United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/SR-93/043 May 1993
vxEPA Project Summary
Radon Reduction and Radon-
Resistant Construction
Demonstrations in New York
Ian Nitschke
The existing house evaluation dem-
onstrated radon mitigation techniques
in houses where the indoor radon con-
centrations exceeded 4 pCi/L. Results
demonstrated that sealing all acces-
sible foundation penetrations in the
basement effectively reduced the ra-
don concentration, although not below
4 pCi/L, and that sealing aids the effec-
tiveness of an active depressurization
system. Active depressurization sys-
tems were usually successful in achiev-
ing 4 pCi/L. The footing drain, sub-slab,
and basement walls were all success-
fully depressurized using a standard
technique after grab samples or radon
sniffing techniques were used to iden-
tify the radon entry source(s). Base-
ment pressurization also effectively
reduced the radon level below the EPA
guideline at one site. Water aeration
systems effectively mitigated radon
from residential water supplies although
the system tested was large and noisy.
Activated charcoal filters adsorbed the
radon in water but eventually became
an unacceptable source of gamma ra-
diation. The inspection of houses where
radon mitigation systems were installed
in 1984 revealed that new systems and
techniques, such as in-line centrifugal
fans, were generally superior to the ear-
lier methods using axial computer-type
fans. Polyurethane caulk was found to
be in good condition; butyl caulk, on
the other hand, had deteriorated. A ra-
don-resistant system was also devel-
oped and tested for integration into
houses during construction.
This Project Summary was devel-
oped by EPA's Air and Energy Engi-
neering Research Laboratory, Research
Triangle Park, NC, to announce key find-
ings of the research project that is fully
documented in two separate volumes
(see Project Report ordering informa-
tion at back).
Introduction
Growing concern about health risks as-
sociated with exposure to indoor radon, a
radioactive gas found in varying amounts
in nearly all houses, has underscored the
need for dependable radon reduction meth-
ods in existing and newly constructed
houses. Responding to this need, the U.S.
Environmental Protection Agency (EPA)
and the New York State Energy Research
and Development Authority (NYSERDA)
cosponsored a project in New York State
to demonstrate radon reduction techniques
in houses with elevated radon concentra-
tions, and to test radon-resistant construc-
tion techniques in new houses.
A primary goal of this research project
was to demonstrate the effectiveness of
radon reduction techniques in houses con-
taining indoor radon concentrations of
more than the current EPA guideline of 4
pCi/L. In addition to demonstrating new
radon reduction techniques, the effective-
ness and durability of previously imple-
mented techniques were assessed. These
radon reduction techniques were pre-
viously implemented during a project
cosponsored by NYSERDA and the
Niagara Mohawk Power Corporation
(NMPC) in 1983 and 1984. Addition-
ally, radon-resistant construction tech-
niques were demonstrated in houses under
construction to gather information and to
provide guidance for houses being built in
Printed on Recycled Paper
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areas with a risk of high radon levels. To
reach these goals, the work was divided
into three tasks:
1. Demonstrating Radon Mitigation
Techniques in Houses Containing
Indoor Radon Concentrations Ex-
ceeding 4 pCi/L.
2. Assessing the Effectiveness and
Durability of Previously Installed
Radon Reduction Techniques.
3. Demonstrating Radon-Resistant
New Construction Techniques.
Demonstrate Radon Mitigation
Techniques in Houses
Containing Indoor Radon
Concentrations Exceeding 4
pCi/L(Task1)
House Selection
The first step was identifying houses in
New York State containing indoor radon
concentrations of more than 4 pCi/L. To
accomplish this, the Bureau of Environ-
mental Radiation Protection of the New
York State Department of Health
(NYSDOH) surveyed houses in areas likely
to contain high radon levels. From this
survey, Orange, Putnam, Albany, and
Rensselaer counties were selected for in-
clusion in this portion of the study. Initial
screening tests were conducted between
August and November 1986. Soil radium
content, soil radon, and water supply ra-
don concentration were measured at the
houses. The final house selection was
completed in November 1986. Eight
houses in Albany and Rensselaer coun-
ties, designated by the prefix AR, and
eight houses in Orange and Putnam coun-
ties, designated by the prefix OP, were
selected for inclusion in this study.
Geology of Areas Selected
The geologies of the two areas in this
study are vastly different. The Albany/
Rensselaer county bedrock consists of
graywacke, a conglomerate of sandstone
and shale. The bedrock is covered with a
layer of gravelly glacial outwash 15-200 ft
deep. This layer of gravel is generally
well-drained and highly permeable.
The Orange/Putnam county bedrock is
dominated by a granitic gneiss of the
Reading Prong geological formation.
Outcroppings of unweathered gneiss and
detached boulders are common through-
out this area. Several outcroppings of the
Orange County bedrock show elevated
gamma levels. There were no reports of
elevated gamma readings in the Putnam
County area. Surficial soil in both counties
is very shallow. Typically, the surface layer
is a 15 in. gravelly silt.
Design of Tasks I and 2
The objective of Tasks 1 and 2 was to
install mitigation systems in the houses in
order to determine the effect each system
had on the indoor radon concentration.
Each system is referred to as a Phase.
For example, Phase 1 may have been the
installation of a sub-slab depressurization
system. Phase 2 may have involved seal-
ing a French drain and deactivating the
sub-slab depressurization system. Phase
3 may have required adding a wall de-
pressurization system to work in combina-
tion with the sealed French drain and the
activated sub-slab depressurization sys-
tem. Using this approach, data could be
gathered to demonstrate the effectiveness
of a sub-slab depressurization system, of
sealing as a stand-alone mitigation tech-
nique, and of a sub-slab/wall depressur-
ization system with floor and wall
penetrations sealed. It was clearly under-
stood in most of the houses that some of
the phases installed were not expected to
reduce the indoor radon concentration be-
low the 4 pCi/L guideline set for this
project. A combination of all phases in-
stalled, however, was expected to result
in indoor concentrations of below 4 pCi/L.
Radon Sampling Methods
A variety of radon sampling methods
were used throughout this project. The
initial screening tests conducted by the
NYSDOH used short-term activated char-
coal canisters (CCs). Longer-term moni-
toring at each house using alpha-track
detectors (ATDs) was performed before
any mitigation work was started, and after
all mitigation work was completed. Radon
grab samples (GRs) were used during
diagnostic testing to help determine radon
entry points and source strengths. Radon
sniffing (RS) techniques were developed
in this and other research projects con-
ducted at the time. Finally, continuous ra-
don monitors (CRMs) were used to provide
information on the immediate effective-
ness of an installed mitigation technique.
Diagnostic Testing
Diagnostic testing was performed at the
Orange/Putnam county houses during No-
vember 1986, and at the Albany/
Rensselaer county houses during Febru-
ary 1987. The purpose of the diagnostic
testing was to investigate building charac-
teristics (such as foundation integrity) and
building dynamics (such as air pressure
relationships) and to determine the effect
these parameters had on indoor radon
concentrations
Field teams investigating each house
performed a series of tests. Grab samples
of the indoor ambient air were taken at
each house. These ambient air samples
served two purposes: 1) to give diagnosti-
cians an indication of their exposure to
radon; and 2) to provide a reference point
for the comparison of subsequent grab
samples from suspected radon entry
points. The comparison of the grab
samples taken at suspected radon entry
points to the ambient air grab samples
classified the relative concentration of the
suspected radon entry point. In this project
as a rule of thumb, any suspected radon
entry point that exhibited radon concen-
trations three times higher than the ambi-
ent sample was considered a source
requiring treatment.
Communications testing, also called con-
nectivity testing, was conducted to deter-
mine the ability to move air under the floor
slab, within hollow-core concrete block
foundation walls, and between the area
beneath the floor slab and the hollow-core
walls. Essentially, a vacuum (air pressure
negative relative to the basement air pres-
sure) was developed beneath the floor
slab or within the hollow-core walls. Pres-
sure differential instruments were then
used to map the extent and strength of
the pressure field being developed. The
data gathered during communication test-
ing helped the diagnostician choose the
fan type and size to use in the active
depressurization systems.
The house was visually inspected to
catalog building characteristics that en-
hance radon entry. Typical characteristics
noted were the number and size of ex-
haust fans, number and type of combus-
tion appliances, and integrity of the
building's foundation.
All information obtained from the site,
including the data gathered during the di-
agnostic testing period, was used to de-
termine the mitigation systems that should
be applied. These systems were applied
in phases to determine the effectiveness
of each system in reducing the radon level.
The final goal was to reach the EPA ra-
don level guideline of 4 pCi/L when all
phases were complete and operating.
Mitigation Systems
Demonstrated
Three elements must be present for a
house to have an indoor radon problem:
1) a source of radon, 2) a driving force
that transports the radon from the source
to the ambient air in the house, 3) path-
ways for the radon to move from the
source into the building if the source is
outside the building. The house will not
have a radon problem if any one of these
conditions does not exist.
-------
Mitigation systems installed during this
project included the sealing of soil gas
entry points, variations of sub-slab and
soil depressurization, sub-membrane de-
pressurization, wall depressurization, base-
ment pressurization, and, water treatment.
Each of these mitigation techniques at-
tempts to remove at least one of the three
prerequisites.
Mitigation System Results
The reduction of the radon level within
each house on a percentage reduction
basis showed the effectiveness of each
mitigation technique. This was obtained
by comparing the pre- and post-mitigation
time-weighted average radon concentra-
tions. Time-weighted average radon con-
centrations are hourly concentrations in
the house quantified using a continuous
radon monitor, and averaged over the
length of the monitoring period. It must be
understood, however, that all parameters
affecting the final indoor radon concentra-
tion must be considered when comparing
pre- and post-mitigation radon concentra-
tions. Any conclusion judging the effec-
tiveness of a system based solely upon
the short-term (less than a week) radon
concentrations is tenuous at best. The
relative short-term measurements should
be considered an indication of the effec-
tiveness of each system versus another
system rather than an indication of the
annual average radon concentration.
Tables 1 to 4 present the results of the
mitigation systems installed. Trend plots
illustrating the continuous data used in
calculating the time-weighted averages
presented in these tables can be found in
the full report.
Sealing of Soil Gas Entry Points
One way to eliminate the pathway from
the radon source to the inside of a house
is by sealing all of the cracks, holes, and
other penetrations that pierce the founda-
tion. Sealing soil gas entry points as a
stand-alone mitigation technique was
tested in six houses. Typical penetration
points found in the project houses included
French drains, utility and plumbing pen-
etrations through side walls in the base-
ment, floor drains, and floor and wall
cracks. These penetrations were sealed
as part of this task. Results of the sealing
efforts are presented in Table 1.
The percentage of radon reduction in
these houses due to sealing of soil gas
entry points ranged from a low of 2%
(AR-01) to a high of 74% (AR-20). This
large difference in radon level reductions
can be attributed to several factors. The
primary factor was the relative contribu-
tion of the original penetration to the total
indoor radon concentration. In other words,
if the penetration, such as a French drain,
was responsible for permitting 70% of the
total radon gases to enter the house, then
sealing this penetration produced a sig-
nificant reduction in radon level. Similarly,
sealing a small wall crack that was a mi-
nor contributor to the total radon level,
produced only a small reduction. Another
factor was the existence of inaccessible
entry points that were not sealed in each
house. Finally, the indoor radon concen-
tration may have been caused by sources
which were not affected by sealing.
As shown in Table 1, sealing penetra-
tions usually reduces radon levels. How-
ever, these results show that these
reductions were not sufficient to bring the
radon levels below the EPA guideline of 4
pCi/L.
Sub-slab Depressurization
The predominant transport mechanism
that moves radon from its source to the
openings in the house's foundation is air
movement by pressure differentials. Just
as gravity forces water to flow from a
higher to a lower area, pressure differen-
tials force gases to move from a high
pressure to a low pressure area. Most
buildings, for a variety of reasons, main-
tain an indoor air pressure that is lower
(negative) than the air pressure outside
the building or in soil surrounding the
house. Depressurization systems attempt
to reverse this by creating an area of
pressure in the soil surrounding the house
that is lower than the indoor air pressure.
Sub-slab depressurization systems us-
ing regenerative and centrifugal blowers
were demonstrated in this project.
Sub-slab depressurization systems us-
ing regenerative blowers were tried in two
houses. Regenerative blowers were se-
lected for use in these two houses be-
cause of the compactness of the sub-slab
aggregate. It was theorized that the re-
generative blower, with its low air flow and
high static pressure operating characteris-
tics, would prove to be more effective
than the centrifugal blower in these
houses. One house, OP-01, had no seal-
ing of foundation penetrations performed
during this phase of the demonstration.
Radon concentrations in this house were
reduced to an average of 12.3 pCi/L from
a pre-mitigation average of 20.6 pCi/L.
House OP-09 also had a regenerative
blower depressurization system installed.
Radon concentrations averaged 11.4 pCi/
L prior to the installation of the system,
and were reduced to 3.4 pCi/L after sys-
tem installation.
Sub-slab depressurization using a cen-
trifugal blower with no sealing of founda-
tion penetrations was demonstrated in six
houses. Reductions of 4 to 93% were
achieved. As for nearly all mitigation sys-
tem types demonstrated during this project,
a wide range of reductions was evident.
The data gathered during this project were
informative and valuable because of the
wide ranges of reductions for each sys-
tem type and the reasons for these varia-
tions. For the house with the lowest
reduction (AR-19), very large floor cracks
adversely affected the operation of the
sub-slab depressurization system. Most of
the other houses had minor floor cracks
that did not greatly interfere with the
sub-slab depressurization system.
Two of the houses were to have sealing
performed as the next phase, while the
other houses were scheduled to have seal-
ing and some other mitigation technique
installed, such as the sub-slab depressur-
ization system combined with sealing and
wall depressurization. Sealing of penetra-
tions in House AR-17, in combination with
the sub-slab depressurization system, re-
sulted in a further reduction of 2% (91 to
93%). This small decrease in radon con-
centrations should not be considered as a
cost-effective improvement in effectiveness
because the radon concentrations for both
phases were below the 4 pCi/L guideline
(2.2 versus 1.6 pCi/L). In fact, when con-
sidering the lower level of detection of the
radon monitoring equipment being used,
Table 1.
House
ID
AR-09
AR-16
AR-17
AR-20
OP-09
Results of Sealing Foundation Penetrations
Pre-mitigation
Concentration
(pd/L)
17.5
22.5
15.5
23.6
35.7
23.5
Post-mitigation
Concentration
(pCi/L)
17.1
9.9
5.7
9.1
9.3
14.7
2
56
63
61
74
37
-------
and the natural variation of radon concen-
trations, there really is no difference be-
tween the two phases. The results of the
sub-slab depressurization systems are
summarized in Table 2.
The results of the sub-slab depressur-
ization systems show significant reduc-
tions in radon levels. These reductions,
however, did not necessarily bring the ra-
don concentrations below the EPA guide-
line. In some cases, penetration sealing
or another radon mitigation technique was
necessary to meet this guideline.
Footing Drain Depressurization
Three of the project houses had footing
drains connected to a depressurization
system. The drainage systems in Houses
AR-16 and AR-20 were complete interior
loop footing drains that were terminated
inside sump holes. The footing drain at
House OP-13 was an exterior footing drain
that drained to an area above the ground.
Radon reduction at these three houses
ranged from 79 to 95%. This consistently
high reduction is due to the footing drain
which helped to extend the negative pres-
sure field around the building perimeter.
Note that the sub-slab aggregate at all
three houses consisted of a natural grav-
elly soil and not the clean imported DOT
No. 2 pebbles currently being prescribed
for sub-slab aggregate. Although a very
small sample population, the success of
these three systems indicates that, in ar-
eas where pebbles are not readily acces-
sible for new home construction, a pipe
loop may be a viable option. The results
of the footing drain depressurization sys-
tems are summarized in Table 3.
Wall Depressurization Systems
Outside wall depressurization was dem-
onstrated in three houses. Reductions
ranged frorr 28% (OP-16) to 98% (AR-01).
For the house with the lowest reduction
(OP-16), 1-1/2 in. passive vents were in-
stalled about every 4 ft around the perim-
eter of the building's foundation. Floor
penetrations and accessible hollow-core
block tops sealed during this phase re-
sulted in a 28% reduction in radon levels.
These passive vents were later plugged
and an active system installed. Reduc-
tions for the active system reached 59%.
A final phase at this house involved ex-
tensive and complicated sealing of all
hollow-core block tops. This final sealing
greatly improved the efficiency of the wall
depressurization system. Refer to Table 4
for the results of wall depressurization sys-
tems.
The other houses, where outside wall
depressurization was demonstrated, in-
volved fairly straightforward installations
and provide'd satisfactory results.
Table 2. Results of Sub-Slab Depressurization Systems
House
ID
AR-04 i'2
AR-05 '-2
AR-09 '•*
AR-17'2
AR-1713
AR-19'2
OP-01 '-2
OP-01 2A
OP-09 4-5
OP-13'3
Pre-mitigation
Concentration
(pd/L)
22.8
21.3
22. 5 6
23.6
23.6 6
12.3 6
20.6
20. 6 6
11.4
13.9 6
Post-mitigaticn
Concentration
(pd/L)
4.2
1.5
2.2
1.6
21.6 '
14.3
12.3
3.4
9.1
Reduction
(%)
42
80
93
91
93
N/A
31
40
70
35
Sub-slab depressurization system with centrifugal blower.
No sealing of radon entry points performed.
Radon entry points sealed.
Sub-slab depressurization system with regenerative blower.
Basement walls sealed.
Period not immediately prior to post-mitigation monitoring period.
Pre-mitigation test period was from mid-February through early April 1987, while the post-mitigation
period was for the month of February 1988. Different weather conditions and an ineffective sub-slab
depressurization system installed by the homeowner caused this system to increase its radon level
during the post-mitigation period.
Basement Pressurization
This technique was successfully dem-
onstrated at one site. Radon concentra-
tions were maintained at a level of less
than 4 pCi/L for almost a year. The sys-
tem was unobtrusive and quiet. A device
was installed that would turn off the pres-
surization in case of a fire. Smoke alarms
equipped with normally closed relays were
wired into the fan system. Therefore, if
the smoke alarm was activated, the relay
would open, and the fan would turn off.
A difficulty with the basement pressur-
ization system, although an effective ra-
don mitigation technique, was the ease
with which it could be defeated. For ex-
ample, if the basement door or window
was left open, the basement would not
pressurize and, consequently, radon con-
centrations would increase. However, pro-
visions to lessen this problem, such as
making the basement windows inoperable
and providing automatic door closers,
could be implemented.
Water Treatment
The water supply was a major source
of indoor radon in two houses. Two types
of water treatment devices were demon-
strated, an activated charcoal filter that
adsorbs the radon, and a water aeration
system that aerates the water and causes
the radon to outgas. Both systems per-
formed well, but because the water sup-
ply contained unusually high radon
concentrations, the activated charcoal fil-
ter quickly became a source of gamma
radiation from the decay of the adsorbed
radon. Since this was unacceptable, a
water aeration unit was installed before
the charcoal filter to remove radon from
the water. The charcoal filter was left in
place to help improve the taste of the
water. The water aeration systems per-
formed very well in reducing radon con-
centrations. However, the systems installed
during this project occupied a large area
in the garage and crawl space and were
extremely noisy.
Overall Results
The overall systems and results from
Task I, which demonstrated radon mitiga-
tion techniques in houses containing in-
door radon concentrations of more than 4
pCi/L, varied from site to site depending
on the location of the radon source. Seal-
ing all accessible penetrations in the base-
ment effectively reduced the radon
concentration, even though this method
did not result in radon levels that would
satisfy the EPA guideline. Results demon-
strated, however, that sealing foundation
penetrations increases the effectiveness
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Table 3. Results of Footing Drain Depressurization Systems
House
ID
AR-1612
AR-20 ''2
OP-1334
Pre-mitigation
Concentration
(pd/L)
15.5
35.7
13.9
Post-mitigation
Concentration
(pd/L)
0.8
2.3
2.9
Reduction
95
94
79
Depressurization of interior footing drain connected to sump hole.
French drains and other floor penetrations not sealed during this phase.
Depressurization of exterior footing drain that drains to daylight.
Floor penetrations also sealed during this phase.
of the overall active depressurization sys-
tems.
The decision to depressurize the foot-
ing drain, sub-slab, or basement wall de-
pends on the location of the radon source
and the construction of the house. Grab
samples or radon sniffing techniques were
used to identify these sources prior to
installation of the depressurization sys-
tem. In some cases, such as House
OP-01, the house had two sources of
radon entry which required the depressur-
ization of both locations. Radon mitigation
contractors should be aware of the possi-
bility of multiple sources in existing houses
and be prepared to address this problem.
All data presented to this point reflect
the results of the mitigation efforts on a
system-by-system basis. The effectiveness
of each system has been derived from
short-term pre- and post-mitigation moni-
toring. While this type of information is
useful to illustrate an immediate effect of
any mitigation effort, the final conclusions
as to the effectiveness of any complete
mitigation system should be based on
long-term measurements.
Assess Effectiveness and Dura-
bility of Previously Installed Ra-
don Mitigation Techniques
(Task 2)
Fourteen houses contained elevated lev-
els of radon in a pioneering indoor air
quality and ventilation study sponsored by
NYSERDA and NMPC. Low-cost mitiga-
tion systems were installed in these houses
in 1984. These houses were revisited dur-
ing this project to assess the long-term
effectiveness of the original systems.
During the original study, many mitiga-
tion systems were installed in the houses,
including sub-slab depressurization, seal-
ing of radon entry points, and increased
ventilation through the use of heat recov-
ery ventilators.
Each house was visited in 1986 and
1987, during which a thorough inspection
was made to determine the condition and
effectivene:?s of the original mitigation sys-
tem. In mcst houses, detailed diagnostic
testing included visual inspections and
pressure differential measurements.
Short-term radon measurements using
charcoal canisters were also made. If parts
of the systems were working improperly,
those components were replaced, updated,
or redesigned Short-term measurements
using charcoal canisters were then re-
peated, followed by long-term measure-
ments using alpha-track detectors.
Table 4.
Results of Wall Depressurization Systems
Post-mitigation
Concentration
(pd/t )
3.1
40.1
2.9
Passive depressurization.
Active depressurization and sealing of tops of ho/low-core concrete blocks.
House
ID
AR-01
OP-01
OP-161
OP-162
Pre-mitigation
Concentration
(pCi/L)
17.5
19.9
55.4
13.9
Reduction
98
84
28
79
Of the 11 homes in the original study
that contained radon concentrations of
more than 4 pCi/L (three were below 4
pCi/L in the original study, but were miti-
gated nevertheless), seven were brought
below 4 pCi/L by the original systems. It
was found during the reinvestigation that
six of the original 11 homes contained
short-term levels above 4 pCi/L. With the
original systems modified, nine houses
contained average long-term concentra-
tions below 4 pCi/L.
Problems found in the original systems
included weak pressure fields being de-
veloped by the sub-slab depressurization
systems. This was caused primarily by
the use of axial computer-type fans in the
original study. These fans were replaced
with more appropriate in-line centrifugal
fans that are now in widespread use.
The design of some of the sub-slab
systems was also a problem in some
houses. Low points in the exhaust piping
allowed water to collect and block the air
flow. Exhausts near ground level allowed
foreign objects to be placed in the ends of
the pipes, blocking air flow.
The condition of the sealants used in
the original study was varied. Generally,
polyurethane caulk was found to be in
good condition. Butyl caulk, on the other
hand, had deteriorated.
The heat recovery ventilators had little
or no impact on the indoor radon concen-
trations, due to the low air exchange rates
produced by the particular heat recovery
ventilator. All ventilators, however, were
operating satisfactorily.
Demonstrate Radon-Resistant
Techniques in New House Con-
struction (Task 3)
In this task, radon-resistant construc-
tion techniques were applied to 15 new
houses. Emphasis was placed on the de-
velopment of cost-effective passive meth-
ods of radon-resistant construction with
potential applicability to building codes.
Housing site selection was critical to
the success of this task because of the
need to presume high radon levels in
houses not yet built. A study of 210 homes
by the Onondaga County Health Depart-
ment identified a band of bedrock with
high radon levels running through parts of
the county. Based on this information, sev-
eral sub-divisions were identified as pos-
sible participants in this task. The four
mitigation methods installed in the
houses during construction were seal-
ing foundation floors, sealing concrete
block foundation walls, passive
sub-slab depressurization, and active
sub-slab depressurization
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Table 5. Results From New Construction Test Sites'
House
ID
ON-0623
ON-073
ON-0823
ON-09
ON- 10
ON- 11
ON-12
ON- 13
ON-14*
ON- 15
ON- 16
ON- 17
ON-186
ON- 19
ON-20
As-built
Concentration
(pd/L)
3-5
4-7
5
29
6-8
8
4
13-18
N/A
7
25
8
25-58
12- 16
25
Passive
Ventilation
Concentration
(pd/L)
3-5
N/A
5
19-20
6-8
7-8
4
10
N/A
6-7
14
7
28
10
21 -23
Active
Depressurization
Concentration
(pCi/L)
N/A4
N/A
N/A
1
<1
2
2
2
2
1 -2
2
1 -2
8
3-4
2-3
' All results are from various measurement devices including A TDs, CCs, and GRs.
2 Vented drains discharged to daylight.
3 Homeowner decided not to install active depressurization system.
4 N/A = not available; phase was not investigated.
5 Results from as-built and with passive ventilation are not available.
6 Radon-resistant techniques installed incorrectly including a severed sub-slab drain.
Sealing Foundation Floors
The foundation floor was sealed on all
test houses except ON-18 by installing a
continuous airtight plastic film over the
sub-slab aggregate prior to pouring the
slab. Joints, tears, punctures, or other pen-
etrations were sealed with builder's tape.
The interior and/or exterior footing drains
were discharged to an area above the
ground whenever possible to avoid intro-
ducing an interior sump. If the footing
drains discharged into an interior sump,
the sump was fitted with an airtight cover.
The water content of the concrete mix
was kept as low as possible to reduce
shrinkage and cracks. Houses ON-06, -09,
and -10 were extensively inspected be-
fore, during, and after the slab was poured
to ensure adherence to the guidelines set
by the designer. Less extensive
spot-checking was done on the remainder
of the houses.
Sealing Concrete Block
Foundation Walls
All houses in this task had concrete
block walls. An obvious problem with con-
crete block walls is the necessity to build
sub-foundations below the normal level of
the footing. The sub-foundation normally
consists of a footing poured on solid un-
disturbed soil on which the concrete block
wall is built up to the level of the normal
footing. Since the primary concern in coat-
ing the outside walls is to prevent water
migration through the walls into the base-
ment, sub-foundation walls are not nor-
mally coated below the slab level.
However, this allows radon to migrate
through the uncoated concrete blocks be-
low the slab into the block cavity, and up
through the blocks into the basement. In
order to avoid this problem, the builder
was instructed to install a course of solid
concrete blocks level with the aggregate.
The exterior of the foundation walls from
the top of the foundation wall to the foot-
ing level was pargeted with either a Port-
land cement with bituminous coating or a
surface-bonding cement.
Passive Sub-slab
Depressurization
All houses in this study had interior and/
or exterior footing drains surrounded by a
layer of crushed stone. Passive sub-slab
ventilation would be expected to be most
effective if the sub-slab aggregate and
sub-slab drainage pipes were vented from
a central location with a large diameter
vent pipe directly to the peak of the roof;
however, to keep installation costs to a
minimum, ail (except one) of the passive
sub-slab ventilation systems consisted of
4-in. PVC pipes connected to the footing
drains, which were then routed outdoors
at the rim joist in one, two, or three loca-
tions on each side of the test site. The
side of the house that received the pre-
vailing wind did not include a passive vent.
Active Sub-slab
Depressurization
The primary emphases of Task 3 were
the development of effective radon barrier
techniques and the testing of passive
methods of providing sub-slab ventilation.
However, if the passive mitigation system
was not effective in reducing the radon
level below the EPA guideline, a centrifu-
gal fan was connected to the sub-slab
ventilation system to form an active de-
pressurization system. In houses with two
or more passive sub-slab vents, all but
one of the vents were capped and a cen-
trifugal fan was connected to the remain-
ing vent. The fan was placed in the
basement as close to the rim joist as
possible due to strong objections of
homeowners who did not want a fan vis-
ible on the house's exterior. The obvious
disadvantage to that configuration is the
possibility of leaks in the fan and piping
allowing radon to be blown into the house.
Results and Conclusions
Radon-resistant construction techniques
demonstrated during this task proved to
be successful in lowering the overall ra-
don level in the houses studied. Addition-
ally, the cost of incorporating these
techniques into construction was shown
to be three times lower than the cost of
retrofitting mitigation techniques.
Sealing and passive ventilation tech-
niques incorporated into newly constructed
houses were successful in reducing ambi-
ent radon concentrations in three of the
15 houses. In the remaining 12 sites, how-
ever, installing active sub-slab depressur-
ization systems was required to bring the
radon levels successfully below the EPA
guideline. (Despite an active system, one
site, House ON-18, did not meet the EPA
guideline because of incorrect application
of the mitigation techniques by the builder.)
Table 5 presents the results from the 15
test sites.
Because multiple passive sub-slab de-
pressurization systems generally do not
reduce radon levels below the EPA guide-
line, it is suggested that only one passive
vent be installed during construction. This
will minimize the cost of the passive venti-
lation system and still permit the addition
of a centrifugal fan to create an active
depressurization system. As previously
stated, this radon-resistant technique was
effective in reducing radon levels below
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the EPA guideline when a site was fitted
with a correctly installed active depressur-
ization system.
The five control sites, located in the
same developments as the 15 test sites,
but without radon mitigation systems, had
an average pre-mitigation radon level of
22 pCi/L (Table 6). The control sites en-
sured that the new houses built in the
developments with radon-resistant tech-
niques were lower in radon concentration
because of these construction techniques
and not because of low radon levels in
the immediate area. All of these sites were
successfully mitigated using sub-slab de-
pressurization systems. However, the cost
for retrofitting these sites was three times
higher than the total cost of the system at
the houses where the radon-resistant tech-
niques were integrated during construc-
tion.
Table 6. Results From New Construction Control Sites1
House
ID
ON-01
ON-02
ON-03
ON-04
ON-05
As-built
Concentration
(pd/L)
33
7
27
25
19
Active
Depressurization
Concentration
(pd/L)
3
3
2
3
3
All results are from various measurement devices including A IDs, CCs,
and GRs.
•U.S. Government Printing Office: 1983 — 760-071/60238
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Ian Nitschke is with The Fleming Group, East Syracuse, NY 13057.
Michael C. Osbornels the EPA Project Officer (see below).
The complete report consists of two volumes entitled" Radon Reduction and Radon-
Resistant Construction Demonstrations in New York."
'Volume 1 (Order No. PB93-163061; Cost: $36.50; subject to change) is the
technical report.
"Volume 2" Order No. PB93-163079; Cost: $27.00; subject to change) consists of
the appendices.
The above reports will be available only from
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$3(30
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
EPA/600/SR-93/043
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