INDIANA DEPARTMENT OF ENVIRONMENTAL MANAGEMENT 

We Protect Hoosiers and Our Environment. 

Michael R. Pence 

Govemor 

Mr. John Mooney 

Chief, Air Programs Branch 

100 N. Senate Avenue • Indianapolis, IN 46204 

(800) 451-6027 • (317) 232-8603 • www.idem.IN.gov 

November 13, 2015 

U. S. Environmental Protection Agency 

77 West Jackson Boulevard 

Chicago, IL 60604-3590 

Carol S. Comer 

Commissioner 

Re: Indiana's Review of Sierra Club's 

Comments on Indiana's 1-Hour S02 

Consent Decree' Recommendations 

Dear Mr. Mooney: 

On March 2, 2015, the U.S. District Court for the Northern District of California accepted, as an 

enforceable order, an agreement between U.S. EPA, the Sierra Club, and the Natural 

Resources Defense Council to resolve litigation concerning the deadline for completing air 

quality designations under the 2010 Sulfur Dioxide National Ambient Air Quality Standards 

(NAAQS) for the remainder of the country. The court's order directed U.S. EPA to complete 

remaining designations in three additional rounds; the first round by July 2"d, 2016, the second 

round by December 31, 2017, and the final round by December 31, 2020. Indiana provided 

recommendations for five Indiana sources identified in the court's order by the September 181

h, 

2015 deadline for the first round of designations. 

In response to your October 20, 2015 letter requesting Indiana's review of Sierra Club's 

modeling information provided for attainment recommendations under the 2010 Sulfur Dioxide 

NAAQS, the Indiana Department of Environmental Management- Office of Air Quality (IDEMOAQ) is providing the following comments. There were four sources (of the five Indiana 

sources named in the court order) that the Sierra Club provided modeling information. IDEM 

has reviewed the modeling for all sources and provides comments for each source separately 

along with summary tables, comparing IDEM and Sierra Club's modeled results of actual 

emissions for each source: 

A.B. Brown: 

1. Sierra Club included several additional sources in their inventory modeling located 

within a 50 kilometer radius. IDEM conducted explicit modeling on nearby sources to 

determine if those sources' modeled impacts warranted inclusion in the A.B. Brown 

An Equal Opportunity Employer A State that~ ® Recycled Paper 
modeling. Modeling results showed no appreciable impacts from several of the 

sources. IDEM included two of the inventory sources that were found to have potential 

significant concentration gradients in its modeling. 

2. Sierra Club used a background concentration of 47.1 1Jg/m3 based on 2011-2013 

monitoring data. The 2011-2013 monitoring data does not correspond with the 2012-

2014 monitoring data used by IDEM to characterize the air quality in the area as 

referenced in the "Updated Guidance for Area Designations for the 2010 Primary Sulfur 

Dioxide National Ambient Air Quality Standard". 

3. The Sierra Club methodology for determining the background concentrations did not 

account for double counting of sources through modeling and monitoring. 

4. IDEM used a temporally varying seasonal background dataset for each modeled source 

instead of an overall1-hour S02 monitored value that Sierra Club used in their analysis. 

5. AERMOD version 14134 was used, not the latest available version of AERMOD 

(version 15181) that IDEM used to model impacts to characterize air quality in the area. 

6. AERMET version 14134 was used, not the latest available version of AERMET (version 

15181) that IDEM used to process the surface and upper air meteorological data. 

7. Sierra Club modeled all flagpole receptor heights at 1.5 meters, IDEM used ground level 

receptor heights, consistent with U.S. EPA's "S02 NAAQS Designations Modeling 

Technical Assistance Document, Section 4.2" 

8. Sierra Club modeled both allowable and actual emissions; IDEM modeled 2012-2014 

Continuous Emissions Monitoring Data (CEM) and a compliance emission limit on Units 

1 and 2 to characterize air quality for the area attainment designations. 

9. Sierra Club used the Clean Air Markets Database (CAMD) hourly emissions data which 

does not include the hourly varying stack temperatures and stack gas flow rates. IDEM 

used A.B. Brown's CEM data as supplied by the source. The varying stack parameter 

approach is considered more representative. 

10. Sierra Club did not address building downwash considerations. IDEM included building 

downwash in its modeling although actual stack heights were modeled. AERMOD no 

longer turns off downwash above the U.S. EPA formula height. Rather, the AERMOD 

code allows the Plume Rise Model Enhancement (PRIME) algorithms within the model 

to determine when and how to apply downwash. 

11. Sierra Club did not use fence line receptors. IDEM did use fence line receptors and 

also followed Appendix W, Section 7.2.2. Sufficient receptor detail was used for the grid 

to estimate the highest concentration and identify possible violations of the NAAQS. 

12. Sierra Club processed its own meteorology and made several assumptions concerning 

seasonal moisture conditions as average with winter months having continuous snow 

cover that differ from the U.S. EPA Region V approach on pages 7-9 of the document, 

"Regional Meteorological Data Processing Protocol EPA Region V and States". This 

approach recommends the AERSURFACE surface characteristics be adjusted based 

on the number of days with snow cover on the ground during the winter months and the 

Page 2 of7 
Bowen ratio adjustment based on soil moisture and precipitation data. This is the 

methodology IDEM uses to process all meteorological data. 

991

h Percentile 1-hour Daily Maximum Modeled 502 Concentration Comparison 

for A B Brown 

Modeled Concentration Facility Models 

with background 1-hour 502 NAAQ5 Attainment? 

Sierra Club 1,278.7 196.2 No 

IDEM 196.08 196.2 Yes 

Clifty Creek: 

1. Sierra Club used a background concentration of 47.1 1Jg/m3 (although listed as 41.7 

1Jg/m3 in the Section 2.2, paragraph 4) based on 2011-2013 monitoring data measured 

in Vanderburgh County. This monitor is located in southwest Indiana and is not the 

nearest S02 monitor to Clifty Creek, located in Jefferson County. IDEM used the New 

Albany, Floyd County S02 monitoring data from 2012-2014 as more representative data 

for southeastern Indiana as referenced in the "Updated Guidance for Area Designations 

for the 2010 Primary Sulfur Dioxide National Ambient Air Quality Standard". 

2. The Sierra Club methodology to determine the background concentrations did not 

account for double counting of sources through modeling and monitoring. 

3. IDEM used a temporally varying seasonal background dataset for each modeled source 

instead of an overall 1-hour S02 monitored value that Sierra Club used in their analysis. 

4. AERMOD version 14134 was used, not the latest available version of AERMOD 

(version 15181) that IDEM used to characterize air quality in the area. 

5. AERMET version 14134 was used, not the latest available version of AERMET (version 

15181) that IDEM used to process the surface and upper air meteorological data. 

6. Sierra Club modeled all flagpole receptor heights at 1.5 meters, IDEM used ground level 

receptor heights, consistent with U.S. EPA's "S02 NAAQS Designations Modeling 

Technical Assistance Document, Section 4.2" 

7. Sierra Club modeled both allowable and actual emissions; U.S. EPA guidance 

recommended actual emissions to characterize area attainment designations. It 

appears that Sierra Club used the actual hourly emissions before Clifty Creek installed 

and began operation of its Flue Gas Desulfurization (FGD) emission control unit in July 

of 2013. Based on the continuous emissions monitoring (GEM) data, both pre-control 

and post-control, there was a significant reduction in S02 emissions from Clifty Creek. 

IDEM modeled the post-control GEM data and showed maximum modeled 1-hour S02 

concentrations were well below the 1-hour S02 NAAQS. IDEM considers this emission 

dataset as representative of the area. 

8. Sierra Club used the Clean Air Markets Database (CAMD) hourly emissions data which 

does not include the hourly varying stack temperatures and stack gas flow rates. IDEM 

Page 3 of7 
used Clifty Creek's Continuous Emissions Monitoring Data (CEM) as supplied by the 

source. The varying stack parameter approach is considered more representative. 

9. Sierra Club did not address building downwash considerations. IDEM included building 

downwash in its modeling although actual stack heights were modeled. AERMOD no 

longer turns off downwash above the U.S. EPA formula height. Rather, the AERMOD 

code allows the Plume Rise Model Enhancement (PRIME) algorithms within the model 

to determine when and how to apply downwash. 

10.Sierra Club did not use fence line receptors. IDEM did use fence line receptors and 

also followed Appendix W, Section 7.2.2. Sufficient receptor detail was used for the grid 

to estimate the highest concentration and identify possible violations of the NAAQS. 

11. Sierra Club processed its own meteorology and made several assumptions concerning 

seasonal moisture conditions as average with winter months having continuous snow 

cover that differ from the U.S. EPA Region V approach on pages 7-9 of the document, 

"Regional Meteorological Data Processing Protocol EPA Region V and States". This 

approach recommends the AERSURFACE surface characteristics be adjusted based 

on the number of days with snow cover on the ground during the winter months and the 

Bowen ratio adjustment based on soil moisture and precipitation data. This is the 

methodology IDEM uses to process all meteorological data. 

ggth Percentile1-hour Daily Maximum Modeled 502 Concentration Comparison 

for Clifty Creek 

Modeled Concentration Facility Models 

with background 1-hour 502 NAAQS Attainment? 

Sierra Club 283.6 196.2 No 

IDEM 71.6 196.2 Yes 

Rockport: 

1. Sierra Club used a background concentration of 47.1 1Jg/m3 based on 2011-2013 

monitoring data. The 2011-2013 monitoring data does not match up with the 2012-2014 

monitoring data used by IDEM to characterize the air quality in each of the areas. 

2. The Sierra Club methodology for determining the background concentrations did not 

account for double counting of sources through modeling and monitoring. 

3. IDEM used a temporally varying seasonal background dataset for each modeled source 

instead of an overall 1-hour S02 monitored value that Sierra Club used in their analysis. 

4. AERMOD version 14134 was used, not the latest available version of AERMOD 

(version 15181) that IDEM used to characterize air quality in the area. 

5. AERMET version 14134 was used, not the latest available version of AERMET (version 

15181) that IDEM used to process the surface and upper air meteorological data. 

Page 4 of7 
6. Sierra Club modeled all flagpole receptor heights at 1.5 meters, IDEM used ground level 

receptor heights, consistent with U.S. EPA's "S02 NAAQS Designations Modeling 

Technical Assistance Document, Section 4.2" 

7. Sierra Club modeled both allowable and actual emissions; U.S. EPA guidance 

recommended actual emissions to characterize area attainment designations. 

8. Sierra Club used the Clean Air Markets Database (CAMD) hourly emissions data which 

does not include hourly varying stack temperatures and stack gas flow rates. IDEM 

used Rockport's Continuous Emissions Monitoring Data (CEM) as supplied by the 

source. The varying stack parameter approach is considered more representative. 

13. Sierra Club did not address downwash considerations. IDEM modeled building 

downwash as Rockport's actual stack heights were below Good Engineering Practice 

(GEP) as the cooling towers are the controlling structures. 

14. Sierra Club processed its own meteorology and made several assumptions concerning 

seasonal moisture conditions as average with winter months having continuous snow 

cover that differ from the U.S. EPA Region V approach on pages 7-9 of the document, 

"Regional Meteorological Data Processing Protocol EPA Region V and States". This 

approach recommends the AERSURFACE surface characteristics be adjusted based 

on the number of days with snow cover on the ground during the winter months and the 

Bowen ratio adjustment based on soil moisture and precipitation data. This is the 

methodology IDEM uses to process all meteorological data. 

991

h Percentile 1-hour Daily Maximum Modeled 802 Concentration Comparison 

for Rockport 

Modeled Concentration Facility Models 

with background 1-hour S02 NAAQS Attainment? 

Sierra Club 283.6 196.2 No 

IDEM 152.1 196.2 Yes 

Duke- Gibson: 

1. IDEM opted to demonstrate attainment of the 1-hour S02 NAAQS by monitoring; 

therefore air dispersion modeling was not used to demonstrate attainment, only to show 

the maximum modeled impacts from Duke-Gibson occur in close proximity of the two 

existing S02 monitors located north-northeast and northwest of the facility. 

2. Sierra Club included several sources in their source inventory that would be captured by 

the background concentrations measured at the Duke - Gibson S02 monitors. Sources 

were not included in any modeling IDEM conducted for Duke-Gibson. 

3. Sierra Club used a background concentration of 47.1 1Jg/m3 based on 2011-2013 

monitoring data taken from Evansville. There are source-specific S02 monitors with 

Page 5 of7 
more representative monitoring data for 2012-2014 used by IDEM to characterize the 

air quality in the area. 

4. The Sierra Club methodology to determine the background concentrations did not 

account for double counting of sources through modeling and monitoring. 

5. AERMOD version 14134 was used, not the latest available version of AERMOD 

(version 15181) that IDEM used to characterize air quality in the area. 

6. AERMET version 14134 was used, not the latest available version of AERMET (version 

15181) used to process the surface and upper air meteorological data for the other 

consent decree sources. 

7. Sierra Club modeled all flagpole receptor heights at 1.5 meters, IDEM used ground level 

receptor heights, consistent with U.S. EPA's "S02 NAAQS Designations Modeling 

Technical Assistance Document, Section 4.2" 

8. Sierra Club modeled both allowable and actual emissions; U.S. EPA guidance 

recommended modeling actual emissions to characterize area attainment designations 

and monitoring locations. 

9. Sierra Club used the Clean Air Markets Database (CAMD) hourly emissions data which 

does not include the hourly varying stack temperatures and stack gas flow rates. IDEM 

used Duke-Gibson's Continuous Emissions Monitoring Data (CEM) as supplied by the 

source. The varying stack parameter approach is considered more representative. 

1 O.IDEM included building downwash in its modeling. Sierra Club did not address building 

downwash considerations which affects the location of maximum modeled impacts. 

11. Sierra Club processed its own meteorology and made several assumptions concerning 

seasonal moisture conditions as average with winter months having continuous snow 

cover that differ from the U.S. EPA Region V approach on pages 7-9 of the document, 

"Regional Meteorological Data Processing Protocol EPA Region V and States". This 

approach recommends the AERSURFACE surface characteristics be adjusted based 

on the number of days with snow cover on the ground during the winter months and the 

Bowen ratio adjustment based on soil moisture and precipitation data. This is the 

methodology IDEM uses to process all meteorological data. 

In summary, based on the modeling information supplied by Sierra Club, IDEM feels each of 

the Sierra Club's recommendations for A.B. Brown Generating Station, Clifty Creek Station, 

Gibson Generating Station and Rockport Plant are based on several factors that are not 

consistent with U.S. EPA guidance germane to the attainment designation process: 

• Sierra Club used overly conservative emission estimates 

• Sierra Club used inappropriate background concentrations 

• Sierra Club overstated modeled impacts from sources within 50 kilometers 

• Sierra Club used outdated versions of U.S. EPA approved models 

Page 6 of7 
Therefore, IDEM recommends that the U.S. EPA disregard the modeling evaluations submitted 

by Sierra Club as misrepresenting the air quality characteristics of each area surrounding the 

sources mentioned in the consent decree. 

This is IDEM's review of the information provided by the Sierra Club for the 1-hour S02 

modeling for four of the five areas in Indiana mentioned in the U.S. District Court for the 

Northern District of California's enforceable order agreement. If there are questions or a need 

for clarification, please contact me at (317) 232-8222 or by e-mail at kbaugues@idem.IN.gov 

or Mark Derf- Section Chief, Technical Support and Modeling Section, Air Programs Branch 

at (317) 233-5682 or by e-mail at mderf@idem.IN.gov. 

Page 7 of7 

Sincerely, 

Keith Baugues 

Assistant Commissioner, 

Office of Air Quality