^   -
Environmental Protection
Agency    "~
1    > u/  **X $ if **-*ť• f

11 ~ "" Office of Radatiorf Programs'
   Office of Research ana Development

 *"" r~Washington, DC 20460
    \  V  V f ** "" -=r *^* iff 1
*.  	X	ff. -K \,	^"	I "* '
            -    -
          EPA 520/1*89-020
          October tS69

   - .-, ,r,.v AV * J1  - * ' ^ ,, r1 *^Ť
  ^  ^  ^-^ ' -^> ^  J?at* - ^ ^ -^ *"^ js
Interim Technical Guidance
/Ť i ,.*<
                                   *> *,-• Ł*" -;
                                     * l^v" *6 |
                                   ^  ^

•*        K.
        1   t  If   ,,, ^   J

       "   -            *   VI   J -
                                                              I        *•

                                           EPA 520/1-89-020

             Interim Technical Guidance
              Office of Radiation Programs
               Office of Air and Radiation
      Air and Energy Engineering Research Laboratory
           Office of Research and Development

       United States Environmental Protection Agency
                    Washington, DC
                     October 1989


                                  EPA DISCLAIMER NOTICE

The U.S. Environmental Protection Agency (EPA) strives to provide accurate, complete, and useful
information.  However, neither EPA nor any person contributing to the preparation of this document
makes any warranty, expressed or implied, with respect to the usefulness or effectiveness of any
information, method, or process disclosed in this document

Mention of firms, trade names, or commercial products in this document does not constitute
endorsement or recommendation for use.


The information contained in this technical document is based largely on research conducted in
Washington County, Maryland, by the Air and Energy Engineering Research Laboratory (AEERL) of
EPA's Office of Research and Development and their contractor, INFILTEC.  The research was
conducted with  the assistance of H. Winger of the Washington County Schools (Maryland).

A.B. Craig and  K.W. Leovic of AEERL and D. W. Saum of INFILTEC contributed to authorship of this
document.  F. L. Blair in the Radon Division  of EPA's Office of Radiation Programs  (ORP) served  as
Work Assignment Manager for contractor support.  J. Harrison also of ORP's Radon  Division provided
substantive information and comments.  Of the contributors outside of EPA, we are particularly indebted
to T. Brennan of Camroden Associates and W. A. Turner of Harriman Associates for  their input.

Drafts of this document have been reviewed by a large number of individuals in the Government and in
the private and  academic sectors. Comments from these reviewers  in addition to those from the
individuals listed above have helped significantly to improve the completeness, accuracy, and clarity of
the document.   The following reviewers offered substantial input:  A. Persily of the National Institute of
Standards  and Technology; P.A. Giardina and  L. G. Koehler of EPA Region 2; W.E. Bellanger of EPA
Region 3;  F. P.  Wagner of EPA Region 4; R.  Dye of EPA  Region 7; L. Feldt, J. Hoornbeek, D.
Murane, and L.  Salmon of ORP's Radon Division; J. Puskins of ORP's Analysis and Support Division;
C. Phillips of Fairfax County Public Schools (Virginia); D. Shiftlet of Prince George's  County Schools
(Maryland); H. M. Mardis of Environmental Research and Technology, Inc.; R. J. Shaughnessy of the
University of Tulsa; T. Meehan of Safe-Aire; G. Bushong and R. McNally of EPA's Office of Toxic
Substance's Asbestos Program.  Technical editing was provided by W. W. Whelan of AEERL and I.
McKnight  of ORP.




       1.1  Purpose	  1
       1.2  Additional Sources of Information	  1
       1.3  Radon Facts  .,	  2


       2.1  Radon Entry	  5
       2.2  Radon Variations Within Schools .	  6
       2.3  Radon Mitigation Techniques	  6



       4.1  School Substructures	11
       4.2  HVAC Systems	 12
       4.3  Location of Utility Lines  	14


       5.1  Application	15
       5.2  Diagnostic Testing	15
       5.3  Design and Installation	17


       6.1  Classroom Pressurization  	23
       6.2  Increasing Ventilation  	24
       6.3  Crawl Space Depressurization	24


       7.1  Building Codes  	25
       7.2  Worker Protection	'.. . 25
       7.3  Asbestos	 25

       A.1 Using Construction Documents  . .	29
       A.2 Fan and Pipe Selection	30
       A3 Diagnostic Measurement Tools	32
       A4 Installation Tools  	33
       AS School SSD Installation Variations	33

       School A' Prince George's County, MD	35
       School B: Washington County, MD	36
       School C: Washington County, MD	40
       School D: Washington County, MD	41
       School E: Fairfax County, VA	[42
       School F: Washington County, MD  .	44
       School G: Arlington County, VA	45
       School H: Washington County, MD		46

         OFFICES	49
       State Radon Offices	49
       EPA Regional Offices	53

                                     1.  INTRODUCTION
This technical document is intended to assist
school facilities maintenance personnel, State
officials, and other interested persons in the
selection, design, and operation of radon
reduction systems in schools.  School officials
should work in conjunction with a person
experienced in radon mitigation, preferably in
schools, to  diagnose the problem and determine
which mitigation options are feasible.  School
officials can contact their State Radon Office or
EPA Regional Office for guidance on selecting
a qualified  radon mitigation contractor. (See
Appendix C.)

The guidance contained in this document is
based largely  on research conducted in 1987 and
1988 in schools located in Maryland and
Virginia. In these initial efforts, researchers
from the U.S. Environmental Protection Agency
(EPA) adapted radon reduction techniques
proven successful in residential housing and
installed them in eight schools. Results indicate
that radon  mitigation and diagnostic techniques
developed for houses can be applied successfully
in these schools. The applicability of these
mitigation approaches to other schools will
depend on  the unique characteristics of each

Because school design,  construction, and
operation patterns vary considerably, it is not
always possible to recommend "standard"
corrective actions that apply to all schools.
Costs for radon reduction will also be school
specific and will depend on the initial radon
level, the extent of the radon problem in the
school, the school design and construction, the
design and operation of the heating, ventilating,
and air-conditioning (HVAC) system, and the
ability of the school maintenance  personnel to
participate  in the diagnosis and mitigation of
the radon problem. With the guidance of an
experienced radon mitigator, maintenance
personnel may be able  to install radon reduction
systems themselves.

This technical document covers background
information on radon and radon mitigation
experience, important school building
characteristics relative to radon entry and
mitigation, problem analysis, radon diagnostic
testing, and radon mitigation system design and
installation. Appendices include technical
information, case studies of the Maryland and
Virginia schools mitigated, and lists of State
Radon Offices and EPA Regional Radiation
Program Offices.

It is important to understand that this is
preliminary guidance. A major research
program is under way in the Air and Energy
Engineering Research Laboratory in EPA's
Office of Research and Development, and
guidance on recommended radon reduction
actions for schools will be updated as soon as
                                             1.2     ADDITIONAL SOURCES OF

                                             The publications listed below are available from
                                             State Radon Offices or from EPA Regional
                                             Offices. (See Appendix  C.)

                                             PUBLICATIONS ON RADON IN SCHOOLS

                                             For guidance on how to measure radon levels in
                                             schools, you should consult "Radon
                                             Measurements in Schools - An Interim Report"
                                             (EPA 520/1-89-010).

                                             OTHER PUBLICATIONS ON RADON

                                             EPA has been studying the effectiveness of
                                             various methods of reducing radon
                                             concentrations in houses.  Although this work is
                                             not yet complete, considerable progress has
                                             been made over the last several years, and a
                                             number of EPA publications have been issued.
                                             A general familiarity with these publications on
                                             radon reduction in houses will be useful in
                                             understanding and reducing elevated radon
                                             levels in school buildings.

                                             "A Citizen's Guide to  Radon: What It Is And
                                             What To Do About It"  (EPA OPA-86-004)
                                             provides general background information for the

  homeowner on radon and its associated health
  risks.  It should be noted that this guide is
  being updated, and the next edition should be
  available in mid-1990.

  "Radon Reduction Methods: A Homeowner's
  Guide" (Second and Third Editions)
  (OPA-87-010 and OPA-89-010) describe in
 general terms  the various radon reduction
 methods available to homeowners.

 "Radon Reduction Techniques for Detached
 Houses: Technical  Guidance" (Second Edition)
 (EPA/625/5-87/019) is a reference manual
 providing information on the sources of radon
 and its health  effects as well as detailed
 guidance on the selection, design, installation,
 and operation  of radon reduction systems.

 "Application of Radon Reduction Methods"
 (EPA/625/5-88/024) supplements the second
 edition of the  technical manual (above) as a
 decision guidance document directing the user
 through the steps of diagnosing a  radon
 problem and selecting a radon reduction
 approach.  Mitigation system design, installation,
 and operation  are also  detailed.

 "Radon Reduction in New Construction, An
 Interim Guide" (EPA OPA-87-009) and
 "Radon-Resistant Residential New Construction"
 (EPA-600/8-88-087) provide information on
 radon prevention techniques for new

1.3.1    Radon Gas

Radon is a colorless, odorless, and tasteless
radioactive gas which results from the decay of
uranium.  Since uranium occurs naturally in
small quantities in most rocks and soil, radon is
continually released into soil gas, underground
water, and outdoor air.  Radon is chemically
inert, and it moves freely without combining
with other materials.  In outdoor air the radon
emitted from the soil is quickly diluted to very
low concentrations. However, relatively high
concentrations of radon can accumulate inside
buildings if radon-containing soil gas infiltrates
 into the building through openings such as
 cracks, building joints, and utility penetrations.
 Normal building ventilation may dilute the
 incoming radon gas, but depending on the soil
 gas radon levels and the amount of soil gas
 entry, the radon concentration in the building
 may accumulate to high levels.  Since radon
 source strengths vary and radon entry routes are
 so unpredictable, testing each building is the
 only practical way to determine the extent of
 the problem.

 EPA currently recommends taking action to
 reduce radon levels in homes where the annual
 average concentration of radon exceeds 4
 picocuries per liter (pCi/L). (As a comparison,
 average outdoor radon concentrations  tend to
 range from about 0.1 to 0.2 pCi/L.)  The greater
 the reduction in radon, the greater the
 reduction in health risk. Consequently, an
 effort should be made to reduce radon levels in
 all buildings as far below 4 pCi/L as possible.
 It should also be noted that the 1988 Indoor
 Radon Abatement Act establishes as a national
 long-term goal that the air within buildings be
 as free of radon as the air outside of the

 1.3.2   Health Effects

 Radon differs from most other carcinogens in
 that human epidemiological evidence links
 radon to lung cancer, and this evidence is well
 supported by laboratory studies and
 experimental research.  Although uncertainties
 remain and considerable research is continuing
 in this field, the health risks of radon  have been
 clearly recognized by the National Academy of
 Sciences, the U. S. Public Health Service, and

 Lung cancer is the only health risk which
 significant data clearly associate with radon.
 Radon gas decays into other radioactive
 elements (often referred to  as radon decay
 products or radon progeny) which can lodge in
 the lungs.  Bombardment of sensitive lung tissue
by alpha radiation released from the decay
products can increase the risk of lung  cancer. It
is estimated that radon causes roughly 20,000
lung cancers each year in the United States.

It should be emphasized that estimates of the
number of lung cancers resulting from radon
vary widely, but even the lowest estimate
represents the largest cause of lung cancer for
non-smokers.  Not everyone exposed to  elevated
levels of radon will develop lung cancer.
However, most scientists believe that children
are at an equal or greater risk from exposure to
radon than adults and that smokers are at a
greater risk from exposure to radon than
nonsmokers.   There is also consensus among
scientists that the risk of developing lung cancer
increases as the concentration and length of
exposure increase.


                                   2.  RADON MITIGATION
 Since  1984, when elevated levels of indoor
 radon were discovered in the Reading Prong
 area of Pennsylvania, many thousands of houses
 have had radon reduction systems installed. In
 many areas of the United States, it is not
 uncommon to find a contractor with house
 mitigation experience. In fact, many states
 maintain lists of radon mitigation contractors.
 (See Appendix C for a list of State Radon

 Radon mitigation experience in schools  is
 relatively recent. However, initial research
 indicates that radon reduction technologies
 proven successful in houses are applicable to
 some schools.  The applicability of these
 mitigation approaches to other schools will
 depend on the unique characteristics of each
Radon normally enters a building from soil gas
that is drawn in by pressure differentials
between the soil surrounding the substructure
and the building interior.  If the building
interior is at a lower pressure than the soil
surrounding the substructure and radon is
present in the soil, the radon can be pulled in
through cracks and openings that are in contact
with the soil.  The amount of radon  in a given
classroom will depend on the level of radon in
the underlying material, the ease with which the
radon moves as a component of the soil gas
through the soil, the magnitude and direction of
the pressure differentials, and the number and
size of the radon entry routes.

2.1.1    Causes of Pressure Differentials

Pressure differentials that contribute  to radon
entry can result from operation of an HVAC
system under conditions that cause negative
pressures (in the building relative to  the subslab
area), indoor/outdoor temperature differences
(including the  "stack effect"), use of appliances
or other mechanical devices that depressurize
the building, and wind.
 HVAC systems in schools and other large
 buildings vary considerably and tend to have a
 much greater impact on radon levels than do
 heating and air conditioning systems in houses.
 If the HVAC system induces a negative pressure
 in the building relative to the subslab area,
 radon can be pulled into the building through
 floor and wall cracks or other openings in
 contact with the soil.

 Even if the HVAC system does not contribute
 to pressure differentials in the building, thermal
 stack effects can induce localized negative
 pressure at the base of the building causing
 radon-containing soil gas to be pulled into the
 school.  As air inside the structure is heated, it
 becomes less dense, and rises, exiting out
 through openings in the top of the structure.
 Cooler air is drawn into the building to replace
 the warm air leaving at the top of the structure.
 This phenomenom, which acts much like a
 chimney, is referred to as the stack effect.

 If the HVAC system pressurizes the building,
 which is common in many systems, it can
 prevent radon entry as long  as the fan  is
 running.   However, school HVAC systems are
 normally set back or turned  off during  evenings
 and weekends, and even if the HVAC system
 pressurizes the  school during operation, indoor
 radon levels may build up during setback
 periods.  Once  the HVAC system is turned back
 on, it may take several hours for radon levels to
 be adequately reduced.  Adjustment of the
 setback timing may, in some cases, achieve
 acceptable indoor radon levels during periods of
 occupancy. Measurements with continuous
 radon monitoring equipment in each classroom
with elevated radon levels are necessary to
determine the appropriate setback configuration
 in such situations.

2.1.2   Radon  Entry Routes

Typical radon entry routes include cracks in the
slabs and walls, floor/wall joints, porous
concrete block walls, open sump pits, and
openings around utility penetrations. Radon
accumulated in  crawl spaces  may also enter a
building.   In addition, many schools have other

 radon entiy points such as slab pour joints
 (control joints) and subslab utility tunnels.
 These are discussed in more detail in Section
 4.3, Location of Utility Lines.

 In houses, radon problems caused by radon
 emanations from building materials or by radon
 released from radon-contaminated water
 (normally well water) occur in isolated
 instances.  We would expect few schools to
 have this type of radon problem.

 Experience has shown that there can be large
 differences between radon levels  in classrooms
 on the same floor.  Causes for these
 room-to-room differences are thought to include
 variations in the soil under the class rooms,
 variations in the construction between rooms,
 variations in the number and size of cracks in
 different rooms, and variations in the design  and
 operation of the HVAC system.  This
 room-to-room variability makes it difficult to
 detect and mitigate all the rooms with high
 radon levels unless every classroom on or below
 ground is tested.

Although the selection of the most appropriate
radon mitigation technique depends on the
unique characteristics of each building, five
mitigation approaches have been common in
house mitigation, either alone or in
combination.  These include:  subslab
depressurization (SSD), submembrane
depressurization (SMD) in crawl space areas,
sealing, pressurizatfon, and natural and
mechanical ventilation.  (For additional details
on these and other mitigation techniques for
houses,  refer to the technical manuals previously

These techniques and their applicability to
schools are briefly discussed below.  Because
current radon mitigation experience in schools is
largely limited to SSD, this guidance document
focuses on that approach. Where available,
 guidance for other techniques is also given.
 The reader should review Sections 5 and 6 for
 more detail.

 EPA feels that many of the radon reduction
 approaches for houses will be applicable to
 school mitigation, and research is in progress to
 conduct additional testing of these techniques in
 school buildings.  It should be understood that
 in many types of schools there is little or no
 experience in radon mitigation.  Examples of
 schools that may be difficult to mitigate include:
 schools with poor subslab permeability
 (explained under SSD); schools with subslab
 ductwork; schools with exhaust fans to increase
 fresh-air infiltration (potentially causing large
 negative pressures and increased radon  entry);
 and schools constructed over crawl spaces.

 2.3.1    Subslab Depressurization (SSD)

 SSD has been the most successful and widely
 used radon reduction technique in slab-on-grade
 and basement houses.  Installation of an SSD
 system involves inserting pipes through  the
 concrete slab to access the crushed rock or soil
 beneath.  A fan is then used to suck
 radon-containing soil gas from under the slab
 through the pipes, releasing it outdoors. SSD
 works by creating a negative pressure field
 under the slab relative to the building interior;
 this interior/exterior pressure relationship
 prevents radon-containing soil gas from  entering
 the building.

 The material under the foundation slab  must  be
 permeable enough to allow air movement  under
 the slab so that adequate suction can be induced
 across the entire slab.  (Subslab permeability  or
 air flow is often referred to as subslab
 "communication" or "pressure field extension.")
 When subslab pressure field extension is
 inadequate, additional suction pipes may be able
 to increase the area that can be depressurized.

 Initial results indicate that SSD can successfully
 reduce radon levels in some schools by over 90
percent if crushed aggregate or other permeable
material is under the slab to allow for adequate
pressure field extension. However, schools with
poor subslab communication and those using
return-air ductwork beneath the slab may

require an alternative mitigation approach to
2.3.4    Pressurizatidn (Through HVAC System
2.3.2    SubmembraBe Depressurization (SMD't

A variation of SSD, often referred to as
submembrane depressurization (SMD), bas been
very successful in reducing radon levels in
houses constructed over crawl spaces. A
polyethylene or rubber membrane is laid over
the earth floor and sealed to the crawl space
walls and internal piers.  Suction is applied to
the soil underneath the membrane and the soil
gas is exhausted to the outdoors. EPA has not
yet researched this method in schools; however,
SMD may prove more difficult in many school
crawl spaces because of all the internal
foundation walls, the large areas to be treated,
and the possible presence of asbestos.

2.3.3    Sealing

The effectiveness of sealing alone as a radon
reduction technique is limited by the ability to
identify, access, and seal major radon entry
routes.  Most buildings have so many radon
entry routes that sealing only the obvious ones
may not result in a significant degree of radon
reduction.  Complete sealing of all radon entry
routes is often impractical.  In some buildings,
certain areas will be difficult, if not impossible,
to access and/or seal without significant expense.
In addition,  settling foundations and expanding
floor cracks  continue to open new entry routes
and reopen old ones. Typical initial radon
reduction from extensive sealing in houses is
usually about SO percent
A potential mitigation approach for schools is
adjustment of the air-handling system to
maintain a positive pressure in the school
relative to the subslab area, discouraging the
inflow of radon. This technique, referred to as
pressurization, has been shown to be an
effective temporary means of reducing radon
levels in some schools, depending on the design
of the HVAC system.  If pressurization through
the HVAC system is under consideration as a
long-term radon mitigation solution in a given
school, proper operation and maintenance of
the system are critical. Responses to changes in
environmental conditions and any additional
maintenance costs  and energy penalties
associated with the changes in operation of  the
HVAC system must also be carefully considered.
There may also be potential moisture and
condensation problems if pressurization is
implemented in very cold climates.

2.3.5    Increasing BuildingVentilation (Without
        HVAC  System Control)

An increase in building ventilation rate, by
opening lower-level windows, doors, and vents
or by blowing outdoor air into  the building  with
a fan, reduces radon levels by diluting indoor air
with outdoor air and by minimizing the pressure
differentials that draw radon into the building.
However, EPA's preferred radon reduction
strategy has been to prevent radon entry into
buildings, rather than to reduce radon levels
once it has entered. Experience has shown  that
it is usually impractical to lower radon levels in
houses much more than 50 percent through
increased ventilation.  Therefore, in most
climates, reducing  radon levels  through
ventilation should  only be considered as a
temporary measure.


                             3.  ANALYZING THE PROBLEM
Understanding a school radon problem and
developing a mitigation strategy involves a
careful review of all 'radon testing data, a
walk-through audit, and a review of relevant
building documents.  Applicable critical building
components  (as discussed in Section 4) should
be examined. These  include the building
structure, the HVAC system, and the location of
utility lines.  Special  radon diagnostic tests will
also be useful.  These might include continuous
monitoring of radon  levels during various
building operating conditions, mapping of
subslab radon, and measuring subslab
communication and pressure  field extension to
determine if SSD is applicable. Diagnostic tests
are discussed in more detail in Section 5.  A
general outline of the steps involved follows.


Write down  all radon test results on copies of
the school floor plan so that rooms with high
readings can be correlated. Test data should
include type of measurement device, length of
measurement period, HVAC operating
conditions, school occupancy,  and weather
conditions during the test period.  In developing
a mitigation plan, emphasis should be on the
confirmatory measurements rather than the
screening measurements, as described in "Radon
Measurements in Schools - An Interim Report".
(See Section 1.2, Additional Sources of
Thoroughly examine all parts of the building in
contact with the soil  (In a basement school,
examine both the basement and first floor.)
Note the presence of possible radon entry
routes  such as floor/wall cracks and other
openings to the sofl and determine if they
correlate with areas having elevated radon
                                     (either positive or negative) can be exerted
                                     during system operation. Where possible,
                                     obtain a complete description of the HVAC
                                     system design and operation from the building
                                     facilities personnel and determine if HVAC
                                     operation is causing any negative pressures in
                                     the building relative to the subslab area. If the
                                     original school has any additions, be sure to
                                     note if there are different types of HVAC
                                     systems, as well as structural differences between
                                     the additions.  In some  cases, consultation with
                                     a qualified firm experienced in HVAC system
                                     design may be useful in understanding possible
                                     sources of HVAC depressurization.
                                     STEP 4:
Depending on the design and operation of the
HVAC system, relatively strong indoor pressures
Study the foundation plans and specifications
for information on aggregate or gravel beneath
the slab, for the layout of footings and subslab
walls that could limit subslab communication in
an SSD system, and for the presence of subslab


School personnel with little experience in radon
reduction should use experienced or certified
radon mitigation firms to gain the advantage of
their experience and specialized knowledge of
local problems. These firms may also be able
to provide specialized equipment such as
continuous radon monitors, core drills, and
sensitive pressure gauges. Since radon
mitigation in schools is a relatively new field, it
is probable that mitigators in many parts of the
country will be more experienced in mitigation
of houses than schools.

Local and state health departments and EPA
regional offices maintain lists of persons who
have attended  EPA mitigation training courses.
Several states have initiated programs for
certification of radon mitigation companies,  and
several trade associations have been offering
membership or educational courses for
professionals in the field. In 1990, EPA will
publish a national list of mitigators who have

 met the requirements of the Radon Contractor
 Proficiency Program.


 Radon mitigation is not an exact science. In
schools  it is often best to proceed in phases:
install the simplest  system that promises the
biggest payback and re-test to  determine
effectiveness; then use this information to
proceed with subsequent phases, as necessary.
The phased approach should be especially
helpful in schools because experience is limited
and the buildings tend to be more complex than
houses. Because we often do not know all the
radon entry routes or forces drawing radon into
the building, the first phase of mitigation can
usually provide valuable information.  The
following sections cover the critical building
components relative to radon entry and
mitigation, the design and installation  of SSD
systems, and other mitigation approaches.  The
case studies in Appendix B are examples of the
phased approach to mitigation.

For help in understanding the causes of elevated
radon levels in schools and to better design
school mitigation systems, three building
components are of primary concern:  the
building substructure(s), the design and
operation of the HVAC system(s), and the
location of utility lines. This section discusses
how these aspects of school buildings relate to
house mitigation experience, how these building
components tend to affect radon entry in
schools, and how they may impact mitigation
system design and operation.

An understanding of these critical building
components and how they relate to a specific
situation are important when designing a school
mitigation system.
The three basic substructure types are
slab-on-grade, basement, and crawl space.  The
majority of substructures in the school districts
studied  thus far were slab-on-grade. Schools
often  have one or more additions, and each
addition may have a different type of

Because of larger building and room sizes,
schools  often have interior footings and subslab
foundation elements.  These may create subslab
communication barriers between areas. The
location of subslab barriers and their influence
on subslab communication will depend on
building size and  configuration, and on
architectural preferences for carrying roof load.
The locations of these barriers may affect the
number and placement of SSD suction points in
a slab-on-grade or basement structure, and
foundation plans, if available, should always be
examined when selecting suction point locations.
This increases the opportunity for all areas with
elevated radon levels to be adequately treated by
the SSD system.

4.1.1    Slab-on-Grade

Since  current research indicates that SSD is the
most successful technique  for reducing radon
levels in slab-on-grade schools with good
subslab communication, the construction
documents should be checked for information
on the type and amount of subslab gravel or
aggregate. Even if aggregate is specified, the
air-flow resistance of different  aggregate types
has been found to differ significantly.  Subslab
communication measurements  and visual
inspections are often necessary to efficiently
design an SSD system.

Interior footings and rolled footings (grade
beams) may pose substantial barriers to
communication between areas; therefore, it  is
necessary to carefully examine  the foundation
plans when designing an SSD system.
Depending on the type of subslab barrier and
the material underneath the barrier  (e.g., clay,
sand, gravel) there may be limited
communication, if any,  across these barriers.
Often, it may be necessary to locate additional
subslab suction points if areas  to be mitigated
do not communicate across subslab barriers. In
other cases, coverage of the SSD system may be
increased if a larger fan and/or pipe diameter
are used.  Evaluation of subslab communication,
as discussed  in Section  5.2, will indicate the
effect that these subslab barriers will have on
SSD system design.

4.1.2   Basements

Schools with basements may present a difficult
problem because a large area is in contact with
the soil.  Some school basements are completely
below-grade  and others are walk-out basements.
Walk-out basements are commonly used as
classrooms or  workspace.  Many full basements
in older buildings have also been converted to
classroom space. Below-grade walls, the slab,
and floor/wall  cracks can be significant sources
of radon entry. If there is adequate subslab
communication, SSD is probably the most
desirable approach to radon mitigation in most
basement schools.  All  of the comments on SSD
systems in the above section on slab-on-grade
schools are applicable to basement schools.  In
addition, any asbestos in the basement should
be removed or encapsulated according to the
Asbestos Hazard Emergency Response Act

 (AHERA) before attempting any radon
 reduction activities in the basement.

 4.1.3   Crawl Spaces

 Most crawl space schools tend to be constructed
 on concrete slabs supported by periphery and
 internal foundation walls, although schools with
 conventional wood joist and floor  construction
 over a crawl  space and "portable" classrooms do
 exist.  Crawl  spaces are usually divided into
 compartments that are all interconnected by
 open passages allowing access to utility pipes.
 To avoid freezing  of inadequately insulated
 pipes, some school crawl spaces have no vents.
 As a result, high levels of radon may collect in
 the crawl space. (Elevated levels of radon can
 accumulate in a vented crawl space as well.)

 Increasing  natural ventilation by opening crawl
 space vents may be a possible solution as long
 as the changes in temperature do not cause
 problems such as freezing pipes, condensation,
 or cold floors.  Whether this will adequately
 reduce radon levels will be school  specific.
 Depressurization of the crawl space has been
 more effective in reducing radon levels in
 houses than natural ventilation  of  the crawl
 space; again,  experience in schools has been
 limited.  Submembrane depressurization (SMD)
 has also been successful in reducing radon levels
 in houses built on crawl spaces.  However, SMD
 has not yet been researched by  EPA in any
 schools.  It is possible that the application of
 this  technique may be difficult in many schools
 because of the large area to be  treated and
 complicating  interior crawl space walls.

 More detailed guidance on these approaches for
schools will be available following  further
 research. In  any case, any asbestos in the crawl
space area  should be removed or encapsulated
according to AHERA before attempting any
 radon reduction  activities in the crawl space.

Understanding the school's HVAC system often
plays an important role in determining the
 source of, and the solution to, the radon
 problem.  The American Society of Heating,
 Refrigerating and Air-Conditioning Engineers
 (ASHRAE) Standard 62-1981R "Ventilation for
 Acceptable Indoor Air Quality" should be
 consulted to determine if the installed HVAC
 system is designed and operated to achieve
 recommended minimum ventilation standards
 for indoor air quality.  Sometimes schools and
 similar buildings were not designed with
 adequate ventilation, and in other instances,
 ventilation systems are not operated properly
 due to factors such as increased energy costs or
 uncomfortable conditions caused by a design or
 maintenance problem.  It is advisable to achieve
 the recommended minimum ventilation
 standards in a school in conjunction with or in
 addition to installation of a system for radon
 reduction.  Consultation with a qualified HVAC
 firm or a registered Professional Engineer
 experienced  in HVAC system design is
 recommended for evaluating the HVAC system
 both in terms of radon mitigation options and
 indoor air quality.

 HVAC systems in the school districts initially
 researched by EPA include: central air-handling
 systems, room-sized unit ventilators, and radiant
 heat. Unit ventilators and  radiant heat can exist
 with or without a separate ventilation system.
 Central air-handling systems and unit ventilators
 tend to  be most prevalent in newer schools,
 particularly if air-conditioned.  Often, because of
 additions, schools may have more than one type
 of HVAC system.

 4.2.1    Central-Air Handling Systems

 In many buildings with air-conditioning, the
 HVAC system contains some type  of central
 air-handling system. The systems can vary
widely in size and configuration, and the
 different types of systems will tend to have
 unique effects on radon entry and subsequent
 mitigation.  Three types of  central air-handling
systems  common in schools are summarized
below: single-fan systems, dual-fan systems, and
exhaust-only systems.

 In single-fan systems the air is distributed to the
rooms (normally under pressure) by the
air-handling  fan, and the return air is brought

back by the same fan.  These systems are similar
to forced-air systems in houses, except that fresh
air can usually be mixed with the return air.
The air-handling fans may operate continuously
during the day, or they may operate only when
heated or cooled air is required, cycling on and
off throughout the day with thermostat control.
In any case, the systems are normally set back
or turned off during evenings and weekends.
These single-fan systems are normally designed
to generate neutral or positive pressures in all
rooms. In a single-fan system, stale air leaves
the building either through  a separate exhaust
system, by relief, or by exfiltration through
cracks  and openings due to  overpressurization
by the fan (if  fresh air is brought into the

Larger air-handling systems  often employ a
dual-fan  system: an air-distribution fan and  a
smaller return-air fan.  The return-air fan  allows
for forced exhaust of return air.  Louvers
regulate  the amount of fresh air brought into
the air supply and the amount of return air  that
is exhausted.  Dual-fan systems are usually
designed so that they generate positive pressures
in all rooms when operating; however, if the
return-air fan  pulls more air from a room than
the supply fan is furnishing, then the room can
be run under  negative pressure causing soil gas
to enter  the room through openings to the soil
beneath  the slab.  The fans  usually operate
continuously during  the day and are either set
back or turned off during evenings and

Although single- and  dual-fan systems are
commonly designed to operate at positive or
neutral pressures, pressure measurements in
schools have indicated that  such systems can
cause significant negative pressures in the
building. HVAC system modifications (such as
reducing the amoral of fresh-air intake), lack of
maintenance (suck as dirty filters), unrepaired
damage,  or other factors can result  in
substantial negative pressures in some rooms,
thus increasing soil gas entry.

The third type of central air-handling system is
an exhaust-only system in which no supply air is
provided mechanically. Such systems are
generally used for ventilation in schools that
heat with radiant systems or unit ventilators and
have no central air-handlers.  The fans exhaust
air through a central ceiling plenum above the
rooms or with roof mounted exhausts in many
locations. These systems are designed to draw
fresh air into the rooms by infiltration through
above grade cracks and openings; however,
radon can enter through below grade cracks and
openings. The fans in exhaust-only systems
usually are normally off at night  but may
operate continuously during the day.  This can
generate a negative pressure in all rooms and,
consequently, increase the  potential for radon

4.2.2   Unit Ventilators

These self-contained units  provide heating
and/or air-conditioning in individual rooms.
They are usually installed on outside walls with
an enclosure which contains finned radiators
and/or coils.  They can also be located overhead
in each room and are sometimes above  the
drop ceiling.  Unit ventilators normally contain
one  or more fans and  a vent to the outdoors  so
that fresh air can be pulled in by the fah(s).
An adjustable damper allows a variation in the
mix  of recycled room air and fresh air fed to
the circulating fan. Fresh-air intake can be
minimal because of obstruction of the outdoor
vents due to poor maintenance or energy
conservation practices.  (Units that do not
provide any outdoor air by design are referred
to as fan coil units, not unit ventilators.)

In some cases there is a central-building
exhaust-fan system in schools with  unit
ventilators, as discussed above.  This exhaust  fan
is intended to provide ventilation by pulling air
in through the unit ventilators (if their fresh-air
vents are open), but it also creates a significant
negative pressure in the room. . This negative
pressure can pull radon into the rooms with the
soil  gas. If fresh-air intakes in the unit
ventilators are blocked for any reason, operation
of exhaust-only fans will increase the negative
pressure in the building relative  to the subslab

Radon mitigation strategies in schools with unit
ventilators might include (1) opening the
fresh-air vents to improve ventilation and

 running the unit ventilator fans continuously to
 pressurize the room, (2) replacing an
 exhaust-only ventilation system with a system
 that operates under a slight positive pressure, or
 (3) installation of an SSD system that could
 overpower all negative pressures in the building.
 If the current HVAC system is providing
 adequate ventilation to the building or if
 options (1) and (2) are not feasible, option (3),
 SSD, would be the most practical strategy if
 there is good subslab communication.

 4.2.3    Radiant Heat Systems

 Radiant heat systems in schools tend to be of
 three types: hot water radiators, baseboard
 heaters, or warm water radiant heat within the
 slab. Schools heated with radiant systems
 should have a ventilation  system to achieve the
 fresh air requirements recommended by
 ASHRAE; however, many of these schools
 provide no ventilation other than infiltration.
 In other schools, there are exhaust ventilators
 on the roof. These can be passive,  allowing
 some ventilation through the stack effect, or
 they can be powered. Powered Roof
 Ventilators (PRVs) can cause significant
 building depressurization,  particularly if a fresh
 air supply is not provided.  This can cause
 considerable radon entry into the building while
 such exhaust systems are operating.

 If SSD is under consideration as a mitigation
 option in a school with intra-slab radiant heat,
 the building plans should be carefully studied to
 avoid damaging any piping when placing the
 SSD points.  An infrared scanning device can be
 used to help locate the exact position of subslab
 pipes.  Satisfactory locations for SSD pipes may
 be very limited in such schools.

The location of entry points for utility lines can
have a significant influence on radon entry in
 schools since they can provide an entry route
 from the soil into the indoor air.  Utility line
 locations depend on many factors such as
 substructure type, HVAC system, and
 architectural needs or practices.  Utility lines
 located above  grade should not cause significant
 radon entry problems.

 In slab-on-grade and crawl space schools, the
 utility penetrations from the subslab or crawl
 space area  to individual rooms are frequently
 not completely sealed, leaving openings between
 the soil and the  building interior.  For example,
 there is a potential for radon entry around
 plumbing penetrations and electrical conduits.

 If utility lines,  such as electrical conduits and
 water and sewer  pipes, are located under the
 slab, their exact locations should be carefully
 noted from the plans, and caution should be
 taken when drilling holes through the slab
 during diagnostic measurements.  This is
 discussed in more detail in Section 5.

 In some slab-on-grade schools, the utility lines
 are located  in a subslab utility tunnel that tends
 to follow the building perimeter or central hall.
 Utility tunnels  often have many openings to  the
 soil beneath the slab-on-grade and,
 consequently, can be a potential radon entry
 route.  In addition, risers to the unit ventilators
 frequently pass through unsealed penetrations in
 the floor so that  soil gas in the utility tunnel
 can readily enter the rooms.  If the surrounding
 soil has elevated  radon levels, a utility tunnel
 could be a major radon entry route in schools.

 It is possible that the utility tunnel could be
 used as a radon collection chamber for an SSD
system, and  this approach will be studied.  Any
asbestos in the utility tunnel should be removed
or encapsulated according to AHERA before
attempting any radon reduction activities in the

  Experience has shown that SSD is the most
  successful radon reduction technique in houses
  that have aggregate or permeable soil beneath
  the slab. There is much less experience with
  SSD in schools; however, the results to date,
  although limited, have been promising in
  schools that have aggregate or clean, coarse
  gravel  under the slab. Current guidance on
  radon reduction in schools is focused on
  designing and installing SSD systems, since
  experience in mitigating schools using other
  techniques (Section 6) is very limited.

  Experience to date has  identified certain types
  of schools where SSD may not be applicable.
  These include:

          Schools that  do not have crushed
          aggregate, coarse gravel, or permeable
          soil  underneath the slab. (Experience
          has shown that SSD systems perform
          best when the subslab material is
          approximately 3/4 to 1-1/4 inches in
          diameter, with few fines.)  An SSD
          system may work in other situations if
          enough suction points are installed to
          create a sufficient pressure field.
          However, in other cases an alternative
          mitigation approach will be necessary.

          Schools with  subslab ductwork.  In
          house mitigation, the subslab ductwork
          is sometimes  sealed off and replaced
          with new above-slab ductwork.  This
          could be difficult and expensive in, many
          schools, and impossible in others.

          Schools with  crawl space construction.
          Depending on crawl space size and
          configuration, increased crawl space
          ventilation, crawl space depressurization,
          or submembrane depressurization
          (SMD)  may be applicable provided no
          asbestos is present

  Future school mitigation studies will research
  radon reduction strategies for mitigating these
  types of schools, and  technical guidance will be
published as soon as possible.  If diagnostic test
results or other reasons indicate that an SSD
system is not appropriate for a given school or
if an SSD system can not be installed as soon as
desired, refer to Section 6, Other Approaches to
Radon Reduction.
                                            Diagnostic measurements will help to better
                                            understand the nature of the radon problem so
                                            that an effective mitigation strategy can be
                                            developed. Aggregate inspection and subslab
                                            communication testing are the simplest, least
                                            expensive, and most important diagnostics to
                                            determine the applicability of an SSD system.
                                            Other diagnostics require more expensive
                                            equipment and may be more difficult to
                                            interpret, but they also may be required to
                                            understand the complex radon problems
                                            associated with larger buildings and HVAC
                                            system operation. Diagnostics that have proven
                                            useful in school mitigation are described below.

                                            5.2.1   Evaluation of the Footing Structure

                                            It is important to determine the types and
                                            locations of potential subslab barriers, such as
                                            footings, subslab walls, and grade beams and
                                            how they may impact subslab communication
                                            and mitigation system design.  The presence of
                                            building walls does not necessarily indicate the
                                            position of a footing or grade beam because not
                                            all walls are load-bearing.  The building plans
                                            (foundation drawings) are the best source of
                                            information on the location of footings.  Note
                                            that thickened areas of the slab  (called "grade
                                            beams") are sometimes found in schools to
                                            support a block wall. Their effect on subslab
                                            communication will depend on the depth of
                                            aggregate or gravel under them.

                                            Experience to date has shown that, in some
                                            cases, subslab communication will reach across
                                            these barriers. However, in many cases, areas
                                            surrounded by footings, subslab walls, or grade
                                            beams may each need at least one suction point.
                                            (This is why the subslab communication test,

  which follows, is important in confirming the
  presence, extent, and effects of subslab barriers.)

  5.2.2   Evaluation of Subslab Communication

  The most important parameter in assessing the
  applicability of SSD is subslab communication
  or pressure field extension.  Permeable
  aggregate, screened, coarse, and approximately
  3/4 to 1-1/4 inches in diameter, is preferable.
  Building plans and specifications have been
  found to be generally accurate in determining
  the presence of aggregate, but the aggregate
  quality must be determined by inspection.  If
  aggregate is not mentioned in the specifications,
  it may not be present even though it is shown
  on the foundation drawings.

  Subslab communication can be evaluated by
  using a shop-type vacuum for suction at one
  larger hole (normally located at the potential
  SSD point) and pressure sensors at other
  smaller holes.  The suction hole should be at
  least 1-inch in diameter or larger, and the test
  holes should  be approximately 3/8-inch in
 diameter and should be located at various
 distances and in various directions from the
 suction hole, depending on building size and
 configuration. This approach will indicate the
 feasibility of developing a pressure field under
 various parts  of the slab and will also help  to
 identify the influence of subslab barriers such as
 grade beams or below grade foundation walls.
 It will also help to indicate competing pressures
 or excessive leakage from subslab ductwork
 which would inhibit pressure field development
 in an SSD system.

 Experience has shown that the size of the area
 that can be mitigated by each SSD point varies
 from a few hundred to several thousand square
 feet The coverage will be  dependent  on
 subslab communication, the flow capacity of the
 fan and pipe,  the presence of subslab barriers,
 and on the strength of the building pressures
 and leakage that the system must overcome.  Of
 course, if subslab permeability is limited, then
 the pressure field may extend only a few feet
and many SSD points may be necessary to
adequately treat the entire area.
  Pressures at the primary (1-inch plus) suction
  point are typically measured at suctions of about
  8, 6, 4, 2, and 0 inches WC The pressures at
  the test hole can be measured either
  qualitatively (with a smoke stick) or
  quantitatively (with a pressure gauge). If
  communication testing indicates a pressure of
  0.001 inch WC (0.25 Pascal) or lower at  a given
  test hole or if smoke stick tests show that air
  flows into the hole, it may be possible that an
  SSD system will be able to  reach the area.

  This procedure requires an  electric-pneumatic
  hammer drill, a vacuum, and a sensitive pressure
  sensor.  Before drilling into the slab, utility
  pipes and conduits should be noted from the
  plans and confirmed to avoid drilling through
  them.   Refer to Section 7.2 on worker
  protection for safety suggestions.

 Aggregate quality can also be inspected by
 drilling at least one hole in  the slab, large
 enough  (at least 4-inches in diameter) to  extract
 a sample.  Holes larger than 4-inches will allow
 for a better estimate of the depth and porosity
 of aggregate,  but holes of this size may also
 cause more damage to floor tiles and be more
 difficult  to repair. Again, proper precautions
 should be taken when drilling through the slab.
 Although this approach will indicate  the
 presence of subslab aggregate and the potential
 for subslab communication, it will not indicate
 the extent of pressure field development that is
 possible  with  the communication test

 5.23   Evaluation of Pressure Differentials

 If the radon tests were made with the HVAC
 system or other ventilation fans on, it may be
 useful to re-test the rooms (at least the ones in
 question) with aU fans turned off in order to
 isolate the major sources of radon and to
 determine if HVAC operation is influencing
 radon levels.  Changes in radon levels due to
 HVAC operation may indicate the significance
 of the pressures (both positive and negative)
 generated by HVAC operation and the potential
 for mitigation by HVAC modifications (See
Sections 4.2 and 6). Pressure differentials and
air flow measurements in classrooms can be
used to identify any HVAC flow imbalances that
may cause negative pressures in the building

 relative to the subslab area.  These
 measurements require sensitive pressure gauges
 and/or air flow meters. Qualitative information
 can be obtained by using a smoke stick to
 indicate the direction of air flow.

 If the HVAC system pressurizes the building, it
 can prevent soil gas entry as long as the
 air-circulating fan is running.  However,
 installation of an SSD system may still be
 necessary if radon levels build up to
 unacceptable levels inside the school when the
'fans are off and it takes too long to reduce the
 radon to acceptable levels when the system is
 turned back on.

 If HVAC system operation or the natural stack
 effect exerts a negative pressure in the building
 relative to the subslab area, then a successful
 SSD system must overcome this negative
 pressure.  Recent experience with SSD in a
 limited number of schools indicates that a
 well-constructed SSD system can provide
 considerable reductions in radon despite strong
 HVAC counter pressures.  However, it may be
 difficult for  an SSD system to overcome the
 negative pressures exerted by return-air ducts
 located under the slab.

 Continuous  radon measurements (typically
 averaged over 1-hour intervals) collected for
 several days will show variations in radon levels.
 These variations can result from changes in
 HVAC operation, diurnal effects, weather
 conditions, and occupancy patterns. These data
 may lead to a greater understanding of the
 pressure dynamics in the building; however, a
 relatively expensive continuous radon monitor is
 required.  Continuous differential pressure
 measurements (inside/outdoor/subslab)  collected
 concurrently with the continuous radon
 measurements, are also extremely useful in
 understanding HVAC system influence on radon

 5.2.4  Measurement of Subslab Radon Levels

 Subslab radon measurements are used to map
 radon source strengths so that the suction
 point(s) can be placed near the major sources.
 The subslab radon measurements can be
 collected through the 1/4-inch diameter holes
drilled into the slab in the subslab
communication test detailed above. To obtain
the most representative results, the subslab
radtin levels should be measured prior to the
communication test.   This diagnostic technique
requires a hammer drill and a continuous or
grab radon monitor that can pump air samples
into a measuring chamber.  Before drilling  into
the slab, utility pipes and conduits should be
noted from the plans and confirmed to avoid
drilling  through them.

Installation of SSD systems is primarily a matter
of plumbing because of the extensive use of
PVC pipe. Electrical work, concrete work, and
roof work are often also involved.   Due to the,
nature of the work, it is important that the
installer take into account all applicable codes
that may affect construction and/or
modifications to school buildings. Typically,
these may include electrical, mechanical, fire
protection, plumbing, and building codes
(Section 7).

A typical SSD system for a school is shown in
Figure 1 and should be referred to throughout
the section.

5.3.1    Suction Hole Location

The location of the suction hole is selected once
an area or room to be treated has been
identified based on radon measurements, subslab
communication tests, and any other diagnostic
measurements.  For optimum mitigation it
would be best to  locate the suction hole closest
to the highest known radon source.  Of course,
if the rooms with higher radon  levels are widely
separated, then they are probably independent
and must be treated separately. Often, the
source  may be widespread or  unidentified or the
suction  hole may need to be located in an
out-of-the-way place that will cause  minimum
disruption to the -room occupants.

Another consideration when locating suction
points is the accessibility of the exhaust pipe
and exhaust fan.  In many cases the suction hole
position is chosen on the basis of aesthetics, fan

                    Exhaust (released away from
                       •    any air intakes or
                       J  ,  open windows)
Exhaust Fan
Mounted Outiida
 Optional Piping
         Drip Guard
                                              Slope Horizontal Leg    /
                                              Down Toward Sub-slab L	,

                                              H°"v   '            ^-'_-_r --'
                                                                     i         i
                                                              Optional Piping
                                                                       '   T  iTo Exhaust Fan
                                                               ''ng	ť|      i Mounted on Roof  Roof Structur.
bi 	 m.







                                                                       '                                Connection to Other
                                                                     Manifold Line                 -Ť	Suction Point(s) if
                                                                             , — —  	   —    —  — applicable
                                                            Exit Piping (Minimum
                                                            Schedule 40 PVC)
                                                                                              Drop Ceiling

                                                                              1. Closing of major slab openings
                                                                               (e.g. major cracks, utility penetrations.
                                                                               gaps Ťt the wall/floor joint) is important.
                                                                                           Verticil Drop
                                                                                           (Suction Pipe. Minimum
                                                                                           Schedule ŤO PVC)
                                                                                                   Indoor Air Through Unctosod
                                                                                                   Cracks. Joints. Utility
                                                                                                   Openings. Etc.
                                                                                              Lip of undisturbed
                                                                                              aggregate/soil of
                                                                                              suffkaen- -vidthto
                                                                                              help support weight
                                                                                              of restored concrete
                                                                                              until set.
                                                                             •  Soil
                             Figure 1. Typical Subslab Depressurization (SSD) Design for a School

location, or exhaust pipe routing.  Often a
location equidistant from both outside walls,
such as a hall or a closet on the hall side of a
classroom, is a good location if subslab
communication is sufficient

5.3.2    Pipe and Fan Layout

In order to adequately depressurize school slabs,
which may be much larger than  house slabs,
larger fans and larger pipes to carry the
increased air flows are typically used.  Appendix
A contains information on fan and pipe
selection which lists a number of fans with the
capability of drawing over 300 cubic feet per
minute  (cftn) at 3/4-inch WC (which may be
three to four times the capacity  of home
mitigation fans).

The typical 4-inch pipe used in most home
mitigation systems may have too much flow
resistance when used with this larger fan;
therefore, 6-inch pipe is often used.   The
piping used should be  fire-rated (minimum
Schedule 40 PVC).

If the permeability of the aggregate is high, then
a single 6-inch suction point can be  used with
the larger pipe and fan.  However, with typical
aggregate permeability, a wider area can be
mitigated by using two or three suction points
manifolded to one of the more powerful fans.
The location for  the SSD point(s) should be
selected based on the results of the diagnostic
measurements. A typical manifold system might
consist of a 6-inch PVC pipe running
horizontally within a dropped ceiling and
extending 20- to 60-feet between vertical drops.
Connected to the manifold would be an exterior
mounted fan, and 4-inch PVC vertical pipes
which penetrate the slab and transmit vacuum
to that area of the floor slab.  This arrangement
can be used to mitigate a long classroom wing
with the suction points located in the central
corridor or on the corridor side  of a classroom.
Experience in schools has shown that locating
the suction points remote from the outside wall
will help to reduce  short circuiting (satisfying
fan demand for air) of the  system.

If any of the pipe is either outside the building
or in an unheated section of the building, then
condensation may form inside the pipe because
of the high moisture content of the exhausted
subslab &>il gas.  The pipes should always be
slanted so that this condensation can drain back
into the subslab cavity where it originated.
(The in-line fans should be mounted vertically
to prevent water accumulation in the
bell-shaped housings.)  Experience has shown
that SSD systems in homes can fail due to a
buildup of condensation in improperly oriented
fans and pipes.  In  humid climates,  condensation
will also form on the outside of pipes in
exposed areas, and  insulation or boxing in may
be necessary.  Rain entry into uncapped exhaust
pipes has not been  reported as a problem,
probably because the volume of rain is small
compared to the volume of condensation that is
continually flowing  back down the exhaust pipes.
Ice buildup on the  fan or on the exhaust stack
has not been reported  as a significant problem,
probably because the soil gas is warm enough to
melt any ice or to prevent  it from forming.

5.3.3    Suction Point and Pipe Installation

Once the location of a suction point is
determined, a  hole  must be drilled through the
concrete slab.  Typically, the slab hole diameter
corresponds to the  pipe's outside diameter,
usually slightly larger than  4- to 6-inches. The
hole must be large  enough to  accommodate the
suction pipe and to allow the excavation of a
cavity beneath the slab. Before drilling into the
slab, utility pipes and conduits should be noted
from the plans and  confirmed to avoid drilling
through them.  Recommended concrete drill
types are discussed  in Appendix A.
Alternatively, core drilling companies can be
hired to drill this type  of hole. If a school
district anticipates mitigating a large number of
schools using SSD,  they should consider
purchasing a drill.  Worker protection should
include respirators and eye protection,  in
addition to ventilation  of the work area to
dilute radon that is released by opening up the

An open hole or cavity, as  seen in Figure 1,
should be excavated beneath the slab with a
diameter of approximately 3-feet and a depth of
about 1-foot  Experience has shown that when
1-foot diameter cavities have been enlarged to

 2- to 3-feet and the depth increased to 1-foot,
 the negative pressure fields have often doubled
 because of the decreased resistance. Although
 performance improvements have been variable,
 this larger cavity size has proven most
 worthwhile in nonporous soils (where the most
 improvement is sought).  Aggregate can
 sometimes be removed from the subslab either
 by hand or with a powerful shop vacuum.  If
 the aggregate is  packed tightly, a crowbar and
 hand excavation may be necessary.  Large
 subslab cavities may require opening up a larger
 slab hole just for aggregate removal.  This hole
 will have to be resealed with concrete.

 The exhaust pipe should be well supported so
 that it will not be knocked loose if it is jostled.
 In school environments it is advisable  to enclose
 the pipe for both security and  aesthetics.

 5.3.4   Fan Installation

 The EPA recommends  that SSD fans be
 installed outside the building because of the
 chance of leakage of highly concentrated radon
 from the fan or the pipe exhausting from the
 fan into the building interior (since the fan and
 exhaust pipe are under positive pressure).
 Figure 1 shows two possible fan mounts.  In
 houses the fans are usually placed in attics, but
 in schools they have been placed on the roof or
 on the upper sidewall of the building exterior.
 (See Appendix A for a discussion of SSD fan
 installation variations.)  Wall penetrations are
 usually preferable because roof penetrations may
 lead to roof leaks.  Several fan configurations
 are possible: in-line mounts that couple to
 pipes, pedestal  mounts with a vertical discharge,
 and pedestal mounts with a horizontal
 discharge.  However, the piping configuration
 and fan placement must be guided by building
 codes in addition to practical considerations.

 The system should exhaust above the roofline to
 prevent high concentrations of  radon from
 re-entering the building. A location should be
chosen which provides a reasonable distance
between the discharge point and HVAC
fresh-air intakes,  windows, doors, or any other
openings to  the building interior.
 5.3.5    Sealing of Radon Entry Routes

 To enhance the performance of the SSD system,
 an effort should be made to seal as many radon
 entry routes as possible.  This  increases the
 strength and extent of the negative pressure
- field and also  reduces the amount of treated
 indoor air that will be drawn into the SSD
 system.   Entry routes that should be sealed
 include  cracks in the slab and walls, the
 floor/wall joint, the surface of porous concrete
 block walls, and openings around utility
 penetrations.  Fibrous expansion joints, that are
 commonly used when the slabs are poured, can
 also serve as radon entry routes.  These and all
 other cracks and porous surfaces should be
 properly prepared and sealed with a suitable

 5.3.6    Troubleshooting

 Troubleshooting SSD systems may involve
 taking a number of diagnostic measurements.  If
 radon levels are not adequately reduced, the
 suction in the subslab cavity  should be
 measured.  Law pressure may indicate high air
 flow or poor fan performance;  high pressure
 indicates poor  subslab permeability or low air
 flow.  The air flow in the pipe  may have to be
 measured to determine whether the fan is
 operating properly.  The pressure field extension
 can be measured at various distances from the
 suction hole(s) to determine  the coverage of the
 SSD system.

 53.7    Improving System Performance

 Some  causes of insufficient subslab  pressure
 field development include: poor subslab  •
 permeability, the presence of subslab barriers,
 competing pressures from subslab return-air
 ductwork, and air leaks into the system (either
air-supply ductwork or from cracks or
openings).  If the performance of an SSD
system is not adequate, a number of different
steps can be attempted to improve system
effectiveness. These include:

        Additional  suction  points  can be
        installed  to  increase coverage area.
        (This approach is most suitable when

        communication is poor or pressure and
        flow are low.)

        Larger pipe diameters, larger fans, and
        larger subslab cavities have been shown
        to improve SSD system performance in
        some cases.  (A larger fan and pipe
        diameter are most appropriate when the
        pressure is low  and the flow is high.)

        Sealing of cracks and  holes can also
        improve the  negative pressure field
        extension and, consequently, radon
        reduction.  Sealing will also help to
        reduce the energy penalty associated
        with the increased exhaust of indoor air
        into the SSD system.

        Reductions in room depressurizatipn (if
        applicable) may also improve radon

        Finally, it is  possible that the suction
        point has been located in a spot with
        such poor  permeability that major
        improvements can only be made by
        abandoning the current hole and drilling
        a new hole in an area with better

5.3.8    System Maintenance and Monitoring

One of the chief advantages of SSD systems is
that there is relatively little maintenance
required for their operation, and the fans have
long lives.  Periodic system inspection and
annual retesting of the radon levels may be
sufficient if fans with an expected service life of
10-20 years are installed.

The SSD system pressure  levels  could be
checked and all measurements recorded
routinely, as is done with  the inspection of fire
extinguishers.  A pressure gauge is the most
common type  of monitoring device that is used
to evaluate the continued  performance of a SSD
system.  Typically a dial pressure gauge (about
$50) is used to monitor the subslab cavity or
suction pipe pressure.  The gauge is  usually
mounted on or near the suction pipe where it
can be checked to determine if the suction
pressure is adequate.  Other devices  that
contain  pressure switches  to turn on a light or
sound an alarm if the pressure falls below a
given value are also available and are the
preferred method.

Each SSD  system should be labeled with its
installation date, nominal  subslab cavity or pipe
pressure depending on monitoring system, and
the name and  telephone number of the persons
to contact .in case of failure.  Once the  final
system is installed, post-mitigation radon levels
should be monitored annually (during cold
weather) to ensure that the system is operating


Other mitigation approaches, in addition to
SSD, have been used in some schools.  These
approaches may be implemented either as a
temporary solution prior to installation of a
permanent SSD system, or they be considered as
the first phase of a more extensive mitigation
plan.  In some cases, implementation of these
approaches alone may adequately reduce radon
levels in the school.  After confirming adequate
reductions with short-term tests, follow up with
long-term measurements to ensure that the
system continues to maintain an adequate level
of radon reduction.

Classroom pressurization, increasing ventilation,
and crawl space depressurization are discussed
below.  It should be emphasized that these
approaches have not yet been thoroughly
researched by the EPA in school applications,
and more definitive guidance will be published
following additional research.  Other mitigation
techniques, such as extensive sealing and
submembrane depressurization (SMD) in a
crawl space will also require extensive testing.
For technical details on how these techniques
have been used in  house mitigation, refer to the
manuals on radon  reduction listed in Section

Maintaining a positive pressure in the building
(relative to the subslab area) through HVAC
system operation has been used successfully for
temporary mitigation in a limited number of
schools.  Whether pressurization is a feasible
long-term mitigation solution depends upon
factors such as the proper operation of the
HVAC system by maintenance personnel,
performance with changing climatic conditions,
and any additional maintenance costs and energy
penalties associated with the changes in
operation of the HVAC system.  Any HVAC
modifications should be made in cooperation
with a qualified HVAC system specialist

Since central HVAC systems are normally
designed to  operate in a  forced supply mode,
the occupied spaces may be maintained under a
slight positive pressure (relative to the
outdoors) depending on the balance between
the supply and the exhaust in the building.
These systems should be checked periodically
for proper operation to ensure that a positive
pressure is maintained, and adjustments should
be made as necessary.  HVAC modifications
that reduce fresh air intake, reduce supply air,
or increase return air in a given  area, and
improper system maintenance can lead to
pressure imbalances, and, consequently increase
radon entry.

If positive pressures are not being achieved in a
single-fan  system, the system should be checked
to ensure that the fresh-air intake meets design
specifications and that the intake has not been
closed or restricted.  Increasing the fresh-air
intake and operating the fans for a sufficient
time prior to occupancy and continuously while
the school is occupied will help to reduce radon
levels that accumulate during night or weekend
setback  periods.  This approach will maintain
low levels during occupied hours by maintaining
a positive pressure to prevent radon entry and
providing fresh (dilution) air.

In dual-fan systems, the return-air fan can be set
back or  restricted so that all the rooms are
under a positive  pressure with only the supply
fan operating. The fresh-air intake to the
supply fan can also be increased  up to the
design limit  of the system.  Another option
might be to  consult with a HVAC engineer to
redesign a fresh-air intake or to add one to a
system.  Diagnostic measurements made with
continuous radon monitoring equipment in  each
classroom with elevated radon levels  can help to
determine the necessary fan operation schedule
in such  situations.

In schools with unit ventilators, increasing the
fresh-air intake to the design limit and
operating  the fans continuously while the school
is occupied will help to maintain a positive
pressure in the building. A central exhaust-only
ventilation system used in conjunction with
unit ventilators or fan coil heaters might  need
to be modified or replaced with a system that
operates under a slight positive pressure.  For

  schools with no-active ventilation systems or
  exhaust-only fan systems, positive pressurization
  will probably require major modifications, such
  as addition of a fresh-air supply, as part of a
  HVAC strategy.  For more detail on classroom
  pressurization and how it would apply to a
  specific type of HVAC system refer to Section

  If these modifications to HVAC system
  operation are to be feasible long-term
  mitigation  approaches in a given school, then
  proper operation and maintenance of the system
  is critical.  Performance during various climatic
  conditions  and any additional maintenance costs
  and energy penalties associated with  the changes
  in operation of the HVAC system must also be
  carefully considered.   In addition, there may be
  potential moisture and condensation problems if
  pressurization is implemented in very cold
  climates. The applicability of this approach will
 need to be determined by qualified personnel on
 a case-by-case basis.  Changes made in HVAC
 system design and/or operation should not
 reduce the  ventilation rate below the  minimum
 standards in ASHRAE guidelines. In addition,
 any changes in HVAC controls  should be
 documented, labeled, and checked regularly.
 Increasing ventilation by simply opening
 windows, doors, or vents may be effective, but
 weather, security problems, the lack of operable
 windows, and increased energy costs often make
 this impractical as a permanent approach in
 most schools.  If the windows cannot be opened
 at night, it rnay be desirable to use a fan to
 blow fresh air into the building to lower the
 radon levels in the morning when the school is
 opened.  Although this approach has been
 shown to reduce radon levels in some houses,
 its applicability to schools has not yet been
 studied.  Therefore, ventilation should only be
 considered as a temporary approach to radon
 reduction until further research identifies its

 If an increase in ventilation is attempted, crawl
spaces and unoccupied basements can sometimes
be sealed off from the rest of the building and
                                              treated separately.  By treating these spaces
                                              separately, ventilation reductions can be
                                              achieved in adjacent classrooms with smaller
                                              fresh air requirements and reduced energy
                                              penalty.  However,  the practicality of this
                                              approach in most climates will be  limited due to
                                              increased heating and/or cooling costs.

                                              For reducing the energy costs associated with an
                                              increase in ventilation, a heat recovery ventilator
                                              (HRV) may be cost-effective.  HRVs allow fresh
                                              air to be delivered indoors with reduced heating
                                              or cooling costs (depending on season) as
                                              compared to natural ventilation. Through a
                                              heat exchanger core, heat is transferred between
                                              exhaust and fresh air streams, without mixing
                                              the two airstreams.  However, for an HRV  to
                                              be a reasonable mitigation option,  the savings
                                              resulting  from the reduced energy penalty
                                              should more than offset the initial  cost of the

 In a variation of crawl space ventilation, an
 exhaust fan is installed in a crawl space vent
 and all other vents are closed.  This is referred
 to as crawl space depressurization or forced-air
 exhaust of the crawl space  and can prevent
 radon entry into the building Interior by
 creating a pressure barrier across the floor.  In
 houses, this approach has been more effective in
 reducing radon levels than passive crawl space
 ventilation. Experience with crawl space
 depressurization in schools is limited.

 A diagnostic fan door test will indicate the
 suitability of a crawl space for this mitigation
 technique.  A fan-door (e.g., blower door) will
 measure the leakiness of the space and will help
 to indicate the size of fan needed to adequately
 depressurize the crawl space. If radon
 measurements show that the crawl space is the
 primary source of the problem, and if asbestos
 is  not present in the crawl space,  then this
 technique may be feasible for reducing indoor
radon levels.  More detailed guidance on this
approach for schools will be available following
further research.

                              7.   SPECIAL CONSIDERATIONS
Building codes are typically written to reflect
minimum design and construction techniques
that must be adhered to by the construction
industry.  They are developed to ensure the
public safety, health, and welfare.  Building
codes are not only directed toward new
construction but also apply to renovation of
existing structures.  They can be developed by
the national model code organizations or by
local jurisdictions. In general, the model codes
published by such organizations as Building
Officials and Code Administrators International
(BOCA), International Conference of Building
Officials (ICBO), and the Southern Building
Code Congress International  (SBCCI) are
adopted  by state or local jurisdictions or serve
as the basis for locally amended building codes.

It is important that the installer take into
account all applicable codes and laws regarding
qualifications for design and type of equipment
used when designing and installing radon
mitigation systems in any building.  Typically,
this may include electrical, mechanical, fire
protection, plumbing, and building codes.
However, since these codes can vary between
different areas, the applicable codes for a given
locality should be referred  to when retrofitting a
school with a radon mitigation system. It is
anticipated that specific additions or
amendments to these codes will be made in the
future to address both  retrofit of school
buildings for radon reduction and radon
preventative new construction.
consideration for all school administrators.
Normal safety precautions  must be observed
when performing any type  of construction or
remodeling work.  Exposure to radon gas and
its decay products creates an additional health
risk.  Therefore, it is important to reduce that
exposure as much as possible.  Specifically, this
may mean increasing ventilation in the work
area and/or utilizing respirators in areas where
the radon concentration is  elevated.  Attention
should also be given to other potential hazards,
such as organic solvents in sealants and coatings
and potential biological hazards growing in
crawl spaces or HVAC systems.

Before drilling into the slab, utility pipes and
conduits should be noted from  the plans and
confirmed to avoid drilling through them.
(However, it should be mentioned that subslab
plumbing  and conduit are sometimes located,
where the installer finds it  convenient and do
not always conform to the  plans.)  One
suggestion for avoiding an  electrical shock in
this situation is to ground  the case of the drill.
If the tool itself is properly grounded, it will
prevent the tool from becoming "hot" and
should cause the breaker to disconnect the
conduit that was hit.  Shutting off the supply to
the drill will stop the drill  but will not shut off
the subslab conduit that was hit unless they
happen to be on the same  breaker.
Worker protection during radon mitigation
system installation is a legal, safety, and ethical
Any potential airborne asbestos fibers identified
in a basement, crawl space, utility tunnel, boiler
room, or any other part of the school that may
be entered as part of radon diagnostics or
mitigation should be removed or encapsulated
according to AHERA before attempting any
radon reduction activities.


1.      ASHRAE Draft Standard 62-1981R. Ventilation for Acceptable Indoor Air Quality. ASHRAE,
       Atlanta, Georgia, 1986.

2.      Leovic, K. W., Craig, A B. and Saum, D.  The Influences of HVAC Design and Operation on
       Radon Mitigation of Existing School Buildings, presented at ASHRAE Conference IAQ 89,
       April 1989.

3.      Leovic, K. W., Craig, A B. and Saum, D. Characteristics of Schools With Elevated Radon
       Levels, In: Proceeding: The 1988 Symposium on Radon and Radon Reduction Technology,
       Volume 1, EPA-600/9-89-006a  (NTIS PB 89-167480), March 1989.

4.      McKelvey, W. R, Radon  Remediation of Pennsylvania School Administration Building,  In:
       Proceedings: The  1988 Symposium on Radon and Radon Reduction Technology, Volume 2,
       EPA-600/9-89-006b (NTIS PB 89-167498), March 1989.

5.      Messing, M. and Saum, D.  West Springfield Elementary School Report on Diagnostic Analysis
       for Radon Remediation on The South Wing, Infiltec, Falls Church, Virginia, 1987.

6.      Messing, M. and Saum, D. Worker Protection for Radon Mitigators and Diagnosticians, In:
       Proceedings: The  1988 Symposium on Radon and Radon Reduction Technology, Volume 2,
       EPA-600/9-89-006b (NTIS PB 89-167498), March 1989.

7.      Saum, D. and Messing, M.  Guaranteed Radon Remediation Through Simplified Diagnostics, In:
       Proceedings: The Radon Diagnostics Workshop, April 13-14. 1987, EPA-600/9-89-057, June 1989.

8.      Saum, D.,  Craig, A B. and Leovic, K.W. Radon Reduction Systems in Schools, In: Proceedings:
       The  1988 Symposium on  Radon and Radon Reduction in Technology, Volume 1, EPA-600/9-89-
       006a (NTIS PD 89-167480), March 1989.

9.      Witter (Leovic), K., Craig, A B. and Saum, D. New-Construction Techniques and HVAC
       Overpressurization for Radon Reduction in Schools, Proceedings of the ASHRAE Conference
       IAQ 88, 1988.



The term "constriction documents" refers to the
formally agreed upon construction drawings and
specifications (project manual), as well as all
subsequent addenda and change orders.  The
documents are a complete pictorial depiction of
the project and consist of the architectural,
structural, mechanical, and electrical drawings.
The specifications include the bidding
documents, the conditions of the contract, and
the technical information that outlines materials
and workmanship for the entire project

Both the specifications manual and the drawings
should be obtained to aid in the understanding
of the building's radon problem.  Each of these
will provide useful information. Table A.1
summarizes the information provided in these
                A.1.1   Specifications

                The specifications will primarily aid the
                mitigator in identifying subslab aggregate
                composition and soil compaction requirements.
                Both of these are usually found in the section
                detailing concrete work and/or fill (typically
                Division 3 - Concrete). The mechanical section
                (Division 15) summarizes the heating,
                ventilating, and air-conditioning (HVAC)
                systems applicable to the building.  This section
                will give details on the mechanical equipment
                and offer design information that may or may
                not be found on the drawings.  The electrical
                section  (Division 16) summarizes the electrical

                       Note:  The specifications have
                       precedence over the drawings if there
                       are contradictions.  For instance,  it is
                       unlikely that aggregate was provided  if
                Table A.1 Radon Mitigation Information In Construction Documents

  Document                                Information
       Concrete (Division 3)

       Mechanical (Division IS)

       Electrical (Division  16)




Subslab composition; aggregate identification

HVAC system summary; equipment identification

Electrical system summary, equipment identification

Typical wall sections

Foundation plan; footing locations and communication
barriers, subslab fill and material thickness
HVAC system design; including duct system design, duct run
length;  supply/return flow design; fresh-air introduction;
exhaust systems
Electrical equipment design and location; conduit location

         the specifications do not call for it, even
         if the drawings show aggregate under
         the slab.

 A. 1.2   Drawings

 The drawings provide a wealth of information
 that may be useful for radon mitigation.  The
 architectural drawings usually show a typical
 wall section. Subslab fill information is usually
 shown and labeled on this section.  The
 structural drawings include a foundation plan
 which locates footings of load-bearing walls and
 columns. This  is useful when identifying
 potential barriers to subslab. The mechanical
 drawings should include all plumbing and
 HVAC drawings. Supply and return duct runs
 show the amount of supply and return air flow
 serving a room or area. By simply adding
 together all of the flows, it can be determined if
 the  room was designed to  be under positive or
 negative pressure.  Most sophisticated HVAC
 systems are designed to be balanced or
 pressurized in most, if not all, rooms.  The
 drawings should note whether or not fresh air is
 introduced into the mechanical system and if
 room air is removed by exhaust fans.

 The electrical drawings should be consulted to
 ensure that no unusual conduit routes (e.g.,
 under the slab) are present in areas where the
 slab may be drilled (either for placement of
 suction points or for communication testing).


 SSD systems in  houses and schools require fans
 that are quiet, long-lived, energy efficient,
 resistant to  moisture, and that have good air
 flow at pressures around 1 inch WC A number
 of centrifugal duct fans manufactured by various
 companies have the performance characteristics
 required for most radon mitigation with an
 expected service life of 10 to 20 years.  Fans
 that  utilize the vane-axial fan blade which
surrounds the motor can be mounted in a
variety of enclosures.  Specifications of some
typical in-line and pedestal fans used in radon
mitigation are shown in Table A.2.

The in-line fans are designed to be mounted
between two sections of pipe. The fan and pipe
 are usually coupled with the black rubber pipe
 couplings fitted with stainless steel hose clamps
 that are used for plumbing pipe connections.
 These couplings are available in a wide variety
 of sizes so that pipes  and fans of various sizes
 can be coupled. Pedestal fans are designed to be
 mounted on a square base that can be
 constructed of pressure-treated wood.  This base
 is attached.over a pipe penetration on a roof or
 a wall, and the fan is  screwed onto and sealed
 to the base.

 In houses, mitigators often attempt to install the
 smallest, quietest, least obtrusive, lowest power
 SSD system possible.  Pipes are generally 4
 inches in diameter or  smaller; fans are rated
 generally less than 100 watts power consumption
 and move less than 150 cfm air at 0.75-inch WC
 pressure.  In schools, however, the
 considerations of noise, energy loss, and size are
 not as important.  Larger fans and pipes should
 be considered if they produce simpler and more
 effective mitigation. It is recommended that
 fire-rated PVC piping, Schedule 40 PVC as a
 minimum, be used.

 Mitigation experience  in schools, although
 limited, has shown that it is advisable to use
 fans that are at least twice as large (200 W and
 300 cfm at 1-inch  WC pressure) and pipes that
 are 6-inches in diameter. The higher air flow
 requires larger pipe diameters so that the
 increased fan capacity  is not lost in pipe
 resistance. For example, these larger pipes can
 be used to provide a low restriction manifold to
 the fan that is connected to two vertical 4-inch
 pipes penetrating the slab. The 6-inch pipe can
 carry 300 cfm to the fan while each of the two
 4-inch pipes carries about 150 cfm. If the  larger
 fans are attached directly to 4-inch pipes, then a
 large part of the increased fan performance will
 be lost to flow resistance of the pipe.  In
 summary, the larger slab areas found in schools
 normally require larger fans and pipes for the
 most  effective SSD installations.

 Table A3 shows the flow resistance for 100-feet
 of pipe with diameters from 2- to 6-inches.  The
 length of pipe that would produce the
equivalent resistance of a system that contains
pipe,  pipe fittings, and subslab flow resistance is
assumed  to be about 100-feet, although typical

       Table A.2      Typical Fans Used for Radon Mitigation
" Pedestal
Press. Max
@No Flow
(in. WC)
 * flow measured at 0.75 inch WC pressure
** INFILTEC measured value
             Table A3  Air Flow Resistance in 100 Feet of Round Pipe
2-in. Pipe
(in. WC)
3 in. Pipe
(in. WC)
4 in. Pipe
(in. WC)
6 in. Pipe
(in. WC)
               These values show the approximate flows for each pipe
               for which the resistance is closest to 0.75-inch WC

  mitigation systems usually do not have pipe runs
  of more than 40-feet.  For example, if a
  particular fan draws 310 cfm at 0.75-inch WC
  and 100 feet of 4-inch pipe has a resistance
  close to 5.1-inches WC at a flow of 300 cfm, it
  would be advisable to use 6-inch pipe to avoid.
  wasting most of the fan power on pipe
  resistance.  However, large pipe is unnecessary
  if little or no subslab air flow due to low
  subslab permeability.  Pressure drops caused by
  bends  (e.g., elbows) in  the pipes should also be
  considered when designing  the SSD piping

 Several types of tools" are useful in gathering
 diagnostic data in schools.  They include an
 electric-pneumatic hammer drill, a large shop
 vacuum, a continuous or grab-sample radon
 monitor, a sensitive pressure measurement
 device, an air-flow indicator, and an air-flow

 Depending on the number of schools to be
 mitigated in a given district, it may be
 cost-effective to purchase some of this
 equipment or it may be more practical to
 employ the services of an experienced radon
 mitigator.  It may be possible to purchase some
 of this equipment from experienced mitigators
 in the area or they may be able to recommend a
 local source  for purchase or rental of radon
 mitigation supplies.

 A3.1   Small Hammer Drill

 Drills capable of drilling holes through concrete
 slabs of at least 3/8- to  1-inch in diameter are
 useful for subslab pressure, communication, and
 radon measurements. The suction hole  should
 be 1-inch or  larger in diameter, and the
 communication test holes are usually 1/4- to 3/8-
 inch in diameter. The inexpensive hammer
 drills sold in hardware stores are often
 incapable of drilling through concrete which has
 hard aggregate embedded in it  Professional
quality, lightweight hammer drills with spline
bits are recommended.  This type of drill costs
approximately S250.
 A.3.2   Vacuum

 Most of the shop-type vacuum systems can draw
 a vacuum of 60- to 120-inches WC and have a
 maximum air flow of about 100 cfm: This is
 quite adequate for inducing flow through drilled
 holes approximately  1 1/2-inches in diameter for
 communication tests. These vacuums are
 available for $40 to S250.

 A.3.3   Continuous Radon Monitor

 Continuous radon monitoring (typically
 averaging at 1-hour intervals) is very useful in
 evaluating the effects of HVAC interactions on
 school radon levels.  Pylon, Femto Tech, and At
 Ease are types of continuous monitors
 commonly used. A number of school systems
 have purchased continuous radon monitors to
 aid in their school mitigation work.  A
 continuous monitor allows each stage to be
 evaluated quickly when mitigation is performed
 in stages or a number of rooms need to be

 A.3.4   Grab-Sample Radon Monitor

 In order to map sub-slab radon, a radon
 monitor is needed that can pump a sample into
 its measurement chamber and hold it long
 enough for a measurement.  It is very
 convenient to use a Pylon AB-5 monitor which
 has a built-in pump and  scintillation counter
 although a separate pump, Lucas cell, and
 scintillation counter can  be used. This
 instrument can be used to take grab samples
 from holes for subsequent counting, or it can be
 used for continuously "sniffing" from a series of
 holes.  The Pylon system costs about $4500.

 A.3.5   Pressure Gauge

 A sensitive pressure gauge is necessary to
 measure the pressure  fields generated by SSD
 systems.  Pressure differentials as low as 0.001-
 inch WC are common. The most sensitive
 Dwyer Magnahelic pressure gauge, which costs
about $50, is sensitive only to about 0.01-inch
WC The slant-tube manometer is difficult to
read, to set up, and to transport It costs about
$100 and has a sensitivity of about 0.001-inch
WC The best type of pressure gauge for these

 measurements is the electronic digital
 micromanometer which can read from 0.001- to
 20-inches WC   These micromanometers cost
 about $1500.

 A3.6   Air-Flow Indicators

 The direction of pressure or air flow in a test
 hole can provide an indication of system
 performance even if it cannot be measured.
 Smoke pencils or guns are  most commonly used
 as flow or pressure indicators.  The smoke is
 generated by a chemical reaction with the
 moisture in the  air  and has an acrid odor
 because of its high  acid content  Chemical
 smoke is used because it is not associated with
 heat; therefore, it will respond more accurately
 to minimal air flows.  The smoke pencils cost
 about S3 to $4 each and can last a couple of
 hours if they are used carefully. A refutable
 smoke gun is also available  for about S70.

 A.3.7  Air-Flow Meters

 Measuring air flow  through  HVAC registers
 requires a "flow  hood" which costs from $1500
 to $4000.  These devices are most commonly
 used to balance  air  flows in large  buildings.  For
 air flow measurements in ducts or pipes, a Pitot
 tube (about $20) can be used in conjunction
 with a sensitive pressure gauge. Alternatively, a
 hot wire or  hot  film anemometer, costing about
 $700 to $1,500, can be used. Pinwheel
 anemometers, vortex shedders, and mass flow
 sensors are examples of other air-flow meters
 that can also be  used.

Most of the tools used for installing radon
mitigation systems are conventional tools used
by home improvement contractors. The only
specialized tool that may be required is a drill
to cut 4- to 6-inch holes through the concrete
floor slab.  The following options are available:

        Use a large rotary hammer drill, costing
        about $400, which has a chisel action
        and regular drill bits.  Experience shows
        that in about 20 minutes this drill can
        make a large hole by drilling a circular
        pattern of smaller holes and punching
        the core out with the chisel.

        Use a hammer drill with a carbide core
        bit. The carbide core bits are expensive
        (as much as $800) and may not be
        available for your drill  in larger size
        diameters.  They can drill a neat hole in
        about 10 minutes.

        Use a core drill with diamond bits and
        water cooling.  This equipment costs  as
        much as $2000 and is verytheavy and
        bulky.  However, it is the fastest way to
        drill precise holes in concrete.

All of these tools can usually be rented  from
tool rental shops.  It may be economical to hire
a core drilling company to come to your
location with a diamond core drill if you have a
number of holes to drill.

All SSD installations should have the exhaust
pipe exiting the building shell.  The fan should
be mounted on the pipe outside the building
shell to avoid leakage of the radon-laden air
from cracks in the fan or from the exhaust end
pipe which is under positive pressure.  EPA
recommends that the system exhaust point be
installed above roof level and be situated to
avoid any possible  human exposure to high
radon levels from the SSD vented soil gas.  For
any type of ran mount, extreme care should be
taken to prevent high concentrations of radon
from re-entering the building through HVAC
fresh-air intakes, windows, doors, or any other
openings to the building interior.  Following
are the  types of installations, and their
advantages and disadvantages, which have been
used in  schools.

A5.1   Pedestal Fan on Roof

In this type of installation the pipe penetrates
the roof and connects to a pedestal fan.
Disadvantages of this type of installation are the
need to construct and seal a pedestal on the
roof for the fan to be mounted  on and  the need

 to cut a hole in the root (This may lead to
 roof leaks or may invalidate warranties on the
 roof.)  Advantages are a vertical pipe run
 without high resistance bends, and the low
 visibility (aesthetics) of the installation.

 A.5.2   In-Line Fan on Side Wall

 In this type of installation the pipe penetrates
 the side wall and an in-line fan is mounted
vertically on the pipe.  Disadvantages of this
type of installation are the necessity of securing
the fan and ihe pipe and the potential for
damage or injury if someone climbs the pipe.
Advantages are the ease in venting above the
roof line and the fact that the  roof is not

A.5.3   Pedestal Fan on Side Wall

In this type of installation the pipe penetrates
the side wall and discharges horizontally with a
 pedestal fan mounted on the wall. A significant
 disadvantage of this type of installation is the
 possibility of someone coming into contact with
 the discharge if the fan is not  mounted high
 enough or radon from the discharge leaking
 back into the building through HVAC fresh-air
 intakes, windows, doors, or any other  openings
 to  the building interior.  An advantage is the
 lack of roof penetration.

 A.5.4   In-Line Fan Above Suspended Ceiling

 In this type of installation the  pipe penetrates
 the roof and connects to a fan which is
 mounted inside the building above the
 suspended ceiling.  This is generally not
 acceptable because  of possible  leakage from the
 fan or exit pipe inside the building.  Any radon
 leakage could be distributed throughout the
building if the area above the suspended ceiling
is a return plenum  for the HVAC system.

 These case studies illustrate the staged approach
 that characterizes many radon mitigation
 projects in large buildings and complex houses.
 Instead of trying to solve the radon problem in
 an initial step, most of these projects consisted
 of multiple stages where one solution was
 attempted and then the results were evaluated
 before initiating the next stage.  The case
 studies show examples of the step-by-step
 procedure for radon reduction in schools.  Some
 of these projects (Schools A, B, C, D,  E, F, G,
 and H) were previously documented in the
 technical paper "Radon Reduction Systems in
 Schools" (Saum, Craig, and  Leovic).

 School A; Prince George's County. MD

 This school had a sophisticated dual-fan HVAC
 system that produced unbalanced flow  and
 exacerbated a radon problem in several rooms.
 Sealing of cracks and replacement of the HVAC
 fan were tried without much effect on  the radon
 levels.  SSD systems will be installed in the
 rooms with the highest radon levels since the
 problem of room depressurization could not be
 readily eliminated.

 A.1    School Description

 The school building, which was built in 1969, is
 two-story, slab-on-grade construction.  It uses a
 large dual-fan air handling system for HVAC
 Each room has separate supply and return
 louvered vents in the suspended ceiling. The
 HVAC system is designed to operate
 continuously during occupied hours and to
 provide positive pressurization in all rooms.

 A.2    Initial Radon Tests

 Radon levels in this school were initially
 measured in February 1988.  One classroom
 tested above 40 pCi/L, a teachers' lounge tested
 above 20 pCi/L, and several  other classrooms
 tested between 4 and 20 pCi/L.

A3    Building Plan Inspection

The foundation drawings call for a 4-inch gravel
bed and a 6-mil plastic vapor barrier under a
 4-inch slab.  A %-inch expansion joint runs
 across the entire building. The footings run
 below virtually all interior and exterior walls.
 Square footings support columns.

 The HVAC system fans have a rated capacity of
 51,000 cfm of air supply and 34,000 cfm of
 return air. This would result in positive
 pressure in all rooms if the system were
 properly balanced.

 A4    Walk-Through Building Inspection

 Examination of the air-handling system showed
 that the air supply fan had been damaged and
 part of the housing cut away; this  resulted in a
 great loss of capacity.  It was determined that
 the distribution fan was actually supplying less
 air than the return air fan was removing; this
 resulted in a negative pressure in many rooms.

 The room with the highest radon level had the
 greatest negative pressure and also had  a very
 large floor-to-wall crack along one wall.  This
 particular floor-to-wall crack was an expansion
 joint where two parts of the building were
 joined.  The expansion joint had disintegrated
 and the two building sections appeared  to have
 separated an  additional it-inch, leaving a full
 1-inch gap  between the floor and wall.   This gap
 was concealed by an aluminum angle iron
 installed when  the building was built. The
 expansion joint and the angle iron continued
 vertically up both corners so  that they were
 serving as an expansion/contraction joint
 between the two parts of the building.

 AS     Pre-Mitigation Diagnostics

 Pressure measurements indicated that many of
 the rooms were under negative pressure when
 both the supply and return fans were in
 operation.  The room with the highest radon
 level measured  0.060-inch WC negative pressure
 (relative to the subslab). There was a good
 correlation  between negative pressure and radon
 levels in all rooms, with the highest radon levels
 in the rooms  with the highest negative
 pressures.  All  rooms  in the school with any
amount of positive pressure had  low radon

  levels.  Subslab radon levels were about 500
  pCi/L in all rooms.  When the return air fan
  was turned off, the pressure in all rooms
  became positive and radon levels decreased to
  less than 2 pCi/L.

  A.6    Temporary Mitigation

  As a temporary solution to reduce radon levels,
  the return air fan was left off and the HVAC
  system operated with only the air distribution
  fan. Under these conditions all rooms showed
  positive pressure and had radon levels below 2

 A.7     First-Stage Mitigation

 The floor-to-wall building expansion crack was
 sealed with a backer rod and polyurethane
 caulking. This sealing decreased radon levels
 only slightly when both fans were off, which
 indicated that there were other soil gas entry
 points in the room.  This poor result from
 sealing a major crack was surprising because
 this crack was about 1-inch wide and soil gas
 with 500 pCi/L flowed out of it when the
 pressure was negative.

 A.8    Second-Stage Mitigation

 Little effect was seen on the negative pressures
 in the problem rooms although the damaged
 supply fan was replaced.  Building personnel
 have attempted to identify the cause of the  flow
 imbalance to these rooms. This will be further

 A.9    Third-Stage Mitigation

 A decision was made to install SSD systems in
 the two rooms with the highest radon levels
 since an HVAC modification was not found to
 solve the negative pressure problem in the
 rooms.  Installation of SSD systems would also
 reduce radon entry when the air handlers are
 not operating during night or weekend setbacks.
T3B fans were installed on 6-inch pipes in the
two rooms with the highest radon levels.  The
return air grill was permanently disconnected
from the return air duct in the teacher's  lounge
to alleviate the problem there.  Since the lounge
is used for smoking, it is probably not a good
 idea to recirculate the air.  The return grill is
 now directly vented to the outdoors.
 Post-mitigation tests from this stage are not yet

 A.10   Conclusions

 Although mitigation of this school is not yet
 complete, SSD in this case appeared to be a
 more reliable solution  to the radon problem
 than crack sealing or HVAC modifications.
 SSD should solve the radon problem both
 during the day while the HVAC system is
 turned on and during the night when it is
 turned off.
 School B; Washington County. MD

 This is an example of a school with a complex
 radon problem that was mitigated in multiple
 steps. A large number of SSD suction points
 had to be used because of the school's complex
 footing structure and poor aggregate.  The
 mitigation performance was evaluated by
 retesting as each suction system was installed or
 improved with a  larger fan, larger pipe, or
 larger subslab cavity. With hindsight it is clear
 that some of these steps could have been
 consolidated; radon mitigation is not an exact
 science and it is often beneficial to try a simple
 solution and evaluate the results before
 continuing.  In this case, the simplest solution
 was installing a single suction point in the
 center of the basement slab near the highest
 concentrations of subslab  radon.  Although  this
 single suction point did provide  considerable
 radon reduction in the basement, it was
 necessary to install several other suction points
 around the edges of the slabs to bring the levels
 well below 4 pCi/L.

 B.1     School Description

 This is a small school, 80  by 150 feet, built on
 the side of a hill.  The school has a 21 by 150
 foot walk-out basement along its lower side.
 The unexcavated area is slab-on-grade, with  the
 slab extending over the basement area and
 resting on steel-bar joists.  The foundation walls
 are constructed of concrete blocks.  The interior
walls of the basement support the end of the

 bar joists and the slab.  This wall is not painted
 or waterproofed on either side.  Separate
 single-fan, roof-mounted HVAC systems with
 ceiling-mounted duct work are provided for the
 basement and upstairs.

 B.2    Initial Radon Tests

 Charcoal canister measurements taken over a
 weekend in March 1988 averaged 10.5 pCi/L in
 the basement and 4.3 pCi/L on the first floor.
 It is unknown how the air handlers were
 operating during the test. All rooms were
 retested over a weekend in May 1988 with air
 handlers turned off.  Measurements ranged from
 78 to 82 pCi/L in the basement and from 18 to
 33 pCi/L on the first floor.

 B.3    Building Plan Inspection

 The building plans indicate that the first floor
 and unfinished basement were constructed in
 1971.  In 1976 the basement was converted into
 classrooms and a slab-on-grade greenhouse was
 added. The foundation plans show a complex
 footing structure upstairs that would limit the
 extent of pressure fields from SSD systems.
 There are, however, basement footings at the
 periphery of the slab which would allow any
 basement SSD pressure fields to be limited only
 by the aggregate porosity. One specification
 notes that "completed fill, prior to laying of
 floor slabs, shall have density and compressive
 value of not less than 95% of the normal
 undisturbed soil value....The fill directly under
 concrete slabs on grade shall be clean crushed
 limestone; 1/2 in. minimum, 1 in. maximum size
 leveled, compacted to 4 in.  minimum thickness
 or as shown on drawings."  No soil test results
 are provided.

 B.4    Walk-Through Building Inspection

 The upstairs and downstairs are mostly open
areas subdivided by movable low partitions.
The HVAC supply and return grills are
 positioned so that there are only a few offices
and storage areas where the HVAC system
could cause depressurization.  No major radon
entry routes were noted other than typical small
 (1/8-inch) cracks between the walls and  the floor
slabs and expansion joints.
 B.5     Pre-Mitigation Diagnostics

 Radon mapping was conducted by drilling small
 holes in the floor and walls and "sniffing" with a
 continuous radon monitor. These tests resulted
 in measurements of about 1500 pCi/L in the
 floor and block walls around  the central stair
 well. Other floor and wall samples were below

 Hourly continuous radon monitoring over
 several weeks showed that radon levels were low
 when the HVAC systems were operating.
 During nights and weekends when the system
 was  in a "setback" mode, radon levels rose quite
 rapidly to as high as 150 pCi/L downstairs and
 80 pCi/L upstairs.  Pressure measurements
 through  holes in the slab showed  that the
 HVAC systems resulted in small positive
 pressures within the building  that  provided
 complete remediation as long as they were
 operating.  However, the HVAC fans only
 operated when heating or cooling  was
 demanded; during mild weather they  seldom
 operated. The March charcoal measurements
 were made during cold weather that probably
 required more HVAC operation than the May
 tests which showed much higher radon levels.
 Communication tests showed  that  a trace  of
 suction could be measured across  20-feet of the
 center of the basement floor and in the nearby
 walls.  This suction  confirmed that some
 aggregate was present, that the permeability was
 marginal, and that an SSD system might be  able
 to produce significant mitigation.

 B.6    Temporary Mitigation

 When the radon problem was discovered in
 March, the students were moved out  of the
 basement classrooms where the levels were the
 highest  Tests in May showed the levels
 increasing upstairs, probably because  of the
 diminished cycling of the HVAC system in mild
weather.  For temporary mitigation, until the
school recessed for the summer, the HVAC fans
were turned on continuously both  upstairs and
downstairs when the building was occupied.
Although this provided complete mitigation
 under spring conditions, it was not considered
an acceptable permanent solution  because of the
increased wear on the HVAC fans and the

 unknown level of performance in the winter.
 Even with closed fresh-air dampers, a very slight
 positive pressure which produced complete
 remediation was generated in the building.  If
 HVAC mitigation had not been possible, one
 option might have been to install a large
 portable fan which would have been used to
 blow air in through an  open door while classes
 were in session, or the  school might have been
 closed early for the summer.

 B.7     First-Stage Mitigation

 A 4-inch diameter suction hole was drilled
 through the slab in a centrally located basement
 closet near the highest  subslab radon
 measurements. The aggregate  exposed by this
 hole was about 4-inches deep; it contained fine
 material which limited its permeability.  A
 1-foot diameter cavity was excavated in the
 aggregate and a 4-inch diameter suction pipe
 was installed across a dropped ceiling, out a
 back wall on the downhill side, and vented up
 above the roof line.  Larger 6-inch  diameter
 pipe would have been installed to allow more
 air flow and a bigger fan, but the clearance
 above the suspended ceiling was too low. A
 Kanalflakt T2 in-line fan was coupled to the
 pipe to provide about 1-inch WC of suction in
 the subslab cavity. After  several days of
 operation, a continuous radon  monitor showed
 a drop in the basement radon to about 40
 pCi/L.  These tests had to be made during the
 weekend when the temporary mitigation scheme
 involving the HVAC system could be
 discontinued without exposing the students to
 high radon levels.  The upstairs levels dropped
 to about 20 pCi/L.  (All air-handlers were off.)
 These results suggested that the SSD system had
a significant effect on the major radon source in
 the building, but other sources remained to be
 mitigated  and/or the main source was not
 completely mitigated.

 B.8     Second-Stage Mitigation

 In order to improve the performance of the
single suction-point system, the subslab cavity
was expanded from about 1-foot in  diameter to
about 2 by 3  feet  This significantly increased
 the air flow as indicated by a drop  in cavity
 pressure from about  1-  to 0.5-inch WC  It also
doubled the pressure field under the slab as
indicated by the fact that the pressures in a hole
13-feet from the suction point increased from
0.012- to 0.025-inch WC Radon levels upstairs
and downstairs also decreased slightly.

B.9    Third-Stage Mitigation

In the next attempt to increase the performance
of the single point  SSD system in the basement,
the fan was increased from a Kanalflakt T2 to a
T3B.  This increased the suction in the cavity
from  0.5- to 0.7-inch WC which was not as large
as might be expected since the T3B is capable
of moving more than twice the air flow of the
T2 at the same pressure.  The increase that was
smaller than expected in subslab pressure is
probably due to the flow restriction and
pressure loss in the 4-inch diameter pipe.  A
slight decrease in radon levels was noted, but
the levels downstairs and upstairs were still
about 20 and 15 pCi/L, respectively, after the
HVAC fans were off for 24 hours.

B.10    Fourth-Stage Mitigation

Since some radon was thought to be coming
from  under the first floor slab, a suction system
was installed near the woodworking shop where
the highest upstairs subslab air measurements
had been taken. A T2 fan and 4-inch pipe were
installed and a T fitting was coupled to the
pipe and sealed so that a second suction point
could be added to this system.  The subslab
aggregate was  found to be only 2 inches deep
and full of fine material, limiting its
permeability.   Continuous radon measurements
showed very little change after the system was
turned on.

B.11    Fifth-Stage  Mitigation

To improve the performance of the upstairs
system, a second suction point was installed
about 20 feet away  from the first  In addition,
the fan was replaced with a T3B and the pipe
near the fan was replaced with 6-inch diameter
pipe to handle the increased flow from the two
suction pipes.  The  initial suction point cavity
beneath the slab was increased from 1-foot in
diameter to 3 by 2 feet to increase the subslab

air flow.  A slight decrease in the upstairs radon
levels was observed.

B.12    Sixth-Stage Mitigation

In order to complete the mitigation system
downstairs, two more suction systems were
installed at the ends of the basement  These
systems used 4-inch pipe and T2 fans, with
about 1-foot cavities in the aggregate beneath
the slab.  In  addition, all three downstairs
systems had T fittings installed in the pipe
about 6-feet above the floor, horizontal 4-inch
pipes penetrated  the hollow concrete block
walls.  Unfortunately, the wall suction  created
so much air flow in the pipes that the subslab
cavity pressures in all the systems fell to about
0.2-inch WC, and the continuous radon monitor
in the basement showed that the net result was
a significant increase in basement radon.

B.13    Seventh-Stage Mitigation

When the wall suction pipes were cut and
sealed, the subslab cavity pressures in all the
systems rose  to about 0.7-inch WC and the
basement continuous radon monitor showed
levels below 2 pCi/L.  Pressure field
measurements in the basement showed
measurable depressurization under all of the

B.14    Eighth-Stage Mitigation

The upstairs  radon levels were still observed to
range from 4 to 10 pCi/L, so three more subslab
suction points were installed along  the uphill
side of the upstairs slab. These systems were
separated by  about 30 feet  and consisted of
6-inch pipe with two points manifolded to a T2
fan and a third connected to a CV9
wall-mounted fan that discharged horizontally
about 10 feet off the ground.

B.1S    Ninth-Stage Mitigation

Continuous radon measurements showed that
some peaks above 4 pCi/L  were associated with
the greenhouse area which had two of the three
new suction points. After  the fan on these
points was increased to a T4, the radon levels
remained  below 2 pCi/L.
B.16    Cost Estimates

The cost estimates given below are higher than
the actual expenses because of the research
nature of this project, but the following
breakdown may be useful:

1.      Labor for SSD installations:

        6 SSD Systems @ 2 person days per
        system =  12 person days.

2.      Parts  cost for SSD installations (fans,
        pipe,  electrical):

        6 SSD Systems @ S500  per system =

3.      Labor for post-mitigation testing:

        9 stages @ 0.5 person day for
        distribution and pickup  = 4.5 person

4.      Charcoal canisters for post-mitigation
        testing at each stage:

        9 stages with 10 canisters each @ S10
        per canister  = $900

5.      Pre-mitigation diagnostic work by
        experienced home mitigator:

        2 days @ S500 per day = $1000

6.      Continuous radon monitoring by
        consultant to monitor progress:

        30  days  @ $1007 per day = $3000

The'total is 16.5 person days of labor and
$7,900 in parts and consultant fees.  Since
continuous radon monitors are available for
about $3000, it may be cost effective  for school
systems with extensive radon problems to
purchase their own monitors.

B.17    Conclusion

Houses with marginal subslab porosity can often
be mitigated with SSD if enough suction points
can be installed.  This school required a similar

  mitigation system.  Winter testing with long
  term alpha-track monitors measured below 4
  pCi/L with most of the rooms measuring below
  2 pCi/L.  Pressure  gauges were placed on most
  of the suction pipes so that the fan performance
  can  be quickly checked.
 School C; Washington County. MD

 This successful school mitigation project is an
 example where large SSD fans can be used to
 mitigate large slab areas with 6-inch diameter
 pipe used as a manifold to connect the fan to
 several 4-inch diameter pipes that penetrate the

 C.1     School Description

 This entire school building is slab-on-grade with
 block walls and no utilities below grade except
 sanitary sewers. The original building was
 constructed in 1956 and has four area air
 handlers  for heating and ventilating with a
 central boiler room.  A classroom wing was
 added in 1968 and unit ventilators were used in
 each room.  No part of the building  is

 C2    Initial Radon Tests

 Elevated  radon levels were found in the locker
 rooms on each  side of the gymnasium in the
 original building and in the new classroom wing.
 The April 1988 screening tests with charcoal
 canisters showed that 21 of 72 tests were above
 4 pCi/L: 7 were above 8 pCi/L, and 1 was above
 20 pCi/L  (26.7). The highest levels were in the
 new classroom wing.

 C.3     Pre-Mitigation Diagnostics

 Although the locker rooms and gymnasium are
 on the same air handler, the gymnasium
 measured 1.8  pCJ/L whereas the girls' locker
 room measured 4.9 to 63 pCi/L and the boys'
 locker room measured 53 to  19 pCi/L.  Further
 examination indicated that each locker room
area had a large exhaust fan to remove odors
and shower steam.  Differential pressure
measurements (using a micromanometer), with
the air handler and exhaust fans operating,
  correlated with the radon levels showing that
  the gym pressure was slightly positive, the girls'
  locker room area slightly negative, and the boys'
  locker room area significantly negative.

  In April 1988 weekend charcoal canister
  measurements were made in the new classroom
  wing with the unit ventilators turned off.  All
  rooms but one were above 4 pCi/L;  a room in
  the northeast corner of the building measured
  26.7 pCi/L.  Radon levels decreased  from north
  to south in this wing as did subslab radon
  levels.  A continuous radon monitor was placed
  in the room with the highest radon levels.
  When the unit ventilator was off, levels above
  20 pCi/L were reached nightly but remained
  below 2 pCi/L when  the unit ventilator was
  operating continuously. Pressure measurements
  made with a micromanometer confirmed that
  the unit ventilator was pressurizing the room

 C4    First-Stage Mitigation

 Construction plans showed  that each locker
 room area was a continuous slab with aggregate
 beneath it.  As a result, a 6-inch subslab suction
 point was placed in each of the two locker
 room areas with a 1-foot diameter subslab hole
 and a Kanalflakt GV-9 fan  (rated at 200 cfm at
 0.75 inch static pressure). Both locker room
 areas measured less than 4  pCi/L with the
 exhaust fans and  the subslab depressurization
 systems operating.

 In the new wing, the  unit ventilators  are turned
 off at night except in extremely cold weather
 when they are cycled.  It was decided to install
 two subslab depressurization points in this wing
 to provide mitigation when  the unit ventilators
 were not operated.  The two 4-inch pipes were
 installed in the hall and manifolded with an
 above-ceiling 6-inch pipe running to  a
 Kanalflakt GV-12 fan (rated at 510 cfm at 0.75
 inch static pressure) at the north end of the
 building.  One suction point was installed with a
 3-foot diameter subslab  hole about 20 feet from
 the east end of the hall. The other suction
 point was installed with a 1-foot diameter
subslab hole about 60 feet from the end of the
hall.  Pressure field extension measurements
indicated that the two fields  overlapped; all slab

areas of the wing, except the most southern
classrooms, were depressurized to the outside

C.5     Second-Stage Mitigation

Since the new wing pressure field extension
around the 1-foot diameter suction hole was not
as great as around the 3-foot suction hole, the
1-foot subslab suction hole was  increased  to 3
feet in diameter.  This extended the measurable
depressurization area by 10 feet to the south,
which was sufficient to reach the last two
classrooms. The amount of depressurization in
the test holes in all directions around the
suction point was doubled.  With the subslab
depressurization system operating, radon levels
were below 4 pCi/L in all classrooms with the
unit ventilator fans off.
This school was relatively simple to mitigate
and, although the subslab communication was
not very good due to low quality aggregate, the
three SSD systems performed adequately
because of large fans, large diameter pipe, and
large subslab suction pits.
School D: Washington County. MD

This successful school mitigation showed that
schools with radiant heating coils in the slab
can be mitigated with SSD if a deep layer of
aggregate is under the slab. The project was
expected to be difficult because of the limited
number of places where the slab could be
penetrated without the danger of drilling
through a hot water pipe.  A newer section of
the school, heated with unit ventilators, was
mitigated with two multi-point  SSD systems.

D.I     School Description

The original building of this school was built in
1958 and is heated with hot water radiant heat
in the slab.  In 1978 a kindergarten room was
added in an off set to the original building, and
a separate building (Building B) was built which
contains  four classrooms, a library, a teachers'
workroom, a conference room, and restrooms.
The kindergarten room is heated with hot water
radiant heat, and the new building is heated
with unit ventilators. Office space in the
original building is air-conditioned with a
window unit  No  other area of either building
is air-conditioned.

The original building has two 3600 cfm
roof-mounted fans that can be used  to exhaust
air in plenums over the hall ceiling.   Each room
has a ceiling vent  which connects to these hall
plenums.  However, the exhaust fans are never
used.  Consequently, the building has no active
ventilation system.

D.2    Initial Radon Tests

All rooms in both buildings were tested with
charcoal canisters  over a weekend in mid-April.
Of 24 tests, 21 were over 4 pCi/L, 16 were over
8 pCi/L, and 3 were over 20 pCi/L.  The eight
rooms in Building B measured between 17 and
20  pCi/L.  It is believed that the unit
ventilators were off during the testing weekend,
but this could not be confirmed.  Seven tests in
the classrooms, library, and multi-purpose room
in the original building measured between 12
and 23 pCi/L.

D.3    Building Plan Inspection

Plans showed that the initial building and
kindergarten addition had 6 inches of aggregate
under a 6-inch thick slab containing hot water
pipes for heating.  Building B had 4 inches of
aggregate under a  4-inch slab.

D.4    Pre-Mitigation Diagnostics

A continuous radon monitor was placed in one
of the classrooms in Building B to measure the
effect of unit ventilator operation on radon
entry.  It was  found that radon levels would rise
overnight to above 20 pCi/L with the ventilator
off but would remain below 2 pCi/L with  the
ventilators operating. Again, this shows that a
unit ventilator can reduce radon levels by
pressurizing the room slightly.  When run
continuously this type of unit ventilator can
prevent radon entry.

  D.S     First-Stage Mitigation

  Since the Building B ventilators are off during
  night setback, a four-point, two-fan subslab
  depressurization system was installed to reduce
  radon entry. The risers are 4-inch pipes
  connected to two 6-inch manifold pipes above
  the dropped ceiling.  (Two risers are manifolded
  to each pipe.)  A Kanalflakt GV-9 fan (rated at
  200 cfm at 0.75-inch static pressure) is used to
  exhaust each system.  Pressure field extension
  measurements indicated that subslab
  depressurization extended 50 feet, the minimum
  distance necessary to reach all parts of the slab.

  With the Building B subslab system operating
  and the unit ventilators off, all rooms remained
  below 4 pCi/L.  However, based on  the
  pressure field extension measurements, the
 system may be of marginal value during cold
 weather. If radon levels rise above 4 pCi/L it is
 believed  that subslab depressurization can be
 improved by sealing the floor-to-wall opening.
 A K-inch expansion joint around all of the slabs
 in the building is deteriorating, leaving
 significant openings to the subslab. This
 probably leads to some short-circuiting of the
 subslab depressurization system.

 D.6    Second-Stage Mitigation

 Subslab suction on this original building (the
 intra-slab radiant-heat building) was a challenge
 since construction plans showed that the hot
 water pipes in the slab were separated by no
 more than 15 inches over the entire building.
 As a  result, it was difficult to locate an area
 where a 6-inch subslab  suction point could be
 put through the slab without running the risk of
 damaging a hot water pipe.  Building plans
 identified a 3-foot square area without water
 pipes in each room. A hole was successfully cut
 through one of these areas.  The plans indicated
 that the aggregate was a minimum of 6 inches
 deep, much deeper than at any other school
 examined.  A 6-inch suction point was installed
with a 3-foot diameter hole with a Kanalflakt
KTR150-8 fan (rated at 510 cfm at 0.75-inch
static  pressure).  Pressure field extension was far
greater than expected; depressurization could be
measured as far as 90 feet from the suction
hole.  These results were surprising since the
  aggregate appeared to be some type of "crusher
  run" aggregate with a certain amount of fines.
  However, in leveling the aggregate before
  pouring the concrete, it is probable that most of
  the  fines had sifted to the lower portion of the
  aggregate bed leaving a fairly thick area of
  large-diameter aggregate immediately under the
  concrete. It is believed that this layer of coarse
  stone enhanced pressure field extension; this
  will be studied further.  It appears  that this one
  suction point will solve the problem in the
  original building.  If this one suction point is
  not sufficient to treat the entire building, it may
  take a second point, operated on a separate fan,
  to completely mitigate the building.

 Since the kindergarten room is an addition, the
 subslab area does not communicate with the
 original building. Consequently, a suction  point
 was put in a closet adjacent to  a restroom
 where the hot water pipes were spaced 24
 inches apart to clear the commode's sewer  line.
 A Kanalflakt T-2 fan (rated at  140 cfm at 0.75
 inch static pressure) installed on this point
 lowered radon levels to below 2 pCi/L.  No
 pressure field extension measurements were
 made for fear of damaging a heating water pipe.

 This school has been retested over the winter to
 determine if the SSD systems continue  to
 mitigate during cold weather conditions; results
 should be available soon.

 D.7    Conclusion

 The ease of mitigating several thousand  square
 feet with one SSD suction point in the older
 section of this school was an encouraging result.
 Building B was a standard installation with  two
 suction points on each of two SSD systems.
School E; Fairfax County. VA

This successful school mitigation project showed
that radon problems can be aggravated by
exhaust-only ventilation systems that produce
continuous negative pressures in all rooms
(relative to the subslab area). However, it was
also shown that, with sufficient subslab
permeability, SSD systems can achieve successful

 radon mitigation under these adverse conditions
 of negative pressure.

 E.1     School Description

 This slab-on-grade building is "L-shaped," and
 each wing has a central hall with classrooms on
 each side.  The rooms are heated by hot water
 fin heaters along the outside walls. Each room
 had ceiling exhaust vents  into a plenum over the
 rooms and halls.  Since there was  no supply air
 fan, the roof-mounted exhaust fans in this
 plenum caused severe depressurization (0.060
 inch WC negative pressure) of the entire
 building, and any make-up air entered the
 building only through infiltration induced by the

 The building was designed so that each
 classroom would be ventilated adequately only if
 one of the windows was left open.
 Unfortunately, the severe depressurization was
 also drawing subslab soil gas containing radon
 into the building.
Initial Radon Tests
Tests during the fall of 1987 in this school were
the first to suggest that radon levels in
classrooms varied widely from room to room,
and that the test results were difficult to predict
from room location and construction.  Initially,
charcoal screening tests were conducted in a few
classrooms with the highest test showing
approximately 6 pCi/L.  Subsequent tests in all
classrooms by the PTA showed several
classrooms over 20 pCi/L.  The two end
classrooms of the southwest wing had levels of
22 and  17 pCi/L with three other rooms above
4 pCi/L. The southeast wing had three rooms
with moderately elevated levels of 5, 6, and 7

E.3     Building Plan Inspection

The building plans and specifications called for
4 inches of aggregate under the slab.  The
foundation plans showed that the slab was
thicker along the hall between the classrooms.
E.4     Temporary Mitigation

The students were moved out of the rooms with
the highest radon levels until the problem could
be corrected.  Since there was little experience
with school radon mitigation in Fairfax County
at this time, it was not known how long it
would take to fix the problem.

E.S     Pre-Mitigation Diagnostics

Subslab communication tests and radon tests
were performed to locate the radon sources and
to determine whether SSD was a possibility.
Radon levels from 25 to 2000 pCi/L were found
under the slab and were consistent with the
location of rooms with highest screening
measurements. The subslab communication was
found to be good, except in the thickened area
of the slab. Separate suction points would have
to be placed on each side of the hall.  There
was good communication under the interior
walls that are perpendicular to the hall.  This
was consistent with the foundation plans that
showed that these walls were non-load-bearing.

E.6    First-Stage Mitigation

A number  of mitigation strategies were
considered, including reversal of the exhaust
fans  to create pressurization, drilling ventilation
holes through the walls behind the radiators to
provide more fresh air, and replacing the entire
HVAC system with a positive pressurization
system.  Before these expensive solutions were
attempted,  it was decided to try the simple
techniques  recommended by the EPA for house
mitigation: eliminating depressurization, sealing
cracks, and SSD. For eliminating
depressurization, the HVAC exhaust fans were
turned off and the rooms were retested to
determine if the building could be mitigated by
simply removing the negative pressure.
Surprisingly, some of the rooms were still above
10 pCi/L under these conditions. It seems that
the lower pressure probably reduced radon entry
rates, but it also reduced the entry of fresh air
that was diluting the radon.

  E.7    Second-Stage Mitigation

  The rooms with the highest radon levels were
  found to have cracks between the floor and wall
  that varied from    to % inch wide.  These cracks
  were carefully sealed and re-testing of the room
  indicated a reduction of radon levels from 0 to
  50 percent.

  It is not unusual  to get marginal mitigation
  results from crack sealing in  houses.  This is
  thought to be due to the difficulty in sealing all
  the radon entry routes such as porous hollow
  block walls. In addition, the radon levels often
  build up behind effective sealants, so that any
  unsealed leaks may provide more radon.

  E.8     Third-Stage Mitigation

 Subslab suction points were put  in the two end
 rooms of the southwest wing.  The subslab
 suction points were manifolded overhead and
 connected to one Kanalflakt GD-9 fan (rated at
 310 cfm at 0.75-inch static pressure).  Subslab
 excavation  revealed that the aggregate was
 present and that it did  not have  significant fine
 material that would impede air flow.  With this
 SSD system in operation there was good
 pressure field extension to at  least three rooms
 on each side of the hall.  In addition, all of the
 floor-to-wall joints were carefully sealed in all of
 the rooms'of both wings.  Following sealing and
 installation of the two suction points, all of the
 rooms in both wings tested below 4 pCi/L.

 E.9     Fourth-Stage Mitigation

 During December 1988, short-term tests
 revealed that radon  levels were again above 4
 pCi/L (despite  the previous sealing work) in the
 southeast wing that  did not have an SSD
 installed.  Although longer term  tests indicated
 that the long-term averages were below 4 pCi/L,
 school personnel decided  to install an SSD
 system in this wing.  This work has been
 completed, and all classrooms are below 4

 E.10    Conclusion

 Mitigation of this school showed  that, since
subslab permeability was good, SSD was
 applicable despite the large size and complex
 ventilation system.  Sealing and the reduction of
 depressurization were marginally effective, but
 SSD was very effective despite the
 depressurization of the building by the HVAC
 exhaust fans.
 School F; Washington County, MD

 This ongoing, initially unsuccessful school
 mitigation project shows that mistakes can be
 made easily in selecting an appropriate radon
 mitigation method.  In this case, an attempt to
 use SSD to overcome subslab return air duct
 leakage was a failure; a  more expensive solution
 will probably be necessary.

 F.I     Initial Radon Tests

 In April 1988, 39 charcoal canister radon tests
 showed that 28  were above 4 pCi/L, 8 were
 above 8 pCi/L, and none were above 20 pCi/L.
 All of the screening and confirmation tests were
 made when the  building was unoccupied and the
 HVAC system was turned  off.

 F.2    Building Plan Inspection

 The original school was built in 1954, and
 additions were made in 1964. Both are
 slab-on-grade  construction.  The additions have
 an HVAC system with return air ducts that are
 underneath the slab.  The foundation plans and
 specifications  call for 4 inches of aggregate
 under the slabs.

 F3     Pre-Mitigation Diagnostics

 Radon grab samples showed about 20 pCi/L in
 the HVAC supply air when the system was
 turned on. This indicated that the return air
 ducts under the  slab were drawing in soil  gas
 and recirculating it through the school. Subslab
 pressure measurements indicated a pressure field
 that ranged from 0.1- to  0.001-inch WC of
 negative pressure. The largest pressures were
 nearest the return air exhaust vent that went up
 to the roof mounted fan  system. These
 measurements suggested that if a SSD system
were installed  which would produce a larger
competing pressure under the slab, the soil gas

 could not enter the cracks in the return air

 F.4     First-Stage Mitigation

 A Kanalflakt GV9 fan was mounted on the
 roof, connected by a 6-inch manifold pipe to
 two  4-inch diameter pipes. Suction points for
 these smaller pipes were drilled though the slab
 near the return exhaust stack in order  to
 maximize the suction  where diagnostics had
 indicated that the return air subslab suction was
 the highest. These slab penetrations uncovered
 good aggregate without excessive fine material.

 However, it soon became obvious that  this SSD
 system could not overcome radon entry into the
 return air ducts.  The diagnostic measurements
 of the  return air pressure field  had been made
 through holes drilled  through the slab  and not
 through holes drilled  through the actual return
 air pipe under the slab.  When this pipe was
 exposed through the holes drilled for the 4-inch
 pipe, pressure measurements showed 0.8-inch
 WC  inside the  pipe. The diagnostics had
 confused the small subslab negative pressure
 that  was caused by duct leakage with the much
 larger negative pressure in the pipe.  It is  very
 unlikely that a  SSD system could realistically
 depressurize all areas  of the slab to a level
 (approximately 0.8-inch WC in  this case) that
 would be required to  prevent soil gas from
 entering any cracks in the pipe.  Subsequent
 radon tests indicated that the installed  system
 had a negligible effect on the radon levels in
 the school.
Schools with subslab HVAC ductwork create a
major problem that may require an alternative
mitigation approach to SSD.  Although it is
generally a good idea to try a simple,
inexpensive mitigation technique before trying
the more complex and expensive techniques,
there should be some experience or theory that
provides some confidence that the technique
will work.

A new overhead air-return system is now being
installed in this school, and follow up diagnostic
measurements are planned.
School G; Arlington County. VA

This successful school mitigation project showed
that schools with minor radon problems in a
few rooms may be mitigated by craclc sealing or
correction of HVAC imbalances.  However, it is
unlikely that these measures would be effective
for radon levels significantly over 8 pCi/L since
reductions  from these approaches are usually
about 50 percent

G.I    School Description

Half of this older school building is one-story
slab-on-grade; the other half is two-story with a
walk-out basement  The walls are constructed
of hollow blocks and the exterior of the school
is brick veneer.  The HVAC system combines
unit ventilators with a single-fan air handling
system with overhead duct work.

G.2    Initial Radon Tests

Initial and  follow-up charcoal canister tests
showed only two basement rooms between 4
and 8 pCi/L. All other rooms were below 4
pCi/L.  The measurements were made during
unoccupied periods.

G3   Walk-Through Building Inspection

The HVAC supply vent in one of the problem
rooms was found to be inoperative  and the
other room was found to have a 1/2-inch wide
building expansion crack that was loosely
covered by baseboard molding.

G.4   Pre-Mitigation Diagnostics

Subslab radon levels of 500  to 1000 pCi/L were
measured in the basement area.  A negative
pressure in the room with the inoperative
supply vent could be detected by air movement
into the room when  the HVAC fan was

G.5   First-Stage Mitigation

An HVAC contractor was called in to correct
the HVAC supply duct problem, and the
building separation crack was sealed with a
pourable polyurethane caulk. After these

  mitigation efforts were complete, continuous
  radon monitoring and short-term charcoal tests
  showed that the room with supply vent
  problems was below 2 pCi/L, but the room with
  the building separation crack still had daily
  peaks above 4 pG/L.  Further examination of
  the slab in this room showed an additional &
  inch wide and  30-foot long crack between the
  floor and the wall underneath a unit ventilator
  system along one wall.

  G.6    Second-Stage Mitigation

  The unit ventilator covers in the remaining
  problem room  were removed to gain access to
  the crack and pourable polyurethane caulk was
  used to seal it.  Continuous monitoring and
  charcoal canister tests showed that the radon
  levels were now consistently below 4 pCi/L.
  Both problem rooms will be retested over the
 winter to determine if the mitigation continues
 to be effective.

 G.7    Conclusion

 When radon levels are slightly elevated (less
 than 8 pCi/L), then mitigation solutions such as
 crack sealing and elimination of gross HVAC
 depressurization may be effective. However, in
 many cases these techniques fail to reduce radon
 levels by as much as 50 percent, and the
 problem may recur during the winter. Sealing
 may not be very effective because many entry
 routes such as porous hollow block walls are
 hard to seal.  Effective sealing causes a higher
 concentration of radon to build up behind the
 seal so that the few remaining entry routes may
 leak soil gas with higher radon concentrations.
 When HVAC depressurization is eliminated,
 there is still a slight depressurization of the
 upper surface of the slab due to the buoyancy
 of wanner air in the building (natural stack •
 effect).  The more effective and dependable
 mitigation techniques rely on positive
 pressurization above the slab, or negative
 pressurization beneath the slab.
School H; Washington County. MD

This ongoing school mitigation project is
attempting to mitigate a combination
  crawl-space/slab-on-grade school. A large
  exhaust fan has been installed in the crawl space
  and the radon levels in the crawl space and the
  building have been slightly reduced.  Future
  plans call for increased air sealing of the crawl
  space, retesting of the pressure and radon levels,
  evaluation of the mitigation effects of the
  HVAC system, and installation of a subslab
  suction system under the slab-on-grade section
  of the school.

  H.1     School Description

  Half of this single story building is over a crawl
  space and the other half is slab-on-grade.  The
  HVAC system is a single-fan system with
  overhead duct work.  The exterior of the school
  is brick veneer.  All exterior entrances  to the
 crawl space appear to be sealed.

 H.2    Initial Radon Tests

 In April 1988, 35 charcoal canister radon tests
 showed that 34 were above 4 pCi/L, 15 were
 above 8 pCi/L, and 1 was above 20 pCi/L (23.5
 pCi/L).  The radon levels were generally higher
 in the rooms over the crawl space. All of the
 screening and confirmation tests were made
 when the building was unoccupied and the
 HVAC system was turned off.

 H.3    Building Plan Inspection

 The original school, which is approximately
 150,000 square feet in area, was built in 1936
 over a crawl space.  In 1967 a slab-on-grade
 addition was built onto two sides of the old
 building.  The crawl space has a dirt floor and
 the wooden floor joists rest on a maze of
 masonry walls. The foundation plans and
 specifications for the slab call for 4 inches of
 aggregate under the slabs.  The addition was
 constructed so that its floor would be at the
 same level as the crawl space floor. Retaining
 walls  were built and shale fill was used to raise
 the leveL

 H.4     Walk-Through Building Inspection

The crawl space is accessible through hatches in
the floor, but the crawl space size and maze of
support walls do not appear to offer good

 access for laying down a ground cover for
 submembrane depressurization (SMD), as is
 often done in houses built over crawl spaces.
 Some plumbing pipes are in the crawl space and
 all exterior vents appear to have been sealed for
 security and to prevent the pipes from freezing.

 H.S    Pre-Mitigation Diagnostics

 Since there is little experience with radon
 mitigation of large crawl spaces, there are no
 guidelines for diagnostic analysis.  Blower door
 testing of the crawl space was considered, but
 the installation of a 500 cfm exhaust fan was
 simpler to evaluate.  Radon grab samples taken
 before the fan installation showed about 30
 pCi/L in the crawl space.

 H.6    First-Stage Mitigation

 A Kanalflakt GV9 fan was mounted on one of
 the wooden panels that covered the crawl space
 vents.  This fan  can move 510 cfm at 0.0
 pressure.  It was mounted so that it would
 exhaust air from the crawl space.   No crawl
 space sealing was done before evaluation of the
 system's performance.

 The fans were turned off over the Christmas
 holiday weekend, and continuous  radon
 monitors were placed in the crawl space and the
 main office to determine if the crawl space
 exhaust fan was  reducing the radon.  The
 monitoring showed that the crawl space levels
dropped slightly when the fan was running. In
addition, the office radon seemed to be well
below 4 pCi/L when school was in session and
the HVAC fans  were  operating. Pressure
differentials in the crawl space did not change
measurably (less than 0.001 inch WC) due to
crawl space exhaust Can operation. Calculations
 of these results estimate that there is at least 10
 square feet of leakage in the crawl space

 H.7    Second-Stage Mitigation

 The school will be retested with the HVAC
 system operating to determine the mitigation
 effect.  If the HVAC system induces a positive
 pressure in all parts of the building, then  the
 radon problems may be mitigated while the
 HVAC fans are operating. Further investigation
 will be required  to determine if the HVAC
 mitigation can be relied on under all operating
 conditions, and whether there is a remaining
 radon exposure problem to those who use the
 school outside of normal operating hours  when
 the HVAC fans are off.  The crawl space
 exhaust fan seems to be lowering the radon
 levels slightly, but it does not seem to be
 creating much of a pressure barrier to prevent
 soil gas from moving into the building. To
 increase the depressurization, several large holes
 between the crawl space and the boiler room
 will be sealed.

 A SSD system will be installed in the
 slab-on-grade part of the school.  This system
 will be mounted externally by drilling a 6-inch
 diameter hole in  the retaining wall, just below
 the slab level A Kanalflakt T3B in-line fan will
 be mounted on a 6-inch stack that exhausts
 above roof level.

 H.8     Conclusion

 Several more mitigation stages are anticipated in
order to obtain an effective radon mitigation
system for this complex school.  The final
 mitigation system will probably combine a
 number of methods due to the school's complex



 Radiological Health Branch
 Alabama Department of Public Health
 State Office Building
 Montgomery, AL 36130
 (205) 261-5313

 Alaska Dept. of Health and Social Services
 P.O. Box H-06F
 Juneau, AK 99811-0613
 (907) 586-6106

 Arizona Radiation Regulatory Agency
 4814 South 40th Street
 Phoenix, AZ 85040
 (602) 255-4845

 Div.  of Radiation Control and Emergency
 Arkansas Department of Health
 4815 Markham Street
 Little Rock, AR 72205-3867
 (501) 661-2301

 Indoor Quality Program
 California Department of Health Services
 2151 Berkeley Way
 Berkeley, CA 94704
 (415) 540-2134

 Radiation Control Division
 Colorado Department of Health
 4210 East llth Avenue
 Denver, CO 80220
 (303) 331-4812

 Connecticut Department of Health Services
Toxic Hazards Section
 150 Washington Street
 Hartford, CT 06106
 (203) 566-3122

 Division of Public Health
 Delaware Bureau of Environmental Health
P.O.  Box 637
Dover, DE 19903
 (302) 736-4731
                                      DC Dept of Consumer and Regulatory Affairs
                                      614 H Street, NW, Room 1014
                                      Washington, DC 20001
                                      (202) 727-7728

                                      HRS Office of Radiation Control/Radon
                                      1317 Wirewood Boulevard
                                      Tallahassee, FL 32399-0701
                                      (904) 488-1525
                                      (800) 543-8279 (Consumer inquiries only)

                                      Georgia Dept of Natural Resources
                                      Environmental Protection Division
                                      205 Butler Street,  NE
                                      Floyd Towers East, Suite 1166
                                      Atlanta, GA 30334
                                      (404) 656-6905

                                      Environmental Protection and Health Services
                                      Hawaii Department of Health
                                      591 Ala Moana Boulevard
                                      Honolulu, HI 96813
                                      (808) 548-4383

                                      Bureau of Preventive Medicine
                                      450 West State Street
                                      Fourth Floor
                                      Boise, ID 83720
                                      (208) 334-5927

                                      Illinois Department of Nuclear Safety
                                      Illinois State Board of Health
                                      1301 Knotts Street
                                      Springfield, IL 62703
                                      (217) 786-6399
                                      (800) 225-1245

                                      Division of Industrial Hygiene and Radiological
                                      Indiana State Board of Health
                                      1330 W. Michigan Street
                                      P.O. Box 1964
                                      Indianapolis, IN 46206-1964
                                      (800) 272-9723

  Bureau of Environmental Health
  Iowa Department of Public Health
  Lucas State Office Building
  Des Moines, IA 50319-0075

  Bureau of Air Quality and Radiation Control
  Attention: Radon
  Forbes Field, Building 740
  Topeka, KS 66620-0110
  (913) 296-1560

  Radiation Control Branch
  Cabinet for Human Resources
 275 East Main Street
 Frankfort, ICY 40621
 (502) 564-3700

 Louisiana Nuclear Energy Division
 P.O. Box 14690
 Baton Rouge, LA 70898-4690
 (504) 925-4518

 Division of Health Engineering
 Maine  Department  of Human Services
 State House  Station 10
 Augusta, ME 04333
 (207) 289-3826

 Division of Radiation Control
 Maryland Dept of Health and Mental Hygiene
 201 W. Preston Street
 Baltimore, MD 21201
 (301) 631-3300
 (800) 872-3666

 Radiation Control Program
 Massachusetts Department of Public Health
 23 Service  Center
 Northhampton, MA 01060
 (413) 586-7525
 (617) 727-6214 (Boston)

Michigan Departtkfcat of Public Health
Division of Radjofcfkal Health
3500 North Logan
P.O. Box 30035
Lansing, MI 48909
(517)  335-8190
 Section of Radiation Control
 Minnesota Department of Health
 P.O. Box 9441
 717 SE Delaware Street
 Minneapolis, MN 55440
 (612) 623-5348
 (800) 652-9747

 Division of Radiological Health
 Mississippi Department of Health
 P.O. Box 1700
 Jackson, MS 39125-1700
 (601) 354-6657

 Bureau of Radiological Health
 Missouri Department of Health
 1730 E. Elm, P.O. Box 570
 Jefferson City, MO  65102
 (800)  669-7236 (Missouri only)

 Occupational Health Bureau
 Montana Dept of Health and Environmental
 Cogswell Building A113
 Helena, MT 59620
 (406) 444-3671

 Division of Radiological Health
 Nebraska Department of Health
 301 Centennial  Mall South
 P.O. Box 95007
 Lincoln, NE 68509-5007
 (402) 471-2168

 Radiological Health Section
 Health Division
 Nevada Department of Human Resources
 505 East King Street, Room 203
 Carson City, NV 89710
 (702) 885-5394

New Hampshire Radiological Health Program
Health and Welfare  Building
6 Hazen Drive
Concord, NH 03001-6527
(603) 271-4588

 New Jersey Dept of Environmental Protection
 380 Scotch Road, CN-411
 Trenton, NJ 08625
 (609) 530-4000/4001 or (800) 648-0394 (in state)
 or (201) 879-2062 (Northern NJ Radon Field

 New Mexico Environmental Improvement Div.
 Community Services Bureau
 1190 St. Francis Drive
 Harold  Runnels Building
 Santa Fe, NM 87503
 (505) 827-2948

 Bureau  of Environmental Radiation Protection
 New York State Health Department
 2 University Place
 Albany, NY 12203
 (800) 342-3722 (NY Energy Research &
 Development Authority)

 Radiation Protection Section
 North Carolina Department of Human
 701 Harbour Drive
 Raleigh, NC 27603-2008
 (919) 733-4283

 Division of Environmental  Engineering
 North Dakota Department of Health and
 Consolidated Laboratory
 Missouri Office Building
 1200 Missouri Avenue, Room 304
 P.O. Box 5520
 Bismarck, ND 58502-5520
 (701) 224-2348

 Radiological Health Program
 Ohio Department of Health
 1224 Kinnear Road, Suite 120
Columbus, OH 43212
 (614)  644-2727 or
 (800)  523-4439 (ta *t*te only)

Radiation and Spedal Hazards Service
Oklahoma State Department of Health
P.O. Box 53551
Oklahoma City, OK 73142
(405)  271-5221
 Oregon State Health Department
 1400 S.W. 5th Avenue
 Portland, OR 97201
 (503) 229-5797
 Bureau of Radiation Protection
 Pennsylvania Department of Environmental
 P.O. Box 2063
 Harrisburg, PA 17120
 (717) 787-2480 or
 (800) 237-2366 (in state only)

 Puerto Rico Radiological Health Division
 G.P.O. Call  Box 70184
 Rio Piedras, PR 00936
 (809) 767-3563

 Division of Occupational Health and Radiation
 Rhode Island Department of Health
 206 Cannon Building
 75 Davis Street
 Providence, RI 02908
 (401) 277-2438

 Bureau of Radiological  Health
 South Carolina Department of Health and
 Environmental Control
 2600 Bull Street
 Columbia, SC 29201
 (803) 734-4700/4631

 Office of Air Quality and Solid Waste
 South Dakota Department of Water and
 Natural Resources
Joe Foss Building, Room 416
523 E. Capital
Pierre, SD 57501-3181
 (605) 773-3153

Division of Air Pollution Control
Custom House
701 Broadway
Nashville, TN 37219-5403
(615) 741-4634   ..

Bureau of Radiation Control
Texas Department of Health
 1100 West 49th Street
Austin, TX 78756-3189
(512) 835-7000

 Division of Environmental Health
 Bureau of Radiation Control
 288 North 1460 West
 P.O. Box 16690
 Salt Lake City, UT 84116-0690
 (801) 538-6734

 Division of Occupational and Radiological
 Vermont Department of Health
 Administration Building
 10 Baldwin Street
 Montpelier, VT 05602

 Bureau  of Radiological Health
 Department of Health
 109 Governor Street
 Richmond, VA 23219
 (804)  786-5932 or
 (800)  468-0318 (in state)

 Environmental Protection Section
 Washington Office of Radiation Protection
Thurston Airdustrial  Center
Building 5, LE-13
Olympia, WA 98504
(206)  753-5962
Radon Hotline (800) 323-9727
Industrial Hygiene Division
West Virginia Department of Health
151 llth Avenue
South Charleston, WV 25303
(304) 348-3526/3427
(800) 922-1255

Division of Health
Section of Radiation Protection
Wisconsin Department of Health and Social
5708 Odana Road
Madison, WI 53719
(608) 273-6421

Radiological Health Services
Wyoming Department of Health and Social
Hathway Building, 4th Floor
Cheyenne, WY 82002-0710
(307) 777-7956


Region         Address/Telephone

  1             U.S. Environmental Protection Agency
               John F. Kennedy Federal Building
               Boston, MA 02003
               (617) 565-3234
                                               States in Region

                                               Connecticut, Maine, Massachusetts,
                                               New Hampshire, Rhode Island,
U.S. Environmental Protection Agency
26 Federal Plaza
New York, NY 10278
(212) 264-4418
                                                             New Jersey, New York, Puerto Rico,
                                                             Virgin Islands
U.S. Environmental Protection Agency
841 Chestnut Street
Philadelphia, PA 19107
(215) 597-8320
                                                             Delaware, District of Columbia,
                                                             Maryland, Pennsylvania, Virginia,
                                                             West Virginia
U.S. Environmental Protection Agency
345 Courtland Street, N.E.
Atlanta, GA 30365
                                                             Alabama, Florida, Georgia, Kentucky,
                                                             Mississippi, North Carolina, South
                                                             Carolina, Tennessee
U.S. Environmental Protection Agency
230 South Dearborn Street
Chicago, IL 60604
(800) 572-2515 (Illinois)
(800) 621-8431 (other states in region)
                                                             Illinois, Indiana, Michigan,
                                                             Minnesota, Ohio, Wisconsin

              U.S. Environmental Protection Agency
              1445 Ross Avenue
              Dallas, TX 75202-2733
              (214) 655-7208
                                              Arkansas, Louisiana, New Mexico,
                                              Oklahoma, Texas
              U.S. Environmental Protection Agency
              726 Minnesota Avenue
              Kansas City, KS 66101  ,
              (913) 236-2893
                                              Iowa, Kansas, Missouri, Nebraska
              U.S. Environmental Protection Agency
              999 18th Street, Suite 500
              Denver, CO 80202-2405
              (303) 293-1709

              U.S. Environmental Protection Agency
              215 Fremont Street
              San Francisco, CA 94105
              (415) 974-8378
                                              Colorado, Montana, North Dakota,
                                              South Dakota, Utah, Wyoming
                                              American Samoa, Arizona, California,
                                              Guam, Hawaii, Nevada
U. S. Environmental Protection Agency
1200 Sixth Avenue
Seattle, WA 98101
(206) 442-7660
Alaska, Idaho, Oregon, Washington