EPA’s Proposed Fenceline Monitoring Requirements for Synthetic Organic Chemical Manufacturing Industry (SOCMI) and Group I and II Polymers and Resins Industries

Preparing for the Proposed EPA HON Fenceline Monitoring Rule

On April 25, 2023, the United States Environmental Protection Agency (EPA) published proposed amendments to the New Source Performance Standards (NSPS) that apply to the Synthetic Organic Chemical Manufacturing Industry (SOCMI) and to the National Emission Standards for Hazardous Air Pollutants (NESHAP) that apply to the Hazardous Organic NESHAP (HON) and Group I & II Polymers and Resins. These amendments include fenceline monitoring requirements based on the December 2015 Refinery Sector Rule (RSR) MACT Subpart CC requirements.

Affected Facilities

The EPA estimates these amendments will impact approximately 200 facilities and will include fenceline monitoring requirements, which is a new compliance program for these industries. These amendments would require fenceline monitoring for facilities that use, produce, store, or emit any of six key air toxics (ethylene oxide (EtO), chloroprene, benzene, 1,3-butadiene, ethylene dichloride, and vinyl chloride). If concentrations of these six key air toxics exceed action levels, the facilities are required to identify the cause of the exceedance and correct it.

Proposed Fenceline Monitoring and Sampling Requirements

The proposed requirements for fenceline monitoring require sampling using passive diffusion tubes on a 14-day schedule and 24-hour summa canister sampling every 5 days, translating to over 160 days of annual field deployments and at least 5,500 discrete samples. This will require considerable facility resources for fieldwork, data management, and quarterly compliance report preparation.

Proactive Measures for Facility Compliance

The EPA has a deadline to issue a final rule by March 29, 2024, and facilities have one year to begin fenceline monitoring once it is finalized. After one year of sampling at these facilities, the data will be made available to the public through EPA’s WebFIRE database.

There is still time to perform pre-compliance period sampling to evaluate your facility’s site conditions and identify areas that may need corrective actions to reduce site emissions below the proposed action levels.

Questions? Connect with our air compliance specialists.

Trihydro recognizes the complexities associated with navigating these evolving fenceline monitoring compliance regulations. Building upon our extensive experience since the implementation of the 2018 Refinery Sector Rule, Trihydro offers comprehensive fenceline monitoring programs to support you in maintaining compliant operations and reporting.

Connect with us if you would like to discuss how the EPA’s proposed NSPS amendments affect your facility and what you can do now to prepare.


Contact Us
Jeremy Sell, P.E.
Senior Vice President, Air and Process Services, Laramie, Wyoming

Jeremy has more than 22 years of experience conducting and managing environmental projects at sites across the western United States. He supports air compliance programs including leak detection and repair (LDAR), Benzene Waste Operations NESHAP (BWON), annual air emission inventories (AEI), cooling tower Maximum Achievable Control Technology (MACT), and refinery sector rule gap assessments.

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