United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S9-89/057 Dec. 1989
Project Summary
Proceedings of the Radon
Diagnostics Workshop,
April 13-14, 1987
David T. Harrje and Lynn M. Hubbard
Diagnostic approaches offer im-
proved evaluations of radon-related
Indoor air quality problems. An in-
formed solution Involves knowledge
of the building, the building site, and
the interaction of radon sources with
the living space. The diagnostics are
applicable in four phases of the miti-
gation process: 1) diagnostics that
assess the radon problem; 2) pre-
mltlgatlon diagnostics, from which a
suitable mitigation approach must be
chosen; 3) diagnostics that check the
performance of the radon mitigation
solution; and 4) diagnostics that de-
termine If the radon problem has
been solved and that guideline radon
concentrations have not been ex-
ceeded over the different seasonal
conditions experienced.
A consensus of current knowledge
on important radon diagnostic tech-
niques and how they may be best
applied are the result of the 2-day
workshop at Princeton University,
April 13-14, 1987. That knowledge is
summarized, placing the various
radon diagnostic techniques In
perspective.
This Project Summary was devel-
oped by EPA's Air and Energy
Engineering Research Laboratory, Re-
search Triangle Park, NC, to announce
key findings of the research project
that Is fully documented In a separate
report of the same title (see Project
Report ordering Information at back).
Introduction
The scope and objectives of the work-
shop were to gain an improved
perspective and develop guidelines on
the usefulness and range of applicability
of different diagnostic techniques. To
categorize state-of-the-art diagnostic
techniques and to treat questions that
diagnostic techniques seek to answer
regarding radon emanation, transport,
entry, and indoor distribution, four phases
of radon diagnostics were highlighted:
1. Radon Problem Assessment Diag-
nostics: radon source strength, loca-
tion, house characteristics, and
house occupancy characteristics.
2. Premitigation Diagnostics: selecting
the best mitigation system for the
building, taking into account radon
source strength and location, partic-
ularly involving the substructure.
3. Mitigation Installation Diagnostics:
used during installation of mitigation
systems to ensure proper operation.
4. Post-Mitigation Diagnostics: assur-
ance that the radon guidelines have
been met and that the mitigation
system is adjusted properly.
The backgrounds of the attendees
were varied, but much of their experience
with radon had been a direct result of the
U.S. Environmental Protection Agency,
U.S. Department of Energy, and state
programs to understand and mitigate
radon problems, primarily in residential
buildings. Examples of that experience
come from numerous areas in the U.S.
and Canada. Questions that were applied
to the diagnostic methods included:
1. How good is the rationale for the
diagnostic measurement?
2. How easy is the diagnostic pro-
cedure?
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3. What resources and expenses are
required to implement the
diagnostic?
4. What information can be obtained
from using the diagnostic?
The workshop included formal presen-
tations summarizing the four phases of
diagnostics as well as discussion ses-
sions emphasizing the individual diag-
nostic procedures.
The emphasis on diagnostics in radon-
troubled homes is a quest for knowledge
of the nature and severity of the problem,
the mitigation approach that may be used
to solve the problem, and evaluation of
the performance of each solution. It was
clear from the workshop discussions that
such diagnostics are absolutely
necessary in certain homes, but many of
the procedures are not cost effective in
the homes that are simple to mitigate.
For example, anticipating possible radon
problems during the house design phase
and incorporating mitigation possibilities
in the design is likely to prove more cost
effective than extensive soil probing to
quantify the radon problem potential for
the individual building lot.
Measurements to determine radon
levels for most homes are generally rec-
ommended. In areas of high incidence of
homes with radon levels greater than the
EPA guidelines and/or regions where
very high house radon levels have been
observed, every homeowner should
check for radon concentration levels.
Where radon problems exist, it is im-
portant to evaluate exactly what should
be done.
In homes with concrete basement floor
slabs, the diagnostic approach receiving
wide acceptance is to check for com-
munication under the slab. Subslab de-
pressurization is commonly used to
remove the radon gas using a fan and
piping that exhausts to the outdoors; but
diagnostics are necessary to ensure that
the suction, and thus airflow, extends
over the entire subslab area. The total
openings through the slab or basement
walls need be only a few square centi-
meters for significant radon entry to take
place. Just sealing the basement or
crawlspace may not be enough, since
sealing techniques rarely cover every
possible floor or wall radon leakage site.
Diagnostics, after mitigation devices
are in place, are necessary to ensure that
the job has been done correctly. An
informed homeowner or private testing
agency is recommended for these
checks, to avoid the conflict of interest of
a mitigator being asked to evaluate his
own work. The workshop treated these
radon diagnostic subjects in depth, look-
ing at the pros and cons of diagnosing
the radon troubled house before, during,
and after mitigation. The techniques
described here are evolving rapidly in a
field where discoveries are being made
daily. However, many of the diagnostic
approaches may already be viewed as
"standard," while many others are in the
process of being developed.
Radon Problem Assessment
Diagnostics
Gamma scans may provide the initial
phase of the radon diagnostics. In the
U.S., the National Uranium Resource
Evaluation (NURE) uses an overflight
approach to document broad land
expanses. Because of local geological
differences and local hotspots, low gam-
ma readings should not be viewed as
nonproblem areas; rather, the high level
locations should be viewed as the first
places to check. Such scans needn't be
from aircraft but may use vans or on-foot
surveys. Vans are limited to access roads
and on-foot surveys may be limited by
time constraints. Surveys may be very
detailed using miniature gamma sensors
which can supply very local readings.
Soil gas measurements are another
approach to assessing the probability of
local indoor radon problems. High radon
levels in the soil gas (thousands of pCi/L),
combined with soil information, can
indicate the potential for elevated indoor
levels. However, the number of
measurements necessary to identify the
radon problem potential for a particular
construction lot could cost more than
designing radon prevention into a house.
Hotspots may be missed in the survey,
even with a large number of samples.
The best correlation between soil and
indoor radon levels is provided by a
homogeneous soil such as that found in
sandy soils, for example in Florida. In
npnuniform soils, 100- to 1000-fold
differences in radon concentrations in the
soil gas within a few meters may be
observed. Rock fractures and direct soil
gas conduits are one extreme in
permeability and impermeable clay soils
are the other; moisture and the mix of
clay and sand can greatly influence radon
passage. Soil gas measurements would
appear to be useful in the general
identification on a regional or "housing
development" scale, but would require
excessive testing for detailed, single
building lot prediction. The preferred
methods for soil gas measurement are
grab samples for single point meas-
urements or the charcoal canister method
for time-averaged measurements. Sam-
pling from at least 1 m depths is recom-
mended to avoid atmospheric dilution.
Problem house identification depends
on indoor screening/measurement sur-
veys. The way the house is operated, the
tightness of the below grade construction,
and the surrounding soil influence the
resulting radon concentration in the
house. It is essential that "closed house"
measurements be made and that "fan
out" approaches be considered carefully
when the first high radon levels are
measured in problem houses. Thus, the
radon screening should be based on: 1)
sampling during winter "closed house"
seasons, 2) testing areas where houses
have indicated very elevated indoor
radon levels, and 3) increased sampling
in areas where a high percentage of the
homes exceed the 4 pCi/L EPA guideline.
Screening questionnaires are impor-
tant to radon problem assessment diag-
nostics. Not only are such questionnaires
useful in research house selection but
they are important to the radon mitigator
in evaluating whether confirmation meas-
urements have been performed to sub-
stantiate the indoor radon levels. Basic
questions concerning house construction,
operation, possible major entry routes,
etc., are also part of the questionnaire.
Questions can guide the homeowner on
the need for professional assistance.
Visual inspection and use of a ques-
tionnaire can prove to be the diag-
nostician's most useful tool. Photographs
of house construction and blueprints may
prove very valuable and serve to check
the accuracy of the occupant's answers
to the questionnaire. Identification of prin-
cipal radon entry routes, using the
questionnaire, may preempt the need for
other diagnostics.
Research needs are evident in radon
problem assessment diagnostics. Al-
though certain housing types are rela-
tively well understood, slab-on-grade and
basements with exposed soil and other
complicating factors are not well charac-
terized and need a larger data base.
Basic research on radon availability,
transport, and entry into buildings is
needed to better understand the phe-
nomenon being dealt with and develop
better mitigation and prevention tech-
niques. Modeling radon entry, to correlate
geological factors and indoor radon
levels, is an area in which little research
has been carried out.
Premltlgatlon Diagnostics
Promulgation diagnostics concentrated
on specific features of the home, the
radon transport involved, and diagnostic
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techniques to choose the appropriate
mitigation approach. Between the
researcher and mitigator, premitigation
diagnostics moves from detailed time
consuming techniques aimed at im-
proved understanding to measurements
sufficient to guide the mitigator to
successful solutions.
Mitigators at the workshop explained
the approaches currently in use. The
simplest diagnostics included only visual
inspection. The more complex diagnostic
procedures added grab samples of local
radon concentrations, differential pres-
sure measurements to document "radon
driving potential," and subslab and wall
airflow communications testing. In one
instance, the mitigator quantified the
airflows through test openings in the floor
to better understand the nature of the
below-slab airflow and thereby determine
the size of the mitigation system needed.
Recent construction offers the best
chance for success, where sufficient
aggregate under the slab tends to ensure
good airflow communication.
Visual inspection is a natural diagnostic
tool if the type housing is well understood
and the mitigation method has proven to
be effective. For example, the
experienced mitigator using subslab
depressurization in housing where there
is good communication via the subslab
aggregate will use visual inspection to
locate the subslab penetrations, exhausts,
and fans. Without diagnostic
measurements, one will not know whether
too little or too much air is being
exhausted. Nor will the mitigation system
yield a best mode of operation, especially
if more than one floor/wall de-
pressurization point is being used. Even
with these factors in mind, many mitiga-
tors are using no premitigation diagnos-
tics, rather they are installing mitigation
systems and using post-mitigation radon
concentrations to motivate any necessary
system alternations.
Communication testing has proved
very useful. Subslab depressurization ap-
proaches to radon mitigation have
prompted this type of diagnostic meas-
urement. Typically a vacuum cleaner is
used to pull air through a test hole drilled
through the slab. At other slab
penetrations, airflow and direction are
monitored with smoke tracers, sensitive
flow measurement methods, etc. The dif-
ferential pressure change between the
basement and subslab is also a direct
indication that flow is present and
communication exists under the slab. An
electronic digital manometer has proven
to be an effective differential pressure
measurement device. Several test holes
are drilled to test various locations under
the slab. Adding wall holes allows
wall/floor communication to be checked.
In each case measurable flows indicate
that the final subslab ventilation system
will be effective. Major airflow "short
circuits" (e.g., an easy flow path to
sumps or perimeter drains) make it
difficult to achieve sufficient airflow
across the subslab area. It also should be
recognized when measuring differential
pressures that heating, ventilating, and air
conditioning systems that are not well
balanced will often exert as much as a 5
Pa negative pressure when the air
handler is on. Thus, it is necessary to
achieve at least that magnitude of dif-
ferential pressure to ensure that the miti-
gation system is immune to such
interactions.
Grab samples using Lucas cells
through the same test holes (prior to
communication testing) indicates the
radon source strength and variability.
These samples may also be taken at
crack sites or other points of possible
radon entry, including hollow block walls.
The purpose is to better locate the prin-
cipal radon sources and from that deter-
mine the mitigation approach. The same
grab sampling technique may be used in
the soil surrounding the house. From
these 1 m deep locations, soil perme-
ability can also be measured. The prob-
lem is that correlation between what the
soil reveals and the radon problems in
the house is yet to be established. Cases
of high inside radon concentrations on
the sides of the houses that indicated
lower soil readings are not uncommon;
hence this diagnostic procedure has not
proven very useful. (How readily the
radon can be transported, and very local
variability in soil properties and source
strength help determine the severity of a
particular radon problem.)
Blower door tests are used for a
variety of purposes in premitigation diag-
nostics. Regular blower door tests, which
relate the amount of air flow into (or out
of) a house under a specific amount of
pressurization (or depressurization), are
used to determine the effective leakage
area; i.e., the "leakiness" associated with
a particular house. If the test is applied
only to the basement area, it is possible
to determine the amount of air flow
necessary to maintain a basement pres-
surization of between 5 and 10 Pa. This
is the amount of "counter-pressure"
which should be sufficient to prevent con-
vective entry of radon gas. If the air flow
determined from the blower door test is
less than about 600 m3/hr (ideally below
350 m3/hr), basement pressurization may
be a viable mitigation strategy if subslab
depressurization is not suitable. Another
use of a blower door test is to determine
how much air exchange is needed in the
basement or crawlspace for a heat
recovery ventilator to effectively
remediate a radon problem using dilution.
A depressurization of the substructure
to -10 Pa by the blower door can be
used in the summer to simulate winter
stack effect, although there is some
question of the reality of this simulation.
In this -10 Pa depressurized mode, grab
samples, pressure differentials, and air
velocities through the substructure test
holes can be recorded and used to deter-
mine radon source strengths at specific
points (in the depressurized mode).
Tracer gas measurements can be used
in premitigation diagnostics to augment
communication testing. Also, leaks
through the exterior of the substructure
can be located using tracer gas tech-
niques (and sealed if a tighter basement
is necessary for success of a basement
pressurization system). One example is
that tracer gases can be used to find a
footing drain.
Mitigation Installation
Diagnostics
Four radon mitigation approaches were
discussed in the workshop, along with re-
lated diagnostic procedures.
Sealing was the first mitigation method
mentioned, where Canadian studies in-
dicate that a total area equal to 1 cm2
opening in the basement slab or walls is
all that can be allowed if the sealing
approach is to be successful. Quality
control is thus extremely important, as
well as the choice of materials. Epoxies
often don't bond well with themselves;
they require special surface preparation,
and bonding to the surroundings is vital.
Sealing, properly done, is viewed as
expensive and difficult but not impos-
sible. The best success would be antic-
ipated in new construction where an
experienced team is required, using com-
mon sense in the choice of sealing meth-
ods. A specific recommendation was the
use of a sealant such as solvent-harden-
ing, rubberized asphalt. Tracer gas meth-
ods are also recommended in assessing
radon leakage paths and determining the
success of sealing.
Dilution was the second general meth-
od discussed for radon mitigation. Pre-
cautions with this approach include
ensuring that the air intake isn't near
radon sources or near the ground, and
avoiding short circuiting (air exiting prior
to complete mixing). Diagnostics for dilu-
tion methods include the use of the
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blower door to evaluate the envelope
leakage rate of the house as well as to
catalog bypass leakage areas which allow
radon to move within the building. For
example, unless appropriate tightness
levels are present it may make no sense
to use heat recovery ventilation. The
blower door tests can also be used to
evaluate communication between zones.
Pressure measurements can be used to
ensure that indoor pressures are slightly
positive (by a few pascals) rather than
negative, to avoid drawing radon into a
living area. Airflow measurements may
make use of pilot tubes, heated-wire
anemometers, vane-type anemometers,
etc., in ducts or pipes. A grid-type
measurement, such as a pitot tube grid,
is a superior approach to averaging flow
profiles. Tracer gas measurements are
also very useful in flow measurement and
air movement, as well as detecting leaks
in the system. Use of a continuous radon
monitor as a diagnostic tool allows
exhaust air radon concentrations to be
evaluated, and to ensure that exhaust
flow isn't being reintroduced to the house
by the supply air. Because of shorter air
residence times, dilution may result in
reduction of working levels greater than
the radon levels themselves. Radon pro-
files (as a result of multilocation testing)
may be used to check for hotspots. One
approach is to flush out the radon with
high initial ventilation and then observe
the ingrowth of radon. This diagnostic
method may be used to evaluate the
amount of ventilation required to meet the
4 pCi/L EPA guideline (this is an annual
average concentration).
Pressurization of the basement was
the third category discussed. Separation
of the basement/crawlspace from the up-
stairs is an initial requirement. If upstairs
air is used to pressurize the basement,
care must be taken with the venting of
upstairs combustion devices. Use of the
blower door is recommended to check for
air leaks between zones, crack leakage to
the outdoors, and back-drafting of
appliances. Flow of approximately 850
m3/hr, and pressure differences of at
least 3 Pa are representative numbers for
judging airflow requirements for pres-
surization. Turning on all venting appli-
ances is one way to check if a mitigation
system maintains proper pressurization.
Subslab depressurization was the
fourth approach discussed. Using the
slab as the separation between house
space and soil gas, depressurization of
the subslab must be sufficient to
overcome stack effects (buoyant airflow
in the house that depressurizes the
basement) and venting appliance opera-
tion since the resulting basement depres-
surization can move soil gas through the
slab and walls to the living space.
Sensitive pressure measurement tech-
niques (such as electronic digital
manometers) may be used to evaluate
the pressure differences, and smoke
tracers can determine the direction of air
movement. The lowest pressure drop
locations across the slab are the critical
zones and should not be located near
any radon hotspots. Since the exhaust
from the subslab depressurization
contains high radon concentrations,
avoiding reentrainment is essential; tracer
gas techniques work well in this check.
The exhaust also often contains high
levels of moisture, making it essential to
design piping to avoid water ac-
cumulation and eliminate pipe blockage
or fan damage. Again back-drafting of the
combustion appliance can be influenced
by the operation of the radon mitigation
system since air is being removed from
the house substructure. Indication of
spilling of exhaust products into the
space may be documented by a small
temperature-sensitive "tab" at the flue
entry. Spillage tends to be worst at the
start of combustion appliance operation.
Use of blower door techniques can also
supply information on the required air
leakage necessary to supply combustion
devices. Dedicated makeup air to the
appliance is highly desirable.
Post-mitigation Diagnostics
Radon monitoring is the principal post-
mitigation diagnostic test commonly
utilized by commercial mitigators. The
first question is: Should the emphasis be
on measurement of radon or progeny?
Currently most people measure radon
gas. One reason is that it is simpler to
measure radon gas, with charcoal canis-
ters and alpha-track detectors. Radon
measurements might provide a less
ambiguous indication of mitigation perfor-
mance. Radon might even provide a
better indication of health risk (given that
only a relatively inexpensive measure-
ment can be made, and that the working
level (WL)-versus-particle size measure-
ments needed for dosage/risk models are
thus impractical for routine use); the
radon is tracked by reading the value for
Polonium-218, which—as the daughter
with the greatest fraction unattached --
probably represents the largest co-
ntribution to the health risk. There is a
need for technical clarification of the EPA
guideline of 4 pCi/L or 0.02 WL because
the equilibrium value between radon and
radon progeny is variable (sometimes as
much difference as 50%). However,
because the EPA guideline is expressed
as 4 pCi/L or 0.02 WL, with no reference
to a specific equilibrium relationship, it is
sufficient guidance from a policy
perspective.
Who makes the measurement is an-
other question in post-mitigation radon
monitoring. A mitigator faced with the
question of liability needs direct knowl-
edge of how the mitigation system is
functioning. Also, information on the
success of the mitigation method aids the
mitigator in selecting mitigation ap-
proaches for other homes. The home-
owner wonders if the problem has really
been solved and might want an inde-
pendent measurement, made by some-
one other than the mitigator. Federal or
state government representatives may be
most interested in how well the mitigators
are performing from a public health
standpoint, and therefore may desire an
independent evaluation of radon levels.
These results may dictate which mitiga-
tors are placed on a "recommended list,"
where local or state government main-
tains such a list.
Wow long to test is the next question.
Short-term monitoring is essential, im-
mediately after radon mitigation system
installation, to confirm that the system is
functioning properly. In addition to this
immediate measurement, an integrated
measurement over 2 to 3 months (alpha
track) in the winter is a recommended
minimum evaluation. The need to de-
velop 2-week monitors as an intermediate
measure was also discussed. Arriving at
an annual average radon exposure is a
point that needs further clarification; if the
4 pCi/L guideline is interpreted as the
annual average that a homeowner should
try to achieve, then measurements might
cover a full year. Multi-year monitoring
could be valuable in evaluating changes
in mitigation system efficiency and/or
variations in the radon source strength
over time. Annual and multi-year
measurements would probably not be
conducted by the mitigator, but would be
the responsibility of the homeowner, or
might be carried out by researchers or
state agencies. Inexpensive monitoring
devices may be heading to the
marketplace to help solve some of these
radon monitoring problems.
Where do you monitor is the next
logical question. Measurements are nor-
mally taken in more than one location: in
the living area, both upstairs and
downstairs, in the basement/crawlspace,
and in other locations cited by the home-
owner as important. Protocols must spec-
ify monitoring location. By surveying the
radon levels throughout the house (radon
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profile), one is less likely to miss a high
radon area, and also these data can be
the basis for estimating total occupant
radon exposure. The basement (or per-
haps crawlspace) area normally registers
the highest radon levels and thus is most
sensitive in revealing if any radon prob-
lem still exists after mitigation.
Which monitoring technique is another
question. Charcoal canisters and alpha-
track detectors are popular because of
ease of use and relatively low cost. For
immediate information on radon concen-
trations, grab and continuous radon sam-
pling are popular. There remain several
uncertainties associated with the vari-
ability in indoor radon levels (which are
evident from continuous radon data). In
view of all the uncertainties, there would
appear to be a need for a standardized
procedure that could be routinely applied
in the post-mitigation period.
Other diagnostics should also be
considered. Diagnostics other than
checking radon concentrations are
usually not done routinely by commercial
mitigators. Testing of the final pressure
field under the slab after installation of a
subslab ventilation system was empha-
sized by several workshop participants as
important to consider as a post-mitigation
diagnostic measurement. Assurance that
combustion devices are not back-drafting
is also an important post-mitigation
measurement. Measurement of flows and
pressures in piping associated with the
mitigation system can be important in the
post-pressure-mitigation diagnostics as
well as during system installation.
Mounting a pressure gauge (or pressure
switch) on the piping to indicate proper
system function is being used and is a
form of a post-mitigation diagnostics that
assures the homeowner that the system
is functioning satisfactorily.
Acknowledgments
The authors wish to acknowledge the
contributions of Michael Mardis, Michael
Osborne, and Bruce Henschel who
served as session chairmen for the work-
shop and provided guidance in sum-
marizing the diagnostic methods dis-
cussed in this summary. The authors also
wish to acknowledge the sponsorship of
the U.S. Environmental Protection
Agency for the workshop under EPA Co-
operative Agreement CR814014-01-0.
#U.S. GOVERNMENT PRINTING OFFICE 1989/748-012/07187
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