PERMIT REVIEW SUMMARY

Permit Writer:	Jeffrey Bland 					Date:	October 22, 2025

Company Name:	Amazon Data Services Inc, Madison Mega Site,
Madison County Mega Site

Facility Location:	1978 Highway 22
Canton, MS  39046

Source Number:	1720-00098

County: 		Madison

FACILITY DESCRIPTION

Amazon Data Services, Inc (Amazon) is a proposed data processing center that was issued Air Construction Permit No. 1720-00098, on December 4, 2024. Amazon proposes to construct a greenfield data processing facility in Canton (Madison County), Mississippi. Amazon’s operations fall under SIC code 7374: Computer Processing and Data Preparation and Processing Services.

Amazon has submitted a complete air modification application to Air Construction Permit No. 1720-00098 for the following changes:
1.	Add fourteen (14) additional 2,750-kW critical emergency generators (CEGs) resulting in an increase from 312 to 326 2,750-kW CEG units.
2.	Remove seven (7) permitted 750-kW house emergency generators (HEGs) resulting in a decrease from 12 to 5 750-kW HEG units.
3.	Add fourteen (14) additional 6,561 gallon-each diesel fuel storage belly tanks for the proposed CEG units resulting in an increase from 312 to 326 CEG belly tanks.
4.	Remove seven (7) permitted 2,700 gallon-each diesel fuel storage belly tanks for the permitted HEG units resulting in a decrease from 12 to 5 HEG belly tanks and change the capacity of the 5 tanks to 1,367-gallons each. 

The draft modification permit includes necessary changes to the Section 2 – Emission Point Description Table.  No changes to any permit terms or conditions were necessary.

The site is referred to as the Madison Mega Site (Site). The Site will include 336 emergency backup electrical power generator engines in various sizes with a total power generation capacity of 904.25 Megawatts (MW). The emergency backup generator engines will consist of:

•	Three-hundred and twenty-six (326) 2,750-Kilowatt (kW) Critical Emergency Backup Electrical Power Generator (CEG) Engines.
Each engine will consist of a 4,043-Horsepower (HP) Caterpillar 3516E Compression Ignition (CI) diesel-fired Tier-2 certified emergency generator engine, equipped with SCR, DOC, and DPF to meet Tier 4 equivalent emission limits.

•	Five (5) 750-kW House Emergency Backup Electrical Power Generators (HEG) Engines.
Each engine will consist of a 1,112 HP Caterpillar C12 CI diesel-fired Tier-2 certified emergency generator engine.

•	Two (2) 1,500-kW Water Treatment System Emergency Backup Electrical Power Generators (WTP) Engines.
Each engine will consist of a 2,206 HP Caterpillar 3512C CI diesel-fired Tier-2 certified emergency generator engine.

•	Two (2) 400-kW Building (Logistics Building and Administration Building) Emergency Backup Electrical Power Generators Engines.
Each engine will consist of a 619 HP Caterpillar C15 CI diesel-fired Tier-3 certified emergency generator engine.

•	One (1) 250-kW Security Building Emergency Backup Electrical Power Generator Engine.
A 398 HP Caterpillar C9 CI diesel-fired Tier-3 certified emergency generator engine.

Each emergency generator engine will be equipped with an associated diesel fuel storage tank. In addition to the belly tanks, the Site will also have twelve (12) bulk diesel fuel storage tanks, with a volume capacity of 12,000 gallons each.

PROJECT/PERMIT ACTION DESCRIPTION

The permitting action is to modify the initial Permit to Construct Air Emissions Equipment.

EMISSION SUMMARY1

Pollutant	PTE Emissions (tons/yr)	
Particulate Matter (TSP)	15.50	
PM10	15.50	
PM2.5	15.50	
Sulfur Dioxide (SO2)	1.94	
Nitrogen Oxides (NOx)	249.0	
Carbon Monoxide (CO)	249.0	
Volatile Organic Compounds (VOC)	38.10	
Total Reduced Sulfur (TRS)	—	
Lead	Not Listed	
CFC/HCFC	—	
Total HAP 	0.69	
1 The PTE emissions reflect any emission limits or enforceable restrictions included in the proposed permit.

APPLICABLE/PROPOSED PERMIT LIMITATIONS

Each of the critical emergency generators CEG 1 – 326 (Model CAT 3516E, 2750 kW each) will be equipped with a selective catalytic reduction (SCR) unit, diesel oxidation catalyst (DOC), and
diesel particulate filter (DPF) to meet Tier 4 equivalent emission limits. The three (3) control devices will be installed as one (1) individual control unit on each engine. The purpose of the control devices is for the Site to avoid exceeding major source PSD permitting. 

Two (2) sets of control systems, manufactured by Miratech and Safety Power, respectively, will be installed. The manufacturer provided control efficiencies of each system are provided below. 

Pollutant	Miratech Provided
Control Efficiency	Safety Power Provided Control Efficiency	
NOx	91.7%	91.9%	
CO	70%	80%	
NMHC or VOC	50%	40%	
Filterable PM	68.6%	75.6%	

The Site proposes to equip a portion of CEG 1 – 326 with the Miratech control system and the remaining CEGs will be equipped with the Safety Power control system. The post-controlled potential emissions from CEG 1 – 326 are conservatively calculated based on the lower control efficiency between the two systems for each listed pollutant.

As described in the NSPS Applicability section below, each emergency engine at the Site is limited to 100 hours per year of operation in for readiness and/or maintenance testing, including non-emergency service. However, were each engine to operate 100 hours for purposes of reading and/or maintenance testing, PSD emission thresholds for NOx and CO would be exceeded. When operating for purposes of readiness and/or maintenance testing, some engines are expected to be operated under “No Load” conditions; therefore, the engine control devices will not meet their stated control efficiencies due to decreased engine exhaust temperature. However, some readiness and/or maintenance testing will be performed at higher loads level (e.g., >70% engine load), which will be high enough to trigger SCR control. Stated control efficiencies will only be met when engines are operated for emergency purposes at full engine load conditions. Therefore, in order to monitor and record monthly and rolling, consecutive twelve-month NOx and CO emissions, several variables must be recorded during each engine’s operations.  

Each engine within Emission Group AA-000 will be equipped with a control system that will continuously measure and record the following:
•	The SCR catalyst bed exhaust temperature. The information will be recorded at a minimum frequency of once every minute, and correlated to run date, engine load/kilowatt output, and engine operating hours.
•	The NOx emissions measured after the catalyst, expressed in ppm. The information shall be recorded at a minimum frequency of once every minute, and correlated to run date, engine load/kilowatt output, and engine operating hours.
•	The differential pressure drop across the entire emissions control system to demonstrate proper function of the SCR, DPF, and DOC. The backpressure monitor shall notify the permittee when the high backpressure limit of the engine is approached. The emissions control system shall be observed by the permittee with a frequency as recommended by the process/control equipment manufacturer.

Further, each monitoring device will be equipped with a mechanism to detect parameters which exceed manufacturer’s recommended thresholds and trigger an alarm to operators when the unit is not operating within the manufacturer’s recommended conditions.

For CO emissions, the facility will apply the uncontrolled emission factor for any runtime that the catalyst bed is not within the manufacturer’s recommended range for control.

Following each month, total monthly NOx and CO emissions will be tabulated on a monthly and for each consecutive twelve-month period on a rolling basis.

PSD Applicability

Amazon is not one of the 28 categorical facilities listed in 40 CFR 52.21(b)(1)(i)(a); therefore, the PSD threshold for a major source is 250 tpy.  Amazon has the potential to emit more than 250 tons per year (tpy) of the following regulated NSR pollutants: nitrogen oxides (NOx) and carbon monoxide (CO). However, Amazon is proposing to limit facility-wide emissions of NOx and CO to 249.0 tpy, each; therefore, the facility will be considered a moderate stationary source. With potential emissions calculated based on each engine operating 100 hours per year, NOx is the only pollutant with potential emissions greater than 250 tpy. However, with potential emissions calculated based on each engine operating 500 hours per year, CO emissions also exceed 250 tpy.

Title V Source Applicability
Amazon’s potential-to-emit (PTE) exceeds the Title V major source threshold of 100 tons per year (tpy) for each of the following criteria air pollutants: Nitrogen Oxides (NOx) and Carbon Monoxide (CO). The facility’s potential-to-emit hazardous air pollutants (HAPs) does not exceed the Title V major source thresholds of 25 tpy of total HAPs or 10 tpy for any individual HAP. Therefore, the facility will operate as an area source. 

NSPS APPLICABILITY

40 CFR Part 60, Subpart IIII—Standards of Performance for Stationary Compression Ignition Internal Combustion Engines
Subpart IIII applies to owners and operators of stationary compression ignition (CI) internal combustion engines (ICE) that commence construction (i.e. date the engine is ordered by the owner or operator) after July 11, 2005, and manufactured as a certified National Fire Protection Association (NFPA) fire pump engine after July 1, 2006. 

The 326 CEG 2,750-kW diesel-fired emergency engines, 5 HEG 750-kW diesel-fired emergency engines, and 2 WTP 1,500-kW diesel-fired emergency engines, are each CI ICE and are subject to Subpart IIII. Each purchased engine must be certified to the emission standards in 40 CFR 60.4205(b) and Tier 2 of Appendix I of 40 CFR 1039, which include: 6.4 grams per kilowatt-hour (g/kW-hr) of Nitrogen Oxides (NOx) emissions; 3.5 g/kW-hr of Carbon Monoxide (CO) emissions; and to 0.2 g/kW-hr of Particulate Matter (PM) emissions.

The two (2) 400-kW diesel-fired emergency engines and one (1) 250-kW diesel-fired emergency engine are each CI ICE and are subject to Subpart IIII. Each purchased engine must be certified to the emission standards in 40 CFR 60.4205(b) and Tier 3 of Appendix I of 40 CFR 1039, which include: 4.0 grams per kilowatt-hour (g/kW-hr) of Nitrogen Oxides (NOx) emissions; 3.5 g/kW-hr of Carbon Monoxide (CO) emissions; and to 0.2 g/kW-hr of Particulate Matter (PM) emissions.

Each emergency backup generator engine must also meet the operating and emergency operational requirements of 40 CFR 60.4211(a)-(f).

40 CFR Part 60, Subpart JJJJ—Standards of Performance for Stationary Spark Ignition Internal Combustion Engines
Subpart JJJJ applies to owners and operators of stationary spark ignition (SI) internal combustion engines (ICE) that commence construction (i.e. date the engine is ordered by the owner or operator) after June 12, 2006, and are manufactured on or after January 1, 2009, for emergency engines with a maximum engine power greater than 19 KW (25 HP). All emergency engines are CI engines. Therefore, Subpart JJJJ is not applicable.

40 CFR Part 60, Subpart Kb—Standards of Performance for Volatile Organic Liquid Storage Vessels (Including Petroleum Liquid Storage Vessels) for Which Construction, Reconstruction, or Modification Commenced After July 23, 1984
Subpart Kb applies to any storage vessel with a capacity greater than or equal to 75 m3 (≈19,813 gal) that is used to store volatile organic liquids (VOL) for which construction, reconstruction, or modification is commenced after July 23, 1984. Subpart Kb does not apply to storage vessels with a capacity greater than or equal to 75 m3 but less than 151 m3 (≈39,890 gal) storing a liquid with a maximum true vapor pressure less than 15.0 kPa. Amazon is proposing to construct a total of twelve (12) diesel fuel storage tanks and one (1) dedicated belly/day tank for each emergency backup generator engine. Each tank will have a capacity much less than 75 m3; Therefore, Subpart Kb is not applicable. 

MACT APPLICABILITY

40 CFR Part 63, Subpart ZZZZ—National Emissions Standards for Hazardous Air Pollutants for Stationary Reciprocating Internal Combustion Engines
Subpart ZZZZ applies to owners or operators of stationary reciprocating internal combustion engines (RICE) at area and major sources of HAP emissions. 

Each proposed diesel-fired emergency generator engine is considered ‘new stationary RICE’, as defined in 40 CFR 63.6590(a)(2)(iii), at an area source of HAP emissions. As such, each engine must meet the requirements of 40 CFR 63, Subpart ZZZZ by meeting the requirements of 40 CFR 60, Subpart IIII, for CI engines.  No further requirements apply for such engines under 40 CFR 63, Subpart ZZZZ or the General Provisions in Subpart A.

PUBLIC PARTICIPATION

The 30-day public notice period began on , when the notice was posted on MDEQ’s website and ends .

RECOMMENDATION

The staff has preliminarily decided to recommend issuance of the permit to the Mississippi Environmental Quality Permit Board as shown in the draft permit.  However, the staff recommendation to the Board will be made only after a thorough consideration of all public comments.