PERMIT RATIONALE FOR REISSUANCE
Rawls Springs Utility District, 
Lakewood Estates Subdivision
Forrest County
Maybank, Mississippi
Water NPDES No. MS0038792
January 2023

I.	CLASSIFICATION – Domestic NPDES Minor

II.	DECRIPTION 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.  No increase in flow is proposed within the application.  

IV.	RECEIVING WATERS – Big Creek thence into Bowie River.  The receiving waters are located within the Pascagoula River Basin and are classified as Fish and Wildlife.  At the point of discharge the receiving stream does not appear on the 2004 State of Mississippi 303(d) list of evaluated impaired waterbodies.  However, the discharge is listed in the Phase I TMDL for organic enrichment/low dissolved oxygen and nutrient for Bowie Creek and Bowie River (June 2005). The 7Q10 for the receiving stream at the point of discharge is 2.0 cfs.  The instream wastewater concentration (IWC) 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, 0.03 MGD or 0.05 cfs.
	Qr = Receiving stream 7Q10, 2.0 cfs.

IWC = {(0.05 cfs)/(2.0 cfs + 0.05 cfs)}*100 = 2.27 %
	
	Only one discharge to surface waters is described within the application with no increase in flow proposed.  

V.	APPLICABLE GUIDELINES – 11 MS Admin Code pt. 6, Wasteload Allocation,	 Commercial (Domestic) Facility Guidelines

VI.	SUMMARY OF LIMITATIONS –

	
Parameter	Limitation	Basis	
Flow	0.03 MGD		
BOD5	30 mg/l	Modeled	
TSS	60 mg/l	Technology 	
Ammonia Nitrogen	8.0 mg/l 	MSWQS	
Dissolved Oxygen	> 6.0 mg/l	MSWQS	
E. Coli	126 Col./100 ml	MSWQS	
Chlorine, Total Residual 	0.485	MSWQS	
pH	6.0 – 9.0 SU	MSWQS	

	Note: MSWQS, Mississippi State Water Quality Standards
	Non-Conventional Pollutants
	Dilution Ratio	2.27% 
	
	Typical Calculation

{(Water Quality Criteria)/(Dilution Ratio %)} = Permit Limitation

	Chlorine Acute Limitation

Chlorine Acute Freshwater Stream Standard = 0.019 mg/l from State’s Water Quality Criteria 
{(0.019 mg/l)/(0.0227)} = 0.837 mg/l 

0.837 mg/l = Acute Limitation for Chlorine

Chlorine Chronic Limitation

Chlorine Chronic Freshwater Stream Standard = 0.011 mg/l from State’s Water Quality Criteria
{(0.011 mg/l)/(0.0227)} = 0.485 mg/l

0.485 mg/l = Chronic Limitation for Chlorine