PERMIT RATIONALE FOR REISSUANCE
Pelahatchie POTW, West
Rankin County
Pelahatchie, Mississippi
Water NPDES No. MS0021008
October 30, 2025

I.	PURPOSE FOR MODIFICATION-The town of Pelahatchie sent a formal letter requesting the Office to modify its current permit. An antidegradation was submitted with the letter, mentioning the facility’s inability to comply with the current ammonia and BOD limitations for the existing outfall. The antidegradation report was approved. Moreover, The permit was reopened to include limitations for the new outfall under construction. 

II.	CLASSIFICATION – NPDES Minor Municipal

III.	DESCRIPTION OF WASTEWATER – Municipal Wastewater

IV.	DESCRIPTION OF WASTEWATER TREATMENT – Wastewater is biologically treated by means of an aerated lagoon followed by a wetlands cell and a rock reed filter.  Disinfection is provided by chlorination; the wastewater also is dechlorinated prior to discharge.  Construction of the second outfall directly into Pelahatchie Creek is anticipated to be complete by the end of 2026.  

OUTFALL 001 (existing outfall)

RECEIVING WATERS – Unnamed Wetlands thence into Pelahatchie Creek. The receiving water is located within the Pearl River Basin, and is classified as Fish and Wildlife. Pelahatchie Creek does not appear on the updated current 303(d) list of Impaired Waterbodies.  The facility is listed in a completed Total Maximum Daily Load (TMDL) for Fecal Coliform (March 2009) and Nutrients (June 2009). The facility utilizes chlorine disinfection. 

The 7-day, 10-year minimum flow (7Q10) of the receiving stream is 0 cfs. The Instream Wastewater Concentration (IWC) at the point of the discharge is determined by the following calculation:

IWC = {(Qw)/(Qw + QR)} * 100
            Where:
            Qw = Design flow of the wastewater treatment facility 0.84 MGD or 1.30 cfs.  
            QR = Receiving stream 7Q10, 0 cfs.

IWC = {(1.30 cfs)/(1.30 cfs + 0 cfs)} * 100 = 100 %

APPLICABLE GUIDELINES – 11 MS Admin Code Pt 6, Municipal Facility Guidelines (Technology), MS Water Quality Standards, Wasteload Allocation (WLA), TMDL

SUMMARY OF LIMITATIONS –

	Parameter					Value			Basis
	Flow						0.84 MGD		Design
	BOD5						3 mg/l 			WLA		
	TSS						30 mg/l 		Technology
	BOD5, % Removal		       		65%, Minimum	Technology 
TSS, % Removal		       		65%, Minimum	Technology 
	E. coli						126 (#col/100ml)	MSWQS	
	NH3-N						1 mg/l 			WLA
	Dissolved Oxygen				6.0 mg/l, Minimum	WLA
	pH						6.0 – 9.0 SU		MSWQS
	Chlorine, Total Residual			0.011 mg/l		MSWQS
	Total Nitrogen					80.62 lbs/day		TMDL
	Total Phosphorus				36.45 lbs/day		TMDL

The permit requires that outfall 001 be decommissioned after outfall 002 is placed into operation.

OUTFALL 002 (new outfall)

RECEIVING WATERS – Discharges into Pelahatchie Creek. Pelahatchie Creek is located within the Pearl River Basin and is classified as Fish and Wildlife. Pelahatchie Creek does not appear on the updated 2018 303(d) list of Impaired Waterbodies.  The facility is listed in a completed Total Maximum Daily Load (TMDL) for Fecal Coliform (March 2009) and Nutrients (June 2009). The facility utilizes chlorine disinfection.

The 7-day, 10-year minimum flow (7Q10) of the receiving stream is 2.9 cfs. The Instream Wastewater Concentration (IWC) at the point of the discharge is determined by the following calculation:

IWC = {(Qw)/(Qw + QR)} * 100
            Where:
            Qw = Design flow of the wastewater treatment facility 0.84 MGD or 1.30 cfs.  
            QR = Receiving stream 7Q10, 2.9 cfs.

IWC = {(1.30 cfs)/(1.30 cfs + 2.9 cfs)} * 100 = 30.96 %

APPLICABLE GUIDELINES – 11 MS Admin Code Pt 6, Municipal Facility Guidelines (Technology), MS Water Quality Standards, Wasteload Allocation (WLA), TMDL

SUMMARY OF LIMITAIONS-

	Parameter					Value			Basis
	Flow						0.84 MGD		Design
	BOD5						10 mg/l 		WLA		
	TSS						30 mg/l 		Technology
	BOD5, % Removal		       		65%, Minimum	Technology 
TSS, % Removal		       		65%, Minimum	Technology 
	E. coli						126 (#col/100ml)	MSWQS	
	NH3-N						3 mg/l 			WLA
	Dissolved Oxygen				6.0 mg/l, Minimum	WLA
	pH						6.0 – 9.0 SU		WLA	
	Chlorine, Total Residual			0.036 mg/l		WLA
	Total Nitrogen					80.62 lbs/day		WLA
	Total Phosphorus				36.45 lbs/day		WLA

V.	CHANGES MADE-

None from permit modification issued in 2024.