Proper Collection of Soil Samples for VOC Analysis

The procedure for the sampling and analysis of soils for volatile organic compounds (TPH GRO, BTEX,
MTBE and naphthalene by GC, and volatiles by GC/MS) was updated by the USEPA in June, 1997 to
Method 5035, and later in 2002 to Method 5035A. This update eliminated Method 5030 (using a soil
packed jar) for soil volatile organic analyses because studies had shown that the results for many target
analytes were biased low. For example, figure 1 shows the loss of a VOC, TCE, in a narrow mouth vial
completely filled with sample and held at ambient temperature for 1 hour in the field.

Figure 1: Loss of TCE in soil sample in the field by volatilization at ambient temperature.   Alan D. Hewitt USACE 1999

Figure 2 shows the loss of VOCs by microbial degradation even when stored and transported at <60C.

Figure 2: Effects of Microbial degradation.  Alan D. Hewitt USACE 1999

To minimize the bias, the USEPA developed Method 5035, and now Method 5035A, incorporating
changes that greatly reduced the handling of soil samples in open air in the field by samplers and by
analysts and also incorporating preservation within 48 hours. Method 5030 is now basically for volatiles
in aqueous samples only.

USEPA Recommended Sample Collection Devices for VOCs

Method 5035 provides a couple of options for collecting soil samples – Terra Core kits and En Core®
Sampling Device.

1. Terra Core Soil Sampler
The Terra Core Soil Sampler is used for soil sampling for low and high level analyses. The sample is
collected using a syringe-like coring device and then extruded into pre-preserved vials. Each kit consists
of a foam block containing a total of three vials and a 60ml plastic jar in addition to the coring device.
The 60ml jar is to be filled for laboratory use for percent solids analysis and the reporting of results on
a corrected dry weight basis. Two vials with sodium bisulfate will be filled for low level analysis and the
third vial with methanol for a high level analysis.

Low level samples: The two vials that are preserved with sodium bisulfate are used for low level
samples. Having two vials with sodium bisulfate enables the laboratory to perform the low level analysis
twice in situations where a reanalysis is required. The low level analysis technique utilizes a closed
system purge and trap procedure. Only one analysis can be performed on each vial. For this reason, a
second vial must be collected in case reanalysis is necessary.

High level samples: Additionally, a third vial that is preserved with methanol is required in case the
sample must be re-analyzed as a high level sample. An aliquot of the methanol containing the VOCs of
concern is introduced to the instrument. For high level samples only one vial is required as multiple
analyses can be made from that vial.

2. En Core® Sampling Device
The En Core® Sampling Device can be used for low or high level analysis. The En Core® sampler is a
device made of an inert composite polymer, designed to collect, store and deliver soil in a sealed,
headspace-free state. In order to collect the sample, the En Core® sampler is attached to a reusable
metal T-handle that serves to assist in pushing the sampler in the soil. An airtight sealing cap is then
attached creating a self-contained package.

Similarly, three En Core® samplers are required for each sample providing the laboratory with two for
low level analysis and one for high level analysis. The devices are transported to the laboratory on ice
where the cap is opened and the undisturbed sample is immediately placed in the appropriate
preservation fluid, methanol or sodium bisulfate. This preservation step must take place within 48 hours
of sample collection.

The Terra Core sampling kit has at least one advantage over the En Core® sampling devices since the
samples are preserved in the field and arrive the laboratory preserved with a 14-day holding time.

If your laboratory has not fully adopted Method 5035 for the sampling of soil for VOC analysis by GC or
GCMS as illustrated above, then there is a high chance that your results are biased low. You may want
to make the necessary changes now.


Posted by Muyiwa Adebola

[email protected],

07084594001, 07084594004