&EPA
United States Office of Air Quality EPA-451/R-93-004
Environmental Protection Planning and Standards April 1993
Agency Research Triangle Park, NC 27711
Air/Superfund
AIR/SUPERFUND
NATIONAL TECHNICAL GUIDANCE
STUDY SERIES
ESTIMATION OF AIR IMPACTS
FROM AREA SOURCES OF
PARTICULATE MATTER EMISSIONS
AT SUPERFUND SITES
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EPA 451/R-93-004
ESTIMATION OF AIR IMPACTS FROM AREA
SOURCES OF PARTICULATE MATTER EMISSIONS
AT SUPERFUND SITES
•
Report ASF - 32
U.S. Environmental Protection Agency
Region 5, Library (PL-12J)
77 West Jackson Boulevard, 12th Floor
Chicago, IL 60604-3590
Prepared for:
Office of Air Quality and Standards
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
April 1993
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DISCLAIMER
This report has been reviewed by the
Office of Air Quality Planning and Standards,
U.S. Environmental Protection Agency, and has
been approved for publication as received from
the contractor. The contents reflect the
views and policies of the Agency, but any
mention of trade names or commercial products
does not constitute endorsement or
recommendation for use.
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TABLE OF CONTENTS
Page
INTRODUCTION 1
PROCESS DESCRIPTION 2
ESTIMATION OF PARTICULATE MATTER AIR EMISSIONS 4
ESTIMATION OF AMBIENT AIR CONCENTRATIONS 14
ESTIMATION OF HEALTH EFFECTS 17
Cancer Effects Due to Long-Term Exposure 17
Non-Cancer Effects Due to Long-Term Exposure 29
Short-Term Exposure 30
EXAMPLE 31
CONCLUSIONS 36
REFERENCES 36
LIST OF FIGURES
1 Mean Annual Number of Days with at Least 0.01 inches of Precipitation . 12
2 One-Hour Average Downwind Dispersion Factor Versus Distance
Stabilization/Solidification Processes with No Air Controls 16
11
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LIST OF TABLES
Page
1 Default Values for Estimating Emissions from Materials Handling 11
2 Metal Concentration and Enrichment Data (Z) 11
3 Default Values for Estimating PM Emissions from Other Area Sources ... 13
4 Example Scenarios for Area Sources of PM Emissions 15
5 Long-Term and Short-Term Health-Based Action Levels for Organic
Compounds in Ambient Air 18
*
6 Long-Term and Short-Term Health-Based Action Levels for Selected
Semi-Volatile Organic Compounds in Air 26
7 Long-Term and Short-Term Health-Based Action Levels for Metals
in Ambient Air 28
8 Estimated Emission Rates and Ambient Air Concentrations 35
9 Action Level Concentrations 35
111
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INTRODUCTION
The U.S. Environmental Protection Agency's Office of Air Quality Planning and
Standards and the Regional Air Offices have been given the responsibility to evaluate air
impacts from Superfund sites. An important part of this program is the analysis of air
impacts from various alternatives for cleaning up Superfund sites. Since these analyses are
frequently required for planning purposes prior to actual cleanup, they depend on estimated
emissions and ambient concentrations rather than on field measurements.
This report provides procedures for roughly estimating the ambient air concentrations
associated with the emissions of participate matter (PM) from soils handling operations at
Superfund sites. These procedures are analogous to procedures for air strippers, soil vapor
extraction systems, and excavation that have previously .been published.u>3 Materials
handling operations are necessary at any site where ex-situ treatment is performed. In
addition, soils handling operations, such as excavation or grading, are frequently performed
as part of site preparation. Procedures are given to evaluate the effect of handling rate and
contaminant concentration on the emission rates and on the ambient air concentrations at
selected distances from the treatment area.
Health-based ambient air action levels are also provided for comparison to the
estimated ambient concentrations. Many of the health levels have not been verified by EPA
or are based on extrapolations of oral exposures or occupational exposures. Their use could
either under or over estimate the potential health effects. The use of action levels that are
neither EPA-verified nor EPA-approved should be considered on a case-by-case basis. The
statements and conclusions presented in this report are those of the authors and do not reflect
U.S. EPA policy.
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PROCESS DESCRIPTION
Materials handling covers such activities as excavation, dumping, grading, short-term
storage, and sizing and feeding soil or waste into treatment processes. Information on
equipment and operating practices for material handling operations are available.4-5
Excavation and removal of contaminated soils and sludges is a common practice at
Superfund sites. Excavation and removal may be the selected remediation approach or it
may be a necessary step in a remediation approach involving treatment. If removal is the
preferred approach, the excavated soil typically is transported off-site for subsequent disposal
at a landfill. If the soil contains large amounts of fuel or highly toxic contaminants, the soil
may need to be treated off-site prior to final disposal. Excavation activities are also typically
part of on-site treatment processes such as incineration, thermal desorption, batch
biotreatment, landtreatment, and certain chemical and physical treatment methods. The soil
is excavated and transported to the process unit and the treated soil typically is put back into
place on the site.
Since digging soil and immediately transferring it directly to transport vehicles or
treatment systems is rarely feasible or efficient, soil will be handled several times. In most
cases, soil will be excavated and placed into a temporary holding area and then handled one
to two more times on-site. Each handling step may involve dumping the material. If ex-situ
treatment is performed, the contaminated material usually will need to be sized and fed into
•
the treatment unit. Elevated levels of PM (and VOC) emissions are possible each time the
soil is handled.
Site preparation activities often involve some amount of excavation, grading, etc. to
constuct roadways and prepare areas for office trailers and other support equipment. Whiie
site preparation tends to be limited to non-contaminated areas, PM emissions are still likely
to occur and some tracking of contaminated material into clean areas may inadvertently take
place.
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The rate of materials handling operations at Superfund sites tend to be controlled by
factors such as safety concerns, storage capacity or treatment capacity, rather than being
limited by the operational capacities of the equipment that is used. For these reasons, actual
materials handling rates tend to be far below typical handling rates at construction sites.4
Multiple potential emission points exist for each of the various soils handling
operations. For excavation, the main emission points of concern are emissions from:
• Exposed waste in the excavation pit;
• Material as it is dumped from the excavation bucket; and
• Waste/soil- in short-term storage piles.
In addition, emissions of paniculate matter, VOC, nitrogen oxides, etc. will also occur from
the engines of the earth-moving equipment. While these emissions will not require any
additional control devices (beyond those provided by the manufacturer), the equipment
emissions should be considered when evaluating any air monitoring data.
Paniculate matter (PM) emissions will depend primarily on the particle size
distribution of the soil, its moisture content, the wind speed, and the operating practices that
are followed. The longer or more energetic the moving and handling, the greater likelihood
that PM emissions will occur. The magnitude of emissions from soils handling operations
will vary with the operating conditions. Add-on control technologies are available for
minimizing PM emissions, but they are relatively ineffective and costly to implement.
Control of emissions can also be achieved by controlling the operating conditions within
preset parameters. The rate of excavation and dumping, the drop height, the amount of
exposed surface area, the length of time that the soil is exposed, the shape of the storage
piles, and the dryness of the surface soil layers will all influence the levels of PM emissions.
Large reductions in emissions can be achieved by identifying and operating within acceptable
ranges of operating conditions.
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A number of methods are available for controlling paniculate matter emissions from
soils. In general, any method designed primarily for paniculate control will also reduce
VOC emissions and vice versa. Compared to point source controls, emission controls for
excavation and other area sources are difficult to implement and only moderately effective.
Controls such as water sprays or foams will alter the percent moisture, bulk density, and
average heating value of the soil and may affect treatment and disposal options. Emission
•
controls for soil area sources include:6
Covers and physical barriers;
Temporary and long-term foam covers;
Water sprays;
Water sprays with additives;
Operational controls;
Complete enclosures;
Wind screens; and
Collection hoods.
ESTIMATION OF PARTICULATE MATTER AIR EMISSIONS
Simple air emission estimation procedures are presented in this section for area
sources of paniculate matter (PM) and metals, including: materials handling and other area
sources such as storage piles and dry surface impoundments. Soils handling is a very
common source of paniculate matter emissions at Superfund sites; excavation of soils, soil
transport, dumping and formation of soil storage piles, and grading are all routinely
performed. The PM emissions arising from these operations should be evaluated, whether
the material is contaminated or not since PM emissions (less than 10 microns in diameter)
are a criteria pollutant. Few emissions models for PM from materials handling exist. A
comprehensive collection of empirically based screening models developed by Cowherd et
al.7 was used as the principal source of all models in this document.
The emissions of PM from all transfer operations - adding to or removing from piles,
conveyor belts, truck dumping - are expressed in Equation 1:
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k (0.0016)(
VIJ
(Eq. 1)
where E =
k
0.0016 =
M
U
2.2 =
PM emissions [g];
particle size multiplier [unitless];
empirical constant [g/Kg]; and
mass of waste handled [Kg];
mean wind speed [m/sec];
empirical constant [m/sec]; and
percent moisture content [%].
Reference 8 provides a more detailed equation for this same activity that takes into account
the drop height, the silt content of the material, and the capacity of the dump bucket. The
particle size multiplier, k, for several sizes of particles for use with Equation 1 are:
size
(microns)
<50
<30
<15
<10
<5
<2.5
multiplier, k
1.0
0.74
0.48
0.35
0.20
0.11
For emissions from the erosion of intermittently active piles, use erosion Equation 9
for each period between activity; use the above equation during the activity itself.
For emissions during materials handling involving mixing and tilling (waste
incorporation and cultivation), a simple model is:
where E
k
0.00538
SA
s
E = k (0.00538) SA 10^ (s)°-6
PM emissions [g];
particle size multiplier (0.21 for PM1Q) [unitless];
empirical constant [g/hectare];
conversion factor [hectare/m2];
area treated [m2]; and
percent silt content [%].
(Eq. 2)
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Particle size multipliers for size fractions other than PM10 are not available for Equation 2.
If wastes or soil are being graded by a bulldozer or any other tractor with a blade, then the
following equation should be used to predict the PM10 (paniculate matter of less than 10
microns) emissions:
X1.4
AH,O
'where ER = PMto emission rate [g/sec];
0.094 = empirical constant [g/sec] ;
s = percent silt content [%]; and
= percent moisture content [%].
The emission rate of traffic on paved roads in grams per vehicle kilometers traveled
(VKT) is given by Equation 4.
\OJ ^' *)
EF =220 | —I
Iw
where EF = PMIO emission factor [g/VKT];
220 = empirical constant [g/VKT];
sL = silt surface loading [g/m2];
12 = empirical constant [g/m2]; and
0.3 = empirical constant [unitless].
For unpaved roads, the PM,0 emission model is given by Equation 5:
. 610 fj.) (*.} pur (~r (365 - p> (Eq'5)
12) (48) (2.7) (4) 365
where EF = PM10 emission factor [g/VKT];
610 = empirical constant [g/VKT];
s = percent silt content of road surface [%];
12 = empirical constant [unitless];
S = mean vehicle speed [km/hrj;
48 = empirical constant [km/hr];
W = mean vehicle weight [Mg];
2.7 = empirical constant [Mg];
w = mean number of wheels per vehicle [unitless];
4 = empirical constant [unitless];
365 =» no. of days per year [days]; and
p = number of days with < 0.01 inches precipitation [days].
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The emission factors can be converted into a total mass emitted if multiplied by the number
of vehicle kilometers traveled.
If the dust is contaminated, the PM or PM10 emission rates given in this document
may be translated to emission rates of the contaminant as follows:
EFj = Xj EF (Eq. 6)
where EFj = emission factor of contaminant i [g/VKTJ; and
X; = fraction of contaminant i in paniculate matter [unitless].
In general, the dust and silt at a site will contain a higher fraction of the metal species than
the bulk soil at the site; i.e. the particulate matter is enriched with the metals.9 Therefore, Xj
is equal to:
Xj = C Z 10^ (Eq. 7)
•where C = concentration of metal in the bulk soil
Z = enrichment factor [unitless]; and
= conversion factor
Fugitive dust may be released from a variety of origins other than materials handling.
A remediation activity that may be a significant area sources of fugitive dust is solidification/
stabilization. Non-remediation sources include storage piles and dry impoundments.
Equations based on fundamental physical laws have been reported for windblown
dust10-11, but the most widely accepted equations are those empirically derived by Cowherd,
et al.8-12'13. The most suitable equations for inclusion in this manual are those given by
Cowherd, et al.7 for open waste piles and staging areas, dry surface impoundments, and
waste stabilization. These are incorporated in the manual along with the metal enrichment
factors for dust presented in Volume HI of the National Technical Guidance Series (NTGS)
documents.9
A simple model of erosion from level areas such as dry surface impoundments during
a time period t between disturbances is given by:
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ER
(Eq. 8)
t 86,400
where ER = PM emission rate from surface material during period t [g/sec];
k — particle size multiplier [unitless];
SA = area of contamination [m2];
p, = erosion potential corresponding to fastest mile of wind during period t
[g/m2];
t = no. of days between disturbances [day]; and
86,400 — conversion factor [sec/day].
Particle size multipliers for Equation 8 are:
Size (microns)
< 30
< 15
< 10
< 2.5
Multiplier, k
1.0
0.6
0.5
0.2
Total suspended particulates (TSP) from wind erosion of continuously active piles can
be estimated as:
(_s\ (365 - p) (J\ ^ 9)
(l5)i 235 (IS)
EF = 1.9
where EF
0.19
s
1500
365
P
235
f
15
PM emission factor (g/m2-day);
empirical constant (g/m2-day);
percentage silt of aggregate (%);
empirical constant (unitless);
no. of days/year (days);
number of days of precipitation > 0.01 inch per year (days);
empirical constant (days);
fraction of time wind > 5.4 m/sec at mean pile height (unitless); and
empirical constant (unitless).
The fraction of TSP. that is PMj0 can be assumed, to be 50%. Equation 9 is valid for piles
that are active at least once per day.
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PM emissions from the transfer of the stabilized waste can be estimated as:
0.00056
E
f u V
(l2")
a.4
where E = PM emissions [g];
0.00056 = empirical factor [g/kg];
U = wind speed [m/sec];
2.2 = empirical factor [m/sec];
M = mass of material handled [kg];
XHZO ~ moisture fraction [%]; and
2 = empirical factor [%].
•
For all the equations given above, site-specific field data must be collected (e.g.,
during the RI/FS) to provide the input data necessary to generate reasonably accurate
estimates of paniculate matter emissions. The minimum field data required to estimate
emissions for the various sources covered in this document are:
• Transfer operations: percent moisture content of the material;
• Mixing and tilling: area treated and silt content of soil;
• Grading: percent moisture content and silt content of material;
• Traffic on paved roads: silt surface loading;
• Traffic on unpaved roads: silt content of road surface;
• Metal emissions for any operation: average concentration of metal in bulk soil;
• Dry surface impoundments: surface area of contamination and the number of
days between disturbances;
• Continuously active piles: percentage silt of aggregate and the fraction of time
with high winds; and
• Stabilization and solidification: percent moisture content and mass of material
handled.
Aerodynamic particle size multipliers for Equations 1, 2, and 8 are provided above.
In general, meteorological data will be available from an on-site monitoring station. If not,
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meteorological data may be obtained from a local airport or government monitoring station.
Soil data is available from the state agricultural service or the federal Soil Conservation
Service.
Default values for equation input parameters are provided in Table 1. Some input
variables, such as mass of material handled and surface area graded, are extremely site- and
operation-specific, so no default values for these variables are given. Table 2 contains
default values for metal enrichment of soils for use in Equation 7. Figure 1 shows a
geographic map of areas of the U.S. and the average number of days with >0.01 inch of
precipitation annually.
Procedures for calculating the erosion potential are given in Reference 7. Table 3
provides default values for the input parameters needed for Equations 8 and 9. For Equation
10, the fraction of TSP made up of PM,0 is estimated to be 0.5.
These emission models assume that after a disturbance, only a certain fraction of the
soil's surface will erode, regardless of the time exposed. That is why Equation 8 does not
depend on time, except for the length of the period between disturbances. Equation 9 is for
continuously active disturbances, and so it assumes that at any point in time, a disturbance
has just occurred, and the same fraction is able to erode. For in-place contaminated soil,
over-prediction of the emissions is possible as a soil crust tends to form, reducing the
erosibility of the pile or field.
These models are equally applicable to a wide variety of materials handling activities.
•
They are based on the premise that a certain percentage of a soil's surface area has a high
"erosion potential", and that the rest of the surface will not be emitted. The equations
presented in this section are all empirically based and drawn from measurements at actual
sites; they are meant to predict the behavior of average sites. If a particular site has unusual
meteorological conditions, rubble, debris, or high silt content of soil, etc., the accuracy of
these models may be affected. It is prudent to always monitor actual field emissions, at least
from some test location, to verify the model predictions.
10
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Table 1.
Default Values for Estimating Emissions from Materials Handling
Parameter
Mean wind speed
Moisture content
Silt content
Silt surface loading
Mean vehicle speed
Mean vehicle weight
Mean # of wheels
Symbol
U
XH»
s
sL
S
W
w
Unite '
m/sec
%
%
g/m2
km/hr
Mg
unitless
Defiult Value
4.4
10
8 (<75 foa)
5
20
3 (plant vehicle)
20 (Commercial haulers)
30 (plant haul trucks)
10
Expected
Range
0 - 4.47
—
2-20
0.3 - 30
8-45
2-9
9-45
20-50
4- 18
Reference
*
*
7
7
7
7
7
7
7
Author's estimate.
Table 2.
Metal Concentration and Enrichment Data (Z)
CAAA* Metals
Antimony (Sb)
Arsenic (As)
Beryllium (Be)
Cadmium (Cd)
Chromium (Cr)
Cobalt (Co)
Lead(Pb)
Manganese (Mn)
Mercury (Hg)
Nickel (Ni)
Selenium (Se)
Other Metals
Barium (Ba)
Silver (Ag)
Median Enrichment Factor (Z)
—
1.28
—
1.31
4.72
—
7.34
—
3.00
—
2.00
1.85
1.00
Source: Reference 9
*CAAA = Clean Air Act Amendments of 1990
11
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Table 3.
Default Values for Estimating PM Emissions from Other Area Sources
- : -'-:. ••' Ptntniwuit
Surface area
Erosion potential
Percentage of silt
Fraction of time with high winds
Wind speed
Moisture fraction
Symbol
SA
P,
s
f
U
X,no
Units
nr
g/m2
%
unitless
m/sec
%
Default Value
2000
33
2.2
20
4.4
2
Expected Range
Site specific
0-525
0.44 - 19
Site specific
0.6 - 6.7
0.25 - 4.8
Reference
—
7
7
—
7
7
'Moisture content of stabilized material.
Note: For use with Equations 8, 9, and 10.
13
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ESTIMATION OF AMBIENT AIR CONCENTRATIONS
Estimates of short-term, worst-case ambient concentrations should be obtained by
using site specific release parameters in the EPA's TSCREEN model.14 Estimates of long
term concentrations should be obtained by using EPA's Industrial Source Complex (ISCLT)
model. Here, for simplicity, the annual average estimates are derived by multiplying the
short term estimate obtained from the TSCREEN model, by a conversion factor to account
for variations of wind direction over time. This approach results in a higher estimate of the
annual average concentration than if the ISCLT model, with site specific data, is used.
Table 4 presents remediation scenarios for area sources of PM or PM10 emissions.
The scenarios were developed based on experience and scientific judgment. The traffic
scenario asumes back and forth traffic in a confined area on-site; therefore, emissions should
be modeled as an area source rather than a line source. Figure 2 can be used to estimate the
maximum hourly ambient air concentration for an emission rate of 1 gram per second at
selected distances downwind from a source. The curves were calculated according to the
following assumptions: 1) the emission rate is 1 gram per second; 2) a flat terrain without
any structures near the emission source; and 3) the emission plume is of low, positive
buoyancy; 4) the emissions are uniformly distributed over the emitting area and constant
over time; and 5) the receptors are at ground level. A release height of 2m was used for
dumping/active piles, all other sources were assumed to be at ground level. The dispersion
model used is not reliable for estimating air concentrations close-in to area sources.
Estimates should not be made for any downwind location that is closer to the source than the
side length of the source.
If multiple sources are present, each should be evaluated separately (i.e., the
downwind concentration due to each source should be calculated and these values summed to
get the total concentration at a given location). If a given source is larger than the example
scenario, the appropriate curve in Figure 2 may still be used. The dispersion factor, in
micrograms/m3 per g/sec, obtained from Figure 2 can be used in Equation 11 to estimate the
maximum hourly ambient concentration and into Equation 12 to estimate the annual average
ambient air concentration for a given downwind distance. Since TSCREEN provides
maximum short-term estimates, the factor of 0.08 in Equation 12 is used to convert the
short-term estimate to an annual average estimate.
14
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Table 4.
Example Scenarios for Area Sources of PM Emissions
Parameter
Dumping Active, Piles
Dimensions
Area
Release height
Mixing. Tilling. Grading. Waste Transfer
Dimensions
Area
Release Height
Pry Surface Impoundments
Dimensions
Area
Release Height
Traffic
Dimensions
Area
Release Height
Units
m
m2
m
m
m2
m
m
m2
m
m
m2
m
Scenario
10 x 10 x 2
100
2
50x50
2500
0
100 x 100
10,000
0
50x50
2500
0
15
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0, = (ER)(F) (Eq. 11)
C. = (ER)(F)(0.08) (Eq. 12)
where Cm = Maximum hourly ambient air concentration(/ig/m3);
C, = Annual average ambient air concentration (jig/m3);
ER = Emission rate (g/sec); and
F = Dispersion Factor from Figure 2 Otg/mVg/sec).
The 0.08 factor in Equation 12 was developed by the U.S. EPA for point sources.
This factor has recently been revised and it is still under review by EPA and may be subject
to further change. There is no EPA policy for converting from hourly to annual estimates
for area sources. Various factors have been published that range up to 0.08.13 Factors up to
0.20 have been suggested for certain specific locations.16 Graphical estimation tools in lieu
of these factors also have been proposed.7-17 It is assumed that this point source factor can be
applied to area sources without greatly increasing the overall uncertainty of the air impact
estimate. As previously stated, the recommended approach is to use ISCLT to estimate long-
term concentrations.
ESTIMATION OF HEALTH EFFECTS
Cancer^ Effects Due to Long-Term Exposure
Potential cancer effects resulting from long-term exposure to substances emitted to the
air can be evaluated using inhalation unit risk factors. Inhalation unit risk factors are a
measure of the cancer risk for each /ig/m3 of concentration in the ambient air. They are
available on EPA's Integrated Risk Information System (IRIS), the Agency's preferred
source of toxicity information. User Support can be contacted at (513) 569-7254. The next
best source of inhalation unit risk factors is EPA's Health Effects Assessment Summary
Tables (HEAST) which are updated annually.18 Inhalation unit risk factors listed in IRIS as
of January 1993 or in HEAST (FY 1992) are given in Table 5 for 168 volatile and semi-
volatile organic compounds. This is an updated version of the same table contained in
References 2 and 3. Similar information is given in Tables 6 and 7 for selected semi-volatile
organic compounds and metals, respectively.
17
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Equation 13 can be used to estimate the cancer risk at a specified distance downwind
of the excavation area. Cancer risk is a measure of the increased probability of developing
cancer in a lifetime as a result of the exposure in question. Equation 13 assumes continuous
exposure (24 hours/day, 365 days/year for 70 years) to the estimated annual average
concentration in air.
R - (CJ(IUR) (Eq. 13)
R is the cancer risk from long-term exposure to a specific compound in air, (unitless);
C. is the annual average ambient concentration estimated from Equation 12, Og/m3); IUR is
the inhalation unit risk factor, (/xg/m3)'1 obtained from Tables 5, 6, or 7.
If the source operates for less than 70 years, multiply C. by x/70, where x is the
expected operating time of the source in years before using Equation 13. If more than one
contaminant is present, the cancer risks for each contaminant can be summed to derive the
total cancer risk at a specified distance downwind of the source.
Non-Cancer Effects Due to Long-Term Exposure
Non-cancer effects can be evaluated by using chronic inhalation reference
concentrations (RfCs). An inhalation RfC is an estimate (with uncertainty spanning perhaps
an order of magnitude) of continuous exposure of the human population to contaminants in
the air that is likely to be without appreciable risk of deleterious effects during a lifetime.
During the past three years, the EPA has become increasingly active in the development of
chemical specific RfCs.
If inhalation RfCs were not available from either IRIS or HEAST, then chronic oral
reference dose (RfD) data (in mg/kg/day) were multiplied by 70 kg (average body weight of
an adult), then divided by 20 nrVday (average adult inhalation rate), and finally multiplied by
1000 ttg/rng to derive a value in /xg/m3. This methodology was selected as the best available
approach for this screening document. The EPA, however, does not condone derivation of
RfCs from data for other routes of exposure on a chemical specific basis.
29
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The EPA considers the minimum basis for the derivation of an RfC to be a properly
conducted inhalation study that examines portal of entry effects. Portal of entry effects are
particularly important with respect to inhalation. There are many known cases where
respiratory effects due to inhalation exposure are much more severe than effects resulting
from equivalent oral doses. Therefore, ambient air action levels based on extrapolated oral
data should be used cautiously since there may be significant differences between the oral
and inhalation exposure pathways.
For compounds lacking RfC or RfD values, action levels were based on occupational
exposure levels recommended by the Occupational Safety and Health Administration
(OSHA)19 and the American Conference of Governmental Industrial Hygienists (ACGIH).20
The action levels were estimated by using the lower of the OSHA Permissible Exposure
Limit-Time Weighted Average (PEL-TWA) level (or ceiling value) or the ACGIH Threshold
Limit Value-Time Weighted Average (TLV-TWA) level (or ceiling value). The lower value
was divided by 1000 to compensate for differences between occupational and residential
exposures. It should be noted that occupational exposure levels are not intended for
evaluation or control of community air pollution or in estimating the toxic potential of
continuous, uninterrupted exposures. Therefore, ambient air action levels based on
occupational exposure limits are not precise distinctions between safe and dangerous ambient
air concentrations, nor are they necessarily indices of toxicity.
Long-term ambient air action level concentrations for non-carcinogens based on RfCs,
extrapolated RfDs and occupational exposure levels are also listed in Tables 5, 6, and 7.
The action levels are in units of ftg/m3 to facilitate comparison to the ambient air
concentrations estimated from Equation 12.
Short-Term Exposure
The short-term (one hour) action levels, in uglrn1, are presented in the last coiumn of
Tables 5, 6, and 7. The listed values were obtained by dividing the lowest of (1) the OSHA
PEL-TWA or (2) the ACGIH TLV-TWA (or ceiling limits if 8-hour averages are not
available) by 100. Division by 100 accounts for variations in human sensitivity (occupational
30
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levels are designed to protect healthy adult workers) and for uncertainties in using
occupational exposure levels to derive ambient air action levels.
The occupational exposure levels on which the short-term action levels are based are
subject to change. To check the values in Tables 5, 6, and 7 (or to derive values for
compounds not listed in the tables), determine the current OSHA PEL-TWA values by con-
sulting 29 CFR Section 1910 and the most recent edition of the ACGIH publication entitled
Threshold Limit Values and Biological Exposure Indices.
The short-term action levels listed in Tables 5, 6, and 7 can be compared directly
with the estimated maximum hourly ambient air concentrations obtained by using
Equation 11 and Figure 2. Use of the short term action levels should consider that no EPA
accepted method exists to determine the short-term concentrations of airborne chemicals
acceptable for community exposure.
EXAMPLE
The following steps illustrate the use of the estimation procedures presented in this
document. The goal is to estimate the maximum hourly and annual average ambient air
concentrations at the nearest receptor to area sources of PM emissions and compare these
values to the action level concentrations listed in Tables 5, 6, and 7.
Step 1 First, collect all necessary information. For this example, assume that a
Superfund site exists in Durham, NC and soil is excavated from a pit and
transported to a storage pile 500 m away. The backhoe moves 4 m3 of soil at
a time, and dumps the excavated soil directly into trucks. Ten truckloads a
day are moved with each truck containing 20 m3 of soil. In addition, a
bulldozer works over the storage pile for an hour each day. The soil moisture
content is 10% and the average wind speed at the site is 2 m/sec. The lead
content of the soil is 100 jig/g. The removal is expected to be in continual
operation for 20 days (1.728 x 106 seconds). The nearest off-site downwind
receptor is 400 merers away. The site also contains a one acre dry surface
impoundment. The soil has a silt content of 8%. A subset of the
contaminated soil is excavated every other day, placed in an (active) storage
pile, and then fed into a stabilization process. The storage pile has a surface
area of 2000 m2. One thousand kilograms per day-of the stabilized material is
placed in a lined portion of the dry surface impoundment.
31
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Step 2 Estimate the PM10 emission rate from each activity. To find the total PM10
emissions from this site, first convert the 20 m3 of soil for ten trucks to a
mass, using the default soil density of 1.5 g/cm3:
(20 m3)(1.5 g/cm3)(0.001 kg/g)(106 cm3/m3)(10 trucks) = 300,000 kg soil.
The particle size multiplier for < 10 /tm is 0.35. Use Equation 1 for the
backhoe emissions:
ER = 0.35 * (0.0016) * 300,000 * (2/2.2)1-3 / (10/2)14 = 15.6 g.
This number should be multiplied by 2, because the soil will be dumped once
into the trucks and dumped a second time onto the storage pile. Thus the total
emissions from dumping are 31 g and the average emission rate is 31 g/day
'(3.6 x 104 g/sec).
To find the lead emissions from the backhoe operations, first calculate the
fraction of lead in the windblown dust using Equation 7 with the lead content
of the soil (100 /*g/g) and the enrichment factor for lead from Table 2 (7.34):
Xj - (100)(7.34)(1(TS) = 7.34x10* (g lead/g windblown dust)
This value is then used with the average emission rate calculated above (31
g/day) and Equation 6:
EF^ = (7.34x10^(31) = 0.023 g/day (2.6 x 10"7 g/sec).
To find the PM,0 emissions from transport, the silt content of the unpaved
surface is needed, as well as the number of wheels per truck, the vehicle
weight, and the vehicle speed. Assume that these all equal the default values
from Table 1. The number of days with precipitation > 0.01" for North
Carolina is found from Figure 1. From Equation 5, the transport emissions
are:
EF = 610 (8/12)(20/48)(30/2.7f 7(10/4)03(365-120)/365 = 970 g/km.
A total of 10 truckloads are driven over a 1 km roundtrip, so the total
emissions (ignoring the weight difference between the empty and full truck)
are 9,700 g or 9.7 kg. The average emission rate is 9.7 kg/day.
Finally, to find the emission rate due to the bulldozing, use Equation 3:
ER - SSLSJH . 0.085 g/sec
(10)"
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Since the activity is underway for one hour, the total emissions are about 300
g per day.
Example calculations for paniculate matter emissions of less than 10 microns
from the other sources are given below. Emissions from the surface impound-
ment are estimated using Equation 8. The surface area of the impoundment is
one acre or 4050 m2. The particle size multiplier for < 10 pm is 0.5, the time
between disturbances is two days, and the default erosion potential is 33 g/m2.
The emission rate from the surface impoundment is:
m (0.5)(4050)(33) =
(2X86,400) * * "
Paniculate matter from wind erosion of continuously active piles can be
estimated using Equation 9. The number of rainy days from Figure 1 is 120:
Assuming 50% of the TSP is PM10, the emissions of PM10 from the storage
pile are:
ER = (1.41)(50/100)(2000) = 1400 g/day.
The emissions of PM10 emissions from the transfer of the stabilized waste can
be estimated using Equation 10 (assuming that all the PM is PM10):
—
(f
(1,000)
= 0.49 g per day
The emissions can be summed from ail activities. Emissions of paniculate
matter are equal to the sum of emissions from the backhoe operation,
transport, bulldozer operation, dry surface impoundment, storage piles, and
waste transfer:
31 -I- 9,700 + 300 + 33,000 -I- 1400 + 0.49 =* 44,000 g/day = 0.51 g/sec
33
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Emissions from the dry surface impoundment and transfer operations represent
the vast majority of the PM10 emissions. Assuming all of the soil is
contaminated with lead, then the emission rate for lead is (7.34 x
= 3.7x10"* g/sec. The fraction of lead in the windblown dust, 7.34 x 1C*4,
was calculated in Step 2.
Step 3 Estimate the downwind ambient air concentrations. Several activities are
performed at this site, so separate calculations could be performed for the
backhoe emissions, transport emissions, surface impoundment emissions, and
so forth. For simplicity, all emission sources are assumed to be located
together and only the most conservative dispersion factor is used. From
Figure 2, the maximum dispersion factor at a distance of 400 meters for any
of the activities is approximately 3000 ug/m3 per g/sec emission rate. This
corresponds to an annual average dispersion factor of 240 ug/m3 per g/s (3000
x 0.08 = 240). The ambient air concentrations estimated from Equations 11
and 12 are presented in Table 8. Using Equation 11, the hourly average
ambient air concentration for lead would be:
•
Cm = (0.00037)(3000) =1.1 ug/m3
Using Equation 12, the annual average air ambient concentration for lead
would be:
C. = (0.00037)(240) = 0.089 ug/m3
Step 4 Compare the downwind concentrations to the action level ambient air
concentrations. The short-term and long-term action levels from Table 7 for
lead are presented in Table 9. The estimated maximum hourly ambient
concentration for lead is slightly below the applicable action level. The annual
average ambient concentration also is somewhat below the long-term action
level.
Step 5 Document the results of the air pathway analysis and define a future course of
action. Based on these screening level results, a more rigorous analysis of the
air impacts is not warranted. The air impacts should be re-examined,
however, when site-specific input data are available, if the inputs differ from
the default values. Also, it would still be adviseable to perform an ambient air
monitoring program during the remediation to document actual worker and
community exposures.
34
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Table 8.
Estimated Emission Rates and Ambient Air Concentrations
"•"."::>' '•:
Lead
Soil Concentration
For Example Problem Qtg/g)
100
Emission Rate
(g/s)
3.7 x 10-1
Ambient Concentrations (/tg/m3)
Maximum Hourly
1.1
Annual Average
0.089
Table 9.
Action Level Concentrations
Lead
Table 7 Action Levels /ig/m3
Short-Term
1.50
Long-Term
0.15
35
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CONCLUSIONS
The procedures presented here are not intended to negate the need for rigorous
analyses that consider site specific meteorological conditions and the health effects of the
specific compounds involved. Although the procedures are based on what is typical and
reasonable for cleaning up Superfund sites, the underlying assumptions need to be kept in
mind. For example, emission models assume typical operating conditions, dispersion models
assume Gaussian distribution of the plume, and many of the health levels are not endorsed by
the Environmental Protection Agency. EPA's Regional lexicologist should be contacted for
general lexicological information and technical guidance on evaluation of chemicals without
established toxicity values.
REFERENCES
1. Eklund, B., S. Smith, and M. Hunt. Estimation of Air Impacts For Air Stripping of
Contaminated Water. EPA-450/1-91-002. May 1991.
2. Eklund, B., S. Smith, P. Thompson, and A. Malik. Estimation of Air Impacts For
Soil Vapor Extraction (SVE) Systems. EPA Contract No. 68-D1-0031, WA13.
December 2, 1991.
3. Eklund, B., S. Smith, and A. Hendler. Estimation of Air Impacts for the Excavation
of Contaminated Soil. EPA-450/1-92-004. March 1992.
4. Church, H. Excavation Handbook. McGraw-Hill, NY, NY. 1981.
5. U.S. EPA. Survey of Materials - Handling Technologies Used at Hazardous Waste
Sites. EPA/540/2-91/010. U.S. EPA-ORD, Washington, D.C. June 1991.
6. Eklund, B., et al. Control of Air Emissions From Superfund Sites. EPA/625/R-92-
012. November 1992.
7. Cowherd, C., P. Englehart, G. Muleski, and J. Kinsey. Hazardous Waste TSDF
Fugitive Particulate Matter Air Emissions Guidance Document. EPA 450/3-89-019.
May 1989.
8. U.S. EPA. AP-42: Compilation of Air Pollutant Emission Factors, Fourth Edition.
U.S. EPA, Office of Air Quality Planning and Standards, Research Triangle Park,
NC. September 1985.
9. Eklund, B., et al. Air/Superfund National Technical Guidance Study Series. Volume
IQ. Estimation of Air Emissions from Cleanup Activities at Superfund Sites. EPA-
450/1-89-003. NTIS PB89-180061/AS. January 1989.
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10. Momeni, M.H., Y. Yuan, and A.J. Zielen. The Uranium Dispersion and Dosimetry
(UDAD) Code. U.S. NRC. NTIS NUREG/CR-0553. May 1979
11. RTI. A Method for Estimating Fugitive Particulate Emissions from Hazardous Waste
Sites. EPA/600/2-87/066. NTIS PB87-232203. August 1987.
12. U.S. EPA> User's Guide - Emission Control Technologies and Emission Factors for
Unpaved Road Fugitive Emissions. EPA/625/5-87/022. September 1987.
13. Cowherd, C., G. Muleski, P. Englehart, and D. Gillette. Rapid Assessment of
Exposure to Particulate Emissions from Surface Contamination Sites. EPA/600-8-
85/002. February 1985.
14. U.S. EPA, A Workbook of Screening Techniques for Assessing Impacts of Toxic Air
Pollutants. EPA-450/4-88-009. September 1988.
15. Huey, N.A. and GJ. Schewe. Empirical Factor Emission of Air Toxic Source
Impacts. In: Proceedings of HMC/Superfund '92. Published by Hazardous Materials
Control Resources Institute, Greenbelt, MA. 1992.
16. Huey, N.A. (U.S. EPA, Region VII). Personal communication to Bart Eklund
(Radian Corporation). April 1993.
17. Guinnup, D.E. A Tiered Modeling Approach for Assessing the Risks Due to Sources
of Hazardous Air Pollutants. EPA-450/4-92-001. March 1992.
18. Health Effects Assessment Summary Tables (BEAST). U.S. Environmental Protection
Agency, Washington, D.C., OERR 9200.6-303 (92-1), NTIS No. PB91-92199,
March 1992.
19. 29 CFR ch. XVII. Subpart Z. Section 1910.1000. July 1, 1990.
20. 1992 - 1993 Threshold Limit Values for Chemical Substances and Physical Agents
and Biological Indices. American Conference of Governmental Industrial Hygienists,
Cincinnati, Ohio, 1992.
U S Environmental Protection Agency
Region 5, Library (PL-12J)
77 West Jackson Boulevard, 12th rioor
Chicago, IL 60604-3590
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