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RULE 4625 WASTEWATER SEPARATORS (Adopted April 11, 1991; Amended May 21, 

1992; Amended December 17, 1992; Amended December 15, 2011) 

1.0 Purpose 

 The purpose of this rule is to limit VOC emissions from wastewater separators by 

requiring vapor loss control devices, recordkeeping, inspection and test methods. 

2.0 Applicability 

 This rule applies to wastewater separators including air flotation units as defined in this 

rule. The requirements of this rule only apply to the separation of crude oil and water 

after custody transfer. 

3.0 Definitions 

 3.1 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. 

3.2 APCO: the Air Pollution Control Officer of the San Joaquin Valley Unified Air 

Pollution Control District, or any person authorized to act on behalf of the APCO. 

3.3 ARB: California Air Resources Board as established by the California Health and 

Safety Code Section 39510, or any person authorized to act on its behalf. 

3.4 Custody transfer: the physical and contractual ownership transfer of produced 

fluids from an oil producer to another entity. 

 3.5 District: San Joaquin Valley Unified Air Pollution Control District. 

3.6 EPA: United States Environmental Protection Agency. 

3.7 Operator: includes but is not limited to any person who owns, leases, 

supervises, or operates a facility and/or equipment. 

3.8 Volatile Organic Compound (VOC): as defined in Rule 1020 (Definitions). 

 3.9 Wastewater Separator: any device or piece of equipment that is used to remove 

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

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

wastewater. 
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 3.10 Wastewater Separator Forbay: that section of a gravity-type wastewater 

separator which receives the untreated, oil-water waste from the preseparator 

flume; and acts as a header which distributes the influent to the separator 

channels. 

4.0 [Reserved] 

 

5.0 Requirements 

 5.1 A person shall not use any compartment of any vessel or device operated for the 

recovery of oil or tar from effluent water, from any equipment which processes, 

refines, stores or handles petroleum or coal tar products unless such 

compartments are equipped with one of the following vapor loss control devices, 

except when gauging or sampling is taking place: 

 5.1.1 A solid cover with all openings sealed and totally enclosing the liquid 

contents of the compartment, except for such breathing vents as are 

structurally necessary; or 

 5.1.2 A floating pontoon or double-deck type cover, equipped with closure 

seals that have no holes or tears, installed and 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 perimeter of the tank. No gap between 

the compartment wall and the seal shall exceed one-half inch; or 

 5.1.3 A vapor recovery system with a combined collection and control 

efficiency of at least 95 percent by weight. 

 5.2 Any gauging and sampling device in the compartment cover shall be equipped 

with a cover or lid. The cover shall be in a closed position at all times, except 

when the device is in actual use. 

 5.3 All wastewater separator forbays shall be covered. 

 

 5.4 Skimmed oil or tar removed from wastewater separating devices 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. 

 

 
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 5.5 Inspection 

 On and after January 1, 2013: 

5.5.1 An operator complying with Section 5.1.1 shall visually inspect, the 

manholes, roof hatches, or other openings on the fixed roof, at least once 

every 12 months after the tank is initially filled with an organic liquid. 

No holes, tears, or other openings are allowed that would permit the 

escape of hydrocarbon vapors. Any defects found are violations of this 

rule. 

5.5.2 An operator complying with Section 5.1.2 shall visually inspect, the 

internal floating roof and its appurtenant parts, fittings, etc., and the 

primary seal and/or secondary seal at least once every 12 months after 

the tank is initially filled with an organic liquid. Other than the gap 

criteria specified by this rule, no holes, tears, or other openings are 

allowed that would permit the escape of hydrocarbon vapors. Any 

defects found are violations of this rule. 

5.5.3 An operator complying with Section 5.1.3 shall visually inspect the 

manholes, roof hatches, other openings, fittings, etc., at least once every 

12 months after the tank is initially filled with an organic liquid. No 

holes, tears, or other openings are allowed that would permit the escape 

of hydrocarbon vapors. Any defects found are violations of this rule. 

6.0 Administrative Requirements 

 6.1 Test Methods 

Compliance with the requirements of Section 5.0 shall be determined in accordance 

with the following test methods or their equivalents as approved by the EPA and the 

APCO:

 6.1.1 Efficiency of VOC control device shall be determined by EPA Test 

Method 25 and analysis of halogenated exempt compounds shall be by 

ARB Method 422. 

 6.1.2 Where add-on control equipment is utilized, collection efficiency shall be 

determined by the EPA document "Model Regulatory Language for 

Capture Efficiency Testing," August 3, 1990. 

 
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6.2 Recordkeeping 

 Any operator subject to Section 5.0 of this rule shall: 

 6.2.1 Maintain records of the type and location of each wastewater separator. 

 

 6.2.2 Record the date of inspections pursuant to Section 5.5. 

 

 6.2.3 Maintain required records for at least five years and made available to 

the APCO, ARB, and EPA upon request.