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
1-1
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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
2-3
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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
2-5
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Combustion
devices
Source: EPA91A
Figure 2-1. Negative Pressure Sources in a Typical House
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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
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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
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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
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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.
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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
-------
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
-------
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
-------
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.
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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
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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
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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)
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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—
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TIGHT
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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.
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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.
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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.
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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.
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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
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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
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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
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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.
3-18
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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)
3-19
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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
3-20
-------
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:
3-21
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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.
3-22
-------
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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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Moke a Copy
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Select
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No
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Satisfying Objective
Use Copy of
Master Matrix
Delete all Un-checked
And Un-flagged ICs
Check Highest Rated Control
For Each Objective and
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Delete all Un-checked
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Technical Controls
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Control for Satisfying Objective
Figure 3-2. STRATEGY 1 - MOST TECHNICAL
3-28
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• 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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Strategy 1 = Strategy 2
End Process
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Satisfying Objective
Delete all Un-checked
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Technical Controls
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Control for Satisfying Objective
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
And Un-flagged ICs
Select
Technical Controls
No
Make a Copy
for Strategy 5
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 Flogged
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 3-5. STRATEGY 4 - MOST ICs
3-39
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• 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
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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
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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
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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
Development
Status
Current Uses
Intended
Future Uses
Pollutant
Levels, Current
Pollutant
Levels, Future
Structural
Information
Proposed Technical and Institutional Controls
Control 1
Control 2
Control 3
Control 4
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
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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
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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
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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-
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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
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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
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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.
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APPENDIX
CASE STUDIES
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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.
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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
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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
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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
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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.
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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-
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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-
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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.
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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
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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.
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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
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2O. SECURITY CLASS (This page)
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EPA Form 2220—1 (Rev. 4-77) PREVIOUS EDITION is OBSOLETE
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