INDIANA DEPARTMENT OF ENVIRONMENTAL MANAGEMENT We ProtectHoosiers andOurEnvironment.

Michael R. Pence Govemor

Mr. John Mooney Chief, Air Programs Branch 100 N. SenateAvenue • Indianapolis, IN 46204 (800) 451-6027 • (317) 232-8603 • www.idem.IN.gov

November 13, 2015

U. S. Environmental Protection Agency 77 WestJackson Boulevard Chicago, IL 60604-3590 Carol S. Comer Commissioner

Re: Indiana's Review ofSierra Club's Comments on Indiana's 1-Hour S02 Consent Decree' Recommendations

Dear Mr. Mooney:

On March 2, 2015, the U.S. District Courtfor the Northern District ofCalifornia 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 deadlinefor completing air quality designations underthe 2010 Sulfur Dioxide National AmbientAir Quality Standards (NAAQS) forthe remainder ofthe country. The court's orderdirected U.S. EPAto 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 forfive Indiana sources identified in the court's order by the September 181 h, 2015 deadlineforthe first round ofdesignations.

In response to your October20, 2015 letter requesting Indiana's review ofSierra Club's modeling information provided for attainment recommendations underthe 2010 Sulfur Dioxide NAAQS, the Indiana Department of Environmental Management- Office ofAir Quality (IDEMOAQ) is providing the following comments. There were four sources (ofthe 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 ifthose sources' modeled impacts warranted inclusion in theA.B. Brown

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## ®RecycledPapermodeling. Modeling results showed no appreciable impactsfrom several ofthe
sources. IDEM included two ofthe inventory sources thatwere found to have potential significant concentration gradients in its modeling. 2. Sierra Club used a background concentration of47.1 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 GuidanceforArea Designations forthe 2010 Primary Sulfur Dioxide National AmbientAir Quality Standard". 3. The Sierra Club methodology for determining the background concentrations did not account for double counting ofsources through modeling and monitoring. 4. IDEM used a temporally varying seasonal background datasetfor each modeled source instead ofan overall1-hour S02 monitored value that Sierra Club used in their analysis. 5. AERMOD version 14134was used, notthe latest available version ofAERMOD (version 15181)that IDEM used to model impacts to characterize airquality in the area. 6. AERMETversion 14134was used, notthe latest available version ofAERMET (version 15181) that IDEM used to process the surface and upperair meteorological data. 7. Sierra Club modeled all flagpole receptor heights at 1.5 meters, IDEM used ground level receptor heights, consistentwith 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 forthe area attainmentdesignations. 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 notaddress building downwash considerations. IDEM included building downwash in its modeling although actual stack heights were modeled. AERMOD no longerturns offdownwash above the U.S. EPAformula height. Rather, the AERMOD code allows the Plume Rise Model Enhancement (PRIME) algorithms within the model to determine when and howto apply downwash. 11.Sierra Club did not use fence line receptors. IDEM did use fence line receptors and also followed AppendixW, Section 7.2.2. Sufficient receptor detail was used for the grid to estimate the highest concentration and identify possible violations ofthe NAAQS. 12.Sierra Club processed its own meteorology and made several assumptions concerning seasonal moisture conditions as average with winter months having continuous snow coverthat differfrom the U.S. EPA Region V approach on pages 7-9 ofthe document, "Regional Meteorological Data Processing Protocol EPA Region V and States". This approach recommends the AERSURFACE surface characteristics be adjusted based
on the numberofdays with snow cover on the ground during the winter months and the



### Page 2of7Bowen ratio adjustment based on soil moisture and precipitation data. This is the methodology IDEM usesto process all meteorological data.

991h 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 of47.1 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 notthe nearest S02monitorto Clifty Creek, located in Jefferson County. IDEM used the New Albany, Floyd County S02monitoring datafrom 2012-2014 as more representative data for southeastern Indiana as referenced in the "Updated GuidanceforArea Designations forthe 2010 Primary Sulfur Dioxide National AmbientAir Quality Standard". 2. The Sierra Club methodologyto determinethe background concentrations did not account for double counting ofsources through modeling and monitoring. 3. IDEM used a temporally varying seasonal background datasetfor each modeled source instead ofan overall 1-hourS02 monitored value that Sierra Club used in their analysis. 4. AERMOD version 14134was used, notthe latest availableversion ofAERMOD (version 15181)that IDEM used to characterize airquality in the area. 5. AERMETversion 14134 was used, notthe latest available version ofAERMET (version 15181) that IDEM used to process the surface and upperair meteorological data. 6. Sierra Club modeled all flagpole receptor heights at 1.5 meters, IDEM used ground level receptor heights, consistentwith 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 appearsthat 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 of2013. Based on the continuous emissions monitoring (GEM) data, both pre-control and post-control, there was a significant reduction in S02emissionsfrom Clifty Creek. IDEM modeled the post-control GEM data and showed maximum modeled 1-hour S02 concentrations were well belowthe 1-hourS02 NAAQS. IDEM considers this emission dataset as representative ofthe area. 8. Sierra Club used the Clean Air Markets Database (CAMD) hourly emissions datawhich does not includethe hourlyvarying stacktemperatures and stack gas flow rates. IDEM



### Page 3of7used Clifty Creek's Continuous Emissions Monitoring Data (CEM) as supplied bythe
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 offdownwash above the U.S. EPAformula height. Rather, the AERMOD code allows the Plume Rise Model Enhancement (PRIME) algorithms within the model to determine when and howto apply downwash. 10.Sierra Club did not use fence line receptors. IDEM did use fence line receptors and also followed AppendixW, Section 7.2.2. Sufficient receptor detail was used forthe grid to estimate the highest concentration and identify possible violations ofthe NAAQS. 11.Sierra Club processed its own meteorology and made several assumptions concerning seasonal moisture conditions as average with winter months having continuous snow coverthat differfrom the U.S. EPA Region V approach on pages 7-9 ofthe document, "Regional Meteorological Data Processing Protocol EPA Region V and States". This approach recommends theAERSURFACE surface characteristics be adjusted based
on the number ofdays 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-hour502 NAAQS Attainment? Sierra Club 283.6 196.2 No IDEM 71.6 196.2 Yes

Rockport:

1. Sierra Club used a background concentration of47.1 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 ofthe areas. 2. The Sierra Club methodologyfor determining the background concentrations did not accountfor double counting ofsources through modeling and monitoring. 3. IDEM used a temporally varying seasonal background datasetfor each modeled source instead ofan overall 1-hourS02 monitored value that Sierra Club used in theiranalysis. 4. AERMOD version 14134 was used, not the latest available version ofAERMOD (version 15181)that IDEM used to characterize air quality in the area. 5. AERMETversion 14134was used, notthe latest available version ofAERMET (version 15181) that IDEM used to process the surface and upper air meteorological data.



### Page 4of76. Sierra Club modeled all flagpole receptor heights at 1.5 meters, IDEM used ground level receptor heights, consistentwith U.S. EPA's "S02NAAQS 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 stacktemperatures and stack gasflow 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 coverthat differfrom the U.S. EPA Region V approach on pages 7-9 ofthe document, "Regional Meteorological Data Processing Protocol EPA Region V and States". This approach recommends theAERSURFACE surface characteristics be adjusted based
on the numberofdays 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.

991h Percentile 1-hour Daily Maximum Modeled 802 Concentration Comparison for Rockport Modeled Concentration Facility Models with background 1-hourS02 NAAQS Attainment? Sierra Club 283.6 196.2 No IDEM 152.1 196.2 Yes

Duke- Gibson:

1. IDEM opted to demonstrate attainment ofthe 1-hourS02NAAQS by monitoring; therefore airdispersion modeling was not used to demonstrate attainment, only to show the maximum modeled impacts from Duke-Gibson occur in close proximity ofthe two existing S02 monitors located north-northeast and northwest ofthe facility. 2. Sierra Club included several sources in their source inventorythatwould 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 of47.1 1Jg/m3 based on 2011-2013 monitoring data taken from Evansville. There are source-specific S02monitors with



### Page 5of7more representative monitoring data for 

### 2012-2014 used by IDEM to characterize the air quality in the area. 4. The Sierra Club methodologyto determinethe background concentrations did not accountfor double counting ofsources through modeling and monitoring. 

### 5. AERMOD version 

### 14134was used, not the latest available version ofAERMOD (version 

### 15181) that IDEM used to characterize air quality in the area. 6. AERMETversion 

### 14134 was used, not the latest available version ofAERMET (version 

### 15181) used to process the surface and upperair meteorological data forthe other consent decree sources. 7. Sierra Club modeled all flagpole receptor heights at 

### 1.5 meters, IDEM used ground level receptor heights, consistentwith 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 hourlyvarying 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 parameterapproach is considered more representative. 1O.IDEM included building downwash in its modeling. Sierra Club did not address building downwash considerations which affects the location ofmaximum 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 coverthat differfrom the U.S. EPA Region V approach on pages 7-9 ofthe document, "Regional Meteorological Data Processing Protocol EPA Region V and States". This approach recommends theAERSURFACE 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 forA.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 germaneto 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 6of7Therefore, IDEM recommends thatthe U.S. EPA disregard the modeling evaluations submitted by Sierra Club as misrepresenting the airquality characteristics ofeach area surrounding the sources mentioned in the consent decree.

This is IDEM's review ofthe information provided bythe Sierra Club forthe 1-hourS02 modeling forfour ofthe five areas in Indiana mentioned in the U.S. District Court forthe Northern District of California's enforceable order agreement. Ifthere are questions or a need for clarification, please contact me at (317) 232-8222 or bye-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 7of7 Sincerely,

Keith Baugues Assistant Commissioner, Office ofAir Quality