NSPS OOOOb
Deep-Dive

Affected Sources

OOOOb covers the same crude oil and natural gas source category as OOOOa, but with broader scope:

• Well sites (including single-well and multi-well sites)
• Centralized production facilities
• Gathering and boosting compressor stations
• Natural gas processing plants
• Natural gas transmission compressor stations
• Natural gas underground storage compressor stations

Affected Equipment Within Each Source

• Storage vessels (tanks)
• Centrifugal and reciprocating compressors
• Natural gas-driven pneumatic controllers and pumps
• Process controllers and pumps in general
• Fugitive emissions components (valves, connectors, flanges, open-ended lines, pressure relief devices)
• Liquids unloading operations
• Associated gas from oil wells
• Wet seal centrifugal compressors
• Sweetening units

Monitoring Frequency by Site Type

• Compressor stations: Quarterly OGI fugitive emissions surveys.
• Well sites with major equipment: Periodic OGI surveys, with frequency determined by the site classification and the equipment present.
• Wellhead-only sites: Less-frequent OGI plus periodic AVO inspections, depending on site characteristics.
• AVO inspections: Required between formal OGI surveys for nearly every covered site.

Specific frequencies vary by source classification — consult the rule text for the exact monitoring schedule that applies to a given site type.

Detection Methods

OOOOb provides for OGI under EPA's Optical Gas Imaging Alternative Work Practice criteria, plus EPA Method 21 as an option. Operators can also propose alternative test methods (including continuous monitoring with advanced sensors) through an EPA approval process. See our comparison of EPA Method 21 vs OGI cameras for the trade-offs.

Repair Timeline

First repair attempt within 30 days of leak identification; final repair within typically 30 days under most categories, with delay-of-repair provisions when shutdown is required. Re-inspection is required after each repair to confirm the leak is below the applicable threshold.

Coverage

OOOOb covers single tanks and "tank batteries" with potential to emit (PTE) of 6 tons per year or more of VOC. The PTE-based threshold pulls more tanks into coverage than older single-tank capacity-based thresholds did.

Control Requirements

Affected tanks must reduce VOC emissions by at least 95 percent, typically through closed-vent systems routed to a flare or vapor recovery unit (VRU). Tanks must be operated under closed-loop conditions during operation, with thief hatch and PRV inspections to confirm no chronic openings.

Pneumatic Controllers

OOOOb generally requires zero-emission natural gas pneumatic controllers at most affected sites. Acceptable alternatives include compressed instrument air, mechanical or electric controllers, or natural gas vented to a closed-vent system. Limited exceptions exist for specific safety-critical applications and remote sites without access to electric power.

Pneumatic Pumps

Natural gas-driven pneumatic pumps must either be replaced with non-emitting alternatives or routed to a control device achieving at least 95 percent VOC reduction. The rule also imposes recordkeeping on the in-service pump count and any temporary outages.

Best Management Practices

Liquids unloading from gas wells must follow a written best-management-practices plan designed to minimize methane and VOC venting. Practices include monitoring downhole pressure, optimizing the unloading event timing, and routing vented gas to a sales line, control device, or beneficial use whenever feasible.

Flare Restrictions

OOOOb places significant restrictions on flaring of associated gas from oil wells. Operators must demonstrate that routing the gas to a sales line, beneficial use, or reinjection is technically and economically infeasible before flaring is allowed. When flaring is permitted, the flare must achieve at least 95 percent VOC destruction with continuous pilot monitoring.

Annual Reports

Operators must submit annual reports to EPA documenting equipment counts, monitoring events, leaks identified and repaired, control device performance, deviations, and corrective actions. Reports are submitted electronically through EPA's CEDRI (Compliance and Emissions Data Reporting Interface).

Records to Retain

Five-year retention applies to: monitoring plans, component inventories, OGI video and Method 21 readings, calibration records, repair documentation, training records, super-emitter event responses, and tank/control device performance data.