United States
Environmental Protection
Agency
Research and Development
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 27711
EPA/600/S8-91/046 Aug. 1991
EPA Project Summary
Feasibility and Approach for
Mapping Radon Potentials in
Florida
Kirk K. Nielson and Vern C. Rogers
The feasibility and approach have
been analyzed for developing statewide
maps of radon potentials In Florida.
The maps would provide a geographic
basis for implementing new radon-pro-
tective building construction standards
to reduce public health risks from ex-
posure to indoor radon. Previous ra-
don mapping efforts, geographic clas-
sification systems, radon Indices, and
radon entry algorithms were analyzed
to estimate the suitability of existing
technology. A new, deterministic ap-
proach Is proposed that would rely
heavily on existing soil survey data to
define geological and lithological fea-
tures and detailed soil properties. State-
wide radium distributions would be es-
timated partly from existing data bases,
but would require supplementary mea-
surements, mostly on archived soil
samples.
In the new mapping approach, varia-
tions in Indoor radon are partitioned by
source, house, and time variations. The
time variations are minimized by using
Invariant or long-term average param-
eters. Source variations are partitioned
from house variations by computing
radon entry rates for a reference house
that is modeled as if located on vary-
ing, layered soils that represent the
source variations throughout the state.
House variations finally are represented
from existing indoor radon data after
normalizing to the source potential at
each location.
Two kinds of maps would result from
this approach: radon source maps
(showing source as a radon entry rate,
mCl yr1), and radon probability maps
(showing the probability of exceeding
prescribed indoor radon levels). The
expected Indoor radon concentrations
could be computed from a particular
source datum and nominal house char-
acteristics. A mapping scale of
1:100,000 to 1:250,000 appears feasible,
with more detailed mapping (to 200 m
resolution) In certain areas of radium
anomalies with non-uniform lithology.
Summary maps at 1:1,000,000 to
1:2,000,000 also would be useful.
This Project Summary was developed
by EPA's Air and Energy Engineering
Research Laboratory, Research Tri-
angle 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
Statewide maps of radon potentials in
Florida have been proposed as a means
of assessing the need for radon-protec-
tive construction features for new hous-
ing. Suitable radon maps would reduce
costs and increase benefits from radon-
based building code requirements being
promulgated by the Florida Department of
Community Affairs (DCA) by defining local
radon risks that could be keyed to the
need for prescribed levels of radon pro-
tection. Radon potentials are dominated
by concentrations of the naturally occur-
ring radium-226 parent nuclide and by the
gas-transport properties of soils in the top
few meters beneath a house. The poten-
tials thus correlate with regional geology,
mineralogy, and physiographic features.
*£§ Printed on Recycled Paper
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An analysis was made of the feasibility
of developing radon maps that would meet
DCA programmatic needs and of the ap-
proach that would be required. The analy-
sis included a review of previous radon
mapping approaches and experience, as
summarized in presentations and discus-
sions at a DCA workshop on radon map-
ping, and a subsequent critical review of
pertinent scientific literature and math-
ematical approaches.
Previous Mapping
Prior radon maps were aimed at identi-
fying radon-prone areas for prioritizing test-
ing programs and alerting the public to
testing needs. They generally have used
3-5 tier classifications of state- or region-
sized land areas on a scale of county or
physiographic units. The classifications
generally are qualitative or probabilistic,
and represent broad correlations of indoor
radon concentrations with surface geol-
ogy, lithology, aeroradiometric data, soil
permeability, and/or soil radium concen-
trations. A few" have resolutions approach-
ing a 10-acre (4047m2) parcel, but most
show only broader trends.
Several deterministic approaches have
utilized radon indices based on simple
correlations of indoor radon with two or
three soil or house parameters, including
soil radium or uranium concentration, soil
permeability, soil radon concentration,
house ventilation rate, and house founda-
tion parameters. More detailed calcula-
tions have utilized steady-state analytical
calculations of advective or combined ad-
vective/diffusive radon entry rates into
nouses.
Proposed Approach
To provide a basis for requiring radon-
protective construction, a more precise,
theoretically based approach is needed to
quantify radon potentials throughout
Florida and to interpret them in terms of
probable indoor radon concentrations.
Greater precision can be achieved by par-
titioning radon variations into the three
categories: source variations, house varia-
tions, and time variations. By using only
long-term average or invariant parameters,
the time component is minimized. Source
and house variations are partitioned by
computing radon entry rates (mCi yr1) for
a reference house, typical of Florida hous-
ing stock, located on layered soils repre-
senting the source variations throughout
the state. From the resulting statewide
distribution of radon source potentials,
housing variability is assessed by statisti-
cal summaries of indoor radon variations
for a constant or normalized source po-
tential.
Statistical analyses of Florida indoor ra-
don data-suggest^ relatively constant,
house-dominated variations within similar
geologic or physiographic units, but
broader variations when areas are grouped
by county or other institutional boundaries.
Methods are described to obtain unbiased
estimates of the variations, which are use-
ful indicators of the presence of local "hot
spots" within a region. These were shown
to occur mainly in northern and central
Florida, and to demonstrate the impor-
tance of localized, high-resolution analy-
ses of source potentials from soils, geo-
logic, and radiological data.
Feasible Maps and Their Basis
The proposed mapping approach will
generate two kinds of radon maps. A
radon source map will display isopleths of
the deterministic estimates of radon entry
rates for the reference house. A radon
probability map then will utilize the source
information with probability distributions to
display isopleths of the probabilities of ex-
ceeding prescribed indoor radon concen-
trations at each map location. A nominal
statewide .mapping scale,,of .1:1 QP.QPQ to
1:250,000 is proposed for the main, initial
mapping effort. For certain populated ar-
eas where radium anomalies and near-
surface lithology (0-5 m) are non-uniform,
higher-resolution mapping to a 200 m scale
will be needed for radon zoning purposes.
Radon source maps can utilize present
multi-region, multi-phase analytical equa-
tions for diffusive and advective radon
transport. The reference house is defined
from average Florida and U. S. param-
eters for slab-on-grade housing. Layered
soil data are mostly available from exist-
ing borings, geology, lithology, and Soil
Conservation Service (SCS) data. These
will define the required layer boundaries,
densities and porosities. From SCS soil
textural classifications and porosities, long-
term average water contents will be esti-
mated from soil matric potentials. The wa-
ter contents in^turn can be used with soil
porosities and textures to estimate soil
permeabilities and diffusion coefficients
using existing empirical correlations. SCS
water percolation data also may prove
useful.
The remaining radium and emanation
parameters will use existing data where
available, but will require supplementary
measurements on samples archived at the
University of Florida and the Florida Geo-
logical Survey. The measurements should
characterize these radiological properties
by geological formation and/or lithological
unit. Precisions of the mapped radon
source potentials are anticipated to ap-
proach a geometric standard deviation of
about 2.5.
The probability maps will utilize a simple
indoor radon dilution model based on the
radon entry rate, house volume, and ven-
tilation rate. Log-normal radon distributions
appear appropriate, and will be used to
compute the probabilities of exceeding 4
pCi liter1 or other criteria using log-normal
distribution statistics.
•&U.S. GOVERNMENT PRINTING OFFICE: 1991 - S48-OZ8M0063
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K. Me/son and V. Rogers are with Rogers and Associates Engineering Corp., Salt
Lake City, UT 84110-0330.
David Sanchez is the EPA Project Officer (see below).
The complete report, entitled "Feasibility and Approach for Mapping Radon Poten-
tials in Florida,"(OrderNo. PB91-217372/AS; Cost: $15.00, subject to change)
will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental
Research Information
Cincinnati, OH 45268
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
Official Business
Penalty for Private Use $300
EPA/600/S8-91/046
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