PERMIT RATIONALE FOR REISSUANCE
Belzoni POTW
Humphreys County
Belzoni, Mississippi
Water NPDES No. MS0020371
March 31, 2025

I.	CLASSIFICATION – Municipal Major

II.	DESCRIPTION OF WASTEWATER – Municipal Domestic

III.	DESCRIPTION OF WASTEWATER TREATMENT - Wastewater is biologically treated by means of a conventional lagoon.  Disinfection is provided by chlorination.  The wastewater then goes through post-aeration prior to being pumped to the discharge point.  A process schematic is attached to the site’s application.  The current design capacity of the facility is 1.30 MGD.

IV.	RECEIVING WATERS – Yazoo River.  The 7Q10 of the receiving stream is 1050 cfs; this along with the facility’s design flow of 1.30 MGD (2.01 cfs) results in an Instream Waste Concentration (IWC) of 0.19%.  The current State of Mississippi List of Waterbodies denotes the Yazoo River, Waterbody ID No. MSYAZR3E, from confluence of Tallahatchie and Yalobusha Rivers to the confluence with the North end of the lower auxiliary channel to be on the 303(d) list of evaluated, impaired waterbodies for the use of aquatic life support. The impairments listed in a 2008 TMDL for nutrients and organic enrichment-low dissolved oxygen in the Tallahatchie and Yazoo Rivers.  Suspended solids are addressed in Section IX. However, TAN reporting limitations have been added to this permit to comply with the TMDL and for protective of water quality. This waterbody is in the Yazoo River drainage basin.  The Yazoo River is classified as Fish and Wildlife.  A location map is attached to the site’s application.

V.	APPLICABLE GUIDELINES – 11 Mississippi Admin Code pt. 6, Wasteload Allocation (WLA), Municipal Guidelines

VI.	SUMMARY OF LIMITATIONS –

Parameter				Value					Basis
Flow				1.3 MGD					Design
BOD5				45 mg/l (Monthly Average)			WLA
Dissolved Oxygen		6.0 mg/l (Minimum)				WLA
TSS				90 mg/l (Monthly Average)			Admin Code
E. Coli				126 #col/100ml					Admin Code
Chlorine				1.0 mg/l (Maximum Weekly Average)	Admin Code
Total Phosphorus		56.4 lbs/day				        	WLA
Total Nitrogen			124.8 lbs/day				         	WLA
pH 				6.0-9.0 S.U				         	Admin Code
Ammonia Nitrogen	          Report mg/l				WLA

VII.	CHANGES FROM PREVIOUS PERMIT

Effluent monitoring and reporting for Total Ammonia Nitrogen has been added to the draft permit in accordance with Waste Load Allocation.

VIII.	BIOASSAY AND CHEMICAL SPECIFIC EVALUATION

BIOASSAY

In accordance to State Regulation 11 MS Admin Code pt. 6, VI.B.2b, Belzoni POTW was required to perform Whole Effluent Toxicity (WET) tests as part of the renewal application. The applicant was to have tested in accordance with Short – Term Methods for estimating the Acute Toxicity of Effluents and Receiving Water to Freshwater Organisms.  Short – term acute WET tests were performed on Ceriodaphnia dubia (invertebrate) and Pimephale promelas (vertebrate).  The results of the wet tests are as follows:

July 2023
Ceriodaphnia dubia		48-hour LC50 		0.38%
Pimephales promelas		96-hour LC50		0.38%

January 2024
Ceriodaphnia dubia		48-hour LC50 		0.38%
Pimephales promelas		96-hour LC50		0.38%

April 2024
Ceriodaphnia dubia		48-hour LC50 		0.38%
Pimephales promelas		96-hour LC50		0.38%

October 2024
Ceriodaphnia dubia		48-hour LC50 		0.38%
Pimephales promelas		96-hour LC50		0.38%

January 2025
Ceriodaphnia dubia		48-hour LC50 		0.38%
Pimephales promelas		96-hour LC50		0.38%

All of the inhibition concentrations were greater than the predicted IWC of 0.19%.  Based upon the results of the WET testing, bioassay requirements will not be placed in the 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 State of Mississippi and/or National water quality criteria to determine any possible toxic effect to the receiving waters.  A synopsis of these calculations is listed in Attachment 5.  A column by column description of the calculations in Attachment 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

Chemical specific analysis has been performed in accordance with State Regulations 11 MS Admin Code pt. 6, V1.B1.  Municipalities shall determine the toxic characteristics of their wastewater by analyzing for the toxic pollutants listed in Table III of appendix D of 40 CFR 122. Municipalities shall submit twelve (12) 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).  

Belzoni POTW submitted three (3) of the twelve (12) sets of samples. The permit, as drafted, requires the facility to submit 9 samples in order to complete the full set of twelve (12) samples one (1) year from the permit’s date of issuance.

Due to a data set less than 12 samples, a 10 times (10x) multiplier was applied to determine the reasonable potential of the compound’s concentration to violate the Water Quality and Human Health Criteria. For Belzoni POTW, the chemical specific data results did not indicate a reasonable potential for violation of the appropriate criteria in Table III of Appendix D of 40 CFR 122. 

Chemical Specific Analysis for Volatile Organic Compounds, Acid – Extractable Compounds, and Base – Neutral Compounds and Results

For Volatile Organics, the permittee had an average daily concentration for the following compounds: Chloroform

	Average Daily Concentration
	Chloroform				0.010 mg/l

According to the most recent National Recommended Water Quality Criteria, the Human Health criteria for these compounds are shown below (organisms only):

Human Health Criteria for Organisms Only 
Chloroform				2.0 mg/l

Average Concentration
Chloroform				0.010 mg/l

Multiplying the average concentration above by the power of 10, due to less than 12 samples, then by the IWC of 0.0019 % determines the reasonable potential of the compound’s concentration to violate the Human Health Criterion.

IWC = 0.19 % = 0.0019

Chloroform:
[(0.010 mg/l)*(10)*(0.0019)] = 0.00019 mg/l < 2.0 mg/l

The average concentrations do not present a reasonable potential to violate Human Health Criterion

The chemical specific data results submitted had no detects for Acid – Extractable Compounds or Base Neutral Compounds.

Attachments

Attachment No. 1 – Wastewater treatment plant flow diagram – See Application
Attachment No. 2 – Discharge location map – See Application
Attachment No. 3 – Wasteload Allocation (WLA)
Attachment No. 4 – Chemical Specific Analysis
Attachment No. 5 – Toxicity Screening

Attachment 3

Attachment 4

Attachment 5