U.S. EPA Region 4 Comments on the Georgia BART Exemption Modeling Protocols 

Date: June 1, 2006 

The following are comments on the CALPUFF-based modeling protocols which are developed to 

address source-specific dispersion modeling to demonstrate whether a source should be exempt from 

Best Available Retrofit Technology (BART) controls in compliance with the Regional Haze Rule. 

General Comments for all Georgia BART Exemption Modeling Protocols

1. Rayleigh Scattering and Sea Salt: This comment applies to the protocols for the Georgia Power and 

Savannah Electric and Power Company power plants (i.e., Branch, McIntosh, McDonough, Wansley, 

Yates, Bowen and Mitchell), International Paper (Augusta Mill) and the Tronox Pigments Incorporated 

facility. Some protocols indicate that the Rayleigh Scattering term will be modified from the default 

value of 10 Mm-1 to account for elevation of the specific Class I area receptors. Some protocols propose 

the use of sea salt for coastal areas. The use of a site-specific Rayleigh scattering value or sea salt is part 

of the revised-IMPROVE extinction equation for calculating light extinction from particle 

concentrations. The revised equation is based on recommendations by the IMPROVE Steering. The 

revised-IMPROVE extinction equation has not been peer reviewed, nor has the Environmental 

Protection Agency (EPA) made a decision regarding its use. Also, there does not appear to be consensus 

among the participants on the national RPO data workgroup on how or when this new equation should 

be implemented. It is also unclear if selectively choosing to use only a portion of the new IMPROVE 

equation (e.g., site-specific Raleigh scattering value or sea salt) is a valid use of the equation. 

Therefore, it is not clear how or if the new IMPROVE extinction equation, which considers geographical 

variation in PM2.5 species, should be used at the present time. There does not appear to be consensus 

among the participants on the national Regional Planning Organization (RPO) data workgroup on how 

or when this new equation should be implemented. It is also unclear if selectively choosing to use only a 

portion of the new IMPROVE equation (e.g., site-specific Raleigh scattering values) is a valid use of the 

equation. Until a decision is made on the use of the new IMPROVE extinction equation, the existing 

approved equation should be used in the compliance demonstration for the Regional Haze Rule. 

However, if a state chooses to develop an alternative approach to estimating natural conditions or 

background data for a Class I Area, a technical rationale that discusses the assumptions and methodology 

for the deviation from the EPA recommended extinction equation should be developed per the 

"Guidance for Estimating Natural Visibility Conditions Under the Regional Haze Rule." We 

recommend that the new IMPROVE extinction equation be used in its entirety, not in pieces. Merely 

referencing the IMPROVE Steering Committee recommendation would not be adequate. The rationale 

would need to be specific to a Class I Area or show how it is applicable to all Class I areas being 

modeled and submitted to the reviewing agencies and EPA on a case-by-case basis. It should 

demonstrate how the alternative methodology is consistent: across applications (e.g., BART and 

Reasonable Progress), across time (e.g., baseline and future calculation for natural conditions), and 

among the stakeholders involved and who need to consult on the development of a long term strategy for 

the Class I Area (i.e., Federal Land Managers (FLMs), states, industry). 

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2. GEP Stack Heights: It is unclear if the stack heights presented in the protocols represented the good 

engineering practice (GEP). Modeling with GEP stack heights is required under 6.2.2 of 40CFR Part 51, 

Appendix W: Guideline on Air Quality Models. Using stack heights greater than the GEP derived stack 

height in 40 CFR Part 51.100 (hh)(1)(v) is a prohibitive dispersion technique for regulatory modeling 

applications. The modeling protocols do not contain any discussion on how the GEP stack heights were 

determined for modeling those sources with stack heights greater than the de minimis GEP height of 65 

meters. These sources must provide justifications that emission units modeled with stack heights above 

65 m represent GEP according to 40 CFR Part 51.100 (hh)(1)(v) or they must redo the modeling. This 

documentation should be included in the BART exemption modeling reports. The sources with stacks 

heights potentially greater than the GEP de minimis height in the NC BART modeling protocols are 

listed in the following table. 

Stacks with Heights Potentially Greater than GEP Height in the GA BART Modeling Protocols 

Facility Emissions Units / permit 

ID/Stack ID 

Stack 

height 

Plant Mitchel Unit 3 152.4 m 

Plant Branch Units 1, 2, 3, 4 304.8 m 

Plant McIntosh Unit 1 121.9 m 

Plant Bowen Units 1,2,3,4 304.8 m 

Plant McDonough Units 1,2 254.8 m 

Plant Wansley Units 1,2 304.8 m 

Plant Kraft Units 3,4 83.8 m 

Plant Yates Units 6,7 254.4 m 

ST06 216 ft 

ST11 272 ft 

ST33 272 ft 

ST15 285 ft 

ST27 285 ft 

ST28 285 ft 

ST29 272 ft 

ST30 285 ft 

PCS Nitrogen Fertilizer 

ST13 285 ft 

DSM Chemicals North S016 280 ft 

America, Inc. S014 220 

Rayonier Performance No. 5 Recovery Furnace 78.8 m 

Fibers, LLC No. 5 Smelt Dissolving Tank 78.8 m 

Recovery boiler No.3 246 ft 

Smelt Tank No.3 248 ft 

Power Boiler No. 1 350 ft 

Georgia-Pacific 

Corporation Cedar 

Springs Mill 

Power Boiler No. 2 350 ft 

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No. 5 Recovery Furnace –R401 82.9 m 

No. 5 Recovery Furnace –R401 82.9 m 

Georgia-Pacific 

Corporation Brunswick 

Mill No. 5 Smelt Dissolver Tank 80.5 m 

3. Documentation: 

a. The BART exemption modeling protocols did not, in some cases, detail the specific input choices that 

will be used to run the various programs for the CALPUFF modeling system (i.e., CALMET, 

CALPUFF, POSTUTIL, CALPOST, etc.). The BART exemption modeling reports should include a 

table that shows the inputs used in running each module in CALPUFF. Even though the CALMAT 

program was run by the Visibility Improvement - State and Tribal Association of the Southeast 

(VISTAS), that information should be obtained for the modeling report. A table similar to the one 

included in the March 16, 2006 EPA Model Clearinghouse memo, “Dispersion Coefficients for 

Regulatory Air Quality Modeling in CALPUFF,” from Tyler Fox to Kay Prince is recommended. This 

table provides a list of the regulatory default modeling options for use in the CALPUFF modeling 

system. The memo is located on the EPA website at 

http://www.epa.gov/ttn/scram/guidance/mch/cfym109.pdf. The BART CALPUFF input table would 

indicate the regulatory defaults and the inputs that the modeler chooses to use for all of the CALPUFF 

processors. A rationale for why a non-regulatory default was chosen would be included in a revised 

modeling protocol or in the modeling report that documents the BART modeling. 

b. A table that lists all of the emission units that were considered prior to determining the BART-eligible 

sources in the facility should be included in the modeling report. The table would include the 

appropriate date(s) that show why that emission unit was or was not BART –eligible and any other 

rationale used to exclude an emission unit. If this information is not included in the modeling report, it 

should be included in the RH SIP documentation. EPA Region 4 is willing to assist the state in 

reviewing the assumptions and decisions that the state used to determine a BART-eligible unit and 

source prior to the submittal of the Regional Haze SIPs. 

c. The protocol should not merely state that the approach recommended by the Visibility Improvement –

State and Tribal Association of the Southeast (VISTAS) or the VISTAS protocol will be followed. The 

source-specific protocol should indicate how with specifics the VISTAS protocol and EPA guidance will 

be followed. 

Georgia Power and Savannah Electric Power Plants

1. Rayleigh Scattering: See the above general comments for EPA concerns on alternative Rayleigh 

scattering. 

2. Emission Rates for Plant Bowen and Wansley: The protocols for Plants Bowen and Wansley propose 

to use seasonal emission rates for the visibility impairment pollutants (VIPs). Maximum 24-hour emission rates 

for non-seasonal and seasonal rates are proposed. The 24-hr emission rate from the highest emitting day of 

the meteorological period modeled must be used.

International Paper (IP) Augusta Mill

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In addition to the following comments on the International Paper Augusta Mill BART exemption 

modeling protocol, we agree with all of the comments on the this protocol as presented in the May 18, 

2006 letter from Bill Jackson (US Department of Agriculture’s Forest Service) to Peter Courtney (GA 

EPD). In some cases a brief portion of those comments are repeated in this document.

1. Use of 98th percentile for visibility threshold comparison: The VISTAS 12-km screening approach 

has been discussed among the EPA Regional Offices, the FLMs and the VISTAS states. The VISTAS 

states have agreed with this approach and to its incorporation in the VISTAS protocol. We are in 

agreement that if the no-observation (NO-OBS) non-regulatory option is used in CALMET, the 

screening would be acceptable if the peak values are used with the visibility threshold. In comments on 

the draft versions of the VISTAS BART protocol, EPA Region 4 expressed concerns on how the 

visibility threshold comparison should be performed for the screening methodology if the 98th percentile 

is used as opposed to the peak value. The highest visibility impact over three years is used in the 

screening modeling because of the uncertainty in using CALMET without observations; this a departure 

from how the CALPUFF model was evaluated. It is unclear how the processing of the meteorological 

data (i.e., specifically the 36-km MM5 data) with the NO-OBS input would affect the performance of the 

CALPUFF modeling system, especially in areas of complex winds, and still provide a conservative 

model while using the 98th percentile for the impact test. Finally, the use of the 98th percentile is not a 

regulation that must be applied for the BART assessment. 

2. AERMOD Turbulence-based dispersion: The protocol does states that the appropriate model codes 

for the dispersion scheme will be used (section 4.3). This is stated after mentioning that CALPUFF can 

use either AERMOD-turbulence or Pasquill-Gifford (P-G) dispersion coefficients. Section 4.3.5 states 

that P-G curves will be used. However, the regulatory default (i.e., option 3) representing the P-G 

dispersion option for the MDISP and MDISP2 CALPUFF inputs are not proposed for use, but should be, 

in the modeling. In the CALPUFF Model Input Group2: Technical Options in Appendix A, option 2 for 

turbulence based-dispersion is indicated. It is unclear which approach will be used in the BART 

modeling, but the P-G dispersion coefficients should be used. 

EPA continues to recommend the use of the P-G dispersion parameters with CALPUFF. The March 16, 

2006 EPA Model Clearinghouse memo, “Dispersion Coefficients for Regulatory Air Quality Modeling 

in CALPUFF,” from Tyler Fox to Kay Prince, discusses the Agency’s position on dispersion coefficients 

for CALPUFF. The memo also provides a list of the regulatory default modeling options for use in the 

CALPUFF modeling system. The memo is located on the EPA website at 

http://www.epa.gov/ttn/scram/guidance/mch/cfym109.pdf. The International Paper (Augusta) BART 

modeling protocol should be revised to clearly indicate that P-G dispersion parameters will be used in 

the BART modeling. 

3. Ammonia-Limiting Method: The Ammonia-limiting method is proposed to be used. It appears that 

hourly ammonia data from the CMAQ model will be used. The protocol should state that monthlyaveraged CMAQ data that is unmodified will be used. 

4. Alternative methodologies when VISTAS BART Protocol methods fail: Chapter 7 discusses several 

alternative modeling methodologies that will be used should the facility’s BART sources fail to indicate 

a need for determining BART controls. These alternative approaches include the use of line-of-sight, 

Method 7, actual relative humidity and the EPA f(RH) curve to determine a new delta deciview (dv) 

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value, limiting CALPOST to only those periods with higher EPA f(RH) values, adjustment for Rayleigh 

scattering, addition of sea salt, and the new EPRI coefficients for calculating extinction. 

a. Sea Salt and Rayleigh Scattering Adjustments: See the above general comments on this topic for 

revising the protocol. 

b. Line-of-Sight (LOS): EPA Region 4 reiterates the comments that were submitted to the North and 

South Carolina on the BART exemption modeling protocols proposing to use this methodology. 

EPA Region 4 does not recommend the use of LOS for evaluating compliance with the BART rule. 

The use of a LOS calculation is an alternative methodology departure from the VISTAS protocol. 

We do not recommend or support this proposed alternative modeling methodology. The preamble of 

the regional haze rule, 64 Federal Register 35726-35727 (July 1, 1999), provides some direction on 

this issue. “...The EPA also acknowledges the technical point made by some commenters that for 

other types of scenes with other site-specific conditions, {for example, where the sight path to a 

scenic feature is less than the maximum visual range} a change of more than 1 deciview might be 

required in order for the change to be perceptible. However, EPA wishes to emphasize that the 

overall goal of the regional haze program is not to track changes in visibility for only certain vistas at 

a specific Class I area. Rather, the program is designed to track changes in regional visibility for the 

range of possible views of sky and terrain found in any Class I area, and to assure progress toward 

the national goal.” While the LOS concept is technically valid for evaluating visibility impacts on an 

instantaneous basis from a specific observer’s viewpoint, it is not appropriate for evaluating regional 

visibility impacts. Therefore, the use of LOS does not ensure that the goals of the Regional Haze 

Rule (RHR) will be met. 

The VISTAS BART modeling protocol has been discussed and has obtained general consensus from 

the EPA, FLM and state reviewers to not use LOS for the BART modeling. Also a LOS calculation 

was not used by EPA in developing the threshold value. The goal of the BART assessment is not to 

determine visibility improvement along a specific line of sight but rather improvement in regional 

haze. If this and other options are used to fine tune the model or significantly change the model as 

EPA used it to develop the threshold criteria, then maybe the criterion might also change. One could 

choose a host of options to adjust the model to predict what may or may not be a better approach in 

using the CALPUFF modeling system. EPA Region 4 is supporting and recommending the use of 

the regulatory defaults for the BART modeling (with the exception agreed upon for the screening 

modeling). 

c. Method 7: EPA disagrees with the use of Method 7 as an alternative method for the BART 

exemption or determination modeling. This is one of many alternative methods that has been 

previously discussed in the development of the VISTAS protocol. As previously stated by Bill 

Jackson of the Forest Service in comments on the VISTAS BART protocol, Method 7 attempts “to 

address the issue of “natural obscuration” solely by modifying the background visibility conditions in 

the CALPOST calculations. This approach addresses only one of the CALPUFF modeling problems 

that occur when “natural obscurations” such as clouds and precipitation are present. As stated in the 

VISTAS protocol, sulfate and nitrate formation rates may increase greatly in the presence of liquid 

water vapor. However, the increased sulfate/nitrate formation in the presence of liquid water is not 

simulated by CALPUFF. Method 7 and Method 7 Prime modify the visibility extinction calculations 

such that the effects are generally lowered (with respect to change in dv), without accounting for the 

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compensating effect of the increased sulfate/nitrate formation that occurs in the presence of liquid 

water. Also, during periods of “natural obscuration”, the primary FLM interest would be in the 

visibility impacts that might occur during the non-obscured hours. The application of Method 7 has 

the effect of double counting the perceived importance of “natural obscurations” in the BART 

modeling.” Method 7 should not be used in the BART CALPUFF modeling. 

d. Other alternative methodologies: Deviations for the BART modeling should be presented with a 

technical rationale that discusses the assumptions and methodology for the deviation from the 

VISTAS BART protocol and any EPA recommendations. The rationale would need to be specific to 

a Class I Area or show how it is applicable to all Class I areas being modeled and submitted to the 

reviewing agencies and EPA on a case-by-case basis. It should demonstrate how the alternative 

methodology is consistent: across applications (e.g., BART and Reasonable Progress), across time 

(e.g., baseline and future calculation for natural conditions), and among the stakeholders involved 

and who need to consult on the development of a LTS for the Class I Area (i.e., FLMs, states, 

industry). 

PCS Nitrogen Fertilizer

1. PCS Nitrogen Fertilizer was identified in the VISTAS ammonia (NH3) modeling to be one of the 

large sources that should be specifically modeled for NH3. The protocol states that the facilities NH3 

emissions will be modeled. It does not, but should also, address modeling particulate matter emissions. 

2. The protocol did not clearly state that 12 km screening modeling will be performed using the 

maximum 24-hoour results to compare with the 0.5 deciview (dv) threshold; and that finer grid modeling 

(i.e., 4 km) will be developed using the 98th percentile results. EPA assumes this is what was implied. If 

this is incorrect, please submit a revised section 1.3 for review. 

3. The protocol is vague in many areas in describing the CALPUF modeling system inputs. It was 

difficult to determine the input choices that will be used in the modeling. Please see the documentation 

comment under the general comments presented above for more information on this topic. 

4. There are several versions of the CALPUFF model on the website maintained by the model 

developer. The protocol should state the version number of the models (CALMET and CALPUFF) that 

will be used in the BART modeling and the website location for obtaining the model. 

5. A map of the modeling domain should be included in the protocol and/or the modeling report. 

Interstate Paper, LLC

1. Section 2.2. - BART-eligible source: Based on the data presented, we agree the bubbling fluidized 

bed boiler does not pass the Step 2 "date test" for BART eligibility. (See Section II.A. of 40 CFR Part 

51, Appendix Y, "Guidelines for BART Determinations under the Regional Haze Rule," for a detailed 

description of the Step 2 test.) However, we disagree with the conclusion in subsection 2.2.1 that the 

lime kiln is not BART-eligible for the following reason. 

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The BART-eligibility assessment in Section 2.2 is not performed correctly and needs to be revised. It 

appears that the potential emissions from each BART-eligible unit were incorrectly compared on a unit 

by unit basis to the 250 tons per year (tpy) or more threshold. The correct procedure is to sum the 

potential emissions for each visibility-impairing pollutant listed in Table 2-1 across all the potentially 

BART-eligible emission units that pass Steps 1 and 2 for BART eligibility, i.e., the lime kiln, power 

boiler, and recovery boiler. (For further details on the Steps, please see Section II.A. of Appendix Y.) 

Thus, potential emissions of NOx would sum to 149+409+350 = 908 tpy NOx. Similarly, potential 

emissions across all three units would sum to 128 tpy PM10 and 311 tpy SO2. 

Since the lime kiln, power boiler, and recovery boiler passed Steps 1, 2, and 3 for BART eligibility, 

these three emission units are considered BART eligible. Some confusion may have resulted from 

portraying the order of the steps to determine BART-eligibility in reverse order from what is presented 

in Appendix Y. We recommend clarifying the step by step analysis in Section 2.2 to reflect the order in 

Appendix Y. 

2. The facility is within 50 km of the Wolf Island Class I Area. For facilities within 50 km of Class 1 

areas, the 12-km screening approach should not be used. At a minimum, the 4-km CALMET data 

should be used and a refinement to 1-km may be necessary. Building downwash should be used. 

3. The version numbers of the CALMET and CALPUFF models that will be used in the modeling should 

be included in the protocol. The location (i.e., website) that the models were obtained should be 

included in the protocol. 

4. Please see the documentation comment under the general comments presented above for more 

information on this topic.

Tronox Pigments Incorporated 

1. Please see the documentation comment under the general comments presented above for more 

information on this topic 

2. The third paragraph on page 2-1 states that additional emission limits are being considered that could 

exempt sources based on emission levels and distance to Class I areas. It is not entirely clear what this 

means. It appears that the facility is considering implementing controls to reduce emission and develop 

a Q/d number that could exempt sources from BART. The Q/d approach cannot be used to exempt a 

BART-source or a Class I area from BART modeling. VISTAS is using Q/d was to determine those 

facilities that the VISTAS contractor would perform 12 km screening modeling for the BART exemption 

assessment. This appears to be a circumvention of the BART rule. If this interpretation of the Tronox 

protocol is correct, then the state could pursue the following. 

a. Assume that the source is subject to BART and proceed to the BART determination modeling 

and engineering assessment for the controls. This would assist the facility in developing 

BART controls. 

b. The source could take an enforceable permit limit to avoid BART-eligibility so long as the 

source takes the limit before the BART determination is made by the state. The enforceable 

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permit limit would have to maintain emissions below 250 tpy of each VIP. Permit limits 

cannot be based on modeling results; they must be based on maintaining emissions below 250 

tpy. 

3. The protocol does not, but should list or discuss the pollutants that will be modeled. 

4. Section 3.2 on page 3-1 sates that hourly CMAQ ammonia data will be used as provided by VISTAS. 

VISTAS has agreed to provide monthly CMAQ ammonia data. Hourly CMAQ data is not 

recommended for the BART modeling. 

5. Tronox proposes to adjust the f(RH) values for the 20% best day’s humidity conditions because the 

monthly f(RH) values in Table A-3 of Appendix A of the EPA “Guidance for Tracking Progress Under 

the Regional Haze Rule," correspond to annual average background conditions which do not capture the 

drier conditions of the 20% best conditions. Consultation with the FLMs is suggested in adjusting the 

humidity factors. It may be that there are other parameter, distributions, scattering efficiencies that 

should be considered in making this adjustment. 

6. The version numbers for the CALMET and CALPUFF models that will be used should also be 

included in the protocol. 

7. Rayleigh Scattering: See the above general comments for EPA concerns on alternative Rayleigh 

scattering choices. 

8. A more detailed protocol is recommended. 

Packaging Corporation of America (PCA) – Valdosta Mill

1. Bradwell Bay Wilderness is not a mandatory Class I area. It should not be modeled for the BART 

requirement. 

2. The potential VIP BART emissions by individual emission units for the VIPs should be included in 

the protocol. 

3. The protocol should discuss how integrated puff sampling methodology will be used in the BART 

modeling. 

4. The protocol does not, but should list or discuss the pollutants that will be modeled. 

DSM Chemicals North America, Inc.

1. Rayleigh Scattering: See the above general comments for EPA concerns on alternative Rayleigh 

scattering choices. 

2. GEP: See General Comment number 3 for concerns in this topic. 

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3. The protocol does not, but should list or discuss the pollutants that will be modeled. A table is 

provided that lists information about potential BART sources for all VIPS at DSM but this does not 

indicate which VIPs will be modeled. 

Rayonier Performance Fibers, LLC

1. Use of Q/d to exempt from BART modeling: The Cape Romain and St. Marks Class I areas were 

proposed to be exempt from modeling because the Q/d number for the facility was less than 10. The Q/d 

approach cannot be used to exempt a BART-source or a Class I area from BART modeling. The 

VISTAS use of Q/d was to merely determine those facilities that the VISTAS contractor would perform 

the 12 km screening modeling for the BART exemption assessment. The Rayonier facility must perform 

BART modeling for all BART-eligible sources and those Class I areas that are within 300 km of the 

facility.

2. The protocol states that if the highest 24-hr average screening visibility impact is greater than 0.5 dv 

then some exceedances are allowed for exemption purposes. No exemptions are allowed under the 

screening modeling. Refined modeling using a finer grid is the only other option allowed if screening 

indicates that a BART determination is required. 

3. The protocol should indicate how the VISTAS protocol will be applied, not merely reference that is 

will be used. The VISTAS protocol did not provide the input choices that could be used in setting up 

each CALPUF modeling system module for execution. 

4. GEP: See General Comment number 3 for concerns in this topic. 

Prayton, Inc.

1. It is unclear if the 24-hr emission rates in Table 2-1 represent the maximum 24-hr emission rate 

during the 2000-2004 time period. The protocol should discuss how the emission rates that comply with 

the BART rule were developed. 

2. The protocol should indicate how the VISTAS protocol will be applied, not merely reference that is 

will be used. The VISTAS protocol did not provide the input choices that could be used in setting up 

each CALPUF modeling system module for execution. 

3. The protocol states that only particulate emissions will be modeled. The protocol should list the VIPs 

for all BART-eligible units at the facility. 

4. Rayleigh Scattering: See the above general comments for EPA concerns on alternative Rayleigh 

scattering choices. 

Georgia-Pacific Corporation Mills in Cedar Springs and Brunswick

1. GEP: See the GEP comment in the General Comment section above. 

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