(Adopted: 05/07/76; CARB Ex. Ord. G-73: 02/01/77; Readopted: 

07/25/77; Amended: 08/24/94; Amended: mm/dd/yy)

MDAQMD Rule 464 464-1

Oil-Water Separators 

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RULE 464 

Oil-Water Separators 

(A) General 

(1) Purpose: 

(a) The purpose of this rule is to reduce emissions of Vvolatile Oorganic 

Ccompounds (VOCs) from Ooil-Wwater Sseparators. 

(2) Applicability: 

(a) This rule applies to Oil-Water Separators including Air Flotation Units as 

defined in this rule, and process units or containers used to store skimmed 

oil or tar from Oil-Water Separators. any structure or system which 

collects process effluent water contaminated with oil or other petroleum 

products and recovers 760 liters (201 gallons) a day or more of any 

petroleum products with a Reid vapor pressure of 25 mm Hg (0.5 pound 

per square inch) or greater. [Derived from SJVUAPCD Rule 4625. Size 

limitation moved to exemption section (D)(1)(b).]

(B) Definitions 

For the purposes of this rule only, the following definitions shall apply: 

(1) “Air Flotation Unit” – Equipment used to remove suspended matter, both oil and 

solid, from water by dissolving air under pressure and then releasing the air at 

atmospheric pressure in a tank or basin. [Derived from SJVUAPCD Rule 4625 

§3.1.] 

(2) “Air Pollution Control Officer” (APCO) - The person appointed to the position of Air 

Pollution Control Officer of the District pursuant to the provisions of California 

Health & Safety Code §40750 and his or her designee. [Derived from MDAQMD 

Rule 1113.] 

(3) “California Air Resources Board (CARB)” - The California State Air Resources 

Board, the Executive Officer of CARB and his or her authorized representative, 

the powers and duties of which are described in Part 2 of Division 26 of the 

California Health & Safety Code (commencing with Section 39500). [Derived 

from MDAQMD Rule 1113.] 

(4) “Control Device” - Any device for reducing emissions of VOC to the atmosphere. 
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(52) “Effluent Water” - Any wastewater generated as a byproduct of industrial 

processes and containing dissolved, particulate organic materials. Consists of a 

mixture of water with a petroleum product, including but not limited to the 

following: gasoline, kerosene, distillate fuel oils, residual fuel oils and lubricants. 

(63) “Fixed Cover” - Any cover made out of metal(s), polymer(s) or other material, 

and installed in a permanent position over the liquid. 

(74) “Floating Cover” - Any cover made out of metal(s), polymer(s) or other material, 

which is in contact with a liquid surface at all times. 

(85) “Forebay” - That section of a gravity-type separator which (a) receives the 

untreated, contaminated Eeffluent Wwater from the preseparator flume, and (b) 

acts as a header which distributes the influent to the separator channels. 

(96) “Fugitive Vapor Leak (Leak)” - The detection of 10,000500 ppm or greater above 

background (expressed as methane), measured at the interface of the component 

using an appropriate hydrocarbon analyzer when sampling is performed according 

to the procedures specified in EPA Method 21. [Derived from BAAQMD Rule 8-

8-204 definition for “vapor-tight.”]

(107) “Non-Contact Water Cooling Systems” - Any system which involves the cooling 

of organic vapors via coolant injected through piping. There is no contact 

between the cooling fluid and the vapors being cooled. 

(118) “Oil-Water Separator” - Any device or piece of equipment, which utilizes the 

difference in density between oil or petroleum products and water to remove the 

oil or associated chemicals from the water, or any device, such as a flocculation 

tank, clarifier, etc. that removes petroleum-derived compounds from wastewater. 

[Definition updated to match SJVUAPCD Rule 4624 definition for “Wastewater 

Separator” more closely.] 

(12) “Operator” – Includes, but is not limited to, any person who owns, leases, 

supervises, or operates a facility and/or equipment. [Derived from SJVUAPCD 

Rule 4625 §3.7.]

(139) “Organic Materials” - Chemical compounds of carbon, excluding carbon 

monoxide, carbon dioxide, metallic carbides, metallic carbonates and ammonium 

carbonate. 

(140) “Organic Vapors” - Chemical compounds of carbon, excluding carbon monoxide, 

carbon dioxide, metallic carbides, metallic carbonates and ammonium carbonate 

in their gaseous state. 

(151) “Overall Control Efficiency” - Is tThe product of the capture efficiency multiplied 

by the control efficiency; the weight per unit time of VOC removed by a control 

device divided by the weight per unit time of VOC emitted by an emission source, 

expressed as a percentage. 
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(162) “Petroleum Products” - Any crude oil or oil distillate derived from tar sands, shale 

or coal, including, but not limited to gasoline, kerosene, distillate fuel oils, 

residual fuel oils and lubricants. 

(173) “Reid Vapor Pressure” - The absolute vapor pressure of volatile crude oil and 

volatile nonviscous petroleum liquids, except liquified petroleum gases, as 

determined by ASTM D 323-89. 

(18) “United States Environmental Protection Agency” (USEPA) - The United States 

Environmental Protection Agency, the Administrator of the USEPA and his or her 

authorized representative. [Derived from MDAQMD Rule 1113.]

(194) “Vapor Recovery System” - A vapor-gathering system capable of collecting VOC 

vapors and gases emitted during the operation of equipment. 

(2015) “Volatile Organic Compound (VOC)” - Any volatile compound containing at 

least one atom of carbon, excluding methane, carbon monoxide, carbon dioxide, 

carbonic acid, metallic carbides or carbonates, and ammonium carbonate, and 

those compounds listed in 40 CFR 51.100(s). containing at least one atom of 

carbon, except for the following: [Derived from MDAQMD Rule 1113 for 

consistency.] 

methane 

carbon monoxide, 

carbon dioxide, 

carbonic acid, 

metallic carbides or carbonates, 

ammonium carbonate, 

1,1,1-trichloroethane, 

methylene chloride, 

trichlorofluoromethane (CFC-11), 

dichlorodifluoromethane (CFC-12), 

chlorodifluoromethane (HCFC-22), 

trifluoromethane (HFC-23) 

1,1,1- trichloro-2,2,2-trifluoroethane (CFC-113), 
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1-chloro-1,1-difluoro-2-chloro-2,2-difluoroethane (CFC-114), 

chloropentafluoroethane (CFC-115), 

2,2-dichloro-1,1,1-trifluoroethane (HCFC-123), 

2-chloro-1,1,1,2-tetrafluoroethane (HCFC 124), 

pentafluoroethane (HFC-125), 

1,1,2,2-tetrafluoroethane (HFC-134), 

1,1,1,2-tetrafluoroethane (HFC-134a), 

1,1-dichloro-1-fluoroethane (HCFC-141b), 

1-chloro-1,1-difluoroethane (HCFC-142b), 

1,1,1-trifluoroethane (HFC-143a), 

1,1-difluoroethane (HFC-152a), 

and the following four classes of perfluorocarbon (PFC) compounds: 

(i) cyclic, branched, or linear, completely fluorinated alkanes, 

(ii) cyclic, branched, or linear, completely fluorinated ethers with no unsaturations, 

(iii) cyclic, branched, or linear, completely fluorinated tertiary amines with no 

unsaturations, and 

(iv) saturated perfluorocarbons containing sulfur with sulfur bonds only to carbon and 

fluorine. 

(C) General Requirements 

(1) Fugitive Vapor Control Devices 

(a) A person shall not use any Ooil-Wwater Sseparator subject to the 

provisions of Section (A)(2), unless it has been equipped with one of the 

following vapor loss control devices, except when gauging or sampling is 

taking place: 

(i) A Ffixed Ccover with all openings sealed and totally enclosing the 

liquid contents of the compartment, except for such breathing vents 

as are structurally necessary; or 

(ii) Aa Ffloating Ccover or double-deck type cover, equipped with 

with closure seals that have no holes or tears, installed and 
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maintained so that gaps between the compartment wall and seal 

shall not exceed one-eighth inch for an accumulative length of 97 

percent of the perimeter of the tank, and shall not exceed one-half 

inch for an accumulative length of the remaining three percent of 

the tank. No gap between the compartment wall and the seal shall 

exceed one-half inch; to enclose any space between the cover's 

edge and compartment wall or

(iii) Route all vapors to a Ccontrol Ddevice with an Ooverall Ccontrol 

Eefficiency (collection and control efficiencies) of at least 950

percent by weight of VOCs, measured according to the test method 

specified in Section (G)(34). [Overall control efficiency increased 

to meet RACT limit in SJVUAPCD Rule 4625 §5.1.3. Updated rule 

citation.]

(b) Any oil-water separator subject to this rule shall provide the following 

vapor loss control device: 

(i) Aa Ffixed Ccover for all Fforebays, such that no liquid surface is 

exposed to the atmosphere.

(c) Skimmed oil or tar removed from Oil-Water Separators shall be either 

charged to process units with feed or transferred to a container with a 

control system with at least 90 percent control efficiency by weight. A 

Control Device must be under District permit. [Control efficiency added to 

meet RACT requirement in SJVUAPCD Rule 4625 §5.4.]

(2) Requirements for Covers 

(a) Covers for oil-water separators shall meet the following requirements: 

(i) The cover material shall be impermeable to VOCs, and free from 

holes or openings. 

(ii) Any gauging or sampling devices on the compartment cover shall 

be covered. The latter cover shall be kept closed, with no visible 

gaps between the cover and the compartment, except when the 

sampling device is being used. 

(iii) Hatches on covers shall be kept closed and free of gaps, except 

when opened for inspection, maintenance or repair. 

(iv) The perimeter of a cover, except for a Ffloating Ccover, shall form 

a seal free of gaps with the foundation to which it is installed. 

(3) Fugitive Vapor Leak Monitoring 

(a) When an instrument reading of 10,000500 parts per million [(ppm)] or 

greater is measured, a leak has been detected and the reading shall 

constitute a violation of this rule. [Updated for RACT.]
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(D) Exemptions 

(1) The provisions of this rule shall not apply to:

(a) Ssegregated storm water runoff drain systems or to non-contact cooling 

water systems, where applicable.

(b) Any system which collects and processes effluent or process water 

contaminated with oil or other petroleum products and recovers less than 

760 liters (201 gallons) a day or more of oil or other petroleum products 

(c) Oils, tars and petroleum products with a Reid Vapor Pressure of less than 

25 mm Hg (0.5 pound per square inch). 

[(D)(1)(b) and (c) relocated from applicability section and separated to address 

comment from Searles Valley Minerals of 4/9/14.]

(E) Monitoring 

(1) Monitoring for Ffugitive Vvapor Lleaks shall be performed on a monthly basis 

and in accordance to test method specified in Section (G)(1). Monitoring records 

shall be kept on file as prescribed in Section (F)(1). 

(2) Monitoring of the control device shall be performed on an annual basis and in 

accordance to the test method specified in Section (G)(4). 

(F) Record Keeping 

(1) A log of the monthly leak inspection shall be kept on file at the facility. The log 

shall record, at a minimum, the following information: 

(a) Date of the inspection. 

(b) Findings, (statement of no leaks or the location, nature and severity of the 

leak(s)) including instrument readings.Documentation of all written or 

machine recorded operator inspections, VOC measurements including 

corresponding background levels, source tests, repairs, replacements, and 

reinspection records. [Updated to more comprehensive recordkeeping 

requirements in SCAQMD Rule 1176 §(g)(C)(i).]

(c) Leak determination method (shall be in accordance to the test method 

specified in Section (G)(1), using an appropriate hydrocarbon analyzer). 

(d) Corrective action (date of leak repair and a written justification for any 

repair interval in excess of 15 calendar days). 
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(e) Inspector's name and signature. 

(2) Any person using an emission control device/system pursuant to Section (C)(1) as 

a means of complying with provisions of this rule shall maintain records of key 

system operating and maintenance data for the purpose of demonstrating 

continuous compliance during periods of emission producing activities. The data 

shall be recorded in a manner as prescribed by the District. 

(3) Any facility claiming exemption pursuant to Sections (D)(1)(a) or (DA)(12)(b) of 

this rule shall keep records to substantiate the claimed exempt status. [Rule 

citations updated.]

(4) Any record required or produced pursuant to this rule shall be retained on site for 

a minimum of two five (5) years and shall be made available to the APCO upon 

request. [Updated to meet SJVUPACD Rule 4625 §6.2.3.]

(G) Test Methods For Compliance Verification 

A violation determined by any one of these test methods shall constitute a violation of the 

rule: 

(1) Fugitive Vapor Leaks - Detection of VOCs - EPA Method 21 shall be used to 

determine compliance with this rule in regards to fugitive or VOC leaks. 

Instrument shall be calibrated with Method 21 using zero air (less than 10 parts 

per million ([ppm)] of hydrocarbon in air) with a mixture of methane or n-hexane. 

(2) Determination of Exempt Compounds Content - Determination of the content of 

exempt compounds in solvents or any diluents shall be determined by ASTM D 

4457-85. Perfluorocarbon compounds shall be assumed to be absent from a 

product or process unless a manufacturer or facility operator identifies the specific 

individual compounds (from the broad classes of perfluorocarbon compounds) 

and the amounts present in the product or process and identifies a validated test 

method which can be used to quantify the specific compounds. [Removed test 

method as superfluous. If test method for determination of exempt compounds is 

needed, it can be determined under §(G)(4).]

(23) Determination of Reid Vapor Pressure - Shall be determined by measuring the 

Reid Vapor pressure in accordance with Test Method for Vapor Pressure for 

Petroleum Products (Reid Method), ASTM D 323-82 (April 8, 1987). 

(34) Control Device Efficiency - Determining the destruction or removal efficiency of 

a control device shall be: 

(a) Ffor systems utilizing add-on control equipment, EPA Method 25 or 25A, 

as applicable and analysis of halogenated exempt compounds shall be by 

ARB Method 22. [Additional test method from SJVUAPCD Rule 4625 

§6.1.1.]
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(b) Ffor incinerators or catalytic incinerators, EPA Method 25, unless the 

concentration of VOC in the outlet stream is below 50 ppm as carbon, in 

which case EPA Method 25A shall be used.

(c) Where add-on control equipment is utilized, collection efficiency shall be 

determined by EPA document “Model Regulatory Language for Capture 

Efficiency Testing,” August 3, 1990. [Derived from SJVUAPCD Rule 

4625 §6.1.2.] 

(4) Any applicable alternative test method may be used so long as such method has 

been approved by USEPA, CARB and the APCO. [Derived from AVAQMD Rule 

1124 §(E)(3)(f). This provision allows the District to use the most recent 

approved ASTM method and allows use of other official test methods if 

necessary.]

[SIP: See SIP Table at 

http://www.mdaqmd.ca.gov/Modules/ShowDocument.aspx?documentid=45 ] 

[SIP: Approved 9/27/95, 60 FR 49722, 40 CFR 52.220(c)(202)(i)(D)(1); Approved 9/8/78, 43 

FR 40011, 40 CFR 52.220(c)(39)(iv)(C); Approved 6/14/78, 43 FR 25684, 40 CFR 52.220 

(c)(32)(iv)(A)]