PERMIT RATIONALE FOR REISSUANCE
Meridian POTW
Lauderdale County
Meridian, Mississippi
Water NPDES No. MS0020117
August 28, 2025

I.	CLASSIFICATION – NPDES Municipal Major

II.	DESCRIPTION OF WASTEWATER – Municipal Wastewater

III.	DESCRIPTION OF WASTEWATER TREATMENT – For Outfall 101, wastewater is collected and treated via two stage nitrification activated sludge followed by chlorination disinfection. For Outfall 201 wastewater is collected and treated via a sequencing batch reactor (SBR). Outfall 002 provides additional treatment via dechlorination. See application for flow diagrams. Only one discharge to surface waters is described in the application with no increase in treated effluent flow proposed.  

IV.	RECEIVING STREAM – Sowashee Creek. 

Sowashee Creek previously appeared on the 2020 State of Mississippi 303(d) List of Impaired Waterbodies for aquatic life use support impairment due to nutrients and organic enrichment/low dissolved oxygen. Nutrient limitations were incorporated into the permit, with recognition that a future TMDL could impose more stringent effluent limits. The facility is also listed in completed TMDLs for fecal coliform in Okatibbee Creek (December 1999) and for biological impairment due to organic enrichment/low dissolved oxygen in Sowashee Creek (March 2012). The effluent limitations included in this permit comply with the applicable load allocations.

	In August 2025, EPA Region 4 approved MDEQ’s request to delist the Sowashee Creek segment (MS400911) from the State’s 303(d) List based on biological monitoring data demonstrating that water quality standards are being met. This delisting is documented in the EPA approval letter included as Attachment 7.

Outfall 101 is the previous discharge from Meridian POTW which is now an internal outfall. Outfall 201 is the wastewater from East Meridian POTW.  Outfall 002 is the combined treated wastewater from Outfall 101 and 201. The facility is located in the Pascagoula River drainage basin, and is classified as Fish & Wildlife. Sowashee Creek has a 7Q10 of 2.3 cfs. See application for discharge location map.  

The 7-day, 10-year minimum flow (7Q10) of the receiving stream is 2.3 cfs. The Instream Wastewater Concentration (IWC) at the point of the discharge is determined by the following calculation:

IWC = {(QW)/(QW + QR)}*100
	Where:
	QW = Design flow of the wastewater treatment facility, 13 MGD or 20.12 cfs.
	QR = Receiving stream 7Q10, 2.3 cfs.

IWC = {(20.12 cfs)/(2.3 cfs + 20.12 cfs)}*100 = 89.74 %

V.	APPLICABLE GUIDELINES – 11 Mississippi Admin Code pt. 6, Municipal Facility Guidelines (Technology), Wasteload Allocation (WLA, see Attachment No. 3), TMDL

VI.	CHANGES FROM PREVIOUS PERMIT – 

E. coli has replaced fecal coliform as the bacterial indicator for all freshwaters in MS designated as Recreation, Fish and Wildlife Support, and/or Public Water supply. 

Based on the results of the WET testing, chronic bioassay requirements will be placed in the permit.

*Copper limitations were adjusted based on a chemical translator hardness study performed in Sowashee Creek. The 95th percentile value was determined from the Discharge Monitoring Reports. The 95th percentile value is cap limited in Outfall 002. (See Attachment 5). Meridian also performed a study demonstrating that the copper values did not demonstrate any correlation with previous bioassays failures. (See AGREED ORDER NO. 7144-21 TOTAL RECOVERABLE COPPER REPORT)

**Data collected as part of the MBISQ program in January 2025 indicated attainment of the Aquatic Life Use. MBISQ score was 78.97, with a bioregional threshold of attainment of 71.6. The MBISQ score is greater than the threshold of attainment, so the waterbody is attaining the use and should be delisted. (See Attachment 6 and 7)

VII.	SUMMARY OF LIMITATIONS –

Outfall 002 (Combined effluent from internal Outfalls 101 and 201 into Sowashee Creek)	
	
Parameter						Value				Basis

Flow							13.0 MGD				Design
CBOD5 (May-Oct)						7 mg/l (Monthly Avg.)			WLA
CBOD5 (Nov-Apr)						10 mg/l (Monthly Avg.)			WLA	
TSS							30 mg/l (Monthly Avg.)			Technology
NH3-N (May-Oct)						1 mg/l (Monthly Avg.)			WLA
NH3-N (Nov-Apr)						2 mg/l (Monthly Avg.)			WLA	
Dissolved Oxygen						> 6.0 mg/l 				WLA
E. coli							126 (#col./100ml) 			MS WQS
pH							6.0 – 9.0 SU				MS WQS
Chlorine, Total Residual					0.011 / 0.019 mg/l			MS WQS
Copper, Total Recoverable					0.011 / 0.012 mg/l			*
Total Nitrogen						Report lbs				**
Total Phosphorus						Report lbs				**
Ceriodaphnia dubia	IC25 >89.74%	Admin Code	
Pimephales promelas		IC25 >89.74%	Admin Code	

Outfall 101 (Internal outfall after final treatment by Meridian POTW)
	
Parameter						Value				Basis

Flow							13.0 MGD				Design
CBOD5 (May-Oct)						7 mg/l (Monthly Avg.)			WLA
CBOD5 (Nov-Apr)						10 mg/l (Monthly Avg.)			WLA	
CBOD5 (Percent Removal)					85% Minimum				Technology
TSS							30 mg/l (Monthly Avg.)			Technology
TSS (Percent Removal)					85% Minimum				Technology
NH3-N (May-Oct)						1 mg/l (Monthly Avg.)			WLA
NH3-N (Nov-Apr)						2 mg/l (Monthly Avg.)			WLA	
pH							Report Minimum/Maximum		MS WQS
Chlorine, Total Residual					0.3 mg/l minimum			Calculation
Total Nitrogen						Report lbs				WLA
Total Phosphorus						Report lbs				WLA 

The minimum and maximum values for Dissolved Oxygen in aeration unit and 30-Minute Sludge Settleability in aeration unit must be reported

Outfall 201 (Internal outfall after final treatment by East Meridian POTW)
	
Parameter						Value				Basis

Flow							1.0 MGD				Design
CBOD5 (May-Oct)						7 mg/l (Monthly Avg.)			WLA
CBOD5 (Nov-Apr)						10 mg/l (Monthly Avg.)			WLA	
CBOD5 (Percent Removal)					85% Minimum				Technology
TSS							30 mg/l (Monthly Avg.)			Technology
TSS (Percent Removal)					85% Minimum				Technology
NH3-N (May-Oct)						1 mg/l (Monthly Avg.)			WLA
NH3-N (Nov-Apr)						2 mg/l (Monthly Avg.)			WLA	
pH							Report Minimum/Maximum		MS WQS
Total Nitrogen						Report lbs				WLA
Total Phosphorus						Report lbs				WLA

The minimum and maximum values for Dissolved Oxygen in aeration unit and 30-Minute Sludge Settleability in aeration unit must be reported.

VIII.	PRETREATMENT PERMITS –

MSP090465 – Chambers Clearview Environmental Landfill Inc.
MSP090562 – Waste Management of Mississippi Inc, Pine Ridge Sanitary Landfill and
	Recycling Center
MSP091085 – Kemper County Lanfill Company LLC, a subsidiary of Waste Pro of 
	Mississippi Inc.
MSP092420 – Hermes Hialeah Warehouse LLC

BIOASSAY AND CHECMICAL SPECIFIC EVALUATIONS

BIOASSAY

Main Plant

In accordance to State Regulation 11 Mississippi Admin Code pt. 6, VI.B.2b., Meridian POTW is required to perform a Whole Effluent Toxicity (WET) evaluation 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 tests were performed on Ceriodaphnia dubia (invertebrate) and Pimephale promelas (vertebrate).  The results of the wet tests are as follows:

March 2020
		Ceriodaphnia dubia		IC25 		>100%
		Pimephales promelas		IC25		>100%

		August 2020
		Ceriodaphnia dubia		IC25 		>25.03%
		Pimephales promelas		IC25		>27.09%

August 2020
		Ceriodaphnia dubia		IC25    	 	<100%
		Pimephales promelas		IC25		<100%

		November 2020
		Ceriodaphnia dubia		IC25 		>100%
		Pimephales promelas		IC25		>100%

February 2021
		Ceriodaphnia dubia		IC25 		>25.03%
		Pimephales promelas		IC25		>27.09%

All of the inhibition concentrations were not greater that the predicted IWC of 89.74%. Based on the results of the WET testing, chronic bioassay requirements will be placed in the permit.

East Plant

In accordance to State Regulation 11 Mississippi Admin Code pt. 6, VI.B.2b., Meridian POTW East is required to perform a Whole Effluent Toxicity (WET) evaluation 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 tests were performed on Ceriodaphnia dubia (invertebrate) and Pimephale promelas (vertebrate).  The results of the wet tests are as follows:

August 2020
		Ceriodaphnia dubia		IC25 		>61.86%
		Pimephales promelas		IC25		>100%

		August 2020
		Ceriodaphnia dubia		IC25 		>1.514%
		Pimephales promelas		IC25		>100%

November 2020
		Ceriodaphnia dubia		IC25    	 	<100%
		Pimephales promelas		IC25		<100%

		February 2021
		Ceriodaphnia dubia		IC25 		>100%
		Pimephales promelas		IC25		>100%

All of the inhibition concentrations were not greater that the predicted IWC of 89.74%. Based on the results of the WET testing, chronic bioassay requirements will be placed in the permit.

CHEMICAL SPECIFIC ANALYSIS

Chemical specific analysis has been performed in accordance with State Regulations 11 Mississippi 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 No. 2.  The reported values are then analyzed and compared to water quality criteria (see Attachment No. 3) to determine any possible toxic effect to the receiving waters.  A synopsis of these calculations is listed in Attachment No. 4.  A column by column description of the calculations in Attachment No. 4 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

Minor toxic municipalities shall determine the toxic characteristics of their wastewater by analyzing for toxic pollutants listed in Table III 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).

For Meridian POTW, the chemical specific data results submitted with the reapplication indicated there was reasonable potential for violation of Total Recoverable Copper in Table III of Appendix D of 40 CFR 122.  See Attachment No. 4 for chemical specific screening sheet and results.	

Main Plant

Chemical specific analysis for Volatile Organic 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: 

Dichlorobromomethane
Avg. Daily Concentration = 1.31 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: 

Dichlorobromomethane
Recommended Water Quality Criteria = 27 μg/L
 
Multiplying the average daily concentration above by 10 (due to a data set of less than 12 samples) determines the reasonable potential of the compound’s concentration to violate the Human Health Criteria. 
[1.31 μg/L * 10]= 13.1 μg/L 
13.1 μg/L < 27 μg/L 

The above results demonstrate that the average concentration(s) for Dichlorobromomethane
do not present a potential to violate Human Health Criteria. 
                                                          
Chloroform
Avg. Daily Concentration = 2.02 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: 

Chloroform
Recommended Water Quality Criteria = 2000 μg/L
 
Multiplying the average daily concentration above by 10 (due to a data set of less than 12 samples) determines the reasonable potential of the compound’s concentration to violate the Human Health Criteria. 
[2.02 μg /L * 10]= 20.2 μg/L 
198 μg/L < 2000 μg/L 

The above results demonstrate that the average concentration(s) for Chloroform do not present a reasonable potential to violate Human Health Criteria.

The chemical specific data results submitted had no detects for all Base-Neutral Compounds and Acid-Extractable Compounds.

East Plant

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

The chemical specific data results submitted had no detects for all Volatile Organic Compounds, Base-Neutral Compounds, nor Acid-Extractable Compounds.

ATTACHMENTS

Please see the application for Flow Diagrams, Discharge Location Map.

Attachment No. 1 – Wasteload Allocation
Attachment No. 2 – MS State Water Quality Standards
Attachment No. 3 – Tabulated Metals Testing Data
Attachment No. 4 – Chemical Specific Screening
Attachment No. 5 – Copper Translator Results and Limit Development
Attachment No. 6 – Sowashee Creek Delisting Form 
Attachment No. 7 – Sowashee Creek Delisting Approval

Attachment 1

Attachment 2

Attachment 3

Attachment 4

Attachment 5

Attachment 6

Attachment 7