Model Clearinghouse Information Storage and Retrieval System
Record Details

Issue:  EPA Region III is seeking concurrence with the Model 
Clearinghouse on the use of the BETA Adjust U* option that was a 
part of a modeling analysis recently received from the Maryland
Department of the Environment (MDE) for the Herbert A. Wagner 
Generating Station located near the City of Baltimore. MDE sought 
permission to use the BETA Adjust U* option in a formal request 
sent to the Regional Administrator under 40 CFR Part 51, specifically
Section 3.2.2 of Appendix W - Guideline on Air Quality Models. The 
formal request letter from MDE dated April 14, 2016 and its attachment
are included as part of this concurrence request package.

C/H Response:  
The Model Clearinghouse concurs that a reasonable justification was 
thoroughly documented and demonstrates that the ADJ_U* Beta option 
in AERMET selected for the Herbert A. Wagner Generating Station 
(Wagner) modeling demonstration performs better than the default 
regulatory version of AERMET for the given application where high 
modeled concentrations are likely to occur under low wind, stable 
conditions. In the case of the Wagner facility, excessive 1-hour SO2 
concentrations on terrain at elevations above the lowest effective 
stack height at distances of 20 km to 34-37 km from the source were 
predicted by the regulatory default version of the AERMOD Modeling 
System, specifically during low wind/stable conditions when u* values 
were relatively small. This parallels similar excessive 1-hour SO2 
concentrations predicted on distant terrain during similar low wind/
stable conditions for the Region 1 Schiller Station situation. Given 
this model response and our similar concurrence of ADJ_ U* for a nearly 
identical circumstance, we agree that it was appropriate for the 
ADJ_ U* Beta option in AERMET to be considered for this regulatory 
modeling application at the Wagner facility.

While not an issue in this particular case, we continue to evaluate 
the potential that the use of the ADJ_U* Beta option in combination 
with site-specific meteorological data that includes the sigma-theta 
and/or sigma-w turbulence parameters may introduce a bias toward 
concentration underprediction and caution anyone considering the use 
of both the ADJ_U* Beta option and meteorological data that includes the 
derived sigma-theta and/or sigma-w turbulence parameters in regulatory 
applications without consultation and approval from the appropriate 
permitting authority and the respective EPA Regional Office.

Memo:  Model Clearinghouse Review of the Use of the ADJ_U* 
Beta Option in the AERMET Meteorological Processor (Version 15181) 
for the Herbert A. Wagner Generating Station Modeling Demonstration
          Dated: June 20, 2016
          From:  George Bridgers, Model Clearinghouse Director
                   Air Quality Modeling Group, EPA
            To:  Tim Leon-Guerrero, Meteorologist
                   Office of Air Monitoring & Analysis, EPA Region 3
                 Alice Chow, Associate Director
                   Office of Air Monitoring & Analysis, EPA Region 3

Memo:  Concurrence Request for the use of BETA Adjust U* for
the Herbert A. Wagner Generating Station near Baltimore, MD
          Dated: May 13, 2016
          From:  Timothy A. Leon Guerrero, Meteorologist
                   Office of Air Monitoring & Analysis, EPA Region III
          Thru:  Alice Chow, Associate Director
                   Office of Air Monitoring & Analysis, EPA Region III
            To:  George Bridgers, Director of Model Clearinghouse
                   Air Quality Modeling Group, Office of Air Quality
                   Planning and Standards