PB88-161534
Radon Reduction
Strategies and Approaches
(U.S.) Environmental Protection Agency
Research Triangle Park, NC
Jan 38
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EPA/600/D-88/022
January 1988
PBdd-lto 1S44
RADON REDUCTION STRATEGIES AND APPROACHES
Judith E. Cook
Air and Energy Engineering Research Laboratory, OEETD
Office of Research and Development (MD-60)
U. S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
Daniel J. Egan
Office of Radiation Programs (ANRf-460)
U. S. Environmental Protection Agency
Washington. D. C. 20460
AIR AND ENERGY ENGINEERING RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT!
U.S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, NC 27711
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TECHNICAL REPORT DATA
(Pleae read Irjumcriom cn (he reverse bit fart completing)
i. report rjo.
EPA/600/D-38/022
2.
1 "S'TWTts 4® .
4. TITLE AND SUBTITLE
| Radon Reduction Strategies and
.Approaches
i. REPORT DATE
January 1938
3. PERFORMiMfi ORGANIZATION CODE
1. AUTKORttSI
J.E. Cook (EPA/AEERL) and D.J. Egan (EPA/ORP)
3. PERFORMING ORGANIZATION REPORT KO.
3. fERFORMING ORGANIZATION (MAMS AND ADDRESS
U.S. Environmental Protection Agency
Office of Radiation Programs (ANRf-460)
Washington, D. C. 20460
10. PROGRAM ELEMENT MO.
it. coNrsACT/CK&wr «o.
NA (Inhouse)
11. SPONSORING AOENCV KAME AND ADDF1ESS
SPA, Office of Research and Development
Air and Energy Engineering Research Laboratory
Research Triangle Park, Iv!C 27711
13. TVPC OF REPORT AND PERIOD COVERED
Book Chapter; 3-12' 37
i«. sponsoring asency code
EPA/600/13
ulcupplementauvnoteb AEEkl project officer is Judith E, Cook. Mail Drop 60, 918/541- \
2923.
chapter is for inclusion in a textbook, Environmental Radon, for grad-
uate students. It gives a flavor of what radon mitigation entails,, rather than being a
detailed handbook treatment of the subject. It emphasizes the removal or reduction
of soil-gas-borne raden (the major source of radon in most houses) and briefly des-
cribes the following methods of reducing/removing indoor radon: natural ventilation;
forced air ventilation; forced air ventilation with heat recovery; reducing entry
points (sealing); venting radon from the soil surrounding a house by drain-tile soil
ventilation, sub-slab ventilation, or wall ventilation; reducing pressure differentials;
removing radon from water; and air cleaning. It gives background information on
house construction types* the significance of weather phenomena, sad the signifi-
cance of the sSack effect in elevating indoor radon levels.
!
17. KEY WORDS AMD DOCUMENT ANALYSIS
l. DESCRIPTORS
b.fOCNTIFIERS/OPEN ENDED TERIWS
£ C.03ATI Fie££,'Group
Pollution Soil Water
| Radon Ventilation
Atmospheric Con- Sealing
tamination Control
Houses Drain Tiles
Soils Weather
Pollution Control
Stationary Sources
Indoor Air
Soil Gas
13B 08H
07B 13A
13H
06K
13 M 13C.11B
00G.08M 04B !
1B. OI5TH'.euT>ON STATEMENT
Release So Public
13. SICURITV CtASS (TkU Repcri)
Unclassified
21. KO. OP PACES i
UH ]
SO SECURITY CLASS (Ttlitps^r)
Unclassified
2J. PRICE j
CPA Form l?2))
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NOriCE
This document has been reviewed in accordance with
U.S. Environmental Protection Agency policy and
approved for publication. Mention of trade names
or commercial products does not constitute endorse-
ment or recommendation for use.
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2
Table of Contents
Chapter 8
8.1. Introduction
8.1.1. Overview of Mitigation Techniques
8.1.1a. Ventilating Indoor Concentrations
8.1.1b. Reducing Radon Entry
8.1.1c. Removing the Radon Source
8.1. id. Removing Radon and Radon Decay Products from indoor Air
8.1.2. Short-Term Mitigation Actions
8.1.3. Limitations of Radon Mitigation
8.2. Evaluation of Sources and Entry Mechanisms
8.2.1. House Construction Types
8.2.2. Possible Entry Points
8.2.3. Possible Depressurlzation Mechanisms
8.2.4. Water and Building Materials
8.3. Options for Radon Reduction
8.3.1. Ventilation - Diluting and Replacing R3don-Laden Indoor Air
8.3.1 a. Natural Ventilation
8.3.1b. Forced Air Ventilation
8.3.1c. Forced Air Ventilation with Heat Recovery
8.3.2. Reducing Radon Entry
8.3.2a. Reducing Entry Points
8.3.2b. Venting Radon from Soil Surrounding the House
Drain-Tile Soil Ventilation
Sufr-M Ventilation
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wan Ventilation
8.3.2c. Reducing Pressure Differentials
8.3.21 Removing Radon from Water
8.3.3. Air Cleaning - Removing Radon and Radon Decay Products
from Indoor Air
8.4. Evaluation and Maintenance of Radon Mitigation Systems
8.5. Developing a Mitigation Strategy
References
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8.1. Introduction
The application of radon reduction strategies and approaches - known
as radon mitigation - Is a new, specialized field within the home-building
industry, as well as the subject of much ongoing research and development
activity. Because it is virtually impossible to completely free the Indoor
environment of radon, the goal of radon mitigation ts to reduce radon In the
Indoor environment as much as possible. Using currently developed
methods, It Is possible to get substantial indoor radon reductions, often to
the 4 pCl L_1 (0.02 WL, or 143 Bq nr-) level recently suggested as guidance
by the U. S. Environmental Protection Agency.
The major source of radon in most structures 1s radon-containing soil-
gas. it is believed that the basic mechanism that brings soil-gas into a
house is the pressure difference between the Indoor and the outdoor
environment. Pressure inside closed houses is generally slightly lower than
the outdoor pressure. This pressure difference is increased In winter., as a
"stack effect" (as in "smoke stack") Is created by the continual rising of
heated air. At the lower levels of the house - Including places where the
house contacts the soil - pressure is lowered, creating a "sucking" action
that draws the radon-containing soli-gas Into the house. At the higher
levels the heated air "exf titrates" around the upper stories and the roof. In
addition to the stack effect, wind effects, use of appliances that consume
indoor air, anc! unbalanced airflow through the house contribute to house
"depressurization." Because the degree of depressur 1 zat 1 on varies with
weather and household activities, radon concentrations will vary within a
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structure over time. If indoor air cannot move freely from one area to
another, there can be spatial variations in radon concentrations as vvell.(
This chapter emphasizes techniques for mitigating the naturally
occurring radon that enters houses. It also emphasizes techniques for
mitigating radon in existing houses as opposed to new houses. These
emphases reflect the focus of research to date. The techniques have not
been applied to office or other public-use buildings, because it is generally
believed that public-use buildings are safer. People usually spend less
time in them; they are better ventilated; and they are multi-story. Further
surveys of building cedes, commercial heating/ventilating/cooling systems
Der formance, and radon levels are needed to confirm this supposition.
8.1.1. Overview of Mitigation Techniques (
There are four possible means of reducing radon in indoor air: The
indoor concentration can be diluted by ventilation, the entry of radon can be
reduced, the source of the radon can be removed, or the ration itself (and its
decay products) can be removed.
8.1.1 a Ventilating indoor Concentrations. Ventilation simply means
increasing the flow of outdoor air into the house which dilutes and replaces
the radon-laden indoor air. Ventilation Is a simple method to use, because
all that Is required is that windows and vents on all sides of an area be
opened equally. In addition, opening windows and vents neutralizes indoor
depressurization, which reduces substantially the pressure-driven flow of
radon into the house. Unfortunately, ventilation isn't practical in extreme
weather, or in areas where houses are susceptible to unauthorized entry.
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8 Mb. Reducing Ftedon Entry. Another means of reducing radon in
Indoor air Is to reduce its entry. Al! cracks and openings In a house's
structure are pathways for the entry of radon-containing soil-gas, so it
follows that sealing them will reduce radon entry. More effective reduction
of radon soil-gas entry can likely be achieved by using mechanical systems
or natural phenomena to draw, or force, the soil-gas away from the house's
lowest level. Radon can be removed from Incoming water by using aeration
or granular activated carbon. Radon removed by aeration can be vented to
the outside. Carbon adsorbs radon and Its decay products.
8.1.1 c Removing the Radon Source. Removing the radon source is a
special case involving the waste products of uranium production, mill
tailings, which were used In the construction of some houses in the p?*st.
The process of separating uranium from the waste had the effect of
concentrating the radium content of the mill tailings, and they became
significant sources of indoor radon in houses where they had been used as
"gravel" under the slabs. In these houses, the slabs were torn out, the mill
tailings excavated, and new slabs poured
8.1.1 d Removing Radon and Radon Decay Products from indoor Air. In
theory, It should be possible to pass indoor air through some type of filter
to which the radon and Its decay products would adhere, thereby removing
them from the air. There are several types of air cleaners now on the
market for particle removal, and the radon decay products are in particle
form. However, the issue of whether these devices can actually reduce the
risk of lung cancer, as discussed in chapters 5 and 6, is complex.
8.1.2. Short-Term Mitigation Actions.
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When extremly high concentrations of radon are found in houses,
local radiation officials may urge temporary relocation of the occupants.
In these instances, further exposure, even for another week, may be judged
untenable.
Fortunately, most elevated indoor radon concentrations are not In this
range, and homeowners can use a number of fairly simple interim measures
to reduce their exposure, whiie they contemplate permanent radon
mitigation measures. Occupants should stop smoking, especially in the
house, and visitors should be discouraged from smoking. Occupants should
reduce the amount of time they spend in part? of the house where radon
concentrations are highest; for example, the basement. If possible,
windows should be opened on all sides of the house to increase ventilation
and reduce depressurization. Fans can be used tr increase air flow through
the house, especially through the basement (they should always blow into
the house), if the house is bui't over a crawl space, all crawl space vents
should be fully opened and remain so throughout the year.(2) of course,
exposed pipes would have to be protected from freezing, if there are
obvious radon entry points that can be closed easily, these should be closed
at once. For example, cover a dirt sump in a basement, and Isolate from the
rest of the house and discontinue use of a dirt basement. Avoid further
depressurizing the house by opening windows when depressurizing
appliances, such as furnaces, clothes dryers, woodstoves: and space heaters,
are in use, and discontinue the use of ceiling fans.(')
6.1.3. Limitations of Radon Mitigation (')
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Radon mitigation is a developing field and not yet as exact a science
as, for instance, designing a heating system. Much has been iearned recently
about designing mitigation systems, but there are still a number of areas
where trial and error are necessary. For instance, many design and
construction characteristics of a house that Influence the performance of
radon mitigation systems are hidden from view. In trtsse cases, some
modifications to the mitigation systems may be necessary after they are
installed and tested.
8.2. Evaluation of Sources and Entry Mechanisms
6.2.1. House Construction Types
Aside from the uranium/radium content and the permeability of the
soil where the house is built, house type is one of the major parameters
that Influence the degree- of radon entry. Most houses In this country are
variations and combinations of three basic house types: Basement houses,
houses on crawl space, and houses built on concrete slabs. Each presents a
different mitigation problem.
Basement houses have an excavated room, or rooms, below ground
level that serve the dual function of being the house's foundation and living
or storage space for the occupants. The excavated space can be constructed
with foundation walls of different materials; e.g., concrete- or cinder-
blocks, poured-concrete, and sometimes field ctone or treated wood. They
can have either a concrete or dirt f !oor. Being below grade (below ground
level), 2 basement offers a wide floor and wall surface area with many
(sometimes concealed) cracks, gaps, and openings through which radon soil-
gas can be drawn into the house. In addition, if the basement has block
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walls, radon soli-gas can be drawn through their porous surface Into the
house.
A crawl space house Is built on a low foundation, partially above and
partially below grade. All living areas are above grade, and the crawl space
below them generally accommodates heating/air conditioning ducts and
pipes In a space sui'fli 'ent for a person to crawl about to service them.
Crawl spaces usually offer the simplest means of radon mitigation, since
they can effectively serve as a ventilated, neutral-pressur e buffer between
house and soil. To ventilate a crawl space year round may require that the
sub-flooring and the water pipes be Insulated. Crawl spaces can be less
amenable to mitigation If they open into the living space of the home. That
Is, they are actually "mini-basements."
A slab house uses a concrete slab %s the base of the house with living
spaces constructed directly over it. Some houses are slab-on-grade, while
others are built on slabs below grade. As with basement houses, these slabs
offer a wide surface area with many (sometimes concealed) cracks, gaps,
and openings through which radon soil-gas can be drawn into the house.
8.2.2. Possible Entry Points
Any opening that somehow comes In contact with the soil surrounding
and below a house can be an entry point for radon. For example, radon-
containing soli-gas can be drawn Into a house through the sump pits that
exist In many basement houses. When water rises high enough In the ground
to enter the house's foundation, the sump pump in the pit automatically
begins to function, pumping water out of the network of drain pipes that
encircle and protect the foundation. However, when the drain pipes are dry,
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radon soil gas can be drawn through their tiny perforations into the drain
system, and through the sump pit Into the basement.*
Common entry points for radon, shown in Figure 5.4, are: cracks In
basement walls and floors, seams where basement walls and floors meet,
seams in concrete floors poured intentionally as expansion joints, floor
drains connected to the soil with no trap to prevent gas entry, holes through
basement walls or floors for pipes and the like, the porous surface of
concrete blocks, and concealed openings in structures associated with
masonry chimneys or fireplaces.*')
Another source of radon in some houses has been water from private
wells (or possibly from small municipal well systems). If the radon in the
water is in sufficiently high concentrations, its release into the indoor air
through showering, clothes washing, etc., can contribute to airborne indoor
radon.(3) (See Chapter 5.)
8.2.3. Possible Depressurization Mechanisms *1 >
Since the basic mechanism that brinos radon soil-gas into a house is
depressurization, activities that increase depressurization must be
minimized, especially in winter. Homeowners can unwittingly increase the
depressurization of the house by using appliances that "consume" indoor air.
A fire in a fireplace, for instance, consumes air.
8.2.4. Water and Building Materials
Radon can enter the house in dissolved form in the water supply and
be released into the Indoor air by such activities as bathing and clothes
washing. The concentration In water must be very high to Influence the
indoor air concentration. A commonly used rule of thumb is that 10,000
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pCI L~' (370,000 Bq m-3) of radon In water will produce 1 pCI L~l (37 Bq
m~3) when released into the air. Researchers have, however, found houses
where the major cause of elevated indoor radon concentrations was radon In
the drinking water supply. In these cases, systems were installed to
remove the radon before it entered the house. Radon in water is a problem
mainly for homeowners with private wells, and occasionally for small
municipal ground water supplies. Radon that may be dissolved in larger
municipal water supplies is usually released Into the air before it reaches
the consumer.^)
Radon can also be introduced Into the house when radium is present in
building materials. The solution, of course, is to avoid the use of such
materials. Granite can be a source of radon, but It is important to note that
the incidence of naturally occurring radium in building materials is almost
aiways a minor problem, compared to the incidence of radon entering a
house in soil-gas. The most widely publicized example of radon
contemlnation from building materials was In uranium mining areas where
builders used the waste products of uranium mining, mill tailings, as a
substitute for gravel under the concrete slabs of some houses.
8.3. Options for Radon Reduction
8.3.1. Ventilation - Diluting and Replacing Radon-Laden Indoor Air
Some degree of house ventilation occurs cont'.uaily, even in closed
houses, as the lower pressure inside draws outside air in through any
available pathway. This continual replacement of Indoor air with outdoor
air, however small, is referred to as "air change," and the rate at which this
replacement occurs is measured In "air changes per hour" (abbreviated 3Ch).
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Ach Is a measure of how long it takes to completely replace all the air in a
house with outside air. In the average American house, one complete air
change occurs approximately every 1 to 2 hours (I.e., a rate of 1 to 0.5 ach).
Newer, more energy-efficient houses could have as little as 0.1 ach. Older,
draftier houses could have as much as 2 ach.(1)
One of the purposes of the ventilation techniques discussed in this
section is to increase the number of air changes per hour, which Increases
the dilution and replacement of radon-laden indoor air. The other purpose -
which may turn out to be primary with further research - is to neutralize
the pressure difference between indoors and outdoors. Since the exchange
rate is much less in energy-efficient houses, they are likely to benefit more
from increased ventilation than are houses that already have higher
exchange rates. In other words, it may be realistic to Increase a ventilation
rate of 0.25 ach to 0.50 ach, while it may not be realistic to increase a
ventilation rate of 1.5 ach to 3 ach (the house could be uncomfortably cold),
although each of these increases would give the same percent reduction in
radon concentration. Based on dilution considerations and excluding the
effects of pressure neutralization, each doubling of the ventilation rate
would reduce radon concentrations by a factor of two. For example, an
initial indoor radon concentration of 20 pCI L"1 (0.1 WL, or 740 Bq rrr3) in a
house with a ventilation rate of 0.25 ach can be reduced to about 2.5 pCI L-1
(0.01 WL, or 92.5 Bq rrr3) by increasing the ventilation rate to 2 ach. Actual
reductions would probably be even higher as a result of the pressure
neutralizing effect of opening windows and vents. (0
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Clearly, the limiting factors In Increasing ventilation rates are human
comfort and energy expense. Generally, temperatures between 68° and
78° F (20° and 25° C) and relative humidities between 30% and 703 are
comfortable to most people.*National data on temperatures indicate
that, on the -verage, there are up to four months each year when ventilation
can be used without discomfort to the occupants of the house and without
Increasing heating or cool tag costs. Beyond these four months, occupants
may have to live with some discomfort and some increased heatlng/coollng
expense/')
Since the most Important area to ventilate is the area nearest the
soil - wftere the radon-containing soil-gas is entering the house - one
option for applying ventilation, if it is feasible, is to close-off and not use
a basement that is being ventilated during extreme weather. The human
comfort problem is thereby avoided, ss is the energy increase In some
measure, although ieakage from the basement Into the living areas will stfl!
Increase energy costs by about 20%. The only requirements in this instance
are that pipes in the.basement be protected from freezing, and that the
basement be abandoned^ - not always an attractive option.
Three ventilation alternatives are discussed in the following
sections, with information on their expense and their ability to reduce radon
levels.
8.3.1a. Natural Ventilation. The easiest form of ventilation to use is
natural ventilation. All that is required is that windows, or doors, and
crawlspace vents be opened equally on all sides of an area. Opening
windows and vents on more than one side of the house is Important in order
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to ensure that the pressure indoors and out remains neutral. If, for example,
windows were opened only on the downwind side of a house, It would
depressurize further, Increasing the flow of soil-gas-borne radon into the
housed1)
Because natural ventilation Is driven, by winds, and pressure and
temperature differences between the Indoor and outdoor environments, It
cannot be well controlled. Therefore, one can have only moderate confidence
that natural ventilation will constantly keep radon concentrations in an
acceptable ranged5) Natural ventilation would not be effective for radon
concentrations above about 40 pCI L~' (0.2 WL, or 1480 Bq m-3) (3) jf
dilution were the only mechanism at work. However, the pressure
neutralizing effect of opening windows and vents (mentioned In section
8.3.1) could likely make natural ventilation effective on even higher
concentrations/If natural ventilation is used year-round in most of the
country, it will Increase heating/cooling costs up to three times normal in a
house with an initial exchange rate of 0.25 ach/1)
8.3.1b. Forced Air Ventilation. Forced air ventilation, too, is
relatively simple in that fans are used to force air through an area, rather
than relying on prevailing winds to do this/1) The advantage of forced air
ventilation is that it enables the control of airflow through an area. Thus,
one can have Increased confidence that it will keep radon concentrations in
an acceptable range/') Forced air ventilation would not be effective for
radon concentrations above 40 pCI L"1 (0.2 WL, or i 480 Bq rrr3)/3) if
dilution were the only mechanism at work. However, the pressure
neutralizing effect of opening windows and vents (mentioned in section
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8.3.1) could likely make forced air ventilation effective on even higher radon
concentrations.^')
If forced air ventilation is used year-round in most of the country, it
will Increase heating/cooling costs up to three times normal in a house
with an initial exchange rate of 0.25 ach. In addition, operating fans year-
round would cost about $100. This estimate does not include more elaborate
installations with new wiring, duct work, dampers, filters, and the 11ke.(
For both natural and forced air ventilation, balanced airflow is of
utmost importance. Mistakes can mean the difference between reduced
radon concentrations, no reduction at all, or - in some cases - increased
entry of radon soil-gas into the house. Opening only upstairs windows, or
using an attic exhaust fan could create negative pressure on the basement.
Hence, the primary area to ventilate Is always the basement, or lowest
level, and fans are always placed so that they blow Ma an area.(1)
8.3. ic. Forced Air Ventilation with Hc-at Recovery. The use of heat
recovery ventilators enables the use of forced air ventilation without the
complete loss of all heated, or cooled, air as the air exchange rate is
increased. Heat recovery ventilators, also called air-to-air heat
exchangers, use a heat transfer surface to warm - or cooi - incoming air.
The heat transfer surface is heated or cooled by the air being exhausted
from the house.O
The heat recovery ventilator offers reasonable potential for treating
houses with radon concentrations up to about 40 pCi L~' (0.2 VVL, or 1480 Bq
m-3).(3) By making use of the heat or cooling in the outgoing air, heat
recovery ventilators reduce considerably the amount of extra energy needed
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to heat or cool a ventilated area. Typically, whole-house heating/cooling
costs are only about 1.5 times normal, or less. These devices range in
cost from $400ti $1500, and are capable of energy recoveries up to
70&d>
8.3.2. Reducing Radon Entry
8.3.2a. Reducing Entry Points.C') 11 i s poss! bl e to reduce radon en try
to some degree simply by sealing all entry points that can be found. In most
cases, however, sealing by itself will probably .iot be sufficient, because
radon entry routes are too numerous and many of them are concealed.
Sealing is usually recommended as.a first step in any radon mitigation
strategy, because it is something that most homeowners can do themselves.
It can't hurt, and might help, especially it-there are some big holes. It may
ultimately be needed anyway to make other mitigation systems, like sub-
slab ventilation, work effectively.
The first sealing step would be to seal the largest and most obvious
radon entry routes, including dirt basements, sump pits, and floor drains
connecting to the sell without traps. The best solution for dirt basements
is to excavate the fill dirt in the area and replace it with concrete. Sump
pits can be capped with an impermeable covering, like sheet metal, sealed
at all joints, and a fan used to draw radon-laden air from under the cap and
exhaust it to the outside. For floor drains to soil, traps can be added, or, if
necessary, removable stoppers used to prevent radon soil-gas entry. Holes
in the top row of concrete blocks and large holes in walls and floors should
also be among the first openings sealed.
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Concrete blocks have hollow spaces inside that connect and form a
network Inside block walls. Radon can be drawn tn through the network of
spaces and enter the house from the openings in the top row of blocks. To
seal these, one may stuff crumpled newspaper into the hollow spaces and
concrete ;ver it if the top blocks are easily accessible. If they are not
easily accessible, then a urethane foam can be extruded into the hollow
spaces through a hose and nozzle assembly.
In addition to large, obvious openings, a conscientious homeowner
could also seal smaller openings, although the impact will be much less.
These include openings where pipes and ducts enter the basement, mortar
Joint cracks between blocks, gaps between block and brickwork surrounding
basement fireplaces, and pores in the surface o? concrete blocks.
Cracks and utility openings can be sealed by first enlarging them 3nd
then filling them with caulk, grout, or sealant. Joints between the wall and
the slab can be enlarged, filled with sealant, and then covered with mortar.
Epoxy sealants or waterproof paints are used to reduce the flow of
radon through porous walls, especially block walls. Meticulous surface
preparation is required to ensure that these coatings will adhere to the
surface.
The effect of sealing on the radon concentration in specific houses Is
unpredictable, because of wide variations In the strength of the source
material in the soil, because each house Is different, ar.d because the unseen
- cracks and openings In a house's foundation may be letting In more radon
than those that can be found and seaied. Also, houses continue to settle
over time, and this settling can create new pathways for radon entry. In
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addition, sealing cannot be expected to provide a constant barrier over time;
house settling and other wear and tear can reopen cracks and gaps. Thus,
one can have only low to moderate confidence that sealing will effectively
control indoor radon concentrations. Sealing major sources, like dirt
basements and sump pits, will have a more marked effect on indoor
concentrations than will the sealing of small cracks and openings.
Sealing major exposed radon sources within the house structure can
range in cost from as low as $100 to several thousand dollars, as, for
example, when concreting a dirt basement. Most cracks and small openings
can be sealed for under $ 100.
8.3.2b. Venting Radon from Soil Surrounding the House. There are
three techniques by which radon soil gas can be vented from the soil
surrounding a house. The basic mechanism in all three is to draw a suction
greater than the suction created by the depressurizatlon of the house. This
reverses the predominant flow of air so that it flows aw3y from the house.
To understand these techniques, it is first necessary to explain briefly a
few basics of house construction.
Houses of either the basement or crawl space type begin below grade
with footings of poured concrete. Trenches somewhat bigger than the
planned walls are dug, and concrete is poured into them to provide a firm
"footing" for the foundation walls that they will support. Block foundation
walls have hollow spaces Inside. Each successive course of blocks is laid so
that the center of the top block covers the ends of the two blocks below.
This "ties" the wall of blocks together, and also creates a network of hollow
spaces Inside the wall that connects both vertically and horizontally.
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Foundation walls can also be made of field stone or timbers, but In all these
cases the foundation walls are usually built over footings of concrete.
Mortar is used to attach the bottom of the foundation walls to the
footings.^ D
It Is believed that a significant amount of radon soil-gas may enter
the house in the area of the footings; th3t is, around the mortar that
attaches the bottom of the foundation walls to the footings, around the
mortar that holds the blocks or stones together, and through the porous
exterior surface of blocks in the foundation walls.f
In many basement houses, construction is also characterized by a
concrete slab which forms the floor of the excavated room. Basement, slab-
below-grade, and slab-on-grade houses have this slab-over-soil
construction in common, and in this case it is believed that radon soil gas
enters through utility perforations, cracks, spaces, and joints in the floor,
as well as through sumps and floor drains. Slabs are usually
poured over aggregate, most often, crushed rock, to give them a firm
base.d)
The sections that follGw-^escribe drain-tile soil ventilation, sub-slab
ventilation, and wall ventilation, all of which are designed around the
unique construction characteristics of different types of houses to draw
radon away from the house's foundation.
Drain-Tile Soil Ventilation. Drain-tile soil ventilation Is a good
radon reduction option for a house with a drain-tile system completely
encircling it. As described in section 8.2.2, drain-tile systems encircle the
foundations of many houses to protect them from water, if such a system
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loops the entire house, Is completely intact with no tiles crushed, silted in,
or missing, and attached to each other, rather than simply touching each
other, It offers a relatively simple and cheap ready-made means of drawing
suction on the soil surrounding the house's foundation. This option is the
most esthetically pleasing of the soil ventilation alternatives, and can be
very effective If the full loop gives good distribution of the suction/1) Of
course, the only way one can be sure if a drain-tile system meets the above
criteria is to have a completely new system Installed, and this would be
quite expensive. Adding drain-tile soil ventilation to an existing drain tile
system is fairly inexpensive, however, so it is generally cost-effective to
try this method/')
Drain-tile soil ventilation uses a fan to draw suction on the network
of drain tiles. This suction draws radon soil-gas into the tile network,
thereby preventing tt from entering the house in the vicinity of the footings.
Since the drain-tile network encircles the house at the base of the
foundation, the suction in the system can also draw soil-gas from under the
house's slab (if it has one) as well/1) Adding such a system to an existing
drain-tile network is fairly simple. In the case of a drain-tile system that
connects to a sump pump In the basement, the entire sump pit area Is capped
with an impermeable material, sealed, and a fan is used to draw suction on
the sump pit and the drain-tile system attached to It/ D
In the case of a drain-tile system that drains to a location remote
from the house - to an above-grade discharge or a dry well - the drain line
is located and cut, and a fan, trap, and riser assembly is added (see Figure
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21
8.1). Thus, water can still drain from the drain tiles, and the fan can draw
suction on the drain tiles without drawing in air from the discharge area.O)
In both of the above methods, the fan is located outside and must be
enclosed to protect it from weather and debris and to protect animals and
children. Since the radon concentration in the air exiting the fan can be
very high, homeowners are cautioned to locate it either in an area remote
from the house, or at a safe height. The fan should also be Inaccessible to
children/')
Drain-tile soil ventilation can be used for reducing any radon
concentration; although for concentrations above 200 pCl L-' (1.0 WL, or
7400 Bq m~3)/3) it may not be able get below 4pC1 L-1 (148 Bq
m~3). Since drain-tile soil ventilation functions by drawing soil gas away
from the house's footings, it might not work as effectively if there are
interior walls in the basement sitting on footings of their own. In this
latter case, the fan might not always draw sufficient suction to keep soil-
gas from entering around the footings of these walls. !t would be extremely
unusual for such Interior walls to have drain tiles of their own. Even in
this latter case, drain-tile soil ventilation may be made to work adequately
by using a higher powered fan.( >)
If a homeowner were to have a contractor install a new drain-tile
system and Include in the installation the fan, trap, and riser, the entire
system would cost about $1200, assuming that no unusual problems were
encountered. A do-it-yourself installation would probably require about
$300 in materials/1) Power to operate the fan in the drain-tile system
year-round would cost about $25. Since the suction would draw some
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warmed or cooled air out of the house, heating or cooling costs could be
expected to Increase by about $ 125 per year.f1)
Sub-Slab Ventflatfon.( i) For basement houses and slab-on-grade
houses, ventilation of the area below the slab may be used to draw
accumulated radon soil-gas out of the aggregate, or soil, beneath the slab.
Suction on the sub-slab area can be drawn 1n several ways: (1)
Individual pipes can be inserted into the slab and a fan used tc draw suction
(see Figure 8.2); (2) if drain pipes exist below the slab, these can be used
with a fan to draw suction on the sub-slab area; (3) a network of perforated
pipes can be laid, the slab poured over them, and a fan used to draw suction;
or (4) an extensive network of perforated pipes can be laid, attached to a
stack, and natural phenomena possibly used to draw radon out of the sub-
slab area.
For existing houses, the most practical solutions are the individual
pipe method and the drain-pipe method. In the Individual pipe method,
severai pipes are inserted vertically into the aggregate through holes
drilled in the slab. The number of pipes needed Is dictated by the
permeability under the slab and the size of the slab. The Inserted pipes are
connected to each ether by horizontal pipes, usually running around the
ceiling and connected to a fan. The fan draws suction on the entire sub-slab
area through the inserted pipes, and exhausts the radon soil-gas outside the
house, usually at roof level. Another possibility for existing houses Is a
variation on drain-tile soil ventilation. The perforated drain pipes that
were laid for water drainage under some slabs during construction usually
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drain Into a sump within the house's footings. By using a fan to draw
suction on the sump and the drain pipes, the sub-sl3b area is ventilated.
Both these methods rely on a good layer of aggregate or a permeable
soil below the slab to allow the effects of a few suction points or the drain
pipes" to radiate to the entire slab. Permeability can be tested fairly easily
before installation is begun by drilling a hole into the slab, Inserting a pipe
into It, and attaching a fan to it temporarily. With the fan operating, smoke
tracer tests at joints and cracks remote from the fan (see section 8.4) will
give a good indication of how much air can move through the aggregate or
soil. If permeability is poor, more suction points may be needed, or a
network of perforated pipes will have to be laid.
In the perforated pipe network method, an extensive layer of
perforated pipes is laid horizontally, a fan attached to it, and the slab
poured over the pipes. Because of the expense of tearing out an existing
slab and replacing it, this method is best suited to new construction. It has
also been used In existing houses when the slab had to be torn out anyway,
because there was contaminated material under It (e.g., uranium mill
tailings), or because there were structural problems.
In some houses, an extensive sub-slab piping network may provide
adequate ventilation in a passive mode, without a fan. By connecting the
piping network to a stack that exhausts at roof level, suction is created
through natural thermal effects inside the stack and a reduced pressure at
the roofline caused by wind movement. If the flow resistance through the
aggregate is low, the weak suction created by this stack effect may be
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sufficient to ventilate the sub-slab. Passive ventilation appears to work
cnly In cold weather.
Another variation of sub-slab ventilation that Is being tested is
forcing air into the sub-slab area, rather than drawing suction on ft; tnat is,
pressurizing, rather than depressurizing. This would have the effect of
pushing radon soil-gas away from the slab and foundation.
None of the methods described above will function effectively
without sealing openings in the slab. Without sealing, house air could be
drawn into the system, overwhelming Its suction power. Holes in the slab,
large seams (cold Joints), openings around utility penetrations, large
settling cracks, snd large joints where the wail and floor meet must bs
sealed with mortar. Small openings can be sealed with asphalt, caulk, or
similar sealants.
Sub-slab ventilation is one of the most effective radon reduction
methods known at the present time and can be used for any radon
concentration. Because of the cost, however, homeowners might elect to
use less expensive methods for radon concentrations below 40 pCt L-1 (0.2
WL, or 1480 Bq m~3). The effectiveness of sub-slab ventilation may be
reduced by the existence of block walls in a basement, because it is
difficult to draw enough suction to keep radon soil-gas from entering
through the walls. Closing the hollow spaces in the top course of blocks, as
well as other gaps and openings in the walls, will improve sub-slab
ventilation of block-wall houses considerably, and using higher powered
fans can overcome much of the leakage into a system.
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Having a contractor install an uncomplicated individual pipe sub-slab
system could cost between $ tOOQ and $2500. A similar installation of a
piping network, Including the labor to cut channels into an existing slab to
lay the pipe, could cost between $2000 and $7500. A sub-slab ventilation
system would place about the same annual energy load on a house as wall
ventilation and drain-tile soil ventilation: power to operate a fan year-
round could be about $25 and, assuming the fan draws some house air into
the system, heating/cooling costs could Increase about $125.
Wall Ventilation) if a basement has block walls, another option
for reducing radon soil-gas entry is to draw suction on the walls
themselves. The same network of hollow spaces that enables radon to enter
the house can be used to draw radon away from the house.
The basic approach in wall ventilation is to attach a fan to the
network of spaces inside each wall, draw radon soil-gas out of the walls,
and exhaust 1t to the outside. There are two variations of wall ventilation:
(1) the single-point pipe method, and (2) the baseboard method (see Figure
8.3). For either of these methods to work effectively, all walls must be
treated, including any interior walls that penetrate the concrete floor. Both
methods also require that all l?rge openings in the walls be closed.
Otherwise, the house air being drawn in through these openings will simply
overwhelm the system, and it will have very little suction power left for
radon soil-gas control.
Closing a!! large openings in the walls means the same sealing of the
hollow spaces in the top row of blocks as W3S described in Section 8.3.2a.
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Other large openings must be closed. These include space around pipes
where thev enter the basement, and any other visible holes and gaps.
With large openings effectively closed, the wall ventilation system
can be Installed. Usually, the choice between the single-point pipe method
and the baseboard method is dictated by the conditions in the basement, by
the expense involved, and by the relative Importance of the usability and
appearance of the area.
The single-point pipe method is the cheaper. It involves drilling one
hole into a hollow space In each wall and inserting a pipe into each drilled
hole. The pipes usually lead up to connecting pipes encircling the entire
perimeter of the inside of the basement. At the end of the pipe network is a
fan that draws suction on the walls. Many variations of this method are
possible, depending on the unique requirements of the basement. For
Instance, the pipes could be inserted into the network of hollow spaces from
outside the house, and the fan could be inside, or outside, the house.
In the more expensive baseboard method, holes are drilled into the
hollow spaces around the entire perimeter of the walls near the floor. Then
a two-sided baseboard "duct" Is constructed of sheet metal, or some other
suitable material, and attached with sealant and screws to the wall above
the drilled holes auu to the floor in front of them. In this way, all holes -
and the joint where the wall meets the floor - are completely covered by
the baseboard duct, and the duct system is attached to a fan. Because there
are holes all along the perimeter of the basement, a more uniform suction is
drawn on the walls than with the single-point pipe metnod.
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If wall openings are not sufficiently closed, the fan used to draw
suction or to pressurize the walls cannot work effectively. Among possible
openings that may require closing are the hollow spaces fn the top row of
blocks, the space between brick veneer and the exterior wall, and spaces
between fireplace structures and the walls of the basement. A higher
powered fan may help to increase the efficiency of a wall ventilation
system. In some cases, wall ventilation may simply not be adequate to keep
radon-containing soil-gas from entering through openings in the slab.
Wall ventilation is usually added as a supplement to sub-slab
ventilation if sub-slab ventilation does not function effectively alope. To
have a contractor Install an uncomplicated singte-point pipe system In an
unfinished basement would probably cost about $2500. A similarly
uncomplicated contractor Installation of a baseboard system in an
unfinished basement would probably cost about $5000. An uncomplicated
installation would be one in which the hollow spaces in the top course of
blocks are easy to access and close, and in which there are few appliances
or other obstacles around which the pipes must be installed.
The cost of a do-it-yourself installation, although not generally
recommended, could be as little as $100 to $500 for pipes, sheet metal,
fans, and miscellaneous supplies, depending on the number of fans required
and the size of the basement.
A wall ventilation system would place about the same annual energy
load on a house as drain-tile soil ventilation. Operating a fan year-round
could cost about $25 and, assuming the fan draws seme house air into the
system, heating/cooling costs could Increase about Si25.
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8.3.2c. Reducing Pressure Differentials. Because pressure-driven
flows are believed to be the basic mechanism by which radon soil-gas
enters a structure, It Is Important to minimize any additional
depressurlzatlon of the house, especially In winter and In the areas where
radon soil-gas enters - basements, or rooms directly over the soil.*') It
appears that the major sources of depressurlzatlon inside the house are
combustion appliances which consume indoor air, further lowering indoor
air pressure, and thermal bypasses which facilitate the stack effect.
Among these are furnaces, water heaters, clothes dryers, wocdstoves,
fireplaces, and space heaters. Of these, furnaces and water heaters
probably depressurlze the house the most, because they generally operate a
much greater percentage of the time than do any of the others.^) The
American Society of Heating, Refrigerating, and All—Conditioning Engineers
(ASHRAE) has recommended since 1981 that direct outside supplies of
"makeup" air be provided for combustion appliances, because they believe
this is necessary for effective and controlled ventilation and acceptable
indoV air quality (6). By supplying each air-consuming appliance with Its
own air supply through separate ductwork to the outside, further
depressurlzatlon of the house Is prevented, and Increased flow of radon
soil-gas into the house is prevented. In the case of a fireplace,
depressurlzatlon can be prevented simply by cracking a window while the
fireplace Is 1n use.O
Another possible source of depressurlzatlon inside the house is local
exhaust fans; e.g., ceiling fans that are used intermittently. They are not as
Important as combustion appliances, but they do draw suction on the
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Interior of the house when they are operating. Thus, It would be advisable
to keep use of such fans to a minimum, especially In winter. Also, tf
portable fans are used to ventilate the house, always ensure that fans blow
Into, not out of, the house/1)
It Is difficult to generalize about the Impact on indoor radon
concentrations of preventing appliance depressurlzatlon. There are too
many variables. Among these variables are the number and operating
conditions of the appliances, the type of house In which they are Installed,
and the strength of the radon source material. Best estimates are that the
average annual radon reduction benefit may be between 0% and 50%. It is
impossible to estimate the cost of installing separate ductwork to an
unknown array of appliances/1)
8.5.2(1. Removing Radon from Water. The two methods available for
removing radon from drinking water involve the use of aeration and granular
activated carbon (GAC). Beth methods can be used in the house, or at the
source of the water.
When water containing radon ilTe'xjfosed to air, some of the radon
escapes. Thus, aeration Is a viable means of removing radon from water. A
diffused aeration tank typically can remove more- than 95% of the radon, and
spray aeration has achieved efficiencies of 93%.(?) Packed tower aeration,
which has been shown to be effective in removing volatile compounds from
water, also appears to have potential for removing radon from water,
althougn it has yet to be tested at pilot- or full-scale.
Granular activated carbon has been used to adsorb noble gases such as
i
radon. Efficiencies aS/hlgh as 96% have been reported/7) Because of Its
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short half-life (3.8 days), much of the radon decays on the 6AC bed before
breakthrough.
An aeration system for an average house would cost about $ 1000.
Annual operating costs would be about $80. A GAC system for an average
house would cost between $500 and $1500 with annual operating costs of
about $20 to $40. The disadvantage of the GAC system is that the occupants
are exposed to the radioactive material adsorbed on the GAC.
8.3.3. Air Cleaning - Removing Radon and Radon Decay Products from indoor
Air
Another approach to reducing the risks of radon is to remove radon
and its decay products from the indoor air. There are various types of
devices on the market that can remove particulates from the air, and these
devices ccn remove radon decay products that have attached to these
particulates. However, it is unclear whether these air cleaners can
effectively remove r3don Itself from the air.
This uncertainty exists because there Is Insufficient data to enable
precise description of the ways in which radon and Its decay products may
cause lung cancer. It is generally believed that the most dangerous
situation involves inhaling decay products attached to relatively small
particulates that are more likely to deposit In the deepest, most sensitive
parts of the lung. Air cleaners are thought to be more efficient at removing
larger particulates than smaller ones. If this is so, then the radon still In
the air after it has passed through an air cleaner will generate decay
products that will attach to smaller particulates than would have been the
case without air cleaning. Thus, although the risks may have been somewhat
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reduced by removing larger particulates and the decay products attached to
them, the risks may also have been somewhat increased because the
remaining decay products can become attached to particulates that will
make them more dangerous.
The same issue arises even if the air cleaner is very effective at
removing particulates of all sizes, because the remaining radon can then
generate decay products that will not attach to any particulates, becoming
"unattached decay products." Although data are inconclusive, some
scientists believe that such unattached decay products may be even more
effective at causing lung cancer than decay products attached to
particulates. (See Chapter 7.)
Thus, while air cleaners that are now available are likely tc be
effective at reducing the overall concentration of radon decay products 1n
Indoor air by reducing particulate concentrations, it appears that they may
not be as effective In reducing the corresponding health risks. Additional
research is needed to resolve these uncertainties, although the necessary
scientific studies may be analytically complex. On the other hand,
development of air cleaning systems that simultaneously remove radon
itself, if this can be accomplished in a practical fashion, would offer
significant benefits.
8.4. Evaluation and Maintenance of Radon Mitigation Systems (1)
None of the methods described above can be installed and forgotten.
They all must be evaluated periodically to ensure that they are still
working, and they all require maintenance.
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Evaluation of the radon mitigation methods described In Section
8.3.2b. after they are Installed Is usually done by smoke tracer tests. The
goal Is to determine If the system is drawing sufficient suction to keep
radon soll-gas out of the house. With the mitigation system operating, a
smoke generator (e.g., a smoke tube) Is passed over the surface of walls,
along the wall-to-floor joint, and any other likely entry points. Smoke
should be consistently drawn Into the area being tested. In those places
where it Is not, there is reason to suspect that radon Is still entering the
house because of insufficient suction. Other diagnostics that would he
conducted by the system's installer Include flow and pressure
measurements in vent pipes, and pressure measurements under the slab and
In block wall cores.
Maintenance of radon mitigation methods Involves Inspecting outside
fans for damage or icing, periodic oiling of fans, checking seals where fans
are attached to pipes, checking seals over basement cracks, gaps, and
openings, and checking traps to be sure they are still filled with water. In
the case of natural and forced-air ventilation, maintenance would also
involve periodic checking to ensure that all windows and vents remain
uniformly open on all four sides of the area being ventilated. For heat
recovery ventilation, it would be necessary to check periodically to ensure
that there is a balanced flow of air into and out of the system.
8.5. Developing a Mitigation Strategy
in the previous sections an array of mitigation methods together with
their relative effectiveness and costs have been presented. These are only
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33
the raw material with which a homeowner would develop a mitigation
strategy. A complete strategy would likely Include the following steps:
1. Screening measurement to determine if radon levels are
elevated;
2. Follow-up measurements to determine the extent of the problem;
3. Taking short-term measures to protect occupants while long-term
mitigation measures are being decided upon;
4. Contacting local radiological health officials, environmental
health officials, or an experienced radon mitigation contractor to
seek guidance;
5. Contractor conducting house diagnostics to determine where radon
Is entering;
6. Contractor Installing radon mitigation system;
7. Contractor conducting post-mitigation measurements to
evaluate the effectiveness of the installed system;
8. Contractor making any necessary modifications to the system;
9. Contractor again conducting post-mitigation measurements;
10. Homeowner conducting periodic checks of system to ensure that
it continues to function effectively.
As outlined above, many homeowners will understandably need the
assistance of radiation and radon mitigation experts in dealing with a
suspected indoor radon problem. Assistance with radon measurements can
be obtained from laboratories and businesses who routinely conduct radon
measurements. The U. S. EPA conducts a voluntary Radon Measurement
Proficiency Program which allows firms to demonstrate their capabilities
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34
In measuring Indoor radon. Lists of participating firms in various areas are
s
available from EPA regional offices/?)
Assistance in making important decisions about how to proceed Is
available tfom the radiation health officials in most states. In some states
this assistance Is available from the state's environmental protection
agency.
Som^ states are also conducting training courses for building
contractors who wish to become proficient In radon mitigation.
Information on which contractors have taken such training are also
available frjom the state's raaiologlcal health office or environmental
protection Agency.
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References
1. D. C. Sanchez aon o. B. Henscnel, Radon Reduction Techniques for Detached
• Houses - Technical Guidance, U. S. Environmental Protection Agency
Report EPA/625/5-86/019, Center for Environmental Research Informa-
tion, Cincinnati, Ohio (June 1986).
2. U. S. Environmental Protection Agency and U. S. Department cf Health and
Human Services, A Citizen's Guide to Radon - What it Is and Vfcat to do
About it, U. S. Environmental Protection Agency Pamphlet Nizr&er
OPA-86-004, Office of Public Awareness, Washington, D. C (August
1986).
3. I). 5. Environmental Protection Agency, Radon Reduction Methods - A
Homeowner's Guide, U. S. Environmental Protection Agency Booklet
Number 0PA-86-005, Office of Public Awareness, Washington, D. C.
(August 1986).
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4 American Society of Heating, Refrigerating, and Alr-Condltlonlng
Engineers, Inc., ASHRAE Handbook 1935 Fundamentals. ASHRAE, Atlanta,
Georgia (1985).
5. U. S. Department of Commerce, Statistical Abstract of the United States
1982 - 1983. Bureau of the Census, Washington, D. C. (1982).
6. American Society of Heating, Refrigerating, and Alr-Condltlonlng
Engineers, Inc., Ventilation for Acceptable indoor Air Quality. ASHRAE
Standard 62-1981, ASHRAE, Atlanta, Georgia (1981).
7. 6. W. Reld, P. Lasscvszky, and S. Hathaway, Treatment, Waste Management
and Cost for Removal of Radioactivity from Drinking Water, Health
Pby£l£L4& 671 (1985).
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Figure 8.1. Drain-tile soil ventilation system, draining to remote
discharge ?rea.J3)
/~
~ ~ .
Drain-tile system
&
X
Fan draws radon
from drain tiles
Riser for
CI5 maintaining
waler love I
Drein exit
V
Water in trap v
prevents airflow
from drain exit
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38
Figure 8.2. Individual pipe variation of sub-slab ventilation.*
Outside fan
draws radon
away from house
I
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39
Figure 8.3. Two variations of wall ventilation: lert - tne DsseDoard
method, and right - the single-point pipe meOod.<3)
Outside fan
draws radon
away from house
i
•Rfidon is drawn
through holes
drilled in blocks
Outside fan
^draws radon
'away from house
Radon is drawn
from walls
through pipes
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