HON Fenceline Monitoring – Are You Ready?

On April 25, 2023, the U.S. Environmental Protection Agency (U.S. EPA) proposed amendments to the National Emission Standards for Hazardous Air Pollutants (NESHAP) that apply to the Synthetic Organic Chemical Manufacturing Industry (SOCMI), more commonly referred to as the Hazardous Organic NESHAP or HON, and Group I Polymers and Resins Industries (P&R I). As part of the proposed amendments, the U.S. EPA will require fenceline monitoring at these facilities (where fenceline is equivalent to the perimeter) that use, produce, store, or emit the following six hazardous air pollutants (HAPs): benzene, chloroprene, 1,3-butadiene, ethylene dichloride, ethylene oxide, and vinyl chloride.

Two distinct methods will be required for fenceline monitoring based on the HAP used, produced, stored, or emitted at the facility: passive (sorbent tube) sampling for benzene, chloroprene, 1,3-butadiene and ethylene dichloride, and canister (silicon-ceramic coated stainless-steel canisters) sampling for ethylene oxide and vinyl chloride. Each method is different, and this article summarizes proposed requirements, action levels, reporting, and expected challenges.

Passive Sampling

Passive sampling involves using small inert-coated metal tubes filled with an adsorbent and a special cap that allows ambient air to diffuse onto the sorbent at a fixed rate, thereby retaining the compounds of interest. Samples are taken over a two-week (14-day) period, and the tubes are sent to a laboratory for analysis, with new tubes installed to maintain continuous sampling. The number of sampling sites (minimum of twelve, depending on the acreage and configuration of the facility), location of the sites, field quality control (QC) samples, and analysis will follow U.S. EPA Method 325, which is currently in use for fenceline monitoring of benzene emissions in the petrochemical refining sector.

Canister Sampling

Canister sampling includes collecting a 24-hour air sample through a particulate filter with a mechanical flow controlling device (MCFD) into an evacuated, chemically inert, specially prepared canister. Following a 24-hour sampling period, the canister is sent to a laboratory for analysis using U.S. EPA Method 327. Eight samples are proposed every fifth day, with the addition of a field blank, field duplicate and field spike, for QC, per U.S. EPA Method 327. Siting of the canisters will follow 40 CFR Part 63, Subpart H (40 CFR §63.184).

Based on the size of the facility, the U.S. EPA is proposing that facilities would be required to move the canister sampling locations with alternating sampling periods in order to ensure complete spatial coverage of the facility. In addition, U.S. EPA has proposed that all canister sampling locations initiate sampling within 60 minutes of each other.

Proposed Action Levels

The U.S. EPA is proposing the following action levels:

• 9 µg/m³ (2.82 ppbv) – Benzene
• 3 µg/m³ (1.36 ppbv) – 1,3-butadiene
• 4 µg/m³ (0.998 ppbv) – Ethylene dichloride
• 3 µg/m³ (1.17 ppbv) – Vinyl chloride
• 3 µg/m³ (0.083 ppbv) – Chloroprene
• 2 µg/m³ (0.111 ppbv) – Ethylene oxide

These action levels were derived based on U.S. EPA’s risk modeling. To account for background, the U.S. EPA proposes that each facility would determine a delta concentration (Δc), calculated as the lowest sample value subtracted from the highest sample value for each sampling period. This approach is intended to correct any estimated contribution from background emissions that do not originate from the facility. A facility would exceed an action level when the highest of the rolling annual average fenceline concentrations (corrected for background) is greater than the action level.

If the facility exceeds the action level, the facility must initiate a root cause analysis, within five days, to determine the cause. If the facility cannot determine the cause of the exceedance within 30 days, the facility would be required to use real-time sampling techniques (e.g., mobile gas chromatographs) to determine the root cause. If the exceedance is from sources under the control of the facility, they would be required to take corrective action within 45 days to bring concentrations back below the action level as soon as possible. If the facility requires longer than 45 days to implement corrective actions, they would be required to submit a corrective action plan no later than 60 days after completion of the root cause analysis.

Data Reporting

To report and submit results, facilities will be required to calculate a rolling annual average within 30 days of completion of each sampling episode and report the data for each sampler within 45 days of the end of each quarterly period through U.S. EPA’s public electronic reporting and data retrieval portal. This submittal will include the individual sample results from each sampler, coordinates of all sampler locations, annual rolling average concentration values, and notes for each sample (e.g., background corrections used, if the value was under the analytical method detection limit (MDL), or an outlier that was removed from the data set). Once submitted, the data will be publicly available.

Challenges

Fenceline monitoring is a new proposed requirement for HON facilities and as such, presents the following challenges based on U.S. EPA’s proposal:

• Different passive and canister sampling periods, with the proposed canister periods being the most stringent.
• Short analytical hold times for canister samples (7 days) which will demand quick collection and expedited shipping and analysis.
• Available canisters and capacity for the analytical laboratories based on proposed sampling periods (every 5 days), alternating locations, and analytical hold times.
• Measurement imprecision and potential false positives for ethylene oxide in canisters given the low action level (based on previous ethylene oxide studies).
• Calculation of Δc for samples that are below the analytical MDL.
• Timelines for corrective actions based on the needs/plan of the facility.

How can ALL4 help?

The U.S. EPA has a deadline to issue a final rule by March 29, 2024, and once finalized, facilities have one year to begin fenceline monitoring. As you plan and implement fenceline monitoring, do not hesitate to ask ALL4 for support. ALL4 has helped several facilities with fenceline monitoring for voluntary emissions reduction agreements, consent decrees, information requests, as well as U.S. EPA Method 325 for the petrochemical sector. ALL4 would be glad to assist with any of the following:

• Developing a fenceline monitoring plan.
• Conducting a pilot study to understand emissions, areas of concern, and potential corrective actions ahead of the finalized rule and required monitoring.
• Installation and placement of passive/canister samplers to meet the proposed rule.
• Collecting, processing, and submitting samples.
• Training for facility personnel.
• Creation of spreadsheet-like tools to record and calculate annual rolling averages.
• Analyzing raw data to subtract out background concentrations as appropriate.
• Installation and maintaining meteorological equipment for on-site ambient meteorological data if nearby data is not available (U.S. EPA Method 325 requires using meteorological monitoring data within twenty-five miles of the facility).
• Conducting quality assurance audits to verify the collection of representative samples.
• Preparing electronic reports for U.S. EPA.
• Preparing root-cause analysis and corrective action plans to submit to U.S. EPA if the facility exceeds concentration action levels.

For more information on Fenceline Monitoring and ways we can help, please contact me at khunt@all4inc.com or 512.705.0123 or contact your ALL4 project manager.