PERMIT RATIONALE FOR REISSUANCE
Philadelphia POTW
Neshoba County
Philadelphia, Mississippi
Water NPDES No. MS0021156
January 2023

I.	CLASSIFICATION – Municipal NPDES Major

II.	DESCRIPTION OF WASTEWATER - Domestic Wastewater

III.	DESCRIPTION OF WASTEWATER TREATMENT – Wastewater is collected and treated by a conventional lagoon with a hydrograph-controlled release discharge. The treatment capacity for the treatment system is 2.1 MGD. No increase in the permitted flow is proposed within the application.

IV.	RECEIVING WATERS – Kentawka Canal. The waterbody is in the Pearl River Basin and is classified as Fish and Wildlife.   The receiving stream does not appear on the current State of Mississippi 303(d) List of Impaired Waterbodies. 

The discharge is denoted on:

The Pearl River TMDL for Total Nitrogen and Total Phosphorus. Although the TMDL report prescribes concentration based limitations for nutrients, the limitations have been applied as mass loadings in the permit to be consistent with other permitted HCRs.  MDEQ TMDL staff has reviewed the permit and confirmed that the limitations comply with the TMDL.

The Pearl River and Yockanookany River Phase I TMDL for Mercury (February 2004). The facility has completed a mercury minimization plan to comply with the TMDL. 

The effluent shall not be discharge to the receiving stream when the stream flow is less than 16 cfs. A dilution ratio of 5 to 1 (steam flow to discharge) shall be maintained until such time as the stream flow is equal to or greater than 44 cfs. At the time instream monitoring station indicates a stream flow of at least 44 cfs, the dilution ratio shall be adjusted to 3 to 1, equivalent to an instream wastewater concentration (IWC) of 25.0%

The instream wastewater concentrations (IWCs) were calculated as followed:

	IWC = {(Qw)/(Qw + Qr)
	Where:
	Qw = Discharge of the wastewater treatment facility (cfs)
	Qr =  Receiving stream flow (cfs)
	
	5:1 Dilution ratio for 16 cfs < Qr < 44 cfs; Qw = 3.2 cfs		
			IWC = {(3.2)/(3.2+16)} * 100 = 16.67%

3:1 Dilution ratio for 44 cfs < Qr; Qw	=14.67 cfs		
			IWC = {(14.67)/(14.67+44)} * 100 = 25.00%

For maximum protection of the receiving water, the highest ratio of mixing, IWC = 25.0%, will be used in all calculations of chemical specific data results.

V.	APPLICABLE GUIDELINES- 11 Mississippi Admin Code pt. 6, Municipal Facility Guidelines (Technology), State of Mississippi Water Quality Criteria (MSWQS), Wasteload Allocation (WLA), Chemical Specific Analysis, and WET 
VI.	
VII.	SUMMARY OF LIMITATIONS – 

Parameter				Value			Basis
	Flow					2.1 MGD		Design
	BOD					30 mg/l 		WLA
	TSS					90 mg/l		Technology
	NH3-N (Phase I)				9	mg/l		Municipal Guidelines
	NH3-N (Phase II)				7 mg/l		WLA
	Phase I Dissolved Oxygen		Report mg/l		WLA	
	Phase II Dissolved Oxygen		6.0 mg/l		WLA					
	E. Coli					126 Col./100ml		WLA
	BOD % Removal				65%		Technology
	pH   					6.0 – 9.0 SU		WLA
	Total Nitrogen 				128.61 lbs./day		WLA
	Total Phosphorus 				30.62 lbs./day		WLA
	C. dubia					IWC ≥ 25%
	P. promelas					IWC ≥25%

VIII.	CHANGES FROM PREVIOUS PERMIT – 

A new ammonia limit and dissolved oxygen limit has been established by the current Waste Load Allocation and is added to the proposed draft permit.

Chronic Bioassay Requirements have been added to the permit in order to complete the toxicity testing required during reapplication.

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.

The Permittee shall Submit engineering report: Due once within 6 months (180 days) after effective date. Said report shall outline the improvement activities needed to upgrade the wastewater treatment facility to comply with the site's Phase II limitations and shall include a proposed schedule for those improvement activities.

The Permittee shall Submit progress report: Due annually - every 1 year after effective date. Said report shall update the Permittee's progress in addressing needed upgrades to the wastewater treatment facility in order to meet the site's Phase II limitations. Said report should also include an updated schedule for completing these activities.

As a condition of the draft permit, Philadelphia POTW will be required to begin the chemical specific monitoring within 10 days of the date of permit issuance and complete the required testing within one year following the effective date of the permit.

BIOASSAY AND CHEMICAL SPECIFIC EVALUATIONS

Bioassay
	 
In accordance to State Regulation 11 MS Admin Code, pt. 6, Philadelphia POTW 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 Chronic Toxicity of Effluents and Receiving Water to Freshwater Organisms.  Short-term chronic WET tests should be performed on Ceriodaphnia dubia (invertebrate) and Pimephales promelas (vertebrate).

As a condition of the draft permit, Philadelphia POTW will be required to begin the WET testing monitoring no later than 10 days of the date of permit issuance and complete the required testing within one year following effective date of the permit.  Philadelphia POTW has a water salinity of less than 1,000 mg/l, so freshwater testing organisms will be used.  If any one (1) chronic toxicity test indicates the IC25 is less than the IWC%, then that test has failed whole 	effluent toxicity. Regulations require that those facilities with an IWC of than or equal to 1% performs 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 test results submitted were as follows:

	August 2021
	Ceriodaphnia dubia							IC25>100%
	Pimephales promelas							IC25>100%

	October 2021
	Ceriodaphnia dubia							IC25>100%
	Primephales promelas							IC25>100%

	July 2022
	Ceriodaphnia dubia							IC25>100%				
	Primephales promelas							IC25>100%

The facility only submitted three (3) bioessays with the application. Therefore, bioessay requirements have been added to the permit. The facility will be required to submit one (1) bioassay afor a total of four (4) to fully assess WET of the discharge.

Chemical Specific Analysis for Metals Results

Municipal Major facilities 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.  Chemical specific 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 indicated that reasonable potential for violations of the appropriate criteria (acute, chronic, and human health).

Facility submitted five (5) samples out twelve (12) with its application Multiplying the average and maximum daily concentrations from 10 (due to a data set of less than 12 samples) determines the reasonable potential of the compound’s concentration to violate the Water Quality and Human Health Criteria. The chemical specific analysis of the metals did not demonstrate the reasonable potential of concern.

As a condition of the draft permit, Philadelphia POTW will be required to begin the chemical specific monitoring no later 10 days of the date of permit issuance and complete the required testing of seven (7) samples for a total of twelve (12) within one year following the effective date of 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. Waste Load Allocation
Attachment 2.  Chemical Specific Analysis
Attachment 3. Water Quality Numeric Criteria
Attachment 4. Toxicity Screening

Attachment 1: Wasteload Allocation 

Attachment 2. Chemical Specific Analysis

Attachment 3. Mississippi Water Quality Numeric Criteria

	

Attachment 4. Toxicity Screening