PERMIT RATIONALE FOR REISSUANCE
Pontotoc, City of, Activated Sludge Facility
Pontotoc County
Pontotoc, Mississippi
Water NPDES No. MS0058581
February 20, 2019

I.	      CLASSIFICATION -  Municipal Major

II.	     DESCRIPTION OF WASTEWATER – Domestic/ Municipal Wastewater

III.	      DESCRIPTION OF WASTEWATER TREATMENT –  Wastewater is collected and treated biologically by means of an activated sludge process. 

IV.	     RECEIVING WATERS- Unnamed tributary of Lyon Creek.  The receiving stream is located within the Yazoo River Basin.  Lyon Creek at the point of discharge is classified as Fish and Wildlife.  The receiving stream at the point of discharge does appear on the Updated State of Mississippi 303(d) list for Impaired Waterbodies with monitoring data for Aquatic Life Support due to Biological Impairment.  One discharge to surface waters is described within the application with no increase in flow.  

V.	     The 7-day, 10 year minimum flow, 7Q10, for Lyon Creek at the point of discharge is 0.0 cfs.  Based upon the 7Q10 at the point of discharge the instream wastewater concentration (IWC) at the point of discharge is 100%.  Only one discharge to surface waters is described within the application with no increase in flow proposed.

VI.	      APPLICABLE GUIDELINES – 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)

VII.	SUMMARY OF LIMITATIONS –
		Parameter			Value		  		Basis
		Flow				1.5 MGD		  	Design
		BOD5				6.0 mg/l			WLA 	
BOD5 (Percent Removal)	85% Minimum		Technology
		TSS				30 mg/l (Monthly Avg.)	Technology
TSS (Percent Removal)	85% Minimum		Technology 
E. Coli				126 Col./100 ml		MSWQS
		NH3-N			2.0 mg/l (Monthly Avg.)	Previous Permit
		Phosphorus, Total 		Report mg/l (Monthly Avg.) 	TMDL
		Nitrogen, Total 		Report mg/l (Monthly Avg.) 	TMDL
		Dissolved Oxygen		> 6.0 mg/l (Monthly Avg.)	WLA	
		pH				6.0 – 9.0 SU		   	MSWQC
		Chlorine, Total Residual	0.011/ 0.019 mg/l		MSWQC, IWC
		Copper, Total Recoverable	0.024/ 0.036 mg/l		*
		Zinc, Total Recoverable	0.357/0.357 mg/l		*	

CHANGES FROM PREVIOUS PERMIT

E. Coli will now be the bacterial indicator used for all freshwaters in MS designated as Recreation, Fish and Wildlife Support, and /or Public Water supply (replacing the use of fecal coliform).

*Total Recoverable Copper limitations are based on a hardness/ chemical translator study addressed in a 2012 permit modification.  Total recoverable Copper data was recalculated based on the chemical specific analysis data that was received with the permit renewal application and the last two years discharge monitoring report (attachment no. 7). 

	*The proposed draft permit contains Zinc Effluent requirements. The limitations for the 
Total Recoverable Zinc based on the chemical specific analysis data that was received with the permit renewal applications and the last two years discharge monitoring report (attachment no.7)

WHOLE EFFLEUNT TOXICITY AND CHEMICAL SPECIFIC EVALUATION

WHOLE EFFLEUNT TOXICITY EVALUATION

In accordance to State Regulation WPC – 1 VI.B.2b, a whole effluent toxicity evaluation was performed 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 Pimephales promelas (vertebrate). The results of the wet tests are as follows:

January 2017
Ceriodaphnia dubia					IC25	100%
Pimephales promelas				IC25	100%

October 2017
Ceriodaphnia dubia					IC25	100%
Pimephales promelas				IC25	100%

April 2018
Ceriodaphnia dubia					IC25	100%
Pimephales promelas				IC25	100%

June 2018
Ceriodaphnia dubia					IC25	100%
Pimephales promelas				IC25	100%

All of the inhibition concentrations were greater that the predicted IWC of 100%. Based upon the results of the WET testing, chronic bioassay requirements will not be placed within the permit.  

Chemical Specific Analysis

Chemical specific analysis has been performed in accordance with State Regulations WPC-1 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 (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. 5 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 Zinc. Chemical specific limits have been placed in the permit for the Total Recoverable Copper and Total Recoverable Zinc. 
 
Chemical specific analysis for Volatile Organics Compounds, Acid-Extractable Compounds, 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	See Application
Attachment 2	See Application
Attachment 3	Waste Load Application 
Attachment 4	Tabulated Metals Results 
Attachment 5	Synopsis of Metals Results 
Attachment 6 	MS State Water Quality Criteria 
Attachment 7 	Hardness/ Chemical Translator Study Results

Attachment No. 3

Attachment 4

Attachment 5

Attachment 6

Attachment 7