United States
                              Environmental Protection
                              Agency

                              Super-fund
Office of Emergency and
Remedial Response
Washington, DC 20460
Office of
Research and Development
Cincinnati, OH 45268
EPA/540/S-92/013
November 1992
                              Engineering  Bulletin
                              Air  Pathway  Analysis
Purpose

    Section 121(b) of the Comprehensive Environmental Re-
sponse, Compensation, and Liability Act (CERCLA) mandates
the Environmental Protection Agency (EPA) to select remedies
that "utilize permanent  solutions and alternative treatment
technologies or resource recovery technologies to the maxi-
mum extent practicable" and to prefer remedial actions in
which treatment  "permanently and significantly reduces tin:1
volume, toxicity, or mobility of hazardous  substances, pdlut
ants and contaminants as a principal element."  1 he Engineer-
ing Bulletins are a series of documents that sumrnaiize the
latest information available on selected treatment and site
remediation technologies and related issues.  They provide
summaries of and references for the latest information to help
remedial project managers, on-scene coordinators, ton trac-
tors, and other site cleanup managers understand the typ;? of
data and site characteristics needed to evaluate 
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FIGURE 1.  FLOWCHART OF ACTIVITIES FOR DEVELOPING SCREENING AND IN-DEPTH EMISSION ESTIMATES (3, p. 24)
                   (1) Define the APA Objectives
                J8833S8JJ8JS883SSS8SJSSSS8S8SSSS8SJgS^^
                    (2) Design and Conduct the
                          Site Scoping
                       Evaluate the Available
                            Site Data
                                   S3J^^
No Potential
                         Document No Potential for
                         Air Pathway Contamination
                      Potential Exists for Air
                      Pathway Contamination
                 (3) Design and Conduct a Screening
                    APA To Determine If In-Depth
                     Baseline Emission Estimate
                        Data Are Necessary	

        In-Depth Baseline
      Emission Estimate Data
        Are Not Necessary
                                                         Document Screening
                                                        Emission Estimate Data
                    In-Depth Baseline Emission
                   Estimate Data Are Necessary

                  (4) Design and Conduct Detailed
                    APA To Determine In-Depth
                    Baseline Emission Estimate
    Insufficient
    APA Data
                      Report In-Depth Baseline
                        Emission Estimate
 Sufficient APA Data
                                Site Mitigation
                                                             Engineering Bulletin: Air Pathway Analysis

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ties, such  as excavation or treatment technologies, do not
create a short term health  risk.  Most sites have a significant
increase in air emissions when the waste is disturbed.

    One important aspect of designing and conducting a suc-
cessful APA is understanding the pathways by which air con-
taminants  leave the site and factors that influence site emis-
sions.  Figures 2 and 3 provide conceptual schematics of likely
emission sources for landfills (i.e. any subsurface waste) and
lagoons.  There are both surface and subsurface pathways.
Some pathways are important in the undisturbed state; while
others are important  in the disturbed state.  Most sites have
weathered, aged surfaces that inhibit air emissions so the sub-
surface sources are more dominant for undisturbed sites. Sub-
surface migration pathways form through the soil and along
subsurface conduits. Emissions generally will be dominated by
materials handling operations and exposure of freshly disturbed
waste (e.g. open pits, stockpiles).
APA Techniques

    In general, all screening and in-depth emission assessment
techniques fall into one of four basic approaches for obtaining
APA data.  The techniques include: direct measurement, indi-
rect measurement, fenceline monitoring/modeling and predic-
tive modeling. The variety of available methods allows for cost-
effective  data collection.   Some methods for  conducting
screening and in-depth air pathway analyses and their applica-
tions are shown in  Table 1.  Selection  of the  type of the
screening  or in-depth  technology will depend  on project re-
sources, schedule, personnel capabilities, emission contaminant
type(s) present, site emission potential, and the intended use of
the APA data [3].

    The direct measurement approach consists of techniques
that provide  an  empirical measurement of emissions.   This
approach allows for accurate estimates of emissions with known
uncertainty but these techniques may be more  expensive and
time consuming  than  other techniques.  If emission data are
needed for health risk assessment, the direct emission measure-
ments may be the most appropriate approach.

    Indirect emission measurement techniques involve the col-
lection of ambient concentration data and meteorological infor-
mation under specific conditions. These data typically are used
to develop inputs for a numerical model to estimate the emis-
sion rate.  These methods are usually less precise than direct
methods, but an emission estimate can be calculated without
having the specific field data.

    The fenceline monitoring/modeling approach requires op-
eration of a monitoring network to tabulate ambient upwind
and downwind concentration data with simultaneously col-
lected meteorological data. A dispersion model, based on field
study data or published emission factors, can give estimates of
downwind concentrations. The model output can be refined
by adjusting the hypothetical input until the output matches
the actual ambient air monitoring data. The fenceline monitor-
ing/modeling approach is often preferred to other assessment
methods when valid, comprehensive ambient air monitoring
data are available.
    Predictive modeling may be useful in estimating emissions
from a site.  An appropriate theoretical model is selected to
represent the site (i.e., landfill, non-aerated lagoon with oil
layer, etc.) and site information is used to estimate gross emis-
sions from the site. Since many variables affect emission rates
from a site, this approach is limited by the representativeness of
the model and by the input used.  This approach is usually used
as a screening-level evaluation to support or refute the need for
additional APA, but should  not be used without site-specific
data to support planning or decision-making activities (e.g.
health risk assessments).
Screening Level Assessment Techniques

    Head space analysis of bottled waste is a simple but
effective direct screening measurement technique that involves
collecting waste material in a bottle with "significant"  head
space and allowing the waste/head space to reach equilibrium.
The head space gas is then  analyzed for volatile compounds
with simple real time analyzers. This activity can be conducted
in conjunction with a soils investigation.  These data are often
used to make field decisions regarding which soil/sludge samples
should undergo compound specific analyses. If the screening
consistently shows little or no volatile emissions from samples
across the site, then an in-depth study may not be necessary.
Subsurface soils may need to be assessed in addition to surface
soils.  Little or no volatile emissions are defined as less than
three  times the analytical detection limit.  It is recommended
that a few gas samples be collected for a gas chromatograph/
mass spectrometry speciation analyses to confirm the emission
levels.  If these screening level data suggest a strong potential
for emissions, then they can be used to help design the in-
depth APA.

    Particulate matter emissions can also be tested in a screen-
ing manner.  Collected samples can be analyzed for particle
size and  soil moisture or tested for "dustiness" [6] or can be
estimated via modeling techniques [3].  Experimental waste
handling and visual observation can also indicate the emissions
potential of PM. These data are used to make the decision as to
whether or not further APA activities are needed.

    Upwind/downwind  survey monitoring  is an indirect
screening method used to study emissions by monitoring up-
wind/downwind concentrations of ambient target compounds.
A conventional monitoring strategy and air sampling/monitor-
ing approach is used.  Often, real time analyzers with flame
ionization and photoionization detection are used for organic
emission detection. Integrated air samples (e.g., grab samples)
are collected using techniques such as evacuated, stainless steel
canisters for VOCs and high-volume filter samples for particu-
late matter.  Advanced techniques  such as optical  remote
sensing can also be used to quantify emission potential for the
detection of compounds.

    A realtime instrument survey is similar to upwind/down-
wind  screening except that the screening usually takes  place
directly over the waste to obviate modeling by testing the air
above the surface. This approach can identify "hot spots" of
emissions and zones of similar emissions.
Engineering Bulletin: Air Pathway Analysis

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FIGURE 2. CONCEPTUAL SCHEMATIC SHOWING AIR CONTAMINANT PATHWAYS FROM AN UNLINED LANDFILL (3, p. 13)
                                       Direct Air Emissions of
                                   Volatiles and Participate Matter
        Gas Venting from Vents
                                     ^v******-:*^-* •»* • **»W*fe
                                     * x:v, * ./** • •' .* -- .";  o*
         Volatilization of Dissolved
         Species in Groundwater

   Lateral Migration
   of Volatiles from
     Solid Waste

 Lateral Migration
 of Volatiles from
  Contaminated
Soils and Leachate
        FIGURE 3. CONCEPTUAL SCHEMATIC SHOWING AIR CONTAMINANT PATHWAYS FROM AN UNLINED
                                   LAGOON WITH NO COVER (3, p. 14)
                 Lateral Migration
                 of Volatiles from
               Liquid/SludgeWaste
  Lateral Migration of Volatiles from
          Contaminated
        Soils and Leachate
  Volatilization of Dissolved Species
          in Groundwater
                                                  Direct Air Emissions
                                                of Volatiles and Aerosols
                                                          Engineering Bulletin: Air Pathway Analysis

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                                 TABLE 1. DATA COLLECTION OPTIONS AND APPLICATIONS
   TECHNIQUES
   Head Space Analysis
   Static Chamber
   Realtime Instrument
   Survey
   Upwind/Downwind
   Survey
   Modeling
   Surface Flux Chamber
   Soil Vapor Probes
   Downhole Flux
   Chamber
   Transect
   Fenceline
   Monitoring/
   Interactive
   Modeling
COLLECTION
METHOD
                                             LEVEL OF EFFORT
                        Bottle
                        Canisters; Tedlar Bags
Instrument on/near
Waste Surface
Polyurethane Foam;
Solid Sorbent; Filter
Data Required: Soil
Contaminants/Con-
centrations; Porosity;
Moisture
                        Enclosure
                        Probes
                        Enclosure
                        Optical Remote
                        Sensing or Array of
                        Point Samples
Any of Above
Methods
                     Screening
                     Screening/ In-Depth
Screening
Screening
Screening/I n-Depth
                                             In-Depth
                     In-Depth
                     In-Depth
                     In-Depth
In-Depth
r

jth


th





APPLICATION
Field Measurement
Field Measurement
Field Measurement
Field Measurement
Field Measurements
for Soil Characteristic
Data or can use
Model Defaults
Field
Measurement;(can
use directly on freshly
disturbed soil)
Field Measurement;
Conduct Limited
Transect (One
Upwind, Two or Three
Downwind)
Field Measurement
Field Measurement
Field Measurement
COMPOUNDS '
VOC, SVOC; VIC
VOC, SVOC; VIC
VOC, SVOC; VIC; PM
VOC, SVOC; VIC; PM
VOC, SVOC; VIC; PM
VOC, SVOC; VIC; PM
VOC, SVOC; VIC; PM
VOC, SVOC; VIC
VOC, SVOC; VIC
VOC, SVOC; VIC
DETECTORS 2
OVA, PID for VOCs
and SVOCs; SD for
VICs
OVA, PID for VOCs
and SVOCs; SD for
VICs
OVA, PID for VOCs
and SVOCs;SD, H/S
for VICs; DM for PM
OVA , PID for VOCs
and SVOCs;SD, H/S
for VICs; DM for PM;
CC/MS
N/A
OVA, PID for VOCs
and SVOCs; SD,
CS/MS
OVA, PID for VOCs
and SVOCs; SD,
CS/MS
OVA, PID for VOCs
and SVOCs; SD,
CC/MS
FTIR, UV-DOAS, CFC,
FBPA, Laser, PAS,
LIDAR, etc.3
OVA PID for VOCs
and SVOCs; SD
   1 VOC = Volatile Organic Compounds
    SVOC = Semivolatile Organic Compounds
    VIC = Volatile Inorganic Compounds
    PM = Paniculate Matter

   2 OVA = Organic Vapor Analyzer
    PID = Photoionization Detector
    SD = Specific Compound Detector
    H/S = Health/Safety Director
    DM = Dust Monitor
                                               3 Optical Remote Sensing Detectors
                                                 FTIR = Fourier Transform Infrared
                                                 UV-DOAS = Ultraviolet-Differential Optical Absorbance
                                                 GFC = Gas Filter Correlation
                                                 FBPA = Filtered Band Pass Absorption
                                                 Laser = Laser Absorption
                                                 PAS = Photoacoustic Spectroscopy
                                                 LIDAR = Light Detection And Ranging
                                                 ETC = Diode-Laser Spectroscopy
Engineering Bulletin: Air Pathway Analysis

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    Predictive models can be used to determine if the site has
an emissions potential.  This is a good  screening approach
provided that waste composition and concentration data are
available. (Since most models are conservative, predictive mod-
eling is generally used to determine if a site does not have a
significant emissions potential and that no further APA is re-
quired.) This approach can also be used for an in-depth APA,
provided that measured and representative model input, in-
cluding waste composition and physical data, are used with an
appropriate model.
In-Depth Level Technologies

    Surface flux chamber is a preferred direct measurement
approach  applicable  to many types of waste sites  [3] and
capable of generating both undisturbed and disturbed emis-
sion rate data for volatile  and semivolatile compounds. The
technology uses  a chamber to isolate a surface emitting gas
species (organic or inorganic); emission rates are calculated by
measuring the gas concentration in the chamber and using the
chamber sweep airflowrate and surface area.

    Soil vapor probe is a direct measurement method that
uses a chamber and sweep air to measure emission rates [3].
The chamber is a small exposed area at the end of a ground
probe where sweep air is added at a fixed, known rate and gas
samples are collected and analyzed for volatile and semivolatile
compounds. While this technology is typically used for plume
mapping  it is capable of  generating emission rate data that
represent waste emissions as if the land surface were disturbed
and exposed.

     Downhole flux chamber,  a third direct measurement
technology, is similar to the soil vapor probe method  in that it
obtains subsurface  gas emission rates that represent disturbed
waste.  However, this technology is used with a hollow-stem
drilling  rig, and  emission  rates are obtained from subsurface
waste up to 100 feet below the surface (or more if necessary).  A
cylindrical chamber is lowered down the annulus of the hollow-
stem auger and the air at the freshly exposed waste  at the
depth of the borehole is sampled. Both the soil vapor probe
and the downhole flux chamber technologies provide useful
disturbed waste emission  rate data without the need to exca-
vate the waste.

     Transect technology is an indirect method that involves
 the collection of ambient concentration data for gaseous com-
 pounds and/or particulate matter using a two-dimensional ar-
 ray of point samplers. These data, along with micro-meteoro-
 logical  data, can be used to estimate the emission rate of the
 source  by using a specific dispersion model.  Data can  be
 obtained that represent emissions from a complex or heteroge-
 neous site or an activity that generates fugitive air  emissions.

     Ambient concentration data can also be collected using
 path averaged techniques or line integration such as  optical
 remote sensing techniques.

     Fenceline monitoring/modeling can be used to develop
 screening or in-depth emission rate data. Data quality depends
 on the  type of air monitoring conducted, the extent of the data
set, the quality of the meteorological data, and the dispersion
model used to simulate the emission event. This approach is
often used to support emission rate data obtained from other
approaches or when fenceline  monitoring  is conducted for
other purposes. It is typically not performed for the sole pur-
pose of providing emission rate data.
Limitations
Screening Level Technologies

    Head space analysis of a sample in a bottle is limited by
the procedure and instrument used to perform the screen.
Typically, a broad-band realtime gas analyzer is used (e.g., an
Organic Vapor Analyzer). This type of analyzer provides useful
information but is often subject to interferences.

    Upwind/downwind survey monitoring is generally lim-
ited in its ability to identify properly the emission potential of
the site for the following reasons: testing out of the plume; not
accounting for upwind interferences; or using survey instru-
ments that are incapable of detecting the compounds emitted.

    Realtime instrument survey has the same limitations as
upwind/downwind screening except that measurements are
generally made over the waste; therefore meteorological condi-
tions have less of an influence on the results.

    Predictive models are inherently limited by the assump-
tions  of the model itself.  It is important that an appropriate
model be selected and site-specific input data are used where
possible.
 In-Depth Level Technologies

     Surface flux chamber is limited by the number of data
 points that are needed or required to describe the source. If the
 site is heterogeneous, each area of similar emissions potential
 requires an assessment. The number of data points needed to
 describe each unit may be significant.  The technology is not
 applicable to particulate matter and is of limited use for assess-
 ing emissions from active processes with fugitive emissions.

     Soil vapor probe technology has the same limitations as
 the surface flux chamber regarding the number of data points
 required to assess the source and is also limited to gaseous
 emissions. Further, the depth of the investigation is limited to
 assessing emissions typically  up to 10 feet below the land
 surface. While the waste source may be deeper, the exposed
 surface is small, resulting in emission rate estimates of higher
 uncertainty than other direct technologies.

     Downhole flux chamber limitations are similar to those of
 the soil vapor probe technology, but the maximum depth is
 generally up to 100 feet below land surface.  A drilling rig is
 required, increasing the costs of the operation.  Combining
 downhole flux chamber measurements with other site assess-
 ment activities using hollow-stem augers can substantially re-
 duce costs.
                                                                    Engineering Bulletin: Air Pathway Analysis

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    Transect technology is limited by upwind interferences,
analytical limits of detection, meteorological influences, and
the need to use a model to estimate emission rate.  It can be
time consuming and expensive to collect the required field
data since the meteorological conditions of the model must be
met prior to  data collection in order for the model to be
effective.

    Fenceline monitoring/modeling is generally limited by
the extent of the  monitoring network,  the quality of these
data, upwind  interferences, analytical sensitivity, and the need
to use modeling to estimate emission rates. This method has
the same limitations as the transect technology and, in addi-
tion, is usually considered  less accurate because the model
used is not specific to the  conditions by which the ambient
data were collected.
Site Requirements

    There are no specific site requirements for an APA assess-
ment other than a secure site, site access, and standard support
facilities. As with all site investigation work, a site trailer equipped
with 110 volt, 50 or 100 amp electric service, lighting, and a
telephone provides  a functional  work area.   Portable  field
instruments usually are battery powered and require charging
overnight. A trailer with 110 volt power permits recharging of
the analyzers on the trailer overnight, thereby keeping the
equipment onsite. Since many field analyzers require calibra-
tion, an area, perhaps  along the side of the trailer, can  be
equipped with a gas bottle rack for safe storage and use of
compressed  gases (e.g., calibration and support gases). An
ambient monitoring network may require weatherproof, AC-
powered shelters. Worker support  facilities are also recom-
mended but are not  required. A facilities trailer equipped with
storage and decontamination areas is often useful.
Status of the APA Process

     EPA has provided technical guidance for conducting an
analysis of the air pathways for air toxic species at waste sites
and for conducting air monitoring. This technical guidance is
contained in a four-volume series:

         VOLUME I Application of Air Pathway Analysis for
         Superfund Activities

         VOLUME II Estimation of Baseline Air Emissions at
         Superfund Sites

         VOLUME III Estimation of Air Emissions from
         Cleanup Activities at Superfund Sites

         VOLUME IV Procedures for Dispersion Modeling
         and Air Monitoring for Superfund Air Pathway
         Analysis

     These volumes are currently being revised.  Any of the
EPA contacts will be  aware of the current status of the APA
documents.
    The amended National Contingency Plan expands upon
the requirement to conduct and fully document an air pathway
analysis.  The process is defined as a "systematic approach
involving a combination of modeling and monitoring methods
to assess actual or potential receptor exposure to air contami-
nants" [2, p. 2-1 ]. Volume I explains this approach and how the
APA  integrates into the site remediation  process.  Volume II
provides the "how to" information needed to conduct an APA
including all recommended screening and in-depth technolo-
gies for assessing air emissions [3]. Estimating emissions from
remedial processes is covered in Volume III [4], and air modeling
and air monitoring approaches are presented in Volume IV [5].
This series was written with the EPA RPM as the target audience.

    Research efforts are underway to improve these assessment
methods and explore further applications.  Current research is
focused on using these methods to design and then test the
effectiveness of various air emission control technologies. Other
studies have  been proposed to provide correlations for data
obtained from screening and in-depth methods so that better
estimates of emission rates can be obtained from cost-effective
field studies.
EPA Contact

    Technology-specific questions regarding air emissions as-
sessment and air monitoring at hazardous waste sites may be
directed to:

        Michelle Simon
        U.S. Environmental Protection Agency
        Risk Reduction Engineering Laboratory
        26 W. Martin Luther King Drive
        Cincinnati, Ohio 45268
        (513)569-7469

    Or to one of the Regional Air/Superfund Coordinators:
     Rose Toscano, Region I
          Boston, MA
        (617) 565-3280

     Alison Devine, Region II
         New York, NY
        (212)264-9868

     Patricia Flores, Region III
        Philadelphia, PA
        (215)597-9134

       Lee Page, Region IV
          Atlanta, GA
        (404) 347-2864

      Charles Hall, Region V
          Chicago, IL
        (312)886-9401
Mark Hansen, Region VI
       Dallas, TX
    (214)655-6582

Wayne Kaiser, Region VII
    Kansas City, KS
    (913)551-7603

Norm Huey, Region VIII
      Denver, CO
    (303) 293-0969

 Kathy Diehl, Region IX
   San Francisco, CA
    (415)744-1133

  Chris Hall, Region X
      Seattle, WA
    (206) 553-1949
 Engineering Bulletin: Air Pathway Analysis
                                                                  •U.S. Government Printing Office: 1993 — 750-071/60161

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   Acknowledgments

      This bulletin was prepared for the U.S. Environmental Pro-
   tection Agency, Office of Research and Development (ORD),
   Risk Reduction Engineering Laboratory (RREL), Cincinnati, Ohio,
   by Science Applications International Corporation (SAIC) under
   contract no. 68-C8-0062.

      Mr. Eugene Harris served as the  EPA Technical Project
   Monitor. Mr. Gary Baker was SAICs Work Assignment Man-
ager.  Dr. Charles E. Schmidt was the primary author.  The
following other Agency and contractor personnel have contrib-
uted their time and comments by participating in the expert
review meetings  and/or peer reviewing the document:
        Mr. Joseph Padgett
        Mr. Paul dePercin
        Mr. Ed Bates
        Mr. Bart Eklund
                            U.S. EPA, OAQPS
                            U.S. EPA, RREL
                            U.S. EPA, RREL
                            Radian Corp.
                                                   REFERENCES
   1.   Engineering Bulletin: Control of Air Emissions from
       Materials Handling During Remediation. EPA/540/2-91/
       022, U.S. Environmental Protection Agency, Cincinnati,
       OH, October 1991.

   2.   Air Superfund National Technical Guidance Study Series,
       Volume 1: Application of Air Pathway Analysis for
       Superfund Activities, Interim Final. EPA/450/1-89/001,
       U.S. Environmental Protection Agency, Research Triangle
       Park, NC,  1989.

   3.   Air Superfund National Technical Guidance Study Series,
       Volume 2: Application of Air Pathway Analysis for
       Superfund Activities, Appendix, Interim Final.  EPA/450/1 -
       89/002, U.S. Environmental Protection Agency, Research
       Triangle Park, NC, 1989.
6.
Air Superfund National Technical Guidance Study Series,
Volume 3: Estimation of Air Emissions from Cleanup
Activities at Superfund Sites, Interim Final.  EPA/450/1 -89/
003, U.S.  Environmental Protection Agency, Research
Triangle Park, NC, 1989.

Air Superfund National Technical Guidance Study Series,
Volume 4: Procedures for Dispersion Modeling and Air
Monitoring for Superfund Air Pathway Analysis, Interim
Final.  EPA/450/1-89/004, U.S. Environmental Protection
Agency, Research Triangle Park, NC, 1989.

Cowherd, Chatten, etal., An Apparatus and Methodol-
ogy for Predicting Dustiness of Materials, American
Industrial Hygiene Association Journal, Volume 50, No.3,
March 1989.
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268

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