How the Fenceline Monitoring Data Should Be Used

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 Δc for a nearby monitor exceeds the benzene action level. The publicly available data provides transparency and allows for public review.  Since samples are taken every two weeks, 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.

How the Fenceline Monitoring Data Should Not Be Used

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 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 (e.g., 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 sites to oversee their emissions sources, there may be situations where the monitors identify benzene emissions that do not originate from and thus does not perfectly isolate site’s emission sources.