top of page

NSPS Method 21 

Surface Emissions Monitoring


For compliance to New Source Performance Standards (NSPS), Emission Guidelines (EG), Federal Plan and National Emission Standards for Hazardous Air Pollutants (NESHAP) for Municipal Solid Waste Landfills in 40 CFR Part 60, Subpart XXX and Cf, Part 62, Subpart OOO, and Part 63, Subpart AAAA.


In accordance with the prescribed regulatory standards, our technicians visually inspect the landfill cover system while monitoring fugitive methane gas emissions using a compliant methane detector.  

Confidence in Results  

People, process, and technology.

US EPA regulations require methane emissions monitoring for MSW landfills under federal regulations, promulgated through the states, as defined above. This manual method for surface emissions monitoring is commonly referred to as Method 21 inspection, and is performed manually by field technicians walking a landfill while holding a methane detector to identify surface leaks on the landfill cover system.


While Method 21 is the industry's traditional method for surface emissions monitoring, the US EPA recently approved OTM-51 / ALT-150 - the SnifferDRONE method using an drone-based unmanned aerial system that automates most of the inspection. Consider using this alternative US EPA approved method. 

Our technicians are properly trained on the specifics of regulatory requirements, including calibration of the equipment, monitoring weather conditions, equipment set-up and utilization, walking path requirements, identification of additional areas to inspect, reporting methods, and more


Technicians utilize Sniffer's designed apps on their mobile devices to record their walking path and to record locations where exceedances (methane concentrations above the prescribed threshold) are found. Details of the location, the cause of the exceedances, and additional information are recorded onsite at the location when observed.

Detailed inspection reports are provided to customers promptly at the end of each daily inspection. The report contains:


  • Methane concentration (PPM)

  • GPS coordinates with location details (e.g. distance to gas well)

  • Site map with pinned locations where issues were found

  • Walking path 

  • Potential cause and/or suggested corrective action

  • Photograph of exceedance location

  • Detector calibration report(s) & calibration gas certs

  • Additional notes


At the end of the 30-day inspection, a formal report is provided for regulatory compliance purposes. Learn more about how our reports are designed to 'Inform for Action'.

Customers may also license Sniffer's Field Ops™ (SFO) software solution.  The app, available for mobile devices, provides real-time feedback of our technicians' inspection activities. Automated email alerts notify customers when exceedances are found by our technicians with a link to view details from a mobile device. 


SFO was designed to provide customers with instant information about found exceedances, allowing an opportunity to quickly remediate the location while technicians are onsite. 


Sniffer's Field Ops app is used by our technicians to precisely and accurately record issues. Customers can also use the app to view our technicians' work and reported issues.

Daily Report Sample.png

Our daily reports provide customers detailed and precise information to help remediate issues quickly and effectively. 

Download a sample daily report.

bottom of page