PERMIT RATIONALE FOR REISSUANCE
Entergy Mississippi Inc, Grand Gulf Nuclear Station
Water NPDES No. MS0029521
Thomas Kelly, Water I Branch
April 8, 2026

I.	FACILITY INFORMATION

Facility Address: 7003 Bald Hill Road, Port Gibson, MS  39150
	Facility County: Claiborne
EPA ID: 110007109547
SIC: 4911

II.	NATURE OF BUSINESS

Nuclear Powered Steam Electric Plant Generation which consists of a boiling water reactor rated at 1250 MW.  The facility operations fall within SIC Code 4911 - Electric Services.  This facility is classified as a NPDES major source.

III.	EFFLUENT AND RECEIVING STREAM FLOW DATA

External Outfalls

Outfall 001 (Categorical: Cooling Tower Blowdown): Discharge from the Natural Draft Cooling Tower Discharge/Mixing basin. Effluent from this outfall consist of cooling tower blowdown from the Auxiliary Cooling and Natural Draft Cooling tower and effluent from internal outfalls(s) 004, 005, 006, 011. These effluent streams commingle in the Mixing/Discharge Basin located at the base of the Natural Draft Cooling Tower. This outfall has a maximum daily flow of 26.27 MGD and discharges to the Mississippi River.  

The Mississippi River is classified as “Fish and Wildlife” and has a 7Q10 flow of 82,082 MGD. 

Outfall 013: Discharge from Sediment Basin A. Effluent from this outfall consists of standby service water leakage, site storm water runoff, treated sanitary wastewater, and the combined discharge of Internal Outfalls 010 and 016. This outfall has a maximum 30-day flow of 2.03 MGD. 

Outfall 014: Discharge from Sedimentation B. Effluent consists of storm water runoff and wastewater from internal Outfall 007. This outfall has a maximum 30-day flow of 0.62 MGD. 

Outfalls 013 and 014 discharge to an unnamed creek thence to Hamilton Lake. The receiving stream is classified as “Fish and Wildlife” and has a 7Q10 flow of 0 MGD.  

Internal Outfalls

Outfall 002 Removed (Categorical: Cooling Tower Blowdown): Since the effluent from this outfall is the exact same effluent as external Outfall 001, this Outfall will be removed from the permit, and the Categorical limitations will be moved to Outfall 001.

Outfall 004 (Categorical: Cooling Tower Blowdown): Unit A cooling tower blowdown, and occasional wastewater resulting from routine testing of the standby service water system (SSW A). This outfall has a maximum 30-day flow of 2.8 MGD and discharges via external Outfall 001. 

Outfall 005 (Categorical: Cooling Tower Blowdown): Unit B cooling tower blowdown, and occasional wastewater resulting from routine testing of the standby service water system (SSW B). This outfall has a maximum daily flow of 0.529 MGD and discharges via external Outfall 001.

Outfall 006 (Categorical: Low Volume): Low volume waste discharge consisting of demineralizer wastewater, carbon filter backwash, and water treatment building sump wastewater. This outfall has a maximum daily flow of 0.65 MGD and discharges via external Outfall 001.

Outfall 007 (Categorical: Low Volume): Low volume waste discharge consisting of miscellaneous wastewaters discharged into Sedimentation Basin B. These include wastewater from the administrative building drains, yard and storm drains, fire water pump house, oily waste sumps, ionic reject water, turbine building cooling water Blowdown, HVAC blowdown, HVAC once-through cooling, outage air compressor once-through cooling, intermittent standby service water leakage and releases. This outfall has a maximum 30-day flow of 0.415 MGD and discharges via external Outfall 014.

Outfall 010 (Non-categorical):   Sanitary wastewater. This outfall has a maximum daily discharge flow of 0.824 MGD and discharges via external Outfall 013.

	Outfall 011 (Categorical: Low Volume): Low volume waste discharge consisting of wastewater from the liquid radwaste treatment system including borated water. Wastewater consists of floor drains and lab drain waste. This outfall has a maximum 30-day flow of 0.0479 MGD.

Outfall 016 (Categorical: Low Volume): Low volume waste discharge consisting of miscellaneous wastewater from the energy services center inclusive of ECS water softener backwash and HVAC cooling tower blowdown, plant water softener backwash, and storm water runoff. This outfall has a maximum 30-day flow of 0.004 MGD and discharges via external Outfall 013.

IV.	303(d) and TMDL ISSUES

None.
V.	TYPE OF WASTEWATER TREATMENT:

Outfall 001 - None. Commingling of waste streams from Outfalls 004, 005, 006, 011.
Outfall 004 - No treatment.
Outfall 005 - No treatment.
Outfall 006 - Sedimentation and neutralization.
Outfall 007 - Oil/Water separation provided for selected internal waste streams.
Outfall 010 - Sanitary Wastewater Treatment Plant with treatment including activated sludge, aeration, chlorination, and Dechlorination. 
Outfall 011 - Ion exchange and neutralization.
Outfall 013 - Oil/Water separation provided for selected internal waste streams.  Settling provided for commingled wastewater.
Outfall 014 - Oil/Water separation provided for selected internal waste streams.  Settling provided for commingled wastewater.
Outfall 016 - No treatment.

VI.	EPA APPLICABLE CATEGORICAL GUIDELINES

40 CFR Part 423 - Steam Electric Power Generation Point Source Category; Sections 423.12 (BPT-Best Practicable Control Technology Currently Available) and 423.13 (BAT-Best Available Technology Economically Available).

VII.	DATA FROM APPLICATION FORM (2C)

External Outfalls:

	Maximum Daily Value	
Parameter	Outfall 001	Outfall 013	Outfall 014	
BOD5	ND	15.3 mg/L	ND mg/L	
COD	31.1 mg/L	< 11.7 mg/L	< 11.7 mg/L	
TOC	13.6 mg/L	5.81 mg/L	4.4 mg/L	
TSS	5.8 mg/L	47 mg/L	5 mg/L	
Ammonia (as N)	ND 	9.19 mg/L	< 0.117 mg/L	
Flow	26.27 MGD	2.8 MGD	1 MGD	
Temperature (Winter)	33.9 °C	18.5 °C	19.2 °C	
Temperature (Summer)	36 °C	21.9 °C	23.1 °C	
pH (minimum)	7.88 SU	7.01 SU	6.86 SU	
pH (maximum)	8.7 SU	8.18 SU	8.74 SU	
Antimony	1.95 ug/L	< 1.72 ug/L	< 1.72 ug/L	
Arsenic	7.44 ug/L	4.3 ug/L	1.87 ug/L	
Copper	2.11 ug/L	1.08 ug/L                 (12)2	1.08 ug/L            (12)2	
Lead	< 0.513 ug/L	< 0.513 ug/L           (12)2	0.516 ug/L          (12)2	
Mercury1	< 0.1 ug/l	< 0.1 ug/L                 (12)2	< 0.1 ug/L        	
Nickel	5.44 ug/L	1.66 mg/L                (12)2	1.36 mg/L           (12)2	
Selenium	1.33 ug/L	< 0.437 ug/L	< 0.437 ug/L	
	Maximum Daily Value	
Parameter	Outfall 001	Outfall 013	Outfall 014	
Zinc	558 ug/L	48 ug/L                   (13)2	34 ug/L                (12)2	
Di-n-Butyl phthalate	0.677 ug/L	< 0.453 ug/L	< 0.453 ug/L	
Bromide	1.56 mg/L	< 0.2 mg/L	--	
Chlorine, TR	--	--	--	
Color	50 pcu	20 pcu	30 pcu	
Fluoride	0.664 mg/L	--	--	
Nitrate-Nitrite	1.15  mg/L	1.25 mg/L	--	
Nitrogen, Total Organic (as N)	1.28 mg/L	1.61 mg/L	--	
Phosphorus	1.06 mg/L	1.33 mg/L	< 0.035 mg/L	
Sulfate (as SO4)	649 mg/L	--	47.8 mg/L	
Barium	-- 	0.124 mg/L	--	
Iron	-- 	0.431 mg/L	0.356 mg/L            (12)2	
Magnesium	-- 	38.3 mg/L	32.9 mg/L	
Manganese	-- 	0.327 mg/L	--	

	Internal Outfalls:

		Maximum Daily Value	
Parameter	Outfall 002	Outfall 004	Outfall 005	Outfall 0063	
BOD5	ND mg/L	3.51 mg/L	< 3.33 mg/L mg/L	1.5 mg/L	
COD	28 mg/L	33.5 mg/L	62.1 mg/L	< 20.0 mg/L	
TOC	13.2 mg/L	11.8 mg/L	18.7 mg/L	4.6 mg/L	
TSS	4.1 mg/L	< 2.5 mg/L	< 2.5 mg/L	16 mg/L	
Ammonia (as N)	< 0.117 mg/L	< 0.117 mg/L	< 0.117 mg/L	< 0.10 mg/L	
Flow	26.27 MGD	2.8 MGD	0.529 MGD	0.65 mg/L	
Temperature (winter)	18.3 °C	18.5 °C	18.8 °C	18.9 °C	
Temperature (summer)	27.3 °C	25.3 °C	25.1 °C	25.4 °C	
pH (minimum)	8.63 SU	6.86  SU	6.96 SU	8.51 SU	
pH (maximum)	8.63 SU	8.01 SU	25.1 SU	8.51 SU	
Arsenic	7.27 ug/L	2.74 ug/L	--	12 ug/L	
Cadmium	<0.0050 ug/L	--	--	0.8 ug/L	
Nickel	5.34 ug/L	43.7 ug/L	81.4 ug/L	136 ug/L	
Zinc	0.815 ug/L	0.45 mg/L	538 ug/L	270 ug/L	
Chromium, Total	--	--	--	125 ug/L	
Copper, Total 	--	58.4 ug/L	58.4 ug/L	98 ug/L	
Lead, Total	--	--	--	3 ug/L	
Mercury, Total	--	--	--	5.5e-6 mg/L	
Selenium, Total	--	--	--	7 ug/L	
Bromide	--	0.353 mg/L	< 0.353 mg/L	0.52 mg/L	
Chlorine, TR	0.102 mg/L	--	--	<0.1 mg/L	
		Maximum Daily Value	
Parameter	Outfall 002	Outfall 004	Outfall 005	Outfall 0063	
Fluoride	0.516 mg/L	0.23 mg/L	0.342 mg/L	0.35 mg/L	
Color	40 pcu	1 pcu	50 pcu	30 pcu	
Nitrate-Nitrite	1.2 mg/L	1.17 mg/L	0.528 mg/L	--	
NitrogenTotal Organic	1.1 mg/L	0.171 mg/L	3.27 mg/L	0.40 mg/L	
Phosphorus	1.04 mg/L	0.705 mg/L	4.84 mg/L	3.38 mg/L	
BOD5	ND mg/L	3.51 mg/L	< 3.33 mg/L mg/L	1.5 mg/L	
COD	28 mg/L	33.5 mg/L	62.1 mg/L	< 20.0 mg/L	
TOC	13.2 mg/L	11.8 mg/L	18.7 mg/L	4.6 mg/L	
TSS	4.1 mg/L	< 2.5 mg/L	< 2.5 mg/L	16 mg/L	
Ammonia (as N)	< 0.117 mg/L	< 0.117 mg/L	< 0.117 mg/L	< 0.10 mg/L	
Flow	26.27 MGD	2.8 MGD	0.529 MGD	0.65 mg/L	
Temperature (winter)	18.3 °C	18.5 °C	18.8 °C	18.9 °C	
Temperature (summer)	27.3 °C	25.3 °C	25.1 °C	25.4 °C	
pH (minimum)	8.63 SU	6.86  SU	6.96 SU	8.51 SU	
pH (maximum)	8.63 SU	8.01 SU	25.1 SU	8.51 SU	
Arsenic	7.27 ug/L	2.74 ug/L	--	12 ug/L	
Cadmium	<0.0050 ug/L	--	--	0.8 ug/L	
Nickel	5.34 ug/L	43.7 ug/L	81.4 ug/L	136 ug/L	
Zinc	0.815 ug/L	0.45 mg/L	538 ug/L	270 ug/L	
Chromium, Total	--	--	--	125 ug/L	
Copper, Total 	--	58.4 ug/L	58.4 ug/L	98 ug/L	
Lead, Total	--	--	--	3 ug/L	
Mercury, Total	--	--	--	5.5e-6 mg/L	
Selenium, Total	--	--	--	7 ug/L	
Bromide	--	0.353 mg/L	< 0.353 mg/L	0.52 mg/L	
Chlorine, TR	0.102 mg/L	--	--	<0.1 mg/L	
Color	40 pcu	1 pcu	50 pcu	30 pcu	
Fluoride	0.516 mg/L	0.23 mg/L	0.342 mg/L	0.35 mg/L	
Nitrate-Nitrite	1.2 mg/L	1.17 mg/L	0.528 mg/L	--	
NitrogenTotal Organic	1.1 mg/L	0.171 mg/L	3.27 mg/L	0.40 mg/L	
Phosphorus	1.04 mg/L	0.705 mg/L	4.84 mg/L	3.38 mg/L	
Sulfate	604 mg/L	190 mg/L	121 mg/L	3370 mg/L	
Aluminum	--	--	--	5.46 mg/L	
Barium	0.354 mg/L	0.0772 mg/L	0.0742 mg/L	0.04 mg/L	
Boron	0.244 mg/L	0.0798 mg/L	0.0757 mg/L	--	
Iron	2.65 mg/L	1.77 mg/L	2.21 mg/L	48.6 mg/L	
Manganese	0.714 mg/L	0.091 mg/L	0.0968 mg/L	1.47 mg/L	
Magnesium	66.3 mg/L	24.3 mg/L	24.5 mg/L	54.3 mg/L	

	Maximum Daily Value	
Parameter	Outfall 007	Outfall 011	Outfall 016	Outfall 010	
Chlorine, TR	< 0.01 mg/L		0.057 mg/L	0.05 mg/L	
Color	10 pcu	200 pcu	50 pcu	--	
Fluoride	0.21 mg/L	--	< 0.064 mg/L	--	
Nitrate-Nitrite	< 0.707 mg/L	--	--	--	
Oil and grease	<1.4 mg/L	ND	--	--	
Phosphorus		1.24 mg/L	0.242 mg/L	--	
Sulfate	53.4 mg/L	--	3.98 mg/L	--	
Copper	--	5.31 ug/L		--	
Zinc	13.9 ug/L	--	< 7.96 ug/L	--	
Barium	0.0959 mg/L	--	5.39 ug/L	--	
Arsenic	--	--	0.669 ug/L	--	
Chromium	--	--	5.6 ug/L	--	
Mercury1	--	--	<0.1 ug/L	--	
Cobalt	--	0.567 ug/L	--	--	
Iron	0.383 mg/L	3.1 mg/L	--	--	
Magnesium	31.1 mg/L	--	1.02 ug/L	--	
Manganese	--	--	5.9 ug/L	--	
Alpha, total	--	12 ± 5.74 pCi/L	--	--	
Beta, total	--	14.1 ± 4.49 pCi/L	--	--	
Radium, total	--	0.892 ± 0.321 pCi/L	--	--	
Radium 226, total	--	0.4 ± 0.296 pCi/L	--	--	

All of the detectable concentrations provided on the application are listed above. The remaining pollutant data provided on the application for each outfall was reported as non-detectable (ND). 

1Mercury was reported as < 0.1 ug/L. Because the facility did not use a test method with enough sensitivity, the screen will be run at the detection level of 0.1 ug/L (0.0001 mg/L).

2This represents the number of analyses reported on the renewal application for copper, lead, nickel, zinc, and iron for Outfalls 013 and 014. The facility only conducted 1 analysis for the renewal application; the remaining 11 samples were estimated from historical application sampling. The facility currently has a 12-sample monitoring requirement for these pollutants. Because the facility has not completed this sampling, the 12-sample monitoring requirement will remain in the permit.

3Outfall 006 has not discharged in 15 plus years. The data provided on the application are estimates based on reported data in a previous application.

VIII. 	WATER QUALITY LIMITATIONS BASED ON WASTELOAD ALLOCATION 

	None. 

VII.	CATEGORICAL GUIDELINE LIMITATIONS CALCULATIONS

Not Applicable.

VIII.	CHEMICAL SPECIFIC SCREENING

Grand Gulf Nuclear Station has three external discharge points.  Outfall 001 is a combination of internal outfalls 004, 005, 006 and 011 which discharge directly into the Mississippi River via an underground pipeline. Outfall 013 is the combined discharge from the Bechtel Shop, vehicle maintenance shop, Standby Service Water Leakage, HVAC once-through cooling water, internal Outfall 010 (Sanitary), and internal Outfall 016 (Energy Service System) which discharges to an unnamed creek thence to Hamilton Lake. Outfall 014 consists of a discharge from sedimentation Basin B, which includes effluent from internal Outfall 007, standby service water leakage and releases, intermittent circulation water basin overflows, and storm water runoff. 

For Outfalls 001

Qr	= Receiving Stream Flow (Mississippi River)
 	= 82,082 MGD (7Q10 Flow) - Acute Screening 
  	= 653,272.60 MGD (Mean annual flow) 
  	 
Qw	= Maximum 30-day value flow.
= 22.84 MGD
	
 IWC = Qw /(Qr + Qw)*100
 = (22.84)/(653,272.7+22.84)*100 = 0.0035 %  (Mean Annual)
 = 100 * (22.84)/(82,082+22.84)*100  = 0.028 %  (7Q10)

For Outfall 013 

Qr  = Receiving Stream Flow  (Unnamed creek thence to Hamilton Lake)
  = 0 MGD (7Q10 flow) - Acute and Chronic Screening 
= 5.8401 MGD (Mean annual flow) - Human Health Screening

Qw = Maximum 30-day value flow. 
 = 2.03 MGD 

IWC = 2.03/(5.881+2.03)*100 = 25.7 %  (Mean Annual)
= 2.03/(0+2.03)*100 = 100 %  (7Q10 = 0)

For Outfall 014  

Qr  = Receiving Stream Flow    (Unnamed creek thence to Hamilton Lake)
        = 0 MGD (7Q10 flow) - Acute and Chronic Screening 
        = 5.8401 MGD (Mean annual flow) - Human Health Screening 

Qw = Maximum 30-day flow.
      = 0.62 MGD

  IWC = Qw /(Qr + Qw)*100
 = 0.62/(5.8401+.62)*100 = 9.6 %  (Mean Annual)
 = 0.62/(0+0.62)*100 = 100 %  (7Q10 = 0) 

The following calculations for external Outfall(s) 001, 013, and 014 are shown on the tables that follow: (See tables on pages 8-10)

Xt =  (Qr * Xr) + (Qw * Xw)
       (Qr + Qw)
Xr =  Receiving stream concentration.  
Xw =  Historical effluent data from the application.
Xt = The calculated in-stream concentration is based on historical effluent data from the application.
 
Until 12 samples can be analyzed, the effluent is multiplied by 10 as seen in the following equation:

Xt = (Qr * Xr) + (Qw * Xw  * 10)
       Qr + Qw)

The procedure for the above chemical specific screen is described in 11 Miss. Admin. Code Pt.6, R.1.2.6.

For Outfall 014 when the Mixing Basin Discharges to Basin B (Emergency Discharge Option)
 
Wastewater from internal Outfalls 004, 005, 006, and 011 pass through the mixing basin at the base of the Natural Draft Cooling tower. During normal operations including outages and maintenance, the mixing basin discharges to Outfall 001 via an underground pipeline (approximately 2.5 miles) until it discharges into the Mississippi River.  If a catastrophic failure occurs preventing the basin from discharging via Outfall 001, water from the mixing basin can be pumped manually into the adjacent 100-year storm ditch which flows to Basin B and thence to external Outfall 014. Because this scenario has not occurred, the facility has not been able to sample effluent from Outfall 014 containing water from the discharge/mixing basin. Therefore, an accurate chemical specific
 screen on this type of discharge scenario cannot be performed. 
Outfall 001

Outfall 013

1Mercury was reported as <0.1 ug/L. Because the facility did not use a test method with enough sensitivity, the screen will be run at the detection level of 0.1 ug/L (0.0001 mg/L). Permit Condition T-1 contains a requirement to collect 12 samples for mercury using the appropriate test method and minimum level of sensitivity.

      Outfall 014

1Mercury was reported as <0.1 ug/L. Because the facility did not use a test method with enough sensitivity, the screen will be run at the detection level of 0.1 ug/L (0.0001 mg/L). Permit Condition T-1 contains a requirement to collect 12 samples for mercury using the appropriate test method and minimum level of sensitivity.

IX.	PROPOSED FINAL LIMITATIONS

1.	Average Permit Limitations

Outfall	Parameter	Categorical Limitation	Water Quality Limitation	Present Permit Limitation	Proposed Permit Limitation	Monitoring Frequency	Sample Type	DMR Reporting Frequency	Basis1	
001	Flow (MGD)	--	--	Report 	Report	Continuously	Measurement	Monthly	PPL, TJ	
001	Temperature °F	--	--	Report	Report	Continuously	Continuous Recorder	Monthly	PPL, TJ	
001	Chlorine, FA1	0.2 mg/L	--	0.2 mg/L	0.2 mg/L	See Permit	Check Requirements	Monthly	PPL, Cat. 	
001	Chromium, TR	0.2 mg/L	--	--	0.2 mg/L	Twice per Month	24-hr Composite 	Monthly	Cat. 	
001	Zinc, TR	1.0 mg/L	--	--	0.2 mg/L	Twice per Month	24-hr Composite 	Monthly	Cat. 	
001	pH	--	6.0 SU	6.0 SU	6.0 SU	Weekly	Grab Sampling	Monthly	PPL, MSWQS	
002	Flow (MGD)	--	--	Report 	Removed	--	--	--	TJ1	
002	Chlorine, FA1	0.2 mg/L	--	0.2 mg/L	Removed	--	--	--	TJ1	
002	Chromium, TR1	0.2 mg/L	--	--	Moved to Outfall 001	See Outfall 001	See Outfall 001	See Outfall 001	TJ1	
002	Zinc, TR1	1.0 mg/L	--	1.0 mg/L	Moved to Outfall 001	See Outfall 001	See Outfall 001	See Outfall 001	TJ1	
004	Flow (MGD)	--	--	Report 	Report	Once per Batch During Operation	Check Requirements	Monthly	PPL, TJ	
004	Chlorine, FA1	0.2 mg/L	--	0.2 mg/L	0.2 mg/L	Once per Batch During Operation	Check Requirements	Monthly	PPL, Cat. 	
004	Chromium, TR1	0.2 mg/L	--	0.2 mg/L	0.2 mg/L	Once per Batch During Operation	Check Requirements	Monthly	PPL, Cat. 	
004	Zinc, TR1	1.0 mg/L	--	1.0 mg/L	1.0 mg/L	Once per Batch During Operation	Check Requirements	Monthly	PPL, Cat. 	
005	Flow (MGD)	--	--	Report 	Report	Once per Batch During Operation	Instantaneous Sampling	Monthly	PPL, TJ	
005	Chlorine, FA1	0.2 mg/L	--	0.2 mg/L	0.2 mg/L	Once per Batch During Operation	Check Requirements	Monthly	PPL, Cat. 	
005	Chromium, TR1	0.22 mg/L	--	0.2 mg/L	0.02 mg/L	Once per Batch During Operation	Check Requirements	Monthly	PPL, Cat. 	
005	Zinc, TR1	1.0 mg/L	--	1.0 mg/L	1.0 mg/L	Once per Batch During Operation	Check Requirements	Monthly	PPL, Cat.	
006	Flow (MGD)	--	--	Report 	Report	Once per Batch During Operation	Instantaneous Sampling	Monthly	PPL, TJ	
006	Oil and grease	15 mg/L	--	15 mg/L	15 mg/L	Once per Batch During Operation	Grab Sampling	Monthly	PPL, Cat. 	
										
Outfall	Parameter	Categorical Limitation	Water Quality Limitation	Present Permit Limitation	Proposed Permit Limitation	Monitoring Frequency	Sample Type	DMR Reporting Frequency	Basis1	
006	TSS	30 mg/L	--	30 mg/L	30 mg/L	Once per Batch During Operation	Grab	Monthly	PPL, Cat.	
007	Flow (MGD)	--	--	Report 	Report	Twice per Month	Instantaneous	Monthly	PPL, TJ	
007	Oil and grease	15 mg/L	--	15 mg/L	15 mg/L	Twice per Month	Instantaneous	Monthly	PPL, Cat. 	
007	TSS	30 mg/L	--	30 mg/L	30 mg/L 	Twice per Month	Grab	Monthly	PPL, Cat. 	
007	Chlorine, total residual	--	--	Report 	Report	Twice per Month 	Grab	Monthly	PPL, TJ	
010	Flow (MGD)	--	--	Report 	Report	Continuously	Continuous Recorder	Monthly	PPL, TJ	
010	BOD (5-Day)	--	--	30 mg/L	30 mg/L	Twice per month	24-hour composite	Monthly	PPL, Domestic Guidelines	
010	TSS	--	--	30 mg/L	30 mg/L 	Twice per month	24-hour composite	Monthly	PPL, Domestic Guidelines	
010	Chlorine, total residual	--	--	Report 	Report	Twice per month	Grab	Monthly	PPL, TJ	
010	E.Coli		126 per 100 ml	126 per 100 ml	126 per 100 ml	Twice per month	Grab	Monthly	PPL, MSWQS	
010	pH	--	6.0 SU	6.0 SU 	6.0 SU 	Twice per month	Grab	Monthly	PPL, MSWQS	
011	Flow (MGD)	--	--	Report 	Report	Continuously	Pump Log	Monthly	PPL, TJ	
011	TSS	30 mg/L	--	Report 	Report	Monthly	Grab	Monthly	PPL, TJ	
011	Oil and grease	15 mg/L	--	--	15 mg/L	Monthly	Grab 	Twice Per Month	PPL, Cat.	
013	Flow (MGD)	--	--	Report 	Report	Quarterly	Instantaneous Sampling	Annually	PPL, TJ	
013	TSS	--	--	Report 	Report 	Quarterly	Grab	Annually	PPL, TJ	
013	pH	--	6.0 SU	6.0 SU 	6.0 SU 	Quarterly	Grab	Annually	PPL, MSWQS	
013	Zinc, TR1	--	0.065  mg/L	--	Report	Monthly	24-hr Composite	Quarterly	PPL, TJ	
014	Flow (MGD)	--	--	Report 	Report	Quarterly	Instantaneous Sampling	Annually	PPL, TJ
	
014	TSS	--	--	Report 	Report 	Quarterly	Grab	Annually	PPL, TJ	
014	Zinc, TR1	--	--	--	Report	Monthly	24-hr Composite	Quarterly	PPL, TJ	
014	pH	--	6.0 SU	6.0 SU 	6.0 SU 	Quarterly 	Grab	Annually	PPL, MSWQS	
016	Flow (MGD)	--	--	Report 	Report	Twice per Quarter	Instantaneous Sampling	Annually	PPL, TJ	
016	Chlorine, TR1	--	--	Report 	Report 	Twice per Quarter	Grab	Annually	PPL, TJ	
016	pH	--	6.0 SU	6.0 SU 	6.0 SU 	Twice per Quarter	Grab	Annually	PPL, MSWQS	
016	TSS	30 mg/L	--	--	30 mg/L	Twice per Quarter	Grab	Annually	PPL, Cat. 	
016	Oil and grease	15 mg/L	--	--	15 mg/L	Twice per Quarter	Grab	Annually	PPL, Cat. 	

2.	Maximum Permit Limitations

Outfall	Parameter	Categorical Limitation	Water Quality Limitation	Present Permit Limitation	Proposed Permit Limitation	Monitoring Frequency	Sample Type	DMR Reporting Frequency	Basis1	
001	Flow (MGD)	--	--	Report 	Report	Continuously	Measurement	Monthly	PPL, TJ	
001	Temperature °F	--	--	Report	Report	Continuously	Continuous Recorder	Monthly	PPL, TJ	
001	Chlorine, FA1	0.5 mg/L	--	0.5 mg/L	0.5 mg/L	See Permit	Check Requirements	Monthly	PPL, Cat.	
001	Chlorination Duration1	120 min	--	120 min	120 min	See Permit	Measurement	Monthly	PPL, Cat.	
001	Chromium, TR	0.2 mg/L	--	--	0.2 mg/L	Twice per Month	24-hr Composite	Monthly	Cat.	
001	Zinc, TR	1.0 mg/L	--	--	1.0 mg/L	Twice per Month	24-hr Composite	Monthly	Cat.	
001	pH	--	9.0 SU	9.0 SU	9.0 SU	Weekly	Grab	Monthly	PPL, MSWQS	
002	Flow (MGD)	--	--	Report 	Report	Twice per Month 	Instantaneous 	Monthly	PPL, TJ	
002	Chlorine, FA1	0.5 mg/L	--	0.5 mg/L	Removed	--	--	--	TJ1	
002	Chlorination Duration	120 min	--	120 min	Removed	--	--	--	TJ1	
002	Chromium, TR1	0.2 mg/L	--	0.2 mg/L	Moved to Outfall 001	See Outfall 001	See Outfall 001	See Outfall 001	TJ1	
002	Zinc, TR1	1.0 mg/L	--	1.0 mg/L	Moved to Outfall 001	See Outfall 001	See Outfall 001	See Outfall 001	TJ1	
004	Flow (MGD)	--	--	Report 	Report	Once per Batch During Operation	Instantaneous 	Monthly	PPL, TJ	
004	Chlorine, FA1	0.5 mg/L	--	0.5 mg/L	0.5 mg/L	Once per Batch During Operation	Check Requirements	Monthly	PPL, Cat.	
004	Chlorination Duration	120 min	--	120 min	120 min	Once per Batch During Operation	Measurement	Monthly	PPL, Cat. 	
004	Chromium, TR1	0.2 mg/L	--	--	0.2 mg/L	Once per Batch During Operation	Check Requirements	Monthly	PPL, Cat. 	
004	Zinc, TR1	1.0 mg/L	--	1.0 mg/L	1.0 mg/L	Once per Batch During Operation	Check Requirements	Monthly	PPL, Cat. 	
005	Flow (MGD)	--	--	Report 	Report	Once per Batch During Operation	Measurement	Monthly	PPL, TJ	
005	Chlorine, FA1	0.5 mg/L	--	0.5 mg/L	0.5 mg/L	Once per Batch During Operation	Check Requirements	Monthly	PPL, Cat. 	
005	Chlorination Duration	120 min	--	120 min	120 min	Once per Batch During Operation	Measurement	Monthly	PPL, Cat. 	
005	Chromium, TR1	0.2 mg/L	--	--	0.2 mg/L	Once per Batch During Operation	Measurement	Monthly	PPL, Cat. 	
005	Zinc, TR1	1.0 mg/L	--	1.0 mg/L	1.0 mg/L	Once per Batch During Operation	Check Requirements	Monthly	PPL, Cat. 	
006	Flow (MGD)	--	--	Report 	Report	Once per Batch During Operation	Instantaneous 	Monthly	PPL, TJ	

Outfall	Parameter	Categorical Limitation	Water Quality Limitation	Present Permit Limitation	Proposed Permit Limitation	Monitoring Frequency	Sample Type	DMR Reporting Frequency	Basis1	
006	Oil and grease	20 mg/L	--	20 mg/L	20 mg/L	Once per Batch During Operation	Grab 	Monthly	PPL, Cat. 	
006	TSS	100 mg/L	--	100 mg/L	100 mg/L	Once per Batch During Operation	Grab	Monthly	PPL, Cat	
007	Flow (MGD)	--	--	Report 	Report	Twice per Month	Instantaneous	Monthly	PPL, TJ	
007	Oil and grease	20 mg/L	--	20 mg/L	20 mg/L	Twice per Month	Grab	Monthly	PPL, Cat. 	
007	TSS	100 mg/L	--	100 mg/L	100 mg/L 	Twice per Month	Grab	Monthly	PPL, Cat. 	
007	Chlorine, total residual	--	--	Report	Report	Twice per Month	Grab	Monthly	PPL, TJ	
010	Flow (MGD)	--	--	Report 	Report	Continuously	Continuous Recorder 	Monthly	PPL, TJ	
010	BOD (5-Day)	--	--	45 mg/L	45 mg/L	Twice per Month	24-hr Composite	Monthly	PPL, Domestic Guidelines	
010	TSS	--	--	45 mg/L	45 mg/L	Twice per Month	24-hr Composite	Monthly	PPL Domestic Guidelines	
010	Chlorine, total residual	--	--	0.5 mg/L	0.5 mg/L	Twice per Month	Grab	Monthly	PPL, TJ	
010	E.Coli		410 col./100 ml	410 col./100 ml	410 col./100 ml	Twice per Month	Grab	Monthly	PPL, MSWQS	
010	pH	--	9.0 SU	9.0 SU	9.0 SU	Twice per Month	Grab	Monthly	PPL, MSWQS	
011	Flow (MGD)	--	--	Report 	Report	Continuously	Pump Log	Monthly	PPL, TJ	
011	TSS	100 mg/L	--	30 mg/L	30 mg/L	Monthly	Grab	Monthly	PPL, TJ	
011	Oil and grease	20 mg/L	--	--	20 mg/L	Monthly	Grab	Twice per month	PPL, Cat.	
013	Flow (MGD)	--	--	Report 	Report	Quarterly	Instantaneous	Annually	PPL, TJ	
013	TSS	--	--	Report 	Report 	Quarterly	Grab	Annually	PPL, TJ	
013	pH	--	9.0 SU	9.0 SU	9.0 SU	Quarterly	Grab	Annually	PPL, MSWQS	
013	Zinc, TR1	--	0.065 mg/L	--	0.065 mg/L	Quarterly	Grab	Annually	PPL, MSWQS	
014	Flow (MGD)	--	--	Report 	Report	Quarterly	Instantaneous	Annually	PPL, TJ	
014	TSS	--	--	Report 	Report 	Quarterly	Grab	Annually	PPL, TJ	
014	Zinc, TR1	--	0.065 mg/L	--	0.065mg/L	Quarterly	24-hr Composite	Annually	PPL, MSWQS	
014	pH	--	9.0 SU	9.0 SU	9.0 SU	Quarterly	Grab	Annually	PPL, MSWQS	
016	Flow (MGD)	--	--	Report 	Report	Twice per Quarter	Instantaneous	Annually	PPL, TJ	
016	Chlorine, total residual	--	--	0.5 mg/L	0.5 mg/L	Twice per Quarter	Grab	Annually	PPL, TJ	
016	TSS	100 mg/L	--	--	100 mg/L	Twice per Quarter	Grab	Annually	PPL, Cat. 	
016	Oil and grease	20 mg/L	--	--	20 mg/L	Twice per Quarter	Grab	Annually	PPL, Cat. 	
016	pH	--	9.0 SU	9.0 SU	9.0 SU	Twice per Quarter	Grab	Annually	PPL, MSWQS	

1Basis: TR = Total Recoverable, FA = Free Available, MSWQS = Mississippi Water Quality Standards, TJ = Technical Judgement, Categorical (Cat.) = 40 CFR 423.12 (BPT) and 423.13 (BAT),  PPL = Previous Permit Limits. Because effluent from internal Outfall 002 is the exact same effluent as Outfall 001, the Outfall 002 limitations were moved to Outfall 001.  Since Outfall 001 already had limitations for FAC and Chlorination duration, the limitations for Chromium and Zinc were the only limits added to Outfall 001.
126 Priority Pollutants Certification

The permittee shall certify, not less than once per year (with the DMR on January 28th of each year), that chemical products added for cooling tower maintenance, including such chemical used for corrosion inhibition, do not result in the discharge via cooling tower blowdown of any of the 126 priority pollutants (including but not limited to chromium and zinc) in detectable concentrations. Additionally, once for each product used for cooling system and/or boiler maintenance, compliance shall be demonstrated by submission of certification from the manufacturer that such product contains no priority pollutants. See permit condition S-1 on page 4 of this permit.

The addition of any chemical product to the cooling system and/or the boiler system other than those submitted with the application is prohibited unless prior written approval is obtained in accordance with condition S-10 on page 8 of this permit.  Chemicals used for the maintenance of cooling water chemistry and boiler water chemistry, or otherwise to operate or maintain these systems, shall not cause a violation of the terms and conditions contained in condition S-1 on page 4 of this permit.

Thermal Mixing Zone

The receiving water shall not exceed a maximum water temperature change of 2.8 degrees Celsius (5.0 degrees Fahrenheit) relative to the upriver temperature, outside a mixing zone not exceeding a maximum width of 60 feet from the river edge and a maximum length of 6,000 feet downstream from the point of discharge, as measured at a depth of 5 feet. The river edge shall be defined as being no further east than the mouth of the barge slip.  The maximum water temperature shall not exceed 32.2 degrees Celsius (90 degrees Fahrenheit) outside the same mixing zone, except then ambient temperatures approach or exceed this value. See condition L-6 on page 2 of this permit.

Thermal Modeling

Thermal monitoring shall be performed any time the river stage is less than 0.5 feet (Vicksburg gauge) during winter months (November-April) or, is less than minus 1.2 feet (Vicksburg gauge) during the summer months (May-October). If these conditions occur and the plant is generating power, monitoring shall be performed upriver at PT.1 (surface/5 feet sub-surface), Discharge Outlet, Barge Slip Outlet, and down river at PT.7.  However, once monitoring has been performed at river stages less than those cited (0.5 feet during the winter months and minus 1.2 feet during the summer months), the river stages which existed at the time of thermal modeling, will then become the standard river stage during which a subsequent monitoring exercise must be performed if the river falls below that stage. Thorough documentation shall be maintained on file of the river stage during each period of thermal monitoring. This policy is subject to modification if any data collected during a particular stage indicates temperature variations not previously measured. See condition L-6 on page 2 of this permit.

Treated Liquid Rad Wastewater (Outfall 011)

This narrative condition states that the radioactive component of this discharge is regulated by the Nuclear Regulatory Commission (NRC). See condition T-1 on page 33 of this permit.

Metal Monitoring (Iron, Copper, Lead, Nickel, Mercury)

During the previous permit renewal, discharges from Outfall 013 and 014 failed the toxicity screen because of a variability factor, i.e. only one sample was provided on the application. Based on technical judgment, the permittee was required to monitor each outfall once per month when discharging, until 12 samples were analyzed for total iron, total copper, total lead, and total nickel.  Because the facility has not completed this sampling, this requirement will remain in the permit. The monitoring frequency for these pollutants has been changed from once per month to twice per month. 

Discharges from Outfalls 013 and 014 failed the total mercury toxicity screen because the test method used did not utilize an appropriate level of sensitivity. The permittee will be required to monitor Outfalls 013 and 014 twice per month when discharging, utilizing 24-hour composite sampling, until 12 effluent samples have been analyzed for each outfall. Total mercury shall be monitored using Method 245.7 or an approved equivalent with a minimum level of quantification (ML) of 5.0 ng/L.  Following completion of the 12-sample collection, the permittee shall submit a report listing the testing date and analytical result for each sampling event. The report shall be submitted to the MDEQ Environmental Permits Division no later than the 28th day of the Month following completion of the 12-sample collection. If this data indicates a violation of water quality standards, the NPDES permit may be reopened and modified. 

Application Submittal Requirements

Upon commencement of discharge from Outfall 006, the permittee shall collect one effluent sample from Outfalls 006 and test for the Table A, Table B, and Table C pollutants listed on EPA Form 2C, Section 7. For Table A pollutants, the application must contain the results for at least one analysis for each pollutant listed in the table. For Table B and Table C pollutants, the application must contain the results of at least one analysis for each pollutant that is believed to be present. This application should be submitted no later than the 28th day of the month following the completion of the effluent sampling.  The NPDES Permit may be modified if data indicates a violation of water quality standards for any of the above-mentioned parameters. The permit includes this requirement because the effluent characteristics provided on the renewal application for this outfall were estimated utilizing historical sampling data because Outfall 006 has not discharged in 15 plus years.  

Removal of internal Outfall 002

Historically, internal Outfall 002 was the comingling of effluent from internal outfalls(s) 004, 005, 006, 011 that discharged from the Natural Draft Cooling Tower mixing basin. The mixing basin discharge (Outfall 002) would then be discharged via external Outfall 001 and thence to the Mississippi River via an underground pipeline. Monitoring of Outfall 001 is conducted as it enters the discharge pipeline near the mixing basin. During this permit renewal, it was determined that the effluent from internal Outfall 002 is the same as Outfall 001.  Therefore, the limitations for Outfall 002 were moved to Outfall 001, and Outfall 002 was removed from the permit. 

Emergency discharge of from the Natural Draft Cooling Tower Mixing Basin

Historically, the cooling tower mixing basin has always been discharged wastewater from the Natural Draft Cooling Tower Mixing Basin via external Outfall 001 during normal operations and plant outages. Based on the renewal application and conversations with the facility during the current renewal process, the facility said that in the event of a catastrophic failure (i.e., where the cooling tower could not discharge via Outfall 001) they would like to have the option to manually pump the water from the cooling tower basin directly into the adjacent 100-yr storm ditch which flows to Basin B and thence to external Outfall 014. During this situation, the pollutants limited on Outfall 001, including the FAC and chlorination duration, will continue to be monitored and reported. 

It should be noted that there is no treatment on Outfall 001, so the manual discharge option to the 100-yr storm ditch is not considered a bypass. Because the limitations and monitoring at Outfall 001 will continue during this alternate discharge option, no additional limitations are required for Outfall 014.

X.	BPJ STATEMENT: 

It is our judgment that the foregoing limitations represent 11 Miss. Admin. Code Pt.6, Ch. 1 and 2 (MSWQS), and the applicable Categorical Guidelines (Cat.) for low volume wastes (40 CFR 423.12(b)(3)), and cooling tower blowdown (40 CFR 423.13(c)(2) and (d)(1)), and technical judgment (TJ).