Sweeny Plant

A fenceline monitoring program utilizes a monitoring technology to measure the ambient air concentration at the fenceline (property line or perimeter) of a manufacturing site (i.e., petroleum refinery, chemical plant) for a specific chemical.

A work practice standard for fenceline monitoring was promoted by the United States Environmental Protection Agency (EPA) as an appropriate method to provide open and transparent evaluation of a site’s emissions monitoring and control methods on a continuous basis. To achieve that goal, the EPA developed this work practice and published it in December 2015. This work practice specified the monitoring technology to be used, an implementation approach, and a benzene fenceline concentration action level above which owners or operators would be required to implement corrective actions to reduce their fenceline concentration below this action level. The details of the fenceline monitoring work practice are prescribed in EPA Test Methods 325A and 325B.

This is the work practice that Chevron Phillips Chemical uses for our fenceline monitoring programs. In fact, there are over 150 different refineries and chemical plants in the United States and Canada utilizing this technology and work practice for fenceline monitoring.

Did you know?

The science of absorption is one we are familiar with in our daily lives. Examples are using paper towels to absorb liquids from the counter or baby diapers. The difference in fenceline monitoring is that after absorbing the chemicals in the sampling tubes, they are later desorbed (i.e., absorbed chemicals removed from the absorbent) in the laboratory so that how much was collected can be measured.

What is the process for fenceline monitoring?

The monitoring technology being used at Chevron Phillips Chemical is a series of passive (diffusive) sorbent tubes sampling locations to monitor fenceline concentrations for benzene. Air samples are collected by the sampling tubes that are filled with an absorbent material. Basically, we a have series of small sampling tubes filled with an absorbent material in which hydrocarbons (benzene) will be absorbed and retained on the sorbent tube over a 14-day sampling period.

The sampling tubes are safely detached, re-sealed, and sent to an independent accredited laboratory for a Thermal Desorption-Gas-Chromatography/Mass Spectrometry (TD-GC/MS) analysis to determine the benzene concentration every 14 calendar days. Then a set of freshly conditioned and qualified sampling tubes are immediately replaced to begin monitoring the subsequent 14-day sampling period.

Monitoring sampling locations are in place and collect data for ambient air concentrations every day.

What does Chevron Phillips Chemical do if the concentrations are greater than the action level?

We will conduct a Root Cause Analysis (RCA) if the annual average benzene concentration Δc value exceeds the action level of 9 µg/m3. The RCA process includes the identification of corrective actions and has specific timelines for completion and reporting to the EPA, if required. These steps include:

• Initiate the RCA within 5 days of determining an action level exceedance

• Complete the RCA and corrective actions within 45 days

• First 14-day sampling period results after completing the corrective actions Δc value must be ≤ 9 µg/m3 to demonstrate effectiveness

• A Corrective Action (CA) Plan, which is publicly available, must be submitted to the EPA within 60 days after the action level exceedance is identified if:

  • First 14-day sampling period  results after completing the corrective actions Δc value is >9 µg/m3; or

  • Identified corrective actions cannot be implemented within 45 days

If there are any questions on the RCA process, CA Plan, or activities, please contact us.

The fenceline data allows sites to have additional insight into their emission sources and their potential impact such that they can take appropriate actions to address the emissions from these sources in the event the annual average benzene concentration Δc value for a nearby monitor exceeds the action level of 9 µg/m3. The publicly available data provides transparency and allows for public oversight.  Since samples are taken every 14 calendar days, sites may also be able to identify sources that might lead to elevated fenceline concentrations and can correct issues early, in efforts to avoid exceeding the benzene action level. The data is being provided to the public so that they can stay informed on the status of the site’s emissions sources and the actions the site is taking to address them, as necessary.

The benzene action level is not an ambient air standard. The fenceline monitors are not intended to provide a measure of benzene levels in the community. There is no correlation between the benzene action level and any health-based benzene or other hazardous air pollutant exposure standard. The benzene action level does not correlate to a benzene emissions level that presents a risk to the public. EPA did not establish the fenceline monitoring program as a risk reduction step under Clean Air Act section 112(f)(2). Rather, the fenceline monitoring requirements are a development of practices that will provide additional information on the status of emission sources to the manufacturing site and the public. It is also important to note that the fenceline monitoring program is not an appropriate tool for monitoring and assessing emergency releases since the data from the monitors are not available immediately.

The fenceline monitors are not limited to measuring emissions from only the site. The passive diffusive tubes may collect benzene from nearby sources that the site does not manage, such as neighboring facilities, roadways, airports, marine ports and from environmental events (i.e., smoke from forest fires). External emission sources may contribute to elevated background readings that are measured by the site’s fenceline monitors. Consequently, while this monitoring program is a reasonable means for the site to oversee their emission sources, there may be situations where the monitors identify benzene emissions that do not originate from the site because they do not perfectly isolate the site’s emission sources.