PERMIT RATIONALE FOR REISSUANCE
University of Mississippi
Lafayette County
Oxford, Mississippi
Water NPDES No. MS0021873
February 23, 2023

I.	CLASSIFICATION – NPDES Major Municipal 

II.	DESCRIPTION OF WASTEWATER – Domestic/Municipal Wastewater

III.	DESCRIPTION OF WASTEWATER TREATMENT – Wastewater is collected and treated using screening, grit removal, biological treatment via activated sludge/oxidation ditch, UV disinfection, and post aeration prior to discharge. See Attachment 1 for a flow diagram. The current design capacity of the facility is 1.5 MGD. The permit contains Only one discharge to surface waters is described in the application.

IV.	RECEIVING WATERS – Unnamed Tributary of Burney Branch. The receiving waters are located in the Yazoo River drainage basin and are classified as Fish & Wildlife. See Attachment 2 for discharge location map. At the point of discharge, the receiving stream does not appear on the 2020 State of Mississippi 303(d) List of Impaired Waterbodies. The discharge does appear on a completed Total Maximum Daily Load (TMDL) for Mercury in The Yocona River and Enid Reservoir (January 2003). The facility is required to perform Mercury monitoring and reporting as part of the permit renewal process, which complies with the conditions of the TMDL.

The 7-day, 10-year minimum flow (7Q10) of the receiving stream is 0.0 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, 1.5 MGD or 2.32 cfs 
QR = Receiving stream 7Q10, 0.0 cfs

IWC = {(2.32 cfs)/(2.32 cfs + 0.0 cfs)}*100 = 100 %

V.	APPLICABLE GUIDELINES – 11 Mississippi Admin Code pt. 6, Mississippi Water Quality Standards (MSWQS, Attachment 5), Wasteload Allocation (WLA, Attachments 3a and 3b), Municipal Facility Guidelines (Technology), TMDL

VI.	CHANGES FROM PREVIOUS PERMIT – 

1.	Total residual chlorine limitations have been included in the draft permit in the event chlorine is utilized as a backup to the UV disinfection system. See Condition L-1 of the draft permit for applicability. 

2.	E. coli has replaced fecal coliform as the bacterial indicator for all freshwaters in Mississippi designated as Recreation, Fish and Wildlife Support, and/or Public Water supply. 

3.	Influent monitoring and reporting requirements for Total Nitrogen and Total Phosphorus have been added to the draft permit in accordance with municipal facility guidelines. 

4.	Limitations for Copper and Zinc (Total Recoverable) have been placed in the draft permit based on the results of the Effluent Chemical Screening Analysis. 

5.	Whole Effluent Toxicity (WET) limitations have been added to the draft permit based on the results of the Bioassays submitted as part of the reapplication. 

6.	Monitoring frequencies for Phase II have been updated in accordance with Municipal Facility Guidelines.

7.	Ammonia toxicity limitations have been adjusted to comply with the current freshwater water quality standard. 

8.	Removed the proposed expansion flow of 3.0 MGD based on facility’s communication that the future expansion was not needed.

9.	The permit is phased based on monitoring frequencies, the permit states, “

Upon issuance of this permit, the permittee shall achieve compliance with the effluent limitations specified for the parameters without a phase designation and for the parameters noted as Phase I. Once the monthly average flow through the treatment plant is greater than or equal to 1.0 million gallons per day (mgd), then the permittee shall achieve compliance with the effluent limitations and monitoring frequencies specified for the parameters noted as Phase II.  

VII.	SUMMARY OF LIMITATIONS – 

Parameter				Value				Basis
Flow					1.5 MGD			Design
	BOD5					10 mg/l 			WLA
	TSS					30 mg/l 			Technology
	*Ammonia Nitrogen			1.37 mg/l 			WLA
	Dissolved Oxygen			> 6.0 mg/l 			WLA
	Chlorine, Total Residual		0.011 mg/l 			MSWQS, IWC
E. coli					126 Col. /100 ml		MSWQS
	pH					6.0 – 9.0 SU			MSWQS
	Nitrogen, Total			Report lbs/day			WLA
	Phosphorus, Total			Report lbs/day			WLA
	Copper, Total Recoverable		0.005 mg/l			MSWQS
Zinc, Total Recoverable		0.065 mg/l			MSWQS
Ceriodaphnia dubia			IC25 >100 %			Admin Code
Pimephale promelas			IC25 >100 %			Admin Code

Influent pH, 30-minute Sludge Settleability and Dissolved Oxygen in the aeration basin must also be monitored.

VIII.	BIOASSAY AND CHEMICAL SPECIFIC EVALUATION –

BIOASSAY

In accordance with State Regulation 11 Mississippi Admin Code pt. 6, VI.B.2b., The University of Mississippi 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 Chronic Toxicity of Effluents and Receiving Water to Freshwater Organisms.  Short – term chronic WET tests were performed on Ceriodaphnia dubia (invertebrate) and Pimephale promelas (vertebrate).  The results of the wet tests are as follows:

September 2020
		Ceriodaphnia dubia		IC25 		 5.46 %
		Pimephale promelas		IC25		>100 %

December 2020
		Ceriodaphnia dubia		IC25 		>100 %
		Pimephale promelas		IC25		>100 %

March 2021
		Ceriodaphnia dubia		IC25 		>100 %
		Pimephale promelas		IC25		66.91 %

May 2021
		Ceriodaphnia dubia		IC25 		  4.85 %
		Pimephale promelas		IC25		18.19 %

The above submitted bioassays demonstrate a reasonable potential to violate Whole Effluent Toxicity based on the IC25 shown above being less than the IWC of the discharge (100%). Based on the results of the WET testing, chronic bioassay requirements will be placed in the permit.

CHEMICAL SPECIFIC EVALUATION

	Chemical specific analysis has been performed in accordance with State Regulations 11 Mississippi 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 4.  The reported values are then analyzed and compared to water quality criteria (see Attachment 5) to determine any possible toxic effect to the receiving waters.  A synopsis of these calculations is listed in Attachment 6.  A column-by-column description of the calculations in Attachment 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 Evaluation for Metals and Results

Major municipalities shall determine the toxic characteristics of their wastewater by analyzing for toxic pollutants listed in Table III 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 The University of Mississippi, the chemical specific data results submitted with the reapplication indicated the reasonable potential for violation of the appropriate criteria (shown below) found in Table III of Appendix D of CFR 122.
	
	Copper, Total Recoverable – chronic, acute
	Zinc, Total Recoverable – acute	 

Based on the results of the Chemical Screening Evaluation, limitations for Copper and Zinc (Total Recoverable) have been placed in the draft permit.

See Attachment 6 for Chemical Specific Evaluation data sheet and screening results.

Chemical Specific Evaluation for Volatile Organic Compounds, Acid-Extractable Compounds, and Base-Neutral Compounds

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

IX.	ATTACHMENTS –

Attachment 1 – Flow Diagram
Attachment 2 – Topographic Map
Attachment 3 – Wasteload Allocation (1.5 MGD) 
Attachment 4 – Chemical Specific Tabulated Test Results
Attachment 5 – MS Water Quality Criteria
Attachment 6 – Chemical Specific Screening

Attachment 1 – Flow Diagram

Attachment 2 – Topographic Map

Outfall 001

Plant Location

Attachment 3 – Wasteload Allocation (1.5 MGD)

Outfall 001

Plant Location

Attachment 4 – Chemical Specific Tabulated Results

Attachment 5 – MS Water Quality Criteria

Attachment 6 – Chemical Specific Screening