PERMIT RATIONALE FOR REISSUANCE
Pearl River County Utility Authority, Neal Road POTW
Pearl River County
Picayune, Mississippi
Water NPDES No. MS0061174
September 2018

I.	CLASSIFICATION – Major Municipal

II.	DESCRIPTION OF WASTEWATER – Domestic/Municipal Wastewater

III.	DESCRIPTION OF WASTEWATER TREATMENT – Wastewater is collected and treated biologically by means of an oxidation ditch followed by ultraviolet (UV) disinfection and post-aeration prior to discharge. See Attachment No. 1 for a flow diagram. The treatment capacity of the facility is 2.4 MGD. Only one discharge to surface waters is described in the application with no increase in treated effluent flow proposed. 

IV.	RECEIVING WATERS – Direct conveyance to Hobolochitto Creek. The receiving waters are located within the Pearl River Basin and are classified as Fish and Wildlife. See Attachment No. 2 for discharge location map. At the point of discharge, the receiving waters do not appear on the current State of Mississippi 303(d) List for Impaired Waterbodies.  The discharge does appear on a complete Total Maximum Daily Load (TMDL) for the Pearl River for Nutrients (June 2009). The proposed draft permit incorporates Total Nitrogen and Total Phosphorus limits developed in accordance with the TMDL.

The 7-day, 10-year minimum flow (7Q10) of the receiving stream is 23 cfs. The Instream Wastewater Concentration (IWC) at the point of the discharge is determined by the following calculation:
IWC = {(Qw)/(Qw + Qr)}*100

Qw = Design flow of the wastewater treatment facility, 2.4 MGD or 3.72 cfs
Qr = Receiving stream 7Q10, 23 cfs.

IWC = {(3.72 cfs)/(3.72 cfs + 23 cfs)} * 100 = 13.9 %

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

VI.	CHANGES FROM PREVIOUS PERMIT – 

1.	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. 

2.	Total Nitrogen and Total Phosphorus limits have been modified in accordance with limits developed in the Pearl River Nutrient TMDL (2009).

VII.	SUMMARY OF LIMITATIONS –

Parameters			Value		Basis
Flow				2.4 MGD		Design
BOD5				10 mg/l		WLA
BOD5 (Percent Removal)	85% Minimum		Technology
TSS				30 mg/l		Technology
TSS (Percent Removal)	85% Minimum		Technology
Ammonia Nitrogen		2 mg/l 		WLA
E. coli				126 Col./100 ml		Admin Code
Dissolved Oxygen		6.0 mg/l (Minimum)		WLA
pH 				6.0 – 9.0 S.U.		Admin Code
Nitrogen, Total		230.34 lbs/day		TMDL
Phosphorus, Total		55.20 lbs/day		TMDL

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

BIOASSAY AND CHECMICAL SPECIFIC EVALUATIONS

BIOASSAY

In accordance to State Regulation 11 Mississippi Admin Code pt. 6, VI.B.2b., PRCUA, Neal Road 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 2017
		Ceriodaphnia dubia		IC25 		>100%
		Pimephales promelas		IC25		>100%

		May 2017
		Ceriodaphnia dubia		IC25 		 28.8%
		Pimephales promelas		IC25		>100%

		August 2017
		Ceriodaphnia dubia		IC25      	>100%
		Pimephales promelas		IC25		>100%

November 2017
		Ceriodaphnia dubia		IC25 		 40.9%
		Pimephales promelas		IC25		>100%

All of the inhibition concentrations were greater that the predicted IWC of 13.9%. Based on the results of the WET testing, chronic bioassay requirements will not be placed within 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. 4.  The reported values are then analyzed and compared to water quality criteria (see Attachment No. 5) to determine any possible toxic effect to the receiving waters.  A synopsis of these calculations is listed in Attachment No. 6.  A column by column description of the calculations in Attachment No. 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 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).
	
For PRCUA, Neal Road POTW, the chemical specific data results submitted with the reapplication did not indicate the reasonable potential for violation of the appropriate criteria in Table III of Appendix D of CFR 122.  See Attachment No. 6 for Chemical Specific Screening sheet and results.  Therefore, chemical specific limits have not been placed in the permit.  

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 No. 1 – Flow Diagram
Attachment No. 2 – Discharge Location Map
Attachment No. 3 – Wasteload Allocation
Attachment No. 4 – Tabulated Metals Testing Data
Attachment No. 5 – MS State Water Quality Standards
Attachment No. 6 – Synopsis of Metals Results
Attachment No. 1 – Flow Diagram

Attachment No. 2 – Discharge Location Map

Outfall 001

Plant Location

Attachment No. 3 – Wasteload Allocation

Attachment No. 4 – Tabulated Metals Testing Data

Attachment No. 5 – MS State Water Quality Standards

Attachment No. 6 – Synopsis of Metals Results