AQ_F_1900138_20221216_MOD_ModRvw_pdf

DIVISION OF AIR QUALITY
December 16, 2022
MEMORANDUM
TO: Emily Supple, Environmental Engineer, RCO
Dena Pittman Permit Coordinator, RRO
FROM: Nancy Jone eteorologist, Air Quality Analysis Branch(AQAB)
THROUGH: Tom Anderso , Supervisor, AQAB
7-4
SUBJECT: Review of Toxics Air Dispersion Modeling for Wolfspeed, Inc.
Siler City, Chatham County, North Carolina Facility No. 1900138
1 have reviewed the dispersion modeling analysis, received November 8, 2022, for Wolfspeed
located in Siler City, Chatham County, North Carolina. The modeling was conducted to
accompany a greenfield permit application to construct and operate a silicon carbide substrate
production facility. This action triggers modeling requirements to evaluate those toxics whose
rates are expected to exceed the levels outlined in 15A NCAC 2Q .0700. The modeling
adequately demonstrates compliance, on a source-by-source basis, for all toxics modeled.
Three air toxics, hydrogen chloride, hydrogen fluoride and sulfuric acid, were evaluated facility
wide in the modeling. AERMOD (21112) was used with five years(2013-2017) of
meteorological surface data from Chapel Hill and upper air data from Greensboro. Direction-
specific building dimensions, determined using EPA's BPIP-Prime program (04274), were used
as input to the model for building wake effect determination. Receptors were spaced at 50-meter
intervals along the fenceline and at 100-meter intervals out to a distance of 1 km. Source inputs
and emission rates used in the modeling analysis are attached.
Maximum Impacts —Wolfspeed
Siler City, Chatham County, NC
TAP Averaging Max. Conc. AAL % ofAAL
Period /m3 /m3
Hydrogen Chloride 1-hour 7.20 700 l
Hydrogen Fluoride 1-hour 6.90 250 3
24-hour 2.58 30 9
Sulfuric Acid 1-hour 4.95 100 5
24-hour 1.85 12 15
This compliance demonstration assumes the source parameters and pollutant emission rates used
in the analysis are correct.
cc: Tom Anderson
Nancy Jones

Model Inputs for Wolfspeed, Siler City, Chatham County, NC
Source Easting Northing Base Stack Exit Stack
ID X Elevation Height Temp. Velocity Diameter HO BF Sulfuric Acid
m m m ft °F (fps) ft lb/hr lb/hr lb/hr
SCRUB4 632514.5 3956961 192 28 75 50 0.46 1.19E-03 1.11E-03 7.94E-04
SCRUB3 632572.9 3956781 198 64 75 50 1.53 1.27E-02 1.27E-02 8.73E-03
SCRUBI 632444.9 3956824 190 64 75 50 4.83 1.29E-01 1.24E-01 8.89E-02
SCRUB2 632449.5 3956834 190 64 75 50 4.83 1.29E-01 1.24E-01 8.89E-02