MODEL CLEARINGHOUSE: FY-93 SUMMARY REPORT OCTOBER 1993 Source Receptor Analysis Branch Technical Support Division Office of Air Quality Planning and Standards U.S. Environmental Protection Agency Research Triangle Park, North Carolina 27711 TABLE OF CONTENTS MODEL CLEARINGHOUSE: FY-93 SUMMARY REPORT PAGE 1.0 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . 1 2.0 FY-92 CLEARINGHOUSE ACTIVITIES . . . . . . . . . . . . . . . 2 2.1 Background and Responsibilities . . . . . . . . . . . . 2 2.2 Summary of Regional Office Requests and Clearinghouse Responses . . . . . . . . . . . . . . . . . . . . . . . 5 2.3 Recurring Coordination . . . . . . . . . . . . . . . . 10 2.4 Support Center for Regulatory Air Models Bulletin Board System (SCRAM BBS) . . . . . . . . . . . . . . . 11 3.0 CLEARINGHOUSE RESPONSES TO RECURRING OR GENERIC ISSUES . . . 13 3.1 Ambient Credits for Emission Reductions Using Screening Techniques . . . . . . . . . . . . . . . . . . . . . . 13 3.2 Credits for Stack Height Increases to Avoid Downwash Problems Created by Newly Constructed Nearby Structures 13 3.3 Rounding of Model Estimates in Ozone Attainment Demonstrations . . . . . . . . . . . . . . . . . . . . 18 3.4 Further Clarifications of Stack-Structure Relationships 20 Appendix A FY-92 MODEL CLEARINGHOUSE MEMORANDA . . . . . . . . . A-1 Appendix B MODEL CLEARINGHOUSE CONTACTS . . . . . . . . . . . . B-1 Appendix C SUMMARY OF THE EPA MODEL CLEARINGHOUSE . . . . . . . C-1 1.0 INTRODUCTION This report summarizes major activities of the Model Clearinghouse from August 22, 1992 to August 31, 1993. The report is divided into two parts. First, the FY-93 activities of the Clearinghouse are summarized. The second section summarizes Clearinghouse responses to major categorical modeling problems occurring during FY-93; within each of these there were several issues/questions of a similar nature. Appendix A provides a list of Model Clearinghouse memoranda covering the period October 1, 1992 to September 30, 1993. Appendix B contains a list of EPA Model Clearinghouse contact personnel. Appendix C provides a brief summary of the EPA Model Clearinghouse responsibility, structure and operational procedures. 2.0 FY-93 CLEARINGHOUSE ACTIVITIES 2.1 Background and Responsibilities The Model Clearinghouse was established on November 20, 1980. The Regional Offices were notified of its general purposes, procedures and limitations on that date. A detailed operational plan describing the functions, structure, procedures, and schedule for implementation was issued on February 25, 1981. Initially the operation of the Model Clearinghouse was limited to the review of proposed deviations from modeling guidance for the regulatory modeling of iron/steel facilities, smelters, and power plants. As such, the reviews were usually limited to sulfur dioxide (SO2), total suspended particulates (TSP), and lead (Pb). On a gradual basis the limitation to these facilities was relaxed to the point where the Clearinghouse, by the mid- 1980's, was accepting referrals for all point sources of stable pollutants. Beginning in 1986, the Clearinghouse began accepting referrals for mobile source problems involving carbon monoxide (CO). During FY-88, the Model Clearinghouse was expanded to cover ozone (O3) and nitrogen dioxide (NO2). A revised Model Clearinghouse operational plan* was issued to reflect that the Model Clearinghouse purview includes all criteria pollutants. During FY-92, the Clearinghouse operation was further expanded to include noncriteria (toxic) pollutants. _______________________ *Model Clearinghouse: Operational Plan, Revised, Source Receptor Analysis Branch, Office of Air Quality Planning and Standards, May 1988 The Model Clearinghouse Operational Plan states that the primary purposes of the Model Clearinghouse are to provide: 1. A mechanism whereby the proposed acceptance by a Regional Office of a nonguideline model or alternative technique can be reviewed for national consistency before final approval by the Regional Administrator. Such reviews promote the use of equivalent acceptance criteria by all Regions. 2. A mechanism whereby the in-depth technical evaluation and/or performance evaluation of a proposed technique can be reviewed by those EPA personnel who are most familiar with the types of techniques to be employed. 3. A communication outlet for EPA's experience with the use of nonguideline models, data bases or other deviations from current guidance. The Clearinghouse maintains a high level of expertise on the applicability of various models and classes of models and allowed deviations from accepted procedures in specified circumstances. This information is communicated on a periodic basis to EPA personnel involved in regulatory model applications. The Clearinghouse is formally located in the Source Receptor Analysis Branch (SRAB) of the Office of Air Quality Planning and Standards (OAQPS). However, the Air Quality Management Division (AQMD) also participates in Clearinghouse matters involving State implementation plan (SIP) attainment strategies and other regulatory functions. The primary responsibility for managing the Clearinghouse and ensuring that all of its functions are carried out is performed by a person full-time within SRAB. A Clearinghouse support person in SRAB maintains the Clearinghouse's electronic communications interface through the computerized data base and bulletin board systems described below. The responsibility for responding to requests for review of modeling issues is assigned, on a pollutant/program basis to four SRAB individuals. In addition, AQMD supports the Clearinghouse with staff who are also knowledgeable in modeling policy. These individuals are responsible for screening SIP submittals and related documents, referring modeling issues to SRAB through the Clearinghouse, and documenting the final (and any significant interim) decision on disposition of the issues. A current list of OAQPS and Regional Office Model Clearinghouse contacts is provided in Appendix B. The FY-93 activities for the Model Clearinghouse included: 1. Responding to Regional Office requests for review of nonguideline models proposed for use. 2. Reviewing draft and formally submitted Federal Register actions. 3. Documenting Clearinghouse decisions and discussions. 4. Summarizing Clearinghouse activities at various meetings. 5. Issuing, internally, a summary report for activities of FY-92. 6. Inputting FY-93 Clearinghouse records into a computerized data base. 7. Providing for Regional Office direct access to the computerized data base by modem. 8. Disseminating Clearinghouse memoranda and reports to the public through a bulletin board system. 2.2 Summary of Regional Office Requests and Clearinghouse Responses The number and type of contacts from the Regional Offices to the Clearinghouse during FY-93 are summarized in Table 1. The data in the table under "Recommendations" include those issues where a coordinated clarification of policy was involved or an investigation had to be undertaken by the Clearinghouse. In addition, there were numerous other inquiries to the Clearinghouse regarding procedures, technical considerations, and policies which were readily resolved or referred elsewhere. Note from the table that there were a total of 19 regulatory modeling problems referred to the Clearinghouse which required a written response and another 77 referrals in which the issues were resolved orally. In addition, there were another 22 referrals where discussions took place but a Clearinghouse recommendation was not requested. Note also that requests for assistance, either written or by telephone, came from all of the Regional Offices. This suggests that there is an awareness and a desire for Clearinghouse support throughout the Agency. Table 2 contains a summary, by category, of the nature of the referrals and requests for assistance. The table is useful for identifying commonly recurring problems and problem areas. Table 3 tabulates the regulatory/modeling subject area involved in resolution of issues for each referral. More than one subject area was involved in the resolution of issues for most referrals. Also, it should be noted that in Table 3 referrals for Interpretation of Modeling Guidance and Interpretation of Regulatory Guidance usually involved broad issues where the applicability of the guidance, in general, was either called into question or that the issue involved a subject not included in the remainder of the subject area list. TABLE 1. TYPES OF CLEARINGHOUSE RESPONSES DURING FY-93 RECOMMENDATIONS REGION WRITTEN ORAL DISCUSSION/INFORMATION* TOTAL I 1 2 3 6 II 2 5 2 9 III 0 4 2 6 IV 4 5 0 9 V 4 12 5 21 VI 1 11 0 12 VII 3 6 0 9 VIII 4 11 6 21 IX 0 14 2 16 X 0 7 2 9 19 77 22 118 *Did not include a specific Clearinghouse recommendation. TABLE 2. CHARACTERIZATION OF 118 CLEARINGHOUSE REFERRALS DURING FY-93. ONLY REFERRALS CONTAINING SIGNIFICANT MODELING ISSUES ARE INCLUDED. SOME REFERRALS INVOLVED MORE THAN ONE POLLUTANT, SOURCE TYPE OR REGULATION. Pollutants Involved Number of Referrals SO2 29 TSP 15 CO 10 Pb 5 NOx 6 O3 14 Dioxin 1 PM-10 34 Unspecified 1 Unspecified Non-criteria 5 Generic 5 Source Types Power Plant 15 Power Boiler 3 Smelter 10 Steel Facility 2 Paper Mill 9 Aluminum Plant 2 Refinery 3 Cogeneration Unit 1 Incineration 6 Mine 1 Chemical Plant 3 Roadway 11 Sugar Mill 1 Open Burning 1 Gas Compressor 1 Cement Plant 1 Open Dust Fugitive 1 Drilling Rig 3 Unspecified Stationary Source 4 Mixed/Multiple Sources 37 Generic to Any Stationary Source 4 Generic to Any Source 1 Urban or Rural Model Involved Urban Only 39 Rural Only 72 Both Urban and Rural 3 Not Relevant 4 Types of Response Written 19 Oral 77 Not Relevant 22 Applicable Regulations Number of Referrals SIP 60 SIP Revision 12 SIP Revision - GEP 3 PSD 32 EIS 1 State Regulation 3 NESHAPS 1 FIP 2 RCRA 5 Generic 1 Terrain Setting High Terrain (above stack height) 9 Low Terrain (below stack height) 66 Both High and Low Terrain 25 Essentially Flat Terrain 15 Not Relevant 3 Guideline or Nonguideline Model Involved Guideline 66 Non-guideline 24 Guideline and Non-guideline 15 Not Relevant 12 Data Bases Used for Model Input On-site 39 Off-site 50 Both Off-site and On-site 7 Not relevant 22 TABLE 3. SUBJECT AREAS INVOLVED IN FY-93 CLEARINGHOUSE REFERRALS Subject Area Number of Occurrences Adjustment of Model Estimates 1 Ambient Air 5 Ambient Monitoring 5 Area Wide Analysis 1 Block/Running Average 1 Calibration 1 Clearinghouse Operating Procedures 1 Deposition 1 Downwash 9 Emissions Characterization 7 Emission Rates for Model Input 9 Equivalency 2 Grandfathering of Guidance 3 Interpretation of Guideline Language 1 Interpretation of Modeling Guidance 13 Interpretation of Regulatory Guidance 11 Length of Record - Meteorological Data 8 Load Level 2 Long-Range Transport 5 Meteorological Monitoring 7 Mixed Terrain Modeling 9 Modeled Background 5 Monitored Background 10 Monitoring in Lieu of Modeling 6 Open Dust Fugitives 1 Performance Evaluations 7 Plume Rise 4 PSD Increment Calculation 2 Reactive Pollutant Modeling/Chemical Transformations 11 Receptor Modeling 9 Receptor Networks 1 Representativeness of Meteorological Data 10 Screening Procedures 4 Shoreline/Offshore Modeling 2 Significant Air Quality Impacts 4 Stability Classes 4 State Modeling Guidelines 2 Technical Credibility of Nonguideline Techniques 5 Time Scaling 1 Urban/Rural 4 Worst Case Meteorology 8 Stagnation 5 Visibility 2 2.3 Recurring Coordination During FY-93, the Clearinghouse conducted or participated in a number of activities that can be categorized as coordination and information exchanges with the Regional Offices. One of the first activities was to prepare and distribute to the Regional Offices in October 1992, a Clearinghouse report; this report served to inform Clearinghouse users about the issues and responses which occurred in FY-92. The report included summaries of generic issues which occurred during the fiscal year. During FY-93, the Clearinghouse continued its policy of sending copies of its written responses (along with incoming requests) to all the Regional Offices. In this way, the Regional Offices are made aware, in a timely fashion, of decisions that may affect their modeling activities. Also, in order for the Regions to be assured that their records are complete, the Clearinghouse attaches to each response, an updated list of all Clearinghouse memoranda issued during the fiscal year. The complete list for FY-93 is provided as Appendix A. During FY-93, the Clearinghouse continued inputting records of Regional Office referrals to the Model Clearinghouse Information Storage and Retrieval System (MCHISRS). During FY-93, the Clearinghouse added approximately 118 entries to the approximately 1068 FY-81 to FY-92 referrals into MCHISRS. The Regional Offices can access by modem the MCHISRS in a search and retrieve mode for any national precedents that might affect their position on a current specific modeling issue. The Model Clearinghouse has a policy whereby an advance opinion of the Regions is sought on particularly sensitive issues with national implications. During FY-93, three such cases arose. One involved the interpretation of Table 9.1 of the Guideline on Air Quality Models (Revised) as it applies to secondary PM-10 precursors in the Denver area. Another advanced opinion issue involved the rounding of ozone model estimates in the Georgia SIP demonstration. The third involved the justified raising of a stack height because an obstruction was built which caused downwash of the existing stack. The resolution of each of these issues is documented under "Current Year Memos" on the Support Center for Regulatory Air Models Bulletin Board System (SCRAM BBS). The latter two issues are also summarized in Section 3 of this report. 2.4 Support Center for Regulatory Air Models Bulletin Board System (SCRAM BBS) During FY-91, EPA began disseminating Agency memoranda and reports generated by the Clearinghouse to the public through the SCRAM BBS. Three types of information are included: 1) selected historical memoranda on generic/recurring issues that have been generated by the Clearinghouse in the FY-81 through FY-93 time frame; 2) the most recent, i.e., FY-89 through FY-93 Clearinghouse memoranda; and 3) the FY-89 through FY-92 Model Clearinghouse annual reports. Information on the SCRAM BBS is not intended to be a complete set of information relative to any subject. Rather, it serves as a means to communicate to regulatory model users significant decisions involving the interpretation of current modeling guidance and experience with the use of nonguideline models, data bases and other deviations from the current guidance. The SCRAM BBS cautions users to consult the Guideline on Air Quality Models (Revised) and contact the appropriate State or Regional Office before using the information for individual/regulatory applications. As new Clearinghouse information becomes available, it is placed on the bulletin board in one of the three categories mentioned above. However, in regard to the current year Model Clearinghouse memoranda, a one to two month delay occurs before the information is placed on the bulletin board. 3.0 CLEARINGHOUSE RESPONSES TO RECURRING OR GENERIC ISSUES During FY-93, the Clearinghouse responded to a number of queries/referrals which had common themes or common consistency/technical issues. The more significant issues, and their resolution, are described below. 3.1 Ambient Credits for Emission Reductions Using Screening Techniques In November 1992, in response to a request from Region I, the Model Clearinghouse reviewed the Region's position with respect to the equivalency between applying the proposed ISCRDT model to the Boise Cascade paper mill in Maine and applying the Industrial Source Complex Short Term (ISCST) model and the Rough Terrain Dispersion Model (RTDM) in accordance with the Intermediate Terrain Policy (ITP). The Region's position was that equivalency between ISCRDT and the ITP has been demonstrated for application to Boise Cascade, but only for assessing the impacts of increment consuming sources and the impacts of sources that are in the existing baseline. For sources which are shutting down or reducing emissions, the Region believed that the ISCRDT model would need to be modified such that the lesser of the simple terrain and complex terrain concentration "credits" are chosen (on an hour-by-hour, source-by-source and receptor-by-receptor basis). The reason for that position was that the Region recognized that providing ambient credits with a screening technique would allow for too much credit, since the screening technique may be overpredicting the source's true impact. The Model Clearinghouse agreed with the Region's position in general, but suggested that there may be some room for flexibility with respect to concentration credits for sources reducing emissions. The source should not be given credit for increment expansion or for reductions in the total concentration by choosing the higher of the simple terrain or complex terrain modeled concentration credits. As the Region pointed out, doing so would result in a nonconservative credit, i.e., a larger credit than is really available if a refined model yielding unbiased estimates were applied. While the Clearinghouse agreed that the lower of the two credits would indeed be conservative but also offered an alternative scheme, one that would still be conservative but at the same time not penalize the source quite so much. The reasoning is as follows. RTDM is a screening model, designed to produce conservative estimates within its applicability domain. ISCST is a refined model, designed to yield unbiased estimates, but again within its applicability domain. The problem in intermediate terrain is that both models are being applied outside of their stated limitations. However, when applying ISCST in intermediate terrain, following the ITP, the terrain is "cut off" at stack height and the estimate is made at that elevation and applied at a higher elevation. Since it is postulated by the guidance that: (1) ISCST is unbiased at stack top, and (2) as one goes up in elevation above stack top, the true concentration would be expected to increase, it follows that the true concentration should be at least as high as the ISCST estimate. Following this rationale it is reasonable to believe that crediting the ISCST estimate as increment expansion or as a concentration offset would still be protective of air quality in intermediate terrain. The Clearinghouse suggested that if the source wants to go back and modify their program to reflect this concept and again demonstrate equivalency to the ITP, the Environmental Protection Agency should accept such an approach. The Clearinghouse further clarified however, that the above suggestion of allowing ambient credit for emissions reductions according to ISCST can only apply in intermediate terrain. For receptors above plume height, i.e., in true complex terrain, crediting the ISCST estimate could easily be nonconservative. Also, crediting RTDM or Complex I estimates at such receptors would also be nonconservative since such screening estimates would normally be higher in absolute magnitude than the true concentration. If the true concentration could be estimated from an unbiased refined model, it could be credited. Also, an estimate from a model that was designed to yield a minimum concentration (hour-by-hour) could also be credited as being conservative. The Clearinghouse suggested that the source may want to try and develop a technique for making minimum estimates in complex terrain, and demonstrate that such estimates would be lower than a refined model estimate, we would be willing to entertain such a proposal. However, the Clearinghouse recognized that such an undertaking is not a trivial problem. This particular issue of allowing for ambient credits for emission reduction using screening techniques was discussed further among all of the Regional Offices and the several States/local agencies that took part in the 1993 Modelers Workshop. The Workshop participants agreed that there is considerable technical difficulty in developing a general solution to this problem but also recognized that in many individual cases, an acceptable solution can be worked. Sources should be encouraged to consider innovative approaches on a case-by-case basis and submit them to their States/EPA for approval. 3.2 Credits for Stack Height Increases to Avoid Downwash Problems Created by Newly Constructed Nearby Structures In October 1992, the Clearinghouse was asked to deal with an issue involving the Dade County Resource Recovery Facility which had submitted a prevention of significant deterioration (PSD) application to add two new boilers and to modify the existing four boilers. The existing boilers (units 1-4) vent through two 150-foot stacks. Two new 250-foot stacks will be built with dual liners (one per liner). The current stacks must be removed in order to replace the existing control equipment with more stringent control devices. In addition to the modifications to units 1-4, two new boilers will be added which will vent through a third 250-foot dual liner stack. The building dimensions of the new boiler building will be 146 feet high by 141 feet long by 136 feet wide. All stacks are within the influence of this building. The existing boiler building for units 1-4 is 118 feet high and good engineering practice (GEP) for the existing stacks is 295 feet. The GEP for the new stacks will be 354 feet. Total SO2 emissions for the facility will be reduced by 117.4 tons per year after modifications and additions are made. In light of a June 29, 1992 memorandum from AQMD on credit for stack height increases due to the siting of new nearby structures, Region IV had taken the position that the facility can be given credit for the proposed increase up to 250 feet. Before deciding to concur with the Region IV position, the Clearinghouse discussed this matter via a conference call with representatives from Regions I-VI, VIII, and IX. The Office of General Counsel was unable to participate in the call but had been consulted beforehand. This was done because there had been some concern raised over the possibility that this change in position could be seen by some sources as an opportunity to erect frivolous structures upwind of their stacks in order to qualify for the exemption from fluid modeling demonstrations possible under the AQMD memorandum. While some Regions expressed concern over allowing credit for any stack height increases for sources with short stacks, whatever their justification, all of the Regions that took part in the discussions agreed that Region IV's interpretation of the AQMD memorandum is appropriate. There was a consensus that it is highly unlikely that sources will attempt to qualify for the exemption under the AQMD memorandum by building frivolous structures. No other objections were raised by any other parties on the call. The Clearinghouse also agreed that the Region IV interpretation is appropriate and thus concurred with the Region's position. However, protecting the national ambient air quality standards (NAAQS) and PSD increments is still of paramount importance. Therefore, the Clearinghouse recommended that the facility be modeled using the downwash option of any approved model at the proposed height (250 feet) so that the resulting emission limit is sufficient to ensure that the source will not cause or contribute to a violation of the NAAQS or PSD increments. If a violation is predicted by the model, either the emission limit must be lowered or the stacks increased, possibly all the way up to GEP height (354 feet) to eliminate the violation. Additionally, Region IV was reminded that the facility's emission limit may have to be revisited some time in the future if a Court-remanded merged gas stream issue is resolved. Finally, it is worth noting that the AQMD memorandum also allows both States and EPA to require fluid modeling to justify stack height increases in those situations where they feel it is warranted. 3.3 Rounding of Model Estimates in Ozone Attainment Demonstrations In October 1993, the Model Clearinghouse responded to a request from Region IV concerning the appropriate modeled air quality value to demonstrate attainment of the NAAQS for ozone in Atlanta. In this case, the State of Georgia wanted their SIP demonstration to be acceptable if the design concentration is reduced to 0.124 ppm, after controls are applied. Before responding to the issue, the Clearinghouse consulted with the staff of AQMD, surveyed Regional Office Modeling Contacts, reviewed related past AQMD decisions on other pollutants and reviewed pertinent portions of the 1990 Clean Air Act. The Clearinghouse recommendation provided below is consistent with the results of that review. The level specified in the ozone NAAQS is 0.12 ppm. The "Guideline for Regulatory Application of the Urban Airshed Model" ("UAM Guideline") is clear (p.63) that to demonstrate attainment, predicted ozone must be 0.12 ppm or less throughout the modeling domain. Thus, a prediction of 0.13 ppm is not sufficient, whereas a prediction of 0.12 ppm is so. The question is whether the value of 0.121 ppm or greater is acceptable in showing attainment in a SIP demonstration. More specifically, the Clearinghouse's review of prior work addressing this issue for ozone and other criteria pollutants included: 1. section 181(a) of the Clean Air Act, in which Congress defines a "marginal area" as one having an ozone design value of 0.121 - 0.138 ppm (Attachment 1); nonattainment areas having modeled values within this range are consistent with the Act's classification as a marginal nonattainment area. 2. past correspondence from AQMD concerning interpretations of control targets for carbon monoxide and lead; model estimates for comparison to the target value should not be rounded. 3. a survey of Regional Office Modeling Contacts in which the most common practice, with regard to rounding of model estimates, appears to interpret values like 0.121 ppm of ozone as not meeting the target concentration level. Based on the information gleaned, it appears in the majority of situations involving various criteria pollutants, for NAAQS demonstrations the numerical value of the standard is the "target" level to which model estimates should be reduced. For ozone this implies that for application of a model that estimates concentrations to three significant figures, the target level is actually 0.120 ppm. Based on this analysis, the Clearinghouse concluded that the State of Georgia's proposal to use 0.124 ppm as the target level would not be acceptable. Moreover, any value between 0.121 and 0.125 would also generally not meet the target for an acceptable attainment demonstration. However, if the State has previously developed a protocol that specifically contains a value greater than 0.120 ppm as the SIP demonstration target level, and the Environmental Protection Agency has approved that protocol, it may qualify for grandfathering. 3.4 Further Clarifications of Stack-Structure Relationships In 1987, a revision to the Industrial Source Complex Model made it possible to use wind direction dependent height and width for certain building wake effects calculations. Separate values of building height and width can be input to the model for each wind direction. For cases where a stack is separated from the building causing the wake effects, the 1987 model revision made it possible for the model to account for wake effects when the stack is upwind or downwind from the building and to ignore the effects when the stack is crosswind from the building. Guidance at that time indicated that wake effects should be considered when the stack is within 5L of the building, where L is the lesser of the height or width of the building. In conjunction with the modeling of a specific power plant, Region VII asked the Clearinghouse whether the 5L should really apply in the crosswind direction. In reply to the Region VII question, the Model Clearinghouse found that the 5L rule for the region of influence is appropriate for stacks in the downwind direction but that the region of influence should be considered to be 2L in the upwind direction. The Clearinghouse further recommended that wake effects calculations be applied when modeling the impact of emissions from a stack that is within 1/2 L of the side of the building in the crosswind direction, provided the stack is also within the 5L distance downwind, or 2L upwind, of the building. This is determined from the projection of the building and stack on a plane perpendicular to the direction of the wind, for example, as shown in Figure 1. Wind direction ---------------> ______________________________________ __ | ____ _ _ _ _ _ _ _ _ _ _ | __ 1/2 L | ___| |___ | | | | | | |Building| | | |_____ | | | |___| _ _ _ _ _ _ _ _ _ | __ |____________________________________| __ 1/2 L |<--2L->| |<--------5L------->| Figure 1 Plan View of Area of Influence of Building Wake Effects In 1989, in response to an inquiry from the private sector, the Clearinghouse recognized that the simplistic diagram in Figure 1 sometimes resulted in a requirement for downwash calculations when the stack, by definition, is considered to be at GEP stack height. This is because the corners of the rectangular area may be outside of the "rounded edge" area of influence provided in the GEP stack height definition. As a consequence, the Clearinghouse clarified that its 1988 reply to Region VII should not be interpreted for other cases to extend the area of influence beyond the GEP stack height definition. In FY-93, another private sector inquiry questioned whether following the above capsulized Clearinghouse memoranda of May 11, 1988 and June 28, 1989 still might leave some situations, for tall buildings, where a calculation for wake effects would be indicated for stacks that by definition would be at GEP stack height. In response to this inquiry, the Clearinghouse agreed that there could indeed by some situations where mechanically following the previous recommendations to Region VII could result in downwash calculations being made for GEP stacks. In a July 1, 1993 memorandum to Region VII, the Clearinghouse reiterated that it was never intended that stacks at GEP height should be modeled for downwash. The recently identified problem can occur only for tall building, i.e., a building whose height is greater than its projected width for at least some directions. The GEP stack height is a function of the projected building height and the projected building width, which varies by wind direction. The maximum GEP height is determined only from those circumstances when the wind crosses the building blowing to or from the stack. For circumstances when the wind does not cross the building, but the stack is close to the building, the projected building dimensions provided to the Industrial Source Complex model (ISC2) should be restricted to be no greater than that used in defining the maximum GEP height. Otherwise, ISC2 may calculate downwash from stack that meets GEP, as if it did not meet GEP criteria. APPENDIX A FY-93 MODEL CLEARINGHOUSE MEMORANDA FY-93 MODEL CLEARINGHOUSE MEMORANDA Date Region Subject 10/7/92 IV Response to Proposal to Allow Credit for a Stack Height Increase at the Dade County Resource Recovery Facility, Dade County, Florida 10/28/92 V Demonstrating Attainment of the Ozone National Ambient Air Quality Standards (NAAQS) with the Urban Airshed Model (UAM) for Detroit 10/28/92 VII Demonstrating Attainment of the Ozone National Ambient Air Quality Standards (NAAQS) with the Urban Airshed Model (UAM) for St. Louis 10/28/92 IV Attainment Demonstrations using the Empirical Kinetics Modeling Approach (EKMA) 11/5/92 I Proposal to Use ISCRDT to Model Intermediate Terrain (Boise Cascade, Rumford, Maine) 11/12/92 VIII Denver PM-10 State Implementation Plan (SIP) Modeling Issues 12/11/92 V Proposal for Resolving Part D Sulfur Dioxide State Implementation Plan Revision for Rhinelander, Wisconsin 12/15/92 IV The Ozone Attainment Test in the State Implementation Plan (SIP) Modeling Demonstrations 2/22/93 VIII Carbon Monoxide State Implementation Plan Attainment Demonstrations 2/23/93 II AES Guayama, Puerto Rico Proposal to Use the Rough Terrain Dispersion Model with Off-Site Meteorological Data FY-93 MODEL CLEARINGHOUSE MEMORANDA (Cont'd) Date Region Subject 3/2/93 VIII E. Helena Lead SIP Attainment Demonstration 4/6/93 V Nonmethane Organic Compounds (NMOC) and Nitrogen Oxides (NOx) Monitoring Required for the Empirical Kinetics Modeling Approach (EKMA) for Nonattainment Areas in Ohio 5/19/93 VI Technical Comparison Document-- Phelps Dodge Smelter 6/9/93 VII Wind Field Development for the Urban Airshed Model (UAM) 6/18/93 V Draft Protocol for Modeling a Sewage Sludge Incinerator 7/9/93 II Proposal for Calculating Plume Rise for Stacks with Horizontal Releases or Rain Caps for Cookson Pigment, Newark, New Jersey 7/1/93 VII Stack-Structure Relationships-- Further clarification of our memoranda dated May 11, 1988 and June 28, 1989 7/22/93 IV Draft Protocol for the Urban Airshed Model V (UAM-V) APPENDIX B MODEL CLEARINGHOUSE CONTACTS MODEL CLEARINGHOUSE CONTACTS 9/7/93 OAQPS CONTACTS Division Branch Name Number Responsibility TSD SRAB Dean Wilson 919-541-5683 Clearinghouse Coordinator SRAB Dean Wilson 919-541-5683 SO2, PM, Pb, NO2 Modeling SRAB Ellen Baldridge 919-541-5684 O3 Modeling SRAB Tom Braverman 919-541-5383 CO Modeling SRAB Tom Coulter 919-541-0832 Receptor Modeling SRAB Joe Touma 919-541-5381 Toxics Modeling AQMD SDPMPB Gary Blais 919-541-3223 SO2, PM-10, Pb SIPs OCPB Doug Grano 919-541-3292 O3, NO2 SIP's PPB Dan deRoeck 919-541-5593 PSD/NSR for all criteria pollutants OCPB Kimber Scavo 919-541-3354 CO SIP's REGIONAL MODELING CONTACTS Region Regional Contact Telephone No. I Brian Hennessey 617-565-3223 II Robert Kelly 212-264-2551 III Todd Ellsworth 215-597-2906 IV Brenda Johnson 404-347-2864 V Rebecca Calby 312-886-6065 VI Quang Nguyen 214-655-7238 VII Richard Daye 913-551-7619 VIII Kevin Golden 303-293-0955 IX Carol Bohnenkamp 415-744-1298 X Rob Wilson 206-553-1531 CO CONTACTS Region Regional Contact Telephone No. I Donald Cooke 617-565-3227 II Henry Feingersh 212-264-7669 III Larry Budney 215-597-0545 IV Yasmin Yorker 404-257-2864 V Rebecca Calby 312-886-6065 VI Quang Nguyen 214-655-7238 VII Royan Teter 913-551-7609 VIII Kevin Golden 303-293-0955 IX Carol Bohnenkamp 415-744-1298 X Bill Ryan 206-553-8561 OZONE MODELING CONTACTS Region Regional Contact Telephone No. I Ian Cohen 617-565-3229 II Robert Kelly 212-264-2551 III Todd Ellsworth 215-597-2906 IV Brenda Johnson 404-347-2864 V Rebecca Calby 312-886-6065 VI Quang Nguyen 214-655-7238 VII Royan Teter 913-551-7609 VIII Kevin Golden 303-293-0955 IX Carol Bohnenkamp 415-744-1298 X Rob Wilson/Dave Bray 206-553-1531 RECEPTOR MODEL CONTACTS Region Regional Contact Telephone No. I Brian Hennessey 617-565-3223 II Marlon Gonzales 212-264-2517 III Tom Casey 215-597-2906 IV Brenda Johnson 404-347-2864 V John Summerhays 312-886-6067 VI Quang Nguyen 214-655-7238 VII Richard Daye 913-551-7619 VIII Dale Wells 303-293-0957 IX Barbara Bates 415-744-1239 X Rob Wilson 206-553-1531 APPENDIX C SUMMARY OF THE EPA MODEL CLEARINGHOUSE EPA Model Clearinghouse Summary The Model Clearinghouse is the single EPA focal point for reviewing the use of modeling techniques in specific regulatory applications. The Clearinghouse also serves to compile and periodically report for Regional Office benefit Agency decisions concerning deviations from the requirements of the Guideline on Air Quality Models (Revised) (Guideline). Need for the Model Clearinghouse The Guideline states that when a recommended model or data base is not used, the Regional Administrator may approve the use of other techniques that are demonstrated to be more appropriate. However, there is also a need to provide for a mechanism that promotes fairness and consistency in modeling decisions among the various Regional Offices and the States. The Model Clearinghouse promotes this fairness and uniformity and also serves as a focal point for technical review of "nonguideline" techniques proposed for use/approval by a Regional Administrator. Functions of the Model Clearinghouse The major function of the Clearinghouse is to review specific proposed actions which involve interpretation of modeling guidance, deviations from strict interpretation of such guidance and the use of options in the guidance, e.g., Regional Office acceptance of nonguideline models and data bases. This is handled in two ways: (1) the Clearinghouse, on request from the Regional Office, will review the Region's position on proposed (specific case) use of a nonguideline model for technical soundness and national consistency, and (2) the Clearinghouse will screen Federal Register regulatory packages for adherence to modeling policy and make recommendations for resolution of any issues identified. A secondary function of the Model Clearinghouse is to communicate to regulatory model users in EPA significant decisions involving the interpretation of modeling guidance. This is accomplished through an annual "Clearinghouse Report" which itemizes the significant decisions that have been made and the circumstances involved. This report serves to improve consistency in future decisions and as a source of technical information for the Regional Offices. In addition to the annual report the Clearinghouse informs users on a contemporary basis of significant decisions through copies of written decisions and briefings at various meetings and workshops; the public has access to Agency memoranda and reports through an EPA electronic bulletin board system. Structure of the Clearinghouse The Clearinghouse is formally located in the Source Receptor Analysis Branch (SRAB) of the Office of Air Quality Planning and Standards. However, the Air Quality Management Division (AQMD) also participates in Clearinghouse matters involving State Implementation Plan attainment strategies and other regulatory functions. The primary responsibility for managing the Clearinghouse and ensuring that all of its functions are carried out is performed by a person full-time within SRAB. The responsibility for responding to requests for review of modeling issues is assigned, on a pollutant/program basis to four SRAB individuals. In addition, AQMD supports the Clearinghouse with staff who are also knowledgeable in modeling policy. These individuals are responsible for screening SIP submittals and related documents, referring modeling issues to SRAB through the Clearinghouse and documenting the final (and any significant interim) decision on disposition of the issues. Communication Chain The Model Clearinghouse functions within the organizational structure of EPA. As such the Clearinghouse serves the EPA Regional Offices. It coordinates with and communicates decisions to the Regional Offices. Any coordination with State and local agencies and individual sources on Clearinghouse activities is a function of the EPA Regional Offices.