For the last decade, EPA has been revising, updating, fixing bugs, and introducing beta options in the AERMOD Model with the goal of offering a dispersion modeling tool that is dependable, accurate, and reflective of the best current science. Dispersion models provide a tool used for a key part of both the permitting process as well as air management for nonattainment areas and thus, their use is important and it is imperative that their output provide a representative picture of atmospheric concentrations associated with industrial and urban-wide sources of emissions. From 2006-2016 this process has resulted in 117 bug fixes, 56 enhancements, and 65 miscellaneous changes included in a total of 12 updated versions of AERMOD. Frequent revisions to the model makes the permitting and state implementation plan process difficult as updated and new versions often provide different ambient concentration estimates with little model performance evaluation updates provided by EPA to assist local, state, regional, and national modelers in determining how to interpret results for decision-makers.

The EPA Office of Inspector General (OIG) performed an audit of the EPA Office of Air Quality Planning and Standards (OAQPS) Air Quality Modeling Group (AQMG) procedures for reviewing the development and evaluation of new and revised models. The conclusion of the report after reviewing the Guideline on Air Quality Models, Clearinghouse memoranda, user's guides, model formulation and evaluation studies and other EPA reports was that guidance was available for new models but not available nor followed for model revisions. The focus in the OIG report was on AERMOD. Other models current and future, though not reviewed, are assumed to fall under the same criteria evaluated in the report. OIG made four recommendations as corrective actions to bring EPA guidance for updating models into compliance with government specifications. These include:

  • Developing Standard Operating Procedures (SOP) to guide and document the process for reviewing and approving revisions to EPA recommended models.
  • Developing Quality Assurance Program Plans (QAPP) to describe the results of systematic planning, updating, and evaluation of model revisions.
  • Updating the OAQPS Quality Management Plan to include the SOP and QAPP documents.
  • Training staff in OAQPS in using and following the SOPs and QAPPs.

So what does this mean to industrial sources and to Trinity modelers? Basically it means that more thoughtful programming elements in these SOP and QAPP documents will improve EPA's research, use, and release of revisions to the work-horse of permitting, i.e., the AERMOD Model. Part of that process has already been established and is being used now in the current version of AERMOD, Version 18081. Instead of new options being introduced in a beta format, a two layer alpha (for research) and beta (for testing in a regulatory setting) system of proposed enhancements and changes has been introduced. Also as EPA follows the new QAPP, changes may come a bit more slowly allowing the permitting process to proceed with the knowledge that a proposed model in a modeling protocol or air permit application will still be acceptable when the modeling is complete rather than model versions changing as frequently in the middle of projects.

The AQMG has responded positively to all of OIG recommendations and the status of EPA responses is summarized on page 15 of the OIG report. The OIG has accepted the current and planned corrective actions from EPA which are summarized in a letter from the Assistant Administrator of EPA, William Wehrum and included as Appendix A in the OIG report.