PERMIT RATIONALE FOR REISSUANCE
Macon POTW
Noxubee County
Macon, Mississippi
Water NPDES No. MS0020796
June 19, 2024

I.	CLASSIFICATION – Municipal NPDES Minor

II.	DESCRIPTION OF WASTEWATER – Domestic Wastewater

III.	DESCRIPTION OF WASTEWATER TREATMENT – Domestic wastewater is collected and treated by means of a conventional lagoon.  No increase in treatment capacity is proposed within the application.  

IV.	RECEIVING WATERS – Noxubee River.  The receiving stream is located within the Tombigbee River Basin and is classified as Fish and Wildlife.  At the point of discharge the receiving stream does appear on the current State of Mississippi 303(d) list for evaluated or impaired waterbodies.  The discharge is listed in the Total Maximum Daily Load (TMDL) for nutrients and organic enrichment/low dissolved oxygen for Noxubee River. The 7Q10 for the receiving stream is 32.0 cfs.  The instream wastewater concentration at the point of discharge is determined by the following calculation:

IWC = {(Qw)/(Qw + Qr)}*100 

	Where:
	Qw = Design flow of the wastewater treatment facility, 0.93 cfs.
	Qr = Receiving stream 7Q10, 32.0 cfs.

	IWC calculation for the Macon POTW is as follows:

IWC = {(0.93 cfs)/(0.93 cfs + 32.0 cfs)}*100 = 2.82 %

Only one discharge to surface waters is described within the application with no increase in flow proposed.  

V.	APPLICABLE GUIDELINES – State of Mississippi Wastewater Regulations, 11 MS admin code part 6 

VI.	SUMMARY OF LIMITATIONS –
Parameter				Value				Basis
Flow					0.6 MGD			Design
BOD5					40 mg/l (Yearly Average)	Modeled
TSS					90 mg/l (Yearly Average)	Technology 
Dissolved Oxygen 			> 6.0 mg/l 			MSWQS
E. Coli					126 Col./100 ml		MSWQS
Chlorine, Total Residual		    0.4 mg/l 			See Calculations
Total Nitrogen 		  	  57.550 lbs/day		TMDL
Total Phosphorus 		   	 29.050 lbs/day		TMDL
pH					   6.0 – 9.0 SU			MSWQS
Total Ammonia Nitrogen		   report			WLA

Ammonia Nitrogen has been changed to “Report Only” in this permit due to ammonia having no reasonable potential to neither violate ammonia toxicity nor cause an oxide depletion scenario in the stream. It is a component of Total Nitrogen and that limitation has been added to the permit.