PERMIT RATIONALE FOR MODIFICATION
Hancock County Utility Authority, Southern Regional WWTP
Hancock County
Waveland, Mississippi
Water NPDES No. MS0027847
January 2025

I.	PURPOSE FOR MODIFICATION-Hancock County Utility Authority, Southern Regional submitted a copper translator study. The study was reviewed and approved by the Office. The facility requested to be permitted based on the results of the study.

II.	CLASSIFICATION – Municipal NPDES Major

III.	DESCRIPTION OF WASTEWATER – Municipal / Domestic Wastewater

IV.	DESCRIPTION OF WASTEWATER TREATMENT – Municipal / Domestic wastewater is treated biologically by means of an activated sludge process. Part of the wastewater is treated through an activated sludge facility followed by circular clarifiers; the remaining wastewater is treated through an oxidation ditch followed by boat clarifiers.  After recombination of the streams, disinfection is provided by chlorination and de-chlorination facilities.  The wastewater then goes through post-aeration prior to being pumped to the discharge point. See Flow Diagram (Attachment 1). The current design capacity of the treatment facility is 4.9 MGD with no increase in treatment capacity proposed.  

V.	RECEIVING WATERS – Edward’s Bayou.  Edward’s Bayou is tidally influenced and does not appear on the current version of the State of Mississippi Section 303 (d) list of impaired waterbodies. A mixing zone study was performed in November of 2011, and results give an Acute IWC of 64% and Chronic IWC of 78%. The facility appears on a completed Total Maximum Daily Load for Fecal Coliform (July 2001. This waterbody is in the Coastal Streams drainage basin and is classified as Fish and Wildlife. 

VI.	APPLICABLE GUIDELINES – 11 Mississippi Admin Code pt. 6 (Admin. Code), Total Maximum Daily Load (TMDL), Wasteload Allocation (WLA, Attachment 3), and Municipal Facility Guidelines (Technology)

VII.	SUMMARY OF LIMITATIONS

Parameter	Proposed      Values	Basis	
Flow	4.9 MGD	Design	
BOD5	10 mg/l	WLA	
TSS	30 mg/l	Technology	
Ammonia Nitrogen	2 mg/l	WLA	
Enterococci	35 Col./100 ml	WLA	
Dissolved Oxygen	6.0 mg/l, minimum	WLA	
pH	6.0 - 9.0	WLA	
BOD5, % removal	85%	Technology	
TSS, % removal	85%	Technology	
Chlorine	0.053 mg/l	WLA	
Total Phosphorus	224.8 lbs/day	WLA	
Total Nitrogen	470.0 lbs/day	WLA	
Copper (Total Recoverable)	0.011 mg/l	Translator	

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

VIII.	CHANGES FROM PREVIOUS PERMIT
Copper (Total Recoverable) permit limitation has been modified based on approved Copper Translator Study. The following conditions were added to permit:

“Within 1 year (365 days) of the issuance of this permit, the permittee must submit a report that demonstrates the chemical translator hardness adjusted limitations for total recoverable copper are protective. The permit may be re-opened and modified based on the results of the study.”

BIOASSAY AND CHEMICAL SPECIFIC EVALUATION

BIOASSAY
	In accordance to State Regulation 11 Mississippi Admin Code pt. 6, Chp.1, a whole effluent toxicity evaluation was performed as part of the renewal application.  The applicant tested in accordance with the Short-Term Methods for estimating the Chronic Toxicity of Effluents and Receiving Water to Saltwater organisms.  Short-term chronic WET tests were performed on Mysidopsis bahia (invertebrates) and Menidia beryllina (vertebrates).

	The facility used in the WET testing a dilution ratio of 78.0 %.  The results of the WET tests are as follows and included with the application:

	January 2022 

	Species				IC25 Results

Amercamysis bahia		> 100%
	Menidia beryllina			> 100%

March 2022

	Species				IC25 Results

Amercamysis bahia		> 100%
Menidia beryllina			> 100%

May 2022

	Species				IC25 Results

Amercamysis bahia		> 100%
Menidia beryllina			> 100%

July 2022

	Species				IC25 Results

Amercamysis bahia		> 100%
Menidia beryllina			> 100%

	The applicant is required to perform four (4) whole effluent toxicity evaluations, two per dry and wet season. Based upon the results of the WET testing, Chronic Bioassay Requirements will not be placed within the municipal NPDES draft permit. 

Chemical Specific Analysis

Chemical specific analysis has been performed in accordance to State Regulation 11 Mississippi Admin Code pt. 6, Chp.1.  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 reported values are then analyzed and compared to water quality criteria to determine any possible toxic effect to the receiving waters. A column by column description of the 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 sum of the 12 samples divided by 12 (months).

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

	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 (Attachment 4).  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,
The chemical specific data results submitted with the reapplication did indicate the reasonable potential for violation of the appropriate criteria in Table II of Appendix D of CFR 122 for Copper (Total Recoverable).  See attached Chemical Specific Screening (Attachment 5) and Toxicity results for both the Acute IWC of 64% and Chronic IWC of 78% (Attachment 6 and 7).  

Chemical Specific Analysis for Volatile Organic 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: 7.68 µg/L
            Dichlorobromomethane- Average Daily Concentration: 4.64 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
Dichlorobromomethane - Human Health Criteria: 27 µg/L

Multiplying the average daily concentrations above by 10 (due to a data set of less than 12 samples) and the Chronic IWC 78% determines the reasonable potential of the compound’s concentration to violate the Human Health Criteria.

Chloroform - [7.68 µg/L*10*0.78] = 59.9 µg/L < 2000 µg/L
Dichlorobromo-methane - [1.82 µg/L*10*0.78] = 14.1 µg/L < 27 µg/L

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

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

Attachments
Attachment 1 Flow Diagram 
Attachment 2 Map of Discharge Location 
Attachment 3 Wasteload Allocation
Attachment 4 Table II MS State Water Quality Standards
Attachment 5 Chemical Specific Analysis
Attachment 6 Acute Chemical Specific Toxicity Screening
Attachment 7 Chronic Chemical Specific Toxicity Screening
Attachment 8 Copper Translator Study Calculations (Section 4)
Attachment 1

Attachment 2

Attachment 3

Attachment 4
Attachment 4

Attachment 5

Attachment 6

Attachment 7 

Attachment 8