PERMIT RATIONALE FOR REISSUANCE
Hancock County Utility Authority, Southern Regional WWTP
Hancock County
Waveland, Mississippi
Water NPDES No. MS0027847
October 2017

I.	CLASSIFICATION – Municipal NPDES Major

II.	DESCRIPTION OF WASTEWATER – Municipal / Domestic Wastewater

III.	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.  

IV.	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 nutrient and organic enrichment/low dissolved oxygen Total Maximum Daily Load (TMDL) for the Saint Louis Bay.  The TMDL recommends nutrient limits for this site, and are included in the permit. Edward’s Bayou also is denoted in a completed TMDL for the use of secondary contact recreation with the pollutant cause of pathogens. Enterococci limits have been included in this draft to comply with the TMDL. This waterbody is in the Coastal Streams drainage basin and is classified as Fish and Wildlife. 

V.	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)

VI.	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	TMDL	
Enterococci	35 Col./100 ml	TMDL	
Dissolved Oxygen	6.0 mg/l, minimum	Admin. Code	
pH	6.0 - 9.0	Admin. Code	
BOD5, % removal	85%	Technology	
TSS, % removal	85%	Technology	
Chlorine	0.009 mg/l	Admin. Code	
Total Phosphorus	470.0 lbs/day	TMDL	
Total Nitrogen	224.8 lbs/day	TMDL	

The minimum and maximum values for Dissolved Oxygen TMDL, and 30-Minute Sludge Settleability in aeration unit must be reported. 
BOD5, NH3-N, and DO limits are based on a Wasteload Allocation(WLA) and modeled for oxygen depletion in the receiving stream, and the toxicity limit for NH3-N and were determined for the parameters that are potentially acutely and chronically toxic.  The more stringent of the modeled limit and the toxicity limit (for NH3-N) is what is given in the Wasteload Allocation, to meet 11 Mississippi Admin Code pt. 6.

CHANGES FROM PREVIOUS PERMIT

1.	Removed Fecal Coliform limits. 

2.	The proposed draft permit will remove testing for Cyanide and Hexavalent Chromium in effluent requirements. Neither parameter was detected while being monitored during the life of the previous permit. 

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.

	December 2015 

	Species				IC25 Results

Mysidopsis bahia		> 100%
	Menidia beryllina			> 100%

March 2016

	Species				IC25 Results

Mysidopsis bahia		> 100%
Menidia beryllina			> 100%

July 2016

	Species				IC25 Results

Mysidopsis bahia		> 100%
Menidia beryllina			> 100%

September 2016

	Species				IC25 Results

Mysidopsis 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, chronic, and human health).

	The chemical specific data results submitted with the reapplication did not indicate the reasonable potential for violation of the appropriate criteria in Table II of Appendix D of CFR 122 for Mercury.  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: 4.79 µg/L
            Dichlorobromo-methane - Average Daily Concentration: 1.82 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

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 - [4.79 µg/L*10] = 47.9 µg/L < 2000 µg/L
Dichlorobromo-methane - [1.82 µg/L*10] = 18.2 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 1

Attachment 2

Attachment 3

Attachment 4

Attachment 5

Attachment 6

Attachment 7