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-
-------
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'.
-------
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
-------
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
------- |