United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S8-89/071 Oct. 1989
f/EPA Project Summary
Testing of Indoor Radon
Reduction Techniques in
Central Ohio Houses:
Phase 1 (Winter 1987-88)
W. O. Findlay, A. Robertson, and A. G. Scott
Developmental radon reduction
techniques have been installed in 16
houses near Dayton, Ohio, in Phase 1
of a two-phase project in that area.
Sub-slab suction and sump (drain
tile) suction have reduced radon
levels in five basement houses below
4 picocuries per liter (pCi/L)*, based
on short-term measurements. In one
of these houses, the reduction was
achieved despite the fact that soil
gas flow in the system was only 2
L/sec. In two other houses, which had
a basement plus an adjoining slab on
grade, sub-slab suction In the
basement alone adequately reduced
radon levels in the entire house,
without any direct treatment of the
adjoining slab. Radon was reduced
by over 90 percent in each of four
slab-on-grade houses using a single
sub-slab suction point from outdoors,
even though forced-air heating sup-
ply ducts under the slabs appeared
to prevent effective extension of the
suction field under the slab. Forced-
air exhaust of the crawl space in four
crawl-space houses proved more
effective in reducing radon in the
living area than did natural ventilation
of the crawl space. Closure of the
wall/floor joint in two basement
houses with concrete foundation
walls, and of a sump in one of the
houses, appears to have given, at
O 1 pCi/L = 37 becquerels per cubic meter
(Bq/m3>
best, moderate reductions In the
house with the sump, and limited (If
any) reduction in the other house.
Operation of sub-slab ventilation
systems in suction proved consis-
tently more effective in reducing
radon than did operation of the
systems in pressure.
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
separate report of the same title (see
Project Report ordering information at
back).
Introduction
As part of the U. S. Environmental
Protection Agency (EPA) program to
develop and demonstrate cost-effective
methods for reducing concentrations of
radon inside houses, developmental
radon reduction measures were installed
and tested in 16 existing houses near
Dayton, Ohio. This testing, conducted
during the 1987-88 heating season, was
intended to develop understanding of the
design and performance of selected
radon reduction systems in selected
house sub-structure types, with
geological and house construction
characteristics representative of Ohio (as
well as of other areas of the country).
The test program had five objectives.
1. To verify that traditional sub-slab
ventilation systems and sump (drain
tile) ventilation systems can provide
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high radon reductions in "pure"
basement houses in Ohio (i.e., base-
ment houses having no adjoining
slab on grade or crawl space). These
active soil ventilation systems have
proven very effective in testing
elsewhere.
2. To demonstrate whether sub-slab
ventilation in the basement alone can
sufficiently reduce radon levels
throughout basement houses with
adjoining slabs on grade (i.e., to
determine whether separate vent
pipes directly treating the adjoining
slab can be avoided).
3. To explore alternative mitigation
methods for slab-on-grade houses
having forced-air heating supply
ducts underneath the slab. Methods
tested included: operating the central
furnace fan continuously to pres-
surize the sub-slab space using the
heating ducts; sealing accessible
slab openings; and single-point sub-
slab ventilation.
4. To test alternative methods for
treating crawl-space houses, in-
cluding: natural ventilation of the
crawl space, by opening foundation
vents; and forced-air ventilation of
the crawl space (with the ventilation
fan operating to exhaust air from the
crawl space).
5. To test sealing alone as a method for
reducing radon in basement houses
particularly amenable to sealing (i.e.,
poured concrete foundation walls,
basement unfinished, and slab and
walls reasonably free of cracking).
Measurement Methods
The performance of the radon reduc-
tion systems was determined using two
types of radon measurements on the in-
door air. One involved 2 - 4 days of hou-
rly measurements with a Pylon contin-
uous radon monitor ("short-term" mon-
itoring). This monitoring provided an
immediate indication of the approximate
percentage radon reduction. The Pylon
monitoring was conducted 2-4 days
before, and 2 - 4 days after, any changes
to the system; system on/off measure-
ments were made back-to-back, to the
extent possible, to reduce temporal
variations. Measurements were made in
different parts of the house, as warranted,
under closed-house conditions. Much of
the monitoring was completed during the
heating season, although some of the last
measurements were not completed until
mid-April 1988.
The other involved alpha-track
detectors (ATD's), to provide a longer-
term measure of system performance.
Premitigation ATD's were exposed for
approximately 2-3 months during cold
weather, just prior to installation of the
mitigation systems. Quarterly postmitiga-
tion ATD measurements are now planned
for a 1- year period.
In addition to the radon measurements,
various diagnostic tests were conducted
(e.g., sub-slab communication tests, and
suction/flow measurements in mitigation
system piping).
Results and Conclusions
Objective 1 - Sub-slab ventilation
and sump ventilation In
basement houses
1. In three basement houses without
sumps, traditional active sub-slab
suction (involving a single sub-slab
suction pipe through the basement
slab) typically achieved reductions
greater than 90%, consistent with
experience in other states where
sub-slab communication was as
good as that in the Dayton houses.
2. In two basement houses with sumps
and reasonably complete drain tile
loops, active sump suction achieved
radon reductions greater than 95%,
again consistent with experience
elsewhere when sub-slab communi-
cation was good.
3. With sub-slab suction, one suction
pipe through the slab was sufficient
even in one house where the pipe
had to be placed at one end of a
large basement slab (170 m2). Thus,
where communication is good and
where fan performance specifications
are sufficient, it would appear that, at
least in some cases, high reductions
can be achieved with a limited
number of suction pipes and with
reasonable flexibility in pipe location.
(The fans in these installations were
capable of 127 L/sec at zero static
pressure, and could develop 350 Pa
suction before stalling.)
4. The sub-slab suction systems in two
of the houses gave high reductions
despite unusually low flow rates (2-
10 L/sec). It would thus appear that
high flows are not necessary to
obtain high radon reductions, as long
as the suction field extends well.
Premitigation sub-slab communica-
tion tests had suggested that high
flows would be expected in these
houses, indicating that the premitiga-
tion diagnostic testing does not fully
reveal all aspects of the sub-slab
condition.
5. Operation of these active soil
ventilation systems with the fans
drawing suction was always distinctly
superior to operation with the fans
reversed to pressurize the sub-slat
region. Reduction of 80-96% with th«
fans in suction fell to 47-89% witt
the fans in pressure. Sub-slat
pressurization depends on creatior
of a good flow of air under the slab
to dilute the radon in the sub-slat
gas, and flows are not high in man;
of these homes.
Objective 2 - Sub-slab ventllatloi
In the basement of basement
plus slab-on-grade houses
1. Sub-slab suction in the basements c
two basement plus slab-on-grad
houses effectively reduced rado
levels throughout the houses, givin
reductions of 96% in the basement
(consistent with the goo
communication under the basemei
slab) and about 93% above th
adjoining slab.
2. Available data did not indicate if tr
radon reductions upstairs were
fact due to extension of the basi
ment suction field under tr
adjoining slab, actually treating U
entry routes associated with th
adjoining slab; or if the observed u
stairs reductions resulted only b
cause the system reduced tl
amount of radon migrating upstai
from the basement.
3. Both of these houses had poun
concrete foundation walls. If tl
basement sub-slab suction field we
to extend under the adjoining s\i
there is a greater likelihood that tl
would occur with concrete walls th
with hollow-block walls. A hollc
block stem wall could provide
channel for air leakage into 1
system which could interrupt I
suction field.
4. As with the "pure" basement hou;
in Objective 1, reversal of the fan
pressurize the sub-slab resulted
distinctly poorer radon reducti<
than when the fan operated
suction.
Objective 3 - Slab-on-grade
houses (with sub-slab heating
ducts)
1. Premitigation sub-slab commun
tion testing confirmed that the ;
slab heating ducts did in fact apj
to prevent extension of a suction 1
underneath the slab. Thus, in
efforts on the four slab-on-gr
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houses focussed on approaches
other than sub-slab suction.
2. Initial efforts on the slab-on-grade
houses involved continuous opera-
tion of the central furnace fan, in an
effort to pressurize the sub-slab via
the forced-air heating supply ducts
under the slab. This approach
resulted in moderate radon reduc-
tions (51-74%) in two of the houses,
and little, if any, effect in the other
two.
3. The second effort in the slab-on-
grade houses was to close the major
accessible opening through the slab,
namely, the opening under the
bathtub where the bath plumbing
comes up through the slab. This step
was not expected to be sufficient by
itself to reduce radon levels below
150 Bq/m3, in view of the other slab
openings left unclosed (such as the
heating supply registers and the
inaccessible wall/floor joint).
However, the approach was tested as
a measure which homeowners could
easily implement them-selves.
Closing the bathtub opening ap-
peared to give limited radon
reductions (33-49%) in two of the
houses, and no meaningful reduction
in a third. (The fourth house had no
opening under the bathtub.) Closure
of the bathtub opening improved the
radon reduction effectiveness of
central fan operation in the two
houses where fan operation had had
a significant effect prior to closure.
Radon reductions with fan operation
in those two houses increased to 67-
94% after closure.
4. A simple sub-slab suction approach
proved very effective in all four slab-
on-grade houses, even though the
sub-slab ducts were preventing
effective distribution of the suction
field under the slab. This approach
involved mounting a 127 L/sec soil
ventilation fan over a single hole
cored horizontally through the
foundation wall from outdoors, below
slab level. The hole was cored either
at one end of the house, or near the
middle of the rear of the house.
Radon reductions ranged from 94 to
97%.
5. Of these sub-slab suction results, the
most tentative are those from the
house which had a block foundation,
and which also had a slab area (190
m2) twice the size of the other three.
This house was the only one which
rose above 4 pCi/L (to 10.6 pCi/L)
when the central furnace fan was
operated continuously in conjunction
with sub-slab suction, suggesting
that high reductions might not be
maintained if the mitigation system is
challenged. The problem in this
house might be the block foundation,
with the block cores facilitating the
short-circuiting of house air into the
system. Or perhaps the slab is too
large for one suction point, in view of
the obstructions presented by the
heating ducts.
6. Reversal of the sub-slab ventilation
fan to operate in pressure distinctly
decreased the performance of these
sub-slab systems, relative to opera-
tion in suction.
Crawl-space
Objective 4
houses
1. Initially, the four crawl-space houses
were tested using natural ventilation
of the crawl space as the mitigation
approach. Each house had between
five and seven foundation vents
around the perimeter of the crawl
space foundation wall. Indoor radon
levels were measured with these
vents open and closed, in an effort to
reduce indoor levels by diluting the
radon concentrations in the crawl
space and by reducing the forces
drawing soil gas up out of the soil.
Opening the vents caused radon
reductions of 37-84% in the living
area, and reductions of 56-91% in
the crawl space.
2. The houses were also tested with
forced ventilation of the crawl space,
with the 127 L7sec ventilation fan ex-
hausting crawl space air. In addition
to increasing ventilation, forced-air
exhaust might be expected to
depressurize the crawl space relative
to the living area, thus reducing
migration of radon from the crawl
space into the living area. To
increase crawl space depressuriza-
tion, the foundation vents were
closed during forced exhaust ventila-
tion; however, no additional sealing
of the crawl-space foundation wall or
of the subflooring under the living
area was attempted. In all four
houses, radon levels in the living
area were reduced to a distinctly
greater extent by forced exhaust than
by natural ventilation of the crawl
space. Reductions in the living area
with forced exhaust were 69-93%.
However, reductions in crawl space
concentrations with forced ventilation
(8-50%) were distinctly poorer than
with natural ventilation, as expected.
In depressurizing the crawl space,
forced exhaust draws more soil gas
into the crawl space, largely offset-
ting the benefits of increased
ventilation. The potential of the crawl
space depressurization mechanism
is demonstrated by the fact that con-
centrations in the living area can be
substantially decreased while the
crawl space concentrations are being
decreased only slightly to
moderately.
Objective 5 - Sealing alone In
amenable basement houses
1. In one of the two houses tested
under this objective, closure of the
sump, caulking of the wall/floor joint,
and sealing around utility line
penetrations through the slab re-
sulted in a radon reduction of about
62% in the basement. But in the
second house, which had no sump,
caulking of the wall/floor joint
appeared to result in no significant
reduction. If only slight to moderate
reductions can be achieved with this
type of closure in "textbook-case"
houses, the incentive for attempting
such closure by itself in more com-
plex cases (e.g., combined substruc-
tures, block foundations, finished
basements) might be questioned.
2. The wall/floor joints in these two
houses were closed using non-flow-
able polyurethane caulk after wire-
brushing and carefully cleaning the
surfaces. Flowable urethane caulk
was tried, but was unsatisfactory
because it flowed out onto the slab,
and disappeared down the 1 - 3 mm
wide wall/floor crack. The sump was
closed using a circular clear plastic
cover cut to fit the sump opening,
sealed around the perimeter and
around the sump penetrations (water
discharge line, electrical connection
to pump).
3. Diagnostic testing indicates that
radon is still entering these houses
through the wall/floor joint, despite
the fact that the caulk bead visually
appears to be adhering well to both
the concrete foundation wall and the
slab. One hypothesis is that the
radon might be bypassing the caulk
bead, moving through the porous
surface of the concrete (the
"laitance") near the base of the foun-
dation wall. If this hypothesis is
correct, and if a suitable primer will
not close the laitance, then the re-
ductions that can be achieved using
the type of sealing effort that
homeowners could reasonably per-
form themselves will be limited.
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W. 0. Findlay is with Acres International Corp., Amherst, NY 14228-1180. A.
Robertson and A. G. Scott are with American Atcon, Inc., Wilmington, DE
19899.
D. Bruce Henschel is the EPA Project Officer (see below).
The complete report, entitled "Testing of Indoor Radon Reduction Techniques in
Central Ohio Houses: Phase 1 (Winter 1987-88)," (Order No. PB 89-219
984/AS; Cost: $36.95, 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
UNOFFICIAL MAIL
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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