United States
                     Environmental Protection
                     Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
                     Research and Development
EPA/600/S8-90/061 Jan. 1991
&EPA         Project Summary

                     Radon  Mitigation  Studies:
                     Nashville Demonstration
                     Bobby E. Pyle and Ashley D. Williamson
                      In this EPA  radon  mitigation
                    demonstration project, 14 houses  in
                    the Nashville, TN area with indoor
                    radon levels  of 5.6 - 47.6 pCi/L* were
                    mitigated using  a  variety  of tech-
                    niques. These techniques were de-
                    signed to be the most cost-effective
                    methods possible to implement, and
                    yet adequately  reduce the  radon
                    levels  to <4 pCi/L.  For the crawl
                    space houses, these  techniques in-
                    cluded sealing the openings between
                    the living areas and the crawl space
                    and then passively venting the crawl
                    space, depressurizing  the  crawl
                    space, depressurizing  under poly-
                    ethylene sheeting in the crawl space,
                    and depressurizing  the crawl  space
                    soil itself. For  the basement  and
                    basement-crawl  space combination
                    houses, the techniques included sub-
                    slab pressurization and depressuriza-
                    tion, block wall depressurization, and
                    combinations' of these techniques
                    with some of those  above for the
                    exposed soil areas. Post-mitigation
                    worst case  radon  levels in  these
                    houses were generally  from <1 to
                    about 5 pCi/L with one house near 15
                    pCi/L. These houses are currently be-
                    ing  followed  with alpha-track detec-
                    tors to  assess the  long  term
                    exposure levels.
                        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
                     * Readers more familiar with metric units may
                      use the factors listed at the end  of this
                      Summary to convert to that system.
separate report of the same title (see
Project Report ordering information at
back).

Introduction

Purpose
  The  primary purpose of the  work
described  in this  report was to  develop
cost-effective techniques  for  radon
mitigation  in crawl space  houses in the
Nashville  Metropolitan Area.  These
techniques should also be applicable to
crawl space designs in other parts of the
country. Other types of houses mitigated
during this study were basement houses
in which the  basement was  excavated
from an existing  crawl space.  Unlike
many houses with basements and ad-
joining crawl  spaces, in  many of these
houses  there  remain areas  of exposed
soil  in  open  communication with the
basement. This type of construction is
also typical of the mid-South, offering yet
another opportunity to expand  the
existing  data  base of radon reduction
techniques.
  Another purpose for this  mitigation
demonstration  was to train local
contractors  in the  proper  techniques of
radon mitigation  and  thereby encourage
radon mitigation efforts by the  private
sector.  This  will  hopefully result  in
providing sources  of cost-effective and
successful  mitigation  installations  to
homeowners in this region. The results
described  in  this report are  the initial
results of an ongoing, EPA funded, radon
mitigation  demonstration in  existing
houses in the Nashville area.

History
  The State  of Tennessee, operating
through  the Tennessee Department  of
                                                                         Printed on Recycled Paper

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Health  and  Environment's  (TDHE's)
Division of Air  Pollution Control  and in
cooperation with the  U.S. Environmental
Protection Agency's (EPA's) State Radon
Survey Program, conducted a survey to
identify areas  in  Tennessee  with  the
potential for  elevated  radon levels in
privately  ov/ned houses.  During  the
months  of January through  April 1987,
approximately 1.787 measurements were
carried out  in  single-family  owner-
occupied houses Based on the results of
that  survey, the TDHE estimated  that
84.2% of  the houses in the state have
radon  levels <4  picocuries per  liter
(pCi/L). 14.5% have levels of 4 - 20 pCi/L,
and  1.3% have  levels  >20 pCi/L.  The
highest level detected in this survey  was
99.9 pCi/L From the geological character
of the soils and rocks in the various parts
of the state,  four risk  levels for  indoor
radon  were  developed  (High,  Inter-
mediate, Moderate, and Low). The High
Risk areas form a  two-pronged band
through the  central part  of the state
including  most  of Davidson County,
which also happens to be one of the most
populated counties in the state


Problem
   Tennessee, along with  several other
states, contain  a substantial number of
crawl space houses for which there are
very little  data regarding the appropriate
technique to  use  for radon mitigation.
This construction type  represented  16  -
28%  of the housing  starts nationwide
between 1963 and 1983. States having a
significant fraction of crawl  space houses
include  Oregon, South  Carolina,, North
Carolina, Nevada, Tennessee, Delaware,
Arkansas. New  Jersey, Idaho, Washing-
ton, West Virginia. Alabama, and Virginia.
Several other states  have <25% each.
Thus crawl space houses represent a
significant fraction of the existing housing
stock in diverse regions of the U.S.
   In general, crawl space houses can be
defined as those in which a part or all of
the living areas of the house are  built
over an  enclosed  area  containing
exposed earth.  Prior to the collection of
recent radon data, crawl  spaces were
even considered to be a viable alternative
for radon control in new construction.


House Screening and Selection
   The  houses  for this demonstration
were selected  from respondents to a
media announcement  for homeowners
whose  houses had  previously been
tested and found to contain radon levels
 >4 pCi»L). From about 100 respondents,
30 houses werej selected for screening as
possible  candidates for participation in
the  radon mitigation  demonstration.
These 30 houses in  Davidson  and
Williamson  Counties (in and  near
Nashville, TN) |were screened between
September 8  and 11,1987, by scientists
from  EPA, TDHE, Southern Research
Institute (SRI), and Camroden Associates.
The  purpose  of the screening effort was
to evaluate  the  houses  for  possible
inclusion  in  Plhase  1  of the  Middle
Tennessee -radon mitigation demonstra-
tion.          ]
   As  a  result  of the screening,  15
houses were  selected for  the mitigation
demonstration: program.  The  houses
selected  include nine  crawl  space
houses, three Houses  with basements
converted frqm crawl  spaces,  two
combination  pasement/crawl  space
houses, and onjs slab-below-grade house.
This cross section is representative of the
existing housesj in the Nashville area and
in portions of other states in the  mid-
south.        \


Intensive Diagnostic  Evaluation
of Selected Houses
   An additional extensive diagnostic visit
to each  house was conducted  between
October  21 and 27, 1987  During this
visit,  measurements and  investigations
were carried out to develop radon reduc-
tion  plans  that  would fit into the overall
research  objectives of the  project.  Char-
coal  canisters (CCs)  and alpha  track
detectors (ATDs) were  placed in either
the crawl space or the  basement and on
the first habitable level of  each house to
obtain a pre-mitigation  radon background.
In each location, duplicate detectors were
collocated  to determine the precision of
the measurement devices.  The CCs were
recovered  by bie  homeowner after  48
hours and mailed to  the  analysis lab-
oratory (Scientific Analysis, Inc., Mont-
gomery,  AL). The ATDs were left in the
houses until just prior to installation of .the
mitigation equipment.  At that time, they
were returned to the supplier for analysis
(Terradex  Corp., Glenwood,  IL).  The
results from the collocated CC measure-
ments in October 1987  are shown in
Table 1.


Development of Mitigation
Plans
   The mitigation techniques for  each of
the   15  houses were developed  by
Camroden Associates and SRI following
the  diagnostic  visits  to  each  of the
houses in Octo'ber 1987. For each of the
houses a 2- or 3-phase mitigation strat-
egy was developed following  guidelines
established by the EPA Project Officer.
These guidelines were as follows:
•  Phase   1  should  be  a  low-cost
   alternative {less than $500 if possible)
   that can be easily removed or turned
   off
•  Phase 2 should be a technique with a
   high probability of lowering the house
   radon levels to 4 pCi/L or less and of
   moderate cost ($500  - $2,000)
•  Phase  3 should  be as close  to  a
   guaranteed  reduction  method  as
   possible with  correspondingly higher
   cost ($2,000 - $5,000).
   During  the planning stages  it was
anticipated that no more than 25% of the
houses would require implementation of a
Phase 3 system. To obtain the maximum
scientific benefit,  it was also assumed
that Phase 2 systems would be  installed
and  tested even if  Phase  1  systems
achieved levels <4 pCi/L.
   The  mitigation  strategies for each
house  were  developed using  the  in-
formation  obtained during  both the
screening  and diagnostic visits.  This  in-
formation  incSuded  the type of house
construction, condition of  the house
flooring, whether there  was heating and
air conditioning ducting  in the  crawl
space, the extent and  condition of any
existing polyethylene sheeting under the
house, the existence of a basement and
the condition of the slab, the existence of
any exposed soil areas in the basement,
and the condition of the soil in the crawl
space  From these site conditions and a
list of  the possible  mitigation systems
that  could be applied  to  the  Nashville
houses, a matrix of mitigation strategies
was developed that would hopefully eval-
uate, demonstrate and allow comparisons
of each technique to arrive at methods
that would be  both successful and  cost-
effective  for houses  similar to those in
Nashville.  The mitigation matrix is shown
in Table 2.


Mitigation of the Nashville
Houses
   Local contractors in the  Nashville area
carried out  most  of  the  mitigation
installations. The houses mitigated during
December 1987 were  DW 31,  DW  43,
DW 82, DW 60,  DW 66, and DW 90.  All
of these are crawl space houses except
DW 43 which is  a  basement- converted
from  a crawl  space.   The  remaining
houses were mitigated either singularly,
or at most, two houses were mitigated
concurrently.  The only house  not
•mitigated  during this first year (1987-88)

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                        Table 1.  Nashville Pre-rnitigation Two-day Charcoal Results for October, 1987 (pd/L)

                         House ID (DW)    Crawl Space        Basement      1st Habitable Level
03
12
14
27
29
31
41
43
58
60
66
78
82
84
90
22.0
NA
NA
64.1
13.2
29.0
NA
NA
NA
34.8
20.0
NA
27.3
8.9
18.0
21.9
-AM
NA
65.2
b
16.5°
NA
NA
NA
32.2
19.2
NA
27.2
9.1
16.9
NAa
26.4
33.2
NA
NA
NA
30.1
48.3
43.0
NA
NA
41.2
NA
NA
NA
NA
25.7
31.0
NA
NA
NA
28.6
48,4
43.5
NA
NA
42.3
NA
NA
NA
9.6
20.2
16.0
39.9
5.8
22.7
18.7
16.5
36.1
20.5
12.1
21.8
15.4
5.7
8.4
9.5
19.1
16.0
40.3
5.7
23.2
19.2
17.0
36.0
20.5
9.9
21.4
14.2
5.5
7.7
                        a Not applicable
                        b This detector lost
                        0 Top left off can in shipment
of the  project was DW  58.  This house
was scheduled for mitigation during the
early part of the  second year  of the
project (1988-89).
   Additional CC  measurements were
carried out just prior to mitigation work on
each of the  houses. These measure-
ments were carried out over either 48 or
72 hour periods between November 29,
1987, and April  11,  1988.  These  later
measurements occurred  primarily during
the peak heating season  for the Nashville
area. These later  results are shown in
Table 3. In most cases the  radon levels
were  higher than those measured in
October (Table 1).


Discussion of  Results
   One of the objectives  of this research
project was  to  develop  cost-  effective
techniques for radon mitigation in crawl
space,  basement,  and combination
houses in the Southeastern regions of the
U.S.  In order to accomplish this task, the
houses in this  study were  not  simply
mitigated but were used as vehicles to
test concepts of the  mitigation process.
While the same tests were not carried out
at each individual  house, the results can
be grouped  by  house  geometry for
comparision  and discussion.

Crawl Space Houses
   Six  mitigation  techniques  were
evaluated in  the nine  crawl space  houses
as shown in the mitigation matrix of Table
2. Except  for the  IPCS (isolate  and
pressurize the crawl space) and the IOCS
(isolate and  depressurize the  crawl
space) methods, all the techniques were
applied to two  or  more houses.  The
resulting evaluation of these techniques
based on continuous radon monitor CRM
data is shown  in Table 4, and  based on
CC  measurements  (pre-  and  post-
mitigation) is shown in Table 5.

ICS -  Isolation of Crawl Space
   The technique of  isolating  the living
areas from the crawl  space and thereby
stopping  or greatly  reducing the  radon
entry was tried  on houses DW 29  and
DW  66. In theory the method seemed
simple and  straightforward.  In  practice
the method was  difficult to apply.  In the
Nashville houses the  sub-flooring  was
typically 1  by 6 in. boards laid diagonally
to the floor joists. Air movement, from the
crawl space up into the cracks between,
these boards,  could be demonstrated at
every location. The air  flow was  much
greater near the  points at which the HAC
cold air return plenum was  constructed
between  the  floor joists.  Sealing  the
cracks between  the sub-flooring boards
was  difficult and achieved  only limited
success,  even in houses that had  no
insulation under the floor. In houses  with
insulation,  it was more time consuming
(and more  costly)  and even jess
successful. Attempts to  seal the floor,
using a variety of spray foams and plastic
liners applied or  attached  to  the  floor
joists, were  ruled out as too expensive
and therefore not cost-effective. The floor
openings that were routinely sealed in
these houses were the utility penetrations
(electrical  wiring, water  and gas  pipe
entries,  and  waste pipe  penetrations  for
drains a~nd under  the bath tub openings)
and the larger openings in the box joists
used for air return plenums.
   In the two Nashville houses (DW  29
and  DW 66) where  this  ICS technique
was applied, the results of sealing alone
were not impressive. In DW 29 the radon
reduction was only about  3% and in DW
66 the levels actually increased by about
15%.  These  reductions  were based  on
CRM measurements  in the living space
of the houses as  shown  in Table 4.  No
CC,measurements were  carried out  for
this technique.
   Thus it  appeared that  attempts  at
isolating the crawl space  from  the living
areas are  a questionable means  of
reducing the indoor  radon levels  when
used as the only mitigation technique. .

IVCS - Isolation and ventilation  of
crawl space
   This  technique of isolating the crawl
space  and opening   the  existing
foundation  vents was  tried  on  four
houses: DW 03, DW 60, DW 82, and DW
90. The radon  reductions ranged  from

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-60% (an increase) for DW 82, to 75%
(decrease) for DW 90 as shown in Table
4. No CC measurements  were carried
out for the IVCS technique.
   In the worst case, DW 82, the garage
had  been  converted to a  den and was
open to the rest of the living areas. In
building  the  den,  the floor  was
constructed using typical wood floor joist
techniques. Unfortunately, the  floor joists
were so close to the old garage slab that
access to this area was impossible. The
number of entry points into the den was
unknown. For the remainder of the house,
(he overhead floor was readily accessible
from the craw! space. In this area  all the
major openings (those >0.25 in.) and
many of the minor cracks  and openings
were closed. However, the radon levels in
the living area increased.
   In summary,  for the applications here,
it  appeared  that isolation and passive
ventilation of the crawl space alone would
not likely reduce  the  levels of upstairs
radon <4 pCi/L level unless the leakage
area between the house and crawl space
was or could have been reduced  to very
low values and ihe ventilation area of the
crawl space increased.

IOCS - Isolation and
Depressurizdition of the Crawl
Space
   Although three houses were scheduled
for mitigation  by  the technique  of
isolation  and depressurization  of  the
crawl space, ohly  one house  (DW  82)
actually had  the system implemented.
The reduction  achieved  was  rather
dramatic. Based on the CRM  data,  the
levels in the den were reduced by 90%,
and from the pr'e- and post-mitigation CC
measurements the reduction  was 96%;
however, the levels in  the  crawl space
increased. The levels here rose from 29.8
to 61.7 pCi/L, arj increase of 107%. While
this posed no problem for this house, it
could lead to problems in others.  If there
were HAG ducts in the crawl space, the
increased radon levels could leak into the
return  ducting  and  be  distributed
throughout  the  house.  Also,  since  the
openings between the living area and the
crawl space can never be entirely closed,
fairly  large amounts  of conditioned air
could  be drawn into the  crawl space,
resulting in a substantial energy penalty
for the  homeowner. In  house DW 82  it
was found  that  the foundation walls  had
enough  leakage areas  that the  major
portion of the air flow into the crawl space
was from outdoors. Thus no substantial
energy penalty was expected.

IPCS - Isolation and
Pressurization of the Crawl
Space
   The  technique  of  isolation  and
pressurization of  the crawl  space was
originally scheduled to be tried  as  a
Phase 1 mitigation on  house DW  82.
However, at the time  of installation, there
were  several  uncertainties as to  the
                          Table 2.  Mitigation Techniques   ;
                            Tech- 	Mitigatidn Phase by House ID (DW)
nique 03
ICS
IVCS 1
/DCS
IPCS
SSoD
SPD 2
SSD-W
SSD-N
SSD-P
SSBWD
SSSPD
PB
SSP
DTD
27

2
3


1








29
1<>




2








31


2

1









60

1



2








66
1




2








82


2
1




i





84




1
2








90

1



2























43






2
1

3




58






1




2


78






2
1

3
4b
5"

















12








1

2

3

14








1
2
3


















41






2





1
3
                          3 = Numbers refer to phases of mitigation application.
                          >> = In house DW 78, two additional, phases were scheduled.
                          ICS     =    Isolation of Crawl Space.
                          IVCS   =    Isolation and Ventilation of Crawl Space.
                          IOCS   =    Isolation and Dep'ressurization of Crawl Space.
                          IPCS   =    Isolation and Pressurization of Crawl Space.
                          SSoD   =    Sub-soil Depressurization.
                          SPD    =    Sub-poly Depressurization.
                          SSD-W =    Sub-slab Depressurization Wide Pit.
                          SSD-N  =    Sub-slab Depressurization Narrow Pit.
                          SSD-P  =    Sub-slab Depressurization Progressive Pit.
                          SSBWD =    Sub-slab + fl/oc/f Wall Depressurization.
                          SSSPD =    Sub-slab + Sub-poly Depressurization.
                          PB     =    Pressurization of Basement.
                          SSP    =    Sub-slab Pressurization.
                          DTD    =    Drain Tile Depressurization.

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                                                                                                                                1
                   Table 3.  Nashville Pre-mitigation Collocated Charcoal Results (Nov'87 to Apr'88) (pCi/L)

                   House ID (DW) Start Date Stop Date   Crawl Space       Basement     1 st Habitable Level
03
12
14
27
29
31
41
43
58
60
66
78
82
84
90
4/08/88
2/05/88
2/08/88
1/22/88
2/19/88
11/29/87
1/22/88
11/29/88
3/29/88
12/01/87
12/01/87
2/19/88
11/29/87
3/28/88
12/01/87
44/11/88
2/08/88
2/10/88
1/25/88
2/22/88
12/1/87
1/25/88
12/1/87
3/31/88
12/3/87
12/3/87
2/22/88
12/1/87
3/30/88
12/3/87
21.6
NA
NA
45.7
27.1
29.4
NA
NA
NA
55.2
26.1
NA
29.5
9.4
29.6
22.1
NA
NA
46.4
27.2
30.3
NA
NA
NA
55.0
25.9
NA
30.0
9.7
29.7
NAa
10.3
89.9
NA
NA
NA
19.2
58.6
56.2
NA
NA
41.2
NA
NA
NA
NA
11.8
86.7
NA
NA
NA
19.3
59.7
57.3
NA
NA
41.5
NA
NA
NA
7.0
7.7
47.1
32.8
15.9
26.3
13.3
23.2
20.4
27.9
12.3
19.6
14.7
1.5
15.8
7.1
7.8
48.1
33.0
16.2
25.7
13.4
22.9
27.4
27.8
11.9
19.9
1.5.1
2.3
15.8
                    Not applicable
                     Table 4.
Percent Radon Reduction for Each Crawl Space Mitigation Scheme (Based on
Average Continuous Monitor Data in Living Area)
                                  House ID Code (DW)
Mitigation Technique
Isolate Crawl Space (ICS)
Isolate Vent C/S (IVCS)
Isolate Dep. C/S (IDCS)
Isolate Pres. C/S (IPCS)
Sub-Poly Dep. (SPD)1 Point
(SPD)2 Point
Sub-Soil Dep. (SSoP) 2 Pts
(SSoP) 4 Pts
03

18


69

27




60
87

29
3



64
84

31





61
84
60

27


77

66
-15a



72

82

-60
90



84





58"
86C
90

75


92

                     a Negative values indicate increased radon levels.
                     b Worst case condition.
                     c House open during part of test.
correct method of installing the available
device (Current Indoor Air Systems, Inc.,
Boulder,  CO, model 300). Consequently,
installation  of  the IPCS  technique was
cancelled for this house. The  device was
later installed in another  crawl space
house, DW 60,  but no  data as to  its
operation or effectiveness were available
at the time of this report.

SSoD - Sub-Soil
Depressurization

   The technique of  depressurizing  the
soil directly was implemented  on two
houses, DW 31  and  DW 84.  The soil in
the crawl space of  DW  31  was fairly
loose and permeable to air movement (as
measured during the  diagnostic  visits in
            October 1987). The soil under house DW
            84 was quite different. The surface of this
            soil  was  very  hard  and  had  large
            desiccation cracks up  to 0.5 in. wide
            throughout. The system installed in each
            house  was  basically  identical.  Four,
            evenly  spaced, suction  pits about 24 in.
            wide and 12 - 18  in. deep were dug in the
            soil  and connected to a  single fan (model
            K6,  R.B. Kanalflakt, Inc.,  Sarasota,  FL)
            exhausting to the outdoors. The area of
            the crawl space under DW 31 was about
            780 ft2  and under DW 84 was about 1360
            ft2. Thus the number of suction points per
            square  foot of soil was one per 195 ft2 for
            DW 31  and one per 340 ft2 for DW  84.
              The  pressure field extension in the soil
            was  measured   by  carefully drilling  a
            series of 3/8-in.  diameter holes into the
soil. These holes were generally 12-18
in. deep, although in some instances the
soil was sufficiently loose that it tended to
slide into the bottom of the hole. In those
cases  it was difficult to  estimate  the
depth  of the test hole.  The  test holes
were located at varying distances from a
suction pit.  In  carrying out the
measurements,  a 12 in. length of 1/8 in.
diameter  steel  tubing  was carefully
inserted into the hole. The top of the hole
was sealed  as  tightly  as possible by
means of a  rubber stopper at the top of
the tube. The steel tube was connected
to an electronic manometer (Neotronics,
Gainesville,  GA,  model  EDM-I)  with  a
sensitivity of 0.001 in. of water.
   The depressurization in the soil could
reliably be measured at  distances of up

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to 6 ft from the suction pit, and in several
cases up to 12 ft. For House DW 31, the
pressure field dropped  to about 10% of
the pit pressures  within 2 ft and around
1% at distances of about 6  ft. In the soil
under  House DW 84,  the pressure
decrease was  even more drastic. Here,
the pressure  dropped to approximately
1% of  the  pit  pressure  within 2  ft,
although some pressures were measured
as far out as 6 ft.
   These results were consistent with the
observed nature  of the soils under the
two houses. The soil under DW  31 was
moderately loose and should have had a
higher  permeability than  the soil under
DW 84,  which was hard packed  clay.
Thus, each suction point of the  system
was capable of producing a measurable
soil depressurization over an area of at
least 113 ft2 and perhaps as large as 452
ft2.
   In terms of  the reduction of the radon
levels  in  the  living space,  the SSoD
technique achieved  reductions  of
approximately  85% as seen in  Table 4
for the  CRM measurements, and up to
92% based on the CC measurements as
shown  in Table  5. Unfortunately, the
method has been applied  to  only two
houses. If the technique is to be used on
any large scale  it should be tested  for
other types  of  soils and   at different
locations.

SPD - Sub-Poly Depressurization
   The  technique  of depressurizing the
soil under a  plastic membrane had the
widest application in the current group of
houses. Six  of  the nine  crawl  space
houses had an SPD system installed and
evaluated. This mitigation technique is a
variation  of  the  successful  sub-slab
depressurization  method used  for slab-
on- or below-grade houses. In  many of
the nine houses  there was  at least some
polyethylene sheeting covering the dirt in
the crawl  space. This  covering is a
popular method used to control moisture
in  living areas.  The  intent  of  this
technique was to supplement the existing
sheeting  with new  6 mil  sheeting to
completely cover the  exposed dirt. This
gaslight barrier  formed a  small-volume
plenum above the soil in which the radon
gas collected. At one or  more suction
points, a shallow pit approximately 24 in.
wide and 12 in. deep was dug in the soil.
Each hole was then covered with a 36 by
36 in. piece of treated plywood.  The 4 in.
diameter polyvinyl chloride  (PVC) suction
pipe was mounted through the plywood
and the sheeting sealed around the pipe
and plywood.  A  fan was installed to pull
the collected  soil gas  from under  the
sheeting and exhaust it outdoors. Initially,
no  attempts  vyere  made to  seal  the
sheeting to the foundation walls or to any
support piers  located in the crawl space.
The sheets were laid directly on the earth
in most cases overlapping at least  1  ft at
the joints.
  Only one  house  had  any type of
perforated pipe  or  ducting network
installed under; the  sheeting.  In house
DW  27,  drainage material  (Enkadrain
Type 9010,  BASF Corp.  Fibers  Div.,
Enka, NC) was placed under the sheeting
to  improve airj flow. In  general,  this is
necessary only; where the soil surface is
excessively hard and smooth or the crawl
space  area is  exceptionally large  (DW
27). When excessive air leaks prevented
effective removal of the  radon, the joints
between the  sheets were  sealed with a
bead  of caulkipg  (DW 27). Also,  where
the number of support piers was large or
located close to the suction point (within
12  ft)  the shebting was sealed  to the
piers nearest  the  suction  points  with
caulking and wood strips (DW 03, DW 29,
and DW 60).  In one house (DW 27) the
sheeting  waŁ  also  sealed  to  the
foundation walls to reduce air leaks.
   Pressure  ujnder the  sheeting  was
measured in  all but one house (DW 27).
Measurements utilized  an  electronic
micromanometer (Neotronics, Gainesville,
GA, model EDM-I)  with a  sensitivity of
0.001 in. of water column. In  each house,
measurable pressures were  detected at
distances  of  up to 6 ft from the suction
point,  and in some  cases up to  12 ft.
Farther away, rthe pressures  were  not
measurable with the  manometer but, in
most cases,  air flow under the sheeting
was observed using a smoke tracer.
   In two  houses (DW 27 and DW 29), a
second suction  point  was added to
increase th|e  extension  of  the
depressurizatibn  under the  sheeting.
These two hoUses had the largest crawl
space area of any of the houses. In  both
cases, the same fan  was used for  both
suction points.
   Based  upon the CRM data, the  SPD
technique achieved  reductions ranging
from 60 - 92% (Table 4). Based on pre-
and post-mitigation  CC  measurements
(Table 5), the reductions range from 45 -
85%.
   In summary, the  SPD technique was
the most widely used and appears to be
the  most  applicable to crawl  space
houses in which the upstairs levels are in
the  10 -  30  pCi/L. There are questions
regarding the ; technique that have not
been fully answered in this study. In the
SPD  installations,  the material  used for
the houses  in  this study  was standard,
builder-grade, ,6 mil polyethylene sheet-
ing.  The  properties  of this  material
(thickness,  puncture resistance, perme-
ability, and resistance to ultraviolet light
and temperature degradation) vary  from
location to location in a single sheet and
perhaps from source to source. Also, the
tear  and  puncture resistance  are not
believed  to  be  sufficiently  high  to
withstand normal  traffic (such  as  by
service personnel  from  utility companies,
termite control organizations,  or the
homeowner) that might be expected in a
crawl space. Other materials  such  as
cross-laminated high-density polyethyl-
ene  films or lagoon  liners  need to  be
examined for use  in these applications.
Other  questions  that  have not  been
addressed include, the amount  of energy
penalty resulting  from  the  SPD  system
withdrawing house air down into the  crawl
space, and  the effects of the  system
upon  the house  frame as  a  result of
moisture;removal from the crawl space.

Basement or Combination
Houses
   One- or two-point sub-slab depressur-
ization (SSD) systems were installed  in
five basement/combination houses.  Mea-
surements of the pressure field extension
under the slab showed a wide, shallow pit
in the soil where the  pipe penetrated the
slab to be more effective than  a narrow,
deep  pit.  The surface  area  of soil
exposed in the pit was found to be  more
important than the shape of the pit. Sub-
slab  pressure,  measured  at a  fixed
distance from the suction hole,  increased
dramatically as the size of the hole  in the
soil  under  the  slab  penetration  was
increased. In mapping  the pressure field
extension as a function of the distance
from  the suction point, the  pressure
became  unmeasurable farther  than 20  -
25 ft from the suction point.
   The  radon  reductions achieved  were
28 - 98%, as shown by the CRM data in
Table  6.  The house  with  the greatest
reduction (DW  41) had a single suction
point installed near the  edge of the slab
under the front foyer. The slab had good
communication which  allowed the  sub-
slab area to  be ventilated from a  single
point.  Also, the  area of exposed soil
located under the front porch  was  small
(less than 100 ft2) and was easily isolated
from the living areas  by construction of a
treated plywood barrier wall with a sealed
access door.
   The lowest reduction for SSD was also'
achieved using  a single suction  point
(DW 43). However,  in this house  the
communication under the slab was poor

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                   Table 5.  Nashville Radon Reduction Summary (Based on Charcoal Canister Measurements
                            in pCi/L)
                                     Crawl Space          Basement            1st Floor
House ID (DW)*
03
27
29

31
60
66
82
84
90
43
58
78
12
14

41
Pre
21.9
46.1
27.2

29.9
55.1
26.0
29.8
9.6
29.7
NA
NA
NA
NA
NA

NA
Post
A/Ob
9.2
5.7
2.8
2.0
23.3
7.6
61.7
ND
7.1
NA
NA
NA
NA
NA

NA
%Red
ND
80
79
90
93
58
71
-107<*
ND
76
NA
NA
NA
NA
NA

NA
Pre
NA<=
NA
NA
NA
NA
NA
NA
NA
NA
NA
59.2
56.8
41.4
11.1
88.3

19.3
Post
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
4.8
ND
2.8
4.4
11.3
3.0
1.4
%Red
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
92
ND
93
61
87
97
93
Pre
7.1
32.9
16.1

26.0
27.91
12.1
14.9
1.9
15.8
23.1
23.9
19.8
7.8
47.6

13.4
Post
2.6
5.3
7.0
3.0
2.2
15.2
2.8
0.7
ND
2.4
1.4
ND
1.5
4.8
3.8

1.0
%Red
64
84
56
82
92
45
77
96
ND
85
94
ND
92
39
92

93
Notes
1,10
2
1
3
4
1
1
5
4,11
1
6
12
6,13
8
9,14
9,15
7
                   a See Table 2 for mitigation codes
                   b No Data
                   c Not Applicable
                   d Negative values indicate increased radon levels
                    Notes:   1.  ICS + SPD
                           2.  Two Point SPD
                           3.  ICS + Two Point SPD
                           4.  Four Pit SSoD
                           5.  /DCS
                           6.  Two Point SSBWD
                           7.  SSD-W
                           8.  Two Point SSD-W
                           9.  Two Point SSBWD + SSSPD
                           10.  No measurements in crawl space
                           11.  No Post-Mitigation CC measurements
                           12.  House not mitigated
                           13.  No duplicate done upstairs
                           14.  Basement readings on top of crawl space wall
                           15.  Basement readings 4 ft from floor and 6 ft from C/S wall
so that an additional suction  point was
required. Also, this  house had a cement
capped perimeter shelf around most of
the basement. This shelf was constructed
of coarse cinder blocks which allowed
radon gas to  enter the basement through
their face openings. Incorporating  block
wall suction achieved a reduction of 42 -
60%.  Because of the high porosity of the
block  comprising the  wall, acceptable
reductions were not achieved until  the
wall was coated with a  sealer (SurWall
Brand). The final reduction for this house
was 92%.
   For house  DW 12 the exposed soil in
the crawl space  was covered with  6 mil
polyethylene  sheeting  but  no
depressurization under the sheeting was
implemented.  Final reduction for this
house was 92%.
   The exposed soil in the crawl space of
house  DW 14  was covered  with  6 mil
sheeting sealed to the surrounding walls.
Depressurization under the sheeting was
accomplished  by breaking through  the
adjoining  wall (and  under  the sheeting)
with the sub-slab system. The open block
tops of the wall were filled with expanding
closed-cell  foam.  This  combination
achieved a reduction  of  85%. After the
top of the wall  was  covered with treated
2 x 12 in.  boards sealed to the top of the
blocks  with  urethane  sealant  a  final
reduction of 93% was achieved.
   The  remaining basement/combination
house (DW 78) had a two-point sub-slab
suction  system installed and  achieved  a
radon reduction of 78%. The  area of the
crawl space in this  house (600 ft2) was
roughly  twice  the area of the slab  (300
ft2) and was  probably the major source
for radon entry into the basement. After
covering the  soil with  6 mil sheeting
sealed to the slab  perimeter wall  and
sealing  the open  block tops of that wall
with  expandable foam, the SSD  system
was  extended into  the  wall  and  thus
under the sheeting covering the soil. The

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                          Table 6.  Percent  Radon Reduction for  Each Basement  Type  Mitigation
                                   Scheme (Based on Continuous Monitor Data in Basement)
[
Mitigation Technique I
Sub-Slab Pressurization (SSP) j
Sub-Slab Depressurization (SSD)>>
SSD + Block Wall Depress.(BWD) ,
SSD + BWD + Seal Exposed Soil
SSD + BWD + Seal Wall Face
43

28C
42-60

92
58





House
78

78

93

D(DW)
12

92



14

70
85
93d

41
70a
98C



                          » Single sub-slab depressurization "point
                          t> Unless specified otherwise, all SSD systems include two suction points
                          c Single sub-slab pressurization point
                          a Top of wall sealed            ',
final reduction was 93% as measured in
the basement with the CRM.
   The only house in  which  the  SSP
technique was implemented was DW 41.
Here the fan was initially installed to force
outside air under the slab.  The reduction
achieved (70%)  was surprising in view of
the  fact  that  a polystyrene  foam
beadboard at  the edge  of  the  slab
allowed air from under  the  slab to easily
enter the  basement  interior via  the
finished walls and  baseboards. This entry
was verified by use of a smoke bottle and
was confirmed by the homeowner as an
increase  in  humidity  and  odor  in  the
basement   Concurrently, measurements
of the levels of  termaticide  (aldrin) in two
rooms of  the basement were  increased
from premitigation concentrations of 0.3
and 0 12 pg.'ms  to levels of 1.40 and 1.03
ng?m3 with pressurization under the slab.
Subsequent measurements in these two
rooms after the system was run in the
sub-slab  depressurization mode for
approximately  10 weeks   showed  the
levels of  aldrin  (and  dieldrin) to  be
< 0.066 vgmz.  Thus, while SSP  can be
effective in lowering radon  levels,  it could
also  lead  to other problems for the
homeowner.

Conclusions and
Recommendations
   Several techniques  have  been tested
in crawl space  and combination  houses
typical of the  Southeast.  Based on the
results  described  in  this  report, the
following conclusions can be drawn.
Methods Applied to Crawl
Space Houses
• Isolation of  the crawl space from  the
   living areas of  the house was found to
   be difficult if not impossible to achieve
   and its use as the only  mitigation
   technique is; risky,  questionable, and
   not recommended.
•  Isolation and! passive ventilation of the
   crawl space  using  only  the  existing
   foundation vents  was found to be
   ineffective due to the limited area of
   the  vents installed  in  most  houses.
   This  technique is not  recommended
   as the sole mitigation method even if it
   is combined1 with covering the soil in
   the  crawl space  with some  type  of
   plastic  film. iWithout active ventilation
   under the film, the radon levels in the
   living areas will, in all likelihood, not be
   reduced to apceptable limits.
•  Isolation and  depressurization of the
   crawl space  was  found to be an
   effective method of reducing the radon
   levels in the living areas of one house.
   However,   this   technique   can
   substantially, increase the levels in the
   crawl space; This technique  may be
   difficult to  apply when there  are cold
   air return ducts in the crawl space and
   could also incur an  energy loss  from
   the conditioned air space above.
o  Sub-soil depressurization was found to
   be  an  effective technique  for two
   houses in this  study. Its  effectiveness
   is greatly influenced by  the soil con-
   ditions  in the crawl space and should
   be used with  caution  until additional
   results  from other geographic  loca-
   tions and soil conditions  become
   available.   .
«  Sub-membrane depressurization in the
   crawl  space was  the  most widely
   applicable technique in this study and
   proved a reliable method of removing
   radon before it enters the crawl space.
   The  number of suction points needed
   under  the  membrane will depend  on
   both the crawl space area  and the
   condition of|the soil. For areas > 1,200
   ft2  or  crawl space with excessively
   damp  soil [Conditions,  at least two
  suction  points should be installed  at
  opposite ends of the crawl space. The
  membrane  used in these houses was
  standard   6 mil  clear  builder's
  polyethylene. However,  due  to its
  limited  puncture and  tear resistance
  and  its  instability to  ultraviolet  (UV)
  light  degradation, it  is  not  recom-
  mended for more general use. Instead,
  a cross-laminated, high  density poly-
  ethylene material with  UV stabilizers is
  recommended.  Sealing of the mem-
  brane lap joints and to the surrounding
  foundation  walls and support piers is
  recommended at locations within  12 ft
  of the  suction  point(s) and  at  all
  locations  if  the crawl  space  is
  exceptionally large. In this case it may
  even be necessary  to  install some
  type  of drainage system under the
  membrane to improve the air flow.

Methods Applied to Basement
or Combination Houses
• Sub-slab pressurization  was found to
  be  somewhat  effective  for  radon
  reduction  in one house but  not  as
  effective as  depressurization  of the
  sub-slab region. It also can produce
  other problems  such as  increased
  moisture or even increased levels of
  termaticide in the basement. It may be
  difficult to  apply  when  sub-slab
  communication is poor.
• Sub-slab depressurization (or sub-slab
  ventilation)  was  found  to  be  an
  effective technique in the five  houses
  studied even   when  the  sub-slab
  communication was not very good. In
  thesei cases, more than one  suction
  hole will likely  be required. The soil
  under the  slab, at the suction  point
  should  be  excavated to at least a
  diameter  of about 36  in.  and  to a
  depth of about 12 - 18 in. The  amount

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   of soil surface area exposed in the pit
   is more important than the depth or
   shape of the pit.  Filling the pit with
   crushed stone was  not found to  be
   necessary.
•  Block wall depressurization was found
   to improve the  effectiviness of  sub-
   slab  systems in the three houses in
   which it was applied. In these houses,
   large areas  of the  block  wall were
   either below grade or separated the
   crawl space from the  basement.
   Sealing of the wall was  found  to  be
   necessary in one  case in which the
   porous  blocks short-circuited  the
   negative  pressures generated under
   the slab.
•  Consideration of the exposed soil in
   direct  communication  with  the
   basement was found to be essential to
   lowering  the  radon   levels  to
   acceptable  limits. The  methods used
   for these areas are similar to those for
   crawl spaces above.

Mitigation Costs
   The  actual contractor  costs  for
installing the systems in the crawl space
houses of  this study were $850 - $1,859
with an average of  $1,282. For the
basement and basement-combination
houses,  the costs were $785 -$1,995 with
an  average  of  $1,496. However, these
costs do not include any time spent in
diagnostics or  in design of the mitigation
systems.  The  expenses  incurred  by
private  mitigators  for  diagnostics  and
design could increase the costs by  as
much as 50%.
Recommendations for
Additional Research

   Questions  need to be addressed in
future studies of mitigation  using  the
techniques described above. In the sub-
poly depressurization technique,  the
material  used for these  houses was
standard  builder's grade  6  mil
polyethylene sheeting. The properties of
this material  (thickness,  puncture
resistance, permeability)  vary  from
location  to location  in a single sheet.
Also, the tear and puncture resistance is
not believed to  be  sufficiently  high to
withstand normal traffic  (such as by
service personnel from utility companies,
termite  control  organizations,  or  the
homeowner) that  might be expected in a
crawl  space.  Other  materials such as
cross-laminated high-density  poly-
ethylene films or  l.agoon liners need to be
examined for use in these applications.
   In houses where  sub-slab depressur-
ization cannot be made to function cost-
effectively, other techniques such as
basement  pressurization  need to be
developed and demonstrated.
Conversion Factors

   Readers more familiar with metric
units may use  the following factors  to
convert nonmetric units  used  in  this
Summary to their metric equivalents.

  Nonmetric   Multiplied by  Yields Metric
      ft
     fp
     in.
   in. H2O
     mil
    pd/L
 0.305

 0.093

 2.54

 0.249

25.4

37.0
  m


 cm
 kPa


Bq/m3

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   Bobby E. Pyte and Ashley D. Williamson are with Southern Research Institute,
        Birmingham, AL 35255-5305.
   Michael C. Oslborne is the EPA Project Officer (see below).
   The complete  report,  entitled  "Radon Mitigation  Studies: Nashville
        Demonstration," (Order No. PB 90-257 791/AS; post: $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/S8-90/061

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