1PA450/1-92-002
United States
Environmental Protection
Agency
Office of Air Quality
Planning and Standards
Research Triangle Park NC 27711
EPA-450/1 -92-002
January 1992
Air/Superfund
AIR/SUPERFUND
NATIONAL TECHNICAL
GUIDANCE STUDY SERIES
AGENCY
Guideline for
Predictive Baseline Emissions
Estimation Procedures for
Superfund Sites
Interim Final
-------
GUIDELINE FOR PREDICTIVE
BASELINE EMISSIONS ESTIMATION
PROCEDURES FOR SUPERFUND SITES
INTERIM FINAL
Prepared by
Environmental Quality Management, Inc.
3109 University Drive, Suite B
Durham, North Carolina 27707
Contract No. 68-DO-0124
Work Assignment No. 1-80
PN 5025-8
Alison Devine, Work Assignment Manager
U.S. ENVIRONMENTAL PROTECTION AGENCY
REGION II
26 FEDERAL PLAZA
NEW YORK, NEW YORK 10278
January 1992
-------
PREFACE
This document was developed for the U.S. Environmental Protection Agency,
Region II through the Air/Superfund Technical Assistance Program. The document has
been reviewed by the National Technical Guidance Study Technical Advisory Committee
as well as the EPA, Region II Air Programs and Superfund staff. This document is an
interim final manual offering technical guidance for use by EPA Air and Superfund staff,
remedial and removal contractors, and potentially responsible parties. Because
assumptions and judgments are required in many parts of the analysis, the user of this
manual needs a strong technical background in emissions and atmospheric dispersion
modeling.
It is envisioned that this manual wili be periodically updated to incorporate new
data and information on air pathway analysis procedures. The Agency reserves the
right to act at variance with these procedures and to change them as new information
becomes available without formal public notice.
-------
DISCLAIMER
Mention of trade names or commercial products does not constitute
endorsement or recommendation for use by the U.S. Environmental Protection Agency.
The contents of this report are reproduced herein as received from the contractor. The
opinions, findings, and conclusions expressed are those of the authors and are not
necessarily those of the U.S. Environmental Protection Agency.
in
-------
CONTENTS
Preface ii
Disclaimer iii
Figures v
Acknowledgment vi
Objective 1
Background/Approach 1
How to Use These Procedures 2
Major Steps 3
Step 1 - Review Site Background and Gather Data Necessary
to Conduct the Baseline Emissions Estimate 4
Step 2 - List Air ARARs and TBCs 6
Step 3 - Estimate Air Emission Rates of Each Applicable
Site Contaminant 7
Step 4 - Estimate Ambient Air Concentrations and/or
Deposition Concentrations at Receptors of
Interest 31
Step 5 - Compare Ambient Concentrations to Air ARARs and
TBCs 37
Step 6 - Organize Concentration Data for Input to the
Baseline Risk Assessment 38
Appendix A Case Example A-1
IV
-------
FIGURES
Number
1 Decision flowchart 20
1a Threshold friction velocity versus aggregate size distribution 23
1 b Increase in threshold friction velocity with L,. 24
2 Function curve used in "unlimited reservoir" model 26
3 Thornthwaite's precipitation - evaporation index (PE)
for State Climatological Divisions 29
versus distance for six area source sizes 34
-------
ACKNOWLEDGMENT
This manual was prepared for the U.S. Environmental Protection Agency by
Environmental Quality Management, Inc. under Contract No. 68-DO-0124, Work
Assignment No. 1-80. Mr. Craig Mann (Project Manager) and Ms. Alison Devine (Work
Assignment Manager) managed the project. The principal authors were Mr. Craig
Mann of Environmental Quality Management, Inc. and Mr. John Carroll of International
Technology Corporation.
Mr. Joseph Padgett and his staff of the Office of Air Quality Planning and
Standards, U.S. Environmental Protection Agency, provided overall program direction.
Peer review of the manual was provided by the Air/Superfund Technical Advisory
Committee and by others including: Grace Musumeci (EPA, Region II), Donna Abrams
(EPA, Region III), and Marina Stefanidis (EPA, Region II).
VI
-------
GUIDELINE FOR PREDICTIVE BASELINE EMISSIONS
ESTIMATION PROCEDURES FOR SUPERFUND SITES
OBJECTIVE:
The objective of the following predictive procedures is to provide conservative
baseline emissions estimates of air pathway contaminants for use in the Baseline Risk
Assessment.
BACKGROUND/APPROACH:
In accordance with the National Oil and Hazardous Substances Pollution
Contingency Plan (NCP), the overriding purpose of an air pathway analysis (APA) is to
ensure the protection of human health and the environment. Protectiveness includes
compliance with Federal and State applicable or relevant and appropriate requirements
(ARARs) and other nonbinding criteria to be considered (TBCs) as well as a
demonstration that potential exposures are within the "acceptable risk range" for
carcinogenic contaminants, and are at or below other health-based criteria for toxicants
exhibiting noncarcinogenic effects. ARARs/TBCs and health-based criteria should be
considered mutually exclusive. That is, ARARs/TBCs may or may not be as protective
as the health-based criteria defined in the NCP. For example, many State air toxics
regulations are based on occupational exposure limits (e.g., TLVs, PELs, etc.) or are
simply based on best control technology with no assessment of actual exposure. In
addition, risk-based ARARs may not include all pathways of exposure pertinent to the
air pathway. Finally, compliance with air ARARs on a contaminant-specific basis may
not prove to be protective when the risks from each pollutant are aggregated for the air
pathway.
Unlike other environmental media, the air pathway is characterized by short
migration times, relatively large exposure areas, and a virtual inability to mitigate the
consequences of a release after the contaminants enter the atmosphere. Exposure
times may range from only a few minutes to many years, and exposure rates may vary
considerably due to the fluidity of atmospheric processes. The very nature of the air
pathway, therefore, is conducive to error in the measurement or prediction of the fate of
airborne contaminants over time and distance. To reduce this relative error,
procedures for estimating baseline air emissions must be conservative whether the
procedures incorporate measurement techniques (e.g., monitoring) or predictive
modeling.
-------
HOW TO USE THESE PROCEDURES:
These procedures are designed to be used during the RI/FS stage as a
guideline to predict air pathway emissions for use in determining exposure point
concentrations in the Baseline Risk Assessment. In addition, these data may also be
used to demonstrate compliance or noncompliance with air ARARs and/or TBCs for
the baseline case (undisturbed site).
The intent of this document is to provide the sequential series of steps necessary
to accomplish the baseline air pathway analysis. These steps incorporate the preferred
EPA predictive models (as of the date of publication) that may be applied to the air
pathway analysis. The models herein have been extracted from various EPA sources;
and therefore as a guideline, all the relevant information concerning the applicability,
limitations, and assumptions of each model are not necessarily included. To properly
use these procedures, the user is required to thoroughly understand all relevant
information from the original references cited throughout this document.
These procedures utilize predictive techniques based on theoretical mass
transfer and dispersion of contaminants into the atmosphere. Fate and transport
models incorporate conservative values to be consistent with the "reasonable maximum
exposure" scenario defined in the NCP. These models are also consistent with those
described in the Risk Assessment Guidance for Superfund, Human Health Evaluation
Manual, Part A, July 1989.
Use of these procedures, however, does not preclude the use of techniques for
measuring emission rates and/or ambient air concentrations of airborne contaminants.
Where site-specific conditions do not lend themselves to these predictive techniques
(e.g., heterogeneous distribution of contaminants, inappropriate meteorological data,
heightened community/State concerns, etc.), more rigorous techniques involving
refined emissions and air quality modeling or measurement techniques may be
necessary.
Emission and ambient air measurement techniques as well as other modeling
techniques which may be more suited to site-specific conditions can be found in the
Air/Superfund National Technical Guidance Study Series, Volumes I through IV, Office
of Air Quality Planning and Standards, EPA-450/1 -89-001, 002a, 003, and 004.
Finally, it should be understood that these procedures are hierarchical in nature,
building upon preceding steps. Mistakes or inaccurate data in individual steps,
therefore, will cause the final predicted values to have considerably greater relative
error. If problems or questions arise, contact your Regional Air/Superfund Coordinator
for assistance.
-------
MAJOR STEPS:
I. Review site background information and gather site characterization and other
data to conduct the baseline emissions estimate.
II. List all air ARARs and TBCs.
III. Estimate air pathway emission rates of each applicable contaminant.
IV. Estimate ambient air concentrations and/or deposition concentrations at
receptors of interest.
V. Compare ambient air concentration estimates to air ARARs and TBCs.
VI. Organize concentration data for input to the Baseline Risk Assessment.
-------
STEP I. REVIEW SITE BACKGROUND AND GATHER DATA NECESSARY TO
CONDUCT THE BASELINE EMISSIONS ESTIMATE
1. Review the nature of contamination at the site and identify potential air exposure
pathways and receptors (e.g., inhalation of volatile organics by an adult resident
100 m from the fenceline, etc.).
2. Assemble all relevant site data. This information may include but is not limited
to:
0 Site configuration and features (maps)
0 List of identified chemical contaminants
0 Sampling concentration data for each media (soil, water, and/or
air)
0 Spatial coordinates of each sample in three dimensions
0 Soils data (porosity, bulk density, and/or particle density, moisture
content)
0 Presence of soil crust and crust thickness, friability and soil particle
size distribution
0 Location and distance to receptors of interest
0 Local meteorological data (annual and/or seasonal average
temperature, windspeed and prevailing direction, if applicable)
0 Extent of surface vegetation and/or surface coverings.
3. Assemble chemical property data for all site contaminants. Data requirements
will vary depending on the type of compound and specific emission rate
equation(s) used in Step III. Chemical properties for volatile compounds may
include:
0 Molecular weight
0 Vapor pressure
0 Henry's Law constant
0 Diffusion coefficient in air
0 Liquid and gas-phase mass transfer coefficients (or overall mass
transfer coefficient)
0 Organic carbon partition coefficient
-------
0 Solubility limit in water
Reference for Physical and Chemical Properties of Contaminants: Air/Superfund
National Technical Guidance Study (NTGS) Series, Volume II - Estimation of
Baseline Air Emissions at Superfund Sites. Appendices F and G, Office of Air
Quality Planning and Standards, Research Triangle Park, North Carolina, EPA-
450/1-89-002a, NTIS PB90-270588, August 1990.
-------
STEP II. LIST AIR ARARs AND TBCs
1. List All Air ARAR and TBC Acceptable Ambient Levels and Averaging Times
(e.g.,/;g/m3 annual average, ppmv never to exceed, etc.):
A. National Ambient Air Quality Standards (NAAQS) for PM10, Pb, NOX, SO2,
CO, and ozone (as applicable)
B. National Emission Standards for Hazardous Air Pollutants (NESHAPs) as
applicable
C. State Ambient Air Concentration Guidelines or Standards (SAACGS)
D. Others as applicable
Note: Compliance with an ARAR or TBC acceptable
ambient level must be demonstrated on the same
averaging time basis (e.g., annual average, 24-hour
average, never to exceed, etc.).
Reference for Step II. 1: CERCLA Compliance With Other Laws Manual Part II,
OSWER Directive 9234.1-02, Office of Emergency and Remedial Response,
Washington, D.C., EPA-540/G-89/009.
2. Develop a set of air pathway pollutants for inclusion in the analysis.
Note: It may be advantageous to reduce the number of potential airborne
contaminants in the analysis or to combine certain pollutants by chemical
class. In some cases, however, the time required to implement the
selection/reduction procedures may exceed the time needed to simply
carry all potential airborne pollutants through the analysis. The
procedures described in the following reference should be used for
selection of potential pollutants. Particular attention should be given to
applying these procedures to the air pathway.
Reference for Step II. 2: Risk Assessment Guidance for Superfund (RAGS),
Volume 1, Human Health Evaluation Manual (Part A), Sections 5.8 - 5.9, Office of
Emergency and Remedial Response, Washington, D.C., EPA-540/1 -89-002.
December 1989.
-------
STEP III. ESTIMATE AIR EMISSION RATES OF EACH APPLICABLE SITE
CONTAMINANT
Background:
Predictive modeling techniques include calculation of theoretical emission rates
for both gaseous and particulate matter contaminants. Emission rate models predict
emission rates as a function of contaminant concentration and contaminant physical
and chemical properties within the surrounding media (e.g., within soils, surface water,
etc.) and through measured or theoretically derived mass transfer coefficients. Some
models have been evaluated against pilot-scale and field test results. Because these
models attempt to predict complex physical and chemical phenomena, their potential
relative error may be considered to span perhaps one order of magnitude.
It should be noted that many of these emission rate models require physical data
about the surrounding media (e.g., soil porosity, moisture content, etc.) as well as
physical and chemical properties of the contaminants (e.g., Henry's Law constants,
diffusivity in air, etc.). In addition, proper use of these emission rate models assumes
that a thorough site characterization has been accomplished and that media-specific
concentrations of all contaminants have been adequately determined within the site
volume in all three dimensions (i.e., all contaminant-specific "hot spots" have been
identified to a known depth). The emission rates calculated from these models must
accurately represent the site or gross under/overprediction of the resulting ambient air
concentrations will result.
1. Gaseous Emissions from Subsurface Soils:
A. For air release potential of contaminants from subsurface soils, measure
contaminant-specific soil gas concentrations. As an alternative, soil bulk
concentrations can also be used for predicting air release potential of
contaminants; however, soil gas measurements are preferred. Care must
be taken to ensure adequate site coverage.
Note: For baseline conditions, relatively shallow soil gas
measurements can be taken. Soil gas measurements
at greater depths will be advantageous if soil
excavation is contemplated during remediation.
Measurements should be made during periods of
stable atmospheric pressure to avoid "barometric
pumping" effects. Great care must be taken not to
disturb soil equilibrium conditions and thus dilute the
sample. For both soil gas and bulk concentration
samples, use the 95 percent upper confidence limit
(UCL) on the arithmetic mean for each homogeneous
-------
subsection of the area of contamination unless this
concentration is greater than the maximum detected
concentration. In this case, the maximum observed
value should be used. Data used in calculating
contaminant concentrations for this analysis should
include all detected concentrations of a substance
plus half the quant'rtation limit for each sample in
which that substance was not detected. Only
substances that were detected in at least one sample
from the site should be included in this analysis.
Reference for Step III. 1. A: RAGS Part A, Sections 5-6. December
1989.
B. If soil bulk concentrations are to be used to calculate emission rates,
estimate the saturation concentration (Csat) for each contaminant in the
vadose zone. Csat for each contaminant is the concentration at which the
adsorptive limit of the soil plus the theoretical dissolution limit of the
contaminant in the available soil moisture has been reached.
Concentrations > Csat indicate "free-phase" contaminants within the soil
matrix.
Csat = (Kdx s x nj + (sx 0J (D
where Csat = Saturation concentration, mg/kg (ppm)
Ky = Soil/water partition coefficient, I/kg (or m!/g)
s = Solubility of contaminant in water, mg/l-water
r^ = Soil moisture content expressed as a weight fraction, kg-water/
kg-soil
Qm = Soil moisture content, l-water/kg-soil (or ml/g).
Reference for Equation No. 1: Risk Assessment Guidance for Superfund
(RAGS), Volume I, Human Health Evaluation Manual (Part B, Development
of Risk-based Preliminary Remediation Goals), Interim, Section 3.3.1,
Office of Emergency and Remedial Response, Washington, D.C., EPA
Publication No. 9285.7-01 B, October 1991.
-------
Estimation of Ky if not available in the scientific literature:
/C = K x f (2)
oc oc
where Ky = Soil/water, partition coefficient, I/kg (or ml/g)
K^. = Organic carbon partition coefficient, I/kg (or ml/g)
foc = Fraction of organic carbon in soil, mg/mg (default = 0.02).
Estimation of K^ if not available in the scientific literature:
Use one of the following equations based on the chemical class closest to
the subject contaminant. If the contaminant does not fit any given class,
use Equation No. 3 (based on largest sampling):
Based on a wide variety of contaminants (mostly pesticides):
Koc = 10"
((0-544 loaK'^ " 1 -3771
Based on aromatics. polvnuclear aromatics. triazines. and dinitroaniline
herbicides:
K = 1 o"°'937 /0<7*~' " °-0061 (3a)
Based on aromatics or polynuclear aromatics:
-0.21)
Based on s-triazines and dinitroaniline herbicides:
K = 1 o"°-94 logK'-} * °-021 (3c)
-------
Based on insecticides, herbicides, and fungicides:
IS _ 1Q«1 -029 logKJl - 0.18)
(3d)
Based on substituted phenvlureas and alkvl-N-phenvlcarbamates:
K = 1 o<(0-524 heK'-1 * °-8551
(3e)
where H^. = Organic carbon partition coefficient, I/kg (or ml/g)
K^ = Octanol/water partition coefficient, I/kg (or ml/g).
Reference for Step III. 1. Equation Nos. 2-3e: Superfund Exposure
Assessment Manual (SEAM), Section 3.5.2.4, Office of Emergency and
Remedial Response, Washington, D.C., EPA-450/1 -88-001, 1988.
Reference for Values of t^c and logK^ in Step III. 1. B: Superfund Public
Health Evaluation Manual (SPHEM), Exhibit A-1, Office of Emergency
Remedial Response, Washington, D.C., EPA-540/1-86-060, October 1986.
C. From the vapor-phase contaminant concentrations (soil gas) or from bulk
concentrations determined in "A" above, calculate an emission rate for
each contaminant.
1. With measured soil gas concentrations:
El =
(4)
where
D.
= Emission rate of component i, g/s
= Diffusion coefficient of component i in air, cm2 /s (scientific
literature or Equation No. 7)
10
-------
Q = Vapor concentration of component i measured in the soil pore
spaces, g/cm3 (Equation No. 4a)
A = Exposed surface area, cm2
Pt = Total soil porosity, dimensionless (Equation No. 6). Pt assumes
dry soil (worst-case); if soil is wet more often than dry,
substitute the term (Pa10/3/P,2) f°r tne term Pt4/3 (see Equation
No. 6a)
dsc = Effective depth of soil cover, cm (from sample depth to soil
surface).
If soil gas measurements are given in ppm on a volume per volume basis,
use the following equation to convert to a weight per volume basis:
, ,„ ,
C, = Cnr x (4a)
' S° 2.404x1010
where Q = Vapor concentration of component i in the soil pore spaces,
g/cm3
CSQ = Measured soil gas concentration of component i, ppmv
MW| = Molecular weight of component i, g/mole.
2. With measured bulk concentrations > Csat (Equation No. 1):
Note: Under this scenario, "free-phase" contaminants exist in the
soil vadose zone, usually as a liquid-phase waste layer or
discrete film. Representative concentration measurements
should be used from the discrete waste layer at depth and
not from composite samples.
Et = D, C* A(P )• (5)
11
-------
where ^ = Emission rate of component i, g/s
D, = Diffusion coefficient of component i in air, cm2/s (scientific
literature or Equation No. 7)
Csi = Saturation vapor concentration of component i, g/cm3
(Equation No. 8)
A = Exposed surface area, cm2
Pt = Total soil porosity, dimensionless (Equation No. 6). Pt assumes
dry soil (worst-case); if soil is wet more often than dry,
substitute the term (Pa10/13/Pt2) f°r tne term Pt4'3 (see Equation
No. 6a).
M; = Mole fraction of component i in the waste, gmole/gmole
d,.c = Effective depth of soil cover, cm.
Note: When calculating Mj, include the number of moles of all
contaminants plus the water within the waste. Do not include the
number of moles of soil because soil is assumed to be nonvolatile.
Calculation of total soil porosity (Pt):
/», - 1 - (6)
P
where Pt = Total soil porosity, dimensionless
P = Soil bulk density, g/cm3: generally between 1.0 and 2.0 g/cm3
(default = 1.5 g/cm3)
p = Particle density, g/cm3: usually 2.65 g/cm3 for most mineral
material.
Note: Pt assumes dry soil and thus worst-case diffusion conditions. If the
soil cover is wet more often than dry on a long-term basis, air-filled
porosity (Pa) may be substituted for Pt. For estimation, Pt can be
12
-------
assumed to be between 0.55 for dry, noncompacted soils and 0.35
for compacted soils.
Calculation of air-filled porosity (PJ:
Pa=Pt- 6mp (6a)
where Pa = Air-filled soil porosity, dimensionless
Pt = Total soil porosity, dimensionless (Equation No. 6)
0m = Soil moisture content, cm3-water/g-soil (or ml/g)
ft = Soil bulk density, g/cm3.
Estimation of diffusion coefficient of component i in air (D,) if not available from the
scientific literature:
o.ooi r1
.75
N
1 1
MW{
MWa
(7)
a
/V^ \r \1/3l2
\Li ya ) J
where D, = Diffusion coefficient of component i in air, cnf/s
T = Absolute temperature of ambient air, ° K (annual average)
MVX; MWa = Molecular weight of component i and air (28.8), respectively,
g/mole
P^ = Absolute pressure, atmospheres
IX; zy, = Molecular diffusion volumes of component i and air (20.1),
respectively, cm3/mole. This is the sum of the atomic diffusion
volumes of the compound's atomic constituents.
13
-------
Atomic diffusion volumes for use in estimating D,:
C = 16.5 Cl = 19.5 Aromatic ring = -20.2
H = 1.98 Br = 35.0 Heterocyclic ring = -20.2
O = 5.48 F = 25.0
N = 5.69 S = 17.0
Example of calculating lVf for carbon tetrachloride, CCI4:
C = 16.5
Cl* = 4x19.5 = 78.0 +
94.5 cm3/mole
Note: Equation No. 7 may not be appropriate for polar compounds.
Where possible, values of Q in the scientific literature should be
used.
Calculation of saturation vapor concentration (Csi):
(8)
R T
where C6i = Saturation vapor concentration of component i, g/cm3
p = Vapor pressure of the chemical i, mm Hg
R = Molar gas constant, 62,361 mm Hg-cm3/mole-°K
T = Absolute temperature of waste (in situ), ° K
MW, = Molecular weight of component i, g/mole.
3. With measured bulk concentrations < Csat (Equation No. 1):
Note: Under this scenario all contaminants are assumed to
be in solution with the available soil moisture and
adsorbed to soil particles within the soil matrix (fully
incorporated). Soil samples should not show
evidence of discrete waste layers or films.
14
-------
where
A 2 D.; e K C:
In a t
(9)
Ej = Average emission rate of component i for exposure interval t,
g/s
D^ = Effective diffusivity of component i, cm2/s ( = DI e0'33)
Dj = Molecular diffusivity of component i in air, cm2/s (scientific
literature or Equation No. 7)
^ = Soil/air partition coefficient, g/cm3 (Equation No. 9b)
Q = Bulk soil concentration of component i, g/g
t = Exposure interval, s (exposure time x exposure frequency x
exposure duration in seconds)
€ = Soil porosity, dimensionless. e = Pt for dry soil or e = Pa when
soil is more often wet than dry (see Equation Nos. 6 and 6a)
A = Exposed surface area, cm2.
and:
a =
(9a)
where
p = Particle density, g/cm3 (default = 2.65 g/cm3).
Calculation of soil/air partition coefficient
41
(9b)
15
-------
where K^ = Soil/air partition coefficient, g/cm3
H = Henry's Law constant of component i, atm-nf/mole
Ky = Soil/water partition coefficient, ml/g or crrf/g (Equation No. 2)
41 = Conversion factor to change H to dimensionless form.
Reference for Step III. 3: Development of Advisory Levels for Poly-
chlorinated Biphenyl (PCB) Cleanup, Office of Research and
Development, Exposure Assessment Group, Washington, D.C. EPA-
600/6-86-002, 1986.
Reference for Step III. 3: RAGS Part B, Section 3.3.1, October 1991.
2. Gaseous Emissions From Nonaerated Surface Impoundments and Contaminants
(In Solution) Pooled at Soil Surfaces:
A. For air release potential of contaminants from nonaerated surface
impoundments and for diluted contaminants pooled at soil surfaces,
measure contaminant-specific liquid-phase concentrations of each
contaminant.
1. Take sufficient samples to ensure representative sampling of the
impoundment/pool.
2. Conduct analysis of samples to quantify content on a contaminant-
specific basis.
B. From the liquid-phase contaminant concentrations determined in "A"
above, calculate an emission rate for each contaminant:
E: = K.CA HO)
'I "( 5
where E; = Emission rate of component i, g/s
^ = Overall mass transfer coefficient, cm/s (Equation No. 11)
Cs = Liquid-phase concentration of component i, g/cm3
(1 mg/l = 1x10s g/cm3)
16
-------
A = Exposed surface area, cm2.
Calculation of overall mass transfer coefficient
R T
Ht klG
(11
where K; = Overall mass transfer coefficient, cm/s
k;L = Liquid-phase mass transfer coefficient, cm/s (Equation No. 12)
R = Ideal gas constant, 8.2x10~5 atm-m3/mole-°K
T = Absolute temperature, ° K
Hj = Henry's Law constant of component i, atm-rrf/mole
k;G = Gas-phase mass transfer coefficient, cm/s (Equation No. 13).
Estimation of liquid-phase mass transfer coefficient (k,L):
kir =
'* I MWi } (298 J [ v
(12)
where
= Liquid-phase mass transfer coefficient, cm/s
= Molecular weights of oxygen (32.0) and component i, respectively,
g/mole
T = Absolute temperature, ° K
= Liquid-phase mass transfer coefficient for oxygen at 25° C, cm/s
(default = 0.002 cm/s).
17
-------
Estimation of gas-phase mass transfer coefficient (kjG):
,0.335
nr» \ 1.005
fee. H,,
where k;G = Gas-phase mass transfer coefficient, cm/s
MWH 0; MWj = Molecular weights of water (18.0) and component i, respectively,
2 g/mole
T = Absolute temperature, ° K
KG, H2O = Gas-phase mass transfer coefficient of water vapor at 25° C, cm/s
(default = 0.833 cm/s).
Reference for Default Values of k^O; and k;G.K,O: Evaluation and Selection
of Models for Estimating Air Emissions From Hazardous Waste Treatment,
Storage, and Disposal Facilities, Section 2, Office of Air Quality Planning and
Standards, Research Triangle Park, NC. EPA-450/3-84-020, NTIS PB85-
156115, December 1984.
3. Volatile Nonmethane Organic Compound (NMOC) Emissions From Codisposal
Landfills:
Codisposal sites contain toxic wastes in combination with
municipal or sanitary wastes which generate landfill gases (e.g.,
methane, hydrogen gas, and carbon dioxide). These "sweep"
* gases greatly increase the upward migration of volatile NMOCs
and their subsequent release to the atmosphere. In fact, the
landfill gas velocity becomes the controlling factor so that soil and
gas-phase diffusion become essentially insignificant.
A. Measure soil gas concentrations of each volatile NMOC.
B. From the soil gas concentrations determined in "A" above, calculate an
emission rate for each volatile NMOC:
ECVA (14)
18
-------
where Ej = Emission rate of component i, g/s
Q = Concentration of component i in the soil pore spaces, g/cm3
Vy = Mean landfill gas velocity in the soil pore spaces, cm/s (default
= 1.63x10"3 cm/s average)
A = Exposed surface area, cm2.
Note: The default value of Vy is an average value. Various site factors such
as saturated soils will tend to reduce the rate of volatilization. The degree to
which this model is able to accurately predict release rates under conditions
of moist or wet soils is unknown. Under such conditions, emission flux
measurements at soil surfaces may be necessary.
Reference for Step III.1.2.&3: SEAM, Section 2.3.2.1., April 1988.
4. Free-phase Volatile Contaminants Directly Exposed to the Atmosphere:
For any and all free-phase volatile contaminants directly exposed to the
atmosphere, in-depth APA is warranted. Source monitoring is recommended to
determine emission rates, supplemented by ambient monitoring and/or refined
modeling. Applicable situations include open drums/containers, fresh spills, etc.
where free product exists.
5. Solids and Semivolatiles Emitted as Particulate Matter:
A. For solids and semivolatile contaminants with air release potential (e.g.,
metals, semivolatiles, and pesticides adsorbed to fugitive dust, etc.), measure
contaminant-specific bulk concentrations of erodible surface materials.
Note: If onsite data are not available, assume that the
contaminant concentrations measured from bulk
samples of surface materials are constant across the
entire soil particle size range.
For estimating emissions from wind erosion, either of two emission flux
(g/rrf-h) models are used depending on the credibility classification of the
site surface material. These two models are: 1) "unlimited reservoir," and 2)
"limited reservoir." Each site surface of homogeneous contaminant
concentration must be placed into one of these two classifications. The
following decision flowchart (Figure 1) is used to determine: 1) whether no
19
-------
No.1
No.4a
No.4d
No. 4«
Figure 1. Decision flowchart.
20
-------
wind erosion potential exists, or 2) which of the two emission flux models is
applicable for site conditions. The instructions within each box of the
flowchart are detailed in the list of steps following the flowchart.
It should be noted that the two emission flux models (Equations 15 and 18)
represent average annual emissions. This assumes continuous emissions
over time. In actuality, emissions do not occur except during periods when
the windspeed meets or exceeds the threshold friction velocity for the given
soil particle size. A continuous average emission flux is calculated to
account for a continuous exposure interval (i.e., hours/day x days/year x
years).
Detailed Steps for Flowchart:
No. 1 Continuous Vegetation?
Continuous vegetation means "unbroken" vegetation covering 100 percent of
the site or site sector to be analyzed.
No. 2 Is Crust Present?
Crusted surfaces are regarded as having a "limited reservoir" of erodible
particles. Check for crust thickness/strength during the site inspection.
No. 3a Determine Threshold Friction Velocity
Threshold friction velocity (u't) is that wind velocity at which erodible site
particles are suspended. To determine u't) the mode of the surface
aggregate size distribution must be determined. The distribution mode is the
particle size containing the highest percentage of material from a
representative sample. This can be determined with a field sieving procedure
as follows:
1. Prepare a nest of sieves with the following openings: 4 mm, 2 mm, 1
mm, 0.5 mm, and 0.25 mm. Place a collector pan below the bottom
sieve (0.25 mm opening).
2. Collect a sample representing the surface layer of loose particles
(approximately 1 cm in depth for an uncrusted surface), removing any
objects larger than about 1 cm in average physical diameter
(nonerodible material). The area to be sampled should not be less than
30 cm x 30 cm.
3. Pour the sample into the top sieve (4 mm opening), and place a lid on
top.
21
-------
4. Rotate the covered sieve/pan by hand using broad sweeping arm
motions in the horizontal plane. Complete 20 rotations at a speed just
necessary to achieve some relative horizontal motion between the sieve
and the particles.
5. Inspect the relative quantities of catch within each sieve and determine
where the mode in the aggregate size distribution lies, i.e.., between the
opening size of the sieve with the largest catch and the opening size of
the next largest sieve (e.g., 0.375 mm lies between the 0.5 mm and the
0.25 mm sieve).
With the aggregate size distribution mode, determine the threshold friction velocity
(u't) in cm/s from the relationship in Figure 1a.
No. 3b Correct for Nonerodible Elements
Mark off a representative site area 1m x 1m and determine the fraction of
total area, as viewed from directly overhead, that is occupied by nonerodible
elements (e.g., stones, clumps of grass, etc.). Nonerodible elements can be
said to exceed 1 cm in diameter. Correct the overhead fractional area of
nonerodible elements to the equivalent projected frontal area. An example
would be that a spherical stone with an area of 10 cm2 as viewed from
overhead but half-buried in the soil, would have a frontal projected area of 5
cm2. Determine the ratio of the frontal projected area of nonerodible
elements to the total overhead area of the erodible soil. This ratio (LJ is
used with the relationship shown in Figure 1b to determine the appropriate
correction factor. Multiply u't by the correction factor to obtain the corrected
threshold friction velocity (u*t).
Note: If data for determining L,. is not available, a conservative default
value of 0.01 may be used for nonsmooth soil surfaces. This
results in a correction factor of approximately 1.5.
No. 3c Is Corrected Threshold Friction Velocity >75 cm/s?
75 cm/s is an empirical number determined through observation of actual
soil types.
No. 4a Determine Crust Thickness/Strength
and
No. 4b Crust Easily Crumbled?
If the crust thickness is <0.6 cm or if the crust can be easily crumbled by
hand pressure it exhibits a potential for wind erosion.
22
-------
o
o
\
o
03
O
to
o
IN
to
CO
o
o
•O
O
.g
L.
To
Q
L.
O)
O)
re
en
D
w
^
o
c
o
o
f-
o
L.
H
r:
O
L_
O)
LL
O O o
O O o
o co to
o
o
o
o
CM
o o
O CO
o
ID
o
ex
(oas/Luo) \n
23
-------
CO
ID
CO
o
_o
o
c
o
eo
(O
2
o
to
o
x.
o
c
JQ
O
CO tO
(ltn) AiiooiaA UOUOMJ
(\n) Ajioo|3A uo
-------
No. 4c Loose Material Present?
Determine if there is loose erodible material above any hardened crust.
No. 4d Estimate Size Distribution Mode and Threshold Friction Velocity
Estimate the aggregate size distribution mode of the loose material above the
hardened crust and determine the threshold friction velocity (u't) (Step 3a).
No. 4e Correct for Nonerodible Elements (u*t)
(Step 3b)
B. Using either the "unlimited reservoir" or the "limited reservoir" model as
determined from Figure 1, calculate an annual average emission flux (g/m2-h)
for each contaminant found in the erodible surface material.
1. Using the "unlimited reservoir" model
a. Emission flux for inhalable particles j< 10//m (PM10):
£10 = 0.036 (1 -V) (M ] F(x ) C (15)
where E,0 = PM10 annual average emission flux of component i, g/m2-h
V = Fraction of contaminated surface with continuous vegetative cover
(equals 0 for bare soil)
[u] = Mean annual windspeed at 10 m anemometer height, m/s (from
local climatological data)
\\ = Equivalent threshold value of windspeed at 7 m anemometer height,
m/s (Equation No. 16)
C = Fractional percent by weight of component i from bulk samples of
surface material
F(x) = Function obtained from the relationship in Figure 2
(x=0.886 Ut/[u], dimensionless ratio).
25
------- An error occurred while trying to OCR this image.
-------
Calculation of the equivalent threshold value of windspeed at a 7 m
anemometer height (u,):
«, = 18.1 (u'0/100 (16)
where (\ = Equivalent threshold value of windspeed at a 7 m anemometer
height, m/s
(u*t) = Threshold friction velocity corrected for nonerodible elements, cm/s
(5.A, detailed Steps 3a and 3b)
Note: This calculation is based on an assumed roughness
height for flat terrain of 0.5 cm, between natural snow
(0.1) and a plowed field (1.0). Refer to the reference
for Step III.5. to calculate u, if a roughness height of 0.5
cm is not appropriate for site-specific conditions.
b. Emission flux for particles _<30x/m (for deposition modeling):
where £30 = Annual average emission flux of component i as
particles j< 30/y m, g/m2-h
EK) = PM10 annual average emission flux of component i,
g/m2-h (Equation No. 15).
2. Using the limited reservoir" model.
a. Emission flux for inhalable particles _< 10/vm (PM10):
27
-------
£10 = 0.83
(1000) (P£/50)
where E,0 = PM1? annual average emission flux of component i,
g/nf-h
f = Frequency of disturbances per month (1/month for abandoned sites
or sites with no activity)
u* = Observed (or probable) fastest mile of wind (at 10 m anemometer
height) for the period between disturbances, m/s (from local
climatological data)
P(u+) = Erosion potential, i.e., quantity of erodible particles at the surface
prior to the onset of erosion, g/m2 (Equation No. 19 or 19a)
V = Fraction of surface area covered by continuous vegetation (equals O
for bare soil)
C = Fractional percent by weight of component i from bulk samples of
surface material
PE = Thornthwaite's Precipitation-Evaporation Index used as a measure of
soil moisture content (Figure 3).
Calculation of erosion potential [P(u+)]:
P(u*) = 6.7 (t/* - ut) for u* >ut (19)
P(u+) = 0 for u' < ut <19a)
where P(u+)= Erosion potential, g/m2
28
-------
M
C
Q
"5
_o
"5
£
o
**
a
E
O
0
*->
TO
53
UJ
a,
x
o
T3
C
o
o
a
N
UJ
C
o
o
o
a!
M
2
~n
SI
o
.C
3
O)
-------
u+ = Observed (or probable) fastest mile of wind (at 10 m anemometer
height) for the period between disturbances, m/s (from local
climatological data)
u, = Equivalent threshold value of windspeed at a 7 m anemometer height,
m/s (Equation No. 16).
b. Emission flux for particles _< 30//m (for deposition modeling):
£30 • *io x 2 {20)
where £30 = Annual average emission flux of component i as particles
_< 30 //m, g/rtf-h
E,0 = PM1J? annual average emission flux of component i,
g/rrr-h (Equation No. 18).
Reference for Step III. 5: Rapid Assessment of Exposure to Particulate Emissions
from Surface Contamination Sites, Sections 1 - 4.1.2. Office of Health and
Environmental Assessment, Washington, DC. EPA-600/8-85/002. February 1985.
C. Calculate a total emission rate (g/s) of each contaminant from the emission
flux rate using the following formula:
ET = L (20a)
r 3600
where ET = Annual average emission rate of component i for particles _<
9/s
EX = EIO °r £30 emission flux obtained from Equation Nos. 15, 17, 18, or
20, g/mf-h
A = Contaminated surface area, m2.
30
-------
STEP IV. ESTIMATE AMBIENT AIR CONCENTRATIONS AND/OR DEPOSITION
CONCENTRATIONS AT RECEPTOR LOCATIONS OF INTEREST
Background:
Once emission rates have been calculated, atmospheric dispersion models are
used to predict ambient air concentrations and/or deposition concentrations at
receptors of interest. Dispersion models may include simple hand calculations or
special computer models. Upper bound values can be approached by making
conservative modeling assumptions (e.g., worst-case meteorological conditions, source
configuration, etc.). A number of other more refined EPA-approved dispersion models
may be substituted for models in the procedures listed below if an in-depth APA is
warranted. Use of the procedures below should generally produce a more
conservative estimate.
1. Model the emissions of each contaminant (gaseous or particulate) for each source
using the appropriate EPA atmospheric dispersion model and source configuration
data (i.e., size, location, height, etc.).
A. Determine if the release is negative, positive or neutrally buoyant.
Note: Under various release scenarios more applicable to
CERCLA Removal Actions (e.g., sudden release of
dense gases) negatively buoyant releases may be
encountered. Impacts from negatively buoyant
releases are likely to be most severe during stable
atmospheric conditions and light windspeeds. Under
these conditions, buoyancy effects may dominate
atmospheric turbulent energy reducing dispersion and
resulting in higher concentrations close to the site. If
negatively buoyant releases are anticipated, perform
the calculations referenced below to determine if
negative buoyancy effects are applicable.
Reference for Step IV. 1.A: A Workbook of Screening Techniques
for Assessing Impacts of Toxic Air Pollutants (Workbook), Section
5.1. Office of Air Quality Planning and Standards, Research
Triangle Park, North Carolina. EPA-450/4-88-009. NTIS PB89-
134340. September 1989.
Note: The Workbook contains hand calculation procedures
for estimating emission rates, dispersion parameters,
and ambient air concentrations for 18 different release
scenarios typically found at treatment, storage, and
31
-------
disposal (TSDF) facilities (e.g., pipe leaks, tank leaks,
etc.). These procedures may be used in conjunction
with or in lieu of the procedures described herein if the
baseline case accurately approximates one of the 18
scenarios described in the Workbook. Care should be
taken, however, to carefully analyze and compare the
emission rate scenarios in the Workbook with that of
the baseline case to ensure that the Workbook
emission scenarios are appropriate. The Workbook
procedures have been converted to a PC-based
system called TSCREEN. TSCREEN is available free of
charge from the EPA Support Center for Regulatory Air
Models (SCRAM) Bulletin Board System at (919) 541-
5742.
B. For neutral or positively buoyant point or area source emissions, use the
EPA SCREEN atmospheric dispersion model to predict short-term (if
applicable) downwind ambient air concentrations t/g/m3). The SCREEN
model predicts one hour average concentrations at receptors, independent
of wind direction, for point, area, and flare sources. Because the SCREEN
model can accommodate only one source for each run, model each source
separately and aggregate the predicted concentrations at the receptors of
interest. Aggregating will yield a conservative one hour average estimate.
The following reference should be reviewed to fully understand the
capabilities and limitations of the SCREEN dispersion model. SCREEN may
be obtained free of charge from the SCRAM Bulletin Board at (919) 541-
5742.
Reference for Step 1V.1.B: Screening Procedures for Estimating
the Air Quality Impacts of Stationary Sources. Office of Air Quality
Planning and Standards, Research Triangle Park, North Carolina.
EPA-450/4-88-010. NTIS PB89-159396. August 1989.
C. As applicable, estimate 3-, 8-, 24-hour, or annual average concentrations
(e.g., to demonstrate compliance with ARARs/TBCs of the same averaging
times) at receptors of interest by multiplying one hour concentrations fc/g/m3)
by the following factors:
Averaging time Multiplying factor
3 hours 0.9
8 hours 0.7
24 hours 0.4
annual 0.025 (for point sources only)
32
-------
Reference for Step IV.1.C: Workbook. Appendix E.
Reference for Annual Point Source Multiplying Factor: Estimation of Air
Impacts From Air Stripping of Contaminated Water. Air/Superfund NTGS
Series, Office of Air Quality Planning and Standards, Research Triangle Park,
North Carolina. EPA-450/1-91-002. NTIS PB91-21888, May 1991. (The
referenced value is presently under review and subject to change.)
D. Estimate downwind annual average concentrations for area sources using
the following procedures:
1. Estimate the combined area source size by summing the sizes of all
individual area sources.
2. Determine the square area of the combined area source (example:
2,500 m2 = 50 m x 50 m).
3. Determine the total annual emission rate for the combined area source
and convert to kg/m2-yr.
4. From the set of curves in Figure 4, locate the //Q value for the
appropriate downwind receptor distance and source size.
5. Multiply the//Q value (10~9 yr/m) by the annual emission rate per
square meter, Q (kg/mf-yr) to derive the annual average concentration,
X (fJQ/m3) for the combined source.
Note: For downwind distances <50 meters and for onsite
receptors, the model presented in the following step
(Step IV,1,E) may be used.
Reference for Step IV.1.D: Hazardous Waste TSDF-Fugitive Particulate Matter
Air Emissions Guidance Document, Appendix C. Office of Air Quality
Planning and Standards, Research Triangle Park, North Carolina. EPA-
450/3-89-019. NTIS PB90-103250. May 1989.
E. If the receptor is located at the edge of the area source or within the
contaminated area, use the following procedure to estimate the annual
average concentration at the center of the area source.
Given the horizontal dimension of the square area source (X in meters) and
the total source emission rate (Q,- in g/s):
33
-------
o
o
0
o
IO
X
o
o
IO
t
i
i
i
_-**"
1 1 1
0
O
CO
X
o
o
CO
(
i
i
i
.-•*•*
t I
1 II i
CM If: r£ c
X X X ^
1 I I i
0 S 0 C
CM 5 ;£ u
(
1
1
1
_s
,s'
./'
s"'
^••'"
^••^ .^
~~ — •
I 1 1 1 I 1 1 1
1 /(}
< /Mi
/ | |:.
- I ! ,;t
— : i |:i
3 / «!
• 1 •:
/ l' ' = '
/ » 'i;
/ i ':":
/ i J|:
/ / ' i •
• i : ]
/ / '!•
/ / 'l\
/ ! 1 ': •
/ / //?
/ / //'
/ / ' M
/ ' -; •'
- / •" / I
/" / / ; I
S ,' ..-•' / /
-^ s ..-' / 1
^ -"."--••"",'-''' J__
i
I 1 1 I 1 i [ 1 I il i
CO
- O
_ o
- "•"
- O
o
CM
- O
_ O
0
- ^~
- o
— o
_ 00
- o
- 0
_ CO
-
~ o
- 0
^J"
—
- o
— o
_ CM
O
O
O
CO
(0
o
o
o
O)
T3
01
I
i
o
Q
O
VL.
O
o
C
CO
0)
N
O
o
^
3
O
(/)
C5
O
^
C3
X
O
£
3
cn
II
to
CM
O
O
IO
O
IO
10
CM
34
-------
1. Determine the natural logarithm of the horizontal dimension of the
subject area source (InX).
2. Enter the value produced in (1) above into the following polynomial
equation to produce the natural logarithm of the normalized
concentration:
InfC/Or) = 13.0-0.261 (InX) -0.241 (InX)2 + 0.0124(!nX)3
3. Take the exponential of the value produced in (2) above to produce the
normalized concentration:
C/Q, = dn(C/cV
4. Multiply the normalized concentration by the emission rate to produce
the long-term (annual average) concentration in/yg/m3:
C = (C/QJQ,
Note: The above polynominal equation is based on the modeling results of
progressively larger square area sources utilizing the U.S. EPA Point-
Area-Line (PAL) dispersion model. A single receptor was located at the
center of each source negating the effects of wind direction.
Windspeed was set at 2 m/s and atmospheric stability was set at
Pasquill-Gifford class D (neutral) as typical average annual values.
Emissions are assumed to be continuous, uniform over the surface of
the area, nonbuoyant, inert, and emitted at a concentration less than
approximately one percent (10,000 ppmv), so that density differences
relative to air are not important. These procedures may not be
conservative for sites in very sheltered locations where windspeeds may
average less than 2 m/s and/or where very stable conditions may be
typical. In these cases, refined modeling and/or monitoring may be
required.
The procedures in Step IV,1,D and E are presently under review and
subject to change.
Reference for Step IV.1.E: Memorandum from Robert Wilson, U.S. EPA, Region X
Meteorologist, to Pat Cirone, Chief, Health and Environmental Assessment
Section. June 1991.
2. If the Baseline Risk Assessment ultimately indicates that the incremental or
aggregate risk for carcinogenic contaminants from onsite incidental ingestion of
contaminated soil exceeds the acceptable risk range (i.e., 10~4 to 10~6) or if the
35
-------
Hazard Index for noncarcinongenic contaminants for the same pathway exceeds
unity, determine the deposition concentration (g/m2) of each applicable
contaminant at receptors of interest. Deposition concentrations are used to
calculate exposures from atmospheric deposition of contaminants. Applicable
pathways may include incidental ingestion of soil, uptake in edible biota, indoor
exposures due to track-in of outdoor dustfall, etc.
A. Model the particulate emissions of each applicable contaminant using the
EPA Industrial Source Complex (ISC) model or the EPA Fugitive Dust Model
(FDM) to determine deposition concentrations.
Reference for Step IV.2.A. User's Guide for the Fugitive Dust Model (FDM)
(Revised), User's Instructions, U.S. EPA, Region X, Seattle, Washington.
EPA-910/9-88-202R. NTIS PB90-215203, PB90-502410 (program diskette).
January 1991.
Reference for Step IV.2.A: Industrial Source Complex (ISC) Dispersion
Model User's Guide-Second Edition (Revised), Volumes I, II, and User's
Supplement. Office of Air Quality Planning and Standards, Research
Triangle Park, North Carolina. EPA-450/4-88-002a and 002b. NTIS
PB88-171475, PB88-171483, and PB88-171491. December 1987.
Note: The most recent and fully capable editions of ISC and FDM may
be obtained free of charge from the SCRAM Bulletin Board at
(919) 541-5742.
B. For sites that are suspected of having deposited contaminants (especially
low mobility contaminants) offsite over an extended period of time, measure
contaminant-specific concentrations of surface materials at receptors of
interest. The potential contributions from other sources in the area (if any)
should be considered and separated from the analysis.
36
-------
STEP V. COMPARE AMBIENT AIR CONCENTRATIONS TO AIR ARARs AND TBCs
1. From dispersion modeling results performed in Step IV, compare estimated
ambient air concentrations with air ARARs and/or TBCs listed in Step II.
Comparisons must be made on a chemical-specific basis and estimated
concentrations must represent the same averaging time(s) as the ARARs/TBCs
(e.g., annual average, 24-h average, etc.).
Note: Most ARAR's specify that the applicable standard must be complied
with at the point of public access. For ground level nonbouyant
sources this will be the site fenceline. For such ARARs, dispersion
modeling must include such a receptor whether or not the receptor also
represents the maximum exposed individual.
2. If any air ARAR or TCB is exceeded, an in-depth air pathway analysis is warranted
which may include in-depth modeling and/or air monitoring.
37
-------
STEP VI. ORGANIZE CONCENTRATION DATA FOR INPUT TO THE BASELINE
RISK ASSESSMENT
1. In tabular form, list the long-term (annual average) ambient air concentrations of
each potential airborne contaminant derived from Step IV. Include these air
concentrations in the summary of exposure point concentrations for all pathways.
Note: For baseline conditions, long-term concentration averages
representative of the reasonable maximum exposure scenario are most
applicable for the Baseline Risk Assessment. If emission potentials are
significant, however, short-term or acute concentration estimates (e.g.,
1-h, 3-h, 8-h, or 24-h average) may be required. In addition, deposition
concentration estimates (g/m2) may be applicable (see Step IV, 1, B
and Step IV, 2).
2. List all variables and assumptions used in the emission and dispersion modeling
analyses and discuss the uncertainty associated with each as well as how this
uncertainty may affect the final estimates.
38
-------
APPENDIX A
CASE EXAMPLE
A-1
-------
PREDICTIVE BASELINE EMISSIONS ESTIMATION FOR
CAS EX SITE
STEP I. REVIEW SITE BACKGROUND AND GATHER NECESSARY DATA
Background:
The hypothetical Casex Superfund site is located in a mixed
rural/residential/commercial area of a northeastern state. The site contains an inactive
scrap metals and polymer processing facility. Wastes from the polymer reclamation
process were stored in underground storage tanks, and other wastewaters were
discharged to a ditch located onsrte. The facility was in operation for approximately 25
years and was closed in 1985. Removal actions were conducted in 1990 to remove
tanks, drums, and debris.
Various volatile and semivolatile organics and metals have been identified in the
soils and groundwater. Soil gas survey data for volatile organic compounds (VOCs) is
available in addition to soil boring sample data.
1. Review the nature of contamination at the site and identify potential exposure
pathways and receptors.
The primary air exposure pathways are:
0 Inhalation of volatile contaminants released from near-surface and
subsurface soils
0 Inhalation of metals and semivolatile contaminants (adsorbed to soil
particles) released as fugitive particulate matter from surface soils.
The potential receptors are residents located at a house on the property east of
the areas of contamination, and residents of apartments located just south of the
property. Distances will be tabulated in the site data to follow. A secondary
potential exposure pathway is ingestion of metals and semivolatile contaminants
redeposited offsite from fugitive dust.
-------
2. Assemble all relevant site data.
The site consists of 17.5 acres of which about one-half is wooded. The plant area
contains five buildings on the west side of the property and the major areas of soil
contamination. This area is fenced and contains approximately 5 acres. Figure
1 shows the general site map.
The list of chemicals identified in soils, the 95 percent UCL of the arithmetic mean
of the bulk concentrations and soil gas concentrations, and sampling depths were
assembled and are shown in Table 1. The reference chemical properties are also
shown in this table. Rgure 2 will be used to define the limits of volatile organic
contaminants in soils as measured in the soil gas. The fenceline represents the
approximate limits of metal contamination in surface soils. Surface vegetation in
these areas was not reported.
Soil types include mainly sand and loamy sand. Grain size analyses of surface
soils and average soil moisture content (2%) of subsurface (vadose zone) soils
were obtained, but other properties such as soil porosity were not reported. The
grain size analysis for surface soils is shown in Table 2. Permanent groundwater
is present at a depth of 15 to 20 feet, and the land is relatively flat.
The following were taken from Figures 1 and 2:
For volatile and semivolatile organics and metals:
Area of contamination
Distance to house
Distance to apartments
150 m x 150 m = 22,500 m2
175 mE
210 mS
TABLE 2. GRAIN SIZE ANALYSIS FROM SURFACE SOIL SAMPLES
Soil type
Gravel
Coarse sand
Medium sand
Fine sand
Silt
Clay
Grain size, mm
2.00 - 4.75
0.42 - 2.00
0.25 - 0.42
0.075 - 0.25
0.006 - 0.075
< 0.006
Average fraction, %
6.5
12.3
36.6
28.1
6.6
9.9
100.0
-------
a.
<
5
u
z
u
o
w
**
oS
o
cr>
a
re
E
a
**
"w
"w
^
a
c
a
V
3
-------
O CT
1
S3
fe
LU
0_
O
cc
CL
O
LU
X
O
Q
CD
Z
CO
11!
_J
CD
LO O
cnoo
Q
o
OOOOOCOOOO
.... ff) LO CD CD ^"
COCOCOCJCOCJCOCOCO
ooooooooo
I I I I I I I I I
i. i LU tii 1.1 LIJ ii i iii LU LU
co CD co cn •—4 ^f f*«> co ^~
—tCJCJCJCJCJCJCJCJ
CDCDCDCDOCDOOCD
t I t I I I I t I
LU LU LLJ UJ LU LU LU CU LU
OOOOOOOOI--
cjocjcocjco—«t
to • • - co cj •
co i**- LO r-* -H •—« co
to CD •-« cj
LO—iCOtDOirOCSJtOtD
CD O O CD CD O
CD CD CD O O O
CO CD CD O CD O
r-» T o co co O
—« r-. co co O
,—i tn
LO
—t LO -^-t *r ^r m to to en
M- • O CD O O O O
) f-. CJ CJ —i CO
» CO —H LO O LO
—I -^ CJ
- O CO tO •— < lT> CJ
ooooooooooo
OOOOOOOCOOOO
r— t-* co LO —< to c-j ca »—»
C <0 QJ
QJ JC O
-C -fJ I-
4-» QJ O
QJ O-—
o t-jr c i
t- O O CD -t
O.— -r- M--
C t. r-JC U C
CD O CD -C O (— QJQJ1
^- r— c O •-- 1 C -Q i
>>-C QJ (O Q —•• CU .— i
t- QJ
O C
•— CU
_C-C
O -4->
OJ
QJ O
QJ -
CDOOOCJOOOOOO
CDOcOCJLOOOt^OCDO
1*^. CO CO r«— ^T CD CO LO CD I***
-=a- co co cj o -^
JZ
4->
Q.
-r- 4J Q.C
O QJ JC QJr— Q)
< C Q. C >>-C
000000
_J Of— >, C O
> 'o o-c *j i- •
— C M +J CU O
JC CI O QJ*-^ NI
r-^.— c-«-«— >>— cu
-------
0 T5
fCALE IN FEET
SCALE
AS SHOWN
DATE
JUNE 1990
SOIL GAS ORGANIC DATA-DECEMBER 1988
SAMPLING DEPTH 8 FEET
FIGURE
Figure 2. Areas of volatile organics in soil gas.
-------
3.
Available meteorological data:
Mean annual temperature = 54.7° F (13°C)
Average wind direction: October - April NW
May - August SW
September SE
Windspeed data taken from National Climatic Data Center Publications is
shown in Table 3. The nearest representative station available was within
5 miles of the site.
Assemble reference chemical property data for all contaminants.
This information is included in Table 1.
TABLE 3. LOCAL CLIMATOLOGICAL DATA
Windspeed data
Normal mean
mi/h
9.6
m/s
4.29
Direction
WSW
Fastest mile data (1983)
Month
January
February
March
April
May
June
July
August
September
October
November
December
Mean
Fastest mile
mi/h
27
36
31
28
26
26
23
34
24
26
30
35
28.83
m/s
12.89
-------
STEP II. LIST AIR ARARs AND TBCs
1. List All Air ARARs and TBC Acceptable Ambient Levels and Averaging Times:
A. NAAQS for applicable site contaminants:
PM10: 50/yg/m3 annual average
150//g/m3 24-h average
Ozone: 0.12 ppm 1-h average
B. NESHAPs:
Not applicable.
C. State Ambient Air Concentration Guidelines or Standards:
The State does not publish specific AALs for air toxics but does require
control of air emissions from industrial processes that emit more than 0.1
Ib/h (45.4 g/h) of each of 11 toxic volatile organic substances. The
following site contaminants are included in the State's list of toxic air
pollutants:
Benzene
Tetrachloroethene
Trichloroethene.
This rule is not an ARAR under baseline conditions, but may be a potential
TBC and will be evaluated as such.
D. Others as applicable.
No other ARARs or TBCs were identified.
2. Develop a set of air pathway pollutants for inclusion in the analysis.
The set of contaminants with the highest site concentrations and lowest levels of
concern are of greatest interest and should be carried through the analysis.
Therefore, for each contaminant, the concentration in the soil was divided by the
ambient health level of concern for that contaminant. Volatile organic compounds
(soil gas concentrations) were assessed separately from metals and semivolatiles
(surface soil bulk concentrations). The resulting quotients were summed and the
percent contribution of each contaminant was computed to provide a relative
indication of the importance of that contaminant. Contaminants contributing less
-------
than one percent of the total of the ratios of concentration in soil to level of
concern were eliminated. This operation is shown in Table 4. The remaining
contaminants, or indicator compounds, are listed in Table 5 along with the health
levels of concern and the ARARs/TBCs.
Note: The procedure used in (2) above was developed to simplify the calculations
for this case example and should not necessarily be used as guidance.
TABLE 4. CALCULATIONS FOR SELECTION OF INDICATOR COMPOUND
COMPOUND
PRELIMINARY
HEALTH LEVEL
OF CONCERN
(ug/m3) *
CONC.
BASIS (ppb or
ug/kg)
CONC./
HLOC
CONTRIBUTION INDICATOR
{%) CHEMICAL
VOLATILE ORGANICS
Methylene chloride
1.1-Dichloroethane
1.1.1-Tri chlorothane
Trichloroethene
Benzene
Tetrachloroethene
Toluene
Ethyl benzene
Xylenes (total)
SEMIVOLATILES/METALS
Phenol
Benzole acid
Napthalene
Dimethylphthal ate
Fluorene
Anthracene
Di-n-butylphthalate
Fluoranthene
Pyrene
6-,s(2-ethylhexyl)phtha
Benzo(a)pyrene
Arsenic
Barium
Cccimi urn
C'rcrr.l UTi
"ercury
2.13
500
1000
0.588
0.12
1.92
2000
1000
300
10-6 Risk
RfC
RfC
10-6 Risk
10-6 Risk
10-6 Risk
RfC
RfC
RfC
2100
14000
14
3500
140
1050
350
140
105
0.25
0.00059
0.00023
0.5
0.00056
8.3E-05
0.3
0.0042
Oral
Oral
Oral
Oral
Oral
Oral
Oral
Oral
Oral
Oral
10-6 Risk
10-6 Risk
RfC
10-6 Risk
10-6 Risk
RfC
10-6 Risk
RfO
RfD
RfD
RfD
RfD
RfD
RfD
RfD
RfD
SF
96654
1343
9735
10640
40714
17500
20111
24905
20702
45377.46
2.69
9.74
18095.24
339283.33
9114.58
10.06
24.91
69.01
11.0143
0.0007
0.0024
4.3922
82.3529
2.2123
0.0024
0.0060
0.0167
411987.01
100.0000
4700
3300
830
720
52
400
23000
370
2500
630000
1700
1070000
243000
58000
13000
1400
13000
2.24
0.24
59.29
0.21
0.37
0.38
65.71
2.64
23.81
2520000.00
2881355.93
4652173913.04
486000.00
103571428.57
156625506.02
4666.67
3095238.10
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0512
0.0585
94.5303
0.0099
2.1045
3.1826
0.0001
0.0629
4921359263.2174
100.0000
Oral RfDs or oral slope factors are used ONLY to derive
preliminary health levels of concern for indicator compound analysis.
8
-------
TABLE 5. AIR PATHWAY COMPOUNDS AND LEVELS OF CONCERN
CASEX AIR PATHWAY COMPOUNDS AND LEVELS OF CONCERN
Compound
VOLATILE ORGANICS
Methylene chloride
Trichloroethene
Benzene
Tetrachloroethene
INORGANICS
Arsenic
Cadmium
Chromium
Preliminary
health level
of concern,
//g.m3
2.13
0.588
0.12
1.92
0.00023
0.00056
8.3E-05
Basis
10-6 Risk
10-6 Risk
10-6 Risk
10-6 Risk
10-6 Risk
10-6 Risk
10-6 Risk
ARAR,
//9/m3
NA
NA
NA
NA
NA
NA
NA
TBC
emissions
45.4 g/h
45.4 g/h
45.4 g/h
Basis
SAACGS
SAACGS
SAACGS
-------
STEP III. ESTIMATE AIR EMISSION RATES OF EACH APPLICABLE SITE
CONTAMINANT
1. Gaseous Emissions from Subsurface Soils:
A. Obtain contaminant-specific soil gas or soil bulk concentrations.
Both soil gas and bulk samples were taken for this site (at different
locations). Emissions calculations will be made using both sets of data for
comparison purposes. The higher emission rates will be used for the
indicator compounds.
B. Estimate the saturation concentration (Csat) for each contaminant in the
vadose zone.
For methylene chloride (dichloromethane) Csat is calculated from Equation
1 as:
= (Kd x ^ x n J + (s x 6 J
where Ky = K^ x foc (Equation 2).
Without site-specific data, the value of foc is assumed to be the default value
of 0.02. The values of K^ and s were taken from the Superfund Public
Health Evaluation Manual, Exhibit A-1.
Therefore K« = 35.0 x 0.02 = 0.7
and,
Csat = (0.7 x 20,000 x 0.02) + (20,000 x 0.02)
Csat = 680 ppm = 680,000 ppb
Values of Csat similarly calculated for all volatile indicator compounds are
given in Table 6.
10
------- An error occurred while trying to OCR this image.
-------
Obtain diffusion coefficients of compounds in air (DJ.
Contamination is above the permanent and seasonal groundwater table.
For worst-case conditions, calculate total soil porosity, Pt (Equation 6):
Assume bulk density/? = 1.5 g/cm3 and particle density
p = 2.65 g/cm3.
P, = 1 - 1.5/2.65 = 0.434
Exposed surface area, A = 22,500 m2 = 2.25 x 10s cm2
Using Equation 4:
,, _ (0.10)(3.42x10-7)(2.25x108)(0.4344/3) _nn,A/1 ,
E, = — = 0.0104 gls
Emission rate calculations for other indicator compounds are
shown in Table 7.
2. N/A
3. All bulk concentrations are less than their respective values of Csat.
Therefore, emission rates for each contaminant will be calculated
using Equation 9:
A 2 D* C *- C> (8)
\]if.a.t
0 The exposed surface area, A = 22,500 m2 = 2.25 x 108 cm2.
0 The effective diffusivity, D^ = D, Pt033.
12
-------
TABLE 7. EMISSION RATE CALCULATIONS FROM SOIL GAS SAMPLES
COMPOUND
Methyl ene chloride
Tn chloroethene
Benzene
Tetrachl oroethene
CONC.
(ppbv) 1
96654
10640
40714
17500
MU
[g/mol )
85
131
78
166
Di
(cm2/s)
l.OOE-01
7.90E-02
8.80E-02
7.20E-02
Ci
(g/cm3)
3.42E-07
5.80E-08
1.32E-07
1.21E-07
DEPTH
dSC
(cm)
244
244
122
122
POROSITY
Pt
(unitless
0.434
0.434
0.434
0.434
AREA
A
) (cm2)
2.25E+08
2.25E+08
2.2SE+08
2.25E+08
Ei
(g/s)
1.04E-02
1.39E-03
7.04E-03
5.28E-03
TOTALS
165508
2.41E-02
Values of D, were obtained from the NTGS Series, Volume II,
Appendices F and G.
The soil/air partition coefficient,
Equation 9b.
is calculated using
0 The 95 percent UCL of the soil bulk concentrations, C , is
obtained from Table 1 .
0 a is calculated from Equation 9a, where e is calculated using
the default values in Equation 6.
0 The exposure interval, t = 60 s/min x 60 min/h x 24 h/day x
350 days/yr x 30 yr = 9.07 x 108 s which represents upper
bound residential exposure.
Table 8 gives the values of each variable in Equation 9 and the calculated
emission rate for each volatile indicator compound.
TABLE 8. EMISSION RATE CALCULATIONS FROM BULK SAMPLES
COMPOUND
Methyl ene chloride
Tri cm oroethene
Benzene
Tetrachl oroethene
95XUCL
BULK CONC.
(ug/kg)
170
5300
2500
220
95XUCL
BULK CONC.
(g/g)
1.70E-07
5.3E-06
2.5E-06
2.2E-07
Oi
(cm2/s)
l.OOE-01
7.90E-02
8.80E-02
7.20E-02
POROSITY
Pt
(unitless)
tf.434
0.434
0.434
0.434
AREA
A
(onZ)
2.25E+08
2.25E+08
2.25E+08
2.25E+08
Del
(cm2/s)
0.075923
0.059979
0.066812
0.054664
Kas
(g/on3)
0.1189
0.1481
0.1381
0.0146
2
1
2
1
alpha
.03E-03
.99E-03
.07E-03
.79E-04
TIME
t
(s)
9.07E+08
9.07E+08
9.07E+08
9.07E+08
Ei
(g/s)
1.25E-04
3.86E-03
1.85E-03
4.80E-05
TOTALS
8190
5.89E-03
13
-------
2. N/A. No surface impoundments or pooled diluted volatiles at the surface.
3. N/A. Not a codisposal landfill.
4. N/A. No free-phase volatiles directly exposed.
5. Solids and semivolatiles emitted as PM:
A. Obtain bulk concentrations of metals and semivolatiles in surface soils from
Table 1. Use the decision flowchart, Guideline, Figure 1, to determine if
wind erosion potential exists and which emission rate model is applicable.
Assume no vegetation in the areas of surface contamination at this site.
Flowchart steps:
No. 1 Continuous vegetation? No.
No. 2 Is crust present? No.
No. 3a Determine threshold friction velocity.
From Table 2, the aggregate size distribution mode lies
between 0.25 mm and 0.42 mm. With a value of 0.3 mm for
surface soil, the threshold friction velocity (Guideline, Figure
1a) is approximately 40 cm/s.
No. 3b Correct for nonerodible elements. Data not reported.
Assume L, = 0.01 (default). From Guideline, Figure 1b, the
correction factor is 1.5. Therefore, u*t = 1.5x40 = 60 cm/s.
No. 3c Is threshold friction velocity > 75 cm/s? No. Select "unlimited
reservoir" model.
B. Calculate an emission flux (g/m2-h) for each contaminant found in the
erodible surface material.
1. Use the "unlimited reservoir" «Todel
a. Use Equation 15 for emission flux of PM10:
£10 = 0.036(1 -V)
M
u.
F(x)C
Input variables:
V=0 (Without data, assume no vegetative cover)
[u] = Mean annual windspeed (Table 3) = 4.29 m/s
14
-------
Calculate equivalent threshold windspeed at 7 m height using
Equation 16:
ut = 18.1(u*t)/100
18.1(60)/100
10.9 m/s
Fractional percent of contaminant (example for arsenic):
C = 1070 mg/kg x (1 kg/105 mg)
0.00107
Obtain F(x) from Guideline, Rgure 2:
x = 0.886 ut/[u]
0.886 (10.9J/4.29
2.25
F(x) = 0.18 (Sx3 + 12x)ex
2
2
0.18 [8(2.25)3 + 12(2.25)]e(225)
0.1346
Therefore,
£10 = 0.036(1 -0)
[4.29
10.9
(0.1346)(0.00107) = 3.16x10-7 glmz-h
b. Not applicable at this time.
C. Calculate total emission rates from the calculated emission flux rates using
Equation 20a:
EXA
ET = ——
r 3600
For arsenic, the contaminated surface area, A = 22,500 m2
T __ (3.16x10-')(22.500) . 1
3600
15
-------
Note: Emission rates of each indicator compound were computed from
both soil gas and bulk samples. The greater of the two emission
rate calculations for each indicator compound are summarized in
Table 9.
TABLE 9. SUMMARY OF EMISSION RATE ESTIMATES
CASEX CONTAMINANT EMISSION RATES
Compound
VOLATILE ORGANICS
Methylene chloride
Trichloroethene
Benzene
Tetrachloroethene
INORGANICS
Arsenic
Cadmium
Chromium
Emission rate, g/s
1.04E-02
3.86E-03
7.04 E-03
5.28E-03
1.98E-06
8.88E-08
1.98E-08
16
-------
STEP IV. ESTIMATE AMBIENT AIR CONCENTRATIONS AND/OR DEPOSITION
CONCENTRATIONS AT RECEPTOR LOCATIONS OF INTEREST
1. Model the emissions of each contaminant for each source using the appropriate
EPA atmospheric dispersion model and source configuration data.
A. The release will be neutrally buoyant.
B. No stack emissions, and 1-h average concentrations for area sources are
not applicable (i.e., no 1-h average ARARs/TBCs).
C. No stack emissions, and 3, 8, and 24-h average concentrations for area
sources are not applicable (i.e., no 3, 8, or 24-h average ARARs/TBCs).
Note: Calculation of less than annual average concentrations (short-term)
may be necessary if potential emissions are of enough magnitude to
cause ambient air concentrations to exceed subchronic or acute
health-based criteria. Consult with a toxicologist or the Superfund
Health Risk Technical Support Center if excessive short-term
exposures are anticipated.
D. Estimate annual average concentrations of contaminants from the area
source using the following procedures:
1. Total area source size = 22,500 m2
2. Square area = (150 m)2
3. Convert the previously calculated emission rates to the form
kg/rrf-yr.
£,. gls x 31,536,000 s/yr x 1 Jtg/1000 g
22,500 mz
Q = Ei x 1.4016 kglmz-yr
For methylene chloride, Q = 0.0104x1.4016 = I.46x10"2 kg/nf-yr.
See Table 10 for other calculated values.
17
-------
TABLE 10. CALCULATIONS FOR ANNUAL AVERAGE AMBIENT CONCENTRATION
ESTIMATES
CASEX SITE
Compound
VOLATILE
ORGANICS
Methylene
chloride
Trichloroethene
Benzene
Tetrachloro-
ethene
INORGANICS
Arsenic
Cadmium
Chromium
Emission
rate, g/s
1.04E-02
3.86E-03
7.04E-03
5.28E-03
1.98E-06
8.88E-08
1.98E-08
Area, m2
22500
22500
22500
22500
22500
22500
22500
Emissions
Q, kg/m2-yr
1.46E-02
5.41 E-03
9.87E-03
7.40E-03
2.78E-06
1.24E-07
2.78E-08
X/Q value,
10~9 yr/m
27.5
27.5
27.5
27.5
27.5
27.5
27.5
Annual
avg. con-
centration,
X, //9/m3
0.402
0.149
0.271
0.204
7.65E-05
3.42E-06
7.63E-07
4. Obtain^/Q value from Guideline, Figure 4 curves. Distance from the
downwind side of the source to the closest receptor is 175 m. From
the curve for the 150 x 150 m area source, x/Q = 27.5 (10"9 yr/m).
5. Compute annual average concentration,
X = jr/Q x Q
For methylene chloride,
X = (27.5)(1.46x10'2)
X = 0.402 /yg/m3
See Table 10 for other calculated values.
18
-------
Predict annual average concentrations of PM10 contaminants.
1 . Area source size = 22,500 m2
2. Square area = (150 m)2
3. Convert the emission rate to kg/m2-yr. For arsenic,
__ 1.98x10-^/5 x _Ug_ x 31.536.000. = ^M* kglm*-yr
22,500m2 1000£ yr
4. Obtain x/Q value from Guideline, Figure 4 curves. Using downwind
edge distance of 175 m and the 150 x 150 m area source, //Q =
27.5(10 '9 yr/m).
5. Compute annual average concentration, /(tyg/m3):
X = x/Q x Q
For arsenic, / = (27.5) (2.78 x 10'6)
X = 7.65x10'5;/g/m3
Other contaminants are shown in Table 10.
E. Not applicable.
2. As applicable, determine deposition concentrations (g/m2) by modeling particulate
emissions of each applicable contaminant as particles _< 30 /vm using the ISC or
FDM dispersion model.
Not applicable if Baseline Risk Assessment indicates risk from onsite incidental
ingestion of contaminated soil is within the acceptable risk range or if the hazard
index is less than one.
19
-------
STEP V. COMPARE AMBIENT AIR CONCENTRATIONS TO ARARs AND TBCs
1. Compare predicted ambient air concentrations to ARARs/TBCs.
The ARARs for PM10 and ozone (NAAQS) will not be approached.
The State air toxics TBCs are compared below:
Contaminant Predicted emission rate TBC Status
Benzene 25.3 g/h 45.4 g/h O.K.
Tetrachloroethene 19.0 g/h 45.4 g/h O.K.
Trichloroethene 13.9 g/h 45.4 g/h O.K.
20
-------
STEP VI. ORGANIZE CONCENTRATION DATA FOR INPUT TO THE BASELINE
RISK ASSESSMENT
1. List the annual average ambient air concentrations for each pollutant (indicator
compound) - Table 10.
2. List variables and assumptions used in emission and dispersion modeling analyses
and discuss their uncertainty and how this uncertainty may affect the final
estimates.
The following discussion of assumptions is exemplary only. Site-specific
conditions will dictate the extent to which assumptions and their possible effects
on emissions and ambient concentration estimates will need examination.
Equation 1: Both the soil/water partition coefficient (K^) and the contaminant
solubility(s) used in Equation 1 assume that each contaminant will
behave in multicomponent systems (mixtures) as they would in two-
component systems (i.e., one contaminant and soil/water). If
mixture values of K* and s are less than published two-component
values, the value of Csat will be less than that calculated in
Equation 1.
Equation 4: The 95 percent UCL soil gas concentrations (Q) used in Equation 4
are assumed to be homogeneous across the exposed surface area
(A). If significantly higher concentrations exist within this area and
are closer to receptors of interest, higher ambient air concentrations
are expected. Total soil porosity (Pt) used in Equation 4 was derived
from Equation 6 using default values (i.e., air-filled porosity = total
porosity). Use of total porosity instead of true air-filled porosity will
tend to overpredict emissions.
Equation 9: As with Equation 4, the 95 percent UCL soil bulk concentrations (Q)
and total porosity (Pt) were used in Equation 9 and will have similar
effects on calculated emissions and resulting ambient air
concentrations. The soil/air partition coefficient (K^) assumes that
each contaminant will behave according to its Henry's Law constant
in multicomponent systems (i.e., activity coefficient = 1). If a
contaminant's activity coefficient is less than one, emissions will be
less than calculated. Equation 9 represents the time-averaged
emission rate over exposure interval t. Actual emissions, therefore,
will be greater at the beginning of this interval and decrease with
time.
21
-------
Equation 15: The relationships used to compute the threshold friction velocity and
the function F(x) used in Equation 15 were derived from wind tunnel
observations of various surface types. The annual average emission
flux rates calculated using Equation 15 represent a continuous
emitting source. In actuality, emissions occur only when windspeeds
meet or exceed the threshold friction velocity for the given particle
size. Therefore, short-term emissions will be considerably higher
than the long-term average which includes a considerable period of
no emissions. No site-specific information was available for extent
of surface vegetation. The surface vegetation (V) was therefore set
equal to zero to promote a conservative analysis.
Step IV, 1,D: Annual average ambient air concentrations of contaminants
determined from the relationship between downwind distance and
X/Q (Figure 4) are based on conservative refined modeling of fugitive
emissions from several treatment, storage, and disposal facilities in
the United States. The set of curves represented in Figure 4 are
based on conservative modeling assumptions and upper bound data
points. Actual concentrations may, therefore, be less than values
predicted from this relationship.
22
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1 "EW-430/1-92-002
4- W/StprriWfcf National Technical Guidance Study Seri
Guideline for Predictive Baseline Emissions Estimation
Procedures for Superfund Sites
7. AUTHOR(S)
Craig S. Mann
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Environmental Quality Management, Inc.
1310 Kemper Meadow Drive, Suite 100
Cincinnati, Ohio 45240
12. SPONSORING AGENCY NAME AND ADDRESS
U.S. Environmental Protection Agency
Office of Air Quality Planning and Standards
Research Triangle Park, NC 2771 1
15. SUPPLEMENTARY NOTES
3. RECIPIENT'S ACCESSION NO.
es, S-"6P3SHBSV1992
6. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION REPORT NO.
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
68-DO-0124
13. TYPE.OF .REPORT AND PERIOD COVERED
Interim Final
14. SPONSORING AGENCY CODE
16. ABSTRACT
The purpose of the project was to develop a guideline for using the preferred EPA-
approved predictive models to estimate air pathway exposure point concentrations for input to
Superfund site Baseline Risk Assessments. The document provides the sequential series of
steps necessary to accomplish the baseline air pathway analysis by predictive means.
17. KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS b.lDENTIFI
Air Pathway Analysis Air Path
Air Pollution
Superfund
18. DISTRIBUTION STATEMENT 19. SECURI
20 SECURI
ERS/OPEN ENDED TERMS C. COSATI Field/Group
way Analysis
TY CLASS (This Report! 21. NO. OF PAGES
TY CLASS i This page/ 22 PRICE
EPA Form 2220—1 (Rev. 4-77) PREVIOUS EDITION is OBSOLETE
-------
INSTRUCTIONS
1. REPORT NUMBER
Insert the EPA report number as it appears on the cover of the publication.
2. LEAVE BLANK
3. RECIPIENTS ACCESSION NUMBER
Reserved for use by each report recipient.
4. TITLE AND SUBTITLE
Title should indicate clearly and briefly the subject coverage of the report, and be displayed prominently. Sot subtitle, if used, in smaller
type or otherwise subordinate it to main title. When a report is prepared in more than one volume, repeat the primary title, add volume
number and include subtitle for the specific title.
5. REPORT DATE
Each report shall carry a date indicating at least month and year. Indicate the hasis on which it was --elected (e.g.. date of issue, date of
approval, date of preparation, etc.).
6. PERFORMING ORGANIZATION CODE
Leave blank.
7. AUTHOR(S)
Give name(s) in conventional order (John R. Doe. J. Robert Doc. etc.). List author's affiliation if it differs from (he performing organi-
zation.
8. PERFORMING ORGANIZATION REPORT NUMBER
Insert if performing organization wishes to assign this number.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Give name, street, city, state, and ZIP code. List no more than two levels of an organujlion.il hireardiy.
10. PROGRAM ELEMENT NUMBER ^
Use the program element number under which the report was pr^)ared. Subordinate numbers may be included m parentheses.
11. CONTRACT/GRANT NUMBER
Insert contract or grant number under which report was prepared.
12. SPONSORING AGENCY NAME AND ADDRESS
Include ZIP code.
13. TYPE OF REPORT AND PERIOD COVERED
Indicate interim final, etc., and if applicable, dates covered.
14. SPONSORING AGENCY CODE
Insert appropriate code.
15. SUPPLEMENTARY NOTES
Enter information not included elsewhere but useful, such as: Prepared in cooperation with. Translation of, Presented at conference of.
To be published in. Supersedes, Supplements, etc.
16. ABSTRACT
Include a brief (200 words or less) factual summary of the most significant information contained ID the report. If the report contains a
significant bibliography or literature survey, mention it here.
17. KEY WORDS AND DOCUMENT ANALYSIS
(a) DESCRIPTORS - Select from the Thesaurus of Engineering and Scientific Terms the proper authon/cd terms that identify the major
concept of the research and are sufficiently specific and precise to be used as index entries for cataloging.
(b) IDENTIFIERS AND OPEN-ENDED TERMS - Use identifiers for project names, code names, equipment designators, etc. Use open-
ended terms written in descriptor form for those subjects for which no descriptor exists
(c) COS.AT1 FIELD GROUP - Field and group assignments are to be taken from the 1965 COSATI Subject Category List. Since the ma-
jority of documents are multidisciplinary in nature, the Primary Field/Group assignmcnt(s) will be specific discipline, area of human
endeavor, or type of physical object. The application(s) will be cross-referenced with secondary I icld/Group assignments that will follow
the primary posting(s).
18. DISTRIBUTION STATEMENT
Denote releasability to the public or limitation for reasons other than security for example "Release Unhmilcd." Cite any availability l»
the public, with address and price.
19. & 20. SECURITY CLASSIFICATION
DO NOT submit classified reports to the National Technical Information service.
21. NUMBER OF PAGES
Insert the total number of pages, including this one and unnumbered pages, but exclude distribution list, if any.
22. PRICE
Insert the price set by the National Technical Information Service or the Government Printing Office, if known.
EPA Form 2220-1 (Rev. 4-77) (Reverse)
------- |