## Additional Plant Scherer Dispersion Modeling for the SO 2 

## NAAQS February 2, 201 6

GA EPD performed additional dispersion modeling to supplement the 1

- hour SO 2 NAAQS modeling that was originally submitted to EPA on September 17, 2015 and supplemented on November 24, 2015. The new modeling used the identical model set

- up and emissions as the original modeling but expanded the modeling domain from 20 km to 50 km from Pl ant Scherer

. A Cartesian receptor g rid was used with discrete receptors placed according to the following configuration based on the center of the plant:

 0 km

- 2km  100 meters apart

 2 km

- 3 km  250 meters apart

 3 km

- 10 km  500 meters apart

 10 km

- 50 km  1,000 meters apart

This domain is sufficient to capture the maximum impact. All receptor locations are represented in the
Universal Transverse Mercator (UTM) projections, Zone 17, North American Datum 1983. Fig ure 1
shows the new modeling domain and receptor location s.

Figure 1. Modeling domain and receptor location s for new Plant Scherer SO 2 modeling.Figure 2 contains the 4th highest modeled maximum 1

- hour SO 2 concentration averaged over 3 years

using the surface characteristics at the Macon NWS station. The maximum value was located at approximately 4.4 kilometers southwest of Plant Scherer. Figure 3 contains the 4th highest modeled
maximum 1

- hour SO 2 concen tration averaged over 3

- years using the surface characteristics at the facility
site.

Figure 2. Plot of the 4th highest maximum daily 1

- hour SO 2 (ppb) averaged over 3 years using surface
characteristics at the Macon NWS station.Figure 3. Plot of th e 4th highest maximum daily 1

- hour SO 2 (ppb) averaged over 3 years using surface

roughness at the Plant Scherer facility site.

Table 1 contains the AERMOD modeling results (  g/m 3 ) using the surface characteristics at the Macon
NWS station and the Plant Scherer facility site. Table 2 contains the AERMOD modeling results (ppb) using the surface characteristics at the Macon NWS station and the Plant Scherer facility site. The results
from both model runs indicate that SO 2 emissions from Plant Scherer do n ot cause or contribute to any
violations of the 1

- hour SO 2 NAAQS.Table 1. Summary of 1

- hour SO 2 NAAQS (  g/m 3 ) analysis using the surface roughness at the Macon

NWS station and the Plant Scherer facility site.

Surface Roughness Location SO 2 Model Design

Concentration (  g/m 3 ) SO 2 Background

Concentration (  g/m 3 ) SO 2 Total

Concentration (  g/m 3 ) SO 2

NAAQS (  g/m 3 ) Below SO 2

NAAQS (Y/N)

Macon NWS Station 98.21 30.3 128.51 196 Y
Facility Site 94.66 30.3 124.97 196 Y

Table 2. Summary of 1

- hour SO 2 NAAQS (ppb) analysis using the surface roughness at the Macon NWS station and the Plant Scherer facility site.

Surface Roughness Location SO 2 Model Design

Concentration (ppb) SO 2 Background

Concentration (ppb) SO 2 Total

Concentration (ppb) SO 2

NAAQS (ppb) Below SO 2

NAAQS (Y/N)

Macon NWS Station 37.5 11.6 49.10 75 Y
Facility Site 36.1 11.6 47.73 75 Y

The original Plant Scherer dispersion modeling for the 1

- hour SO 2 NAAQS designations has been supplemented by additional modeling that expanded the modeling domain from 20 km to 50 km from Plant Scherer

. Based on the original and the supplemental modeling analysis, SO 2 emissions from Plant Scherer do not cause or contribute to any violations of the 1

- hour SO 2 NAAQS in the following counties : Monroe, Bibb, Jones, Jasper, Butts, Lamar, Upson , or Crawford

. Therefore, Georgia EPD continues to recommend that the following c ounties be designed unclassifiable/attainment for the 2010 1

- hour SO 2 NAAQS:

 Monroe County

,

 Bibb County

,

 Jones County

,

 Jasper County

,

 Butts County

,

 Lamar County

,

 Upson County , and

 Crawford County

.