PERMIT RATIONALE FOR REISSUANCE 
Enterprise Gas Processing LLC, Pascagoula Gas Processing Plant
Water NPDES No. MSS061719
May 1, 2023
Samar Patel, Water I Branch

I.	FACILITY INFORMATION

Facility Address:  6800 Stennis Boulevard, Moss Point, MS  39562-7609
Facility County: Jackson
	SIC:  1321

II.	NATURE OF BUSINESS

Enterprise Gas Processing is a natural gas refinement/treatment facility. Crude natural gas is piped on site from several offshore platforms in the Gulf of Mexico via the Destin Pipeline. The plant separates heavier hydrocarbons from crude natural gas. Light end hydrocarbons and condensates are removed, and the gas is dehydrated. The refined natural gas is delivered to a pipeline for compression and shipment.

III.	EFFLUENT AND RECEIVING STREAM FLOW DATA

•	Outfall 001 (Fed by OWS-1, OWS-2, & OWS-8) – Storm water collected from truck loading/unloading area and stabilization area including the berm area around the bulk storage tanks and the chemical drum storage area drains to an oil/water separator (OWS)-1, OWS-2, and OWS-8. After storm water processed in the OWSs, it drains into the aeration lagoon, then into a lined secondary treatment lagoon prior to discharge into Outfall 001– average flow – 0.0819 MGD1

•	Outfall 002 (Fed by OWS-7) – Storm water collected from northwest area of the site and from NGL Lube oil pumps and lube oil reservoir located in a secondary containment structure drains to OWS-7. – average flow – 0.0002 MGD1

•	Outfall 003 (Fed by OWS-3) – Storm water collected from the northeast area of the site and from a containment area with the residue compressor lube oil reservoirs and compressor skids drains to OWS-3 – average flow – 0.0005 MGD1

•	Outfall 004 (Fed by OWS-5 and OWS-6) – Storm water collected from the refrigeration compressor area, from the Hot Oil Pump containment area and the Train A and Train B Expander skids drains to OWS-5 and OWS-6 – average flow – 0.0010 MGD1

•	Outfall 005 (Fed by OWS-4) – Storm water collected from the East Residue Building and from the NGL lube oil pumps and lube oil reservoir located in a secondary containment structure drains to OWS-4 – average flow – 0.0003 MGD1

•	Outfall 006 (Fed by Sluice Gate-4) – Storm water collected from the eastern side of the facility. This drainage is permitted for the first time with this renewal, and considered existing discharge activity since it is always present and left the site like their other storm water outfalls. The drainage is routed through Sluice Gate No.4, which can be closed if the discharge has a sheen and treated before discharge. 

	1 The average flow for Outfalls 001-005 is based on Discharge Monitoring Reports                           (DMRs) from the most recent two-year period (i.e., 2021-2022). 

		Receiving Stream: Unnamed tributary to Bayou Cassotte, which is located approximately 6,000 feet southwest of the site. 

IV.	303(d) ISSUES

The State of Mississippi 2022 Section 303(d) List of Impairment Water Bodies list segment of Bayou Casotte (Water Body ID 200312) that is listed as impaired for Organic Enrichment/Low Dissolved Oxygen. Bayou Casotte is in Coastal Streams Basin and classified as Fish and Wildlife. The actual discharge from Enterprise first enters an unnamed tributary (drainage ditch) west of the property, adjacent to Hwy 611 (Industrial Road) and flows approximately one mile southwest of the site prior to entering Bayou Casotte. The unnamed tributary is in Coastal Streams Basin and has classified as Fish and Wildlife. The unnamed tributary by itself does not appear on The State of Mississippi 2022 Section 303(d) List of Waterbodies. However, the impairment listed influencing an unnamed tributary is due to Bayou Casotte, which is on the Impairment List for Organic Enrichment/Low Dissolved Oxygen.

The storm water discharged from the site is not expected to significantly influence the water quality / impairment listed in the Section 303(d) List for Bayou Casotte. Based on the type of operations, intermittency of storm water discharges, distance to Bayou Casotte, and implementation of Storm Water Pollution Prevention Plan (SWPPP), impacts to Bayou Casotte are expected to be negligible from the facility’s discharge.

The facility is required to sample oil & grease at all permitted outfalls. Based on the facility operations, monitoring for oil & grease will give an indication of any presence of hydrocarbons in storm water discharges from the facility. Upon review of the DMRs from the most recent three years, oil and grease was reported either non-detect or well-below their permitted levels. Further, highest level at which BOD and COD reported in the application submitted on May 6, 2022, are less than 4.0 mg/l and 33 mg/l; thus, MDEQ believes that storm water discharged from the facility will not contribute to organic enrichment problems in Bayou Casotte. 

A TMDL for Phenol was approved on May 24, 2002, for Bayou Casotte. The facility is not subject to this TMDL since phenol is not used or stored at the site. 

V.	EPA APPLICABLE CATEGORICAL GUIDELINES

Not Applicable

VII.	DATA FROM APPLICATION FORM

Parameter	Maximum Daily Value	
Outfall 001		
BOD	< 4.0 mg/l	
COD	9 mg/L	
TSS	11 mg/L	
Total Nitrogen	<1.80 mg/l	
Total Phosphorous	< 0.222 mg/l	
pH2	8.55 S.U.	
Oil & Grease2	5.70 mg/l	
BTEX	ND (MRL3 = 5.0 ug/l)	
Outfall 002		
BOD	< 3.0 mg/l	
COD	33 mg/L	
TSS	8.8 mg/L	
Total Nitrogen	<1.80 mg/l	
Total Phosphorous	< 0.141 mg/l	
pH2	9.85 S.U.	
Oil & Grease2	5.4 mg/l	
BTEX	ND (MRL3 = 5.0 ug/l)	
Outfall 003		
BOD	< 3.0 mg/l	
COD	7.0 mg/L	
TSS	9.5 mg/L	
Total Nitrogen	<1.80 mg/l	
Total Phosphorous	0.106 mg/l	
pH2	9.61 S.U.	
Oil & Grease2	6.2 mg/l	
BTEX	ND (MRL3 = 5.0 ug/l)	
Outfall 004		
BOD	< 3.0 mg/l	
COD	16.0 mg/L	
TSS	27.5 mg/L	
Total Nitrogen	<1.80 mg/l	
Total Phosphorous	0.05 mg/l	
pH2	8.7 S.U.	
Oil & Grease2	5.8 mg/l	
BTEX	ND (MRL3 = 5.0 ug/l)	
Outfall 005		
BOD	< 3.0 mg/l	
COD	12.0 mg/L	
TSS	42.6 mg/L	
Total Nitrogen	<1.80 mg/l	
Total Phosphorous	0.071 mg/l	
pH2	9.62 S.U.	
Oil & Grease2	5.60 mg/l	
BTEX	ND (MRL3 = 5.0 ug/l)	
Outfall 006 		
BOD	< 3.0 mg/l	
COD	7.0 mg/L	
TSS	13.4 mg/L	
Total Nitrogen	<1.80 mg/l	
Total Phosphorous	0.062 mg/l	
pH	7.77 S.U.	
Oil & Grease	<5.00 mg/l	
BTEX	ND (MRL3 = 5.0 ug/l)	

2 The pH and oil & grease data for Outfalls 001-005 is based on Discharge Monitoring        Reports (DMRs) from the most recent two-year period (i.e., 2021-2022).

           3 MRL = Minimum Reporting Limit

VIII. 	WATER QUALITY LIMITATIONS BASED ON WASTELOAD ALLOCATION 

	Not Applicable

IX.	CATEGORICAL GUIDELINE LIMITATIONS CALCULATIONS

	Not Applicable

X.	TOXICITY SCREENING

Not Applicable

XI.	PROPOSED FINAL LIMITATIONS 

1.	Average Permit Limitations

Outfall	Parameter	Categorical Limitation	Water Quality Limitation	Present Permit Limitation	Proposed Permit Limitation	Basis	
MSS061719-001	Flow (MGD)
			R	R	EJ	
	Oil & Grease
			10 mg/L	10 mg/L	PPR/EJ	
	pH (min.)
		6.0 S.U.	6.0 S.U.	6.0 S.U.	MSWQS	
MSS061719-002	Flow (MGD)
			R	R	EJ	
	Oil & Grease
			10 mg/L	10 mg/L	PPR/EJ	
	pH (min.)
		6.0 S.U.	6.0 S.U.	6.0 S.U.	MSWQS	
MSS061719-003	Flow (MGD)
			R	R	EJ	
	Oil & Grease
			10 mg/L	10 mg/L	PPR/EJ	
	pH (min.)
		6.0 S.U.	6.0 S.U.	6.0 S.U.	MSWQS	
MSS061719-004	Flow (MGD)
			R	R	EJ	
	Oil & Grease
			10 mg/L	10 mg/L	PPR/EJ	
	pH (min.)
		6.0 S.U.	6.0 S.U.	6.0 S.U.	MSWQS	
MSS061719-005	Flow (MGD)
			R	R	EJ	
	Oil & Grease
			10 mg/L	10 mg/L	PPR/EJ	
	pH (min.)
		6.0 S.U.	6.0 S.U.	6.0 S.U.	MSWQS	
MSS061719-006	Flow (MGD)
			-	R	EJ	
	Oil & Grease
			-	10 mg/L	EJ	
	pH (min.)
		6.0 S.U.	-.	6.0 S.U.	MSWQS	

2.	Maximum Permit Limitations

Outfall	Parameter	Categorical Limitation	Water Quality Limitation	Present Permit Limitation	Proposed Permit Limitation	Basis	
MSS061719-001	Flow (MGD)
 			R	R	EJ	
	Oil & Grease
			15 mg/L	15 mg/L	PPR/EJ	
	pH (max.)
		9.0 S.U.	9.0 S.U.	9.0 S.U.	MSWQS	
MSS061719-002	Flow (MGD)
			R	R	EJ	
	Oil & Grease
			15 mg/L	15 mg/L	PPR/EJ	
	pH (max.)
		9.0 S.U.	9.0 S.U.	9.0 S.U.	MSWQS	
MSS061719-003	Flow (MGD)
			R	R	EJ	
	Oil & Grease
			15 mg/L	15 mg/L	PPR/EJ	
	pH (max.)
		9.0 S.U.	9.0 S.U.	9.0 S.U.	MSWQS	
MSS061719-004	Flow (MGD) 
			R	R	EJ	
	Oil & Grease
			15 mg/L	15 mg/L	PPR/EJ	
	pH (max.)
		9.0 S.U.	9.0 S.U.	9.0 S.U.	MSWQS	
MSS061719-005	Flow (MGD)
			R	R	EJ	
	Oil & Grease
			15 mg/L	15 mg/L	PPR/EJ	
	pH (max.)
		9.0 S.U.	9.0 S.U.	9.0 S.U.	MSWQS	
MSS061719-006	Flow (MGD)
			-	R	EJ	
	Oil & Grease
			-	15 mg/L	EJ	
	pH (max.)
		9.0 S.U.	-	9.0 S.U.	MSWQS	
MGD = Million Gallons per Day, R = Report only, PPR = Previous Permit Requirement, EJ = Engineering Judgment, MSWQS = State of Mississippi Water Quality Criteria for Intrastate, Interstate and Coastal Waters

All parameters shall be monitored once per quarter and submitted in a yearly report. Flow shall be monitored instantaneously, and all other parameters shall be monitored through grab sample. The monitoring for oil and grease will be required to ensure that proper BMPs will be practiced so that the amount of oil and grease or other materials exposed to storm water will be minimized.