United States
Environmental Protection
Agency
Research and Development
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 2771T
EPA/600/S8-90/081 Feb. 1991
EPA Project Summary
Follow-Up Annual Alpha-Track
Monitoring in 40 Eastern
Pennsylvania Houses with
Indoor Radon Reduction
Systems (December 1988 -
December 1989)
A. G. Scott and A. Robertson
Between June 1985 and June 1987,
developmental indoor radon reduction
techniques were installed in 40 houses
in the Reading Prong region of eastern
Pennsylvania. Most of these systems
involved some form of active soil venti-
lation, although three involved heat re-
covery ventilators and two included
carbon filters to remove radon from well
water. The initial reductions in indoor
radon concentrations achieved in each
house were described in an earlier report.
Follow-up alpha-track detector (AID)
measurements of radon concentrations
in these houses during the winters of
1987-88 and 1988-89 were also described
earlier.
The purpose of the current study was
to make follow-up ATD measurements in
the living area of these houses over an
entire year (December 1988-December
1989), 2 to 4 years after the installations
were completed. Since these figures re-
flect annual averages in the living area,
they are the best measures to date of the
effectiveness of the mitigation systems
in reducing occupant exposures after
several years of operation.
Of the 28 houses where the radon
mitigation system was in operation
during the entire year, the annual aver-
age radon levels measured in the living
area were within 1 pCi/L* of the previous
winter-quarter averages In all but six.
Almost half of the houses were below 2
*1 pCi/L = 37Bq/m1
pCi/L, and three-quarters were below 4
pCi/L. It Is believed that most of the
residual radon in these houses results
from re-entrainment of fan exhaust back
into the house, and, to a lesser extent,
from radon released from well water.
Inadequate treatment of the floor slab by
the active soil depressurization system
does not appear to be the primary cause
of the residual radon in most of these
houses.
Of 34 soil depressurization fans oper-
ating under this project, 6 have failed to
date. Five of these six failures resulted
from failure of the capacitor in the fan
circuitry.
This Project Summary was developed
by ERA'S Air and Energy Engineering
Research Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
The U.S. Environmental Protection
Agency (EPA) is conducting a program to
develop and demonstrate cost-effective
methods for reducing the concentrations of
naturally occurring radon gas inside houses.
As part of this program, EPA sponsored the
installation of developmental radon reduc-
tion measures in 40 existing houses in east-
ern Pennsylvania having high initial radon
levels—above 20 picoCuries per liter (pCi/
L). These houses had substructures repre-
sentative of the region—basements having
^g§> Printed on Recycled Paper
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block or poured concrete foundation walls,
sometimes with an adjoining slab-on^grade
or crawl-space wing. Active soil ventilation,
utilizing a fan—sub-slab suction, drain tile
suction, or block wall suction or pressur-
iration—were tested in most of the houses.
Heat recovery ventilators (air-to-air heat
exchangers) were tested in three houses
having only moderately elevated radon lev-
els, and charcoal treatment of well water
was tested in two houses. The installations
in these 40 houses, and the initial system
performances, were reported earlier.
To test the durability of these installa-
tions, 3-to 4- month ATD measurements of
radon concentrations were made during the
winter periods since the installations were
completed. Measurements during the win-
ters of 1987-88 and of 1988-89 were re-
ported earlier. Measurements in the living
area between December 1988 and De-
cember 1989 are reported here. This 1 -year
measurement period was selected to de-
termine the annual average levels to which
the occupants were being exposed.
The measurements reported here were
completed in the 38 of the 40 houses which
still have operating systems. Of the 2 houses
no longer with operating systems, 1 was
moved from its original site afterthe system
was installed; intheother.theownerdecided
to discontinue participation in the project.
Measurement Procedures
The measurements were made using
Terradex "Type SF" Track Etch ATDs. In
each house, a cluster of two ATDs were
hung together in the living area (the story
above the basement), from an interior wall
or ceiling. Clusters of two were used to
permit identification of outliers.
The detectors were deployed in mid-De-
cember 1988, and retrieved in mid-Decem-
ber 1989, by an experienced professional.
The exposed detectors were returned to the
Terradex laboratories for analysis.
For quality assurance, six unexposed
detectors were returned to Terradex as
blind blanks, to determine the zero correc-
tion. Also, as part of the previous winter-
quarter measurements, 10 detectors were
exposed to known radon environments in a
test chamber for a selected duration, and
returned to Terradex as blind spikes, to
determine the gain correction.
Results and Discussion
Of the 38 houses in which ATDs were
deployed, it was found upon retrieval of the
detectors that the mitigation system fans
had been off in 10 houses during some
portion of the measurement period. In three
houses, the soil depressurization fan failed;
in five other houses, the fan had deliberately
been turned off during mild weather when
the homeowner usually opened the win-
dows, in the belief that increased natural
house ventilation would compensate forthe
system's being off; in a another house, the
soil depressurization fan was inadvertently
unplugged; and in another house, the fan
motor in a heat recovery ventilator failed.
Thus, in only 28 houses do the ATD results
give radon concentrations representative of
uninterrupted system operation over the
year.
The results from these 28 houses are
presented in Table 1. The radon concentra-
tions listed in the column "1989 Annual" are
from this measurement effort; each number
is theaverage of the two ATDs inthe cluster,
corrected using thezero and gain corrections
from the blanks and spikes. Results are also
shown for post-mitigation ATD measure-
ments during the previous winter quarters
where available ("1989 Winter'forthe winter
of 1988-89, etc.). Pre-mitigation results,
usually from an ATD measurement during
an earlier heating season, are also shown
for each house.
A review of the data for all 28 houses in
Table 1 shows that the annual average
concentration in the living area measured
throughout 1989 is not as greatly different
from the 1988-89 winter-quarter average as
might have been expected. Within a toler-
ance of ± 0.3 pCi/L: 10 of the 28 houses
have annual averages in the living area
equal to the Winter 1989 value, ± 0.3 pCi/L;
8 houses have annual averages lower than
the winter-quarter value; and 10 houses
have annual averages greaterthan the win-
ter-q'uarter value. This is a fairly uniform
distribution. When the band of allowable
difference is increased to ±1.0 pCi/L (not an
unreasonable allowance, given the variabil-
ity of radon levels in a given house, and
giventhe accuracy of the ATD measurement
method at these low concentrations): 22 of
the 28 houses have annual averages equal
to the Winter 1989 quarterly value; 2 have
lower annual averages (Houses 18 and 28,
both with HRVs); and 4 have higher annual
averages (Houses. 10, 25, 27, and 39).
Among that group of four houses having
annual averages greaterthan their winter-
quarter means, all but House 27 are among
the group having annual averages above 4
pCi/L In summary, in only six houses does
the 1988-89 winter-quarter concentration in
the living area differ from the annual aver-
age by more than 1.0 pCi/L, and in four of
those cases, the winter-quarter concentra-
tion is towerthan the annual average. Simi-
lar results are obtained when this analysis is
expanded to include winter-quarter data for
the prior winters.
Since radon measurements have often
been made in the winter with the expecta-
tion of maximizing the radon concentration,
it is to be noted that, more often than not
among these houses, the winter-quarter
post-mitigation average can be lower than
the annual average. There are thoughtto be
two reasons why the annual average is
commonly higher. First, opened windows
during mild weather probably increased the
amount of fan exhaust re-|entrained back
into the house. Second, there are probably
additional, unreported cases where the
occupant turned off the system during peri-
ods of mild weather when the windows are
opened. (Of the five houses where it is
known that the fan was turned off when
windows were opened, radon levels in the
living area increased significantly in four of
these, probably due to the very high source
term in this region, and to the likelihood that
the windows were not constantly open.)
Almost half of the 28 houses with continu-
ously-operating systems have been reduced
to below 2 pCi/L in the living area on an
annual average, compared to pre-mitigation
(cold-weather) values in the hundreds of
pCi/L in many cases. Over three-quarters
are below 4 pCi/L on an annual average.
Based upon testing conducted after this
year-long measurement period was com-
pleted, it is believed that most of the residual
radon in many of these houses is due to re-
entrainment of fan exhaust, and, to a lesser
extent, airborne radon resulting from radon
in the well water. Most of the active soil
depressurization systems in this project are
maintaining at least a marginal (and some-
times a very good) suction field beneath the
floor slabs; thus, the residual radon is often
not the result of poor sub-slab communica-
tion and insufficient suction field extension,
as had previously been thought. Care in the
design of the fan exhaust, to reduce re-
entrainment, is clearly important when the
exhaust contains such high radon concen-
trations as com monly encountered in eastern
Pennsylvania (often greater than 1,000-
2,000 pCi/L). It is believed that essentially
all of these houses could be reduced below
2-4 pCi/L if the re-entrainment and well
water contributions were addressed.
The generally consistent performance of
these mitigation systems over the two to
four years since installation demonstrates
the durability of these systems over that
time period. Only where the soil depressur-
ization fan failed, or where the system had
been turned off by the occupant, did radon
levels show a significant increase. Five of
the six fan failures to date have resulted
from failures of the electrolytic capacitor in
the fan circuitry, ft was learned from the fan
manufacturerthatthe capacitors installed in
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most of the fans in this project were rated at
a 40,000-hour lifetime, which would corre-
spond to 4 to 5 years of continuous opera-
tion. If this lifetime rating is accurate, more
fan failures might be anticipated in the near
future as some of these systems approach
5 years of operation.
In House 40, where the capacitor failed
while the fan was operating, the fan contin-
ued to operate, at greatly reduced suction
and flow, for up to a year following the
capacitorfailure. (If the fan had been turned
off during that period, it would not have re-
started.) To the occupant, the fan sounded
as if it were operating normally. Thefact that
the fan can continue to operate, but at
greatly reduced performance, following ca-
pacitorfailure is further indication that pres-
sure- and/or flow-actuated alarms are nec-
essary on active soil depressurization sys-
tems.
The performance was checked of the two
activated charcoal water treatment units
installed in 1986 under the original project.
The one unit containing a charcoal specifi-
cally selected for radon removal was still
achieving 97% removal, within the range
(95-99%) that has been observed since
installation. However, the radon removal
efficiency of the second unit—containing a
generally available charcoal not specifically
selected for radon—continued a steady
decline, now down to 38%.
Tab/el. Living Area ATD Results to Date Houses with Mitigation Fans Operating Throughout the 12/88-12/89
Annual Measurement Period
Average Radon Concentration (pd'/L)
House
ID#
3
4
5
6
8
10
12
15
16
18
20
21
23
24
25
26
27
28
29
30
32
33
34
35
Type*
1
1
1
1
1
1
1
1
2
1
2
•1
3
4
4
1
1
1
5
1
1
4
4
4
Final
Mitigation System
Wall + sub-slab
suction
Sub-slab suction
Wall pressurization
Sub-slab suction
Wall suction
Drain tile suction
Drain tile suction
Drain tile suction
Wall suction
Heat recovery
ventilator
Sub-slab + wall
suction in bsmt;suction
under crawl-space slab
Sub-slab suction
Sub-slab suction
(basement + slab)
Sub-slab suction
Sub-slab suction
Drain tile suction
Drain tile suction
Heat recovery
ventilator
Drain tile suction
(interior sump)-i-
suction under crawl-
space liner
Carbon adsorption
treatment of well
water
Sub-slab suction
Sub-slab suction
Sub-slab suction
Sub-slab suction
Premiti-
gation**
350
25
(110)
60
183
626
(11)
(18)
395
12
. 210
172
98
66
122
(89)
21
21
61
17
(6)
82
470
144
1989
Annual
1.8
0.5
4.0
2.3
1.1
12.1
1.3
0.9
1.5
3.6
10.0
3.7
1.6
3.2.
6.4
1.0
3.9
3.6
3.0
1.9
4.0
0.6
5.8
0.7
Post-Mitigation""
1989 1988 1987
Winter Winter Winter
1.9
1.0
4.4
2.7
1.0
8.9
2.1
1.3
1.1
5.1
9.3
2.7
1.5
3.7
5.3
1.1
2.1
5.1
2.3
2.1
3.2
0.7
5.5
1.0
2.3
3.1'
4.4
3.2
1.5
9.9
2.2
11. Of
2.5
3.4
10.0
2.7
1.6
3.8
6.0
1.6
2.2
4.4
2.0
1.6
4.4
1.2
5.5
. 0.9
2.1
0.8
4.3
4.9
1.8
6.5
2.5
1.0
1.7
2.1
9.9
2.6
4.6
3.0
1.5
2.2
5.3
1.4
1.3
3.2
1:1
3.7
0.7
1986
Winter
1.7
1.3
3.0
— .
.
• '
___.
(continued)
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Tablet 1. (Continued)
Average Radom Concentration (pCi/U
House
/D#
36
37
38
39
Type
3
3
1
1
Final
Mitigation System
Sub-slab suction
(basement + slab
Sub-slab suction
(basement only)
Sub-slab suction
Sub-slab suction
Permiti-
gation"
300
87
309
111
1989
Annual
0.7
0.9
6.6
4.1
Post-Mitigation"'
1989 1988 1987 1986
Winter Winter Winter Winter
0.7
0.5
7.3
1.8
1.0 0.7 —
0.7 1.7 —
72 _-_ —
17.5" — —
•House Type:
1 -Block basement walls
2 - Block basement waits + paved crawl space
3 - Poured concrete basement walls + slab on grade
4 m Poured concrete basement walls
5 - Block basement walls + unpaved crawl space
"Many ol these pro-mitigation radon concentrations were probably obtained in the basement, and thus might not be directly compa
rablo to the living-area post-mitigation results in the remainder of the table. Pre-mitigation concentrations reported here represent
a single Terradex Track Etch alpha-track detector measurement arranged by the Pennsylvania Department of Environmental
Resources during a heating season prior to installation of EPA's radon mitigation system. The exact location of these detectors is
not always known; In some cases, this pre-mitigation measurement might have been made in the basement. Where it is known that
the pro-mitigation ATD was not placed in a representative location, or where the ATD result was clearly not representative of
subsequent Pylon measurements made by EPA, the pre-mitigation concentration shown here is the average of at least 48 hours
of hourly radon measurements made in the basement during cold weather using a Pylon AB-5 continuous radon monitor. (Pylon
measurements were generally not made in the living area during this early testing.) Where Pylon measurements have been used,
the pro-mitigation value Is shown in parentheses. The Pylon measurements were made during the 1965-87 system installation
period.
'"Post-mitigation living-area radon concentrations reported here represent the average of clusters of two (1989) or three (pre-1989)
ATDs. The 1989 annual detectors were exposed between December 1988 - December 1989; the values shown in this table
are the corrected averages. The Winter 1989 detectors were exposed for 4 months (December 1988 -April 1989); the Winter
1988 detectors were exposed for 3 months (December 1987 - March 1988). The Winter 1987 ATD measurements
(December 1986 - March 1987) and the Winter 1986 ATD measurements (December 1985 - March 1986) were
reported hi the final report on the original project. All results in this table have been corrected using the zero and gain corrections.
• A superscript "a" indicates that the ATD measurements in that house during thatyear are not representative of an operating mitigation
system, because the system fan was off for part or all of that measurement period.
—Absence of results for 1986 or 1987 for a given house indicates that: alpha-track measurements were not made in that house that
winter; or the radon mitigation system was changed significantly between that winter and the following winter; or the alpha-track
measurement was made significantly outside the December - March window due to the system installation schedule..
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A.G. Scott and A. Robertson are with American Atcon, Inc., Wilmington, DE 19899.
D. Bruce Henschel is the EPA Project Officer (see below).
The complete report, entitled "Follow-Up Annual Alpha-Track Monitoring in 40 Eastern
Pennsylvania Houses with Indoor Radon Reduction Systems (December 1988-
December 1989)," (Order No. PB91-127 779/AS; Cost: $15.00, 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 Off her 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/S8-90/081
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