PERMIT RATIONALE FOR REISSUANCE
Hattiesburg North Lagoon
Forrest County
Hattiesburg, Mississippi
Water NPDES No. MS0020826
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 permitted treated effluent flow is proposed within the application.  Please see attachment no. 1 for a flow schematic.

IV.	RECEIVING STREAM – Bouie River.  The receiving stream is located within the Pascagoula River Basin and is classified as Fish and Wildlife.  See attachment no. 2 for discharge location map.  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 Organic Enrichment/Low Dissolved Oxygen and Nutrients (June 2005) in the Bouie Creek and Bouie River. The BOD5 limitation and the monitoring requirement for Ammonia Nitrogen have been added to the permit to comply with the TMDL. Only one discharge to surface waters is described within the application.  
The 7-day, 10 year minimum flow, 7Q10, for Bouie River at the point of discharge is 190 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, 4.0 MGD or 6.2 cfs.
	QR = Receiving stream 7Q10, 190 cfs.

IWC = {(6.2 cfs) / (6.2 cfs + 190 cfs)} * 100 = 3.16 %
	
V.	APPLICABLE GUIDELINES – 11 Miss. Admin Code pt. 6, TMDL, WLA

VI.	SUMMARY OF LIMITATIONS – 
Parameter			Value				Basis
Flow				4.0 MGD			Design
BOD5				30 mg/l (Monthly Avg.)	Modeled
TSS				30 mg/l (Monthly Avg.)	WLA
Ammonia Nitrogen		Report mg/l (Monthly Avg.)	WLA
Dissolved Oxygen		> 6.0 mg/l 			WLA

Parameter			Value				Basis
E Coli				126 Col./100 ml		Admin Code
Chlorine, Total Residual	0.35 mg/l 			Admin Code
pH				6.0 – 9.0 SU			Admin Code
Phosphorus, Total 		Report (Monthly)		TMDL
Nitrogen, Total 		Report (Monthly)		TMDL

See attached modeling data results attachment no. 3

Dilution Ratio 3.16 %

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)/(0.0316)} = 0.35 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)/(0.0316)} = 0.6 mg/l

BIOASSAY AND CHEMICAL SPECIFIC EVALUATION

BIOASSAY

In accordance to 11 Miss. Admin Code pt. 6, Ch. 1, Hattiesburg North 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 Chronic Toxicity of Effluents and Receiving Water to Freshwater Organisms.  Short-term acute WET tests should be performed on Ceriodaphnia dubia (invertebrate) and Pimephales promelas (vertebrate).

As a condition of the draft permit, Hattiesburg North Lagoon, will be required to begin the WET testing monitoring no later than 10 days of the date of permit issuance and complete the required testing within one year following effective date of the permit.  Hattiesburg North 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 a 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).
	
In accordance to 11 Miss. Admin Code pt. 6, a whole effluent toxicity (WET) evaluation was performed as part of the renewal application.  The applicant tested in accordance with Short – Term Methods for estimating the Chronic Toxicity of Effluents and Receiving Water to Freshwater organisms.  Short – term chronic WET tests were performed on Ceriodaphnia dubia (invertebrate) and Pimephales promelas (vertebrate). 
	The Hattiesburg North Lagoon in the WET testing used a dilution ratio of 3.16%.  The WET tests on the species were performed in September 2019, October 2019, February 2020 and April 2020.  The results of the WET tests are as follows:

September 2019

	Species				IC25 Results

	Ceriodaphnia dubia			>100 %
Pimephale promelas			>100 %

October 2019

	Species				IC25 Results

	Ceriodaphnia dubia			>100 %
Pimephale promelas			>100 %

February 2020

	Species				IC25 Results

	Ceriodaphnia dubia			>100 %
Pimephale promelas			>100 %

April 2020

	Species				IC25 Results

	Ceriodaphnia dubia			>100 %
Pimephale promelas			>100 %

All of the inhibition concentrations were greater than the predicted IWC of 3.16% for all species in all tests; it appears the effluent is not toxic to aquatic species.  Additional whole effluent toxicity tests will not be required as a permit condition.
CHEMICAL SPECIFIC ANALYSIS

Chemical specific analysis has been performed in accordance with 11 Miss. Admin Code pt. 6. Municipalities shall determine the toxic characteristics of their wastewater by analyzing for the toxic pollutants listed in Table III of Appendix D of 40 CFR 122.  The results of this analysis are tabulated as attachment no. 5.  The tabulated results are then analyzed and compared to water quality criteria to determine any possible toxic effect to the receiving waters.  A synopsis of these calculations is listed in attachment no. 6.  A column by column description of the calculations in attachment no. 6 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 Results

	Municipalities with pre-treatment programs 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 the NPDES permit if any of the parameters evaluated in the toxic screening procedures indicate the reasonable potential for violation of the appropriate criteria (acute, chronic, and human health). 
	For the City of Hattiesburg POTW North the chemical specific data results submitted with the reapplication did not indicate the reasonable potential for violation of the appropriate criteria in Table III of Appendix D of CFR 122.  See attached Chemical Specific Screening sheet and results.  Therefore, chemical specific limits have not been placed within the NPDES permit.  

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

For Volatile Organics, the permittee had an average daily concentration for the following compounds: Chloroform and dichlorobromomethane.

Average Daily Concentrations
Chloroform 					0.049 mg/l
Dichlorobromo-methane		0.00765 mg/l

According to the 2009 National Recommended Water Quality Criteria, the Human Health criteria for these compounds are shown below (organisms only):

Human Health Criteria for Organisms Only
Chloroform					0.47 mg/l
Dichlorobromo-methane		0.017 mg/l

Multiplying the average concentrations above by the IWC of 3.16 % determines the reasonable potential of the compound’s concentration to violate the Human Health Criteria.  The average concentration is multiplied by the power of 10 due to less than 12 samples.  

IWC = 3.16 %

Chloroform

[(0.049 mg/l)*(10)*(0.0316)] = 0.0155 mg/l < 0.47 mg/l

Dichlorobromo-methane

[(0.00765 mg/l)*(10)*(0.0316)] = 0.00242 mg/l < 0.017 mg/l 

The above results demonstrate that the average concentrations for both compounds do not present a reasonable potential to violate Human Health Criteria.  

The chemical specific data results submitted had no detects for Acid – Extractable Compounds.

The chemical specific data results submitted detected the following Base – Neutral Compounds: 

*from application

Average Daily Concentrations
Bis (2-chloroethyl) ether 			1.53 ug/l
di-n-octyl phthalate 					1.53 ug/l

According to the 2009 National Recommended Water Quality Criteria, the Human Health criteria for these compounds are shown below (organisms only):

Human Health Criteria for Organisms Only
Bis (2-chloroethyl) ether 			2.2 ug/l
di-n-octyl phthalate 					*no criteria available

Bis (2-chloroethyl) ether

[(0.00153 mg/l)*(10)*(0.0316)] = 0.0005 mg/l < 0.0022 mg/l
The above results demonstrate that the average concentration does not present a reasonable potential to violate Human Health Criteria.

di-n-octyl phthalate

No criteria is available to determine if there is a potential toxic effect.

Attachments

Attachment 1. Flow Schematic (See Application)
Attachment 2. Discharge Location Map (See Application)
Attachment 3. Wasteload Allocation (WLA)
Attachment   4. Chemical Specific Tabulated Results
	Attachment 5. State of Mississippi Water Quality Criteria
	Attachment 6. Toxicity Screening

Attachment 3

Attachment 4

Attachment 5

Attachment 5 (continued)

Attachment 6