PERMIT RATIONALE FOR REISSUANCE
Morton POTW
Scott County
Morton, Mississippi
Water NPDES No. MS0036234
September 9, 2024

I.	CLASSIFICATION – NPDES Major Municipal

II.	DESCRIPTION OF WASTEWATER – Municipal Wastewater

III.	DESCRIPTION OF WASTEWATER TREATMENT – Municipal wastewater is collected and treated biologically by means of a Sequential Batch Reactor. The application does not describe any increase in flow. See Attachment No. 1 for a flow diagram.

IV.	RECEIVING WATERS – Unnamed ditch thence into the Strong River. See Attachment No. 2 for a discharge location map. The receiving waters do not appear on the current State of Mississippi 303(d) List of Impaired Waterbodies. The facility is included in a Total Maximum Daily Load (TMDL) for Total Nitrogen and Total Phosphorous for the Pearl River (June 2009). As permitted, the facility complies with the conditions proposed in the TMDL. The receiving streams are located in the Pearl River drainage basin, and are classified as Fish & Wildlife. This discharge should not further impair water quality.

The 7-day, 10-year minimum flow (7Q10) of the receiving stream is 0.06 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 2.97 MGD or 4.60 cfs.  
            QR = Receiving stream 7Q10, 0.06 cfs.

IWC = {(4.60 cfs)/(4.60 cfs + 0.06 cfs)} * 100 = 98.71 %

V.	APPLICABLE GUIDELINES – 11 MS Admin Code pt. 6, 2019 Wasteload Allocation (WLA), Total Maximum Daily Load (TMDL), Municipal Facility Guidelines (Technology)

VI.	SUMMARY OF DISCHARGE LIMITATIONS – 

Parameter				Value			Basis
Flow					2.97 MGD			Design
BOD5					10 mg/l (Monthly Average)		WLA
BOD5 (Percent Removal)		85% Minimum			Technology
TSS					30 mg/l (Monthly Average)		Technology
TSS (Percent Removal)		85% Minimum			Technology
NH3-N (Phase I)			2.0 mg/l (Monthly Average)	WLA
NH3-N (Phase II)			1.39 mg/l (Monthly Average)	WLA
Dissolved Oxygen			> 6.0 mg/l			WLA
E Coli					126 Col./100ml			MS WQS
	Phosphorus, Total			138.7 lbs/day			TMDL
Nitrogen, Total			337.1 lbs/day			TMDL
pH					6.0 – 9.0 S.U.			MS WQS
Copper, Total Recoverable		0.0160 mg/L			Translator Study
	*Chlorine, Total Residual		0.011 mg/L			MS WQS

*Facility must meet limitations when utilizing disinfection as a backup for the UV system. If not in use, facility must report NODI_CODE 9 on the monthly Discharge Monitoring Report (DMR).

This permit contains the phased limitations of Ammonia Nitrogen. 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 notes as Phase I; Phase II limitations shall not 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; Phase I limitations shall no longer apply at this time. 

The permittee shall submit an engineering report that describes how the facility will come into compliance with the Phase II limitations.

The permitted Copper limit is established based on a chemical translator/hardness study. A chemical translator study establishes a limit based on the site specific environmental conditions of the interaction between the permitted effluent and receiving stream. This method can be utilized to establish a limit in lieu of a chemical specific screening per 11 MS Admin Code Part 6, Ch. 1, Rule 1.2.6.C.(2).(b). 

BOD5, NH3-N and DO limits are based on the 2024 WLA (Attachment No. 3) and modeled for oxygen depletion in the receiving stream, and the toxicity limit for NH3-N and Cl2 were determined for the parameters that are potentially acutely and chronically toxic. The more stringent of the modeled limit and the toxicity limit (for NH3-N) is what is given in the Wasteload Allocation, to meet Water Quality Based Effluent Limitations (WQBELs).

MDEQ received 12 samples of Total Recoverable Zinc with the permit renewal application and all were no detects (attachment no. 5). We also reviewed the DMR/Historic data from previous two years. Total Recoverable Zinc did not exceed water quality standard for that time period and therefore was removed from the current draft permit.

BIOASSAY AND CHEMICAL SPECIFIC EVALUATION

BIOASSAY

In accordance to State Regulation 11 Mississippi Admin Code pt. 6, VI.B.2b., Corinth 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 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:

May 2023
			Ceriodaphnia dubia		IC25	   	>98.71%
			Pimephales promelas		IC25	  	>98.71%
			
August 2023
			Ceriodaphnia dubia		IC25	   	>98.71%
			Pimephales promelas		IC25 	    	>98.71%

			October 2023
			Ceriodaphnia dubia		IC25	   	>98.71%
			Pimephales promelas		IC25	   	>98.71%

			January 2024
			Ceriodaphnia dubia		IC25	   	>98.71%
			Pimephales promelas		IC25	     	>98.71%
			
All the inhibition concentrations were greater that the predicted IWC of 98.71%. Based upon the results of the WET testing, chronic bioassay requirements will not be placed within the permit.

Chemical Specific Analysis

Chemical specific analysis has been performed in accordance with State Regulations 11 Mississippi Admin. Code Pt. 6 Ch. 1.  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 (Attachment No. 6) to determine any possible toxic effect to the receiving waters.  A synopsis of these calculations is listed in Attachment No. 5.  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.

Chemical Specific Analysis 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). 

The chemical specific data results submitted did indicate the reasonable potential for violation of the appropriate criteria in Table III of Appendix D of CFR 122 for Total Recoverable Copper. The Copper limit is established based on a chemical translator/hardness study and placed in the permit. 

Chemical specific analysis 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, Base-Neutral Compounds 

Attachments 
Attachment 1 See Application 
Attachment 2 See Application 
Attachment 3 Wasteload Allocation 
Attachment 4 Tabulated Metal Results 
Attachment 5 Synopsis of Metals Results 
Attachment 6 MS State Water Quality Criteria 
Attachment 7 Copper translator/hardness study calculations

Attachment No. 3

Attachment No. 4 

Attachment No. 5

Attachment No. 6

Attachment No. 7