PERMIT RATIONALE FOR REISSUANCE
Pearl River County Utility Authority, Old Mill Landing Subdivision
Pearl River County
Picayune Mississippi
Water NPDES No. MS0060640
October 14, 2025

I.	CLASSIFICATION – NPDES Commercial

II.	DESCRIPTION OF WAASTEWATER – Domestic wastewater

III.	DESCRIPTION OF WASTEWATER TREATMENT – Domestic wastewater is collected and treated by an aerated lagoon followed by chlorine disinfection prior to discharge.  Only one discharge to surface waters is described in the application with no increase in treated effluent flow proposed.  

IV.	RECEIVING WATER – Unnamed tributary of Boardpile Branch. The receiving waters are located within the Coastal Streams Basin and are classified as Fish and Wildlife.  At the point of discharge, the receiving stream does not appear on the updated State of Mississippi 303(d) list of Impaired Waterbodies.  The discharge must comply with a Total Maximum Daily Load (TMDL) for pathogens. E.coli limitations are included in the permit to comply with the TMDL.

The 7-day, 10-year minimum flow (7Q10) of the receiving stream is 0.77 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, 0.08 MGD or 0.12 cfs 
QR = Receiving stream 7Q10, 0.035 cfs

IWC = {(0.12 cfs)/(0.12 cfs + 0.035 cfs)}*100 = 77.4 %

V.	APPLICABLE GUIDELINES – 11 Mississippi Admin Code pt. 6, Mississippi Water Quality Standards (MSWQS), Wasteload Allocation (WLA), Commercial Facility Guidelines (Technology)

VI.	CHANGES FROM PREVIOUS PERMIT – 

The previous permitted Phase 2 limitations for Ammonia Nitrogen and Dissolved Oxygen are now enforceable in the new permit. 

VII.	SUMMARY OF LIMITATIONS - 

Parameter				Value		Basis
Flow					0.08 MGD		Design
BOD					30 mg/l		Technology
NH3-N	(Previously Phase II)		3 mg/l		WLA
	DO (Previously Phase II)		≥6.0 mg/l		WLA
TSS					60 mg/l 		Technology
E. coli					126 Col./100 ml		MSWQS
pH					6.0 - 9.0 S.U.		MSWQS
Chlorine				0.014 mg/l		MSWQS, IWC