United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/S8-90/056 Aug. 1990
&EPA Project Summary
Testing of Indoor Radon
Reduction Techniques in 19
Maryland Houses
Daniel G. Gilroy and William M. Kaschak
Indoor radon reduction techniques
were tested in 19 existing houses in
Maryland. The focus was on passive
measures: various passive soil
depressurization methods, where
natural wind and temperature effects
are utilized to develop suction in the
system; and sealing of radon entry
routes into the house. Active (fan-
assisted) soil depressurization
techniques were also tested.
Passive soil depressurization
systems typically gave moderate
radon reductions (30 to 70%),
although the reductions ranged from
zero to 90%. Only two houses were
reduced below 4 pCi/L* with the
passive systems. A passive system
is most likely to be successful when
sub-slab communication is very
good, when the house is a basement
with no adjoining slab-on-grade or
crawl-space wings, and when the
foundation walls are poured concrete
instead of hollow block.
Entry route sealing as a stand-
alone radon mitigation measure gave
0 to 50% reduction in the one house
where it was tested.
Active soil depressurization, tested
in 18 houses, reduced 16 of them
below 4 pCi/L, and 12 of them below 2
pCi/L; reductions were often in
excess of 90%. Poor sub-slab
communication prevented this
1 pCi/L = 37 Bq/m3
approach from being fully successful
in the other two houses; later
modifications to these two systems
reduced these houses below 4 pCi/L
also.
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
The U.S. EPA is conducting a radon
mitigation research, development, and
demonstration program to identify and
evaluate cost-effective techniques for
reducing elevated radon levels in houses.
The total EPA program will evaluate the
full range of radon reduction methods
(i.e., house ventilation, sealing of entry
routes, soil ventilation, house pressure
adjustment, radon removal from well
water, and air cleaning), in the full range
of housing substructure types,
construction methods, and geological
conditions representative of the U. S.
housing stock. The program described in
this report was to demonstrate selected
radon reduction methods in housing and
geology typical of Maryland.
This project involved testing of radon
mitigation systems in 19 existing
Maryland houses. These houses have
structures that are representative of this
region: 18 have basements with concrete
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slabs (sometimes with an adjoining slab-
on-grade or crawl-space wing), while the
remaining house is of slab-on-grade
construction. The foundation walls are
hollow block in 13 of the houses, and
poured concrete in the 6 others. Pre-
mitigation radon levels ranged from 7 to
298 pCi/L, with most houses having
radon levels greater than 10 pCi/L.
The major objective of this project was
to evaluate passive systems (i.e.,
systems not requiring the operation of a
fan). Such systems have not been widely
tested in other projects. Passive systems
include: passive soil depressurization,
i.e., soil depressurization not involving the
use of a fan; sealing of soil gas entry
routes; and natural ventilation of the
house or crawl space. A key potential
advantage of passive systems is that
they do not require homeowner
maintenance of a fan, and avoid the cost
and any noise associated with fan
operation. Disadvantages include
potentially limited and variable radon
reduction performances due to, e.g., the
limited nature of the natural suction that
is developed in passive soil
depressurization stacks by thermal and
wind effects, and the difficulty in
effectively accessing and addressing
essentially all soil gas entry routes when
attempting sealing as the sole mitigation
measure. In this project, the intent was
to determine the degrees of radon
reduction that could be achieved with a
reasonable best effort to retrofit passive
systems into typical existing houses.
In view of this objective, passive
systems were initially installed in 13 of
the houses where structural features
appeared reasonably conducive to this
approach. Twelve of these were passive
soil depressurization systems (often in
conjunction with sealing or natural crawl-
space ventilation), and one involved
purely sealing. (In all cases, active, or
fan-assisted, soil depressurization was
considered a backup approach to be
installed if the initial passive systems did
not achieve sufficient reductions.) In the
remaining six houses, where conditions
appeared less favorable for passive
measures, active soil depressurization
systems were the initial approach of
choice.
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 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. Measurements were made
both in the basement and the upstairs
living area, under closed-house
conditions.
The other measurement method
involved alpha-track detectors, (ATDs) to
provide a longer-term measure of system
performance. Quarterly post-mitigation
ATD measurements were conducted for 1
to 4 quarters, depending upon how early
in the project the mitigation installation
was completed.
In addition to the radon measurements,
various diagnostic tests were conducted
in selected houses (e.g., sub-slab
communication tests, ^and-suetion/flow
measurements in mitigation system
piping).
Results and Conclusions
1. Passive soil depressurization
techniques, relying upon temperature
and wind effects to create natural
suction in the system, were tested
with 14 mitigation installations in 12
houses. The passive techniques
tested included sub-slab de-
pressurization (SSD), drain tile
(sump) depressurization (DTD), and
sub-liner depressurization (SLD) in
crawl spaces; these techniques were
tested both by themselves, and in
certain combinations with each other
and with block wall depressurization
(BWD). Commonly, some degree of
entry route sealing and/or crawl-
space isolation/natural ventilation was
conducted in conjunction with the
passive soil depressurization. House
substructure types tested included
basement houses, and basement
houses having adjoining slab-on-
grade or crawl-space wings.
2. The passive soil depressurization
systems typically provided
moderate radon reductions (30 to
70%), although the reductions
ranged from as low as zero to as
high as 90%. In only two houses
(Houses 047 and 079) was the
passive system sufficient to
consistently reduce radon below 4
pCi/L both in the basement and in
the living area.
"s/ The house which gave the best
reductions consistently (House 079,
which achieved 70 to 90% reduction
with each measurement as the
result of a one-pipe passive SSD
system) was a textbook-case house
for a passive system: a) it had a
"pure" basement, without an
adjoining wing; b) it had very good
sub-slab communication; and c) it
had poured concrete foundation
walls, thus minimizing wall-related
entry routes. The one other house
which also met all three of these
criteria (House 004) also achieved
good reductions, 60 to 80% in the
basement.
4. The other house which achieved
radon concentrations below 4 pCi/L
was House 047, a basement-plus-
crawl-space house which achieved
20 to 70% reduction in the basement
(and 90 to 96% in the crawl space)
—•—-using—a^- passive SLD system
combined with basement sealing.
This house, too, apparently was a
textbook case: a) the exposed crawl-
space soil was the primary radon
source; b) the crawl space was
unobstructed, small, and had
reasonable head room; c) the furnace
flue was used as the passive stack,
enhancing the natural suction
developed on the SLD system; and
d) the foundation walls were poured
concrete, again minimizing wall-
related entry.
5. One of the most important single
variables influencing the
performance of passive soil
depressurization systems is the
communication beneath the slab. All
houses which had poor performance
from the passive system (Houses
054 and 074) had poor/uneven sub-
slab communication (and block
foundations). However, the existence
of good communication was not
sufficient, by itself, to ensure high
radon reductions from the passive
system.
6. The performance of passive
depressurization systems appeared
to be somewhat better in houses
having poured concrete foundation
walls. In all of the houses having
poured walls, the upper end of the
performance range with a passive
system was above 70% reduction.
By comparison, of the seven block-
foundation houses to receive passive
systems, only three achieved upper-
end reductions greater than 50%.
This could be due in part to difficulty
by the low-suction passive systems
in treating the wall-related entry
routes. In House 106, a basement-
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plus-slab-on-grade house with a
block foundation, performance
improved perceptibly (from 0 - 50%,
to 30-85%) when the original passive
SSD system was expanded to
include a BWD component, con-
firming the failure of the original SSD
system to adequately treat the wall in
this case.
7. For a given degree of sub-slab
communication, and for a given
material of construction for the
foundation wall, it is not possible
from these data to determine a
significant effect of the substructure
type on the performance of the
passive systems. Except perhaps for
textbook-case Houses 004 and 079
-... (which had pure basements), it is not
possible, within the error bar of these
results, to identify whether the
passive systems give better
performance in pure basement
houses than they do in basements
with adjoining wings.
8. In the passive SSD installations, a
limited number of suction points
were installed to minimize installation
costs. The installation of additional
sub-slab suction holes, or of a
passive BWD component when block
foundation walls were present, might
have improved the performance of
the passive systems.
9. The performance of a given passive
system is presented as a range in
this report because: a) the pre- and
post-mitigation measurements are
separated in time in many cases,
and the radon source term might
have changed between measure-
ments; and b) the performance of the
passive systems appears to be
varying over time, depending upon
wind conditions and temperature.
10. The suctions developed in the piping
of these passive systems were
typically in the range of 0.0 to 0.10
in. WG.* If sub- slab communication
was very good, the resulting
depressurization underneath the slab
was observed to extend as far as 40
ft*" from the suction pipe in one
house, although the magnitude of
this depressurization fluctuated,
presumably due to varying winds.
1 in. WG = 0.249 kPa.
1 ft = 0.305 m.
11. Entry route sealing, as a passive
mitigation measure by itself, was
tested in one house which appeared
amenable to this approach. The
house was a pure basement house;
the basement was unfinished, with all
apparent entry routes accessible;
and radon levels were only slightly
elevated, so that high radon
reductions were not necessary. The
house had block foundation walls,
capped with solid blocks. After
sealing all apparent entry routes -
including painting the block walls
with a waterproofing paint -- the
radon reduction, if any, was limited
(0 to 50%). This limited performance
may be due in part to the fact that
the paint did not appear to fully seal
the block pores.
12. Active soil depressurization was
tested in 18 of the 19 houses. All but
one of the 13 houses with passive
systems, discussed above, were
converted to active systems by the
end of the project. In addition, six
houses received active systems
immediately, because they did not
appear to be amenable to passive
testing (due to highly elevated pre-
mitigation radon levels or to poor
communication). The active tech-
niques tested covered the range
indicated for the passive systems in
item 1 above. The house sub-
structure types included basement
and basement-plus-adjoining-wing
houses, and one slab-on-grade
house.
13. Radon levels were reduced to below
4 pCi/L, in both the basement and
the living area, in 16 of the 18
houses where active de-
pressurization systems were in-
stalled. Levels were reduced below 2
pCi/L on both stories in 12 of these
houses. The radon reductions
typically were above 90% in the 16
houses, and often ranged as high as
97 to 99 + %, although the per-
centage reduction sometimes ranged
as low as 50 to 80% where the pre-
mitigation concentrations were only
slightly elevated.
14. In the two houses which were not
reduced below 4 pCi/L with the
active systems (Houses 054 and
074), the reason was poor and
uneven communication underneath
the basement slab. (These two
houses were subsequently reduced
below 4 pCi/L by adding additional
suction pipes in regions of the slabs
where the suction field had not been
extending with the initial single pipe.)
15. It is not apparent from these data
that active systems performed any
better in houses with block
foundations than they did in houses
with poured foundations. Thus, within
the sensitivity of these data, it would
appear that these active systems
were adequately treating any block-
wall-related entry routes, even
though only two of the systems
included specific BWD components.
(However, both of the houses which
failed to be reduced below 4 pCi/L
did have block walls; block walls may
be significant when sub-slab-
communication is poor.)
16. In four of the houses which had
basements with adjoining slab-on-
grade or crawl-space wings (Houses
008, 069, 076, and 106), radon levels
on both stories were reduced below
4 pCi/L with active soil de-
pressurization treating the basement
only. Three of these houses were
reduced below 2 pCi/L. All four of
these houses were observed to have
good aggregate under the basement
slab, and/or suction field extension
measurements showed good com-
munication. Thus, it appears that --
with these combined-substructure
houses -- it is possible to reduce
radon in the entire house by treating
the basement only, without
specifically treating the adjoining
wing, if the basement sub-slab
communication is good (and,
presumably, if the adjoining wing is
not the primary radon source).
17. In general, the active systems
achieved high suctions in the system
piping (usually 0.4 to 1.6 in. WG,
except where suctions were reduced
by high flows from BWD legs or
some other source). Suctions
developed under the slabs at points
remote from the suction pipes (20 to
40 ft away) ranged from zero to 0.9
in. WG from house to house,
depending upon communication. In a
few cases (Houses 096, 126, 143,
and 163), good radon reductions
were achieved despite the fact that
no sub-slab depressurization could
be measured at some test holes.
if.U.3. GOVERNMENT PRINTING OFFICE: 1990/748-012/20079
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D. Gitroy and W. Kaschak are with COM Federal Programs Corp., Fairfax, VA
22033.
D. Bruce Henschel is the EPA Project Officer (see below).
The complete report, entitled "Testing of Indoor Radon Reduction Techniques in
19 Maryland Houses," (Order No. PS 90-244 393/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
Penally for Private Use $300
EPA/600/S8-90/056
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