United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/SR-94/052
June 1994
EPA Project Summary
Characteristics of Florida Fill
Materials and Soils—1990
C.E. Roessler, R. Morato, D.L. Smith, and J. Wherett
This report presents results of labo-
ratory work by the University of Florida
in support of the Foundation Fill Data
Base project of the Foundation Fill Ma-
terials Specifications Task Area of the
Florida Radon Research Program
(FRRP). Work included determination
of radon concentrations in soil gas
samples and physical and radiological
characterization of soil/fill samples to
provide data for further use in model-
ing radon production, transport, and
entry. This work adds to the 35-site,
54-sample data base developed in an
earlier study by the University of Florida
under the State University System
Board of Regents Radon Research Pro-
gram. The earlier study emphasized
materials being used as fill at construc-
tion sites; only one-third of the samples
were native surficial soil at construc-
tion or existing house sites. The study
being reported here emphasized sites
as prepared for construction. Twenty-
three sites were sampled. Two sites
were selected in each of 11 regions
designated to represent population cen-
ters covering the range of geographic,
topographic, and geological features in
Florida. Also included was a Brooksville
school construction site being studied
in another FRRP project.
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
The most prevalent source of elevated
indoor radon* in Florida is from the entry
of radon-bearing soil gas from beneath
the structure. Radon in this soil gas origi-
nates from radium in underlying and sur-
rounding soil and fill materials. The radon
source potential of a particular site is a
function of the soil gas radon concentra-
tion and the radon transport characteris-
tics of the substrate. Transport character-
istics determine the ease with which this
soil gas can be moved into a structure
and the extent to which the exhausted soil
gas radon can be replenished. The ease
of movement of radon-bearing soil gas
can be characterized in terms of the soil
air permeability coefficient. Permeability is
also an important parameter in the design
and performance of the sub-barrier de-
pressurization method of radon mitigation.
Alternative soil characteristics can also
be used to estimate radon source term
and entry. Soil radium concentration and
radon emanation coefficient jointly deter-
mine the radon production. Particle size
distribution influences the air permeability
and radon diffusion coefficient of the soil.
Soil classification can be a qualitative in-
dicator of the other, quantitative, param-
eters.
Initial work to characterize the radon
source potential and the permeability char-
acteristics of Florida soils and fill materi-
als was conducted by the University of
Florida as part of the State University Sys-
tem Board of Regents Radon Research
* In this report, the term "radon" is used to designate the
radon isotope, radon-222, and the term "radium" is
used to designate the radium isotope radium-226.
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Program. This report presents data for
appearance, physical characteristics, and
radiological characteristics for fill material
samples collected at 23 sites in 11 desig-
nated regions of the State of Florida. In
addition, a sand fill sample was collected
at the Brooksville school site. The data
from this laboratory work are presented
for further use in modeling radon produc-
tion, transport, and entry under the FRRP
Foundation Fill Materials Specifications
task effort.
Field Measurements and
Sampling
Sampling regions were designated to
represent population centers covering the
range of geographic, topographic, and geo-
logical features in Florida. Typically two
sampling sites were designated per re-
gion. One additional sampling location,
Brooksville, was included because of a
FRRP project involving a school under
construction in that vicinity.
Sites were selected, field work was per-
formed, and results were reported by
Geohazards, Inc. under a separate FRRP
contract. Most of the sampling sites con-
sisted of sites that had been leveled and
contoured for construction with fill (if any)
in place. A small number of sites were on
raw land or in the vicinity of existing
houses.
Sites were typically visited twice. At the
initial visit, in-situ permeability, penetrom-
eter, and density measurements were per-
formed, and alpha-track soil gas radon
detectors were deployed. In addition, soil
gas samples were collected in conjunc-
tion with the in-situ permeability measure-
ments at the maximum depth at which
these measurements were made (0.30 to
0.75 m or 12 to 30 in.). Soil samples were
also collected for laboratory classification
and measurement of physical and radio-
logical properties. Soil samples were col-
lected at a depth of 0.61 m (2 ft) or shal-
lower, but usually 0.3 m (1 ft) or deeper.
Approximately 6 weeks later, the sites were
revisited, the alpha track detectors were
retrieved, and additional soil gas samples
were collected.
Laboratory Measurements
Samples were classified by texture and
appearance with reference to the grain
size scale used by American geologists
(the modified Wentworth scale). Perme-
ability values were determined for samples
in dry unconsolidated, dry compacted,
moist unconsolidated, and moist com-
pacted states. Size distributions were de-
termined by sieve analysis. The samples
were also classified by sedimentation
analysis.
The radon concentration in soil gas was
determined by using a radon scintillation
cell counting system to analyze the cells
that had been filled during soil gas sam-
pling in the field. For radiological analysis
of soil samples, dried portions were sealed
in a container, counted with a high resolu-
tion gamma-ray spectrometry system
shortly after sealing, held for ingrowth of
radon-222, and counted at least one more
time. Radon emanation coefficient and ra-
dium-226 concentration were calculated
from the activity associated with the 295-,
352-, and 609-keV peaks of the short-
lived radon daughters. The radium-226
was based on the projected equilibrium
radon-222 activity; radon emanation coef-
ficient was determined from the pair of
values corresponding to pre-ingrowth and
equilibrium radon concentrations.
Appearance and Physical
Characteristics
All of the regional soil samples were
sand or sandy materials with loamy sand
and clayey sand the more prevalent ma-
terials. In contrast, the Brooksville school
site samples were clay. Most of the sandy
samples had moisture contents in the
range of 2-10%; the clay samples had
moisture contents on the order of 30- 40%.
Laboratory permeability measurements are
reported for four combinations of compac-
tion and moisture for each sample and
ranged from below the detection level to
48.71 x 10"12m2. In-situ permeabilities were
measured at four depths and ranged from
<0.0005 to 1050 x 10'12m2. Particle size
data are reported for 46 samples. The
predominant particle size was noted for
each sample as a simple screening clas-
sification. Sieve analyses for eight size
categories based on seven sieve sizes
ranged from 0.074 to 2.00 mm. The re-
sults of sedimentation (hydrometer) analy-
sis are presented in terms of the fractions
classified as sand, silt, and clay.
Radiological Characteristics
Soil gas radon concentrations include
both the initial sampling at a single depth
at the two primary stations at each site
and the later sampling in the vicinity of the
alpha tract burial stations. At 11 sites,
samples were collected at two depths at
the alpha tract (second visit). At 10 of the
sites, no soil gas sample was collected at
the second visit; this was usually due to
the fact that the buried alpha track detec-
tors could not be located as a result of
construction activities between the two vis-
its.
Soil gas radon concentrations ranged
from a few to over 10,000 pCi/L. The data
were not submitted to statistical analysis;
however, some observations can be made
by inspection:
1) The two primary stations at a site
generally had comparable levels on
the same sampling date.
2) About half of the 13 alpha track sta-
tions (sampled 6 weeks later) had
levels that were noticeably different
from those at the primary stations.
However, since the two types of sta-
tion were not sampled at the same
visit, it is not possible to determine
whether this is a time effect or a
spatial effect.
3) In the limited multi-depth sampling
at 11 alpha track stations, concen-
trations generally increased with
depth in the range of 0.30-0.75 m
(12-30 in.) when the concentrations
were greater than 100 pCi/L.
Radium-226 concentrations were 2 pCi/
g or less in 87% of the samples and less
than 1 pCi/g in 67%. One exception was
the Bartow samples which had concentra-
tions on the order of 11-13 pCi/g. At this
site, the upper 0.6 m (2 ft) consisted of
white/grey sand with pebbles and cobbles
and appeared to be a fill material placed
over the original natural soil. The other
exceptions were the Brooksville samples
(clay) and the Tallahassee A samples
which had concentrations on the order of
2-4 pCi/g. The fact that soil gas radon
concentrations at some of the sites where
soil concentrations were <1 pCi/g ap-
proached or exceeded 1000 pCi/L sug-
gests a radon source deeper than that
from which the soil sample was taken.
Results of emanation coefficient mea-
surements ranged from a few to about
40%. Since most of these samples had
low radium concentrations, the associated
emanation coefficient determinations have
a high degree of uncertainty.
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C.E. Roessler, R. Morato, D.L Smith, and J. Wherett are with The University of
Florida, Gainesville, FL 32611.
David C. Sanchez is the EPA Project Officer (see below).
The complete report, entitled "Characteristics of Florida Fill Materials and Soils—
1990," (Order No. PB94-176906; 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 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
Official Business
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