Operators use enforceable limits in air permits to avoid triggering NSPS OOOOa applicability for crude oil, condensate and produced water storage tanks. To obtain an enforceable limit, the limits must be included in a legally and practically enforceable air permit or other authorization. Air permits granted by a federal, state, local or tribal authority typically meet these requirements. Consult your permitting agency to ensure that the permit or other authorization is enforceable.


If a new (after September 18, 2015) storage tank is not permitted using enforceable permit limits and VOC emissions are equal to or greater than 6 tons per year, then the storage tank is subject to NSPS OOOOa emission controls, recordkeeping and reporting requirements. This is true even if the facility later permits the storage tanks in an enforceable permit with emissions less than 6 tons VOCs per year. This is because the rule states, “A storage vessel affected facility that subsequently has its potential for VOC emissions decrease to less than 6 tpy shall remain an affected facility under this subpart.”

Emission calculations used to establish enforceable air permit limits are based on potential to emit (PTE) emissions, not using actual emissions. PTE permit limits can be based on one or a combination of the following:

  • Production throughput limits
  • After controls emissions
  • Operating hours limits
  • Other operation or design limitation (e.g., circulation rate of glycol for dehydrators)

To be enforceable, the PTE limits and associated limits on production throughput, emission controls and operating hours must be included in the air permit application and approved by the permitting agency.

Be sure to maintain copies of the basis for PTE calculations used for the air permit obtained. This is especially true for some State agency General Permits and permits by rule (PBR) since the air permit documents received from the State agency may be generic “boilerplate” documents. These generic documents may not include a detailed listing of emission controls used, throughput limits or operating hour limits.


Advantages of limiting PTE

Beside avoiding NSPS OOOOa for storage tanks, lowering PTE can:

  • Lower facility emissions to qualify as minor source and avoid Title V/Part 70 major source permitting.
  • Lower facility emissions to qualify for a permit by rule (PBR) or General permit. These types of permits have quicker approval timelines than individual permits for new and modified facilities.
  • Lower emissions to below threshold for annual reporting of criteria pollutants and hazardous air pollutants.
  • Meet regulatory set limits on operating hours for emergency use and backup engines (e.g., generators, compressors, pumps)


Limiting Storage Tank PTE

For oil and gas operations, storage tanks’ PTE are most often limited by one or a combination of:

  • Limit the barrels of oil per year throughput
  • Recover vent gas using a vapor recovery unit (VRU)
  • Combust vent gases using a vapor combustion unit (VCU) or a candlestick flare

Examples for Storage Tanks:

Uncontrolled storage tank emissions:            100 tons per year VOCs

Vapor recovery unit (VRU) efficiency:            99% based on expected runtime

Storage tank controlled PTE emissions:        1 ton per year VOCs

Added benefit of VRU is that the vent gas is recovered and sent to sales.

Uncontrolled storage tank emissions:            100 tons per year VOCs

Vapor combustion unit (VCU) efficiency:       99.9% (based on stack testing)

Storage tank controlled PTE emissions:        0.1 ton per year VOCs

Note that NSPS OOOOa does not require the VRU be included in an enforceable permit provided the operator meets the specifications for tank covers (hatches) and closed vent system and maintains records specified in § 60.5365a(e)(3). Most State regulatory agencies require the VRU to be included in the air permit to get credit for the reduction for emissions not associated with NSPS OOOOa.


Cimarron Services and Products

Cimarron uses its Identify, Quantify, Rectify (IQR) methodology to reduce and manage air emissions. Our IQR services include LDAR leak monitoring for NSPS OOOOa compliance.

Use our best in class Vapor Recovery Units, Vapor Recovery Tower (VRT), and Enclosed Combustors (ECD) to minimize emissions and optimize production with minimal regulatory burdens.

Contact Cimarron now to find out how we can assist your operations. Company specific webinars tailored to your operations are available.

Contact us at +1 (844) 746-1676

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