PERMIT RATIONALE FOR REISSUANCE
Corinth POTW
Alcorn County
Corinth, Mississippi
Water NPDES No. MS0061328
April 24, 2019

I.	CLASSIFICATION	- Municipal Major

II.	DESCRIPTION OF WASTEWATER – Domestic/ Municipal Wastewater

III.	DESCRIPTION OF WASTEWATER TREATMENT –  Domestic wastewater is collected and treated biologically by means of an oxidation ditch process.  The discharge point was moved to the Tuscumbia River Canal and the plant has been upgraded to increase capacity to treat 6.0 MGD.  See attachment No. 1 for flow diagram.

IV.	RECEIVING WATERS-  Tuscumbia River Canal.  The receiving stream is located within the North Independent Stream Basin.  The Tuscumbia River at the point of discharge is classified as Fish and Wildlife.  See attached “Location Map” for plant site and discharge point (Attachment No. 2).   The receiving stream at the point of discharge does not appear on the current State of Mississippi 303(d) list for Impaired Waterbodies.  One discharge to surface waters is described within the application.  The facility is included in a completed TMDL for pathogens and a TMDL for Biological Impairment due to Nutrients and Organic Enrichment/Low DO.

The 7-day, 10 year minimum flow, 7Q10, for the Tuscumbia River at the point of discharge is 5.8 cfs.  Based upon the 7Q10 at the point of discharge the instream wastewater concentration (IWC) at the point of discharge is 61.56%.  Only one discharge to surface waters is described within the application with no increase in flow proposed.

V.	APPLICABLE GUIDELINES – 11 MS admin code part 6, Water Quality Certification” applicable. Wasteload Allocation (WLA), Total Maximum Daily Load (TMDL)

VI.	SUMMARY OF LIMITATIONS –
	Parameter						Value			Basis
	Flow						6.0 MGD			Design
	BOD5 						10 mg/l (Monthly Average)		Model			
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 					125 lbs/day (Monthly Avg.)	TMDL
	Nitrogen, Total						575 lbs/day (Monthly Avg.)	TMDL
	Dissolved Oxygen					> 6.0 mg/l (Monthly Avg.)		WLA	
	pH						6.0 – 9.0 SU			MSWQC
	Chlorine, Total Residual				0.018/ 0.031 mg/l			MSWQC, IWC
	Zinc, Total Recoverable				0.106/0.106 mg/l			MSWQC, IWC

BOD5, NH3-N and DO limits are based on the Wasteload Allocation and modeled for oxygen depletion in the receiving stream, and the toxicity limit for NH3-N and Cl2 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 Water Quality Based Effluent Limitations ( WQBELs).	

Facility did not submit any Beryllium data with the permit renewal application. MDEQ required facility to submit 3 sample data. Facility submitted 3 Beryllium samples which were detects, therefore the DMR will not require any limitations either. Facility will be required to submit the additional influent/effluent samples upon the permit issuance. 

MDEQ received 12 samples of Chromium Hex. with the permit renewal application and all were no detects. We also reviewed the DMR/Historic data from previous two years. Chromium Hex. did not exceed water quality standard for that time period and therefore was removed from the current draft permit. 

MDEQ reviewed past 2 year of DMR data for Total Recoverable Zinc and it indicates the reasonable potential violation for Zinc. Therefore, the Total Recoverable Zinc limitation has been placed in the permit. 

BIOASSAY AND CHEMICAL SPECIFIC EVALUATION

BIOASSAY

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 test were performed on Ceriodaphnia dubia (invertebrate) and Pimephale promelas (vertebrate).  The results of the wet tests are as follows:

			August 2018
			Ceriodaphnia dubia		IC25    		  22.5%
			Pimephales promelas		IC25   		>100%

			September 2018
			Ceriodaphnia dubia		IC25   		>100%
			Pimephales promelas		IC25   		>100%

			December 2018
			Ceriodaphnia dubia		IC25     		>100%
			Pimephales promelas		IC25     		>100%

			January 2019
			Ceriodaphnia dubia		IC25  		>100%
			Pimephales promelas		IC25   		>100%

Not all the inhibition concentrations were greater that the predicted IWC of 61.56%.  Based upon the results of the WET testing, chronic bioassay requirements will 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

	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).
	
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 CFR 122 but as stated previously, the Total Recoverable Zinc limitation has been placed in the permit. See attached Chemical Specific Screening sheet and results. 

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 No. 1 – Wastewater treatment plant flow diagram – See Application
Attachment No. 2 – Discharge location map – See Application
	Attachment No. 3 – Wasteload Allocation (WLA)
	Attachment No. 4 - Tabulated Metals Results 
Attachment No. 5 - Synopsis of Metals Results 
Attachment No. 6 - MS State Water Quality Criteria 3

Attachment No. 3

Attachment 4

Attachment 5

Attachment 6