Final Modelling Review Feb. 19, 2018

MEMORANDUM
DIVISION OF AIR QUALITY
February 19, 2018
TO: Charles McEachern, Environmental Engineer, RRO
Permit Coo · at01\ RRO
SUBJECT: Revised Review of Toxics Air Dispersion Modeling -
Dominion Energy Transmissions, Inc. Atlantic Coast Pipeline, LLC
Northampton County Compressor Station
Northampton County, North Carolina Facility No. 6600169
I reviewed the updated dispersion modeling analysis, received on February 15, 2018, for the
Dominion Energy Transmissions, Inc. Atlantic Coast Pipeline, LLC Northampton County
Compressor Station, Northampton County, North Carolina. Revisions were made to the
emission rates estimates for the modeling previously conducted for the facility described in a
memo dated January 31, 2018. The changes to the emission rates were minimal and did not
significantly affect the modeled impact's overall percentage of the AAL's from those previously
reported in the January memo. The owner has submitted a pennit application for a greenfield
facility, which triggered modeling requirements to evaluate those toxics whose rates are expected
to exceed the levels outlined in 1 SA NCAC 2Q .0700. The modeling continued to adequately
demonstrates compliance, on a source-by-source basis, for all toxics modeled.
Three air toxics were evaluated facility wide in the modeling. Details of the emission rates and
source parameters used in the modeling are attached. AERMOD (16216r) using five years
(2012-2016) of meteorological surface data from Rocky Mount/Wilson and upper air data from
Greensboro was used to evaluate impacts in both simple and elevated terrain. Direction-specific
building dimensions, detennined using EPA' s BPIP-P1ime program (0427 4), were used as input
to the model for building wake effect detennination. Receptors were placed around the facility's
property line at SO-meter intervals and extended outward to 1,500 meters. Additional receptors
were spaced at 100-meter intervals from 1,500 to 2,500 meters, at 250-meter intervals out to
5,000 meters, and at 500-meter intervals out to 10,000 meters from the facility.
Maximum Impacts -Dominion Energy Transmissionst Inc. Atlantic Coast Pipeline, LLC
Northampton County Compressor Station, North Carolina
TAP Averaging Max. Cone. AAL %ofAAL
Period (uf!.l m3) (µg!m3)
Benzene Annual 0.006 0.12 5%
F01maldehyde I-hour 26.4 150 18 %
n~Hexane 24-hour 588.2 1,100 53%
This compliance demonstration assumes the source parameters and pollutant emission rates used
in the analysis are correct.
cc: Mike Abraczinskas
Michael Pjetraj
Tom Anderson
Nancy Jon~s
Dominion Energy Transmissions, Inc. Atlantic Coast Pipeline, LLC
Northampton County, NC Compressor Station Emission Rates
Source BENZENE FORMALDEHYDE HEXANE
(lb/hr) {lb/hr) (lb/hr)
CTOl 6.90E-04 4.70E+OO
CT02 3.90E-04 l.17E+OO
CT03 3.42E-04 1.16E+OO
EGEN 5.13E-04 1.36E+OO 2.06E-03
EGN2 3.97E-05 2.06E-02 1.68E-04
BOIL 1.08E-05 3.86E-04 9.26E-03
BLR2 3.29E-07 7.94E-06 2.82E-04
TNK.l 2.38E-04 2.00E-03
TNK2 5.02E-06 5.0lE-06
UNTl 14 3.07E-01
UNT2 14 3.49E-Ol
UNT3 14 5.97E-01
STNI 14 LSIE+OO
STN2 14 l.08E+OO
STN3 14 8.58E-Ol
CTOIBLDG l.00E-02
CT23BLDG 2.00E-02
Dominion Energy Transmissions, Inc. Atlantic Coast Pipeline, LLC
Northampton County, NC Compressor Station Volume Source Release Characteristics
Initial
Easting Northing Base Release lnit. Hor. Vert.
Source ID (X) (Y) Elevation Height Dimension Dimension
(m) (m) (m) (ft) (ft} (ft}
CT0lBLDG 275,698 4,047,188 28.65 22.5 16.5 20.9
CT23BLDG 275,744 4,047,187 28.65 17.7 26.5 16.5
Dominion Energy Transmissions, Inc. Atlantic Coast Pipeline, LLC Northampton County, NC Compressor Station Point Source Release Characteristics Stack Release Easting Northing Base Stack Exit Stack Source ID Type (X) (Y) Elevation Heil!ht Temperature Velocity Diameter (m) (m) {m) (ft) (Of) (fus) (ft) CT0l DEFAULT 275,717 4,047,189 28.35 60 750 83 6 CT02 DEFAULT 275,722 4,047,187 28.04 60 750 59 6 CT03 DEFAULT 275,767 4,047,188 28.35 60 750 50 6 EGEN DEFAULT 275,734 4,047,234 28.96 27 974 184 1.2 EGN2 DEFAULT 275,337 4,047,254 38.1 5 1200 423 0.21 BOIL DEFAULT 275,740 4,047,235 28.96 26 838 247 0.67 BLR2 DEFAULT 275,341 4,047,263 38.1 10 838 247 0.67 TNKI DEFAULT 275,606 4,047,186 28.35 9 Ambient 0 0.33 TNK2 DEFAULT 275,605 4,047,182 28.35 8 Ambient 0 0.33 UNTI 14 RAINCAP 275,719 4,047,130 27.13 19 Ambient 43 1.85 UNT2 14 RAINCAP 275,734 4,047,130 27.13 19 Ambient 49 1.85 UNT3 14 RAINCAP 275,752 4,047,131 27.13 25 Ambient 60 2.19 STNl 14 RAINCAP 275,601 4,047,146 28.35 11 Ambient 48 6.37 STN2 14 RAINCAP 275,601 4,047,143 28.35 11 Ambient 26 7.32 STN3 14 RAINCAP 275,601 4,047,122 28.35 11 Ambient 27 6.37