Additional Plant Scherer Dispersion Modeling for the SO2 NAAQS

February 2, 2016

GA EPD performed additional dispersion modeling to supplement the 1-hour SO2 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 Plant Scherer. A Cartesian receptor grid 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. Figure 1 

shows the new modeling domain and receptor locations.

Figure 1. Modeling domain and receptor locations for new Plant Scherer SO2 modeling.
Figure 2 contains the 4th highest modeled maximum 1-hour SO2 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 SO2 concentration averaged over 3-years using the surface characteristics at the facility 

site.

Figure 2. Plot of the 4th highest maximum daily 1-hour SO2 (ppb) averaged over 3 years using surface 

characteristics at the Macon NWS station.
Figure 3. Plot of the 4th highest maximum daily 1-hour SO2 (ppb) averaged over 3 years using surface 

roughness at the Plant Scherer facility site.

Table 1 contains the AERMOD modeling results (g/m3) 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 SO2 emissions from Plant Scherer do not cause or contribute to any 

violations of the 1-hour SO2 NAAQS.
Table 1. Summary of 1-hour SO2 NAAQS (g/m3

) analysis using the surface roughness at the Macon 

NWS station and the Plant Scherer facility site.

Surface 

Roughness

Location 

SO2 Model Design 

Concentration 

(g/m3)

SO2 Background 

Concentration 

(g/m3)

SO2 Total 

Concentration 

(g/m3)

SO2

NAAQS 

(g/m3)

Below SO2

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 SO2 NAAQS (ppb) analysis using the surface roughness at the Macon NWS 

station and the Plant Scherer facility site. 

Surface 

Roughness

Location 

SO2 Model Design 

Concentration 

(ppb)

SO2 Background 

Concentration 

(ppb)

SO2 Total 

Concentration 

(ppb)

SO2

NAAQS 

(ppb)

Below SO2

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 SO2 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, SO2 emissions from Plant 

Scherer do not cause or contribute to any violations of the 1-hour SO2 NAAQS in the following counties:

Monroe, Bibb, Jones, Jasper, Butts, Lamar, Upson, or Crawford. Therefore, Georgia EPD continues to 

recommend that the following counties be designed unclassifiable/attainment for the 2010 1-hour SO2

NAAQS:

 Monroe County,

 Bibb County,

 Jones County,

 Jasper County,

 Butts County,

 Lamar County,

 Upson County, and

 Crawford County.