NSPS OOOO (Quad O) 1.5 Update - Revised March 31, 2015
December 26, 2014

On December 31, 2014, the EPA published in the Federal Register updates and clarifications to 40 CFR 60 Subpart OOOO (aka Quad O). The notification includes a summary fact sheet for the Quad O revisions at: http://www.epa.gov/airquality/oilandgas/pdfs/20141219fs.pdf

These changes are expected to be followed by other proposed modifications to Quad O in 2015. 

March 23, 2015 Proposed Changes to NSPS OOOO - Updated March 31, 2015

In a Federal Register Notice dated March 23, 2015, the EPA proposed changes to NSPS OOOO. One change proposed included amending NSPS OOOO to remove provisions in the rule regarding storage vessels connected or installed in parallel and to revise the definition of ‘‘storage vessel’’.

In the Federal Register Notice, EPA stated it was soliciting "comment on other approaches to help avoid or discourage installation or operation of storage vessels that would unnecessarily reduce the potential to emit (PTE) of a single storage vessel." and EPA stated, it seeks comments on, "other approaches to help avoid or discourage installations or operations of storage vessels that would unnecessarily reduce the PTE of a single storage vessel."

No guidance was given by EPA on compliance with the existing, promulgated storage tank definition in NSPS OOOO. 

HY-BON VRU Vent Gas Management

 A short list of affected sections of the rule are listed below. 

  • Changes the definition of a storage vessel. NOTE: the March 23, 2015 Federal Register notice proposal may rescind this defintion change. 
  • Defines stages of flowback process in the definitions in 40 CFR 60.5430. 
  • Defines low-pressure wells (important for Reduced Emission Completion exemption)
  • Allows other mechanisms besides weighted thief hatches to ensure hatch lids remain sealed. 
  • Allows leaks from reciprocating compressors rod packing seals to be used fuel in lieu of periodic replacement of seals. 
  • Revised the definition of “responsible official” 
  • Clarified certain requirements for leak detection at natural gas processing plants
  • Included language that operator can use a VRU to lower the VOC potential to emit (PTE) of a tank even if the VRU is not in the facility’s air permit
  • Changed defintion of a storage vessel - discussed below. 
  • Clarified how replacement storage tanks are regulated, how storage tanks removed from service are regulated and how storage tanks placed into/returning to service are regulated
  • Affirmative Defense – EPA removed the regulatory affirmative defense provision from the rule. If a source is unable to comply with emissions standards as a result of a malfunction, the EPA may use its case-by-case enforcement discretion to provide flexibility, as appropriate. 

Note that for case-by-case enforcement determinations, the use of backup emission control systems (VRU, VRT and vapor combustor), maintenance contracts, spare parts inventory and routine inspections can help reduce or eliminate a monetary penalty. 


Storage Vessel Definition NOTE: the March 23, 2015 Federal Register notice proposal may rescind this defintion change. 

The new definition states, "Storage vessel means a tank or other vessel that contains an accumulation of crude oil, condensate, intermediate hydrocarbon liquids, or produced water, and that is constructed primarily of nonearthen materials (such as wood, concrete, 
steel, fiberglass, or plastic) which provide structural support. Two or more storage vessels connected in parallel are considered equivalent to a single storage vessel with throughput equal to the total throughput of the storage vessels connected in 

Why is this storage tank definition change important?

This can impact how a facility determines the applicability of NSPS OOOO to their crude, condensate and produced water storage tanks. Based on this definition, if all storage tanks are connected in parallel and are considered one storage tank, then the facility cannot divide by the number of tanks to get the per tank VOC emissions (i.e., average VOC emissions across tanks). This could mean that the facilities storage tanks trigger NSPS OOOO requirements even with the use of a flare or vapor combustion device.

Qualification: The addition of the language regarding storage vessels connected in parallel is proposed to be rescinded according to the Federal Register Notice dated March 23, 2015. .

Compliance Heads-Up

Operators may want to review their air permits to determine how this new storage tank definition affects current and future operations. 

Quad OOOO Reminder

Group 1 storage vessels that emit 6 or more tpy VOC must reduce VOC emissions by 95.0% or greater by April 15, 2015.  This is a per storage tank emission limitation.

Group 1 storage vessels are those constructed after August 23, 2011, and on or before April 12, 2013. 

Control methods used include vapor recovery and vapor combustion units


Future NSPS OOOO Changes (Quad O 2.0)

Below is a short discussion of information indicating oil and gas emission sources that might be included in a future NSPS OOOO modification. The next modification is sometimes referred to as Quad O 2.0. 

University of Texas Papers on Liquids Unloading and Pneumatic Controllers

The results of two studies conducted by the University of Texas on Liquids Unloading and Pneumatic Controllers was published December 9, 2014, in Environmental Science & Technology. The primary author of the two papers was Dr. David T. Allen of the University of Texas at Austin. 

The papers discuss sampling and measurements made at oil and gas production facilities for venting from liquids unloading and pneumatic controllers using natural gas.

Copies of the papers can be found at the links below: 

Methane Emissions from Process Equipment at Natural Gas Production Sites in the United States: Liquid Unloadings.

Methane Emissions from Process Equipment at Natural Gas Production Sites in the United States: Pneumatic Controllers

A summary of the two papers can be found at:  http://www.utexas.edu/news/2014/12/09/methane-emissions-dave-allen/


EPA White Papers and Future NSPS OOOO Revisions Expected

Future changes to Quad O are expected based on the directives in the Climate Action Plan – Strategy to Reduce Methane Emissions.  To meet the Climate Action Plan, the EPA published in April 2014 five White Papers on Methane and VOC  from oil and gas emission sources. Besides the White Papers, the EPA is reviewing other issues. The results of studies by Dr. David Allen will probably be used in the rule making.


The EPA White papers focused on the emission source types listed below.

  • Liquids Unloading 
  • Leaks 
  • Completions and ongoing production of hydraulically fractured oil wells
  • Compressors seals
  • Pneumatic Devices

Along with the EPA White Papers, feedback comments from peer reviewers are supplied online.

The EPA’s review and public/industry feedback may result in further regulation of VOC emissions from these venting sources. Some of the issues discussed in the in the white papers are discussed below.


Liquids Unloading Venting

Methane venting from liquids unloading of wells has been reported by companies in their annual greenhouse gas (GHG) reports. Dr. Allen’s liquids unloading paper included sampling results for wells using plunger lifts and those not using plunger lifts. The study found most wells without plunger lifts unload/vent

The EPA White Paper discusses information EPA understands about well unloading. The peer reviewers supplied their comments.


Leaks – Fugitives, Storage Tanks

Leaks are getting much more attention by regulators, nongovernmental organizations and the general public. This includes fugitive leaks from valves, flanges, threaded fittings, seals and pressure relief devices. Also getting attention are leaks from equipment that is not operating properly. This includes a leaking tank hatch (leaking thief hatch).

Several states already require leak detection and repair (LDAR) programs for certain oil and gas air permits – state wide and/or in certain geographic areas. These include:  

  • Colorado Department of Public Health and Environment
  • Texas Commission on Environmental Quality
  • Ohio Environmental Protection Agency
  • Wyoming Department of Environmental Quality 

Expect the EPA or other states to require more LDAR programs in the future for oil and gas facilities.

The EPA White Paper entitled Oil and Natural Gas Sector Leaks lists leak sources result from seals, valves, flanges, connectors, hatches, instruments, meters, open ended lines, pressure relief devices and pump seals. 

Also of concern are leaks from equipment that is not operating properly including storage tank thief hatches that are left open and separator dump valves that are stuck open and venting through the tank. The White Paper cites some studies indicating that maintenance-related issues such as open thief hatches, failed/leaking pressure relief devices or stuck dump valves are significant contributor to leaks.

Other White Papers

The White Papers regarding completions and ongoing production of hydraulically fractured oil wells; compressors seals and pneumatic devices indicate that EPA considers these as potentially significant VOC and methane sources. More data gathering and/or studies are being conducted to determine future regulatory changes.

Ongoing Compliance and Preparation for NSPS OOOO

EPA and state regulators have focused on reducing venting and flaring of natural gas from oil and gas operations. This will continue into the future.

Many expect that after the Quad O regulatory deadlines pass (e.g., Group 1 Storage Tank deadline), regulators will conduct more compliance checks. Compliance checks may include field surveillance visits and review of reports required to be submitted by operators. As these air quality regulations get more and more complex, it is important for operators to have a system vent gas management. HY-BON can help you with your continued compliance system for Quad O.