PERMIT RATIONALE FOR REISSUANCE
Clinton POTW, Southside
Hinds County
Clinton, Mississippi
Water NPDES No. MS0054992
February 5, 2024

CLASSIFICATION

Municipal Major

DESCRIPTION OF WASTEWATER

Domestic/ Municipal Wastewater

DESCRIPTION OF WASTEWATER TREATMENT  

Wastewater is collected and treated by means of an oxidation ditch followed by UV disinfection. 

RECEIVING WATERS

Bakers Creek. The receiving waters, at the point of discharge, are classified as Fish and Wildlife, and are in the Big Black River Basin. This discharge is listed in the TMDL for Pathogens.  The facility utilizes UV disinfection, which complies with the conditions of the TMDL. The discharge is included in a draft TMDL for Fourteen Mile Creek. Nutrient limitations are included in the draft permit to comply with the TMDL. Bakers Creek appears on the current Section 303(d) List of Impaired Water Bodies, for biological impairment.  

The instream wastewater concentration (IWC) 7Q10   at the point of discharge is determined by the following calculation:

IWC calculation for the Clinton POTW, Southside is as follows:

Qw = Design flow of the wastewater treatment facility = 3.5 MGD or 5.42 cfs
Qr =  Receiving stream 7Q10 = 0 cfs
IWC = (Qw/ (Qw + Qr)) * 100 =  (5.42/ 5.42 + 30) =  100 %

APPLICABLE GUIDELINES 

Mississippi Wastewater Regulations (11 MS admin code part 6), State of Mississippi Water Quality Criteria & “Wastewater Regulations for National Pollutant Discharge Elimination System Permits, Underground Injection Control Permits, State Permits, Water Quality Based Effluent Limitations , Water Quality Criteria (MSWQC), Water Quality Certification” applicable. Wasteload Allocation (WLA), Total Maximum Daily Load (TMDL)

SUMMARY OF LIMITATIONS –

	Parameter						Value				Basis
	Flow						3.5 MGD				Design
	BOD5 						8 MGD				TMDL
	BOD5 (Percent Removal)				85% Minimum				Technology
	TSS						30 mg/l (Monthly Avg.)			Technology
	TSS (Percent Removal)					85% Minimum				Technology
	NH3-N (Phase I)						2 mg/l (Monthly Avg.)			TMDL
	NH3-N (Phase II)						1.37 mg/l (Monthly Avg.)			WLA
	Dissolved Oxygen					> 6.0 mg/l (Monthly Avg.)			WLA
	E. Coli						126 mg/l (Monthly Avg.)			MSWQC
	pH						6.0 – 9.0 SU				MSWQC
	Copper, Total Recoverable			0.024 / 0.033 mg/l 				*
	Zinc, Total Recoverable					0.094 / 0.094 mg/l				Translator Study
	Chromium, Hexavalent 					0.011/0.016 mg/l				CSA
	Total Nitrogen						396.9 lbs/day (Monthly Avg.)			TMDL
	Total Phosphorus 					103.4 lbs/day (Monthly Avg.)			TMDL
	Pimephale promelas					100% Minimum				Admin code
Ceriodaphnia dubia	100% Minimum				Admin code

The minimum and maximum values for Dissolved Oxygen in aeration unit and 30-Minute Sludge Settleability in aeration unit must be reported.

	See attached modeling data results attachment no. 1.

Upon issuance of this permit, the permittee shall achieve compliance with the effluent limitations specified for the parameters noted as Phase I.  Beginning upon the completions and start-up of the improvements needed to comply with Phase II limitations, three (3) years after the permit effective date, the permittee shall achieve compliance with the effluent limitations specified for the parameter noted as Phase II.

The permittee shall submit an engineering report that describes how the facility will come into compliance with the Phase II limitations.

*Total Recoverable Copper and limitations are based on the hardness/ chemical translator in which was addressed in the 2005 permit modification. At the request of the permittee the data was also used to recalculate the Total Recoverable Zinc limitations in a 2009 reapplication. Facility submitted the data to recalculate the Total Recoverable Zinc limitations in 2024 and the limit has been updated based on the data received in this reissuance (attachment no. 6).  In further establishing the Copper criteria the permittee developed a site specific biological translator that relates the existing water quality standard to a specific permit limit using the water effects ratio (WER), as described in EPA guidance (No. 823-B-94-001), and Mississippi Wastewater Regulations (11 MS admin code part 6). The study demonstrated that a WER of 24 would protect the designated use of the receiving stream. The 2009 reapplication established a WER of 3.0 to protect designated use of the receiving stream, and cap the existing Copper load. As required by EPA guidance the permittee will be required to perform chronic whole effluent monitoring. The WER study was reconfirmed in 2015, and the facility will be required to reconfirm the study prior to the next reapplication.
	
	Copper limit = (Adjusted State Criteria for Copper attachment no. 5 ) * (WER of 3.0)
	Copper Monthly Average = 0.008*3.0 = 0.024 mg/l
	Copper Maximum Weekly Average = 0.011*3.0 = 0.033 mg/l

Zinc passed according to the renewal Chemical Specific data submitted with the renewal application, but failed according to the last 2 years of DMR data. Since there is still potential to violate the Zinc, Zinc limits will not be removed from the permit. 

Facility is actively performing Copper hardness/ chemical translator study. The permit will be modified based on the data received from the facility to reconfirm and adjust the limitations in future. 

Chromium, Hexavalent failed during the data received with renewal application listed in attachment 2, therefore, the limitations have been placed within the permit. 
	
WHOLE EFFLEUNT TOXICITY AND CHEMICAL SPECIFIC EVALUATION

WHOLE EFFLEUNT TOXICITY EVALUATION

In accordance to State Regulation 11 Mississippi Admin Code pt. 6, VI.B.2b., Clinton POTW, Southside is required to perform a Whole Effluent Toxicity (WET) evaluation as part of the renewal application. The applicant was to have 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 Pimephale promelas (vertebrate).  The results of the wet tests are as follows:

February 2023
Ceriodaphnia dubia					IC25	100%
Pimephales promelas				IC25	100%

April 2023
Ceriodaphnia dubia					IC25	7.8 %
Pimephales promelas				IC25	7.4 %

July 2023
Ceriodaphnia dubia					IC25	100%
Pimephales promelas				IC25	100%

August 2023
Ceriodaphnia dubia					IC25	100%
Pimephales promelas				IC25	100%

All of the inhibition concentrations were not greater than the predicted IWC of 100%. Bioassays results demonstrated a reasonable potential to violate Whole Effluent Toxicity based on the data received with the renewal application. Therefore, WET limitations will be placed within the permit. 

Chemical Specific Analysis

Chemical specific analysis has been performed in accordance with State Regulations 11Mississippi 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 No. 2.  The reported values are then analyzed and compared to water quality criteria (see Attachment No. 4) to determine any possible toxic effect to the receiving waters.  A synopsis of these calculations is listed in Attachment No. 3.  A column by column description of the calculations in Attachment No. 3 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 indicate the reasonable potential for violation of the appropriate criteria in Table III of Appendix D of CFR 122 for Total Recoverable Copper and Total Recoverable Chromium Hexavalent which addressed above. 

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

For Volatile Organic Compounds, the permittee had an average daily concentration for the following compounds: 

	Chloroform - Average Daily Concentration: 44.3 µg/L
	Dichlorobromo-methane - Average Daily Concentration: 25.5 µg/L
	Chlorodibromo-methane - Average Daily Concentration: 2.7 µg/L 

According to EPA’s National Recommended Water Quality Criteria, the Human Health Criteria (consumption of organism only) for the following compounds are shown below:

	Chloroform - Human Health Criteria: 2000 µg/L
	Dichlorobromo-methane - Human Health Criteria: 27 µg/L
	Chlorodibromo-methane - Human Health Criteria: 21 µg/L 

Multiplying the average daily concentrations above by 10 (due to a data set of less than 12 samples) determines the reasonable potential of the compound’s concentration to violate the Human Health Criteria.

	Chloroform - [44.3 µg/L*10] = 443 µg/L < 2000 µg/L
	Dichlorobromo-methane - [25.5 µg/L*10] = 255 µg/L > 27 µg/L
	Chlorodibromo-methane - [2.7 µg/L*10] = 27 µg/L < 10,000 µg/L

The above results demonstrate that the average concentrations for Chloroform, and Chlorodibromo-methane do not present a reasonable potential to violate Human Health Criteria.

The results also demonstrate that the average concentrations for Dichlorobromo-methane do present a reasonable potential to violate Human Health Criteria. The permit will require ten (10) samples of Dichlorobromo-methane be submitted to further determine the potential impacts on water quality. 

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

Attachments
Attachment 1	Waste Load Application 
Attachment 2	Tabulated Metals Results 
Attachment 3 	Synopsis of Metals Results 
Attachment 4 	MS State Water Quality Criteria 3
Attachment 5 	Hardness/ Chemical Translator Study Results
Attachment 6     Zinc Hardness/Chemical Translator Study Results (2024)

Attachment 1

Attachment 2

Attachment3

Attachment 4

Attachment 5

Attachment 6