United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S.8-88/002 Feb. 1988
&EPA Project Summary
Installation and Testing of
Indoor Radon Reduction
Techniques in 40 Eastern
Pennsylvania Houses
Arthur G. Scott
Indoor radon reduction measures
were tested in 40 existing houses
with significantly evaluated radon
concentrations in eastern
Pennsylvania. In all but one, soil gas
was the predominant source of the
radon. The houses all had
basements, sometimes with an
adjoining slab-on-grade or crawl-
space wing. Most of the radon
mitigation techniques involved some
form of active soil ventilation. In
addition, three heat recovery
ventilators (HRVs) were tested, and
two carbon filters were tested for
removing radon from well water.
The tests showed that significant
radon reductions (90 - 99%) can be
achieved with properly designed
active soil ventilation systems. In
basement houses with concrete floor
slabs, suction on perimeter drain
tiles can be very effective when a
reasonably complete loop of drain
tiles exist. Sub-slab suction (with
individual suction pipes penetrating
the sub-slab region) would be the
next technique of choice, though it
can be important that the suction
pipes be carefully located when
sub-slab permeability is poor.
Ventilation of block wall cavities can
give less predictable results. HRVs
can provide moderate radon
reductions (usually no greater than
about 50% for reasonably sized
HRVs), although their effectiveness
in different parts of a house cannot
always be reliably predicted. Carbon
filtration can remove significant
amounts of radon from water (up to
95-99%), at least over the 9-month
period that they were tested in this
study. The source of the carbon can
be very important.
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 program
to develop and demonstrate cost-
effective methods for reducing the
concentrations of naturally occurring
radon gas inside houses. This program
is investigating the full range of radon
reduction measures, in an effort to
demonstrate suitable mitigation
approaches for the full range of housing
substructure types, housing design and
construction methods, initial radon
concentrations, and geological 'conditions
representative of U.S. houses.
This report describes one project in
the overall EPA radon mitigation
program. Specifically, it describes the
installation of developmental radon
reduction measures in 40 existing high-
radon houses located in the Reading
Prong region of eastern Pennsylvania.
The 40 houses were selected to be
representative of the substructure types
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common in that region. All of the houses
have basements with concrete floor
slabs, sometimes with an adjoining
slab-on-grade or crawl-space wing.
The foundation walls are constructed of
hollow block in 30 of the houses, and
poured concrete in the remaining 10. The
houses were selected to have initial
indoor radon concentrations of at least
740 becquerels/cubic meter (Bq/m3)-or
20 picocuries/Iiter (pCi/L)-as determined
by measurements by the Pennsylvania
Department of Environmental Resources
(PDER). One house had an initial level of
1 200 pCi/L (44,000 Bq/m3). In all but
oie house, soil gas is the predominant
source of the radon. Well water is the
predominant source in the remaining
house (with up to 11.5 MBq/m3, or
310,000 pCi/L in the water), and is an
important secondary contributor in
several other houses. Extensive gamma
measurements in and around the houses
gave no suggestion that building
materials are an important radon
contributor.
Active soil ventilation approaches for
radon reduction were selected for testing
in most of the houses. Where soil gas is
the predominant source, these
approaches appear to offer the potential
for achieving, at moderate cost, the very
high levels of reduction needed to reach
the EPA guideline of 148 Bq/m3 (4 pCi/L)
in some of these houses (sometimes
over 99%). Air-to-air heat exchangers
(or HRVs) for increased house ventilation
were tested in three houses, where the
initial radon level is less severely
e'svatod (generally where reductions no
greater than 75% are required). Greater
reductions with HRVs were not
considered practical in view of the natural
infiltration rates in these houses. Well
water treatment systems were tested in
two houses.
The general principle of soil ventilation
is to draw or blow the soil gas away from
th© house before it can enter. Most
commonly, fans are used: a) to draw
suction on the soil around the foundation
in an attempt to suck the soil gas out of
the soil and to vent it away from the
house: or b) to blow outdoor air into the
soil, creating a "pressure bubble"
underneath the house which forces the
soil gas away. When fans are used to
ventilate soil in either manner, the
approach is referred to as active soil
ventilation.
In this project, soil was actively
ventilated in several different ways.
• Suction on drain tiles which are
sometimes located beside the footings
for water drainage purposes. The
drain tiles can be present around the
outside of trie footings (exterior drain
tiles), or around the inside, under the
slab (interior drain tiles). If the tiles
drain to sump inside the house, drain
tile suction involves suction on the
sump.
Suction on tie region underneath the
concrete floor slab, by inserting
suction pipes vertically down through
the slab from; inside the house.
Suction on (or pressurization of) the
network of voids inside hollow-block
foundation | walls. This can be
accomplishpd either by inserting
individual ventilation pipes into the
void, network, or by installing a
baseboard duct which covers holes
drilled into trie block cavities.
Measurement Procedures
The performance of the radon
reduction syste'ms was determined using
two types of radon measurements on the
indoor air. The first type was 2 to 4 days
of hourly Pylon measurements in the
basement with all basement doors and
windows closed, both before and after
system activation ("short-term").
Sometimes measurements were also
made .upstair^. These measurements
provided an immediate indication of the
approximate percentage radon reduction,
and of whether the post-mitigation
concentration had been reduced below
148 Bq/m3 (4 !pCi/L). The second type
involved 3-mohth alpha-track detector
exposure during cold weather ("long
term"). This measurement indicated
whether the house was being reduced
below 148 Bq/m3 under cold-weather
conditions, whi|ch would be expected to
challenge tl)e mitigation system
performance. By comparison against any
alpha-track measurements made by the
PDER the previous winter, these long-
term measurements could also suggest
the winter-tim;e long-term percentage
reduction. [
In addition j to the radon measure-
ments, various diagnostic tests were
conducted be'fore mitigation to help
design the system, and after mitigation to
help evaluate system performance. .
Results j
Table 1 summarizes the result from
the 40 houses. For simplicity, only the
ultimate reduction system for each house
is listed. Some of the houses had more
than one installation during the course of
this project, arjd some installations were
modified as the testing proceeded, as
described in the report.
The radon measurements reported in
Table 1 are the arithmetic averages of at
least 48 hours of hourly measurements
using a Pylon AB-5 semi-continous
radon monitor, both before and after the
mitigation system was activated. For all
except House 18, the measurements
were in the basement with doors and
windows closed. In essentially all cases,
the post-mitigation values were
measured during cold weather.
Conclusions
The following conclusions are based
on the results of this testing:
1. If a complete loop of perimeter drain
tiles is present, suction on this loop
should be one of first reduction
approaches considered because: a)
the tiles permit suction to be drawn
effectively where it is generally
needed the most, and high reductions
are often achieved; b) drain tile suction
is generally the least expensive active
soil ventilation approach, and is the
most amenable to do-it-yourself;
and c) where tiles drain to a point
outside the house, the entire
installation is outdoors, thus offering
advantages in convenience and
aesthetics. Unfortunately, loops are
not always complete.
2. Even where only a partial drain tile
loop exists, drain tile suction can
sometimes provide significant
reductions and under some
circumstances, might still be cost-
effective to install before attempting
additional measures.
3. Sub-slab suction, using pipes
• penetrating the sub-slab region, can
be very effective in houses with either
hollow-block or poured concrete
foundation walls. Accordingly, it
should be considered as a candidate
control approach whenever significant
levels of reduction are needed. If
sub-slab permeability is good, one or
two suction points might be sufficient,
if the system is properly designed. If
sub-slab permeability is not good,
more suction pipes might be needed,
and location of the pipes near the soil
gas entry routes can become more
important. In such cases, best results
appear to be achieved when one or
more suction points are placed near
each load-bearing block wall
(including interior as well as perimeter
walls). The actual number and location
of suction points required in a given
house will depend on the nature and
uniformity of sub-slab permeability,
the location of major soil gas entry
routes, and system design parameters
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Table 1. Summary of Results from Radon Mitigation Tests in 40 Eastern Pennsylvania Houses
Mean Radon Levels,
House No. Substructure Type Final Mitigation pCi/L Reduction, %
Before
After
1
Block basement
Block basement
Wall and sub-slab 161
pressurization
(baseboard duct)
Wall and sub-slab 238
pressurization
(baseboard duct
and carbon filter on
well water)
97
99
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
Block basement
Block basement
Block basement
Block basement
Block basement
Block basement
Block basement
Block basement
Block basement
Block basement
Block basement
Block basement
Block basement
Block basement &
paved crawl space
Block basement
Block basement
Block Basement
Block basement &
paved crawl space
Block Basement
Poured concrete
basement & slab on
rtrarlf*
Wall and sub-slab
suction
Sub-slab suction
Wall pressurization
Sub-slab suction
Sub-slab and wall
suction
Wall suction
Wall & Sub-slab
pressurization
(baseboard duct
over French' drain)
Drain tile suction
(exterior)
Wall & sub-slab
suction (baseboard
duct over French
drain)
Drain tile suction
(exterior)
Drain tile suction
(exterior)
Wall suction
Drain tile suction
(exterior)
Wall suction
HRW
HRV
Wall Suction
Sub-slab & wall
suction, & suction
on interior drain
tiles in crawl space
Sub-slab suction
Sub-slab suction
(basement & slab)
1205
20
110
60
402
88
360
209
60
11
94
61
18
240
60
2
35
282
111
34
5
3
5
5
4
6
7
7
21
3
2
1
1
4
38
1
11
4
3
9
99
86
95
92
99
93
98
97
65
75
98
98
98
98
37
50
68
99
97
74
(Continued)
aHeat recovery ventilator
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Table 1. (Continued)
House No. Substructure Type
Final Mitigation
Mean Radon Levels,
pCi/L
Reduction, %
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
Poured concrete
basement & slab on
grade
Poured concrete
basement
Poured concrete
basement
Block Basement
Block Basement
Block Basement
Block basement &
unpaved crawl
space
Block Basement
Block Basement
Block Basement
Poured concrete
basement
Poured concrete
basement
Poured concrete
basement
Poured concrete
basement & slab on
grade
Poured concrete
basement & slab on
grade
Block Basement
Block Basement
Poured concrete
basement
Sub-slab suction
(basement & slab)
i
Sub-slab suction
Sub-slab suction
Draft tile suction
(exterior)
Draft tile suction
(exterior)
HRV
Draft tile suction
(interior, sump) &
crawl space
liner/vent
Carbon filter on well
water
Sub-Slab suction
Sub-Slab suction
SubLSlab suction
Sub-Slab suction
Sub-Slab suction
Sub-slab suction
(basement & slab)
Subrslab suction
(basement only)
Sub-Slab suction
Sub-Slab suction
Sub-Slab suction
Before
95
44
148
89
42
16
47
29
485
6
84
696
164
142
19
375
24
113
After
3
3
8
T
3
10
2
5
4
1
5
5
1
2
1
5
2
3
97
93
93
99
93
38
96
83
99
80
94
99
99
99
97
99
93
97
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(e.g., if a hole is excavated under the
slab where the pipe penetrates, in
order to reduce system pressure
loss). It appears that, through proper
system design, sub-slab suction can
be made to give high reductions even
in houses with limited or poor sub-
slab permeability. Diagnostic testing
of the permeability before installation
could aid in assessing the complexity
of the sub-slab system that will be
required in a given house.
4. In houses with block foundation walls,
ventilation of the yoid network inside
the walls can give high degrees of
radon reduction, if major wall
openings can be adequately closed
and if there are no major slab-related
soil gas entry routes remote from the
walls, Current results suggest that a
well-designed sub-slab suction
system by itself might be expected to
effectively treat both slab- and wall-
related entry routes more often than
might a wall ventilation system alone.
Accordingly, in many block basement
houses needing high reduction, it
might be advisable to initially consider
sub-slab suction rather than wall
ventilation. Wall ventilation might
sometimes be required in combination
with sub-slab suction to reduce high
radon block houses below 148 Bq/m3
(4 pCi/L).
5. With any active soil ventilation
technique, it is crucial that major
openings in the slab and wall be
closed, before effective suction can be
drawn. Sumps should be capped even
if suction on the sump is not planned.
!n houses with French drains that are
needed to handle water drainage, the
closure must retain the water drainage
capabilities. Floor drains connecting to
the soil should be trapped or plugged
to prevent soil gas entry.
6. With any active sub-slab technique,
best results have been achieved when
the fan being used can maintain at
least 150 Pa at the suction points with
the soil gas flows encountered,
typically 20 to 70 L/sec.
7. As expected, dilution appears to be a
major mechanism in determining the
performance of HRVs. However, other
mechanisms (e.g., changes in soil gas
influx) can also play a role, so that the
radon reduction performance of an
HRV on different floors of a given
house cannot always be reliably
predicted a priori based solely on
dilution considerations. Moderate
reductions (up to 80% in some parts
of the house under some circum-
stances) can be achieved with a
reasonably sized HRV in houses with
typical natural infiltration rates,
sometimes at the expense of lesser
reductions in other parts of the house.
One issue in selecting an HRV is
whether it will be cost-effective
relative to a comparable increase in
natural ventilation without heat
recovery.
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A. G. Scott is with American ATCON, Inc., P. O. Box 1347,
Wilmington, DE 19899.
D. Bruce Henschel is the EPA Project Officer (see below).
The complete report', entitled "Installation and Testing of Indoor Radon
Reduction Techniques in 40 Eastern Pennsylvania Houses," (Order No. PS 88-
156617/AS; Cost: $32.95, 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
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA^600/S8-88/002
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