PERMIT RATIONALE FOR REISSUANCE
Columbus, City of, Reynolds R Ridgley Wastewater Treatment Plant
Lowndes County
Columbus,, Mississippi
Water NPDES No. MS0056472
October 15, 2025

I.	FACILITY INFORMATION

Facility Name:  Columbus, City of, Reynolds R Ridgley Wastewater Treatment Plant
Facility Address:  168 Yorkville Road West 
		      Columbus, MS  39702   Columbus, 
Permit No.:  MS0056472
SIC:  4952
Permit Writer:  James “Luke” Wall
EPD Branch:  Municipal and Private Facilities Branch

II.	NATURE OF BUSINESS

Applicant engages in the collection and treatment of domestic wastewater.

III.	EFFLUENT AND RECEIVING STREAM FLOW DATA

Luxapallila Creek.  The receiving stream is classified as Fish and Wildlife, and is in the Tombigbee River Basin. Luxapallila Creek does appear on the current 303(d) List of Impaired Water Bodies for pH. The discharge is listed in the Aliceville Pool TMDL. Biological Oxygen Demand, Ammonia Nitrogen, and Nutrient (Phosphorus and Nitrogen) limitations are based on EFDC/WASP model created by Columbus consultant and will comply with the conditions of the TMDL.

The instream wastewater concentration (IWC) 7Q10 at the point of discharge is determined by the following calculation:

	IWC calculation is as follows:

	Qw = Design flow of the wastewater treatment facility = 10 MGD or 15.5 cfs
	Qr =  Receiving stream 7Q10 = 59 cfs
             IWC = (Qw/ (Qw + Qr)) * 100 =  (15.5/ 15.5 + 59)*100 =  20.77 %

IV.	TYPE OF WASTEWATER TREATMENT:

Wastewater is collected and treated biologically via an activated sludge treatment plant followed by chlorine disinfection.

V.	EPA APPLICABLE CATEGORICAL GUIDELINES

Mississippi Wastewater Regulations (11 MS admin code part 6), State of Mississippi Water Quality Criteria & “Wastewater Regulations for National Pollutant Discharge Elimination System Permits, Water Quality Based Effluent Limitations, Water Quality Criteria (MSWQC), Water Quality Certification” applicable. Wasteload Allocation (WLA), Total Maximum Daily Load (TMDL)

VI.	PROPOSED FINAL LIMITATIONS 

Parameters			Value					Basis
Flow				10 MGD				Design
BOD5 				26 mg/l 				WLA
TSS				30 mg/l 				Technology Based
Ammonia Nitrogen 		6.0 mg/l 				WLA
E. Coli				126 Col./100 ml		11 MS admin code part 6
Dissolved Oxygen		6.0 mg/l				WLA
pH				6.0 – 9.0 SU		11 MS admin code part 6
Residual Chlorine		0.053 mg/l / 0.091 mg/l		Toxicity
Total Nitrogen 		Report					TMDL
Total Phosphorus 		Report					TMDL
	
The minimum and maximum values for Dissolved Oxygen in aeration unit and 30-Minute Sludge Settleability in aeration unit must be reported.
The toxicity limit for NH3-N and Total Residual Chorine was determined. The Total Residual Chlorine limit was updated to reflect the Instream Waste Concentration of the discharge in the receiving stream. For NH3-N the more stringent of the TMDL limit and the toxicity limit is what is given in the Wasteload Allocation.

See attached modeling data results attachment no. 3.

VII.     CHANGES FROM PREVIOUS PERMIT: 

Facility submitted eight sample sets, and an additional four sample sets will be required to fully assess water toxicity.

Chemical Specific Limitation Statement
Mississippi Wastewater Regulations require that the influent to and the effluent from the wastewater treatment facility must be analyzed twice per month for a 6 month period for the chemicals listed below. 
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 
Phenol 
Pentachlorophenol 
Hardness (in mg/l as CaCO3)

Please be aware that the chemical specific analysis must be performed by a method listed in 40 CFR 136 and with a Method Minimum Level (ML) at or below the level of the applicable water criterion for the measured pollutant parameter or the method has the lowest ML of the EPA approved analytical for the measured pollutant parameter. 
Sampling shall be initiated no later than the reissuance of the permit and results shall be compiled and submitted to Mississippi Environmental Quality Board, POSTMARKED NO LATER THAN THE 28TH DAY OF THE MONTH FOLLOWING THE COMPLETION OF THIS MONITORING. 
[11 Miss. Admin. Code Pt. 6, Ch. 1, Subch. 1.]

WHOLE EFFLEUNT TOXICITY AND CHEMICAL SPECIFIC EVALUATION

WHOLE EFFLEUNT TOXICITY EVALUATION

In accordance to State Regulation WPC-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 Pimephale promelas (vertebrate).  The results of the wet tests are as follows:

September 2025
Ceriodaphnia dubia			IC25    	>83.0%
Pimephales promelas		IC25   	>83.0%

March 2025
Ceriodaphnia dubia			IC25   	>83.0%
Pimephales promelas		IC25   	>83.0%

May 2025
Ceriodaphnia dubia			IC25     	  38%
Pimephales promelas		IC25     	>83.1%

July 2025
Ceriodaphnia dubia			IC25     	>83.1%
Pimephales promelas		IC25	>83.1%

All of the inhibition concentrations were greater that the predicted IWC of 20.77%.  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 WPC-1 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 (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 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).

During DEQ’s review of the lab sheets provided with the application it appeared that the 4th set in the series performed on 4/29/20 had the samples switched between the influent and effluent. DEQ contacted the lab, and the lab confirmed that the samples appeared switched. DEQ determined to not include the 4th set in the analysis. In addition, DEQ required the facility to complete four additional sets for 12 sets after the invalid 4th set.  The data is included in attachments 4(a) and 4(b)

The chemical specific data results submitted did not indicate the reasonable potential for violation of the appropriate criteria in Table III of Appendix D of CFR 122.

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 Acid-Extractable, Volatile Organic Compounds and Base-Neutral Compounds. 

Attachments
Attachment 1		See Application
Attachment 2		See Application
Attachment 3		Waste Load Application 
Attachment 4(a) 	Tabulated Metals Results
Attachment 4(b) 	Tabulated Metals Results 
Attachment 5 		Synopsis of Metals Results 
Attachment 6 		MS State Water Quality Criteria 

Attachment 3

Attachment 4

Attachment 5

I.	
Attachment 6