United States Air and Energy Environmental EPA/600/9-90/005C
Environmental Protection Research Laboratory January 1990
Agency Research Triangle Park NC 27711
Research and Development
ve/EPA The 1990 International
Symposium on Radon
and Radon Reduction
Technology:
Volume III. Preprints
Session IV: Radon Surveys
Session V: Radon Entry
Dynamics
Session VI: Radon in the
Natural Environment
Session C-V: Radon Entry
Dynamics—POSTERS
Session C-VI:
Radon in the Natural
Environment—POSTERS
February 19-23,1990
Stouffer Waverly Hotel
Atlanta, Georgia
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Session IV:
Radon Surveys
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IV-1
RADON EXPOSURE IN CONNECTICUT: ANALYSIS OF THREE STATEWIDE SURVEYS
OF NEARLY ONE PERCENT OF SINGLE FAMILY HOMES
by: Alan J. Siniscalchi, M.S., M.P.H. (1), Lynne M. Rothney, M.P.H. (2),
Brian F. Toal, M.S.P.H. (1) , Margaret A. Thomas, M.S. (3),
David R. Brown, Sc.D. (1), Maria C. van der Werff, B.S. (4),
Carolyn J. Dupuy, M.S., S.M. (1)
(1) State of Connecticut Department of Health Services
Hartford, Connecticut 06106-4474
(2) Yale University School of Medicine
(3) State of Connecticut Department of Environmental Protection
(4) U.S. Environmental Protection Agency Region I - work
performed while employed with the State of Connecticut
ABSTRACT
Statewide radon measures are needed to establish comprehensive population
estimates of risk. The Connecticut Department of Health Services has
measured indoor radon concentrations in over 5,000 living units which
represent nearly 1% of the homes statewide. Short-term exposure data
were obtained from both lowest livable areas (i.e., basements) and lowest
living areas in 3,378 houses. Long-term living area data were collected
in over 500 homes. Analysis of these data has shown associations with
home construction type including a strong positive correlation with house
age. Analysis of over 1,000 homes with energy use data did not reveal an
association between energy efficient homes and high radon levels.
Differences in air and water levels have been identified among various
geologic units. Consistent findings among the three surveys include
geometric mean basement and living area radon levels and percent of homes
exceeding 4 pCi/L.
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INTRODUCTION
The State of Connecticut Department of Health Services (DHS) began
receiving numerous telephone inquiries on radon following the discovery
of elevated indoor air radon levels in Pennsylvania (1). Since the DHS
lacked information on radon exposure in Connecticut, plans were made to
investigate the distribution of radon in the state. In addition to
providing information to residents concerned about radon, the Department
wanted to determine the extent of the radon problem in Connecticut. The
risk reduction priorities of the DHS needed to be refined by under-
standing the true hazard posed by this newly discovered residential
risk. Moreover, if elevated radon levels were identified in certain
areas of the state, then local health agencies could focus their risk
reduction resources in these areas. Since risk determinations require
exposure data, the DHS proceeded to assess Connecticut population
exposure to radon.
A pilot project and three studies have been performed. The first
study was the 1985-87 "Connecticut Radon Survey" (2). This study was
followed by an expanded 1986-87 "EPA-Connecticut Radon Survey" of
basement radon levels in 168 of Connecticut's 169 municipalities.
Results of the EPA-Connecticut Radon Survey were then utilized to
plan the 1987-88 "Household Testing Program" where 3,400 homeowners were
given radon testing kits in towns which were selected based on radon
potential or in towns not previously sampled.
THE CONNECTICUT RADON SURVEY
The Connecticut Radon Survey was conducted between 1985 and 1987 to
assess the predictive ability of geologic, hydrologic and household
factors on well water and indoor air radon. In the first phase, homes
were chosen in six areas thought to be potentially high in radon levels
on the basis of the Bedrock Geological Hap of Connecticut (3), and later,
on the basis of an aeroradioactivity survey (4). The second phase
expanded the survey to also include low and intermediate radon areas.
Information from local health department well completion reports were
also used. Private well water was sampled using the EPA scintillation
method from 262 homes. The indoor air radon level was sampled with a
single alpha track device placed in the living area for three winter
months in 202 of the homes from which water samples were taken. These
homes were located in 44 towns and represent sampling from 26 geologic
formations.
The private well water radon levels ranged from 100 to 130,240
picocuries per liter (pCi/L) with a geometric mean level of 3,179 pCi/L.
Twenty-six percent (26%) of the wells had water radon levels greater than
10,000 pCi/L. The long-term living area indoor air radon levels ranged
-------
from 0.1 pCi/L to 25.6 pCi/L, with a geometric mean level of 1.25 pCi/L.
Eleven percent (11%) of the homes with radon had levels greater than 4
pCi/L. Regression analysis estimated that 18% of the variation in indoor
air radon can be attributed to radon in private well water, with a water
to air ratio of 10,000 pCi/L to 1.6 pCi/L (C.I. - 0.80 to 3.40 pCi/L).
Figure 1 shows this relationship.
Geologic, hydrologic and household parameters were analyzed for their
ability to predict radon levels. Figures 2 and 3 show the mean water and
air radon levels respectively, compared to the bedrock classifications as
shown on the Connecticut portion (Figure 4) of a generalized bedrock
mapping scheme of New England (5). Geology was a significant predictive
factor of radon in both private well water and indoor air with granitic
and sedimentary formations associated with higher and lower radon levels
respectively, while the radon potential of bedrock may be generally
characterized by such data, it is possible that water radon levels alone
are sufficient to estimate the geologic radon potential. Indoor air
radon measurements represent radon emissions not only from bedrock, but
also from surficial materials and also appear to vary significantly with
various household factors.
Hydrologic factors, foundation type and energy efficiency were
examined. Only the depth of unconsolidated material overlaying the
bedrock had a strong positive correlation with private well water radon
levels. Homes with block wall foundations had higher indoor air radon
levels than those with other types of foundations. Homes characterized
by the homeowner as being more energy efficient did not have higher
indoor air radon levels than homes characterized as being less energy
efficient.
EPA-CONNECTICUT RADON SURVEY
During the summer of 1986 the DHS cooperated with the U.S.
Environmental Protection Agency (EPA) to conduct a survey of basement
radon levels in Connecticut using charcoal testing devices supplied and
analyzed by the EPA Eastern Environmental Radiation Facility in
Montgomery, Alabama. The survey design called for differing sampling
densities based upon radon potential estimations conducted by a geologist
from the Connecticut Department of Environmental Protection (DEP). The
radon potential was estimated using geological mapping, the Connecticut
Radon Survey results and aeroradioactivity mapping. A target sample
number from 7 to 15 samples per town was established based on the radon
potential estimation for each of Connecticut's 169 towns. The survey
design called for distribution of charcoal testing devices to 1600 homes,
and for placement in the lowest livable area (i.e. basement) of the house
for two days. The devices were placed during the winter of 1986-87 by
energy auditors from CONN SAVE, a non-profit energy conservation
organization. Homeowners were offered a radon test when they requested
-------
an energy audit. Testing was on a first-come first-served basis until
the target sample number was reached in each town. At the time of kit
placement, information on housing characteristics, air infiltration rate,
and house location were recorded by the energy auditor. Air infiltration
rates were later estimated with a computer model commonly used by energy
conservation organizations.
A total of 1,572 homeowners agreed to participate in the survey, with
a refusal rate of less than 1%. One hundred and forty seven or 9.4% of
the tests, were dropped from the analyses due to improper testing or
mail-in procedures. A total of 1,157 tests of detached home basements
were included for the detailed analysis reported here. Nineteen percent
(19%) of the basements tested exceeded the EFA guideline of 4 pCi/L.
There were significant differences (p/ 0.05) in the percentage of homes
with radon levels greater than 4 pCi/L between major areas of the state.
These regions were established by their estimated geological potential
for radon. Furthermore, correlation analysis demonstrated strong
associations between radon levels and geology. Detailed analysis with
regard to specific bedrock units also showed strong associations, with
homes above granitic rock units having higher radon values than homes
overlaying sedimentary rock units. Of the many housing characteristics
studied, the age of the house was the most predictive factor with older
housing having higher levels (see Figure 5). Fieldstone and block
foundations were also accompanied by higher radon levels compared to
concrete and concrete mix foundations (see Figure 6). No association was
found between radon levels and the estimated air infiltration rate.
These findings are consistent with those of the previous survey.
Geographic Information System (CIS) analyses of indoor radon data
with digitized aeroradioactivity mapping (4) showed a strong correspon-
dence between the percentage of homes with basement levels that were
greater than or equal to 4 pCi/L and the generalized aeroradioactivity
mapping as measured in counts per second gamma radiation (see Figure 7).
Since a review of radon distribution revealed that some elevated
radon occurs in all areas, the DHS issued an advisory in August 1987
stating that all Connecticut homeowners should have their houses tested
for radon. The DHS then established a full-time Connecticut Radon
Program.
HOUSEHOLD TESTING PROGRAM
In December of 1987 the Connecticut Radon Program began distribution
of free radon testing devices under the Household Testing Program (HTP).
The objectives of the HTP were: to provide free radon testing devices
-------
and appropriate placement instructions to residents living in areas
suspected of having high radon levels; to obtain additional data on radon
concentrations in selected Connecticut municipalities; and to examine the
ratio between basement and living area radon concentrations.
In planning the HTF, fifty-three cities and towns were identified by
a geologist employed with the Connecticut Department of Environmental
Protection (DEP) based on results of the previous two radon surveys and
existing information on terrestrial radiation and bedrock geology.
Thirty-eight of these municipalities were selected for the HTP based on
the ability and interest of the local health departments or other local
agencies to participate in the distribution of testing devices (see
Figure 8).
Each municipality was given 200 charcoal testing devices and asked to
recruit 100 volunteer households. One charcoal testing device was placed
in the basement or other "lowest livable area" and the second device
placed in the "lowest lived-in area." All testing device analyses were
conducted by the same contract laboratory. Three hundred and forty
households with living area radon concentrations over 4 pCi/L and/or
basement radon concentrations over 20 pCi/L received alpha-track devices
for long-term follow-up testing.
The results of the HTP were not different from those of the
EPA-Connecticut Survey and the Connecticut Radon Survey (see Table 1).
The data also revealed an apparently consistent 3:2 ratio between
basement and living area radon concentrations (6). Analysis indicated
that the basement radon level is strongly predictive of the upstairs or
living area radon level (R2-0.48, P/ 0.00001).
The program is now evaluating results of long-term (9-12 month) alpha
track devices provided to the 340 participants (10%) whose living area
radon levels exceeded 4 pCi/L or basement levels that exceeded 20 pCi/L.
The program also examined the influence of waterborne radon on indoor air
radon levels. Figure 1 showed the analysis of variation between radon in
water and indoor air radon levels for the Connecticut Radon Survey. When
HTP homes on private well water were compared to homes with public water
the ratio of living area to basement air levels was 0.75 ± 0.46 versus
0.49 ± 0.29 respectively (mean ± SD, N - 50). This effect was non-linear
which suggests that higher levels of water radon are more significant
contributors to indoor living area radon exposure.
DISCUSSION
The Connecticut DHS and DEP have collected radon data on 5,036
households. Information on housing characteristics and detailed
locations is available on nearly all of the units tested. Household
locations have been mapped on U.S. Geological Survey topographic maps at
-------
1:24,000 scale and digitized into the DEP computerized Geographic
Information System (CIS). This information has proven to be extremely
useful in evaluating the radon potential of specific areas of the state.
The CIS is being used to test correlations of radon occurance at
various concentrations with geophysical data, specific geological
materials and modifying environmental conditions. Statistical analyses
of radon indoor air and water data with respect to Connecticut geological
terranes and individual bedrock formations have produced geologically
stratified sampling schemes for the EPA - Connecticut Radon Survey and
the Household Testing Program. For the EPA - Connecticut Radon Survey,
CIS analyses have shown a strong correspondence between aeroradioactivity
mapping (4) and basement radon testing (see Figure 7). These analyses
produced statewide radon potential mapping that is being used as a tool
to increase our understanding of the locations of,homes with radon levels
above 4 pCi/L.
The aeroradioactivity data was also utilized by earlier researchers
in conducting an epidemiological study of cancer rates in Connecticut
(7). The weighted regression analysis by towns used by Walter, et al.
did not reveal an increased cancer rate by radiation level. However, the
authors cited the limited statistical power of the study which provided
only a small probability of detecting a radiation effect if a two-fold
excess cancer risk existed in the higher gamma areas. The present survey
data suggests that towns are too large a unit to detect cancer increases
from radon exposure.
The similarity in the results for both the percentage of homes above
the guideline and geometric mean radon levels are especially notable when
one considers the methodological differences in both device (short-term
charcoal and long-term alpha track) and home selection among each of the
three studies. For example, differences in bias of the selection among
the three studies is shown in Table 1. The selection of households for
the Connecticut Radon Survey and the Household Testing Program tended to
be toward areas with higher radon levels (although to a lesser degree in
the HTP). The homes tested in the EPA-Connecticut Survey were not
selected in areas that were known for high or low levels. Thus, the
selection bias of this study was neutral.
The results of these studies provided information to the Department
that suggested radon exposure in Connecticut was higher than expected.
Many local health departments then initiated their own surveys. This
information was also used to plan a number of educational campaigns
designed to encourage further testing among Connecticut residents.
The studies also provided information useful to the Department's
evaluation of its risk reduction priorities. An analysis of the survey
data has been used to generate estimates of the risk for developing lung
cancer from radon exposure in Connecticut. Table 2 displays the
-------
distribution of living area radon concentrations for the three studies.
Analysis of the distribution of this data using the risk tables provided
in the National Academy of Sciences BEIR IV report (8) and smoking
information would predict 280 excess lung cancers could occur each year
in Connecticut from exposure to radon in homes. Risk calculations using
a U.S. EPA model (9) predict similar rates.
An extrapolation of this information yielded estimates of additional
exposures to radon that occur in schools. Assuming a school population
of 542,000 students with 10 years of exposure, an estimated 425
additional cases of lung cancer could result from radon exposure in
schools alone (10). If, as chronic disease surveys (11) imply, that 19%
of elementary and secondary school of students smoke, the excess cancer
cases due to radon alone would be much higher.
This series of surveys illustrate the complexity of predicting radon
exposures from limited measures of radon. Additional factors which are
being investigated further are: the contribution of water radon in homes
with private wells, the influence of differences in bedrock type within
small geographic areas, and the radon contribution from unconsolidated
materials, differences in housing characteristics and lifestyles of the
population.
SUMMARY
The three Connecticut radon surveys show that a radon problem exists
in the state. The studies also provided information on the differences
in risk due to variability in exposure from housing type and location.
Information on the relationship between radon levels and geology will
continue to be developed to refine our knowledge of the locations and
conditions in Connecticut where radon may be of the highest risk. Local
agencies can then focus educational and outreach efforts in these areas.
The studies have been the foundation for the establishment of a
formal radon program within the DHS. Information from these studies will
continue to guide the Program's efforts in public outreach and
educational campaigns designed to encourage testing and appropriate
mitigation within all Connecticut structures.
With the exception of the charcoal testing devices provided by the
U.S. Environmental Protection Agency (EPA) for use in the EPA Connecticut
Radon Survey, the work described in this paper was not funded by the
EPA. Therefore, the contents do not necessarily reflect the views of the
Agency and no official endorsement should be inferred.
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ACKNOWLEDGEMENTS
The authors wish to thank Ms. Suzanne Lessard for her expert word
processing assistance in the preparation of this paper, Ms. Laurie Gokey
and Mr. Zygmunt Dembek for their review of the manuscript, and Mr. Marc
T. Rothney for the preparation of Figures 1, 2, and 3. The authors also
express their appreciation to the staff of CONN SAVE for their assistance
in the EPA-Connecticut Radon Survey, the local health and other officials
who participated in the Household Testing Program, and all the households
who participated in these surveys.
REFERENCES
1. Logue, J. and Fox, J. Health hazards associated with elevated levels
of indoor radon - Pennsylvania. Morbidity and Mortality Weekly
Report (MMWR). 34:657, 1985.
2. Rothney, L.M. Connecticut radon survey of private well water and
indoor air: assessing geologic, hydrologic and household
parameters. Connecticut Department of Health Services, Toxic Hazards
Section, Hartford, Connecticut, 1987. 45 pp.
3. Rogers, J. Bedrock geological map of Connecticut. Scale 1:125,000,
Connecticut Geological and Natural History Survey. 1985.
4. Popenoe, P. Aeroradioactivity and generalized geologic maps of parts
of New York, Connecticut, Rhode Island and Massachusetts. U.S.
Geologic Survey Geophys, Inv. Map. GP-359, Scale 1:250,000, U.S.G.S.
1966.
5. Olszewski, W., Jr. and Boudette, E.L. Generalized bedrock map of New
England, Scale 1:1,000,000, New Hampshire Water Supply and Pollution
Control Commission and U.S. EPA Region I, 1986.
6. Toal, B.F., Dupuy, C.J., Rothney L.M., Siniscalchi, A.J., Brown,
D.R., and Thomas, M.A. Radon exposure assessment - Connecticut.
Morbidity and Mortality Weekly Report (MMWR). 38:713, 1989.
7. Walter, D.S., Meigs, J.W., and Heston, J.F. The relationship of
cancer incidence to terrestrial radiation and population density in
Connecticut 1935-1974. American Journal of Epidemiology 123:1,
1986.
8. National Research Council Committee on the Biological Effects of
Ionizing Radiations. Health Risks of Radon and Other Internally
Deposited Alpha-Emitters (BIER IV). National Academy Press,
Washington, D.C., 1988. 602 pp.
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9. Oge, M. Current ORP estimate of radon-induced lung cancer deaths in
the general population. U.S. EPA memorandum, August 17, 1989.
10. Dupuy, C.J. and Rothney, L.M. Radon risk in schools. DHS
memorandum, December 21, 1988.
11. Unpublished data. Center for Chronic Disease, Urban/Rural Health,
Connecticut Department of Health Services. Connecticut Health Check
data 1988.
pCi/L
(air)
4.5.
4
3.5.
3-
2.5.
2.
1.5.
1.
STATE E3 GRANITIC GNEISS
n = NUMBER OF HOMES
n-116
0-5K 5-1 OK IO-20K 20-40K 40K
pCi/L (water)
Figure 1. Connecticut Radon Survey: geometric mean indoor air radon
levels by range of water radon levels.
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Sedtrrentary Besln
Extrusive Igneous'Sedimentary Basin
Two-Mica Granite
Mafic Plutonic
General Gneiss
Granitic Gneiss
Intermediate to Mafic Gneiss
Stratified Metamorphic
Carbonate Stratified Melamorphic
Quartzite Stratified Metamorphic
General Mixture
5
12
I
J7
63
II
61
9
J
16
5000 10000 15000 20000 25000 30000
pCi/L (water)
n - NUMBER OF HOMES
Figure 2. Connecticut Radon Survey: geometric mean water radon level by
generalized bedrock type.
Sedimentary Basin
Extrusive Igneous Sedimentary Basin
Two-Mica Granite
Mafic Plutonic
General Gneiss
Granitic Gneiss
Intermediate to Maftc Gneiss
Stratified Metamorphic
Carbonate Stratified Metamorphic
Quartzite Stratified Metamorphic
General Mixture
X'X'XvXvX'X]
•
•
XvX-XvX-XvX-X-X-
:x:::x:x;::>::::x::::::::::::::::::::;:;::x:::::l
i i i
.1
n
:::x:x:x:xvx:::x:::::::::x:::::x:::x:
X'X'X-X-X-XvXvX.X.X'X'XvX
x:Xv:::W::x:x:x:x:
F -4 1
0 0.5
JO
5
//
/
23
45
to
46
7
J
13
.5 2 2.5 3 3.5 4
pCi/L (air)
n ' NUMBER OF HOMES
Figure 3. Connecticut Radon Survey: geometric mean air radon levels by
generalized bedrock type.
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LEGEND
1. SEDIMENTARY BASIN
la. EXTRUSIVE IGNEOUS
SEDIMENTARY BASIN
2. TWO-MICA GRANITE
GNEISSES - GENERAL
GNEISSES OF GRANITIC
COMPOSITION
GNEISSES OF INTERMEDIATE
TO MAFIC COMPOSITION
3. GRANITES OF CALC-ALKA-
LINE COMPOSITION
10. ULTRAMAFIC ROCKS
4. ALKALIC PLUTONIC
ROCKS
5. PLUTONIC ROCKS OF
INTERMEDIATE
COMPOSITION
6. MAFIC PLUTONIC
ROCKS
11. STRATIFIED METAMORPHIC
ROCKS
lla. CARBONATE STRATIFIED
METAMORPHIC ROCKS
lib. QUARTZITE STRATIFIED
METAMORPHIC ROCKS
12. GENERAL MIXTURES OF ABOVE
UNITS (AREAS NOT SHOWN)
Figure 4. Connecticut portion, generalized bedrock map of New England
(modified from reference 5)
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0.0
(2-9) (10-24) (25-50) (> 50)
AGE OF HOUSE (YRS)
Figure 5. EPA - Connecticut Radon Survey: geometric mean radon levels
by age of house.
FIELD STONE
OTHER MIXTR.
o
5 BLOCK
1
g BLOCK&OTHER
b
o
w
STONE&CONCR.
CONCRETE
197
129
IB
20
755
0.0 0.3 0.5 0.8 1.0 1.3 1.5 1.8 2.0 2.3 2.5
PICOCURIES PER LITER
Figure 6. EPA - Connecticut Radon Survey: geometric mean radon levels
by type of foundation wall.
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— Basement Air Radon vs. Aeroradioactivity
^ < 300 300-500 500-700 700-900
°~ Aeroradioactivity (counts per second gamma)
Figure 7. EPA - Connecticut Radon Survey: percent frequency of
basements with 4 pCi/L radon levels by aeroradioactivity.
HOUSEHOLD TESTING PROliRfltl
CONNECTICUT TOUN SELECTION
H SELECTED FOR TESTING, UIMTER 1987-
'//. RECOrrtNDED FOR FUTURE TESTING
Figure 8. Household Testing Program: municipalities recommended and
selected for testing.
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TABLE 1. SUMMARY OF INDOOR AIR RADON SURVEYS CONDUCTED BY CONNECTICUT
DEPARTMENT OF HEALTH SERVICES
Characteristic
Bias*
Survey device
Connecticut
Radon Survey
(n=202)
High
Alpha-track
EPA-Connecticut
Survey
|n = 1157»)
Neutral
Charcoal
Household
Testing Program
In =3409!
High
Charcoal
Results
Location
of measurement
Basement
Lived-in area
pCi/L1
NT1
11%
Geometric
mean
(pCi/L)
NT
1.3
pCi/L
19%
NT
Geometric
mean
(pCi/L)
2.1
NT
pCi/L
21%
10%
Geometric
mean
(pCI/U
2.1
1.3
•Number of detached houses out of 1425 total homes tested.
fBias toward geologic locations with a higher probability of finding high radon homes.
'Picocuries per liter.
fNot tested.
(from reference 6)
TABLE 2. DISTRIBUTION OF HOME LIVING AREA RADON CONCENTRATIONS (HOUSE-
HOLD TESTING PROGRAM DATAl
Percent
Radon Concentration (pCi/L)
90
6
3
0.5
0.4
0.1
4 (geometric mean
4 - 9.9
10 - 19.9
20 • 49.9
50 - 99.9
& 100
-1.3 pCl/L)
2745F
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IV-2
RESIDENTIAL RADON SURVEY OF TWENTY-THREE STATES
by: Jacolyn A. Dziuban1
Maureen Anderson Clifford1
S. B. White2
Jane U. Bergstein2
Barbara V. Alexander2
1. U. S. Environmental Protection Agency
2. Research Triangle Institute
ABSTRACT
This paper describes the cumulative results from 23 states that
conducted surveys with the assistance of the Environmental Protection Agency
(EPA) during the 1987, 1988 and 1989 heating seasons. It also describes the
survey designs, provides population estimates of medians and means, and
defines the proportion of households in each state exceeding specified
exposure levels.
The goal of these surveys was twofold: to locate areas with elevated
radon levels, and to characterize the statewide frequency distribution of
radon screening measurements. Each survey was designed to provide a
statistically valid comparison of radon levels in households in defined areas
within each state and for each state as a whole. Overall, approximately
34,400 randomly-selected households provided screening measurements.
Experience gained through these surveys will be highlighted and applied to the
next series of state surveys scheduled for the winter of 1990.
This paper has been reviewed in accordance with the U. S. Environmental
Protection Agency's peer and administrative review policies and approved for
presentation and publication.
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IV-3
SURVEYS OF RADON LEVELS IN HOMES BY UNIVERSITY OF
PITTSBURGH RADON PROJECT
Bernard L. Cohen
University of Pittsburgh
Pittsburgh, PA 15260
ABSTRACT
Data are analyzed on measurements of radon levels in numerous U.S. homes, accompanied
by responses to questionnaires. Substantial bias reduction was accomplished by use of ques-
tionnaire responses, leaving 37,000 measurements in living areas and 33,000 in basements for
the analysis. Variables studied include level with respect to ground where measurement was
made, room type, age of house, recent weatherization actions, draftiness, location (urban-
suburban- rural), air pollution, market value of house, annual household income, educational
attainment of head of household, cigarette smoking, whether the house is rented or owner-
occupied, and geographic section of U.S. Mean radon levels are determined for each response
to questionnaire items (correlations), and for each pair of responses (cross correlations).
Many interesting correlations and cross correlations are found, and their explanation and
consequences are discussed.
From July, 1985 to January, 1988 the University of Pittsburgh Radon Project and its
successor (starting in May, 1987), The Radon Project provided measurements of radon levels
in homes almost exclusively in response to mail orders (cost - $12.00) stimulated by media
publicity. This yielded a fairly broad national coverage. Each measurement was accompanied
by a questionnaire which was filled out by the householder and returned before the result
of the measurement was known. The purpose of this paper is to present results of the
statistical analysis of these data. Preliminary reports on this work have been published in
connection with presentations at conferences (Cohen and Gromicko 1988), but they were
based on portions of the data and incomplete analysis.
The measurement and quality control procedures have been described previously (Cohen
and Nason 1986, Cohen 1988, Cohen and Cohen 1989). Diffusion barrier charcoal adsorption
collectors were exposed for seven days, after which the quantity of radon collected was
measured by 40 minute counts of gamma rays under the 295 KeV, 352 KeV, and 609 KeV
photoelectric peaks with Nal (Tl) scintillation detectors. Results are corrected for seasonal
variations to best represent annual averages (Cohen 1989). Statistical uncertainties are about
45% at 18 Bq m~3, 25% at 37 Bq m'3, and less than 10% above 120 Bq m'3.
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Bias Reduction
Since our purpose is to obtain statistically meaningful data, it is important to reduce the
biases in selection of houses measured as much as possible. Since these measurements are
purchased by the householder, the potential for bias is very great. Bias reduction is done by
use of the questionnaires.
One obvious source of bias is that poor people are less able to afford purchase of a
measurement. To overcome this, the questionnaire includes questions about socioeconomic
status, and data can be stratified on that basis. Another source of bias is that houses with
high radon levels are much more likely to be remeasured. The questionnaire asks* "Has the
radon level in this house been measured previously?" The ratio of mean radon levels for
yes/no answers is 1.93 [1-61]; here and elsewhere in this paper, the first figure is for the main
living areas of houses, and the figure in brackets is for basements. The expected effect is
clearly evident, and it has been eliminated by requiring a "no" answer to the question. Our
study is therefore restricted to first measurements on houses.
Another obvious source of bias is that a person is more likely to purchase a measurement
if a nearby neighbor has a high radon level. The questionnaire therefore asks "How far away
is the closest house you know to have a high radon level". The ratios of mean radon levels for
distance D to distance 16 km or more (or don't know) are: 0=0-1.6 km, 1.88 [2.11]; D=1.6-8
km, 1.20 [1.26]; D=8-16 km, 1.03 [1.15]. Based on these results, data were eliminated if 0 is
less than 8 km.
The remainder of this paper deals with analysis of the 70,000 measurements described
above. We will present mean radon levels for various situations. This raises the question
of whether to use geometric or arithmetic means. A problem with the latter is that it is
heavily influenced by very large measurements which, since they occur infrequently, intro-
duces "random" fluctuations into the results. This is avoided by using geometric means. The
latter would be heavily influenced by measurements close to zero which have large statistical
uncertainty but this problem is avoided by setting a lower limit of 11 Bq in~3 (0.3 p Ci IT1);
any measurements below that were set equal to this lower limit. Mean radon levels will be
presented, in units of the widely accepted world mean for houses, r0, where r0 = 37 Bq m~3
(1.0 p Ci L-1).
*This question was suggested to the author by David Gur.
-------
Questionnaire Items
The questionnaires were changed frequently, but the most persistently asked questions
(names for later reference given in capital letters) were:
- LEVEL - "Is the room where test was made (a) mostly below ground level, (b) lowest floor
above ground, (c) second floor above ground, (d) third or higher."
- ROOM - "Type of room where test was made (e.g., livingroom, bedroom) "
- AGE - "Age of house (If not known, best guess)"
- WEATHERIZE - "How much has been done since 1975 to reduce heat loss from your
house by weather-stripping, closing gaps under doors, sealing windows, etc.?
much, little, nothing"
- DRAFTY - "How drafty is your house compared to other houses in your area?
more than average, about average, less
than average"
- LOCATION - "The location of the house is (check one):
urban, suburban, rural"
- POLLUTION - "Is the air pollution in your area (check one):
less than average, about average, worse
than average?"
- VALUE - "What is the approximate market value of your house?"
- INCOME - "Annual household income?"
- EDUCATION - "Head of household's years of formal education beyond eighth grade (for
example, high school graduate = 4)?"
- CIGARETTES - "How many cigarettes per day are smoked by all members of your house-
hold combined?"
- OWN - RENT - "Do you own or rent this house?"
Results
The analysis consists mainly of determining mean radon levels for each response to each
questionnaire item for the total file and for each geographic area, and also for each pair of
responses which we refer to as cross correlations. Since complete tables of cross correlations
would be far too voluminous for this paper, these results will mostly be presented through
discussion.
-------
In Tables 1-3, for the total file the first entry (in parenthesis) is the number of responses
in hundreds, the second entry is the mean radon level in units of r0, and the third entry is
the ratio of the mean radon level to the one designated l.QO. For the separate geographic
areas, the second of these entries is omitted.
Level and Room
Table 1 gives the results for LEVEL and ROOM. It is evident that basements which are
mostly below ground have about twice the radon level of first floor living areas. Levels on
second floors are a few percent lower than on first floors. Only 4% of our measurements are
from above the first floor, and only 0.2% are from above the second floor but, while statistics
are poor, they are consistent in indicating substantially lower radon levels on third floors
and above. High rise apartment dwellers are clearly grossly under-represented in our data.
The results on ROOM types in Table 1 can be better understood with the aid of the
cross-correlation with level, shown in Table 4, with the last column giving the percent of
cases where the room was mostly below ground. We see that the reason why family rooms,
bedrooms, and halls in Table 1 have higher average radon levels than living rooms, dining
rooms, and kitchens is because they are more frequently below ground. This represents
another type of measurement bias: it seems probable that far less than 27% of U.S. bedrooms
are below ground, but that below ground bedrooms are an incentive to purchase radon
measurements. The residual room-to-room variations in Table 4 may be due to variations in
the fraction of the room that is below ground; for example, "mostly below ground" rooms
may average 60% below ground for living rooms vs. 90% for basements. Another factor is
that below ground rooms that are used as living areas are less likely to have cracked walls
and floors.
There have been claims that kitchens are not a suitable place for radon measurements.
The fact that average levels are similar in living rooms, dining rooms, and kitchens in Tables
1 and 4 is strong evidence to the contrary.
Results for other questionnaire items are listed separately for living areas in Table 2
and for basements in Table 3. The first row of these gives mean radon levels for the entire
data files - 1.68 for living areas and 3.34 for basements - and also shows the number of
measurements in each geographic area.
Age
The results on AGE (of houses) indicate that radon levels increase during the first year.
Houses 1 - 9 y old have the highest levels, and levels decrease monotonically with increasing
age up to 80 y old where they are only about | as high. For houses more than 80 y old,
radon levels increase. The decrease out to 80 y and the increase beyond is observed for
both living areas and basements; for all geographic areas; for all degrees of weatherization,
draftiness, or pollution; for urban, suburban, or rural locations; for houses of all value above
$40,000; for occupants of all EDUCATION, and of all incomes above $15,000 per year; and
for both owner-occupied and rented houses. The only exceptions are houses valued at less
than $40,000, or with occupant annual incomes below $15,000. For these, radon levels seem
to increase slowly with AGE beyond 5 y.
-------
Data on the former are shown in Table 5. The bottom row, which gives the ratio of radon
levels for age 0-9/age 50-79, shows that this ratio increases monotonically from the lowest
to the highest value houses. Also notable from Table 5 is the fact that expensive houses are
predominantly new while low cost houses are predominantly old, with a steady progression
between these extremes as the value changes.
Weatherize
The WEATHERIZE results in Tables 2 and 3 yield the surprising conclusion that
tightening houses to conserve fuel has done essentially nothing to increase radon levels except
perhaps in the SC-W area. With that exception, the most consistent finding is that houses
where "little" has been done to weatherize have lower radon levels than those that have done
"nothing" or "much". It is difficult to imagine an explanation for that behavior.
The ratio of mean radon levels for houses where "much"/"nothing" has been done is
1.06 for living rooms, 1.06 for dining rooms, 1.00 for kitchens, 0.97 for family rooms, 1.07
for bedrooms, 1.08 for halls and 0.99 for basements; there are no large differences among
the various rooms. It is 1.02 [1.06] for houses less than 10 y old, increasing with age to
1.27 [1.21] for houses 50-79 y old, which seems reasonable since new houses would not have
as many cracks, but it drops back to 1.12 [1.10] for ages over 80 y. It is 1.21 [1.09] for
urban houses, 1.07 [0.98] for suburban, and 0.98 [0.95] for rural; perhaps weatherizing rural
houses includes measures which prevent entry of radon from the ground(?). For houses that
are more drafty than average, average, and less drafty than average, the "much"/"nothing"
ratio is respectively 1.23 [1.67], 0.98 [0.96], and 0.93 [0.84]. This means that weatherizing
increases radon levels only in exceptionally drafty houses, where the weatherization probably
consisted mainly of sealing openings. In houses that are not drafty, this was presumably not
done and perhaps insulation was added which might act to reduce radon entry. Of course,
the judgement of how drafty the house is refers to the time of the measurement which is
after the weatherizing has been completed.
The "much"/"nothing" ratio decreases monotonically with increasing values of the house:
1.26 [1.01] for less than $40,000; 1.14 [1.08] for $40-75,000; 1.01 [0.97] for 875-130,000; 0.93
[0.97] for $130-200,000; and 0.97 [0.88] for over $200,000; apparently weatherizing does most
to reduce air exchange with outdoors in lower cost housing. A similar pattern for the ratio
appears in the cross correlation with income: 1.15 [1.12] for incomes less than $15,000 per
year; 1.04 [1.04] for $15-25,000; 1.07 [1.01] for $25-45,000; 0.99 [0.97] for $45-70,000; and 0.90
[0.92] for over $70,000. For owner-occupied houses, the ratio is 0.98 [0.94] vs. 1.19 [1.14] in
rented houses. In summary weatherizing has increased radon levels by 15-20% in low cost
houses, occupied by low income families, but has actually reduced radon levels in expensive
houses owned and occupied by high income families. Perhaps wealthier people weatherize by
improving insulation which does not affect air exchange, whereas poorer people seal cracks
which inhibits air exchange and thereby increases radon levels.
It is interesting to note that the fraction of respondents who did much/little/ nothing
to weatherize is about the same for all income levels, roughly 2/2/1. One might think that
high income people would have done more because they are better able to afford the costs
-------
of weatherizing, but on the other hand they are also better able to afford the cost of heating
fuels.
Only 20% of our respondents said they have done nothing to weatherize their houses since
1975, whereas typical estimates are that about 50% of all houses have been weatherized. This
can be explained by the fact that people who purchase radon measurements are untypically
interested in home improvement.
Drafty
The correlations with how drafty a house is are large and consistent in Tables 2 and 3,
as is expected from the fact that drafty houses have more air exchange with outdoors where
radon levels are much lower than indoors. The ratio of mean radon levels in houses less
drafty/more drafty than average is 1.56 [1.47] for our total files, and for geographic areas it
is 1.58 [1.48] in NE (-NJ), 1.47 [1.38] in NJ, 1.48 [1.34] in SE, 1.59 [1.36] in MW, and 1.57 in
SC-W. It is 1.39 in living rooms, 1.40 in kitchens, 1.76 in family rooms, 1.64 in bedrooms,
and 1.46 in basements, with much of this variation explainable by statistics. There is no
clear trend with age of the house, although there may be a peak at 10-19 y where the ratio
is 1.80 [1.68], and the effect seems to be reduced for houses over 80 y old, ratio = 1.09 [1.22].
There does seem to be a dependence on weatherization activities; for houses where much,
little, and nothing has been done to weatherize, the ratio is respectively 1.44 [1.12], 1.55
[1.40], and 1.91 [2.23]. As suggested above, perhaps weatherizing drafty houses consisted
largely of sealing openings, which did increase radon levels.
For urban, suburban, and rural houses, the ratio is respectively 2.08 [1.55], 1.52 [1.41],
and 1.49 [1.53], which seems to indicate that draftiness plays a more important role in urban
homes. There is no consistent trend in the ratio with socioeconomic factors.
The ratio is substantially higher for owner-occupied than for rented houses, 1.58 [1.41]
vs. 1.16 [1.25]. Perhaps rented houses have more very small openings which contribute in
an important way to air exchange rates without affecting draftiness. Only 4.5% [4.0%] of
owner-occupied houses, vs. 17% [17%] of rented houses were judged to be more drafty than
average.
Location
The data in Tables 2 and 3 clearly indicate that rural houses have substantially higher
radon levels than urban and suburban houses. One possible explanation is that rural areas
are more windy, leading to stronger chimney effects which cause radon to be sucked in from
the ground. Another suggestion^ is that urban sewer drains go into storm sewers whereas
rural drains go into the ground, leaving an open path for radon to come out of the ground,
into the house. There may be other construction differences between urban and rural houses
to explain this effect. The result is quite important since it means that urban people, who
have more lung cancer, have lower radon exposure.
For most geographic areas, Tables 2 and 3 indicate that radon levels are substantially
higher in suburban than in urban houses, but a major exception here is the Midwest (MW).
This last is a "fluke" resulting from the fact that urban and suburban measurements came
-------
from different areas; urban measurements came heavily from Columbus and Dayton, OH and
Des Moines, IA, where radon levels are high, while one third of the suburban measurements
are from the Chicago area where radon levels are comparatively low.
Since this case represents a potential serious weakness in this type of study, we consider
it in more detail with reference to Table 6 where the geogrphic area is divided into its three
principal components by zip codes. Note that the middle zip code range has much higher
radon levels than the other two, and it includes far fewer suburban cases but more urban
cases (note that what is perceived as "urban" in Iowa is not necessarily the same as in the
Chicago area). It is easy to calculate averages from the data given, and in doing so one finds
that, although the urban/suburban ratio (last column of Table 8) is less than unity for each
of the three components, it is substantially greater than unity when all three are combined.
On the other hand, it should be recognized that when the whole nation is considered,
with its multitude of variations in types of urban and suburban areas located in various
geologic settings, the correct conclusion, that suburban areas have higher radon levels, does
come through, and it also comes through in the majority of individual geographic areas.
While the question of urban vs. suburban radon levels involves some complications, there
can be no question but that rural houses have appreciably higher radon levels than either.
For our entire data file, the rural/suburban ratio is 1.31 in living rooms, 1.26 in dining rooms,
1.28 in kitchens, 1.29 in bedrooms, 1.34 in halls, but 1.47 in basements and 1.49 in family
rooms. It is 1.45 for rooms mostly below ground vs. 1.28 on first floors and 1.24 on second
floors. This may indicate that the reason for the difference is in the basement source.
The rural/suburban ratio vs. age of the house is 1.30 [1.26] for age 0-4, 1.23 [1.39] for
age 5-9, 1.23 [1.44] for 10-19, 1.23 [1.43] for 20-29, 1.24 [1.47] for 30-39, 1.26 [1.38] for age
40-49, 1.53 [1.48] for age 50-79, and 1.50 [1.25] for ages over 80 y. It is 1.26 [1.46] for houses
that have done much to weatherize, and 1.27 [1.48] for those that have done nothing. It is
1.29 [1.31] for drafty houses vs. 1.27 [1.42] in houses that are less drafty than average. We
see in Table 7 that the ratio increases with increasing value of the house; expensive rural
houses have much higher radon levels than expensive suburban houses, but there is far less
difference for low cost houses. However, there is no indication of such a trend with income:
progressing from the lowest to the highest income bracket gives rural/suburban ratios 1.24
[1.51], 1.35 [1.45], 1.30 [1.46], 1.28 [1.56], 1.28 [1.41]. The ratio is somewhat higher for rented
than for owner-occupied houses, 1.51 [1.63] vs. 1.33 [1-44].
Pollution
The results in Tables 2 and 3 indicate that there is a clear negative correlation between
air pollution and mean radon levels. High air pollution regions have lower levels than low
pollution regions for each geographic section of the nation in both living areas and basements.
It is difficult to concoct a direct cause-effect explanation; the most obvious one would be
that in polluted areas people do not open their windows as much, but that would increase
indoor radon levels, contrary to our finding. An obvious confounding relationship is that air
pollution is highest in urban areas where we have found radon levels to be low.
The cross-correlation between LOCATION and POLLUTION is shown in Table 8. It is
true that the great majority (71%) of rural houses are in regions of below average pollution,
-------
while most suburban (62%) and urban (64%) houses are in areas of "average" pollution.
Moreover 9% of urban houses, vs. only 4% of suburban and 1% of rural houses are in "above
average" pollution areas. But still, among rural houses only, or among suburban houses only,
or among urban houses only, low pollution areas have higher radon levels than high pollution
areas by substantial factors both in living areas and in basements. One might assign part of
the explanation to varying judgements on what is high or low pollution, or what is urban or
suburban, or what is suburban or rural. But even suburban and rural highpollution areas
have substantially lower radon levels than low pollution urban areas. This would seem to
imply that the negative correlation between air pollution and radon is not due only to urban-
rural effects.
The low/high pollution ratio of mean radon levels is 1.43 in basements, 1.31 in first floors,
and 1.19 on second floors. This might be interpreted as indicating that the difference is due
to basement entry. There is little variation in this ratio with room type (other than it is
somewhat higher in basements and family rooms), with age of the house, with how much
has been done to weatherize, or with how drafty the house is. There is also no systematic
variation with any of our socioeconomic factors, value of the house, household income, or
education of head of household. It is higher in rented than in owner-occupied houses, 1.83
[1.53] vs. 1.23 [1.37]. In summary, radon levels are substantially higher in low pollution than
in high pollution areas, there is evidence that this is not simply due to urban-rural effects,
but there is no clear hint from our studies of what these other causes might be.
Value
The results in Tables 2 and 3 seem to indicate that houses valued at less than $40,000
have about 15% lower radon levels than others, and there is a tendency for expensive houses
to have lower levels than intermediate value houses. Mean radon levels in the cheapest houses
are lower than in any other value category in 4 [3] of the 5 geographic areas and are second
lowest in the remaining 1 [2] categories. They have the lowest mean radon level in kitchens,
bedrooms, and basements, but the most expensive houses have the lowest in living rooms,
dining rooms, family rooms and halls. Explanations for this are difficult to concoct.
The cross correlation between value and age is shown in Table 5. We see there that for
living areas of houses less than 30 y old, the least expensive houses have substantially lower
radon levels than the others, but for houses more than 30 y old, the least expensive houses
have the highest radon levels. For basements, they have the lowest levels up to age 20, and
the second highest levels above age 50. This switch-over can perhaps be explained by the
fact that older low-value houses were often originally constructed as expensive houses but
their value deteriorated by aging or by changes in the neighborhood.
*t This suggestion was offered by David Gur.
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About 10% of the "more drafty than average" houses, but only 3% of the "less drafty
than average" houses are valued at less than $40,000. Among the more drafty houses, radon
levels are nearly constant but declining with increasing value of the house, but for houses
of average or lower draftiness, radon levels are lowest for the least and most expensive,
and highest at intermediate value. About 13% of the urban houses, but only 2.5% of the
suburban and 6% of the rural houses are valued below $40,000.
The cross correlation between LOCATION and VALUE is given in Table 7. We see there
that lowest value houses have higher radon levels than expensive houses in urban areas, but
the former have by far the lowest levels in rural houses. Intermediate value houses have the
highest radon levels for all locations.
The cross correlation between VALUE and INCOME is given in Table 9. As expected
we see that low income people live in low value houses and high income people live in high
value houses with a steady progression between. But for each income level independently,
intermediate value houses have the highest radon levels.
For owner-occupied houses, radon levels are lowest for the least and most expensive
houses with a peak at about $75,000, but for rented houses low value houses have higher
radon levels and these levels decline steadily with value.
Income
Table 2 indicates that houses of lowest income people have about 15% lower radon con-
centration than others, with no clear trend for incomes above $15,000 per year. According
to Table 3, there is essentially no variation of radon level with income for basements.
The ratio of radon levels for annual incomes <$15,000/>$70,000 is 0.87 for living rooms,
0.70 for dining rooms, 0.92 for kitchens, 0.95 for family rooms, 0.69 for bedrooms, 0.87 for
halls, and 0.94 for basements. The cross- correlation between INCOME and AGE is similar
to that between VALUE and AGE (Table 5), with low income families having lower radon
levels in new houses and higher levels in old houses, but the differences are less sharply
defined here.
The ratio of radon levels for <$15,000/>$70,000 is 0.83 [1.04] for those who have done
"much" to weatherize, 0.76 [0.93] for those who have done "little" and 0.65 [0.85] for those
who have done "nothing". This monotonic trend confirms our previous conclusion that
weatherizing increases radon exposure for poor people much more than for rich people. This
ratio is 0.82 [0.84] for drafty houses, 0.78 [0.95] for houses of average draftiness, and 0.93
[1.02] in "less drafty than average" houses. Apparently the effect of income is largest in
drafty houses, and almost disappears in houses that are not drafty.
This ratio is 0.84 [0.96] for urban, 0.76 [0.90] for suburban, and 0.73 [0.96] for rural
houses, and it is 0.89 [0.96] for owner-occupied houses vs. 0.72 [0.82] for rented houses.
From Table 9 we note that for expensive houses radon levels increase monotonically with
increasing income, but for houses valued at less than $40,000, averaging between living areas
and basements there is a slow monotonic decrease with increasing income. Low income people
living in expensive houses and high income people living in cheap houses have substantially
lower radon levels than people living in houses matched to their income.
-------
Education
The questionnaire item on head of household's years of formal education beyond eighth
grade was apparently widely misunderstood because the majority of responses correspond
to post-baccalaureate college education. Perhaps it was interpreted as total years of formal
education. Nevertheless, the data do provide some information on trends of mean radon
levels vs. education on a relative scale.
There is some indication in Tables 2 and 3 of a slight trend for more educated people to
have higher radon levels. The ratio of mean radon levels for most/least educated is 1.03 in
living rooms, 1.09 in dining rooms, 1.03 in kitchens, 1.15 in family rooms, 1.04 in bedrooms,
1.05 in halls, and 1.14 in basements.
The least educated have the lowest radon levels, averaging between living areas and
basements, for houses of all ages, although the differences are by only a few percent for houses
over 40 y old. They have the lowest radon levels for each response to the WEATHERIZE
question, for each response to the DRAFTY question, for each response to the LOCATION
question, for each response to the POLLUTION question, for each but the lowest VALUE
of the house response, for all but one INCOME bracket, and for owner-occupied - but not
for rented-houses. One reason for this unusually high degree of consistency is that there are
reasonably good statistics for all responses to the EDUCATION question. The conclusion is
that homes in which the head of household did not finish high school have about 10% lower
radon levels than average.
Cigarettes
The results in Tables 2 and 3 clearly indicate that households with cigarette smokers
have substantially lower radon levels than the others, but for some strange reason it seems
like the difference decreases with increasing number of cigarettes smoked. It should also be
noted from those tables that only 17% of all people who purchased radon measurements
have smokers in their households, whereas 33% of American adults are smokers.
The ratio of mean radon levels between non-smokers and the average of the three cate-
gories of smokers (CIGARETTES=0/>0) is 1.13 in living rooms, 1.19 in dining rooms, 1.13
in kitchens, 1.06 in family rooms, 1.11 in bedrooms, 1.08 in halls, and 1.12 in basements.
Our earlier indication that this ratio is much larger in living rooms and dining rooms (Cohen
and Gromicko 1988) proved to be misleading.
The ratio is 1.06 [1.07] for houses of age 0-4, 1.12 [1.12] for age 5-9, 1.10 [1.10] for age
10-19, 1.06 [1.10] for age 20-29,1.08 [1.11] for age 30-39, 1.08 [1.08] for age 40-49, 1.10 [1.07]
for age 50-79, and 1.03 [1.12] for age over 80. Clearly there is little or no correlation with age
of the house. There is similarly little correlation with how much has been done to weatherize
and with whether the location is urban, suburban, or rural. For drafty houses, the ratio is
1.30 [1.15] whereas for average and less drafty houses it is respectively 1.03 [1.21] and 1.11
[1.07]. 7.7% [5.0%] of smokers vs 4.3% [3.8%] of non-smokers reported their houses to be
excessively drafty.
There does seem to be a correlation with value of the house and income. The 0/>0
ratio is 1.32 [1.30] for house values below $40,000, 1.17 [1.18] for $40-75,000, 1.11 [1.01] for
10
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$70-130,000,1.10 [1.10] for $130-200,000, and 0.95 [1.03] for > $200,000, and it is 1.22 [1.22]
for incomes below $15,000 per year vs. 1.10 [1.10] for annual incomes over $70,000. The
ratio is about the same for owner-occupied as for rented houses — 1.14 [1.13] vs. 1.16 [1.10].
In summary, houses of cigarette smokers have about 15% lower radon levels than houses
of non-smokers, with the effect almost twice as large for low income families living in low
value houses, and almost disappearing for high income people living in high value houses.
Own-rent
The results listed in Tables 2 and 3 clearly indicate that owner-occupied houses have
higher radon levels than rented houses; the own/rent ratio is 1.28 [1.14]. This is important
because rented houses are grossly under-represented in our data base.
Cross correlations are hindered by the small numbers of rented houses, leading to rela-
tively large statistical uncertainties. The own/rent ratio is 1.21 for living rooms, 1.23 for
dining rooms, 1.31 for kitchens, 1.16 for family room, 1.23 for bedrooms, 1.50 for halls (with
poor statistics), and 1.14 for basements. There is little systematic variation with age of
the house except that for houses over 50 years old basement ratios fall below 1.00. The
ratio is 1.24 [1.12] in houses where "much" has been done to weatherize, vs. 1.50 [1.36]
where "nothing" has been done. Apparently weatherized rented houses are more like owner-
occupied houses. The ratio is only 0.99 [1.07] in drafty vs. 1.35 [1.21] in "less drafty than
average" houses. The ratio is 1.48 [1.20] in urban, 1.28 [1.17] in suburban, and 1.13 [1.04] in
rural houses, a monotonic relationship. It is 1.08 [1-19] in areas where air pollution is below
average vs. 1.60 [1.34] where pollution is above average, a rather large difference which is at
least partly related to the urban- rural difference.
The own/rent ratio is below unity, 0.82 [1.06], for houses valued at less than $40,000,
but increases with value to 1.16 [0.98] for $40-75,000, 1.38 [1.14] for $75-130,000, 1.21 ]1.52]
for $130-200,000, and 1.48 [1.27] for >$200,000. The cross correlation with income seems to
behave differently, 1.39 [1.38] for income <$15,000 per year, 1.08 [1.12] for $15-25,000, 1.36
[1.07] for $25-45,000, 1.56 [1.31] for $45-70,000, and 1.13 [1.19] for >$70,000. It is difficult
to reconcile this difference except as statistical fluctuations. There is no systematic trend in
the own/rent ratio vs. education of head of household.
In summary, the own-rent ratio seems to vary systematically with several factors but the
reasons for these variations are obscure. Perhaps many of them are due to poor statistics as
there are less than 100 rented homes in most categories.
References
Cohen, B.L.; Nason, R. A diffusion barrier charcoal adsorption detector for measuring radon
concentrations in indoor air. Health Phys. 50: 457-463; 1986.
Cohen, B.L.; Gromicko, N. Variation of radon levels in U.S. homes with various factors.
Jour. Air Polltuion Control Assn. 38: 129-134; 1988.
Cohen, B.L.; Performance characteristics of DBCA radon detectors. Had. Protection mag-
net. 5:47-54; 1988.
11
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Cohen, B.L.; Cohen, F.B. Error prevention at a radon measurement service lab. Rad.
Protection Mngmt. 6:43-47; 1989.
Cohen, B.L.; Seasonal variations of radon levels in homes. Health Phys. - submitted; 1989.
The work described in this paper was not funded by the U. S. Environmental
Protection Agency and therefore the contents do not necessarily reflect the
views of the Agency and no official endorsement should be inferred.
12
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Table 1: Mean radon concentration vs level with respect to ((round and v« room i\pv
for various geographic areas of the United States -living" refers to the rooms luted
other than •basement1' Geographic areas refer to up codes- NJ 07000-0899!). M:
0-19999. bK - 20000-39999, MW - 4000-69999. SC + VV 70000 99999 Under • I'S
total" column, the figure in parenthesis is number of measurements (in hundreds), the
next number is the mean radon level in units of r0 and the third number is the ratio of
the mean radon level to the one marked LflQ in the game column in other columns.
the second of these numbers is not included
RESPONSE
LEVEL :
below ground :
•baMaane
-living
lit above grd :
•baMDnnt
-living
2nd above grd :
)rd or higher •
ROOM
beeeaenc
living rood
dining roooj
bedroea
fully rooei
hall
klcehon :
U S TOTAL
(251)- 3 39-1 96 •
( 3l)-2 86-1 65 :
( S)-2 43-1 40 :
(1S7}-1 73-1.00 •
( 20) -1 (2- 94 '.
( 1)-1 04- 60
:
(298)-J 32-2.27 .
(106)-1 46-1.00 :
( 26)-l 40- 96 :
( 60)-1.«3-1.25 .
( 80) -2 05-1 40 .
( 12)-1.77-1.21 .
( 50) -1 46-1.00 :
NE (-NJ)-
(92) -2 09 •
( 8)-l 68
( 3)-l 41 .
(47).JJ)fl :
( 7)- 91
( 3)- 51 .
(104) -2 44 .
( 33).JJffi. .
( 8). .92 :
( 13)-1 14 .
( 20) -1 70 •
< 3)-l 17 .
( 14). 1 02 .
NJ
(47)- 2 12 :
{ 2)-1.62 •
( 1)-1.«4 !
(23)-UUl .
( 4). 94 .
( 2)- 70
•
(70). 2. 46 :
(28)-.U|Q. :
( 8)- 98 i
(12)-1.21 :
(22)-l J4 •
( 3)-l 24 :
(14). 1.07 :
SE
(31)- 2. 02 .
( J)-1.J6 •
-
( 1)-1 46
(3D-XJIO..
( *>• 99
( 2)- .63 .
(40). 2. 38
(16)OJia
( 4). 1. 01 •
(14). 1 28 :
(IS)- 1.44
( 2)-l 22 •
( 8)-l 08 '.
KU
(69) -I 77 .
(ll)-l 4J :
( 1)-1 22 •
(33)-U)Q_:
( 3)- 88 •
( 2)- 54
(72). 1.92 .
(17)-.Lm
( 4). 1.01 :
(ll)-l 33
(17)-1 26
( 3)-1.29 !
( 8)-l 04
SOW
( 8)-2 52
( 4). 2 07
( 5)-l 00
(2U-UU1
( 2)-l 16
( 2)- 72
( 9). 2 30
(12).J_flO,
( 2). 96
( 9)-l 17
( 0-1 25
( I)- 95
( 5)- 89
-------
Table 2: Mean radon levels from measurements in living areas for various responses to
questionnaire items See caption (or Table I
RESPONSE
0-1
1-9
10-19
20-29
30-19
40-49
SO -79
80*
much
llttla
nothing
mora
drafty
avcraga
drafty
urban
auburban
rural
avaraga
$200.000
<$15.000
$15E-$2SK
$2SK-$4SIC
$4SK-$70K
>$70.000
<4
4
5-7
8
>8
0
1-5
6-20
>20
own
rant
U.S. TOTAL
(374)-l.SS
(4). 1. 61-. 84
(10D-1.92-1.00
(84)-l.lS-.96
(6S)-1.65-.86
(49)-l.}7-.82
(19). 1.47. .77
(33J-1. 22-. 64
(24)-1.46-.76
(129J-1 76-1 02
(147M.60- 92
(63). 1.73-1. 00
(11). 1 38- IS
(67)- 2. 17-1. 33
(26)-1.65-.98
(137). 1.69-1.00
(67)-2. 16-1731"
(89) -2. 09-1. 24
(103M.69-1.00
( 9). 1.64-79T"
(11). 1. 56-. 86
(61)- 1.82-1. 10
(IQH-l. 81-1.00
(100)-1.S6..86
(36). 1. 61-. 89
( 9)-1.39-.85
(28)- 1.72-1. OS
(87)-1.7S-1.07
(122)-1 64-1.00
(42)-1.79-1.09
(85)-l.S8-.96
(35). 1. 61-. 99
HB1- 1.65-1. 00
(J8)-1.66-1.01
(172)- 1.76-1. 07
(12)-1.50- 87
( 34). 1. 55-. 90
(18)- 1. 62-. 94
( 6). 1.49- 1.00
HE (-NJ)
TOTAL LIVING
(105)- 1.74
ACE
(.7)-.9S
(2S)-1.00
(20) -.95
(16) -.81
(14).. 87
( 6)-. 71
(11)-. SB
(12)- .67
VEATHERIZE
(37)- 87
(42)-. 84
(17). 1.00
DRAFTY
( D-.80
(48) -1 00
(20). 1.26
LOCATION
(41). I ' 00
(21). 1.11
POLLUTION
(27)- I. 11
(12)-1.00
( 2)T7?
VALUE
< 4). .69
(20)-. 94
(28). 1.00
(24).. 76
(12)-. 7S
INCOME
( 3)- .84
( 9)- 1.01
(26)- 1.07
(29)-1.00
(12)- 1.10
EDUCATION
(2D-1.08
(ll)-l.Ol
Ull.l.OQ
(46)-1.0S
CIGARETTES
( 4). 82
( 8). .92
( S>-.96
OWH - RENT
(4D-1.13
NJ
UEAS
(94).1.1S
(2) -.96
(21)-. 96
(18) -.82
(13)-. 72
( 5)-. 75
( 8)- .58
( 5)-. 88
(24).. 99
(16)-. 91
(14). 1.00
( 2)-. 92
(40). 1.00
( 7)- 1.35
( D-.69
(22). 1.00
(l2)-l77T
(ID-1.49
(IS)- 1.00
(.6)-. 92
(.D-.77
( 2). .94
(15). 1.00
(18)TT02
(14). 1.21
( D-.74
( D-.89
(15) -.97
(34). 1.00
(ll)-l.Ol
( 8). 1.00
(15)-U20.
(Il)-l!o8
(76)-U2S.
( 3)- .91
( 6). .89
( 4).. 98
: (17)- 1.92
SB
(71)- 1.75
(.7)- .72
(27)-1.0C
(12)-. 96
( 7). .82
( D-.69
( 4). .61
( 2)-. 71
(25)- 1.06
(27). .98
(16). 1.00
( 2)-. 86
(3S)-1.00
(11). 1.27
( 4)-. 84
(29)- 1.00
(14)- 1.12
(2D-1.00
( 2)-78T'
( 2). .71
(11). .85
(25)-1.00
(22)-T755
( D-.74
(16)-i95
(30)- 1.00
(10)-. 90
( 5)-. 97
(12)-JL2ft,
(12)- .99
(40) -1.01
( 2)-. 85
( 7)- .87
( 4). 90
(22J-1.24
Ml
(67). 1.84
(.I)-. 82
(ll)-l.OO
(15)-. 91
(1D-.95
(11)-. 86
( 4)-. 82
( 7)-. 71
( 4).. 81
(27)- 1.07
(28). .96
( 9). 1.00
( 2). .82
(17)- 1.30
( 9). 1.18
(3D- 1.00
(12)-T72T
{25)-l!oO
( 2>.T7T
(20)-i.04
(22)- 1.00
(10)-. 91
( D-.84
( D-.74
( 6)- .95
(lO)-l.OO
( 7)-. 96
(14)-AJKL
(10)-. 97
(11). 1 17
(53)-ma
( 2)-. 86
( 3)-. 90
( 2)- .77
(34). 1.21
: ( 2)-U|0.
SMI
(41). 2. 06
(.2)-. 90
(14). 1.00
(10).. 94
( 6)- .81
( 4)- .91
( 2)-. 86
( D-.H
(11)-. 97
(ISM 21
(14). 1.05
( 7). 1.00
( I)-. 76
(17). 1.00
(11) -1 19
( 6). .89
(ll)-l 00
do)-rrnr
(14)- 1 26
( 9)-1.00
( D-TTTf
( 2). .81
( 9). .96
(ll)-lOO
( 2)-!s8
( 2)-. 90
( 5)- 1.25
(1D-1.1S
(10) -1 00
( 4).T7HT
(10)-. 91
( 3)-1.02
( 5)- 99
(19). 94
( 1M OS
<19)-1 11
• ( D-.LP£
-------
Table 3: Mean radon levels from measurements in basements for various responses to ques-
tionnaire items See caption for Table 1
RESPONSE
0-1
1-9
10-19
20-29
30-39
40-49
50-79
SO*
much
Heel.
nothing
nor*
draft/
average
less
drafcy
urban
auburban
rural
laia than av :
average
•ere than av
<540.000
S40K.$75K
S75K-S130K
5130K-S200K
>$200,000
<$1S.OOO
$15K.$25K
S25K-S4SK
S4SK-$70K .
>$70.000
<4
4
5-7
a
>8
0
1-5
6-20
>20
own
rent
U S. TOTAL
(32S)-3 34
( 3)-) 23-. 77 :
(80)-4.18-1 00 •
(6D-3.74. 89 .
(55)-3 19-. 76
(46)-2 67- 64
(20)-2 72- 6) •
(37)-2 69- 64 •
(21)-3 40- 81
(116)-3 49- 99 •
(136)-3 14- 89
(49)-3 51-1.00
(ll)-2 71- 86
(178)- 3 14-1 00
(80)-3 96-1 26
(31)-3 10-1.02 •
(166)-3 05-1 0* •
(64)-4.43-1.4S
(100) -3 96-1.31 :
(142)-3.02-1.00
( 9)- 2 85- 94
(1D-2.96. 83 :
(51)-3 40- 95
(8D-3 S8-JLJ20.
(7})- 3 30- 92 .
(56)-3 28- 92
( 6)- 3. 30- 96 :
(19)- 3. 34-. 97 •
(7D-3.37- 98 :
(92)-3.44-1.00 :
(56)-3.45-l 00 :
(«S)-3 00.89
(10) -3 41-1.01 .
(22j-3.38-J.jaL •
(23). 3 54-1. OS
(215)-3 42-1.01 :
(258)- 3. 42-1. 00
(9)-2.92-.81
(34)-1.55-.90 •
(16)-3 07-. 85 .
(203) -3 37-1.14 :
( 5)-2.95-1.00 •
HE (-NJ)
TOTAL BASEMENTS
(113J-3 69
AM
( 9). 64
(26) -1 00
(19)- .92
(18)-. 81
(16)-. 69
( 7)- 66 .
(14)- 62
(U)- 72 •
WEATHERIZE
(41). 94
(48)- 88
(16) -1 00
DRAfTY
< 5)- 82
(62) -1 00
(30)- 1 21
LOCATION
( 9)-. 82
(61)-1 00
(26)-1.17
POLLUTION
(36)-l 18 •
(53)-l 00
( 3). 95
VALUE
( 4). .64 •
(19)- 89
(281-1.00
(23)- 81
(19)- 76
INCOME
( 2>- 86 .
( 8). .86 •
(2J)-.94
(27)-1.00 :
(M^TT .
EDUCATION
(25). 83
(4)-. 96
(7)-OO_
(7)-l 07
(73)- 97 .
CIGARETTES
(88)-l 00
( J)> 85 .
(10)- 95
( 5)- 91
OUR • RENT
(74). 1 24
( 2)-l 00
NJ
(75)- 2. 97 •
(D-.72
(19)-1 00
(14)-. 84
(15)-. 64
(10)-. J4
( 4)..J4
( 8)- 48
( 4)- 71
(21)-. 87
(32)- 82
(12)-1 00 •
( 2)- 91 •
(40) -1 00 •
(12)-1 26 •
( D-.64 :
(35). 1 00 :
(14) -1.84 :
(20). 1.49 •
(26) -1 00 •
(l)-~77~
(.!)•!. 06 :
( 9)-. 82 :
(8)-l 00 •
(2SM.16
(26)-l 33
(.»)•!. 07 :
( 2)-. 88 :
(10). 90 :
(24)-1.00 :
(17) -TUT:
(19) -.87 :
( 3)- 91 .
(6)-UBL •
(7)-1.0i .
(44)-1.00 •
(60)-1 00 •
( 2)-. 92 :
( 6)-. 89 •
( 3)-1.01 •
OS)- 1.23 •
(.7)-!. 00 :
SE
(45)- 3 47:
(.7)-.9S :
(17)-1 00:
(10)- 1.05:
(6). .81 :
( *)-.59
( 3). 65 :
< 3). 61 :
( I)- 85
(15)-. 97 •
(17)- 90 •
(9)-l 00
( D-.94 •
(24). 1.00.
(10)-1 26
( 3)-. 76 :
(22)-l 00-
(8)-1.63 :
(1D-1.41:
(20)-l 00:
( D-.75 :
(.4). .84 :
(4). 1.01 .
(1S)-1 00-
(»)•!. 13.
( 6)- 94
(.3)-!. 14
( 2)-1.07
(9)-. 97
(17)- 1.00
( 8).TW~
(6) -.86
( 2)-1.12
(3)-i1OJL
-T"2T
( 6). .99 :(.2)- 53
(26)- 1 01:( 2)-. 68
<2S)-1.00:(5M 00
(9)-~9f-( 2>T"P
( 4)- 87 •( 7)-l 12
( 2)-. 99 :(.2)-.94
( 7)-1.06:(.6)- 90
(235-1.01: (3)-. 99
(20}-1.00:(3)-1.00
(10).798~:( 2FTTS
(ll)-l.lO: (2)-. 76
( 2)-1.09:(.5).l 14
t5).1.00 :( 1)-1 00
(4).l 07 .( 9)-l 03
(58)-1.21:(7)-l 14
(61)-1^00:(9)-1 00
( 2)-. 76 :(.3)- 91
( 8)-. 87 :( 7)-1.05
( 5). 80 ( 3) -.89
(57)- .96 :(6)-l 65
( 2) -1.00.: (.2) -1^00.
-------
Table 4. CTOM correlation between room type and level with respect to ground Number
in parenthesis is number or measurements (in hundreds), and other number 11 mean
radon level in units or r0 Last column is the percent of cases for each room type where
level is below ground
ROOM TYPE
BELOW GROUND
FIRST ABOVE
SECOND ABOVE
% BELOW GROUND
LIVING ROOM
DINING ROOM
KITCHEN
FAMILY ROOM
BEDROOM
HALL
BASEMENT
( 2)-241
( })•! 40
( 1)-1 92
( 17) -2 Sk
( 9)-3 17
( I) -2 94
(25D-3 39
(42)-l 58
(10)-1 55
U6)-l 60
(22)-l 92
(18)-1 62
( 4>-l 73
( 8)-2 43
( 3)-l 54
(.8)-! 31
( 1)-1 36
(.8)-! 83
( 7)-l 69
( 8)-l 57
...
4 0
2.5
3 1
43
27
21
97
Table 5. Crosi correlation between age of house and value of house L and B refer to living
areaa and baicments respectively See caption for Table 4 Last column u ratio of
radon levels for value OIO.OUO/>S20U,000 bottom row is ratio of radon levels for ace
0-9/age 50-79
VALUE
ACE
0-4
5-9
10-19
20-29
30-39
40-49
50-79
80+
0-9
50-79
<$40.000
L(.6)-1.57
B(.2)-3.7J
• L(.9)-l 20
B( 2)-2 81
. L( D-1.31
B( 6)-2 99
L( 1)-1 42
B( 9J-3.1S
L( 2)-l 96
B( 2)-2 58
L( D-1.84
B( D-2.47
L( 3J-1.S3
B( 3)-3.00
. L< 2)-l 59
B( 2)-3.63
L - 90
B -1.09
. $40-75.000
: L( S)-2 02
B( 2)-3.83
L( 7>-l 80
: B( 3)-3 95
• L(12)-l 98
• B( 7)-3 48
• L(ll)-l 96
B( 9)-3.65
. L(1D)-1 95
B(12)-3 06
. L( 5)-1.63
. B( 5)- 3. 18
L( 7)-l 46
B( 8). 3 14
: L( 4>-l.S5
: B( 4)- 3 87
. L -1 31
: B -1 24
. $75-130.000
. L(14)-l 96
B(10)-4 32
L(16>-2 14
• B(10)-4 48
L(25)-2 OS
B(18)-4 15
L(19)-l 77
• B<16). 3 58
L(13)-l 58
B(ll)-2 74
L( 5) -I 37
: B( 5>- 2. 82
L( 7)-l 26
• B( 8). 2 26
L( 5)-l 58
B( 4)- 3. 43
L -1 63
B -1 68
: $130-200.000
• L(18)-l 79
: B(13)-4 10
. L(15)-l 91
: B(10)-4 07
• L(23)-l 78
: B(13)-3 84
L(17)-l 47
: B(12)-2 90
• L(ll)-l 27
B( 9)-2 27
: L( 4)-l 27
. B( 4). 2 42
. L( 7)-0 91
• B( 6) -2 44
• L( 5>-l 29
: B( 4)- 3 61
: L -2 03
: B -1 67
>$200.000 :
L( 8)- .86 :
B(14)- .39 :
'. U 5)- .88 :
B( 7)- .05 .
. L( 7)- 78
BUD- il
L( 5)-l 48 .
B( 8)-2.62
L( 4)- I 49
B( 6)-2 43
L< 1)-1 36
B( 2)-2 68
L( 3)-l 07 .
B< 5) -2 37
L< 2)-l 33 .
B( 3)-2 73
L -2 05
B -1 78 .
*9 au.uuu
>$200.000
1 18
1 17
1.57
1 44
I 36
L 17
1 04
0 83
0 76
0 95
0 74
1 09
0 70
0 79
0 84
0 75
-------
Table 8: Breakdown of geometric medn dud arithmetic average radon levels for location
= urban (U), suburban (S), and rural (Ft) Last column u ratio of U/S for previous
column
ZIP CODES
40000
•49*9*
50000
-59999
60000
-69999
40000
•69*99
STATES
(NUMBER) :
OH
IN
UI (2)
ND (.8)
IL
KS
(10).
(3).
, KN
. SD
(20).
<1>.
HI
KY
(2),
(.5)
HO
HE
(IS).
(2)
•
IA (9).
. HT (.5) :
(J).
( 3)
t
ALL OF ABOVE
:
NUMBER :
U-
S-
R.
U-
S-
R-
U-
S.
R.
U-
S-
R.
309 .
1436 •
S48 .
164 •
409
416 .
206
1231 .
186
(81
3074
11JO
HEAK
1
1
1
3
3
2
1
1
2
2
1
2
7i
.6*
.9*
.21
61
.70
.13
.4S
02
0}
.74
22
. AVERAGE
: 2
2
3
4
4
: A
: 1
2
3
3
2
3
7i
91
.43
67
.91
44
.69
.IS
.09
J«
.47
.72
AV U/S
0 93
0 99
.
'. 0 79
1 18
Table 7: Cross correlation between location and value of house Last column u ratio of
mean radon levels in previous two columns See caption (or Table 5
VALUE
<$40.000
$40-75.000
$75.130.000 :
$130-200.000
>$200.000
URBAN
L-
B-
L-
B-
L-
L-
B-
< 3)
( A)
( B)
.
1
2
1
( 7). 3
( 3)
( »
( 2)
( 2)
.
-
1
2
1
2
66
76
85
32
49
31
76
17
04
SUBURBAN
. ( 3)-l
: ( 3)- 2
: (22)-l
(23)- 3
.S3
70
89
01
(41). 1 86
: (43). 3. 22
: (3D- 1
• (38). 3
(24)- 1
(39). 3
63
07
47
02
RURAL RURAL/SUBURBAN
: ( 3>- 3
(12)-4
(19)- 2
• (16) -4
: (12) -7.
(12)-4
'. ( «>-2
(13) -4
.A3
26
42
.87
.23
.49
14
32
1
1
1
I
1
1
1
1
1
1
10
28
12
42
30
31
38
46
46
30
-------
IV-4
RADON IN NORWEIGAN DWELLINGS
12 3
T.Strand , B.M.R. Green and E.Stranden
National Institute of Radiation Hygiene, Osteras, Norway
2 National Radiological Protection Board, Oxfordshire, United Kingdom
3Radforsk A/S, Fjellhamar, Norway
ABSTRACT
The results of a large scale survey of radon concentrations in Norwegian dwellings
are reported. Measurements of radon have been made in 7500 dwellings representing all 450
municipalities. The dwellings were selected by a random sampling procedure based on data from
the Central Bureau of Statistics. The number of measurements in each municipality is proportional
to its population. The measurements were performed by nuclear track detectors from the National
Radiological Protection Board in United Kingdom. The results will be used in an epidemiological
study on radon and lung cancer.
INTRODUCTION
From 1983 to 1986 a pilot survey of radon in Norwegian dwellings was carried out (1). In the
winter seasons measurements of radon were performed in a total of about 1500 detached houses
from 79 out of the 450 municipalities of Norway. These municipalities included about 30% of the
total population. Taking into account seasonal differences in radon concentration and that
multifamily houses were not included in the survey, the year average of radon concentration in
Norwegian dwellings was estimated to be between 80 and 100 Bq/m*. Comparing these estimates
with those from other surveys in other countries, it was concluded that the overall level of radon
in Norwegian dwellings is about the same as in Sweden and Finland (2,3). Owing to weaknesses in
the sampling procedure (no random selection of dwellings) and because the integration time in the
measurements was only 5-7 days, it was recognised that it would be difficult to use this material in
any kind of epidemiological study on radon and lung cancer.
In 1986, financial support for a large scale epidemiological study on radon and lung cancer
in Norwegian dwellings were given from the Norwegian Cancer Society. The study was started in
early 1987 and has been conducted as a collaboration between the National Institute of Radiation
Hygiene, the Cancer Registry of Norway and the National Radiological Protection Board in United
Kingdom. The objectives and strategy of the study have been presented in an earlier paper (4).
-------
In this paper, some initial results of the radon survey are reported. These data are combined
with earlier radon data and information on the building stock and indoor occupancy patterns to
give a better estimate of the average radon concentration in Norwegian dwellings. The results from
the epidemiological part of the study will be presented later.
MATERIAL AND METHODS
SELECTION OF DWELLINGS
The aim of the survey is to obtain a representative average value of the indoor radon
concentration for each of the 450 municipalities in Norway for use in an epidemiological study of
radon and lung cancer. The number of dwellings in each municipality is proportional to the
population except for the two largest cities, Oslo and Bergen, where somewhat smaller samples
were taken due to the higher population density.
Influx of radon from the subsoil and bedrock is the main source of indoor radon in
Norwegian dwellings. For an average Norwegian detached or undetached house about 90% of the
source term is due to the influx of radon from the ground. For blocks of fiats and other multifamily
houses the picture is somewhat different: The radon concentrations are generally much lower, and
building materials, which are not usually correlated with geology, are usually the most important
source of indoor radon. Less than 15% of the population live in flats or other multifamily houses
(5). In Oslo, die largest city, about 65% of die population are living in flats. Due to die significant
differences in radon levels between houses and flats, it was necessary to stratify die sampling
procedure. A census data base with information on die building stock is available at die
Central Bureau of Statistics. This data base was used for die selection of dwellings. The sampling
procedure is similar to that used in a large scale survey of natural 7 radiation in Norwegian
dwellings (6).
Because die financial resources were limited, is was necessary to limit die number of
measurements to about 10,000. From an epidemiological point of view it was found more
appropriate to do one measurement in 10,000 dwellings instead of two measurements in 5,000
dwellings. From an earlier study (1), die radon concentration in bedrooms was found to be on die
average about 10% lower than in living rooms. This difference can be explained by die fact that in
a large proportion of single family houses die bedrooms are often better ventilated and are on a
floor above die living room. However, die higher occupancy in die bedroom compared to other
parts of die house means that die measurements in bedrooms would be a good indicator of die
relative radon exposure of die population at die municipality level.
THE MEASUREMENTS
The measurements were performed by NRPB type nuclear track detectors (7,8). Preparation,
calibration and analyses were performed at die NRPB in United Kingdom, while die distribution of
dosemeters to die householders were organized from die National Institute of Radiation Hygiene in
Norway. Each month, for a period of 18 mondis (from March 1987 to October 1988), about 550
detectors were issued to householders in different municipalities. The integration time for die
measurements was 6 mondis. In order to avoid any difficulties from long-term variations in radon
concentration in die estimates of annual average of radon concentration for each municipality, die
detectors were spread evenly over all seasons of die year. After six mondis, die householder was
asked to return die detector and a questionnaire to die National Institute of Radiation Hygiene.
The detectors were stored in a very low radon atmosphere (<10 Bq/m>) for a maximum of a week
at the institute before it was sendt to die NRPB for analysis.
-------
The detectors were sent to the householders without first asking for their agreement to take
part in the study. It was anticipated that this procedure would increase the percentage of selected
households taking part in the study. A variety of reasons, such as detectors returned without
completed questionnaire, changes of address, an unwillingness to participate, lost detectors and so
on, meant that the final number of valid measurements was about 7,500 out of the initial 10,000,
a success rate of 75%. There was no geographical pattern in the missing fraction of measurements.
RESULTS AND DISCUSSION
In figure 1, a frequency distribution of the measurements for the whole country is shown.
The distribution is found to be log-normal. The arithmetic mean of the measurements is calculated
to be 53 Bo/nP. Owing to the fact that the sampling procedure was population based and that the
measurements in each municipality were evenly distributed in time, this mean value is a good
estimation of the annual average radon concentration in Norwegian bedrooms. On an individual
level it may be necessary to correct for the seasonal variations in radon concentration. Owing to
climatic conditions, concentrations in winter are usually somewhat higher than in summer.
900
BOO
700 -
600
soo -
b ** "
O
« 300
200 -
100-
100
180
RAOON CONCENTRATION (Bq/n>)
Figure 1. Frequency distribution for radon concentration in bedrooms in Norwegian dwellings.
The frequency distribution in figure 1 has been truncated at 200 Bq/m>. However, about 4%
of the results were above 200 Bq/m* and about 0.3% above 800 Bq/m*. The highest values were
found in die eastern pan of southern Norway. In this region of the country there are relatively
large occurrences of precambrian to Silurian rocks like alum shales and granites. Measurements on
samples of alum shale from the upper cambrian or lower ordovician period have shown
-------
concentrations of radium up to 4,500 Bq/kg, which is about 100 times higher than the normal
level in rocks and soils. In an ealier survey of radon in dwellings on typical alum shale ground (9),
more than 75% of the dwellings had an average radon concentration in the heating season above
200 Bq/m>. In our survey, the lowest concentrations were found in dwellings on Caledonian ground
with large occurrences of gneisses.
In most detached and undetached houses, living room and kitchen are located on the first
floor (ie groundlevel). However, in a large proportion of the dwellings, the bedrooms are located
one floor higher. In such houses the radon level is assumed to be somewhat lower in the
bedroom(s) than in the rooms on the first floor. On the questionnairies, information on "what floor
the main bedroom is located" were recorded. In figure 2, the average radon level is shown for
bedrooms in the basement, on the first floor and on the second floor. On the average, the radon
level was found to be about 20% higher if the main bedroom was on the first floor and 240% in
the basement relative to a bedroom on the second floor. According to census data from the Central
Bureau of Statistics (5) we may assume that the living room are located on the first floor in all
detached and undetached houses in Norway. Assuming that the average radon concentration for
the category "bedroom on the first floor* is a representative average for the radon concentration in
living rooms for detached and undetached houses, it is possible to correct the annual average of
radon concentration in bedrooms to become a more representative estimate for the average in the
dwelling. In these estimates it is assumed that 50% of the time indoors is spent in the bedroom,
40% of the time in the living room and 10% of the time in the basement. If the bedroom in
located on the basement floor, it is assumed in the calculations that 40% of the time is spent on
the first floor. From these calculations the average radon concentration in Norwegian dwellings was
estimated to 60 Bq/m>. This average is somewhat lower than the estimate from the pilot study.
This may partly be explained by the unrandomized sampling in the pilot study and partly by the
fact that the pilot measurements were performed during the heating season in detached houses
only.
BASEMENT
FIRST
FLOOR
SECOND
FLOOR
Figure 2. Average radon concentration in bedroom for different categories of dwelling according to
on what floor the bedroom is.
-------
In figure 3, the arithmetic averages are calculated for different categories of dwelling. As
illustrated the average concentration in detached and undetached houses is 30-35% higher than in
blocks of flats. The higher level of radon in detached/undetached houses was expected owing to
the fact that the influx of radon from the ground has been found to be the most the most
significant source of radon in Norwegian dwellings.
60
40
20
DETACHED
HOUSES
UNDETACHED
HOUSES
MULTI-FAMILY
HOUSES
Figure 3. Average radon concentration in the bedrooms for different categories of dwellings in
Norway.
In figure 4, average radon concentration in bedrooms are calculated for different categories of
dwellings according to year it was built. All types of dwellings are included the estimates.
The average radon level does appear to be higher in newer dwellings. This may be attributed in
part to the "save energy campaign" in the seventies. It is to be expected that the air exchange rate
in newer houses will be less than in older houses.
V
2. 60 •
§
a
i 40"
§ 20"
I
8.2*
6.9*
,.«
1.0*
9.3*
19*
23*
17%
1*01 1M1 1941 It4« 1991
1*10 1*40 IMS 1*50 !•«« 1»7« 1MO
Figure 4. Average radon concentration in bedrooms according to the year die house was
built Percentage of the total sample are included in the histogram for each category.
-------
CONCLUSIONS
The annual average of radon concentration in Norwegian bedrooms is calculated to be
53 Bq/m>. The radon concentrations were found to be about 30-35 % higher for bedrooms in
detached and undetached houses than in blocks of flats. There was no significant seasonal
dependence in the results. The highest concentrations were found in the eastern pan of southern
Norway. However, it is assumed that the radon level in bedrooms on the average is somewhat
lower than in the living room. In a large proportion of Norwegian houses, the bedrooms are
located one floor higher than the living room and kitchen. By assuming that most living rooms are
located on the first floor, by using an average factor for the ratio between bedrooms on the second
and first floors to estimate the level in the living room and by assuming that that an average of
the concentration in the bedroom and living room is representative for the dwelling, we estimate
the average radon concentration in Norwegian dwellings to be 60 Bq/m3. This is 30-40% lower
than the earlier estimates (1).
ACKNOWLEDGEMENTS
This work was supported by the Norwegian Cancer Society - Landsforeningen mot
kreft.
The work described in this paper was not funded by the U.S. Environmental Protection
Agency and therefore the content do not necessarily reflect the views of die Agency and no official
endosrement should be inferred.
REFERENCES
1. Stranden, E. Radon in Norwegian dwellings. In: Proceedings of the Symposium Radon and its
Decay Products: Occurrence, Properties, and Health Effects, New York, April 13-18, 1986.
American Chemical Society Symposium Series 331, p.70-83.
2. Swedjemark, GA and Mjones, L. Radon and radon daughter concentrations in Swedish homes.
Radiat.Prot.Dosim. 7 (1-4): 341-345, 1984.
3. Castren, O., Winquist, XL, Makelainen, I. and Voutilainen, A. Radon measurements in Finnish
houses. Radiat-ProcDosim. 7 (1-4): 333-336, 1984.
4. Stranden, E., Magnus, JC, James, A.C., Green, B.M.R. and Strand, T. Radon and lung cancer:
an epidemiological study in Norway. Radiat.Prot.Dosim. 24 (1-4): 471-474, 1988.
5. Central Bureau of Statistics. Census data. Personal Communications, 1986.
6. Strand, T., Magnus, K. and Stranden, E. Sampling strategy for a large scale indoor radiation
survey - a pilot project Radiat.ProtDosim. 14 (3): 251-255, 1986.
7. Bartlett, D.T., Gflvin, OJ., Still, R., Dixon, D.W. and Miles, J.C.H. The NRPB radon
personal dosimetry service. Jour.Radiol.Prot. 8: 19-24, 1988.
8. Bartlett, D.T. and Bird, T.V., Technical specification of the NRPB radon personal dosemeter.
Chilton, NRPB-r208 (London, HMSO).
9. Stranden, E. and Strand, T. Radon in an alum shale rich Norwegian area.
RadiatProLDosim. 24(1-4): 367-370, 1988.
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Session V:
Radon Entry Dynamics
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V-I
A Simplified Modeling Approach and Field Verification
of Airflow Dynamics in SSD Radon Mitigation Systems
Kenneth J. Gadsby, T. Agami Reddy, Rajiv de Silva, and David T.Harrje
Center for Energy and Environmental Studies
Princeton University
Princeton, NJ 08544, USA
Abstract
The airflow characteristics in the subslab area of a building must be
known in order to provide engineering guidance for designing a subslab
depressurization (SSD) radon mitigation system. An earlier study had described
our research effort to model subslab flows as radial airflow through a porous
media confined between two impermeable disks. A laboratory device was also
built to experimentally determine the aerodynamic pressure drop versus flow
model coefficients for a variety of subslab gravel materials and to test the
validity of our modeling approach.
This paper will address the issue of how the simplified model approach
along with the laboratory-determined pressure drop coefficients can be used as
a rational means of assessing subslab connectivity in actual houses.
Preliminary field verification results in a house with gravel under the
basement slab are presented and discussed. The way in which the simplified
modeling approach could be useful to professional mitigators is described.
Illustrative figures of the pressure field extension map from closed-form
solutions are presented. Experimental results of the subslab pressure field
under single and dual suction penetrations (perimeter and central locations)
are shown. Finally, certain practical aspects relating to proper engineering
design of the SSD system are addressed and initial recommendations are made.
This paper has been reviewed in accordance with the U.S. Environmental
Agency's peer and administrative review policies and approved for presentation
and publication.
Introduction
An EPA sponsored workshop was held at Princeton University to summarize
available knowledge on various radon mitigation diagnostic techniques (1). The
emphasis of the workshop was on diagnostics since each house, housing sub-
division, and region may have different characteristics which would require
that special attention be paid to system design in order to maximize mitigation
system performance and minimize installation cost. This issue was of particular
importance since it was found that a large number of mitigated houses still had
-------
radon levels above the recommended guideline of 4 pCi/L. In fact a recent study
(2) found that 64% of the mitigated houses in New Jersey, where post-mitigation
measurements have been made, remained above the recommended radon level.
Diagnostics are therefore crucial for providing information relevant and
necessary to the successful design and implementation of a radon mitigation
system.
A survey of the workshop participants indicated that systems based on SSD
account for more than 50% of all installed systems. (Another promising
technique involves subslab pressurization. Since the two techniques are similar
in terms of subslab dynamics of induced airflow, they can both be treated in
the same scientific framework.) In the pre-mitigation diagnostics phase, the
degree of "connectivity" under the slab as well as the permeability
characteristics of the subslab medium must be determined before a suitable SSD
system can be designed. Proper attention to these aspects will ensure that
reasonable flows, and hence the desired degree of depressurization, will
prevail at all points under the slab. Lowering the pressures at all points of
the subslab to values below those of the basement/crawlspace/living area will
then greatly reduce the flow of radon-rich soil-gas into the building.
Parallel with the above aspect is the concern that presently mitigators
tend to over-design the SSD system in order to err on the safe side. In doing
so, more radon (a 10-fold increase has been cited in Ref.3) from the soil is
removed and vented to the ambient air than would have occurred naturally.
There is the need to try to prevent these overly robust SSD mitigation systems
and therefore decrease exhaust emissions of radon and conditioned indoor air,
while simultaneously ensuring that the indoor radon levels do not exceed the
recommended value.
We are currently involved in the formulation and verification of a rapid
diagnostic protocol for subslab and wall depressurization systems designed to
control indoor radon levels (4). It is hoped that the protocol will lead not
only to the ability to distinguish between houses that are hard or easy to
mitigate, but also to the articulation of a more rational and scientific
approach which would be of special usefulness to the ever-increasing body of
professional mitigators.
Our approach to the formulation of the diagnostics protocol consists of:
(i) a practical component in that specific guidelines would be suggested so
'that the effectiveness of the engineering design of the radon mitigation system
would be enhanced, and (ii) involvement of scientific studies at a more
fundamental level which would both lend credence and enable defining the
guidelines more rationally. This paper will briefly address the scientific
component of the protocol and present preliminary validation of the previously
suggested simplified modeling approach to predict the subslab pressure-induced
flow by a single central suction hole (5). This paper will also show how the
closed-form solutions thereby obtained could be conveniently used to generate
figures useful to the professional mitigator. Aspects relating to the proper
engineering design of the piping system will also be addressed.
-------
Previous Work
Following an earlier study (6), we had forwarded arguments to support the
suggestion that subslab airflow of a residence with either gravel or soil under
the concrete slab be visualized as occurring in radial streamlines terminating
at the central suction point (5). It was pointed out that the Reynolds number
(Re) indicates the flow regime, where Re is defined as:
Re - (q/A) (l/va) (oV4) (1)
where q - total volumetric flow rate,
A - cross sectional area of the flow (in the case of radial flow
through a circular bed of radius r and thickness h, the area -2wrh) ,
va - kinematic viscosity of air,
dy - equivalent diameter of pebbles, and
$ - void fraction or porosity of the gravel bed.
It was then shown that subslab airflow under actual operation of
mitigation systems is likely to be turbulent if a gravel bed is present under
the slab, and laminar when soil is present (6).
The core of any model is the formulation of the correlation structure
between pressure drop and Re (or flow rate). For laminar flow, Darcy's law
holds and we have (7) :
- a (q/A) (2)
where pf - density of the flowing fluid, and
g - gravitational constant.
In the case of turbulent flows, a model such as the following is widely
used:
U/Pf g) (dp/dx) - a (q/A)b (3)
The left side is the pressure drop in head per unit bed length, and the
parameter "a" can be loosely interpreted as the resistivity of the porous bed
to the flow of the particular fluid. The permeability k of the porous bed is
given by:
* - ( VS) (l/a> (4)
It was then shown in Ref. 5 that the following closed- form solutions are
obtained for the pressure drop (in units of head of water) in a homogeneous bed
with a circular boundary and with a single suction hole at the center of the
disk, see Fig. 1:
For laminar flow:
[p(r)-pa]/(pw g) - a (pa//>w) (q/2>rh) In(r/r0) (5)
-------
where pv and pa are the densities of water and air respectively.
For turbulent flow:
[P(r)-pa]/(pw g) - a a/Pw) [(q/2irh)b] [l/(l-b)J (r1^-^1^) (6)
The practical implications of the parameters a and b are that, if they are
really constant for a given bed material and can be determined by actual
experiments in the field, they will serve as indices by which a mitigator will
be able to assess how much of the area from the suction hole he can hope to
access for a given suction pressure.
In order to evaluate the soundness of the mathematical derivation
presented above and also to determine the numerical - values of the empirical
coefficients, a laboratory model consisting of a 2.4 m diameter circular
section and 0.15 m deep was constructed as shown in Figs. 2 and 3. The top and
bottom impermeable disks were made from 2 cm thick plywood, and a wire mesh at
the outer periphery of the disks was used to contain the gravel between the
disks. The apparatus allowed experiments to be conducted with a maximum disk
spacing (depth of gravel bed) of 9.5 cm.
A 3.8 cm diameter hole was drilled at the center of the disk to serve as
the suction hole. Nine holes, whose layout is shown in Fig. 3, were drilled on
three separate rays of the top disk and fitted with a sleeve of 1.3 em inner
diameter FVC pipe with chamfered entrances at either end. Pressure measurements
at these nine holes would then yield an accurate picture of the pressure field
over the entire bed.
A number of different experimental runs were performed on the laboratory
apparatus using two different sizes of river-run gravel (1.3 and 1.9 cm
diameter) . Least square regression for both the constant "a" and exponent "b"
was performed on the observed experimental pressure drop data using eq.(6)
(since the flow in the gravel bed was determined to be turbulent) . Table 1
summarizes the different experiments performed using the laboratory apparatus
and the values of the physical parameters obtained.
Field Verification
The irregular boundary conditions and the non-homogeneity in subslab beds
that arise in practice are however not easily tractable with a simple
expression such as eqs. (5) and (6), and resorting to a numerical computer code
may be the only rigorous way to proceed in order to predict pressure fields
under actual situations (8,9). We shall show in this section that our
simplified approach nevertheless has practical relevance in that it could be
used to determine which areas under the slab have poorer connectivity.
The house under investigation (H21) has a partial basement with a gravel
bed under the basement slab. As shown in Fig. 4, the basement though
rectangular, is close to being square (6.45 x 7.60 m) . It has two sides exposed
to the ambient air above grade, while the other two sides are adjacent to slab-
on- grade construction. Initially, one suction hole of 0.1 m diameter was
-------
drilled at roughly the center of the basement slab to which a temporary
mitigation system was installed. Though 19 holes were drilled across the slab
(Fig. 4), two of them (holes 11 and 12) were found to be blocked beneath the
slab. Consequently, data from only 17 holes have been used in this study. This
blockage was later found to be due to the presence of an oversized footing for
a support column.
Three sets of runs were carried out which, depending on the airflow rate
through the single suction pipe, are termed:
i) 28 L/s - High flow,
ii) 23.4 L/s - Hedium flow, and
iii) 18.1 L/s - Low flow,
Note that our analytical expression for the pressure field under turbulent
flow given by eq. (6) is strictly valid for a circular disk with boundary
conditions at r - ro and p - pa. We approximate the rectangular basement by a
circle of 3.5 m mean radius. We need to also include the extra path length of
ambient air flowing down the outer basement wall, going under the footing, and
then flowing through the subslab gravel into the suction hole. We estimate this
to be about 2 m. Consequently, we find that r0 - 5.5 m. The thickness of the
subslab gravel bed, h, has been found to be about 5 cm.
The gravel under the slab, though river-run, was found to be highly
heterogeneous in size and shape. In general, its average size was slightly less
than 1.3 cm. However, we decided to use the properties of the 1.3 cm gravel
determined experimentally in the laboratory (see Table 1).
Fig. 5 shows the observed and calculated pressure drops for the high and
low flow rates. Readings from holes 13 and 14 are lower and we suspect poorer
connectivity to these holes; i.e., some sort of blockage in this general area.
Ve note that the agreement between model and observation (Fig. 5) is indeed
striking, given the simplification in our model and also the various
assumptions outlined above.
Fig. 5 indicates which areas under the slab are non-uniform. A better way
of illustrating how well the model fares against actual observations is shown
in Fig. 6. The solid line represents the model predictions while observations
are shown by discrete points. Ve note again the satisfactory predictive ability
of this modeling approach and also the fact that certain holes have pressure
drop values higher than those predicted by the model.
In order to illustrate the fact that our approach is sensitive to the
selection of type of gravel bed, Fig. 7 presents the experimental observations
plotted against model predictions with gravel bed coefficients taken to be
those that correspond to the 1.9 cm gravel. Ve note the very large differences
between model prediction and observed pressures over the entire basement,
thereby suggesting that our approach has enough sensitivity to be of practical
relevance.
-------
An alternate approach, to the one adopted here and described above, would
be not to assume specific gravel bed coefficients but to determine these from
regression. This entails using eq.(6) along with the data set of actual
observations and determining the parameters k and b by regression. Since b is
not a parameter that varies greatly (5), we have chosen two different values of
b (1.6 and 1.7) to see what difference this leads to in terms of the
coefficient of determination (R2) and in the values of k.
Regression results are summarized in Table 2. We have performed three
trial runs. Trial 1 uses all data points while, in trial 2, pressure drop
observations from holes 11 and 12 (holes that are blocked) have been removed.
We note that the R2 improves dramatically, from O.BO to 0.96. For trial 3,
holes 9 and 10 have been equally removed in order not to bias the regression
since these holes have high pressure drop values. We note that the R2 of trial
3 is 0.88, an improvement over that of trial 1.
o
Other than the very high R values found, the most striking feature is
that regression yields a value of k which is practically identical to that of
the 1.3 cm gravel determined experimentally in our laboratory apparatus. This
suggests that even a visual inspection of the porous material under the slab
can be an indicator good enough for a mitigator to select a standard bed
material before using the physical properties of the material get a sound
estimate of what the suction pressure ought to be in order to generate a
certain pressure field under the slab. The need to categorize commonly found
subslab material, deduce their aerodynamic pressure drop coefficients in
laboratory experiments, and then tabulate these in handbooks seems to be an
avenue worth pursuing.
Graphical Representation
The approach developed here will show how closed-form solutions for the
pressure drop in porous beds can be represented in graphical form suitable for
professional radon mitigators. Let us illustrate our approach using the
simplest case of a circular porous bed with radial inflow between two
impermeable disks. From the discussion in the above section, it would seem that
we could apply our model equally to square basements and to houses with a
partial basement.
Eq. (5) is valid for laminar flow which would prevail where soil is the
subslab material (5). It can be written as:
Aph(r) k - (ua/g) (/>a/pw) (1/2*) (q/h) In(r/r0) (7)
where Ap^ is the pressure drop in head of water and is equal to
lp(r)-pa]/0»w 8>-
Four curves have been plotted in Fig. 8 for four values of
(q/h): l.OxlO'3, 5xlO'3, IxlO'2, and 2xlO'2 m2/s. Thus, if the values of
(r/r0), (q/h), and k are known, [Aph(r)l can be obtained from this figure.
-------
For gravel under the slab, the flows will probably be turbulent and the
pressure drop is given by eq. (6) which can be rewritten as:
Aph(r) F-
-------
Pressure Drop Considerations
There are basically three different sources of pressure drops in the
mitigation system:
APtotal - APbed + APent + APpipe
where ApDe(j - pressure drop in porous bed,
** pressure drop due to change of direction and that
associated with entrance effects into the mitigation
pipe, and
~ pressure drop in the mitigation pipe.
The pressure drop in the subslab bed is given by equations akin to eq. (5)
or (6) . The pressure drop at the entrance to the suction pipe involves
accounting for the following effects: (i) change in flow direction, (ii) change
in cross-sectional area, and (iii) entrance effects at the throat of the
suction pipe. From an engineering viewpoint, it is more convenient to treat
these together. In accordance with actual practice (10), we propose the
following simplified empirical equation for the head loss:
APent/Pw g - Kp [l-(Ap/Ab)]2 (Vp2/2g) (10)
where Kp is the dimensionless pressure loss coefficient which should not
depend on the velocity or the bed thickness, and is a constant
for a specific type of bed material,
Ap is the cross -sectional area of the suction pipe,
AD is the surface area of a cylinder of diameter equal to that of
the suction pipe and height equal to the thickness of the porous
bed, and
Vp is the velocity of air in the suction pipe.
If dp is the diameter of the suction pipe, then:
- (irdp2/4) (l/ffdph) - dp/4h (lla)
and
Vp - q/Ap - 4q/wdp2 (lib)
Table 3 assembles the results of determining the entry pressure loss
coefficient for three flow rates. We note that Kp values are exactly the same,
a gratifying result. This enables us to place a certain amount of confidence in
our model for the entrance losses.
The pressure drop in the piping includes losses due to elbows, fittings,
as well as straight pipe. Following Ref. 10, losses in the straight pipe are
given by:
- f a/dp) (q/A)/2g (12)
Pressure losses in bends and fittings are normally expressed in terms of
-------
an equivalent pipe diameter. For example, a 90° elbow has the same pressure
drop as a straight pipe of length equal to about 25 times the pipe diameter
(10).
Since the primary objective of the mitigation system is to create a
suction pressure under the slab only, we can define a hydrodynamic
effectiveness of the mitigation system based on these three pressure drops:
Hydrodynamic effectiveness - Apbed / APtotal (13)
We have computed these various pressure drop values for house H21 in order
to get an idea of their relative magnitude. The mitigation system (with one
suction hole only) in house H21 has about 7 m of straight pipe of 0.1 m
diameter and three 90° elbows. This translates into a total length of
7 + (3 x 2.5 x 0.1) - 14.5 m.
Table 4 assembles the various pressure drops in the three elements of the
mitigation system. While AP^ed and APent have been measured, APpipe has been
calculated from eq. (12). The hydrodynamic effectiveness defined by eq. (13)
is also given.
Table 4 shows that APpipe is negligible compared to APDed> while AP is
about one third of AP^,e
-------
Acknowledgements
The assistance of R. Gafgen during the experimental phase of this study is
acknowledged.
Nomenclature
A cross-sectional area of flow
a parameter representative of the resistivity to flow of the porous bed
b pressure drop exponent for turbulent flow in gravel beds
d diameter
dy equivalent diameter of pebbles
F correction factor given by eq. (8b)
f friction factor
g acceleration due to gravity
h thickness of porous bed
Kp pressure loss coefficient at entry to suction pipe
k permeability of porous bed
L length of pipe
Ap pressure drop
p pressure
pa atmospheric pressure
q total volume flow rate
R2 coefficient of determination of regression
Re Reynolds number
r radial distance from center of the suction hole
r0 outer radius of the laboratory apparatus
SEM standard error of the mean of the regression estimate
V air velocity
x distance along flow
p density
v dynamic viscosity
4 porosity of porous bed
Subscripts
a air, ambient
b porous bed
ent entrance
f fluid
P Pipe
w water
-------
References
1. D.T. Harrje & L.M. Hubbard, Proceedings of the Radon Diagnostics Workshop,
April 13-14, 1987 (EPA-600/9-89-057) (NTIS PB89-207898), June 1989.
2. J. Wang & M. Cahill, Radon reduction efforts in New Jersey, paper presented
at the Annual Meeting of the National Health Physics Society, Boston, MA, July
4-8, 1988.
3. D.C. Sanchez, Technical issues related to emission releases from subslab
radon mitigation systems, presented at ASCE National Conference on
Environmental Engineering, Austin, TX, July 9-12, 1989.
4. K.J. Gadsby, L.M. Hubbard, D.T. Harrje & D.C. Sanchez, Rapid Diagnostics:
Subslab and Wall Depressurization Systems for Control of Indoor Radon,
Proceedings: The 1988 Symposium on Radon and Radon Reduction Technology,
Volume 2, EPA-600/9-89-006b (NTIS PB89-167498), March 1989.
5. T.A.Reddy, H.E.Black III, K.J.Gadsby, D.T.Harrje & R.G.Sextro, Modeling air
flow dynamics through a homogeneous porous bed with relevance to proper design
of radon mitigation systems using subslab depressurization, PU/CEES draft
report, Center for Energy and Environmental Studies, Princetion University,
Jan. 1990; also, "Airflow dynamics under subslab depressurization: Simplified
model approach and preliminary validation" paper presented at the Third Annual
AARST Conference, Baltimore, Oct. 16-17, 1989.
6. T.G. Matthews, D.L. Wilson, P.K. TerKonda, R.J. Saultz, G. Goolsby, S.E.
Burns & J.W. Haas, Radon diagnostics: Subslab communication and permeability
measurements, Proceedings: The 1988 Symposium on Radon and Radon Reduction
Technology, Volume 1, EPA-600/9-89-006a (NTIS PB89-167480), March 1989.
7. M. Muskat, The Flow of Homogeneous Fluids through Porous Media,
McGraw-Hill, 1937.
8. C. de 0. Loureiro, "Simulation of the Steady-State Transport of Radon from
Soil into Houses with Basement under Constant Negative Pressure", LBL-24378,
Lawrence Berkeley Laboratory, Berkeley CA 1987.
9. J.M.Barbar & D.E.Hintenlang, Computer modeling of subslab ventilation
systems in Florida, paper presented at the 34th Annual Meeting of Health
Physics, Abstract No. TAM-E8, Albuquerque, NM, 1989.
10. ASHRAE, Handbook of Fundamentals. American Society of Heating,
Refrigeration and Air-Conditioning Engineers, Atlanta, 1985.
-------
Table 1. Summary of laboratory experiments using river run gravel
and the physical parameters deduced in Ref. 5
Experiment Diameter of Measured Pressure Permeability
particles porosity drop of bed
nominal measured exponent (m2)
(m) fin)
A1+A2
0.013 0.011
0.374 1.60
9.4 x 10
-9
A3
0.019 0.022
0.424 1.40
34 x 10
-9
Table 2. Results of regressing experimental data using eq,(6)
Trial
run
k
Cm2)
SEM
Remarks
1.6 9.13 x 10'9
1.7 7.5 x 10'9
6-7%
O.BO With all data points
0.80
1.6
1.7
7.1 x 10'9
5.8 x 10'9
3%
0.96
0.97
With data of holes 11 and 12
removed
1.6
1.7
10.0 x 10'9
7.3 x 10"9
5%
0.88
0.87
With data of holes 9, 10, 11
and 12 removed
-------
Table 3. Determination of the pressure loss coefficient at the
throat of the mitigation suction pipe in house H21
Run
1
2
3
Total
airflow
(L/s)
18.3
23.4
28.4
Suction
pressure
before
entry
(cm water)
1.300
1.938
2.700
Suction
pressure
after
entry
{en water)
1.664
2.540
3.589
Kp
0.053
0.053
0.053
Table 4. Relative pressure drops in the mitieatlon system of house H21
Run
1
2
3
Total
airflow
(L/s)
18.3
23.4
28.4
APbed
(cm water)
1.30
1.94
2.70
APent
(cm water)
0.363
0.602
0.889
*Ppil
(cm wat
8.0 x
13.0 x
17.7 x
)e Hydrodynamic
:er) effectiveness
m
10-3
10-3
10-3
77.8
75.9
74.9
-------
I
gravelx
Imperaeable
disks
\1
Suction
x" pipe
'dr
. Tap to measure static pressure
Fig. 1 Schematic of a model to duplicate flow conditions
occurring beneath the concrete slab of a residence
when induced by a single suction point. The air-
flow is assumed to be radial flow through a
homogenous porous bed of circular boundary.
Attachement Co measure
flow and pressure
Suction tube
Top plywood disk
Foam cover
Gravel bed
Bottom plywood disk
Floor
Fig. 2 Cross-section of the experimental laboratory apparatus.
Fig. 3 Layout of the test holes to measure static
pressures in the porous bed.
-------
6.45
e
o
• 1
• 5
•17
•16
7 .6
10 V9
12U
»15
H3
,f
14
18
19
•3
cu
•a
re
t-
eo
c
C/}
Slab on grade
J
Fig. 4 Plan of the basement slab showing the relative
positions of the various subslab penetrations.
The suction hole of the temporary mitigation
system is marked as +, while the location of
the central and perimeter suction holes (M) of
the final mitigation system are also shown.
-------
I
to
en
O
CM
vl
I
s
s
2.5 -
2.0 -
1.5 -
1.0 -
0.5 -
n Observed
+ Calculated
H21
HIGH FLOW
28L/S
0 -F-T
I 1 3 4 8 a 7 • • 10 11 14 IS II 17 II II
DISTANCE (m)
10 11 14 19 II 17 ia It
Houmnian
Fig. 5 Using coefficients for 1.3 cm grave] (b = 1.6 Fig. 6 Comparison of observed and computed pressure
and k = 9.4 x 10~9m2). Data of holes 11 nnd 12 drops us!nj.', coelT !.c. ients of 1.3 cm Rr.nvcl.
not included. Data of holes 11 and 12 not included.
-------
10 II 14 IS U IT 11 It
Fig. 7 Using coefficients of 1.9 cm gravel (b = 1.4
and k = 3.4 x 10~9 m2).
-------
Fig.
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
FRACTIONAL RADIAL DISTANCE r/r0
8 Pressure drop in a sand bed with radial
airflow between two impermeable disks.
GRAVEL BED
River-run gravel
Small 1.3 cm
Large 1.9 Cm
Fig. 9
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
FRACTIONAL RADIAL DISTANCE r/rQ
Pressure drop in a gravel bed with radial
airflow between two impermeable disks. The
correction factor F can be determined from
Fig. 10.
(a)
§
O
CJ
g
O
O
§
O
CJ
12343678 9 10
1234567 89 10
0.15
0.13 •
0.11
0.09 ^
0.07 •
0.05
0.03
(4) -7.5=1
Large gravel
' Snail gravel
Fig.
1234 5678 9 10
ro (m)
10 Correction factor F for gravel beds to he
used in Fig. 9.
-------
I
a
CO
3
40
35 -
30 -
25 -
20
15 -
10
Both suction
pipes open
Central
pipe only
open
Perimeter
pipe only
open
1 2 S 4 5 S 7 8 9 10 13 14 15 16 17 18 1»
HOIX NUUBER
Fig. 11 Subslab suction pressure fields generated by the
mitigation system when different suction pipes
are used.
-------
V-2
THE ROLE OF DIFFUSION IN RADON ENTRY INTO HOUSES
by: Allan B. Tanner
U.S. Geological Survey
Reston, VA, 22092
ABSTRACT
Pressure-driven flow of radon-bearing soil gas is commonly accepted as
Che usual mechanism whereby radon moves from outside house foundations to
cause elevated indoor radon concentrations. It is less clear how radon moves
to the backfill-and-subslab zone just outside the foundation. Fourteen houses
having elevated indoor radon concentrations were investigated by the U.S.
Environmental Protection Agency and its contractors. The permeability of the
ground to gas flow was measured next to and several meters from each house
foundation. For 6 of the 14 houses none of the intrinsic permeability values
exceeded 7.6xlO~12 m2, below which diffusion is likely to be the dominant mech-
anism of radon movement. Because it can be significant in unsaturated soils
of moderate-to-low permeability, diffusion should not be ignored in consider-
ing radon movement to house foundations.
INTRODUCTION
Radon (222Rn) in the ground moves by two principal mechanisms. In res-
ponse to a gradient of radon concentration, there is a net movement of radon
atoms in the direction of lessening concentration by the process of diffusion.
In a porous medium such as soil, the effective diffusion coefficient, which
characterizes the rate of diffusion, depends primarily on the degree of liquid
saturation of the soil and secondarily on the porosity, pore sizes, adsorptive
properties of the soil grains, and absorptive properties of the liquid phase.
Diffusion can occur with or without soil-gas flow, which is caused by a
pressure gradient in the soil. The rate of soil-gas flow is controlled mainly
by the pressure gradient and the soil's permeability to gases. Permeability
depends strongly on pore and grain size; like the diffusion coefficient, it
decreases greatly as the fractional saturation of the soil by liquids
increases.
-------
It is generally accepted that where enough radon enters a house to cause
concern, entry Is usually due to pressure-driven flow of radon-bearing soil
gas (1,2). Diffusion of radon through concrete slabs and walls is slow enough
to reduce the radon concentration greatly by decay (3). Radon movement
through local cracks, sumps, and utility openings by soil-gas flow is favored
over diffusion if the air pressure within a house at the slab level is less
than that in the soil, and if the zone comprising the backfill and subslab
material is fairly permeable. Both conditions often exist, particularly if
the house slab is laid on the layer of coarse aggregate required by many
building codes. It is less clear to what degree each of the two mechanisms is
responsible for radon movement from the soil to the foundation wall or to the
underside of the slab. Presumably because of evidence that pressure-driven
flow causes the actual radon entry, most modeling to date has assumed that
diffusion can be neglected. I know of no study that justifies such an assump-
tion for other than very permeable soils.
The purpose of this paper is to present the several factors most impor-
tant to diffusion and flow, to relate them to various soil types and condi-
tions, and to show that diffusion, rather than flow, is likely to be the
dominant mechanism of radon movement to the foundations of some houses having
moderately elevated indoor radon levels.
COMBINED DIFFUSION AND FLOW
The first equation for steady-state, one-dimensional radon movement
incorporating both diffusion and flow velocity was derived by Grammakov (4).
Clements (5) derived an equation for the steady-state radon flux density
crossing the Earth's surface into the atmosphere. Multiplying the radon flux
density by the mean life of radon (the reciprocal of the decay constant)
yields the maximum amount-of radon per unit area that can be sustained by
steady migration from the source soil (6). Dividing that amount by the
concentration of radon that would build up in the soil gas if there were no
migration yields a distance, K, which is the volume of undepleted soil gas per
unit surface area that would contain the amount of radon sustained externally.
I call M the "mean migration distance." It is calculated as follows:
M - [l/(2L)][(-k/u)(dp/dx)+/(-k/u)2(dp/dx)2+4eLD], (1)
where H is in meters, L is the radon decay constant, e is the soil porosity,
k (mz) is the soil's intrinsic permeability to gas, u is the viscosity of air
(1.8xlO"s Pa-s at typical soil temperatures), dp/dx (Pa/m) is the pressure
gradient, and D (nr/s) is the (bulk) effective diffusion coefficient (see
references 3 and 7), equal to the interstitial effective diffusion coefficient
times the soil porosity.
The bulk effective diffusion coefficient can be estimated by the
following equation (8):
D/e - 7xl
-------
Typical permeabilities of soils range from 10~16 m2 for clays to
10~7 m2 for clean gravels (7). Although the mean migration distance in clays
is only of the order of 1 cm, diffusion is the dominant mechanism, and flow
can be neglected. For even very low pressure gradients, flow is dominant in
gravels and coarse sands. Because of their mixed grain sizes, most soils have
permeability values between the extremes, and the relative contributions by
flow and by diffusion depend not only on permeability and diffusion
coefficient, but also on the pressure gradient.
Figures 1 through 4 are graphs computed from equation (1) in order to
show the relative importance of diffusion and soil-gas flow for different
values of permeability, porosity, diffusion coefficient, and pressure
gradient. Because of interaction among the variables, the graphs should not
be used to infer the effect of changing a single variable on the flux density
of radon.
4
VERY FINE SANDS
ORGANIC AND INORGANIC SILTS
MIXTURES OF SANDS
SILT AND CLAY
5
M
W
I
CLEAN SANDS
CLEAN SAND AND GRAVEL MIXTURES
-14
-13 -12 -11
DDG10 PERMEABILITY (m2)
-10
Figure 1.
Mean radon migration distance for soils of 40 percent porosity,
50 percent water saturation, and -1 Fa/m pressure gradient. The
correlations of soil types with permeability values or ranges are
from reference (7).
-------
Figure 1 has been computed for a soil porosity of 0.4, a pressure
gradient of -1 Pa/m, a bulk effective diffusion coefficient of 4.8x10"7 mz/s,
corresponding to 50 percent water saturation, and the range of permeability
extending from that of a sandy clay to that of a uniform medium sand. The
permeability ranges of the soil types are taken from reference (7). Figure 1
shows that the mean interstitial migration distance is nearly independent of
permeability below several times 10'12 m2 under the specified conditions.
Soil-gas flow should contribute little to radon migration in poorly graded
soils containing substantial fractions of clay, silt, or fine sand. With
well-graded grains and larger grain sizes, soil-gas flow is more important
than diffusion.
W 3
1-1
Q
-14
-13 -12 -11
LDG10 PEBMEABIUTY (m2)
-10
Figure 2. Mean radon migration distance for soil of SO percent water satura-
tion, -1 Pa/m pressure gradient, and porosities of 20, 30, 40, 50,
and 60 percent (uppermost to lowest curves, respectively).
Figure 2 presents a family of curves computed for a pressure gradient of
-1 Fa/n, a diffusion coefficient corresponding to 50 percent water saturation,
and different values of porosity in the range from 20 to 60 percent. Soil-gas
-------
flow is significant at slightly lower values of permeability in low-porosity
soils than in high-porosity soils.
-14
•13 -12 -11
LOG10 PERMEABILITY (m2)
-10
Figure 3. Mean radon migration distances for soils of 40 percent porosity, 50
percent water saturation, and pressure gradients of -20, -5, -3,
-1, -0.5, and -0.1 Pa/m (uppermost to lowest curves, respectively).
Figure 3 presents a family of curves computed for soils of 40 percent
porosity, a diffusion coefficient corresponding to 50 percent water satura-
tion, and pressure gradients ranging from -20 to -0.1 Pa/m. Pressure differ-
ences of -5 Pa between U.S. houses and the soil are considered to be fairly
high (9). If a -5 Pa difference were distributed over the typical radon
diffusion length of about 1 m in soil, the resulting -5 Pa/m gradient should
cause soil-gas transport of radon to be more important than diffusion in soils
of permeability greater than about 10"12 m2. Such gradients are likely where
the radon flux converges at entry points such as cracks and utility openings,
and the gradients decrease markedly with distance from the entry points. At a
-------
house site where radon is effectively gathered from a zone several meters from
the foundation, the gradients should be much less than 1 Pa/m. Where radon
entry occurs over a broad front, such as through porous block walls or a
distributed crack system, the one-dimensional migration regime discussed in
this paper should be suitable.
-~» 4
E
-14
-13 -12 -11
DOG10 PERMEABILITY (m2)
-10
Figure 4. Mean radon migration distance for -1 Pa/m pressure gradient in
soils of 40 percent porosity and 10, 30, SO, 70, and 90 percent
water saturation (uppermost to lowest curves, respectively).
Figure 4 presents a family of curves computed for a pressure gradient of
-1 Pa/m in soils of 40 percent porosity and 10, 30, 50, 70, and 90 percent
water saturation. In the drier soils, soil-gas flow should be significant
with permeability exceeding 10"ll m2; in the wetter soils, soil-gas flow should
be significant at somewhat lower values. Increasing saturation of a given
soil reduces both its radon diffusion coefficient and its gas permeability.
-------
I am not aware of studies of the effects of increasing saturation on both
permeability and diffusion coefficient on the same material. However, Rogers
and others (10) presented figures showing approximately 30-fold reduction of
permeability from dry to saturated state and a three order-of-magnitude reduc-
tion of diffusion coefficient over the same range. Nazaroff and others (7)
gave data indicating a decrease of gas permeability by a factor of 50 to 100
between the dry and saturated states of loamy sand. Because the diffusion
coefficient enters into equation (1) to the 1/2 power, the effect of satur-
ating soil on the mean migration distance in it by diffusion should be
comparable with that for soil-gas flow.
Loureiro (11) included both diffusive and soil-gas flow mechanisms in
modeling radon entry from dry soil via a slab-to-footing gap. He concluded
that the diffusive mechanism was dominant for soils of permeability less than
10*12 m2, and that the soil-gas flow mechanism was dominant above that value.
FIELD DATA
Two sets of field data were available that included soil permeability
measurements for houses having indoor radon measurements exceeding the lowest
action level. The first set was obtained as part of the U.S. Environmental
Protection Agency's House Evaluation Program in work performed by Agency
personnel and contractors. Radon in soil gas and the permeability of the
ground close to and several meters from house foundations were measured by
soil-probe methods at locations in Colorado Springs and Denver, Colorado, in
northern Virginia, in Bartow and Lakeland, Florida, and in northern New
Jersey. Of 14 different houses having indoor radon measurements exceeding the
148 Bq/m3 (4 pCi/L) level, six had no measurement exceeding 7.6xlO"12 m2. The
maximum values measured were 2.2xlO'12, 7.6xlO'12, 7.4x10'", 1.2xlO'12,
3.3xlO"12, and 6.4xlO"12 m2. Permeabilities at the sites typically ranged to
values one to two orders of magnitude lower than the maximum. The greatest
permeability was usually found in the backfill zone near the foundation wall.
I investigated three homesites that were included in the House Evaluation
Program at the times of those tests. The three houses had indoor radon
concentrations of about 800 Bq/m3 (20 pCi/L) but are not included among the
six houses discussed above because the House Evaluation Program permeability
measurements exceeded 1x10"u m2 for those houses. By means of the procedure
described in reference (6), I measured permeabilities ranging from l.SxlO"12
to 7xlO'14 and from 2.2xlO'12 to 1.2x10'" m2 at two of the houses; two meas-
urements at different sites at the third house gave a value of 1.4x10'" m2.
At two houses in northern New Jersey, both of which had indoor radon levels
exceeding 7 kBq/m3 (200 pCi/L), I measured permeabilities of 7x10'" and
2xlO"10 m2, which were consistent with other observations of high permeabil-
ities associated with severe indoor radon levels (12).
-------
CONCLUSIONS
There is little doubt that severe indoor radon levels are very likely to
be associated with highly permeable soils. However, moderately elevated
indoor radon levels are sometimes associated with soils of low average perme-
ability. At such sites, diffusion is probably the dominant mechanism of radon
movement in the soil, particularly beyond the disturbed zone comprising the
backfill and subslab aggregate.
ACKNOWLEDGMENTS
This study was supported in part by the Office of Health and Environ-
mental Research of the U.S. Department of Energy under interagency agreement
no. DE-A105-87-ER60578. I thank R. Thomas Peake of the Office of Radiation
Programs, U.S. Environmental Protection Agency, for making some of the House
Evaluation Program data available.
The work described in this paper was not funded by the U.S. Environmental
Protection Agency and therefore the contents do not necessarily reflect the
views of the Agency and no official endorsement should be inferred.
-------
REFERENCES
1. Akerblom, G., Andersson, P., and Clavensjfl, B. Soil gas radon--a source
for indoor radon daughters. Radiation Protection Dosimetry. 7: 49, 1984.
2. Nero, A.V. and Nazaroff, W.W. Characterising the source of radon indoors.
Radiation Protection Dosimetry. 7: 23, 1984.
3. Culot, M.V.J., Olson, H.G., and Schiager, K.J. Effective diffusion
coefficient of radon in concrete, theory and method for field
measurements. Health Phys. 30: 263, 1976.
4. Grammakov, A.G. On the influence of some factors in the spreading of
radioactive emanations under natural conditions [in Russian]. Zhur.
Geofiziki. 6: 123, 1936.
5. Clements, W.E. The effect of atmospheric pressure variation on the
transport of Z22Rn from the soil to the atmosphere [Ph.D. dissertation].
New Mexico Inst. Mining and Technology, Socorro, N.M. 110 p.
6. Tanner, A.B. A tentative protocol for measurement of radon availability
from the ground. Radiation Protection Dosimetry. 24: 79, 1988.
7. Nazaroff, W.W., Hoed, B.A., and Sextro, R.G. Soil as a source of indoor
radon: generation, migration, and entry. In: W.W. Nazaroff and A.V.
Nero, Jr. (eds.), Radon and Its Decay Products in Indoor Air. John Wiley,
New York, 1988. p. 57.
8. Rogers, V.C., Nielsen, K.K., and Kalkwarf, D.R. Radon attenuation
handbook for uranium mill tailings cover design. NUREG/CR-3533, U.S.
Nuclear Regulatory Commission, Washington, D.C., 1984. 85 p.
9. Sextro, R.G. Oral communication, 1986.
10. Rogers, V.C., Nielson, K.K., and Merrell, G.B. Radon generation,
adsorption, absorption, and transport in porous media. RAE-8810-1 and
DOE/ER/60664-1, Rogers and Associates Engineering Corp., Salt Lake City,
Utah. 48 p.
11. Loureiro, C. de 0. Simulation of the steady-state transport of radon from
the soil into houses with basements under constant negative pressure
[Ph.D. dissertation). LBL-24378, Lawrence Berkeley Laboratory, Berkeley,
Calif. 278 p.
12. Sextro, R.G., Nazaroff, W.W., and Turk, B.H. Soil permeability and radon
concentration measurements and a technique for predicting the radon source
potential of soil. In: Proceedings of the 1988 Symposium on Radon and
Radon Reduction Technology, Vol. 1, Symposium Oral Papers.
EPA/600/9-89/006a. [U.S. Environmental Protection Agency] Radian Corp.,
Research Triangle Park, N.C., 1989. p. 5-61.
-------
V-3
SOIL GAS AND RADON ENTRY POTENTIALS £QR SUBSTRUCTURE SURFACES
Bradley H. Turk
Rm. 109, 105 E. Marcy St.
Santa Fe, New Mexico 87501
Jed Harrison
U.S. EPA Office of Radiation Programs
Washington, D.C. 20460
Richard J. Prill
Washington Energy Extension Service
Spokane, Washington 99201
Richard G. Sextro
Indoor Environment Program
Lawrence Berkeley Laboratory
Berkeley, California 94720
ABSTRACT
Measurement techniques and parameters that describe the potential for
areas of a building substructure to have high soil gas and radon entry rates
have been developed. Flows and pressures measured at test holes in
substructure surfaces while the substructure was intentionally depressurized
were used in a highly simplified electrical circuit to model the
substructure/soil network. Data from four New Jersey houses indicate that (1)
the soil was a factor of two to six times more resistant to soil gas flow than
substructure surfaces, (2) concrete slab floors, including perimeter gaps,
cracks, and other penetrations, were approximately five times more resistant
to soil gas movement than hollow block walls, and (3) radon entry potentials
were highest for slab floors. These Indices of entry potential may be useful
for characterizing the relative leakiness of below-grade substructure surfaces
and for determining the selection and placement of radon control systems.
INTRODUCTION
It is widely accepted that the pressure-driven flow of soil air into
buildings is the most frequent cause of elevated indoor radon levels. Several
studies have proposed techniques that define the ability of soil at a
particular site to supply radon to a building structure via this convective
flow (1,2,3,4,5). In some of these studies, the magnitude of the pressure
field extending from a mechanically-depressurized house has also been mapped
(6,7,8). The pressure coupling between the house and the soil location can be
defined as the ratio of the pressure difference between the measurement
location and the substructure to the depressurization of the substructure
relative to outside. A snail value for the pressure coupling indicates the
existence of pathways connecting the house and soil location. The pathways
-------
consist of openings through the substructure surfaces (cracks, holes,
perimeter drains, etc.) and regions in the materials around the house that
permit relatively unrestricted transport of soil air (permeable soil, gravel
layers, and air gaps). Other work, some related to the control of indoor
radon, has attempted to identify soil air pathways near substructures and to
locate radon entry points in the building envelope (9,10,11,12).
Various measurements of the air permeability of the soil performed during
many of the above studies are indicators of the mobility of soil gas in
materials around a house. The air permeability can vary widely over both
vertical and horizontal dimensions. High permeability zones were often found
near substructures and were caused by less tightly-packed soil in the area
disturbed by construction, layers of material provided for drainage (gravel),
and air gaps below slab floors or near walls - some extended to the soil
surface - created by expansion/contraction cycles and settling (4,13).
In this paper, we describe entry potentials for soil gas and radon
through substructure surfaces that are based on the developments from the
research mentioned above and on flows, pressures, and radon concentrations
measured at the substructure/soil interface. This approach simplistically
considers the below grade substructure surfaces, near-house materials, and
nearby soils as elements of a "black box" whose aggregate characteristics
assist in estimating the likelihood and relative magnitude of soil gas and
radon entry. We do not include transport by diffusion. In addition, the
analysis enables comparisons of the resistance of soil and of the below-grade
substructure surfaces to air flow.
SOIL GAS AND RADON ENTRY POTENTIALS
Below grade, most houses are surrounded by a very complex matrix of
soils, rock, and construction-related materials or structures, each having
different capacities for radon production and soil gas and radon transport. In
most situations, details of the geometry, characteristics, and interactions
between these features and with the substructure cannot be known. Plus, the
condition and construction details of the substructure surfaces in contact
with these exterior materials are not fully known.
In order to account for these complexities without knowing their
specifics, a method to integrate the flow and pressure characteristics is
useful. If we assume a linear pressure dependence for air flow through soils
and materials around the substructure (i.e., Darcy flow), the passage of soil
gas through soil and into a substructure depends on the resistance of the flow
path through the materials around the substructure and through the surfaces of
the substructure. Therefore, a simplified electrical resistance analog of a
typical basement/soil system can be created, as shown in Figures la and Ib, to
simulate the flows, pressure drops, and resistances in the soils, near-house
materials, and substructure surfaces.
A blower door that enhances depressurization in the substructure is
represented by the battery in the circuit. The test holes drilled through the
floor and walls permit measurements of air flows (current) and pressure drops
(voltage) at various nodes in the circuit. While the blower is operating, the
system is tested in two conditions: with the test hole closed and with the
test hole open. With the test hole sealed, good pressure coupling between the
interior of the substructure and the exterior at a test hole location (pathway
with low effective resistance) may result from nearby cracks and openings in
the substructure surfaces or from more distant openings through the
substructure that are connected by high permeability pathways to the test
-------
hole. Good coupling does not, however, necessarily mean that large quantities
of soil gas will enter through the nearby openings. The soil, aggregate, or
backfill material around the substructure must also be sufficiently permeable
so that substantial quantities of soil gas can be transported to the openings.
Therefore, with the test hole open (indicated in Figure Ib by the dotted lines
representing the current, IH, and resistance, R^, of the test hole and flow
measurement adaptor), a high air flow rate through the test hole suggests high
permeability (low effective resistance) in the materials around the
substructure and relatively rapid transport of soil gas to the nearby openings
in the substructure surfaces. In general, when both good pressure coupling
and high flow rates are measured at a test hole, then it is likely that
significant amounts of soil gas will enter the house around that location.
A more quantitative interpretation of the data requires analysis of the
analogous electrical circuit. Following are symbols and definitions (and the
corresponding electrical parameters) used in the derivations. The subscript
"C" identifies the condition with the test hole closed.
QH (IH) = measured (corrected) flow through open test hole and flow adaptor
(m3/s),
QF (Jp) " defined flow through cracks and openings in below-grade substructure
surfaces with test hole open (m3/s),
QT (IT) = defined total flow through cracks, openings, and test hole (m3/s),
PB (VB) - measured pressure difference between inside of basement and
outside, point a to c (Fa),
PH (VH) = calculated pressure drop across open test hole and flow adaptor,
point a to b (Pa),
Ps (Vs) - pressure drop across soil paths between point b and outside with
test hole open, PB - PH (Pa),
RH = defined resistance of open test hole and flow adaptor (Pa-s/m3),
RF-EFF = calculated effective resistance that lumps resistances of cracks
and openings in substructure surfaces and resistances of near-
substructure materials surrounding the open test hole (RF1, RF2»
RF3, etc.) (Pa-s/m3), and
Rg.gpp - calculated effective resistance of soil paths to measurement
point b (Rg!, R^, Rgg, etc.), with test hole open (Pa-s/m3).
We assume that the complex network of resistances through the soil and
substructure surfaces is represented approximately by the simplified circuit
shown to the left in Figure Ib. With the test hole closed, a resistance
ratio, Z (i.e., the resistance of the substructure surfaces and
near-substructure materials divided by the resistance of the soil), can be
defined as
~" 17 ID D
V sc 'TCKSC-SFF KSC-BFF
-------
Using Kirchoff's rule for circuit analysis when the test hole is open, the
following three independent equations are derived
^8 - IHRH ~ h*S-EFt - 0 , [3]
IF&F-F.FF ~ IH*H = 0 , and [4]
IT ~ If ~ IH = 0 ' [5]
If we assume that
RFC-CFF " RF-SFF ano<
RSC-EFF " &S-SFF
then we can solve for Rg-gpy, using equations 2 through 5 and substituting for
analogous air flow and pressure parameters, to obtain the effective soil
resistance,
s'
fFF
RF-EFP is found by solving equation 2. These two resistance parameters enable
comparisons of the resistance to air flow created by the soil and substructure
surfaces .
Combining these resistances, we now define the entry potential of soil
gas at a location, G (a3/Pa-s), as the net conductance through the surrounding
soil, near- substructure materials, and substructure surface materials from
;r
S-SFF * Kf-tFF
fr - » - ;r» - . or [7]
K- *
'-IFF
Qr • [8]
Thus, larger values of either Rg.gpp or Rp.Epp result in a smaller soil gas
entry potential.
Note that the area over which to apply the effective resistances and
entry potential is not defined. In an ideal situation, where the subfloor
materials are highly permeable (RF2 is small) and the substructure surfaces
and surrounding soils are homogeneous - without discontinuities such as
impermeable barriers or large short circuits, a single test hole location
would suffice to calculate the total resistance of the substructure surfaces
and of the soils. However, many of these discontinuities may exist around
typical houses. Consequently, more than one measurement location is required
to determine the local resistances at different locations. Unfortunately, in
this situation with many test locations, it is difficult to know the distance
from each test location over which the resistances are derived. Indeed, for
those test locations in homogeneous materials such as subfloor gravel layers,
identical conditions may be measured over a large area. While at the same
house, measurements made at test locations in different materials could
represent conditions very near to the test location.
-------
The entry potential of radon, E (Bq/Pa-s), may be defined as the mass
transfer of radon found near the substructure surfaces, C (Bq/m3), with the
prevailing pressure -normalized flow of soil gas into the building (soil gas
entry potential):
£ = CC • [9]
Similar to the soil gas entry potential, the radon entry potential should
indicate the likelihood that significant amounts of radon can enter a building
through an area of the substructure surface. Both high soil gas entry rates
(soil gas entry potential) and high radon concentrations at the exterior of
the substructure will cause a higher radon entry rate (radon entry potential).
EXPERIMENTAL PROCEDURES
At four New Jersey houses , a blower door depressurized the substructure
by -10 Pa to -37 Pa while air velocities and pressure differences were
measured at indoor test holes. Measurements were made at up to three
different pressures in two houses, LBL13 and LBL14C. By artificially
depressurizing the building, the magnitude of most parameters was increased so
that they were more easily measured and so that many environmental effects
were minimized. All tests were conducted during June 1987. These houses were
part of a larger research project investigating radon entry and control (14).
In each house, approximately 30 test holes (6 mm to 13 mm in diameter)
had been drilled through substructure slab floors and hollow block walls, and
into the block cavities of these walls (approximately 0.25 m above the floor)
for a variety of measurement purposes. Some of the test holes through the
floors penetrated only to the space or gravel layer directly below the slab,
while at other holes, probes extended approximately 1 m into soil that was
compacted before the slab was poured. At one location on each exterior wall,
a probe completely penetrated the block wall to the soil.
In separate experiments conducted while the house was depressurized by
the blower door, a pressure field map was made of the pressure coupling at
some indoor test holes and at approximately 25 locations in the soil around
the house. The soil probes were 13 mm OD and were placed at depths ranging
from 0.2 m to 2.2 m and distances of 0.5 m to 3.5 m from the houses. The
pressure coupling data for the soil probes provides an interesting comparison
to those data measured at the test holes in the substructure surfaces.
Pressure differences were measured between each soil probe or exterior of
each test hole, VK (test hole sealed), and the basement. All other test
holes and soil probes were kept sealed. The basement depressurization, PB,
was measured relative to outside. All pressures were measured using an
electronic micromanometer with a minimum resolvable pressure difference of 0.5
Pa and an accuracy of 1%.
Air velocities as small as 0.025 m/s at the open test holes were measured
with a hot wire anemometer attached to a flow adaptor designed to mate with
the various-sized holes (Figure 2). Where necessary, flow rates (IH) were
corrected for the effects of the size of the test hole. The pressure drop
across the flow adaptor and test hole (PH) was estimated using the engineering
formula for laminar flow through a tube
_ m [10]
x nr4
-------
where PH - pressure drop (Pa),
x = length of the test hole plus flow adaptor (m),
H . absolute viscosity of air, 1.8 x 10~s kg/in-s, and
r = radius of the tube (in our case, we used the radius of the
flow adaptor - 0.0045 m).
Estimated pressure drops in the test hole and flow adaptor ranged from 0.01 Pa
to 3.5 Pa. In theory, a more accurate value for this pressure drop could be
determined by direct measurement; however, the small pressure differences are
difficult to measure in practice.
To determine the radon concentration in soil gas near the substructure,
G, grab samples of soil gas from the test holes were collected in evacuated
alpha scintillation flasks. The radon activity in the flasks was counted on a
portable photomultiplier tube and sealer. Because grab samples were not
always collected concurrently with measurements of flow and pressure
difference, samples collected at other times during the study were used to
compute average radon concentrations for the test holes. Uncertainties in the
radon concentrations measured with this procedure are estimated to be ± 20 X.
RESULTS AND DISCUSSION
A total of 117 measurements were made at 75 test holes in the four
houses. The average calculated effective resistances for soil (RS-EH?) and
substructure surfaces (1^-^) are summarized in Table 1. The data are grouped
according to location of the test hole. There is considerable variability in
the resistances among test holes as indicated by the large standard
deviations. By examining the geometric means, several patterns are apparent
and statistically significant: 1) the effective soil resistance that is 'seen'
by the test locations across the slab floors and in block wall cavities is
similar, probably because large surface areas of soil (and for the block walls
- wall areas exposed directly to the outside air) are accessible to the test
holes; (2) the slab floors are approximately five times more resistant to soil
gas movement than the interior surface of the porous block walls; and (3) for
all locations, except those in the soil exterior to the walls, the
substructure 'sees' the soil as being a factor of 2 to 6 times more resistant
to soil gas flow than the substructure surfaces and the materials very near to
the substructure. We also find that the entire thickness of a block wall is
many times more resistant to soil gas flow than only the interior surface of
the block - presumably because of the coatings and sealants that are applied
to the exterior surface for waterproofing. These data support the view that
the flow of soil gas into buildings depends to a lesser degree on the
resistance of the building surfaces below grade than on the resistance of the
surrounding soil and materials. It is important to recognize that low
resistance values can result from low resistance in the materials near to the
test locations or from the sum of many parallel resistances when the test
location 'sees' a large area of soil and building material.
Average soil gas entry potentials, G, for each of the 75 test holes are
shown on Figures 3 through 6. Pressure coupling ratios from the pressure
field mapping tests are also shown so that comparisons can be made among the
test locations. See Table 3 for a description of the symbols used on these
figures. Values for G ranged from less than 0.01 x ID'9 m3/Pa-s to 3.2 x lO'*
mVPa-s. These data are summarized in Table 2 by the same groupings as in
Table 1 The geometric mean soil gas entry potential is highest for the
hollow block walls, probably because of the high porosity (lower effective
-------
resistance) of the block wall material and because the large exterior surface
area exposed to soil and/or outdoor air is available to most entry locations
on the interior surface via the interconnecting network of cavities. Similar
conclusions were reached by Garbesi and Sextro (6).
For the two houses where G was calculated for different basement
pressures, the mean coefficient of variation for replicates at 35 test holes
was 49%. The entry potential did not appear to be biased by level of
depressurization.
If we assume the average soil gas entry potential (0.73 x 10'6 m3/Pa-s)
is for an effective area of 1 m2, then for a house with 175 m2 of below grade
surface area at a natural depressurization of 3 Pa, the soil gas entry rate
is predicted to be 1.4 m3/h. This soil gas entry rate is similar to the 1 m3/h
calculated by other researchers (6,15,16,17), and lower than that measured in
houses on highly permeable soils (18).
Data for the radon entry potentials, E, at each house are also shown on
Figures 3 to 6 and are summarized in Table 2. For 73 test holes, the
geometric mean radon entry potential was highest for the test locations in
subslab aggregate. Although the test holes into the block wall cavities had a
slightly higher soil gas entry potential, the subslab test holes had greater
concentrations of radon in the soil gas which compensated for their smaller
soil gas entry potential. Calculated values of E ranged from less than 0.1 x
10'3 Bq/Pa-s to 1300 x 10'3 Bq/Pa-s.
When reviewing the radon entry potential plotted on Figures 3 to 6, we
find that the areas of highest potential generally coincide with the locations
where the pipes of successful subsurface ventilation-depressurization (SSD)
radon control systems were placed through the slabs. For these houses, a
'high' radon entry potential would be considered greater than approximately
15 x 10'3 Bq/Pa-s. Since the entry potentials were calculated after
installation of the SSD systems, these indices appear to provide a
quantitative method for replicating the intuitive approach of successful
mitigation contractors. House LBL12 is an exception, where it was difficult
to bring indoor radon levels below the target concentration of 148 Bq/m3.
There were areas of high radon entry potential in this house that were not in
proximity to an SSD pipe, and may have been the sources of inadequately
controlled radon entry (Figure 4).
In general, the radon entry potential may indicate the preferred
locations for SSD pipes, but will not provide information about the ability of
a specific SSD system to reduce radon entry rates. The pressure field
extension test that uses a vacuum cleaner or depressurizing blower remains the
best technique to measure the extent to which a SSD system can reverse the
natural pressure gradient around a substructure, and therefore control radon
entry (10). Combining results from the pressure field extension test with
identified areas of high radon entry potential may assist contractors deciding
on the placement of SSD pipes. When the soil gas (and radon) entry potential
is high for a particular location, but the pressure field extension or
connection to the vacuum .is poor, obstructions or high permeability short
circuits are probably blocking or intercepting the pressure field from the
vacuum. The problem then is to provide access to the areas of high radon
entry potential.
The geometric mean radon entry potential for each of the four houses was
compared with the average indoor radon concentration, measured between
September 1 and May 1 and weighted by the volumes for various zones where
indoor radon was measured. From the lowest to the highest average indoor
radon concentration; 540, 620, 650, and 660 Bq/m3, the geometric mean radon
entry potentials were 6.4, 10, 7.2, and 18 x 10'3 Bq/Pa-s, respectively. Only
-------
for the third house listed (LBL13), does the geometric mean radon entry
potential fail to trend with increasing indoor radon concentrations. The
geometric mean radon entry potential (assumed to be for an effective area of 1
m2} can also be used in a mass balance equation along with actual surface
areas and structure volumes and an assumed pressure difference of 3 Pa and
ventilation rate of 0.5 h'1 to calculate a steady-state indoor radon
concentration for each house. The correlation is poor between these
calculated values (42, 39, 24, and 103 Bq/m3, respectively) and the actual
radon levels. And we see that using the radon entry potentials under-predicts
actual radon levels by factors of 6 to 30.
LIMITATIONS
That the current development and application of these new parameters may
still have weaknesses, is suggested in some of the data just presented. The
electrical analog is imperfect since it assumes linear flow characteristics -
which may not occur either under natural depressurization at entry locations
or under the greater mechanically-induced depressurization at both entry
locations and test holes. A more appropriate analogous circuit would also
include capacitance to represent the storage and discharge of radon that is
assumed to occur in spaces near the substructure in response to time-varying
driving forces.
In addition, the assumptions, REC-EFF = &F-EFF an<* RSC-EFF ° &S-EFF> are not
exactly valid, since the paths for air flowing through the soil and building
surfaces are different in the two measurement conditions. The effects of
inhomogeneities in soils, near-house materials, and substructure surface
materials on the assumption have not been examined. Although the derivation
is generally not sensitive to the pressure drop across the test hole and flow
adaptor (right hand term in the numerator of Equation 6), the term was
occasionally as large as 55% of the substructure depressurization (PB). This
term has the greatest impact when the pressure drop across the test hole is
large or when substructure surfaces are leaky (small Z). Since the test hole
diameter will also have an important effect on the measured flow rate, all
test holes should be drilled to the same size or corrections to a standard
hole size (for this study, a 9 mm dia. hole) should be made. Then entry
potentials may be more accurately compared between test holes and between
houses.
The soil gas entry potential at a particular location is affected by all
soils, materials, and openings in the below-grade surfaces around a building,
but to a greater degree by those nearby or connected by a high permeability
path. More study is required to determine the distance from a test hole over
which the soil gas entry potential is applicable. For example, if RF2 in
Figure Lb is small (i.e., highly permeable subfloor material), then the
distance is large. If RF2 is large, then the entry potential is more
localized. When these relationships are better understood, the test holes can
be better placed to best represent the soil gas entry throughout the entire
substructure.
The time-varying nature of many of the measured parameters may create
difficulty in using a one-time determination of soil gas and radon entry
potentials to represent typical entry potentials for a house. For example,
the radon concentrations measured in grab samples collected from the test
holes under natural conditions showed large variations. Repeated samples
(between two and seven) were collected from 45 test holes at six houses over a
12-month period when radon control systems were not operating. The mean
-------
coefficient of variation for the radon concentration at each test hole was
79%. Concentrations at the same test hole varied by up to a factor of 1000
from one sample to another. It is possible that these large variations in
radon concentrations were caused by changes in wind, radon production in the
soil, or soil gas flow rates into the houses. The radon concentration in grab
samples from individual test holes collected during mechanically-induced
depressurization can also be considerably different from concentrations during
natural conditions. However, when concentrations measured at 99 test holes in
seven houses during mechanically-induced depressurization were correlated with
corresponding concentrations during natural conditions, we found a correlation
coefficient (R) of 0.68 and that the means for the two conditions were not
significantly different. This suggests that radon concentrations in samples
collected during a brief period of mechanically-induced depressurization may,
on average, be representative of concentrations under natural conditions.
In addition to variations in radon concentrations, it would not be
surprising to also observe changes in the soil gas entry potential due to
changes in soil permeability (for example, caused by precipitation or a moving
water table). More study on the time-dependent variation of these parameters
is required.
SUMMARY
A procedure has been described to determine the potential for soil gas
and radon to enter a house at substructure surfaces by convective flow from
the soil. The necessary field measurements of flow, pressure, and radon
concentration are relatively simple and utilize commonly available equipment.
These parameters for entry potential may be useful to: (1) identify areas in a
substructure with the potential for comparatively high soil gas entry rates;
(2) compare the relative leakiness of below-grade surfaces in different
houses; (3) provide approximate measures of the resistance of the substructure
surfaces and soils/materials around the substructure and provide a basis for
establishing the relative importance of these features to radon entry; and (4)
identify areas in a substructure with potentially high radon entry rates for
placement of radon control systems.
Initial measurements in four houses indicate that the soils surrounding
the houses are approximately three times more resistant to the transport of
soil gas than the substructure surfaces and the materials near the
substructure. Soil gas has approximately twice the entry potential at the
surfaces of hollow block walls than at slab floors, but the slab floors have
much higher radon entry potentials because of the greater radon concentrations
below the slabs.
Modifications to the simple electrical resistance circuit used in this
development to represent the substructure/soil system may improve the
predictive capability of the procedure. In addition, determination of these
new parameters in additional houses and under changing seasonal conditions is
necessary to more fully examine their suitability as diagnostic and research
tools.
ACKNOWLEDGMENTS
We appreciate the insightful comments of William Fisk. Ashok Gadgil, and
Mark Modera; the program support of David Sanchez at AEERL, U.S. EPA; and the
cooperation of the families of the seven New Jersey houses.
This work was supported by the Assistant Secretary for Conservation and
-------
Renewable Energy, Office of Building and Community Systems, Building Systems
Division; by the Director, Office of Energy Research, Office of Health and
Environmental Research, Human Health and Assessments Division and Pollutant
Characterization and Safety Research Division of the U.S. Department of Energy
(DOE) under Contract No. DE-AC03-76SF00098; and by the U.S. Environmental
Protection Agency (EPA) through Interagency Agreement DW89931876-01-0 with
DOE. This paper has been reviewed in accordance with the U.S. EPA's peer and
administrative review policies and approved for presentation and publication.
REFERENCES
1. Nazaroff, W.W. Predicting the rate of radon-222 entry from soil into the
basement of a dwelling due to pressure-driven air flow. Radiation
Protection Dosimetry. 24: 199-202, 1988.
2. Nazaroff, W.W. and Sextro, R.G. Technique for measuring the indoor 222Rn
potential. Environmental Science and Technolpgy. 23: 451, 1989.
3. Schery, S.D. The design of accumulators and their use in determining the
radon availability of soil. In: Proceedings of the 82nd Annual Meeting of the
Air and Waste Management Association. 89-79.2, Anaheim, CA., 1989.
4. Sextro, R.G., Nazaroff, W.W., and Turk, B.H. Spatial and temporal
variation in factors governing the radon source potential of soil. In:
Proceedings of the U.S. EPA Symposium on Radon and Radon Reduction Technology.
EPA-600/9-89/006a. pp. 5-61 to 5-74. Research Triangle Park, N.C., 1989.
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(ed.), ACS Symposium Series No. 331, Radon and Its Decay Products: Occurrence,
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9. Figley, D.A. and Dumont, R.S. Techniques for measuring the air leakage
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Anaheim, CA., 1989.
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10. Gadsby, K.L., Hubbard, L.M., and Harrje, D.T. Rapid diagnostics: subslab
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und Lufthygiene: Berlin. 2: pp. 316-320, 1987.
17. Nazaroff, W.W., Feustel, H., Nero, A.V., Revzan, K.L., Grimsrud, D.T.,
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Characterizing the occurrence, sources, and variability of radon in Pacific
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1989.
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(a)
BRSEtlENT INTERIOR
HOLLOU-CORE
BLOCK UflLLS
(b)
EFFECTIVE
RESISTflNCES
Figure 1 Drawing of substructure during pressure field mapping and basement depreaauriiation (a).
A simplified electrical analog of the various flows, pressure drop*, and reaiatancea during the teat
depicted in (a) is shown in (b). The dotted line indicates the variables associated with an open
teat hole. A further simplification ia shown by the circuit on the left aide of (b).
-------
26
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Figure 2. Flow adaptor device used to measure the flows through the teat holes. The bottom opening
of the adaptor seals against the test hole surfaces, while flows are measured with a hot wire
anemometer probe placed Inside the open end of the adaptor.
-------
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Figure 3. A site plaa of house LBL08 that shows the locations of probes in the soil around the
house, holes drilled through the slob floors (solid dots), test holes drilled into and through
hollow block walls (vertical and horizontal lines), and the pipes for the radon control systems.
Data for pressure coupling ratios during pressure field mapping tests (PFM), and for soil gas (6)
and radon (E) entry potentials are placed under the identification code for the test holes. See
Table 3 for more complete descriptions of the codes and symbols that are used.
-------
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-------
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-------
Table 1. Statistical Summary of Effective Resistances for Soils and
Substructure Surfaces from Four Houses
Material
Category
Below Slab
Gravel
Test Hole Location
Block Wall Hall
Cavity Exterior
All
Locations
Soils, Rs-EFF (1C6 Pa-s/m3)
Geom. Mean
Geom Std Dev
Arith Mean
Arith Std Dev.
Number
Substructure Surfaces
Geom Mean
Geom Std Dev.
Arith Mean
Arith Std Dev
Number
Table 2 Statistical
Four Houses
Entry
Potential
1.2
5.0
5.3
11
22
, RF-EFF <106 Pa"s/
0 65
4 8
3 0
7.7
22
Summary of Soil Gas
Below Slab
Gravel
0.68
2 2
1.1
2.1
44
n>3)
0.12
2.1
0.16
0.12
44
and Radon
Test Hole
Block Wall
Cavity
2.5
5.8
8.1
12
9
5.7
7 8
19
26
9
0.93
3 6
3.2
7.7
75
0.32
6.0
3.2
11
75
Entry Potentials from
Location
Wall
Exterior
All
Locations
Soil Gas Entry Potential, G (ID'S m3/Pa-s)
Geom. Mean
Geom Std Dev
Arith Mean
Arith Std Dev
Number
Redon Entry Potential
Geom. Mean
Geom Std. Dev.
Arith Mean
Arith Std Dev.
Number
0.5
4 8
1.1
0.85
22
, E (10-3 Bq/Pa-s)
23
6 7
110
280
22
1.2
1.6
1.4
0.52
44
7.9
5.1
24
42
42
0.11
4 3
0.24
0.28
9
3.2
6.4
21
54
9
0 73
3 6
1.1
0.70
75
9.7
6.2
48
160
73
-------
Table 3. Key to Symbols for Figures 3 to 6
LOCATIONS
I = Indoor
W = Wall
(B) = Into block wall cavities
Blank = Through wall, into soil
Top = Opening into block at top of wall
F = Through floor
FS = Floating slab
0 = Outdoor
A « 0.5 m from house
B « 1.5 m from house
C « 3.0 m from house
N,E,W,S = Orientation to compass direction
1,2,3,... = Arbitrary sample location number
SSD PIPE = Subsurface depressurization pipe for radon control
system
BWV PIPE = Block wall ventilation pipe for radon control system
VAC. HOLE = Test hole where vacuum was placed for pressure field
extension tests
MEASUREMENTS AND DATA
PFM = Pressure field map coupling ratio [•= """"" I
\' OUTSIDE ~ r BASEMENT J
I = Initial test, basement depressurized to -30 Pa
10 = Basement depressurized to -10 Pa
30 = Subsequent tests with basement depressurized
to approx. -30 Pa
OR = Over range
G = Soil gas entry potential (10~6 m3/Pa-s)
E = Radon entry potential (10~3 Bq/Pa-s)
-------
V-4
MEASUREMENTS AND MODELLING OF RADON INFILTRATION INTO A DWELLING*
by: F. Stoop, F.J. Aldenkamp, E.J.T. Loos, R.J. de Meijer and
L.W. Put
Kernfysisch Versneller Instituut
Rijksuniversiteit Groningen, Zernikelaan 25, 9747 AA
Groningen, the Netherlands
In situ measurements in a Dutch test dwelling of radon exhalation of
walls, floor and soil in and under the dwelling are interpreted in terms of
source strengths. Continuous measurements of radon concentration in various
compartments (e.g. crawl space and living room) of the same dwelling
together with measurements of leakage parameters, temperature, pressure
differences between compartments and ground-water table are used to obtain
information on the dynamic aspects of the radon infiltration. Source
strengths and dynamic variables are used as input for a multi-room model to
describe the variations and interrelations of radon concentrations in
various compartments. Despite the relatively low radon concentration in the
soil gas (~ 10000 Bq.nf ) and the low permeability of the soil, preliminary
analyses suggest pressure driven flow through the soil to the crawl space to
be an important radon source. A possible influence of precipitation on this
flow and on the source strength for the soil of the crawl space is
discussed.
*) Research supported in part by the Dutch Government and the Commission of
the European Communities.
-------
1. INTRODUCTION
Radon being a noble gas has the property to move from its location of
birth by two physical processes: diffusion and pressure driven flov.
Diffusion is the process by which radon is transported due to concentration
differences. Pressure differences cause transport through e.g. porous
materials and openings in walls. The importance of the transport is
determined by the product of current and concentration; a low current with a
high concentration may be equally important as a high current with a low
concentration.
To design effective countermeasures against elevated radon
concentrations, source strengths, entry routes and driving forces have to be
known. Source strengths can be estimated for a dwelling by measuring in situ
the exhalation rate of various components of a dwelling. Entry routes and
driving forces may be determined from measurements of radon concentrations
simultaneously with other relevant physical parameters.
The dynamic aspects have been measured in houses in New Jersey by the
groups of Berkeley and Princeton-Oak Ridge. So far, to our knowledge, no
results have been published in the open literature. Also in Finland
continuous measurements of radon have been made by Arvela tt al. (1). They
compare the variation in measured radon concentrations of 33 houses with
variations calculated with a model which relates indoor radon concentrations
to radon entry rate, air infiltrations and meteorological factors. In houses
with a slab on ground the measured seasonal variations are often explained
almost entirely by pressure driven flow. Diffusion is according to ref. (1)
a significant source in case of large porous concrete walls against the
soil. According to their measurements and calculations the diurnal maximum
in the radon concentrations occurs in the morning and is caused by pressure
driven flow.
Median radon concentrations in the Netherlands (2-3) are comparable to
values found in the Federal Republic of Germany and England. However, due to
the absence of rock near the surface, except for the far south eastern tip,
the percentage of dwellings with high concentrations is smaller. In the
absence of the need for immediate mitigation an investigation of radon entry
and transport for a "typical" house may provide knowledge which leads to
reduction of the population dose due to exposure to radon.
In the present investigation measurements are carried out in a test
dwelling in Roden in the northern part of the Netherlands. As most Dutch
dwellings it has a crawl space which is the result of excavating a part of
the soil and refilling it partly with sand. The soil in the 50 cm high crawl
space is uncovered. Radon concentrations in the crawl space and the living
room have been monitored with time-integrating detectors since 1980.
-------
Unexpected variations (4) were observed in the year average radon
concentrations, which are likely due to fluctuations in the ground water
level often inundating the crawl space.
The aim of the present investigation is to obtain better understanding
of the behaviour of radon concentrations in dwellings. This goal is thought
to be achieved by developing a dynamic model in which the radon
concentrations are calculated from static source strengths and air currents.
For the source strengths the exhalation by walls, floors, ceilings and soil
were measured; air currents were deduced from measured pressure differences
and measured or estimated leak sizes. Moreover a number of possibly relevant
parameters as ground water level, relative humidity, temperature, barometric
pressure, and precipitation rate were measured and ventilation rates were
deduced.
In this paper we present measurements and calculations for two periods
of one week with different characteristics. An hypothesis is formulated in
which rainfall plays an important role in changes of values of exhalation
rate, source strength and pressure driven flow.
2. TEST DWELLING AND EXPERIMENTAL PROCEDURES
2.1. TEST DWELLING
The test house is located in Roden, southwest of the city of Groningen
in the northern part of the Netherlands. It is located on the edge of the
"Drents Plateau"; the local soil consists of silty fine sand with
intercalations of boulder clay upon "pot clay". The impermeability of the
pot clay causes large and rapid variations in the groundwater level. Prior
to the installation of a water drainage system in February 1989 the ground-
water levels often almost reached the soil surface. Such situations are not
uncommon for recently build houses in various parts of the Netherlands.
The dwelling is a single family house, built in 1973. It has a
rectangular floor shape with a wall extending from the crawl space to the
roof, which divides the house into a northern and southern part which can be
regarded as reasonably independent. In the present investigation only the
southern part is investigated. This part consists of a crawl space and a
high loft living room, with an "open kitchen", directly covered by the roof.
The ceiling of the crawl space consists of prefab hollow concrete bars which
are covered by a layer of a few centimeters cement; in the living room this
layer is covered with ceramic tiles. The outside walls are cavity walls
consisting of masonry (about 10 cm thick); the cavity has been filled in
1976 with a polyurethane foam for thermal insulation. The floor of the crawl
space consists of uncovered sand and is situated at about 40 cm below the
-------
surrounding soil of the yard. Around the house, at a distance of 1 to 1.5 m,
a ring type drain has been installed in February 1989 at a depth of 70-90 cm
belov the surface. The dividing vail in the crawl space has tvo crawl
openings in addition to feed throughs for central heating (water) and
utilities. In June 1989 these openings have been closed by 5 cm thick foam
board. All remaining openings in the wall were sealed with caulk. In October
1989 a 20 cm diameter ventilation duct plus fan was installed in order to
(de)pressurize the southern part of the crawl space. Natural ventilation of
the crawl space occurs via ventilation shafts to the outside air; in
principle these shafts should have no connection with the cavity wall.
2.2. EXPERIMENTAL TECHNIQUES
Radon exhalation rates were measured with a device developed from a
prototype designed by Ackers (5). A description of the modified version and
its collection properties is given in ref. (6). For a measurement the device
is placed on a surface; soft-rubber rings at the ends of the two coaxial
cylinders are supposed to fit air-tight to the surface. For rough surfaces
caulk is applied to the surface and the outer ring after the device has been
mounted. For measurements in soil a 30 cm long cylinder with a flat and
smooth top surface is placed in the soil on which the device is mounted.
Prior to each measurement the device is flushed with dry nitrogen.
The exhalation rate, E, is determined from a fit to the growth curve
for the radon concentration C
C(t) = * (1 - e'Xt). (2.1)
In this equation A is the area covered by the inner cylinder and V is the
measuring volume. The quantity X is the effective decay constant and is the
sum of the nuclear decay constant of radon and a constant associated with
leakage by diffusion from the measuring volume to its surrounding.
Radon concentrations were measured with a radon meter based on the
Lucas cell principle. The device is designed for low background, high
efficiency and short measurement time. The efficiency for radon with respect
to radon daughters was optimized by segmenting a 13 cm diameter, 30 cm long
cylindrical cell into 8 longitudinal sections. The cell and segment wall are
covered by ZnS(Ag) except for the side where the cell is mounted onto a 13
cm diameter, low background photo multiplier tube. Due to this geometry a
high efficiency for radon is obtained: about 50%. The efficiency for each of
the two a-emitting radon daughters is about 60%.
The setup was operated in a quasi-continuous mode: a sample is taken by
flushing the cell over a filter and a drying column for five minutes;
subsequently the sample is counted for 25 minutes and the number of counts
-------
is stored in the memory of a data logger. Simultaneously the values of the
following parameters averaged over 25 minutes are stored in the memory:
pressure differences between the outside air at three sides of the dwelling
at the crawl space ventilation openings, the pressure difference between
living room and crawl space, temperature and relative humidity of outside
air, air in the living room and in the crawl space, temperature of the soil
near the house and in the yard and barometric pressure.
After transfer of the data to the central computer the counts from the
radon meters were converted to radon concentrations after corrections for
daughter activity and background.
3. RESULTS
3.1. EXHALATION RATES
TABLE 1. EXHALATION RATES (E), EFFECTIVE DECAY CONSTANT (\f{), AND SURFACE
AREA (A), FOR VALLS, FLOOR AND SOIL OP THE CRAWL SPACE AND LIVING ROOM IN
THE SOUTHERN PART OF THE TEST DWELLING.
crawl space
soil d = 58
11 d = 48
" d = 46
inner wall
outer wall
ceiling2'
living room
floor
wall
E
(Bq.nf'.h'1)
(V*26 m)
11 1.78 ± 0.08
0.88 ± 0.06
1.02 ± 0.06
2.44 ± 0.06
1.96 ± 0.04
3.40 ± 0.05
(V=208 m)
1.34 ± 0.04
0.26 ± 0.05
(h'1)
0.014
0.011
0.011
0.11
0.043
0.054
0.032
0.074
A
48
10
15
48
48
97
E.A
(Bq.lT1)
85
42
49
24
29
173
65
25
water level relative to the soil surface, averaged over the measuring
. period
taken identical to the value of the floor in the study
-------
Table 1 lists exhalation rates, effective decay constants and surface
areas for the perimeters in the crawl space and living room. The exhalation
rate for the ceiling is taken equal to the value obtained for the floor in
the study because the value for the ceiling could not be measured directly
due to its curved surface. In the study the prefab concrete bars are covered
by a few centimeters of cement. In the table three measurements are reported
taken at different levels of the ground-water in the crawl space. Here one
notes a decreasing exhalation rate with a decreasing thickness of the sand
layer between the exhalation meter and the ground-water. In the crawl space
the exhalation rate of the soil is a factor of two to three smaller than of
the walls and the ceiling. The product of surface area and exhalation rate
makes that the ceiling yields the largest contribution to the diffusive
source strength in the crawl space. From the values of X one notices the
af f
large value for the inner wall. This value indicates the roughness of the
surface which made it difficult to mount the device leak-tight.
3.2. QUASI-CONTINUOUS RADON MONITORING
Fig. 1 shows from top to bottom four pressure differences P -P with
i cs
i=west, south, east and living room, respectively, and P is the pressure
in the crawl space, the deduced ventilation rate, the radon concentration in
the crawl space, and the barometric pressure in week 24 (June 11th - 17th)
of 1989. This week was characterized by absence of wind, high temperatures
during day time and cool nights. In the figure one notices that during the
night time the living room is at a lower pressure than the crawl space and
the crawl space is at lower pressure than the outside air. This is
attributed to the temperature difference between living room and outside
air. In the absence of wind or forced ventilation this stack effect is
considered the driving force for the pressure difference between crawl space
and living room. The ventilation rate is calculated from conservation of air
mass and the flow calculated from the pressure differences and the measured
leak of the crawl space ventilation shafts. From the figure one notices that
both ventilation rate and radon concentration in the crawl space are in
phase with each other and the pressure differences over the wall.
Fig. 2 shows the time dependence of a number of parameters during week
31, 1989. In this week there has been almost continuously wind from the
southwest, resulting in over pressure at the south and west walls and under
pressure in the living room, all with respect to the crawl space. Heavy rain
fall occurs on Sunday afternoon and evening as showers. No obvious effect on
the radon concentration is observed. On Tuesday and Vednesday evening the
open fire was lit causing a sharp increase in the pressure difference
between living room and crawl space. Surprisingly no effect of this
increased under pressure is observed on either radon concentrations and/or
pressure difference of the crawl space with the outside world. The radon
-------
concentration in the crawl space shows the diurnal cycle similar to the one
in fig. 1. Also in the pressure differences such a cycle is noticeable. The
difference with fig. 1, however, is that the maxima in the crawl space radon
concentration are more pronounced and that for Tuesday, Wednesday and
Thursday they coincide with the minima in the ventilation rate. However,they
are more pronounced than the variations in the ventilation rate. The overall
trend of the crawl space radon concentration is decreasing towards the
middle of the week and increasing afterwards. For the radon concentration in
the living room no diurnal cycle is observed; the concentration diminishes
somewhat on Wednesday and Thursday.
4. ANALYSIS AND INTERPRETATION
4.1. STATIC VENTILATION MODEL
In the extremely simplified model for the radon concentration in a room
which is ventilated with radon-free air one considers constant static
sources and a constant ventilation rate. For the equilibrium situation one
may write for the radon concentration C in a room with ventilation rate X
(A » X ) and volume V:
Rn
C = 1- I E. A , (4.1)
XV i L i
where the summation is over all radon exhaling surfaces indicated by i with
exhalation rate E. and surface area A . Here it is assumed that the radon
concentration in the incoming ventilation air may be neglected.
For the crawl space with volume V=26 m3, a ventilation rate X=0.5 h"1
(based on the average value in fig.2e) and E and A taken from table 1 one
obtains a value of C=21 and 17 Bq.nT3 for a dry soil (d=46 cm) and a barely
inundated (d=0 cm) crawl space, respectively. In the latter case the
contribution from the soil has been neglected. In the period 1980-1987 time
averaged radon concentrations were measured (4); the average value was 50±20
Bq.nT . The large uncertainty in this value is due to large fluctuations in
the radon concentration, presumably due to variations in the ground-water
level (4).
From the numbers one may conclude that based on the exhalation
measurements the radon concentration in the crawl space is two to three
times higher than expected on diffusion from the materials. This discrepancy
indicates another source of radon which, for this crawl space, is equally or
even more important.
-------
A similar simplified model yields for the living room with
constant source terms and a constant ventilation with a constant fraction,
a, of air from the crawl space:
Cl, - « Cc. * "-I C. * W f EiV <4'2>
Substituting C =22 Bq.m'3 (ref. 4). C =50 Bq.nf3, C =3 Bq.nf3, X =0.5 and
lr CB 0 ^ It
E and A from table 1 one obtains o=0.4. This value would correspond to a
crawl space ventilation rate of at least 3 h"1 and hence a discrepancy
between the radon contribution calculated from static sources and the
observed value for the crawl space of a factor of 15.
4.2. DYNAMIC VENTILATION MODEL
A dwelling is considered with N rooms, each having a radon
concentration C (t) and a volume V ; outdoor parameters are indicated by
N+l. The radon concentration in room i is determined by the total strength
of radon sources in the room, S. , and the transport of radon by air
currents. If q denotes the air current from room k into room i the
following mass-balance equation for room i can be written:
H+l
V <4'3>
Defining X. = «- Z q as the ventilation rate of room i and f = » — ,
1 i k=i ik i
eq. (4.3) transforms into:
N+I
Eq. (4.4) can be written for each of the N rooms, giving a system of N
coupled linear non-homogeneous differential equations. The set of equations
can be described more comprehensively using vector and matrix notation. In
principle the equations can be solved analytically, in practice, however,
instabilities occur and a numerical solution is preferred. The algorithms
have been implemented in a computer programme (CARACO).
-------
Essential for the calculation are the input parameters: the currents
q and the source strengths S . The currents q have been deduced from the
pressure difference between room i and k, Ap. =p -p., and the air
transparency of a barrier between the compartments i and k, T .
B
c
l 1 Pa
The values of T and n are taken from a previous study on the air leaks in
this test dwelling (7). For the source term in the crawl space a pressure
driven flow term (S ) was added to the static sources (S ) as discussed
pdf at
in sect. A.I. This pressure driven flow stems from the pressure difference
between the outside and the crawl space and causes a small, Darcy-type flow,
through the soil (and the walls of the crawl space). This flow becomes
important due to the relatively high concentration of radon in soil. The
relative intensity of this term depends on the permeability of the soil (and
walls), the radon concentration in the soil and the length of the crawl
space perimeter. As starting values were taken: for the permeability 5.10"
ra . the value for fine sand, and for the radon concentration in the soil gas
10 Bq.nf .
Fig. 3 shows the radon concentration in the crawl space measured during
week 24, 1989. The dashed curve is the calculated concentration based on
measured leakage parameter, measured S and a pressure driven flow (PDF)
term with a strength 40 times the estimated value of S based on the
pdf
starting parameters. Without the adjustment of S the magnitude of the
pdf
concentration is a factor of three too low and the oscillations are out of
phase. For the radon concentration in the living room (not measured during
that week) a value of about 75 Bq.nf3 was assumed at the rare moments that
the flow was from the living room to the crawl space. The results indicate
that the missing radon concentration in the crawl space may be accounted for
by a values of the S which is almost two orders of magnitude larger than
pdf
estimated from rather arbitrary starting parameters.
Fig. 4 shows radon concentrations in the living room (top) and crawl
space (bottom) measured during week 31, 1989. The dashed curves represent
the concentrations calculated with a two-room model. First the crawl space
concentration was optimized by starting from values for parameters as found
for week 24, 1989. The result in the bottom part of fig. 4 is obtained with
a seven times larger value than the measured value of S and a value for
S equal to the value estimated from the original starting parameters.
pdf
With these values of S and S the average concentration in the crawl
at pdf
space is reproduced; in the living room the concentration is a factor of two
-------
too lov. The larger static source term is necessary to reproduce the dips in
the cravl space radon concentration at times of increased ventilation; the
smaller S to obtain the correct average values.
pdf
At first sight it seems rather strange that the size of the terms
changes in time and one may argue that the infiltration of radon is still a
large puzzle. Without trying to reduce such a conclusion one could think of
a possible explanation. During week 31 the ground-water level reached one of
its lowest values of the year (d=58 cm). The exhalation of the soil in this
period, measured at one location increases sharply (d=58 cm in table 1). The
increase of the exhalation rate is larger than expected on basis of
difference of water level at d=48 and 46 cm.
As a hypothesis we propose a role to rainfall to qualitatively account
for both the increase in exhalation rate and the reduction of the PDF-term.
The concentrated precipitation did hardly change the ground-water level
until the latter part of the week. This means that the percolating rain has
been forming a type of piston on the soil closing of pores in air with water
thereby reducing the porosity and permeability of the soil. The slowly
moving piston blocks the diffusion of radon to the outdoor soil and thus
causes an increase of the radon in the soil gas below the piston. This will
enhance the exhalation of the soil in the crawl space, especially near the
perimeters (the measurement of the exhalation was made close to the centre).
Moreover the reduction of permeability will reduce the PDF-term. It should
be stressed again that this is only a hypothesis, which qualitatively
accounts for these rather large changes.
CONCLUSIONS
Radon concentrations in crawl spaces and living rooms are larger than
calculated from measured static source strengths. Time evolution of radon
concentrations measured simultaneously with pressure differences indicates
that pressure driven flow may account for the missing contribution to the
concentration as well in the crawl space as the living room. This is the
result of the preliminary analysis of two weeks in the summer of 1989 with
different weather characteristics.
From this analysis we conclude that the effective strength of diffusive
and pressure driven terms are not constant in time. It is proposed as a
hypothesis that changes in water content of the soil due to precipitation
may temporarily increase the radon concentration below the wetted layer and
that the increased water content may reduce the pressure driven flow.
Although we are still at the beginning of the analysis of the data and
our hypothesis may be replaced by others we would be tempted to state that
10
-------
understanding radon infiltration into dwellings is not so much a problem of
transport in the dwelling than it is a problem of radon transport of soil.
In our present opinion the way to better understanding is a combination of
analysing measurements, as described in this paper, over a longer period of
time to identify possible important parameters and investigations of these
parameters under controlled conditions in the laboratory.
This work is part of the research programme of the Environmental
Radioactivity Research Group at the KVI and has been financed by the Dutch
Government, as part of the National Research Programme RENA, and by the
Commission of the European Communities, as part of the 1985-1989 Radiation
Protection Programme.
REFERENCES
1. Arvela, H., Voutilainen, A., Makelainen, I., Castren, 0. and Winquist, K.
Comparison of predicted and measured variations of indoor radon
concentration. Radiat. Prot. Dosim. 24: 231-235, 1988.
2. Put, L.W., de Meijer, R.J. and Hogeweg, B. Survey of radon concentration
in Dutch dwellings. Sci. Total Environ. 45: 441-448, 1985.
3. Put, L.W., de Meijer, R.J. and Bosniakovic, B.F.M. Radon in the
Netherlands. In: Indoor RADON II. Proc. 2 APCA. Int. Spec. Conf. Cherry
Hill, APCA, Pittsburgh, U.S.A., pp. 107-119, 1987.
4. Put, L.W., de Meijer, R.J. Variation of time-averaged indoor and outdoor
radon concentrations with time, location and sampling height. Radiat.
Prot. Dosim. 24: 317-320, 1988.
5. Ackers, J.G. Direct measurements of radon exhalation from surfaces.
Radiat. Prot. Dosim. 7: 199-201, 1984.
6. Aldenkamp, F.J., de Meijer, R.J., Put, L.W. and Stoop, P. Removal
processes for charged radon decay products, submitted to Radiat. Prot.
Dosim.
7. Phaff, J.C., de Gids, W.F. and Knoll, B. Ventilatie van gebouwen.
Metingen van de luchtlekken en voorspelling van de ventilatie van een
woning in Roden, IMG-TNO Technical Report C535, Sept. 1983, TNO-Delft.
11
-------
(c)
-i
ISO
(f)
1D40
(g)
1010
— i— —i— —i— —i
1 1 1 1 i i
Sun
Mon
Tue
Wed
Thu
Fri
Sat
Fig. 1 Pressure differences P -P (Pa) with P being the pressure at the
i as i
west (a), south (b) and east (c) outside wall and in the living room (d) and
with P being the pressure in the crawl space. The calculated ventilation
rate (If1) of the cravl space and the measured radon concentration (Bq.nf3)
and the barometric pressure (hPa) are presented in parts (e), (f) and (g),
respectively. All data were collected in week 24, 1989 (June 11-17).
12
-------
(b)
(c)
-1
-5
(e)
50
(0-
0
150
(g)
0
75
(h)
o
1020
(0
990
^/^-W^V^
Sun
Mon
Tue
Wed
Thu
Fri
Sat
Fig. 2 Pressure differences PI-PCI (Pa) with PA being the pressure at the
west (a), south (b), and east (c) outside wall and the living room (d), the
calculated ventilation rate (h~ ) of the crawl space, part (e) the measured
radon concentrations(Bq.m~ ) in living room (f) and crawl space (g),
precipitation rate (mm.h~ ) in part (h), and barometric pressure (hPa) in
the bottom part. All data are collected in week 31, 1989 (July 30 - August
5).
13
-------
150
Sun
Mon
Tue
Wed
Thu
Fri
Sat
Fig. 3 Radon concentration in the crawl space of the test dwelling in Roden
during week 24, 1989 (June 11-17). The solid curve represents the
measurement, the dashed curve the calculated concentration with a dynamic
model. Multiplication factors for the measured S and estimated S are 1
at pdf
50
(a)
150
(b)
T
T
T
T
/\
. * ^V\
V
Sun
Mon
Tue
Wed
Thu
Fri
Sat
Fig. 4 Radon concentration in the crawl space and living room of the test
dwelling in Roden during week 31, 1989 (July 30 - August 5). (See fig. 3).
Multiplication factors for the measured S and estimated S are 7
St pdf
and 1, respectively.
14
-------
Session VI:
Radon in the Natural Environment
-------
VI-1
BENCHMARK AND APPLICATION OF THE RAETRAD MODEL
by: V.C. Rogers
K.K. Nielson
Rogers and Associates Engineering Corporation
Salt Lake City, Utah 84110-0330
ABSTRACT
Field measurements were used to benchmark a simple new predictive
correlation between soil gas permeability and soil grain size, moisture, and
porosity. The correlation was incorporated with a previous diffusion
correlation into the new RAETRAD code, that calculates radon generation and
two-dimensional transport in soils, and radon entry into structures. RAETRAD
generalizes the one-dimensional RAETRAN model, combining advective and
diffusive radon transport with radon emanation, decay, absorption, and
adsorption. RAETRAD calculations suggest 0.03 percent radon-entry efficiency
for slab-on-grade homes on low-permeability soils «10 ° cm'), increasing to
0.1 percent for sandy soils. Soil or fill properties in the first few feet
dominate radon entry efficiency and limiting radium concentrations for
prescribed indoor radon levels. For indoor radon concentrations of 2
pCi/liter. sandy soils may contain only 2-3 pCi/g radium compared to 10-20
pCi/g for more clayey soils.
This paper has been reviewed in accordance with the U.S. Environmental
Protection Agency's peer and administrative review policies and approved for
presentation and publication.
INTRODUCTION
Radon generation and transport in soils and its subsequent entry into
dwellings is a complex process requiring characterization of the soil
conditions, meteorological conditions, and the structure. Radon emanates
from radium-bearing minerals into the soil pore space, followed by diffusive
and advective transport in both liquid and gas phases into the dwelling.
entering via cracks, sumps, porous building materials, and other routes. The
RAECOM (Radon Attenuation Effectiveness and £over Optimization with Moisture)
(1) multlregion. one-dimension radon generation and transport code has been
used widely to predict radon migration through porous media. RAETRAN (RAdon
Emanation and TRANsport) (2) provides similar capabilities, but also includes
Idvective transport mechanisms. These codes are easy to use and require very
little input data: however, because they are one-dimensional, they have
limited application for radon entry into structures.
-------
The mathematics of the RAETRAN code have been extended to two
dimensions. In addition, the pressure-driven flow equation now is solved in
the code instead of externally as required with RAETRAN. The resulting
position-dependent velocities have corresponding boundary conditions to those
used for the radon generation and transport calculations. The resulting
code, called RAETRAD (RAdon Emanation and TRAnsport into Dwellings) (3).
retains the general simplicity of operation and minimal inpUt requirements
as the earlier RAECQM and RAETRAN codes. However, it provides a more
detailed description of radon movement through porous materials such as soil
and concrete and subsequent radon entry into structures coupled to the soils.
Key factors in the simplicity of the RAETRAD input data are the simple
correlations for predicting gas permeabilities and radon diffusion
cpefficients for the porous materials. These correlations and their use are
discussed in the next section. After that the RAETRAD code is briefly
described, and finally is applied to typical Florida soils and structures to
obtain radon entry efficiency factors and radon entry rates into dwellings.
and to estimate example maximum soil radium concentrations for foundation
fill materials.
AIR PERMEABILITY AND RADON DIFFUSION COEFFICIENT CORRELATIONS
Radon migration through soils and entry into dwellings depend strongly
on values of radon diffusion coefficients and air permeabilities for the
soils and for the applicable house construction materials. Simple
correlations for the radon diffusion coefficient have been developed and have
been widely used (4-5). The diffusion coefficient correlation that is
incorporated in RAETRAD is (6-7):
3p(l+p)d 7p(l+p)d
D - a-exp [ a m - 7m5]. (1)
8(2+ndg) 2+dg
where
D - pore average radon diffusion coefficient (cmV1)
p - soil porosity
dg - geometric mean particle diameter (pm)
m - fraction of moisture saturation.
Predictive correlations for gas permeability have been proposed previously
(7-8). A recently improved permeability correlation for shallow soils (9)
was incorporated into RAETRAD:
y2
- Pi—1 d«'3. (2)
where
K - air permeability in porous material (cm2)
da - arithmetic average particle diameter (cm).
Equations (1) and (2) reveal that soil gas permeability and radon
-------
diffusion coefficients both can be estimated from soil moisture, porosity,
and particle diameter averages d_ and da. In turn, the particle diameter
averages can be estimated from standard soil classifications such as the 1Z
categories used by the U.S. Soil Conservation Service (SCS) (10).
Furthermore, the appropriate soil moisture near a dwelling can be estimated
from the soil classification and soil matric potential (11).
As an example of the above methodology, measurements were made of the
in-situ moisture, gas permeability, porosity, and soil particle sizes for
several soils in Florida. Soil samples were obtained at depths of 60 t9 75
cm from several locations around the state. The data for the soils are given
in Table 1. The soil gas permeabilities were estimated from Equation (Z)
using the field soil data. The resulting correlation-predicted
permeabilities and measured field permeabilities are also given in Table 1.
In general, the agreement is within the experimental uncertainties. Two-
thirds of the predictions were within a factor of 2 of the field-measured gas
permeabilities.
From the particle size and moisture information in Table 1. soil matric
potentials were estimated using the methodology, described in4Reference 11.
The estimated matric potentials ranged from 1x10* Pa to 3.4xlOn Pa. A matnc
potential of 5xl04 Pa was selected as a reasonably conservative dry-side
average for conditions in the locations sampled in Florida. Using the
5x10* Pa matric potential and soil particle size distribution parameters from
the soil samples, soil moisture, permeabilities, and diffusion coefficients
were estimated for the broader range of soils defined by the U.S. Soil
Conservation Service classifications (10). These data are given in Table Z.
and were used in the example radon migration and house entry analyses
performed by RAETRAD.
TABLE 1. COMPARISON OF IN-SITU SOIL GAS PERMEABILITIES
WITH CALCULATED VALUES
Location
Ocala
Leesburg
Leesburg
E Orlando
N Orlando
SH Orlando
SH Orlando
Klsslmee
Lakeland
NE Tampa
Tampa
S Tampa
Clay
wt.X
5.9
74.6
1.7
2.0
1.9
2.1
1.2
0.9
2.2
2.2
2.0
3.2
Silt
wt.X
7.4
24.8
5.4
3.9
3.0
3.1
2.2
1.9
2.9
5.1
5.7
4.9
Sand
wt.S
86.7
0.6
92.9
94.0
95.1
94.8
96.5
97.2
94.9
92.7
92.3
92.0
Density
(g/cm3)
1.54
1.45
1.51
1.48
1.50
1.75
1.52
1.52
1.56
1.69
1.67
1.52
Moist.
Safn.
0.17
0.86
0.12
0.12
0.19
0.49
0.13
0.15
0.10
0.40
0.73
0.13
Measured
Permeabl 1 1 ty
(cm7)
B.SxlO"8
3.6xlO'12
1.2xlO'7
l.OxlO'7
2.4xlO'7
4.2xlO'8
9.0xlO'8
7.2xlO'8
6.8xlO'8
l.lxlO"7
4.5X10'10
8.6xlO'8
Calculated
Permeability
(cmz)
5.4xlO"8
l.SxlO'11
S.OxlO"8
6.5xlO'8
4.4xlO"8
2.1xlO"8
6.6xlO'8
7.6xlO'8
6.3xlO'8
3.0xlO'8
4.1xlO'9
6.7xlO'8
Ratio of
Cal c.Perm./
Heas.Perm.
0.63
3.52
0.66
0.65
0.18
0.51
0.73
1.05
0.93
0.27
9.21
0.78
-------
TABLE 2. MOISTURES. DIFFUSION COEFFICIENTS, AND PERMEABILITIES
OF STANDARD SCS SOILS AT 0.5-BAR MATRIC POTENTIAL*
SCS Soil
Classification
Sand
Loamy Sand
Sandy Loam
Sandy Clay Loam
Sandy Clay
Loam
Clay Loam
Silt Loam
Clay
Silty Clay Loam
Silty Clay
Silt
Moisture
Saturation
Fraction
0.073
0.196
0.377
0.411
0.488
0.576
0.664
0.780
0.813
0.900
0.932
0.938
Radon Diffusion
Coefficient1
(cmz/s)
B.lxlO"2
3.1xlO'z
1.5xlO"z
1.3xlO"z
9.4xlO"3
B.OxlO"3
2.7xlO'3
5.4xlO'4
7.9xlO"4
7.2xlO"5
4.8xlO"5
1.4xlO"5
Soil Gas
Permeability*
(cm2)
1.6xlO"7
1.4xlO"7
6-lxlO"8
S.lxlO"8
3.2xlO"8
1.7xlO'8
7.5xlO'9
1.7xlO~9
l.OxlO"9
1.2xlO"10
3.3xlO'n
l.SxlO"11
*At 1.6 g/cm3 bulk dry density: 0.407 porosity.
Estimated from Equation 1.
'Estimated from Equation 2.
THE RAETRAD CODE
RAETRAD solves the-two dimensional radon balance and air pressure
balance equations in cylindrical geometry. The two-dimensional rate balance
equation for radon in the gas component of the soil pore space is given by:
/d2Ca 1 dCa dzCa\
I— + + —-) - xc
\drz r dr dzz /
/dP dCa dP dCa\
I + 1
\dr dr dz dz /
p(l-m)
mX dC=
(l-m)kd a tit
where
D. - radon diffusion coefficient in air, including tortuosity
C. - radon concentration in the air-filled pore space
(3)
-------
r
z
X
Pa
m
K
-air
kd
Twa
radial distance from center of house
vertical depth from ground surface
radon decay constant
air-surface adsorption coefficient for radon
bulk dry density
fraction of moisture saturation
pore gas permeability
total porosity
pore gas pressure
radium concentration in the solid matrix
component of emanation coefficient that is a direct pore air
source of radon . .
equilibrium distribution coefficient for radium in sond-to-
pore-liquid
transfer factor of radon from pore water to pore air
The T transfer factor from pore water to pore air is obtained from
combining Equation (3) with a similar rate balance equation for radon in pore
water (6). The derivatives of the atmospheric and soil air pressures are
obtained by solving the following equation using the same approach as for the
radon transport equation:
d2P
1 dP d'P dP
K [— r + -- +— y] --
(4)
dr
dr
dt
The boundary conditions for Equation (4) are the indoor air pressure
applied to the inside surface of the dwelling floor, and the outdoor air
pressure (typically averaging zero) applied to the outdoor soil surface. If
the dwelling is at a negative pressure compared to the outdoors, then air
movement proceeds from the outdoor soil surface downward through the soil and
then inward and upward towards the structure as shown in Figure 1. Radon
entry into the slab-on-grade dwelling in Figure 1 is assumed to be through
a perimeter crack, such as may occur between the slab and foundation
footings.
House Area- 141 mz(1SOOsq ft)
Indoor Pressure. -2 4 Pa
Perimeter Crack Area: 4%
Fiqure 1. Flow lines and peripheral air entry locations
for a structure on a 61-cm deep foundation in
sandy soil (K - 1.7 x 10"' cm').
-------
After the pressure field is determined. RAETRAO solves the radon
generation and transport equations to obtain values for the following
parameters (3):
1. Radon concentration in soil air pores as a function of position.
2. Average radon concentration under the dwelling slab (if
applicable).
3. Diffusive, advective. and total surface radon fluxes.
4. Radon entry rates through dwelling floors, walls, and cracks in
contact with the soil.
5. Air entry rates from the soil.
6. Radon entry efficiency factors for the dwelling-soil system.
The radon entry efficiency factor is defined as the average indoor radon
concentration divided by the area-weighted average sub-slab radon
concentration in the soil pores.
APPLICATION OF RAETRAD
The RAETRAO code was applied to the soils and soil conditions given in
Table 2. A slab-on-grade structure was coupled to the soils as shown in
Figure 1, and it was assumed that radon entered the dwelling through a
perimeter crack between the 10-cm thick concrete slab and a 60-cm deep
foundation footing. The dwelling is assumed to be at a -2.4 Pa pressure
compared to the atmosphere. The radon emanation coefficient of the soil is
0.25. Other parameters used in the analyses are shown in Figure 1.
Radon entry efficiency factors computed by RAETRAD for the dwelling on
each of the SCS soils are shown in Figure 2. They increase with increasing
soil permeability mainly for coarse-grained soils. The entry efficiency
factor becomes less dependent on permeability for permeabilities less than
about 10 cm. because diffusion processes dominate the radon entry rate
into the dwelling for the low-permeability soils. For these examples, the
entry efficiency varies from about 0.025 to 0.1 percent. The radon entry
efficiency factors are determined from the radon entry rates, dwelling air
volumes, and air exchange rates. The average air exchange rate can be either
input directly or estimated from procedures published by the American Society
of Heating. Refrigerating and Air-Conditioning Engineers (12). The present
example used an air exchange rate of 1 hr .
-------
0.10
0.08
o
c
0)
'5
£
Hi
c
o
•o
CO
DC
0.06
0.04
0.02
Soil Moistures: 5x104 Pa matric potential
Soil Densities: 1.6 g/cm3
Sandy Loam
Sandy Clay Loam
• sit0"* Loam
Clay
Clay
Loam
10
-11
,-10
10'1U 10'9 10'8 10
Soil Gas Permeability (cm*)
-7
10-'
Figure 2. Radon entry efficiencies computed by RAETRAD
for a slab-on-grade structure (Figure 1) on
uniform soils defined in Table 2.
Maximum soil radium concentrations can also be determined from the
example analyses by assuming a maximum indoor radon concentration guideline.
A guideline of 2 pCi/liter applied to the example calculations gives the
maximum soil radium concentrations shown in Figure 3. The maximum soil
radium increases with decreasing soil permeability. Calculations were also
made of the maximum soil radium concentrations for a layer of foundation fill
material placed over the natural soil. Fill material properties generally
obscured effects from the underlying soils when the fill layer thickness
exceeded approximately 1 m. For thinner fill layers, high or low radium
contents in the underlying soil affected the acceptable radium content of the
fill material. As shown in Figure 3. the maximum soil radium for the fill
material also becomes insensitive to the natural soJl conditions for low-
permeability fill materials (less than about 10 cnr permeability). Sandy
soils permitted only 2-3 pCi/g radium before exceeding the 2 pCi/liter indoor
radon concentration, while finer-grained soils could have 10-20 pCi/g due to
their lower permeabilities and diffusion coefficients (Figure 3).
-------
100
O>
o
Q.
•o
a
QC
o
co
X
(0
10
Silt, Silty Clay, &
Silty Clay Loam
Clay Loam
Loam
Sandy Clay
Clay Loam
Sandy Loam
Loamy
Sand
Uniform Soil
30-cm Layer on 1 pCi/g Silt Loam
30-cm Layer on 24 pCi/g Silt Loam
Sand
10
-11
,-8
1Q-10 1Q-9 10'° 10
Soil Gas Permeability (cm*)
-7
10"
Figure 3. Maximum soil radium concentrations to maintain
2 pCi/liter radon in a slab-on-grade structure
(Figure 1) on SCS soils that are uniform (solid
line) or used for a 30 cm fill layer over a
silt-loam base soil (broken lines). Soil
properties are defined in Table 2.
Radon entry efficiency factors and maximum soil radium concentrations
also vary according to the perimeter crack width. Figure 4 shows the
variation of the entry efficiency factor with the perimeter crack area for
a sandy soil. The perimeter crack area is expressed as a percentage of the
total slab area, and also may be used to approximate the effects of perimeter
utility penetrations through the slab.
-------
0.12
0.08
0.06
0.04
"g 0.02
DC
0.00
12345
Perimeter Crack Area (%)
Figure 4. Variation of radon entry efficiencies with the
size of perimeter crack for the slab-on-grade
structure (Figure 1) on SCS sandy soil.
As a benchmark for RAETRAD, an analysis was performed for a house-soil
system in Florida for which some field data are available. The indoor radon
concentration for a 203 m slab-on-grade dwelling was measured to average
about 10 pCi/liter.
The radium concentration in the top 30 cm of subslab soil is about 0.9
pCi/g. the soil moisture is about 15 percent of saturation, and the measured
permeability is 8 x 10 cm*. A subslab radon concentration of 4.200
pCi/liter indicates the presence of a deeper soil layer with elevated radium.
This is represented by a 5 pCi/g soil radium layer beneath the top 31 cm
layer characterized above. A radon emanation coefficient of 0.25 is also
used in the analysis. The RAETRAD calculation gives a subslab radon
concentration of 4.000 pCi/liter and an indoor radon concentration of 7
pCi/liter, for a house pressure differential of 1.0 Pa. The estimated indoor
concentration is within 30 percent of the measured value of 10 pCi/liter.
ACKNOWLEDGEMENT
This work was supported in part by U.S. Department of Energy grant
DE-FG02-88ER60664 and in part under subcontract IAG-RWFL933783 to the U.S.
Environmental Protection Agency.
-------
REFERENCES
1. Rogers. V.C.. and Nielsen. K.K.. "Radon Attenuation Handbook for
Uranium Mill Tailings Cover Design," U.S. Nuclear Regulatory Commission
report NUREG/CR-3533. April 1984.
2. Nielsen, K.K.. and Rogers, V.C., "Radon Generation. Absorption and
Transport in Porous Media -- The RAETRAN Model." EOS. 70. 497 (1989).
3. Nielson, K.K., and Rogers, V.C.. "A Mathematical Description of Radon
Generation. Transport and Entry Into Structures," in preparation.
4. Nielson. K.K.. Rogers. V.C.. and Gee. G.W.. Soil Science Society of
America Journal 52, 898 (1988).
5. U.S. Nuclear Regulatory Commission Regulatory Guide 2.64. "Calculation
of Radon Flux Attenuation by Earthen Uranium Mill Tailings Covers,"
June 1989.
6. Rogers, V.C., Nielson, K.K., and Merrell, G.B.. "Radon Generation.
Adsorption. Absorption, and Transport in Porous Media." U.S. Department
of Energy report DOE/ER/60664-1, May 1989.
7. Rogers. V.C.. and Nielson. K.K.. "Radon Emanation and Transport in
Porous Media," in Proceedings: The 1988 Symposium on Radon and Radon
Reduction Technology. Volume 1. EPA-600/9-89/006a (NTIS PB89-167480).
March 1989.
8. Shepherd. R.G.. "Correlations of Permeability and Grain Size."
Groundwater 27. 633-638. 1989.
9. Rogers. V.C.. and Nielson. K.K.. "Predictive Correlations for Air
Permeabilities and Radon Diffusion Coefficients in Porous Media," in
preparation.
10. Dunn. I.S.. Anderson, L.R., and Kiefer. F.W.. Fundamentals of
Geotechnical Analysis. New York: Wiley & Sons. 1980.
11. Nielson, K.K., and Rogers, V.C., "Moisture, Radon Diffusion and Air
Permeability Characteristics of SCS Soil Classifications." in
preparation.
12. Fundamentals Handbook. "Ventilation and Infiltration." American Society
of Heating. Refrigerating and Air-Conditioning Engineers (1981).
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VI-2
GEOLOGIC CONTROLS ON RADON OCCURRENCE IN GEORGIA
L.T. Gregg
Atlanta Testing & Engineering, Inc.
11420 Johns Creek Parkway
Duluth, Georgia 30136
Gene Coker
United States Environmental Protection Agency
345 Courtland Street, N.E.
Atlanta, Georgia 30365
ABSTRACT
Through a combination of geologic models and field measurements, each of the four
geologic provinces of Georgia can be characterized for radon concentration. The
combinations of bedrock lithology and soil characteristics most likely to exhibit higher
radon concentration in Georgia are granites, granodiorites, granite gneisses, pegmatites,
mylonites, carbonaceous shales, phosphates, and monazite/heavy mineral placers, coupled
with high to medium permeability soils such as gravels, sands, and uniformly-graded silts
and sandy silts. Saprolite and surficial soil may either enhance or impede radon migration,
as may hydrogeologic characteristics and rock structures such as faults and joint/fractures.
INTRODUCTION
The four radioisotopes considered in this paper are uranium, thorium, radium, and
radon. The principal uranium isotope is U238, which decays to Ra226. Radium-226 decays
to Rn222, which decays to polonium, bismuth and finally lead. The principal thorium
isotope is Th230, which decays to Ra228, then to Rn220, polonium, bismuth and finally lead.
Because of its half-life of 3.8 days, Rn222 is of much more concern and interest from an
environmental standpoint than Rn220 (56 seconds half-life).
The basic properties of radon are: it is gaseous and therefore highly mobile, it is an
alpha and gamma emitter so its presence can be measured (usually with an alpha-particle
measuring device), it is a daughter or decay product of radium, it is moderately soluble in
water and its solubility decreases with increasing temperature, and it does not readily
combine chemically with other elements. These properties form the framework for our
understanding of radon generation, occurrence and migration in rocks, soils, and
groundwater.
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In considering the geologic setting of Georgia and the Southern Appalachians, the
major structural and lithologic trends run from northeast to southwest. The principal rock
types in the Cumberland Plateau and the Valley and Ridge Provinces are limestones,
dolomites, shales, and sandstones, in the Blue Ridge and Piedmont Provinces igneous and
metamorphic rocks such as granites, gneisses, and schists, and in the Coastal Plain
limestones, sandstones, phosphates, and unconsolidated sediments.
URANIUM GEOCHEMISTRY
Uranium abundance typically ranges from 2 to 5 parts per million (ppm) in granites
to as high as 9 ppm in nepheline syenites, from 0.5 to 2 ppm in the andesites and mafic
rocks and much less in the ultramafic rocks, to as high as 34 ppm in the Marcellus Shale
(an analog of the Chattanooga Shale) and 120 to 140 ppm in the phosphates and
phosphorites. Thorium shows similar ranges, as high as SO ppm in granites.
Why is uranium so widely distributed? Uranium is polyvalent, with the three principal
ions being +4, +5, and +6. It has a large atomic radius of 0.8 to 0.97 angstroms; it is
highly active chemically and forms strong complexes with many ligand species; and the
hexavalent compounds are more soluble than the tetravalent compounds, the latter being
isomorphic with Ca, Th, Zr, W, Mo, and so forth. This suite of properties results in a
complex geochemistry.
During magmatic differentiation, uranium does not seem to form separate mineral
precipitates. There is isomorphic substitution in some rock-forming minerals. Uranium
tends to concentrate in late stage crystallization in acidic rocks and minerals such as
granites and felsic volcanics, and through hydrothermal action in pegmatite dikes and veins.
This is primarily due to its large atomic radius and to its affinity for late forming members
in the reaction sequence such as quartz, potassium feldspar and muscovite. In igneous
rocks, the petrofabrics play an important role in uranium concentration (or enrichment).
The petrofabrics provide microstructural control of uranium movement and deposition such
as coatings around mineral grains, and within microfractures and along crystal cleavage
planes (which provide a type of porosity for the uranium bearing waters). In felsic
volcanics, both acidic and alkalic, uranium may be highly dispersed and thus readily
leachable. Some concentration of uranium has been observed in ashes and tuffs and in
cross-cutting dikes and veins.
In sedimentary rocks, uranium concentration is more dependent upon the geochemical
cycle, including such mechanisms as oxidation-reduction, absorption, adsorption by
substrates such as iron oxide, silica, and organic material, formation of fluoride, sulfate,
phosphate, carbonate, and organic complexes, the relative mobility of the hexavalent and
tetravalent ions, and the weathering and solution of the uranium source and the transport,
precipitation and deposition of the weathered uranium. Figure 1 shows the processes
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controlling the occurrence of syngenetic uranium in the sedimentary environment. Through
various mechanisms - oxidation, reduction, adsorption, ionic substitution, and evaporation -
uranium concentrates in different sedimentary rocks. Figure 2 shows the processes
controlling epigenetic uranium deposition. Concentration mechanisms here are primarily
adsorption, precipitation, evaporation, and changes in redox potential and pH.
Figure 3 shows an idealized sequence of the processes that control uranium
concentration in metamorphic rocks, where recrystallization may cause a grain size increase,
porosity reduction, and liquid-gas expulsion, resulting in uranium movement into fractures,
shear zones, and lower pressure zones and concentration in them.
To summarize, the principal factors in uranium mobility and concentration are the long
half-life, ionic size, polyvalence, mineralogy and uranium content of the source, petrofabric,
and geochemical conditions such as the amount and rate of circulating water, climatic
factors, pH and Eh, the presence or absence of complexing agents, and the presence or
absence of sorptive materials.
RADIONUCLIDE MOBILITY
Uranium is more mobile than its daughter product radium. Generally, uranium may
be considered much more mobile in oxidizing environments than in reducing environments,
whereas radium is most mobile in chloride-rich reducing environments. Radium tends to
behave chemically somewhat similar to the alkaline earths such as calcium and may
complex with sulfate, carbonate, or chloride.
Since radon is a gas, the oxidation-reduction environment is immaterial. Radon has
two principal components to its movement: diffusion, which is generally thought to be a
minor component (probably an average of about 1 meter from its radium parent source),
and convection, which is the major component. Radon can move many meters by
convection, but it has to be carried in some type of "geo-gas" that can be either a mixture
of helium, nitrogen, methane, CO2, and so forth, or groundwater, or both.
Once radon is liberated (or "emanates") from its radium parent source, within rock,
soil, or water, it will tend to migrate by diffusion and convection to zones of lower
pressure, for example vertically toward the surface. A high permeability soil will allow
radon to more readily permeate upward to the surface than will soils high in the clay
minerals that have resultant high porosity but low permeability. Figure 4 shows an
idealized cross-section of the Piedmont from surface soils down through massive saprolite,
structured saprolite, partially weathered rock and fresh bedrock. Circulating meteoric
waters near the surface should more actively dissolve and transport leachable uranium than
at greater depths, where these waters may concentrate iron, silica, and clay substrates
which would tend to act as scavengers to concentrate uranium. Relict structures within the
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structured saprolite such as joints, fractures, faults, mineral veins, and foliation planes
would provide pathways for percolating waters and deposition of substrates and organic
material, resulting in sites for precipitation of radionuclide complexes and concentration
of uranium, thorium, and radium. These relict structures should also act as conduits for
radon migration, through diffusion and convection, toward the surface.
NURE STREAM SEDIMENT DATA
Under the NURE Program, uranium and thorium were measured in stream sediments.
The mean in Georgia stream sediments for uranium was 11.62 ppm and 56.62 ppm for
thorium. The average upper continental crustal abundances are 2.5 ppm and 10 ppm for
uranium and thorium respectively. Thus, the ratio of the mean to the crustal abundance
in Georgia is about 4.5 for uranium and 5.5 for thorium.
Figure 5 shows the NURE stream sediment data for uranium (1). The outlined zones
include the two highest concentrations of uranium, ranging from 6.1 ppm to 426 ppm.
Note the trends from northeast to southwest. The NURE thorium data in stream
sediments is almost a perfect overlay of the uranium data, which is not too surprising if
one considers the location of the so-called monazite belt as it traverses the Carolinas and
Georgia. However, it should be noted that heavy minerals, as they are weathered and
eroded from host rocks, tend to concentrate in stream sediments at highly variable
transport distances. Thus uranium and thorium stream sediment concentrations are at best
an imperfect indicator of adjacent host rock concentrations.
GEOLOGIC CONTROLS IN THE PIEDMONT PROVINCE
We have categorized the geologic factors controlling radon occurrence in the Piedmont
Province as bedrock, saprolite, soil, groundwater, and surface processes.
Obviously these factors must interact with one another, but the degrees and types of
interaction are not well known, except in a few instances. In examining bedrock, we must
consider the lithology and mineralogy, the mobility of radium in either an oxidizing or
reducing environment, the amount and continuity of near-surface jointing and fracturing,
the proximity of major faults and shear zones, the depth of the water table, and the
proximity of pegmatite dikes and veins. Radon concentration and migration in saprolite
is influenced by the lithology of the parent rock, the amount and degree of jointing and
fracturing and interconnection, the degree of water saturation, permeability and porosity,
thickness, zonation (whether the saprolite is structured or massive), and the distribution
and extent of nanopores (pores less than one micron in width). In surface and near
surface soil the principal influences are thickness, zonation (A, B, and C zones), moisture
content (8 to 15 percent has been suggested (2) as optimum for radon emanation),
permeability and porosity of the soil, and finally the temperature gradient from the surface,
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which determines the water vapor pressure of the soil. The major groundwater influences
are the recharge area, the flow directions and flow rates, seasonal fluctuations and the
presence of water supply wells (both of which cause a pumping effect), and the infiltration
of surface precipitation. Finally, there are meteorologic and topographic effects on radon
migration that can be enumerated but are not well understood. Meteorologic controls on
soil-gas transport that have been identified are temperature, humidity, precipitation,
barometric pressure, presence or absence of snow cover, and wind speed and direction.
Topographic effects are primarily the varying thickness of soil cover on ridge tops and
hillsides versus that in valleys.
RADON OCCURRENCE IN GROUNDWATER
Until recently, radon occurrence in groundwater has in general been the subject of less
research than in soil and bedrock, although there is a fairly large body of empirical
groundwater data for the U.S. and some quantitative analysis of that database. There have
been several published physical models of radon release from soil and rock into
groundwater and transport through aquifers into pumping wells. Together with aquifer
lithology, the width and frequency of fractures and pores/nanopores in the aquifer are key
determinants of both radon release and transport.
Aquifer lithology has been shown (3) to be a useful and relatively accurate predictor
of radon concentrations in groundwater across a wide suite of rock types in North
Carolina: granite, metasediments and metavolcanics, gneisses and schists, mafics,
nonmarine and marine clastic sediments. The average radon concentrations measured in
each of these rock types were generally consistent with relative abundances of uranium in
these rocks.
EPA GROUNDWATER SAMPLING PROGRAM
In recognition of the need for additional research, EPA initiated a groundwater
sampling program in 1988 in Georgia and Tennessee (4). In Georgia, nine aquifer units
or rock types, with more or less homogeneous geologic conditions, were selected for
sampling. These nine units or sampling cells are somewhat representative of portions of
the four geologic provinces in Georgia. Within each sampling cell, ten private well sample
sites were located and sampled. The sampling protocol required continuous pumping and
measurements every five minutes of temperature, specific conductance, dissolved oxygen,
and pH until these parameters stabilized. After purging and stabilization, the water
sampling took place at the faucet nearest the wellhead. For each sample, a total of forty-
eight chemical parameters and fourteen radionuclide parameters, including radon and
uranium, were analyzed by EPA analytical laboratories.
Some preliminary results from the EPA groundwater sampling program in Georgia
-------
show a range of radon in groundwater in a Piedmont granite gneiss from 3,160 to 268,500
picocuries per liter (pCi/1) with an average of nearly 82,000 pCi/1. In the Blue Ridge, as
expected, the minimums, maximums and average are much lower, as is the case in the
Valley and Ridge and the Coast Plain.
SUMMARY
The most suspect terranes for radon occurrence in Georgia are granite, granodiorite,
granitic gneiss, pegmatites, mylonites and other cataclastics, carbonaceous shales,
phosphates and phosphorites, and monazite/heavy mineral placers, which are overlain by
high to medium permeability soils and which have conduits for radon migration from the
source to the surface, such as joints, fractures, faults, bedding planes and foliation planes.
Much research remains to be done. The E.P.A. groundwater sampling program
currently underway will be an important contributor to understanding radon occurrence in
groundwater in the Southeast.
The work described in this paper was not funded by the U.S. Environmental Protection
Agency and therefore the contents do not necessarily reflect the views of the Agency and
no official endorsement should be inferred.
REFERENCES
1. Koch, George S., Jr., A Geochemical Atlas of Georgia, Georgia Geologic Survey,
Geologic Atlas 3, 1988.
2. Otton, James K., et al, Map Showing Radon Potential of Rocks and Soils in Fairfax
County, Virginia, U.S. Geological Survey, Miscellaneous Field Studies Map MF-
2047, 1988.
3. Loomis, Dana P., Aquifer Lithology As a Predictor of Radon Concentration in
Groundwater: Research Results in North Carolina, U.S. E.P.A. Conference on
Indoor Radon, EPA 904/9-87 145, 1987.
4. Coker, Gene and Olive, Robert, Radionuclide Concentrations from Waters of
Selected Aquifers in Georgia, U.S. Environmental Protection Agency, Region IV,
1989.
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SOURCES
CONCENTRATION
MECHANISM
OCCURRENCE
CLASSIFICATION
HEAVY MINERALS
1
(FLU
1
OXIDATION
(FLUVIAL; MARGINAL
MARINE)
REDUCTION
PLACERS
CONGLOMERATES
U-BEARING
WATERS
ADSORPTION
IONIC SUBSTITUTION
EVAPORATION
*• MARINE BLACK SHALES
PHOSPHATES
EVAPORITES
FIGURE 1. SYNGENETIC URANIUM IN SEDIMENTARY ENVIRONMENTS
-------
SOURCES
SURFACE AND NEAR.
SURFACE WATERS
HYDRO-THERMAL
FLUIDS
CONCENTRATION
MECHANISM
ADSORPTION
PRECIPITATION;
EVAPORATION
Eh-pH
CHANGES
OCCURRENCE
CLASSIFICATION
COAL
SHALE
PRECIPITATES;
EVAPORITES
SANDSTONE
(ROLL FRONT)
LIMESTONE
VEINS, FAULTS, ETC.
(STRUCTURALLY
CONTROLLED)
FIGURE 2. EPIGENETIC URANIUM IN SEDIMENTARY ENVIRONMENTS
-------
RECRYSTALUZATION
\
GRAIN SIZE INCREASE
\
POROSITY REDUCTION
\
LIQUID-GAS EXPULSION
\
URANIUM LOSS INTO
- FRACTURES
• SHEAR ZONES
• LOWER PRESSURE ZONES
FIGURE 3. URANIUM IN METAMORPHIC ROCKS
-------
UJh^Q
% REMOVAL
HIGH
DEPTH
LOW
UJh,Ra
CONCENTRATION
LOW
HIGH!
Fe & Mn CONCENTRATION
(U SCAVENGERS)
STRUCTURE
-JOINTS, FRACTURES,
FAULTS, ETC.
- POSSIBLE ZONES OF
CONCENTRATION OF
U,Th,Ra
FIGURE 4. IDEALIZED PIEDMONT SUBSURFACE MODEL
-------
U (Uranium!
TOTAL NUMBER OF SAMPLES: 58SI
Symbol
FIGURE 5. NURE STREAM SEDIMENT DATA
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VI-3
CORRELATIONS OF SOIL-GAS AND INDOOR RADON WITH GEOLOGY IN
GLACIALLY DERIVED SOILS OF THE NORTHERN GREAT PLAINS
R. Randall Schumann1, R. Thomas Peake2, Kevin M. Schmidt3, and Douglass E. Owen1
iU.S. Geological Survey, MS 939 Denver Federal Center, Denver, CO 80225-0046
2U.S. EPA, 401 M St. SW, Washington, DC 20460
3USGS, 345 Middlefield Rd., Menlo Park, CA 94025
ABSTRACT
A higher percentage of homes in parts of the northern Great Plains underlain by soils
derived from continental glacial deposits have elevated indoor radon levels (greater than 4 pCi/L)
than any other area in the country. Soil-gas radon concentrations, surface radioactivity, indoor
radon levels, and soil characteristics were studied in areas underlain by glacially-derived soils in
North Dakota and Minnesota to examine the factors responsible for these elevated levels. Clay-rich
till soils in North Dakota have generally higher soil-gas radon levels, and correspondingly higher
indoor radon levels, than the sandy till soils common to west-central Minnesota. Although the
proportions of homes with indoor radon levels greater than 4 pCi/L are similar in both areas,
relatively few homes underlain by sandy tills have screening indoor radon levels greater than
20 pCi/L, whereas a relatively large proportion of homes underlain by clayey tills have screening
indoor radon levels exceeding 20 pCi/L. The higher radon levels in North Dakota are likely due to
enhanced emanation from the smaller grains and to relatively higher soil radium concentrations in
the clay-rich soils, whereas the generally higher permeability of the sandy till soils in Minnesota
allows soil gas to be drawn into structures from a larger source volume, increasing indoor radon
levels in these areas.
This paper has been reviewed in accordance with the U.S. Environmental
Protection Agency's peer and administrative review policies and approved for
presentation and publication.
INTRODUCTION
Preliminary testing by the U.S. Environmental Protection Agency (EPA) as part of the
EPA/State Indoor Radon Survey (1) indicates that a large proportion of homes built on soils
derived from continental glacial deposits have screening indoor radon concentrations greater than
EPA's recommended action level of 4 pCi/L. Although a correlation between highly permeable
glacial deposits and elevated indoor radon levels has been documented by previous researchers,
notably in northern Europe (2,3,4), the magnitude of the problem in the northern Great Plains
States (Table 1) was unexpected because the deposits have low to moderate permeability and low
surface gamma radioactivity signatures.
A regional-scale correlation between radon potential and surface gamma radioactivity of
areas underlain by bedrock or soils derived from underlying bedrock (5,6,7,8) allows
preliminary predictions of radon potential to be made from equivalent uranium or radium data
calculated from gamma radioactivity, one of the best sources of which is the map of NURE aerial
radioactivity data for the conterminous United States compiled by the U.S. Geological Survey
-------
(USGS) (9). However, the number of homes in North Dakota, Minnesota, and Iowa with
elevated indoor radon levels (Table 1) is disproportionately high compared to the generally low
aerial radiometric signature of the area. Glacial drift derived largely from the Pierre Shale in North
Dakota and from crystalline rocks of the Canadian Shield in Minnesota generate elevated indoor
radon levels in a large number of homes in those States. Soils in the area are not necessarily highly
permeable; in fact, some of the highest indoor radon levels in North Dakota were measured in
homes in the Red River Valley along the eastern border of the State, which is underlain primarily
by silty-clay lacustrine deposits of glacial Lake Agassiz (10,11).
As part of the EPA-USGS joint effort to identify and characterize the radon potential of the
United States, a field investigation was initiated to quantitatively identify and describe the geologic
factors responsible for anomalous indoor radon concentrations in the northern Great Plains and
Great Lakes States underlain by continental glacial deposits. This report presents preliminary
observations from field investigations in North Dakota and Minnesota.
GLACIAL GEOLOGY
Most of North Dakota and Minnesota are underlain by Wisconsin-age continental glacial
deposits, except for the southwest corner of North Dakota, which is unglaciated and underlain by
Tertiary and Upper Cretaceous sandstones and shales (Figure 1), and the southeast comer of
Minnesota, which is underlain by pre-Wisconsin glacial drift (Figure 2). In North Dakota, ice
advanced from the north and northwest in six separate glacial advances during Wisconsin time
(Figure 1). The tills of all the ice advances are lithologically similar and are derived primarily from
Tertiary and Upper Cretaceous shales, siltstones, and sandstones that comprise the underlying
bedrock in North Dakota and southwestern Manitoba. Some of the deposits in the northeastern
part of the State also include carbonate-rich till derived from Paleozoic limestone and dolomite in
southern Manitoba (11). Most of the tills consist of nearly equal parts sand, silt, and clay (12,13).
Lacustrine deposits of glacial Lakes Agassiz, Souris, and Devil's Lake (Figure 1) are composed
primarily of silty clays and clays, and are commonly interbedded with tills. The unoxidized tills
are generally dark olive gray to bluish gray. Iron oxidation and accumulation of calcium carbonate
are common weathering effects (14); both were noted in nearly all of the soils sampled in the study
area.
Wisconsin-age glacial drift covers most of Minnesota. The drift can be classified into
deposits of four major ice lobes that advanced at different times and in different directions, from
areas with different source lithologies (Figure 2). Each lobe experienced multiple phases of ice
advance, some of which overlapped other lobes in time and space. In order of roughly decreasing
age, the major lobes are the Wadena, Rainy, Superior, and Des Moines (15). Drift of the Wadena
lobe is exposed only in central Minnesota (Figure 2). The Wadena lobe advanced southward from
the north and northwest, moving in a generally north-south direction in central Minnesota.
Wadena drift is dominantly gray to buff-colored, sandy, calcareous till derived from carbonate
rocks of southern Manitoba. The Rainy lobe moved from northeast to southwest. Rainy lobe drift
covers parts of northeastern and central Minnesota and varies in both color and constituent
lithology. In the northeast the drift is derived primarily from gabbro and basalt, giving it a gray
color. Further west the drift is light gray to light brown, reflecting a dominantly granite source. In
central Minnesota, Rainy lobe drift is derived mostly from metamorphic rocks and has a brown
color resulting from oxidation of the initially gray metamorphic rock fragments.
The Superior lobe advanced from northeast to southwest in the eastern part of the State,
roughly parallel to the Rainy lobe. It carried generally sandy red till containing sandstone and slate
pebbles. Drift of the Des Moines lobe was primarily derived from Upper Cretaceous shales of
-------
southern Manitoba, eastern North Dakota, and western Minnesota. Sublobes of the Des Moines
lobe moved eastward across northern Minnesota and southward to central Iowa. Till derived from
the Des Moines lobe is generally gray to buff, calcareous, silty to clayey (16). Silty and clayey
lacustrine deposits of Lake Agassiz cover much of the Red River Valley in the northwestern pan of
the State (Figure 2).
METHODS
Field sampling was conducted at 132 locations along four traverses, each 100-150 km
long, along highway rights-of-way (Figure 1,2). Sample stations were spaced about 4 km apart.
The field measurements were made during two weeks in August, 1989 during which the weather
was mostly warm and dry, so any variations in measured values due to climate or weather-related
effects are estimated to be negligible compared to variations caused by geologic factors. At each
station, soil-gas radon was sampled at 1 m depth using the method of Reimer (17) and surface
gamma radioactivity was measured with a portable gamma-ray spectrometer. The gamma-ray
spectrometer gives an estimate of the concentrations of uranium, radium, thorium, and potassium
in the upper 30 cm of soil. At alternate stations, an additional soil-gas sample was collected and
soil permeability was estimated using soil-gas probes and equipment developed by V.C. Rogers
and Associates (18), and soil profiles were examined, described, and sampled with a bucket auger.
Soil samples were collected at the surface and at 1 m at alternate stations. Laboratory analyses of
these samples were not completed at the time of this writing.
PRELIMINARY FIELD DATA
Results of field sampling of soil gas, permeability, and surface radioactivity are
summarized in Table 2. Each traverse generally characterizes a specific glacial lobe or group of
similar lobes. Traverse ND-1 crosses deposits of advances 2,3, and 4. Most of traverse ND-2
characterizes deposits of advances 5 and 6, except for those samples at the eastern end of the
traverse, which were collected in sediments of glacial Lake Agassiz, and which are treated
separately from the rest of ND-2 (Figure 1; Table 2). In Minnesota, traverse MN-1 crosses
deposits of the Wadena and Rainy lobes, and traverse MN-2 primarily crosses deposits of the Des
Moines lobe (Figure 2).
Average soil-gas radon concentrations, equivalent uranium (eU), and permeabilities for
each transect are compared in Figure 3 and Table 2. Soil-gas radon concentrations and eU are
generally higher in North Dakota than in Minnesota,. The highest soil radon and eU
concentrations and lowest permeabilities were measured in soils derived from sediments of glacial
Lake Agassiz. A good correlation exists between eU measured at the surface and soil radon
measured at 1 m (Figure 4a). Average ratios of eU to soil-gas radon concentration are significantly
lower in this study than for similar ratios in unglaciated areas, such as those reported by
Gundersen (19) and Gundersen and others (6).
Permeability appears to exhibit a weak inverse correlation with soil-gas radon concentration
(Figure 4b), although the range of permeability values is relatively small; all the average values are
between 2xlQ-8 and 9xlQ-8 cm2, and all 39 permeability measurements fall between 10"10 and 10"7
cm2. It was expected that the Minnesota soils, especially the sandy and silty soils derived from
Wadena and Rainy lobe deposits (traverse MN-1), would have higher permeabilities than were
measured (U.S. Soil Conservation Service soil surveys for the area describe many of the soils as
moderately to rapidly permeable). The lower measured values may have been due to localized wet
soil conditions, or to better development of the B horizon, which is generally a zone of
-------
accumulation of fines and therefore less permeable than over- or underlying horizons, in the older
Wadena and Rainy lobe soils. Soils sampled along the Minnesota transects have somewhat higher
and generally more variable permeability than those sampled in North Dakota (Figure 3).
DISCUSSION
The physical, chemical, and drainage characteristics of soils formed on glacial deposits
vary according to source bedrock type and the glacial features on which they are formed. Although
the effects of glaciation have modified the relationship between the bedrock source and the soil's
radon generation and transport characteristics, source rock lithology exerts a major control on
radon potential because it determines the initial uranium and/or radium concentrations in the glacial
drift and the type of soil (clayey or sandy, for example) that develops. Soils formed on ground or
stagnation moraine deposits, which underlie most of the study area, tend to be more poorly drained
and contain more fine-grained material than soils formed on outwash or eskers, which are
generally coarser and well drained.
In general, soils developed from glacial deposits are moderately to highly permeable and
rapidly weathered, because crushing and grinding of the rocks by glacial action may enhance and
speed up soil weathering processes (20). Grinding of the rocks increases the radionuclide mobility
in the resulting soils by exposing the uranium and radium at grain surfaces, where they are more
easily leached and moved downward through the soil profile with other mobile ions.
Accumulations of CaCOj and iron oxides were observed below about 75 cm in most soils in the
study area. CaCOs and iron oxides form soil-grain coatings or concretions that sorb or associate
with uranium (21,22), providing a possible mechanism for uranium accumulation and enhanced
radon emanation in deeper soil horizons. The low surface radioactivity and comparatively high soil
radon concentrations of the glacial soils suggests that radionuclides have been removed from the
upper soil layers and are probably concentrated in deeper horizons. This may explain why
preliminary radon potential predictions based primarily on aerial gamma-ray data typically provide
an underestimate of the number of homes with indoor radon problems in some areas underlain by
glacial drift
Clayey till soils, such as those underlying most of North Dakota, have high emanation
coefficients (23) and usually have low to moderate permeability, depending on the degree to which
the clays are mixed with coarser sediments. Soils formed on tills consisting of mostly coarse
material, such as the sandy tills that underlie much of Minnesota, tend to emanate less radon
because the larger grains have lower surface area-to-volume ratios, but because these soils have
generally higher permeability, radon transport distances are longer, so buildings constructed in
these materials are able to draw soil air from a larger source volume, and moderately elevated
indoor radon concentrations may be achieved from comparatively lower radioactivity soils
(24, 25). In till soils with extremely high permeability, atmospheric dilution may become
significant, so elevated indoor radon levels are less common.
Two general classes of glacial soils can be identified from this study: 1) clay-rich soils
with lower permeability and higher emanation coefficients, and 2) coarser-grained soils with lower
emanation coefficients and higher permeability. The effect of this difference in soil characteristics
can be clearly seen by comparing the distributions of indoor radon levels in North Dakota
(Figure 5) and Minnesota (Figure 6). Although both types of soils can generate indoor radon
levels greater than 4 pCi/L, till soils with high emanation coefficients can generate a significant
number of indoor radon levels greater than 20 pCi/L (Figure 5), whereas soils with high
permeability tend to generate few indoor radon levels greater than 20 pCi/L (Figure 6).
-------
SUMMARY
A comparison of glacial geology, soil-gas radon and gamma radioactivity data, and indoor
radon data for Minnesota and North Dakota indicates that glaciation modifies the relation among
source bedrock, soils, and their resulting radon emanation and transport characteristics, but radon
potential predictions are possible if the nature of these modifications is understood. The
preliminary observations presented in this paper suggest that two factors are important to consider
when predicting radon potential in glaciated terranes. 1) Glaciers transport and redistribute
bedrock, so a bedrock geologic map may not accurately reflect the parent material lithology of
glacially-derived soils, but knowledge of source rock lithology (or lithologi&f, as glaciers may also
mix rocks from several sources together) will aid in determining the radon emanation and transport
characteristics of the derivative tills. 2) Grinding of the rocks by glaciers reduces grain size and
therefore increases grain surface area, enhancing radon emanation by exposing more radium at
grain surfaces than in coarser-grained soils. Glacial mixing and crushing also speeds up the
weathering process, so radionuclides may be leached from shallow horizons of till soils more
rapidly than in soils developed on untransported bedrock, thus giving a surface gamma
radioactivity reading that may underestimate the uranium and radium concentrations at depth.
ACKNOWLEDGEMENTS
This study was conducted in cooperation with, and funded in part by, the U.S.
Environmental Protection Agency under Interagency Agreement DW14933884-0. Thanks are due
to S.S. Agard and G.M. Reimer for reviewing the manuscript and to L.C.S. Gundersen for
helpful discussions.
-------
REFERENCES
1. Ronca-Battista, M., Moon, M., Bergsten, J., White, S.B., Holt, N., and Alexander, B.,
Radon-222 concentrations in the United States-Results of sample surveys in five states.
Radiation Protection Dosimetry 24:307-312,1988.
2. Akerblom, G., Andersson, P., and Clavensjo, B., Soil gas radon—A source for indoor radon
daughters. Radiation Protection Dosimetry 7:49-54,1984.
3. Castre'n, O., Makelainen, I., Winqvist, K., and Voutilainen, A., Indoor radon measurements in
Finland: A status report. la: Hopke, P.K. (ed.), Radon and Its Decay Products.
American Chemical Society Symposium Series 331:97-103,1987.
4. Stranden, E, Radon-222 in Norwegian dwellings. In: Hopke, P.K. (ed.), Radon and Its
Decay Products. American Chemical Society Symposium Series 331:70-83,1987.
5. Duval, J.S., Use of aerial gamma-ray data to estimate relative amounts of radon in soil gas. In:
Gundersen, L.C.S., and Wanty, R.B. (eds), Field studies of radon in natural rocks, soils,
and water. U.S. Geological Survey Bulletin, in press.
6. Gundersen, L.C.S, Reimer, G.M., Wiggs, C.R., and Rice, C.A., Map showing radon
potential of rocks and soils in Montgomery County, Maryland. U.S. Geological Survey
Miscellaneous Field Studies Map MF-2043, scale 1:62,500,1988.
7. Peake, R.T., and Schumann, R.R., Regional radon characterizations. la: Gundersen, L.C.S.,
and Wanty, R.B. (eds), Field studies of radon in natural rocks, soils, and water. U.S.
Geological Survey Bulletin, in press.
8. Schumann, R.R., and Owen, D.E., Relationships between geology, equivalent uranium
concentration, and radon in soil gas, Fairfax County, Virginia. U.S. Geological Survey
Open-File Report 88-18,1988,28 p.
9. Duval, J.S., Jones, W.J., Riggle, F.R., and Pitkin, J.A., Equivalent uranium map of the
conterminous United States. U. S. Geological Survey Open-File Report 89-478,1989.
10. Clayton, Lee, Moran, S.R., and Bluemle, J.P., Explanatory text to accompany the geologic
map of North Dakota. North Dakota Geological Survey Report of Investigation 69,1980,
93 p.
11. Moran, S.R., Arndt, M., Bluemle, J.P., Camara, M., Clayton, L., Fenton, M.M., Harris,
K.L., Hobbs, H.C., Keatinge, R., Sackreiter, D.K., Salomon, N.L., and Teller, J.,
Quaternary stratigraphy and history of North Dakota, southern Manitoba, and northwestern
Minnesota. In: Mahaney, W.C. (ed.), Quaternary stratigraphy of North America.
Stroudsburg, Pennsylvania, Dowden, Huchinson, and Ross, 1976, p. 133-158.
12. Lemke, R.W., Geology of the Souris River area, North Dakota. U.S. Geological Survey
Professional Paper 325, 1960,138 p.
13. Winters, H.A., Geology and ground water resources of Stutsman County, North Dakota, Part
I: Geology. North Dakota Geological Survey Bulletin 41,1963,84 p.
-------
14. Lemke, R.W., Laird, W.M., Tipton, M.J., and Lindvall, R.M., Quaternary geology of the
northern Great Plains. In: Wright, H.E., Jr., and Frey, D.G. (eds), The Quaternary of the
United States. Princeton, NJ, Princeton University Press, 1965, p. 15-27.
15. Hobbs, H.C., and Goebel, J.E., Quaternary geologic map of Minnesota. Minnesota
Geological Survey Map S-l, scale 1:500,000,1982.
16. Wright, H.E., Jr., and Ruhe, R.V., Glaciation of Minnesota and Iowa. IQ: Wright, H.E.,
Jr., and Frey, D.G. (eds.), The Quaternary of the United States. Princeton, NJ, Princeton
University Press, 1965, p. 29-41.
17. Reimer, G.M., Simple techniques for soil-gas and water sampling for radon analysis. In:
Gundersen, L.C.S., and Wanty, R.B. (eds), Field studies of radon in natural rocks, soils,
and water. U.S. Geological Survey Bulletin, in press.
18. Nielson, K.K., Bollenbacher, M.K., Rogers, V.C., and Woodruff, G., Users guide for the
MK-II radon/permeability sampler. U.S. Environmental Protection Agency report, in
press.
19. Gundersen, L. C. S., Anomalously high radon in shear zones. In: Osborne, M., and
Harrison, J., symposium cochairmen, Proceedings of the 1988 Symposium on Radon and
Radon Reduction Technology, Volume 1, oral presentations. U.S. Environmental
Protection Agency publication EPA/600/9-89/006A, 1989, p. 5-27 to 5-44.
20. Jenny, H., The clay content of the soil as related to climatic factors, particularly temperature.
Soil Science 40:111-128,1935.
21. Hansen, R. O., and Stout, P. R., Isotopic distributions of uranium and thorium in soils. Soil
Science 105:44-50,1968.
22. Nash, J. T., Granger, H. C, and Adams, S. S., Geology and concepts of genesis of
important types of uranium deposits. Economic Geology, 75th Anniversary volume: 63-
116, 1981.
23. Grasty, R. L., The relationship of geology and gamma-ray spectrometry to radon in homes.
EOS 70:496,1989.
24. Duval, J.S., Otton, J.K., and Jones, W.J., Estimation of radon potential in the Pacific
Northwest using geological data. U.S. Department of Energy, Bonneville Power
Administration report DOE/BP-1234,1989.
25. Kunz, C, Laympn, C. A., and Parker, C., Gravelly soils and indoor radon. In: Osborne,
M., and Harrison, J., symposium cochairmen, Proceedings of the 1988 Symposium on
Radon and Radon Reduction Technology, Volume 1, oral presentations. U.S.
Environmental Protection Agency publication EPA/600/9-89/006A, 1989, p. 5-75 to 5-86.
-------
TABLE 1. PERCENT OF HOMES IN THE EPA/STATE INDOOR RADON SURVEY WITH
SCREENING INDOOR RADON MEASUREMENTS GREATER THAN 4 PCI/L FOR STATES
UNDERLAIN PRIMARILY BY GLACIAL DEPOSITS
STATE
Iowa
Michigan
Minnesota
North Dakota
Wisconsin
PERCENT > 4 pCi/L
71
12
47
65
27
# OF HOMES TESTED
1381
1989
919
1596
1191
(data from EPA press releases, 1987-89)
TABLE 2. RADON IN SOIL GAS, GAMMA RADIOACnVrTY, AND PERMEABILITY DATA
FOR 132 SAMPLE LOCATIONS IN MINNESOTA AND NORTH DAKOTA
See figures 1 and 2 for locations of sampling traverses. Rn=soil-gas radon concentration at 1m,
eU=equivalent uranium measured at the surface by gamma spectrometer, S.D.=sample standard
deviation, n=number of measurements.
ND-1
eU (ppm)
MINIMUM
MAXIMUM
MEAN
MEDIAN
S.D.
n
1.1
2.3
1.7
1.7
0.4
29
PERMEABILITY (cm2)
MINIMUM
MAXIMUM
MEAN
MEDIAN
S.D.
ND-2 LakeAgassiz MN-1
0.7
2.2
1.5
1.6
0.4
22
7.5xlO'9
1.2xlO-7
4.6x10-8
3.0xlO-8
4.5x10-8
6
1.2
3.0
2.0
0.6
2.2
11
2.6xlO-9
2.9x10-8
1.7x10-8
1.9x10-8
1.3x10-8
3
0.1
1.2
0.4
0.4
0.3
35
2.3xlO'9
2.1xlO-7
3.1x10-8
1.4x10-8
5.7x10-8
12
MN-2
Rn (pd/L)
MINIMUM
MAXIMUM
MEAN
MEDIAN
S.D.
n
310
2325
883
792
440
29
400
3750
1357
1065
900
21
570
2865
1739
1527
738
11
120
1485
416
270
359
35
170
2700
832
687
567
35
0.3
2.7
1.2
1.2
0.5
35
2.7xlO'10
l.SxlO-7
8.3x10-8
9.5x10-8
5.6x10-8
18
-------
Glacial
Devil's
Lake
**' V V V ^ V V
'XUngladated A'X>v
20 40
60 80 100
i i I
Figure 1. Map of North Dakota showing Wisconsin-age glacial deposits and locations of sampling
traverses (ND-1 and ND-2). Numbered lines indicate maximum extent of each glacial
advance. Modified from (14).
-------
EXPLANATION
Glacial Lake
deposits
Oes Moines
Superior
Rainy
Wadena
Pre-Wisconsin
30 60 Miles
Figure 2. Map of Minnesota showing Wisconsin-age glacial deposits and locations of s
traverses (MN-1 and MN-2). Patterned areas indicate deposits of named glacial lobes,
as indicated in map legend. Modified from (15).
-------
EQUIVALENT URANIUM, ppm
4000
3000
2000 H
1000
ND-1 ND-2 LakoAg. MN-1 MN-2
TRAVERSE
SOIL RADON, pCi/L
ND-1 ND-2 LakaAg. MN-1 MN-2
TRAVERSE
SOIL PERMEABILITY, cm'
ND-1 ND-2 LakeAg. MN-1 MN-2
TRAVERSE
• AVERAGE
O minimum
+ maximum
• AVERAGE
O minimum
+ niBxbnum
• AVERAGE
O mWmum
^ irojufflum
Figure 3. Average, minimum, and maximum equivalent uranium (eU), soil-gas radon, and
permeability for soils in the study aiea. See Figures 1 and 2 for locations of traverses.
-------
2000
7 1500 -
1000-
500-
B
2000
z 1500 -
1000
UJ
500-
1 2
AVERAGE eU.ppm
Lake Agassiz
ND-2
MN-2
MN-1
2 4 6 8 10
AVERAGE SOIL PERMEABILITY, cm 2 x10 "*
Figure 4. a) eU versus soil radon. Each point represents the average for one traverse.
b) Permeability versus soil radon. Each point represents the average for one traverse.
Line fitted visually, excluding the point representing MN-1.
-------
20 40 60
80 100
I I
L_E
MB
Data
10 25 50 75 100
20 40
•0 100
UUM
% QTMMr than 20 pCW.
M> o 1 5 10 25*
Figure S. Percent of homes tested in the State/EPA Indoor Radon Survey with basement screening
indoor radon values in excess of 4 pCi/L and 20 pCi/L in North Dakota, by county.
-------
HIM
0 30 60
I* o 10 25 50 76 100
% graatcr than 20 pCM.
30 60
I tv
Dai.
10 2S»
Figure 6. Percent of homes tested in the State/EPA Indoor Radon Survey with basement screening
indoor radon values in excess of 4 pCi/L and 20 pCi/L in Minnesota, by county.
-------
VI-4
GEOLOGIC FACTORS AND HOUSE CONSTRUCTION PRACTICES
AFFECTING INDOOR RADON IN ONONDAGA COUNTY. NEW YORK
by: Charles Laymen and Charles Kunz
Wadsworth Center for Laboratories and Research
New York State Department of Health
Albany, New York 12201-0509
ABSTRACT
Indoor radon in Onondaga County, New York is largely controlled by
bedrock and surficial geology. At more local scales, these alone are insuf-
ficient to characterize indoor radon potential. A detailed study of the
concentration of indoor radon, soil radium, soil-gas radon, soil and bedrock
type, permeability, and home construction practices indicates that above-
average indoor radon concentrations are associated with gravelly moraine and
glaciofluvial deposits, the radium-bearing Marcellus Shale, and high
permeability zones around the substructure of houses built into limestone
bedrock.
INTRODUCTION
Indoor radon*- produced by the radioactive decay of radium-226 in rocks
and soil, is the product of a complex system of interrelated variables.
Because of the inherent relationship between geology and indoor radon, geolo-
gists have been challenged in recent years with the problems of identifying
areas of potential public health risk and developing protocols for evaluating
indoor radon potential prior to new house construction. It is recognized
that many factors affect indoor radon, but the importance of these factors at
different scales is not well understood. New York is geologically very
diverse and the New York State Department of Health has been actively
involved in trying to better understand the geologic controls on indoor
radon. Onondaga County in central New York is one of several counties in the
state that has received special attention.
occurs in three forms, Rn-119, Rn-220, and Rn-222. The longest-lived
isotope, Rn-222, is the most important with regard to public health and will
be referred to exclusively in this paper.
-------
For the past several years, the New York State Department of Health has
provided activated charcoal canister radon detectors to state residents at a
minimal cost. Over 4300 measurements have been made in Onondaga County as
part of this program. In this paper, we examine the county-wide distribution
of indoor radon and the radon problem at several local areas. Results of
this investigation demonstrate that bedrock and surficial geology are
adequate to characterize indoor radon potential at the county-wide scale, but
at smaller scales of a few square kilometers or less, many other character-
istics need to be considered. Particularly important is an understanding of
the variability within the major controls and how homes within the area
interface with their environment.
GEOLOGIC SETTING
PHYSIOGRAPHY
Onondaga County is centrally located in New York State and at the
northeastern edge of the Finger Lakes Region (Figure 1). The county spans
the border between two physiographic provinces, the Erie-Ontario Lowland to
the north and the Appalachian Upland to the south. The Erie-Ontario Lowland
encompasses the relatively low, gently undulating plain lying south of Lakes
Erie and Ontario. Glacial scour has produced numerous ridges of till and
rock, which are surrounded by extensive and thick deposits of stratified
glaciolacustrine sand and mud (3).
Onondaga County is underlain by Upper Silurian to Upper Devonian shales,
limestones, and minor sandstones that are exposed in east-west trending bands
and dip slightly to the south beneath progressively younger strata (1,2).
Differing resistance of the bedrock to weathering processes has produced a
scarp at the northern edge of the Appalachian Upland that rises sharply to
the south more than 300 m in elevation (Figure 1). The scarp is comprised of
several benches formed primarily on the Onondaga and Helderberg Limestones
and is, therefore, referred to as the Onondaga or Helderberg Escarpment
(2,4,5).
The Appalachian Upland is characterized by greater relief as a result of
fluvial dissection of the uplifted bedrock. The northern edge of the upland
is cut by the Finger Lakes and adjacent through valleys, which are glacially
modified valleys of preglacial river drainage. A segment of the largest
moraine in New York, the Valley Heads Moraine, crosses the southern end of
Onondaga County (3,6). Thick sequences of gravelly outwash fill the deeply
cut through valleys of the upland and thin till covers the upland interfluves
between the valleys (3).
The dominant soils in Onondaga County are derived from glacial deposits
containing varying amounts of limestone, shale, and sandstone. For the most
part these soils are deep, medium-textured, well drained to moderately well
drained, and medium to high in lime content (7).
BEDROCK LITHOLOGIES OF THE ONONDAGA ESCARPMENT
Before discussing the geologic controls on indoor radon along the
Onondaga Escarpment, a review of the bedrock lithologies found on the
-------
44° N
43° N
Onondaga & Halderberg Limestone
:^3 Marcvllut Formation
Figure 1. Maps showing the physiographic provinces of New York
State and location of Onondaga County, and the study
areas along the Onondaga Escarpment.
-------
escarpment is beneficial. The Upper Silurian Rondout Dolostone is a poorly
exposed gray dolostone at the base of the escarpment (5). The Rondout
Dolostone grades upward into the overlying Lower Devonian Helderberg Group,
which consists of about 45 m of limestone and generally forms the middle part
of the escarpment (4,5). The Middle Devonian Oriskany Sandstone overlies the
Helderberg Group. This sandstone is absent from the western part of the
county, but increases in thickness from about 1 cm southwest of Syracuse
(Figure 1) to about 5 m on the eastern edge of the county (5). Although the
Oriskany Sandstone is relatively thin, it is notable for containing radium-
bearing, black nodules of calcium phosphate such that it is readily detected
in gamma-ray logs from wells (4,8,9) (Figure 2). Despite this, indoor radon
has not been attributed to the nodules. The Onondaga Limestone, which is
about 24 m thick, overlies the Oriskany Sandstone and is the most durable
rock in the escarpment, cropping out at or near the top (5).
Immediately overlying the Onondaga Limestone are thick beds of black,
bituminous, argillaceous shale collectively known as the Marcellus Formation
(5,9). This formation increases in thickness from about 30 m at the western
edge of the county to about 90 m at the eastern edge (9). The Marcellus
Formation is most noted in New York State for its radioactivity and it is
consequently easily recognized in gamma-ray logs of wells (8,9,10) (Figure
2). In general, radioactivity of the Marcellus Formation is greatest at the
base and decreases progressively upward to the top with the exception of a
1 m thick limestone bed of relatively low activity about 5 m above the base
of the formation.
Results of whole-rock gamma spectrometry analysis of the Marcellus
Formation are given in table 1. Similar results for the Onondaga and
Helderberg Limestones are also given in table 1 for comparison. It is
apparent from these results that the Marcellus Formation shales are enriched
in uranium and radium compared to the underlying limestone units. In
addition, the uranium-to-radium ratio is nearly one to one for both rock
types (taking analytical error and the geometric standard deviation into
account) suggesting that the radium is in equilibrium with the uranium and
there is no evidence of preferential removal of radium by solution.
TABLE 1. RADIONUCLIDE CONTENT OF BEDROCK
226Ra 232Th
Marcellus Formation
Geom. Mean
Geom. Std. Dev.
n
3.5
1.4
10
2.6
1.2
10
1.2
1.1
10
Onondaga and Helderberg Limestones
Geom. Mean 0.3 0.3 0.1
Geom. Std. Dev. 1.8 1.6 1.8
n 31 32 32
-------
I
Steimle
Permit 11632
II
Van Patten
Permit 12148
III
Shepard
Permit 9578
Marcellus
Formation
. — _ _**^«»^^^.
Onondaga
Limestone
^^^^^^^^*
Helderberg
Group
Figure 2. Gamma-ray logs of the Marcellus Formation, Onondaga
Limestone, and upper Helderberg Group from three wells
in and adjacent to Onondaga County.
-------
METHODS
INDOOR RADON
Indoor radon survey results reported in this paper are based on volun-
teered two or four day screening measurements primarily in the basement using
activated charcoal canister detectors. Measurements were made at any time of
the year, but most were made during the fall, winter, and spring. Follow-up
measurements were made in homes with screening results greater than 20 pCi/L.
SOIL-GAS RADON
Soil-gas samples were collected by driving a 2.5 cm diameter steel pipe
into the soil to bedrock or a depth of 120 cm (11). Soil gas was withdrawn
through perforations at the tip of the pipe and the concentration of radon
was measured by alpha scintillation using Lucas cells.
PERMEABILITY
Permeability is measured using the same apparatus used to sample soil
gas. Soil gas is withdrawn from the ground at a fixed flow rate while the
pressure differential required to maintain that flow is measured (11).
Permeability can then be calculated using a standard equation (11,12).
SOIL AND ROCK CHEMISTRY
Soil samples were prepared for radionuclide analysis by placing approx-
imately 100 g of air-dried soil less than 2 mm in diameter in a sealed
polyethylene bottle and set aside for three weeks to allow the radon and
radon daughters to obtain equilibrium with the radium of the sample. Approx-
imately 100 g of each rock sample was crushed and ground to a powder and
similarly sealed in a bottle and set aside for three weeks. The uranium-
238, radium-226, and thorium-232 concentrations were determined after
measuring the rate of gamma emissions by spectroscopy with a Ge(Li) detector.
RESULTS AND DISCUSSION
COUNTY-WIDE DISTRIBUTION OF INDOOR RADON
Over 4300 indoor radon screening measurements in Onondaga County yield a
mean and geometric mean of 10.1 and 4.4 pCi/L, respectively. Examination of
the distribution of indoor radon survey results grouped by zip code area can
be helpful in identifying large-scale geologic controls on indoor radon (13).
Indoor radon in the Erie-Ontario Lowland physiographic province is generally
below 4 pCi/L (Figure 3). This can be attributed to the low concentration of
uranium and radium in the bedrock (9) and an extensive and thick cover of
glacial lacustrine sediments (3) (Figure 3). These sediments are generally
fine-grained and well sorted with almost no gravel-size clasts, resulting in
moderate to low permeability for gas flow (7). Much of the area covered by
these sediments is poorly drained, resulting in large swamps. Only a few
-------
Indoor Radon Concentration
Surficial Geology
< 2.0 pCi/L
^ 2.0 - 3.9 pCi/L
4.0 • 10.0 pCi/L
> 10.0 pCi/L
1 Till [V] Outwiih Qravtt
PI Licuttrfte Sand & Mud
J2 Moraine
Bedrock
Figure 3. Maps of Onondaga County showing indoor radon concentrations
and surficial geology
-------
drumlins and areas covered with gravelly loamy till remained above the ice
marginal lake levels and were not covered with glaciolacustrine sediments
(3). In spite of the gravel component of the till, the fine-grained nature
of its matrix restricts permeability to moderate or lower.
In the southern part of the county, including the Onondaga Escarpment,
indoor radon concentrations greater than 4 pCi/L are more common (Figure 3).
These higher concentrations are attributed to a) the radium-bearing, black
Marcellus Shale, b) building practices in the limestone bedrock, and c) the
highly permeable moraine and glaciofluvial deposits. Almost the entire
Appalachian Upland of Onondaga County is covered by till, outwash, or moraine
deposits (3) (Figure 3). Numerous permeability measurements in these
deposits throughout New York State show variability depending on the texture
and degree of sorting, but in general, demonstrate relatively high permea-
bility for gas flow ranging between 10"° and 10'^ nr (11). Above-average
concentrations of indoor radon are often associated with permeable surficial
deposits, even in the absence of above-average concentrations of radium in
the soil and bedrock (11,14,15). We attribute many of the elevated concen-
trations of indoor radon in southern and central Onondaga County to the
highly permeable nature of these glacial deposits.
Many homes with indoor radon concentrations greater than 4 pCi/L occur
along a narrow east-west trending band across the central part of the county
corresponding to the Onondaga Escarpment. Although some of the elevated
indoor radon concentrations can be attributed to the Marcellus shale,
detailed field investigations with laboratory analyses reveal that many homes
along the escarpment underlain by Onondaga or Helderberg Limestone also
possess elevated concentrations of indoor radon. Hand and Banikowski (16)
attributed elevated indoor radon concentrations on, and north of, the
Onondaga Escarpment to redistribution of uranium from the Marcellus Formation
into subjacent limestones by ground water. No direct evidence for this has
been observed. Below, we present results from several small study areas
along the escarpment that illustrate the complex nature of the association
between topography, bedrock, erosion and transport processes, soils, and home
construction practices that occur along the Onondaga Escarpment leading to
elevated radon levels.
STUDY AREA 1
This study area is located on the Marcellus Formation and forms the basis
for comparison with the other study areas located on the underlying lime-
stones (Figure 1). Indoor radon concentrations in 19 single-family homes
located within the study area yield a mean and geometric mean of 8.5 and 6.0
pCi/L, respectively. The soil derived from rapidly weathered Marcellus shale
is silt loam with shale fragments and is typically less than one-meter thick
and poorly drained (7). Permeability of the soil is generally moderate to
high, ranging from 5 x 10'12 to 1 x 10'9 m2, and in most cases, it is fairly
consistent with depth (Figure 4). The soil contains above-average concentra-
tions of uranium and radium (Table 2). Soil-gas radon concentrations range
up to 5300 pCi/L. The mean soil-gas radon concentration near the foundation
of homes is about 1650 pCi/L, whereas in less disturbed soil in the yard away
from the homes it averages about 2200 pCi/L.
-------
Study Area 1
Permeability (m2)
10'13 10'" 10'11 10'
10
10'
Study Area 2
Permeability (m*)
ID'14 ID'13 10"* 10'"
Study Area 3
Permeability (m2)
IP'14 IP"'3 10"2 10"' 10'10 10'9
30
E6°
I
o
BO
120
30 •
?60
u
a
a>
O
90
120
E
u
30
60
Ltowilont TU
90
120
Figure 4. Permeability profiles for each study area.
-------
TABLE 2. RADIONUCLIDE CONTENT OF SOIL
226Ra 232^
Study Area 1 (n=47)
Geom. Mean
Geom. Std. Dev.
Study Area 2 (n=14)
Ceom. Mean
Geom. Std. Dev.
Study Area 3 (n=16)
Geom. Mean
Geom. Std. Dev.
2.5
1.4
1.1
1.3
2.1
1.5
2.0
1.4
0.7
1.3
2.0
1.8
1.1
1.2
0.6
1.2
0.9
1.3
STUDY AREA 2
This study area is located on the Onondaga and the Helderberg Limestones
on the escarpment downslope from Study Area 1 (Figure 1). Indoor radon
concentrations in 39 homes have a mean and geometric mean of 12.7 and 7.4
pCi/L, respectively. The overburden in this area is variable in thickness
and ranges in texture from gravelly loam to silty clay loam reflecting its
multiple sources (7). Some of the overburden in this area is calcareous till
derived from limestone and shale bedrock to the north that was transported
southward over the escarpment. Elsewhere, there is evidence that Marcellus
shale has been transported northward over some parts of the area by slope
wash and fluvial processes. Disturbance of the overburden during home
construction has made it difficult to separate soils derived from both of
these sources. The radionuclide content of the till is average to slightly
below average for soils (Table 2). In general, permeability of the till is
low to moderate, ranging from 5 x 10"^ to 1 x 10"^ m , but permeability of
the soil in cracks between limestone blocks and buried limestone talus is
higher, approximately 5 x 10*^-^ or (Figure 4). The radon concentration of
several soil-gas samples from undisturbed soil in these cracks and buried
talus range from about 1400 to 1700 pCi/L. For homes built into the
limestone bedrock, permeability is slightly higher adjacent to the home in
the backfilled area around the basement than it is in the undisturbed soil
nearby.
STUDY AREA 3
This study area also is located downslope from the Marcellus Formation on
Onondaga and Helderberg Limestones (Figure 1). Indoor radon concentrations
in 56 homes yield a mean and geometric mean of 46.0 and 20.8 pCi/L, respec-
tively. The soil is shaly loam or silt loam, often less than one-meter thick
(7), and contains above-average concentrations of uranium and radium (Table
2). Permeability of the soil is generally moderate to high, ranging from
-------
5 x 10'12 to 5 x 10"10 m2, and in general, is fairly consistent with depth
(Figure U). As in Study Area 2, permeability is higher in the backfilled
area adjacent to homes than in the undisturbed soil farther away. Soil-gas
radon concentrations range from about 400 to 5000 pCi/L. The mean soil-gas
radon concentration near the foundation of homes is about 1600 pCi/L, whereas
less disturbed soils in the yard away from the home have a mean of about 1900
pCi/L.
It has become increasingly clear after intensive study that several
important factors are acting together to increase the radon potential of
homes in this area. Even though these homes are built on limestone that
possesses very little radon source potential (Table 1), the overlying soil,
which infiltrates joints and solution cavities in the limestone bedrock
provides a sufficient source of radium for radon production. From the
texture of the soil, abundance of shale fragments, and similar radionuclide
content to the Marcellus shale and corresponding soil, it is clear that much
of the soil in this area is derived from the Marcellus Formation and not the
underlying limestone bedrock. It is unclear if the Marcellus shale was
incompletely eroded by glaciers from the Onondaga Limestone, or if it was
transported beyond its bedrock limits and over both the Onondaga and the
Helderberg Limestones by mass movement or fluvial processes. Inconclusive
evidence exists for both mechanisms.
The choice of home construction practices by builders in Study Area 3
also influences indoor radon potential. Most homes in the area are two-
story, colonial, single-family homes between 10 and 30 years old with full
basements or combination basements and crawl spaces. Most of these homes are
heated by forced air from gas furnaces located in the basement. Basement
walls were made with cement blocks, open at the top, and penetrated by the
utilities. Slabs were poured up to the wall and now slab-wall separations
occur in at least 50 percent of the homes examined. Floor drains, rather
than sump holes, were used almost exclusively, and floor cracks are common.
Indoor radon measurements on the first floor and in the basement of homes
in Study Area 3 shows that radon concentrations on the first floor are on
average 18 percent of the concentration in the basement. Radon concentra-
tions in crawl spaces are about 50 percent higher than in the adjacent
basement. Radon concentrations in the block walls are about the same or
slightly higher than in the basement, and concentrations below the slab, as
indicated by grab samples from floor drains, cracks, and slab-wall separa-
tions, are about 100 percent higher than in the basement.
HOME BUILDING IN LIMESTONE BEDROCK
Excavation of limestone bedrock is a difficult, time-consuming, and
expensive task for the home builder, particularly when drilling and blasting
are required. Consequently, builders are forced to either build a split-
level home partially below grade, build the home with a full basement only
partially below grade, or build combination partial basements with crawl
spaces. Below-grade combinations seem to be more common in the limestone
bedrock terrain along the Onondaga Escarpment. Basement and crawl space
slabs were poured directly on the underlying limestone bedrock and rubble
that was generated in the excavation process or over an intervening gravel
-------
bed. In either case, sub-slab communication is excellent and the sub-slab
area becomes a part of a large network of interconnected joints and solution
cavities in the limestone bedrock underlying and surrounding the house.
Joints developed in most beds of the limestone bedrock are widely spaced,
resulting in large blocks commonly more than one meter to a side. Large
numbers of these boulders are excavated for basement construction. In the
absence of much overburden on the limestone bedrock along the escarpment,
backfilling around the below-grade foundation with the excavated material
produces a poorly compacted zone with void spaces. One builder, who needed
to import top soil to cover the bedrock around some homes that were built
into the limestone bedrock, stripped top soil from its source along with the
brush that was growing on it to help prevent the top soil from infiltrating
the cracks and cavities. In Study Area 3, soil derived from Marcellus shale
was incorporated in the backfill, adding a fine-grained, radium-bearing
component to the matrix of the gravelly limestone backfill. The result of
these practices is the formation of a highly permeable zone around the
foundation of the homes that may even be interconnected with the network of
joints and solution cavities in the bedrock. The potential soil-gas
collection area of these homes is so large that, even in the absence of a
substantial radon source, indoor radon concentrations can become very high.
SUMMARY AND CONCLUSIONS
The radium content of bedrock and permeability of surficial materials are
the primarily factors controlling indoor radon in Onondaga County. However,
at smaller scales, additional factors also affect indoor radon to the same
extent. The most important of these factors is how each house interfaces
with its environment. Along the Onondaga Escarpment, where overburden is
thin and many homes are built into limestone bedrock and surrounded by a
highly permeable zone, there is a high potential for these homes to have
elevated levels of indoor radon even though the radium content of the bedrock
is well below average. The effectiveness with which a home draws soil gas
from this zone is dependent on many design characteristics. Other factors
affecting indoor radon in Onondaga County include dispersal of radium-bearing
rock or soil by glacial, mass movement, and fluvial processes. These
processes extend the effect of the radon source rock beyond the mapped limits
of its bedrock source. Consequently, identification of radon risk based on
geologic contacts can greatly underestimate the area affected. The
complexities of the radon system identified in this paper are not unique to
Onondaga County. They most certainly occur elsewhere in New York State and
may be prevalent throughout much of the eastern U.S., particularly in the
Appalachian Mountain region.
The work described in this paper was not funded by the U.S. Environ-
mental Protection Agency and therefore the contents do not necessarily
reflect the views of the Agency and no official endorsement should be made.
-------
ACKNOWLEDGEMENTS
Funding for this research was provided by the New York State Department
of Health Radon Program and the New York State Energy Research and
Development Authority. We are grateful for the field and laboratory
assistance of R. Mahoney, C. Parker, M. Reynolds, and D. Gordon.
REFERENCES
1. Broughton, J.G., Fisher, D.W., Isachsen, Y.W. and Rickard, L.V. Geology
of New York. New York State Museum and Science Service, Educational
Leaflet 20, Albany, New York, 1966, 49 pp.
2. Rickard, L.V. and Fisher, D.W. Geologic map of New York, Finger Lakes
sheet. 1:250,000. New York State Museum and Science Service, Map and
Chart Series No. 15. 1970.
3. Muller, E.H. and Cadwell, D.H. Surficial geologic map of New York,
Finger Lakes sheet. 1:250,000. New York State Museum and Science
Service, Map and Chart Series No. 40. 1986.
4. Clarke, J.M. and Luther, D.D. Geologic map of the Tully Quadrangle. New
York State Museum, Bulletin 83. 1905. 70 pp., map.
5. Hopkins, T.C. The geology of the Syracuse quadrangle. New York State
Museum, Bulletin 171. 1914. 80 pp., map.
6. Muller, E.H. Surficial geology of the Syracuse field area. In: J.J.
Prucha (ed.), Guidebook, New York State Geological Association, 36th Ann.
Mtg., May 8-10, 1964. p. 25.
7. Hutton, Jr., F.Z. and Rice, C.E. Soil survey of Onondaga County, New
York. U.S. Department of Agriculture, Soil Conservation Service and
Cornell University Agricultural Experiment Station, 1977. 235 pp., maps.
8. Vickers, R.C. A radioactivity study of the sedimentary rocks of central
New York State and a description of the methods and apparatus used.
M.Sc. Thesis, Syracuse University. Syracuse, New York. 1951. 39 pp.
9. Rickard, L.V. Stratigraphy of the subsurface Lower and Middle Devonian
of New York, Pennsylvania, Ohio and Ontario. New York State Museum, Map
and Chart Series, No. 39. 1989. 59 pp., maps.
10. Leventhal, J.^S., Crock, J.G. and Malcolm, M.J. Geochemistry of trace
elements and'uranium in Devonian shales of the Appalachian Basin. U.S.
Geological Survey Open-File Report 81-778. 1981. 72 pp.
11. Kunz, C., Laymon, C.A. and Parker, C. Gravelly soils and indoor radon.
In: Proceedings of the 1988 Symposium on Radon and Radon Reduction
-------
Technology, U.S. Environmental Protection Agency, Denver, CO. 1988.
12. DSMA, Atcon, Ltd. Review of existing instrumentation and evaluation of
possibilities for research and development of instrumentation to
determine future levels of radon at a proposed building site. Report for
the Atomic Energy Control Board, Ottawa, Ont. 1983.
13. Mose, D.G., Chrosniak, C.E. and Mushrush, G.W. State-size radon hazard
maps based on zip code compilations. In: Abstracts with Programs,
Geological Society of America. 1989. p. A143.
14. Grace, J.D. Radon anomalies in southern Michigan. In: Abstracts with
Programs, Geological Society of America. 1989. p. A144.
15. Smith, G.W., Mapes, R.H., Hinkel, R.J. and Darr, R.L. Radon hazards
associated with glacial deposits in Ohio. In: Abstracts with Programs,
Geological Society of America. 1989. p. A144.
16. Hand, B.M. and Banikowski, J.E. Radon in Onondaga County, New York:
Paleohydrogeology and redistribution of uranium in Paleozoic sedimentary
rocks. Geology 16: 775, 1988.
-------
VI-5
GEOLOGIC CONTROLS ON INDOOR RADON IN THE PACIFIC NORTHWEST
by: James K. Otton
Joseph S. Duval
U. S. G. S.
Reston, VA 22092
ABSTRACT
Indoor radon data for some townships in the Pacific Northwest
(Washington, Oregon, Idaho, western Montana and western Wyoming) have been
compared with aerial gamma-ray data which show the radium content of surface
materials. Surface radium measurements provide a first-order estimate of the
average levels of indoor radon where soils have low to moderate intrinsic
permeability. Areas with significantly higher average indoor radon are almost
all characterized by soils that have higher permeabilities, based on county
soil descriptions. The permeability effect is greatest in the dry areas (less
than 50 cm annual precipitation) in the eastern part of the study area. In
the wet Puget lowland, elevated indoor radon levels occur only in houses on
soils with extremely high permeability. Some of the areas above the general
trend are also characterized by steep slopes.
-------
Session C-V:
Radon Entry Dynamics—POSTERS
-------
C-V-1
SUB-SLAB SUCTION SYSTEM DESIGN FOR LOW PERMEABILITY SOILS
by: David E. Hintenlang, Ph.D.
Department of Nuclear Engineering Sciences
University of Florida
Gainesville, FL 32611
Richard A. Furman
School of Building Construction
University of Florida
Gainesville, FL 32611
ABSTRACT
Soils having permeabilities in the range of 10-"-10-18 m2 have sometimes
proven to be difficult subjects for the successful implementation of radon-
mitigating sub-slab suction systems. The characteristics of soils having
permeabilities in this range have been studied and a model developed that
describes the pressure fields and airflows that may be expected due to sub-slab
suction points. The model has been computerized to permit its use as a design
tool for a variety of slab and sub-slab suction system configurations. Methods
of using this model to help optimize sub-slab suction system design and the
effectiveness of mitigation will be presented. Pressure-field and airflow
predictions that have been made using this technique, as well as the resulting
decreases in indoor radon concentrations, will be compared with measurements
made on the University of Florida Test Slabs and for whole-house installations.
Funding Statement. Research sponsored by the Environmental Protection Agency
(CR 814-925-010) and the State of Florida Board of Regents State University
System Radon Research Program. This paper has been reviewed in accordance with
the U.S. Environmental Protection Agency's peer and administrative review
policies and approved for presentation and publication.
INTRODUCTION
Sub-slab depressurization systems have proven to be an effective means of
reducing indoor concentrations of radon-222 gas in single-family houses. Their
effectiveness has been demonstrated in the northeast portion of the United
States, and these systems are now being implemented in other areas of the country
-------
that may utilize different construction techniques and materials. The
performance of sub-slab depressurization systems is strongly dependent on the
characteristics of specific construction features and,in particular, the sub-
slab medium. In order to adapt these systems to the conditions that may be
encountered in different geographical areas, it is imperative to develop a
precise understanding of the operation of these systems and their interactions
with the house/soil system in which they are located.
The development of a complete understanding of sub-slab depressurization
systems is also necessary for the practical aspects of optimizing the design and
installation procedures for these systems. Some considerations encountered when
optimizing these mitigation systems are the minimization of the number of suction
points, accounting for the limited availability of locations to install the
suction points, and the optimization of ventilation pipe and mitigation fan
sizes.
In order to address some of these issues, a mathematical/computer model
that simulates the performance of sub-slab depressurization systems has been
developed and applied to buildings of slab-on-grade construction type, including
slab-on-stemwall and monolithic poured slabs. These types of construction
represent the dominant construction types in Florida. This area also utilizes
sandy, sub-slab fill materials almost exclusively. The mathematical/computer
model is, therefore, specifically designed to accommodate these conditions but
may be applied equally well in any region where the sub-slab materials are
homogeneous and the air velocities in the sub-slab materials induced by the
ventilation system are sufficiently low to avoid turbulent flow.
THEORY
Sub-slab depressurization systems contribute to reduced indoor radon
concentrations through two mechanisms: 1) they may provide sufficient airflow
and dilution of the soil gas immediately underneath a slab so that the radon gas
concentrations at that point are significantly reduced, or 2) they may eliminate
or reverse the direction of pressure-driven flow of radon containing soil gas
by reversing the sub-slab pressure differentials. Source strengths are
frequently strong enough, and the airflow rates small enough (for sub-slab
materials having air permeabilities less than about 5 x 10"" m2)- that mechanism
2) is frequently dominant. This results in the necessity of ensuring that any
installed sub-slab depressurization system can, in fact, depressurize a
significant area under a slab, relative to the above-slab pressure.
Airflow through porous media, such as the fill encountered below a slab,
is governed by several fundamental laws (1). These are the conservation of mass
for a fluid moving through porous media,
V(p-V) = 0
where p is the fluid density, V is the fluid velocity and Darcy's Law,
V = - S vp (2)
-------
where k is the air permeability of the porous medium, y is the fluid viscosity,
and y.p is the applied pressure gradient. The simultaneous solutions of these
equations for appropriate boundary conditions describe the airflow and pressure
fields developed by a sub-slab depressurization system.
Substituting Darcy's Law into the equation of mass conservation, assuming
that the fluid (air) is incompressible, yields:
V' (K V-P) = 0 (3)
which must then be solved for appropriate boundary conditions.
In order to obtain solutions for a wide variety of boundary and sub-slab
conditions in three dimensions, a computer solution utilizing finite difference
methods was developed. The methodology of this approach involves dividing the
sub-slab volume into a number of small discrete volumes, referred to as cells.
Each cell is permitted to communicate (have a flow of air) with its nearest
neighbor cells. The program iterates a series of steps where the flow of soil
gas from cell to cell is governed by equation (3). The iterative process
continues until steady-state conditions are achieved; i.e., the flow into the
sub-slab volume is equal to the flow out of the sub-slab volume.
Boundary conditions that govern the generic operation of sub-slab
ventilation systems are determined by the presence of sources and sinks for the
air current. In practical sub-slab depressurization systems, air must be drawn
into the sub-slab volume to replace the air that is forced out of that volume
by the suction fan. The precise sources of this replacement air vary according
to the physical conditions unique to that site. For slab-on-grade construction,
there are several common sources for this replacement air. Cinderblock stemwalls
frequently provide a dominant source, since they have permeabilities equal to,
or larger than, those of the soils of interest and allow outdoor air to be pulled
into the sub-slab volume. Where the block stemwalls are well sealed, air must
be pulled into the soil around the building from the outdoor air. This air is
then transported below the stemwalls and footings to the sub-slab volume. Cracks
in and around the concrete slab also allow indoor air to be transported to the
sub-slab volume. The primary sink for sub-slab depressurization systems is the
suction pressure applied to the sub-slab materials, either in the form of a
suction pit or an extended suction scheme such as a drainage mat.
The boundary conditions that characterize each of these sources or sinks
may be specified as a pressure measured relative to atmospheric pressure. The
pressures at boundaries that permit the infiltration of outdoor air are therefore
equal to atmospheric pressure, and the pressures at the suction points simply
become the applied suction pressures.
The implementation of this technique for computer solutions requires the
complete specification of all boundary conditions. These correspond to physical
quantities such as slab dimensions, construction type and geometry, the sizes
and locations of cracks, and the number, location, and size of the suction
points. Following the specification of these parameters, the finite difference
-------
methods discussed previously are utilized to obtain a three-dimensional
simulation of the pressure and velocity fields present in the sub-slab volume.
Although the calculations are performed in full three dimensions, it is
usually most effective to present the data in the form of a two-dimensional slice
(vertical or horizontal) in which the pressure or velocity field contours may
be easily evaluated. For the purposes of designing and evaluating sub-slab
depressurization systems for radon mitigation, the pressure fields of primary
interest are those in the horizontal plane immediately below the concrete slab.
The pressure fields generated for this location also lend themselves well to
experimental measurements for verification of the computer simulations.
EXPERIMENTAL
Experimental evaluations of the pressure fields in the plane immediately
below the concrete slab have been made on a number of different slabs for
comparison with the computer predictions. These tests have been performed both
at houses where active sub-slab depressurization systems have been installed and
at the University of Florida Test Slab Site. The Test Slab Site was explicitly
built to investigate the performance of and changes associated with sub-slab
depressurization systems under a variety of conditions (2). The University of
Florida Test Slab site consists of four test slabs built with the slab-in-stem-
wall construction technique using standard construction practices. Each slab
has dimensions of 24 ft x 48 ft (7.3 m x 14.6 m) and represents a typical Florida
house construction technique through the completion of the slab, with no
additional building shell. The measurements reported here are obtained from Test
Slab #2 which is constructed with 24 in (0.6 m) of sand fill material above the
natural soil, which is also sandy in nature (Figure 1). This test slab utilizes
a polyethylene curtain placed along the stem wall for half the perimeter of the
slab. This effectively seals the block walls from air infiltration for that
portion of the slab.
The site provides an excellent facility for mapping the pressure field
created by a variety of different suction point configurations and comparing them
with the pressure fields generated from the computer simulation for those
experimental conditions.
The Test Slab has a series of 22 3/4-in. (0.02 m) holes drilled through
the concrete slab in a regular pattern across the slab (Figure 1). These holes
serve as the measurement points for pressure field mapping and velocity
measurements. A suction pit in the form of a 12 in. (0.3 m) radius hemisphere
was created below the suction point penetration and was not backfilled with any
material in this series of experiments.
The experimental procedure for pressure field mapping consisted of applying
a suction pressure of 500 Pa to a central suction point while all other
penetrations remained sealed. Suction pressure was created by an industrial
vacuum cleaner fitted to a regulating valve. Pressure at the suction point was
monitored throughout the experiment using a Neotronics micromanometer, Model
MP20SR. Airflow out of the suction point was calculated from a measurement of
-------
(a)
1 2 3
4.5 6
19 y*J
20
. * •
789
°SP
10* 11 12
V 21
22
13 U 15
16 17 18
1
A
•— B
••-C
(b)
Figure 1. University of Florida Test Slab Configuration, (a) A hori-
zontal cut-away of the footing, stemwall, slab, and fill
construction, (b) A vertical view of the test slab illus-
trating the plumbing rough-in (A), stemwall curtain (B) stem-
wall (c), suction point (SP), and test points.
-------
the velocity of the air flowing through a pipe from the suction point. Air
velocity was measured with a Kurz Model 440 air velocity meter. The induced
pressure was sequentially measured at each of the test points by inserting the
measurement hose of a micromanometer (Neotronics, Model MP20SR) through the test
hole and sealing it from the above slab atmosphere. All pressures were measured
and reported relative to atmospheric pressure. A commercial software package
(Surfer, Golden Software) was used to interpolate between data points, using a
Kriging algorithm, and to develop contour lines of constant pressure. The
empirical pressure fields developed for the central suction point configuration
are illustrated in Figure 2a.
Pressure field extension measurements, total system airflow, and indoor
radon measurements were also made on four research houses. These houses were
initially evaluated using EPA Diagnostic Protocols(3). Based upon the
information obtained during these visits, sub-slab depressurization systems were
designed for each of these houses utilizing the computer simulation. The
parameters describing the operation and performance for each of these systems
are measured and compared to the predictions. The airflows are predicted from
measurements of the soil permeability and applied suction pressure, along with
the geometric dimensions of the specific house slab and compared to the
measurements made at each suction point which are shown in Table 1. All but one
of these sub-slab depressurization systems consist of two suction points
connected to a single fan.
The system is also configured so that the suction points may be
individually valved off. By valving one suction point off and measuring the
pressure induced at that point by the other suction point, it is possible to
obtain a measure of the pressure field that may be compared with the predicted
pressure field. The pressure field due to single suction point operation as
predicted by the computer model for House 789 is illustrated in Figure 3 with
the measurement of the pressure induced at the opposite suction point posted at
that location. The reduction of indoor radon concentration by the designed
pressure fields is listed in Table 1.
RESULTS AND DISCUSSION
The pressure fields generated under the test slabs are simulated by
utilizing the computer model configured to the same boundary conditions as the
test slab. This configuration permits the comparison of the model results with
experimental results for two different sets of boundary conditions: sealed and
unsealed stemwalls. The boundary conditions utilized for the model that
correlate with the test slab are: 1) no interaction of the sub-slab environment
with the outdoor atmosphere along the outer perimeter of the slab to a depth of
1 m, corresponding to the case of the polyethylene-curtained stemwalls, and 2)
differential pressure equal to atmospheric pressure at the outer perimeter of
the slab, corresponding to unsealed stemwalls. The test slab pressure-field
contours developed from the computer simulation, Figure 2b, may be directly
compared with the contours developed from the experimental test points, Figure
2a. The simulated contours coincide with the experimental data over the entire
-------
Table 1. COMPARISON OF EXPERIMENTAL MEASUREMENTS AND MODEL PREDICTIONS FOR RESEARCH HOUSES
House
Suction
789-1
789-2
797-1
797-2
892-1
892-2
062-1
Ro *
Po -
Qexp -
°-pred~
kd *
R0(cm) P0(Pa)
46 385
40.7 388
46 387
46 388
46 378
42 325
46 241
Qexp(cfm) Qpred(cfm) kd(m2) kc(m2) [Rn]Before [Rn]After
3.6 4.
2.2 3.
3.0 4.
3.2 4.
2.0 4.
20.4 4.
2.6 2.
3 e.Oxlo"11 S.oxio"11 12 1.9
9 6.0X10"11 3.5X10"11
4 6.0X10"11 4.2X10"11 17.5 1.4
4 6.0X10'11 4.2X10"11
5 6.5X10'11 3.0X10"11 18.9 7.1
9 6.5X10"11
7 e.oxio'11 e.oxio'11 8.9 2.0
The hemispherical suction pit radius.
The empirically measured
The empirically measured
Values are ± 0.3 cfm (1.
The flow rate predicted
The air permeability of
«*_.!..._._ «*•.**. -L. ^ S\ ft.
pressure at the suction point. Values are ± 3 Pa.
flow rate from
4xlO~4m3/s) .
the suction point.
by the computer model calculations.
the sub-slab soils determined by diagnostic communication tests.
[Rn]
The corrected air permeability that permits the computer model calculations to reproduce Qexp.
Indoor radon concentrations averaged over several weeks of lived-in conditions,
Berore/Arter before and after the installation of sub-slab depressurization systems.
-------
u
•a
4J
•o
24
22
20
18
16
14
12
10
s
6
4
2
0
24
22
20
18
16
14
12
10
3
6
4
2
0
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 JO 32 34 36 38 40 42 44 46 48
Slab Length, ft.
(a)
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48
Slab Length, ft.
(b)
Figure 2. Test Slab Pressure Fields. The vertical and horizontal
axes are the slab dimensions in feet, and the right half
of the slab incorporates the stemwall curtain, (a)
Measured pressure field contours (Pa) from an applied
suction pressure of -500 Pa, plotted for pressures
greater than -60 Pa. (b) Pressure field predicted by
the computer simulation of the experimental conditions.
-------
slab, indicating that the model accurately predicts the pressure fields for both
sealed and unsealed stemwall conditions.
Both the experimental results and those from the computer model demonstrate
how polyethylene-curtained stemwalls extend the pressure field immediately under
the slab. Figure 2 demonstrates that, although sealing the stemwall does not
dramatically change the pressure-field extension along the long axis of the slab,
it does permit the pressure field to reach the edges of the slab across the short
axis. In this example, if a pressure differential of 4 Pa were required to
neutralize the natural depressurization of a house, the sealed stemwall could
account for an additional 4% of the slab area being maintained below this
differential pressure. These results demonstrate how sealing stemwalls from
airflow extends the pressure field and that the effect of stemwall sealing will
be most evident for small pressures, on the order of a few Pascals. These
pressure field extensions can dramatically reduce radon entry by encompassing
major entry routes such as the slab/footing joint.
The test slab experiments provide verification of the operation of the sub-
slab computer model under well-characterized conditions. Additional experiments
and tests were performed using houses participating in a U.S. EPA mitigation
research project. Unlike the test slabs, the sub-slab nature of these houses
could only be inferred from the results of diagnostic tests performed at each
of the houses. These houses, located in Alachua and Marion Counties, Florida,
provide data on the range of applicability for the sub-slab computer model in
Florida houses, provide the opportunity for whole house verification, and
demonstrate the facility of using the computer simulations as an aid in the
design of sub-slab depressurization systems. The initial data for these
simulations were obtained from diagnostic visits in the fall of 1988. Once a
particular design was chosen and installed, experimental measurements were made
for comparison with the simulation predictions.
The pressure at the suction point may be predicted by developing a sub-
slab system performance curve, applied pressure vs. airflow, and matching it
against the fan performance curve. The sub-slab system performance curve is
developed by running computer simulations of the sub-slab environment for several
applied pressures. The fan performance curve is obtained from the fan
manufacturer and verified empirically. The intersection of these two curves
describes the pressure and airflow where the entire sub-slab depressurization
system will operate, assuming that the system is designed such that there are
negligible pressure drops from other sources. Since each of the installations
examined here utilizes a single fan, when two suction points are utilized,
slightly different pressures may be measured at each of the suction points due
to several variables such as differences in suction pit size, length of pipe run,
number of elbows, and airflow rates.
While the predicted pressure may be corrected to account for these
variables, for the purpose of evaluating the sub-slab computer model and the
predicted flowrate, it is most straightforward to perform a simulation utilizing
the empirically determined applied pressure. Predicted airflow rates are listed
in Table 1 along with the measured flow rates. There is agreement between all
-------
of these measurements except for suction point 892-2. The extraordinarily high
flow rate here may be attributed to a crack in the cement floor that runs
directly into the suction point.
All of these flow rates were predicted utilizing effective permeability
values obtained from the diagnostic sub-slab communication testing. From
measurements of the applied pressure and airflow rates, we can use the computer
model to calculate an updated value of the permeability. It is therefore likely
that some of the variations between the predicted and experimentally measured
permeabilities may be attributed to some variation in the sub-slab soil
permeability from the fall of 1988 to the installation time.
Since these houses are occupied, it is not possible to obtain a high
resolution map of the pressure fields created underneath the slab. As previously
discussed, it is, however, possible to obtain a simple measure of the pressure
field extension in the houses that utilize multiple suction points. The pressure
field induced under such a configuration for one house is demonstrated in Figure
3, along with the predicted pressure field contours from the single suction point
operation. These figures indicate that the predicted pressure fields are in
agreement with the measured pressure point along the axis connecting the suction
points. The pressure fields predicted by simultaneous operation of both suction
points are also illustrated in Figure 3. Since the magnitude of the pressure
fields from single-point operation and test slab data is correctly predicted,
it is reasonable that the pressure fields created from the simultaneous operation
of two suction points are also correctly predicted.
The effectiveness of the designed pressure fields in overcoming the
pressure-driven flow of radon-222 into these houses is demonstrated by the
reduction of the indoor radon concentrations shown in Table 1. One house, House
892, continues to have elevated radon concentrations, although they are reduced
from the original concentrations. It is most likely that this is caused by a
significant reduction in the pressure field produced at suction point #2 by the
crack adjacent to the suction point as previously discussed. It is expected
that, when this crack is sealed, the pressure fields will extend to the designed
contours and the indoor radon concentrations will be reduced to levels comparable
to that achieved through the use of sub-slab depressurization in the other
research houses.
The preceding results indicate that the computer model that has been
developed accurately matches experimental conditions. The usefulness of such
a model lies in its ability to make useful predictions. These may include the
use of the computer model as a design tool to increase the efficiency of sub-
slab depressurization systems, or as a means of predicting the behavior of sub-
slab depressurization systems under conditions that are time-consuming,
expensive, or otherwise difficult to measure experimentally.
The ability of this computer model to simulate the operation of a sub-slab
depressurization system prior to installation makes it a valuable design tool.
For sub-slab depressurization systems to be acceptable to homeowners, it is
necessary to install the suction points in inconspicuous locations. These are
not usually the optimum locations for the suction points. By performing computer
-------
"O
•H
.o
cd
iH
CO
0 2 5 7 10 12 15 17 20 22 25 27 30 32 35 37 40 42 45 47 50 52 55 57 60
Slab Length, ft.
(a)
0 2 5 7 10 12 15 17 20 22 25 27 30 32 35 37 40 42 45 47 50 52 55 57 60
Slab Length, ft.
(b)
Figure 3. Research House 789 Pressure Fields (a) Predicted contours
for pressures greater than -60 Pa from a single suction
point. (b) Predicted contours for pressures greater than
-60 Pa for the simultaneous operation of both suction
points.
-------
simulations, it is possible to evaluate the performance of a sub-slab system
utilizing the discrete locations that are available for use. Utilizing this
methodology, it is possible to design a sub-slab depressurization system that
provides for the optimum number and location of suction points, that maximizes
system efficiency, and that minimizes the visual impact to the homeowner.
Predictions of the physical processes that occur during sub-slab
depressurization are also possible through these modeling techniques. One of
the most important aspects of these modeling techniques concerns the development
of pressure fields under conditions of homogeneous permeability. Under these
conditions the magnitude of the pressure fields established by the sub-slab
depressurization system is independent of the permeability. For a given set of
boundary conditions, the pressure fields will always be the same, regardless of
the soil permeability. In the case of non-homogeneous soil permeability, the
pressure fields created will be modified by the inhomogeneities, but these
changes will be a function of the ratios of the different permeabilities, and
are still independent of the permeability magnitude.
Permeability does, however, affect soil gas velocity and flow. From
Darcy's Law, for a given pressure field gradient, the greater the permeability,
the greater the flow rate. Since the pressure field gradients are determined
solely by the boundary conditions and are the same regardless of permeability,
it follows that changes in the soil permeability must affect the flow rate
accordingly. Both of these effects are predicted by the computer model and may
also be derived analytically for simple geometries.
An interesting application of the computer model is the simulation of the
effects of cracks and other openings in a concrete slab on a sub-slab
depressurization system. In order to model this case we have assumed that the
crack, or opening, is large enough and that the air velocity moving through it
is small enough (small soil permeability) so that the pressure drop across the
opening can be neglected. The opening, therefore, permits atmospheric pressure
to be maintained under the slab immediately below the opening. This becomes an
additional boundary condition for this problem.
The incorporation of this boundary condition leads to two effects on the
physical conditions present beneath the slab. The induced pressure in the sub-
slab volume surrounding the penetration will be reduced and the flow through the
sub-slab volume, and out of the suction point, will be increased. The increased
flow, predicted by the computer model, will provide an indirect reduction in the
applied pressure by changing the sub-slab performance curve in such a manner that
it intersects the fan performance curve at a higher flow rate, and therefore a
smaller applied pressure. In most practical cases the increase in flow rate is
small enough that these effects are negligible.
The computer model predicts that the area under the slab affected by the
penetration will be determined by its proximity to the suction point. Figure
4 illustrates the pressure fields produced in two situations for a constant
applied pressure and where only the position of the penetration has been changed.
This demonstrates that a penetration closer to the suction point affects a
smaller slab area than one farther away. The penetration near a suction point
-------
•o
•H
0)
rH
01
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48
Slab Length, ft.
(a)
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48
Slab Length, ft.
(b)
Figure 4. Effects of slab penetrations on the pressure field: (a)
A 12 x 36 in. (0.3 x 0.9 m) penetration close to the
suction point, (b) A 12 x 36 in. (0.3 x 0.9 m) pene-
tration far from the suction point.
-------
nay decrease the pressure field below that required to overcome the negative
house pressure only in the immediate vicinity of the penetration. The pressure
field quickly recovers in this case and develops nearly unperturbed except for
that small area. When the penetration is farther from the suction point, where
the pressure gradients are smaller, a much larger slab area is affected. Under
these conditions, the lower limit of the pressure fields are greatly perturbed,
and can greatly affect the area under the slab where sub-slab depressurization
is effective.
These results indicate that, unless cracks near a suction point are so
extensive that the applied pressure cannot be maintained, it is not worth a large
expenditure of effort to seal them. Conversely, cracks near the perimeter of
the pressure field should be sealed if the sub-slab depressurization system is
required to maintain its effectiveness at distances beyond that from the suction
point.
CONCLUSIONS
A computer simulation that describes the operation of sub-slab
depressurization systems has been developed by modeling the physical processes
that occur when this mitigation technique is applied to slab-on-grade
construction. The model has been verified by extensive pressure field mapping
at the University of Florida Test Slab Site and has demonstrated its
effectiveness in the design of sub-slab depressurization systems for several
radon mitigation research/demonstration houses. The physical processes predicted
by the model make it a useful tool for the design of these systems, and permit
it to make valuable predictions concerning the performance of these systems for
a variety of physical conditions. These simulations permit accurate evaluations
of various sub-slab depressurization configurations that can be performed without
the time and expense associated with the construction of elaborate test
facilities and extensive instrumentation.
REFERENCES
1. Bear, J. The Fundamental Fluid Transport Equations in Porous Media, in:
Dynamics of Fluids in Porous Media. Dover Publications, New York, 1988.
2. Furman, R.A. and Hintenlang, D.E. Sub-Slab Pressure Field Extension
Studies on Four Test Slabs Typical of Florida Construction. In1.
Proceedings of the 1990 International Symposium on Radon and Radon
Reduction Technology, Atlanta, Georgia, to be published.
3. Harris, D.B., Henschel, D.B., Sanchez, D.C. and Witter, K.W. Field
Measurements in the EPA/AEERL Radon R&D Program. In: Proceedings: The 1988
Symposium on Radon and Radon Reduction Technology, Volume 2, EPA-600/9-
89-0066 (NTIS PB86-167498), March 1989.
-------
C-V-2
INTERPRETING THE VACUUM SUCTION TEST
by: Terry Brennan
Camroden Associates
Oriskany, NY 13440
ABSTRACT
Some Investigators use a vacuum cleaner to temporarily induce a low air
pressure field beneath concrete slabs. This test is performed to gain insight
into the prospects for soil depressurization as a radon control method. A
protocol is suggested that can provide a basis for deciding whether sub-slab
depressurization or pressurization is likely to succeed or fail. Enough data
can be collected to select a fan with appropriate performance characteristics.
Examples are drawn from field work to illustrate the collection and
interpretation of the data.
-------
Lacking X-ray vision, a vacuum suction test can be done to explore
strength and size that a low air pressure field can be extended beneath a
floor slab. How far the pressure field is extended and at what strength
depends two things:
• how resistant to airflow is the material immediately beneath the slab
• how tight the surrounding soil and covering foundation are
The results of this test can yield insight into both of these important
variables. First a vacuum cleaner is used to apply suction to a hole through
the slab, called FA by convention. The amount of suction created by the
vacuum pulling on the 'system * beneath the slab is measured in the
vacuum nozzle (FA), at a hole 10 inchs away (FB, again by convention) and
at other test holes (FC, FD etc.) several feet away (usually 10 to 30 feet). If
the material beneath the slab is loose (say stone pebbles) and foundation
and surrounding soil are fairly resistant to airflow, then a low pressure can
be induced a great distance from the suction point. If there is loose
material beneath the slab and there are large airleaks through the
foundation or the surrounding soil or bedrock, then a weak pressure field
will be induced and will extend only as far as the leaks (eg. French drain or
shattered bedrock). If there is fine but porous material beneath the slab
then a strong vacuum will be induced at the suction point (FA) but it will be
defeated by the resistance to airflow of the fine material and not extend
very far from the suction point. See Figure 7 for a conceptual model and
illustration of these ideas.
Figure 1 - The Vacuum Suction Test
VACUUM NOZZLE
Pressure Differential Gauges
-------
Figure 2 - Measure the vacuum in the closed nozzle (zero airflow) and
open nozzle (maximum airflow). This establishes a rough guide to the
amount of air the vacuum can pull from under the slab, which can be
used with Figure 3 to select the fan type. Alternately the airflow could
actually be measured.
Cover the vacuum nozzle
with your hand. The airflow
thru the vac is zero. The
amount of suction measured
in the nozzle is the most the
vacuum can pull. For a
Eureka Mighty Mite with a
clean bag this is about 40
inchs WC.
Measure the suction in the
nozzle with the vacuum
nozzle in open air. This is the
lowest amount of suction the
vacuum will pull because it
is the minimum resistance to
airflow it can have. For a
Eureka Mighty Mite with a
clean bag this is about 5
inchs WC.
Figure 3 - Select Fan Type
Suction at
FA
FB
Fan Type
Low-Medium
High
Medium-High
<1.5inchsWC
<1.5inchsWC
>1.5 Inchs WC
In Line Centrifugal
Vortex
Radial
-------
Figure 4 - Fan and "System " Curves
In Line
200 T /S**1*1^
Stone Pebbles v
J3fc-—
.^•^
Radial Fan
W* I
Vortex Fan
*— Fine sand
or silt
4 5
AP (Inchs WC)
The four "system" curves are measured field data that appear
"typical" for the conditions listed. As with all things radon it is
likely that there are many exceptions to these "typical" curves.
Notice that for different sub-slab conditions the in line
centrifugal fans normally used for soil depressurization systems
is probably not appropriate. Both the coarse sand and fine sand
and silt curves!ntersect the in line centrifugal fan curve below
the manufacturers suggested minimum airflow.
The power consumed by an air handler depends on how much air it
is moving. This table shows the measured Wattage range of the
fans whose curves are shown in the graph.
In Line Centrifugal 63-83 Watts
Radial 87-245 Watts
Vortex 67-132 Watts
-------
Figure 5 - Select Number of Suction Points
Suction at
FA
| FC, F D etc.
Probable Sub
Slab Condition
Number of
Suction Points
Low-Medium Good everywhere (stone pebbles)
Good around
slab edge
(sand with
perimeter
drain tile)
1 anywhere
1 anywhere
at slab edge
High Drops off quickly
(6 to 10 feet)
Medium-High Drops off quickly
(10 to 15 feet)
(clay or silt)
(coarse sand)
1/300 square feet
1/600 square feet
Low
Drops off quickly
(8 to 15 feet) or
marginal
everywhere
large leaks under
the slab through
the foundation or
underlying soil or
bedrock.
(Shattered shale
or limestone,
glacial outwash or
riverbed gravels)
pressurize
beneath the slab
or more suction
points or
seal foundation
leaks if they are
large (french
drain, sump hole)
Figure 6 - Select Pipe Diameter
Suction at
FA
Pipe Diameter
High Four inch
Medium Three Inch
Low Two inch legs, three inch headers
-------
Figure 7 - A Conceptual Model for Soil Depressurization
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'f 't 'f 'f 'f 'f ~f 't 'f ~f ~f "f ~f 't't't ~f "f "f 't't't't't't 't't't t t f
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VxVxxxVxVxVxVxVxVxVxVxVxVxVxVxVxVxVxVxVxVxxxVxVxVxXxV
\x\\\\\\\\\\\\\\\\\s\\\\\\\\ \ \ \ \,v v>»>>»>>>>>>>^^^
If the material beneath the slab has very little resistance to airflow
compared to that of the surrounding soil or bedrock (Rs,a) and that of
the leaks through the foundation to the sub slab air (Rb.a), then the
amount of air and vacuum induced by the sub slab fan is a function of
these two variables and the fan performance curve.If the material
beneath the slab is fine enough so that the resistance to airflow
through a few feet of it is comparable to the other two (Rb.s and Rs.a)
then this model is too simple. The material beneath the slab would
have to be divided up into numerous "bits" and the resistance between
each bit the and the surrounding "bits", outside air and basement air
would need to be accounted for.This is the case when fine sands, silts
and clays are found directly beneath the slab and it has important
implications for both radon entry and the prevention of radon entry by
soil depressurization.
-------
C-V-3
SEASONAL VARIATIONS OF INDOOR RADON CONCENTRATIONS
by: Benny Majborn
Rise National Laboratory
DK-4000 Roskilde, Denmark
ABSTRACT
Seasonal variations of indoor radon concentrations have been stud-
ied in a cluster of 10 single-family houses. Eight of the houses are
of a similar construction with slab-on-grade foundations. The remaining
two nouses have different substructures, one of them having a crawl
space, and the other having partly a basement and partly a crawl space.
A "normal" seasonal variation of the radon concentration with a maximum
in winter and a minimum in summer was observed in most of the houses. In
these houses the variation showed a strong correlation with the indoor-
outdoor temperature difference on a 2-month basis. However, deviating
seasonal variations were observed in some of the houses, notably in the
two houses having different substructures.
A re-examination of the data obtained in a previous study indicates
that winter/summer ratios of indoor radon concentrations in Danish houses
depend on the house substructure. The mean winter/summer ratios were
about 2.1 for houses with slab-on-grade foundations, 1.5 for houses having
a basement, and 1.0 for houses with a crawl space (geometric mean values).
However, a study with more houses in each substructure category will be
needed to show whether or not the indicated differences are generally valid
for Danish houses.
INTRODUCTION
In this paper some results on seasonal variations of indoor radon
concentrations in Danish single-family houses are reported and discussed.
The results have been obtained in two different studies. One of these is
an extension of an investigation of factors influencing indoor radon
concentrations carried out in 1986-87 (1). The investigation comprised 16
houses built on the same site, and included integrating radon measurements
-------
in the living-room and in a bedroom of all the houses on a two-month
basis throughout the two years. These measurements have been extended
through 1988 in ten of the houses. The other study is a pilot investiga-
tion of natural radiation in Danish houses carried out in 1983-84 (2). In
that work integrating radon measurements were made in 70 single-family
houses and 12 apartments during three months in winter and three months
in summer. The data on seasonal variations obtained in the pilot study
have been re-examined after obtaining additional information on the sub-
structure of the houses.
Knowledge of temporal variations of indoor radon concentrations and
the variability of such variations is needed for a proper appraisal of
the significance of results obtained from short-term measurements and for
estimating the uncertainties involved in attempts to predict annual aver-
ages from measurements covering shorter time periods (3,4). Knowledge of
temporal variations and the identification of causes of such variations
can also contribute to improve our understanding of the mechanisms of
radon entry into houses (5,6).
METHODS
Integrating radon measurements were made with passive closed dose-
meters equipped with CR-39 track detectors. The dosemeter design and its
properties have been described elsewhere (2,1). The performance of the
dosemeter was tested in CEC radon dosimetry intercomparisons in 1984 (8),
1987 (9), and 1989, in all cases with good results.
HOUSE TYPES
The 10 houses in which radon was measured on a two-month basis dur-
ing 1986-88 are situated next to Ris0 National Laboratory. The site of
the houses forms an area of about 150 m by 300 m, and the soil below the
houses is mainly moraine clay. The houses are one-storey single-family
houses built of bricks. Eight of the houses have slab-on-grade foundations
and differ only in length, having one bedroom more or less. The remaining
2 houses have different substructures, one having a crawl space and the
other having partly a basement and partly a crawl space. A special feature
is a district-heating duct which is extended into each house, where it
proceeds circumferentially along the outer walls as an integral part of
the foundation.
The 70 single-family houses included in the pilot study in 1983-84
are distributed throughout Denmark. They were not chosen to be repre-
sentative for the Danish building stock as the purpose of the in-
vestigation was primarily to establish and test measurement procedures.1
^A representative survey was conducted in 1985-86 (10), but in that
work two six-month integration periods were used, and the seasonal
variation was not measured in each single house.
-------
Out of the 70 single-family houses 25 had a basement, but no further
differentiation of the nouses according to substructure was made at the
time when the study was carried out. Recently, additional information on
the type of substructure has been acquired for most of the houses, so
that these may be grouped into the categories: 1) full basement, 2) base-
ment + crawl space, 3) basement + slab-on-grade, 4} crawl space, and 5)
no basement or crawl space, i.e. mostly slab-on-grade houses.
RESULTS
Figure 1 shows the seasonal variations during 1986, 1987 and 1988
of the mean radon concentrations in seven of the Rise houses. The figure
shows the geometric mean value of the radon concentrations for each 2-
month period for all 14 rooms (7 living-rooms and 7 bedrooms). The geo-
metric standard deviations range from 1.6 to 2.1 for the 18 measurement
periods. In the remaining 3 houses, including the two houses having a
different substructure, there was not a pronounced seasonal variation
_ 300
j=
200
8 100
8
O
10
UJ
-10
1986
1987
YEAR
1988
Figure 1. Seasonal variations during 1966, 1987 and 1988 of 1) the
geometric mean value of the radon concentrations in 7 houses,
and 2) the average outdoor temperature.
-------
of the radon concentration, except that the house with a crawl space
appeared to snow a summer maximum in 1986. Figure 1 also shows the
average outdoor temperature (2-month averages) at the nearby meteorologi-
cal station at Rise National Laboratory. The correlation coefficients
(linear regression) between outdoor temperature and indoor radon (geome-
tric mean value for 14 rooms) were found to be -0.97 for 1986, -0.98 for
1987, and -0.91 for 1988. As the variations of the average indoor tempe-
rature are small compared with those of the outdoor temperature, the
results indicate a strong correlation on a 2-month basis between the
average indoor-outdoor temperature difference and the average indoor
radon concentration in this group of houses.
In the pilot study integrating radon measurements were made in a 3-
month winter (1 Dec. 1983 to 29 Feb. 1984) and a 3-month summer period
(22 May to 13 Aug. 1984). Figure 2 is a plot of the summer results for
UJ
300
200
•E 100
a-
CO
HI
o
§ 300
o
o
200
100
Bedroom
Living-room
0 100 200 300 &00
RADON CONCENTRATION (Bq/m3) WINTER
Figure 2. Summer versus winter radon concentrations in 38 houses with-
out basement or crawl space. The straight lines represent a
slope = 1.
-------
each of the houses without a basement or crawl space (i.e. mostly slab-
on-grade houses) versus the winter results for the same houses. Similarly,
figure 3 shows the summer versus winter results for the houses having a
basement. In Table 1 the winter and summer radon concentrations and the
winter/summer ratios (geometric mean values and geometric standard devi-
ations) are given for 1) houses with a basement, 2} houses with a crawl
space, and 3) houses without a basement or crawl space. The houses with
a full basement or basement + crawl space have been grouped together,
because the mean radon concentrations and winter/summer ratios did not
differ significantly between the two groups. Three houses having a base-
ment + slab-on-grade foundation had mean radon concentrations in the
0 100 200 300 400
RADON CONCENTRATION (Bq/knJ) WINTER
Figure 3. Summer versus winter radon concentrations in houses having
a full basement (circles), basement + crawl space (squares),
or basement + slab-on-grade foundation (triangles). The
straight lines represent a slope = 1.
-------
TABLE 1. WINTER AND SUMMER RADON CONCENTRATIONS AND WINTER/SUMMER
RATIOS (GEOMETRIC MEAN VALUES AND GEOMETRIC STANDARD DEVI-
ATIONS) FOR DIFFERENT HOUSE TYPES.
House type Number Radon concentration
Roan of Winter Summer
houses GM GSD GM GSD
(Bq/m3) (Bq/m3)
Winter/summer
ratio
GM GSD
Basement* 16
Living-room
Bedroom
Basement
Crawl space 3
Living-room
Bedroom
No basement or
crawl space 38
Living-room
Bedroom
68
60
115
59
48
122
92
2.2
2.2
1.7
2.6
2.4
1.7
2.0
47
38
88
63
49
57
46
1.6
1.8
1.9
2.5
2.6
1.9
2.0
1.46 1.7
1.57 1.7
1.32 1.6
0.93
0.97
2.13
2.02
1.3
1.1
1.5
1.8
* Include 11 houses with full basement and 5 houses with basement + crawl
space.
living-rooms and bedrooms that were close to the mean values found for
the slab-on-grade houses. The results from these 3 houses have not been
included in Table 1. There are only 3 houses with a crawl space in this
sample. All 3 houses had winter/summer ratios close to unity in both
rooms (range 0.7 - 1.2). The average radon concentrations were about 20,
70, and 120 Bq/m3 in the 3 houses.
Within each category of houses the mean winter/summer ratios are
not different between living-rooms and bedrooms (98% of the living-rooms
and 79% of the bedrooms were on the first floor). For the 16 houses hav-
ing a basement or basement + crawl space the lower mean winter/summer
ratio found for basement rooms (1.3) is not significantly different from
that found for living-rooms and bedrooms (1.5). The differences between
the mean winter/summer ratios found for living-rooms and bedrooms in 1)
houses without basement or crawl space (2.1), 2) houses with basement
(1.5), and 3) houses with crawl space (1.0) are significant at the 95%
level.
-------
DISCUSSION AND CONCLUSIONS
Seasonal variations of indoor radon concentrations may depend on
a number of factors, including geological factors, climate, house cha-
racteristics and living habits. Figure 1 shows an example of the in-
fluence of climate. The figure shows the seasonal variations during
3 years of the mean radon concentrations in a group of houses with slab-
on-grade foundations. The variations show a strong correlation with the
indoor-outdoor temperature difference on a 2-month basis. A major dif-
ference between the 3 years was an unusually cold January-February in
1986 and 1987 and an unusually mild January-February in 1988. This dif-
ference is clearly reflected in the observed radon concentrations.
The results.reported in this paper on winter/summer ratios indicate
that houses with slab-on-grade foundations have higher mean winter/summer
ratios than houses with a basement or crawl space. Similar observations
have been reported in a Finnish study (11), where measured seasonal
variations of indoor radon concentrations were compared with model cal-
culations. Data from the USA suggest that winter/summer ratios tend to be
greater for the first floor than for the basement of houses (4). The same
tendency was observed in the present work. It should be noted, however,
that the results reported in this paper are based on a limited number
of houses. A study with more nouses in each substructure category will
be needed to show whether or not the indicated differences are generally
valid for Danish houses.
The work described in this paper was not funded
by the U.S. Environmental Protection Agency and
therefore the contents do not necessarily reflect
the views of the Agency and no official endorsement
should be inferred.
ACKNOWLEDGEMENTS
This paper is partly based on two studies that were partly funded by
the Commission of the European Communities. The author would like to
thank S.P. Nielsen for valuable discussions.
-------
REFERENCES
1. Majborn, B., Serensen, A., Nielsen, S.P., and Better-Jensen, L.
An investigation of factors influencing indoor radon concentra-
tions. Riso-M-2689, Ris0 National Laboratory, Roskilde, Denmark,
1988. 58 pp.
2. Sorensen, A., B0tter-Jensen, L., Majborn, B., and Nielsen, S.P.
A pilot investigation of natural radiation in Danish houses. Rise
-M-2483, Risa National Laboratory, Roskilde, Denmark, 1985. 40 pp.
3. Swedjemark, G.A. Radon and radon daughters indoors, problems in
the determination of the annual average. SSI Scientific Report
84-11-12, National Institute of Radiation Protection, Stockholm,
Sweden, 1984. 47 pp.
4. Bierma, T.J., Croke, K.G., and Swartzman, D. Accuracy and preci-
sion of hone radon monitoring and the effectiveness of EPA moni-
toring guidelines. JAPCA 39: 953, 1989.
5. Nazaroff, W.W., Moed, B.A., and Sextro, R.G. Soil as a source of
indoor radon: Generation, migration and entry. In; W.W. Nazaroff
and A.V. Nero, Jr. (ed.), Radon and its decay products in indoor
air. J. Wiley & Sons, New York, ISBN 0-417-62810-7, 1988, p. 57.
6. Arvela, H., and Winqvist, K. Influence of source type and air
exchange on variations of indoor radon concentration. STUK-A51,
Finnish Centre for Radiation and Nuclear Safety, Helsinki, Finland,
1986. 32 pp.
7. Majborn, B. Measurements of radon in dwellings with CR-39 track
detectors. Nuclear Tracks 12: 763, 1986.
8. Miles, J.C.H., and Sinnaeve, J. Results of the second CEC inter-
comparison of active and passive dosemeters for the measurement of
radon and radon decay products. EUR 10403 EN, Commission of the
European Communities, Brussels, Belgium, 1986. 64 pp.
9. Miles, J.C.H., and Sinnaeve, J. Results of the third CEC inter-
conparison of active and passive detectors for the measurement
of radon and radon decay products. EUR 11882 EN, Commission of
the European Ccmrounities, Brussels, Belgium, 1988. 80 pp.
10. Ulbak, K., Stenum, B., S0rensen, A., Majborn, B., Better-Jensen,
L., and Nielsen, S.P. Results from the Danish indoor radiation
survey, Radiat. Prot. Dosim. 24: 401, 1988.
11. Arvela, H., \foutilainen, A., Makelainen, I, Castren, p., and
Winqvist, K. Comparison of predicted and measured variations of
indoor radon concentration. Radiat. Prot. Dosim. 24:231, 1988.
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C-V-4
DYNAMIC MULTI-COMPARTMENT MODELLING: THE TRANSPORT
OF RADON AND ITS DECAY PRODUCTS INDOORS
by: Craig P. Wray, P.Eng. and
Grenville K. Yuill, Ph.D., P.Eng.
G.K. Yuill and Associates Ltd.
Winnipeg, Manitoba R3T 2C4
ABSTRACT
A microcomputer program has been developed so systematic radon and radon
progeny control techniques of optimal effectiveness can be formulated for
designing or retrofitting houses. An existing multizone airflow/contaminant
dispersal analysis computer program was modified by adding a model of radon
progeny plate-out on indoor surfaces.
Three simulation exercises of radon and radon progeny levels in the
rooms of a hypothetical house for two different HVAC systems were carried out
using the new program. Comparisons of these parameters were made with those
for the same house with only natural ventilation. The simulations showed that
significant differences in average radon levels and total EEDCs can occur
between rooms of a house. These differences demonstrate the need for a
multizone model and indicate caution should be used in applying radon and
radon progeny level measurements taken in one room to any other room in a
house. The simulation exercises also showed that radon and radon progeny
levels in a house strongly depend on the type of ventilation system in the
house.
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INTRODUCTION
In a large fraction of Canadian houses, radon concentrations Indoors are
significantly higher than those outdoors. These elevated levels can
compromise the health of occupants who are exposed to them over long periods
of time. Although several mitigation techniques have been used recently to
reduce these concentrations to acceptable levels, the reasons for their
effectiveness are not well understood, and no systematic approach has been
established for implementing an appropriate procedure in each situation.
The behavior of radon and its progeny in houses is too complex to
predict without simulation. Although field monitoring could be used to study
radon and radon progeny transport, this approach is prohibitively expensive if
even a few common combinations of house geometry, ventilation system types,
and soil characteristics are to be examined.
As a step towards the improvement of existing mitigation techniques and
the formulation of mitigation strategies, it is desirable to synthesize
previous research about radon and radon progeny transport with current
multizone modelling techniques to produce a model that can predict the
accumulation of these pollutants in a house on a time-varying basis. In the
work described here, an existing multizone airflow/pollutant analysis
microcomputer program was modified. Parametric studies using the modified
program (CONAIR 89-2) can be carried out in the future to gain a better
understanding of radon transport, so systematic radon and radon progeny
control techniques of optimal effectiveness can be developed for new and
existing houses.
CONAIR 89-1: AN EXISTING SIMULATION TOOL
CONAIR 89-1 is an existing multizone airflow/contaminant dispersal
network analysis microcomputer program that has most, but not all, of the
capabilities required for the work described here. It was developed by G.K.
Yuill and Associates Ltd. using two computer programs (AIRNET and CONTAM 87)
obtained from the U.S. National Bureau of Standards as its core (1). CONAIR
89-1 begins by modelling airflows between zones and between indoors and
outdoors in a multizone building. It simulates wind and stack effects on
envelope leaks, friction in ducts, fan characteristics and two-way buoyancy-
driven flow through large openings such as doors. Calculations are done using
hourly mass-balances on a macroscopic basis assuming well-mixed zones.
Recirculation within a single room is not simulated. Steady-state
calculations are done for each set of hourly operating conditions supplied,
such as weather data, fan settings, or damper settings. The program ignores
subhourly pressure transients, because their time constants are typically too
short to be of significance in this kind of calculation.
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CONAIR 89-1 also has the capability to model pollutant concentrations.
This part of the program uses the airflows determined in the first part, along
with source strengths and reaction and decay rates for the various pollutants
present, to predict the pollutant concentrations in each zone. The program
does a steady-state analysis, but can also do a dynamic analysis to predict
time-varying concentrations.
RADON DAUGHTER PLATE-OUT MODEL
CONAIR 89-1 assumes all pollutants are airborne and thus are subject to
transport in ventilation airflows. However, this assumption is inappropriate
for some pollutants such as radon progeny (218Po, 214Pb, and 214Bi), which
plate-out on surfaces within a house such as walls or furniture. With the
exception of 218Po, once these progeny are deposited on these surfaces, they
do not produce significant numbers of progeny that return to the air where
they can be transported from room to room or from indoors to outdoors. Thus,
surface-deposited 214Pb and 214Bi remain trapped in the particular room in
which they plated-out. The concentrations of these two surface-deposited
radon daughters are of no significance from a health standpoint therefore,
because they cannot be inhaled once they plate-out. However, 214Pb formed
from decaying surface-deposited 218Po can return to the air through a recoil
mechanism, so CONAIR 89-1 needed upgrading to model surface-deposition of
with recoil.
CONAIR 89-1 uses air and pollutant mass-balances to determine the mass
transport rate of up to eight different species through simple flow elements
with or without filters. The flow through an element is assumed to be
instantaneous and well-mixed. Axley (2) defines the transport of a pollutant
species a between two nodes by flow element equations from node i to node j
due to an air mass flow rate we(t) as follows:
M = W(t)°
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Since CONAIR 89-1 assumes all species are airborne, equations 1 and 2
state that all species are transported into element e where they can be
removed to some degree by a filter. Thus, to account for surface-deposition
of a particular species at a node, it is necessary to eliminate the mass
transport of that species into element e. This blocking of airborne transport
in CONAIR 89-2 was achieved by defining a surface-deposition coefficient «s
that affects the species mass transport rates as follows:
(3)
(4)
For airborne transport of a particular species, as is set to unity, so
it has no effect on the mass transport rate of that species. For a particular
species that is surface-deposited, xs is set to zero, so the mass transport
by ventilation of that species through all flow elements connecting every node
is eliminated.
The nature of each pollutant (airborne or surface-deposited) is
identified in the CONAIR 89-2 contaminant input file by specifying the
pollutant type as either type "A" (airborne, «s = 1.0) or type "S" (surface-
deposited, "s = 0.0).
INPUT PARAMETERS FOR THE RADON AND RADON PROGENY MODEL
RADON AND RADON PROGENY KINETICS
In the Jacobi model (3), the sources of radon in the indoor air are the
entry of radon in soil gas infiltrating into the basement through foundation
penetrations and in the outdoor air infiltrating through above-grade leaks in
the building envelope. The removal of radon and the removal and production of
radon progeny in the Jacobi model by radioactive decay, attachment,
deposition, and recoil can be described by a set of linear first-order
differential equations for each room. CONAIR 89-1 already has the capability
to model these processes (2), with the exception of surface-deposition that
involves recoil. Therefore, it was only necessary to define the differential
equations and to select a value for each of the rate constants in these
equations for each room.
The Jacobi model can be simplified for the purposes of this project.
There is no need to determine the concentrations of surface-deposited 214Pb or
214Bi, because these species do not pose a health risk once they are removed
from the air by the plate-out process. The probability they will produce
recoiling atoms once deposited is negligible. This leaves eight species to
consider: airborne-unattached ^Rn (URn2), airborne-unattached 218Po (UPo8),
airborne-unattached 21«Pb (UPb4), airborne-unattached 214Bi (UBi4), airborne-
attached 218Po (APo8), airborne-attached 214Pb (APb4), airborne-attached 214Bi
(ABi4), and surface-deposited 218Po (SPo8).
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The differential equations describing the radon and radon progeny
kinetics indoors (excluding ventilation) for any given room are:
d[URn2]
dt
d[UPo8]
dt
d[UPb4]
dt
drUBJ41
dt
d[APo8]
dt
d[APb4]
dt
d[ABi4]
dt
d[SPo8]
dt
where
Ao
Ai
A2
A3
Aa
A3
Pi
Po
[X]
= -A0[URn2] (5)
= Ao [URn2] - (Xa + A3 + A,) [UPo8] (6)
= A, [UP08] - (Xa + A3 + A2) [UPb4]
+ Pi A1 [APo8] + Po A1 [SPo8] (7)
= A2 [UPb4] - (\a + A3 + A3) [UBi4] (8)
= Aa[UPo8]-(\i+AS)[APo8] (9)
= (1-Pi)Ai[APo8]+Aa[UPb4]-(x3+A2)[APb4] (10)
= A2 [APb4] + Aa [UBi4] - (\3 + A3) [ABi4] (11)
= A3 [UP08] + A3 [AP08] -Ai [SP08] (12)
radioactive decay constant of 222Rn, h-1.
radioactive decay constant of 218Po, h-1.
radioactive decay constant of 214Pb, Ir1.
radioactive decay constant of 214Bi, h-1.
attachment rate of free species onto aerosols, h-1.
surface-deposition rate of unattached species, h-1.
surface-deposition rate of species attached to
aerosols, h~1.
recoil probability of 214Pb from aerosols, d'less.
recoil probability of 214Pb from surfaces in the room,
d'less.
concentration of species X in the room, nuclei/gair.
Based on the eight differential equations listed here, a set of five key
parameters that characterizes radon and radon progeny kinetics must be
specified in CONAIR 89-2 for each room. These parameters are: the attachment
rate, the unattached species deposition rate, the attached species deposition
rate, the recoil probability of 214Pb from aerosols, and the recoil
probability of 214Pb from room surfaces.
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SELECTION OF INPUT PARAMETER VALUES
The radioactive transmutation coefficients (A0, AI, A 2, and AS) used in
the Jacobi model are not unique to each room. Instead, they are physical
constants related to the isotope half -lives.
Porstendorfer (4,5), Bruno (6), and Nazaroff and Nero (7) report that
the attachment rate of radon progeny onto aerosols can vary widely indoors (4
to 2000 h'1). The attachment rate strongly depends on the aerosol size
distribution and aerosol concentration. Maximum attachment rates correspond
to particle sizes in the range of 0.1 to 0.2 fjm (7) and to high aerosol
concentrations. These concentrations vary from 2 to 500,000 particles/cm3
depending on the amount of cooking and smoking and on the effectiveness of air
filtration systems, if any are used. Cooking and smoking can increase
aerosol concentrations indoors by two to three orders of magnitude (7), which
in some cases can result in significant variations in attachment rates from
room to room in a house.
An attachment rate of 50 h-1 was used indoors. This rate was selected
from values listed in the literature for clean air (approximately 10,000 to
20,000 aerosol particles/cm3). Unfortunately, reported attachment rates tend
to list only the corresponding aerosol concentration, but not the particle
size distributions, so it is difficult to determine a typical value for
typical conditions. The attachment rate used here was assumed to be constant
everywhere in the house for simplicity in demonstrating the new models. An
attachment rate of 40 fr1 was used outdoors based on Jacobi (3). This lower
rate recognizes that although the aerosol concentrations outdoors usually are
higher than those indoors when there is no cooking or smoking (7), these
activities generally would be expected to result in higher average aerosol
concentrations indoors.
CONAIR 89-2, which implements the modified flow element equations
described earlier, can model the surface-deposition of radon-daughters by
specifying the unattached and attached species deposition rates. The
deposition rate of a particular unattached species in a specific room is
dependent on the area of exposed surfaces in that room, on the volume of that
room, and on the deposition velocity of the particular species as follows:
(13)
where
Ad = surface deposition rate of unattached
species in a given room, h'1.
i/d = average deposition velocity of free (unattached)
species in the room, m/h.
S = total area of enclosure surfaces in the room exposed
to air (including walls, doors, windows, floors, and
ceilings, but excluding other surfaces such as
furniture), m2.
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F = correction factor to account for additional exposed
area of furniture or other surfaces in the room,
d'less.
V = volume of air in the room, m3.
This rate expression assumes all surfaces exposed to air in a given room
are equally effective in removing any radon daughter through the use of an
average deposition velocity that is the same for all radon progeny. Although
an analogous equation can be applied to attached species, this was not done
because the deposition velocities of attached species are usually much smaller
than those for unattached species. Nazaroff and Nero (7) report that the
ratio of unattached to attached deposition velocities is approximately 100.
Deposition velocities are strongly influenced by air motion. Equation
13 assumes there is sufficient air motion in each room so the radon progeny
concentration in the room is uniform. However, most deposition velocities
found in the literature are not accompanied by quantitative descriptions of
the air movement conditions during the deposition velocity experiments. Bruno
(6) reports a deposition velocity for unattached 218Po in still air of 0.54
m/h, which is not typical of real houses. He also reports that the deposition
velocity for unattached 218Po in rooms with low ventilation is 7 m/h and with
moderate ventilation is 22 m/h. Bigu (8) lists values of 2-19 m/h for a 26 m3
chamber equipped with a circulating fan. The higher value corresponds to
operation of the fan, while the lower value corresponds to periods when the
fan was off. The circulation rate of the fan is not provided by Bigu. Scott
(9) reports unattached deposition velocities in the range of 3.6 to 18 m/h,
with the higher values corresponding to higher ventilation rates.
Unattached deposition velocities of 8 m/h in rooms and 20 m/h in ducts
were assumed. The value for rooms was selected as an average value (7).- The
value for ducting was selected in recognition of their high airflow rates.
This value may be an underestimate, since it is based on maximum room
deposition velocities, but there does not appear to be any literature
available on radon progeny deposition rates in ducting.
Room surface areas and volumes as required for equation 13 were
estimated from building plans. A correction factor of 2.5 (10) was applied to
increase the surface area exposed to air in each room, except in hallways
where furnishings tend to be sparse. A factor of 1.0 was used in hallways.
Porstendo'rfer (10) does not quantify room or furnishing surface areas, so
these factors are somewhat arbitrary. The deposition rate for attached
progeny in a given room was assumed to be 1/100 of the unattached deposition
rate in that room.
The unattached deposition velocity outdoors was assumed to be 17 m/h so
the outdoor equilibrium fraction would be 0.56 (7). Therefore, the outdoor
value has little direct basis on real conditions. It is assumed all
deposition rates described here are constant over time for simplicity in
demonstrating the new models.
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The literature reviewed here does not differentiate between radon
progeny when specifying deposition rates or attachment rates, so the Jacobi
model described here assumes the same attachment rate or the same deposition
rate can be applied to each of the three radon progeny considered. Research
should be carried out in a future project to determine the impact of this
assumption on CONAIR's predictions of radon progeny concentrations.
When atoms of attached or surface-deposited 218Po decay, a fraction of
the 214Pb atoms produced can become detached and move into the room air. The
recoil probability describes the chance this process will occur for any given
atom. The maximum probability is 1.0. In this case, all of these 214Pb atoms
are released into the room air. The recoil probability depends on whether the
218Po is attached to an aerosol or to a surface in the room.
For 218Po attached to aerosols, a range of 214Pb recoil probabilities
from 0.4 to 0.83 has been reported (11, 12). The higher recoil probabilities
are expected to correspond with smaller aerosol sizes (12). Field
investigations to determine this recoil probability in the real house were
beyond the scope of this project, so a typical indoor value of 0.5 (3, 5) was
assumed for the case considered here.
A different recoil probability of 0.83 was used outdoors for 214Pb
produced by 218Po attached to aerosols. This value was selected so the
outdoor equilibrium fraction would be 0.56 (7).
For surface-deposited 218Po, 21«Pb recoil probabilities tend to be
lower. Due to the presence of a laminar boundary layer on indoor surfaces, it
is unlikely all recoiling 214Pb atoms will escape into the room air. Instead,
a significant fraction (as much as 50%, (6)) will escape into the boundary
layer, from which they will redeposit on the surface they escaped from.
Typically, this recoil probability is estimated to be 0.25 (7, 13). For lack
of any other evidence, this typical value has been used indoors and outdoors
in the case considered here.
EXAMPLE ANALYSES USING CONAIR 89-2
INTRODUCTION
Three simulation exercises were carried out using CONAIR 89-2. The
purpose of these exercises was to demonstrate the capabilities of the modified
program through analyses of the radon levels and EEDCs in the rooms of a
hypothetical house for two different HVAC systems, and through comparisons of
these parameters with those for the same house with only natural ventilation.
Hypothetical soil properties and radon progeny transport phenomena
characteristics used in these simulations were based on ranges of values cited
in the literature and not on field trials, because the purpose of these
simulations did not justify the expense of an Intensive measurement effort to
determine these values.
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NATURALLY-VENTILATED HOUSE DESCRIPTION
A hypothetical house based on a real single-storey house located in a
suburban area of Winnipeg, Manitoba was simulated. The house has an
Equivalent Leakage Area (ELA) of 1540 cm*. The total surface area indoors
exposed to air (subject to radon progeny plate-out) is 1769 m2, including
furnishings. The house was divided into the following eight zones: basement;
kitchen/dining room/living room; hallway joining living room, bathroom, and
bedrooms; bathroom (sink area); bathroom (tub area); master bedroom; bedroom
2- and bedroom 3. The kitchen, living room, and dining room were lumped
together as one zone because there are no significant flow resistances between
these regions.
Using the total ELA of the house and assumptions of leakage area
distributions, inputs were developed for CONAIR 89-2 to characterize the
magnitude and location of unintentional leaks in the building envelope. The
only leaks considered between zones were interior doorways, which were
simulated as if the doors were wide open.
The soil surrounding the hypothetical house was a wet sandy silt, with
coarse sand backfill around the walls and beneath the floor slab. The total
ELA of the combination of soil leakage and the 5 mm wide crack at the wall-
floor interface was 4 cm2 or 0.26% of the total ELA of the house.
The hypothetical house is heated electrically with baseboard heaters and
has no mechanical ventilation system. All windows and exterior doors were
simulated in their closed position, so the only source of ventilation in the
house was natural infiltration and exfiltration driven by wind and stack
effects through leaks in the house envelope.
HRV-VENTILATED HOUSE DESCRIPTION
A second hypothetical house was simulated with characteristics identical
to those described for the naturally-ventilated house, but with two changes.
The baseboard heating system was replaced with a central electric forced-air
furnace, and a balanced heat recovery ventilator (HRV) system was added. The
supply airflow rates from the furnace to each zone were sized to meet the same
design heating load as the baseboard heaters. Return airflows for each zone
were also specified. Indoor air was exhausted continuously through the HRV
from the kitchen/dining room/living room area at a rate of 30.6 L/s and from
the bathroom tub area at a rate of 14.2 L/s.
An extra zone was simulated in this case to represent the estimated
combined volume of the added ducting and furnace (5 m3). The surface area of
these components exposed to the air was estimated to be 60 m2. The plate-put
and attachment rates for the combined ducting and furnace were described
earlier, along with appropriate 214Pb recoil probabilities.
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LAFSW-VENTILATED HOUSE DESCRIPTION
A third hypothetical house was simulated with characteristics identical
to those described for the naturally-ventilated house, but with two changes.
An LAFSW system with damper-controlled air inlets on the windows in the living
room and in the three bedrooms (14) was added, along with a central exhaust
fan in the basement. The central exhaust fan was connected through short
pieces of ducting to the kitchen/dining room/living room area and to the
bathroom tub area. Exhaust airflow rates identical to those of the HRV were
specified.
Each air inlet had an ELA of 23.6 cm2 with the damper in the fully-open
position. These inlets were controlled on a diurnal schedule corresponding to
normal residential activity. From 8 a.m. to 11 p.m., the air inlets in the
living room were fully open, while those in the bedrooms were fully closed.
From 11 p.m. to 8 a.m. when people would occupy the bedrooms, the air inlets
in the bedrooms were fully open, while those in the living room were fully
closed.
WEATHER DATA AND OUTDOOR CONCENTRATIONS
*
The three simulations were carried out using hourly Winnipeg weather
data from a four-day period in August 1981. In all cases, every indoor zone
had a constant temperature of 21° C. The average outdoor dry-bulb temperature
during this period was 20.3° C. The average wind speed was 3.3 km/h. Real
wind direction data were not available, so the wind was simulated by rotating
it around the house on a 59 hour cycle.
The infiltration of radon in outdoor air can be a significant
contribution to typical indoor levels, even though it is negligible at higher
indoor levels. Radon concentrations in outdoor air are usually in the range
of 0.1 to 0.4 pCi/L (7). A typical value of 0.2 pCi/L (15) was assumed for
the cases simulated in this project. A constant equilibrium fraction of 0.56
was assumed outdoors (7). The total EEDC outdoors based on this equilibrium
fraction was 0.11 pCi/L.
SIMULATION RESULTS AND ANALYSES
Tables 1 through 3 summarize the CONAIR 89-2 predictions of radon and
radon progeny concentrations by listing zonal and whole-house average radon
levels, unattached EEDCs, attached EEDCs, total EEDCs, and equilibrium
fractions for the three cases considered here. Whole-house averages were
calculated as the sum of the zonal averages, weighted by the fraction of the
total volume of the house in each zone. To understand how the two different
ventilation systems affect radon and radon progeny concentrations in different
areas of the house, consider the basement, living room and one bedroom
-------
(Bedroom 2) separately. Bedroom 2 was selected for illustration purposes, but
either of the other two bedrooms could have been used instead, since all three
bedrooms have similar radon and radon progeny levels.
A particularly interesting set of comparisons is that of the living room
to basement average radon concentration and total EEDC ratios. These ratios
provide an insight into the inaccuracies that can result from measuring the
radon level or total EEDC in one region of the house such as the basement and
attempting to apply the same results to other regions of the house, such as
the living room.
For the naturally-ventilated house the average radon level in the living
room was only 50% of that in the basement, while the average total EEDC in the
living room was 48% of that in the basement. The average radon level and the
average total EEDC in the living room of the HRV-ventilated house were closer
to those in the basement (ratios of 68% and 71% respectively) than in the
naturally-ventilated house. These reduced differences between the living room
and basement averages were due to the effects of air mixing caused by the
furnace air-handling system in the house with the HRV. Table 2 shows this
mixing effect in particular through the lack of variation in main floor
average zonal radon level and total EEDC predictions. For the house equipped
with the LAFSW system, the average radon level and the average total EEDC in
the living room were further from those in the basement (ratios of 37% and 37%
each) than in the naturally-ventilated house. The LAFSW system was
intentionally designed to have this effect. By providing outdoor air
specifically only to occupied regions that require ventilation, the LAFSW
system saves the energy an HRV system wastes by not ventilating the entire
house when all of the house is not occupied.
These observations indicate that significant differences in average
radon levels and total EEDCs could occur between basements and living rooms,
so caution should be exercised in applying measured radon level or total EEDC
data from one region to another.
The advantage of the LAFSW system in providing local ventilation is
emphasized by the average radon levels and total EEDCs in the bedrooms. In
bedroom 2 of the LAFSW-ventilated house, the average radon level was slightly
below that outdoors (0.20 pCi/L) because of the combined effects of direct
ventilation with only outdoor air and the radioactive decay process. The HRV-
ventilated bedroom had a lower average radon level (0.34 pCi/L) than that in
the naturally-ventilated bedroom (0.71 pCi/L), but it was higher than that for
the LAFSW-ventilated bedroom due to mixing with other regions of the house
caused by the furnace air-handling system. Bedroom 2 of the LAFSW-ventilated
house had an average total EEDC of 0.08 pCi/L, which was lower than that
outdoors (0.11 pCi/L) due to the combined effects of direct ventilation with
only outdoor air, radioactive decay, and plate-out in the bedroom. As for the
average radon level, the HRV system lowered the average total EEDC in bedroom
2 slightly to 0.14 pCi/L compared with 0.26 pCi/L in the naturally-ventilated
house. However, due to the effects of mixing with other regions of the house
caused by the furnace air-handling system, the HRV-ventilated house could not
achieve a reduction in bedroom average total EEDC to below the outdoor level.
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Since people normally spend a large fraction of their time at home sleeping In
their bedrooms, these results Indicate that local ventilation provided by the
LAFSW system in these bedrooms could significantly reduce the total long-term
exposure of occupants to radon progeny.
CONCLUSIONS
CONAIR 89-2, which is based on an existing computer program, was
developed so it could simulate the accumulation of radon and its progeny
within houses. A radon progeny plate-out model was implemented in the program
and a set of typical coefficients describing radon progeny kinetics was
suggested for a hypothetical house.
Three simulations of different ventilation strategies were carried out
using CONAIR 89-2. Average radon levels and total EEDCs in several rooms of
the naturally-ventilated hypothetical house with baseboard heat were compared
with those of a similar house equipped with a furnace/HRV system and with
those in one having a baseboard-heat/LAFSW system. There were significant
differences in average radon levels and total EEDCs between rooms of the
house, which demonstrated the importance of using a multizone model instead of
a single-zone model to predict radon and radon progeny levels indoors. These
differences also indicate caution should be exercised in extrapolating radon
and radon progeny level measurements taken in one room to any other room in a
house.
The simulations predicted that the baseboard-heat/LAFSW system can
control radon levels in the bedrooms better than the furnace/HRV system.
Since the average radon levels and total EEDCs in the bedrooms ventilated
using the LAFSW system were below those outdoors, and since people normally
spend a large fraction of their time at home sleeping in these bedrooms, it
appears that the LAFSW system could significantly reduce the risk of lung
cancer.
ACKNOWLEDGEMENTS
This project was carried out with the support of National Research
Council Canada, Energy, Mines and Resources Canada, the Canada Mortgage and
Housing Corporation, and Manitoba Hydro. We gratefully acknowledge the
contributions of George Walton of the U.S. National Institute of Standards and
Technology and Jim Axley of the Massachusetts Institute of Technology. The
use of their programs (AIRNET and CONTAM 87) in CONAIR 89-2 greatly
facilitated program development. The work described in this paper was not
funded by the U.S. Environmental Protection Agency and therefore the contents
do not necessarily reflect the views of the agency and no official endorsement
should be inferred.
-------
REFERENCES
1. Yuill, G.K. and Wray, C.P. A microcomputer program for evaluating the
performance of buildings equipped with ventilator window/baseboard
heating systems. In: Proceedings of the 1989 Annual SESCI Conference,
Penticton, 1989.
2. Axley, J. Progress toward a general analytical method for predicting
indoor air pollution in buildings - Indoor air quality modelling: Phase
III report. U.S. National Bureau of Standards to U.S. EPA, NBSIR 88-
3814, July 1988.
3. Jacobi, W. Activity and potential a-energy of 222radon- and ^radon-
daughters in different air atmospheres. Health Physics. 22(May): 441-
450, 1972.
4. PorstendSrfer, 0., Wicke, A., and Schraub, A. The influence of
exhalation, ventilation and deposition processes upon the concentration
of radon (^Radon), thoron (^Radon) and their decay products in room
air. Health Physics. 34(May): 465-473, 1978.
5. Porstendorfer, J. Indoor radon exposure in the Federal Republic of
Germany. In: Proceedings of the Second Air Pollution Control
Association Specialty Conference: Indoor Radon II, 1987. pp. 57-67.
6. Bruno, R.C. Sources of indoor radon in houses: A review. Journal of
the Air Pollution Control Association. 33:(2, February): 105-109, 1983.
7. Nazaroff, W.W. and Nero, A.V. Jr. Radon and its decay products indoors.
New York: John Wiley and Sons, 1988.
8. Bigu, J. Radon daughter and thoron daughter deposition velocity and
unattached fractions under laboratory-controlled conditions and in
underground uranium mines. Journal of Aerosol Science. 16(2): 157-165,
1985.
9. Scott, A.G. Radon daughter deposition velocities estimated from field
measurements. Health Physics. 45(2): 481-485, 1983.
10. Porstendorfer, J. Behavior of radon daughter products in indoor air.
Radiation Protection Dosimetry. 7(1-4):107-113, 1984.
11. Kruger, J. and Not hi ing, J.F. A comparison of the attachment of the
decay products of radon-220 and radon-222 to monodisperse aerosols.
Journal of Aerosol Science. 10: 571, 1979.
12. Mercer, T.T. The effect of particle size on the escape of recoiling RaB
atoms from particulate surfaces. Health Physics. 31: 173-175, 1976.
-------
13. Shimo, M., Asano, Y., Hayash1, K., and Ikebe, Y. On some properties of
^Rn short-lived decay products in air. Health Physics. 48(1): 75-86,
1985
14. Yin 11, G.K. and Comeau, G.M. Demonstration and performance testing of
the laminar airflow super window - humidity controlled air inlet -
baseboard heating (LAFSW/HCAI/BH) system in a Winnipeg house. in:
Proceedings of the 1989 Annual SESCI Conference, Penticton, 1989.
15. Bodansky, D., Robkin, M.A., and Stadler, D.R. Indoor radon and its
hazards. Seattle: University of Washington Press, 1989.
TABLE 1
&maivy of Averago Radon Lmla. EEDCa.
ana Equibrun Fractions Natural Valuation
Volume
(m-J)
20683
US 07
780
19 SI
791
6*2
3972
2320
Total
446 48
Zont
Nomi
BoMnunt
Living Room
Hofcoy
Blfroom 3
Both (Sink)
Both CTub)
Waiter Bldroom
Bedroom 2
Outdoon
Soil
Wholi-houfi
*»( Cone
Rn222
(pOA)
159
080
OBI
073
000
000
072
071
020
30459
1 13
EEOCu
(oGA)
003
002
002
001
000
000
001
001
001
000
oo:
EEDCo
-------
C-V-5
A DATA ACQUISITION SYSTEM FOR
MONITORING RADON ENTRY AND DISTRIBUTION
R.P. Sieber D.A. Flgley
Graduate student Research officer
Department of Mechanical Engineering Prairie Regional Station
University of Saskatchewan Institute for Research in Construction
Saskatoon, Sk., Canada, S7N OWO National Research Council of Canada
Saskatoon, Sk., Canada, S7N OW9
R.W. Besant G.J. Schoenau
Head Professor
Department of Mechanical Engineering Department of Mechanical Engineering
University of Saskatchewan University of Saskatchewan
Saskatoon, Sk., Canada, S7N OWO Saskatoon, Sk., Canada, S7N OWO
ABSTRACT
This paper describes the development of a micro-computer based Radon Data
Acquisition System (RDAS) for monitoring the entry and distribution of radon
gas in houses. The information obtained will be valuable for the evaluation of
control measures used to reduce radon concentrations to acceptable levels.
There are many proposed control measures for reducing radon levels.
However, these methods are not always reliable since they do not accurately
account for uncontrolled interacting factors. Some of these factors include
interzonal and building air leakage, ventilation rate, pressure and temperature
gradients, radon concentrations in soil gas, and environmental factors such as
wind and relative humidity. The RDAS simultaneously measures pressure,
temperature, and radon gas concentration at several points. In addition, the
RDAS characterizes the interzonal air exchange rate using tracer gas techniques.
Radon is measured with semiconductor sensors capable of measuring concentrations
continually over a period of time; the output is transmitted to the data logger.
Careful design of an experimental protocol will account for other uncontrolled
factors.
-------
INTRODUCTION
The presence of elevated radon gas concentrations in residential housing
can lead to serious health problems for the occupants if they are exposed over
an extended period of time. Some control measures for minimizing radon
concentration levels include increased ventilation, sub slab depressurization
using externally vented fans, and sealing potential leakage passages (1-2).
Typically, evaluation of these control measures have been limited to a
before/after air sample analysis and are unlikely to account for temporal
variations in the environment or building factors. Conclusions drawn from
studies of this nature can contain substantial errors. The purpose of this
paper is to outline briefly the experimental variables that must be measured to
conduct detailed building science based studies on radon and to describe a data
acquisition system designed to continuously monitor these variables.
The Institute for Research in Construction (IRC) of the National Research
Council of Canada (NRC) is developing a data acquisition system, the RDAS,
capable of continuous measurement of experimental parameters necessary to
evaluate the effectiveness of radon control measures. The parameters include
ventilation rate, indoor/outdoor pressure difference at various surfaces above
and below grade, indoor and outdoor air temperature, and radon gas and radon
daughter concentrations in the air and soil gas. An important component of this
research activity is the development of analytical models that describe the
functional relationships between the various parameters. These models will
provide a broader understanding of the dynamic processes involved, but they must
be validated with well characterized experimental data to be reliable.
The RDAS will allow accurate evaluation of radon characterization in case-
control (paired) studies and assist in the development of relationships based
on building science principles. This will provide valuable information to guide
development of design and construction techniques for buildings.
BUILDING SCIENCE PRINCIPLES
There are many potential sources of radon gas in buildings. One of the
most important is the soil surrounding the foundation. To accurately assess
radon in buildings, various parameters such as the indoor concentration,
ventilation rate, and transportation of radon gas into the space need to be
quantified. Considering a well mixed, single zone chamber with an outdoor air
supply, indoor and outdoor radon sources and internal space conditioning (Figure
1), a simple mass balance model yields the equation:
-------
V C
SOURCES
(S)
REMOVAL
(R)
V C
Figure 1. Single zone steady-state mass balance model
Ci - C0 + S - R (1)
K • V
where: Ct - indoor radon gas concentration (pCi/m3)
C0 - outdoor radon gas concentration (pCi/m3)
S - indoor radon gas source strength (pCi/s)
R - radon gas removal rate (pCi/s)
K - ventilation efficiency
V - outdoor air exchange rate (m3/s)
Equation 1 is a simplified expression that can be used to identify the
major parameters that must be considered and the impact that changes in the
parameters will have on the resulting indoor radon gas concentration. In
practice, temporal and spacial variations in these factors must be accurately
monitored to avoid errors in analysis. Other potential interacting factors
including soil porosity and relative humidity may also effect the radon
concentration level. In multi-zoned buildings, data will be required on
conditions within individual zones and on communication among zones which add
to the complexity of the data acquisition system requirements.
-------
SYSTEM COMPONENTS
A schematic diagram of the RDAS is shown in Figure 2.
Sciemetrica InsL
System 200
Modules
Toshiba 3200 AT
Portable, using
Custom software
Figure 2. Schematic diagram of RDAS
The system includes a central MS DOS portable computer and a Sciemetrics
System 200 data acquisition module. The System 200 is a modular, general
purpose, measurement system suited to numerous applications including data
acquisition and process control. Included in the RDAS are two model 220 relay
cards, a model 231 analog/digital converter, and two model 252 expansion card
(32 channels each). Communication between the modules and the personal computer
is accomplished with the System 200 I/O module 802 interface card. Customized
software is added to set up channel sampling frequency, feedback control and data
processing and storage.
The menu driven software allows the RDAS operator flexibility in setting
up individual experiments. The number of transducers, gains or calibration
coefficients and scan rate can be input from the keyboard to suit the
experimental requirements.
The techniques to measure pressure difference across the building envelope
surfaces, air ventilation and infiltration in the various internal zones,
internal and external temperature distribution, and radon gas concentrations are
presented in more detail below.
-------
1) PRESSURE MEASUREMENT
Below grade air infiltration due to lower pressures in basement air
compared to surrounding soil gas pressures has been identified as the primary
cause of high radon gas levels in houses (1,3). Potential entry points of
airborne radon gas include floor and wall cracks, floor drains, and line cracks
where the slab and wall intersect (Figure 3). Methods to reduce radon gas
infiltration into basements are to eliminate or reduce the flow of soil gas into
the basement by sealing entry points or by eliminating the air pressure
differences which cause air infiltration into the basement foundation.
Figure 3. Potential soil gas entry sites
The rate of airflow through an opening such as a crack or a hole is given by:
Q - C(AP)n (2)
where: Q - airflow rate (m3/s)
C - flow coefficient (m3/s-Pan)
P - pressure difference across opening (Pa)
n - flow exponent (between 0.5 - 1.0)
The total pressure difference across the opening is the sum of the pressure
gradients due to wind, stack, changes in atmospheric pressure, and pressure
differences created by the mechanical system. In the case of radon gas in soil,
equation 2 can be coupled with the radon concentration in the soil gas to
determine the radon source strength due to airflow as:
-------
SP-Q
(3)
where: Sp - radon source strength due to airflow (pCi/s)
R - radon concentration in the soil gas (pCi/m3)
For a foundation, the flows and pressure fields are coupled in a complex
network as shown in Figure 4. The flow coefficient is more complex than the
case of a simple crack or hole. The overall flow resistance is a combination
of the flow resistance of the foundation opening, Rt, and the adjacent soil,
Rf - FOUNDATION AIR FLOW RESISTANCE
R,-SOIL AIR FLOW RESISTANCE
Psg (SOIL GAS)
Figure 4. Soil gas and resistor network
For below grade components, the airflow resistance of the soil can cause
large time shifts between the atmospheric pressure and the soil gas pressure on
the outside of the below grade building envelope. It is necessary to measure
the pressure difference across individual building components in order to
calculate component specific airflows.
The movement of air and airborne pollutants within a building is driven
by pressure gradients. Although the RDAS estimates air movement by tracer gas
techniques, the pressure regime inside and outside the building must be measured
independently for inputs to the analytical models.
The RDAS can record the output from 10 individual pressure transducers.
Modus T10 differential pressure transducers with 0-5 VDC outputs were selected
for the system. The range of the transducers is matched to the expected range
in pressure to minimize measurement errors. Maximum error is specified as ± 2%
of full scale capacity.
-------
2) VENTILATION MEASUREMENT
The total ventilation rate of a building is a combination of infiltration
and mechanical ventilation. While techniques exist for estimating or calculating
these components, they may not be sufficiently accurate for research purposes.
Further, the distribution of the ventilation will directly affect the indoor
pollutant concentrations.
Ventilation rates are determined through the use of tracer gas techniques.
The tracer gas decay rate is an exponential time function related to ventilation.
The tracer decay method consists of an initial injection of tracer into the space
followed by recording tracer gas concentrations as a function of time. For a
well mixed zone with no sources or sinks, the tracer gas concentration is given
by the equation:
c(t) - c0 • exp[-(q/V)t] (4)
where: c - tracer concentration
c0= initial tracer concentration
V = space volume (m3)
q - outdoor air exchange rate (m3/hr)
t - time (hr)
Knowing the effective zone volume and the current and initial tracer
concentrations enables the infiltration rate to be determined. The air change
rate (air changes/hour) is the ratio of the air exchange rate, q, and space
volume, V.
A four zone Air Change per Hour Measuring Apparatus (ACHMA) was designed
to evaluate ventilation and air movement within and between zones. N20 was
selected as the tracer gas for estimating ventilation rates. N20 is easy to
measure and suitable for small and medium sized buildings. To estimate air
leakage characteristics between zones additional tracer gases (C02 and SF6) can
be incorporated into the system.
The requirements for the ACHMA are:
1) Set tracer gas maximum and minimum zone concentrations (0-100 ppm).
2) Discharge N20 tracer gas into one or a combination of four well mixed
zones.
3) Sample in one or a combination of four zones.
4) Return sample to zone or purge outside.
A small amount of N20 is injected into the zone and the decay in gas
concentration is measured as a function of time. Once the tracer concentration
has decayed below the minimum allowed concentration, additional tracer can be
injected into the zone. This allows for an extended testing period. Proper
mixing of air within the zone is essential for unbiased sampling since equation
4 assumes perfect mixing within the zone. The time period selected for the
solution of equation 4 must be carefully considered. Initially, following a
tracer gas injection, the tracer will not be well mixed. During a test, changes
in the air exchange rate can occur which will confuse the analysis if the change
-------
is not recorded within the time step. A shorten time step requires a higher rate
of sampling and increases the load on the sampling system. A zone sampling rate
of five minutes was selected as the best compromise between system requirements
and accuracy of estimation of air exchange rate.
A schematic of the ACHMA is shown in Figure 5. The ACHMA consists of a
network of solenoid valves, tubing, an air pump, gas analyzer, and tracer gas
source tank equipped with a pressure regulator. The N20 analyzer is a Beckman
Model 865 infrared gas analyzer with a span of 0 to 100 ± 1 ppra (0-100mVOC
output}. Rotameters are used to monitor and control flow since only approximate
flow rates are required.
N20 Detector
Figure 5. Four zone ACH measuring apparatus
3) TEMPERATURE MEASUREMENT
Temperature differences across the skin of a building often cause air
infiltration while internal temperature differences may or may not cause air
circulation. Temperatures are measured with Type T (copper-constantan)
thermocouples. The original data logger was modified to include an isothermal
junction for the thermocouple connections. This improved the original accuracy
from ± 2*C to ± 0.1°C. The isothermal Junction can accommodate 24 individual
thermocouple inputs.
-------
4) RADON MEASUREMENT
In general, radon concentrations can be determined by measuring the time-
average value, where the average radon concentration is calculated over a
specified period of time, or by instantaneous measurement, otherwise known as
grab sampling. Time-averaging does not identify transient variations .while
manual grab sampling becomes time consuming and laborious when sampling a large
population. Due to various interacting factors, radon levels can fluctuate
substantially over an extended period of time (Figure 6). The RDAS includes
radon meters capable of continuous "real time" measurement. This allows analysis
of both the transient and steady state response associated with various control
measures or disturbances.
RADON. mWL
12
24 36 48
60 72 84
TIME. HOURS
Figure 6. Temporal variations of radon levels
108 120 132 144
While many previous studies on radon measurement focused on the house as
a whole, information is needed at suspected radon gas entry points and to examine
the spacial distribution of radon within the building. Spacial variations of
radon gas within a zone or between zones are often large enough to warrant the
use of several detectors. The RDAS incorporates 10 radon meters into its design.
The radon meters are designed by Thomson & Nielsen Electronics Ltd. They
produce a time integrated measurement similar to that of other radon meters,
however, the time constant is relatively small (five minutes) compared to other
radon detectors. Although the radon data is not actually instantaneous, the
integrated values are acceptable since radon levels are not expected to change
-------
significantly over the five minute interval.
Semiconductor sensors are used to produce a voltage signal proportional
to the radon concentration, or alpha activity. An integral pump draws air
through the an intake filter, into a chamber, then out through an exhaust filter.
The intake filter absorbs radon daughters which are present. As the radon gas
continues through the chamber, the gas decays and the daughters are deposited
on the second filter. With both filters in place, radon gas is detected. With
no intake filter, only the daughters are detected. Alpha activity on the filters
is counted and processed into a zero to five volt DC output and recorded on the
data logger. Each meter has its own power source and pump for air sampling.
The accuracy of the radon meters are within ± 10% of the true value.
FUTURE APPLICATIONS
The RDAS is being installed in an experimental house to examine the effect
of various ventilation system operating modes on the distribution of pollutants
within the house. Initial studies will focus on line source and point source
pollutants originating at the foundation. Tracer gas sources will be used to
simulate radon entering through cracks and holes in the foundation. Subsequent
studies will investigate the effect of building envelope and mechanical system
operation modifications on the radon entry and distribution characteristics.
The work described in this paper was not funded by the U.S. Environmental
Protection Agency and therefore the contents do not necessarily reflect the
views of the Agency and no official endorsement should be inferred.
ACKNOWLEDGMENTS
Special thanks are extended to D.H. Guenter of IRC, Saskatoon for
assistance in the design and construction of the RDAS, to M.E. Lux of IRC.
Saskatoon for valuable discussion, and to Canada Mortgage and Housing Corp.
(CMHC) for their financial assistance in the form of a scholarship.
REFERENCES
1. Radon Reduction Techniques for Detached Houses - Technical Guidance,
EPA/625/5-86/019, United States Environmental Protection Agency, Research
Triangle Park, NC., June, 1986.
2. Figley, D.A., Dumont, R.S. Techniques For Measuring The Air Leakage
Characteristics Of Below Grade Foundation Components. In: Proceedings of
the 82nd Annual Meeting of the Air and Waste Management Association, Anaheim,
Ca., June, 1989.
-------
3. Indoor Air Quality Environmental Information Handbook: Radon, DOE/PE/72013-
2, United States Department of Energy, Washington, D.C. February, 1985. pp.
2-1.
4. Figley, D.A., Dumont, R.S. Radon in Houses - A Building Science Approach,
Accepted for presentation at the Proceedings of the 5th Conference on Building
Science and Technology, February, 1990.
5. Dumont, R.S., Figley, D.A. Control of Radon in Houses. In: Canadian
Building Digest 247, February, 1988.
6. Determining Air Leakage Rate By Tracer Dilution. In: Annual Book of ASTM
Standards, Vol 04.07, E741-83, November, 1983.
7. ASHRAE Handbook 1989 Fundamentals, American Society of Heating, Refrigeration
and Air Conditioning Engineers, Atlanta, Ga., 1989. pp. 23-1 - 23-10.
8. Discussions with M.E. Lux., Research officer, Prairie Regional Station,
Institute for Research in Construction, National Research Council of Canada,
Saskatoon, Sk., Canada, S7N OW9
-------
Session C-VI:
Radon in the Natural Environment—POSTERS
-------
C-VI-1
PRELIMINARY IDENTIFICATION OF HIGH RADON POTENTIAL
AREAS IN TWENTY-FIVE STATES
R. Thomas Peake
U. S. Environmental Protection Agency
ABSTRACT
A preliminary radon potential nap of 25 states has been
prepared shoving areas of high radon potential. The data used to
create this map include:
1) National Uranium Resource Evaluation (NURE) aerial radiometric
data. NURE data in glaciated and non-glaciated areas have to be
interpreted differently because the properties of the surficial
material can be as important as the radium concentration.
2) State/EPA Indoor Radon Survey Data. Indoor radon data for 25
states have been analyzed by house construction by county and
regionally.
Both sets of data have been compared to geology to produce a
county scale map. Areas of high radon potential include, but are
not limited to, the Upper Midwest, the Rocky Mountain region and
portions of the Applachian Mountains. This map will be used in
EPA's efforts to identify and characterize high radon potential
areas for school and workplace surveys, and for building code
development.
This paper has been reviewed in accordance with the U. S. Environmental
Protection Agency's peer and administrative review policies and approved for
presentation and publication.
-------
C-VI-2
SECULAR VARIATIONS OF RADON IN METROPOLITAN VANCOUVER,
BRITISH COLUMBIA. CANADA
By: M.M. Ghomshei1 and W.F. Slawson2
1. Orchard Geothermal Inc. 401-134 Abbott Street, Vancouver, B.C.
V6B 2K4 (Canada)
2. Department of Geophysics and Astronomy, University of British
Columbia, Vancouver, B.C. V6T 1W5 (Canada)
ABSTRACT
Sampling of radon within the soil from three sites in
metropolitan Vancouver is reported. Alpha track bi-weekly
measurements during a period of 4 years show secular variations
with a period of 8-15 months. There are low-radon and high-radon
episodes enduring several months to a year. Average radon level
during the high-radon episodes reaches 5-10 times that of the low-
radon periods. During high-radon episodes the high-frequency
variations show very high amplitudes. After filtering of the high-
frequency fluctuations, the data from different sites demonstrate
remarkably similar trends. It is suggested that along with
hydrogeological events, stress relaxation in rocks, earthquake, and
magma emplacement may contribute to the sources of secular
variations of radon. Because of long-term variations, radon level
in urban areas should be monitored on a continuous basis. Single
measurements, even those integrating radiation over a period of few
months, may sample a low-radon episode, and provide a false
assurance, or occur during a high-radon episode and give a false
alarm.
-------
INTRODUCTION
Temporal variation of atmospheric radon is a known fact
especially to those involved in uranium, and geothermal
exploration/ hydrogeology, and environmental science (e.g.
1/2,3/4,5,6). These variations are controlled by: 1- factors which
affect the release of radon from the source geological material
(e.g. radium-bearing mineral) and 2- factors which affect the radon
transport systems. The emanation and diffusion of radon from the
radium-bearing mineral to a porous media containing a fluid phase
(e.g. water, steam, or other gases) is mainly controlled by the
volume, shape and structure of the porosity (e.g. 7). Continuously
varying factors such as temperature and the pressure of the fluid
secondary phase have some control on the emanation process (e.g.
8). Co-seismic activities in ground may have a major control on the
release of radon to atmosphere. This control is mainly through
producing microfractures which speed the process of diffusion of
radon from the source rock into the highly mobile fluid phase.
Since the discovery of hazardous radon levels in the urban
areas (e.g. 9), the prime concern of the environmental researchers
have been the spatial variations of radon. Study of temporal
variations have comparatively been neglected/ resulting in a lack
of a long-term data base. It is often wrongly assumed that alpha
track "single-shot" surveys with an exposure time of few months
would average out the temporal fluctuations. Besides the common
high-frequency (diurnal and weekly or monthly) fluctuations, the
low-frequency (seasonal or secular) variations demonstrate high
amplitudes which should be taken into account in the risk
assessment calculations.
The present work introduces data on the significance of short-
term and long-term temporal variations. Possible causes of these
variations are discussed. The data were collected during the period
of 1977 - 1981 and are being reported now in view of the recent
wide-spread interests in radiation protection and earthquake
prediction.
EXPERIMENT
SITES
A number of sites within the Greater Vancouver (British
Columbia, Canada) area were selected for long-term monitoring (Fig.
1). The selection was made to include a variety of geological and
hydro-geological environments. Site YVR was located in the Fraser
River delta, lying over several hundred meters of Recent Sediments.
The UBC site was located above about 90 meters of Glacio-marine
-------
Pig. 1. Location map, Greater Vancouver Area.
-------
deposits. Several meters of glacial outwash overlying the Late
Cretaceous Coast Range granodiorite made the host for site CGN.
Only UBC and CGN were operated over the more than 4 year period.
We report here the sites UBC, CGN and YVR. Data from two other
sites were not considered reliable due to frequent flooding.
ANALYTICAL PROCEDURE
Alpha-track measurement system (10,11,9) was employed for all
the sites. Detectors were placed in 60 cm deep cased holes and were
exposed for approximately two week periods (Fig. 2). The plastic
track detector (from Terradex) was placed at the closed end of a
cup. The open end was covered with a thoron filter. The filter
consisting of a single layer of "Gladwrap" delays the diffusion of
gases into the cup by almost a day, eliminating all the thoron and
a small fraction of radon. The data is reported as counted alpha
particles per square meter of detector per second. Average
background (blank) signal was determined by another study and
did not exceed 2 -± 1.5 counts nf2 s"1. The linear correlation
between track density (cm"2) and dose (pCiL^Day) are reported by
Fleischer and coworkers (9).
HOLE COVER
s
/•
• -
_ •'' .
Ill
1
7/y7^'-
//&//,
'ALPHA PARTICLE
DETECTOR /
^--PLASTIC CUP /"' ' .<
Figure 2. The installation of a TRACK-ETCH detector.
RESULTS AND DISCUSSION
The results are presented in the Figure 3. A low pass filter
was applied to smooth the high-frequency fluctuations and better
highlight the longer-term effects.
-------
RADON HMANATON FROM SOIL
. mm (con sast
40 -
M -
ao -
a -
10 -
6 -
0
1. II
1000
BAZA
RADON DONATION PROM SOIL
ran (UK an>
D41X
RADON EMANATION PROM SOIL
TiNCOUVn. SOUTH (YVB SIB)
oar j. oat
— ""'•""
BtXk
MAX. Affi THMP. AYS. INTHBVAL « IS DATS
nncoDTB, na (me am)
BA»
1000
nur t. lor?
Fig. 3
-------
The spectrum of data appears to contain two main frequencies:
1- variations with a period of several weeks (few data points) . 2-
Variations with a longer period of several months to a year. A
third longer-term variation can be depicted from the overall rising
trend visible in all the sites. The 4 year data collection period
does not seem sufficient to detect any periodicity in this trend.
The short-period variations are controlled to some extent by the
transient atmospheric perturbations such as precipitation, pressure
and temperature (e.g. 6,4,3) . Our data did not show any significant
correlation with atmospheric parameters. It is possible that the
bi-weekly time-averaged measurements have filtered the fluctuations
related to relatively rapid atmospheric perturbations. As to the
low-frequency variations, most of the data (first 1000 days)
demonstrate a periodicity close to 1 year which might be
tentatively correlated with seasonal temperature patterns. This
correlation is not however consistent over the entire data spectrum
(Fig. 3). The variations induced by the atmospheric events may be
overshadowed by more vigorous changes induced by non-atmospheric
dynamic factors such as stress relaxation in the bedrock, related
degassing, and some fluid mobilization. It should also be noted
that the combination of the meteorological changes which affect the
soil parameters is not necessarily of yearly frequency. Radon
episodes, therefore, may not coincide with yearly temperature
seasons. To avoid confusion, we suggest the term episode (instead
of season) to be employed for these long-term variations of radon.
According to our data the frequency of the high- and low-radon
episodes is not necessarily associated with the calendar year.
An interesting observation can be made on the amplitude of
the short-term and long-term variations. It seems the amplitude of
the short-term variations is positively correlated with that of the
long-term variations. The short-term fluctuations demonstrate a
higher amplitude during the high-radon episodes (crest of the long-
term variations). This observation strongly suggests that the long-
term background enhancement is the major source of radon
fluctuations. The short-term atmospheric factors do not have a
causal relation with radon emanation. These factors act only as
transient mobilizers. The mobilization is naturally proportional
to the existing free radon in the rock-soil system. By free radon
we mean the radon which has been released from the rock to a
secondary fluid media and consequently more dynamic environment.
The geological factors which may contribute to the background
enhancement are either of a pulse nature such as seismic
activities, or of events of longer duration such as stress
relaxation in the rock formation due to plate adjustment
(dilatancy-diffusion). Some relatively fast stress relaxations
precede brittle deformations and can be used as an earthquake
precursor. Fast relaxation may induce extremely high radon
-------
background in the roclc-soil system. The degassing of this radon to
the atmosphere can cause "radon storms" or "impulsive radon
emanation" (12). On our data the relatively sharp increase in radon
in 1981 may be related to this type of phenomenon.
A second observation suggesting a lithospheric origin for the
long-term variation is the similarity of data-spectra from
different sites. The general rising trend is remarkable on all 3
sites. Other shorter-period variations appear also to reflect
regional behaviour. The coincidence of the "episodic" variations
from the three sites is obvious. Although these variations may be
to some extent related to long-term meteorological cycles, the
remarkable similarities of the data spectra are suggestive of a
common subsistent lithospheric component.
CONCLUDING REMARKS
The data presented in this work suggest that the temporal
variations of radon are composed of high- and low-frequency
components. The high-frequency variations may reflect the effect
of the transient atmospheric perturbations on the dynamic
properties of soil and its contained fluids. These variations
demonstrate large amplitude when they are superimposed on the crest
of the low-frequency variations. The low-frequency variations are
the main source of overall radon enhancement at regional scale.
These variations may be related to a combination of long-term
meteorological cycles and crustal events. Therefore, only
measurement spanning several years constitutes valid base-line
data.
ACKNOWLEDGEMENTS
Data collection project was supported by grants to WFS from
the Geophysics Division of the DEMR. C.Y. King of USGS (Menlo
Park), and J. Gingrich of Terradex Corp. were very helpful and
supportive during the period of 1979 - 1981.
The work described in this paper was not funded by the U.S.
Environmental Protection Agency and therefore the contents do not
necessarily reflect the views of the Agency and no official
endorsement should be inferred.
REFERENCES
1. Malmqvist, L., Isaksson, M. and Kristiansson, K. Radon migration
through soil and bedrock. Geoexploration, 26: 135, 1989.
2. Kruger, P. and Semprini, L. Radon as in-situ tracer in
geothermal reservoirs. Electric Power Research Institute Inc.
-------
(EPRI), Report No. AP-5315, 1987.
3. Ghomshei, M.M. Concentrations des radioelements naturels
(!'uranium, le thorium et le potassium) et evolution des magmas
(exemple de quatre series volcaniques) . Doctoral Thesis/ University
of Paris - XI, 1983. 201 pp.
4. Fleischer, R.L. and Mogro-Campero, A. Radon enhancements in the
Earth: Evidence for intermittent upflows. Geophysical Research
Letters, 5: 361, 1979.
5. Pearson, J.E. Natural environmental radioactivity from radon
222. Public Health Service Publications (U.S. Government), 1967.
6. Pearson, J. E. and Moses, H. Atmospheric radon 222
concentration variations with height and time. J. of Applied
Meteorology, 5: 175, 1965.
7. Tanner, A.B. Radon migration in the ground: A supplementary
review: United States Geological Survey Open-File, Report 78-1050/
1978. 62 pp.
8. Satomi, K. and Kruger, P. Radon emanation mechanism from finely
ground rocks. Proceedings of Fourth International Symposium on
Water-Rock Interactions, Misasa, Japan, August, 1983.
9. Fleischer, R.L., Girard, W.R., Mogro-Campero, A., Turner, L.G.,
Alter, H.W. and Gingrich, J.F. Dosimetry of environmental radon:
Methods and theory for low-dose integrated measurements. Health
Physics, 39: 957, 1980.
10. King, C.Y. Episodic radon changes in subsurface soil gas along
active faults and possible relation to earthquakes. J. of
Geophysical Research, 85: 3065, 1980.
11. Fleischer, R.L. Price, P.B., and Walker, R.M. Nuclear Tracks
in Solids: Principles and Applications: University of California
Press, Berkeley, California, 1975. 605 pp.
12. King, C.Y. Impulsive radon emanation on a creeping segment of
the San Andreas Fault, California. Pageoph., 122: 1.
-------
C-VI-3
RADON IN HOMES. SOILS. AND CAVES
OF NORTH CENTRAL TENNESSEE
by: Paul D. Collar
U.S.G.S.
G.F.O. Box 4424
San Juan, PR 00936
and
Albert E. Ogden
Center for the Management, Utilization, and
Protection of Water Resources
Tennessee Technological University
Cookeville, TN 38505
ABSTRACT
Radon concentrations were measured in soils, caves, and
homes of north central Tennessee. Soil radon concentration ranged
from 72.5 to 349.2 picoCuries/Liter (pCi/L) and had a mean of
130.5 pCi/L; the maximum was measured within a soil developed on
the uraniferous Chattanooga Shale. Cave radon ranged from 7.2
pCi/L to 386 pCi/L. Caves within Ordovician limestones had a mean
radon concentration of 129.1 pCi/L while caves in Mississippian
limestones had a mean radon concentration of 30.1 pCi/L. Home
radon concentration ranged from 0.2 pCi/L to 37.6 pCi/L and had a
mean of 2.02 pCi/L; twenty-three percent of the home radon
concentrations exceeded 4 pCi/L.
Homes built on Fort Payne limestone had the highest
geometric mean (2.91 pCi/L) of lithologically classified samples;
homes built on the Warsaw limestone had the lowest mean (1.58
pCi/L). A weak inverse correlation between radon concentration
and distance above the Chattanooga Shale was indicated by a
Pearson correlation coefficient of -0.165. The confidence the
relation was not coincidental, however, was only 81.4 percent.
Crawl space homes and basement homes were found to have
statistically similar mean radon concentrations. The depth of
home excavation varied directly with radon concentration at a
confidence of 99.9 % using the Pearson product-moment correlation.
-------
INTRODUCTION
Radon concentrations were measured in 9 soils, 22 caves, and 98 homes of
north central Tennessee. The radon concentration of soils and caves were
analyzed in order to characterize the local geologic environment for its
potential to introduce radon to houses located in the field area. Radon
levels in homes were correlated with several geological and home construction
factors in an attempt to determine if geological and engineering controls on
radon's distribution in the indoor environment could be quantified for
incorporation into mitigative home construction strategies.
FIELD AREA
Physiographically, the field area encompasses terrain from both the
Outer Central Basin and Eastern Highland Rim Provinces of north central
Tennessee (Figure 1). A simplified northwest-southeast trending cross-
section is provided in Figure 2 and shows that rocks cropping out in the field
Wlllfrn vilify
Cotllll Pill"
ol Ttnnfssti Wvtr
W.ilSfn
Mississippi Hivtr Vallty
Unaka Mount.m.
Mississippi EtKbaymcnt
Nathvill. Dome
Appalachian Foldb.lt
Figure 1. Physiography of central Tennessee showing location
of study area (modified after (1)).
area include Ordovician and Mississippian carbonates and the Devonian
Chattanooga Shale. Table 1 summarizes the insoluble percentages and the
phosphate content associated with each of the major rock units exposed in the
field area. The differing solubilities of the various lithologies in the
field area strongly govern the physiography of central Tennessee (2). The
Central Basin is a rolling lowland which has resulted from the greater
solubility of the Ordovician carbonates relative to the siliceous,
Mississippian Fort Payne and Warsaw limestones. Soils develop to a maximum
thickness of about 20 feet in the Central Basin (3); for the most part,
however, soils do not exceed six feet in depth.
Formations contain a high percentage of silica.
The Fort Payne and Warsaw
In the Fort Payne, silica
occurs predominantly as thick-bedded cherts; in the Warsaw silica occurs
mostly as silt and sand. As a result, these units are erosionally resistant
-------
WNW
ESE
u.
Ul
Ul
OUTER
CENTRA!
BASIN
;i,'i t' 'X C«tfc»y«-
^^^
Figure 2.
Table 1,
Cross-section within study area showing the principal
lithologies.
Percentage of insoluble constituents and phosphate
in each of the major carbonate lithologies of the
field area (modified after (5) and (6).
Rock Unit
Monteagle
St. Louis
Warsaw
Fort Payne
Leipers
Catheys
Percent
Insoluble
Constituents
3.15
1.8 to 7.3
4.04
7.48
7.48
Percent
Phosphate
(as P2O5)
0.030
0.033
0.017
0.179
0.179
-------
and constitute a plateau surface known as the Highland Rim Province. Soil
thicknesses often exceed 50 feet in the Highland Rim and have been reported up
to 100 feet (4). The Mississippian lithologies above the Warsaw Formation are
for the most part relatively pure and highly subject to dissolution. The St.
Louis Limestone forms a sinkhole plain on the easternmost flank of the
Highland Rim Plateau surface. A steep escarpment abuts the sinkhole plain and
rises to the Cumberland Plateau. This escarpment is underlain by the
Monteagle, Hartselle, and Bangor Formations. Despite the fact that the Warsaw
Limestone contains abundant silica, several caves are present in this unit as
a result of the vertical continuity of cave systems originating in the St.
Louis Limestone. The Fort Payne Formation, although abundantly fractured and
highly porous relative to adjacent lithologies, is characterized by small
pocket caves. The caves analyzed for radon in the present survey were all in
either the Ordovician carbonates or the Mississippian Warsaw or Monteagle
Limestones.
The Chattanooga Shale has been shown (7 and 8) to contain relatively
high quantities of uranium throughout most of its geographic extent. Whole
rock uranium analyses of the organic-rich Gassaway Member of the Chattanooga
Shale ranged from 13 to 97 microgram per gram (ug/g) and averaged 55 ug/g (8).
The uranium content of the Chattanooga Shale is therefore significantly higher
than most granites and comparable to highly uraniferous granites. The
Chattanooga Shale's potential as a source of environmentally threatening radon
is probably minimized, however, by the limited thickness of the rock unit.
Throughout central Tennessee, the Chattanooga Shale averages about 30 feet in
thickness, and the uranium-rich Gassaway Member averages only 15 feet in
thickness (9).
RESULTS AND DISCUSSION
SOIL AND CAVE RADON MEASUREMENTS
Soil Radon Survey
Track-etch radon measurements in nine soil associations yielded a range
from 78 to 345 picoCuries per liter (pCi/L), a geometric mean of 130.5 pCi/L,
and an arithmetic average of 153.6 pCi/L (Table 2). The limited number of
samples prohibitted the clear definition of the type of data distribution, but
the data appear to be lognormally distributed. The two lowest soil radon
measurements were taken in floodplains of creeks during the wet months of
December and January, when the water table was near the land surface. These
lower measurements may reflect the inhibitting effect of a nearby water table
on radon's diffusive migration through soil. Nevertheless, the geometric mean
and average of all soil radon measurements are both higher than the national
average soil radon concentration of 100 pCi/L (10), suggesting that north
central Tennessee soils may introduce slightly more radon to area homes than
do soils on the national average.
Cave Radon Survey
Radon analyses in 22 regional caves were made with carbon canisters over
a 4 to 5 day exposure period. Elementary statistics are summarized in Table
-------
Table 2. Summary of elementary statistics of variously
classified radon data sets.
Datasot
i«° #° «* ^ £
> + v*x y i*
A° -*v oK «
.»
•T
HOME RADON
Overall
98
2.02
3.07
2.54 125.74X 23.47X
LITHOLOGIC POPULATIONS
Warsaw 42 1.58 2.46
Fort Payne 25 2.91 3.53
Chattanooga 10 1.7 2.03
Ordovician 21 2.31 4.24
2.8 177.22X 21.43X
1.84 63.23X 32.00X
1.98 116.47X 10.00X
2.8 121.21X 19.05X
HOME TYPES
Crawl space
Concrete slab
64 1.87 2.61 2.4 128.34X 20.97%
34 2.31 3.87 2.78 120.35X 30.56X
DEGREE OF
UEATHERIZATION
Very Low
Below Average
Average
Above Average
Very High
SOIL RADON
CAVE RADON
Overall
Mississippian
Ordovician
9
16
49
17
7
1.62
1.52
2.03
2.81
2.46
2.28
1.75
2.85
5.43
2.93
2.63
1.77
2.48
3.63
1.53
162. 35X
116.45X
122.17%
129.18%
62.20X
16.67X
0.00%
23.26%
31.58%
16.67X
22
16
6
130.5 153.6
41.3
30.13
129.1
84.7
62.6
164.1
1.78
4.26
4.2
2.33
1.36X
10.31%
13.94X
1.80%
N/A
N/A
N/A
N/A
-------
2. Caves in Ordovician rocks had a significantly higher geometric mean (129.1
pCi/L) than did caves in Mississippian rocks (30.1 pCi/L). This is thought to
reflect mineralogical differences between the two limestones. The
Mississippian Monteagle Formation is a relatively pure limestone (Table 1)
with an average of 0.03 percent phosphate (as P205); similarly, the underlying
Warsaw Formation contains an average of 0.033 percent phosphate and the Fort
Payne an average of only 0.017 percent phosphate. The Ordovician Leipers and
Catheys Formations, on the other hand, have phosphate-rich horizons with up to
20 percent phosphate by weight (5). The average phosphate concentration in
the Catheys and Leipers formations is 0.179 percent. Insoluble constituents
average 7.48 percent within the Catheys and Leipers (Table 1). Unlike the
overlying siliceous Fort Payne and Warsaw limestones, however, the majority of
the insoluble portion of the Ordovician strata consists of interbedded shales
and disseminated clays.
The lattices of calcium phosphate minerals have been shown to readily
accomodate uranium as an isomorphic substituent (11). Uranium is also commonly
adsorbed onto the surfaces of clay minerals. The relatively higher proportion
of clay minerals and phosphate in the Ordovician rocks is therefore likely to
provide a suitable environment for the regional incorporation of uranium into
the Ordovician rock matrix. Although some of the uranium may have been
introduced into the sedimentary basin by the deposition of clays, it is also
possible that ground water mobilization of uranium from the Chattanooga Shale
has resulted in the concentration of uranium in phosphatic horizons below the
Chattanooga Shale.
GEOLOGICAL CONTROLS ON INDOOR RADON MEASUREMENTS
Basements and crawl spaces were tested for radon with carbon canisters
in homes built upon the Catheys, Leipers, Chattanooga, Fort Payne, and Warsaw
Formations. Measurements ranged from 0.1 to 37.6 pCi/L. The data were
lognormally distributed, with a geometric mean of 2.02 pCi/L (Table 2).
Twenty three percent of the measurements were above the U.S. Environmental
Protection Agency recommended maximum of 4 pCi/L (12). The mean of 2.02 pCi/L
was higher than the national geometric mean of 0.89 pCi/L (13). However, the
maximum of 37.6 pCi/L was one or two orders of magnitude below the extremes
measured in other parts of the United States. The 37.6 pCi/L maximum of the
present study was measured in a home constructed within 100 feet of the cave
passage possessing the highest cave radon measurement (386 pCi/L) made in this
study. Radon was shown to enter the home via a fracture system connecting the
cave and the substructure of the house (14), demonstrating that near surface
cave systems can pose a potential avenue of radon entry to nearby houses.
Indoor radon measurements were classified according to underlying
bedrock; the data from each lithological class was found to possess a
lognormal distribution. The elementary statistics describing these classes
are given in Table 2. Homes built on the Fort Payne Formation possessed the
highest geometric mean (2.9 pCi/L) while homes built on the Warsaw Formation
possessed the lowest geometric mean (1.6 pCi/L). These were the only two
populations which proved to be statistically separable at an alpha of 0.05
with the Student's t-test.
-------
Despite the fact that the Chattanooga Shale has a uranium content
significantly greater than the overlying and underlying limestone lithologies,
homes built on the Shale did not have anomalously high radon concentrations.
The low observed measurements (Table 2) may be due to the very limited 2 to
2.5 feet soil thickness developed on the Chattanooga. A thin soil can
minimize soil radon concentrations and the radon introduced to overlying homes
in several ways. At soil depths less than 3 feet, only a portion of the
diffusion length of radon is utilized, thereby limiting radon production. A
thin mantle of soil is furthermore subject to atmospheric influences to a
greater extent than is a thick soil. Consequently, wind and temperature
fluctuations are potentially more effective in removing radon from the soil.
Precipitation is more likely to produce a saturated zone near the land surface
within a thin soil, thereby decreasing the effective diffusivity of the soil.
Besides the soil thickness, another factor which may explain the low
radon content of Chattanooga homes is the location of radium ions within the
soil matrix. The emanation coefficient of a given soil is strongly controlled
by the location of radium ions in the solid matrix (15). If radium is
primarily present as adsorbed ions on the exterior of clay grains, then the
emanating fraction of the total volume of radon produced by the decay of
radium is likely to be high. If, however, radium is bound in individual
grains a distance greater than a few microns from interstitial pore space,
then the radon that actually escapes the grains and enters the pore space is
likely to be significantly lower and result in a lower overall emanation
coefficient. The proportion of clays in Chattanooga-derived soils was found
to be noticeably lower than that characterizing soils weathered from carbonate
lithologies. Correspondingly, rock fragments were more abundant within
Chattanooga soils than within any of the other soils augered. The relative
abundance of rock fragments and paucity of clay in the Chattanooga soil,
combined with the low radon measurements in homes, may suggest that radium is
bound within the interior of rock fragments and not predominantly attached to
the exterior of clay surfaces by adsorption.
Based on a radon survey of 1733 homes in Tennessee and the knowledge
that the Chattanooga Shale was the most highly uraniferous stratum exposed
statewide, Tennessee Department of Health and Environment (16) characterized
the surface outcrop of the Chattanooga Shale and downslope areas in Tennessee
with its highest "radon occurrence potential" ranking. In order to further
assess the effects of the Chattanooga Shale in promoting high radon
concentrations in adjacent homes, the stratigraphic distance above and beneath
the Chattanooga Shale was calculated for each of the homes tested during the
present survey using geologic maps, topographic maps, structure contour maps,
and well logs. The distance from the Chattanooga Shale was plotted against
the logarithm of the radon concentration for the two sets of homes (those
beneath the shale and those above the shale). Logarithmic transformation of
the raw data was necessary in order to permit the parametric statistical
comparison of the two variables by calculation of Pearson correlation
coefficients.
As Figure 3 shows, no relation was manifested between distance beneath
the shale and radon concentration, suggesting that downslope drift of
weathered Chattanooga Shale residuum does not appear to be a significant
-------
control on radon distribution in Central Basin soils adjacent to the
Chattanooga Shale outcrop. The plot of radon concentration versus distance
above the Chattanooga Shale is shown in Figure 4 and appears to manifest a
weak inverse correlation between the two variables. A mathematical
correlation of the two variables yielded a Pearson coefficient of -0.165 at an
alpha of 0.186, implying only an 81.4 percent probability that the relation
is not coincidental. The weak dependence of radon concentrations on distance
above the shale appears to be lost altogether beyond about 180 feet above the
Shale. The degree of home weatherization is identified in Figure A and shows
that highly insulated homes plot generally in the uppermost portion of the
field whereas poorly insulated homes plot generally in the lowermost portion
of the field. These generalizations are not all-encompassing, however,
suggesting that radon distribution is influenced by other factors as well.
The strength of the correlation is insufficient to conclude that the
location of the Chattanooga Shale has a predictable effect on the radon
concentration within overlying lithologies. Nevertheless, the weak trend
cannot be dismissed outright as coincidence either. What the distribution of
the data appear to indicate is that radon distribution in the subsurface and
indoor environment is an extremely complex function of a large number of
variables. As a result, the analysis of one or two factors which may
partially control its distribution cannot be expected to yield perfect data
fits with low covariance. The apparent relationship between radon
concentration of homes and distance above the Chattanooga Shale—if it is in
fact real and not coincidental—may be the result of at least three
fundamentally separate processes. These are briefly summarized below.
1. The inverse relationship could indicate that radon is produced
within the Chattanooga Shale and migrates through the subsurface
to overlying homes. Homes more removed from the Shale would
therefore be expected to have a lower radon concentration. One
problem with this interpretation is that the Chattanooga Shale
forms the lower boundary of an aquifer developed within the Fort
Payne and Warsaw. Consequently, radon produced in the Chattanooga
Shale would have to travel a tortuous subsurface path through
ground water and ground air, all within the time constraint
imposed by its limited decay period.
2. The upward diffusion of uranium throughout geologic time as a
result of ground water reworking could have promoted higher
uranium concentrations within overlying rock. In such a case,
uranium content would be expected to be progressively reduced with
increasing distance above the Shale. Under this circumstance,
radon would be derived from the decay of radium grains contained
within Fort Payne soils and not the underlying Chattanooga itself.
3. Finally, the apparent reduction in average radon concentration
moving away from the Chattanooga Shale could reflect a change in
the source or quantity of clays introduced into the sedimentary
basin and be completely independent of the uranium content of the
underlying shale. This possibility would imply that radon is
-------
8
O
o
<
I.D
1.4
1.2
1
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
_i
I I I I I I Lk I I
-
-
-
_
A A ^
A A A -
A A A A .
A A
A
A
A A
A *
-
_
A
-
I i i i i i i i
50
100 150 200 250 300 350 400 450
STRATIGRAPHIC DISTANCE BENEATH CHATTANOOGA (FT)
Figure 3. Log(radon content) plotted against stratigraphic
distance beneath the Chattanooga Shale.
^
1
8
O
|
I.D
1.4
L2
1
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
i i i i i i i
-
-
r>D
0 * ^
- A o ° ° ** OD
A A O D ° n
A OFQ
A A
°0 ° D
-
f£> O
- WEATHERIZAHON A
_A i«w O
" O AvnuK Q
_ D mm
1 1 1 1 In 1 1
40
80
120
160
200 240 280 320
STRATIGRAPHIC DISTANCE ABOVE CHATTANOOGA (FT)
Figure 4. Log (radon content) plotted against stratigraphic
distance above the Chattanooga Shale for populations
classified according to degree of home weather izat ion.
-------
derived from clays within the soils underlying homes and not from
distant subsurface sources.
HOME CONSTRUCTION CONTROLS ON INDOOR RADON CONCENTRATIONS
Although geological environment is expected to provide an important
control on the magnitude of radon's localized availability, home construction
characteristics have been shown (17) to play a strong role in determining the
extent to which radon is admitted into a structure and concentrated there.
The effects of three construction factors were considered in describing the
radon distribution in this study. These factors were: 1) home type, 2)
degree of home weatherization, and 3) depth of basement excavation.
Home Type
Homes surveyed were of two types: homes with basements and concrete
foundations, and homes with crawl spaces and earthen foundations. Both data
sets exhibitted lognonnal distributions, and Table 2 summarizes simple
statistics calculated for the two populations. Homes with basements had a
larger geometric mean (2.3 pCi/L) than homes with crawl spaces (1.9 pCi/L),
but the difference was not statistically significant with the t-test at an
alpha of 0.10 (evaluated with log-transformed data). This implies that the
greater air exchange characteristic of the crawl space homes studied is
sufficient to overcome their heightened susceptibility to radon entry
resulting exclusively from the absence of a concrete foundation radon
diffusion barrier. Correspondingly, the data strongly indicate that the
presence of a concrete foundation does not ensure that homes with excavated
basements are immune from the effects of radon entry.
Degree of Home Weatherization
Figure 5 shows that the degree of home weatherization is a factor which
influences the magnitude of indoor radon concentrations. Highly weatherized
homes had higher geometric means than homes which were poorly insulated. The
coefficients of variation indicate that well insulated homes similarly had the
most homogeneous radon concentrations, suggesting that air exchange promoted
by "leaky" houses had a diagnostic effect on the variability of measured radon
concentrations.
Depth of Home Excavation
Depth of excavation was determined onsite for each of the homes tested.
This parameter was correlated with log-transformed radon concentration using
the Pearson product-moment correlation, yielding a coefficient of 0.51 at an
alpha of 0.001. The relationship is depicted in Figure 6 in which a linear
regression is plotted. Excavation depth was similarly correlated with
log(radon) for each lithology. None of the lithologically classified data
sets provided statistically significant correlations at an alpha level of 0.1
or lower except for the Fort Payne data set, which yielded a Pearson
coefficient of 0.47 at an alpha of 0.012. A linear regression of the Fort
Payne data is also shown in Figure 6. Comparison of the two trends indicate
that the minimum radon concentrations of Fort Payne homes is higher than the
-------
1,000
o
Q
CD
LOW
AVERAGE
DEGREE OF HOME WEATHERIZATION
HIGH
Figure 5. Plot showing the geometric mean and coefficient of
variation of populations classified on the basis of
degree of home weatherization.
8
O
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
-0.2
-0,4
-0.6
-0.8
-1
LOG(RADON)=0.056(DEPTH)+6.3 IS
LOG(RADON)=0.028(DEPTH)+0.318
DATA SET
O SJISMS5..«.
0 1 23456789 10 11 12 13 1415 16 17 18
DEPTH OF EXCAVATION (FT)
Figure 6. Log(radon content) plotted against depth of home
excavation showing overall and Fort Payne populations.
-------
minimum concentrations of homes built within other lithologies, that is, the
y-intercept of the Fort Payne regression has a higher magnitude. Conversely,
the overall data set manifests the greater slope, indicating that the
probability of higher radon concentrations at greater excavation depths is
higher among lithologies other than the Fort Payne. The regression equations
loosely represent data with high covariance. The error in their prediction of
radon concentration based on excavation depth was generally less than 15
percent but as high as 30 percent. The regression functions suggest that on
the average, 4 pCi/L radon will be exceeded in the overall data set at
excavation depths greater than 8.2 feet and among Fort Payne homes at
excavation depths greater than 10.1 feet.
The close correspondence between depth of excavation and radon
concentration in homes built on the Fort Payne is thought to reflect the fact
that the radon source lies within the soil itself and not in the Chattanooga
Shale. An additional indication that the source of radon is within the soil
among the Fort Payne homes is the relatively low coefficient of variation for
the Fort Payne population (63 percent) compared to the other lithologic
populations, which ranged from 116 percent to 177 percent. If radon were
derived from the Chattanooga Shale and transported along solutionally enlarged
fracture systems within the Fort Payne, radon concentrations in the Fort Payne
soil would be expected to be variable with high radon concentrations above
fracture zones and low radon concentrations above non-fractured rock. The
fact that the coefficient of variation is the lowest among Fort Payne samples
argues that radon is not transported along fracture systems but is derived
from radium grains within the soil itself.
CONCLUSIONS
Radon concentrations in north central Tennessee homes and soils are
slightly higher than indoor radon concentrations on a national average.
However, radon is present in quantities much lower than in areas of the United
States considered by the Environmental Protection Agency and equivalent state
agencies to be radon "hot spots".
In the homes surveyed, radon was shown to vary as a function of many
different factors related to both geology and home construction. Homes built
upon soil derived from the Fort Payne Formation had the highest mean radon
concentration, and homes built upon the overlying Warsaw Formation had the
lowest radon concentration. There was an apparent inverse correlation between
distance above the Chattanooga Shale and radon concentration; the confidence
that this relation was not coincidental, however, was only 81.4 percent.
Homes possessing crawl spaces were shown to have a geometric mean
statistically similar to homes having basements with concrete foundations.
Depth of home excavation and log(radon) manifested a direct correlation with a
confidence of 99.9 % that the relation was not coincidental. A linear
regression predicted that the U.S. Environmental Protection Agency recommended
maximum of 4 pCi/L would be exceeded on the average at excavation depths
greater than 8.2 feet for the overall data set and 10.1 feet within Fort Payne
homes•
-------
The work described in this paper was not funded by the U.S.
Environmental Protection Agency and therefore the contents do not necessarily
reflect the views of the Agency and no official endorsement should be
inferred.
ACKNOWLEDGEMENTS
The authors wish to acknowledge the Center for Management,
Utilization, and Protection of Water Resources at Tennessee Technological
University for funding of the research summarized herein. Acknowledgments are
due Brad Neff, who collected most of the cave radon measurements.
Additionally, we would like to thank Joe Troester and Gregg Hileman of the
U.S.G.S. for the technical reviews each provided.
REFERENCES
1. Miller, R.A., 1979, The Geologic History of Tennessee: Dept. of Cons.,
Div. of Geol., Bulletin 74, 59 p.
2. Reesman, A.L., and Godfrey, A.E., 1972, Chemical Erosion and Denudation
Rates in Middle Tennessee: Tenn. Dept. of Cons. Div. Water Resources
Series 4, 35 p.
3. Burchett, C.R., and Moore, G.K., 1971, Water Resources in the Upper
Stones River Basin, Central Tennessee: Tenn. Dept. Cons. Div. Water
Resources series 8, 62 p.
4. Moore, G.K., and Wilson, J.M., 1972, Water Resources of the Center Hill
Lake Region, Tennessee: Dept. of Cons. Div. of Water Resources Series 9,
77 p.
5. Hershey, R.E. and Maher, S.W., 1985, Limestone and dolomite resources of
Tennessee: Tenn. Div. of Geol. Bull. // 65, 252 p.
6. Milici, R.C., Briggs, G., Knox, L.M., Sitterly, P.O., and Statler, A.T.,
1979, The Mississippian and Pennsylvanian Systems in the United
States--Tennessee: U.S. Geological Survey Professional Paper 110-G.
7. Glover, L., 1959, Stratigraphy and uranium content of the Chattanooga
Shale in northeastern Alabama, northwestern Georgia, and eastern
Tennessee: U.S. Geological Survey Bulletin 1087-E, pp. 133-168.
8. Leimer, H.W., and Matthews, R.D., 1981, Chattanooga Shale of the Eastern
Highland Rim, Tennessee, and methods of sampling; Synthetic Fuel from Oil
Shale II, symposium and field trip, Institute of Gas Technology.
9. Conant, L.C. and Swanson, V.E., 1961, Chattanooga Shale and related rocks
of central Tennessee; U.S. Geological Survey Professional Paper 357.
-------
10. Brookins, D.G., 1988, The indoor radon problem: studies in the
Albuquerque, New Mexico area: Environ. Geol. Water Sci., v. 12, n. 3,
pp. 187-196.
11. Rogers, J.J.W. and Adams, J.A.S., 1969: Uranium; IN: Handbook of
Geochemistry, Springer, Berlin, Chapter 92, 1962.
12. U.S. Environmental Protection Agency, 1986-a, A Citizen's Guide to Radon:
USEPA/OPA-86-004, 14 p.
13. Nero, A.V., 1988, Radon and its decay products in indoor air: an
overview: in: Radon and its Decay Products in Indoor Air, Nazaroff W.W.
and Nero, A.V. eds, Wiley-Interscience; 518 p.
14. Collar, P.D. and Ogden, A.E., 1989, Radon in homes, soils, and caves of
north central Tennessee and implications for the home construction
industry: Third Interdisciplinary Conference on Sinkholes and
Environmental Problems in Karst Terranes; St. Petersburg, Florida, Oct.
14, 1989.
15. Nazaroff, W.W., Hoed, B.A., and Sextro, R.G., 1988, Soil as a source of
indoor radon: generation, migration and entry: in: Radon and its Decay
Products in Indoor Air, Nazaroff W.W. and Nero, A.V. eds,
Wiley-Interscience; 518 p.
16. Tennessee Department of Health and Environment, 1987 Summary Report of
the Tennessee Radon Survey.
17. U.S. Environmental Protection Agency, 1987, Radon Reduction in New
Construction: an Interim Guide: EPA/OPA-87-009.
-------
C-VI-4
GRAIN SIZE AND EMANATION AS CONTROLLING FACTORS IN SOIL RADON
Linda C. S. Gundersen
U. S. Geological Survey
ABSTRACT
A comparison of two soQ radon sampling techniques, die Reimer grab sampling
technique (RG) and die EPA flow through grab sample technique (EFT), reveals a
strong control of grain size and sorting on the soil radon measured. Moisture
produces secondary effects on sampling, sometimes determining whether a sample
can be obtained at all. Emanation, however is the ultimate control on the amount of
radon sampled and h appears to be influenced most by the abundance of metal-
oxides and the siting of uranium and radium in and around grains.
In well sorted, medium to coarse grained sands the two sampling techniques obtain
similar radon concentrations, usually within 10% of each other. In poorly sorted
sands, especially clayey sands, the RG obtains higher concentrations than the EFT.
Under high moisture conditions including saturated conditions, the EFT cannot
obtain a radon sample while the RG will obtain a sample approximately 50% of the
time. Permeability measured at all of these sites has no apparent correlation with the
radon concentration.
Equivalent uranium from gamma spectrometry at the surface and uranium and
radium measured chemically in the soil have been compared with the soil radon
concentrations. Although a generally positive correlation exists, anomalous amounts
of soil radon with respect to its parent radionuclides are found in a variety of
geologic settings. The common factor causing these anomalous concentrations is the
occurrence of metal oxides, particularly iron, and the sorption or precipitation of
uranium and radium in association with the metal oxides, dramatically enhancing the
emanation in the rocks and soils.
This paper has been reviewed in accordance with the U. S. Environmental
Protection Agency's peer and administrative review policies and approved for
presentation and publication.
-------
C-VI-5
EFFECTS OF REGIONAL AND SEASONAL VARIATIONS IN SOIL MOISTURE AND
TEMPERATURE OK SOIL GAS RADON
Arthur W. Rose, Department of Geosciences
Edward J. Ciolkosz, Department of Agronomy
John W. Washington, Department of Geosciences
Pennsylvania State University
University Park, PA 16802
ABSTRACT
Radon in houses depends partly on Rn concentration in soil
gas, which is affected by water in a variety of ways. In this
paper, temperature-dependent effects of Rn partitioning between
changing proportions of air and water in pore space are shown to
be capable of causing variations in Rn concentration up to 5-
fold. A map of regional soil moisture and temperature regimes,
in combination with the moisture/temperature effects on Rn,
suggests that soil gas Rn will be most elevated by moisture
effects in eastern U.S. and other regions with the Udic soil
moisture regime. Large seasonal differences are also predicted
for soils of the Udic moisture regime, with soils of the Frigid
temperature regime having higher Rn in summer than winter.
Aridic (dry) soils show negligible effects. Clay-rich soils
will generally be most strongly affected by moisture variations.
-------
INTRODUCTION
The main source of radon (Rn) in houses is now generally
accepted Co be soil gas entering through the foundation, driven
by small pressure gradients between the outside and inside of the
house (1). The total flux of Rn into a house via soil gas is a
function of two factors, the flow rate of soil gas into the
house, and the concentration of radon in the soil gas. The
first factor, the flow rate of soil gas, varies with time owing
to changes in the pressure gradient with changing conditions
inside and outside the house, and temporal changes in air-filled
porosity due to moisture changes. In addition, the flow rate
varies from one house to another because of differences in
construction details, as well as differences in permeability of
soil and backfill along the path of air flow into the house.
The second factor, the Rn concentration in the entering soil gas,
depends largely on the radium (Ra) content, moisture and physical
properties of the soil and backfill around the house. In
general, increased Rn in soil gas is expected to lead to
increased flux of Rn into the house, given equal influx rate of
soil air.
The intent of this paper is to discuss some effects of soil
moisture and temperature variations on the Rn content of soil
air. The main emphasis is on effects involved in Rn equilibrium
between air and water in the soil. This phenomenon has an
important influence on absolute soil gas Rn concentrations as
well as the nature of changes with time in the Rn concentration
available to enter a house. The same phenomena are also
important considerations in the interpretation of soil gas Rn
surveys to predict Rn hazard.
TYPES OF MOISTURE EFFECTS
A large number of processes involving water have been
proposed to affect the Rn content of soil gas. The following
processes involving liquid water (but not ice) can be
distinguished (2, 3, 4, 5, 6): (1) The sealing effect of a water-
saturated zone at the surface or within the soil profile; (2)
inhibition of diffusion in water-saturated pores because of much
slower diffusion in water than air; (3) the flushing effect of
water percolating through the soil and either pushing air ahead
of it or transporting dissolved radon; (4) changes in volume of
the soil due to changes in moisture, leading to cracking and
swelling; (5) for relatively dry soils, an increase in Rn
emanation coefficient with increasing moisture; (6) for radon
transport into houses, the effect of the water table in limiting
the depth of air flow; (7) temperature-dependent partition of Rn
between water and air in soil pore space (2). Host of these
processes must be considered theoretical, because unambiguous
-------
field evidence demonstrating one cause of Rn variability and
eliminating all other causes is scarce.
In most soil profiles, the Rn concentration decreases toward
the surface because of diffusion from the relatively high
concentrations (200-5000 pCi/1) generated in the soil compared to
negligible concentration in open air (0.2 pCi/1). In soils with
dominantly air-filled pores, this zone of markedly varying
concentrations ranges from a few tens of centimeters to several
meters in thickness, depending on the effective diffusion
coefficient and air-filled porosity of the soil. However, the
Rn diffusion coefficient in water is smaller by a factor of about
10* than the diffusion coefficient in air (2). Because the
concentration gradient due to diffusion depends on the square
root of the diffusion coefficient, the zone of changing
concentration in water- saturated soil is condensed to about 1%
of its thickness in soil with air-filled pores.
One result of this phenomenon is that a rainfall event
intense enough to saturate the surface soil can create a seal for
Rn, leading to high Rn levels beneath the water- saturated zone.
Several half lives of Rn are required for the full increase to
occur. A low permeability zone within the soil can have a
similar effect.
As a soil is progressively wetted, the pores fill with water
in the order of smallest to largest because of surface tension
effects. Because of the low diffusion rate of Rn in water,
transport of Rn in water-filled micropores is very slow. Thus,
saturated micropores may effectively cause a dual pore system: a
small proportion of air-filled pores separated by water-filled
micropores and having high Rn concentration, and a separate set
of connected macropores in which Rn concentration is controlled
by diffusion in air, and flushing effects discussed below. This
condition may be further complicated during intense rainfall
events when the network of connected macropores may be the
preferred pathway for rapid water movement through the soil.
Rainfall or other precipitation leading to percolation of
water through the soil can displace Rn-rich air upwards. Some Rn
is expected to dissolve from the soil air into the downward
percolating water, resulting in additional Rn transport downward
with the water. These processes can lead to a temporary
depletion of Rn in the zone above the percolating water.
In a soil, Rn atoms are generated by radioactive decay of Ra
atoms occurring in soil grains. The proportion of Rn atoms that
escape into the pore space is termed the emanation coefficient.
Emanation coefficients in very dry soils are markedly lower than
in moist soils (7). Typical values in soils with at least 5% of
the pore space filled by water are 0.15 to 0.35, with about 0.2 a
-------
common value. Although this effect has been clearly
demonstrated in experiments, it appears that few soils are dry
enough to have significantly decreased emanation coefficients.
In most soils, the pore space is filled with a mixture of
air and water. These phases are expected to be in close enough
contact that Rn will redistribute itself between air and water by
local diffusion between pores. At depths below the zone of
significant diffusive loss to the atmosphere, when the soil air
and water have remained long enough for emanated Rn to reach
radioactive equilibrium, the concentration of Rn per unit volume
of air-filled pore space (CR ) is given by the following relation
(6):
CRn -
where CRfl is the concentration of Ra per unit mass of soil
particles, E is the emanation coefficient, D is the dry bulk soil
density, P is the volume fraction of total pore space, F is the
volume fraction of total pore space occupied by water, and K is
the partition coefficient of Rn between unit volumes of water and
air (CR water/cRn air)- Tne v*l"e of K depends on temperature
(T), and'ranges from 0.54 at 0°C to 0.23 at 25°C (6).
The effects of air-water partition may be isolated from
equation (1) and expressed as Q, the factor by which variations
in moisture and temperature increase Rn concentration in air-
filled pore space:
Q - 1 (2)
(F(K-l)-H)
Given this relation, Figure 1 shows the effects of changes
in F and T on Rn concentrations of soil air, given fixed values
of CRa, E, D and P. CR_ is seen to vary by a factor of 5
between F-0, T-0°C and F-1.0, T-30°C. Variations of a
significant fraction of this range can occur at a single site at
different times, and most of the above range occurs within soils
of the United States.
REGIONAL AND LOCAL VARIABILITY OF SOIL MOISTURE AND TEMPERATURE
Soil moisture and temperature are very important in the
growth of crops, so soils are classified partly in terms of these
properties (8). Based on mean annual soil temperature (MAST),
soils of temperate regions are classified as Frigid (MAST-0-8°C),
Mesic (MAST-8-15°C), Thermic (MAST-15-22°C) or Hyperthermic
(MAST>22°C). Soil moisture regimes are basically defined by
groundwater level and proportion of the year in which moisture is
held at tensions of 1500 kPa or less, the maximum tension at
which common crops can grow. Most U. S. soils are classified as
-------
Aridic, Ustic or Udic in order of increasing length of the
growing season with moist soil. In addition, the Xeric soil
moisture regime occurs in areas of Mediterranean climate, i. e.,
moist cool winters and hot dry summers, in contrast to moist
summers and dry winters of the Ustic regime.
Figure 2 gives a generalized distribution of soil
temperature and soil moisture regimes for the U.S., compiled from
references 9-12. In the eastern and central U. S., soil
temperature regimes follow a simple pattern of Frigid, Mesic,
Thermic and Hyperthermic from north to south. East of about
97°W Long., soils are relatively moist (Udic), and westward to
the Rocky Mountains they are Ustic. In the western U. S.,
Frigid regimes extend southward along the Rocky Mountains, and
Aridic regimes are common in the southwest. Regions of Xeric
soil moisture regime are common in California and nearby areas.
Based on Figures 1 and 2, soils with identical values of
CRa, E, D and P would be expected to increase in CRn in the
sequence Aridic-Ustic-Udic eastward across the U. S, and to
increase in the order Frigid-Mesic-Thermic-Hyperthermic
southward. Table 1 lists a few sites for which the relevant
parameters have been measured or estimated. For most sites in
regions of Udic moisture regime, the observed Rn (especially the
maximum observed Rn) exceeds the values calculated for dry soil
by factors of 1.5 to 5, as expected for soils of Udic moisture
regime. For site 14-80, where measurements of moisture and
temperature have been made, the values calculated from equation
(1) match the measured values within measurement error (6). The
sole exception, site 14-82, is strongly affected by water
saturation effects for much of the year. In contrast, at the
site at Socorro, NM, in an Aridic moisture regime, the calculated
and observed Rn agree closely. The moisture content of this
soil is reported as 4 wt.%, equivalent to F-0.17, a reasonable
value for the aridic regime. For the site at Denver, CO, the
observed Rn levels for moist seasons distinctly exceed the values
calculated for dry conditions, and during dry seasons the soil
cracks to allow air penetration to depth. These data are
consistent with a significant moisture effect.
Extension of the relations discussed above leads to the
hypothesis that radon in houses should vary according to the
moisture and temperature regimes, if not obscured by variations
in CRa, E, D and P, and flux of soil air. This hypothesis was
tested using statewide averages of Rn in homes from a compilation
of 175,000 measurements by The Radon Project of Pittsburgh, PA,
as compiled by Dr. Bernard Cohen of the University of Pittsburgh.
The data on houses do not fit the hypothesis. In eastern
and central U. S., the highest values are in IA, SD, and several
other northern plains states with an Ustic moisture regime and
-------
Frigid or Mesic thermal regime, rather than in states with a
Udic-Thermic regime. Values tend to be low in most states of
southeastern U. S. with a Thermic temperature regime. Likely
explanations of the failure of the hypothesis are regional
differences in Ra and U, lower indoor-outdoor temperature
differences in the southeast leading to lower pressure gradients,
regional differences in home construction (specifically the use
of slab-on-grade construction in the southeast vs. basements in
northern states), and error from grouping by state. Also, in
areas of high soil moisture, the air permeability may be greatly
decreased by blockage of small pores by water.
Local differences in drainage and moisture are probably also
of significant importance in soil gas Rn. Many relatively flat
valley areas are floored by alluvium or soil that is water
saturated at the surface, to form the Aquic moisture regime.
Other poorly drained areas may have a thin zone of moist soil
above the water table. Radon content of soil gas is expected to
be relatively high in such areas, but air permeability may be so
low that little Rn transport is possible.
EFFECTS OF SEASONAL VARIATIONS IN SOIL MOISTURE / TEMPERATURE
Soils literature also allows estimates of seasonal change in
moisture and temperature, leading to estimates of seasonal
changes in Rn concentrations. Tables 2, 3, and 4 give these
estimates.
The soil moisture states and soil moisture tension ranges
given in Table 2 were developed by the USDA Soil Conservation
Service (14). The data given in Table 2 for the sandy loam and
silty clay loam was calculated as follows: A bulk density of
1.60 g/cm (sandy loam) and 1.45 g/cm (silty clay loam) was used
to calculate (assuming a particle density of 2.65 g/cm ) a total
pore space of 40% for the sandy loam and 45% for the silty clay
loam. Soil moisture content based on data from Petersen et al.
(15) and Ciolkosz and Dobos (16) for 1500 and 33 KPa tensions was
used to interpolate the values given in Table 2 using the soil
moisture tension/moisture content relations given by Thome and
Thorne (17). These data were used to compute the percent pore
space filled with water (% soil moisture x bulk density/total
pore space). Table 3 gives estimated winter and summer soil
moisture regimes for the upper 1.5 meters of soils of the United
States. These data are based on numerous soil moisture state
evaluations (18, 19) for various soils of the United States. The
soil temperatures given in Table 4 were calculated from mean
monthly air isotherms (20) using the method of van Wambeke (21)
for the various soil temperature/moisture regions given in Figure
3. This method may give conservative values for bare soil areas
(22), therefore the soil temperatures may have a greater range
than given for the arid area.
-------
These data have been used Co derive the estimates of Q shown
in Table 5. Several conclusions of interest may be drawn from
this data:
1. The largest seasonal effects of moisture and temperature
are expected in the Udic moisture regime. In the warmer parts
of Udic regions, winter Rn values may be more than double the
summer values.
2. Summer Rn values higher than winter values are predicted
for the Frigid-Udic regime, and are possible in the Mesic-Udic
regime. This behavior has been recognized at several sites in
central Pennsylvania (14-80, 14-81, 14-82, 14-83), which is on
the cold edge of the Hesic thermal regime.
3. Summer Rn exceeding winter Rn is possible in the Ustic
regime, but in general, large changes are not expected.
4. In the aridic regime, moisture is low enough that
seasonal effects are very small, but typically winter levels will
slightly exceed summer values.
5. In the Xeric regime, winter Rn values are expected to
markedly exceed summer values.
6. Seasonal effects are expected to be much larger in clay-
rich soils than in sandy soils, because of the generally higher
moisture saturation of clay-rich soils.
CONCLUSIONS
Although many effects of water on Rn in soil gas are
proposed, the effect of varying proportion of pore space occupied
by water appears to be among the largest and most universal.
Temperature also affects soil gas Rn because of its effect in
varying the partition of Rn between water and air. The process
affects moist soils at all depths, but can be evaluated best for
depths where diffusion toward the surface is negligible.
In the soils literature, major regional differences in soil
moisture and temperature are well documented, and have been
compiled as a map. The meager data on Rn in soil gas agrees with
the proposed moisture temperature effects. However, within
houses the effects of soil moisture and temperature are masked by
other Rn-determining factors (regional differences in Ra, house
construction, house pressurization, etc.) so that a clear
regional effect of the soil moisture and temperature is not
obvious in a large data set on Rn in houses.
Seasonal variability in soil gas Rn has been predicted from
estimated temporal soil moisture and temperature variations.
Large seasonal variations are predicted for soils of the Udic
moisture regime, characteristic of the eastern U.S. For the
northeastern U.S., from New England through Minnesota, summer
soil gas radon is predicted to exceed winter values, as found at
several sites in Pennsylvania. Contrastingly, in soils of the
-------
Xeric moisture regime, distinctly higher values are predicted in
the winter than the summer. Clay-rich soils are more susceptible
to moisture-induced elevated Rn than are sandy soils. However,
local variations of moisture caused by variability in drainage
are undoubtedly also of considerable importance.
The work described in this paper was not funded by the U.S.
Environmental Protection Agency and therefore the contents do not
necessarily reflect the views of the Agency and no official
endorsement should be inferred.
ACKNOWLEDGEMENTS
The authors acknowledge the financial support of the U.S.
Department of Energy (Grant DE-FG02-87ER60577).
REFERENCES
1. Environmental Protection Agency. A citizen's guide to
radon. USEPA, Doc. OPA-86-004, 1986. 13 pp.
2. Tanner, A.B. Radon migration in the ground: A review. In:
J.A.S. Adams and W.M. Lowder (ed.), The Natural Radiation
Environment. University of Chicago Press. 1963. p. 161.
3. Tanner, A.B. Radon migration in the ground: A supplementary
review. I_n: T.F. Gesell and W.M. Lowder (ed.), The Natural
Radiation Environment III. DOE Symposium Series, CONF-780422.
1980. p. 5.
4. Schery, S.D., Gaeddert, D.H., and Wilkening, M.H. Factors
affecting exhalation of radon from a gravelly sandy loam. J.
Geophys. Res. 89: 7299, 1984.
5. Schumann, R.R., Owen, D.E., and Asher-Bolinder, S. Weather
factors affecting soil-gas radon concentrations at a single
site in the semiarid western U.S.. In: Proceedings of the 1988
E.P.A. Symposium on Radon and Radon Reduction Technology. EPA-
600/9-89/006B, U.S. Environmental Protection Agency,
Cincinnati, Ohio, 1989. p. 3.1.
6. Washington, J.W. and Rose, A.W. Regional and temporal
relations of radon in soil gas to soil temperature and
moisture. Geophys. Res. Lett, in press: 1990.
7. Nielson, K.K., Rogers, V.C., Mauch, M.L., Hartley, J.N., and
Freeman, H.D. Radon emanation characteristics of uranium mill
tailings. I_n: Symposium on Uranium Mill Tailings Management.
Colorado State University, Fort Collins, CO, 1982. p. 355.
8. Soil Survey Staff. Soil Taxonomy. Agricultural Handbook No.
436, Soil Conservation Service, U.S. Department of
Agriculture, 1975. 754 pp.
9. Soil Survey Staff. Soil areas of the midwest region. Soil
Conservation Service, U.S. Department of Agriculture. Midwest
Nat. Tech. Center, Lincoln, NE. 1972. 1 page map.
10. Soil Survey Staff. Soil moisture regime and soil temperature
map. Soil Conservation Service, U.S. Department of
-------
Agriculture. South Nat. Tech. Center, Fort Worth, TX. 1975. 1
page map.
11. Soil Survey Staff. Composite map of soil moisture and
temperature as presented by individual states. Soil
Conservation Service, U.S. Department of Agriculture. West
Nat. Tech. Center, Portland, OR. Draft of the WRRC-50
committee project. Map and text.
12. Smith, H. Soil temperature regimes of the northeastern United
States. Soil Conservation Service, U.S. Department of
Agriculture. Northeast Nat. Tech. Center, Chester, FA. 1984.
1 page map.
13. Schumann, R.R., and Owen, D.E. Relationships between geology,
equivalent uranium concentration, and radon in soil gas,
Fairfax County, Virginia. Open-File Report 88-18, Geological
Survey, U.S. Department of the Interior, Denver, Colorado,
1988. 27 pp.
14. Quandt, L.A. and Grossman, R.B. Soil water states for select
soils in the northeast region. Soil Conservation Service,
U.S. Department of Agriculture. Northeast Nat. Tech. Center,
Chester, PA. 1983. 51 pp.
15. Petersen, G.W., Cunningham, R.L., Hatelski, R.P. Moisture
characteristics of Pennsylvania soils: I. Moisture tension as
related to texture. Soil Sci. Soc. Am. Proc. 32: 271, 1968.
16. Ciolkosz, E.J., and Dobos, R.R. Penn State Soil
Characterization Laboratory Data Base. Department of
Agronomy, Penn State University. University Park, PA.
17. Thorne, D.W. and Thorne, M.D. Soil, water, and crop
production. AVI Pub. Co., Westport, CT. 1979. 353 pp.
18. Soil Survey Staff. Proceedings of the 1981 national technical
work-planning conference of the cooperative soil survey. Soil
Conservation Service, U.S. Department of Agriculture,
Washington, D.C., 1982. p. 19.
19. Soil Survey Staff. Proceedings of the 1983 national technical
work-planning conference of the cooperative soil survey. Soil
Conservation Service, U.S. Department of Agriculture,
Washington, D.C., 1983. p. 114.
20. Environmental Data Service. Climatic atlas of the United
States. Superintendent of documents, Environmental Science
Services Administration, U.S. Department of Commerce.
Washington, D.C. 1968.
21. van Wambeke, A. Calculated soil moisture and temperature
regimes of South America. SMSS Tech. Monogr. No. 2, Soil
Conservation Service, U.S. Department of Agriculture,
Washington, D.C. 1981.
22. Murtha, G.G. and Williams, J. Measurement, prediction, and
interpretation of soil temperature for use in soil taxonomy:
Tropical Australian experience. Geoderma. 37: 189, 1986.
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0.0 0.2 0.4 0.6
Fraction Saturation (F)
0.8
1.0
Figure 1: Values of Q (factor by which soil gas Rn is
increased) as a function of temperature (T°C) and
fraction moisture saturation (F)
Mud
TEMPERATURE
REGIMES
F- Frigid
M- M..IC
T • Thtrmle
H • Hyp.rth.rmlc
MOISTURE
REGIMES
ud'Udlc
u • Uitlc
0 -Arldlc
X • Xerlc
Figure 2: Generalized distribution of soil moisture
temperature regimes in the U.S.
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Table 1. Comparison of calculated and observed radon in soil gas.
Site* CRab(pCi/g)
14-80 (PA)
14-81 (PA)
14-82 (PA)
14-83 (PA)
6-10 (PA)
NC-1 (NC)
Socorro,
NM
Denver .
CO
Fairfax
Co, VA1
2.37
1.15
0.85
0.54
1.32
2.37
0.90
0.8
0.8+0.12
Ec
0.20
(0.2)
(0.2)
0.21
(0.2)
(0.2)
0.38
(0.2)
(0.2)
D(g/cm3)
1.46
1.65
1.87
1.91
1.15
1.30
1.5
(1.5)
(1.5)
P Calc(dry)d
0.45
0.38
0.29
0.28
0.56
0.51
0.35
(0.43)
(0.4)
1540
997
1096
775
542
1210
1465
560
600
obs . mean
2433
1584.
860?J
51 Oh
1300
5841
1400
1000
obs , max
4690
2560
1323
1115
1556
8674
1200
3700
Moisture^ Reference
ud
ud
ud
ud
ud
ud
a
u
ud
This study
This study
This study
This study
This study
This study
(4)
(5)
(13)
a. Sites 14-80 through 14-83 are in Centre Co., PA; site 6-10 is in Berks Co.. PA; and NC-1 is at
Justice, NC.
b. Radium or uranium in soil.
c. Measured value, or assumed as 0.2 if in parentheses.
d. Calculated from equation 1.
e. Mean value for 1-2 years by alpha-track detector at sites of this study.
f. Maximum reported value for alpha track detectors exposed 2-3 months, or single reported value.
g. Moisture regime: ud, udic; u, ustic; a, arldic
h. Alpha track detector submerged part of year.
i. Based on samples with 1.5 to 2.5 ppm eU on plot of soil gas Rn vs eU (Figure 7). The observed "mean"
is the approximate median.
-------
Table 2. Soil moisture states, percent moisture, and percent saturated pore space for a
typical sandy loam and silty clay loan soil.
Soil Moisture
State ~~ Tension~KPay
Dry
Very Dry (VD) 100, 000*-10 . 000
Slightly Dry (SD) 10.000-1,500
Moist
Slightly Moist (SM) 1.500-200
Moderately Moist (MM) 200-33
Very Moist (VM) 33-1
Wet < 1
Sandy
perc
Moisture*
0-1
1-6
6-11
11-14
14-24
Loam
ent
Pore space
Saturated**
0-4
4-24
24-44
44-56
56-96
100
Silty Clay Loam
percent
Pore space
Moisture* Saturated**
0-2 0-6
2-12 6-39
12-18 39-58
18-23 58-74
23-31 74-99
100
* Air dry (50% relative humidity); oven dry = 1,000,000 KPa
+ by weight
•ft by volume
Table 3. Estimated average soil moisture states for the soil temperature regimes of the
United States. See Table 2 for abbreviations.
Soil
Temperature
Regime
Frigid
Mesic
Thermic
Hyperthermic
Soil Moisture States
Xeric
Winter
VM
VM
MM
--
Summer
MM
SM
SD
--
Aridic
Winter
SM
SM
SM
SD
Summer
SD
SD
SD
SD
Ustic
Winter Summer
MM
MM
MM
SM
SM
SM
SM
SM
Udic
winter
VM
VM
VM
VM
Summer
MM
MM
SM
SM
-------
Table 4. Approximate mean January and July air and soil temperature (degrees C at 51 cm
depth) for the various soil temperature-moisture regime areas of the United
States. Mean annual soil temperature: Frigid 0-8°C; Masic B-15°C; Thermic 15-
22°C; and Hyperthermic > 22°C mean.
Soil Temperature Regime
Air and Soil Temperature
frigid
Air
January
July
Soil
January
July
Meslc
Air
January
July
Soil
January
July
Ib.er.Hic
Air
January
July
Soil
January
July
Hffier. thermic
Air
January
July
Soil
January
July
Xeric
-4
16
2
14
2
18
7
18
9
23
14
23
--
--
--
—
Western
Aridic
-7
18
1
16
-3
21
4
19
7
29
14
28
11
33
18
32
States
Ustic
-9
18
-2
16
-2
24
5
22
7
28
13
27
13
29
19
29
Udic
-6
16
1
14
4
21
10
21
--
--
--
—
--
--
--
—
Eastern States
Udlc
-9
19
-2
16
-2
24
5
22
7
27
13
26
18
28
22
28
-------
Table 5. Estimated winter and summer values of Q for soil moisture-temperature regimes.
Winter (Jan.)
Summer (July)
Regime* T°C
Range
Midpoint T"C
Range
Higher.
Midpoint Season
A. Silty
Fud
Mud
Tud
Hud
Fu
Mu
Tu
Hu
Fa
Ma
Ta
Ha
Fx
MX
Tx
B. Sandy
Fud
Mud
Tud
Hud
Clay Loam
-5.4
5
13
22
-2.2
5
13
19
0.6
4
14
18
2.2
7.2
13.8
Loam
-5.4
5
13
22
.74-. 99
.74-. 99
. 74- . 99
.74-. 99
.58-. 74
.58-. 74
.58-. 74
.39-.S8
.39-. 58
.39-. 58
.39-. 58
.06-. 39
.74-. 99
.74-. 99
.58-. 74
.74-. 99
.74-. 99
.74-. 99
.74-. 99
(1.39-1.60)
1.73-2.30
1.99-2.99
2.26-3.93
(1.35-1.49)
1.50-1.73
1.64-1.99
1.64-1.73
1.24-1.41
1.28-1.48
1.36-1.66
1.04-1.39
1.64-2.09
1.80-2.47
1.65-2.01
(1.06-1.10)
1.09-1.16
1.10-1.19
1.11-1.22
(1.498)
2.011
2.448
2.967
(1.418)
1.605
1.797
1.539
1.316
1.364
1.487
1.188
1.866
2.128
1.816
16.1
21.6
26.1
28
16.1
21.6
27.4
29
16.1
19
28
32
14.4
17.7
22.7
16.1
21.6
26.1
28
.58-. 74
.58-. 74
.39-. 58
.39-. 58
.39-. 58
.39-. 58
.39-. 58
.39-. 58
.06-. 39
.06-. 39
.06-. 39
.06-. 39
.58-. 74
.39-.S8
.06-. 39
.58-. 74
.58-. 74
.39-. 58
.39-. 58
1.69-2.08
1.77-2.25
1.44-1.83
1.45-1.85
1.38-1.69
1.41-1.77
1.45-1.85
1.45-1.87
1.04-1.38
1.05-1.40
1.05-1.45
1.05-1.47
1.66-2.03
1.39-1.71
1.05-1.42
1.08-1.11
1.09-1.12
1.05-1.09
1.05-1.09
1.866
1.981
1.601
1.616
1.510
1.563
1.611
1.623
1.183
1.191
1.212
1.219
1.829
1.526
1.200
S
0
W
W
S
0
W
S
W
W
W
0
0
W
W
S
S
S
a. Moisture-temperature regime. Temperature regimes: F, Frigid; M. Mesic; T, Thermic; H, Hyperthermic;
Moisture regimes: ud. udic; u, ustic; a. aridic; x, xeric.
b. Season with highest predicted Rn: S, summer; W, winter; O, subequal.
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