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Appendix
J
A Tiered Modeling Approach for Assessing the Risks Due to Sources of Hazardous Air Pollutants

David E. Guinnup

Disclaimer

This report has been reviewed by the Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, and has been approved for publication. Any mention of trade names or commercial products is not intended to constitute endorsement or recommendation for use.

U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air Quality Planning and Standards
Technical Support Division
Research Triangle Park, NC 27711
February 1992



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Page 537 Appendix J A Tiered Modeling Approach for Assessing the Risks Due to Sources of Hazardous Air Pollutants David E. Guinnup Disclaimer This report has been reviewed by the Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, and has been approved for publication. Any mention of trade names or commercial products is not intended to constitute endorsement or recommendation for use. U.S. ENVIRONMENTAL PROTECTION AGENCY Office of Air Quality Planning and Standards Technical Support Division Research Triangle Park, NC 27711 February 1992

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Page 538 Table Of Contents DISCLAIMER 537 FIGURES 539 TABLES 539 1.0 Introduction 540   1.1   Background and Purpose 540   1.2   Risk Assessment in Title III 541   1.3   Overview of Document 544   1.4   General Modeling Requirements 545 2.0     Tier I Analyses 549   2.1   Introduction 549   2.2   Long-term Modeling 549     2.2.1 Maximum Annual Concentration Estimation 550     2.2.2 Cancer Risk Assessment 552     2.2.3 Chronic Noncancer Risk Assessment 553   2.3   Short-term Modeling 554     2.3.1 Maximum Hourly Concentration Estimation 554     2.3.2 Acute Hazard Index Assessment 557 3.0     Tier 2 Analyses 558   3.1   Introduction 558   3.2   Long-term Modeling 558     3.2.1 Maximum Annual Concentration Estimation 558     3.2.2 Cancer Risk Assessment 560     3.2.3 Chronic Noncancer Risk Assessment 561   3.3   Short-term Modeling 562     3.3.1 Maximum Hourly Concentration Estimation 562     3.3.2 Acute Hazard Index Assessment 563 4.0     Tier 3 Analyses 564   4.1   Introduction 564   4.2   Long-term Modeling 564     4.2.1 Maximum Annual Concentration Estimation 565     4.2.2 Cancer Risk Assessment 567     4.2.3 Chronic Noncancer Risk Assessment 568   4.3   Short-term Modeling 569     4.3.1 Maximum Hourly Concentration Estimation 570     4.3.2 Acute Hazard Index Assessment 572 5.0     Additional Detailed Analyses 575 6.0     Summary of Differences Between Modeling Tiers 576       References 577 Appendix A - Electronic Bulletin Board Access Information 579 Appendix B - Regional Meteorologists/Modeling Contacts 580

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Page 539 Figures Number   1 Schematic of Example Facility with Long-Term Impact Locations 567 2 Schematic of Example Facility with Short-Term Impact Locations 573 Tables Number   1 Normalized Maximum Annual Concentrations, (µg/m3)(T/yr) 551 2 Normalized Maximum 1-Hour Average Concentrations, (µg/m3)(g/s) 556 3 Summary of Differences Between Modeling Tiers 576

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Page 540 1.0 Introduction 1.1 Background and Purpose Title III of the Clean Air Act Amendment of 1990 (CAAA) sets forth a framework for regulating major sources of hazardous (or toxic) air pollutants which is based on the implementation of MACT, the maximum achievable control technology, for those sources. Under this framework, prescribed pollution control technologies are to be installed without the a priori estimation of the health or environmental risk associated with each individual source. The regulatory process is to proceed on a source category-by-source category basis, with a list of source categories to be published by the end of 1991, and a schedule for their regulation to be published a year later. After the implementation of MACT, it will be incumbent on the United States Environmental Protection Agency (EPA) to assess the residual health risks to the population near each source within a regulated source category. The results of this residual risk assessment will then be used to decide if further reduction in toxic emissions is necessary for each source category (refer to §112(f) of the CAAA). These decisions will hinge primarily on a determination of the lifetime cancer risk for the "maximum exposed individual" for each source as well as the determination of whether the exposed population near each source is protected from noncancer health effects with an "ample margin of safety". The determination of lifetime cancer risk involves the estimation of long-term ambient concentrations of toxic pollutants whereas the determination of noncancer health effects can involve the estimation of long-term and short-term ambient concentrations. Since the measurement of long-term and short-term ambient concentrations for each toxic air pollutant (189 pollutants as listed in §112(b)) in the vicinity of each source is a prohibitively expensive task, it is envisioned that the process of residual risk determination would involve performing analytical simulations of toxic air pollutant dispersion for all sources (or a subset of sources) within each source category. Such simulations will subsequently be coupled with health effects information and compared to available data to quantify human exposure, cancer risk, noncancer health risks, and ecological risks. In addition to mandating the residual risk assessment process, the CAAA provide for the exemption of source categories and pollutants from the MACT-based regulatory process if it can be demonstrated that the risks associated with that source category or pollutant are below specified levels of concern. EPA-approved risk assessments would need to be performed to justify such an exemption, and the CAAA provide for petition processes to approve or deny claims that a source category or a specific pollutant should not be subject to regulation.

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Page 541 The purpose of this document is to provide guidance on the use of EPA-approved procedures which may be used to assess risks due to the atmospheric dispersion of emissions of hazardous air pollutants. It is likely that the techniques described herein will be useful with respect to several decision-making processes associated with the implementation of CAAA Title III (e.g., petition to add or delete a pollutant from the list of hazardous air pollutants, petition to delete a source category from the list of source categories, demonstration of source modification offsets, etc.). In addition, the procedures may serve as the basis for the residual risk determination processes described above. The guidance addresses the estimation of long-term and short-term ambient concentrations resulting from the atmospheric dispersion of known emissions of hazardous air pollutants, and subsequently addresses the techniques currently used to quantify the cancer risks and noncancer risks associated with the predicted ambient concentrations. It describes a tiered approach which progresses from simple conservative screening estimates (provided in the form of lookup tables) to more complex modeling methologies using computer models and site-specific data. In addition to providing guidance to assist in the CAAA Title III implementation process, it is being provided to the general public to assist State and local air pollution control agencies as well as sources of hazardous pollutants in their own assessment of the impacts of these sources. While the methods described herein comprise the most up-to-date means for assessing the impacts of sources of toxic air pollution, they are subject to future revision as new scientific information becomes available, possibly as a result of the risk assessment methodology study being conducted by the National Academy of Sciences (NAS) under mandate of section 112(o) of the CAAA (report due to Congress from NAS in May, 1993) 1.2 Risk Assessment in Title III As mentioned above, several provisions of CAAA Title III describe the need to consider ambient concentration impacts and their associated health risks in establishing the regulatory processes for sources of toxic air pollutants. Specifically, these are: 1. A pollutant may be deleted via a petition process from the list of hazardous or toxic pollutants subject to regulation if the petition demonstrates (among other things) that ''ambient concentrations…of the substance may not reasonably be anticipated to cause any adverse effects to the human health." (§112(b)(3)(C)) 2. A pollutant may be added to the list if a petition demonstrates that "ambient concentrations…of the substance are known or may reasonably be

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Page 542   anticipated to cause to cause adverse effects to human health." (§112(b)(3)(B)) 3. An entire source category may be deleted form the list of source categories subject to regulation if a petition demonstrates, for the case of carcinogenic pollutants, that "no source in the category…emits (carcinogenic) air pollutants in quantities which may cause a lifetime risk of cancer greater than one in one million to the individual in the population who is most exposed to emissions of such pollutants from the source," (§112(c)(9)(B)(i)) and, for the case of noncarcinogenic yet toxic pollutants, that "emissions from no source in the category…exceed a level which is adequate to protect public health with an ample margin of safety and no adverse environmental effect will result from emissions from any source." (§112(c)(9)(B)(ii)) 4. Within eight years after a source category has been subject to a MACT regulation, EPA must determine whether additional regulation of that source category is necessary based on an assessment of the residual risks associated with the sources in that category. Based on such an assessment, additional regulation of the source category is deemed necessary if "promulgation of such standards is required in order to provide an ample margin of safety to protect the public health" with respect to noncancer health effects, or if the MACT standards "do not reduce lifetime excess cancer risks to the individual most exposed to emissions from a source in the category or subcategory to less than one in one million" with respect to carcinogens, or if a determination is made "that a more stringent standard is necessary to prevent…an adverse environmental effect." (§112(f)(2)(A)) In the context of these provisions, decisions are to be made based on whether or not the predicted impact of a source exceeds some level of concern. For comparison to specified levels of concern, source impacts are quantified in four ways: 1. lifetime cancer risk; 2. Chronic noncancer hazard index; 3. acute noncancer hazard index, and; 4. frequency of acute hazard index exceedances. These impact measures are discussed in more detail in the next few paragraphs. It is worth noting at this point that insofar as knowledge is available regarding the effects of specific hazardous pollutants on the environment, it may be possible to use ecological hazard index values to quantify such impacts. Such calculations would proceed on a track which is parallel to the calculation of health hazard index values.

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Page 543 For carcinogenic pollutants, the level of concern is the risk of an individual contracting cancer by being exposed to the ambient concentrations of that pollutant over the course of a lifetime, or lifetime cancer risk. For the purposes of §112(c), the criterion specified in the CAAA is 1 in 1,000,000 lifetime cancer risk for the most exposed individual, or the individual exposed to the highest predicted concentrations of a pollutant. (For other purposes, the lifetime cancer risk specifying the level of concern may be higher or lower.) Lifetime cancer risks are calculated by multiplying the predicted annual ambient concentrations (in µg/m3) of a specific pollutant by the unit risk factor or unit risk estimate (URE)1for that pollutant, where the unit risk factor is equal to the upper bound lifetime cancer risk associated with inhaling a unit concentration (1 µg/m3)of that pollutant. Since predicted annual pollutant concentrations around a source vary as a function of position, so do lifetime cancer risk estimates. Thus, decisions involving whether the impact of a source or group of sources is above some level of concern typically focus on the highest predicted concentration (and hence the highest predicted lifetime cancer risk) outside the facility fenceline. The EPA has developed unit risk factors for a number of possible, probable, or known human carcinogens, and will be developing additional cancer unit risk factors as more information becomes available. For the purposes of this document, cancer risks resulting from exposure to mixtures of multiple carcinogenic pollutants will be assessed by summing the cancer risks due to each individual pollutant, regardless of the type of cancer which may be associated with any particular carcinogen.2 For pollutants causing noncancer health effects from chronic or acute exposure, the levels of concern are chronic and acute concentration thresholds, respectively, which would be derived from health effects data, taking into account scientific uncertainties. For purposes of estimating potential long-term impacts of hazardous air pollutants, EPA has derived for some pollutants (and will derive for others) chronic inhalation reference concentration (RfC)1 values, which are defined as estimates of the lowest concentrations of a single pollutant to which the human population can be exposed over a lifetime without appreciable risk of deleterious effects. For purposes of specific chronic noncancer risk assessment, EPA may designate the RfC value, or some fraction or multiple thereof, as the appropriate long-term noncancer level of concern. For purposes of specific acute noncancer risk assessment, the EPA may designate acute reference thresholds as the appropriate short-term noncancer level of concern. For the purposes of this document, long-term noncancer levels of concern will be referred to as chronic concentration thresholds, and short-term noncancer levels of concern will be referred to as acute concentration thresholds. For ease of implementation, acute concentration thresholds will be designated for 1-hour averaging times. This does not necessarily mean that exposure data indicate deleterious health effects from exposure times of 1 hour, but rather that the 1-hour acute

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Page 544 concentration threshold has been derived such that it is protective of the exposure duration of concern. The risk with respect to long- or short-term deleterious noncancer health effects associated with exposure to a pollutant or group of pollutants is quantified by the hazard index. The chronic noncancer hazard index is calculated by dividing the modeled annual concentration of a pollutant by its chronic concentration threshold value. The acute noncancer hazard index is calculated by dividing the modeled 1-hour concentration of a pollutant by its acute concentration threshold value. If multiple pollutants are being evaluated, the (chronic or acute) hazard index at any location is calculated by dividing each predicted (annual or 1-hour) concentration at that location by its (chronic or acute) concentration threshold value and summing the results.2If the hazard index is greater than 1.0, this represents an exceedance of the level of concern at that location. For pollutants which can cause deleterious health effects from acute exposures, exceedances of a level of concern may occur at any location and at any time throughout the modeling period. Thus, the frequency with which any location experiences an exceedance also becomes a measure of the risk associated with a modeled source. Frequency of acute hazard index exceedances is only addressed by the most refined analysis methods referred to in this document. Information on UREs and RfCs is accessible through the Integrated Risk Information System (IRIS), EPA Environmental Criteria and Assessment Office (ECAO) in Cincinnati, Ohio, (513) 569-7254. 1.3 Overview of Document This document is divided into three major sections, each section addressing a different level of sophistication in terms of modeling, referred to as "tiers". The first tier is a simplified screening procedure in which the user can estimate maximum off-site ground-level concentrations without extensive knowledge regarding the source and without the need of a computer. The second tier is a more sophisticated screening technique which requires a bit more detailed knowledge concerning the source being modeled and, in addition, requires the execution of a computer program. The third tier involves site-specific computer simulations with the aid of computer programs and detailed source parameters. Since the effects of toxic air pollutants may be of concern from both a long-term and a short-term perspective, each tier is divided into two parts. The first part addresses dispersion modeling to assess long-term ambient concentrations (important from a cancer-causing or chronic noncancer effects standpoint) and the second addresses dispersion modeling for the estimation of short-term concentrations (important from an acute toxicity perspective).

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Page 545 It should be noted that this document is intended to be used in conjunction with the User's Guides for the models described: SCREEN,3TOXST,4and TOXLT.5It is not intended to replace or reproduce the contents of these documents. In addition, the reader may wish to consult the "Guideline on Air Quality Models (Revised)"6for more detailed information on the consistent application of air quality models. Modelers may also wish to use the EPA's TSCREEN7modeling system to assist in the Tier 2 computer simulation of certain toxic release scenarios. It should be noted, however, that toxic pollutant releases which TSCREEN treats as heavier-than-air are not to be modeled using techniques described herein. Atmospheric dispersion of such pollutants requires a more refined analysis, such as those described in Reference 8. Model codes, user's guides, and associated documentation referred to in this document can be obtained through the Technology Transfer Network (TTN) of the EPA's Office of Air Quality Planning and Standards (OAQPS), and access information is provided in Appendix A. The modeling tiers are designed such that the concentration estimates from each tier should be less conservative than the previous one. This means that, for a given situation, a Tier 1 modeled impact should be greater than, or more conservative than, the Tier 1 modeled impact, and the Tier 2 modeled impact should be more conservative than the Tier 3 modeled impact. Progression from one tier of modeling to the next thus involves the use of levels of concern, as defined above. For example, if the results of a Tier 1 analysis indicates an exceedance of a level of concern with respect to either (1) the maximum predicted cancer risk, (2) the maximum predicted chronic noncancer hazard index, or (3) the maximum predicted acute hazard index, the analyst may wish to perform a Tier 2 analysis. If all three of these impact measures are below their specified levels of concern, there should be no need to perform a more refined simulation, and thus, there should be no need to progress to the next tier of modeling. Since the establishment of levels of concern for each specific hazardous air pollutant is not a part of this effort, this document will refer to generic levels of concern, and users will need to consult subsequent EPA documents to determine the specific levels of concern for their particular pollutant or pollutant mixture and for the particular purpose of their modeling efforts. 1.4 General Modeling Requirements, Definitions, and Limitations This document describes modeling methologies for point, area, and volume sources of atmospheric pollution. A point source is an emission which emanates from a specific point, such as a smokestack or vent. An area source is an emission which emanates from a specific, well-defined surface, such as a lagoon, landfarm, or open-top tank. Sources referred to as having "fugitive" emissions (e.g., multiple leaks within a specific processing area) are typically mod-

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Page 546 eled as area sources. The methods used in this document are generally considered to be applicable for assessing impacts of a source from the facility fenceline out to a 50 km radius of the source or sources to be modeled. There is no particular upper or lower limit on emission rate value for which these techniques apply. For the purposes of this document, "source" means the same thing as "release", and "air toxic" means the same as "hazardous air pollutant". It should be noted that ''area source" as defined in the previous paragraph is not the same as the "area source" defined by the CAAA. Modeling techniques described in this document are specifically intended for use in the simulation of a finite number of well-defined sources, not for simulation of a large number of ill-defined small sources distributed over a large region, as might well be the case for some "area sources" specified in the CAAA. Simulation of the acute and chronic impacts of such area sources may utilize the RAM model9and the CDM 2.0 model,10respectively. Consult the "Guideline on Air Quality Models (Revised)"6for additional information. The reader should note that relatively small, well-defined groups of sources, however, may be modeled using the techniques described herein. This document does not address the simulation of facilities located in complex terrain. Those interested in modeling facilities with possible complex terrain effects are directed to consult the "Guideline on Air Quality Models (Revised)"6or their EPA Regional Office modeling contact for assistance in this area (see listing Appendix B). In order to conduct an impact assessment, it is necessary to have estimates of emission rates of each pollutant from each source or release point being included in the assessment. Emission rates may be best estimated from experimental measurements or sampling, where such test methods are available. Alternatively, mass balance calculations or use of emission factors developed for specific types of processes may be used to quantify emission rates. The procedures discussed in this document do not address the emission estimation process. Guidance for source-specific emission rate estimation and emission test methods is available in other EPA documentation (e.g., see References 11 through 15). Additional information concerning specific emission measurement techniques is available through the OAQPS TTN (see Appendix A). Since many sources of hazardous air pollutants are intermittent in nature (e.g., batch process emissions), the techniques in this document have been developed to allow the treatment of intermittent sources as well as continuous types of sources. It is important to understand the different treatment of emission rates for both types of sources when carrying out either the analysis of a long-term

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Page 547 impact or a short-term impact. In a long-term impact analysis, the emission rate used for modeling is based on the amount of pollutant emitted over a 1-year period, regardless of whether the emission process is a continuous or intermittent one. In addition, to assess the worst-case impact of a source or group of sources, long-term emission rates used in model simulations should reflect the emission rates for a plant or process which is operating at full design capacity. In a short-term impact analysis, the emission rate used for modeling is based on the maximum amount of pollutant emitted over a 1-hour period, during which the source is emitting. The Tier 1 and Tier 2 procedures evaluate the combined worst-case impacts of intermittent sources as if they are all emitting at the same time, whereas the Tier 3 procedures incorporate a more realistic treatment of intermittent sources by turning them on and off throughout the simulation period according to user-specified frequency of occurrence of each release. This frequency of occurrence should reflect the normal operating schedule of the source when operating at maximum design capacity. In addition to emission rate estimates, it is necessary to have quantitative information about the sources to conduct a detailed impact assessment. Tier 1 analyses require information about the height of the release above ground level and the shortest distance from the release point to the facility fenceline. Higher tiers of analysis require additional information including, but not limited to: Stack height Inside stack diameter Exhaust gas exit velocity Exhaust gas exit temperature Dimensions of structures near each source Dimensions of ground-level area sources Exact release and fenceline location Exact location of receptors for determining worst-case impacts Land use near the modeled facility Terrain features near the facility Duration of short-term release Frequency of short-term release Where appropriate, this document will address the best means of obtaining these input data. In some more complex cases, the modeling contact at the nearest EPA Regional Office may need to be consulted for specific modeling guidance (see listing in Appendix B). Depending on the specific purpose of the impact assessment, it may be difficult for the modeler to decide which sources (or release points) and which pollutants should be included in a particular analysis or simulation. Since these

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Page 572   sible concern. Although it may be set higher, a good rule of thumb for setting this value is: where LACT is the lowest acute concentration threshold value in the group of pollutants being modeled, and Npoli is the number of pollutants emitted from ISCST source group i. The printed ISCST output will indicate the top 50 impacts for each ISCST source group, and the TOXFILE will contain all of the concentrations above the cutoff value from each ISCST source group at each receptor. The ISCST model was exercised for the example facility. The maximum 1-hour concentrations for each source/pollutant combination were determined to be as follows: Source Compound Max. Impact Location Stack 1 Pollutant A 34.5 µg/m3 Q Stack 2 Pollutant A 67.9 µg/m3 R Stack 2 Pollutant B 29.1 µg/m3 R Stack 3 Pollutant B 39.2 µg/m3 S Stack 4 Pollutant B 47.5 µg/m3 S The locations of the predicted maximum 1-hour concentrations are shown in Figure 2. The maximum impacts from each source were only slightly lower than those from the Tier 2 analysis. 4.3.2 Acute Hazard Index Exceedance Assessment Concentrations from the ISCST master file inventory are used by the TOXX post-processor to calculate acute hazard index values for each hour of a multiple-year simulation period at each receptor site in the ISCST receptor array. The program then counts the number of times a hazard index value exceeds 1.0 (an exceedance) and prints out a summary report which indicates the average number of times per year an exceedance occurs at each receptor. The use of the TOXX post-processor requires the following considerations: 1. As stated above, in most cases unit emission rate multipliers for each pollutant from each source are used as inputs to the TOXX post-processor.

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Page 573 Figure 2. Schematic of Example Facility with Short-term Impact Locations 2. Acute threshold concentration values are provided to TOXX as the health effects thresholds in the TOXX post-processor input file. 3. The TOXX output option should be chosen to output the exceedances in polar grid format. Exceedance counts at discrete fenceline receptors will appear at the end of this table in the order in which discrete receptor locations were input to ISCST. 4. If only one pollutant is being modeled, the additive exceedance calculation option should not be chosen. If multiple pollutants are being modeled, the additive exceedance calculation option should be chosen. The TOXX post-processor should be set to perform 400 or more simulation years (maximum 1000). Unless otherwise specified by EPA guidance, background concentrations for toxic air pollutants should be set equal to 0. 5. The frequency of operation for each emission source is specified by providing values for the probability of the source switching on and the duration of the release. For each continuous emission, the probability of the source switching on is 1.0, and for each intermittent emission source, the probability of the source switching on is equal to the average number of releases per year divided by 8760 (the number of hours in a non-leap year).

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Page 574   The duration of release for each continuous source should be set equal to 1.0, and the duration of release for each intermittent release should be specified as the nearest integer hour which is not less than the release duration. (For example, if the average release duration is less than 1 hour, the duration of the release should be set equal to 1; if the average release duration is 3.2 hours, the duration of release should be set equal to 4.) If the maximum number of acute hazard index exceedances in the receptor grid is less than some specified value (e.g., 0.1, equivalent to an average of 1 hourly exceedance every 10 years), the modeled source is considered to be in compliance with the acute threshold concentration criteria. However, resimulation with placement of additional receptors in the ISCST receptor array should be considered as a means of assuring that the simulation is not underestimating the maximum acute hazard index. If the maximum number of hazard index exceedances in the receptor array is greater than the specified value, additional runs of the TOXX post-processor with reduced emissions rate multipliers may be performed to assess the impacts of possible emission control scenarios. In the case of non-compliance, it may be desirable on the part of the modeler to conduct a more refined analysis. Section 5.0 of this document discusses such possibilities. The TOXX post-processor was exercised for the example facility using the results form the ISCST simulation. The frequency of operation for each source ranged from 0.14 to 0.84, reflecting the actual yearly frequency of "on" time for each source. The output showed that none of the receptors experienced an impact resulting in a hazard index value of 1.0 or greater. Comparing this result with the Tier 2 result indicates that the hazard index never exceeds 1.0 because in a Tier 3 analysis the maximum impacts are seen not to occur at the same place and time. This indicates that the facility does not cause a significant health risk from acute exposure in its current configuration.

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Page 575 5.0 Additional Detailed Analyses If any Tier 3 analyses indicate non-compliance with any of the user-specified criteria, it may be desireable to conduct an additional, more refined analysis. This may mean the use of on-site meteorological data or it may mean that a more appropriate modeling procedure is deemed applicable for the specific case. The determination of an appropriate alternative modeling procedure can only be made in a manner consistent with the approach outlined in the "Guideline on Air Quality Models (Revised)."6 In some cases, the EPA may allow exposure assessments to incorporate available information on actual locations of residences, potential residences, businesses, or population centers for the purpose of establishing the probability of human exposure to the predicted levels of toxic pollution near the source being modeled. In such cases, use of the Human Exposure Model (HEM II)19with the ISCLT dispersion model is preferred. Again, if the use of other modeling procedures is desired, the approval of a more appropriate alternative modeling procedure can only be made in a manner consistent with the approach outlined in Section 3.2 of the "Guideline on Air Quality Models (Revised)."6

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Page 576 6.0 Summary Of Differences Between Modeling Tiers To summarize the major differences between the 3 modeling tiers described in this document, Table 3 below briefly lists the input requirements, output parameters, and assumptions associated with each tier. This Table may be used to quickly determine whether a given scenario may be modeled at any particular tier. Within each tier, cancer unit risk estimates, chronic noncancer concentration thresholds, and acute concentration thresholds are required to convert concentration predictions into cancer risks, chronic noncancer risks, and acute noncancer risks, respectively. Modeling Tier Input Requirements Output Parameters Major Assumptions Tier 1 emission rate, stack height, minimum distance to fenceline maximum off-site concentrations, worst-case cancer risk or worst-case noncancer hazard index (short- and long-term) worst-case meteorology, worst-case downwash, worst-case stack parameters, short-term releases occur simultaneously, maximum impacts co-located, cancer and noncancer risks additive Tier 2 emission rate, stack height, minimum distance to fenceline, stack velocity, stack temperature, stack diameter, rural/urban site classification, building dimensions for downwash calculations maximum off-site concentrations, worst-case cancer risk and/or worst-case noncancer hazard index (short- and long-term) worst-case meteorology, short-term releases occur simultaneously, maximum impacts co-located, cancer and non-cancer risks additive Tier 3 emission rate, stack height, actual fenceline and release point locations, stack velocity, stack temperature, stack diameter, rural/urban site classification, local meteorological data, receptor locations for concentration predictions, frequency and duration of short-term (intermittent) releases concentrations at each receptor point, long-term cancer risk estimates, chronic noncancer hazard index estimates at each receptor point, annual hazard index exceedance rate at each receptor. cancer and noncancer risks additive

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Page 577 References 1. Environmental Protection Agency, 1988. Glossary of Terms Related to Health, Exposure, and Risk Assessment. EPA-450/3-88-016. United States Environmental Protection Agency, Research Triangle Park, NC 27711. 2. Environmental Protection Agency, 1987. The Risk Assessment Guidelines of 1986. EPA-600/8-87-045. United States Environmental Protection Agency, Washington, DC 20460. 3. Brode, Roger W., 1988. Screening Procedures for Estimating the Air Quality Impact of Stationary Sources (Draft). EPA-450/4-88-010. United States Environmental Protection Agency, Research Triangle Park, NC 27711. 4. Environmental Protection Agency, 1992. Toxic Modeling System Short-Term (TOXST) User's Guide. EPA-450/4-92-002. United States Environmental Protection Agency, Research Triangle Park, NC 27711 (in preparation). 5. Environmental Protection Agency, 1992. Toxic Modeling System Long-Term (TOXLT) User's Guide. EPA-450/4-92-003. United States Environmental Protection Agency, Research Triangle Park, NC 27711 (in preparation). 6. Environmental Protection Agency, 1988. Guideline on Air Quality Models (Revised). EPA-450/2-78-027R. United States Environmental Protection Agency, Research Triangle Park, NC 27711. 7. Environmental Protection Agency, 1990. User's Guide to TSCREEN: A Model for Screening Toxic Air Pollutant Concentrations. EPA-450/4-90-013. United States Environmental Protection Agency, Research Triangle Park, NC 27711. 8. Environmental Protection Agency, 1991. Guidance on the Application of Refined Dispersion Models for Air Toxic Releases. EPA-450/4-91-007. United States Environmental Protection Agency, Research Triangle Park, NC 27711. 9. Catalano, J.A., D.B. Turner, and J.H. Novak, 1987. User's Guide for RAM - Second Edition. United States Environmental Protection Agency, Research Triangle Park, NC 27711. 10. Irwin, J.S., T. Chico, and J.A. Catalano. CDM 2.0 - Climatological Dispersion Model-User's Guide. United States Environmental Protection Agency, Research Triangle Park, NC 27711. 11. Environmental Protection Agency, 1991. Procedures for Establishing Emissions for Early Reduction Compliance Extensions. Draft. EPA-450/3-91-012a. United States Environmental Protection Agency, Research Triangle Park, NC 27711. 12. Environmental Protection Agency, 1978. Control of Volatile Organic Emissions from Manufacturers of Synthesized Pharmaceutical Products. EPA-450/2-78-029. United States Environmental Protection Agency, Research Triangle Park, NC 27711. 13. Environmental Protection Agency, 1980. Organic Chemical Manufacturing Volumes 1-10. EPA-450/3-80-023 through 028e. United States Environmental Protection Agency, Research Triangle Park, NC 27711. 14. Environmental Protection Agency, 1980. VOC Fugitive Emissions in Synthetic Organic Chemicals

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Page 578 Manufacturing Industry - Background Information for Proposed Standards. EPA-450/3-80-033a. United States Environmental Protection Agency, Research Triangle Park, NC 27711. 15. Environmental Protection Agency, 1990. Protocol for the Field Validation of Emission Concentrations from Stationary Sources. EPA-450/4-980-015. United States Environmental Protection Agency, Research Triangle Park, NC 27711. 16. Pierce, T.E., Turner, D.B, Catalano, J.A., Hale, F.V., 1982. "PTPLU: A Single Source Gaussian Dispersion Algorithm." EPA-600/8-82-014. United States Environmental Protection Agency, Washington, DC 20460. 17. California Air Pollution Control Officers Association (CAPCOA), 1987. Toxic Air Pollutant Source Assessment Manual for California Air Pollution Control District and Applications for Air Pollution Control District Permits, Volumes 1 and 2. CAPCOA, Sacramento, CA. 18. Environmental Protection Agency, 1987. Industrial Source Complex (ISC) User's Guide- Second Edition (Revised), Volumes 1 and 2. EPA-450/4-88-002a and b. United States Environmental Protection Agency, Research Triangle Park, NC 27711. 19. Environmental Protection Agency, 1991. Human Exposure Model (HEM-II) User's Guide. EPA-450/4-91-010. United States Environmental Protection Agency, Research Triangle Park, NC 27711.

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Page 579 Appendix A Electronic Bulletin Board Access Information The Office of Air Quality Planning and Standards (OAQPS) of the EPA has developed an electronic bulletin board network to facilitate the exchange of information and technology associated with air pollution control. This network, entitled the OAQPS Technology Transfer Network (TTN), is comprised of individual bulletin boards that provide information on OAQPS organization, emission measurement methods, regulatory air quality models, emission estimation methods, Clean Air Act Amendments, training courses, and control technology methods. Additional bulletin boards will be implemented in the future. The TTN service is free, except for the cost of the phone call, and may be accessed from any computer through the use of a modem and communications software. Anyone in the world wanting to exchange information about air pollution control can access the system, register as a system user, and obtain full access to all information areas on the network after a 1 day approval process. The system allows all users to peruse through information documents, download computer codes and user's guides, leave questions for others to answer, communicate with other users, leave requests for technical support from the OAQPS, or upload files for other users to access. The system is available 24 hours a day, 7 days a week, except for Monday, 8-12 a.m. EST, when the system is down for maintenance and backup. The model codes and user's guides referred to in this document, in addition to the document itself, are all available on the TTN in the bulletin Board entitled SCRAM, short for Support Center for Regulatory Air Models. Procedures for downloading these codes and documents are also detailed in the SCRAM bulletin board. Documentation on EPA-approved emission test methods is available on the TTN in the bulletin board entitled EMTIC, short for the Emission Measurement Testing Information Center. Procedures for reading or downloading these documents are also detailed in the EMTIC bulletin board. The TTN may be accessed at the phone number (919)-541-5742, for users with 1200 or 2400 bps modems, or at the phone number (919)-541-1447, for users with a 9600 bps modem. The communications software should be configured with the following parameter settings: 8 data bits; 1 stop bit; and no (N) parity. Users will be asked to create their own case sensitive password, which they must remember to be able to access the network on future occasions. The entire network is menu-driven and extremely user-friendly, but any users requiring assistance may call the system operator at (919)-541-5384 during normal business hours EST.

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Page 580 Appendix B Regional Meteorologists/Modeling Contacts Ian Cohen EPA Region I (ATS-2311) J.F.K. Federal Building Boston, MA 02203-2211 FTS: 853-3229 Com: (617) 565-3225 E-mail: EPA9136 FAX: FTS 835-4939 Robert Kelly EPA Region II 26 Federal Plaza New York, NY 10278 FTS: 264-2517 Com: (212)-264-2517 E-mail: EPA9261 FAX: FTS 264-7613 Alan J. Cimorelli EPA Region III (3AM12) 841 Chestnut Building Philadelphia, PA 19107 FTS: 597-6563 Com: (215) 597-6563 E-mail: EPA9358 FAX: FTS 597-7906 Lewis Nagler EPA Region IV 345 Courtland Street, N.E. Atlanta, GA 30365 FTS: 257-3864 Com: (404) 347-2864 E-mail: EPA9470 FAX: FTS 257-5207 James W. Yarbough EPA Region VI (6T-AP) 1445 Ross Avenue Dallas, TX 75202-2733 FTS: 255-7214 Com: (214) 255-7214 E-mail: EPA9663 FAX: FTS 255-2164 Richard L. Daye EPA Region VII 726 Minnesota Avenue Kansas City, KS 66101 FTS: 276-7619 Com: (913) 551-7619 E-mail: EPA9762 FAX: FTS 276-7065 Larry Svoboda EPA Region VIII (8AT-AP) 999 18th Street Denver Place-Suite 500 Denver, CO 80202-2405 FTS: 776-5097 Com: (303) 293-0949 E-mail: EPA9853 FAX: FTS 330-7559 Carol Bohnenkamp EPA Region IX (A-2-1) 75 Hawthorne Street San Francisco, CA 94105 FTS: 484-1238 Com: (415) 744-1238 E-mail: EPA9930 FAX: FTS 484-1076 Rebecca Calby EPA Region V (5AR-18J) 77 W. Jackson Chicago, IL 60604 FTS: 886-6061 Com: (312) 886-6061 E-mail: EPA9553 FAX: FTS 886-5824 Robert Wilson EPA Region X (ES-098) 1200 Sixth Avenue Seattle, WA 98101 FTS: 399-1530 Com: (206) 442-1530 E-mail: EPA9051 FAX: 399-0119

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Page 581 TECHNICAL REPORT DATA FORM

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Page 582 TECHNICAL REPORT DATA FORM (continued)