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

On May 16, 2024, the United States Environmental Protection Agency (EPA) published a final rule that regulates emissions and establishes new emission control requirements for various sources (e.g., storage tanks, process vents, wastewater systems, etc.). The rule also requires fenceline monitoring at over 200 chemical plants across the country.

The publication finalizes amendments to the New Source Performance Standards (NSPS) that apply to the Synthetic Organic Chemical Manufacturing Industry (SOCMI) and amendments to the National Emission Standards for Hazardous Air Pollutants (NESHAP) that apply to the SOCMI (more commonly referred to as the Hazardous Organic NESHAP or HON) and Group I and II Polymers and Resins (P&R I and P&R II, respectively). The rules will be effective July 15, 2024. 

Fenceline Monitoring Affected Facilities

The rule requires fenceline monitoring for affected 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). Non-affected sources (boilers, housekeeping, building maintenance, or lab/research activities) will not trigger fenceline monitoring if they are the only sources emitting target analytes.

This is a substantial expansion of the EPA’s fenceline monitoring requirements, which began with benzene monitoring for oil refineries (2018 Refinery Sector Rule). If concentrations of these six key air toxics exceed EPA action levels, the facilities must identify the cause of the exceedance and implement corrective actions to reduce detected levels below the action levels. 

Fenceline Monitoring Schedule

The fenceline monitoring requirements vary by type of facility and chemical. 

  • Chloroprene monitoring at neoprene production facilities starts 90 days after the rule takes effect (August 14, 2024).

  • Monitoring for other chemicals begins two years after the effective date on July 15, 2026 (instead of the proposed one year). 

Facilities will need to conduct:

  • Passive diffusion tube sampling every 14 days.

  • 24-hour summa canister sampling every 5 days.

This translates to over 160 days of annual field deployment and potentially over 5,500 samples collected per year, depending on facility operations. 

Reduced Fenceline Monitoring Frequency

In the final rule, the EPA established alternative sampling frequencies to reduce the burden of monitoring on facilities. These allow for less frequent monitoring when levels are consistently below certain thresholds. Chloroprene and ethylene oxide monitoring are not eligible for alternative sampling frequencies due to their very low action levels. Additionally, vinyl chloride monitoring can only take advantage of the alternative sampling frequencies at facilities with a perimeter under 5,000 meters, where sampling is required at each of the 8 monitoring locations during every event. A summary of the alternative sampling frequency scenarios is provided below:

  • Facilities maintaining acceptable levels for benzene (0.9 µg/m3), 1,3-butadiene (0.3 µg/m3), and ethylene dichloride (0.4 µg/m3) for two years can switch to monthly monitoring (every other sampling event).

  • Facilities with continued good performance for an additional two years of monthly monitoring can move to quarterly monitoring.

  • Eventually, facilities with consistent compliance can transition to semiannual and annual monitoring schedules.

Reporting Schedule & Requirements

Facilities must submit quarterly reports using the EPA's CEDRI system one year after starting within 45 days of each quarter's end. The EPA will then make this emissions data publicly available.

Questions? Connect with our Air Compliance Specialists

Recognizing the complexities of these evolving regulations, Trihydro leverages its extensive experience from the 2018 Refinery Sector Rule to provide comprehensive fenceline monitoring services, software, and programs. Our services are designed to efficiently and effectively guide you through this challenge, from program implementation and monitoring to data management and reporting.

With a fenceline monitoring implementation deadline of July 15, 2026, Trihydro can help you get ahead of the curve. Our services include pilot studies to assess current site conditions and identify potential emission sources. This allows you to take corrective actions before data is made publicly available through EPA's mandated quarterly CEDRI reporting. 


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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