PERMIT RATIONALE FOR REISSUANCE
DeSoto County Regional Utility Authority, Olive Branch POTW Ross Road
Desoto County
Olive Branch,, Mississippi
Water NPDES No. MS0029513
May 2026

I.	CLASSIFICATION – NPDES Major Municipal 

II.	DESCRIPTION OF WASTEWATER – Domestic / Municipal Wastewater

III.	DESCRIPTION OF WASTEWATER TREATMENT – Wastewater is collected and treated using screening, grit removal, biological treatment via activated sludge/oxidation ditch, UV disinfection, and post aeration prior to discharge. See Attachment 1 for a flow diagram. The current design capacity of the facility is 3.0 MGD. Only one discharge to surface waters is described in the application with no increase in treated effluent flow proposed.

IV.	RECEIVING WATERS – Lick Creek thence Camp Creek. The receiving stream is located in the Yazoo River drainage basin and is classified as Fish & Wildlife. See Attachment 2 for discharge location map. At the point of discharge, the receiving stream does not appear on the 2024 State of Mississippi 303(d) List of Impaired Waterbodies. The discharge does appear on a completed Total Maximum Daily Load (TMDL) for Biological Impairment due to Nutrients, Organic Enrichment/Low Dissolved Oxygen and Ammonia Toxicity in Camp Creek (June 2008). The permit contains limits in accordance with the wasteload allocation developed by the TMDL. The discharge also appears on a Pathogen TMDL for the Coldwater River (December 2003). The facility utilizes UV disinfection, which complies with the conditions of the TMDL.

The 7-day, 10-year minimum flow (7Q10) of the receiving stream is 0.0 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, 3.0 MGD or 4.64 cfs 
QR = Receiving stream 7Q10, 0.0 cfs

IWC = {(4.64 cfs)/(4.64 cfs + 0.0 cfs)}*100 = 100 %

V.	APPLICABLE GUIDELINES – 11 Mississippi Admin Code pt. 6, Mississippi Water Quality Standards (MSWQS, Attachment 5), Wasteload Allocation (WLA, Attachment 3), Municipal Facility Guidelines (Technology), TMDL

VI.	CHANGES FROM PREVIOUS PERMIT – 

Chronic Bioassay Requirements have been added to the permit in order to complete the toxicity testing required during reapplication.
 
In accordance to State Regulation 11 Mississippi Admin Code pt. 6, VI.B.2b., DeSoto County Regional Utility Authority, Olive Branch POTW Ross Road
is required to perform Whole Effluent Toxicity (WET) tests 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 should be performed on Ceriodaphnia dubia (invertebrate) and Pimephales promelas (vertebrate).
 
The applicant did not submit any of the four (4) bioassays, therefore, chronic bioassay requirements have been placed in the draft permit in order to satisfy the reapplication testing requirements and determine the toxicity of the discharge.

VII.	SUMMARY OF LIMITATIONS – 
Parameter				Value				Basis
Flow					3.0 MGD			Design
	CBOD5				5 mg/l 				TMDL
	TSS					30 mg/l 			Technology
	Ammonia Nitrogen			1 mg/l 				TMDL
	Dissolved Oxygen			> 6.0 mg/l 			WLA
	Chlorine, Total Residual		0.011 mg/l 			MSWQS, IWC
E. coli					126 Col. /100 ml		MSWQS
	pH					6.0 – 9.0 SU			MSWQS
	Nitrogen, Total			287.93 lbs/day			TMDL
	Phosphorus, Total			42.82 lbs/day			TMDL
	Zinc, Total Recoverable		0.136 mg/l			MSWQS
	Copper, Total Recoverable		0.011 mg/l			MSWQS
Ceriodaphnia dubia			IC25 >100 %			Admin Code
Pimephale promelas			IC25 >100 %			Admin Code

BIOASSAY AND CHEMICAL SPECIFIC EVALUATION

BIOASSAY

In accordance with State Regulation 11 Mississippi Admin Code pt. 6, VI.B.2b., DCRUA, Olive Branch POTW Ross Road 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).  

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 4.  The reported values are then analyzed and compared to water quality criteria (see Attachment 5) to determine any possible toxic effect to the receiving waters.  A synopsis of these calculations is listed in Attachment 6.  A column by column description of the calculations in Attachment 6 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 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 DCRUA, Olive branch POTW Ross Road, the chemical specific data results submitted with the reapplication indicated the reasonable potential for violation of the appropriate criteria (shown below) found in Table III of Appendix D of CFR 122.

	Zinc, Total Recoverable – acute
	Copper, Total Recoverable – chronic, acute 

DCRUA, Olive Branch POTW Ross Road’s current permitted Total Recoverable Zinc limit of 0.136 mg/l was developed from a 2009 chemical translator method for dissolved zinc based on a 15th percentile value for Total Suspended Solids (TSS) of 2 mg/l and an average hardness of 39.7 mg/l. From the reapplication data and the previous two (2) years of DMR data, the current 15th percentile TSS value and average hardness were found to be 1.74 mg/l and 48.3 mg/l, respectively. Using these values to re-confirm the chemical translator study, the average monthly Total Recoverable Zinc limit of 0.136 mg/l was confirmed to be protective of the receiving stream.  Using the current average hardness and 15th percentile TSS values, the Total Recoverable Copper limit was also adjusted. See Attachment 7 for calculations of the adjusted limits.

See Attachment 6 for Chemical Specific Screening sheet and results.

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, and Acid-Extractable Compounds.

ATTACHMENTS:

Attachment 1 – Flow Diagram
Attachment 2 – Location Map
Attachment 3 – Wasteload Allocation 
Attachment 4 – Chemical Specific Screening
Attachment 5  – MS Water Quality Criteria
Attachment 6 –  Chemical Specific Screening 

Attachment 1 – Flow Diagram

Attachment 2 – Location Map

	

  

Outfall 001

Plant Location

Attachment 3 – Wasteload Allocation

	

Attachment 4 – Chemical Specific Tabulated Results

	

Attachment 5 – MS Water Quality Criteria

Attachment 6 – Chemical Specific Screening