PERMIT RATIONALE FOR REISSUANCE
Raymond POTW, East
Hinds County
Raymond, Mississippi
Water NPDES No. MS0025852
March 31, 2026

I.	CLASSIFICATION – Municipal Minor Toxic

II.	DESCRIPTION OF WASTEWATER – Municipal/ Domestic Wastewater

III.	DESCRIPTION OF WASTEWATER TREATMENT – Wastewater is collected and treated biologically by means of an aerated lagoon followed by disinfection with chlorination. No increase in flow is proposed within the application.

IV.	RECEIVING WATER – Snake Creek. The receiving water is located within the Big Black River Basin, and is classified as Fish and Wildlife.  Snake Creek is listed on the State of Mississippi 303(d) list of impaired waterbodies. It is listed as an impaired waterbody with monitoring date for aquatic life support due to biological impairment. The facility is listed in a completed TMDL for Pathogens.  

The instream wastewater concentration at the point of discharge is determined by the following calculation:

IWC = {(Qw) /(Qw + Qr)}*100

	Where:
	Qw = Design flow of the wastewater treatment facility, 0.93 cfs.
	Qr = Receiving stream 7Q10, 0.22 cfs.

IWC = {(0.93 cfs) / (0.93 cfs + 0.22 cfs)}*100 = 80.85 %

V.	APPLICABLE GUIDELINES – State of Mississippi Wastewater Regulations (11 MS admin code part 6),  State of Mississippi Water Quality Criteria (11 MS admin code part 6), Municipal Facility Guidelines

VI.	SUMMARY OF LIMITATIONS –

	Parameter						Value			Basis
	Flow						0.6 MGD			Design
	BOD5 						     8 mg/l (Max Monthly Avg)	TMDL
	BOD5 (Percent Removal)			    	85% Minimum			Technology
	TSS						     30 mg/l (Max Monthly Avg)	Technology
	TSS (Percent Removal)			          	85% Minimum			Technology
	NH3-N						     1 mg/l (Max Monthly Avg)	TMDL
	Dissolved Oxygen					     6.0 mg/l Minimum		TMDL
	E. coli					          126 Col./100 ml			TMDL	
	pH						     6.0 – 9.0 SU			11 MS admin code part 6
	Chlorine, Total Residual			          	0.014 / 0.023 mg/l		IWC
	Chronic Ceriodaphnia					80.85% Minimum		WET, IWC
	Chronic Pimephales					     80.85% Minimum		WET, IWC						
	Total Nitrogen 						     57.55 lbs/day (Max Monthly Avg)	TMDL
	Total Phosphorus					    	16.39 lbs/day (Max Monthly Avg)	TMDL

Wasteload Allocation (WLA), Chemical Specific Analysis (CSA), Whole Effluent Toxicity (WET), Instream Waste Concentration (IWC), Mississippi Water Quality Criteria (11 MS admin code part 6), Total Maximum Daily Load (TMDL)

The TMDL allocation is modeled for oxygen depletion in the receiving stream, and the toxicity limit 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).

VII.	CHANGES FROM PREVIOUS PERMIT

Permit application data for total recoverable copper, total recoverable cadmium, and total recoverable lead did not exceed applicable water quality standards. Additionally, a review of DMR and historic data from the previous two years showed no exceedances of water quality standards for these parameters. Therefore, limitations for these parameters have been removed from the current permit.

WHOLE EFFLEUNT TOXICITY AND CHEMICAL SPECIFIC EVALUATION

WHOLE EFFLEUNT TOXICITY EVALUATION

In accordance to 11 Miss. Admin Code pt. 6, Ch. 1, Raymond POTW, East is required to perform Whole Effluent Toxicity (WET) tests as part of the renewal application.  The applicant should test in accordance with Short – Term Methods for estimating the ChronicToxicity of Effluents and Receiving Water to Freshwater Organisms. Regulations require that those facilities with an IWC of greater than 1% to perform a chronic whole effluent toxicity evaluation.  This test should be performed in accordance with Short-Term Methods for Estimating the Chronic Toxicity of Effluents and Receiving Water to Freshwater Organisms (EPA/600/4-91/002) or most recent addition.  The chronic WET tests should be performed on Ceriodaphnia dubia (invertebrate) and Pimephales promelas (vertebrate). The result of the wet tests are as follows:

September 2024
Ceriodaphnia dubia					IC25	80.85%
Pimephales promelas				IC25	80.85%

February 2025
Ceriodaphnia dubia					IC25	44.63%
Pimephales promelas				IC25	80.85%

April 2025
Ceriodaphnia dubia					IC25	80.85%
Pimephales promelas				IC25	80.85%

September 2025
Ceriodaphnia dubia					IC25	80.85%
Pimephales promelas				IC25	80.85%

Not all the inhibition concentrations were greater that the predicted IWC of 80.85%.  Based upon the results of the WET testing, chronic bioassay requirements will 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. 3.  The reported values are then analyzed and compared to water quality criteria to determine any possible toxic effect to the receiving waters.  A synopsis of these calculations is listed in attachment No. 2.  A column by column description of the calculations in attachment No. 2 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).

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. See Attachment 2 for the chemical specific analysis for metals and Attachment 3 for results of the toxicity screening.

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 Base-Neutral Compounds and Acid-Extractable Compounds.	

For Volatile Organics, the facility had an average daily concentration of 0.0081 mg/l for Chloroform. According to the 2006 National Recommended: Water Quality Criteria, the Human Health criteria for Chloroform is 0.470 mg/l, Organisms Only. The average concentration, multiplied by the power of 10 (0.081 mg/l), due to less than 12 samples, does not present a reasonable potential to violate Human Health Criteria.  

Attachments
Attachment 1	Waste Load Application 
Attachment 2	Synopsis of Metals Results
Attachment 3 	Tabulated Metals Results 
Attachment 4 	MS State Water Quality Criteria 

Attachment 1

Attachment 2

Attachment3

Attachment 4