PERMIT RATIONALE FOR REISSUANCE
Grenada POTW, Holcomb Facility
Grenada County
Holcomb, Mississippi
Water NPDES No. MS0036242
July 24, 2017

I.	CLASSIFICATION – Municipal NPDES Minor

II.	DESCRIPTION OF WASTEWATER – Domestic Wastewater 

III.	DESCRIPTION OF WASTEWATER TREATMENT – Domestic wastewater is collected and treated biologically by means of a three cell lagoon followed by disinfection.  No increase in treatment capacity is proposed within the application.  

IV.	RECEIVING WATERS – Cane Creek.  The receiving waters are located within the Yazoo River Basin and are classified as Fish and Wildlife.  At the point of discharge the receiving stream does appear on the most recent State of Mississippi 303(d) list of evaluated or impaired waterbodies.  Specifically, waterbody ID 916811 is listed for biological impairment and pathogens.  The listing is from the head waters to the mouth at the Yalobusha River.  At the point of discharge the 7Q10 for the receiving stream is 1.25 cfs.  The instream wastewater concentration at the point of discharge can be determined by the following calculation:

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

	Where
	Qw = Design flow of the wastewater treatment facility, 0.065 MGD or 0.1 cfs.
	QR = Receiving stream 7Q10, 1.25 cfs

IWC = {(0.1 cfs)/(0.1 cfs + 1.25 cfs)}*100 = 7.4 %

	The existing discharge from this facility should not further the impairment in the 	receiving 	stream.  No increase in treated effluent flow is proposed with only one 	discharge to surface 	waters described in the application.  

V.	APPLICABLE GUIDELINES – State of Mississippi Wastewater Regulations, WPC – 1 

VI.	SUMMARY OF LIMITATIONS –
	Parameter					Value			Basis
	Flow						0.065 MGD			Design
	BOD5						25 mg/l (Yearly Avg.)			Modeled
	Ammonia Nitrogen				5.0 mg/l (Yearly Avg.)		MSWQS
	TSS						90 mg/l (Yearly Avg.)			Technology
	Minimum D.O. 					> 6.0 mg/l (Yearly Avg.)		MSWQS
	E. Coli						126 Col./100 ml			MSWQS
	Chlorine, Total Residual			0.15 mg/l 			See Calculation
	pH						6.0 – 9.0 SU			MSWQS
	Total Nitrogen					Report (lbs/day)			WLA
	Total Phosphorus				Report (lbs/day)			WLA

E. Coli will now be the bacterial indicator used for all freshwaters in MS designated as Recreation, Fish and Wildlife Support, and /or Public Water supply (replacing the use of fecal coliform). 
BOD5, DO limits are based on the Wasteload Allocation and modeled for oxygen depletion in the receiving stream, and the toxicity limit for Cl2 was determined for the parameters that are potentially acutely and chronically toxic. 	

Total Residual Chlorine Calculations:

Dilution Ratio = 7.4 % 

Typical Calculation:

	Limitation = (Numeric Criteria) / (IWC)

	Chlorine Acute Limitation Calculation

	Freshwater Acute Chlorine Numeric Criteria = 0.019 mg/l

0.019 mg/l / 0.074 = 0.26 mg/l

	Chlorine Chronic Limitation Calculation

	Freshwater Chronic Chlorine Numeric Criteria = 0.011 mg/l

0.011 mg/l / 0.074 = 0.15 mg/l