United States
Environmental Protection
Agency
Office of Research and
Development
Washington, DC 20460
Air and Energy Engineering
Research Laboratory
Research Triangle Park,
NC 27711
Technology Transfer
EPA/625/5-88/024 Aug. 1988
vvEPA
Application of
Radon Reduction Methods
Is
homeowner
diagnostician/
mitigator
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EPA/625/5-88/024
August 1988
Application of Radon Reduction Methods
by
Ronald B. Mosley
D. Bruce Henschel
Air and Energy Engineering Research Laboratory
Research Triangle Park, NC 27711
AIR AND ENERGY ENGINEERING RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, NC 27711
U.S. Environmental Protection Agency
Region 5, Library (PL-12J)
77 West Jackson Boulevard, 12th Floor
Chicago, IL 60604-3590
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DISCLAIMER
The U. S. Environmental Protection Agency (EPA) strives to provide accurate,
complete, and useful information. However, neither EPA--nor any person
contributing to the preparation of this document-makes any warranty, express or
implied, with respect to the usefulness or effectiveness of any information, method,
or process disclosed in this material. Nor does EPA assume any liability for the use
of, or for damages arising from the use of, any information, method, or process
disclosed in this document.
Mention of firms, trade names, or commercial products in this document does not
constitute endorsement or recommendation for use.
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FOREWORD
This document is intended to aid homeowners and contractors in diagnosing and
solving indoor radon problems. It will also be useful to State and Federal regulatory
officials and many other persons who provide advice on the selection, design and
operation of radon reduction methods for houses.
This document represents the third publication of EPA's technical guidance for indoor
radon reduction methods. It is not intended to replace but rather to supplement the
previous document, "Radon Reduction Techniques for Detached Houses: Technical
Guidance (Second Edition)," (EPA/625/5-87-019) published in January 1988. While
the present document incorporates updated information reflecting new results and
perspectives gained since the previous document, its primary purpose is to address a
broader audience by condensing and organizing the material to form a decision
guidance instrument.
Several recent EPA publications on radon may be of interest to the reader. These
publications and their contents are listed below:
• "A Citizen's Guide to Radon: What It Is and What to Do About lt,"OPA-86-
004 - This brochure provides general information on radon and its associated
health risks.
• "Radon Reduction Methods - A Homeowner's Guide (3rd Edition)," OPA-88-
010 - This booklet provides a concise overview of the radon reduction
techniques available to homeowners who have discovered an indoor radon
problem.
• "Radon Reduction Techniques for Detached Houses: Technical Guidance
(Second Edition)," EPA/625/5-87/019 -- This reference manual provides
detailed information on sources of radon and its health effects as well as
guidance for selection, design, and installation of reduction techniques.
• "Application of Radon Reduction Methods," EPA/625/5-88/024 - The current
document is a decision guidance instrument intended to direct the user through
the steps of diagnosing a radon problem and selecting a reduction method;
followed by designing, installing, and operating a mitigation system.
• "Radon-Resistant Residential New Construction," EPA/600/8-88/087 - This
manual provides builders and new home buyers with information on materials and
building techniques that are effective in reducing radon levels in new houses.
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Copies of these documents can be obtained from the State agencies and the EPA
Regional Offices listed in Section 11. Copies can also be obtained from EPA's Center
for Environmental Research Information, Distribution, 26 W. Martin Luther King Drive,
Cincinnati, OH 45268.
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CONTENTS
Page
Foreword iii
Figures iv
Tables viii
Acknowledgments ix
Glossary x
Metric Equivalents xvii
1. Introduction 1
1.1 Purpose 1
1.2 Scope 1
1.3 How to Use This Manual 3
2. Background 7
2.1 Sources of Radon 7
2.2 Health Effects 7
2.3 Potential Strategies for Reducing Indoor Radon Concentrations 7
3. Measuring Radon Concentrations 17
3.1 Screening Measurements 18
3.2 Follow-Up Measurements 18
3.3 EPA Action Level and Guidance for Action 19
4. Determining the Sources of Radon 21
4.1 Choice of Diagnostician/Mitigator 21
4.2 Identification of Radon Entry Routes 22
4.3 Factors Influencing Driving Forces 28
4.3.1 Weather Effects 28
4.3.2 House Design Effects 28
4.3.3 Homeowner Activity Effects 30
5. Diagnostic Testing to Select a Mitigation Method 31
5.1 Visual Survey of Entry Routes and Driving Forces 31
5.2 Radon Measurements in Room Air 33
5.3 Radon Measurements at Potential Soil Gas Entry Points 33
5.4 Radon Measurements in Well Water 34
5.5 Pressure Measurements 34
5.6 Measurement of Sub-Slab Communication 34
5.7 Measuring the Pressure Field Inside Block Walls 36
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CONTENTS (Continued)
6. Selecting and Designing a Mitigation System 37
6.1 Selecting a Technique 37
6.1.1 Soil Ventilation 37
6.1.2 Crawl-Space Ventilation 37
6.1.3 Basement Pressurization 41
6.2 Designing the System 41
6.2.1 Primary Considerations 41
6.2.2 Phased Approach 43
7. Installing a Mitigation System 45
7.1 Drain Tile Ventilation Installed Outside 45
7.2 Drain Tile Ventilation Installed in a Sump 47
7.3 Sub-Slab Ventilation Installed Through the Floor 49
7.4 Wall Ventilation 51
7.5 Methods of Closing the Top Row of Blocks 52
7.6 Closing the Gap Behind Brick Veneer 54
8. Post-Installation Diagnostics 55
9. Post-Mitigation Monitoring 57
9.1 Short-Term Monitoring 57
9.2 Long-Term Monitoring 57
10. Additional Radon Reduction Techniques 59
10.1 Passive Soil Ventilation 59
10.2 Crawl-Space Ventilation 59
10.3 House Ventilation 60
10.4 Sealing 62
10.5 House Pressure Adjustments 63
10.5.1 Reduce Depressurization 63
10.5.2 House Pressurization 67
10.6 Air Cleaning 67
10.7 Radon Removal from Well Water 68
10.8 Radon Reduction in New Construction 69
11. Sources of Information 71
12. References 81
APPENDIX 83
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FIGURES
Number Page
1 Steps Involved in Diagnosing and Solving an Indoor Radon
Problem 2
2 Some Potential Soil Gas Entry Routes into a House 26
3 Steps in Diagnostic Testing 32
4 Selecting a Mitigation Approach (See Table 1 for a Summary
of the Mitigation Techniques.) 38
5 Choosing a Method of Soil Ventilation (Details of these
installations are presented in Section 7.) 39
6 Choosing a Crawl Space Ventilation System (For additional
information see Section 10.2.) 40
7 Deciding Whether to Use Basement Pressurization (Additional
considerations are discussed in Section 10.5.2.) 42
8 Drain Tile Ventilation Where Tile Drains to an Above-Grade
Discharge 46
9 Dram Tile Ventilation Where Tile Drains to Sump 48
10 Sub-slab Ventilation Using Pipes Inserted Down Through Slab ... 50
11 One Method for Creating Open Hole Under Sub-Slab
Depressurization Point When Slab Hole Has Been Created by
Jackhammer 51
12 Some Options for Closing Major Wall Openings in Conjunction
with Block Wall Ventilation 53
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TABLES
Number Page
1 Summary of Radon Reduction Techniques 9
2 Possible Soil Gas Entry Routes into a House 23
3 Factors That Might Contribute to the Driving Force for Soil
Gas Entry 29
4 Sealant Information 64
5 Radon Contacts for Individual States 72
6 Radiation Contacts for EPA Regional Offices 79
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ACKNOWLEDGMENTS
This manual compiles and documents the experience of many different individuals
who have worked in radon mitigation and related fields. Many of these individuals are
recognized in the list of references in Section 12. It is through the innovative efforts
of these workers that this document is possible.
Drafts of this document have been reviewed by a large number of individuals in
Government and in the private sector. Comments from these reviewers have helped
significantly to improve the completeness, accuracy, and clarity of the document.
Within EPA, reviews were provided by. AEERL's radon mitigation staff, the Office of
Radiation Programs, and the Regional Offices. The authors wish to thank the
following EPA personnel in particular for their substantive recommendations,
comments, and guidance: A.B. Craig, M.C. Osborne, E.L Plyler, J.S. Ruppersberger,
M. Samfield, W.G. Tucker, and K.A. Witter of AEERL; D.M. Murane of the Office of
Radiation Programs; P.A. Giardina and L. Koehler of Region 2; W.E. Belanger and L.
Felleisen of Region 3; Paul Wagner of Region 4; R.E. Dye of Region 7; and J. Leiten
of Region 10.
Of the reviewers outside EPA, we are particularly indebted to the following for their
substantial input: A.G. Scott of American ATCON; T. Brennan and S. Galbraith of
Camroden Associates; and A. Williamson, B.E. Pyle, and C. Fowler of Southern
Research Institute.
Editing and typing services were coordinated by C.B. Brickley of Radian Corporation,
Research Triangle Park, NC.
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GLOSSARY
Air changes per hour (ach) - The number of times within 1 hour that the volume of
air inside a house would nominally be replaced, given the rate at which outdoor
air is infiltrating the house. If a house has 1 ach, it means that all of the air in
the house will be nominally replaced in a 1-hour period.
Air exchange rate - The rate at which the house air is replaced with outdoor air.
Commonly expressed in terms of air changes per hour.
Airflow bypass - Any opening through the floors between stories of a house (or
through the ceiling between the living area and the attic) which facilitates the
upward movement of house air under the influence of the stack effect. By
facilitating the upward movement, airflow bypasses in effect facilitate exfiltration
at the upper levels, which in turn will increase infiltration of outdoor air and soil
gas.
Alpha particle - A positively charged subatomic particle emitted during decay of
certain radioactive elements. For example, an alpha particle is released when
radon-222 decays to polonium-218. An alpha particle is indistinguishable from
a helium atom nucleus and consists of two protons and two neutrons.
Back-drafting - A condition where the normal movement of combustion products
up a flue, resulting from the buoyant forces on the hot gases, is reversed, so
that the combustion products can enter the house. Back-drafting of
combustion appliances (such as fireplaces and furnaces) can occur when
depressurization in the house overwhelms the buoyant force on the hot gases.
Back-drafting can also be caused by high air pressures at the chimney or flue
termination.
Band joist - Also called header joist, header plate, or rim joist. A board the same
width as the floor joist that rests (on its 2-in.* dimension) on top of the sill plate
around the perimeter of the house. The ends of the floor joists are nailed into
the header joist that maintains spacing between the floor joists.
Barrier coating(s) - A layer of a material that obstructs or prevents passage of fluid
through a surface that is to be protected. More specifically, grout, caulk, paints,
or various sealing compounds, perhaps used with polyurethane membranes to
prevent soil-gas-borne radon from moving through walls, cracks, or joints in a
house.
"Readers more familiar with the International System of Units (SI) may use the
equivalents listed at the end of the front matter.
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Baseboard duct - A continuous system of sheet metal or plastic channel ducting
that is sealed over the joint between the wall and floor around the entire
perimeter of the basement. Holes drilled into hollow blocks in the wall allow
suction to be drawn on the walls and joint to remove radon through the ducts to
a release point away from the inside of the house.
Basement - A type of house construction where the bottom livable level has a slab
(or earthen floor) which averages 3 ft or more below grade level on one or more
sides of the house and is sufficiently high to stand in.
Blower door - A device consisting of an instrumented fan which can be mounted in
an existing doorway of a house. By determining the air flows through this fan
required to achieve different degrees of house pressurization and
depressurization, the blower door permits determination of the tightness of the
house shell, and an estimation of the natural in-filtration rate.
Cold air return - The registers and ducting which withdraw house air from various
parts of the house and direct it to a central forced-air furnace or heat pump.
The return ducting is at low pressure relative to the house because the central
furnace fan draws air out of the house through this ducting.
Cold joint - The contact joint between two adjacent concrete slabs or parts of a slab
that were poured at different times.
Convective movement - As used here, the bulk flow of radon-containing soil gas
into the house as the result of pressure differences between the house and the
soil. Distinguished from diffusive movement.
Crawl space - An area beneath the living space in some houses, where the floor of
the lowest living area is elevated above grade level. This space (which generally
provides only enough head room for a person to crawl in), is not living space,
but often contains utilities. Distinguished from slab-on-grade or basement
construction.
Cubic feet per minute (cfm) - A measure of the volume of a fluid flowing within a
fixed period of time.
Depressurization - In houses, a condition that exists when the air pressure inside
the house or in the soil is slightly lower than the air pressure outside. The lower
levels of houses are almost always depressurized during cold weather, due to
the buoyant force on the warm indoor air (creating the natural thermal stack
effect). Houses can also be depressurized by winds and by appliances which
exhaust indoor air.
Detached houses - Single family dwellings as opposed to apartments, duplexes,
townhouses, or condominiums. Those dwellings which are typically occupied by
one family unit and which do not share foundations and/or walls with other
family dwellings.
Diffusive movement - The random movement of individual atoms or molecules, such
as radon atoms, in the absence of (or independent of) bulk (convective) gas
flow. Atoms of radon can diffuse through tiny openings, or even through
unbroken concrete slabs. Distinguished from convective movement.
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Duct work - Any enclosed channel(s) which direct the movement of air or other gas.
Effective leakage area - A parameter determined from blower door testing, giving a
measure of the tightness of the house shell. Conceptually, this leakage area
reflects the square inches of open area through the house shell, through which
air can infiltrate or exfiltrate.
Entry routes - Pathways by which soil gas can flow into a house. Openings through
the flooring and walls where the house contacts the soil.
E-Perm - The Electret-Passive Environmental Radon Monitor is a device that
uses an electrostatically charged plastic disk-called an electret--to sense
radon in air. When radon decays it produces ions, which are collected by the
electret, resulting in a measurable decrease in the charge on the disk.
Exfiltration - The movement of indoor air out of the house. The opposite of infil-
tration.
Exhaust fan - A fan oriented so that it blows indoor air out of the house. Exhaust
fans cause outdoor air (and soil gas) to infiltrate at other locations in the house,
to compensate for the exhausted air.
Footing(s) - A concrete or stone base which supports a foundation wall and which is
used to distribute the weight of the house over the soil or subgrade underlying
the house.
Forced-air furnace (air conditioner or heat pump) - A central unit that functions by
recirculating the house air through a heat exchanger. A forced-air furnace is
distinguished from a central hot-water space heating system, or electric
resistance heating.
French drain (also perimeter drain, channel drain, or floating slab) - A water
drainage technique installed in basements of some houses during initial
construction. If present, typically consists of a 1- or 2-in. gap between the
basement wall and the concrete floor slab around the entire perimeter inside the
basement to allow water to drain to aggregate under the slab and then soak
away.
Gamma radiation - Electromagnetic radiation released from the nucleus of some
radionuclides during radioactive decay.
Grab sample - A sample of air or soil gas collected in an airtight container for later
measurements of radon concentration.
Grade (above or below) - The term by which the level of the ground surrounding a
house is known. In construction typically refers to the surface of the ground.
Things can be located at grade, below grade, or above grade relative to the
surface of the ground.
MAC system - A heating and air conditioning system.
Heat exchanger - A device used to transfer heat from one stream to another. In
air-to-air heat exchangers for residential use, heat from exhausted indoor air
is transferred to incoming outdoor air, without mixing the two streams.
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Heat recovery ventilators (HRVs) - Also known as air-to-air heat exchangers.
Hollow-block wall, Block wall - A wall constructed using hollow rectangular
masonry blocks. The blocks might be fabricated using a concrete base
(concrete block), using ash from combustion of solid fuels (cinder block), or
expanded clays. Walls constructed using hollow blocks form an interconnected
network with their interior hollow cavities unless the cavities are filled with
concrete.
House air - Synonymous with indoor air. The air that occupies the space within the
interior of a house.
HVAC system - The heating, ventilating, and air conditioning system for a house.
Generally refers to a central furnace and air conditioner.
Indoor air - That air that occupies the space within the interior of a house or other
building.
Infiltration - The movement of outdoor air or soil gas into a house. The infiltration
which occurs when all doors and windows are closed is referred to in this
document as the natural closed-house infiltration. The reverse of exfiltration.
Joist - Any of the parallel horizontal beams set from wall to wall to support the floor
or ceiling.
Livable space - Any enclosed space that residents now use or could reasonably
adapt for use as living space.
Microrem - A unit of measure of "dose equivalence," which reflects the health risk
resulting from a given absorbed dose of radiation. A microrem (prem) is 1
millionth (10 ) of a rem (roentgen equivalent man).
Microrem per hour - A unit of measure of the rate at which health risk is being
incurred as a result of exposure to radiation.
Mitigator - A building trades professional who works for profit to correct radon
problems, a person experienced in radon remediation. At present, training
programs are underway to provide working professionals with the knowledge
and experience necessary to control radon exposure problems. Some State
radiological health offices have lists of qualified professionals.
Neutral Plane - A roughly horizontal plane through a house defining the level at
which the pressure indoors equals the pressure outdoors. During cold weather,
when the thermal stack effect is occurring, indoor pressures below the neutral
plane will be lower than outdoors, so that outdoor air and soil gas will infiltrate.
Above the neutral plane, indoor pressures will be higher than outdoors, so that
house air will exfiltrate.
Permeability (sub-slab) - A measure of the ease with which soil gas and air can
flow through a porous medium. High permeability facilitates gas movement
under the slab, and hence generally facilitates the implementation of sub-slab
suction.
XIII
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Picocurie (pCi) - A unit of measurement of radioactivity. A curie is the amount of
any radionuclide that undergoes exactly 3.7 x 1010.radioactive disintegrations
per second. A picocurie is one trillionth (10 ) of a curie, or 0.037
disintegrations per second.
Picocurie per liter (pCi/L) - A common unit of measurement of the concentration of
radioactivity in a fluid. A picocurie per liter corresponds to 0.037 radioactive
disintegrations per second in every liter of air.
Pressure field extension - A spatial extension of a variation in pressure as occurs
under a slab when a fan ventilates at one or a few distinct points.
Punk stick - A small tube used to generate smoke from smoldering materials.
Radionuclide - Any naturally occurring or artificially produced radioactive element or
isotope which is radioactive; i.e., which will release subatomic particles and/or
energy, transforming into another element.
Radon - The only naturally occurring radioactive element which is a gas.
Technically, the term "radon" can refer to any of a number of radioactive
isotopes having atomic number 86. In this document, the term is used to refer
specifically to the isotope radon-222, the primary isotope present inside
houses. Radon-222 is directly created by the decay of radium-226, and has a
half-life of 3.82 days. Chemical symbol Rn-222.
Radon progeny - The four radioactive elements which immediately follow radon-
222 in the decay chain. These elements are polonium-218, lead-214,
bismuth-214, and polonium-214. These elements have such short half-lives
that they exist only in the presence of radon. The progeny are ultrafine solids
which tend to adhere to other solids, including dust particles in the air and solid
surfaces in a room. They adhere to lung tissue when inhaled and bombard the
tissue with alpha particles, thus creating the health risk associated with radon.
Also referred to as radon daughters and radon decay products.
RPISU - A radon progeny integrated sampling unit is a radon decay product
measurement system consisting of a low flow-rate air pump that pulls air
continuously through a detector assembly containing a thermoluminescent
dosimeter. The unit is operated for 100 hours or longer and then the detector
assembly is returned to the laboratory for analysis.
Sill plate - A horizontal band (typically 2 x 4 or 2 x 6 in.) that rests on top of a block
or poured concrete foundation wall and extends around the entire perimeter of
the house. The ends of the floor joists which support the floor above the
foundation wall rest upon the sill plate. For slab-on-grade, the sill plate is the
bottom plate of the wall.
Slab - A layer of concrete, typically about 4 in. thick, which commonly serves as the
floor of any part of a house whenever the floor is in direct contact with the
underlying soil.
Slab below grade - A type of house construction where the bottom floor is a slab
which averages between 1 and about 3 ft below grade level on one or more
sides.
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Slab on grade - A type of house construction where the bottom floor of a house is a
slab which is no more than about 1 ft below grade level on any side of the
house.
Smoke stick - A small tube, several inches long, which releases a small stream of
inert smoke when a rubber bulb at one end of the tube is compressed. Can be
used to visually define bulk air movement in a small area, such as the direction
of air flow through small openings in slabs and foundation walls.
Soil gas - Gas which is always present underground, in the small spaces between
particles of the soil or in crevices in rock. The major constituent of soil gas is air
with some components from the soil (such as radon) added.
Stack effect - The upward movement of house air when the weather is cold, caused
by the buoyant force on the warm house air. House air leaks out at the upper
levels of the house, so that outdoor air (and soil gas) must leak in at the lower
levels to compensate. The continuous exfiltration upstairs and infiltration
downstairs maintain the stack effect air movement, so named because it is
similar to hot combustion gases rising up a fireplace or furnace flue stack.
Sump - A pit through a basement floor slab, designed to collect water and thus
avoid water problems in the basement. Water is often directed into the sump by
drain tiles around the inside or outside of the footings.
Sump pump - A pump to move collected water out of the sump pit, to an above-
grade discharge remote from the house.
Thermal bypass - As used here, the same thing as an airflow bypass.
Tight house - A house with a low air exchange rate. If 0.5 to 0.9 air changes per
hour is typical of modern housing, a tight house would be one with an exchange
rate well below 0.5 ach.
Top voids, Block voids, Voids - Air space(s) within masonry walls made of concrete
block or cinder block. Top void specifically refers to the air space in the top
course of such walls; that is, the course of block to which the sill plate is
attached and on which the walls of the house rest.
Unattached radon progeny - Refers to radon decay products which have not yet
adhered to other, larger dust particles in the air (or to other surfaces, such as
walls). Unattached progeny might result in a higher lung cancer risk than will
progeny that are attached to larger particles, because the unattached progeny
can selectively deposit in limited areas of the lung.
Veneer, Brick veneer - A single layer or tier of masonry or similar materials securely
attached to a wall for the purposes of providing ornamentation, protection, or
insulation, but not bonded or attached to intentionally exert common action
under load.
Ventilation rate - The rate at which outdoor air enters the house, displacing house
air. The ventilation rate depends on the tightness of the house shell, weather
conditions, and the operation of appliances (such as fans) influencing air
movement. Commonly expressed in terms of air changes per hour, or cubic feet
per minute.
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Warm air supply - The ducting and registers which direct heated house air from the
forced-air furnace, to the various parts of the house. The supply ducting is at
elevated pressure relative to the house because the central furnace fan is
blowing air through this ducting.
WC - The height (in inches) of a water column that represents a unit of measure for
pressure differences.
Working level (WL) - A unit of measure of the exposure rate to radon and radon
prcweny defined as the quantity of short-lived progeny that will result in 1.3 x
10° MeV of potential alpha energy per liter of air. Exposures are measured in
working level months (WLM); e.g., an exposure to 1 WL for 1 working month
(170 hours) is 1 WLM. These units were developed originally to measure
cumulative work place exposure of underground uranium miners to radon and
continue to be used today as a measurement of human exposure to radon and
radon progeny.
XVI
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METRIC EQUIVALENTS
Although it is EPA's policy to use the International System of Units (SI) in its
documents, nonmetric units are used in this report for the reader's convenience.
Readers more accustomed to the metric system may use the following factors to
convert to that system.
Nonmetric
atmosphere (atm)
British thermal unit (Btu)
cubic foot (ft3)
cubic foot per minute
(cfm, or ft3/min)
degree Fahrenheit (°F)
foot (ft)
gallon (gal)
horsepower (hp)
inch (in.)
inch of water column
(in. WC)
microrem (prem)
picocune per liter
(PCi/L)
square foot (ft2)
Times
101
1060
28.3
0.47
5/9 (°F-32)
30.5
3.78
746
2.54
248
0.01
37
0.093
Yields metric
kiloPascal (kPa)
joule (J)
liter (L)
liter per second (L/sec)
degree Centigrade (°C)
centimeter (cm)
liter (L)
watt (W), or joule/sec
centimeter (cm)
Pascal (Pa)
microSievert (jiSv)
Becquerel per cubic
meter (Bq/m3)
square meter (m2)
XVII
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Sect/on f
Introduction
1.1 Purpose
Much attention has been given recently to increased
risks of lung cancer associated with elevated levels of
radon gas in indoor air. Only in recent years has it
been recognized that a large number of houses in the
United States have elevated levels of indoor radon as
a result of natural sources. Several comprehensive
documents have been published recently (EPA88a,
Br88a, Br88b) that describe the nature of the
problem. The present document will not attempt a
comprehensive description of the background
information or health risks analysis associated with
indoor radon, but will refer the reader to existing
references for detailed information.
The purpose of this manual is to provide guidance in
diagnosing radon problems in houses as well as in
selecting, designing, and installing radon reduction
systems. For an overview, see Figure 1, in which a
flow chart illustrates the steps to take in analyzing
and solving an indoor radon problem. The
organization of this manual is designed to guide the
user through decision making by stages to the point
of operating and maintaining a successful radon
reduction system. Note that advice is provided on
choosing a professional mitigator to recommend
and/or install a mitigation system.
This document is intended to condense the
information contained in "Radon Reduction
Techniques for Detached Houses: Technical
Guidance (Second Edition)" (EPA88a). Particular
emphasis is given to selecting, designing, and
installing an effective radon reduction system. The
earlier document (EPA88a) is viewed as a companion
reference document with supporting information to aid
in a more complete understanding of indoor radon
problems. Much of the background information and
details on sources of radon, the assessment of
associated health risks, and mitigation design detail
are not reproduced here. Rather, the present
document focuses on actions that can be taken to
reduce the risks associated with indoor radon
exposure once a problem has been recognized.
1.2 Scope
A brief description of where radon comes from as well
as its health risk implications and strategies for
reducing radon levels in houses are discussed in
Section 2. Radon measurements and EPA's
recommended actions are presented in Section 3.
A critical step in developing a plan for reducing indoor
radon levels is to identify the important radon entry
routes and recognize the factors (e.g., weather
effects, house construction features, and occupant
activities) that influence the driving forces bringing
radon into the house. These effects are discussed in
Section 4.
A number of diagnostic measurements presented in
Section 5 may be useful in selecting and designing a
radon reduction system. Both the strategy and the
specifics of designing a radon mitigation system are
discussed in Section 6. Section 7 gives some detailed
descriptions and recommendations for installing
reduction systems. Post-installation diagnostics are
presented in Section 8.
After installation, it is necessary to make both short -
and long-term measurements and observations to
determine whether the system is operating as
intended. These measurements are described in
Section 9. Once the mitigation system is operating,
routine monitoring and maintenance must be carried
out to ensure continued performance.
Several of the more frequently used reduction
techniques are described at various points (especially
in Sections 6 and 7) throughout the first nine
sections. The methods of crawl-space ventilation,
house ventilation, and house pressure adjustments
are further developed in Section 10. Although sealing
(or closure) is referred to throughout the document,
the most complete presentation is in Section 10. The
less frequently applied techniques of passive soil
ventilation, air cleaning, removal of radon from well
water, and radon reduction in new construction are
treated almost exclusively in Section 10.
-------
Figure 1. Steps involved in diagnosing and solving an indoor radon problem.
Measure
Radon
Sec 31,32
Is Action
Indicated
Design
Mitigation
System
Sec. 6.2
Install
System
Sec 7
Is
Homeowner
Diagnostician/
Mitigator
Choose
Diagnostician/
Mitigator
Sec 4 1
Is
System
Operating
as Designed
Inspect
House
Sec 42, 43,5.1
Check
System
Performance
Sec 8
Perform
Diagnostic
Measurements
Sec 5
Monitor
Short-Term
Sec 9 1
Choose
Mitigation
Method
Sec 6 1
Monitor
Long-Term
Sec 9 2
Is
Radon
Reduction
Adequate
Operate and
Maintain
System
Sec 1.3
-------
1.3 How to Use This Manual
This section describes the steps in the decision
process illustrated in Figure 1 and directs the reader
to other sections of the manual for additional
information.
A step-by-step approach for using this document
to identify and solve indoor radon problems is
recommended below:
Step 1. Make radon (or radon decay product)
measurements to determine the severity of
the existing radon problem. This typically
involves both screening and follow-up
measurements.
Section 3.1 contains a brief description of
methods commonly used to perform initial
radon (or radon decay product) mea-
surements. For more complete coverage of
both initial screening measurements and
follow-up measure-ments, see EPA's
interim protocols (EPA86b, EPA87a). The
radon levels determined by these
measurements will aid in deciding upon the
degree of radon reduction required and the
urgency of the need for action. In cases of
elevated radon levels in the indoor air, water
supplied from a private or small community
well should also be tested to determine
whether the well water might be an
important contributor to the airborne radon.
Further guidance on measurements in water
is available in Reference EPA87c. In most
states, the health department, the radiation
protection office, or the drinking water office
have been designated to help in testing
private water supplies.
Step 2. Decide whether action to reduce the radon
level is required.
If the annual average radon concentration is
greater than 4 pCi/L, action to reduce it is
recommended. The urgency with which
action is recommended depends upon how
much the measurement exceeds 4 pCi/L.
1. For radon concentrations greater than 200
pCi/L, action is recommended within a
few weeks.
2. For radon concentrations in the range of
20 to 200 pCi/L, action is recommended
within several months.
3. For radon concentrations in the range of
4 to 20 pCi/L, action is recommended to
reduce the levels below 4 pCi/L within a
few years. The higher the value the more
urgent the need for action (EPA86a).
4. If the radon concentration is less than 4
pCi/L, EPA does not specifically recom-
mend that any action be taken. However,
since there may be no safe level of indoor
radon, some homeowners may wish to
reduce the levels further. If action to
reduce the radon concentration is taken,
the goal should be to reduce the level as
much below 4 pCi/L as reasonably
possible because of significant health
risks even at 1 pCi/L. It should be noted,
however, that it is not very practical to try
to reduce indoor radon levels below the
ambient values.
Step 3. Choose an advisor/mitigator.
If, after studying this manual and Reference
EPA88a, the reader does not feel confident
in tackling the task of diagnosing the radon
problems in the house, then guidance in
choosing a professional advisor (dia-
gnostician) is provided in Section 4.1.
Step 4. Inspect the house to identify radon entry
routes, factors which influence the driving
forces for radon entry, and construction
features which lend themselves or present
obstacles to specific mitigation techniques.
Section 4.2 provides a detailed discussion
along with a checklist (Table 2) x>f many
potential routes through which soil gas might
enter a house, while Section 4.3 provides a
checklist (Table 3) of appliances, house
design features, and other factors which can
contribute to depressurization. Knowledge of
the processes through which the soil gas is
entering will be important in the selection
and design of any radon reduction system.
Step 5. Implement near-term radon reduction
measures that can be applied fairly simply
and at low cost.
A homeowner discovering elevated radon
levels might wish to take some immediate
action to reduce these levels before more
comprehensive, permanent steps can be
taken. Section 3.3 describes some
techniques that can be readily implemented
by a homeowner at limited cost, such as
increased house ventilation and closure of
major entry routes that are accessible.
Some of these near-term approaches (in
particular, house ventilation via open
windows and doors) can be very effective,
but are not practical as a permanent
-------
reduction method (e.g., during extreme hot
or cold weather). Closure of major entry
routes might provide significant radon
reductions. However, these near-term
approaches will often not be adequate by
themselves to address the elevated levels
permanently.
Step 6. Conduct diagnostic testing as warranted to
aid in the selection and design of a radon
reduction technique.
Section 5 describes some of the diagnostic
testing that can be considered to provide
information to aid in the selection and design
of a mitigation system. Many of these
diagnostic tests are intended to measure
inherent properties of the house or soil (e.g.,
the permeability of the soil and crushed rock
beneath the concrete slab) to determine
suitability for sub-slab soil ventilation.
Some of the tests are intended to evaluate
the relative importance of different potential
radon sources within the house. The
particular diagnostic tests that are cost
effective for a given house will depend upon
the particular radon reduction techniques
that are being considered and the
construction features of the house. Some of
this pre-mitigation diagnostic testing might
best be completed before Step 7 is initiated
to aid in choosing between radon reduction
options. Other diagnostic testing would best
be performed after the selection process is
completed, to aid in designing (Step 8) the
particular reduction options that have been
selected. Therefore, Steps 6, 7, and 8 are
not always distinct.
Step 7. Review the alternative radon reduction
options that appear suitable for the particular
house, and select a mitigation method. The
radon reduction options available are
summarized in Section 2.3 (Table 1).
Some of the less frequently used radon
reduction options, including pertinent
information for each (such as applicability,
and estimated effectiveness), are
summarized in Section 10. This selection
will be based upon the degree of radon
reduction desired, the construction features
of the house, and the confidence levels,
costs, and other factors acceptable to a
particular homeowner. Such factors might
include aesthetics, maintenance require-
ments, lifestyle adjustments, and noise.
Where a combination of techniques is to be
installed, or where a single technique can be
designed in various ways with various costs,
it might sometimes be cost-effective to
install the system in phases. This topic is
further explored in Section 7. Selection of
the method is also discussed in Section 6.
Step 8. Design the radon reduction system.
Obviously, the design of the mitigation
system depends upon which reduction
method is selected. The details of the
design depend primarily upon the
construction features of the house and the
results of the diagnostic measurements. The
principles of design are to maximize the
performance of the system while minimizing
both the installation and the operating costs.
The location, the appearance, and the noise
level of an active system must meet the
approval of the homeowner. Further
guidance on the design of the mitigation
system is offered in Section 6.
Step 9. Install the mitigation system.
Because the actual installation is often
contracted to local building contractors or
subcontractors, the supervision and
inspection of the work is very important. The
actual installer should be made aware of the
objectives of the particular techniques being
applied. For instance, when sealing is to be
applied the installer must be aware not only
of the characteristics of the sealant being
used, but also of the degree of care required
in applying the sealant. Minor modifications
in the installation plans will often be required
as obstacles are discovered during drilling or
digging. It is important that these minor
modifications be consistent with the
principles of the original design, and not
interfere with the performance of the final
installation. When pipes and other parts of
the system are to be hidden for aesthetic
reasons, it is important that careful
inspection and testing be performed before
critical joints or other parts are obscured by
finishing materials. Ventilation systems, as
well as closures of radon entry routes,
should be leak tested before being covered
with finishing materials. Every effort should
be made to provide access for inspection of
any potentially major radon entry routes.
Further discussion of the principles of
installation can be found in Section 7.
Step 10. Check the installation and operation of the
system.
A variety of diagnostic tests can be
conducted on the system in order to confirm
that it is operating as it should, and to
identify modifications to improve
-------
performance. Such post-mitigation dia-
gnostic testing is described in general in
Sections 8 and 9, with specific applications
described as warranted in the detailed
discussions in Section 10.
Step 11. Determine the effectiveness of the mitigation
system through both short- and long-term
monitoring.
Following installation, the radon/progeny
measurement methods described in Section
3 can be used to assess the degree of
reduction and the final levels achieved.
(Care must be taken to ensure that the
before and after measurements can be
reliably compared to yield a meaningful
indication of the reduction achieved.)
1. Short-term performance measurements
are required to determine whether further
diagnostic, design, or installation work is
required.
2. Long-term performance measurements
are required to estimate the potential
exposure to radon related health risks.
Both the methods and rationales for these
two types of measurements are dis-
cussed in Section 9.
Step 12. Establish a schedule for maintenance of the
system.
All installed reduction techniques (active and
passive) must be checked periodically to
determine whether they are continuing to
function properly. In this regard the mitigator
should provide a checklist and schedule for
regular inspection and maintenance of the
installation. Materials used to seal radon
entry routes should be inspected periodically
for cracks or openings. Passive ventilation
systems should be inspected periodically for
cracks or blockage of the ventilation pipes. It
would be desirable to measure the draft in
the passive stack. Active ventilation systems
should be inspected more often because of
the potential for mechanical wear. In addition
to looking for cracks and leaks in the pipes,
it is necessary to ascertain that the fan is
operating properly. With an active system, it
is desirable to install an indicator (alarm)
such as a light or buzzer to announce that
the fan is not generating sufficient air flow
for the system to perform adequately. The
ultimate test for how well the mitigation
system is working will be a periodic radon
measurement such as a 3- or 4-month
alpha-track measurement during winter.
-------
-------
Section 2
Background
2.1 Sources of Radon
Radon-222 is an inert radioactive gas resulting from
the radioactive decay of radium-226. Since radium is
naturally present at trace concentrations in most soil
and rock, radon is continuously being released in the
ground almost everywhere, becoming a trace
constituent of the soil gas, and also dissolving in
underground water. Soil gas containing radon can
enter a house through any opening between the
house and the soil. The pressures inside houses are
often slightly lower than the pressures in the
surrounding soil, so that the soil gas flows into the
house as a result of the pressure difference. The
amount of radon that can build up inside a house due
to in-flowing soil gas will depend upon the radium
content in the surrounding rock or soil (and,
consequently, the radon level in the soil gas), the
ease with which soil gas can move through the soil,
the size and number of openings between the house
and the soil, the extent to which the house is
depressurized relative to the soil, and the above-
grade ventilation rate in the house. If a house
receives water from an individual or small community
well, airborne radon can also occur as a result of
radon's being released from water used in the house.
However, well water is usually only a secondary
radon source compared to soil gas.
2.2 Health Effects
Radon is a health concern because it decays into
other radioactive elements (radon decay products)
that are solid particles. These particles can lodge in
the lungs when inhaled. Bombardment of sensitive
lung tissue by alpha radiation released from these
lodged particles can increase the risk of lung cancer.
Current EPA guidelines suggest that remedial action
be considered when radon concentrations inside a
house exceed an annual average of 4 picocuries of
radon per liter of air (4 pCi/L), or when the radon
decay products exceed roughly 0.02 "working levels"
(0.02 WL). See Reference EPA88a for a discussion
of working levels. According to estimates
(unpublished) based on screening measurements,
12% of U.S. houses may have radon concentrations
exceeding this guideline.
The primary concern with radon in drinking water is
that the radon will be released when the water is used
in the house and will thus contribute to the airborne
levels. Scientists have considered the alpha dosage
received by various organs in the body—the
stomach, for example-from the radon that remains
in the water when it is ingested. The current
conclusion is that the lung cancer risks from radon
released into the air are much more significant than
the risks from radon that remains in the water (Na85).
2.3 Potential Strategies for Reducing
Indoor Radon Concentrations
A number of methods can be considered for reducing
indoor radon levels. For radon from natural sources,
these methods fall into two generic categories:
methods aimed at preventing the radon from entering
the house, and those aimed at removing radon or its
decay products after entry. The selection and design
of a cost-effective radon reduction system for a
specific house will depend upon a number of factors
specific to that house, including, for example, the
initial radon concentration and a variety of house
construction details. Table 1 summarizes the radon
reduction methods that are most prevalent in current
mitigation practices. Detailed discussions of these
reduction methods are presented in Sections 6
through 10 of this document. Certain information,
such as the degree of radon reductions achievable
with specific techniques and estimated cost, is found
almost exclusively in this summary table. It should be
stressed that the order in which the techniques are
presented is not intended to convey their relative
priority for application.
The prevalent radon reduction strategy is to prevent
entry into the house. Radon entry can be prevented
by any one or combinations of the three processes:
(1) remove the source of the radon, (2) eliminate or
reverse the driving forces causing radon entry, or (3)
eliminate the entry routes. Many of the reduction
techniques discussed in this manual will address one
or more of these processes. Soil ventilation, crawl-
space ventilation, sealing, house pressure
adjustments, and radon removal from water are all
reduction techniques that attempt to prevent radon
-------
from entering the house, while house ventilation and
air cleaning are techniques that attempt to remove
radon (or its decay products) from inside.
-------
Table 1. Summary of Radon Reduction Techniques
Method
Principle of Operation
Applicablity
Radon
Reductions
Achievable, %
Confidence
in Installation and Operation
Performance Considerations
Estimated Installation and
Operating Costs*
House
Ventilation
-Natural
(Sec. 10.3)*
Increased movement
of fresh outdoor air
into the house (or
crawl space) without
the use of fans. This
reduces convective
radon influx, and
dilutes the radon that
does enter.
All house types. All
initial radon levels.
Application would
have to be limited
during extreme
weather conditions, or
unacceptable energy
and comfort penalties
would result.
To 90 and above,
depending upon
extent to which inflow
of fresh air is
increased. In no case
can radon levels be
reduced below levels
in outdoor air (usually
a fraction of 1 pCI/L).
High Open windows, doors, or vents
uniformly around the house (not
on one side only). Open
especially on lower levels of
house. Windows might be
opened only slightly to reduce
energy/comfort penalties in cold
weather (reducing reduction
performance). Can ventilate just
crawl space, with insulation
around water pipes and under
subflooring, to permit ventilation
during cold weather.
No (or minimal) installation cost.
Easily implemented by
homeowners. No operating cost
during mild weather. During
cold weather, heating costs
could increase by a factor of
1.1 to 3 or more, depending
upon extent of ventilation and
efforts to maintain temperature
in the ventilated part of the
house. There would be a
comparable increase in air
conditioning costs in hot
weather.
-Forced Air
no heat
recovery
(Sec. 10.3)
Increased movement
of fresh air into the
house or crawl space,
as above, except with
the use of one or
more fans.
All house types. All
initial radon levels.
Application would
have to be limited
during extreme
weather conditions, or
unacceptable energy
and comfort penalties
would result.
To 90 and above,
depending upon
increase in inflow of
fresh air (i.e., size of
fan).
High, if fan is
large enough, and
if forced air is
distributed
effectively.
Fan can be installed to
continuously blow fresh air into
house through existing central
forced-air furnace ducting. Or
window fans could blow air in
through windows in lower levels
of house. For typical house, fan
capacity for 90% radon
reduction would likely have to
be greater than 500 to 1000
cfm, depending on house size
and natural infiltration rate. Fans
should always be oriented to
blow outside air in. Commercial
whole-house fans are not
recommended because they
typically suck indoor air out.
Installation costs vary from
perhaps $30 to $200 for a
single window fan, to perhaps
as much as $1000 to modify a
central furnace for fresh air
addition. Operating costs
include an increase in heating
and cooling costs, comparable
to those for natural ventilation,
plus cost for electricity to
operate fans (about $50/year
for a less powerful window fan,
$300/year for a more powerful
window fan or a central furnace
fan).
(continued)
-------
Table 1. Continued
Method
Principle of Operation
Applicablity
Radon
Reductions
Achievable, %
Confidence
in
Performance
Installation and
Operation
Considerations
Estimated Installation and
Operating Costs**
House Ventilation
(continued)
-Forced Air with
Heat Recovery
(heat recovery
ventilators or
HRVs) (Sec. 10.3)
Sealing of Soil Gas
Entry Routes
(Sec. 10.4)
Increased movement
of fresh outdoor air
into the house;
exhaust of a similar
amount of house air,
with transfer of heat
from the exhausted
house air to the
incoming fresh air.
Dilutes radon levels in
the house; reduction
of radon influx might
not occur when
exhaust flow equals
intake flow.
Reduce or eliminate
convective and
diffusive radon
movement into the
house by closing
openings between the
house and the soil.
All house types. Applicable as
standard-alone method to
achieve 4 pCi/L only when
initial radon levels is below
about 10-15 pCi/L in houses
with typical infiltration rates.
Best reductions in tight houses.
Heat recovery might reduce
energy and comfort penalties of
ventilation during extreme
weather, but there will still be
some heat penalty (heat
recovery efficiency is 50 to
80%). Also, the net savings in
reduced heat penalty (relative
to natural ventilation) can be
offset by capital cost of HRV.
Most likely to be cost-effective
in cold or very hot and humid
climates.
All houses having the various
individual types of entry routes.
Can be effectively applied to
individual entry routes,
however, total sealing of all
routes (to totally prevent all soil
gas entry) is probably
impractical.
50 to 75 for houses
having typical size
and infiltration rate,
assuming between
200 and 400 cfm or
HRV capacity.
Reductions can be
greater in tight
houses (low
infiltration rate).
Reductions can vary
throughout house,
depending on ducting
configuration.
0-90 extremely
case-specific,
depending on
importance of entry
routes sealed, nature
of remaining unclosed
entry routes, and
effectiveness of
closure.
Moderate for fully
ducted
ventilators. Low
to moderate for
wall-mounted
ventilators.
Performance not
always
predictable, can
vary over time.
Low to high,
extremely case-
specific
(depending on
importance of
sealed route and
residual unclosed
routes). Some
openings can be
very difficult to
seal effectively.
Seals can reopen
over time as
house settles.
Ducted ventilator
supplies fresh air to
all or part of the
house, withdraws
stale house air from
all or part of house.
Capacity of ventilator,
location of
supply/withdrawal
vents must be
selected based upon
size and tightness of
house, location of
living areas most
needing ventilation.
Care is required to
maintain the desired
balance between inlet
and outlet flows.
Major openings in
floor and walls closed
with mortar, caulk, or
other sealants.
Smaller openings
closed by more
extensive caulking
effort, or sealed using
coatings or
membranes. Open
water-collection
systems (sumps, floor
drains, French drains)
covered and trapped
Contractor installed cost for a
single 150-200 cfm fully
ducted HRV might range from
$800 to $2500, depending
upon extent of ductwork
installed, amount of wall/floor
finish affected, and brand of
HRV. The lower cost possible
in cases where existing central
forced-air furnace ducting use
for HRV. Increasing capacity to
300-400 cfm would increase
installed cost by roughly 25-
50% if single larger unit used,
or by roughly 100% if second
1 50-200 cfm unit installed.
Operating costs include: an
increase in heating and cooling
costs (roughly 20 to 50% of the
increase incurred by
comparable ventilation without
heat recovery); the cost of
electricity for fans (roughly $50
per year for a 200 cfm unit) and
for inlet air preheat (if used).
Highly variable. Costs can be
low for do-it-yourself closure
of accessible major entry
routes. Costs can be low to
moderate for trapping drains,
covering sujmps. Costs can be
high for application of
membranes and coatings.
(continued)
-------
Table 1. Continued
Method
Active Soil
Ventilation
- Drain Tile
Ventilation
(Sec. 7.1 and 7.2)
Principle of Operation
Uses a fan to draw
suction on the
perforated footing
drain tiles that
surround some
houses for water
drainage. In this
manner, uses the tiles
to maintain a low-
pressure field in the
soil/aggregate under
and around the
house, drawing soil
gas into the tiles and
exhausting it
outdoors, preventing
it from entering the
house.
Applicability
Houses with slabs
which have a
reasonably complete
loop of drain tiles
around the outside or
the inside of the
footings. Any initial
radon level.
Radon
Reductions
Achievable, %
90-99, if drain tile
loop is reasonably
complete. Lower
(40-95) if loop only
partial, depending on
sub-slab perme-
ability.
Confidence
in
Performance
Moderate to high.
(Confidence high
when complete
loop known to
exist, permeability
good, no major
entry routes
through slab
remote from
perimeter
footings.)
Installation and Operation
Considerations
Tap into dram tile loop with a
PVC pipe which rises above
grade level. Mount fan on riser
capable of maintaining at least
0.5-1.0 in. WC suction at the
soil gas flows encountered. If
tiles drain to an interior sump,
cap the sump and draw suction
on the sump cavity.
Estimated Installation and
Operating Costs**
Installation by contractor would
likely cost between $700 and
$1,500 where tiles dram to
point outside house, and
between $800 and $2,500
where titles dram to a sump.
Costs depend upon: depth of
tiles; height of, finish around
exhaust stack; and (for sump
systems) location of stack,
location of fan, and interior
finish. Operating costs roughly
ISO/year for electricity to run
the fan, $lOO/year heating and
cooling penalty resulting from
increased house ventilation.
— *
- Sub-Slab
Ventilation
(Sec. 7.3)
Uses fan to establish
low-pressure field
under slab, as above,
but in this case by
drawing suction on
pipes inserted into the
soil/aggregate under
the slab.
Any house with a
slab, having
reasonable perme-
ability under the slab
(e.g., good aggregate
on permeable soil).
Moderate to high
initial radon levels, in
view of the cost of
the system.
80-99, with high
reductions expected
when permeability
good.
Moderate to high.
(Confidence high
when permeability
is known to be
good.)
Insert individual PVC pipes
down through slab, or
horizontally through foundation
wall beneath slab. Mount fan
capable of mamtaiing at least
0.5-1.0 in. WC suction at the
gas flows encountered.
Installation by contractor would
likely cost between $800 and
$2,000, depending on system
configuration and degree of
house finish, if no unusual
complexities are encountered.
Poor sub-slab permeability,
high degrees of finish could
increase costs. Operating costs
roughly $30/year for electricity,
$100/year heating and cooling
penalty.
(continued)
-------
Table 1. Continued
ro
Method
Principle of Operation
Apphcablity
Radon
Reductions
Achievable, %
Confidence
in
Performance
Installation and
Operation
Considerations
Estimated Installation
and Operating Costs"
Active Soil
Ventilation
(continued)
- Block-wall
Ventilation
(Sec. 7.4)
- Isolation/Venting
of Area Sources
(Sec. 10.2)
Use a fan to draw
suction on, or to blow
outdoor air into, the
void network inside
hollow- block
foundation walls. In
this manner, use the
void network as a
collector for soil gas
(to establish a low-
pressure field,
drawing soil gas from
entry routes into the
house) or as a
plenum to distribute
air under pressure (to
force soil gas away).
Install an enclosure
over a floor or wall
which is an area
source; use a fan to
ventilate the
enclosure.
Houses having hollow-block
foundation walls, where major
wall openings can be
reasonably closed. Houses
where sub-slab suction is not
adequate by itself (sub-slab
suction would in many cases be
the preferred choice, if
applicable) Sub-slab suction
and wall vent can be
considered in combination.
Moderate to high initial radon
levels, in view of the system
cost.
Houses with earthen -floored
crawl spaces where crawl
space ventilation is not
preferred. Houses with badly
cracked slabs or walls where
sub- slab suction not an option.
In general, isolation/ventilation
would be considered only after
other options are determined to
be less cost effective.
90-99 where walls
adequately closed,
and no major slab-
related entry routes
remote from walls.
Lower (as low as
50-70) where walls
not sufficiently tight,
slab badly cracked.
Definitive
data limited.
Moderate (since
ease of wall
closure,
importance of
slab-related
entry routes
cannot always be
reliably
predicted)
Moderate for
crawl-space
lining/venting.
Low for other
systems, due to
limited nature of
available data..
Insert one or more
individual PVC pipes
into each perimeter
foundation wall and
interior block wall.
Alternatively, install
"baseboard duct"
over wall/floor joint of
all perimeter and
interior walls, with
holes drilled into the
block cavities inside
the duct. Connect
piping to suitable fan
in pressure (or
suction).
Install gastight liner
over earthen floor of
crawl space, with
perforated vent pipes
between liner and
soil. Build gastight
false floor or false
wall over existing slab
or foundation wall.
Use fan to ventilate
enclosed space.
Installation by
contractor would
likely cost between
$1,500 and $2,500
for an individual-
pipe system, and
$2,000 and higher
for a baseboard duct
system. Additional
wall closure efforts,
other complexities,
could increase costs.
Operating costs
roughly $30 to
$60/year for
electricity, $200 to
$500/year heating
and cooling penalty.
Highly variable.
(continued)
-------
Table 1. Continued
CO
Method
Passive Soil
Ventilation
(Sec. 10.1)
House Pressure
Adiustments
- Reduce
Depressunzation
(Sec. 10.5)
Principle of
Operation
Use systems
similar to the active
soil ventilation
systems above, but
rely on natural
phenomena to
draw the suction
(wind-related
depressunzation
near rooflme,
thermal stack
effect). In this
manner, avoid the
maintenance
requirements,
noise, and
operating cost of a
fan.
Take steps to
reduce the degree
to which a house
becomes
depressunzed, in
an effort to reduce
soil gas influx. Or,
for a given degree
of depressunzation,
take steps to
reduce air
movement out ot
the house, to
reduce soil gas
influx.
Applicabhty
Sump/dram tile suction
in houses having
complete drain tile
loops and good sub-
slab permeability.
Sub-slab suction
systems where an
adequate perforated
piping network is laid,
and good permeability
is ensured. Houses with
poured concrete
foundation walls and an
integral slab, to reduce
the treatment required
from the system.
All houses. Most
applicable when can be
implemented directly by
homeowner at low cost,
since radon reductions
resulting from these
steps are variable and
since utility will be for
short-term periods if
source of
depressunzation is
intermittent (e.g., use of
fireplace). Most
applicable when
measurements have
confirmed that source
of depressurization is
indeed increasing radon
levels.
Radon
Reductions
Achievable, %
Insufficient long-
term data to
determine.
Insufficient data to
cite reductions that
can generally be
expected with
individual steps. Will
depend on
charactenzatics of a
specific house (e.g.,
tightness). However,
benefits can
sometimes be
significant, at least for
short periods, if
depressurization is
largely neutralized.
Confidence
in Installation and Operation
Performance Considerations
Cannot be stated A network of perforated pipe
at this time due to laid under the slab is attached
lack of data. to a passive stack which rises
through the house and
terminates on the roof.
Cannot be stated Slightly open windows near
at this time due to exhaust fans and combustion
lack of data. appliances (such as fireplaces
and woodstoves) to facilitate
flow of makeup air from
outdoors. Install a permanent
system to supply combustion air
from outdoors for combustion
appliances. Seal off cold air
return registers in basement for
central forced-air heating and
cooling systems, and seal low-
pressure return ducting in
basement to reduce leakage of
basement air into duct. Close
airflow bypasses (openings
through floors between stories)
and openings through house
shell on upper levels, to reduce
air outflow resulting from
buoyant forces. Other steps can
also be considered.
Estiamted Installation and
Operating Costs'"
Installation by contractor
roughly $2,000 where sub-
slab tiles exist, dram into sump.
If slab must be removed in
order to lay new pipes, cost
could be on the order of
$10,000. No operating cost.
Installation and operating costs
will generally be relatively low
for those systems which can be
implemented directly by the
homeowner (opening windows,
sealing cold air return ducts,
closing accessible airflow
bypasses and upper house shell
penetrations). Other steps will
be more expensive, might not
be warranted unless radon
measurements confirm that the
depressurization source being
addressed is indeed a
significant contributor to indoor
radon levels.
(continued)
-------
Table 1 Continued
Method
Principle of
Operation
Applicablity
Radon
Reductions
Achievable, %
Confidence
in
Performance
Installation and Operation
Considerations
Estimated Installation and
Operating Costs'*
House Pressure
Adjustments
(continued)
- House
Pressunzation
(Sec. 6.1.3)
Air cleaning
(Sec. 10.6)
Maintain that part
of the house which
is in contact with
the soil at a
pressure higher
than the soil, so
that soil gas cannot
enter.
Remove the
particulate decay
products of radon
from the indoor air,
by continuously
circulating the
house air through a
particle removal
device.
Houses with tight
basements or heated
crawl space. This
technique is
developmental, should
be applied as stand-
alone measure only on
experimental basis.
All houses. There are
insufficient data to
evaluate the health
benefits of using
particle removal air
cleaners lor radon
progeny reduction.
These cleaners can
reduce the total decay
product levels in the
house air, but they will
also remove the other
dust particles to which
the progeny atttach.
Therefore, the amount
of progeny which are
unattached can
increase. Unattached
progeny are a
potentially more serious
health risk than
attached progeny.
Thus, while total
progeny can be
reduced, the health risk
might be increased.
EPA is not in a position
Insufficient long-
term data to
determine. Short-
term reductions of
about 90% have
sometimes been
observed.
Up to 90% removal
of total radon progeny
(attached plus
unattached) in a
typical house, if a
2,000 cfm high
efficiency air cleaner
operates full time. 50
to 70% reduction of
total progeny if the air
cleaner capacity is
250-500 cfm. The
concentration of
unattached progeny
could increase with
the 2,000 cfm air
cleaner and almost
certainly would
increase with the
250-500 cfm units.
Performance is highly
dependent upon the
rate at which house
air is circulated
through the cleaning
device.
Cannot be stated
at this time due to
lack of data.
The confidence
that an air
cleaner will
reduce the heatlh
risk from radon
exposure cannot
be stated at this
time, due to
uncertainty in the
health risk
resulting from the
potentially
increased levels
of unattached
progeny.
Confidence that
total progeny
(attached plus
unattached) will
be decreased is
moderate to high,
if house air is
circulated through
the cleaner at a
high enough rate.
Tighten basement (or crawl
space) shell, between basement
and upstairs and between
basement and outdoors. Blow
upstairs air down into
basement.
A device such as an
electrostatic precipitator or an
efficient filter is placed in the
ducting of the central forced -
air furnace, treating all
recirculating house air.
Alternatively, smaller stand-
alone units can be placed on
the floor or in the ceiling in
individual rooms.
Installation by contractor
roughly $1,000 to $2,500,
perhaps higher if greater
tightening required. Operating
cost roughly $40/year for
electricity to run the fan, roughly
$500/year heating and cooling
penalty due to increased
ventilation.
Installation of an air cleaner in a
central forced-air furnace
system (capable of treating
about 2,000 cfm) roughly $500
to $2,000. Stand-alone units
capable of treating up to 250
cfm can be installed for $500-
$1 ,000, depending upon
amount of associated ducting (if
any) and ease of mounting;
eight such units would be
required to treat 2,000 cfm.
Operating cost include
electricity to operate fan(s)
circulating the air through the
cleaner and to develop charge
in cleaner where cleaner
operates on electrostatic
principles.
(continued)
-------
Table 7 Continued
Method
Radon Confidence
Principle of Reductions in Installation and Operation Estimated Installation and
Operation Applicablity Achievable, % Performance Considerations Operating Costs"
House Pressure
Adjustments
(continued)
Air Cleaning
(Sec. 10.6
continued)
to recommend either
the use of particle-
removal air cleaners for
radon reduction, or
discontinued use of
existing air cleaners.
Removal from
Water (Sec. 10.7)
Remove dissolved
radon gas from well
water before the
water is used in the
house, thus
preventing the
dissolved radon
from being released
into the house air.
All houses which
receive water from an
individual well (or
perhaps a small
community well), when
radon levels in the
water are high enough
to potentially make a
significant contribution
to indoor airborne radon
concentrations. On this
basis, water treatment
might be considered
when water radon
levels are above
perhaps 40,000 pCi/L.
Above 99 with
properly designed
granular activated
carbon (GAC)
treatment unit. Up to
95 with currently
available aeration
units; higher removals
achievable at
increased cost.
Moderate to high
for GAC units.
Cannot be stated
for aeration units
due to limited
experience with
residential
aerators.
Confidence
should increase
after more
extensive
commercial
experience with
both GAC and
aeration units.
Install GAC tank in incoming
water line from well,
immediately after pressure tank,
to adsorb radon out of the
water.Provide suitable shielding
around tank to reduce gamma
radiation. Replace spent carbon
bed (with adsorbed radon
decay products) when
necessary, perhaps after a
number of years. Waste carbon
might have to be disposed of as
radioactive waste. Or install
suitably sized aerator in water
line, usually prior to pressure
tank, to release radon from the
water before use in house.
Depending on design, aerator
could require air compressor
and auxiliary pump to re-
pressurize water after
treatment. Vent released radon
gas away from house.
Plumber installation of GAC unit
$750 to $1,200, excluding
gamma shielding; shielding
could add about $200.
Operating cost of GAC nominal.
(Maintenance includes
replacement of carbon bed, at
infrequent intervals.) Installation
of aeration unit $2,500 to over
$4,000, depending upon type
of aerator. Operating cost
includes electricity to run
compressor, pump. For either
type of unit, pretreatment to
remove iron or manganese, if
needed, could add $600 to
$1,000 to the installed cost.
"Detailed discussions of the individual radon reduction methods can be found in the sections of this document indicated in parentheses.
"The costs shown here do not include: (a) estimates of maintenance and repair costs or (b) the costs of monitoring to ensure continued satisfactory performance.
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Section 3
Measuring Radon Concentrations
In order to determine whether a particular house has
elevated radon levels prior to a decision regarding the
need for radon reduction, measurements of radon or
radon progeny in the house air are required.
Measurement techniques are divided into two
categories: "active" and "passive." Passive methods
do not require the pumps or specialized sampling
equipment that active methods do. Charcoal canisters
and alpha-track detectors are convenient mea-
surement methods to use because, as passive
methods, they are simple and relatively inexpensive
for homeowners to use. These passive methods also
have the advantage of providing averaged (integrated)
measurements over a period of time (a few days for a
charcoal canister, a few months for an alpha-track
detector). Averaging over several months provides a
meaningful measure of the concentration to which
homeowners are exposed. Time averaging is
important because radon concentrations often vary
significantly over the period of a day as well as from
season to season.
The EPA has recently issued a protocol for the use of
a new passive radon measurement method. This new
device, called an Electret-Passive Environmental
Radon Monitor (E-PERM), is capable of making both
short- and long-term radon measurements. The
device works on the same principle as the ionization
chamber detector, which has been used as a
radiation detector for many years. Although EPA's
experience with this measurement device (EPA88c) is
limited, the device does have attractive features. It is
reported to provide good integrated measurements of
radon with time exposures that can range from 1 day
to 1 year. The results can be read in the field (using a
special surface potential voltmeter). It is also reported
to be insensitive to relative humidity, which makes it a
candidate for measuring in situ radon concentrations
in soil gas.
Other measurement methods are also available.
These methods, referred to as active methods,
require an experienced sampling team with
specialized equipment to visit the house (although it
is possible for one person to set up and operate this
equipment, it is more typical for two or more people
to be involved). Active methods include continuous
monitoring, grab sampling, and use of a Radon
Progeny Integrated Sampling Unit (RPISU). Because
of the need for special equipment and for a sampling
team, these measurements are relatively expensive.
Thus, active methods are less commonly used for
initial radon measurements in a house. However, they
find greater application in pre-mitigation diagnostic
testing and in evaluation of the performance of
installed radon reduction systems.
The EPA has issued protocols for making
measurements in houses using alternative
measurement methods, with the objective of
determining occupant exposure (EPA86b, EPA87a).
The EPA protocols recommend a two-step
measurement strategy in which: (1) an initial
screening measurement is made to provide a
relatively quick and inexpensive indication of the
potential radon/progeny levels in a house and (2)
additional follow-up measurements are recom-
mended, if the screening measurement is above
about 4 pCi/L (about 0.02 WL). Persons making
measurements are advised to apply the methods in a
manner consistent with these protocols.
Two general types of passive measurement devices
are currently in common use (with a third device
gaining prominence):
1. The charcoal canister (or charcoal pouch), which
uses activated carbon in a small container to
adsorb radon;
2. The alpha-track detector, which consists of a
container with a small piece of plastic sensitive to
the alpha particles released by the radon and
radon progeny. The user can purchase both
devices from any one of a number of suppliers,
generally through the mail. The user exposes the
device in the house for a specified period The
device is then returned to the laboratory for
analysis. For both devices, the result is the radon
gas concentration in pCi/L; these devices do not
determine the concentration of radon progeny;
and
3. The E-PERM, which uses an electret to detect
the ions generated by radon decay.
17
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The Agency has also established a Radon
Measurement Proficiency Program enabling
organizations which provide radon measurement
services to voluntarily demonstrate their proficiency in
making radon/radon progeny measurements
(EPA86c). Lists of firms which have successfully
demonstrated their proficiency under this program are
published periodically (e.g., EPA87b). Anyone wishing
to hire a firm to conduct indoor radon monitoring can
check these periodic lists for the names and
addresses of candidate firms. Publication of the next
update (Round 5) is expected in October 1988.
Copies of the current list can be obtained through the
State contact or the appropriate EPA Regional office
identified in Section 11.
3.1 Screening Measurements
A few of the key procedures indicated in the EPA
protocol documents are listed below. If no prior radon
measurement has been made in the house, the initial
measurement should be viewed as a screening
measurement, and the exposure times for the devices
should be:
• Charcoal canister -- 2 to 7 days, as specified
by supplier,
• Alpha-track detector -- 3 months to 1 year
(or less, if specified by supplier), and
• E-PERM -- 1 day to 1 year depending on
electret selected.
The objective of the screening measurement is to
provide a quick and inexpensive indication of whether
the house has the potential for causing high occupant
exposures.
For the screening measurement, the device should be
placed in the lowest livable space, such as the
basement. Within that livable space, the device
should be placed in the room expected to have the
lowest ventilation rate. Livable space does not have
to be finished or even be used as living space.
The devices should not be placed in sumps, or in
small enclosed areas such as closets or cupboards.
Further precautions and recommendations for locating
the measurement devices are offered in Section 3.2.
The objective is to measure the highest radon levels
that might be expected anywhere in the livable part of
the house. If low radon levels are found at the
worst-case location, the house may be presumed to
have low levels everywhere.
Screening measurements should be made under
closed-house conditions (doors and windows closed
except for normal entry and exit), with minimum use
of ventilation systems that mix indoor and outdoor air
(such as attic and window fans). Closed-house
conditions should also be maintained for 12 hours
prior to beginning the screening measurement, if the
measurement is shorter in duration than 72 hours. If
possible, it is recommended that measurements be
made during cold weather, which usually corresponds
to the highest radon levels. As above, the objective of
maintaining these conditions is to obtain the highest
expected radon measurement for the livable part of
the house so that a low level measured under these
conditions can be presumed to mean that the dwell-
ing will likely remain at least as low under less
challenging conditions.
3.2 Follow-Up Measurements
In selecting a measurement technique and a schedule
for determining occupant exposure, the reader should
be aware that radon levels in a given house can vary
significantly over time. While the magnitude of this
variation is house dependent, it is not uncommon to
see concentrations in a dwelling vary by a factor of 2
to 3 or more over a 1-day period, even when the
occupant has not done anything that might be
expected to affect the levels (such as opening a
window). Seasonal variations can be even more
significant (sometimes as much as a factor of 10, with
typical values in the range of 3 to 5). In some houses,
the daily and seasonal variations will not be this great.
If a meaningful measure of the occupants' exposure
to radon is desired, it is best to obtain measurements
over an extended period (3 months to 1 year) and
during different seasons. Since the highest levels in
most climates are likely to occur during cold-wea-
ther periods, it would be wise to ensure that some
measurements are made during winter months.
If the screening result is greater than about 4 pCi/L,
follow-up measurements should be considered to
more rigorously determine the radon levels to which
occupants are being exposed (and hence the urgency
of remedial action). If the screening measurement
yields a result less than about 20 pCi/L, follow-up
measurements should include:
• Charcoal canister-canister measurements
made once every 3 months for 1 year, with each
canister exposed for 2 to 7 days, as specified by
supplier.
• Alpha-track detector--alpha track device
exposed for 12 months. This approach is
preferred over the quarterly charcoal canister
approach because the year-long alpha-track
measures for the entire year rather than just for
2- to 7-day periods, thus giving a more reli-
able measure of occupant exposure.
• E-PERM - exposed for 12 months.
These measurements should be made in the actual
living area on each floor of the house that is most
18
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frequently used as living space. Measurements
should be made under normal living conditions, rather
than the closed-house conditions recommended for
screening. The year-long measurement period is
suggested because the health risks at 20 pCi/L and
less are felt to be sufficiently low that the homeowner
can take time to make a good measurement of annual
exposure before having to decide upon action to
reduce the levels.
If the screening measurement yields a result greater
than about 20 pCi/L, but not greater than about 200
pCi/L, follow-up measurements are again suggested
for confirmation before taking remedial action.
However, an expedited schedule for these
measurements is suggested due to the higher risks
associated with continued exposure to these higher
levels. Follow-up measurements should be
completed within several months after obtaining the
screening result. Suggested follow-up mea-
surements are:
• Charcoal canister--a one-time measurement
on each floor having living space, under
closed-house conditions (during the winter if
possible), with exposure for 2 to 7 days.
• Alpha-track detector—a one-time mea-
surement on each floor having living space,
under closed-house conditions, with exposure
for 3 months (or less, if specified by supplier).
• E-PERM -- a one-time measurement on
each floor having living space, under closed-
house conditions, with exposure for 1 month.
If the screening measurement yields a result greater
than about 200 pCi/L, the follow-up measurement
should be expedited and conducted under closed-
house conditions over a period of days or weeks; a
3-month alpha-track exposure might not be
appropriate in this case. Short-term actions to
reduce the radon levels should be considered as
soon as possible. If this is not possible, it should be
determined, in consultation with appropriate state or
local health or radiation protection officials, whether
temporary relocation is appropriate until the levels can
be reduced.
In both screening and follow-up measurements, the
charcoal, alpha track, and E-PERM should be
positioned within a room according to the following
criteria:
• The device should be in a position where it will
not be disturbed during the measurement
period;
• It should not be placed in drafts caused by
heating/air conditioning vents, or near windows,
doors, or sources of excessive heat (such as
stoves, fireplaces, or strong sunlight);
• It should not be placed close to the outside walls
of the house; and
• It should be at least 8 in. (20 cm) below the
ceiling and 20 in. (50 cm) above the floor, with
the top face of charcoal canisters at least 4 in.
(10 cm) away from other large objects which
might impede air movement.
For further details regarding the protocols for using
charcoal canisters and alpha-track detectors, the
reader is referred to References EPA86b and
EPA87a.
3.3 EPA Action Level and Guidance for
Action
The EPA has established an action level for indoor
radon at 4pCi/L as an annual average. This means
that, while the radon concentration may fluctuate from
day to day and season to season, its yearly average
should not exceed 4 pCi/L. If the annual average does
exceed 4pCi/L, it is recommended that action be
taken to reduce the radon level. If such action is
initiated, the objective should be to reduce the radon
concentration to as low a level as is practical. The
bulk of this document is intended to provide advice
on reducing the indoor radon concentration.
This action level of 4 pCi/L does not imply that radon
levels below 4 pCi/L are safe. Exposure to any
measurable level of radon has an associated health
risk. There are no absolutely safe levels of exposure.
The individual must judge whether it is prudent to
further reduce radon levels that are below 4 pCi/L.
Note that, with current technology, it is not practical
to reduce indoor radon levels below the local ambient
values (typically 0.25 pCi/L).
On the opposite end of the spectrum, where radon
concentrations are significantly higher than 4 pCi/L,
urgency of the recommendation to reduce the radon
concentration increases with the level of the radon.
For high radon concentrations, it is also more
important to implement temporary measures to
reduce radon.
In summary, it is recommended that:
• For radon concentrations greater than 200 pCi/L,
action be initiated within a few weeks;
• For radon concentrations in the range of 20 to
200 pCi/L, action be initiated within several
months;
19
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• For radon concentrations in the range of 4 to 20
pCi/L, action be initiated within a few years (the
higher the radon the more urgent the need for
action); and
• For radon concentrations less than 4 pCi/L, no
action is specifically recommended. However,
many individuals may elect to further reduce
radon concentrations in the range of 1 to 4
pCi/L.
Some radon reduction measures will require
installation by a professional mitigation firm or by
skilled homeowners. However, there are some steps
which essentially any homeowner can take
immediately, often at little cost. These steps might
not always be sufficient by themselves to ensure an
annual average of 4 pCi/L or less, but they should
give some reduction, and they can be implemented
fairly easily pending installation of more
comprehensive measures. Such steps include:
• Increase ventilation of the house whenever
possible, by opening windows on two or more
sides of the lower level of the house (and on
upper levels if these are the primary livingareas).
In crawl-space houses, any existing crawl-
space vents should be left open year- round
(with insulation added around water pipes and
under the sub-flooring if necessary).Properly
implemented increases in ventilation should give
major radon reductions for as long as the
windows or vents remain open.
Close major soil gas entry routes, such as open
sumps, any distinct holes in slabs and foun-
dation walls, untrapped floor drains, and any
accessible open voids in the top course of block
foundation walls. The radon reductions that can
be achieved by such closure will be variable, but
can be significant in some cases.
Take steps to reduce the driving force for soil
gas entry, including; closure of major accessible
thermal bypasses (such as open stairwell doors,
fireplace dampers, and laundry chutes); opening
a nearby window to provide an outdoor air
source when combustion appliances and
exhaust fans are in use; and, where possible,
placing ventilation fans such that they blow
outdoor air indoors rather than exhausting indoor
air. The radon reductions that might be achieved
will be variable, but short-term effects could be
significant in some cases.
20
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Sect/on 4
Determining the Sources of Radon
4.1 Choice of Diagnostician/Mitigator
The person primarily responsible for diagnosis of the
problem is called the "diagnostician." The person
who will be primarily responsible for the design,
installation, and post-installation evaluation of the
radon reduction system is referred to here as the
"mitigator." These may or may not be the same
person.
Depending upon the types of radon reduction
systems that are being considered for a particular
house, and depending upon the skills of the individual
homeowner, some might feel that they can install a
system in their house on a do-it-yourself basis,
without a professional mitigator's help. The steps
involved in installing these systems are all consistent
with common construction practice (although special
equipment is desirable in a few cases). Thus,
homeowners with knowledge and experience in house
repairs and improvement may be able to install some
of these systems themselves. Effective, pro-
fessional-looking, and successful systems have
been installed by homeowners.
If the radon reduction steps that homeowners feel
comfortable in undertaking themselves are not
sufficient to reduce indoor radon concentrations to
acceptable levels, then the homeowners should hire a
mitigator experienced in house diagnostics and radon
mitigation. To obtain a list of candidate mitigators who
can do this type of work in the area, the homeowner
might have to inquire through a number of channels,
since no one organization maintains a list of active
contractors on a national basis. To obtain a local list,
contact state radiological health officials, local public
health officials, local building trade associations and
realtor associations, local building supply houses,
chambers of commerce, house improvement firms, or
perhaps energy conservation consultants. A list of
state contacts can be found in Section 11.
Companies listed in the most recent report by EPA on
measurement proficiency (e.g., EPA87b) may also be
a good source to consult. However, the potential for
conflict of interest with a company doing both radon
measurements and mitigation work should be noted.
Neighbors who have had mitigation work performed
are also a good source.
Radon mitigation is a relatively new field.
Consequently, many contractors have been in this
particular field for a relatively short time (although
some may have been involved in related building
trades for a number of years). Contractor experience
varies widely. Currently, no organization certifies
mitigation contractors on a national basis as being
qualified and experienced, although some States are
developing contractor certification programs. Thus,
the responsibility for evaluating candidate contractors
will often fall on the homeowner. The homeowner
should attempt to obtain a list of other buildings that
each contractor has mitigated. The mitigation
contractor may be unable to provide a comprehensive
list of references because many homeowners
consider the work that the mitigator has done for
them to be confidential. However, a mitigator who has
done work on a large number of houses should have
a few clients willing to serve as references. Other
sources with which the homeowner might check
include state radiological health officials, the Better
Business Bureau, and perhaps some of the other
sources identified in the previous paragraph.
Other factors that homeowners might consider in
evaluating mitigators are suggested below.
1. How many houses has the mitigator worked on?
How many of the houses were similar to yours, in
terms of substructure type and design features?
What were the radon levels before and after
mitigation?
2. Is the mitigator able to clearly explain the
proposed work? If the approach differs from the
recommendations given here, are the reasons
clear? Does the proposed design include features
that would alert you if the reduction system were
to malfunction?
3. How will the performance of the system be
determined after installation? Will radon
measurements of sufficient duration be conducted
after installation?
21
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4. What type of "guarantee" is provided? The state
of knowledge regarding radon mitigation is such
that many contractors will generally not be able to
guarantee the degree of radon reduction that will
be achieved (unless the house presents a
particularly clear-cut case, or unless the cost
estimate includes a cushion to cover potential
additional work that might be needed). However,
a contractor could guarantee the cost of the
specific proposed installation. The mitigator could
also ensure that the installation will meet certain
criteria (e.g., that all sealing will be completed
satisfactorily, or that any associated fans will
function for a specified period of time).
5. If the cost estimate is significantly different from
that of other prospective contractors, is it
apparent why? Is the mitigator proposing more or
less work than the others? Is the additional work
needed? One bidder might be proposing more
diagnostic testing, while another bidder might be
devoting more effort in improving aesthetics. Also,
one bidder may route exhaust pipes above the
eaves, while another may have them exit at
ground level. After proposals from different
contractors have been received, a homeowner
might wish to discuss the proposed systems with,
say, state radiological officials or other
homeowners who have had mitigation work done.
4.2 Identification of Radon Entry Routes
If elevated indoor radon levels are discovered, a
logical next step is to identify where the radon might
be entering. Radon-containing soil gas can enter a
house anyplace it finds an opening where the house
contacts the soil. Some such openings will always be
present, even in well-built houses. Potential entry
routes include:
• Openings in the foundation wall (such as holes
around utility penetrations, unclosed voids in the
top course of hollow-block foundation walls,
pores and mortar j6int cracks in block walls, and
settling cracks in block or poured concrete
walls);
• Openings in concrete slabs (such as holes
through the slabs, sumps, untrapped floor drains
which connect to the soil, the joint between the
slab and the foundation wall, cracks, and cold
joints);
• For crawl-space houses, openings between the
crawl space and the living area (such as utility
penetrations through the subflooring);
• For crawl-space houses, leakage of crawl-
space air into the cold air return ducts of a
central forced-air furnace located in the crawl
space;
• For slab-on-grade houses, openings in the
slab around penetrations (such as under
commodes and bathtubs, utility penetrations,
and heating ducts under the slab).
The void network inside hollow-block foundation
walls (or inside block fireplace structures) can serve
as a hidden conduit for soil gas into the house.
Table 2 is a checklist of possible entry routes that
might exist in a given house. If elevated radon levels
have been measured in a house, this checklist can be
used in inspecting the house to identify likely entry
routes. While not all of the entry routes into a house
can be sealed effectively, knowledge of where entry
is occurring (or might be occurring) will be important
in the ultimate design of a radon reduction system.
This checklist is subdivided according to routes
associated with the foundation wall, routes associated
with the concrete slab (including routes unique to
slab-on-grade houses), and routes unique to
crawl-space houses (which may have neither a slab,
nor a foundation wall, extending up into the living
area). In this discussion, the foundation wall is defined
as the wall which rests upon underground footings,
and which supports the weight of the house.
Foundation walls can be constructed of hollow
construction blocks, poured concrete, or (less
commonly) fieldstone or treated wood. Internal walls
should be treated as foundation walls if they penetrate
the slab and rest on footings.
Figure 2 depicts many of the entry routes listed in
Table 2. For convenience, this illustration shows a
hybrid house with some hollow block foundation walls,
and some poured concrete walls in order to aid
depiction of the full range of entry routes. Probably no
house would be built with all these construction
features. The entry routes shown in the figure are
identified according to their number in Table 2. Not all
entry routes in the table are identified.
The building substructure plays an important role in
determining the number and type of entry routes.
Table 2 indicates which entry routes are applicable to
the various substructure types. The three basic types
of substructures are;
1. basement, in which the floor (slab) is below grade
level;
2. slab on grade, in which the floor (slab) is at grade
level; and
3. crawl space, in which the floor is above grade
level, and the enclosed region between the floor
and the soil (the crawl space) is not livable area.
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Table 2. Possible Soil Gas Entry Routes into a House*
A. Entry routes associated with the foundation wall
Applicability: Wherever the foundation wall forms any portion of the wall area in the living space, including
houses in which a portion or all of the house includes:
a basement (over 3 ft below grade),
a slab below grade (1 to 3 ft below grade),
a slab on grade with hollow-block foundation wall in which the foundation wall extends up to form
the wall for the living area, or
a crawl space with hollow-block foundation walls where the foundation wall extends into the living
area, or in which the crawl space is open to the living area
1. Holes in foundation walls around utility penetrations through the walls (water, sewer, electrical, fuel oil, natural
gas lines).
2. Any other holes in the walls (such as defects in individual blocks in hollow-block walls, holes drilled for
electrical junction boxes or for other purposes, chinks between fieldstones in fieldstone foundation walls).
3. Any locations in which the wall consists of exposed soil or outcroppmgs of rock.
4. With hollow-block walls, unclosed voids in the top course of block, at the top of the wall (i.e., absence of a solid
cap block).
5. With hollow-block walls, unclosed voids in blocks around window and door penetrations.
6. With hollow-block walls, pores in the face of the blocks. (All hollow blocks are porous, but some blocks are
more porous than others. For example, true cinder block is generally more porous than concrete block.)
7. With hollow-block walls, cracks through the blocks or along the mortar joints (including fine cracks as well as
wider cracks and missing mortar).
8. With poured concrete foundation walls, settling cracks in the concrete, pressure cracks, and flaws from imperfect
pours.
9. In a split-level house in which a slab-on-grade or partial basement section adjoins a lower basement, the
joint between the lower basement wall and the floor slab of the next higher level.
10. Any block or stone structure built into a wall (in particular, a fireplace structure, or a structure supporting a
fireplace on the floor above), where a cavity can serve as a hidden conduit permitting soil gas to migrate into the
house (also ash pits).
Note: With hollow-block walls, the above list applies not only to the exterior perimeter walls, but also to any
interior block walls which penetrate the floor slab and rest on footings underneath the slab.
B. Entry routes associated with concrete slabs
Applicability: Wherever the floor of all or a portion of the house consists of a poured concrete slab in direct
contact with the underlying soil, including houses with:
a basement,
a slab below grade,
a slab on grade, or
a paved crawl space which opens to the living area.
1. Any exposed soil and rock in which concrete is absent and a portion of the house has an earthen floor, such as
sometimes found in fruit cellars, attached greenhouses, and earthen-floored basements. Rock outcroppmgs
protruding through the slab are another example.
2. Any holes in the slab exposing soil. These might be due to wooden forms or posts which have been removed or
have rotted away, or due to openings which were made for some particular purpose during construction but were
never filled in.
3. Sumps (a special case of B.2 above) which have:
- exposed soil at the bottom, and/or
drain tiles opening into the sump.
Where dram tiles drain into the sump, the tiles (installed to collect water) are probably serving as a collector for
soil gas, routing it into the house via the sump.
4. Floor drains, if these drains are untrapped (or if there is not water in the trap), and if the dram connects to the
soil in some manner (i.e., if the floor dram connects to perforated dram tiles, to a septic system, or to a dry well).
Trapped drains which are equipped with a cleanout plug might still be a source of soil gas, even if there is water
in the trap, if the plug is missing.
5. Openings through the slab around utility penetrations (e.g., water, sewer).
6. Cold joints in the slab.
7. Settling cracks in the slab.
8. The wall/floor joint (i.e., the crack around the inside perimeter of the house where the slab meets the foundation
wall). In some houses, this perimeter crack is in fact a gap 1 to 2 in. in width, for water drainage or soil
expansion (alternatively referred to as a French drain, channel dram, or floating slab). The wall/floor joint
associated with any interior wall which penetrates the slab can also be an entry route, not just the joint
associated with the perimeter walls.
9. Any hollow objects which penetrate the slab and provide a conduit for soil gas entry. A few examples are:
hollow metal load-bearing posts which rest on a footing under the slab (and which support a
crossbeam across the ceiling above the slab),
hollow concrete blocks which penetrate the slab (e.g., serving as the base for a furnace or water
tank), with the open central cores exposing earth,
hollow pipes which penetrate the slab (e.g., serving as the legs for a fuel oil tank), or
heating ducts under the slab.
(continued)
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Table 2. Continued
10. Hole in the slab under the tub for installation of the trap.
11. Hole under the commode on a slab.
C. Entry routes associated with decoupled crawl-space houses
Applicability: Houses with crawl spaces which do not open to the living area (i.e., which are decoupled from the
living area):
1. Seams and openings in the subflooring between the crawl space and the living area (e.g., openings around utility
penetrations through the floor, hole under the tub for the trap, and leaks around floor heating vents).
2. If a central forced-air HAC system is situated in the crawl space, leaks in the cold-air return ducting which
would permit crawl space air to leak into the house circulating air.
'Some entry routes are illustrated by number in Figure 2.
There are many variations and combinations of these
three basic substructure types. For example, some
common combinations of these basic substructures
include a basement with an adjoining slab on grade,
or a slab on grade with an adjoining crawl space.
Some houses include different wings representing all
three substructure types. A split-level house is a
common and somewhat unique combination of
substructure types. These houses have a basement
adjacent to a wing that is either a slab on grade or a
crawl space. The uniqueness of these houses lies
primarily in the openness of the internal space, which
means the separate sections of the house do not
interact like a normal upstairs and basement.
Sometimes the distinction between the substructure
types becomes blurred, as when the bottom level of a
house has a front foundation wall completely below
grade (thus having the characteristics of a full
basement) and a rear foundation wall totally above
grade (similar to a slab on grade). For the purposes
of this document, the following terminology is used to
distinguish between houses having lower levels at
varying depths below grade:
• The house is considered to have a basement if
the floor (slab) of the lower livable level
averages 3 ft or more below grade level on one
or more sides of the house.
• The house is considered a slab on grade if the
floor slab is no more than 1 ft below grade level
on any side.
• The house is considered a slab below grade if
the floor slab averages between 1 and 3 ft below
grade level on one or more sides.
Thus, the example cited above (of a house with the
front wall below grade and the rear wall above grade)
would be considered a basement house by this
terminology. Although the description of houses near
the borders of these three categories may be less
than ideal, they are accepted here for the
convenience of having only three categories.
If all other factors were equal (i.e., the soil radium
content, the soil permeability, the degree of house
depressurization, and the house's ventilation rate)
then the house with the greatest number of entry
routes (assuming the distribution of entry route sizes
is the same for all houses) would probably have the
greatest indoor radon level. Basement houses provide
the greatest amount of contact between the house
and the soil, and thus generally offer the greatest
opportunity for entry routes to exist. Thus, one might
anticipate that basement houses would tend to offer
the greatest risk of elevated radon. By comparison, a
crawl-space house where the crawl space does not
open into the living area, and where vents for natural
circulation are kept open, will have a ventilated,
pressure-neutral buffer space between the living
area and the soil. Crawl-space houses with
ventilated crawl spaces would be expected to offer
the least risk of elevated radon. However, crawl-
space houses are often observed to have elevated
radon levels. Since the type and size distribution of
entry routes depend, among other things, on the
house design and local construction practices, all
other factors are not likely to be equal. Consequently,
the expected trend for highest radon levels in
basement houses may be partially obscured by
variations in construction practices. Limited and
statistically nonsignificant data collected by EPA
suggest that basement houses may have the highest
radon levels.
The type of foundation wall can also play an important
role in determining the entry routes. When the
foundation wall is made of poured concrete, soil gas
will generally be able to move into the house through
the wall by pressure-driven flow only at those points
where there is a complete penetration all the way
through the wall somewhere below grade level.
However, when the foundation wall is made of hollow
blocks, soil gas can enter more easily. The voids
within the blocks form an interconnected network
throughout the wall. Once soil gas has entered that
void network (by penetrating through accessible
pores, mortar joint cracks, etc., in the exterior face of
the blocks below grade), the gas can move anywhere
within that network. The network, however, does not
extend around a corner from one perpendicular wall
to another. The soil gas can then enter the house
anywhere it finds an opening in the interior face of the
blocks, even above grade. The interior opening might
be a utility penetration, a mortar joint crack, or the
24
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pores in the interior face. If the top course in the
block wall is open, the easiest place for the gas to
enter the house will be the open voids in the top of
the wall. Even if the top voids appear to be covered
by the sill plate, the soil gas can still make its way out
of the blocks at that point. Since the sill plate does
not seal the open voids, the block wall serves as a
chimney, providing a convenient conduit for soil gas
entry.
Likewise, even if the foundation wall is largely above
grade, soil gas entering the blocks at footing level
underground can move up into the above-grade
portions of the wall and emerge into the house
through, say, the uncapped top voids 8 ft above
grade level. Or if there is a load-bearing block wall
inside the house (a wall which penetrates the
concrete slab and rests on footings underneath the
slab), soil gas can enter the blocks below the slab
and move up into the house through the wall.
Therefore, the wall can be a soil gas entry route,
even though no face of the wall appears to be
contacting soil. This ability of hollow blocks to serve
as a conduit for soil gas is illustrated in a number of
instances in Figure 2, and is reflected in a number of
the entry routes listed in Part A of Table 2.
In some cases a block foundation wall with open top
voids can serve as a conduit in a slab-on-grade or
crawl-space house even when the blocks do not
extend up into the living area. Depending upon how
the sill plate, outer sheathing, and any brick veneer
are configured at the top of the block foundation wall,
soil gas moving up through the open top voids could
enter the space between the sheathing and the
wallboard in the living area, and then migrate into the
house.
One potentially important entry route which will
sometimes be present is associated with hollow-
block structures which contain fireplaces and
chimneys, or which support fireplaces on the floor
above. Such block structures are commonly built into
the perimeter foundation wall, an interior load-
bearing wall, or sometimes a free-standing central
structure. These structures are of potential concern
whenever they penetrate the slab (or flooring) and
rest on footings of their own, which is often the case.
The potential problem is that there can be openings
concealed within the structure which can provide a
ready conduit for soil gas up into the basement or
into the upper living area of the house. For example,
if the structure consists of a block-walled chimney of
rectangular cross section, with a firebrick fireplace
built into one face of the chimney, there can quite
possibly be a space between the back of the firebrick
and the block wall of the surrounding chimney. The
exact nature and extent of such concealed openings
will depend upon the specific procedures used by the
masons during construction. If present, these
openings cannot be effectively closed without at least
partially dismantling the structure.
Another type of entry route is that in which
underground perforated drain tiles connect into the
house, thus serving as a soil gas collector facilitating
entry. Sumps (B3 in Figure 2) and floor drains (B4 in
Figure 2) are the two specific examples of this type of
entry route. Many sumps (although not all) connect to
perimeter drain tiles which surround at least part of
the house at footing level (B3 in Figure 2). These tiles
can be located on the outside of the footings, on the
inside (underneath the slab), or on both the outside
and the inside. Their purpose is to drain water away
from the vicinity of the foundation. The water
collected by the tiles drains to the sump, from which
a sump pump lifts the water to an above-grade
discharge remote from the house or to the house
sewer line (see sump in Figure 2). These drain tiles
can also collect soil gas, which can then move into
the house via the sump. Thus radon can enter the
house through the sump not only as the result of any
exposed soil which might be visible in the sump itself,
but also from soil around the entire foundation
(through drain tile). As a consequence, sumps are
almost universally a major radon source when they
are present and not sealed.
Some floor drains (B4 in Figure 2) also drain to the
perimeter drain tiles, to a separate segment of drain
tile, and/or to a dry well (sometimes under the floor).
In some cases, the floor drain might drain to a septic
tank, a storm sewer, or a sanitary sewer. Whenever
the floor drain connects to the soil in this manner, soil
gas can be drawn into the house via the drain unless
the drain includes a trap which is always full of water,
a waterless trap, or a reverse flow valve. Floor drains
which connect to a septic tank sometimes are
installed with a trap that includes a cleanout
permitting the trap to be bypassed for purposes of
cleaning the line. This cleanout extension is normally
blocked with a removable plug. If this cleanout plug is
missing, then soil gas (and septic odors) can enter
the house via the cleanout extension even if the trap
is filled with water. Floor drains which drain via non-
perforated pipe to an above-grade discharge would
not be expected to be a source of soil gas. However,
unless it is known that the drain definitely does not
connect to the soil in some manner, the drain should
be viewed as a potential entry route.
In using Table 2 to inspect a house for soil gas entry
routes, the reader should recognize that, in many
cases, some entry routes will be hidden. For example,
they may be concealed behind or under paneling,
carpeting, wood framing, or other structures or
appliances. Using the table, it should be possible to
identify where such entry routes might be hidden, as
well as to identify the major visible potential entry
routes. Understanding where important entry routes
are, and where they might be concealed, is important
25
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Figure 2. Some potential soil gas entry routes into a house.
Key
+• Soil Gas Flow
A1 Identifier of Soil Gas Entry Route,
from Table 2
House Air Flow Through Airflow Bypass
Air up
Stairwell
(if door
is open)
Poured Concrete
Foundation Wall
Footing
26
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Air up ,
Flue
Chase
Fireplace
Flue
Footing
Dram Tile
interior)
Sump
Note: Hybrid house containing both hollow-block and poured concrete foundation
walls shown for convenience to illustrate range of entry routes
27
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in selecting the diagnostic testing which should follow
and in determining the logical radon reduction
alternatives for that house.
4.3 Factors Influencing Driving Forces
Along with the identification of soil gas entry routes, it
is also important to identify those features which
might be contributing to the driving force which is
causing soil gas to flow into the house through these
entry routes. The features influencing the driving
force include: (a) those which increase the soil gas
flow by contributing to depressurization of the house;
and (b) those which facilitate the flow of soil gas
without increasing depressurization.
Specific potential contributors to the driving force are
listed in Table 3. The contributors are subdivided into
three categories: those associated with the weather,
those associated with house design features, and
those associated with homeowner activities. The
contributors in the weather and homeowner activity
categories directly influence house depressurization.
Contributors in the house design category facilitate
house air exfiltration (and hence, perhaps, soil gas
infiltration) under the depressurization created by the
contributors from the other two categories. While
nothing can be done to alter the weather, some steps
can be taken to reduce some of the individual
contributors in the other categories.
4.3.7 Weather Effects
Low outdoor temperatures contribute an important
driving force. Whenever the indoor temperature is
maintained at a level higher than the outdoor
temperature, the buoyancy of the warm indoor air will
tend to cause it to rise. The colder the temperature
outdoors, the greater the buoyancy of the indoor air.
The warm air leaks out of the house through
openings in the upper levels (e.g., around upstairs
windows, and through penetrations into unheated
attics). To compensate for the warm air that is thus
lost, outdoor air leaks into the house around doors
and windows at the lower levels (and through the
seam between the house frame and the foundation
wall). Also, soil gas leaks in through entry routes.
Once inside, the infiltrating air and soil gas
themselves become heated, then rise and leak out
through the upper levels, thus continuing the process.
The shell of a closed house can thus be pictured as a
chimney through which air is constantly moving
upward whenever the temperature is warmer indoors
(although the air movement is too small for the
homeowner to notice). Due to the similarity of this
process to that of warm air rising up a chimney or
smokestack, the effect is commonly referred to as the
natural stack effect.
The buoyant force on the warm house air
depressurizes the lower levels of the house, sucking
in the outdoor air and soil gas needed to replace the
out-leaking (exfiltrating) warm air. On the other
hand, the buoyant force pressurizes the upper levels
of the house (relative to the outdoors), forcing heated
air upstairs and out.
In addition to temperature, another weather-related
contributor to the driving force for soil gas entry is the
wind. Winds create a low-pressure zone along the
roofline and on the downwind side of the dwelling.
Depending upon the air exfiltration routes existing on
the roof and on the downwind side, portions of the
house can become depressurized.
4.3.2 House Design Effects
Nothing can be done to prevent the natural buoyant
force that makes warm indoor air want to rise during
cold weather. However, the air flows created by this
buoyant force (and hence the infiltration of soil gas)
can potentially be reduced by appropriate attention to
certain house design features. The principles involved
in reducing these air flows have been applied for
some time by energy conservation consultants whose
objective has been to reduce the amount of warm air
flowing out of the house, to improve energy
efficiency. These same steps can simultaneously
reduce the amount of soil gas flowing in.
Openings through the house shell (between indoors
and outdoors) above the neutral plane will facilitate
the exfiltration of warm house air. The neutral plane is
an effective horizontal plane in the house located at
the height at which the inside pressure is equal to the
outside pressure. To the extent that such openings
through the shell can be closed above the neutral
plane, the effect will be to partially cap the "chimney"
created by the house shell, reducing the
temperature-induced flows. Also, many concealed
openings cannot easily be closed; for example, efforts
to make the upper levels almost gastight (by
installation of plastic sheeting as an air barrier inside
the walls and over the attic floor) would be expensive,
and perhaps not cost effective. Note that, if openings
to the outdoors are closed below the neutral plane,
the effect would be to reduce the openings available
for outdoor air to infiltrate in order to compensate for
the exfiltrating warm air at higher levels. Hence,
closure of openings (e.g., around windows and doors)
below the neutral plane could increase the amount of
infiltrating soil gas, relative to infiltrating outdoor air,
making radon problems worse. Closure of openings
through the house shell can also reduce exfiltration
(and depressurization) caused by low-pressure
zones created by winds.
If the upper portion of a house can be pictured as a
cap over a figurative chimney, then the floors
between stories might be pictured as dampers in this
chimney. Just as openings through the upper house
28
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Table 3. Factors That Might Contribute to the Driving Force for Soil Gas Entry
A. Weather factors
1. Cold temperatures outdoors (creating an upward buoyant force on the warm air inside the house, thus causing
depressurization of the lower levels of the house).
2. High winds (depressurizing the roofline and downwind side of the house) can be important if the downwind side
of the house has more openings through the shell than does the upwind side.
8. Design factors
1. Openings through the house shell (between indoors and outdoors). Openings above the neutral plane (i.e.,
openings in the attic and upper levels) contribute to the out-leakage (exfiltration) of rising warm air resulting
from temperature-induced buoyant forces, potentially increasing soil gas infiltration. Such openings can include:
Spaces between windows and window frames.
Uncaulked gaps between window frames and the exterior house finish.
Penetrations through roofs (e.g., where attic ventilation fans are mounted).
Attic soffit vents, gable vents, passive roof vents, and ridge vents (must remain open for moisture control
reasons).
Open dampers in chimneys and flues (permitting house air to flow directly from lower levels of the house
to the outdoors above the roofline).
Concealed openings through walls and roof (e.g., openings around electrical junction boxes and switch
plates in the walls, seams between strips of siding).
Openings through the house shell on the downwind side of the house, and through the roof, can increase
exfiltration and depressurization due to wind effects.
2. Openings through the floors and ceilings inside the house, facilitating the movement of air between stories (also
between the living space and the attic, as well as basement and first floor). Such internal openings-referred
to as airflow (or "thermal") bypasses-facilitate the rise of warm air resulting from the temperature-induced
buoyant forces, and thus can potentially increase warm air exfiltration and soil gas infiltration. Internal airflow
bypasses include!
Stairwells between stories which cannot be closed off.
Chases for flues, ducts, and utilities.
Laundry chutes.
The cavity inside frame walls, where the walls penetrate the floor above (especially in the case of
internal frame walls, where the cavity is not partially blocked).
Attic access doors that are not weatherstnpped.
Recessed ceiling lights, which require a penetration through the sheet rock.
Openings concealed inside block structures which penetrate floors between stories.
Central forced-air heating/air conditioning ducts which connect upstairs, downstairs, and basement.
C. Homeowner activities and appliance use
1. Using combustion appliances which draw combustion air (and flue draft air) from inside the house and exhaust
the products of combustion outdoors.
Fireplaces.
Wood or coal stoves.
Central gas or oil furnaces or boilers for house heating, if air is drawn from inside the livable area.
Fuel-fired water heaters, if air is drawn from livable area.
Gas dryers.
A separate supply of combustion air from outdoors can reduce the depressurization caused by these appliances.
2. Using any exhaust fan (a fan which sucks air from indoors and blows it outdoors).
Window fans or portable fans for home ventilation, when operated to blow indoor air out.
Clothes dryers which exhaust outdoors.
Kitchen exhaust fans (especially high-volume range exhaust hood fans).
Bathroom exhaust fans.
Attic exhaust fans, including fans intended to ventilate just the attic (sized below 1,000 cfm) and fans
intended to ventilate the entire house (up to several thousand cfm).
3. Using the fan in any central forced-air heating/air conditioning system where the return ducting preferentially
withdraws house air from the lower story of the house (due either to the location of the return air registers or to
leaks into the return air ducting). Depressurization of the basement can arise, for example, when the central fan
and much of the return ducting is located in the basement; basement air can be sucked into the return ducting
(e.g., via unsealed seams in the ductwork and poor connections) and "exhausted" to the upstairs by the central
fan.
4. Leaving doors open in the stairwell between stories (thus creating an internal airflow bypass).
5. Opening of windows or doors on just the downwind side of the house.
6. Operating a heat recovery ventilator in an unbalanced mode resulting in exhausting more air than is brought in.
shell permit rising warm air to escape, openings internal airflow bypasses (since they permit the rising
through the floors facilitate the upward flow of warm warm air to bypass the damper). They are also
air inside the house, thus also facilitating the ultimate commonly referred to as thermal bypasses, since
escape of the air through the shell. Such openings they facilitate the flow of heated air up and out of the
through the floors-- which are effectively holes house. Where major airflow bypasses can be closed,
through the damper-are referred to here as the upward air movement can be reduced-and, as
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a result, the exfiltration of warm air and the infiltration
of outdoor air and soil gas can be reduced. Some
bypasses cannot be closed easily, due either to
inaccessibility or to practical considerations. For
example, houses having large open stairwells without
doors between stories offer a major flow route for
rising warm air which cannot be closed without
installing a wall and door across the stairwell. In
houses having such major bypasses, it might not be
possible to significantly reduce the upward air
movement by closing other, secondary, bypasses so
long as the stairwell remains open.
4.3.3 Homeowner Activity Effects
As listed in Item C of Table 3, a number of appliances
remove air from the house, and thus might have a
depressurizing effect. Fans which draw air from the
house and exhaust it outdoors are present in most
houses, in the form of window and attic fans, range
hoods (not all range hoods are exhaust fans; some
merely recirculate the air through a filter), and
bathroom exhaust fans. A clothes dryer is a form of
exhaust fan whenever the moist air leaving the dryer
is exhausted outdoors. A stove, fireplace, furnace, or
boiler inside the house also removes air in order to
burn the fuel, and in order to maintain the proper draft
up the flue. This air (including products of
combustion) goes up the flue and is exhausted
outdoors. These appliances are important in daily
living, so that ceasing their use is generally not an
acceptable option. Some of these appliances are
used only intermittently (e.g., fireplaces are often
used only occasionally during the winter); thus their
impact on indoor radon levels may sometimes be of
limited duration.
The Appendix is an example of a house inspection
form that can be used during a visual inspection. Not
all parts of the form are applicable to every house.
However, much of the information on this form will be
useful to a diagnostician in selecting and designing a
radon reduction system. Along with the checklists in
Tables 2 and 3, this inspection form directs the
inspector's attention to the variety of issues that may
be important in diagnosing the house's radon
problems and then mitigating them.
30
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Section 5
Diagnostic Testing to Select a Mitigation Method
A collection of observations and measurements
(referred to as "diagnostic tests") can be made prior
to mitigation to aid in the selection and design of the
radon reduction method for a particular house. The
type and extent of diagnostic measurements
conducted by radon diagnosticians and remediation
firms currently varies among individuals. While no one
set of diagnostic testing procedures can be
considered universally applicable, EPA is compiling an
appropriate set of diagnostics to be used in Agency-
sponsored projects. This will not necessarily be the
most appropriate set for other mitigators. Several
studies in progress (Ma87, Se87, Tu87, Ha87) are
attempting to identify the minimum set of diagnostic
measurements needed to design an efficient
mitigation system for a given house. One important
consideration in choosing the appropriate diagnostic
procedures is cost effectiveness to the homeowner,
since the time spent by diagnosticians will generally
be paid for by the homeowner. Unless a specific
diagnostic test offers some reasonable potential for
leading to a successful installation in a given house
more efficiently and more cheaply, the need for
conducting that diagnostic test should be questioned.
Since there is not currently a universally accepted set
of diagnostic protocols, the following discussion can
list only some of the specific diagnostic tests that
have been used by various diagnosticians and EPA
engineers, with a discussion of the conditions under
which the individual tests might be most applicable.
Diagnostics described in this section fall into two
groups: one contains the minimum set required for
the simplest diagnosis, while the other contains
additional procedures to be performed by more
experienced mitigators especially when a house is
expected to present difficulties in mitigation. Figure 3
shows a logical sequence of steps that could be
followed in performing diagnostic measurements.
These observations and measurements are discussed
in the following subsections.
5.1 Visual Survey of Entry Routes and
Driving Forces
The first and most important step in the diagnosis is
an inspection of the house to identify potential radon
entry routes and driving forces. During this step one
notes both the general and the unique features of the
house which could be important in the selection and
design of a mitigation system. From these features,
potential strategies of mitigation are formulated, and
specific system designs are visualized. These
visualizations of system designs are then used to
develop a plan of action for diagnostic testing either
to confirm the applicability of the most promising
reduction method or to distinguish between
competing designs. Additional features to be
observed are whether extensive wall and floor finishes
exist in the lowest level. From the house plan or from
the homeowner, it may be possible to determine
whether a complete loop of drain tile exists around
the footings. A major difficulty in diagnosing radon
problems in a house is that entry routes, certain
house features contributing to the stack effect, and
other structural features influencing mitigation design
are often concealed behind or under wall paneling,
carpeting, wood framing, and plumbing fixtures.
In many such cases, the cost-effective approach will
be simply to make some reasonable assumptions
about the concealed features, and to design the
radon reduction system to be modified if performance
after installation suggests that the assumptions were
not correct. If large hidden openings in the slab or
foundation walls prevent an active soil ventilation
system from maintaining adequate depressurization,
the paneling, flooring, commode, etc., may have to be
temporarily removed so that the openings can be
closed. If the current homeowner observed the house
being built, or if the builder is available, information
about some of these and other concealed features
might be obtainable from them (such as whether a
good layer of clean, crushed rock was placed under
the slab, or whether there is a complete loop of drain
tile around the footings).
In conducting the visual inspection, the primary tools
required will generally be a flashlight, a screwdriver,
and a stiff wire, or other similar tool for probing in
joints and openings. A small stepladder can
sometimes be useful. A mirror to enable viewing
features in difficult-to-reach locations is advisable,
since hidden crevices could contain mouse traps or
worse hazards to bare fingers. A plumber's "snake"
31
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Figure 3. Steps in diagnostic testing.
Inspect House for Potential
Entry Routes and Driving Forces
Measure Radon Concentration in
Air by Grab Samples
Measure Flow Rates and
Radon Source Strengths
at Apparent Entry Routes
Measure Radon in Water if
Source is a Private or
Small Community Well
This Manual
May Not
Apply
Map Radon Source
Strength Under Slab
(and in walls if hollow)
Measure Radon in
Crawl Space
Measure Communication
Between Sub-Slab Points
(also wall points if hollow)
Estimate Degree of
Communication Between
Crawl Space and Living Space
Measure Extension of
Pressure Field Under Slab
(and hollow walls)
Estimate Ventilation
Rate in Crawl Space
32
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can be valuable for probing the extent of openings
(for example, the extent of the drain tiles that open
into a sump). Another very useful tool is a smoke
stick or a punk stick, which generates a small stream
of smoke. When released next to cracks and other
openings, the smoke can reveal whether there is a
distinct movement of air into or out of the opening.
This indicates whether there might be a significant
soil gas flow into the house through that opening. A
smoke stick uses chemicals to produce smoke
without generating significant heat. A punk stick
generates smoke from a smoldering substance. Since
the punk stick generates heat, the smoke tends to
rise, which may interfere with the proper interpretation
of the air flows. Punk sticks are more readily
available. Despite the fact that smoke sticks are less
common, they are preferred over punk sticks.
However, the smoke flow can sometimes be
ambiguous. Moreover, the fact that a distinct smoke
flow is not observed at a given time does not
necessarily mean that that opening is not an
important entry route. Conversely, in some locations,
an observed smoke flow might be attributable to
outside air or house air flow, not soil gas. Therefore,
smoke testing is not always definitive, but it can be
useful when distinct air movement is present. (Note:
Whenever a smoldering object such as a punk stick is
used as a smoke source, care should be taken to
prevent fires-for example, in basements cluttered
with flammable materials. It also is not advisable that
the diagnostician breathe excessive amounts of the
fumes from chemical smoke sticks.)
In many cases, the mitigator will be sufficiently
confident of his initial diagnosis that additional testing
will not be considered necessary. Rather than
spending additional time performing diagnostic
measurements, the mitigator begins immediately to
install the reduction system. A number of mitigators
have been quite successful with this approach
(especially with sub-slab depressurization systems).
Their success is based primarily upon their
knowledge of local building codes and practices. For
instance, the mitigator may know that in a certain
locality there will almost always be a good layer of
aggregate under the slab. In some localities, the
mitigator may be aware that the soil is sufficiently
permeable that aggregate is not required to ensure
the applicability of a sub-slab system. Similarly, if
there is no central air circulation system and the
basement is well isolated from the upstairs, one might
be inclined to try basement pressurization without
further diagnostic testing. Natural or forced ventilation
of the crawl space might also be attempted without
further testing, if no appliances or air handling
systems are located in the crawl space.
However, in many circumstances, some minimal
number of diagnostic measurements are needed to
guide the design and installation of the radon
reduction system. One of the most universal
diagnostic measurements will be a simple test of
sub-slab communication. In a simple form, this test
consists of using a vacuum cleaner or other fan at a
single location to depressurize the region beneath the
slab, while smoke sticks or other devices are used to
determine whether air flow from the basement to the
sub-slab region is induced at some distance through
existing holes or through drilled test holes. Good air
movement induced at large distances indicates good
sub-slab communication and, consequently, high
probability of success for a sub-slab ventilation
system.
5.2 Radon Measurements in Room Air
The initial measurements that a homeowner makes to
determine occupant exposure inside the house are
not considered in this discussion to be part of
diagnostic testing. If radon measurements in the bulk
house air have already been completed in
accordance with the EPA protocols, there will
generally not be a need for a diagnostician to repeat
them. However, there may be individual cases where
further measurements in the house air are desirable
as part of the diagnostic process. For example, grab
samples for radon in the room air might be taken at
the same time that entry route radon measurements
are made, to permit a direct comparison of the entry
route concentrations with the simultaneously existing
room air concentrations. Grab samples are samples
of air collected in a container during a short period of
time (nominally 5 minutes) to be analyzed for radon
concentration. These grab samples are usually stored
in an airtight container and measured for radon
concentration at a later time using a scintillation
counter,
5.3 Radon Measurements at Potential
Soil Gas Entry Points
Some diagnosticians believe that radon
measurements made in (or near) suspected entry
routes are useful in suggesting the relative
importance of the various routes, as an aid in the
design of the radon reduction system (Tu87). Grab
samples can be taken from: inside the sump; inside
floor drains; inside the voids of each block foundation
wall (via small holes drilled in the face of the wall); in
the space between paneling/wallboard and the
foundation wall behind; and from cracks and joints in
the slab and walls (including French drains), by taping
over a segment of these openings and drawing the
sample from within the taped area (Tu87). Those
entry routes exhibiting higher radon concentrations
might reasonably be assumed to be relatively more
important than those having lower concentrations.
Thus, the routes with higher concentrations might
receive some priority in the design of the mitigation
system. For example, if an active sub-slab suction
system is planned, more suction points might be
33
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placed near the block foundation walls that appear to
have the higher radon levels in the voids.
If holes are being drilled through the slab in order to
measure the sub-slab pressure field extension, as
discussed in Section 5.6 below, the radon levels
under the slab can be measured by grab samples
taken through the several holes. If the results show
that radon levels are distinctly higher under certain
segments of the slab, the sub-slab suction points
can be placed in (or biased toward) those segments.
Note that these measurements only suggest the
relative importance of an entry route. They do not
provide a rigorous measure of the actual contribution
of that route to the radon levels in the house. The
actual amount of radon entering a house through a
given opening is determined not only by the radon
concentration in the entering gas, but also by the flow
rate of the gas through the opening. For example an
opening with a less elevated radon level, but a high
flow, might be more important than one with a higher
level but a low flow. Since flow rates are not easily
measured in these circumstances, the actual amount
of radon entering through a given opening is not
known. It is being assumed that two similar types of
entry routes (e.g., two block walls or two slab cracks)
probably have similar entry flow rates. Thus, the one
with the higher radon concentration is probably the
more important contributor to indoor levels. This
assumption, while reasonable, will not always be
correct. Two dissimilar types of routes (e.g., a block
wall versus a slab crack) cannot reliably be compared
based on radon measurements alone.
5.4 Radon Measurements in Well Water
If a house receives its water from a private or small
community well, it will generally be necessary to
measure the water radon level as part of the
diagnostic effort. A qualitative test can be performed
by using either grab samples or a continuous radon
monitor (EPA86b, EPA87b) to measure the radon
concentrations in a closed bathroom before and after
the hot shower runs for 10 to 15 minutes. If the well
water contains more than, say, 40,000 pCi/L of radon,
the water might be contributing a significant portion of
the indoor airborne radon. Under these conditions,
water treatment will be required in addition to (or
rather than) soil-gas-related reduction measures.
For more information, see References EPA87c and
EPA88a. The only documented health risk associated
with radon in the water is from its release into the air
and, consequently, from lung cancer. There is no
documented health risk from ingestion of the radon in
the water. The commonly used rule of thumb is that
10,000 pCi/L of radon in water will result in about 1
pCi/L of radon in the indoor air. The actual range is
0.2 to 3 pCi/L. This rule of thumb relates to the
average concentration in the house. Local
concentrations in the bathroom may be much higher.
5.5 Pressure Measurements
Since most mitigators agree that radon entry into
houses is controlled primarily by a pressure-driven
flow of soil gas into the house, useful information can
be obtained by measuring appropriate pressure
differentials. For example, the pressure differential
between indoors and outdoors during a radon
measurement will give some perspective regarding
the degree of house depressurization and,
consequently, the strength of the driving forces
bringing outside air into the house. Pressure
differentials measured while air-exhausting
appliances are in operation indicate the degree of
depressurization caused by these appliances. The
mitigation system must be designed to counteract
these pressure differences. Pressure differences
between the house and the soil give a more direct
measure of the driving force bringing soil gas into the
house (at the time of measurement). The mitigation
system also must be designed to offset this driving
force.
The small pressure differences that exist in these
situations, no more than a small fraction of an inch of
water, expressed as in. WC (water column), can be
measured using either a micromanometer or a
pressure transducer.
5.6 Measurement of Sub-Slab
Communication
If a sub-slab ventilation system is being considered,
it is helpful to know the ease or difficulty with which
gas can move through the soil and crushed rock
under the slab (i.e., the sub-slab "communication").
Sub-slab systems rely upon the ability of the system
to draw (or force) soil gas away from the entry routes
into the house. If an active (fan-assisted) sub-slab
ventilation system is to be used, and if this system is
to maintain reduced pressure at all of the entry routes
around the slab, the number and location of the
needed ventilation points will depend on the
communication under the various portions of the slab.
The better the communication, the easier it will be for
a ventilation point to maintain reduced pressure at an
entry route remote from that point.
In some cases, some diagnosticians might feel that it
would be more cost effective to install a sub-slab
ventilation system without measuring communication.
By that approach, the initial sub-slab installation
would be made using best judgment (based upon
visual inspection) and experience. If radon levels are
not sufficiently reduced by the initial system, post-
mitigation diagnostics (including sub-slab pressure
measurements) could then be conducted to
determine where additional ventilation points are
needed. This approach avoids the cost of the pre-
mitigation communication measurement, but
34
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increases the risk that the initial installation willhave
to be modified later at some expense. Among the
circumstances under which it might be a reasonable
risk to skip the pre-mitigation communication testing
would be when it is reasonably certain that there is a
good layer of clean, coarse aggregate under the slab.
Evaluation of sub-slab communication can consist
simply of visually inspecting the nature of the
aggregate under the slab, by drilling several small test
holes through the slab at several points. This
approach would not necessarily detect some barriers
to gas flow that might exist under the slab such as
heating ducts, interior footings, or bedrock with no
aggregate over it.
A more quantitative approach for assessing sub-slab
communication is to measure what is referred to as
the "pressure field extension." The pressure field
extension reflects the ability of ventilation applied at
one point under the slab to maintain reduced
pressure at various other points remote from the first.
One convenient technique for measuring the pressure
field extension (Ha87) involves the use of an industrial
vacuum cleaner, capable of producing up to 80 in.
WC of pressure differential, to depressurize a hole
through the slab at some central location. The vent
hole through the slab should be as large as 1.5 in. in
diameter, in which case the hose from the vacuum
cleaner can be inserted all the way through the slab
and temporarily sealed using putty. Care must be
exercised to ensure that a reliable seal is obtained.
While the vacuum cleaner operates, pressure
differences are measured across the slab at several
test points around the perimeter of the slab, remote
from the vent point. The pressure difference is also
measured at a closer point, within perhaps 8 to 12 in.
of the vent point.
These pressure differences can be measured using a
suitably sensitive micromanometer or pressure gauge
sealed with putty into 3/8- or 1/2-in. holes through
the slab. Some diagnosticians use a smoke stick,
rather than a pressure measurement, to determine
qualitatively whether the depressurization is capable
of inducing an air flow down into the test hole. If this
condition were maintained under the most adverse
conditions of basement depressurization (during
winter, with appliances operating), a distinct flow into
the test holes should be adequate to ensure good
performance of a mitigation system producing
equivalent sub-slab depressurization. The exhaust
from the vacuum cleaner should be vented outdoors,
since it will consist of soil gas from under the slab
which can be very high in radon. Of course, all holes
must be permanently closed after testing.
The primary objective of this test is to determine the
degree of depressurization to be maintained under
the slab to ensure that the direction of flow at the
remote perimeter points will be from the basement
into the sub-slab region, despite the thermal stack
effect, the wind, or appliance operation. At present, it
is estimated that the sub-slab pressure differential
depressurization around the slab perimeter must be at
least 0.015 in. WC (about 4 Pa) to prevent soil gas
entry when the basement becomes depressurized
under normal conditions.
The results of this diagnostic test include the
pressure differences in the closer test hole, and in the
remote perimeter test holes. Under favorable
conditions (good communication), the pressure
difference in the closer test hole will be no greater
than several tenths of an inch of water, despite the
high depressurization in the vacuum cleaner. The
pressure differences at the remote points will often
not be much greater than 0.015 in. WC, and will
sometimes be less. The reduction in pressure
difference between the closer and the remote test
points is a measure of the flow resistance under the
slab. If the slab contains cracks and other openings,
this reduction in pressure difference may also be a
measure of the amount of house air leaking down
through the slab openings.
A sub-slab ventilation installation can be more
effective by using a hole excavated in the soil under
the slab having a radius equal to the distance to the
closer test point discussed above (see Section 7.3 for
an illustration). The pressure at the closer test point
(8 to 12 in.) can be viewed as the pressure which the
sub-slab ventilation system must maintain in that
vent hole if the sub-slab depressurization around the
slab perimeter is to be maintained at 0.015 in. WC.
The manufacturer's performance curve of the fan and
the diameter and length of the ventilation pipe (and
hence the pipe pressure loss) can be used to
determine the needed pressure difference in the vent
hole at the indicated flows.
This diagnostic test procedure has been used by
private mitigators in designing a number of sub-slab
ventilation installations. Where sub-slab
communication is relatively good, the procedure
appears fairly successful. When the pressure field
extension is good, indicating high sub-slab
communication, one sub-slab ventilation point is
often adequate to treat an entire slab in a small- to
medium-sized house. In large houses, or where the
communication is lower (although still good), a
second ventilation point may be needed. The second
point might be installed without any further vacuum
diagnostic testing, on the assumption that the flow
resistance under the slab near the second point will
be generally similar to that where the vacuum test
was conducted. This assumption is probably
reasonable when communication is good.
The rationale for pressure field extension
measurements as a cost-effective diagnostic test
lies in the argument that the system can be properly
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sized and located based on these measurements. If
more vent points and a larger fan than necessary are
installed, both the initial cost and the operating costs
will be greater than for an optimized system. The
excess operating costs include not only the additional
energy required to operate the larger fan but also the
heating and cooling penalties associated with
removing excessive amounts of conditioned indoor
air. On the other hand, if the system is undersized
there are both capital and labor costs associated with
modifying the system.
The greatest difficulties with sub-slab pressure field
measurements arise where communication is not
good. When the pressure field extension is poor, a
vacuum cleaner test at one or two vent holes will
generally not give the mitigator much information with
which to design a sub-slab ventilation system. The
vacuum cleaner depressurization might not extend at
all to any of the remote test points. Thus, calculation
of sub- slab flow resistance near those test points is
impossible (one just knows that resistance is high);
and one cannot reliably determine from the results
where sub-slab suction points would have to be
located to adequately treat those remote areas of the
slab. The pressure field extension test here simply
serves as a warning that permeability is poor (and
probably variable from place to place), and that the
sub-slab system will thus have to be designed
conservatively including multiple suction points,
careful placement of the points, and perhaps fans.
Sometimes less remote test points could be used to
estimate the maximum extent of the pressure field.
Testing has shown that "poor" pressure field
extension does not necessarily mean that sub-slab
depressurization is not applicable. One option for
obtaining more quantitative design guidance when the
permeability is poor might be to conduct vacuum
cleaner tests through a number of test holes around
the slab, more extensively mapping the distribution of
sub-slab flow resistance. However, so many test
points might be required that this approach would not
be cost effective, since diagnostic time and costs will
rise with the significantly increased effort. Also, some
sections of the slab might not be accessible, due to
carpeting or other floor finish. Moreover, the results
may not be accurately interpreted. Results from some
installations suggest that a sub-slab system might
still be reasonably effective even if the system does
not maintain 0.015 in. WC suction everywhere
(Sc87). Thus, if the results from the pressure field
mapping suggest that many suction points would be
needed to achieve 0.015 in. WC everywhere, a
mitigator might be inclined to start with fewer points in
the initial installation with the location of the points
selected using best judgment. The number of points
could be increased later if warranted. This approach
is what the mitigator would have done in the absence
of extensive mapping.
Therefore, if the initial test of sub-slab pressure field
extension shows poor extension (poor
communication), some mitigators might decide that
the most cost-effective approach would then be to
install a system based on best judgment and
experience, rather than proceed with further pressure
field diagnosis. Developmental work is underway to
define what further pressure field testing is cost
effective and practically useful where permeability is
poor.
5.7 Measuring the Pressure Field Inside
Block Walls
If active ventilation of the void network inside hollow-
block foundation walls is planned, it might be useful to
make measurements on the wall voids, analogous to
those described above regarding sub-slab
communication. The objective would be to determine
how far any pressure effects within the voids (either
depressurization or pressurization) extend out from
the wall ventilation point. The concern with wall voids
is not whether flow resistance will be too high to
permit good pressure field extension (as can be the
case under the slab), because the flow resistance in
the void network will be quite low. Rather, the
concern is that the pressure field might not extend
very far because the walls can permit so much air to
leak into (or out of) them when depressurization (or
pressurization) is applied (Mar88). The information on
pressure field extension could be used to help select
the number and location of wall ventilation points
needed to handle this leakage, and thus to adequately
treat all of the wall-related entry routes. The results
might also help identify major wall openings that must
be closed.
For wall testing, the industrial vacuum cleaner would
be connected to the void network by holes drilled into
the block cavities at appropriate points around the
foundation walls. The small test holes would also
penetrate into block cavities at appropriate locations
radiating out from the vent holes. Again, some
diagnosticians feel that this type of testing might not
be cost effective unless poor performance of the
initial mitigation system suggests that it is needed.
Measurement of pressure field extension inside block
walls has not been widely used. Thus, its practical
usefulness as a diagnostic test procedure cannot be
confirmed at present.
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Section 6
Selecting and Designing a Mitigation System
6.1 Selecting a Technique
The selection of a radon reduction method for a given
house by the owner or mitigation contractor will be
determined by a number of factors including: the
degree of reduction required; the degree of reduction
that the homeowner is willing to pay for; the desired
convenience and appearance of the installed system;
the desired confidence in system performance; the
construction features of the house; and the results of
the pre-mitigation diagnostic testing. Figure 4
illustrates a number of the decisions involved in
selecting a mitigation approach. Considerations
leading to the choice of specific techniques are
discussed below.
6.1.1 Soil Ventilation
When radon reductions of more than 80% are
required (i.e., when the initial radon levels are above
about 20 pCi/L assuming a target level of 4 pCi/L),
some type of active soil ventilation approach is
usually used. From a risk standpoint, the target level
should be as low as reasonably achievable, rather
than 4 pCi/L. The effectiveness of alternative
techniques to active soil ventilation for achieving such
high reductions is not well demonstrated. If smaller
reductions are sufficient, other techniques can more
readily be considered (e.g., heat recovery ventilators,
sealing of entry routes, or perhaps passive soil
ventilation). These methods are discussed in Section
10. However, if the homeowner is willing to pay the
price, an active ventilation system should be
considered for maximum risk reduction.
The radon reduction approach that has received the
greatest amount of attention to date is active soil
ventilation. If the initial radon concentrations (from an
appropriate follow-up test) are greater than 20 pCi/L
and the homeowner is willing to spend $800 to 2,000,
an active soil ventilation system should be
considered. Also, if maximum reduction regardless of
cost is the goal, active soil ventilation should be
considered. Figure 5 illustrates the considerations
applicable in choosing the most appropriate soil
ventilation technique.
Since drain tile ventilation systems are often the least
expensive and the easiest to install, they are usually
the first choice, if the tiles are present and
accessible. If the drain tile installation is not viable,
the second choice is usually sub-slab ventilation.
The applicability of a sub-slab system depends
primarily on whether there is good air communication
under the slab. If the communication under the slab
and with the walls is poor, the slab has no cracks or
apparent entry routes, the radon levels in the block
walls are very high, and the tops of the blocks are
sealed or are sealable, a wall ventilation system may
be indicated. For poured basement walls with poor
communication under the slab, consider a baseboard
duct ventilation system or, alternatively, a sub-slab
ventilation system with ventilation points about every
20 ft around the perimeter. This spacing assumes
that no detectable communication was observed with
a smoke test. Often, multiple sub-slab points around
the perimeter will compete favorably with point-
penetration wall ventilation systems.
6.1.2 Crawl-Space Ventilation
For a crawl-space house, ventilation of the crawl
space is usually the first option. Figure 6 shows how
to choose the type of ventilation system. If the radon
concentrations in the living space are comparable to
those in the crawl space, the following considerations
will apply. As a rule, reductions by dilution become
difficult when the required reductions exceed 90%.
Consequently, when the radon concentrations in the
crawl space exceed about 40 pCi/L, an alternative to
simple dilution should be considered. When the
concentration in the living space is much less than
that in the crawl space, this critical value, 40 pCi/L,
could be somewhat greater. The first alternative to
simple dilution might be to cover the soil with an
impermeable film and ventilate the soil beneath the
film. Six mil polyethylene film is often used for this
purpose. Although the film has proven adequate so
far, its durability is unknown. In principle, this
technique is very similar to sub-slab ventilation.
Whether it is necessary to seal the edges of the film
and overlaps depends on the radon level, the
permeability of the soil, the number of piers, and the
size of the crawl space. For maximum efficiency in
radon reduction, both (edges and overlaps) should
always be sealed.
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Figure 4. Selecting a mitigation approach (see Table 1 for a summary of the mitigation techniques).
Radon
Concentration Greater
Than 20 pd/L
Basement
or Slab
House
Basement
or Slab
House
7
Crawl-Space
House
Consider
Crawl-Space
Ventilation
Sec 6 1.2, 102
Maximum
Radon Reduction
Desired
7
Homeowner
Willing to
Spend $800 - 2,000 on
Mitigation
System
Close Known
Entry Routes
Central
Air Circulation
System
Basement
Tight
Consider Soil
Ventilation
Sec 61 1,7 1-7.4
Radon
Concentration
Less Than
10pCi/L
7
Consider
Natural or
Forced Ventilation
Sec. 103
Consider Basement
Pressunzation
(sealing or passive
ventilation may also
be viable)
Sec 62,1052
(Sec 104, 10 1)
Consider Heat
Recovery
Ventilation
(sealing or
passive ventilation
may also be viable)
Sec. 10.3
(Sec. 10.4, 10.1)
38
-------
Figure 5. Choosing a method of soil ventilation (details of these installations are presented in Section 7).
With Any Soil Ventilation
Method, Close Sumps, as Well
as Major Cracks and Openings
Dram
Tile Present and
Accessible
Interior
Footings or
Fireplaces
Tiles
Drain to
Sump
Install Tile
Ventilation
System in Sump
No (or unknown)
Install Sub-Slab
Ventilation System
Install Drain Tile
Ventilation System
on the Outside
Install Sub-Slab Ventilation
Points Around Perimeter
(add supplemental wall
ventilation if necessary)
Install Baseboard
Ventilation or Sub-Slab
Ventilation with Multiple
Points at Perimeter
Good
Communication
Under the
Slab
Block
Basement with
Elevated Radon
Levels in
Walls
Poured
Basement with No
Cracks
7
Consider
Alternative
Approach
39
-------
Figure 6. Choosing a crawl space ventilation system (for additional information see Section 10.2).
To Ventilate a Crawl Space, Close
Major Openings Between Crawl
and Living Spaces
Yes
No
Radon
Concentration in
Crawl Space Greater
Than 40 pCi/L
Crawl
Space Could be
Allowed to
Freeze
Floor
Unsuitable for
Poly Film and Crawl
Space is Fairly
Tight
Yes
Cover Floor with
Poly Film and
Ventilate by
Depressunzmg
Under the Film
Yes
Isolate from Living Space,
Insulate Critical Components,
and Ventilate. If Natural
Ventilation is Insufficient,
Increase it by Blowing Air
from Inside to Outside
Close Openings and
Depressunze the
Crawl Space
40
-------
One important consideration relating to crawl-space
ventilation is whether the crawl space can be allowed
to freeze. If certain components such as water lines
and fuel lines can be insulated (heat tracing may be
required), allowing the remainder of the crawl space
to freeze, then a possible mitigation technique is to
isolate the crawl space from the living space, insulate
critical components, and ventilate the crawl space. If
natural ventilation is insufficient, it can be increased
by blowing air from inside to outside. Exhausting air
from inside the crawl space may result in a slight
depressurization which ensures that the flow of
crawl-space air to the living space is not increased.
This does not mean that pressurization of the crawl
space would not prevent radon entry in many cases.
Experience with crawl-space pressurization,
however, is very limited. If the crawl space cannot be
allowed to freeze and sub-film ventilation is not
appropriate, but it is relatively leaktight, then all
openings should be closed and the crawl space
depressurized or pressurized.
Depressurizing the crawl space is likely to increase its
radon concentration. Consequently, this technique
should not be applied when the crawl space is
entered often; for example, when the washer and
dryer are located there. This technique also should
not be used when the air circulation system has the
cold air return ducts in the crawl space. In fact, no
technique that allows high concentrations of radon in
the crawl space should be used when the cold air
return ducts are located there because radon could
be transported into the living space through leaky
return ducts.
Where the living space can be effectively isolated
from the crawl space, it may be possible to reduce
the radon significantly by reducing the
depressurization in the crawl space using a single
vent to the outside without inducing freezing in the
crawl space. This would work only in mild climates
and for soils with moderate concentrations of radon.
6.1.3 Basement Pressurization
An alternative to depressurizing under a basement
slab to reverse the direction of flow of soil pas is to
pressurize the basement relative to the sub-slab
region. Many basements are not appropriate for this
technique. Figure 7 illustrates how to decide whether
to apply basement pressurization. If it is impractical to
isolate the basement from the living space, then
basement pressurization will not be practical. Open
stairwells between the upstairs and the basement as
well as fireplaces or woodstoves in the basement are
examples in which basement pressurization would be
impractical. If the heating and/or air conditioning
(HAC) system is a forced air unit, it will probably not
be possible to isolate the basement; hence basement
pressurization will not be applicable. A fireplace or
woodstove in the living space would make it
impractical to pressurize the basement by blowing air
from upstairs into the basement. It might be possible
in some circumstances to blow outside air into the
basement. The most straightforward test for
determining the applicability of basement
pressurization is a blower door test between the
basement and either the upstairs or the outside,
whichever is considered the source of air. A rule of
thumb is that basement pressurization will not be
practical unless a positive pressure of at least 5 Pa
can be sustained with a flow rate of not more than
300 cfm under the most challenging conditions. If the
test is performed during the winter, the most
challenging conditions would presumably be simulated
by operating all the air-exhausting appliances in the
basement during the test.
6.2 Designing the System
The principles of design are to maximize the
performance of the system while minimizing both the
installation and the operating costs. For a soil
ventilation system, the soil gas is prevented from
entering the house either by directing it away from the
house by pressurizing the soil under the slab or by
collecting it in a ventilation system and exhausting it
away from the house (preferably above the eaves).
The bulk of EPA's experience has been with the latter
type of ventilation system. Limited experience
suggests that pressurization works well only in high
permeability soils which allow sufficient air flow to
dilute the radon under the slab without increasing the
pressure to force more soil gas into the basement.
The presence of a good aggregate layer may not be
sufficient to ensure good movement of soil gas away
from the house.
The construction details of the house will nearly
always be important to the design of a mitigation
system. The location of doors, windows, and other
structures inside the house, the location of potential
entry routes, the degree of wall and floor finish, the
permeability under the slab, and, of course, the
substructure type will all influence where the
ventilation points can reasonably be located, and
where they need to be located in order to maintain
adequate sub-slab depressurization at all significant
entry routes. Many of these features will also
influence the location of the exhaust pipe for a
ventilation system. If the house is a slab on grade
with a highly finished interior, lack of access from the
interior could suggest that the ventilation points be
inserted under the slab from outside the house
through the foundation wall below slab level rather
than penetrating through the slab from inside the
house (more studies are planned on this method).
6.2.1 Primary Considerations
For a depressurization system to be highly effective, it
must treat all the soil gas entry routes in the
substructure of the house. The most efficient system
41
-------
Figure 7. Deciding whether to use basement pressurization (additional considerations are discussed in 'Section 10.5.2).
Open
Stairwell
Between Upstairs
and Basement
Fireplace
or Woodstove in
Basement
Forced
Air MAC
Perform Blower Fan Test
Between Outside and
Basement, Pressurizing
the Basement
Fireplace
or Woodstove on
Upper Level
Consider an
Alternative
Mitigation
Method
Perform Blower Fan
Test Between Upstairs
and Basement, Pressurizing
the Basement
Operate the Air
Circulation Fan and
Clothes Dryer During Test
Operate the Air
Circulating Fan and
Clothes Dryer During Test
Positive
Pressure Greater
Than 5 Pa and Flow
Less Than 300
cfm
Positive
Pressure Greater
Than 5 Pa and Flow
Less Than 300
cfm
Pressurize
Basement from
Outside
After
Retest, Pressure
Greater than 5 Pa
and Flow Less Than
300 cfm
Pressurize Basement
from Upstairs
After
Retest, Pressure
Greater than 5 Pa
and Flow Less Than
300 cfm
42
-------
would maintain sufficient flow to direct the soil gas
away from all the entry routes, but not sufficient flow
to extract any excess indoor air through those same
entry routes. Extracting excess indoor air adds to the
operating costs both in energy to move the excess air
and in an energy penalty for removing treated indoor
air. Practically, some of these increased operating
costs must be accepted in order to obtain an
operating margin of safety in the design of the
mitigation system. Since the natural driving forces
which control the radon entry rate vary significantly
from hour to hour and from month to month, the
minimum fan speed required to prevent radon entry
varies accordingly. At present, a mitigation system
has not been developed with sensing and feedback
controls to allow the speed of the fan to adjust to the
current strengths of the driving forces. It is not
currently known whether such a system would be
practical or cost-effective. The present philosophy is
to design the mitigation system to handle the most
challenging set of circumstances that it is likely to
experience during the annual cycle of variations.
For U.S. houses, the typical air exchange rate is in
the range of 0.5 to 1.0 air changes per hour (ach).
For a house with 1500 ft2 of floor space and
exchange rate of 1.0 ach, the infiltration rate is 200
ft3 per minute (cfm). Some researchers have
estimated that as much as 20% (5% is probably
more typical) of the infiltrating air in some houses
may be soil gas (i.e., infiltration below grade). In that
case, the above example would have about 40 cfm of
soil gas entering the house. An effective mitigation
system would then be expected to handle at least 40
cfm of air flow. However, to treat the entire slab from
a central point would probably require a greater flow,
because the average pressure difference imposed
across the slab to compensate for the naturally
occurring driving forces must be higher. The imposed
pressure difference decreases significantly from the
central ventilation point to the perimeter of the house.
In fact, the induced pressure due to the mitigation
system must compensate for the natural driving
forces at the most remote entry point. Consequently,
entry points closer to the ventilation point will
experience pressure differences considerably in
excess of that required to compensate for the natural
driving forces. The amount of excess indoor air
extracted through the nearby soil gas entry paths
increases with the increased pressure difference
imposed along the gas flow paths. Consequently, if
the sub-slab is to be ventilated through a single
central point, the required fan capacity will probably
exceed the rate at which the soil gas initially enters.
This emphasizes the importance of sealing all entry
routes to minimize the amount of house air that is
removed.
6.2.2 Phased Approach
Often, it will be cost effective to select and design the
radon reduction system for installation in phases. It
will sometimes make sense to begin by installing the
simplest, least expensive mitigation which offers
reasonable potential for achieving the desired radon
reductions. The system could then be expanded in a
series of pre-designed steps, until the desired
degree of reduction is achieved. The alternatives to
this phased approach include performing increased
diagnostic testing beforehand (at an increased cost)
to ensure an improved initial system design, or
installing a more extensive (and more expensive)
mitigation system to begin with, to ensure that radon
levels will be sufficiently reduced on the first try.
The cost effectiveness of the phased approach,
versus efforts to reduce phasing by increased
diagnostics and/or more extensive initial systems, will
have to be determined case by case. This decision
will be based on the judgment of the
diagnostician/mitigator and the desires of the
homeowner. In practice, some phasing will sometimes
be unavoidable. Even with increased diagnostics and
more extensive initial systems, the initial installation
still might not achieve the desired reduction.
Some of the initial, simple steps that homeowners
might take can be considered the first phase of
mitigation, to the extent that such steps are
permanent (e.g., closure of entry routes and airflow
bypasses). A more serious effort of sealing entry
routes as a reduction technique will often turn into the
first phase of the mitigation technique (sealing as a
technique is discussed in Section 10.4). A few other
specific examples of phasing are suggested below for
illustration.
1. A house having slightly elevated radon levels (20
pCi/L or less) has an open sump with
substantially elevated levels inside the sump,
suggesting that the sump could be the
predominant source. Sealing the top of the sump
and passively venting the enclosed sump to the
outdoors could be implemented prior to any more
extensive measures. Additional known entry
routes would also be sealed.
2. A house with slightly elevated radon levels has
only a partial drain tile system. If the drain tile is
easily accessible, ventilation of the partial tile
system could be applied readily. This effort would
be encouraged if good aggregate were known to
exist under the slab. If this installation were not
fully successful, sub-slab ventilation points could
be added where the drain tile was missing.
3. A house for which sub-slab suction would
appear to be the preferred approach has a
basement which is partially finished. Unless there
is an obvious major source in the finished section,
43
-------
it might be both cost effective and convenient for 4. A basement house with hollow-block foundation
the homeowner if an initial sub-slab suction walls and high radon levels might ultimately
system is installed with ventilation points only in require ventilation of both the sub-slab and the
the unfinished portion. If this system turns out to wall void network. The initial installation might be
be insufficient, then appropriate ventilation points designed to depressurize the sub-slab, with
can be added in the finished section of the treatment of the wall voids added later, if needed.
basement.
44
-------
Sect/on 7
Installing a Mitigation System
Some mitigators use local contractors to install the
radon reduction system in a house. The installation
process should be supervised by the
diagnostician/mitigator, or by someone else familiar
with the principles of the system being installed.
While some steps might seem inconsequential to an
installer who is unfamiliar with the principles of the
technique, these steps might be very important in the
system's ultimate performance. For instance, if an
objective is to mortar closed the partially visible open
top voids in a block foundation wall, then it is
important that the mortar be forced all the way under
the sill plate so that the entire void is closed.
Mortaring only the exposed part of the void would
greatly reduce the effectiveness of the closure. It
would be very difficult to check on the completeness
of this mortaring job, or to get mortar into any
unclosed segment of the void under the sill plate,
once the mortar in the visible part of the void had
hardened.
As a practical matter, many detailed decisions
regarding the precise configuration of the system will
often be made during installation. For example,
unanticipated obstacles might be encountered as the
installers drill or dig into places the diagnostician
could not see during inspection. A run of piping for an
active soil ventilation system might not fit around
existing features of the house exactly as visualized
during initial design. Therefore, the supervisor of the
installation crew must ensure that any detailed
adjustments made during the installation phase are
consistent with the principles of the technique, so that
performance is not reduced, and installation is
consistent with the desires of the homeowner for a
neat, attractive appearance.
7.1 Drain Tile Ventilation Installed
Outside
Drain tiles are pipes intended to collect water and
drain it from around the foundation of a house.
Because the drain tiles are located near the floor/wall
joint, a prominent soil gas entry route, ventilation of
these pipes is often very effective in reducing radon
levels in the house. Sometimes drain tiles also extend
under the slab. If the tiles extend under the slab, or if
the communication under the slab is good, tile
ventilation can effectively treat the entire sub-slab
region. Water collected by the tile system will be
drained to a point above grade, to a dry well, or to an
interior sump. If an extensive drain-tile network is
present, then drain-tile ventilation should be one of
the first reduction techniques considered. Even if the
drain-tile loop is not complete, this technique can be
very effective in reducing the radon levels.
First consider the situation in which the tile system
drains to a point above grade. Such an installation is
illustrated in Figure 8. The circle beside the footing in
Figure 8 represents the cross section of a drain tile
which, ideally, forms a continuous loop around the
perimeter of the house. The ventilation system,
consisting of the trap and riser with the fan, is
installed by the mitigator in the discharge line that
drains the water from the collection loop. The trap
ensures that the fan ventilates the loop near the
footings rather than drawing air from the discharge
point. The removable plate on the riser allows the
homeowner to add water to the trap during dry
periods. A water hose connection or even a
permanent water line could be installed. The
permanent water line should be installed underground
to avoid freezing. If the trap becomes dry enough to
allow air to pass through, the ventilation system will
become ineffective. To decrease the likelihood that
the trap will dry out, the vertical arms of the traps
should be made as long as practicable. A useful
alternative to the water trap is to install a reverse flow
valve on the above-grade discharge end of the drain
pipe. This reverse valve eliminates the concern over
the trap's drying out. Some drain-tile systems have
more than one discharge line. All discharge lines
must have traps installed. So long as all the tiles are
connected, only one fan is required. Note that the
trap must always be on the drain discharge side of
the fan. In fact, while the traps must be installed in
the drain discharge lines, the fan can be installed as
shown in Figure 8 or anywhere in the loop. However,
it is usually cheaper to install the fan at the same
location as the trap. Although one is not shown in the
figure, it is advisable to install an alarm to announce if
the trap goes dry, if the reverse valve fails, or if the
fan becomes ineffective for any other reason.
45
-------
Figure 8. Drain tile ventilation where tile drains to an above-grade discharge.
Exhaust (preferably released
above eaves)
Note
1. Closure of major
slab openings is
important
Riser Connecting
Dram Tile to Fan
;•.;?•"Ł,' Footing -'.».•'.'%••}>'.:'•
vy^-^y^^v*
ta*^V;^:'tt*!#r:
Reverse
Flow
Valve
(alternative to
the water trap)
./"•> ' -L ^.V'Jj
4- Existing Drain
.*• y.. .-L y.-. '•• y. j
Tile Circling the
Above-
Grade
Discharge
Water Trap to Prevent Air from
Being drawn up from Discharge
46
-------
After the discharge line is exposed, a section must be
removed to allow the trap and riser to be inserted.
The trap, riser, and connections must be airtight so
that the effectiveness of the fan is not reduced.
Consequently, the trap and riser cannot be made of
perforated pipe like the drain tiles. The trap can be
purchased as a unit or constructed from elbows and
tee's cemented together. The longer the vertical arms
of the trap, the longer the time required for all the
water to evaporate.
The distance from the house to install the trap and
fan depends on aesthetics (whether the riser can be
hidden by shrubbery, etc.), whether the noise of the
fan can be isolated by distance, and the length of
electrical cable required to run the fan. Consideration
should also be given to whether people will spend
much time in the vicinity of the exhaust. If so, the
exhaust should be elevated above breathing level to
aid in dispersing radon-laden gas or made
inaccessible by shubbery, etc. If the exhaust is near
the house, it is recommended that it be extended
above the eaves. Whether the exhaust is mounted on
the roof or away from the house, consideration should
be given to the possibility that it could become
covered either by debris or by snow and ice. The fan
should be durable and resistant to weather conditions,
capable of sustaining a pressure differential of 0.5 -
1.0 in. WC (124 - 248 Pa) at a flow rate of 150 -
200 cfm (0.071 - 0.094 cms).
7.2 Drain Tile Ventilation Installed in a
Sump
Drain tile ventilation systems are installed somewhat
differently when the tiles drain to an interior sump.
Figure 9 illustrates such an installation. Although the
figure shows the tile loop outside the footings, it may
be located on the inside or both. If there is a history
of water problems, a sump pump is likely to have
been installed already. However, just because a sump
is present does not necessarily mean that the exterior
tiles drain into the sump. If the homeowner does not
know whether the tiles drain into the sump or if
additional exterior drain lines exist, their presence can
be learned only by observation and conducting tests
such as those using tracer gases or a plumber's
snake. When the sump is covered, as shown in
Figure 9, it is recommended that the existing sump
pump be replaced by a submersible pump if such a
pump is not already present. The submersible pump
is recommended to avoid problems with corrosion of
the pump motor and/or for ease of sealing the sump.
For the sump ventilation to be effective, the cover
must be sealed airtight. Figure 9 shows a flat cover
with penetrations. This cover can be made of sheet
metal, plywood, or another suitable material. It will
usually be convenient to fabricate the cover in two
pieces so it can be fitted around the pipes which
penetrate the sump. The possibility of needing to
service the sump pump should be taken into
consideration when designing the sump cover. Caulk
and sealants can be used to ensure an airtight fit.
The cover should be secured to the floor with
masonry bolts. If water sometimes enters the sump
from the top of the slab, then an airtight seal that
allows water to drain must be installed. A drain with a
water trap can be used for this purpose (EPA88a,
Br87, Bro87a, Sc87). While water traps are relatively
simple to install, they are effective only so long as
they retain water. Alternatively, waterless traps are
also available. As an alternative to constructing a
sump cover, complete airtight sump units can be
purchased to replace leaky, incomplete sumps, or
where sump holes have been left for sump installation
at a later date.
The ventilation pipe that penetrates the sump cover
must extend up through the house shell to exhaust
the soil gas extracted through the sump. Figure 9
shows two alternative exits for the exhaust pipe. In
one, the pipe penetrates the house shell through the
band joist and extends up outside the house. It is
recommended that the exhaust be above the eaves of
the house and away from windows in such an
instance. In the other case, the pipe extends up
through the house to the roof and exhausts the soil
gas above the roofline. Where the pipe penetrates the
roof, the fan should be mounted either in the attic or
on the roof. Mounting the fan on the roof is preferable
because both noise and the risk of leaking radon
back into the house are reduced (no part of the pipe
inside the house is under positive pressure).
However, the roof-mounted option is more
expensive and exposes the fan housing to the
elements.
To reduce pressure losses in the pipe, the number of
turns and length of pipes should be held to a
minimum. Unfortunately, one has limited control over
the location of the ventilation point in the sump.
Consequently, the least tortuous path acceptable to
the homeowner should be chosen. Typically, the
homeowner will insist that the exhaust pipe pass
through an upstairs closet. The pipe must be
supported with mounting brackets either on the
basement wall or at the floor penetrations. Horizontal
piping runs should be supported by clamps or
brackets attached to floor joists. Pipe joints must be
completely airtight and should be leak tested. Further,
horizontal runs of pipe should be sloped slightly so
that condensed water can drain to the ground or to an
outside drain. It is imperative that no traps or low
points exist in the line. If a natural trap exists in the
exhaust line, condensed water can collect and block
the air flow.
47
-------
Figure 9. Drain tile ventilation where tile drains to sump.
Exhaust
To Exhaust Fan
Mounted in Attic
or on Roof
Outside
Fan
(optional)
Optional
Piping
Configuration
Drip
Guard
Sealant
Note:
1 Closure of major
slab openings is
important.
Slope Horizontal
Leg Down
Toward Sump —
ri"- Footin9 :- .*
t:*"?v
-------
7.3 Sub-Slab Ventilation Installed
Through the Floor
While drain tile ventilation may be the first choice in
some circumstances, sub-slab ventilation is by far
the most widely applicable soil ventilation technique.
In reality, the two techniques represent variations on
the principle of diverting soil gas from entering the
substructure by changing the direction of movement
of the soil gas. The sub-slab ventilation technique
attempts to treat the entire region under the slab,
taking particular advantage of the communication in
the aggregate bed when one is present. A typical
penetration through the slab directly into the
aggregate bed is illustrated in Figure 10. Options for
exhausting the soil gas above the eaves of the house
include either penetrating through the roof from inside
the house or extending the exhaust pipe outside the
house. The options for installing the exhaust are very
similar to those discussed above for sump ventilation
(Figure 9).
The greatest concern with sub-slab ventilation arises
when the communication under the slab is poor.
However, the inability to measure air movement under
the slab is no guarantee that sub-slab ventilation will
not work. It has been demonstrated on several
occasions that sub-slab ventilation can be effective
in spite of the failure of an air communication test. A
similar instance recently occurred with four slab-
on-grade houses in Dayton, Ohio. These houses
have heating ducts under the slab which appear to
block communication. However, installed sub-slab
systems were effective.
If an unused sump is present with openings under the
slab and communication under the slab is good, the
simplest option is to cover and ventilate the sump. If
no sump is present, or communication tests indicate
that multiple ventilation points are needed, then it is
necessary to make holes in the slab. A number of
methods are available to do this. The difficulty of
making a hole through the slab is determined by the
size of the hole that is needed. In EPA's experience,
the ventilation system usually consists of 4-in. PVC
pipes.
The easiest way to cut holes of this size is with a
coring drill, which removes a core of the proper size
for the pipe to fit neatly in the hole. Holes cut this
way are perhaps easier to seal around the pipe.
Coring drills with diamond bits (and the operators to
handle them) can usually be hired from local
construction firms. The bits of these drills are usually
continuously cooled with water and, consequently,
tend to be somewhat messy for use in finished living
areas. It is practical in most cases to make a 4-in.
hole using small bits. For instance, a circular pattern
can be made by drilling small (1/4 to 1/2 in.) holes
with a masonry drill and then knocking the center out
with a chisel or a rotary hammer (Sa87). If a larger
hole (1 to 2 ft2) is required, a jackhammer may be the
proper tool. Although electrically driven hammers can
be rented, they may not always be powerful enough
to break through the concrete. In some cases a more
powerful jackhammer handled by an experienced
operator may be required. A jackhammer might be
necessary when the sub-slab communication is so
poor that an excavated pit around the ventilation point
would improve the pressure field extension (EPA88a).
This type of installation is illustrated in Figure 11. In
this case a 2-ft2 hole is made in the slab and a large
cavity is excavated in the soil. Alternatively, if a core
drill and 4-in. bit are available, eight 4-in. adjacent
holes forming the outline of a 1 -ft square can be
quickly opened. The center can then be knocked out
to open a 1-ft2 hole. The pit is covered with plywood
and the vent pipe installed with the end extending
slightly into the pit. The hole in the slab is then
repoured to seal the vent pipe in place. Note that the
plywood is supported by aggregate and that the hole
in the concrete was jackhammered with a slope
around the edge so that the weight of the new
concrete will ultimately be supported by the original
slab. An alternative to leaving a large open pit would
be to fill the pit with coarse aggregate (2-in. stone).
The permeability of coarse aggregate is high enough
that the pit's effectiveness would not be compromised
significantly. If aggregate is used, it should be
covered with a material such as polyethylene liner to
keep wet concrete from plugging the aggregate. The
vent pipe would penetrate the film. The purpose of
the pit is to distribute the region of depressurization
over a larger surface of the soil resulting in better
extension of the pressure field into the surrounding
soil. The diagnostician/mitigator and homeowner must
weigh the advantages and disadvantages of
aesthetics and cost of sub-slab ventilation pits
against additional ventilation points installed in holes
drilled in the slab. The type of pit excavation just
described is expensive because it is labor intensive. If
soil and not stone exist under the slab, it is practical
to excavate a sizable pit through a 4-in. drill hole. In
this case pits are probably less costly than extra
ventilation points.
Piping used to construct ventilation systems should
be made of plastic such as PVC (thin wall) sewer
pipe for durability, as well as for corrosion and leak
resistance. Flexible hose such as clothes dryer vent
hose is not recommended because it is easily
damaged and not conducive to draining water that
condenses in the line. It will tend to sag under the
weight of condensed water, forming traps which could
result in reduced effectiveness of the ventilation
system. PVC pipe is readily sealed with the
appropriate cement familiar to contractors. It is critical
that the joints in the system be airtight. Before a fan
is installed in a line, it should be leak checked since
the housings of many fans are not designed to be
airtight. All the joints in a system including those
49
-------
Figure 10. Sub-slab ventilation using pipes inserted down through slab.
Exhaust (preferably released
A above eaves)
T/T
Outside
Fan
(optional)
Optional
Piping
Configuration
Drip
Guard
-^ Slope Horizontal Leg
| Down Toward Sub-Slab
Hole
To Exhaust Fan
Mounted in Attic
or on Roof
Connection to Other
Suction Point(s)
Note-
1. Closing of major slab openings
(e g , major settling cracks, utility
penetrations, gaps at the wall/
floor joint) is important
Suction
Pipe
House Air Through Unclosed
Settling Cracks, Cold Joints,
Utility Openings1
•^^>Xi>'K-^-'rif;>'/f;. ?,••!>'.<Ł;J^P
X.V:.V'. ^'^;.;^>>i^;' 4# '••• Ł-:
**-r. Open Hole
• (as large as
. , reasonably
'.• •'. practical)
50
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Figure 11. One method for creating open hole under sub-
slab depressurization point when slab hole has
been created by jackhammer.
Suction
Pipe
Plywood or
Sheet Metal
Restored
Concrete
Undisturbed
Soil . . .' .
regale
Lip of undisturbed
aggregate/soil of
sufficient width to help
support weight of
restored concrete
where the vent penetrates the slab should be leak
tested. If any part of the line on the exhaust side of
the fan is indoors, it should be carefully leak tested
because it will release radon in the house if it leaks.
For this reason, the fan should be mounted in the
attic, on the roof, or outside whenever possible.
Leaks on the intake side of the fan will reduce the
effectiveness of the system by reducing the capacity
of the system to depressurize the soil.
The size of the pipe can also influence system
performance. If the diameter of the pipe is too small,
the fan cannot depressurize the soil because of
increased pressure drop in the pipe. Long runs of
pipe or turns and elbows have a similar effect. Since
small diameter pipe takes up less space and is more
easily hidden, it my be desirable to use small pipe in
some instances. If using smaller diameter pipe is
contemplated, the pressure drop at realistic flow rates
should be computed to estimate its effects on system
performance. In all cases, care should be taken to
ensure adequate support for all pipes and fans
installed. All fans should be mounted vertically to
Wevent water from collecting and all horizontal runs
of pipe should be sloped toward the sub-slab vent
point so that condensed water can drain back to the
soil. If there are any low points in the line that cannot
drain properly, a special drain with a water or
waterless trap or a reverse valve must be installed to
prevent accumulation of water that could impede
performance. If the exhaust line penetrates through
the band joist, the exterior penetration should be
carefully sealed and a drip guard installed to prevent
rainwater's running down the pipe and damaging the
band joist. Consideration should be given to
preventing the exhaust from blockage by birds' nests,
bees' nests, or debris. Vents through the roof should
be capped with a rain guard that does not impede
flow. The possibility that the outlet could be covered
by snow accumulation or drifts should also be
considered. In cold climates, insulation might be
needed on the exhaust pipe to prevent ice from
blocking it.
7.4 Wall Ventilation
Although wall ventilation is discussed here as a
stand-alone mitigation technique, it finds its widest
application as a supplemental aid to methods such as
sub-slab ventilation. Wall ventilation would be a
preferred technique only in special situations such as
no measurable communication under the slab or with
51
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the walls, no apparent entry routes in the slab, and
high radon levels in the walls. For wall ventilation to
be applicable, all major wall openings must be closed
and there must be no major slab entry routes away
from the wall. There are two types of wall ventilation
installations: point-penetration systems and
baseboard duct systems. Baseboard duct systems
are more expensive and find fewer applications than
point-penetrations systems.
Point-penetration systems attempt to ventilate the
wall void networks by inserting individual pipes into
void cavities at various points. Each block wall,
interior or exterior, that rests on a footing should have
at least one vent pipe. The fan can be oriented to
either pressurize or depressurize the wall void
network. Because of their high porosity, untreated
block walls often require high flow rates to
depressurize the void network, resulting in
depressurization of the basement. Problems with
backdrafting of combustion appliances and increased
radon flow through slab entry routes can occur when
the basement is highly depressurized by wall
ventilation. There is some concern that pressurization
of the wall might increase radon entry through some
points. There have been some instances in which
sub-slab pressurization increased radon entry
(Se87), thus illustrating the potential for adverse
effects of pressurization, even in block walls.
Concerns also exist that wall or sub-slab
pressurization could increase indoor air levels of other
contaminants such as termiticides or biological
components. Moisture condensation and freezing
around footings is another potential concern with wall
pressurization. Although the Agency's experience is
limited, EPA has had some success in reducing radon
levels by both pressurizing and depressurizing block
walls (He87a, Sc88).
Usually one block wall does not communicate very
well with the wall sharing a common corner.
Consequently, at least one ventilation point per wall is
recommended. EPA's limited experience with block
wall ventilation suggests installing at least two
ventilation points in a wall that is longer than about 25
ft (He87a, Sc88). Ventilation points in a wall are
typically placed to treat equal surface areas (one
point located in the center, two points located a
quarter of the way from each end). Walls with
fireplaces might need an extra vent point. If diagnostic
measurements have identified certain walls as having
particularly elevated radon concentrations, additional
ventilation points might be advised for those walls. If
the wall ventilation system is supplemental to a sub-
slab system, only the identified "hot" walls may
require a ventilation point. Wall ventilation points
should be placed near the bottom of the wall to
enhance the treatment there.
For installation, a hole will be drilled or chiseled
through one face of a single block into one of the
cavities of the block. The ventilation pipe inserted into
the block cavity must be well sealed to prevent air
leakage around the pipe. Caulk or asphaltic sealant
should be worked into the gap to form a good seal.
The considerations relating to sizing the pipes are
same as those for the other ventilation techniques.
7.5 Methods of Closing the Top Row of
Blocks
Closure of major openings is important in all soil
ventilation systems. It is especially important with wall
ventilation because the flow rates through the walls
tend to be high anyway. Open voids at the top of the
wall make wall ventilation impractical if they cannot be
closed. Fortunately, in many areas, the building code
requires a row of solid cap blocks. When cap blocks
are not present, closing the openings can present
quite a challenge.
If the sill plate leaves sufficient access to the
openings (perhaps 4 in.), the recommended
procedure is to stop each void with crumpled
newspaper (or some other suitable support) and fill it
with mortar to a depth of at least 2 in. The mortar
must be forced under the sill plate and worked to
ensure complete sealing of the hole. This procedure
is illustrated in Figure 12a.
If the sill plate allows sufficient space (1 to 3 in.) to
force newspapers into the void, but not sufficient
working space to ensure that the mortar completely
fills the void, an expanding foam such as a single-
component urethane foam can be substituted for the
mortar. These foams are available in aerosol cans or,
for commercial applications, can be extruded through
a hose and nozzle. Such a void is also illustrated in
Figure 12a.
If the top of void is not sufficiently accessible to force
newspaper or some equivalent supporting material
into the opening, closure becomes much more
difficult. A hole could be drilled in the block to inject
the foam; however, the foams tested by EPA were
not sufficiently self-supporting to remain in the top of
the void while they cured. In some cases supports for
the foam can be improvised. For instance, it has been
suggested that balloons be inserted into the cavity
through drilled holes and then inflated to support the
foam. It has also been suggested that dowel pins be
inserted through a series of small, closely spaced
holes to support the expanding foam. Another
suggestion was to saw out the first mortar joint to a
depth of a few inches, allowing plastic, cardboard, or
sheet metal supports to be inserted through the slots.
Although some of these techniques could be made to
work, they are judged to be too expensive to be
practical.
52
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Figure 12. Some options for closing major wall openings in conjunction with block wall ventilation.
Siding
Sheathing
Wallboard
Floor
Band Joist
Sill Plate
Concrete Block
Mortar/Foam
to Close Void
Crushed
Newspaper Support
Top Void
a) Closure of top void
when void is reasonably
accessible.
Siding
Sheathing
Wallboard
Floor
Band Joist
Coated Wood Strip
to Close Void
Sill Plate
Top Void
Concrete Block
b) One option for closure
of top void when a
fraction of an inch of
the void is exposed.
- Veneer Gap
m^
Sheathing
Brick Veneer
. Wallboard
. Band Joist
Floor
Drilled Access Hole
Closure Plate
Coated Wood Strip
to Close Void
Sill Plate
Foam to Close
Veneer Gap
Concrete Block
c) One option for closing gap
between exterior brick veneer
and interior block and sheathing.
53
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When the top void was inaccessible, EPA has
successfully used the sill plate to close the tops. In
cases in which the openings along the edge of the sill
plate were sufficiently small, a bead of caulk was
used to seal between the sill plate and the block.
When the openings along the edge of the sill plate
were too large to be caulked, but too small to work
mortar into, a wood strip with caulk on two sides was
nailed to the edge of the sill plate covering the
openings. Both the edge along the block and the
crack between the strip and the sill plate were then
caulked. This technique is illustrated in Figures 12b
and 12c. Although this technique is less effective than
using foam (note that the outside edge of the sill plate
is not accessible for caulking), it is less expensive
and appears to be adequate in many cases (He87a,
Sc88).
7.6 Closing the Gap Behind Brick
Veneer
In houses with exterior brick veneer, a gap usually
exists between the veneer and the sheathing, as well
as between the veneer and the block behind it. This
situation is illustrated in Figure 12c. This gap could
reduce the effectiveness of wall ventilation systems
by allowing air to flow into or out of the block void
network, thus negating the wall depressurization or
pressurization. While it is not clear how often this gap
seriously limits the performance of wall ventilation, it
is clear that effective wall ventilation can be
accomplished in some cases without closing this gap.
For at least one house in an EPA study an effort was
made to close the veneer gap by drilling through the
band joist and extruding urethane foam into the gap.
This procedure is illustrated in Figure 12c. There was
no clear evidence that the foam improved the
performance of the ventilation system.
Obvious holes and cracks in the walls should be
closed using grout, caulk, or other sealants. Examples
are holes around utility penetrations, chinks in blocks,
and mortar joint cracks where pieces of mortar are
missing. Pores in the concrete blocks represent a
significant amount of air leakage. Coating concrete
block walls has not been a standard practice when
installing a ventilation system. However, when
installing a wall ventilation system on cinder block
walls it is advisable to coat the wall to close the pores
(pore closure will also help with concrete block walls).
Cinder blocks are more porous than concrete blocks.
For discussion of the options for closing the pores in
a block wall see Reference EPA88a.
Openings in the slab should be closed to assist a wall
ventilation system in extending the pressure field
under the slab. Of particular concern is the wall/slab
joint. Sumps and major cracks should be closed,
while floor drains should be either trapped or closed.
54
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Sect/on 8
Post-Installation Diagnostics
Diagnostic measurements should be performed to
assess whether the system is performing mechan-
ically the way it is supposed to, and to identify further
modifications that might need to be undertaken to
improve radon reduction.
Post-mitigation diagnostic tests should also be
conducted to ensure that the reduction system is
operating properly. While such diagnostic testing will
vary from mitigator to mitigator, some key tests are:
• Visual inspection of the system to ensure that it
has been installed properly. For active soil
ventilation systems, one particularly useful tool
is a smoke stick. A smoke stick releases a small
stream of smoke which can reveal air
movement. The smoke stick can be used, for
example, to confirm whether pipe joints and
slab/wall closures leak.
• Pressure and flow measurements in the pipes of
active soil ventilation systems and heat recovery
ventilators. Such measurements can reveal
installation and operating problems of various
types.
• Sub-slab pressure field measurements, where
a sub-slab soil ventilation system has been
installed. Such measurements will reveal
whether the system is maintaining the desired
pressure reduction underneath the entire slab.
These measurements can be made with a
micromanometer or with a smoke stick.
• Grab sample radon measurements in individual
pipes associated with active soil ventilation
systems (to identify "hot spots" around the
house), and grab measurements to detect the
location of soil gas entry routes not being
treated by the current system.
• Flow measurements in the flues of existing fur-
naces, water heaters, and other combustion
appliances when an active soil ventilation
system has been installed, in order to ensure
that house air being removed by the system is
not depressurizing the house enough to cause
back-drafting of the combustion appliances.
55
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Sect/on 9
Post-Mitigation Monitoring
9.1 Short-Term Monitoring
After the radon reduction system is installed, a
several-day measurement of radon gas should be
made to give an initial indication of the success of the
system. Possible measurement techniques include
charcoal canisters, E-PERMs, or continuous moni-
tors. One or a few grab samples, by themselves, are
not recommended for the purpose of determining
reduction performance, because the 5-minute
sampling period is considered to be too brief to
provide a meaningful measure. If this initial short-
term measurement indicates adequate reductions,
then it should be followed up by at least one alpha-
track detector measurement. As a minimum, the
measurement should be made over 3 months
(preferably during the winter) to evaluate sustained
system performance. In the event that the mitigation
system is installed doing the spring and a 3-month
alpha track measurement indicates adequate
reductions, it is recommended to begin an annual
average, measurement in the form of quarterly alpha
track measurements. An effort should be made to
have winter months comprise one quarterly
measurement. This quarter should represent the most
challenging period for the mitigation system.
9.2 Long-Term Monitoring
After all modifications/improvements to the radon
reduction system have been completed, a radon
measurement of longer duration than that described
above is recommended. This longer term
measurement will provide a more definitive picture of
how the occupants' exposure has been reduced over
an extended term by the final installation. Since the
EPA guideline of 4 pCi/L is based upon an annual
average exposure, this longer duration, post-
mitigation measurement would ideally cover a 1-year
period. A 12-month alpha-track measurement (or
average of four consecutive quarterly tests) would
give the most reliable measure of annual average
exposure. However, the other methods for making
"follow-up" measurements, as described in the EPA
protocols (EPA87a), can also be considered. These
other methods include charcoal canisters, E-
PERMs, or continuous monitors, used once every 3
months during the year. Grab samples are never
adequate for final characterization of reduction
technique performance.
A disadvantage of a 12-month track-etch
measurement is that the level of performance would
not become known for a year after installation. This
delay is unacceptable. If the technique is not
providing adequate performance, corrective action
should not be delayed for a year. Therefore, it is
recommended that the initial longer duration, post-
mitigation measurement be a 3-month alpha-track
or E-PERM measurement. Although it is preferred
that the test be performed under the challenging
conditions of cold weather, it is not recommended
that the test be postponed several months. However,
it is recommended that measurements be performed
during cold weather at the first opportunity. If the
results of this winter measurement are below 4 pCi/L,
it is probably reasonable to assume that the annual
average levels in the house will be below 4 pCi/L If
the results of the winter alpha-track measurement
are above 4 pCi/L, then a decision concerning further
action is required. If the radon level is sufficiently
high, immediate improvements to the mitigation
system should be considered. On the other hand, if
the radon concentration is only slightly above 4 pCi/L,
it is possible that the annual average might be below
4 pCi/L. The objective should be to achieve as low a
level as practicable.
The positioning of measurement devices inside the
house, and other considerations in the use of the
various measurement techniques, should be
consistent with EPA's monitoring protocols (EPA86b).
Initial, short-term measurements should be made in
the basement under closed-house conditions, in
accordance with the "screening" protocols (EPA87a).
Final, long-term measurements should be made
both upstairs and downstairs under normal living
conditions, in accordance with the "follow-up"
protocols (EPA87a). It is important that both the pre-
and post-mitigation measurements be made using
the EPA protocols, so that the results will be
comparable.
The above discussion addresses measurements
made immediately after, or within the first year after,
57
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installation of the system, for initial verification of
system performance. Homeowners would be well
advised to make periodic measurements on a
continuing basis, after these initial measurements are
completed, to ensure that system performance does
not degrade over the years. An ideal approach would
be to conduct a single alpha-track measurement
each year in the primary living space (or, if preferred,
in the lowest livable area of the house). The alpha-
track detector could be exposed for the entire 12
months, to provide a measure of the annual average
exposure. Some homeowners might consider it more
practical to conduct a 1-year alpha-track mea-
surement every third year or so. The more frequent
monitoring would be appropriate for houses that
initially had high radon levels (greater than 100 pCi/L)
and, consequently, the potential for significant health
risks over a short period of time should the mitigation
system fail.
58
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Sect/on 70
Additional Radon Reduction Techniques
The preceding discussion addressed the overall
approach for implementing radon reduction measures
in houses as well as detailed descriptions of the most
frequently used reduction techniques. The following
discussion summarizes some of the key features
regarding a few of these techniques, but mainly
describes additional reduction techniques that are
less frequently applied. Passive soil ventilation is an
attractive technique whose practicality remains to be
demonstrated. Crawl-space ventiliation, house
ventilation, and sealing are further developed because
of their growing importance as mitigation techniques.
The topics of house pressure adjustments, air
cleaning, removal of radon from well water, and radon
reduction in new construction are discussed to form a
complete list of techniques.
10.1 Passive Soil Ventilation
The active (fan-assisted) soil ventilation approaches
discussed previously might also be considered for
operation as passive soil ventilation systems. This
would dictate that the system be designed to take full
advantage of natural driving forces to create a draft in
the exhaust pipe in the absence of the fan. This
application could represent an example of the phased
approach to design in which a system is first
designed to operate in the passive mode with the
option to add a fan later if needed. Since passive
systems do not use fans, they avoid the maintenance
requirements, noise, and operating costs associated
with fans. These systems rely upon wind-related
depressurization near the house roofline, and the
thermal stack effect (during cold weather) to create a
natural draft in the passive vent stack. Further work is
needed to develop and adapt solar energy techniques
to enhance the natural thermal stack effect as a
driving force for passive ventilation. The depressu-
rization which can thus be established is very small,
relative to that possible with a fan, and a very
effective network for distributing this depressurization
is needed if a passive system is to be able to
maintain sufficient depressurization in the soil.
Installation of such an effective network (e.g., a
network of perforated pipe under the slab with a good
layer of crushed rock) can be expensive if it is not
already in place (e.g., in the form of sub-slab drain
tiles installed when the house was built). In addition,
since depressurization levels are so low, a passive
system would be more likely to be overwhelmed
when the house is depressurized by weather or
occupant activities. The performance of passive
systems could thus be more variable over time than
that of active systems. In addition, passive systems
can rarely if ever reduce radon levels to as low values
as can active systems.
Insufficient data exist to permit a reliable assessment
of the long-term performance and cost-effective-
ness of passive systems. Thus, although the potential
benefits of maintenance-free passive systems are
apparent, their performance is too uncertain for them
to be recommended until more information becomes
available. If a fairly substantial piping network is
already in place (such as sub-slab drain tiles), the
ventilation system that is installed connecting to these
tiles might initially be designed and operated in a
passive mode to determine if passive operation is
sufficient. However, performance should be monitored
closely, and conversion to an active system
undertaken if passive operation proves to be
insufficient.
10.2 Crawl-Space Ventilation
Crawl spaces are a major type of substructure.
Crawl-space houses have living space built over an
enclosed area that is usually exposed earth. Even if
the living space appears to be well separated from
soil gas by the crawl-space volume, these houses
often have elevated radon levels. In some cases the
radon-laden soil gas is transported through the
foundation wall into the house. More often, however,
the crawl-space air contains high concentrations of
radon, which enters the house through leaks in the
floor. When the air circulation system has return
ducts in the crawl space, this system can be a major
transporter of radon into the house. This happens
because the return ducts are often very leaky. When
the return ducts are depressurized by the operation of
the circulation fan, crawl-space air containing high
radon concentrations flows into the return plenum and
is transported to the outlet vents. This effect is
especially pronounced when a part of the return duct
and plenum has been formed by enclosing the floor
joist with sheet metal. Much air can leak into these
59
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pan ducts. Although it is very difficult, if not
impossible, to seal these leaky return ducts once they
are in place, tape and caulking can be used to close
those major leaks that are accessible.
The general strategy for reducing the radon levels in
a crawl-space house is to isolate and ventilate.
Isolation is accomplished either by sealing the
interface between the living space and the crawl
space, or by separating the soil from the crawl space
using an impermeable film such as polyethylene.
Ventilation is accomplished either by increasing the
air exchange rate in the crawl space or by ventilating
underneath the film.
In some cases, crawl-space air can be diluted
adequately by opening the foundation vents. Even if
the resulting natural (passive) ventilation is not
sufficient, it may be possible to obtain the required
radon reduction by actively blowing air from inside the
crawl space to the outside using a fan. The
foundation vents should remain open to provide
adequate dilution. The primary drawback to this type
of ventilation occurs when the crawl space cannot be
allowed to freeze. In cold climates, the subfloor, water
lines, and fuel lines passing through the crawl space
have to be adequately insulated and, if necessary,
heat traced. In some cases, the increased costs of
heating might make this type of ventilation
impractical. In other cases, the foundation vents may
have to be closed and the crawl space depressurized
by a fan. Even if the radon concentration in the living
space were reduced significantly, the concentration in
the crawl space would increase as a result of the
depressurization. Therefore, this may not be an
acceptable solution. An alternative approach would be
to pressurize the crawl space by blowing outside air
in. If the crawl space is well isolated from the living
space, this pressurization can prevent radon from
entering the crawl space. In practice, this technique
appears to be another example of radon reduction by
dilution. There is a danger that if the living space is
not well isolated higher levels of radon will be forced
into the living space.
For sub-film ventilation, the increased infiltration
should be much less than when the foundation vents
are open with no sub-film ventilation. Ventilation
under a polyethylene film uses an approach similar to
sub-slab ventilation. The intent is to collect and
exhaust to the outside all the soil gas that might
otherwise find its way into the crawl space or the
house. In order to completely isolate the soil from the
crawl space, it is necessary to either tape or bond the
overlapped edges of the impermeable film, and to
seal the edges of the film to the foundation walls. One
method of attaching the film to the wall is to wrap the
edges around wood furring strips and nail the strips
either to the sill plate or to the foundation wall. The
pdint of contact between the wall and plastic can then
be caulked. Penetrations through the plastic film such
as sewer, water, and fuel lines, as well as foundation
piers must also be sealed by taping and caulking. The
better the film is sealed, the less crawl-space air will
be exhausted through the fan, resulting in increased
infiltration of outside air and increased heating costs.
In milder climates, effective sealing of the film may be
less critical. Subliner ventilation has been tested on a
number of occasions (Br87, Bro87b, He87b, Os87,
Sc88, Si87). In many of these installations, perforated
pipe networks were placed between the soil and the
plastic film and depressurized. Although these
systems appeared to work well in most cases,
interpretation of the results was complicated by the
fact that most of the houses had combinations of
crawl spaces with other substructure types.
Consequently, more than one radon reduction method
was operating. More recently, in EPA's Tennessee
Project (Py88) purely crawl-space houses have
been successfully mitigated using subliner ventilation.
10.3 House Ventilation
Natural ventilation (opening of windows, doors, and
vents) is a very effective, universally applicable radon
reduction technique that can be readily implemented
by the homeowner. During mild weather, there is
essentially no cost for implementing this technique. If
done properly, natural ventilation is consistently
capable of high reductions, probably above 90% if a
sufficient number of windows or vents are opened.
The high reductions result because natural ventilation
both reduces the flow of soil gas into the house (by
facilitating the infiltration of outdoor air to compensate
for temperature- and wind-induced exfiltration) and
dilutes any radon in the house air with outdoor air
which is almost radon-free. Proper implementation
of natural ventilation involves ensuring that windows
are open on the lower level of the house; opening
windows on only the upper level might make radon
problems worse by increasing the depressurization in
the lower level. Also, windows should be opened on
more than one side of the house, preferably on all
sides, to provide proper cross-ventilation; under
some conditions, radon levels might be made worse
by wind-induced depressurization if windows are
opened only on the downwind side. Windows and
vents must remain open essentially all the time for
continuous effectiveness. A special case is natural
ventilation of the crawl-space house by opening
crawl-space vents on all sides of the house, creating
a pressure-neutralized buffer zone between the soil
and the living area.
The primary shortcoming of natural ventilation is that
extreme temperatures could make this technique
impractical to use 365 days a year in most parts of
the country, due to discomfort and/or increased
heating (and cooling) costs during winter (and
summer). Open windows can also compromise the
security of the house. One possible way to reduce
the discomfort and energy penalty would be to leave
60
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windows open only an inch or two during extreme
weather, which would reduce the radon reduction
effectiveness. In the case of crawl-space houses,
the crawl-space vents could be left open all year if
water pipes and the subflooring under the living area
were adequately insulated.
If natural ventilation is used during the winter, heating
costs might increase by as little as 10% (if windows
are left open only slightly, or if a crawl space is
ventilated), or by more than 300% if windows in
heated living space are left wide open, which is
generally not practical from a comfort standpoint.
There would be a comparable increase in air
conditioning costs in the summer. In view of the
effectiveness and ease of implementation of natural
ventilation, it is recommended that a homeowner
whose house has elevated radon levels seriously
consider this approach for as much of the year as
possible, at least until some other radon reduction
approach is implemented. Natural ventilation can also
be used in conjunction with some of the other
mitigation approaches.
Rather than relying upon natural air movement,
forced-air fans can be used to provide a controlled
amount of forced ventilation. For example, a fan could
be installed to blow fresh air into the house
continuously through the existing central forced-air
heating ducts and supply registers, with windows and
doors remaining closed. Alternatively, fans could blow
air into the house through protected intakes through
the side of the house, or could be mounted in
windows. A fan could also be installed to blow
outdoor air into a crawl space. Advantages of
forced-air ventilation relative to natural ventilation
include reduction or elimination of house security
concerns that can arise when windows are left open.
Also, the amount of fresh air entering the house could
be controlled. However, a fan system will involve
some initial capital cost, and a continuing cost for
electricity to run the fan(s), which natural ventilation
does not require. Forced-air ventilation can also
result in the condensation and freezing of moisture
inside exterior walls of humidified houses during cold
weather. For a given increase in the ventilation rate,
the increase in the heating and cooling costs will be
the same for either natural ventilation or forced-air
ventilation (without heat recovery).
Natural and forced-air ventilation would be expected
to provide similar radon reductions for a given
increase in ventilation rate, if the forced-air system
effectively distributes the air (including sufficient air
delivery to the lower levels of the house). The same
reduction mechanisms would come into play in both
cases; i.e., reduction of soil gas influx, and dilution.
However, to achieve a comparable increase in
ventilation using fans to match the natural flows which
produce 90% radon reductions, the fans will probably
have to provide at least 750 to 1,000 cfm of fresh air,
and perhaps more, in a house of typical size and
natural infiltration rate. By comparison, an individual
window fan might move about 500 cfm, and a central
furnace fan about 2,000 cfm. If the house shell is
sufficiently tight, inward-blowing forced-air systems
might slightly pressurize the house (or the basement),
providing reductions above those with comparable
natural ventilation.
With forced-air systems, it is crucial that the fan be
oriented to blow outdoor air into the house, because
fans operating to exhaust indoor air could depres-
surize the house and possibly increase radon entry
rates. Typical ceiling-mounted whole-house fans
on the market are designed to operate in the exhaust
mode, exhausting house air into the attic. Whole-
house fans are thus not currently recommended for
radon reduction.
Heat recovery ventilators (HRVs)--also known as
air-to-air heat exchangers—are forced-air
ventilation systems intended to reduce the energy
penalty and the comfort penalty associated with
ventilation. The heated (or air-conditioned) house
air--which would otherwise exfiltrate without any
energy recovery when outdoor air is simply blown into
the house--is exhausted through the HRV,
transferring between 50 and 80% of its heat to the
incoming fresh air. HRVs provide no greater radon
reduction than a comparably sized ventilation fan
without heat recovery. HRVs can be fully ducted, with
supply and return ducts leading to different parts of
the house, analogous to central forced-air furnace
ducting. Alternatively, wall-mounted HRVs are
analogous to wall-mounted air conditioners, without
external ducting.
The applicability of HRVs for radon reduction will
likely be limited to situations where only moderate
reductions are needed. Due to the cost and
commercially available capacities for residential
HRVs, it is believed that no more than 200 to 400 cfm
of HRV ventilation capacity might be installed
practically in a house of typical size. This amount of
ventilation is low relative to what might be achieved
with increased natural ventilation, and could typically
produce radon reductions of 50 to 75%. Thus, if an
HRV were intended to serve as a stand-alone
measure to achieve 4 pCi/L in a house of typical size
and infiltration rate, the initial radon level in the house
could be no greater than 10 to 15 pCi/L. Greater
reductions can sometimes be achieved in tight
houses (i.e., low natural infiltration rates).
HRVs will most likely be cost-effective, relative to
comparable ventilation without heat recovery, only in
areas with cold winters and/or hot, humid summers.
High fuel costs and high HRV heat recovery
efficiencies could also improve HRV cost
effectiveness. For the HRV to be cost effective, the
operating cost savings resulting from the reduced
61
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energy penalty must more than offset the initial capital
cost of the HRV (and the cost of electricity to run the
two fans). Where winters are not particularly cold, or
summers particularly hot, it can prove less expensive
to achieve the desired degree of ventilation simply by
opening windows. It is recommended that, before a
decision is made to install an HRV, the cost
effectiveness of the unit for that part of the country
be determined.
While the overall radon reduction performance of fully
ducted HRVs is usually consistent with the increase
in ventilation rate, the performance in different parts
of the house cannot always be reliably predicted prior
to installation based solely upon the anticipated
increase in ventilation. Air and soil gas flows
throughout the house apparently can sometimes be
affected in a complex manner. Also, performance can
be sensitive to proper balancing of fresh air inlet
versus stale air exhaust flows. This balance can vary
over time (due to dirt or ice buildup in the HRV core,
to changes in wind velocity, or to changes in
occupancy habits such as opening doors). The
homeowner must conduct the maintenance that is
required (e.g., cleaning or replacing air filters,
cleaning the core, annual rebalancing of flows). A
word of caution is in order; balancing HRVs is tricky,
and only individuals thoroughly familiar with their
operation should attempt balancing them.
HRVs are typically balanced such that the inlet and
outlet flows are equal, which is the condition providing
the best heat recovery performance. Under these
conditions, the HRV will generally not reduce the
influx of soil gas, an important mechanism for radon
reduction in the cases of natural ventilation and
forced-air ventilation without heat recovery.
Balanced HRVs reduce radon by the dilution
mechanism only. If the HRV is deliberately operated
in an unbalanced mode, with the inlet flow being
greater than the exhaust, it could contribute to
neutralization of the pressure between indoors and
outdoors (or perhaps even to pressurization of the
house), reducing soil gas influx. Unbalanced operation
would reduce the energy efficiency of the system.
There are not sufficient data to confirm whether such
unbalanced HRV operation--or whether HRV
ducting configurations designed to pressurize a
basement-can consistently improve HRV radon
reduction performance.
10.4 Sealing
The term "sealing," as commonly used, can have two
different meanings from the standpoint of this
document. In the first meaning, sealing refers to the
treatment of a soil gas entry route into the house in a
manner which provides a true gastight physical barrier
to soil gas. Such a barrier is intended to prevent the
convective movement (and sometimes the diffusive
movement) of soil gas containing radon from the soil
into the house through the treated entry route. In the
second meaning, the term is used to refer to
treatment of entry routes in a manner which prevents
most gas flow through the route, but is not truly
gastight. Such treatment is referred to in this manual
as "closure" of the entry route, rather than true
sealing. As discussed later, the purpose of the entry
route treatment determines whether true sealing is
required, or whether simple closure is sufficient. True
gastight seals are difficult to establish and maintain.
Sealing of all soil gas entry routes is difficult and
challenging. Many different sealants with different
properties are required for the numerous surfaces
through which entry routes may penetrate. A thorough
job of sealing entry routes will typically result in a
50-70% reduction in radon. However, greater than
90% reduction has been achieved occasionally.
For the purposes of this discussion, soil gas entry
routes are divided into major and minor categories.
Major routes are usually relatively large, distinct
openings between the house and the soil. Major
routes include areas of exposed soil inside the house,
sumps, floor-to-wall cracks, floor drains, French
drains, large cracks, and uncapped top blocks in
hollow-block foundation walls. Minor routes are
small, but can be distributed over broad areas.
Examples of minor routes include small cracks and
the pores in block walls. Because they are often
numerous and widespread, minor routes collectively
can be very important sources of radon entry in the
house.
Accessible major entry routes should always be
closed as a matter of course to reduce soil gas entry
with or without additional mitigation. A reasonable
effort should be made to ensure that these closures
are true gastight seals. However, the openings
associated with these entry routes are generally so
large that some meaningful radon reduction will be
achieved even if it is not practical to establish a
gastight seal. Closure methods generally involve
cementing shut holes in slabs and walls, and covering
and/or installing traps in water collection systems. In
addition to these large routes, intermediate-sized
holes and cracks in slabs and walls should be closed
with mortar, caulk, or other sealant. Intermediate
holes and cracks include those where there is a
distinct opening amenable to closure, and exclude
minor entry routes such as hairline cracks and the
pores in block walls. The degree of radon reduction
which can be achieved through closure of major and
intermediate-sized entry routes will vary from house
to house, and will probably not often be sufficient by
itself to reduce high-radon houses below 4 pCi/L if
the initial level is above 10 pCi/L. However, some
degree of reduction will generally be achieved,
depending upon the relative importance of the entry
routes which are closed, the nature of the remaining
unclosed entry routes, and the effectiveness of the
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closures (i.e., whether they are gaslight seals). In
some cases, the reduction can be significant.
Because these closures can often be implemented
relatively easily by the homeowner at relatively little
cost, the homeowner is well advised to take these
steps. These closures would also be needed if a soil
ventilation system were subsequently installed in the
house.
Simple closure of major and intermediate routes is
generally sufficient when the purpose is to prevent
house air from flowing out through the entry route
when suction is being applied by an active soil
ventilation system. Large amounts of house air
leakage into the soil ventilation system might reduce
the effectiveness of the system. However, small
amounts of leakage can be handled by the soil
ventilation system, so that gastight sealing is not
required. Even if a gastight seal were established for
a given entry route, the soil ventilation system would
probably still receive comparable degrees of air
leakage from the numerous other small entry routes
which were not sealed. Thus, the expense and effort
involved in true sealing of entry routes may not be
justified for reducing leakage into active soil
ventilation systems.
If an attempt were to be made to reduce high radon
levels in a house below 4 pCi/L using sealing
techniques alone, it would be necessary to apply a
permanent, true gastight seal over essentially every
soil gas entry route. Special care would be required
to ensure that the major and intermediate routes were
sealed gastight. Also, the minor routes such as small
cracks and block pores would have to be sealed,
requiring special surface preparation (such as routing
of the cracks prior to sealing) and materials (such as
coatings or membranes to seal the pores in block
walls). Inaccessible entry routes (such as those
concealed within block fireplace structures) would
have to be sealed, possibly requiring partial
dismantling of the structure. Because entry routes are
often numerous, with some concealed and
inaccessible, because gastight seals are often difficult
to ensure, and because sealed routes can reopen
(and new routes can be created) as the house settles
over the years, sealing alone is not felt to be a viable
technique for treating houses with high radon levels.
At present, it appears that homeowners will be best
served simply by executing reasonable closure or
sealing of the accessible major and intermediate entry
routes--and by then moving on to some other
approach if that level of sealing does not give
adequate reductions.
The pores in a block wall can be significant radon
entry routes. This is especially true with cinder
blocks. Paints and other pore-filling coatings can be
effective in reducing air flow through these porous
surfaces; however, cracks should first be filled with
caulk or another sealant. Latex paints may require
three or more coats (a minimum of three is
recommended) to be highly effective in stopping air
flow through a hollow-block concrete wall.
Waterproof and epoxy paints may be as effective with
only one or two coats. Further studies of block wall
sealing are under way.
If openings are to be closed using sealants, the first
step is to choose the appropriate material. Table 4
gives a partial listing by category of the available
sealants, along with some suggestions for
applicability. The information in this table was
obtained from sources including manufacturers'
literature, laboratory research study reports, and field
study reports. This information does not constitute an
exhaustive list of sealants or of pertinent information
relating to these particular products. Particular
attention should be paid to information relating to
safety concerns. If there is any suspicion that the
safety precautions supplied with a particular product
are inadequate, the manufacturer should be contacted
for further advice. Manufacturers' addresses could be
obtained from reference books (such as the Thomas
Register) in the local library. Since many sealants are
designed to bond to specific surfaces, more than one
type of sealant may be required to close all the entry
routes in a particular house. Table 4 compares the
properties and applicability of several products. Listing
of a product in this table does not imply EPA approval
or recommendation. Further information on new
products may be available from the manufacturers.
10.5 House Pressure Adjustments
70.5.7 Reduce Depressurization
Depressurization of the lower levels of the house
(relative to the surrounding soil) is a primary factor
contributing to the flow of soil gas into the house.
Some steps can be taken to reduce the effects of
some of the contributors to this depressurization. In
addition, steps can be taken to reduce flow of house
air up through, and out of, the house as a
consequence of depressurization. Reduction in air
outflow should reduce soil gas inflow.
There are currently insufficient data to estimate the
contributions of the various sources of
depressurization to the radon levels in the house.
Their effects will vary from house to house.
Therefore, the radon reductions that might generally
be achieved by addressing these sources cannot now
be predicted. Moreover, since some of these sources
exert only intermittent influence (such as fireplaces
and exhaust fans), any radon reductions that are
achieved by controlling these sources will apply only
over short time periods. However, it is known that
such sources can sometimes be significant
contributors to indoor radon, and that the benefits of
addressing them can be significant. Therefore, it
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Table 4. Sealant Information
Sealant Name
Small Cracks
Fomofill
Geocel Construction
1200
Geocel Construction
2000
Geocel SPEC 3000
Sikatop
Sikadur
Silastic
Insta-Seal Kit, I-S 550
Handi-Foam,
Model 1-160
Large Cracks
Versi-foam 1
Versi-foam 15
Froth PakFP-180
Dow Corning Fire Stop
Foam Kit #2001
Insta-Seal Kit, I-S 550
Handi-Foam,
Model 1-160
Sealant Type
One component, caulk bead
Caulk, silicons
Copolymer caulk
Caulk, urethane
Nonshrink grout w/binder
Nonshrink grout w/bmder
Caulk, silicons
One component, caulk bead
One component, caulk bead
Two component urethane
foams
Two component urethane
foams
Two component urethane
foams
Two component silicone
liquid
One component, caulk bead
One component, caulk bead
Safety Concerns
Nontoxic, water-
based solvent
Ventilation required
during installation
Use respirators
w/organic vapor
cartridges
Ventilation required
during installation
Ventilation required
during installation
Ventilation required
during installation
Ventilation required
during installation
Ventilation required
during installation
Application
Effectiveness
(%) Cost
$11/Cf
$2/tube
$2.50/tube
$3/tube
$79/2.2cf
$89/2.2cf
$22/1 Cf
$220/1 5cf
$254/1 5Cf
1-2lb.
kit:$1 2.75/1 cf
$78/2.2cf
$89/2.2cf
Sealant
Manufacturer
Fomo Products, Inc.
Geocel Corp.
Geocel Corp.
Geocel Corp.
Sika Chemical Corp
Sika Chemical Corp.
Wright/Dow Corning
Insta-Foam Products,
Inc.
Fomo Products, Inc.
Universal Foam System,
Inc.
Universal Foam System,
Inc.
Insta-Foam Products,
Inc.
Insta-Foam Products,
Inc.
Insta-Foam Products,
Inc.
Fomo Products, Inc.
(continued)
-------
Table 4. Continued
Application
O)
01
Sealant Name
Large Cracks
(continued)
Froth Pak Kit FP-9.5
Fomofill
Geocel Construction
1200
Geocel Construction
2000
Geocel SPEC 3000
Tremco THC-900
Zonolite 3300
Polycel One
Pores
Foil-Ray
Thiocol WD-6
Rock Coat 82-3
Resitron II
HydrEpoxy 1 56
HydrEpoxy 300
Aerospray 70
Sealant Type
Two component, spray foam
One component, caulk bead
Caulk, silicone
Copolymer caulk
Caulk, urethane
Flowable urethane,
two-part
Spray foam and fire proofing
Expanding foam,
polyurethane
Reflective insulation
Alkylpolysulfide copolymer
(0.102 cm thickness)
P.V.C. copolymer solution
(0.127 cm thickness)
Two component furan
Two component, water-based
epoxy
One component
Safety Concerns
Nontoxic, water-
based solvent
Ventilation required
during installation
Use respirators
w/organic vapor
cartridges
Ventilation required
during installation
Check ventilation
requirements
Not used in living
space; may cause
allergic reactions on
skin
Flammable, non-
toxic
Non-hazardous;
choking fumes when
burned; wear masks,
gloves, shield; avoid
inhalation
Fire hazard, exhaust;
wear goggles, gloves
Self-extinguishing
Self-extinguishing
Effectiveness
(%) Cost
$11/1Cf
$2/tube
$2.50/tube
$3/tube
$49/1 .5 gal.
$80/16 Ib. tank
99 $0.36/sq.ft
tape-$8.50/roll)
90
26
97 $6.75/gal.
($0.33/sq.tt)
94 $7.30/gal.
($0.l9/sq.ft)
85 $6.37/gal.
($0.31/sq.ft)
99 $2.96/gal.
Sealant
Manufacturer
Insta-Foam Products,
Inc.
Fomo Products, Inc.
Geocel Corp.
Geocel Corp.
Geocel Corp.
Tremco
W. R. Grace and Co.
W. R. Grace and Co.
Thiokol Corp.
Halltech, Inc.
Ventron Corp.
Acme Chemicals &
Insulation Co.
Acme Chemicals &
Insulation Co.
American Cyanamid
(continued)
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Table 4. Continued
05
OT
Sealant Name
Pores
(continued)
Blockbond
Shurewall
Acryl 60
Trocal, etc.
Polyester
Saran Latex XD4624
Design Openings
Versi-foam 1
Versi-foam 15
Froth PakFP-1 80
Froth Pak Kit FP-9.5
Vulkem
Zonolite 3300
Sealant Type
Surface bonding cement
w/binder
Surface bonding cement
w/bmder
Surface bonding cement
w/bmder
Sheeting: polymer.AI-mylar,
PVC, polyethylene
Polyethylene terephthalate
(0.009 cm thickness)
One component, medium
viscosity, unsaturated polyester
Experimental Saran Latex
Two component urethane
foams
Two component urethane
foams
Two component urethane
foams
Two component, spray foam
Flowable urethane, 1 part
Spray foam and fire proofing
Application
Effectiveness
Safety Concerns (%) Cost
Check ventilation
requirements
Check ventilation
requirements
Check ventilation
requirements
99
Self-extinguishing 95 $2. 11 /gal.
($0.13/sq. ft.)
89 $2.72/gal.
($0.12/sq.ft)
Ventilation required $22/cf
during installation
Ventilation required $220/1 5cf
during installation
Ventilation required $254/1 5cf
during installation
Ventilation required $lO/qt. tube
during installation
Check ventilation
requirements
Sealant
Manufacturer
Standard Dry Wall
Products
Dynamit Nobel of
America, Inc.
Essex Chemical Corp.
Dow Chemical Co.
Universal Foam
System, Inc.
Universal Foam
System, Inc.
Insta-Foam
Products, Inc
Insta-Foam
Products, Inc.
W. R. Grace and Co.
NOTE: Inclusion of a sealant in this table should not be construed as an endorsement by EPA of the product or its manufacturer. This table is not
represented as a complete listing of suitable products or manufacturers. This table is intended only as a partial listing of some of the sealants
known to be commercially available.
-------
serves the homeowner well to take whatever steps
are possible to reduce depressurization.
Some steps which homeowners might easily and
inexpensively implement include:
• Slightly opening windows near exhaust fans and
combustion appliances when these appliances
are in use to facilitate the inflow of outdoor air to
make up for the house air exhausted by these
devices;
• Sealing off cold-air return registers in the
basement for central forced-air heating and
cooling systems and sealing around the return
ducting in the basement to reduce the extent to
which the basement is depressurized; and
• Closing accessible airflow bypasses (between
stories) and accessible openings through the
house shell on the upper levels to reduce air
movement up through, and out of, the house as
the result of the thermal stack effect.
Before considering more expensive measures for
addressing a depressurization source (e.g.,
installation of a permanent source of outdoor
combustion air for a fireplace), the homeowner might
wish to make radon measurements with and without
the fireplace in operation. Such measurements would
suggest whether that source is a sufficiently important
contributor to indoor radon levels to make the
investment worthwhile.
70.5.2 House Pressurization
If the pressure difference between the house and the
soil can be reversed so that the house is higher in
pressure than is the soil, the convective flow of soil
gas inward will be stopped altogether. House
pressurization is a developing reduction technique
which has been tested in only a few basement
houses to date. Radon reductions as high as 90%
have sometimes been observed using this approach.
For houses with basements (or with heated crawl
spaces) it might be possible to isolate the basement
(crawl space) from the remainder of the house, and to
pressurize it by blowing air into the basement (crawl
space) from the other parts of the house.
The ability to isolate and tighten that portion of the
house in contact with the soil is a key consideration.
If the portion in contact with the soil could not be
isolated, it would be necessary to pressurize the
entire house, by blowing in outdoor air--a
potentially impractical approach which would have a
large heating penalty. Even with the isolation and
tightening, the heating penalty could be significant,
because of increased infiltration upstairs when large
amounts of upstairs air are blown into the basement.
While basement pressurization appears to offer
potential, the technique requires further testing before
it can be designed and operated with confidence.
One concern that has been expressed about this
technique is the collection of moisture in the walls as
a result condensation as warm moist air contacts the
colder surfaces of the outer parts of the wall.
Increased moisture could damage wood components
and freezing might damage concrete blocks.
10.6 Air Cleaning
Since radon decay products are solid particles, they
can be removed from the air, after the entry of the
radon gas into the house, by continuously circulating
the house air through a device which removes
particles. Such air cleaning devices have been
available for residential use for many years. These
devices include mechanical filters and electrostatic
devices which can be incorporated into the air
handling system associated with a central forced-air
heating and cooling system, or which can stand alone
inside the house.
Radon decay products will rapidly attach to other,
larger dust particles in the house air. If no air cleaner
is in use, the concentration of dust particles will be
sufficient such that only a small fraction of the decay
products will not be thus attached. Air cleaners
remove the dust particles so that newly created
decay products, which are continuously being
generated by the radon gas throughout the house,
find many fewer dust particles to adhere to.
Therefore, while air cleaners can reduce the total
concentration of radon decay products, they can
actually increase the concentration of unattached
decay products.
At present, particle-removal air cleaners cannot be
recommended for the purpose of reducing the health
risk due to radon and its decay products. Unattached
decay products may result in a greater health risk
than those attached to dust particles, because the
unattached progeny could deposit selectively in a
fairly small portion of the lung, giving that portion a
high dosage of alpha particle bombardment. The
health data currently available are not sufficient to
confirm whether the potential increase in unattached
progeny caused by an air cleaner, combined with the
net decrease in total progeny, would typically cause
an increase or a decrease in the lung cancer risk to
the homeowner. While the use of air cleaners cannot
currently be recommended for radon progeny
reduction due to this uncertainty, neither can it be
recommended that air cleaners be turned off in cases
where they are being used for reasons other than
radon (e.g., to reduce allergy problems).
Air cleaners, if designed for high efficiency, can be
highly effective in removing the radon progeny (both
attached and unattached) which pass through them.
However, a difficulty arises in circulating the house air
67
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through the devices fast enough to provide high
house-wide reductions. Progeny are constantly
being generated by radon decay in every corner of
the house. The challenge is to remove these progeny
in the air cleaner before they can be inhaled. To
achieve 90% reduction of the total decay products in
a house of typical size and infiltration rate, the air
would have to circulate through a highly efficient air
cleaner at a rate of about 2000 cfm. This is
approximately the capacity of a central forced-air
furnace fan for a house of typical size. Thus, to
achieve 90% total reduction, an efficient air cleaner
could be installed in the central furnace ducting and
the furnace fan operated continuously (not being
allowed to cycle off). The alternative of installing
stand-alone air cleaners in individual rooms to
achieve 90% reduction is considered impractical;
about eight such units would be needed (almost one
in every room), if each air cleaner handles 250 cfm. A
more realistic number of one or two 250-cfm units in
the entire house could give 50 to 70% reduction in
the total progeny concentration, if the total house air
could be effectively circulated through such localized
units (e.g., via ducting). Many stand-alone air
cleaners on the market are much smaller than 250
cfm, some treating only a few cubic feet per minute.
Such small units would provide no meaningful
reduction of the total progeny.
The percentage reductions discussed in the
preceding paragraph are the reductions in the total
decay product concentration. The effects of those air
cleaners on the concentration of the unattached
progeny would depend on a number of factors and
are difficult to predict. With a 2,000-cfm unit, it is
possible that the concentration of unattached progeny
would not decrease at all as a result of air cleaner
operation, and might even increase. With one or two
250-cfm units, the unattached concentration would
very likely be increased by the air cleaner(s). The
smaller units could circulate the house air fast enough
to reduce the dust particle concentration (thus
increasing the fraction of unattached progeny), but
not fast enough to remove the unattached progeny
which are being generated.
The above discussion has focused on air cleaners
which remove particles (and hence radon decay
products). Air cleaners which might remove radon gas
are in a developmental stage and are not considered
here.
10.7 Radon Removal from Well Water
Radon gas from the surrounding soil can dissolve in
groundwater. If the groundwater is drawn directly into
a house from an individual well (or perhaps from a
small community well), the dissolved radon can
escape into the air, contributing to airborne radon
levels. Houses receiving water from a municipal water
treatment plant will not have this potential problem,
because any radon in the water supply will have been
released during treatment and handling before the
water reaches the house. As a rule of thumb, 10,000
pCi/L of radon in well water will contribute roughly 1
pCi/L of airborne radon to the house air on the
average, although localized airborne levels can be
much higher. If water concentrations are sufficiently
high (above perhaps 40,000 pCi/L), some effort to
address the water source of radon would be
advisable, in addition to efforts addressing the soil
gas source.
One option for addressing the radon in water is to
ventilate the house near the point of usage whenever
water is used. A second option-- more practical as
a long-term solution—is to treat the well water
before it is used in the house.
One approach for treating the water is to install a
granular activated carbon (GAC) treatment unit on the
water line entering the house from the well, following
the pressure tank. These GAC units have been used
in residential applications for removing water
contaminants other than radon (for example,
organics). A number of GAC units have been installed
over the past 6 years specifically for radon removal. If
the unit is properly sized and contains a brand of
carbon specifically selected for radon removal, radon
removals of over 99% have sometimes been
obtained. The reported performance of those carbon
units which have been in operation for several years
suggests that the units can operate with no
degradation in radon reduction performance for at
least several years, with minimal maintenance. One
major consideration with GAC units is that they must
be properly shielded (or else located remote from the
house), in order to protect the occupants from
gamma radiation resulting from radon and radon
decay products accumulated on the carbon bed.
Another consideration is that, depending upon State
regulations, the spent carbon might in some cases
have to be disposed of as a low-level radioactive
waste. An additional concern which will not be
discussed here is the possible bacterial growth that
has been reported to occur in the carbon bed.
Aeration of the well water is another treatment option,
to release and vent the dissolved radon before the
water is used in the house. Several aerator designs
have been tested for residential use, and reductions
above 90% have been reported with some of them.
Aerators will avoid the need for gamma shielding that
carbon units have, and will avoid concerns regarding
the disposal of waste carbon. However, aeration units
are more expensive to install and operate than are
GAC units, and the radon removal capabilities of the
aerators that are currently being marketed are
generally lower than the 99 + % that has sometimes
been reported for GAC. Although home aeration units
are commercially available, experience with aerators
for residential use is limited to date. In addition,
68
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aerators will be more complex than GAG units,
generally requiring at least one additional water pump
(to boost the low-radon water from the aerator back
up to the pressure needed to move it through the
house plumbing) and a fan or air compressor (to
provide the stripping air).
10.8 Radon Reduction in New
Construction
When a house is under construction, steps can be
taken to reduce the risk that the house will have
elevated radon levels. In addition, measures can be
installed that will facilitate the activation of an effective
radon reduction system if levels do turn out to be
elevated after the house is built. The actual
effectiveness of these individual steps has not yet
been demonstrated in new construction; the
necessary demonstration is being initiated now.
However, these techniques are logical extensions of
current knowledge and of the experience to date in
existing houses. These steps can be implemented
with less expense, and with greater effectiveness,
during the construction stage than they can after the
house is completed. Therefore, persons who are
concerned about a potential for elevated radon levels
in houses they are building should consider these
steps.
Steps that can be taken to reduce the risk of elevated
radon levels in a new house are:
• Efforts to reduce soil gas entry routes, including,
for example, avoiding cracks in the concrete
floor slab, sealing around utility penetrations
through the slab and foundation walls, capping
the top of hollow-block foundation walls, and
sealing the top of sumps.
• Efforts to reduce the house depressurization and
house air exfiltration that can increase soil gas
influx, including, for example, avoiding thermal
bypasses throughout the house, providing an
external air supply for certain combustion
appliances, and ensuring the presence of
adequate vents in crawl spaces. These steps
are discussed in EPA's "Radon-Resistant
Residential New Construction" (EPA88b) and
"Radon Reduction in New Construction, an
Interim Guide" (EPA87d).
As a further precaution, provisions can be made
during construction that will enable effective sub-
slab suction after the house is built, if radon levels
turn out to be elevated despite the preventive steps
mentioned above. These provisions include a 4-in.
deep layer of clean, crushed rock under the slab, with
an exterior or interior drain tile loop which drains into
a sump or which is stubbed-up and capped outside
the house or through the slab. Alternatively, one or
more 1-ft lengths of PVC pipe can be embedded
into the aggregate through the slab and capped at the
top. These standpipes can later be uncapped and
connected to a fan in suction (or to a passive
convection stack) if needed.
69
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Sect/on 11
Sources of Information
The first point of contact for information concerning
indoor radon and radon reduction measures should
be the appropriate state agency. In most states these
agencies have copies of EPA publications for
distribution. They can also provide information about
any state radon programs that may exist. They are
the best source of information about radon
occurrence in an individual state. Table 5 lists the
agency to contact for each of the states.
If you desire further information, additional assistance
and contacts can be provided by the EPA Regional
Office for the region that includes your state. Table 6
lists the address and telephone number of the
radiation staff for each of EPA's 10 Regional Offices.
The table also includes the appropriate Regional
Office to contact for each state.
71
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Table 5. Radon Contacts for Individual States
Alabama
Radiological Health Branch
Alabama Department of Public Health
State Office Building
Montgomery, AL 36130
(205)261-5313
Alaska
Alaska Department of Health and Social Services
P.O. Box H
Juneau, AK 99811-0613
(907)465-3019
Arizona
Arizona Radiation Regulatory Agency
4814 South 40th Street
Phoenix, AZ 85040
(602) 255-4845
Arkansas
Division of Radiation Control and Emergency Management
Arkansas Department of Health
4815 Markham Street
Little Rock, AR 72205-3867
(501)661-2301
California
Indoor Quality Program
California Department of Health Services
2151 Berkeley Way
Berkeley, CA 94704
(415) 540-2134
Colorado
Radiation Control Division
Colorado Department of Health
4210 East 11th Avenue
Denver, CO 80220
(303) 331-4812
Connecticut
Connecticut Department of Health Services
Toxic Hazards Section
150 Washington Street
Hartford, CT06106
(203) 566-8167
Delaware
Division of Public Health
Delaware Bureau of Environmental Health
P.O. Box 637
Dover, DE 19903
(302) 736-4731
(continued)
72
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Table 5. Continued
District of Columbia
DC Department of Consumer and Regulatory Affairs
614 H Street, NW, Room 1014
Washington, DC 20001
(202) 727-7728 or (202) 727-7722
Florida
Florida Office of Radiation Control
Building 18, Sunland Center
P.O. Box 15490
Orlando, FL 32858
(305) 297-2095
Georgia
Georgia Department of Natural Resources
Environmental Protection Division
205 Butler Street, SE
Floyd Towers East, Suite 1166
Atlanta, GA 30334
(404) 656-6905
Hawaii
Environmental Protection and Health Services Division
Hawaii Department of Health
591 Ala Moana Boulevard
Honolulu, HI 96813
(808) 548-4383
Idaho
Radiation Control Section
Idaho Department of Health and Welfare
Statehouse Mail
Boise, ID 83720
(208) 334-5879
Illinois
Illinois Department of Nuclear Safety
Office of Environmental Safety
1035 Outer Park Drive
Springfield, IL 62704
(217) 785-9900
Indiana
Division of Industrial Hygiene and Radiological Health
Indiana State Board of Health
1330 W. Michigan Street
P.O. Box 1964
Indianapolis, IN 46206-1964
(317)633-0153
Iowa
Bureau of Radiological Health
Iowa Department of Public Health
Lucas State Office Building
Des Momes, IA 50319-0075
(515) 281-7781
(continued)
73
-------
Table 5. Continued
Kansas
Bureau of Air Quality and Radiation Control
Attention: Radon
Forbes Field, Building 321
Topeka, KS 66620-0110
(913)296-1560,296-1568
Kentucky
Radiation Control Branch
Cabinet for Human Resources
275 East Mam Street
Frankfort, KY 40621
(502) 564-3700
Louisiana
Louisiana Nuclear Energy Division
P.O. Box 14690
Baton Rouge, LA 70898-4690
(504) 925-4518
Maine
Division of Health Engineering
Maine Department of Human Services
State House Station 10
Augusta, ME 04333
(207) 289-3826
Maryland
Division of Radiation Control
Maryland Department of Health and Mental Hygiene
201 W. Preston Street
Baltimore, MD 21201
(301) 333-3130 or (800) 872-3666
Massachusetts
Radiation Control Program
Massachusetts Department of Public Health
23 Service Center
Northampton, MA 01060
(413) 586-7525 or (617) 727-6214 (Boston)
Michigan
Michigan Department of Public Health
Division of Radiological Health
3500 North Logan, P. O. Box 30035
Lansing, Ml 48909
(517)335-8190
Minnesota
Section of Radiation Control
Minnesota Department of Health
P.O. Box 9441
717SE Delaware Street
Minneapolis, MN 55440
(612) 623-5350 or (800) 652-9747
(continued)
74
-------
Table 5. Continued
Mississippi
Division of Radiological Health
Mississippi Department of Health
P.O. Box 1700
Jackson, MS 39215-1700
(601) 354-6657
Missouri
Bureau of Radiological Health
Missouri Department of Health
1730 E. Elm, P. O. Box 570
Jefferson City, MO 65102
(314) 751-6083
Montana
Occupational Health Bureau
Montana Department of Health and Environmental Sciences
Cogswell Building A113
Helena, MT 59620
(406) 444-3671
Nebraska
Division of Radiological Health
Nebraska Department of Health
301 Centennial Mall South
P.O. Box 95007
Lincoln, NE 68509-5007
(402)471-2168
Nevada
Radiological Health Section
Health Division
Nevada Department of Human Resources
505 East King Street, Room 203
Carson City, NV 89710
(702) 885-5394
New Hampshire
New Hampshire Radiological Health Program
Health and Welfare Building
6 Hazen Drive
Concord, NH 03301-6527
(603)271-4588
New Jersey
New Jersey Department of Environmental Protection
380 Scotch Road, CN-411
Trenton, NJ 08625
(609) 530-4000/4001 or (800) 648-0394 (in State) or
(201) 879-2062 (N.NJ Radon Field Office)
(continued)
75
-------
Table 5. Continued
New Mexico
Dr. Margo Keele, Radon Project Manager
New Mexico Environmental Improvement Division
Community Services Bureau
P.O. Box 968
Santa Fe, NM 87504-0968
(505) 827-2957
New York
Bureau of Environmental Radiation Protection
New York State Health Department
2 University Place
Albany, NY 12203
(518) 458-6461 or (800) 458-1158 (in State) or
(800) 342-3722 (New York State Energy Office)
North Carolina
Radiation Protection Section
North Carolina Department of Human Resources
701 Barbour Drive
Raleigh, NC 27603-2008
(919) 733-4283
North Dakota
Division of Environmental Engineering
North Dakota Department of Health and Consolidated Laboratory
Missouri Office Building
1200 Missouri Avenue, Room 304
P.O. Box 5520
Bismarck, ND 58502-5520
(701) 224-2348
Ohio
Robert M. Quillin, Program Administrator
Radiological Health Program
Ohio Department of Health
1224 Kmnear Road, Suite 120
Columbus, OH 43212
(614) 644-2727 or (800) 523-4439 (in State only)
Oklahoma
Radiation and Special Hazards Service
Oklahoma State Department of Health
P.O. Box 53551
Oklahoma City, OK 73152
(405) 271 -5221
Oregon
Oregon State Health Department
1400 S.W. 5th Avenue
Portland, OR 97201
(503) 229-5797
(continued)
76
-------
Table S. Continued
Pennsylvania
Bureau of Radiation Protection
Pennsylvania Department of Environmental Resources
P.O. Box 2063
Harnsburg, PA 17120
(717) 787-2480 or (800) 237-2366 (in State only)
Puerto Rico
Puerto Rico Radiological Health Division
G.P.O. Call Box 70184
Rio Piedras, PR 00936
(809) 767-3563
Rhode Island
Division of Occupational Health and Radiation Control
Rhode Island Department of Health
206 Cannon Building
75 Davis Street
Providence, Rl 02908
South Carolina
Bureau of Radiological Health
South Carolina Department of Health and Environmental Control
2600 Bull Street
Columbia, SC 29201
(803) 734-4700/4631
South Dakota
Office of Air Quality and Solid Waste
South Dakota Department of Water & Natural Resources
Joe Foss Building, Room 416
523 E. Capital
Pierre, SD 57501-3181
(605) 773-3153
Tennessee
Division of Air Pollution Control
Custom House
701 Broadway
Nashville, TN 37219-5403
(615) 741-4634
Texas
Bureau of Radiation Control
Texas Department of Health
1100 West 49th Street
Austin, TX 78756-3189
(512) 835-7000
(continued)
77
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Table 5. Continued
Utah
Division of Environmental Health
Bureau of Radiation Control
288 North 1460 West
P.O. Box 16690
Salt Lake City, UT 84116-0690
(801) 538-6734
Vermont
Division of Occupational and Radiological Health
Vermont Department of Health
Administration Building
10 Baldwin Street
Montpeher, VT 05602
(802) 828-2886
Virginia
Bureau of Radiological Health
Department of Health
109 Governor Street
Richmond, VA 23219
(804) 786-5932 or (800) 468-0138 (in State)
Washington
Environmental Protection Section
Washington Office of Radiation Protection
Thurston Airdustnal Center
Building 5, LE-13
Olympia, WA 98504
(206) 753-5962 (within the state, 800-323-9727)
West Virginia
Industrial Hygiene Division
West Virginia Department of Health
151 11th Avenue
South Charleston, WV 25303
(304) 348-3526/3427
Wisconsin
Division of Health
Section of Radiation Protection
Wisconsin Department of Health and Social Services
5708 Odana Road
Madison, Wl 53719
(608)273-5180
Wyoming
Radiological Health Services
Wyoming Department of Health and Social Services
Hathway Building, 4th Floor
Cheyenne, WY 82002-0710
(307) 777-7956
78
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Table S. Radiation Contacts for EPA Regional Offices
Address and Telephone States in EPA Region
Region 1
U.S. Environmental Protection Agency
APT-2311
John F. Kennedy Federal Building
Boston, MA 02203
(617)565-3234
Region 2
2AWM:RAD
U.S. Environmental Protection Agency
26 Federal Plaza
New York, NY 10278
(212) 264-4418
Region 3
SAM 12
U.S. Environmental Protection Agency
841 Chestnut Street
Philadelphia, PA 19107
(215) 597-8320
Region 4
U.S. Environmental Protection Agency
345 Courtland Street, N.E.
Atlanta, GA 30365
(404) 347-2904
Region 5
5AR-26
U.S. Environmental Protection Agency
230 South Dearborn Street
Chicago, IL 60604
(312) 886-6175
Region 6
6T-AS
U.S. Environmental Protection Agency
1445 Ross Avenue
Dallas, TX 75202-2733
(214) 655-7208
Region 7
U.S. Environmental Protection Agency
726 Minnesota Avenue
Kansas City, KS 66101
(913)236-2893
Region 8
8HWM-RP
U.S. Environmental Protection Agency
999-18th Street, Suite 500
Denver, CO 80202-2405
(303) 293-1709
Region 9
A-1-1
U.S. Environmental Protection Agency
215 Fremont Street
San Francisco, CA 94105
(415)974-8378
Region 10
AT-082
U.S. Environmental Protection Agency
1200 Sixth Avenue
Seattle, WA 98101
(206) 442-7660
Connecticut, Maine,
Massachusetts, New Hampshire,
Rhode Island, Vermont
New Jersey, New York, Puerto
Rico, Virgin Islands
Delaware, District of Columbia,
Maryland, Pennsylvania, Virginia, West Virginia
Alabama, Florida, Georgia,
Kentucky, Mississippi, North Carolina, South Carolina,
Tennessee
Illinois, Indiana, Michigan,
Minnesota, Ohio, Wisconsin
Arkansas, Louisiana, New
Mexico, Oklahoma, Texas
Iowa, Kansas, Missouri,
Nebraska
Colorado, Montana, North
Dakota, South Dakota, Utah,
Wyoming
American Samoa, Arizona,
California, Guam, Hawaii,
Nevada
Alaska, Idaho, Oregon,
Washington
(continued)
Correspondence should be addressed to the EPA Radiation Representative at each address.
79
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Table 6. Continued
EPA Region
EPA Region
Alabama
Alaska
American Samoa
Arizona
Arkansas
California
Colorado
Connecticut
Delaware
District of Columbia
Florida
Georgia
Guam
Hawaii
Idaho
Illinois
Indiana
Iowa
Kansas
Kentucky
Louisiana
Maine
Maryland
Massachusetts
Michigan
Minnesota
Mississippi
Missouri
4
10
9
9
6
9
8
1
3
3
4
4
9
9
10
5
5
7
7
4
6
1
3
1
5
5
4
7
Montana
Nebraska
Nevada
New Hampshire
New Jersey
New Mexico
New York
North Carolina
North Dakota
Ohio
Oklahoma
Oregon
Pennsylvania
Puerto Rico
Rhode Island
South Carolina
South Dakota
Tennessee
Texas
Utah
Vermont
Virginia
Virgin Islands
Washington
West Virginia
Wisconsin
Wyoming
8
7
9
1
2
6
2
4
8
5
6
10
3
2
1
4
8
4
6
8
1
3
2
10
3
5
8
80
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Section 12
References
Br87 - Brennan, T., Camroden Associates, Inc.,
Rome, NY, private communication, July 1987.
Br88a - Brennan, T., W. Brodhead, S. Galbraith, W.
Makafske, C. Silver, and V. Edward. Reducing
Indoor Radon: Training Manual, New York State
Energy Office, Albany, NY, 1988.
Br88b - Brennan, T., and S. Galbraith. Practical
Radon Control for Homes, Cutter Information
Corp., Arlington, MA. 1988.
Bro87a - Brodhead, W., Mitigation Quality Control
Checklist in Reducing Radon in Structures:
Student Manual, prepared for U.S. Environmental
Protection Agency Radon Reduction Training
Course under contract number 68-01-7030,
January 1987. (An updated EPA report is in
preparation.)
Bro87b - Brodhead, W., Buffalo Homes,
Riegelsville, PA, private communication, July
1987.
EPA86a - U.S. Environmental Protection Agency, A
Citizen's Guide to Radon, OPA-86-004,
Washington, DC, August 1986.
EPA86b - Ronca-Battista, M., P. Magno, S.
Windham, and E. Sensintaffer, Interim Indoor
Radon and Radon Decay Product Measurement
Protocols, U.S. Environmental Protection Agency,
EPA-520/1-86-04 (NTIS PB86-215258),
Washington, DC, February 1986.
EPA86C - Singletary, H. M., K. Starner, and C. E.
Howard, Implementation Strategy for the
Radon/Radon Progeny Measurement Proficiency
Evaluation and Quality Assurance Program, U. S.
Environmental Protection Agency, EPA-520/1-
86-03, Washington, DC, February 1986.
EPA87a - Ronca-Battista, M., P. Magno, and P.
Nyberg, Interim Protocols for Screening and
Follow-Up Radon and Radon Decay Product
Measurements,U.S. Environmental Protection
Agency, EPA-520/1-86-014, Washington, DC,
February 1987.
EPA87b - U. S. Environmental Protection Agency,
Radon/Radon Progeny Cumulative Proficiency
Report, EPA-520/1-87-002, January 1987.
EPA87c - U.S. Environmental Protection Agency,
Removal of Radon from Household Water, OPA-
87-009, August 1987.
EPA87d - U.S. Environmental Protection Agency,
Radon Reduction in New Construction, An Interim
Guide, OPA-87-009, August 1987.
EPA88a - Henschel, D. B., Radon Reduction
Techniques for Detached Houses, Technical
Guidance (Second Edition), U.S. Environmental
Protection Agency, EPA/625/5-87-019,
Research Triangle Park, NC, January 1988.
EPA88b - Osborne, M.C., Radon-Resistant
Residential New Construction, U.S. Environmental
Protection Agency, EPA-600/8-88-087,
Research Triangle Park, NC, July 1988.
EPA88c - U.S. Environmental Protection Agency,
Protocols for Screening and Followup Radon and
Radon Decay Product Measurements (in
preparation).
Ha87 - Harrje, D. T., Hubbard, L. M., and Sanchez,
D.C."Proceedings of the Radon Diagnostics
Workshop, April 13-14, 1987," PU/CEES Report
No. 223, 1987. (EPA report is in preparation.)
He87a - Henschel, D.B., and A. G. Scott, Testing of
Indoor Radon Reduction Techniques in Eastern
Pennsylvania: An Update, in Indoor Radon II:
Proceedings of the Second ARC A International
Specialty Conference on Indoor Radon, pp. 146-
159, Cherry Hill, NJ, April 1987.
He87b - Henschel, D. B., and A. G. Scott, Some
Results from the Demonstration of Indoor Radon
Reduction Measures in Block Basement Houses,
81
-------
in Indoor Air '87: Proceedings of the 4th
International Conference on Indoor Air Quality and
Climate, Vol. 2, pp. 340-346, Berlin, West
Germany, August 1987.
Ma87 - Matthew, T. G. et al. from Oak Ridge
National Laboratory, and Hubbard, L. M. et al.
from Princeton University, "Investigation of Radon
Entry and Effectiveness of Mitigation Measures in
Seven Houses in New Jersey: Midproject
Report," ORNL/TM-10544, 1987.
Mar88 - Marynowski, J. M., "Measurement and
Reduction Methods of Cinder Block Wall
Permeabilities," Senior Thesis in Chemical
Engineering, Princeton University, 1988.
Na85 - Nazaroff, W. W., S. M. Doyle, A. V. Nero,
and R. G. Sextro, Potable Water as a Source of
Airborne Radon-222 in U.S. Dwellings: A
Review and Assessment, Lawrence Berkeley
Laboratory, Report LBL-18154, December 1985.
Os87 - Osborne, M. C., Resolving the Radon
Problem in Clinton, NJ, Houses, presented at the
4th International Conference on Indoor Air Quality
and Climate, Berlin, West Germany, August 1987.
Py88 - Pyle, B. E., A. D. Williamson, C. S. Fowler,
F. E. Belzer III, M. C. Osborne, and T. Brennan,
Radon Mitigation in Crawl Space Houses in
Nashville, Tennessee, presented at the 81st
Annual Meeting of APCA, Dallas, TX, June 19-
24, 1988.
Sa87 - Saum, D., INFILTEC Radon Control
Services, Falls Church, VA, private
communication, June 1987.
Sc87 - Scott, A. G., American ATCON, Wilmington,
DE, private communication, July 1987.
Sc88 - Scott, A. G., A. Robertson, and W. O
Findlay, "Installation and Testing of Indoor Radon
Reduction Techniques in 40 Eastern
Pennsylvania Houses," EPA-600/8-88-002
(NTIS PB88-156 617). Research Triangle Park,
NC, January 1988.
Se87 - Sextro, R. G. et al., "An Intensive Study of
Radon and Remedial Measures in New Jersey
Homes: Preliminary Results," Lawrence Berkeley
Laboratory, University of California, LBL-23128,
1987. (EPA report in preparation under
interagency agreement DW89931876-01 with
the U.S. Department of Energy.)
Si87 - Simon, R., Barto, PA, private communication,
April 13, 1987.
Tu87 - Turk, B. H., J. Harrison, R. J. Prill, and R. G.
Sextro, "Preliminary Diagnostic Procedures for
Radon Control," EPA-600/8-88-084 (NTIS
PB88-225 115), June 1988.
82
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Appendix
The following house inspection form is to be used in much information is preferable to collecting too little,
conjunction with the visual inspection. It is quite since the latter may require a second visit to the
detailed, but not all entries are pertinent to all houses. house. Survey type information is quickly obtained
The form is designed to be fairly complete and, and, therefore, should be collected as completely as
consequently.may call for information that is not possible on the first visit. This form is organized to
always needed. Experience shows that collecting too facilitate incorporating the information into a report.
83
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EXAMPLE OF A HOUSE INSPECTION FORM THAT CAN BE USED DURING A VISUAL SURVEY
(from Reference Tu87)
RADON SOURCE DIAGNOSIS
BUILDING SURVEY
NAME: HOUSE INSPECTED: (i.d.)
ADDRESS: DATE:
ARRIVAL TIME:
DEPARTURE TIME:_
PHONE NO.
SURVEY TECHNICIANS:
I. BASIC CHARACTERIZATION OF BUILDING AND SUBSTRUCTURE
Site
1. Age of house
2. Basic building construction:
Exterior materials
Interior materials
3. Earth-based building materials in the building - describe:
4. Domestic water source:
a. municipal surface
b. municipal well
c. on-site well
d. other
5. Building infiltration or mechanical ventilation rate:
a. building shell - leaky, moderate, tight
b. weathenzation - caulk, weatherstrip, etc.
c. building exposure: (1) heavy forest
(2) lightly wooded or other nearby buildings_
(3) open terrain, no buildings nearby
exhaust fans: (1) whole house attic fans
(2) kitchen fans (4) others_
(3) bath fans (5) frequency of use_
other mechanical ventilation
(continued)
84
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HOUSE INSPECTION FORM (Continued)
6. Existing radon mitigation measures
Type
Where
When
7. Locale - description:
8. Unusual outdoor activities: farm
construction_
factories
heavy traffic_
Substructure
1. Full basement (basement extends beneath entire house)
2. Full crawl space (crawl space extends beneath entire house)
3. Full slab on grade (slab extends beneath entire house)
4 . House elevated above ground on piers
5. Combination basement and crawl space (% of each)
6. Combination basement and slab on grade (% of each)
7. Combination crawl space and slab on grade (% of each)
8. Combination crawl space, basement, and slab on grade (% of each)
9. Other - specify
Occupants
1. Number of occupants Number of children
2. Number of smokers Type of smoking
Frequency
Air quality
1 Complaints about the air (stuffiness, odors, respiratory problems, watery eyes, dampness, etc.)
2. Are there any indications of moisture problems, humidity or condensation (water marks, molds, condensation , etc.)?
When
Note: Complete floor plan with approximate dimensions and attach.
II. BUILDINGS WITH FULL OR PARTIAL BASEMENTS
1. Basement use: occupied, recreation, storage, other_
2. Basement walls constructed of:
a. hollow block: concrete, cinder
b. block plenums: filled, unfilled,
top block filled or solid: yes, no
c. solid block: concrete, cinder
d. condition of block mortar joints: good, medium, poor
e. poured concrete
f. other materials - specify:
g. estimate length and width of unplanned cracks:_
h. interior wall coatings: paint, sealant, other
exterior wall coatings: parget, sealant, insulation (type_
(continued)
85
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HOME INSPECTION FORM (Continued)
3. Basement finish:
a. completely unfinished basement, walls and floor have not been covered with paneling, carpet, tile, etc.:
b. fully finished basement - specify finish materials:
c. partially finished basement - specify:
4. Basement floor materials:
a. contains unpaved section (i.e., exposed soil) - specify site and location of unpaved area(s):
b. poured concrete, gravel layer underneath
c. block, brick, or stone - specify
d. other materials - specify
e. describe floor cracks and holes through basement floor
f. floor covering - specify
5, Basement floor depth below grade - front rear_
side 1 side 2
6. Basement access:
a door to first floor of house
b. door to garage
c. door to outside
d. other - specify
7. Door between basement and first floor is:
a. normally or frequently open "
b. normally closed
8. Condition of door seal between basement and first floor - describe (leaky, tight, etc.):
9. Basement wmdow(s) - specify:
a. number of windows
b. type
c. condition
d. total area:
10. Basement wall-to-floor joint:
a. estimate total length and average width of jomt:_
b. indicate if filled or sealed with a gasket of rubber, polystyrene, or other materials - specify materials:
c. accessibility - describe:
11. Basement floor drain:
a. standard drain(s) - location:.
b. French drain - describe length, width, depth:_
c. other - specify:
(continued)
86
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HOUSE INSPECTION FORM (Continued)
d. connects to a weeping (drainage) tile system beneath floor - specify source of information (visual inspection,
homeowner comment, building plan, other):
e. connects to a sump
f. connects to a sanitary sewer
g. contains a water trap or waterless trap
h. floor drain water trap is full of water:
(1) at time of inspection
(2) always
(3) usually
(4) infrequently
(5) insufficient information for answer
(6) specify source of information
12. Basement sump(s) (other than above) - location:_
a. connected to weeping (drainage) tile system beneath basement floor - specify source of information:
b. water trap is present between sump and weeping (drainage) tile system - specific source of information:
c. wall or floor of sump contains no bottom, cracks, or other penetrations to soil - describe:
e. sump contains water:
(1) at time of inspection
(2) always
(3) usually
(4) infrequently
(5) insufficient information for answer
(6) specify source of information:
(7) pipe or opening through which water enters sump is occluded by water:
(a) at time of inspection
(b) always
(c) usually
(d) infrequently
(e) insufficient information for answer
(f) specify source of information
f. contains functioning sump pump:
13. Forced air heating system ductwork: condition of seal - describe:
supply air:
return air
- basement heated: a. intentionally
b. incidentally
14. Basement electrical service:
a. electrical outlets - number (surface or recessed)
b. breaker/fuse box - location
15. Penetrations between basement and first floor:
a. plumbing:
b. electrical:
c. ductwork:
d. other:
16. Bypasses or chases to attic (describe location and size):
17. Floor material type, accessibility to flooring, etc.:
18. Is caulking or sealing of holes and openings between substructure and upper floors possible from:
a basement?
b. living area?
(continued)
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HOUSE INSPECTION FORM (Continued)
III. BUILDINGS WITH FULL OR PARTIAL CRAWL SPACES
1. Crawl space use: storage, other
Crawl space walls constructed of:
a. hollow block: concrete, cinder
b . block plenums: filled, unfilled
top block filled or solid: yes, no
c. solid block: concrete, cinder
d. condition of mortar joints: good, medium, poor
e. poured concrete
f. other materials - specify:
g. estimate length and width of unplanned cracks:
h. interior wall coatings: paint, sealant, other
i. exterior wall coatings: parget, sealant, insulation (type
3. Crawl space floor materials:
a. open soil
b. poured concrete, gravel layer underneath:
c. block, brick, or stone - specify:
d. plastic sheet condition:
e. other materials - specify.
f. describe floor cracks and holes through crawl space floor:
g. floor covering - specify:
4. Crawl space floor depth below grade:_
5. Describe crawl space access:_
condition:
Crawl space vents:
a number
b. location
c. cross-sectional area
d. obstruction of vents (soil, plants, snow, intentional)
7. Crawl space wall-to-floor joint:
a. estimate length and width of crack
b. indicate if sealed with gaskets of rubber, polystyrene, other - specify
c. accessibility - describe
8. Crawl space contains:
a. standard drain(s) - location
b. French drain - describe length, width, depth
c. sump
d. connect to: weeping tile system
(1) sanitary sewer
(2) water trap (trap filled, empty)
9. Forced air heating system ductwork: condition and seal - describe
10; Crawl space heated: a. intentionally
b. incidentally
11. Crawl space electrical service:
a. electrical outlets - number _
b. breaker/fuse box - location
12. Describe the interface between crawl space, basement, and slab:
(continued)
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HOUSE INSPECTION FORM (Continued)
13. Penetrations between crawl space and first floor:
a. plumbing
b. electrical
c. ductwork:
d. other:
14. Number and locations of bypasses or chases to attic
15. Caulking feasible from: a. basement
b. living room
IV. BUILDINGS WITH FULL OR PARTIAL SLAB FLOORS
1. Slab use: occupied, recreation, storage, other:
2. Slab room(s) finish:
a. completely unfinished, walls and floor have not been covered with paneling, carpet, tile, etc.
b. fully finished - specify finish materials
c. partially finished - specify
3. Slab floor materials:
a. poured concrete
b. block, brick, or stone - specify
c. other materials - specify
d. fill materials under slab: sand, gravel, packed soil, unknown
source of information
e. describe floor cracks and holes through slab floor
f. floor covering - specify
4. Elevation of slab relative to surrounding solid (e.g., on grade, 6 in. above grade):
is slab perimeter insulated or covered? yes, no
5. Slab area access to remainder of house - describe:
normally: open, closed
6. Slab wall-to-floor joint (describe accessibility):
a. estimate length and width of crack
b. indicate if sealed with gasket of rubber, polystyrene, other - specify
c. accessibility - describe
7. Slab drainage:
a. floor drain - describe
b. drain tile system beneath slab or around perimeter - describe
c. source of information
(continued)
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HOUSE INSPECTION FORM (Continued)
8. Forced air heating system ductwork:
a. above slab condition and seal - describe
b. below slab: '
(1) length and location
(2) materials
9. Slab area electrical service:
a. electrical outlets - number _
b. breaker/fuse box - location
10. Describe the interface between slab, basement, and crawl space:
11. Penetrations between slab area and occupied zones:
a. plumbing
b. electrical
c. ductwork
d. other
12. Bypasses or chases to attic:
(continued)
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HOUSE INSPECTION FORM (Continued)
V. SUBSTRUCTURE SERVICE HOLES AND PENETRATIONS
(Note on Floor Plan)
Complete table to describe all service penetrations (i.e., pipes or conduit for water, gas, electricity, or sewer) through subfloors and walls.
Indicate on floor plan.
Description of service,
size, location, accessibility
Example: water, 3/4-in. cooper
pipe, through floor, accessible.
Size of crack or gap around
service and type and condition of seal
Example: Approx. 1/8-in. gap around
circumference of pipe with sealing
polystyrene gasket.
(continued)
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HOUSE INSPECTION FORM (Continued)
VI. APPLIANCES
MAJOR APPLIANCES LOCATED IN SUBSTRUCTURE (CRAWL SPACE, SLAB ON GRADE, BASEMENT)
Location Description
Appliance (Crawl, slab, base) (Fuel type, style, operation)
Furnace
Water heater
Water conditioners
Air conditioner
Clothes dryer
Exhaust fans
Other:
Forced air duct/plenum seals - describe
Combustion appliances: combustion air supplied (yes, no)
U.SGP.O 1988- 548-158/87040
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