Fenceline Monitoring Requirements of the Proposed Revisions to the Hazardous Organic NESHAP (HON)

WASHINGTON, D.C., JULY 27, 2023 -

On April 6, 2023, the U.S. Environmental Protection Agency (EPA) issued EPA’s proposed revisions to 40 CFR 63 Subparts F, G, H, and I. The rule affects the over 200 facilities in the US that produce synthetic organic chemicals, polymers and resins. The intent of the proposed revisions is to reduce air pollution from the Synthetic Organic Chemical Manufacturing Industry (SOCMI) and the polymers and resins industry.

What type of monitoring is required?EPA’s proposed rules would require plants to conduct fenceline monitoring if they use, produce, store, or emit any of six air toxics. Those air toxics include ethylene oxide (EtO), chloroprene, benzene, 1,3-butadiene, ethylene dichloride and vinyl chloride. If annual average air concentrations of the chemicals are higher than an “action level” at the fenceline, owners and operators would have to find the emissions source and make repairs. The proposed action levels vary depending on the chemical and are summarized in the table below, along with the fenceline sampling method:

As part of the proposed rule, EPA is also proposing Method 327 for ethylene oxide and vinyl chloride. In EPA Method 327, ambient air samples are collected using specially prepared and pre-cleaned evacuated stainless-steel canisters. For analysis, a known volume of air is directed from the canister to a pre-concentrator, and the targeted VOC from the sample is measured using a gas chromatograph mass spectrometer (GC–MS). EPA Method 327 is modeled after the techniques outlined in EPA Method TO-15. The proposed Method 327 however includes requirements that are aimed at improving the quality and consistency of the data. These changes also vastly increase the QA/QC burden on both the laboratories and the persons collecting the field samples. For chloroprene, benzene, 1-3 butadiene and ethylene dichloride the EPA is proposing to use Method 325A/B. EPA Method 325A defines the deployment of prepared passive samplers (sorbent tubes), including the determination of the number of passive samplers and locations of the samplers. EPA Method 325B describes the procedures for collection and analysis of the sorbent tubes. EPA Methods 325A/B were first introduced to monitor benzene for the refinery sector rule.

What is the sampling period and how are the results presented?For benzene, chloroprene, 1,3-butadiene, and ethylene dichloride, measured in accordance with EPA Methods 325A/B, EPA is proposing a fenceline monitoring period of 14-days. For EtO and vinyl chloride, measured in accordance with EPA Methods 327, EPA is proposing 24-hour sampling periods conducted once every 5 days. Similar to what is required in the refinery sector rule, for each sampling period (2-week period for passive tubes or 24-hour period for canisters), the facility would determine a delta c, calculated as the lowest sample value for the compound of interest subtracted from the highest sample value for the compound of interest. This approach is intended to subtract out the estimated contribution from background emissions that do not originate from the facility. The delta c for the most recent year of samples (26 sampling periods for passive tubes and 73 sampling periods for canisters) would be averaged to calculate an annual average delta c.


What happens when an action level is exceeded?If the annual average concentration, as determined on a rolling average every sampling period, exceeds the action level, facilities have to perform a root cause analysis. The root cause analysis would be required to be initiated within 5 days of determining that an action level was exceeded. If the underlying causes of the action level exceedance are deemed to be from sources under the control of the facility, the facility would be required to take corrective action to address the underlying cause of the exceedance and to bring concentrations back below the action level as expeditiously as possible. If the owner or operator cannot determine the root cause of the exceedance within 30 days of determining there was an exceedance of an action level, the owner or operator would be required to use real-time sampling techniques (e.g., mobile gas chromatographs, sensors, UV-DOAS, FTIR) to determine the root cause of the exceedance. Completion of the root cause analysis and initial corrective action would be required within 45 days of determining that there was an exceedance of an action level. If the owner or operator requires longer than 45 days to implement the corrective actions identified by the root cause analysis, the owner or operator would be required to submit a corrective action plan no later than 60 days after completion of the root cause analysis.

What will the challenges be for this type of fenceline monitoring?Laboratory capacity and availability of sampling equipment will be of concern for companies complying with this rule. Laboratories will have to invest in additional analytical and sampling equipment as well as chemists to meet the anticipated demand. Companies complying with this rule will want to collect data to determine if there is a risk of non-compliance well ahead of the effective date. The challenge with the methods prescribed by EPA is that they don’t provide real-time data and the time from sample collection to having results is usually a few weeks. Real-time data collection can provide determinations of compliance that can also be tied to process operations. For example, if a short-term spike in a given pollutant is observed, the facility can correlate that spike with process observations and mitigate that event moving forward. Modern monitoring tools also offer the ability to identify the source of the emission event, based upon wind speed and wind direction as well as the sensor data. Once the rule is implemented, if concentrations are found to be above the action level facilities have 45 days to identify the cause and correct it. Without real-time data being tied to process operations and source identification, it will be challenging for a facility to determine the cause of the exceedance exposing a facility to notice of violations and fines.

How can Sensible EDP Help?The team at Sensible EDP can monitor both at the fenceline and in the facility, where events occur. Sensible EDP integrates various advanced monitoring technologies such as:

● Point or open path optical techniques such as UV-DOAS, FTIR, TDL, and CRDS.● Gas chromatography, employing different detectors such as FID, PID, and TCD.
● Sensors using various detection principles to precisely monitor air samples.

These techniques combined with meteorological data and our proprietary stand-alone software, pinpoint the source of leaks or equipment issues early, before they escalate. This allows for swift response and mitigation.

For more information contact Montrose at info@sensible-edp.com.