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
-------
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
Official Business
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