PERMIT RATIONALE FOR REISSUANCE
McComb POTW
Pike County
McComb, Mississippi
Water NPDES No. MS0061077
2/21/2013

I.	CLASSIFICATION – Municipal Major

II.	DESCRIPTION OF WASTEWATER - Industrial and Domestic

III.	DESCRIPTION OF WASTEWATER TREATMENT – Wastewater will be collected and treated biologically by means of an activated sludge process, followed by UV disinfection. An outline of the components included in the treatment system can be found in the application. The design capacity of the treatment system will be 5.0 MGD.  The design capacity does include anticipated growth. The City is currently under an administrative order to comply with the conditions of the Little Tallahatchie River TMDL.  The City has opted to consolidate existing systems and upgrade treatment. 

IV.	APPLICABLE GUIDELINES – State of Mississippi Wastewater Regulations (WPC-1),  State of Mississippi Water Quality Criteria (WPC-2), Municipal Facility Guidelines

V.	RECEIVING WATERS – Town Creek thence into Little Tallahatchie River. Town Creek at the point of discharge is classified as Fish and Wildlife.  Town Creek is in the South Independent Streams Basin. Town Creek does appear on the State of Mississippi 303(d) List of Impaired Waterbodies. It is listed for a Completed TMDL due to pathogens. The TMDL for pathogens requires disinfection. The facility will utilize UV disinfection.  Little Tallahatchie River is listed for a Complete TMDL due to  organic enrichment/ low dissolved oxygen, and ammonia nitrogen. The limits for DO, BOD, and NH3-N were developed to comply with the conditions of the TMDL. An antidegradation demonstration was provided with the application.  Review of the final antidegradation report indicated conformance with review criteria

The  7Q10 of the Town Creek at the point of proposed discharge is 1.1 cfs.  The instream wastewater concentration (IWC) at the point of proposed discharge is determined by the following calculation.

IWC   =   Qw                    * 100  
	    Qr  + Qw   

Where, Qw = Design flow of the wastewater treatment facility
Qr = Receiving stream 7Q10

IWC calculation for the proposed McComb POTW is as follows:

Qw = 5.0 MGD or 7.75 cfs
Qr = 1.1 cfs
IWC =    (7.75/(7.75+1.1))*100 = 87.6 %

VI.	SUMMARY AND BASIS OF DISCHARGE LIMITATIONS
		
	Parameter				Value				Basis
	Flow				5.0 MGD			Design
	NH3-N				1.46/ 2.19 mg/l			WLA, TMDL 
	BOD5				7.3/ 10.95 mg/l			WLA, TMDL 
	BOD5 Percent Removal		85% Minimum			Technology
	TSS				30/ 45 mg/l			Technology
	TSS Percent Removal		85% Minimum			Technology
	Fecal Coliform			200/400 col/100ml		MSWQS
	Dissolved Oxygen			> 6.0 mg/l			WLA, TMDL
	PH				6.0-9.0 SU		MSWQS
	Total Nitrogen				Report		WLA	
	Total Phosphorus				Report		WLA
	Copper, Total Recoverable		0.0057 mg/l		Toxicity	
	Lead, Total Recoverable			0.0013 mg/l		Toxicity
		
The minimum and maximum values for Influent ph, Dissolved Oxygen in aeration unit, and 30-Minute Sludge Settleability in aeration unit must be reported

	NOTE:  	MSWQS = Mississippi State Water Quality Standards
			TMDL = Total Maximum Daily Load (Little Tallahatchie River)
			WLA = Wasteload Allocation
				
The limits for DO, BOD, and NH3-N were developed to comply with the conditions of the TMDL for the Little Tallahatchie River.

ATTACHMENT A

CATEGORICAL GUIDELINE LIMITATIONS CALCULATIONS

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 the table below.  The reported values are then analyzed and compared to water quality criteria to determine any possible toxic effect to the receiving waters.  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 or Discharge Monitoring Results submitted in the last 2 years 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 Lead. Chemical specific limits have been place in the permit for both parameters.

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 Acid-Extractable Compounds.

For Volatile Organics, the facility had an average daily concentration of 0.167 µg/l for Benzene. According to the 2006 National Recommended: Water Quality Criteria, the Human Health criteria for Benzene is 51 µg/l, Organisms Only. The average concentration, multiplied by the power of 10 (0.005 mg/l), due to less than 12 samples, does not present a reasonable potential to violate Human Health Criteria.  

For Base-Neutral Compounds, the facility had an average daily concentration of 36 µg/l for 2,4-Dinitrotoluene. According to the 2006 National Recommended: Water Quality Criteria, the Human Health criteria for 2,4-Dinitrotoluene is 3.4 µg/l, Organisms Only. The average concentration, multiplied by the power of 10 (36 µg/l), due to less than 12 samples, does present a reasonable potential for violation based on 3 effluent samples.  

The permittee shall sample for 2,4-Dinitrotoluene at least once per month using a 24 hour composite for the first 12 consecutive months after the issuance of this permit in order to determine the long term average concentration for 2,4-Dinitrotoluene in the effluent.  Sampling shall be performed in accordance to an EPA approved method.  After 12 samples are collected, the permit will be modified to require the facility to meet a 2,4-Dinitrotoluene monthly average limitation if the long term average demonstrates a reasonable potential to violate Human Health Criteria; as listed in the U. S. EPA's National Recommended Water Quality Criteria. If the long term average does not demonstrate a reasonable potential to violate Human Health Criteria, then the permittee will not be required to continue sampling of 2,4-Dinitrotoluene.

2,4-Dinitrotoluene limit calculations are below:
	
Parameter	Human Health criteria (µg/L)	Human Health criteria (mg/L)	Instream Waste Concentration Based on Mean Annual Flow (%)	Monthly Average (mg/L)	
2,4-Dinitrotoluene	3.4	0.0034	43.63	0.0157	

For Base-Neutral Compounds, the facility had an average daily concentration of 0.25 µg/l for 1,2,4-Trichlorobenzene. According to the 2006 National Recommended: Water Quality Criteria, the Human Health criteria for 1,2,4-Trichlorobenzene is 70 µg/l, Organisms Only. The average concentration, multiplied by the power of 10 (0.773 mg/l), due to less than 12 samples, does not present a reasonable potential to violate Human Health Criteria.  Permit requires monitoring of this parameter.

ATTACHMENT B

TOXICITY SCREENING

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 pimephales promelas (vertebrate).  The WET tests on the species were performed in March 2010, June 2010, October 2011, November 2011, and December 2011.

March 2010
Pimephales promelas		ICp25 > 100%
Ceriodaphnai dubia		ICp25 > 100%

June 2010
Pimephales promelas		ICp25 > 100%
Ceriodaphnai dubia		ICp25 > 100%

October 2011
Pimephales promelas		ICp25 > 100%
Ceriodaphnai dubia		ICp25 > 100%

November 2011
Pimephales promelas		ICp25 > 100%
Ceriodaphnai dubia		ICp25 > 100%

December 2011
Pimephales promelas		ICp25 > 100%
Ceriodaphnai dubia		ICp25 > 100%

The data in the application have not shown a failure in a WET testing.  With this demonstration of compliance, the Bioassay requirements from the previous permit were removed.