United States
Environmental Protection Agency
                            Office of Solid Waste
                            Washington, DC 20460
EPA 530-R-99-005
December T998
&EPA
Industrial Waste Air Model (IWAIR)
User's Guide

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                                 Table of Contents
Section
Page
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    RiskModel	1-4
       1.3    Estimation Process	1-5
       1.4    Capabilities and Limitations of the Model	1-7
       1.5    About This User's Guide	1-9

2.0    Getting Started	2-1
       2.1    Hardware and Software Requirements  	2-1
       2.2    Installing the Program	2-1
       2.3    Running IWAIR	2-3
       2.4    Starting the Program	2-3
       2.5    Navigating the Tool	2-3
       2.6    Online Help  	2-6
       2.7    Troubleshooting	2-6

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 	3-2

4.0    Completing Forward Calculation to Risk  	4-1
       4.1    Method, Meteorological Station, WMU (Screen 1A) 	4-6
       4.2    Wastes Managed (Screen 2)	4-9
       4.3    Enter WMU data for Using CHEMDAT8 Emission Rates	4-10
       4.4    Emission Rates	4-16
             4.4.1    Using CHEMDAT8 Emission Rates (Screen 4A) 	4-16
             4.4.2    User-Specified Emission Rates (Screen 4B)	4-17
       4.5    Dispersion Factors	4-18
             4.5.1    Using ISCST3 Default Dispersion Factors (Screen 5A)	4-18
             4.5.2    User-Specified Dispersion Factors (Screen 5B)	4-20
       4.6    Results (Screen 6) 	4-22

5.0    Completing Backward Calculation to Protective Waste Concentration  	5-1
       5.1    Method, Meteorological Station, WMU (Screen 1A)	5-7
       5.2    Wastes Managed (Screen 2)	5-10
       5.3    Enter WMU Data for Using CHEMDAT8 Emission Rates  	5-11
       5.4    Emission Rates	5-16
             5.4.1    Using CHEMDAT8 Emission Rates (Screen 4A)  	5-16
                                           111

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                          Table of Contents (continued)
Section
       5.5
             5.4.2   User-Specified Emission Rates (Screen 4B)
             Dispersion Factors
             5.5.1   Using ISCST3 Default Dispersion Factors (Screen 5A)
             5.5.2   User-Specified Dispersion Factors (Screen 5B)
             Results (Screen 6)
6.0

7.0
5.6

Example Calculations

References 	
 Page

. 5-17
. 5-18
, 5-18
, 5-20
. 5-21
                                                                                   6-1
                                                                                   7-1

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                                   List of Figures
Figure
1-1
IWAIR Approach for Developing Risk or Protective Waste Concentrations:
This figure shows the steps in the tool to assist the user in developing risk or
protective waste concentration estimates	
                                                                          Page
                                                                                  1-6
2-1    Menu bar in the IWAIR program	2-4

3-1    Receptor Locations  	3-6

4-1    IWAIR Approach for Completing Forward Calculation to Risk:  Pathway 1 - Using
       CHEMDAT8 Emission Rates and ISCST3 Default Dispersion Factors	4-2
4-2    IWAIR Approach for Completing Forward Calculation to Risk:  Pathway 2 - Using
       CHEMDAT8 Emission Rates and User-specified Dispersion Factors 	4-3
4-3    IWAIR Approach for Completing Forward Calculation to Risk:  Pathway 3 - Using
       User-specified Emission Rates and ISCST3 Default Dispersion Factors  	4-4
4-4    IWAIR Approach for Completing Forward Calculation to Risk:  Pathway 4 - Using
       User-specified Emission Rates and Dispersion Factors	4-5

5-1    IWAIR Approach for Completing Backward Calculation to Protective Waste
       Concentration:  Pathway 1 - Using CHEMDAT8 Emission Rates and ISCST3
       Default Dispersion Factors	5-3
5-2    IWAIR Approach for Completing Backward Calculation to Protective Waste
       Concentration:  Pathway 2 - Using CHEMDAT8 Emission Rates and User-specified
       Dispersion Factors	5-4
5-3    IWAIR Approach for Completing Backward Calculation to Protective Waste
       Concentration:  Pathway 3 - Using User-specified Emission Rates and ISCST3 Default
       Dispersion Factors	5-5
5.4    IWAIR Approach for Completing Backward Calculation to Protective Waste
       Concentration:  Pathway 4 - Using User-specified Emission Rates and Dispersion
       Factors  	5-6
                                   List of Tables

Table                                                                           Page

1-1    Constituents Included in IWAIR	1-3

2-1    IWAIR Menu Tabs and Associated Screens 	2-5

6-1    Parameter Values Used in Estimating Time Weighted Average Exposure	6-3

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Section 1.0
Introduction
1.0  Introduction

       This document describes how to use the Industrial Waste Air Model (IWAER). A companion
document, the Industrial Waste Air Model (IWAIR) Technical Background Document, provides technical
background information. This section provides an overview of IWAIR, its purpose, operation, and
application. The three major components of the system, the emissions, dispersion, and results models,
are described, and an overview of the remainder of this User's Guide is provided.

1.1   Guide for Industrial Waste Management and IWAIR

       EPA and representatives from 12 state environmental agencies have developed a voluntary Guide
for Industrial Waste Management to recommend a baseline of protective design and operating practices
to manage industrial non-hazardous waste throughout the country. The guidance is designed for facility
managers, regulatory agency staff and the public and reflects four underlying principles:

       •     Adopt a multimedia approach to protect human health and the environment;

       •     Tailor management practices to risk in this 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 their programs;

       •     Foster partnerships among facility managers, the public and regulatory agencies.

       The Guide recommends best management practices and the key factors to take into account to
protect groundwater, surface water and ambient air quality in siting, operation, design, monitoring,
corrective action, closure and post closure care. In particular the guidance recommends risk-based
approaches to choose liner systems and waste application rates for groundwater protection and to
evaluate the need for air controls. The CD ROM version of the Guide includes user friendly air and
ground-water models to conduct these risk evaluations.

       The chapter of the Guide entitled "Protecting Air Quality" highlights several key
recommendations:

       •     Adopt controls  to minimize paniculate emissions.

       •     Determine whether waste management units at a facility are addressed by Clean Air Act
             requirements and comply with those requirements.
                                                                                         1-1

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Section 1.0
Introduction
       •      If waste management units are not specifically addressed by Clean Air Act requirements,
             use IWAIR to assess risks associated with volatile air emissions from units.

       •      Implement pollution prevention, treatment or controls to reduce volatile air emission
             risks.

       EPA developed the Industrial Waste Air Model (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 the fetus or neurological effects in an adult). With a limited amount of site-
specific information IWAIR can estimate whether specific wastes and management practices may pose
an unacceptable risk to human health.

1.2    Model Design

       IWAIR is an interactive computer program with three main components: an emission model; a
dispersion model to estimate fate and transport of constituents through the atmosphere and determine
ambient air concentrations at specified receptor locations; and 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. 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 the user to provide the
required waste- and unit-specific data. Once these data are entered, the model calculates and displays
chemical-specific emission rates.  If users decide not to develop or use the CEEMDAT8 rates, they can
enter their own site-specific emission rates (g/m2-s).
 1-2

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Section 1.0
                                                              Introduction
                              Table 1-1.  Constituents Included in IWAIR
      Chemical
     Abstracts
        -(CAS)
     "" Number
Compound Name
Chemical
Abstracts"
'   ^(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-1,3-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                           Propyiene oxide
                          110861                                  Pyridine
                          100425                                  Styrene
                         1746016                           TCDD, 2,3,7,8 -
                          630206                  Tetrachloroethane, 1,1,1,2-
                           79345                  Tetrachloroethane, 1,1,2,2-
                          127184                        Tetrachloroetnylene
                          108883                                  Toluene
                        10061026                 trans-1,3-Dichloropropylene
                           75252                          Tribromomethane
                           76131          Trichloro-1,2,2-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
                                                                                                          1-3

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Section 1.0
Introduction
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 ug/m2 - s) to obtain a unitized air
concentration (UAC), also called a dispersion factor, which is measured in ug/m3 per ug/m2 -s. The total
air concentration estimates are then developed by multiplying the constituent-specific emission rates
derived from CHEMDAT8 (or from another source) with a site-specific dispersion factor. Running
ISCST3 to develop a new dispersion factor for each location/WMU is very 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:

       •       29 meteorological stations, chosen to represent the nine general climate regions of the
              continental U.S.;

       •       4 unit types;

       •       14 surface area sizes for landfills, land application units, and surface impoundments, and
              7 surface area sizes and 2 heights for waste piles;

       •       6 receptor distances from the unit (25, 50,75,  150, 500, 1000 meters);

       •       16 directions in relation to the edge of the unit.

       The default dispersion factors  were derived by modeling each of these scenarios, then choosing
as the default the maximum dispersion factor for each waste management unit/surface
area/meteorological station/receptor distance combination.

       Based on the size and location of a unit,  as specified by a user, IWAIR. selects an appropriate
dispersion factor from the default dispersion factors in the model. If the user specifies a unit surface area
that falls between two of the sizes already modeled, a linear interpolation method will estimate
dispersion in relation to the two closest unit sizes.

       Alternatively, a user 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 waste
 1-4

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Section 1.0
Introduction
concentration (Cw) in the unit that must not be exceeded to protect 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.  IWAJR
maintains standard health benchmarks (cancer slope factors for carcinogens and reference concentrations
for noncarcinogens) for 95 constituents.  These health benchmarks are from the Integrated Risk
Information System (IRIS) and the Health Effects Assessment Summary Tables (HEAST) (U.S. EPA,
1998a, 1997b).  IWAIR uses these data to perform either a forward calculation to obtain risk estimates
or a backward calculation to obtain protective waste concentration estimates.

1.3    Estimation Process

       Figure 1-1 provides an overview of the stepwise approach the user follows to calculate risk or
protective waste concentration estimates 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 the user provides input data, the program proceeds to the next step.  Each step of the estimation
process is discussed below.

1.     Select Calculation Method. Select one of two calculation methods. Use the forward calculation
       to arrive at chemical-specific and cumulative risk estimates if the user knows the concentrations
       of constituents in the waste. Use the backward calculation method to estimate protective waste
       concentrations not to be exceeded in new units.

2.     Identify Waste Management Unit. Four WMU types can be modeled: surface impoundments
       (Sis), land application units (LAUs), active landfills (LFs), and wastepiles (WPs).  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 wastepiles,
       and tilling depth for LAUs. The  amount of unit-specific data needed as input will vary
       depending on whether the user elects to develop CHEMDAT8 emission rates. IWAIR provides
       default values for several of the operating parameters that you may use, if appropriate.

3.     Define Waste Managed. Specify constituents and concentrations in the waste if you choose a
       forward calculation to arrive at chemical specific risk estimates.  If you choose a backward
       calculation to estimate protective waste concentrations, then specify constituents of concern.

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 29 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 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.
                                                                                           1-5

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Section 1.0
                                                                                                   Introduction
  User Specifies:
  • Calculation option
/"llserSpacffle*:
I  * WMUtype              *
I  • WMU Information (e.g., operating
I    parameters   .
           Clear SpecHta*:
            Constituents
            (choose up to 6 from list of 95)
            Concentration for forward calculation
            .
           Usar Specifies:                     5
           •  Emission rate option     .          '""-')
           •  Facility location for meteorological input  .)
        (•User Specifies:                   ^
        I  • Dispersion factor option         •    j
        |  • Recaptof Information (e.g., distance,   i
        ^ andtype)..     :  '•• ^
        fUaer Specifies:

        I • RJsfc level for backward calculation

         ^'**~-«..4.J-J.H.>ltWTT-I"	     " •'"--—
                                                             Select Calculation Method
                                                              Forward Calculation to Risk
                                                                       Or
                                                            Backward Calculation to Protective
                                                            Waste Concentration
                                                                                  .<--*f.»*a3*-i>*v«j
                                                                    Identify WWIU
                                                               Land Application Unit (LAU)
                                                               Waste Pile (WP)
                                                               Surface Impoundment (SI)
                                                               aerated and quiescent
                                                              .  Landfill (LF)	
                                                             Determine Emission Rates
                                                            CHEMDAT8
                                                                 Or
                                                     User Specified Emission Rates
                                                           Determine Dispersion Factors   |
                                                    ISCST3 Default Dispersion Factors
                                                                 Or
                                                      User-specified Dispersion Factors
                                                          Calculate Ambient Air Concentration
                                                         Calculates ambient air concentrations for
                                                         each receptor based on emission and
                                                         dispersion data
                                                       Forward Calculation to Risk

                                                 1. Chemical-specific Carcinogenic Risk
                                                 2. Chemical-specific Non-carcinogenic Risk
                                                 3. Total Cancer Risk
                                                                  Or
                                                         Backward calculation
                                                  to protective waste concentration (Cw)

                                                   •  Cwforwastewaters(mg/L)

                                                   •  Cw for solid wastes (mg/kg)

       Figure 1-1.  IWAIR Approach for Developing Risk or Protective Waste Concentrations: This
       figure shows the steps in the tool to assist the user in developing risk or protective waste
       concentration estimates.
 1-6

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Section 1.0
Introduction
4.     Determine Dispersion. You can provide site-specific unitized dispersion factors (ug/m3 per
       |ag/m2-s) or have the model develop dispersion factors based on user-specified WMU information
       and the IWAIR default dispersion data. 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 which 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.

5.     Calculate Ambient Air Concentration. For each receptor, the model combines emission rates
       and dispersion data to estimate ambient air concentrations for all waste constituents of concern.

6.     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 a forward or backward
       calculation:

       Forward calculation: Results are estimates of cancer and non-cancer risks from inhalation
       exposure to volatilized constituents in the waste. If risks are too high, options are: 1) implement
       unit controls to reduce volatile air emissions; 2) implement pollution prevention or treatment to
       reduce volatile organic compound (VOC) concentrations before the waste enters the unit; or 3)
       conduct a full site-specific risk assessment to more precisely characterize risks from the unit.

       Backward 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., 1 x 10~6 or hazard
       quotient 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 or treatment to reduce
       VOC concentrations in the waste; 2) modify waste management practices to better control VOCs
       (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 Limitations 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 not be appropriate or when another
model would be a better choice.
                                                                                            1-7

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Section LO
                                                                                   Introduction
Capabilities
Limitations
              The model provides a reasonable, conservative representation of VOC inhalation risks
              associated with waste management units.

              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 run a forward calculation from the unit or a backward calculation
                     from the receptor point.

              •       You can modify health benchmarks (HBNs) and target risk level, when
                     appropriate and in consultation with other stakeholders.
              Chemicals of Concern. If waste contains chemicals that (1) are not included in the model
              (see Table 1-1) and (2) have human health effects and may be present in concentrations
              sufficient to pose a risk to public health via inhalation exposure, the model will not fully
              characterize risks for that WMU since these additional chemicals would be excluded from
              consideration.

              Release Mechanisms and Exposure Routes. The model considers exposures from
              breathing ambient air. It does not address potential risks attributable to paniculate
              releases nor does it address risks associated with indirect routes of exposure (i.e,
              noninhalation routes of exposure). 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 waste management units. Competing mechanisms such as runoff,
              erosion, and leaching are not accounted for in the model.  In so much as these competing
              processes actually occur, the model would tend to slightly overestimate the volatile
              emissions.  On the other hand, one could interpret this situation as being representative of
              WMUs that have leachate controls, such as liners, or erosion and runoff controls. Such
              controls would tend to inhibit these processes and result in more volatile emissions.

              Waste Management Practices. The user specifies a number of unit-specific parameters
              that significantly impact the inhalation pathway (e.g., size, type, and location of WMU,
              which is important hi identifying meteorological conditions). However, the model cannot
 1-8

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Section 1.0
Introduction
              accommodate information concerning control technologies such as covers that might
              influence the degree of volatilization (e.g., whether a wastepile 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.

       •       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 (1) generate site-specific air dispersion modeling results for the site and enter those
              results into the program, or (2) use a site-specific risk modeling approach other than
              IWAIR. The model will inform the user which of the 29 meteorological stations is used
              for a facility. If the local meteorological conditions are very different from the site
              chosen by the model, it would be more accurate to choose a different model.

              The terrain type surrounding a facility can impact 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 simple
              or flat terrain. The Guideline on Air Quality Models (U.S. EPA, 1993) can assist users in
              determining whether a facility is in an area of simple, intermediate, or complex terrain.

       •       Receptors Type and Location. IWAIR has predetermined worker and resident receptors,
              six receptor locations, and predetermined exposure factors. The program cannot be used
              to characterize risk for other possible exposure scenarios. For example, the model can
              not evaluate receptors that are closer to the unit than 25 meters or those that are further
              from the unit than 1000 meters.

1.5    About This User's Guide

       The focal point of this User's Guide is to encourage management practices that are protective of
human health and the environment.  The remainder of this document is organized into five sections:

       •       Section 2, Getting Started, identifies system requirements for running IWAIR, provides
              stepwise guidance for installing the program, and introduces the user to program screens
              and navigational tools (e.g., menu tabs, toolbar, and buttons).  It also includes the
              troubleshooting guide.

       •       Section 3, Selecting Calculation Method, WMU Type, and Modeling Pathways, assists
              you, in selecting the appropriate calculation method (i.e., forward calculation to risk
              estimates or backward calculation to protective waste concentration), waste management
              unit type, and modeling pathway. After selecting a calculation mode, the WMU type is
              selected. This section describes the types of units addressed by the model.

              With both forward and backward calculation, you can select from four modeling
              pathways. These four pathways are:
                                                                                             1-9

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Section 1.0
Introduction
              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 forward calculation or Section 5 for
              completing a backward calculation. Each of these sections provides pathway-specific
              guidance as needed.

       •      Section 4, Completing Forward Calculations to Risk, 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 Backward Calculation to Protective Waste Concentration,
              provides detailed guidance to predict protective waste levels based on a user-specified
              risk level. Again follow the screen-by-screen guidance to complete a backward
              calculation.

       •      Section 6, Example Calculation, provides a detailed example of how the program can be
              used to perform forward calculations to estimate inhalation risk or backward calculations
              to estimate protective waste concentrations.

       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.
 1-10

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Section 2.0
Getting Started
2.0 Getting Started

2.1   Hardware and Software Requirements

      The IWAIR tool is a 16-bit Visual Basic application designed to run on an IBM®-conipatible
machine with Windows® 3.1 or Windows® 95 operating systems. It is recommended that the computer
on which this program is installed have at least 16 megabytes (preferably 32 MB) of RAM and a 486
CPU processor (preferably Pentium® processor).  About 10 Mb of free hard drive space is required.
The program does not require any additional software.

2.2   Installing the Program

      The IWAIR computer program is provided to the user on the Guidance CD ROM. Instructions
for installing and uninstalling the program on a computer running either the Windows 3.1 or
Windows 95 operating system are provided below.

Installing from Windows 3.1:

1.     Insert CD ROM into your CD ROM drive.
2.     Open File Manager.
3.     Select the CD ROM drive.
4.     Double click on Setup.exe.
5.     The setup program will prompt you to enter a name for the directory in which IWAIR 1.0 will be
      installed.
6.     Follow the instructions  on the screen.

OR

1.     Insert CD ROM into your CD ROM drive.
2.     From the Windows FILE menu, select Run.
3.     Type 'D:\SETUP' or, as appropriate, replace D: in this command with the correct drive
      designation.
4.     Press Enter or select OK.
5.     The setup program will prompt you to  enter a name for the directory in which IWAIR 1.0 will be
      installed.
6.     Follow the instructions on the screen.
                                                                                      2-1

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Section 2.0
                                                                         Getting Started
Uninstalling from Windows 3.1:

1.      Open File Manager.
2.      Open IWAIR directory folder.
4.      Double click on UninstalLexe (or Unwise.exe).
5.      The uninstall program will navigate you through removing the program from your computer.
6.      Follow the instructions on the screen.

Installing from Windows 95

1.      Insert CD ROM into your CD ROM drive.
2.      Open My Computer.
3.      Select the CD ROM drive.
4.      Double click on Setup.exe.
4.      The setup program will prompt you to enter a name for the directory in which IWAIR 1.0 will be
       installed. If no directory is specified, the program will automatically be installed in a directory
       called IWAIR under the Windows 95 Program Files subdirectory.
5.      Follow the instructions on the screen.
OR

1.
2.
3.

4.
5.
6.
Insert CD ROM into your CD ROM drive.
Select Start, Run.
Type 'D:\SETUP' or, as appropriate, replace D: in this command with the correct drive
designation.
Press Enter or select OK.
The setup program will prompt you to enter a name for the directory in which IWAIR 1.0 will be
installed. If no directory is specified, the program will automatically be installed in a directory
called IWAIR under the Windows 95 Program Files subdirectory.
Follow the instructions on the screen.
Uninstalling from Windows 95

1.     Select Start.
2.     Navigate system and select Windows Explorer.
3.     Open IWAIR directory folder.
4.     Double click on UninstalLexe (or Unwise.exe).
5.     The uninstall program will navigate you through removing the program from your computer.
6.     Follow the instructions on the screen.
 2-2

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Section 2.0
Getting Started
2.3    Running IWAIR

       To run the program from Windows 3.1, double click on the IWAIR icon. From Windows 95,
navigate the Windows 95 Start menu to find and select the IWAIR folder and double-click the
IWAIR.exe file, or double click on the IWAIR icon on the desktop.

2.4    Starting the Program

       Start IWAIR by clicking on the START button of the program title page. During a single run,
the program can be used to conduct modeling for one unit (choice of four unit types:  surface
impoundment, land application unit, active landfill, and wastepile) and will simultaneously evaluate up
to six chemicals of concern and up to five different receptors.  Once the START button is selected, the
program automatically opens the Method, Met Station, WMU menu tab.

2.5    Navigating the Tool

       The following tools facilitate user interaction with the IWAIR program:

       •     Menu tabs
       •     Menu bar
       •     Command buttons
       •     Message prompts.

Each of these tools is explained in more detail in this section.

Menu Tabs

       Menu 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 opened screen. There
are six menu tabs, one for each of the following screens:

             Method, Met.  Station, WMU
       •     Wastes Managed
             WMU data for CHEMDAT8
       •     Emission Rates
       •     Dispersion Factors
       •     Results.

       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.
Specifically, all calculated values on subsequent screens will be lost, as will any entered data on the
Emission Rates, Dispersion Factors, and Results screens if those are after the changed screen. Entered

                               .                                            —           —

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Section 2.0
                                                                   Getting Started
data on the Wastes Managed and WMU Data for CHEMDAT8 screens will be retained if they are still
relevant. 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 has 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 Rate 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
Rate screen.

       Table 2-1 describes each of these menu 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
DONE command button is clicked. To return to a previously completed input screen, click on the menu
tab of choice.

Menu Bar

       As shown in Figure 2-1, a menu bar is also provided with IWAIR that allows the user to perform
tasks  such as starting a new run, importing data from a previous run, and exiting the program.

Command Buttons

       In addition to the menu tabs and menu bar, several command buttons are provided on each screen
that initiate an action by the program. For instance,  click the DONE command button after all data have
been entered on a screen and you are ready to proceed to the next screen.
                                                      Z. Select W«t«Man«aem«mWt(V«MU) type
                               Fwwwdralcuistai to estimate
                               specified chemical ccrcwirations
                               Back rafcuMBontoesttnofe chemical:
                               coocairaflora based on specified risk
                a. S«^cflonof BMtMatoofok>alc»l Satkmfof Ste--!^ _
                               Back rakajiabonto estimate chemtarf
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              Figure 2-1. Menu bar in the IWAIR program.
2-4

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                                                     Table 2-1. IWAIR Menu Tabs and Associated Screens
            Menu Tab
                                  Description of Screen Associated with Menu Tab
          Method, Met
          Station, WMU
    Select calculation method (i.e., forward calculation to inhalation risk or backcalculation to a protective waste concentration).
    Select waste management unit (WMU) Type.  The WMU choices include surface impoundment, land application unit, active landfill, and wastepile.
    Enter zip code or latitude and longitude of site to allow the program to select the most representative meteorological station from the program's 29
    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 6 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 in the IWAIR program).
    If you selected to perform a forward calculation to risk, then the concentration of each chemical will need to be provided under this screen.
          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. A variety of site-specific data (e.g., unit dimensions and waste loading information) will need to be provided.  Default values are provided adjacent to
the data box for several of the input parameters.
          Emission Rates
CHEMDAT8 emission rates are viewed and confirmed or user-specified emission rates are entered.  Source and justification for user-specified emission
rates should also be entered on this screen.
          Dispersion
          Factors
Calculate dispersion factors or provide user-specified dispersion factors. When this tab is clicked, the dispersion factors screen allows you to identify up to
5 receptors (i.e., potentially exposed individuals). For each receptor, the user specifies the distance to the receptor and the receptor type (i.e., resident or
worker). Dispersion factors are calculated by the program based on these data. Alternatively, you may enter you own dispersion factors.  Source and
justification for the user-supplied dispersion factors should also be entered on this screen.
          Results
Two different result screens are associated with this tab, one for forward calculation to risk and one for backward calculation to protective waste
concentrations. You will be able to:
•   Select the receptor(s) (up to 5 receptors) for which the calculation is to be performed.
•   View the chemicals of concern that were selected under the wastes managed screen.
•   View to confirm input data determined in previous screens.  These data include the distance from the unit to the receptor, receptor type, and
    dispersion factors. These data are to be used by IWAIR in the risk/waste concentration calculations.
•   View and override program-supplied health benchmarks. If you choose to override these data, the source and justification for the user-supplied
    benchmarks must be provided.
•   Calculate results by clicking the CALCULATE button on the forward calculation screen results in the generation and displaying of risk estimates for
    carcinogens and hazard quotients for noncarcinogens. Clicking the CALCULATE button on the backward calculation screen results in the generation
    and displaying of protective waste concentrations for each of the chemicals of concern.
•   Select target risk level (e.g., 1x10'5,1x10'6) and/or a hazard quotient (e.g., 0.5,1) that will serve as the starting point for the backward calculation for
    each chemical.
to
Ul

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Section 2.0
Getting Started
   Every screen in the IWAIR has a HELP button so you can easily access the system's online help
associated with the screen in use. The format of the help system is the same as mat of a standard
Windows application.

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.

2.6    Online Help

   The program provides online help that can be accessed from any screen by clicking on the HELP
command button. The HELP command button has a standard Windows format with a contents and
searchable index. The online help contains information presented in this document.

2.7    Troubleshooting
Problem
Category
Display
Printing
Uninstalling
Miscellaneous
Description of problem
The gray screens in the
program appear "blotched"
and are not uniformly gray in
color.
Large fonts on screen, text
that drops off the screen,
incomplete display tables,
etc.
Screens are not displayed
correctly, display not
optimized.
Margins on the printed
reports are not adjusted, or
text is "cut off at the edges.
No uninstall.exe file in folder
Low system resources
message is displayed, or
program is crashing
frequently
Solutions
Changing your monitor's display settings will fix this problem. For
Windows 95 users, 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). Note that these options may not be available on
all machines, depending on the type of monitor and the drivers used.
This problem occurs when the computer's memory resources are
very low. There are two ways to fix it:
• Exit IWAIR and restart the program, or if this does not work,
• Restart the computer.
If this behavior persists, try closing all other programs except for
IWAIR when using it. (See Miscellaneous)
The IWAIR program display is optimized for screen resolutions of
800 x 600 pixels or higher. To vastly improve the display of IWAIR
screens, increase your screen resolution to 800 x 600 pixels or
higher.
Due to the large quantity of data to be displayed on the reports, the
margins selected for the reports are only 0.25 inches. Printing
functions were tested on an HP Laser Jet 4/4M and higher grade
printers. Using older or dissimilar printers may cause problems
during printing.
If you cannot find an Uninstall.exe file in the IWAIR folder, search
your drive for Unwise.exe. This file will uninstall the IWAIR program.
IWAIR may be unstable when other applications are also open due
to the memory required for running IWAIR. Close out of all other
applications when running IWAIR to free up the maximum
resources for the program.
2-6

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Section 3.0
Selecting Calculation Method, WMU Type, and Modeling Pathways
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: forward and backward. Click on the option button associated with either the
forward (Risk) or the backward (Concentration) calculation option.  Each of these options is discussed
below.

Forward Calculation Method

       The first calculation method is a forward calculation that allows you to develop inhalation risk
estimates based on user-specified waste concentrations. Results from the forward 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., hazard quotients for
noncarcinogens in the waste). Use the forward calculation option to develop risk estimates if the
concentrations of the constituents in the waste are known. 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 organic
compound (VOC) concentrations before the waste enters the unit or applying unit control technologies
or practices to reduce volatile air emissions. The "Protecting Air Quality" chapter of the Guide for
Industrial Waste Management identifies and discusses some emission control options.

Backward Calculation Method

       The second calculation method is a backward calculation that results in the development of waste
concentrations (Cw) that are protective of human health. The calculation method can be applied in
calculating waste concentrations for both wastewaters (Cw in mg/L) and solid waste (Cw in mg/kg).
These concentrations are estimated based on user-defined target cancer and noncancer risk levels (e.g.,
IxlO"5 or IxlO"6 for carcinogens, or hazard quotient [HQ] of 0.5 or 1 for noncarcinogens). You will set
these risk levels on a later screen, the Results Screen.  The program uses information gathered on the
IWAIR screens to calculate a waste concentration for each chemical that would not pose an inhalation
risk to the receptor greater than the selected target level.  The backward calculation option can be used
for estimating protective waste concentrations for those users with units that have not yet received a
waste to determine what concentration(s) would pose an unacceptable risk to potentially exposed
individuals.
                                                                                         3-1

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Section 3.0
Selecting Calculation Method, WMUType, and Modeling Pathways
3.2    Selecting WMU Type

       Identify the WMUs that are used to manage wastes of concern at your facility and ran the model
separately for each unit. Each of the four IWAIR unit types (described below) reflect waste
management practices that are likely to occur at Industrial Subtitle D facilities.

       Surface Impoundment (SB -  In the IWAIR tool, Sis are considered to be ground-based,
flowthrough units. The major source of volatile emissions associated with Sis is the uncovered liquid
surface exposed to the air (U.S. EPA, 1991). Impoundments can be quiescent or aerated. Aeration
and/or agitation are applied to aid in 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 non-aerated Sis. Parameters to which
emissions are most sensitive include surface area, unit depth, waste concentration, retention time,
windspeed for quiescent systems, and biodegradation.

       Tilled Land Application Units (LAUs) - The waste can be tilled or sprayed directly onto the soil
and subsequently mixed with the soil by discing or tilling.  Waste in an LAU is a mixture of sludge and
soil.  IWAIR allows the modeling of tilled LAUs.  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.
Important characteristics for the tilled LAU include surface area (the exposed area from which volatile
emissions can be released) and the application rate (affects  the depth of the contamination, which,  along
with area, defines the extent of the source for volatile emissions).

       Landfills (LFs) - 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-based emission source.

       Wastepiles fWPs) - Wastepiles are typically elevated sources used as temporary storage units for
solid wastes.  Important characteristics for the wastepile include surface area and height. These
parameters define the exposed area from which volatile emissions can be released. Two representative
pile heights (2m and 5m) were used in developing the IWAIR default dispersion factors. These values
are based on the height a frontloader might be able to reach.

3.3   Determining Appropriate Modeling Pathway

       Regardless of the calculation method selected (forward or backward), determine which modeling
pathway to follow in using the tool. After deciding upon the appropriate calculation method and
modeling pathway, proceed to either Section 4 for detailed guidance for completing forward calculations
or Section 5 for backward calculations.
 3-2

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Section 3.0
Selecting Calculation Method, WMU Type, and Modeling Pathways
       You can choose from four pathways that provide you 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, 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).

       CHEMDAT8 considers most of the
competing removal pathways that might limit air
emissions, including adsorption and hydrolysis in
surface impoundments, and biodegradation in all
                      IWAIR Assumptions Made for
                            Modeling Volatile
                       Emissions with CHEMDAT8
              •   Annual average temperature is determined by
                  assigned meteorological station.
              •   Waste is homogeneous.

              Quiescent and Aerated Surface Impoundment
              Assumptions:
              •   Flow-through unit operating at steady state.
              •   SI is well mixed.
              •   Biodegradation rate is first order with respect to
                  biomass concentrations.
              •   Biodegradation rate follows Monod kinetics
                  with respect to contaminant concentrations.
              •   Hydrolysis rate is first order with respect to
                  contaminant concentrations.

              Tilled LAU Assumptions:
              •   Biodegradation occurs

              Landfill Assumptions:
              •   The active cell is modeled as instantaneously
                  filled at time t=0 and open for 1 year.
              •   Cells are either depleted of the constituent or
                  capped after 1 year.
              •   No biodegradation.

              Wastepile Assumptions:
              •   Wastepile operates with fixed volume.
              •   Biodegradation occurs.
                                                                                              3-3

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Section 3.0
Selecting Calculation Method, WMU Type, and Modeling Pathways
types of units. Adsorption is the tendency of a chemical to attach or bind to the surface of particles in
the soil or waste and therefore not volatilize into the air. This tendency to adsorb to particles is an
important process for estimating the concentration of the chemical on particles emitted to the air due to
wind erosion. Biodegradation is the tendency of a chemical to be broken down or decomposed into
less-complex chemicals by organisms in the waste or soil; for IWAIR, biodegradation is not modeled for
landfills, but is modeled for all other WMU types. Similarly, hydrolysis is the tendency of a chemical to
be broken down or decomposed into less-complex chemicals by reaction with water. Chemicals that
decompose due to either biodegradation or hydrolysis have lower potential for emission to the air as
gases or particles. 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
emission to the air as gases or particles.  CHEMDAT8 is considered to provide reasonable to slightly
high (environmentally conservative) estimates of air emissions from the various emission sources.  A
more detailed discussion of the  emissions modeling is provided in the IWAIR Technical Background
Document.

Using ISCST3 Default Dispersion Factors

       The IWAIR default dispersion factors were developed by conducting air dispersion modeling
with EPA ISCST3 (U.S. EPA, 1995).  This model is capable of modeling ground-level and elevated area
sources. As part of this effort, landfills, LAUs, and Sis were modeled as  ground-level area sources and
wastepiles were treated 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 area) using meteorological data
obtained from 29 meteorological stations. The
representative WMUs were selected from the 1985
Screening Survey of Industrial Subtitle D
Establishments  (Shroeder et al., 1987).  This database
is the most comprehensive database that EPA has to
date on waste unit characteristics. This database
contains data on 6,254 Sis, 1,281 WPs, 702 LAUs,
and 790 LFs. The IWAIR program is designed to
cover the range of unit characteristics contained in the
database. To facilitate dispersion modeling, the range
was divided into strata using a modified version of a
statistical method called the Dalenius Hodges
procedure. This procedure divided into strata the
skewed distribution of areas found in the Industrial D
Survey database so that all WMUs in the database
would be adequately represented. The median area in
each stratum was then used in the dispersion
modeling. As a result,  14 surface areas were selected
                 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 (tg/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 since the types of WMUs being
                  assessed are typically in nonurban areas.
                  Flat terrain was assumed.
 3-4

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Section 3.0
Selecting Calculation Method, WMU Type, and Modeling Pathways
for modeling for the landfills, land application units, and surface impoundments. Seven surface areas
were selected for wastepiles.
       The ISCST3 modeling was conducted with
data obtained from 29 representative meteorological
stations. These stations were selected in an
assessment for EPA's Superfund Soil Screening
Level (SSL) program (EQM, 1993) as being
representative of the nine general climate regions of
the continental United States.  The dispersion
modeling was conducted using 5 years of data from
each of the 29 meteorological stations. The
meteorological data required as input to the ISCST3
model included hourly readings for the following
parameters: wind direction, windspeed (m/s),
ambient temperature (K), mixing height, and stability
class.
                       Key Meteorological Data for
                    the ISCST3 Model without Depletion

              Wind Direction: determines the direction of the
              greatest impacts.

              Windspeed: ground-level air concentration is
              inversely proportional to windspeed, so the lower the
              windspeed the higher the concentration.

              Stability Class: impacts rate of lateral and vertical
              diffusion. The more unstable the air, the greater the
              diffusion.

              Mixing Height: determines the height to which can
              be diffused vertically.
       Unitized air concentrations (UACs) were
obtained as output by running the model with a unit
emission rate (i.e., 1 |ig/m2-s). The selected areas for each type of WMU were modeled using
meteorological inputs obtained from the 29 representative meteorological locations in the continental
United States. Receptors were placed in 16 directions at distances of  25, 50, 150, 500, and 1,000 meters
from the edge of the WMU. Figure 3-1 illustrates the pattern of receptor placement around the unit.
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 UACs at each distance serve as the IWAIR default
dispersion factors.

       Based on the WMU surface area provided by the user, the IWAIR tool selects an appropriate
dispersion factor. If the entered WMU surface area lies between two area strata, dispersion factors for
the WMU are estimated by a linear interpolation between dispersion factors for WMUs in the database
with areas above and below that of the user's entered WMU area. For example, if a user specifies 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 estimates 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.
                                                                                               3-5

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Section 3.0
                        Selecting Calculation Method, WMU Type, and Modeling Pathways
       -400
     400-
-300
 -200
	L_
-100
                                                               100         200        300        400
                                                                                 400
     300-
     200-
     100-
       0-
    -100-
    -200-
    •300-
    -400-
                         Land
                                                            UDIL
                                                                                                  -300
                                                                                                  -200
                                                                                                  -100
                                                                                                  -0
                                                                                                  -100
                                                                                                   -200
                                                                                                  -300
                                                                                                   -400
       -400        -300        -200        -100
                                                                100        200         300         400
                                                 ("meters')


                                     Figure 3-1. Receptor Locations.
 3-6

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Section 4.0
Completing Forward Calculation to Risk
4.0  Completing Forward Calculation to Risk

       IWAIR allows you to complete a forward calculation to develop inhalation risk estimates for
wastes of known chemical concentrations. Results from the forward calculation method include
chemical-specific cancer risk estimates, total cancer risk estimates (i.e., the summation of the chemical-
specific risk estimates),  and noncancer risk estimates (i.e., hazard quotients for noncarcinogens in the
waste).

       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;
             and
       •      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 forward 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 forward calculation. You will not need to
reference all of the information provided in this section since the guidance addresses all four of the
modeling pathways. Follow only those subsections that are applicable to your chosen pathway.
                                                                                         4-1

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Section 4.0
               Completing Forward Calculation to Risk
           User Specifies:     •

           » Calculation option  j
           Ucer Specifies:
           • WMUtypa
         ^UsarSpeclftes:
           • Constituents      .     ,
             (choose up to 6 from list of 05)
           * Concentrations
           User Specifies:
           • CHEMDATBopflon                   I
           • Facility location for meteorological Input  •
           • WMU information (i.e., cJeaign and       j
          y^operating parameters)              ___.;••
           User Specifies:
             Raceptorlnfomiation (i.e., distance    •
             ahdtype)                         I
                                                           Select Calculation Method
                                                             Forward Calculation to Risk
                                                                  Identify WMU
 • Land Application Unit (LAU)

 • Waste Pile (WP)

 • Surface Impoundment (SI)
 • Landfill (LF)
   Define Wastes Managed
                                                            Determine Emission Rates
       CHEMDAT8
                                                          Determine Dispersion Factors
ISCST3 Default Dispersion Factors
                                                                      /?^'4'-?*'.ag''?.''ire*'i-Yg
                                                                       Y
                                                         Calculate Ambient Air Concentration
                                                        Calculates ambient air concentrations tor
                                                        each receptor based on emission and
                                                        dispersion data
                                                              Forward Calculation to Risk

                                                        1. Chemical-specific Carcinogenic Risk
                                                        2. Chemical-specific Non-carcinogenic Risk

                                                        3. Total Cancer Risk
       Figure 4-1.  IWAIR Approach for Completing Forward Calculation to Risk: Pathway 1 - Using
       CHEMDAT8 Emission Rates and ISCST3 Default Dispersion Factors.
4-2

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Section 4.0
                                                             Completing Forward Calculation to Risk
         •f User Specifies:   A
         :  *  ?^<"«v» «"*^ ""„  - ,'
         ^•Calculation option ^/
           User Specifies:
        1
  User Specifies:     •
?• Constituents   \   ^   <
'   4 (chose up,to 6 from list of95)5 ^
  9 Concentrations j> \.f^ T x ^
                                                           Select Calculation Method
                                                             Forward Calculation to Risk
                                                                               st^^
                                                                  Identify WMU
                                                   •  Land Application Unit (LAU)

                                                   •  Waste Pile (WP)

                                                   •  Surface Impoundment (SI)
                                                   •  Landfill (LF)
                                                              Define Wastes Managed
                                                                                      _i
                                                                         |^^^r?B^^
                                                            Determine Emission Rates
                                                                   CHEMDAT8
                                                          Determine Dispersion Factors   I.
                                                           User-specified Dispersion Factors
                                                         Calculate Ambient Air Concentration
                                                        Calculates ambient air concentrations for
                                                        each receptor based on emission and
                                                        dispersion data
                                                              Forward Calculation to Risk

                                                        1. Chemical-specific Carcinogenic Risk
                                                        2. Chemical-specific Non-carcinogenic Risk
                                                        3. Total Cancer Risk
       Figure 4-2. IWAIR Approach for Completing Forward Calculation to Risk: Pathway 2 - Using
       CHEMDAT8 Emission Rates and User-specified Dispersion Factors.
                                                                                                          4-3

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Section 4.0
            Completing Forward Calculation to Risk
           User Specifies:     )
          • Calculation Option   j
           User Specifies:
           •  WMUtype
         i^User Specifies:                 "-j
         I •  Constituents                    ;i
         1    (chose up to 6 from list of 9        j
                    '
           User Specifies:
         1  • Emission rates
          J*                  ' '       • •":  ^^X
         / User Specifies:                 :,'A
           •  WMU area (and height for WP)      1
             Facility location for meteorological     i
           "                       '''     "
                                         ..
            Receptor information (i.e., distance
                                                            Select Calculation Method
                                                              Forward Calculation to Risk
                                                                   Identify WWIU
  • Land Application Unit (LAD)
  • Waste Pile (WP)
  • Surface Impoundment (SI)
  • Landfill (LF)
     Define Wastes Managed
                                                             Determine Emission Rates
                                                              User-specified Emission Rates
                                                                                         m

Determine Dispersion Factors    pi
 ISCST3 Default Dispersion Factors
                                                          Calculate Ambient Air Concentration
                                                        Calculates ambient air concentrations for
                                                        each receptor based on emission and
                                                        dispersion data
                                                              Forward Calculation to Risk
                                                        1. Chemical-specific Carcinogenic Risk
                                                        2. Chemical-specific Non-carcinogenic Risk
                                                        3. Total Cancer Risk
       Figure 4-3. IWAIR Approach for Completing Forward Calculation to Risk: Pathway 3 - Using
       User-specified Emission Rates and ISCST3 Default Dispersion Factors.
4-4

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Section 4.0
         Completing Forward Calculation to Risk
          UserSpeclfles:  ,
          •  Calculation option
           User Specifies:
          * WMUtype
           User Specifies:
             ^'yvx^ *
        riisti
                                                          Select Calculation Method
                                                           Forward Calculation to Risk
                                                                Identify WMU
. Land Application Unit (LAU)
• Waste Pile (WP)
• Surface Impoundment (SI)
• Landfill (LF)
                                                                        ^
  Define Wastes Managed
                                                          Determine Emission Rates
                                                           User-specified Emission Rates
                                                        Determine Dispersion Factors
                                                         User-specified Dispersion Factors
                                                          "~""~™"Ta
                                                       Calculate Ambient Air Concentration
                                                      Calculates ambient air concentrations for
                                                      each receptor based on emission and
                                                      dispersion data
                                                            Forward Calculation to Risk
                                                      1.  Chemical-specific Carcinogenic Risk
                                                      2.  Chemical-specific Non-carcinogenic Risk
                                                      3.  Total Cancer Risk
       Figure 4-4. IWAIR Approach for Completing Forward Calculation to Risk: Pathway 4 - Using
       User-specified Emission Rates and Dispersion Factors.
                                                                                                       4-5

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Section 4.0
Completing Forward Calculation to Risk
                                        ;C>^-«,k,is^SA^Sfc^j**Si,^^SiSS
                       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 forward (Risk) calculation 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 (Sis) (aerated and quiescent), active landfills (LFs), wastepiles (WPs), and tilled
land application units (LAUs). A detailed description of these unit types is provided in Section 3.2.
Select from 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 the site's 5-digit zip code or 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 29IWAIR meteorological stations. Data from the 29 stations
(shown on a map of the continental United States in Screen  IB, viewed by clicking on the VIEW MAP
button shown on Screen 1 A) are used as input to CHEMDAT8 emission modeling (e.g., temperature and
4-6

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Section 4.0
Completing Forward Calculation to Risk
windspeed), and as inputs to the air dispersion modeling effort conducted to develop the default
dispersion factors maintained in the IWAIR tool. Additional information on this dispersion air modeling
effort and the 29 representative meteorologic stations is provided in Section 3.3.

       Enter 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.

       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 SEARCH FOR MET.
       STATION 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 appear
       to 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 view the map of the United States (VIEW
MAP button, Screen 1 A) showing the 29 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 assist you in
identifying this error prior to proceeding with the calculations.

E.     Select Emission and Dispersion Option (IWAIR-Generated or User-Specified) (Screen 1A)
       You  must  select from the IWAER emission and dispersion data options. Under these options,
you have the flexibility of conducting modeling using IWAIR-generated emission rates and dispersion
factors, user-specified emission and dispersion estimates, or a combination of both IWAIR-generated
and user-specified estimates.

       The tool uses emission rate and dispersion factor estimates in both the forward and backward
calculations. As seen in Screen 1 A, you must select one of the three options provided for obtaining
emission and dispersion data:

              Option 1 - Use CHEMDAT8
              Select Option 1  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 be
                                                                                           4-7

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Section 4,0
Completing Forward Calculation to Risk
             allowed to override the IWAIR emission estimates on subsequent screens. Option 1 is
             most appropriate for use if Pathway 1 or 2 was selected in Section 3.3.  Select this option
             by clicking the Use CHEMDAT8 command button.

             Option 2 - Enter Emission Rates
             Select Option 2 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 unitized dispersion factors (ug/ m3 per ug/m2-s).  Option 2 is
             most appropriate for use if Pathway 3 was selected in Section 3.3.  Select this option by
             clicking the ENTER EMISSION RATES command button.   Once 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.
             Screen IB. Map of Continental USA Showing 29 Meteorological Stations
 4-8

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Section 4.0
Completing Forward Calculation to Risk
               Option 3 -  Enter Emission, Dispersion Data.
               Select Option 3 to enter your own emission estimates (g/m2-s) and unitized dispersion
               factors (ug/ m3 per ug/m2-s). Option 3 is most appropriate for use if Pathway 4 was
               selected in Section 3.3. This option is selected by clicking the ENTER EMISSIONS,
               DISPERSION DATA command button.
                                           CtwinicaHo remove

                                            /"*-•
                  Acetatdehyde
                  Acetone (67*1-1]
                  AcdonWe [7S-05«]
                  Acraleln [T07-02-8]
                  Acrvlamde [79-OS.1]
                     acid [7910-7]
                  Acrytonfcte {107-13-1]
                  AnJne 1625331
                  Benzeoe
                  Benntfine [9287-5!
                  Benzo(a)pyren8 [50-32-8]
                  BfomodicWoromethane [7S-27-4J
                  1 3-Buladiene {108-99-0]
                  Hexachloro-1 3-butaaene [87-68^3]
                  Carbon titeuWde 175-15-01
                  GarbcnietracWorids [5823^5]
                  Chlorobenzwie [108^0-7)
                  Chlorodibromomettiane [124-45-1]
                  CMdrofbrffi [67-^66^31
                                     Screen!. Wastes Managed
4.2   Wastes Managed (Screen 2)

       To perform a forward calculation risk, 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.

A.     Select Sorting Option for Identifying Chemicals (Screen 2)
       IWADR. includes a predetermined list of 95 chemicals from which you can identify waste
constituents.  These constituents are shown with their Chemical Abstracts (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 2, select a sort
order by clicking on the button to the left of the sorting option of choice.
                                                                                                  4-9

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Section 4.0
Completing Forward Calculation to Risk
B.     Identify Chemicals in Waste (Screen 2)
       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.

C.     View Selected Chemicals (Screen 2)
       The chemicals you identified for consideration are displayed in text boxes shown on Screen 2.
You can remove waste constituents from consideration by selecting the check box to the left of the
chemical and clicking the «Remove command button.

Z>.     Enter Waste Concentrations (Screen 2)
       If you are using CHEMDAT8, enter a chemical-specific waste concentration for each chemical
identified. This is not necessary if you will enter your own emission rates. The concentration should be
expressed as mg/L for wastewaters and mg/kg for solid wastes.  The concentration entered for a single
compound can not exceed its solubility limit (identified to the right of the concentration textbox) nor
should the total organic concentration exceed 1,000,000 mg/kg or mg/L (equivalent to ppm). If these
conditions are not met, an error message will be displayed.

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
CHEMDAT8 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.

       The section provides guidance in 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, windspeed for quiescent systems, and
       biodegradation.

       Land Application Units. The waste can be tilled or sprayed directly onto the soil and
       subsequently mixed with the soil by discing or tilling. Waste in a LAU is a mixture of sludge
       and soil.  IWAIR allows the modeling of tilled LAUs. Another model may be more appropriate
       if your LAU uses spray application. 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.
4-10

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Section 4.0
Completing Forward Calculation to Risk
       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), constituent concentration in the waste, and the volatility of the constituent (U.S. EPA,
       1991).

       Wastepiles. The waste pile emission model is sensitive to the air porosity of the solid waste, the
       liquid loading in the solid waste, the wastepile height, 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 wastepiles. Guidance for completing each
screen is provided below. For several of the required inputs, default values are provided to the right of
the screen textboxes. 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. The basis for
these default values is provided in the IWAIR Technical Background Document.
                Screen 3A. WMU Data for CHEMDAT8:  Surface Impoundment
                                                                                           4-11

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Section 4.0
Completing Forward Calculation to Risk
               t,f'""ii"; ^;>"«?' ?ft^"'Sl!fl';-%g^^S-r55!f"^:
                Screen 3B. WMU Data for CHEMDAT8:  Land Application Unit
                                              :": :'^aiimaleiStS£^SIIIiis^^^!^^&y,&lS!S^^^^ff^^^^:
                        Screen 3C.  WMU Data for CHEMDAT8: Landfill
4-12

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Section 4.0
Completing Forward Calculation to Risk
                      Screen 3D. WMU Data for CHEMDAT8:  Wastepfle
A.     View Meteorological Data for Site (Screens 3A, 3B, 3C, and 3D)
       Both windspeed and temperature can affect the volatilization rate of a chemical. Average
temperature and windspeed are used as input to the CHEMDAT8 model. Drawing from the
meteorological data stored in IWAIR, the program will display the average annual temperature and
windspeed available for the representative meteorological station that was determined for the site in
Screen 1 A. Alternatively, you can enter average windspeed and temperature for your site if the default
values are significantly different.
B.     Enter Unit Design and Operating Data
       Enter Surface Impoundment Design Data (Screen 3A):
       Enter the unit dimensions and loading information in the textboxes shown in each Screen 3A.
       The data include the depth of the surface impoundment in meters, the area of the surface
       impoundment in square meters, and the annual flow of the waste in cubic meters per year.

       Enter LAU Design and Operating Information (Screen 3B)
       Enter the unit dimensions and loading information, including the operating life of the unit in
       years, tilling depth of the unit (m), area of the unit in square meters (m2), annual waste quantity
       in megagrams per year, number of application per year, and waste bulk density in grams per
       cubic centimeter (g/cm3).
                                                                                         4-13

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Section 4.0
Completing Forward Calculation to Risk
       Enter Landfill Design and Operating Information (Screen 3C):
       Enter the unit dimensions and loading information in the textboxes in Screen* 3B. 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 in
       years, total area of the unit in square meters (m2), depth of the unit (m), number of cells in your
       unit, annual quantity of wastes disposed in landfill (Mg/year), and bulk density of waste (g/cubic
       centimeter).

       Enter Wastepile Design and Operating Information (Screen 3D):
       The unit dimensions and loading information to be entered include the height of the pile in
       meters (m), area of the unit in square meters (m2), annual quantity of v/aste in pile (Mg/year), and
       bulk density of the waste in g/cm3.

C.     Enter Waste Characteristics Data (Screens 3A, 3B, 3C, and 3D)
       For Surface Impoundments Only - Enter Waste Characteristics Data (Screens 3A)
       The waste characteristic information to be entered for surface impoundments include active
       biomass (grams/liter), total suspended solids into WMU (milligrams/liter), total organics into
       WMU (milligrams/liter), total biorate (milligrams/ gram bio-hr), and molecular weight of oil
       (grams/gram-mole).

       LAUs, LFs, and WPs Only - Enter Waste Characteristics Data (Screens 3B, 3C, and 3D)
       Specify if the waste being modeled is an aqueous- or oily-phase waste. If a waste is identified as
       oily, then you will also need to enter a waste density.

       In making the determination of whether a waste is oily or aqueous, you should examine the
       fraction of the waste that is organic. Consider the following guidance in making this
       determination.

       Oily:     If the total concentration of all organics in the waste is greater than 10%, then the
                 waste should be identified as oily.  IWAIR does this automatically if the combined
                 concentration of all chemicals entered is greater than 100,000 mg/kg or mg/L, or
                 10%.

       Aqueous:  If the total concentration of all organics in the waste is less than 10%, then the waste
                 should be identified as aqueous.

       Based on this distinction, the model will apply either the aqueous or the oily waste equilibrium
       partitioning algorithm. For oily (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 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.
4-14

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Section 4.0
Completing Forward Calculation to Risk
D.     For LAUs, Landfills, and WPs Only - Enter Waste Porosity Information (Screens 3B, 3C,
       and 3D)
       Waste (or soil/waste mixture for LAUs) 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 (TJ), also sometimes call saturated water content,
can be calculated from the bulk density (BD) of the waste and particle density (ps) as follows:
                                        •n =  i  -
                                                 BD
       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.

E.     For Surface Impoundments Only - Identify Unit as Aerated or Quiescent (Screen 3A)
       IWAIR models both quiescent (not aerated) or 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).  Identify your unit as aerated or quiescent (i.e., not aerated)
by clicking the appropriate option button.

F.     For Aerated Surface Impoundments Only - Enter Aeration Data  (Screen 3A)
       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., air diffuse aerated). If
your surface impoundment is aerated, provide information to characterize the operation. This
information includes fraction of surface area agitated (unitless) and an indication of whether the unit is
aerated through the use of air diffusion or mechanically aerated, or both. If the unit has diffused
aeration, you will also need to enter a submerged air flowrate (m3/s) in this screen.

G.     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/hour-HP), number of aerators,
total power (HP), powers efficiency (fraction), impeller diameter (cm), and impeller speed
(radian/second).

       Done. Once you provide the required WMU inputs, click the DONE button to enable the
Emission Rates menu tab and open the Emission Rates screen. Proceed to Section 4.4, Emission Rates.
                                                                                           4-15

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Section 4.0
Completing Forward Calculation to Risk
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., selected the ENTER EMISSION RATES or ENTER
EMISSIONS, DISPERSION DATA command buttons shown previously on Screen 1 A), proceed to
Section 4.4.2, User-Specified Emission Rates.

       Please note that all calculated and entered values on the Emission Rate screen will be lost if you
return to a previous screen and make changes. This includes both calculated and entered override
emission rate values.
Aectekfehyde-
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Section 4.0
Completing Forward Calculation to Risk
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 data.  Confirm
the emission rates to be used in the calculations by clicking the DONE button. The program will then
automatically enable the Dispersion Factors menu tab and open the Dispersion Factors screen.  Proceed
to Section 4.5, Dispersion Factors.
                            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.  The source and
the justification for these data and the estimation method employed should also be documented using the
textbox on the screen.

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.
                                                                                           4-17

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Section 4.0
Completing Forward Calculation to Risk
       Done. Once you have entered the 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 4.5, Dispersion Factors.

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 Section 4.5.1 and 4.5.2, respectively. If you elected to use
ISCST3 dispersion factors provided in IWAIR (i.e., selected the USE CHEMDAT8 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 values on the Dispersion Factor screen will be lost if
you return to a previous screen and make changes. This includes receptor locations and types, and
calculated and entered override dispersion factor values.
                         C. View IWAIR
                         dispersion
                         factor or enter
                         user-specified
                         dispersion
                         factors
                    Rocsptor Dwiancsto
                    l*>«   Receptor <&&
                                                                                       B. Direct
                                                                                       IWAIR to
                                                                                       estimate
                                                                                       dispersion
                                                                                       factors
                      Screen 5A. Using ISCST3 Default Dispersion Factors
4-18

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Section 4.0
Completing Forward Calculation to Risk
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 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 Distance to Receptor and 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.

       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 smaller distance will
overestimate risk, and selecting a larger 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, a worker and a resident, can be
modeled with IWAIR. 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.  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
assumptions for residents reflect males and females from birth through age 30. Use the drop-down box
positioned under the Receptor Type column heading to select either a 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 IWAER 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.

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). If you choose to provide
alternative dispersion factors, document the source and the justification for these data in the text box that
                                                                                           4-19

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Section 4.0
Completing Forward Calculation to Risk
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 menu tab.  Proceed to Section 4.6, Results.
                 f*
                   "1.,; >-• 'lw_^^:\{w^JHHrt^
                    &	'* '.^sa:" ^^^^M^^^^^^^^^^^^^^'
                   ,^;,,.;_;' i'fg^'l^h^y^^fS^^^ilgi^
                          Screen 5B. User Specified Dispersion Factors
4.5.2  User-Specified Dispersion Factors (Screen SB)

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 Distance to Receptor and
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.

       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.
4-20

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Section 4.0
Completing Forward Calculation to Risk
       Receptor Type - Two different types of exposed individuals, a worker and a resident, can be
modeled with IWAIR. 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. 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
assumptions for residents reflect a males and females from birth through age 30. Use the drop-down box
positioned under the Receptor Type column heading to select either a worker or resident.

B.     Enter User-Specified Dispersion Factors (Screen SB)
       For each receptor specified, enter site-specific unitized dispersion factors (ug/m3 per fig/m2-s) in
the text box located under User Override.

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 data.

       Done.  Once you have entered dispersion data, click on the DONE button to open the Results
menu tab. Proceed to Section 4.6, Results.
                 ndustrial Waste - IS. Results: Risk basedjon Chemical Concentrations (Forward Calculation))
                                       Screen 6.  Results
                                                                                            4-21

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Section 4.0
Completing Forward Calculation to Risk
4.6   Results (Screen 6)

       The cancer and non-cancer risk estimates attributable to emissions from a WMU can be
calculated using IWAIR for residents and workers. 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 adult), 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 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 (cancer slope factors for carcinogens and reference
concentrations for noncarcinogens) for 95 constituents. These health benchmarks were obtained
primarily from the EPA's Integrated Risk Information System (IRIS) and the Health Effects Assessment
Summary Tables (HEAST) (U.S. EPA, 1998a, 1997b).  IWAIR uses these data to perform a forward
calculation to obtain risk estimates.

       Please note that all calculated and entered values on the Results screen will be lost if you return
to a previous screen and make changes. This includes entered override health benchmarks as well as all
calculated 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 5 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.

B.     View or Enter Health Benchmarks (Screen 6)
       Screen 6 allows you to view the health benchmarks that IWAIR will use in calculating risk
estimates. If you choose not to use these data, you can enter alternate health benchmarks.  Enter cancer
slope factors (per mg/kg-d) in textboxes located under Cancer Slope Factors (CSF) and reference
concentrations (mg/m3) under Reference  Concentration (RfC). Do not use a reference dose in the place
of a reference concentration.

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 textbox. 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 the risk. Hazard quotients (unitless) and cancer
risk estimates  (unitless), respectively, are displayed for each noncarcinogen and carcinogen identified as
4-22

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Section 4.0
Completing Forward Calculation to Risk
being managed.  In addition, a total cancer risk estimate, which is the sum of the chemical-specific risk
estimates, is displayed.

       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 restarting the model or saving the current run.
                                                                                            4-23

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Section 5.0
Completing Backward Calculation to Protective Waste Concentration
5.0  Completing Backward Calculation to Protective

       Waste Concentration

       IWAIR allows you to complete a backward calculation to develop protective waste
concentrations (Cw). The calculation method can be applied in calculating waste concentrations for both
wastewaters (Cw in mg/L) and solid waste (Cw in mg/kg). These concentrations are estimated based on
user-defined target cancer and noncancer risk levels (e.g., IxlO"5 or IxlO"6 for carcinogens, or hazard
quotient of 0.5 or 1 for noncarcinogens). The user defines these risk levels on the results screen.

       The release of a chemical to the atmosphere is impacted by whether a waste is an aqueous- or
oily-phase waste. This determination  depends on the fraction of the waste that is organic. Oily wastes
are defined in this model as having a total concentration of all organics in the waste greater than 10%
while aqueous wastes have a total organic concentrations less than 10%. Based on this distinction, the
model will apply either an aqueous or the oily waste equilibrium partitioning algorithm. For oily
(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 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.

       The backcalculation is initially based on an aqueous-phase waste, as this is more conservative for
most chemicals. For some chemicals in some units, it may not be possible to reach the target risk
without the concentration exceeding the solubility (in waste waters) or the soil saturation limit (in solid
wastes) of the chemical. Once these limits are exceeded, the waste would be considered oily. In this
case, IWAIR will switch to oily-phase emission rates and continue. 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.

       For a very few chemicals, the oily phase emissions are more conservative, and the
backcalculation is then always based on an oily-phase waste.

       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;
                                                                                        5-1

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Section 5.0
Completing Backward Calculation to Protective Waste Concentration
       •      Pathway 3: Using user-specified emission rates and ISCST3 default dispersion factors;
              and

       •      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 a backward 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 a backward calculation. You will not
need to reference all of the information provided in this section since 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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Section 5.0
Completing Backward Calculation to Protective Waste Concentration
          User Specifies:
                      *   I „
          * Calculation option  _,
           User Specifies:
                                                         Select Calculation Method
                                                            Backward Calculation to
                                                             Waste Concentration
                                                                Identify WML)
                                                          • Land Application Unit (LAU)

                                                          • Waste Pile (WP)

                                                          • Surface Impoundment (SI)

                                                          • Landfill (LF)
                                                                        B6^fl^^^
                                                            Define Wastes Managed
                                                          Determine Emission Rates
                                                                CHEMDAT8
                                                        Determine Dispersion Factors
                                                         ISCST3 Default Dispersion Factors
                                                       Calculate Ambient Air Concentration
                                                      Calculates ambient air concentrations for
                                                      each receptor based on emission and
                                                      dispersion data
                                                           Backward Calculation to
                                                           Protective Waste Concentration

                                                           Cw forwastewaters (mg/L)
                                                           Cw for solid wastes (mg/kg)

       Figure 5-1. IWAIR Approach for Completing Backward Calculation to Protective Waste
       Concentration: Pathway 1 - Using CHEMDAfS Emission Rates and ISCST3 Default Dispersion

       Factors.
                                                                                                              5-3

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Section 5.0
Completing Backward Calculation to Protective Waste Concentration
          User Specifies:

          » Calculation option

           .User Specifies:
           >  WMU type
           User Specifies:

             Constituents
             (chose up to 6 from list of 95)
         >  User Specifies:
           'CHEMpAt8 option
          •  Facility kx^tion for meteorological input
         '•V  WMU infbrmaton (i.e., design and
          ,   operating parameters    :
        f  User Specifies:   '  .  _  '-•    •._,"

           » Dispersion iactors  i ';  .'.Ji,',."/'.•
           • Receptor information (i.e., distance
             and type)
         fuser Specifies:

         i • Rl^cfeva!
                                                            Select Calculation Method
                                                               Backward Calculation to
                                                                Waste Concentration
                                                                   Identify WMU
                  • Land Application Unit (LAD)

                  • Waste Pile (WP)

                  • Surface Impoundment (SI)
                  • Landfill (LF)
                    Define Wastes Managed
                                                            Determine Emission Rates
                        CHEMDAT8
                Determine Dispersion Factors
                 User-specified Dispersion Factors
                                                         Calculate Ambient Air Concentration
                                                        Calculates ambient air concentrations for
                                                        each receptor based on emission and
                                                        dispersion data
                                                              Backward Calculation to
                                                              Protective Waste Concentration

                                                              Cw for wastewaters (mci/L)
                                                              Cw for solid wastes (mg/kg)
                                                                                SiiStSisissicsitS&Si
       Figure 5-2. IWAIR Approach for Completing Backward Calculation to Protective Waste
       Concentration: Pathway 2 - Using CHEMDAT8 Emission Rates and User-specified Dispersion
       Factors.
5-4

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Section 5.0
                               Completing Backward Calculation to Protective Waste Concentration
           • ^-vw".-.- A,- '-.-,-.-. •"~-'->'
           (' User Specifies:
             User Specifies:

               Constituefrts
    {cftose up to Strom list of 95)* ^ *
  User Specifies: -

  • Emission rates  ^ ,
        "**#"          
       ,. -^  - ~ ^^~  ~i~s^^ ~ $, ^-~

  User Specifies:  /-   " J" ^*^-,fA
       '  *    > ^ <<^v^*  '?>' ^i*   ^
 jf^WMU area(ariS height forWP)   s   »"
 •' Facility location for meteorological input"
I*  Receptor information (i.e;i distance   ^
*    «*n«4 t«fvm\     . 1.   •>„       ^ ^  . ,
                                                              Select Calculation Method
                                                                 Backward Calculation to
                                                                   Waste Concentration
                                                                           '^
                                                                     Identify WMU
                                                                 Land Application Unit (LAU)

                                                                 Waste Pile (WP)

                                                                 Surface Impoundment (SI)
                                                                 Landfill (LF)
                                                                       m?
                                                      Define Wastes Managed
                                                                 ,,^m™Mwa
                                                               Determine Emission Rates
                                                                User-specified Emission Rates
                                                                                          J
                                                                                        j»-;!B5a
                                                                                        „_
                                                                 aaiaaagBi»«gaiaMB»»'CT'"'«m""'^SBB»
                                                               I
                                                             Determine Dispersion Factors
                                                              ISCST3 Default Dispersion Factors
                                                            Calculate Ambient Air Concentration
                                                           Calculates ambient air concentrations for
                                                           each receptor based on emission and
                                                           dispersion data

                                                                Backward Calculation to
                                                                Protective Waste Concentration

                                                                Cw for Wastewaters (mg/L)
                                                                Cw for solid wastes (mg/kg)
                                                                                      I
                                                                            Kisarja«ggge3a«am«5aK3*si«ssi
         Figure 5-3. IWAIR Approach for Completing Backward Calculation to Protective Waste
         Concentration: Pathway 3 - Using User-specified Emission Rates and ISCST3 Default Dispersion

         Factors.
                                                                                                           5-5

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Section 5.0
                                Completing Backward Calculation to Protective Waste Concentration
           User Specifies:     ;
          • Calculation option   j
           User Specifies:
           • WMUtype
            Jser Specifies:
           " Constituents 	  '•' '"
            (chose up to 6 from list of 95)
           User Specifies:
           • Emission rates
User Specifies: '       •  -.. 7,/ '••   i
• Dispersion factors                  j
• Receptor ftiformatfbn (i-e^ distance  '; 1
  andtype}                      \y
          U User Specifies:
           • Rfeklevel...
                                                             Select Calculation Method
                                                                Backward Calculation to
                                                                 Waste Concentration
                                                                    Identify WW1U
                                                  •  Land Application Unit (LAU)
                                                  •  Waste Pile (WP)

                                                  •  Surface Impoundment (SI)
                                                  •  Landfill (LF)

                                                     Define Wastes Managed


                                                              Determine Emission Rates
                                                               User-specified Emission Rates
                                                            User-specified Dispersion Factors
                                                           Calculate Ambient Air Concentration
                                                          Calculates ambient air concentrations for
                                                          each receptor based on emission and
                                                          dispersion data
                                                    Backward Calculation to
                                                    Protective Waste Concentration
                                                               Cw for wastewater (mg/L)
                                                               Cw for solid wastes (mg/kg)
       Figure 5-4. IWAIR Approach for Completing Backward Calculation to Protective Waste Concentration:
       Pathway 4 - Using User-specified Emission Rates and Dispersion Factors.
 5-6

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Section 5.0
Completing Backward Calculation to Protective Waste Concentration
               ^Industrial Waste • (1a. Waste Management Unit Type I
                               jfoMesttttans Mesotron sosafiea nsk
                                                             '   t    -^fi

                      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 option button associated with the backward
(Concentration) calculation option. 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 and run the model separately for
each unit type.  The four unit types that are addressed as part of this guidance include surface
impoundments (Sis) (aerated and quiescent), active landfills (LFs), wastepiles (WPs), and tilled land
application units (LAUs). A detailed description of these unit types is provided in Section  3.2.  Select
from 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 the site's 5-digit zip code or 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 29IWAIR meteorological stations. Data from the 29 stations
(shown on a map of the continental United States in Screen IB, viewed by clicking on the VIEW MAP
button shown on Screen 1A) are used as input to CHEMDAT8 emission modeling (e.g., temperature and
windspeed), and as inputs to the air dispersion modeling effort conducted to develop the default
                                                                                             5-7

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Section 5.0
Completing Backward Calculation to Protective Waste Concentration
dispersion factors maintained in the IWAIR tool. Additional information on this dispersion air modeling
effort and the 29 representative meteorologic stations is provided in Section 3.3.

       Enter 5 Digit Zip Code of Site
       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 the user can supply
       the needed data.

       Enter Latitude and Longitude of Site
       As shown in Screen 1A, 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 SEARCH button. If the
       latitude and longitude information 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 the user
       can supply the needed data.

JD.     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 view the map of the United States showing the
29 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 assist you in identifying this error prior to proceeding
with the calculations.

E.     Select Emission and Dispersion Option (Screen 1A)
       Select from IWAIR emission and dispersion data options.  These options provide the flexibility
of conducting modeling using IWAIR-generated emission rates and dispersion factors, user-specified
emission and dispersion estimates, or a combination of both IWAIR-generated and user-specified
estimates.

       The tool uses emission rate and dispersion factor estimates in both the forward and backward
calculations. As seen in Screen 1 A, you must select one of the three options provided for obtaining
emission and dispersion data:

              Option 1 - Use CHEMDAT8
              Select Option 1 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 be
              allowed to override the IWAIR emission estimates on subsequent screens. Option 1 is
 5-8

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Section 5.0
Completing Backward Calculation to Protective Waste Concentration
             most appropriate for use if Pathway 1 or 2 was selected in Section 3.3.  Select this option
             by clicking the Use CHEMDAT8 command button.

             Option 2 - Enter Emission Rates
             Select Option 2 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 unitized dispersion factors (ug/ m3 per ug/m2-s).  Option 2 is
             most appropriate for use if Pathway 3 was selected in Section 3.3.  Select this option by
             clicking the ENTER EMISSION RATES command button. Once 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.

             Option 3 - Enter Emission, Dispersion Data.
             Select Option 3 to enter your own emission estimates (g/m2-s) and unitized dispersion
             factors (ug/ m3 per ug/m2-s).  Option 3 is most appropriate for use if Pathway 4 was
             selected in Section 3.3. This option is selected by clicking the ENTER EMISSIONS,
             DISPERSION DATA command button.
                Waste - [1 fa. Map showing the 2S Met Stations]


           Screen IB.  Map of Continental USA Showing 29 Meteorological Stations
                                                                                           5-9

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Section 5.0
Completing Backward Calculation to Protective Waste Concentration
                  «ol by OB Nuntar': •
                  „,.,.,.- »« v,^* ,»%*,-..
                Acebnirie I7&-054]
                AcnMt [107-02-8]
                Acryfcadd [73-10-7]
                Ar*w [S2-S3-3J
                Benzene [71*t3-2]
                BenixSne [92-87-5]
                Benzo((0pyrene [50-32-8]
                BrcmodcHoronethane [75-27-4]
                13-Butadene 1106-33*1
                             [87-63-31
                Carbon dsuHide
                Carbon tebachjorBe'. [58-23-5]
                Chkxobennne [10erSO-7)
                CNcrodbroanriethane' [124-48-1]
                                   Screen 2.  Wastes Managed
5.2   Wastes Managed (Screen 2)

       To perform a backward calculation to arrive at protective waste concentration estimates, identify
the chemical(s) of concern in the waste.

A.     Select Sorting Option for Identifying Chemicals (Screen 2)
       IWAIR includes a predetermined list of 95 chemicals from which you can identify waste
constituents. These constituents are shown with their Chemical Abstracts (CAS) numbers 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 2, select a sort
order by clicking on the button to the left of the sorting option of choice.

B.     Identify Chemicals in Waste (Screen 2)
       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 displayed chemical
name and click the «Remove command button.
5-10

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Section 5.0
Completing Backward Calculation to Protective Waste Concentration
C.     View Selected Chemicals (Screen 2)
       The chemicals you identified for consideration are displayed in text boxes shown on Screen 2.
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
CHEMDAT8 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.

       The section provides guidance in 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,  windspeed for quiescent systems, and
       biodegradation.

       Land Application Units. The waste can be tilled or sprayed directly onto the soil and
       subsequently mixed with the soil by discing or tilling. Waste in a LAU is a mixture of sludge
       and soil. IWAIR allows the modeling of tilled LAUs.  Another model may be more appropriate
       if your LAU uses spray application. 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), constituent concentration in the waste, and the volatility of the constituent (U.S.
       EPA, 1991).

       Wastepiles. The waste pile emission model is  sensitive to the air porosity of the solid waste, the
       liquid loading in the solid waste, the wastepile height, 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 wastepiles. Guidance for completing each
                                                                                          5-11

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Section 5.0
     Completing Backward Calculation to Protective Waste Concentration
                                           '      Suffro Jmpomidmer* WomMtioo
                                           ==^Terop«a(weandV«oc^i^tl»ilaxBdarev«Bie»fty^^ Staflt»%s(«*a
                                        17-22
                                                        r—Waste-Cftaradertstfes Wormrtion
                   ^Otaeodons, LMtfcgkvfonMtGQ
                    Depth of Una On)
                    Anwo»Uni(r«2)
                    Annual FkW of Waste
[500    [     .
   "
                       Aerated
                                                Befauf
                     pmuse Aerated
                     MeehertcalyAenrted
                    Subroaged Air flow A           '
                                                          '   ^?^l;fefi'|SSW|f?S;sftft'i|lS!i
                                                                                 >     '
                    Screen 3B. WMU Data for CHEMDAT8:  Land Application Unit
 5-12

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Section 5.0
Completing Backward Calculation to Protective Waste Concentration
                                               s.    ^              ?-
                                               K'AnnuaJ Quantity o< Waste Bispos«d-tn,
                                               1              •   *^"
                       Screen 3C. WMU Data for CHEMDAT8: Landfill
                       Screen 3D. WMU Data for CHEMDAT8:  WastepUe
                                                                                           5-13

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Section 5.0
                                    Completing Backward Calculation to Protective Waste Concentration
screen is provided below. For several of the required inputs, default values are provided to the right of
the screen textboxes. 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.  The basis for
these default values is provided in the IWAIR Technical Background Document.

A.     View Meteorological Data for Site  (Screens 3A, 3B, 3C, and 3D)
       Both windspeed and temperature can affect the volatilization rate of a chemical. Average
temperature and windspeed are used as input to the CHEMDAT8 model. Drawing from the
meteorological data stored in IWAIR, the program will display the average annual temperature and
windspeed available for the representative meteorological station that was determined for the site in
Screen 1 A. Alternatively, you can enter average windspeed and temperature for your site if the default
values are significantly different.
B.
      Enter Unit Design and Operating Data
      Enter Surface Impoundment Design Data (Screen 3A):
      Enter the unit dimensions and loading information in the textboxes shown in each Screen 3 A.
      The data include the depth of the surface impoundment in meters, the area of the surface
      impoundment in square meters, and the annual flow of the waste in cubic meters per year.

      Enter LAU Design and Operating Information (Screen 3B)
      Enter the unit dimensions and loading information, including the operating life of the unit in
      years, tilling depth of the unit (m), area of the unit in square meters (m2), annual waste quantity
      in megagrams per year, number of application per year, and waste bulk density in grams per
      cubic centimeter (g/cm3).

      Enter Landfill Design and Operating Information (Screen 3C):
      Enter the unit dimensions and loading information in the textboxes in Screen 3B. 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 in
      years, total area of the unit in square meters (m2), depth of the unit (m), number of cells in your
      unit, annual quantity of wastes disposed in landfill (Mg/year), and bulk density of waste (g/cubic
      centimeter).

      Enter Wastepile Design and Operating Information (Screen 3D):
      The unit dimensions and loading information to be entered include the height of the pile in
      meters (m), area of the unit in square meters (m2), annual quantity of waste in pile (Mg/year), and
      bulk density of the waste in g/cm3.
C.
       For Surface Impoundments Only - Enter Waste Characterization Data (Screens 3A)
       The waste characteristic information to be entered for surface impoundments include active
biomass (grams/liter), total suspended solids into WMU (milligrams/liter), total organics into WMU
(milligrams/liter), total biorate (milligrams/ gram bio-hr), and molecular weight of oil (grams/gram-
mole).
5-14

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Section 5.0
Completing Backward Calculation to Protective Waste Concentration
D.     For LAUs, LFs, and WPs Only - Enter Waste Porosity Information (Screens 3B, 3C, and 3D)
       Waste (or soil/waste mixture for LAUs) porosity information required as input includes total
porosity (unit less) and air porosity (unitless). Total porosity includes air porosity and the space
occupied by oil and water within waste. Total porosity (r)), also sometimes call saturated water content,
can be calculated from the bulk density (BD) of the soil and particle density (ps) as follows:
                                                 BD
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.

E.     For Surface Impoundments Only - Identify Unit as Aerated or Quiescent (Screen 3A)
       IWAIR models both quiescent (not aerated) 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). Identify your unit as aerated or quiescent (i.e., not aerated)
by clicking the appropriate option button.

F.     For Aerated Surface Impoundments Only - Enter Aeration Data (Screen 3A)
       Aeration is achieved through the use of mechanical mixers such as impellers (i.e., mechanically
aerated) and/or by sparging air which bubbles up from the bottom of the unit (i.e., air diffuse aerated). If
your surface impoundment is aerated, provide information to characterize the operation.  This
information includes fraction of surface area agitated (unitless) and an indication of whether the unit is
aerated through the use of air diffusion or mechanically aerated, or both.  If the unit has diffused
aeration, you will also need to enter a submerged air flowrate (m3/s) in this screen.

G.    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/hour-HP), number of aerators,
total power (HP), powers efficiency (fraction), impeller diameter (cm), and impeller speed
(radian/second).

       Done. Once you provide the required WMU inputs, click the DONE button to enable the
Emission Rates menu tab and open the Emission Rates screen. Proceed to Section 5.4, Emission Rates.
                                                                                           5-15

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Section 5.0
Completing Backward Calculation to Protective Waste Concentration
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 elected to use CHEMDAT8 (i.e., selected the ENTER EMISSION RATES or ENTER
EMISSIONS, 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 Rate screen will be lost if you
return to a previous screen and make changes.  This includes both calculated and entered override
emission rate values.
                   V :'T;,; j "^..;~j;-;;'",;|,V^:EA^g$^gfa^£|^;|'igg"r:?l@ "*  . t  *"* *! >r». ,..f. '
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                               -'^' ;?"? -,':>'•".-•.< . -• l.->^'V'-'-'sl ^-i-;.-^*"?-'.'-^'-''W- ^     /x
                   '•'.•' i-: <• > ^"^i^rr? ^c$^.^^^^^^® ^
                           Screen 4A.  CHEMDAT8 Emission Rates
5.4.1  Using CHEMDAT 8 Emission Rates (Screen 4A)

A.     View CHEMDAT8 Emission Rates (Screen 4A)
       Screen 4A shows the both the oily- and aqueous-phase waste CHEMDAT8 emission rates.
Confirm the emission rates to be used in the calculations by clicking the DONE button. The program
will automatically enable the Dispersion Factors menu tab and open the Dispersion Factors screen.
Proceed to Section 5.5, Dispersion Factors.
5-16

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Section 5.0
Completing Backward Calculation to Protective Waste Concentration
                             Screen 4B. User Specified Emission Rates
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 provide alternate rates, the source and the justification for these data and estimation method
employed should also be documented using the textbox on the screen.
B.     Enter Source and Justification for User-specified Emission Rates (Screen 4B)
       The program will prompt the user 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.
                                                                                          5-17

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Section 5.0
Completing Backward Calculation to Protective Waste Concentration
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 Section 5.5.1 and 5.5.2, respectively. If you elected to use
ISCST3 dispersion factors provided in IWAIR (i.e., selected the Use CHEMDAT8 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 values on the Dispersion Factor screen will be lost if
you return to a previous screen and make  changes. This includes receptor locations and types, and
calculated and entered override dispersion factor values.
                                                                                      C. View IWAIR
                                                                                      dispersion
                                                                                      factor or enter
                                                                                      user-specified
                                                                                      dispersion
                                                                                      factors
                                                                                      B. Direct
                                                                                      IWAIR to
                                                                                      estimate
                                                                                      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.
5-18

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Section 5.0
Completing Backward Calculation to Protective Waste Concentration
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 Distance to Receptor and Receptor Type. You can
specify two receptor types at six distances (25,50,75,150,500, and 1000 meters) from the edge of the
WMU.

       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 dropdown box
under the Distance to Receptor heading. Note that selecting a smaller distance will overestimate risk,
and selecting a larger 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, a worker and a resident, can be
modeled with IWAIR. 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.  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
assumptions for residents reflect a males and females from birth through age 30. Use the drop-down box
positioned under the Receptor Type column heading to select either a 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.

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).  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 menu tab. Proceed to Section 5.6, Results.
                                                                                           5-19

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Section 5.0
Completing Backward Calculation to Protective Waste Concentration
                   'ifti. i- v.5^-^rr-".?3;;^sr':"T^^
                   l.i;i'if	, ," -.:•":' ,ri'  , , '"-«•"> :l^l';i • .j.vl, ^'-^S'!^^*<^;-i.:f£^;toS£^&3KV^^/^j^^w'^^^^sfe&^t'.
                           Screen SB.  User Specified Dispersion Factors
5.5.2  User-Specified Dispersion Factors (Screen SB)

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 5 receptors. The receptor information includes Distance to Receptor and Receptor
Type.  You can specify 2 receptor types in 16 directions at 6 distances (25, 50,75, 150, 500, and 1,000
meters) from the edge of the waste  management unit.

       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, a worker and a resident, can be
modeled with IWAIR.  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. 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
assumptions for residents reflect a males and females from birth through age 30. Use the drop-down box
positioned under the Receptor Type column heading to select either a worker or resident.
 5-20

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Section 5.0
Completing Backward Calculation to Protective Waste Concentration
B.     Enter User-Specified Dispersion Factors (Screen SB)
       For each receptor specified, enter site-specific unitized dispersion factors (ug/m3 per g/m2-s) in
the text box located under User Override.

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 menu
tab.  Proceed to Section 5.6, Results.
              {Industrial Waste - [6. Results: Threshold Chemical Concentrations (Back Calculation)]


                                       Screen 6. Results
5.6   Results (Screen 6)

       Protective 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 adult), 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
                                                                                             5-21

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Section 5.0
Completing Backward Calculation to Protective Waste Concentration
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 (cancer slope factors for carcinogens and reference concentrations for
noncarcinogens) for 95 constituents. These health benchmarks were obtained primarily from the EPA's
Integrated Risk Information System (IRIS) and the Health Effects Assessment Summary Tables
(HEAST) (U.S. EPA, 1998a, 1997b). IWAIR uses these data to perform a backward calculation to
obtain protective waste concentrations estimates.

       The approach applied by IWAIR includes an iterative forward 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-based unit and have elected to use CHEMDAT8 to calculate
emissions, IWAIR will perform backcalculations for both an aqueous-phase waste and an oily-phase
waste, and will output the lower 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.  If you elected to enter your own emission rates, or if you are modeling a
surface impoundment, IWAIR will only backcalculate and output concentrations for an aqueous-phase
waste.

       In performing backcalculations, IWAIR ensures that backcalculated aqueous-phase
concentrations do not exceed the soil saturation limit (for land-based units) or the solubility (for surface
impoundments) for that chemical. This prevents impossible results from occurring. Similarly, the
program also ensures that backcalculated oily-phase concentrations do not exceed 1,000,000 mg/kg. If
the target risk or hazard quotient cannot be achieved by any possible concentration (i.e., in an aqueous-
phase waste up to the soil saturation or solubility, or in an oily-phase waste up to 1,000,000 mg/kg), then
the program will note the maximum risk or hazard quotient that can be reached, and the backcalculated
concentration will be set to the concentration that results in the maximum possible risk or hazard
quotient. This will be either the soil saturation limit or 1,000,000 if you are modeling a land-based unit
using CHEMDAT8, or 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.

       Please note that all calculated and entered values on the Results screen will be lost if you return
to a previous screen and make changes. This includes entered override health benchmarks and entered
target risk and hazard quotients, as well as all calculated 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 5 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 of concern by
clicking on one of the other receptor option buttons.
 5-22

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Section 5.0
Completing Backward Calculation to Protective Waste Concentration
B.     Specify Risk Level (Screen 6)
       Specify a target cancer and noncaner risk levels. As shown in Screen 6, a drop down box is used
to allow to select an appropriate risk levels (e.g., a hazard quotient of 1 for noncarcinogens or 1 x 10~6 for
carcinogens).

C.     View or Enter Health Benchmarks (Screen 6)
       Screen 6 allows the you to view the health benchmarks IWAIR uses in the calculations. If a you
chooses not to use these data, alternate health benchmarks can be entered. Cancer slope factors (per
mg/kg-d) will be entered in textboxes located under Cancer Slope Factors (CSF) and reference
concentrations (mg/m3) under Reference Concentration (RfC). Do not use a reference dose in the place
of a reference concentration.

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 textbox.  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 Protective Waste Concentration (Screen 6)
       Click on the CALCULATE button to calculate waste concentration estimates.  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 oily) that served as the basis for these rates
will be displayed to the right of the waste concentration textboxes.

       When using the IWAIR tool in backward 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.
To estimate the cumulative risk posed to the receptor of concern, you can multiply the number of
carcinogens in the waste by the specified target risk level. For example, if a waste being managed
contains 5 carcinogens  and the single target risk level specified is IxlO"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 (IxlO'6) or 5xlO'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 restarting the model or saving the current run.
                                                                                          5-23

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Section 6.0
                                                                   Example Calculations
6.0  Example Calculations
       IWAJR allows the user to conduct forward calculations to estimate cancer and noncancer
inhalation risk estimates or back calculations to estimate protective waste concentrations from a
specified target risk level.  The following example calculations were prepared to demonstrate the
calculation approaches applied by IWAIR.

       The example calculations are performed for a tilled land application unit with a surface area of
1000 square meters. It was assumed that the waste managed in the unit contains the carcinogen
formaldehyde and noncarcinogen acrolein.  The default emission rates and dispersion rates used in the
calculations were developed using EPA's models  CHEMDAT8 and the Industrial Source Complex Short
Term model, version 3 (ISCST3 model), respectively.  The meteorological inputs used in conducting
emission and dispersion modeling were developed based on data obtained for Huntington, West
Virginia, which is one of the 29 IWAIR meteorological stations. The exposed individual is assumed to
be located 25 meters from the edge of the unit.  .

Carcinogens
       As discussed above, it was assumed that the waste managed in the land application unit
contained the carcinogen formaldehyde.  The cancer slope factor (CSF) from formaldehyde is 4.6E-02
(per mg/kg-d).

Forward Calculation:
       Using constituent-specific information for formaldehyde, Equations 1 through 3 illustrate the
process of completing a forward calculation to arrive at risk. For this example, it is assumed that
formaldehyde is present in the waste at a concentration of 6.5 mg/kg. The model combines emission
rates and dispersion data to predict an ambient air concentration at the point of exposure (i.e., 25 meters
from the unit).
Calculation of C.
                      C  = C
                            x ER x DF xlO3  mg/g = 2E-4
(6-1)
where
ER    =
                    air concentration (mg/m3)
                    waste concentration (mg/kg) = 6.5 mg/kg
                    unitized emission rate ([g/m2-s]per[mg/kg]) associated with a waste concentration
                    of 1 mg/kg. ER for Formaldehyde is 3E-8 [(g/m2-s)per(mg/kg)].

-------
Section 6.0
                                                                    Example Calculations
       DF    =     dispersion factor [(mg/m3) per (mg/m2-s)] associated with an emission rate of 1
                    g/m2-s.  DF for an assumed receptor located 25 meters from the unit is 1
                    [(mg/m3)per(mg/m2-s)].

The resulting air concentration can be combined with receptor exposure factors and toxicity benchmarks
to calculate the risk from concentrations managed in the unit.
Risk for carcinogens can be calculated as follows:

                                   C . x CSF x IR x  ED x EF
                           Risk =
                                      BW  x AT x  365 d/yr
                                                                                 (6-2)
where
       Risk   =     Individual risk (unitless)
       Cjj,.    =     air concentration (mg/m3)
       CSF   =     cancer slope factor (per mg/kg-d)
       IR     =     inhalation rate (m3/d)
       ED    =     exposure duration (yr)
       EF    =     exposure frequency (d/yr)
       BW   =     body weight (kg)
       AT    =     averaging time (yr).

       To reflect exposure that would occur in a lifetime (i.e., from childhood through adult), the model
applies a modified version of Equation 6-2 that employs 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).
IWAIR calculates lifetime risk as follows:
                                   C^xEFxCSF
                                 ~ AT x 365  d/yr X-r1
                                                                                 (6-3)
 where
Risk   =

EF    =
CSF   =
AT    =
FA   =
                     risk (unitless)
                     air concentration (mg/m3)
                     exposure frequency (day/yr) = 350 for all ages
                     cancer slope factor (mg/kg/day)'1 = 4.6E-2 for formaldehyde
                     averaging time (yr) = 70
                     inhalation rate for age group i (m3/day)
                     exposure duration for age group i (yr)
                     body weight for age group i (kg)
 6-2

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Section 6.0
                                            Example Calculations
          Table 6-1. Parameter Values Used in Estimating Time Weighted Average Exposure
"5 H <
Body Weight
Adult
Child < 1 year
Child 1-5 years
Child 6-11 years
Child 12-18 years
s
Body Weight
" tkg)
69.1
9.1
15.4
30.8
57.2
Inhalation
Rate
(nrVday)
13.3
4.5
7.55
11.75
14.0
•* \ /s
Exposure 'Duration
(years)'
11
1
5
6
7
Exposure Frequency
(days/year)
350
350
350
350
350
       The exposure factors addressed as part of this approach include inhalation rate, body weight,
exposure duration, and exposure frequency. The Table 6-1 identifies the default values that were applied
for each age group.

       These default values were identified based on data presented in EPA's Exposure Factors
Handbook (U.S. EPA, 1997a) and represent average exposure conditions.

Substituting these values into Equation 6-3 gives:
     _,. .   2E-4x350x4.6E-2
     Risk =	x
                 70x365
( 13.3 x
{   69.1
3x11  4.5x1   7.55x5   11.75x6  14.0x7
         9.1
15.4
30.8
57.2
                                            = lE-6
Backward Calculation:
       IWAIR performs backward calculations using an interative forward calculation algorithm. Using
Equations 1 through 3 above, the program sets an initial waste concentration, calculates risk, compares
the resulting risk estimate to the user-specified risk level, then adjusts the waste concentration and
recalculates until the target risk is achieved. For example, the program would begin with a waste
concentration of 1 mg/kg and solve Equation 6-1 to obtain an air concentration of 3E-5 mg/m3.  Based
on this air concentration, Equation 6-3 would result in a risk estimate of 1.7E-7.  This risk estimate
would then be compared to the specified risk level (e.g., 1 x 10"6).  Based on this comparison, the waste
concentration would be adjusted upward and the estimation process repeated until the program arrived at
a protective waste concentration of 6.5 mg/kg. As demonstrated above, this waste concentration
corresponds to inhalation risk estimate of 1 x 10"6.

Noncarcinogens
       To demonstrate the calculation process for noncarcinogens, it is assumed that the waste managed
in the model land application unit contains the noncarcinogen acrolein. Acrolein has a reference
concentration (RfC) of 2E-05 (mg/m3).
                                                                                           6-3

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Section 6.0
                                                                    Example Calculations
Forward Calculation:
       Using constituent-specific information for acrolein, Equations 6-4 and 6-5 illustrate the process
of forward calculating to noncarcinogenic risk (i.e., hazard quotient). For this example, it is assumed
that acrolein is present in the waste at a concentration of 1 mg/kg.
The hazard quotient for noncarcinogens can be calculated as follows:
                                       HQ -
                                              RfC
                                                                                (6-4)
where
       HQ    =     hazard quotient (unitless)
       Qor    =     afr concentration (mg/m3)
       RfC   =     reference concentration (mg/m3) = 2E-05 (mg/m3).

Substituting Equation 6-1 into Equation 6-4 and solving for HQ:

                                  cwaste x  ER x DF xl03mg/g
                           HQ  =
                                              RfC
                                                                                (6-5)
where
ER    =

DF    =


RfC   =
                     waste concentration (mg/kg) = 1 mg/kg
                     unitized emission rate ([g/m2-s]per[mg/kg]) associated with a waste concentration
                     of 1 mg/kg. ER for Acrolein is 2E-08 [(g/m2-s)per(mg/kg)].
                     unitized dispersion factor [(mg/m3) per (mg/m2-s)] associated with an emission
                     rate of 1 g/m2-s. DF for a receptor assumed to be located 25 meters from the unit
                     is 1 [(mg/m3)per(mg/m2-s)].
                     reference concentration (mg/m3) = 2E-05 (mg/m3).
 Substituting in parameter values:
                              HQ  =
                              1 x 2E-8  x 1 x  103mg/g
                                        2E-5
                                            HQ=1
 6-4

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Section 6.0
Example Calculations
Backward Calculation:
       IWAIR performs backward calculations using an interative forward calculation algorithm. Using
the above equations, the program sets an initial waste concentration (Cwaste), calculates risk, compares the
resulting risk estimate to the user-specified risk level, then adjusts the waste concentration and
recalculates until the target risk is achieved. For example, the program would begin with a waste
concentration of 1 mg/kg and solve Equation 6-1 to obtain an air concentration of 2E-5 mg/m3.  Based
on this air concentration, Equation 6-5 would result in a hazard quotient of 1. This risk estimate would
then be compared to the specified risk level (e.g., HQ of 0.5). Based on this comparison, the waste
concentration would be adjusted downward and the estimation process would be repeated until the
program arrived at a protective waste concentration of 0.5 mg/kg which corresponds to a hazard quotient
of 0.5 for acrolein.
                                                                                             6-5

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Section 7.0
References
7.0 References

Bailey, Robert G.; Avers, Peter E.; King, Thomas; McNab, W. Henry, eds. 1994. Ecoregions and
      subregions of the United States (map). Washington DC.; U.S. Geological Survey.  Scale
      1:7,500,000; colored. Accompanied by a supplementary table of map unit descriptions compiled
      and edited by McNab, W. Henry, and Bailey, Robert G. Prepared for the U.S. Department of
      Agriculture, Forest Service, http://www.epa.gov/docs/grdwebpg/bailey/

Environmental Quality Management, Inc. and E.H. Pechan & Associates. 1993. Evaluation of
      Dispersion Equations in Risk Assessment Guidance for Superfund (RAGS): Volume I - Human
      Health Evaluation Manual.  Prepared for U.S. Environmental Protection Agency, Office of
      Emergency and Remedial Response, Toxics Integration Branch. Washington, DC.

Shroeder, K., R. Clickner, and E. 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. Environmental Protection Agency.  1990. Methodology for Assessing Health Risks Associated with
      Indirect Exposure to Combustion Emissions (COMPDEP).  EPA/600/6-90/003.  Office of Health
      and Environmental Assessment, Washington, DC.

U.S. Environmental Protection Agency.  1991. Hazardous Waste TSDF - Background Information for
      Proposed RCRA Air Emission Standards. EPA-450/3-89-023a. Office of Air Quality Planning
      and Standards, Research Triangle Park, NC.               *

U.S. Environmental Protection Agency.  1993. Guideline on Air Quality Models, Office of Air Quality
      Planning and Standards, Research Triangle Park, NC.

U.S. Environmental Protection Agency.  1994. CHEMDAT8 User's Guide.  EPA-453/C-94-080B.
      Office of Air Quality Planning and Standards, Research Triangle Park, NC.
      EPA's web page (http://www.epa.gov/ttn/chief/software.html).

U.S. 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. Environmental Protection Agency.  1997a.  Exposure Factors Handbook. Draft. Office of Research
       and Development, National Center for-Environmental Assessment.
                                                                                        —

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Section 7.0
References
U.S. Environmental Protection Agency. 1997b.  Health Effects Assessement Summary Tables
       (HEAST). EPA-540-R-97-036. FY 1997 Update. Office of Solid Waste and Emergency
       Response, Washington, DC.

U.S. Environmental Protection Agency. 1998a.  Integrated Risk Information System (IRIS) - online.
       Duluth, MN. Http://www.epa.gov/iris/
 7-2

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