PERMIT RATIONALE FOR REISSUANCE
Harrison County Utility Authority, Tradition Development
Harrison County
Woolmarket, Mississippi
Water NPDES No. MS0057011
June 2025

I.	CLASSIFICATION – NPDES Municipal Major

II.	DESCRIPTION OF WASTEWATER – Domestic/Municipal Wastewater

III.	DESCRIPTION OF WASTEWATER TREATMENT – Domestic wastewater is collected and treated biologically by means of an activated sludge system. The draft permit contains three phases. All three phases will utilize the same outfall. Phase I will utilize a series of activated sludge package plants and is permitted to discharge up to 0.35 MGD of treated effluent. For Phase II, the package plant locations are to be removed from service and become pump stations to an oxidation ditch, and the treatment capacity will increase to 1.0 MGD. Phase III will add an additional orbital oxidation ditch increasing the plant capacity to 2.0 MGD. Only one discharge to surface waters is described within the application with no increase in treated effluent flow proposed.

IV.	RECEIVING WATERS – Tiger Creek thence into the Biloxi River. The receiving streams are located in the Coastal Streams drainage basin and are classified as Fish & Wildlife. At the point of discharge, the receiving waters do not appear on the 2018 State of Mississippi 303(d) List of Impaired Waterbodies. There is a completed Pathogen Total Maximum Daily Load (TMDL) for the Biloxi River (December 1999). The facility utilizes chlorine disinfection, which complies with the conditions of the TMDL. 

The 7-day, 10-year minimum flow (7Q10) of the receiving stream is 2.3 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, 0.35 MGD or 0.54 cfs 
QR = Receiving stream 7Q10, 2.3 cfs

IWC = {(0.54 cfs)/(0.54 cfs + 2.3 cfs)}*100 = 19.1 %

V.	APPLICABLE GUIDELINES – 11 Mississippi Admin Code Pt. 6 Ch. 1, Municipal Facility Guidelines (Technology), State of Mississippi Water Quality Criteria (MSWQS), Wasteload Allocation (WLA- Attachment 2)

VI.	SUMMARY OF DISCHARGE LIMITATIONS – 

Phase I
Parameter			Value			Basis
	Flow				0.35 MGD		Design
	BOD5				10 mg/l 		WLA
	TSS				30 mg/l 		Technology
	Ammonia Nitrogen		2 mg/l 		WLA
	Dissolved Oxygen		> 6.0 mg/l		MSWQS
	E. coli				126 Col./100ml		MSWQS
	Chlorine, T.R.			0.011 mg/l		MSWQS
	pH				6.0 – 9.0 S.U.		MSWQS
	Total Nitrogen			Report lbs/day		WLA
	Total Phosphorus		Report lbs/day		WLA

Phase II
Parameter			Value			Basis
	Flow				1.0 MGD		Design
	BOD5				10 mg/l 		WLA
	TSS				30 mg/l 		Technology
	Ammonia Nitrogen		2 mg/l 		WLA
	Dissolved Oxygen		> 6.0 mg/l		MSWQS
	E. coli				126 Col./100ml		MSWQS
	Chlorine, T.R.			0.011 mg/l		MSWQS
	pH				6.0 – 9.0 S.U.		MSWQS
	Total Nitrogen			Report lbs/day		WLA
	Total Phosphorus		Report lbs/day		WLA
	
Phase III
Parameter			Value			Basis
	Flow				2.0 MGD		Design
	BOD5				10 mg/l 		WLA
	TSS				30 mg/l 		Technology
	Ammonia Nitrogen		2 mg/l 		WLA
	Dissolved Oxygen		> 6.0 mg/l		MSWQS
	E. coli				126 Col./100ml		MSWQS
	Chlorine, T.R.			0.011 mg/l		MSWQS
	pH				6.0 – 9.0 S.U.		MSWQS
	Total Nitrogen			Report lbs/day		WLA
	Total Phosphorus		Report lbs/day		WLA

Phase I limitations shall apply when the monthly average effluent discharge is less than or equal to 0.35 MGD.  The permittee shall provide written notification to the Office of Pollution Control within 180 days of exceeding the monthly average effluent discharge of 0.35 MGD. 

Phase II limitations shall apply when the monthly average effluent discharge is greater than 0.35 MGD, and less than or equal to 1.0 MGD.  The permittee shall provide written notification to the Office of Pollution Control within 180 days of exceeding the monthly average effluent discharge of 1.0 MGD.

Phase III limitations shall apply when the monthly average effluent discharge is greater than 1.0 MGD, and up to 2.0 MGD.

CHEMICAL SPECIFIC ANALYSIS

Chemical specific analysis has been performed in accordance with State Regulations 11 Mississippi Admin Code pt. 6, V1.B1.  Municipalities shall determine the toxic characteristics of their wastewater by analyzing for the toxic pollutant listed in Table III of appendix D of 40 CFR 122.  The results are tabulated in Attachment 3.  The reported values are then analyzed and compared to water quality criteria (see Attachment 4) to determine any possible toxic effect to the receiving waters.  A synopsis of these calculations is listed in Attachment 5.  A column by column description of the calculations in Attachment 5 is hereby provided:

Column No. 1 – Maximum concentration.  The highest effluent reading of the parameter

Column No. 2 – The maximum concentration mixed with the receiving water IWC.  This is 			calculated by the following equation:

		{Maximum Concentration (Column 1) * IWC %} / 100

Column No. 3 – Acute allowable – Chemical Specific State Water Quality Criteria                                   
	Column No. 4 – Pass or Fail. If column 2 > column 3 water quality criteria is exceeded                                		and failure occurs.

Column No. 5 – Long term average (LTA) of all tests.  The summation of the 12 samples divided                                         by 12.

Column No. 6 – The long term average concentration mixed with the receiving water                                		 	IWC.  This is calculated by the following equation:

		{LTA Concentration (Column 5) * IWC%} / 100

Column No. 7 – Chronic allowable – Chemical Specific State Water Quality Criteria                                   
Column No. 8 – Pass or Fail. If column 6 > column 7 water quality criteria is exceeded                               			and failure occurs.

Column No. 9 – Human health determination.  Long term average (Column 5) is mixed                  		with the mean annual flow IWCMA .  This is calculated by the following equation:

{LTA Concentration (Column 5) * IWCMA %} / 100

Column No. 10 – Human health allowable – State Water Quality Criteria   Note: Organisms only                              column is used if receiving waters are not drinking water supply. 

	Column No. 11 – Pass or Fail.  If column 9 > column 10 water quality criteria is exceeded                       	         	 and failure occurs.

Chemical Specific Analysis for Metals and Results

Major municipalities shall determine the toxic characteristics of their wastewater by analyzing for toxic pollutants listed in Table III of Appendix D of 40 CFR 122.  Metal analysis shall be for total recoverable metals.  Municipalities shall submit twelve influent and effluent samples collected.  Chemical specific limits shall be placed in a permittee’s permit if any of the parameters evaluated in the toxic screening procedure indicate the reasonable potential for violation of the appropriate criteria (acute, chronic, and human health).

For HCUA, Tradition Development, the chemical specific data results submitted with the reapplication did not indicate reasonable potential for violation of the appropriate criteria  in Table III of Appendix D of CFR 122. See Attachment 5 for Chemical Specific Screening sheet and results.

Chemical Specific Analysis for Volatile Organic Compounds, Acid – Extractable Compounds, and Base – Neutral Compounds and Results

For Volatile Organic, Acid-Extractable, and Base-Neutral compounds, the permittee had an average daily concentration for the following compounds: 

Bis(2-ethylhexyl) phthalate, Chloroform, Dichlorobromomethane, and Chlorodibromomethane. 

The average daily concentrations reported for the above compounds were compared to the EPA’s National Recommended Water Quality Criteria for Human Health Criteria for consumption of organism only (See Attachment 6) to determine their potential to violate Human Health Criteria. 

The results of the screening shown in Attachment 6 demonstrate that the average concentrations for Bis(2-ethylhexyl) phthalate, Chloroform, Dichlorobromomethane, and Chlorodibromomethane do not present a reasonable potential to violate Human Health Criteria. 

ATTACHMENTS

Attachment 1 – Discharge Location Map
Attachment 2 – Wasteload Allocation 
Attachment 3 – Chemical Specific Tabulated Results
Attachment 4 – MS Water Quality Criteria
Attachment 5 – Chemical Specific Screening for Metals
Attachment 6 – Volatile Organic, Acid-Extractable, and Base-Neutral Screening

Attachment 1 – Discharge Location Map

Attachment 2 – Wasteload Allocation 

Attachment 3 – Chemical Specific Tabulated Results

Attachment 4 – MS Water Quality Criteria

Attachment 4 – MS Water Quality Criteria (continued)

Attachment 5 – Chemical Specific Screening for Metals

Attachment 6 – Volatile Organic, Acid-Extractable, and Base-Neutral Screening

Parameter	Average Daily Concentration (µg/L)	10X Multiplier (µg/L)	EPA Water Quality Criteria (µg/L)	Pass/Fail	
Bis(2-ethylhexyl) phthalate***	9.77	NA	0.37	***	
Chloroform	20.236	NA	2000	PASS	
Dichlorobromomethane	3.744	NA	27	PASS	
Chlorodibromomethane	0.917	NA	21	PASS	

***EPA has issued a Maximum Contaminant Level (MCL) for this chemical which may be more stringent. Refer to EPA’s National Primary Drinking Water Regulations. No limitations are being placed in the draft permit at this time.