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vention and Control Division, 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 Florida Department of Community
Affairs, under the Florida Radon Research
Program (FRRP), has developed radon-
protective building standards for new resi-
dential construction. An earlier version of
the standards contained more detailed re-
quirements for passive and active radon
controls in areas identified by a radon
protection map to have elevated radon
potential. Although not part of the adopted
standard, the radon protection map and
the related system for selecting different
levels of radon control still provide useful
guidance for residential radon control.
The radon protection map was devel-
oped by calculating the soil radon poten-
tials for each of 3,919 regions of Florida
from soil, geological, radiological, and hy-
drological properties. The regions were
defined by the digital intersection of soil
maps and surface geology maps. The ra-
don potentials were expressed as the rate
of radon entry into a reference slab-on-
grade house that was numerically simu-
lated to be located in each region. The
regions were then classified into low, in-
termediate, and elevated radon potential
categories, depending on whether indoor
radon levels for the reference house could
range as high as 4 pCi L1, as high as 8.3
pCi L1, or greater than 8.3 pCi L1.
A site-specific test protocol was devel-
oped under the FRRP for measuring the
soil radon potential category of specific
sites in a way that corresponds to the
radon protection map designations. How-
ever, the protocols for site-specific tests
were designed to represent small site ar-
eas of 1 acre (4x103 m2) or less, com-
pared with the larger 8,800-acre (3.6x107
m2) regions typically shown on the radon
protection map. The site-specific measure-
ments were designed to supersede the
regional map designations because of their
better representation of specific sites. The
site-specific measurement protocol uses
the same theoretical basis as the radon
protection map. However, the protocol has
not been previously evaluated by field
measurements to determine its consistency
with the radon protection map.
This report examines the consistency of
analyses from the site-specific radon po-
tential measurements with the Florida ra-
don protection map. It also presents and
evaluates a simplified alternative method
for estimating soil radium profiles for use
in the protocol. The consistency between
the site-specific measurements and the
map is examined from a series of bench-
mark measurements using the site-spe-
cific protocol in different Florida regions
that lie within the red, yellow, and green
areas of the radon protection map. The
resulting data are analyzed by the
RAETRAD-F computer code, which was
developed for analyzing data from the site-
specific measurements. The measurement
results give the radon protection category
of each site, which is compared with the
category shown on the radon protection
map.
Site Selection
The locations for the benchmark site-
specific tests included seven Florida sites:
two in the green category on the radon
protection map, three in the yellow cat-
egory, and two in the red category. The
sites were selected considering criteria for
representativeness, accessibility, and con-
venience. The general color regions were
selected from the elevated frequency of
red regions in central Florida, the elevated
frequency of yellow-regions in north-cen-
tral Florida, and the nearly complete domi-
nance of green regions in the Florida
panhandle. Representativeness was based
on qualitative field judgements that ex-
cluded areas that were obviously disturbed
or otherwise atypical of the map region.
For example, highway embankments were
excluded. Related considerations included
avoidance of buried utility lines, approxi-
mate 1-acre minimum areas, and conve-
nient proximity to access roads.
The sites where the field sampling and
measurement protocols were conducted
are shown in Figure 1. The two red-cat-
egory sites were selected for accessibility.
The Polk-1 site was located at an FRRP
research site already used for radon stud-
ies. An adjacent commercial building prop-
erty in Bartow (Polk-2) was also available
because of participation in another FRRP
project. The three yellow-category sites
were chosen in Hernando and Sumter
Counties during the field trip. The
Hernando County site was located in a
highway median that contained old and
apparently undisturbed native soil and veg-
etation. This site was selected to test the
"smaller than 1 acre" option of the proto-
col (using only three boreholes). The
Sumter County sites were on cleared but
otherwise undisturbed land of a power
line corridor (Sumter-1) and on cleared
land of an interstate highway right-of-way
(Sumter-2). The green-category site in
Wakulla County was on undisturbed land
of a power line corridor. The Jefferson
County site was on vegetation-cleared land
in the margin between private land and a
U.S. highway right-of-way.
Latitude and longitude coordinates of
each sampling and measurement site were
measured using a global positioning sys-
tem. The coordinates were subsequently
analyzed by a Geographic Information Sys-
tem to positively determine the radon map
polygon containing the site. Individual sam-
pling locations at each site were located
at least 10 m apart in an approximately
square configuration.
Field Procedures
Field sampling and measurement pro-
cedures used the FRRP procedures given
in "Standard Measurement Protocols,
Florida Radon Research Program," the
American Society for Testing and Materi-
als (ASTM) procedures where applicable,
or Rogers and Associates Engineering
Corporation procedures. The field sam-
pling and measurements were conducted
between March 12 and 15, 1995. The
field procedures used portable equipment
that could be hand-carried onto the site
without requiring vehicle-mounted drilling
or measuring equipment.
The site-specific protocol requires sam-
pling of site soils and measurement of five
parameters from the samples or from field
measurements: (a) soil 226Ra concentra-
tion, (b) soil density, (c) soil textural clas-
sification, (d) 222Rn concentration in soil
gas, and (e) water table minimum depth
and duration.
Soil sampling used five boreholes
spread over the site at locations corre-
sponding to planned or potential building
sites. For sites smaller than 1 acre, sam-
pling used at least one borehole for every
planned or potential residential building
location. Soils were collected from each
borehole to represent the 0-61, 61-122,
122-183, and 183-244 cm depth intervals.
The samples were collected from the drill
cuttings of a 5-cm diameter soil auger
attached to a hand-held gasoline-powered
drill. Samples were immediately sealed
into heavy gauge (0.1 mm) polyethylene
bags and labeled by site, location, and
depth for transport to the Rogers and As-
sociates laboratory for radium assays. Ap-
proximately 350 g of soil was collected
from each depth increment.
In situ soil density samples were col-
lected at each site using a thin-walled
steel drive cylinder, as prescribed by ASTM
D 2937. The cylinder was inserted in the
0-30 cm depth range and was then exca-
vated with a hand trowel. After removing
excess material from the cylinder, the mea-
sured volume of soil was transferred to a
heavy gauge (0.1 mm) re-sealable poly-
ethylene bag for weighing and moisture
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Wakulla
Jefferson
(Green) Sumter-2
Sumter-1
Polk-1
(Red)
Figure 1. Field sampling locations.
measurement in the laboratory. Soil den-
sity was determined in grams per cubic
centimeter on a dry mass basis.
Soil textural classifications were made
from visual and tactile observations while
bagging the auger cuttings for the radium
samples. The textures were classified into
one of the 12 classes defined by the U.S.
Soil Conservation Service: sand, loamy
sand, sandy loam, sandy clay loam, sandy
clay, loam, clay loam, silty loam, clay, silty
clay loam, silty clay, and silt.
Water table depths were observed,
where possible, by measuring the distance
from the soil surface to the surface of the
water that occurred in the borehole prior
to backfilling. Where water was not ob-
served, estimates were obtained subse-
quently from the data used for the
statewide radon maps.
The concentration of 222Rn in soil gas
was determined by drawing air from a
driven tube into a calibrated radon mea-
surement system. The tube (6 mm I.D.
steel pipe) was driven to a depth of ap-
proximately 1 m and was connected by
plastic tubing to the scintillation cell and
pump of a radon monitor. The monitor
drew approximately 2 L min-1 of soil gas,
and was operated for several minutes to
establish background before connecting
to the pipe. The sampler was operated for
10 to 35 minutes on the pipe, after which
the plastic tube was disconnected to purge
the cell with surface air. The alpha activity
in the scintillation cell was recorded over
2-minute intervals. Soil gas radon con-
centrations were computed from the con-
tinuously measured alpha counts. The
efficiency of the scintillation cell was de-
termined previously from measurements
at the U.S. Department of Energy's Tech-
nical Measurement Center radon cham-
ber at Grand Junction, CO.
Borehole gamma ray logs were mea-
sured before backfilling each hole for com-
parison with the results of laboratory
radium assays. The borehole logs used a
2.5-cm diameter sodium iodide gamma
ray scintillation probe connected to a digi-
tal sealer. Individual 1-min counts were
recorded at 30.5-cm intervals throughout
the depth of each borehole. The same
probe was calibrated in a separate study
to yield 4,600 counts min-1 in boreholes
with 2.1 pCi g-1 226Ra and 0.2 pCi g-1 228Ra
and a background rate of 590 counts
min-1 in low-radium boreholes.
Laboratory Analyses
The borehole soil samples were weighed
into tared steel cans and sealed for ra-
dium assay by the procedures described
previously. Radium assays were performed
after approximately 18 days equilibration
in the sealed cans. Laboratory assays used
a calibrated gamma ray spectrometer to
determine concentrations of 226Ra in pico-
curies per gram on a dry mass basis. At
least 10% duplicates, blanks, and stan-
dards were also analyzed for quality as-
surance purposes. Samples were dried
as specified by ASTM D 2216-80 for mois-
ture determinations. The soil density
samples were transferred to laboratory
beakers and dried as specified by ASTM
D 2216-80 to determine dry sample den-
sity according to ASTM D 2937-83.
Test Results
Soil radium concentrations measured by
laboratory assays of the borehole soils
ranged from 0.1 to 20.8 pCi g-1, compared
to a range of 0.2 to 13.2 pCi g-1 based on
the borehole gamma ray measurements.
The individual borehole measurements had
a correlation coefficient of r2 = 0.84 in a
least-squares regression of radium on
gamma ray intensity. An independent cali-
bration of gamma activity was used to
estimate radium concentrations from the
gamma ray measurements, and the re-
sulting radium concentrations were aver-
aged by depth interval for comparison
radium concentrations.
Extra laboratory radium analyses for
quality assurance purposes included ap-
proximately 10% duplicate assays, 10%
blanks, and 10% replicate analyses of
standards. The precision as estimated from
counting statistics for samples exceeding
2 pCi g-1 was 6.0% (100 x standard devia-
tion •*• mean), compared to a data quality
objective of 20% for this parameter. The
corresponding analytical precision esti-
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mated from duplicate assays averaged
4.3%. The duplicate assays showed no
net bias. The analyses of blanks aver-
aged 0.1 + 0.2 pCi g-1, well within the
analytical standard deviation of +0.2 pCi
g-1. The analyses of a 15.12 + 0.23 pCi g-1
226Ra standard showed an average bias of
only 2%, well within the 10% accuracy
objective.
Soil moisture measurements on the
laboratory radium samples ranged from
3.2 to 53.7% of dry mass. The soil tex-
tures were mostly (69%) sand, with the
next most prevalent textures including clay
(10%), loamy sand (8%), and sandy loam
(7%).
Soil density measurements among the
seven sites averaged 1.53 g crrr3 with a
standard deviation of 0.10 g crrr3 and a
range of 1.41 g cnr3 (Jefferson site) to
1.68 g cnr3 (Wakulla site). Soil radon con-
centrations ranged from 91 pCi L1 at the
Jefferson site to 4,100 pCi L1 at the Polk-
2 site. The water table was observed only
at the Wakulla site; therefore the mini-
mum depths and durations were primarily
estimated from the Statsgo data used pre-
viously in developing the Florida radon
maps.
Model Analyses of Radon
Protection Category
The measured data were analyzed with
the RAETRAD-F computer code to deter-
mine the radon potential category of each
site. The code simulated radon entry into
the reference house in a way that corre-
sponded to the radon protection map. The
site-specific calculations were then com-
pared with the mapped categories. More
general sensitivity analyses were also per-
formed with the RAETRAD-F model to
assess the general, statewide agreement
between the site-specific modeling ap-
proach and the statewide radon protec-
tion map.
The RAETRAD-F code computed sta-
tistical parameters from the site measure-
ments to characterize the site radium
distributions, the annual water table distri-
bution, the soil moisture profiles, and other
parameters. It then computed the annual
average indoor radon distribution for the
reference house. From this distribution,
the code computed the 95% confidence
limit for the annual average indoor radon
concentration in the reference house (C95)
to correspond with the radon protection
map. The code finally compared C95 to the
4.0- and 8.3-pCi L1 cut points used in the
radon protection map, and designated the
site to have low, intermediate, or elevated
radon potential.
The potential radon concentrations and
site classifications from these analyses
are given in the third and fourth columns
of Table 1 for comparison with the classi-
fications of the radon protection maps.
Both sites located in a red (elevated) ra-
don potential category on the radon pro-
tection map were determined to have a
corresponding elevated radon potential
classification by the site-specific tests us-
ing the laboratory radium assays. Two of
the three sites that were mapped in the
intermediate radon potential category
(Sumter-1 and Hernando) were determined
to have a corresponding intermediate (yel-
low) radon potential classification by the
site-specific tests using the laboratory ra-
dium assays. The other site mapped in
the intermediate radon potential category
(Sumter-2) was determined to have a low
(green) classification by the site-specific
tests but was within 8% of the boundary
between the green and yellow categories.
The two sites mapped in the low-radon
potential category were both determined
to have a corresponding low-radon (green)
potential classification by the site-specific
tests.
Corresponding separate model analy-
ses used the alternative radium distribu-
tions estimated from the borehole gamma
ray measurements instead of the labora-
tory radium assays. The potential radon
concentrations and site classifications from
these analyses are given in the fifth and
sixth columns of Table 1. Both sites
mapped in an elevated (red) radon poten-
tial category were again determined to
have a corresponding elevated radon po-
tential classification by the tests using bore-
hole gamma ray logs. Two of the three
sites mapped in the intermediate radon
potential category (Sumter-1 and
Hernando) were also found to have an
elevated (red) radon potential classifica-
tion using the alternative radium distribu-
tions from the borehole logs. The other
site mapped in the intermediate radon po-
tential category (Sumter-2) was again de-
termined to have a low (green)
classification by the alternative radium dis-
tributions. The two sites mapped in the
low-radon potential category were deter-
mined to have a corresponding low-radon
(green) potential classification by the al-
ternative analyses.
The comparisons in Table 1 show agree-
ment or conservative differences between
the map and site-specific analyses. The
differences for the Sumter-2 site result
from the conservative land classification
by the radon potential map. Although lo-
cally elevated conditions were found for
the other six sites, this site reflects the
general conservatism (95% confidence
limit) of the radon potential map. The only
other sites showing differences, Sumter-1
and Hernando, were correctly modeled
from the laboratory radium assays but were
Table 1. Potential Radon Concentrations and Site Radon Potential Categories from RAETRAD-F Analyses
Using Lab Radium Assays
Using Borehole Gamma Logs
Site
Polk-1
Polk-2
Sumter-1
Sumter-2
Hernando
Wakulla
Jefferson
Radon
Protection
Map
Category
Red
Red
Yellow
Yellow
Yellow
Green
Green
Potential
Radon
Cone.
(pd L-i)
35.2
104.5
8.1
3.7
6.8
2.1
2.1
Site Radon
Potential Category
Elevated (Red)
Elevated (Red)
Intermediate (Yel.)
Low (Green)
Intermediate (Yel.)
Low (Green)
Low (Green)
Potential
Radon
Cone.
(pd L-i)
27.7
70.4
9.0
3.5
13.3
1.8*
2.4
Site Radon
Potential Category
Elevated (Red)
Elevated (Red)
Elevated (Red)
Low (Green)
Elevated (Red)
Low (Green)
Low (Green)
^Assumes 1 pCi g-' radium concentrations in holes where water precluded gamma ray measurements.
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conservatively modeled by the borehole
gamma ray logs. In general, the compari-
sons show good correspondence between
the detailed field tests and the map pre-
dictions and comprise an acceptable
benchmark between measured and
mapped radon potentials.
The conservatism in the gamma ray
measurements could have resulted from
any of several recognized systematic
sources, including contributions from natu-
ral thorium-chain radionuclides to the ra-
dium estimates and to a lesser extent,
auger smearing of elevated-radium soils
from the deepest strata into upper, low-
radium soil regions around the borehole.
The differences for the Sumter-1 and -2
sites could also be attributed to random
variation, since they are within approxi-
mately 8-12% of the respective 8.3- and
4.0-pCi L1 map category cut points.
The simplified alternative protocol for
site radium estimates proved to give gen-
erally equivalent or conservative results.
Although the simpler method gave faster
results at lower cost, it was potentially
less accurate because of the added un-
certainty in calibrating gamma ray inten-
sity to soil radium concentration. The
potential errors were conservative, how-
ever, because the potentially increased
radium variations served to raise the 95%
confidence limits of potential radon con-
centration calculated by RAETRAD-F. The
alternative protocol was also conservative
because thorium-chain gamma rays in-
creased the total radium estimate from
gamma radiation, even though the tho-
rium-chain radionuclides do not produce
222Rn.
Generalized Model-Map
Comparisons
A second, more generalized compari-
son was also made between RAETRAD-F
calculations and the data used for the
statewide radon protection map. This com-
parison addressed most of the 3,919 map
polygons, but it relied on generic data
rather than site-specific measurements for
input to the RAETRAD-F code.
The generalized comparisons used the
statewide polygon definitions of soil ra-
dium distributions. The geometric mean
radium concentrations were plotted against
their geometric standard deviations for
each polygon. Polygons mapped in the
red (elevated radon potential) category
were plotted with circles; polygons mapped
in the yellow (intermediate radon poten-
tial) category were plotted with triangles;
and polygons mapped in the green (low-
radon potential) category were plotted with
small dots. The resulting scatter plot
showed distinct grouping that corresponds
to map categories.
For comparison with RAETRAD-F, cal-
culations were performed to estimate
where the green-yellow and yellow-red cut
points would fall on the above scatter plot.
For the RAETRAD-F calculations, all soils
were represented conservatively by sand.
This conservative texture provided maxi-
mum permeability and diffusivity and mini-
mal water retention, permitting as much
surface radon release as possible. Water
tables were also defined conservatively
low. Soil radium distributions were defined
to be log-normal with geometric means
and geometric standard deviations (GSDs)
that were varied to obtain different radon
potentials corresponding to the green-yel-
low and yellow-red cut points.
The generic cut point lines calculated
by RAETRAD-F had similar shape and
spacing trends to those of the three cat-
egories of polygon points but were biased
lower than the GSDs of the polygon points.
The difference in GSD was expected, since
the maps use large-area regional GSDs
dominated by aeroradiometric and soil
variations, while the RAETRAD-F analy-
ses use local GSDs controlled by radium
and moisture variations over a 1-acre site.
An increase of only 0.5 in the site-specific
GSDs gave good agreement between the
calculated generic site radon potentials
and the statewide clusters of red, yellow,
and green polygon data.
Summary
Site-specific measurements using the
measurement and analysis methods pre-
scribed by the original site characteriza-
tion protocol gave identical radon
protection categories to those shown on
the radon protection map at six of the
seven sites that were tested. At the re-
maining site, the potential radon concen-
tration (C95=3.7 pCi L1) was slightly below
the map cut point of 4 pCi L1 that would
have placed it into an equivalent category.
The conservative display by the map is
expected, since the map categories are
defined to contain significant areas with
lower radon potentials.
Slightly more conservative site catego-
ries were obtained using the alternative
protocol that replaces laboratory radium
assays with field borehole gamma ray logs.
Although all sites mapped with low or el-
evated classifications retained the same
category under the alternative protocol,
two intermediate-class sites were indicated
as elevated. This conservatism could po-
tentially be eliminated by alternative cali-
brations or field instruments that reduce
232Th-chain radionuclide interference.
On a broader scale, less-specific com-
parisons of the radon protection map with
the site-specific data analysis model
(RAETRAD-F) also show consistency. This
comparison is complicated by an inherent
difference in scale between large regional
variations and local site variations. Never-
theless, the comparison suggests that even
the complete statewide distribution of ra-
don potentials is consistent with the trends
shown by the RAETRAD-F model, which
is prescribed for analyzing site-specific
measurement data.
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Kirk K. Me/son, Rodger B. Holt, and Vern C. Rogers are with Rogers and
Associates Engineering Corp., Salt Lake City, UT 84110-0330.
David C. Sanchez is the EPA Project Officer (see below).
The complete report, entitled "Site-Specific Measurements of Residential Radon
Protection Category,"(OrderNo. PB97-104707; Cost: $21.50, 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 Pollution Prevention and Control Division
National Risk Management 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
Official Business
Penalty for Private Use
$300
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
EPA/600/SR-96/108
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