PERMIT REVIEW SUMMARY

Permit Writer:	Chappell Ford				Date:	August 1, 2025

Company Name:	Enchanted Rock LLC, Entergy ERDC-EGUs

Facility Location:	Whitten Street
			Vicksburg, MS 39180

Source Number:	2780-00119

County: 		Warren

FACILITY DESCRIPTION

Enchanted Rock is proposing to build and operate Entergy ERDC - EGUs facility (ERDC) in Vicksburg, Warren County, Mississippi. Enchanted Rock will provide a non-emergency power source for Entergy. This synthetic minor operating permit submittal is to authorize the operation of 16 natural gas-powered spark ignition reciprocating engines, each operated for a maximum of 4,250 hours per year at ERDC (Title V Avoidance Limit). 

The facility will operate under SIC 4911 and NAICS 221112.

PROJECT/PERMIT ACTION DESCRIPTION

Enchanted Rock is seeking a Synthetic Minor Operating Permit for sixteen (16) natural gas fired spark ignition engines to provide non-emergency power for Entergy. There are currently eight (8) existing emergency generators near the location of the planned eight (8) new engines. 

Enchanted Rock constructed eight (8) natural gas fired spark ignition emergency engines in 2021. The potential to emit (PTE) for those eight engines was based on 500 hours/year and 100 hours/year.  The PTE for Engines 1-8 (AA-001 through AA-008) were below the threshold to require a construction and operating permit in the intervening years. Permits were not required for Engines 1-8 to operate as emergency engines. 

Pollutant	PTE, 
500 hr/yr	PTE, 
100 hr/yr	< 10 tpy,
< 2.5 tpy HAPs	
Particulate Matter	0.2	0.04	Yes/Yes	
PM10	0.2	0.04	Yes/Yes	
PM2.5	0.2	0.04	Yes/Yes	
Sulfur Dioxide	0.14	0.03	Yes/Yes	
Nitrogen Oxides	0.12	0.02	Yes/Yes	
Carbon Monoxide	5.74	1.15	Yes/Yes	
Volatile Organic Compounds	0.32	0.06	Yes/Yes	
Total HAPs	0.3	0.06	Yes/Yes	

Enchanted Rock plans to construct an additional eight (8) natural gas fired spark ignition engines (AA-009 through AA-016). The PTE for those 8 engines is below the threshold to require a permit to construct and qualify under the de minimis modification definition in 11 Miss. Admin Code Pt. 2, R. 2.1.C.(5)., where the increase in emissions is less than three-fourths (3/4) of the threshold for a major modification (250 tpy). Therefore, a construction permit for the eight (8) new engines is not required. 

Pollutant	PTE, Uncontrolled	PTE, 
4,250 hr/yr	< 187.5 tpy, 
< 18.75 tpy HAPS	De Minimis?	
Particulate Matter	3.6	1.7	Yes	Yes	
PM10	3.6	1.7	Yes	Yes	
PM2.5	3.6	1.7	Yes	Yes	
Sulfur Dioxide	2.64	1.19	Yes	Yes	
Nitrogen Oxides	2.16	1.02	Yes	Yes	
Carbon Monoxide	100.72	48.79	Yes	Yes	
Volatile Organic Compounds	5.52	2.72	Yes	Yes	
Total HAPs	5.36	2.55	Yes	YEs	

After issuance of the Synthetic Minor Operating Permit (SMOP), Enchanted Rock plans to run the original eight (8) emergency engines as full-time, non-emergency engines alongside the eight (8) new engines. Therefore, the facility has the uncontrolled potential to emit (PTE) for all 16 engines of 201 tons per year (tpy) of Carbon Monoxide (CO). The facility does not have the uncontrolled PTE to emit more than 100 tpy of any other Criteria Pollutant and less than 25 tpy of total hazardous air pollutants (HAPs) and less than 10 tpy of any individual HAP. The facility has requested a run time limit of 4,250 hours per generator per year to reduce the PTE of CO to less than 100 tpy, the Title V threshold, for the 16 engines. 

The following table shows the proposed emission sources.

Emission Point	Facility ID	Description	
AA-001 (existing)	Engine 1	5.03 MMBTU/hr natural gas fired, 652 hp, 448 kW, rich-burn SI ICE, 2019/2020 model year, controlled with a catalytic converter	
AA-002 (existing)	Engine 2	5.03 MMBTU/hr natural gas fired, 652 hp, 448 kW, rich-burn SI ICE, 2019/2020 model year, controlled with a catalytic converter	
AA-003 (existing)	Engine 3	5.03 MMBTU/hr natural gas fired, 652 hp, 448 kW, rich-burn SI ICE, 2019/2020 model year, controlled with a catalytic converter	
AA-004 (existing)	Engine 4	5.03 MMBTU/hr natural gas fired, 652 hp, 448 kW, rich-burn SI ICE, 2019/2020 model year, controlled with a catalytic converter	
AA-005 (existing)	Engine 5	5.03 MMBTU/hr natural gas fired, 652 hp, 448 kW, rich-burn SI ICE, 2019/2020 model year, controlled with a catalytic converter	
AA-006 (existing)	Engine 6	5.03 MMBTU/hr natural gas fired, 652 hp, 448 kW, rich-burn SI ICE, 2019/2020 model year, controlled with a catalytic converter	
AA-007 (existing)	Engine 7	5.03 MMBTU/hr natural gas fired, 652 hp, 448 kW, rich-burn SI ICE, 2019/2020 model year, controlled with a catalytic converter	
AA-008 (existing)	Engine 8	5.03 MMBTU/hr natural gas fired, 652 hp, 448 kW, rich-burn SI ICE, 2019/2020 model year, controlled with a catalytic converter	
AA-009 (proposed)	Engine 9	5.03 MMBTU/hr natural gas fired, 652 hp, 448 kW, rich-burn SI ICE, 2023/2024 model year, controlled with a catalytic converter	
AA-010 (proposed)	Engine 10	5.03 MMBTU/hr natural gas fired, 652 hp, 448 kW, rich-burn SI ICE, 2023/2024 model year, controlled with a catalytic converter	
AA-011 (proposed)	Engine 11	5.03 MMBTU/hr natural gas fired, 652 hp, 448 kW, rich-burn SI ICE, 2023/2024 model year, controlled with a catalytic converter	
AA-012 (proposed)	Engine 12	5.03 MMBTU/hr natural gas fired, 652 hp, 448 kW, rich-burn SI ICE, 2023/2024 model year, controlled with a catalytic converter	
AA-013 (proposed)	Engine 13	5.03 MMBTU/hr natural gas fired, 652 hp, 448 kW, rich-burn SI ICE, 2023/2024 model year, controlled with a catalytic converter	
AA-014 (proposed)	Engine 14	5.03 MMBTU/hr natural gas fired, 652 hp, 448 kW, rich-burn SI ICE, 2023/2024 model year, controlled with a catalytic converter	
AA-015 (proposed)	Engine 15	5.03 MMBTU/hr natural gas fired, 652 hp, 448 kW, rich-burn SI ICE, 2023/2024 model year, controlled with a catalytic converter	
AA-016 (proposed)	Engine 16	5.03 MMBTU/hr natural gas fired, 652 hp, 448 kW, rich-burn SI ICE, 2023/2024 model year, controlled with a catalytic converter	

EMISSION SUMMARY

Facility-Wide Potential-to-Emit Summary1
Pollutant	PTE Emissions (tons/yr)	
Particulate Matter (TSP)	3.52	
PM10	3.52	
PM2.5	3.52	
Sulfur Dioxide (SO2)	2.56	
Nitrogen Oxides (NOx)	2.08	
Carbon Monoxide (CO)	97.76	
Volatile Organic Compounds (VOC)	5.28	
Total HAP 	5.28	
1 The PTE emissions here reflect any emission limits or enforceable restrictions included in the proposed permit.

APPLICABLE/PROPOSED PERMIT LIMITATIONS

Enchanted Rock will limit its operating hours to a maximum of 4,250 hours per engine in order to restrict carbon monoxide emissions below the Title V threshold of 100 tpy. 

NSPS APPLICABILITY

40 CFR 60, Subpart A – General Provisions
40 CFR 60, Subpart A applies to any owner or operator of a stationary source which contains an affected facility if any part of 40 CFR 60 is applicable to the facility. Some provisions of Subpart A are applicable to the facility. 

40 CFR 60, Subpart IIII—Standards of Performance for Stationary Compression Ignition Internal Combustion Engines
40 CFR 60, Subpart IIII applies to stationary compression ignition internal combustion engines. The proposed engines are Spark Ignition Reciprocating Internal Combustion Engines (SI RICE). Therefore the requirements of 40 CFR 60, Subpart IIII do NOT apply.

40 CFR 60, Subpart JJJJ—Standards of Performance for Stationary Spark Ignition Internal Combustion Engines
40 CFR 60, Subpart JJJJ applies to Stationary Spark Ignition Internal Combustion Engines. The 16 proposed engines are all SI ICE. Therefore, the requirements of 40 CFR 60, Subpart JJJJ are applicable.

40 CFR 60, Subpart TTTT—Standards of Performance for Greenhouse Gas Emissions for Electric Generating Units
40 CFR 60, Subpart TTTT applies to steam generating units, integrated gasification combined cycle (IGCC) facilities, or stationary combustion turbines. The proposed engines are NOT steam generating units, IGCC facilities, or stationary combustion turbines. Therefore, the requirements of 40 CFR 60, Subpart TTTT do NOT apply.

40 CFR 60, Subpart TTTTa—Standards of Performance for Greenhouse Gas Emissions for Modified Coal-Fire Steam Electric Generating Units and New Construction and Reconstruction Stationary Combustion Turbine Electric Generating Units
40 CFR 60, Subpart TTTTa applies to any steam generating unit of IGCC that combusts coal. None of the proposed engines combust coal. Therefore, the requirements of 40 CFR 60, TTTTa do NOT apply.

MACT APPLICABILITY

40 CFR 63—National Emission Standards for Hazardous Air Pollutants (NESHAP) Applicability
The facility is an area source of Hazardous Air Pollutants (HAP) since the facility does not have the controlled potential to emit more than 25 tons per year of total HAPs or 10 tpy of any individual HAP..

40 CFR 63, Subpart ZZZZ—National Emissions Standards for Hazardous Air Pollutants for Stationary Reciprocating Internal Combustion Engines
40 CFR 63, Subpart ZZZZ applies to any stationary RICE at major or area sources of HAP emissions. The facility is proposing eight (8) existing non-emergency stationary RICE and eight (8) new stationary RICE for a total of 16 stationary RICE and is considered an area source of HAPs. However, the requirements of Subpart ZZZZ are met by meeting the requirements of 40 CFR 60 Subpart JJJJ. No further requirements shall apply under Subpart ZZZZ. 

PUBLIC PARTICIPATION

The 30-day public notice period began on September 24, 2025, when the notice was posted on MDEQ’s website and ends October 24, 2025.

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.