PERMIT RATIONALE FOR REISSUANCE
Saltillo POTW
Lee County
Saltillo, Mississippi
Water NPDES No. MS0021733
October 2019

I.	CLASSIFICATION – Municipal NPDES Major

II.	DESCRIPTION OF WASTEWATER –Municipal/Domestic Wastewater

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

IV.	RECEIVING WATERS – Sand Creek. The receiving stream is located within the Tombigbee River Basin and is classified as Fish and Wildlife.  At the point of discharge, Sand Creek (MS ISD 804811) appears on the current State of Mississippi 303(d) List of Impaired Waterbodies for Biological Impairment.  At the point of discharge the 7Q10 for the receiving stream is 0.06 cfs.  The instream wastewater concentration at the point of discharge is determined to be 97.48%.  Only one discharge to surface waters is described within the application with no increase in flow.

V.	APPLICABLE GUIDELINES – 11 MS Admin Code pt. 6, 2019 Wasteload Allocation (WLA), Chemical Specific Calculations

VI.	SUMMARY OF LIMITATION – 

Parameter				Value			Basis
Flow					1.5 MGD			Design
BOD5					6 mg/l (Monthly Avg.)		WLA
TSS					30 mg/l (Monthly Avg.)		Admin Code
Ammonia Nitrogen 			2 mg/l (Monthly Avg.)		WLA
E. Coli					126 Col./100ml			Admin Code
Dissolved Oxygen			6.0 mg/l (Minimum)			Admin Code
Chlorine				0.011 mg/l (Monthly Avg.)		WLA
Total Phosphorus			47.44 lbs/day			TMDL
Total Nitrogen				111.23 lbs/day			TMDL
Copper, Total Recoverable		0.00682 mg/l			Chemical Specific Calcs
Zinc, Total Recoverable			0.065 mg/l			Chemical Specific Calcs
Mercury, Total Recoverable		Report mg/l			Chemical Specific Calcs
pH 					6.0 – 9.0 S.U.			MSWQS
Ceriodaphnia dubia 			97.48% min 			Admin Code
Pimephales promelas 			97.48% min 			Admin Code

VII.	CHANGES FROM PREVIOUS PERMIT – 

1)	Fecal Coliform has been replaced with E. Coli as the pathogen indicator in accordance to 11 MS Admin Code part 6.

The following requirement has been added for sampling due to test results submitted with the reapplication: 

“The Permittee shall submit results of 9 effluent samples of the following pollutant(s) listed in Section D of the application:

Bis-(2-ethylhexyl) Phtalate
Chlorodibromo-Methane
Dichlorobromo-Methane 
Mercury

In addition, 9 influent samples shall be submitted for Mercury, concurrent with effluent sampling.

Sampling of the wastewater treatment facility's effluent and influent (if applicable) shall be performed twice per month for a total of 9 samples. Sampling shall begin 10 days after the issuance date of permit and continuing for 9 consecutive months. Sample results shall be submitted by the 28th day of the month following completion of sampling.”

Ammonia-Nitrogen (NH3-N) has been updated to reflect the 2019 Wasteload Allocation (attached.)

BIOASSAY AND CHECMICAL SPECIFIC EVALUATIONS

BIOASSAY

In accordance to State Regulation 11 Admin Code pt. 6, Saltillo POTW 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 should be performed on Ceriodaphnia dubia (invertebrate) and Pimephales promelas (vertebrate).

May 2019
Ceriodaphnia dubia					IC25	67.6%
Pimephales promelas				IC25	78.1%

Inhibition concentrations were below the predicted IWC of 97.48%. 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 Regulation 11 MS Admin Code, part 6.  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. 4.  The reported values are then analyzed and compared to water quality criteria (attachment No. 6) to determine any possible toxic effect to the receiving waters.  A synopsis of these calculations is listed in attachment No. 5.  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

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 indicated the reasonable potential for violation for the following parameter(s): Copper, Mercury, and Zinc

The Limitations for Copper and Zinc will remain unchanged from the previous permit. Mercury has been added as “Report Only” until further testing has been completed, upon which the toxicity screening will be re-evaluated to determine if numeric limitations are needed.

In accordance to an agreed order issued by MDEQ, the facility will initiate further sampling upon the completion of facility improvements for the parameters below:

Total Recoverable Antimony
Total Recoverable Arsenic
Total Recoverable Beryllium 
Total Recoverable Cadmium
Total Recoverable Chromium
Chromium (Hex) 
Total Recoverable Copper
Total Recoverable Lead 
Total Recoverable Nickel (Freshwater) 
Total Recoverable Selenium 
Total Recoverable Silver
Total Recoverable Thallium
Total Recoverable Zinc 
Free Cyanide
Phenolic Compound
Pentachlorophenol
Hardness (in mg/l as CaCO3)	 

Sampling shall be performed for a total of twelve (12) samples from the influent to and effluent from the wastewater treatment facility. Analytical procedures must be in accordance to methodologies listed in 40 CFR 136 for the above pollutants. 

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

The following Volatile Organic compounds were detected and evaluated for a potential to violate Human Health Criteria: 

1)	Chlorodibromo-Methane
2)	Dichlorobromo-Methane	
3)	Chloroform

1) Chlorodibromo-Methane

Average Daily Concentration		
2.44 ug/l

According to the most recent National Recommended Water Quality Criteria, the Human Health criteria for Chlorodibromo-Methane is shown below (organism only): 

Human Health Criteria for Organisms Only
21 ug/l 

Multiplying the average concentration above by the power of 10, due to less than 12 samples, then by the IWC of 97.48 (0.9748) % determines the reasonable potential of the compound’s concentration to violate the Human Health Criteria. 

[(2.44 ug/l)*(10)*(0.9748)] = 23.78 ug/l

23.78 ug/l > 21 ug/l

The above results demonstrate that the average concentration(s) for presents a potential to violate Human Health Criteria. A condition requiring the facility for 9 additional samples has been added to the permit.

	2) Dichlorobromo-Methane 

Average Daily Concentration:
3.62 ug/L

According to EPA’s National Recommended Water Quality Criteria, the Human Health Criteria (consumption of organism only) for Dichlorobromo-Methane is shown below:

Human Health Criteria for Organisms Only: 
	27 ug/l 

Multiplying the average concentration above by the power of 10, due to less than 12 samples, then by the IWC of 97.48 (0.9748) % determines the reasonable potential of the compound’s concentration to violate the Human Health Criteria. 

[(3.62 ug/l)*(10)*(0.9748)] = 35.3 ug/l

35.3 ug/l > 27 ug/l

The above results demonstrate that the average concentration(s) for presents a potential to violate Human Health Criteria. A condition requiring the facility for 9 additional samples has been added to the permit.

3) Chloroform	

Average Daily Concentration:
0.00214 mg/l 

According to the most recent National Recommended Water Quality Criteria, the Human Health criteria for these compounds are shown below (organisms only): 

Human Health Criteria for Organisms Only: 
2.0 mg/l 

Multiplying the average concentration above by the power of 10, due to less than 12 samples, then by the IWC of 97.48 (0.9748) % determines the reasonable potential of the compound’s concentration to violate the Human Health Criteria. 

[(0.00214 mg/l)*(10)*(0.9748)] = 0.0208 mg/l
0.0208 < 2.0 mg/l

The average concentration for Chloroform does not present a reasonable potential to violate Human Health Criteria.

The following Base-Neutral compound was detected and evaluated for a potential to violate Human Health Criteria:

Bis-(2-ethylhexyl) Phtalate
	Avg. Daily Concentration
	10.38 μg/L

According to EPA’s National Recommended Water Quality Criteria, the Human Health Criteria (consumption of organism only) for the following compound(s) are shown below:

Human Health Criteria for Organisms Only: 
0.37 μg/L

Multiplying the average daily concentration above by 10 (due to a data set of less than 12 samples) then by the IWC of 97.48 (0.9748) % (determines the reasonable potential of the compound’s concentration to violate the Human Health Criteria.

[10.38 ug/L * 10 * 0.9748]= 103.8 μg/L
101.2 μg/L > 0.37 μg/L

The above results demonstrate that the average concentration(s) for presents a potential to violate Human Health Criteria. A condition requiring the facility for 9 additional samples has been added to the permit. 

The chemical specific data results submitted had no detects for Acid-Extractable Compounds.

Attachments

Attachment 1	         Wastewater treatment plant flow diagram (See Application)
Attachment 2 		Discharge location map (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 3

Attachment 4

Attachment 5

Attachment 6