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EPA 325, fenceline monitoring

EPA Method 325, Volatile Organic Compounds from Fugitive and Area Sources, was created for monitoring the fencelines of refineries for benzene and includes two sub-part methods:

  • EPA Method 325A: Sampler Deployment and VOC Sample Collection
  • EPA Method 325B: Sampler Preparation and Analysis.

These complementary US EPA methods outline the design, deployment, preparation, and analysis of a series of passive sampling devices suspended around the refinery property line.

In an effort to adequately provide spatial coverage to determine representative pollutant concentrations, the US EPA has specified 12 to 24 diffusive samplers must be deployed on a bi-weekly basis to monitor benzene concentrations around the fenceline of every refinery property. The number of samplers is based on the size of the refinery (<750 acres, 750 to 1,500 acres, and >1,500 acres).

The concentration of benzene on the samplers must be monitored on an annual rolling average basis in order to determine if there are significant excess emissions of fugitive sources that need to be addressed.


Analytical method & sampling procedure

Samples are analyzed using a thermal desorption device. This works by heating the sample tube and releasing the compounds into a flow of inert gas. Once sample is focused, it is heated again and rapidly injected into the GC column in a narrow band of vapor.

Samples are collected using a 3.5’’ long x ¼’’ OD stainless steel tube packed with a carbon-based sorbent, in which one end of the tube is outfitted with an open mesh diffusion cap for volatile compound collection.

Sorbent tubes are extremely versatile and can be deployed for weeks at a time. The tubes are deployed for 14 days at location points outlined per EPA Method 325A (either equal linear distance between samplers or equal degrees of separation around the geometric center of a facility). After sampling is complete, the tubes are capped and sent to the laboratory for analysis.

The method covers 10 of the most common illicit drugs

Example of compounds included in method EPA 325



EPA 325 B Fenceline Monitoring Canada


EPA 325 B Sampling Instructions USA


EnviroMail 03 USA Fenceline Monitoring EPA 325B

01 NOV 2017

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