PERMIT RATIONALE FOR REISSUANCE
NRG Wholesale Generation LP
Choctaw County
French Camp, Mississippi
Water NPDES No. MS0057606
June 18, 2018

I.	FACILITY INFORMATION

Facility Name:  NRG Wholesale Generation LP
Facility Address:  2446 Highway 407 
French Camp, MS  39745    
	Permit No.:  MS0057606
SIC:  4911
Permit Writer:  Thomas Kelly
EPD Branch:  Water I

II.	NATURE OF BUSINESS

NRG Wholesale Generation LP is a dry-cooled combined-cycle electrical generation facility with a nominal electrical generating capacity of approximately 800 megawatts.  The facility has three natural gas fired combustion turbines to generate electricity for the power grid.  The facility obtains potable water from the local municipal water utility.  Water from two onsite wells is used for makeup for the steam cycle, for inlet air cooling, for service water, and fire protection water.  This facility is classified as an NPDES Major Source.

III.	EFFLUENT AND RECEIVING STREAM FLOW DATA

Outfall 001:   External outfall consisting of the combined discharge of treated sanitary wastewater and low volume wastewater from internal outfalls 003 and 004. The maximum daily discharge flow from this outfall is approximately 0.2001MGD.

Outfall 002:  External outfall consisting of facility storm water.  The maximum daily discharge flow is 0.6163 MGD.

Outfall 003 (Removed): Internal outfall consisting of treated sanitary wastewater. The water quality based effluent limitation for this wastewater were placed on external outfall 001 in lieu of this internal outfall. As a result, the discharge monitoring requirements for internal outfall 003 have been removed. The maximum daily discharge flow is 0.00076 MGD.

Outfall 004:	Internal outfall consisting of low volume wastewater (wastewater from raw water filters, wastewater from combustion turbine inlet air coolers, oil/water separator, reverse osmosis and electro-deionization unit, and HRSG blowdown). The maximum 30-day discharge flow is 0.1781 MGD.

External Outfalls 001 and 002 both discharge into an unnamed tributary of Poplar Creek (7Q10=0).

IV.	303(d) ISSUES

None.
V.	TYPE OF WASTEWATER TREATMENT:

Outfall 001:	Equilibration in a wastewater surge tank, aeration to increase dissolved oxygen levels, and dechlorination.
Outfall 002:	Sedimentation.
Outfall 003:	Package sanitary treatment system consisting of primary treatment, activated sludge, settling/clarification, and chlorine disinfection.
Outfall 004:	Oil/water separation and mechanical cooling.

VI.	EPA APPLICABLE CATEGORICAL GUIDELINES

1.	40 CFR Part 423 - Steam Electric Power Generation Point Source Category; Sections 423.12 (BPT-Best Practicable Control Technology Currently Available) and 423.15 (New Source Performance Standards).  See Attachment A.

VII.	STATE APPLICABLE GUIDELINES

The Mississippi environmental regulations have been renumbered and reformatted pursuant to the amended Administrative Procedures Act passed by the state legislature. While the numbering and citation of the regulations have changed, the content of the regulations have not.

1.	Mississippi Commission on Environmental Quality National Pollutant Discharge Elimination System (NPDES) Permits, Underground Injection Control (UIC) Permits, State Permits, Water Quality Based Effluent Limitations, and Water Quality Certification [11 Miss. Admin Code Pt. 6, Ch.1.]

2.	 Mississippi Commission on Environmental Quality Regulations for Intrastate, Interstate, and Coastal Waters [11 Miss. Admin Code Pt. 6. Ch. 2].
VIII.	DATA FROM APPLICATION FORM (2C):
		        Maximum Daily Value	
Parameter	Outfall 001	Outfall 002	Outfall 003	Outfall 004	
BOD	< 6.0 mg/L	<6.0 mg/L	13 mg/L	< 6.0 mg/L	
COD	15 mg/L	<15 mg/L	42 mg/L	32 mg/L	
TOC	1.32 mg/L	2.76 mg/L	16.7 mg/L	1.94 mg/L	
TSS	5 mg/L	7 mg/L	16 mg/L	12 mg/L	
Ammonia (as N)	1.36 mg/L	0.111 mg/L	21.6 mg/L	0.228 mg/L	
Flow	0.2001 MGD	0.6163 MGD	0.000076 MGD	0.1781 MGD	
Temp. (Winter)	27.3 ºC	Ambient 	Ambient	Ambient	
Temp. (Summer)	28 ºC	28.3 °C	27.6 °C	27.8 °C	
pH	8.98SU	7.84 SU	6.58 SU	7.69 SU	
Bromide, Total	<0.01 mg/L	--	--	--	
Chlorine, TR	0.01 mg/L	<0.01 mg/L	8.8 mg/L	0.02 mg/L	
Color	--	--	30 CU	<5 CU	
Fecal Coliform 	--	--	62.8 col/100mL	--	
Fluoride, Total	0.135 mg/L	--	--	--	
Nitrate-Nitrite	0.762 mg/L	<0.100 mg/L	97.9 mg/L	0.701 mg/L	
Nitrogen, Total Organic (as N)	<0.5 mg/L	<0.5 mg/L	<0.5 mg/L	<0.5 mg/L	
Oil and Grease	<1.6 mg/L	1.7 mg/L	<1.6 mg/L	2.1 mg/L	
Phosphorus, Total	1.19 mg/L	<0.005 mg/L	20.7 mg/L	1.84 mg/L	
Sulfate (as SO4)	7.1 mg/L	--	44.5 mg/L	4.68 mg/L	
Sulfide (as S)	<1.0 mg/L	--	--	--	
Aluminum, Total	<0.1 mg/L	--	--	<0.1 mg/L	
Barium, Total	0.008 mg/L	--	--	0.1 mg/L	
Boron, Total	0.092 mg/L	--	--	--	
Iron, Total	0.1 mg/L	--	--	0.1 mg/L	
Magnesium, Total	0.344 mg/L	--	--	0.401 mg/L	
Molybdenum, Total	0.036 mg/L	--	--	--	
Manganese, Total	0.344 mg/L	--	--	0.024 mg/L	
Titanium, Total	0.0012 mg/L	--	--	--	
Cadmium, Total	0.0005 mg/L	--	--	--	
Copper, Total	0.0016 mg/L	--	--	--	
Mercury, Total	0.00000013 mg/L	--	--	--	
Zinc, Total	0.006 mg/L	--	--	--	
Many of the parameters listed previous table were reported at a concentration greater than the appropriate minimum quantification level (MQL). All other parameters listed on the Form 2C application are not shown due to one of the following reasons: (1) testing was not required, (2) the parameters were believed absent, (3) the reported concentrations were non-detect or less than the appropriate MQL for each parameter tested.

IX.	WATER QUALITY LIMITATIONS BASED ON WASTELOAD ALLOCATION 

Parameter	Average Concentration	Average Loading	
Ammonia (as N)	2 mg/L	--	
Chlorine, TR	0.011 mg/L	--	
e.Coli	126 col./100 mL	--	
DO	6 mg/L	--	
BOD5	9 mg/L	20.27 lb/day	

IX.	CATEGORICAL GUIDELINES

See Attachment A

X.	CHEMCAL SPECIFIC SCREENING

See Attachment B.

XI.	PROPOSED FINAL LIMITATIONS 

1.	Average Permit Limitations
Outfall	Parameter	Categorical Limitation	Water Quality Limitation	Present Permit Limitation	Proposed Permit Limitation	Basis	
001 (External)	Ammonia (as N)	--	2 mg/L	2 mg/L	2 mg/L	WLA	
	Chlorine, Total Residual	--	0.011 mg/L	0.011 mg/L	0.011 mg/L	WLA, 11 Miss. Admin Code Pt. 6, Ch.2	
	E. Coli	--	--	126 col./100ml	126 col./100ml	WLA, 11 Miss. Admin Code Pt. 6, Ch.2	
	Flow	--	Report (MGD)	Report (MGD)	Report (MGD)	Technical Judgment	
	CBOD5	--	--	--	9 mg/L	WLA	
	DO (minimum)	--	6.0 mg/L	6.0 mg/L	6.0 mg/L	WLA	
	pH	--	6.0 SU	6.0 SU	6.0 SU	11 Miss. Admin Code Pt. 6, Ch.2	
	TDS	--	750 mg/L	750 mg/L	750 mg/L	11 Miss. Admin Code Pt. 6, Ch.2	
	Temperature (ºF)	--	Report ( ºF)	Report ( ºF)	Report ( ºF)	Technical Judgment	
002 (External)	Flow 	--	--	Report (MGD)	Report (MGD)	Technical Judgment	
	Oil and Grease	--	--	10 mg/L	10 mg/L	EPA Guidance	
	pH (minimum)	--	6.0 SU	6.0 SU	6.0 SU	11 Miss. Admin Code Pt. 6, Ch.2	
	TSS	--	--	45 mg/L	45 mg/L	Technical Judgment	
004 (Internal)	Flow 	--	--	Report (MGD)	Report (MGD)	Technical Judgment	

Outfall	Parameter	Categorical Limitation	Water Quality Limitation	Present Permit Limitation	Proposed Permit Limitation	Basis	
004 (Internal)	Oil and Grease	15 mg/L	--	15 mg/L	15 mg/L	Categorical	
	TSS	30 mg/L	--	30 mg/L	30 mg/L	Categorical	

2.	Maximum Permit Limitations

Outfall	Parameter	Categorical Limitation	Water Quality Limitation	Present Permit Limitation	Proposed Permit Limitation	Basis	
	Ammonia (as N)	--	3 mg/L	3 mg/L	3 mg/L	WLA, Technical Judgment	
001 (External)	Chlorine, TR	--	0.019 mg/L	0.019 mg/L	0.019 mg/L	WLA, 11 Miss. Admin Code Pt. 6, Ch.2	
	E. Coli	--	--	410 col./100 ml	410 col./100 ml	WLA	
	CBOD5	--	--	--	13.5 mg/L	WLA, Technical Judgment	
	Flow	--	Report 	Report	Report	Technical Judgment	
	DO 	--	Report (mg/L)	Report (mg/L)	Report (mg/L)	Technical Judgment	
	pH 	--	9.0 SU	9.0 SU	9.0 SU	11 Miss. Admin Code Pt. 6, Ch.2	
	TDS	--	1500 mg/L	1500 mg/L	1500 mg/L	11 Miss. Admin Code Pt. 6, Ch.2	
	Temperature	--	90 ºF	90 ºF	90 ºF	11 Miss. Admin Code Pt. 6, Ch.2	
002 (External)	Flow 	--	--	Report (MGD)	Report (MGD)	Technical Judgment	
	Oil and Grease	--	--	15 mg/L	15 mg/L	Technical Judgment	
	pH	--	6.0 SU	6.0 SU	6.0 SU	11 Miss. Admin Code Pt. 6, Ch.2	
	TSS	--	--	45 mg/L	45 mg/L	Technical Judgment	
004
(Internal)	Flow 	--	--	Report (MGD)	Report (MGD)	Technical Judgment	
	Oil and Grease	20 mg/L	--	20 mg/L	20 mg/L	Categorical	
	TSS	30 mg/L	--	30 mg/L	30 mg/L	Categorical	

According to the application, internal Outfall 003 (treated sanitary wastewater) and Outfall 004 (low volume wastewater) flow to a wastewater surge tank where it is retained until enough water is collected for a batch discharge. 
MONITORING TYPE AND FREQUENCY

•	Effluent “Flow” shall be monitored at Outfall 001 continuously utilizing a continuous recorder and reported on a monthly basis; Outfall 002 shall be monitored twice per quarter utilizing instantaneous sampling and reported on a quarterly basis; Outfall 004 shall be monitored daily utilizing a totalizer and shall be reported on a monthly basis.

•	“Oil and Grease” shall be monitored at Outfall 002 twice per quarter with a grab sample of effluent and reported on a quarterly basis; Outfall 004 shall be monitored twice per month with a grab sample of effluent and reported on a monthly basis.

•	“Total Suspended Solids (TSS)” shall be monitored at Outfall 002 twice per quarter with a grab sample of effluent and reported on a quarterly basis; Outfall 004 shall be monitored twice per month with a grab sample of effluent and reported on a monthly basis.

•	“Total Dissolved Solids (TDS) shall be monitored at Outfall 001 twice per month utilizing composite sampling and reported on a monthly basis.

•	“E-coli” shall be monitored at Outfall 001 twice per month with a grab sample of effluent and reported on a monthly basis.

•	 “Total Residual Chlorine (TRC)” shall be monitored at Outfall 001 twice per month with a grab sample of effluent and reported on a monthly basis. 

•	“Oxygen Demand, carbonaceous biochemical, 5-day (20 degrees C)” shall be monitored at Outfall 001 twice per month with a grab sample of effluent and reported on a monthly basis.

•	“Dissolved Oxygen” shall be monitored at Outfall 001 twice per month with a grab sample of effluent and reported on a monthly basis.

•	“Temperature (Deg. F)” shall be monitored at Outfall 001 weekly with a grab sample of effluent and reported on a monthly basis.

•	“pH” shall be monitored at Outfall 001 weekly with a grab sample of effluent and reported on a monthly basis; Outfall 002 twice per quarter with a grab sample of effluent and reported on a quarterly basis.

XI.	BASIS FOR PROPOSED EFFLUENT LIMITS AND PERMIT CONDITIONS

pH:

The minimum and maximum pH effluent limits of 6.0 SU and 9.0 SU are water quality based effluent limits (WQBELs) that reflect the 11 Miss. Admin Code Pt. 6, Ch.2 requirement for the normal pH of waters to be in the range of 6.0 to 9.0 SU.

Flow:

The average and maximum limits of “Report” are based on technical judgment.

Oil and Grease:

The average and maximum effluent limit of 15 mg/L and 20 mg/L are categorical limitations defined in 40 CFR 423.15 (NSPS) for low-volume wastes. The average and maximum loading limits of “Report” are based on technical judgment and were carried forward from the previous permit.

Total Suspended Solids (TSS):

The average and maximum effluent limits of 30 mg/L and 100 mg/L are categorical limitations defined in 40 CFR 423.12 (BPT) for low-volumes wastes. The average and maximum loading limits of “Report” are based on technical judgment and were carried forward from the previous permit.

Total Dissolved Solids (TDS):

11 Miss. Admin Code Pt. 6, Ch.2 specifies that there shall be no substances added to the receiving waters to cause the dissolved solids to exceed 750 mg/l as a monthly average value, nor exceed 1500 mg/L at any time.

Total Residual Chlorine (TRC):

The average and maximum limitations of 0.011 mg/L and 0.019 mg/L are WQBELs that were determined using the acute and chronic water quality criteria, the 7Q10 river flow (Qr7Q10), and the effluent discharge flow limitation (Qw). Since the Qr7Q10 is 0 MGD for all outfalls, the in-stream waste concentration is 100%. Therefore, the acute and chronic WQBELs will be the same as the acute and chronic water quality standards for those pollutants at each outfall.

E.Coli

As part of the recent triennial review of Mississippi’s Water Quality Standards, revisions were made regarding the bacterial indicator for Mississippi’s freshwaters. The following information summarizes the revisions made regarding bacteria as part of the recently approved revisions to the WQS regulations:

(1)	E.coli will now be the bacterial indicator used for all freshwaters in MS designated as Recreation, Fish and Wildlife Support, and/or Public Water Supply (replacing the use of fecal coliform).
(2)	The specific language from the WQS regulations states that ‘Culturable E.coli should not exceed a geometric mean of 126 per 100 ml over a 30-day period, nor should the samples examined during a 30-day period exceed 410 per 100 ml more than 10% of the time.’

Accordingly, fecal coliform has been removed from the proposed permit and replaced with E. coli.  

Total Ammonia Nitrogen (as N)

The average and maximum limitations of 2 mg/L and 3 mg/L are based on the WLA and technical judgment. The average and maximum loading limitations of 1.67 mg/L and 3.83 mg/L are based on technical judgment and were carried forward from the previous permit.

Carbonaceous Biochemical Oxygen Demand, 5-day (CBOD5)

The average and maximum concentration limitations of 9 mg/L and 13.5 mg/L are based on the WLA and technical judgment. The average and maximum loading limitation of 20.27 lb/day and “Report” were based on the WLA and technical judgment.

Dissolved Oxygen (DO)

The minimum concentration limit of 6 mg/L is based on the WLA and technical judgment. 

pH

The minimum and maximum pH effluent limits of 6.0 SU. and 9.0 SU are WQBELs that reflect the 11 Miss. Admin Code Pt. 6, Ch.2 requirement for the normal pH of waters shall be 6.0 to 9.0.  

126 Priority Pollutants Certification
	
The permittee shall certify annually that chemicals added for cooling system maintenance, including such chemicals used for corrosion inhibition, do not result in the discharge via evaporative cooler blowdown and/or HRGS 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 maintenance (unless subsequent changes in the product formulation occur or, the product is obtained from a different source), compliance shall be demonstrated by submission of certification from the manufacturer that such product contains no priority pollutants or, if any of the 126 priority pollutants are contained in such product, calculations which show that the addition of such products does not result in the discharge of that individual priority pollutant at concentrations greater than 10 micrograms per liter due to dilution within the cooling system.

Report Submittal Requirement

Discharges from the following outfall 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 will be required to monitor twice per month when discharging until 12 effluent samples have been analyzed.

•	Outfall 001 – Total Cadmium, Total Copper, Total Mercury

If this data indicates a violation of water quality standards, the NPDES permit may be reopened and modified. Once all 12 samples have been collected for each pollutant, the permittee shall submit a report summarizing the results. 

ATTACHMENT A

EPA CATEGORICAL GUIDELINES

423.11 Specialized Definitions

(1)	The term low volume waste sources means, taken collectively as if from one source, wastewater from all sources except those for which specific limitations are otherwise established in this part. Low volume wastes sources include, but are not limited to: wastewaters from wet scrubber air pollution control systems, ion exchange water treatment system, water treatment evaporator blowdown, laboratory and sampling streams, boiler blowdown, floor drains, cooling tower basin cleaning wastes, and recirculating house service water systems. Sanitary and air conditioning wastes are not included.

423.12 (BPT-Best Practicable Control Technology Currently Available) and 423.15 (New Source Performance Standards).  

(2)	The pH of all discharges shall be within the range of 6.0 - 9.0.

(3)	There shall be no discharge of polychlorinated biphenyl compounds

(4)	The quantity of pollutants discharged from low volume waste sources (Outfalls 004) shall not exceed the quantity determined by multiplying the flow of low volume waste sources times the concentration listed in the following table:

Pollutant or Pollutant Property	
BPT effluent limitations	

Maximum for any 1 day
(mg/l)	
Average of daily values for 30 consecutive days shall not exceed
(mg/l)	

TSS	
Oil and grease		
100.0
20.0	
30.0
15.0	

(5)	At the permitting authority’s discretion, instead of the monitoring specified in 40 CFR 122.11(b) compliance with the limitations for the 126 priority pollutants may be determined by engineering calculations which demonstrate that the regulated pollutants are not detectable in the final discharge by the analytical methods in 40 CFR 136.

(6)	When waste streams from various sources are combined for treatment or discharge, the quantity of each pollutant or pollutant property controlled shall not exceed the specified limitation for that waste source

ATTACHMENT C

CHEMICAL SPECIFIC SCREENING

The facility effluent discharges to an unnamed tributary of Poplar Creek. The stream has a 7Q10=0 cfs and a Mean Annual stream flow of 2.231 MGD (3.452 cfs).  A toxicity screen was performed on all pollutant data provided in the application that has an applicable water quality standard.  A NRWQC of 100 ug/L (0.1 mg/L) is listed for manganese; however, this standard was originally recommended in the Red Book and subsequently published in the Gold Book for marine water in order to protect against a possible human health hazard to humans by manganese accumulation in shellfish. Because Poplar Creek is a freshwater stream, this standard is not applicable and a toxicity screen will not be performed on this pollutant.

Stream Flows:
Qr	= 7Q10 of receiving stream (Acute and Chronic Screenings) 
= 0 MGD (for all outfalls)

Qr	= Mean Annual Flow (Human Health Screening) 
= 3.452 CFS = 2.231 MGD (Outfalls 001 and 002)

Qw	= Maximum 30-day flow
= 0.0885 MGD (Outfall 001) 
= 0.3086 MGD (Outfall 002) 

  	IWC	(%) = Qw /(Qr + Qw)*100

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

Xr	= Receiving stream concentration.  
Xw 	= Historical effluent data from the application.
Xwa	= Permit limits from previous permit or from effluent guidelines.
Xta	= The calculated in-stream concentration based on existing permit limits or the calculated limit based on current effluent guidelines.
Xt	= The calculated in-stream concentration is based on historical effluent data from the application.

Note:       To calculate Xta substitute Xwa for Xw.

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)
To view screening results, see the toxicity screening tables on the following pages.