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Support Center for Regulatory Atmospheric Modeling (SCRAM)

Air Quality Model Clearinghouse

The Model Clearinghouse is a focal point for interpretation of modeling guidance in specific regulatory applications. The Model Clearinghouse is the mechanism by which an EPA Regional Office can obtain EPA Headquarters concurrence on resolving implementation issues and non-regulatory applications related to regulatory air quality modeling. Archival of Model Clearinghouse decisions are located in the Model Clearinghouse Information Storage and Retrieval System (MCHISRS). In addition to MCHISRS, EPA issues formal "Clarification Memos" for general issues related to permit modeling under Appendix W, as appropriate.

The statutory authority of the Model Clearinghouse is provided within 40 CFR, Part 51, Appendix W (PDF)(54 pp, 761 K, 01-17-2017), Section 3.3(b). This section states that "The Regional Office should always be consulted for information and guidance concerning modeling methods and interpretations of modeling guidance, and to ensure that the air quality model user has available the latest most up-to-date policy and procedures. As appropriate, the Regional Office may request assistance from the Model Clearinghouse after an initial evaluation and decision has been reached concerning the application of a model, analytical technique or data base in a particular regulatory action."

Public access to policy-related memoranda are available from the "Title V, NSR/PSD Policy and Guidance Database", courtesy of EPA Region 7. This policy-oriented database provides an excellent compliment to the technical-oriented information within MCHISRS.

Model Clearinghouse Operational Plan

The 2016 Model Clearinghouse Operational Plan (PDF)(56 pp, 1 MB, 12-19-2016, 454-B-16-008) outlines the Model Clearinghouse process by defining the roles and responsibilities of all parties, providing thorough descriptions and flow diagrams, referencing the current databases that store all formal Model Clearinghouse decisions, making available templates for request memoranda and other pertinent information, and providing “best practice” examples of request memoranda that highlight how to best inform the Model Clearinghouse process.

Model Clearinghouse Process

The need for a Model Clearinghouse action begins when there is an unresolved regulatory modeling issue that arises at a State or local office in a particular permitting action that is then forwarded to the Regional Office (RO) for resolution. After the State/local agency contacts the RO, the Model Clearinghouse (MCH) process is initiated to resolve the issue and involves the following steps:

1. The RO makes a determination that the issue is a precedent-setting decision or may have national implications.

2. The RO submits a formal request memorandum (on RO letterhead) detailing issue and proposed solution for concurrence to the MCH Director (via email), along with supporting technical and related documentation.

3. The MCH facilitates review across the RO and EPA Headquarters to determine appropriateness of proposed solution.

4. After review, the MCH generates a formal response memorandum of findings (on EPA letterhead) and submits to the RO.

5. The MCH Director sends formal MCH response memo via email to all ROs and archives in MCHISRS for public access and reference.

Questions about the Model Clearinghouse should be provided to George Bridgers, the MCH Director.

Model Clearinghouse Memorandum Requirements

The following elements are required as part of a MCH request from the ROs:
1. Background and explanation of issue
2. Technical proposal of solution
3. Defensibility of solution, including Appendix W or technical evaluation references
4. Language which isolates this solution to this particular application

Example Regional Office Request Memo (PDF)(3 pp, 180 K, 11-05-1992).

The formal MC memorandum from EPA Headquarters will contain the following elements:
1. Brief acknowledgement of receipt of Model Clearinghouse request
2. Background and explanation of issue
3. Overview of proposed solution
4. MC concurrence of proposal solution, with technically defensible rationale
5. Language indicating that this solution is for the specific application; similar applications must be approved on a case-by-case basis

Example MCH Response Memo (PDF)(3 pp, 165 K, 11-13-1992).