EPA-600/R-9 5~ 149 a
September 1995
DESIGN AND TESTING OF SUB-SLAB DEPRESSURIZATION
FOR RADON MITIGATION IN NORTH FLORIDA HOUSES
Part I - Performance and Durability
Volume 1. Technical Report
By
C. E. Roessler, R. Morato, R. Richards, and H. Mohammed
Department of Environmental Engineering Sciences
D. E. Hintenlang
Department of Nuclear Engineering Sciences
and
R. A. Furman
School of Building Construction
University of Florida
Gainesville, FL 32611
EPA Assistance Agreement CR 814925-01
DCA Project Officer:
Richard Dixon
Florida DCA
2740 Centerview Drive
Tallahassee, FL 32399
EPA Project Officer:
David C. Sanchez
National Risk Management
Research Laboratory
Research Triangle Park, NC 27711
Prepared For:
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460
and
FLORIDA DEPARTMENT OF COMMUNITY AFFAIRS
Codes and Standards Division
2740 Centerview Drive
Tallahassee, FL 35255-5305

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NOTICE
This document has been reviewed in accordance with
U.S. Environmental Protection Agency policy and
approved for publication. Mention of trade names
or commercial products does not constitute endorse-
ment or recommendation for use.
ii

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FOREWORD
The U.S. Environmental Protection Agency is charged by Congress with pro-
tecting the Nation's land, air, and water resources. Under a mandate of national
environmental laws, the Agency strives to formulate and implement actions lead-
ing to a compatible balance between human activities and the ability of natural
systems to support and nurture life. To meet this mandate, EPA's research
program is providing data and technical support for solving environmental pro-
blems today and building a science knowledge base necessary to manage our eco-
logical resources wisely, understand how pollutants affect our health, and pre-
vent or reduce environmental risks in the future.
The National Risk Management Research Laboratory is the Agency's center for
investigation of technological and management approaches for reducing risks
from threats to human health and the environment. The focus of the Laboratory's
research program is on methods for the prevention and control of pollution to air,
land, water, and subsurface resources; protection of water quality in public water
systems; remediation of contaminated sites and groundwater; and prevention and
control of indoor air pollution. The goal of this research effort is to catalyze
development and implementation of innovative, cost-effective environmental
technologies; develop scientific and engineering information needed by EPA to
support regulatory and policy decisions; and provide technical support and infor-
mation transfer to ensure effective implementation of environmental regulations
and strategies.
This publication has been produced as part of the Laboratory's strategic long-
term research plan. It is published and made available by EPA's Office of Re-
search and Development to assist the user community and to link researchers
with their clients.
E. Timothy Oppelt, Director
National Risk Management Research Laboratory
i i i

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ABSTRACT
A demonstration/research project was conducted to evaluate sub-slab depressurization
(SSDJ techniques for radon mitigation in North Florida where the housing stock is primarily
slab-on-grade and the sub-slab medium typically consists of native soil and sand. Objectives
included developing and testing the use of a soil depressurization computer model as a design
tool, optimization of SSD design for North Florida houses, and observation of the performance
and durability of the installed systems.
Between May 1989 and August 1990, SSD systems were designed and installed in
nine houses - seven with simple, rectangular floor plans and two with more complex, L-shaped
designs. Installations included a single-suction point system in one house and two-suction
point/single-fan systems in eight houses. The installation in one of the larger, L-shaped
houses consisted a single-suction point system in addition to a two-suction point/single-fan
system. All systems used small diameter, nominal 50-mm (2-in), piping.
AH houses were equipped with continuous radon monitors and integrating radon
monitors were also deployed. All houses were visited on a regular schedule for measurements
and observations.
The mitigation successfully reduced indoor radon concentrations, originally on the order
of 10 to 30 pCi/L, to post-mitigation values of <4 pCi/t in all nine houses. Levels were
reduced to values on the order of 2 pCi/L or less in three houses.
Installation experiences demonstrated the importance of avoiding "short-circuit" air-
flow leakage near suction points, providing drainage for moisture that condenses in the
system during cooler weather (even in Florida), and sealing around discharge ducts at roof
penetrations to prevent re-entry of exhausted sub-slab gases.
System manipulations indicated that a single suction point was sufficient on two
houses with 160 to 170 m2 (1700 to 1800 ft2} slabs but that passive ventilation is not likely
to be effective for this type of sub-slab medium.
During the limited time available for durability observations (3 to 18 months), the
systems retained effectiveness in maintaining reduced indoor radon concentrations, no fan
failures occurred, and no structural effects were observed.
i v

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CONTENTS
Abstract		i v
Tables 		vi
Figures 		vi
Acknowledgments		vii
1.	Introduction 	 1
Background	 1
Objectives	 2
2.	Conclusions and Recommendations	 3
Effectiveness		3
Design Considerations 		3
Installation Considerations 		3
Performance and Durability		3
Further Work		4
3.	Methods 		5
Diagnostic Methods	 5
Mitigation System Design and Installation	 6
Monitoring 	 6
4.	Results and Discussion 	11
House Characterization	11
Installation of Demonstration SSD Mitigation Systems	13
Observations on the Installed Systems 	24
Design and Installation Experiences	30
Optimization Studies 	31
Durability 	32
5.	Quality Assurance 	34
Calibrations and Intercomparisons of Radon Measurement Instruments 	34
Data Review	35
References 	36
Appendix A. House Characterization Data 		A-1"
Appendix B. Data Collection Procedures for Routine House Visits 		B-1 '
Appendix C. Data by house 		C-1*
Appendix D. Weather Data		D-1*
(*) In Volume 2.
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8
10
12
14
25
26
27
29
34
15
16
17
18
19
20
21
22
23
Tables
Parameters Recorded by Continuous Monitoring Systems	
Post-installation Data Collection and Observations	
Summary of Characterization Measurements on 12 Candidate Houses
Characteristics of Mitigation Demonstration Houses, SSD Systems, and
Monitoring 	
Indoor Radon Concentrations and Reduction Factors 	
Average Initial Pressures and Flows at Suction Holes	
Summary of SSD Initial Operating Conditions 	
Sub-Slab and/or Suction-Hole Radon Concentrations 	
Results of Participation in EML Radon Gas Intercomparison Exercises .
Figures
House
234797
(Ocala 1) 	
House
234789
(Ocala 2) 	
House
234892
(Gainesville-1)	
House
235001
(Gainesville-2)	
House
235062
(Gainesville-3)	
House
234912
(Gainesviile-4) 	
House
235059
(Ocala-3) 	
House
234839
(Gainesville-5)	
House
234873
(Gainesvi!le-6>	
VI

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ACKNOWLEDGMENTS
The investigators wish to acknowledge the many persons who contributed to this
study. The participating homeowners are thanked for their cooperation. Special appreciation
is expressed to Laura Pendlebury who wrote procedures, developed forms, organized data,
and performed editing; to Frank Roessler who was responsible for the data acquisition
instrumentation, performed calibrations, and conducted house visits; and to Leon Pendlebury
who performed house visits and collected data.
We would also like to thank Rad Elec Corporation for loaning E-PERM ionization
chambers and an electret reader and for donating electrets during the start up of the project.
Likewise, we thank the Sun Nuclear Corporation for donating some of the At-Ease continuous
radon monitors.
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SECTION 1
INTRODUCTION
A demonstration/research project was conducted to evaluate sub-slab depressurization
(SSD) techniques for radon1 mitigation in North-central Florida. This work was conducted in
this locality because of the presence of elevated indoor radon levels and the need to
investigate mitigation techniques successful for the housing stock and conditions represented.
BACKGROUND
In late 1986, results from a statewide indoor radon survey (Nagda 1987) identified two
focal areas of elevated indoor radon in Florida. One of these occurs in the Bone Valley
phosphate mining region of West Central Florida (Polk, Hillsborough, and surrounding
counties). The other is the North Florida Hawthorn formation region - with the greatest
affected populations in the Gainesville-Ocala area (Alachua and Marion counties). Several
other studies have confirmed the presence of indoor radon levels ranging from < 1 to about
200 pCi/L in this area.
In Florida, the housing stock is primarily of slab-on-grade construction with several
variations of floor-wall joining. There is a small percentage of crawl-space and slab/crawl-
space combination houses (both open and enclosed crawl spaces), and there are very few
houses with basements.
The U. S. Environmental Protection Agency (EPA) has suggested that soil
depressurization is the most successful method of limiting indoor radon; thus sub-slab
depressurization (SSD) appeared to be a promising mitigation method for Florida houses.
However, at the time this project was initiated, most mitigation experience in the country had
been with basement homes. Furthermore, the sub-slab materials commonly used in Florida
construction consist of native soil and sand. These would be expected to have lower air
permeabilities than the coarse gravel used under basement slabs in regions of the country
where SSD had been highly successful. This suggested that more complex and more robust
systems might be required to successfully control radon in construction typical of Florida.
Radon mitigation demonstration work in Florida was begun with the 1 987 initiation of
the EPA-sponsored Florida Radon Mitigation Project - Phase I in Central Florida (Polk County)
with the Southern Research Institute as contractor. In late 1987, EPA also sponsored a
University of Florida (UF) project to identify elevated radon houses that might serve as
candidates for a parallel North Florida mitigation project. During the 1987-88 winter,
screening measurements (charcoal collector method) were made in nearly 400 Gainesville and
Ocala vicinity slab-on-grade houses in neighborhoods designated on the basis of geological
potential for elevated radon. In these screening measurements on this selected group of
houses, about 70% of the indoor radon concentrations exceeded 4 pCi/L and about 20% of
the total exceeded 20 pCi/L (Roessler et al., 1990). The North Florida effort was then
'in this report, the terms "radon" and "Rn" are used to designate the radon isotope, radon-222; and "radium"
is used to designate radium-226.
1

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continued with the August 1988 initiation of the research and demonstration project, Florida
Radon Mitigation Project Phase II - North Florida, under Assistance Agreement CR 814925-01.
OBJECTIVES
This project had a demonstration objective and a series of research objectives. The
demonstration objective was to demonstrate mitigation methods that are effective for the
substrate and construction type characteristic of the North Florida region. Initial emphasis was
placed on sub-slab depressurization (SSD). The project had three research objectives:
1.	Develop tools for design of SSD systems. This includes testing the use of a soil
depressurization computer model2.
2.	Optimize SSD design for North Florida houses.
3.	Observe the short-term and long-term performance and durability of the installed SSD
system in this environment.
"'Amendment 3 of the Assistance Agreement authorized further development and testing of a computer model
previously developed at UF for simulating sub-slab pressures and flows during the operation of soil
depressurization systems. The work, which included expanding the model, developing it as an SSD design tool,
and validation, is presented in the companion report to this document, Design and Testing of Sub-slab
Depressurization for Radon Mitigation in North Florida Houses: Part II - Design and Modeling.
2

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SECTION 2
CONCLUSIONS AND RECOMMENDATIONS
EFFECTIVENESS
1. SSD was effective in reducing indoor radon levels in North Florida slab-on-grade
houses from pre-mitigation values on the order of 10 to 30 pCi/L to post-mitigation
values on the order of 2.0 to 3.5 pCi/L.
DESIGN CONSIDERATIONS
1.	SSD was effective in houses of both simple rectangle and L-shaped floor plans.
2.	For the sub-slab media found in this region, low flows permitted the use of smaller
diameter, nominal 50 mm (2-in) pipes.
3.	Two suction points were successful for slab areas up to 200 m2 (2100 ft2}. -
4.	A single suction point was sufficient on two houses with single-level, rectangular
slabs with areas on the order of 160 to 170 m2 (1700 to 1800 ft2).
5.	Experiments with installed active systems (fan off, vent line open) indicated passive
ventilation is not likely to be effective for this type of sub-slab medium.
INSTALLATION CONSIDERATIONS
1.	Air leakage near the suction point can compromise the system effectiveness;
special care should be taken in new construction to minimize such leakage through
the slab or at the perimeter. Leakage at points more remote from the suction point
have much less influence on effectiveness.
2.	Even in Florida, moisture condensation can occur in the system during cooler
weather and, thus, it is important to avoid low points in horizontal attic runs where
possible and to install traps and drains if water trapping points cannot be avoided.
3.	It is important to seal around the discharge duct at the roof penetration to prevent
re-entry of the exhausted sub-slab gases. Examination for other sources of re-
entrainment is also warranted.
PERFORMANCE AND DURABILITY
The post-installation observation periods in these houses were rather short -- 3 to
18 months. From these limited observation times it is concluded:
1.	Pressure and flow values in SSD systems may exhibit some temporal variability; a
series of measurements should be taken on different days and averaged when
documenting post-installation performance from single-point-in-time measurements.
2.	On a near-term basis, SSD systems, as installed in this project, retain effectiveness
in maintaining reduced indoor radon concentrations.
3.	Continued integrity of sealing of potential short-circuit air flow sources near suction
points is essential to continued effectiveness. System maintenance should include
inspection of such sealing.
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4.	During cooler weather, unintended trapping of moisture condensation in horizontal
attic runs can compromise system performance. Maintenance should include
inspections for such inadvertent effects.
5.	Fan failures have not been identified as a problem in the short term (a conclusion
limited by the small number of systems).
6.	Structural effects have not been identified in the short term.
7.	With the exception of noises associated with the water condensation before
correct/on, these systems have not generated homeowner complaints.
Short-term durability information wouid be enhanced by following all houses for at
least a year and long-term durability information would be gained by following all the
houses for a longer time period.
FURTHER WORK
Further work is needed to demonstrate effective systems in houses with fills containing
clay and in houses with more complex designs such as multi-level slabs.
4

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SECTION 3
METHODS
This project involved the following work areas:
1.	Select and characterize a candidate pool of houses.
2.	Mitigate a subset of these houses -- select houses, design mitigation systems, and
install mitigation systems.
3.	Monitor:
3a. Collect baseline data prior to mitigation.
3b. Monitor initial post-mitigation performance.
3c. Conduct special studies on installed systems for the purpose of system
optimization.
3d. Evaluate durability of installed systems -- continue monitoring and observations
for the duration of the project.
DIAGNOSTIC METHODS
From the data obtained in the House Identification Study(Roessler et al. 1990), 12
elevated radon houses were selected as potential candidates for the mitigation demonstration.
These houses were then visited and the EPA diagnostic measurements were performed
(Harris, et al., 1989). These diagnostic observations included descriptive information, sub-slab
measurements and sampling, radon measurements, and house dynamics observations.
Sub-slab measurements included determination of soil gas radon by "sniff" and "grab"
sampling, sub-slab communication testing, and calculation of effective permeability. Effective
permeability was calculated from sub-slab communication measurements as
follows:
Kclf = 3.21 x 109 _V_	(1)
d P
where : KBff = effective permeability (m2)
V = velocity of air flow (m/s)
d = diameter of suction pit (m)
P = pressure (Pa)
3.21 x 10 9 = units reconciliation constant.
For measurements using an air-flow meter reading in ft/min, this becomes:
Keff = 1.63 x 10"11 _\T	(2)
d P
where: Keff = effective permeability (m2)
V' = velocity of air flow (ft/min)
d = diameter of suction pit (m)
P = pressure (Pa)
1.63 x 10 11 = units reconciliation constant.
5

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Cores of sub-slab material were collected by pushing a 25-mm (1 -in) diameter tube to
a series of depths in 0.1 5-m (6-in) increments through holes drilled in the slab and then
extruding the tube contents into labeled containers.
Indoor radon measurements included short-term measurements of concentrations in the
living space and also measurements of radon in the building shell. House dynamics
measurements included inside/outside and inside/sub-slab pressure differential measurements
under various conditions and blower door pressurization/depressurization tests.
MITIGATION SYSTEM DESIGN AND INSTALLATION
The design procedures are described in the Part II companion to this report. Briefly,
potential suction points were located on the basis of accessible, unobtrusive locations -
usually in interior closets. The UF soil depressurization computer model was then used as a
design tool. For an initial set of five houses selected for mitigation in 1989, the model was
used to simulate pressure fields under proposed designs. Suction system pressures and flows
were predicted by superimposing the sub-slab "system curve" on the respective performance
curves of candidate fans. For each house, the number of suction points, their locations, and
the fan size were selected from the combination giving the pressure field coverage believed
to be adequate to overcome the inflow of radon-bearing soil gas. Subsequently, the computer
model was used to develop soil depressurization system guidelines for the Florida radon-
resistant building code. For a second set (four houses) selected for mitigation in 1990,
system designs were specified using the evolving code guidelines.
As a means of saving cost, space, and installation effort, the pipes specified for the
major runs of the SSD systems were nominal 50-mm (2-in) PVC pipes rather than the nominal
100 mm (4-in) pipes reported in the literature for previous mitigation projects. It was
anticipated that, because of the low flows associated with the low permeability Florida sub-
slab medium, pressure losses due to flow would be minimal with the smaller pipe sizes.
At each suction point, sub-slab fill and/or soil was removed to form a pit of roughly
hemispherical shape and approximately 0.5 to 0.9 m (20 to 36 in) in diameter. Nominal 100
mm (4-in) PVC pipes with a clean-out branch to serve as an access port were installed through
the slabs. The remainder of the suction system consisted of nominal 50 mm (2-in) PVC pipe.
Suction pipes were run vertically from the pit to the attic. Fans were located in the attic. For
the systems with two suction points, lateral pipes were run from the vertical rises to a tee
located under the suction fan. For the single suction point systems, the vertical pipe was run
directly up to the fan.
Systems were installed by the research team. Electrical hook-up was provided by
licensed electrical contractors.
MONITORING
Individual measurement procedures were consistent with the Florida Radon Research
Program (FRRP) Standard Measurement Protocols (Williamson and Finkel, 1991).
6

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Approach. Parameters, and Measurements
At each house, monitoring was conducted during three time realms:
1.	The baseline data collection period,
2.	The system installation and tuning period, and
3.	The post-installation performance/durability monitoring period.
Data collection consisted of a combination of:
1.	Continuous multi-parameter data acquisition (in a sub-set of four houses!,
2.	Continuous radon monitoring,
3.	Integrated radon monitoring, and
4.	Point measurements and observations in conjunction with site visits.
Data-acquisition systems for continuous recording of various parameters as indicated
in Table 1 were installed in a subset of four houses (referred to as "instrumented houses"),
usually prior to the mitigation installation. Continuous indoor radon monitoring was performed
in most of the houses, either as part of the data logging system (hourly averages) in the
instrumented houses or by a stand-alone continuous radon monitor (four-hour averages) in the
other houses. Integrating radon monitors (E-PERM electret ionization chambers, Rad Elec
Incorporated) were also used.
Beginning with the baseline data collection period and continuing through the first year of
the project, daily weather data for Gainesville and Ocala were obtained on a monthly basis
from the University of Florida Agronomy Department and the City of Ocala Water Treatment
Plant, respectively.
Baseline Measurements
Baseline data collection was targeted for at least a month-long period prior to
installation of the SSD system. Measurements included indoor radon concentration by
integrating detectors, indoor radon concentration by continuous monitoring, pressure
differentials (in some instrumented houses), and weather data (in some instrumented houses).
Post-installation Performance/Durability Monitoring
Following installation and tuning of the mitigation system, continuous data acquisition
systems (instrumented houses) or continuous radon monitors (non-instrumented houses) were
operated, integrating radon monitors were deployed, and periodic house visits were
performed.
Post-installation monitoring was conducted according to the following general 3-stage
schedule:
• Stage 1 Monitoring (in service <6 months) - Continuous and/or integrating indoor
radon monitoring was performed and houses were visited on a biweekly basis to
observe system operation, measure pressures and flows, and service radon monitoring
equipment.
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Table 1. Parameters Recorded by Continuous Monitoring Systems.
A.
Data Acauisition Svstems in Instrumented Houses - Data loaaers* with sensors

for:


1.
Pressure Differential
•	Outside vs. inside
•	Sub-slab vs. inside

2.
3.
Indoor Radon*
Temperature
•	Indoor
•	Outdoor

4.
Rainfall

5.
Wind Speed

The above parameters are sampled every 30 seconds and then summed or
averaged and hourly sums or averages are averaged and stored in memory.
B.
Continuous Radon Monitorina in Non-instrumented Houses - Continuous

monitor* for indoor radon. Four-hour averages are stored in memory.
Notes:
* Model 21X Micrologger Campbell Scientific Inc., Logan, UT, with sensors for
the various parameters,
t At Ease Model 1021, Sun Nuclear Corp., Melbourne, FL.
t At Ease Model 1023
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•	Stage 2 Monitoring (in service 6 to 12 months) -- Houses without data loggers were
visited on a monthly schedule. For houses with data loggers, data acquisition was
continued, data were reviewed, arid visits were performed as necessary.
•	Staoe 3 Monitorina (in service >12 months) -- As a longer-term follow-up, visits were
conducted on an approximately 6-month schedule to inspect the systems, measure
pressures and flows, and deploy radon monitors for a week-long measurement.
Measurements and observations taken during house visits are summarized in Table 2. In
addition, responses were made to homeowner questions or homeowner-identified problems.
The procedures and data collection forms for the post-mitigation routine house visits are
included in Appendix B (Volume 2).
Performance/durability data were evaluated in terms of the following characteristics:
•	System Performance and Interaction with the Sub-slab Medium - System pressures
and flows, noise and vibration, and requirements for adjustments and maintenance.
•	The Sub-slab Environment -- Effective permeability calculated from pressures and
flows, and exhaust air and/or sub-slab radon concentrations.
•	Effectiveness - Indoor radon concentrations.
•	Structural Effects - Observations for evidence of subsidence, heaving, cracking,
separation of joints, etc.
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Table 2.
Post-installation Data Collection and Observations.
A.
Condition of Sub-slab Environment
1.	Soil moisture at each suction hole:
•	Visible evidence of condensation in the clean out.
•	Collection of small soil sample for laboratory analysis (as required).
•	Qualitative observation of pipe internal moisture: dry, moist, or wet.
2.	Visible evidence of mold at or in the suction hole.
3.	Radon concentration in sub-slab exhaust air at each suction hole.
4.	Soil gas radon concentration (if fan is turned off).
5.	Suction-hole-to-suction-hole communication (on special schedule).
6.	Effective permeability calculated from flow and pressure measurements.
B.
Condition of Sub-slab Medium and Ventilation Eauioment System

1.	In instrumented houses: pressure monitored continuously.
2.	In all houses: system-induced pressure and air flow at time of visit.
3.	Comments and observations on changes; possible causes of atypical
values.
C.
Ventilation Svstem Performance
1.	Occurrence of noise, vibrations, etc.; diagnosis of causes; actions taken.
2.	Ambient temperature at fan location (if attic is entered).
3.	Record of any adjustment, maintenance, or equipment change out.
D.
Continued Effectiveness
1.	Indoor radon - integrated and continuous (instrumented houses).
2.	Meteorological and other variables potentially influencing indoor radon
concentrations.
E.
Structural Effects (if any)
1.	Evidence of structural effects (i.e., heaving, subsidence, failing integrity
of sealing joints, stair-step cracking at corners of masonry walls)
observed during biweekly visits.
2.	Evidence of structural effects as observed during detailed non-routine
visits; quantification of effects.
Note: Observations are biweekly unless noted otherwise.
10

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SECTION 4
RESULTS AND DISCUSSION
HOUSE CHARACTERIZATION
Diagnostics were performed on 12 Gainesville and Ocala slab-on-grade houses with
elevated indoor radon leveis (screening measurement levels on the order of 20 to 50 pCi/L)
during the last week of November 1988. Selected results are tabulated in Table 3; a more
detailed tabulation is presented in Appendix A (Volume 2). The houses represented a variety
of slab areas, foundation shapes, and slab-wall configurations. All of the houses had central
heating/air conditioning systems, but a variety of fuels, air handler locations, and return air
routing.
The Sub-slab Medium
The sub-slab material typically consisted of sand, either native material from the lot or
fill from off-site sources. This is in contrast to the coarse aggregates being advocated
elsewhere in the country. The permeability of this material is significantly less than for
coarser aggregates and consequently communication is often poor. Communication distance
was defined as the farthest distance at which a pressure differential of at least 0.025 mm
(0.001 in) of water can be measured when a pressure of 500 Pa is applied at a suction hole.
The distribution of communication distances was as follows for the 12 houses:
•Good(>3m) 	 3 houses (25%)
•	Fair (> 0.3 - 3.0 m) 	 6 houses (50%)
•	Poor (<0.3 m) 	 3 houses (50%).
This suggests that in the majority of cases, SSD systems will have to deal with
communication distances considerably less than half the major dimension of the house.
Consequently, for many houses, more than one sub-slab suction point is likely to be required
to provide an adequate pressure field.
In some cases, the communication increased when the test hole was extended farther
(approximately 1 5 cm) beneath the slab. This suggests that the fill placement practice
produced a compaction gradient with the lowest permeability immediately under the slab.
Thus, suction pits should be excavated sufficiently deep to penetrate through the compacted
layer to the more permeable material.
The moisture content of the sub-slab material was in the range of 1 to 5% for the
majority (78%) of the samples examined. However, for several houses the moisture content
was in the range of 9 to 14%. This suggests that the sub-slab soil/fill under some houses
may be susceptible to drying upon ventilation; this should be examined in studies of SSD
system performance. There did not seem to be a correlation between moisture content and
effective permeability or pressure communication.
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Table 3. Summary of Characterization Measurements on 1 2 Candidate Houses
Visit
1
2
3
4
5
6
7
8
9
10
11
12
House ID
234839
234892
234797
234789
234804
234873
235062
235001
234901
234912
234932
235059
Visit Date
M-N
MP
T*A
TN
T P
W-A »
WN
WP
Th-A
Th-N
Th-P
F-A
City
Gainesville
Gainesville
Ocala
Ocala
Ocala
Gainesville
Gainesville
Gainesville
Gainesville
Gainesville
Gainesville
Ocala
Mitigation ID
G-5
G-l
0-1
0-2

G-6
G-3
G*2

G-4

0-3
HOUSE FEATURES












Slab type
S
S
f
S
S
F
F
F
S
F
F
P
Slab size. m}
195
164
167
164
112
203
158
194
186
181
195
149
nt'i
(2100)
(1760)
(1800)
(1760)
(1 200)
(2188)
(1700)
(2087)
(2000)
(1950)
(2100)
(1608)
Foundation shape
*L"
Rect
Rect
Rect
Rect
2 Rect
Rect
Rect
Complex
Pact
Rect
Rect
Wall construction
FRM + STV
FRM/BV +C
CCB
FRM
FM/VN
CCB
CCB
CCB/VN
CCB+FRM
CCB/BV
CCB
CCB
Attic space adequate?
Y
Y
Y
Y
N
Y
Y
Y
N
Y
Y
Y
Fireplace type
PF
PF
None
MAS
None
PF
None
PF
PF
Nona
None
WS
Heating fuel
Gas
HP
Elect
Gas
Elect
Gas
Elect
Propane
Gas
Gas
Gas
Elect
Air handler
Garage
Garage
UTIL
Garage
UTIL
Garage
Closet
Garage
Closet
O
0
UTIL
Attic
Return air
Attic + TW
TW
Attic
Attic+ TW
Attic
TW
TW(Ooor)
Attic
Ceiling
AttiC
Attfc
Attic
SUB-SLAB FEATURES












Commun. distance, m
6 20
0.3
0.3
5.5
1.8
4.6
4.9
0.3
2.4
2.4
3.0
2.4
(ft)
1 (6.5)
(1.0)
(1.0)
(18.0)
(6.0)
(15.0)
(16.0)
(1.0)
(8.0)
(8.0)
(10.0)
(8.0)
Commun. category
Fair
Poor
Poor
Good
Poor
Good
Good
Poor
Fair
Fair
Fair
Fair
RADON. AVQ dCI/L












Sub-slab, sniff
4305
2824
3879
3945
4658
3400
8599
4272
1347
3257
7818
9255
grab
3855

3564
4422

4250
7160

3117
3033
7647
9928
In-wall, max
33
55

55
..
40
161
20
50
267
127
65
min
1
6

2

16
9
2
3
-32
31
14
Indoor, screening
29.0
34.9
45.7
21.1
28.1
20.8
38.1
41.5
21.9
38.4
42.5
44.0
alpha track
11.0
4.6
11.3
10.7
7.6
10.1


15.4
19.9
30.2
8.9
canister
15.7
16.6
25.0
22.7
14.4
8.1
12.6
18.9
15.8
28.7
35.9
28.1
grab
6.5
9.6
8.0
6.4
8.0

11.0

9.8
7.9
28.4
"
HOUSE DYNAMICS












Delta P, House Closed:












Appliances off • low
ND
0.125
0.075
0.250
NR
-0.025
-0.050
-0.050
-0.100
-0.100
-0.025
-0.150
high

0.200
0.225
0.300

-


-

-
-0.025
Furnace fan on
NM
NM
NM
0.125
NR
Var
-0.075
-0.050
NM
NM
VS
-0.400
Leakage:












Eff. leakage area. m}
85
150
78
100
179
196
109
167
184
131
230
54
KEY
Slab type:
Wall construction:
Fireplace type:
Heating fuel:
Air handler:
Return air:
Date of visit:
Commun. distance
Common, category
S« sealed stem-wall, F- floating. P« partially sealed
FRM * frame. CCB = concrete block, BV « brick veneer.
STV « stone veneer, VN = vinyl siding
PF ¦ prefab. MAS ¦ masonry, WS = wood stove
HP « heat pump
UTll » utility room (a conditioned space)
TW • through the wall
M. T, W, Th, & F ¦ Mon 28 Nov through Fri 2 Dec 1 988
•A. -N, -P ¦ AM. noon. PM
Delta P's are mm of water with EDM
NO » none detected with EDM
NM « not measured
NR * not recorded
NE • no effect of fan or appliance(s)
VS * very slight effect
Var = Variable. House f 234873 with furnace on:
Negative near return air intake (-0.05 to -0.012)
Positive in hall near front door {+ 0.001 to + 0.011)
¦ communication distance
= communication category.
e farthest distance at which a pressure differential of 20-025 mm of water can be measured when a pressure of 500 Pa is applied at the suction hole.
Based on communication distances Poor =• 0*0.3 m (0*1 ft); Fair = 0.3-3 m (1 *1 0 ft); Good =• > 3 m (> 10 ft).

-------
Slab\Wall Configuration
A major variable characteristic of Florida slab-on-grade house construction, potentially
affecting the route of radon entry and potentially impacting on the design, installation, and
performance of SSD systems is the slab\wall configuration. Three types were observed
among the 12 houses:
•	Floating slab\Concrete block wall (F\CCB) 		6 houses (50%)
•	Slab on sealed stem wall\Frame wall (S\FRM) 		5 houses (42%)
•	Slab, partialJy-sealed stem wall\Concrete block wall (P\CCB) 		1 house ( 8%).
The highest in-wall radon concentrations were observed in the floating slab houses.
Return Air Routing
The return air system was considered another variable potentially affecting design and
performance of SSD systems because of the potential effect on pressure differentials. The
following distribution of configurations occurred in the 1 2 houses:
•	Overhead ducting in attic or false ceiling 	 7 houses (58%)
•	Through-the-wall grill, no ducting (TW) 	 3 houses (25%)
•	Combination (ATTIC + T) 	 2 houses (17%).
INSTALLATION OF DEMONSTRATION SSD MITIGATION SYSTEMS
Between May 1989 and August 1990, SSD systems were installed in a total of nine
of the previously characterized slab-on-grade houses in the Gainesville-Ocala vicinity. The
installations were performed in two series - a 1989 set and a 1990 set. House descriptions
and the installed systems are summarized in Table 4; floor plans are included in Figures 1
through 9. Results of observations, measurements, and data acquisition are presented by
house in Appendix C (Volume 2) and are summarized in the following sections.
In 1989, five houses, three in Gainesville and two in Ocala were selected for
mitigation. These houses were all of simple, single rectangular slab configuration with slab
areas ranging from 158 to 195 m2 (1700 to 2100 ft2). Mitigation systems were designed
using the UF soil depressurization model and were installed during the time period May
through November 1989. Two-suction point, single-fan systems were installed in four of the
houses. The Gainesville-3 house was of smaller dimensions (slab area = 158 m2 or 1700 ft2),
its sub-slab communication was rated as "Good", and it had a convenient location for a
central suction point - hence only a single suction point was used. The Gainesville houses
were equipped with continuous data acquisition systems.
During the summer of 1990, systems were installed in two additional houses with
simple rectangular slabs (149 to 181 m2 or 1600 to 1950 ft2) and in two larger (195 to 203
m2 or 2100 to 2200 ft2) houses with L-shaped floor plans. System designs were specified
using the evolving guidelines of the Florida radon-resistant building code. All of these systems
had two suction points connected to a single fan. The system in the largest house also had
a third suction point with a second fan. A continuous data acquisition system was installed
in one of the rectangular houses.
13

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Table 4. Characteristics of Mitigation Demonstration Houses, SSD Systems, and Monitoring.
House *
#234797
0CALA-1
#234789
0CALA-2
#234892
GVL-1
#235001
GVL-2
#235062
GVL-3
#234912
GVl-4
#235059
OCALA-3
#234839
GVL-5
#234873
GVL-6
House Features:
Age, yrs
14
17
9
14
19
20
14
9
13
Slab Footprint
Type'
Size, m2
(ft7)
Rectangle
F
167
(1800)
Rectangle
S
164
(1760)
Rectangle
S
164
(1760)
Rectangle
F
194
(2087)
Rectangle
F
158
(1700)
Rectangle
F
181
(1950)
Rectangle
P
149
(1608)
L-shaped
S
195
(2100)
L-shaped
F
203
(2188)
Wall Construction*
CB
FR
FR/BV + CB
CB/VN
CB
CB/BV
CB
FR + STV
CB
Air Handler Location
Return Air Route*
Utility Rm
ATTIC
Garage
Attic + TW
Garage
TW
Garage
Attic
Closet
TW(door)
Closet
Attic
Attic
Attic
Garage
Attic+ TW
Garage
TW
Pre-Mitiaation Conditions:
Sub-slab Commuoication*
Radon, pCi/L*
Poor
3880
Good
3940
Poor
2820
Poor
4270
Good
8600
Fair
3260
Fair
9260
Fair
4300
Good
3400
Indoor Rn (avg), pCi/L*
16
10
11
25
9
11
30
25
26
SSD System Features:
Suction Pit #1 Diameter, m
#2 Diameter, m
#3 Diameter, m
0.91
0.91
0.91
0.84
0.91
0.84
0.91
0.52
0.91
0.61
0.66
0.71
0.71
0.86
0.71
0.56
0.61
0.61
Fan Type*
R-1 50
R-1 50
R-150
R-150
T-1
R-150
R-150
R-150 & RW
R-150
Date Operation Began
May 1989
May 1989
July 1989
Nov 1989
Oct 1989
May 1990
Aug 1990
July 1990*
July 19905
Monitoring:
Continuous Acquisition
No
No
Yes
Yes
Yes
Yes
No
No
No
Date Rn Monitoring Began
April 1989
April 1989
June 1989
Oct 1989
Oct 1989
Jan 1990
Aug 1990
Aug 1990
Dec 1990
"Key: GVL = Gainesville	Slab Type: S = Sealed stem-wall; F = Floating; P = Partially-sealed stem-wall
Wall Construction: CB = Concrete block; FR = Frame; BV = Brick veneer; STV = Stone veneer; VN = Vinyl siding
Return Air Route: TW = Through wall with no ducting; Attic = Ducts, in attic
Sub-Slab Communication: Based on communication distances. Poor = 0-0.3 m (0-1 ft); Fair = 0.3-3 m (1-10 ft); Good = >3 m (>10 ft)
Communication Distance: Farthest distance at which a pressure differential of M).025 mm of water can be measured when a pressure of 500 Pa is applied at the suction hole.
Fan Type: R-1 50 = Fantech Model R-1 50, 270 cfm, 21 50 rpm, 1/20 HP; T-1 = R.B. Kanalflakt Turbo Model T-1, 1 58 cfm, 2800 rpm, 1/40 HP;
RW = Radon Win Mitigator Series One (based on Fuji Model VCF 083 Ring Compressor) 19.5 cfm, 0.11 HP
t Sub-slab radon is average for "sniff" measurements. t Avg. indoor radon values are for measurements made shortly before mitigation. See Table 5 for range of pre-mitigation values.
§ Although systems in GVL-5 and GVL-6 were turned on July 1990, they required further adjustment and became successful Oct 1990.

-------
House 234797
Ocala-1
Figure 1. House 234797 (Ocala 1)
15

-------
House 234789
OcaIa-2


'	J

If
Legend	1 cm = 4 ft
—•	2" PVC Pipe air suclion
	 0.5" PVC Pipe condensation drainage
®	Fan
•	Suction point
N
Figure 2. House 234789 (Ocaia 2)
16

-------
0)
>

CD
C
"(D
o
CM
CTi
00
CO
CV|

-------


bn
r>k
1 f]
tj CP CP t
oo
C3 C-
¦e
3	C
Legend
1 cm = 4 ft
'	2" PVC Pipe air suction
	 0.5" PVC Pipe condensation drainage
<8>	Fan
•	Suction point
¦	Data logger
-0~	Weather station

I
Q
9?.
O
c
3*
CD
CD
CO
ro
<_
0)
01
o
fO
o
•Jk
Figure 4. House 235001 (Gainesville-2)

-------
J
1 ®L ,,	,
L) <^3 cLi C	i eri
n
U—
n II n
r=3
a
5?.
zj'
(D
0)
<
CD
I
O
c
0)
(D
ro
CO
oi
w §
ro
Legend	1 cm = 4 ft
"""	2" PVC Pipe air suction
		0.5" PVC Pipe condensation drainage
®	Fan
•	Suction point
¦	Data logger
-0~	Weather station
Figure 5. House 235062 (Gainesville-3)

-------
Legend	1 cm = 4 ft
1	2" PVC Pipe air suction
		0.5" PVC Pipe condensation drainage
®	Fan
•	Suction point
¦	Data logger
-0~	Weal ier station
Figure 6
House 234912
(Gainesville-
4)

-------
House 235059
Ocala-3
N
Legend	1 cm = 4 ft
" ~ 2" PVC Pipe air suction
	 0.5* PVC Pipe condensation drainage
® Fan
• Suction point
Figure 7. House 235059 (Ocala-3)
21

-------
House 234839
Galnesville-5
u u
J ^
2
Al
rn:

3	C
fi==M
(1
Legend	1 cm = 4 ft
—- 2" PVC Pipe air suction
0.5" PVC Pipe condensation drainage
® Fan
• Suction point
¦ Data logger
-0- Weather station
Figure 8. House 234839 (Gainesvifle-5)
22

-------
House 234873
Gainesville-6
Figure 9. House 234873 (Gainesvil!e-6>
23

-------
In summary, SSD systems were installed in a total of nine slab-on-grade houses with
central heating/air conditioning systems, six in Gainesville and three in Ocala. Several
combinations of slab and wall type, return air system, and measured sub-slab communication
are represented. Floor plans included seven rectangular and two more complex, L-shaped
designs. A single-suction point system was installed in one house. Two-suction point/single-
fan systems were installed in eight of the houses. One of these houses had a complex floor
plan with several slab rectangles and a single-point, single-fan system was installed in addition
to the two-point, single-fan system. Suction pits ranged from 0.5 to 0.9 m (20 to 36 in) in
diameter. The major piping runs of the SSD systems were of nominal 50 mm (2-in) PVC pipe.
A total of four houses were instrumented for continuous data acquisition.
OBSERVATIONS ON THE INSTALLED SYSTEMS
System Effectiveness (Indoor Radon)
Pre-mitigation indoor radon concentrations and concentrations for various system
operating configurations are presented in Table 5. The systems were generally effective in
reducing indoor radon levels that were originally in the range of 10 to 30 pCi/L to levels of < 4
pCi/L. Levels were reduced to values on the order of 2 pCi/L or less in three houses.
The effectiveness of the SSD systems was confirmed by performance when the systems
were switched off and then back on. When the SSD systems were shut off, indoor radon
concentrations returned to levels comparable to those before the beginning of operation of the
system; when the systems were turned on, levels were again reduced.
System OoeratinQ Characteristics (Pressure and Flow)
Pressure and flow values, as observed by single-point-in time measurements during
house visits, exhibited fluctuations on the order of 10 to 20 Pa and 0.02 to 0.5 L/s (0.5 to
1 cfm), respectively. Therefore, initial operating characteristics were taken as the average
over the first several months of operation. These are listed in Table 6 and summarized in
Table 7 for operation with the fans at the "high" speed setting. For the two-suction-point
systems with R-1 50 fans, the system pressures near the suction holes were typically on the
order of -200 to -400 Pa, while the flows ranged from 0.5 to 13 L/s (1 to 28 cfm). Similar
characteristics were observed for the lone single-suction point system with a T-1 fan -
average pressure of -246 Pa and average flow of 1.1 L/s (2.3 cfm). Flows for 11 (65%) of
the 17 suction points with these fans were clustered in the range of 0.5 to 2.0 L/s (1 to 4
cfm). Flows for the remaining six suction points (35%) were distributed over the broad range
of 3.6 to 13 L/s (8 to 28 cfm). When expressed on a log basis, the flow data suggest a
bimodal distribution. The low flows for the majority of these systems are presumably related
to the nature of the sand fill under the slabs at these houses.
The second system in House Gainesville-6 utilized a high pressure fan; consequently,
operating conditions were different from those exhibited by the other systems -- pressure of -
1600 Pa and flow of 5 Us (11 cfm).
In the two-suction-point systems, pressures were typically the same at the two suction
holes (SH's) - the holes were connected to the same exhaust system and flow rates were too
low to present appreciable differences in pressure loss between the two branches of the
24

-------
Table 5. Indoor Radon Concentrations and Reduction Factors.
House
#234797
OCALA-1
#234789
0CALA-2
#234892
GVL-1
#235001
GVL-2
#235062
GVL-3
#234912
GVL-4
#235059
OCALA-3
#234839
GVL-5
#234873
GVL-6
Pre-mitiaation:
Average, pCi/L
(Range, pCi/L)
16
(13-17)
10
(9-11)
11
( 4-23)
25
(19-32)
9
( 7-14)
11
( 6-15)
30
(11-44)
25
(19-29)
26
(10-46)
Passive Ventilation:
Average, pCi/L
[Reduction]*
NM
8
[0.84]
21
[none]
27
[none]
9
[none]
NM
NM
NM
NM
Hole #1 Active:
Average, pCi/L
(Range, pCi/L)
[Reduction]
NM
3
[0.32]
6
( 5- 6)
[0.52]
NM
2
[0.22]
NM
NM
NM
NM
Hole #2 Active:
Average, pCi/L
(Range, pCi/L)
[Reduction]
NM
NM
9
( 7-11) t
[0.56]
NM
NA
NM
NM
NM
NM
All Holes Active:
Average, pCi/L
(Range, pCi/L)
[Reduction]
2.5
(1-4)
[0.13
2
( 1-4)
[0.20]
3.5
( 1- 9) t
[0.32]
2.5
(2.5-11)t
[0.10]
NA
2.6
(1.8-3.9)
[0.24]
2
[0.07]
2.5
[0.1]
2.5
[0.1]
Svstem Off:
Average, pCi/L
25
12
NM
NM
NM
NM
NM
NM
NM
•Reduction = (Concentration at test)/(Pre-mitigation concentration).	Definition of Conditions:
tSome data collected before sealing of floor crack.


Condition
Fan
Hole #1
Hole #2
GVL =
= Gainesville
Pre-mitigation
NONE
NONE
NONE
NM =
Not Measured
Passive Ventilation
OFF
OPEN
OPEN
NA =
Not Applicable (only one suction point)
Hole #1 Active
ON
OPEN
CLOSED


Hole #2 Active
ON
CLOSED
OPEN


All Holes Active
ON
OPEN
OPEN


System Off
OFF
CLOSED
CLOSED

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Table 6. Average Initial Pressures and Flows at Suction Holes.
House (1989 Set)
#234797
#234789
#234892
#235001
#235062

OCALA-1
OCALA-2
GVL-1
GVL-2
GVL-3
Operation Date
May 1989
May 1989
July 1989
Nov 1989
Oct 1989
Fan*
R-150
R-150
R-150
R-150
T-1
Suction Hole
1 2
1 2
1 2
1 2
1
Pit, m
0.91 0.91
0.91 0.84
0.91 0.84
0.91 0.52
0.91
Pressure, Pa
384 384
377 377
370 328
277 310
246
Flow, Us
1.9 1.9
2.0 1.3
1.4 10.4
13.4 8.4
1.1
(cfm)
(4.1) (4.0)
(4.2) (2.8)
(2.9) (22.1)
(28.3) (17.8)
(2.3)
House (1990 Set)
#234912
GVL-4
#235059
OCALA-3
#234839
GVL-5
#234873
GVL-6
Operation Date

May 1990
Aug 1990
July 1990**
July 1990**
Fan*

R-150

R-150
R-150
RW

R-150
Suction Hole
1

2
1 2
1
2
3
1
2
Pit, m
0.61

0.62
0.71 0.71
0.86
0.71
0.56
0.61
0.61
Pressure, Pa
211

203
347 428
342
121
1611
198
331
Flow, L/s
(cfm)
1.6
(3.4)

3.6
(7.7)
5.7 0.5
(12.1) (1.1)
1.2
(2.6)
6.2
(13.2)
5.2
(11.0)
0.6
(1.3)
0.9
(2.0)
*Fan Type: R-150 = Fantech Model R-150, 270 cfm, 2150 rpm, 1/20 HP;
T-1 = R.B. Kanalflakt Turbo Model T-1, 158 cfm, 2800 rpm, 1 /40 HP;
RW = Radon Win Mitigator Series One (based on Fuji Model VCF 083 Ring Compressor) 19.5 cfm, 0.11 HP
** Although systems in GVL-5 and GVL-6 were turned on July 1990, they required further adjustment and became successful Oct 1990.

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Table 7. Summary of SSD initial Operating Conditions

Pressure,
Pa
Flow, L/s (cfm)
R-150 Fan: 2-hole svstems. 0.6-0.9 m Dits.
installed in 8 houses {16 holes)


• Range of values {16 holes)
121-428
0.5-13.4 (1.1-28.3)
• Typical values {10 holes)
200-400
0.5-2 (1-4)
• Installations with atypical values (6 holes):
- House GVL-1
SH-1 <0.91 m pit)
[After sealing crack]*
SH-2 (0.84 m pit)
[After sealing crack]*
370
[444]
328
[436]
1.4 ( 2.9)
[0.7 ( 1.6)]
10.4 (22.1)
[4.2 ( 8.8)]
- House GVL-2
SH-1 (0.91 m pit)
SH-2 (0.52 m pit)
277
310
13.2 (28.3)
8.4 (17.8)
- House Ocala-3
SH-1 (0.71 m pit)
SH-2 (0.71 m pit)
347
428
5.7 (12.1)
0.5 { 1.1)
- House GVL-5
SH-1 (0.86 m pit)
SH-2 (0.71 m pit)
342
121
1.2 { 2.6)
6.2 (13.2)
T-1 Fan: 1-hole svstem. 0.91 m Dit. installed in
1 house


• Observed values
246
1.1 (2.3)
RW Fan: 1-hole svstem. 0.56 m Dit, installed in
1 house in addition to an R-150/2-hole system


• Observed values
1611
5.2 (11.0)
SH = Suction hole.
•House GVL-1 has a crack near SH-2. Values after partially sealing crack are indicated in I ).
Fan Types:
R-150 = Fantech Model R-150, 270 cfm, 2150 rpm, 1/20 HP;
T-t = R.B. Kanalflakt Turbo Model T-1, 158 cfm, 2800 rpm, 1/40 HP;
RW = Radon Win Mitigator Series One {based on Fuji Model VCF 083 Ring Compressor) 19.5 cfm, 0.11 HP.
27

-------
system. On the other hand, the sub-slab medium does not always present the same
resistance at both suction points in the same house. Consequently, differences in flows (and,
correspondingly, effective permeability) between the two branches of the system were
typically greater than any differences in pressure.
There were exceptions to the "typical" operating conditions. At Gainesvil!e-1 (SH-2),
Ocala-3 (SH-1), and Gainesville-5 (SH-2), flows were atypically high (5 to 10 X the values for
the "partner"hote) with pressure reductions of 11, 19, and 65% from those in the partner
hole. At Gainesville-1, SH-2 actually was installed through the house stem wall from inside
the garage and was located near the floor-wall joint of the garage floor. The nearby joint
apparently provided a leak with significantly less resistance than the general sub-slab medium;
this resulted in a considerable ambient air leakage which was reflected in a high flow and
lower pressure. Sealing leaks near this suction point (in November, 113 days after start up)
resulted in sharp increases in pressure in the system, especially at SH-2 and a decrease in
flow at SH-2. The sealing effort, however, was only partially successful. Pressures observed
during the balance of the year were variable, and flows at SH-2 were variable and generally
higher than what appears to be typical for these houses.
Another exception was the Gainesville-2 house at which flows at both holes were an
order of magnitude higher than typical - on the order of 13 L/s (28 cfm) at SH-1 and 8 L/s
(18 cfm) at SH-2. The higher flow at SH-1 relative to SH-2 might be due to the fact that SH-
1 is located near the end of the house and near the wall to the garage. This hole was possibly
drawing considerable ambient air as a result of being located so close to two outside walls.
The leakage/dilution hypothesis is supported by the lower suction hole radon concentration
observed- at SH-1 (Table 8). The reason for the relatively high flow at SH-2 remains an
enigma. While high flows would be associated with sub-slab fills of higher permeability than
typical for the study houses, no unusual characteristics were noted for the fill examination at
the time of house characterization. Also, while high flows at this hole could result from
nearby slab leakage or channeling from the foundation perimeter, the radon concentration at
SH-2 (Table 8) did not provide strong evidence of excessive entry of ambient air into the
system and concomitant dilution of the soil gas radon concentration.
Trends with Time
Trends with time for system characteristics (pressure, flow, effective permeability, and
suction hole radon concentration) are presented in tables and figures by house in Appendix
C (Volume 2). System characteristics were followed with time for four months or longer in
six of the nine houses; three of the installations in the 1990 set were completed too late in
the project to observe trends with time.
Except for a transient condensation-related flow perturbation, the systems were
characterized by small short-term flow fluctuations and a general trend at five of the six
houses of relatively constant or slightly decreasing flows in the presence of steady or slightly
increasing pressures (also expressed as constant to slightly decreasing effective sub-slab
permeability). The exception to this pattern was Gainesville-2 where flows and effective
permeability were initially atypically high and increased with time while the system pressures
decreased. This is suggestive of channeling in, or drying of, the sub-slab medium.
28

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Table 8. Sub-slab and/or Suction-Hole Radon Concentrations, pCi/L
House (1989 Set)
#234797
OCALA-1
#234789
OCALA-2
#234892
GVL-1
#235001
GVL-2
#235062
GVL-3
Pre-installation,
Sub-slab -
3720
4180
2820
4270
7880
Post-installation,
Suction Hole:
Pre-operation*
System off*
Passive Vent*
Active Vent5
SH-1 SH-1
NM NM
NM NM
8050 6380
2620 3210
SH-1 SH-2
NM NM
5500 9400
2000 NM
5300 8070
SH-1 SH-2
126 133
NM NM
8190 598
15400 1440
SH-1 SH-2
NM NM
NM NM
2590 5660
390 3050
SH-1
NM
NM
6920
3250

House (1990 Set)
#234912
GVL-4
#235059
OCALA-3
#234839
GVL-5
#234873
GVL-6
Pre-installation,
Sub-slab -
3140
9590
4080
3820
Post-installation,
Suction Hole:**
Active Vent
SH-1 SH-2
10400 4088
SH-1 SH-2
3821 296
SH-1 SH-2 SH-3
1922 1862 4458
SH-1 SH-2
17241 15278
NM = Not Measured	SH = Suction Hole
* Pre-operation = Pre-operational condition = System installed, prior to operation,
t System off = Fan off and suction hole valves closed.
$ Passive vent = Passive ventilation = Fan off and one or more suction hole valves open.
§ Active vent = Active ventilation = Fan on and suction holes open.
** For houses mitigated in 1990, post-installation suction hole radon measurements were conducted only for the active ventilation condition.

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The most striking system perturbation was related to moisture condensation in the
early installations. With the advent of cool weather in 1989, there was a dramatic increase
in condensation due to moist (nearly saturated) air coming in contact with the cooler
ventilation system in the attic in the three systems on line at that time. The first indication
was a gurgling sound in the system in the Ocala-1 house in late October. In systems with an
undrained low point in the horizontal run, water built up to a sufficient degree to affect the
performance of the system. This was manifested as reduced pressure in houses Ocala-1 and
Ocala-2. A program of biweekly draining was initiated, and the systems were routinely
drained before making pressure and flow measurements. Shortly thereafter, drain lines were
installed to facilitate draining the attic traps. Following initiation of the drainage program in
the two Ocala houses where condensate-induced system pressure reductions were observed,
pressures resumed the earlier values and trends. The observations from house Gainesville-1
were confounded by the fact that the appearance of condensation occurred in about the same
time frame as the efforts to seal cracks to reduce leakage.
The Sub-slab Environment
Sub-slab moisture was difficult to monitor. One continuous moisture probe stopped
operating due to voltage scaling problems. Data from laboratory analysis of soil samples
collected at the diagnostic visit, at the time of installation of the suction pit, and from the
suction holes near the end of 1989 did not indicate any significant change in moisture content
during this relatively short period of operation. Better measurement methods should be
developed to follow this parameter over a longer period of time.
Sub-slab radon concentrations as determined at the diagnostic visits and suction hole
radon as determined under various system conditions are summarized in Table 8. For three
of the nine houses (Gainesville-1, -4, and -6) suction hole radon concentration was a factor
of 2 or more times the sub-slab soil gas radon concentration measured under static conditions;
in these cases the sub-slab was apparently isolated from the ambient atmosphere and soil gas
was being drawn from deeper depths. In another third of the houses (Gainesville-2, -3, and
Ocala-3), the suction hole/sub-slab radon concentration ratio was less than 0.5, indicating
dilution by house air or by influx of ambient air. The remaining three houses presented a more
"balanced" situation with the suction hole radon concentrations representing the static sub-
slab radon within a factor of two (ratio in range of 0.5 to 2.0).
DESIGN AND INSTALLATION EXPERIENCES
Mitigation Design
As stated above, the UF soil depressun'zation model was used as a design tool in
placing suction points and sizing system components. The results of this work are presented
in the companion Part U report.
Moisture Condensation
Because the air being exhausted has a high moisture content, condensation will occur
in attic systems during cold weather and this must be considered. Build-up of water in
undrained low portions of suction pipes can be sufficient to compromise the operation of the
exhaust system. Exhaust systems should be insulated to reduce the problem of condensation.
30

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In addition, any horizontal runs in the attic should be sloped downward toward the vertical
rises from the suction hole with no low spots for collection of water. If available space does
not permit sloping toward the vertical pipe, traps should be installed at low points and
provision made for drainage. The drainage method should be a minimum-maintenance system
requiring only infrequent attention by the homeowner.
Sub-slab Leakage
Since resistance to flow is relatively high for such media, SSD systems for houses with
sand as the sub-slab fill are sensitive to short circuits and leakage of house or ambient air into
the depressurized space. It was observed that air leakage near the suction point can
compromise the system effectiveness. For example, in one case "short-circuit" flows from
a leakage crack near one suction point of a two-point, single-fan system resulted in excessive
flows at that suction point, an imbalance of the system, a compromise of the pressure field,
and unsatisfactory effectiveness. Caulking the crack resulted in satisfactory performance.
Subsequent failure of the silicone caulking resulted in degraded performance; this was
remediated by re-caulking with a urethane elastomer. Other experimental work and simulation
with the computer model indicated that leakage at points more remote from the suction point
have much less of an influence on effectiveness. Special care should be taken in new
construction to minimize such leakage through the slab or at the perimeter.
Re-entrainment
An adventitious experience indicated the potential for re-entrainment problems.
Following the initial installations in two houses, indoor radon levels were 2:10 pCi/L when the
systems were operating. Attic levels of 10's of pCi/L were found in subsequent radon
monitoring. Investigation revealed that the roof penetration was not sealed around the vent
pipe, apparently providing the opportunity for discharged sub-slab gases to enter the attic and
be drawn into the house ventilation system. Sealing the roof penetrations resulted in reduced
concentrations in the attics and indoor levels of -2.5 pCi/L (see Table 51.
OPTIMIZATION STUDIES
Pipe Sizing
Nominal 50-mm (2-in) suction pipes were installed as planned. As stated previously,
for the 18 suction holes, the majority (11 or 61%) had flows of <2 L/s (4 cfm). According
to friction loss charts, the pressure loss in a 50-mm (2-in) pipe would be <15 Pa/10 m for a
flow of <2 L/s. Five of the remaining seven suction points had flows between 3.6 and 10
L/s (8 and 22 cfm); the calculated pressure loss for a 10 L/s flow in a 50-mm pipe would be
100 Pa/10 m. Thus friction Josses would be <15 Pa/10 m for the typical case and <100
Pa/10 m for 90% of the cases.
At Gainesville-1/SH-2, for which the flow was 10.4 L/s with a calculated friction loss
of 100 Pa/10 m, the observed pressure was -328 Pa. The partner suction point in this house
(SH-1) had a flow of 1.4 L/s with a pressure of -370 Pa. This combination effected a
reduction in indoor radon from 11 pCi/L to 3.5 pCi/L (32% of unmitigated value). At
Gainesville-2/SH-2, for which the observed flow was 13.4 L/s with a calculated pressure loss
of 167 Pa/10 m, the observed pressure was -277 Pa. The partner suction point (SH-2) had
31

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a flow of 8.4 L/s and a pressure of 310 Pa. This combination effected an indoor radon
reduction from an original 25 pCi/L to a mitigated 2.5 pCi/L (reduction to 10%).
In summary, with this use of 50-mm (2-in) pipe, for the majority of the cases (61 % of
the suction holes), flows were sufficiently low that calculated pressure losses due to flow
were <15 Pa/10 m, and for 90% of the holes losses were calculated to be <100 Pa/10 m.
In the two cases of the highest flows where the calculated loses were >100 Pa/10 m, actual
pressures on the order of -300 Pa (-277 to -328 Pa) were observed. The systems, involving
these suction points in combination with a second suction point, were effective in reducing
indoor radon levels by factors of 3 to 10, thus resulting in indoor radon levels of 3.5 pCi/l or
less for these houses. The use of the smaller pipe permits savings in cost, space, and
installation effort.
Suction Points
Two suction points successfully maintained levels below 4 pCi/L for slab areas up to
195 m2 (2100 ft2). A single-point system was effective in house Gainesville-3. In addition,
several of the two-hole systems were tested for single-suction point effectiveness by making
radon measurements after one hole or the other had been closed for a period of time. In one
case (Ocala-2), the concentration was maintained at <4 pCi/L. In the other case
(Gainesville-1), the concentration was reduced significantly from the unmitigated case -- but
not to a level below 4 pCi/L. These experiences indicate that a single suction point can be
sufficient for at least some houses with 160 -170 m2 (1700-1800 ft2) slabs.
Passive Ventilation
The potential effectiveness of passive sub-slab ventilation was tested in several of the
houses by monitoring indoor radon with the fans off and the suction lines open. These
experiments indicated that passive venting (fan off, vent line open) was not effective for a
packed sand/soil sub-slab medium. Because of the low permeability of this medium, the
effect is more one of sub-slab depressurization than of sub-slab ventilation. While passive
systems might induce ventilation of a permeable sub-slab medium, they cannot induce the
required negative pressure in this much less permeable medium.
Fan Speed
Fans were typically operated at maximum speed. Reducing fan speed from high to low
generally resulted in a small reduction in pressure at both holes but had little, if any, effect on
flow and consequently no discernable effect on indoor radon concentration.
DURABILITY
Special questions were posed concerning durability for systems operating under Florida
conditions. Would continued operation impact the sub-slab environment in a manner that
affects the continued effectiveness of the system? If there were effects on the sub-slab
environment, would these have structural effects on the building? Would continued
performance of the fans be compromised by the low flow and high temperature in Florida
installations?
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As of the end of 1990, the 1989 installations had been monitored for post-mitigation
periods on the order of 13 to 19 months. Insufficient time had elapsed for significant
durability monitoring on the 1990 systems which had been installed during the period May
through August. During the limited observation period (3 to 18 months), the following were
observed:
1.	With the transient exceptions noted below, the systems settled to relatively constant
performance after an initial adjustment/stabilization period and retained their
effectiveness in maintaining reduced indoor radon concentrations.
2.	In one case, failure of the silicone caulking of a leakage crack near a suction point
resulted in increased "short-circuit" flows. This was remedied by re-caulking with
urethane elastomer, a more durable material.
3.	With the advent of cold weather, condensation formed in horizontal attic runs that
were not self-draining. This resulted in an audible gurgling noise, reduced flow and
increased fluctuations in indoor radon concentrations. This condition was remediated
by installing traps and drains.
4.	No fan failures were observed -- any effect of low flow on fan life was not expressed
during the available observation period.
5.	No structural effects were observed.
6.	With the exception of the "gurgling" associated with the water condensation before
installation of traps and drains, there were no homeowner complaints of noise or other
annoyances.
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SECTION 5
QUALITY ASSURANCE
CALIBRATIONS AND INTERCOMPARISONS OF RADON MEASUREMENT INSTRUMENTS
Scintillation cells (Pylon Model 300 used in conjunction with Pylon Model AB-5
Radiation monitors, Pylon Electronic Development Co., Inc., Ottawa, Ontario, Canada) were
employed as the reference instrument for airborne radon measurements. Cells in a selected
set were calibrated against the radon chamber of the Environmental Measurements Laboratory
(EML) of the U.S. Department of Energy and were then used as reference cells for calibrating
the UF radon chamber.
Pylon Radon Monitors
The University participates in the EML Radon Gas Intercomparison Exercises. For these
exercises, sets of three scintillation cells are shipped to EML where they are filled from a
known radon atmosphere. The filled cells are returned to UF for counting and calculation of
the radon concentration. Later, the known radon concentrations are supplied by EML for
evaluation of the participants' performance. If the UF values vary more than 10% from the
EML values, calibration factors are updated for subsequent measurements. The University
participated in three of the intercomparison exercises during the time period bracketing this
study. Results are presented in Table 9.
Table 9. Results of Participation in EML Radon Gas Intercomparison Exercises.
Exercise, Date
UF Mean*
EML Mean
UF/EML
#14, February 1988
#16, January 1 989
#19, April 1991
13.2 ± 2.0
20.0 + 1.9
26.0 ± 1.1
12.5 + 0.2
24.0 ± 0.6
16.4 ± 0.5
1.06 ± 0.16
0.84 ± 0.07
1.58 ± 0.05
*UF measurements were performed with scintillation cells (Pylon Model 300 used in
conjunction with Pylon Model AB-5 Radiation Monitors). Tabulated values are the
means of three cells.
All ± values represent one standard deviation.
The other scintillation cells in use were calibrated against the reference cells using the
UF radon chamber as the radon source.
34

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At Ease Continuous Radon Monitors
At Ease continuous radon monitors were initially calibrated by the supplier.
Calibrations were periodically checked against calibrated scintillation cells by simultaneous
exposure in the same atmosphere.
Electret Ion Chamber Radon Monitors
The electret readers (voltmeters) were periodically tested by reading a reference
electret. Electret calibration factors were supplied by the vendor. The EIC system were
periodically intercompared with other airborne radon instruments by simultaneous exposure
in the same atmosphere.
DATA REVIEW
The data in this report were reviewed for consistency. Inconsistencies that could not
be attributed to instrument malfunction, transcription error, or any other obvious cause are
identified in the data presentation (Volume 2). Unexplainabie air flow-pressure inconsistencies
with fan speed manipulations (higher flows with lower pressures at "Low" fan speed as
compared to "High" fan speed) were noted for six occasions:
•	House 234797 (Ocala-1), Volume 2, Table C1-4 (pg C-10), two occasions,
•	House 234789 (Ocala-3), Volume 2, Table C2-4 (pg C-28), two occasions, and
•	House 234892 (Gainesville-1), Volume 2, Table C3-4 (pg C-45), two occasions.
In addition, at one house, the indoor radon data reported by the At Ease continuous monitor
for the two averaging periods during the month of January 1990 were noted as "suspect":
•	House 234892 (Gainesville-1), Volume 2, Table C3-5 (pg C-49) and Figure C3-5 (pg
C-51). At Ease radon data for days 361-375 and days 375-394 were an order of
magnitude lower than the Electret Ion Chamber (E-PERM) readings for the same time
periods and were inconsistent with the previous and subsequent At Ease
measurements in this house.
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REFERENCES
Harris, D. B.; Henschel, D. B.; Sanchez, D. C.; Leovic, K. W. Field Measurements in the
EPA/AEERL Radon R&D Program. In Proceedings: the 1988 Symposium on Radon
and Radon Reduction Technology, Vol. 2, EPA-600/9-89-006b (NTIS PB 89-167498).
U. S. Environmental Protection Agency,March 1989.
Nagda, M. L.; Koontz,M.D.; Fortman, R. C.; Schoenborn, W. A.; Mehegan, L. L. Florida
Statewide Radiation Study. Publication #05-029-057, Florida Institute of Phosphate
Research, Bartow, FL 33830, 1987.
Roessler, G. S.; Hintenlang, D. E.; Roessler, C.E.; Furman, R.A. Identification of Candidate
Houses for the North Florida Portion of the Florida Radon Mitigation Project. EPA-
600/8-90-070 (NTIS PB90-274077), U. S. Environmental Protection Agency,
September 1990.
Williamson, A. D.; Finkel, J. M.. Standard Measurement Protocols, Florida Radon Research
Program. EPA-600/8-91-212 (NTIS PB 92-115294), U.S. Environmental Protection
Agency, November 1991.
36

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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before complei
1. REPORT NO. 2.
EPA-600 / R- 9 5-149 a
a
4. title and subtitle Desj.gn and Testing of Sub-slab Depres-
surization for Radon Mitigation in North Florida Hou-
ses, Part I--Performance and Durability, Volume 1.
Technical Report
5. REPORT DATE
September 1995
6. PERFORMING ORGANIZATION CODE
7.author(s) Roessler, R. Morato, R. Richards, IT. Moham-
med, D. Hintenlang, and R. Furman
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
University of Florida
Gainesville, Florida 32611
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
CR 814925-01
12. SPONSORING AGENCY NAME AND ADORESS
EPA, Office of Research and Development
Air Pollution Prevention and Control Division
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOO COVERED
Task Final; 8/88 - 12/90
14. SPONSORING AGENCY CODE
EPA/600/13
16.supplementary notes t^PPCD project officer is David C. Sanchez, Mail Drop 54, 919/
541-2979. This is Parti (which has two volumes) of a two-part report.
16. abstractrepQrt gives results of a demonstration/research project to evaluate
sub-slab depressurization (SSD) techniques for radon mitigation in North Florida
where the housing stock is primarily slab-on-grade, and the sub-slab medium typi-
cally consists of native soil and sand. Objectives were to develop and test the use of
a soil depressurization computer model as a design tool, to optimize the SSD design
for North Florida houses, and to observer the performance and durability of the in-
stalled systems. Between May 1989 and August 1990, SSD systems were designed and
installed in nine houses: seven with simple rectangular floor plans and two with more
complex, L-shaped designs. Installations included a single-suction-point system in
one house and two-suction-point/single-fan systems in eight houses. The installation
in one of the larger, L-shaped houses consisted of a single-suction-point system in
addition to a two-suction-point/single-fan system. All systems used small-diameter,
nominal 50-mm (2-in.) piping. The mitigation successfully reduced indoor radon con-
centrations, originally on the order of 10-30 pCi/L, to post-mitigation values of 
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