United States
                     Environmental Protection
                     Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
                     Research and Development
EPA/600/S9-91/044 Dec. 1991
\yEPA       Project Summary
                     Proceedings  of  the Workshop
                     on  Radon  Potential Mapping,
                     Florida  Radon Research
                     Program
                     Kirk K. Nielson and Vern C. Rogers
                       The Workshop on Radon Potential
                     Mapping was organized as part of the
                     Florida Radon Research  Program
                     (FRRP), which Is aimed at developing
                     radon-related building construction
                     standards for Florida. The workshop
                     was designed to Identify and discuss In
                     an expert forum the technical Issues
                     associated with radon potential charac-
                     terization of Florida lands. If developed,
                     radon potential maps would be used to
                     Identify geographic areas with greatest
                     potential for indoor radon problems so
                     that appropriate precautions, specified
                     by related building construction stan-
                     dards, could be taken.
                       The workshop Included background
                     presentations by the FRRP  program
                     manager and the Soils Committee chair-
                     man, and topical presentations by four
                     invited speakers on various Issues and
                     aspects of radon potential mapping. It
                     also included two task group meetings
                     that included all participants In discuss-
                     ing technical and institutional issues
                     related to radon potential mapping.
                       Existing radon maps for Florida and
                     other states and regions were reviewed
                     and their uses of aeroradlometric, geo-
                     logical, indoor radon, and other data
                     were identified. The technical basis for
                     defining an Indoor radon potential was
                     presented, and the rationale and level
                     of detail for radon maps was analyzed.
                     Available data sources were reviewed.
                     Task  groups identified general  ap-
                     proaches and uses of the radon maps,
                     with consensus on some issues.
                        This Project Summary was devel-
                     oped by EPA's Air and Energy Engi-
                     neering Research Laboratory, Research
                     Triangle Park, NC, to announce key find-
                     Ings of the research project that Is fully
 documented In a separate report of the
 same title (see Project Report ordering
 Information at back).

 Introduction
    The Workshop on Radon Potential Map-
 ping  was held  on April 20, 1990,  in
 Gainesville, FL, as an activity of the Florida
 Radon Research Program (FRRP), which
 is jointly sponsored  by the Florida Depart-
 ment of Community Affairs (DCA) and the
 U.S.  Environmental Protection Agency
 (EPA). It was  designed to bring together
 recognized  experts in characterizing and
 mapping the potentials for elevated indoor
 radon concentrations in different geographi-
 cal areas based on distributions of soil
 radium concentrations, soil physical and
 hydrological properties, and foundation in-
 teractions with the soils. The objective of
 the workshop was to examine the feasibil-
 ity and pertinent issues for pursuing a map-
 ping  effort for  radon potentials in Florida,
 based on the  experiences gained in na-
 tional, regional, state, county, and local
 radon mapping efforts that have been con-
 ducted elsewhere or are in progress.
    The workshop was organized under
 the direction of the program managers for
 the  sponsoring  organizations  (Richard
 Dixon, Florida DCA, and David Sanchez,
 U.S.  EPA).  Technical direction and sup-
 port was assigned to the FRRP's. Founda-
 tion Fill Materials Committee, which is one
 of several standards development commit-
 tees  of the workshop followed a 1-day
 format, with prepared presentations in the
 first half,  and workshop task group meet-
 ings in the second. The presentations and
 task  group  meetings are summarized in
 Figure 1.
    The  Florida perspective summarized
 by Richard Dixon includes radon issues as
                                                                     Printed on Recycled Paper

-------
                United States
                Environmental Protection
                Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
                Research and Development
EPA/600/S9-91/044 Dec. 1991
EPA       Project Summary

                Proceedings  of the  Workshop
                on  Radon  Potential  Mapping,
                Florida  Radon  Research
                Program
                Kirk K. Nielson and Vern C. Rogers
                  The Workshop on Radon Potential
                Mapping was organized as part of the
                Florida Radon Research Program
                (FRRP), which Is aimed at developing
                radon-related building construction
                standards for Florida. The workshop
                was designed to Identify and discuss In
                an expert forum the technical Issues
                associated with radon potential charac-
                terization of Florida lands. If developed,
                radon potential maps would be used to
                identify geographic areas with greatest
                potential for indoor radon problems so
                that appropriate precautions, specified
                by related building construction stan-
                dards, could be taken.
                  The workshop Included background
                presentations by the FRRP program
                manager and the Soils Committee chair-
                man, and topical presentations by four
                invited speakers on various issues and
                aspects of radon potential mapping. It
                also included two task group meetings
                that included all participants In discuss-
                ing technical and institutional issues
                related to radon potential mapping.
                  Existing radon maps for Florida and
                other states and regions were reviewed
                and their uses of aeroradlometric, geo-
                logical, indoor radon, and other data
                were Identified. The technical basis for
                defining an indoor radon potential was
                presented, and the rationale and level
                of detail for radon maps was analyzed.
                Available data sources were reviewed.
                Task  groups identified general  ap-
                proaches and uses of the radon maps,
                with consensus on some Issues.
                   This Project Summary  was devel-
                oped by EPA's Air and Energy Engi-
                neering Research Laboratory, Research
                Triangle Park, NC, to announce key find-
                ings of the research project that Is fully
 documented In a separate report of the
 same title (see Project Report ordering
 Information at back).

 Introduction
    The Workshop on Radon Potential Map-
 ping  was held  on April 20, 1990,  in
 Gainesville, FL, as an activity of the Florida
 Radon Research Program (FRRP), which
 is jointly sponsored by the Florida Depart-
 ment of Community Affairs (DCA) and the
 U.S.  Environmental Protection Agency
 (EPA). It was  designed to bring together
 recognized  experts in characterizing and
 mapping the potentials for elevated indoor
 radon concentrations in different geographi-
 cal areas based on distributions of soil
 radium concentrations, soil physical and
 hydrological properties, and foundation in-
 teractions with the soils. The objective of
 the workshop was to examine the feasibil-
 ity and pertinent issues for pursuing a map-
 ping  effort for  radon potentials in Florida,
 based on the  experiences gained in na-
 tional, regional, state, county, and local
 radon mapping efforts that have been con-
 ducted elsewhere or are in progress.
    The workshop was organized under
 the direction of the program managers for
 the sponsoring  organizations  (Richard
 Dixon, Florida DCA, and David Sanchez,
 U.S.  EPA).  Technical direction and sup-
 port was assigned to the FRRP's. Founda-
 tion Fill Materials Committee, which is one
 of several standards development commit-
 tees  of the workshop followed a 1-day
 format, with prepared presentations in the
 first half,  and workshop task group meet-
 ings in the second. The presentations and
 task  group  meetings are summarized in
 Figure 1.
    The  Florida perspective summarized
 by Richard Dixon includes radon issues as
                                                                Printed on Recycled Paper

-------
one of several areas of responsibility of the
Florida DCA. The Building Code Standards
Office, tasked with developing radon build-
ing code standards, also deals with other
state policies such  as the energy code,
accessibility code, wind loads, and other
issues  to be enforced  by local govern-
ments under the state-mandated building
code. The broader issues of housing re-
quire DCA to blend the radon  issue  with
other concerns in developing statewide
uniform building codes.  Since only about
5% of the Florida housing  population has
radon problems, there is potential for con-
flicts between the affordability of housing
and protection of the population from ra-
don problems.
   The  FRRP was  established  by the
Florida legislature to develop building con-
struction standards related to radon con-
trol. From the beginning, the DCA sought
to bring in the U.S.  EPA, the Florida De-
partment of Health and Rehabilitative Ser-
vices, and others to participate in the FRRP,
and DCA still is pursuing overtures to the
U.S. Department of  Energy (DOE), which
also has a radon  research  project in
progress in Florida. The overall  goal of the
DCA is to bring to full development, and to
the benefit of Florida, the  efforts of all
funding  agencies and  projects involved,
and to have their contractors participate in
this program to share ideas and interests.
The DCA will ensure that the various  pro-
gram directions are  consistent  or at  least
complementary.
   Various tasks within the FRRP are or-
ganized  by different components of the
Introduction

Overview—Florida Programmatic Goals

Meeting Scope, Objectives, & Issues

Review, Use & Basis of Existing Radon Maps


Technical Basis for Radon Mapping

Rationale & Level of Detail for State and
  County Radon Maps

Data Available for Florida Radon Mapping

Discussion of Issues & Priorities;
  Task Group Scopes

Workshop Task Group 1             —

Workshop Task Group 2             —
building construction standards. They in-
clude radon barriers, HVAC (heating, ven-
tilation, and  air-conditioning)  systems,
house dynamics,  soil  and backfill materi-
als, and alternate performance standards.
The workshop was organized by the Soil
and Backfill Committee to identify and dis-
cuss in an expert forum the technical is-
sues  associated with  radon  potential
characterization of Florida lands. Its spe-
cific purpose  was to assess the possibili-
ties of extending the building construction
standards to be tied to the actual potential
for indoor radon problems in a given geo-
graphic area. The technical assessment
was to examine the feasibility (in terms of
time, costs, and human resources) of iden-
tifying radon potential zones to inform build-
ers and regulators of  the needs in a
particular jurisdiction. The zones would be
commensurate with the  precedent wind
load, seismic, and other zones established
for  regulating building construction.  The
DCA was to evaluate the monetary, timing,
and institutional aspects of pursuing a ra-
don mapping effort as summarized from
the workshop and subsequent analyses by
the Soils and  Backfill Materials Committee.
If developed, a Florida radon map would
be based solely on physical boundaries,
and would require  flexibility so  that the
mapped parameter would remain suitable
for use with alternative limits, if the present
4 pCi L1 standard is revised.
   The technical  objectives of the work-
shop,  as  summarized by  Vern  Rogers,
were to assess the technical feasibility of
creating a Florida map of radon potentials
   Vern Rogers, RAE Corp.

   Richard Dixon, Florida DCA

   Vem Rogers, RAE Corp.

   James Otton,
   U.S. Geological Survey (USGS)

   Allan Tanner, USGS

   Charles Layman, New York Department of
     Health

   Walter Schmidt, Florida Geological Survey

   Richard Dixon, Florida DCA


   Technical Issues

   Institutional Issues
Figure 1.     Agenda of the Florida workshop on radon potential mapping.
that would be useful to builders, to assess
the resources needed to develop the map,
and to develop technical mapping recom-
mendations for DCA. Significant  issues
identified by the Soils Committee for con-
sideration by participants are summarized
in Figure 2.

Existing Radon Maps
   Existing foreign and U.S. radon maps
reviewed by James  Otton included both
geology-based  and empirical maps of el-
evated indoor radon  frequencies. Foreign
radon mapping is dominated by Swedish
work, based on prior geologic mapping
that enabled lithologic estimates of impor-
tant  near-surface  uranium deposits and
high-permeability materials. The Swedish
maps are regional in scale.  For site-spe-
cific  estimates, soil-gas radon  at  10,000
Bq rrv3 (270 pCi L1) divides low- and mod-
erate-risk soils, and concentrations of
50,000 Bq nr3  (1,350 pCi L1) distinguish
moderate-risk from high-risk soils. Soil per-
meability is a secondary consideration.
   U.S. radon mapping efforts  date back
to the 1950s  in Florida,  but are  mostly
recent. A U.S.  radon potential map was
developed for EPA in 1986, focussing on
lithologies with elevated  radon risk and
known uranium occurrences or districts
with  uranium potential. Several updates
have  been  completed.  USGS  and EPA
recently started a new national radon map
with  oversight  from  the  Association of
American State Geologists. It should be
available within about 1 year. A geology-
based regional  radon map has been com-
pleted for New England, and a map based
on correlating  aeroradiometric data and
lithology with indoor radon was completed
for the Pacific Northwest. The notable state-
scale radori mapping was done in Florida;
however, other  state-scale radon mapping
has been done for Alabama, Georgia, Indi-
ana, Maryland, North Carolina, New Jer-
sey,  Rhode Island,  South Carolina,  and
Utah. Typical scales ranged from 1:250,000
to 1:7,500,000.  Regional radon maps also
have  been developed for  some of these
states, plus  New York, Virginia, and other
areas. The multi-tiered Fairfax County, Vir-
ginia, map is a good example of a detailed
probabilistic approach combining aerora-
diometric data, geology maps, soils maps,
and indoor radon data.
   An empirical assessment of radon map-
ping efforts  indicates that the controlling
parameters are soil  radium, emanation frac-
tion,  permeability,  and moisture content.
Surrogates generally are  used for these
parameters. The recommended approach
for state  and  county-level maps uses
aeroradiometric data for soil radium con-

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1.   Usefulness of radon potential maps.
    •   How should they be used?
        What can they be used for?
        What accuracy and confidence are needed/possible ?

2.   Technical basis of radon potential maps.
        What parameter should be mapped?
    •   How should Ra, water table depths, and climate be considered?
        How should house type and occupancy variations be considered?

3.   Deterministic or probabilistic approach.

4.   Level of detail of maps.
    •   What geographic scale is needed/appropriate ?
    •   What accuracy and confidence level is needed/appropriate ?

5.   Data availability and adequacy.
        What data exist for geology, Ra, emanation distributions ?
        Are correlating soil gas and indoor radon data available ?
    •   What data exist on radon transport in soils ?

6.   Institutional issues.
        What are FRRP objectives ?
        What were previous NY, NJ, and Swedish uses?

Figure 2.      Florida radon mapping workshop issues.
centrations and supporting data from geol-
ogy, uranium occurrence, and soil perme-
ability maps. Field measurements of soil
gas  radon  should be used to rank geo-
graphic areas, generally by Irthotogy or soil
units. The form  of the final radon potential
map will be  driven more by policy than
geology.

Technical Basis and Rationale
   The technical basis for estimating ra-
don potentials, reviewed by Allan Tanner,
emphasized the importance of radon diffu-
sion and convection. Both are controlled
by soil water content; soil permeability ad-
ditionally is affected by  soil  pore sizes.
Several indices potentially suitable for ra-
don mapping have been proposed for rep-
resenting radon potentials. Most consider
the basic properties of radium, emanating
power, permeability, and diffusion coeffi-
cients,  and then  use mathematical func-
tions to  characterize  radon  movement
toward a building.  The proposed radon
availability and index numbers differ in their
consideration of either the soil only or the
combined effect of the soil properties with
some standard house design. One-dimen-
sional analyses suggest that soil diffusivity
is dominant except when  soil permeability
exceeds 10"11 m2. Multidimensional analy-
ses suggest significant permeability effects
at somewhat lower permeabilities.  Radon
availability  or index numbers will not tell
whether a house will exceed 4 pCi  L1, but
can be used with on-site measurements to
estimate the magnitude of expected prob-
lems. On-srte measurements also are use-
ful to check  predictions  and get ground
truth.
   Field measurements for estimating ra-
don  potential  include surface radon flux
and  soil gas  radon.  A forced-air radon
accumulator was proposed as a new con-
ceptual approach for site assessment of
radon potentials. Moisture-related  biases
may occur when using passive radon  de-
tectors buried in soil cavities for estimating
soil-gas radon concentrations unless  ap-
propriate corrections are made. Invariant
soil parameters may be preferable to site-
specific measurements for estimating ra-
don  potentials. The invariant parameters
include  soil radium, emanation, density,
diffusion coefficient, and permeability on a
dry basis, with corrections to account for
the effects of soil-water contents. The re-
sulting moisture-corrected invariant param-
eters may  better represent the basis for
long-term average radon potentials.
   The  rationale and level of detail for
developing radon potential maps was dis-
cussed  by  Charles Layman, summarizing
the data,  map scale, and precision and
accuracy perspectives from New York ra-
don studies. Site-specific data help identify
proxy parameters for local controls that
determine indoor radon. The controls  are
geologic, building, and meteorologic char-
acteristics. Radon data often are collected
as classifications or attributes, but these
are weaker and less versatile than numeri-
cal measurement data. Information from
numerical data is maximized by statistical
interpretations, and its quality and resolu-
tion are affected by precision (random er-
rors), accuracy  (systematic errors), and
mistakes (illegitimate errors). Indoor radon
measurements may be biased by targeting
or volunteer studies, and the biases should
be reduced by normalization to appropri-
ate controls whenever possible. Sampling
may utilize grid pattern, random, and com-
bined designs, but the number of mea-
surements required depends on geologic
variability and acceptable precision. As the
number of measurements is increased, the
range increases until it stabilizes. In New
York studies,  approximately 5-10 measure-
ments sometimes were sufficient. Field
sampling density must be sufficient to de-
tect  the smallest features  of interest. A
mean radon  index for  a region is best
computed from individual radon indices at
points within  the region, rather than from
averaged parameters for the region.

Available Data
   The  data  available for mapping radon
potentials  in Florida were  reviewed by
Walter  Schmidt.  The Florida Geological
Survey  (FGS) has 10-20 county bulletins
that cover geology,  economic  geology,
groundwater,  surface mapping, contour
maps, and other information for selected
counties. The FGS environmental geology
series maps  (1:50,000) were targeted at
land use planners, and are based on  soil
C-horizons (beneath A- and B- horizons)
to aim at the  soil parent material. In some
cases these are at the surface, in others at
1-2 ft,*  and in others at 10-12 ft. A 10-ft
cutoff was  used  for the environmental ge-
ology map series. Several (12-18) mineral
resource county maps also are available,
showing lithologic units instead of soil  for-
mations. The FGS  maintains a library of
17,000  sets of cores and cuttings, which
equates to one  for every 3  mi2** in  the
state. FGS also has 6,000 to 8,000 sets of
wire line logs (total count gamma logs) of
wells,  aeroradiometric  mylars on a
1:250,000 scale, and  comparisons of out-
crop gamma  profiles with subsurface pro-
files.
   Other agencies with significant radon-
related  data  include  water  management
districts (hydrogeology, core, and perme-
ability data), the DCA (FRRP project data),
the state university system (topical data),
and the Department of Health and Reha-
bilitative Services (indoor radon data).  No-
table radon related reports include a Florida
Institute of Phosphate  Research  report,
  1 ft - 0.3 m.
  1 mi1 - 2590 km'.

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and the 1987 Transactions of the Health
Physics Society and Southeastern Geo-
logical Society Symposium on the Natural
Radiation Environment in Florida. The U.S.
Soil Conservation Service has generated
valuable soils maps that are complete for
most  Florida counties. About 20-30% of
these  have been encoded into  digitized
files.  USGS   is  releasing   a   new
aeroradiometric  map  for Florida that is
based on a 1:250,000 scale. Open scien-
tific literature also contains Florida radon
data.

Data, Accuracy, and
Instrumentation Task Group
   Group discussions indicated the need
for quantitative input data at a county or
smaller scale. Higher resolution data were
desirable,  but their  basis was  not identi-
fied. The parameter to be mapped was
described variously  as "radon source po-
tential" or  "radon availability." It was  dis-
cussed at length with no ultimate consensus
for its exact definition. It generally was
considered to be computed from more ba-
sic parameters,  which  were identified as
the emanating radium concentration (Ra-
dium  x Emanation), the soil permeability,
and the soil radon diffusion coefficient.
Surrogates  for these  parameters were
deemed acceptable and in  some cases
necessary.  The combination of the impor-
tant variables may vary due to diffusive or
advective transport dominance. Use of a
Radon Availability Number (kBq rrr2) or a
Radon Index Number (dimensionless) was
discussed,  as was  the invariant param-
eters approach (Figure 3), which attempts
to partition out the moisture effects for
localized model representation. Surrogate
data sources also are represented.
   To represent house differences, a par-
titioning diagram was drawn (Figure 4) to
illustrate the preference to represent only
soil properties in the mapping effort and to
leave  house variations to the user in inter-
preting the map. This partitioning was con-
sidered desirable by the task group. The
desirability of using a single parameter to
represent house conditions led the group
to ignore house diversity for mapping pur-
poses, and represent houses by a model
typical of most. Variations from this model
configuration would be recognized in map
interpretation (right-hand side, Figure 4).
   Possible mapping  scales were esti-
mated from surrogate data scales.  Na-
tional  Uranium Resource Evaluation
(NURE) aeroradiometric data for Florida
are mapped on 2 km pixels for most of the
state,  and on 1 km pixels for the northern
part of the state. These data would support
mapping at a scale no finer than 1:250,000.
   Emanation
      Ra/Rn
     Porosity
 Permeability
 Gr. Size Dist.

Moist
Properties
4


Radon
[Index.
Availability]
Number
Figure 3.
Estimation of a radon number from invariant properties.
Figure 4.     Partitioning of radon availability from radon entry for mapping.
To repeat the aeroradiometric data collec-
tion on 1 -mi* flightline spacings in Florida
would cost about $1  million, and would
yield combined data on potassium, ura-
nium, and thorium. The present approach
for interpreting aeroradiometric data would
be (1) group and designate land areas by
aeroradiometric signatures and geology,
lithotogy, or soil information; (2) identify the
radon source for each grouping; and (3)
estimate radon availability numbers for each
unit. The scales at which other surrogate
data are available are summarized in Table
1.
   The data needs  indicated that surro-
gates would be required to represent most
model parameters. The proposed forced-
air radon accumulator could be used as a
                                            1 mi-1.6 Km.
                             reference measurement, but would not be
                             practical for statewide measurements of a
                             mapping parameter. The need was identi-
                             fied for analyzing existing data to recom-
                             mend  what  additional  data should  be
                             measured.

                             Institutional Issues, Uses and
                             Costs Task Group
                                The uses  and objectives of radon po-
                             tential  maps  suggested  addressing them
                             to one- and two-family dwellings, as ad-
                             dressed in the national building code. The
                             maps eventually should become available
                             as county-level  maps for use  by builders,
                             incorporating  detail on the nominal level of
                             a 10-acre (40,470 m2) plot.  Line divisions
                             to distinguish  one area from another must
                             be clear.  To  get maps adopted  for their
                             intended  uses,  defensible  physical  and

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technical boundaries are required. If many
anomalies  are noted in field  verification,
maps may require revision with more de-
tail. Less characterization may be justified
in areas with few houses. The fraction of
state area versus the fraction of state popu-
lation should be considered in  allocating
resources  to  obtain  adequate  statistical
definition of the radon potential parameter.
   The information on radon maps poten-
tially may mislead people in low-tier radon
potential areas to not test for indoor radon,
thus becoming  a  self-fulfilling prophesy.
By encouraging testing in  high-radon ar-
eas, high results will be found; and by not
emphasizing testing  in  lower areas, few
additional high results will be found.  How-
ever, overall the maps  should help focus
future  indoor radon  testing  in  the  most
important areas. The radon maps should
be directly  compatible  with the present
draft radon  building code,  giving builders
options for testing and compliance.
   The costs of radon mapping were com-
pared  to the  value obtained.  Maps can
save money overall by focusing on areas
that really need  extra radon controls. Map
use should  be well-defined, whether only
for guidance or for regulation, and should
establish exact lines for decisionmaking by
builders. Map costs suggest  reliance on
ZIP-Code level  indoor  radon  data when
possible to minimize expenses of  addi-
tional field work.
Table1.      Data Source*, SC«/M. and Coverage

         Data                          Scales
                                Coverage
NUREmaps
Total count aerorad maps
State geologic maps
Environmental geologic maps
Local/county maps
SoH photos
SoH associations
    1:250,000
    1:100,000

    1:500,000
    1:250,000
124,000 to /.-65,000
     1:24,000
    1:250,000
   Entire state
North half of state
   Entire state
   Entire state
     Varied
  70% of state
  70% of state
                                                                         &U.S. GOVERNMENT PRINTING OFFICE: I99Z - 648-080/40121

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