PERMIT RATIONALE FOR REISSUANCE
Philadelphia POTW
Neshoba County
Philadelphia, Mississippi
Water NPDES No. MS0021156
January 2018

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 (1999) for Fecal Coliform. E. coli limitations have been developed and incorporated into the permit to comply with the TMDL. 

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 TMDL for Mercury. 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 – Mississippi Administrative Code, pt. 6; State of Mississippi Water Quality Criteria (MSWQS) & “Wastewater Regulations for National Pollutant Discharge Elimination System Permits, Underground Injection Control Permits, State Permits, Water Quality Based Effluent Limitations, and Water Quality Certification”; Municipal Guidelines; Wasteload Allocation (WLA).	

VI.	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)				Report		Municipal Guidelines
	NH3-N (Phase II)				9 mg/l		WLA
	Dissolved Oxygen				6.0 mg/l		WLA						
	E. Coli					126 Col./100ml		WLA
	BOD % Removal				65%		Technology
	pH   					6.0 – 9.0 SU		MSWQS
	Total Nitrogen 
		Phase I			Report		WLA
		Phase II		128.6 lb/day		WLA
	Total Phosphorus 			
		Phase I			Report		WLA
		Phase II		30.8 lb/day		WLA

VII.	CHANGES FROM PREVIOUS PERMIT – 

The proposed draft permit contains Phase I and Phase II Ammonia-Nitrogen effluent requirements.  The Phase II limitation is based on the Wasteload Allocation (WLA) dated November 3, 2017. 

The proposed draft permit contains Phase I and Phase II Total Nitrogen effluent requirements.  The Phase II limitation is based on the Wasteload Allocation (WLA) dated November 3, 2017. 

The proposed draft permit contains Phase I and Phase II Total Phosphorus effluent requirements.  The Phase II limitation is based on the Wasteload Allocation (WLA) dated November 3, 2017. 

The bacteria indicator, Fecal Coliform, has been substituted with E. Coli; the limitations have been updated to reflect this change.  

Beginning upon the completion and start-up of the improvements needed to comply with Phase II limitations, but no longer than the expiration date of the permit, the permittee shall achieve compliance with the effluent limitations specified for the parameters noted as Phase II.  The permittee shall notify our office orally at least 48 hours prior to start-up of the wastewater treatment units designed to meet the Phase II parameters and in writing no later than 5 days after start-up

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 within 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).

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).
	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.

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.	

Attachment 1: Wasteload Allocation