PERMIT RATIONALE FOR MODIFICATION
Derma POTW
Calhoun County
Derma, Mississippi
Water NPDES No. MS0034975
March 2019

I.	CLASSIFICATION – Municipal Minor NPDES

II.	DESCRIPTION OF WASTEWATER – Domestic Wastewater

III.	TYPE OF WASTEWATER TREATMENT: Domestic wastewater is collected and treated via a conventional lagoon with a hydrograph controlled release (HCR) discharge.  The treatment capacity of the facility is 0.06 MGD. No increase in flow is proposed within the application.    

IV.	RECEIVING WATERS—Yalobusha River. This waterbody does not appear on the current 303(d) list of impaired waterbodies.  The location of this discharge is included in a TMDL for Organic Enrichment/Low DO and Nutrients.  The discharge from this facility is prohibited at critical stream conditions and will comply with the conditions of the TMDL. This discharge will only occur when the stream flow of the Yalabusha River is above 5 cfs.

V.	 This waterbody is located in the Yazoo River drainage basin, and is classified as Fish and Wildlife. 
IWC = {(Qw)/(Qw + Qr)}*100

	Where, Qw = Design flow of the wastewater treatment facility, 0.06 MGD or 0.09 cfs
		 Qr = Receiving stream 7Q10, 5 cfs.
IWC = {(0.09 cfs)/(0.09 cfs + 5.0 cfs)}*100 = 1.77 %

VI.	APPLICABLE GUIDELINES – 11 MS Admin Code pt. 6, 2019 Wasteload Allocation (WLA), Total Maximum Daily Load (TMDL), Municipal Guidelines (Technology)

VII.	 SUMMARY OF LIMITATIONS –
	
	Outfall 002: 
	
	Parameter						Value				Basis
	Flow						0.06 MGD				Design
	BOD5						30 mg/l (Max Monthly Avg.)		WLA	
	BOD5 (Percent Removal)			65% Minimum				Technology
	TSS 						90 mg/l (Max Monthly Avg.)		Technology	
	TSS (Percent Removal)				65% Minimum				Technology
	Total Nitrogen						20.1 lbs/day (Annual Avg.)			TMDL
	Total Phosphorus					9.1 lbs/day  (Annual Avg.)			TMDL
	Dissolved Oxygen					> 6.0 mg/l 				WLA
	pH						6.0 – 9.0 SU				MSWQS

Discharge from Outfall 002 shall not occur if the stream flow in the Yalobusha River at the point of discharge is lower than 5 cfs.

Permittee shall Submit a report: Due annually by the 28th of January detailing date, time, and stream stage when the discharge begin; date, time, and stream stage when the discharge ceased; and the volume of wastewater released for each discharge from Outfall 002 occurring in the previous year.