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?

-------
  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

-------
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

-------
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

-------
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

-------