PERMIT RATIONALE FOR REISSUANCE
Mississippi Department of Corrections, South Mississippi Correctional Institution
Greene County
Leakesville, Mississippi
Water NPDES No. MS0050750
December 2025

I.	CLASSIFICATION –Municipal NPDES Minor 

II.	DESCRIPTION OF WASTEWATER – Municipal Wastewater

III.	DESCRIPTION OF WASTEWATER TREATMENT –
The existing wastewater treatment plant (WWTP) is an activated sludge treatment
process designed to treat an average daily flow of 0.45 million gallons per day
(MGD). Currently raw sewage flows to the WWTP by gravity to the headworks
through a magnet installed to catch metal objects, a 3/16-inch bar screen, and then a
duplex influent pump station. Flow is then directed to either the aerator lagoon or the
oxidation ditch by use of gate valves. The center of the oxidation ditch serves as a
secondary clarifier which effluent from the clarifier flows to a manhole where
chlorine solution is added for disinfection if the UV disinfection system is not
operational before effluent flows to the UV disinfection system. Effluent then flows
through a V notched weir located inside a manhole for flow measurement. The treated
effluent then flows to the duplex effluent pump station and is pumped to the discharge
point (Outfall No. 001) located on Martin Creek.

Once construction is completed for the new plant, flow will be directed from the
existing plant to the newly constructed SMCI WWTP. The newly constructed SMCI
WWTP is designed to treat a daily average of 0.9 MGD with a peak flow of 3.1
MGD. The newly constructed WWTP receives raw sewage by gravity at the new
headworks. There it flows through the coarse mechanical bar screen, the triplex
influent pump station, and the fine mechanical bar screen to remove any large debris.
Both Coarse and Fine Screens have parallel, 100% redundant screens. At the Fine
Screen, Soda ash is introduced to the effluent to adjust the PH of the water. From
there process water moves to the East Lagoon where it is converted into a complete
mix treatment system with suspended diffusers off the bottom of the lagoon and two
(2) concrete secondary clarifiers on the west end of the lagoon. The West Lagoon
receives and stores any wasted sludge. After leaving the biological treatment system,
flow moves through a tertiary filtrations system to consistently achieve the permitted
BOD limit. Following the tertiary filtrations system, flow is measured via a flowmeter in the Parshall Flume as it moves to the UV disinfections system. There, three (3)
50% UV banks are available, with two (2) banks operating and one (1) serving as a
backup. Flow from the UV disinfection system then enters the new triplex effluent
pump station and is pumped to the discharge point (Outfall No. 002) located on
Martin Creek.
	
South Mississippi Correctional Institution will comply with permit limitations designated for Outfall 002 after Outfall 001 has been fully decommissioned. At this time, the facility will comply with permit limitations designated for Outfall 001.

IV.	RECEIVING WATERS – Martin Creek.  The receiving water is located within the Pascagoula River Basin and is classified as Fish and Wildlife.  Martin creek appears on the current State of Mississippi 303(d) list of impaired waterbodies. The discharge is listed in a Total Maximum Daily Load (TMDL) for Organic Enrichment / Low Dissolved Oxygen (DO) and Nutrients on the Chickasawhay River. The TMDL requires nutrient monitoring (Total Nitrogen and Total Phosphorus) to be included in the permit.

Outfall 001
The 7-day, 10-year minimum flow (7Q10) of the receiving stream is 0.022 cfs. The Instream Wastewater Concentration (IWC) at the point of the discharge is determined by the following calculation:
IWC = {(Qw)/(Qw + QR)} * 100
            Where:
            Qw = Design flow of the wastewater treatment facility 0.45 MGD or 0.696 cfs.  
            QR = Receiving stream 7Q10, 0.022 cfs.

IWC = {(0.696 cfs)/(0.696 cfs + 0.022 cfs)} * 100 = 96.94 %
	
Outfall 002
The 7-day, 10-year minimum flow (7Q10) of the receiving stream is 0.022 cfs. The Instream Wastewater Concentration (IWC) at the point of the discharge is determined by the following calculation:

IWC = {(Qw)/(Qw + QR)} * 100
            Where:
            Qw = Design flow of the wastewater treatment facility 0.90 MGD or 1.39 cfs.  
            QR = Receiving stream 7Q10, 0.022 cfs.

IWC = {(1.39 cfs)/(1.39 cfs + 0.022 cfs)} * 100 = 98.45 %

V.	APPLICABLE GUIDELINES – 11 MS Admin Code Pt 6, Municipal Facility Guidelines (Technology), MS Water Quality Standards, Wasteload Allocation (WLA), TMDL

VI.	SUMMARY OF LIMITATIONS –

Outfall 001
Parameter			Flow				Basis
Flow				0.45 MGD			Design
BOD5				10 mg/l 			WLA
Ammonia Nitrogen		2 mg/l				WLA
Minimum DO			6.0 mg/l 			WLA
E. coli				126 (#Col/100ml)		MS WQS
Total Nitrogen			Report				WLA
Total Phosphorous		Report				WLA
TSS				30 mg/l			Technology
pH				6.0 – 9.0 SU			MS WQS
**Chlorine				0.011 mg/l		WLA
Outfall 002
Parameter			Flow				Basis
Flow				0.90 MGD			Design
BOD5				5 mg/l 				WLA
Ammonia Nitrogen		1 mg/l				WLA
Minimum DO			6.0 mg/l 			WLA
E. coli				126 (#Col/100ml)		MS WQS
Total Nitrogen			Report				WLA
Total Phosphorous		Report				WLA
TSS				30 mg/l			Technology
pH				6.0 – 9.0 SU			MS WQS
**Chlorine			0.011 mg/l			WLA

**Chlorination may be utilized by facility in the event the ultraviolet (UV) system is not available for disinfection. When chlorine is used as the method for disinfection, the facility must comply with the Chlorine, Total Residual limitations provided in the permit.  If chlorination is not being utilized, the permittee shall report NODI_CODE 9 (Conditional Monitoring - Not Required This Period) in the monthly Discharge Monitoring Report (DMR).