PERMIT RATIONALE FOR REISSUANCE
Amory POTW
Monroe County
Amory, Mississippi
Water NPDES No. MS0045489
November 2024

I.	CLASSIFICATION – NPDES Major Municipal

II.	DESCRIPTION OF WASTEWATER – Municipal Wastewater

III.	DESCRIPTION OF WASTEWATER TREATMENT – Wastewater is biologically treated by means of a facultative lagoon wastewater treatment facility, which is followed by disinfection by chlorination prior to discharge. The current design capacity of the facility is 2.0 MGD. See Attachment No. 1 for flow diagram.  Only one discharge to surface waters is described in the application with no increase in treated effluent flow proposed.  

IV.	RECEIVING STREAM – Tennessee-Tombigbee Waterway. At the point of discharge the receiving stream does not appear on the updated current State of Mississippi Section 303(d) List of Impaired Waterbodies. The facility is listed in a completed State of Alabama TMDL for the Aliceville Pool for Organic Enrichment and Dissolved Oxygen. No limitation increases have been proposed in this draft permit. This draft permit proposes effluent limitations consistent with that TMDL and the corresponding Wasteload Allocation. The receiving water is located in the Tombigbee River Drainage Basin, and is classified as a Public Water Supply.

The 7-day, 10-year minimum flow (7Q10) of the receiving stream is 337 cfs. The Instream Wastewater Concentration (IWC) at the point of the discharge is determined by the following calculation:

IWC = {(QW)/(QW + QR)}*100
	Where:
	QW = Design flow of the wastewater treatment facility, 2.0 MGD or 3.10 cfs.
	QR = Receiving stream 7Q10, 337 cfs.

IWC = {(3.10 cfs)/(3.10 cfs + 337 cfs)}*100 = 0.91 %

V.	APPLICABLE GUIDELINES – 11 Mississippi Admin Code pt. 6, Municipal Facility Guidelines (Technology), Wasteload Allocation (WLA, see Attachment No. 3)

VI.	CHANGES FROM PREVIOUS PERMIT – 

No change from last reissuance.

VII.	SUMMARY OF LIMITATIONS –

	Parameter				Value				Basis
	Flow					2.0 MGD			Design
	BOD5 					30 mg/l			WLA
	TSS					90 mg/l 			Technology
	Dissolved Oxygen, Minimum				6.0 mg/l 			WLA
	E. coli								126 col./100 ml		MS WQS	
	Chlorine, Total Residual				1.208 mg/l 			WLA
	pH								6.0 – 9.0 SU			MS WQS
	Total Nitrogen							Report lbs/day			WLA		
	Total Phosphorus						Report lbs/day			WLA
		
The minimum and maximum values for Dissolved Oxygen in the aeration unit and the 30-minute sludge settleability in the aeration unit must be reported.

BIOASSAY AND CHECMICAL SPECIFIC EVALUATIONS

BIOASSAY

In accordance to State Regulation 11 Mississippi Admin Code pt. 6, VI.B.2b., Amory POTW 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 Acute Toxicity of Effluents and Receiving Water to Freshwater Organisms.  Short – term acute WET tests were performed on Ceriodaphnia dubia (invertebrate) and Pimephale promelas (vertebrate). If the LC50 is less than the IWC of 0.91% with a 3x multiplier, the test demonstrates reasonable potential of concern. The results of the wet tests are as follows:

				Criteria = 3*IWC = 2.73%

August 2023
		Ceriodaphnia dubia		LC50		>3.6%
		Pimephales promelas		LC50		>3.6%

		September 2023
		Ceriodaphnia dubia		LC50		>3.6%
		Pimephales promelas		LC50		>3.6%

November 2023
		Ceriodaphnia dubia		LC50   	 	>3.6%
		Pimephales promelas		LC50		>3.6%

		March 2024
		Ceriodaphnia dubia		LC50 		>3.6%
		Pimephales promelas		LC50		>3.6%

All of the lethality concentrations were greater that the predicted 3*IWC (2.73%). Based on the results of the WET testing, acute bioassay requirements will not be placed in the permit.

CHEMICAL SPECIFIC ANALYSIS

Chemical specific analysis has been performed in accordance with State Regulations 11 Mississippi 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. 4.  The reported values are then analyzed and compared to water quality criteria (see Attachment No. 5) 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 for Metals and Results

Major municipalities 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 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).

For Amory POTW 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 40 CFR 122.  See attached Chemical Specific Screening sheet and results.

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

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

ATTACHMENTS

Attachment No. 1 – Flow Diagram
Attachment No. 2 – Discharge Location Map
Attachment No. 3 – Wasteload Allocation
Attachment No. 4 – Tabulated Metals Testing Data
Attachment No. 5 – MS State Water Quality Standards
Attachment No. 6 – Synopsis of Metals Results

Attachment No. 1 – Flow Diagram

Attachment No. 2 – Discharge Location Map

Attachment No. 3 – Wasteload Allocation

Attachment No. 4 - Tabulated Metals Testing Data

Attachment No. 5 - MS State Water Quality Standards

Attachment No. 6 - Synopsis of Metals Results