xvEPA
           United States     Office of Air Quality       EPA-451/R-93-012
           Environmental Protection Planning and Standards     September 1993
           Agency        Research Triangle Park, NC 27711

           Air/Superfund
AIR/SUPERFUND
NATIONAL TECHNICAL
GUIDANCE STUDY SERIES
           OPTIONS FOR DEVELOPING AND
           EVALUATING MITIGATION STRATEGIES
           FOR INDOOR AIR IMPACTS AT CERCLA
           SITES

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              AIR/SUPERFUND NATIONAL TECHNICAL
                   GUIDANCE STUDY  SERIES
                       Report ASF-36
OPTIONS FOR DEVELOPING AND EVALUATING  MITIGATION STRATEGIES
           FOR INDOOR AIR IMPACTS AT CERCLA SITES
                   Contract No. 68D30032
                   Work Assignment No.  4
                  Work Assignment Manager
              Kathy Diehl, U.S. EPA  Region  IX
            U.S.  Environmental  Protection Agency
       Office  of Air Quality Planning and Standards
       Research Triangle Park, North  Carolina   27711
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                                DISCLAIMER

      NOTICE: The materials and  descriptions complied for this paper are
not to be considered Agency guidance  or policy,  but are provided for
informational and discussion purposes only.   They are not intended,  nor can
they be relied upon, to create any rights enforceable by any party in
litigation with the United States. Mention  of companies, trade names,  or
commercial products does not constitute endorsement or recommendation for
use.

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                               TABLE OF CONTENTS
DISCLAIMER 	  i
TABLES	  iv
FIGURES	  iv

1.0    INTRODUCTION	 1-1
       1.1    BACKGROUND  	 1-1
       1.2    PURPOSE 	 1-1
       1.3    SCOPE  	 1-2
       1.4    RELATIONSHIP TO EXISTING REGULATIONS AND GUIDANCE 	 1-2

2.0    MITIGATION TECHNIQUES  	 2-1
       2.1    CONTAMINANT PATHWAYS	 2-1
       2.2    TECHNICAL MEASURES	 2-3
             2.2.1   Source Removal	 2-3
             2.2.2   Prevention of Soil Gas Entry	 2-4
             2.2.3   Removal From Indoor Air	 2-29
             2.2.4   Techniques for New Construction	 2-38
       2.3    INSTITUTIONAL	 2A6
             2.3.1   Governmental ICs  	 2-49
             2.3.2   Proprietary Institutional Controls	 2-51

3.0    DEVELOPING AND SELECTING MITIGATION STRATEGIES  	 3-1
       3.1    DEFINING THE OBJECTIVE	 3-2
             3.1.1   Mitigation Level Desired	 3-4
             3.1.2   Reduce Impacts for Current Property Usage	 3-5
             3.1.3   Prevent/Reduce Impact for Future Property Usage	 3-5
       3.2    BASIC INFORMATION NEEDS	 3-5
             3.2.1   Source Type, Strength, Route of Impact	 3-6
             3.2.2   Building Structural Features	3-9
             3.2.3   Current and Potential Future Uses  	 3-12
       3.3    EVALUATION OF OPTIONS 	 3-13
             3.3.1   Estimated Effectiveness of Potential Technical Measures 	 3-13
             3.3.2   Estimated Effectiveness of Institutional Controls	 3-18
       3.4    DEVELOPING MITIGATION STRATEGY ALTERNATIVES	 3-21
             3.4.1   Combinations of Mitigation Options Meeting/Exceeding Objectives .. 3-21
             3.4.2   Probable costs to Implement and Operate	 3-46

4.0    EVALUATING A PROPOSED MITIGATION STRATEGY	 4-1
       4.1    OBJECTIVE OF EVALUATION 	 4-1
       4.2    REVIEW SITE RELATED INFORMATION	 4-1
             4.2.1   Contaminant Source and  Route of Impact 	 4-2
             4.2.2   Duration of Impacts 	 4-2
             4.2.3   Comparison of Site Information to the Strategy	 4-3
       4.3    REVIEW IMPACTED STRUCTURE/AREA INFORMATION	 4-6
             4.3.1   Developed vs Undeveloped Land	 4-8
             4.3.2   Current and Potential Future Uses	 4-9
             4.3.3   Measured and Estimated  Level of Impact	 4-9

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             4.3.4   Structural Characteristics	 4-9
             4.3.5   Proposed Technical and Institutional Controls	 4-11
             4.3.6   Completion of Review	 4-11
       4.4    REVIEW PROPOSED MITIGATION STRATEGY TECHNIQUES	4-13
             4.4.1   Comparability to Strategies Used in Similar Cases	 4-13
             4.4.2   Applicable to Specific Case 	 4-15
             4.4.3   Reduction Estimates Reasonable	 4-16
             4.4.4   Cost Estimates Reasonable 	 4-16
             4.4.5   Enforceability	 4-17

5.0    EVALUATING EFFECTIVENESS OF IMPLEMENTED MITIGATION STRATEGY	5-1
       5.1    TECHNICAL EFFECTIVENESS	 5-2
             5.1.1   Direct Indoor Air Measurements	 5-2
             5.1.2   Diagnostic Testing for Effectiveness	 5-4
             5.1.3   Diagnostic System Testing with Corrective Action	 5-5
       5.2    INSTITUTIONAL CONTROLS  	 5-10

APPENDIX    CASE STUDIES	A-1
                                          in

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                                     LIST OF TABLES
Table
2.1     Factors Contributing to the Driving Force For Soil Gas Entry	2-7
2.2    Possible Soil Gas Entry Routes Into a Typical House 	2-9
2.3    Sealing of Entry Routes	 2-11
2.4    Sealant Manufactures/Suppliers	 2-12
2.5    Sealant Information 	 2-13
2.6    Drain Tile Soil Ventilation (Active)	 2-20
2.7    Sub-Slab Soil Ventilation (Active) 	 2-24
2.8    Block Wall Ventilation  (Active)	 2-26
2.9    Sub-Slab Soil Ventilation (Passive)	 2-29
3.1     Technical Control Options 	 3-16
3.2    Institutional Control Options	 3-23
3.3    Master Matrix Table	 3-27
3.4    Strategy 1 Matrix Table 	 3-31
3.5    Strategy 2 Matrix Table 	 3-34
3.6    Strategy 3 Matrix Table  	 3-37
3.7    Strategy 4 Matrix Table  	 3-42
3.8    Strategy 5 Matrix Table 	 3-45
4.1     Example Format for Comparison of Site Information	4-4
4.2    Example Review of Site Information  	4-7
4.3    Example Format for Reviewing Impacted Structure/Area Information	4-8
4.4    Example Reviewing Impacted Structure/Area Information 	 4-14
                                     LIST OF FIGURES

 Figure
 2-1     Negative Pressure Sources In a Typical House	2-6
 2-2     Major Soil Gas Entry Routes	2-8
 2-3     Theory of Operation of a Sub-slab Depressurization System	 2-16
 2-4     Drain Tile Ventilation Where Tile Drains to Sump	 2-18
 2-5     Sub-slab Suction Using Pipes Inserted Through Foundation Wall	 2-21
 2-6     Sub-slab Suction Using Pipes Inserted Down Through Slab	 2-22
 2-7     Wall Ventilation wfth Individual Pressurization Point Walls	 2-25
 2-8     Passive Sub-slab Ventilation System	 2-28
 2-9     Possible Configuration for a Fully Ducted HRV	 2-33
 2-10    New  Construction Techniques	 2-39
 2-11    Post  Construction Soil Gas Removal	 2-40
 2-12    Passive Sub-slatxVentilation System	 2-42
 2-13    Summary of Mechanical Barrier Approach  	 2-43
 2-14    Methods to Reduce the Vacuum Effect	 2-47
 3-1     Mitigation Strategy  Development  	  3-3
 3-2     Strategy 1 - Most Technical 	 3-28
 3-3     Strategy 2-- Best Technical  	 3-32
 3-4     Strategy 3 - Least Technical	 3-35
 3-5     Strategy 4 - Most ICs	 3-39
 3-6     Strategy 5 - Best fCs  	 3-44
                                             iv

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                                 SECTION  1
                               INTRODUCTION

1.1   BACKGROUND
    The Comprehensive  Environmental  Response, Compensation,  and Liability
Act of 1980 (CERCLA or "Superfund")  and its  reauthorization  in the Super-
fund Amendments and Reauthorization  Act (SARA) of  1986 established a na-
tional program for responding  to  releases of hazardous substances into the
environment.  The mandate  of the  CERCLA program  is to protect human health
and the environment from current  and potential threats posed by these
releases.

    Occupants of existing  structures proximate to  a CERCLA site may be
exposed to the released chemicals from their transport into  the indoor
environment.  The potential  also  exists for  similar exposures to occupants
of future structures proximate to the site.   Mitigation may  be needed when
investigations of the  site and proximate  areas demonstrated  that these
exposures reach levels determined unacceptable for occupants of current
structures, or are likely  to be reached for  occupants of potential new
structures.

    Many EPA Regions have  sites where such  impacts have occurred and
mitigation has been required.   Methods used  to  select the mitigation
procedure(s) for those impacts vary within  and  among Regions.  Although
information and reference  documents exist for mitigation techniques for
certain types of impacts,  most notably for  radon,  no information or
guidance document exists for developing  or  evaluating indoor air impact
mitigation strategies.

1.2    PURPOSE
    The purpose of this document is to present  and analyze approaches that
may be used to mitigate CERCLA site impacts on  the indoor air  quality of
nearby structures.  This document is based  on relevant published lit-
erature, information on specific cases made available by EPA,  and  expertise
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and experience provided by its  review committee.  The document  is designed
to provide information that may assist  in  resolution of indoor  air  quality
concerns at CERCLA sites.   The  procedures  and  methods, however, may also be
useful  in developing mitigation strategies for indoor air impacts from
other hazardous wastes and hazardous materials sources.

1.3   SCOPE
    This document assumes  that  the  need for mitigation of indoor air
impacts related to the site has been established.   Assessment procedures
are, therefore, not included.   The  reader  may  refer to the Air/Superfund
National Technical Guidance Study Series Report "Assessing potential Indoor
Air Impacts for Superfund  Sites", EPA-451/R-92-002, for assistance  in
assessing the potential impacts.

    This document focuses  primarily on  mitigation methods which may be
applied in the immediate vicinity of the impacted or  potentially  impacted
structure(s).  Reference is made to CERCLA site remediation  methods which
may also have a beneficial impact on indoor air quality,  but these  are not
discussed  in detail here.   The document includes summary  level  information
on technical methods to prevent or  reduce the intrusion of  site related
chemicals  into the  indoor environment and institutional methods to  restrict
the use of developed and undeveloped property to the  extent  necessary to
reduce risks to acceptable levels.

1.4    RELATIONSHIP TO EXISTING REGULATIONS  AND GUIDANCE
    This document  provides supplemental information to assist the reviewer
in  focusing  on mitigation  of indoor air impacts occurring at a CERCLA site
using techniques  that  involve  little or no  treatment to reduce or prevent
indoor  air exposures.   This document assumes  that  other actions designed  to
eliminate  the  contaminants  at  the  site  through  treatment or removal  may be
occurring  that  also reduce or  eliminate indoor  air impacts.

     The  RI/FS  guidance requires that,  while developing alternatives,
 screening  procedures  be used that  consider  effectiveness, implementability,
 and costs  for media-specific technologies and to assist with reducing the
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number of alternatives  prior to  detailed  evaluation.   Section  3 of this
document, which discusses  procedures  for  developing  alternative strategies
for detailed evaluation,  assists in the screening  of the alternatives
regarding effectiveness,  costs,  and reduction of the number of alterna-
tives.

    The NCR and RI/FS guidance requires that  remedy  selection  for a site be
accomplished by detailed  evaluation of alternatives  against nine criteria.
The suggested alternative strategies  development procedures in Section 3
and the review procedures of Section  4 were designed to consider these
criteria.  The review procedures of Section 4 assist in addressing specific
concerns relevant to the  criteria for the indoor air pathway.

    CERCLA and the NCP  require a periodic review of  remedial actions, at
least every five years  after initiation,  for  so long as hazardous substanc-
es, pollutants, or contaminants  that  do not allow  unrestricted use remain
at the site.  Section 5 provides procedures that may be of use in conduct
of such reviews for the indoor air mitigation efforts at a site as well as
for effectiveness reviews that may be desirable following implementation of
the mitigation.
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                          REFERENCE  FOR  SECTION  1

EPA88 Guidance for Conducting Remedial Investigations and Feasibility
      Studies under CERCLA.  EPA/540/G-89/004, OSWER Directive 9355.3-01
      October 1988.

EPA92 National Oil and Hazardous Pollution Contingency Plan (The NCP).
      Publication 9200.2-14.  NTIS PB92-963261.  January 1992.
                                      1-4

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                                SECTION  2
                          MITIGATION TECHNIQUES
     The techniques  described in this document  are provided as options  that
may assist in the development of mitigation strategies for the  indoor air
impacts at CERCLA sites.   These techniques may  be considered  as  supplement
to state-of-the-art source control  technologies,  such as soil gas extrac-
tion wells, ground water  pumping systems,  etc.

     The mitigation techniques presented are intended to address  indoor air
contaminants that migrate into  a building  from  external sources.   The
primary transport mechanisms for indoor air impacts  on proximate structures
are ambient air (to include wind driven),  soil  gas intrusion,  and ground
water migration.  Development of the mitigation strategy may  be influenced
by the transport mechanism.

     The techniques are presented  in one of two broad classes:  technical
measures; and institutional controls.  Technical  measures are mitigation
techniques that employ engineering principles to  reduce the  indoor air
impact.  Institutional controls are mitigation  techniques based on legal
principles that reduce indoor air  impacts  by restricting the  use of the
affected property.  Institutional  controls are  used  to supplement engineer-
ing controls at the site.

2.1 CONTAMINANT PATHWAYS
     Air emissions from the site,  both  gaseous  and particulate,  may be
carried by ambient air to the impacted  structure.  The rate  at which ambi-
ent air infiltrates a building  is  a function of several factors including
wind speed, indoor-outdoor temperature  differences,  height of the building,
and leaks in the building envelope.  The use of vented equipment, such  as
mechanical ventilation systems,  bathroom and kitchen fans, or oil and gas
furnaces and fireplaces also affects infiltration.  Typical  buildings ex-
                                    2-1

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change between about 0.5 and  1.0  building  volumes  of  air per hour.   "Tight"
buildings may have exchange rates as  low as 0.25 building volumes per  hour.

     Volatile pollutants in migrating soil gases,  such as from a landfill
or groundwater plume, may also enter  the ambient air  at the ground  surface
near the structure and enter  with the ambient  air.  While generally these
concentrations would be expected  to be  low, they may  be high enough to be
of concern in cases where the pollutant is highly  toxic.

     Contaminated soil  gases  can  enter  a structure through any opening in
that part of the building shell directly  above or  in  contact with the
ground.  This includes, among others, cracks  in below-grade floors  and
walls, porous structural components such  as cinder blocks, sumps, and  open-
ings where utilities such as  electrical,  water, or gas  or oil  lines enter.
Soil gases may diffuse  into the building  or be drawn  in due to reduced
pressure in the building.  Air pressures  below ambient  can develop  in  the
lower stories of a building as a  result of indoor-outdoor thermal differ-
ences, the use of vented equipment, or  it may be wind induced.   Although
these pressure differences are small, typically between  1  and  10 pascals,
they can result in the  building literally sucking in  soil  gases through
cracks and openings.

     If the water table is near the ground surface, direct intrusion of
contaminated  groundwater into  below-grade parts of the structure is possi-
ble.  Contamination  may be from  a migrating plume of contaminated ground-
water or from groundwater  contact with contaminated soil  near the struc-
ture.

     Many commercial and residential  buildings use wells  as  a  water supply.
 If these wells  intersect the  contaminated groundwater, the pollutants  may
 be volatilized  from indoor uses  of that water.  Typical residential
 activities which  may result  in volatilization  of  the pollutants are
 showering, cooking,  and clothes  washing.
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2.2  TECHNICAL MEASURES
     Much of the technical information contained  in this  Section  is  based
on techniques found to  be  applicable  to  radon  reduction in indoor air.
Although that information  was  intended only  for the mitigation of radon,
the principles  of  operation  and  the primary  entry routes  are theoretically
comparable to those for other  gases.  They are applicable, therefore, to
the development  of mitigation  strategies for the  indoor air impacts  related
to CERCLA sites.

     The following technical measures are  offered as  available options to
be considered when developing  a  mitigation strategy.   The list is not ex-
haustive.  It is likely that combinations of,  or  adaptations to,  the listed
techniques may produce  the most  benefit.  This technology is in its  infancy
and innovation and ingenuity are often required to obtain the desired re-
sults.  The technical measures discussed in  this  Section  are:

     •      Source Removal

     •      Prevention  of Soil Gas Entry

     •      Removal from Indoor  Air

     •      New Construction Techniques

2.2.1 Source Removal
     Source removal requires substantial or  complete  removal of the  source
generating the indoor air contaminant.   This technique may  involve the
removal of contaminated soil and the back fill of uncontaminated soil or
the removal of the remote source of the  contamination.  Applicability is
limited to situations in which a significant amount of the  source can be
isolated and removed.  Obviously, the cost-effectiveness  and  feasibility of
this  alternative  should be evaluated.

     Building materials may be contaminated  by settled particulate matter
or groundwater intrusion.  In some cases, removal of these  contaminants
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from the building materials,  or removal  of the contaminated building
materials that have been identified as causing elevated indoor contaminant
levels, may be indicated.  Applicability is limited to situations in which
the contaminant source has been isolated and can be effectively remediated
or removed.  The cost-effectiveness and feasibility of this alternative can
restrict its application.

2.2.2 Prevention of Soil Gas Entry
     Soil permeability is a function of the void to solid  ratio of soil.
The voids between the solids will be occupied by either liquids or gases.
Pressure and/or concentration differentials between adjacent voids cause
the liquids or gases to migrate.  This migration is a primary pathway for
contaminant transport from the source to an impacted building.

     In order for contaminated soil gas to have a deleterious effect on the
indoor air of an impacted building, the soil gas must enter the building
envelope.  The driving  forces influencing the entry of soil gas are
somewhat complex.  Examples of the driving forces  influencing soil gas
entry  are weather, building design, indoor/outdoor temperature differences,
and mechanical depressurization  (e.g., exhaust fans).  Figure 2-1 illus-
trates some of the driving forces  acting on a residential building which
may induce a negative pressure differential between the building  and the
soil.  A checklist of factors that may contribute  to the driving  force of
soil gas entry are listed  in Table 2-1.   In general, soil gas entry can  be
prevented  or controlled through:

       •     Sealing  soil gas entry routes,

       •     Ventilating the  soil  or crawl  space  beneath the  building to
            divert soil gas  away from the  building substructure,  and

       •     Adjusting the  pressure inside  the building  to  reduce or elimi-
            nate the driving force for soil  gas entry.
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2.2.2.1     Sealing  of Soil Gas  Entry Routes
     Soil  gas  may enter a building via numerous pathways or entry  routes.
Soil gas entry routes can be  categorized  by their  relative  potential  for
soil gas influx.  Major entry routes allow virtually  unrestricted  flow of
soil gas into the building.   Examples of  major entry  routes  include exposed
soil, sumps, floor drains, French drains, and uncapped hollow block walls.
Minor entry routes include slab/wall cracks and block wall  pore openings.
Although minor entry routes have a lower  potential  for soil  gas influx than
major entry routes,  they are  considered a significant pathway for  soil gas
migration into a building (EPA88).  Figure 2-2 diagrams potential  entry
routes into a building.  Table 2-2 lists  possible  soil gas  entry routes
into a residential building.   These can be used to assist with a visual
inspection to identify entry  routes.  Visual  inspection alone is not likely
to locate all entry  routes.   Some actual  examples  of  locating and  sealing
entry routes are described in the Appendix  (Case examples 3  and 5).

     In order to effectively  seal an entry route,  a gas-tight physical
barrier must be placed in the pathway between the  source and the interior
space.  Numerous sealants, caulks, and membranes are  commercially available
to seal entry routes.  When  properly  selected and  applied,  these products
effectively seal entry routes.  One-part  gun  grade or flowable urethane
caulks are most effective for cement  surfaces and  when permanent sealing  is
being considered.   Silicon caulks are not as  effective on  cement surfaces
and are easily removed.  Gas-tight sealing  of minor entry  routes and
inaccessible major entry routes  is often  impractical  or impossible.   In
some cases it is possible to  partially  seal  or  close  entry  routes.  Closure
of an entry route will restrict  gas  flow  but  not necessarily provide  a gas-
tight seal.  Periodic  inspection of  the  installed  seals will help to  ensure
the seals or closures  effectively minimize  soil gas entry.

     The complexity  of the sealing effort is dependent on the level of
mitigation required and  is  site  specific.  Some form of entry route sealing
is recommended for almost  all mitigation  techniques.   Sealing is often used
in conjunction with other  remediation techniques.   The sealing of potential
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                                   Combustion
                                   devices
Source:  EPA91A

         Figure 2-1. Negative Pressure Sources in a Typical  House
                                    2-6

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 Table 2-1.   Factors Contributing to the Driving Force for Soil  Gas Entry*
WEATHER FACTORS

Cold temperatures outdoors create a buoyant force on the
inside warm air and depressurize lower levels.
High winds contribute to depressurizing the building.
DESIGN FACTORS

Openings through the building shell above the neutral plane
contribute to exfiltration of warm air, potentially in-
creasing soil gas infiltration. Such openings can include:
spaces between windows and window frames; uncaulked gaps
between window frames and the exterior house finish; attic
soffit vents (must remain open); open dampers in chimneys
and flues; concealed openings through walls and roof (e.g.,
openings around electrical junction boxes and switch plates
in the walls, seams between strips of siding).
Openings through the floors and ceilings inside the house
can potentially increase warm air exfiltration and soil gas
infiltration. Internal airflow bypasses include: open
stairwells; utility and duct chases; laundry chutes; cavity
inside frame walls; attic access doors; recessed ceiling
lights; hollow block walls; HVAC ducts.
OCCUPANT ACTIVITIES AND APPLIANCE USE

Appliance which draw combustion air from inside and exhaust
to the outside such as: fireplaces; wood or coal stoves;
central gas or oil furnaces and fuel fired water heaters
located indoors.
Fans which exhaust indoor air outdoors such as: window or
portable fans in exhaust mode; clothes dryer exhausts;
kitchen, bath, and attic fans.
HVAC systems where the return ducts, by design or through
leaks, preferentially withdraws air from, and depressuriz-
es, the lower floors of the structure.
Open doors in the stairwells between floors.
Open doors or windows only on downwind side of building.
* - Adapted from EPA88
                                     2-7

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••*:".:•> •••••;•  •,. .   .
    A.   Cracks in concrete slabs
    B.   Spaces behind  brick veneer walls that rest on uncapped
            hollow-block foundation
    C.   Pores and cracks  in concrete blocks
    D..   Floor-wall joints
    E.   Exposed soil,  as  in a sump
    F.   Weeping (drain) tile, if drained to  open sump
    G.   Mortar joints
    H.   Loose fitting  pipe penetrations
    I.   Open tops of block walls
    J.   Openings around fireplace and chimney supports
    K.   Hater (from  some  wells)
  Source: EPA87
                   Figure 2-2.  Major Soil Gas Entry Routes
                                    2-8

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Table 2-2.   Possible Soil Gas Entry Routes  into  a Typical House
ENTRY ROUTES ASSOCIATED WITH THE FOUNDATION WALL

Holes in foundation walls around utility penetrations
through the wall (e.g., water, sewer, electrical, fuel oil)
Any other holes in the walls, such as defects in individual
blocks in hollow-block walls, drilled holes for electrical
junction boxes, chinks between fieldstones in this type wall
Any location in which the wall consists of exposed soil or
underlying rock
With hollow-block walls, unclosed voids in the top course,
unclosed voids in blocks around windows and door penetra-
tions, pores in the face of the blocks, cracks through the
blocks or along mortar joints (including hairline cracks).
Applies to exterior walls and interior walls which penetrate
the floor slab and rest on footings beneath the slab.
With poured concrete foundation walls, settling cracks in
the concrete, pressure cracks, and pouring flaws
In split-level houses with slab-on-grade or partial basement
section adjoining lower basement, joint between the lower
basement wall and the floor slab of the higher level
Any block or stone structure built into a wall, such as
fireplace or fireplace support, where a cavity can serve as
hidden conduit for soil gas entry
ENTRY ROUTES ASSOCIATED WITH CONCRETE FLOORS

Any exposed soil or rock in which concrete is absent, such
as sometimes found in fruit cellars, attached greenhouses,
and earthen floor basements
Any holes in the slab exposing soil, such as from wooden
forms or posts that have been removed or rotted
Sumps which have exposed soil at the bottom and/or drain
tiles opening into the sump (drain tiles can serve as soil
gas collectors and route it into the house via the sump
Floor drains, if untrapped or no water in trap or cleanout
plug missing, and if drain connects to the soil (e.g., con-
nects to perforated drain tiles or to septic system.
Openings through the slab around utility penetrations
Cold joints in the slab
Settling Cracks in the slab
                               2-9

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                           Table 2-2.   (Cont'd)

Wall/floor joint around the perimeter where the slab meets
the foundation wall. The crack can be 1 to 2 in. wide in
houses with French drains. Wall/floor joints for interior
walls which penetrate the slab can also be entry points.
Any hollow objects which penetrate the slab, such as:
metal load-bearing posts; hollow concrete blocks (e.g.
ving as base for furnace or water tank); hollow pipes
serving as legs for fuel oil tank)
hollow
, ser-
(e.g.,
ENTRY ROUTES ASSOCIATED WITH DECOUPLED CRAWL SPACE HOUSES

Seams and openings in the subfl coring between the crawl space
and the living area (e.g., openings around utility penetra-
tions)
If a central forced- air HVAC is situated in the crawl
leaks in the low-pressure return ducting which permits
space air to leak into the house circulating air
space,
crawl
 entry routes can be a simple quick fix  to  reduce the  infiltration  of con-
taminated soil gas or a major effort to  form  a gas-tight membrane over
exposed soil in the basement of a building.   In most cases,  in  order to
significantly reduce the infiltration of soil gas,  sealing must be  supple-
mented with another mitigation technique (EPA88).

     Foundation and/or soil  settling can cause a building's  sub-structure
to move or shift.  These dynamics often  cause sealed entry routes to reopen
over time and to introduce new entry routes.  Therefore,  periodic  inspec-
tions of the sealed openings and condition  of the  unsealed  substructure are
critical aspects of ensuring the long-term effectiveness  of  this mitigation
technique.  Table 2-3 identifies some of the  advantages and  disadvantages
of using sealing entry routes as the primary  mitigation technique.

     The application of this mitigation  strategy  is, in theory, relatively
simple.  The  first  step is to identify major and minor soil  gas entry
routes, which  can be difficult  in many cases.  Once these are  identified,
the mitigator  should compare possible alternatives and select  the most
appropriate  and  cost effective  products  to achieve the desired results.
                                     2-10

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                    Table 2-3  SEALING OF ENTRY ROUTES
ADVANTAGES DISADVANTAGES
Applicable to all buildings
Relatively simple to implement
30 to 90 percent reduction in
contaminant level possible if all
major entry routes sealed
Sealants recommended for specific
applications are readily avail-
able
Extensive surface preparation may
be required
Requires periodic inspections to
ensure airtight seals over time
Difficult to seal all entry
routes. Access to floor/wall
joints is difficult and can be
labor intensive

Detailed preparation of the substrate will  often  be  required to  form an
effective gas-tight seal.   This preparation can be time  consuming  and ex-
pensive.  The manufacturer's installation instructions should  be followed
during application of the selected product.

     After installation,  periodic inspection  of the  sealed areas should be
conducted to identify damage from physical  contact,  degradation, or water.
The inspection should include damaged seals,  seals that  may have reopened,
and new cracks that have opened due to movement and  shifting of  the sub-
structure caused by normal settling of the foundation over the life of the
building.  Identified new openings and damaged seals should be repaired.

     The cost of materials for sealing soil gas entry routes can range from
$100 to $500 depending on the extent of the sealing  effort  (EPA88).  Labor
costs could cause significant increases when extensive surface preparation
or elaborate membrane systems are required (EPA88).

     A list of manufacturers is provided in Table 2-4.   A list of  commer-
cially  available products is provided in Table 2-5.
                                    2-11

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Table 2-5.  Sealant  Information
Sealant Name
Sealant type
Manufacturer
SMALL CRACKS
Fomofill
Geocel Construction 1200
Geocel SPEC 3000
Sikatop
Silastic
Intra-Seal Kit, I-S 550
Handi-Foam, Model 1-160
Bead caulk
Caulk, silicone
Caulk, urethane
Nonshrink grout w/
binder
Caulk, silicone
Bead caulk
Bead caulk
Fomo Products
Geocel
Geocel
Sika Chemical
Wright/Dow Corning
Insta-Foam
Fomo Products
LARGE CRACKS
Versi-foam 1
Versi-foam 15
Froth Pak FP-180
Dow Corning Fire Stop Foam
Kit # 2001
Insta-Seal Kit, I-S 550
Handi-Foam, Model 1-160
Froth-Pak Kit FP-9.5
Fomofill
Geocel Construction 2000
Temco THC-900
Zonolite 3300
Polycel One
2-part urethane foams
2-part urethane foams
2-part urethane foams
2-part silicone liquid
Bead caulk
Bead caulk
2-part spray foam
Bead caulk
Caulk, silicone
Flowable urethane,
two-part
Spray foam
Expanding foam, ure-
thane
Universal Foam
Universal Foam
Insta-Foam
Insta-Foam
Insta-Foam
Fomo Products
Insta-Foam
Fomo Products
Geocel
Geocel
W.R. Grace
W.R. Grace
               2-13

-------
                            Table 2-5  (Cont'd)
Sealant Name
Sealant type
Manufacturer
PORES
Thiocol WD-6
Rock Coat 82-3
Resitron II
HydrEpoxy 300
Aerospray 70
Acryl 60
Trocal, etc.
Alkylpolsulfide copol-
ymer (0.102 cm thick)
PVC copolymer solution
2-part furan
2-part water based
epoxy
One component
Surface bonding cement
Sheeting; polymer, Al-
mylar, PVC, polyethyl-
ene
Thiokol
Hall tech
Ventron
Acme Chemical
American Cyanamid
Standard Dry Wall
Products
Dynamit Nobel Of
America, Inc.
DESIGN OPENINGS
Versi-foam 1 & 15
Froth Pak FP-180
Froth Pak Kit FP-9.5
Vel kern
Zonolite 3300
2-part urethane foam
2-part urethane foam
2-part spray foam
Flowable urethane
Spray foam
Universal Foam
Insta-Foam
Insta-Foam

W.R. Grace
Note:  Inclusion of a sealant in this  table  should  not  be  construed as an
endorsement by EPA of this sealant or  its  manufacturer.  This  table is not
represented as a complete listing of suitable  products  or  manufacturers.
This table is intended only as a partial listing of some of the  sealants
known to be commercially available.
                                    2-14

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2.2.2.2  Diverting Soil  Gas Away from  Foundation
     Active  and  passive  systems to effectively divert soil  gases  away from
a building's foundation  have been developed.  These  systems fall  into one
of three general categories: the system may mechanically introduce a nega-
tive pressure on sub-floor soil and  vent  contaminated gas away from the
foundation;  the  system may mechanically introduce  a  positive pressure on
the sub-floor soil to dilute the contaminated soil gas  before it enters the
building (not recommended); the system may afford  the soil  gas a controlled
means to vent away from  the house without active mechanical assistance.
Based on currently available information, negative pressure soil  ventila-
tion has been a  consistently effective method of mitigation for radon
reduction (EPA88).

     In the  pressurization mode, outdoor  air is forced  into the sub-floor
region to create a "pressure bubble" under the  building to force soil gases
away from the foundation.  This technique can cause  re-entry of sub-slab
contaminants into the building through unsealed entry routes.  EPA has
experienced pesticide re-entry when  using positive pressurization.

     In the  depressurization mode, a negative pressure  is mechanically
applied to the sub-floor region which  causes  soil  gases to be evacuated be-
fore they can enter the  building  (Figure  2-3).  Gas  movement through un-
sealed entry routes should  be  toward the  gas  collection system when the
system is properly operating.

     Particular  care should be used  when  installing  any of the active
depressurization systems discussed  below  due  to the  potential to cause
backdrafting of combustion  equipment.   If significant  amounts of indoor air
are drawn into the depressurization  system through unsealed entry routes,
the relative negative pressure created in the building  may draw combustion
products from fireplaces and  fired  furnaces into  the structure.  Diagnostic
testing should be performed after installation  to assess this possibility.
                                    2-15

-------
Source: EPA91A
                          Medium pressure zone
                        Low pressure zone
                         High pressure zone
  Figure 2-3.  Theory of Operation of a Sub-slab Depressurization  System
                                    2-16

-------
     Gases from  the system vents should be exhausted  above  the  building
roofline in a location  that  will minimize  the  potential  for the exhausted
gases to reenter the  building.   Generally, the gases  are exhausted directly
to the atmosphere.   In  a few cases,  control  devices,  such as activated
carbon, have been used  to capture  the  pollutants  in the  system exhaust.
These exhaust emissions may  be  included  as part of the pathway in calculat-
ing risks to determine  if controls are actually warranted.

     Passive venting  of contaminated soil  gas  may  be  accomplished in some
instances.  Soil gases  are vented  from the sub-floor  region as a result of
the buoyancy caused by  temperature and pressure differentials across the
building envelope.

     The types of soil  ventilation techniques  that have  been used include:
     •      Drain Tile  Soil  Ventilation  (Active)
     •      Sub-Slab Ventilation (Active)
     •      Block Wall  Ventilation (Active)
     •      Isolation and Ventilation  of Sources  (Active and Passive)
     •      Passive Ventilation

2.2.2.2.1  Drain Tile Soil Ventilation
     Drain tiles are  frequently used to  control water intrusion into a
building.  They are placed during  construction and can either circle the
perimeter of the building on the interior or exterior of the foundation
wall.   Interior (or sub-floor)  drain tiles can be placed either  around the
perimeter adjacent to footings  or in a pattern under the floor.  Water col-
lected  in the drain tiles is routed to a remote above-grade discharge, a
dry well, or to a sump for mechanical  pumping to an above grade  discharge.

     Drain tiles provide a convenient  in-place network that enables the
suction or pressure field to be applied over a relatively wide area.  Ac-
tive drain tile ventilation may be applied to buildings  having drain tile
loops which surround most or all of the perimeter of the foundation or
buildings with  open sumps with connected drain tiles  (Figure 2-4).   This
                                    2-17

-------
Outside
fan
(optional)
                                                       To exhaust fan
                                                       mounted in attic
                                                       or on roof
     Optional
     piping       x
     configuration  **•-•
      Sealant
                                                        Note:
                                                        1. Closure of major
                                                          slab openings is
                                                          important.
Slope horizontal
leg down
toward sump —
                            Existing exterior drain
                      '••'••:'/•'•' tile circling the house
                                                                       Sealant
                                                                          Water discharge
                                                                          pipe (to remote discharge)

                                                                          Masonry bolts
                                                                          • Sealant
                                                                          Sump
                                         Submersible
                                         pump
   Source:  EPA87
           Figure 2-4.  Drain  Tile Ventilation Where  Tile Drains to  Sump
                                               2-18

-------
technique has demonstrated  a  high degree of  success  in the mitigation of
radon.  Reductions  as  high  as 99 percent have  been  achieved (EPA88).   As-
suming an intact unclogged  drain tile network,  a  marked reduction in  soil
gas contaminant entry  may be  achieved using  this  mitigation technique.

     Ventilation of drain tile systems should  receive  first consideration
if it is in place and  soil  ventilation appears appropriate.  Because  a
considerable amount of outside air may be drawn into the suction system, in
some cases an adequate lowering of sub-slab  pressure may not be practically
achieved.  Diagnostic  testing is required to assess  the practicality  of
this technique.  However, alternative mitigation  techniques are likely to
be more cost effective than retrofitting a drain  tile system around an
existing structure.

     The design and installation costs for a drain tile ventilation system
(not including drain tile installation) for  a  single family residential
building might cost between $700 and $2,500  (EPA88).  This cost estimate is
dependent on the depth of the drain tile network, the presence of a sump,
the location of the exhaust fan, the length  of piping, and the number of
vertical connections to the drain tile required to achieve adequate venti-
lation of the sub-slab region.  Existing building finishes, performance
requirements, the level of  diagnostic testing  performed, and the specific
construction characteristics  of  the building will influence the cost.
Table 2-6 identifies  some  advantages and disadvantages of using drain tile
soil ventilation as the primary  mitigation  technique.

2.2.2.2.2  Sub-slab Ventilation  (Active)
     In the application of  this technique, either a  suction or pressure
field may be applied  to the gravel  fill  beneath a concrete slab.  The field
is mechanically induced by  installing  a  venting system with an attached
fan.  Sub-slab depressurization  (SSD)  has  been the most successful and
widely used radon reduction technique  in  slab-on-grade and basement  houses.
It has been proven capable  of achieving  very high radon reductions in
single-family residential  buildings.   Its  applicability to larger  struc-
                                    2-19

-------
tures has been tested in schools and proven  effective.   It has also been
used successfully in controlling VOC intrusions for

              Table 2-6  DRAIN TILE SOIL VENTILATION (Active)
            ADVANTAGES
DISADVANTAGES
Applies ventilation at major
entry routes. Effective on
hollow block wall construction
Provides an in-place network for
pressure field
90 percent or higher reduction in
contaminant level possible
Can be installed where tiles
drain to an internal sump
Drain tile loops difficult to ac-
cess
Requires intact, undamaged drain
tile loop for optimum performance
Major entry routes should be
sealed
Outside air flow into system can
reduce performance
Flooding may reduce performance
Energy penalty for fan use
Fan maintenance required
detached houses, townhouse clusters, and a school (see the Appendix).  As-
suming good permeability of the sub-slab region and sufficient ventilation
points to create a pressure field beneath the entire slab, it is likely
that a marked reduction in soil gas contaminant entry will be achieved
using this mitigation technique.

     In the depressurization (suction) mode, soil gases are drawn from the
sub-slab region and exhausted  via a network of pipes to the outside of the
building (Figures 2-5 and 2-6).  The  intent of the system is to create a
continuous low-pressure region beneath the entire slab sufficient to pre-
vent soil gas from entering the building.  Systems operating in suction
mode rather  than  in pressure mode have a greater  likelihood of success.
Results have been mixed with pressure systems  and there  is evidence  that
pressurization  can result  in an increase of soil  gas influx and resuspen-
 sion of contaminants  through some entry routes.
                                     2-20

-------
                                                Exhaust
Note:

1. Closing of major slab openings
  (e.g., major settling cracks, utility
  penetrations, gaps at the wall/
  floor joint) is important.
                                                                               House air
                                                                               leakage through
                                                                               wall/floor joint1
              •.'.'..•:•• '•'.- ••;. Connection to
              • .:'•-'•' V '.':•• ;•. • other suction
               •' •.  •; •-". ••/•' points
       Soured:  EPA87
        Figure 2-5. Sub-slab Suction  Using  Pipes  Inserted  Through Foundation Wall

                                                    2-21

-------
               Exhaust
 Outside
 fan
 (optional)

Optional
piping
configuration
To exhaust fan
mounted in attic
or on roof
Slope horizontal leg
down toward sub-slab
hole
                                                                        Connection to other
                                                                        .suction point(s)
                                                         Note:
                                                         1. Closing of major slab openings
                                                           (e.g., major settling cracks, utility
                                                           penetrations, gaps at the wall/
                                                           floor joint)  is important.
                                                                   House air through unclosed
                                                                   settling cracks, cold joints,
                                                                   utility openings1
                                                                Open hole '••
                                                                (as large as.
                                                                reasonably
                                                                practical)
 Source:  EPA87
     Figure  2-6.   Sub-slab Suction Using  Pipes  Inserted  Down Through  Slab
                                              2-22

-------
     Typical  systems  installed use  3  to  6  inch diameter  PVC  pipes (size
depends on length of pipe run, number of bends,  etc.)  for gas collection
and venting.   Exhaust fans are generally sized to  produce about 0.5 to 1
inch water column vacuum at the point the  suction  pipe enters the floor
slab.  In-line 250 cubic feet per minute fans are  frequently used.  Howev-
er, the actual fan selected for a given  installation will depend on the
sub-slab permeability,  the air leakage into the  system,  the  piping pressure
losses, among other considerations.

     This mitigation  technique may  be applied to any building or any area
of a building that has  an impermeable floor slab.   However,  the permeabili-
ty of the sub-slab region is a significant factor  in the effectiveness of
this mitigation technique.  Good permeability will  permit the ventilation
effects of a limited number of suction points to extend effectively under
the entire slab.  Slabs having limited permeability under all or part of
the sub-slab region will require a  greater number  of ventilation points.

     A variation of SSD is referred to as  sub-membrane depressurization
(SMD).  SMD has been successful in  reducing radon  levels in  a number of
houses constructed over crawl spaces.  A polyethylene  or rubber membrane is
laid over the soil 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.

     The design and installation costs for a sub-slab  ventilation system
for a single-family residential building might cost between  $900 and $2,500
(EPA88).  This cost estimate is influenced by the  presence of a permeable
sub-slab region, the location of the  exhaust fan,  the  length of piping, and
the number of vertical  ventilation  points  required to  achieve adequate
ventilation of the sub-slab region.  Existing interior finishes, perfor-
mance requirements, the level of diagnostic testing performed, and the
specific construction characteristics of the building  will influence the
cost of design and installation. Table  2-7 list some  advantages and disad-
vantages of this technique.
                                    2-23

-------
               Table 2-7   SUB-SLAB SOIL VENTILATION (Active)
ADVANTAGES
Can be applied to any building
with a concrete floor slab under
all or part of the building
Extensive installation perfor-
mance documentation available
90 percent or higher reduction in
contaminant level
Sub-slab region likely to consist
of gravel layer

DISADVANTAGES
Soil permeability unknown prior to
diagnostic testing
Low permeability sub-slab regions
require numerous ventilation
points
Exhaust of high concentration of
contaminated air when in suction
mode
Major entry routes should be
sealed
Energy penalty related to fan op-
eration and exhaust of room air
through unsealed entry routes
Fan maintenance required
2.2.2.2.3  Block Wall Ventilation (Active)
     Hollow block walls have been identified  as  potential major  soil  gas
entry routes.  The voids within hollow block walls can serve as  a conduit
for soil gas to enter a building through mortar joints,  pores,  and other
wall penetrations (Figure 2-7).  Mitigators have used hollow block walls as
an in-place network  to apply a negative pressure to remove  soil  gas from
the void or apply a  positive pressure to keep soil gas from entering the
void.

     Block wall ventilation may only be applied to buildings with hollow
block walls.   Buildings where satisfactory mitigation is not achieved with
a sub-slab suction system may have supplemental ventilation points in-
stalled  in the wall  cavity.  This mitigation technique when used  in con-
junction with  other  mitigation techniques can be very effective.

     The design and  installation costs for a block wall  ventilation system
for  a  single  family  residential  building might  cost  between $300  and  $2,500
                                     2-24

-------
            Protective
            grille
                                                                 6 in. dia.
                                                                 collection pipe
                                                                           To connections
                                                                           into other walls
                     • Outdoor alrajfj'TrVjO          R
                    • pressurizing•;";-•; '•''•.'    /N/
                    • void network'-:-'

                   Concrete block
                                                                    Notes:
                                                                    1. Closing the veneer gap may
                                                                      be Important in some cases.
                                                                    2. Top voids must be closed as
                                                                      effectively as possible to
                                                                      avoid excessive leakage of
                                                                      outdoor air out of the void
                                                                      network.
                                                                    3. Closing major slab openings
                                                                      is important.
-Close major mortar cracks and holes in wall
 Outdoor air through block pores.
 unclosed cracks, and holes
                                                                 Utility pipe

                                                             Sealant
                                                       Outdoor air1
                     '••  :"'• • '-'•'•'.•••.•':'•'•'•',' '•' •: .''••:.:!' : :'".•'•'.•"••• . Soil gas":";.'-: •.';-.•;..-..-" '•.'. .'•_' /•:-/.••;; "•/• -
Source:    EPA87
  Figure  2-7.    Wall  Ventilation  with  Individual  Pressurization  Point
                                                     2-25

-------
(EPA88).  This cost estimate is  dependent  on the  accessibility of major
entry routes requiring closure,  the  location of the exhaust  fan,  the length
of piping, and the number of ventilation points required  to  achieve ade-
quate ventilation of the wall  cavity.   Existing interior  finishes, perfor-
mance requirements, the level  of diagnostic testing performed, and the
specific construction characteristics  of the building will  influence the
cost of design and installation.  Some of  the  advantages  and disadvantages
of block wall ventilation are given  in Table 2-8.

                 Table 2-8 BLOCK WALL  VENTILATION (Active)
ADVANTAGES
Can be applied to any building
with hollow concrete block walls
Wall cavity provides an in-place
network to apply ventilation over
a wide area

DISADVANTAGES
May require numerous ventilation
points
Energy penalty related to fan op-
eration and exhaust of room air
through unsealed entry routes
Exhaust of high concentration of
contaminated air when in suction
mode
Major entry routes should be
sealed
Percent reduction in contaminant
level difficult to estimate
Fan maintenance required
2.2.2.2.4   Isolation and Active Ventilation of Areas Sources
     Where a large soil gas entry route (or a collection of entry routes)
exists,  it  may be economical to cover (or enclose) the large route, and  to
ventilate the enclosure with a fan.  Thus, the source of the soil gas  is
isolated, and the soil gas can not enter the living space.  Examples of
such  an  isolation/ventilation approach would be:

      •       Covering an earth-floored crawl space or basement with  an  air-
             tight plastic  sheet  ("liner"), and actively ventilating the
             space between  the liner and the soil  (for example,  using a
             network of perforated  piping under the liner).

                                    2-26

-------
     •       Building  an  airtight  false wall  over  an existing  foundation
            wall  which  is  a  soil  gas  source,  and  ventilating  the  space
            between the  false wall  and the  foundation wall.
     •       Building  an  airtight  false floor over a cracked concrete slab,
            and ventilating  the space between the false  floor and the slab.

     This mitigation  technique is best applied to  crawl  spaces with  soil  or
gravel  floors for which  it is infeasible or uneconomical  to use  natural or
forced air ventilation.  This mitigation technique has been applied in
conjunction with other  mitigation techniques and  has been fairly success-
ful.  No data are available  on the  effectiveness  of this technique as the
sole form of mitigation.

2.2.2.2.5  Passive Soil  Ventilation
     Theoretically, any  of the fan-assisted ("active") soil ventilation
approaches described  in the  previous  sections could be attempted without
the aid of a fan (that  is, "passively").  With passive systems,  natural
phenomena are relied  upon  to develop  the suction  needed  to draw the soil
gas away from the entry routes  into the  building. Passive systems require
the use of a vertical stack, connected  to the ventilation piping network,
that rises through the  building  and penetrates the roof  (Figure 2-8).  A
natural suction is created in the stack by two phenomena:  1) the movement
of wind across the top  of  a  properly positioned vertical stack can create a
negative pressure  in  the stack;  2)  the  buoyancy created  when  the stack
(indoors) is warmer than outdoor air causing the  stack to act as a pathway
for soil gas to raise.   Depending on the outdoor  temperature  and wind cur-
rents, the pressure differential  created in the stack  (but not under the
slab which can be  considerably  less)  of a passive system is typically on
the order of several  hundredths  of an inch of water,  considerably less than
that developed by  fan-assisted  systems.

     Passive soil ventilation may be  best applied to buildings with
slightly elevated  levels of contaminants in the indoor air that  have
entered with soil  gas.   If properly designed, the system may be  retrofitted
with a fan,  if required, for warm weather operation.   Sub-slab permeability
                                     2-27

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                                      2-28

-------
is a significant factor in  the success of  passive ventilation.   If the
permeability is good enough to allow soil  gas ventilation  with  the slight
suction created passively,  the system has  a much better  opportunity for
success.  Advantages and disadvantages are summarized  in Table  2.9.

2.2.3 Removal from Indoor Air
     Once a contaminant has been introduced into the indoor  air of a buil-
ding, the control  options are limited to dilution to control  the indoor
concentrations or removal by mechanical air cleaners.

               Table 2-9  SUB-SLAB SOIL VENTILATION (Passive)
ADVANTAGES
Can be applied to any building
with a concrete floor slab under
all or part of the building
Fan maintenance is not required
70 to 90 percent reduction in
contaminant level possible in
some cases
Sub-slab region likely to consist
of gravel layer
DISADVANTAGES
Soil permeability unknown prior to
diagnostic testing
Low permeability sub-slab regions
require numerous ventilation
points
Likely not to work in warm weather
without fan assist
Major entry routes should be
sealed
2.2.3.1  Ventilation/Dilution
     Contaminants infiltrating the  sub-structure  and  entering a building
can be controlled by diluting the indoor concentrations with uncontaminated
outdoor air.  The objective of this mitigation technique is to increase the
building's air exchange rate.  Typical  air exchange rates in U.S. homes are
approximately 0.5 to 1.0 air changes per hour (ACH).   The air exchange rate
is a function of mechanical air exchange,  and infiltration/exfiltration
rates.  Infiltration/exfiltration rates are influenced by weather condi-
tions and air tightness of the building.  Air exchange in residential
construction is typically achieved by local exhaust ventilation, and air
exfiltration/infiltration.  In other types of construction, mechanical
ventilation systems may draw or force outdoor air into the building.
                                    2-29

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     The stack effect  phenomena  accounts for much of the passive air ex-
change in residential  buildings.  The upward buoyant force  of warm air
creates, relative to outdoors,  a positive  pressure  region  in  the  upper
portions of the house and a negative pressure  region in  the lower  portions
of the house.  Between these pressure regions  lies  a neutral  plane at  which
no detectable pressure differential  exists.  As  indoor air  rises,  it  leaks
out  (exfiltrates) through penetrations in  the  building envelope on the
upper levels of the building (above the neutral  plane).  To compensate for
the exfiltration, outdoor air and soil gases leak into the  lower levels of
the building  (below the neutral  plane).  Only  about 1 to 5  percent of the
outdoor infiltration air is composed of soil gases  (EPA88).

     House ventilation can be used as a mitigative  technique  by following
one  or more of the following techniques:

      •      Increase ventilation using natural ventilation
      •     Mechanically induce air movement and air exchange without
             energy recovery
      •      Mechanically induce air movement and air exchange with energy
             recovery

2.2.3.1.1   Increase Ventilation using  Natural  Ventilation
     This method is based on keeping windows and doors  open to the maximum
extent  practical.   It  can generally  be used in any building with  operable
windows and doors.  The  principle governing this technique is  that contami-
nated  indoor air is diluted  with  uncontaminated outdoor air.   This tech-
nique will  obviously  only be effective if outdoor contaminant  concentra-
tions  are  below  acceptable  levels.   Ninety percent reductions  have been
observed in the  mitigation  of indoor radon using this method.

     Due to the  obvious  problems with  this method (e.g., security, heating
 and cooling costs),  it is  unlikely  to be  used as part of any strategy for
 mitigating the impacts addressed  in this  document.
                                     2-30

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2.2.3.1.2  Mechanical Outdoor Air Introduction without Energy Recovery
     The mechanical  introduction  of outdoor  air can act  to  dilute indoor
contaminant concentrations and pressurize the building to reduce the influx
of soil gas through entry routes.  Most existing residential  buildings are
not designed with the capacity to introduce  outdoor air into  the building.
It is possible to reconfigure an  existing HVAC system to introduce outdoor
air.  Alterations to an existing  HVAC system should only be made by quali-
fied HVAC contractors.  Outdoor air may also be introduced through a sepa-
rate system, such as a window mounted fan or a ducted outdoor air fan.  The
fan should discharge into the building below the neutral plane.  Fans must
not be operated in the exhaust mode as this  depressurizes the building and
can increase soil gas intrusion.

     Several important considerations should be addressed prior to select-
ing mechanical outdoor air introduction with an existing HVAC system:

       1.    The existing fan and motor must  be sized  correctly to provide a
            sufficient volume of outdoor air to dilute indoor contaminants
            to a satisfactory level.  The addition of a second fan, a two
            speed fan, or a variable speed fan may be necessary  to attain
            the desired results.
       2.    The heating and cooling capacities of the system must be sized
            correctly to handle the increased heating, cooling,  and mois-
            ture loads caused by the introduction of outdoor air.  Humidi-
            fication may be required in some locations.
       3.    Increased filtration may be required to ensure dust, pollen,
            microbes, etc. are removed from the outdoor air being intro-
            duced into the system.
       4.    An energy analysis is  recommended to determine the energy
            penalty  associated with the introduction of outdoor  air.

2.2.3.1.3   Mechanical Air Exchange with Energy Recovery
     By using an energy recovery device to pre-condition the outdoor air,
the  energy  penalty for mechanical  outdoor air  introduction will  be  reduced.
Energy recovery devices, heat recovery ventilators (HRVs), or  air-to-air
                                     2-31

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heat exchangers,  are devices which  use  fans  to  accomplish a controlled
degree of forced-air ventilation, while recovering some of the energy from
the exhaust air stream (Figure 2-9).  HRVs typically include two fans, one
blowing a controlled amount of outdoor  air into the building, and a second
blowing an equal  amount of indoor air to the outside.  The incoming and
outgoing air streams pass near each other in the core of the exchanger.  In
cold weather, the warmer indoor air being exhausted heats the incoming air.
In hot weather, the cooler indoor air cools  the incoming air.  Thus, some
of the energy used to condition indoor  air is recovered.  Several types of
HRVs are commercially available.  Three basic types of HRVs are presently
available:  1) fixed-plate; 2) rotary wheel; and 3) heat transfer fluid
pipes.

     HRVs have been installed for radon mitigation.  Their effectiveness as
a control device is questionable.  Success has been achieved in single-
family homes only when installed to treat basements.  A 50 to 75 percent
reduction in radon concentrations has been reported  (EPA88).  Whole-house
residential HRV treatment is not usually recommended unless the house  is
extremely tight (i.e., hourly air exchange rates of 0.25 or less) because
of the limited air handling capacity of appropriate units.  The principle
reduction mechanism acting when using HRVs is dilution.  As previously
discussed, two reduction mechanisms are acting when mechanical outdoor  air
introduction  is implemented.  First, the driving  force  drawing soil  gas
into  the  building  is reduced by facilitating the  introduction of outdoor
air below the  neutral  plane to  compensate for exfiltration  above the
neutral  plane.  Second,  soil gases that do enter  the building are  diluted
by  the  increased  influx  of  outdoor air.  By  comparison,  the advantages of
the first mechanism  are  virtually  lost when  using  HRVs.   HRVs typically
provide  no net supply  of outdoor air below  the  neutral  plane to  compensate
 for the  exfiltration  above  the  neutral  plane.
                                     2-32

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     As with  other  outdoor  air  introduction techniques, several important
factors  should be addressed when  considering  the  installation  of  an  HRV:

     •       The heating and cooling  capacities  of the  existing HVAC  system
            may be unable to condition  the  increased volume of outdoor air.
     •       Increased levels of dust, pollen, microbes, etc. are  likely due
            to the increased volume  of  outdoor  air.
     •       Depending on the climate, an  energy penalty may be realized due
            to the introduction of increased  volumes of outdoor air.

     The  relative impact of each  will be  reduced  by a  factor determined by
the efficiency of the HRV selected.

     The  design and installation  of  an  HRV  might  cost  between  $1,000 and
$3,000.   The installed cost is a  function of the efficiency of the HRV and
the operating air flow volume.  Factors influencing  the cost of design and
installation are the accessibility of major entry routes  requiring closure,
and the retrofit of existing HVAC components.  Existing building  finishes,
performance requirements, the level  of  diagnostic testing performed, and
the  specific construction characteristics of the building will influence
the cost of design and installation.

     Depending on the local climate, the  HRV efficiency,  and the  volume of
air  exchanged by the HRV, a significant energy penalty can be  experienced.
Therefore, an operating  cost for the operation of the HRV fan  and increased
energy costs for heating and cooling should be estimated  and  included  in
the  mitigation plan.

2.2.3.2  Indoor Air  Cleaning  (EPA90)
     Air cleaners are devices that attempt to remove particulate  or gaseous
pollutants  from  the  indoor  air.  Typically, residential  furnace  filters  are
installed  in  prepackaged blower  units  and  are  the simplest form  of  air
filtration  to  remove particles.  This  basic  filtration system may be
upgraded by  installing more efficient  filters  that trap smaller  pollutants
or by adding additional  air cleaning devices such as  portable air cleaners.
                                     2-34

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Air cleaners generally rely on filtration  or  ionization  to  remove particles
from the air.  The use of air cleaning to  remove  pollutants from the air in
residential applications is in its infancy.

     There are three  general  types of air  cleaners to remove particles
presently available in the market:  mechanical  filters;  electronic air
cleaners; and ion generators.  Mechanical  filters may  be installed in
buildings with central heating and or air  conditioning  or may  be used in
portable devices.

     There are two major types of mechanical  air  filters:   flat  or panel
filters, and pleated or extended surface filters.  Flat  or  panel filters
consist of either a low packing density of course glass  fibers,  animal
hair, vegetable fibers or synthetic fibers which  are often  tactified to
increase the holding capability and adhere to particulate materials.  Flat
filters may efficiently collect large particles,  but remove only a small
percentage of respirable sized particulate (RSP).  Flat  filters may also be
made of "electret" media, consisting of a  permanently-charged  plastic film
or fiber.  Particles in the air are attracted to  the charged material.

     Pleated or extended surface filters generally  attain greater effi-
ciency for capture of RSP than flat filters.   Their greater surface area
allows the use of smaller fibers and an  increase  in packing density of the
filter without a large drop in air flow.

     Electronic air cleaners use an electric  field  to  trap  particles.  Like
mechanical filters, they may be installed  in buildings with central HVAC
systems or may be portable units with fans.  Electronic air cleaners are
usually electrostatic precipitators or  charged-media filters.    In elec-
trostatic precipitators, particles are  collected on a series of  flat
plates.   In  charged-media filter devices,  which are less common, the parti-
cles are collected on the fibers of a filter.  In most electrostatic pre-
cipitators and some charged-media filters, the particles are deliberately
ionized  (charged) before the collection  process,  resulting in a  higher
collection efficiency.   Ion generators  also use static charges  to remove
                                    2-35

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particles from the  air.   These  devices come in portable  units  only.   They
act by charging particles in  a  room,  so they are  attracted  to  walls,
floors, tabletops,  draperies, occupants, etc.  In some cases,  these  devices
contain a collector to attract  charged particles  back to the unit.   Note
that the latter two types of  devices  may produce  ozone,  either as  a  by-
product of use or intentionally.   Because  ozone  is a lung irritant,  consid-
eration must be given to the  potential risks of  replacing one  type of pol-
lutant with another.

     Some newer systems  on the  market, referred to as hybrid devices,
contain two or more of the particle removal devices discussed  above.  For
example, one or more types of mechanical filters  may be  combined with an
electrostatic precipitator or an  ion  generator.

     The performance of air cleaners  in removing  particles  from indoor air
depends not only on the air flow rate through  the cleaner and  the efficien-
cy of  its particles capture mechanism, but also  on factors such as:   the
mass of the particles entering  the device, the characteristics of the par-
ticles  (e.g., their size), the  degradation rate  of the efficiency of the
capture mechanism caused by loading,  filter by-pass, and ventilation effec-
tiveness.

     There are at least three standard methods by which  particle removal
efficiency can be assessed:  American Society of Heating, Refrigerating,
and Air-Conditioning Engineers (ASHRAE)  Standard 52-76 weight arrestance
test,  ASHRAE  Standard 52-76 atmospheric dust spot test,   and the dioctyl-
phthlate  (OOP) method in military standard 282.   The weight arrestance  test
is  only used  to evaluate  low efficiency filters designed to remove the
largest and heaviest particles.   It  is of limited value  in assessing  the
removal  of respirable particles.  The dust spot  test is  used  to rate  medium
efficiency filters which  can remove  some  respirable  sized  particles.   The
efficiency rating  is determined  using a complex  mixture  of dusts  and  is not
a size specific  rating.   For example, EPA tests  (EPA90)  of a  filter with  an
ASHRAE rating of 95  percent  found  only 50 to 60  percent  of particles  in the
0.1 to 1 urn size range.   Military  standard 282 is used  only for high
                                     2-36

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efficiency  (i.e.,  rating above  about 98  percent)  filters.   The  test
measures the percentage removal  of 0.3 nm particles  of OOP.

     Removal  of gaseous pollutants requires the use  of a  sorbent material.
As mentioned earlier,  removal  of gaseous  pollutants  has been applied in
industrial and manufacturing processes, but the effectiveness for  removal
of organic compounds in residential  or commercial  settings  is not  well-
documented.  In general, capacities  of current sorbent systems are too low
to be of practical  use in mitigating indoor air impacts addressed  in this
document.

     The most frequently used  process for removing such contaminants from
indoor air is sorption by solid  sorbents. The effectiveness is  dependent
upon:
     •      air flow rate through the sorbent material,
     •      concentration of the pollutants  in the air stream,
     •      presence of other gases  or vapors (e.g., water  vapor),
     •      physical and chemical characteristics  of both the pollutants
            and the sorbent,
     •      configuration of the sorbent  in  the device, and
     •      the quantity of sorbent  used  as well  as  the bed depth.

     Because the rate  of pollutant capture by sorbents (i.e., efficiency)
decreases with the amount of pollutants  captured,  air cleaners for gaseous
pollutants are generally rated in terms  of the  sorption capacity  (i.e.,  the
total amount of the chemical that can be  captured) and penetration time
(i.e., the amount of time before capacity is  reached).  Sorbents  can be
engineered to remove specific gaseous pollutants  such as formaldehyde  or
classes  of compounds such as volatile organic chemicals  (VOCs).

     Activated carbon  has been used  to reduce indoor concentrations of low
molecular weight gases  and odors to imperceptible levels.  Research ad-
dressing  ability to remove high concentration of pollutants,  useful life,
holding  capacity over  time, and ability to adapt  to variations in type and
concentration of indoor pollutants is in progress.
                                    2-37

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     Special  sorbents  have been developed to remove specific gaseous  pol-
lutants such as formaldehyde.  Many of these are "chemi-sorbents",  impreg-
nated with chemically  activated materials,  such  as potassium permanganate
or copper oxide,  which will  react with one  or  a  limited  number of different
reactive gaseous  pollutants.

2.2.4 Techniques  for New Construction  (EPA91A)
     New buildings,  developed on sites in which  there  is  a  potential  for
indoor air impacts from nearby CERCLA  sites, may be designed using con-
struction and mitigation techniques that will  help control  indoor air con-
taminant concentrations (Figure 2-10).  As  with  existing buildings, control
may be accomplished by preventing  its  entry into the building, or by reduc-
           j
ing the indoor concentration of the contaminant  once it is present in the
indoor air.  The principles  and theories applied to existing buildings, in
particular soil ventilation  systems, mechanical  barriers, and modified
mechanical system operation  are also applicable  to new construction.  In
fact, their design and application during  construction may involve less
labor and financial investment.

     Although these techniques have been discussed for the development of
radon-resistant housing, they have not been fully demonstrated and tested.
These techniques are discussed  because they have a sound technical and
theoretical basis and potential  for  success.   The soil ventilation tech-
niques have been applied and have proven  to be applicable for diverting
contaminated soil gas.

2.2.5.1     Soil Ventilation Systems
     Soil ventilation  systems may be used  when the contaminant pathway is
pressure-driven soil gas.  Installation costs for sub-slab depressurization
systems  in  existing houses typically range from $900 to  $2,500.  A roughed-
in  system that would  allow for future installation, as necessary,  would
cost much less.   Figure 2-11 illustrates how a  final  installation  might
appear  so that consideration can be given during  construction  to  locating
vent pipes,  etc.  such  that interior finishes do not have to be removed  for
future  installation.   The figure is a composite of several  construction
                                    2-38

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 SEAL ALL JOINTS
ON PRESSURE SIDE
    OF FANS
                                                            SEAL ALL- JOINTS
                                                          ON PRESSURE SIDE
                                                                   OF FANS
                              PREFERRED
                              FAN LOCATIONS
                          INTERIOR
                          VENT
                          ROUTINO
       SOLID
      BLOCK
     COURSE
                                  SEAL AROUND ALL
                                  PENETRATIONS OF
                                    SUMP COVER
                                       CAP DURING
                                     CONSTRUCTION
                         SUMP  DISCHARGE
                                           CAULK UNDER
                                           SUMP COVER  SUB-SLAB
                                                           VENT
                                                       STANDPIPEV
   EXTERIOR
  DRAIN PIPE
     LOOP
    INTERIOR
   DRAIN PIPE
       LOOP
    (USE WITH
FRENCH DRAIN)
                                     SUMP CASINO

  Source:    EPA87

             Figure 2-11.   Post  Construction  Soil  Gas  Removal
                                          2-40

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techniques not likely to all  be found  at  a  specific  building.   A  properly
roughed-in system would involve a  good layer  of  aggregate  beneath the floor
slab and a capped PVC pipe at a central ventilation  point.  A  network of
perforated drain tiles beneath the slab and tied to  the  ventilation point
has also been used (Figure 2-12).   If  a good  layer of  aggregate is in-
stalled, it is not necessary to install such  a network.

     Passive sub-slab ventilation  systems may be  installed by  the developer
which allow for the future installation of  an in-line  fan.   If elevated
contaminant levels occur when the  system  is operating  passively,  a fan
could easily be mounted on the existing passive  vent stack for little more
that the cost of the fan.  Again,  the  developer  should ensure  a good layer
of permeable aggregate is placed beneath  the  floor slab.

2.2.5.2     Mechanical Barriers
     Theoretically, a gas-tight barrier may be placed  between  the soil  and
the building foundation to eliminate the  possibility of  soil gas  intrusion.
(Figure 2-13).  The types of mechanical barriers that  have been tried or
suggested may be categorized as follows:

      •     Foundation Materials
      •     Coatings
      •     Membranes
      •     "Site" Barriers

     Foundation materials may form a mechanical  barrier.   New  construction
typically incorporates cast-in-place concrete in the foundation.   The en-
tire foundation or merely the footings and  floor slab  are  usually cast-in-
place.  Concrete masonry walls and their  mortar joints can provide minor
entry routes for soil gases.  Solid or filled blocks should  be placed as
the bottom  and top course of a concrete masonry wall.   Dampproofing or
waterproofing treatments inhibit soil  gas migration  and  are  typically re-
quired  by building codes.  If conventional  foundation  construction tech-
niques  are  used, the  constructor should ensure that  possible entry routes
are treated with a sealant after construction is completed.
                                    2-41

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                   Bond beam or
                   solid cap block
                      Reinforce walls and slabs
                      to reduce cracking
                — Coat interior wall
                             Dampproofing  or
                             waterproofing
                     Exterior parge coat
                     and dampproofing
                                         Membrane beneath
                                         slab
                           Gravel drainage
                           layer
                                                  Seal around pipe
                                                  penetrations
                                                  and at joints
Interior and/or
exterior footing
drain
Source:   EPA91A
          Figure 2-13.  Summary of Mechanical  Barrier Approach
                                       2-43

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     Membranes of plastics  and  rubbers that are  used to  control  liquid
water penetration and water vapor diffusion can  be effective gas-tight
barriers.  If they are adequately sealed at the  joints and penetrations and
undamaged during installation,  they could provide an effective soil gas
barrier.  The 4 to 6 mil plastic film presently  being  used during founda-
tion construction as a vapor barrier has been proven to be insufficient to
stop the influx of radon gas (EPA91A).   More  comprehensive installation
measures and more durable vapor barriers may  be  required to control strong
sources or high soil gas flow rates.  Several types of membranes are com-
mercially available:

      •     Polyethylene Films
      •     Foil faced, High Strength Bubble  Pack
      •     Aluminum Foil over Glass Scrim Webbing
      •     PVC Membranes
      •     Ethylene Propylenediene Monomers  (EPDM)

     Polyethylene films have been used as a vapor barrier to prevent mois-
ture entry from beneath the slab for several  decades.   Although these
barriers offer a gas-tight seal when intact,  it  is virtually  impossible to
install  them  without puncturing or  tearing them.  Another issue is the sta-
bility  of the polyethylene vapor barrier.  Ultraviolet  (UV) exposure  is
known to deteriorate polyethylene.  Although their exposure to UV may be
short lived during  construction, the materials deterioration  over  time is
not well known.

     On the other hand, no evidence exists that  polyethylene  deteriorates
with exposure to  soil  chemicals.  High-density  polyethylenes  are used for
storage and transport  of numerous chemicals.  Polyethylene  is chemically
stable,  but may  be  adversely  affected by aliphatic hydrocarbons  (such as
butane,  hexane,  and octane)  and chlorinated  solvents.   Polyethylene-based
membranes  have been used at  hazardous waste  landfills,  lagoons,  and  similar
applications  to  control  subsurface  migration.
                                     2-44

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     Foil faced, High Strength Bubble Pack has a high compression strength
and doubles  as  an  insulator.  This material  is  somewhat  fragile  and  is
susceptible  to  puncture.  Therefore,  its  ability to  endure  the construction
and installation process make its applicability questionable.

     A product  using aluminum foil facing on two sides with an asphalt
coating over a  glass scrim webbing has potential but has not  been tested
for its resistance capability.  The  product  will likely  perform  similarly
to other foil faced products.   It also is susceptible to puncture during
installation.

     PVC and EPDM  membranes are very  durable and have been  used  for  miti-
gation of radon in existing houses.   Both were originally developed  as
roofing membranes  and  can provide air-tight  seals,  if properly  installed.

2.2.5.3     MECHANICAL SYSTEM DESIGN
     Potential  indoor  air impacts should  be  addressed in the  HVAC system
design and operation.   The HVAC system should  be designed to:

     •      help control  soil gas influx,
     •      allow controlled volumes of  outdoor dilution air  to  enter the
            building,  and
     •      maintain  an acceptable  indoor temperature and relative  humidity
            range to  the building.

     Controlling  soil  gas influx by  mechanical  means may be accomplished by
establishing a  positive pressure on  the  lower (at  and below grade)  levels
of the building.   This is  achieved  by simply introducing a  larger volume of
air  into the space than is  exhausted from the space.  That  is,  the total
cubic feet of air supplied  to  the  space  shoulrf be  greater than  the total
cubic feet of air exhausted  from the space.

     Other ventilation system features may be  incorporated  to reduce indoor
contaminant concentrations,  reduce  soil  gas entry, or otherwise increase
the  acceptability of the system.  For example heat recovery ventilators
                                     2-45

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(HRVs) may be incorporated  to  reduce  the  energy penalty associated with
increasing air exchange  rates  and  combustion  appliances should use outdoor
air for combustion.   Figure 2-14 illustrates  ventilation system design
aspects that may help achieve  the  desired results.

2.3  INSTITUTIONAL CONTROLS
     In some cases technical controls may have  to be  supplemented  by
institutional controls (ICs) to  limit exposure.  ICs  differ from technical
controls in that ICs are restrictions on  the  use of property.  ICs may be
used to broadly require  or  prevent certain activities at or near a site or
they may be a narrow, specific restriction such as  restricting use of
contaminated groundwater.

     The material  in this Section  is  intended to provide the reader with a
general overview of the  types  of ICs.  It is  not intended as legal guidance
and should not be construed as such.   For legal advise, the reader should
consult counsel.  For legal guidance, the reader may also consult the
memorandum from D. F. Coursen  to H. F.  Corcoran (see Reference EPA92B).
Portions of that memorandum are restated  here for the reader's benefit.

     There are two fundamentally distinct types of  ICs, which might be
     characterized as governmental  and  proprietary  controls.  Govern-
     mental controls involve a state  or local government using its
     police powers to impose restrictions on  citizens or sites under
     its jurisdiction.  Proprietary controls  involve property owners
     using their rights  as  owners  to  control  the use of, or access to,
     their property.  The two  types of ICs must be  discussed separate-
     ly, since they  differ  significantly  in regard  to scope, reliabil-
     ity, and appropriate mechanisms  for  implementation. (EPA92B)
                                     2-46

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                               SEAL AROUND
                            ATTIC ACCESS STAIRS
                         SEAL SPACES AROUND
                         FLUES AND
                         CHIMNET8
                                                                    AVOID RECESSED
                                                                    CEIUNQ LIGHTS IN
                                                                    UPPER FLOORS
EXTERNAL AIR
 SUPPLY  FOR
  FIREPLACE
                                    SEAL AROUND
                                   DUCT AND FLUE
                                   CHASE OPENINGS
                                  BETWEEN  FLOORS
 SEAL OPENINGS
AROUND PLUMDIHO
 PENETRATIONS
                                       SEAL AROUND
                                   DUCT PENETRATION
                                  BETWEEN BASEMENT
                                   AND CRAWL SPACE
                                                                              VENTS TO
                                                                             MEET CODE
                                                                          REQUIREMENTS
                                        SEAL AROUND
                                        ACCESS DOOR—
                                     TO CRAWL SPACE
                           TIGHT
                           FITTING
                           WINDOWS
                         »-ANO WEATHER
                           STRIPPING
                           TO REDUCE
                           VENTURI
                           EFFECT
         Source:  EPA87
                      Figure 2-14.   Methods  to  Reduce  the  Vacuum  Effect
                                                      2-47

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    The National Contingency Plan (NCR) sets out EPA's expectation
    that  ICs "shall not substitute for active response measures ...
    [that actually reduce, minimize, or eliminate contamination] as
    the sole remedy unless such measures are determined not to be
    practicable, based on the balancing of trade-offs among alterna-
    tives that  is conducted during the selection of remedy."  [40 CFR
    § 300.430(a)(l)(iii)(D)].  Nevertheless, where active remediation
    is not practicable, ICs may be "the only means available to
    provide for the protection of human health."  [55 Federal Regis-
    ter at 8666, 8706  (March 8, 1990)].  However, where controls are
    the sole remedy "special precautions must be made to ensure that
    the controls are reliable."  [55 Federal Register at 8706].
    Controls may also  be  "a necessary supplement where waste is left
    in place as it is  in  most response actions." Id. (EPA92B)

    The NCR does not discuss or identify the precautions needed to
    ensure the  reliability of ICs.  It does specify, however, that  in
    appropriate cases  the Agency cannot provide remedial action
    unless a state assures "that institutional controls implemented
    as part of  the remedial action are in place, reliable, and will
    remain in place after initiation of operation and maintenance."
     [40 CFR § 300.510(c)(l); see also 42 U.S.C. § 9604(c)(3)].  (EPA-
    92B)


    The use of  ICs to  assist with mitigation of indoor air impacts  must

generally  be  considered as supplemental  to  both  technical  measures  used

specifically  for that  purpose  and  to response  measures  selected  to  re-

mediate the CERCLA site.   The  use  of ICs  for mitigation  of indoor  air

impacts may be  considered to  be  most applicable  to  situations in which site

remediation will quickly eliminate or adequately reduce  those impacts, in
which technical  measures are  inadequate or  not cost  effective during long-
term remedial  actions,  in which  active measures  are  not  practical  for the

site and/or the affected property,  and in which  they are a necessary
supplement to other controls  where waste is left in  place  following

remediation.


     "An  1C may  fail  if it is  inadequately  designed  or  not  fully and effec-

tively implemented or if full  and effective implementation cannot be

maintained for  the desired time period." (EPA92B).   It is  critical  to give

careful consideration,  early in the planning process,  to the development of

ICs that will  meet the needs at the site and to determine what measures can

be taken to maximize their effectiveness.  It is strongly recommended that


                                    2-48

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Regional counsel  be consulted as soon as  it appears  that ICs may be needed.

Failure to do so  may negatively impact the range  of  ICs that may be

considered or the timeliness with which they may  be  implemented.  Assessing

effectiveness of  ICs is  discussed in Section 3.3.2.


2.3.1 Governmental  ICs

     As the NCR points out,  institutional  controls typically are
     unlikely to  be implemented by the Agency.  Governmental  ICs,  by
     definition,  involve restrictions that are generally within the
     traditional  police  power of state and local  governments to impose
     and enforce.   Among the more common  governmental  institutional
     controls are water  and  well  use advisories and  restrictions,
     well-drilling  prohibitions,  building permits, and zoning and
     other land use restrictions. (EPA92B).

     	 § 104(c)(3)  expressly requires  that, before  EPA provides
     remedial action at  a site, the state in which the site is located
     must provide certain assurances, including an assurance of all
     future maintenance; if  a state will  not provide this assurance,
     it may be difficult to  implement institutional  controls. (EPA92B)

     Typically, the mechanism for providing such  an  assurance is a
     Superfund cooperative agreement or a Superfund  State Contract
     (SSC) in which the  state,  pursuant to CERCLA §  104(c)(3), assures
     EPA that it  will  operate and maintain a remedy.   In many cases,
     the continued  enforcement of the 1C  can be characterized as an
     aspect of the  effective operation and maintenance (O&M) of a
     site. (EPA92B)

     With a cooperative  agreement or SSC  in place, the state retains
     whatever authority  it has to alter or permit the  alteration of
     zoning or other use restrictions but is contractually obligated
     to EPA to continue  the  ICs to the extent it  has the authority to
     do so.  Thus if the remedy fails, EPA may be able (depending  on
     applicable law),  to pursue a breach  of contract claim against the
     state.  The  ultimate utility of such an action  may depend both on
     whether EPA  prevails in the action,  and, if  it  does, on whether
     it could obtain specific performance or would be  limited to a
     damages remedy. (EPA 92B).


     However, states may have delegated the types of police powers
     that are needed for ICs to local governments,which often are  not
     parties to an  agreement with EPA and are not required, under
     CERCLA, to give an  O&M  assurance.  Since it  is  the state that has
     made the assurance, EPA's remedy for a failure  of the control is
     from the state, which may not have the legal authority to prevent
     the local government from actions that might lead to failure  of
     the 1C, such as a zoning regulation  change.  (EPA92B).

                                     2-49

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    This differs somewhat from other aspects (i.e., those not involv-
    ing ICs) of O&M at a site for which the state has provided assur-
    ances but the local government implements the O&M.  If the local
    government fails to carry out activities necessary to O&M, the
    state's O&M assurance would appear to obligate the state to step
    in.  Nevertheless, while a state typically possesses the legal
    authority to carry out O&M, it may not have the legal authority
    to impose an institutional control. (EPA92B).

    One approach to increasing the reliability of governmental ICs is
    to create a direct contractual relationship between EPAand the
    governmental entity responsible for implementing and enforcing
    the use restriction.  In situations where the state proposes to
    have the local government implement O&M, arguably an adequate
    assurance should include some commitment by the local government
    to EPA  in a three party agreement or to the state in a separate
    agreement, that it will not reduce or eliminate the necessary use
    restrictions; the effectiveness of such a commitment will depend
    in part on the extent that the commitments of the signatory
    government are binding on successive governments.  In some cases,
    this could be done in a three-party SSC or a cooperative  agree-
    ment.   Before entering into such an agreement, Regional councel
    should  be consulted regarding the remedies available in the event
    of a breach.  (EPA92B).

    Where EPA is not providing remedial action, some comparable
    method  of formalizing a contractual relationship between  EPA  and
    the state or local government in which  EPA receives  an assurance
    that the  institutional control will remain in  place  may be useful
    Cf. 40  CFR §§ 35.6200-6205 (authorizing removal response  coopera-
    tive agreements).  The mere fact that CERCLA does not require
    certain types of assurances in certain  circumstances does not
    preclude  the Agency from obtaining assurances  needed to maximize
    protection of health and the  environment at the site.  (EPA92B).

    A less  formal, but perhaps more effective, means  of  ensuring  the
    reliability of this type control is to  emphasize  obtaining commu-
    nity understanding of, and support for, the  1C.  A community's
    belief  in the importance and  appropriateness of an  1C could,  as  a
    practical matter,  increase the likelihood of adequate  implementa-
    tion of the control.  (EPA92B).

     It  should be  remembered, however,  that  political  developments are

unpredictable,  and changes  may render governmental  ICs ineffective for

long-term actions.
     The United States  has  authority under CERCLA §  106(a)  to issue
     orders or take  other appropriate actions taken,  as  "may be neces-
     sary to protect public health and the environment"  if  there "may
     be an imminent  and substantial  endangerment."  An order issued

                                     2-50

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     under  this  authority may,  in appropriate cases,  require  the
     implementation of institutional controls by other  parties.  In
     addition, the order itself, to the extent it effectively re-
     stricts  or  prohibits certain land uses, may function  as  an  insti-
     tutional control with respect to the party to whom it was issued.
     (EPA92B).

2.3.2 Proprietary Institutional Controls

     Proprietary institutional  controls (PICs) involve  some  form of owner-

ship of an  interest  in the  property.   "With  a proprietary control,  a party

owning sufficient rights  in  a property  restricts  the use of the property."

(EPA92B).  "The  rights of  property  owners  are generally defined by the

property laws of the  state  where the  property  is  located.   This makes it

critical to identify  and  understand the applicable  property law principles

as part of the process of  developing  an  1C." (EPA92B).   "Ideally, a

proprietary control  will  be implemented with sufficient flexibility to

allow all appropriate uses  of the property,  and  to  permit the owner to

convey most interest  in  the property."  EPA92B).


     PICs can often be implemented, particularly  in  an  enforcement
     context, under consent  agreements between EPA  and  property own-
     ers.  However,  in some  cases,  implementation may be require the
     acquisition of  an interest in  real property.   Further,  in some
     such situations, a necessary part of  the response  may be for EPA
     to acquire  property on  its own behalf.  Whenever EPA acquires
     property, certain procedures and  rules  apply.  (EPA92B).

     As part  of  a remedial  action,  the Agency may  "acquire,  by pur-
     chase, lease, condemnation,  donation, or otherwise, any real
     property or any  interest in real  property" under CERCLA § 104(j).
     A condition of  the exercise of acquisition authority under CERCLA
     § 104(j) is that, before an interest  in real estate is  acquired,
     "the State  in which the interest  to be  acquired is located as-
     sures. .. [EPA] ... that  the State will  accept  transfer of the in-
     terest following completion of the remedial  action."  §  104(j)(2).
     Where  the property  interest will  be extinguished (e.g.,  a lease
     with a limited  term or  an easement for  a specific  term or pur-
     pose)  by the completion of the  remedial action, no assurance is
     necessary.  (EPA92B).

     EPA's  Facilities Management and  Services Division  (FSMD) has sole
     authority within the Agency to  acquire  real  property under Agency
     Delegation  1-4.   In addition,  CERCLA  Delegation 14-30 requires
     the approval of  the Assistant  Administrator  for Solid Waste and
     Emergency response, with the concurrence of  the General  Counsel,
     for all  real property  acquisitions, "by EPA  or pursuant to a

                                    2-51

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     cooperative  agreement  for  response action, including a removal,
     remedial  planning  activity,  or  remedial action."  After the
     necessary concurrences,  the  Hazardous Site Control Division sends
     a  request for  acquisition  to FSMD.  FSMD may complete the real
     estate  transaction with  its  own personnel, by contract with a
     commercial firm, or through  an  Interagency Agreement with the
     U.S.  Army Corps  of Engineers or U.S. Bureau of Reclamation.
     (EPA92B).

     "Full  fee title  obviously  constitutes an interest in property which  is

sufficiently broad to support an 1C, since  fee  owners  can generally

restrict the uses of their property as they  see fit, within  the  limits

imposed by applicable law." (EPA92B).  Where title  is  held by  a  PRP,  the 1C

can be enforced through an order or enforcement agreement.   Alternatively,

the government may take title itself.  "...  a  sovereign  may  act  in  the

capacity of a property owner and implement  a proprietary 1C  subject  to  the

same conditions that apply to a private party's proprietary  controls."

(EPA92B).  "A lesser interest (preferably recordable)  that encompasses

rights and control over the property sufficient to  enforce a use restric-

tion could also be adequate." (EPA92B).


     To implement a control through a privately held  interest  (either fee

title or less), an enforceable agreement may be entered  into with a party
possessing a  sufficient interest in the property to prevent  the inappropri-

ate use, in which the  party formally agrees to enforce that  right and
prevent the use.


     To ensure the reliability of such an arrangement,  it may  be
     desirable to clarify the terms and conditions  under which the
     owner will enforce the restrictions and to address  the  possible
     conveyance of the property interest that  provides the right to
     enforce the  restriction, and the owner's  continuing responsibili-
     ty to enforce the restriction even where  there has  been a con-
     veyance.  Any such restriction, however,  must  be  framed so that
     it does not  violate the prohibition of restraints on  alienation
     as reflected in the property law of the state  where the restric-
     tion is to be imposed." (EPA92B).


     "An easement is a common, reliable type of property interest suffi-

cient  for implementing a proprietary  1C.  Not only is an easement well-

recognized  at  common law,  but  it  has  sufficient flexibility so that  it can


                                     2-52

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be crafted to give the  holder precisely the  rights  needed to restrict use
of the property."  (EPA92B).  Easements can be  crafted to include prohibi-

tions on certain types  of  development including placement of buildings and

excavation of soil.   Easements can be obtained by purchase,  donation,

condemnation, etc.  Easements "run with the  land" and, therefore, bind

successive owners.
     A covenant  running with the land, restricting  uses  of the  proper-
     ty might  be adequate, so long as some party  has  both  the ability
     and willingness to enforce it.  It might  be  useful  to explore  the
     possibility that a local community group, motivated by a desire
     to ensure adequate environmental protection  of an area, might
     hold such an interest.  In considering  such  a  possibility,  fac-
     tors affecting the long-term viability  of the  group must be exam-
     ined such as its likely longevity, resources for taking legal
     action  to address violations of the control, and its  ability to
     take various actions. (EPA92B).

     Another alternative might be a reverter clause in a deed,  by
     which the property reverts to a former  owner or  some other party
     if it is  ever used in a prohibited way.   Yet another option would
     be the  creation of an irrevocable trust to hold  the interest and
     ensure  that the property is not used  in the  prohibited manner.
     (EPA92B).

     Although  interests less than fee title  may be  adequate to  protect
     an 1C,  it is critical to ensure that, in  fact, the  party oversee-
     ing the 1C  will be able to manage use of  the property in the
     desired ways.  Certain  instruments, for example  those requiring
     privity,  may not reliably ensure this,  since the ability to
     enforce will cease, and the control may fail,  once  the property
     passes  out  of privity.  However, to the extent that failure of
     such a  control results  in a CERCLA release,  the  owner or operator
     may be  liable under CERCLA § 107.  Moreover, the presence  of a
     use restriction or notice in a deed would probably  be relevant to
     the ability of a party  to maintain an innocent landowner defense
     to liability. (EPA92B).


     It should be obvious that if these kinds  of  controls are anticipated,

early planning and consultation with  Regional  counsel is required.
                                    2-53

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                          REFERENCES FOR SECTION 2
AEE92 -     The Association of Energy Engineers,  1992 Innovative Radon
            Mitigation Design Competition,  Atlanta, GA,  1992.
EPA88 -     U.S. Environmental Protection Agency, Radon Reduction Techni-
            ques for Detached Houses, EPA/625/5-87/019, Washington, DC,
            January 1988.


EPA89 -     U.S. Environmental Protection Agency, Radon Reduction Techni-
            ques in Schools, 520/1-89-020, Washington, DC, October 1989.


EPA90 -     U.S. Environmental Protection Agency, Residential Air-Cleaning
            Devices, 400/1-90-002, Washington, DC, February 1990.


EPA91A -    U.S. Environmental Protection Agency, Radon-resistant Construc-
            tion Techniques for New Residential Construction, EPA/625/2-
            91/032, Washington, DC, February 1991.


EPA91B -    U.S. Environmental Protection Agency, Sub-Slab Depressurization
            for Low-Permeability  Fill Material, 625/6-91-029, Washington,
            DC, July 1991.


EPA91C -    U.S. Environmental Protection Agency, Radionuclides  in Drinking
            Water,  570/9-91-700,  Washington, DC, June  1991.


EPA92A -    U.S. Environmental Protection Agency, A Citizen's Guide to
            Radon,  402-K92-001, Washington, DC, May 1992.

EPA92B -    "Use of Institutional  Controls at  Superfund Sites",  Memorandum
            from David  F.  Coursen, Attorney-Advisor,  to Howard. F.  Corcoran,
            Associate General  Council -  Grants, Claims and Intergovernmen-
            tal Division.   July 27,  1992.
                                     2-54

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                                 SECTION 3
              DEVELOPING AND SELECTING MITIGATION STRATEGIES
   Mitigation of indoor air impacts from a CERCLA site may be accomplished
by source control  or by preventing  the  indoor exposure.   The NCR requires
the development and evaluation  of a range  of alternatives in the remedy
selection process  for a CERCLA  site.  There is a  strong  preference for
source control.  However,  the NCR also  requires the development of one or
more alternatives  that involve  little or no treatment,  but provide protec-
tion of human health and the environment by preventing potential exposures.
Indoor air mitigation techniques  that prevent indoor  exposures, such as
sub-slab depressurization and  institutional controls,  are examples of such
alternatives.

   This Section discusses procedures that can be  used to develop alterna-
tive strategies to mitigate indoor  air  impacts occurring as a result of
pollutant releases at a CERCLA  site.  It is recognized that mitigating
these impacts is only a part of the overall activities being taken to
clean-up the site.  The indoor  air  mitigation strategy development process
is considered one component in  the  overall  site remediation plan and the
utility of strategy elements are considered in the context of compatibility
with the overall plan.

   Addressed in this Section are development  of  indoor air mitigation
objectives and the basic information needed in developing the indoor air
mitigation alternatives.  This  Section  also addresses identifying and
selecting potential mitigation  measures, and combining them into workable
strategies from which a final  strategy  can be selected.   Note specifically
that selection of a remedy must be  based on an evaluation of the alterna-
tives against the nine NCR criteria (EPA88b).  This  document may only be
used to assist in developing alternatives  for evaluation; it cannot be used
to conduct the required evaluation  and  select the remedy.
                                    3-1

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   Matrix techniques are used that allow consideration of a wide range of
possible strategies.  Figure 3-1 illustrates the overall  process suggested
in this Section.  These techniques allow the evaluation of a large amount
of information in a relatively straightforward and concise manner.
Although the matrix techniques use quantitative appearing procedures,  it
must be recognized that qualitative and subjective considerations are
involved and, therefore, the result is not a definitive scientific analy-
sis.

   This document does not cover procedures for conducting remedial in-
vestigations, assessment of the indoor air impacts, or environmental  and
health risk assessments.  The procedures assume that the indoor air impact
has already been documented and the risks are such that mitigation has been
determined to be necessary.

   Application  of  the procedures  is  illustrated by development  of a set  of
strategy alternatives for a hypothetical situation which makes use of
information from an actual impacted site supplemented by fabricated
information to  provide  additional complexity.

3.1   DEFINING  THE OBJECTIVE
   Objectives  are  statements  of what  outcome  is desired.  Objectives  are
accomplished by designing and implementing a cohesive set of appropriately
chosen actions  - the strategy.  Before a workable strategy can  be developed
to mitigate specific indoor air impacts from a CERCLA site, it  is essential
that  there be definite  objectives.   If clear objectives are not defined,  it
is quite possible  to develop  strategies that do not solve the existing
problem, do not prevent recurrence of the problem, or that are  excessively
costly, cumbersome  and  complex.   In  some cases, the objective will be sim-
ple  and straightforward.   In  other cases, there may be a number of objec-
tives that cannot  be simultaneously met, and  which require an  evaluation
of strategies that  provide  the  best  overall solution.
                                     3-2

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   Collect and Review Information
        Set Mitigation Objectives
     Screen Technical Controls
     Screen Institutional Controls
       Construct Master  Matrix
Strategy 1
Most Technicals
Strategy 2
 Best Technicals
Strategy  3
Least Technicals
Strategy 4
Most ICs
Strategy 5
Best ICs
  Figure 3-1. MITIGATION STRATEGY DEVELOPMENT
                   3-3

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   Objectives should be both general  and specific.   General  objectives
might be stated, for example,  as  "  reduce the  incremental  site related
cancer risk to the occupants to 10"6."  A specific objective might be,
"prevent indoor use of contaminated groundwater".   The  set of objectives
developed become the standard against which  the utility of the various
technical and institutional  controls  that make up the strategy can be mea-
sured and also provides the focus needed to  assist  with project discussions
with technical and legal experts.

   Objectives can  be easily thought of in three basic areas: selection of
the mitigation level to achieve;  reduction of current impacts; and re-
duction of future  impacts.  Each of these is discussed  below.  Objectives
cannot be properly developed until  the basic information about the site and
affected properties required by Section 3.2  is available.

3.1.1 Mitigation Level Desired
   The objective of mitigation is to reduce risks due to the release  of
pollutants from the CERCLA site.  Reducing risks from pollutants from non-
CERCLA site sources may occur as a side benefit to  the  strategy imple-
mented.  Mitigation of  indoor air impacts may be accomplished by reducing
the  indoor air concentration of the pollutant and/or by reducing the
occupants', or potential occupants' exposure to the pollutants.  It is
important, therefore, when defining the desired mitigation level not  to
focus solely on indoor  air concentrations.  However, the most effective
strategies will likely  be those that reduce the indoor  air concentrations
of the pollutants.

      The first  step  is  setting a goal  for the  mitigated concentration.
This will take  place as part of the feasibility study for the site.   The
information needed to establish this goal may  be obtained from the baseline
risk assessment or other  investigation that concluded mitigation of  indoor
air  impacts was necessary.  The  target level for each pollutant for  each
medium  should be established at  a concentration and intake that corresponds
to an excess  cancer risk  of  10"6 or a hazard index  of 1, whichever is
lower.   Note  that  if  indoor  air  impact  is from several  chemicals  and/or
                                     3-4

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several media, the total  risks  will  likely  exceed  these values.  The goal
is an initial guideline.   It  does  not  establish  that  mitigation to that
level is warranted; preliminary remediation objectives may be modified
during the remedy selection process.

3.1.2 Reduce Impacts for  Current Property Usage
   Impacts for current property usage are those  that are or might occur  as
a consequence of the existing property usage.  For example, if the property
is high-density residential and expected  to remain in this usage, the miti-
gation objective must consider reduction  of both short-term risks and long-
term risks for this usage.

3.1.3 Reduce/Prevent Impacts  for Future Property Usage
   Objectives must also be developed to deal with potential changes in
land use for the period that  adverse CERCLA site impacts are expected.
This includes potential development of undeveloped property as well as
changes in usage.  Typical  changes might  include conversion to higher den-
sity usage, such as agricultural to rural,  rural to urban, and industrial
to residential.  Land use assumptions should be  consistent with the Agency
policies generally applicable to CERCLA risk assessments.

3.2   BASIC INFORMATION NEEDS
   Prior to analyzing mitigation options for a property, information
related to the source of  the  contaminant, the fate and transport of the
contaminant, the structural  features of the building(s) being affected,  and
the mitigation methods available should be  gathered.   This information will
enable evaluation and assessment of the situation and definition of the
mitigation objectives which lead to making  an informed, cost-effective
selection decision.  This information will  generally be obtained in the
Remedial Investigation, assessments of impacts on specific buildings,
removal assessment, and from  Section 2 of this document.  Certain specific
information related to building characteristics  may need to be determined.
Some useful procedures are described in references EPA88a and EPA92.
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3.2.1 Source Type, Strength,  and  Route  of Impact
   An understanding of the source,  the  type of contaminant generated from
the source, and the transport mechanisms  acting on the contaminant are
vital to setting objectives for mitigation.   The chemical  and physical
properties of the contaminants should be  researched and understood.   The
toxicity, flammability, and reactivity  of the contaminant  will  be important
considerations when setting priorities  and selecting mitigation objectives.
The health effects and environmental  impacts of exposure to the contami-
nants should be researched and understood.  It is imperative to know what
one is dealing with when developing a control strategy.

   The physical location of the source  of the contaminant and the extent
of the contamination should be identified.  Whether the source is on a
remote property or on an adjacent property will give some  indication of the
scope of contamination, potential duration of its impact,  and the concen-
trations to be expected.  The presence  of the contaminant  in the local
groundwater, ambient air, soil gas, or  community well should be determined
by acceptable analytical methods.  Hydrogeological surveys, ambient air
monitoring, soil gas testing, and groundwater testing may need to be con-
ducted to fully understand the extent of the contamination and to make any
necessary corrections for background levels.

   The  present  status  of the  source should  be determined.   If the con-
taminant is still being released from the site, an evaluation of the effec-
tiveness of control strategies used at  the  site to limit further release
should be conducted.   If no control strategies are in-place, the first
objective of the mitigation plan may include controlling the source.  The
quantity of contaminant released from the source  should be estimated.
Based on available information the potential duration of the impact should
be estimated.

   The  route  of impact is  a  primary consideration when selecting  a  miti-
gation  strategy.  The  route of impact  is  the physical movement of the con-
taminant from the source to the point of  impact.   Basically, three  compo-
nents comprise  the route of  impact.  First,  the transport mechanism deliv-
                                     3-6

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ers the contaminant from the  source to the building.   Second,  the means of
intrusion allows the contaminant to enter the building envelope to reach
the point of impact.  Finally,  the impact occurs in the form of health
effects from exposure to the  contaminant.

   The transport mechanism causing the migration of the contaminant from
the source to the impacted building should be identified.   Typically, tran-
sport mechanisms fall into one  of the following categories:

      •     Ground Water Migration (or Ground Water Plume)
      •     Soil Gas Migration
      •     Ambient Air (Wind Currents)

   Based on the analytical results conducted to determine the extent of
the contamination, transport  mechanisms should be identified.   The trans-
port mechanisms should be placed in rank order according to their relative
contribution to the transport of the contaminant.  The highest ranking
transport mechanisms should be  identified for control by defining them as
mitigation objectives.

   As there are several transport mechanisms, there are several  means of
intrusion.  The principal means of intrusion may be categorized  as follows:

      •     Infiltration - Ambient Air
      •     Infiltration - Soil Gas Intrusion
      •     Ground Water Intrusion
      •     Diffusion through Building Materials
            Well Water
      •     Carried on clothing or shoes  (e.g., contaminated soil)

   Based on the transport mechanisms  acting  on  the contaminant  and  the
results of the analytical site assessment, the above means of intrusion may
be placed in rank order according to their relative potential contribution
to the intrusion of the contaminant.  The highest ranking should be
identified for control by defining them as mitigation objectives.
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3.2.1 Example - Understanding Source  Type, Strength,  and Route of Impact
   A manufacturing facility is located about 200 yards from a residential
community.  One of the underground chemical  storage tanks  leaked TCE for an
unknown period of time.   The source of the  leak has been stopped,  however
the TCE has migrated into the groundwater.   The plume is currently defined
as 300 yards wide extending 1,000  yards into the residential  community.
TCE has been detected in this plume at all depths between  the top of the
groundwater table, 5 feet below surface,  to  50 feet below  ground surface.
Concentrations are an order of magnitude higher near the source than in the
middle of the plume.  Hydrogeological testing indicated the groundwater is
moving from the facility toward the community at about 0.5 feet per day.
Host of the buildings use water from  a public surface water system located
several miles from the community;  however,  a few of the older residences
use private wells intersecting the plume.

   A site investigation has been conducted.  Monitoring at the site  and
affected buildings included soil gases, ambient air, and  indoor air  in  the
fall and winter.  Indoor air impacts  have been documented  in a number of
buildings.  Indoor air concentrations of TCE ranged from 50 to 100 ppb/v.
The data  indicate that indoor concentrations are significantly higher when
the ground  is frozen or snow covered.  The data also indicate that TCE
volatilizing from the plume escapes through the surface when the ground is
not frozen.  The TCE in the ambient concentrations could migrate into the
homes, however the ambient air concentrations were not high enough to be of
concern during the monitoring period.  Direct intrusion of the contaminated
groundwater is not occurring.

    The results obtained  for frozen or snow  covered ground may be  related
to  increased building stack effects due  to greater  indoor-outdoor  tempera-
ture differences.  The results may also  be related  to the impermeability of
the  soil  surface  causing  increased TCE concentrations in near  surface soil
gases.  The ambient air concentrations of TCE  in the  immediate vicinity of
the  buildings  is  of interest because  it  tells us whether or not the  ambient
air pathway into  the  indoor  air is important or not.
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   The data available,  therefore,  indicate the potential for a long-term
indoor impact,  that the migrating groundwater plume  is likely the source of
contaminated soil gases  in  and  around  the  buildings,  soil  gas intrusion is
likely the only significant impact  route  in most  buildings,  and that vola-
tile chemicals in the well  water are likely of concern in  a  few homes.

   Based on a previous risk analysis,  a mitigation level objective for
indoor air concentrations of TCE of no more than  5 ppb/v,  annual average
may be established.  This requires  90  to 95 percent  reduction from current
levels.

3.2.2 Building Structural Features
   Basic information relative to the  construction characteristics of the
subject building should  be  gathered.   The  following  building characteris-
tics should be determined:

   •  The presence of a  sub-structure  drainage system indicates a potential
      for application of a  drain tile  ventilation system.   Indications that
      a drain tile network  exists  are  a basement  sump, a dry well, and a
      remote above ground discharge pipe.

   •  The type of sub-structure should be  noted to indicate  if using a sub-
      slab ventilation system is feasible. The presence of  a crawl space
      with an earth floor may indicate use of crawl  space ventilation or
      sub-enclosure ventilation.

   •  The composition of the sub-slab  region  should  be determined.  The
      presence and depth of a sub-slab aggregate layer, a moisture barrier,
      and the porosity of the fill  material will  indicate the permeability
      of the materials and  the potential  for  success of a sub-slab ventila-
      tion system.  Diagnostics could  be used to conduct sub-slab commu-
      nication tests to  physically assess  the flow potential of the sub-
      slab.  These tests should be conducted  by an experienced diagnosti-
      cian for reliable  results.
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   •  The type of foundation wall  should be noted.  Typically, foundation
     walls are constructed of cast-in-place concrete, concrete masonry
     units, stone, or brick.  The foundation wall cavity, if present, may
     be ventilated to control the intrusion of contaminated soil gas.

   •  An estimate of the building's infiltration rate should be made  (see
     EPA92).  Loose construction joints and window/door  seals will greatly
     increase the infiltration rate in a building.  Potential major  and
     minor entry routes for intrusion of soil gases and  groundwater, and
     their accessibility for mitigation efforts, should  be identified.

   •  The type of HVAC system in the building should be noted.  Typical
     general systems include:  forced-air, hot water w/baseboard radia-
     tors, etc.  The on/off cycling, and whether the fan delivers a
     constant volume or a variable volume  (usually found only in commer-
     cial buildings) of air during operation indicate  if mitigation  using
     building pressure adjustments with existing HVAC  components is  a
     viable option.

   •  The property's water source(s) should be  identified.  Typically,
     water  is provided by a private or  community well, or  a  public  source.

   Certain  site  characteristics are also necessary to make an informed
mitigation  selection.  The following information  should be  obtained  from
building  records,  site plans, and  soil surveys:

   •  Depth  of Water Table  - monthly depth  variations
   •  Frost  Line - monthly depth variations
   •  Soil  Type  and  Permeability
   •  Well  Depth and Water  Source

3.2.2 Example  -  Building  Structural Features
   There are two types of buildings in the residential community located
near the manufacturing facility:  two-story condominiums built in clusters
of four units  on a common slab, and single-family detached housing on slab
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floors.  Floors of all buildings are at grade  level.   The condominiums have
a drain tile (French) system completely around the exterior perimeter.  The
building plans, and on-site inspection, indicate a 4-inch layer of pea
gravel was placed under  the slab floor.  Foundation walls are constructed
of hollow cinder block.  Exterior  frame walls  are supported by a sill plate
which rests on the top course  of block.  There is brick veneer on the exte-
rior.  There is a solid  block  wall between units.  Utility connections
(water, sewer, and electrical) penetrate both  the slab and walls.  Heating
and cooling is all electrically-operated forced air.   The buildings are
well insulated and have  a  low  air  infiltration rate.   All buildings are
connected to the public  water  supply.

   Structural  information for the  condominiums is  useful for preliminary
assessments of potential soil  gas  entry locations  and possible mitigation
techniques that could be used. The presence of a French drain suggests the
possible presence of a designed gap between the slab  and walls through
which soil gas can enter.  The hollow  cinder block walls also can provide a
pathway for soil gas to  enter  the  building either  through unsealed penetra-
tions (e.g., utilities)  or at  the  wall/sill plate junction.  The opening
between the brick veneer and  the framing materials also can provide a
pathway for soil gas to  enter  the  building above the  sill plate.  The
presence of a good layer of gravel beneath the slab  indicates this area is
probably highly porous  and soil gases  could probably  be ventilated using a
limited number of sub-slab ventilation points  or by depressurizing the
French drain system (assuming it is not plugged).  The fact that the condos
use electric heating and cooling indicates that 1) operation of the system
probably has little effect on  building pressures,  and 2) backdrafting of
furnace combustion products  is not a concern if exhaust fan assisted soil
ventilation methods are  used.

   There are  ten single-family residences located in a heavily forested
section of the community.  All have poured concrete slab and foundation
walls.  There are indications  that gravel  was  not  used below the slab and
that it was poured directly on the ground.  Above grade construction  is
frame with brick veneer finish.  Construction  technique suggests air  infil-
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tration would fall within typical  ranges.   Two-story buildings  predominate
but several are three story.   Utilities  penetrate both  the  slab and above
grade walls.  Heat for all buildings is  by forced air oil furnaces located
on the lower floor.  All homes use private wells and septic systems.   Floor
drains in the utility room connect to the septic system.

   The poured concrete slabs and walls suggest there are probably few
openings through which soil gases could  enter the buildings.  Unsealed
utility penetrations are the most likely entry points.   It  is possible,
however, that some soil gases may be channeled to upper floors  through the
gap between the frame and the brick  veneer.  Because these  homes use wells
that may intersect the contaminated  groundwater plume,  volatilization of
contaminants from  indoor water uses  (i.e., showering, cooking)  is likely.
Also, septic system drain fields provide an excellent collection system for
soil gases which can enter the houses if the floor drains do not include
traps or if the traps are not water filled.  If, as suspected,  the slabs
were poured directly on the ground,  it is likely that sub-slab soil perme-
ability is  low and ventilation of soil gases would be limited to regions
near the ventilation points.  Because fired equipment,  such as the oil
furnaces, withdraw air from the houses,  they can increase the buildings'
underpressurization and cause more soil  gas to be drawn into the buildings.
Also,  if a depressurization system is used for soil ventilation, care must
be exercised to ensure that furnace backdrafting is not caused by withdraw-
ing too much air  from the house through unsealed gaps in the structure.

3.2.3  Current  and Potential Future Uses
    The present,  future,  or intended  uses  of  the building and site should
be identified.  The  selected mitigation method  should be based on goals  and
objectives  that account  for known long-term use  changes and short-term use
adaptations.   Changes  in  use could affect  the types  of systems considered,
the maintenance requirements of the  system(s),  and  the level of  protection
required of the system.
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3.2.3 Example - Reducing Current and Future Impacts
   Only 20 percent of the land immediately above the present position of
the contaminated plume has been developed.   It is composed of moderate to
high density residential.   Another 20 percent of the land is currently
zoned for high density residential.  The remaining land is currently zoned
for light industrial.   Land in the projected path of the plume is undevel-
oped but zoned for residential use.

   Base on the information available, the following additional objectives
were established to approach the mitigation level objective:

Objectives for Reducing Impacts to Current buildings
   •  Prevent indoor usage of well water
   •  Reduce exposure to soil gas intrusion into existing buildings
Objectives for Reducing Impacts from Future Development
   •  Prevent the use of inappropriate construction methods
   •  Reduce contaminant concentrations in groundwater

3.3   EVALUATION OF OPTIONS
   With objectives defined and the exact nature of the problem delineated,
the technical and institutional control measures that are applicable to
mitigating the impacts can be evaluated.  The procedures in this Section
are oriented toward estimating the potential effectiveness of individual
measures in mitigation.  Combining these into workable alternative strate-
gies is discussed in Section 3.4.

3.3.1 Estimated Effectiveness of Potential Technical Measures
   Technical alternatives will be  evaluated either iff the process of
planning a removal or in selecting a remedy or both.  In either case the
likely effectiveness of the alternative is a key consideration.  The design
and installation of the technical mitigation measures requires considerable
technical expertise and experience.  The EPA has provided technical
guidance for design and installation of radon mitigation measures, and
there is limited additional information available to assist in the mitiga-
tion of other indoor air contaminants.
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   This section suggests a method for assessing the effectiveness of
indoor air control  methods.   It does not substitute for the selection
process set out in the NCR;  rather, it suggests an approach that could be
used in assessing one or more of the factors that the NCR requires EPA to
evaluate in making removal  or remedial decisions.

   In order to evaluate potential technical mitigation measures, first
organize all available and necessary information related to the remediation
site.  A table should be prepared, listing in column 1 the objectives
defined above.  Five additional columns will be used to list potential
control methods and subjective ratings  (see example, Table 3.1).  It is
suggested that a zero (infeasible) to 5 (high confidence) rating scale be
used for the subjective rating of criterion used in the decision making
process.

   The  second  column  should  have  the  heading  "Mitigation Methods."   In
this column list all technical control  methods applicable to the objectives
in column 1.   In the third column, rate the potential control effectiveness
of this method.  The likelihood of achieving  the mitigation goals should be
evaluated.  For example, if  a 90% reduction in indoor contaminant levels
were the goal  of a particular mitigation problem,  sub-slab ventilation
might receive  a 5 in certain specific cases,  and sealing of entry routes
might receive  a 1.

   The  fourth  column  should  be given  the  heading "Feasibility."   The
practicability of each mitigation measure  should be  evaluated and rated.
Measures that  can not be implemented, such as constraints due to  the build-
ing's structural features, should be  given a  zero.   For example,  drain tile
ventilation can not be considered a viable option  for  a building  without a
drain tile  system.  Mitigation  measures which require  modifications  to
structural, architectural, mechanical,  or  electrical  systems should  be
subjectively rated  in terms  of their  relative practicality.

    The fifth  column should  be given the heading "Rough Cost".   Ratings for
costs  should  be  in  the  order:  5 for least  cost;  0  for most  expensive.
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   The product of the horizontal rows should be entered in the sixth
column to give a relative effectiveness  rating  for each of the listed
mitigation methods.   The product of the  individual ratings is suggested
here as a means to eliminate controls that,  for one reason or other,  have
been rated "infeasible"  (i.e.,  given a zero  rating).  A simple summation
could result in an infeasible control achieving an overall high rating.
Based on the relative ratings,  the list  of viable controls can be reduced.

3.3.1 Example - Estimated Effectiveness  of Technical Control Options
   The above process is demonstrated through its application to the
manufacturing facility example.  The potential  control options for each
impact route must be evaluated to determine  their applicability.  The
objective is to eliminate inappropriate  methods from further consideration.
In this example the controls and rating  are  for illustration purposes only.
No reliance should be placed on the completeness, accuracy, or applicabili-
ty for this or other cases.

   As  indicated above, the first step in the process  is development of an
evaluation table for technical controls.  Table 3.1 does this.  In the
first column all objectives, except the  overall mitigation goal, are
listed.  In column 2, mitigation methods to  accomplish those objectives are
listed.  Considered for preventing indoor exposures due to use of veil
water in the detached houses are two methods: (1) provide an alternate
water supply, or (2) treat the well water for each of the houses.  Methods
to reduce exposures to soil  gas intrusion are complicated by the fact that
two basic building structural types are  to be mitigated.  Drain tile
ventilation is listed only for the condominiums because the drain tiles are
already in place.  Sub-slab ventilation  could be used for either structural
type, as could reliance on sealing intrusion routes or modifying building
ventilation.  Although new construction  could be designed to reduce
intrusion, no technical  control exists to ensure they are used.  Indoor
exposures can also be reduced by removing the contaminants from the
groundwater.  For this example, we decide there are only two ways to accom-
plish this: extract the water at high concentration locations near the
source/community boundary or by using multiple extraction wells distributed
                                     3-15

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 throughout the community.  Note  that this  would likely be considered as
part of the overall  site remediation plan,  not  just for indoor air con-
cerns.

   Each of these methods must be rated  for control capability, feasibility
and rough costs.  If an uncontaminated  alternative water supply is provided
for the houses, control of this source  is 100 percent; thus,  a 5 rating is
given for control.  Connection to the public water supply, which is already
in the community serving the  condominiums,  is feasible.  However, because
at this point we do  not know  the design capacity of the water lines, a
feasibility rating of 3 is assigned.  A rough cost rating of 3 is assigned
because a water distribution  system is  nearby and there are only a few
houses to service.  Treating  well water at  each of the houses receives
lower ratings in all categories because contaminant removal is not as good,
and significant modifications may be necessary  to install properly sized
systems.

   Passive drain  tile ventilation systems for the condominiums are given
high ratings for feasibility  and rough  cost because the tiles exist and the
systems can be installed simply.   Control capability is rated low, however,
because the system may not achieve the  95 percent mitigation objective in
cold weather and may not perform well in warm weather.  Active drain tile
ventilation is assigned a higher control rating, but is not given a 5
because of uncertainty about  the effectiveness  of control for gases rising
near the center of the slabs.  That is, the tiles and/or aggregate under
the slabs may be partially plugged by silt reducing the vacuum effect far
from the tiles.

   Sub-slab ventilation was assigned uniformly higher  rating for  the
condominiums than for detached houses primarily because of the high proba-
bility of the presence of a permeable gravel layer beneath the condo-
miniums' slabs.  This indicated the likelihood  of good sub-slab ventilation
with a minimum of slab penetrations for vent pipes, associated piping, and
interior remodeling.  Sealing soil gas  intrusion openings as a stand alone
control technique was assigned low rating for the condominiums because of
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the presence of the French drains (likely  large perimeter openings  at
slab/wall interface) and hollow block foundation  wall  construction.
Sealing opening at the detached housing was  assigned higher ratings because
both slab and foundation walls are poured  concrete and,  therefore,  nay have
fewer entry routes.  However,  control is somewhat uncertain because of the
possible presence of cracks behind finished  walls.  Feasibility and rough
cost are downrated because of the possibility of  having to remodel  these
finished areas to repair cracks.

   Ventilation modifications,  including dilution with outdoor air and /or
pressure balancing to reduce depressurization in  the lower levels of the
condos, was assigned generally low ratings due to potential energy pen-
alties in the cold climate, the potential  for many soil gas intrusion
routes, and the possibility of some units  being connected through cracks in
the solid wall separating them.  Ventilation modification, by pressure
rebalancing, in the single-family houses was assigned higher ratings
because of the possibility of fewer entry  routes.

   Reducing  indoor exposures by cleaning up the ground water was given
high ratings for control effectiveness for both options for locating the
extraction wells.  The feasibility and rough costs of locating the wells in
the community received  lower ratings than  locating them near the source be-
cause of the large community area and  likely large number of wells needed
with interconnecting piping.

    The final  rating for each  technical mitigation method was calculated as
the product of the  ratings  in  each of  the three columns.

3.3.2  Estimated  Effectiveness  of Institutional Controls
    Predicting  the effectiveness of institutional  controls is a complex
matter.  Implementing  institutional  controls will  typically require  exten-
sive consultation  with  legal counsel.  There are  legally  mandated  proce-
dures  that must  be  followed in the application of many of the  controls.   It
is strongly  recommended that Regional  Counsel be  consulted  to  assist with
evaluation of  institutional controls potentially  applicable to a site.
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   The procedures below should  be  useful  in estimating  the likely effec-
tiveness; however,  they are  qualitative and should not  be  construed as a
quantitative analysis of a rather  speculative process.  Use of these
procedures is not required by the  NCP or  by EPA  policy.  Rather it is
simply one suggested approach to evaluating effectiveness  of ICs as part of
the remedy selection process set out in the NCP.

   The first step in the process  should  be to  develop a simple matrix
using the objectives as the  focal  point for listing  institutional  controls.
This is most effectively accomplished by  preparing a table with six col-
umns, (see example,  Table 3.2)  listing in the first  column the objectives
desired to be accomplished.  The objectives should be as specific as
possible (e.g., prevent indoor  use of contaminated groundwater).  In the
second column, list all the  ICs that might accomplish each objective (e.g.,
well use restrictions, well-drilling prohibitions, building permits, zoning
laws, deed restrictions, etc.). At this  stage,  it is preferable to include
as many types of ICs as possible.   Title  the third,  fourth, and fifth
columns "Duration",  "Interest", and "Authority",  respectively.

    In the third column, give the  time  period over which the 1C must be  ef-
fective.  In the fourth column, indicate  whether or  not the 1C involves an
interest in property and who would own that interest (e.g., Federal, State,
PRP, private party).  In the fifth column, list  the  party  or parties with
authority to implement or change  the 1C.   For example,  in  the above case
regarding the manufacturing  facility, the State  or local government may
have the police powers adequate to enforce well  use  restrictions.   The
parties holding an interest  in  the property would have  the power to enforce
deed restrictions (subject  to State property laws).   When  this table is
completed, it is likely that several ICs  will  have been repeated for the
objectives.

   The sixth column should  be  entitled  "Likely Reliability".  Entries  in
the sixth column will be somewhat  subjective.   It is suggested that a zero
(1C is unreliable, not implementable, or  excessively costly) to 5 (1C is
easy to implement, likely to perform adequately,  and costs are reasonable)
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rating scale be used.   The following can be considered as a general  guide
although site specific considerations may  affect  the analysis:

   •  The shorter the term of the  1C, the  more  likely it  is to  be  reliable.

   •  ICs based on property interests may  be more effective than those
      based on police powers if the  1C must be  effective  over a long period
      of time and if there is a party with the  authority  and  incentive for
      long-term enforcement of the 1C.

   •  As a general matter, property  interests  are likely  to be  reliable in
      the descending order (remember, however,  that Federal  interests must
      be transferred upon completion of  the remedial action): Federal has
      full fee title , State has full fee  title and a Superfund State
      Contract is in place, Federal  or State  owns a recordable  interest,
      PRP owns interest and a Consent Agreement is in place,  and  private
      party  (e.g., local community group)  owns interest.   In  the  case of
      private party interest, enforcement  would be very difficult.

   •  ICs involving three party agreements (Federal,  State,  and Local
      governments) are effective only to the  extent that the  commitments
      are binding on successive city and county governments.

   The  table now provides  an  estimate of  the relative effectiveness  of
 each  1C  for  each objective.  This table  and the similar one developed  for
 technical measures can now be used in  developing a set  of strategies for
 the mitigation.

 3.3.2 Example -  Estimated Effectiveness of Institutional Controls
   For the example,  the summary for potential  effectiveness  of insti-
 tutional controls  is given  in Table 3.2.  Column 1 of that table  lists the
 mitigation  objectives  as before and in column 2  the potential  institutional
 controls are listed for each  objective (there  is no implication here that
 the  list is complete  or appropriate).   Buying  some or all of the  involved
 properties  is listed  for completeness.   This option will appear frequently
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if the procedures suggested  in  this document are followed.   This does not
imply that such an option should receive  serious consideration in any
except very unusual cases.

   The time period entered  in column  3,  10 years,  was estimated based on
the overall site remediation plan schedule.  Partial  lists  of parties who
might own the property interest and who would  have authority to change
those interests are given in columns  4 and 5.  A subjective reliability
rating for each of the mitigation methods is given in column 6.

   In this example, local health department restrictions are rated higher
than restrictive covenants for preventing indoor use  of well water in the
detached homes primarily because they are more likely to remain effective
for 10 years.  The only 1C  listed in  this example  for indoor exposure
reduction, for either type of properties  with  unacceptable  soil gas intru-
sion rates, is property purchase. For prevention  of  inappropriate con-
struction methods, changes  in the building permit  requirements was rated
more effective than zoning changes because building permit  requirements can
be crafted to achieve exactly the desired construction elements needed and
could apply to both developed and undeveloped  properties.

3.4   DEVELOPING MITIGATION  STRATEGY  ALTERNATIVES
   At this point,  lists of technical  and institutional controls have been
developed addressing each of the objectives and the relative effectiveness
of each control estimated.   These must  now be  combined into workable
strategy alternatives to mitigate the indoor air  impacts.  For simple
cases, and, with experience, for some of the more  complex cases, a prefera-
ble strategy for final evaluation may be  discernable  by inspection of the
tabulated information.  In  the general  case, however, it is preferable to
build a number of alternative strategies  for evaluation.  This is the
approach presented in this  Section.

3.4.1 Combinations of Mitigation Options  Meeting/Exceeding Objectives
   The NCR requires that at the screening stage defined alternatives be
evaluated against the short- and long-term aspects of three broad criteria:
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effectiveness, implementability,  and  costs.   Effectiveness  refers  to the
combined effect of the alternative components in protecting human  health
and the environment.  Implementability refers to the feasibility of
constructing, operating, and maintaining technical  components and  to the
administrative requirements such  as obtaining approvals  from other offices
and Agencies.  Costs include capital,  operating, and maintenance costs for
technical and institutional controls.    For screening purposes,  it is more
important that costs be compared  on a common basis  than  that they  be highly
accurate.

   Review the lists of  technical  and institutional  controls developed for
each objective and eliminate those with poor ratings (however, if  there is
only one control for any objective, retain it even  if it has a poor rat-
ing).  The controls remaining form the set of options from which to choose
to develop the various  strategy options.

   The  straightforward  way to develop the set of strategy  options would be
to begin by  constructing a matrix of all controls and objectives developed
in preceding parts of this Section.  Again, this approach  is not required
by the  NCR or EPA policy;  it is simply one suggested way of performing the
screening process provided for by the NCR.  That matrix could be decomposed
to form strategy options by making all possible combinations of technical
and  institutional controls for the objectives.  This approach is likely to
produce a large number  of  strategies to evaluate, many of which would be
comprised of poorer options.  In the approach below, the matrix is decom-
posed into five strategy types ranging from  as  complete reliance on techni-
cal  controls as possible to as complete reliance on  institutional  controls
as possible. The strategy types are:

Strategy 1   "Most Technical" - A technical control  is chosen  for as many
             objectives  as  possible.   ICs are selected to supplement the
             technical controls, where needed.
Strategy 2   "Best Technical" - Only the best technical controls are used.
             ICs are  selected to supplement the  technical controls, where
             needed.
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Strategy 3  "Least Technical" - The least  number of technical  controls are
            used.  ICs are selected to  supplement the  technical  controls,
            where needed.

Strategy 4  "Most ICs" - ICs are used for  as  many objectives as  possible.
            These are supplemented by technical  controls,  where  needed.

Strategy 5  "Best ICs" - The best ICs are  used.   These are supplemented by
            technical controls, where needed.
   The first three  strategies rely heavily on technical controls, a
preference expressed in the NCP.  They vary in the number of different
types of controls considered and the quality of those controls.  This al-
lows flexibility in choosing controls and strategies that are compatible
with the overall site remediation plan.

   The last two strategies  rely primarily on  institutional controls.
These are provided  to cover situations in which (1) no technical control
strategy provides adequate protection during or following completion of
remedial actions, (2) indoor air impacts will be mitigated quickly by site
remediation activities  and  ICs  would be adequately protective and cost
effective, and  (3)  mitigation of indoor air impacts using ICs best comple-
ments the overall site  remediation plan.

Master Matrix Table:

•   Begin  by  constructing a  matrix  table with  4  columns:  Objective,  Tech-
    nical  Control,  Institutional Control, and  Probable  Costs.   See example,
    Table  3.3.

•   Subdivide the technical  and  institutional  control columns  into three
    columns:  control,  frequency, and  rating.

 •   Fill  in the Objectives column.
                                     3-24

-------
•  Review the list of technical  controls satisfying the objectives and
   count the number of times (the frequency) each control  is listed (i.e.,
   how many objectives a single  control  satisfies).

•  Insert in column two of the table by all objectives it satisfies, the
   most frequently listed technical  control, the frequency, and the effec-
   tiveness rating.

•  Repeat this process for the second,  third, fourth, etc., most fre-
   quently listed technical controls and insert each control sequentially
   by all ob.iectives it satisfies.  Continue this process until a tech-
   nical control is listed for all objectives (assuming a technical con-
   trol was listed for all objectives).

•  Repeat this process for institutional controls, continuing to list the
   ICs in column three in order  of most frequently listed until an 1C is
   entered by all objectives (assuming an  1C was listed for all objec-
   tives).

   The matrix is now complete.  Make several copies of the matrix to use
in developing the strategies.

3.4.1 Example - Master Matrix Table
   As indicated above, the first step is to develop the master matrix
table that gives all the useful  technical and institutional controls
previously developed.  In this example,  several of the lower rated techni-
cal and institutional controls in the Tables 3.1 and 3.2 were eliminated
from further consideration and are not  listed on the master matrix, Table
3.3.

   In Table 3.3, each control method has been listed by each objective  to
which it is applicable in the order of the frequency with which it was
 listed on Tables 3.1 and 3.2.  Host  of the technical controls in Table 3.1
were listed by only one objective; therefore, they received a "1" frequency
score.  Sub-slab ventilation appears by two objectives and is assigned a
                                    3-25

-------
frequency of 2.  Under the institutional controls,  only property purchase
was listed by more than one objective in Table 3.2.   The ICs are listed by
all objectives to which they apply and the appropriate frequency of their
appearance given.  The potential effectiveness ratings given in Tables 3.1
and 3.2 are given in Table 3.3 for each type structure.

   The next step  is  the actual development of the strategies using the
matrix table above.

Strategy 1 - "Most Technical"
   Illustrated in  Figure  3-2  is the process for developing Strategy
alternative 1  which  is described below.
•  Use a copy  of  the master matrix table.
•  In the  second  column  (Technical Controls) of the table, for  each  objec-
   tive  for which  a  technical control  is  given, place  a check mark by  the
   control with  the  highest effectiveness rating for that objective.   Flag
   all occurances  of that control.   If two or more controls have the same
   highest effectiveness  rating for  an objective, additional "Strategy 1"
   options can be developed by  using  each sequentially.
•  Delete  all  unchecked  and unflagged technical controls.

   At this point,  the  best technical  control  for each  objective, even  if
it is a  poor control,  has been selected.  Also shown are the technical  con-
trols selected for other  objectives which supplement the effectiveness  of
the  selected control for  each objective.  Make a copy  at this point  for use
in developing  Strategy 2.

    Institutional  controls must  now be chosen  to  supplement  those technical
controls that  would  not  satisfy the objectives.

•   Begin with  objectives for  which there is  no  technical  control.   Check
    the  lowest  effectiveness rated 1C that will,  at  the least,  ensure that
    the  objective is  satisfied.
                                     3-26

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         Delete all Un-checked
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              Figure 3-2. STRATEGY 1 - MOST TECHNICAL
                                3-28

-------
•  For objectives with a technical  control,  review  the  effectiveness of
   the checked control plus  the  effectiveness  of  any  flagged controls and
   assess whether or not the combined  effectiveness will  likely satisfy
   the objective.  If it does not  appear  that  they  will,  an 1C must be se-
   lected.  It is likely that those objectives for  which  the better
   technical controls were selected, will  not  require supplemental ICs.

•  Place a check mark by the lowest effectiveness rated 1C that will, at
   the least, ensure that the combination of technical  and institutional
   controls satisfy the objective.   Flag  all occurrences  of 1C.

•  Delete all ICs that were not  checked or flagged  for at least one of the
   objectives.

   Strategy 1 is now complete.   It is  composed of the best technical
control for each objective,  even though the  control may be poor,  that could
be used to effect mitigation.  It  also outlines the minimum level  of ICs
necessary to supplement the technical  controls for  each objective.

3.4.1 Example - Strategy 1,  "Most  Technical"
   On  a copy of  the Master Matrix  table,  the highest  rated technical
control for each objective was checked.   In  this  case,  the highest rated
control to mitigate soil gas intrusion was checked  for both types of
buildings.  All technical controls which  were  not checked for at least one
objective were deleted.  It should be  noted  that  Modify Ventilation was
checked for its rating for applicability  to  single-family homes and Active
Drain Tile Ventilation was checked for applicability  to the condominiums.
It should also be noted that sealing openings  in  the  building shells would
be required to some extent for these techniques.

   Institutional controls were then selected to supplement the technical
controls, where needed.  In this case, local health department restrictions
were selected to supplement alternate  water  supply  to ensure that residents
did not continue to use the existing wells.  Because  there was no technical
control to prevent inappropriate new construction,  an 1C  based on the local
                                    3-29

-------
building permit process was  selected.   The  1C  would have  to  ensure that
local building codes included a provision  that any structure built in the
affected area would have to  include  connection to the public water supply
and use construction techniques designed to prevent soil  gas intrusion.  A
consent agreement with the PRP was selected to ensure the pump and treat
technical control was installed,  operated  and  maintained.   The completed
Strategy 1 is shown in Table 3.4.

Strategy 2 - "Best Technical"
   Illustrated in Figure 3-3 is  the  process for developing strategy
alternative 2 which is described  below.

•  Use the copy made previously in developing Strategy 1.
•  Review the checked technical  controls only and delete all except  those
   with the two highest effectiveness ratings.

•  If no technical  controls were deleted, Strategies  1 and 2 will be
   identical  and  there  is no need to proceed with this strategy.

   ICs must now  be  selected  for objectives  for which  there  is  no  technical
control or for which the technical  controls will not satisfy the objective.
The  process for making these selections is the same as described under
Strategy 1.  After  the  ICs are selected, Strategy 2 is complete.  It is
composed of technical controls with  the two highest effectiveness ratings
and  the minimum level ICs necessary  to supplement the technical controls
for  each objective.
3.4.1 Example - Strategy 2, "Best Technical"
    The  checked  ratings  for technical controls  in  Table 3.4  (45,  80,  36,
and 64) were reviewed and the highest two (80 and 64) identified.  Techni-
cal controls not having these two high ratings were deleted from the table.
This  leaves only active drain tile ventilation for the condominiums  and
pump  and  treat  for  the groundwater.  ICs must now be selected  to supplement
the technical controls.  Because in this strategy no source of uncontami-

                                    3-30

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          End Process
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Technical Controls
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             Figure 3-3. STRATEGY 2 - BEST TECHNICAL
                              3-32

-------
nated water is provided,  the options  available are purchase of the single-
family homes (PRP liability should be considered)  or using health depart-
ment restrictions to prevent use of the  well  water, essentially forcing
residents to use bottled water for all needs.   Similarly,  no technical
method is provided for preventing soil gas intrusion into  the single-family
homes.  Purchasing the single-family  homes is again selected as the 1C
necessary (PRP liability should be considered).   The rest  of this strategy
alternative is identical to Strategy  1,  above.  The completed table is
shown in Table 3.5.

Strategy 3 - "Least Technical"
    Illustrated in Figure 3-4 is the process for developing strategy
alternative 3 which is discussed below.

•   Use a copy of the Master Matrix.

•   Identify the technical control(s)  with the highest frequency.

•   Place a check by this(these) control(s) for all objectives where
    it(they) appear(s).

•   Examine the objectives for which no  control was checked and determine
    the most frequently listed technical  control.

•   Place a check by this control  for each of  these objectives and  check
    all  other occurrences for other objectives.

•   Repeat this iterative process  for each remaining group of objectives
    until a technical control has  been selected for all objectives.   For
    objectives having only technical controls  with  frequencies of  1,  select
    the control with the highest rating  for that objective.

•   Delete all unchecked technical controls.
                                    3-33

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              Figure 3-4.  STRATEGY 3 - LEAST TECHNICAL

                             3-35

-------
   The checked controls represent the minimum number of technical controls
that could be used  for all  objectives which  have a possible technical  solu-
tion.   ICs must now be selected  for objectives  for which there is no
technical  control or for which the technical  controls will  not satisfy the
objective.  The process for making these  selections is the same as de-
scribed under Strategy 1.'  After the  ICs  are selected, Strategy 3 is
complete.   It is composed of the minimum  number of different technical
controls,  without considering their effectiveness, which can be applied to
the most objectives and the minimum level  ICs necessary to supplement the
technical  controls  for each objective that could be used for mitigation.

3.4.1 Example - Strategy 3, "Least Technical"
   The technical control with the highest frequency  (2) is sub-slab
ventilation.  For the first and  last  objectives, which have multiple
technical  controls  with frequencies of 1,  only the highest rated controls
were checked.

   ICs are  now chosen  to supplement  the technical  controls.  For prevent-
ing use of well water, using local health department restrictions is chosen
to supplement the technical control.   Because,  in  this case, it is believed
that sub-slab ventilation is adequate for control  of soil gas  intrusion
into the condos, no supplemental 1C  is chosen.   For reducing soil gas
intrusion into the single-family houses,  the low rating suggests that sub-
slab ventilation may be inadequate.   Therefore, a  strong 1C, the only one
listed in this example, was selected as a supplement.  Again,  the use of
the local building permit process is  chosen to prevent  inappropriate
construction and a consent agreement  with the PRP  is chosen to supplement
the pump  and treat technical control.  The strategy  alternative  is  shown  in
Table 3.6.
                                    3-36

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Strategy 4 - Most ICs"
   Illustrated in Figu
alternative 4 which is  discussed  below.
  •ategy 4  -  Most  ICs"
   Illustrated in  Figure 3-5  is  the  process  for developing strategy
  •.prnativp 4 whirh  ic  Hi smcspH hfOnw
•  Use a copy of the Master Matrix.

•  In the third column (Institutional  Controls), for each objective for
   which an 1C is given,  place a check mark by the control with the high-
   est effectiveness rating for that objective.

•  If purchase of the property is the highest rated, also place a check by
   the second highest rated 1C.  The objective here is to try to ensure
   the strategy does not default to  a "purchase the property"  option.

•  Place a flag by all occurrences of the checked controls.

•  Delete all unchecked and unflagged ICs.

•  Note that  if two or more controls have the  same  highest effectiveness
   rating for an objective or if property purchase  was checked, additional
   "Strategy  4" options can be developed by using each of the checked  con-
   trols sequentially.

   At this point, the best 1C for each objective, even if it is a poor
control, has been selected.  Also shown are the ICs selected for other
objectives which supplement the effectiveness of the selected 1C for each
objective.  Make a copy for use in developing Strategy 5.

   Technical  controls must now be chosen to supplement those institutional
controls that would not satisfy the objectives.
 •  Begin with any objective for which there is  no  1C or  for which property
   purchase was the only  1C checked.
                                    3-38

-------
                                           Use Copy of
                                           Moster Matrix
                Select
 Institutional  Controls
            Check Highest Rated Control
            For Each Objective. Check
            2nd Highest Rated if
            Purchase Checked. Flag
            All Occurrences
                                           Delete all Un-checked
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            Select
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                        No
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for Strategy 5
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            Addition to Purchase
                                                     Yes
 Check Lowest Rated Technical
 Control Satisfying Objective
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                                          No
                 Check Lowest Rated
                 Technical Control to
                 Supplement Non—purchase 1C
                                                              Yes
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                       Satisfy Objective
                                     Yes
    Delete all Un—checked and
    Un—flagged Technical Controls
                                    No
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                   Control to Supplement Combi-
                   nation of ICs to satisfy Objective
                       Figure 3-5.  STRATEGY 4 - MOST ICs

                                       3-39

-------
•  Place a check by the lowest  effectiveness rated technical control that
   will, at the least, ensure that the objective is satisfied without
   relying on property purchase as an 1C.

•  Repeat until all objectives  which have  no institutional control or
   property purchase as the only 1C are satisfied.

•  For objectives which have only property purchase and one additional  1C,
   select a technical control to supplement the secondary 1C, if neces-
   sary.

•  For all other objectives, review the effectiveness of the checked con-
   trol plus the effectiveness  of any supplemental controls (those select-
   ed for other objectives that also appear for this objective) and
   determine if the combined effectiveness will satisfy the objective.   If
   they will not,  a technical control must be selected.

•  Place a check by the lowest effectiveness rated technical control that
   will, at the least, ensure that the combination of technical and
   institutional controls satisfy the objective.   It is likely that those
   objectives  for  which the better institutional  controls were selected,
   will not require supplemental technical controls.

 •  Delete all  technical controls that were not  checked or flagged  for  at
   least one of the objectives.

   Strategy 4  is now  complete.  It is composed  of the best  institutional
 control, even  though  the control may be poor, for each objective and the
 minimum level  technical control necessary to supplement the ICs for each
 objective, that could be used to effect mitigation.
 3.4.1  Example  - Strategy 4, "Most ICs"
    The first step is  to place checks  by the highest  rated institutional
 controls.   This 1C  is property purchase  for all except the  last  objective.

                                    3-40

-------
Therefore, a secondary 1C is  selected where possible;  no  alternative 1C is
given for reducing soil  gas exposures.  Using  local health department
restrictions is checked as the secondary  1C for preventing use of well
water and using the local building permit process  is  chosen as the second-
ary 1C for preventing inappropriate  construction.

   The next step is to select technical  controls  for objectives with no
ICs or those with property purchase  as the only 1C.   In these cases the
technical controls must be adequate  to meet the mitigation objective
without regard to the 1C.  Technical controls  are  needed to reduce soil gas
intrusion in all occupied buildings. Modifying the  ventilation, which will
include sealing of major entry routes, is selected for the detached houses.
Sub-slab ventilation is selected for the  condominiums.   Following the
instructions, this control is also flagged for the single-family houses.
However, it will not provide supplemental control  in  this case because the
control is not applied to the same intrusion route.

   Next,  technical controls are selected to  supplement the secondary 1C
for those objectives with property purchase as the primary 1C.  An alterna-
tive water supply is needed to supplement the  health department restric-
tions on well usage.  For reducing groundwater contaminant concentrations,
it is assumed,in this case, that the consent agreement with the PRP is
adequate and no supplemental  technical controls are  needed.

   The completed matrix  is shown  in Table 3.7.  Based on  the  controls
selected, there are two possible Strategy 4's; one based on purchasing the
property and holding it until the groundwater  is  cleaned-up sufficiently
that indoor air impacts are not of concern, and one  based on using the sec-
ond highest rated ICs supplemented by providing an alternate water source
for single-family homes, installing  sub-slab ventilation for the condomin-
iums, and modifying the ventilation  in  the single-family homes.

Strategy 5 - Best ICs"
    Illustrated  in Figure 3-6  is the process  for  developing strategy
alternative 5 which is discussed below.
                                    3-41

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•  Use the copy made while developing ICs for Strategy 4.

•  Review the checked institutional  controls only and mark through all
   except those with the two highest effectiveness ratings.   If no insti-
   tutional controls were deleted,  Strategies 4 and 5 will be identical
   and there is no need to proceed with this strategy.

   Technical controls must now be selected for objectives for which there
is no 1C or for which the ICs will  not  satisfy the objective.   The process
for making these selections is the  same as described under Strategy 4.
After the technical  controls are  selected, Strategy 5 is complete.   It is
composed of institutional controls  with the two highest effectiveness rat-
ings and the minimum level technical  controls necessary to supplement the
ICs for each objective,  that could  be used to effect mitigation.

3.4.1 Example - Strategy 5, "Best ICs"
   In this case, property purchase is checked by all objectives except
reducing contaminant concentrations in groundwater.  A consent agreement
with the PRP is the 1C for this objective.  Technical controls must be
selected to supplement the ICs.  First, technical controls are examined for
objectives having only property purchase as an 1C to determine if any would
be adequate without the 1C.  For preventing use of well water, it is
assumed that simply providing an alternate water source without some
control in place to prevent continued use of the existing well systems
would be inadequate.  Therefore,  on technical control is chosen for this
objective.  For the condominiums, it is assumed that sub-slab ventilation
would adequately control the soil gas intrusion and it is chosen as a stand
alone control.   None of the technical controls are considered adequate as
stand alone methods for preventing soil gas intrusion into the single-
family homes and there is no technical  control given for preventing
inappropriate construction.  For this case, it will be assumed that the
consent agreement with the PRP is adequate and no supplemental technical
control is needed.  The strategy alternative, shown in Table 3.8, would
comprise purchasing all the developed and undeveloped impacted properties
and requiring the PRP to cleanup the groundwater.  It is apparent that this
                                    3-43

-------
               Select
 Institutional Controls
                                          Use Copy from
                                          Strategy 4
                                          Delete all ICs Except
                                          Two Highest Rated
           Strategy 4 = Strategy 5
              End Process
                                   No
        ICs Deleted
           Select
Technical  Controls
                        No
                                                  Yes
       Objective Has an 1C in
       Addition to Purchase
                                                    Yes
 Check Lowest Rated Technical
 Control Satisfying Objective
Objective Has More Than One 1C
in Addition to Purchase
                                          No
                 Check Lowest Rated
                 Technical Control to
                 Supplement Non—purchase 1C
                                                             Yes
                  Checked and Flagged
                  Non—purchase 1C will
                  Satisfy Objective
                                    Yes
    Delete all Un-checked and
    Un-flagged Technical Controls
                              No
             Check Lowest Rated Technical
             Control  to Supplement Combi-
             nation of ICs to satisfy Objective
                       Figure 3-6.  STRATEGY 5 - BEST ICs
                                      3-44

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would be an expensive alternative and may likely be  eliminated without
further consideration.

   At this point, a number of strategies have been developed that should
be effective in mitigating the indoor air impacts.   These will need to be
compared using the NCR evaluation criteria (EPA88b)  to determine which
strategy will be recommended for implementation.  In principle, all of the
strategies, as a subpart of overall site remediation efforts,  should be
effective.
3.4.2 Probable Costs to Implement and Operate
    Costs  should be considered in terms of the costs to implement the
remedy, the costs to operate and maintain the systems, and the length of
time that the systems must remain effective.  Ranges for installation and
operating cost were given in Section 2 for a number of technical mitigation
measures.  These costs are based on radon mitigation experience.  It should
be  taken  into account that cost may rise substantially if more sophisticat-
ed  equipment is used.  For example, when mitigating for high levels of
methane or other combustible gases, explosion proof installation may be
required  for electrical systems, fan motors, etc.  Likewise, installation
of  systems with backup power systems, monitors, or alarms will also
increase  costs.

    The time  the remedy must remain  in place  should be considered  in
determining  how a particular technical method will be implemented.  Note
that the  technical methods in the strategies developed above may be accom-
plished using different types of equipment and installation methods.  Vari-
ous tradeoffs should be considered  in estimating the costs  involved.

    For short-term  requirements,  these tradeoffs  might  include  selecting
less durable, and thus cheaper, equipment.   In these cases, the costs of
replacing components, both time and materials, should be  considered  in
determining  the total costs over the time period.
                                     3-46

-------
   In general, as the length of time that the method  must be in place in-
creases, the more reliable and aesthetically  appealing  the  installation
should become.  This invariably leads to higher  initial  costs  which may be
offset to some extent by lower operating,  including maintenance,  costs.

   The costs of implementing ICs must also be considered.  In addition to
the actual compensation paid,  when necessary,  cost may  also include
recording fees and other legal fees.  In many cases,  EPA contracts for many
of the legal services needed.   Because State  laws are quite variable, the
costs of implementing identical ICs in different areas  may  deviate consid-
erably.  It is recommended that Regional Counsel be consulted  for assis-
tance.

   The  costs of ensuring that  some  ICs remain effective for the required
period may be affected by the time period required.   For example,  ICs based
on contractual agreements, such as restrictive covenants, may vary in the
amount of legal effort required depending on  the time the covenant must be
effective.  If only short-term effectiveness  is  required, and conveyance is
not an issue, less extensive legal work may be adequate.  However, as the
effectiveness time increases, additional effort  may be  required to ensure
future owners would be bound by the agreement.
3.4.2 Example - Probable Cost to Implement and Operate
    In the  example used, for prevention of use of well water all strategies
rely on either purchase of the 10 homes using well water or providing an
alternate water source and using health department restrictions to ensure
use of existing wells does not continue.   Because public water is already
available  in the community, connecting the 10 homes to this supply would
likely be  the least expensive option.

    For reducing soil gas  intrusion  into existing buildings, several  types
of  technical controls are considered.  Institutional controls range  from
none, to purchasing single-family homes only, to purchasing all existing
homes.  Because drain tiles are already in place for the condominiums,
                                     3-47

-------
active ventilation of the tiles  would be fairly  inexpensive.   Drain tile
ventilation would be cheaper than  sub-slab ventilation, primarily because
less remodeling of the highly finished  lower floors  would be  needed.   For
single-family homes, drain tile  ventilation  is not  a possibility and sub-
slab ventilation is questionable due to the high likelihood of poor under
slab permeability.  If sub-slab  ventilation were used,  it is  likely the
costs would be high because all  lower  levels are highly finished and many
suction points may have to be used.  Because the slab floor and foundation
wall are poured concrete, it is  possible that  sealing major opening and
modifying the building ventilation would be both effective and relatively
inexpensive.  Ventilation improvements  would probably include providing
outdoor air as combustion air for  the  oil  furnaces  to reduce  depressuriza-
tion, and increasing the proportion of  return  air that is supplied to the
lower floor to increase pressure on that  level.

   For preventing  inappropriate new construction techniques,  no technical
controls are available and institutional controls are either  using restric-
tions available through  local building codes  or purchase  of the property.
Using the building  code  restrictions would appear to be significantly less
expensive and more  easily implement able.

    Reducing contaminant  concentrations in the groundwater  is part  of  the
overall site remediation plan.  The need to reduce  indoor air  impacts be-
comes part  of the  input  to remediation goals.   Cost would not be a consid-
eration for mitigating indoor air impacts  unless the indoor impact risks
drive the groundwater remediation levels required.
                                     3-48

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                          REFERENCES FOR SECTION 3
EPA88a Radon Reduction Techniques for Detached Houses: Technical  Guidance.
       Second Edition, EPA/625/5-87/019,  January 1988.

EPA88b Guidance  for Conducting Remedial Investigations and Feasibility
       Studies Under CERCLA.  EPA/540/G-89/004, OSWER Directive 9355.3-01,
       October 1988.

EPA89  Risk Assessment Guidance for Superfund: Volume 1 - Human Health
       Evaluation Manual  (Part A).  EPA/540/1-89/002, December 1989.

EPA91  Risk Assessment Guidance for Superfund: Volume 1- Human Health
       Evaluation Manual  (Part B, Development of Risk Based Preliminary
       Remediation Goals). Publication 9285.7-01B, October 1991.
EPA92  Assessing  Potential Indoor Air Impacts for Superfund Sites.
       451/R-92-002, October, 1992.
EPA-
                                    3-49

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                                SECTION  4
                 EVALUATING  A  PROPOSED  MITIGATION  STRATEGY
     This  Section  discusses general procedures that could be used  in
conducting a screening  review  of  indoor  air mitigation  strategies  that have
been proposed.   This is not general guidance for the  screening  analysis;
                                            *
rather, it represents a process that  may be a useful  tool for conducting
such an analysis.   The  review  is  useful  as  part  of  the  alternatives
screening process  described in section 430(e)(7) of the NCP.  The  proce-
dures in this section do not include, nor do they substitute for,  the
detailed evaluation of alternatives required for remedy selection.  Note  -
the screening referred  to here is only a preliminary  screening  to  eliminate
alternatives that  are significantly less effective, infeasible,  or grossly
excessive in cost.  The procedures in this  section  assume that  the reviewer
was not involved in the development of the  indoor air mitigation part of
the alternatives being  considered. The  procedures, however, may also be  of
benefit in reviewing mitigation strategies  under development.

4.1  OBJECTIVE  OF  EVALUATION
     The objective of this screening  evaluation  is  to determine  which
alternatives are adequate to proceed  to  detailed evaluation.  Comparisons
made during screening are generally made between similar alternatives with
only the most promising carried forward  for further analysis.   As  indicated
in Section 3, the  NCP requires that defined alternatives be evaluated
against the short- and  long-term  aspects of effectiveness,  implement-
ability, and costs.  The objective of Section 4  is  to assist the reviewer
in addressing these objectives and to provide procedures to ensure specific
concerns relevant  to the indoor air  impacts are  considered.

4.2  REVIEW SITE RELATED INFORMATION
     Any review of a proposed  strategy should begin with a  review  of the
information about  the site.  The  purpose of this review is  to determine if
                                    4-1

-------
all  pertinent information regarding  the  site  was  considered.  The  purpose
is also to determine if the  information  relevant  to  the  site  impacts  and
their possible mitigation approaches were properly assessed.  Most relevant
to this review are the contaminant  source type(s) and  strength(s),  the
route(s) of potential  impacts,  and  the estimated  duration  of  those impacts.

4.2.1 Contaminant Source and Route  of  Impact
     The background information  for  the  site  should  first  be  compared with
information from site investigation reports.   The objective  is  to  check for
consistency and completeness.  The  easiest way to conduct  this  check  is to
prepare a list during review of the information detailing  the types of
contaminants cited, the amounts or  concentrations in the various media, the
area and depth of those contaminations,  and the pathways for  pollutant
transport off-site and to receptors.  This information should then be
compared with site investigation reports to determine its  consistency.
Information which is inconsistent should be flagged.

     Pollutants and their potential  pathways  listed  in the site investiga-
tion reports, but not in the proposed  strategy background  information,
should be noted.  Any additional pathways for pollutants listed in the
strategy should also be noted.   These  pollutants and their pathways should
be evaluated to determine if additional  impacts  not considered  previously
may be present.  This is an  important  step because  it is possible  that  the
strategy may have been developed solely on documented current indoor  air
impacts and not considered additional  potential  future impacts.

4.2.2 Duration of  Impacts
     Duration of impacts is a significant driver for mitigation method
selection.  Therefore, it is important that the  proposed strategy has  taken
duration properly  into account.  The duration of indoor air  impacts given
in the  proposed strategy should be compared to the  time estimated for
completion  of remedial actions which treat or remove  the contaminants
responsible  for the impacts.  A similar  comparison  should be performed
regarding the time  estimated for residual pollutants, impacting on-site  and
off-site receptors, to remain at the site.
                                    4-2

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4.2.3 Comparison of Site Information to the Strategy
     The proposed strategy  should  be reviewed to determine whether or not
the information developed during the review of  background  information per
Section 4.2.1 has been considered.  Note that,  at  this point,  the review is
only to determine if all potential pollutants and  pathways  have been
addressed for the appropriate time frames.   The likely effectiveness of
those measures proposed by the strategy will  be reviewed  in  Section 4.4.

     Using the information  developed above,  prepare a table giving,  in the
first column, a list of all impact pathways,  the expected  duration of im-
pacts by this pathway, and the pollutants potentially impacting through
those pathways (i.e., those included in the proposed strategy  and those
added by the reviewer).  Pathways and pollutants added by  the  reviewer
(i.e., those potentially missed during strategy development)  should be
distinguishable, perhaps by using different color  writing,  from those in
the proposed strategy.  Review the various technical and  institutional
controls utilized in the strategy and list them individually across the top
as headings for each additional column.  Table  4.1 shows  the general
appearance such a table would have.  Individual technical  and  institutional
controls would be entered as headings for the columns under "Proposed
Technical and Institutional Controls".

     Beginning in column 2, place a check by each  pathway  to which that
control method is applicable and the pollutant(s)  it is  expected to control
to some degree (should be stated in the proposed strategy).   The reviewer
should also place a different mark in this column, such  as an  asterisk, by
each pollutant in column 1 the reviewer has reason to believe  would also be
controlled by this method.  Complete the table  for all proposed control
methods.  Place a flag, such as a red "x", in column 1 by any pathway, or
pollutant listed for a pathway, not addressed by at least one  control meth-
od.  Use a different kind of flag to indicate pathways  included in the
proposed strategy for which there is no supporting evidence in the site
investigation reports.
                                     4-3

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       Table 4.1  Example Format for Comparison of Site Information
Impact
Pathways
Ambient Air
Duration
Pollutant A
Pollutant B
Soil Gas
Duration
Pollutant A
Pollutant B
Groundwater
Duration
Pollutant A
Pollutant B
Proposed Technical and Institutional Controls
Control 1



Control 2



Control 3



Control 4



     The consistency and completeness  check  for  inclusion of source  infor-
mation is now complete.  It indicates  whether or not all  appropriate path-
ways and pollutants have been considered.   It does not indicate the  con-
trols are adequate for the mitigation.

4.2  EXAMPLE REVIEU SITE RELATED INFORMATION
     The Strategy 1 alternative presented  in Section 3 will be  used  for the
example application of the methods described in this Section.   It will be
assumed that only the  information given in that Section was provided to the
reviewer.  Information in that Section should be consulted as  necessary.

     The first step is to create the review table (see Table 4.1 and Table
3.4).  The completed table is shown as Table 4.2.  Begin by reviewing the
information provided for the source of the contamination in Table 3.4 such
as pollutants, amounts, area/volume contaminated, and transport pathways.
The proposed strategy  mentions only one pollutant, TCE.  However, the
source was identified  as a storage tank for a manufacturing facility, and
based on the groundwater migration rate, 0.5 ft/d, and the extent of
contamination, pollutant found 1,200 yds from the tank, it is  likely the
                                     4-4

-------
release has been occurring for at least  20 years.   It  is likely,  therefore,
that other pollutants,  either from material stored in  the tank over 20
years or degradation of the JCE in the groundwater,  should have been found.
Analytical data from the monitoring conducted should be obtained and
reviewed.  In Table 4.2, additional pollutants are listed as Pollutant B.
The duration expected was determined from remediation  plans for the site.
These plans indicated site remediation would take  no more than 10 years.

       The proposed strategy indicated monitoring  was  done in fall and
winter and that only low concentrations of JCE were detected in the ambient
air.  The ambient air pathway was not considered further.  As no informa-
tion was provided regarding potential changes in the depth of the water
table, due to snow melt or spring rains, and the effect that might have on
surface emissions, this pathway for pollutants released into the air near
the buildings and possibly drawn into the indoor environment may have been
incorrectly discounted.  Additional information on variations in water
table depth are needed.  Monitoring or modeling may be needed to estimate
the importance of this pathway.  This additional potential pathway was
added to the table.

     Soil gas intrusion and indoor uses  of the contaminated groundwater
were pathways given in the strategy.  Because other pollutants besides TCE
are expected, a "Pollutant B" was added to each pathway.

     The proposed technical and institutional controls given in Table 3.4
are listed across the top of the table.   For ambient air impacts  (soil gas
rising to surface near the building), it is likely that the "Pump and
Treat" and "Consent Agreement" controls would reduce the indoor air
impacts.  Therefore, a check is placed by TCE, listed in the strategy, and
an asterisk by Pollutant B, added by the reviewer.  None of the other
controls are expected to reduce the ambient air impact.

     For the soil  gas intrusion pathway, check marks are placed by 5 of the
controls.  The first two are technical controls that work to prevent soil
gas entry into existing buildings.  The "Building  Restriction" control
                                     4-5

-------
works to prevent entry into any additional  buildings  constructed.   The
remaining two controls, "Pump and Treat" and "Consent Agreement",  work to
reduce the contaminant concentration in the groundwater and,  thus, the
potential for impact by any pathway.

     For the indoor use of groundwater pathway, 5  controls work to reduce
or prevent impact from use of groundwater.   These  range from stopping
current usage to ensuring clean water is used for  new construction to
remediating the groundwater in order that unrestricted usage may occur.

4.3  REVIEW IMPACTED STRUCTURE/AREA INFORMATION
     A critical  review of information presented  for the impacted area and
structures involved should be conducted.  The presumption should be that
the strategy proposed  is based solely on information  in the documentation
provided to the reviewer supporting that strategy.  It is important,
therefore, to assess whether or not all appropriate issues were addressed
and whether or not the information  is consistent with information developed
during the assessment  phase of the  investigation.   Review will be most
easily accomplished if a table is prepared similar to that developed in
Section 4.2.  Place in column 1 the review areas listed below, leaving
space under each for sub-issues.  Significant areas for review to be
included in the table  are the expected duration of impacts, the develop-
mental status of the affected area, current uses,   intended future uses,
pollutant  levels measured or estimated  for existing structures, pollutant
levels estimated for future development, and structural characteristics  of
the  soil and  buildings.  See Table  4.3.
                                     4-6

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Table 4.3  Example Format for Reviewing Impacted Structure/Area Information
Review Areas
Duration
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Current Uses
Intended
Future Uses
Pollutant
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Structural
Information
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4.3.1 Developed vs Undeveloped Land
     Using information from site  investigations,  indoor  air impact  assess-
ments, and the proposed strategy, determine if the impacted area is devel-
oped or undeveloped.  Strategies  proposed for developed  areas may rely
heavily on technical controls for specific properties whereas strategies
for undeveloped areas may rely on source control  and institutional  con-
trols.

     Strategies for developed areas may address only those properties known
to be currently impacted.  If the expected duration of impacts is short as
a result of site remediation efforts or other factors which will reduce
pollutant concentrations in the affected area and little or no additional
development is expected in this time frame, such a strategy may be accept-
able.  However, if similar or greater impacts are expected to occur for
several years, the strategy should address mitigation of potential  new
structures.
                                     4-8

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4.3.2 Current and Intended Future Uses
     The proposed strategy should state  the  current uses of the  impacted
area.  Current usage information should  include whether the area is used
for heavy or light industrial,  commercial  office buildings, high density
residential, single-family detached housing, and schools.   It should
indicate whether the area is urban or rural, or other information to
indicate population density.  If mitigation  is  proposed for only a small
number of structures, the strategy should  indicate the current usage of
those structures.

     If adverse impacts  for the  area  are projected to continue for several
years, the proposed strategy should include  a discussion of intended future
uses.

4.3.3 Measured and Estimated Level of Impact
     The proposed strategy and supporting  impact assessment information
should be compared to determine  if measured  and estimated  impact levels  are
consistent.  In this section of the table  being created, list the pollut-
ants contained in the table created in Section  4.2 above (Table  4.1).
Beside each, insert information  given in the proposed strategy for the
measured or estimated indoor air concentration  of that pollutant which is
attributed to impacts from the  site.   If no  concentration  data are given
for a pollutant, insert  an "N"  in this space.  Compare these  to  the concen-
trations given in the indoor air impact  assessment document.   Place a check
by those that are in substantial agreement,  a question mark by those in
significant disagreement, and an "x"  by  any  of  the pollutants not listed in
the assessment document.

4.3.4 Structural Characteristics
     The strategy should be reviewed  to  determine if  the characteristics of
structures for which mitigation  is proposed  have been adequately addressed.
For cases in which future development must also be considered, the assumed
characteristics of those structures should be reviewed.
                                    4-9

-------
     Structural  characteristics  are most  important when  the  impact pathway
is by intrusion of groundwater or soil  gases.   In these  cases,  the con-
struction details must be reasonably  well described  to provide the basis
for an adequate review of the applicability of mitigation techniques.  The
basic information that should be addressed in  the proposed strategy or
supporting assessment document include  (adapted from EPA88b):

General
     •      Type of building construction; brick, frame, etc,
     •      Building shell leakage; leaky, moderate, tight,
     •      Building exposure; open terrain, nearby  woods or buildings,
            heavily forested,
     •      Water source; private well  or off-site supply,
     •      Substructure type; full  slab on grade, full  crawl  space, full
            basement, or combination  of above,
     •      Evidence of moisture problems; water marks,  mold or mildew,
     •      Vented combustion devices;  fireplace, oil  or gas furnace,
     •      Evidence of asbestos-containing materials
Floor in contact with ground
     •      Depth/height of floor below/above  grade,
     •      Material; open soil, poured concrete, block, brick, stone,
     •      Drains; floor drain, French drain, weeping tile system beneath
            floor, connect to sump septic tank or sewer,
     •      Soil beneath floor; gravel  (4 to 6 inches),  soil permeability,
     •      Floor joint to wall; length and width of crack,  type of sealing
            material,
     •      Floor condition; utility  openings, floor cracks,
     •      Floor covering; unfinished, carpeted, etc.,
Walls connecting with floor in contact with ground
     •      Depth/height below/above  grade,
     •      Material; poured concrete,  solid block,  hollow block  (top
            blocks filled or solid?), hollow block with  plenums concrete
            filled, other,
     •      Wall condition; utility openings,  vents, windows, cracks,
                                    4-10

-------
     •      Wall covering; unfinished,  partially finished,  fully finished
            as living area.

     Assumptions made for new construction  in  currently  developed areas or
in undeveloped areas should be reviewed to determine if they are in general
agreement with normal construction practices for the area.   Assumptions
made based on significantly more expensive construction  techniques should
be flagged for comparison with any proposed institutional  control that
might require such construction.

4.3.5 Proposed Technical and Institutional  Controls
     Complete the table  under development  by listing  the various  technical
and institutional controls utilized in  the strategy individually across the
top as headings for each additional column.  Beginning in  column 2, place a
check by each item of column 1 which is addressed for that  control method
in the proposed strategy.  The reviewer should also place  a different mark
in this column, such as an asterisk, by each item of column 1 the reviewer
has reason to believe would also be addressed  by this method.  Complete the
table for all proposed control methods.  Place a flag,  such as a red "x",
in column 1 by any item not addressed by at least one control method.  This
would also include pathways or pollutants  added by the reviewer and
potentially overlooked during strategy  development.  Use a  different kind
of flag to indicate which, if any, of the  items in column  1 lack adequate
documentation to justify their inclusion in the strategy.

4.3.6 Completion of Review
     The consistency and completeness check for inclusion of information
for the impacted area is now complete.   It indicates whether or not all
appropriate items have been considered.  It does not indicate that the con-
trols are adequate for the mitigation.   If there are significant data gaps,
the reviewer should obtain missing information deemed necessary to complete
the review.
                                    4-11

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4.3  EXAMPLE REVIEW IMPACTED STRUCTURE/AREA INFORMATION
     Information related to the  impacted area may be  reviewed by developing
the information suggested by  Table 4.3.  In  table  4.4,  information from the
strategy description (see Section 3)  is  included in the  Review  Areas
column.   In an actual case, more information,  as discussed in the  preceding
sections, would be included for pollutants and for structural details.   The
technical and institutional controls  from Strategy 1  are listed across the
top as column headings.  The  "N's" are placed by the  pollutants for both
current and future concentrations indicating that  the discussion in Section
3 did not give actual or estimated indoor pollutant concentrations.
Concentration data are needed for both condominiums and single-family homes
to assess whether the 90 to 95 percent reduction objective given is
realistic.

     For current purposes,  the discussion provided in Section 3 for the
proposed strategy adequately  addressed the developmental status and the
likely future uses of the property, developed and undeveloped.   All of the
structural  information requested by Section  4.3.4  was included  and ad-
dressed  in  the  strategy except that pertaining to  asbestos, floor cracks,
and the utility room drain to the septic system for the single-family
homes.  Asbestos is unlikely in the construction described.  Because the
lower floors of the buildings are fully  finished,  floor cracks  probably
cannot be fully assessed until mitigation begins.   However, because French
drains, hollow  block walls, a sill plate,  and a brick veneer were used in
the condominiums, all of which provide excellent pathways for intrusion of
soil gases, cracks are  a minor issue at  this stage.

     In each of the columns,  checks are  placed by  each review item ad-
dressed by  the  particular control.  Asterisks are placed by review  items
added during  the previous review  step to which  the control is also  applica-
ble.  The effect of  the  "Alternate Water Source" control is primarily on
current homes  and  checks are placed by 5 items, all  related to current
single-family  homes, and one  item for future impacts.  The latter is added
because  installing  the  alternative water system to the single-family homes
provides  an in-place system to service some new or modified construction.
                                     4-12

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For "Drain Tile Ventilation",  additional  checks are placed by several
structural items because these items were specifically considered in
selecting this control  for the Strategy 1 alternative.  Checks are placed
by all items for "Building Restrictions"  except for current concentrations
of indoor air pollutants.   Note that checks are also placed by current uses
because the building restrictions would apply to any modifications to
existing structures.  This is the only control that addresses soil gas
intrusion from the septic systems through the floor drains and then only
for new/modified construction.  The strategy did not specifically address
mitigation of current structures for this potential soil gas intrusion
through the floor drain, the trap of which likely is not consistently water
filled.  This can be a major entry route and must be addressed.

4.4  REVIEW PROPOSED MITIGATION STRATEGY  TECHNIQUES
     Assuming the necessary information has been obtained,  the reviewer
should proceed with assessing whether or not the proposed strategy is like-
ly to satisfy the mitigation requirements.  Elements of this review which
are discussed below are:
•    comparing the strategy to those successfully used in previous cases,
•    modifications of prior successful  strategies needed to satisfy the
     specific case,
•    reasonableness  of control effectiveness estimates,
•    reasonableness  of cost estimates,
•    enforceability  of institutional controls proposed.

4.4.1 Comparability to Strategies Used in Similar Cases
     Confidence in a proposed strategy is increased if it uses similar
mitigation methods to those that have been successful  in comparable cases.
There are only a limited number of  implemented indoor  air impact mitigation
strategies at CERCLA sites at which EPA was the lead Agency.  Although
                                    4-13

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confidence will  not be as high for proposed  strategies  not using those
control methods,  they should not necessarily be  discarded.   Performance
information for the control  methods,  as discussed  in  Sections 4.4.2 and
4.4.3 below, may be useful  for assessing their applicability in specific
cases.  Performance information is also indicated  in  the case examples in
the Appendix.

     Information  about the  performance  of indoor air  impact  mitigation
strategies may also be available for sites at which  a State Agency had the
lead.  Performance information may also be available  for Radon program
activities and RCRA program cleanups.

4.4.2 Applicable to Specific Case
     Using the information  developed  in Sections 4.2  and 4.3,  information
contained in the proposed strategy document, and other technical informa-
tion such as that in Section 2, the reviewer can assess the applicability
of each control proposed to the particulars  of the specific case.  Informa-
tion in the proposal on the applicability of the method and its limitations
should be reviewed and compared to the site  specific information developed
in Tables 4.2 and 4.4.  For each control method  on these tables, review the
information provided to determine if the method  is applicable to the items
checked.  Look particularly for items that may be major impediments.  For
example, drain tiles blocked with water during wet weather are a major
impediment to drain tile ventilation.  If major  defects are found, the
strategy should be eliminated from those that will be subjected to detailed
evaluation for selection of the remedy.

     If no major defects are found,  the reviewer should consider the meth-
ods being proposed to mitigate a specific type of impact, such as use of
contaminated groundwater, as a group.  Attention should be given to any
group of methods that rely on several substantially similar techniques to
effect incremental control  as this may be an unreliable approach.  Atten-
tion should also be given to groups that contain a large number of differ-
ent techniques for the control of a type of impact.   This may indicate that
the strategy proposed is more conservative than  necessary.
                                     4-15

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4.4.3 Reduction Estimates Reasonable
     Estimates of indoor contaminant reductions for each  specific  type  of
indoor impact in the proposed strategy should  be  compared to known or
estimated performance for the controls proposed.   See Section 2.   Most
confidence in the reduction estimates occurs when only one or two control
methods are responsible for most of the contaminant  reduction and the
estimated control effectiveness is less than the  demonstrated performance
in similar applications.  Least confidence occurs when several methods,
each with estimated effectiveness at the limit of demonstrated or theoreti-
cal performance, are proposed to control a single indoor impact pathway.
Attention should be given to the methodology used to arrive at the overall
control effectiveness estimated.  In general,  performance information is
based on each control as the only one in use.   The combined effectiveness
for several controls based on similar techniques  may be less than expected
for simple addition of the effectivess of individual  controls.

     The reviewer should tabulate the control  effectiveness information in
the proposed  strategy for each specific type of indoor impact and compare
it to the estimates developed during the review.   Estimates substantially
above or below  those in the strategy should be flagged for additional
review.  All  estimates  should be compared to the objectives stated in the
proposed strategy to determine if those objectives are met.

4.4.4 Cost  Estimates Reasonable
     Cost estimates in the proposed strategy should be compared to pub-
lished  ranges,  or recent Agency experience, for  installation  and  operation
of the  methods  used.  Regional counsel  should be contacted to verify costs
of implementing ICs unless concurrence  of the counsel regarding costs  is
contained  in  the proposed  strategy.  Cost estimates  should be examined  to
determine  if  they have  been  properly  adjusted for the region  of the country
and  escalated properly  from  the base year for which  the  cost  were reported.
Cost  for post-mitigation diagnostics  and costs for checks  to  verify
technical  and institutional  controls  remain effective should  also be in-
cluded.
                                     4-16

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     Cost estimates  should be reviewed to determine  if  site  specific con-
ditions have been taken into account.  These might  include such items as
additional expenses for ICs due to complex  state  laws and contractor
expenses in support of property acquisition.  They  may  also  include
temporary relocation expenses of affected  parties,  and  remodeling expenses
due to installation of technical controls.

4.4.5 Enforceability
     Enforceability applies to the institutional  controls used.   The pro-
posed strategy should contain regional counsel concurrence with the con-
trols proposed.  If the proposed strategy  does not  contain this concur-
rence, possibly indicating counsel review  was not obtained,  counsel should
be contacted for an opinion.  Particular attention  should be given to un-
usual ICs, those that rely on police powers of local governments, those
that rely on PRP property interests, and any 1C that must be effective
beyond the end of the remedial action.   The remedy  available in the event
of a breach should also be considered.   If remedy is limited to damages  and
does not allow enforcement of the 1C,  effectiveness of the 1C is substan-
tially reduced.
4.4  EXAMPLE - REVIEW MITIGATION STRATEGY TECHNIQUES
     Comparability to Strategies Used in Similar Cases -- The technical
controls "Alternate Water Source" and "Pump and Treat" proposed are proven
technology and have been shown to be effective for the general type
applications proposed.  "Drain Tile Ventilation"  and "Modify Ventilation"
have been used, primarily for radon mitigation, with mixed success (see
Section 2).  There is little experience with these techniques at CERCLA
sites.  All of the institutional controls, except the consent agreement
with the PRP, rely on police powers of the local government.  There is a
mixed history using this type of control.  Thus, although there is some
experience with the controls, the experience is not extensive and thus
there is some cause for concern with the methods used in this strategy
alternative.
                                    4-17

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     Applicable to Specific Case  --  The  information provided indicates  that
site specific consideration have been taken into account.   Specifically,
the likely permeability of subsurface soils and building construction
details were considered in selection of techniques for the alternative.  No
more than one technical control and one institutional control were given
for control of any single objective.  Thus, the alternative is likely not
to be overly conservative.  Thus, the reduction achieved should be similar
to that achieved  in prior applications.

     Reduction Estimates Reasonable --  Although not  specifically stated in
the proposed strategy, all technical methods proposed have been shown,   in
similar or related applications, to equal or exceed the 90 to 95 percent
reduction stated  as the objective.  And because no more than one technical
control and one institutional control were given for control of any single
objective, the reduction achieved should be similar to that achieved in
prior applications.

     Cost Estimates Reasonable -- The proposed strategy discusses likely
costs in  relative terms rather than specifics.  There is no way to know
from the  discussion what  the  likely final cost would be.

     Enforceability -- Enforceability of the ICs was not discussed.  No
information was given  on  assurances or binding  agreements made to  ensure
these would not be changed.   Considering the pressure to develop for this
area, such assurances  should  be  obtained or the ICs should  be considered
unreliable for the 10  year period proposed.

     The  strategy has  several flaws, pointed out above, that should be
addressed before  the  strategy is accepted  as a  potential remedial  alterna-
tive.   These  include  the  ambient air pathway,  soil gas  intrusion  through
floor drains,  and reliability of the ICs proposed.
                                     4-18

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                         REFERENCES FOR SECTION 4

EPA88a  "Guidance for Conducting  Remedial  Investigations and Feasibility
        Studies Under CERCLA",  EPA/540/G-89/004,  OSWER Directive 9355.3-01,
        October 1988.

EPA88b  Radon reduction Techniques  for  Detached Houses: Technical Guidance
        (Second Edition).   EPA/625/5-87/019.  January 1988.
                                    4-19

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                                 SECTION  5
        EVALUATING EFFECTIVENESS  OF IMPLEMENTED MITIGATION  STRATEGY
     This section includes  evaluation exercises and procedures useful  for
reviewing the basic elements of implemented  indoor  air  impact mitigation
strategies.  Section 5 provides assistance in  conducting  a quantitative
evaluation to determine the technical  effectiveness of  an applied mitiga-
tion technique.  In some instances  information is provided on corrective
actions which may be taken  when technical  systems are found ineffective.
Section 5 provides assistance for the  evaluation of ICs which govern the
strategy's operation.

     Evaluation of the effectiveness of  technical controls  soon  after their
installation is normally done as part  of any CERCLA cleanup.  The site
manager may also require reviews of all  control techniques as deemed
appropriate.  Review of indoor air  mitigation  measures  at a site may also
be part of the 5-year reviews required by CERCLA.   These  reviews are
required at least every five years  after initiation of  cleanup  at sites
where hazardous substances, pollutants,  or contaminants remain  on-site at  a
level that does not allow for unlimited use  and unrestricted exposure.
Section 5 provides assistance with  the conduct of 5-year  reviews that may
be required.  This assistance is supplemental  to CERCLA and does not
supersede any CERCLA requirements.

5.0  EXAMPLE - BACKGROUND
     Application of evaluation procedures  discussed in  this Section will be
applied to a soil gas migration problem experienced at  a  group  of townhouse
clusters built on land next to an active landfill.  Methane was detected
entering into basements and slab on-grade structures  of buildings proximate
to the landfill.  The source of the methane was the decomposition of buried
refuse.
                                    5-1

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     The  land adjacent  to  the  landfill was  initially undeveloped but zoned
for residential.   Development  of the property was desirable.   Local
authorities were,  however, concerned that  some impacts  from  soil gas migra-
tion, due the presence of buried refuse, might occur  in buildings  con-
structed on the property.   Therefore,  an  institutional  control was utilized
that worked through the building permit.   Any developer of the property was
required to remove any refuse  buried beneath proposed building foundations
and to install passive venting systems.  A number of  townhouse clusters
were subsequently built in accordance  with the institutional controls.

5.1  TECHNICAL EFFECTIVENESS
     Quantitative  testing  of the building  indoor air  should  be conducted to
determine if the projected reduction  in pollutant levels has been  achieved.
It is recommended that the monitoring  methods and procedures described in
"Assessing Potential Indoor Air Impacts for Superfund Sites", EPA  451/R-92-
002, be used for this purpose.  It should be noted, however, that  proce-
dures in that manual for estimating the intrusion of pollutants  into the
structure will likely not be applicable if soil gas ventilation  systems
have been installed.  In these cases,  sampling only the ambient  and  indoor
air  and comparing the results  to premitigation concentration levels  may
provide a measure of the reduction achieved.  Any sampling methodology used
should be designed and implemented by qualified individuals.

     Two types of monitoring may be required:  direct indoor air pollutant
measurements under existing conditions and diagnostic type testing to
assess control probability under conditions less favorable to control
techniques in place.  Diagnostic testing may  also be used to ensure the
system is operating as intended and to find the cause of system failure  so
that corrective actions may be  taken.

5.1.1 Direct  Indoor Air Measurements
     Comparison of short-term direct indoor air measurements to  premiti-
gation conditions can  serve as  an  indicator of  the level of mitigation
achieved.  However, because many variables may  have changed,  the  reduction
determined may not  be  completely attributable to the mitigation systems.
                                     5-2

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If direct testing is conducted under conditions  expected to result in
worst, or near worst, case conditions for impacts,  or if impact is from a
pollutant not normally found in indoor environments this type testing may
be adequate.

     Air sampling may need to be conducted periodically  to  account for
seasonal variations.  Direct testing for soil gas impacts during warm
weather will likely be inappropriate in some regions of  the country because
building stack effects and permeability of surface soils may not be ade-
quately addressed.  Building stack effects tend  to be greater during cold
weather because the temperature difference between the indoor and outdoor
environments is larger.  In addition, ground surface permeability is
reduced when it is rain soaked, frozen, or snow  covered, resulting in a
lower transport of soil gas contaminants through the ground surface.  Under
these conditions, pollutant concentrations in the soil gas may increase and
an increased volume of soil gas will tend to move towards and through
openings in the building shell in contact with the ground.   Testing for
control of  impacts from groundwater intrusion during protracted dry periods
is likely to overestimate control effectiveness.

5.1.1 Example - Direct Indoor Air Measurements
     After three townhouse clusters were constructed,  indoor air sampling
measurements were made using spot and continuous monitoring.  The measure-
ment results showed one housing cluster reached  explosive methane concen-
trations; another cluster had moderate methane concentrations; and a third
cluster was unaffected.

     Testing was conducted in late winter and early spring when the ground
surface in  the area was saturated from winter snow melts.  It was felt that
soil gas intrusion would be at a maximum at these times because the ground
surface would have a low permeability under these conditions, and because
there would be a  large stack effect in the buildings due to the substantial
indoor/outdoor temperature differences.  A large stack effect was expected
to result in good performance of the passive ventilation system.
                                     5-3

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     The indoor only testing,  although  definitely  indicating  indoor
impacts, did not provide adequate information to determine if soil gas
concentrations had substantially increased in certain areas of the complex
or if some of the passive systems were not functioning properly.

5.1.2 Diagnostic Testing for Effectiveness
     Diagnostic testing using  building  depressurization may be used  to
simulate building stack effects.  The building may be depressurized  either
using mechanical means (e.g.,  blower doors; see Section 2) or by increasing
the indoor temperature to well above the outdoor temperature.  Mechanical
depressurization does not, in general,  provide a realistic test of passive
ventilation systems which rely on indoor/outdoor temperature differences to
create  the vacuum needed for ventilation.

     By monitoring the indoor air while artificially lowering the building
pressure, an  indication of control effectiveness during cold weather
operation may be obtained during warm weather.  However,  the method is
likely  to give  inaccurate indications of control effectiveness if soil gas
pollutant concentrations are  substantially below those upon which the
strategy was  based.  Soil gas concentrations may be low due to a number of
possible factors including lower water table and increased permeability of
non-frozen ground surfaces.

5.1.2 Example - Diagnostic Testing For Effectiveness
        Several  engineering studies of the site were conducted over the
spring  and summer months.  These studies  included detailed mapping of soil
gas  concentrations  throughout the complex.   Concurrent with  the soil  gas
napping,  indoor temperatures  were increased  to  simulate winter operations.
One  study  indicated that  a significant amount of the methane  was migrating
from refuse present within property  boundaries  and  recommended removal of
All  or  part  of the  on-site refuse and  the possible  installation of  a
perimeter gas-control  system.   Gas collection systems at  the property
boundaries were installed but the indoor testing showed that  this was
ineffective  in controlling methane entry into basements.
                                     5-4

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5.1.3 Diagnostic System Testing with Corrective  Actions
     If it is determined that  the  level of mitigation  is  insufficient,
diagnostic testing of the system may be conducted.   Diagnostic testing can
aid in the identification of design or installation  errors or omissions
and/or system modifications that may improve  the efficiency of the system's
operation.  Basically, there are three reasons for performing post-mitiga-
tion diagnostics on a system:   1)  to ensure that the system is operating as
intended; 2) to identify system modifications that might increase the level
of mitigation; and (3) to provide some indication of cold weather operation
during warm weather testing as discussed  in Section  5.1.2 above.

     No definitive set of diagnostic procedures  exists for the testing of
mitigation systems.  Post-mitigative radon diagnostics have been performed
by researchers and mitigators.  A portion of  the testing may be done with
the building artificially depressurized.  This technique is useful during
mild weather to simulate the behavior of  the  building during cold weather.
A "blower door" is useful to achieve the  desired negative pressure (about
0.05 inches water column).  The blower door  is simply a large fan that may
be attached to an exterior door and exhausted outdoors until the desired
indoor to outdoor pressure differential  is  achieved.  Some of the tests
that have been used by diagnosticians are:

     Visual inspection and smoke stick testing.-- Inspection of system
components should be performed, including the integrity of sealed entry
routes, system duct connections and hangers,  fan wiring, etc.  Each compo-
nent should be inspected for proper installation and operation.  The diag-
nostician should pay .particular attention to  the effects of HVAC system
operation relative to the mitigation system operation.

     A smoke tube with an attached aspirator  bulb or a smoke punk is a use-
ful tool when conducting visual inspections.  The smoke permits the evalu-
ator to see otherwise invisible and/or imperceptible air movement.  Air
movement across unsealed entry routes or  across  separate floors of the
building may be easily tested by releasing  smoke in  or near the opening to
                                    5-5

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be tested.  Even slight air flow across  an opening will  cause  the smoke
pattern to drift in the direction of the air movement.

     The pressure field created  by sub-slab depressurization systems  can
easily be tested with smoke tubes.  Test holes may be  created  by drilling
through the slab with a 3/8 inch bit remote to the suction point.  The
system's pressure field may be tested by gently  releasing a steady stream
of smoke from the tube near the test hole opening.   A  good sub-slab suction
field will draw the smoke stream into the test hole.   This test may also be
performed using unsealed openings rather than test holes.  Incomplete suc-
tion fields may then be addressed by modifying the system.

     An example of a typical smoke tube  aided inspection might proceed as
follows.  Measurements of the indoor air indicate an insufficient reduction
in indoor contaminant levels.  Diagnostic testing of the single suction
point,  sub-slab depressurization system indicates a  portion of the sub-slab
region  is unaffected by the mitigation system.   The  diagnostician identi-
fies a  concrete footing obstructing the extension of the pressure field.

     The system is modified by installing a second suction point through
the  slab  on the other  side  of the footing.  Diagnostic testing of the modi-
fied system indicates  full  extension of the  sub-slab depressurization
field.  Screening measurements of the indoor air indicate a significant
reduction in  indoor contaminant  levels.  Follow-up measurements will be
taken to  ensure  seasonal weather variations  do not cause  indoor contaminant
concentrations to  increase.

     Pressure and flow measurements.-- Active  soil  ventilation systems and
forced-air ventilation  systems require  the mechanical  movement of air  for
proper  operation.   Pressure and  air  flow measurements taken at points  along
the  system can  indicate system  imbalances, blockages, and/or  excessive air
leakage.   Inadequate  pressure and  air flow could require  an increase  in  fan
capacity  or a reduction in  the  systematic resistance caused by excessively
long duct runs,  numerous directional changes,  etc.  Flow  velocities  in
pipes  and ducts  can  be measured  using pitot tubes or hot-wire anemometers.
                                     5-6

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     Sub-slab and wall  void  pressure field measurements.-- Active  soil
ventilation systems can be tested for  proper  operation  by measuring the
suction at various points under the  slab.  An evaluation  of  how well  the
suction field is extending to various  sections of the slab may be  made.
Measured pressure differentials will likely be very small.   A micromanome-
ter sufficiently sensitive to detect differentials of 0.01  inches  water
column is a useful tool when conducting  pressure  field  measurements.

     On/off cycling of the mitigation  system  and  recording of pressure
differentials may be useful  in verifying proper system  operation.   Pressure<
field extension measurements can be  made through  3/8-in.  test holes drilled
through the slab at various points remote to  the  ventilation point.  Such
measurements can be particularly useful  if the initial  level of mitigation
is unsatisfactory.  Modification of  the  system, to include additional ven-
tilation points, may be indicated in areas in which the pressure field of
the system is insufficient.

     Measurements to ensure proper venting of combustion  appliances should
be performed.  Active mitigation systems may  draw indoor air from the buil-
ding through former entry routes and in  effect depressurize  portions of the
building.  This depressurization may effect the draw of exhaust flues.  Air
flow measurements and smoke pencil testing should demonstrate that air
movement in exhaust flues is consistently upward during mitigation system
operation.

     Spot contaminant measurements.--  If the  level of mitigation is unsat-
isfactory, direct-reading instruments  (such  as an OVA), adequately sensi-
tive for the particular pollutant(s) of concern,  may be used to identify
"hot spots" in the building.  Identification  of these hot spots may
indicate unaddressed entry routes or additional sources.   System modifica-
tions can be designed based on these spot contaminant measurements.

     Ventilation measurements.-- The effects  of the mitigation system on
the ventilation rate should be evaluated.  A  qualitative estimation of the
effects of the system on the building's indoor air flow patterns can be
                                    5-7

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made using the smoke stick testing procedures above.   Combustion  appliances
should be checked to ensure back-drafting of exhaust  flues  does not  occur
due to the operation of the mitigation system.   Excessive air flow through
the building may cause occupant discomfort generating complaints  of
"drafts".

     Mitigation systems relying on the dilution of indoor concentrations of
contaminants with uncontaminated outdoor air can be evaluated by  determin-
ing the ventilation effectiveness of the combined HVAC/mitigation system.
Increased outdoor air exchange may exceed HVAC system capabilities and/or
cause heating and cooling expenses to dramatically increase.   Determining
ventilation effectiveness in a building is complex and should only be
performed by experienced and well qualified diagnosticians.  Whole building
air exchange rates may be estimated, but in order to test the entire
building, tracer gases must be used.  When interpreting the tracer gas
data, the diagnostician must consider the dynamics related to weather
conditions, mitigation system operation, and HVAC system operation.

5.J.3 Example  - Diagnostic Testing with Corrective Action
     After perimeter soil gas extraction proved unsuccessful, alternative
strategies were investigated.  Numerous families had already been evacuat-
ed.  Control to at  least 100 ppm methane in a confined space was set as  the
objective  (This study, which was not conducted  in the United States,
contained  the  following rationale for  this objective: "...a proposed
standard of 100 ppm has been suggested  in the United States for a methane
concentration  in a  confined space.").  Because  a passive venting system  had
been  installed (required by the  institutional  control) using a drain tile
system  around  each  townhouse cluster,  the next  logical step was to convert
the system to  an active drain  tile  ventilation  system which was accom-
plished by attaching  suction fans to  the existing passive venting systems.

     However,  after the fans were installed negligible sub-slab soil
depressurization resulted  and  the required reduction of methane gas entry
was not achieved.   Diagnostic  testing of the mitigation  system components
was conducted.  Smoke testing  of entry routes  was conducted  and sub-slab
                                     5-8

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pressures were measured in test holes drilled into the townhouse floors.
Smoke released near the entry routes was not draw into the opening and the
pressure tests showed that the sub-slab pressure was nearly the same as
ambient pressures.  These tests indicated" ttnt a pressure field had not
been established.  Pressure gauges were- installed at various points in the
drain tile collector pipes and relative vacuum measured while the fans were
in operation.  In some parts of the system, a good vacuum (e.g., < -25 Pa)
was achieved.  However, in large sections of the system, there was no
measurable difference between the pressure fn the drain tiles and ambient
air.  This revealed that the perimeter drain tfles connected to the modi-
fied venting system were severely blocked with silt and debris and major
zones were, in effect, not connected to the vacuum system.  These blockages
drastically reduced the performance of the system.

     After numerous attempts to remove the blockages from the perimeter
drain tiles failed, a sub-slab depresst/rization (SSD) system was installed
and activated.   The SSD system incorporated two suction points through the
interior basement floor slab into the underlying  layer of aggregate and
visible entry routes were sealed.  Smoke testing of test holes and entry
routes was again conducted.  Visible air movement generated by the opera-
tion of the SSD  system indicated that a negatively pressurized sub-slab
region had been  achieved.

     Pressure and flow measurements taken at points along the systems using
manometers did not indicate system imbalances, blockages, or excessive air
leakage.  A sub-slab pressure differential of approximately -15 Pa was
found indicating a good pressure field extensfon under the slab (pressure
differences less than -5 Pa would indicate a poor pressure field exten-
sion).

     Air monitoring, using an organic vapor analyzer with a flame ioniza-
tion detector),  for the presence of methane indicated a significant reduc-
tion in indoor concentrations.  Indoor concentrations of methane were
reported to be below 100 ppm with few exceptions.  In townhouses or clus-
                                     5-9

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ters which showed consistently elevated methane levels,  additional suction
points were installed with favorable results.

     System failures were simulated to  determine the effect  of possible
system down time on indoor methane concentrations.  The system failure
simulations indicated that elevated indoor methane levels might occur under
some conditions (such as immediately following heavy rainfalls or during
periods when the ground was snow-covered or frozen) and that secondary
technical measures should be considered.  Because indoor concentration rose
rapidly when the fans were not operating, an auxiliary power source was
considered to ensure limited system down time during power failures.
However, the local utility company was contacted and indicated that the
maximum power failure duration reported for the community over the  last 2-
1/2 years was 84 minutes.  Therefore, costly back-up power or other
technical measures were not considered warranted.   Meticulous entry route
sealing was considered adequate to reduce the short-term entry rate of
methane-laden soil gases.

5.2  INSTITUTIONAL CONTROLS
     Institutional controls implemented as part of the strategy should be
reviewed to ensure they  are achieving the desired objective(s), are being
followed,  and remain  in  effect.  This will generally involve efforts of
both on-site evaluators  and legal  professionals.

     The mechanics of the ICs should be reviewed to determine if they are
working.   Examples  include determining  if property-based restrictions, such
as easement and covenants, are included in deeds  resulting  from property
transfers  and determining  if  restrictions based on  police powers,  such as
well use  restrictions, zoning classifications,  building permit require-
ments,  etc., have  been changed.

     It should  be determined  if the property is being used  inconsistently
with the  ICs.   The inspector  should  compile  a  list  of  activities  prohibited
 by the ICs prior to on-site  inspection.  Examples which the inspector
 should look for include  inappropriate  well  usage  and excavations.    If the
                                     5-10

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ICs include restrictions on development,  the inspector should look for, for
example, inappropriate land use,  such as  increased residential  construc-
tion, and construction techniques inconsistent with the restriction.  For
example, standard construction techniques may have been used rather than
techniques required to resist soil  gas intrusion.

     The ultimate measure of whether or not an 1C  is achieving  its objec-
tive, however, is the reduction in risk that resulted from its  use.  If the
1C is being followed as planned and exposures have not been reduced by the
projected levels, then the 1C is not adequately effective.  If the 1C has
been ignored or circumvented and appropriate legal actions are either not
being taken or are inadequate to enforce the 1C, the 1C is inadequate.

     In some cases, it may be difficult to separate the effectiveness of an
1C from the effectiveness of technical controls applied.  For example,
consider a hypothetical case in which landfill gases are migrating in the
near surface soil and impacting a nearby occupied building.  Because on-
site monitoring showed that most of the indoor air impact was from soil
gases entering through the slab floor, a sub-slab ventilation system was
installed to control the primary impact pathway and an 1C prohibiting exca-
vation on the property was applied to ensure no channel was opened for the
gas to escape to the surface.  Follow-up testing showed indoor air concen-
trations were still elevated, that the sub-slab ventilation system was
operating as designed, and that ambient air concentration were higher than
previously measured.  These data are not adequate to determine if the
technical control failed because it did not control a significant pathway
into the building, or whether the 1C failed because it inadequately
addressed the potential for gases to migrate to the surface and be drawn
into the building.  More extensive diagnostic testing would be required to
determine the appropriate additional measures to take.

5.2  Example - Institutional Controls
     In this example, a fairly simple 1C was used that operated through the
building permit process.  It required only that refuse buried directly
below proposed townhouse foundations be removed and that a passive drain
                                    5-11

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tile ventilation system be installed.   The information provided for the
example indicates the 1C was complied  with exactly as written.   That
information also shows that the 1C was inadequate.

     Because the drain tile systems were  plugged,  it is  impossible  to
determine whether or not the 1C could  have worked.  However,  it is  likely
that either specifications for the installation were  inadequate or  that
installation inspection requirements were inadequate  or  not followed.
Also, because the sub-slab depressurization system performed well,  it is
quite possible that the fan assisted drain tile ventilation system  would
also have worked.  Thus, the failure of the 1C to ensure an adequate drain
tile system also prevented the use of  an efficient and inexpensive  technol-
ogy.

      In this case example, it would have been appropriate to examine the
1C for  the above concerns as soon as  it was discovered that the drain tiles
were plugged.  It may have been possible at that stage to modify the 1C for
construction of additional townhouse  clusters.  As this case was concluded,
the ICs for future development require removal of buried refuse and
installation of sub-slab ventilation systems operated in vacuum mode.
                                     5-12

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  APPENDIX
CASE STUDIES
     A-l

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                           APPENDIX:  CASE STUDIES

      The case studies presented in this Appendix  are  examples  of mitigation
activities used in real situations.  Information upon  which  they are based was
obtained from a survey of the Regional  Air/Superfund Coordinators and discus-
sions with other Agency personnel  knowledgeable of, or directly involved in,
the mitigation activities.  The examples do not include all  case examples
obtained, nor do they represent all indoor air mitigation  activities that have
been conducted.  They were selected to  present a range of  situations and miti-
gation activities that might be encountered.   However, because  the number of
cases obtained is small, not all situations or mitigation  techniques could be
included.  There are currently several  cases,  in which indoor air impacts are
documented or considered highly likely, for which  mitigation strategies are
being developed or implemented.

      Two of the six case examples presented illustrate techniques used to
mitigate indoor air impacts in buildings in which  the  pollutant of concern was
radon released from improperly disposed radioactive wastes.   These cases do
not  include all of the activities undertaken to mitigate all impacts associat-
ed with radioactive wastes.  This document is not  intended as a manual on
radon mitigation methods.  Techniques used to mitigate radon have been used to
mitigate indoor air impacts from other types of pollutants in soil gases and,
thus, their inclusion  is relevant to the purpose of this document.
A.I   CASE  STUDY  1  - VOCS IN GROUNDWATER UNDERLYING SLAB ON GRADE CONSTRUCTION
      A  plume  of  contaminated groundwater, containing trichloroethylene (TCE)
and other chlorinated solvents, migrated from a near surface discharge at a
manufacturing  facility into an adjacent residential subdivision.  The plume is
moving along underground pathways, apparently in both shallow, 10 to 20 feet
below ground surface, and intermediate, 40 to 50 feet below surface, flow
zones.
                                      A-2

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      The plume passes beneath several  residences,  down  a  steep  hill,  and
beneath the library of an elementary school.   TCE  concentrations in  groundwa-
ter near the school of over 7,500 ppb have  been  measured.   Soil  gas  monitoring
wells were installed around the school.   The  maximum concentrations  of soil
gas VOCs detected, 99 ppm v/v 1,2 DCE and TCE, were found,  at 3  foot depth,  10
feet from the school library on the side  facing  the plume  source.   Indoor air
monitoring was conducted in the school.   Elevated  levels of VOCs were found  in
several areas.  The maximum concentration found  was for  TCE,  100 ppb v/v, in
the library.

A.1.1 Structural Characteristics
      The 6 residences which were mitigated are  all duplexes constructed over
slabs on grade.  The school is a two-story  building constructed  slab on grade.
However, because the building was built on  a grade, the  library  connects with
the second floor of the building.  There is at least one above grade crawl -
space adjacent to the library.  Heating and ventilation  in the library is
accomplished  using self-contained forced-air exterior wall  units to which
steam is piped from the boiler room.  The steam pipes penetrate  the floor
slab.  Additional  cracks along the slab/floor interface are present.  Although
as built construction drawings were not obtained,  it was suspected that a
French drain  tile  system was  installed to facilitate water drainage beneath
the library structure because a possible drainage pipe was found in a catch
basin manhole.

A.1.2 Systems Installed
       Initial  efforts at the  school  included increased ventilation of the
library  and  installing  a fan  to ventilate the crawl space.  These proved to  be
inadequate.   A sub-slab depressurization system, based on radon mitigation
guidance similar  to  that described  for Case  Example 3 below, was installed.
This  system  includes  alarms  to  indicate malfunction of the system.  The  ex-
haust  from the sub-slab depressurization system is  treated by activated  carbon
to reduce VOC emissions  and  possible reintroduction to the building  through
the  air intake system.

       Sub-slab depressurization systems  were also  installed  at  each  of  the  6
                                      A-3

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impacted duplexes.  Although these systems included malfunction alarms, carbon
adsorbers were not installed on the exhausts.

A.1.3 System Effectiveness
      The systems have been in operation for 2  years.   Overall  operation has
been good.  Indoor air monitoring has been conducted.   TCE levels of about 1
ppb v/v were found.

A.2   CASE EXAMPLE 2 - LANDFILL GAS MIGRATION,  METHANE
      Indoor air impacts from migrating gases from landfills entering into
basement and slab on-grade structures is frequently encountered.  This case
example summarizes such a soil gas intrusion problem experienced by a develop-
ment of townhouse clusters sited adjacent to an active landfill.  The study
focused almost exclusively on methane, which in some units exceeded explosive
limits.  Limited data on VOCs, which were also present, were contained in the
investigation report.

A.2.1 Building and Site Characteristics
      The townhouse community is comprised of 14 townhouse clusters of 3 to 12
units.  There are a total of 81 townhouse units in the development.  Each two-
story unit has a full basement, a gas-fired hot water heater, and a forced air
furnace.  Some foundation walls are constructed of concrete masonry units and
others are cast-in-place, poured concrete.

      Prior to construction, local authorities anticipated the potential for
methane intrusion problems due to the presence of buried refuse on the site
and the adjacent landfill.  Therefore, an institutional control was placed on
the undeveloped property via the permitting process.  Prior to the issuance of
a building permit, the local authorities required the developer to agree to
install a passive venting system on each townhouse cluster and remove  any
buried refuse from beneath the proposed building foundations.

      The passive venting systems were installed during building construction
for all townhouse clusters with the exception of the two clusters furthest
away from the landfill.  The passive  venting systems consisted of a 150 mm
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diameter perforated plastic big "0"  pipe  laid around  the  exterior of the per-
imeter building foundation.  A 100 mm  diameter non-perforated  riser was at-
tached to the big "0" pipe at the end  of  each townhouse cluster and extended
vertically to the top of the building.  Passive venting systems rely on two
natural phenomena to develop the suction  needed to draw soil gas away from
sub-slab entry routes:  1) air movement generated by  wind currents across the
roofline that develop a low-pressure region near the  roof;  and 2) the natural
thermal effects resulting from buoyant forces inside  the  vertical riser.

      Three perimeter methane collection  systems were also installed on the
landfill/townhouse development property border.  The  collection systems were
intended to control the migration of methane laden soil gas from the adjacent
landfill.  Indoor air sample results indicated that the perimeter collection
systems were ineffective.  The occupants  of a majority of the  townhouse units
were evacuated.

       Several  studies were conducted to evaluate the methane migration  and
intrusion problems experienced on the  site.  One investigator hypothesized
that a significant portion of the methane was being generated from the  decom-
position of refuse buried within the townhouse community boundaries.  His
recommendation was to remove the buried refuse and install a perimeter  gas-
control  system.  No mention of the application of soil ventilation technology
was made in his  recommendations.  The property owners questioned  the feasi-
bility of the  recommendations  and decided to explore alternative  possibili-
ties.

       Another  investigation of the  site was  conducted  by a firm familiar  with
radon  mitigation using  soil gas  ventilation  and  suggested that  active  soil
ventilation may  be  a  cost-effective and suitable control strategy.   An  objec-
tive  of the  strategy  involved  using a  phased  approach  under experimental  con-
ditions to derive  a  technical  control  measure  applicable to the entire  town-
house community.

A.2.2 Methane  Levels
       While  the  engineering studies of the site  were being  conducted,  indoor
                                      A-5

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air samples were being collected and  analyzed.   The source of the methane was
the decomposition of buried refuse and  the  transport mechanism was soil  gas
migration.   Air monitoring for the presence of  methane in the indoor air,
outdoor air, and soil gas was conducted using spot and continuous monitoring.
The measurement results showed elevated concentrations of methane in the in-
door air of several of the townhouse  units.  In order to efficiently and me-
thodically mitigate the entire townhouse community, three townhouse clusters
were selected to undergo an experimental mitigation study.  Of the three clus-
ters selected for mitigation, the indoor methane concentrations in one housing
cluster reached explosive concentrations; another cluster had moderate methane
concentrations; and the third was used  as the control.  However, during the
time the study was being conducted, methane levels in the control cluster
remained low.

      A measurement protocol was defined and calibration of instrumentation
using calibration gases and cross-referencing with a continuous monitor was
performed throughout the data collection process.  All measurements were col-
lected on the basement level.  A box fan was used in the basement to circulate
and mix the air in an attempt to identify an average concentration in the
basement air.  Basement doors were closed during the sampling except to allow
entry into  and exit from the building.   Air monitoring was conducted in four
phases:

            1)    the pre-pumping phase,
            2)    the active-pumping phase,
            3)    the post-pumping phase, and
            4)    the alternative assessment phase.

      The purpose of the pre-pumping phase monitoring phase was to create  a
baseline for methane levels  in the subject clusters  and  to evaluate the  ini-
tial concentrations  in passive vent stacks.  Active-pumping monitoring evalu-
ated whether the depressurization of the sub-slab  region would  be effective  in
reducing methane entry into  the basements of the townhouse units.  The post-
pumping phase was designed to establish  the rate of  methane build-up  in  the
event of system failure.  The alternative  assessment phase was  performed to
                                     A-6

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optimize system performance and to resolve outstanding  issues.   A methane con-
centration of 100 ppm was selected as an  appropriate  mitigation  level.

A.2.3 System Installed
      The proposed initial technical  control  involved attaching  an in-line fan
to the existing passive venting system to apply a suction  field  of -25  pascals
in the vent pipe at the furthest point from the fan.   Upon connectivity test-
ing, the perimeter big "0" piping system  was found to be severely blocked with
silt and debris.  These blockages drastically reduced the  performance of the
system.  Where possible the blockages were removed or the  big "0" piping was
replaced.  Three in-line Kanalflakt fans  were installed on the vertical risers
and the active sub-slab depressurization  (SSD) system was  activated.   In sev-
eral instances where the existing venting system was  of negligible use, a se-
ries of interior suction points were installed and tied into the unperforated
big "0" pipe mounted on the exterior of the building.  The interior suction
points were installed by penetrating through the interior basement floor slab
into the underlying layer of aggregate.  Pressure and flow measurements taken
at points in the sub-slab region and in the vent stacks were collected to
determine optimum system performance.

      System failures were simulated during the Alternatives Assessment Phase
to determine the effect of possible system down time on indoor methane concen-
trations.  The  system failure  simulations indicated that indoor methane levels
rose substantially  in some townhouses over several hours.   Local utility com-
pany records indicated that the maximum power failure duration reported for
the community over  the last 2-1/2 years was 84 minutes.  Therefore, back-up
power was not considered  likely to be warranted.

A.2.4 Volatile  Organic Compound
      Many volatile organic compounds were detected  in the soil gas, base-
ments,  and  in the  system  exhaust  pipes.  These  included several freons,  halo-
genated organics,  benzene, toluene,  and  aliphatic  hydrocarbons. • Vinyl  chlo-
ride,  about  2 ng/rt?, was detected in the system exhaust gases at one cluster.
The investigators  did  not consider the VOCs  to  be  of concern  and no  informa-
tion was presented  on  the percent reduction  achieved by the  installed  systems.
                                      A-7

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One set of 10-minute grab samples of VOCs in basement air and  vent gases was
collected while the depressurization system was active to determine if a cor-
relation existed between the pollutant concentrations in the vent gas and the
basement air.  The results were inconclusive.

A.2.5 Conclusions Reached
      This study was conducted on a limited number of the affected buildings
to determine the feasibility of active soil gas ventilation as a technical
control measure for the entire complex.  The conclusions were:

      1.    Active soil gas ventilation in a depressurization mode is an ef-
            fective technical control measure for reducing methane entry into
            the residential structures.  During the course of the investiga-
            tion, reductions up to 99.9% were achieved.
      2.    Active soil ventilation in a pressurization mode did not prove
            effective  in reducing methane entry into the structures.  Poor
            soil porosity and the decomposition of buried refuse below the
            structures may have contributed to the system's ineffectiveness.
      3.    Individual sub-slab depressurization systems were more effective
            than the modified perimeter venting system.  A poor connection
            between the sub-slab aggregate layer and perimeter perforated pipe
            was assumed to be the cause of the ineffective remediation.
      4.    Based on the analysis of the unit with the highest initial methane
            concentrations, a depressurization of 15 pascals was sufficient to
            reduce ambient basement methane levels to less than 15 ppm.
            Therefore, a depressurization of 15 Pa was recommended as an
            effective  operating sub-slab pressure differential.
      5.     In the event of fan failure, elevated methane concentrations may
             still be realized.  Therefore,  implementation of auxiliary control
            measures may be necessary.
      6.    Air monitoring for volatile organic compounds in the exhaust air
             stream was performed.  The concentrations measured were suffi-
             ciently low that their uncontrolled discharge was not considered  a
             problem.
      7.    Carbon monoxide monitoring was  also performed and low concentra-
                                      A-8

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            tions reported.   Therefore,  carbon  monoxide was not considered a
            concern.

A.3   CASE EXAMPLE 3 - RADON MITIGATION FOR BASEMENT AND CRAWLSPACE
      The contaminant source was improperly disposed radium and related radio-
nuclides.  The material was  disposed at various location and has impacted
several different buildings, both commercial  and residential.  Similar
mitigation techniques were used in all locations,  although details of the
installations are highly site specific.  This example considers the mitigation
at only one of the affected  properties.

      Some of the general specifications for all work were:

      •     Source control.   Remove as much of the contaminated soil and de-
            bris as practical.
      •     Cut and patch structural elements so as to not reduce load-carry-
            ing capacity or load-deflection ratio.
      •     Cut and patch construction exposed on the exterior or in occupied
            spaces  so  as to not reduce the building's aesthetic quality or
            result  in  visual evidence of the cut and patch.
      •     Use materials identical to, or which match, existing materials.
            Remove  existing floor or wall coverings and replace with new mate-
            rials,  if  necessary to achieve uniform color and appearance.
      •     Avoid  interference with use of, or free passage  to, adjoining
            areas  so as  to  allow for  owner occupancy and use by the public.
      •     Install products, materials, and system components to provide
            adequate space  for  inspection, adjustment,  future  connections,  or
            replacement, where  appropriate, avoiding interference with  other
            building components requiring  similar access.
       •     Maintain  a set  of  "as  built" drawings.
       •     Upon  completion,  clean  each  surface or  unit to the condition  ex-
            pected in  a normal  building  cleaning  and maintenance  program.

 A.3.1 Building  Characteristics
       The impacted structure is two-story  single-family residence with  a  par-
                                      A-9

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tial basement and two crawlspaces.   The main  structure  is  built over a partial
basement that has been extensively remodeled  (See Figure A-l).   It has been
partitioned into four areas including an office,  laundry room with enclosed
toilet, heater room (gas-fired hot water system), and general purpose room.
The basement floor is concrete.  It is covered with 9 x 9  inch tiles in the
heater and general purpose rooms and carpet in the other areas.  All walls,
except the interior of the heater room, are covered with patterned boards or
sheet paneling.  The ceiling joists, except in the heater  room, are covered
with decorative tiles.  Foundation walls are  poured concrete, 12 inch thick to
grade level and 8 inch thick from grade to framing level.

      There is an attached crawl space at the  rear of the basement with access
from a hatch cut into the paneling in the laundry area. The crawl space is
exposed sandy soil.  Heat piping running through the space to service above
living areas is suspected of containing asbestos.  Joists  are exposed and have
thermal insulation in place.  There is an operable window  in the rear founda-
tion wall.

      There is also a crawlspace in the front of the building below a single
story porch remodeled for use during temperate weather.  Soil is exposed in
the crawlspace.  Areas between the brick foundation piers  are enclosed around
the front  steps with open lattice work in the remaining front and side areas.

      The  main floor is finished and contains the living  room, kitchen and
pantry.   Bedrooms are located on the second floor which was  in the process of
being  remodeled.

      The  roof is a gable-type structure with sheathing boards and asphalt
shingle cover.

A.3.2  Radon Levels
       Radon levels recorded in the basement air  averaged 11  pCi/1.  Samples
taken  at  two locations within floor areas measured 700 and 2,850  pCi/1.
                                     A-10

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Fan
        o
                 •J,  CRAWLSPACE
      OFFICE
    H
                       LAUNDRY
                                   CXQ
                      Stairs
                       RECREATION
                 PORCH
        Foundation Wall
        Solrd Pipe
      '• Perforated Pipe
o Vertical Pipe
^ Sewage Pipe
* Floor Suction
     Figure A-1 Soil Ventilation System
                     A-ll

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      Minimum expectation of the mitigation system installed was to provide a
radon level below the current EPA Action Level  of 4.0 pCi/1.  The intention
was to provide an indoor radon level approaching outdoor levels.

A.3.3 System Installed
      Mitigation at this location included installation of lead shielding to
provide reduction in gamma radiation levels to exposure levels of at or below
20 micro-roentgens per hour.  Details of this installation are not included in
this example.

      Penetrations of the basement floor and foundation walls were sealed.
The sewage drain line penetrated the basement floor.   The area between the
pipe and the concrete floor was thoroughly cleaned and sealed with gun grade
urethane.  Water and gas lines penetrated the foundation wall.  The openings
were cleaned and filled with hydraulic cement.  After the cement cured, gun
grade urethane was applied to the cement/pipe interface.  The toilet in the
basement was removed and the base and floor thoroughly cleaned.  Silicone
sealant was applied and the fixture replaced.  A crack in the basement floor,
approximately 20 feet long, was expanded with a small hand held grinder.   Dust
generated was controlled using a vacuum cleaner, with a HEPA filter, that ex-
hausted to the outside.  The crack was filled with flowable urethane.

      Suction points for the sub-slab depressurization system were opened in
the basement floor at two points.  One was in the heater room and located in
the northeast corner of the building near the front foundation wall.  The
second point was located near the south foundation wall of the basement in the
corner of the laundry room nearest the center of the basement wall.  In both
places, a 5-inch diameter hole was drilled through the floor (dust controlled
as above) and approximately 4 gallons of sub-slab material removed forming a
hemispherical shape.  Three-inch diameter PVC pipe was installed in the hole.
The opening was filled with hydro-cement and sealed around the pipe/cement
interface with flowable urethane.   In-line dampers were installed in both
pipes.  The two points were manifolded by running PVC pipe up the walls and
along the 12 to 8 inch foundation wall transition shelf.
                                     A-12

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      Ten feet of perforated 3-inch  diameter  pipe was placed  in  the  crawl
space and connected to a solid wall  riser  pipe.  An  inline damper  was  placed
in the riser pipe and the riser was  connected to the manifold.   The  perforated
pipe and entire crawl space floor was covered  with an EPDM membrane.  The mem-
brane was sealed to the foundation walls with an expandable urethane spray
foam.

      A 5-inch diameter hole was drilled through the crawl space  wall and the
manifold pipe routed through the hole.  The manifold was connected to  an in-
line fan using a vibration and sound absorbing rubber coupling.  The installa-
tion was sealed using urethane caulk.  The fan exhaust  was routed  vertically
from fan housing to above roofline using ultra-violet light tolerant PVC pipe.

      A flow verification switch was installed on the negative  pressure side
of the fan and an "on when running"  indicator light  and audible  alarm  with
override switch installed.  The fan  was wired to run continuously  and  connect-
ed to a different circuit from those used  for the  indicator light  and  alarm.
All  system electrical connections were made to a separate  panel, located in
the  heater room, which was identified as the  Sub-slab Depressurization Control
Panel.

      The system was activated and all leaks  sealed.  The  pressure field under
the  slab was measured, making use of several  small  holes drilled in the floor,
and  the adjustable dampers positioned to  achieve  the desired  vacuum at all
locations.  The dampers were sealed  in place and  the diagnostic holes  patched.

A.3.4 System  Effectiveness
      Discussions with the RPM for the site  indicated the system reduced  in-
door air radon levels to  design specifications given in Section A.3.2.

A.4   CASE  EXAMPLE 4 - AMBIENT AIR  PCB DUST,  SOURCE CONTROL
      Indoor  air  impact  at  several  residences occurred from wind borne dusts
from a  nearby unpaved road.   Dust control  measures for the roadway  had  includ-
ed oil  application.   The  oil  used contained  PCBs.   Dusts in the buildings were
collected by  taking  wipe  samples.   No  indoor air monitoring was done.   The
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contaminated soil  surface of the road was removed and treated to destroy the
PCBs.  The treated soil  was reused as backfill  for the road and the road was
paved.

      Access agreements  with the residents were obtained and each residence
was thoroughly cleaned to remove the PCB dust.   This included vacuuming, sham-
pooing carpets and dust  removal  from all surfaces.  Follow-up dust wipe sam-
ples were negative for PCBs.  Mitigation was complete and no further action
was needed.

A.5   CASE EXAMPLE 5 -   RADON MITIGATION, MULTIPLE TECHNIQUES
      Following demolition in 1985 of a building used for radium dial  painting
from about 1932 to 1978, aerial  and ground level radiation surveys of the
surrounding area detected 20 areas with abnormally high gamma radiation lev-
els.  Subsequent investigations  and site consolidations reduced the number of
sites to 14 with elevated levels due to an industrial source.  The suspected
sources of the contamination are improperly disposed trash and debris  from a
second building demolished in 1968 which also housed a similar radium dial
painting operation.   The affected areas included unrestricted public access
areas, residential  properties, businesses, and  school areas.   Radium contami-
nated soils were present at both surface and depths exceeding 3 feet.

      Radon screening tests were conducted in several homes in 1986.  Two
homes with indoor radon  levels greater than 200 pCi/1 and a third home with
levels exceeding 1,000 pCi/1 were found.  About 800 ft3 of contaminated soil
was removed at one home.  The State purchased the third home as this was more
cost effective than  remediation.

      A second survey was conducted in 1988 using the following criteria from
the U.S.  EPA's "Citizen's Guide  to Radon":

      Tier I      200 pCi/1  or Higher
                  Action should  be taken within weeks to reduce levels to as
                  far below 200  pCi/1  as possible.   Temporary relocation may
                  be appropriate if mitigation  must be delayed.
                                     A-14

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      Tier II      20  to  200  pCi/1
                  Actions  should  be  taken within months to  reduce  levels  to  as
                  far below  20  pCi/1  as possible.

      Tier III    4 to 20  pCi/1
                  Actions  should  be  taken within a few years  to  reduce  levels
                  to  4 pCi/1  or lower.

      Tier IV     4 pCi/1  or Below
                  No  action  indicated.  Exposures are considered average  to
                  slightly above  average.

      For buildings falling  in  Tier  III, confirmatory measurements were made.
Alpha-track monitors  were  placed  in  the buildings for one month  to confirm
levels.  If the screening  level was  above  10  pCi/1,  confirmatory testing  also
included 7-day working level monitors.  If the  levels were  confirmed,  a gamma
radiation survey was  also  conducted.  Only buildings with elevated gamma  lev-
els were considered radium-contaminated properties.

      Only 62 of the 67 buildings designated  for  radon  screening were tested
because either the owner could  not be contacted,  the canisters were not re-
turned, or the owner refused.  One building was designated  Tier I, 3 buildings
Tier  II, 8 buildings Tier III,  and 50 buildings Tier IV.  Gamma surveys were
required at 6 buildings but one owner refused.  Mitigation  plans were prepared
for the four buildings in Tiers I and II.   The  estimated  costs to mitigate
these 4 buildings was $98,000.   Mitigation systems  were installed at only
three of the locations.  The fourth home  owner  rejected the mitigation plan
and,  in 1990, an action memorandum was signed to  move  that  home to an uncon-
taminated property owned by the homeowner.

A.5.1 Mitigation of Buildings  1 and 2
      Mitigation at two of the affected structures  used sealing and sub-slab
depressurization much as described  in Case 1  above.   A brief description  of
the building  and specific differences in  mitigation procedures  are given  be-
low.
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      Building 1 is an auto repair garage.   The  walls are hollow cement block
capped with vitreous tile coping.   The walls sit directly on the concrete
floor.  Two interior enclosed spaces, an office  and two washrooms, are con-
structed with cement block.  The shop floor is open and has several floor
drains, "alligator " cracking over the entire surface, and several large stru-
ctural cracks, including a continuous shrinkage  crack at the floor wall joint
indicating the building is settling unevenly. The floor is also penetrated by
plumbing for two toilets and a water line.

      Standard mitigation procedures were used to seal the floor cracks and
utility penetrations.  A sub-slab depressurization system was installed using
three suction points.  None of the floor drains  had traps and all had to be
completely replaced.  This involved removal of about 18 inches of concrete
floor around each drain, replacing the drain with a trapped drain with inte-
gral clean-out, replacing the concrete, and sealing around the new joints.

      Building 2 is a 50 year old one and one-half story frame house with an
800 ft2 full  basement.  The basement has a  concrete slab floor and concrete
foundation walls to 4 ft high with the remainder of the wall constructed of 12
in. by 12 in. terra-cotta hollow block layered on mortar.  Each course is laid
at right angles to the adjacent course, providing a seal between courses.  The
stair horses, for the stairway leading to the first floor, and wooden support
posts for the main beam penetrate the basement floor.  The 2 to 3 inch thick
concrete floor is cracked throughout the entire  area.  A floor drain by the
shower also penetrates the floor and connects to the city sewage system.

      The cracks around the shower drain and wood penetrations were sealed by
removing damaged concrete, replacing that concrete, and sealing the new joints
with urethane.  A sub-slab depressurization system with three suction points
was installed, running the manifold  into a. storage area on the first floor
where the inline fan was installed, with the riser pipe penetrating the roof.
Major cracks  in the basement floor were patched  by grinding out a small sur-
face channel  and filling it with flowable urethane.  The entire surface was
coated with a mixture of sand and Velkum 351.   It  is expected that this mate-
rial will flex with the floor and accommodate future settlement of the struc-
                                     A-16

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ture.

A.5.2 Mitigation of Building 3
      This residential structure was built in the  1950's.   The property had
been a strip mine, a swamp,  and then filled in and divided into lots.   The
structure is built over both crawl space and a partial  basement.  The crawl -
space, which covers 60 percent of the area, is composed  of several  subcompart-
ments with poor accessibility.  The basement is not livable space.   There is a
high water table and a sump is located in the basement to  collect and remove
water from under the slab.

      Initial mitigation efforts focused on sub-slab depressurization in the
basement  and pressurizing the crawl space.  The depressurization system was
installed by placing a cover over the sump, inserting the  suction pipe through
the cover, running the manifold into the attic where the fan was installed,
and exhausting through the roof.  All floor and wall penetrations were sealed.
Heat ducts were removed, replaced, and the new duct joints sealed.   Prepara-
tions for crawlspace pressurization included sealing all exterior openings,
all  connections to the basement,  and installing plywood on the joists above
the crawlspaces.  A hole was cut  in a closet floor above the crawlspace and a
pressure  verification switch with alarm  placed in the crawlspace.  A duct was
inserted  through  the  hole and sealed in  place.  The duct was connected to a
fan installed  in  the  closet wall.  Performance requirement was that the system
maintain  a minimum pressure difference between the living  area and the crawl-
space of  4 pascals.

      Testing  over the  next two years  indicated that  radon concentrations were
slightly  above the objective  of 4 pCi/1  but  that  in the last  6 months  the
system  performance was  deteriorating.   In  addition, the crawlspace  fan had
failed  at least twice and,  on  the last occasion,  a  new  type fan  was  installed.
A decision  was made  to  modify the system.

       The sub-slab depressurization  system was checked  by  drilling  a  small
 hole in the floor & ft  from the  sump  with the intent  of measuring  the pres-
 sure.   The soil on the drill  bit  was  wet clay.  In addition,  the hole quickly
                                      A-17

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filled with water.  The sump cover was removed and the sump examined.   The
solid plastic sump had 2 inches of water.   Several 0.5 inch holes were drilled
into the sump sides and floor to extend the depressurization under the base-
ment floor.  Also, a more powerful suction fan was installed.  The following
day the system was checked with the system in operation.  No pressure connec-
tion to the sump was observed at the test  hole 6 ft away.  Radon levels in the
test hole were <10 pCi/1.  No further changes were made to this part of the
system.

      The access hatch to the crawl space pressurization fan was opened.  It
was observed that, when the new type fan was installed, its position was al-
tered such that dust and dirt collected on, and blocked, the intake screen re-
sulting in gradual degradation in performance of that part of the system.  In
each accessible crawlspace, perforated pipe was laid down below a membrane
soil cover.  The cover was not sealed to the walls as this was impractical.
The perforated pipes were manifolded with solid PVC pipe and routed through
the closet into the attic where an inline fan was installed.  Exhaust was
routed through the roof.

The modified system has controlled indoor radon levels to within the objective
of 4 pCi/1.

A.6 CASE EXAMPLE 6 - MITIGATION IN PROGRESS, VINYL CHLORIDE FROM LANDFILL
      This case example is presented to illustrate actions being taken to
prevent indoor impacts from occurring.  It contains some of the administrative
and institutional controls needed to effect this  proactive measure.  Assess-
ment of the problem is still underway and the final mitigation strategy for
the site is not complete.

A.6.1 Site Description
      The  70-acre landfill, closed in 1983 after  reaching permitted capacity,
is situated in an abandoned sand  and gravel quarry.  The landfill is divided
into three waste disposal areas;  the solid waste  area  is about 30 acres, the
sewage sludge area is about 15 acres, and the bulky waste area is about  11
acres.  Records indicate that drums of waste glue containing VOCs had  been
                                     A-18

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routinely buried in the solid waste area.   There  is  an active gravel  quarry to
the west with several  residences between it and the  solid waste area  of the
landfill.  The site is partly owned by the  town and  a  private citizen.   The
Town operates an active waste transfer station  on the  site.   The private citi-
zen has a dog kennel,  firing range, and bird hunting preserve on the  site.

      The site was added to the NPL list in 1989  primarily as a result  of
contaminated groundwater impacting the local residential  water supply.   In
1985, the Town authorized construction of a municipal  water line extension to
the transfer station and eight residential  dwellings in the immediate site
area.  After negotiations with the PRP to conduct an RI/FS were unsuccessful,
a federally financed RI/FS was initiated.   The  soil  gas study conducted as
part of the RI/FS detected methane and non-methane VOCs (vinyl chloride as the
principal component) migrating off-site and toward the residences.  Both gases
are of concern and are being dealt with under removal  action authority.

A.6.2 Access Agreements
      In March 1991, EPA sent access agreements to the residents and citizen
owning part of the site.  The agreement requested permission for access for
the purposes of taking samples to  scope the extent of contamination.  The
citizen/owner refused this request.  EPA met with the citizen/owner to discuss
his concerns and  in May sent a second letter indicating EPA's willingness to
comply with certain request made by him.  This letter also requested that
hunting, target shooting, etc., be curtailed during the hours the response ac-
tivities were occurring.  The Citizen/owner refused this  request but did sign
the original access agreement request.  EPA began limited response activities
under that  agreement.  Discussions were held in  June  and  July over this refus-
al.  On  both occasions, the  citizen/owner  clearly stated  that hunting  activi-
ties would  not  be curtailed.

       In March  of 1992,  EPA  issued an  Administrative  Order to  achieve  compli-
ance with  the previous  requests.   The  order was  issued under the  authority
vested  in  the President  of  the  United  States in  Section  104(e)  of CERCLA,  42
U.S.C  § 9604(e),  the  NCP,  40 CFR  § 300.400 (d) and  cited  the delegation of
that authority  to EPA by  Executive Order  12580,  52  Federal  Register  2923,  and
                                      A-19

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to the Regional Administrator by EPA Delegation No.  14-6.   Compliance with the
order was cited as enforceable under Section 104(e)(5)  of CERCLA,  42 U.S.C. §
9604(e)(5), under which a court could impose civil  penalties of up to $25,000
per day of violation and/or punitive damages up to  three times the costs in-
curred by the United States as a result of such failure as provided in Section
107(c) of CERCLA, 42 U.S.C § 9607(c)(3).  The order detailed precise times,
locations, prohibited activities, and permitted activities related to use on
the site of firearms and dogs.

A.6.3 Pollutant Measurements
      By December 1991, permanent soil gas monitoring wells had been installed
around the landfill, two rounds of sampling had been conducted, and indoor
monitoring had been conducted at 12 residences.  These data showed that
methane had penetrated several residential basements, with levels in one
basement of up to 1,000 ppm and over 1,000 ppm in the outdoor foundation point
of another.  Vinyl chloride was not detected inside the buildings.  However,
it was detected at concentrations up to 4,000 ppm in soil gas 150 feet from
one building.

      The  area was also sampled in October of 1992 following issuance of the
Action Memorandum for removal actions at the site.   These results show methane
concentrations in several soil gas wells exceeding the lower explosive limit
and vinyl  chloride at a number of points, none indoors, at concentrations
ranging up to  5,100 ppb v/v.

A.6.4 Action Memorandum
      The  Action Memorandum, signed in October 1992, concludes that the poten-
tially explosive gas levels detected during daily monitoring at the perimeter
of the landfill and in nearby homes and businesses appear to meet the criteria
for imminent and substantial danger and, thus, response is authorized under
CERCLA Section 104(a)(l).

       Included in the specific proposed actions are:
       •     Continue to monitor the residential area for methane  and other
            VOCs.
                                     A-20

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      •      Notify  PRPs  and give them the opportunity  to  implement  the  removal
            action.
      •      Coordinate with the RPM to ensure the  removal  action will be  con-
            sistent with the  remedial action.
      •      Institute an interagency agreement with  the Corp of Engineers for
            a rapid response  contract to develop engineering and design plans
            to mitigate  the underground migration  of methane, vinyl  chloride,
            and other VOCs.
      •      Activate the EPA  Emergency Response Cleanup Services removal  con-
            tractor to implement the design  and engineering plan upon its
            completion.
      •      Negotiate an operation  and maintenance agreement with  the State,
            local  community,  or  PRP for the  anticipated  active gas collection
            system.  Must be  in  place before construction begins.
      •      Measure and address  emissions  of hazardous gases from  any collec-
            tion system installed.
      •      Provide monitoring adequate to  provide an  early warning system and
            to determine the  effectiveness  of the  actions.

A.6.5 Invitation to PRP
      Based on available data, including  that collected  in October 1992,  it
was recommended that methane  monitors  be  placed  in two homes  and  that  a sub-
slab depressurization system plus  a methane monitor be install  in  another home
while the overall  design is being  completed.  This information  was transmitted
to the PRP in the notice referred  to in  Section  A.6.4 above and in a meeting
among the PRP, EPA, and the State.   The  PRP agreed to immediately implement
the above two recommendations.  They also requested an opportunity to  evaluate
the feasibility of  assuming the costs associated with the overall  mitigation
design and the implementations of the recommendations.
                                     A-21

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                                   TECHNICAL REPORT DATA
                            (Please read Instructions on the reverse before completing)
1. REPORT NO.
  EPA-451/R-93-012
                                                           3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
  Air/Superfund National Technical Guidance Study Series
  Options for Developing and Evaluating Mitigation
  Strategies for Indoor Air Impacts at CERCLA Sites	
5. REPORT DATE
       September 1993
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
                                                           8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
  U.S. Environmental Protection Agency
  Region X, 75 Hawthorne Street
  San Francisco, California  94105
                                                            10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
  U.S. Environmental Protection Agency
  Office of Air Quality Planning and Standards
  Research Triangle Park, North Carolina  27711
13. TYPE OF REPORT AND PERIOD COVERED
	Final	
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTR/
       'tffe purpose of this document is to present and analyze approaches that may be used to
 mitigate the Comprehensive  Environmental  Response, Compensation, and Liability Act of 1980
 (CERCLA) site impacts on the indoor air quality of nearby structures.  This document is based on
 relevant published literature, information on specific cases made  available by EPA, and expertise
 and experience provided  by its  review  committee.  The document  is designed to provide
 information that may assist in resolution of indoor air quality concerns at CERCLA sites.  The
 procedures and methods,  however, may also be useful in developing mitigation strategies for
 indoor air impacts from other hazardous wastes and hazardous materials sources.

       This  document focuses  primarily  on  mitigation methods that  may be   applied  in the
 immediate vicinity of the impacted or  potentially impacted structure(s).  Reference is made to
 CERCLA site remediation methods that may also have a beneficial impact on  indoor air quality,
 but these  are not discussed  in detail.  The document includes summary level  information on
 technical  methods to prevent or reduce the intrusion of site related chemicals  into the  indoor
 environment and institutional methods to restrict the use of developed and  undeveloped property
 to the extent necessary to reduce risks to  acceptable levels.
17.
                                KEY WORDS AND DOCUMENT ANALYSIS
                  DESCRIPTORS
                                              b.lDENTIFIERS/OPEN ENDED TERMS
              c. COSATI Field/Group
        Air Pollution
        Superfund
        Indoor Air
        Indoor Air Mitigation
18. DISTRIBUTION STATEMENT
                                              19. SECURITY CLASS (This Report)
                                                                         21. NO. OF PAGES
                                              2O. SECURITY CLASS (This page)
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