# Maryland Department

of the Environment April14, 2016 Mr. Shawn M. Garvin Regional Administrator USEPA Region

3 1650 Arch Street Mail Code: 3RAOO Philadelphia,
PA 19103-2029 

# DearM~

Larry Hogan Governor Boyd Rutherford Lieutenant Governor Ben Grumbles Secretary I am writing to you regarding the 1-hour S02 Characterization Modeling for the area around the H.A. Wagner and Brandon Shores power plants air quality modeling protocol that was recently submitted
to the Maryland Department

of the Environment (MOE), Air and Radiation Management Administration (ARMA). This modeling protocol was prepared
to describe the approach being taken to demonstrate that the H.A. Wagner (Wagner) power plant located
in Anne Arundel County, Maryland would be in attainment

of the 1-hour S0 2 National Ambient Air Quality Standard (NAAQS). On March 20, 2015, EPA informed Maryland that the Wagner Power Plant would be part of the expedited round of designations under the 1-hour S0 2 NAAQS due to terms of the S0 2 Consent Decree negotiated between the Sierra Club and EPA (Sierra Club 

### v. McCarthy). The EPA intends to designate the Wagner Power Plant area as either unclassifiable/attainment, nonattainment

or unclassifiable

by July 2, 2016 after a review of available modeling
or monitoring data to support the S0 2 concentration characterization. The model selected for this modeling application

is the EPA American Meteorological Society/Environmental Protection Agency Regulatory Model (AERMOD) modeling system version 15181, including the American Meteorological Society/Environmental Protection Agency Regulatory Improvement Committee (AERMIC) meteorological (AERMET)nonregulatory default/beta ADJ_U* option (EPA,2015a). EPA has indicated support for this change as part of their July 29, 2015 Appendix
W proposal.

In addition, Roger Brode's (USEPA) Proposed Updates to AERMOD Modeling System presentation (EPA, 2015b) delivered
at the 11th Modeling Conference
on August 12, 2015 indicated that the ADJ_U* option be incorporated into the regulatory versions
of AERMOD and AERMET

in the notice of proposed rulemaking (NPRM). Section 3.2.2.b of Appendix
W to 40 CFR Part 51, ("Revision
to the Guideline on Air Quality Models", November

9, 2005), details the approach for approval
of an alternative model. Specially, the request must meet one of the following three conditions

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. gov1 . If a demonstration can be made the model produces concentrations estimates equivalent

to the estimates obtained using
a preferred model; 2. If a statistical performance evaluation has been conducted using measured air quality data and the results of that evaluation indicate the alternative model performs better for the given application than a comparable model; or 3. If the preferred model
is less appropriate for the specific application,

or there is no preferred model. The Wagner power plant request falls under condition

3. Appendix
W (Section 3.2.2.e) states that for condition

3 in paragraph

b of section 3.2.2 of Appendix
W to 40CFRPart 51, "an alternative refined model may be used provided that: 1 . The model has received

a scientific peer review; 2. The model can be demonstrated

to be applicable
to the problem on a theoretical basis; 3. The databases which are necessary
to perform the analysis are available and adequate; 4. Appropriate performance evaluations

of the model have shown that the model
is not biased toward underestimates; and, 5. A protocol on methods and procedures

to be followed has been established." These five (5) points are discussed below separately. 

### Condition

1 : The model has received

a scientific peer review EPA has acknowledged poor AERMOD performance during low wind-speed conditions (Robinson and Brode 2007). The proposed AERMET formulation changes
to the friction velocity computation
for low wind speeds are referenced

in a Boundary-Layer Meteorology Qian and Venkatram (2011) peer-reviewed paper which demonstrated that the AERMOD meteorological preprocessor (AERMET) tends to grossly under-predict surface friction velocity (u*) under low wind-speed conditions (less than two meters per second). When simulating emission sources with AERMOD, the under-prediction

of u* leads to inappropriately
low mechanical mixing heights, consequently resulting

in overly conservative (excessively high) ambient concentration estimations (EPA 2015c; Paine and Connors 2013; Qian and Venkatram 2011, Robert Paine 2015). Qian and Venkatram (2011) suggested

a new method for calculating

u* and showed results that support improved
u* and model concentration predictions

in the low wind-speed regime. EPA has incorporated this calculation methodology

in AERMET as ADJ_U* (EPA 2013), most recently

in AERMET version 15181. The ADJ_ U* method
is a processing option for calculating

u* for low wind speeds during stable (nighttime) conditions (EPA 2015a}. Several study results support the conclusion that the application

of the ADJ_U* option significantly improves AERMOD performance
for low wind-speed conditions while maintaining

a conservativelyhigh bias in predicted concentrations (EPA 2013; EPA 2015c; EPA 2014; Paine and Connors 2013). These studies indicate that the ADJ_U* option has been sufficiently peer-reviewed. 

### Condition

2: The model can be demonstrated

to be applicable
to the problem on a theoretical basis There
is no theoretical limitation
to the application

of the AERMET ADJ_U*-

it is generally applicable. The current default algorithm

in AERMET has been demonstrated

to be faulty and needs to be replaced by the ADJ_U* approach. 

### Condition

3: The databases which are necessary
to perform the analysis are available and adequate The necessary data needed for implementing ADJ_U* within the AERMOD modeling system
is routine meteorological data are already available and are sufficient for exercising this low wind option. The use of the Baltimore Washington International Thurgood Marshall Airport (BWI) National Weather Service (NWS) data is sufficient. There are no special database requirements
for the use of the ADJ_U* option. 

### Condition

4: Appropriate performance evaluations

of the model have shown that the model is not biased toward underestimates There have been many model evaluation studies that illustrate improved performance

of the AERMOD modeling system with the use of the ADJ_U* option. Most notably
is the performance evaluation referenced

in Appendix

F of the AERMOD User's Guide (EPA 2015c) that was conducted
by EPA. This performance evaluation performed
by EPA utilizes three evaluation databases:
(1) Idaho Falls (NOAA Technical Memorandum ERL ARL-52, August 1974), (2) Oak Ridge (NOAA Technical Memorandum ERL ARL-61, August 1976), and (3) Lovett. The first two databases were part of the API-sponsored evaluation

of AERMOD conducted
by AECOM, that were submitted
as part of API's public comments
on EPA's 10th Conference
on Air Quality Models held in March 2012

. The two NOAA field studies were low-level, non-buoyant tracer releases with three arcs of samplers located at 1 00 m, 200 m, and 400 m from the release point. The Idaho Falls study was located
in a flat terrain, while Oak Ridge was located
in complex terrain. The third database utilized by EPA to evaluate the ADJ_U* option presented

in Appendix

F of the AERMOD User's Guide (EPA 2015c) was the Lovett database. Lovett
is a historical AERMOD evaluation database and features

a single 145 meter stack located within
a few kilometers

of complex terrain. The Lovett field study was a year-long 

### 80 2 field program with monitors located on the primary terrain features
to the north of the stack. The most representative field program that could be used to predict the performance

of ADJ_U* for a modeling study at the Wagner power plant is the Lovett field program.Overall for Lovett, the Q-Q plots on pages F-35 through F-37 (EPA 2015c) demonstrate that the inclusion
of the ADJ_U* option improves model performance. Whether the ADJ_U* option
is correcting
an under-prediction bias as shown on page F-35 (Figure
1) or anoverprediction bias as shown on pages F-36 (Figure 2) and F-37 (Figure 3), the model performance

is better. In Attachment

A (Modeling Analysis
to Support Use of ADJ_U* Option) of this letter is an additional analysis completed
to demonstrate that the model using ADJ_U*

is not biased toward underestimate.

In addition, the modeling files used in this analysis to support the use of ADJ_U* are also enclosed. In the proposed revisions
to the Guideline (EPA 2015d), EPA intends for the ADJ_U* option to be part of the regulatory default AERMOD modeling system. EPA made this proposal

in the preamble
to the proposed changes
to the Guideline, referred to below as NPRM. Due to several initial comments from stakeholders, members
of the EPA modeling group provided clarifications (EPA 2015e and 2015f) that reinforced EPA's intent to include ADJ_U* as a regulatory default option. These clarifications were provided during EPA's 11th Conference
on Air Quality Modeling and Public Hearing for the Proposed Revisions
to the Guideline held on August 12-13, 2015 (2015 Conference). EPA's statements regarding the ADJ_U* option as presented

in the NPRM and the 2015 Conference are provided below. From NPRM section IV.A.2., "Updates
to EPA's AERMOD Modeling System" (EPA 2015g): "Based on studies presented and discussed
at the Tenth Modeling Conference, and additional relevant research since 2010, the EPA and other researchers have conducted additional model evaluations and developed changes

to the model formulation
of the AERMOD modeling system
to improve model performance

in its regulatory applications.
We propose the following updates
to the AERMOD modeling system
to address

a number of technical concerns expressed by stakeholders: 1. A proposed option incorporated

in AERMET

to adjust the surface friction velocity (u*) to address issues with AERMOD model over prediction under stable, low wind speed conditions. This proposed option is selected by the user with the METHOD STABLEBL ADJ_U* record in the AERMET Stage 3 input file." As presented
on the public record at the 2015 Conference
by Tyler Fox in his presentation "Overview
of Proposed Revisions
to Appendix W" (EPA 2015e): "In the NPRM, EPA has proposed

to incorporate specific updates
to the regulatory version that are the subject of public review and comment and then would be codified as part of the final rule action, as appropriate.-These options have thus remained ltbeta" in v15181
to allow for public testing
& evaluation" As presented
on the public record at the 2015 Conference
by Roger Brode
in his presentation "Proposed Updates
to AERMOD Modeling System" (EPA 2015f): ltEPA has proposed

in the NPRM that the ADJ_U* option (with or without BULKRN) be incorporated into the regulatory version of AERMET." It is clear that EPA, pending review and comments during the public comment period, intends to incorporate ADJ_U* as a regulatory default option. At this time, ADJ_U* remains a nondefault option and requires approval from EPA for use in modeling compliance demonstrations. According
to statements

at the 2015 Conference, the proposed revisions to the Guideline are expected
to be finalized by the spring of 2016 (EPA 2015e). MDE/ARMA believes that these evaluations satisfy this condition. Condition

5: A protocol on methods and procedures

to be followed has been established A modeling protocol addressing the 1-hour S02 characterization

of the Wagner area was prepared by AECOM and submitted
to EPA Region

3 in February 2016. Comments
on the modeling protocol were received from EPA Region

3 in March 2016. MDE/ARMA has reviewed the modeling protocol prepared for utilizing ADJ_U* and EPA Region

3 comments and the implementation

of the ADJ_U*

in the application, and we believe that the comments have been adequately addressed. MDE/ARMA believes for the reasons described previously that the ADJ_U* option
is justified for use in the 1-hour S02 characterization

air quality modeling for the Wagner power plant.

If there are any specific questions related to the technical aspects
of this air modeling issue, please contact Mr. Michael Woodman

of MDE/ARMA

at (410) 537-3229. Sincerely, Ben rumbles Secretary cc: Tim Leon Guerrero, U.S. EPA Region
Ill (e-mail) George (Tad) S. Aburn, Jr., MOE EnclosuresI c w ..J w c 0 

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### References Sierra Club 

### v. McCarthy, Case No. 3:313-cv-3953-SI, Consent Decree (approved Mar. 2, 2015). EPA, 2015a. Addendum, User's Guide for the AERMOD Meteorological Preprocessor (AERMET). (EPA-454/B-03-002, November 2004). Office of Air Quality Planning and Standards, Research Triangle Park, NC. June 2015. http://www.epa.gov/ttn/scram/7thconf/aermod/aermet userguide.zip

. EPA, 2015b. "Proposed Updates
to AERMOD Modeling System." Roger W. Brode, U.S. EPA Office of Air Quality Planning and Standards (OAQPS), Air Quality Assessment Division (AQAD), Air Quality Modeling Group (AQMG). Presentation

at EPA 11th Model

i ng Conference, Research Triangle Park, NC. August 12, 2015. Accessed March 14, 2016. https://www.epa.gov/ttn/scram/11 thmodconf/presentations/1- 5 Proposed Updates AERMOD System.pdf Robinson,

R. and R. Brode. 2007. "AERMOD Implementation Workgroup." Presentation

at EPA Regional/State/Local Modelers Workshop. Virginia Beach, VA. May 15-17,2007. Accessed March 14, 2016. http://www.cleanairinfo.com/regionalstatelocalmodelingworkshop/archive/2007/presentations/ Tuesday%20-%20May%2015%202007



### I AERMOD Implementation Workgroup. pdf Qian, W. and A. Venkatram. 2011. "Performance

of Steady-State Dispersion Models Under Low Wind-Speed Conditions." 

### Boundary-Layer Meteorology (2011) 138:475-491 DOl 10.1 007/s1 0546-010-9565-

1 . Published online December

3, 2010. Accessed March 14, 2016. http://link.springer.com/article/1

0.1 007%2Fs1 0546-010-9565-1 EPA. 2015c. "Addendum: User's Guide for the AMS/EPA Regulatory Model- AERMOD (EPA-454/B-03-001, September 2004." Office of Air Quality Planning and Standards, Air Quality Assessment Division. June 2015. Accessed March 14, 2016. http://www.epa.gov/ttn/scram/models/aermod/aermod userguide.zip

. Paine, B. and J. Connors. 2013. "AERMOD Low Wind Speed Issues: Review of New Model Release." AECOM. EPA 2013 Modeling Workshop Presentation. April23, 2013. Accessed March 14, 2016. http://www.cleanairinfo.com/regionalstatelocalmodelingworkshop/archive/2013/Files/Presentatio ns/Tuesday/1 05-Review

of AERMOD Low Wind Speed Options Paine.pdf Robert Paine, Olga Samani, Mary Kaplan, Eladio Knipping

& Naresh Kumar (2015) Evaluation
of low wind modeling approaches tor two tall-stack databases, Journal of the A ir 

### & Waste Management Association, 65:11, 1341-1353, DOl

: 0.1080/10962247.2015.1085924 Accessed on March 14,2016. http://www.tandfonline

. com/doi/abs/1 0.1080/10962247.2015.1085924

# EPA. 2013. "AERMOD Modeling System Update." Roger W. Brode, Office of Air Quality Planning and Standards, Air Quality Modeling Group. Presentation

at EPA R egionai/State/Local Modelers' Workshop. Dallas, TX. April 23, 2013. Accessed March 14, 2016. http://www .cleanairinfo.com/reqionalstatelocalmodelingworkshop/archive/2013/Files/Present ations!Tuesday/1 04-Brode AERMOD System Update RSL-Dallas 04-23-2013.pdf EPA. 2014. 'Webinar: AERMOD Modeling System Update." Office of Air Quality Planning and Standards, Air Quality Modeling Group. January 14, 2014. Accessed March 24, 2016. https://www3.epa.qov/ttn/scram/webinar/AERMOD

13350 Update/AERMOD System Update Webinar 01-14-2014 FINAL.pdf NOAA Technical Memorandum ERL ARL-52. Diffusion Under Low Wind Speed, Inversion Conditions. Sagendorf, J.F., C . Dickson. Air Resources Laboratory, Idaho Falls, Idaho. August 197 4. NOAA Technical Memorandum ERL ARL-61. Diffusion Under Low Wind Speed Cond

i tions near Oak Ridge, Tennessee. Wilson, R.B., G. Start, C. Dickson,
N. Ricks. Air Resou

r ces Laboratory, Idaho Falls, Idaho. August 1976. EPA. 2015d. "40CFR Part 51, Revis

i on to the Guideline on Air Quality Models: Enhancements to the AERMOD Dispersion Modeling System and Incorporation

of Approaches
To Address Ozone and Fine Particulate Matter; Proposed Rule

. " Federal Reg

i ster. Vol. 80 No.145. July 29. 2015. Accessed March 14, 2016. http://www.epa.gov/ttn/scram/11 thmodconf/EPA-HQ-OAR-2015-031 0-0001.pdf

. EPA. 2015e. "Overview
of Proposed Revisions
to Appendix
W ." Tyler Fox, Office of Air Quality Planning and Standards. 11th Modeling Conference, Research Triangle Park

, NC

. August 12, 2015. Accessed March 14, 2016. https://www .epa.gov/ttn/scram/11 thmodconf/presentations/1-3 Overview

11 thMC.pdf EPA. 2015f. "Proposed Updates to AERMOD Modeling System." Roger W. Brode, Office of A

i r Quality Planning and Standards, Air Quality Assessment Division, Air Quality Modeling Group. 11th Modeling Conference, Research Triangle Park, NC. August 12, 2015. Accessed March 14, 2016. https://www .epa.gov/ttn/scram/11 thmodconf/presentations/1- 5 Proposed Updates AERMOD System.pdf EPA. 2015g. "40 CFR Part 51

, Revision
to the Guideline on Air Quality Models: Enhancements to the AERMOD

D

i spersion Modeling System and Incorporation

of Approaches
To Address Ozone and Fine Particulate Matter; Proposed Rule." Federal Register

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