PERMIT RATIONALE FOR MODIFICATION
Enterprise POTW
Clarke County
Enterprise, Mississippi
Water NPDES No. MS0037826
December 2025

I.	CLASSIFICATION – Minor Municipal NPDES 

II.	DESCRIPTION OF WASTEWATER – Domestic Wastewater

III.	DESCRIPTION OF WASTEWATER TREATMENT – Domestic wastewater is collected and treated by means of a conventional lagoon followed by disinfection by chlorination.  No increase in treated effluent flow is proposed within the application.  

IV.	RECEIVING WATERS – Chickasawhay River.  The receiving stream is located within the Pascagoula River Basin and is classified as Fish and Wildlife.  At the point of discharge the receiving stream does not appear on the most recent State of Mississippi 303(d) list of evaluated or impaired waterbodies.  At the point of discharge the 7Q10 for the receiving stream is 54.65 cfs.  The instream wastewater concentration (IWC) 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, 0.08 MGD or 0.124 cfs
	QR = Receiving stream 7Q10, 29 cfs

IWC = {(0.124 cfs)/(0.124 cfs + 54.65 cfs)}*100 = 0.23 %

V.	APPLICABLE GUIDELINES –  11 Miss. Admin Code pt. 6, Municipal Guidelines, 2021 WLA

VI.	SUMMARY OF LIMITATIONS – 
	Parameter						Value			Basis
	Flow							0.08 MGD			Design
	BOD5							30 mg/l (Max Mo. Avg.)		Modeled
	TSS							90 mg/l (Max Mo. Avg.)		Technology
	Ammonia Nitrogen					Report mg/l (Max Mo. Avg.)	Admin Code
	E. Coli							126 Col./100 ml			Admin Code
	Chlorine, Total Residual		 	0.011 mg/l (Maximum)		Admin Code
	pH							6.0 – 9.0 SU			Admin Code
	Dissolved Oxygen 					6.0 (Minimum)			Admin Code
	Total Nitrogen						Report (mg/l)			WLA
	Total Phosphorus					Report (mg/l)			WLA

VII.	CHANGES FROM PREVIOUS PERMIT
Per the wasteload allocation, 7Q10 is based on the 2023 update for USGS stream gage 02477000.