PERMIT RATIONALE FOR REISSUANCE
Florence POTW
Rankin County
Florence, Mississippi
Water NPDES No. MS0025275
October 2023
1.	CLASSIFICATION – NPDES Municipal Minor. This reissuance will be the last issuance under this classification. The categorical pretreatment permit, MS090294, which discharges into Florence POTW has been revoked.

2.	DESCRIPTION OF WASTEWATER – Municipal Wastewater

3.	DESCRIPTION OF WASTEWATER TREATMENT – Municipal wastewater is collected and treated by means of an Oxidation Ditch followed by chlorine disinfection.

4.	RECEIVING WATERS – Steen Creek.  The 7Q10 of the receiving stream at the point of discharge is 0.26 cfs; this along with the facility’s design flow of 0.75 MGD results in an Instream Waste Concentration (IWC) of 82%.  Steen Creek is not denoted in the most recent State of Mississippi Section 303(d) list of impaired waterbodies. The discharge is listed on a completed TMDL for Fecal Coliform. The facility utilizes chlorine disinfection, and complies with the TMDL. Steen Creek is in the Pearl River drainage basin and is classified as Fish and Wildlife.  	

5.	APPLICABLE GUIDELINES –11 Mississippi Admin Code pt. 6, Municipal Facility Guidelines (Technology), State of Mississippi Water Quality Criteria (MSWQS), Wasteload Allocation (WLA)

6.	SUMMARY OF LIMITATIONS –
Parameter			       Flow				Basis
Flow 				       0.75 MGD			Design
	Phase I BOD5						6.0 mg/l 			WLA
	Phase II BOD5						5.0 mg/l			WLA
	BOD (Percent Removal)			85% Minimum			Technology
	Minimum DO						6.0 mg/l			WLA
	TSS							30 mg/l 			Technology
	TSS (Percent Removal)			85% Minimum			Technology
	Chlorine, Total Residual			0.013 mg/l			WLA
	Ammonia						1 mg/l 			WLA
	E. Coli							126 Col./100 ml			WLA
	pH							6.0-9.0 SU			MSWQS
	Lead (Total)						0.00147/0.038 mg/l		MSWQS	
	Zinc (Total)						0.065/0.065 mg/l			MSWQS
	Cyanide						0.0052/0.022 mg/l		MSWQS
	Nitrogen (Total)					Report lbs./ day			WLA
	Phosphorus (Total)					Report lbs./ day			WLA
	Ceriodaphnia Dubia					82% Minimum			Previous Permit
	Pimephales Promelas				82% Minimum 			Previous Permit

7.	CHANGES FROM PERVIOUS PERMIT- 

Waste Load Allocation established a new BOD limit. Silver, Copper, and WET monitoring requirements have been removed from the draft permit. Due to facility showing consistent compliance for those parameters in the last 2 years.

The following conditions were added to the proposed draft 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. 

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.

Condition L-1 was added in the proposed draft permit.

BIOASSAY AND CHEMICAL SPECIFIC EVALUATION

In accordance to condition in permit, Florence POTW submitted additional bioessays for modification of permit..  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 pimephales promelas (vertebrate). WET tests on the species were performed totaling three (3) bioessays completed. Florence POTW has shown consistent compliance from past DMR submittals and data submitted. Their effluent does not show a reason of potential of concern. The results of the data submitted are below:

			August 2019
Pimephales promelas		IC25 > 100%
Ceriodaphnai dubia		IC25 > 100%

March 2020
Pimephales promelas		IC25 > 100%
Ceriodaphnai dubia		IC25 > 100%

October 2021
Pimephales promelas		IC25 > 100%
Ceriodaphnai dubia		IC25 > 100%
Florence will not be required to submit additional WET reports.

CHEMICAL SPECIFIC ANALYSIS

Categorical Guideline Limitations Calculations

The chemical specific analysis for the reissuance of permit has been performed in accordance with State Regulations 11 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.  Florence POTW submitted set of samples required by the permit to attain a total of twelve (3) sample sets. The results are tabulated in Attachment 2. A toxicity screening is performed by analyzing and comparing the results to water quality criteria (Attachment 3) to determine any possible toxic effect to the receiving waters.  See Attachment 4 for the toxicity screening results.  A column by column description of the toxicity screening calculations 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).
	
Florence POTW submitted twelve (3) metal samples ot of twelve (12) required.. The chemical specific data results submitted indicate a reasonable potential of concern for Copper, Lead, and Zinc. See Attachment 2 for the chemical specific analysis for metals and Attachment 4 for results of the toxicity screening.. Since the facility has not submitted a total of twelve (12) metal sample sets, Florence POTW will be required to submit nine (9) additional samples initiated no longer than 10 days from the reissuance of this permit.

The limitations for metal concentrations that exceeded water quality criteria were developed using the following calculations:

	Monthly Average (mg/l) = chronic criteria (column [7] ÷ instream waste concentration

	Max Weekly Average (mg/l) = acute criteria (column [3]) ÷ instream waste concentration
Lead
Copper exceeds the chronic water quality criteria based on the data received through the permit application, therefore, the following limitations have been added to the draft permit:
			Monthly Average:                                            Maximum Weekly Average:	
0.0014 mg/l					 	0.0036 mg/l	

Cyanide
Cyanide exceeds the acute and chronic water quality criteria based on the data received through the permit application, therefore, the following limitations have been added to the draft permit:
			Monthly Average:                                            Maximum Weekly Average:	
0.0063 mg/l						0.026 mg/l

Zinc
Cyanide exceeds the acute and chronic water quality criteria based on the data received through the permit application, therefore, the following limitations have been added to the draft permit:
			Monthly Average:                                            Maximum Weekly Average:	
0.00792 mg/l						0.0792 mg/l

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 all Volatile Organics Compounds, Acid-Extractable Compounds or Base-Neutral Compounds.

Attachment 1—Wasteload Allocation
Attachment 2—Chemical Specific Tabulated Results
Attachment 3—MS Water Quality Criteria
Attachment 4—Metal Toxicity Screening
Attachment 5- Calculations

Attachment 1.

Attachment 2.

Attachment 3.

Attachment 4.

Attachment 5.

Calculations for Cyanide, Lead, and Zinc

Calculation of Cyanide Acute Limit 

Cya = CA / IWC 

Where: 

Cya =Acute Cyanide limit to be placed in proposed draft permit
 
CA= Acute Allowable Criteria for Cyanider in fresh water (0.007 mg/l) 

IWC= Chronic Instream Waste Concentration (82%) 

Cya = (0.022 mg/l) / (0.82) = 0.026 mg/l 

Calculation of Cyanide Chronic Limit 

Cya = CA/ IWC 

Where: 

CyA =Chronic Cyanide imit to be placed in proposed draft permit 

CA= Chronic Allowable Criteria for Cyanide (0.005 mg/l) 

IWC= Chronic Instream Waste Concentration (82%)

CnA = (0.0052 mg/l) / (0.82) = 0.0063 mg/l

Calculation of Lead Acute Limit 

Pb = PbA / IWC 

Where: 

Pb =Acute Lead limit to be placed in proposed draft permit
 
PbA= Acute Allowable Criteria for Lead in fresh water (0.007 mg/l) 

IWC= Chronic Instream Waste Concentration (82%) 

Pba = (0.03 mg/l) / (0.82) = 0.0365 mg/l 

Calculation of Lead Chronic Limit 

Pb = PbA / IWC 

Where: 

Pb =Acute Lead limit to be placed in proposed draft permit
 
PbA= Acute Allowable Criteria for Lead in fresh water (0.00118 mg/l) 

IWC= Chronic Instream Waste Concentration (82%) 

Pba = (0.00118 mg/l) / (0.82) = 0.0014 mg/l
Calculation of Zinc Chronic Limit 

Zna = ZnA / IWC 

Where: 

Zn =Acute zinc limit to be placed in proposed draft permit
 
Znb= Acute Allowable Criteria for Zinc in fresh water (0.007 mg/l) 

IWC= Chronic Instream Waste Concentration (82%) 

Zn = (0.065 mg/l) / (0.82) = 0.0792 mg/l 

Calculation of Zinc Chronic Limit 

Zn = Zna/ IWC 

Where: 

Zn =Chronic Zinc imit to be placed in proposed draft permit 

Zna= Chronic Allowable Criteria for Zinc (0.065 mg/l) 

IWC= Chronic Instream Waste Concentration (82%)

Zn = (0.065 mg/l) / (0.82) = 0.0792 mg/l