PERMIT RATIONALE FOR REISSUANCE
Como POTW
Panola County
Como, Mississippi
Water NPDES No. MS0030104
September 20, 2021

I.	CLASSIFICATION – Municipal NPDES Minor

II.	DESCRIPTION OF WASTEWATER – Domestic / Municipal Wastewater

III.	DESCRIPTION OF WASTEWATER TREATMENT – Domestic / Municipal wastewater is collected and treated biologically by means of an oxidation ditch followed by disinfection.  No increase in treatment capacity is proposed within the application.  

IV.	RECEIVING WATERS – Porter Creek.  The receiving stream is located within the Yazoo River Basin and is classified as Fish and Wildlife.  At the point of discharge the receiving stream does not appear on the current State of Mississippi 303(d) list of evaluated or impaired waterbodies.  The discharge is included in the Total Maximum Daily Load (TMDL) for Organic Enrichment / Low Dissolved Oxygen and Nutrients for Coldwater River. At the point of discharge the receiving stream’s 7Q10 is 0.02 cfs.  The instream wastewater concentration (IWC) at the point of discharge can be determined by the following calculation:

IWC = {(Qw)/(Qw + QR)} * 100 

	Where:
	Qw = Design flow of the wastewater treatment facility, 0.25 MGD or 0.39 cfs.
	QR = Receiving stream 7Q10, 0.02 cfs

IWC = {(0.39 cfs)/(0.39 cfs + 0.02 cfs)} * 100 = 95 %

V.	APPLICABLE GUIDELINES – 11 MS admin code part 6

VI.	SUMMARY OF LIMITATIONS –
	Parameter				Value					Basis
	Flow					0.25 MGD				Design 
	BOD5								10 mg/l (Monthly Avg.)		Modeled
	TSS								30 mg/l (Monthly Avg.)		Technology
	Ammonia Nitrogen						2 mg/l (Monthly Avg.)		MSWQS
	Dissolved Oxygen						> 6.0 mg/l 				MSWQS
	E. coli							    126 Col./100 ml			MSWQS
	Chlorine, Total Residual				0.011 mg/l / 0.019 mg/l		MSWQS
	pH								6.0 – 9.0 SU				MSWQS
	Total Nitrogen						     Report 				WLA
	Total Phosphorus						Report				WLA

The minimum and maximum values for dissolved oxygen and 30-minute sludge settleability in the aeration unit must be reported.  	
  
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). 

Facility is currently under construction to improve their wastewater treatment system and are planning to complete by June 1, 2022. 

BIOASSAY AND CHEMICAL SPECIFIC EVALUATION

BIOASSAY

	The permit includes limitations requiring the facility to perform the testing required in order to perform the Whole Effluent Toxicity Testing, which will meet the requirements of the Form 2A application.   The applicant shall test in accordance with Short – Term Methods for estimating the Chronic toxicity of Effluents and Receiving Water to Freshwater organisms.  Short term chronic WET tests are to be performed on Ceriodaphnia dubia (invertebrates) and Pimephales promelas (vertebrates).  Monitoring shall be required once per quarter for a period of one year.  Monitoring shall begin no later than one year after the issuance date of the permit. The chronic toxicity value is equivalent to the facilities instream waste concentration (IWC) which is 95%.  Should any of the analysis demonstrate amounts that violate water quality standards a reopener clause has been included in permit.

CHEMICAL SPECIFIC ANALYSIS

	The permit includes limitations requiring the facility to perform the testing required in order to perform the chemical specific analysis screening, which will meet the requirements of the Form 2A application.  Monitoring shall be conducted twice per month for a six month period for total recoverable metals, free cyanide, phenol, pentachlorophenol, and hardness.  Sampling is to be conducted on the influent to and effluent form the treatment works. Additionally, monitoring shall be required for all other pollutants listed in Table C of the 2A application.  Sampling for these pollutants shall be performed once per month for a three month period.  Sampling is to be conducted on the effluent only.  Monitoring shall begin no later than one year after the issuance date of the permit.  Should any of the analysis demonstrate amounts that violate water quality standards a reopener clause has been included in permit.

Attachments

Attachment No. 1 – See application
Attachment No. 2 – See application
Attachment No. 3 – Wasteload Allocation (WLA)
Attachment No. 4 – MS state water quality criteria

Attachment 3 – Wasteload Allocation

Attachment 4