PERMIT RATIONALE FOR MODIFICATION
Diamondhead Water and Sewer District
Hancock County
Diamondhead, Mississippi
Water NPDES No. MS0046078
July 2023

PURPOSE OF MODIFICATION

After submitting all the required data to fully access effluent toxicity, Diamondhead Water & Sewer sent a formal letter requesting removal of Copper, Zinc, and WET monitoring requirements. The permit was reopened to determine the facility’s compliance with Copper and Zinc by looking at the facility’s DMR submittals from the past two years. After review, the data indicate that the facility has shown consistent compliance. Therefore, Copper and Zinc permit limitations were removed from permit. WET monitoring requirements were removed due to the facility passing its four (4) bioessays.

I.	CLASSIFICATION	- Municipal Major

II.	DESCRIPTION OF WASTEWATER –Domestic

III.	DESCRIPTION OF WASTEWATER TREATMENT – See attachment No. 1 for flow diagram. Wastewater is treated by means of an activated sludge plant wastewater treatment facility, which is followed by Chlorine disinfection prior to discharge. Only one discharge to surface waters is described in within the application with no increase in effluent flow

I.	RECEIVING WATERS – Jourdan River thence to St. Louis Bay. The receiving waters are located in the Coastal Streams drainage basin and are classified as Recreational. At the point of discharge, the receiving stream does not appear on the current State of Mississippi 303(d) List of Impaired Waterbodies, but the discharge does appear on a completed Total Maximum Daily Load (TMDL) for Fecal Coliform.
II.	
The instream wastewater concentration (IWC) 7Q10 at the point of discharge is determined by the following calculation:
		
		IWC 7Q10 = 
Qw = Design flow of the wastewater treatment facility
Qr = Receiving stream 7Q10

IWC calculation for the Diamondhead Water & Sewer District is as follows:
	Outfall 001:

Qw = 2.5 MGD or 3.87 cfs
Qr = 14.9 cfs

IWC 7Q10 = 

IV.	APPLICABLE GUIDELINES – 11 Mississippi Admin Code pt. 6, Wasteload Allocation (WLA, Attachment # 3), and Municipal Facility Guidelines (Technology), State of Mississippi Water Quality Criteria (MSWQS)

V.	CHANGES FROM PREVIOUS PERMIT
2022 Waste Load Allocation established new Ammonia limit. The new Ammonia limit has been added to the proposed draft permit. Zinc reporting and monitoring is added to draft permit.
After reviewing the facility’s copper and zinc DMR for the past two years, the facility has been shown to comply with the copper limit. Therefore, copper and zinc have been removed from final permit.
Outfall 001:
Parameter			   Value			Basis
Flow				   2.5 MGD 			Design
BOD5				   25 mg/l 			WLA
Phase I Ammonia Nitrogen	     9 mg/l 			WLA
Phase II Ammonia-Nitrogen	    6 mg/l			WLA
Total Nitrogen 		   239.78 lbs/day		WLA
Total Phosphorus		   114.7 lbs/day 		WLA
TSS				   30 mg/l			WLA
Enterococci			   35 mg/l			TMDL
	pH				   6.0 to 9.0 S.U.		MSWQS
	Chlorine, Total Residual	   0.053 mg/l			WLA
Dissolved Oxygen		   6.0 mg/l, Minimum		WLA
	BOD5, % Removal		   85%, Minimum		Technology 
TSS, % Removal		   85%, Minimum		Technology 
The permittee shall achieve compliance with the effluent limitations specified for discharge in accordance with the following schedule:
Upon issuance of this permit, the permittee shall achieve compliance with the effluent limitations specified for the parameters without a phase designation and for the parameters noted as Phase I; Phase II limitations shall not apply at this time.
Beginning upon completion and start-up of improvements needed to comply with Phase II limitations or three (3) years after the issuance of the permit, whichever comes first, the permittee shall achieve compliance with the effluent limitations specified for the parameters without a phase designation and for the parameters noted as Phase II; Phase I limitations shall no longer apply at this time. 
The Permittee shall Submit engineering report: Due once within 6 months (180 days) after effective date. Said report shall outline the improvement activities needed to upgrade the wastewater treatment facility to comply with the site's Phase II limitations and shall include a proposed schedule for those improvement activities. 

The Permittee shall Submit progress report: Due annually - every 1 year after effective date. Said report shall update the Permittee's progress in addressing needed upgrades to the wastewater treatment facility in order to meet the site's Phase II limitations. Said report should also include an updated schedule for completing these activities.
The permittee shall notify our office orally at least 24 hours prior to start-up and in writing no later than 48 hours after start-up.

BIOASSAY AND CHEMICAL SPECIFIC EVALUTION

BIOASSAY

	In accordance to State Regulation 11 Mississippi Admin Code, pt. 6, VI.B.2b., Diamondhead Water and Sewer District 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 Seawater organisms.  Short-Term Chronic WET tests are to be performed on Menidia beryllina (vertebrates) and Mysidopsis bahia (invertebrates). The results of the effluent biomonitoring report submitted was as follows:

		January 2018						
		Menidia beryllina 							IC25>82.5%	
		Mysidopsis bahia						I	IC25>82.5%

		July 2018
		Menidia beryllina							IC25<82.5%
		Mysidopsis bahia							IC25<82.5%	

		October 2022
		Menidia beryllina							IC25>82.5%			Mysidopsis bahia							IC25>82.5%

		January 2023
		Menidia beryllina							IC25>82.5%			Mysidopsis bahia							IC25>82.5%

Facility was able to submitted all four (4) bioessays. Chronic bioassay requirements have been removed from the permit

Chemical Specific Analysis

	Major 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.  Chemical specific 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 indicated that reasonable potential for violations of the appropriate criteria (acute, chronic, and human health).

	Diamondhead Water and Sewer District submitted the data described below, submitting twelve (12) samples. Furthermore, the average and max concentrations do not cause a reason of potential of concern shown in Attachment # 4

VOLATILES, ACID EXTRACTABLES, AND BASE-NEUTRAL COMPOUNDS AND RESULTS

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

ATTACHMENTS

	Attachment # 1 – Flow Diagram 
	Attachment # 2 – Discharge Location Topography Map 
	Attachment # 3 – Wasteload Allocation
	Attachment #4 – Toxicity Screen Spreadsheet
	Attachment #5 – Chemical Specific Analysis Spreadsheet (Effluent)
	Attachment #6 – Table II. Numeric Criteria, MS State Water Quality Standards
	
Attachment #1- Flow Diagram

Attachment #2- Dischage Location Topography Map

Attachment #3- Wasteload Allocation

Attachment #4 – Toxicity Screening Spreadsheet 

Attachment #5 – Chemical Specific Analysis Spreadsheet (Effluent)

Attachment #6 – Numeric Criteria (Table II) MS State Water Quality Standards