United States
                   Environmental Protection
                   Agency
National Risk Management
Research Laboratory
Research Triangle Park NC 27711
                   Research and Development
EPA/600/SR-96/108  November 1996
4>EPA       Project Summary
                   Site-Specific
                   Measurements  of Residential
                   Radon  Protection  Category

                   Kirk K. Nielson, Rodger B. Holt, and Vern C. Rogers
                     The report describes a series  of
                   benchmark measurements  of soil ra-
                   don potential at seven Florida sites and
                   compares the measurements with re-
                   gional estimates of radon potential from
                   the Florida radon protection map. The
                   measurements and map were both de-
                   veloped under the Florida  Radon Re-
                   search Program to identify the amount
                   of radon resistance that is  needed for
                   new  buildings in different parts  of
                   Florida. While the measurement proto-
                   col and the radon map have a common
                   theoretical basis, the tests were de-
                   signed to represent  small  site areas
                   (
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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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