EPA Method 325 allows for the same sorbent tubes used for passive fenceline monitoring to be used in an active sample collection mode. A volumetric syringe or personal sampling pump can quickly pull a grab sample for instantaneous measurements. Two types of samples may be collected – source vapors and ambient samples collected at various distances from the source. Since the source vapors are expected to contain high concentrations of VOCs, we recommend small sample collection volumes using a provided disposable syringe. For the ambient samples collected between the source and the station, a metered sampling syringe or a battery operated sampling pump can be provided to allow for larger volumes and reporting limits similar to the 14‐day fenceline monitoring reporting limits. The actively collected samples are handled the same by the laboratory with analysis conducted by EPA 325B. With an analytical reporting limit of 5 ng, the volume required to reach the 9 μg/m3 benzene action level would be approximately 600 mL.
Passive Sorbent collection via EPA 325B (1 to 14 days)
Battery Operated Sampling Pump
The laboratory can provide some additional detailed compositional information from the EPA 325 sample data which can be valuable in root cause analysis and source identification. While EPA 325 sorbent tubes measure benzene concentrations, the tubes also retain other chemicals in the environment which are indicated by peaks on instrument’s output called the total ion chromatogram. Each peak can be tentatively identified by matching the mass spectral pattern of the peak to the NIST library of chemical spectra. The overall chromatographic pattern and the tentative identification of the uncalibrated chemicals coupled with refinery specific data on materials and processes near the monitoring station can be helpful in identifying the benzene source. Comparing the chromatographic patterns across the refinery and/or over a range of monitoring periods can also be a useful tool.
Directional VOC is a powerful new Source ID feature in the TubeTrack/Explorer Dashboard. This will allow you to pin down the likely direction of measured VOC concentration on fenceline monitoring tube samples. See the example of the Directional VOC module indicating the locally sampled emission value at tube shelter #1 originating from the NE of the current sampling location.
Utilizing the same tube used for fenceline monitoring, Benzene measurements can be determined over periods from 1 to 14 days with reporting limits below the action level of 9 μg/m3 . (Shortening the collection period raises the reporting limit proportionally.)
Source ID Options
Active Sorbent Collection via EPA 325B
Chromatographic Fingerprinting & Sample Review
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Directional VOC in the TubeTrack™/Explorer Dashboard
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Metered Sampling Syringe
Evacuated canisters can be paired with a flow controller to collect time integrated samples over periods from 30 minutes to 24 hours. Alternatively, a filter can be connected to the canister inlet to collect an instantaneous, grab sample. The canister method allows for the measurement of a large suite of calibrated VOCs including benzene via TO-15. With our significant canister inventory, we can quickly deploy canisters to the site. The expected sample reporting limit for benzene using a 1 liter canister grab sample is 3.2 μg/m3.
Canister Sample Collection via EPA TO-15
As a full-service air specialty laboratory, Eurofins Air Toxics has an advanced suite of methods available to provide additional monitoring resources. One of the challenges with fenceline monitoring is appropriately identifying on-site & off-site benzene sources for background concentration determination as well as root cause analysis when concentrations exceed the action level. Both sorbent-based and canister-based tools can be easily deployed for shorter-term sample collection and are described as follows: