Solutions for HON MACT Fenceline Monitoring with Sensible EDP and Enthalpy Labs

October 18, 2023 —


In April 2023, the U.S. EPA issued National Emission Standards for Hazardous Air Pollutants (NESHAP) for the Synthetic Organic Chemical Manufacturing Industry (SOCMI) and Group I & II Polymers and Resins Industry (P&R I and P&R II). This proposed new rule introduces changes to 40 CFR 63 Subparts F, G, H, and I, impacting more than 200 U.S. facilities. As part of this rulemaking (which is expected to be finalized March 31, 2024) there is a significant and ongoing burden for fenceline monitoring if facilities use, produce, store, or emit any of six volatile organic compounds (VOC):

  • Ethylene oxide (EtO)
  • Chloroprene
  • Benzene
  • 1,3-butadiene
  • Ethylene dichloride
  • Vinyl chloride

Once the rule is final, ongoing fenceline monitoring will consist of collecting and analyzing samples using Method 325A/B (passive adsorbent tubes) or Method 327 (canisters) or a combination of both methods. If there is an exceedance of an action level (for one of the six VOCs) and the facility cannot determine the root cause of the exceedance within 30 days, the owner or operator will be required to use real-time monitoring techniques (e.g., mobile gas chromatographs, sensors, UV-DOAS, FTIR) to determine the root cause of the exceedance.

Montrose Environmental Group (MEG) is uniquely qualified to support industry with implementation/citing, in-field sample collection, laboratory analysis, a unified data platform and root cause investigation of exceedances. As part of this turnkey service, data will be collected, aggregated and reported allowing facility operators to pinpoint operational induced variances of the VOCs being monitored with the Sensible Environmental Data Platform (EDP), helping ensure compliance with this new rule.

Implementation/Siting & In-field Sample Collection

Montrose Air Quality Services, the air quality monitoring division of MEG, has field technicians currently servicing Method 325 fenceline monitoring programs across the United States and has reviewed and participated in the comment period on the proposed Method 327. Montrose field technicians and project managers complete rigorous training and certification on applicable methods and regulatory requirements prior to being qualified to participate in fenceline monitoring projects. Montrose has sited field locations to meet Method 325 requirements, and developed dozens of fenceline monitoring plans with EPA approval. Montrose deploys and collects over 5,000 samples annually ensuring our clients meet their regulatory commitments.

Laboratory Analysis

Enthalpy Analytical ( the laboratory division of MEG, operates a network of 9 environmental laboratories across the United States. Enthalpy has over 10 years’ experience with EPA Method 325B, analyzes over 50,000 samples annually, and is closely monitoring and engaging with EPA on the pending Method 327. EPA Method 327, which is based on EPA MEthod TO-15/15A, provides a heightened expectation for field sample collection and laboratory analysis. A standard 7-day turnaround time, mobile field application for sample collection and custom electronic data deliverables makes Enthalpy the clear choice for fenceline monitoring laboratory support.

Data Platform & Root Cause Analysis

Sensible EDP, powered by Montrose Environmental, is the leading Environmental Data Platform for industries and communities who are monitoring air, water, and soil data continuously. The Sensible EDP ( collects emissions data from a variety of sensors and mechanisms in real time. When fugitive emission leaks are detected, alerts are sent via phone, email, text, or app, pinpointing the leak location, ensuring they are repaired promptly. Reporting is available to verify compliance with federal and state regulations. Emissions data across a variety of toxics is securely stored in one place, for ongoing analysis and real time monitoring, making Sensible EDP the single source of truth for all of your emissions data management needs.

MEG’s turnkey integrated solution from citing to root cause investigations allows facility operations to focus on safe and environmentally compliant production. The ability to aggregate data quickly and monitor trends, will help affected facilities meet new environmental monitoring requirements.

Key Takeaways

The combined Montrose, Enthalpy and Sensible teams are experienced in existing fenceline monitoring programs and are diligently preparing to meet the enhanced requirements of facilities covered by the updated HON MACT regulations.

Contact for more information and please sign-up for our live webinar on December 6th where MEG's experts will help you get started on your fenceline monitoring program and answer questions. The webinar will help viewers:

  1. Understand the recent HON MACT rulings
  2. Determine if you are affected by the updated regulations
  3. Learn about various solutions to make sure you're in compliance with the new regulations.