EPA Method 325 requires low-level monitoring of benzene at the refinery fenceline via passive sorbent tubes sampling over 2 week intervals. Compliance will be costly to refineries; but to make the most of the dollars invested and to fully comply with the regulation, operators need to understand the why and how of refinery fenceline monitoring.
Understanding The Why
Rather than acting on a mandated "because I said so" approach. It's better to understand why EPA is taking action on monitoring benzene and potentially other toxic VOC's at the fenceline. According to EPA, 85% of benzene emissions from refineries occur from fugitive sources. Typical emission sources are:
- Process piping leaks
- Wastewater streams leaks, vents, cooling towers, and drains
- Tank leaks, vents, pump leaks, maintenance related emissions
Emissions are likely to have the highest concentrations at ground level and because monitoring specific sources in the refinery will be impossible, perimeter ground level sampling makes sense and will provide the refinery operator the best data for monitoring and addressing potential benzene emissions. The ultimate payoff of will be protecting and improving the health of area communities.
How To Get The Most Out Of EPA 325
- Require perimeter monitoring and corrective action upon exceeding trigger of 9 ug/m3 (2.8 ppbv)
- Require sub-3 ppb level monitoring capability for benzene.
- Monitor by Auto-GCs and passive monitoring using thermal desorption tubes.
- Trigger is based on highest concentration modeled at any fenceline.
- Continuous, 2-week sampling periods.
- Complete coverage of fenceline, average concentration over the 2 week period.
- Trigger for Root Cause Analysis / Corrective Action based on annual average concentration.
EPA has mandated that thermal desorption tubes be inert coated to prevent adsorption of active and reactive compounds. According to EPA the analytical approach will be based on the TO-17 method which specifies pumped sampling into tubes with thermally stable adsorbents.
Potential sampling related issues with EPA 325 are:
- Other non target VOC's and coelution of sample peaks
- Sorbent decomposition
- VOC's not completely cleaned from tubes
- Contamination from sample handling.
SilcoNert® coating is recognized industry-wide as the leading inert surface that enables refiners to sample their processes reliably with high accuracy and reproducibility. If left uncoated, even low surface area parts will adsorb compounds of interest and lead to invalid results, causing expensive retesting.
Figure 1: Uncoated surfaces within the GC flow path adsorb benzene, toluene, xylenes
and other target analytes, leading to severe peak distortion and missing peaks.
Benzene, organosulfur compounds, and other hazardous air pollutants (HAPs) that can be measured with Method 325 protocol are known to be highly reactive with bare, untreated stainless steel. SilcoNert® provides a uniform barrier between substrate and sample while preventing analytes of interest from adsorbing onto the surface, ensuring they reach the analyzer and can be accurately assessed at low levels (ppb or lower).
Figure 2: SilcoNert-coated GC flow paths produce sharp peaks with high resolution, giving refineries superior analytical accuracy and full compliance with EPA regulations.
Coat the entire sample flowpath
To assure complete inertness, coat the entire sample flowpath with an inert coating like SilcoNert® 2000. Be sure high surface area internal components are coated:
Image courtesy of US EPA.