United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/S8-90/076 Feb. 1991
Project Summary
Testing of Indoor Radon
Reduction Techniques in
Basement Houses Having
Adjoining Wings
Marc Messing
Indoor radon reduction techniques
were tested in 12 existing houses in
Maryland. These houses had pre-
mitigation radon concentrations rang-
ing from 2 to 23 pCi/L*. The primary
objectives were to assess active soil
depressurization methods in basement
houses having either an adjoining
slab-on-grade wing or an adjoining
crawl-space wing. The intent was to
determine: a) under what conditions ra-
don levels could be adequately reduced
throughout the entire house through
sub-slab depressurization (SSD) or drain
tile depressurization (DTD) in the base-
ment alone; and b) what additional (in-
cremental) reductions could be achieved
by also applying SSD under the adjoin-
ing slab-on-grade wing, or sub-liner de-
pressurization (SLD) in the adjoining
crawl space. The houses were selected
to include both good and poor commu-
nication beneath the basement slab, and
different degrees of importance of the
adjoining wing as a radon source. An-
other objective of this project was to
determine whether a simple, one-pipe
SSD system would provide high reduc-
tions in a large slab-on-grade house
having forced-air heating supply ducts
under the slab.
In the five basement-plus-slab-
on-grade houses, simultaneous treat-
ment of both slabs always gave better
performance (relative to treatment of
either one of the slabs alone), providing
an incremental additional reduction
ranging from 0.1 to 5.2 pCi/L in the
basement, and from 0 to 2.9 pCi/L in the
living area above the slab on grade.
With simultaneous treatment, levels in
all five houses were reduced below 1
pCi/L in the living areas and below 1-2
pCi/L in the basements. Basement-only
treatment always reduced levels
throughout the house below 4 pCi/L,
even when communication was poor
and the adjoining slab was a source,
and sometimes reduced levels below 2
pCi/L. Treatment of only the adjoining
slab reduced living area levels below 2
pCi/L, but often left basement levels
above 4 pCi/L.
In the six basement-plus-crawl-space
houses, basement-only treatment
achieved reductions throughout the
house comparable to the reductions
obtained with simultaneous treatment
of both wings (i.e., to less than 1 pCi/L),
even when the crawl space was a radon
source, if communication beneath the
basement slab was very good. When
sub-slab communication was poor,
treatment of both wings was required.
Treatment of only the crawl space al-
ways reduced concentrations through-
out the house below 3 pCi/L. However,
the incremental additional reductions
achieved with simultaneous treatment,
compared to crawl-space SLD alone,
were significant (ranging from 1.0 to 2.7
pCi/L In the basement, and from 0.7 to
2.1 pCi/L in the living area); in no case
would it appear desirable to install a
crawl-space SLD system without also
installing SSD in the basement.
Radon levels in the one slab-
on-grade house were effectively re-
* 1 pCi/L = 37 Bq/m3
Printed on Recycled Paper
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duced, from 7.1-15.7 pCl/L to below 1
pCl/L, with the one-pipe SSD system,
despite the large size and the sub-slab
ducts.
This Project Summary was devel-
oped by EPA's Air and Energy Engi-
neering 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 (seo Project Report
ordering Information at back).
Introduction
The U. S. Environmental Protection
Agency (EPA) is conducting a radon miti-
gation program to develop, demonstrate
and optimize cost-effective techniques for
reducing elevated radon concentrations in
houses, schools and other types of build-
ings. The total EPA program addressing
houses will evaluate the full range of radon
reduction methods (i.e., house ventilation,
sealing of entry routes, soil depressuriza-
tion/pressurization, house pressure ad-
justment, radon removal from well water,
and air cleaning), in the full range of hous-
ing substructure types, construction meth-
ods, and geological conditions
representative of the U. S. housing stock.
The program described in this report was
to demonstrate radon reduction methods
in selected housing types and with the
geology typical of Maryland.
The major objective of this project was
to evaluate the application of active
(fan-assisted) soil depressurization as the
mitigation approach in basement houses
having an adjoining slab-on-grade or
crawl-space wing. The active soil depres-
surization methods tested included sub-slab
depressurization (SSD), drain tile depres-
surization (DTD) via a sump, and sub-liner
depressurization (SLD) in unpaved crawl
spaces (i.e., crawl spaces with dirt floors).
The intent of the testing was to identify
under what conditions SSD or DTD in the
basement alone is sufficient to treat the
entire house in such basement-
plus-adjoining-wing houses, and what ad-
ditional reductions might be achieved by
also treating the adjoining wing. It was also
desired to determine whether simple diag-
nostic tools could be used prior to mitiga-
tion, to predict whether the adjoining wing
should also be treated.
To address this objective, testing was
carried out in six basement houses having
an adjoining crawl space, and five base-
ment houses having an adjoining slab on
grade. In each case, an SSD system (usu-
ally with only one suction pipe) or a DTD
system was installed in the basement, and
another suction pipe was installed beneath
the adjoining slab on grade or through
polyethylene sheeting placed over the un-
paved floor of the adjoining crawl space.
Radon concentrations were then measured
in the basement and in the upstairs living
area with: none of the suction pipes oper-
ating; SSD or DTD applied to the base-
ment slab only; SSD beneath the adjoining
slab on grade only, or SLD in the crawl
space only; and simultaneous treatment of
both the basement slab and the adjoining
wing. Another variable investigated during
the testing in basement-plus-crawl-space
houses was the effect of increased sealing
of the polyethylene liner in the crawl space,
and of increased isolation of the crawl
space from the basement.
Another objective of this project was to
determine whether a simple SSD system
(with only one or two suction pipes) would
^be "sufficient unreal a pure^slabnon^grade"
house with forced-air heating supply ducts
under the slab, when th'ere is good sub-slab
aggregate. The concern is whether the
sub-slab ducts might prevent effective ex-
tension of the suction field under the slab,
requiring a large number of SSD pipes in a
substructure type where locating suction
pipes can often be complicated by the
presence of a highly finished living area on
most of the slab. This objective was ad-
dressed by testing one slab-on-grade
house.
Measurement Methods
The performance of the radon reduc-
tion methods was determined utilizing sev-
eral radon measurement methods. The
primary method involved hourly measure-
ments with a Pylon continuous radon
monitor as the mitigation system was cycled
through various test configurations over a
10- to 14-day period. This monitoring pro-
vided an immediate indication of the ap-
proximate percentage radon reduction. A
typical test cycle [n the basement houses
having adjoining wings involved collecting
Pylon data for 2 to 4 days in each of five
mitigation system configurations: 1) sys-
tem off; 2) basement leg operating alone;
3) adjoining wing leg operating alone; 4)
both legs operating simultaneously; and 5)
system off. Measurements were made both
in the basement and in the living area
above the adjoining wing.
Another measurement method involved
alpha-track detectors (ATDs), to provide a
longer-term measure of system perfor-
mance. Quarterly post-mitigation ATD
measurements, both upstairs and in the
basement of each house, were conducted
over the first (summer) quarter following
completion of the mitigation installations,
with the most effective of the mitigation
configurations in operation. Subsequently,
year-long ATDs were deployed from Sep-
tember 1989 to September 1990.
Radon measurements using Electret
Ion Chambers were conducted in parallel
with the Pylorj and ATD measurements.
In addition to the radon measurements,
varbus diagnostic measurements were also
completed in 6ach house. These diagnos-
tic measurements included: suction and
flow measurements in system piping;
sub-slab communication measurements
prior to mitigation, using-a vacuum cleaner
to induce suction; suction field extension
measurements beneath the basement and
adjoining slabs, and beneath the
crawl-space liners, with the mitigation sys-
tem operating; and measurement of the
effective leakage area of the houses using
a blower door.
Results and Conclusions
i
Basement Houses Having
Adjoining Slabs on Grade
Active soil depressurization techniques
were tested in five Maryland houses hav-
ing basements with adjoining slabs on
grade. Pre-mitigation radon concentrations"
in these houses ranged from 9.5 to 23.4
pCi/L in the basement, and from 2.3 to
15.7 pCi/L in the living area above the slab
on grade. !
This testing led to several conclusions.
1. In all five houses tested here, simul-
taneous, treatment of both slabs al-
ways gave better radon reductions,
in both the basement and the living
area above the slab on grade, than
did operation of either the basement
or the s'lab-on-grade system alone.
The percentage radon reduction in
the basement was increased by 2 to
25 percentage points by simultaneous
operation (compared to treatment of
either one of the slabs ajqne), and
percentage reduction in the living area
was increased by 0 to 11 percentage
points. With both slabs being treated,
concentrations were reduced below
1 pCi/L in the living area in all houses;
four of the houses were reduced be-
low 1 pCi/L in the basement, and all
were reduced below 2 pCi/L in the
basement.
2. In all five study houses, SSD or DTD
in the basement alone, without direct
treatment of the adjoining slab, was
sufficient to reduce concentrations
throughout the house below 4 pCi/L.
In three of the houses, concentra-
tions were reduced below 2 pCi/L
throughout the house. The incre-
mental benefit of treating both slabs
simultaneously, relative to base-
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ment-only treatment, was an addi-
tional reduction of 0.3 to 2.9 pCi/L in
the basement, and of exactly the
same range in the living area above
the slab on grade. Thus, it would
appear to be generally advanta-
geous to add a slab-on-grade leg to
a basement treatment system; how-
ever, it will not always be neces-
sary, depending upon the radon
reduction desired and the impor-
tance of the adjoining slab as a
radon source.
3. In all five houses, SSD under the
adjoining slab alone, without direct
treatment of the basement, was suf-
ficient to reduce concentrations be-
low 4 pCi/L in the living area above
the slab on grade; concentrations
- ~were reduced below 2 pCi/L in the
living area in four of the houses.
Living-area reductions were usually
greater than they had been with
basement-only treatment. However,
adjoining-slab-only treatment re-
duced concentrations in the base-
ment below 4 pCi/L in only three of
the five houses, and below 2 pCi/L
in only one. The incremental benefit
of treating both slabs simultaneously,
relative to adjoining-slab-only treat-
ment, was 0.1 to 5.2 pCi/L in the
basement (averaging 2.9 pCi/L), and
0 to 0.5 pCi/L in the living area.
Thus, if the basement is rarely oc-
cupied, it might be sufficient to treat
the adjoining slab alone; however,
in terms of house-wide reductions, it
would appear generally not desir-
able to install a system to treat the
adjoining slab without also installing
a leg to treat the basement.
4. If the adjoining slab is ah important
contributor to radon levels inside the
house, the chances appear in-
creased .that treatment of both slabs
will be necessary in order to achieve
high house-wide reductions. In no
case where the adjoining slab was
an important source, was
basement-only treatment adequate
to reduce basement levels below
3.3 pCi/L, even when sub-slab com-
munication was good. However, in
the one case where communication
was good, basement-only treatment
was sufficient to reduce living-area
levels below 2 pCi/L despite the ap-
parent importance of the adjoining
slab as a source.
5. Houses where sub-slab communi-
cation is poor are most likely to re-
quire simultaneous treatment of both
slabs, especially when both wings
are important contributors to indoor
radon levels.
6. Where sub-slab communication is
good, performance of the basement
treatment system (either by itself, or
in conjunction with the adjoining slab
system) is not noticeably influenced
by whether or not a sump/drain tile
system is present. That is, where
communication is good, a SSD sys-
tem performs as well as a DTD sys-
tem in otherwise comparable houses.
7. While a definitive conclusion is not
possible from these data regarding the
effects of house size, the results are
consistent with the expectation that
larger houses (e.g., with a house foot-
print larger than 1,250 ft2*) are more
likely to require simultaneous treat-
—* ment of both slabs to achieve high
house-wide radon reductions.
8. In the houses tested here, the pres-
ence of forced-air supply ducts be-
neath the adjoining slab on grade did
not appear to detract from the perfor-
mance of the mitigation systems, in
any of the system configurations.
Basement Houses Having Adjoining
Crawl Spaces
Active soil depressurization techniques
were tested in six Maryland houses having
basements with adjoining crawl spaces.
Pre-mitigation radon concentrations in these
houses ranged from 4.2 to 12.7 pCi/L in the
basement, and from 3.0 to 5.4 pCi/L in the
living area above the crawl space.
This testing led to several conclusions.
1. Where communication beneath the
basement slab was excellent, treat-
ment of the basement alone gave ra-
don reductions, in both the basement
and the living area, comparable to (or
only marginally poorer than) those
achieved when both wings were
treated. In the two houses where
communication was excellent and
where testing was successfully com-
pleted, concentrations were reduced
below 1 pCi/L both by basement-only
treatment and by simultaneous treat-
ment of both wings. This effective
basement-only result was obtained
despite the fact that the crawl space
clearly appeared to be a major radon
source in one of the two houses. Thus,
where sub-slab communication is very
good, it might not always be neces-
sary to incur the cost of treating the
crawl space.
2. In the one house where sub-slab
communication was very poor and
* 1 ft2 = 0.093 m2
where the crawl space appeared to
be a radon source, SSD in the base-
ment alone gave only moderate
house-wide reductions (about 50%),
failing to reduce the basement below
4 pCi/L. But combined SSD in the
basement and SLD in the crawl space
reduced concentrations to about 1
pCi/L. Thus, these worst-case condi-
, tions (communication is poor and
crawl space is an important source)
increase the likelihood that simulta-
neous treatment of both wings will be
necessary.
3. In all three houses where crawl-
space-only treatment was success-
fully tested, SLD in the crawl space
alone was sufficient to reduce con-
centrations below 3 pCi/L throughout
the house (reductions of 17 to 76%).
In the two houses where sub-slab
communication was very good,
basement-only treatment gave clearly
better reductions than did crawl-
space-only treatment. But in the third
house, with poor communication and
with the crawl space being an impor-
tant radon source, crawl-space-only
treatment gave better reductions than
did basement-only treatment. In all
cases, simultaneous treatment of both
wings gave distinctly superior reduc-
tions compared to crawl-space-only
treatment. The incremental benefit of
treating both the basement and the
crawl space, relative to crawl-
space-only treatment, was an addi-
tional reduction of 1.0 to 2.7 pCi/L in
the basement, and of 0.7 to 2.1 pCi/L
in the living area. Thus, in no case
would it appear desirable to install a
crawl-space SLD system without also
installing a leg to treat the basement.
4. With the SLD system in the crawl
space operating alone, without direct
treatment of the basement, :the sys-,
tern was tested with alternate de- *
grees of sealing of the polyethylene
liner. In one case, the liner was sealed
only at seams between the sheets of
plastic, but not around the perimeter
where the liner met the foundation
wall. In the second case, the liner
was also sealed to the foundation
wall, as well as at seams between
sheets. In all cases, sealing around
the perimeter resulted in a small but
noticeable improvement in radon re-
ductions on both stories, giving an
incremental reduction in concentra-
tions of 1.2 to 1.6 pCi/L in the base-
ment, and of 0.5 to 1.2 pCi/L in the
living area.
5. When the crawl space is an impor-
tant radon source, performance of the
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mitigation system does not appear to
be significantly affected, so long as
the communication beneath the
basement slab Is good. That is,
basement-only treatment can appar-
ently still treat the entire house, as
indicated previously. But if sub-slab
communication is poor, simultaneous
treatment of both wings is more likely
to be required when the crawl space
is an important source.
6. When communication beneath the
basement slab is poor, a simple
one-pipe SSD system in the base-
ment combined with a SLD system in
the crawl space will not always be
sufficient. In one house tested here,
three SSD pipes In the basement
were required in order to achieve
concentrations below 4 pCi/L -in the —
basement.
7. The results from this testing do not
permit any definitive conclusions re-
garding any possible effect or mitiga-
tion performance of: a) the presence
of a sump in the basement, permit-
ting installation of a DTD system,
which might improve the distribution
of suction under the slab; b) the size
of the house; c) the material of con-
struction of the foundation wall (hol-
low block vs. poured concrete); or d)
the nature of the crawl-space floor
(bare soil vs. gravel over soil).
Slab-on-grade House Having Sub-
slab Forced-air Supply Ducts
An active SSD system was tested in
one large (2,700 ft2) slab-on-grade house
in Maryland, having forced-air heating sup-
ply ducts beneath the slab. The SSD sys-
tem included one suction pipe at a central
location in the house; The objective of this—
testing was to determine whether such a
simple SSD system could achieve high
radon reductions in a slab-on-grade house
having several complications (sub-slab
heating ducts, large slab, block foundation
wall), in cases where there is good aggre-
gate under the slab. This testing was to
confirm results on similar slab-on-grade
houses in Ohio, where high reductions
were achieved with one- or two-pipe SSD
systems despite the concern that the
sub-slab ducts would prevent the effective
distribution of suction under the slab.
Pre-mitigation concentrations of 7.1 to
21.0 pCi/L were reduced below 1 pCi/L by
operation of the one-pipe SSD system in
the Maryland house. This performance was
even better than had been achieved in the
one house in Ohio which was completely
comparable (sub-slab ducts, large, block
foundation). The Ohio house (with a
pre-mitigation level of 15.7 pCi/L) had been
reduced to 1.7 pCi/L with two suction pipes,
~ and to 6:7-7.7 pCr/L"withone"suction piper
This testing demonstrates that, when there
is a good layer of aggregate beneath the
slab, large slab-on-grade houses can be
treated with relatively simple SSD sys-
tems, even when there are sub-slab ducts.
Marc MessingIs with Infiltec, Falls Church, VA 22041.
D. Bruca Henschel is the EPA Project Officer (see below).
The complete report, entitled "Testing of Indoor Radon Reduction Techniques in
Basement Houses Having Adjoining Wings," (Order No. PB91-12S 831'/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
BULK RATE
POSTAGE & FEES PAID
EPA PERMIT NO. G-35
Official Business
Penalty for Private Use $300
EPA/600/S8-90/076
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