PERMIT RATIONALE FOR MODIFICATION
Pelahatchie POTW, West
Rankin County
Pelahatchie, Mississippi
Water NPDES No. MS0021008
April 2024

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 incapability 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.  No increase in flow is proposed within the application.  

OUTFALL 001 (existing outfall)

V.	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 %

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

VII.	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)			MS WQS	
	NH3-N						1 mg/l 			WLA
	Dissolved Oxygen					6.0 mg/l, Minimum		WLA
	pH						6.0 – 9.0 SU			MS WQS
	Chlorine, Total Residual			0.011 mg/l			MS WQS
	Total Nitrogen						80.62 lbs/day			TMDL
	Total Phosphorus					36.45 lbs/day			TMDL

OUTFALL 002 (new outfall)

VIII.	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 %

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

X.	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)			MS WQS	
	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

XI.	CHANGES MADE-

Outfall 002 permit limitations and receiving stream have been added to the proposed draft permit. Facility will comply with Condition T-15 of the permit:

“The permittee shall achieve compliance with the effluent limitations specified for discharge in accordance with the following schedule: Upon Permit Issuance. The permittee shall comply with limitations designated as Outfall 001 until existing outfall is decommissioned. After Outfall 001 is decommissioned, permittee shall comply with limitations designated as Outfall 002.”

Outfall 001 permit limitations will be removed after permit renewal application is submitted for reissuance required by Condition S-8:

“At least 180 days prior to the expiration date of this permit pursuant to the State law and regulation, the permittee who wishes to continue to operate under this permit shall submit an application to the Permit Board for reissuance. The Permit Board may grant permission to submit an application later than this, but no later than the expiration date of the permit.”