Fenceline Monitoring Data Collection and Reporting

The fenceline monitoring provisions require refineries to monitor the concentration of benzene emissions along their property boundary, or fenceline. To do this, refineries place passive diffusion tubes along their boundary, each tube collecting a continuous 2-week sample. Refineries use the measurements to calculate a benzene concentration difference (Δc) for each sampling period by subtracting the lowest individual monitor reading from the highest individual monitor reading. Refineries then calculate a rolling annual average Δc, meaning an average Δc that is updated every 2-week sampling period. Refineries report monitoring results to EPA on a quarterly basis. Quarterly reports must be submitted no later than 45 calendar days following the end of the reporting period, after which there is a 30-day period for data quality review before the results are made public.

Please Note

  • The benzene action level is 9 micrograms per cubic meter (µg/m3) for the annual average Δc. An exceedance of the action level is not a violation of the regulation, rather it requires the refinery to conduct a root cause analysis and take corrective action to reduce emissions.
  • A select number of refineries have site-specific monitoring plans, allowing them to account for known sources of benzene emissions external to the refinery when calculating the sampling period Δc value.

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