PRETREATMENT RATIONALE FOR RENEWAL

Westlake Chemicals and Vinyls LLC
Monroe
Aberdeen, MS
Water I Branch

MSP091451
SIC: 4011
November 2025
Permit Engineer: Samar Patel

I.	FACILITY INFORMATION

A.	Nature of Business: Production of PVC resins, compounds, and plasticizers

B.	Process Wastewater Description:  Wastewater results from the following sources: 1) process wastewater, 2) non-contact cooling water, 3) boiler feed water, 4) storm water, and 5) wastewater resulting from initial water treatment.  Treatment includes above-ground solid separating unit, air strippers for removal of vinyl chloride, an equalization pond, 3 rotating biological contactors, 2 aerated lagoons, and a polishing pond.

C.	Proposed Flowrate: 2.5 MGD maximum

D.	Applicable Federal Guidelines: 40 CFR 403 General Pretreatment Regulations and 40 CFR 414 Organic Chemicals, Plastics, and Synthetic Fibers (OCPSF), specifically 40 CFR 414.45, 40 CFR 414.85, and 40 CFR 414.111

II.	RECEIVING POTW INFORMATION

A.	POTW and Permit Number: Aberdeen POTW East (MS0055581)

B.	POTW Treatment Type: Aerated lagoon with disinfection by chlorination followed by dechlorination

C.	POTW Design Flowrate: 5.2 MGD, permitted monthly average flow of 4.0 MGD

D.	POTW Receiving Stream: Tennessee-Tombigbee Waterway (recreational classification)

E.	POTW Receiving Stream 7Q10 (Q7/10): 337 cfs (218 MGD)

I.	
III.	PROPOSED PERMIT LIMITATIONS

Parameter	Reported Max. Conc. 
mg/L	Categorical Limits	Current Permit Limits	Proposed Permit Limits	Sampling Frequency 	Sample Type	Basis of Decision1	
		Max 
lb/day (mg/L)	Avg. lb/day (mg/L)	Max. lb/day (mg/L)	Avg. lb/day
(mg/L)	Max. lb/day (mg/L)	Avg. 
lb/day (mg/L)				
Flow	2.183
 MGD	--	--	2.5
 MGD	Report	2.5
MGD	Report
	Continuously	Continuous Recorder	Engr Judgment & Existing permit 	
pH, S.U.	6.51(Min.) 7.69(Max)	--	--	9.0 S.U.
(Max)	6.0 S.U. (Min)	9.0 S.U.
(Max)	6.0 S.U. (Min)	Weekly	Grab	Existing Permit & TBEL	
BOD5
lb/day (mg/l)	703.6
(60)	--	--	Report
 (60)	Report
(40)	Report
(60)	Report
(40)	Weekly	24-hr composite	Existing permit & POTW	
TSS
lb/day (mg/l)	789.8
(58)	--	--	Report
 (100)	Report
 (90)	Report
 (100)	Report
 (90)	Weekly	24-hr composite	Existing permit & POTW	
Zinc 
lb/day (mg/l)	0.14
(0.0203)	27.6 (2.61)	11.1 (1.05)	4.08 (Report)	1.63 
(Report)	4.08 
(Report)	1.63 
(Report)	One / six months	Grab	Existing Permit & TBEL	
Acenaphthene	ND	0.498
(Report)	0.201
(Report)	0.498
(Report)	0.201
(Report)	0.498 (Report)	0.201
(Report)	One / six months	Grab	Existing Permit & TBEL	
Anthracene	ND	0.498
(Report)	0.201
(Report)	0.498
(Report)	0.201
(Report)	0.498 (Report)	0.201
(Report)	One / six months	Grab	Existing Permit & TBEL	
Benzene  
	ND
	1.42
(Report)	0.604
(Report)	1.42
(Report)	0.604
(Report)	1.42 (Report)	0.604
(Report)	One / six months	Grab	Existing Permit & TBEL	
Bis (2-ethylhexyl) phthalate	ND
	2.73
(Report)	1.01
(Report)	2.73
(Report)	1.01
(Report)	2.73
(Report)	1.01
(Report)	One / six months	Grab	Existing Permit & TBEL	
Carbon Tetrachloride	ND
	4.02
(Report)	1.50
(Report)	4.02
(Report)	1.50
(Report)	4.02
(Report)	1.50
(Report)	One / six months	Grab	Existing Permit & TBEL	
Chlorobenzene	ND
	4.02
(Report)	1.50
(Report)	4.02
(Report)	1.50
(Report)	4.02
(Report)	1.50
(Report)	One / six months	Grab	Existing Permit & TBEL	
Chloroethane	ND
	3.12 (Report)	1.17 (Report)	3.12 (Report)	1.17 (Report)	3.12 (Report)	1.17 (Report)	One / six months	Grab	Existing Permit & TBEL	
Chloroform	ND
	3.442 (Report)	1.18 (Report)	3.442 (Report)	1.18 (Report)	3.442 (Report)	1.18 (Report)	One / six months	Grab	Existing Permit & TBEL	
Di-n-butyl Phthalate	ND
	0.455 (Report)	0.212 (Report)	0.455 (Report)	0.212 (Report)	0.455 (Report)	0.212 (Report)	One / six months	Grab	Existing Permit & TBEL	
1,2-Dichlorobenzene	ND
	8.41 (Report)	2.08 (Report)	8.41 (Report)	2.08 (Report)	8.41 (Report)	2.08 (Report)	One / six months	Grab	Existing Permit & TBEL	
1,3-Dichlorobenzene	ND
	4.02 (Report)	1.50 (Report)	4.02 (Report)	1.50 (Report)	4.02 (Report)	1.50 (Report)	One / six months	Grab	Existing Permit & TBEL	
1,4-Dichlorobenzene	ND
	4.02 (Report)	1.50 (Report)	4.02 (Report)	1.50 (Report)	4.02 (Report)	1.50 (Report)	One / six months	Grab	Existing Permit & TBEL	
1,1-Dichloroethane	ND
	0.625 (Report)	0.233 (Report)	0.625 (Report)	0.233 (Report)	0.625
(Report)	0.233 (Report)	One / six months	Grab	Existing Permit & TBEL	
1,2-Dichloroethane	ND
	6.08 (Report)	1.91 (Report)	6.08 (Report)	1.91 (Report)	6.08 (Report)	1.91 (Report)	One / six months	Grab	Existing Permit & TBEL	
1,1-Dichloroethylene	ND
	0.636 (Report)	0.233 (Report)	0.636 (Report)	0.233 (Report)	0.636 (Report)	0.233 (Report)	One / six months	Grab	Existing Permit & TBEL	
1,2-trans-Dichloroethylene	ND
	0.699 (Report)	0.265 (Report)	0.699 (Report)	0.265 (Report)	0.699
(Report)	0.265 (Report)	One / six months	Grab	Existing Permit & TBEL	
1,2-Dichloropropane	ND
	8.41 (Report)	2.08 (Report)	8.41 (Report)	2.08 (Report)	8.41 (Report)	2.08 (Report)	One / six months	Grab	Existing Permit & TBEL	
1,3 Dichloropropylene	ND
	8.41 (Report)	2.08 (Report)	8.41 (Report)	2.08 (Report)	8.41 (Report)	2.08 (Report)	One / six months	Grab	Existing Permit & TBEL	
Diethyl Phthalate	ND
	1.20
(Report)	0.487 (Report)	1.20 (Report)	0.487 (Report)	1.20 (Report)	0.487 (Report)	One / six months	Grab	Existing Permit & TBEL	
Dimethyl Phthalate	ND
	0.498 (Report)	0.201 (Report)	0.498 (Report)	0.201 (Report)	0.498 (Report)	0.201 (Report)	One / six months	Grab	Existing Permit & TBEL	
4,6-Dinitro-o-cresol	ND
	0.045 (Report)	0.013 (Report)	0.045 (Report)	0.013 (Report)	0.045 (Report)	0.013 (Report)	One / six months	Grab	Existing Permit & TBEL	
Ethylbenzene
	ND
	4.02 (Report)	1.50 (Report)	4.02 (Report)	1.50 (Report)	4.02 (Report)	1.50 (Report)	One / six months	Grab	Existing Permit & TBEL	
Fluoranthene	ND
	0.572 (Report)	0.233 (Report)	0.572 (Report)	0.233 (Report)	0.572 (Report)	0.233 (Report)	One / six months	Grab	Existing Permit & TBEL	
Fluorene	ND
	0.498 (Report)	0.201 (Report)	0.498 (Report)	0.201 (Report)	0.498 (Report)	0.201 (Report)	One / six months	Grab	Existing Permit & TBEL	
Hexachlorobenzene	ND
	8.41 (Report)	2.08 (Report)	8.41 (Report)	2.08 (Report)	8.41 (Report)	2.08 (Report)	One / six months	Grab	Existing Permit & TBEL	
Hexachlorobutadiene	ND	4.02 (Report)	1.50 (Report)	4.02 (Report)	1.50 (Report)	4.02 (Report)	1.50 (Report)	One / six months	Grab	Existing Permit & TBEL	
Hexachloroethane	ND	8.41 (Report)	2.08 (Report)	8.41 (Report)	2.08 (Report)	8.41 (Report)	2.08 (Report)	One / six months	Grab	Existing Permit & TBEL	
Methyl Chloride	ND	3.12 (Report)	1.17 (Report)	3.12 (Report)	1.17 (Report)	3.12 (Report)	1.17 (Report)	One / six months	Grab	Existing Permit & TBEL	
Methylene Chloride	ND	1.80 (Report)	0.381 (Report)	1.80 (Report)	0.381 (Report)	1.80 (Report)	0.381 (Report)	One / six months	Grab	Existing Permit & TBEL	
Naphthalene	ND	0.498 (Report)	0.201 (Report)	0.498 (Report)	0.201 (Report)	0.498 (Report)	0.201 (Report)	One / six months	Grab	Existing Permit & TBEL	
Nitrobenzene	ND	67.8 (Report)	23.7 (Report)	67.8 (Report)	23.7 (Report)	67.8 (Report)	23.7 (Report)	One / six months	Grab	Existing Permit & TBEL	
2-Nitrophenol	ND	2.45 (Report)	0.688 (Report)	2.45 (Report)	0.688 (Report)	2.45 (Report)	0.688 (Report)	One / six months	Grab	Existing Permit & TBEL	
4-Nitrophenol	ND	6.10 (Report)	1.72 (Report)	6.10 (Report)	1.72 (Report)	6.10 (Report)	1.72 (Report)	One / six months	Grab	Existing Permit & TBEL	
Phenanthrene	ND	0.498 (Report)	0.201 (Report)	0.498 (Report)	0.201 (Report)	0.498 (Report)	0.201 (Report)	One / six months	Grab	Existing Permit & TBEL	
Pyrene	ND	0.508 (Report)	0.212 (Report)	0.508 (Report)	0.212 (Report)	0.508 (Report)	0.212 (Report)	One / six months	Grab	Existing Permit & TBEL	
Tetrachloroethylene	ND	1.74 (Report)	0.551 (Report)	1.74 (Report)	0.551 (Report)	1.74 (Report)	0.551 (Report)	One / six months	Grab	Existing Permit & TBEL	
Toluene           	ND	0.784 (Report)	0.297 (Report)	0.784 (Report)	0.297 (Report)	0.784 (Report)	0.297 (Report)	One / six months	Grab	Existing Permit & TBEL	
1,2,4-Trichlorobenzene	ND	8.41 (Report)	2.08 (Report)	8.41 (Report)	2.08 (Report)	8.41 (Report)	2.08 (Report)	One / six months	Grab	Existing Permit & TBEL	
1,1,1-Trichloroethane	ND	0.625 (Report)	0.233 (Report)	0.625 (Report)	0.233 (Report)	0.625 (Report)	0.233 (Report)	One / six months	Grab	Existing Permit & TBEL	
1,1,2-Trichloroethane	ND	0.636 (Report)	0.233 (Report)	0.636 (Report)	0.233 (Report)	0.636
(Report)	0.233 (Report)	One / six months	Grab	Existing Permit & TBEL	
Trichloroethylene	ND	0.731 (Report)	0.275 (Report)	0.731 (Report)	0.275 (Report)	0.731 (Report)	0.275 (Report)	One / six months	Grab	Existing Permit & TBEL	
Vinyl Chloride	ND	1.82 (Report)	1.03 (Report)	1.82 (Report)	1.03 (Report)	1.82 (Report)	1.03 (Report)	One / six months	Grab	Existing Permit & TBEL	
* ND = Non-detect

IV.	STATEMENT OF BASIS (narrative)

1 The POTW design flow is 5.2 MGD, therefore the POTW is well able to handle the facility’s proposed flow of 2.5 MGD. The parameter limits for BOD5 and TSS were established by the POTW during the previous permitting actions and will be continued in the proposed permit. Per application, these pollutants are found well below the permitted levels and, as such, the requirements to monitor for these conventional pollutants will remain unchanged in the proposed permit. The long-term average values reported in the application for BOD5 and TSS are 17.46 mg/l and 21.3 mg/l, respectively.

2 The categorical limits, found in 40 CFR 414.111, were evaluated using a flow rate of 1.27 MGD.  The former average flow was used because the facility has not had issues meeting the categorical limitations evaluated at this rate.  Because Westlake mostly does not detect the categorical pollutants, only semiannual testing is required.
•	The only categorical limits not utilized in this permit are those for cyanide, lead, and zinc.  Cyanide and lead are not permitted for the following reasons: 
o	Westlake does not have any metal-bearing streams or cyanide-bearing waste streams listed in 40 CFR 414, Appendix A.  
o	Per application, past sampling resulted in non-detects or very low concentrations.  Westlake does usually detect some zinc in their effluent; therefore, these limits will remain the same since they are protective of water quality.