UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

REGION 4

Technical Support Document

For

Georgia Rule (sss) Impact Analysis

EPA’s Notice of Proposed Rulemaking For:

Air Plan Approval and Air Quality Designation; GA; Redesignation of the Atlanta, 

GA, 1997 Annual Fine Particulate Matter Nonattainment Area to Attainment

November 2015
A. BACKGROUND

The Atlanta Area attained the 1997 Annual PM2.5 NAAQS in 2009. Data substitution resulted in 

maximum design value estimates of 14.2 μg/m3and 13.6 μg/m3for the 3-year periods 2007-2009 

and 2008-2010, respectively. See 76 FR 56701, September 14, 2011. Rule (sss) required a 

phase-in of flue gas desulfurization (FGD) controls that started achieving SO2 emission 

reductions from electric generating units (EGUs) in 2009. However, this state rule has not been 

approved into Georgia’s SIP. Therefore, in January 2015, GA EPD provided Region 4 with an 

analysis to show that the emission reductions achieved by the rule were not necessary for the 

Area to achieve attainment. In this analysis, Georgia focused on the impact of SO2 reductions 

because in previous analyses they have been determined to be the dominant contributor to PM2.5 

secondary formation in the Southeast, including the Atlanta Area. The State determined that the 

maximum impact of all SO2 controls installed by 2010 on EGUs subject to Rule (sss) was a 

reduction in the Atlanta Area DV of 0.6 μg/m3. Thus, for the period 2008-2010, the maximum 

DV without Rule (sss) reductions is estimated to be 14.2 μg/m3. For the period 2007-2009, the 

maximum impact of the Rule (sss) reductions would be less than 0.6 μg/m3since most of the 

relevant controls did not start achieving emission reductions until 2009.

B. CAA REQUIREMENT

For redesignating a nonattainment area to attainment, the CAA requires EPA to determine that 

the air quality improvement in the area is due to permanent and enforceable reductions in 

emissions resulting from implementation of the SIP and applicable Federal air pollution control 

regulations and other permanent and enforceable reductions (CAA section 107(d)(3)(E)(iii)). 

C. EPA’S ANALYSIS OF GA EPD’S SUBMITTAL

FGD controls installed by 2010

Because GA EPD performed their impact analysis based upon the period 2008-2010, the State 

looked at the four power plants in the Atlanta Area that had FGD controls installed by the end of 

2009 and thus in operation for the entire year 2010. Plant Bowen had FGD installed on Units 3 

and 4 by December 31, 2008, and on Unit 2 by June 1, 2009. Plant Hammond had FGD installed 

on Units 1-4 by December 31, 2008. Plant Wansley had FGD installed on Unit 1 by December 

31, 2008, and Unit 2 by December 31, 2009. Plant Yates had FGD installed on Unit 1 by 

December 31, 2008. These are summarized in Table 1 below.
Table 1. EGUs included in the State’s Rule (sss) sensitivity analysis (i.e., EGUs with FGD 

installed by the end of 2009)

Plant Units Control

Measure

Date Control

Measure Was 

Required by GA 

Rule (sss)

Date Control 

Measure 

Began 

Operation

Annual 

Average SO2

Reductions 

Achieved 2008-

2010 (tpy)

Bowen 3, 4; 2 FGD 12/31/08; 6/1/09 10/1/08; 4/1/09 119,247

Hammond 1, 2, 3, 4 FGD 12/31/08 4/1/08 27,872

Wansley 1; 2 FGD 12/31/08; 

12/31/09

10/1/08; 4/1/09 53,573

Yates 1 FGD 12/31/08 10/1/99 5,157

SO2 Emission Reductions Achieved

To estimate the impact of the above FGD emission controls, GA EPD first determined the 

average annual SO2 reductions that were obtained from those controls during 2008-2010 (shown 

in Table 1 above). To do this, GA EPD determined the average tons per year of SO2 emitted per 

megawatt of power generated at each facility, using the years 2003-2007 to establish a baseline. 

GA EPD multiplied this factor by the actual annual power produced during the years 2008, 2009 

and 2010 to estimate plant-wide “uncontrolled” SO2 emissions during those years. GA EPD then 

subtracted the actual plant-wide SO2 emissions each year from the uncontrolled number to obtain 

the tons per year of SO2 reduced at each plant. (See Appendix 1 for detailed calculations.) 

Sensitivity of Monitors to Plant SO2 Emissions

To be able determine the impact of the SO2 emission reductions (shown in Table 1) on the PM2.5

concentrations measured by the monitors in the Atlanta Area, GA EPD needed to determine the 

sensitivity of each ambient monitor to the reductions in SO2 emissions from each plant. The 

sensitivity would show, for each monitor, the expected annual reduction in PM2.5 concentration 

per quantity of SO2 emissions reduced at each plant.

GA EPD used the results of existing VISTAS photochemical grid modeling1to determine the 

sensitivity of PM2.5 concentrations in the Atlanta Area to the reductions in SO2 emissions due to 

the installation and operation of scrubbers at three large coal-fired power plants in Georgia 

(Bowen Units 1 and 2, Wansley Unit 2, and Yates Units 2-7), as shown in Table 2 below (the 

 

1 The sensitivity analysis was based on the Visibility Improvement State and Tribal Association of the Southeast 

(VISTAS) modeling, using the base-year emission inventory for 2002 and the projected 2009 “future year” 

emissions inventory, and CMAQ version 4.5 with the CB-IV chemical mechanism. The methodology and 

procedures used in the CMAQ modeling and calculation of PM2.5 concentrations followed the recommendations in 

EPA’s modeling guidance (EPA, Guidance on the Use of Models and Other Analyses for Demonstrating Attainment 

of Air Quality Goals for Ozone, PM2.5, and Regional Haze, EPA-454/B-07-002, April 2007). 
“existing sensitivity analysis”2

). Modeling for these units was used because it had already been 

performed and, therefore, no additional modeling was necessary. 

Table 2. Power plants for which earlier sensitivity analysis was performed (to evaluate 

EGU control strategies to be implemented in 2009 and later)

Plant Units Control

Measure

Date Control

Measure Was 

Required by GA 

Rule (sss)

Date Control 

Measure Began 

Operation

Bowen 2; 1 FGD 6/1/09; 6/1/10 4/1/09; 3/1/10

Wansley 2 FGD 12/31/09 4/1/09

Yates 2, 3, 4, 5 6, 

7

Conversion to 

natural gas

4/16/15 5/1/99

The State then used the results of existing previous sensitivity analysis to calculate the 

“normalized sensitivity” values for the SO2 emissions reductions from Rule (sss) controls 

installed prior to 2010 for each facility (see Table 1 for a list of these controls, Appendix 2 for 

calculations, and Table 3 for the normalized sensitivity values). The normalized sensitivity 

values represent the impact on annual PM2.5 concentrations due to the amount of modeled SO2

emissions reductions from each facility. This analysis assumes that the EGUs included in the 

earlier sensitivity analysis (i.e., Table 2 units) are representative of the EGUs that had controls 

installed prior to 2010 (i.e., Table 1 units).3 These normalized sensitivity values were then used 

by GA EPD to calculate estimate the amount that the annual PM2.5 concentration would increase 

in the Atlanta Area without if Rule (sss) SO2 controls were not in place.4

Table 3. Normalized sensitivities to SO2 controls at each plant

Normalized Sensitivity (ng/m3/TPD)

Plant Bowen 0.973

Plant Hammond 0.973

Plant Wansley 0.947

Plant Yates 1.308

Impact of Reductions on DV

 

2 This sensitivity analysis had been done for the 2010 PM2.5 Attainment demonstration for the Atlanta Area.

3 All four units at Plant Hammond had controls installed prior to 2009, so they were not included in the earlier 

sensitivity analysis. In its current analysis, GA EPD conservatively used the normalized sensitivity value from Plant 

Bowen to calculate the potential impact from Plant Hammond emissions. Substituting the sensitivity of Plant Bowen 

for Plant Hammond is conservative because Plant Hammond is located farther away from all the Atlanta monitors 

than Plant Bowen and is located in the same general direction from the ambient monitors as Plant Bowen.
The maximum impact on annual PM2.5 concentrations at each Atlanta PM2.5 monitor due to SO2

emission reductions that can be attributed to Rule (sss) controls installed prior to 2010 at Plant 

Bowen, Plant Hammond, Plant Wansley, and Plant Yates is calculated as shown in Table 4 

below. 

Table 4. Annual PM2.5 impact on Atlanta monitors from SO2 controls on Plant Hammond, 

Plant Bowen, Plant Wansley, and Plant Yates in 2008-2010

SO2 Emission

Reductions 

(TPY)

SO2 Emission

Reductions 

(TPD)

Normalized 

Sensitivity

(ng/m3/TPD)

Annual PM2.5

Impact 

(g/m3)

Plant Bowen 119,246.70 326.70 0.973 0.318

Plant Hammond 27,872.21 76.36 0.973 0.074

Plant Wansley 53,573.25 146.78 0.947 0.139

Plant Yates 5,156.60 14.13 1.308 0.018

TOTAL 0.550 

The maximum total impact on the PM2.5 annual measurements at the Atlanta Area PM2.5

monitors from the application of SO2 controls from Georgia’s Rule (sss) is 0.6 g/m3(rounded 

up from 0.550 g/m3). If this this quantity is added to the measured 2008-2010 annual PM2.5

design value (13.6 g/m3), the result would be a design value of 14.2 g/m3, well below the 1997 

annual PM2.5 NAAQS of 15.0 g/m3. Therefore, removal of these controls would not have 

resulted in a 2008-2010 annual PM2.5 design value over the 1997 annual PM2.5 NAAQS.

D. CONCLUSIONS AND RECOMMENDED AGENCY ACTION

The sensitivity analysis performed by GA EPD conservatively estimates that the maximum 

potential impact of measures required by Georgia Rule (sss) by 2010 was to reduce the Area 

design value by 0.55 μg/m3. Thus, with a measured 2010 design value of 13.6 g/m3, the design 

value without the Georgia Rule (sss) measures in place would have been 14.2 g/m3. On the 

basis of this review, EPA has concluded that the Atlanta Area would have attained the 1997 

annual PM2.5 NAAQS of 15.0 μg/m3 by the same time that it did even if there had been no 

emission reductions achieved from the State’s Rule (sss). Therefore, EPA recommends that lack 

of federal approval of Georgia Rule (sss) have no impact on the determination of whether the air 

quality improvement in the Atlanta Area is due to permanent and enforceable reductions in 

emissions resulting from implementation of the federally SIP and applicable federal air pollution 

control regulations as described in the Federal Register notice of proposed rulemaking.
Appendix 1 – Calculations of SO2 Emission Reductions Achieved through 2010 by Rule (sss)

Plant Hammond, Controlled SO2 emissions from in 2008 - 2010

2003 2004 2005 2006 2007 2008* 2009* 2010*

Actual SO2 Emissions (tpy) 35,900 37,700 39,500 40,600 47,800 12,500 900 2,427

Annual Power Generation (MW) 4.79 4.11 4.64 4.27 5.09 4.32 3.73 3.23

Annual SO2/Gen 7,495 9,173 8,513 9,508 9,391 2,894 241 751

AVG SO2/gen, 2003-2007 8,816

Uncontrolled SO2 Emissions 38,085 32,883 28,475

Controlled SO2 Emissions 25,585 31,983 26,048

Avg Controlled SO2 Emissions, 2008-2010 27,872

Plant Bowen, Controlled SO2 emissions from in 2008 - 2010

2003 2004 2005 2006 2007 2008* 2009* 2010*

Actual SO2 Emissions (tpy) 164,900 165,900 186,500 206,400 196,800 148,100 54,800 7,618

Annual Power Generation (MW) 21.9 21.9 23.3 23.7 24 23.4 22.9 24.7

Annual SO2/Gen 7,530 7,575 8,004 8,709 8,200 6,329 2,393 308

AVG SO2/gen, 2003-2007 8,004

Uncontrolled SO2 Emissions 187,285 183,283 197,690

Controlled SO2 Emissions 39,185 128,483 190,072

Avg Controlled SO2 Emissions, 2008-2010 119,247

Plant Wansley**, Controlled SO2 emissions in 2008 - 2010

2003 2004 2005 2006 2007 2008* 2009* 2010*

Actual SO2 Emissions (tpy) 94,000 99,000 101,500 96200 93,900 74,300 7400 2,343

Annual Power Generation (MW) 13.7 14 15.1 14.8 16.1 15.5 11.8 9.8

Annual SO2/Gen 6,861 7,071 6,722 6,500 5,832 4,794 627 239

AVG SO2/gen, 2003-2007 6,597

Uncontrolled SO2 Emissions 102,259 77,849 64,654

Controlled SO2 Emissions 27,959 70,449 62,311

Avg Controlled SO2 Emissions, 2008-2010 53,573

Plant Yates (Unit 1), Controlled SO2 emissions in 2008 - 2010

2003 2004 2005 2006 2007 2008* 2009* 2010*

Actual SO2 Emissions (tpy) 352 175.9 286

Uncontrolled SO2 Emissions 7,040 3,518 5,726

Controlled SO2 Emissions 6,688 3,342 5,440

Avg Controlled SO2 Emissions, 2008-2010 5,157

Source: EPA Clean Air Markets Division

* SO2 control, required by Georgia Rule (sss), was operational on one or more EGUs for partial or full year.

** Does not include emissions from facility’s gas-fired units.
Appendix 2 – Summary of sensitivity analysis results for SO2 emission controls.

5

Plant Bowen and Plan Hammond6

Site Name

TPD 

reduction7

Annual Reduction in 

PM2.5 (g/m3)

Normalized annual 

reduction in PM2.5

(ng/m3/TPD)8

Doraville (13-089-2001) 217.72 0.1682 0.772

E. Rivers School (13-121-0032) 217.72 0.1564 0.718

Fire Station No. 8 (13-121-0039) 217.72 0.1553 0.713

Forest Park-Georgia DOT (13-063-0091) 217.72 0.1417 0.651

Gainesville-Fair Street School (13-139-0003) 217.72 0.1692 0.777

Gwinnett Tech (13-135-0002) 217.72 0.1717 0.788

Kennesaw-National Guard (13-067-0003) 217.72 0.2117 0.973

South DeKalb (13-089-0002) 217.72 0.1411 0.648

Yorkville (13-223-0003) 217.72 0.1549 0.711

Plant Wansley

Site Name

TPD 

reduction

Annual Reduction1in 

PM2.5 (g/m3)

Normalized annual 

reduction in PM2.5

(ng/m3/TPD)

Doraville (13-089-2001) 103.88 0.0858 0.826

E. Rivers School (13-121-0032) 103.88 0.0902 0.868

Fire Station No. 8 (13-121-0039) 103.88 0.0906 0.872

Forest Park-Georgia DOT (13-063-0091) 103.88 0.0976 0.940

Gainesville-Fair Street School (13-139-0003) 103.88 0.0612 0.589

Gwinnett Tech (13-135-0002) 103.88 0.0714 0.687

Kennesaw-National Guard (13-067-0003) 103.88 0.0839 0.807

South DeKalb (13-089-0002) 103.88 0.0928 0.893

Yorkville (13-223-0003) 103.88 0.0983 0.947

Plant Yates

Site Name

TPD 

reduction

Annual Reduction1in 

PM2.5 (g/m3)

Normalized annual 

reduction in PM2.5

(ng/m3/TPD)

Doraville (13-089-2001) 137.20 0.1530 1.115

E. Rivers School (13-121-0032) 137.20 0.1673 1.220

Fire Station No. 8 (13-121-0039) 137.20 0.1680 1.224

 

5 Scaled relative to the observed speciated 5-year concentrations (weighted for 2000-2004).

6 GA EPD did not include Plant Hammond in its earlier sensitivity analysis because all four units were already required to 

have scrubbers installed by December 31, 2008. Since Plant Hammond is located farther away, but in the same general 

direction, from all the Atlanta monitors than Plant Bowen, a conservative approach is to use the Plant Bowen SO2 normalized 

sensitivities (from the Kennesaw-National Guard monitor) to represent the impact from Plant Hammond at all the Atlanta 

monitors.

7 The “Tons Per Day (TPD) Reduction” values represent the reduction of SO2 emissions compared to pre-controlled 

emissions (assuming a 95% control efficiency for the scrubbers). The values were actually calculated from the 2009 

projected emissions inventory used in the VISTAS modeling. The 2009 projected emissions for each unit modeled in the 

sensitivity analysis were reduced by 95% to arrive at the “TPD reduction” values presented in the table.

8 The normalized sensitivity value in the last column in Appendix 2 is calculated by dividing the values in the “Annual 

Reduction in PM2.5” column by the values in the “TPD reduction” column.
Forest Park-Georgia DOT (13-063-0091) 137.20 0.1795 1.308

Gainesville-Fair Street School (13-139-0003) 137.20 0.0988 0.720

Gwinnett Tech (13-135-0002) 137.20 0.1207 0.880

Kennesaw-National Guard (13-067-0003) 137.20 0.1589 1.158

South DeKalb (13-089-0002) 137.20 0.1641 1.196

Yorkville (13-223-0003) 137.20 0.1579 1.151

Map of Plants Bowen, Hammond, Wansley and Yates relative to the ten Atlanta PM2.5

monitors.