United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/S8-90/050 Aug. 1990
&EPA Project Summary
Testing of Indoor Radon
Reduction Techniques in
Central Ohio Houses: Phase 2
(Winter 1988-11989)
W. O Findlay, A-Robertson, and A. G.Scott
Developmental radon reduction
techniques have been tested in nine
slab-on-grade houses and four crawl-
space houses near Dayton, Ohio, in
Phase 2 of a two-phase project in that
area. Testing in slab-on-grade houseis
indicated that, where a layer of
aggregate was under the slab, sub-
slab ventilation (SSV) with one or two
suction pipes generally reduced
indoor radon concentrations below 2
pCi/L* (86 to 99% reduction), even
when forced-air supply ducts were
under the slab. Large slabs, block
foundation walls, and sub-slab duclts
sometimes required additional care
in SSV design (number, location of
vent pipes). SSV from inside and
outside the slab-on-grade house gave
generally comparable performance;
however, interior SSV was preferable
for one large house. Increasing the
number of suction pipes from one to
two, and increasing fan capacity,
generally appeared to improve SSV
performance. Operation of SSV
systems in pressure never gave
better reductions than did operation
in suction. Testing in crawl-space
houses indicated that
depressurization under a poly-
ethylene liner over the crawl-space
floor was able to reduce
concentrations below 2 pCi/L in the
living area (81 to 96% reduction),
• 1 pCi/L = 37 Bq/rri3.
consistently giving better living-area
reductions than did any of the crawl-
space ventilation approaches.
Complete coverage of the crawl-
space floor with the liner, and
complete sealing of the liner at
seams and around the perimeter, was
not always necessary. Among the
crawl-space ventilation approaches,
forced exhaust (a fan blowing crawl-
space air outdoors) consistently gave
the best performance (70 to 92%
reduction); natural ventilation
(opening the foundation vents) gave
46 to 83% reduction; and forced
supply gave 0 to 73%. In none of the
slab-on-grade or crawl-space houses
did "site ventilation" provide
significant indoor radon reductions.
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
Much of the testing to date in EPA's
radon reduction program has addressed
basement houses. Phase 2 of the field
project in Ohio was designed to focus on
the two other primary substructure types:
slab on grade, and crawl space. The
testing reported here supplements earlier
testing carried out under Phase 1 of the
Dayton project.
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The objectives of Phase 2 were:
1. To demonstrate alternative radon
mitigation methods, and alternative
mitigation design/operating conditions, for
slab-on-grade houses representing
different house design/construction
conditions, and
2. To demonstrate alternative methods
for treating crawl-space houses.
During Phase 2. testing of radon
reduction approaches was completed on
five additional slab-on-grade houses in
the Dayton area, bringing to nine the
number of slab-on-grade houses tested
during the Dayton project. (Limited
testing was carried out on a tenth house.)
The premitlgation radon concentrations in
these houses ranged between 10 and 30
pCi/L. The houses were selected to cover
a range of house design/construction
variables: slab size; foundation material
(hollow block vs. poured concrete);
presence or absence of forced-air supply
ducts under the slab; and presence or
absence of a sunken living room, as one
example of interior obstructions that
might disrupt the extension of a suction
field under the slab when applying sub-
slab depressurization. Much of the
testing focussed on SSV as the radon
reduction approach. Also tested were:
continuous operation of the central
furnace fan, in an effort to pressurize the
sub-slab region via the forced-air supply
ducts; sealing of major slab openings
(i.e., the plumbing opening under the
bathtub); and "site ventilation" (i.e.,
suction on a pipe embedded in the
ground outside the house, in an effort to
draw soil gas from the entire site). Two
variations of SSV were tested: "exterior"
SSV, with the SSV pipes penetrating
horizontally into the sub-slab aggregate
through the foundation wall from
outdoors; and "interior" SSV, with the
SSV pipes penetrating the slab vertically
from indoors. All of the houses tested had
a good layer of aggregate under the slab,
with the underlying soil being clay.
The four crawl-space houses tested
during Phase 1 of the Dayton project
were the subject of further testing during
Phase 2. The premitigation con-
centrations in the living area of these
houses ranged between 5 and 17 pCi/L.
Mitigation approaches tested during
Phase 1 had included: natural ventilation
of the crawl space (i.e., opening the
foundation vents, with no fan); and forced
exhaust ventilation of the crawl space
(i.e., using a fan to blow crawl-space air
out, depressurizing the crawl space). The
approaches tested during Phase 2 were:
forced supply ventilation of the crawl
space (i.e., with the fan blowing outdoor
air into the crawl space, possibly
pressurizing it); depressurization under
polyethylene sheeting laid over the
unpaved crawl-space floor (sub-liner
depressurization); and site ventilation.
The testing of sub-liner depressurization
addressed the effects of alternative
degrees of coverage of the crawl-space
floor by the sheeting, and alternative
degrees of sealing of this liner; since
placement and sealing of the liner can be
difficult and labor-intensive, it is desirable
to determine to what extent this effort can
be reduced. In all cases, the sub-liner
depressurization systems tested here
involved drawing suction on a length of
perforated piping laid under the liner. -
Measurement Methods
The performance of the radon
reduction systems was determined using
two types of radon measurements on the
indoor air. One involved 2-4 days of
hourly measurements with a Pylon
continuous radon monitor ("short-term"
monitoring). This monitoring immediately
indicated the approximate percentage of
radon reduction. The Pylon monitoring
was conducted 2-4 days before, and 2-4
days after, any changes to the system;
system on/off measurements were made
back-to-back, to the extent possible, to
reduce temporal variations. Measure-
ments were made in different parts of the
house, as warranted, under closed-house
conditions. Most of the monitoring was
completed during the heating season.
The other measurement method
involved alpha-track detectors (ATD's), to
provide a longer-term measure of system
performance. Premitigation ATD's were
exposed for about 2-3 months during
cold weather, just prior to installing the
mitigation systems. Quarterly post-
mitigation ATD measurements were
conducted over 3 to 4 quarters for the
Phase 1 study houses; 12-month ATD
measurements are underway for the
Phase 2 houses.
In addition to the radon measurements,
various diagnostic tests were conducted
in selected houses (e.g., sub-slab com-
munication tests, and suction/flow
measurements in mitigation system
piping).
Results and Conclusions
Slab-on-Grade Houses
Based on test results in the slab-on-
grade houses, the following conclusions
are apparent:
1. Continuous operation of the central
furnace fan was tested in four additional
slab-on-grade houses under Phase 2 of
the Dayton project. The conclusion
regarding HVAC fan operation is
unchanged from what it was after testing
the first four houses during Phase 1.
Specifically, continuous operation of the
HVAC fan in an effort to pressurize the
sub-slab region via the sub-slab supply
ducts will provide no better than
moderate radon reductions. Observed
reductions in the eight houses ranged
between 0 and 84%, compared to when
the central fan was cycling normally.
There was no clear correlation between
the effectiveness of central fan operation
and the key house variables - size or
foundation material.
2. Sub-slab ventilation ~ with the SSV
system operated to depressurize the sub-
slab ~ was very effective in all nine of the
slab-on-grade houses tested, consistent
with the results observed in the first four
houses during Phase 1. With appropriate
SSV design, radon was reduced 86 to
99% in these houses, with the SSV
mitigation fan operated at full capacity.
The aggregate under the slabs is likely
contributing to this success.
3. Forced-air (HVAC) supply ducts
under the slabs did not appear to reduce
the effectiveness of sub-slab depressur-
ization by the SSV system. Where
houses with similar characteristics other
than the presence of ducts could be
compared, the SSV system achieved
comparable reductions in houses with
and without ducts.
4. Two SSV approaches were tested
back-to-back in four houses: "exterior"
SSV, where the system pipes penetrate
__the sub-slab region horizontally,through
the foundation wall from outdoors; and
"interior" SSV, where the pipes penetrate
vertically through the slab indoors. The
two SSV approaches appeared to
perform about equally in three of the
houses; interior SSV appeared superior in
the fourth. The better performance of
interior SSV in the one house could not
be clearly linked to any particular house
characteristic (size, foundation,
presence/absence of sub-slab ducts).
5. The largest house tested (240 m2, or
2,600 ft2) -- which had sub-slab HVAC
supply ducts - required two interior SSV
pipes to reduce premitigation radon
levels of 16 pCi/L to below 2 pCi/L; one
pipe (at either of two locations) was
insufficient to reduce levels below 4
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pCi/L. Another large house (220 m2, or
2,350 ft2), which did not have sub-slab
HVAC ducts and which had a pre-
mitigation level of 24 pCi/L, achieved
levels of 2-4 pCi/L with only one pipe
(although a second pipe provided even
greater reductions, to below 1 pCi/L).
Thus, large houses may require more
than one pipe, especially if ducts are
under the slab. All of the other slab-on-
grade houses tested, ranging from 90 to
160 m2 (1,100 to 1,700 ft2), achieved
levels below 2 pCi/L with only one SSV
pipe.
6. In the two large houses referred to in
5 above, two suction pipes were better
than either one alone, and any one pipe
alone was about as effective as the other
pipe alone. However, in a third house
where a two-pipe system was tested, one
of the pipes alone gave better
performance than the other one alone or
than both pipes together.
7. Slab-on-grade houses having poured
concrete foundations appeared to
consistently achieve the better radon
reductions (97 to 99% reduction at best
conditions) than did houses having
hollow-block foundations (usually 81 to
93% reduction at best conditions). This
may have been due in part because
block-foundation houses tend to be
larger.
8. In slab-on-grade houses having block
foundation walls and sub-slab ducts, the
wall ventilation component of an exterior
SSV system can sometimes be bene-
ficial.
9. In many of the SSV installations,
operating the mitigation fan at reduced
capacity was sufficient to reduce indoor
concentrations below 4 pCi/L; in some
cases, reduced-capacity operation
reduced levels below 2 pCi/L. (In most
cases, reduced-capacity consisted of
reducing fan power to where system flow
rates were half those at full power; this
point would generally be about 15% of
full power.) But in most cases, operation
at full capacity provided radon reductions
beyond those achieved at reduced
capacity.
10. Operating these SSV systems with
the fan pressurizing the sub-slab region,
was never as effective as operatiing them
in suction, in the seven slab-on-grade
houses where both pressurization and
depressurization were tested. Reductions
ranged from 88 to 99% in suction, and
only 43 to 90% in pressure.
Crawl-Space Houses
Based on the tests in the crawl-spacs
houses, the following conclusions are
apparent:
1. In the four crawl-space houses tested,
forced-supply ventilation of the crawl
space reduced radon in the living area
sometimes more than, and sometimes no
better than, achieved by natura.1
ventilation of the crawl space. In all
cases, forced exhaust was superior to
either forced supply or natural ventilation.
Radon reductions in the living area
ranged from 0 to 73% with forced-air
supply to the crawl space; 46 to 83%
with natural ventilation; and 70 to 92%
with forced exhaust.
2. Sub-liner depressurization systems
were able to reduce all four houses below
2 pCi/L in the living area, achieving radon
reductions of 81 to 96%. Sub-liner de-
pressurization consistently gives better
living-area reductions than do any of the
crawl-space ventilation approaches.
3. With sub-liner depressurization sys-
tems, complete coverage of the crawl-
space floor with the plastic sheeting is
not always necessary, depending upon
system configuration and perhaps other
variables. In two houses having a loop of
perforated drain tile around the perimeter,
the plastic sheeting extended out from
each perimeter wall for 3 m (10 ft); the
central area of the crawl space was not
completely covered, with the pre-existing
vapor barrier spread out to cover this
central area. With the depressurization
fan operating at full capacity, these
systems achieved reductions of 81 to
89%, reducing living-area concentrations
to about 1 pCi/L
4. Sealing the seams between the sheets
of plastic, and sealing where the lineir
contacts the perimeter foundation wall,
can be important with sub-liner
depressurization systems; the importance
depends upon such variables as fan
capacity. In one house ~ where the
plastic covered the entire floor, and
where the perforated piping was in the
form of two straight, parallel lengths in
the interior of the crawl space — sealing
the liner at seams between plastic and
around the perimeter increased living
area reductions to 90% with the fan at full
capacity; by comparison, with the liner
completely unsealed (neither at seams
nor around the perimeter), reductions
were 80%. Good reductions (comparable
to what had been achieved in this house
with forced crawl-space exhaust, which
the sub-liner system may have been
simulating in this case) could be
achieved with no sealing, with the fan at
full capacity. In another house - with the
liner covering the entire floor, and the
perforated piping forming three parallel
lengths in the interior of the crawl space
— sealing the liner at seams between
sheets and around the perimeter
increased living-area radon reductions to
94% at reduced fan capacity; by
comparison, with the liner sealed at
seams but not around the perimeter, the
reduction was only 20%. This dramatic
effect of perimeter sealing might have
resulted because of the reduced fan
capacity.
5.With sub-liner depressurization,
increased fan capacity appears generally
to increase radon reductions, all other
variables being constant. Reducing fan
capacity appears to have the least impact
when the liner is largely sealed.
Reducing fan capacity from medium to
low decreased radon reductions by 4 to
14 percentage points in two houses with
fully-sealed liners. But in a house with
the liner not sealed around the perimeter,
reducing fan capacity from full to low
decreased reduction by over 75
percentage points (from 98 to 20%).
With the liner sealed, it appears that good
reductions can be achieved even at
reduced fan capacity.
Site Ventilation
"Site ventilation" involves drawing
suction on a pipe embedded in the
ground outside the house, with the intent
of drawing soil gas away from the vicinity
of the house, in effect treating the entire
lot. If effective, this approach could be
attractive, since it requires no work inside
the house, and the exterior work is
relatively simple. For this approach to be
effective, it would be expected that the
horizontal permeability of the soil would
have to be relatively high, and the vertical
permeability relatively low. This approach
has proven to be fairly effective in some
areas of Canada and Sweden where
these permeability requirements are met.
In most of the Dayton area houses in this
project, the underlying soil is clay, and it
would thus appear that these
permeability requirements would not
generally be met; if site ventilation were
successful in Dayton, it might be
expected to be fairly widely applicable.
In some cases, native gravel lies under
the clay; if the site ventilation pipe could
penetrate into the gravel, this approach
could be effective.
U. S. GOVERNMENT PRINTING OFFICE: 1990/748-012/20077
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On these bases, site ventilation was
tested on 13 houses in this project. In all
cases, a 10-cm (4-in.) diameter PVC pipe
was embedded in an augered hole up to
3 m (10 ft) deep, about 2 m (7 ft) from
the house. A Kanalflakt T2 fan was
mounted on the above- grade end of the
pipe, drawing suction at full power.
In none of the houses did the site
ventilation pipes penetrate the clay layer
into gravel; thus, in no case were the
conditions favorable for site ventilation.
And, as might be expected, reductions in
the indoor radon concentrations were
limited at best, varying from +65% to -
48%; the average reduction, averaged
over all 13 houses, was only 3%. Indoor
levels appeared to increase in about as
many houses as they decreased with the
application of site ventilation, suggesting —
that the observed changes in indoor
radon levels might be due in part simply
to temporal variations in premitigation
radon concentrations. Tests of flows and
radon concentrations in the vent pipe,
and tracer gas studies to evaluate gas
movement through the soil toward the
pipe, suggested that gas was being
drawn into the vent pipe, but that it was
likely largely air being drawn down from
grade level; tracer testing suggested that,
beyond about a meter away from the
vent pipe, the influence of the vent pipe
was not strong.
W. Findlay is under contract to Acres International Corp., Amherst, NY 14228;
and A. Robertson and A. 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 2 (Winter 1988-1989)," (Order No. PB 90-222
7041 AS; Cost: $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
Official Business
Penalty for Private Use S300
EPA/600/S8-90/050
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