Oklahoma department of environmental quality

G-P added background concentrations of SO₂ to the modeling results. As summarized in Table D-29, when adding the background concentrations, the 3-hour, 24-hour, and annual concentrations are less than the respective NAAQS. Therefore, G-P has demonstrated that the Mill-wide emissions will not cause or contribute to a violation of the NAAQS.

Particulate Matter – PM₁₀

The analysis predicted exceedances of the 24-hour NAAQS for PM₁₀ on a single receptor on the American Foundry Group property when modeling all sources, including the American Foundry Group source, Model ID 13673. The placement of receptors was automatically set by a Cartesian grid and included one receptor within a short distance of the modeled emission source. G-P further analyzed for NAAQS by using two analyses. The first analysis includes all sources and excludes the one receptor on American Foundry Group property. The second analysis includes all receptors and excludes model source 13673. Table D-30 presents the results of these analyses.

(b) Impacts off the American Foundry Group Property only exclude receptor (291600, 3956300) [ISC file PMAQS*_1]

G-P added background concentrations to the modeling results. Table D-31 summarizes the total concentrations for both analyses. With these two sets of data, the analysis predicted that the NAAQS would not be exceeded. Further, the modeling output files for the significant impact analysis of PM₁₀ demonstrate that the project emissions will not cause any significant impact near the American Foundry Group property.

Table D-31	Concentrations in μg/m3
Averaging Period	Annual	24-Hour High 6th High
Maximum Predicted Impact	12.54	42
Background Concentration	23.2	72
Total Concentration	35.74	114.40
NAAQS	50	150

By modeling the increment-affecting emissions from the Mill and competing source, G-P determined that the maximum annual mean NO₂ increment predicted impact is 14.3 μg/m³. The maximum impact location is in an area that did not require additional refined receptor grids. Table D-32 summarizes the NO₂ model results. This impact is less than the allowable increment of 25 g/m³. Therefore, G-P has demonstrated that the Mill emissions will not cause or contribute to a violation of the PSD Class II Increment.

Sulfur Dioxide

Particulate Matter – PM₁₀

PSD review rules require that controls required for emission sources using the Best Available Control Technology Analysis (see Attachment E) cannot be affected by a stack height that exceeds Good Engineering Practice (GEP) or any other dispersion technique. In other words, emission rates specified in a source impact analysis must demonstrate compliance with stack heights at or below GEP, even if the physical height of the stack is greater. On July 8, 1985, EPA defined GEP stack height in the final stack height regulations (see 40 CFR 51.100(hh)). GEP stack height is defined as the greater of the following.

(2) (i) For stacks in existence on January 12, 1979, and for which the owner or operator had obtained all applicable permits or approvals required under 40 CFR parts 51 and 52, Hg = 2.5H, provided the owner or operator produces evidence that this equation was actually relied on in establishing an emission limitation, where

Hg = good engineering practice stack height, measured from the ground-level elevation at the base of the stack, and

H = height of nearby structure(s) measured from the ground-level elevation at the base of the stack.

(ii) For all other stacks, Hg = H + 1.5L, where

L = lesser dimension, height or projected width, of nearby structure(s) provided that the EPA, State or local control agency may require the use of a field study or fluid model to verify GEP stack height for the source.

(3) The height demonstrated by a fluid model or a field study approved by the EPA, State or local control agency, which ensures that the emissions from a stack do not result in excessive concentrations of any air pollutant as a result of atmospheric downwash, wakes, or eddy effects created by the source itself, nearby structures or nearby terrain features. “Nearby” is defined as a distance up to five times the lesser of the height or projected width dimensions of a structure or terrain feature but not greater than 0.8 kilometer (km).
The proposed project includes one new stack: Model ID PPRTO. To determine if the stack meets GEP regulations, G-P assembled stack height and building information from the source impact analysis.
D.3.2 GEP CALCULATIONS

Table D-35 presents a summary of stack construction date and computed GEP value for the proposed source modeled at the Mill. For this stack, the applicable GEP equation is GEP = (Height of structure) + 1.5  (Lesser of structure height or width).

The proposed stack height is 20.7 m. This value is less than the computed GEP height; therefore, the proposed stack at its physical height complies with GEP regulations.