PERMIT RATIONALE FOR MODIFICATION
Mantachie POTW
Itawamba County
Mantachie, Mississippi
Water NPDES No.MS0047350
May 2025

I.	CLASSIFICATION – Municipal NPDES Minor

II.	DESCRIPTION OF WASTEWATER – Domestic Wastewater

II.	DESCRIPTION OF WASTEWATER TREATMENT – Domestic wastewater is collected and treated by a conventional lagoon with a hydrograph controlled release.  No increase in treatment capacity is proposed within the application.  

IV.	RECEIVING WATERS – Mantachie Creek.  The receiving stream is located within the Tombigbee River Basin and is classified as Fish and Wildlife.  As indicated above, wastewater is treated by means of a conventional lagoon and stored until such time that the receiving stream reaches a prescribed hydrograph.  No effluent from outfall 001 is allowed until instream monitoring stations indicate a stream flow of not less than 60.0 cfs.  At such time as the stream flow reaches 60.0 cfs, discharge may begin and continue at a ratio of no more than 9:1 (stream to discharge).  At the point of discharge the receiving stream does not appear on the updated State of Mississippi 303(d) list for impaired waterbodies. Although this discharge is listed in a TMDL for Fecal Coliform, the TMDL does not require fecal coliform limitations or for the HCR to disinfect.  Only one discharge to surface waters is described within the application with no increase in flow proposed.  The discharge is an existing source with no proposed increase in discharge flow; therefore, the facility will not further impair water quality.  

V.	APPLICABLE GUIDELINES – 11 Miss. Admin Code pt. 6, WLA
 
VI.	SUMMARY OF LIMITATIONS – 
Parameter				Value				Basis
Flow					0.24 MGD			Design
BOD5					45 mg/l  			WLA
BOD5 (Percent Removal)		65% Minimum		11 MS Admin Code
TSS					90 mg/l			WLA		
TSS (Percent Removal)		65% Minimum		11 MS Admin Code
	Dissolved Oxygen			6.0 mg/l Minimum		WLA
	Ammonia Nitrogen			20 mg/l			WLA
	Ammonia Nitrogen 			40 lbs/day (Annual Avg.)	Calculations
pH					6.0 – 9.0 SU			11 MS Admin Code
	Total Nitrogen						    Report lbs/day 			WLA
	Total Phosphorus					    Report lbs/day 			WLA

* 	Effluent shall not be discharged to the receiving stream when the stream flow is less than 60 cfs.  At such time as the stream flow reaches 60 cfs, discharge may begin and continue at a ratio of no more than 9:1 (stream to discharge)

**	The measurement frequency shall be reported as the total number of discharge events during the month.  BOD5, TSS, and pH samples shall be taken from the effluent during each discharge event. 

VII.	CHANGES FROM PREVIOUS PERMIT
	
Effluent monitoring for Total Nitrogen and Total Phosphorous has been added to the draft permit.