Transitioning a Gas Plant from Method 21 to Appendix K OGI Monitoring (NSPS OOOOb LDAR)

Trihydro supported a midstream operator in the Permian Basin transition a natural gas processing facility’s leak detection and repair (LDAR) program from Method 21 (M21) to Appendix K optical gas imaging (OGI) monitoring under New Source Performance Standards (NSPS) 40 CFR Part 60, Subpart OOOOb (OOOOb). The facility’s regulatory applicability had changed, bringing additional process units under LDAR requirements and necessitating a structured transition to meet Appendix K monitoring, documentation, and compliance expectations.

The gas processing facility included approximately 40,000 components across multiple process units, requiring a deliberate transition strategy to maintain compliance while aligning with the Appendix K monitoring methodology. Because the facility already maintained a tagged component inventory, routing structure, and database under Method 21, Trihydro focused on adapting existing program elements rather than rebuilding the LDAR framework from the ground up.

Trihydro developed and implemented an Appendix K–compliant monitoring program supported by regulatory-aligned procedures, defensible documentation, and structured scheduling to meet compliance deadlines. Additional process units not previously monitored under Method 21 were incorporated into the updated LDAR program, expanding coverage and improving compliance posture.

OGI Monitoring Implementation and Method 21 Transition Strategy

Trihydro applied its internal Appendix K training program to support implementation readiness. The program combined regulatory instruction with field execution training, including thermal tuning, image interpretation, and mitigation of common interferences to improve consistency and data quality.

Field data, including quality assurance videos, leak identification, meteorological conditions, and fatigue-break documentation, were maintained using LeakTracker Pro™ to support Appendix K recordkeeping and provide traceable, audit-ready documentation for compliance teams.

At the operator’s request, Trihydro performed a pre-sweep of components in residue and fuel gas service to proactively identify and address leaks ahead of the Appendix K program transition. The effort focused on areas not historically monitored under Method 21. Early action mitigated transition risk, supported timely repairs, and positioned the facility for smoother compliance once Appendix K monitoring began.

Appendix K OGI Monitoring Approach for OOOOb Compliance

To support implementation, Trihydro conducted facility walkdowns to develop compliant monitoring routes and establish defined component counts for each process unit. Routes were designed to meet Appendix K requirements such as appropriate dwell time and simplified scene development, while providing repeatable workflows between operators and improving monitoring consistency.

These walkdowns translated regulatory requirements into practical, repeatable workflows. Clearly defined monitoring paths established the beginning and end of each process unit, providing OGI technicians with the expected monitoring duration and supporting consistent execution across operators, while demonstrating compliance with the Appendix K methodology.

Trihydro documented monitoring activities and leak identification using LeakTracker Pro™, supporting traceable records for environmental and compliance teams. Monitoring was primarily conducted within the OGI manufacturer’s operating envelope, with Appendix K–approved procedures developed to support extended conditions when needed.

OGI Monitoring Results and LDAR Performance Improvements

The Method 21-to-Appendix K transition began in early 2026, with a senior OGI operator conducting the initial monitoring event across the entire facility. With the additional process unit surveys, a substantial number of leaks were identified and documented in LeakTracker Pro. The surge in open leaks required close coordination among operations, environmental, and Trihydro’s OGI operators to ensure repairs and verification were completed within the required timeframes. Removing gaps between all affected groups was key to maintaining compliant leak custody and close-out. 

Subsequent bimonthly OGI events showed a downward trend in leak counts and improved program sustainability. The value of transitioning from M21 to OGI-Appendix K was realized by the second quarter of implementation.

Method 21 to OGI Monitoring Transition Results Under OOOOb

• Transitioned an existing Method 21 LDAR program to Appendix K OGI monitoring under NSPS Subpart OOOOb
• Expanded LDAR coverage to additional process units not previously monitored
• Implemented compliant monitoring routes and repeatable workflows to support audit readiness
• Delivered Appendix K training, procedures, and documentation to support sustained compliance
• Reduced transition risk through targeted pre-sweep leak identification and early repairs
• Achieved measurable reductions in leak counts across subsequent monitoring events