United States
Environmental Protection
Agency
Air and Radiation
(6604J)
402-R-93-028
September 1993
EPA's Map of Radon Zones
DELAWARE

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

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

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

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

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            TABLE OF CONTENTS
               I. OVERVIEW
     II. THE USGS/EPA RADON POTENTIAL
        ASSESSMENTSrINTRODUCTION
  III. REGION 3 GEOLOGIC RADON POTENTIAL
                SUMMARY
V. PRELIMINARY GEOLOGIC RADON POTENTIAL
        ASSESSMENT OF DELAWARE
 V. EPA'S MAP OF RADON ZONES - DELAWARE

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                                       OVERVIEW


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

 BACKGROUND

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

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

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

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

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

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

 Development of the Map of Radon  Zones

       The technical foundation  for the Map of Radon Zones is the USGS Geologic Radon
Province Map.  In order to examine the radon potential for the United States, the USGS
began by identifying approximately 360 separate geologic  provinces for the U.S. The
provinces are shown on the USGS Geologic Radon  Province Map (Figure 2). Each of the
geologic provinces was evaluated by examining the available data for that area:  indoor radon
measurements, geology, aerial  radioactivity,  soil parameters, and foundation types.  As stated
previously, these five factors are considered to be of basic importance  in assessing radon
                                           1-2

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

 Map Validation

       The Map of Radon Zones is intended to represent a preliminary assessment of radon
potential for the entire United States.  The factors that are used in this effort --indoor radon
data, geology, aerial radioactivity,  soils, and foundation type ~ are basic indicators for radon
potential.  It is important to note, however, that the map's county  zone designations are not
"statistically valid" predictions due to the  nature of the data available for these 5 factors at  the
county level.  In order to validate the map in light of this lack of statistical confidence, EPA
conducted a number of  analyses. These analyses have helped  EPA to identify the best'
situations  in which to apply the  map, and  its limitations.
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Figure 3
                 Geologic  Radon  Potential  Provinces  for Nebraska
         Lincoln County
           Hiji      Uoieraie      Low
Figure 4
         NEBRASKA  -  EPA  Map  of Radon  Zones
         Lincoln County
         Zoae I     Zone 2    Zone 3
                                       1-6

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

 Review Process

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

 BACKGROUND

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


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

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

 RADON GENERATION AND TRANSPORT IN SOILS

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


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

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 and moisture infiltration rates and depth of wetting may be limited when the cracks in the
 surface soil layers swell shut.  Clay-rich B horizons, particularly those with massive or platy
 structure, can form a capping layer that impedes the escape of soil  gas to the surface
 (Schumann and others, 1992).  However, the shrinkage of clays can act to  open or  widen
 cracks upon drying, thus increasing the soil's permeability to gas flow during drier  periods.
        Radon transport in  soils occurs by two processes:  (1) diffusion and  (2) flow (Tanner,
 1964). Diffusion is the process whereby radon atoms  move from areas of  higher
 concentration to  areas of lower concentration in response to a concentration gradient.  Flow is
 the process by which soil air moves through soil pores in response  to differences in pressure
 within the soil or between the soil and  the atmosphere, carrying the radon atoms along with it.
 Diffusion is the dominant radon transport process in soils of low permeability, whereas flow
 tends  to dominate in highly permeable soils (Sextro and others,  1987).  In low-permeability
 soils,  much of the radon may decay before it is able to enter a building because its  transport
 rate is reduced.   Conversely, highly permeable soils, even those  that are relatively low in
 radium, such as those derived from some types of glacial deposits, have been associated with
 high indoor radon levels in Europe and in the northern United States (Akerblom and others,
 1984;  Kunz and others, 1989; Sextro  and others,  1987).  In area's of karst topography formed
 in carbonate rock (limestone or dolomite) environments, solution cavities and fissures can
 increase soil permeability at  depth by providing  additional pathways for gas flow.
    Not all radium contained in soil grains and grain coatings will result in mobile  radon
 when  the radium decays.  Depending  on where the radium is distributed in  the soil, many of
 the radon atoms may remain imbedded  in the soil grain containing the parent radium atom, or
 become imbedded in adjacent soil grains.  The portion of radium that releases radon into the
 pores  and fractures of rocks and soils is called the emanating fraction.  When a radium atom
 decays to radon, the energy generated is strong enough to send the radon atom a distance of
 about  40 nanometers (1 nm = 10'9 meters), or about 2x10* inches—this is known as alpha
 recoil  (Tanner, 1980).  Moisture in the soil lessens the chance of a recoiling radon atom
 becoming imbedded in an adjacent grain.  Because water is more dense  than air, a radon  atom
 will travel  a shorter distance  in a water-filled pore than in an air-filled pore, thus increasing
 the likelihood that the radon  atom will remain in the pore space. Intermediate moisture levels
 enhance radon emanation but do not significantly affect permeability.  However, high
 moisture levels can significantly decrease the gas permeability of the soil and impede radon
 movement through the soil.
    Concentrations of radon in soils are generally many times higher than those  inside of
 buildings, ranging from tens of pCi/L to more than 100,000 pCi/L, but typically  in the range
 of hundreds to low thousands of pCi/L.  Soil-gas radon concentrations can vary in response to
 variations in climate and weather on hourly, daily, or seasonal time scales.  Schumann and
 others  (1992) and Rose and others (1988) recorded order-of-magnitude variations in soil-gas
 radon  concentrations between seasons in Colorado and Pennsylvania.  The most important
 factors appear to  be (1) soil moisture  conditions,  which are controlled in large part by
precipitation; (2)  barometric pressure; and (3) temperature. Washington and Rose (1990)
suggest that temperature-controlled partitioning of radon between water and gas in soil pores
also has a significant influence on the amount of mobile radon in soil gas.
    Homes in hilly limestone regions  of the southern Appalachians were found to have higher
indoor radon concentrations during the summer than in the winter.   A suggested  cause for this
phenomenon involves temperature/pressure-driven flow of radon-laden air from  subsurface


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

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

  RADON ENTRY INTO BUILDINGS

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

 METHODS AND SOURCES OF DATA

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

 GEOLOGIC  DATA

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


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

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 igneous rocks, and basalts.  Exceptions exist within these general lithologic groups because of
 the occurrence of localized uranium deposits, commonly of the hydrothermal type in
 crystalline rocks or the "roll-front" type in sedimentary  rocks. Uranium and radium are
 commonly sited in heavy minerals, iron-oxide coatings on rock and soil grains, and organic
 materials in soils and sediments.  Less common are uranium  associated with phosphate and
 carbonate complexes in rocks and soils, and uranium minerals.
    Although many cases of elevated indoor radon levels can be traced to high radium and
 (or) uranium concentrations in parent rocks, some structural features, most notably faults and
 shear zones, have been identified as sites of localized uranium concentrations (Deffeyes and
 MacGregor, 1980) and have been  associated with some  of the highest reported indoor radon
 levels (Gundersen, 1991).  The two highest known indoor radon occurrences are associated
 with sheared fault zones in Boyertown, Pennsylvania (Gundersen and others, 1988a; Smith
 and others, 1987), and in Clinton,  New Jersey (Henry and others, 1991; Muessig and Bell,
 1988).

 NURE AERIAL RADIOMETRIC DATA

    Aerial radiometric data are used to  quantify the radioactivity of rocks and soils.
 Equivalent uranium (eU) data provide an estimate of the surficial concentrations of radon
 parent materials (uranium, radium) in rocks and soils. Equivalent uranium is calculated from
 the counts received by a gamma-ray detector from the 1.76 MeV (mega-electron volts)
 emission energy corresponding to bismuth-214  (214Bi), with the assumption that uranium and
 its decay products are  in secular equilibrium. Equivalent uranium is expressed in units of
 parts per million (ppm).  Gamma radioactivity also may be expressed in terms of a radium
 activity; 3 ppm eU corresponds to approximately 1 picocurie  per gram (pCi/g) of radium-226.
 Although radon is highly mobile in soil and its concentration is affected by meteorological
 conditions (Kovach, 1945; Klusman and Jaacks, 1987; Schery and others, 1984; Schumann
 and others, 1992), statistical correlations between average soil-gas radon concentrations and
 average eU values for  a wide  variety of soils have been  documented (Gundersen and others,
 1988a,  1988b; Schumann and Owen, 1988).  Aerial radiometric data can provide an estimate
 of fadon source strength over  a region, but the  amount  of radon that is able to  enter a home
 from the soil is dependent on  several local  factors, including soil structure, grain size
 distribution, moisture content, and permeability, as well  as type of house construction and its
 structural condition.
    The aerial radiometric data used for these characterizations were collected as part of the
Department of Energy  National Uranium Resource Evaluation (NURE) program of the 1970s
and early 1980s.  The purpose of the NURE program was to identify and describe areas in the
United  States having potential uranium  resources (U.S. Department of Energy, 1976).  The
NURE aerial radiometric data were collected by aircraft in which a gamma-ray spectrometer
was mounted, flying approximately 122 m  (400 ft) above the ground surface. The equivalent
uranium maps presented in the state chapters were generated from reprocessed NURE data in
which  smoothing, filtering, recalibrating, and matching of adjacent quadrangle data sets were
performed to compensate for background, altitude, calibration, and other types of errors and
inconsistencies in the original  data set (Duval and others, 1989). The data were then gridded
and contoured to produce maps of eU with a pixel size corresponding to approximately 2.5 x
2.5 km (1.6 x 1.6 mi).


                                           II-6     Reprinted from USGS Open-File Report 93-292

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                   FLIGHT  LINE SPACING Of  SORE  AEKlAL  SURVEYS
                     2  KM (1 MILE)
                     5  EH (3 MILES)
                     2  i  5  KM
                 ES 10 IU  (6 MILES)
                     5  t  10  KM
                     NO DATA
Figure 2. Nominal flightline spacings for NURE aerial gamma-ray surveys covering the
contiguous United States (from Duval and others, 1990). Rectangles represent I°x2° quadrangles.

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

 SOIL SURVEY DATA

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

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

 INDOOR RADON DATA

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

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

  RADON INDEX AND CONFIDENCE INDEX

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


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

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

FACTOR
INDOOR RADON (average)
AERIAL RADIOACTIVITY
GEOLOGY*
SOIL PERMEABILITY
ARCfflTECTURE TYPE
INCREASING RADON POTENTIAL ^

POINT VALUE
1
<2pCi/L
< 1.5 ppm eU
negative
low
mostly slab
2
2-4pCi/L
1.5 - 2.5 ppm eU
variable
moderate
mixed
3
>4pCi/L
> 2.5 ppm eU
positive
high
mostly basement
'GEOLOGIC FIELD EVIDENCE (GFE) POINTS: GFE points are assigned in addition to points
   for the "Geology" factor for specific, relevant geologic field studies. See text for details.

   Geologic evidence supporting:   HIGH radon        +2 points
                              MODERATE       +1 point
                              LOW              -2 points
                  No relevant geologic field studies    0 points
SCORING:
            Radon potential category
                      Point ranee
      Probable average screening
       indoor radon for area
            LOW
            MODERATE/VARIABLE
            HIGH
                      3-8 points
                      9-11 points
                     12-17 points
           <2pCi/L
           2-4pCi/L
           >4pCi/L
                     POSSIBLE RANGE OF POINTS = 3 to 17
TABLE 2.  CONFIDENCE INDEX MATRIX
                                    INCREASING CONFIDENCE
FACTOR
INDOOR RADON DATA
AERIAL RADIO ACnVlTY
GEOLOGIC DATA
SOIL PERMEABILITY
POINT VALUE
1
sparse/no data
questionable/no data
questionable
questionable/no data
2
fair coverage/quality
glacial cover
variable
variable
3
good coverage/quality
no glacial cover
proven geol. model
reliable, abundant
SCORING:
LOW CONFIDENCE
MODERATE CONFIDENCE
HIGH CONFIDENCE
 4-6  points
 7-9  points
10 -12 points
                     POSSIBLE RANGE OF POINTS = 4 to 12
                                    II-12     Reprinted from USGS Open-File Report 93-292

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

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

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

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

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

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

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

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                                 REFERENCES CITED

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

 Tanner, A.B., 1980, Radon migration in the ground: a supplementary review, in Gesell, T.F.,
        and Lowder, W.M. (eds), Natural radiation environment m, Symposium proceedings '
        Houston, Texas, v.  1, p. 5-56.

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

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

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

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

White, S.B., Bergsten, J.W., Alexander, B.V., and Ronca-Battista, M., 1989, Multi-State
       surveys of indoor 222Rn: Health Physics, v. 57, p. 891-896.
                                         11-19     Reprinted from USGS Open-File Report 93-292

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                                               APPENDIX A
                                      GEOLOGIC TIME SCALE
Subdivisions (and their symbols)
Eon or
Eonothem
Phanerozoic2

Proterozoic
(P\


Archean
(At
l«J
Era or
Erathem
Cenozoic 2
(Cz)
Mesozoic2
(Mt)

Paleozoic2
(Pa


UW.
rotBror&ic 0'C rf\
£«ny
'rmvroToiC (X)
laia
Arttivan IW1
MlOdM
Afthtan (V)
t»nv
Aretwn (Ul
Per od. System,
Subperiod. Subsystem
Quaternary
(Q)
Neopene J
Subperiod or
T.rrJ.ry Subsystem (N)
m Paleogene2
Suboeriodor
Subsystem (Pi)
Cretaceous
(K)
Jurassic

Triassic
C5)
Permian
(P)
Pennsylvanian
Carboniferous (P)
(O Mississippian
(M)

Devonian
in)


Silurian
IC\
(a)

Ordovician
/Ol
(Ul

Cambrian
K.)
Epoch or Series
Holocene
Pleistocene
Pliocene
Miocene
Oligocene
Eocene
Paleocene
Late
Early
Late
Middle
Early
Late
Middle
Early
Late
Early
Late
Middle
Early
Late
Early
Late
Middle
Early
Late
Middle
Early
Late
Middle
Early
Late
Middle
Early
Upper
Lower
Upper
Middle
Lower
Upper
Middle
Lower
Upper
Lower
Upper
Middle
Lower
Upper
Lower
Uooer
Middle
Lower
Upper
Middle
Lower
Upper
Middle
Lower
Upper
Middle
Lower
None defined
None defined
None defined
None defined
None defined
None defined
pr*-Arch«n (pA) *
Age estimates
of boundaries
in mega-annum
(Ma)1

































-570*







    1R*nots reflect uncertainties of bolopie and bbstratigraphic agi assignments. Ape boundaries not closely bracketed by existing
data shown by -> Decay constants and bolopic ratios employed are cited in Steiger and Jiger (1977). Designation m.y. used for an
Interval of time.
    * Modifiers (tower, middle, upper or early, middle, late) when used with these Hems are Informal divisions of the larger unit; the
tint letter of the modifier is lowercase.
    'Rocks older than 570 Ma also called Precambrian (p€). a time term without specific rank.
    'informal time term without specific tank.
                                      USGS Open-File Report 93-292

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

-------
  delta, deltaic Referring to a low, flat, alluvial tract of land having a triangular or fan shape
           OT     *  °                                                           '
                          °f •* *?* *.**** ^ ^ ^cumulation of sediment depo'by a

                                                   the smTounding rock' that commoniy
 ™                      rock that is medium in color and contains visible dark minerals that
 make up less than 50% of the rock. It also contains abundant sodium plagioclase and minor
 Quartz.
                    -e sedimer"arv ™.ck of which more than 50% consists of the mineral dolomite
                    is commonly white, gray, brown, yellow, or pinkish in color.       uolormie
 drainage  The manner in which the waters of an area pass, flow off of, or flow into the soil
 Also refers to the water features of an area, such as lakes and rivers, that drain it
 eolian Pertaining to sediments deposited by the wind.
 esker A long, narrow  steep-sided ridge composed of irregular beds of sand and gravel deposited
 by streams beneath a glacier and left behind when the ice melted.                     deposited
                         of water from a land ~ by evaporation from
 extrusive  Said of igneous rocks that have been erupted onto the surface of the Earth.
 fault A fracture or zone of fractures in rock or sediment along which there has been movement.
 fluvial, fluvial deposit Pertaining to sediment that has been deposited by a river or stream.
 ™t^^^                                                                   *
 formation A mappable body of rock having similar characteristics.
 glacial deposit Any sediment transported and deposited by a glacier or processes associated
 with glaciers, such as glaciofluvial sediments deposited by stteaL fl?w^f from Sg gSers.
 gneiss A rock formed by metamorphism in which bands and lenses of minerals of similar
 SffiS" aea          ^ ^ *"** °f ***** comPosition' ^ing the rockTslriped or
        " appeae.
                           COa5Sely crysteMne, quartz- and feldspar-bearing igneous plutonic
65%
                                                                                  of
heavy minerals Mineral grains in sediment or sedimentary rock having higher than average
specific gravity. May form layers and lenses because of wind or water sortil  b
                                                      or water sortig byweigh    size

                                         11-23     Reprinted from USGS Open-File Report 93-292

-------
 and may be referred to as a "placer deposit." Some heavy minerals are magnetite, garnet, zircon,
 monazite, and xenotime.

 igneous Said of a rock or mineral that solidified from molten or partly molten rock material. It is
 one of the three main classes into which rocks are divided, the others being sedimentary and
 metamorphic.

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

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

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

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

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

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

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

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

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

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

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

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

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

outcrop That part of a geologic formation or structure that appears at the surface of the Earth, as
in "rock outcrop".

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

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

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


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

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

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

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

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

 uraniferous Containing uranium, usually more than 2 ppm.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

 Arizona         John Stewart
                Arizona Radiation Regulatory Agency
                4814 South 40th St.
                Phoenix, AZ 85040
                (602) 255^845
Arkansas       Lee Gershner
               Division of Radiation Control
               Department of Health
               4815 Markham Street, Slot 30
               Little Rock, AR 72205-3867
               (501) 661-2301
California      J. David Quinton
               Department of Health Services
               714 P Street, Room 600
               Sacramento, CA 94234-7320
               (916)324-2208
               1-800-745-7236 in state
Colorado       Linda Martin
               Department of Health
               4210 East llth Avenue
               Denver, CO 80220
               (303) 692-3057
               1-800-846-3986 in state
 Connecticut  Alan J. Siniscalchi
             Radon Program
             Connecticut Department of Health
               Services
             150 Washington Street
             Hartford, CT 06106-4474
             (203) 566-3122

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

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

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

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

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

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

Kentucky        JeanaPhelps
                Radiation Control Branch
                Department of Health Services
                Cabinet for Human Resources
                275 East Main Street
                Frankfort, KY 40601
                (502)564-3700
     Louisiana  Matt Schlenker
               Louisiana Department of
                 Environmental Quality
               P.O. Box 82135
               Baton Rouge, LA 70884-2135
               (504) 925-7042
               1-800-256-2494 in state

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

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

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

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

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

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

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

 Montana        Adrian C. Howe
                Occupational Health Bureau
                Montana Department of Health and
                 Environmental Sciences
                Cogswell Building Al 13
                Helena, MT 59620
                (406)444-3671
Nebraska       Joseph Milone
               Division of Radiological Health
               Nebraska Department of Health
               301 Centennial Mall, South
               P.O. Box 95007
               Lincoln, NE 68509
               (402)471-2168
               1-800-334-9491 In State

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

New Hampshire David Chase
               Bureau of Radiological Health
               Division of Public Health Services
               Health and Welfare Building
               Six Hazen Drive
               Concord, NH 03301
               (603)271-4674
               1-800-852-3345 x4674
    New Jersey  Tonalee Carlson Key
               Division of Environmental Quality
               Department of Environmental
                 Protection
               CN415
               Trenton, NJ 08625-0145
               (609) 987-6369
               1-800-648-0394 in state

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

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

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

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

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

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  Oklahoma
  Oregon
 Pennsylvania
 Puerto Rico
Rhode Island
South Carolina
  Gene Smith
  Radiation Protection Division
  Oklahoma State Department of
    Health
  P.O. Box 53551
  Oklahoma City, OK 73152
  (405) 271-5221
  George Toombs
  Department of Human Resources
  Health Division
  1400 SW 5th Avenue
  Portland, OR 97201
  (503)73W014
 Michael Pyles
 Pennsylvania Department of
   Environmental Resources
 Bureau of Radiation Protection
 P.O. Box 2063
 Harrisburg, PA 17120   -
 (717) 783-3594
 1-800-23-RADON In State

 David Saldana
 Radiological Health Division
 G.P.O. Call Box 70184
 Rio Piedras, Puerto Rico 00936
 (809) 767-3563
Edmund Arcand
Division of Occupational Health and
  Radiation
Department of Health
205 Cannon Building
Davis Street
Providence, RI02908
(401) 277-2438
               Bureau of Radiological Health
               Department of Health and
                 Environmental Control
               2600 Bull Street
               Columbia, SC 29201
               (803)734^*631
               1-800-768-0362
  South Dakntq  MikePochop
               Division of Environment Regulation
               Department of Water and Natural
                 Resources
               Joe Foss Building, Room 217
               523 E. Capitol
               Pierre, SD 57501-3181
               (605) 773-3351

     Tennessee  Susie Shimek
               Division of Air Pollution Control
               Bureau of the Environment
               Department of Environment and
                 Conservation
               Customs House, 701 Broadway
               Nashville, TN 37219-5403
               (615) 532-0733
               1-800-232-1139 in state

        Texas  Gary Smith
               Bureau of Radiation Control
               Texas Department of Health
               1100 West 49th Street
               Austin, TX 78756-3189
               (512) 834-6688
        Utah  John Hultquist
              Bureau of Radiation Control
              Utah State Department of Health
              288 North, 1460 West
              P.O. Box 16690
              Salt Lake City, UT 84116-0690
              (801)536^250

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

Virgin Islands  Contact the U.S. Environmental
              Protection Agency, Region JJ
              in New York
              (212)264-4110
                                              H-31      Reprinted from USGS Open-File Report 93-292

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

 Washington     Kate Coleman
                Department of Health
                Office of Radiation Protection
                Airdustrial Building 5, LE-13
                Olympia, WA 98504
                (206)7534518
                1-800-323-9727 In State

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

 Wisconsin       Conrad Weiffenbach
                Radiation Protection Section
                Division of Health
                Department of Health and Social
                 Services
                P.O. Box 309
                Madison, WI53701-0309
                (608) 2674796
                1-800-798-9050 in state

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

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

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

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

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

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

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

Delaware       Robert R. Jordan
               Delaware Geological Survey
               University of Delaware
                101 Penny Hall
               Newark, DE 19716-7501
               (302)831-2833
 Florida Walter Schmidt
        Florida Geological Survey
        903 W. Tennessee St.
        Tallahassee, FL 32304-7700
        (904)488-4191
        William H. McLemore
        Georgia Geologic Survey
        Rm. 400
        19 Martin Luther King Jr. Dr. SW
        Atlanta, GA 30334
        (404)656-3214
 Hawaii  Manabu Tagomori
        Dept. of Land and Natural Resources
        Division of Water & Land Mgt
        P.O. Box 373
        Honolulu, HI 96809
        (808) 548-7539

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

Illinois  Morris W. Leighton
        Illinois State Geological Survey
        Natural Resources Building
        615EastPeabodyDr.
        Champaign, IL 61820
        (217)333-4747

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

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

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

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

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

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

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

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

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

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

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

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

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

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

    New York Robert H. Fakundiny
               New York State Geological Survey
               3136 Cultural Education Center
               Empire State Plaza
               Albany, NY 12230
               (518)474-5816
                                               11-34      Reprinted from USGS Open-File Report 93-292

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

 North Dakota    John P. Bluemle
                North Dakota Geological Survey
                600 East Blvd.
                Bismarck, ND 58505-0840
                (701)224^109
 Ohio           Thomas M. Berg
                Ohio DepL of Natural Resources
                Division of Geological Survey
                4383 Fountain Square Drive
                Columbus, OH 43224-1362
                (614) 265-6576

 Oklahoma       Charles J. Mankin
                Oklahoma Geological Survey
                Room N-131, Energy Center
                lOOE.Boyd
                Norman, OK 73019-0628
                (405) 325-3031
                Donald A. Hull
                DepL of Geology & Mineral Indust.
                Suite 965
                800 NE Oregon St. #28
                Portland, OR 97232-2162
                (503)73W600
Pennsylvania    Donald M. Hoskins
               Dept. of Environmental Resources
               Bureau of Topographic & Geologic
                 Survey
               P.O. Box 2357
               Harrisburg, PA 17105-2357
               (717)787-2169

Puerto Rico     Ram<5n M. Alonso
               Puerto Rico Geological Survey
                 Division
               Box 5887
               Puerta de Tierra Station
               San Juan, P.R. 00906
               (809)722-2526

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

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

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

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

        Utah  M. Lee Allison
              Utah Geological & Mineral Survey
              2363 S. Foothill Dr.
              Salt Lake City, UT 84109-1491
              (801)467-7970
     Vermont  Diane L. Conrad
              Vermont Division of Geology and
                Mineral Resources
              103 South Main St.
              Waterbury, VT 05671
              (802)244-5164
     Virginia  Stanley S. Johnson
              Virginia Division of Mineral
               Resources
              P.O. Box 3667
              Charlottesville, VA 22903
              (804) 293-5121
  Washington Raymond Lasmanis
             Washington Division of Geology &
               Earth Resources
             Department of Natural Resources
             P.O. Box 47007
             Olympia, Washington 98504-7007
             (206)902-1450
                                               H-35
       Reprinted from USGS Open-File Report 93-292

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  West Virginia  Lairy D. Woodfoik
               West Virginia Geological and
                 Economic Survey
               Mont Chateau Research Center
               P.O. Box 879
               Morgantown, WV  26507-0879
               (304)594-2331

Wisconsin      James Robertson
               Wisconsin Geological & Natural
                 History Survey
               3817 Mineral Point Road
               Madison, WI 53705-5100
               (608)263-7384

Wyoming       Gary B. Glass
               Geological Survey of Wyoming
               University of Wyoming
               Box 3008, University Station
               Laramie, WY 82071-3008
               (307)766-2286
                                              11-36      Reprinted from USGS Open-File Report 93-292

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                EPA REGION 3 GEOLOGIC RADON POTENTIAL SUMMARY
                                            by
                  Linda C.S. Gundersen, James K. Otton, and Sandra L. Szarzi
                                   U.S. Geological Survey

        EPA Region 3 includes the states of Delaware, Maryland, Pennsylvania, Virginia, and
  West Virginia.. For each state, geologic radon potential areas were delineated and ranked on the
  basis of geologic, soil, housing construction, and other factors. Areas in which the average
  screening indoor radon level of all homes within the area is estimated to be greater than 4 pCi/L
  were ranked high. Areas in which the average screening indoor radon level of all homes within the
  area is estimated to be between 2 and 4 pCi/L were ranked moderate/variable, and areas in which
  the average screening indoor radon level of all homes within the area is estimated to be less than"
  2 pCi/L were ranked low. Information on the data used and on the radon potential ranking scheme
  is given in the introduction to this volume. More detailed information on the geology and radon
  potential of each state in Region 3 is given in the individual state chapters. The individual chapters
  describing the geology and radon potential of the states in EPA Region 3, though much more
  detailed than this summary, still are generalized assessments and there is no substitute for having a
  home tested. Within any radon potential area homes with indoor radon levels both above and
 below the predicted average will likely be found.
        Figure 1 shows a generalized map of the major physiographic/geologic provinces in EPA
 Region 3.  The summary of radon potential in Region 3 that follows refers to these provinces
 Figure 2 shows average screening indoor radon levels by county. The data for Maryland
 Pennsylvania, Virginia, and West Virginia are from the State/EPA Residential Radon Survey  Data
 for Delaware were compiled by the Delaware Department of Health and Social Services Figure 3
 shows the geologic radon potential areas in Region 3, combined and summarized from the
 individual  state chapters in this booklet.

 DELAWARE

 Piedmont
       The Piedmont in Delaware has been ranked moderate in geologic radon potential Average
 measured indoor radon levels in the Piedmont vary from low (<2 pCi/L) to moderate (2-4 pCi/L)
 Individual readings within the Piedmont can be locally very high (> 20 pCi/L). This is not
 unexpected when a regional-scale look at the Atlantic coastal states shows that the Piedmont is
 consistently an area of moderate to high radon potential.  Much of the western Piedmont in
 Delaware is underlain by the Wissahickon Formation, which consists predominantly of schist
 This formation has moderate to  locally high geologic radon potential. Equivalent schists in the
 Piedmont of Maryland can have uranium concentrations of 3-5 ppm, especially where faulted.
 The Wilmington Complex and James Run Formation, in the central and eastern portions of the
 Delaware Piedmont, are variable in radon potential.  In these units, the felsic gneiss and schist may
 contribute to elevated radon levels, whereas mafic rocks such as amphibolite and gabbro, and
relatively quartz-poor granitic rocks such as charnockite and diorite are probably lower iii radon
potential. The average indoor radon is distinctly lower in parts of the Wilmington Complex than in
surrounding areas, particularly in areas underlain by the Bringhurst Gabbro and the Arden pluton
The permeability of soils in the Piedmont is variable and dependent on the composition of the rocks
from which the soils are derived. Most soils are moderately permeable, with local areas of slow to
                                          m-1    Reprinted from USGS Open-File Report 93-292-C

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                                                                                               100
                                                                                   miles
Figure 1. Geologic radon potential areas of EPA Region 3.  1-Central Lowland; 2-Glaciated Pittsburgh Plateau-
3-Pennsylvanian rocks of the Pittsburgh Low Plateau; 4-Permian rocks of the Pittsburgh Low Plateau; 5-High Plateau
Section; 6-Mountainous High Plateau; 7-Allegheny Plateau and Mountains; 8-Appalachian Mountains- 9-Glaciated
Low Plateau. Western Portion; 10-Glaciated Pocono Plateau; 11-Glaciated Low Plateau, Eastern Portion;
12-Reading Prong; 13-Great Valley/Frederick Valley carbonates and elastics; 14-Blue Ridge Province-
15-Gettysburg-Newark Lowland Section (Newark basin) 16,34-Piedmont; 17-Atlantic Coastal Plain; 18-Central
Allegheny Plateau; 19-CumberIand Plateau and Mountains; 20-Appalachian Plateau; 21-Silurian and Devonian rocks
in Valley and Ridge; 22.23-Valley and Ridge (Appalachian Mountains); 24-Western Piedmont Phyllitc,
25-Culpeper, Gettysburg, and other Mesozoic basins; 26-Mesozoic basins; 27-Eastern Piedmont, schist'and gneiss;
28-Inner Piedmont; 29-Goochland Terrane; 30,31-Coasta! Plain (Cretaceous, Quaternary, minor Tertiary sediments)-
32-Carolina terrane; 33-Coastal Plain (Tertiary sediments); 35,37,38-Coastal Plain (quartz-rich Quaternary
sediments); 36-Glauconitic Coastal Plain sediments.

-------
100 Miles
    Indoor Radon Screening
Measurements: Average (pCi/L)
                                       0.0 to 1.9
                                       2.0 to 4.0
                                       4.1 to 10.0
                                       10.1 to 32.6
                                       Missing Data
                                       or < 5 measurements


-------
         GEOLOGIC
      RADON POTENTIAL
    j   | LOW

    HU MODERATE/VARIABLE
        HIGH

                                                                                  100
                                                                         mile*
Figure 3. Geologic radon potential of EPA Region 3. For more detail, refer to individual state
radon potential chapters.

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  rapid permeability. Limited aereal radioactivity data for the Delaware Piedmont indicates that
  equivalent uranium is generally moderate (1.5-2.5 ppm).

  Coastal Plain
         Studies of radon and uranium in Coastal Plain sediments in New Jersey and Maryland
  suggest that glauconitic marine sediments equivalent to those in the northern portion of the
  Delaware Coastal Plain can cause elevated levels of indoor radon.  Central New Castle County is
  underlain by glauconitic marine sediments of Cretaceous and Tertiary age that have moderate to
  locally high radon potential. Aerial radiometric data indicate that moderate concentrations of
  uranium occur in rocks and soils associated with the Piedmont and parts of the Coastal Plain of
  northern Delaware. Chemical analyses of Cretaceous and Tertiary glauconitic marine sediments
  and fluvial sediments of the Columbia Formation performed by the Delaware geological survey
  indicate variable but generally moderate concentrations of uranium, averaging 1.89 ppm or greater
  The permeability of soils in these areas  is variable but generally moderate to high, allowing radon
  gas to move readily through the soil. Data for New Castle County from the State indoor radon
  survey shows that areas underlain by the Cretaceous fluvial sediments (not glauconitic) have lower
  average indoor radon levels than the glauconitic parts of the upper Cretaceous and lower Tertiary
  sequence to the south.  Kent County and all of Sussex County are underlain by quartz-dominated
  sands, silts gravels, and clays with low radon potential. These sediments are low in radioactivity
  and generally have a low percentage of homes with indoor radon levels greater than 4 pCi/L.

 MARYLAND

 Coastal Plain

 *nH *  ™etWeS'!;rn Su°rl°f Maryland has tee*1 ranked moderate to locally high in radon potential
 and the Eastern Shore has been ranked low in radon potential. The Coastal Plain Province is
 under am by relatively ^consolidated fluvial and marine sediments that are variably phosphatic
 and glauconitic on the Western Shore, and dominated by quartz in the Eastern Shore
 Radioactivity in the Coastal Plain is moderate over parts of the Western Shore sediments,

 LTnlt7 T^  ^ Creta<;eoUS and Tertiary Sediments of P^6 George's' Anne Arundel,
 and northern Calvert counties. Moderate radioactivity also appears to be associated with the
 Cretaceous and Tertiary sediments of the Eastern Shore where these sediments are exposed in
 major drainages in Kent, Queen Anne's, and Talbot counties. Soil-gas radon studies in Prince
 George s County indicate that soils formed from the locally phosphatic, carbonaceous  or
 glaucoma sediments of the Calvert, Aquia, and Nanjemoy Formations can produce significantly
 high radon (average soil radon > 1500 pCi/L).  The Cretaceous Potomac Group had more
 moderate levels of soil radon, averaging  800-900 pCi/L, and the Tertiary-Cretaceous Brightseat
 Formation and Monmouth Group had average soil radon of 1300 pCi/L.  Soil permeability on the
 Western Shore vanes from low to moderate with some high permeability in sandier soils.  Well-
 ?h7t0plp fpy B^°nz1°"S With low Permeability are common. Indoor radon levels measured in
 the State/EPA Residential Radon Survey are variable among the counties of the Western Shore but
 are generaUy low to moderate. Moderate to high average indoor radon is found in most of the
 Western Shore counties.

inri H- F^S aS*eSSment we have ranked P3* of the Western Shore as high in radon potential,
uicluding Calvert County, southern Anne Arundel County, and eastern Prince George's County
This area has the highest radioactivity, high indoor radon, and significant exposure of Tertiary rock
                                          ffl-5    Reprinted from USGS Open-File Report 93-292-C

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units. The part of the Western Shore ranked moderate consists of Quaternary sediments with low
radon potential, Cretaceous sediments with moderate radon potential, and lesser amounts of
Tertiary sediments with high radon potential. The Quaternary sediments of the Eastern Shore have
low radioactivity associated with them and are generally quartzose and thus low in uranium.
Heavy-mineral concentrations within these sediments may be very local sources of uranium.
Indoor radon appears to be generally low on the Eastern Shore with only a few measurements over
4 pCi/L reported.

Piedmont
       Gneisses and schists in the eastern Piedmont, phyllites in the western Piedmont, and
Paleozoic metasedimentary rocks of the Frederick Valley are ranked high in radon potential.
Sedimentary and igneous rocks of the Mesozoic basins have been ranked moderate in radon
potential. Radioactivity in the Piedmont is generally moderate to high. Indoor radon is moderate
to high in the eastern Piedmont and nearly uniformly high in the  western Piedmont.  Permeability
is low to  moderate in soils developed on the mica schists and gneisses of the eastern Piedmont,
Paleozoic sedimentary rocks of the Frederick Valley, and igneous and sedimentary rocks of the
Mesozoic Basins.  Permeability is moderate to high in the soils developed on the phyllites of the
western Piedmont The Maryland Geological Survey has compared the geology of Maryland with
the Maryland indoor radon data. They report that most of the Piedmont rocks, with  the exception
of ultramafic rocks, can contribute to indoor radon readings exceeding 4 pCi/L. Their data indicate
that the phyllites of the western Piedmont have much higher radon potential than the schists in the
east Ninety-five percent of the homes built on phyllites of the Gillis Formation had indoor radon
measurements greater than 4 pCi/L, and 47 percent of the measurements were greater than 20
pCi/L. In comparison, 80 percent of the homes built on the schists and gneiss of the Loch Raven
and Oella Formations had indoor radon readings greater than 4 pCi/L, but only 9 percent were
greater than 20 pCi/L.
       Studies of the phyllites in Frederick  County show high average soil-gas radon (>1000
pCi/L) when compared to other rock types in the county.  Limestone and shale soils of the
Frederick Valley and some of the Triassic sedimentary rocks may be significant sources of radon
(500-2000 pCi/L in soil gas). Because of the highly variable nature of the Triassic sediments and
the amount of area that the rocks cover with respect to the county boundaries, it is difficult to say
with confidence whether the high indoor radon in Montgomery,  Frederick, and Carroll counties is
partly attributable to the Triassic sediments.  In Montgomery County, high uranium  concentrations
in fluvial crossbeds of the upper Manassas Sandstone containing gray carbonaceous clay intraclasts
and drapes have been documented. Similar  lithologic associations are common in the upper New
Oxford Formation. Black shales and gray sandstones of the Heidlersburg Member are similar to
uranium-bearing strata in the Culpeper basin in Virginia and may be a source of radon.  Black
shales in  the overlying Gettysburg Formation may also be locally uranium rich. The lower New
Oxford Formation, the lower Manassas Sandstone, the lower Gettysburg Formation, and the Balls
Bluff Siltstone in Maryland are not likely to  have concentrations  of uranium except where altered
by diabase intrusives and/or faulted.  The diabase bodies are low in radon potential.

Appalachian Mountains
       The Appalachian Province is divided into the Blue Ridge, Great Valley, Valley  and Ridge,
and Allegheny Plateau. Each of these areas is underlain by a distinct suite of rocks with a
particular geologic radon potential. The Blue Ridge is ranked low in radon potential but may be
                                           IH-6    Reprinted from USGS Open-File Report 93-292-C

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  locally moderate to high. The Catoctin volcanic rocks that underlie a significant portion of the Blue
  Ridge have low radioactivity, yield low soil radon and have low soil permeability.  The quartzite
  and conglomerates overlying the Catoctin also have low radioactivity and low soil-gas radon
  Further, the Pennsylvania Topographic and Geologic Sn—jy calculated the median uranium
  content of 80 samples of Catoctin metabasalt and metadiaoase to be less than 0.5 ppm. The
  Harpers Formation phyllite bordering the Catoctin volcanic rocks yields high soil-gas radon
  (>1000 pCi/L), has greater surface radioactivity than the surrounding rocks and is a potential
  source of radon. The Precambrian gneiss that crops out in the Middletown Valley of the southern
  Blue Ridge appears to have moderate radioactivity associated  with it and yielded some high radon
  in soil gas. It is difficult, given the constraints of the indoor radon data, to associate the high
  average indoor radon in the part of Frederick County underlain by parts of this province with the
  actual rocks. The Blue Ridge is provisionally ranked low in geologic radon potential, but this
  cannot be verified with the presently  existing indoor radon data.
        Carbonates and black shales in the Great Valley in Maryland have been ranked high in
 radon potential. Radioactivity is moderate to high over the Great Valley in Washington County
 Washington County has more than 100 indoor radon measurements, has an average indoor radon
 concentration of 8.1 pCi/L in the State/EPA Survey, with over half of the readings greater than
 4 pCi/L. To the north in Pennsylvania, carbonate rocks of the Great Valley and Appalachian
 Mountain section have been the focus of several studies and the carbonate rocks in these areas
 produce soils with high uranium and radium contents that generate high radon concentrations  In
 general, indoor radon in these areas is higher than 4 pCi/L. Studies in the carbonates of the Great
 Valley in West Virginia suggest that the deepest, most mature  soils have the highest radium and
 radon concentrations and generate moderate to high indoor radon. High radon in soils and high
 indoor radon in homes over the black shales of the Martinsburg Formation  of the Great Valley
 were also measured in West Virginia.
        The Silurian and Devonian rocks of the Valley and Ridge have been ranked moderate to
 locally nigh in geologic radon potential.  Indoor radon measurements are generally moderate to
 high in Allegany County. Soil permeabmty is variable but is generally moderate. Radioactivity in
 this part of the Valley and Ridge is moderate to locally high. The Tonoloway, Keyser, and Wills
 Creek Formations, and Clinton and Hamilton Groups have high equivalent uranium associated
 with them and the shales, limestone soils, and hematitic sands  are possible sources of the high
 readings over these units.
       The Devonian through Permian rocks of the Allegheny Plateau are ranked moderate in
 geologic radon potential.  Indoor radon measurements are generally moderate to high
 Radioactivity in the Allegheny Plateau is low to moderate with  locally high equivalent uranium
 associated with the Pocono Group and Mauch Chunk Formation.  Soil permeability  is variable but
 generally moderate.

 PENNSYLVANIA

New England Province
       The New England Province is ranked high in geologic radon potential. A number of
studies on the correlation of indoor radon with geology in Pennsylvania have been done. The
Reading Prong area in the New England Province is the most notable example because of the
national publicity surrounding a particularly severe case of indoor radon. These studies found that
shear zones within the Reading Prong rocks enhanced the radon potential of the rocks and created
                                           m-7    Reprinted from USGS Open-File Report 93-292-C

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local occurrences of very high uranium and indoor radon. Several of the rock types in the Reading
Prong were found to be highly uraniferous in general and they are the source for high radon levels
throughout much of the province.

Piedmont
       The Piedmont is underlain by metamorphic, igneous, and sedimentary rocks of
Precambrian to Mesozoic age that have generally moderate to high radon potential. Rock types in
the metamorphic crystalline portion of the Piedmont that have naturally elevated uranium
concentrations include granitic gneiss, biotite schist, and gray phyllite. Rocks that are known
sources of radon and have high indoor radon associated with them include phyllites and schists,
such as the Wissahickon Formation and Peters Creek Schist, shear zones in these rocks, and the
faults surrounding mafic bodies within these rocks.
       Studies in the Newark Basin of New Jersey indicate that the black shales of the Lockatong
and Passaic Formations and fluvial sandstones of the Stockton Formation are a significant source
of radon in indoor air and in water. Where these rock units occur in Pennsylvania, they may be the
source of high indoor radon as well.  Black shales of the Heidlersburg Member and fluvial
sandstones of the New Oxford Formation may also be sources of locally moderate to high indoor
radon in the Gettysburg Basin.  Diabase sheets and dikes within the basins have low eU. The
Mesozoic basins as a whole, however, are variable in their geologic radon potential. The Narrow
Neck area is distinctly low in radioactivity and Montgomery County, which is underlain almost
entirely by Mesozoic basin rocks, has an indoor radon average less than 4 pCi/L. Other counties
underlain partly by the Mesozoic basin rocks, however, have average indoor radon greater than
4 pCi/L. The Newark basin is high in radon potential whereas the Gettysburg basin is low to
locally moderate. For the purposes of this report the basins have been subdivided along the
Lancaster-Berks county boundary. The Newark basin comprises the Mesozoic rocks east of this
county line.

Blue Ridge
       The Blue Ridge Province is underlain by metasedimentary and metavolcanic rocks and is
generally an area of low radon potential. A distinct low area of radioactivity is associated with the
province on the map, although phyllite of the Harpers Formation may be uraniferous.  Soils
generally have variable permeability. The metavolcanic rocks in this province have very low
uranium concentrations. It is difficult, given the constraints of the indoor radon data, to associate
the high average indoor radon in counties underlain by parts of this province with specific rock
units. When the indoor radon data are examined at the zip code level, it appears that most of the
high indoor radon is attributable to the Valley and Ridge soils and rocks. The conclusion is that the
Blue Ridge is provisionally ranked low in geologic radon potential although this cannot be verified
with the presently available indoor radon data.

Ridge and Valley and Appalachian Plateaus
       Carbonate rocks of the Great Valley and Appalachian Mountain section have been the focus
of several studies and the carbonates in these areas produce soils with high uranium and radium
contents and soil radon concentrations.  In general, indoor radon in these areas is higher than
4 pCi/L and the geologic radon potential of the area is high, especially in the Great Valley where
indoor radon is distinctly higher on the average than in surrounding areas. Soils developed on
                                           m-8     Reprinted from USGS Open-File Report 93-292-C

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  limestone and dolomite rock at the surface in the Great Valley, Appalachian Mountains, and
  Piedmont are probably sources of high indoor radon.
        The clastic rocks of the Ridge and Valley and Appalachian Plateaus province, particularly
  the Ordovician through Pennsylvanian-age black to gray shales and fluvial sandstones, have been
  extensively cited in the literature for their uioiiium coni^,. as well as their general uranium
  potential. It appears from the uranium and radioactivity data and comparison with the indoor radon
  data that the black shales of the Ordovician Martinsburg Formation, the lower Devonian black
  shales, Pennsylvanian black shales of the Allegheny Group, Conemaugh Group, and Monogahela
  Group, and the fluvial sandstones of the Devonian Catskill and Mississippian Mauch Chunk
  Formation may be the source of most moderate to high indoor radon levels in the Appalachian
  Plateau and parts of the Appalachian Mountains section.
        Only a few areas in these provinces appear to have geologically low to moderate radon
  potential. The Greene Formation in Greene County appears to correlate with distinctly low
  radioactivity. The indoor radon for Greene County averages less than 4 pCi/L for the few
  measurements available in the State/EPA survey.
        Somerset and Cambria Counties in the Allegheny Mountain section have indoor radon
  averages less than 4 pCi/L, and  it appears that low radioactivity and slow permeability of soils may
 be factors in the moderate geologic radon potential of this area. These two counties and most of
 the Allegheny Mountain section are underlain by Pennsylvanian-age sedimentary rocks.  The
 radioactivity map shows low to  moderate radioactivity for the Pennsylvanian-age rocks in the
 Allegheny Mountain section and much higher radioactivity in the Pittsburgh Low Plateau section.
 Most of the reported uranium occurrences in these rocks appear to be restricted to the north and
 west of the Allegheny Mountain section. Approximately half of the soils developed on these
 sediments have slow permeability and seasonally high water tables.

 Coastal Plain
       Philadelphia and Delaware Counties, in the southeastern corner of Pennsylvania, have
 average indoor radon less than 4 pCi/L and  have low radioactivity.  Part of Delaware County and
 most of Philadelphia County are underlain by Coastal Plain sediments with low uranium
 concentrations. Soils  developed on these sediments are variable, but a significant portion are
 clayey with slow permeability.

 Glaciated Areas of Pennsylvania
       Radiometric lows and relatively lower indoor radon levels appear to be associated with the
 glaciated areas of the State, particularly the eastern portion of the Glaciated Low Plateau and
 Pocono Plateau in Wayne, Pike, Monroe, and Lackawanna Counties. Glacial deposits are
 problematic to assess for radon.  In some areas of the glaciated portion of the United States, glacial
 deposits enhance radon potential, especially where the deposits have high permeability and are
 derived from uraniferous source rocks. In other portions of the glaciated United States, glacial
 deposits blanket more uraniferous rock or have low permeability and corresponding low radon
 potential.  The northeastern corner of Pennsylvania is covered by the Olean Till, made up of 80-90
 percent sandstone and siltstone clasts with minor shale, conglomerate, limestone, and crystalline
 clasts. A large proportion of the soils developed on this till have seasonally high water tables and
poor drainage, but some parts of the till soils are stony and have good drainage and high
permeability. Low to moderate indoor radon levels and radioactivity in this area may be due to the
seasonally saturated ground and  to the tills being made up predominantly of sandstones and
                                           m-9    Reprinted from USGS Open-FUe Report 93-292-C

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 siltstones with low uranium contents. A similar situation exists in the northwestern part of the
 State, which is covered by a wide variety of tills, predominantly the Kent Till, which contains
 mostly sandstone, siltstone, and shale clasts.  Many of the soils in this area also have low
 permeabilities and seasonally high water tables. Where the tills are thinner, the western portion of
 tne Glaciated Low Plateau has higher indoor radon and high radioactivity.

 VIRGINIA

 Coastal Plain
       The Coastal Plain of Virginia is ranked low in geologic radon potential.  Indoor radon is
 generally low; however, moderate to high indoor radon can occur locally and may be associated
 with phosphatic, glauconitic, or heavy mineral-bearing sediments. Equivalent uranium over the
 Tertiary units  of the Coastal Plain is generally moderate. Soils developed on the Cretaceous and
 Tertiary units  are slowly to moderately permeable. Studies of uranium and radon in soils indicate
 that the Yorktown Formation could be a source for elevated levels of indoor radon.  The
 Quaternary sediments generally have low eU associated with them.  Heavy mineral deposits of
 monazite found locally within the Quaternary sediments of the Coastal Plain may have the potential
 to generate locally moderate to high indoor radon.

 Piedmont
       The Goochland terrane and Inner Piedmont have been ranked high in radon potential.
 Rocks of the Goochland terrane and Inner Piedmont have numerous well-documented uranium and
 radon occurrences associated with granites; pegmatites; granitic gneiss; monazite-bearing
 metasedimentary  schist and gneiss;  graphitic and carbonaceous slate, phyllite, and schist; and shear
 zones. Indoor radon is generally  moderate but significant very high radon levels occur in several
 areas. Equivalent uranium over the Goochland terrane and Inner Piedmont is predominantly high
 to moderate with areas of high eU more numerous in the southern part. Permeability of soils
 developed over the granitic igneous and metamorphic rocks of the Piedmont is generally moderate.
 Within the Goochland terrane and Inner Piedmont, local areas of low to moderate radon potential
 will probably be found over mafic rocks (such as gabbro and amphibolite), quartzite, and some
 quartzitic schists.  Mafic rocks have generally low uranium concentrations and slow to moderate
permeability in the soils they form.
       The Carolina terrane is variable in radon potential but is generally moderate.  Metavolcanic
rocks have low eU but the granites and granitic gneisses have moderate to locally high eU.  Soils
developed over the volcanic rocks are slowly  to moderately permeable. Granite and gneiss soils
have moderate permeability.
     The Mesozoic basins have moderate to locally high radon potential. It is not possible to make
 any general associations between county indoor radon averages and the Mesozoic basins as a
whole because of the limited extent of many the basins. However, sandstones and siltstones of the
 Culpeper basin, which have been lightly metamorphosed and altered by diabase intrusion, are
mineralized with uranium and cause documented moderate to high indoor radon levels in northern
Virginia. Lacustrine black shales and some of the coarse-grained gray sandstones also have
significant uranium mineralization, often associated with green clay clasts and copper. Equivalent
uranium over the Mesozoic basins varies among the basins. The Danville basin has very high eU
associated with it whereas the other basins have generally moderate eU. This radioactivity may be
related to extensive uranium mineralization along the Chatham fault on the west side of the Danville
                                           HMO    Reprinted from USGS Open-File Report 93-292-C

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 basin.  Localized high eU also occurs over the western border fault of the Culpeper basin. Soils
 are generally slowly to moderately permeable over the sedimentary and intrusive rocks of the
 basins.

 Valley and Ridge
        The Valley and Ridge has been ranked high in geologic radon potential but some areas have
 locally low to moderate radon potential.  The Valley and Ridge is underlain by Cambrian dolomite,
 limestone, shale, and sandstone; Silurian-Ordovician limestone, dolomite, shale, and sandstone;
 and Mississippian-Devonian sandstone, shale, limestone, gypsum, and coal. Soils derived from
 carbonate rocks and black shales, and black shale bedrock may be sources of the moderate to high
 levels of indoor radon in this province. Equivalent uranium over the Valley and Ridge is generally
 low to moderate with isolated areas of high radioactivity.  Soils are moderately to highly
 permeable. Studies of radon in soil gas and indoor radon over the carbonates and shales of the
 Great Valley in West Virginia and Pennsylvania indicate that the rocks and soils of this province
 constitute a significant source of indoor radon. Sandstones and red siltstones and shales are
 probably low to moderate in radon potential.  Some local uranium accumulations are contained in
 these rocks.

 Appalachian Plateaus
        The Appalachian Plateaus Province has been ranked moderate in geologic radon potential.
 The plateaus are underlain by Pennsylvanian-age sandstone, shale, and coal. Black shales,
 especially those associated with coal seams, are generally elevated in uranium and may be the
 source for moderate to high radon levels. The coals themselves may also be locally elevated in
 uranium. The sandstones are generally low to moderate in radon potential but have higher soil
 permeability than the black shales.  Equivalent uranium of the province is low to moderate and
 indoor radon is variable from low to high, but indoor radon data are limited in number.

 WEST VIRGINIA

 Allegheny Plateau
       The Central Allegheny Plateau Province has moderate geologic radon potential overall, due
 to persistently moderate eU values and the occurrence of steep, well-drained soils. However,
 Brooke and Hancock counties, in the northernmost part of this province, have average indoor
 radon levels exceeding 4 pCi/L. This appears to be related to underlying Conemaugh and
 Monongahela Group sedimentary rocks which have elevated eU values in this area and in adjacent
 areas of western Pennsylvania.
       The Cumberland Plateau and Mountains Province has low radon potential. The eU values
 for the province are low except in areas of heavy coal mining, where exposed shale-rich mine
 waste tends to increase values. Indoor radon levels average less than 2 pCi/L in most counties.
       The Eastern Allegheny Plateau and Mountains Province has moderate radon potential
 overall. Locally high indoor radon levels are likely in homes on dark gray shales of Devonian age
and colluvium derived from them in Randolph County. The southern part of this province has
somewhat lower eU values and indoor radon averages.
                                          ffl-11    Reprinted from USGS Open-File Report 93-292-C

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Ridge and Valley Province
       The southern part of the Appalachian Ridge and Valley Province in West Virginia has
moderate radon potential overall. The eU signature for this province is elevated (> 2.5 ppm eU).
Locally high radon potential occurs in areas of deep residual soils developed on limestones of the
Mississippian Greenbrier Group, especially in central Greenbrier County, where eU values are
high. Elevated levels of radon may be expected in soils developed on dark shales in this province
or in colluvium derived from them.
       The northern part of the Appalachian Ridge and Valley Province in West Virginia has high
geologic radon potential. The soils in this area have an elevated eU signature.  Soils developed on
the Martinsburg Formation and on limestones and dolomites throughout the Province contain
elevated levels of radon and a very high percentage of homes have indoor radon levels exceeding
4 pCi/L in this province. Karst topography and associated locally high permeability in soils
increases the radon potential.  Structures sited on uraniferous black shales may have very high
indoor radon levels. Steep, well-drained soils developed on phyllites and quartzites of the Harpers
Formation in Jefferson County also produce high average indoor radon levels.
                                           m-12   Reprinted from USGS Open-File Report 93-292-C

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     PRELIMINARY GEOLOGIC RADON POTENTIAL ASSESSMENT OF DELAWARE
                                          by
                                 Linda C. S. Gundersen
                                 U.S. Geological Survey
INTRODUCTION

       The Office of Radiation Control in the Delaware Department of Health and Sotial Services
assisted Delaware citizens in testing for indoor radon from 1985-1990 (Eichler and Wright 1991)
Of more tfian 7000 indoor radon measurements performed in the State, 10.5 percent of the homes '
tested had indoor radon levels exceeding the U.S. Environmental Protection Agency's 4 pCi/L
guideline. Statewide radon levels ranged from 0.5 to 164 PCi/L and averaged 2 pCi/L Ninety-
eight percent of the testing was done by means of charcoal canister. The Delaware Geological
s
                                                            .


        Examination of the indoor radon data in the context of geology, soil permeability, and
 radioactivity suggest that some of the metamorphic and igneous rocks of the Piedmont and some
 sediments of the northern portion of the Atlantic Coastal Plain have moderate to locally high radon
 potential.  Much of the Atlantic Coastal Plain in the central and southern portion of the State has
 low radon potential.
        This is a generalized assessment of geologic radon potential of rocks, soils, and surficial
 deposits of Delaware. The scale of this assessment is such that it is inappropriate for use in
 identifying the radon potential of small areas such as neighborhoods, individual building sites  or
 housing tracts. Within any area of a given radon potential ranking there are likely to be areas with
 higher or lower radon levels than characterized for the area as a whole.  Indoor radon
 concentrations, both high and low, can be quite localized, and there is no substitute for testing
 individual homes.  For more information, the reader is urged to consult the Office of Radiation
 Control, Delaware Department of Health and Social Services, or the EPA regional office  More
 detailed information on state or local geology may be obtained from the state geological survey
 Addresses and phone numbers for these agencies are listed in chapter 1 of this booklet
 PHYSIOGRAPHIC AND GEOGRAPHIC SETTING
       Delaware lies within parts of two physiographic provinces (fig. 1). The Piedmont is
underlain by igneous and metamorphic rocks with gently rolling, wooded and open uplands
averaging 250 feet in elevation, but with as much as 300 feet of local relief.  The rest of Delaware
is within the Atlantic Coastal Plain. The northern portion of the Atlantic Coastal Plain is
characterized by gently rolling hills with minor relief, underlain by fluvial and marine sediments
ine central, southern, and coastal portions of the Atlantic Coastal Plain consist of bottom land
pine woods, and marshes, which  are also underlain by fluvial and marine sediments  The entire
Mate is well drained, with a central divide postulated to be controlled by tectonic tilt of the
Delmarva Peninsula (Spoljaric, 1980).
      In 1990, the population of Delaware was 666,168 (U.S. Census Bureau fig 2)  The
majority of its population resides  in the northernmost county of New Castle, where technological
marine, and heavy industries support the population centers of Wilmington, Newark, and New  '
Castle. The two southern counties of Kent and Sussex are dominantiy agricultural.
                                         IV-l    Reprinted from USGS Open-File Report 93-292-C

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                                             Piedmont
                        Figure 1. Physiographic areas of Delaware.

GEOLOGY AND SOILS

       The following discussion of bedrock and surficial geology is condensed from Jordan
(1962,1964,1974,1983), Pickett and Spoljaric (1971), Woodruff (1985,1986), Woodruff and
Thompson (1972,1975), Pickett and Benson (1977,1983), Kraft and Carey (1980), Thompson
(1980), Talley (1982,1987), Andres (1986), Benson and Pickett (1986), Ramsey and Schenck
(1990), and Wagner and others (1991).  Discussion of soils is based on Richmond and others
(1987) and the Soil Conservation Service county soil surveys (Mathews and Lavoie, 1970;
Mathews and Ireland, 1971; and Ireland and Mathews, 1974).  A generalized geologic map of
Delaware is shown in figure 3, cross sections of the Coastal Plain are given in figure 4a and b, and
a generalized surficial geologic map of Delaware is shown in figure 5.

The Piedmont
       The Piedmont is underlain by a complex sequence of high-grade metamorphic and igneous
rocks that have been folded and faulted. These crystalline rocks are generally weathered to a depth
of 10 feet or more, and in some cases, depth of weathering may exceed 70 feet. Soils formed on
these rocks are saprolitic and reflect the original composition of the rock.  Because the crystalline
rocks are so complex, the soils formed on them are also complex. The descriptions of soils
presented here are generalized and do not reflect site-specific conditions that one would expect to
observe in the field.
       The oldest rocks in the Piedmont are Precambrian Grenville gneisses that occur along the
Pennsylvania border in the core of the Mill Creek dome in the northwestern part of the Piedmont.
They have been correlated with the Baltimore Gneiss and consist of quartz-feldspar gneisses,
biotite schist, and minor amphibolite.  Saprolite soils developed on the gneiss are sandy to silty
loams and clayey, silty sands. Permeability in the sandy, silty loams ranges from moderate to
moderately rapid. Deeply developed soils and soils from the micaceous schist tend to be more
                                          IV-2    Reprinted from USGS Open-FDe Report 93-292-C

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                                         POPULATION (1990)

                                        C2  100000 to 200000
                                        E3  200001 to'300000
                                        0  300001to400000
                                        H  400001 to 500000
                                             10 Miles
Figure 2. Population of counties in Delaware (1990 U.S. Census data).

-------
Figure 3. Generalized geologic map of Delaware showing rock units ranging in age from
Precambrian to Tertiary (after Pickett, 1976). Quaternary units are shown on the surficial
geologic map (fig. 5).

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    GENERflLIZED GEOLOGIC MflP OF DELRUJRRE (PRECflMBRIBN-TERTIflRV)
                                  EHPLRNRTION
 TERTIRRV


 PLIOCENE

         Beaverdam Formation - Fairly well sorted medium sand, some gravel.
 PLIOCENE?
         Bryn Mawr Formation - Red and brown quartz sand with silt, clay and fine gravel
         (in Piedmont).
 MIOCENE-PLIOCENE(?)

         Chesapeake Group - Bluish gray silt with quartz sand and some shell beds.
 PflLEOCENE-EOCENE{?)
 -.0.«
   Vt
 Vincentown Formation - Green, gray and reddish-brown fine to coarse, highly
        quartzose glauconitic sand with some silt.
 CRETflCEOUS-PRLEOCENE
        Hornerstown Formation - Green, gray and reddish-brown fine to medium, silty
        highly glauconitic sand and sandy silt.                                   '
CRETRCEOUS
 .» X
 X X
 X X
Mount Laurel -Monmouth Formations - Gray, green and red-brown, glauconitic
fine to medium, quartz sand with some silt                        s*uiwniuc

Matawan Group
                              ion " Dark greenish-gray, massive, very glauconitic silty,


          Englishtown Formation - Light gray and rust brown, well sorted micaceous sand
          with thin mterbedded layers of dark gray silty sand; abundant fossil burrows.
                                              micaceous'
                                                                     itic sandy
   I   Magothy Formation - White and buff quartz sand with beds of gray and black clayey


       Potomac Formation - Variegated silts and clays with beds of quartz sand.

-------
PRECflMBR IBN-PflLEOZO IC

        Wissahickon Formation - Gneiss, schist, amphibolite, and minor serpentine.

        Setters Formation & Cockeysville Marble of the Lower Glenarm Series - Quartz -
        mica schist and dense white crystalline marble.


        Baltimore Gneiss - Feldspathic biotite gneiss and minor schist.


        Anorthosite - Andesine anorthosite and anorthositic gabbro.


        James Run Formation - Amphibolite; hypersthene gneiss and minor pelitic gneiss.

        Wilmington Complex - Hypersthene-bearing felsic gneiss, minor amphibolite, with
        gabbro, norite, and anorthosite plutons.

-------
       A.
            1000
           LOCATION OF
         CROSS-SECTIONS
                                                                              2000
                               Qhl - Holocene Deposits
                               QToml, Qomu - Omar Formation
                               Qcl - Columbia Formation
                               Tbd • Beaverdam Formation
                               Tbt - Bethany Formation
                               Tma, Tmb - Manokin Formation
                               Tsm - St. Marys Formation
                               Teh - Choptank Formation
                               Tc - Calvert Formation
EXPLANATION
          Tna-
          Tvt-
          TM-
          Kml.
          Kmt
          Ket-
          Kmv
          Km-
          Kpt-
• Nanjemoy Formation
Vincentown Formation
Hornerstown Formation
• Mount Laurel Formation
- Marshalltown Formation
Englishtown Formation
- Merchantville Formation
Magothy Formation
Potomac Formation
         B.
                NNW
                         KENT COUNTY
                                                   SUSSEX COUNTY
                                                                  Oomu
                                                                           SSE
                                                                             .Tbt
    « r  »i  £g  ? , f  S^PS10 cross-sections of (A) the Middletown-Odessa area,
-New Castle County (after Pickett and Spoljaric, 1971), and (B) Kent and Sussex
 counties, southern Delaware (after Ramsey and Schenck  1990)

-------
                                                             10
Figure 5. Generalized surficial geologic map of Delaware (after Richmond and others, 1987, and
Ramsey and Schenck, 1990).

-------
                    GENERflLIZEO SURFICIflL GEOLOGIC MBP OF DELflUJflRE
                                             EKPLflNHTION
                    (After Richmond and others, 1987, and Ramsey and Schenck, 1990)
  HOLOCENE
           Beach, Barrier, and Spit Deposits - White'to gray, fine to coarse sand with scattered gray silty clay beds  Well
           sorted, laminated, and crossbedded, mostly quartz, includes some organic matter and shells.

           Swamp and Saline-Marsh Deposits - Interbedded dark-gray, black, or greenish-gray silty clay to clayey fine
           sand and carbonaceous clay; dark-brown to black organic debris, muck, and local peat, mixed with muck
           composed of fine sand, silt and kaolinitic clay. Commonly bioturbated; local marl in calcareous clay at depth
  PLEISTOCENE
           Alluvial and Estuarine Sand and Silt - White to light reddish-brown medium to coarse sand, gravelly sand
           gravel, silty clay, and organic-rich silty clay. Sand commonly crossbedded. Fossiliferous in places (Delaware
           Jisy deposits}.

           Alluvial Gravelly Sand - Gray to brown, fine to medium sand, gravelly sand, clayey silt, and silty clay  Both
           sand and gravel are chiefly quartz. Deposit is poorly sorted, thin to medium bedded, and locally crossbedded
           Capped in places by well-sorted fine sand associated with dunes.(Nanticoke deposits).


   IHT]   ftoeto coa^Snd6 ^"^ ^ *** -CIay" ™* *° ** to WuiSh ffay ^ ^ Sa"d'dayey ^ **F clay'and
          Sandy and Silty Decomposition Residuum - Tan to dark gray silty and clayey sand and sandy silt (Staytonville

          Sandy Decomposition Residuum - Orange-red, reddish-brown, tan, light gray, or white sandy loam that grades
          downward into medium to coarse feldspathic sand with minor gravel and silt; with reddish-brown or orange
          brown iron oxide stains.  Residuum is chiefly on broad upland surfaces (Columbia Formation)
 QURTERNRRV RND TERTIHRV
          Sandy Clay Saprolite and Alluvium - Red, yellowish-red, strong-brown , yellow, light-gray, or greenish-grav
          shghtly clayey sand to sandy clay. Clays are mixed smectite and kaolinite if, saproUtf. wS souSSJS
         Micaceous Saprolite and Alluvium - Red, reddish-brown, strong-brown, yellowish-red, or gray, micaceous
         clayey to shghfly clayey sand to clayey sandy silt. Clay is kaolinite and lesser amounts of gibbsite  Mica mostly
         weathered to micaceous clay and (or) kaolinite near ground surface                                     y
TERTIHRV
  ~^   Sand and Sandy Decomposition Residuum - Pale white, buff, or greenish-gray, medium sand with scattered
  LHJ   beds of coarse sand gravelly sand, and silty clay. Unit fines upwards; contains rare glauconite. Residuum is
         chiefly on broad upland surfaces (Beaverdam Formation)                                 «»uuui,,»

-------
clayey and have slow to moderate permeability.  Soils derived from amphibolite are clayey loams
to clayey silts and silty, sandy clays that are slowly to moderately permeable.
       The Baltimore Gneiss is unconformably overlain by the Setters Formation and
Cockeysville Marble of the Lower Glenarm Series. The Setters Formation comprises thin lenses
of quartzitic mica schist and is very limited in exposure. The Cockeysville Marble is a calcitic to
locally dolomitic, coarse-grained marble that underlies the Hockessin-Yorklyn Valley and Pleasant
Valley near Newark. Where soils are well developed, the marble weathers to form silty clays and
clayey loams of slow permeability. Steeper slopes of the marble tend to have soils that are less
deep and stony soils of moderate permeability that vary from sandy loam to silty clay.
       Much of the western part of the Piedmont is underlain by the Wissahickon Formation,
consisting of quartzitic to micaceous, felsic schists and gneisses, amphibolite, and small areas of
serpentinite and granitic pegmatite. Soils developed on the quartzitic schist are sandy to silty loams
and clayey, silty sands with moderate to moderately rapid permeability. Soils developed on the
micaceous schist tend to be more clayey and have slow to moderate permeability. Soils derived
from amphibolite and serpentinite are clayey loams to silty clays with slow permeability.  Lying in
an elongate belt between the Wissahickon Formation and the Wilmington Complex is the James
Run (?) Formation (fig. 3). Interpretation and distribution of this rock type is the subject of
debate. The James Run (?) Formation as shown on the map of Pickett (1976) in figure 3 is similar
to the distribution of the James Run (?) Formation in Thompson (1980). On the geologic maps of
Woodruff and Thompson (1972,1975) these rocks are included in the Wilmington Complex.
They are described in the western Piedmont as felsic and mafic gneiss with minor pelitic schist.
The mafic and felsic gneisses may also contain hornblende and hypersthene. In the eastern
Piedmont, they are described as hornblende-plagioclase gneiss interlayered with smaller amounts
of pyroxene-bearing felsic gneiss, amphibolite, and quartz-feldspar gneiss (Woodruff and
Thompson, 1975).  Wagner and others (1991) show the James Run Formation only in the
southwesternmost corner of the Piedmont in contact with a small body of granitic gneiss.  They
place most of the western felsic and mafic gneisses in the Wissahickon Formation and include the
eastern hornblende- and pyroxene-bearing gneisses in the Wilmington Complex.
       The Wilmington Complex underlies much of the eastern third of the Piedmont. It
comprises hypersthene-bearing felsic gneiss, minor amphibolite, and small plutons. Two of the
largest plutons are in the eastern and southeastern portions of the Wilmington Complex. The
Arden Pluton has been described as anorthosite, noritic anorthosite, norite, and minor charnockite
by Woodruff and Thompson (1975), and as a granodiorite-norite-charnockite by Wagner and
others (1991). The other major pluton is the Bringhurst Gabbro, which underlies part of the city
of Wilmington and consists of gabbro and norite. The felsic rocks of the Wilmington Complex
form silty sands ^nd sandy loams of moderate to moderately rapid permeability. The mafic rocks
of the Wilmington Complex (gabbro, amphibolite) form silty clays and clayey loams with slow
permeability.

The Coastal Plain
       The Coastal Plain consists of relatively unconsolidated Cretaceous and Tertiary sediments
that are unconformably overlain by Tertiary, Quaternary, and Holocene sediments (fig. 4). At the
surface, the Cretaceous portion of the Coastal Plain consists of the fluvial and marine sediments of
the Potomac and Magothy Formations, Matawan Group, and the Mount Laurel (Monmouth)
Formation. Other units exist in the subsurface and are shown in figure 4.  Only surface units are
described in this section.
                                         IV-10    Reprinted from USGS Open-File Report 93-292-C

-------
         The Potomac Formation consists of fluvial channel sands with variegated, locally lignitic
  silt and clay deposited in an alluvial plain. Iron oxide concretions and cements are common  The
  Magothy Formation consists of quartz sands and lignitic, gray and black clayey silt of estuarine
  and marginal deltaic origin. The Matawan Group is subdivided into the Marshalltown
  Englishtown, and Merchantville Formations. Downdip, the lithologies in these three formations
  grade into a single unit and the Matawan Group is changed to formation rank.  It consists
  predominantly of marine silty sands and sandy silt with abundant glauconite. The Mount Laurel
  Formation (also known as the Monmouth in the subsurface) is made up of glauconitic silty sands
  and silt. Glauconite may locally comprise more than 80 percent of the sediment in the Matawan
  Group and Mount Laurel Formation (Spoljaric, 1980).  These Cretaceous units are generally
  exposed in some of the major river drainages, canals, and estuaries, as well as where the overlying
  Quaternary sediments are absent. The fluvial sands of the Potomoc Formation tend to have
  moderate to moderately rapid permeability.  Marine sands with abundant glauconite or sands that
  have abundant iron-oxide content tend to be more clayey and have slow to moderate permeability
  Silt and fine sandy sediments are slowly to moderately permeable and the clays (except where drv
  and fractured) are slowly permeable.
        The oldest part of the Tertiary sequence exposed at the surface is the glauconitic sands and
  sandy silts of the Rancocas Group, consisting of the Hornerstown and Vincentown Formations
  Soils derived from these formations are sandy to clayey loams with slow to moderate permeability
  I he rest of the Tertiary sequence exposed at the surface, the Chesapeake Group, includes the
  Calvert and Choptank Formations.  The Calvert Formation is predominantly fine sand with shelly
 mterbeds. The Choptank Formation consists of several fining-upward sequences varying from
 shelly sand to sandy, clayey silt. These deposits generally lack glauconite. Soils formed on the
 Chesapeake Group typically have slow to moderately rapid permeability. Other Tertiary units exist
 in the subsurface of the Coastal Plain and are shown in figure 4.
        Quaternary and late Tertiary sediments, where present, vary from 5 to 100 feet in thickness
 and blanket much of the Atlantic Coastal Plain (fig. 5). The Quaternary fluvial deposits in the
 northern and central portion of the Atlantic Coastal Plain are called the Columbia Formation and
 they unconformably overlie the older Cretaceous and Tertiary sediments. They consist of rusty-
 weathering, feldspathic quartz sands with gravel and silt beds that are derived primarily from older
 units to the northeast and north. The Staytonville unit is a silty to clayey sand and sandy silt that
 overlies the Columbia and is exposed in a limited area in southwestern Kent County near the
 county line. The Staytonville unit's relationship to the Columbia Formation is not known  The
 Columbia Formation overlaps an older fluvial unit in southern Delaware, the Pliocene Beaverdam
 Formation. This unit is siltier than the Columbia Formation, is partly unconformable with older
 Tertiary units, and crops out only in Sussex County.  The Beaverdam Formation is predominantly
 sand with some gravelly sand and silty clay layers. The sand has a silt matrix in the upper half of
 the unit. In southeastern Delaware, the Tertiary-Quaternary Omar Formation overlies the
 Beaverdam Formation.  It consists of silty fine sand, clayey silt and silty clay, and fine to coarse
 sand. The upper Omar  Formation is the principal part of the unit exposed at the surface; the lower
 part of the Omar Formation is restricted to a paleovalley cut into the Beaverdam Formation
 Permeability of the Quaternary sediments is generally moderate to moderately rapid, but areas of
 slow permeability exist in more clay-rich or water-saturated sediments. In the Nanticoke River
 Valley, deposits of silty clay, gravelly sand, and fine- to medium-grained sand are termed the
 Nanticoke deposits and are Quaternary in age. In Delaware Bay, Quaternary deposits of sand
minor gravel, silty clay, and organic-rich silty clay comprise the Delaware Bay deposits  Shoreline
                                         IV-11    Reprinted from USGS Open-FUe Report 93-292-C

-------
deposits of Holocene age dominate in southeasternmost Delaware and along the Atlantic coastline.
These sediments include: organic rich silty clay and sand of marsh and swamp deposits; fine to
coarse, white quartz sand and silty clay beds found in the present day beach, barrier, and spit
deposits; and organic-rich silty clay and clayey silty sand in present day lagoon and estuary
deposits.

RADIOACTIVITY

       An aeroradiometric map of Delaware (fig. 6) was compiled from spectral gamma-ray data
acquired during the U.S. Department of Energy's National Uranium Resource Evaluation (NURE)
program (Duval and others, 1989). For the purposes of this assessment, low equivalent uranium
(eU) is defined as less than 1.5 parts per million (ppm) of uranium, moderate eU is defined as
1.5-2.5 ppm, and high eU is defined as greater than 2.5 ppm. Low radioactivity appears to be
associated with most of the Atlantic Coastal Plain sediments. Moderate eU is found in parts of the
central and northern portions of the State associated with the Piedmont and parts of the Coastal
Plain. There are no areas of high radioactivity on the map. The pattern of radioactivity over the
Coastal Plain in figure 6 cannot be readily correlated with any specific geologic units.
       A recent study of radon and radioactivity in part of the Coastal Plain by the Delaware
Geological Survey  (Woodruff and others, 1992) used portable gamma radiation detectors to survey
the surface areas underlain by glauconitic sediments in southern New Castle County. They found
that, despite the cover of Columbia Formation, ranging from 10 to 70 feet thick, gamma-ray
measurements over subcrops of the glauconite-rich Mount Laurel Formation and Rancocas Group
displayed typically higher radioactivity (72-139 counts per second, cps) than the non-glauconitic
deposits of the Chesapeake Group (60-80 cps) to the south. The highest gamma radiation
measurements were associated with the Hornerstown Formation (130-140 cps). They measured
uranium concentrations ranging from 0.8-114 ppm with an average of 8.2 ppm in samples of the
Mount Laurel Formation and Rancocas Group, and ranging from 0.6-4.9 ppm with an average of
1.89 ppm (J.H. Talley, written commun., 1993) in the Columbia Formation. Soil radon
measurements by Woodruff and others (1992) in the Columbia Formation ranged from 53.9-
419.1 pCi/L in areas underlain by glauconitic sediments and 25.7-259.9 pCi/L hi areas underlain
by non-glauconitic sediments; however, the authors do not feel that the differences in the radon
concentrations are statistically significant. The authors suggested that gamma radiation and,
possibly, radon gas from the glauconitic sediments beneath the Columbia Formation, were
contributing to the natural radioactivity measured at and near the surface.

INDOOR RADON DATA

       During the period from November, 1985, to June, 1990, the Office of Radiation Control in
the Delaware Department of Health and Social Services assisted homeowners and others in testing
for indoor radon, and compiled test data to map indoor radon levels in the State. Results of this
study are presented in a report by Eichler and Wright (1991). This data set includes all 150 public
schools in Delaware and more than 30 private schools. Ninety-eight percent of the tests were done
by charcoal canister. The average indoor radon level for the more than 7000 tests in the State
survey was 2 pCi/L. Table 1 summarizes the data by zip code. Figures 7a and b are maps of the
average indoor radon and percent of indoor radon measurements exceeding 4 pCi/L, plotted by zip
code centroid—each point is located hi the center of the zip code area. These zipcode maps show
                                         IV-12    Reprinted from USGS Open-File Report 93-292-C

-------
                                             EQUIVALENT URANIUM
                                                    > 1.5 ppm
                                                (==:l 1.0-1.5 ppm
                                                    < 1 -0 ppm
                                                |   | NO DATA
                                                         10
                                                  Miles
Figure 6.  Aerial radiometric map of Delaware (after Duval and others, 1989).

-------
TABLE 1.  Screening indoor radon data complied by the Delaware Department of Public Health
for homes tested during the period 1986-1990. Data represent 2-7 day charcoal canister
measurements. Units for all columns of radon data are pCi/L.
ZIP
CODE
19701
19702
19703
19706
19707
19708
19709
19710
19711
19713
19714
19715
19720
19730
19731
19732
19733
19734
19735
19736
19800
19801
19802
19803
19804
19805
19806
19807
19808
19809
19810
19901
19930
19931
19933
19934
19936
19938
19939
19940
19941
19942
CITY
BEAR
NEWARK
CLAYMONT
DEL. CITY
HOCKESSIN
KIRKWOOD
MEDDLETOWN
MONTCHANIN
NEWARK
NEWARK
NEWARK
NEWARK
NEW CASTLE
ODESSA
PORTPENN
ROCKLAND
ST. GEORGES
TOWNSEND
YORKLYN
YORKLYN
WILMINGTON
WILMINGTON
WILMINGTON
WILMINGTON
WILMINGTON
WILMINGTON
WILMINGTON
WILMINGTON
WILMINGTON
WILMINGTON
WILMINGTON
DOVER
BETHANY
BETHAL
BRTDGEVILLE
CAMDEN
CHESWOLD
CLAYTON
DAGSBORO
DELMAR
ELLENDALE
FARMINGTON
COUNTY
NEW CASTLE
NEWCASTLE
NEWCASTLE
NEW CASTLE
NEW CASTLE
NEWCASTLE
NEWCASTLE
NEWCASTLE
NEWCASTLE
NEWCASTLE
NEWCASTLE
NEWCASTLE
NEWCASTLE
NEW CASTLE
NEW CASTLE
NEW CASTLE
NEWCASTLE
NEW CASTLE
NEW CASTLE
NEW CASTLE
NEW CASTLE
NEWCASTLE
NEWCASTLE
NEWCASTLE
NEW CASTLE
NEW CASTLE
NEWCASTLE
NEWCASTLE
NEW CASTLE
NEWCASTLE
NEWCASTLE
KENT
SUSSEX
SUSSEX
SUSSEX
KENT
KENT
KENT
SUSSEX
SUSSEX
SUSSEX
KENT
NO. OF
MEAS.
140
175
132
33
352
5
240
15
821
197
2
4
269
47
13
6
5
106
1
15
2
39
114
688
171
194
78
178
572
234
691
295
21
3
49
58
5
48
32
24
7
1
AVERAGE
1.8
1.5
1.8
1.0
2.4
0.9
3.0
1.7
2.7
1.5
2.7
1.7
1.7
3.2
1.2
1.7
2.9
1.6
0.8
2.3
0.5
1.5
1.7
2.1
1.9
1.6
1.6
2.2
2.2
2.1
2.6
1.6
0.7
1.0
1.0
1.1
0.9
1.1
1.5
0.8
0.6
0.5
MEDIAN
1.3
1.0
1.3
0.6
1.6
0.5
2.0
1.5
1.5
0.9
2.7
1.8
1.3
2.0
0.5
1.5
2.2
1.0
0.8
1.3
0.5
1.1
1.1
1.6
1.7
1.0
1.1
1.7
1.6
1.5
1.8
1.2
0.5
1.0
0.8
0.9
0.5
0.8
0.5
0.5
0.5
0.5
GM
1.3
1.1
1.3
0.9
1.7
0.8
2.0
1.4
1.5
1.0
2.6
1.6
1.2
2.0
0.9
1.3
2.5
1.1
0.8
1.4
0.4
1.2
1.2
1.5
1.4
1.0
1.2
1.6
1.6
1.5
1.8
1.1
0.6
0.9
0.9
0.9
0.8
0.9
0.8
0.7
0.6
0.5
STD
1.9
1.5
1.5
0.7
2.5
0.6
4.0
1.1
7.5
1.6
0.2
0.6
1.8
3.1
1.4
1.2
1.9
1.8
***
3.3
0.3
1.1
1.6
1.8
1.4
3.0
1.3
1.9
2.3
1.9
2.7
1.4
0.4
0.4
0.5
0.9
0.5
1.0
3.1
0.4
0.4
***
MAX
15.8
13.4
7.5
3.0
17.5
1.7
38.9
4.2
163.9
13.1
2.8
2.4
21.0
13.0
5.4
3.2
6.2
9.6
0.8
13.3
0.7
5.6
10.2
12.3
6.5
37.2
7.4
12.8
26.5
13.0
40.5
9.5
2.0
1.4
3.3
5.5
1.5
6.0
17.1
2.1
1.5
0.5
%>4
pCi/L
11
4
11
0
15
0
19
7
14
5
0
0
7
30
8
0
20
9
0
7
0
3
9
14
8
6
5
13
13
13
19
6
0
0
0
3
0
2
6
0
0
0
%>20
pCi/L
0
0
0
0
0
0
1
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

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TABLE 1 (continued). Screening indoor radon data for Delaware.
ZIP
CODE
1994
19944
1994
1994
19947
19950
1995
19952
19953
19954
19955
19956
19958
19960
19961
19962
19963
19964
19966
19968
19969
19970
19971
19973
19975
19977
19979
19980
CITY
FELTON
FENWICKIS.
FRANKFORD
FREDERICA
GEORGETOWN
GREENWOOD
HARBESON
HARRINGTON
HARTLY
HOUSTON
KENTON
LAUREL
LEWES
LINCOLN
LITTLE CREK
MAGNOLIA
MILFORD
MARYDEL
MILLSBORO
MILTON
NASSAU
MDLLVILLE
REHOBOTH
EAFORD
ELBYVILLE
MYRNA
VIOLA
WOODSIDE
COUNTY
KENT
SUSSEX
SUSSEX
KENT
SUSSEX
KENT
SUSSEX
KENT
•CENT
SENT
CENT
SUSSEX
SUSSEX
SUSSEX
CENT
CENT
SUSSEX
KENT
SUSSEX
SUSSEX
USSEX
USSEX
USSEX
USSEX
USSEX
KENT
NEW CASTLE
CENT
NO. OF
MEAS
5

3
2
7
3«
12
38
17
16

52
88
2'
]
2J
81
e
64
55
3
50
63
105
36
99
3
1
AVERAGE
1.
0.
0.
1.
0.
\J-
0.
o.;
0.!
1.
0.5
0.<
1.:
o.<
2.]
1.6
l.f
0.',
0.9
1.0
1.5
0.8
1.2
1.1
0.5
1.6
1.2
0.5
MEDIAN
0.
0.
0.
0.
0.
0.
0.5
0.5
0.5
0.8
0.5
0.5
0.7
0.5
2.]
i.:
1.0
0.7
0.5
0.6
1.C
0.5
0.7
0.8
0.5
1.0
1.5
0.5
GM
0.
0.
o;
l.:
0.'
0.
1)
0.7
0.7
0.9
0.5
0.7
O.J
0.7
2 ]
1.2
1.]
0.7
0.7
0.8
1.3
0.7
0.9
0.9
0.5
1.2
1.0
0.5
STD
1.
0.
0.
1.;
0.
1.7
0.6
0.7
0.6
0.6
***
().!
0.9
O.I

1.^
1.2
0.2
0.6
0.*
1.0
0.5
1.2
1.0
0.2
1.6
0.6

MAX
8.
0.
3.
4.
c
9.3
1.
4.6
2.6
2
0.5
4.7

4.1
2.1
6.3
7.C
1.1
3.0
5.0
27
2.3
8.1
5.2
1.7
11.7
1.5
0.5
%>4
pCi/T



1


0
0
0
0
0

1

0


0
0
2
0
0
3
3
0
6
0
0
%>20
pCi/L







0
0
0
0
0
0
0
o
0
o
o
o
o
o
o
o
o
o
o
o
0

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                                                       f
                                                       N
                                               Bsmt &  1st Floor Rn
                                         Average Concentration (pCi/L)
                                                 •fr  0.0 to 1.0
                                                 *  1.1 to 2.0
                                                 *  2.1 to 3.0
                                                 *  3.1 to 4.0
                                                       10 Miles
#
#
^ * #
*• ^
^r ^
Figure 7a. Average indoor radon levels of homes sampled in each zip code area, plotted
by zip code centroid. Points are plotted only for those zip code areas containing 5 or
more measurements. Points representing the average indoor radon reading are plotted at
the center of each zip code area. Data compiled by the Delaware Department of Public
Health for homes tested between 1986-1990 (see Table 1).

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                                                      t
                                                      N
                                           Bsmt & 1st Floor Rn
                                                 %>4pCi/L
                                                # 0 to 10
                                                * 11  to 20
                                                * 21  to 30
                                                    10 Miles
Figure 7b. Percent of homes tested with indoor radon measurements greater than 4 pCi/L
plotted by zip code centroid. Points are plotted only for those zip code areas with 5 or   '
more measurements. Points representing the percent of readings greater than 4 pCi/L
are plotted at the center of each zip code area. Data compiled by the Delaware Department
of Public Health for homes tested between 1986-1990 (see Table 1)

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data only for those zipcodes with 5 or more indoor radon readings. Figure 8 is a map of counties
for reference. Figure 9 shows the frequency distribution of individual indoor radon measurements
by county. In general, the indoor radon measurements were highest in New Castle County and
lowest in Sussex County. New Castle County had 16 measurements exceeding 20 pCi/L whereas
Kent and Sussex Counties had no readings over 20 pCi/L.

GEOLOGIC RADON POTENTIAL

       An examination of aerial radioactivity, geologic, and indoor radon data, and radioactivity
surveys conducted by the Delaware Geological Survey (Woodruff and others, 1992) allows us to
make some observations about the geologic radon potential of the State. It appears that the
Piedmont and northern portion of the Atlantic Coastal Plain have the highest geologic radon
potential. Average indoor radon in the Piedmont varies from low (<2 pCi/L) to moderate (2-4
pCi/L). Individual readings within the Piedmont can be locally very high (> 20 pCi/L). This is not
unexpected when a regional-scale examination of the Atlantic coastal states shows that the
Piedmont is consistently an area of moderate to high radon potential. Much of the western
Piedmont in Delaware is underlain by the Wissahickon Formation, which is predominantly schist.
Soils developed on this schist have generally moderate permeability. This formation is moderate to
locally high in geologic radon potential.  Studies of equivalent schists in the Piedmont of Maryland
(Gundersen  and others, 1988) indicate that these rocks can have uranium concentrations of 3-5
ppm, especially where faulted.  The soils developed on these schists can also have soil-gas radon
concentrations greater than 1000 pCi/L.  The Wilmington Complex and James Run Formation in
the central and eastern portions of the Delaware Piedmont are variable in radon potential.  In these
units, the felsic gneiss and schist may contribute to the elevated radon  levels, whereas mafic rocks
such as amphibolite and gabbro, and quartz-poor rocks such as charnockite and diorite, are
probably lower in radon potential. The soils developed on the felsic rocks also tend to have higher
permeability than the soils developed on the mafic rocks. The average indoor radon (fig. 7a) is
distinctly lower in parts of the Wilmington Complex than in surrounding areas, particularly in
zipcode areas underlain by the Bringhurst Gabbro and the Arden pluton. Plotting of individual
indoor radon readings may better delineate specific geologic units; however, given the present
format of the data,  this is not possible. .
       Studies of radon and uranium in Coastal Plain sediments in New Jersey (Gundersen and
others, 1991) and Maryland  (Reimer and others, 1991) suggest that glauconitic marine sediments
equivalent to those in the northern portion of the Delaware Coastal Plain can generate elevated
levels of indoor radon. Central New Castle County is underlain by glauconitic marine sediments
of Cretaceous and Tertiary age that have moderate to locally high geologic radon potential. Aerial
radiometric data indicate that moderate concentrations of uranium occur in rocks and soils
associated with the Piedmont and parts of the Coastal Plain of northern Delaware. Chemical
analyses of Cretaceous and Tertiary glauconitic marine sediments and  fluvial sediments of the
Columbia Formation performed by the Delaware Geological Survey indicate that variable but
generally moderate concentrations of uranium occur, averaging 1.89 ppm or greater. The
permeability of soils in these areas is variable but generally moderate to high, allowing radon gas to
move readily through the soil. Data from the State indoor radon survey for New Castle County
indicates that areas underlain by the non-glauconitic Cretaceous fluvial sediments have lower
average indoor radon levels than the glauconitic parts of the upper Cretaceous and lower Tertiary
sequence to the south.  Kent County and all of Sussex County are underlain by quartz-dominated
                                         IV-18    Reprinted from USGS Open-File Report 93-292-C

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Figure 8. Counties in Delaware.

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                                        New Castle
                    10000
                  ffl



                  I
                  in
                  TO
                  OJ
                  
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  sands, silts, gravels, and clays that have low geologic radon potential. These sediments are low in
  radioactivity and generally have a smaU percentage of homes with indoor radon levels greater than
  4 pCi/L.

  SUMMARY

        For the purpose of this assessment, Delaware has been divided into 3 geologic radon
 potential areas and each area assigned a Radon Index (RI) and a Confidence Index (CI) score
 (Table 2) using the information outlined in the sections above (please see the introduction chapter
 to this report for a detailed explanation of the indexes). The RI is a relative measure of radon
 potential based  on geology, soils, radioactivity, architecture, and indoor radon. The CI is a
 measure of the confidence of the RI assessment based on the quality and quantity of the data used
 to assess geologic radon potential.
        New Castle County has generally moderate but variable radon potential. Northern New
 Castle County is underlain by the metamorphic and igneous rocks of the Piedmont that have
 moderate radon potential, but that may be locally high or low, as discussed in the previous section.
 Central New Castle County is underlain in part by glauconitic marine sediments of Cretaceous and
 Tertiary age that have moderate to locally high geologic radon potential. Aerial radiometric data
 indicate that moderate concentrations of uranium occur in rocks and soils associated with the
 Piedmont and parts of the Coastal Plain of northern Delaware.  Chemical analyses (Woodruff and
 others, 1992) of Cretaceous and Tertiary glauconitic marine sediments and fluvial sediments of the
 Columbia Formation indicate that moderate concentrations of uranium, generally averaging 1 89
 ppm or greater, occur. The permeability of soils in these areas is variable but generally moderate to
 high, allowing radon gas to move readily through the soil. Data from the State indoor radon
 survey also indicate that these areas of New Castle County have the highest percentage of homes
 with elevated indoor radon as well as the highest indoor radon concentrations found in the State
 Kent County and all of Sussex County are underlain by quartz-dominated sands, silts, gravels  and
 clays that have lowgeologic radon potential. These sediments are low in radioactivity and generally
 have a low percentage of homes with indoor radon levels greater than 4 pCi/L.
       This is a  generalized assessment of the State's geologic radon potential and there is no
 substitute for having a home tested. The conclusions about radon potential presented in this report
 cannot be applied to individual homes or building sites. Indoor radon levels, both high and low,
 can be quite localized, and within any radon potential area there will likely be areas with higher'or
 lower radon potential than assigned to the area as a whole. Any local decisions about radon should
 not be made without consulting all available local data. For additional information on radon and
how to test, contact your State radon program or EPA regional office. More detailed information
on state or local geology may be obtained from the state geological survey. Addresses and phone
numbers for these agencies are listed in chapter 1 of this booklet.
                                         IV-21   Reprinted from USGS Open-FUe Report 93-292-C

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TABLE 2. Radon Index and Confidence Index scores for Delaware.
      FACTOR
                  (2) Coastal Plain           (3) Coastal Plain
                  Upper Cretaceous      Cretaceous, Tertiary, Quaternary
(1) Piedmont         and lower Tertiary           quartzitic
                glauconitic marine sediments  fluvial and marine sediments
RI     CI            RI      CI             RI    CI
INDOOR RADON
RADIOACTIVITY
GEOLOGY
SOIL PERM.
ARCHITECTURE
GFE POINTS
TOTAL

2
2
2
2
3
0
11
Mod
2
2
2
3
-
-
9
Mod
2
2
2
2
2
0
10
Mod
2
2
2
3
-
.
9
Mod
1
1
1
2
2
0
7
Low
2
2
2
3
-
_
9
Mod
RADON INDEX SCORING:
Radon potential cateeorv
LOW
MODERATE/VARIABLE
HIGH
Point range
3-8 points
9- 11 points
> 1 1 points
Probable screening indoor
radon average for area
<2pCi/L
2-4pCi/L
>4pCi/L
                           Possible range of points = 3 to 17

CONFIDENCE INDEX SCORING:
         LOW CONFIDENCE
         MODERATE CONFIDENCE
         HIGH CONFIDENCE
                        4-6 points
                        7-9 points
                       10 - 12 points
                           Possible range of points = 4 to 12
                                      IV-22   Reprinted from USGS Open-File Report 93-292-C

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                         REFERENCES CITED IN THIS REPORT
         AND GENERAL REFERENCES PERTAINING TO RADON IN DELAWARE

 Andres, A.S., 1986, Stratigraphy and depositional history of the post-Choptank Chesapeake
        Group: Delaware Geological Survey, Report of Investigations No. 42, 39 p.

 Benson, R.N., and Pickett, T.E., 1986, Geology of south central Kent County, Delaware:
        Delaware Geological Survey, Geologic Map Series No. 7, scale  1:24,000.

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

 Eichler, Thomas P, and Wright, Lester N., 1991, The Delaware Radon Program: Department of
        Health and Social Services, Division of Public Health, Authority on Radiation Protection,
        29 p.

 Elsinger, R.J., 1982, Estuarine geochemistry of 224 Ra, 228 Ra, 226 Ra, and 222 Rn: Doctoral
        Thesis, Univ. of South Carolina, Columbia, SC, 95 p.

 Gundersen, L. C.S, Peake, R.T., Latske, G.D., Hauser, L.M., and Wiggs,C.R., 1991, A
        statistical summary of uranium and radon in soils from the Coastal Plain of Texas,
        Alabama, and New Jersey, in Proceedings of the 1990 International Symposium on Radon
        and Radon Reduction Technology,Volume 2: Symposium Oral Papers, U.S. EPA report
        EPA-600/9-91/026b,p.CVI4-l-13.

 Gundersen, L.C.S., Reimer, G.M., Wiggs, C.R. and Rice, C.A., 1988, Radon Potential of
       Rocks and Soils in Montgomery County, Maryland: U. S. Geological Survey
       Miscellaneous Field Studies Map 88-2043, scale 1:62,000.

 Hammond, D., Simpson, H.J., and Mathieu, G., 1976, Distribution of radon-222 in the Delaware
       and Hudson estuaries as an indicator of migration rates of dissolved species across the
       sediment-water interface: Eos, Transactions of the American Geophysical Union v 57
       p. 151.                                                                      '

 Ireland, W., Jr., and Matthews, E.D., 1974, Soil survey of Sussex County, Delaware: U.S.
       Department of Agriculture, Soil Conservation Service, 74 p.

 Jordan, R.R., 1962, Stratigraphy of the sedimentary rocks of Delaware: Delaware Geological
       Survey, Bulletin No. 9, 51 p.

Jordan, R.R., 1964, Columbia (Pleistocene) sediments of Delaware: Delaware Geological Survev
       Bulletin No. 12, 61 p.                                                          *'

Jordan, R.R., 1974, Pleistocene deposits of Delaware, in Oakes, R.Q., and Dubar, J.R., eds.,
       Post-Miocene Stratigraphy, Central and Southern Atlantic Coastal Plain: Logan, Utah,
       Utah State University Press, p. 30-52.
                                        IV-23   Reprinted from USGS Open-File Report 93-292-C

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 Jordan, R.R., 1983, Stratigraphic nomenclature of nonmarine Cretaceous rocks of inner margin of
        Coastal Plain in Delaware and adjacent states: Delaware Geological Survey, Report of
        Investigations No. 37,43 p.

 Kraft, J.C., and Carey, W., eds., 1980, Selected Papers on the Geology of Delaware: Special
        publication of the Delaware Geological Survey, 268 p.

 Matthews, E.D., and Lavoie, O.L., 1970, Soil survey of New Castle County, Delaware: U.S.
        Department of Agriculture, Soil Conservation Service, 97 p.

 Matthews, E.D., and Ireland, W., Jr., 1971, Soil survey of Kent County, Delaware:  U.S.
        Department of Agriculture, Soil Conservation Service, 66 p.

 Pickett, T.E., 1976, Generalized Geologic Map of Delaware: Delaware Geological Survey Special
        Publication No. 9, scale approx. 1:576,000.

 Pickett, T.E., and Benson, R.N., 1977, Geology of the Smyrna-Clayton area, Delaware:
        Delaware Geological Survey, Geologic Map Series No. 6, scale 1:24,000.

 Pickett, T.E., and Benson, R.N., 1983, Geology of the Dover area, Delaware: Delaware
        Geological Survey, Geologic Map Series No. 7, scale 1:24,000.

 Pickett, T.E., and Spoljaric, N., 1971, Geology of the Middletown-Odessa area, Delaware:
        Delaware Geological Survey, Geologic Map Series No. 2, scale 1:24,000.

 Pierce, A.P., 1956, Radon and helium studies: U.S. Geological Survey Rept  TEI-620
       p. 305-309.

 Ramsey, K.W., and Schenck, W.S.,  1990, Geologic map of southern Delaware: Delaware
       Geological Survey, Open-File Report No. 32, scale 1:100,000.

 Reimer, G.M., Gundersen, L.C.S., Szarzi, S.L., and Been, J.M., 1991, Reconnaissance
       approach using geology and  soil-gas radon concentrations for rapid and preliminary
       estimates of radon potential,  in Gundersen, L.C.S., and Wanty, R.B., eds., Field Studies
       of Radon in Rocks Soils and Water: U. S. Geological Survey Bulletin 1971, p. 177-181.

 Richmond, G.M., Fullerton, D.S., and Weide, D.L., compilers, 1987,  Quaternary geologic map
       of the Chesapeake Bay 4°x6° quadrangle, United States and Canada:  U.S. Geological
       Survey Miscellaneous Investigations Map 1-1420 (NJ-18), scale 1:1,000,000.

 Spoljaric, R, 1980, The geology of the Delaware Coastal Plain, in Kraft, J.C., and Carey, W.,
       eds., Selected Papers on the Geology of Delaware: Special publication of the Delaware
       Geological Survey, p. 87-114.

Talley, J.H., 1982, Geohydrology of the Milford area, Delaware: Delaware Geological Survey,
       Hydrologic Map Series No. 4, scale 1:24,000.
                                         IV-24   Reprinted from USGS Open-File Report 93-292-C

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 Talley, J.H., 1987, Geohydrology of the southern coastal area, Delaware: Delaware Geological
        Survey, Hydrologic Map Series No. 7,2 sheets, scale 1:24,000.

 Thompson, A.M., 1980, A summary of the geology of the Piedmont in Delaware, in Kraft, J.C.,
        and Carey, W., eds., Selected Papers on the Geology of Delaware: Special publication of
        the Delaware Geological Survey, p. 115-1"''
 van Assendelft, A.C.E., and Sachs, H.M., 1982, Soil and regional uranium as controlling factors
        of indoor radon in eastern Pennsylvania: Princeton University, Center for Energy and
        Environmental Studies Report 145, 68 p.

 Wagner, Mary Emma, Srogi, LeeAnn, Wiswell, C. Gil, and Alcock, James, 1991, Taconic
        collision in the Delaware-Pennsylvania Piedmont and implications for subsequent geologic
        history, in Schultz, A., and Compton-Gooding, E., eds., Geologic evolution of the eastern
        United States, Field trip guidebook, Geological Society of America, NE-SE section,
        p. 91-119.

 Woodruff, K.D., 1980, Geohydrology of Delaware, in Kraft, J.C., and Carey, W., eds., Selected
        Papers on the Geology of Delaware: Special publication of the Delaware Geological
        Survey, p. 135-166.                                                    *

 Woodruff, K.D., 1985, Geohydrology of the Wilmington area, Delaware: Delaware Geological
        Survey, Hydrologic Map Series No. 3,4 sheets, scale 1:24,000.

 Woodruff, K.D., 1986, Geohydrology of the Chesapeake and Delaware Canal area, Delaware-
       Delaware Geological Survey, Hydrologic Map Series No. 6,  2 sheets, scale 1:24,000.

 Woodruff, K.D., and Thompson, A.M., 1972, Geology of the Newark area, Delaware: Delaware
       Geological Survey, Geologic Map Series No. 3, scale 1:24,000.

Woodruff, K.D., and Thompson, A.M., 1975, Geology of the Wilmington area, Delaware:
       Delaware Geological Survey, Geologic Map Series No. 4, scale 1:24,000.

Woodruff, K.D., Ramsey,  K.W., and Talley, J.H., 1992, Radon potential of the glauconitic
       sediments in the Coastal Plain of Delaware: Final Report to Delaware Department of Health
       and Social Services, Division of Public Health, Health Systems Protection, Radiation
       Control, Contract No. 92-105,43  p.
                                        IV-25    Reprinted from USGS Open-FUe Report 93-292-C

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                             EPA's Map of Radon Zones


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

 DELAWARE MAP OF RAnnxr
       The Delaware Map of Radon Zones and its supporting documentation (Part IV of this
 report) have received extensive review by Delaware geologists and radon program experts
 The map for Delaware generally  reflects current State knowledge about radon for its counties
 Some States have been able to conduct radon investigations in  areas smaller than  geologic
 provinces and  counties, so it is important to consult locally available data
       Although the information  provided in Part IV of this report - the State chapter entitled
 Preliminary Geologic Radon Potential Assessment of Delaware" - may appear to be quite
 specific, it cannot be applied to determine the radon levels of a neighborhood, housing tract
 individual house, etc  THE ONLY WAY TO DETERMINE  IF A HOUSE HAS
 ELEVATED INDOOR RADON IS TO TEST.  Contact the Region 3  EPA  office or the
Delaware radon program for information on testing and fixing homes.  Telephone numbers
and addresses can be found in Part II of this report.
                                         V-l

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I

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