•&EPA Industrial Waste Air Model
(IWAIR) User's Guide
United States
Environmental Protection
Agency
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Solid Waste and EPA 530-R-02-011
Emergency Response August 2002
(5306W) www.epa.gov/industrialwaste
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February 2002
Industrial Waste Air Model (IWAIR)
User's Guide
Office of Solid Waste
U.S. Environmental Protection Agency
Washington, DC 20460
Printed on Recycled Paper
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IWAIR User's Guide Table of Contents
Contents
Section Number
List of Figures v
List of Tables vi
List of Acronyms and Abbreviations vii
1.0 Introduction 1-1
1.1 Guide for Industrial Waste Management and IWAIR 1-1
1.2 Model Design 1-2
1.2.1 Emission Model 1-2
1.2.2 Dispersion Model 1-4
1.2.3 Risk Model 1-4
1.3 Overview of Approach to Estimating Risk or Allowable Concentration 1-5
1.4 Capabilities and Appropriate Application of the Model 1-8
1.5 About This User's Guide 1-10
2.0 Getting Started 2-1
2.1 Hardware and Software Requirements 2-1
2.2 Installing and Uninstalling the Program 2-1
2.3 Running IWAIR 2-3
2.4 Navigating in IWAIR 2-3
2.5 Menus 2-7
2.5.1 Start a New Analysis 2-7
2.5.2 Save and Re-Open an Analysis 2-7
2.5.3 Print Reports 2-9
2.5.4 Exit IWAIR 2-10
2.6 Online Help 2-10
2.7 Troubleshooting 2-10
3.0 Selecting Calculation Method, WMU Type, and Modeling Pathway 3-1
3.1 Selecting Calculation Method 3-1
3.2 Selecting WMU Type 3-2
3.3 Determining Appropriate Modeling Pathway 3-3
4.0 Completing Risk/Hazard Quotient Calculations 4-1
4.1 Method, Meteorological Station, WMU (Screen 1A) 4-6
4.2 Wastes Managed (Screen 2A) 4-10
4.3 Enter WMU Data for Using CHEMDAT8 Emission Rates 4-15
4.4 Emission Rates 4-23
4.4.1 Using CHEMDAT8 Emission Rates (Screen 4A) 4-24
4.4.2 User-Specified Emission Rates (Screen 4B) 4-25
in
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IWAIR User's Guide Table of Contents
Contents (continued)
Section Number
4.5 Dispersion Factors 4-26
4.5.1 Using ISCST3 Default Dispersion Factors (Screen 5A) 4-26
4.5.2 User-Specified Dispersion Factors (Screen 5B) 4-29
4.6 Risk Results (Screen 6) 4-30
5.0 Completing Allowable Waste Concentration Calculations 5-1
5.1 Method, Meteorological Station, WMU (Screen 1A) 5-7
5.2 Wastes Managed (Screen 2A) 5-11
5.3 Enter WMU Data for Using CHEMDAT8 Emission Rates 5-15
5.4 Emission Rates 5-21
5.4.1 Using CHEMDAT8 Emission Rates (Screen 4A) 5-22
5.4.2 User-Specified Emission Rates (Screen 4B) 5-24
5.5 Dispersion Factors 5-24
5.5.1 Using ISCST3 Default Dispersion Factors (Screen 5A) 5-25
5.5.2 User-Specified Dispersion Factors (Screen 5B) 5-27
5.6 Allowable Concentration Results (Screen 6) 5-29
6.0 Example Calculations 6-1
6.1 Calculation of Risk and Hazard Quotient 6-1
6.2 Calculation of Allowable Concentration 6-5
7.0 References 7-1
Appendix A Considering Risks from Indirect Pathways A-l
Appendix B Parameter Guidance B-l
Appendix C Physical-Chemical Property Values C-l
IV
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IWAIR User's Guide Table of Contents
Figures
Number Page
1-1 IWAIR approach for estimating risk or allowable waste concentrations 1-6
2-1 Menu bar in the IWAIR program 2-6
3-1 Receptor Locations 3-6
4-1 IWAIR approach for completing risk calculations, Pathway 1: Using CHEMDAT8
emission rates and ISCST3 default dispersion factors 4-2
4-2 IWAIR approach for completing risk calculations, Pathway 2: Using CHEMDAT8
emission rates and user-specific dispersion factors 4-3
4-3 IWAIR approach for completing risk calculations, Pathway 3: Using user-specified
emission rates and ISCST3 default dispersion factors 4-4
4-4 IWAIR approach for completing risk calculations, Pathway 4: Using user-specified
emission rates and dispersion factors 4-5
5-1 IWAIR approach for completing allowable waste concentration calculations,
Pathway 1: Using CHEMDAT8 emission rates and ISCST3 default dispersion
factors 5-3
5-2 IWAIR approach for completing allowable waste concentration calculations,
Pathway 2: Using CHEMDAT8 emission rates and user-specified dispersion
factors 5-4
5-3 IWAIR approach for completing allowable waste concentration calculations,
Pathway 3: Using user-specified emission rates and ISCST3 default dispersion
factors 5-5
5-4 IWAIR approach for completing allowable waste concentration calculations,
Pathway 4: Using user-specified emission rates and dispersion factors 5-6
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IWAIR User's Guide Table of Contents
Tables
Number Page
1-1 Constituents Included in IWAIR 1-3
2-1 IWAIR Tabs and Associated Screens 2-5
2-2 Troubleshooting Common Problems in IWAIR 2-10
6-1 Inputs Used for Example Calculation: Landfill 6-2
6-2 Parameter Values Used in Estimating Time-Weighted-Average Exposure 6-4
6-3 Unitized Emission Rates for Allowable Concentration Mode Example Calculation
([g/m2-s]/[mg/kg]) 6-6
VI
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IWAIR User's Guide
Table of Contents
Acronyms and Abbreviations
ATSDR Agency for Toxic Substances and Disease Registry
BAF Bioaccumulation factor
BCF Bioconcentration factor
BOD Biological oxygen demand
CAA Clean Air Act
CalEPA California Environmental Protection Agency
CAS Chemical Abstract Service
COD Chemical oxygen demand
CSF Cancer slope factor
DCOM Distributed component model
EPA Environmental Protection Agency
HEAST Health Effects Assessment Summary Tables
HQ Hazard quotient
HSDB Hazardous Substances Databank
IRIS Integrated Risk Information System
ISCST3 Industrial Source Complex, Short-Term Model, Version 3
IWAIR Industrial Waste Air Model
IWEM Industrial Waste Management Evaluation Model
MLVSS Mixed-liquor volatile suspended solids
MLSS Mixed-liquor suspended solids
MRL Minimum risk level
PAH Polycyclic Aromatic Hydrocarbons
RfC Reference concentration
REL Reference exposure level
SCDM Superfund Chemical Data Matrix
TOC Total organic carbon
TSS Total suspended solids
WMU Waste management unit
vn
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IWAIR User's Guide Section 1.0
1.0 Introduction
This document describes how to use the Industrial Waste Air Model (IWAIR). A
companion document, the Industrial Waste Air Model Technical Background Document,
provides technical background information. This section of the User's Guide provides an
overview of IWAIR, its purpose, operation, and application; describes the three major
components of the system—the emissions, dispersion, and results models; and provides an
overview of the remainder of the User's Guide.
1.1 Guide for Industrial Waste Management and IWAIR
The U.S. Environmental Protection Agency (EPA) and representatives from 12 state
environmental agencies developed a voluntary Guide for Industrial Waste Management
(hereafter, the Guide) to recommend a baseline of protective design and operating practices to
manage nonhazardous industrial waste throughout the country. The guidance is designed for
facility managers, regulatory agency staff, and the public, and it reflects four underlying
objectives:
• Adopt a multimedia approach to protect human health and the environment;
• Tailor management practices to risk in the enormously diverse universe of waste,
using the innovative, user-friendly modeling tools provided in the Guide;
• Reaffirm state and tribal leadership in ensuring protective industrial waste
management, and use the Guide to complement state and tribal programs;
• Foster partnerships among facility managers, the public, and regulatory agencies.
The Guide recommends best management practices and key factors to consider to protect
groundwater, surface water, and ambient air quality in siting, operating, and designing waste
management units (WMUs); monitoring WMUs' impact on the environment; determining
necessary corrective action; closing WMUs; and providing postclosure care. In particular, the
guidance recommends risk-based approaches to choosing liner systems and waste application
rates for groundwater protection and to evaluating the need for air controls. The CD-ROM
version of the Guide includes user-friendly air and groundwater models to conduct these risk
evaluations.
Chapter 5 of the Guide, entitled "Protecting Air Quality," highlights several key
recommendations:
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IWAIR User's Guide Section 1.0
• Adopt controls to minimize particulate emissions.
• Determine whether WMUs at a facility are addressed by Clean Air Act (CAA)
requirements and comply with those requirements.
• If WMUs are not specifically addressed by CAA requirements, use IWAIR to
assess risks associated with volatile air emissions from units.
• Implement pollution prevention programs, treatment measures, or emissions
controls to reduce volatile air emission risks.
EPA developed IWAIR and this User's Guide to accompany the Guide to evaluate
inhalation risks. Workers and residents in the vicinity of a unit may be exposed to volatile
chemicals from the unit in the air they breathe. Exposure to some of these chemicals at sufficient
concentrations may cause a variety of cancer and noncancer health effects (such as
developmental effects in a fetus or neurological effects in an adult). With a limited amount of
site-specific information, IWAIR can estimate whether specific wastes or waste management
practices may pose an unacceptable risk to human health.
1.2 Model Design
IWAIR is an interactive computer program with three main components: (1) an emission
model to estimate release of constituents from WMUs; (2) a dispersion model to estimate fate
and transport of constituents through the atmosphere and determine ambient air concentrations at
specified receptor locations; and (3) a risk model to calculate either the risk to exposed
individuals or waste constituent concentrations that can be protectively managed in the unit. The
program requires only a limited amount of site-specific information, including facility location,
WMU characteristics, waste characteristics, and receptor information. A brief description of
each component follows. The IWAIR Technical Background Document contains a more detailed
explanation of each.
1.2.1 Emission Model
The emission model uses waste characterization, WMU, and facility information to
estimate emissions for 95 constituents (identified in Table 1-1) for four types of units: land
application units, landfills, waste piles, and surface impoundments. You can also add chemical
properties to model additional chemical constituents. The emission model selected for
incorporation into IWAIR is EPA's CHEMDAT8 model. This model has undergone extensive
review by both EPA and industry representatives and is publicly available from EPA's Web page
(http://www.epa.gov/ttn/chief/software.html).
To facilitate emission modeling with CHEMDAT8, IWAIR prompts you to provide the
required waste- and unit-specific data. Once you have entered these data, the model calculates
and displays chemical-specific emission rates. If you decide not to develop or use the
CHEMDAT8 rates, you can enter your own site-specific emission rates (g/m2-s).
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IWAIR User's Guide
Section 1.0
Table 1-1. Constituents Included in IWAIR
CAS
Number
Compound Name
CAS
Number
Compound Name
75070 Acetaldehyde
67641 Acetone
75058 Acetonitrile
107028 Acrolein
79061 Acrylamide
79107 Acrylic acid
107131 Acrylonitrile
107051 Allyl chloride
62533 Aniline
71432 Benzene
92875 Benzidine
50328 Benzo(a)pyrene
75274 Bromodichloromethane
106990 Butadiene, 1,3-
75150 Carbon disulfide
56235 Carbon tetrachloride
108907 Chlorobenzene
124481 Chlorodibromomethane
67663 Chloroform
95578 Chlorophenol, 2-
126998 Chloroprene
10061015 cis-1,3-Dichloropropylene
1319773 Cresols (total)
98828 Cumene
108930 Cyclohexanol
96128 Dibromo-3-chloropropane, 1,2-
75718 Dichlorodifluoromethane
107062 Dichloroethane, 1,2-
75354 Dichloroethylene, 1,1-
78875 Dichloropropane, 1,2-
57976 Dimethylbenz[a]anthracene, 7,12-
95658 Dimethylphenol, 3,4-
121142 Dinitrotoluene, 2,4-
123911 Dioxane, 1,4-
122667 Diphenylhydrazine, 1,2-
106898 Epichlorohydrin
106887 Epoxybutane, 1,2-
111159 Ethoxyethanol acetate, 2-
110805 Ethoxyethanol, 2-
100414 Ethylbenzene
106934 Ethylene dibromide
107211 Ethylene glycol
75218 Ethylene oxide
50000 Formaldehyde
98011 Furfural
87683 Hexachloro-l,3-butadiene
118741 Hexachlorobenzene
77474 Hexachlorocyclopentadiene
67721 Hexachloroethane
78591 Isophorone
7439976 Mercury*
67561 Methanol
110496 Methoxyethanol acetate, 2-
109864 Methoxyethanol, 2-
74839 Methyl bromide
74873 Methyl chloride
78933 Methyl ethyl ketone
108101 Methyl isobutyl ketone
80626 Methyl methacrylate
1634044 Methyl tert-butyl ether
56495 Methylcholanthrene, 3-
75092 Methylene chloride
68122 N,N-Dimethyl formamide
91203 Naphthalene
110543 n-Hexane
98953 Nitrobenzene
79469 Nitropropane, 2-
55185 N-Nitrosodiethylamine
924163 N-Nitrosodi-n-butylamine
930552 N-Nitrosopyrrolidine
95501 o-Dichlorobenzene
95534 o-Toluidine
106467 p-Dichlorobenzene
108952 Phenol
85449 Phthalic anhydride
75569 Propylene oxide
110861 Pyridine
100425 Styrene
1746016 TCDD, 2,3,7,8-
630206 Tetrachloroethane, 1,1,1,2-
79345 Tetrachloroethane, 1,1,2,2-
127184 Tetrachloroethylene
108883 Toluene
10061026 trans-1,3-Dichloropropylene
75252 Tribromomethane
76131 Trichloro-l,2,2-trifluoroethane, 1,1,2-
120821 Trichlorobenzene, 1,2,4-
71556 Trichloroethane, 1,1,1-
79005 Trichloroethane, 1,1,2-
79016 Trichloroethylene
75694 Trichlorofluoromethane
121448 Triethylamine
108054 Vinyl acetate
75014 Vinyl chloride
1330207 Xylenes
*Chemical properties for both elemental and divalent forms of mercury are included.
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IWAIR User's Guide Section 1.0
1.2.2 Dispersion Model
IWAIR's second modeling component estimates dispersion of volatilized contaminants
and determines air concentrations at specified receptor locations, using default dispersion factors
developed with EPA's Industrial Source Complex, Short-Term Model, version 3 (ISCST3).
ISCST3 was run to calculate dispersion for a standardized unit emission rate (1 n-g/m2- s) to
obtain a dispersion factor, which is measured in |J,g/m3 per |J,g/m2 -s. The total air concentration
estimates are then developed by IWAIR by multiplying the constituent-specific emission rates
derived from CHEMDAT8 (or the rates you specified) with a site-specific dispersion factor.
Running ISCST3 to develop a new dispersion factor for each location/WMU is time consuming
and requires extensive meteorological data and technical expertise. Therefore, IWAIR
incorporates default dispersion factors developed using ISCST3 for many separate scenarios
designed to cover a broad range of unit characteristics, including
• 60 meteorological stations, chosen to represent the different climatic and
geographical regions of the contiguous 48 states, Hawaii, Puerto Rico, and parts
of Alaska;
• 4 unit types;
• 17 surface areas for landfills, land application units, and surface impoundments,
and 11 surface areas and 7 heights for waste piles;
• 6 receptor distances from the unit (25, 50, 75, 150, 500, 1,000 meters);
• 16 directions in relation to the edge of the unit (only the one resulting in the
maximum air concentration is used).
The default dispersion factors were derived by modeling each of these scenarios, then
choosing as the default the maximum dispersion factor of the 16 directions for each
WMU/surface area/height/meteorological station/receptor distance combination.
Based on the size and location of the unit you specify, IWAIR selects an appropriate
dispersion factor from the default dispersion factors in the model. If you specify a unit surface
area or height that falls between two of the sizes already modeled, an interpolation method will
estimate dispersion in relation to the modeled unit sizes.
Alternatively, you may enter a site-specific dispersion factor developed by conducting
independent modeling with ISCST3 or with a different model and proceed to the next step, the
risk calculation.
1.2.3 Risk Model
The third component combines the constituent's air concentration with receptor exposure
factors and toxicity benchmarks to calculate either the risk from concentrations managed in the
unit or the allowable waste concentration (Cwaste) in the unit that must not be exceeded to protect
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IWAIR User's Guide Section 1.0
human health. In calculating either estimate, the model applies default values for exposure
factors, including inhalation rate, body weight, exposure duration, and exposure frequency.
These default values are based on data presented in EPA's Exposure Factors Handbook (U.S.
EPA, 1997a) and represent average exposure conditions. IWAIR contains standard health
benchmarks (cancer slope factors [CSFs] for carcinogens and reference concentrations [RfCs] for
noncarcinogens) for 94 of the 95 constituents included in IWAIR.1 These health benchmarks are
obtained primarily from the Integrated Risk Information System (IRIS) and the Health Effects
Assessment Summary Tables (HEAST) (U.S. EPA, 2001, 1997b); for a complete list of sources,
see Appendix B, Section B.2.2.3. IWAIR uses these data to estimate risk or hazard quotients
(HQs) or to estimate allowable waste concentrations. You may override the IWAIR health
benchmarks with your own values.
1.3 Overview of Approach to Estimating Risk or Allowable Concentration
Figure 1-1 provides an overview of the stepwise approach you will follow to estimate risk
or allowable waste concentrations with IWAIR. The seven steps of the estimation process are
shown down the right side of the figure, and the user input requirements are specified to the left
of each step. As you provide input data, the program proceeds to the next step. Each step of the
estimation process is summarized below (later sections of this User's Guide provide more
detailed instructions):
1. Select Calculation Method. To begin, select one of two calculation
methods—risk or allowable concentration. Use the risk calculation to arrive at
chemical-specific and cumulative risk estimates; you must know the
concentrations of constituents in the waste to use this option. Use the allowable
concentration calculation method to estimate waste concentrations that may be
managed protectively in new units.
2. Identify Waste Management Unit. Four WMU types can be modeled: surface
impoundments, land application units, active landfills, and waste piles. For each
WMU, you will be asked to specify some design and operating parameters, such
as waste quantity, surface area, and depth for surface impoundments and landfills;
height for waste piles; and tilling depth for land application units. The amount of
unit-specific data needed as input will vary depending on whether you elect to
have IWAIR calculate CHEMDAT8 emission rates or enter your own. IWAIR
provides default values for several of the operating parameters that you may use,
if appropriate.
1 At the time IWAIR was released, no accepted health benchmark was available for 3,4-dimethylphenol
from the hierarchy of sources used to populate the IWAIR health benchmark database, nor were data available from
these sources to allow the development of a health benchmark with any confidence. In addition, IWAIR contains
chemical properties for both elemental and divalent forms of mercury, but contains a health benchmark only for
elemental mercury; no accepted benchmark was available for divalent mercury.
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IWAIR User's Guide
Section 1.0
User Specifies:
• Calculation option
User Specifies:
• WMU type
• WMU information (e.g.,
operating parameters)
User Specifies:
• Constituents (choose up to 6)
• Concentration for risk calculation
User Specifies:
• Emission rate option
• Facility location for meteorological input
User Specifies:
• Dispersion factor option
• Receptor information (e.g., distance and type)
User Specifies:
• Risk level for allowable concentration
calculation
Risk calculation
or
Allowable waste concentration
calculation
T
Identify WMU
Land application unit
Waste pile
Surface impoundment, aerated
and quiescent
Landfill
Define the Waste Managed
Add/modify properties data, as
desired
CHEMDAT8
or
User-specified emission rates
Determine Dispersion Factors
Interpolated from ISCST3 default
dispersion factors
or
User-specified dispersion factors
Calculate Ambient Air Concentrations
Calculates ambient air concentrations for
each receptor based on emission and
dispersion data
T
Calculate Results
Risk Calculation
1. Chemical-specific carcinogenic risk
2. Chemical-specific noncarcinogenic risk
3. Total cancer risk
or
Allowable Waste Concentration
(CV3.t.) Calculation
* '-'waste f°r wastewaters (mg/L)
* Cwastefor solid wastes (mg/kg)
Figure 1-1. IWAIR approach for estimating risk or allowable waste concentrations.
This figure shows the steps in the tool to assist you in developing risk or
allowable waste concentration estimates.
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IWAIR User's Guide Section 1.0
3. Define the Waste Managed. If you choose to calculate chemical-specific risk
estimates, specify constituents and concentrations in the waste. If you choose to
calculate allowable waste concentrations, then specify only constituents of
concern (no concentrations). You can also add chemicals or modify chemical
property data in this step.
4. Determine Emission Rates. You can elect to develop CHEMDAT8 emission
rates or provide your own site-specific emission rates for use in calculations.
IWAIR will also ask for facility location information to link the facility's location
to one of the 60 IWAIR meteorological stations. Data from the meteorological
stations provide wind speed and temperature information needed to develop
emission estimates. In some circumstances, you may already have emissions
information from monitoring or from a previous modeling exercise. As an
alternative to using the CHEMDAT8 rates, you may provide your own site-
specific emission rates developed with a different model or based on emission
measurements.
5. Determine Dispersion Factors. You can provide site-specific dispersion factors
(|j,g/m3 per |o,g/m2-s) or have the model develop dispersion factors based on WMU
information that you specify and the IWAIR default dispersion data. These
dispersion factors are specific to the meteorological station selected. Because a
number of assumptions were made in developing the IWAIR default dispersion
data (for example, flat terrain was assumed), you may elect to provide site-specific
dispersion factors that can be developed by conducting independent modeling
with ISCST3 or with a different model. Whether you use IWAIR or provide
dispersion factors from another source, specify distance to the receptor from the
edge of the WMU, and the receptor type (i.e., resident or worker). These data are
used to define points of exposure and exposure duration.
6. Calculate Ambient Air Concentration. For each receptor, the model combines
emission rates and dispersion data to estimate ambient air concentrations for up to
six waste constituents you have specified.
7. Calculate Results. The model calculates results by combining estimated ambient
air concentrations at a specified exposure point with receptor exposure factors and
toxicity benchmarks. Presentation of results depends on whether you chose to
calculate risk or the allowable waste concentration.
Risk Calculation: Results are estimates of cancer and noncancer risks from
inhalation exposure to volatilized constituents in the waste. If risks are too high,
your options are to (1) implement unit controls to reduce volatile air emissions;
(2) implement pollution prevention programs or treatment measures to reduce
volatile compound concentrations before the waste enters the unit; or (3) conduct
a full, site-specific risk assessment to more precisely characterize risks from the
unit.
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IWAIR User's Guide Section 1.0
Allowable Concentration Calculation: Results are estimates of constituent
concentrations in waste that can be protectively managed in the unit so as not to
exceed a defined risk level (e.g., 1E-6 or an HQ of 1) for specified receptors.
This information should be used to determine preferred characteristics for wastes
entering the unit. There are several options if it appears that planned waste
concentrations may be too high: (1) implement pollution prevention programs or
treatment measures to reduce volatile compound concentrations in the waste;
(2) modify waste management practices to better control volatile compounds (for
example, use closed tanks rather than surface impoundments); or (3) conduct a
full site-specific risk assessment to more precisely characterize risks from the unit.
1.4 Capabilities and Appropriate Application of the Model
In many cases, IWAIR will provide a reasonable alternative to conducting a full-scale
site-specific risk analysis to determine if a WMU poses unacceptable risk to human health.
However, because the model can accommodate only a limited amount of site-specific
information, it is important to understand its capabilities and recognize situations when it may be
most appropriate to use in a specific way, when it may not be appropriate to use at all, or when
another model would be a better choice.
Capabilities
The model provides a reasonable, protective representation of volatile compound
inhalation risks associated with WMUs.
The model is easy to use and requires a minimal amount of data and expertise.
The model is flexible and provides features to meet a variety of user needs.
You can enter emission and/or dispersion factors derived from another model
(perhaps to avoid some of the limitations below) and still use IWAIR to conduct a
risk evaluation.
The model can calculate risk from specified waste concentrations or allowable
concentrations based on a target risk or HQ.
You can modify health benchmarks and target risk level, when appropriate and in
consultation with other stakeholders.
You can add additional volatile organic chemicals to the 95 chemicals included
with IWAIR.
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IWAIR User's Guide Section 1.0
Appropriate Applications
• Release Mechanisms and Exposure Routes. The model considers exposures from
breathing ambient air. It does not address potential risks attributable to particulate
releases, nor does it address risks associated with indirect routes of exposure (i.e,
noninhalation routes of exposure). Appendix A discusses the potential for
indirect risks. Additionally, in the absence of user-specified emission rates,
volatile emission estimates are developed with CHEMDAT8 based on unit- and
waste-specific data. The CHEMDAT8 model was developed to address only
volatile emissions from WMUs. The model does not account for all competing
removal mechanisms; specifically, runoff, erosion, and leaching are not modeled.
In so much as these competing processes actually occur, the model would tend to
slightly overestimate the volatile emissions.
• Waste Management Practices. Although you specify a number of unit-specific
parameters that have a significant impact on the inhalation pathway (e.g., size,
type, and location of WMU, which is important in identifying meteorological
conditions), the model cannot accommodate information concerning control
technologies, such as covers, that might influence the degree of volatilization
(e.g., whether a waste pile is covered immediately after application of new waste).
In this case, it may be necessary to generate site-specific emission rates and enter
those into IWAIR. In addition, IWAIR cannot be used to estimate emissions from
land application units using spray techniques for waste application; the emissions
model component for land application units is only applicable to tilled land
application units; again, in this case, it will be necessary to generate site-specific
emission rates and enter them into IWAIR. IWAIR also cannot be used to model
tanks; the surface impoundment component should not be used to model tanks, as
most tanks have some height above the ground, and the dispersion factors used in
IWAIR for surface impoundments are all for a ground-level source.
• Terrain and Meteorological Conditions. If a facility is located in an area of
intermediate or complex terrain or with unusual meteorological conditions, it may
be necessary to either generate site-specific air dispersion modeling results for the
site and enter those results into the program, or use a site-specific risk modeling
approach other than IWAIR. The model will inform you which of the 60
meteorological stations is used for a facility. If the local meteorological
conditions are very different from the meteorological conditions at the site chosen
by the model, it would be more accurate to choose a different model or enter a
different location that results in the selection of a more appropriate meteorological
station.
The terrain type surrounding a facility can influence air dispersion modeling
results and, ultimately, risk estimates. In performing air dispersion modeling to
develop the IWAIR default dispersion factors, it was assumed that the facility was
located in an area of flat terrain. The Guideline on Air Quality Models (U.S. EPA,
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IWAIR User's Guide Section 1.0
1993) can assist you in determining whether a facility is in an area of simple,
intermediate, or complex terrain.
• Receptor Type and Location. IWAIR has predetermined worker and resident
receptors and predetermined exposure factors. The program cannot be used to
characterize risk for other possible exposure scenarios. The model contains
dispersion factors for six receptor locations. IWAIR cannot evaluate other
receptor locations unless you enter your own dispersion factors.
1.5 About This User's Guide
The focus of this User's Guide is to help you understand how to use IWAIR. The
remainder of this document is organized into five sections and three appendices:
• Section 2, Getting Started, identifies system requirements for running IWAIR,
provides stepwise guidance for installing the program, and introduces you to
program screens and navigational tools (e.g., tabs, menus, and buttons). This
section covers saving and retrieving data and printing reports. It also includes a
troubleshooting guide.
• Section 3, Selecting Calculation Method, WMUType, and Modeling Pathway,
assists you in selecting the appropriate calculation method (i.e., calculation of risk
estimates or calculation of allowable waste concentration), WMU type, and
modeling pathway. This section describes the types of units IWAIR addresses.
With both risk and allowable concentration calculations, you can select from the
following four modeling pathways:
— Pathway 1: Using CHEMDAT8 emission rates and ISCST3 default
dispersion factors
— Pathway 2: Using CHEMDAT8 emission rates and user-specified
dispersion factors
— Pathway 3: Using user-specified emission rates and ISCST3 default
dispersion factors
— Pathway 4: Using user-specified emission rates and dispersion factors.
Depending on the calculation method, you will be directed to follow the detailed
guidance provided in Section 4 for completing a risk calculation or in Section 5
for completing an allowable concentration calculation. Each of these sections
provides pathway-specific guidance, as needed.
1-10
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IWAIR User's Guide Section 1.0
• Section 4, Completing Risk/Hazard Quotient Calculations., provides detailed
guidance to develop risk estimates for wastes of known chemical concentration(s).
Follow the screen-by-screen guidance to arrive at risk estimates.
• Section 5, Completing Allowable Waste Concentration Calculations., provides
detailed guidance to predict allowable waste levels based on a user-specified risk
level. Again, follow the screen-by-screen guidance to complete an allowable
concentration calculation.
• Section 6, Example Calculations, provides a detailed example of how the program
calculates air concentration and inhalation risk or allowable waste concentrations.
It does not cover emission or dispersion calculations.
• Appendix A, Considering Risks from Indirect Pathways, describes the types of
pathways by which an individual may be exposed to a contaminant, explains
which pathways are accounted for in IWAIR, and discusses exposures
unaccounted for in IWAIR.
• Appendix B, Parameter Guidance, describes and provides additional information
on all parameter values needed to run IWAIR.
• Appendix C, Physical-Chemical Property Values, provides molecular weights and
densities for IWAIR constituents.
A separate document, Industrial Waste Air Model Technical Background Document,
provides detailed discussions on the CHEMDAT8 emission model, the ISCST3 model and
modeling efforts conducted to develop the IWAIR default dispersion factors, and health
benchmarks included in IWAIR.
1-11
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IWAIR User's Guide Section 2.0
2.0 Getting Started
2.1 Hardware and Software Requirements
The IWAIR tool consists of a 32-bit Visual Basic application and an Access 2000
database. It is designed to run on an IBM-compatible computer with Windows 95, 98, NT4, or
2000. The recommended hardware configuration to run IWAIR includes at least 32 MB of RAM
(preferably 64 MB), a Pentium 120 MHz CPU processor (preferably Pentium n or above), and 30
MB of free hard-drive space (preferably 50 MB).
The most recent version of the appropriate Windows operating system must be installed
on the computer. As of the publication of this document, the most recent versions are Windows
95B, Windows 98 SE, Windows NT4 with Service Pack 6a, and Windows 2000 with Service
Pack 2. Service packs are available from the Microsoft Web site (www.microsoft.com).
Microsoft recommends that these service packs be re-installed after any software is installed or
uninstalled. If the computer is running Windows 95B or Windows 98SE, the distributed
component model (DCOM) software also must be installed. This software is available from the
Microsoft Web site (www.microsoft.com/com/dcom/dcom95/dcoml_3.asp for Windows 95,
www.microsoft.com/com/dcom/dcom98/dcoml_3.asp for Windows 98). The program does not
require any additional software when running under Windows NT or Windows 2000 (other than
the latest service packs mentioned above).
2.2 Installing and Uninstalling the Program
You receive the IWAIR computer program on the Guidance CD-ROM. The installation
consists of three files: setup.exe, setup.1st, and iwair.cab. Depending on the security settings of
your operating system, this software may need to be installed and uninstalled by someone with
administrator privileges. Instructions for installing and uninstalling the program are provided
below. Any updated instructions are located on the Guidance CD-ROM in readme.txt.
Installing
1. Close all applications, such as word processors and e-mail programs. Close or
disable virus protection software.1
2. Insert the CD-ROM into your CD-ROM drive.
1 Many vims protection programs interfere with or slow down the installation of software. You should scan
any software files for viruses before installing.
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IWAIR User's Guide Section 2.0
3. Open MY COMPUTER.
4. Select the CD-ROM drive.
5. Double-clickonsetup.exe.
6. You will see some files being copied to your hard drive. The WELCOME TO THE IWAIR
INSTALLATION PROGRAM screen then appears. If all your other applications were closed
(Step 1), then click |OK|.
7. The next screen is IWAIR SETUP. This screen displays the default location for the
IWAIR files to be installed. If you want to change the location, click the I CHANGE
DIRECTORY] button and specify a different directory. Otherwise, just click the large
button (shows a computer with an open box in front of it).
8. The next screen is IWAIR - CHOOSE PROGRAM GROUP. The default is to create a new
program group named "IWAIR." You can change the program group if you prefer
a different one. Press the I CONTINUE | button to install the program.
9. The next screen is IWAIR SETUP. The progress bar shows the progress of the files
that are being installed to your hard drive.
10. The final screen displays the message, "IWAIR setup was completed
successfully." Click on the I OKI button.
11. If you are using Windows 2000 or Windows NT4, you should install the latest
Service Pack.
12. Restart your computer.
OR
1. Close all applications, such as word processors and e-mail programs. Close or
disable virus protection software.2
2. Insert the CD-ROM into your CD-ROM drive.
3. Click on the Windows I START] button and select RUN.
4. Type "D:\SETUP" or, as appropriate, replace "D:" in this command with the
correct drive designation for your CD-ROM drive.
5. Proceed with Step 6 above.
2 Many vims protection programs interfere with or slow down the installation of software. You should scan
any software files for viruses before installing.
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IWAIR User's Guide Section 2.0
Uninstalling
1. Click on the Windows I START] button.
2. Select SETTINGS, and then CONTROL PANEL.
3. Select ADD/REMOVE PROGRAMS.
4. Select IWAIR and then CHANGE/REMOVE. When asked "Are you sure you want to
completely remove IWAIR and all of its components," select the I YES I button.
5. If you are using Windows 2000 or Windows NT4, you should re-install your latest
Service Pack and restart your computer.
2.3 Running IWAIR
To execute the program, press the Windows I START] button. Select PROGRAMS, IWAIR, IWAIR.
(If you selected a different name for the group during the installation process, you must select
PROGRAMS, then the group name you selected, then IWAIR.)
Begin working in IWAIR by clicking on the I START] button of the program title screen.
IWAIR can model one unit (choice of four unit types: surface impoundment, land application
unit, active landfill, and waste pile), up to six chemicals of concern, and up to five different
receptors during a single simulation. Once IWAIR's I START] button is selected, the program
automatically opens the METHOD, MET. STATION, WMU screen.
2.4 Navigating in IWAIR
The following tools facilitate interaction with the IWAIR program:
• Tabs
• Menus
• Command buttons
• Message prompts.
Each of these tools is explained in more detail in this section. Although this guide assumes the
use of a mouse to navigate through the screens and features, you may also navigate using key
strokes (see the "Navigation without the Mouse" explanation at the end of this section).
Tabs
Tabs facilitate navigation between the different screens in the program. Clicking a tab
opens the screen associated with it. You can enter information and edit data on an open screen.
There are six tabs, one for each of the following screens:
• METHOD, MET. STATION, WMU
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IWAIR User's Guide Section 2.0
WASTES MANAGED
WMU DATA FOR CHEMDAT8
EMISSION RATES
DISPERSION FACTORS
RESULTS.
Table 2-1 describes each of these tabs and how each screen associated with a tab assists
you in providing the program with the inputs needed to perform the calculations. The program
automatically opens the next screen after the required information is entered into the data fields
and the I DONE | command button is clicked.
At any time in the program, you can return to a screen that has already been visited by
clicking the tab associated with the screen. You can view information entered on the screen and
can also change any information entered on a previously visited screen. Changing data on a
previously visited screen has no effect on screens before the changed screen, but does affect
screens following the changed screen. Whenever you change data on a previously visited screen,
you will have to proceed through the following screens in order (even if the data on them have
been retained) to return to where you were before you went back and made the change; this is so
that calculated values will be recalculated with the new data. For example, if you were on the
EMISSION RATES screen and returned to the METHOD, MET STATION, WMU screen to change meteorological
stations, you would still have to proceed through the WASTES MANAGED and WMU DATA FOR CHEMDAT8
screens, clicking on | DONE |, to return to the EMISSION RATES screen. If you enter data on a screen,
return to a previous screen without clicking | DONE |, and make changes to the previous screen, the
new data you entered will be lost, and you will need to re-enter them when you return to the
screen you were working on. These data will not be lost if you do not change anything on the
previous screen and if you return to the subsequent screen using | TAB | rather than | DONE |.
Menus
As shown in Figure 2-1, a menu is also provided with IWAIR that allows you to perform
tasks such as starting a new run, loading data from a previous run, saving data from the current
run, printing reports, and exiting the program. The menu options are covered in detail in
Section 2.5.
Command Buttons
In addition to tabs and menus, one or more command buttons are provided on each screen
that initiate an action by the program. For instance, click the I DONE | command button after you
have entered all data on a screen to calculate and proceed to the next screen.
Message Prompts
The program uses message boxes to communicate important information and to confirm
actions before executing a command. For instance, an error message is shown when incorrect,
invalid, or incomplete information is entered.
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IWAIR User's Guide
Section 2.0
Table 2-1. IWAIR Tabs and Associated Screens
Tab
Description of Screen Associated with Tab
Method, Met.
Station, WMU
Select calculation method (i.e., risk calculation or allowable waste concentration
calculation).
Select WMU type. The WMU choices include surface impoundment, land application
unit, active landfill, and waste pile.
Enter zip code or latitude and longitude of site to allow the program to select the most
representative meteorological station from the program's 60 stations.
Select whether estimations will be made based on program-generated CHEMDAT8
emission rates and default ISCST3 dispersion factors, user-specified emission rates
and default dispersion factors, or a combination of both IWAIR-generated and user-
specified estimates.
Wastes Managed
Identify up to six chemicals that are present in the waste managed in the WMU of
concern. You can choose to view chemicals by CAS number or by chemical name (95
chemicals are included in the database that is installed with the IWAIR program).
Add or modify chemical data.
If you selected to perform a risk calculation and to use CHEMDAT8, you must
provide the concentration of each chemical in the WMU.
WMU Data for
CHEMDAT8
This tab is enabled and its associated screens are opened if you elected to have IWAIR
develop chemical-specific emission rates using EPA's CHEMDAT8 model. You must
provide a variety of site-specific data (e.g., unit dimensions and waste loading
information). Default values are provided adjacent to the data box for several of the input
parameters.
Emission Rates
View and confirm CHEMDAT8 emission rates or enter user-specified emission rates.
Enter source and justification for user-specified emission rates on this screen.
Dispersion Factors
Calculate dispersion factors or provide user-specified dispersion factors. Identify up to
five receptors (i.e., potentially exposed individuals). For each receptor, specify the
distance to the receptor and the receptor type (i.e., resident or worker). The program
calculates the dispersion factors based on distance to the receptor, as well as WMU area
and meteorological station. Alternatively, you may enter your own dispersion factors.
Enter source and justification for the user-supplied dispersion factors on this screen.
Results
Two different results screens are associated with this tab, one for risk calculation and one
for allowable concentration calculation. You can
• Select the receptor for which the calculation is to be performed.
• View the chemicals of concern that were selected under the WASTES MANAGED screen.
• View input data determined in the previous screen (distance from the unit to the
receptor, receptor type, and dispersion factors). IWAIR uses these data in the risk or
waste concentration calculations.
• View and override program-supplied health benchmarks. If you choose to override
these data, you should also provide the source and justification for the user-supplied
benchmarks.
• In the risk calculation mode, click the I CALCULATE | button to generate and display risk
estimates for carcinogens, and HQs for noncarcinogens.
• In the allowable concentration mode, select target risk level (e.g., 1E-5, 1E-6) and/or
an HQ (e.g., 0.5, 1) to serve as the starting point for the allowable concentration
calculation for each chemical. Then click the I CALCULATE | button to generate and
display the allowable waste concentrations for each chemical of concern.
2-5
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IWAIR User's Guide
Section 2.0
Industrial Waste - [la. Waste
AIR
lie Help
Open Analysis,,,
Save Analysis,,,
Print Report...
Exit
concentration
rtion,WMU f • --' ,•: ; = ' --/-:! ] vlU Data for CHEMDAT8 ]
Calculation to estimate risk for specified
chemical concentrations
Calculation to estimate chemical
concentrations based on specified risk
-2. Select Waste Management Unit (WMU) Type — ,
(• Surface impoundment
C Land application unit
f Afiiup landfill
3. Selection of Best Meteorological Station for Site
f* Search by zip code
C Search by latitude and longitude coordinates
C Waste pile
B3 Industrial Waste - [la. Waste
File
Mi
Help
View Help for Screen
Contents
T
'MU f
Dispersion Factors
Waste s M an aq e d
I
I
Results
WMU for CHEW DAI
8 )
1. Select Calculation Method
(* Calculate risk Calculation to estimate risk for specified
chemical concentrations
f Calculate allowable Calculation to estimate chemical
concentration concentrations based on specified risk
3. Selection of Best Meteorological Station for Site
(* Search by zip code
C Search by latitude and longitude coordinates
2. Select Waste Management Unit (WMU) Type
(• Surface impoundment
C" Land application unit
r Active landfill
r Waste pile
Figure 2-1. Menu bar in the IWAIR program.
Navigation without the Mouse
Although you typically navigate IWAIR's graphical user interface using a mouse or other
pointing device, the keyboard may be used to make selections and proceed through the screens.
The I TAB | key moves the cursor from one input box or control (e.g., command button, option
button, drop-down list) to the next. The I BACK-TAB | key (I SHIFT | + | TAB |) moves the cursor in the
reverse order on the current screen. When the cursor is on a command button, press the I ENTER |
key to "click" the button. Option buttons always appear in a set of at least two options; when the
cursor is on any option button, press a cursor arrow key to mark a different option button as
being selected and then use the I TAB | key to move out of that option button group. A drop-down
box displays one choice of several; when the cursor is on the box, use the up-arrow and down-
arrow keys to display the desired choice. At any time, you can press the | ALT| key to access the
FILE and HELP menus at the top of the window.
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IWAIR User's Guide Section 2.0
2.5 Menus
As shown in Figure 2-1, the IWAIR menu bar consists of two choices: FILE and HELP. HELP
is described in Section 2.6. The FILE menu options are described in this section.
The FILE menu provides the following features: start a new analysis, save and re-open an
analysis, print reports, and exit IWAIR. Each of these features is discussed below.
2.5.1 Start a New Analysis
During an IWAIR session, you may want to discard all data and start over with a new
analysis, so as to model a different WMU, different chemicals, or a different scenario. The NEW
ANALYSIS option lets you clear the current analysis without exiting and restarting IWAIR. It is not
necessary to select NEW ANALYSIS when you start IWAIR.
NEW ANALYSIS clears all entered data and resets IWAIR to initial defaults, with one
exception: the facility information for printed report headers is retained when you select NEW
ANALYSIS. This information may be edited when you print a report.
To start a new analysis, select FILE, NEW ANALYSIS. You will be prompted with "Discard all
changes and restart calculations?"
• Click on | YES I to start a new analysis.
• Click on | No I to return to your existing analysis.
2.5.2 Save and Re-Open an Analysis
You can save an analysis and re-open it later using the FILE, SAVE ANALYSIS and FILE, OPEN
ANALYSIS features. IWAIR saves all user-entered data, as well as calculated and user-override
emission rates and dispersion factors, and current facility information for report headers (if any
has been entered during the session). It does not save calculated values from the RESULTS screen
(air concentrations, risks, HQs, and allowable concentrations); these must be recalculated from
the RESULTS screen.
IWAIR does not save chemical properties data or user-defined health benchmarks with a
saved analysis, but uses the current chemical properties and user-defined health benchmark
values in the chemical database at the time an analysis is re-opened. Therefore, the results may
change if you have changed the chemical properties or user-defined health benchmarks of any
chemical in the saved analysis since you saved the analysis. Changes to user-defined health
benchmarks will be reflected when you recalculate the results, as you are required to do. Changes
to other chemical properties that affect emission rates will not be reflected unless you recalculate
emission rates by clicking | DONE | on the WMU DATA FOR CHEMDAT8 screen. In addition, the chemical
database must contain entries for all chemicals in the saved analysis, or the analysis will not
reload. This would only occur if you had saved an analysis containing user-defined chemicals,
then subsequently deleted any of those chemicals from the chemical database, or if you tried to
open a file saved by another user containing user-defined chemicals specific to his or her
2-7
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IWAIR User's Guide Section 2.0
chemical database and not found in yours. See Appendix A, Sections A.4.2 and A.5.2, for more
details on adding or modifying chemical data.
IWAIR can only reload analyses saved from the current version of IWAIR.
You can save an analysis only from the RESULTS screen. You can open a saved analysis
from any screen, but once the analysis is reloaded, you will be returned to the METHOD, MET. STATION,
WMU screen. You should then move through the tabs in sequence by clicking | DONE |, even if you
have not changed anything. This will recalculate your analysis (though you will have to re-enter
any user-override emission rates or dispersion factors) and ensure the accuracy of the results. If
you wish to view saved user-override emission rates or dispersion factors before you do this, you
can use the tabs to move directly to other screens without clicking | DONE | on each screen.
IWAIR was not designed to do calculations other than as part of a complete sequence through the
screens. Therefore, although you may be able to view results by recalculating only on the RESULTS
screen (without clicking through the previous screens using the I DONE | buttons), doing so may
result in model errors.
If an analysis fails to reload (either because it is missing a chemical or was saved from a
previous version of IWAIR), you will be returned to the METHOD, MET. STATION, WMU tab with all
values reset, as if you had selected NEW ANALYSIS.
To save the current analysis, navigate to the RESULTS screen, and select FILE, SAVE ANALYSIS.
This opens a SAVE As dialog box.
• Enter the desired file name in the FILE NAME box and click on | SAVE | to save the
analysis to a new file.
• Click on an existing file name and click on | SAVE | to save the analysis over an
existing file. You will be warned that the file already exists and asked if you want
to replace it.
- Click on | YES I to replace the existing file.
- Click on | No I to return to the SAVE As box and change the file name.
• Click on | CANCEL | to abort saving the analysis; you will be returned to the current
analysis.
To reload a previously saved analysis, select FILE, OPEN ANALYSIS. You will be prompted
with "You will lose unsaved data. Continue?"
• Click on | YES I to open a FILE OPEN dialog box; from this box, select the desired file
by clicking on it.
- Click on | OPEN I or double-click on the file name to open it. You may see
the IWAIR screens flashing on your screen as IWAIR reloads your data.
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IWAIR User's Guide Section 2.0
Click on | CANCEL | to abort opening a saved analysis and return to your
existing analysis.
• Click on | No I to return to your existing analysis.
2.5.3 Print Reports
You can print a report containing the data and results from the current analysis using the
PRINT REPORT function. Reports are divided into five sections:
• Part la: General Parameters. This section includes facility information;
information on the meteorological station, WMU type, and computation options
used; and WMU characteristics. The facility information for the header includes
facility name, facility type, address, date of sample analysis, name of user, and
additional information; you will be prompted to enter or edit this, if you desire,
before printing the report.
• Part Ib: Chemical Properties. This section includes the CAS number and all
chemical properties except health benchmarks for each chemical in the analysis.
• Part 2: Health Benchmark Information. This section includes the IWAIR and user-
defined health benchmarks and references for each chemical in the analysis.
• Part 3: Receptors and Dispersion Factors. This section includes the receptor data,
IWAIR and user-override dispersion factors, and exposure duration for each
receptor.
• Part 4: Final Results. This section includes the waste concentration, IWAIR and
user-override emission rates, and the risk and HQ for each chemical and receptor.
The exact data in each report vary somewhat depending on the type of WMU and the type of
analysis. The reports are 5 to 8 pages long, depending on how many chemicals and receptors you
have selected. The report only prints in full and to the default printer. You cannot print selected
pages or sections, nor can you print reports to a file.
The facility information you enter for the report header is retained until you exit IWAIR;
each time you print a report, you have the option to edit it. This information is saved in a saved
analysis; therefore, if you open a saved analysis, the saved information will overwrite the current
information.
You can print a report only once you have completed an analysis (i.e., you have reached
the RESULTS screen). Once you have done this, you can print a report from any screen (i.e., if you
have gone back to look at a previous screen); however, printing a report always returns you to the
RESULTS screen, regardless of where you printed from.
To print a report, select FILE, PRINT REPORT. You will be prompted with "Edit facility
information for report header?"
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IWAIR User's Guide
Section 2.0
• Click on | YES I to enter or edit facility information to be printed in the report
header.
• Click on | No I to retain the current facility information for the report header (or to
leave it blank if you have not entered facility information during the current
IWAIR session).
• Click on | CANCEL | to abort printing.
Once you have edited (or chosen not to edit) the facility information for the report header, you
will be prompted to "Click OK to route the reports to local printer." The report cannot be
aborted at this point. Reports are printed to the default printer defined on your system.
2.5.4 Exit IWAIR
To exit IWAIR, select FILE, EXIT, or click on the X in the upper right corner of the screen.
IWAIR will ask "Do you want to exit IWAIR?"
• Click on | YES I to exit IWAIR. Any unsaved data will be lost.
• Click on | No I to return to your analysis.
2.6 Online Help
The program provides online help that can be accessed from any screen, either by
pressing the IF11 key or by selecting the HELP menu. The IF11 key and the VIEW HELP FOR SCREEN
selection on the HELP menu display the information corresponding to Sections 4 and 5 of this
document that is pertinent to the currently displayed program screen. A hyperlink at the top of
the HELP screen brings up the parameter guidance help corresponding to Appendix B of this
document. In some cases, this may be preceded by hyperlinks for risk versus allowable
concentration calculations. The CONTENTS selection on the HELP menu displays the table of contents
for the online help.
2.7 Troubleshooting
Table 2-2 lists some common problems you may encounter and how to solve them.
Table 2-2. Troubleshooting Common Problems in IWAIR
Problem Category
Description of Problem
Solutions
Installation
Windows 95B and NT4 SP6a
ask to restart computer to
update Windows system
files.
Click on | YES |. After restart is complete, double-click on
setup.exe again to finish the install. Windows system files
updated will be in the system folders in the Windows
directory, and the old ones will be renamed
"filename.dll.old".
(continued)
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IWAIR User's Guide
Section 2.0
Table 2-2. (continued)
Problem Category
Description of Problem
Solutions
Windows NT4 SP6a, error
occurs installing
CRVIEWER.DLL.
Choose | IGNORE |, and the program will install completely.
This does not in any way affect the functionality of the
software.
Display
The gray screens in the
program appear "blotched"
and are not uniformly gray.
Changing your monitor's display settings will fix this
problem. Under the CONTROL PANEL, DISPLAY, SETTINGS
tab, make sure that the Color Pallette is set for High Color
(16 bit) or True Color (32 bit) or higher. Note that these
options may not be available on all machines, depending
on the type of monitor, graphics card, and video driver
used.
Screens are not displayed
correctly, display is not
optimized.
The IWAIR program display is optimized for screen
resolutions of 800 x 600 pixels. At lower resolutions, not
all of the IWAIR screens are displayed. The screens
appear smaller at higher resolutions.
Printing
Text is cut off at the edges.
Due to the large quantity of data to be displayed on the
reports, the margins selected for the reports are only 0.25
inches. Text may be cut off if the printer has a larger
unprintable area. Printing functions were tested on an HP
Laser Jet 4/4M and higher-grade printers.
Override values print in
reports even though no
override values were entered.
If no override values are entered, IWAIR may repeat the
calculated emission rates or dispersion factors in the
override column of the printed report.
Miscellaneous
Low system resources
message is displayed,
program crashes, program
runs slowly.
IWAIR may be unstable when other applications are also
open because of the memory required for running IWAIR.
Close all other applications before starting IWAIR to free
up the maximum resources for the program. If your
computer's resources are still low, reboot the computer
and restart IWAIR.
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IWAIR User's Guide Section 3.0
3.0 Selecting Calculation Method, WMU Type,
and Modeling Pathway
3.1 Selecting Calculation Method
Each time you begin the program, select the mode of calculation. You can choose from
two calculation methods: risk and allowable concentration. Click on the option button associated
with either the risk calculation or the allowable concentration calculation mode. Each of these
options is discussed below.
Risk Calculation Method
The first calculation method, risk calculation, allows you to develop inhalation risk
estimates based on waste concentration levels that you specify. Results from the risk calculation
method include (1) chemical-specific cancer risk estimates, (2) total cancer risk estimates (i.e.,
the summation of the chemical-specific risk estimates), and (3) noncancer risk estimates (i.e.,
HQs for noncarcinogens in the waste). Use the risk calculation option to develop risk estimates
when you know the concentrations of the constituents in the waste. If the program results
indicate that the waste poses an unacceptable risk to exposed individuals, then you should
consider conducting a more site-specific analysis or implementing corrective measures to reduce
the fraction of constituents released to the atmosphere. Such measures could include
pretreatment of waste to reduce volatile chemical concentrations before the waste enters the unit
or applying unit control technologies or practices to reduce volatile air emissions. Chapter 5 of
the Guide for Industrial Waste Management, "Protecting Air Quality," identifies and discusses
some emission control options.
Allowable Concentration Calculation Method
The second calculation method is an allowable concentration calculation that results in
the development of waste concentrations (Cwaste) that are protective of human health when
managed as described. The calculation method can be applied in calculating waste
concentrations for both wastewaters (Cwaste in mg/L) and solid waste (Cwaste in mg/kg).
Concentrations are estimated based on user-defined target cancer and noncancer risk levels (e.g.,
IE-5 for carcinogens, or an HQ of 1 for noncarcinogens), which you will set on a later screen,
the RESULTS SCREEN. The program uses information gathered on the IWAIR screens to calculate for
each chemical an allowable waste concentration that would not pose an inhalation risk to the
receptor greater than the selected target level. You can use the allowable concentration
calculation option to estimate waste concentrations for a WMU that has not yet received a waste,
5-1
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IWAIR User's Guide Section 3.0
to determine what concentration(s) would pose an unacceptable risk to potentially exposed
individuals.
3.2 Selecting WMU Type
Identify the WMUs that are used to manage wastes of concern at your facility and run the
model separately for each WMU. Each of the four IWAIR unit types (described below) reflects
waste management practices that are likely to occur at Industrial Subtitle D facilities.
Surface Impoundment. In the IWAIR tool, surface impoundments are considered to be
ground-level, flowthrough units. The major source of volatile emissions associated with surface
impoundments is the uncovered liquid surface exposed to the air (U.S. EPA, 1991).
Impoundments can be quiescent (nonaerated) or aerated. Aeration or agitation is applied to aid in
the treatment of the waste. Emissions tend to increase with an increase in surface turbulence
because of enhanced mass transfer between the liquid and air (U.S. EPA, 1991). IWAIR can
conduct emission modeling for both aerated and nonaerated surface impoundments. Parameters
to which emissions are most sensitive include surface area, unit depth, waste concentration,
retention time, wind speed for quiescent systems, and biodegradation.
The surface impoundment component of the IWAIR tool should not be used to model
tanks. Although tanks have many common characteristics with surface impoundments with
respect to volatile emissions, tanks are usually aboveground units, and height of the unit above
the ground has a significant effect on dispersion factors. Therefore, the dispersion factors
included in IWAIR for surface impoundments (which are presumed to be ground-level) are
inappropriate for tanks and would produce erroneous results if so used.
Tilled Land Application Units. Wastes managed in land application units can be tilled or
sprayed directly onto the soil and subsequently mixed with the soil by discing or tilling. Waste in
a land application unit is a mixture of waste and soil. IWAIR allows the modeling of tilled land
application units only. Spray application was not included because the degree of volatilization
associated with this type of application practice is very site-specific and is influenced by a
number of variables, including meteorological conditions and application equipment. Therefore,
IWAIR is unsuitable for modeling spray land application units. Important characteristics for the
tilled land application unit include surface area (the exposed area from which volatile emissions
can be released) and the application rate (which affects the depth of the contamination, which,
along with area, defines the extent of the source for volatile emissions).
Landfills. IWAIR allows modeling of emissions released from the surface of an active
(i.e., receiving wastes) landfill. Volatilization can occur from the surface of the landfill.
Important unit characteristics for the landfill include surface area and unit depth. IWAIR
assumes that the landfill being modeled is a ground-level emission source.
Waste Piles. Waste piles are typically elevated sources used as temporary storage units
for solid wastes. Important characteristics for the waste pile include surface area and height.
These parameters define the exposed area from which volatile emissions can be released.
5-2
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IWAIR User's Guide Section 3.0
3.3 Determining Appropriate Modeling Pathway
Regardless of the calculation method selected (risk or allowable concentration),
determine which modeling pathway to follow in using the tool. After deciding on the appropriate
calculation method and modeling pathway, proceed to either Section 4 for detailed guidance on
completing risk calculations or Section 5 for guidance on allowable waste calculations.
You can choose from four pathways that provide you with the flexibility of conducting
modeling using IWAIR-generated emissions rates and dispersion factors, user-specified emission
and dispersion estimates, or a combination of both IWAIR-generated and user-specified
estimates:
• Pathway 1: Using CHEMDAT8 emission rates and ISCST3 default dispersion
factors
• Pathway 2: Using CHEMDAT8 emission rates and user-specified dispersion
factors
• Pathway 3: Using user-specified emission rates and ISCST3 default dispersion
factors
• Pathway 4: Using user-specified emission rates and dispersion factors.
In selecting a pathway, consider the availability of site-specific information. For
example, if you have access to a limited amount of site-specific data and do not have access to
emissions measurement data, then you will likely want to follow either Pathway 1 or 2 to allow
IWAIR to develop CHEMDAT8 emissions rates. Similarly, if you do not have the ability (i.e.,
resources or access to technical capabilities) to conduct site-specific air dispersion modeling,
then you will want to follow either Pathway 1 or 3 to allow IWAIR to develop dispersion factors.
If site-specific emission and dispersion rates are accessible or if resources are available to
develop these data, Pathway 4 will provide the most refined site-specific results.
Additionally, consider model assumptions and capabilities. Because a number of
assumptions are made by IWAIR in modeling emissions and dispersion, use of these features
may not be appropriate in all cases. Review the following overviews of CHEMDAT8 emission
modeling and ISCST3 default dispersion factors, as well as Section 1.4 on IWAIR's capabilities
and limitations, prior to choosing a pathway.
Using CHEMDAT8 Emission Rates
EPA's CHEMDAT8 model has been incorporated into the IWAIR program to assist you
in the development of chemical-specific emission rates. This model has undergone extensive
review by both EPA and industry representatives and is publicly available from EPA's Web page
(http://www.epa.gov/ttn/chief/software.html).
5-3
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IWAIR User's Guide
Section 3.0
CHEMDAT8 considers many of the
competing removal pathways that might limit
air emissions, including adsorption and
hydrolysis in surface impoundments and
biodegradation in all types of units.
Adsorption is the tendency of a chemical to
attach or bind to the surface of particles in the
waste and therefore to not volatilize into the
air. Biodegradation is the tendency of a
chemical to be broken down or decomposed
into less-complex chemicals by organisms in
the waste or soil; because this is a highly site-
specific process, IWAIR allows you to choose
whether to model biodegradation for all
WMU types. Similarly, hydrolysis is the
tendency of a chemical to be broken down or
decomposed into less-complex chemicals by
reaction with water. IWAIR does not model
these breakdown products produced as a
result of biodegradation or hydrolysis.
Chemicals that decompose by either
biodegradation or hydrolysis have lower
potential for volatile emission to the air.
Loss of contaminant by leaching or
runoff is not included in the CHEMDAT8
model. Both leaching and runoff are a
function of a chemical's tendency to become
soluble in water and follow the flow of water
(e.g., due to rainfall) down through the soil to
groundwater (leaching) or downhill to surface
water (runoff). These two mechanisms would
also result in less chemical being available for
volatile emission to the air. CHEMDAT8 is
considered to provide reasonable to slightly
high (environmentally conservative) estimates
of air emissions from the various emission
sources. See the IWAIR Technical
Background Document for a more detailed
discussion of the emissions modeling.
IWAIR Assumptions Made for
Modeling Volatile
Emissions with CHEMDAT8
• Annual average temperature is determined by
assigned meteorological station; user may override.
• Waste is homogeneous.
Quiescent and Aerated Surface Impoundment
Assumptions'.
• Flowthrough unit is operating at steady state.
• For aqueous-phase wastes, waste in the surface
impoundment is well mixed.
• Organic-phase wastes are modeled under plug flow
conditions.
• For aqueous-phase wastes, biodegradation rate is
first order with respect to biomass concentrations.
• For aqueous-phase wastes, biodegradation rate
follows Monod kinetics with respect to
contaminant concentrations.
• For aqueous-phase wastes, hydrolysis rate is first
order with respect to contaminant concentrations.
• For aqueous-phase wastes, biodegradation is
modeled by default; user may turn off.
Tilled Land Application Unit Assumptions:
• The volume of the land application unit remains
constant. As new waste is applied, an equal
volume of waste/soil mixture becomes buried or
otherwise removed from the active tilling depth.
• Biodegradation is modeled by default; user may
turn off.
• For organic-phase wastes, biodegradation and
hydrolysis are not modeled.
Landfill Assumptions:
• Only one cell is active at a time.
• The active cell is modeled as instantaneously filled
at time t = 0 and open for the life of the landfill
divided by the number of cells. Cells are either
depleted of the constituent or capped at the end of
this period.
• Biodegradation is not modeled by default; user
may turn on.
Waste Pile Assumptions:
• Waste pile operates with fixed volume.
• Waste pile is modeled as a square box with
essentially vertical sides.
• Biodegradation is not modeled by default; user
may turn on.
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IWAIR User's Guide
Section 3.0
Using ISCST3 Default Dispersion Factors
The IWAIR default dispersion factors
were developed by conducting air dispersion
modeling with EPA's ISCST3 (U.S. EPA,
1995). This model is capable of modeling
ground-level and elevated area sources. For
IWAIR, landfills, land application units, and
surface impoundments were modeled as
ground-level area sources and waste piles were
modeled as elevated area sources.
Because the ISCST3 model has
considerable run times for area sources,
modeling was conducted for a limited number
of WMUs of representative sizes (i.e., surface
areas, and heights for waste piles) using
meteorological data obtained from 60
meteorological stations. The representative
WMU sizes were selected from the range of
sizes seen in the 1985 Screening Survey of
Industrial Subtitle D Establishments
(Shroeder et al., 1987). This database was the
most comprehensive database that EPA had on waste unit characteristics. It contains data on
6,254 surface impoundments, 1,281 waste piles, 702 land application units, and 790 landfills.
The IWAIR program is designed to cover the range of unit characteristics contained in the
database. Specific areas to be modeled were selected from the skewed distribution of areas
found in the Industrial D Survey database so that all WMUs in the database would be adequately
represented and interpolation errors would be minimized. As a result, 17 surface areas were
selected for modeling for the landfills, land application units, and surface impoundments. Eleven
surface areas were selected for waste piles. In
addition, 7 heights were selected to be
modeled for waste piles, and waste piles were
modeled at all possible combinations of the
11 areas and 7 heights.
Assumptions Made for Dispersion Modeling
An area source was modeled for all WMUs.
To minimize error due to site orientation, a
square area source with sides parallel to x- and
y-axes was modeled.
Modeling was conducted using a unit emission
rate of 1 ug/nf-s.
Receptor points were placed on 25, 50, 75, 150,
500, and 1,000 m receptor squares starting from
the edge of the source, with 16 receptor points
on each square.
Dry and wet depletion options were not activated
in the dispersion modeling.
The rural option was used in the dispersion
modeling because the types of WMUs being
assessed are typically in nonurban areas.
Flat terrain was assumed.
The ISCST3 modeling was conducted
with data obtained from 60 meteorological
stations chosen to represent the various
climatic and geographical regions of the
contiguous 48 states, Hawaii, Puerto Rico,
and parts of Alaska. The dispersion modeling
was conducted using 5 years of data from
each of the 60 meteorological stations. The
meteorological data required as input to the
ISCST3 model included hourly readings for
Key Meteorological Data for
the ISCST3 Model without Depletion
Wind direction determines the direction of the
greatest impacts.
Wind speed is inversely proportional to ground-level
air concentration, so the lower the wind speed, the
higher the concentration.
Stability class influences rate of lateral and vertical
diffusion. The more unstable the air, the lower the
concentration.
Mixing height determines the maximum height to
which emissions can disperse vertically. The lower
the mixing height, the higher the concentration.
5-5
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IWAIR User's Guide
Section 3.0
the following parameters: wind direction, wind speed (m/s), ambient temperature (K), mixing
height, and stability class.
Dispersion factors were obtained as output by running the model with a unit emission rate
(i.e., 1 |j,g/m2-s). The selected areas for each type of WMU were modeled using meteorological
inputs obtained from the 60 representative meteorological locations. Receptors were placed in
16 directions at distances of 25, 50, 75, 150, 500, and 1,000 meters from the edge of the WMU.
Figure 3-1 illustrates the pattern of receptor placement around the unit for a 10,000 m2 unit; only
receptors at 150 m or less are shown for clarity reasons. Receptor placement was made based on
a sensitivity analysis that was conducted to determine the locations and spacings that would
provide adequate resolution without modeling an excessive number of receptors. The resulting
maximum annual average air concentrations at each distance serve as the IWAIR default
dispersion factors.
200 <
100 <
0)
*> o <
£
-100 <
-200 <
-2
> • 4
» • • •
*
> • 4
DO -100
> • 4
WMU
0
(meters)
> • 4
• • • 4
> • 4
>
>
>
100 200
Figure 3-1. Receptor Locations.
5-6
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IWAIR User's Guide Section 3.0
Based on the WMU surface area (and height, for waste piles) that you provide, the
IWAIR tool selects an appropriate dispersion factor. If the entered WMU surface area or height
lies between two modeled areas or heights, dispersion factors for the WMU are estimated by an
interpolation between dispersion factors for WMUs in the database with areas and heights above
and below that of the WMU area you entered. For example, if you specify a landfill with a
surface area of 8,000 m2, the program will determine that this surface area falls between two
modeled units with surface areas of 4,047 m2 and 12,546 m2. A linear interpolation method is
then applied to estimate a dispersion factor for the 8,000 m2 landfill, based on the default
dispersion factors stored in the IWAIR database for two similarly sized units. For waste piles, a
two-dimensional nonlinear interpolation method (called a spline) is used. See the IWAIR
Technical Background Document for more information on the spline approach.
5-7
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IWAIR User's Guide Section 4.0
4.0 Completing Risk/Hazard Quotient
Calculations
IWAIR allows you to develop inhalation risk estimates for wastes of known chemical
concentrations. Results from the risk calculation method include chemical-specific cancer risk
estimates, total cancer risk estimates (i.e., the summation of the chemical-specific risk estimates),
and chemical-specific noncancer risk estimates (i.e., HQs for noncarcinogens in the waste).1
IWAIR is structured in a stepwise framework. Through the use of a series of screens,
IWAIR assists in selecting calculation options, identifying and entering required inputs, and
generating desired outputs. There are four different pathways you can follow in performing a
calculation:
• Pathway 1: Using CHEMDAT8 emission rates and ISCST3 default dispersion
factors
• Pathway 2: Using CHEMDAT8 emission rates and user-specified dispersion
factors
• Pathway 3: Using user-specified emission rates and ISCST3 default dispersion
factors
• Pathway 4: Using user-specified emission rates and dispersion factors.
Guidance for determining which modeling pathway to follow is provided in Section 3.3. The
stepwise approach employed by IWAIR to assist in calculating risk, whether you are following
Pathway 1, 2, 3, or 4, is shown in Figures 4-1, 4-2, 4-3, and 4-4, respectively. The seven steps of
the estimation process are shown down the right side of each figure, and the user input
requirements are specified to the left of each step. The types of input data required will vary
depending on the modeling pathway chosen. Screen-by-screen, IWAIR walks you through the
steps of a risk calculation to arrive at inhalation risk estimates.
This section provides screen-by-screen guidance that describes the data that are required
as input to each screen and the assumptions that are interwoven in the calculation being
performed. The guidance provided in this section will assist you in completing a risk calculation.
You will not need to reference all of the information provided in this section because the
guidance addresses all four of the modeling pathways. Follow only those subsections that are
applicable to your chosen pathway.
1 Noncancer risks are not summed across chemicals, because summation is only appropriate when the same
target organ is affected.
-------
IWAIR User's Guide
Section 4.0
User Specifies:
• Calculation option
User Specifies:
• WMU type
Identify WMU
Land application unit
Waste pile
Surface impoundment
Landfill
User Specifies:
• Constituents (choose up to 6)
• Concentrations
User Specifies:
• CHEMDAT8 option
• Facility location for meteorological input
• WMU information (i.e., design and
operating parameters)
j
User Specifies: ^
• Receptor information (i.e., distance
and type) J
Define the Waste Managed
Add/modify chemical properties
data, as desired
Determine Dispersion Factors
Interpolated from ISCST3 default
dispersion factors
Calculate Ambient Air Concentrations
Calculates ambient air concentrations for
each receptor based on emission and
dispersion data
Calculate Results
Risk Calculation
1. Chemical-specific carcinogenic risk
2. Chemical-specific noncarcinogenic risk
3. Total cancer risk
Figure 4-1. IWAIR approach for completing risk calculations, Pathway 1: Using
CHEMDAT8 emission rates and ISCST3 default dispersion factors.
4-2
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IWAIR User's Guide
Section 4.0
User Specifies:
• Calculation option
User Specifies:
• WMU type
Identify WMU
Land application unit
Waste pile
Surface impoundment
Landfill
User Specifies:
• Constituents (choose up to 6)
• Concentrations
User Specifies:
• CHEMDAT8 option
• Facility location for meteorological input
• WMU information (i.e., design and
operating parameters)
User Specifies:
• Dispersion factors
• Receptor information (i.e., distance
and type) for reference only
Define the Waste Managed
Add/modify chemical properties
data, as desired
User-specified dispersion factors
Calculate Ambient Air Concentrations
Calculates ambient air concentrations for
each receptor based on emission and
dispersion data
Calculate Results
Risk Calculation
1. Chemical-specific carcinogenic risk
2. Chemical-specific noncarcinogenic risk
3. Total cancer risk
Figure 4-2. IWAIR approach for completing risk calculations, Pathway 2: Using
CHEMDAT8 emission rates and user-specific dispersion factors.
4-3
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IWAIR User's Guide
Section 4.0
User Specifies:
• Calculation option
User Specifies:
• WMU type
Identify WMU
Land application unit
Waste pile
Surface impoundment
Landfill
User Specifies:
• Constituents (choose up to 6)
Define the Waste Managed
Add/modify chemical properties
data, as desired
User Specifies:
• Emission rates
User-specified emission rates
User Specifies:
• WMU area (and height for waste pile)
• Facility location for meteorological input
• Receptor information (i.e., distance and
type)
Determine Dispersion Factors
Interpolated from ISCST3 default
dispersion factors
Calculate Ambient Air Concentrations
Calculates ambient air concentrations for
each receptor based on emission and
dispersion data
Calculate Results
Risk Calculation
1. Chemical-specific carcinogenic risk
2. Chemical-specific noncarcinogenic risk
3. Total cancer risk
Figure 4-3. IWAIR approach for completing risk calculations, Pathway 3: Using user-
specified emission rates and ISCST3 default dispersion factors.
4-4
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IWAIR User's Guide
Section 4.0
User Specifies:
• Calculation option
User Specifies:
• WMU type
Identify WMU
Land application unit
Waste pile
Surface impoundment
Landfill
User Specifies:
• Constituents (choose up to 6)
User Specifies:
• Emission rates
User Specifies:
• Dispersion factors
• Receptor information (e.g., distance
and type) for reference only
Define the Waste Managed
Add/modify chemical properties
data, as desired
Determine Emission Rates
User-specified emission rates
User-specified dispersion factors
Calculate Ambient Air Concentrations
Calculates ambient air concentrations for
each receptor based on emission and
dispersion data
Calculate Results
Risk Calculation
1. Chemical-specific carcinogenic risk
2. Chemical-specific noncarcinogenic risk
3. Total cancer risk
Figure 4-4. IWAIR approach for completing risk calculations, Pathway 4: Using user-
specified emission rates and dispersion factors.
4-5
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IWAIR User's Guide
Section 4.0
A. Select
calculation
method
C. Select met
station search
option
Enter zip code
and search for
met station
Enter latitude
and longitude
and search for
met station
D. View
selected met
station
File Help
Emission R.ates | ' * i .dors j Results
Method, Met. Station, WMU } -ed J WMU Data for CHEMDAT3 1
i 1. Select Calculation Method p2. Select Waste Management Unit (WMU) Type _
(• fcaicuiate risk' Calculation to estimate risk for specified W
•4 ! ' chemical concentrations ** Surface impoundment
f* Calculate allowable Calculation to estimate chemical f Land application unit
concentration concentrations based on specified risk
1 C Active landfill
1 3. Selection of Best Meteorological Station for Site i ^ Waste pile
Y (* Search by zip code
f* Search by latitude and longitude coordinates
Enter 5 digit Zip Code of Site
' • Search
i . in ii ] .1 I i i 1 . ' i'.»
-» r r r
1 I
Selected Meteorological Station for Site
4 View Map
! 4. Select Emissions and Dispersion Option *
Use CHEMDAT8 to estimate emission ^
Use CHEMDAT8 rates and use dispersion factors
provided
1 OR 1
Enter Emission Directly enter emission rates without
_, using CHEMDAT8 and use disperion
factors provided
OR
Enter Emission & Directly enter emission rates and
Dispersion Data aspersion factors
- B. Select
WMU type
_ E. Select
emission and
dispersion
option
Screen 1A. Method, Meteorological Station, WMU
4.1 Method, Meteorological Station, WMU (Screen 1A)
A. Select Calculation Method (Screen 1A)
Select the calculation method by clicking on the | CALCULATE RISK | option button. Detailed
guidance for selecting the appropriate mode of calculation is provided in Section 3.1.
B. Select Waste Management Unit (WMU) Type (Screen 1A)
Identify the WMUs that are used to manage wastes of concern at your facility and run the
model separately for each unit type. The four unit types that are addressed as part of this
guidance include surface impoundments (aerated and quiescent), active landfills, waste piles, and
tilled land application units. A detailed description of these unit types is provided in Section 3.2.
Select one of the four WMU types shown in Screen 1A by clicking on the appropriate option
button.
C. Select Meteorological Station Search Option (Screen 1A)
The two search options available include searching by the site's 5-digit zip code or by its
latitude and longitude. Select the appropriate search option and enter the appropriate
information. This information is used to link the facility's location to one of the 60 IWAIR
meteorological stations. The 60 stations cover the 48 contiguous states, Hawaii, Puerto Rico, and
parts of Alaska. Data from the 60 stations (shown on maps in Screen IB, viewed by clicking on
4-6
-------
IWAIR User's Guide Section 4.0
the | VIEW AMP | button shown on Screen 1 A) were used as inputs to the air dispersion modeling
effort conducted to develop the default dispersion factors contained in the IWAIR tool. They are
also used as inputs to CHEMDAT8 emission modeling (e.g., temperature and wind speed).
Additional information on this air dispersion modeling effort and the 60 representative
meteorological stations is provided in Section 3.3.
Enter 5-Digit Zip Code and Search for Meteorological Station
Enter a 5-digit zip code and click on the | SEARCH | button to identify the default
meteorological station. If the zip code was entered incorrectly or if no data were provided
at all, message boxes will appear to indicate the specific problem that the tool
encountered so that you can supply the needed data. The zip code database includes zip
codes established through 1999. If your facility has a new zip code that was established
more recently, you will get an error message indicating that it is not a valid zip code
because it is not in IWAIR's database. If this occurs, you can use your old zip code, use a
nearby zip code, or select a meteorological station using latitude and longitude.
Enter Latitude and Longitude Information and Search for Meteorological Station
As shown in Screen 1 A, enter the latitude and longitude of the site in degrees, minutes,
and seconds. At a minimum, the program requires degrees for latitude and longitude to
be entered. If available, the minutes and seconds should be supplied to ensure that the
most appropriate station is selected for a site. After these data are entered, click on the
I SEARCH | button to identify the default meteorological station. If the latitude and longitude
information was entered incorrectly or if no data were provided at all, message boxes will
be displayed that indicate the specific problem that the tool encountered so that you can
supply the needed data.
D. View Selected Meteorological Station (Screen 1A)
The meteorological station selected by the tool will be displayed in the text box. Once
the meteorological station is selected, you are encouraged to click on the VIEW MAP | button to
view the maps showing the 60 meteorological stations to ensure that the selection was made
correctly. For example, if the latitude of a site was entered incorrectly, then the selected
meteorological station would likely not be the most representative station. In this case, the map
will help you identify this error before proceeding with the calculations. Clicking on the | VIEW
MAP | button will bring up a map of the 48 contiguous states (Screen IB, shown here). You may
view six additional maps (regional maps for the northeastern, southeastern, and western areas of
the 48 contiguous states, as well as maps of Hawaii, Alaska, and Puerto Rico) by clicking on the
appropriate button at the bottom of Screen IB. The | CLOSE| button returns you to the METHOD, MET.
STATION, WMU Screen (Screen 1 A).
4-7
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IWAIR User's Guide
Section 4.0
Industrial Waste - [Ib. Maps showing the Met Stations]
IfllR
File Help
Met
Continental U.S. Western U.S. Northeastern U.S. Southeastern U.S. I Alaska I Hawaii I Puerto Rico j Close
Screen IB. Map of 48 Contiguous States Showing 60 Meteorological Stations
E. Select Emission and Dispersion Option (IWAIR-Genemted or User-Specified)
(Screen 1A)
You must select from the IWAIR emission and dispersion data options. Under these
options, you have the flexibility of conducting modeling using IWAIR-generated emission rate
and dispersion factor estimates, user-specified emission and dispersion estimates, or a
combination of IWAIR-generated and user-specified estimates.
The tool uses emission rate and dispersion factor estimates in both the risk and allowable
concentration modes. As seen in Screen 1 A, you must select one of the three options provided
for obtaining emission and dispersion data:
• Use CHEMDAT8
Select | USE CHEMDAT81 to use CHEMDAT8 for calculating the emissions from
your unit regardless of whether you want to calculate or enter dispersion factors.
This allows you to enter a variety of unit-specific information that IWAIR will use
4-8
-------
IWAIR User's Guide Section 4.0
to develop chemical-specific emission rate estimates through the use of EPA's
CHEMDAT8 model. These inputs also provide the information needed to use the
ISCST3 dispersion factors provided with IWAIR; however, you may also enter
your own dispersion factors. You will be allowed to override the IWAIR
emission estimates on subsequent screens. This option corresponds to Pathways 1
and 2 (see Section 3.3 and Figures 4-1 and 4-2).
• Enter Emission Rates
Select | ENTER EMISSION RATES | to enter your own site-specific emission rates (g/m2-s)
on a subsequent screen. Rates may be developed based on monitoring data or
measurements or by conducting modeling with a different emission model. Under
this option, IWAIR can be used to estimate dispersion based on ISCST3 default
dispersion factors. If this option is selected, you will still be allowed to override
the IWAIR dispersion factors on subsequent screens with site-specific dispersion
factors (|J,g/m3 per |j,g/m2-s). Once the | ENTER EMISSION RATES | command button is
selected, a message box will appear that directs you to enter WMU area (m2). If a
waste pile is being modeled, a subsequent box will appear for the height of the
unit to be entered. These WMU data are used by the model to calculate dispersion
estimates. This option corresponds to Pathway 3 (see Section 3.3 and Figure 4-3).
Enter Emission, Dispersion Data.
Select | ENTER EMISSION & DISPERSION DATA| to enter your own emission estimates
(g/m2-s) and dispersion factors (n-g/m3 per |j,g/m2-s). This option corresponds to
Pathway 4 (see Section 3.3 and Figure 4-4).
4-9
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IWAIR User's Guide
Section 4.0
B. Select
sorting option
for identifying
chemicals
A. Add/
modify
chemicals
C. Identify
chemicals in
waste
Industrial Waste - [Za. Wastes Managed in WMUs]
File Help
Method, Met. Station, WMU
Wastes Managed
Identify Chemicals of Concern
To select chemical in management unit, click on chemical in list and click "Add »", or double-click on chemical in list
To remove chemical in management unit, select chemical to remove and click "«Remove"
To add a chemical to the list or to modify properties for a user-defined chemical, click "AddModify Chemicals"
Sort by chemical name
Sort by CAS number
Add/Modify Chemicals
Benzo(a)pyrene [50-32-8]
Bromodichloromethane [75-27-4]
JSBIBBBBIBBnBMSffiSil^^B
Carbon tetrachloride [56-23-5]
£hlorobenzene [108-90-7]
Chlorodibromomethane [124-48-1 ]
Chloroform [67-66-3]
Chloroprene [126-99-8]
cis-1,3-Dichloropropylene [10061 -01 -5]
Cresols (total) [1319-77-3]
Cumene [98-82-8]
Cyclohexanol [108-93-0]
Dichlorodifluoromethane [75-71 -8]
Epichlorohydrin [106-89-8]
Bhylbenzene [100-41-4]
Ethylene dibromide [106-93-4]
Hhylene glycol [107-21-1]
Bhylene oxide [75-21-8]
Select
chemical to
remove
Chemicals in waste
1,1,1,2-Tetrachloroethane
Carbon disulfide
Screen 2A. Wastes Managed
4.2 Wastes Managed (Screen 2A)
To perform a risk calculation, identify the chemical(s) in the waste being managed, and if
you are using CHEMDAT8, enter the concentration (mg/L or mg/kg) of each chemical. You may
also choose to add or modify chemical data from this screen.
A. Add/Modify Chemicals (Screen 2A)
IWAIR includes a list of chemicals from which you can identify waste constituents. As a
convenience to the user, IWAIR includes data on 95 constituents (shown with their CAS number
in Section 1, Table 1-1). However, this list of chemicals may not include all the organic
chemicals in your waste, and the data for these 95 chemicals may not match your site-specific
conditions for some properties. Therefore, IWAIR has the capability to add or modify chemicals.
To add or modify chemical data, click on the | ADD/MODIFY CHEMICALS | button. This will bring up
Screen 2B, ADD/MODIFY CHEMICALS.
4-10
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IWAIR User's Guide
Section 4.0
53 Industrial Waste - [2b. Add/Modify Chemicals]
File Help
,,Ja.|x|
AS. Clear entry
Wastes
Enter information for new chemical into form or double-dick chemical from list box on which to base new entry.
A6. Save entry
r Chemical Properties —
Chemical name:
f*
CAS number:
Molecular wt
(g/g-mole):
Density (g/cm3):
{-•
Vapor pressure
(mmHg):
Henry's law constant
Catm-m3/mol-K):
SolubBy (mgjL):
Soil biodegradation
rste(s-1):
Antoine's constants: A:
Health benchmarks:
Cancer slope factor
(mgjkgM)-1:
(enter leading spaces if necessary)
Diffussvity in water
(cm2/s):
Diffusivity in air
(cm2/s):
log(Kow):
K1 (L/g-h):
Kmax (mg VO/g-h):
Reference
concentration (mg/m3):
Chemicals currently in database:
Sort by chemical name
Sort by CAS number
1,1,1,2-Tetrachloroethane [630-20-6]
1,1,1-Trichloroethane [71-55-6]
1,1,2,2-Tetrachloroethane [79-34-5]
1,1,2-Trichloro-1,2,2-trifluoroethane [76-13-1 ]
1,1,2-Trichloroethane [79-00-5]
1,1-Dichloroethylene [75-35-4]
1,2,4-Trichlorobenzene [120-82-1]
1,2-Dibromo-3-chloropropane [96-12-8]
1,2-Dichloroethane [107-06-2]
1,2-Dichloropropane [78-87-5]
1,2-Diphenylhydraiine [122-66-7]
1,2-Epoxybutane [106-88-7]
1,3-Butadiene [106-99-0]
1,4-Dioxane [123-91-1]
Delete User-Defined Chemical
Screen 2B. Add/Modify Chemicals
The ADD/MODIFY CHEMICALS screen will initially appear with no data in any of the fields. You
have four options:
• Add a new chemical. To do this, enter all data, including chemical name and
CAS number, manually.
• Add a new entry for a chemical already in the database To do this, select an
existing entry for the chemical for which you wish to add an entry; if you select a
user-defined entry, IWAIR will ask if you want to create a new entry. Click on
I YES |. If you select an original IWAIR entry, IWAIR will automatically create a
new entry.
• Modify the data in an existing user-defined entry. To do this, select the
chemical to modify; when IWAIR asks if you want to create a new entry, click on
I No |. Original IWAIR entries may not be modified; if you select one, IWAIR will
automatically create a new entry.
• Delete an existing user-defined entry. Select the entry to delete. Original
IWAIR entries may not be deleted.
4-11
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IWAIR User's Guide Section 4.0
To ensure the integrity of the original IWAIR data and distinguish user-defined entries,
IWAIR will automatically generate a unique identifier for each chemical entry added to the data
set in the format "User X," where "X" is an entry number and "User" indicates it is a user-
defined entry. This identifier will be appended to the chemical name to uniquely identify each
entry. This identifier will be shown on screens and reports whenever the chemical is identified to
clearly indicate which chemical entry has been used.
Mercury is included in the IWAIR database in both divalent and elemental forms, but
because of code modifications needed for mercury (to reflect differences in its behavior, since it
is not an organic chemical), you may not create additional or modified entries for mercury.
Al. Select Sorting Order for Identifying Chemicals (Screen 2B)
The list of chemicals that is currently available in the database is shown here so that you
can select constituents to modify. This list includes the 95 constituents included with
IWAIR, as well as any you have already added to the IWAIR database. To facilitate the
chemical selection process, IWAIR allows you to sort this list of chemicals alphabetically
by chemical name, or by CAS number. As shown in Screen 2B, select a sort order by
clicking on the button to the left of the sorting option of choice.
A2. Select a Chemical to Modify (Screen 2B)
If you wish to add a new entry for an existing chemical or modify an existing user-defined
entry, double-click on the chemical name in the list of chemicals. This will display the
data for that chemical on the ADD/MODIFY CHEMICALS screen. If you select one of the 95
original IWAIR chemicals, a new entry will be generated automatically with a new,
unique identifier. If you select a user-defined entry, IWAIR will ask if you want to create
a new entry. Click on | YES | to create a new entry (you will be able to modify the data) or
I No | to edit the existing entry.
A3. Enter or View Chemical Name and CAS Number (Screen 2B)
If you selected a chemical to modify or to update with a new entry, the chemical name
and CAS number will be displayed. These may not be edited, to preserve the integrity of
the unique chemical identifiers. If you are adding a new chemical and therefore entering
all data manually, you will need to enter an appropriate chemical name and CAS number
in these text boxes. Do not include a "User X" designation in your chemical
name—IWAIR will append that automatically. Chemical names may not contain
apostrophes (') or quotation marks ("). CAS numbers that are shorter than the maximum
length should be prefaced with leading spaces, not zeros.
A4. Enter Chemical Properties Data (Screen 2B)
Enter values for all chemical properties shown on the screen. Use the mouse to click in
each text box, or use the | TAB | key to move between the boxes. Except for health
benchmarks, you may only enter numeric values (although you may enter numeric values
4-12
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IWAIR User's Guide Section 4.0
in scientific notation). For health benchmarks, "NA" may also be entered. Be sure to
enter values in the units shown. Additional guidance on obtaining values for these
parameters is available in Appendix B, Section B.2.2.3.
You may enter user-defined health benchmarks both here, in a user-defined chemical
record, and on the RESULTS screen. On the RESULTS screen, you can enter them directly into
an IWAIR chemical record without overwriting the original IWAIR value. If you are
entering a new or modified chemical entry, you should enter any user-defined health
benchmarks here. However, you need not create a new chemical entry here just to change
the benchmark of an IWAIR chemical; you can enter the user-defined health benchmark
on the RESULTS screen.
AS. Clear Entry (Screen 2B)
To clear an unwanted entry from the ADD/MODIFY CHEMICALS screen without saving, click on
the | CLEAR | button. You will be asked to confirm that you want to clear the data.
A6. Save Entry (Screen 2B)
Once all data have been entered, you can save by clicking on the | SAVE| button. IWAIR
does some limited range checking to ensure values are within physically possible ranges;
if an entry is not in the acceptable range, IWAIR will display an error message with the
accepted range. These ranges are intended to eliminate only impossible entries (e.g.,
negative values for many properties) or values that will cause the model to fail. The
actual range for most of the chemical properties is likely smaller than the accepted range.
Once all data values have been validated and the entry added to the database, the form
will be cleared.
A 7. Delete a Chemical (Screen 2B)
You may delete a user-defined chemical entry on the ADD/MODIFY CHEMICALS screen by
selecting the chemical from the list of chemical entries and clicking on the | DELETE USER-
DEFINED CHEMICAL | button. It is not necessary to double-click on the chemical to bring up its
data before deleting; a single click to select the entry in the list is sufficient. If you have
selected an original IWAIR chemical entry, an error message will appear indicating that
the entry cannot be deleted. If you have selected a user-defined entry, a message will
appear to confirm that you want to delete the entry. If you select I YES |, the entry will be
deleted from the database and you will be returned to the ADD/MODIFY CHEMICALS screen. The
list of chemicals on this screen will be updated to reflect the removal of the entry. If you
select I No |, you will be returned to the screen, and the chemical will not be deleted.
Note that the deletion of a chemical entry used in a saved analysis will lead to the failure
of the saved analysis to reload.
4-13
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IWAIR User's Guide Section 4.0
A8. Return to Wastes Managed Screen (Screen 2B)
Once you have completed all desired data additions, modifications, and deletions, click
the | RETURN | button to return to the WASTES MANAGED screen. If you have unsaved data,
IWAIR will warn you and ask if you want to proceed. If you select I YES |, the unsaved
data will be lost. If you select I No |, you will be returned to the ADD/MODIFY CHEMICALS
screen, where you can save your data by selecting | SAVE |.
The list of available chemicals in the WASTES MANAGED screen will be updated to include any
new entries and to omit any deleted entries.
B. Select Sorting Option for Identifying Chemicals (Screen 2A)
Once you have returned to the WASTES MANAGED screen, you can identify waste constituents
from the list of chemicals included in IWAIR. This list includes the 95 constituents included
with IWAIR, as well as any you add to the IWAIR database using the ADD/MODIFY CHEMICALS feature.
The 95 constituents included with IWAIR are shown with their CAS number in Section 1, Table
1-1. To facilitate the chemical identification process, IWAIR allows you to sort this list of
chemicals alphabetically by chemical name, or by CAS number. As shown in Screen 2A, select a
sort order by clicking on the button to the left of the desired sorting option.
C. Identify Chemicals in Waste (Screen 2A)
Identify up to six chemicals in a waste for modeling with IWAIR. Identify a chemical by
clicking on the chemical name or CAS number and clicking on the | ADD» | command button. To
remove a waste constituent from consideration, select the check box located to the left of the
chemical name and click the | «REMOVE| command button. User-defined entries are identified in
this list by the modifier "User X" appended to the chemical name, where "X" is a unique
number.
You may choose to simultaneously model the same chemical using multiple entries from
the chemical database. You may want to do this to compare results based on changes you have
made in chemical properties. However, you should note that the resulting total risk (across all
chemicals modeled) presented on the RESULTS screen will reflect double-counting for any
chemicals duplicated and will, therefore, not be an accurate estimate of total risk. Chemical-
specific risk results will be accurate.
D. View Selected Chemicals (Screen 2A)
The chemicals you identified for consideration are displayed in text boxes shown on
Screen 2A. You can remove waste constituents from consideration by selecting the check box to
the left of the chemical and clicking the | «REMOVE| command button.
4-14
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IWAIR User's Guide Section 4.0
E. Enter Waste Concentrations (Screen 2A)
If you are using CHEMDAT8, enter a chemical-specific waste concentration for each
chemical identified. This is not necessary if you are not using CHEMDAT8. The concentration
should be expressed as mg/L for wastewaters and mg/kg for solid wastes.
The total concentration (the sum of all concentrations entered) may not exceed the
physical limit of 1,000,000 mg/L or mg/kg; if this occurs, an error message will be displayed and
the program will not proceed until the total concentration is less than or equal to 1,000,000 mg/L
or mg/kg. In addition, if the total concentration exceeds 10 percent (100,000 mg/L or mg/kg), a
message will be displayed advising you to consider characterizing the waste as an organic waste
in the WASTE MANAGEMENT UNITS screen (Screen 3 A, 3B, 3C, or 3D). The distinction between aqueous
and organic wastes is discussed briefly in Section 4.3C and in more detail in Appendix B,
Sections B.3.1.4, B.3.2.4, B.3.3.4, and B.3.4.4.
Chemicals with entered waste concentrations that lead to concentrations in the unit in
excess of the solubility limit in the IWAIR database (for surface impoundments) or the soil
saturation limit calculated by IWAIR (for other unit types) for that chemical will be modeled
somewhat differently by CHEMDAT8. Typically, chemicals above saturation or solubility limits
in the unit will come out of solution, and if this is occurring, the waste would be best modeled as
an organic-phase waste. However, these limits can be somewhat site-specific; therefore, IWAIR
does not prevent you from entering waste concentrations in excess of these limits, nor does it
require you to model wastes with concentrations in excess of these limits as organic-phase
wastes. Instead, IWAIR assumes that the chemical remains in solution, either because of waste
matrix effects in your unit or because the actual solubility or soil saturation limit in your unit is
higher than that specified in the database or calculated by IWAIR because of site-specific
conditions. However, even though IWAIR continues to model such wastes as aqueous-phase
wastes (unless you select organic-phase), it uses a different partition coefficient that more
appropriately models this situation. IWAIR will notify you that this was done after emissions are
calculated (because determining when this is the case depends on data entered after the WASTES
MANAGED screen). In addition, printed reports will document the use of the alternative emissions
modeling approach.
4.3 Enter WMU Data for Using CHEMDAT8 Emission Rates
If you elected to use CHEMDAT8 emission rates in the risk calculations (i.e., selected the
USE CHEMDAT81 command button shown previously on Screen 1 A), you will need to enter WMU
data as specified in this section. If you did not elect to use CHEMDAT8 emission rates, then you
should proceed to Section 4.4, Emission Rates. If you elected to enter emission rates and use
ISCST3 dispersion factors, you will be asked to enter the WMU area (and height, if a waste pile)
for ISCST3 before proceeding to the emissions screen.
This section provides guidance on providing input data needed to develop CHEMDAT8
emission estimates for the four unit types addressed by IWAIR.
4-15
-------
IWAIR User's Guide Section 4.0
Surface Impoundments. The major source of volatile emissions associated with surface
impoundments is the uncovered liquid surface exposed to the air (U.S. EPA, 1991).
Aeration and/or agitation are applied to aid in treatment of the waste, and emissions tend
to increase with an increase in surface turbulence because of enhanced transfer of liquid-
phase contaminants to the air (U.S. EPA, 1991). Parameters to which emissions are most
sensitive include surface area, unit depth, waste concentration, retention time, wind speed
for quiescent systems, and biodegradation. Retention time is not an explicit input, but is
a function of impoundment volume and flow.
Land Application Units. Waste can be tilled or sprayed directly onto the soil and
subsequently mixed with the soil by discing or tilling. Waste in a land application unit is
a mixture of sludge and soil. IWAIR allows the modeling of tilled land application units.
If your unit uses spray application, another model may be more appropriate. Air
emissions from land treatment units are dependent on the chemical/physical properties of
the organic constituents, such as vapor pressure, diffusivity, and biodegradation rate.
Operating and field parameters affect the emission rate, although their impact is not as
great as that of the constituent properties.
Active Landfill. IWAIR allows the modeling of emissions released from the surface of
an active (i.e., receiving wastes) landfill. The landfill model is sensitive to the air
porosity of the solid waste, the liquid loading in the solid waste, the waste depth
(assumed to be the same as the unit depth), the constituent concentration in the waste, and
the volatility of the constituent (U.S. EPA, 1991).
Waste Piles. The waste pile emission model is sensitive to the air porosity of the solid
waste, the liquid loading in the solid waste, the waste pile height, the constituent
concentration in the waste, and the volatility of the constituent (U.S. EPA, 1991).
Screens 3A, 3B, 3C, and 3D, respectively, identify the CHEMDAT8 input requirements
for surface impoundments, land application units, landfills, and waste piles. Guidance for
completing each screen is provided below. For some of the required inputs, default values are
provided in the screen text boxes, as well as to the right of the text boxes. These default values
were selected to represent average or typical operating conditions. If appropriate, the defaults
can be applied in the absence of site-specific data; however, you always have the option of
overriding any defaults. The basis for these default values is provided in the IWAIR Technical
Background Document.
4-16
-------
IWAIR User's Guide
Section 4.0
A. View met
data for site
B. Enter
surface
impoundment
design data
C. Enter
aeration data
File Help
Emissic IT" | | -•- n --i-- -> | ! ^ suits
Method, Met. Station, WMU ] Wastes Managed J WMU Data for CHEMD
Surface Impoundment Information
V\find speed (m/s) |3.473 |
Temperature (C) |15.45 |
Biodegradation {*" on C Off
Operating life (yr) |20
Depth of unit (m) 1
Area of unit (m2) 1 0000
rmStyrl
h
No aeration (quiescent) f"
Diffused air aeration r*
Mechanical aeration f
Both (diffused air & mechanical) **"
Fraction of surface area agitated
Submerged air flow (m3/s)
ATB I
> A (•=.=•+= |"i-.=r=ll-v4.prj^jr^. infnrmitrnn
Type of waste: Aqueous C* Otysnic C
De
ault
Active biomass (gjL) I0-05 | 0.05
Total suspended solids in Influent (g/L) |o.2 | 0.2
Total organics into WMU (mgrt_) |200 | 200
Total biorate (mg/g biomass-h) 19 I 19
Oxygen transfer rate (Ib O2/h-hp) p ^
Number of aerators
Total power (hp)
Power efficiency (fraction) |o.83 | 0.83
Impeller diameter (cm) |61 | 61
impeller speed (rad/s) |^30 | 1 30
Done
E. Enter waste
data
D. Enter
mechanical
aeration
information
Screen 3 A. WMU Data for CHEMD ATS: Surface Impoundment
File Help
A. View met
data for site
F. Enter waste
porosity
information
Emission Rates | Dispersion Factors \ Restits
Method, Met. Station, WMU ] Wastes Managed J WMU Data for CHEMDAT8
Land Appl
Wind speed (m/s) J3.473 I
- •
Temperature (C) |15.45 I
r- Waste/Soil Mixture Porosity Information ,
- • Default
Total porosity (volume rj^j I Q 61
fraction) l_ I
Air porosity (volume [g~5 I g ,
fraction) ' '
Done
cation Unit Information
Biodegradation f? Qn C Off
Default
Operating life (yr) 20
Tilling depth of unit (in) 1
Area of unit (m2) 500
Annual waste quantity (Mg/yr) jioo 1
Number of applications per year JTij 1
Waste bulk density (g/cm3) Fs 1 1 .3
Aqueous (•" Organic C
••
I
B. Enter land
application
unit design
and operating
information
E. Enter waste
— characteristics
data
Screen 3B. WMU Data for CHEMD ATS: Land Application Unit
4-17
-------
IWAIR User's Guide
Section 4.0
Industrial Waste - [3c. Active Landfill]
File Help
Method, Met. Station, WMU
Wastes Managed
WMU Data for CHEMDAT8
i-Meteorological Station Parameters
Wind speed (m/s) 13.473
Temperature (C) 15.45
,—Waste Porosity Information-
Default
Total porosity (volume fraction) h.5 0.5
Air porosity (volume fraction) p.25 0-25
Landfill Information
—Lanatm uimensions ana Loaamg information
Biodegradation C On (• Off
Operating life (yr) |20
Total area ot landfill (m2) |SOO
Total depth of landfill (m) |2
Total number of cells in landfill H 2
Annual quantity of waste disposed in [-KKJO
landfill (Mg/yr) I
Bulk density of waste (g/cm3) p -2
Default
4
1.2
Waste Characteristics Information (Only for Risk Calculation)'
Aqueous (* Organic C"
Screen 3C. WMU Data for CHEMDAT8: Landfill
Industrial Waste - [3d. Waste Pile]
File Help
JSJxJ
Emission Rates |
M eth o d, M et Stati o n, WM U f
«
Wind speed (mis) |3'473 |
Temperature (C) |15.4S |
D spers
on Factors | Results
Wastes Managed f WMU Data for CHEMDATB
w
aste Pil
Waste F
Biode
Operer
Height
Area c
Avera
Bulkd
e Information
yadation (~ On (• Off —
r- 1 Default
ing life (yr) |20 |
of waste pile unit (m) 4
f unit (m2) J300 I
ge quantity of waste in waste pile (Mgfyr) 1 00
snsity of waste (g/cm3) R~4 I ^ ^
Default
Total porosity (volume i 1
fraction) F | °-s
Air porosity (volume fraction) |g 25 I 0.25
Aqueous (f Organic C
•
Nuiecular weiqht ut wa.;.te : q/q-trio!e I
Done
Screen 3D. WMU Data for CHEMDAT8: Waste Pile
4-18
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IWAIR User's Guide Section 4.0
A. View Meteorological Data for Site (Screens 3A, 3B, 3C, and 3D)
Both wind speed and temperature can affect the volatilization rate of a chemical.
Average wind speed and temperature are used as input to the CHEMDAT8 model. Average
annual wind speed is used to select the most appropriate empirical emission correlation equation
in CHEMDAT8; there are several of these correlations, and each one applies to a specific range
of wind speeds and unit sizes. Average annual temperature is used to adjust Henry's law
constant and vapor pressure values (temperature-dependent chemical properties) from a standard
temperature to the ambient temperature at the unit. Drawing from the meteorological data stored
in IWAIR, the program will display the average annual temperature and wind speed available for
the representative meteorological station that was determined for the site in Screen 1 A. You can
enter average wind speed and temperature for your site if the default values are significantly
different.2
B. Enter Unit Design and Operating Data
For all unit types, you may select whether or not biodegradation occurs in your unit.
Select the | ON | option to turn biodegradation on and the | OFF | option to turn it off. The default
setting varies by unit type. See Appendix B, Sections B.3.1.2, B.3.2.3, B.3.3.3, and B.3.4.3, for
further details about the implications of turning biodegradation on or off and the appropriateness
of difference choices for different unit types.
Enter Surface Impoundment Design Data (Screen 3A)
Enter the unit dimensions and loading information in the text boxes shown in Screen 3 A.
The data include the operating life at the unit (yrs), the depth of the unit (m), the area of
the unit (m2), and the annual flow of the waste (m3/yr).
Enter Land Application Unit Design and Operating Information (Screen 3B)
Enter the unit dimensions and loading information in the text boxes shown in Screen 3B.
The data include the operating life of the unit (yrs), tilling depth of the unit (m), area of
the unit (m2), annual waste quantity (Mg/yr), number of applications per year, and waste
bulk density (g/cm3).
Enter Landfill Design and Operating Information (Screen 3C)
Enter the unit dimensions and loading information in the text boxes in Screen 3C. The
model assumes that the landfill is divided into cells, with only one cell active at a time.
Emissions are modeled from the active cell. The data to be entered include the operating
life of the unit (yrs), total area of the unit (m2), depth of the unit (m), number of cells in
your unit, annual quantity of wastes disposed in the unit (Mg/yr), and bulk density of
waste (g/cm3).
These inputs are not used in the dispersion modeling, which uses hourly data, not annual averages.
Therefore, changes to these inputs will not affect the dispersion factors.
4-19
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IWAIR User's Guide Section 4.0
Enter Waste Pile Design and Operating Information (Screen 3D)
Enter the unit dimensions and loading information in the text boxes in Screen 3D. The
data include the operating life of the unit (yrs), the height of the pile (m), area of the unit
(m2), annual quantity of waste in the pile (Mg/yr), and bulk density of the waste (g/cm3).
C. For Aerated Surface Impoundments Only — Enter Aeration Data (Screen 3A)
IWAIR models both quiescent (nonaerated) and aerated impoundments. Aeration or
agitation of a liquid waste in an impoundment enhances transfer air (oxygen) to the liquid to
improve mixing or to increase biodegradation (U.S. EPA, 1991). Aeration is achieved through
the use of mechanical mixers, such as impellers (i.e., mechanically aerated), or by sparging air,
which bubbles up from the bottom of the unit (i.e., diffused air aerated). First, select the aeration
option that best describes your unit by clicking the appropriate option button. If you selected one
of the aerated options, provide information to characterize the aeration in your unit. For all
aeration options, you will need to enter the fraction of the surface area agitated (unitless). If you
selected an option including diffused air aeration (diffused air only or both diffused air and
mechanical aeration), you will also need to enter the total submerged air flow (m3/s) of all
diffusers in the impoundment.
If you choose to model an aerated impoundment, you will not have the option of
modeling an organic-phase waste; IWAIR cannot model an organic-phase waste in an aerated
impoundment because of limitations in CHEMDAT8.
D. For Mechanically Aerated Surface Impoundments Only - Enter Mechanical Aeration
Information (Screen 3A)
If a surface impoundment is mechanically aerated, you will need to provide additional
operating parameter information. These data include oxygen transfer rate (Ib O2/hr-hp), number
of aerators, total power (hp), power efficiency (fraction), impeller diameter (cm), and impeller
speed (rad/s).
E. Enter Waste Characteristics Data (Screens 3A, 3B, 3C, and 3D)
For Surface Impoundments Only - Enter Waste Characteristics Data (Screens 3A)
For nonaerated impoundments, specify whether the waste being modeled is an aqueous-
or organic-phase waste. IWAIR cannot model organic-phase wastes for aerated
impoundments; therefore, if you selected an aeration option other than nonaerated, the
organic option will not be enabled. Appendix B, Section B.3.1.4 contains detailed
guidance on determining whether your waste is aqueous or organic, including definitions
of those terms. Briefly, in making the determination of whether a waste is aqueous or
organic, you should examine the fraction of the waste that is organic. Consider the
following guidance in making this determination.
4-20
-------
IWAIR User's Guide Section 4.0
Organic: If the total concentration of all organics in the waste is greater than 10
percent, then the waste is probably most appropriately modeled as organic.
IWAIR will suggest this if the combined concentration of all chemicals
entered is greater than 100,000 or mg/L, or 10 percent, but it will not
automatically select the organic option; IWAIR always defaults to
aqueous, and you must explicitly select the organic option if you determine
that it is more appropriate.
Aqueous: If the total concentration of all organics in the waste is less than 10
percent, then the waste is probably more appropriately modeled as
aqueous. The default in IWAIR is always aqueous.
Based on your selection of aqueous or organic, IWAIR will apply either the aqueous or
the organic waste equilibrium partitioning algorithm. For organic wastes, the model uses
Raoult's law, and the liquid-to-air partition coefficient becomes proportional to the
contaminant's partial vapor pressure. For aqueous wastes, which are assumed to partition
predominantly to water (e.g., rain and water in the soil), the model uses Henry's law and
the liquid-to-air partition coefficient becomes proportional to the contaminant's Henry's
law coefficient.3 This is discussed in greater detail in Appendix B, Section B.3.1.4.
If you choose to model an organic-phase waste, you will also need to enter the waste
density (g/cm3) and the average molecular weight of the waste (g/mol). Appendix B,
Section B.3.1.4, provides details on how to estimate these parameters.
Additional waste characteristics information to be entered for surface impoundments
includes active biomass (g/L), total suspended solids into WMU (mg/L), total organics
into WMU (mg/L), and total biorate (mg/g biomass-hr). These parameters are discussed
in more detail in Appendix B.
Land Application Units, Landfills, and Waste Piles Only -Enter Waste
Characteristics Data (Screens 3B, 3C, and 3D)
Specify whether the waste being modeled is an aqueous- or organic-phase waste.
Appendix B, Sections B.3.2.4, B.3.3.4, and B.3.4.4, contain detailed guidance on
determining whether your waste is aqueous or organic, including definitions of those
terms. Briefly, in making the determination of whether a waste is aqueous or organic,
you should examine the fraction of the waste that is organic. Consider the following
guidance in making this determination.
Organic: If the total concentration of all organics in the waste is greater than 10
percent, then the waste is probably most appropriately modeled as organic.
IWAIR will suggest this if the combined concentration of all chemicals
3 This assumes the chemical concentration in the impoundment is at or below the chemical's solubility limit.
If it is above the solubility limit, IWAIR uses a hybrid of the aqueous-phase and organic-phase modeling approaches.
See Appendix B, Section B.3.1.4.
4^21
-------
IWAIR User's Guide Section 4.0
entered is greater than 100,000 mg/kg, or 10 percent, but it will not
automatically select the organic option; IWAIR always defaults to
aqueous, and you must explicitly select the organic option if you determine
that it is more appropriate.
Aqueous: If the total concentration of all organics in the waste is less than 10
percent, then the waste is probably more appropriately modeled as
aqueous. The default in IWAIR is always aqueous.
Based on your selection of aqueous or organic, IWAIR will apply either the aqueous or
the organic waste equilibrium partitioning algorithm. For organic wastes, the model uses
Raoult's law and the liquid-to-air partition coefficient becomes proportional to the
contaminant's partial vapor pressure. For aqueous wastes, which are assumed to partition
predominantly to water (e.g., rain and water in the soil), the model uses Henry's law, and
the liquid-to-air partition coefficient becomes proportional to the contaminant's Henry's
law coefficient.4 This is discussed in greater detail in Appendix B, Sections B.3.2.4,
B.3.3.4, and B.3.4.4.
If you choose to model an organic-phase waste, you will also need to enter the average
molecular weight of the waste (g/mol). Appendix B, Sections B.3.2.4, B.3.3.4, and
B.3.4.4, provide details on how to estimate this parameter.
F. For Land Application Units, Landfills, and Waste Mies Only — Enter Waste Porosity
Information (Screens 3B, 3C, and 3D)
Waste (or soil/waste mixture for land application units) porosity information required as
input includes total porosity (unitless) and air porosity (unitless). Total porosity includes air
porosity and the space occupied by oil and water within waste. Total porosity (et), also
sometimes called saturated water content, can be calculated from the bulk density (BD) of the
waste and particle density (ps) as follows:
. BD
et = * - —
where BD and ps are expressed in the same units.
In the absence of site-specific data, IWAIR identifies default values of 0.5 and 0.25,
respectively, for total porosity and air porosity. Air porosity cannot exceed total porosity.
Done. Once you provide the required WMU inputs, click the |DONE| button to enable the
EMISSION RATES tab and open the EMISSION RATES screen. Proceed to Section 4.4, Emission Rates.
4 This assumes the chemical concentration in the unit is at or below the chemical's solubility limit. If it is
above the solubility limit, IWAIR uses a hybrid of the aqueous-phase and organic-phase modeling approaches. See
Appendix B, Sections B.3.2.4, 3.3.4, and B.3.4.4.
4^22
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IWAIR User's Guide
Section 4.0
IWAIR must calculate emission rates before displaying the EMISSION RATES screen. This is usually
very quick, but if your computer is slow, or if you are modeling a land application unit with a
large number of total applications (i.e., number of applications per year times operating life),
there can be a noticeable delay before the EMISSION RATES screen is displayed. This is normal, but
should typically not exceed 1 minute on a fast machine or 5 minutes on a slow machine.
4.4 Emission Rates
Guidance for using CHEMDAT8 emission rates or entering your own emission rates is
provided in this section. View and confirm the CHEMDAT8 emission rates as directed in
Section 4.4.1. If you did not elect to use CHEMDAT8 (i.e., if you selected the I ENTER EMISSION
RATES] or | ENTER EMISSION ft DISPERSION DATA] command buttons shown previously on Screen 1A),
proceed to Section 4.4.2, User-Specified Emission Rates.
Please note that all calculated and entered values on the EMISSION RATES screen will be lost if
you return to a previous screen and make changes. This includes both calculated and entered
override emission rate values.
^Industrial Waste - [4a. Emission
File Help
Method Met. Station, WMU
Wastes Managed
WMU Data for CHEMDAT8
Emission Rates
Chemical Emissions Estimated Using CHEMDAT8
(Emission of chemical = concentration of waste x emission rate)
Chemical emissions
Aqueous Organic Override
Chemicals selected
For surface impoundments:
Effluent cone. Fraction
(mgjL)
adsorbed
1,1,1,2-Tetrachloroethane
Acetone
Carbon disulfide
Source and Justification for User Override Values
justification
Done
Screen 4A. CHEMDAT8: Emission Rates
4-23
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IWAIR User's Guide Section 4.0
4.4.1 Using CHEMDAT8 Emission Rates (Screen 4A)
A. View CHEMDAT8 Emission Rates or Enter User-Specified Emissions (Screen 4A)
Screen 4A shows the calculated CHEMDAT8 emission rates. For surface
impoundments, this screen also shows the calculated effluent concentrations and fraction
adsorbed for each chemical. With the exception of waste managed in aerated surface
impoundments (assumed to be aqueous because of model limitations), emission rates will be
displayed under the AQUEOUS or ORGANIC column headings depending on how you characterized
your waste on the WMU DATA FOR CHEMDAT8 screens (Screens 3 A, 3B, 3C, or 3D). If you wish to
override the displayed rates, enter alternate rates (g/m2-s) in the text boxes located under the
OVERRIDE heading.
For surface impoundments, landfills, and waste piles, emissions are modeled at
equilibrium and are assumed to reflect a long-term average emission rate, which is shown on this
screen. In contrast, land application units are not assumed to be at equilibrium; rather, emissions
are calculated for each year of the specified operating life plus 30 years postclosure. The
emission rates shown on this screen are the maximum single-year emission rates for each
chemical (which may not reflect the same year for all chemicals). This emission rate is used
directly to calculate the air concentration used for calculating noncarcinogenic risk. However,
for carcinogenic risk, the maximum 7- or 30-year average emission rate (7-year for a worker and
30-year for a resident, corresponding to the default exposure durations for each receptor type) is
used to calculate air concentration and risk. If you enter user-override emission rates for any unit
type, they should reflect a long-term average emission rate. Override emission rates are used as
entered in all risk calculations, including both carcinogenic and noncarcinogenic calculations for
land application units.
B. Enter Source and Justification for User-Specified Emission Rates (Screen 4A)
If alternative emission rates are entered, IWAIR will prompt you to identify the source
and justification for these data. This documentation should be entered in the text box displayed
on the screen. It is important to provide this documentation as a reference that will allow you or
another user to view and understand saved files at a later date. This information is also printed in
reports. Confirm the emission rates to be used in the calculations by clicking the |DONE| button.
The program will then automatically enable the DISPERSION FACTORS tab and open the DISPERSION
FACTORS screen. Proceed to Section 4.5, Dispersion Factors.
4-24
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IWAIR User's Guide
Section 4.0
Industrial Waste - [4b. User Override Emission
File Help
Method, Met. Station, WMU
Wastes Managed
Emission Rates
User Override Chemical Emissions
(Emission of chemical = concentration of waste x emission rate)
User override emissions
Chemicals
1,1,1,2-Tetrachloroethane
Acetone
Carbon disulfide
2e-6
|3e-6
Source and Justification for User Override Values
iustification
Done
Screen 4B. User-Specified Emission Rates
4.4.2 User-Specified Emission Rates (Screen 4B)
A. Enter User-Specified Emissions (Screen 4B)
Enter site-specific emission rates (g/m2-s) in the text box under USER OVERRIDE EMISSIONS. If
you have measured or calculated emission rates in g/s for your entire unit, you will need to divide
that emission rate by the total area of your unit (in m2) to obtain area-normalized emission rates
in g/m2-s. These emission rates should reflect long-term average emissions, not a short-term
peak.
B. Enter Source and Justification for User-Specified Emission Rates (Screen 4B)
The program will prompt you to provide justification for user-specified emission rates
and documentation of the estimation method applied. It is important to provide this
documentation as a reference that will allow you or another user to view and understand saved
files at a later date.
Done. Once you have entered the emission data and source/justification, click the | DONE|
button to enable the DISPERSION FACTORS tab and open the DISPERSION FACTORS screen. Proceed to
Section 4.5, Dispersion Factors.
4-25
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IWAIR User's Guide
Section 4.0
4.5 Dispersion Factors
Dispersion modeling outputs are used to estimate air concentrations to which the various
human receptors are exposed. Guidance for using the ISCST3 default dispersion factors or
entering your own site-specific dispersion factors is provided in Sections 4.5.1 and 4.5.2,
respectively. If you elected to use ISCST3 dispersion factors provided in IWAIR (i.e., selected
the | USE CHEMDAT81 or | ENTER EMISSION RATES | command buttons shown previously on Screen 1 A),
you will need to follow the guidance provided in Section 4.5.1. If you did not elect to use the
default dispersion factors, you should proceed to Section 4.5.2, User-Specified Dispersion
Factors.
Please note that all calculated and entered dispersion factors values on the DISPERSION
FACTORS screen will be lost if you return to a previous screen and make changes. This does not
include receptor locations and types but does include calculated and entered override dispersion
factor values.
53 Industrial Waste - [5. Dispersion Factors]
File Help
Method. Met Station, WMU
Wastes Managed
WMU Data for CHEMDAT8
Emission Rates
Dispersion Factors
Receptor Distance, Type, and Dispersion Factor
To override default dispersion factors, enter values into "User override" column
Dispersion factors for location and unit
size [(ug/m3 per (ug/m2-s)]
Calculated dispersion user override
factors
Receptor Distance to
no. receptor (m)
Receptor type
1.
IWorker "• Click to calculate
dispersion factors
Resident "1 |1.87E-01
Source and Justification for User Override Values
C. View
IWAIR
dispersion
factors or
enter user-
specified
dispersion
factors
D. Enter
source and
justification
for user-
specified
dispersion
factors
Screen 5A. Using ISCST3 Default Dispersion Factors
4.5.1 Using ISCST3 Default Dispersion Factors (Screen 5A)
In Screen 5A, you will provide receptor information (i.e., receptor type and distance to
the receptor) and click the | CALCULATE | button; IWAIR will develop site-specific dispersion factors
based on default dispersion data. If you wish to override the IWAIR-developed dispersion
factors, enter alternate site-specific unitized dispersion factors. If you enter alternative dispersion
4-26
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IWAIR User's Guide Section 4.0
factors, you should document the source and the justification for these data in the text box on the
screen.
A. Select Receptor Type and Distance (Screen 5A)
Enter information concerning the receptors of concern (i.e., potentially exposed
individuals). You can specify up to five receptors, including the distance to receptor and the
receptor type. You can specify two receptor types, resident or worker, at six distances (25, 50,
75, 150, 500, and 1,000 meters) from the edge of the WMU. You can delete the last receptor
entered by deleting both the distance to receptor and receptor type entries.
Distance to Receptor - For each receptor of concern, determine the distance from the
edge of the unit to the receptor. Based on this distance, select from the six default distances (25,
50, 75, 150, 500, and 1,000 meters) the one that best approximates the location of your receptor,
using the drop-down box positioned under the DISTANCE TO RECEPTOR column heading. Note that
selecting a distance smaller than the actual distance to receptors near your unit will overestimate
risk, and selecting a distance larger than the actual distance will underestimate risk. These
distances correspond to the distances for which air dispersion modeling was conducted to
develop the IWAIR default dispersion factors. The IWAIR Technical Background Document
discusses the analysis that was conducted in determining the appropriateness of these default
distances.
Receptor Type - Two different types of exposed individuals, worker and resident, can be
modeled with IWAIR. The dispersion factors do not vary with receptor type; however, receptor
type is chosen here for convenience. The difference between these two receptor types lies in the
exposure factors, such as body weight and inhalation rate, used to calculate risk for carcinogens.
There is no difference between them for noncarcinogens, because calculation of noncarcinogenic
risk does not depend on exposure factors. The IWAIR Technical Background Document
describes the exposure factors used for residents and workers. The assumptions for workers
reflect a full-time, outdoor worker. The exposure duration for workers is the smaller of 7.2 years
or the operating life of the unit. The assumptions for residents reflect males and females from
birth through age 30; it is important to consider childhood exposures because children typically
have higher intake rates per kilogram of body weight than adults. The actual exposure duration
used for residents is the smaller of 30 years or the operating life of the unit that you entered.5 For
exposure durations less than 30 years, exposure starts at birth and continues for the length of the
exposure duration, using the appropriate age-specific exposure factors. Use the drop-down box
positioned under the RECEPTOR TYPE column heading to select either WORKER or RESIDENT.
B. Direct IWAIR to Estimate Dispersion Factors (Screen 5A)
After the requested receptor information is provided, click on the | CALCULATE! button to
direct the program to determine an appropriate dispersion factor based on the IWAIR default
5 An exception to this is that the exposure duration for land application units is 7.2 years for workers and 30
years for residents regardless of the operating life entered for the unit. This allows IWAIR to account for postclosure
exposures, which are assumed to occur with land application units but not with other units.
4^27
-------
IWAIR User's Guide Section 4.0
dispersion data. The resulting dispersion factor will be displayed for each receptor of concern. A
discussion of the development of IWAIR default dispersion data and the methodology used by
the program in selecting an appropriate dispersion factor for each WMU/receptor combination is
provided in Section 3.3. A more detailed discussion of the air dispersion modeling effort is
provided in the IWAIR Technical Background Document.
For waste piles, IWAIR uses a two-dimensional nonlinear spline to interpolate dispersion
factors for areas and heights different from those included in the dispersion factor database. This
technique is more accurate than a two-dimensional linear interpolation and is less likely to
underestimate the actual dispersion factor. However, on rare occasions, the spline may produce
results inconsistent with the data points nearest the actual area and height. If this occurs, IWAIR
shifts to the linear interpolation technique, which generally produces somewhat lower dispersion
factors. If this occurs, you will see a message to that effect. The interpolation techniques used
for dispersion factors are discussed in greater detail in the IWAIR Technical Background
Document.
C. View IWAIR Dispersion Factors or Enter User-Specified Dispersion Factors
(Screen 5A)
You may override the program-calculated dispersion factors by entering alternative
dispersion data in the text box located under the USER OVERRIDE column (see Screen 5A).
D. Enter Source and Justification for User-Specified Dispersion Factors (Screen 5A)
If you choose to provide alternative dispersion factors, document the source and the
justification for these data in the text box that will appear. It is important to provide this
documentation as a reference that will allow you or another user to view and understand saved
files at a later date. This information also appears on printed reports.
Done. Once the program has developed dispersion factors, click the | DONE | button to
open the RESULTS tab. Proceed to Section 4.6, Results.
4-28
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IWAIR User's Guide
Section 4.0
Industrial Waste - [5. Dispersion Factors]
File Help
• ft *•'
Method, Met. Station, WMU
Wastes Managed
Emission Rates
Dispersion Factors
Receptor Distance, Type, and Dispersion Factor
To override default dispersion factors, enter values into "User override" column
Dispersion factors for location and unit
size [(ug/m3 per (ugAn2-s)]
Receptor Distance to Receptor type
no. receptor (m)
Source and Justification for User Override Values
C. Enter
source and
justification
for user-
specified
dispersion
factors
Screen 5B. User-Specified Dispersion Factors
4.5.2 User-Specified Dispersion Factors (Screen 5B)
A. Select Receptor Type and Distance (Screen SB)
Enter information concerning the receptors of concern (i.e., potentially exposed
individuals). You can specify up to five receptors. The receptor information includes the
distance to receptor and the receptor type. You can specify two receptor types (residents or
workers) at six distances (25, 50, 75, 150, 500, and 1,000 meters) from the edge of the WMU.
You can delete the last receptor by deleting both the distance to receptor type and receptor type
entries.
Distance to Receptor - For each receptor of concern, determine the distance from the
edge of the unit to the receptor. Based on this distance, select from the six default distances (25,
50, 75, 150, 500, and 1,000 meters) the one that best approximates the location of your receptor,
using the drop-down box positioned under the DISTANCE TO RECEPTOR column heading. These values
are only for your reference and are not used in calculations, since you are entering your own
dispersion factors.
Receptor Type - Two different types of exposed individuals, WORKER and RESIDENT, can be
modeled with IWAIR. The dispersion factors do not vary with receptor type; however, receptor
type is chosen here for convenience. The difference between these two receptors is in the
exposure factors, such as body weight and inhalation rate, used to calculate risk for carcinogens.
There is no difference between them for noncarcinogens because calculation of noncarcinogenic
4-29
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IWAIR User's Guide Section 4.0
risk does not depend on exposure factors. The IWAIR Technical Background Document
describes the exposure factors used for residents and workers. The assumptions for workers
reflect a full-time, outdoor worker. The exposure duration for workers is the smaller of 7.2 years
or the operating life of the unit. The assumptions for residents reflect males and females from
birth through age 30; it is important to consider childhood exposures because children typically
have higher intake rates per kilogram of body weight than adults. The actual exposure duration
used for residents is the smaller of 30 years or the operating life of the unit that you entered.6 For
exposure durations less than 30 years, exposure starts at birth and continues for the length of the
exposure duration, using the appropriate age-specific exposure factors. Use the drop-down box
positioned under the RECEPTOR TYPE column heading to select either WORKER or RESIDENT.
B. Enter User-Specified Dispersion Factors (Screen SB)
For each receptor specified, enter site-specific unitized dispersion factors (n.g/m3 per
|j,g/m2-s) in the text box located under USER OVERRIDE. You may need to normalize modeled
dispersion factors to a unit concentration by dividing the modeled dispersion factor by the
emission rate used in dispersion modeling (in |j,g/m2-s) if it was not 1 |J,g/m2-s. For example, if
you ran your dispersion model using an emission rate of IE-6 |o,g/m2-s, then you would need to
divide all your dispersion factors by IE-6 to normalize them to a concentration of 1 |J,g/m2-s.
C. Enter Source and Justification for User-Specified Dispersion Factors (Screen SB)
The program will prompt you to provide justification for user-specified dispersion data
and documentation of the estimation method applied. It is important to provide this
documentation as a reference that will allow you or another user to view and understand saved
files at a later date.
Done. Once you have entered dispersion data, click on the | DONE| button to open the
RESULTS tab. Proceed to Section 4.6, Results.
4.6 Risk Results (Screen 6)
The cancer and noncancer risk estimates attributable to emissions from a WMU can be
calculated for residents and workers using IWAIR. The program combines the constituent's air
concentration with receptor exposure factors and toxicity benchmarks to calculate the risk from
concentrations managed in the unit. For each receptor, IWAIR calculates air concentrations
using emission and dispersion data specified or calculated in previous screens. To reflect
exposure that would occur in a lifetime (i.e., from childhood through adulthood), the model
applies a time-weighted-average approach. This approach considers exposure that would occur
during five different phases of life (i.e., Child < 1 year, Child 1-5 yrs, Child 6-11 yrs, Child
12-18 yrs, and Adult). The exposure factors addressed as part of this approach include
inhalation rate, body weight, exposure duration, and exposure frequency. Default values applied
An exception to this is that the exposure duration for land application units is 7.2 years for workers and 30
years for residents regardless of the operating life entered for the unit. This allows IWAIR to account for postclosure
exposures, which are assumed to occur with land application units but not with other units.
4^30
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IWAIR User's Guide
Section 4.0
by IWAIR were identified based on data presented in EPA's Exposure Factors Handbook
(U.S. EPA, 1997a) and represent average exposure conditions. IWAIR incorporates standard
toxicity benchmarks (CSFs for carcinogens and RfCs for noncarcinogens) for 95 constituents.
These health benchmarks were obtained primarily from EPA's IRIS and the HEAST (U.S. EPA,
2001, 1997b). IWAIR uses these data to perform a risk calculation. See the IWAIR Technical
Background Document for documentation of the equations.
Please note that all calculated values on the RESULTS screen will be lost if you return to a
previous screen and make changes.
- 1 6. Results: Risk based an
File Help
f^,.
*4» "
Jfljxj
A. Select
receptor
E. View air
concentration
B. View or
override
health
benchmark
D. Direct
IWAIR to
calculate risk
Method, Met. Station, WMU J Wastes Managed f WMU Data for CHEMDAT8
Emission Rates J Dispersion Factors J Results 1
pp^ilts. r fl|n ||,tp pj^k ,1 spe(.jfjed rendition?
Source and Justification for User Override Values
Receptor type Distance to receptor (mj 1 ,1 ,1 ,2-Tetracriloroethane HI
I Ho 1 (~ I K ~~^
Ho 2 (t jKesident |fs iustfication
Ho. 3 'C Exposure Dispersion factor [(ugrtnS)
duration fyr) per (ugAn2-s)]
ETo |i^87E-01
I 1 Full Citations
ree Rfc RfCref Chemical- * Hazard
Air cone CSF rcF < , K1~ reT' ^^0,,;*:^ Kic.i, ^. ^
I i«pr fl / A ^.^ t a /~i\ t ^^' ' ei i tncj/fnj j spccuic nsK quotient
Chemical name User * t^*"3) (ms*S«)-1
|1,1,1,2-letrachbroethane JD |y.J3b-m jlfc-2 1 U»ei _^NA No ref. J |9.15E-07 |
JAcetone |o J2.34E+H JNA j No ret d |3 1E+01 |ATSDRdI |( :-4E-Lb
|Carton disulfide |o |4.39E+0(|NA | No ref. J J7.0E-01 | IRIS jrj | jb.JtiE-CU
I r~\ I I dl I dl I
I II I I i dl I dl I
I I I I I dl dl I
Total cancer
C. Enter
source and
justification
for user-
specified
values
F. View
risk and
hazard
quotient
Screen 6. Risk Results
A. Select Receptor (Screen 6)
Select a single receptor to serve as the focal exposure point for the calculations by
clicking on the option button associated with the receptor of choice. As discussed above under
Section 4.5, you can specify up to five receptors for consideration. However, results can only be
seen on the screen for one receptor at a time. Once results are calculated and displayed for the
receptor of choice, you can select a different receptor by clicking on one of the other receptor
option buttons. You do not need to enter exposure duration—this is set by IWAIR and will be
displayed when you click on the | CALCULATE | button.
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IWAIR User's Guide Section 4.0
B. View or Override Health Benchmarks (Screen 6)
Screen 6 allows you to view the health benchmarks that IWAIR will use in calculating
risk estimates. For each benchmark, the table on the RESULTS screen shows the value and a brief
reference. To see more-complete citations, click on the | FULL CITATIONS | button in the SOURCE AND
JUSTIFICATION box in the upper right corner of the screen.
IWAIR gives you the option of entering your own health benchmarks. If you choose not
to use the IWAIR data, you can enter alternative health benchmarks by opening the drop-down
box in the RFC REF. column of the desired health benchmark and selecting USER-DEFINED, and then
entering a value in the text box for the benchmark. Enter CSFs (per mg/kg-d) in text boxes
located under the CSF heading and RfCs (mg/m3) under the RFC heading. Do not use a reference
dose in the place of a reference concentration. Once you have entered alternative benchmarks,
they are available in future runs, and you may toggle between them and the IWAIR values using
the drop-down reference box.
You must enter a user-defined health benchmark for two chemicals in IWAIR's chemical
database: divalent mercury and 3,4-dimethylphenol. At the time IWAIR was released, no
accepted health benchmarks were available for these chemicals from the hierarchy of sources
used to populate the IWAIR health benchmark database, nor were there data available from these
sources to allow the development of a health benchmark with any confidence. Thus, if you want
to model one of these chemicals, you will have to enter at least one user-defined health
benchmark. See Section 5 of the IWAIR Technical Background Document for further discussion
of how health benchmarks were developed for IWAIR.
C. Enter Source and Justification for User-Specified Values (Screen 6)
If you choose to override the IWAIR-provided benchmarks, you should specify the source
and the justification of the alternative data in the text box. It is important to provide this
documentation as a reference that will allow you or another user to view and understand saved
files at a later date.
D. Direct IWAIR to Calculate Risk (Screen 6)
Click on the |CALCULATE! button to calculate exposure duration, air concentration, risk, and
HQ for each chemical.
E. View Air Concentration (Screen 6)
Air concentration at the selected receptor point is displayed for each chemical identified
as managed. For land application units, IWAIR calculates three different air concentrations,
based on three different underlying emission rates: a 30-year average for residents for
carcinogens, a 7-year average for workers for carcinogens, and a 1-year maximum for residents
or workers exposed to noncarcinogens. Depending on the receptor selected and the chemical,
IWAIR displays the appropriate air concentration. However, for chemicals that are both
carcinogens and noncarcinogens, only the 30- or 7-year average used for the carcinogenic risk
4-32
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IWAIR User's Guide Section 4.0
calculation is displayed. To calculate the 1-year maximum used in the noncarcinogenic HQ
calculation, multiply the emission rate shown on the EMISSION RATES screen by the dispersion factor,
and then multiply by 1,000,000 (to convert units).
F. View Risk and Hazard Quotient (Screen 6)
Cancer risk estimates and HQs (both unitless), respectively, are displayed for each
carcinogen and noncarcinogen identified as being managed. IWAIR calculates lifetime excess
individual cancer risk. This is the probability that an individual exposed at the specified level,
under the specified exposure assumptions, will consequently contract cancer during his or her
lifetime. Although the risk is unitless, it reflects probability. Thus, a risk of IE-5 means that an
individual has 1 chance in 100,000 of contracting cancer as a result of exposure.
For noncarcinogens, the HQ is a ratio of the air concentration to which an individual is
exposed, to the RfC. The RfC is an estimate (with uncertainty spanning perhaps an order of
magnitude) of a daily exposure to the human population (including sensitive subgroups) that is
unlikely to pose an appreciable risk of deleterious noncancer effects during an individual's
lifetime. It is not a direct estimator of risk but rather a reference point to gauge the potential
effects. At exposures increasingly greater than the RfC, the potential for adverse health effects
increases; however, lifetime exposure above the RfC does not imply that an adverse health effect
would necessarily occur.
In addition, a total cancer risk estimate, which is the sum of the chemical-specific risk
estimates, is displayed. No total noncancer risk is calculated because noncancer risks are
appropriately summed only when the same target organ is affected.
Done. Click the | DONE | button to initiate a new run or save the run that you have just
completed. A dialog box will appear to guide you through starting a new run or saving the
current run.
4-33
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IWAIR User's Guide
Section 5.0
5.0 Completing Allowable Waste Concentration
Calculations
IWAIR allows you to develop allowable waste concentrations (Cwaste) that may be
protectively managed in a WMU. The calculation method can be applied in calculating waste
concentrations for both wastewaters (Cwaste in mg/L) and solid waste (Cwaste in mg/kg). These
concentrations are estimated based on user-defined target cancer and noncancer risk levels (e.g.,
IE-5 or 1E-6 for carcinogens, or an HQ of 0.5 or 1 for noncarcinogens), which you define on
the RESULTS screen.
The release of a chemical into the
atmosphere is influenced by whether a waste
is an aqueous- or organic-phase waste.
IWAIR can apply either an aqueous or
organic waste equilibrium partitioning
algorithm. These partitioning algorithms are
discussed in detail in the IWAIR Technical
Background Document.
EPA anticipates that most Industrial D
wastes managed by the users of IWAIR will
be aqueous-phase wastes with no chemicals
above the typical solubility or saturation
limits; therefore, the allowable concentration
calculation is initially based on an aqueous-
phase waste. For some chemicals in some
units, it may not be possible to reach the
target risk without the concentration
exceeding the solubility limit (in wastewaters) or the soil saturation limit (in solid wastes) of the
chemical. Once these limits are exceeded, the waste is better modeled as organic. In this case,
IWAIR will switch to organic-phase emission rates and continue.1 If the target risk is still not
reached when the concentration reaches the maximum 1,000,000 mg/kg or mg/L, then the
program will output a concentration of 1,000,000 and will note the maximum risk (or HQ)
achievable.
Aqueous-phase waste: a waste that is predominantly
water, with low concentrations of organics. All
chemicals remain in solution in the waste and are
usually present at concentrations below typical
solubility or saturation limits. However, it is possible
for the specific components of the waste to raise the
effective solubility or saturation level for a chemical,
allowing it to remain in solution at concentrations
above the typical solubility or saturation limit.
Organic-phase waste: a waste that is predominantly
organic chemicals, with a high concentration of
organics. Concentrations of some chemicals may
exceed solubility or saturation limits, causing those
chemicals to come out of solution and form areas of
free product in the WMU. In surface impoundments,
this can result in a thin organic film over the entire
surface.
1 For formaldehyde, the organic-phase emissions are higher than aqueous-phase emissions, and in order to
be protective, the allowable concentration calculation is always based on an organic-phase waste.
5-1
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IWAIR User's Guide Section 5.0
IWAIR is structured in a stepwise framework. Through the use of a series of screens,
IWAIR assists in selecting calculation options, identifying and entering required inputs, and
generating desired outputs. There are four different pathways you can follow in performing a
calculation:
• Pathway 1: Using CHEMDAT8 emission rates and ISCST3 default dispersion
factors
• Pathway 2: Using CHEMDAT8 emission rates and user-specified dispersion
factors
• Pathway 3: Using user-specified emission rates and ISCST3 default dispersion
factors
• Pathway 4: Using user-specified emission rates and dispersion factors.
Guidance for determining which modeling pathway to follow is provided in Section 3.3. The
stepwise approach employed by IWAIR to assist in calculating waste concentration, whether you
are following Pathway 1, 2, 3, or 4, is shown in Figures 5-1, 5-2, 5-3, and 5-4, respectively. The
seven steps of the estimation process are shown down the right side of each figure, and the user
input requirements are specified to the left of each step. The types of input data required will
vary depending on the modeling pathway chosen. Screen-by-screen, IWAIR walks you through
the steps of an allowable concentration calculation to arrive at protective waste concentration
estimates.
This section provides screen-by-screen guidance that describes the data that are required
as input to each screen and the assumptions that are interwoven in the calculation being
performed. The guidance provided in this section will assist you in completing an allowable
concentration calculation. You will not need to reference all of the information provided in this
section because the guidance addresses all four of the modeling pathways. Follow only those
subsections that are applicable to your chosen pathway.
5-2
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IWAIR User's Guide
Section 5.0
User Specifies:
• Calculation option
User Specifies:
• WMU type
User Specifies:
• Constituents (choose up to 6)
User Specifies:
• CHEMDAT8 option
• Facility location for meteorological input
• WMU information (i.e., design and
operating parameters)
User Specifies:
• Receptor information (i.e., distance and type)
User Specifies:
• Risk level
Allowable concentration
calculation
T
Identify WMU
Land application unit
Waste pile
Surface impoundment
Landfill
Define the Waste Managed
Add/modify chemical properties
data, as desired
CHEMDAT8
Determine Dispersion Factors
Interpolated from ISCST3 default
dispersion factors
Calculate Ambient Air Concentrations
Calculates ambient air concentrations for
each receptor based on emission and
dispersion data
Calculate Results
Allowable Waste Concentration Calculation
ste for wastewaters (mg/L)
ste f°r solid wastes (mg/kg)
Figure 5-1. IWAIR approach for completing allowable waste concentration calculations,
Pathway 1: Using CHEMDAT8 emission rates and ISCST3 default
dispersion factors.
5-3
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IWAIR User's Guide
Section 5.0
User Specifies:
• Calculation option
User Specifies:
• WMU type
User Specifies:
• Constituents (choose up to 6)
User Specifies:
• CHEMDAT8 option
• Facility location for meteorological input
• WMU information (i.e., design and
operating parameters)
User Specifies:
• Dispersion factors
• Receptor information (i.e., distance and type)
User Specifies:
• Risk level
Allowable concentration
calculation
Identify WMU
Land application unit
Waste pile
Surface impoundment
Landfill
Define the Waste Managed
Add/modify chemical properties
data, as desired
CHEMDAT8
Determine Dispersion Factors
User-specified dispersion factors
Calculate Ambient Air Concentrations
Calculates ambient air concentrations for
each receptor based on emission and
dispersion data
Calculate Results
Allowable Waste Concentration Calculation
ste f°r wastewaters (mg/L)
t for solid wastes (mg/kg)
Figure 5-2. IWAIR approach for completing allowable waste concentration calculations,
Pathway 2: Using CHEMDAT8 emission rates and user-specified dispersion
factors.
5-4
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IWAIR User's Guide
Section 5.0
User Specifies:
• Calculation option
Allowable concentration
calculation
User Specifies:
• WMU type
User Specifies:
• Constituents (choose up to 6)
Land application unit
Waste pile
Surface impoundment
Landfill
Add/modify chemical properties,
as desired
User Specifies:
• Emission rates
Determine Emission Rates
User-specified emission rates
User Specifies:
• WMU area (and height for waste pile)
• Facility location for meteorological input
• Receptor information (i.e., distance and type)
Determine Dispersion Factors
Interpolated from ISCST3 default
dispersion factors
Calculate Ambient Air Concentrations
Calculates ambient air concentrations for
each receptor based on emission and
dispersion data
User Specifies:
• Risk level
Allowable Waste Concentration Calculation
3
for solid wastes (mg/kg)
Figure 5-3. IWAIR approach for completing allowable waste concentration calculations,
Pathway 3: Using user-specified emission rates and ISCST3 default
dispersion factors.
5-5
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IWAIR User's Guide
Section 5.0
User Specifies:
• Calculation option
User Specifies:
• WMU type
User Specifies:
• Constituents (choose up to 6)
User Specifies:
• Emission rates
User Specifies:
• Dispersion factors
• Receptor information (i.e., distance and type)
User Specifies:
• Risk level
Allowable concentration
calculation
Identify WMU
Land application unit
Waste pile
Surface impoundment
Landfill
Define the Waste Managed
Add/modify chemical properties,
as desired
User-specified emission rates
Determine Dispersion Factors
User-specified dispersion factors
T
Calculate Ambient Air Concentrations
Calculates ambient air concentrations for
each receptor based on emission and
dispersion data
Allowable Waste Concentration Calculation
for solid wastes (mg/kg)
Figure 5-4. IWAIR approach for completing allowable waste concentration calculations,
Pathway 4: Using user-specified emission rates and dispersion factors.
5-6
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IWAIR User's Guide
Section 5.0
A. Select
calculation
method
C. Select met
station search
option
Enter zip code
and search for
met station
Enter latitude
and longitude
and search for
met station
D. View
selected met
station
File Help
Emission R.ates | ' M .dors j Results
Method, Met. Station, WMU } -ed J WMU Data for CHEMDAT3 1
| 1. Select Calculation Method p2. Select Waste Management Unit (WMU) Type _
(• fcaicuiate risk' Calculation to estimate risk for specified W
•4 ! ' chemical concentrations ** Surface impoundment
f* Calculate allowable Calculation to estimate chemical f Land application unit
concentration concentrations based on specified risk
1 C Active landfill
1 3. Selection of Best Meteorological Station for Site i ^ Waste pile
Y (* Search by zip code
f* Search by latitude and longitude coordinates
Enter 5 digit Zip Code of Site
' • Search
i . in ii ] .1 I i i 1 . ' i'.»
-> r r r
1 I
Selected Meteorological Station for Site
4 View Map
! 4. Select Emissions and Dispersion Option *
Use CHEMDAT8 to estimate emission ^
Use CHEMDAT8 rates and use dispersion factors
provided
1 OR 1
Enter Emission Directly enter emission rates without
_, using CHEMDAT8 and use disperion
factors provided
OR
Enter Emission & Directly enter emission rates and
Dispersion Data aspersion factors
- B. Select
WMU type
_ E. Select
emission and
dispersion
option
Screen 1A. Method, Meteorological Station, WMU
5.1 Method, Meteorological Station, WMU (Screen 1A)
A. Select Calculation Method (Screen 1A)
Select the calculation method by clicking on the | CALCULATE ALLOWABLE CONCENTRATION | option
button. Detailed guidance for selecting the appropriate mode of calculation is provided in
Section 3.1.
B. Select Waste Management Unit (WMU) Type (Screen 1A)
Identify the WMUs that are used to manage wastes of concern at your facility and run the
model separately for each unit type. The four unit types that are addressed as part of this
guidance include surface impoundments (aerated and quiescent), active landfills, waste piles, and
tilled land application units. A detailed description of these unit types is provided in Section 3.2.
Select one of the four WMU types shown in Screen 1A by clicking on the appropriate option
button.
C. Select Meteorological Station Search Option (Screen 1A)
The two search options available include searching by the site's 5-digit zip code or by its
latitude and longitude. Select the appropriate search option and enter the appropriate
information. This information is used to link the facility's location to one of the 60 IWAIR
meteorological stations. The 60 stations cover the 48 contiguous states, Hawaii, Puerto Rico, and
5-7
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IWAIR User's Guide Section 5.0
parts of Alaska. Data from the 60 stations (shown on maps in Screen IB, viewed by clicking on
the | VIEW AMP | button shown on Screen 1 A) were used as inputs to the air dispersion modeling
effort conducted to develop the default dispersion factors contained in the IWAIR tool. They are
also used as inputs to CHEMDAT8 emission modeling (e.g., annual average temperature and
wind speed). Additional information on this air dispersion modeling effort and the 60
representative meteorological stations is provided in Section 3.3.
Enter 5-Digit Zip Code and Search for Meteorological Station
Enter a 5-digit zip code and click on the | SEARCH | button to identify the default
meteorological station. If the zip code was entered incorrectly or if no data were provided
at all, message boxes will appear to indicate the specific problem that the tool
encountered so that you can supply the needed data. The zip code database includes zip
codes established through 1999. If your facility has a new zip code that was established
more recently, you will get an error message indicating that it is not a valid zip code
because it is not in IWAIR's database. If this occurs, you can use your old zip code, use a
nearby zip code, or select a meteorological station using latitude and longitude.
Enter Latitude and Longitude Information and Search for Meteorological Station
As shown in Screen 1 A, enter the latitude and longitude of the site in degrees, minutes,
and seconds. At a minimum, the program requires degrees for latitude and longitude to
be entered. If available, the minutes and seconds should be supplied to ensure that the
most appropriate station is selected for a site. After these data are entered, click on the
I SEARCH | button to identify the default meteorological station. If the latitude and longitude
information was entered incorrectly or if no data were provided at all, message boxes will
be displayed that indicate the specific problem that the tool encountered so that you can
supply the needed data.
D. View Selected Meteorological Station (Screen 1A)
The meteorological station selected by the tool will be displayed in the text box. Once
the meteorological station is selected, you are encouraged to click on the | VIEW MAP | button to
view the maps showing the 60 meteorological stations to ensure that the selection was made
correctly. For example, if the latitude of a site was entered incorrectly, then the selected
meteorological station would likely not be the most representative station. In this case, the map
will help you identify this error before proceeding with the calculations. Clicking on the | VIEW
MAP | button will bring up a map of the 48 contiguous states (Screen IB, shown here). You may
view six additional maps (regional maps for the northeastern, southeastern, and western areas of
the 48 contiguous states, as well as maps of Hawaii, Alaska, and Puerto Rico) by clicking on the
appropriate button at the bottom of Screen IB. The | CLOSE| button returns you to the METHOD, MET.
STATION, WMU SCREEN (Screen 1 A).
5-8
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IWAIR User's Guide
Section 5.0
Industrial Waste - [Ib. Maps showing the Met Stations]
IfllR
File Help
Met
Continental U.S. Western U.S. Northeastern U.S. Southeastern U.S. I Alaska I Hawaii I Puerto Rico j Close
Screen IB. Map of 48 Contiguous States Showing 60 Meteorological Station
E. Select Emission and Dispersion Option (IWAIR-Genemted or User-Specified)
(Screen 1A)
You must select from the IWAIR emission and dispersion data options. Under these
options, you have the flexibility of conducting modeling using IWAIR-generated emission rate
and dispersion factor estimates, user-specified emission and dispersion estimates, or a
combination of IWAIR-generated and user-specified estimates.
The tool uses emission rate and dispersion factor estimates in both the risk and allowable
concentration modes. As seen in Screen 1 A, you must select one of the three options provided
for obtaining emission and dispersion data:
5-9
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IWAIR User's Guide Section 5.0
• Use CHEMDAT8
Select | USE CHEMDAT81 to use CHEMDAT8 for calculating the emissions from
your unit regardless of whether you want to calculate or enter dispersion factors.
This allows you to enter a variety of unit-specific information that IWAIR will use
to develop chemical-specific emission rate estimates through the use of EPA's
CHEMDAT8 model. These inputs also provide the information needed to use the
ISCST3 dispersion factors provided with IWAIR; however, you may also enter
your own dispersion factors. You will not be allowed to override the IWAIR
emission estimates on subsequent screens in allowable concentration mode. This
option corresponds to Pathways 1 and 2 (see Section 3.3 and Figures 5-1 and 5-2).
• Enter Emission Rates
Select | ENTER EMISSION RATES | to enter your own site-specific emission rates (g/m2-s
per mg/kg of mg/L) on a subsequent screen. Rates may be developed based on
monitoring data or measurements or by conducting modeling with a different
emission model. If your emission rates are in g/s, they will also have to be
normalized by dividing by the area of the unit in m2. In addition, these emission
rates must be unitized (i.e., normalized to a unit waste concentration). This can be
done by dividing the emission rate in g/m2-s by the waste concentration in mg/L or
mg/kg. Under this option, IWAIR can be used to estimate dispersion based on
ISCST3 default dispersion factors. If this option is selected, you will still be
allowed to override the IWAIR dispersion factors on subsequent screens with site-
specific unitized dispersion factors (|a.g/m3 per |j,g/m2-s). Once the | ENTER EMISSION
RATES | command button is selected, a message box will appear that directs you to
enter WMU area (m2). If a waste pile is being modeled, a subsequent box will
appear for the height of the unit to be entered. These WMU data are used by the
model to calculate dispersion estimates. This option corresponds to Pathway 3
(see Section 3.3 and Figure 5-3).
• Enter Emission, Dispersion Data
Select | ENTER EMISSION & DISPERSION DATA| to enter your own emission estimates
(g/m2-s per mg/kg or mg/L) and unitized dispersion factors (|J.g/m3 per |j,g/m2-s).
Emission rates may be developed based on monitoring data or measurements or
by conducting modeling with a different emission model. If your emission rates
are in g/s, they will also have to be normalized by dividing by the area of the unit
in m2. In addition, these emission rates must be unitized (i.e., normalized to a unit
waste concentration). This can be done by dividing the emission rate in g/m2-s by
the waste concentration in mg/L or mg/kg. Dispersion factors may also need to be
unitized by dividing by the emission rate (in g/m2-s) used in dispersion modeling.
This option corresponds to Pathway 4 (see Section 3.3 and Figure 5-4).
5-10
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IWAIR User's Guide
Section 5.0
B. Select
sorting
option for
identifying
chemicals
A. Add/
modify
chemicals
Industrial Waste - [2a. Wastes Managed in WMUs]
File Help
Method, Met. Station, WMU
Wastes Managed
Identify Chemicals of Concern
To select chemical in management unit, click on chemical in list and click "Add »", or double-click on chemical in list
To remove chemical in management unit, select chemical to remove and click "«Remove"
To add a chemical to the list or to modify properties for a user-defined chemical, click "Add/Modify Chemicals"
(* Sort by chemical name
r Sort by CAS number
AddWIodify Chemicals
Benzo(a)pyrene [50-32-8]
Bromodichloromethane [75-27-4]
Carbondlsulfide [75-15-0]
B|||HiiS)|HHIi!JiiBJB!
Chlorobenzene [108-90-7]
Chlorodibromomethane [124-48-1 ]
Chloroform [67-66-3]
Chloroprene [126-99-8]
cis-1,3-Dichloropropylene [10061 -01 -5]
Cresols (total) [1319-77-3]
Cumene [98-82-8]
Cyclohexanol [108-93-0]
Dichlorodifluoromethane [75-71 -8]
Epichlorohydrin [106-89-8]
Bhylbenzene [100-41-4]
Bhylene dibromide [106-93-4]
Bhylene glycol [107-21-1]
Hhylene oxide [75-21-8]
Select
chemical to
remove
Chemicals in waste
1,1,1,2-Tetrachloroethane
Acetone
Carbon tetrachloride
Screen 2A. Wastes Managed
5.2 Wastes Managed (Screen 2A)
To perform an allowable concentration calculation, identify the chemical(s) of concern in
the waste.
A. Add/Modify Chemicals (Screen 2A)
IWAIR includes a list of chemicals from which you can identify waste constituents. As a
convenience to the user, IWAIR includes data on 95 constituents (shown with their CAS number
in Section 1, Table 1-1). However, this list of chemicals may not include all the organic
chemicals in your waste, and the data for these 95 chemicals may not match your site-specific
conditions for some properties. Therefore, IWAIR has the capability to add or modify chemicals.
To add or modify chemical data, click on the | ADD/MODIFY CHEMICALS | button. This will bring up
Screen 2B, ADD/MODIFY CHEMICALS.
5-11
-------
IWAIR User's Guide
Section 5.0
Industrial Waste - [2b. Add/Modify Chemicals]
File Help
A5. Clear entry
Wastes
Enter information for new chemical into form or double-click chemical from list box on which to base new entry.
A6. Save entry
r Chemical Properties
Chemical name: IT
CAS number:
Molecular wt
(g/g-mole):
Density (gfcmS):
-•
Vapor pressure
(mmHg):
Henry's law constant
(atm-mSJmol-K):
SolubilSy (mg/L):
Soil biodegradation
rate(s-1):
Antoine's constants: A:
Health benchmarks:
Cancer slope factor
(mg*g/d)-1:
(enter leading spaces if necessary)
-• Clear
3turn •-
Chemicals currently in database:
f* Sort by chemical name
Sort by CAS number
1,1,1,2-Tetrachloroethane [630-20-6]
1,1,1 -Trichloroethane [71 -55-6]
1,1,2,2-Tetrachloroethane [79-34-5]
1,1,2-Trichloro-1,2,2-trifluoroethane [76-13-1 ]
1,1,2-Trichloroethane [79-00-5]
1,1 -Dichloroethylene [75-35-4]
1,2,4-Trichlorobenzene [120-82-1]
1,2-Dibromo-3-chloropropane [96-12-8]
1,2-Dichloroethane [107-06-2]
1,2-Dichloropropane [78-87-5]
1,2-Diphenylhydraiine [122-66-7]
1,2-Epoxybutane [106-88-7]
1,3-Butadiene [106-99-0]
1,4-Oioxane [123-91-1]
.jj I
Delete User-Defined Chemical
Screen 2B. Add/Modify Chemicals
The ADD/MODIFY CHEMICALS screen will initially appear with no data in any of the fields. You
have four options:
• Add a new chemical. To do this, enter all data, including chemical name and
CAS number, manually.
• Add a new entry for a chemical already in the database. To do this, select an
existing entry for the chemical for which you wish to add an entry; if you select a
user-defined entry, IWAIR will ask if you want to create a new entry. Click on
I YES |. If you select an original IWAIR entry, IWAIR will automatically create a
new entry.
• Modify the data in an existing user-defined entry. To do this, select the
chemical to modify; when IWAIR asks if you want to create a new entry, click on
I No |. Original IWAIR entries may not be modified; if you select one, IWAIR will
automatically create a new entry.
• Delete an existing user-defined entry. Select the entry to delete. Original
IWAIR entries may not be deleted.
5-12
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IWAIR User's Guide Section 5.0
To ensure the integrity of the original IWAIR data and distinguish user-defined entries,
IWAIR will automatically generate a unique identifier for each chemical entry added to the data
set in the format "User X," where "X" is an entry number and "User" indicates it is a user-
defined entry. This identifier will be appended to the chemical name to uniquely identify each
entry. This identifier will be shown on screens and reports whenever the chemical is identified to
clearly indicate which chemical entry has been used.
Mercury is included in the IWAIR database in both divalent and elemental forms, but
because of code modifications needed for mercury (to reflect differences in its behavior, since it
is not an organic chemical), you may not create additional or modified entries for mercury.
Al. Select Sorting Order for Identifying Chemicals (Screen 2B)
The list of chemicals that is currently available in the database is shown here so that you
can select constituents to modify. This list includes the 95 constituents included with
IWAIR, as well as any you have already added to the IWAIR database. To facilitate the
chemical selection process, IWAIR allows you to sort this list of chemicals alphabetically
by chemical name, or by CAS number. As shown in Screen 2B, select a sort order by
clicking on the button to the left of the sorting option of choice.
A2. Select a Chemical to Modify (Screen 2B)
If you wish to add a new entry for an existing chemical or modify an existing user-defined
entry, double-click on the chemical name in the list of chemicals. This will display the
data for that chemical on the ADD/MODIFY CHEMICALS screen. If you select one of the 95
original IWAIR chemicals, a new entry will be generated automatically with a new,
unique user-defined identifier. If you select a user-defined entry, IWAIR will ask if you
want to create a new entry. Click on | YES | to create a new entry (you will be able to
modify the data) or | No| to edit the existing entry.
A3. Enter or View Chemical Name and CAS Number (Screen 2B)
If you selected a chemical to modify or to update with a new entry, the chemical name
and CAS number will be displayed. These may not be edited, to preserve the integrity of
the unique chemical identifiers. If you are adding a new chemical and therefore entering
all data manually, you will need to enter an appropriate chemical name and CAS number
in these text boxes. Do not include a "User X" designation in your chemical
name—IWAIR will append that automatically. Chemical names may not contain
apostrophes (') or quotations marks ("). CAS numbers that are shorter than the maximum
length should be prefaced with leading spaces, not zeros.
A4. Enter Chemical Properties Data (Screen 2B)
Enter values for all chemical properties shown on the screen. Use the mouse to click in
each text box, or use the | TAB | key to move between the boxes. Except for health
benchmarks, you may only enter numeric values (although you may enter numeric values
5-13
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IWAIR User's Guide Section 5.0
in scientific notation). For health benchmarks, you may also enter "NA." Be sure to
enter values in the units shown. Additional guidance on obtaining values for these
parameters is available in Appendix B, Section B.2.2.3.
You may enter user-defined health benchmarks may be entered both here, in a user-
defined chemical record, and on the RESULTS screen. On the RESULTS screen, you can enter
them directly into an IWAIR chemical record without overwriting the original IWAIR
value. If you are entering a new or modified chemical entry, you should enter any user-
defined health benchmarks here. However, you need not create a new chemical entry
here just to change the benchmark of an IWAIR chemical; you can enter the user-defined
health benchmark on the RESULTS screen.
AS. Clear Entry (Screen 2B)
To clear an unwanted entry from the ADD/MODIFY CHEMICALS screen without saving, click on
the | CLEAR | button. You will be asked to confirm that you want to clear the data.
A6. Save Entry (Screen 2B)
Once all data have been entered, you can save by clicking on the | SAVE| button. IWAIR
does some limited range checking to ensure values are within physically possible ranges;
if an entry is not in the acceptable range, IWAIR will display an error message with the
accepted range. These ranges are intended to eliminate only impossible entries (e.g.,
negative values for many properties) or values that will cause the model to fail. The
actual typical range for most of the chemical properties is likely smaller than the accepted
range. Once all data values have been validated and the entry added to the database, the
form will be cleared.
A 7. Delete a Chemical (Screen 2B)
You may delete a user-defined chemical entry on the ADD/MODIFY CHEMICALS screen by
selecting the chemical from the list of chemical entries and clicking on the (DELETE USER-
DEFINED CHEMICAL | button. It is not necessary to double-click on the chemical to bring up its
data before deleting; a single click to select the entry in the list is sufficient. If you have
selected an original IWAIR chemical entry, an error message will appear indicating that
the entry cannot be deleted. If you have selected a user-defined entry, a message will
appear to confirm that you want to delete the entry. If you select I YES |, the entry will be
deleted from the database and you will be returned to the ADD/MODIFY CHEMICALS screen. The
list of chemicals on this screen will be updated to reflect the removal of the entry. If you
select I No |, you will be returned to the screen, and the chemical will not be deleted.
Note that the deletion of a chemical entry used in a saved analysis will lead to the failure
of the saved analysis to reload.
5-14
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IWAIR User's Guide Section 5.0
A8. Return to Wastes Managed Screen (Screen 2B)
Once you have completed all desired data additions, modifications, and deletions, click
the | RETURN | button to return to the WASTES MANAGED screen. If you have unsaved data,
IWAIR will warn you and ask if you want to proceed. If you select I YES |, the unsaved
data will be lost. If you select I No |, you will be returned to the ADD/MODIFY CHEMICALS
screen, where you can save your data by selecting | SAVE |. The list of available chemicals
in the WASTES MANAGED screen will be updated to include any new entries and to omit any
deleted entries.
B. Select Sorting Option for Identifying Chemicals (Screen 2A)
Once you have returned to the WASTES MANAGED screen, you can identify waste constituents
from the list of chemicals included in IWAIR. This list includes the 95 constituents included
with IWAIR, as well as any you add to the IWAIR database using the ADD/MODIFY CHEMICALS feature.
The 95 constituents included with IWAIR are shown with their CAS number in Section 1, Table
1-1. To facilitate the chemical identification process, IWAIR allows you to sort this list of
chemicals alphabetically by chemical name, or by CAS number. As shown in Screen 2A, select a
sort order by clicking on the button to the left of the sorting option of choice.
C. Identify Chemicals in Waste (Screen 2A)
Identify up to six chemicals in a waste for modeling with IWAIR. Identify a chemical by
clicking on the chemical name or CAS number and clicking on the | ADD» | command button. To
remove a waste constituent from consideration, select the check box located to the left of the
chemical name and click the | «REMOVE| command button. User-defined entries are identified in
this list by the modifier "User X" appended to the chemical name, where "X" is a unique
number.
You may choose to simultaneously model the same chemical using multiple entries from
the chemical database. You may want to do this to compare results based on changes you have
made in chemical properties.
D. View Selected Chemicals (Screen 2A)
The chemicals you identified for consideration are displayed in text boxes shown on
Screen 2A. You can remove waste constituents from consideration by selecting the check box to
the left of the chemical and clicking the | «REMOVE| command button.
5.3 Enter WMU Data for Using CHEMDAT8 Emission Rates
If you elected to use CHEMDAT8 emission rates in the calculations (i.e., selected the
| USE CHEMDAT81 command button shown previously on Screen 1 A), you will need to enter WMU
data as specified in this section. If you did not elect to use CHEMDAT8 emission rates, then you
should skip this section and proceed to Section 5.4, Emission Rates. If you elected to enter
5-15
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IWAIR User's Guide Section 5.0
emission rates and use ISCST3 dispersion factors, you will be asked to enter the WMU area (and
height, if a waste pile) for ISCST3 before proceeding to the emissions screen.
This section provides guidance on providing input data needed to develop CHEMDAT8
emission estimates for the four unit types addressed by IWAIR.
Surface Impoundments. The major source of volatile emissions associated with surface
impoundments is the uncovered liquid surface exposed to the air (U.S. EPA, 1991).
Aeration and/or agitation are applied to aid in treatment of the waste, and emissions tend
to increase with an increase in surface turbulence because of enhanced transfer of liquid-
phase contaminants to the air (U.S. EPA, 1991). Parameters to which emissions are most
sensitive include surface area, unit depth, waste concentration, retention time, wind speed
for quiescent systems, and biodegradation. Retention time is not an explicit input, but a
function of impoundment volume and flow.
Land Application Units. Waste can be tilled or sprayed directly onto the soil and
subsequently mixed with the soil by discing or tilling. Waste in a land application unit is
a mixture of sludge and soil. IWAIR allows the modeling of tilled land application units.
If your unit uses spray application, another model may be more appropriate. Air
emissions from land treatment units are dependent on the chemical/physical properties of
the organic constituents, such as vapor pressure, diffusivity, and biodegradation rate.
Operating and field parameters affect the emission rate, although their impact is not as
great as that of the constituent properties.
Active Landfills. IWAIR allows the modeling of emissions released from the surface of
an active (i.e., receiving wastes) landfill. The landfill model is sensitive to the air
porosity of the solid waste, the liquid loading in the solid waste, the waste depth
(assumed to be the same as the unit depth), the constituent concentration in the waste, and
the volatility of the constituent (U.S. EPA, 1991).
Waste Piles. The waste pile emission model is sensitive to the air porosity of the solid
waste, the liquid loading in the solid waste, the waste pile height, the constituent
concentration in the waste, and the volatility of the constituent (U.S. EPA, 1991).
Screens 3A, 3B, 3C, and 3D, respectively, identify the CHEMDAT8 input requirements
for surface impoundments, land application units, landfills, and waste piles. Guidance for
completing each screen is provided below. For some of the required inputs, default values are
provided in the screen text boxes, as well as to the right of the text boxes. These default values
were selected to represent average or typical operating conditions. If appropriate, the defaults
can be applied in the absence of site-specific data; however, you always have the option of
overriding any defaults. The basis for these default values is provided in the IWAIR Technical
Background Document.
5-16
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IWAIR User's Guide
Section 5.0
A. View met
data for site
B. Enter
surface
impoundment
design data
C. Enter
aeration data
Ril Industrial Waste - f3a. Surface Impoundment! I r^lyiliklH^^^ta^^^^^^^^^^^^Kai^^Hi^^^^^^^^^^^^^^^^BVlHtBTti
File Help
Emissic ! ^ ~
Method, Met. Station, WMU
1
1
l •- n --,'- -> | ! -suits
Wastes Managed J WMU Data for CHEMD
Surface Impoundment Information
V\find speed (m/s)
j-^SI Dimensions, Loading Informatior
Biodegradation {* on f
Operating life (yr)
Depth of unit Cm)
Area of unit (m2)
Annual flow of waste
(m3/yr)
M No aeration (quiescent)
Diffused air aeration
Mechanical aeration
Both (diffused air & mechanical)
Fraction of surface area agitated
Submerged air flow (m3fe)
|3.473 |
|15.45 |
Off
10000
2500
r
r
r
(?
c
E
H
H
ATB I
W=.*°fp r~h^r=ir"tprr~fir^- lnfnrm=rtrnn
Type of waste: Aqueous (• Oiiiaiic (~
De
ault
Active biomass (gJL) |°-05 | 0.05
Total suspended solids in influent (g/L) |o.2 | o.2
Total organics into WMU (mgfl_) [200 | 200
Total biorate (mg/g biomass-h) 19 I 19
------ - Detail!!
Oxygen transfer rate (Ib O2/h-hp) p 3
Number of aerators
Total power (hp)
Power efficiency (fraction) |o.B3 | 0.83
Impeller diameter (cm) [61 | 61
Impeller speed (rad/s) |l30 | 130
Done
E. Enter waste
data
D. Enter
mechanical
aeration
information
Screen 3 A. WMU Data for CHEMD ATS: Surface Impoundment
l Waste - 1 3b. Land Application Unit I
File Help
Method, Met Station, WMU
Wastes Managed
WMU Data for CHEMDATB
r-Meteorological Station Parameters
Wind speed (m/s) b.473
Temperature (C) (15.45
pWaste/Soil Mixture Porosity Information
Default
Total porosity (volume l^j I 0.61
fraction) L_ _ I
Air porosity (volume [glj I g ^
fraction) I - 1
Land Application Unit Information
.AU Dimensions and Loading Information
Biodegradation C*" On P Off
Operating life (yr)
Tilling depth of unit (m)
Area of unit (m2)
Annual waste quantity (Mg/yr)
Number of applications per year
Waste bulk density (g/cm3)
j- Waste Characteristics Information (Only for Risk Calculation)_
r c
Screen 3B. WMU Data for CHEMD ATS: Land Application Unit
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IWAIR User's Guide
Section 5.0
al Waste - [3c. Active Landfill]
.JLDJJil
File Help
Method, Met. Station, WMU
Wastes Managed
WMU Data for CHEMDATB
^-Meteorological Station Parameters
Wind speed (rnte) Is .473
Temperature (C)
[—Waste Porosity Information—
Default
Total porosity (volume fraction) h.5 I 0.5
Air porosity (volume fraction) |o.25 0.25
Landfill Information
"LanaTiii uimensions ana Loaamg information
Biodegradalion C On (!" Off
Operating life (yr) 20
Total area of landfill (m2) |500
Total depth of landfill (m) |2
Total number of cells in landfill 1 2
Annual quantity of waste disposed in [1000
landfill (Mg/yr) I
Bulk density of waste (g/cmS) p -2
Default *
1.2
Waste Characteristics Information (Only for Risk Calculation)"
Screen 3C. WMU Data for CHEMDAT8: Landfill
Industrial Wa
-------
IWAIR User's Guide Section 5.0
A. View Meteorological Data for Site (Screens 3A, 3B, 3C, and 3D)
Both wind speed and temperature can affect the volatilization rate of a chemical.
Average wind speed and temperature are used as input to the CHEMDAT8 model. Average
annual wind speed is used to select the most appropriate empirical emission correlation equation
in CHEMDAT8; there are several of these correlations, and each one applies to a specific range
of wind speeds and unit sizes. Average annual temperature is used to adjust Henry's law constant
and vapor pressure values (temperature-dependent chemical properties) from a standard
temperature to the ambient temperature at the unit. Drawing from the meteorological data stored
in IWAIR, the program will display the average annual temperature and wind speed available for
the representative meteorological station that was determined for the site in Screen 1 A. You can
enter average wind speed and temperature for your site if the default values are significantly
different.2
B. Enter Unit Design and Operating Data
For all unit types, you may select whether or not biodegradation occurs in your unit.
Select the | ON | option to turn biodegradation on and the | OFF | option to turn it off. The default
setting varies by unit type. See Appendix B, Sections B.3.1.2, B.3.2.3, B.3.3.3, and B.3.4.3, for
further details about the implications of turning biodegradation on or off and the appropriateness
of difference choices for different unit types.
Enter Surface Impoundment Design Data (Screen 3A)
Enter the unit dimensions and loading information in the text boxes shown in Screen 3 A.
The data include the operating life of the unit (yrs), the depth of the unit (m), the area of
the unit (m2), and the annual flow of the waste (m3/yr).
Enter Land Application Unit Design and Operating Information (Screen 3B)
Enter the unit dimensions and loading information in the text boxes shown in Screen 3B.
The data include the operating life of the unit (yrs), tilling depth of the unit (m), area of
the unit (m2), annual waste quantity (Mg/yr), number of applications per year, and waste
bulk density (g/cm3).
Enter Landfill Design and Operating Information (Screen 3C)
Enter the unit dimensions and loading information in the text boxes in Screen 3C. The
model assumes that the landfill is divided into cells, with only one cell active at a time.
Emissions are modeled from the active cell. The data to be entered include the operating
life of the unit (yrs), total area of the unit (m2), depth of the unit (m), number of cells in
your unit, annual quantity of wastes disposed in the unit (Mg/yr), and bulk density of
waste (g/cm3).
These inputs are not used in the dispersion modeling, which uses hourly data, not annual averages.
Therefore, changes to these inputs will not affect the dispersion factors.
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IWAIR User's Guide Section 5.0
Enter Waste Pile Design and Operating Information (Screen 3D)
Enter the unit dimensions and loading information in the text boxes in Screen 3D. The
data include the operating life of the unit (yrs), the height of the pile (m), area of the unit
(m2), annual quantity of waste in the pile (Mg/yr), and bulk density of the waste (g/cm3).
C. For Aerated Surface Impoundments Only — Enter Aeration Data (Screen 3A)
IWAIR models both quiescent (nonaerated) and aerated impoundments. Aeration or
agitation of a liquid waste in an impoundment enhances transfer air (oxygen) to the liquid to
improve mixing or to increase biodegradation (U.S. EPA, 1991). Aeration is achieved through
the use of mechanical mixers, such as impellers (i.e., mechanically aerated), or by sparging air,
which bubbles up from the bottom of the unit (i.e., diffused air aerated). First, select the aeration
option that best describes your unit by clicking the appropriate option button. If you selected one
of the aerated options, provide information to characterize the aeration in your unit. For all
aeration options, you will need to enter the fraction of the surface area agitated (unitless). If you
selected an option including diffused air aeration (diffused air only or both diffused air and
mechanical aeration), you will also need to enter the total submerged air flow (m3/s) of all
diffusers in the impoundment.
If you choose to model an aerated impoundment, you will not have the option of
modeling an organic-phase waste; IWAIR cannot model an organic-phase waste in an aerated
impoundment because of limitations in CHEMDAT8.
D. For Mechanically Aerated Surface Impoundments Only - Enter Mechanical Aeration
Information (Screen 3A)
If a surface impoundment is mechanically aerated, you will need to provide additional
operating parameter information. These data include oxygen transfer rate (Ib O2/hr-hp), number
of aerators, total power (hp), power efficiency (fraction), impeller diameter (cm), and impeller
speed (rad/s).
E. For Surface Impoundments Only - Enter Waste Characteristics Data (Screens 3A)
The waste characteristic information to be entered for surface impoundments includes
active biomass (g/L), total suspended solids into WMU (mg/L), total organics into WMU (mg/L),
and total biorate (mg/g biomass-hr). These parameters are discussed in more detail in
Appendix B.
F. For Land Application Units, Landfills, and Waste Piles Only - Enter Waste Porosity
Information (Screens 3B, 3C, and 3D)
Waste (or soil/waste mixture for land application units) porosity information required as
input includes total porosity (unitless) and air porosity (unitless). Total porosity includes air
porosity and the space occupied by oil and water within waste. Total porosity (et), also
sometimes called saturated water content, can be calculated from the bulk density (BD) of the
waste and particle density (ps) as follows:
5^20
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IWAIR User's Guide Section 5.0
et =
BD
where BD and ps are expressed in the same units.
In the absence of site-specific data, IWAIR identifies default values of 0.5 and 0.25,
respectively, for total porosity and air porosity. Air porosity cannot exceed total porosity.
Done. Once you provide the required WMU inputs, click the |DONE| button to enable the
EMISSION RATES tab and open the EMISSION RATES screen. Proceed to Section 5.4, Emission Rates.
IWAIR must calculate emission rates before displaying the EMISSION RATES screen. This is usually
very quick, but if your computer is slow, or if you are modeling a land application unit and with a
large number of total applications (i.e., number of applications per year times operating life),
there can be a noticeable delay before the EMISSION RATES screen is displayed. This is normal, but
should typically not exceed 1 minute on a fast machine or 5 minutes on a slow machine.
5.4 Emission Rates
Guidance for using CHEMDAT8 emission rates or entering your own emission rates is
provided in this section. View and confirm the CHEMDAT8 emission rates as directed in
Section 5.4.1. If you did not elect to use CHEMDAT8 (i.e., if you selected the | ENTER EMISSION
RATES | or | ENTER EMISSION & DISPERSION DATA| command buttons shown previously on Screen 1 A),
proceed to Section 5.4.2, User-Specified Emission Rates.
Please note that all calculated and entered values on the EMISSION RATES screen will be lost if
you return to a previous screen and make changes. This includes both calculated and entered
override emission rate values.
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IWAIR User's Guide
Section 5.0
RH Industrial Waste - [4a. Emission Rates for Wastes from
File Help
Method, Met. Station, WMU
Wastes Managed
WMU Data for CHEMDAT8
Emission Rates
Chemical Emissions Estimated Using CHEMDAT8
(Emission of chemical = concentration of waste x emission rate)
I Chemical emissions
Aqueous Organic Override
Chemicals selected (gfm2/s) per (mgfkg)
I3.16E-09
1,1,1,2-Tetrachloroethane
Screen 4A. CHEMDAT8 Emission Rates
5.4.1 Using CHEMDAT8 Emission Rates (Screen 4A)
A. View CHEMDA T8 Emission Rates (Screen 4A)
Screen 4A shows the calculated CHEMDAT8 emission rates. Emission rates for the
allowable concentration mode are unitized to a unit waste concentration (i.e., a waste
concentration of 1 mg/kg). For land application units, landfills, and waste piles, emission rates
are linear with concentration; therefore, this unitized emission rate can be adjusted to any specific
concentration by multiplying by the concentration. For surface impoundments, however,
emissions are not linear in the aqueous phase because of biodegradation, which is first order at
low concentrations and shifts to zero order at higher concentrations. The concentration at which
this occurs is chemical-specific. Therefore, for surface impoundments, this screen does not
display emission rates. The actual emission rate used in risk calculations is calculated later,
during the risk calculations.
For landfills and waste piles, emissions are modeled at equilibrium and are assumed to
reflect a long-term average emission rate, normalized to a waste concentration of 1 mg/kg, which
is shown on this screen. In contrast, land application units are not assumed to be at equilibrium;
rather, emissions are calculated for each year of the specified operating life, plus 30 years
postclosure. The emission rates shown on this screen are the maximum single-year emission
5-22
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IWAIR User's Guide
Section 5.0
rates for each chemical (which may not reflect the same year for all chemicals), normalized to a
waste concentration of 1 mg/kg. This emission rate is used directly to calculate air concentration
for calculating noncarcinogenic risk. However, for carcinogenic risk, the maximum 7- or 30-year
average emission rate (7-year for a worker and 30-year for a resident, corresponding to the
default exposure durations for each receptor type) is used to calculate air concentration and then
risk.
For all unit types other than surface impoundments, emission rates will be displayed
under both the AQUEOUS and ORGANIC column headings; IWAIR will determine which of these to use
during calculation of the allowable concentration depending on the target risk or HQ and the
chemical's solubility or saturation limit.
These emission rates may not be overridden. Confirm the emission rates to be used in the
calculations by clicking the | DONE | button. The program will automatically enable the DISPERSION
FACTORS tab and open the DISPERSION FACTORS screen. Proceed to Section 5.5, Dispersion Factors.
R| Industrial Waste - [4b. User Override Emission
File Help
Method, Mat. Station, WMU
Wastes Managed
Emission Rates
User Override Chemical Emissions
Chemicals
(Emission of chemical = concentration of waste x emission rate)
User override emissions
(gMZ/s)
he-6
1,1.1,2-Tetrachloroethane
Acetone
Carbon disulfide
Source and Justification for User Override Values
justification
Done
Screen 4B. User-Specified Emission Rates
5-23
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IWAIR User's Guide Section 5.0
5.4.2 User-Specified Emission Rates (Screen 4B)
A. Enter User-Specified Emissions (Screen 4B)
Enter site-specific normalized emission rates (g/m2-s per mg/kg or g/m2-s per mg/L) in
the text box located under USER OVERRIDE. Your emission rates must be normalized to a unit
concentration. If you have measured or calculated emission rates in g/s for your entire unit, you
will need to divide that emission rate by the total area of your unit (in m2) to obtain area-
normalized emission rates in g/m2-s. You can normalize this emission rate to a unit
concentration by dividing by the waste concentration in mg/L or mg/kg at the time when the
emission rate was measured or calculated. These emission rates should reflect long-term average
emissions, not a short-term peak.
B. Enter Source and Justification for User-Specified Emission Rates (Screen 4B)
The program will prompt you to provide justification for using user-specified emission
rates and documentation of the estimation method applied. It is important to provide this
documentation as a reference that will allow you or another user to view and understand saved
files at a later date.
Done. Once you have entered emission data and source/justification, click the | DONE|
button to enable the DISPERSION FACTORS menu tab and open the DISPERSION FACTORS screen. Proceed to
Section 5.5, Dispersion Factors.
5.5 Dispersion Factors
Dispersion modeling outputs are used to estimate air concentrations to which the various
human receptors are exposed. Guidance for using the ISCST3 default dispersion factors or
entering your own site-specific dispersion factors is provided in Sections 5.5.1 and 5.5.2,
respectively. If you elected to use ISCST3 dispersion factors provided in IWAIR (i.e., selected
the | USE CHEMDAT81 or | ENTER EMISSION RATES | command buttons shown previously on Screen 1 A),
you will need to follow the guidance provided in Section 5.5.1. If you did not elect to use the
default dispersion factors, you should proceed to Section 5.5.2, User-Specified Dispersion
Factors.
Please note that all calculated and entered dispersion factors on the DISPERSION FACTORS
screen will be lost if you return to a previous screen and make changes. This does not include
receptor locations and types but does include calculated and entered override dispersion factor
values.
5-24
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IWAIR User's Guide
Section 5.0
53 Industrial Waste - [5. Dispersion Factors]
Fjle Help
Method. Met Station, WMU
Wastes Managed
WMU Data for CHEMDAT8
Emission Rates
Dispersion Factors
Receptor Distance, Type, and Dispersion Factor
To override default dispersion factors, enter values into "User override" column
Dispersion factors for location and unit
size [(ug/mS per (ugAn2-s)]
Calculated dispersion user override
factors
Receptor Distance to
no. receptor (m)
Receptor type
1.
IWorker "• Click to calculate
dispersion factors
Resident""! (1.87E-01
Source and Justification for User Override Values
C. View
IWAIR
dispersion
factors or
enter user-
specified
dispersion
factors
D. Enter
source and
justification
for user-
specified
dispersion
factors
Screen 5A. Using ISCST3 Default Dispersion Factors
5.5.1 Using ISCST3 Default Dispersion Factors (Screen 5A)
In Screen 5A, you will provide receptor information (i.e., receptor type and distance to
the receptor) and click on the | CALCULATE | button; IWAIR will develop site-specific dispersion
factors based on default dispersion data. If you wish to override the IWAIR-developed
dispersion factors, enter alternate site-specific unitized dispersion factors. If you enter alternative
dispersion factors, you should document the source and the justification for these data in the text
box on the screen.
A. Select Receptor Type and Distance (Screen 5A)
Enter information concerning the receptors of concern (i.e., potentially exposed
individuals). You can specify up to five receptors, including the distance to receptor and the
receptor type. You can specify two receptor types at six distances (25, 50, 75, 150, 500, and
1,000 meters) from the edge of the WMU. You can delete the last receptor entered by deleting
both the distance to receptor and receptor type entries.
Distance to Receptor - For each receptor of concern, determine the distance from the
edge of the unit to the receptor. Based on this distance, select from the six default distances (25,
50, 75, 150, 500, and 1,000 meters) the one that best approximates the location of your receptor,
using the drop-down box positioned under the DISTANCE TO RECEPTOR column heading. Note that
selecting a distance smaller than the actual distance to receptors near your unit will overestimate
5-25
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IWAIR User's Guide Section 5.0
risk, and selecting a distance larger than the actual distance will underestimate risk. These
distances correspond to the distances for which air dispersion modeling was conducted to
develop the IWAIR default dispersion factors. The IWAIR Technical Background Document
discusses the analysis that was conducted in determining the appropriateness of these default
distances.
Receptor Type - Two different types of exposed individuals, worker and resident, can be
modeled with IWAIR. The dispersion factors do not vary with receptor type; however, receptor
type is chosen here for convenience. The difference between these two receptors is in the
exposure factors, such as body weight and inhalation rate, used to calculate risk for carcinogens.
There is no difference between them for noncarcinogens because calculation of noncarcinogenic
risk does not depend on exposure factors. The IWAIR Technical Background Document
describes the exposure factors used for residents and workers. The assumptions for workers
reflect a full-time, outdoor worker. The exposure duration for workers is the smaller of 7.2 years
or the operating life of the unit. The assumptions for residents reflect males and females from
birth through age 30; it is important to consider childhood exposures because children typically
have higher intake rates per kilogram of body weight than adults. The actual exposure duration
used for residents is the smaller of 30 years or the operating life that you entered for the unit. For
exposure durations less than 30 years, exposure starts at birth and continues for the length of the
exposure duration, using the appropriate age-specific exposure factors. Use the drop-down box
positioned under the RECEPTOR TYPE column heading to select either WORKER or RESIDENT.
B. Direct IWAIR to Estimate Dispersion Factors (Screen 5A)
After the requested receptor information is provided, click on the | CALCULATE! button to
direct the program to determine an appropriate dispersion factor based on the IWAIR default
dispersion data. The resulting dispersion factor will be displayed for each receptor of concern. A
discussion of the development of IWAIR default dispersion data and the methodology used by
the program in selecting an appropriate dispersion factor for each WMU/receptor combination is
provided in Section 3.3. A more detailed discussion of the air dispersion modeling effort is
provided in the IWAIR Technical Background Document.
For waste piles, IWAIR uses a two-dimensional nonlinear spline to interpolate dispersion
factors for areas and heights different from those included in the dispersion factor database. This
technique is more accurate than a two-dimensional linear interpolation and is less likely to
underestimate the actual dispersion factor. However, on rare occasions, the spline may produce
results inconsistent with the data points nearest the actual area and height. If this occurs, IWAIR
shifts to the linear interpolation technique, which generally produces somewhat lower dispersion
factors. If this occurs, you will see a message to that effect. The interpolation techniques used
for dispersion factors are discussed in greater detail in the IWAIR Technical Background
Document.
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IWAIR User's Guide
Section 5.0
C. View IWAIR Dispersion Factors or Enter User-Specified Dispersion Factors
(Screen 5A)
You may override the program-calculated dispersion factors by entering alternative
dispersion data in the text box located under the USER OVERRIDE column (see Screen 5A).
D. Enter Source and Justification for User-Specified Dispersion Factors (Section 5A)
If you choose to provide alternative dispersion factors, document the source and the
justification for these data in the text box that will appear. It is important to provide this
documentation as a reference that will allow you or another user to view and understand saved
files at a later date.
Done. Once the program has developed dispersion factors, click the | DONE | button to
open the RESULTS tab. Proceed to Section 5.6, Results.
Industrial Waste - [5. Dispersion Factors]
File Help
Method, Met. Station, WMU
Wastes Managed
Emission Rates
Dispersion Factors
Receptor Distance, Type, and Dispersion Factor
To override default dispersion factors, enter values into "User override" column
Dispersion factors for location and unit
size [(ug/m3 per (
Receptor Distance to Receptor type
no. receptor (m)
|7S 21
[Tie T]
Worker ^
[Resident ;I
1 Resident •»!
Source and Justification for User Override Values
C. Enter
source and
justification
for user-
specified
dispersion
factors
Screen 5B. User-Specified Dispersion Factors
5.5.2 User-Specified Dispersion Factors (Screen 5B)
A. Select Receptor Type and Distance (Screen SB)
Enter information concerning the receptors of concern (i.e., potentially exposed
individuals). You can specify up to five receptors. The receptor information includes the
5-27
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IWAIR User's Guide Section 5.0
distance to receptor and the receptor type. You can specify two receptor types in sixteen
directions at six distances (25, 50, 75, 150, 500, and 1,000 meters) from the edge of the WMU.
You can delete the last receptor entered by deleting both the distance to receptor and receptor
type entries.
Distance to Receptor - For each receptor of concern, determine the distance from the
edge of the unit to the receptor. Based on this distance, select from the six default distances (25,
50, 75, 150, 500, and 1,000 meters) the one that best approximates the location of your receptor,
using the drop-down box positioned under the DISTANCE TO RECEPTOR column heading. These values
are only for your reference and are not used in calculations, since you are entering your own
dispersion factors.
Receptor Type - Two different types of exposed individuals, worker and resident, can be
modeled with IWAIR. The dispersion factors do not vary with receptor type; however, receptor
type is chosen here for convenience. The difference between these two receptor types lies in the
exposure factors, such as body weight and inhalation rate, used to calculate risk for carcinogens.
There is no difference between them for noncarcinogens because calculation of noncarcinogenic
risk does not depend on exposure factors. The IWAIR Technical Background Document
describes the exposure factors used for residents and workers. The assumptions for workers
reflect a full-time, outdoor worker. The exposure duration for workers is the smaller of 7.2 years
or the operating life of the unit. The assumptions for residents reflect males and females from
birth through age 30; it is important to consider childhood exposures because children typically
have higher intake rates per kilogram of body weight than adults. The actual exposure duration
used for residents is the smaller of 30 years or the operating life of the unit that you entered. For
exposure durations less than 30 years, exposure starts at birth and continues for the length of the
exposure duration, using the appropriate age-specific exposure factors. Use the drop-down box
positioned under the RECEPTOR TYPE column heading to select either WORKER or RESIDENT.
B. Enter User-Specified Dispersion Factors (Screen SB)
For each receptor specified, enter site-specific unitized dispersion factors (n-g/m3 per
|o,g/m2-s) in the text box located under USER OVERRIDE. You may need to normalize modeled
dispersion factors to a unit concentration by dividing the modeled dispersion factor by the
emission rate used in dispersion modeling (in |j,g/m2-s) if it was not 1 |J,g/m2-s. For example, if
you ran your dispersion model using an emission rate of IE-6 |j,g/m2-s, then you would need to
divide all your dispersion factors by IE-6 to normalize them to a concentration of 1 |J,g/m2-s.
C. Enter Source and Justification for User-Specified Dispersion Factors (Screen SB)
The program will prompt you to provide justification for using user-specified dispersion
data and documentation of the estimation method applied. It is important to provide this
documentation as a reference that will allow you or another user to view and understand saved
files at a later date.
Done. Once you have entered dispersion data, click the | DONE| button to open the RESULTS
tab. Proceed to Section 5.6, Results.
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IWAIR User's Guide Section 5.0
5.6 Allowable Concentration Results (Screen 6)
Allowable waste concentrations can be calculated from user-specified risk levels. The
program combines the constituent's air concentration with receptor exposure factors and toxicity
benchmarks to calculate the waste concentrations that are protective of human health. For each
receptor, IWAIR calculates air concentrations using emission and dispersion data specified or
calculated in previous screens. To reflect exposure that would occur in a lifetime (i.e., from
childhood through adulthood), the model applies a time-weighted-average approach. This
approach considers exposure that would occur during five different phases of life (i.e., Child < 1
yr, Child 1-5 yrs, Child 6-11 yrs, Child 12-18 yrs, and Adult). The exposure factors addressed
as part of this approach include inhalation rate, body weight, exposure duration, and exposure
frequency. The default values that are applied in developing these time-weighted-average
exposures were identified based on data presented in EPA's Exposure Factors Handbook (U.S.
EPA, 1997a) and represent average exposure conditions. IWAIR incorporates standard toxicity
benchmarks (CSFs for carcinogens and RfCs for noncarcinogens) for 95 constituents. These
health benchmarks were obtained primarily from the EPA's IRIS and the HEAST (U.S. EPA,
2001, 1997b). IWAIR uses these data to perform an allowable concentration calculation. See
the IWAIR Technical Background Document for documentation of the equations.
The approach applied by IWAIR to calculate allowable concentration employs an
iterative calculation algorithm. The program sets an initial waste concentration, calculates risk,
compares that to the target risk, then adjusts the waste concentration and recalculates until the
target risk is achieved.
If you are modeling a land application unit, landfill, waste pile, or quiescent surface
impoundment and have elected to use CHEMDAT8 to calculate emissions, IWAIR will perform
allowable concentration calculations for both an aqueous-phase waste and an organic-phase
waste and will output the lower (or more protective) of the two resulting concentrations. For
most chemicals, that will be the aqueous-phase concentration, but for a few chemicals (most
notably formaldehyde), it will be the organic-phase concentration.3 If you elected to enter your
own emission rates, or if you are modeling an aerated surface impoundment, IWAIR will only
calculate and output concentrations for an aqueous-phase waste.
In performing allowable concentration calculations, IWAIR ensures that calculated
aqueous-phase concentrations do not exceed the soil saturation limit (for land-based units) or the
solubility limit (for surface impoundments) for that chemical. This prevents impossible results
from occurring. Similarly, the program also ensures that calculated organic-phase concentrations
do not exceed 1,000,000 mg/kg. If the target risk or HQ cannot be achieved by any possible
concentration (i.e., in an aqueous-phase waste up to the soil saturation or solubility limit, or in an
organic-phase waste up to 1,000,000 mg/kg), then the program will note the maximum risk or
HQ that can be reached, and the calculated concentration will be set to the concentration that
3 Any concentration at or below the soil saturation limit or solubility limit may occur in either an aqueous-
phase waste or an organic-phase waste. The phase of the waste is not solely determined by the concentration of any
one chemical. For most chemicals, the same concentration in an aqueous-phase waste will produce higher emissions
than in an organic-phase waste; however, formaldehyde is a notable exception.
5^29
-------
IWAIR User's Guide
Section 5.0
results in the maximum possible risk or HQ. This will be either the soil saturation limit or
1,000,000 if you are modeling a land-based unit using CHEMDAT8; the soil saturation limit if
you are modeling a land-based unit with your own emission factors; or the solubility if you are
modeling a surface impoundment.
For chemicals with both a CSF and an RfC, allowable concentrations are calculated based
on both of these health benchmarks, and the final allowable concentration is based on the one
that leads to the lowest, most protective concentration. This is almost always the one based on
the CSF.
Please note that all calculated values on the RESULTS screen will be lost if you return to a
previous screen and make changes.
^^^^^^Rglndustrlal Waste - T6. Results: Allowable Chemical
A. Select
receptor
F. View air
concentration
C. View or
override health
benchmarks
E. Direct
IWAIR to
calculate
allowable waste
concentrations
File Help
Method, Met. Station, WMU f Wastes Managed
Emission Rates J Dispersion Factors
Results: Allowable Chemical Concentrations at Specified Conditions
M „„„,„,,._. Distance to Select risk value for
»Mo.1 r Ji^/orker p; 11F ^ ^1^
Mo. 3 r Exposure Dispersion factor Select hazard quotif nt va u
duration (yr) [(ug/m3) per for noncarcinogens
f2 (ug*n2-s)] fj ^1
5.10E-01
Air cone CSF CSF ref
User # (Mmhi3i (mgficg/d>1
Chemical name
1 ,1 ,1 ,2-Tetrachloroethane | JO J1 .59E-02 1e-2 User -r
Acetone JO j^l^F.n? NA Nore1JljJ
Carbon tetrachloride lo J2.35E-02 S.3E-02 calc T
I! I ^
I I z.
I ! dl
r— - — | I
! "" ^_j| °nC j '
'•;, :':' ' .Jnlxj
J WMU Data for CHEMDATS
] Results
Source and Justification for User Override Values
1 ,1 ,1 ,2-Tetrachloroethane J
justification
Full Citations
I
i
RfC Allow, cone. Waste
(mgrtnS) RfCref- (mg/kg or mgrt.) type
W Noref.^j 3.12E+03 |org.
J.1E+01 ATSDF. ^||953E+05 |org
7.0E-03 SF ^JJ5.72E+02 |org.
dl I
dl I
I dl I
I
B. Specify
target or HQ
D. Enter
source and
justification
for user-
specified
values
G. View
allowable
waste
concentration
Screen 6. Allowable Concentration Results
A. Select Receptor (Screen 6)
Select a single receptor to serve as the focal exposure point for the calculations by
clicking on the option button associated with the receptor of choice. As discussed above in
Section 5.5, you can specify up to five receptors of concern; however, results can only be seen on
the screen for one receptor at a time. Once results are calculated and displayed for one receptor,
you can select another receptor by clicking on one of the other receptor option buttons. You do
not need to enter exposure duration because it is set by IWAIR and will be displayed when you
click on the | CALCULATE | button.
5-30
-------
IWAIR User's Guide Section 5.0
B. Specify Risk Level (Screen 6)
Specify target cancer and noncancer risk levels. As shown in Screen 6, a drop-down box
is used to allow you to select an appropriate risk level (e.g., an HQ of 1 for noncarcinogens or
IE-6 for carcinogens).
C. View or Override Health Benchmarks (Screen 6)
Screen 6 allows you to view the health benchmarks that IWAIR will use in calculating
risk estimates. For each benchmark, the table on the RESULTS screen shows the value and a brief
reference. To see more-complete citations, click on the | FULL CITATIONS | button in the SOURCE AND
JUSTIFICATION box in the upper right corner of the screen.
IWAIR gives you the option of entering your own health benchmarks. If you choose not
to use the IWAIR data, you can enter alternative health benchmarks by opening the drop-down
box in the RFC REF. column of the desired health benchmark and selecting USER-DEFINED, and then
entering a value in the text box for the benchmark. Enter CSFs (per mg/kg-d) in text boxes
located under the CSF heading and RfCs (mg/m3) under the RFC heading. Do not use a reference
dose in the place of a reference concentration. Once you have entered alternative benchmarks,
they are available in future runs, and you may toggle between them and the IWAIR values using
the drop-down reference box.
You must enter a user-defined health benchmark for two chemicals in IWAIR's chemical
database: divalent mercury and 3,4-dimethylphenol. At the time IWAIR was released, no
accepted health benchmarks were available for these chemicals from the hierarchy of sources
used to populate the IWAIR health benchmark database, nor were there data available from these
sources to allow the development of a health benchmark with any confidence. Thus, if you want
to model one of these chemicals, you will have to enter at least one user-defined health
benchmark. See Section 5 of the IWAIR Technical Background Document for further discussion
of how health benchmarks were developed for IWAIR.
D. Enter Source and Justification for User-Specified Values (Screen 6)
If you choose to override the IWAIR-provided benchmarks, you should specify the source
and the justification of the alternative data in the text box. It is important to provide this
documentation as a reference that will allow you or another user to view and understand saved
files at a later date.
E. Direct IWAIR to Calculate Allowable Waste Concentrations (Screen 6)
Click on the | CALCULATE | button to calculate exposure duration, air concentration, and
waste concentration estimates.
5-31
-------
IWAIR User's Guide Section 5.0
F. View Air Concentration (Screen 6)
Air concentration at the selected receptor point is displayed for each chemical identified
as managed. For land application units, IWAIR calculates three different air concentrations,
based on three different underlying emission rates: a 30-year average for residents for
carcinogens, a 7-year average for workers for carcinogens, and a 1-year maximum for residents
or workers exposed to noncarcinogens. Depending on the receptor selected and the chemical,
IWAIR displays the appropriate air concentration. However, for chemicals that are both
carcinogens and noncarcinogens, only the 30- or 7-year average used for the carcinogenic risk
calculation is displayed. To calculate the 1-year maximum used in the noncarcinogenic HQ
calculation, multiply the emission rate shown on the EMISSION RATES screen by the dispersion factor
and then multiply by 1,000,000 (to convert units).
G. View Allowable Waste Concentration (Screen 6)
Waste concentration estimates will be displayed for each chemical of concern. If
CHEMDAT8 emission rates were used in the calculations, the waste phase (aqueous or organic)
that served as the basis for these rates will be displayed to the right of the waste concentration
text boxes.
For chemicals with both a CSF and an RfC, allowable concentrations are calculated based
on both of these health benchmarks, and the final allowable concentration is based on the one
that leads to the lowest, most protective concentration. This is almost always the one based on
the CSF.
When using the IWAIR tool in allowable concentration calculation mode, you need to
remember that the specified target levels are chemical-specific and do not represent total or
cumulative cancer risk levels (i.e., the summation of the chemical-specific risk estimates). If
multiple chemicals of concern are present in the waste, the cumulative cancer risk will likely be
greater than the specific target risk level unless the target risk could not be reached for some or
all of the chemicals. If the target risk is reached for all chemicals, you can estimate the
cumulative risk posed to the receptor of concern by multiplying the number of carcinogens in the
waste by the specified target risk level. For example, if a waste being managed contains five
carcinogens and the single target risk level specified is IE-6, then the cumulative risk posed to
the receptor of concern would be equal to the product of the number of carcinogens in the waste
(5) times the target risk level (IE-6) or 5E-6.
Done. Click the | DONE | button to initiate a new run or save the run that you have just
completed. A dialog box will appear to guide you through starting a new run or saving the
current run.
5-32
-------
IWAIR User's Guide Section 6.0
6.0 Example Calculations
With IWAIR, you can calculate estimates of cancer and noncancer inhalation risk or
estimates of allowable waste concentration from a specified target risk level. The following
example calculations demonstrate how IWAIR calculates risk or allowable concentration from
emission rates and dispersion factors, using the equations presented in Section 6 of the IWAIR
Technical Background Document, "Calculation of Risk/Hazard Quotient or Allowable Waste
Concentration." You may either use IWAIR-calculated emission rates and dispersion factors or
enter your own values; these example calculations do not cover how IWAIR calculates emission
rates and dispersion factors.
The example calculations are based on a hypothetical exposure situation with the
following conditions:
• The WMU modeled is a landfill.
• The waste managed in the landfill contains the carcinogen hexachlorobenzene and
the noncarcinogen acrolein.
• The emission rates and dispersion factors are IWAIR-calculated values, not user-
override values.
• The exposed individual is a resident living 25 meters from the edge of the unit.
Additional inputs used for the emission and dispersion modeling are summarized in Table 6-1.
6.1 Calculation of Risk and Hazard Quotient
To calculate risk from a specified chemical to a specified receptor, IWAIR uses the
following steps:
1. Calculate emission rates from your inputs or use the emission rates that you
entered; the emission rates are chemical-specific and, if calculated by IWAIR,
depend on the waste concentrations that you entered.
2. Calculate dispersion factors from your inputs or use your entered dispersion
factors; the dispersion factors are receptor-specific.
3. Calculate air concentrations from emission rates and dispersion factors; the air
concentrations are chemical- and receptor-specific.
-------
IWAIR User's Guide
Section 6.0
Table 6-1. Inputs Used for Example Calculation: Landfill
Parameter
Method, Met. Station, WMU Parameters
Meteorological Station
WMU Type
Example Calculation Value
Huntington, WV
Landfill
Wastes Managed Parameters
Chemicals
Concentration (mg/kg)
Waste Management Unit Parameters
Temperature (°C)
Wind speed (m/s)
Total porosity (volume fraction)
Air porosity (volume fraction)
Biodegradation
WMU operating life (yr)
WMU area (m2)
WMU depth (m)
Number of cells
Annual waste quantity (Mg/y)
Waste bulk density (g/cm3)
Hexachlorobenzene, Acrolein
Hexachlorobenzene: 10
Acrolein: 3
13.12 (met station default)
3.179 (met station default)
0.5 (default)
0.25 (default)
Off (default)
30
10,000
2
25
500
1.2 (default)
Receptor Parameters
Receptor type
Receptor distance (m)
Resident
25
6-2
-------
IWAIR User 's Guide Section 6. 0
4. Calculate risks or HQs from air concentrations and, for carcinogens, exposure
factors.
This example calculation does not cover the calculation of emission rates and dispersion factors
in Steps 1 and 2. Using the inputs shown in Table 6-1, IWAIR calculates an emission rate of
1.56E-8 g/m2-s for hexachlorobenzene, an emission rate of 5.36E-9 g/m2-s for acrolein, and a
dispersion factor of 3.37 [|j,g/m3]/[|j,g/m2-s], which is not chemical-specific (but corresponds to a
receptor at 25 m).
Starting with Step 3, IWAIR calculates air concentration, as follows:
Cairj = (EJ X 1Q6) X DF (6-1)
where
Cgjrj = air concentration of chemical y (|J,g/m3)
EJ = volatile emission rate of chemicaly (g/m2-s)
106 = unit conversion (|j,g/g)
DF = dispersion factor ([|j,g/m3]/[|j,g/m2-s]).
Plugging the values for emission rates and dispersion factor shown above into
Equation 6-1 gives the following air concentration values:
c*h* = 1.56E-8xl06x3.37
= 5.26E-2
Cair,acrolein = 5.36E-9 x 106 x 3.37
= 1.806E-2
In Step 4, for carcinogens, IWAIR uses the calculated air concentration, the exposure
factors, and the CSF to calculate carcinogenic risk, as follows:
C . . x 1(T3 x CSF. x EF 5 IR. x ED.
Risk. = -2^ * x E _! 1 (6_2)
J AT x 365 i"! BW. v '
where
Riskj = individual risk for chemicaly (unitless)
6-3
-------
IWAIR User's Guide
Section 6.0
airj
io
-3 =
ED;
EF
365
AT
BW;
air concentration for chemical j (|J,g/m3) = 5.26E-2 for hexachlorobenzene,
calculated above
unit conversion (mg/|ig)
cancer slope factor for chemical y (per mg/kg-d) =1.6 for hexachlorobezene
index on age group (e.g., <1 yr, 1-5 yrs, 6-11 yrs, 12-19 yrs, Adult)
inhalation rate for age group / (m3/d) - varies by age group, see Table 6-2
exposure duration for age group / (yr) - varies by age group, see Table 6-2
exposure frequency (d/yr) = 350
unit conversion (d/yr)
averaging time (yr) = 70
body weight for age group /' (kg) - varies by age group, see Table 6-2.
Table 6-2. Parameter Values Used in Estimating Time-Weighted-Average Exposure
Age Range
Child < 1 year
Child 1-5 years
Child 6-11 years
Child 12- 18 years
Adult
Body Weight
(kg)
9.1
15.4
30.8
57.2
69.1
Inhalation Rate
(nWday)
4.5
7.55
11.75
14.0
13.3
Exposure Duration
(yrs)
1
5
6
7
11
Exposure
Frequency
(d/yr)
350
350
350
350
350
Plugging the air concentration value for hexachlorobenzene and the exposure factors shown
above into Equation 6-2 gives the following carcinogenic risk value:
5.26E-2 x 1Q-3x 1.6x350 f 4.5 x 1 7.55x5 11.75x6 14.0x7 13.3 x
x + + + +
70 x 365
^ 9.1 15.4 30.8 57.2
= 1.04E-5
69.1
In Step 4, for noncarcinogens, IWAIR uses the calculated air concentration and the RfC
to calculate noncarcinogenic risk (HQ), as follows:
-3
HQj =
(6-3)
6-4
-------
IWAIR User 's Guide Section 6. 0
where
= hazard quotient for chemical y (unitless)
Cairj = air concentration for chemical y' (|o,g/m3) = 1.806E-2 for acrolein, calculated
above
10"3 = unit conversion (mg/|j,g)
RfCj = reference concentration for chemical y' (mg/m3) = 2E-5 for acrolein.
Plugging the air concentration value for acrolein into Equation 6-3 above gives the following
HQ, or noncarcinogenic risk value:
Q = 1.806E-2xlQ-3
^acrolein 9 p _ «
= 9.03E-1
6.2 Calculation of Allowable Concentration
To calculate an allowable concentration, IWAIR uses the following steps:
1. Calculate unitized emission rates from your inputs or use your entered unitized
emission rates; the emission rates are chemical-specific and correspond to a waste
concentration of 1 mg/kg or mg/L; if calculated by IWAIR, unitized emission
rates are also specific to waste type (i.e., aqueous- or organic-phase).
2. Calculate dispersion factors from your inputs or use your entered dispersion
factors; the dispersion factors are receptor-specific.
3. Calculate target air concentrations from target risk or HQ, health benchmarks,
and, for carcinogens, exposure factors; the air concentrations are chemical- and
receptor-specific.
4. Calculate waste concentrations from air concentrations, dispersion factors, and
unitized emission rates, for aqueous- and organic-phase wastes.
5. Choose an allowable concentration from the waste concentrations calculated for
aqueous- and organic-phase wastes.
This example calculation does not cover the calculation of unitized emission rates and dispersion
factors in Steps 1 and 2. Using the inputs shown in Table 6-1, IWAIR calculates the unitized
emission rates for aqueous and organic phases for hexachlorobenzene and acrolein, shown in
Table 6-3, and a dispersion factor of 3.37 [|j,g/m3]/[|j,g/m2-s], which is not chemical-specific.
These will be used in Step 4.
6-5
-------
IWAIR User's Guide
Section 6.0
Table 6-3. Unitized Emission Rates for Allowable Concentration
Mode Example Calculation ([g/m2-s]/[mg/kg])
Chemical
Hexachl orob enzene
Acrolein
Aqueous-phase
1.56E-9
1.79E-9
Organic-phase
1.12E-13
7.28E-10
Starting with Step 3, IWAIR calculates target air concentrations by solving Equations 6-2 and 6-3
above for air concentration. For carcinogens,
airj
isk x AT x 365
10
-3
5
E
x
(6-4)
BW;
Plugging a target risk value of IE-5 into Equation 6-4 gives the following air concentration:
air.hcb
lE-Sx 70x365
10-* x 1.6x350 x
( A*v1 TZ**S.
4.5x1 + /.:>:> x:j
( 9.1 15.4
= 5.03E-2
11.75x6 14.0x7
30.8 57.2
+ 13.3 x 11 1
69.1 )
For noncarcinogens,
Cairj
(6-5)
Plugging a target HQ of 1 into Equation 6-5 gives the following air concentration:
Cair,j = 1X
= 2E-2
In Step 4, IWAIR uses an equation comparable to Equation 6-1 to relate target air
concentration to waste concentration. However, this equation must be adapted to reflect the use
of a unitized emission rate associated with a waste concentration of 1 mg/kg. The emission rate,
Ej, is replaced by Cwaste xEjimttized, where Cwaste is waste concentration in mg/kg and Ejimdtimd is the
unitized emission rate for chemical y in [g/m2-s]/[mg/kg]. This new equation, which assumes that
emissions are linear with waste concentration, is as follows:
6-6
-------
IWAIR User 's Guide Section 6. 0
Cai, = (C^te^un* X ^ X DF (6-6)
where
Cair = air concentration (|j,g/m3)
CWaste = waste concentration (mg/kg)
Eunit = normalized volatile emission rate of constituent ([g/m2-s]/[mg/kg])
106 = unit conversion (|j,g/g)
DF = dispersion factor ([|j,g/m3]/[|j,g/m2-s]).
Equation 6-6 may be solved for waste concentration, as follows:
_ air
IWAIR uses this equation with both an aqueous-phase emission rate and an organic-phase
emission rate, to estimate an aqueous-phase waste concentration and an organic-phase waste
concentration.
For hexachlorobenzene in an aqueous-phase waste, plugging the air concentration
calculated above, the unitized emission rate for aqueous-phase waste shown in Table 6-3, and the
dispersion factor shown earlier into Equation 6-7 gives the following waste concentration:
5.03E-2
1.56E-9 x 106 x 3.37
= 9.57
For hexachlorobenzene in an organic-phase waste, plugging the air concentration
calculated above, the unitized emission rate for organic-phase waste shown in Table 6-3, and the
dispersion factor shown earlier into Equation 6-7 gives the following waste concentration:
5.03E-2
waste
1.12E-13 x 106 x 3.37
= 1.33E+5
In Step 5, IWAIR then examines these waste concentrations to ensure that they do not
exceed physical limits (i.e., soil saturation concentration for aqueous-phase wastes and 1E+6
mg/kg for organic-phase wastes). If either waste concentration exceeds the applicable limit, it is
6-7
-------
IWAIR User 's Guide Section 6. 0
discarded.1 If both values are possible, IWAIR selects the lower of the two as the allowable
concentration.
The soil saturation concentration for hexachlorobenzene, given the inputs in Table 6-1, is
26 mg/kg. Because the aqueous-phase concentration for hexachlorobenzene calculated above
(Cwaste = 9.57) does not exceed 26 mg/kg, it is possible and is not discarded. Similarly, the
organic-phase concentration does not exceed 1E+6 mg/kg, and is therefore possible and not
discarded. Since both aqueous-phase and organic-phase concentrations are possible, IWAIR
selects the lower of the two as the allowable concentration. In this case, the aqueous-phase waste
value is lower for the target risk of IE- 5; consequently, the allowable concentration for
hexachlorobenzene is 9.57 mg/kg, based on an aqueous-phase waste.
The calculations for Steps 4 and 5 are similar for acrolein. In an aqueous-phase waste,
plugging the air concentration calculated above, the unitized emission rate for aqueous-phase
waste shown in Table 6-3, and the dispersion factor shown earlier into Equation 6-7 gives the
following waste concentration:
2E-2
1.79E-9 x 106 x 3.37
= 3.32
For acrolein in an organic-phase waste, plugging the air concentration calculated above,
the unitized emission rate for organic-phase waste shown in Table 6-3, and the dispersion factor
shown earlier into Equation 6-7 gives the following waste concentration:
C = 2E-2
waste 7.28E-10 x 106 x 3.37
= 8.15
The soil saturation concentration for acrolein, given the inputs in Table 6-1, is about
45,700 mg/kg. Because the calculated aqueous-phase concentration for acrolein is below this
level, the value is possible and is not discarded.
Similarly, the organic-phase concentration does not exceed 1E+6 mg/kg and is therefore
possible and not discarded. Since both aqueous-phase and organic-phase concentrations are
possible, IWAIR selects the lower of the two as the allowable concentration. In this case, the
aqueous-phase waste value is lower. Thus, for a target HQ of 1, the allowable concentration of
acrolein is 3.32 mg/kg, based on an aqueous-phase waste.
1 If they are both discarded, the soil saturation limit or 1E+6 is used, whichever results in the greatest risk.
-------
IWAIR User's Guide Section 7.0
7.0 References
Shroeder, K., R. Clickner, andE. Miller. 1987. Screening Survey of Industrial Subtitle D
Establishments. Draft Final Report. Westat, Inc., Rockville, MD., for U.S. EPA Office of
Solid Waste. EPA Contract 68-01-7359. December.
U.S. EPA (Environmental Protection Agency). 1991. Hazardous Waste TSDF—Background
Information for Proposed Air Emissions Standards. EPA-450/3-89-023a. Office of Air
Quality Planning and Standards, Research Triangle Park, NC. Pp. C-19-C-30.
U.S. EPA (Environmental Protection Agency). 1993. Guidance on Air Quality Models
(Revised). EPA/450/2-78-027R. Office of Air Quality Planning and Standards, Research
Triangle Park, NC. February.
U.S. EPA (Environmental Protection Agency). 1995. User's Guide for the Industrial Source
Complex (ISC3) Dispersion Models. EPA-454/B-95-003a. Office of Air Quality
Planning and Standards, Research Triangle Park, NC.
U.S. EPA (Environmental Protection Agency). 1997a. Exposure Factors Handbook. Office of
Research and Development, National Center for Environmental Assessment.
U.S. EPA (Environmental Protection Agency). 1997b. Health Effects Assessment Summary
Tables (HEAST). EPA-540-R-97-036. FY 1997 Update.
U.S. EPA (Environmental Protection Agency). 2001. Integrated Risk Information System
(IRIS). National Center for Environmental Assessment, Office of Research and
Development, Washington, DC. Available online at http://www.epa.gov/iris/ Office of
Solid Waste and Emergency Response, Washington, DC.
7-1
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-------
Appendix A
Considering Risks from Indirect Pathways
-------
-------
IWAIR User's Guide
Appendix A
Appendix A
Considering Risks from Indirect Pathways
A. 1 What are "Indirect Risks" ?
Direct Pathways: An individual is directly exposed to
the contaminated medium, such as air or
groundwater, into which the chemical was released.
Indirect Pathways: An individual is indirectly
exposed when a contaminant that is released into one
medium (for example, air), is subsequently
transported to other media, such as water, soil, or
food, to which the individual comes in contact.
IWAIR assesses exposures by direct
inhalation of a contaminant. It is possible,
however, that environmental contaminants
can be transferred to other media resulting in
an indirect exposure to the pollutant. The
purpose of this section is to provide risk
assessors with information on health risks that
may result from volatile emissions other than
from the inhalation pathway. An indirect
pathway of exposure is when a contaminant
that is released into one medium (for
example, air) is subsequently transported to other media, such as water, soil, or food, to which a
receptor is exposed. For example, chemical vapors that are released from a WMU and
transported to an adjacent agricultural field may diffuse into vegetation, deposit on vegetation, or
may be taken up by vegetation from the soil. Individuals who subsequently eat the produce from
that field may be exposed to contaminants in their diet. Additional indirect exposures can occur
through the ingestion of contaminated fish, or animal products, such as milk, beef, pork, poultry,
and eggs.
Figure A-l shows these pathways graphically. The arrows indicate the flow of pollutants
through the pathways. Pollutants are released from a source, dispersed through the air, and
deposited on crops, pastures, soil, and surface water. From there, they may be taken up into
plants or animal tissues. Humans may then be exposed by ingesting soil (through hand-to-mouth
contact), ingesting plant products, or ingesting animal products (including fish). Although not
shown in Figure A-l, humans may also ingest groundwater and surface water as drinking water
sources. Groundwater exposures are modeled by the Industrial Waste Management Evaluation
Model (IWEM), and surface water sources of drinking water are presumed to be treated to
remove contaminants.
A-3
-------
IWAIR User's Guide
Appendix A
Dispersion
Figure A-l. Indirect exposure pathways.
A.2 Determining When Indirect Pathways May Be Important
There are two key factors a facility manager should consider when determining the need
to assess the human health risk from indirect pathways of exposure. First, only certain land uses
near a WMU may pose potential risks through indirect exposure pathways. Second, only certain
chemicals may have properties that favor indirect pathways. These two criteria are explained in
the following paragraphs.
A.2.1 Land Use
As described above, indirect exposures can occur when a vapor-phase constituent in the
air is transported into surface water or taken up by produce or by animal products (via feed plants
or surface water). However, these pathways are unlikely to be of concern unless the land use
near the site includes one or more of the following:
• Residential home-gardening
• Agriculture (including production of produce and animal products for human
consumption)
• Farms that grow feed for animals
A-4
-------
IWAIR User's Guide Appendix A
• Recreational fishing
• Recreational hunting areas.
A.2.2 Chemical Properties
In addition to land use, the chemical properties of the constituents in the waste are
important in determining whether indirect pathways are of potential concern. Some chemicals
exhibit properties that tend to favor indirect pathways, while others do not, or do so to a lesser
extent. The chemical properties of interest are those that reflect the tendency for a chemical to be
persistent in the environment, bioaccumulate in plants or animals, or be toxic when ingested.1 A
facility manager should consider these properties when determining whether an assessment of
indirect pathways may be necessary for the WMU. The following subsections provide a brief
description of some of the chemical properties that can be used to predict a constituent's
persistence, bioaccumulation potential, and toxicity.
Persistence
A chemical's persistence refers to how long the chemical remains in the environment
without being chemically or biologically broken down or altered. A chemical considered to be
highly persistent remains in the environment for a relatively long period of time, although it may
move through different media (e.g., from soil to water to sediment). Because persistent
chemicals remain in the environment, they can accumulate in environmental media and/or plant
and animal tissue. As a result, the temporal window for exposure through both direct and
indirect pathways may be extended, and the likelihood of exposure will increase. Persistence is
frequently expressed in terms of half-life. For example, if a chemical has a half-life of 2 days, it
will take 2 days for a given quantity of the chemical to be reduced by one-half due to chemical
and biological processes. The longer the half-life, the more persistent the chemical. A related
chemical property is degradation rate, which is inversely related to half-life. Thus, the lower the
degradation rate, the more persistent the chemical. Data on soil biodegradation rates are
presented for the IWAIR chemicals in Appendix B of the IWAIR Technical Background
Document; this property may be used as a general indicator of persistence potential.
Bioaccumulation Potential
Bioaccumulation potential refers to a chemical's tendency to accumulate in plants and
animals. For example, plants may accumulate chemicals from the soil through their roots. Some
of these chemicals are transformed or combined with others and used by the plant; others are
simply eliminated; and others accumulate in the plant roots, leaves, or edible parts of the plant.
Animals also bioaccumulate certain chemicals in different tissues or organs. For chemicals that
1 The tendency of chemical constituents to be persistent and bioaccumulate are a function of both the
chemical/physical attributes of the chemical (e.g., Kow) and the environmental setting (such as the physical
characteristics of the system, e.g., dissolved organic carbon, soil pH; or the biology of organisms that inhabit the
system, e.g., crops, fish species); however, it is convenient to think of persistence and bioaccumulation potential as
intrinsic properties when considering indirect exposure pathways.
A-5
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IWAIR User's Guide
Appendix A
bioaccumulate, the concentration in the plants and animals can be higher than the concentration
in the environment. As a result, a human who eats the plant or animal may be exposed to a
higher concentration in the food than in the contaminated medium.2 Bioaccumulation potential
may be expressed as a bioaccumulation factor (BAF) or a bioconcentration factor (BCF); these
factors express the relationship between the concentration in biota and the concentration in the
environmental medium. Bioaccumulation potential may also be expressed as a biotransfer factor
for animal products, representing the relationship between the exposure concentration and the
mass of contaminated plants ingested daily.
Chemicals that tend to accumulate in
plants and animal tissues often have a
characteristically high affinity for lipids (fats).
This tendency is reflected by the octanol-
water partition coefficient (Kow),3 a laboratory
measurement of the attraction of a chemical
to water versus its attraction to lipids (fats).
In these experiments, octanol is used as a
surrogate for lipids. Because chemicals with
higher Kow values have been shown to have a
greater tendency to accumulate in the fatty
tissue of animals, the BAF and BCF are
generally accepted as useful predictors of
bioaccumulation potential (see text box for
definitions and examples of other parameters
that are often used to evaluate indirect
exposures through the ingestion of produce
and animal products). Some chemicals with
high Kow values, such as polycyclic aromatic
hydrocarbons (PAHs), do not accumulate
appreciably in animals that have the capacity
to metabolize the chemical and eliminate it
from their systems. Moreover, this strong
affinity for lipids also means that the
chemical has a strong affinity for organic
carbon in soil and surface water. Chemical
contaminants that are strongly sorbed to the
organic component in soil may not be readily
taken up by plants. For example, dioxin is
poorly taken up from the soil by virtually all
species of plants that have been tested.
Parameters Used to Evaluate Indirect Exposures
BCF: Bioconcentration Factor for Fish. Defined as
the ratio of chemical concentration in the fish to the
concentration in the surface water. Fish are exposed
only to contaminated water.
BAF: Bioaccumulation Factor for Fish. Defined as
the ratio of the chemical concentration in fish to the
concentration in the surface water. Fish are exposed
to contaminated water and plants/prey.
BSAF: Biota-Sediment Accumulation Factor for
Fish. Generally applied only to highly hydrophobic
organic chemicals, and defined as the ratio of the
lipid-normalized concentration in fish to the organic
carbon-normalized concentration in surface sediment.
Fish are exposed to contaminated pore water,
sediment, and plants/prey.
Br: Plant-Soil Bioconcentration Factor. Defined as
the ratio between the chemical concentration in the
plant and the concentration in soil. It varies by plant
group (e.g., root vegetables, aboveground
vegetables).
Bv: Air-Plant Bioconcentration Factor. Defined as
the mass-based ratio between the chemical
concentration in the plant and the vapor-phase
chemical concentration in the air. It is varies by plant
group (e.g., leafy vegetables, forage).
Ba: Plant-Animal Biotransfer Factor. Defined as the
ratio between the chemical concentration in the
animal tissue and the amount of contaminant ingested
per day. It varies by type of animal tissue (e.g., beef,
milk).
Even though the concentration in food may not be significantly higher than in the environmental media,
the consumption rate of produce and meat/dairy products may lead to a substantial exposure to contaminants.
3 Because octanol-water coefficients can span many orders of magnitude, they are normally discussed in
terms of their log values (log Kow).
A-6
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IWAIR User's Guide Appendix A
Consequently, the use of chemical properties should be supplemented with information from
field studies to determine whether the chemical is of potential concern through indirect exposure
pathways. Data on log Kow are presented for the IWAIR chemicals in Appendix B of the IWAIR
Technical Background Document, they may be used as a first-cut indicator of bioaccumulation
potential. As a general rule, chemicals with relatively high Kow values tend to accumulate in
plants and animals to a greater extent than chemicals with relatively low Kow values.
Toxicity
The toxicity of chemicals to humans depends on the route of exposure—inhalation or
ingestion. IWAIR contains health benchmarks for inhalation exposures. However, the indirect
pathways discussed here refer to ingestion exposures. Therefore, even if a chemical is released
into the air and tends to bioaccumulate in plant or animal products, if it is not very toxic by the
ingestion pathway, then indirect pathways will be of less concern. Two benchmarks are used to
predict the toxicity of a contaminant that is ingested: the cancer slope factor (CSF, which
measures the tendency of a chemical to cause cancer) and the reference dose (RfD, which
provides a threshold below which a chemical is unlikely to result in adverse, noncancer health
effects). The CSF is a measure of carcinogenic potency; consequently, a larger value indicates
greater toxicity. However, the RfD is a threshold at which adverse effects are not expected;
therefore, a smaller value indicates greater toxicity.
Oral toxicity benchmarks are not used in IWAIR; therefore, for convenience, the oral
toxicity benchmarks (oral CSF and RfD) are presented for the IWAIR chemicals in Table A-l.
A.3 Additional Information
Indirect risk assessments are often site-specific, require a significant amount of
information about the area surrounding the WMU, and can be complex depending on the
chemicals of concern. However, indirect pathways should not be overlooked as a potential
source of risk if the chemical properties and surrounding land uses suggest potential risks
through indirect exposures.
If it appears that indirect pathways may be of concern, Methodology for Assessing Health
Risks Associated with Multiple Pathways of Exposure to Combustor Emissions (U.S. EPA,
1998b) presents guidance developed by the Agency for conducting indirect risk assessments for
most chemicals. This document can be used to determine whether further assessment of indirect
pathways is needed, and, if so, how to conduct such an assessment. For dioxin-like compounds,
indirect pathways are evaluated somewhat differently; see U.S. EPA (2000a), Exposure and
Human Health Reassessment of 2,3,7,8-Tetrachlorodibenzo-p-Dioxin (TCDD) and Related
Compounds. Part I: Estimating Exposure to Dioxin-Like Compounds.
A-7
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IWAIR User's Guide
Appendix A
Table A-l. Oral Health Benchmarks for IWAIR Chemicals
IWAIR Constituent Name
RfD RfD CSFo (per CSFo
CASRN (mg/kg-d) Source mg/kg-d) Source Comment
1,1, 1 ,2-Tetrachloroethane
1,1,1 -Trichloroethane
1 , 1 ,2,2-Tetrachloroethane
1 , 1 ,2-Trichloro-l ,2,2-trifluoroethane
1 , 1 ,2-Trichloroethane
1 , 1 -Dichloroethylene
1 ,2,4-Trichlorobenzene
1 ,2-Dibromo-3 -chloropropane
630-20-6
71-55-6
79-34-5
76-13-1
79-00-5
75-35-4
120-82-1
96-12-8
3.0E-02
2.8E-01
6.0E-02
3.0E+01
4.0E-03
9.0E-03
l.OE-02
IRIS
SF
SF
IRIS
IRIS
IRIS
IRIS
2.6E-02
2.0E-01
5.7E-02
6.0E-01
1.4E+00
IRIS
IRIS
IRIS
IRIS
HEAST intermediate MRL
1,2-Dichloroethane
107-06-2
available
9.1E-02 IRIS intermediate MRL
available
1 ,2-Dichloropropane
1 ,2-Diphenylhydrazine
1,2-Epoxybutane
1,3 -Butadiene
1,4-Dioxane
2,3,7,8-TCDD
2,4-Dinitrotoluene
2-Chlorophenol
2-Ethoxyethanol
2-Ethoxyethanol acetate
2-Methoxyethanol
2-Methoxyethanol acetate
2-Nitropropane
3 ,4-Dimethylphenol
3 -Methylcholanthrene
7, 12-Dimethylbenz[a]anthracene
78-87-5 9.0E-02 ATSDR 6.8E-02 HEAST
122-66-7 8.0E-01 IRIS
106-88-7
106-99-0
123-91-1 1.1E-02 IRIS
1746-01-6 l.OE-09 ATSDR 1.5E+05 HEAST
121-14-2 2.0E-03 IRIS 6.8E-01 IRIS CSFo is for 2,4-72,6-
mixture
95-57-8 5.0E-03 IRIS
HO-80-5 4.0E-01 HEAST
111-15-9 3.0E-01 HEAST
109-86-4 l.OE-03 HEAST
110-49-6 2.0E-03 HEAST
79-46-9
95-65-8 l.OE-03 IRIS
56-49-5
57-97-6
(continued)
A-8
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IWAIR User's Guide
Appendix A
IWAIR Constituent Name
Acetaldehyde
Acetone
Acetonitrile
Acrolein
Acrylamide
Acrylic acid
Acrylonitrile
Allyl chloride
Aniline
Benzene
Benzidine
Benzo(a)pyrene
Bromodichloromethane
Carbon disulfide
Carbon tetrachloride
Chlorobenzene
Chlorodibromomethane
Chloroform
Chloroprene
cis- 1 , 3 -Dichloropropylene
Table
CASRN
75-07-0
67-64-1
75-05-8
107-02-8
79-06-1
79-10-7
107-13-1
107-05-1
62-53-3
71-43-2
92-87-5
50-32-8
75-27-4
75-15-0
56-23-5
108-90-7
124-48-1
67-66-3
126-99-8
10061-01-5
A-l. (continued)
RfD
(mg/kg-d)
l.OE-01
2.0E-02
2.0E-04
5.0E-01
l.OE-03
3.0E-03
2.0E-02
l.OE-01
7.0E-04
2.0E-02
2.0E-02
l.OE-02
2.0E-02
3.0E-02
RfD CSFo(per CSFo
Source mg/kg-d) Source Comment
IRIS
HEAST
IRIS 4.5E+00 IRIS
IRIS
HEAST 5.4E-01 IRIS
5.7E-03 IRIS
5.5E-02 IRIS upper range estimate
used for CSFo
IRIS 2.3E+02 IRIS
7.3E+00 IRIS
IRIS 6.2E-02 IRIS
IRIS
IRIS 1.3E-01 IRIS
IRIS
IRIS 8.4E-02 IRIS
IRIS
HEAST
IRIS l.OE-01 IRIS RfD & CSFo are for
Cresols (total)
Cumene
Cyclohexanol
Dichlorodifluoromethane
Epichlorohydrin
1319-77-3 5.0E-02 surr
98-82-8 l.OE-01 IRIS
108-93-0 1.7E-05 solvents
75-71-8 2.0E-01 IRIS
106-89-8 2.0E-03 HEAST 9.9E-03
1,3 -dichloropropene
RfD is for m-cresol
IRIS
(continued)
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IWAIR User's Guide
Appendix A
Table A-l. (continued)
IWAIR Constituent Name
Ethylbenzene
Ethylene dibromide
Ethylene glycol
Ethylene oxide
Formaldehyde
Furfural
Hexachloro- 1 , 3 -butadiene
Hexachlorobenzene
Hexachlorocyclopentadiene
Hexachloroethane
Isophorone
Mercury
Methanol
Methyl bromide
Methyl chloride
Methyl ethyl ketone
Methyl isobutyl ketone
Methyl methacrylate
Methyl tert-butyl ether
Methylene chloride
N,N-Dimethyl formamide
Naphthalene
n-Hexane
Nitrobenzene
N-Nitrosodiethylamine
N-Nitrosodi-n-butylamine
CASRN
100-41-4
106-93-4
107-21-1
75-21-8
50-00-0
98-01-1
87-68-3
118-74-1
77-47-4
67-72-1
78-59-1
7439-97-6
67-56-1
74-83-9
74-87-3
78-93-3
108-10-1
80-62-6
1634-04-4
75-09-2
68-12-2
91-20-3
110-54-3
98-95-3
55-18-5
924-16-3
RfD
(mg/kg-d)
l.OE-01
2.0E+00
2.0E-01
3.0E-03
3.0E-04
8.0E-04
6.0E-03
l.OE-03
2.0E-01
l.OE-04
5.0E-01
1.4E-03
6.0E-01
8.0E-02
1.4E+00
6.0E-02
l.OE-01
2.0E-02
1.1E+01
5.0E-04
RfD CSFo(per CSFo
Source mg/kg-d) Source Comment
IRIS
8.5E+01 IRIS
IRIS
l.OE+00 HEAST
IRIS
IRIS
SF 7.8E-02 IRIS
IRIS 1.6E+00 IRIS
IRIS
IRIS 1.4E-02 IRIS
IRIS 9.5E-04 IRIS
surr RfD is for methyl
mercury
IRIS
IRIS
1.3E-02 HEAST
IRIS
HEAST
IRIS
intermediate MRL
available
IRIS 7.5E-03 IRIS
HEAST
IRIS
SF
IRIS
1.5E+02 IRIS
5.4E+00 IRIS
(continued)
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IWAIR User's Guide
Appendix A
Table A-l. (continued)
IWAIR Constituent Name
N-Nitrosopyrrolidine
o-Dichlorobenzene
o-Toluidine
p-Dichlorobenzene
Phenol
Phthalic anhydride
Propylene oxide
Pyridine
Styrene
Tetrachloroethylene
Toluene
trans- 1 , 3 -Dichloropropylene
Tribromomethane
Trichloroethylene
Trichlorofluoromethane
Triethylamine
Vinyl acetate
Vinyl chloride
Xylenes
RfD RfD CSFo(per CSFo
CASRN (mg/kg-d) Source mg/kg-d) Source
930-55-2 2.1E+00 IRIS
95-50-1 9.0E-02 IRIS
95-53-4 2.4E-01 HEAST
106-46-7 2.4E-02 HEAST
108-95-2 6.0E-01 IRIS
85-44-9 2.0E+00 IRIS
75-56-9 2.4E-01 IRIS
110-86-1 l.OE-03 IRIS
100-42-5 2.0E-01 IRIS
127-18-4 l.OE-02 IRIS 5.2E-02 HAD
108-88-3 2.0E-01 IRIS
10061-02-6 3.0E-02 IRIS l.OE-01 IRIS
75-25-2 2.0E-02 IRIS 7.9E-03 IRIS
79-01-6 1.1E-02 HAD
75-69-4 3.0E-01 IRIS
121-44-8
108-05-4 l.OE+00 HEAST
75-01-4 3.0E-03 IRIS 7.2E-01 IRIS
1330-20-7 2.0E+00 IRIS
Comment
intermediate MRL
available
RfD & CSFo are for
1 ,3 -dichloropropene
CSFo is for
continuous adult
exposure
a Sources:
ATSDR = ATSDR oral minimal risk levels (ATSDR, 200 1)
IRIS = Integrated Risk Information System (U.S. EPA, 200 1)
HEAST = Health Effects Assessment Summary Tables (U.S. EPA, 1997a)
HAD = Health Assessment Document (U.S. EPA, 1986, 1987)
SF = Superfund Risk Issue Paper (U.S. EPA, 1998c, 1999a, 1999b, 2000b)
solvents = 63 FR 64371-0402 (U.S. EPA, 1998a)
surr = surrogate
A-ll
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IWAIR User 's Guide Appendix A
Finally, as noted above, various chemical properties indicative of the potential for indirect
pathway concern are presented in the IWAIR Technical Background Document for IWAIR
chemicals. For other chemicals, the following sources may be useful:
• EPA' s Superfund Chemical Data Matrix (SCDM) (U. S. EPA, 1 997b)
• The Merck Index (Budavari, 1996)
• The National Library of Medicine's Hazardous Substances Databank (HSDB),
available on TOXNET (U.S. NLM, 2001)
• Syracuse Research Corporation' s CHEMF ATE database (SRC, 1 999)
• CambridgeSoft.com's ChemFinder database (CambridgeSoft, 2001)
• Agency for Toxic Substances and Disease Registry (ATSDR) Toxicological
Profiles (ATSDR, 2001)
• EPA's Dioxin Reassessment (U.S. EPA, 2000a) — for dioxins only
Half-life
• Howard etal. (1991)
Toxicity (in order of preference)
• Integrated Risk Information System (IRIS) (U.S. EPA, 2001)
• Superfund Technical Support Center Provisional Benchmarks (U.S. EPA, 1998c,
1999a, 1999b, 2000b)
• Health Effects Assessment Summary Tables (HEAST) (U.S. EPA, 1997a)
• Agency for Toxic Substances and Disease Registry oral minimal risk levels
(MRLs) (ATSDR, 2001)
• California Environmental Protection Agency (CalEPA) cancer potency factors
(CalEPA, 1999)
• EPA health assessment documents (U.S. EPA, 1986, 1987, 1998a).
A-12
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IWAIR User's Guide Appendix A
A.4 References
ATSDR (Agency for Toxic Substances and Disease Registry). 2001. Minimal Risk Levels
(MRLs)for Hazardous Substances. http://atsdrl.atsdr.cdc.gov:8080/mrls.html
Budavari, S. (Ed.). 1996. The Merck Index, An Encyclopedia of Chemicals, Drugs, and
Biologicals. 12th Edition. Merck & Co. Inc., Rahway, NJ.
CalEPA (California Environmental Protection Agency). 1999. Air Toxics Hot Spots Program
Risk Assessment Guidelines: Part II. Technical Support Document for Describing
Available Cancer Potency Factors. Office of Environmental Health Hazard Assessment,
Berkeley, CA. Available online at http://www.oehha.org/scientific/hsca2.htm.
CambridgeSoft Corporation. 2001. ChemFinder.com database and internet searching.
http://chemfmder.cambridgesoft.com. Accessed July 2001.
Howard, P.H., R.S. Boethling, W.F. Jarvis, W.M. Meylan, E.M. Michalenko, and H.T. Printup
(Ed.). 1991. Handbook of Environmental Degradation Rates. Lewi s Publi shers,
Chelsea, MI.
Syracuse Research Corporation (SRC). 1999. CHEMFATE Chemical Search, Environmental
Science Center, Syracuse, NY. http://esc.syrres.com/efdb/Chemfate.htm. Accessed July
2001.
U.S. EPA (Environmental Protection Agency). 1986. Addendum to the Health Assessment
Document for Tetrachloroethylene (Perchloroethylene). Updated Carcinogenicity
Assessment for Tetrachloroethylene (Perchloroethylene, PERC, PCE). External Review
Draft. EPA/600/8-82-005FA. Office of Health and Environmental Assessment, Office of
Research and Development, Washington DC.
U.S. EPA (Environmental Protection Agency). 1987. Addendum to the Health Assessment
Document for Trichloroethylene. Updated Carcinogenicity Assessment for
Trichloroethylene. External Review Draft. EPA/600/8-82-006FA. Office of Health and
Environmental Assessment, Office of Research and Development, Washington DC.
U.S. EPA (Environmental Protection Agency). 1997a. Health Effects Assessment Summary
Tables (HEAST). EPA-540-R-97-036. FY 1997 Update.
U.S. EPA (Environmental Protection Agency). 1997b. Superfund Chemical Data Matrix
(SCDM). Office of Emergency and Remedial Response. Web site at
http://www.epa.gov/oerrpage/superfund/resources/scdm/index.htm. June.
U.S. EPA (Environmental Protection Agency). 1998a. Hazardous waste management system;
identification and listing of hazardous waste; solvents; final rule. Federal Register
63 FR 64371-402.
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IWAIR User's Guide Appendix A
U.S. EPA (Environmental Protection Agency). 1998b. Methodology for Assessing Health Risks
Associated with Multiple Pathways of Exposure to Combustor Emissions. Update to
EPA/600/6-90/003 Methodology for Assessing Health Risks Associated with Indirect
Exposure to Combustor Emissions. EPA 600/R-98/137. National Center for
Environmental Assessment, Cincinnati, OH.
U.S. EPA (Environmental Protection Agency). 1998c. Risk Assessment Paper for: Evaluation
of the Systemic Toxicity of Hexachlorobutadiene (CASRN 87-68-3) Resulting from Oral
Exposure. 98-009/07-17-98. National Center for Environmental Assessment. Superfund
Technical Support Center, Cincinnati, OH.
U.S. EPA (Environmental Protection Agency). 1999a. Risk Assessment Issue Paper for:
Derivation of Provisional Oral Chronic RfD and Subchronic RfDsfor 1,1,1-
Trichloroethane (CASRN 71-55-6). 98-025/8-4-99. National Center for Environmental
Assessment. Superfund Technical Support Center, Cincinnati, OH.
U.S. EPA (Environmental Protection Agency). 1999b. Risk Assessment Paper for: An Updated
Systemic Toxicity Evaluation of n-Hexane (CASRN 110-54-3). 98-019/10-1-99. National
Center for Environmental Assessment. Superfund Technical Support Center, Cincinnati,
OH.
U.S. EPA (Environmental Protection Agency). 2000a. Exposure and Human Health
Reassessment of 2,3,7,8-Tetrachlorodibenzo-p-Dioxin (TCDD) and Related Compounds.
Part I: Estimating Exposure to Dioxin-Like Compounds. Volume 3—Properties,
Environmental Levels, and Background Exposures. Draft Final Report. EPA/600/P-
00/001. Office of Research and Development, Washington, DC. September.
U.S. EPA (Environmental Protection Agency). 2000b. Risk Assessment Paper for: Derivation
of a Provisional RfD for 1,1,2,2-Tetrachloroethane (CASRN 79-34-5). 00-122/12-20-00.
National Center for Environmental Assessment. Superfund Technical Support Center,
Cincinnati, OH.
U.S. EPA (Environmental Protection Agency). 2001. Integrated Risk Information System
(IRIS). National Center for Environmental Assessment, Office of Research and
Development, Washington, DC. Available online at http://www.epa.gov/iris/ Office of
Solid Waste and Emergency Response, Washington, DC.
U.S. NLM (National Library of Medicine). 2001. Hazardous Substances Data Bank (HSDB).
http://toxnet.nlm.nih.gov/cgi-bin/sis/htmlgen7HSDB. Accessed July 2001.
A-14
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Appendix B
Parameter Guidance
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IWAIR User's Guide Appendix B
Appendix B
Parameter Guidance
This appendix provides you with guidance on all parameter values needed to run IWAIR.
This guidance covers all parameters that you may enter in text boxes and most selections from
drop-down boxes. It does not include most option buttons, as those are covered in the
operational guidance in Sections 4 and 5. However, a few options are covered here, as well as in
Sections 4 and 5.
This appendix is organized by screen. Some parameters are applicable only to risk mode
or allowable concentration mode; those are so noted.
B.I Method, Met. Station, WMU (Screen 1A)
Most of the options on Screen 1A are covered in the operational guidance in Sections 4
and 5. There are only two parameters for this screen: zip code and latitude/longitude. You will
only need to enter data for one or the other.
Zip Code. This is the 5-digit zip code for the physical location of your facility. IWAIR
uses this zip code to assign the most appropriate meteorological station to your site; therefore,
you should not use the zip code from a mailing address, such as a post office box or a company
headquarters. The zip code database includes zip codes established through 1999. If your
facility has a new zip code that was established more recently, you will get an error message
indicating that it is not a valid zip code, because it is not in IWAIR's database. If this occurs,
you can use your old zip code, use a nearby zip code, or select a meteorological station using
latitude and longitude.
Latitude and Longitude. These are the latitude and longitude coordinates for the
physical location of your facility. At a minimum, the program requires that degrees for latitude
and longitude be entered. If available, the minutes and seconds should be supplied to ensure that
the most appropriate station is selected for a site. Latitude and longitude can be obtained from
most maps of the area where your facility is located.
B-3
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IWAIR User's Guide Appendix B
B.2 Wastes Managed and Add/Modify Chemicals (Screens 2A and 2B)
B.2.1 Wastes Managed
Sections 4 and 5 cover the selection of chemicals for your waste. There is only one
parameter to be entered on Screen 2A: waste concentration. This is only needed for risk
calculations.
Waste Concentration (mg/L or mg/kg). This is the concentration of each chemical in
your waste. It should reflect the waste or influent going into your unit, not the concentration
within the unit. For surface impoundments, it should be in mg/L or ppm. For land application
units, landfills, and waste piles, it should be in mg/kg or ppm. This value must be greater than
zero; the sum of all concentrations entered must be less than or equal to one million.
B.2.2 Add/Modify Chemicals (Screen 2B)
The ADD/MODIFY CHEMICALS screen requires you to enter numerous chemical-specific
parameters. These are organized below into chemical identifiers, physical-chemical properties,
and health benchmarks.
B.2.2.1 Chemical Identifiers
Chemical Name. If you are entering a new chemical, you can enter the chemical name
here. If you are modifying or making a new entry for an existing chemical, you will not need to
enter a chemical name; IWAIR will fill it in automatically. Do not add any user designation to
the end of the chemical name you enter—IWAIR will do that automatically. Enter the chemical
name exactly as you would like it to sort and display. For example, if you want 1,2,4-
trichlorobenzene to sort under T instead of 1, enter it as "trichlorobenzene, 1,2,4-".
CAS Number. If you are entering a new chemical, you can enter the Chemical Abstracts
Service (CAS) number here. If you are modifying or making a new entry for an existing
chemical, you will not need to enter a CAS number; IWAIR will fill it in automatically. IWAIR
does not use leading zeros on CAS numbers; therefore, for consistency with the data provided
with IWAIR, it is recommended that you use leading spaces instead of leading zeros for CAS
numbers shorter than the maximum length.
B.2.2.2 Physical-Chemical Properties. Data on many physical-chemical properties can
be obtained from the following sources:
• EPA's Superfund Chemical Data Matrix (SCDM) (U. S. EPA, 1997b),
• The Merck Index (Budavari, 1996),
• The National Library of Medicine's Hazardous Substances Databank (HSDB),
available on TOXNET (U.S. NLM, 2001),
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IWAIR User's Guide Appendix B
• Syracuse Research Corporation's CHEMFATE database (SRC, 1999),
• CambridgeSoft.com's ChemFinder database (CambridgeSoft, 2001), and
• Agency for Toxic Substances and Disease Registry (ATSDR) Toxicological
Profiles (ATSDR, 2001).
In addition, a useful source of data on chemical properties for dioxins is EPA's Dioxin
Reassessment (U.S. EPA, 2000a).
Molecular Weight (g/mol). Molecular weight is used to estimate emissions. Values can
be obtained from the literature, including from the SCDM; HSDB; and CHEMF ATE. This value
must be greater than or equal to 1 g/mol (the molecular weight of a single hydrogen ion). No
maximum limit is enforced. IWAIR has been tested for molecular weights between 1 and 400
g/mol.
Density (g/cm3). IWAIR uses density to determine if chemicals present in organic phase
in surface impoundments are likely to float (if they are less dense than water) or sink (if they are
more dense that water). Unless the value is very near 1 g/cm3 (the density of water), the model is
not sensitive to variations in the value. Values can be obtained from the literature, including
from the SCDM; Merck Index; and HSDB. This value must be greater than zero. No maximum
limit is enforced. IWAIR has been tested for densities between 0.01 and 14 g/cm3.
Vapor Pressure (mmHg). Vapor pressure and the mole fraction in the liquid phase are
used to calculate the constituent's partial vapor pressure. The partial vapor pressure is
subsequently used as the partition coefficient for organic-phase wastes and aqueous-phase wastes
with chemicals present above solubility or saturation limits. Values can be obtained from the
literature, including from the SCDM and HSDB. Vapor pressure may be reported in other units,
such as atmospheres or torr; torr is equivalent to mmHg, but data in atmospheres will need to be
converted. Different vapor pressures may be reported for the same chemical at different
temperatures. For best results, choose a vapor pressure reported at a temperature around
20-25°C. This value must be greater than zero. No maximum limit is enforced. IWAIR has
been tested for vapor pressures between 0 and 5,300 mmHg.
Henry's Law Constant (atm-n^/mol). Henry's law constant reflects the tendency of
chemicals to volatilize from dilute aqueous solutions; it is used as the partition coefficient for
aqueous-phase wastes with chemicals present below solubility or saturation limits. Values can
be obtained from the literature, including from the SCDM; 2000 Dioxin Reassessment (for
dioxins); HSDB; CHEMF ATE; and ChemFinder. If Henry's law constant is not available, it can
be calculated from the chemical's vapor pressure, molecular weight, and solubility using the
following equation (Lyman et al., 1990):
H =
X
uoooJ
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IWAIR User 's Guide Appendix B
where
H = Henry' s law constant (atm-m3/mol)
VP = vapor pressure (mmHg)
S = solubility (mg/L)
MW = molecular weight (g/mol)
760 = unit conversion (mmHg/atm)
1000 = unit conversion (L/m3)
1000 = unit conversion (mg/g).
The value for Henry's law constant must be greater than zero. No maximum limit is enforced.
IWAIR has been tested for Henry's law constants between 4E- 1 1 and 1.2 atm-m3/mol-K.
Solubility (mg/L). This is the solubility of the individual chemical in water. Solubility is
used for surface impoundments to identify wastes that may be supersaturated so that emissions
equations may be based on the most appropriate partition coefficient (Henry's law for aqueous-
phase wastes below saturation or solubility limits, and partial vapor pressure for wastes above
saturation or solubility limits and organic-phase wastes). Values can be obtained from the
literature, including from the SCDM; Merck Index; Dioxin Reassessment (for dioxins); HSDB;
and CHEMFATE. This value must be greater than zero and less than or equal to one million.
IWAIR has been tested for solubilities from 1.93E-5 to 1,000,000 mg/L.
Soil Biodegradation Rate (s'1). The soil biodegradation rate is a first-order rate constant
used to estimate soil biodegradation losses in land application units, landfills, and waste piles.
The tendency to biodegrade in soil is often reported as half-life; this is not comparable to
biodegradation rate and should not be used in IWAIR. However, you can calculate the soil
biodegradation rate from the half-life as follows:
k =
tl/2
where
ks = soil biodegradation rate (s"1)
ln(2) = natural log of 2
t1/2 = half-life (s).
An excellent reference for soil biodegradation data (and the one used for all soil biodegradation
rates included with IWAIR) is Howard et al. (1991). This reference provides both high-end and
low-end half-life data for soil biodegradation. The high-end values were used in IWAIR. In
general, half-lives are reported in hours. Values for very short half-lives are given in minutes or
seconds. All values, except the ones already given in seconds, must be converted to seconds
before using the above equation to convert to biodegradation rate. The soil biodegradation rate
may be zero if the chemical does not biodegrade; however, because a zero value would cause
IWAIR to try to divide by zero, IWAIR converts values entered as zero to 1E-20, which results
B-6
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IWAIR User's Guide Appendix B
in negligible biodegradation. No maximum limit is enforced. IWAIR has been tested for soil
biodegradation rates from IE-20 to 0.0004 s"1.
Antoine's Constants: A, B, or C. Antoine's constants are used to adjust vapor pressure
and Henry's law constant to ambient temperature. While not explicitly reported with units, they
are intended to adjust vapor pressure in mmHg based on temperature in degrees Celsius. Values
for Antoine's constants are available in Reid et al. (1977). A and B must be greater than or equal
to zero. C may be negative. No maximum limits are enforced. IWAIR has been tested for A
values from 0 to 14; B values from 0 to 5,400; and C values from 0 to 292.
Diffusivity in Water (cnf/s). Diffusivity in water is used to estimate emissions.
Diffusivity in water can be calculated from the chemical's molecular weight and density, using
the following correlation equation based on Water9 (U.S. EPA, 2001c):
» = 0.0001518X
where
Dw = diffusivity in water (cm2/s)
T = temperature (°C)
273.16 = unit conversion (°C to °K)
MW = molecular weight (g/mol)
p = density (g/cm3).
If density is not available, diffusivity in water can be calculated using the following correlation
equation based on U.S. EPA (1987b):
D,= 0.00022 x
The value for diffusivity in water must be greater than zero. No maximum limit is enforced.
IWAIR has been tested for values of diffusivity in water from 5E-6 to 3E-5 cm2/s.
Diffusivity in Air (cnf/s). Diffusivity in air is used to estimate emissions. Diffusivity in
air can be calculated from the chemical's molecular weight and density, using the following
correlation equation based on Water9 (U.S. EPA, 200Ic):
0.00229 X(T +273.16) 1-5xJ0.034 + *MWcor
V V MWy
0.333
B-7
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IWAIR User's Guide Appendix B
where
Da = diffusivity in air (cm2/s)
T = temperature (°C)
273.16 = unit conversion (°C to °K)
MW = molecular weight (g/mol)
p = density (g/cm3).
MWcor = molecular weight correlation:
MWOT = (l-0.000015xMW2)
If MWcor is less than 0.4, then MWcor is set to 0.4.
If density is not available, diffusivity in air can be calculated using the following correlation
equation based on U.S. EPA (1987b):
-f-V
= 1.9x1 MW Uj
For dioxins, diffusivity in air can be calculated from the molecular weight using the following
correlation equation based on EPA's Dioxin Reassessment (U.S. EPA, 2000a):
x0-068
Diffusivity in air values must be greater than or equal to zero. No maximum limit is enforced.
IWAIR has been tested for values of diffusivity in air from 0 to 0.25 cm2/s.
Octanol-Water Partition Coefficient (log Kon). Km is used to estimate emissions and to
calculate the soil saturation concentration limit for land application units, landfills, and waste
piles. Because Km can cover an extremely wide range of values, it is typically reported as the log
of Km and should be entered as the log in IWAIR. Values can be obtained from the literature,
including the SCDM. Log Kow is unitless. Log Kow may have negative values, reflecting Km
values less than 1. Due to model limitations, log Kow may not be less than -10 or greater than 10;
IWAIR has been tested for this entire range.
Hydrolysis Constant (s'1). This value, which is used to estimate losses by hydrolysis, is
the hydrolysis rate constant at neutral pH. An excellent source of data on hydrolysis rate
constants (and the one used for all hydrolysis rate constants included with IWAIR) is Kollig
(1993). The hydrolysis constant may be zero if the chemical does not hydrolyze; it cannot be less
than zero. No maximum limit is enforced. IWAIR has been tested for values of hydrolysis
constants from 0 to 22 s"1.
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IWAIR User's Guide Appendix B
Kj (L/g-h). Kj is used to estimate biodegradation losses in surface impoundments. There
are very few literature sources for K,. The primary source of data is Coburn et al. (1988). Values
for K! in CHEMDAT8 and IWAIR were taken from this source. If you have rate study data at
very low concentrations, that rate can be used for K,. K, may be zero if the chemical does not
biodegrade; it cannot be less than zero. No maximum limit is enforced. IWAIR has been tested
for values of K, from 0 to 25 L/g-h.
Kmax (mg volatile organics/g-h). Kmax is used to estimate biodegradation losses in surface
impoundments. There are very few literature sources for Kmax. The primary source of data is
Coburn et al. (1988). Values for Kmax in CHEMDAT8 and IWAIR were taken from this source.
If you have rate study data at very high concentrations, that rate can be used forKmax. Kmax may
be zero if the chemical does not biodegrade; it cannot be less than zero. No maximum limit is
enforced. IWAIR has been tested for values of Kmax from 0 to 100 mg VO/g-h.
B.2.2.3 Health Benchmarks
Cancer Slope Factor (CSF) (mg/kg/d)'1. The inhalation CSF is used to evaluate risk for
carcinogens. The CSF is an upper-bound estimate (approximating a 95 percent confidence limit)
of the increased human cancer risk from a lifetime exposure to an agent. Inhalation CSFs are
used in the model for carcinogenic constituents, regardless of the availability of an RfC. If a
value for the inhalation CSF is not available, you should enter "NA" in the CSF field, rather than
zero. IWAIR must have a numeric value for either the inhalation CSF or RfC to calculate risk or
allowable concentration. If a numeric value is entered, it must be greater than zero. No
maximum limit is enforced. IWAIR has been tested for CSF values from 0.00001 to 150,000
(mg/kg/d)-1.
Reference Concentration (RfC) (mg/m3). The RfC is used to evaluate noncancer hazards
posed by inhalation exposures to chemicals. The RfC is an estimate (with uncertainty spanning
perhaps an order of magnitude) of a daily exposure to the human population (including sensitive
subgroups) that is unlikely to pose an appreciable risk of deleterious noncancer effects during an
individual's lifetime. If a value for the RfC is not available, you should enter "NA" in the RfC
field, rather than zero. IWAIR must have a numeric value for either the inhalation CSF or RfC to
calculate risk or allowable concentration. If a numeric value is entered, it must be greater than
zero. No maximum limit is enforced. IWAIR has been tested for RfC values from 0.00001 to
40 mg/m3.
Human health benchmarks contained in databases developed by EPA were used
whenever available. Benchmarks were obtained in the following order of preference:
• Integrated Risk Information System (IRIS) (U.S. EPA, 2001b)
• Superfund Technical Support Center Provisional Benchmarks (U.S. EPA, 1998b,
1999a, 1999b, 2000b)
• Health Effects Assessment Summary Tables (HEAST) (U.S. EPA, 1997a)
B-9
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IWAIR User's Guide Appendix B
• Agency for Toxic Substances and Disease Registry (ATSDR) minimal risk levels
(MRLs) (ATSDR, 2001)
• California Environmental Protection Agency (CalEPA) chronic inhalation
reference exposure levels (RELs) and cancer potency factors (CalEPA, 1999a,
1999b, 2000)
• EPA health assessment documents (U.S. EPA, 1986, 1987a, 1998a)
• Various other EPA health benchmark sources.
B.3 WMU Data for CHEMDAT8 (Screens 3A through 3D)
B.3.1 WMU Data for CHEMDAT8 - Surface Impoundment (Screen 3A)
B.3.1.1 Meteorological Station Parameters. These inputs are used only for the
emissions modeling, not the dispersion modeling, which uses hourly meteorological data, not
annual averages. Therefore, changes to these inputs will not affect the dispersion factors.
Wind Speed (m/s). IWAIR uses wind speed to select the most appropriate empirical
emission correlation equation in CHEMDAT8; there are several of these correlations, and each
one applies to a specific range of wind speeds and unit sizes. By default, IWAIR uses the
average annual wind speed from the meteorological station that was assigned to your location.
However, you may wish to override the default if you have site-specific data on wind speed. If
you do override, you should use an overall annual average in all directions, not any measure of
peak wind speed or average only in the prevailing wind direction. Also, wind speed is often
reported in knots or mph. However, for use in IWAIR, wind speed must be converted to m/s.
This value must be greater than zero. No maximum limit is enforced. IWAIR has been tested
for values of wind speed from 0.01 to 100 m/s; however, a realistic range for average annual
wind speed is about 2 to 10 m/s.
Temperature (°C). IWAIR uses temperature to correct various temperature-dependent
chemical properties used in emissions modeling (Henry's law constant and vapor pressure) from
a standard temperature to the ambient temperature. By default, IWAIR uses the average annual
temperature from the meteorological station that was assigned to your location. However, you
may wish to override the default if you have site-specific data on temperature. If you do
override, you should use an annual average temperature. Temperature may be reported in
degrees Fahrenheit (°F); however, for use in IWAIR, temperature must be converted to degrees
Celsius (°C). This value must be greater than or equal to -100°C. No maximum limit is
enforced. IWAIR has been tested for values of temperature from 0 to 50°C.
B.3.1.2 SI Dimensions, Loading Information
Biodegradation (on/off). This option, in conjunction with the ACTIVE BIOMASS input, allows
you to determine what type of biodegradation is modeled for your unit. In biologically active
surface impoundments, two processes occur: growth of biomass, which provides a growing
B-10
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IWAIR User's Guide Appendix B
matrix for chemical adsorption and loss through settling, and direct biodegradation of chemical
constituents as the bacteria that compose the biomass consume constituent mass. Direct
biodegradation cannot occur if there is no active biomass. If an impoundment is biologically
active, it may go through a transitional period during which there is active biomass (so
adsorption and settling losses occur) but the biomass is not yet adapted to consume the specific
chemicals present (so direct biodegradation is not occurring). This transitional period will
usually end as the biomass acclimate and adapt to the chemicals present.
Setting biodegradation to I OFF | turns off direct biodegradation. It does not affect
adsorption loss. Setting active biomass to zero turns off biomass growth, so that adsorption
losses are limited to adsorption to inlet solids. Setting active biomass to zero also turns off direct
biodegradation (in fact, if you have set biodegradation |ON I and then set active biomass to zero,
IWAIR will automatically reset the biodegradation option to I OFF |). If you set biodegradation to
I OFF |, IWAIR will remove the default value for active biomass, and you will have to enter a
value (typically zero, but this is not required, and it may be greater than zero if you wish to model
the transitional period before direct biodegradation occurs).
If your impoundment is biologically active, it recommended that you leave
biodegradation set to I ON I (the default). If your impoundment is not biologically active, it is
recommended that you set biodegradation to I OFF | and active biomass to zero.
Operating Life (yr). This parameter is the expected remaining operating life of your unit,
from the time you are modeling until you expect it to be closed. Operating life does not affect
emissions estimates for surface impoundments, which are modeled at steady state. However,
operating life may affect exposure duration. IWAIR uses default exposure durations of 30 years
for residents and 7.2 years for workers. However, proper closure of a surface impoundment
typically ends all exposures. Therefore, if the operating life you specify is less than 30 or 7.2
years, IWAIR caps the exposure duration at the operating life. Values in excess of 30 years will
not affect the results for residents, and values in excess of 7.2 years will not affect the results for
workers. Operating life should be entered in years. This value must be greater than zero. No
maximum limit is enforced. IWAIR has been tested for values of operating life from 0.01 to 100
years.
Depth of Unit (m). This is the average depth of your unit in meters (m). If your unit is
not a constant depth, use the average or most typical depth. If you have depth reported in units
such as feet, you will need to convert them to meters. This value must be greater than zero. No
maximum limit is enforced. IWAIR has been tested for values of depth from 0.01 to 30 m.
Area of Unit (m2). This is the total surface area of your unit in m2. Areas may be
reported in acres or hectares; these values will need to be converted to m2 for use in IWAIR.
This value must be greater than or equal to 81 m2 and less than or equal to 8,090,000 m2; these
are the smallest and largest areas for which IWAIR can interpolate dispersion factors for ground-
level sources. IWAIR has been tested for this full range.
Annual Flow of Waste (m3/yr). This is the total amount of waste that flows through your
impoundment in a year, in m3/yr. Flow is often reported in millions of gallons per day (MGD) or
B-ll
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IWAIR User's Guide
Appendix B
other units; you will need to convert to m3/yr for use in IWAIR. This value must be greater than
zero. No maximum limit is enforced. IWAIR has been tested for values of annual flow of waste
from 0.01 to 10,000,000 nrVyr.
B.3.1.3 Aeration Option Information
Type of Aeration. This option allows you to identify whether your impoundment is
aerated and, if so, the specific type of aeration. IWAIR can model no aeration (quiescent),
diffused air aeration, mechanical aeration, and both (diffused air and mechanical).
If your impoundment is not aerated, choose No AERATION.
If your impoundment is aerated only by mechanical aerators (these are rotating impellers),
choose MECHANICAL AERATION.
If your impoundment is aerated only by diffused air flow from submerged aerators,
choose DIFFUSED AIR AERATION.
If your impoundment is aerated by both mechanical aerators and diffused air aerators,
choose BOTH (DIFFUSED AIR a MECHANICAL).
Fraction of Surface Area Agitated Unless you chose No AERATION, you will need to enter
the fraction of surface area agitated. If you have data on agitated area, you can divide the agitated
area by the total area (in the same units) to obtain this fraction. Alternatively, you can estimate
this visually. This input is a unitless fraction and must be greater than zero and less than or equal
to one. IWAIR has been tested with values of fraction agitated from 0.01 to 1.
Submerged Air Flow (m3/s). Submerged air flow is used for diffused air systems; you
will need to enter a value if you chose either DIFFUSED AIR AERATION or BOTH (DIFFUSED AIR a MECHANICAL).
This is the total air flow of all diffusers in the impoundment. For example, if you had two
diffusers, each with an air flow of 0.1 m3/s,
you would enter 0.2 m3/s here. If you enter a
value here, it must be greater than zero. No
maximum limit is enforced. IWAIR has been
tested for values of submerged air flow from
0.01 to 100m3/s.
B.3.1.4 Waste Characteristics
Information
Type of Waste. In order to generate
an accurate estimate of a constituent's volatile
emissions, you must define the physical and
chemical characteristics of the waste you are
modeling. In particular, you must identify
whether or not the waste is best described as a
Aqueous-phase waste: a waste that is predominantly
water, with low concentrations of organics. All
chemicals remain in solution in the waste and are
usually present at concentrations below typical
solubility limits. However, it is possible for the
specific components of the waste to raise the
effective solubility level for a chemical, allowing it to
remain in solution at concentrations above the typical
solubility limit.
Organic-phase waste: a waste that is predominantly
organic chemicals, with a high concentration of
organics. Concentrations of some chemicals may
exceed solubility, causing those chemicals to come
out of solution and form areas of free product in the
WMU. In surface impoundments, this can result in a
thin organic film over the entire surface.
B-12
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IWAIR User's Guide Appendix B
dilute mixture of chemical compounds (aqueous) or if the waste should be considered organic,
containing high levels of organic compounds or a separate nonaqueous organic phase. These two
different types of waste matrices influence the degree of partitioning that will occur from the
waste to the air. Partitioning describes the affinity that a contaminant has for one phase (for
example, air) relative to another phase (for example, water) that drives the volatilization of
organic chemicals. Your choice of waste matrix will significantly affect the rate of emissions
from the waste. The following discussion is intended to provide background on emissions
modeling as it relates to waste type, guidance on making this selection, and clarification of the
modeling consequences of choosing AQUEOUS versus ORGANIC in IWAIR. Note that you will only be
asked to choose a waste type for risk calculations; for allowable concentration calculations,
IWAIR calculates emission rates for both aqueous and organic waste types and selects the one
that achieves the target risk or HQ at the lowest concentration applicable to the waste type.
A WMU contains solids, liquids (such as water), and air. Individual chemical molecules
are constantly moving from one of these media to another: they may be absorbed to solids,
dissolved in liquids, or assume a vapor form in air. At equilibrium, the movement into and out
of each medium is equal, so that the concentration of the chemical in each medium is constant.
The emissions model used in IWAIR, CHEMDAT8, assumes that equilibrium has been reached.
Partitioning refers to how a chemical tends to distribute itself among these different
media. Different chemicals have differing affinities for particular phases—some chemicals tend
to partition more heavily to air, while others tend to partition more heavily to water. The
different tendencies of different chemicals are described by partition coefficients or equilibrium
constants.
Of particular interest in modeling volatile emissions of a chemical from a liquid waste
matrix is the chemical's tendency to change from a liquid form to a vapor form. As a general
rule, a chemical's vapor pressure describes this tendency. The pure component vapor pressure is
a measure of this tendency for the pure chemical. A chemical in solution in another liquid (such
as a waste containing multiple chemicals) will exhibit a partial vapor pressure, which is the
chemical's share of the overall vapor pressure of the mixture; this partial vapor pressure is lower
than the pure component vapor pressure and is generally equal to the pure component vapor
pressure times the constituent's mole fraction (a measure of concentration reflecting the number
of moles of the chemical per total moles) in the solution. This general rule is known as Raoult's
law.
Most chemicals do not obey Raoult's law in dilute (i.e., low concentration) aqueous
solutions, but exhibit a greater tendency to partition to the vapor phase from dilute solutions than
would be predicted by Raoult's law. These chemicals exhibit a higher partial vapor pressure than
the direct mole fraction described above would predict.1 This altered tendency to partition to the
vapor phase in dilute solutions is referred to as Henry's law. To calculate the emissions of a
1 There are some exceptions to this behavior in dilute solutions. A notable exception is formaldehyde,
which has lower activity in dilute aqueous solution, which means that formaldehyde will have greater emissions in a
high concentration, organic-phase waste.
B-13
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IWAIR User's Guide Appendix B
constituent from a dilute solution, a partition coefficient called Henry's law constant is used.
Henry's law constant relates the partial vapor pressure to the concentration in the solution.
To account for these differences in the tendency of chemicals to partition to vapor phase
from different types of liquid waste matrices, CHEMDAT8 models emissions in two regimes: a
dilute aqueous phase, modeled using Henry's law constant as the partition coefficient, and an
organic phase, modeled using the partial vapor pressure predicted by Raoult's law as the partition
coefficient. In fact, there is not a clear point at which wastes shift from dilute aqueous phase to
organic phase; this is a model simplification. However, several rules of thumb may be used to
determine when the Raoult's law model would be more appropriate. The clearest rule is that any
chemical present in excess of its solubility limit in a wastewater has exceeded the bounds of
"dilute aqueous" and is more appropriately modeled using Raoult's law. Chemicals exceeding
solubility limits will typically come out of solution and behave more like pure, organic-phase
component. However, solubility limits can vary depending on site-specific parameters, such as
temperature and pH of the waste. In addition, waste matrix effects2 can cause chemicals to
remain in solution at concentrations above their typical solubility limit. This scenario (an
aqueous-phase waste with concentrations above typical solubility limits) is also best modeled
using Raoult's law. Another rule of thumb is that a waste with a total organics concentration in
excess of about 10 percent (or 100,000 ppm) is likely to behave more like an organic-phase waste
than a dilute aqueous-phase waste and be more appropriately modeled using Raoult's law.
For surface impoundments, where the waste is a liquid, the model uses an approach that
considers the resistance to mass transfer (i.e., movement of chemical mass from one phase to the
other) in the liquid and gas phases at the surface of the impoundment. Emissions are calculated
using an overall mass transfer coefficient, which is based on the partition coefficient (as
described above), the liquid-phase mass transfer factor (which accounts for resistance to transfer
in the liquid phase), and the gas-phase mass transfer factor (which accounts for resistance to
transfer in the gas phase). This is referred to as the two-film model. For organic-phase wastes,
the mass transfer is dominated by the gas-phase resistance and the partition coefficient; the
liquid-phase mass transfer resistance is negligible and is, therefore, omitted from the calculation.
This is referred to as the one-film model, or the oily film model.
In the two-film model for surface impoundments, the gas-phase and liquid-phase mass
transfer coefficients are strongly affected by the turbulence of the surface impoundment surface.
Turbulence may be caused by mechanical aeration or, to a lesser extent, diffused air aeration.
Therefore, whether the impoundment is aerated or not and how it is aerated are important inputs.
When in allowable concentration calculation mode, IWAIR calculates both aqueous-
phase and organic-phase emission rates. However, aqueous-phase emission rates, as discussed
above, are only applicable up to the solubility limit. If the use of the aqueous-phase emission
"Waste matrix effects" refers to the effect that the composition of the waste has on a constituent's
solubility in the waste or the tendency for the chemical to evaporate from the waste. For example, hexane has a
solubility in distilled water of approximately 12 mg/L; however, its solubility in methanol is much higher (more than
100,000 mg/L) (Perry and Green, 1984). Therefore, it is likely that hexane will remain dissolved in a solution of 10
percent methanol in water at higher concentrations than the aqueous solubility limit of 12 mg/L suggests.
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IWAIR User 's Guide Appendix B
rate results in an allowable concentration in excess of the solubility limit, IWAIR will use the
organic-phase rate instead.
Molecular Weight of Waste (g/mol) (Only for Risk Calculation). If you choose to
model an organic-phase waste, you will need to enter the average molecular weight of the waste.
This may be calculated from the molecular weights of the component constituents as follows:
E (C.) x (1 m3)
MW = _ _ - _ - _
1~te E (C./MW,) x (1 m3)
where
MWwaste = molecular weight of waste (g/mol)
Q = waste concentration of contaminant / (mg/L = g/m3)
MW; = molecular weight of contaminant /' (g/mol).
This assumes that the average molecular weight of the unspecified fraction of the organic waste
matrix has the same average molecular weight as the specified fraction (i.e., the input
contaminant concentrations). Appendix C provides values for molecular weight for all IWAIR
chemicals.
This value must be greater than or equal to 1 (the molecular weight of a hydrogen ion).
No maximum limit is enforced. IWAIR has been tested for values from 1 to 400 g/mol.
Density of Waste (g/cm3) (Only for Risk Calculation). If you choose to model an
organic-phase waste, you will need to enter the density of the waste. It is best to use a measured
value for this, but you can estimate it as follows:
waste
where
Pwaste = density of waste (g/cm3)
Q = waste concentration of contaminant / (mg/L = g/m3)
pi = density of contaminant /' (g/cm3).
Appendix C provides values for density for all IWAIR chemicals.
This value must be greater than zero. No maximum limit is enforced. IWAIR has been
tested for values from 0.01 to 3 g/cm3.
Active Biomass (g/L). This input, in conjunction with the BIODEGRADATION option, allows
you to determine what type of biodegradation is modeled for your unit. In biologically active
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IWAIR User's Guide Appendix B
surface impoundments, two processes occur: growth of biomass, which provides a growing
matrix for chemical adsorption and loss through settling, and direct biodegradation of chemical
constituents as the bacteria that compose the biomass consume constituent mass. Direct
biodegradation cannot occur if there is no active biomass. If an impoundment is biologically
active, it may go through a transitional period during which there is active biomass (so
adsorption and settling losses occur) but the biomass is not yet adapted to consume the specific
chemicals present (so direct biodegradation is not occurring). This transitional period will
usually end as the biomass acclimate and adapt to the chemicals present. See also the discussion
in Section B.3.1.2 on biodegradation and how active biomass interacts with the biodegradation
setting.
This input refers to the biomass concentration within the surface impoundment. Most of
the biodegradation rate constants use mixed-liquor volatile suspended solids (MLVSS) as the
measure of bioconcentration. Therefore, MLVSS in the impoundment is the preferred source for
this input if you have those data available. If not, you can approximate this (in order of
preference) using biomass concentration in the impoundment, mixed-liquor suspended solids
(MLSS) in the impoundment, MLVSS in the effluent, biomass concentration in the effluent, or
MLSS in the effluent. Alternatively, you may choose to use the IWAIR default of 0.05 g/L;
however, this default is only appropriate for biologically active impoundments. If you are
modeling a biologically inactive impoundment, this value should be set to zero, which turns off
direct biodegradation and biomass growth, so that adsorption losses are limited to adsorption to
inlet solids. This value must be greater than or equal to zero and less than or equal to 1,000 g/L.
IWAIR has been tested for this full range.
Total Suspended Solids in Influent (g/L). Total suspended solids (TSS) is used, in
conjunction with total organics, to estimate growth of solids in the impoundment. This input is
the TSS in the impoundment influent, not within the impoundment. If those data are not
available, you can approximate this (in order of preference) using total solids in the influent,
MLSS in the influent, MLVSS in the influent, biomass concentration in the influent, TSS within
the impoundment, total solids within the impoundment, or MLSS within the impoundment.
Alternatively, you may choose to use the IWAIR default of 0.2 g/L. This value must be greater
than or equal to zero and less than or equal to 1,000 g/L. IWAIR has been tested for this full
range.
Total Organics into WMU (mg/L). Total organics is used, in conjunction with TSS, to
estimate new biomass growth, so it most accurately refers to biodegradable organics. For this
reason, the most preferred data source is biological oxygen demand (BOD) in the influent. If
BOD is not available, you can estimate this using chemical oxygen demand (COD) or total
organic carbon (TOC) in the influent. Values of BOD, COD, or TOC in the effluent may be used
if influent values are not available, but these need to be adjusted up to account for removal in the
impoundment by dividing by (1 - removal efficiency). Alternatively, you can use the IWAIR
default value of 200 mg/L. This value must be greater than or equal to the sum of the
concentrations you entered for organic chemicals in the WASTES MANAGED screen and must be less
than or equal to 1,000,000 mg/L. IWAIR has been tested for this full range.
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IWAIR User's Guide Appendix B
Total Biorate (mg/g biomass-h). This is the degradation rate of total organics in the
impoundment. Total biorate can be measured from the maximum oxygen uptake rate from
respirometry studies, converting the oxygen uptake rate to grams carbon assuming mineralization
(formation of CO2). Alternatively, you can use the IWAIR default value of 19 mg/g biomass-h).
This value must be greater than or equal to zero. No maximum limit is enforced. IWAIR has
been tested for values from 0 to 100 mg/g biomass-h.
B.3.1.5 Mechanical Aeration Information
These inputs are needed for only if you selected MECHANICAL AERATION or BOTH (DIFFUSED AIR a
MECHANICAL).
Oxygen Transfer Rate (Ib Ofli-hp). This is the oxygen transfer rating of your aerator,
measured using water, and should be available from the design specifications of your aerator. If
no data are available, you can use the IWAIR default of 3.0 Ib O2/h-hp. This value must be
greater than zero. No maximum limit is enforced. IWAIR has been tested for values from 0.01
to 3 Ib O2/h-hp.
Number of Aerators. This is the number of impellers in your impoundment. You should
be able to count them visually if you do not have these data readily available. This value must be
greater than or equal to 1 and should be an integer. No maximum limit is enforced. IWAIR has
been tested for values from 1 to 150.
Total Power (hp). This is the power from all impellers in the impoundment combined.
You can calculate it by summing the power of each impeller (make sure they are all in the same
units first). Impeller power should be part of the design specifications for your aerators. In a
survey of surface impoundments managing nonhazardous wastes (U.S. EPA, 200la), the reported
average power per aerator ranged from 4 to 100 hp. If you cannot determine the power of your
aerators, you can estimate aerator power. Aeration and mixing power requirements often depend
on the volume of liquid needing aeration or mixing, although the range of appropriate values can
be wide. Additionally, many impoundments are aerated near the unit's influent, but a large
portion of the impoundment may remain unaerated. Consequently, the lower limit for aeration
may be more difficult to assess than the upper limit. A reasonable upper limit for aeration power
based on high aeration requirements is approximately 150 hp per million gallons of
impoundment volume (Metcalf and Eddy, 1979). This factor can be applied to the total volume
of the unit to assess a maximum power limit. A lower limit based on mixing is approximately 10
hp/million gallons; this factor can be applied to the unit volume times the fraction aerated to
yield a lower limit. The minimum value for total power must be greater the 0.25 hp. No
maximum limit is enforced. IWAIR has been tested for values from 0.26 to 3,000 hp.
Power Efficiency (fraction). Power efficiency is a misnomer that is carried over from
CHEMDAT8. This input is really the oxygen correction factor for the liquid-phase turbulent
mass transfer coefficient. The actual power efficiency, used in the equation for gas-phase
turbulent mass transfer coefficient, is hardwired to a value of 0.85 in CHEMDAT8. In order to
maintain consistency with CHEMDAT8, IWAIR also terms this input "power efficiency" but
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IWAIR User's Guide Appendix B
uses it as the oxygen correction factor, and hardwires the real power efficiency with a value of
0.85.
This correction factor is used to adjust the oxygen transfer rate input (which applies to
pure water) for application to wastewaters. A value for your aerator should be available from
your aerator supplier. If no data are available, you can use the IWAIR default of 0.83; this value
is consistent with its use as the oxygen correction factor. This value must be greater than zero
and less than or equal to 1. IWAIR has been tested for values from 0.01 to 1.
Impeller Diameter (cm). This is the diameter of each impeller, from one end of the
impeller to the other. If you have different impellers of different diameters, use either an average
or the most typical. If this value is in meters, feet, or inches, it must be converted to centimeters
for use in IWAIR. If you cannot determine the diameter of your impellers, you can use the
IWAIR default value of 61 cm. This value must be greater than zero and less than 100 times the
square root of the area of the unit in m2 (i.e., the impeller cannot be longer than the side length of
the unit, assuming the unit is square, which maximizes the smallest side length). IWAIR has
been tested for this full range.
Impeller Speed (rad/s). This is a measure of rotational speed (in radians per second). It
should be part of the specifications of your aerators, although it may be reported in rotations per
minute (rpm). If so, you will need to convert it to radians per second. One rotation is equal to
360 degrees, or 6.28 radians. If your aerators have different speeds, use an average or the most
typical value. If you cannot determine the speed of your impellers, you can use the IWAIR
default value of 130 rad/s. This value must be greater than zero. No maximum limit is enforced.
IWAIR has been tested for a range from 0.01 to 1,000 rad/s.
B.3.2 WMU Data for CHEMDAT8 - Land Application Unit (Screen 3B)
B.3.2.1 Meteorological Station Parameters. These inputs are used only for the
emissions modeling, not the dispersion modeling, which uses hourly meteorological data, not
annual averages. Therefore, changes to these inputs will not affect the dispersion factors.
Wind Speed (m/s). IWAIR uses wind speed to select the most appropriate empirical
emission correlation equation in CHEMDAT8; there are several of these correlations, and each
one applies to a specific range of wind speeds and unit sizes. By default, IWAIR uses the
average annual wind speed from the meteorological station that was assigned to your location.
However, you may wish to override the default if you have site-specific data on wind speed. If
you do override, you should use an overall annual average in all directions, not any measure of
peak wind speed or average only in the prevailing wind direction. Also, wind speed is often
reported in knots or mph. However, for use in IWAIR, wind speed must be converted to m/s.
This value must be greater than zero. No maximum limit is enforced. IWAIR has been tested
for values of wind speed from 0.01 to 100 m/s; however, a realistic range for average annual
wind speed is about 2 to 10 m/s.
Temperature (°C). IWAIR uses temperature to correct various temperature-dependent
chemical properties used in emissions modeling (Henry's law constant and vapor pressure) from
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IWAIR User's Guide Appendix B
a standard temperature to the ambient temperature. By default, IWAIR uses the average annual
temperature from the meteorological station that was assigned to your location. However, you
may wish to override the default if you have site-specific data on temperature. If you do
override, you should use an annual average temperature. Temperature may be reported in
degrees Fahrenheit (°F); however, for use in IWAIR, temperature must be converted to degrees
Celsius (°C). This value must be greater than or equal to -100°C. No maximum limit is
enforced. IWAIR has been tested for values of temperature from 0 to 50°C.
B.3.2.2 Waste/Soil Mixture Porosity Information
Total Porosity (volume fraction). Porosity refers to the spaces in a soil or waste matrix
that are not soil particles. These spaces may be filled with air or water. Total porosity is the sum
of both air- and water-filled porosity. Sometimes porosity is referred to as saturated water
content. Porosity values are used in the emissions model, and they can be used to estimate soil
saturation concentration limits. If measured data on porosity are not available, porosity can be
estimated from the bulk density and particle density of the waste as follows:
et = 1 - BD/ps
where
et = total porosity (unitless)
BD = bulk density of waste (g/cm3)
ps = particle density of waste (g/cm3).
If particle density is not available, a typical value for mineral material is 2.65 g/cm3 (Mason and
Berry, 1968).
Porosity must be greater than zero and less than 1. IWAIR has been tested for values
from 0.01 to 0.99.
Air Porosity (volume fraction). Air-filled porosity is the porosity that is filled with air
instead of water. This can be calculated from volumetric moisture content (which is equivalent
to water-filled porosity) and total porosity as follows:
6a = 6t - 6w
where
ea = air-filled porosity (unitless)
et = total porosity (unitless)
ew = water-filled porosity = volumetric water content (unitless).
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IWAIR User's Guide Appendix B
Air-filled porosity must be greater than zero and less than or equal to the total porosity. IWAIR
has been tested for this full range.
B.3.2.3 LAU Dimensions and Loading Information
Biodegradation (on/off). This option lets you choose whether to model biodegradation
losses in the unit. Land application units are designed to biodegrade wastes; therefore, the
biodegradation option is turned on by default. Biodegradation rates can be very site-specific. If
you believe that the actual rates in your unit are different than those included in the IWAIR
chemical properties database, the best choice would be to enter user-defined chemical entries
using your own soil biodegradation rates and select biodegradation ION I. However, if you wish
to model a land application unit without biodegradation, you can select biodegradation | OFF |.
Operating Life (yr). This parameter is the expected remaining operating life of your unit,
from the time you are modeling until you expect it to be closed. Operating life does not affect
exposure duration for land application units the way it does for other unit types, because
exposures can continue postclosure for land application units. Operating life does affect average
emission rates for land application units. Emissions are estimated for each year of operation plus
30 years postclosure, and then the maximum 7- and 30-year averages are calculated. For land
application units, IWAIR uses default exposure durations used by IWAIR of 30 years for
residents and 7.2 years for workers, regardless of operating life. Operating life should be entered
in years. This value must be greater than zero. No maximum limit is enforced; however, see the
discussion below under number of applications per year on how operating life affects the
maximum number of applications per year. IWAIR has been tested for values of operating life
from 0.01 to 100 years.
Tilling Depth of Unit (m). This is the depth to which your land application unit is tilled
and the depth to which wastes are mixed with soil; once constituents get below this depth, they
are no longer mixed with newly applied waste. Tilling depth should be entered in m; if it is in
other units, it must be converted to m. Tilling depth must be greater than zero. No maximum
limit is enforced. IWAIR has been tested for tilling depths from 0.01 to 1 m.
Area of Unit (m2). This is the total surface area of your unit in m2. Areas may be
reported in acres or hectares; these values will need to be converted to m2 for use in IWAIR.
This value must be greater than or equal to 81 and less than or equal to 8,090,000 m2; these are
the smallest and largest areas for which IWAIR can interpolate dispersion factors for ground-
level sources. IWAIR has been tested for this full range of values.
Annual Waste Quantity (Mg/yr). This is the total amount of waste that you manage in
your land application unit in a year, in Mg/yr. You may need to estimate this by multiplying the
waste quantity applied per application by the number of applications per year. This value must
be greater than zero. The maximum limit depends on the other inputs. The waste quantity,
number of applications per year, bulk density, and area imply a depth of application as follows:
dapp = Q/CNappl >< BD x A)
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IWAIR User's Guide Appendix B
where
dapp = depth of application (m)
Q = annual waste quantity (Mg/yr)
Nappl = number of applications per year (yr"1)
BD = bulk density of waste (g/cm3 = Mg/m3 )
A = area of unit (m2).
This depth of application may not exceed the tilling depth and, realistically, should be
considerably less than the tilling depth. IWAIR has been tested for values of annual waste
quantity from 0.01 to 10,000,000 Mg/yr.
Number of Applications per Year. This is the number of times you apply waste to the
land application unit per year. You may need to convert a frequency of application to the
corresponding number of applications per year. For example, if you apply waste weekly, you
would enter 52 applications per year in IWAIR. This value must be an integer greater than or
equal to 1. The maximum number of applications per year depends on the operating life you
specified. IWAIR models land application unit emissions in time steps equal to the time between
applications (so, if you entered 52 applications per year, IWAIR would model in 1-week time
steps), for a period equal to the operating life of the unit plus 30 years. The total number of time
steps modeled is thus:
Nsteps= (tlife-30)xNappl
where
Nsteps = total number of time steps modeled (unitless)
tiife = operating life of unit (yr)
Nappl = number of applications per year (yr"1).
This total number of time steps, Nsteps, cannot exceed 32,766 because of code limitations for
integer variables. This is unlikely to result in practical limitations, unless the operating life is
very long and the number of applications per year very high. For example, you could have daily
applications (365 applications/year) for 59 years and still be just within this limitation. IWAIR
has been tested for values from 1 to 52.
Waste Bulk Density (g/cm3). This is the overall, or bulk, density of your waste. This
should be available from measurements. Bulk density must be in g/cm3. This value must be
greater than zero. IWAIR has been tested for values from 0.01 to 14 g/cm3.
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IWAIR User's Guide
Appendix B
B.3.2.4 Waste Characteristics Information (Only for Risk Calculation)
Aqueous-phase waste: a waste that is predominantly
water, with low concentrations of organics. All
chemicals remain in solution in the waste and are
usually present at concentrations below typical
saturation limits. However, it is possible for the
specific components of the waste to raise the
effective saturation level for a chemical, allowing it
to remain in solution at concentrations above the
typical saturation limit.
Organic-phase waste: a waste that is predominantly
organic chemicals, with a high concentration of
organics. Concentrations of some chemicals may
exceed saturation limits, causing those chemicals to
come out of solution and form areas of free product
in the WMU.
Type of Waste. In order to generate
an accurate estimate of a constituent's volatile
emissions, you must define the physical and
chemical characteristics of the waste you are
modeling. In particular, you must identify
whether or not the waste is best described as a
dilute mixture of chemical compounds
(aqueous) or if the waste should be
considered organic, containing high levels of
organic compounds or a separate nonaqueous
organic phase. These two different types of
waste matrices influence the degree of
partitioning that will occur from the waste to
the air. Partitioning describes the affinity that
a contaminant has for one phase (for example,
air) relative to another phase (for example,
water) that drives the volatilization of organic chemicals. Your choice of waste matrix will
significantly affect the rate of emissions from the waste. The following discussion is intended to
provide background on emissions modeling as it relates to waste type, guidance on making this
selection, and clarification of the modeling consequences of choosing AQUEOUS versus ORGANIC in
IWAIR. Note that you will only be asked to choose a waste type for risk calculations; for
allowable concentration calculations, IWAIR calculates emission rates for both aqueous and
organic waste types and selects the one that achieves the target risk or HQ at the lowest
concentration applicable to the waste type.
A WMU contains solids, liquids (such as water), and air. Individual chemical molecules
are constantly moving from one of these media to another: they may be absorbed to solids,
dissolved in liquids, or assume a vapor form in air. At equilibrium, the movement into and out
of each medium is equal, so that the concentration of the chemical in each medium is constant.
The emissions model used in IWAIR, CHEMDAT8, assumes that equilibrium has been reached.
Partitioning refers to how a chemical tends to distribute itself among these different
media. Different chemicals have differing affinities for particular phases—some chemicals tend
to partition more heavily to air, while others tend to partition more heavily to water. The
different tendencies of different chemicals are described by partition coefficients or equilibrium
constants.
Of particular interest in modeling volatile emissions of a chemical from a liquid waste
matrix is the chemical's tendency to change from a liquid form to a vapor form. As a general
rule, a chemical's vapor pressure describes this tendency. The pure component vapor pressure is
a measure of this tendency for the pure chemical. A chemical in solution in another liquid (such
as a waste containing multiple chemicals) will exhibit a partial vapor pressure, which is the
chemical's share of the overall vapor pressure of the mixture; this partial vapor pressure is lower
than the pure component vapor pressure and is generally equal to the pure component vapor
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IWAIR User's Guide Appendix B
pressure times the constituent's mole fraction (a measure of concentration reflecting the number
of moles of the chemical per total moles) in the solution. This general rule is known as Raoult's
law.
Most chemicals do not obey Raoult's law in dilute (i.e., low concentration) aqueous
solutions, but exhibit a greater tendency to partition to the vapor phase from dilute solutions than
would be predicted by Raoult's law. These chemicals exhibit a higher partial vapor pressure than
the direct mole fraction described above would predict.3 This altered tendency to partition to the
vapor phase in dilute solutions is referred to as Henry's law. To calculate the emissions of a
constituent from a dilute solution, a partition coefficient called Henry's law constant is used.
Henry's law constant relates the partial vapor pressure to the concentration in the solution.
To account for these differences in the tendency of chemicals to partition to vapor phase
from different types of liquid waste matrices, CHEMDAT8 models emissions in two regimes: a
dilute aqueous phase, modeled using Henry's law constant as the partition coefficient, and an
organic phase, modeled using the partial vapor pressure predicted by Raoult's law as the partition
coefficient. In fact, there is not a clear point at which wastes shift from dilute aqueous phase to
organic phase; this is a model simplification. However, several rules of thumb may be used to
determine when the Raoult's law model would be more appropriate. The clearest rule is that any
chemical present in excess of its soil saturation concentration has exceeded the bounds of "dilute
aqueous" and is more appropriately modeled using Raoult's law. Chemicals exceeding
saturation limits will typically come out of solution and behave more like pure, organic-phase
component. However, saturation limits can vary depending on site-specific parameters, such as
temperature and pH of the waste. In addition, waste matrix effects4 can cause chemicals to
remain in solution at concentrations above their typical saturation limit. This scenario (an
aqueous-phase waste with concentrations above typical saturation limits) is also best modeled
using Raoult's law. Another rule of thumb is that a waste with a total organics concentration in
excess of about 10 percent (or 100,000 ppm) is likely to behave more like an organic-phase waste
than a dilute aqueous-phase waste and be more appropriately modeled using Raoult's law.
For land application units, where the waste is either a solid or mixed with a solid (such as
soil), the CHEMDAT8 emissions model considers two-phase partitioning of the waste into the
liquid (either aqueous or organic) phase and the air phase, using the partition coefficients
described above, to estimate the equilibrium vapor composition in the pore (or air) space within
the WMU. Emissions are subsequently estimated from the WMU by calculating the rate of
diffusion of the vapor-phase contaminant through the porous waste/soil media.
3 There are some exceptions to this behavior in dilute solutions. A notable exception is formaldehyde,
which has lower activity in dilute aqueous solution, which means that formaldehyde will have greater emissions in a
high concentration, organic-phase waste.
4 "Waste matrix effects" refers to the effect that the composition of the waste has on a constituent's
solubility in the waste or the tendency for the chemical to evaporate from the waste. For example, hexane has a
solubility in distilled water of approximately 12 mg/L; however, its solubility in methanol is much higher (more than
100,000 mg/L) (Perry and Green, 1984). Therefore, it is likely that hexane will remain dissolved in a solution of 10
percent methanol in water at higher concentrations than the aqueous solubility limit of 12 mg/L suggests.
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IWAIR User 's Guide Appendix B
When in allowable concentration calculation mode, IWAIR calculates both aqueous-
phase and organic-phase emission rates. However, aqueous-phase emission rates, as discussed
above, are only applicable up to the saturation limit. If the use of the aqueous-phase emission
rate results in an allowable concentration in excess of the saturation limit, IWAIR will use the
organic-phase rate instead.
Molecular Weight of Waste (g/mol). If you choose to model an organic-phase waste, you
will need to enter the average molecular weight of the waste. This may be calculated from the
molecular weights of the component constituents as follows:
v (C) x (1 Mg)
MW
(1 Mg)
where
MWwaste = molecular weight of waste (g/mol)
C; = waste concentration of contaminant /' (mg/kg = g/Mg)
MW; = molecular weight of contaminant /' (g/mol).
This assumes that the average molecular weight of the unspecified fraction of the organic waste
matrix has the same average molecular weight as the specified fraction (i.e., the input
contaminant concentrations). This value must be greater than or equal to 1 (the molecular weight
of a single hydrogen ion). No maximum limit is enforced.
B.3.3 WMU Data for CHEMDAT8 - Landfill (Screen 3C)
B.3.3.1 Meteorological Station Parameters. These inputs are used only for the
emissions modeling, not the dispersion modeling, which uses hourly meteorological data, not
annual averages. Therefore, changes to these inputs will not affect the dispersion factors.
Wind Speed (m/s). IWAIR uses wind speed to select the most appropriate empirical
emission correlation equation in CHEMDAT8; there are several of these correlations, and each
one applies to a specific range of wind speeds and unit sizes. By default, IWAIR uses the
average annual wind speed from the meteorological station that was assigned to your location.
However, you may wish to override the default if you have site-specific data on wind speed. If
you do override, you should use an overall annual average in all directions, not any measure of
peak wind speed or average only in the prevailing wind direction. Also, wind speed is often
reported in knots or mph. However, for use in IWAIR, wind speed must be converted to m/s.
This value must be greater than zero. No maximum limit is enforced. IWAIR has been tested
for values of wind speed from 0.01 to 100 m/s; however, a realistic range for average annual
wind speed is about 2 to 10 m/s.
Temperature (°C). IWAIR uses temperature to correct various temperature-dependent
chemical properties used in emissions modeling (Henry's law constant and vapor pressure) from
a standard temperature to the ambient temperature. By default, IWAIR uses the average annual
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IWAIR User's Guide Appendix B
temperature from the meteorological station that was assigned to your location. However, you
may wish to override the default if you have site-specific data on temperature. If you do
override, you should use an annual average temperature. Temperature may be reported in
degrees Fahrenheit (°F); however, for use in IWAIR, temperature must be converted to degrees
Celsius (°C). This value must be greater than or equal to -100°C. No maximum limit is
enforced. IWAIR has been tested for values of temperature from 0 to 50°C.
B.3.3.2 Waste Porosity Information
Total Porosity (volume fraction). Porosity refers to the spaces in a soil or waste matrix
that are not soil particles. These spaces may be filled with air or water. Total porosity is the sum
of both air- and water-filled porosity. Sometimes porosity is referred to as saturated water
content. Porosity values are used in the emissions model, and they can be used to estimate soil
saturation concentration limits. If measured data on porosity are not available, porosity can be
estimated from the bulk density and particle density of the waste as follows:
et = 1 - BD/ps
where
et = total porosity (unitless)
BD = bulk density of waste (g/cm3)
ps = particle density of waste (g/cm3).
If particle density is not available, a typical value for mineral material is 2.65 g/cm3 (Mason and
Berry, 1968).
Porosity must be greater than zero and less than 1. IWAIR has been tested for values
from 0.01 to 0.99.
Air Porosity (volume fraction). Air-filled porosity is the porosity that is filled with air
instead of water. This can be calculated from volumetric moisture content (which is equivalent
to water-filled porosity) and total porosity as follows:
6a = 6t - 6w
where
ea = air-filled porosity (unitless)
et = total porosity (unitless)
ew = water-filled porosity = volumetric water content (unitless).
Air-filled porosity must be greater than zero and less than or equal to the total porosity. IWAIR
has been tested for this full range.
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IWAIR User's Guide Appendix B
B.3.3.3 Landfill Dimensions and Loading Information
Biodegradation (on/off). This option lets you choose whether to model biodegradation
losses in the unit. Landfills are generally not designed to biodegrade wastes; therefore, the
biodegradation option is turned off for landfills by default. However, biodegradation may occur
in your landfill. If you believe it does and want to model it, you can select biodegradation | ON I.
Soil biodegradation rates can be very site-specific. If you believe that the actual rates in your unit
are different than those included in the IWAIR chemical properties database, you can enter user-
defined chemical entries using your own soil biodegradation rates.
Operating Life (yr). This parameter is the expected remaining operating life of your unit,
from the time you are modeling until you expect it to be closed. For landfills, this value is used
in emissions calculations. In addition, it affects exposure duration. IWAIR uses default
exposure durations of 30 years for residents and 7.2 years for workers. However, proper closure
of a landfill typically ends all exposures. Therefore, if the operating life you specify is less than
30 or 7.2 years, IWAIR caps the exposure duration at the operating life. Values in excess of 30
years will not affect the results for residents, and values in excess of 7.2 years will not affect the
results for workers. Operating life should be entered in years. This value must be greater than
zero. No maximum limit is enforced. IWAIR has been tested for values of operating life from
0.01 to 100 years.
Total Area of Landfill (nt2). This is the total surface area of your unit in m2. Be sure to
enter total area and not just the area of the active cell. Areas may be reported in acres or
hectares; these values will need to be converted to m2 for use in IWAIR. This value must be
greater than or equal to 81 and less than or equal to 8,090,000 m2, which are the smallest and
largest areas for which IWAIR can interpolate dispersion factors for ground-level sources.
IWAIR has been tested for this full range of values.
Total Depth of Landfill (m). This is the average depth of your unit in meters (m). If
your unit is not a constant depth, use the average or most typical depth. If you have depth
reported in units such as feet, you will need to convert them to m. This value must be greater
than zero. No maximum limit is enforced. IWAIR has been tested for values of depth from 0.01
to 30 m.
Total Number of Cells in Landfill. Landfills are typically filled one cell at a time. This
input is the total number of cells in your landfill. IWAIR models one open cell at a time, with
each cell open for a period equal to the operating life divided by the total number of cells. This
value must be greater than or equal to 1. No maximum limit is enforced. IWAIR has been tested
for values from 1 to 10,000.
Annual Quantity of Waste Disposed in Landfill (Mg/yr). This is the total amount of
waste that you manage in your landfill in a year, in Mg/yr. This value must be greater than zero.
The maximum limit depends on other inputs. The waste quantity, operating life, area, and depth
imply a loading rate as follows:
L = (Q x tlife)/(A x D)
B-26
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IWAIR User's Guide
Appendix B
where
L
Q
tlife
A
D
loading rate (Mg/m3 = g/cm3)
annual waste quantity (Mg/yr)
operating life (yr)
area of landfill (m2)
depth (m).
This loading rate may not exceed the bulk density of the waste. IWAIR has been tested for
values of annual waste quantity from 0.01 to 10,000,000 Mg/yr.
Bulk Density of Waste (g/cm3). This is the overall, or bulk, density of your waste. This
should be available from measurements. Bulk density must be in g/cm3. This value must be
greater than zero. IWAIR has been tested for values from 0.01 to 14 g/cm3.
B.3.3.4 Waste Characteristics Information (Only for Risk Calculation)
Type of Waste. In order to generate
an accurate estimate of a constituent's volatile
emissions, you must define the physical and
chemical characteristics of the waste you are
modeling. In particular, you must identify
whether or not the waste is best described as a
dilute mixture of chemical compounds
(aqueous) or if the waste should be
considered organic, containing high levels of
organic compounds or a separate nonaqueous
organic phase. These two different types of
waste matrices influence the degree of
partitioning that will occur from the waste to
the air. Partitioning describes the affinity that
a contaminant has for one phase (for example,
air) relative to another phase (for example,
water) that drives the volatilization of organic
chemicals. Your choice of waste matrix will significantly affect the rate of emissions from the
waste. The following discussion is intended to provide background on emissions modeling as it
relates to waste type, guidance on making this selection, and clarification of the modeling
consequences of choosing AQUEOUS versus ORGANIC in IWAIR. Note that you will only be asked to
choose a waste type for risk calculations; for allowable concentration calculations, IWAIR
calculates emission rates for both aqueous and organic waste types and selects the one that
achieves the target risk or HQ at the lowest concentration applicable to the waste type.
A WMU contains solids, liquids (such as water), and air. Individual chemical molecules
are constantly moving from one of these media to another: they may be absorbed to solids,
dissolved in liquids, or assume a vapor form in air. At equilibrium, the movement into and out
Aqueous-phase waste: a waste that is predominantly
water, with low concentrations of organics. All
chemicals remain in solution in the waste and are
usually present at concentrations below typical
saturation limits. However, it is possible for the
specific components of the waste to raise the
effective saturation level for a chemical, allowing it
to remain in solution at concentrations above the
typical saturation limit.
Organic-phase waste: a waste that is predominantly
organic chemicals, with a high concentration of
organics. Concentrations of some chemicals may
exceed saturation limits, causing those chemicals to
come out of solution and form areas of free product
in the WMU.
B-27
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IWAIR User's Guide Appendix B
of each medium is equal, so that the concentration of the chemical in each medium is constant.
The emissions model used in IWAIR, CHEMDAT8, assumes that equilibrium has been reached.
Partitioning refers to how a chemical tends to distribute itself among these different
media. Different chemicals have differing affinities for particular phases—some chemicals tend
to partition more heavily to air, while others tend to partition more heavily to water. The
different tendencies of different chemicals are described by partition coefficients or equilibrium
constants.
Of particular interest in modeling volatile emissions of a chemical from a liquid waste
matrix is the chemical's tendency to change from a liquid form to a vapor form. As a general
rule, a chemical's vapor pressure describes this tendency. The pure component vapor pressure is
a measure of this tendency for the pure chemical. A chemical in solution in another liquid (such
as a waste containing multiple chemicals) will exhibit a partial vapor pressure, which is the
chemical's share of the overall vapor pressure of the mixture; this partial vapor pressure is lower
than the pure component vapor pressure and is generally equal to the pure component vapor
pressure times the constituent's mole fraction (a measure of concentration reflecting the number
of moles of the chemical total moles) in the solution. This general rule is known as Raoult's law.
Most chemicals do not obey Raoult's law in dilute (i.e., low concentration) aqueous
solutions, but exhibit a greater tendency to partition to the vapor phase from dilute solutions than
would be predicted by Raoult's law. These chemicals exhibit a higher partial vapor pressure than
the direct mole fraction described above would predict.5 This altered tendency to partition to the
vapor phase in dilute solutions is referred to as Henry's law. To calculate the emissions of a
constituent from a dilute solution, a partition coefficient called Henry's law constant is used.
Henry's law constant relates the partial vapor pressure to the concentration in the solution.
To account for these differences in the tendency of chemicals to partition to vapor phase
from different types of liquid waste matrices, CHEMDAT8 models emissions in two regimes: a
dilute aqueous phase, modeled using Henry's law constant as the partition coefficient, and an
organic phase, modeled using the partial vapor pressure predicted by Raoult's law as the partition
coefficient. In fact, there is not a clear point at which wastes shift from dilute aqueous phase to
organic phase; this is a model simplification. However, several rules of thumb may be used to
determine when the Raoult's law model would be more appropriate. The clearest rule is that any
chemical present in excess of its soil saturation concentration has exceeded the bounds of "dilute
aqueous" and is more appropriately modeled using Raoult's law. Chemicals exceeding
saturation limits will typically come out of solution and behave more like pure, organic-phase
component. However, saturation limits can vary depending on site-specific parameters, such as
temperature and pH of the waste. In addition, waste matrix effects6 can cause chemicals to
5 There are some exceptions to this behavior in dilute solutions. A notable exception is formaldehyde,
which has lower activity in dilute aqueous solution, which means that formaldehyde will have greater emissions in a
high concentration, organic-phase waste.
6 "Waste matrix effects" refers to the effect that the composition of the waste has on a constituent's
solubility in the waste or the tendency for the chemical to evaporate from the waste. For example, hexane has a
solubility in distilled water of approximately 12 mg/L; however, its solubility in methanol is much higher (more than
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IWAIR User's Guide Appendix B
remain in solution at concentrations above their typical saturation limit. This scenario (an
aqueous-phase waste with concentrations above typical saturation limits) is also best modeled
using Raoult's law. Another rule of thumb is that a waste with a total organics concentration in
excess of about 10 percent (or 100,000 ppm) is likely to behave more like an organic-phase waste
than a dilute aqueous-phase waste and be more appropriately modeled using Raoult's law.
For landfills, where the waste is either a solid or mixed with a solid (such as soil), the
CHEMDAT8 emissions model considers two-phase partitioning of the waste into the liquid
(either aqueous or organic) phase and the air phase, using the partition coefficients described
above, to estimate the equilibrium vapor composition in the pore (or air) space within the WMU.
Emissions are subsequently estimated from the WMU by calculating the rate of diffusion of the
vapor-phase contaminant through the porous waste/soil media.
When in allowable concentration calculation mode, IWAIR calculates both aqueous-
phase and organic-phase emission rates. However, aqueous-phase emission rates, as discussed
above, are only applicable up to the saturation limit. If the use of the aqueous-phase emission
rate results in an allowable concentration in excess of the saturation limit, IWAIR will use the
organic-phase rate instead.
Molecular Weight of Waste (g/mol). If you choose to model an organic-phase waste, you
will need to enter the average molecular weight of the waste. This may be calculated from the
molecular weights of the component constituents as follows:
MW E (Q x (1 Mg)
MWW , =
E (C/MW;) x (l Mg)
where
MWwaste = molecular weight of waste (g/mol)
C; = waste concentration of contaminant / (mg/kg = g/Mg)
MW; = molecular weight of contaminant /' (g/mol).
This assumes that the average molecular weight of the unspecified fraction of the organic waste
matrix has the same average molecular weight as the specified fraction (i.e., the input
contaminant concentrations). This value must be greater than or equal to 1 (the molecular weight
of a single hydrogen ion). No maximum limit is enforced.
B.3.4 WMU Data for CHEMDAT8 - Waste Pile (Screen 3D)
B.3.4.1 Meteorological Station Parameters. These inputs are used only for the
emissions modeling, not the dispersion modeling, which uses hourly meteorological data, not
annual averages. Therefore, changes to these inputs will not affect the dispersion factors.
100,000 mg/L) (Perry and Green, 1984). Therefore, it is likely that hexane will remain dissolved in a solution of 10
percent methanol in water at higher concentrations than the aqueous solubility limit of 12 mg/L suggests.
B-29
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IWAIR User's Guide Appendix B
Wind Speed (m/s). IWAIR uses wind speed to select the most appropriate empirical
emission correlation equation in CHEMDAT8; there are several of these correlations, and each
one applies to a specific range of wind speeds and unit sizes. By default, IWAIR uses the
average annual wind speed from the meteorological station that was assigned to your location.
However, you may wish to override the default if you have site-specific data on wind speed. If
you do override, you should use an overall annual average in all directions, not any measure of
peak wind speed or average only in the prevailing wind direction. Also, wind speed is often
reported in knots or mph. However, for use in IWAIR, wind speed must be converted to m/s.
This value must be greater than zero. No maximum limit is enforced. IWAIR has been tested
for values of wind speed from 0.01 to 100 m/s; however, a realistic range for average annual
wind speed is about 2 to 10 m/s.
Temperature (°C). IWAIR uses temperature to correct various temperature-dependent
chemical properties used in emissions modeling (Henry's law constant and vapor pressure) from
a standard temperature to the ambient temperature. By default, IWAIR uses the average annual
temperature from the meteorological station that was assigned to your location. However, you
may wish to override the default if you have site-specific data on temperature. If you do
override, you should use an annual average temperature. Temperature may be reported in
degrees Fahrenheit (°F); however, for use in IWAIR, temperature must be converted to degrees
Celsius (°C). This value must be greater than or equal to -100°C. No maximum limit is
enforced. IWAIR has been tested for values of temperature from 0 to 50°C.
B.3.4.2 Waste Porosity Information
Total Porosity (volume fraction). Porosity refers to the spaces in a soil or waste matrix
that are not soil particles. These spaces may be filled with air or water. Total porosity is the sum
of both air- and water-filled porosity. Sometimes porosity is referred to as saturated water
content. Porosity values are used in the emissions model, and they can be used to estimate soil
saturation concentration limits. If measured data on porosity are not available, porosity can be
estimated from the bulk density and particle density of the waste as follows:
et = 1 - BD/ps
where
et = total porosity (unitless)
BD = bulk density of waste (g/cm3)
ps = particle density of waste (g/cm3).
If particle density is not available, a typical value for mineral material is 2.65 g/cm3 (Mason and
Berry, 1968).
Porosity must be greater than zero and less than 1. IWAIR has been tested from 0.01 to
0.99.
B-30
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IWAIR User's Guide Appendix B
Air Porosity (volume fraction). Air-filled porosity is the porosity that is filled with air
instead of water. This can be calculated from volumetric moisture content (which is equivalent
to water-filled porosity) and total porosity as follows:
6a = 6t - 6w
where
ea = air-filled porosity (unitless)
et = total porosity (unitless)
ew = water-filled porosity = volumetric water content (unitless).
Air-filled porosity must be greater than zero and less than or equal to the total porosity. IWAIR
has been tested for this full range.
B.3.4.3 Waste Pile Dimensions and Loading Information
Biodegradation (on/off). This option lets you choose whether to model biodegradation
losses in the unit. Waste piles are generally not designed to biodegrade wastes; therefore, the
biodegradation option is turned off for waste piles by default. However, biodegradation may
occur in your waste pile, particularly if residence times of waste in the waste pile are long (on the
order of 60 days to one year). With such residence times, naturally occurring microorganisms
could potentially acclimate and degrade contaminants within the waste pile. If you believe that
biodegradation does occur in your waste pile and you want to model it, you can select
biodegradation | ON I. Soil biodegradation rates can be very site-specific. If you believe that the
actual rates in your unit are different than those included in the IWAIR chemical properties
database, you can enter user-defined chemical entries using your own soil biodegradation rates.
Operating Life (yr). This parameter is the expected remaining operating life of your unit,
from the time you are modeling until you expect it to be closed. Operating life does not affect
emissions estimates for waste piles, which are modeled at steady state. However, operating life
may affect exposure duration. IWAIR uses default exposure durations of 30 years for residents
and 7.2 years for workers. However, proper closure of a waste pile typically ends all exposures.
Therefore, if the operating life you specify is less than 30 or 7.2 years, IWAIR caps the exposure
duration at the operating life. Values in excess of 30 years will not affect the results for
residents, and values in excess of 7.2 years will not affect the results for workers. Operating life
should be entered in years. This value must be greater than zero. No maximum limit is enforced.
IWAIR has been tested for values of operating life from 0.01 to 100 years.
Height of Waste Pile Unit (m). This is the average height of your waste pile in meters
(m). If your waste pile is not a constant height, use the average or most typical height. If you
have height reported in units such as feet, you will need to convert them to m. This value must
be greater than or equal to 1 m and less than or equal to 10 m; these are the smallest and largest
heights for which IWAIR can interpolate dispersion factors for waste piles. IWAIR has been
tested for this full range.
B-31
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IWAIR User's Guide
Appendix B
Area of Unit (m2). This is the total surface area of your unit in m2. Areas may be
reported in acres or hectares; these values will need to be converted to m2 for use in IWAIR.
This value must be greater than or equal to 20 and less than or equal to 1,300,000 m2; these are
the smallest and largest areas for which IWAIR can interpolate dispersion factors for waste piles.
IWAIR has been tested for this full range of values.
Average Quantity of Waste in Waste Pile (Mg/yr). This is the average amount of waste
in your waste pile over a year, in Mg/yr. This value must be greater than zero. No maximum
limit is enforced. IWAIR has been tested for values of annual waste quantity from 0.01 to
10,000,000 Mg/yr.
Bulk Density of Waste (g/cm3). This is the overall, or bulk, density of your waste. This
should be available from measurements. Bulk density must be in g/cm3. This value must be
greater than zero. IWAIR has been tested for values from 0.01 to 14 g/cm3.
B.3.4.4 Waste Characteristics Information (Only for Risk Calculation)
Type of Waste. In order to generate
an accurate estimate of a constituent's volatile
emissions, you must define the physical and
chemical characteristics of the waste you are
modeling. In particular, you must identify
whether or not the waste is best described as a
dilute mixture of chemical compounds
(aqueous) or if the waste should be
considered organic, containing high levels of
organic compounds or a separate nonaqueous
organic phase. These two different types of
waste matrices influence the degree of
partitioning that will occur from the waste to
the air. Partitioning describes the affinity that
a contaminant has for one phase (for example,
air) relative to another phase (for example,
water) that drives the volatilization of organic
chemicals. Your choice of waste matrix will significantly affect the rate of emissions from the
waste. The following discussion is intended to provide background on emissions modeling as it
relates to waste type, guidance on making this selection, and clarification of the modeling
consequences of choosing AQUEOUS versus ORGANIC in IWAIR. Note that you will only be asked to
choose a waste type for risk calculations; for allowable concentration calculations, IWAIR
calculates emission rates for both aqueous and organic waste types and selects the one that
achieves the target risk or HQ at the lowest concentration applicable to the waste type.
A WMU contains solids, liquids (such as water), and air. Individual chemical molecules
are constantly moving from one of these media to another: they may be absorbed to solids,
dissolved in liquids, or assume a vapor form in air. At equilibrium, the movement into and out
Aqueous-phase waste: a waste that is predominantly
water, with low concentrations of organics. All
chemicals remain in solution in the waste and are
usually present at concentrations below typical
saturation limits. However, it is possible for the
specific components of the waste to raise the
effective saturation level for a chemical, allowing it
to remain in solution at concentrations above the
typical saturation limit.
Organic-phase waste: a waste that is predominantly
organic chemicals, with a high concentration of
organics. Concentrations of some chemicals may
exceed saturation limits, causing those chemicals to
come out of solution and form areas of free product
in the WMU.
B-32
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IWAIR User's Guide Appendix B
of each medium is equal, so that the concentration of the chemical in each medium is constant.
The emissions model used in IWAIR, CHEMDAT8, assumes that equilibrium has been reached.
Partitioning refers to how a chemical tends to distribute itself among these different
media. Different chemicals have differing affinities for particular phases—some chemicals tend
to partition more heavily to air, while others tend to partition more heavily to water. The
different tendencies of different chemicals are described by partition coefficients or equilibrium
constants.
Of particular interest in modeling volatile emissions of a chemical from a liquid waste
matrix is the chemical's tendency to change from a liquid form to a vapor form. As a general
rule, a chemical's vapor pressure describes this tendency. The pure component vapor pressure is
a measure of this tendency for the pure chemical. A chemical in solution in another liquid (such
as a waste containing multiple chemicals) will exhibit a partial vapor pressure, which is the
chemical's share of the overall vapor pressure of the mixture; this partial vapor pressure is lower
than the pure component vapor pressure and is generally equal to the pure component vapor
pressure times the constituent's mole fraction (a measure of concentration reflecting the number
of moles of the chemical per total moles) in the solution. This general rule is known as Raoult's
law.
Most chemicals do not obey Raoult's law in dilute (i.e., low concentration) aqueous
solutions, but exhibit a greater tendency to partition to the vapor phase from dilute solutions than
would be predicted by Raoult's law. These chemicals exhibit a higher partial vapor pressure than
the direct mole fraction described above would predict.7 This altered tendency to partition to the
vapor phase in dilute solutions is referred to as Henry's law. To calculate the emissions of a
constituent from a dilute solution, a partition coefficient called Henry's law constant is used.
Henry's law constant relates the partial vapor pressure to the concentration in the solution.
To account for these differences in the tendency of chemicals to partition to vapor phase
from different types of liquid waste matrices, CHEMDAT8 models emissions in two regimes: a
dilute aqueous phase, modeled using Henry's law constant as the partition coefficient, and an
organic phase, modeled using the partial vapor pressure predicted by Raoult's law as the partition
coefficient. In fact, there is not a clear point at which wastes shift from dilute aqueous phase to
organic phase; this is a model simplification. However, several rules of thumb may be used to
determine when the Raoult's law model would be more appropriate. The clearest rule is that any
chemical present in excess of its soil saturation concentration has exceeded the bounds of "dilute
aqueous" and is more appropriately modeled using Raoult's law. Chemicals exceeding
saturation limits will typically come out of solution and behave more like pure, organic-phase
component. However, saturation limits can vary depending on site-specific parameters, such as
7 There are some exceptions to this behavior in dilute solutions. A notable exception is formaldehyde,
which has lower activity in dilute aqueous solution, which means that formaldehyde will have greater emissions in a
high concentration, organic-phase waste.
B-33
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IWAIR User's Guide Appendix B
temperature and pH of the waste. In addition, waste matrix effects8 can cause chemicals to
remain in solution at concentrations above their typical saturation limit. This scenario (an
aqueous-phase waste with concentrations above typical saturation limits) is also best modeled
using Raoult's law. Another rule of thumb is that a waste with a total organics concentration in
excess of about 10 percent (or 100,000 ppm) is likely to behave more like an organic-phase waste
than a dilute aqueous-phase waste and be more appropriately modeled using Raoult's law.
For waste piles, where the waste is either a solid or mixed with a solid (such as soil), the
CHEMDAT8 emissions model considers two-phase partitioning of the waste into the liquid
(either aqueous or organic) phase and the air phase, using the partition coefficients described
above, to estimate the equilibrium vapor composition in the pore (or air) space within the WMU.
Emissions are subsequently estimated from the WMU by calculating the rate of diffusion of the
vapor-phase contaminant through the porous waste/soil media.
When in allowable concentration calculation mode, IWAIR calculates both aqueous-
phase and organic-phase emission rates. However, aqueous-phase emission rates, as discussed
above, are only applicable up to the saturation limit. If the use of the aqueous-phase emission
rate results in an allowable concentration in excess of the saturation limit, IWAIR will use the
organic-phase rate instead.
Molecular Weight of Waste (g/mol). If you choose to model an organic-phase waste, you
will need to enter the average molecular weight of the waste. This may be calculated from the
molecular weights of the component constituents as follows:
E (C.) x (1 Mg)
MW = - —
1V1VV waste
(C/MW;) X (1 Mg)
where
MWwaste = molecular weight of waste (g/mol)
C; = waste concentration of contaminant /' (mg/kg = g/Mg)
MW; = molecular weight of contaminant / (g/mol).
This assumes that the average molecular weight of the unspecified fraction of the organic waste
matrix has the same average molecular weight as the specified fraction (i.e., the input
contaminant concentrations). This value must be greater than or equal to 1 (the molecular weight
of a single hydrogen ion). No maximum limit is enforced.
"Waste matrix effects" refers to the effect that the composition of the waste has on a constituent's
solubility in the waste or the tendency for the chemical to evaporate from the waste. For example, hexane has a
solubility in distilled water of approximately 12 mg/L; however, its solubility in methanol is much higher (more than
100,000 mg/L) (Perry and Green, 1984). Therefore, it is likely that hexane will remain dissolved in a solution of 10
percent methanol in water at higher concentrations than the aqueous solubility limit of 12 mg/L suggests.
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IWAIR User's Guide Appendix B
B.4 User-Override Emission Rates (Screens 4A and 4B)
Override Emission Rates. You may choose either to enter your own emission rates for
all chemicals modeled or to override IWAIR's calculated emission rates for some or all of the
chemicals modeled. Override emission rates may be based on measured data or modeled results
from an emissions model outside of IWAIR, but regardless of source, should reflect a long-term
average, not a short-term peak.
This input has different units in risk calculation mode versus allowable concentration
mode:
• In risk mode, this input should be the actual measured or modeled emissions from
your unit, normalized on area (in g/m2/s). If emission rates are based on modeled
rates, they should correspond to the actual waste concentrations in your unit.
Emissions in g/s should be normalized to area by dividing by the area of the unit.
• In allowable concentration mode, the emission rate should either be based on
modeled emissions corresponding to a waste concentration of 1 mg/kg or 1 mg/L,
or they should be normalized to concentration by dividing by the actual waste
concentration present when the emissions were measured or modeled. The units
for allowable concentration mode emission rates (g/m2-s per mg/kg or mg/L)
reflect this. Emissions measured or modeled in g/s should also be normalized to
area by dividing by the area of the unit.
You may input one override emission rate per chemical. In risk mode, IWAIR assumes
this emission rate corresponds to the waste type (aqueous or organic) you chose on Screen 3,
WMU DATA FOR CHEMDAT8. In allowable concentration mode, IWAIR assumes this emission rate
corresponds to an aqueous waste. As a result, IWAIR will not output concentrations in
concentration mode in excess of each chemical's solubility or saturation limit if you have entered
user-override emission factors.
Source and Justification for User-Override Values. If you enter override emission
factors, you must document their source in this field. The justification field may not be left
blank.
B.5 ISCST3 or User-Override Dispersion Factors (Screen 5A)
Distance to Receptor (m). This is the distance from the edge of your unit to the receptor
for whom you want to estimate risk or allowable concentration. You must choose from one of
the six values available in IWAIR: 25, 50, 75, 150, 500, or 1,000 m. Choose the distance that
best approximates the location of your receptors. If you are using IWAIR's dispersion factors,
they will correspond to the distance you select; selecting a distance smaller than the actual
distance to receptors near your unit will overestimate risk, and selecting a distance larger than the
actual distance will underestimate risk. If you enter your own dispersion factors, this input is
only for your reference and is not used in calculations. Therefore, you should select the distance
that most closely approximates the distance your dispersion factor applies to.
B-35
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IWAIR User's Guide Appendix B
Receptor Type. Two different types of exposed individuals, worker and resident, can be
modeled with IWAIR. The dispersion factors do not vary with receptor type; however, receptor
type is chosen here for convenience. The difference between these two receptor types lies in the
exposure factors, such as body weight and inhalation rate, used to calculate risk for carcinogens.
There is no difference between them for noncarcinogens because calculation of noncarcinogenic
risk does not depend on exposure factors. The assumptions for residents reflect males and
females from birth through age 30; it is important to consider childhood exposures because
children typically have higher intake rates per kilogram of body weight than adults. The actual
exposure duration used for residents is the smaller of 30 years or the operating life of the unit that
you entered (except for land application units, for which the exposure duration for residents is
always 30 years regardless of operating life). Exposure for residents starts at birth and continues
for the length of the exposure duration, using the appropriate age-specific exposure factors. The
assumptions for workers reflect a full-time, outdoor worker; all exposure is assumed to occur as
an adult. The exposure duration for workers is the smaller of 7.2 years or the operating life of the
unit (except for land application units, for which the exposure duration for workers is always 7.2
years regardless of operating life). For more information on the specific exposure factors used
for residents and workers, see the IWAIR Technical Background Document.
User-Override Dispersion Factors. You may choose either to enter your own dispersion
factors for all receptors modeled or to override IWAIR's calculated dispersion factors for some
or all of the receptors modeled. Note that dispersion factors are not chemical-specific, nor are
they specified to receptor type (resident or worker). Dispersion factors may be based on
measured air concentrations or air concentrations modeled outside of IWAIR. If based on
modeled air concentrations, they should correspond to an emission rate of 1 |j,g/m2-s. If based on
measured air concentration data, they should be normalized to emission rate by dividing by the
actual emission rate measured or modeled. The units for dispersion factors (|J,g/m3 per |j,g/m2-s)
reflect this. Note that when you enter your own dispersion factors, you are not limited to the six
receptor distances included in IWAIR. In this circumstance, those distances are for your
reference only.
Source and Justification for User-Override Values. If you enter override dispersion
factors, you must document their source in this field. If your receptor distances differ from the
distances available in IWAIR, it may be useful to document here the actual receptor distances for
each numbered receptor. The justification field may not be left blank.
B.6 Results Screen (Screen 6)
B.6.1 Target Risk and Hazard Quotient Value
These inputs are needed for allowable concentration mode only. In risk mode, risk and
HQ are calculated by IWAIR.
Risk Value for Carcinogens. Choose one of the five values available. A higher risk
value represents greater risk and will result in lower allowable concentrations. This value is not
required if no carcinogens are being modeled (i.e., CSF is NA for all chemicals modeled).
B-36
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IWAIR User's Guide Appendix B
Hazard Quotient Value for Noncarcinogens. Choose one of the five values available.
A higher HQ value represents greater likelihood of health effects and will result in lower
allowable concentrations. This value is not required if no noncarcinogens are being modeled
(i.e., RfC is NA for all chemicals modeled).
B.6.2 Health Benchmarks
Parameter guidance for health benchmarks is provided in Section B.2.2.3.
B.7 References
ATSDR (Agency for Toxic Substances and Disease Registry). 2001. Minimal Risk Levels
(MRLs)for Hazardous Substances. http://atsdrl.atsdr.cdc.gov:8080/mrls.html
Budavari, S. (Ed.). 1996. The Merck Index, An Encyclopedia of Chemicals, Drugs, and
Biologicals. 12th Edition. Merck & Co. Inc., Rahway, NJ.
CalEPA (California Environmental Protection Agency). 1999a. Air Toxics Hot Spots Program
Risk Assessment Guidelines: Part II. Technical Support Document for Describing
Available Cancer Potency Factors. Office of Environmental Health Hazard Assessment,
Berkeley, CA. Available online at http://www.oehha.org/scientific/hsca2.htm.
CalEPA (California Environmental Protection Agency). 1999b. Air Toxics Hot Spots Program
Risk Assessment Guidelines: Part III. Technical Support Document for the
Determination ofNoncancer Chronic Reference Exposure Levels. SRP Draft. Office of
Environmental Health Hazard Assessment, Berkeley, CA. Available online at
http ://www. oehha. org/hotspots/RAGSII. html.
CalEPA (California Environmental Protection Agency). 2000. Air Toxics Hot Spots Program
Risk Assessment Guidelines: Part III. Technical Support Document for the
Determination ofNoncancer Chronic Reference Exposure Levels. Office of
Environmental Health Hazard Assessment, Berkeley, CA. Available online (in 3
sections) at http://www.oehha.org/air/chronic_rels/22RELS2k.html,
http: //www. oehha. org/air/chroni c_rel s/42kChREL. html,
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(Ed.). 1991. Handbook of Environmental Degradation Rates. Lewi s Publi shers,
Chelsea, MI.
B-37
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IWAIR User's Guide Appendix B
Kollig, H.P. 1993. Environmental Fate Constants for Organic Chemicals Under Consideration
for EPA 's Hazardous Waste Identification Projects. EPA/600/R-93/132., Athens, GA.
August.
Lyman, W.J., W.F. Reehl, and D.H. Rosenblatt. 1990. Handbook of Chemical Property
Estimation Methods: Environmental Behavior of Organic Compounds. American
Chemical Society, Washington, DC.
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Francisco, p. 410.
Metcalf and Eddy, Inc. 1979. Wastewater Engineering: Treatment, Disposal and Reuse. Edited
by Tchobanoglous, G., McGraw-Hill, Inc.
Perry, R.H., and D.W. Green. 1984. Perry's Chemical Engineer's Handbook, 6th Edition.
McGraw-Hill, New York.
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Edition. McGraw-Hill, New York.
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Science Center, Syracuse, NY. http://esc.syrres.com/efdb/Chemfate.htm. Accessed July
2001.
U.S. EPA (Environmental Protection Agency). 1986. Addendum to the Health Assessment
Document for Tetrachloroethylene (Perchloroethylene). Updated Carcinogenicity
Assessment for Tetrachloroethylene (Perchloroethylene, PERC, PCE). External Review
Draft. EPA/600/8-82-005FA. Office of Health and Environmental Assessment, Office of
Research and Development, Washington DC.
U.S. EPA (Environmental Protection Agency). 1987a. Addendum to the Health Assessment
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Trichloroethylene. External Review Draft. EPA/600/8-82-006FA. Office of Health and
Environmental Assessment, Office of Research and Development, Washington DC.
U.S. EPA (Environmental Protection Agency). 1987b. Processes, Coefficients, and Models for
Simulation Toxic Organics and Heavy Metals in Surface Waters. EPA/600/3-87/015.
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Tables (HEAST). EPA-540-R-97-036. FY 1997 Update.
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(SCDM). Office of Emergency and Remedial Response. Web site at
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B-38
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IWAIR User's Guide Appendix B
U.S. EPA (Environmental Protection Agency). 1998a. Hazardous waste management system;
identification and listing of hazardous waste; solvents; final rule. Federal Register
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U.S. EPA (Environmental Protection Agency). 1998b. Risk Assessment Paper for: Evaluation
of the Systemic Toxicity ofHexachlorobutadiene (CASRN 87-68-3) Resulting from Oral
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Appendix C
Physical-Chemical Property Values
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IWAIR User's Guide
Appendix C
Table C-l. Molecular Weights and Densities for IWAIR Constituents
CAS
50000
50328
55185
56235
56495
57976
62533
67561
67641
67663
67721
68122
71432
71556
74839
74873
75014
75058
75070
75092
75150
75218
75252
75274
75354
75569
75694
75718
76131
77474
78591
78875
78933
79005
79016
79061
79107
79345
79469
80626
Chemical Name
Formaldehyde
Benzo(a)pvrene
N-Nitrosodiethvlamine
Carbon tetrachloride
3-Methylcholanthrene
7,1 2-Dimethy Ibenz [al anthracene
Aniline
Methanol
Acetone
Chloroform
Hexachloroethane
N,N-Dimethyl formamide
Benzene
1,1,1- Trichloroethane
Methyl bromide
Methyl chloride
Vinyl chloride
Acetonitrile
Acetaldehyde
Methylene chloride
Carbon disulfide
Ethvlene oxide
Tribromomethane
Bromodichloromethane
1.1-Dichloroethvlene
Proovlene oxide
Trichlorofluoromethane
Dichlorodifluoromethane
1 .1 .2-Trichloro- 1 .2.2-trifluoroethane
Hexachlorocvclopentadiene
Isoohorone
1 ,2-Dichloropropane
Methyl ethyl ketone
1,1 ,2- Trichloroethane
Trichloroethvlene
Acrvlamide
Acrylic acid
1,1 ,2,2-Tetrachloroethane
2-Nitroorooane
Methyl methacrvlate
Molecular Weight (g/mole)
30
252
102
154
268
256
93
32
58
119
237
73
78
133
95
50
63
41
44
85
76
44
253
164
97
58
137
121
187
273
138
113
72
133
131
71
72
168
89
100
Density (g/cm3)
0.82
1.35
0.94
1.59
1.28
1.02
1.02
0.79
0.79
1.48
2.09
0.94
0.88
1.34
1.68
0.91
0.91
0.79
0.78
1.33
1.26
0.89
2.90
1.98
1.21
0.86
1.49
1.49
1.56
1.70
0.93
1.16
0.81
1.44
1.46
1.12
1.05
1.60
0.98
0.94
03
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IWAIR User's Guide
Appendix C
Table C-l. Molecular Weights and Densities for IWAIR Constituents
CAS
85449
87683
91203
92875
95501
95534
95578
95658
96128
98011
98828
98953
100414
100425
106467
106887
106898
106934
106990
107028
107051
107062
107131
107211
108054
108101
108883
108907
108930
108952
109864
110496
110543
110805
110861
111159
118741
120821
121142
121448
Chemical Name
Phthalic anhydride
Hexachloro- 1 ,3-butadiene
Naphthalene
Benzidine
o-Dichlorobenzene
o-Toluidine
2-Chlorophenol
3,4-Dimethylphenol
1 ,2-Dibromo-3-chloropropane
Furfural
Cumene
Nitrobenzene
Ethylbenzene
Styrene
p-Dichlorobenzene
1 ,2-Epoxybutane
Epichlorohydrin
Ethylene dibromide
1,3-Butadiene
Acrolein
Allvl chloride
1 ,2-Dichloroethane
Acrvlonitrile
Ethvlene alvcol
Vinvl acetate
Methyl isobutvl ketone
Toluene
Chlorobenzene
Cvclohexanol
Phenol
2-Methoxvethanol
2-Methoxvethanol acetate
n-Hexane
2-Ethoxvethanol
Pvridine
2-Ethoxvethanol acetate
Hexachlorobenzene
1 ,2,4- Trichlorobenzene
2.4-Dinitrotoluene
Triethvlamine
Molecular Weight (g/mole)
148
261
128
184
147
107
129
122
236
96
120
123
106
104
147
72
93
188
54
56
77
99
53
62
86
100
92
113
100
94
76
118
86
90
79
132
285
181
182
101
Density (g/cm3)
1.53
1.56
1.03
1.25
1.31
1.00
1.26
0.98
2.09
1.16
0.86
1.20
0.87
0.91
1.25
0.84
1.18
2.18
0.61
0.84
0.94
1.24
0.81
1.11
0.93
0.80
0.87
1.11
0.96
1.05
0.96
1.01
0.65
0.93
0.98
0.98
2.04
1.46
1.32
0.73
C4
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IWAIR User's Guide
Appendix C
Table C-l. Molecular Weights and Densities for IWAIR Constituents
CAS
122667
123911
124481
126998
127184
630206
924163
930552
1319773
1330207
1634044
1746016
7439976
7439977
10061015
10061026
Chemical Name
1 ,2-Diphenvlhvdrazine
1,4-Dioxane
Chlorodibromomethane
Chloroprene
Tetrachloroethylene
1 ,1 ,1 ,2-Tetrachloroethane
N-Nitrosodi-n-butylamine
N-Nitrosopyrrolidine
Cresols (total)
Xylenes
Methyl tert-butyl ether
2,3,7,8-TCDD
Mercury
Divalent Mercury
cis- 1 ,3-Dichloropropylene
trans- 1 ,3-Dichloropropylene
Molecular Weight (g/mole)
184
88
208
89
166
168
158
100
108
106
88
322
201
201
111
111
Density (g/cm3)
1.16
1.03
2.45
0.96
1.62
1.54
0.90
1.09
1.06
0.87
0.74
1.83
13.53
5.60
1.22
1.22
C-5
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