MODEL CLEARINGHOUSE: FY-91 SUMMARY REPORT OCTOBER 1991 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-91 SUMMARY REPORT PAGE 1.0 INTRODUCTION 2.0 FY-91 CLEARINGHOUSE ACTIVITIES . . . . . . . . . . . 2 2.1 Background and Responsibilities . . . . . . . . 2 2.2 Summary of Regional Office Requests and Clearinghouse Responses . . . . . . . . . . . . . . . . . . . 4 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 12 3.1 Use of Multiple Meteorological Data Sets . . . 12 3.2 Exceptions to Modeling Guidance for PM-10 State Implementation Plans (SIP's) . . . . . . . . . 14 Appendix A FY-91 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 18, 1990, to August 23, 1991. The report is divided into two parts. First, the FY-91 activities of the Clearinghouse are summarized. The second section summarizes Clearinghouse responses to major categorical modeling problems occurring during FY-91; 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, 1990 to September 30, 1991. 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-91 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 the past year or two the Model Clearinghouse has informally been accepting some referrals on the modeling of toxic air pollutants (see e.g., the seven noncriteria pollutant cases listed in Table 2 of this report). At the close of the fiscal year the Clearinghouse was nearing completion of a procedure for formalizing this expansion of its function. Implementation is planned for FY-92. 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-91 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-90. 6. Inputting FY-91 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-91 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 14 regulatory modeling problems referred to the Clearinghouse which required a written response and another 93 referrals in which the issues were resolved orally. In addition, there were another 19 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-91 RECOMMENDATIONS REGION WRITTEN ORAL DISCUSSION/INFORMATION* TOTAL I 0 7 1 8 II 2 10 2 14 III 1 10 1 12 IV 2 14 3 19 V 3 15 2 20 VI 0 3 3 6 VII 0 5 0 5 VIII 6 15 7 28 IX 0 11 0 11 X 0 3 0 3 (TOTALS) 14 93 19 126 ------------------- *Did not include a specific Clearinghouse recommendation. TABLE 2. CHARACTERIZATION OF 126 CLEARINGHOUSE REFERRALS DURING FY-91. 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 56 TSP 1 CO 12 Pb 9 NOx 4 O3 4 PM-10 30 Unspecified 6 Unspecified Non-criteria 7 Generic 2 Not Relevant 1 Source Types Power Plant 14 Power Boiler 5 Smelter 12 Steel Facility 7 Paper Mill 7 Refinery 7 Cogeneration Unit 10 Incineration 6 Mine 5 Roadway 10 Aircraft 1 Lumber/Wood Products Plant 1 Open Dust Fugitive 1 Unspecified Stationary Source 11 Mixed/Multiple Sources 22 Generic to Any Stationary Source 4 Generic to Any Source 4 Urban or Rural Model Involved Urban Only 32 Rural Only 73 Both Urban and Rural 7 Not Relevant 14 Types of Response Written 14 Oral 93 Not Relevant 19 Applicable Regulations Number of Referrals SIP 31 SIP Revision 22 SIP Revision - GEP 9 PSD 32 EIS 4 NSR 1 Bubble 1 Redesignation 5 State Regulation 7 Study 1 Compliance Order 1 FIP 2 RCRA 1 Generic 3 Generic - SIP 1 Generic - Any Regulation 4 Not Relevant 3 Terrain Setting High Terrain (above stack height) 8 Low Terrain (below stack height) 50 Both High and Low Terrain 41 Essentially Flat Terrain 11 Not Relevant 16 Guideline or Nonguideline Model Involved Guideline 62 Non-guideline 27 Guideline and Non-guideline 22 Not Relevant 15 Data Bases Used for Model Input On-Site 39 Off-Site 43 Both Off-site and On-site 11 Not Relevant 33 TABLE 3. SUBJECT AREAS INVOLVED IN FY-91 CLEARINGHOUSE REFERRALS Subject Area Number of Occurrences Adjustment of Model Estimates 4 Ambient Air 3 Ambient Monitoring 12 Area Wide Analysis 7 Calm Winds 3 Clearinghouse Operating Procedures 5 Data Processing 1 Deposition 2 Downwash 15 Emissions Characterization 8 Emission Rates for Model Input 7 Equivalency 2 Fluid Modeling 5 Grandfathering of Guidance 6 Interpretation of Modeling Guidance 19 Interpretation of Regulatory Guidance 20 Length of Record - Meteorological Data 2 Load Level 1 Long-Range Transport 4 Meteorological Monitoring 15 Mixed Terrain Modeling 13 Modeled Background 5 Monitored Background 2 Monitoring in Lieu of Modeling 13 Open Dust Fugitives 4 Performance Evaluations 7 Plume Rise 4 PSD Increment Calculation 10 Reactive Pollutant Modeling/Chemical Transformations 4 Receptor Modeling 16 Receptor Networks 6 Replicability 1 Representativeness of Meteorological Data 17 Screening Procedures 4 Significant Air Quality Impacts 4 Stability Classes 2 Stack Tip Downwash 1 Supplementary Control Systems 1 Technical Credibility of Nonguideline Techniques 9 Time Scaling 3 Urban/Rural 5 Wind Speed Profiles 3 Stagnation 5 2.3 Recurring Coordination During FY-91 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 1990, a Clearinghouse report; this report served to inform Clearinghouse users about the issues and responses which occurred in FY-90. The report included summaries of generic issues which occurred during the fiscal year. During FY-91 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 list is provided as Appendix A. During FY-91, the Clearinghouse continued inputting records of Regional Office referrals to the Model Clearinghouse Information Storage and Retrieval System (MCHISRS). During FY-91 the Clearinghouse added approximately 125 entries to the approximately 800 FY-81 to FY-90 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-91 one such case arose involving multiple source increment modeling in a Class I area in Virginia. In this case an advance draft response agreeing with the Region III position on the issue was circulated to all the Regional Offices for comment. After a series of discussions with Regional Offices having concerns, the response was revised and finalized; the August 20, 1991 response is contained in the "Current Year" memoranda on the Support Center for Regulatory Air Modeling Bulletin Board System (SCRAM BBS). 2.4 Support Center for Regulatory Air Models Bulletin Board System (SCRAM BBS) During FY-90 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 to FY-91 timeframe; 2) the most recent, i.e. FY-89, FY-90, and FY-91 Clearinghouse memoranda; and 3) the FY-89 and FY-90 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 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-91 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 Use of Multiple Meteorological Data Sets When an emission limit needs to be tested for a source, whether for the PSD or SIP program, the established modeling procedure is to model that source using its own on-site meteorological data or data from an off-site location which is deemed to be representative of transport and dispersion of the source's emissions. If background sources need to be modeled as well, pursuant to guidance provided in Sections 9.1 and 9.2 of the Guideline on Air Quality Models, or if off-site source contributions to increment consumption need to be calculated, these sources are also modeled with the same on-site/representative meteorological data. The rationale behind this procedure is that it is more important to properly characterize the transport and dispersion of the plume from the source whose emission limit is in question than the transport and dispersion from off-site sources. In recent years, and especially so in FY-91, there have been a number of cases where, for one reason or another, strict conformity to this procedure did not lead to a reasonable conclusion. This issue, for the case where there is a need to model multiple increment consuming sources, was debated at the FY-91 Region/State Modelers Workshop. The question posed to the modelers was "Should we allow the use of multiple, concurrent meteorological data sets for refined modeling, particularly Class I increment analyses?" It was correctly pointed out that there is a mismatch between "straight-line" Gaussian models recommended in the Guideline and multiple sets of meteorological data, i.e. using more than one set of data within the same modeling domain is really outside the stated limitations of the modeling technique. It was also recognized that over any sizable modeling domain, even in flat terrain, there will be both spatial and temporal variations in the meteorological parameters. Thus, if there are sources scattered throughout that domain, there will be spatial and temporal variations in source-receptor relationships. The modelers noted that one answer to the problem would be to justify/support the use, on a case-by-case basis, of a nonguideline model that handles spatial variations in the meteorological fields (primarily the wind field). This in fact may be the only technically satisfactory procedure and may be the only answer in complicated situations. However, recognizing that there is currently no obvious choice for such a model and that one might have to expend considerable resources in choosing/justifying the model, it was agreed that for some straightforward situations with only a couple of sources involved, EPA could entertain proposals to use two different sets of concurrent meteorological data with straight line Gaussian models. Thus, there is no change in the procedure of using the meteorological data that is on-site/representative of the source whose emission limit is being tested, but the Clearinghouse will entertain exceptions to that procedure in very limited circumstances and where there is clear need to do so. 3.2 Exceptions to Modeling Guidance for PM-10 State Implementation Plans (SIP's) Modeling analyses for PM-10 SIP's have, over the years, been found to be very difficult to satisfactorily complete. There are a number of reasons for the difficulties, ranging from the lack of applicable models or data bases, to the lack of State resources/time to complete an analysis that conforms with guidance. Because of these problems the Model Clearinghouse, in July 1990, agreed to accept, in certain limited cases, the use of receptor modeling alone as an adequate SIP demonstration. The circumstances and limitations of such demonstrations are specified in a July 5, 1990 memorandum, posted on the SCRAM BBS, and summarized in the "Model Clearinghouse: FY-90 Summary Report." While these criteria were helpful in resolving issues in some simple cases, they were not useful in the more complicated situations where receptor modeling was the optimum technique for establishing source-receptor relationships. The situation became more difficult in FY-91 because the Clean Air Act Amendments of November 1990 established that PM-10 SIP's for designated nonattainment areas would be due on November 15, 1991. To accommodate this due date for SIP submittals, and recognizing that this time frame may be incompatible in some instances with the States' ability to develop SIP demonstrations in accordance with guidance, EPA Management, in March 1991, developed a temporary policy for the acceptance of "modified" SIP demonstrations. This policy states that, generally, all SIP submittals for the initial moderate PM-10 nonattainment areas should follow the existing guidance on PM-10 modeling. In the situation where an area has completed or can complete its demonstration by November 15, 1991 consistent with existing guidance, an attainment demonstration based on the existing guidance should be submitted. However, in those situations where time constraints, inadequate resources, inadequate data bases, lack of a model for some unique situations, and other unavoidable circumstances would leave an area unable to submit an attainment demonstration within the short time frame provided by the Clean Air Act, then a modified demonstration conforming to the prerequisites listed below may be submitted. The policy further notes that Section 189(a)(1)(B) of the Clean Air Act Amendments of 1990 requires that any such modified demonstration be based on some form of "air quality modeling." In addition, 40CFR Part 51.112 requires that a demonstration be shown to be "adequate and appropriate." Accordingly, the policy states that all such modified demonstrations should be accompanied by the following: 1. Documentation of Modified Modeling Method. Documentation of the procedures or analyses used in lieu of those set forth in the previously issued guidance. 2. Rationale for Modified Demonstration. An explanation of why the alternative modeling techniques set forth in the guidance were not used. 3. Justification of Modified Demonstration. A description of how and why the SIP provides an adequate and appropriate demonstration of area-wide attainment. If the design value contained in the demonstration is based on monitoring data, the justification should also: a. Show that the SIP is based on at least one full year of data from an approved network that meets EPA's quality assurance requirement. Also, the justification should contain a review of the monitoring data (e.g., data completeness, prescribed sampling frequency) in accordance with EPA's SIP development guidance. The justification should also include a review of the network's ability to identify the point of maximum concentration and the impact of most significant sources. b. Based on the network and data review in (a) above, the SIP should include appropriate provisions to conduct follow-up monitoring (e.g., daily monitoring, saturation monitoring, expansion or modification of the monitoring network and meteorological data collection) to address those issues raised during the review. The purpose of the follow-up monitoring is to ensure that the monitoring network in place as of January 1, 1994 will be appropriate to evaluate attainment. The modified demonstrations conforming to the above may be considered on a case-by-case basis. The policy is only to apply to those initial moderate PM-10 nonattainment areas which have completed the technical analysis for their SIP submittal and have made a good-faith effort to submit a final SIP by the November 15, 1991 due date. Technical analyses that are being developed on a schedule which goes beyond November 15, 1991 will be expected to follow all previously established guidance for modeling and demonstrations. The SIP's for all other PM-10 nonattainment areas will be reviewed in accordance with the previously issued attainment demonstration guidance. During FY-92 it is expected that the Model Clearinghouse will be reviewing PM-10 SIP's submitted pursuant to this policy. As long as the above listed conditions are met it is expected that the SIP demonstrations will be accepted. APPENDIX A FY-91 MODEL CLEARINGHOUSE MEMORANDA Date Region Subject 1/7/91 V Pit Retention from Stone Quarries 1/8/91 IV Meteorological Data for the Ashland Petroleum Company GEP Modeling Analysis 1/31/91 IV Georgia Power Plant Yates GEP Modeling 2/8/91 VIII Revised ASARCO, East Helena Modeling Protocol 3/4/91 V Particulate Matter from Surface Coal Mining 3/5/91 II New Jersey DEP Comments on Valley Model 3/15/91 II Use of CTDMPLUS in the Virgin Islands Water and Power Authority PSD Application 4/15/91 VIII Revised ASARCO, East Helena Modeling Protocol 4/26/91 V Use of Nonguideline Versions of Urban Airshed Model 5/8/91 I-X PM-10 State Implementation Plan Attainment Demonstration Policy for Initial Moderate Nonattainment Areas 5/24/91 VIII Review of Chemical Mass Balance (CMB) Analysis for the Communities of Polson and Ronan, Montana 6/24/91 IV On-Site Meteorological Data Collected at Ashland Oil Refinery in Catlettsburg, Kentucky 7/2/91 VIII Review of East Helena Pb Source Apportionment Study 8/20/91 III Hadson Power - Buena Vista PSD Permit Class I Increment Issue 9/17/91 IX AES Ohana, Inc. PSD Permit Application APPENDIX B MODEL CLEARINGHOUSE CONTACTS AND PERSONNEL 7/2/91 OAQPS CONTACTS Division Branch Name FTS Number Responsibility TSD SRAB Dean Wilson 629-5683 Clearinghouse Coordinator SRAB Dean Wilson 629-5683 SO2, PM, Pb, NO2 Modeling SRAB Rich Scheffe 629-4650 O3 Modeling SRAB Tom Braverman 629-5383 CO Modeling SRAB Tom Coulter 629-0832 Receptor Modeling AQMD SDPMPB Gary Blais 629-3223 SO2, PM-10, Pb SIPs OCPB Doug Grano 629-3292 CO, O3, NO2 SIPs PPB Dan deRoeck 629-5593 PSD/NSR for all criteria pollutants REGIONAL MODELING CONTACTS Region Regional Contact FTS Telephone No. I Ian Cohen 835-3229 II Robert Kelly 264-2551 III Al Cimorelli 597-6563 IV Lew Nagler 257-1033 V Rebecca Calby 886-6065 VI Jim Yarbrough 255-7214 VII Richard Daye 276-7619 VIII Larry Svoboda (Acting) 776-5102 IX Carol Bohnenkamp (Acting) 484-1238 X Rob Wilson 399-1531 CO CONTACTS Region Regional Contact FTS Telephone No. I Tom Wholley 835-3233 II Annamaria Colecchia 264-4939 III Larry Budney 597-0545 IV Tom Hansen 257-2864 V Rebecca Calby 886-6065 VI Jim Yarbrough 255-7214 VII Royan Teter 276-7609 VIII Larry Svoboda (Acting) 776-5102 IX Carol Bohnenkamp (Acting) 484-1238 X Rob Wilson 399-1531 OZONE MODELING CONTACTS Region Regional Contact FTS Telephone No. I Ian Cohen 835-3229 II Robert Kelly 264-2551 III Todd Ellsworth 597-9325 IV Brenda Johnson 257-2864 V Rebecca Calby 886-6065 VI Jim Yarbrough 255-7214 VII Royan Teter 276-7609 VIII Larry Svoboda (Acting) 776-5102 IX Carol Bohnenkamp (Acting) 484-1238 X Rob Wilson/Dave Bray 399-1531 RECEPTOR MODEL CONTACTS Region Regional Contact FTS Telephone No. I Brian Hennessey 835-3223 II Marlon Gonzales 264-2517 III Tom Casey 597-2906 IV Lew Nagler 257-1033 V John Summerhays 886-6067 VI Quang Nguyen 255-7214 VII Richard Daye 276-7619 VIII Dale Wells 330-1773 IX Barbara Bates 484-1239 X George Lauderdale 399-6511 APPENDIX C SUMMARY OF THE EPA MODEL CLEARINGHOUSE The Model Clearinghouse is the single EPA focal point for reviewing the use of modeling techniques for criteria pollutants 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.