PERMIT RATIONALE FOR REISSUANCE
DeSoto County Regional Utility Authority, Short Fork WWTF
Desoto County
Hernando, Mississippi
Water NPDES No. MS0062227
January 2025

I.	CLASSIFICATION – NPDES Major Municipal 

II.	DESCRIPTION OF WASTEWATER – Domestic / Municipal Wastewater

III.	DESCRIPTION OF WASTEWATER TREATMENT – Wastewater is collected and treated biologically 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 8.0 MGD. Only one discharge to surface waters is described in the application with no increase in treated effluent flow proposed.

IV.	RECEIVING WATERS – Coldwater River. The receiving stream is located in the Yazoo River drainage basin and is classified as Fish & Wildlife. At the point of discharge, the receiving stream does not appear on the current State of Mississippi 303(d) List of Impaired Waterbodies, nor does the discharge appear on a completed Total Maximum Daily Load (TMDL).

The 7-day, 10-year minimum flow (7Q10) of the receiving stream is 22 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 8.0 MGD or 12.38 cfs.  
	QR = Receiving stream 7Q10, 22 cfs.

IWC = {(12.38 cfs)/(12.38 cfs + 22 cfs)} * 100 = 36.02 %

V.	APPLICABLE GUIDELINES – 11 Mississippi Admin Code pt. 6, Municipal Facility Guidelines (Technology), Mississippi State Water Quality Standards (MSWQS), Wasteload Allocation (WLA, Attachment 3), Municipal Facility Guidelines (Technology)

VI.	CHANGES FROM PREVIOUS PERMIT – 

Total residual chlorine limitations have been included in the draft permit in the event chlorine is utilized as a backup disinfection. The following condition has been added into the proposed draft permit

“Chlorination may be utilized by facility in the event the ultraviolet (UV) system is not available for disinfection. When chlorine is used as the method for disinfection, the facility must comply with the Chlorine, Total Residual limitations provided in the permit.  If chlorination is not being utilized, the permittee shall report NODI_CODE 9 (Conditional Monitoring - Not Required This Period) in the monthly Discharge Monitoring Report (DMR).”

Waste Load Allocation established a new ammonia limit basaed on ammonia toxicity. Therrefore, the new ammonia limit has been added to the proposed draft permit. The permittee will be required to comply with the following conditions added to the permit:

“The permittee shall achieve compliance with the effluent limitations specified for discharge in accordance with the following schedule:

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; Phase II limitations shall not apply at this time.

Beginning upon completion and start-up of improvements needed to comply with Phase II limitations or three (3) years after the issuance of the permit, whichever comes first, the permittee shall achieve compliance with the effluent limitations specified for the parameters without a phase designation and for the parameters noted as Phase II; Phase I limitations shall no longer apply at this time. Phase II limitations shall apply as soon as the treatment system has demonstrated compliance with the Phase II limitations, but no longer than three (3) years after the issuance of the permit.

The permittee shall notify our office orally at least 24 hours prior to start-up and in writing no later than 48 hours after start-up.”

“The Permittee shall Submit engineering report: Due once within 6 months (180 days) after effective date. Said report shall outline the improvement activities needed to upgrade the wastewater treatment facility to comply with the site's Phase II limitations and shall include a proposed schedule for those improvement activities.”

“The Permittee shall Submit progress report: Due annually - every 1 year after effective date. Said report shall update the Permittee's progress in addressing needed upgrades to the wastewater treatment facility in order to meet the site's Phase II limitations. Said report should also include an updated schedule for completing these activities.”

VII.	SUMMARY OF LIMITATIONS – 
Parameter				Value				Basis
Flow					8.0 MGD			Design
	BOD5					18 mg/l 			WLA
	TSS					30 mg/l 			Technology
	Ph. I Ammonia Nitrogen		4.0 mg/l 			WLA
	Ph. II Ammonia Nitrogen		3.6 mg/l 			WLA			
	Dissolved Oxygen			> 6.0 mg/l 			WLA
	Chlorine, Total Residual		0.031 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

BIOASSAY AND CHEMICAL SPECIFIC EVALUATION

BIOASSAY

In accordance with State Regulation 11 Mississippi Admin Code pt. 6, VI.B.2b., DCRUA, Short Fork WWTF 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:

October 2022
		Ceriodaphnia dubia		IC25 		>72 %
		Pimephale promelas		IC25		>72 %

February 2023
		Ceriodaphnia dubia		IC25 		>72%
		Pimephale promelas		IC25		>72 %

June 2023
		Ceriodaphnia dubia		IC25 		>72 %
		Pimephale promelas		IC25		>72 %

July 2023
		Ceriodaphnia dubia		IC25 		>72 %
		Pimephale promelas		IC25		>72 %

The above submitted bioassays that demonstrate a reasonable potential to violate Whole Effluent Toxicity based on the IC25 shown above that is less than the IWC for the discharge of 36.02%. The four (4) quarterly bioessays demonstrated no reasonable potential. Furthermore, based on the results of the WET testing and consistent compliance of DMR submittals from last four (4) years WET monitoring and limitations were removed from  the proposed draft permit

CHEMICAL SPECIFIC ANALYSIS

	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 Analysis 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 DCRUA, Short Fork WWTF, the chemical specific data results submitted with the reapplication did not indicate a reasonable potential for violation of the criteria in Table III of Appendix D of CFR 122.

See Attachment 6 for Chemical Specific Screening sheet and results.

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 1 – Flow Diagram
Attachment 2 – Location Map
Attachment 3 – Wasteload Allocation 
Attachment 4 – Chemical Specific Tabulated Test Results
Attachment 5 – MS Water Quality Criteria
Attachment 6 – Chemical Specific Screening

Attachment 1 – Flow Diagram

Attachment 2 – Location Map

Outfall 001

Plant Location

Attachment 3 – Wasteload Allocation

Attachment 4 – Chemical Specific Tabulated Results

Attachment 5 – MS Water Quality Criteria

Attachment 6 – Chemical Specific Screening