PERMIT RATIONALE FOR REISSUANCE
Yazoo City POTW
Yazoo County
Yazoo City, Mississippi
Water NPDES No. MS0020389
January 18, 2023

I.	CLASSIFICATION – Major Municipal 

II.	DESCRIPTION OF WASTEWATER – Domestic/Municipal Wastewater

III.	DESCRIPTION OF WASTEWATER TREATMENT – Wastewater is collected and biologically treated by means of an aerated lagoon, facultative lagoons, and a finishing pond followed by chlorine disinfection prior to discharge. See Attachment No. 1 for flow diagram. The design capacity of the facility is 3.0 MGD. Only one discharge to surface waters is described in the application with no increase in treated effluent flow proposed. 

IV.	RECEIVING WATERS – Yazoo River. The receiving water is located in the Yazoo River Basin and is classified as Fish and Wildlife.  See Attachment No. 2 for discharge location map. At the point of discharge, the receiving stream does not appear on the current State of Mississippi 303(d) List of Impaired Waterbodies. The discharge does appear on a completed Total Maximum Daily Load (TMDL) for Fecal Coliform in the Yazoo River1 (June 2003). The permit contains chlorine limitations, which complies with the conditions of the TMDL. The discharge also appears on a completed TMDL for Total Nitrogen and Total Phosphorus for Selected Large Rivers in the Delta2 (June 2008). The permit contains Total Nitrogen and Total Phosphorus limits prescribed in the TMDL. 

The 7-day, 10-year minimum flow (7Q10) of the receiving stream is 1,250 cfs. The Instream Wastewater Concentration (IWC) at the point of the discharge is determined by the following calculation:

IWC = {(Qw)/(Qw + QR)} * 100 
	Where:
	Qw = Design flow of the wastewater treatment facility 3.0 MGD or 4.64 cfs.  
	QR = Receiving stream 7Q10, 1,250 cfs.

IWC = {(4.64 cfs)/(4.64 cfs + 1,250 cfs)} * 100 = 0.37 %

V.	APPLICABLE GUIDELINES – 11 Mississippi Admin Code pt. 6, Municipal Facility Guidelines (Technology), Wasteload Allocation (WLA, see Attachment No. 3), TMDL2

VI.	SUMMARY OF LIMITATIONS – 

Parameter			Value			Basis
Flow			3.0 MGD			Design
BOD5			45 mg/l			Technology
Ammonia Nitrogen		Report mg/l			WLA
TSS			90 mg/l			Technology	 
Residual Chlorine		1.0 mg/l			WLA
E. coli			126 col./100 ml			Admin Code/ TMDL1
Dissolved Oxygen		6.0 mg/l (Minimum)		WLA
BOD % Removal		65% (Minimum)			Technology
pH			6.0 - 9.0 S.U.			Admin Code
Total Nitrogen			288 lbs/day			TMDL2
Total Phosphorus 		130 lbs/day			TMDL2

BIOASSAY AND CHEMICAL SPECIFIC EVALUATION

BIOASSAY

In accordance to State Regulation 11 Mississippi Admin Code pt. 6, VI.B.2b., Yazoo City POTW is required to perform a Whole Effluent Toxicity (WET) evaluation as part of the renewal application. The applicant was to have tested in accordance with Short – Term Methods for estimating the Acute Toxicity of Effluents and Receiving Water to Freshwater Organisms.  Short – term acute WET tests were performed on Ceriodaphnia dubia (invertebrate) and Pimephale promelas (vertebrate).  The results of the wet tests are as follows:

March 2022
	Ceriodaphnia dubia		48-hour LC50 		> 1.5 %
	Pimephales promelas		96-hour LC50		> 1.5 %

	June 2022
	Ceriodaphnia dubia		48-hour LC50 		> 1.5 %
	Pimephales promelas		96-hour LC50		> 1.5 %

	November 2022
	Ceriodaphnia dubia		48-hour LC50      	> 1.5 %
	Pimephales promelas		96-hour LC50		> 1.5 %

Since, facility was unable to submit all of the WET testing requirements according to the 2A application, therefore, bioassay requirements will be placed in the permit. Facility is required to take one more WET test in June 2023 and based on that data, this permit shall be reopened and modified. Until the permit has been modified, facility is allow to put NODI=9 for conditional monitoring when filling out the DMRs. 

CHEMICAL SPECIFIC ANALYSIS

Chemical specific analysis has been performed in accordance with State Regulations 11Mississippi Admin Code pt. 6, V1.B1.  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 results are tabulated in Attachment No. 4.  The reported values are then analyzed and compared to water quality criteria (see Attachment No. 5) to determine any possible toxic effect to the receiving waters.  A synopsis of these calculations is listed in Attachment No. 6.  A column by column description of the calculations in Attachment No. 6 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.

Chemical specific analysis for Metals and Results

Major municipalities shall determine the toxic characteristics of their wastewater by analyzing for toxic pollutants listed in Table II of Appendix D of 40 CFR 122.  Metal analysis shall be for total recoverable metals.  Municipalities shall submit twelve influent and effluent samples collected.  Chemical specific limits shall be placed in a permittee’s permit if any of the parameters evaluated in the toxic screening procedure indicate the reasonable potential for violation of the appropriate criteria (acute, chronic, and human health).
	
For Yazoo City POTW, the chemical specific data results submitted with the reapplication did not indicate the reasonable potential for violation of the appropriate criteria in Table III of Appendix D of CFR 122.  See Attachment No. 6 for Chemical Specific Screening sheet and results.  Therefore, chemical specific limits have not been placed in the permit.  

Chemical specific analysis for Volatile Organic Compounds, Acid-Extractable Compounds, and Base-Neutral Compounds and Results

The chemical specific data results submitted had no detects for all Volatile Organic Compounds, Base-Neutral Compounds and Acid-Extractable Compounds.

ATTACHMENTS

Attachment No. 1 – Flow Diagram
Attachment No. 2 – Discharge Location Map
Attachment No. 3 – Wasteload Allocation
Attachment No. 4 – Tabulated Metals Testing Data
Attachment No. 5 – MS State Water Quality Standards
Attachment No. 6 – Synopsis of Metals Results

Attachment No. 1 – Flow Diagram

Attachment No. 2 – Discharge Location Map

Outfall 001

Attachment No. 3 – Wasteload Allocation

Attachment No. 4 – Tabulated Metals Testing Data

   *Values reported in mg/L

Attachment No. 5 – MS State Water Quality Standards

Attachment No. 6 – Synopsis of Metals Results