PERMIT RATIONALE FOR REISSUANCE
D Lo POTW
Simpson County
D'Lo, Mississippi
Water NPDES No. MS0061727
March 2017

I.	FACILITY INFORMATION – Municipal NPDES Minor

II.	DESCRIPTION OF WASTEWATER – Domestic Wastewater 

III.	DESCRIPTION OF WASTEWATER TREATMENT – Domestic wastewater is collected and treated biologically by means of an aerated lagoon followed by disinfection by chlorination.  

IV.	RECEIVING WATERS – Strong River.  The receiving stream is located within the Pearl River Basin and is classified as Recreation.  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.  The discharge appears on a completed a Fecal Coliform TMDL for segments of the Pearl River, Strong River, Halls Creek, and Pretty Branch (Jan. 2012). The Facility uses Chlorine disinfection, and complies with the TMDL.  At the point of discharge the 7Q10 for the receiving stream is 19.125 cfs.  The instream wastewater concentration (IWC) at the point of discharge is determined using the following calculation:

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

	Where:
	Qw = Design flow of the wastewater treatment facility, 0.16 MGD or 0.25 cfs.
	QR = Receiving stream 7Q10, 19.125 cfs.

IWC = {(0.25 cfs)/(0.25 cfs + 19.125 cfs)}*100 = 1.28 %

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

V.	APPLICABLE GUIDELINES – 11 Mississippi Admin. Code pt. 6, Facility Guidelines (Technology)

VI.	SUMMARY OF LIMITATIONS –
	Parameter				Value				Basis
	Flow					0.16 MGD			Design
	BOD5					30 mg/l			WLA
	TSS					60 mg/l			Technology
	Ammonia Nitrogen			20 mg/l			WLA
	Minimum Dissolved Oxygen		6.0 mg/l 			WLA
	E. Coli					126 Col./100 ml		TMDL
		
Parameter				Value				Basis
	Chlorine, Total Residual				0.86 mg/l 			WLA
	pH								6.0 – 9.0 SU			Admin. Code

VII.	CHANGES FROM PREVIOUS PERMIT- 
	Fecal Coliform is replaced by E. Coli limits.