Fenceline Monitoring 101: Regulations, Technologies, and Best Practices

February 9, 2024 —

Fenceline Monitoring (FLM) is a pivotal practice in verifying and reducing fugitive emissions from industrial facilities. Companies need to stay ahead of evolving regulations while ensuring compliance and environmental responsibility with a range of tools—from precise point measurements to expansive open-path systems. This blog breaks down the basics of fenceline monitoring, key regulations to be aware of, some actionable, and best practices to support your compliance efforts. It also identifies technology—available today—that will help you meet your organization's monitoring needs now and in the future.

Fenceline Monitoring at a Glance

Fenceline monitoring is the use of monitoring technologies to assess air quality along the perimeter or boundary of industrial facilities (e.g., petroleum refineries, chemical plants). There is a range of pollutants measured including particulate matter, methane, volatile organic compounds (VOC’s) such as benzene and toluene, hazardous air pollutants (HAPs) like mercury and lead and many more.


Regulatory requirements from local, state, and national agencies have increased in response to evolving air quality knowledge, public concerns, and an increasing commitment to environmental sustainability.

There are various reasons outside of regulatory requirements to install FLM. These include fostering positive connections with neighboring communities (i.e. Denver’s Love My Air Program) and validating where emissions sources originated (internal or external).

Hazardous Organic NESHAP and established maximum achievable control technology (HON MACT), expected to be finalized March 31, 2024, will affect over 200 U.S. synthetic organic chemical manufacturing facilities, as well as some facilities that produce polymers and resins. The draft rule proposes significant and ongoing requirements for fenceline monitoring. This rulemaking will require collecting and analyzing fenceline samples using Method 325A/B and/or Method 327, as well as using real-time monitoring techniques if the facility cannot determine the root cause of an action level exceedance. Read more here.

South Coast Air Quality Management District (SCAQMD) is proposing lower ethylene oxide emission limits compared to the NESHAP as well as additional monitoring requirements including fenceline and mobile monitoring. The recently modified Rule 1405 reduces emissions of ethylene oxide to the lowest level of any regulations for commercial sterilizers and related operations. Read more here.

National Emission Standards for Hazardous Air Pollutants (NESHAP) sets standards for pollutants from stationary sources. Hazardous air pollutants (HAPs) refer to substances with known or suspected links to cancer, serious health issues, like reproductive effects or birth defects, and adverse environmental impacts. Read more here.

Best Practices to Consider

Whether it's real time data collected to meet a regulatory requirement or consent decree, or data collected to support a fenceline program involving sample collection and analysis, various advanced techniques and methodologies can provide real time, actionable data, to ensure you stay compliant with regulations, while also remaining cost-efficient. Consider these best practices when creating, developing or evaluating your FLM program:

Regulatory Compliance: Stay informed about relevant regulations and ensure that your fenceline monitoring program aligns with local, state, and federal requirements.

Strategic Siting of Samplers: Carefully choose the locations for placing monitoring equipment. Consider the facility layout, prevailing wind directions, and potential emission sources.

Use of Advanced Technologies: Embrace advanced monitoring technologies, such as open-path monitoring systems, drones, and real-time sensors. These technologies can provide more comprehensive and timely data, improving the overall effectiveness of the fenceline monitoring. All of these can be integrated throughout the Sensible EDP (Environmental Data Platform) software, delivering real-time, actionable data to guarantee your compliance with regulations. [Read more about Sensible FLM]

Data Quality Assurance: Establish strong data quality assurance measures. Regularly calibrate and maintain monitoring equipment to ensure accurate and reliable data.

Documentation and Reporting: Maintain thorough documentation of the monitoring process, including equipment calibration records, sampling locations, and any corrective actions taken. Timely and accurate reporting is essential for regulatory compliance and transparency, ensuring legal adherence and the organization’s reputation. Clear and accessible documentation enhances trust among stakeholders and the community.

Emergency Response Plan: Develop an emergency response plan that outlines the steps to be taken in the event of unexpected releases or exceedances.

Available Monitoring Technologies

A real-time understanding of your fenceline emissions is critical to community safety. Technology is the first step toward proactive monitoring and should address your specific needs. The outcome is a data-driven approach that enables rapid responses to pressing issues. Here are some practical, cost-effective, technologies available today that can help companies address their monitoring needs.

Point Measurements: The Montrose Emerging Technologies division employs a range of point measurement technologies, including UV and IR spectrometry, gas chromatography with different detectors (FID, PID, TCD, TDT-PID) and total VOC sensors, to ensure alignment with customers' unique data quality objectives. Additionally, Montrose leads in the deployment and evaluation of cutting-edge methane sensing techniques, and has evaluated optical, infrared, and TDL based methane sensors.

Passive Tubes & Canister Sampling: Various regulations, including the refinery fenceline rule, proposed HON, consent decrees, and Section 114 requests, follow EPA Method 325A/B (using passive tubes) and EPA Method 327 (using canisters). Montrose, in collaboration with its NELAP-accredited subsidiary Enthalpy Analytical, offers sampler siting, sample collection, analysis, and reporting. Montrose and Enthalpy currently manage over 50 programs nationwide.

Open Path Technologies: Montrose offers open-path air monitoring systems employing techniques such as UV-DOAS, OP-FTIR, and OP-TDL/QCL, capable of covering up to 1 km distances. Our installations meet the criteria of SCAQMD Rule 1180, BAAQMD Regulation 12 - Rule 15, and Colorado House Bill 1189.

Mobile Solutions: Our drone solutions provide a wide and unobtrusive view of your fenceline emissions. With our PTR-TOF-MS mobile van, we enable instant and ultra-low detection of emissions for swift response and accurate tracking from any location, be it on the fenceline or within the facility. Additionally, we can mount any point sensor on a mobile platform for convenient fenceline monitoring.

Sensible EDP Software

Montrose’s Sensible EDP software integrates with any of these technologies or from any number of sources in real time, including hardware from 3rd party manufacturers, giving your organization the ability to monitor all of your environmental data within a single platform. The data is displayed on your personalized dashboard in real time, offering predictive analytics, anomaly detection, and centralized 24/7 data storage.

The Command Center is where your environmental data is processed and monitored. It sends alerts via email, phone, text, and API when emissions are detected. Our proprietary stand-alone software, along with triangulation techniques, pinpoints potential emissions sources early, before they escalate. This allows for swift response, mitigation and emissions reductions.

Our Project Services team will be there to support your organization throughout the entire project lifecycle including Monitoring Program Design, Development of Monitoring Plans, Installation, Operations and Maintenance, Data Acquisition and Management, and Alert Response.

Contact us to learn more about our fenceline monitoring solutions at info@sensible-edp.com or visit our website at https://sensible-edp.com/fenceline-monitoring/. Ready to see the platform? Schedule a demo with one of our experts today.