Reassessment of the Interagency Workgroup on Air Quality Modeling (IWAQM) Phase 2 Summary Report: Revisions to Phase 2 Recommendations

ii NOTICE The information in this document is in DRAFT form and is still under review by the U.S. Environmental Protection Agency (EPA) and the Federal Land Managers (FLMs). The draft revisions to the IWAQM Phase 2 recommendations presented herein are still undergoing internal testing to assess their viability for meeting the technical objectives of this reassessment. Some sections are still under development and will be incorporated in future updates to the DRAFT document. This DRAFT document is being made available at this time to provide additional technical information in support of the May 15, 2009 Model Clearinghouse recommendations to U.S. EPA Region 8 regarding the Otter Tail BART modeling protocol, to inform the modeling community of our concerns regarding the CALPUFF modeling system for long range transport (LRT) applications, and to notify the community of our plans for addressing these concerns. Mention of trade names, products, or services does not convey, and should not be interpreted as conveying official EPA approval, endorsement, or recommendation. iii PREFACE The Interagency Workgroup on Air Quality Modeling (IWAQM) was formed to provide a focus for development of technically sound recommendations regarding assessment of air pollutant source impacts on Federal Class I and Wilderness areas. Meetings were held with personnel from interested Federal agencies, viz. Service. The purpose of these meetings was to review respective modeling programs, to develop an organizational framework, and to formulate reasonable objectives and plans that could be presented to management for support and commitment. The members prepared a memorandum of understanding (MOU) that incorporated the goals and objectives of the workgroup and obtained signatures of management officials in each participating agency. The IWAQM recommended the use of the CALPUFF modeling system for use in Class I increment and air quality related values (AQRV) analyses required under the Prevention of Significant Deterioration of Air Quality (PSD) major source permitting program. In the ten years since the publication of the original IWAQM Phase 2 recommendations, the CALPUFF modeling system has continually evolved. Experience within the modeling community has also expanded with numerous applications of CALPUFF for PSD and Regional Haze Best Available Retrofit Technology (BART). However, the IWAQM guidance did not evolve to reflect the changes in modeling technology and experience gained since the original publication in 1998. In 2005, the EPA convened a federal workgroup to discuss ongoing issues with the development and management of the CALPUFF modeling system recommended …