EN ISO 19258:2011

SLOVENSKI STANDARD
01-november-2011
.DNRYRVWWDO1DYRGLOR]DGRORþDQMHYUHGQRVWLQDUDYQHJDR]DGMD,62
Soil quality - Guidance on the determination of background values (ISO 19258:2005)
Bodenbeschaffenheit - Leitfaden zur Bestimmung von Hintergrundwerten (ISO
19258:2005)
Qualité du sol - Guide pour la détermination des valeurs de bruit de fond (ISO
19258:2005)
Ta slovenski standard je istoveten z: EN ISO 19258:2011
ICS:
13.080.99 Drugi standardi v zvezi s Other standards related to
kakovostjo tal soil quality
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 19258
NORME EUROPÉENNE
EUROPÄISCHE NORM
June 2011
ICS 13.080.99
English Version
Soil quality - Guidance on the determination of background
values (ISO 19258:2005)
Qualité du sol - Guide pour la détermination des valeurs de Bodenbeschaffenheit - Leitfaden zur Bestimmung von
bruit de fond (ISO 19258:2005) Hintergrundwerten (ISO 19258:2005)
This European Standard was approved by CEN on 10 June 2011.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management Centre has the same
status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland,
Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.

EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2011 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 19258:2011: E
worldwide for CEN national Members.

Contents Page
Foreword .3

Foreword
The text of ISO 19258:2005 has been prepared by Technical Committee ISO/TC 190 “Soil quality” of the
International Organization for Standardization (ISO) and has been taken over as EN ISO 19258:2011 by
Technical Committee CEN/TC 345 “Characterization of soils” the secretariat of which is held by NEN.
This European Standard shall be given the status of a national standard, either by publication of an identical
text or by endorsement, at the latest by December 2011, and conflicting national standards shall be withdrawn
at the latest by December 2011.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.
Endorsement notice
The text of ISO 19258:2005 has been approved by CEN as a EN ISO 19258:2011 without any modification.

INTERNATIONAL ISO
STANDARD 19258
First edition
2005-12-15
Soil quality — Guidance on the
determination of background values
Qualité du sol — Guide pour la détermination des valeurs de bruit
de fond
Reference number
ISO 19258:2005(E)
©
ISO 2005
ISO 19258:2005(E)
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ii © ISO 2005 – All rights reserved

ISO 19258:2005(E)
Contents Page
Foreword. iv
1 Scope. 1
2 Normative references. 1
3 Terms and definitions. 1
4 General. 3
5 Procedures. 3
5.1 General. 3
5.2 Objectives and technical approaches . 4
5.2.1 General. 4
5.2.2 Substances and parameters. 4
5.2.3 Study area. 6
5.2.4 Time period. 7
5.2.5 Scale of sampling (Support) . 7
5.3 Evaluation of existing data . 7
5.3.1 General. 7
5.3.2 Completeness of data sets/minimum requirements . 8
5.3.3 Comparability of data (Sampling, nomenclatures, analyses) . 8
5.3.4 Elimination of outliers . 9
5.4 Collection of new data. 9
5.4.1 Sampling. 9
5.4.2 Soil analysis. 12
5.5 Data processing and presentation. 13
5.5.1 Statistical evaluation of data . 13
5.5.2 Data presentation and reporting . 14
6 Data handling/quality control . 15
Annex A (informative) Scale of sampling. 17
Annex B (informative) Outlier tests . 19
Bibliography . 23

ISO 19258:2005(E)
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 19258 was prepared by Technical Committee ISO/TC 190, Soil quality, Subcommittee SC 7, Soil and site
assessment.
iv © ISO 2005 – All rights reserved

INTERNATIONAL STANDARD ISO 19258:2005(E)

Soil quality — Guidance on the determination of background
values
1 Scope
This International Standard provides guidance on the principles and main methods for the determination of
pedo-geochemical background values and background values for inorganic and organic substances in soils.
This International Standard gives guidance on strategies for sampling and data processing and identifies
methods for sampling and analysis.
This International Standard does not give guidance on the determination of background values for
groundwater and sediments.
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 10381-5, Soil quality — Sampling — Part 5: Guidance on the procedure for the investigation of urban and
industrial sites with regard to soil contamination
ISO 11074:2005, Soil quality — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 11074 and the following apply.
3.1
background content
content of a substance in a soil resulting from both natural geological and pedological processes and including
diffuse source inputs
3.2
background value
statistical characteristic (3.8) of the background content
3.3
contaminant
substance or agent present in the soil as a result of human activity
NOTE There is no assumption in this definition that harm results from the presence of the contaminant.
ISO 19258:2005(E)
3.4
diffuse source input
input of a substance emitted from moving sources, from sources with a large area or from many sources
NOTE 1 The sources can be cars, application of substances through agricultural practices, emissions from town or
region, deposition through flooding of a river.
NOTE 2 Diffuse source input usually leads to sites that are relatively uniformly contaminated. At some sites, the input
conditions may nevertheless cause a higher local input such as near the source or where atmospheric deposition/rain is
increased.
[ISO 11074:2005]
3.5
pedo-geochemical content
content of a substance in a soil resulting from natural geological and pedological processes, excluding any
addition of human origin
NOTE It may be hardly possible to determine the precise pedo-geochemical content of certain substances in a soil
due to anthropogenic diffuse contamination.
3.6
pedo-geochemical background value
statistical characteristic (3.8) of the pedo-geochemical content
NOTE Any estimate of pedo-geochemical background value will be prone to a certain amount of error given the
uncertainty associated with determining the pedo-geochemical content.
3.7
soil
upper layer of the Earth's crust composed of mineral parts, organic substance, water, air and living organisms
[ISO 11074:2005]
3.8
statistical characteristic
numerical value calculated from a variate of a chosen parameter of the population
EXAMPLE Examples of the statistical characteristics are the mean, the median, the standard deviation or the
percentiles of the ordered frequency distribution.
3.9
study area
three-dimensional definition of the area where samples are to be obtained from and thus for which the
background value(s) are to be estimated
3.10
support
size, shape and orientation of a soil sample
NOTE For the purpose of analysing spatial variation in soils geostatistically (by estimation of the variogram of a soil
property), the support should be the same at each sampling site.
3.11
variate
set of observed values of a variable
EXAMPLE A variate could for instance be the series of numbers of the concentration of a substance in soil or
numerous, individual soil samples.
2 © ISO 2005 – All rights reserved

ISO 19258:2005(E)
4 General
Soils retain the evidence of their past history including impacts due to natural events or human activities.
Chemical impacts related to human activities can be detected in soils all over the world, even in regions far from
any source of contamination. For this reason, the background contents of inorganic and organic substances in
soils consist of a pedo-geochemical fraction and an anthropogenic fraction. The ratio of these fractions varies
widely depending on the type of substances, the type of soil and land use, and the kind and extent of external
impacts.
For many inorganic substances, the background content of unpolluted soils is dominated by the pedo-
geochemical content and consequently by the mineralogical composition of the soils parent material. Pedogenetic
processes may lead to a redistribution (enrichment/impoverishment) and consequently to a horizon-specific
differentiation of the substances within a soil profile. Persistent organic substances in soils originate more often
from non-natural sources and therefore the background content of soils is governed by the kind and extent of
diffuse contamination from non-soil sources.
In practice, it is often difficult to distinguish clearly between the pedo-geochemical and the anthropogenic fraction
of the background content of soils. Nonetheless, a detailed knowledge of the background content as well as of its
natural fraction for the substances of concern is essential both for any evaluation of the current status of soils for
environmental or land use related aspects or just for scientific purposes within the scope of pedology or
geochemistry. To this end, so-called background values in terms of the statistical characteristics of both, the pedo-
geochemical and the anthropogenic fraction have to be determined.
A variety of different objectives can be identified for the determination of background values of inorganic and/or
organic substances in soils. The objectives themselves provide insufficient information to define the technical
programme that will produce the desired background values. Thus a number of technical approaches have to be
defined which together form the basis of the technical programme.
This guidance provides essential aspects of sampling strategies and procedures, minimum requirements
regarding the necessary steps and ways of sample pre-treatment, analytical methods and statistical
evaluation procedures for determining sound and comparable background values.
Guidance is given for
a) evaluating existing data from different data sources and
b) setting up complete investigation programs aiming to compile background values for a clearly defined
three-dimensional picture of the soil.
These situations are representing the two extreme starting positions for the process of compiling background
values. In practice, a third intermediate situation may be dealt with when additional data need to be collected
because the quantity or quality of the existing data is insufficient.
5 Procedures
5.1 General
The procedures to determine background values encompass aspects of sampling (strategy, procedure), soil
analysis (pre-treatment, extraction and measurement), data processing and presentation. In general, two
starting positions can be distinguished, namely
a) the evaluation of existing data mostly from different data sources, and
b) the collection of new data based on an appropriate investigation strategy.
ISO 19258:2005(E)
5.2 Objectives and technical approaches
5.2.1 General
Before commencing any survey on background values in soils it is of crucial importance to define the objective
of the survey and the related technical approach.
The objective is, in general terms, the definition of 'why' background values are to be determined. The
technical approaches describe aspects like the 'where', 'what', 'how' and 'when'. Together the technical
approaches determine the technical programme that will provide the required background values.
NOTE It should be noted that a technical approach that is fit for one objective, will often be unfit for other objectives.
The objectives for defining background values might be:
⎯ to identify the current contents of substances in soils, e.g. in the context of soil-related directives;
⎯ to assess the degree of contamination by human activities;
⎯ to derive reference values for soil protection;
⎯ to define soil values for reuse of soil material and waste;
⎯ to calculate critical levels and tolerable additional critical loads;
⎯ to identify areas/sites with atypically enhanced levels of element contents due to geogenic reasons or
human impact;
⎯ etc.
In order to meet the objective, the technical approaches might include the following.
⎯ Definition of the substances and parameters
⎯ For example, the background values to be estimated may be the total heavy metal content or the
bioavailable heavy metal content. (See 5.2.2)
⎯ Definition of the study area
⎯ The (three-dimensional) definition of the area where samples are to be obtained from. This has to be
a detailed description of what is to be considered as the study area, and what is not. (See 5.2.3.)
⎯ Definition of the time period of interest:
⎯ Are the historical or current contents relevant for the objective? (See 5.2.4.)
⎯ Definition of the size and geometry (support) of the area sampled at a sampling location. (See 5.2.5.)
5.2.2 Substances and parameters
Background values can be determined for all kinds of inorganic and organic substances in soils as well as soil
characteristics. In practice, the more persistent and immobile compounds are of primary interest because of
their potential to adsorb and accumulate in soil, whereas remobilization and intrinsic biodegradation are of
less significance.
As well as the substances of concern, basic soil parameters and site characteristics (see 5.4.1.3) need to be
provided to assist in interpretation of the contents of substances. A number of so-called basic soil parameters
influence soil processes that affect the contents of inorganic and organic substances. Table 1 lists these
parameters which should be analysed according to the given International Standards.
4 © ISO 2005 – All rights reserved

ISO 19258:2005(E)
Within the group of inorganic substances, trace elements (e.g. heavy metals, micronutrients) are most often
analysed (Table 2). Concerning the analytical methods, a distinction has to be drawn between different
extraction/preparation methods (Table 2), whereof very few determine the total content which may be needed
for instance for calculating element stocks. Besides total contents, the (eco-) toxicologically more relevant
mobile fractions (Table 2) are of increasing interest, e.g. if pathway-related questions are to be examined.
Analysis of parameters in Table 2 should be carried out according to International Standards given in Table 2.
Table 1 — Basic soil parameters
Parameter Method ISO International Standard
Texture Sieving, sedimentation ISO 11277
Fraction of coarse material Sieving ISO 11277
Amount of non-soil material Sieving/visual control ISO 11259, ISO 11277
Bulk density Direct measurement of undisturbed ISO 11272
soil samples, estimation form soil
water retention curves
pH pH-electrode ISO 10390
Content of organic carbon Dry combustion ISO 14235
Cation exchange capacity, exchangeable cations BASECOMP ISO 11260
BaCl ISO 13536
Carbonate content CO-evolution ISO 10693
Table 2 — Examples for the analysis of inorganic substances
Parameter Speciation/form Extraction/preparation ISO International Standard
Method
Extraction/preparation Determination
Metalloids, e.g. ISO 14869-1 ISO 14869-1
Alkaline fusion + X-ray
Total
fluorescence HF + HCIO
arsenic and selenium ISO 14869-2 ISO 11047
Metals, Pseudo total aqua regia ISO 11466 ISO 11047
barium, cadmium, EDTA
Complexing
chromium, cobalt, DTPA ISO 14870 ISO 11047
copper, iron, lead, NaNO
manganese, mercury, NH NO
4 3
Exchangeable
molybdenum, nickel, CaCl
thallium, zinc KCl
Cyanides Water soluble H O, leaching tests See NOTE. See NOTE.
NOTE There are a variety of extraction and analytical methods for soil-water in the series of International Standards on water
quality which may also be applicable. However, it is important to confirm that they will work with the extracts obtained form particular soil
material.
Surveys on organic substances usually refer to persistent compounds. The persistent organic contaminants
listed in Table 3 are some of the more commonly encountered, but the list is not complete. Analysis should be
carried out according to International Standards listed in Table 3.
Various methods are used for the analysis of organic substances. The aim of these methods is usually to
extract the greatest possible quantity of organic substances from soils. It is important to recognize that organic
compounds may be extracted from naturally occurring organic materials (e.g. organic matter, decaying
vegetation, peat, charcoal), and that non-specific analyses in particular may, therefore, give misleading results.
ISO 19258:2005(E)
Table 3 — Examples for the analysis of organic substances
Substance/groups of substances Method ISO International Standard
PAH Soxhlet/HPLC/UV ISO 13877
Thin-layer chromatography ISO 7981-1
RP C-18/HPLC ISO 7981-2
GC/MS ISO 18287
Dioxins/Furane
Chlorophenols Hexane/GC/ECD ISO 8165-1
Chlorpesticides RP C-18/HPLC/UV ISO 11369
PCBs GC-ECD ISO 10382
Chlornaphthalene
Chlorparafin
Bromodiphenylethers
NOTE There are a variety of extraction and analytical methods for water in the series of International Standards on water quality
which may also be applicable. However it is important to confirm that they will work with the extracts obtained from a particular soil
material.
When collecting new data for determining background values, it is recommended that the investigation
program be designed with regard to additional questions that could arise in future. In most cases, carrying out
new sampling campaigns is much more expensive than analysing additional substances in the first place. To
this end, a suitable storage of soil samples for subsequent analyses of organic or inorganic substances is of
crucial importance. Besides the substances of concern (Tables 2 and 3) and additional soil parameters
(Table 1), it is essential to provide a comprehensive site description (see 5.4.1.3) for interpretation purposes.
The documentation of all the actions taken is of utmost importance if the data measured is to be of use for
other assessments in future investigations.
5.2.3 Study area
The definition of the study area (3.9) can be based on two different principles, that is:
⎯ a purely spatial definition (X, Y, Z), defining the contours of the study area by the coordinates within which
the study area lies. Apart from the definition in a horizontal plane, the soil depth that is to be studied
should also be defined;
⎯ a typological definition of the study area, based on one or more characteristic(s), e.g. soil type (for
example, the A-horizon of a specific soil type), land use (also considering the potential effects on the
background values), elevation level, etc.
Of course, it is possible to mix the spatial and typological definition of the study area.
EXAMPLE Examples of a mix of the spatial and typological definition of the study area might be:
— the grassland in a county or province;
— the A-horizon in an area defined by X- and Y-coordinates.
The definition of the study area must be detailed at a level where there cannot be any misinterpretation on
what is and what is not part of the study area. For an unambiguous definition of the study area, all actual point
and diffuse sources within the study area need to be defined. As the general objective is to determine
background values, a safety zone around that (type of) source might be defined and thereby excluding parts
of the more generally defined study area. It might also result in specific zones for which the data is to be
considered separately from the rest of the study area.
6 © ISO 2005 – All rights reserved

ISO 19258:2005(E)
The definition of the study area as described is independent of whether the soil samples are still to be taken,
or whether already existing soil samples (or results) are to be used. In the latter situation, the detailed
definition of the study area will define which samples/results are to be included or excluded.
5.2.4 Time period
Background values are influenced both by the natural processes (pedogenesis, biogeochemical cycles) as
well as by diffuse source input. Two different time scales can be distinguished:
⎯ the period in which the background value may significantly vary due to natural processes;
⎯ the period in which the background value will most probably only change due to human influences
(except for large scale natural phenomena).
The second period is generally smaller than the first one.
It might be that a specific historic period is of interest when measuring background values. When a soil layer is
formed during this same period, it is indeed possible to determine background values for a certain time period.
When background values are to be re-determined after a period of time in order to determine if changes occur,
the time period between measurements should be based on (see also ISO 16133):
⎯ the expected enrichment of substances in soils (accumulation for example due to diffuse source input);
⎯ the expected loss of substances in soils (for example, due to leaching, biodegradation or plant uptake);
⎯ changes in concentration level that can be determined both analytically and statistically.
5.2.5 Scale of sampling (Support)
Variability in concentrations is by definition a scale-related characteristic. Depending on the volume for which
an analytical result is to be considered representative, the variability in concentrations encountered might be
different. The scale — or in more technical terms the (geo-statistical) support (3.10) — is therefore an
important technical aspect on which a decision is to be made prior to data collection.
For (mainly) two-dimensional surveys, the support is the size (and geometry) of the area sampled at a
sampling location.
The study will always involve a certain soil layer of depth. However, as in the horizontal plane, the dimensions
are much larger than in the vertical plane, the support in soil surveys is most often defined in a two-
dimensional way.
More information on support is given in Annex A.
5.3 Evaluation of existing data
5.3.1 General
When using existing data, specific care must be taken concerning the quality and comparability of data
particularly if the data originate from different sources. Data with appropriate information have to be
harmonized in a step-wise procedure with regard to the specific evaluation objectives. In general, the
harmonization of data sets results in a more or less significant reduction of the respective variate. Nonetheless,
the procedure of harmonization of data sets is inevitable to produce a sound and reliable evaluation. The
respective harmonization strategy should encompass aspects like
a) the check of the completeness of the data sets related to minimum requirements,
b) the harmonization of different sampling strategies, references, nomenclatures and analytical procedures,
ISO 19258:2005(E)
c) the identification and elimination of contaminated samples (excluded from the population of background
values by definition).
5.3.2 Completeness of data sets/minimum requirements
In order to ensure a minimum level of data quality, it is essential to provide sufficient and sound information of
the data, for instance
⎯ the date of sampling,
⎯ the procedure used to select sampling locations (plots),
⎯ the scale of sampling (e.g. support),
⎯ the site location (coordinates),
⎯ the sampling depth intervals,
⎯ the number and configuration of samples (e.g. regular grid or random sampling) taken at a sampling
location (plot),
⎯ the method used to extract and analyse the components (including quality assurance and detection limits),
⎯ the site-specific information (e.g. pedology/lithology, land use).
This information can be used to screen the data on their suitability for the objective of compiling background
values.
The definition of minimum requirements on information of the data set depends, amongst others, on the
substances of concern, the area and spatial reference to be considered and the approach pursued to achieve
an adequate spatial representation of the point-related data.
Apart from the information listed above, the type and degree of accuracy, e.g. of site-specific information
depends on soil and other parameters influencing the behaviour and hence the contents of the substances in
soils. For instance, inorganic substances need to be related at first priority to lithogenic soil properties due to
their predominant geogenic origin, whereas the content of organic substances of soils is more strongly
correlated to, e.g. land-use-related parameters.
5.3.3 Comparability of data (Sampling, nomenclatures, analyses)
Different sampling strategies may have a crucial impact on the comparability of data sets. Problems arise here
in particular through the comparison of horizon versus depth level-related samples and that of mixed versus
individual samples. Further on, the representative nature of the variate for a sample population with regard to
the same support for an area needs to be taken into account. Also, an uneven spatial distribution of the
sampling points within an area may cause biased estimates of the parameters of the frequency distribution
due to an overestimation of some parts of the study area. Block-kriging is recommended to deal with this
problem. It is strongly recommended to carefully balance the possible inaccuracies introduced by merging
data sets from different campaigns, versus the advantage of an increasing number of samples and
consequently an increasing representation of a population.
The extent to which different sample pre-treatments and analytical procedures (extraction, measurements)
can be compared and harmonized has to be evaluated in each individual case, e.g. against the intended
accuracy of the background value. For inorganic substances, the analytical results originating from different
analytical procedures may be transformed by applying regression functions or constants provided the
respective relations are known. Alternatively, the analytical procedures may be grouped roughly according to
the operationally defined extracted fractions (see Table 2). The broader the ranges of classified background
values as target variables are, the lower may be the demand of data comparability. Nonetheless, the assessor
should bear in mind, that merging data sets analysed by different analytical procedures invariably requires
compromises to be made.
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ISO 19258:2005(E)
5.3.4 Elimination of outliers
According to definition 3.1, the background content of substances in soils includes the moderate diffuse input
into the soil. Therefore, locally contaminated sites are excluded from the population of background contents.
Consequently, data obviously stemming from locally contaminated sites have to be identified and eliminated
from the respective data set. To this end several statistical tests for identifying outliers are applicable, e.g. test
on distribution of the data, exploratory data analysis (boxplots), principle component analysis, etc. (See also
5.5.1.2.1 and Annex B.)
NOTE The removal of outliers has a significant effect on the resulting definition of the background value. The
statistical identification of an outlier by itself is insufficient for removing a high (or low) measurement out of the database
describing the background value. The statistical test does however provide a good method of defining which data should
be investigated in more detail, in order to see if an explanation can be found for the high value to be an outlier. If such an
explanation is found, the value is indeed an outlier and should be eliminated.
5.4 Collection of new data
5.4.1 Sampling
5.4.1.1 Sampling strategy
5.4.1.1.1 General considerations
The natural pedo-geochemical content and the usual content of substances in soil vary according to soil
parent material. They also depend on soil horizons, as pedogenic processes modify and redistribute
components in soils, leading generally to the formation of several soil horizons that may exhibit different
compositions.
Land use and distance to contamination sources also influence the content of substances in soils. Human
activity modifies soil composition through agriculture, waste spreading, building, atmospheric deposition from
industry, households, traffic, etc. A sampling site is considered here as a small portion of land, from a few
square metres to about 1 ha, where one sample of each of the soil layers or horizons of interest is collected.
This section presents two strategies for selecting the sampling sites within the study area: the systematic
approach and the typological approach. The choice of one of them is generally influenced by the degree of
pre-existing knowledge about the soil and land use. When relatively little is known, the systematic approach is
often more appropriate. However, these two approaches can be considered as typical ones in the continuum
of all possible strategies. Therefore, it is possible to build an intermediate strategy, mixing some aspects of the
systematic approach with others from the typological one.
5.4.1.1.2 Systematic approach
The sampling sites are located using a grid. The interval between the grid points is dependent on the
resolution desired for the determination of the pedo-geochemical and/or background content. In principle, the
interval between the sampling sites should be such that the minimum number of samples can be collected to
represent each of the defined soil units. A square grid can be used, with cells varying in size (available
monitoring recommendations should be considered).
For instance, square cells with a 16 km, 5 km or 2,5 km site can be used at the scale of a country, whilst
square cells of a few hundred meters are more appropriate for the study at the level of a small area.
If sampling at a given grid point is rendered impossible due to buildings, roads, water surface or any other
reason, a new location may be chosen using a systematic procedure. For instance, a deviation may be
permitted from the initial point by steps of a definite distance north, then east, then south and finally west.
For each selected site, consider moving the sampling area if it is potentially highly contaminated by near-by
point sources, or in a pedo-geochemical way, if any source could compromise the purpose of the study (e.g.
overhead power-lines should be avoided if the zinc content of soils is of interest).
ISO 19258:2005(E)
Samples are taken from soil layers of definite depths or from a defined pedological horizon or horizons. If the
surface layers are contaminated by diffuse sources, the contents determined indicate the background content
in these soils. For relatively immobile substances (e.g. heavy metals), the deep layers and particularly those at
a depth below 40 cm are generally uncontaminated (provided local contamination by point sources can be
excluded), and the respective substance content can be considered as the pedo-geochemical content.
A comprehensive site and soil description (Table 5) should be done at the same time as the samples are
taken.
5.4.1.1.3 Typological approach
In the typological approach, the soil is stratified according to soil parent material (for inorganic substances),
soil type and land use. Sites potentially highly contaminated by adjacent point sources are rejected.
The typological approach needs detailed information about the area to be investigated. Information (such as
on geology, pedology, land use and sources of possible contamination) has to be gathered and evaluated in
order to elaborate the sampling scheme.
For inorganic substances, the first step of the stratification of the area refers to the soil parent materials.
Within each type of parent material stratum, the soil is stratified again on the basis of pedogenesis, if this is
considered to have markedly modified the distribution of substances in soil. Further stratification, e.g. for
organic substances is related to land use; it is recommended to distinguish between cultivated and forest soils
and soil under meadow or spontaneous vegetation. On a local scale, the best stratification is based on
pedology, e.g. that of the soil series, as this taxonomic level generally explains most of the variation of the soil
properties. Finally, the horizon to be sampled has to be chosen.
Within one stratum, the sampling sites should generally be chosen in such a way that the area is covered
representatively. The choice of the sampling sites can be carried out within each stratum using a random or
systematic sampling scheme.
NOTE Apart from the degree of pre-existing knowledge, the type of question largely determines the choice between a
random or a systematic sampling scheme. To estimate parameters of a frequency distribution of the background contents,
a random sampling approach is most appropriate. For mapping background contents, in general, a (centred) regular grid is
more appropriate.
5.4.1.2 Number of sampling sites
Background values cannot be summarized in a central parameter such as the mean. It is necessary to
describe the variability of a given content in soil as precisely as possible. In the case of a normal probability
distribution, the number of samples necessary for the estimation of the standard deviation is independent from
the standard deviation of the population. It can be determined using Table 4, which shows that a minimum
number of 30 samples is necessary to estimate the standard deviation of a normal population.
Table 4 — Maximum relative error on the estimation of the standard deviation
of a normal population, with a = 0,05; n: number of samples
n e (%)
r
10 57
20 35
30 27
40 23
50 21
10 © ISO 2005 – All rights reserved

ISO 19258:2005(E)
However, probability distributions of substances in soils are rarely normal. They are often positively skewed
but not necessarily log-normal. The estimation of the required number of samples to assess variability of such
a distribution can then be equal to the number of samples necessary to draw a representative histogram or to
calculate representative percentile. To this end, a minimum number of 30 samples is recommended.
5.4.1.3 Soil description
The interpretation of background contents of soils requires general information about the study area. The most
relevant parameters for the soil description of the study area are listed in Table 5. It is important to bear in
mind that the reliability of data interpretation strongly depends on a profound knowledge of the study area,
hence collection of parameters, indicated in Table 5, should be as comprehensive as possible.
Table 5 — Parameters for site and soil description
Parameter ISO
In
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