in parts of the Uinta and Piceance basins in the Wyoming Basin province.


       Indoor radon data for Colorado (fig. 7; Table 1) from the State/EPA Residential Radon
Survey were compiled from 1986 to 1987 (Colorado Geological Survey, 1991). Data from only
those counties in which five or more measurements were made are presented in figure 7.  A map
showing the counties in Colorado (fig. 8) is provided to facilitate discussion of correlations among
the indoor radon data (fig. 7), geology (fig. 2), aerial radiometric data (fig. 4),  and soils (fig. 6).
In this discussion,  "elevated" refers to screening indoor radon levels greater than 4.0 pCi/L.  For
the counties that have sufficient data to be shown on figure 7, the distribution of elevated indoor
radon levels correlates with the bedrock geology and in general with the aerial radiometric data.
Elevated indoor radon levels occur in the Great Plains region underlain by Cretaceous sedimentary
shales and limestones. Elevated indoor radon levels also occur in the High Plains adjacent to the
Front Range on the eastern flank  of the Rocky Mountains in areas underlain by Permian, Triassic,
Jurassic, and Cretaceous sedimentary rocks, in areas of alluvium derived from  those rocks, and
from the"igneous rocks to" the wesf in tfie~Rocky Mountains. Elevated radon levels also occur "in
the Rocky Mountains, and especially in the Front Range, where the bedrock consists of
Precambrian igneous and metamorphic rocks, some with faults and fracture zones, and numerous
Paleozoic to Cenozoic sedimentary rocks. Elevated indoor radon levels also occur on the Colorado
Plateau in regions underlain by Paleozoic, Mesozoic, and especially Cretaceous sedimentary rocks.
                                           IV-12    Reprinted from USGS Open-File Report 93-292-H


       [;££j  Affisols (moderate permeability)

       ^^  Inceptisols (moderate permeability)

       i?';V!i  Entisols (moderate permeability)

       $8888  Aridisols (moderate permeability)

       I   I  Mollisols (stow to rapid permeability)

       |V£|  Natrargids (moderate permeability)
                                    150 mi
Figure 6.  Map showing generalized soils of Colorado (modified from Erickson and Smith, 1985).

                                                                 Bsmt. & 1st Floor Rn
                                                                     % >4pCi/L
                                                            21 L
11 to 20
21 to 40
41 to 60
61 to 80
Missing Data
or < 5 measurements
                                                                    Bsmt. & 1st Floor Rn
                                                                Average Concentration (pCi/L)
                                                                  5 L^l

                                                            21 L
0.0 to 1.9
2.0 to 4.0
4.1 to 10.0
10.1 to 14.7
Missing Data
or < 5 measurements
                                                                 100 Miles
Figure 7. Screening indoor radon data from the EPA/State Residential Radon Survey of
Colorado, 1986-87, for counties witlr5or more mrastiremen1srDam~areffbTrr2-7"dayl:harcoal"~
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
Colorado conducted during 1986-87.  Data represent 2-7 day charcoal canister measurements
from the lowest level of each home tested.
' 2
%>4 pCi/L

TABLE 1 (continued). Screening indoor radon data for Colorado.
%>4 pCi/L
%>20 pCi/L


       The highest indoor radon levels measured in Colorado as of this writing were greater than
600 pCi/L.  These levels are associated with faults and mineralized shear zones in igneous and
metamorphic crystalline rocks in the Front Range of Jefferson County near Conifer (Schumann,
Gundersen, and others, 1989) and in faulted Sharon Springs Member of the Pierre Shale along the
mountain front in Larimer County near Fort Collins, and in the Highlands Ranch subdivision in the
southern Denver metropolitan area. The highest indoor radon value measured in the State/EPA
Residential Radon Survey of Colorado was 215 pCi/L in Teller County (Table 1).
       The complex geology in each county of Colorado and the scale of maps used in this report
makes it difficult to characterize individual rock units that may be responsible for the specific
elevated radon levels; the reader is referred to the geologic discussion in this report and should note
that the specific geology at any particular site is critical to discerning the factors responsible for
measured elevated radon levels. Each of the geologic terranes with elevated radon levels
corresponds to areas of anomalously high radiometric signatures on the aerial radiometric map
(fig. 4) that reflect uranium-bearing bedrock or alluvium and soils derived from those rocks.


       A comparison of geology (fig. 2) with aerial radiometric data (fig. 4) and indoor radon data
(fig. 7; Table 1) provides preliminary indications of rock types and geologic features suspected of
producing elevated radon levels. An overriding factor in the geologic evaluation is the abundance
and widespread outcrops of known uranium-bearing and uranium-producing formations in the
state (fig. 5; Chenoweth, 1980). Because of the widespread occurrence of uranium-bearing rock
formations and alluvium, and soils derived from them, virtually all areas of Colorado have the
potential for some indoor elevated radon levels; however, even in areas underlain by rocks known
to contain uranium, other mitigating factors locally may interact to produce an  environment that
does not have elevated radon levels.  Colorado has many uranium-bearing rocks throughout the
state, as discussed in the geology section of this report (fig. 5), but all of those rocks are not highly
uraniferous at every locality. The following list is an overview of the rocks that are most likely to
produce elevated indoor radon levels. In the Great Plains, sedimentary rocks such as the Upper
 Cretaceous and Paleocene Dawson Arkose, and various Cretaceous sedimentary rocks including
 the Dakota Formation, Fox Hills Sandstone, and Laramie Formation, the Pierre Shale (especially
 the Sharon Springs Member), all have the potential to produce locally elevated indoor radon  levels.
 In addition, the Upper Cretaceous and Paleocene Denver Formation and the Upper Cretaceous
 Arapahoe Formation, along with Tertiary and Quaternary alluvium and soils derived from these
 rocks and from uplifted Paleozoic and Mesozoic sedimentary rocks and Precambrian igneous rocks
 in the Rocky Mountains also have potential for producing locally elevated radon levels.
        In the Rocky Mountains, outcrops of Precambrian igneous and metamorphic crystalline
 rocks such as the Pikes Peak Granite, the Silver Plume Granite, and the Idaho Springs Formation,
 particularly wherethey arejracture^fojufed^^^
 - --  —•- ------  - - - -   -_->•-—•--«-- • -                          f.._. _J	j__^.l__.rt.1rt T T»i1i-P*-«yI TDnl^a
 concentrations of uranium minerals and to produce elevated radon levels. Uplifted Paleozoic and
 Mesozoic sedimentary rocks, and smaller outcrops of Tertiary volcanic and sedimentary rocks, are
 also locally uraniferous and may produce elevated radon levels.
        On the Colorado Plateau and in the Wyoming Basin, many rock formations are known to
 produce uranium ore and to locally contain low-level concentrations of uranium where ore is not
 present. Outcrops of the Salt Wash Member of the Morrison Formation are probably the most
 likely to contain significant uranium orebodies, but many other formations have produced uranium
                                           IV-18    Reprinted from USGS Open-File Report 93-292-H

 occurrences in Colorado. Locally, the Middle Jurassic Entrada Sandstone, the Oligocene and
 Miocene Browns Park Formation, the Eocene Echo Park Alluvium, the Oligocene Tallahassee
 Creek Conglomerate, and the Paleocene and Eocene Coalmont Formation all have potential to
 produce elevated radon levels. In the San Juan Mountains, various extrusive volcanic rocks locally
 contain above-average uranium concentrations that may produce elevated radon levels.
        Ground water in contact with uranium-bearing bedrock has the potential to accumulate
 radon and to contribute to indoor radon levels (Nazaroff and Nero, 1988). Municipal water
 treatment generally dissipates radon accumulations in water supplies, but individual wells used as a
 source of domestic water that are located in bedrock with high uranium concentrations can
 contribute significant levels of radon to indoor air (Hess and others, 1990; Lawrence and others,
 1989, in press).  In Colorado, domestic water wells that tap ground water in uranium-bearing
 bedrock, especially the fractured, faulted, or sheared Precambrian rocks of the .Rocky Mountains,
 have the potential to significantly contribute to elevated indoor radon levels (Lawrence and others,
 1989), and waterborne radon levels as high as 3,000,000 pCi/L have been found in the Lyons,
 Colorado, area.  The Ogallala aquifer, a principal source of ground water on the Great Plains, and
 the Dakota Group aquifer (Vinckier, 1982), located in the Canon City embayment of Fremont and
 Pueblo Counties, also contain low-level uranium concentrations.  In such areas, ground water may
 contribute significantly to indoor radon but on a highly variable basis depending on water usage.


       For purposes of assessing the radon potential of the state, Colorado can be divided into
 nine general areas (termed Area 1 through Area 9), delineated on the basis of similar geology and
 other factors listed in Table 2 (see figure 9 and Table 2) and scored with a Radon Index (RI), a
 semi-quantitative measure of radon potential, and an associated Confidence Index (CI), a measure
 of the relative confidence of the assessment based on the quality and quantity of data used to make
 the evaluations.  For further details on the ranking schemes and the factors used in the evaluations,
 refer to the Introduction chapter to this booklet.
       Areas 1,  2,3, 4, and 6 each have high radon potential (RI=15, 14, 13, 13, and 12,
 respectively) associated with a high  or moderate confidence index (CI=11, 10, 9, 9, and 8,
 respectively), and area 5 has a high radon potential (RI=12) with a moderate confidence index
 (CI=8) on the basis of high indoor radon measurements, high surface radioactivity as evidenced by
 the aerial radiometric data, and the presence of rock formations such as Precambrian granite,
 Jurassic sandstone and limestone, or Cretaceous to Tertiary sandstone, shale, and volcanic rock
 that are known to contain or produce uranium.  Area 1 encompasses the Rocky Mountains and
 contains primarily Precambrian granite that has low but consistent uranium concentrations and
 abundant shear zones that are known to produce radon in several areas (Schumann, Gundersen,
 and others,  1989); it also contains outcrops of sedimentary rocks shed from the granitic highlands.
 Area 2 just east of the Rocky Mountains in central Colorado contains primarily outcrops of the
 DawsbfrAfkoseTKaf was sKM^~aUuvTal"'fan and riverIdeposits sourcecTIn trie^ffite'mcoiiitainslo"
 the west. Area 3 is primarily underlain by marine shales of the Mancos Shale and by Tertiary
 sandstones. Area 4 is underlain by variable geology and includes uranium-bearing Jurassic
 sedimentary rocks of the Uravan mineral belt. Area 5 is underlain primarily by Tertiary sandstone,
primarily the Ogallala Formation, and in part, is covered to varying degrees by windblown eolian
 sand and silt (loess) deposits. Both the bedrock and the loess have the capacity to contribute to
high radon values, whereas the thicker eolian sand generally is  associated with relatively lower
                                          IV-19    Reprinted from USGS Open-File Report 93-292-H



• I—t





 radon values. Area 6 in eastern Colorado contains variable geology including Quaternary
deposits, Cretaceous marine shales that locally have a high radiometric signature, and small areas
of older sedimentary rocks.
       Areas 7, 8, and 9 have moderate radon potential (RI=11 for each area) associated with
moderate confidence indices (CI=9, 9, and 8, respectively). Area 7 in southwestern Colorado
contains primarily volcanic rocks of the San Juan volcanic field. Area 8 comprises three parts of
western Colorado: sedimentary outcrops of the easternmost Uinta Mountains, west of the Rocky
Mountains, and the northern part of the San Juan Basin in southwestern Colorado. Area 9
contains primarily Teriary sedimentary rocks.
       This is a generalized assessment of the State's geologic radon potential and there is no
substitute for having a home tested.  The conclusions about radon potential presented in this report
cannot be applied to individual homes or building sites.  Indoor radon levels, both high and low,
can be quite localized, and within any radon potential area there will likely be areas with higher or
lower radon potential that assigned to the area as a whole. Any local decisions about radon should
not be made without consulting all available local data. For additional information on radon and
how to test, contact your State radon program or EPA regional office. More detailed information
on state or local geology may be obtained from the State geological survey.  Addresses and phone
numbers for these agencies are listed in chapter 1 of this booklet.
                                          IV-21    Reprinted from USGS Open-File Report 93-292-H

TABLE 2. Radon Index (RI) and Confidence Index (CI) scores for geologic radon potential areas
of Colorado.
Area 4
Area 2
Area 5
Area 8
Area 3
Area 6
Area 9
        RANKING  MOD   MOD


          Radon potential category
Point range
          LOW            *           3-8 points
          MODERATE/VARIABLE      9-11 points
          HIGH                     > 11 points
Probable screening indoor
  radon average for area
                    < 2 pCi/L
                    > 4 pCi/L
                          Possible range of points = 3 to 17

       4-6  points
       7-9  points
      10 - 12 points
                          Possible range of points = 4 to 12
                                      IV-22   Reprinted from USGS Open-File Report 93-292-H

                           REFERENCES CITED IN THIS REPORT

   Alter, H.W., 1980, Track etch radon ratios to soil uranium and a new uranium abundance
         estimate, in Gesell,T.F., and Lowder, W.M. eds., Natural radiation environment IE; Vol.
         1, Proceedings of International Symposium on the Natural Radiation Environment,
         Houston, TX, April 23-28, 1978:  DOE Symposium Series 1, p. 84-89.

   Asher-Bolinder, Sigrid, Owen, D.E., and Schumann, R.R., 1990, Pedologic and climatic controls
         on Rn-222 concentrations in soil gas, Denver, Colorado: Geophysical Research Letters  v
         17, p. 825-828.

   Asher-Bolinder, S., Owen, D.E., and Schumann, R.R., in press, A preliminary evaluation of
         environmental factors influencing day-to-day and seasonal soil-gas radon concentrations, in
         Gundersen, L.C.S., and Wanty, R.B., eds. Field studies of radon in natural rocks, soils,
         and water:  U.S. Geological Survey Bulletin, 26 p.

   Beach, R.A., Gray, A.W., Peterson, E.K., and Roberts, C.A., 1985, Availability of federal land
         for mineral  exploration and development in western states-Colorado, 1984:  U.S. Bureau
         of Mines Special Publication, 40 p.

   Bell, M.W., Allen, J.W., Pacer, J.C., and Roberts, E.H.,  1981, Drilling-mud emanometry; a new
         technique for uranium exploration: U.S. Department of Energy Report GJBX-273(81),
         50 p.

   Bell, M.W., Pacer,  J.C., and Roberts, E.H., 1981 , Drilling-mud emanometry, a new technique
         for uranium exploration:  American Association of Petroleum Geologists Bulletin v 65 D
         898.                                                                       '*'

   Chenoweth, W.L.,  1980, Uranium in Colorado, in Kent, H.C., and Porter, K.W., eds.,
         Colorado geology: Rocky Mountain Association of Geologists, p. 217-224.

   Chronic, J. and Chronic, H., 1972, Prairie, peak, and plateau:  Denver, Colorado, Colorado
         Geological Survey, 126 p.

   Colorado Energy Research Institute, 1983, Radon gas levels in metropolitan Denver homes:
        Prepared for the Executive Committee, Legislative Council of the Colorado General
        Assembly, 42 p.

   Colorado Geological Survey, 1991, Results of the 1987-88 EPA supported radon study in
        91-4, 51 p.                                                               F

  Colorado Land Use Commission, 1973, A land use program for Colorado: Denver, Colorado,
        Colorado Land Use Commission, 247 p.

  Cothern, C.R., and Rebers, P.A., eds., 1990, Radon, radium, and uranium in drinking water,
        286 p.
                                          IV-23    Reprinted from USGS Open-File Report 93-292-H

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.

Erickson, K.A., and Smith, A.W., 1985, Atlas of Colorado: Colorado Associated University
       Press, 73 p.

Evans, H.B., 1957, Natural radioactivity of the atmosphere (Colorado Plateau and Texas): U.S.
      ' Geological Survey TEI-700, 268-272 p.

Felmlee, J.K,. and Cadigan, R.A., 1979, Radium and uranium concentrations and associated
       hydrogeochemistry in ground water in southwestern Pueblo County, Colorado: Geological
       Society of America, Abstracts with Programs, v. 11, p. 272.

Fisher, J.C., 1976, Application of track etch radon prospecting to uranium deposits, Front Range,
      * Colorado, w Weiss, A., ed., World mining and metals technology: Proceedings of third
       joint meeting of the Mining and Metallurgical Institute of Japan and the American Institute
       of Mining, Metallurgical and Petroleum Engineers,World Mining and Metals Technology
       Denver, CO, Sept. 1-3, 1976, p. 95-112.

Franklin, J.C., and Marquardt, R.F., 1976, Continuous radon gas survey of the Twilight Mine:
       U.S. Bureau of Mines, Technical Program Report 93,  16 p.

Gerlach, A.C., ed., 1970, The National Atlas of the United States of America: Washington, D.C.,
       U.S. Geological Survey, 417 p.

Gingrich, J.E., and Fisher, J.C.,  1976, Uranium exploration using the track-etch method:
       Proceedings of exploration for uranium ore deposits, Vienna, Austria, March 29: April 2,
        1976, IAEA, Proceedings Series 434, p. 213-227.

Hazle, A.J., 1987, Colorado; the legacy of uranium mining: Environment, v.  29, p. 13, 15, 17,

 Heil, R.D., Romine, D.S., Moreland, D.C., Dansdill, R.K., Montgomery, R.H.,  and Cipra,
       J.E., 1977, Soils of Colorado: Fort Collins, Colorado, Colorado State  University
       Experiment Station in Cooperation with the Soil Conservation Service-USD A, 40 p.

 Hess, C.T., Vietti, M.A., Lachapelle, E.B., and Guillemette, J.F., 1990, Radon transferred from
        drinking water into house air, in C.R. Cotherm and P.A. Rebers, eds., Radon, radium
        and uranium in drinking water:  Chelsea, Michigan, Lewis Publishers,  p. 51-67.
 Holub, R.F., DrouUard, R.R,. Bprak, XB^Lnkret J&^
        Radon-222 and 222Rn progeny concentrations measured in an energy-efficient house
        equipped with a heat exchanger: Health Physics, v. 49, p. 267-277.

 Jaacks, J.A., and Klusman, R.W., 1981, Seasonal and short-term variations in gas emission at an
        aseismic site: Eos, Transactions, American Geophysical Union, v. 62, p. 962-963 .
                                           IV-24    Reprinted from USGS Open-File Report 93-292-H

Jaacks, J.A., and Klusman, R.W., 1984, A comparison of instantaneous versus integrative
        techniques in soil-gas sampling, in Anonymous, ed., Exploration for ore deposits of the
        North American Cordillera; Abstracts with Program: Proceedings of Symposium of the
        Association of Exploration Geochemists, Reno, NV, Mar. 25-28, 1984, p. 45.

Jacoby, G.C., Jr., Simpson,  H.J., Mathieu, G., and Torgersen, T., 1979, Analysis of
        groundwater and surface water supply interrelationships in the Upper Colorado River basin
        using natural radon-222 as a tracer: John Muir Institute, 46 p.

Kent, H.C. and Porter, K.W., eds., 1980, Colorado Geology:  Denver, Colorado, Rocky
        Mountain Association of Geologists, , 258 p.

Klusman, R.W., 1981, Seasonal and short-term variations in gas emission from the Earth: Eos,
        Transactions, American Geophysical Union, v. 62, p. 1033-1034 .

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.

Klusman, R.W. and Webster, J.D., 1981, Preliminary analysis of meteorological and seasonal
       influences on crustal gas emission relevant to earthquake prediction:  Bulletin of the
        Seismological Society of America, v. 71, p. 211-222.

Landa, E.R., 1983, Radon concentrations in the indoor air of earth sheltered buildings in
        Colorado, in Boyer, L.L., ed., Proceedings of First International Earth Sheltered Buildings
       Conference, Sydney, Australia:  Architectural Extension and University Center for Energy
       Research, Oklahoma  State University, p. 275-279.

Landa, E.R., 1984, Radon in earth-sheltered structures: Underground Space, v. 8, p. 264-269.

Lawrence, E.P., Wanty, R.B. and Briggs, P.H., 1989, Hydrologic and geochemical processes
       governing distribution of U-238 series radionuclides in groundwater near Conifer, CO:
       Geological Society of America, Abstracts with Programs, v. 21, p. A144.

Lawrence, E.P., Wanty, R.B., and Nyberg, P.,  in press, Contribution of 222Rn in domestic water
       supplies to 222Rn in indoor air in homes in Colorado: Health Physics, 20 p.

Mallory, W.W., 1972, Geologic Atlas of the Rocky Mountain Region: Denver, Rocky Mountain
       Association of Geologists, p. 331.
       Geophysics, v. 48, p. 806.

Nazaroff, W.M., and Nero, A.V., eds., 1988, Radon and its daughter products in indoor air,
       518 p.

Nelson-Moore, J.L., Collins, D.B., and Hornbaker, A.L., 1978, Radioactive mineral occurrences
       of Colorado and bibliography: Denver, Colorado, Colorado Geological Survey, 1054 p.
                                         IV-25   Reprinted from USGS Open-File Report 93-292-H

Nielson, K.K,. and Rogers, V.C., 1986, Surface water hydrology considerations in predicting
       radon releases from water-covered areas of uranium tailings ponds, in Abt, S.R., Nelson,
       J.D., Shepherd, T.A., Wardwell, R.E.,  and van Zyl, D., eds., Proceedings of the 8th
       annual symposium on geotechnical and geohydrological aspects of waste management:
       Fort Collins, Colorado, Feb. 5-7, 1986, p. 215-222.

Norton, S.A., Hess, C.T., Blake, G.M., Morrison, M.M., and Baron, J., 1985, Excess
       unsupported 210Pb in lake sediment from Rocky Mountain lakes; a groundwater effect:
       Canadian Journal of Fisheries and Aquatic Sciences, v. 42, p. 1249-1254.

Otton, J.K., 1989, Using geology to map and understand radon hazards in the United States:
       United States Geological Survey Yearbook, p. 52-54.

Otton, J.K., Schumann, R.R.,  Owen, D.E. and Chleborad, A.F., 1988, Geologic assessments of
       radon hazards; a Colorado case history, in Marikos, M.A., and Hansman, R.H., eds.,
       Geologic causes of natural radionuclide anomalies: Proceedings of GEORAD Conference,
       Geologic Causes of Natural Radionuclide Anomalies, St. Louis, MO, Apr. 21-22,1987,
       p.  167.

Owen, D.E. and Asher-Bolinder, S., 1988, Assessment of natural phenomena producing
       fluctuations and variations in soil-gas Radon-222 concentrations:  Geological Society of
       America, Abstracts with  Programs, v. 20, p. A354.

Reimer, G.M., 1985, Gaseous  emanations associated with sandstone-type uranium deposits, in
       Finch, W.I.,  and Davis, J.F., eds.,  Geological environments of sandstone-type uranium
       deposits: Report of the working group on uranium geology organized by the International
       Atomic Energy Agency,  U.S. Geological Survey, Denver, CO,  p. 335-346.

Reimer, G.M., and Rice, R.S., 1977, Linear-traverse surveys of helium and radon in soil gas as a
       guide for uranium exploration, central Weld County, Colorado:  U.S. Geological Survey,
       Open-File Report 77-589,10 p.

Schumann, R.R., Asher-Bolinder,  S., and Owen, D.E., 1989, Factors influencing seasonal
       variations in soil-gas radon concentrations in a fine-grained soil:  Geological Society of
       America, Abstracts with Programs, v. 21, p. 65.

Schumann, R.R., Gundersen,  L.C.S., Asher-Bolinder, S., and Owen, D.E., 1989,  Anomalous
       radon levels in crystalline rocks near Conifer, Colorado: Geological Society of America,
       Abstracts with Programs, v. 21, p. A144-A145.

Schumann, R.R., Owen,JD.E>  and Asher-Bolinder7S.,-t989rWeatherfaetors-affecting-soil-gas—
       radon concentrations at a single site in the semiarid western U.S., in Osborne, M.C., and
       Harrison, J., eds., Proceedings of the 1988 EPA Symposium on Radon and  Radon
       Reduction Technology, v. 2, EPA Report EPA/600/9-89/006B, p. 3-1 to 3-13.
                                          IV-26   Reprinted from USGS Open-File Report 93-292-H

 Spitz, H.B., Cohen, N., and Wrenn, M.E., 1975, Non-occupational radiation exposures from
       radon-222 and daughters to residents of Grand Junction, Colorado, annual report, July 1,
       1974 to June 30, 1975; Volume 2, p. (unknown).

 Stevens, D.N., Rouse, G.E., and De Voto, R.H., 1970, Radon in soil gas; three uranium
       exploration case histories in the western United States: Proceedings of the Canadian
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       Toronto, Third International Geochemical Exploration Symposium, Program and
       Abstracts, p. 57.

 Stevens, D.N., Rouse, G.E. and De Voto, R.H., 1971, Radon-222 in soil gas; three uranium
       exploration case histories in the western United States: Canadian Institute of Mining and
       Metallurgy, Special Volume, v. 11, p. 258-264.

 Stieff, L.R., Stieff, C.B., and Nelson, R.A., 1987, Field measurements of in situ 222Rn
       concentrations in soil based on the prompt decay of the 214Bi counting rate: Nuclear
       Physics, v. 1, p. 183-195.

 Streufert, R.K., and Ohl, J.P., 1989, Colorado metal mining activity map with directory:
       Colorado Geological Survey, Special Map 25, scale 1:500,000.

 Swindle, R.W., 1977, Radon daughter control in the Uravan mineral belts, m Kim, Y.S. ed.,
       Uranium mining technology: Proceedings of First conference on uranium mining
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       1977, (unpaginated).

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Tripp, R.M., 1944, Radon survey of the Fort Collins anticline (Colorado) (abst): Dallas Digest,
      p. 67.

Varani, F.T., Jelinek, R.T., and Correll, R.J., 1987, Occurrence and treatment of uranium in
      point of use systems in Colorado, in Graves, B. ed., Radon, radium, and other
      radioactivity in ground water: National Water Well Association Conference: Radon,
      radium and other radioactivity  in ground water, Somerset, NJ, Apr. 7-9,1987, p. 535-

Vinckier, T.A., 1982, Hydrogeology of the Dakota Group aquifer with emphasis on the radium-
      226 content of its contained ground water, Canon City Embayment, Fremont and Pueblo
      Counties, Colorado: Colorado  Geological Survey, Open File 82-3, 80 p.
                                         IV-27    Reprinted from USGS Open-File Report 93-292-H


                            EPA's Map of Radon Zones

       The USGS1 Geologic Radon Province Map is the technical foundation for EPA's Map
 of Radon Zones. The Geologic Radon Province Map defines the radon potential for
 approximately 360 geologic provinces. EPA has adapted this information to fit a county
 boundary map in order to produce the Map of Radon Zones.
       The Map of Radon Zones is based on the same range of predicted screening levels of
 indoor radon as USGS' Geologic Radon Province Map. EPA defines the three zones as
 follows:  Zone One areas have an average predicted indoor radon screening potential greater
 than 4 pCi/L.  Zone Two areas are predicted to have an average indoor radon screening
 potential between 2 pCi/L and 4 pCi/L.  Zone Three areas are predicted to have an average
 indoor radon screening potential  less than 2 pCi/L.
       Since the geologic province boundaries cross state and county boundaries, a strict
 translation of counties from the Geologic Radon Province Map  to the Map of Radon Zones
 was not possible.  For counties that have variable radon potential (i.e.,  are located in two  or
 more provinces of different rankings), the counties were assigned to a zone based on the
 predicted radon potential of the province in which most of its area lies.  (See Part I for more


       The Colorado Map of Radon Zones and its supporting documentation (Part IV of this
 report) have received extensive review by Colorado geologists and radon  program experts.
 The map for Colorado generally reflects current State  knowledge about radon for its counties.
 Some States have been able to conduct radon investigations in areas smaller than geologic
 provinces and counties, so it is important to consult locally  available  data.
       Although the information  provided in Part IV of this report -- the  State chapter entitled
 "Preliminary Geologic Radon Potential Assessment of Colorado" -- 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
 Colorado radon program for information on  testing and fixing homes.  Telephone numbers
and addresses can be found in Part II of this report.