PERMIT RATIONALE FOR REISSUANCE
Columbia POTW, South
Marion County
Columbia, Mississippi
Water NPDES No. MS0044164
May 2019

I.	CLASSIFICATION – Municipal Major

II.	DESCRIPTION OF WASTEWATER – Municipal Domestic

III.	DESCRIPTION OF WASTEWATER TREATMENT - Wastewater is biologically treated by means of a conventional lagoon.  Disinfection is provided by chlorination.  A process schematic is attached to the facility’s application.  The current design capacity of the facility is 1.47 MGD.

RECEIVING WATERS – Pearl River.  The receiving water, at the point of discharge, is classified as Recreational, and is in the Pearl River Basin. This discharge is included in a TMDL for pathogens and pH.  The permit as drafted will comply with the conditions of both the pH and pathogen TMDL. The facility is also listed in a draft TMDL for nutrients. The permit includes a Total Phosphorus limitation in order to comply with the conditions of the nutrient TMDL. A map of the discharge location is attached to the facility’s application.

The 7-day, 10-year minimum flow (7Q10) of the stream is 765 cfs. At the point of discharge, the Instream Wastewater Concentration (IWC) is determined by the following calculation:

Qw = Design flow of the wastewater treatment facility = 1.47 MGD or 2.28 cfs
Qr =  Receiving stream 7Q10 = 765 cfs

IWC = (Qw/ (Qw + Qr)) * 100 =  (2.28/ 2.28+ 765) =  0.30 %

IV.	APPLICABLE GUIDELINES –11 MS Admin Code pt. 6, Municipal Guidelines (Technology), 2018 Wasteload Allocation (WLA, see Attachment No. 1), Total Maximum Daily Load (TMDL)

V.	SUMMARY OF LIMITATIONS –

	Parameter						Value				Basis
	Flow						1.47 MGD				Design
	BOD5						45 mg/l (Monthly Avg.)			WLA
	BOD5 (Percent Removal)			65% Minimum				Technology	
	Ammonia-Nitrogen					Report				WLA
	Minimum D.O.						6.0 mg/L				Admin Code
	TSS						90 mg/l (Monthly Avg.)			Technology
	TSS (Percent Removal)				65% Minimum				Technology
	Total Phosphorus					*33.81 lbs/day (Monthly Avg.)		TMDL
Total Nitrogen				     141.08 lbs/day (Monthly Avg.)	TMDL
	E. Coli						126 Col./100 ml (Monthly Avg.)		Admin Code
	pH						6.0 – 9.0 SU				Admin Code
Chlorine, Total Residual			     1.0 mg/l (Maximum Weekly Average)	Admin Code	

* See section VI below

VI.	CHANGES FROM PREVIOUS PERMIT

Total Phosphorus has been changed from 28.07 (lb/day) Maximum Weekly Average to 33.81 (lb/day) Monthly Average  to reflect the limitation given in the 2019 Nutrient TMDL for the Pearl River. The limitation in the current permit was given erroneously and will be corrected in this reissuance.

E.coli has replaced Fecal Coliform as the bacteria indicator in Mississippi’s Water Quality Standards (MSWQS) for freshwater. The permit limitations have been updated to reflect this change.

BIOASSAY AND CHEMICAL SPECIFIC EVALUATION

BIOASSAY

In accordance to State Regulation 11 MS Admin Code pt. 6 – 1 VI.B.2b, Columbia POTW, South is required to perform Whole Effluent Toxicity (WET) tests as part of the renewal application.  The applicant should 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 were performed on Ceriodaphnia dubia (invertebrate) and Pimephales promelas (vertebrate)  

September 2018
Pimephales promelas	 ICp25 > 100%
Ceriodaphnai dubia	 ICp25 > 100%

December 2018
Pimephales promelas	 ICp25 > 100%
Ceriodaphnai dubia	 ICp25 > 100%

January 2019
Pimephales promelas	 ICp25 > 100%
Ceriodaphnai dubia	 ICp25 > 100%

	              April 2019
Pimephales promelas	 ICp25 > 100%
Ceriodaphnai dubia	 ICp25 > 100%

All of the inhibition concentrations were greater that the predicted IWC of 0.030%. Based on the results of the WET testing, chronic bioassay requirements will not be placed within the municipal NPDES permit.

CHEMICAL SPECIFIC ANALYSIS

Categorical Guideline Limitations Calculations

The chemical specific analysis has been performed in accordance with State Regulations 11 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 2. A toxicity screening is performed by analyzing and comparing the results to water quality criteria (Attachment 3) to determine any possible toxic effect to the receiving waters.  See Attachment 4 for the toxicity screening results. A column by column description of the toxicity screening calculations 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 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.  

The chemical specific data results submitted did not indicate a reasonable potential for violation of the appropriate criteria in Table III of Appendix D of CFR 122. See Attachment 4 for the chemical specific analysis for metals and Attachment 5 for results of the toxicity screening.

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

The chemical specific data results submitted detected the following Volatile Organics Compounds:

	Chloroform: 
	Of three (3) samples provided, the calculated average effluent concentration is:
	 (12.2 + 6.34 + 0) / 3 = 6.18 ug/L
		Multiplying by a factor of 10: 6.18 * 10= 61.8 ug/L
	According to EPA’s National Recommended Water Quality Criteria for Human Health, the limitation for Chloroform is 2,000 ug/L. 
	61.8 < 2,000 ug/L. 
	Chloroform concentration does not violate Human Health Criteria and will not be added to the permit.

		Toluene:
	Of three (3) samples provided, the calculated average effluent concentration is:
	(2.37+ 0 +0) / 3 = 0.79
	Multiplying by a factor of 10: 0.79*10= 7.9 ug/L
	According to EPA’s National Recommended Water Quality Criteria for Human Health, the limitation for Toluene is 520 ug/L. 
	7.9 < 520 ug/L
	Toluene concentration does not violate Human Health Criteria and will not be added to the permit.

		Chlorodibromo-methane:
	Of three (3) samples provided, the calculated average effluent concentration is:
	(3.07+ 0 +0) / 3 = 1.02
	Multiplying by a factor of 10: 1.02 * 10= 10.2 ug/L
	According to EPA’s National Recommended Water Quality Criteria for Human Health, the limitation for Dichlorobromo-methane is 27 ug/L. 
	10.2 < 27 ug/L
	Dicholorobromo-methane concentration does not violate Human Health Criteria and will not be added to the permit.

The chemical specific data results provided no-detects for Acid-Extractable Compounds or 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 – Chemical Specific Analysis Results
Attachment No. 5 – Toxicity Screening

Attachment 3

Attachment 4

Attachment 5