PERMIT RATIONALE FOR REISSUANCE
Clarksdale Public Utilities, Lewis L Wilkins Generating Station
Coahoma County
Clarksdale, Mississippi
Water NPDES No. MS0001139
March 24, 2020

I.	FACILITY INFORMATION

Facility Name:  Clarksdale Public Utilities, Lewis L Wilkins Generating Station
Facility Address:  240 Hicks Street 
Clarksdale, MS 38614
Permit No.:  MS0001139
SIC:  4911
Permit Writer:  Thomas Kelly
EPD Branch:  Water I

II.	NATURE OF BUSINESS

This facility’s Standard Industrial Classification (SIC) codes is 4911 – steam electgric generation. The facility is a combined cycle power generation facility which produces 52 MW of electrical power. This facility is classified as an NPDES Minor Source.

III.	EFFLUENT AND RECEIVING STREAM FLOW DATA

Outfall 001 (External):	Effluent consisting of once through cooling water from Unit No. 6, Unit No. 7, Unit No. 9, low volume wastes, and effluent from internal Outfall(s) 101, 201, and 102. These waste streams discharge into the Unit No. 6 discharge pit, Unit No. 7 discharge pit, and Unit No. 9 discharge pit and then to Outfall 001. The outfall has an average flow of 13.75 MGD. 

Outfall 002 (External):	 Effluent consisting of once through cooling water from Unit No. 9, low volume wastes, and effluent from internal Outfall 102.  These waste streams discharge into the Unit No. 9 discharge pit and then to Outfall 002.  The outfall has an average flow of 5.76 MGD. 

Outfall 102 (Internal):	 Formerly Outfall 003. Effluent consisting of low volume wastes. The low volume wastes include No. 9 HRSG blowdown, demineralizer waste water, noncontact cooling water from the air compressor, and waste water from floor drains. These waste streams discharge into the Unit No. 9 discharge pit and then to Outfall(s) 002 and 001. This outfall has an average flow of 5.76 MGD. 

Outfall 101 (Internal):	 Formerly Outfall 004. Effluent from this outfall consists of low volume wastes. The low volume wastes include Unit No. 7 boiler blowdown, noncontact cooling water from the Unit No. 7 condenser. These waste streams discharge into the Unit No. 6 and Unit No. 7 discharge pits and then to Outfall 001. This outfall has an average flow of 5.535 MGD. 

Outfall 201 (Internal):	 Formerly Outfall 005. Effluent from this outfall consists of low volume wastes. The low volume wastes include No. 6 HRSG boiler blowdown. This waste stream discharges into the Unit No. 6 and Unit No. 7 discharge pits and then to Outfall 001. This outfall has an average flow of 0.005 MGD.

Wastewater from these outfalls discharge to an unnamed ditch thence into Big Sunflower River. The Big Sunflower River is located in the Yazoo River Basin. This stream is classified as “fish and Wildlife”.

It should be noted that the effluent flow from external outfall(s) 001 and 002 are composed primarily (combined total of approximately 99.8%) of once through cooling water. Because of this, Categorical limitations for once through cooling water were applied to those outfalls. 

IV.	303(d) and TMDL ISSUES

This permit complies with the following applicable TMDLs:

Pollutant		Drainage Area	    Basin	Waterbody ID	TMDL ID
Fecal Coliform		Big Sunflower River	    Yazoo	  MS951011	  None
Fecal Coliform		Little Sunflower River	    Yazoo	  MS950912	  None
Fecal Coliform		Big Sunflower River	    Yazoo	  Multiple	  4087
Organic Enrichment		Big Sunflower River	    Yazoo	  Multiple	  9397
Nutrients		Big Sunflower River	    Yazoo	  Multiple	  9397
Sediment		Big Sunflower River 	    Yazoo	  Multiple	  9397
Sediment		Yazoo River Basin Delta Region    Yazoo	  Multiple	  35359
Legacy Pesticides		Yazoo River Basin	    Yazoo	  Multiple	  12247
DDT and Toxaphene		Yazoo River Basin	    Yazoo	  Multiple	  12247
Total Nitrogen		Selected Large River in the Delta    Yazoo	  Multiple	  35411
Total Phosphorus		Selected Large River in the Delta    Yazoo	  Multiple	  35411

V.	TYPE OF WASTEWATER TREATMENT:

None.

VI.	EPA APPLICABLE CATEGORICAL GUIDELINES

40 CFR 423 – Steam Electric Power Generation Point Source Category; Section 423.12 (BPT) and 423.13 (BAT).
VII.	DATA FROM APPLICATION FORM (2C)

	Outfall 001							Outfall 002
	
Parameter	1Max. 	2LTA	3# 		Parameter	1Max. 	2LTA	3# 	
BOD5, mg/L	< 4 	--	1		BOD5, mg/L	< 4	--	1	
COD, mg/L	< 10 	--	1		COD, mg/L	< 10	--	1	
TOC, mg/L	< 5 	--	1		TOC, mg/L	< 5	--	1	
TSS, mg/L	19 	--	1		TSS, mg/L	25	--	1	
Ammonia, mg/L	0.33 	--	1		Ammonia, mg/L	0.43	--	1	
Flow, MGD	11.5 	4.55	19		Flow, MGD	0.0173	--	18	
Temperature (w), ºC	18	--	21		Temperature (w), ºC	21	--	1	
Temperature (s), ºC	33	--	21		Temperature (s), ºC	21	--	1	
pH, SU (max)	8.9	--	21		pH, SU (max)	9.0	--	1	
Nitrate-Nitrite, mg/L	0.6	--	1		Nitrate-Nitrite	0.8	--	1	
Oil and Grease, mg/L	ND	--	1		Oil and Grease, mg/L	ND	--	1	
Nitrogen (as N)	0.73	--	1		Nitrogen (as N), mg/L	2.42	--	1	
Phosphorus (as P)	0.027	--	1		Phosphorus (as P), mg/L	0.14	--	1	
Sulfate, mg/L	17	--	1		Sulfate, mg/L	5.0	--	1	
Iron, mg/L	17.04	3.86	19		Iron, mg/L	8.015	4.39	16	
Manganese, mg/L	0.42	--	1		Manganese, mg/L	0.52	--	1	
Mercury, mg/L	2.2e-6	--	1		Mercury, mg/L	2.8e-6	--	1	
Selenium, mg/L	<0.05 	--	1		Selenium, mg/L	<0.05	--	1	
Cyanide, mg/L	<0.05	--	1		Cyanide, mg/L	<0.05	--	1	
					Zinc, mg/L	<0.02	<0.02	12	

Outfall 101 (004)							Outfall 201 (005)
	
Parameter	1Max. 	2LTA	3# 		Parameter	1Max. 	2LTA	3# 	
BOD5, mg/L	< 4 	--	1		BOD5, mg/L	< 4	--	1	
COD, mg/L	< 10 	--	1		COD, mg/L	< 10	--	1	
TOC, mg/L	< 5 	--	1		TOC, mg/L	< 5	--	1	
TSS, mg/L	25	--	1		TSS, mg/L	210	--	1	
Ammonia, mg/L	0.43 	--	1		Ammonia, mg/L	0.43	--	1	
Flow, MGD	0.005	--	1		Flow, MGD	0.005	--	1	
Temperature (w), ºC	21	--	1		Temperature (w), ºC	21	--	1	
Temperature (s), ºC	21	--	1		Temperature (s), ºC	21	--	1	
pH, SU (max)	9.0	--	18		pH, SU (max)	11.35	--	1	
Nitrate-Nitrite	0.68	--	1		Nitrate-Nitrite	0.8	--	1	
Oil and Grease, mg/L	ND	--	1		Oil and Grease, mg/L	3.43	--	1	
Nitrogen (as N)	2.42	--	1		Nitrogen (as N)	2.42	--	1	
Phosphorus (as P)	0.14	--	1		Phosphorus (as P)	0.14	--	1	
Sulfate	5.0	--	1		Sulfate	5	--	1	
Iron, mg/L	8.015	4.39	16		Iron, mg/L	8.015	4.39	16	
Manganese, mg/L	0.52	--	1		Manganese, mg/L	0.52	--	1	
Mercury, mg/L	2.8e-6	--	1		Mercury, mg/L	2.8e-6	--	1	
Selenium, mg/L	ND 	--	1		Selenium, mg/L	ND	--	1	
Cyanide, mg/L	ND	--	1		Cyanide, mg/L	ND	--	1	

Outfall 102 (003)

Parameter	1Max. 	2LTA	3# 		
BOD5, mg/L	< 4 	--	1		
COD, mg/L	< 10 	--	1		
TOC, mg/L	< 5 	--	1		
TSS, mg/L	25	--	1		
Ammonia, mg/L	0.43 	--	1		
Flow, MGD	0.005	--	1		
Temperature (w), ºC	21	--	1		
Temperature (s), ºC	21	--	1		
pH, SU (max)	9.0	--	18		
Nitrate-Nitrite	0.68	--	1		
Oil and Grease, mg/L	ND	--	1		
Nitrogen (as N)	2.42	--	1		
Phosphorus (as P)	0.14	--	1		
Sulfate	5.0	--	1		
Iron, mg/L	8.015	4.39	16		
Manganese, mg/L	0.52	--	1		
Mercury, mg/L	2.8e-6	--	1		
Selenium, mg/L	ND 	--	1		
Cyanide, mg/L	ND	--	1		

VIII. 	WATER QUALITY LIMITATIONS BASED ON WASTELOAD ALLOCATION 

	Not Applicable

IX.	CATEGORICAL GUIDELINE LIMITATIONS CALCULATIONS

Not Applicable

X.	TOXICITY SCREENING

See Attachment A
XI.	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	1Basis	
001	Flow (MGD)	--	--	Report 	Report	Continuously	Continuous Recorder	Monthly	TJ	
001	Chlorine, TR2	--	0.011 mg/L	0.011 mg/L	0.011 mg/L	Twice per month	Multiple Grab5	Monthly	MSWQS	
001	Iron, TR2	--	--	Report	Report	Twice per month	8-hr Composite	Monthly	TJ	
001	Temperature (°F)	--	--	Report	Report	Twice per month	Grab Sampling	Monthly	TJ	
001	pH	--	6.0 SU	6.5 SU	6.0 SU	Twice per month	Grab Sampling	Monthly	MSWQS	
002	Flow (MGD)	--	--	Report 	Report	Continuously	Continuous Recorder	Monthly	TJ	
002	Chlorine, TR2	--	0.011 mg/L	0.011 mg/L	0.011 mg/L	Twice per month	Multiple Grab5	Monthly	MSWQS	
002	Iron, TR	--	--	Report	Report	Twice per month	8-hr Composite	Monthly	TJ	
002	Temperature (°F)	--	--	Report	Report	Twice per month	Grab Sampling	Monthly	TJ	
002	pH	--	6.0 SU	6.5 SU	6.0 SU	Twice per month	Grab Sampling	Monthly	MSWQS	
102	Flow (MGD)	--	--	Report 	Report	Monthly	Instantaneous	Monthly	TJ	
102	Oil and Grease	15 mg/L	--	15 mg/L 	15 mg/L 	Monthly	Grab Sampling	Monthly	Categorical	
102	TSS	30 mg/L	--	30 mg/L (18 lb/day)	30 mg/L (18 lb/day)	Monthly	Grab Sampling	Monthly	Categorical	
102	pH	--	6.0 SU	6.0 SU	6.0 SU	Monthly	Grab Sampling	Monthly	MSWQS	
101	Flow (MGD)	--	--	Report 	Report	Monthly	Instantaneous	Quarterly	TJ	
101	Oil and Grease	15 mg/L	--	15 mg/L 	15 mg/L 	Monthly	Grab Sampling	Quarterly	Categorical	
101	TSS	30 mg/L	--	30 mg/L (18 lb/day)	30 mg/L (18 lb/day)	Monthly	Grab Sampling	Quarterly	Categorical	
101	pH	--	6.0 SU	6.0 SU	6.0 SU	Monthly	Grab Sampling	Quarterly	MSWQS	
201	Flow (MGD)	--	--	Report 	Report	Monthly	Instantaneous	Quarterly	TJ	
201	Oil and Grease	15 mg/L	--	15 mg/L 	15 mg/L 	Monthly	Grab Sampling	Quarterly	Categorical	
201	TSS	30 mg/L	--	30 mg/L (18 lb/day)	30 mg/L (18 lb/day)	Monthly	Grab Sampling	Quarterly	Categorical	
201	pH	--	6.0 SU	6.0 SU	6.0 SU	Monthly	Grab Sampling	Quarterly	MSWQS	

2.	Maximum Permit Limitations
Outfall	Parameter	Categorical Limitation	Water Quality Limitation	Present Permit Limitation	Proposed Permit Limitation	Monitoring Frequency	Sample Type	DMR Reporting Frequency	1Basis	
001	Flow (MGD)	--	--	Report 	Report	Continuously	Continuous Recorder	Monthly	TJ	
001	Chlorine, TR2	--	0.019 mg/L	0.019 mg/L	0.019 mg/L	Twice per month	Multiple Grab5	Monthly	MSWQS	
001	Chlorination Duration	120 min/unit	--	120 min/unit	120 min/unit	Daily	Measurement	Monthly	Categorical	
001	Iron, TR2	--	--	Report	Report	Twice per month	8r-Composite	Monthly	TJ	
001	Temperature (°F) 	--	90	90	90	Twice per month	Grab Sampling	Monthly	MSWQS	
001	pH	--	9.0 SU	9.0 SU	9.0 SU	Twice per month	Grab Sampling	Monthly	MSWQS	
002	Flow (MGD)	--	--	Report 	Report	Continuously	Continuous Recorder	Monthly	TJ	
002	Chlorine, TR2	--	0.019 mg/L	0.019 mg/L	0.019 mg/L	Twice per month	Multiple Grab5	Monthly	MSWQS	
002	Chlorination Duration	120 min/unit	--	120 min/unit	120 min/unit	Daily	Measurement	Monthly	Categorical	
002	Iron, TR2	--	--	Report	Report	Twice per month	8r-Composite	Monthly	TJ	
002	Temperature (°F) 	--	90	90	90	Twice per month	Grab Sampling	Monthly	MSWQS	
002	pH	--	9.0 SU	9.0 SU	9.0 SU	Twice per month	Grab Sampling	Monthly	MSWQS	
102	Flow (MGD)	--	--	Report 	Report	Monthly	Instantaneous	Monthly	TJ	
102	Oil and Grease	20 mg/L	--	20 mg/L 	20 mg/L 	Monthly	Grab Sampling	Monthly	Categorical	
102	TSS	100 mg/L	--	100 mg/L 	100 mg/L 	Monthly	Grab Sampling	Monthly	Categorical	
102	pH	--	9.0 SU	9.0 SU	9.0 SU	Monthly	Grab Sampling	Monthly	MSWQS	
101	Flow (MGD)	--	--	Report 	Report	Monthly	Instantaneous	Quarterly	TJ	
101	Oil and Grease	20 mg/L	--	20 mg/L 	20 mg/L 	Monthly	Grab Sampling	Quarterly	Categorical	
101	TSS	100 mg/L	--	100 mg/L 	100 mg/L 	Monthly	Grab Sampling	Quarterly	Categorical	
101	pH	--	9.0 SU	9.0 SU	9.0 SU	Monthly	Grab Sampling	Quarterly	MSWQS	
201	Flow (MGD)	--	--	Report 	Report	Monthly	Instantaneous	Quarterly	TJ	
201	Oil and Grease	20 mg/L	--	20 mg/L 	20 mg/L 	Monthly	Grab Sampling	Quarterly	Categorical	
201	TSS	100 mg/L	--	100 mg/L 	100 mg/L 	Monthly	Grab Sampling	Quarterly	Categorical	
201	pH	--	9.0 SU	9.0 SU	9.0 SU	Monthly	Grab Sampling	Quarterly	MSWQS	

1Basis: 11 Miss. Pt. 6, Ch.1 = 11 Miss. Admin Code Pt. 6, Ch.1, Categorical = 40 CFR Part 423 Steam Electric Power Generation Point Source Category; Section 423.15 New  Source Performance Standards (NSPS),  MSWQS = Mississippi Water Quality Standards, TJ = Technical Judgement.
2TR =Total Residual
3FA = Free Available
4TR = Total Recoverable
5Multiple Grab

Report Submittal Requirement

Discharges from the following outfalls 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 each outfall monthly when discharging until 12 effluent samples have been analyzed for each outfall.

•	Outfall 001 – total recoverable selenium, total recoverable arsenic
•	Outfall 002 – total recoverable selenium, total recoverable arsenic, total recoverable zinc

 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. 

XII.	STATEMENT OF BASIS: 

It is our judgment that the foregoing limitations represent Technical Judgment, 423.12 11 Miss. Admin. Code Pt.6, Ch. 1 and 2, and the applicable Categorical Guidelines. 

ATTACHMENT A

TOXICITY SCREENING
This facility discharges into the Big Sunflower River that has a 7Q10 flow of 19.39 MGD (30 cfs) and a Mean Annual stream flow of 81.64 MGD (126.32 cfs).  A toxicity screen is performed on all pollutant data provided in the application that has an applicable state and/or national 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 the Big Sunflower River is a freshwater stream, this standard is not applicable and a toxicity screen will not be performed on this pollutant.

The effluent flow information used to calculate these limits was taken from the permit renewal application (EPA Form 2C). The receiving stream flow information was provided by our Water Quality Modeling/TMDLBranch.

Stream Flow:
Qr	= 7Q10 of receiving stream (Acute and Chronic Screenings) 
=  19.39 MGD

Qr	= Mean Annual Flow (Human Health Screening) 
= 81.64 MGD

Effluent Flow:
Qw	= Maximum 30 day flow (Outfall 001)
= 11.5 MGD (Outfall 001- Maximum daily value is used in the screen because the Maximum 30 day flow value is not available).
= 5.545 MGD (Outfall 002 - Taken from the August 2019 DMR)
	
  	IWC	(%) = 39.21% (Provided on the Waste Load Allocation)

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.