United States
Environmental Protection
Agency
National Kisk Management
Research Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/SR-95/145
February 1996
& EPA Project Summary
Soil and Fill Laboratory
Support-1992, Radiological
Analyses, Florida Radon
Research Program
C.E. Roessler, H. Mohammed, R. Richards, and H. Nyugen
The report gives results of radiologi-
cal analyses of soil and fill samples
and data interpretations by the Univer-
sity of Florida in support of the Florida
Radon Research Program (FRRP). Mois-
ture, radium-226, and radon emanation
coefficient determinations were per-
formed on samples collected and sub-
mitted during 1992 by the FRRP New
House Evaluation Program (NHEP) and
the FRRP Research House Program.
During this period, 164 samples repre-
senting 31 sites were received and ana-
lyzed; this provided a 1991-92 cumula-
tive of 288 samples from 75 sites. Since
much of the 1992 sampling represented
a continuation of work performed in
1991, the cumulative 1991-92 data were
analyzed.
The North Florida NHEP sites
(Gainesville vicinity) were characterized
by fill with almost exclusively low ra-
dium-226 content (<1 pCi/g). Of the 41
sites sampled in 1991-92, the radium
content of the first 0.9 m of the sub-
strate was <1 pCi/g at 76% of the sites,
1-10 pCi/g at 22%, and in excess of 10
pCi/g (12 pCi/g) at one site. In 1992, the
sampling depth was increased to in-
clude a profile to 1.8 m. The range of
results was comparable for the first
and second 0.9 m depths, but the dis-
tribution shifted toward higher values
(more sites exceeding 2 pCi/g) for the
deeper increment.
For the Central Florida NHEP sites of
both years, most of the fill samples
and a high percentage of the native
soil sites (70-75%) had radium con-
centrations exceeding 1 pCi/g. These
sites are characterized by elevated ra-
dioactivity (1 to >10 pCi/g) fill over a
wide range of substrate concentrations
(<1 to >10 pCi/g).
This work supports conclusions from
previous years. A large portion of the
fill used in Florida construction is of a
low radium content. However, elevated
radium concentrations do occur in soil
at some Florida construction sites, and
fill with elevated radioactivity may be
an issue in selected circumstances. The
extent and source of elevated radioac-
tivity fills should be investigated fur-
ther and building code development
should continue to consider a soil/fill
radioactivity standard. At some loca-
tions (for example, North Florida) near-
surface soil gas radon may originate
from deeper than 1 m, and thus shal-
low soil samples may not be adequate
for identifying radon potential.
With respect to the research houses
and test modules, these laboratory
analyses verified that the sites and test
fills are generally representative of the
conditions observed at the NHEP con-
struction sites in the respective regions.
This Project Summary was developed
by the National Risk Management Re-
search Laboratory's Air Pollution Pre-
vention and Control Division, Research
Triangle Park, NC, to announce key
findings of the research project that is
fully documented in a separate report
of the same title (see Project Report
ordering information at back).
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Introduction
The report gives results of soil and fill
analyses performed by the University of
Florida in support of the Florida Radon
Research Program (FRRP). Radiological
characteristics were determined on
samples collected during 1992 by the Re-
search House Program and the New
House Evaluation Program (NHEP) of the
FRRP.
This work is a continuation of efforts to
characterize the radon1 source potential
of Florida soil and fill materials. In 1989, a
survey of 35 sites distributed statewide
examined fill materials at construction sites
(66.6%) and native surficial soil at con-
struction or existing house sites (33.3%).
In addition, insitu permeability and soil
gas radon measurements were performed
at a subset of these sites. Work in 1990
emphasized insitu permeability and soil
gas radon measurement and soil sam-
pling at 23 statewide sites as prepared for
construction. In 1991, the research con-
tractors for the NHEP program submitted
samples collected at 42 construction sites
in areas of suspected elevated radon po-
tential in North Florida (Alachua County)
and Central Florida (primarily Polk County).
Samples were also received from the
Alachua County and Polk County FRRP
Research House sites.
The work in 1992 involved continued
support of the FRRP NHEP and Research
House projects and analysis of the 1991-
92 cumulative data.
Methodology
Samples were collected to represent
both the sub-slab fill material and the up-
per (1-2 m) portion of the underlying sub-
strate. In the laboratory, soil samples were
dried and portions were sealed in a con-
tainer, counted with high resolution
gamma-ray spectrometry shortly after seal-
ing, held for ingrowth of radon and its
short-lived decay products, and counted
at least one more time. Radium concen-
trations and radon emanation coefficients
were calculated from the activity associ-
ated with 295.2-, 351.9-, and 609.3-keV
peaks of the short-lived radon daughters.
The radium concentration was based on
the projected equilibrium radon-222 activ-
ity; radon emanation coefficient was de-
termined from the pair of values corre-
sponding to pre-ingrowth and equilibrium
radon concentrations.
1 In the report, the term "radon" designates the radon
isotope, radon-222. The term "radium" denotes the
radium isotope, radium-226.
Sample collection methods for the Re-
search House Project are specified in a
separate Florida research houses guid-
ance document.
Results and Discussion
During 1992, 164 samples representing
31 sites were received and processed;
this provided a 1991-92 cumulative of 288
samples from 75 sites.
Radiological Characteristics at
NHEP Sites
The North Florida NHEP sites
(Gainesville vicinity) were characterized by
fill with almost exclusively low radium-226
content (<1 pCi/g) over predominantly low
activity near-surface substrate. Fill samples
had concentrations of <1 pCi/g at 30 of 31
sites. At one site, moderately elevated
radioactivity fill (3 pCi/g) was found over
low activity (<1 pCi/g) surficial substrate.
Compared to the 1991 sites, the 1992
sites had a greater percentage of slightly
to moderately elevated radium concentra-
tions (1-10 pCi/g) in the first 0.9 m. For
the upper 0.9 m of the 41 sites sampled in
1991-92, 76% had <1 pCi/g, 22% had 1 -
10 pCi/g, and only one site exceeded 10
pCi/g (12 pCi/g). Because it appeared that
the radon gas was originating from deeper
than the 0.9 m sampled in 1991, profiles
to 1.8 m were collected in 1992. The range
of results was comparable for the first and
second 0.9 m depths, but the distribution
shifted toward higher values (more sites
exceeding 2 pCi/g) for the deeper incre-
ment.
For the Central Florida NHEP sites of
both years, most of the fill samples and a
high percentage of the native soil sites
(70-75%) had radium concentrations ex-
ceeding 1 pCi/g. These sites are charac-
terized by elevated radioactivity (1 to >10
pCi/g) fill over a wide range of substrate
concentrations (<1 to >10 pCi/g).
Radiological Characteristics at
Research House Sites
At the North Florida Research House,
radium concentrations in the first 1.8 m
for two different cores near the house
were in the range of 4-7 pCi/g. These
values are moderately elevated and indi-
cate that the radon source is near the
surface with a relatively uniform distribu-
tion at this site. This compares to the
several North Florida NHEP house sites
that had elevated radium in the near-sur-
face substrate. The sub-slab material from
the suction pit was much lower in radioac-
tivity and presumably represents fill. The
general material excavated from the pit
had concentrations on the order of only
0.3-0.4 pCi/g, while pieces of clay found
in this material had slightly elevated ra-
dium concentrations in the range of 1-2
pCi/g.
The fill and the substrate at the Central
Florida Test Modules Florida Institute of
Phosphate Research (FIPR) site had ra-
dium concentrations on the order of 5-8
pCi/g; these values are comparable to the
median values observed for soil and fill at
the Central Florida NHEP sites.
In 1992 a module was constructed in
Central Florida to permit testing of the
contribution of fill material to indoor radon.
This site has a low near-surface radon
source — radium concentrations in the
first 1.5 m were on the order of 0.1 to 0.2
pCi/g. The test materials selected to rep-
resent "medium" radioactivity fill (waste
sand tailings from phosphate rock
benefication) had concentrations on the
order of 4 pCi/g. The test materials se-
lected to represent "hot" fill (phosphate
rock concentrate, the benefication prod-
uct), had concentrations on the order of
33 pCi/g. These concentrations are com-
parable to values typically reported for
these materials and verify the selection of
these materials to represent or simulate
two levels of fill radioactivity.
Fill from a Central Florida source and in
use in a test chamber had radium con-
centrations in the range of 4-6 pCi/g. These
concentrations are comparable to those in
the moderately elevated substrate and fill
samples from the Central Florida NHEP
sites.
Conclusions and
Recommendations
The 1991 and 1992 work under this
project leads to the following conclusions
and recommendations.
1. The observations for North
Florida support earlier conclu-
sions (1989 and 1990) that a
large portion of the fill actually
used in Florida construction is of
a low radium content. Availability
of low radioactivity fill should not
be a deterrent to adopting radio-
activity standards for construction
fill.
2. Elevated radium concentrations
do occur in some Florida soil and
fill samples in actual house con-
struction. Building code develop-
ment should continue to consider
a soil/fill radioactivity standard.
3. Fill with elevated radioactivity can
be an issue in selected circum-
stances (this was observed at the
Central Florida NHEP sites). The
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extent and source of these fills
should be investigated further.
4. Mining-related land (such as re-
claimed overburden and/or sand
tailings areas) may present a ra-
don source. These soils may
have characteristics different from
those of undisturbed soils and
directly excavated fills. The pro-
gram should be reviewed to as-
sess whether this land category
is receiving adequate attention in
sampling and radon potential
modeling.
5. These and other studies indicate
that, at some locations in North
Central Florida, the near-surface
soil gas radon may originate from
deeper than 1 m. Therefore, sam-
pling in this region should con-
tinue to be for a 2-m or greater
depth profile, especially if el-
evated soil gas radon has been
detected at the site.
6. The observation that the radon
source may be deeper than 1 m
indicates that shallow soil
samples, in the absence of addi-
tional information about the depth
profile, may not be adequate for
identifying radon potential.
7. With respect to the research
houses and test modules, these
laboratory analyses verified that
the sites and test fills are gener-
ally representative of the condi-
tions observed among the NHEP
construction sites in the respec-
tive regions.
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C. Roessler, H. Mohammed, R. Richards, and H. Nyugen are with The University
of Florida, Gainesville, FL 32611.
David C. Sanchez is the EPA Project Officer (see below).
The complete report, entitled "Soil and Fill Laboratory Support—1992, Radiological
Analyses, Florida Radon Research Program," (Order No. PB96-140579; Cost:
$17.50, 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
Cincinnati, OH 45268
United States
Environmental Protection Agency
National Risk Management Research Laboratory (G-72)
Cincinnati, OH 45268
Official Business
Penalty for Private Use $300
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POSTAGE & FEES PAID
EPA
PERMIT No. G-35
EPA/600/SR-95/145
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