United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S8-90/061 Jan. 1991
&EPA Project Summary
Radon Mitigation Studies:
Nashville Demonstration
Bobby E. Pyle and Ashley D. Williamson
In this EPA radon mitigation
demonstration project, 14 houses in
the Nashville, TN area with indoor
radon levels of 5.6 - 47.6 pCi/L* were
mitigated using a variety of tech-
niques. These techniques were de-
signed to be the most cost-effective
methods possible to implement, and
yet adequately reduce the radon
levels to <4 pCi/L. For the crawl
space houses, these techniques in-
cluded sealing the openings between
the living areas and the crawl space
and then passively venting the crawl
space, depressurizing the crawl
space, depressurizing under poly-
ethylene sheeting in the crawl space,
and depressurizing the crawl space
soil itself. For the basement and
basement-crawl space combination
houses, the techniques included sub-
slab pressurization and depressuriza-
tion, block wall depressurization, and
combinations' of these techniques
with some of those above for the
exposed soil areas. Post-mitigation
worst case radon levels in these
houses were generally from <1 to
about 5 pCi/L with one house near 15
pCi/L. These houses are currently be-
ing followed with alpha-track detec-
tors to assess the long term
exposure levels.
This Project Summary was
developed by EPA's Air and Energy
Engineering Research Laboratory,
Research Triangle Park NC, to
announce key findings of the research
project that is fully documented in a
* Readers more familiar with metric units may
use the factors listed at the end of this
Summary to convert to that system.
separate report of the same title (see
Project Report ordering information at
back).
Introduction
Purpose
The primary purpose of the work
described in this report was to develop
cost-effective techniques for radon
mitigation in crawl space houses in the
Nashville Metropolitan Area. These
techniques should also be applicable to
crawl space designs in other parts of the
country. Other types of houses mitigated
during this study were basement houses
in which the basement was excavated
from an existing crawl space. Unlike
many houses with basements and ad-
joining crawl spaces, in many of these
houses there remain areas of exposed
soil in open communication with the
basement. This type of construction is
also typical of the mid-South, offering yet
another opportunity to expand the
existing data base of radon reduction
techniques.
Another purpose for this mitigation
demonstration was to train local
contractors in the proper techniques of
radon mitigation and thereby encourage
radon mitigation efforts by the private
sector. This will hopefully result in
providing sources of cost-effective and
successful mitigation installations to
homeowners in this region. The results
described in this report are the initial
results of an ongoing, EPA funded, radon
mitigation demonstration in existing
houses in the Nashville area.
History
The State of Tennessee, operating
through the Tennessee Department of
Printed on Recycled Paper
-------
Health and Environment's (TDHE's)
Division of Air Pollution Control and in
cooperation with the U.S. Environmental
Protection Agency's (EPA's) State Radon
Survey Program, conducted a survey to
identify areas in Tennessee with the
potential for elevated radon levels in
privately ov/ned houses. During the
months of January through April 1987,
approximately 1.787 measurements were
carried out in single-family owner-
occupied houses Based on the results of
that survey, the TDHE estimated that
84.2% of the houses in the state have
radon levels <4 picocuries per liter
(pCi/L). 14.5% have levels of 4 - 20 pCi/L,
and 1.3% have levels >20 pCi/L. The
highest level detected in this survey was
99.9 pCi/L From the geological character
of the soils and rocks in the various parts
of the state, four risk levels for indoor
radon were developed (High, Inter-
mediate, Moderate, and Low). The High
Risk areas form a two-pronged band
through the central part of the state
including most of Davidson County,
which also happens to be one of the most
populated counties in the state
Problem
Tennessee, along with several other
states, contain a substantial number of
crawl space houses for which there are
very little data regarding the appropriate
technique to use for radon mitigation.
This construction type represented 16 -
28% of the housing starts nationwide
between 1963 and 1983. States having a
significant fraction of crawl space houses
include Oregon, South Carolina,, North
Carolina, Nevada, Tennessee, Delaware,
Arkansas. New Jersey, Idaho, Washing-
ton, West Virginia. Alabama, and Virginia.
Several other states have <25% each.
Thus crawl space houses represent a
significant fraction of the existing housing
stock in diverse regions of the U.S.
In general, crawl space houses can be
defined as those in which a part or all of
the living areas of the house are built
over an enclosed area containing
exposed earth. Prior to the collection of
recent radon data, crawl spaces were
even considered to be a viable alternative
for radon control in new construction.
House Screening and Selection
The houses for this demonstration
were selected from respondents to a
media announcement for homeowners
whose houses had previously been
tested and found to contain radon levels
>4 pCi»L). From about 100 respondents,
30 houses werej selected for screening as
possible candidates for participation in
the radon mitigation demonstration.
These 30 houses in Davidson and
Williamson Counties (in and near
Nashville, TN) |were screened between
September 8 and 11,1987, by scientists
from EPA, TDHE, Southern Research
Institute (SRI), and Camroden Associates.
The purpose of the screening effort was
to evaluate the houses for possible
inclusion in Plhase 1 of the Middle
Tennessee -radon mitigation demonstra-
tion. ]
As a result of the screening, 15
houses were selected for the mitigation
demonstration: program. The houses
selected include nine crawl space
houses, three Houses with basements
converted frqm crawl spaces, two
combination pasement/crawl space
houses, and onjs slab-below-grade house.
This cross section is representative of the
existing housesj in the Nashville area and
in portions of other states in the mid-
south. \
Intensive Diagnostic Evaluation
of Selected Houses
An additional extensive diagnostic visit
to each house was conducted between
October 21 and 27, 1987 During this
visit, measurements and investigations
were carried out to develop radon reduc-
tion plans that would fit into the overall
research objectives of the project. Char-
coal canisters (CCs) and alpha track
detectors (ATDs) were placed in either
the crawl space or the basement and on
the first habitable level of each house to
obtain a pre-mitigation radon background.
In each location, duplicate detectors were
collocated to determine the precision of
the measurement devices. The CCs were
recovered by bie homeowner after 48
hours and mailed to the analysis lab-
oratory (Scientific Analysis, Inc., Mont-
gomery, AL). The ATDs were left in the
houses until just prior to installation of .the
mitigation equipment. At that time, they
were returned to the supplier for analysis
(Terradex Corp., Glenwood, IL). The
results from the collocated CC measure-
ments in October 1987 are shown in
Table 1.
Development of Mitigation
Plans
The mitigation techniques for each of
the 15 houses were developed by
Camroden Associates and SRI following
the diagnostic visits to each of the
houses in Octo'ber 1987. For each of the
houses a 2- or 3-phase mitigation strat-
egy was developed following guidelines
established by the EPA Project Officer.
These guidelines were as follows:
• Phase 1 should be a low-cost
alternative {less than $500 if possible)
that can be easily removed or turned
off
• Phase 2 should be a technique with a
high probability of lowering the house
radon levels to 4 pCi/L or less and of
moderate cost ($500 - $2,000)
• Phase 3 should be as close to a
guaranteed reduction method as
possible with correspondingly higher
cost ($2,000 - $5,000).
During the planning stages it was
anticipated that no more than 25% of the
houses would require implementation of a
Phase 3 system. To obtain the maximum
scientific benefit, it was also assumed
that Phase 2 systems would be installed
and tested even if Phase 1 systems
achieved levels <4 pCi/L.
The mitigation strategies for each
house were developed using the in-
formation obtained during both the
screening and diagnostic visits. This in-
formation incSuded the type of house
construction, condition of the house
flooring, whether there was heating and
air conditioning ducting in the crawl
space, the extent and condition of any
existing polyethylene sheeting under the
house, the existence of a basement and
the condition of the slab, the existence of
any exposed soil areas in the basement,
and the condition of the soil in the crawl
space From these site conditions and a
list of the possible mitigation systems
that could be applied to the Nashville
houses, a matrix of mitigation strategies
was developed that would hopefully eval-
uate, demonstrate and allow comparisons
of each technique to arrive at methods
that would be both successful and cost-
effective for houses similar to those in
Nashville. The mitigation matrix is shown
in Table 2.
Mitigation of the Nashville
Houses
Local contractors in the Nashville area
carried out most of the mitigation
installations. The houses mitigated during
December 1987 were DW 31, DW 43,
DW 82, DW 60, DW 66, and DW 90. All
of these are crawl space houses except
DW 43 which is a basement- converted
from a crawl space. The remaining
houses were mitigated either singularly,
or at most, two houses were mitigated
concurrently. The only house not
•mitigated during this first year (1987-88)
-------
Table 1. Nashville Pre-rnitigation Two-day Charcoal Results for October, 1987 (pd/L)
House ID (DW) Crawl Space Basement 1st Habitable Level
03
12
14
27
29
31
41
43
58
60
66
78
82
84
90
22.0
NA
NA
64.1
13.2
29.0
NA
NA
NA
34.8
20.0
NA
27.3
8.9
18.0
21.9
-AM
NA
65.2
b
16.5°
NA
NA
NA
32.2
19.2
NA
27.2
9.1
16.9
NAa
26.4
33.2
NA
NA
NA
30.1
48.3
43.0
NA
NA
41.2
NA
NA
NA
NA
25.7
31.0
NA
NA
NA
28.6
48,4
43.5
NA
NA
42.3
NA
NA
NA
9.6
20.2
16.0
39.9
5.8
22.7
18.7
16.5
36.1
20.5
12.1
21.8
15.4
5.7
8.4
9.5
19.1
16.0
40.3
5.7
23.2
19.2
17.0
36.0
20.5
9.9
21.4
14.2
5.5
7.7
a Not applicable
b This detector lost
0 Top left off can in shipment
of the project was DW 58. This house
was scheduled for mitigation during the
early part of the second year of the
project (1988-89).
Additional CC measurements were
carried out just prior to mitigation work on
each of the houses. These measure-
ments were carried out over either 48 or
72 hour periods between November 29,
1987, and April 11, 1988. These later
measurements occurred primarily during
the peak heating season for the Nashville
area. These later results are shown in
Table 3. In most cases the radon levels
were higher than those measured in
October (Table 1).
Discussion of Results
One of the objectives of this research
project was to develop cost- effective
techniques for radon mitigation in crawl
space, basement, and combination
houses in the Southeastern regions of the
U.S. In order to accomplish this task, the
houses in this study were not simply
mitigated but were used as vehicles to
test concepts of the mitigation process.
While the same tests were not carried out
at each individual house, the results can
be grouped by house geometry for
comparision and discussion.
Crawl Space Houses
Six mitigation techniques were
evaluated in the nine crawl space houses
as shown in the mitigation matrix of Table
2. Except for the IPCS (isolate and
pressurize the crawl space) and the IOCS
(isolate and depressurize the crawl
space) methods, all the techniques were
applied to two or more houses. The
resulting evaluation of these techniques
based on continuous radon monitor CRM
data is shown in Table 4, and based on
CC measurements (pre- and post-
mitigation) is shown in Table 5.
ICS - Isolation of Crawl Space
The technique of isolating the living
areas from the crawl space and thereby
stopping or greatly reducing the radon
entry was tried on houses DW 29 and
DW 66. In theory the method seemed
simple and straightforward. In practice
the method was difficult to apply. In the
Nashville houses the sub-flooring was
typically 1 by 6 in. boards laid diagonally
to the floor joists. Air movement, from the
crawl space up into the cracks between,
these boards, could be demonstrated at
every location. The air flow was much
greater near the points at which the HAC
cold air return plenum was constructed
between the floor joists. Sealing the
cracks between the sub-flooring boards
was difficult and achieved only limited
success, even in houses that had no
insulation under the floor. In houses with
insulation, it was more time consuming
(and more costly) and even jess
successful. Attempts to seal the floor,
using a variety of spray foams and plastic
liners applied or attached to the floor
joists, were ruled out as too expensive
and therefore not cost-effective. The floor
openings that were routinely sealed in
these houses were the utility penetrations
(electrical wiring, water and gas pipe
entries, and waste pipe penetrations for
drains a~nd under the bath tub openings)
and the larger openings in the box joists
used for air return plenums.
In the two Nashville houses (DW 29
and DW 66) where this ICS technique
was applied, the results of sealing alone
were not impressive. In DW 29 the radon
reduction was only about 3% and in DW
66 the levels actually increased by about
15%. These reductions were based on
CRM measurements in the living space
of the houses as shown in Table 4. No
CC,measurements were carried out for
this technique.
Thus it appeared that attempts at
isolating the crawl space from the living
areas are a questionable means of
reducing the indoor radon levels when
used as the only mitigation technique. .
IVCS - Isolation and ventilation of
crawl space
This technique of isolating the crawl
space and opening the existing
foundation vents was tried on four
houses: DW 03, DW 60, DW 82, and DW
90. The radon reductions ranged from
-------
-60% (an increase) for DW 82, to 75%
(decrease) for DW 90 as shown in Table
4. No CC measurements were carried
out for the IVCS technique.
In the worst case, DW 82, the garage
had been converted to a den and was
open to the rest of the living areas. In
building the den, the floor was
constructed using typical wood floor joist
techniques. Unfortunately, the floor joists
were so close to the old garage slab that
access to this area was impossible. The
number of entry points into the den was
unknown. For the remainder of the house,
(he overhead floor was readily accessible
from the craw! space. In this area all the
major openings (those >0.25 in.) and
many of the minor cracks and openings
were closed. However, the radon levels in
the living area increased.
In summary, for the applications here,
it appeared that isolation and passive
ventilation of the crawl space alone would
not likely reduce the levels of upstairs
radon <4 pCi/L level unless the leakage
area between the house and crawl space
was or could have been reduced to very
low values and ihe ventilation area of the
crawl space increased.
IOCS - Isolation and
Depressurizdition of the Crawl
Space
Although three houses were scheduled
for mitigation by the technique of
isolation and depressurization of the
crawl space, ohly one house (DW 82)
actually had the system implemented.
The reduction achieved was rather
dramatic. Based on the CRM data, the
levels in the den were reduced by 90%,
and from the pr'e- and post-mitigation CC
measurements the reduction was 96%;
however, the levels in the crawl space
increased. The levels here rose from 29.8
to 61.7 pCi/L, arj increase of 107%. While
this posed no problem for this house, it
could lead to problems in others. If there
were HAG ducts in the crawl space, the
increased radon levels could leak into the
return ducting and be distributed
throughout the house. Also, since the
openings between the living area and the
crawl space can never be entirely closed,
fairly large amounts of conditioned air
could be drawn into the crawl space,
resulting in a substantial energy penalty
for the homeowner. In house DW 82 it
was found that the foundation walls had
enough leakage areas that the major
portion of the air flow into the crawl space
was from outdoors. Thus no substantial
energy penalty was expected.
IPCS - Isolation and
Pressurization of the Crawl
Space
The technique of isolation and
pressurization of the crawl space was
originally scheduled to be tried as a
Phase 1 mitigation on house DW 82.
However, at the time of installation, there
were several uncertainties as to the
Table 2. Mitigation Techniques ;
Tech- Mitigatidn Phase by House ID (DW)
nique 03
ICS
IVCS 1
/DCS
IPCS
SSoD
SPD 2
SSD-W
SSD-N
SSD-P
SSBWD
SSSPD
PB
SSP
DTD
27
2
3
1
29
1<>
2
31
2
1
60
1
2
66
1
2
82
2
1
i
84
1
2
90
1
2
43
2
1
3
58
1
2
78
2
1
3
4b
5"
12
1
2
3
14
1
2
3
41
2
1
3
3 = Numbers refer to phases of mitigation application.
>> = In house DW 78, two additional, phases were scheduled.
ICS = Isolation of Crawl Space.
IVCS = Isolation and Ventilation of Crawl Space.
IOCS = Isolation and Dep'ressurization of Crawl Space.
IPCS = Isolation and Pressurization of Crawl Space.
SSoD = Sub-soil Depressurization.
SPD = Sub-poly Depressurization.
SSD-W = Sub-slab Depressurization Wide Pit.
SSD-N = Sub-slab Depressurization Narrow Pit.
SSD-P = Sub-slab Depressurization Progressive Pit.
SSBWD = Sub-slab + fl/oc/f Wall Depressurization.
SSSPD = Sub-slab + Sub-poly Depressurization.
PB = Pressurization of Basement.
SSP = Sub-slab Pressurization.
DTD = Drain Tile Depressurization.
-------
1
Table 3. Nashville Pre-mitigation Collocated Charcoal Results (Nov'87 to Apr'88) (pCi/L)
House ID (DW) Start Date Stop Date Crawl Space Basement 1 st Habitable Level
03
12
14
27
29
31
41
43
58
60
66
78
82
84
90
4/08/88
2/05/88
2/08/88
1/22/88
2/19/88
11/29/87
1/22/88
11/29/88
3/29/88
12/01/87
12/01/87
2/19/88
11/29/87
3/28/88
12/01/87
44/11/88
2/08/88
2/10/88
1/25/88
2/22/88
12/1/87
1/25/88
12/1/87
3/31/88
12/3/87
12/3/87
2/22/88
12/1/87
3/30/88
12/3/87
21.6
NA
NA
45.7
27.1
29.4
NA
NA
NA
55.2
26.1
NA
29.5
9.4
29.6
22.1
NA
NA
46.4
27.2
30.3
NA
NA
NA
55.0
25.9
NA
30.0
9.7
29.7
NAa
10.3
89.9
NA
NA
NA
19.2
58.6
56.2
NA
NA
41.2
NA
NA
NA
NA
11.8
86.7
NA
NA
NA
19.3
59.7
57.3
NA
NA
41.5
NA
NA
NA
7.0
7.7
47.1
32.8
15.9
26.3
13.3
23.2
20.4
27.9
12.3
19.6
14.7
1.5
15.8
7.1
7.8
48.1
33.0
16.2
25.7
13.4
22.9
27.4
27.8
11.9
19.9
1.5.1
2.3
15.8
Not applicable
Table 4.
Percent Radon Reduction for Each Crawl Space Mitigation Scheme (Based on
Average Continuous Monitor Data in Living Area)
House ID Code (DW)
Mitigation Technique
Isolate Crawl Space (ICS)
Isolate Vent C/S (IVCS)
Isolate Dep. C/S (IDCS)
Isolate Pres. C/S (IPCS)
Sub-Poly Dep. (SPD)1 Point
(SPD)2 Point
Sub-Soil Dep. (SSoP) 2 Pts
(SSoP) 4 Pts
03
18
69
27
60
87
29
3
64
84
31
61
84
60
27
77
66
-15a
72
82
-60
90
84
58"
86C
90
75
92
a Negative values indicate increased radon levels.
b Worst case condition.
c House open during part of test.
correct method of installing the available
device (Current Indoor Air Systems, Inc.,
Boulder, CO, model 300). Consequently,
installation of the IPCS technique was
cancelled for this house. The device was
later installed in another crawl space
house, DW 60, but no data as to its
operation or effectiveness were available
at the time of this report.
SSoD - Sub-Soil
Depressurization
The technique of depressurizing the
soil directly was implemented on two
houses, DW 31 and DW 84. The soil in
the crawl space of DW 31 was fairly
loose and permeable to air movement (as
measured during the diagnostic visits in
October 1987). The soil under house DW
84 was quite different. The surface of this
soil was very hard and had large
desiccation cracks up to 0.5 in. wide
throughout. The system installed in each
house was basically identical. Four,
evenly spaced, suction pits about 24 in.
wide and 12 - 18 in. deep were dug in the
soil and connected to a single fan (model
K6, R.B. Kanalflakt, Inc., Sarasota, FL)
exhausting to the outdoors. The area of
the crawl space under DW 31 was about
780 ft2 and under DW 84 was about 1360
ft2. Thus the number of suction points per
square foot of soil was one per 195 ft2 for
DW 31 and one per 340 ft2 for DW 84.
The pressure field extension in the soil
was measured by carefully drilling a
series of 3/8-in. diameter holes into the
soil. These holes were generally 12-18
in. deep, although in some instances the
soil was sufficiently loose that it tended to
slide into the bottom of the hole. In those
cases it was difficult to estimate the
depth of the test hole. The test holes
were located at varying distances from a
suction pit. In carrying out the
measurements, a 12 in. length of 1/8 in.
diameter steel tubing was carefully
inserted into the hole. The top of the hole
was sealed as tightly as possible by
means of a rubber stopper at the top of
the tube. The steel tube was connected
to an electronic manometer (Neotronics,
Gainesville, GA, model EDM-I) with a
sensitivity of 0.001 in. of water.
The depressurization in the soil could
reliably be measured at distances of up
-------
to 6 ft from the suction pit, and in several
cases up to 12 ft. For House DW 31, the
pressure field dropped to about 10% of
the pit pressures within 2 ft and around
1% at distances of about 6 ft. In the soil
under House DW 84, the pressure
decrease was even more drastic. Here,
the pressure dropped to approximately
1% of the pit pressure within 2 ft,
although some pressures were measured
as far out as 6 ft.
These results were consistent with the
observed nature of the soils under the
two houses. The soil under DW 31 was
moderately loose and should have had a
higher permeability than the soil under
DW 84, which was hard packed clay.
Thus, each suction point of the system
was capable of producing a measurable
soil depressurization over an area of at
least 113 ft2 and perhaps as large as 452
ft2.
In terms of the reduction of the radon
levels in the living space, the SSoD
technique achieved reductions of
approximately 85% as seen in Table 4
for the CRM measurements, and up to
92% based on the CC measurements as
shown in Table 5. Unfortunately, the
method has been applied to only two
houses. If the technique is to be used on
any large scale it should be tested for
other types of soils and at different
locations.
SPD - Sub-Poly Depressurization
The technique of depressurizing the
soil under a plastic membrane had the
widest application in the current group of
houses. Six of the nine crawl space
houses had an SPD system installed and
evaluated. This mitigation technique is a
variation of the successful sub-slab
depressurization method used for slab-
on- or below-grade houses. In many of
the nine houses there was at least some
polyethylene sheeting covering the dirt in
the crawl space. This covering is a
popular method used to control moisture
in living areas. The intent of this
technique was to supplement the existing
sheeting with new 6 mil sheeting to
completely cover the exposed dirt. This
gaslight barrier formed a small-volume
plenum above the soil in which the radon
gas collected. At one or more suction
points, a shallow pit approximately 24 in.
wide and 12 in. deep was dug in the soil.
Each hole was then covered with a 36 by
36 in. piece of treated plywood. The 4 in.
diameter polyvinyl chloride (PVC) suction
pipe was mounted through the plywood
and the sheeting sealed around the pipe
and plywood. A fan was installed to pull
the collected soil gas from under the
sheeting and exhaust it outdoors. Initially,
no attempts vyere made to seal the
sheeting to the foundation walls or to any
support piers located in the crawl space.
The sheets were laid directly on the earth
in most cases overlapping at least 1 ft at
the joints.
Only one house had any type of
perforated pipe or ducting network
installed under; the sheeting. In house
DW 27, drainage material (Enkadrain
Type 9010, BASF Corp. Fibers Div.,
Enka, NC) was placed under the sheeting
to improve airj flow. In general, this is
necessary only; where the soil surface is
excessively hard and smooth or the crawl
space area is exceptionally large (DW
27). When excessive air leaks prevented
effective removal of the radon, the joints
between the sheets were sealed with a
bead of caulkipg (DW 27). Also, where
the number of support piers was large or
located close to the suction point (within
12 ft) the shebting was sealed to the
piers nearest the suction points with
caulking and wood strips (DW 03, DW 29,
and DW 60). In one house (DW 27) the
sheeting waŁ also sealed to the
foundation walls to reduce air leaks.
Pressure ujnder the sheeting was
measured in all but one house (DW 27).
Measurements utilized an electronic
micromanometer (Neotronics, Gainesville,
GA, model EDM-I) with a sensitivity of
0.001 in. of water column. In each house,
measurable pressures were detected at
distances of up to 6 ft from the suction
point, and in some cases up to 12 ft.
Farther away, rthe pressures were not
measurable with the manometer but, in
most cases, air flow under the sheeting
was observed using a smoke tracer.
In two houses (DW 27 and DW 29), a
second suction point was added to
increase th|e extension of the
depressurizatibn under the sheeting.
These two hoUses had the largest crawl
space area of any of the houses. In both
cases, the same fan was used for both
suction points.
Based upon the CRM data, the SPD
technique achieved reductions ranging
from 60 - 92% (Table 4). Based on pre-
and post-mitigation CC measurements
(Table 5), the reductions range from 45 -
85%.
In summary, the SPD technique was
the most widely used and appears to be
the most applicable to crawl space
houses in which the upstairs levels are in
the 10 - 30 pCi/L. There are questions
regarding the ; technique that have not
been fully answered in this study. In the
SPD installations, the material used for
the houses in this study was standard,
builder-grade, ,6 mil polyethylene sheet-
ing. The properties of this material
(thickness, puncture resistance, perme-
ability, and resistance to ultraviolet light
and temperature degradation) vary from
location to location in a single sheet and
perhaps from source to source. Also, the
tear and puncture resistance are not
believed to be sufficiently high to
withstand normal traffic (such as by
service personnel from utility companies,
termite control organizations, or the
homeowner) that might be expected in a
crawl space. Other materials such as
cross-laminated high-density polyethyl-
ene films or lagoon liners need to be
examined for use in these applications.
Other questions that have not been
addressed include, the amount of energy
penalty resulting from the SPD system
withdrawing house air down into the crawl
space, and the effects of the system
upon the house frame as a result of
moisture;removal from the crawl space.
Basement or Combination
Houses
One- or two-point sub-slab depressur-
ization (SSD) systems were installed in
five basement/combination houses. Mea-
surements of the pressure field extension
under the slab showed a wide, shallow pit
in the soil where the pipe penetrated the
slab to be more effective than a narrow,
deep pit. The surface area of soil
exposed in the pit was found to be more
important than the shape of the pit. Sub-
slab pressure, measured at a fixed
distance from the suction hole, increased
dramatically as the size of the hole in the
soil under the slab penetration was
increased. In mapping the pressure field
extension as a function of the distance
from the suction point, the pressure
became unmeasurable farther than 20 -
25 ft from the suction point.
The radon reductions achieved were
28 - 98%, as shown by the CRM data in
Table 6. The house with the greatest
reduction (DW 41) had a single suction
point installed near the edge of the slab
under the front foyer. The slab had good
communication which allowed the sub-
slab area to be ventilated from a single
point. Also, the area of exposed soil
located under the front porch was small
(less than 100 ft2) and was easily isolated
from the living areas by construction of a
treated plywood barrier wall with a sealed
access door.
The lowest reduction for SSD was also'
achieved using a single suction point
(DW 43). However, in this house the
communication under the slab was poor
-------
Table 5. Nashville Radon Reduction Summary (Based on Charcoal Canister Measurements
in pCi/L)
Crawl Space Basement 1st Floor
House ID (DW)*
03
27
29
31
60
66
82
84
90
43
58
78
12
14
41
Pre
21.9
46.1
27.2
29.9
55.1
26.0
29.8
9.6
29.7
NA
NA
NA
NA
NA
NA
Post
A/Ob
9.2
5.7
2.8
2.0
23.3
7.6
61.7
ND
7.1
NA
NA
NA
NA
NA
NA
%Red
ND
80
79
90
93
58
71
-107<*
ND
76
NA
NA
NA
NA
NA
NA
Pre
NA<=
NA
NA
NA
NA
NA
NA
NA
NA
NA
59.2
56.8
41.4
11.1
88.3
19.3
Post
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
4.8
ND
2.8
4.4
11.3
3.0
1.4
%Red
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
92
ND
93
61
87
97
93
Pre
7.1
32.9
16.1
26.0
27.91
12.1
14.9
1.9
15.8
23.1
23.9
19.8
7.8
47.6
13.4
Post
2.6
5.3
7.0
3.0
2.2
15.2
2.8
0.7
ND
2.4
1.4
ND
1.5
4.8
3.8
1.0
%Red
64
84
56
82
92
45
77
96
ND
85
94
ND
92
39
92
93
Notes
1,10
2
1
3
4
1
1
5
4,11
1
6
12
6,13
8
9,14
9,15
7
a See Table 2 for mitigation codes
b No Data
c Not Applicable
d Negative values indicate increased radon levels
Notes: 1. ICS + SPD
2. Two Point SPD
3. ICS + Two Point SPD
4. Four Pit SSoD
5. /DCS
6. Two Point SSBWD
7. SSD-W
8. Two Point SSD-W
9. Two Point SSBWD + SSSPD
10. No measurements in crawl space
11. No Post-Mitigation CC measurements
12. House not mitigated
13. No duplicate done upstairs
14. Basement readings on top of crawl space wall
15. Basement readings 4 ft from floor and 6 ft from C/S wall
so that an additional suction point was
required. Also, this house had a cement
capped perimeter shelf around most of
the basement. This shelf was constructed
of coarse cinder blocks which allowed
radon gas to enter the basement through
their face openings. Incorporating block
wall suction achieved a reduction of 42 -
60%. Because of the high porosity of the
block comprising the wall, acceptable
reductions were not achieved until the
wall was coated with a sealer (SurWall
Brand). The final reduction for this house
was 92%.
For house DW 12 the exposed soil in
the crawl space was covered with 6 mil
polyethylene sheeting but no
depressurization under the sheeting was
implemented. Final reduction for this
house was 92%.
The exposed soil in the crawl space of
house DW 14 was covered with 6 mil
sheeting sealed to the surrounding walls.
Depressurization under the sheeting was
accomplished by breaking through the
adjoining wall (and under the sheeting)
with the sub-slab system. The open block
tops of the wall were filled with expanding
closed-cell foam. This combination
achieved a reduction of 85%. After the
top of the wall was covered with treated
2 x 12 in. boards sealed to the top of the
blocks with urethane sealant a final
reduction of 93% was achieved.
The remaining basement/combination
house (DW 78) had a two-point sub-slab
suction system installed and achieved a
radon reduction of 78%. The area of the
crawl space in this house (600 ft2) was
roughly twice the area of the slab (300
ft2) and was probably the major source
for radon entry into the basement. After
covering the soil with 6 mil sheeting
sealed to the slab perimeter wall and
sealing the open block tops of that wall
with expandable foam, the SSD system
was extended into the wall and thus
under the sheeting covering the soil. The
-------
Table 6. Percent Radon Reduction for Each Basement Type Mitigation
Scheme (Based on Continuous Monitor Data in Basement)
[
Mitigation Technique I
Sub-Slab Pressurization (SSP) j
Sub-Slab Depressurization (SSD)>>
SSD + Block Wall Depress.(BWD) ,
SSD + BWD + Seal Exposed Soil
SSD + BWD + Seal Wall Face
43
28C
42-60
92
58
House
78
78
93
D(DW)
12
92
14
70
85
93d
41
70a
98C
» Single sub-slab depressurization "point
t> Unless specified otherwise, all SSD systems include two suction points
c Single sub-slab pressurization point
a Top of wall sealed ',
final reduction was 93% as measured in
the basement with the CRM.
The only house in which the SSP
technique was implemented was DW 41.
Here the fan was initially installed to force
outside air under the slab. The reduction
achieved (70%) was surprising in view of
the fact that a polystyrene foam
beadboard at the edge of the slab
allowed air from under the slab to easily
enter the basement interior via the
finished walls and baseboards. This entry
was verified by use of a smoke bottle and
was confirmed by the homeowner as an
increase in humidity and odor in the
basement Concurrently, measurements
of the levels of termaticide (aldrin) in two
rooms of the basement were increased
from premitigation concentrations of 0.3
and 0 12 pg.'ms to levels of 1.40 and 1.03
ng?m3 with pressurization under the slab.
Subsequent measurements in these two
rooms after the system was run in the
sub-slab depressurization mode for
approximately 10 weeks showed the
levels of aldrin (and dieldrin) to be
< 0.066 vgmz. Thus, while SSP can be
effective in lowering radon levels, it could
also lead to other problems for the
homeowner.
Conclusions and
Recommendations
Several techniques have been tested
in crawl space and combination houses
typical of the Southeast. Based on the
results described in this report, the
following conclusions can be drawn.
Methods Applied to Crawl
Space Houses
• Isolation of the crawl space from the
living areas of the house was found to
be difficult if not impossible to achieve
and its use as the only mitigation
technique is; risky, questionable, and
not recommended.
• Isolation and! passive ventilation of the
crawl space using only the existing
foundation vents was found to be
ineffective due to the limited area of
the vents installed in most houses.
This technique is not recommended
as the sole mitigation method even if it
is combined1 with covering the soil in
the crawl space with some type of
plastic film. iWithout active ventilation
under the film, the radon levels in the
living areas will, in all likelihood, not be
reduced to apceptable limits.
• Isolation and depressurization of the
crawl space was found to be an
effective method of reducing the radon
levels in the living areas of one house.
However, this technique can
substantially, increase the levels in the
crawl space; This technique may be
difficult to apply when there are cold
air return ducts in the crawl space and
could also incur an energy loss from
the conditioned air space above.
o Sub-soil depressurization was found to
be an effective technique for two
houses in this study. Its effectiveness
is greatly influenced by the soil con-
ditions in the crawl space and should
be used with caution until additional
results from other geographic loca-
tions and soil conditions become
available. .
« Sub-membrane depressurization in the
crawl space was the most widely
applicable technique in this study and
proved a reliable method of removing
radon before it enters the crawl space.
The number of suction points needed
under the membrane will depend on
both the crawl space area and the
condition of|the soil. For areas > 1,200
ft2 or crawl space with excessively
damp soil [Conditions, at least two
suction points should be installed at
opposite ends of the crawl space. The
membrane used in these houses was
standard 6 mil clear builder's
polyethylene. However, due to its
limited puncture and tear resistance
and its instability to ultraviolet (UV)
light degradation, it is not recom-
mended for more general use. Instead,
a cross-laminated, high density poly-
ethylene material with UV stabilizers is
recommended. Sealing of the mem-
brane lap joints and to the surrounding
foundation walls and support piers is
recommended at locations within 12 ft
of the suction point(s) and at all
locations if the crawl space is
exceptionally large. In this case it may
even be necessary to install some
type of drainage system under the
membrane to improve the air flow.
Methods Applied to Basement
or Combination Houses
• Sub-slab pressurization was found to
be somewhat effective for radon
reduction in one house but not as
effective as depressurization of the
sub-slab region. It also can produce
other problems such as increased
moisture or even increased levels of
termaticide in the basement. It may be
difficult to apply when sub-slab
communication is poor.
• Sub-slab depressurization (or sub-slab
ventilation) was found to be an
effective technique in the five houses
studied even when the sub-slab
communication was not very good. In
thesei cases, more than one suction
hole will likely be required. The soil
under the slab, at the suction point
should be excavated to at least a
diameter of about 36 in. and to a
depth of about 12 - 18 in. The amount
-------
of soil surface area exposed in the pit
is more important than the depth or
shape of the pit. Filling the pit with
crushed stone was not found to be
necessary.
• Block wall depressurization was found
to improve the effectiviness of sub-
slab systems in the three houses in
which it was applied. In these houses,
large areas of the block wall were
either below grade or separated the
crawl space from the basement.
Sealing of the wall was found to be
necessary in one case in which the
porous blocks short-circuited the
negative pressures generated under
the slab.
• Consideration of the exposed soil in
direct communication with the
basement was found to be essential to
lowering the radon levels to
acceptable limits. The methods used
for these areas are similar to those for
crawl spaces above.
Mitigation Costs
The actual contractor costs for
installing the systems in the crawl space
houses of this study were $850 - $1,859
with an average of $1,282. For the
basement and basement-combination
houses, the costs were $785 -$1,995 with
an average of $1,496. However, these
costs do not include any time spent in
diagnostics or in design of the mitigation
systems. The expenses incurred by
private mitigators for diagnostics and
design could increase the costs by as
much as 50%.
Recommendations for
Additional Research
Questions need to be addressed in
future studies of mitigation using the
techniques described above. In the sub-
poly depressurization technique, the
material used for these houses was
standard builder's grade 6 mil
polyethylene sheeting. The properties of
this material (thickness, puncture
resistance, permeability) vary from
location to location in a single sheet.
Also, the tear and puncture resistance is
not believed to be sufficiently high to
withstand normal traffic (such as by
service personnel from utility companies,
termite control organizations, or the
homeowner) that might be expected in a
crawl space. Other materials such as
cross-laminated high-density poly-
ethylene films or l.agoon liners need to be
examined for use in these applications.
In houses where sub-slab depressur-
ization cannot be made to function cost-
effectively, other techniques such as
basement pressurization need to be
developed and demonstrated.
Conversion Factors
Readers more familiar with metric
units may use the following factors to
convert nonmetric units used in this
Summary to their metric equivalents.
Nonmetric Multiplied by Yields Metric
ft
fp
in.
in. H2O
mil
pd/L
0.305
0.093
2.54
0.249
25.4
37.0
m
cm
kPa
Bq/m3
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Bobby E. Pyte and Ashley D. Williamson are with Southern Research Institute,
Birmingham, AL 35255-5305.
Michael C. Oslborne is the EPA Project Officer (see below).
The complete report, entitled "Radon Mitigation Studies: Nashville
Demonstration," (Order No. PB 90-257 791/AS; post: $31.00, subject to
change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
Official Business
Penalty for Private Use $300
EPA/600/S8-90/061
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