Status and Role of

EPA’s Model Clearinghouse

11th Conference on Air Quality Modeling

RTP, NC

George M. Bridgers

OAQPS-AQAD-Air Quality Modeling Group

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Regulatory Requirements

• Authority to modify a specified model in Appendix W or use a 

substitution must be granted through writing from the Administrator.

– 40 CFR Part 51 – Section 51.166:

(l) Air quality models. The plan shall provide for procedures which 

specify that—

• (1) All applications of air quality modeling involved in this subpart shall be 

based on the applicable models, data bases, and other requirements 

specified in appendix W of this part (Guideline on Air Quality Models).

• (2) Where an air quality model specified in appendix W of this part 

(Guideline on Air Quality Models) is inappropriate, the model may be 

modified or another model substituted. Such a modification or substitution 

of a model may be made on a case-by-case basis or, where appropriate, on 

a generic basis for a specific State program. Written approval of the 

Administrator must be obtained for any modification or substitution. In 

addition, use of a modified or substituted model must be subject to notice 

and opportunity for public comment under procedures set forth in §

51.102. 08/12/2015 U.S. Environmental Protection Agency 2
Regulatory Requirements (Cont.)

• The regulatory authority for the approval of alternative model and 

techniques is delegated to the Regional Administrators through 

Section 3 of Appendix W.

– Delegated authority is further clarified in the proposed revisions to the 

Guideline.

• However, Regional Offices still must seek concurrence from EPA 

Headquarters on any action that could be inconsistently applied 

across the other Regions (ensuring national consistency).

– 40 CFR Part 56 – Section 56.5:

(b) A responsible official in a Regional Office shall seek concurrence from the 

appropriate EPA Headquarters office on any interpretation of the Act, or rule, 

regulation, or program directive when such interpretation may result in 

inconsistent application among the Regional Offices of the act or rule, 

regulation, or program directive.

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Proposed Revisions to the Guideline

• Importance of consistency is stressed several places 

in the Guideline on Air Quality Models (the Guideline

or Appendix W), including the very first sentence:

– “Industry and control agencies have long expressed a need 

for consistency in the application of air quality models for 

regulatory purposes.”

• In 1988, the Model Clearinghouse Operational Plan 

was developed and shared with the Regional Offices.

– Consistent with the regulations and the proposed revisions to 

the Guideline.

– http://www.epa.gov/ttn/scram/11thmodconf/1988MCHOperationalPlan.pdf

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Proposed Revisions to the Guideline (Cont.)

• The 1993 revision of the Guideline to add Supplement 

B included the first regulatory references to the Model 

Clearinghouse.

– Section 3.3.1 of the 1993 Guideline referenced to the 

Operation Plan.

– Included the first of three primary functions as, “Review of 

decisions proposed by EPA Regional Offices on the use of 

modeling techniques and data bases.”

• Subsequent revisions of the Guideline expanded the 

discussion of the Model Clearinghouse but also lost 

some of the clarity of the formal process that was 

being consistently followed within the EPA.

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Proposed Revisions to the Guideline (Cont.)

• EPA’s OAQPS-AQAD-AQMG and Model 

Clearinghouse are responsible for the development 

and proposal of all preferred models or techniques 

per Appendix W, Section 3.1.

• To ensure national consistency and to respect the 

responsibilities mentioned above, it is appropriate that 

concurrence with the Model Clearinghouse is sought 

on the approval of any alternative model or technique 

per Appendix W, Section 3.2.

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Proposed Revisions to the Guideline (Cont.)

• In the proposed revisions to the Guideline, the EPA 

proposes to codify the long-standing process of the 

Regional Offices consulting and coordinating with the 

Model Clearinghouse on all approvals of alternative 

models and techniques.

– Referencing the 1988 Model Clearinghouse Operational Plan.

– Referencing 40 CFR 51.166(l)(2) with an understanding of 40 CFR 

56.5(b).

– Providing as much transparency to the internal process between the 

Regional Offices and the Model Clearinghouse that has existed for 

over 25 years.

– Allowing broad communication across stakeholder community so 

case-specific decisions are well-understood and applicable 

elsewhere.

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Formal Model Clearinghouse Process

• State contacts Region Office with a regulatory modeling 

situation that requires EPA review and/or approval.

• Regional Office determines if it is an alternative 

modeling situation per Appendix W, Section 3.2.

• Regional Office writes request memorandum to the 

Modeling Clearinghouse:

– Statement of issue.

– Desired approach by the state/local/tribe or applicant.

– Justification per the requirements of Section 3.2.2.

• Clearinghouse is engaged and consulted on solutions 

and writes formal concurrence response memorandum.

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Formal Model Clearinghouse Process (Cont.)

• Clearinghouse summarizes and archives decisions:

– Searchable database (MCHISRS) via web access (SCRAM).

http://cfpub.epa.gov/oarweb/MCHISRS/

– Presents summary at annual Regional/State/Local Workshop 

and Modeling Conferences.

• OAQPS develops guidance or proposes updates to the 

Guideline on Air Quality Models, as appropriate:

– Policy memo, EPA report or guidance document, rulemaking.

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EPA’s Model Clearinghouse

• http://www.epa.gov/ttn/scram/guidance_clearinghouse.htm

• Director of Model Clearinghouse:

– George Bridgers

– OAQPS/AQAD/AQMG

– bridgers.george@epa.gov

– (919) 541-5563

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