PERMIT RATIONALE FOR REISSUANCE
Senatobia POTW
Tate County
Senatobia, Mississippi
Water NPDES No. MS0052221
April 2022

I.	CLASSIFICATION – Municipal Major

II.	DESCRIPTION OF WASTEWATER – Domestic / Municipal Wastewater

III.	DESCRIPTION OF WASTEWATER TREATMENT - Wastewater is collected and biologically treated by means of an Oxidation Ditch, followed by UV Disinfection.  

IV.	RECEIVING WATERS- Hickahala Creek. Hickahala Creek at the point of discharge is classified as Fish and Wildlife.  Hickahala Creek is in the Yazoo River Basin. Hickahala Creek does not appear on the current State of Mississippi 303(d) List of Impaired Waterbodies. It is listed for a Completed TMDL due to organic enrichment/ low do and nutrients. The BOD5 and NH3-N effluent limits are based on the TMDL for organic enrichment/ low D.O. and nutrients. 
	The 7-day, 10 year minimum flow, 7Q10, for Hickahala Creek at the point of discharge is 6.5 cfs.  Based upon the 7Q10 at the point of discharge, the current instream wastewater concentration (IWC) at the point of discharge is 32.3%. The relocation of the discharge point is along Hickahala Creek, where the proposed expansion to 3.0 MGD would increase the IWC to 41.67% (see attachment 3). 

V.	APPLICABLE GUIDELINES – 11 Mississippi Administrative Code Pt. 6,  Mississippi State Water Quality Criteria (MSWQC), Total Maximum Daily Load (TMDL), Wasteload Allocation 2022 (WLA)

VI.	SUMMARY OF LIMITATIONS –
	Parameter						Value				Basis
	Flow (Phase I)						2 MGD				Design
	Flow (Phase II)						3 MGD				Design
	BOD5(Phase I)						14 mg/l (Monthly Avg.)			WLA	
	BOD5(Phase II)						6 mg/l (Monthly Avg.)			WLA
	BOD5 (Percent Removal)			85% Minimum				Technology
	TSS						30 mg/l (Monthly Avg.)			Technology
	TSS (Percent Removal)				85% Minimum				Technology
	NH3-N (Phase I) 					2.0 mg/l (Monthly Avg.)			TMDL
	NH3-N (Phase II) 					1.33  mg/l (Monthly Avg.)			TMDL
	Dissolved Oxygen					> 6.0 mg/l (Monthly Avg.)			WLA
	E. Coli						126/410 Col./100 ml			MSWQC	
	pH						6.0 – 9.0 SU				MSWQC
	Total Nitrogen						Report				WLA
	Total Phosphorus					Report				WLA	
	Copper, Total Recoverable			 Report (mg/l)				App Data
	Zinc, Total Recoverable		         Report (mg/l)				App Data
	Ceriodaphnia dubia					 Report minimum %			IWC
	Pimephale promelas			         Report minimum %			IWC

**BOD, TSS, Ammonia Nitrogen, D.O, and E. Coli sampling frequencies will increase to 3 times per week from Weekly in Phase II.

VII.  TOXICITY SCREENING

Chemical Specific Analysis and Results

Municipalities shall determine the toxic characteristics of their wastewater by analyzing for the toxic pollutant listed in Table III of appendix D of 40 CFR 122. The chemical specific analysis has been performed in accordance with State Regulations 11 Mississippi Admin. Code Pt. 6 Ch. 1. The results are tabulated in attachment No. 4. The reported values are then analyzed and compared to water quality criteria (attachment No. 6) to determine any possible toxic effect to the receiving waters (attachment No. 5). A synopsis of these calculations is listed in below:

A column by column description of the calculations in attachment No. 5 is hereby provided: 

Column No. 1 – Maximum concentration. The highest effluent reading of the parameter 

Column No. 2 – The maximum concentration mixed with the receiving water IWC. This is calculated by the following equation: 
{Maximum Concentration (Column 1) * IWC %} / 100 

Column No. 3 – Acute allowable – Chemical Specific State Water Quality Criteria 

Column No. 4 – Pass or Fail. If column 2 > column 3 water quality criteria is exceeded and failure occurs. 

Column No. 5 – Long term average (LTA) of all tests. The summation of the 12 samples divided by 12. 

Column No. 6 – The long term average concentration mixed with the receiving water IWC. This is calculated by the following equation: 
{LTA Concentration (Column 5) * IWC%} / 100 

Column No. 7 – Chronic allowable – Chemical Specific State Water Quality Criteria 

Column No. 8 – Pass or Fail. If column 6 > column 7 water quality criteria is exceeded and failure occurs. 

Column No. 9 – Human health determination. Long term average (Column 5) is mixed with the mean annual flow IWCMA . This is calculated by the following equation: 
{LTA Concentration (Column 5) * IWCMA %} / 100 

Column No. 10 – Human health allowable – State Water Quality Criteria Note: Organisms only column is used if receiving waters are not drinking water supply. 

Column No. 11 – Pass or Fail. If column 9 > column 10 water quality criteria is exceeded and failure occurs.

A total of three (3) influent and effluent samples were submitted to meet the minimum requirements for application per Table C of form 2A, where a ten times (10x) multiplier was applied to the maximums and averages of the 3 samples for the toxicity screening.

The results of the Chemical Specific Analysis demonstrated that Copper and Zinc have a potential to violate water quality criteria (Attachment No. 5). These parameters have been added to the permit as Report Only. The limitations shall apply until the additional nine (9) samples are submitted for re-evaluation using twelve total (12) samples. The permit may be re-opened when the submittal requirements are satisfied.

Results for Volatile Organics Compounds, Acid-Extractable Compounds, and Base-Neutral Compounds and Results 

The chemical specific data results submitted had no detects for Volatile Organics Compounds, Acid-Extractable Compounds, or Base-Neutral Compounds. 

Bioassay Results

In accordance to State Regulation 11 Mississippi Admin Code pt. 6, Chp.1,VI.B.2b., a whole effluent toxicity evaluation was performed as part of the renewal application.  The applicant was to have tested in accordance with Short – Term Methods for estimating the chronic toxicity of Effluents and Receiving Water to Freshwater organisms.  Short – term chronic WET test were performed on ceriodaphnia dubia (invertebrate) and pimephales promelas (vertebrate).  

The results of the WET tests are as follows:

October 2020
Pimephales promelas		ICp25 > 100%
Ceriodaphnia dubia		ICp25 = 1.609%

March 2021
Pimephales promelas		ICp25 = 34.93%
Ceriodaphnai dubia		ICp25 > 100%

May 2021
Pimephales promelas		ICp25 > 100%
Ceriodaphnia dubia		ICp25 > 11.49%

August 2021
Pimephales promelas		ICp25 > 100%
Ceriodaphnia dubia		ICp25 = 11.9%
Based on the results of the WET testing, inhibition concentrations were not greater that the predicted IWC of 32.3% Chronic bioassay requirements will be placed in the permit as Report Only until upgrades are complete and the new treatment system is online. Permit limitations will be re-evaluated upon completion of testing.

VII.	CHANGES TO PERMIT

As part of facility upgrades, the outfall will be relocated along Hickahala Creek directly to 34°15'29",89°31'50". Upon successful relocation and startup of the SBR treatment system, the permittee shall pull the remaining nine (9) samples to complete testing. 
The following condition has been added to the permit:

“The permittee shall perform the remaining sampling twice per month for nine (9) samples, and shall be initiated upon startup of the Sequence Batch Reactor (SBR) treatment system and lasting for the next nine (9) consecutive months, from the influent to and effluent from the SBR. Sampling shall be conducted by grab sample for the following pollutants per the required EPA Method. Monitoring results shall be compiled and submitted to the Mississippi Environmental Quality Board POSTMARKED NO LATER THAN THE 28TH DAY FOLLOWING NINE (9) MONTHS OF SAMPLING:
 
Total Recoverable Antimony 
Total Recoverable Arsenic
Total Recoverable Beryllium
Total Recoverable Cadmium
Total Recoverable Chromium 
Chromium (Hex)      
Total Recoverable Copper 
Total Recoverable Lead 
Total Recoverable Mercury
Total Recoverable Nickel (Freshwater)
Total Recoverable Selenium
Total Recoverable Silver
Total Recoverable Thallium
Total Recoverable Zinc
Free Cyanide
Phenolic Compound
Pentachlorophenol
Hardness (in mg/l as CaCO3)       
 
Analytical procedures must be in accordance to methodologies listed in 40 CFR 136 for the above pollutants
Attachments

Attachment No. 1 – Process Schematic
Attachment No. 2 – Discharge Location Map 
Attachment No. 3 – Waste Load Allocation(s)
Attachment No. 4 – Chemical Specific Tabulated Results
Attachment No. 5 – Chemical Specific Calculations
Attachment No. 6 – State of Mississippi Water Quality Criteria

Attachment 1

Attachment 2

Attachment 3 								     (1 of 2)

Attachment 3 								         (2 of 2)

Attachment 4

Chemical Specific Analysis Results For Senatobia POTW

Parameters

Test Method

9/29/21

10/21/21

11/3/2021

Avgs.

Max

Avgs. X 10

Max x 10

Antimony

200.8

ND

ND

ND

0

0

0

0

Arsenic

200.8

0.00156

ND

0.00107

0.000219

0.00156

0.00219167

0.0156

Beryllium

200.8

ND

ND

ND

0

0

0

0

Cadmium

200.8

ND

ND

ND

0

0

0

0

Chromium

200.8

0.00205

ND

ND

0.000171

0.00205

0.00170833

0.0205

Chromium HEX

3500 CRB

ND

ND

ND

0

0

0

0

Copper

200.8

0.00534

0.00613

0.00779

0.001605

0.00779

0.01605

0.0779

Lead

200.8

ND

ND

ND

0

0

0

0

Mercury

1631E

9.33E-07

9.89E-07

1.26E-06

2.65E-07

1.26E-06

2.6517E-06

1.26E-05

Nickel

200.8

0.00649

0.00295

0.00275

0.001016

0.00649

0.01015833

0.0649

Selenium

200.8

ND

ND

ND

0

0

0

0

Silver

200.8

ND

ND

ND

0

0

0

0

Thallium

200.8

ND

ND

ND

0

0

0

0

Zinc

200.8

0.058

0.0334

0.0328

0.01035

0.058

0.1035

0.58

Cyanide

4500 CNE

ND

ND

ND

0

0

0

0

Phenol

625

ND

ND

ND

0

0

0

0

Pentachlorophenol

625

ND

ND

ND

0

0

0

0

Hardness

200.8

85.2

93.5

90.7

22.45

93.5

224.5

935

Attachment 5

Attachment 6