PASSIVE, NON-INTRUSIVE SOIL-GAS SAMPLING
METHOD TO TARGET ELEMENTAL MERCURY
Beacon Environmental Services, Inc.
323 Williams Street
Bel Air, MD 21014
323 Williams Street, Bel Air, MD 21014 USA 1-410-838-8780 ●P
1-410-838-8740 ●F
BEACON-USA.COM
PASSIVE, NON-INTRUSIVE SOIL-GAS SAMPLING
METHOD TO TARGET ELEMENTAL MERCURY
1.0
Background
Beacon Environmental Services, Inc. provides passive soil-gas sampling and analytical services
to target elemental mercury contamination in soil and soil vapor. The state-of-the-art sampling
and analytical procedures followed by Beacon Environmental are the foundations for a highly
sensitive technology to identify trace levels of mercury present in the vapor phase. Sample
collection is performed by using either a subsurface sampler emplaced within an approximately
two to three centimeter (2-3 cm) diameter hole advanced to a typical depth of 30 cm to one meter
or by using a completely non-intrusive, surface-placed flux chamber. Either sampling approach
is provided through easy-to-use BESURE Sample Collection KitsTM for the client’s personnel to
collect the samples and ship the samplers to Beacon Environmental’s contract laboratory for
analysis.
The analytical results for a passive soil gas method are not presented as a concentration, but in
units of mass for comparison between sample locations to identify source areas, to delineate the
lateral extent of contamination, including migration pathways, and to monitor remediation
programs. The soil gas concentration reported with an active soil gas method that uses a high
flow pump may not represent the actual concentration in soil gas because of the forced
movement of soil gas. However, valid soil-gas concentrations can be measured using packed
sorbent tubes and a low-flow pump with analyses by Beacon Environmental’s contract
laboratory.
2.0
Survey Design
Passive soil gas surveys targeting elemental mercury utilize samplers that are emplaced
subsurface to capture mercury in soil gas without forcing the flow rate of soil gas. Samplers are
typically placed in a grid pattern to simultaneously sample trace levels of mercury in soil gas that
originate from contamination in the soil. By sampling all locations at the same time, the
temporal variations in soil-gas concentrations that are known to occur daily and even hourly are
normalized. In addition, the spatial variability of contamination is better defined with a passive
soil gas survey because the lower sampling and analytical costs of the method allow for more
locations to be sampled than normally would be with a fixed budget. Passive soil gas methods,
in general, have been demonstrated to be more sensitive and reproducible than active soil gas
methods and are an effective means to characterize sites for targeted compounds.
The survey design varies depending on the amount of historical and other site information that is
available prior to initiating the passive soil gas (PSG) survey. Typically an unbiased grid is
established across the site with additional biased sample locations to target specific features. The
spacing between sample locations is dependent upon the expected depth of the compounds of
concern, the soil types, and the size of the area to be investigated. Tape measures are used to
locate the sample points in the field and record them on a map. As an option, global positioning
system (GPS) equipment can be used to collect the sample location coordinate data.
“BEACON ⎯ A PROVEN LEADER IN SOIL-GAS SURVEYS”
323 Williams Street, Bel Air, MD 21014 USA ph: 1-410-838-8780 www.beacon-usa.com
Passive, Non-Intrusive Soil-Gas Sampling Method to Target Elemental Mercury
Beacon Environmental Services, Inc.
Each PSG Sampler contains a specialized media that binds with mercury in the vapor phase.
Following retrieval, the PSG Samplers are shipped to a laboratory under contract to Beacon
Environmental for analysis. Samples are analyzed following NIOSH Method 6009 or OSHA ID140 procedures, cold vapor-atomic absorption spectrophotometer (CVAA) methods.
Following analysis and review of the data, a
comprehensive survey report is provided by
Beacon Environmental. The report includes
tabular results as well as a color isopleth map
showing the distribution of mercury across the
site. An example color isopleth map is provided
as Figure 1. The survey report also provides a
description of the field and laboratory procedures,
a discussion on the quality assurance/quality
control procedures followed, and a narrative
describing the specifics of the project.
Figure 1 – Example Color Isopleth Map
3.0
Soil-Gas Sampling Procedures
To perform a soil-gas investigation, Beacon Environmental provides BESURE Sample Collection
KitsTM with all the materials necessary to collect the requested number of soil-gas samples.
Beacon Environmental offers two sampling approaches: a completely non-intrusive method and
a minimally intrusive method where the PSG Samplers are installed in the ground to a depth as
shallow as 10 cm. The procedures for each of these sampling methods are described below.
To collect soil-gas samples using the Minimally Invasive Sampling Method, a 2 to 3 cm
diameter hole is made to a depth of 10 cm using a hammer and a metal stake provided in the
Field Kit. When applicable, a hammer drill, slide hammer, or other comparable equipment then
can be used to advance an approximately 1.5- to 2-centimeter
diameter hole to a one-meter depth. In either case, the PSG
Sampler is installed in the top 10 cm of the hole. For locations
covered by asphalt or concrete surfacing, a 3 to 4 cm diameter
hole is drilled through the surfacing to the underlying soils, and
the hole can be sleeved with a sanitized pipe provided in the
Kit. After the Sampler is installed inside the pipe, the hole is
patched with an aluminum foil plug and a thin concrete patch
to protect the sampler. Following the exposure period, the
Samplers are retrieved and shipped to the laboratory for
analysis. Figure 2 shows a PSG Sampler for subsurface
installation as it looks when received in the Field Kit.
Figure 2 – PSG Sampler
Beacon Environmental provides in the BESURE Sample Collection KitsTM pre-cleaned sleeves
when sampling through impermeable surfacing. These sleeves prevent any horizontal migration
of vapors in the more porous subgrade from significantly influencing the soil-gas samplers. The
sleeves are advanced below the subgrade and tapped into the underlying soils so that the
Samplers will only be capturing mercury in soil gas that is moving vertically through the soils
“BEACON ⎯ A PROVEN LEADER IN SOIL-GAS SURVEYS”
323 Williams Street, Bel Air, MD 21014 USA ph: 1-410-838-8780 www.beacon-usa.com
Passive, Non-Intrusive Soil-Gas Sampling Method to Target Elemental Mercury
Beacon Environmental Services, Inc.
beneath, and not in the vapors that may be migrating laterally through the more porous subgrade.
Other soil-gas vendors simply create a hole one meter deep, and leave their samplers unprotected
to the horizontal migration of vapors in the subgrade. This easy-to-perform but important
procedure of using the sleeves is critical to an accurate and reliable soil gas survey (see
Attachment 1).
To collect soil-gas samples using the Non-Intrusive Surface Flux Chambers, the sampling
team prepares the sample location as necessary and removes a laboratory-conditioned cartridge
from a borosilicate glass vial. The cartridge is then hung from a stainless steel hanger, and this
sampler assembly is positioned immediately above the ground surface at the designated location.
The stainless steel flux chamber is then lowered over the sampler assembly, open end down, and
the chamber is surrounded with a collar of sand or local soil. The chamber can be covered with a
camouflage cloth that is secured with a small additional amount of sand or soil. Figure 3
provides a diagram of the Surface Flux Chambers. During retrieval, the cartridges are placed in
borosilicate vials for transport.
Cartridge Hanger
Cartridge Hanger
Camouflage
Cover
(when needed)
Stainless Steel
Flux Chamber
Camouflage
Cover
(when needed)
Stainless Steel
Flux Chamber
18 cm
18 cm
Beacon's
Hydrophobic
Mercury
Sampling
Adsorbent
Cartridges
Media
Beacon's
Hydrophobic
Mercury
Sampling
Adsorbent
Cartridges
Media
Seal
Seal
Soil
Concrete Surface
Figure 3– Non-Intrusive Surface Flux Chamber
With either sampling approach, the sampling media is exposed to subsurface gas for typically
seven (7) to 14 days depending on the objectives of the investigation and the concentrations that
are expected to be present. A trip blank, which remains with the other PSG samples during
preparation, shipment, and storage, is included with each batch of up to 30 field samples.
Beacon Environmental assists in planning the sampling event so that the highest level of
sensitivity and accuracy can be achieved.
A two-person team can install approximately 50 to 100 samplers per day depending on the
number of sample locations that are covered with asphalt, concrete, or gravel surfacing. For
retrieval of the Samplers, one person can retrieve approximately 50 samplers per day and patch
the holes through any surfacing.
Figure 4 provides photos of PSG subsurface samplers being installed using the BESURE Sample
Collection KitsTM .
“BEACON ⎯ A PROVEN LEADER IN SOIL-GAS SURVEYS”
323 Williams Street, Bel Air, MD 21014 USA ph: 1-410-838-8780 www.beacon-usa.com
Passive, Non-Intrusive Soil-Gas Sampling Method to Target Elemental Mercury
Beacon Environmental Services, Inc.
Figure 4 — Installation of Samplers with BESURE Sample Collection KitTM
4.0
Sample Custody Procedures
A chain-of-custody accompanies the field samples at all times from the time the samples are
collected until final analysis. BESURE KitsTM are shipped with tug-tight custody seals to ensure
that samplers are not tampered with during transport (see Figure 5).
Figure 5 -- BESURE KitTM
5.0
Analytical Procedures
Soil gas samples are analyzed by a contract laboratory to Beacon Environmental using cold
vapor-atomic absorption spectrophotometer (CVAAS) instrumentation, following NIOSH 6009
or OSHA ID-140 procedures. Analytical results are based on an external five-point calibration
and internal control blank and internal control verification analyses are performed every 12 hours
to ensure that the system is contaminant free and properly calibrated. The laboratory’s reporting
limit for mercury is 0.06 micrograms (ug).
6.0
Reporting
Following analysis and a data review, a comprehensive survey report is provided that contains:
project objectives,
the plan of investigation,
the QA/QC program and findings,
laboratory data (in micrograms),
“BEACON ⎯ A PROVEN LEADER IN SOIL-GAS SURVEYS”
323 Williams Street, Bel Air, MD 21014 USA ph: 1-410-838-8780 www.beacon-usa.com
Passive, Non-Intrusive Soil-Gas Sampling Method to Target Elemental Mercury
Beacon Environmental Services, Inc.
data converted to emission flux rates (µg/m2/min) if surface flux chambers are employed,
a color isopleth map showing the distribution of mercury,
field procedures,
laboratory procedures,
Field Deployment Reports, and
Chain-of-Custody documentation.
Beacon Environmental requests that a CAD drawing of the site is provided with coordinate data
for each location. Beacon Environmental will return the CAD drawing with the color isopleth
map provided as new layers to the file, if requested. Beacon Environmental will provide post
survey support to assist in interpreting the data, when requested.
“BEACON ⎯ A PROVEN LEADER IN SOIL-GAS SURVEYS”
323 Williams Street, Bel Air, MD 21014 USA ph: 1-410-838-8780 www.beacon-usa.com
Attachment 1
EFFECTIVE PASSIVE SOIL-GAS SAMPLING PROCEDURES
PSG Samplers need only be installed to a 10 centimeter depth because of the sensitivity of the method.
However, the method is extremely versatile and installation procedures can be adapted to meet project
objectives or client requirements.
When a PSG Sampler is installed in the ground,
the top of the hole is completely sealed by
collapsing the soils above the Sampler or
patching the drilled hole through the surfacing.
Other vendors use a permeable cork to plug their
installation hole, which allows subsurface gases
to escape before the adsorbent captures the
organic compounds (reducing sensitivity) and
permits vapors from above the surface, as well as
surface water, to enter the hole (false positives).
Beacon Environmental’s PSG Samplers are not
susceptible to these influences because they are
effectively sealed in the subsurface.
As mentioned above, Beacon Environmental’s
Samplers are versatile and for some projects a
higher
sensitivity
is
required
because
contaminants are present at low concentrations or
soils are fairly impermeable. In these situations,
the sampling hole is advanced to a greater depth using a hammer drill, slide hammer, or direct push
equipment. Because the soil vapors that enter the hole will migrate upwards in this newly created
preferential pathway, it is not necessary to push the Sampler to the bottom of the hole. Therefore, the
Sampler can still be installed in the upper 10 centimeters of the hole
Samplers installed through an impermeable
surface are sleeved in pre-cleaned protective
sleeves (provided by Beacon Environmental).
These sleeves prevent any horizontal
migration of vapors in the more porous
subgrade from influencing the soil-gas
Samplers. As the accompanying diagram
shows, the metal sleeves are advanced below
the subgrade and tapped into the underlying
soils so that the Samplers will only be
adsorbing compounds in soil gas that are
moving vertically through the soils beneath,
and not in the vapors that may be migrating
laterally through the more porous subgrade. Other soil-gas vendors simply create a hole one meter deep,
and leave their samplers unprotected to the horizontal migration of vapors in the subgrade. This easy-toperform but important procedure is yet another reason why Beacon Environmental’s method has achieved
the reputation as being the most accurate and reliable soil gas technology available.
“BEACON ⎯ A PROVEN LEADER IN SOIL-GAS SURVEYS”
323 Williams Street, Bel Air, MD 21014 USA ph: 1-410-838-8780 www.beacon-usa.com