PERMIT RATIONALE FOR REISSUANCE
Monticello POTW
Lawrence County
Monticello, Mississippi
Water NPDES No. MS0024643
June 22, 2022

I.	CLASSIFICATION –Municipal NPDES Minor 

II.	DESCRIPTION OF WASTEWATER – Domestic/ Municipal Wastewater

III.	DESCRIPTION OF WASTEWATER TREATMENT – Wastewater is collected from the Town of Monticello and treated by means of a three cell facultative lagoon, followed by chlorine disinfection. No increase in flow is proposed within the application.  

IV.	RECEIVING WATERS – Halls Creek. The receiving water is located within the Pearl River Basin and is classified as Fish and Wildlife.  The current State of Mississippi 303(d) list of impaired waterbodies, does list Halls Creek as an impaired waterbody for secondary contact due to pathogens. The discharge is also listed in a Completed TMDL for Pathogens. The facility disinfects, so the discharge will comply with the TMDL, and should not contribute to the pathogenic impairment of the receiving waters. The discharge is also listed in a Completed TMDL for pH. The facility monitors pH, so the permit will comply with the TMDL. The discharge is also included in Mercury TMDL.  This facility has already performed a Mercury Minimization Plan.

The 7Q10 of the receiving waters is 16 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, 0.349 cfs.
	Qr = Receiving stream 7Q10, 16 cfs.

IWC = {(0.349 cfs) / (0.349 cfs + 16 cfs)}*100 = 2.1 %

V.	APPLICABLE GUIDELINES – 11 MS admin code part 6

VI.	SUMMARY OF LIMITATIONS –
	Parameter						Value			Basis
	Flow						0.225 MGD			Design
	BOD5						30 mg/l			Model
	BOD5 (Percent Removal)			65% Minimum			Technology
	Ammonia						Report			WLA					
	TSS						90 mg/l			Technology
	E Coli						126 Col./100 ml			11 MS admin code part 6	
	pH						6.0 – 9.0 SU			MSWQS
	Chlorine, Total Residual			0.51/ 0.89 mg/l			MSWQS, IWC
	Mercury, Total Recoverable			Report			TMDL
	Dissolved Oxygen					6.0 mg/l			Model
	Total Nitrogen						Report (lbs/day)			WLA
	Total Phosphorus					Report (lbs/day)			WLA

BOD5, limits are based on the Wasteload Allocation and modeled for oxygen depletion in the receiving stream, and the toxicity limit Cl2 was determined for the parameters that are potentially acutely and chronically toxic.