UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

REGION IX AIR DIVISION

Technical Support Document 

for

EPA’s Direct Final Rulemaking

for the

California State Implementation Plan

Mojave Desert Air Quality Management District 

 

Rule 464 Oil-Water Separators

Prepared by: James Shears

Reviewed by: Andrew Steckel

February 2015
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RULE IDENTIFICATION 

Agency: Mojave Desert Air Quality Management District 

(MDAQMD)

SIP Approved Rule: Rule 464 – Oil-Water Separators

Amended – August 24, 1994

Submitted – October 19, 1994

EPA Approved – September 27, 1995 (60 FR 49772)

Subject of this TSD: Rule 464 – Oil-Water Separators

Amended – June 23, 2014

Submitted – November 6, 2014

RULE SUMMARY –

MDAQMD Rule 464, Oil-Water Separators, is designed to limit VOC emissions 

from oil-water separators consistent with EPA design criteria guidance described 

in the Control Techniques Guidance (CTG) document titled, “Control of Refinery 

Vacuum Producing Systems, Wastewater Separators and Process Unit 

Turnarounds” (EPA – 450/2-77-025). While this CTG states applicability to 

petroleum refinery sources, Rule 464 does not specify the refinery industry 

because this industry is non-existent in the MDAQMD. It applies instead to similar 

wastewater separator equipment used in other industries. To reflect current 

RACT, Rule 464, as amended, will update the rule applicability, definitions, 

floating cover seal tolerances, control device efficiency, fugitive vapor leak 

violation limits, container storage of skimmed oil and tar, recordkeeping, and test 

methods.

MDAQMD regulates portions of Riverside County and San Bernardino County. 

Portions of the MDAQMD were classified as severe nonattainment for the 1997 8-

hour ozone NAAQS (see 40 CFR part 81). Regarding Rule 464, because the 

District had an existing SIP rule for this CTG category, the District committed to 

adopting an updated RACT rule for oil-water separators as part of its 2006 RACT 

SIP.1 

The following are the significant provisions of Rule 464. 

1. Section (A)(2) updates the rule’s applicability to oil-water separators 

including air flotation units, and process units or containers used to store 

skimmed oil or tar from oil-water separators. The size limitation for 

exempted containers has been moved to the exemption section, Section 

(D).

 

1 8-Hour Reasonably Available Control Technology – State Implementation Plan Analysis (RACT SIP 

Analysis), August 2006. 
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2. Section (C)(1)(a)(ii) is modified to specify floating cover or double-deck 

type cover seal tolerances.

3. Section (C)(1)(a)(iii) updates the overall control efficiency from 90% to 95% 

to meet RACT.

4. Section (C)(1)(c) has been added to cover oil or tar skimmed from oil-water 

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

with a control system with at least 90% control efficiency by weight in order 

to meet RACT. 

5. Section (C)(3) reduces fugitive leak violations from 10,000 ppm to 500 

ppm.

6. Sections (D)(1)(b) and (D)(1)(c) clarifies the exemptions for systems 

collecting less than 760 liters/day or for systems with a RVP of less than 25 

mm Hg. 

7. Section (F)(4) updates the recordkeeping requirement from 2 years to 5 

years.

8. Section (G)(3)(a) and (c) includes additional test methods.

EVALUATION CRITERIA - The following criteria were used to evaluate the 

submitted rule. 

1. Enforceability - The Bluebook (Issues Relating to VOC Regulation 

Cutpoints, Deficiencies, and Deviations, EPA, May 25, 1988) and the Little 

Bluebook (Guidance Document for Correcting Common VOC & Other Rule 

Deficiencies, (EPA Region 9, August 21, 2001) were used to help evaluate 

compliance with the CAA §110(a)(2)(A) requirement for enforceability. 

2. Stringency - EPA’s CTG titled, “Control of Refinery Vacuum Producing 

Systems, Wastewater Separators and Process Unit Turnarounds” (EPA –

450/2-77-025, October 1977), and other state and local rules for this 

category were used to help evaluate the RACT requirements of CAA 

§182(b)(2) and §182(f). 

3. SIP Relaxation – Where previous versions of rules have been SIP 

approved, new submittals must comply with CAA §110(l) and §193 

regarding SIP relaxation.

EPA EVALUATION – The submitted MDAQMD Rule 464 is more stringent than 

the CTG and meets RACT requirements. The overall control efficiency of the oilwater separator vapor control device is increased from 90% to 95% by weight. A

new provision is added that skimmed oil or tar removed from the oil-water 
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separator transferred to a secondary system shall have a 90% control efficiency by 

weight. Fugitive vapor leak monitoring now defines a leak at 500 ppm or more 

instead of 10,000 ppm. More extensive documentation/recordkeeping is now 

required of all written or machine-recorded operator inspections, VOC 

measurements including background levels, source tests, repairs, replacements 

and re-inspections. Alternative test methods are allowed as long as the methods 

have been approved by EPA, CARB and the APCO. 

1. The rule requirements and applicability are clear, and recordkeeping, 

reporting and other provisions sufficiently ensure that affected sources and 

regulators can evaluate and determine compliance with Rule 464. 

2. The submitted rule is as stringent as other air district rules, such as the San 

Joaquin Valley United Air Pollution Control District Rule 4625 and the South 

Coast Air Quality Management District Rule 1176, for this category, and it is 

more stringent than EPA’s 1977 CTG. As a result, we have determined that 

this rule fulfils RACT requirements. 

3. We propose to determine that our approval of the submittal would comply 

with CAA §110(l) and §193 because (1) the proposed SIP revision would 

not interfere with the on-going process for ensuring that requirements for 

RFP and attainment of the NAAQS are met, and (2) the requirements in the 

submitted rule are more stringent than the existing control requirements that 

they would replace and are approved for the SIP.

ADDITIONAL RECOMMENDATIONS FOR THE NEXT RULE REVISION – The 

following revision is not currently the basis for rule disapproval, but is

recommended for the next time the rule is amended.

1. Section (G)(3)(a) specifies a CARB test method for analyzing halogenated 

exempt compounds as being ARB Method 22. The correct test method is 

ARB Method 422.

EPA ACTION - The submitted Rule 464 complies with all relevant CAA 

requirements. Therefore, EPA staff recommends a full approval of Rule 464

pursuant to CAA §110(k)(3).

REFERENCES -

1. Mojave Desert Air Quality Management District (MDAQMD), “Final Staff 

Report Proposed Amendments to Rule 464 – Oil-Water Separators”, as 

submitted to the EPA on November 6, 2014.

2. San Joaquin Valley Unified Air Pollution Control District (SJVUAQMD), 

Rule 4625, “Wastewater Separators”, December 15, 2011.
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3. South Coast Air Quality Management District (SCAQMD), Rule 1176, “VOC 

Emissions from Wastewater Systems”, September 13, 1996.

4. Bay Area Air Quality Management District (BAAQMD), Regulation 8, Rule 

8, “Wastewater Collection and Separation Systems”, September 15, 2004.

5. CTG, “Control of Refinery Vacuum Producing Systems, Wastewater 

Separators and Process Unit Turnarounds” (EPA-450/2-77-025, October 

1977).

6. The Little Bluebook, EPA Region 9, August 21, 2001.

7. The Bluebook, EPA, May 25, 1988.