Model Clearinghouse Information Storage and Retrieval System
On Use of Equivalent Building Dimensions in AERMOD - Alcoa
Record No: 11-VII-01 Last Update: 11/10/2011
|EPA Region:||7||Fiscal Year:||2011|
|Oral/Written:||Written||Involvement:||Review and Comment|
Issue: Region VII requests review and concurrence from the Model Clearinghouse regarding the use of fluid modeling studies to develop "equivalent building dimension" (EBD) parameters to replace building parameters generated by BPIPPRM for use in the AERMOD air dispersion model specific to the Alcoa Davenport Works facility. Given the range of technical changes in the AERMOD model generally, and specifically the PRIME downwash algorithm in AERMOD, as compared to the ISC model, we also believe that more studies and additional guidance are needed before the EBD approach for determining building parameters can be accepted for use in AERMOD analyses. C/H Response: We agree with the Region VII position to not approve the use of EBD parameters in the particular case presented for the Alcoa Davenport Works facility due to the technical issues and concerns conveyed in the request memorandum, most notably the inclusion of additional surface roughness elements to account for the surface roughness of the actual facility for the tests conducted to demonstrate the equivalency of the EBDs. Further, we also agree that additional technical challenges with the EBD approach for determining alternative building parameters have been introduced with the promulgation of the AERMOD model, with PRIME downwash algorithms, replacing ISCST3 as the preferred near-field dispersion model under the EPA’s “Guideline on Air Quality Models,” published as Appendix W to 40 CFR Part 51. We feel that it is imperative to reassess the past guidance and practices more broadly to ensure that future studies provide a viable basis for determining equivalent building parameters that are appropriate for use with the AERMOD model. Therefore through this Model Clearinghouse response, all past EPA guidance related to determining EBDs through wind tunnel modeling (Ref: Record 94-IV-09) is hereby suspended until further notice. Please note that this should not be taken to imply that all such studies will be summarily rejected until the process of reassessing the guidance has been completed, but rather to indicate that any EBD studies being considered should be discussed with the appropriate reviewing authority as early in the process as possible and that the Model Clearinghouse should also be engaged as early as possible.
memo: Review Results of Equivalent Building Dimensions for AERMOD Dated: 10/24/2011 From: George Bridgers, Model Clearinghouse Director Air Quality Modeling Group, EPA To: Michael Jay, Chief Atmospheric Programs Section, Region 7 EPA Richard L. Daye, Regional Meteorologist Atmospheric Programs Section, Region 7 EPA Attachment A: Alcoa Wind Study Report Dated: 1/09 From: CPP Inc., Wind Engineering and Air Quality Consultants Ft. Collins, CO 80524 To: Alcoa Davenport Works, Bettendorf, IA Attachment B: Assessment_of_Alcoa_Davenport_Works_EBD_Study Letter: Request to Review of Use of Equivalent Building Dimensions in AERMOD Dated: 6/23/11 From: Michael Jay, Chief Atmospheric Programs Section, Region 7 EPA To: George Bridgers, Model Clearinghouse Director Air Quality Modeling Group, EPA