ISO 10381-7:2005

INTERNATIONAL ISO
STANDARD 10381-7
First edition
2005-09-01
Soil quality — Sampling —
Part 7:
Guidance on sampling of soil gas
Qualité du sol — Échantillonnage —
Partie 7: Lignes directrices pour l'échantillonnage des gaz du sol

Reference number
©
ISO 2005
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ii © ISO 2005 – All rights reserved

Contents Page
Foreword. iv
Introduction . v
1 Scope .1
2 Normative references .1
3 Terms and definitions .1
4 Preliminary points to be considered.4
5 Permanent gases .5
5.1 Investigation objectives .5
5.2 Basic principles.5
5.3 General considerations for sampling .7
5.4 Sampling requirements.7
5.5 Technical equipment .9
5.6 Sampling plan .10
5.7 Sampling.11
5.8 Storage and transport of samples for laboratory analysis .12
5.9 Sampling report .12
5.10 Quality assurance.13
5.11 Interferences .15
6 Volatile organic compounds (VOCs) .16
6.1 Objectives.16
6.2 Basic principles .16
6.3 General considerations for sampling .17
6.4 Sampling requirements.18
6.5 Technical equipment .20
6.6 Sampling plan .22
6.7 Sampling.22
6.8 Storage and transport of samples for laboratory analysis .24
6.9 Sampling report .24
6.10 Quality assurance.24
6.11 Interferences .25
6.12 Interpretation of soil-gas analyses for VOCs.26
Annex A (informative) Sampling protocol.27
Annex B (informative) Anaerobic degradation and the formation of methane and carbon dioxide.29
Annex C (informative) Strategy of soil-gas investigations .31
Annex D (informative) Apparatus for measurement of gas flow rate .34
Annex E (informative) Portable equipment for measurement of concentrations of permanent
gases.35
Bibliography .38

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 10381-7 was prepared by Technical Committee ISO/TC 190, Soil quality, Subcommittee SC 2, Sampling.
ISO 10381 consists of the following parts, under the general title Soil quality — Sampling:
 Part 1: Guidance on the design of sampling programmes
 Part 2: Guidance on sampling techniques
 Part 3: Guidance on safety
 Part 4: Guidance on the procedure for investigation of natural, near-natural and cultivated sites
 Part 5: Guidance on the procedure for the investigation of urban and industrial sites with regard to soil
contamination
 Part 6: Guidance on the collection, handling and storage of soil for the assessment of aerobic microbial
processes in the laboratory
 Part 7: Guidance on sampling of soil gas
 Part 8: Guidance on sampling of stockpiles
iv © ISO 2005 – All rights reserved

Introduction
ISO 10381-7 is one of a group of International Standards to be used in conjunction with each other where
necessary. ISO 10381 (all parts) deals with sampling procedures for the various purposes of soil investigation.
The stated soil-gas and landfill-gas measurements do not give any quantitative statement of the total quantity
of material detected in soil gas or soil. The measurement results can be influenced by, e.g. temperature,
humidity, air pressure, minimum extraction depth, etc.
The general terminology used is in accordance with that established in ISO/TC 190 and, more particularly,
with the vocabulary given in ISO 11074-2.
In addition to the main components (nitrogen, oxygen, carbon dioxide), soil gas can contain other gases
(methane, carbon monoxide, mercaptans, hydrogen sulfide, ammonia, helium, neon, argon, xenon, radon, etc.).
It can also contain highly volatile organic compounds or inorganic vapours (mercury) which are of special interest
within the framework of investigating soil and groundwater contamination.
Due to the different physical properties and ranges of concentrations of gases in soil and landfills as well as the
wide variety of objectives for soil-gas sampling, this part of ISO 10381, after the general clauses 1 to 4, is
subdivided into two sections:
a) permanent gases of soil gas and landfill gas (Clause 5); and
b) volatile organic compounds (VOCs) (Clause 6).
Thus it is inevitable that some details are repeated in both clauses in order to make the guidance
comprehensive.
INTERNATIONAL STANDARD ISO 10381-7:2005(E)

Soil quality — Sampling —
Part 7:
Guidance on sampling of soil gas
WARNING — This part of ISO 10381 concerns on-site soil and sub-soil gas analysis requiring
particular health and personal safety precautions.
1 Scope
This part of ISO 10381 contains guidance on the sampling of soil gas.
This part of ISO 10381 is not applicable to the measurement of gases from the soil entering into the atmosphere,
the sampling of atmospheric gases, or passive sampling procedures.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 10381-1, Soil quality — Sampling — Part 1: Guidance on the design of sampling programmes
ISO 10381-2, Soil quality — Sampling — Part 2: Guidance on sampling techniques
ISO 10381-3, Soil quality — Sampling — Part 3: Guidance on safety
ISO 11074-1, Soil quality — Vocabulary — Part 1: Terms and definitions relating to the protection and
pollution of the soil
ISO 11074-2, Soil quality — Vocabulary — Part 2: Terms and definitions relating to sampling
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 11074-1 and ISO 11074-2 and the
following apply.
3.1
active soil-gas sampling
sampling by extracting a certain volume of soil gas
3.2
biodegradation
the physical and chemical breakdown of a substance by living organisms, mainly bacteria and/or fungi
3.3
borehole
hole formed into soil or landfilled material into which may be installed a standpipe to enable gas monitoring to
be carried out
NOTE A borehole is also used as a means of venting or withdrawing gas.
3.4
concentration/adsorption method
method in which substances to be determined are concentrated adsorptively on an adsorbent (e.g. activated
charcoal or XAD-4 resin), subsequently desorbed and analysed
3.5
dead volume
volume which is present between the suction opening of the soil-gas probe and the sampling vial, including the
volume of the sampling vial or of the absorption tube
3.6
direct method
direct measuring method
method of analysis where the soil-gas sample (aliquot) is directly introduced into a suitable equipment without
first being concentrated and subjected to analysis
3.7
direct-reading detecting tube
glass tube filled with reagents which, after drawing through certain gaseous compounds, show concentration-
dependent chromophoric reactions and which are thus used for qualitative and semi-quantitative analyses as
well
NOTE It is important that attention be paid to cross-sensitivities.
3.8
gas migration
movement of gas and vapour from the wastes within a landfill or through the ground to the adjoining strata, or
emission to the atmosphere
3.9
gas monitoring well
standpipe suitably installed inside a borehole from which gas samples can be taken to measure soil-gas
concentrations and to monitor changes in composition of soil gas or soil-gas migration
3.10
gas sampling
collection of a proportion of material for testing such that the material taken is representative of the gas in the
pore space of the location of sampling
3.11
landfill
deposition of waste into or onto the land as a means of disposal
NOTE It can eventually provide land which may be used for another purpose.
3.12
landfill gas
mixture of permanent gases (main components), dominated by methane and carbon dioxide, formed by the
decomposition of degradable wastes within landfill sites
NOTE It can also include a large number of VOCs (trace components).
2 © ISO 2005 – All rights reserved

3.13
lower explosive limit
LEL
lowest percentage (volume fraction) of a mixture of flammable gas with air which will propagate an explosion
in a confined space at 25 °C and atmospheric pressure
3.14
one-stage soil-gas sampling
sampling of soil gas directly from a soil-gas probe placed in soil, without pre-drilling
3.15
passive soil-gas sampling
sampling based on the adsorption of soil gas on an absorbent placed in soil, without employing negative
pressure
3.16
permanent gas
element or compound with boiling point below − 60 °C at atmospheric pressure
3.17
sample volume
volume of soil from which the soil-gas sample is taken
3.18
soil gas
gas and vapour in the pore spaces of soils
3.19
soil-gas monitoring device
borehole finished with suitable material for stabilisation of the borehole wall and/or for limiting the sampling area.
NOTE Depending on the type and stability of fitting, a difference is made between temporary (for single or short-term
repeated soil sampling) and stationary (for long-term observations) soil-gas measuring points.
3.20
soil-gas probe
soil-gas sampling probe
probe, generally a tube, which is installed directly into soil (one-stage soil-gas sampling), or in a borehole
(two-stage soil-gas sampling) to take soil-gas samples.
NOTE By applying a negative pressure to the upper end of the soil-gas probe (head), the soil gas at the lower end (tip)
is drawn through the suction opening(s) and transferred to a gas collecting equipment and online measurement equipment
(direct measuring method) or to an absorbent (concentration method), which are installed either in or at the head of the
soil-gas probe or subsequently used.
3.21
soil-gas suction test
continuous soil-gas sampling from a borehole well over a controlled longer period of time (mostly several
hours up to days) to observe the variations over time of the gas concentrations and of the pressure distribution
in the soil
3.22
two-stage soil-gas sampling
sampling done firstly through installation of a borehole with the aid of a drilling instrument or by small boring, and
secondly by sampling of soil gas from a soil-gas probe installed in the borehole
3.23
volatile organic compound
VOC
compound which is liquid at room temperature (20 °C) and which generally has a boiling point below 180 °C
EXAMPLES single-ring aromatic hydrocarbons and other low boiling halogenated hydrocarbons, which are used as
solvents or fuels, and some degradation products.
4 Preliminary points to be considered
The choice of sampling technique shall be consistent with the requirements of the investigation (including
subsequent analytical procedures). Consideration should also be given to the nature of ground under
investigation, as well as the nature and distribution of contamination, the geology and the hydrogeology. Every
effort should be made to avoid cross-contamination and at no point should underlying aquifers be put at risk.
Before intrusive works begin, a comprehensive check should be made of the ground to ensure that no
services or structures are at risk and no hazards are present. (For more information on sampling techniques
and safety, see ISO 10381-2 and ISO 10381-3.)
When sampling soil gas close to the surface, the effect of ambient air penetration needs to be considered. The
sampling depth is determined by the presence of impermeable cover over the ground surface, the soil type
(porosity, clay content, etc.) and the depth of bedrock. It is considered unlikely that useful samples can be
collected at depth less than 0,5 m. For routine monitoring of soil gas, a minimum depth of 1 m is
recommended.
Circumstances in cold conditions make soil-gas sampling difficult in many ways. Ground frost greatly limits the
mobility of gas in soil and should be considered in planning and carrying out sampling as well as in interpreting
the measuring results. Similarly water saturated ground can limit mobility.
The main problem with soil-gas sampling below the frozen ground is the loss of air-filled porosity due to the high
moisture content in the zone between frozen and unfrozen parts of the ground. Consequently the samples shall
be taken from greater depths.
All buildings constructed on unfrozen ground act as pathways or barriers for upwards soil-gas migration.
Underpressure and differences in concentration in the buildings can also assist gases to penetrate the
basements of buildings.
Pressure effects caused by the rise of warm air within buildings can assist the entry of gases into buildings.
Some organic pollutants in the gas phase in soil and sub-soil can present toxicological risks of varying severity.
Due to this possibility, personnel should be equipped, according to the potential toxicity (assumed or measured),
with suitable protective material.
Certain organic fumes can form explosive mixtures with air. (Explosivity limits and self-ignition temperatures
should be taken into account.). It is therefore appropriate to use electrical equipment and tools which are suitable
for use in explosive atmospheres.
Health and safety issues should be considered at all times. Training should be given to ensure that personnel
understand the necessary precautions. (For more information on safety, see ISO 10381-3.)
4 © ISO 2005 – All rights reserved

5 Permanent gases
5.1 Investigation objectives
5.1.1 Soil gas
The objectives of the investigation for permanent soil gases are
 analysis of soil-gas composition, and
 determination of the difference of concentration on a site.
5.1.2 Landfill gas
The objective of the investigation for landfill gases is
 analysis of landfill gas composition.
5.1.3 Further objectives
Further objectives may be
 assessment of possible reasons for plant growth inhibition,
 optimization or control of sealings or gas collecting installations,
 rough estimate of gas production potential and duration of gas production,
 detection of underground combustion,
 design of gas protection measures for buildings.
5.2 Basic principles
5.2.1 Physical and chemical principles
Wherever biodegradable material is present in landfill sites or within the soil matrix of the made ground
beneath a brownfield site, microbial activity will produce landfill gas. Similar gas can also be produced in
alluvial deposits and degrading natural organic material (see Annex B). Landfill gas consists primarily of
methane and carbon dioxide (at a ratio of approximately 60:40). Depending on microbial activity, this ratio can
change. A number of additional trace gases can be present.
Permanent gases can also originate from coal deposits, peat, natural deposits (e.g. chalk and alluvial
deposits), from leaks of mains gas (natural gas) and from sewer gas. Information on techniques for identifying
the origin of gas can be found in 5.2.3.
Methane is explosive at concentrations of between 5 % and 15 % (volume fraction) in air; below 5 % there is
insufficient gas to support combustion and above 15 % (volume fraction) there is insufficient oxygen to support
combustion. Carbon dioxide is an asphyxiant and can cause adverse health effects in concentrations greater
than 0,5 % (volume fraction).
Landfill gas is usually saturated with moisture and is corrosive. It can cause vegetation to die back due to the
elimination of oxygen from the plant's root zone or to the presence of phytotoxic compounds. Its density
depends upon the ratio of carbon dioxide to methane: the higher the ratio of carbon dioxide the greater the
density.
Gas pressure within the sub-surface is dependent on the gas generation rate, the permeability of the waste
mass and the surrounding strata, and changes in the level of leachate or groundwater within the site. Other
important factors are temperature and atmospheric pressure.
Depending upon site engineering and local geology, gas can migrate considerable distances and can present
a hazard to nearby developments. In the case of mine gas, the cessation of water pumping can lead to a rise
in water table levels which can increase the gas pressure, and consequently increase surface gas emissions.
It is therefore important to gain an understanding of gas concentrations and flow rates to establish the
potential for gas migration off-site or atmospheric emissions.
5.2.2 Ambient conditions
It is important during the monitoring of a site, that atmospheric conditions, for 3 to 4 days before and during
the sampling, be recorded. Local climatic conditions at the time of monitoring should also be recorded. This
information can help in the interpretation of the data. The most important parameters to record are
 atmospheric pressure, and
 rainfall.
Other useful parameters are
 temperature (ambient air and soil gas),
 wind speed/direction, and
 water table depth.
During dry periods the ground can crack, especially if clay is used to cover sites. This will lead to an increase
in gas emissions at the surface. In periods of wet weather, the clay will become wet and swell, and cracks will
be sealed. This will reduce surface gas emissions and can lead to increased gas concentrations and
increased lateral migration. A measurement of soil permeability and moisture content can be helpful in
assessing these effects.
A rising water table, caused by rainfall for example, can put the gas under pressure and force it to the surface;
however, it can also block migration pathways. The saturation of superficial soils can restrict the venting of
landfill gas to atmosphere. This can result in variations in gas pressure and concentrations.
Falling atmospheric pressure can increase emission rates. Rising atmospheric pressure can have the
opposite effect. The magnitude of this effect depends upon the soil permeability and the rate at which the
pressure changes.
In general, however, it can be difficult to establish the cause of changes in concentrations and emissions since
they may be due to a combination of the above factors.
5.2.3 Identifying the source of gas
Identifying the origin of the gas is important when making decisions regarding its monitoring and control. The
composition of a gas may help identify the source. Examples are given below.
 Gas from a geological source may have a higher proportion of methane than landfill gas.
 Geologically-derived gas generally contains up to 15 % ethane and higher hydrocarbons, while biogenic
methane contains only trace amounts.
 It may be possible to distinguish mains gas from other gases if the exact composition of the local mains
gas is known. Mains gas may have odour compounds such as sulfides and mercaptans added to give the
gas a distinctive odour; it may also contain long chain hydrocarbons such as octane and nonane. Helium
is often removed from mains gas.
6 © ISO 2005 – All rights reserved

Landfill gas may also contain higher than normal concentrations of higher hydrocarbons if the waste contains
substances that generate or release such gases and vapours.
Identification of different components may, however, be limited as the components may be affected by
chemical changes occurring in the ground during migration, by solution in groundwater and by adsorption onto
clays, etc.
Biogenic (formed by microbiological activity) methane and thermogenic (formed by thermal degradation of
organic matter at higher temperatures and pressures) methane have different proportions of carbon isotopes
carbon 12 and carbon 13 which can be measured to identify the origin of the gas. The technique, however,
requires specialist laboratories.
5.3 General considerations for sampling
The strategy should be site specific and should be based upon the particular conditions of the site in question
as well as on the information obtained from the site investigation (see Annex C).
It should be considered that any invasive activity can affect migration patterns and will act as a pathway for
the gas.
In addition to gas monitoring, boreholes are also useful for obtaining hydrogeological, geotechnical and
contamination information and are therefore a useful multi-purpose tool.
If gas concentration measurements are required at different depths the use of multi-level boreholes is
undesirable and multiple well installations are to be preferred.
When results shall be compared to others and especially when monitoring from standpipes, the technique
used should be consistent to ensure comparable results between different operators, techniques and over
different monitoring periods. To achieve this, quality assurance measures as given in 5.10 need to be
followed.
Gas concentration measurements may be taken using portable equipment (see Table E.1) or samples may be
taken for off- site laboratory analysis. It is advisable to collect gas samples, to be submitted for confirmatory
analysis in a laboratory, in order to verify the on-site monitoring results.
5.4 Sampling requirements
5.4.1 Sampling options
Gas may be monitored using a range of different sampling techniques (see Table 1).
Although each technique has its uses, in situations where a detailed, long-term understanding of the site is
required, monitoring wells installed in boreholes tend to be the most favourable option.
5.4.2 Borehole construction
During drilling of the borehole, the borehole atmosphere should be monitored with on-site equipment at 1 m
intervals. Where ground water is encountered, useful information on the content of gas in the underlying
ground can be obtained by measuring the gas concentrations immediately above the water level at 1 m
intervals as the drilling progresses.
5.4.3 Location of sampling
The location and design of monitoring wells or other chosen technique should be planned well in advance, in
accordance with the aims of the site investigation, the conceptual site model and considerations including
health and safety, location of underground services, etc. (see Tables A.1 through A.5). A plan should be
drawn up in detail and adhered to. Any changes to this plan should be noted.
In areas where contamination is thought to be severe, the drilling of boreholes can produce preferential
pathways and as a result information should be sought on specialist drilling precautions.
The spacing of boreholes is dependent on the nature of the strata.
The depth from which samples are taken depends on the objectives. Information on concentrations at different
depths is useful, as it allows for a better understanding of the propensity for the gas to migrate.
Table 1 — Options for sampling of permanent gases
Method Description Advantages Disadvantages
Shallow probes Hollow perforated pipe Very quick Max. depth of 2 m
pushed into the ground
Cheap Can become blocked
and connected to a gas
Easy to install Confirms gas presence but not
detector
absence
Auger Hand-held auger is used to Cheap and easy to use Physically difficult
bore into the ground
Allows unspecified sampling of Cannot penetrate difficult ground
solids
Can be time consuming
Deeper than spiking/shallow probes
Driven probes Hollow tube with solid nose Minimal ground disturbance Will not penetrate obstructions
cone. Mechanically driven
Easily portable thus access Can cause smearing in clayey soils
into the ground. Monitoring
problems unlikely which restricts gas ingress into the
pipe installed inside tube.
probe hole
Max. depth of 10 m
Tube extracted leaving
behind nose cone
Allows soil-gas profile through the
ground to be determined
Boreholes Cased borehole is sunk by Great depths attainable Relatively slow and expensive
(without flushing cable percussion
Minimal disturbance to ground May have access problems
device) techniques into which a
Can install several standpipes in Brings contaminated material to the
perforated standpipe is
one borehole to measure at surface
installed. The pipe is
different depths
surrounded with gravel,
Care is needed to avoid enabling
and the casing withdrawn
Can take samples of strata at contamination of an underlying
different depths during drilling aquifer
Allows groundwater to be monitored
Allows soil-gas profile through the
ground to be determined
Boreholes Similar to above, but the As above but: As above but:
(with flushing hole is drilled by a rotary
 quicker than cable percussion  not intrinsically safe, sparks
device) tool and flushed with air or
may be a hazard on a gassing
water to aid rock  relatively mobile rig
site;
penetration
 water flush can spread
contamination
 air flush can cause migration of
soil gas
Care is needed to avoid enabling
contamination of an underlying
aquifer
Does not allow determination of
soil-gas profile due to the effects of
the flush
8 © ISO 2005 – All rights reserved

5.4.4 Sample volumes and sampling rates
In the case of point soil-gas sampling, a small volume is taken within the horizon layer (about 10 ml) for a
detection, probably not affected by external parameters, of the pore volume filled with gas. When sampling larger
volumes (up to several litres), the sampling area is diffuse and its location cannot be determined. Soil-gas
sampling from a borehole with greater diameter than that of the probe is called “integrating”, as the gas might be
delivered over its entire length. In landfill gas sampling, larger sampling volumes should be taken to determine
the gas components over a greater area.
The gas flow rate shall be ascertained. Several techniques for measuring gas flow rates, including their
advantages and disadvantages, are listed in Annex D.
5.5 Technical equipment
5.5.1 General
Different instruments measure different gases over different concentration ranges, and each has its own
advantages and limitations. It is important for the operator to obtain a good understanding of gas monitoring
equipment and which type should be used in a given situation.
In Table 2, the operational advantages and disadvantages of several portable instruments, along with the
gases analysed, are given. For more details, see Annex E.
The instruments required depend upon conditions at specific sites; it is therefore not appropriate to specify
specific instruments.
Portable instruments which are to be used on gas-contaminated sites should be intrinsically safe; this is
particularly so if the instrument is to be used within a confined space.
5.5.2 Installation of gas-monitoring standpipe
The borehole should reach 1 m into the natural ground or 6 m deep (whichever is the greater) or to a pre-
determined depth as required by the specific site investigation. Where the investigation is related to a landfill,
the borehole outside the landfill should reach at least 1 m beyond the maximum depth of the landfill. If this
depth is not known, it should be established as part of the investigation.
A 50 mm diameter pre-slotted pipe should be installed to the base of the borehole. The pipe should, however,
be un-slotted (plain) within 1 m of the ground surface. The pipe should comprise sections which can be fitted
together with screw threads, as this avoids the need for organic compounds and solvents to seal the lengths
together.
The annulus between the outer wall of the borehole and the slotted pipe should be filled in with pea-shingle or
similar material.
The top of the hole (generally between 1 m and 0,2 m from the ground surface) should be sealed with an
impermeable plug (bentonite grout/bentonite cement, etc.), while the upper 0,2 m from the ground surface
should be sealed with cement which should support a cover. Where possible, pipes should terminate above
ground level as this prevents flooding and makes them easier to identify. This may however not be possible
on sites with public access. A lockable heavy-duty cover is worth considering to prevent vandalism and
tampering.
A screw top should be fitted to the top of the standpipe to allow access into the pipe in order to take ground
water level measurements. A stopcock should be fitted to the cap from which gas samples can be taken; the
stopcock will allow the flow of gas from the standpipe to be opened or shut off as required.

Table 2 — Portable equipment to measure permanent gases
Instrument Gases analysed Advantages Disadvantages
 Specific gases can  Reading may be affected by
Infra-red spectro-photometer Carbon dioxide,
be analysed within moisture
(IR) (methane)
pre-defined ranges
aliphatic
hydrocarbons
 Wide detection range
 Sensitive  Sensing element may deteriorate
Sensor with catalytic oxidation Flammable gases
with age
 Requires adequate oxygen
 Not methane-specific
 Not intrinsically safe
 Sample is destroyed as part of
measurement process
 Wide detection range  Not methane-specific
Thermal conductivity detector Carbon dioxide,
(TCD) flammable gases
 Errors can occur at low
concentrations
 Very sensitive  Not methane-specific
Flame ionization detector Flammable gases
 Good for pinpointing  Not always intrinsically safe

emission sources
 Requires oxygen
 Possible errors if high levels of
carbon dioxide
 Sample is destroyed as part of
measurement process
 Very easy to use  Limited precision and readability
Indicator tubes Most gases
 Wide detection range  high cross sensitivity
 Used for large number
of gases
 Simple to use  Moisture can reduce sensitivity
Electrochemical cells Oxygen
 Limited shelf-life
 Accuracy affected by changes in
Paramagnetic cell Oxygen
atmospheric pressure
 Detection of various  Detection not specific
Photoionization detector (PID) Volatile aromatic
ranges can be excluded
and aliphatic
 Detector signal depends on
hydrocarbons
 Different exitation connection
energies possible
 Elaborate  Single component determination
Gas chromatograph (portable) Aromatic
possible
(GC) equipped with hydrocarbons,
appropriate detectors, e.g. volatile
flame-ionization detector halogenated
(FID), photoionization hydrocarbons
detector (PID), heat
conductivity detector (WLD)
5.6 Sampling plan
The sampling plan depends on the investigation objective and the local site.
To understand the conditions, the following parameters shall be considered:
 meteorological conditions;
 pressure differences;
10 © ISO 2005 – All rights reserved

 gas flow rates;
 gas concentrations.
Before measurements are taken, the following points shall be considered:
 understand exactly what is to be measured in order to ensure that the correct techniques and equipment
are used;
 be aware of the limitations associated with the usage of the equipment chosen;
 whether the very act of setting up and making the measurement has affected the distribution equilibrium
between the solid phase and the gas phase and hence affect the measurements taken;
 whether portable gas monitoring equipment is sufficient or whether off-site analysis is required.
It is good practice to decide upon a sampling protocol that can be used whenever monitoring is undertaken.
This should help ensure that the techniques used by different operators are consistent, which should reduce
uncertainties in data quality. A checklist should help to ensure that key activities are not overlooked. It is
important that when planning a monitoring scheme the requirements of the investigation are kept in mind at all
times.
The protocol given in Annex A is only an example; activities can be omitted or added depending upon the site
and the requirements of the survey.
5.7 Sampling
5.7.1 Sampling for on-site measurements
Where portable instruments are used, they should be connected securely to the sample point and gas should
be allowed to flow through the instrument until a steady reading is obtained. A reading should be taken of both
peak and steady-state concentrations.
If more than one instrument is required to measure different gases, this procedure shall be followed for each
of the gases. If the instruments are fitted with pumps, and provided that the sample is not destroyed in the
measurement process, the instruments can be put in series, with the exhaust from one instrument going into
the inlet of the next instrument. In this case it is advisable to fit non-return valves in the inlets to the
instruments to prevent air being drawn back through them by the other instruments. Instruments shall be
proved gas-tight. If an external pump is applied, then this shall be installed after the series of measuring
instruments.
When taking a gas measurement from a standpipe, a length of sample line is usually required to connect the
borehole to the gas analyser. This should be kept to a minimum, in general no more than 1 m. Care should be
taken when selecting sample lines, as certain compounds can be adsorbed onto them. For example,
poly(vinyl chloride) (PVC) absorbs water vapour and will release it in a dry air stream, while polyethylene is
permeable to oxygen and carbon dioxide. Where possible, internally clean stainless steel should be used, or if
flexibility is required, polypropylene is suitable for most gases. Silicone tubing, polyethylene and PVC should
be avoided where possible.
A column of drying agent can need to be placed along the sampling line to prevent the moisture contained
within the landfill gas from damaging the instrument. Consideration should be given to the type of drying agent
used, as this can affect readings. Silica gel absorbs gases such as carbon dioxide, especially when wet. In
most cases either calcium chloride or anhydrous calcium sulfate is recommended. For sensitive analysis,
magnesium perchloride is probably the most suitable. Instrument manufacturers often supply proprietary
hydrophobic filters, but care should be taken that only specified filters are used. Alternatively, a gas cooling
device, e. g. with a Peltier element and fixed water separator, can be applied.
In some cases, during sampling, it can be beneficial to record the gas concentrations and flow rates observed
in a borehole using a data-logging device. In most cases, the gas analyser will have a data logger connection.
This can be used to log at pre-defined frequencies. When monitoring from a borehole, it is advisable to log
every few seconds. This will show the steady-state concentrations, as well as the range of concentrations. In
most cases the data logger can be downloaded onto a computer software package for further analysis and
data storage.
5.7.2 Sampling for laboratory measurements
The laboratory chosen to carry out the analysis should be independent and competent in the work required,
and preferably have an appropriate accreditation or notification.
Selection of suitable apparatus and sampling procedure shall be agreed between the analyst and the
sampling staff.
A simple and widely used method of collecting gas samples is to use pressurised sampling cylinders, e. g. a
Gresham tube. A hand pump is used to compress the sample into a small cylinder made from either
aluminium alloy or preferably stainless steel. The cylinders can vary in capacity from 15 ml up to 110 ml.
Another method is the use of a gas sampling vessel, which can be sealed at both ends by taps or valves. The
vessel is connected to the sample point with a vacuum pump or hand aspirator in-line to provide suction. Gas
should be drawn through the vessel until at least three to five changes of the vessel volume have passed
through.
Landfill gas samples can be taken using a variety of containers.
It is advisable to flush all containers with an inert gas, such as argon, before the sample is taken. It is
important to be consistent in the methods of sampling, the apparatus used and the analytical and
measurement techniques employed. It is important to consider the possibility of absorption onto the surfaces
of containers and, where necessary, treated containers should be used.
5.8 Storage and transport of samples for laboratory analysis
Storage characteristics (time and
...

SLOVENSKI STANDARD
01-september-2006
.DNRYRVWWDO±9]RUþHQMH±GHO1DYRGLOR]DY]RUþHQMHWDOQLKSOLQRY
Soil quality -- Sampling -- Part 7: Guidance on sampling of soil gas
Qualité du sol -- Échantillonnage -- Partie 7: Lignes directrices pour l'échantillonnage des
gaz du sol
Ta slovenski standard je istoveten z: ISO 10381-7:2005
ICS:
13.080.05 Preiskava tal na splošno Examination of soils in
general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

INTERNATIONAL ISO
STANDARD 10381-7
First edition
2005-09-01
Soil quality — Sampling —
Part 7:
Guidance on sampling of soil gas
Qualité du sol — Échantillonnage —
Partie 7: Lignes directrices pour l'échantillonnage des gaz du sol

Reference number
©
ISO 2005
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ii © ISO 2005 – All rights reserved

Contents Page
Foreword. iv
Introduction . v
1 Scope .1
2 Normative references .1
3 Terms and definitions .1
4 Preliminary points to be considered.4
5 Permanent gases .5
5.1 Investigation objectives .5
5.2 Basic principles.5
5.3 General considerations for sampling .7
5.4 Sampling requirements.7
5.5 Technical equipment .9
5.6 Sampling plan .10
5.7 Sampling.11
5.8 Storage and transport of samples for laboratory analysis .12
5.9 Sampling report .12
5.10 Quality assurance.13
5.11 Interferences .15
6 Volatile organic compounds (VOCs) .16
6.1 Objectives.16
6.2 Basic principles .16
6.3 General considerations for sampling .17
6.4 Sampling requirements.18
6.5 Technical equipment .20
6.6 Sampling plan .22
6.7 Sampling.22
6.8 Storage and transport of samples for laboratory analysis .24
6.9 Sampling report .24
6.10 Quality assurance.24
6.11 Interferences .25
6.12 Interpretation of soil-gas analyses for VOCs.26
Annex A (informative) Sampling protocol.27
Annex B (informative) Anaerobic degradation and the formation of methane and carbon dioxide.29
Annex C (informative) Strategy of soil-gas investigations .31
Annex D (informative) Apparatus for measurement of gas flow rate .34
Annex E (informative) Portable equipment for measurement of concentrations of permanent
gases.35
Bibliography .38

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 10381-7 was prepared by Technical Committee ISO/TC 190, Soil quality, Subcommittee SC 2, Sampling.
ISO 10381 consists of the following parts, under the general title Soil quality — Sampling:
 Part 1: Guidance on the design of sampling programmes
 Part 2: Guidance on sampling techniques
 Part 3: Guidance on safety
 Part 4: Guidance on the procedure for investigation of natural, near-natural and cultivated sites
 Part 5: Guidance on the procedure for the investigation of urban and industrial sites with regard to soil
contamination
 Part 6: Guidance on the collection, handling and storage of soil for the assessment of aerobic microbial
processes in the laboratory
 Part 7: Guidance on sampling of soil gas
 Part 8: Guidance on sampling of stockpiles
iv © ISO 2005 – All rights reserved

Introduction
ISO 10381-7 is one of a group of International Standards to be used in conjunction with each other where
necessary. ISO 10381 (all parts) deals with sampling procedures for the various purposes of soil investigation.
The stated soil-gas and landfill-gas measurements do not give any quantitative statement of the total quantity
of material detected in soil gas or soil. The measurement results can be influenced by, e.g. temperature,
humidity, air pressure, minimum extraction depth, etc.
The general terminology used is in accordance with that established in ISO/TC 190 and, more particularly,
with the vocabulary given in ISO 11074-2.
In addition to the main components (nitrogen, oxygen, carbon dioxide), soil gas can contain other gases
(methane, carbon monoxide, mercaptans, hydrogen sulfide, ammonia, helium, neon, argon, xenon, radon, etc.).
It can also contain highly volatile organic compounds or inorganic vapours (mercury) which are of special interest
within the framework of investigating soil and groundwater contamination.
Due to the different physical properties and ranges of concentrations of gases in soil and landfills as well as the
wide variety of objectives for soil-gas sampling, this part of ISO 10381, after the general clauses 1 to 4, is
subdivided into two sections:
a) permanent gases of soil gas and landfill gas (Clause 5); and
b) volatile organic compounds (VOCs) (Clause 6).
Thus it is inevitable that some details are repeated in both clauses in order to make the guidance
comprehensive.
INTERNATIONAL STANDARD ISO 10381-7:2005(E)

Soil quality — Sampling —
Part 7:
Guidance on sampling of soil gas
WARNING — This part of ISO 10381 concerns on-site soil and sub-soil gas analysis requiring
particular health and personal safety precautions.
1 Scope
This part of ISO 10381 contains guidance on the sampling of soil gas.
This part of ISO 10381 is not applicable to the measurement of gases from the soil entering into the atmosphere,
the sampling of atmospheric gases, or passive sampling procedures.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 10381-1, Soil quality — Sampling — Part 1: Guidance on the design of sampling programmes
ISO 10381-2, Soil quality — Sampling — Part 2: Guidance on sampling techniques
ISO 10381-3, Soil quality — Sampling — Part 3: Guidance on safety
ISO 11074-1, Soil quality — Vocabulary — Part 1: Terms and definitions relating to the protection and
pollution of the soil
ISO 11074-2, Soil quality — Vocabulary — Part 2: Terms and definitions relating to sampling
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 11074-1 and ISO 11074-2 and the
following apply.
3.1
active soil-gas sampling
sampling by extracting a certain volume of soil gas
3.2
biodegradation
the physical and chemical breakdown of a substance by living organisms, mainly bacteria and/or fungi
3.3
borehole
hole formed into soil or landfilled material into which may be installed a standpipe to enable gas monitoring to
be carried out
NOTE A borehole is also used as a means of venting or withdrawing gas.
3.4
concentration/adsorption method
method in which substances to be determined are concentrated adsorptively on an adsorbent (e.g. activated
charcoal or XAD-4 resin), subsequently desorbed and analysed
3.5
dead volume
volume which is present between the suction opening of the soil-gas probe and the sampling vial, including the
volume of the sampling vial or of the absorption tube
3.6
direct method
direct measuring method
method of analysis where the soil-gas sample (aliquot) is directly introduced into a suitable equipment without
first being concentrated and subjected to analysis
3.7
direct-reading detecting tube
glass tube filled with reagents which, after drawing through certain gaseous compounds, show concentration-
dependent chromophoric reactions and which are thus used for qualitative and semi-quantitative analyses as
well
NOTE It is important that attention be paid to cross-sensitivities.
3.8
gas migration
movement of gas and vapour from the wastes within a landfill or through the ground to the adjoining strata, or
emission to the atmosphere
3.9
gas monitoring well
standpipe suitably installed inside a borehole from which gas samples can be taken to measure soil-gas
concentrations and to monitor changes in composition of soil gas or soil-gas migration
3.10
gas sampling
collection of a proportion of material for testing such that the material taken is representative of the gas in the
pore space of the location of sampling
3.11
landfill
deposition of waste into or onto the land as a means of disposal
NOTE It can eventually provide land which may be used for another purpose.
3.12
landfill gas
mixture of permanent gases (main components), dominated by methane and carbon dioxide, formed by the
decomposition of degradable wastes within landfill sites
NOTE It can also include a large number of VOCs (trace components).
2 © ISO 2005 – All rights reserved

3.13
lower explosive limit
LEL
lowest percentage (volume fraction) of a mixture of flammable gas with air which will propagate an explosion
in a confined space at 25 °C and atmospheric pressure
3.14
one-stage soil-gas sampling
sampling of soil gas directly from a soil-gas probe placed in soil, without pre-drilling
3.15
passive soil-gas sampling
sampling based on the adsorption of soil gas on an absorbent placed in soil, without employing negative
pressure
3.16
permanent gas
element or compound with boiling point below − 60 °C at atmospheric pressure
3.17
sample volume
volume of soil from which the soil-gas sample is taken
3.18
soil gas
gas and vapour in the pore spaces of soils
3.19
soil-gas monitoring device
borehole finished with suitable material for stabilisation of the borehole wall and/or for limiting the sampling area.
NOTE Depending on the type and stability of fitting, a difference is made between temporary (for single or short-term
repeated soil sampling) and stationary (for long-term observations) soil-gas measuring points.
3.20
soil-gas probe
soil-gas sampling probe
probe, generally a tube, which is installed directly into soil (one-stage soil-gas sampling), or in a borehole
(two-stage soil-gas sampling) to take soil-gas samples.
NOTE By applying a negative pressure to the upper end of the soil-gas probe (head), the soil gas at the lower end (tip)
is drawn through the suction opening(s) and transferred to a gas collecting equipment and online measurement equipment
(direct measuring method) or to an absorbent (concentration method), which are installed either in or at the head of the
soil-gas probe or subsequently used.
3.21
soil-gas suction test
continuous soil-gas sampling from a borehole well over a controlled longer period of time (mostly several
hours up to days) to observe the variations over time of the gas concentrations and of the pressure distribution
in the soil
3.22
two-stage soil-gas sampling
sampling done firstly through installation of a borehole with the aid of a drilling instrument or by small boring, and
secondly by sampling of soil gas from a soil-gas probe installed in the borehole
3.23
volatile organic compound
VOC
compound which is liquid at room temperature (20 °C) and which generally has a boiling point below 180 °C
EXAMPLES single-ring aromatic hydrocarbons and other low boiling halogenated hydrocarbons, which are used as
solvents or fuels, and some degradation products.
4 Preliminary points to be considered
The choice of sampling technique shall be consistent with the requirements of the investigation (including
subsequent analytical procedures). Consideration should also be given to the nature of ground under
investigation, as well as the nature and distribution of contamination, the geology and the hydrogeology. Every
effort should be made to avoid cross-contamination and at no point should underlying aquifers be put at risk.
Before intrusive works begin, a comprehensive check should be made of the ground to ensure that no
services or structures are at risk and no hazards are present. (For more information on sampling techniques
and safety, see ISO 10381-2 and ISO 10381-3.)
When sampling soil gas close to the surface, the effect of ambient air penetration needs to be considered. The
sampling depth is determined by the presence of impermeable cover over the ground surface, the soil type
(porosity, clay content, etc.) and the depth of bedrock. It is considered unlikely that useful samples can be
collected at depth less than 0,5 m. For routine monitoring of soil gas, a minimum depth of 1 m is
recommended.
Circumstances in cold conditions make soil-gas sampling difficult in many ways. Ground frost greatly limits the
mobility of gas in soil and should be considered in planning and carrying out sampling as well as in interpreting
the measuring results. Similarly water saturated ground can limit mobility.
The main problem with soil-gas sampling below the frozen ground is the loss of air-filled porosity due to the high
moisture content in the zone between frozen and unfrozen parts of the ground. Consequently the samples shall
be taken from greater depths.
All buildings constructed on unfrozen ground act as pathways or barriers for upwards soil-gas migration.
Underpressure and differences in concentration in the buildings can also assist gases to penetrate the
basements of buildings.
Pressure effects caused by the rise of warm air within buildings can assist the entry of gases into buildings.
Some organic pollutants in the gas phase in soil and sub-soil can present toxicological risks of varying severity.
Due to this possibility, personnel should be equipped, according to the potential toxicity (assumed or measured),
with suitable protective material.
Certain organic fumes can form explosive mixtures with air. (Explosivity limits and self-ignition temperatures
should be taken into account.). It is therefore appropriate to use electrical equipment and tools which are suitable
for use in explosive atmospheres.
Health and safety issues should be considered at all times. Training should be given to ensure that personnel
understand the necessary precautions. (For more information on safety, see ISO 10381-3.)
4 © ISO 2005 – All rights reserved

5 Permanent gases
5.1 Investigation objectives
5.1.1 Soil gas
The objectives of the investigation for permanent soil gases are
 analysis of soil-gas composition, and
 determination of the difference of concentration on a site.
5.1.2 Landfill gas
The objective of the investigation for landfill gases is
 analysis of landfill gas composition.
5.1.3 Further objectives
Further objectives may be
 assessment of possible reasons for plant growth inhibition,
 optimization or control of sealings or gas collecting installations,
 rough estimate of gas production potential and duration of gas production,
 detection of underground combustion,
 design of gas protection measures for buildings.
5.2 Basic principles
5.2.1 Physical and chemical principles
Wherever biodegradable material is present in landfill sites or within the soil matrix of the made ground
beneath a brownfield site, microbial activity will produce landfill gas. Similar gas can also be produced in
alluvial deposits and degrading natural organic material (see Annex B). Landfill gas consists primarily of
methane and carbon dioxide (at a ratio of approximately 60:40). Depending on microbial activity, this ratio can
change. A number of additional trace gases can be present.
Permanent gases can also originate from coal deposits, peat, natural deposits (e.g. chalk and alluvial
deposits), from leaks of mains gas (natural gas) and from sewer gas. Information on techniques for identifying
the origin of gas can be found in 5.2.3.
Methane is explosive at concentrations of between 5 % and 15 % (volume fraction) in air; below 5 % there is
insufficient gas to support combustion and above 15 % (volume fraction) there is insufficient oxygen to support
combustion. Carbon dioxide is an asphyxiant and can cause adverse health effects in concentrations greater
than 0,5 % (volume fraction).
Landfill gas is usually saturated with moisture and is corrosive. It can cause vegetation to die back due to the
elimination of oxygen from the plant's root zone or to the presence of phytotoxic compounds. Its density
depends upon the ratio of carbon dioxide to methane: the higher the ratio of carbon dioxide the greater the
density.
Gas pressure within the sub-surface is dependent on the gas generation rate, the permeability of the waste
mass and the surrounding strata, and changes in the level of leachate or groundwater within the site. Other
important factors are temperature and atmospheric pressure.
Depending upon site engineering and local geology, gas can migrate considerable distances and can present
a hazard to nearby developments. In the case of mine gas, the cessation of water pumping can lead to a rise
in water table levels which can increase the gas pressure, and consequently increase surface gas emissions.
It is therefore important to gain an understanding of gas concentrations and flow rates to establish the
potential for gas migration off-site or atmospheric emissions.
5.2.2 Ambient conditions
It is important during the monitoring of a site, that atmospheric conditions, for 3 to 4 days before and during
the sampling, be recorded. Local climatic conditions at the time of monitoring should also be recorded. This
information can help in the interpretation of the data. The most important parameters to record are
 atmospheric pressure, and
 rainfall.
Other useful parameters are
 temperature (ambient air and soil gas),
 wind speed/direction, and
 water table depth.
During dry periods the ground can crack, especially if clay is used to cover sites. This will lead to an increase
in gas emissions at the surface. In periods of wet weather, the clay will become wet and swell, and cracks will
be sealed. This will reduce surface gas emissions and can lead to increased gas concentrations and
increased lateral migration. A measurement of soil permeability and moisture content can be helpful in
assessing these effects.
A rising water table, caused by rainfall for example, can put the gas under pressure and force it to the surface;
however, it can also block migration pathways. The saturation of superficial soils can restrict the venting of
landfill gas to atmosphere. This can result in variations in gas pressure and concentrations.
Falling atmospheric pressure can increase emission rates. Rising atmospheric pressure can have the
opposite effect. The magnitude of this effect depends upon the soil permeability and the rate at which the
pressure changes.
In general, however, it can be difficult to establish the cause of changes in concentrations and emissions since
they may be due to a combination of the above factors.
5.2.3 Identifying the source of gas
Identifying the origin of the gas is important when making decisions regarding its monitoring and control. The
composition of a gas may help identify the source. Examples are given below.
 Gas from a geological source may have a higher proportion of methane than landfill gas.
 Geologically-derived gas generally contains up to 15 % ethane and higher hydrocarbons, while biogenic
methane contains only trace amounts.
 It may be possible to distinguish mains gas from other gases if the exact composition of the local mains
gas is known. Mains gas may have odour compounds such as sulfides and mercaptans added to give the
gas a distinctive odour; it may also contain long chain hydrocarbons such as octane and nonane. Helium
is often removed from mains gas.
6 © ISO 2005 – All rights reserved

Landfill gas may also contain higher than normal concentrations of higher hydrocarbons if the waste contains
substances that generate or release such gases and vapours.
Identification of different components may, however, be limited as the components may be affected by
chemical changes occurring in the ground during migration, by solution in groundwater and by adsorption onto
clays, etc.
Biogenic (formed by microbiological activity) methane and thermogenic (formed by thermal degradation of
organic matter at higher temperatures and pressures) methane have different proportions of carbon isotopes
carbon 12 and carbon 13 which can be measured to identify the origin of the gas. The technique, however,
requires specialist laboratories.
5.3 General considerations for sampling
The strategy should be site specific and should be based upon the particular conditions of the site in question
as well as on the information obtained from the site investigation (see Annex C).
It should be considered that any invasive activity can affect migration patterns and will act as a pathway for
the gas.
In addition to gas monitoring, boreholes are also useful for obtaining hydrogeological, geotechnical and
contamination information and are therefore a useful multi-purpose tool.
If gas concentration measurements are required at different depths the use of multi-level boreholes is
undesirable and multiple well installations are to be preferred.
When results shall be compared to others and especially when monitoring from standpipes, the technique
used should be consistent to ensure comparable results between different operators, techniques and over
different monitoring periods. To achieve this, quality assurance measures as given in 5.10 need to be
followed.
Gas concentration measurements may be taken using portable equipment (see Table E.1) or samples may be
taken for off- site laboratory analysis. It is advisable to collect gas samples, to be submitted for confirmatory
analysis in a laboratory, in order to verify the on-site monitoring results.
5.4 Sampling requirements
5.4.1 Sampling options
Gas may be monitored using a range of different sampling techniques (see Table 1).
Although each technique has its uses, in situations where a detailed, long-term understanding of the site is
required, monitoring wells installed in boreholes tend to be the most favourable option.
5.4.2 Borehole construction
During drilling of the borehole, the borehole atmosphere should be monitored with on-site equipment at 1 m
intervals. Where ground water is encountered, useful information on the content of gas in the underlying
ground can be obtained by measuring the gas concentrations immediately above the water level at 1 m
intervals as the drilling progresses.
5.4.3 Location of sampling
The location and design of monitoring wells or other chosen technique should be planned well in advance, in
accordance with the aims of the site investigation, the conceptual site model and considerations including
health and safety, location of underground services, etc. (see Tables A.1 through A.5). A plan should be
drawn up in detail and adhered to. Any changes to this plan should be noted.
In areas where contamination is thought to be severe, the drilling of boreholes can produce preferential
pathways and as a result information should be sought on specialist drilling precautions.
The spacing of boreholes is dependent on the nature of the strata.
The depth from which samples are taken depends on the objectives. Information on concentrations at different
depths is useful, as it allows for a better understanding of the propensity for the gas to migrate.
Table 1 — Options for sampling of permanent gases
Method Description Advantages Disadvantages
Shallow probes Hollow perforated pipe Very quick Max. depth of 2 m
pushed into the ground
Cheap Can become blocked
and connected to a gas
Easy to install Confirms gas presence but not
detector
absence
Auger Hand-held auger is used to Cheap and easy to use Physically difficult
bore into the ground
Allows unspecified sampling of Cannot penetrate difficult ground
solids
Can be time consuming
Deeper than spiking/shallow probes
Driven probes Hollow tube with solid nose Minimal ground disturbance Will not penetrate obstructions
cone. Mechanically driven
Easily portable thus access Can cause smearing in clayey soils
into the ground. Monitoring
problems unlikely which restricts gas ingress into the
pipe installed inside tube.
probe hole
Max. depth of 10 m
Tube extracted leaving
behind nose cone
Allows soil-gas profile through the
ground to be determined
Boreholes Cased borehole is sunk by Great depths attainable Relatively slow and expensive
(without flushing cable percussion
Minimal disturbance to ground May have access problems
device) techniques into which a
Can install several standpipes in Brings contaminated material to the
perforated standpipe is
one borehole to measure at surface
installed. The pipe is
different depths
surrounded with gravel,
Care is needed to avoid enabling
and the casing withdrawn
Can take samples of strata at contamination of an underlying
different depths during drilling aquifer
Allows groundwater to be monitored
Allows soil-gas profile through the
ground to be determined
Boreholes Similar to above, but the As above but: As above but:
(with flushing hole is drilled by a rotary
 quicker than cable percussion  not intrinsically safe, sparks
device) tool and flushed with air or
may be a hazard on a gassing
water to aid rock  relatively mobile rig
site;
penetration
 water flush can spread
contamination
 air flush can cause migration of
soil gas
Care is needed to avoid enabling
contamination of an underlying
aquifer
Does not allow determination of
soil-gas profile due to the effects of
the flush
8 © ISO 2005 – All rights reserved

5.4.4 Sample volumes and sampling rates
In the case of point soil-gas sampling, a small volume is taken within the horizon layer (about 10 ml) for a
detection, probably not affected by external parameters, of the pore volume filled with gas. When sampling larger
volumes (up to several litres), the sampling area is diffuse and its location cannot be determined. Soil-gas
sampling from a borehole with greater diameter than that of the probe is called “integrating”, as the gas might be
delivered over its entire length. In landfill gas sampling, larger sampling volumes should be taken to determine
the gas components over a greater area.
The gas flow rate shall be ascertained. Several techniques for measuring gas flow rates, including their
advantages and disadvantages, are listed in Annex D.
5.5 Technical equipment
5.5.1 General
Different instruments measure different gases over different concentration ranges, and each has its own
advantages and limitations. It is important for the operator to obtain a good understanding of gas monitoring
equipment and which type should be used in a given situation.
In Table 2, the operational advantages and disadvantages of several portable instruments, along with the
gases analysed, are given. For more details, see Annex E.
The instruments required depend upon conditions at specific sites; it is therefore not appropriate to specify
specific instruments.
Portable instruments which are to be used on gas-contaminated sites should be intrinsically safe; this is
particularly so if the instrument is to be used within a confined space.
5.5.2 Installation of gas-monitoring standpipe
The borehole should reach 1 m into the natural ground or 6 m deep (whichever is the greater) or to a pre-
determined depth as required by the specific site investigation. Where the investigation is related to a landfill,
the borehole outside the landfill should reach at least 1 m beyond the maximum depth of the landfill. If this
depth is not known, it should be established as part of the investigation.
A 50 mm diameter pre-slotted pipe should be installed to the base of the borehole. The pipe should, however,
be un-slotted (plain) within 1 m of the ground surface. The pipe should comprise sections which can be fitted
together with screw threads, as this avoids the need for organic compounds and solvents to seal the lengths
together.
The annulus between the outer wall of the borehole and the slotted pipe should be filled in with pea-shingle or
similar material.
The top of the hole (generally between 1 m and 0,2 m from the ground surface) should be sealed with an
impermeable plug (bentonite grout/bentonite cement, etc.), while the upper 0,2 m from the ground surface
should be sealed with cement which should support a cover. Where possible, pipes should terminate above
ground level as this prevents flooding and makes them easier to identify. This may however not be possible
on sites with public access. A lockable heavy-duty cover is worth considering to prevent vandalism and
tampering.
A screw top should be fitted to the top of the standpipe to allow access into the pipe in order to take ground
water level measurements. A stopcock should be fitted to the cap from which gas samples can be taken; the
stopcock will allow the flow of gas from the standpipe to be opened or shut off as required.

Table 2 — Portable equipment to measure permanent gases
Instrument Gases analysed Advantages Disadvantages
 Specific gases can  Reading may be affected by
Infra-red spectro-photometer Carbon dioxide,
be analysed within moisture
(IR) (methane)
pre-defined ranges
aliphatic
hydrocarbons
 Wide detection range
 Sensitive  Sensing element may deteriorate
Sensor with catalytic oxidation Flammable gases
with age
 Requires adequate oxygen
 Not methane-specific
 Not intrinsically safe
 Sample is destroyed as part of
measurement process
 Wide detection range  Not methane-specific
Thermal conductivity detector Carbon dioxide,
(TCD) flammable gases
 Errors can occur at low
concentrations
 Very sensitive  Not methane-specific
Flame ionization detector Flammable gases
 Good for pinpointing  Not always intrinsically safe

emission sources
 Requires oxygen
 Possible errors if high levels of
carbon dioxide
 Sample is destroyed as part of
measurement process
 Very easy to use  Limited precision and readability
Indicator tubes Most gases
 Wide detection range  high cross sensitivity
 Used for large number
of gases
 Simple to use  Moisture can reduce sensitivity
Electrochemical cells Oxygen
 Limited shelf-life
 Accuracy affected by changes in
Paramagnetic cell Oxygen
atmospheric pressure
 Detection of various  Detection not specific
Photoionization detector (PID) Volatile aromatic
ranges can be excluded
and aliphatic
 Detector signal depends on
hydrocarbons
 Different exitation connection
energies possible
 Elaborate  Single component determination
Gas chromatograph (portable) Aromatic
possible
(GC) equipped with hydrocarbons,
appropriate detectors, e.g. volatile
flame-ionization detector halogenated
(FID), photoionization hydrocarbons
detector (PID), heat
conductivity detector (WLD)
5.6 Sampling plan
The sampling plan depends on the investigation objective and the local site.
To understand the conditions, the following parameters shall be considered:
 meteorological conditions;
 pressure differences;
10 © ISO 2005 – All rights reserved

 gas flow rates;
 gas concentrations.
Before measurements are taken, the following points shall be considered:
 understand exactly what is to be measured in order to ensure that the correct techniques and equipment
are used;
 be aware of the limitations associated with the usage of the equipment chosen;
 whether the very act of setting up and making the measurement has affected the distribution equilibrium
between the solid phase and the gas phase and hence affect the measurements taken;
 whether portable gas monitoring equipment is sufficient or whether off-site analysis is required.
It is good practice to decide upon a sampling protocol that can be used whenever monitoring is undertaken.
This should help ensure that the techniques used by different operators are consistent, which should reduce
uncertainties in data quality. A checklist should help to ensure that key activities are not overlooked. It is
important that when planning a monitoring scheme the requirements of the investigation are kept in mind at all
times.
The protocol given in Annex A is only an example; activities can be omitted or added depending upon the site
and the requirements of the survey.
5.7 Sampling
5.7.1 Sampling for on-site measurements
Where portable instruments are used, they should be connected securely to the sample point and gas should
be allowed to flow through the instrument until a steady reading is obtained. A reading should be taken of both
peak and steady-state concentrations.
If more than one instrument is required to measure different gases, this procedure shall be followed for each
of the gases. If the instruments are fitted with pumps, and provided that the sample is not destroyed in the
measurement process, the instruments can be put in series, with the exhaust from one instrument going into
the inlet of the next instrument. In this case it is advisable to fit non-return valves in the inlets to the
instruments to prevent air being drawn back through them by the other instruments. Instruments shall be
proved gas-tight. If an external pump is applied, then this shall be installed after the series of measuring
instruments.
When taking a gas measurement from a standpipe, a length of sample line is usually required to connect the
borehole to the gas analyser. This should be kept to a minimum, in general no more than 1 m. Care should be
taken when selecting sample lines, as certain compounds can be adsorbed onto them. For example,
poly(vinyl chloride) (PVC) absorbs water vapour and will release it in a dry air stream, while polyethylene is
permeable to oxygen and carbon dioxide. Where possible, internally clean stainless steel should be used, or if
flexibility is required, polypropylene is suitable for most gases. Silicone tubing, polyethylene and PVC should
be avoided where possible.
A column of drying agent can need to be placed along the sampling line to prevent the moisture contained
within the landfill gas from damaging the instrument. Consideration should be given to the type of drying agent
used, as this can affect readings. Silica gel absorbs gases such as carbon dioxide, especially when wet. In
most cases either calcium chloride or anhydrous calcium sulfate is recommended. For sensitive analysis,
magnesium perchloride is probably the most suitable. Instrument manufacturers often supply proprietary
hydrophobic filters, but care should be taken that only specified filters are used. Alternatively, a gas cooling
device, e. g. with a Peltier element and fixed water separator, can be applied.
In some cases, during sampling, it can be beneficial to record the gas concentrations and flow rates observed
in a borehole using a data-logging device. In most cases, the gas analyser will have a data logger connection.
This can be used to log at pre-defined frequencies. When monitoring from a borehole, it is advisable to log
every few seconds. This will show the steady-state concentrations, as well as the range of concentrations. In
most cases the data logger can be downloaded onto a computer software package for further analysis and
data storage.
5.7.2 Sampling for laboratory measurements
The laboratory chosen to carry out the analysis should be independent and competent in the work required,
and preferably have an appropriate accreditation or notification.
Selection of suitable apparatus and sampling procedure shall be agreed between the analyst and the
sampling staff.
A simple and widely used method of collecting gas samples is to use pressurised sampling cylinders, e. g. a
Gresham tube. A hand pump is used to compress the sample into a small cylinder made from either
aluminium alloy or preferably stainless steel. The cylinders can vary in capacity from 15 ml up to 110 ml.
Another method is the use of a gas sampling vessel, which can be sealed at both ends by taps or valves. The
vessel is connected to the sample point with a vacuum pump or hand aspirator in-line to provide suction. Gas
should be drawn through the vessel until a
...

NORME ISO
INTERNATIONALE 10381-7
Première édition
2005-09-01
Qualité du sol — Échantillonnage —
Partie 7:
Lignes directrices pour l'échantillonnage
des gaz du sol
Soil quality — Sampling —
Part 7: Guidance on sampling of soil gas

Numéro de référence
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ISO 2005
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©  ISO 2005
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Publié en Suisse
ii © ISO 2005 – Tous droits réservés

Sommaire Page
Avant-propos. iv
Introduction . v
1 Domaine d’application .1
2 Références normatives .1
3 Termes et définitions.1
4 Points préliminaires à prendre en compte.4
5 Gaz permanents.5
5.1 Objectifs de l’étude.5
5.2 Principes de base .5
5.3 Considérations générales relatives à l’échantillonnage .7
5.4 Exigences relatives à l’échantillonnage.7
5.5 Équipement technique .9
5.6 Plan d’échantillonnage.11
5.7 Échantillonnage .12
5.8 Stockage et transport des échantillons pour l’analyse en laboratoire .13
5.9 Rapport d’échantillonnage .13
5.10 Assurance qualité.14
5.11 Interférences .17
6 Composés organiques volatils (COV) .17
6.1 Objectifs.17
6.2 Principes de base .17
6.3 Considérations générales sur l’échantillonnage.18
6.4 Exigences relatives à l’échantillonnage.19
6.5 Équipement technique .22
6.6 Plan d’échantillonnage.22
6.7 Échantillonnage .24
6.8 Stockage et transport des échantillons pour l’analyse en laboratoire .26
6.9 Rapport d’échantillonnage .26
6.10 Assurance qualité.26
6.11 Interférences .27
6.12 Interprétation des analyses de gaz du sol pour les COV .28
Annexe A (informative) Protocole d’échantillonnage.30
Annexe B (informative) Dégradation anaérobie et formation de méthane et de dioxyde de carbone .32
Annexe C (informative) Stratégie pour l’étude des gaz du sol .35
Annexe D (informative) Équipement pour le mesurage du débit du gaz.39
Annexe E (informative) Équipement portatif pour le mesurage des concentrations de gaz
permanents.40
Bibliographie .40

Avant-propos
L'ISO (Organisation internationale de normalisation) est une fédération mondiale d'organismes nationaux de
normalisation (comités membres de l'ISO). L'élaboration des Normes internationales est en général confiée
aux comités techniques de l'ISO. Chaque comité membre intéressé par une étude a le droit de faire partie du
comité technique créé à cet effet. Les organisations internationales, gouvernementales et non
gouvernementales, en liaison avec l'ISO participent également aux travaux. L'ISO collabore étroitement avec
la Commission électrotechnique internationale (CEI) en ce qui concerne la normalisation électrotechnique.
Les Normes internationales sont rédigées conformément aux règles données dans les Directives ISO/CEI,
Partie 2.
La tâche principale des comités techniques est d'élaborer les Normes internationales. Les projets de Normes
internationales adoptés par les comités techniques sont soumis aux comités membres pour vote. Leur
publication comme Normes internationales requiert l'approbation de 75 % au moins des comités membres
votants.
L'attention est appelée sur le fait que certains des éléments du présent document peuvent faire l'objet de
droits de propriété intellectuelle ou de droits analogues. L'ISO ne saurait être tenue pour responsable de ne
pas avoir identifié de tels droits de propriété et averti de leur existence.
L'ISO 10381-7 a été élaborée par le comité technique ISO/TC 190, Qualité du sol, sous-comité SC 2,
Échantillonnage.
L'ISO 10381 comprend les parties suivantes, présentées sous le titre général Qualité du sol —
Échantillonnage:
 Partie 1: Lignes directrices pour l’établissement des programmes d’échantillonnage
 Partie 2: Lignes directrices pour les techniques d’échantillonnage
 Partie 3: Lignes directrices relatives à la sécurité
 Partie 4: Lignes directrices pour les procédures d’investigation des sites naturels, quasi naturels et
cultivés
 Partie 5: Lignes directrices pour la procédure d’'investigation des sols pollués en sites urbains et
industriels
 Partie 6: Lignes directrices pour la collecte, la manipulation et la conservation de sols destinés à une
étude en laboratoire des processus microbiens aérobies
 Partie 7: Lignes directrices pour l’échantillonnage des gaz du sol
 Partie 8: Lignes directrices pour l’échantillonnage de matériaux en tas
iv © ISO 2005 – Tous droits réservés

Introduction
L’ISO 10381-7 fait partie d’une série de Normes internationales destinées à être utilisées conjointement en
fonction des besoins. L’ISO 10381 (toutes les parties) traite des modes opératoires d’échantillonnage
correspondant aux divers objectifs de l’étude du sol. Les mesurages indiqués pour les gaz du sol et les gaz de
décharge ne fournissent aucune indication quantitative sur la quantité totale de matériaux détectée dans les
gaz du sol ou dans le sol. Les résultats des mesurages peuvent être influencés notamment par la température,
l’humidité, la pression atmosphérique, la profondeur minimale d’extraction, etc.
La terminologie générale utilisée est conforme à celle établie par l’ISO/TC 190 et, plus précisément, à la
terminologie présentée dans l’ISO 11074-2.
Outre les principaux constituants (azote, oxygène, dioxyde de carbone), les gaz du sol peuvent contenir
d’autres gaz (méthane, monoxyde de carbone, mercaptans, hydrogène sulfuré, ammoniac, hélium, néon,
argon, xénon, radon, etc.). Ils peuvent également contenir des composés organiques très volatils ou des
vapeurs inorganiques (mercure) qui présentent un intérêt particulier dans le cadre de l’analyse de la
contamination du sol et des eaux souterraines.
Compte tenu des différentes propriétés physiques et des gammes de concentrations des gaz dans le sol et
dans les décharges, ainsi que de l’étendue des objectifs de l’échantillonnage des gaz du sol, la présente
partie de l’ISO 10381 est divisée en deux sections, après les articles généraux 1 à 4:
a) les gaz permanents des gaz du sol et des gaz de décharge (Article 5); et
b) les composés organiques volatils (COV) (Article 6).
Par conséquent, certains détails sont inévitablement répétés dans ces deux articles afin que les lignes
directrices soient complètes.
NORME INTERNATIONALE ISO 10381-7:2005(F)

Qualité du sol — Échantillonnage —
Partie 7:
Lignes directrices pour l'échantillonnage des gaz du sol
AVERTISSEMENT — La présente partie de l’ISO 10381 concerne l’analyse sur site des gaz du sol et du
sous-sol, nécessitant des précautions particulières en matière d’hygiène et de sécurité.
1 Domaine d’application
La présente partie de l’ISO 10381 donne des lignes directrices sur l’échantillonnage des gaz du sol.
La présente partie de l’ISO 10381 ne traite pas du mesurage des gaz du sol entrant dans l’atmosphère, ni de
l’échantillonnage des gaz atmosphériques ou encore des modes opératoires d’échantillonnage passif.
2 Références normatives
Les documents de référence suivants sont indispensables pour l’application du présent document. Pour les
références datées, seule l’édition citée s’applique. Pour les références non datées, la dernière édition du
document de référence (y compris les éventuels amendements) s’applique.
ISO 10381-1, Qualité du sol — Échantillonnage — Partie 1: Lignes directrices pour l'établissement des
programmes d'échantillonnage
ISO 10381-2, Qualité du sol — Échantillonnage — Partie 2: Lignes directrices pour les techniques
d'échantillonnage
ISO 10381-3, Qualité du sol — Échantillonnage — Partie 3: Lignes directrices relatives à la sécurité
ISO 11074-1, Qualité du sol — Vocabulaire — Partie 1: Termes et définitions relatifs à la protection et à la
pollution du sol
ISO 11074-2, Qualité du sol — Vocabulaire — Partie 2: Termes et définitions relatifs à l'échantillonnage
3 Termes et définitions
Pour les besoins du présent document, les termes et définitions donnés dans l’ISO 11074-1 et l’ISO 11074-2
ainsi que les suivants s'appliquent.
3.1
échantillonnage actif des gaz du sol
échantillonnage par extraction d’un certain volume de gaz du sol
3.2
biodégradation
décomposition physique et chimique d’une substance par des organismes vivants, principalement des
bactéries et/ou des champignons
3.3
sondage
trou formé dans le sol ou dans des matériaux mis en décharge, dans lequel une tuyauterie peut être installée
pour permettre la surveillance des gaz
NOTE Un sondage est également utilisé pour l’évacuation ou l’extraction des gaz.
3.4
méthode par concentration/adsorption
méthode dans laquelle les substances à déterminer sont concentrées par adsorption sur un adsorbant (par
exemple charbon actif ou résine XAD-4), puis désorbées et analysées
3.5
volume mort
volume qui est présent entre l’ouverture d’aspiration de la sonde et le flacon d’échantillonnage, comprenant le
volume du flacon d’échantillonnage ou du tube d’absorption
3.6
méthode directe
méthode de mesurage direct
méthode d’analyse dans laquelle l’échantillon de gaz du sol (aliquote) est introduit directement dans un
dispositif approprié, sans concentration préalable, puis est soumis à une analyse
3.7
tube de détection à lecture directe
tube de verre rempli de réactifs qui, après passage de certains composés gazeux, provoquent des réactions
entraînant des changements de couleur en fonction de la concentration; cet équipement est, par conséquent,
utilisé pour des analyses qualitatives et semi-quantitatives
NOTE Une attention particulière doit être portée aux interférences.
3.8
migration des gaz
mouvement des gaz et des vapeurs issus des déchets dans une décharge ou dans le sol vers les couches
adjacentes, ou émission vers l’atmosphère
3.9
puits de surveillance des gaz
tuyauterie installée de manière appropriée dans un sondage et permettant le prélèvement d’échantillons de
gaz afin de mesurer les concentrations de gaz du sol et de contrôler les variations de la composition des gaz
du sol ou leur migration
3.10
échantillonnage des gaz
prélèvement, en vue de la réalisation d’essais, d’une proportion de matériau représentatif du gaz contenu
dans la porosité du sol à l’emplacement d’échantillonnage
3.11
décharge
dépôt de déchets dans ou sur un terrain pour s’en débarrasser
NOTE Une décharge peut fournir de la terre qui pourra être utilisée à une autre fin.
3.12
gaz de décharge
mélange de gaz permanents (principaux constituants), dominé par le méthane et le dioxyde de carbone,
formé par la décomposition de déchets dégradables sur des sites d’enfouissement
NOTE Le gaz de décharge peut également inclure un grand nombre de COV (composés à l’état de trace).
2 © ISO 2005 – Tous droits réservés

3.13
limite inférieure d’explosivité
LIE
pourcentage minimal (fraction volumique) d’un mélange de gaz inflammable et d’air entraînant une explosion
dans un espace confiné à une température de 25 °C et à la pression atmosphérique
3.14
échantillonnage des gaz du sol en une étape
échantillonnage des gaz du sol réalisé directement à partir d’une sonde placée dans le sol, sans préforage
3.15
échantillonnage passif des gaz du sol
échantillonnage basé sur l’adsorption des gaz du sol sur un adsorbant placé dans le sol, sans utiliser de
dépression
3.16
gaz permanent
élément ou composé dont le point d’ébullition est inférieur à - 60 °C à la pression atmosphérique
3.17
volume d’échantillon
volume de sol à partir duquel l’échantillon de gaz du sol est prélevé
3.18
gaz du sol
gaz et vapeur présents dans la porosité des sols
3.19
dispositif de surveillance des gaz du sol
sondage dont la finition est réalisée avec un matériau approprié pour stabiliser la paroi du sondage et/ou pour
limiter la zone d’échantillonnage
NOTE Selon le type et la stabilité de l’assemblage, une distinction est faite entre les points de mesurage temporaires
des gaz du sol (échantillonnage de sol unique ou répété à court terme) et les points de mesurage fixes (observations à
long terme).
3.20
sonde de gaz du sol
sonde d’échantillonnage des gaz du sol
sonde, généralement un tube, installée directement dans le sol (échantillonnage des gaz du sol en une étape)
ou dans un sondage (échantillonnage des gaz du sol en deux étapes) en vue de prélever des échantillons de
gaz du sol
NOTE En appliquant une dépression à l’extrémité supérieure de la sonde (tête), les gaz du sol à l’extrémité inférieure
(bout) sont aspirés via la ou les ouvertures d’aspiration et transférés vers un équipement de collecte des gaz et un
équipement de mesurage en ligne (méthode de mesurage direct) ou vers un absorbant (méthode par concentration), ces
dispositifs étant installés dans ou au niveau de la tête de la sonde ou utilisés ultérieurement.
3.21
essai d’aspiration des gaz du sol
échantillonnage des gaz du sol à partir d’un sondage pendant une période contrôlée plus longue (souvent de
plusieurs heures à plusieurs jours) en vue d'observer les variations temporelles de la concentration des
substances et la distribution de pression dans le sol
3.22
échantillonnage des gaz du sol en deux étapes
échantillonnage impliquant dans un premier temps l’installation d’un sondage à l’aide d’un instrument de
forage ou au moyen d’un petit sondage, puis dans un deuxième temps l’échantillonnage des gaz du sol à
partir d’une sonde installée dans le sondage
3.23
composés organiques volatils
COV
composés liquides à température ambiante (20 °C), dont le point d’ébullition est généralement inférieur à
180 °C
EXEMPLES Les COV comprennent notamment des hydrocarbures aromatiques à un seul noyau benzénique et des
hydrocarbures halogénés à bas point d’ébullition utilisés comme solvants ou comme combustibles, ainsi que certains
produits de dégradation.
4 Points préliminaires à prendre en compte
Le choix de la technique d’échantillonnage doit être cohérent avec les exigences de l’étude (y compris les
modes opératoires d’analyse ultérieurs). Il convient également de prendre en compte la nature du terrain à
analyser ainsi que la nature et la distribution de la contamination, la géologie et l’hydrogéologie. Il convient
que tout soit mis en œuvre pour éviter une contamination croisée et qu’à aucun moment les couches
aquifères ne soient exposées à des risques.
Avant le début des travaux intrusifs, il convient d’effectuer un contrôle complet du sol afin de garantir la
sécurité des installations ou structures présentes et l’absence totale de dangers (voir l’ISO 10381-2 et
l’ISO 10381-3 pour plus d’informations sur les techniques d’échantillonnage et la sécurité).
Lors de l’échantillonnage des gaz du sol à proximité de la surface, l’effet de la pénétration de l’air ambiant doit
être pris en compte. La profondeur de l’échantillonnage sera déterminée par la présence d’une couche
imperméable à la surface du sol, le type de sol (porosité, teneur en argile, etc.) et la profondeur du socle
rocheux. On considère qu’il est peu probable que des échantillons utiles puissent être prélevés à une
profondeur inférieure à 0,5 m. Pour la surveillance de routine des gaz du sol, une profondeur minimale de 1 m
est recommandée.
Le froid rend difficile l’échantillonnage des gaz du sol. Le gel au sol limite sensiblement la mobilité des gaz
dans le sol, ce qu’il convient de prendre en compte lors de la planification et de la réalisation de
l’échantillonnage ainsi que lors de l’interprétation des résultats de mesurage. De même, la mobilité peut être
limitée par un sol saturé en eau.
Le principal problème de l’échantillonnage des gaz sous un sol gelé est la perte de pores remplis d’air en
raison de la forte teneur en humidité dans la zone comprise entre les parties gelées et les parties non gelées
du sol. Par conséquent, les échantillons doivent être prélevés plus en profondeur.
Tous les bâtiments construits sur un sol non gelé jouent le rôle de voies ou de barrières pour la migration
ascendante des gaz du sol. En outre, une dépression et des différences de concentration dans les bâtiments
peuvent favoriser la pénétration des gaz dans les fondations des bâtiments.
Les effets de pression engendrés par la montée de l’air chaud dans les bâtiments peuvent favoriser l’entrée
des gaz dans les bâtiments.
Certains polluants organiques dans la phase gazeuse du sol et du sous-sol peuvent présenter des risques
toxicologiques plus ou moins graves. Par conséquent, il convient que le personnel dispose d’un équipement
de protection adapté, en fonction de la toxicité potentielle (supposée ou mesurée).
Certaines vapeurs organiques peuvent former des mélanges détonants au contact de l’air (il convient de
prendre en compte les limites d’explosivité et les températures d’auto-inflammation). Par conséquent, il
convient d’utiliser des équipements et des outils électriques adaptés aux atmosphères explosives.
Il convient que les problèmes liés à l’hygiène et à la sécurité soient constamment pris en compte. Il convient
que le personnel suive une formation lui permettant de bien comprendre les précautions à prendre (voir
l’ISO 10381-3 pour plus d’informations sur la sécurité).
4 © ISO 2005 – Tous droits réservés

5 Gaz permanents
5.1 Objectifs de l’étude
5.1.1 Gaz du sol
Les objectifs de l’étude des gaz du sol permanents sont
 l’analyse de la composition des gaz du sol,
 la détermination de la différence de concentration sur un site.
5.1.2 Gaz de décharge
L’objectif de l’étude des gaz de décharge est
 l’analyse de leur composition.
5.1.3 Autres objectifs
D’autres objectifs peuvent être définis, à savoir:
 l’évaluation des raisons possibles de problèmes d’inhibition de croissance des plantes,
 l’optimisation ou le contrôle des couvertures ou des installations de collecte des gaz,
 l’estimation globale du potentiel de production de gaz et de la durée de cette production,
 la détection de combustion souterraine,
 la définition de mesures de protection contre les gaz dans les bâtiments.
5.2 Principes de base
5.2.1 Principes physiques et chimiques
Lorsque des matériaux biodégradables sont présents dans des décharges ou dans la matrice du sol remanié
dans une friche industrielle, l’activité microbienne produit des gaz de décharge. Des gaz similaires peuvent
également être émis dans des dépôts alluvionnaires et la matière organique naturelle en décomposition (voir
l'Annexe B). Les gaz de décharge sont principalement constitués de méthane et de dioxyde de carbone (avec
un rapport d’environ 60:40). En fonction de l’activité microbienne, ce rapport peut varier. Un certain nombre
d’autres gaz traces peuvent être présents.
Les gaz permanents peuvent également être émis par les gisements de charbon, la tourbe, les dépôts
naturels tels que la craie et les dépôts alluvionnaires, ou encore peuvent provenir de fuites dans le réseau de
gaz distribué (gaz naturel) et de gaz d’égouts. Des informations sur les techniques permettant d’identifier
l’origine des gaz sont données en 5.2.3.
Le méthane est explosif à des concentrations comprises entre 5 % et 15 % (fraction volumique) dans l’air; en
dessous de 5 %, la concentration de gaz n’est pas suffisante pour entretenir la combustion et au-dessus de
15 % (fraction volumique), l’oxygène n’est pas suffisant pour entretenir la combustion. Le dioxyde de carbone
est un asphyxiant pouvant avoir des effets néfastes sur la santé lorsque les concentrations sont supérieures à
0,5 % (fraction volumique).
Le gaz de décharge, généralement saturé en humidité, est corrosif. Il peut entraîner l’asphyxie de la
végétation en raison de l’élimination de l’oxygène dans les racines des plantes ou de la présence de
composés phytotoxiques. Sa masse volumique dépend de la proportion de dioxyde de carbone par rapport au
méthane: plus la concentration de dioxyde de carbone est élevée, plus la masse volumique est grande.
La pression du gaz dans le sol dépend du taux d’émission de gaz, de la perméabilité de la masse de déchets
et des couches environnantes, ainsi que des variations du niveau de lixiviat ou des eaux souterraines dans le
site. La température et la pression atmosphérique constituent d’autres facteurs importants.
En fonction de la conception du site et de la géologie locale, le gaz peut migrer sur des distances
considérables et représenter un danger pour les constructions environnantes. Dans le cas du gaz de mine,
l’arrêt du pompage de l’eau peut conduire à une élévation du niveau de la nappe phréatique, ce qui peut
augmenter la pression de gaz et donc les émissions de gaz en surface. Par conséquent, il est important de
connaître les concentrations de gaz et les débits afin d’évaluer le potentiel de migration hors site ou
d’émission vers l’atmosphère.
5.2.2 Conditions ambiantes
Au cours de la surveillance d’un site, il est important d’enregistrer les conditions atmosphériques pendant trois
à quatre jours avant et pendant l’échantillonnage. De même, il convient d’enregistrer les conditions
climatiques locales présentes au moment de la surveillance. Ces informations peuvent faciliter l’interprétation
des données. Les paramètres les plus importants à enregistrer sont
 la pression atmosphérique, et
 la hauteur de précipitation.
Les paramètres suivants sont également utiles:
 la température (air ambiant et gaz du sol),
 la vitesse/la direction du vent, et
 la profondeur de la nappe phréatique.
Au cours des périodes de sécheresse, le sol peut se fissurer, notamment lorsque de l’argile est utilisée pour
couvrir les sites. On constate alors une augmentation des émissions de gaz à la surface. Lors des périodes
de précipitation, l’argile devient humide, elle gonfle et les fissures sont colmatées. Les émissions de gaz à la
surface sont alors réduites et une augmentation des concentrations de gaz ainsi qu’une augmentation de la
migration latérale peuvent être observées. Le mesurage de la perméabilité du sol et de la teneur en humidité
peut faciliter l’évaluation de ces effets.
L’élévation du niveau de la nappe phréatique, par exemple à la suite de précipitations, peut exercer une
pression sur le gaz et forcer sa remontée à la surface; cette élévation peut également bloquer les voies de
migration. La saturation des sols superficiels peut limiter l’évacuation des gaz de décharge vers l’atmosphère.
Il peut alors s’ensuivre des variations de la pression et des concentrations de gaz.
La chute de pression atmosphérique peut augmenter les taux d’émission. La hausse de la pression
atmosphérique peut avoir l’effet inverse. L’amplitude de cet effet dépend de la perméabilité du sol et du taux
de variation de la pression.
En général, il peut toutefois être difficile de déterminer la cause des variations de concentrations et des
émissions car elles peuvent être dues à une combinaison des facteurs précédemment mentionnés.
6 © ISO 2005 – Tous droits réservés

5.2.3 Identification de la source de gaz
L’identification de l’origine des gaz est importante pour la prise de décisions relatives à la surveillance et au
contrôle. La composition d’un gaz peut faciliter l’identification de la source. Des exemples sont donnés ci-
dessous.
 Le gaz issu d’une source géologique peut avoir une plus grande proportion de méthane que le gaz émis
par une décharge.
 Généralement, les gaz d’origine géologique contiennent jusqu’à 15 % d’éthane et des hydrocarbures
supérieurs, tandis que le méthane d’origine biologique n’en contient que des traces.
 Il peut être possible de différencier le gaz distribué des autres gaz si la composition exacte du gaz
distribué local est connue. Des composés à forte odeur tels que les sulfures et les thiols peuvent être
ajoutés au gaz distribué afin de lui donner une odeur distinctive; il peut également contenir des
hydrocarbures à longue chaîne tels que l’octane et le nonane. L’hélium est souvent éliminé du gaz
distribué.
Le gaz de décharge peut également contenir des concentrations d’hydrocarbures supérieurs plus élevées que
la normale si les déchets contiennent des substances générant ou émettant de tels gaz et vapeurs.
L’identification des différents composés peut, toutefois, être limitée car ils peuvent être affectés par des
modifications chimiques se produisant dans le sol au cours de la migration, par une dissolution dans les eaux
souterraines et par une adsorption dans l’argile, etc.
Le méthane d’origine biologique (formé par l’activité microbiologique) et le méthane thermogénétique (formé
par dégradation thermique de la matière organique à une température et une pression élevées) présentent
des proportions différentes d’isotopes de carbone, le carbone 12 et le carbone 13, qui peuvent être mesurées
pour identifier l’origine du gaz. La technique nécessite, toutefois, l’intervention de laboratoires spécialisés.
5.3 Considérations générales relatives à l’échantillonnage
Il convient que la stratégie soit spécifique au site et qu’elle soit basée sur les conditions particulières du site
concerné ainsi que sur les informations obtenues grâce à l’étude du site (voir l’Annexe C).
Il convient de prendre en compte le fait que toute action de pénétration dans le sol peut influencer les
schémas de migration et représenter une voie de migration pour le gaz.
Outre la surveillance des gaz, les sondages permettent également d’obtenir des informations relatives à
l’hydrogéologie, la géotechnique et la contamination. Par conséquent, il s’agit d’outils très utiles à objectifs
multiples.
S’il est nécessaire d’effectuer des mesurages de la concentration de gaz à différentes profondeurs, l’utilisation
de sondages à plusieurs niveaux n’est pas souhaitable et il est préférable d’utiliser des puits différents.
Lorsque les résultats doivent être comparés à d’autres et notamment lors d’une surveillance à partir de
tuyauteries, il convient que la technique utilisée soit cohérente afin de garantir l’obtention de résultats
comparables entre différents opérateurs, différentes techniques et différentes périodes de surveillance. Pour
ce faire, les mesures d’assurance qualité indiquées en 5.10 doivent être respectées.
Les mesurages de la concentration de gaz peuvent être réalisés à l’aide d’un équipement portatif (voir
Tableau E.1) ou des échantillons peuvent être prélevés en vue d’une analyse en laboratoire hors site. Il est
conseillé de prélever des échantillons de gaz à soumettre à une analyse de contrôle en laboratoire afin de
vérifier les résultats de la surveillance sur site.
5.4 Exigences relatives à l’échantillonnage
5.4.1 Options d’échantillonnage
La surveillance des gaz peut être réalisée à l’aide de différentes techniques d’échantillonnage (voir Tableau 1).
Tableau 1 — Options pour l’échantillonnage des gaz permanents
Méthode Description Avantages Inconvénients
Sondes peu Tube creux perforé Très rapide Profondeur maximale de 2 m
profondes enfoncé dans le sol et
Faible coût La sonde peut se boucher
connecté à un détecteur
de gaz
Facile à installer Confirme la présence de gaz mais
pas leur absence
Tarière Utilisation d’une tarière Faible coût et facile à utiliser Effort physique important
manuelle pour faire un trou
Permet, si besoin est, Ne peut pas pénétrer dans un sol
dans le sol
l’échantillonnage des solides difficile
Plus grandes profondeurs qu’avec Peut être longue à mettre en place
les tiges métalliques/sondes peu
profondes
Sondes Tube creux doté d’un Remaniement minimal du sol Pénétration impossible en cas
contrôlées embout conique plein. d’obstacles
Transport facile donc problèmes
Mécaniquement enfoncé
d’accès peu probables Peut provoquer un colmatage dans
dans le sol. Tuyau de
les sols argileux qui limite l’entrée
surveillance installé dans
Profondeur maximale de 10 m
des gaz dans le trou de sondage
le tube. Extraction du tube,
Permet la détermination du profil
sans retirer le cône.
des gaz du sol
Sondages Le sondage tubé est Possibilité d’atteindre de grandes Méthode relativement lente et
(sans dispositif creusé à l’aide des profondeurs coûteuse
d’injection) techniques de percussion
Remaniement minimal du sol Possibilité de problèmes d’accès
par câble. Une tuyauterie
perforée est mise en
Possibilité d’installer plusieurs Ramène les matériaux contaminés
place. Le tube est entouré
tuyauteries dans un seul sondage à la surface
de gravier, puis le tubage
afin de réaliser des mesurages à
Nécessite des précautions pour
est retiré.
différentes profondeurs
éviter la contamination d’un
Possibilité de prélever des aquifère sous-jacent
échantillons de couches de sol à
différentes profondeurs au cours du
forage
Permet la surveillance des eaux
souterraines
Permet la détermination du profil
des gaz du sol
Sondages Similaire à la description Comme ci-dessus, mais: Comme ci-dessus, mais:
(avec dispositif précédente, mais le trou
 plus rapide que la percussion  pas intrinsèquement sûrs. Les
d’injection) est foré à l’aide d’un outil
par câble étincelles peuvent présenter
rotatif et de l’air ou de l’eau
un danger sur un site
 équipement de sondage
est injecté(e) pour faciliter
produisant des gaz
relativement mobile
la pénétration de la roche.
combustibles;
 l’injection d’eau peut répandre
une contamination;
 l’injection d’air peut entraîner
la migration des gaz du sol.
Nécessite des précautions pour
éviter la contamination d’un
aquifère sous-jacent.
Ne permet pas la détermination du
profil des gaz du sol en raison des
effets de l’injection.
8 © ISO 2005 – Tous droits réservés

Bien que chaque technique puisse être utilisée, lorsqu’il est nécessaire d’effectuer une étude détaillée à long
terme du site, les puits de surveillance installés dans des sondages tendent à être l’option la plus favorable.
5.4.2 Construction des sondages
Au cours de la réalisation du sondage, il convient de contrôler l’atmosphère du trou à l’aide d’un équipement
in situ à des intervalles de 1 m. En présence d’eaux souterraines, il est possible d’obtenir des informations
utiles sur le contenu gazeux de la couche sous-jacente en mesurant les concentrations de gaz juste au-
dessus du niveau de l’eau à des intervalles de 1 m au fur et à mesure de la progression du sondage.
5.4.3 Emplacement de l’échantillonnage
Il convient que l’emplacement et la conception des puits de surveillance ou toute autre technique choisie
soient planifiés à l’avance conformément aux objectifs de l’étude du site, au modèle conceptuel du site et aux
considérations telles que l’hygiène et la sécurité, l’emplacement des équipements souterrains, etc. (voir les
Tableaux A.1 à A.5). Il convient qu’un plan détaillé soit établi et respecté, et que toute modification apportée à
ce plan soit consignée.
Dans les zones où la contamination est supposée dangereuse, la réalisation des sondages peut générer des
cheminements préférentiels et, par conséquent, il convient de s’informer sur les précautions à prendre pour la
réalisation du forage.
L’espacement des sondages dépend de la nature des couches.
La profondeur à laquelle les échantillons sont prélevés dépend des objectifs. Les informations relatives aux
concentrations à différentes profondeurs sont donc utiles car elles permettent de mieux comprendre la
propension des gaz à migrer.
5.4.4 Volumes et débits d’échantillonnage
En cas d’échantillonnage ponctuel des gaz du sol, un petit volume est prélevé dans l’horizon (environ 10 ml)
afin de détecter, probablement sans influence de paramètres externes, le volume poreux rempli de gaz. Lors
de l’échantillonnage de volumes plus importants (pouvant atteindre plusieurs litres), la zone d’échantillonnage
est diffuse et son emplacement ne peut pas être déterminé. L’échantillonnage des gaz du sol à partir d’un
sondage dont le diamètre est supérieur à celui de la sonde est dit intégrant car le gaz peut être émis sur toute
la longueur. Lors de l’échantillonnage de gaz de décharge, il convient de prélever des volumes
d’échantillonnage plus importants afin de déterminer la composition du gaz sur une zone plus étendue.
Le débit de gaz doit être déterminé. L’Annexe D présente un certain nombre de techniques de mesurage du
débit de gaz et décrit les avantages et les inconvénients de chacune.
5.5 Équipement technique
5.5.1 Généralités
Chaque instrument mesure un certain type de gaz, à différentes gammes de concentrations. Chacun a ses
propres avantages et limites. Il est important que l’opérateur ait une bonne connaissance de l’équipement de
surveillance des gaz et qu’il sache quel type d’équipement il convient d’utiliser pour chaque situation.
Le Tableau 2 répertorie un certain nombre d’instruments portatifs, les gaz analysés ainsi que les avantages et
les inconvénients opérationnels. Pour plus de détails, voir l’Annexe E.
Tableau 2 — Équipement portatif pour mesurer les gaz permanents
Instrument Gaz analysés Avantages Inconvénients
Photomètre spectral à Dioxyde de  des gaz spécifiques  le résultat peut être influencé par
infrarouge (IR) carbone,
peuvent être analysés l’humidité
hydrocarbures dans des domaines de
aliphatiques
concentration
(méthane) prédéfinis
 large domaine de
détection
Capteur avec oxydation Gaz inflammables  sensible  le capteur peut se détériorer avec
catalytique
l’âge
 nécessite une certaine quantité
d’oxygène
 non spécifique au méthane
 pas intrinsèquement sûrs
 l’échantillon est détruit au cours du
processus de mesurage
Détecteur de Dioxyde de  large domaine de  non spécifique au méthane
conductivité thermique carbone, gaz
détection
 erreurs possibles en cas de faibles
(TCD) inflammables
concentrations
Détecteur à ionisation Gaz inflammables  très sensible  non spécifique au méthane
de flamme
 convient pour détecter  pas toujours intrinsèquement sûrs
les sources d’émission
 nécessite de l’oxygène
 erreurs possibles en cas de niveaux
élevés de dioxyde de carbone
 l’échantillon est détruit au cours du
processus de mesurage
Tubes indicateurs La plupart des gaz
 très faciles à utiliser  précision et lisibilité limitées
 large domaine de  interférences élevées
détection
 utilisés pour un grand
nombre de gaz
Cellules Oxygène  simples à utiliser  l’humidité peut réduire la sensibilité
électrochimiques
 durée de conservation limitée
Cellule paramagnétique Oxygène  la précision est affectée par les
variations de la pression
atmosphérique
Détecteur à photo- Hydrocarbures
 détection de plusieurs  détection non spécifique
ionisation (PID) aromatiques et domaines de
 le signal du détecteur dépend de la
aliphatiques
concentration exclue
connexion
volatils
 différentes énergies
d’excitation possibles
Chromatographe en Hydrocarbures
 élaboré  détermination possible d’un seul
phase gazeuse (portatif) aromatiques, composé
(GC) doté de détecteurs hydrocarbures
appropriés, par exemple halogénés volatils
à ionisation de flamme
(FID), à photoionisation
(PID), à conductibilité
thermique (WLD)
10 © ISO 2005 – Tous droits réservés

Les instruments requis dépendent des conditions présentes sur chaque site; par conséquent, la spécification
d’instruments particuliers n’est pas appropriée.
Il convient que les instruments portatifs devant être utilisés sur des sites contaminés au gaz soient
intrinsèquement sûrs; ceci est encore plus vrai lorsque l’instrument doit être utilisé dans un espace confiné.
5.5.2 Installation d’une tuyauterie de surveillance des gaz
Il convient que le sondage atteigne 1 m dans le terrain naturel ou 6 m de profondeur (retenir la valeur la plus
élevée) ou encore une profondeur prédéfinie selon les exigences de l’étude du site. Lorsque l’étude concerne
une décharge, il convient que le sondage hors de la décharge atteigne au moins 1 m au-delà de la profondeur
maximale de la décharge. Si la profondeur n’est pas connue, il convient qu’elle soit établie au cours de l’étude.
Il convient d’installer un tube préperforé de 50 mm de diamètre à la base du sondage. Toutefois, il est
recommandé que le tube soit non perforé (lisse) sur une distance de 1 m par rapport à la surface du sol. Il
convient que le tube comporte des sections pouvant être assemblées par filetage, car cela évite le recours à
des composés organiques et des solvants pour assembler les longueurs de tube.
Il convient que l’espace annulaire entre la paroi externe du sondage et le tube perforé soit rempli avec des
bardeaux de pois ou tout autre matériau similaire.
Il convient que le haut du trou (généralement entre 1 m et 0,2 m de la surface du sol) soit fermé avec un
bouchon imperméable (coulis/ciment de bentonite, etc.), et que la section comprise entre 0,2 m et le niveau
du sol soit scellée à l’aide de ciment pouvant supporter un couvercle. Lorsque c’est possible, il convient que
les tubes se terminent au-dessus du niveau du sol afin d’empêcher les inondations et de faciliter leur repérage.
Toutefois, cela peut ne pas être réalisable sur des sites à accès public. Il peut être utile d’envisager un
couvercle résistant et verrouillable en vue d’empêcher tout vandalisme et toutes manœuvres abusives.
Il convient de placer un bouchon à vis en haut de la tuyauterie afin d’en permettre l’accès pour la réalisation
de mesurages du niveau des eaux souterraines. Il convient qu’un robinet d’arrêt soit fixé au couvercle à partir
duquel les échantillons de gaz peuvent être prélevés; le robinet permet de laisser passer ou non le flux de gaz
issu de la tuyauterie, selon les besoins.
5.6 Plan d’échantillonnage
Il dépend de l’objectif de l’étude et du site local.
Pour connaître les conditions présentes, les paramètres suivants doivent être pris en compte:
 les conditions météorologiques;
 les différences de pression;
 les débits de gaz;
 les concentrations de gaz.
Avant de procéder aux mesurages, les points suivants doivent être pris en compte:
 il est important de comprendre exactement ce qui doit être mesuré afin de s’assurer que les techniques
appropriées et l’équipement adap
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