PERMIT RATIONALE FOR REISSUANCE
Columbia POTW, North
Marion County
Columbia, Mississippi
Water NPDES No. MS0020222
June 30, 2026

I.	CLASSIFICATION – Municipal NPDES Minor

II.	DESCRIPTION OF WASTEWATER – Domestic/ Municipal Wastewater

III.	DESCRIPTION OF WASTEWATER TREATMENT - Municipal wastewater is collected and treated by means of an aerated lagoon followed by disinfection.  No increase in flow is proposed within the application.

IV.	RECEIVING WATER – Pearl River.  The Pearl River is located in the Pearl River basin and is classified as Recreational. The Pearl River does not appear on the current State of Mississippi 303(d) list of impaired waterbodies. It has a completed TMDL for Pathogens, Nutrients, Sediment, pH, and Pesticides. The facility, as permitted, will be in compliance with the TMDLs.  The 7Q10 of the Pearl River 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, 0.465 cfs
   Qr = Receiving water 7Q10, 765 cfs

IWC calculation for the Columbia POTW North is as follows:

IWC = {(0.465 cfs)/(0.465 cfs + 765 cfs)}*100 = 0.061 %

V.	APPLICABLE GUIDELINES – 11 MS Admin Code pt. 6, Municipal Guidelines, 2021 Wasteload Allocation (WLA)

VI.	SUMMARY OF LIMITATIONS –
Parameter			Flow				Basis
Flow				0.3 MGD			Design
BOD5				30 mg/l			WLA
BOD (Percent Removal)	65% Minimum		Guidelines
TSS				90 mg/l			Guidelines
E. Coli				126 Col/100 ml		Admin Code
	Chlorine, Total Residual	1.0 mg/l (Maximum)		Admin Code & IWC
	Minimum D.O.		6 mg/l 				WLA
pH				6.0 – 9.0 SU			Admin Code
Total Nitrogen			Report lbs/day			WLA
Total Phosphorus		Report lbs/day			WLA
Ammonia Nitrogen		Report mg/l			WLA