PERMIT RATIONALE FOR REISSUANCE
Hattiesburg South Lagoon
Forrest County
Hattiesburg, Mississippi
Water NPDES No. MS0020303
July 2020

I.	CLASSIFICATION – Municipal NPDES Major

II.	DESCRIPTION OF WASTEWATER – Domestic Wastewater

III.	DESCRIPTION OF WASTEWATER TREATMENT – Domestic wastewater is collected and treated by means of a conventional lagoon followed by disinfection.  No increase in treated effluent flow is proposed within the application. 

IV.	RECEIVING WATERS – Leaf River.  The receiving stream is located within the Pascagoula River Basin and is classified as Fish and Wildlife.  At the point of discharge the receiving stream does not appear on the most recent State of Mississippi 303(d) list of evaluated or impaired waterbodies.  The discharge is listed in the Total Maximum Daily Load (TMDL) for Biological Impairment due to Organic Enrichment/Low Dissolved Oxygen and Nutrients (June 2005). 
The 7-day, 10 year minimum flow, 7Q10, for Leaf River at the point of discharge is 347 cfs. The instream wastewater concentration at the point of discharge can be determined using the following calculation:

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

	Where:
	Qw = Design flow of the wastewater treatment facility, 20.0 MGD or 31 cfs.
	QR = Receiving stream 7Q10, 347 cfs.

IWC = {(31 cfs) / (31 cfs + 347 cfs)} * 100 = 8.19 %

V.	APPLICABLE GUIDELINES –11 Miss. Admin Code pt. 6, Total Maximum Daily Load (TMDL), 2020 Wasteload Allocation (WLA), Previous Permit Modification

VI.	SUMMARY OF LIMITATIONS –
Parameter			Value				Basis
Flow				20.0 MGD			Design
BOD5				30 mg/l (Monthly Avg.)		Modeled
TSS				75 mg/l (Monthly Avg.)		Previous Permit
Ammonia Nitrogen		2.0 mg/l (Monthly Avg.)	TMDL
Dissolved Oxygen 		> 6.0 mg/l 			MSWQS
E. Coli				126 Col./100 ml			MSWQS
Chlorine, Total Residual		0.134 mg/l 			See Calculation
pH				6.0 – 9.0 SU			MSWQS
Nitrogen (Total)			Report mg/l 			TMDL
Phosphorus (Total)		Report mg/l			TMDL
Total Kjedahl Nitrogen		Report mg/l			Previous Permit
Nitrate Nitrogen, Total		Report mg/l			Previous Permit
Nitrite Nitrogen, Total		Report mg/l			Previous Permit

Dilution Ratio 8.2 %

Typical Calculation

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

Chlorine Chronic Limitation

Chlorine Chronic Freshwater Stream Standard = 0.011 mg/l from the State’s Water Quality Criteria

{(0.011 mg/l)/(0.082)} = 0.134 mg/l 

Chlorine Acute Limitation

Chlorine Acute Freshwater Stream Standard = 0.019 mg/l from the State’s Water Quality Criteria 

{(0.019 mg/l)/(0.082)} = 0.23 mg/l

BIOASSAY AND CHEMICAL SPECIFIC EVALUATION

BIOASSAY

In accordance to 11 Miss. Admin Code pt. 6, Ch. 1, Hattiesburg South Lagoon is required to perform Whole Effluent Toxicity (WET) tests as part of the renewal application.  The applicant should test in accordance with Short – Term Methods for estimating the ChronicToxicity of Effluents and Receiving Water to Freshwater Organisms. Hattiesburg South Lagoon has a water salinity of less than 1,000 mg/l, so freshwater testing organisms will be used.  Regulations require that those facilities with an IWC of greater than 1% to perform an chronic whole effluent toxicity evaluation.  This test should be performed in accordance with Short-Term Methods for Estimating the Chronic Toxicity of Effluents and Receiving Water to Freshwater Organisms (EPA/600/4-91/002) or most recent addition.  The chronic WET tests should be performed on Ceriodaphnia dubia (invertebrate) and Pimephales promelas (vertebrate). The WET tests on the species were performed in October 2019, February 2020, June 2020, and July 2020.

October 2019 
Pimephales promelas ICp25 > 100% 
Ceriodaphnai dubia ICp25 > 100% 

February 2020
Pimephales promelas ICp25 > 100% 
Ceriodaphnai dubia ICp25 > 100%  

June 2020

Pimephales promelas ICp25 > 100% 
Ceriodaphnai dubia ICp25 > 100% 

July 2020 

Pimephales promelas ICp25 > 100% 
	Ceriodaphnai dubia ICp25 > 100%

CHEMICAL SPECIFIC ANALYSIS

Categorical Guideline Limitations Calculations

The chemical specific analysis has been performed in accordance with State Regulations 11 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 4. A toxicity screening is performed by analyzing and comparing the results to water quality criteria (Attachment 5) to determine any possible toxic effect to the receiving waters.  See Attachment 6 for the toxicity screening results. A column by column description of the toxicity screening calculations 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 II 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).
	
The chemical specific data results submitted did not indicate the reasonable potential for violation of the appropriate criteria in Table III of Appendix D of CFR 122. See Attachment 4 for the chemical specific analysis for metals and Attachment 6 for results of the toxicity screening.

Chemical specific analysis for Volatile Organics Compounds, Acid-Extractable Compounds, and Base-Neutral Compounds and Results

The chemical specific data results submitted detected the following Volatile Organics Compounds
for a potential to violate Human Health Criteria: 1) Chloroform and 2) Bromodichloromethane.

1)	Chloroform:
	
Average Daily Concentration:
0.0612 mg/l

According to the most recent National Recommended Water Quality Criteria, the Human Health criteria for these compounds are shown below (organisms only): 

Human Health Criteria for Organisms Only: 
2.0 mg/l

Multiplying the average concentration above by the power of 10, due to less than 12 samples, then by the IWC of 8.19 (0.0819) % determines the reasonable potential of the compound’s concentration to violate the Human Health Criteria. 

[(0.0612 mg/l)*(10)*(0.0819)] = 0.050 mg/l
0.050 < 2.0 mg/l

The average concentration for Chloroform does not present a reasonable potential to violate Human Health Criteria.

2)	Dichlorobromo-Methane:

Average Daily Concentration:
4.21 ug/L

According to EPA’s National Recommended Water Quality Criteria, the Human Health Criteria (consumption of organism only) for Dichlorobromo-Methane is shown below:

Human Health Criteria for Organisms Only: 
	27 ug/l 

Multiplying the average concentration above by the power of 10, due to less than 12 samples, then by the IWC of 8.19 (0.0819) % determines the reasonable potential of the compound’s concentration to violate the Human Health Criteria. 

[(4.21 ug/l)*(10)*(0.0819)] = 3.44 ug/l

3.44 ug/l < 27 ug/l
The average concentration for Dichlorobromomethane does not present a reasonable potential to violate Human Health Criteria.

The chemical specific data results submitted had no detects for Acid-Extractable Compounds or Base-Neutral Compounds.

Attachment 1— Wastewater treatment plant flow diagram
Attachment 2— Discharge location 
Attachment 3— 2020 Wasteload Allocation
Attachment 4— Chemical Specific Tabulated Results
Attachment 5— MS Water Quality Criteria
Attachment 6—Metal Toxicity Screening

Attachment 1

Attachment 2

Attachment 3

Attachment 4

Attachment 5

Attachment 6