PERMIT RATIONALE FOR REISSUANCE
Tronox LLC, Hamilton Facility
Monroe County
Hamilton, Mississippi
Water NPDES No. MS0002232
September 28, 2016

I.	FACILITY INFORMATION

Facility Name:  Tronox LLC, Hamilton Facility
Facility Address:  40034 Tronox Road 
Hamilton, MS  39746    
Hamilton, 
Permit No.:  MS0002232
SIC:  2816
Permit Writer:  Samar Patel
EPD Branch:  Chemical Branch

II.	NATURE OF BUSINESS

Tronox manufactures Titanium Dioxide from titanium-bearing ore. The impure ore is chlorinated and the resulting titanium tetrachloride is separated from the ore while in a vapor phase and then oxidized to form titanium dioxide.

The Sodium Chlorate Plant at the facility was shut-down and ceased operation on October 30, 2015. 

III.	EFFLUENT AND RECEIVING STREAM FLOW DATA

A.	Outfall 101 – Cooling water and storm water runoff from non-process areas that include old manganese facility, the recently shutdown Chlorate plant, parking areas, and wooded area south of Tronox road between the road and the ditch that leads to Ponds No.3.  Long term average flow is 3.33 MGD and the maximum 30-day average flow is 7.88 MGD.  The receiving stream for this outfall is Dose Maie Creek, which has a 7Q10 of zero.

B.	Outfall 201 – Process wastewater from titanium dioxide plant, storm water runoff from process areas, sanitary and laundry wastewater (from Internal Outfall 301), and contaminated wastewater (i.e., leachate) and storm water from existing Landfill No.11 and new proposed Landfill No.22.  The long term average flow is 8.04 MGD and the maximum 30-day average flow is 13.14 MGD.  The anticipated average flow from Landfill No.2 is projected to be 0.08 MGD. This is about 1% of average flow recorded at Outfall 201. The receiving stream for this outfall is the Tennessee-Tombigbee Waterway, which has a 7Q10 of 96.95 MGD.

1 Landfill No.1 is currently use for disposing only non-hazardous waste sand materials generated during the processing operations (i.e., scour sand used in oxidation process area for cleaning TiO2 out of a heat exchanger). Waste sand is washed couple of times to recover as much TiO2 as possible before it landfilled. According to the permittee, once they use this sand from Landfill No.1 as filling material around the new leachate piping as said in the following paragragh, this will greatly extend life of  Landfill No.1 and it will be years before they have to actually dispose of waste sand in Landfill No.2. 

2 Landfill No.2 will be used for the disposal of non-hazardous wastes generated on-site and will be approximately 42.6 acres in size. The primary waste to be disposed in this landfill are dewatered filter cake solids from the existing wastewater treatment system which consists of a series settling ponds, waste sand materials generated during the processing operations (currently dispose of at active Landfill No.1), in addition to sand from Landfill No.1 that will be used as the 18” fill around the new leachate piping. 

C.	Outfall 301 – Internal outfall going into Outfall 201 made up of sanitary and laundry wastewater.

Both outfalls are in the Tombigbee River Basin 

IV.	303(d) ISSUES

	Outfall 201 – Tennessee-Tombigbee Waterway
           7Q10 of Tennessee-Tombigbee Waterway = 96.95 MGD (150 cfs)
            Mean Annual Flow of Tennessee-Tombigbee Waterway = 2,275 MGD                  (3,520 cfs) 

There are no 303(d) issues for the site.  In October 2008, a TMDL for organic enrichment and dissolved oxygen was finalized by EPA for Tombigbee River (Aliceville Reservoir).  Tronox is not subject to this TMDL. 

V.	TYPE OF WASTEWATER TREATMENT:

A.	Outfall 101 – A settling/equalization pond, identified as pond 3.

B.	Outfall 201 – Process wastewater that is not recycled or reused undergo neutralization prior to treatment in a series of settling ponds (Ponds 16, 14, 11, and 7 in order). Contaminated water from Waste Solids Impoundment Pond No.15 is also cycled through these settling ponds. Leachate and storm water from Landfill No.1 is first routed into Pond 9 (or Ponds 11 or 14 as alternatives). No matter its entry point into the system, this wastewater will be treated with the facility’s process wastewater then be routed ultimately to Pond 7 before discharging through Outfall 201. 

The discharge of leachate and storm water collected from the proposed Landfill No.2 will be routed to a 20,000-gallon storage tank. From the storage tank, the leachate will be routed to either Pond 14 or to Pond 16 to be treated with the facility’s process wastewater before discharging through Outfall 201. Storm water from the two permanently installed sedimentation basins located adjacent to the landfill will be routed to either Pond 14 or to Pond 16 to be treated with the facility’s process wastewater before discharging through Outfall 201. 

C.	Outfall 301 – Sanitary and laundry waste is treated in a conventional lagoon (Pond 8)

VI.	EPA APPLICABLE CATEGORICAL GUIDELINES

The facility is classified under the Standard Industrial Classification (SIC) Code 2816 which is identified as “Inorganic Pigments”. The process waste streams generated by this facility are regulated by 40 CFR §415.223(b), “Titanium Dioxide-Chloride Process.

VII.	DATA FROM APPLICATION FORM 

Outfall 101:

Parameter	Unit	Maximum Daily Concentration	
Aluminum	mg/l	0.232	
Ammonia	mg/l	0.018	
Antimony	mg/l	<0.001	
Arsenic	mg/l	<0.0005	
Barium	mg/l	0.0527	
Beryllium	mg/l	<0.001	
Biochemical Oxygen Demand (BOD)	mg/l	4.0 mg/l	
Bis(2-ethylhexyl) phthalate	mg/l	<0.026 mg/l	
Bis(chloromethyl) ether	mg/l	<0.003 mg/l	
Boron	mg/l	0.0383	
Bromide	mg/l	<0.50	
Cadmium	mg/l	<0.001	
Chemical Oxygen Demand (COD)	mg/l	147.0	
Chlorine, Total Residual	mg/l	<0.002	
Chromium	mg/l	0.00341	
Cobalt	mg/l	<0.001	
Color	CP units	8.0 	
Copper	mg/l	<0.001	
Cyanide	mg/l	<0.005	
Fluoride	mg/l	<0.20	
Fecal Coliform	Col/100 mL	8.0 ec	
Iron	mg/l	3.74	
Lead	mg/l	<0.001	
Magnesium	mg/l	1.87	
Manganese	mg/l	2.07	
Mercury	ng/l	4.21	
Molybdenum	mg/l	<0.001	
Nickel	mg/l	0.0012	
Nitrate+Nitrite	mg/l	0.309	
Oil & Grease	mg/l	6.0	
pH	SU	6.0-10.20	
Phenols	mg/l	<0.0053	
Phosphorous	mg/l	<0.5	
Selenium	mg/l	<0.001	
Silver	mg/l	<0.001	
Sulfate	mg/l	3.69	
Thallium	mg/l	<0.001	
Tin	mg/l	<0.001	
Titanium	mg/l	0.516	
Total Organic Carbon (TOC)	mg/l	11.0	
Total Organic Nitrogen 	mg/l	0.424	
Total Suspended Solids (TSS)	mg/l	24.0	
2,3,7,8-Tetrachlorodibenzo-P-Dioxin (TCDD)	pg/l	ND
(MDL = 2.01 pg/l)	
Zinc	mg/l	<0.005	

Outfall 201:

Parameter	Unit	Maximum Daily Concentration	
Aluminum	mg/l	1.19	
Ammonia	mg/l	<0.015	
Antimony	mg/l	2.96	
Arsenic	mg/l	<0.0025	
Barium	mg/l	0.344	
Beryllium	mg/l	<0.001	
Biochemical Oxygen Demand (BOD)	mg/l	8.0 	
Bis(2-ethylhexyl) phthalate	mg/l	<0.026 	
Bis(chloromethyl) ether	mg/l	<0.003 	
Boron	mg/l	0.161	
Bromide	mg/l	<0.50	
Cadmium	mg/l	<0.005	
Chemical Oxygen Demand (COD)	mg/l	5100	
Chlorine, Total Residual	mg/l	0.01	
Chromium	mg/l	0.08	
Cobalt	mg/l	<0.005	
Color	CP units	100	
Copper	mg/l	0.0381	
Cyanide	ug/l	0.0389	
Fluoride	mg/l	<0.20	
Fecal Coliform	Col/100 mL	<4.0 ec	
Iron	mg/l	2.278	
Lead	mg/l	<0.005	
Magnesium	mg/l	49.7	
Manganese	mg/l	10.0	
Mercury	ng/l	3.12	
Molybdenum	mg/l	0.0863	
Nickel	mg/l	0.0526	
Nitrate+Nitrite	mg/l	10.164	
Oil & Grease	mg/l	7.0	
pH	SU	5.79-9.35	
Phenols	mg/l	<0.0053	
Phosphorous	mg/l	<0.5	
Selenium	mg/l	<0.005	
Silver	mg/l	<0.005	
Sulfate	mg/l	1710	
Thallium	mg/l	<0.005	
Tin	mg/l	<0.005	
Titanium	mg/l	0.264	
Total Organic Carbon (TOC)	mg/l	5.6	
Total Organic Nitrogen 	mg/l	10.264	
Total Suspended Solids (TSS)	mg/l	24.8	
2,3,7,8-Tetrachlorodibenzo-P-Dioxin (TCDD)	pg/l	ND
(MDL = 2.01 pg/l)	
Zinc	mg/l	<0.025	

Outfall 301:

Parameter	Unit	Maximum Daily Concentration	
BOD	mg/l	6.0	
Chemical Oxygen Demand (COD)	mg/l	46.0	
Total Organic Carbon (TOC)	mg/l	1.2	
Total Suspended Solids (TSS)	mg/l	21.0	
Ammonia	mg/l	0.337	
Oil & Grease	mg/l	6.0	
Fecal Coliform	Col/100 mL	50.86 ec	
Color	CP units	45.0	
Bromide	mg/l	<0.50	
Fluoride	mg/l	<0.20	
Phosphorous	mg/l	<0.5	
Nitrate+Nitrite	mg/l	0.961	
Total Organic Nitrogen 	mg/l	2.7	
      	ND = Non-Detect, MDL = Method Detection Limit
	
VIII. 	WATER QUALITY LIMITATIONS BASED ON WASTELOAD ALLOCATION 

	None.

IX.	CATEGORICAL GUIDELINE LIMITATIONS CALCULATIONS

See Attachment A

X.	TOXICITY SCREENING

See Attachment B

XI.	PROPOSED FINAL LIMITATIONS 

1.	Average Permit Limitations

Outfall	Parameter	Categorical Limitation	Water Quality Limitation	Present Permit Limitation	Proposed Permit Limitation	Basis	
Outfall 101 MS002232-101	Flow1	-	-	Report (MGD)	Report
(MGD)	EJ	
	Manganese1*	-	-	1.5 mg/L
(R lbs/day)	1.5 mg/L
(R lbs/day)	PPR/ABS	
	Iron
(Phase I)1,3	-	-	-	R mg/l
(R lbs/day)	EJ	
	Iron
(Phase II)1,3			-	1.0 mg/l
(66.8 lbs/day)	RPA / NRWQS	
	Chromium1,4	-	-	-	R mg/l
(R lbs/day)	EJ	
	Titanium1,4	-	-	-	R mg/l
(R lbs/day)	EJ	
	pH1,2
(continuous)	6.0 
(min.)	6.0 
(min.)	6.0 
(min.)	6.0 
(min.)	PPR / MSWQS 	
Outfall 201 MS002232-201	Flow1	-	-	Report (MGD)	Report
(MGD)	EJ	
	Chromium1*	43.09 lbs/day	0.042 mg/l
(2.81 lbs/day)	0.042 mg/l (2.25 lbs/day)	0.042 mg/l
(2.25 lbs/day)	PPR / ABS / MSWQS	
	Iron1,4	-	-	-	R mg/l
(R lbs/day)	EJ	
	Aluminum1,4	-	-	-	R mg/l
(R lbs/day)	EJ	
	Titanium1,4	-	-	-	R mg/l 
(R lbs/day)	EJ	
	Manganese1,5	-	-	-	R mg/l 
(R lbs/day)	EJ	
	TSS1*	137.03 mg/l
9194.24 lbs/day		30.0 mg/l
1346 lbs/day	30.0 mg/l
1346 lbs/day	ABS / PPR	
	Antimony1*	-		R mg/l
(1.5 lbs/day)	R mg/l
(1.5 lbs/day)	ABS / PPR	
	Chlorine1*	-	0.011 mg/l
(0.73 lbs/day)	0.011 mg/l
(0.59 lbs/day)	0.011 mg/l
(0.59 lbs/day)	PPR / ABS / MSWQS	
	pH1,2
(continuous)	6.0 
(min.)	6.0 
(min.)	6.0 
(min.)	6.0 
(min.)	PPR / MSWQS 	
Outfall (301)
MS002232-301	Fecal
Coliform1,6			200 col/100 ml	200 col/100 ml	PPR / ABS/
MSWQS	

2.	Maximum Permit Limitations

Outfall	Parameter	Categorical Limitation	Water Quality Limitation	Present Permit Limitation	Proposed Permit Limitation	Basis	
Outfall 101
MS002232-101	Flow1	-	-	Report (MGD)	Report
(MGD)	EJ	
	Manganese1*	-	-	3.0 mg/L
(R lbs/day)	3.0 mg/L
(R lbs/day)	PPR/ABS	
	Iron
(Phase I)1,3	-	-	-	R mg/l
(R lbs/day)	EJ	
	Iron
(Phase II)1,3			-	2.0 mg/l
(133.6 lbs/day)	RPA / NRWQS	
	Chromium1,4	-	-	-	R mg/l
(R lbs/day)	EJ	
	Titanium1,4	-	-	-	R mg/l
(R lbs/day)	EJ	
	pH1,2 (continuous)	9.0
(max.)	9.0
(max.)	9.0
(max.)	9.0
(max.)	PPR / MSWQS	
	Temperature1			90ºF	90ºF	ABS / MSWQS	
Outfall 201
MS002232-201	Flow1	-	-	Report (MGD)	Report
(MGD)	EJ	
	Chromium1*	81.88 lbs/day	0.323 mg/l
21.67 lbs/day	0.323 mg/l
17.3 lbs/day	0.323 mg/l
17.3 lbs/day	PPR / ABS	
	Iron1,4	-	-	-	R mg/l
(R lbs/day)	EJ	
	Aluminum1,4	-	-	-	R mg/l
(R lbs/day)	EJ	
	Titanium1,4	-	-	-	R mg/l
(R lbs/day)	EJ	
	Manganese1,5	-	-	-	R mg/l 
(R lbs/day)	EJ	
	TSS1*	33041.8 lbs/day	-	45.0 mg/l
2019 lbs/day	45.0 mg/l
2019 lbs/day	PPR / ABS	
	Antimony1*	-	-	R mg/l
(3.0 lbs/day)	R mg/l
(3.0 lbs/day)	PPR / ABS	
	Chlorine1*	-	0.019 mg/l
1.27 lbs/day	0.019 mg/l
1.02 lbs/day	0.019 mg/l
1.02 lbs/day	PPR / ABS / MSWQS	
	pH1,2 (continuous)	9.0
(max.)	9.0
(max.)	9.0
(max.)	9.0
(max.)	PPR / MSWQS	
MS002232-301	Fecal Coliform1,6			400 col/100 ml	400 col/100 ml	PPR / ABS/
MSWQS	
R = Report Only, PPR = Previous Permit Requirement, EJ = Engineering Judgment, ABS = Anti-backsliding Provisions (40 CFR §122.44(l)), RPA = Reasonable Potential Analysis, NRWQS = Environmental Protection Agency (EPA) - National Recommended Water Quality Criteria, MSWQS = State of Mississippi Water Quality Criteria for Intrastate, Interstate and Coastal Waters

* Water quality-based limitations, existing permit-based limitations and categorical limitations were evaluated as shown in the table above to determine the limits, but a most stringent of all three limits was proposed since it will be more protective of water quality and therefore placed in the permit. The proposed limits are considerably lower than the categorical and water-quality based limitations, but the permittee has demonstrated the ability to comply with these limits. Therefore, the limits originally set in the permit will not be changed during this renewal for the aforementioned parameters based on the Anti-Backsliding provisions of 11 Miss. Admin. Code Pt. 6, R. 1.1.4.A(4)(e). of Wastewater Regulations for NPDES Permits. 

1  Flow, pH, and temperature shall be monitored with a continuous recorder. All other parameters, with the   exception of fecal coliform, antimony, chlorine, and titanium shall be monitored weekly with a 24-hour composite sampling of the effluent. Fecal Coliform shall be monitored once every three months with a grab sample of the effluent. Antimony and chlorine shall be monitored annually with a 24-hour composite sampling. Titanium shall be monitored monthly with a 24-hour composite sampling. 

2  pH limits are based on the State of Mississippi Water Quality Criteria. Since pH shall be monitored continuously at both permitted outfalls, language is also found in the permit which allows for short term unintentional excursions outside the permitted pH range as allowed by 40 CFR §401.17.

3  The chronic water quality criteria for iron is 1.0 mg/l. Based on the RPA in Attachment C of this rationale, there is reasonable potential for water quality standard for iron to be exceeded at Outfall 101. Water high in iron can have an unpleasant taste, and materials washed in water with high iron concentrations could stain. Therefore, the water quality-based effluent limits are necessary for iron in the proposed permit. The maximum concentration limit is determined (using engineering judgment) by multiplying the 1.0 mg/l average limit by factor of 2 to obtain the 2.0 mg/l maximum limit. 

		MDEQ characterized iron limitations in the permit as Phase I and Phase II. Upon issuance of the permit, the permittee should be required to achieve compliance with the effluent limitations specified for the parameters noted as Phase I and the ones noted as phase-specific (i.e. Phase I, Phase II); Phase II limitations shall not apply at this time. Beginning upon completion and start-up of improvements needed to comply with Phase II limitations, the permittee shall achieve compliance with the Phase II effluent limitations; Phase I limitations will cease when Phase II begins. 

   Upon the permit issuance, the permittee shall be required to start monitoring iron once per week with a 24-hour composite sampling of the effluent. During the compliance schedule term of three (3) years from permit issuance date, the permittee shall be required to report only for iron to comply with Phase I. When Phase II begins, the effluent shall be sampled once per week to demonstrate compliance with the monthly average and daily maximum Phase II limitations of 1.0 mg/l (66.8 lbs./day) and 2.0 mg/l (133.6 lbs./day). Mass loadings for iron are calculated using long-term average flow of 8.04 MGD reported in the application.  

4  MDEQ proposed monitoring for chromium and titanium at Outfall 101 and iron, aluminum, and titanium at Outfall 201. This placement, as well as the data submitted in water application dated December 2014, support that these parameters do not have the reasonable potential to contribute to WQS exceedances, and limits are not necessary to protect water quality.  Monitoring is proposed to document any releases of these parameters into surface water since they are commonly found in waste streams at this type of industry. Iron and aluminum were detected consistently in the plant’s effluent. As such, the monitoring is proposed to document that iron and aluminum continue to remain at low levels.  

		Titanium has neither water quality criterion nor Preliminary Remediation Goal (PRG) set by ATSDR. The Mississippi Tier 1 Target Remediation Goal (TRG) for titanium in groundwater is 146 mg/l. Because TRGs are calculated using a similar method as the PRGs, they also represent safe levels for chronic lifetime exposures. In the application, titanium is reported 0.516 mg/l at Outfall 101 and 0.264 mg/l at Outfall 201. It would not be expected to cause any adverse health effects at these levels.

5  Manganese may be present in the effluent due to historical activities on the site. Manganese was reported 10.0 mg/l at Outfall 201, which may not be representative of its actual levels in the effluent and was based on only one data point. MDEQ has performed toxicity screening on this parameter and recommends additional monitoring. The constituent failed the screening procedure due to multiplication by a factor of 10 as a result of the reporting less than 12 sample results. The purpose of the proposed monitoring is to collect additional data on the frequency of occurrence and variability of this parameter in the plant’s effluent. Upon re-evaluation of the additional data, the permit may be modified and new limits will be established for this parameter, if justified during the next permit renewal.

6  Fecal coliform limitations were placed in the permit based on our State water quality standards.  Monitoring should be done at the point of discharge of the conventional lagoon and before mixing with the waste water from the settling ponds.  Monitoring frequency was based on regulations for municipal facilities with the same type of treatment and similar flow.

XII	Effluent Monitoring Requirements:

In addition to providing effluent limits as summarized above, monitoring requirements are included in the permit to determine compliance with these effluent limitations (Section 308 of the CWA and §122.44(i)). The permittee is responsible for conducting the monitoring and reporting these results to MDEQ as a means to ensure that the effluent wastewater treatment system (WTS) is functioning correctly and that the discharge complies with the effluent limits. 

Monitoring frequencies are based on the nature and effect of the pollutant, as well as a determination of the minimum sampling necessary to adequately monitor the facility’s performance. Based on engineering judgment, MDEQ elected to maintain the current monitoring frequencies for all evaluated pollutants in this permit since the applicant’s monitoring history has demonstrated the ability to consistently comply with regulatory limits of the permit.

  Note that the permittee shall be required to submit monitoring results and a completed Item V and VI of the Form 2C application from Outfall 201 to MDEQ as addressed in the proposed permit within one (1) year of commencing the Landfill No. 2 operations. MDEQ will evaluate the results and determine if there is a potential to violate the proposed limits for Outfall 201 or the State water quality standards. New limits or monitoring will be established at that time, if justified. 
 
XIII	Other Monitoring Basis

Outfall 101

Based on the effluent data provided in the application for Outfall 101, the facility failed the toxicity screening for cadmium, copper, selenium, lead, and thallium. For all these parameters, the facility failed the toxicity screening procedure due to the multiplication by a factor of 10 as a result of reporting less than 12 sample results.  For thallium, the detection limit was too high to confirm that it does not exceed the water quality standards for human health (organism only). To determine with certainty whether water quality standards for these parameters are being violated, the facility shall perform additional monitoring twice per month for twelve months with 24-hour composite samples of the effluent beginning the month following the effective issuance date of the permit or until 24 samples are received. All monitoring results shall be submitted to the Mississippi Environmental Quality Permit Board no later than the 28th day of the month following the completed collection of all samples.  The NPDES permit may be modified to include cadmium, copper, selenium, lead, and thallium limits after screening is accomplished with the additional data.
Outfall 201
1.	Based on the effluent data provided in the application for Outfall 201, the facility failed the toxicity screening for cadmium, copper, nickel, selenium, and lead.  For all these parameters, the facility failed the toxicity screening procedure due to the multiplication by a factor of 10 as a result of reporting less than 12 sample results.  To determine with certainty whether water quality standards for these parameters are being violated, the facility shall perform additional monitoring twice per month for twelve months with 24-hour composite samples of the effluent beginning the month following the effective issuance date of the permit or until 24 samples are received. All monitoring results shall be submitted to the Mississippi Environmental Quality Permit Board no later than the 28th day of the month following the completed collection of all samples.  The NPDES permit may be modified to include cadmium, copper, nickel, selenium, and lead limits after screening is accomplished with the additional data.
2.	The facility was previously required to perform analyses for iron, aluminum and mercury until twelve samples were obtained and reported to the agency. Using this data along with the application, the facility passed toxicity screening and RPA for iron, aluminum and mercury at Outfall 201, as determined in Attachment B and Attachment C of this rationale. Thus, the monitoring for mercury has been removed from the proposed permit. Monitoring for iron and aluminum is proposed to document that these pollutants continue to remain at low levels.
3.	The proposed monitoring requirements for molybdenum, thallium, and vanadium are based on our engineering judgment since we have no evidence on the frequency of occurrence and variability of these pollutants in the plant’s effluent. As such, the monitoring will serve to document any releases of these pollutants into surface water, since there is a possibility for presence of these constituents in commingled wastewaters from chloride process operations and in raw material (i.e., ore feedstock) used at the facility. For thallium, the detection limit was too high to confirm that thallium does not exceed the water quality standards (i.e., screening levels of health based and human health (water + organism)). The facility shall perform monitoring twice per month for twelve months with 24-hour composite samples of the effluent for these pollutants or until 24 samples are received. All monitoring results shall be submitted to the Mississippi Environmental Quality Permit Board no later than the 28th day of the month following the completed collection of all samples. Upon re-evaluation of the monitoring data, the permit may be modified and new permit requirements will be established for molybdenum, thallium, and vanadium, if justified.
4.	Whole Effluent Toxicity (WET): The Water Quality Standards for Surface Waters prohibit the discharge of effluent that causes toxic effects in the receiving waters. Many toxic pollutants cannot be analyzed using commonly available detection methods. The Whole Effluent Toxicity (WET) testing is being utilized by MDEQ as a means to ensure that there are no discharges of pollutants in amounts which are harmful to the beneficial uses of the receiving stream. As such, in order to determine the aggregate toxic effect of a mixture of pollutants present in the effluent, WET can be measured directly by exposing living aquatic organisms to the whole effluent wastewater in laboratory tests and measuring the response of the organisms. Toxicity tests measure the aggregate toxicity of the whole effluent, and therefore this approach is called WET testing. There are two types of WET tests: acute and chronic. The chronic conditions apply to a discharge unless the instream waste concentration (IWC) of that discharge in the receiving water after mixing is less than or equal to 1%. Tronox is an existing major facility discharging to a Tennessee-Tombigbee Waterway, which has a 7Q10 flow of 96.95 MGD. Since the calculated IWC is 11.94%, the chronic conditions apply for this discharge in accordance with our Wastewater Regulations, 11 Miss. Admin. Code Pt. 6, Ch.1. 
The inhibition concentration (IC) is the analysis used in chronic WET tests to estimate the sub-lethal effects of the effluent sample. The IC25 is an estimate of the effluent concentration which causes a 25% reduction in growth or reproduction of test organisms. The IC25 is compared to the instream waste concentration (IWC) for the effluent to determine whether there is potential for the effluent to cause sub-lethal effects to aquatic populations, once it has mixed with the receiving water. That is, if the IC25 of any test is less than 11.94%, the effluent may consider to have the potential to cause sub-lethal effects to aquatic populations in the receiving water.
The permittee shall require to test the effluent discharge for chronic toxicity during the first year of the permit term and submit those test results within sixty (60) days following completion of the WET tests data collection. This chronic testing shall conduct in accordance with Short-Term Methods for Estimating the Chronic Toxicity of Effluents and Receiving Waters to Freshwater Organisms, (EPA/600/4-89/001) or the most recent edition. The sampling frequency during effluent characterization shall be at least twice per year and sampling shall be timed to cover the seasonal extremes of the year such as hot-dry and cold-wet. Upon evaluation of the chronic toxicity data, the permit may be reopened and new requirements for chronic WET testing will be established, if justified. After first year of monitoring, provided the IC25 is greater than or equal to 11.94%, the permittee will no longer subject to the requirements of chronic WET testing.

XII.	ANTIDEGRADATION EVALUATION:
 
Tronox submitted an Antidegradation Report according to the MDEQ State of Mississippi Antidegradation Implementation Methods, (January 28, 2010). The antidegradation report titled “Tronox Landfill No.2” received March 12, 2015, and revision received June 1, 2015, have been reviewed by MDEQ. Our review of the antidegradation report is completed, and we have no further comment.

The primary waste to be disposed to Landfill No.2 will consist of dewatered filter cake from the existing wastewater treatment system and waste sand materials generated from the process. The leachate is generated from water contacting these waste streams may potentially contain the following constituents: titanium dioxide (TiO2), hydrocarbons, calcium sulfate (CaSO3), calcium carbonate (CaCO3), chromium, cadmium, and other various metals. The landfill leachate and all contaminated storm water generated from Landfill No. 2 operations will be routed to their existing effluent WTS consisting of a series of wastewater settling ponds before being discharged through Outfall 201. According to the report, the proposed leachate flow is anticipated to be 0.004 MGD and the storm water flow to be 0.073 MGD, resulting in a total flow of 0.077 MGD. The projected total flow from Landfill No.2 operations will be approximately 1% of the average flow of 8.04 MGD recorded at Outfall 201.  Although wastewater associated with the newly proposed Landfill No.2 operations will be allowed to be discharged through the existing Outfall 201, the constituents present in wastewater will not result in degradation of the receiving waters to the extent that human health or the environmental will be adversely impacted. In addition, the detention time in the settling ponds and mixing of proposed minimal flow from landfill operations with the storm water and other process wastewater present in these ponds is anticipated to provide removal of constituents in the leachate. 

The applicant evaluated potential degradation to the receiving stream and alternatives for eliminating the discharge. Specifically, the applicant evaluated a “No net discharge” system, such as spray irrigation, land application , and evaporation pits; pumping the landfill leachate to the nearest existing publicly owned wastewater collection and treatment system (POTW); alternate discharge locations; product or raw material substitution; alternative treatment option; improved operation and maintenance of existing treatment system; seasonal or controlled discharge options; and collect and haul landfill leachate to the nearest wastewater treatment plant. The nearest wastewater facility is the Columbus Light and Water Department’s Reynolds R. Ridgley Wastewater Treatment Plant. Alternatives such as spray irrigation and collect and hauling of leachate to the nearest POTW were technically feasible for purpose of this review but economically non-feasible since the “Total Annualized Project Cost” associated with these options were 145% and 903.6%, respectively, greater than the preferred option of discharging to the facility’s effluent WTS under the NPDES permit limits. According to the report, all other options including connection to an existing POTW are impractical and already found economically non-feasible when dealing with the smaller incremental increase in wastewater (from Landfill No.2 operations) within the facility. 

XIII	ADDITIONAL SUBMITTAL REQUIREMENTS:

-	For Outfall 201, within one (1) year of commencing of discharge from Landfill No.2 operations, the permittee shall complete and submit Items V and VI of NPDES application Form 2C [40 CFR 122.21 (k)(5)(vi) & 40 CFR 122.26(c)(1)(i)(G)].

-	An updated facility-wide Storm Water Pollution Prevention Plan (SWPPP will be required within 180 days from permit issuance date. The revised SWPPP must identify all activities including the new landfill and significant materials which may potentially pollute storm water discharges. The SWPPP shall describe and ensure implementation of Best Management Practices (BMPs), which will help minimize pollutants in storm water discharges and assure compliance with the terms and conditions of the proposed permit. The SWPPP shall, at a minimum, contain the requirements of 40 CFR 122.26(c)(1)(i)(A)-(D).

ATTACHMENT A

CATEGORICAL GUIDELINE LIMITATIONS CALCULATIONS

Federal Effluent Guidelines Calculations
Outfall 201

BAT - Maximum Daily Limitation
				
	Titanium Dioxide Production by the Chloride Process	
	[40 CFR 415.223(b)] 653 tons per day	= 1436.6 (1000 lb./day)	
	 		 	
Parameter
 	Production Rate
(1000 lb./day)	Daily*	BAT Effluent Limit	
TSS	1436.6	23	33041.8
(492.47 mg/l)**	
Total Chromium	1436.6	0.057	81.88
(1.22 mg/l)**	
pH	Minimum 6.0 S.U - Maximum 9.0 S.U. from all sources	
				
*  Pounds of constituent per 1000 pounds of product		
** Based on LTA – 8.04 MGD				

BAT - Average Monthly Limitation			
				
	Titanium Dioxide Production by the Chloride Process	
	[40 CFR 415.223(b)] 653 tons per day	= 1436.6 (1000 lb./day)	
	Production Rate
(1000 lb./day)	Daily*	BAT Effluent Limit	
Parameter
 				
TSS	1436.6	6.4	9194.24 lb./day 
(137.03 mg/l)**	
Total Chromium	1436.6	0.03	43.098
(0.64 mg/l)**	
pH	Mininum 6.0 S.U - Maxiumum 9.0 S.U. from all sources	
				
* Pounds of constituent per 1000 pounds of product
** Based on LTA – 8.04 MGD		

CFR = Code of Federal Regulations
MGD = millions gallons per day
TSS = total suspended solids
LTA = long-term average flow

ATTACHMENT B

TOXICITY SCREENING

Outfall 101

1.            Toxicity Screening Procedures							
										
               A describtion of these procedures is outlined in the State of Mississippi			
               Wastewater Regulations for NPDES Permits.					
										
2.            Definitions								
										
                           IWC       =        Instream waste Concentration, which is defined as the resulting conc.		
                                                   of a specific wastewater discharge flow into a receiving water following		
	                         mixing of the wastewater in the receiving water at the appropriate critical 		
	                         flow (See Qr defined below)						
										
	Qw         =         Average flow for Outfall						
										
	Qr          =         Receiving stream flow. The critical flow normally employed is the 7Q10 		
	                         flow, or the 7-day, 10-year low flow of the receiving water. In the absence 	
	                         of any available 7Q10 dat, 0.0 cfs is assumed.
				
	Xr           =        Background concentration of screened pollutant in the receiving water. 		
	                        Assumed to be zero (0) in the absence of any available data.			
										
	Xw          =        The daily maximum concentration of the screened pollutant as reported in 	
	                         the application or determined from effluent monitoring; or the daily		
	                        maximum permit limit. This value is multiplied by ten (10) when fewer		
	                        than twelve (12) analyses are reported.					
										
	Xwa          =      The monthly average concentration of the screened pollutant as reported in 	
	                        the application or determined from effluent monitoring; or the monthly		
	                        average permit limit. This value is multiplied by ten (10) when fewer		
	                        than twelve (12) analyses are reported.					
										
	Xt            =      Concentration of screened pollutant following discharge and mixing in  		
	                        the receiving water, based on reported maximum discharge concentration.	
										
	Xta           =     Instream Concentration of screened pollutant following discharge and 		
	                       mixing in the receiving water, based on reported average discharge 		
	                       concentration.							
										
	AWQC    =      Acute Water Quality Criterion value, as denoted in Table-2 of the		
	                       State Water Quality Criteria and the EPA- National Recommended Water	
	                       Quality Criteria.							
										
	CWQC    =     Chronic water Quality Criterion value, as denoted in Table-2 of the		
	                       State Water Quality Criteria and the EPA- National Recommended Water	
	                       Quality Criteria.							
										
	HHV       =     Human Health Value for consumption of organism, as denoted by 10-6		
	                      risk factors for carcinogens referenced in Table-2 of the State Water		
	                    Quality Criteria and the  EPA- National Recommended Water Quality		
	                    Criteria.							
3.            Calculations								
										
	Reported Values, Xwa and Xw for each pollutant screened				
										
	          Parameter	 	Xwa	 	Xw				
	 	 	 	μg/l	 	μg/l				
	Total Iron	 	 	1330	 	3740				
	Total Mercury*1	 	0.03	 	0.04				
	Total Cadmium		10		10				
	Total Chromium*1	 	34.1	 	34.1				
	Total Copper*1	 	10	 	10				
	Total Nickel*1	 	12	 	12				
	Total Selenium*1	 	10	 	10				
	Total Zinc*1	 	50	 	50				
	Total Lead*1	 	10	 	10				
	Total Manganese	 	500	 	2070				
	Total Thallium		10		10				
	Total Arsenic*1	 	5	 	5				
	*  As the data reported for these parameters is based on fewer than twelve (12) results,		
	   the reported value is multiplied by a factor of ten (10) for screening purposes.		
										
	1 Only daily maximum values were reported in the application. In that case,			
	   based on our engineering judgment, it was decided to use these values to see  	
	   if there will be potential for these toxics to violate the acute, chronic, and human		
	   health water criteria. Although, the metals that were reported below their method's		
	   detection limit (MDL), these metals may be assumed to be present at the detection		
	   levels of method's reporting limt as reported in the application. 				

	Calculations of IWC							
										
		Qw        =	Max. 30-day Average Flow at Outfall 101 = 	7.88	MGD		
		Qr         =	 7Q10 flow of receiving water =		0.00	MGD		
										
		IWC      =	100 * [Qw / (Qw+Qr)]						
		            =	100 *  [ 7.88 / (7.88+0) ]					
		            =	100 * [7.88 / 7.88]						
		            =	100.000%							

Calculations of Xt and Xta							
										
		Since Xr =	0							
										
		Xt = Xw * (IWC/100) = Xw * [ Qw / (Qw+Qr) ]				
	                    &									
		Xta = Xwa * (IWC/100) = Xwa * [ Qw / (Qw+Qr) ]				
										
Acute Toxicity Screening								
										
          Parameters	Xw	Xt	AWQC	Pass/Fail					
 	 	μg/l	μg/l	μg/l	 					
Total Iron	 	3740	3740	-	N/A					
Total Mercury	0.04	0.0421	1.4	Pass					
Total Arsenic	5	5	340	Pass					
Total Cadmium	10	10	1.03	Fail					
Total Chromium	34.1	34.1	323	Pass					
Total Copper	10	10	7	Fail					
Total Nickel	12	12	260	Pass					
Total Selenium	10	10	11.8	Pass					
Total Zinc	50	50	65	Pass					
Total Manganese	2070	2070	-	N/A					
Total Thallium	10	10	-	Fail					
Total Lead	10	10	30	Pass					
										
Chronic Toxicity Screening								
										
          Parameters	Xwa	Xta	CWQC	Pass/Fail					
 	 	μg/l	μg/l	μg/l	 					
Total Iron	 	1330	1330.00	1000	Fail					
Total Mercury	0.03	0.03	0.77	Pass					
Total Arsenic	5	5.00	150	Pass					
Total Cadmium	10	10	0.15	Fail					
Total Chromium	34.1	34.10	42	Pass					
Total Copper	10	10.00	5	Fail					
Total Nickel	12	12.00	29	Pass					
Total Selenium	10	10.00	4.6	Fail					
Total Zinc	50	50.00	65	Pass					
Total Manganese	500	500.00	-	N/A					
Total Thallium	10	10	-	Fail					
Total Lead	10	10.00	1.18	Fail					
										
Human Health Toxicity Screening							

          Parameters	Xwa	XHH	HHV2	Pass/Fail					
 	 	μg/l	μg/l	μg/l	 		 			
Total Iron	1330	1330.00	-	N/A					
Total Mercury	0.03	0.03	0.153	Pass					
Total Arsenic	5	5.00	24	Pass					
Total Cadmium	10	10	168	Pass					
Total Chromium	34.1	34.10	140468	Pass					
Total Copper	10	10.00	1000	Pass					
Total Nickel	12	12.00	4600	Pass					
Total Selenium	10	10.00	4200	Pass					
Total Zinc	50	50.00	26000	Pass					
Total Manganese	500	500.00	100	Fail					
Total Thallium	10	10	0.47	Fail					
Total Lead	10	10.00	-	N/A					

2 Human Health for the Consumption of   
  Organisms								
										
Conclusions									
										
          Parameters	AWQC	CWQC	HHV						
 	 	Pass/Fail	Pass/Fail	Pass/Fail						
Total Iron	N/A	Fail	N/A						
Total Mercury	Pass	Pass	Pass						
Total Arsenic	Pass	Pass	Pass						
Total Cadmium	Fail	Fail	Pass						
Total Chromium	Pass	Pass	Pass						
Total Copper	Fail	Fail	Pass						
Total Nickel	Pass	Pass	Pass						
Total Selenium	Pass	Fail	Pass						
Total Zinc	Pass	Pass	Pass						
Total Manganese	N/A	N/A	Fail						
Total Thallium	N/A	N/A	Fail						
Total Lead	Pass	Fail	N/A						
										
The facility failed the toxicity screening for cadmium, copper, selenium, lead, and thallium.  For all these parameters, the facility failed the toxicity screening procedure due to the multiplication by a factor of 10 as a result of reporting less than 12 sample results.  To determine with certainty whether water quality standards for these parameters are being violated, the facility shall perform additional monitoring twice per month for twelve months with 24-hour composite samples of the effluent beginning the month following the effective issuance date of the permit or until 24 samples are received. All monitoring results shall be submitted to the Mississippi Environmental Quality Permit Board no later than the 28th day of the month following the completed collection of all 48 samples.  The NPDES permit may be modified to include cadmium, copper, selenium, lead, and thallium limits after screening is accomplished with the additional data.

Outfall 201

1.            Toxicity Screening Procedures							
										
               A description of these procedures is outlined in the State of Mississippi			
               Wastewater Regulations for NPDES Permits.					
										
2.            Definitions								
										
                                 IWC      =         Instream waste Concentration, which is defined as the resulting conc.		
                                                         of a specific wastewater discharge flow into a receiving water following		
	                         mixing of the wastewater in the receiving water at the appropriate critical 		
	                         flow (See Qr defined below)						
										
	Qw         =          Average flow for Outfall						
										
	Qr          =         Receiving stream flow. The critical flow normally employed is the 7Q10 		
	                         flow, or the 7-day, 10-year low flow of the receiving water. In the absence 	
	                         of any available 7Q10 data, 0.0 cfs is assumed.
				
	Xr           =         Background concentration of screened pollutant in the receiving water. 		
	                         Assumed to be zero (0) in the absence of any available data.			
										
	Xw          =        The daily maximum concentration of the screened pollutant as reported in 	
	                        the application or determined from effluent monitoring; or the daily		
	                        maximum permit limit. This value is multiplied by ten (10) when fewer		
	                        than twelve (12) analyses are reported.					
										
	Xwa         =       The monthly average concentration of the screened pollutant as reported in 	
	                        the application or determined from effluent monitoring; or the monthly		
	                        average permit limit. This value is multiplied by ten (10) when fewer		
	                        than twelve (12) analyses are reported.					
										
	Xt            =       Concentration of screened pollutant following discharge and mixing in  		
	                        the receiving water, based on reported maximum discharge concentration.	
										
	Xta          =        Instream Concentration of screened pollutant following discharge and 		
	                        mixing in the receiving water, based on reported average discharge 		
	                        concentration.							
										
	AWQC   =       Acute Water Quality Criterion value, as denoted in Table-2 of the		
	                       State Water Quality Criteria and the EPA- National Recommended Water	
	                       Quality Criteria.							
										
	CWQC   =      Chronic water Quality Criterion value, as denoted in Table-2 of the		
	                       State Water Quality Criteria and the EPA- National Recommended Water	
	                       Quality Criteria.							
										
	HHV       =     Human Health Value for consumption of organism, as denoted by 10-6		
	                      risk factors for carcinogens referenced in Table-2 of the State Water		
	                      Quality Criteria and the  EPA- National Recommended Water Quality		
	                      Criteria.							

3.            Calculations								
										
	Reported Values, Xwa and Xw for each pollutant screened				
										
	          Parameter	 	Xwa	 	Xw				
	 	 	 	μg/l	 	μg/l				
	Total Antimony	 	543	 	2960				
	Total Aluminum	 	320	 	1190				
	Total Cadmium*1			50		50				
	Total Iron	 	 	490	 	2278				
	Total Mercury*1	 	0.02	 	0.03					
	Total Chromium	 	10	 	80					
	Total Copper*1	 	381	 	381					
	Total Nickel*1	 	526	 	526					
	Total Selenium*1	 	50	 	50					
	Total Zinc*1	 	250	 	250				
	Total Lead*1	 	25	 	50				
	Total Manganese*1	 	100000	 	100000				
	Total Thallium*1		50		50				
	Total Cyanide*1	 	0.389	 	0.389				
	Total Arsenic*1	 	25	 	25				
	*  As the data reported for these parameters is based on fewer than twelve (12) results,		
	   the reported value is multiplied by a factor of ten (10) for screening purposes.		
										
	1 Only daily maximum values were reported in the application. So in that case,			
	   based on our engineering judgment, we decided to use these values to check and see  	
	   if there will be a potential for these toxics to violate the acute, chronic, and human		
	   health water criteria. Although, the metals that were reported below their method's		
	   detection limit (MDL), these metals may be assumed to be present at the detection		
	   levels of method's reporting limt as reported in the application. 				

	Calculations of IWC							
										
		Qw        =	  Max. 30-day Average Flow at Outfall 201 =	13.14	MGD		
		Qr         =	  7Q10 flow of receiving water =		 96.95	MGD		
										
		IWC      =	100 * [Qw / (Qw+Qr)]						
		=	100 *  [ 13.14 / (13.14+96.95) ]					
		=	100 * [13.14 / 110.09]					
		=	11.94%							
										
	Calculations of Xt and Xta							
										
		 Since Xr =	0							
										
		Xt = Xw * (IWC/100) = Xw * [ Qw / (Qw+Qr) ]					
	                      &									
		Xta = Xwa * (IWC/100) = Xwa * [ Qw / (Qw+Qr)]					
										
Acute Toxicity Sceening								
										
          Parameter	Xw	Xt	AWQC	Pass/Fail					
 	 	μg/l	μg/l	μg/l	 					
Total Antimony	2960	353.42	-	N/A					
Total Aluminum	1190	142.09	750	Pass					
Total Cadmium	50	5.97	1.03	Fail					
Total Cyanide	0.389	0.05	22	Pass					
Total Iron	 	2278	271.99	-	N/A					
Total Mercury	0.03	0.00	1.4	Pass						
Total Arsenic	25	2.99	340	Pass						
Total Chromium	80	9.55	323	Pass						
Total Copper	381	45.49	7	Fail						
Total Nickel	526	62.80	260	Pass						
Total Selenium	50	5.97	11.8	Pass						
Total Zinc	 	250	29.85	65	Pass					
Total Manganese	100000	11940.00	-	N/A					
Total Thallium	50	5.97	1.73	Fail					
Total Lead	50	5.97	30	Pass					
										
Chronic Toxicity Sceening								
										
          Parameter	Xwa	Xta	CWQC	Pass/Fail					
 	 	μg/l	μg/l	μg/l	 					
Total Antimony	543	64.83	-	N/A					
Total Aluminum	320	38.21	87	Pass					
Total Cadmium	50	5.97	0.15	Fail					
Total Cyanide	0.389	0.05	5.2	Pass					
Total Iron	490	58.51	1000	Pass						
Total Mercury	0.02	0.00	0.77	Pass						
Total Arsenic	25	2.99	150	Pass						
Total Chromium	10	1.19	42	Pass						
Total Copper	381	45.49	5	Fail						
Total Nickel	526	62.80	29	Fail						
Total Selenium	50	5.97	4.6	Fail						
Total Zinc	250	29.85	65	Pass						
Total Manganese	100000	11940	-	N/A					
Total Thallium	50	5.97	1.33	Fail					
Total Lead	25	2.99	1.18	Fail					
										
Human Health Toxicity Screening							
										
Calculations of IWC								
	Qw        =	  Max. 30-day Average Flow at Outfall 201   = 	13.14	MGD			
	Qr         =	  Mean Annual Flow of receiving water =	2275	MGD			
										
	IWCHH       =	100 * [Qw / (Qw+Qr)]							
	=	100 *  [ 13.14 / (13.14+2275) ]						
	=	100 * [13.14 / 2288.14]						
	=	0.574%								
Calculations of XHH									
										
	XHH = Xwa * (IWCHH/100) = Xwa * [ Qw / (Qw+Qr) ]					
										
          Parameter	Xwa	XHH	HHV4	Pass/Fail					
 	 	μg/l	μg/l	μg/l	 		 			
Total Antimony	543	3.12	640	Pass					
Total Aluminum	320	1.84	-	N/A					
Total Cadmium	50	0.29	168	Pass					
Total Cyanide	0.389	0.00	140	Pass					
Total Iron	 	490	2.81	-	NA					
Total Mercury	0.02	0.00	0.153	Pass						
Total Arsenic	25	0.14	24	Pass						
Total Chromium	10	0.06	140468	Pass						
Total Copper	381	2.19	1300	Pass						
Total Nickel	526	3.02	4600	Pass						
Total Selenium	50	0.29	4200	Pass						
Total Zinc	250	1.44	26000	Pass						
Total Manganese	100000	574	100	Fail					
Total Thallium	50	0.29	0.47	Pass					
Total Lead	25	0.14	-	NA					
										
3 Health- and Ecology- Based Screening Levels from “EPA’s Risk Assessment for   the Listing Determination for Inorganic Chemical Manufacturing Waste -            
  August 2000”

4 Human Health for the Consumption of Organisms					

										
Conclusions									
										
          Parameter	AWQC	CWQC	HHV						
 	Pass/Fail	Pass/Fail	Pass/Fail						
Total Antimony	N/A	N/A	Pass						
Total Aluminum	Pass	Pass	N/A						
Total Cadmium	Fail	Fail	Pass						
Total Cyanide	Pass	Pass	Pass						
Total Iron	N/A	Pass	NA						
Total Mercury	Pass	Pass	Pass							
Total Arsenic	Pass	Pass	Pass							
Total Chromium	Pass	Pass	Pass							
Total Copper	Fail	Fail	Pass							
Total Nickel	Pass	Fail	Pass							
Total Selenium	Pass	Fail	Pass							
Total Zinc	Pass	Pass	Pass							
Total Manganese	N/A	N/A	Fail						
Total Thallium	Fail	Fail	Pass						
Total Lead	Pass	Fail	NA						
										
The facility failed the toxicity screening for cadmium, copper, nickel, lead, thallium, selenium, and manganese. For all these parameters, the facility failed the toxicity screening procedure due to the multiplication by a factor of 10 as a result of reporting less than 12 sample results.  To determine with certainty whether water quality standards for these parameters are being violated, the facility shall perform additional monitoring twice per month for twelve months with 24-hour composite samples of the effluent beginning the month following the effective issuance date of the permit or until 24 samples are received. All monitoring results shall be submitted to the Mississippi Environmental Quality Permit Board no later than the 28th day of the month following the completed collection of all 24 samples.  The NPDES permit may be modified to include cadmium, copper, nickel, lead, selenium, and thallium limits after screening is accomplished with the additional data.
Manganese may be present in the effluent due to historical activities on the site. Manganese was reported 10.0 mg/l at Outfall 201, which may not be representative of actual levels in the plant effluent because it was based on only one data point. As such, the monitoring is proposed in the permit to collect additional data on the frequency of occurrence and variability of this parameter in the plant’s effluent. Upon re-evaluation of the additional data, the permit may be modified and new limits will be established for this parameter, if justified during the next permit renewal.

ATTACHEMENT  C

REASONABLE POTENTIAL CALCULATIONS

REASONABLE POTENTIAL ANALYSIS (Outfall 101)

The following analysis and calculations are done based on EPA’s procedure for reasonable potential in Chapter 3 of the Technical Support Document for Water Quality Based Toxics Control EPA/505/2-90-001 (USEPA 1991). To determine if there is reasonable potential for the discharge to cause or contribute to an exceedance of water quality criteria for a given pollutant, EPA compares the maximum projected receiving water concentration to the criteria for that pollutant. If the projected receiving water concentration exceeds the criteria, there is reasonable potential to cause an excursion above the water quality criteria for a given pollutant, and if not, there is no reasonable potential for that pollutant. The procedure to determine the maximum projected receiving water concentration is discussed in the following section.

Data Set 1: Iron

There are 52 total samples collected for Iron during year 2012. Using given data, we have estimated monthly average effluent value for each month based on samples collected during that month. The average values for Jan-Dec for year 2012 are as follows:

Iron (mg/l): 1.75, 1.25, 1.40, 0.88, 1.12, 0.89, 0.75, 0.89, 0.37, 1.03, 1.41, 1.54. 

Since there are a limited number of data points available for iron, the desired Confidence Interval and Probability Basis chosen is 95/95. The 95th percentile is calculated by multiplying the maximum reported concentration (MRC) by a “reasonable potential multiplier” (RPM). The MRC is the highest monthly average effluent value and that value is 1.75 mg/l as listed above under given data set for iron.

RPM is the ratio of the 95th percentile concentration to the MRC. Using the equations in Section 3.3.2 of the TSD, the RPM is calculated based on the coefficient of variation (CV) and the number of the data points as follows. 

First, the percentile represented by the highest reported concentration is calculated. 

	Pn = (1 – confidence level)1/n		(1)

	where,
	Pn = the percentile represented by the highest reported concentration
	n = the number of samples in the data set
	confidence level = 95% = 0.95

Because the above data set for iron contained 52 effluent samples, 

	Pn = (1 – 0.95)1/52
	Pn = 0.94

This means, with 95% confidence, the MRC is greater than the 94th percentile. 

As said previously,

	RPM = C95/Cpn 				(2)

	where,
	C = exp(zσ – 0.5σ2)			(3)

	Where,
	σ2 = ln(CV2 + 1)			(4)
	σ = (σ2)1/2				(5)
	CV = coefficient of variation 
	z = the inverse of the normal cumulative distribution function at a given percentile

Note that for the data set where all values are above the specified reporting limit and the number of data points is 10<=n=<30, the data must be transformed into a lognormal format before standard statistics are applied to calculate CV as follows:

	CV = [exp(σ2y)-1]1/2			(6)
	  where,
	  σ2y = variance = Σ[(yi-μy)2]/n-1	
	  yi = ln(xi) for i=1,2,…n 		
	  μy = mean = Σ(yi)/n			
	  n = number of samples			

In the case of Iron:				
					
samples (n)	
Date	
mg/l (Ave.)	
yi = ln(xi)	(yi-μy)^2	
1	Jan-12	1.75	0.56	0.30	
2	Feb-12	1.25	0.22	0.05	
3	Mar-12	1.4	0.34	0.11	
4	Apr-12	0.88	-0.13	0.02	
5	May-12	1.12	0.11	0.01	
6	Jun-12	0.89	-0.12	0.02	
7	Jul-12	0.75	-0.29	0.09	
8	Aug-12	0.89	-0.12	0.02	
9	Sep-12	0.37	-0.99	1.00	
10	Oct-12	1.03	0.03	0.00	
11	Nov-12	1.41	0.34	0.11	
12	Dec-12	1.54	0.43	0.18	
					
	μy = 	   Σyi /n	0.01		
	σ2y = 	Σ[(yi-μy)2]/n-1	0.04		
					
By substituting the above values in equation (6), CV is calculated as follows:

	CV = [exp(σ2y)-1]1/2
	CV = [exp(0.04)-1]1/2
	CV = 0.20

Now, by using the calculated CV in equation (4) and (5), we can get σ2 & σ and substituting these values in equations (2) and (3) will give us RPM to determine maximum projected effluent concentration (MEC).

	σ2 = ln(CV2 + 1) = ln(0.432+1) = 0.037
	σ = (σ2)1/2 = 0.19
	z = 1.645 for the 95th percentile = 1.554 for the 94th percentile

	C95 = exp (zσ – 0.5σ2) = exp (1.645*0.19-0.5*0.037) = 1.34
	C94 = exp (zσ – 0.5σ2) = exp (1.554*0.19-0.5*0.037) = 1.32

	RPM = C95 / C94 = 1.34 / 1.32
	RPM = 1.017

The projected MEC is calculated by multiplying the highest reported effluent daily maximum concentration of 1.75 mg/l by the RPM:

	MEC (Ce) = (RPM)(MRC)			(7)

In the case of iron,

	MEC (Ce) = (1.017)(1.75) = 1.78 mg/l

The discharge has the reasonable potential to cause or contribute to an exceedance of the water quality criteria for iron if the above maximum projected concentration exceeds the water quality criterion for iron. The maximum projected receiving water concentration is calculated as follows;

	Cd = Ce-Cu  + Cu				(8)
                        D
	where,
	
Cd = Receiving water concentration downstream of the effluent discharge (that is, the 
        concentration at the edge of the mixing zone)
	Ce = Maximum projected effluent concentration 
  	Cu = Receiving water upstream concentration (zero)
	D = dilution factor = Qe + Qu		(9)
                                                   Qe
where,
	
Qe = Effluent flow rate (set equal to the average flow of the facility)
	Qu = Receiving water low flow rate upstream of the discharge (i.e., 7Q10) 

Since the receiving stream (i.e. drainage ditch) is ephemeral in nature, the 7Q10 flow is zero. 

Therefore, the dilution factor, D = 3.33+0 = 1
                                                                       3.33

	and, using this factor in equation (8), the chronic receiving water concentration for Iron is:

	Cd,Fe = (1.78 mg/l) – (0 mg/l)  + (0 mg/l)
                                           1
	Cd,Fe = 1.78 mg/l

The chronic water quality criterion for iron is 1.0 mg/l. Because the above projected receiving water concentration for iron is greater than the chronic criterion, there is reasonable potential for the chronic water quality standard to be exceeded. As a result, a water quality-based effluent limit is necessary for iron in this permit. 

REASONABLE POTENTIAL ANALYSIS (Outfall 201)

The following analysis and calculations are done based on EPA’s procedure for reasonable potential in Chapter 3 of the Technical Support Document for Water Quality Based Toxics Control EPA/505/2-90-001 (USEPA 1991). To determine if there is reasonable potential for the discharge to cause or contribute to an exceedance of water quality criteria for a given pollutant, EPA compares the maximum projected receiving water concentration to the criteria for that pollutant. If the projected receiving water concentration exceeds the criteria, there is reasonable potential to cause an excursion above the water quality criteria for a given pollutant, and if not, there is no reasonable potential for that pollutant. The procedure to determine the maximum projected receiving water concentration is discussed in the following section.

Data Set 1: Iron

There are 52 total samples collected for Iron during year 2012. Using given data, we have estimated monthly average effluent value for each month based on samples collected during that month. The average values for Jan-Dec for year 2012 are as follows:

Iron (mg/l): 0.545, 0.607, 1.68, 0.565, 0.245, 0.8045, 0.765, 0.872, 1.01, 0.528, 1.0375, 1.92.

Since there are a limited number of data points available for iron, the desired Confidence Interval and Probability Basis chosen is 95/95. The 95th percentile is calculated by multiplying the maximum reported concentration (MRC) by a “reasonable potential multiplier” (RPM). The MRC is the highest monthly average effluent value and that value is 1.92 mg/l as listed above under given data set for iron.

RPM is the ratio of the 95th percentile concentration to the MRC. Using the equations in Section 3.3.2 of the TSD, the RPM is calculated based on the coefficient of variation (CV) and the number of the data points as follows. 

First, the percentile represented by the highest reported concentration is calculated. 

	Pn = (1 – confidence level)1/n		(1)
	
where,
	Pn = the percentile represented by the highest reported concentration
	n = the number of samples in the data set
	confidence level = 95% = 0.95

Because above given data set for iron contained 52 effluent samples, 

	Pn = (1 – 0.95)1/52
	Pn = 0.94

This means, with 95% confidence, the MRC is greater than the 94th percentile. 

As said previously,

	RPM = C95/Cpn 				(2)

	where,
	C = exp(zσ – 0.5σ2)			(3)

	Where,
	σ2 = ln(CV2 + 1)			(4)
	σ = (σ2)1/2				(5)
	CV = coefficient of variation 
	z = the inverse of the normal cumulative distribution function at a given percentile

Note that for the data set where all values are above the specified reporting limit and the number of data points is 10<=n=<30, the data must be transformed into a lognormal format before standard statistics are applied to calculate CV as follows:

	CV = [exp(σ2y)-1]1/2			(6)
	  where,
	  σ2y = variance = Σ[(yi-μy)2]/n-1	
	  yi = ln(xi) for i=1,2,…n 		
	  μy = mean = Σ(yi)/n			
	  n = number of samples			

In the case of iron:				
					
samples (n)	
Date	
mg/l (Ave.)	
yi = ln(xi)	(yi-μy)^2	
1	Jan-12	0.545	-0.61	0.30	
2	Feb-12	0.607	-0.50	0.19	
3	Mar-12	1.68	0.52	0.34	
4	Apr-12	0.565	-0.57	0.26	
5	May-12	0.245	-1.41	1.81	
6	Jun-12	0.8075	-0.21	0.02	
7	Jul-12	0.765	-0.27	0.04	
8	Aug-12	0.872	-0.14	0.01	
9	Sep-12	1.01	0.01	0.00	
10	Oct-12	0.528	-0.64	0.33	
11	Nov-12	1.0375	0.04	0.01	
12	Dec-12	1.92	0.65	0.51	
					
	μy = 	   Σyi /n	-0.06		
	σ2y = 	Σ[(yi-μy)2]/n-1	0.08		
					
By substituting the above values in equation (6), CV is calculated as follows:

	CV = [exp(σ2y)-1]1/2
	CV = [exp(0.08)-1]1/2
	CV = 0.28

Now, by using calculated CV in equation (4) and (5), we can get σ2 & σ and substituting these values in equations (2) and (3) will give us RPM to determine maximum projected effluent concentration (MEC).

	σ2 = ln(CV2 + 1) = ln(0.282+1) = 0.08
	σ = (σ2)1/2 = 0.28
	z = 1.645 for the 95th percentile = 1.554 for the 94th percentile

	C95 = exp (zσ – 0.5σ2) = exp (1.645*0.28-0.5*0.08) = 1.53
	C94 = exp (zσ – 0.5σ2) = exp (1.554*0.28-0.5*0.08) = 1.49

	RPM = C95 / C94 = 1.53/1.49
	RPM = 1.03

The projected MEC is calculated by multiplying the highest reported effluent daily maximum concentration of 1.92 mg/l by the RPM:

	MEC (Ce) = (RPM)(MRC)			(7)

In the case of iron,

	MEC (Ce) = (1.03)(1.92) = 1.97 mg/l

The discharge has reasonable potential to cause or contribute to an exceedance of the water quality criteria for iron if the above maximum projected concentration exceeds the water quality criterion for iron. The maximum projected receiving water concentration is calculated as follows;

	Cd = Ce-Cu  + Cu				(8)
                        D
	where,
	
Cd = Receiving water concentration downstream of the effluent discharge (that is, the 
        concentration at the edge of the mixing zone)
	Ce = Maximum projected effluent concentration 
  	Cu = Receiving water upstream concentration (zero)
	D = dilution factor = Qe + Qu		(9)
                                                   Qe
	where,
	
Qe = Effluent flow rate (set equal to the average flow of the facility)
	Qu = Receiving water low flow rate upstream of the discharge (i.e., 7Q10) 

Since the receiving stream is the Tenn-Tom Waterway, the 7Q10 flow is 96.95 MGD. 

Therefore, the dilution factor, D = 8.04+96.95 = 13.06
                                                                         8.04

	and, using this factor in equation (8), the chronic receiving water concentration for Iron is:

	Cd,Fe = (1.97 mg/l) – (0 mg/l)  + (0 mg/l)
                                     13.06
	Cd,Fe = 0.151 mg/l

The chronic water quality criterion for iron is 1.0 mg/l. Because the above projected receiving water concentration for iron is less than the chronic criterion, there is no reasonable potential for the chronic water quality standard to be exceeded. As a result, a water quality-based effluent limit is not necessary at Outfall 201 for iron.

The following tables summarize the reasonable potential procedures for mercury and aluminum. The reasonable potential analysis has been evaluated for mercury and aluminum based on the highest monthly average and daily maximum concentrations reported in the recent years of facility’s operations. The analysis was conducted using zero for background receiving water concentrations for mercury and aluminum. Note that the reasonable potential calculation as shown above is based on the highest effluent monthly average concentration reported for Iron and is documented in the following table for informational purposes.