SIST EN ISO 5667-6:2017

SLOVENSKI STANDARD
01-junij-2017
.DNRYRVWYRGH9]RUþHQMHGHO1DYRGLOR]DY]RUþHQMHUHNLQSRWRNRY,62

Water quality - Sampling - Part 6: Guidance on sampling of rivers and streams (ISO 5667
-6:2014)
Wasserbeschaffenheit - Probenahme - Teil 6: Anleitung zur Probenahme aus
Fließgewässern (ISO 5667-6:2014)
Qualité de l'eau - Échantillonnage - Partie 6: Lignes directrices pour l'échantillonnage
des rivières et des cours d'eau (ISO 5667-6:2014)
Ta slovenski standard je istoveten z: EN ISO 5667-6:2016
ICS:
13.060.10 Voda iz naravnih virov Water of natural resources
13.060.45 Preiskava vode na splošno Examination of water in
general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 5667-6
EUROPEAN STANDARD
NORME EUROPÉENNE
September 2016
EUROPÄISCHE NORM
ICS 13.060.10; 13.060.45
English Version
Water quality - Sampling - Part 6: Guidance on sampling of
rivers and streams (ISO 5667-6:2014)
Qualité de l'eau - Échantillonnage - Partie 6: Lignes Wasserbeschaffenheit - Probenahme - Teil 6: Anleitung
directrices pour l'échantillonnage des rivières et des zur Probenahme aus Fließgewässern (ISO 5667-
cours d'eau (ISO 5667-6:2014) 6:2014)
This European Standard was approved by CEN on 30 April 2016.

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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2016 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 5667-6:2016 E
worldwide for CEN national Members.

Contents Page
European foreword . 3
Annex ZA (informative) A-deviation . 4
European foreword
The text of ISO 5667-6:2014 has been prepared by Technical Committee ISO/TC 147 “Water quality” of
the International Organization for Standardization (ISO) and has been taken over as EN
ISO 5667-6:2016 by Technical Committee CEN/TC 230 “Water analysis” the secretariat of which is held
by DIN.
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 March 2017, and conflicting national standards shall
be withdrawn at the latest by March 2017.
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.
Please see informative Annex ZA (A-deviation), which is an integral part of this document.
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, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 5667-6:2014 has been approved by CEN as EN ISO 5667-6:2016 without any
modification.
Annex ZA
(informative)
A-deviation
A-deviation: National deviation due to regulations, the alteration of which is for the time being outside
the competence of the CEN-CENELEC national member.
This European Standard does not fall under any Directive of the EU.
In the relevant CEN-CENELEC countries (Estonia), these A-deviations are valid instead of the provisions
of the European Standard until they have been removed.
Clause Deviation
1 According to the regulation of Estonian Minister of the Environment no 30,
06.05.2002 "Sampling procedure", paragraph 15, only three methods described in the
standard, are permitted to use for sampling from surface water in Estonia – discrete
sampling, composite sampling or continuous sampling.
6 According to the regulation of Estonian Minister of the Environment no 30,
06.05.2002 "Sampling procedure", paragraph 9, clause 4, temperature for storage and
transportation of sample must be between 2 °C-5 °C.
7 According to the regulation of Estonian Minister of the Environment no 30,
06.05.2002 "Sampling procedure", paragraph 16, clause 3 , a sample must be collected
from the depth of surface water of 25 cm. If the depth of water in the stream is less
than 50 cm, the sample must be collected at a depth of 1/3.
7.2 According to the regulation of Estonian Minister of the Environment no 30,
06.05.2002 "Sampling procedure", paragraph 14, clause 3, sampling from near the
bridges is not recommended. If it is necessary, a sample must be collected from the
upstream side of the bridge.
INTERNATIONAL ISO
STANDARD 5667-6
Third edition
2014-07-15
Water quality — Sampling —
Part 6:
Guidance on sampling of rivers and
streams
Qualité de l’eau — Échantillonnage —
Partie 6: Lignes directrices pour l’échantillonnage des rivières et des
cours d’eau
Reference number
ISO 5667-6:2014(E)
©
ISO 2014
ISO 5667-6:2014(E)
© ISO 2014
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
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Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2014 – All rights reserved

ISO 5667-6:2014(E)
Contents Page
Foreword .v
Introduction .vii
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Design of sampling programme . 3
5 Sampling location . 4
5.1 Sampling point selection . 4
5.2 Frequency and time of sampling . 8
6 Preparation for sampling . 8
7 Sampling at specific locations. 9
7.1 General . 9
7.2 Sampling from bridges .10
7.3 In-stream sampling .11
7.4 Sampling from the bank side .11
7.5 Sampling from craft .12
7.6 Sampling under ice .12
8 Sampling methods .12
8.1 Single, discrete samples .12
8.2 Sampling from specific depths .12
9 Sampling equipment .13
9.1 Single, discrete samples .13
9.2 Sampling of surface layers for LNAPL (e.g. oils) or surface films .14
9.3 Devices for sampling from specific depths .14
9.4 Automatic sampling devices .14
9.5 Other sampling equipment .15
10 Taking the sample .15
10.1 Risk factors .15
10.2 Arrival on site .15
10.3 Rinsing the equipment .16
10.4 Direct sampling .16
10.5 Indirect sampling using a sampling vessel .16
10.6 Sampling through ice .17
10.7 Sampling of surface layers or films.17
10.8 Sampling by increments.17
10.9 Adding preservatives in the field.17
10.10 Labelling .17
11 Stabilization, transport, and storage of samples .17
11.1 Stabilization .17
11.2 Transportation .18
11.3 Security and traceability of samples during storage and delivery .18
12 Quality assurance .18
12.1 Avoidance of contamination .18
12.2 Sample identification and records .19
12.3 Assurance and quality control .19
13 Reports.19
13.1 Analytical reports .19
13.2 Sampling protocols .20
ISO 5667-6:2014(E)
14 Certification, registration, or accreditation .20
15 Safety precautions .20
Annex A (informative) Calculation of complete mixing distance .22
Annex B (informative) Example of a report - Sampling from rivers and streams .23
Bibliography .26
iv © ISO 2014 – All rights reserved

ISO 5667-6:2014(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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
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. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers
to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 147, Water Quality, Subcommittee SC 6, Sampling.
This third edition cancels and replaces the second edition (ISO 5667-6:2005), which has been technically
revised.
ISO 5667 consists of the following parts, under the general title Water quality — Sampling:
— Part 1: Guidance on the design of sampling programmes and sampling techniques
— Part 3: Preservation and handling of water samples
— Part 4: Guidance on sampling from lakes, natural and man-made
— Part 5: Guidance on sampling of drinking water from treatment works and piped distribution systems
— Part 6: Guidance on sampling of rivers and streams
— Part 7: Guidance on sampling of water and steam in boiler plants
— Part 8: Guidance on the sampling of wet deposition
— Part 9: Guidance on sampling from marine waters
— Part 10: Guidance on sampling of waste waters
— Part 11: Guidance on sampling of groundwaters
— Part 12: Guidance on sampling of bottom sediments
— Part 13: Guidance on sampling of sludges
— Part 14: Guidance on quality assurance and quality control of environmental water sampling and
handling
— Part 15: Guidance on the preservation and handling of sludge and sediment samples
ISO 5667-6:2014(E)
— Part 16: Guidance on biotesting of samples
— Part 17: Guidance on sampling of bulk suspended solids
— Part 19: Guidance on sampling of marine sediments
— Part 20: Guidance on the use of sampling data for decision making — Compliance with thresholds and
classification systems
— Part 21: Guidance on sampling of drinking water distributed by tankers or means other than distribution
pipes
— Part 22: Guidance on the design and installation of groundwater monitoring points
— Part 23: Guidance on passive sampling in surface water
vi © ISO 2014 – All rights reserved

ISO 5667-6:2014(E)
Introduction
An understanding of the purpose of sampling is an essential prerequisite to identifying the principles
to be applied to a particular sampling problem. Examples of the purposes of sampling programmes
commonly devised for rivers and streams are as follows:
a) to determine the suitability of the water quality of a river or stream within a river basin for a
particular use, such as
1) a source of drinking water,
2) for agricultural use (e.g. all types of irrigation, live-stock watering),
3) for the maintenance or development of fisheries,
4) for amenity use (e.g. aquatic sports and swimming), and
5) for conservation and protection of aquatic life;
b) to assess the impact of human activities on the quality of water, such as
1) study of the effects of waste discharge or accidental spillages on a receiving water,
2) assessment of the impact of land use on river or stream quality,
3) assessment of the effect of the accumulation and release of substances including contaminants
from bottom deposits on aquatic biota within the water mass, or on bottom deposits,
4) study of the effects of abstraction, river regulation, and river-to-river water transfers on the
chemical quality of rivers and their aquatic biota, and
5) study of the effects of river engineering works on the water quality (e.g. addition or removal of
weirs, changes to channel or bed structure).
INTERNATIONAL STANDARD ISO 5667-6:2014(E)
Water quality — Sampling —
Part 6:
Guidance on sampling of rivers and streams
WARNING — The focus of this part of ISO 5667 is the collection and integrity of water samples. The
collection of these samples can be hazardous and attention is therefore drawn to the existence
in some countries of legislative requirements for the safety of personnel. It is essential that all
sampling personnel have had thorough health and safety training for the conditions they are
likely to encounter.
1 Scope
This part of ISO 5667 sets out the principles to be applied to the design of sampling programmes,
sampling techniques, and the handling of water samples from rivers and streams for physical and
chemical assessment.
It is not applicable to the sampling of estuarine or coastal waters nor for microbiological sampling.
[10]
NOTE 1 Procedures for microbiological sampling are given in ISO 19458.
This part of ISO 5667 is neither applicable to the examination of sediment, suspended solids or biota, nor
to dammed stretches of rivers or streams. Also, it is not applicable to passive sampling of surface waters
(see ISO 5667-23).
NOTE 2 In cases where naturally occurring or artificially constructed dams result in the retention or storage
of water for several days or more, the stretch of the river or stream should be considered as a standing water body.
For sampling purposes, see ISO 5667-4.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 5667-1, Water quality — Sampling — Part 1: Guidance on the design of sampling programmes and
sampling techniques
ISO 5667-3, Water quality — Sampling — Part 3: Preservation and handling of water samples
ISO 5667-11, Water quality — Sampling — Part 11: Guidance on sampling of groundwaters
ISO 5667-14, Water quality — Sampling — Part 14: Guidance on quality assurance and quality control of
environmental water sampling and handling
ISO 6107-2:2006, Water quality — Vocabulary — Part 2
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 5667-11, ISO 6107-2, and the
following apply.
ISO 5667-6:2014(E)
3.1
automatic sampling
process whereby samples are taken either discretely or continuously, independently of human
intervention, and according to a predetermined programme
[SOURCE: ISO 6107-2:2006, 9]
3.2
composite sample
two or more samples or sub-samples, mixed together in appropriate known proportions (either
discretely or continuously), from which the average value of a desired characteristic can be obtained
Note 1 to entry: The proportions are usually based on time or flow measurements.
[SOURCE: ISO 6107-2:2006, 29]
3.3
continuous sampling
process whereby a sample is taken continuously from a body of water
[SOURCE: ISO 6107-2:2006, 32]
3.4
discrete sampling
process whereby single samples are taken from a body of water
[SOURCE: ISO 6107-2:2006, 40]
3.5
incremental sampling
technique in which small samples are taken because of a low flow rate (with the possibility of
contamination by bottom deposits) or because of restricted access (e.g. where a sample is obtained
through a small aperture), these small samples then being aggregated to form a composite sample
Note 1 to entry: All the liquid contained in the small samples is used, unlike blending of aliquots used to make a
flow-proportional sample (see 9.4).
3.6
isokinetic sampling
technique in which the sample from a water stream passes into the orifice of a sampling probe with a
velocity equal to that of the stream in the immediate vicinity of the probe
[SOURCE: ISO 6107-2:2006, 56]
3.7
light non-aqueous-phase liquid
LNAPL
organic compound that has low water solubility and a density less than that of water
EXAMPLE Petroleum products.
[SOURCE: ISO 5667-11:2009, 3.15, modified — Singular forms replace plural forms.]
3.8
random sampling
form of sampling whereby the chances of obtaining different concentration values of a determinand are
precisely those defined by the probability distribution of the determinand in question
2 © ISO 2014 – All rights reserved

ISO 5667-6:2014(E)
3.9
river
natural body of water flowing continuously or intermittently along a well-defined course into an ocean,
sea, lake, inland depression, marsh, or other watercourse
[SOURCE: ISO 6107-2:2006, 109]
3.10
sampling site
general area or location from which samples are taken
3.11
sampling point
precise position within a sampling location from which samples are taken
[SOURCE: ISO 6107-2:2006, 117]
3.12
stream
water flowing continuously or intermittently along a well-defined course, as for a river, but generally on
a smaller scale
[SOURCE: ISO 6107-2:2006, 137]
3.13
sub-sample
portion removed from a sample and intended to be representative of that sample
3.14
systematic sampling
sampling whereby the samples are taken at predetermined intervals, often equally spaced in time
4 Design of sampling programme
Sampling is usually the first step in carrying out an investigation and largely determines the quality
of the whole investigation. It is therefore recommended that a detailed sampling strategy be drawn
up, often based upon a preliminary investigation in which an assessment has identified the important
aspects. Both the purpose and the ambient situation determine the way in which the sampling is carried
out. Consideration of time-of-travel data can influence choice of sampling locations depending on the
objective of the survey. General aspects for sampling programme design can be found in ISO 5667-1.
The sampling plan should give consideration to at least the following aspects.
General aspects:
a) purpose of the investigation;
b) parameters to be analysed for each sampling point;
c) the measurements to be carried out at the sampling point (with specification of the methods to be
used) such as temperature, dissolved oxygen, degree of acidity, or discharge;
d) frequency and times of sampling and the type of sample;
e) sampling site and the number and locations of sampling points (also see 5.1);
f) sampling equipment;
g) quality assurance procedures to be followed;
h) transport, preservation, and storage of samples.
ISO 5667-6:2014(E)
Aspects relating to the ambient situation of the sampling point:
a) safety aspects;
b) hydrodynamic and morphological characteristics of the water to be sampled;
c) local circumstances such as water depth, floating layers, vegetation, and accessibility of the location;
d) the sampling depth(s);
e) anticipated composition and quantity of the water to be sampled, among other things whether there
are any floating and/or sludge layers present.
In addition, many characteristics can influence the behaviour of contaminants in river systems. An
understanding of the nature of these characteristics is important when planning and carrying out river
sampling programmes. Important factors include temperature, turbidity, depth, velocity, turbulence,
slope, changes in direction and in cross-sections, and the nature of the river bed.
These factors are so interrelated that it is difficult to assign more or less importance to each one. For
example, slope and roughness of the stream channel affect both depth and velocity of flow, which together
control turbulence. Turbulence in turn affects rates of mixing of effluents and tributary streams, re-
aeration, sedimentation or scour of solids, growths of attached biological forms and rates of natural
purification. In addition, chemical and biological processes can occur, e.g. photosynthesis, respiration,
and metabolic effects.
Practical sampling issues, such as accessibility, can make the ideal sampling point impractical. It is
essential that any change to the designated sampling point on any grounds be discussed and agreed
with the sampling programme originator. The outcome of the deliberations should be recorded in a
sampling point file which contains directions to the sampling site, the detailed location of the sampling
point, the method of sampling, and specific details (e.g. keys required, health, and safety issues). It can
differentiate between equivalent sampling points that can be used if, for instance, river conditions
change. It can also specify the type of sampling to be carried out, e.g. the depth to sample.
5 Sampling location
5.1 Sampling point selection
5.1.1 Choice of sampling site
In choosing the exact point from which samples are required, two aspects are generally involved:
a) the selection of the sampling site (i.e. the location of the sampling cross-section within the river
basin, river, or stream);
b) the identification of the precise point at the sampling site.
The purpose of sampling often defines sampling sites (as in the case of the determination of the quality
of an effluent discharge), but sometimes the purpose only leads to a general idea of the sampling site,
as in the characterization of quality in a river basin. Where possible, sampling site locations should be
[9]
defined by a grid reference in accordance with the international grid system in ISO 19112.
The choice of sampling sites for single sampling stations is usually relatively straightforward. For
example, a monitoring station for a baseline record of water quality can be chosen to permit the use of
a convenient bridge, or to allow an upstream effluent discharge or tributary to be well mixed laterally
before the station. Stations for monitoring water supply abstraction points might need to be fixed within
narrow limits (i.e. in proximity to the abstractions).
In regions that receive seasonal rainfall only, and that have long periods without rain, river volumes and
flows can vary tremendously, and sampling sites for regular use should be chosen so as to ensure that
4 © ISO 2014 – All rights reserved

ISO 5667-6:2014(E)
they remain appropriate and practical for sampling during periods of both maximum and minimum
flow.
Where it is necessary to carry out sampling through ice in winter, the chosen sampling site should be as
close as possible to the sampling site used during other seasons of the year. If sampling is to be carried
out near a bridge, the site should be located far enough upstream to avoid contamination from road
salt and sand. Any deviations from the routine sampling point or given sampling coordinates should be
discussed where possible with the sampling originator, and should be detailed as part of the data set and
recorded with the analytical results, together with the new coordinates where applicable.
5.1.2 Importance of mixing
When the effects of a tributary or an effluent on the quality in a particular identified stretch of river
or the main stream are of interest, at least two sampling sites should be chosen; one should be just
upstream of the confluence and the other should be sufficiently far downstream to ensure that mixing
is complete.
It is also important that the sample be collected at a well-mixed and flowing sampling point, i.e. not in an
eddy or a backwater where the flow is not typical of the main water body.
The physical characteristics of the channels of watercourses largely control distances required for the
complete mixing of effluents with stream flow.
Effluents mix in three dimensions in a stream, namely
a) vertically (from top to bottom),
b) laterally (from one side to the other), and
c) longitudinally (levelling out of peaks and troughs in the concentration of effluent constituents as
water passes downstream).
The distances over which effluents mix in these three dimensions should be considered in the selection
of sampling sites and points, and are affected by, amongst other factors, the water velocity. Tracer
techniques using dyes can be useful in studying mixing processes and conductivity measurements can
also be helpful.
NOTE The use of tracer techniques might be subject to licensing by the authority responsible for the
watercourse, as there might be concerns over the release of chemicals into the environment. Where this is the
case, it might be better to use determinants already present, such as pH, temperature, or conductivity, to study
mixing processes.
Where mixing is relevant to the sampling regime, the sampling location and other associated parameters
should preferably be defined clearly before the beginning of sampling.
The sampler should acknowledge that in watercourses near the coast there might be a tidal influence
on the flow, quality, and mixing capability of the water body. Account of this should be taken where
appropriate, and the sampler should take measurements of the flow and water depth to give an indication
of the tidal status. Sampling at different states of the tide is usually necessary.
Vertical mixing, almost always, is the first of the three types to be complete in a stream. Shallow water
and high velocities result in rapid vertical mixing, but even in deep water with low velocities, vertical
mixing is relatively rapid. Effluents discharged to most streams mix vertically, within 100 metres or
within a few hundred metres at most. Normally therefore a stream need not be sampled at more than
one depth, although stratification can be induced in slow-moving rivers and streams by thermal and
other density effects. In these cases, sampling at several depths might be necessary and preliminary
tests should be carried out to assess the degree of stratification (see 5.2).
Lateral mixing usually occurs after vertical mixing has occurred, but before longitudinal mixing is
complete. Differences in solids content and especially in temperature of effluents and stream water
can cause the effluents to stratify and travel across the stream more rapidly on surface or bottom than
ISO 5667-6:2014(E)
they would if mixed vertically at the point of discharge. This phenomenon is most significant at very low
velocities since even moderate turbulence quickly destroys stratification, causes vertical mixing and
slows the lateral movement of the wastes.
Change in direction of stream flow is also effective in lateral mixing. This, combined with normal
vertical mixing, can cause rapid and fairly complete lateral mixing. However, even when a stream passes
through two approximately 90° reverse bends that are reasonably close together it cannot be assumed
that lateral mixing of upstream effluents is complete. For example, coloured effluents and turbidity from
small tributaries have been observed to hug one bank of a stream for many kilometres in wide, shallow,
swift streams, with rocky bottoms, in spite of several reverse bends in these distances.
Whereas turbulence can cause vertical mixing within a few hundred metres, the distance for lateral
mixing generally is dependent on the occurrence of relatively sharp reverse bends. As a general rule, the
distance for adequate lateral mixing is in kilometres rather than hundred metres. Frequently a stream
needs to be sampled at two or more points at one or more locations downstream from an effluent
discharge or a tributary stream because of slow lateral mixing.
Consideration of longitudinal mixing distances can be important in deciding on the frequency of
sampling. To give representative results just below an irregular discharge, more frequent sampling
is required than would be necessary some distance downstream where longitudinal mixing has been
completed to a greater extent. See Informative Annex A for more information on longitudinal mixing.
5.1.3 Consideration of time-of-travel data
Time of travel is the time taken for a given mass of water to move between two defined points. This can
be from a point of discharge to the next point of discharge or from a point of discharge to an abstraction
point, etc. Information on the time of travel or river retention of substances in this mass of water is
important for the following main reasons.
a) It provides information on the lateral mixing characteristics of a given stretch of river which assists
in defining the most representative point on that river system from which to take a sample.
b) It provides information on the longitudinal velocity profiles in the river, which can be used to
calculate re-aeration rates to predict the assimilative capacity of a reach for biodegradable organic
matter. The self-purification, or river recovery rate, can be presented as a mathematical model. Such
models are very important as they assist in the prediction of oxygen sag curves, and the re-use
capability of a river. Time-of-travel measurements can also be used to study the rates of change of
other unstable constituents in rivers, e.g. the oxidation of ammonia, the decomposition of phenol
and the decay of radionuclides.
c) It provides information on mean flow velocities under a set of given discharge conditions which
is extremely valuable in assessing the distance travelled from pollution source. This information
can enable remedial action to be taken before the pollution arrives at a water abstraction point, or
allow the water treatment processes to be varied to compensate for the effects of the pollution or to
predict the time interval necessary for the abstraction to be stopped.
d) Time-of-travel data can often be of relevance to the choice of sampling location. For example,
sampling sites might have to be arranged to allow certain constituents or pollutants to be traced
through a system, particularly from a discrete source of pollution. This necessitates knowledge of
the residence time within the system under investigation (i.e. the time of travel). Knowledge of the
time of travel is also important in sampling studies to investigate the rate of change of unstable
constituents (e.g. in the self-purification of a water body, the time of travel can provide information
on kinetic rate coefficients). It therefore provides information on the selection of sampling locations
and for deciding the length of a river reach to be studied. It can be used to estimate the subsequent
downstream position of a mass of water in which some abnormal result was obtained at one or
more sampling locations. This allows additional sampling to be carried out to confirm or revise any
idea or conclusion based on the abnormal result.
6 © ISO 2014 – All rights reserved

ISO 5667-6:2014(E)
In determining the time of travel, one of the three principal methods should be used, namely the use of
[5] [3]
surface floats (see ISO 748 ), the use of tracers (see ISO 9555 ), or the measurement of flow rate with
[5] [6]
knowledge of cross-sectional areas (see ISO 748 and ISO 1070 ).
Measurements should be made at a minimum of five different flow rates and the resulting times of travel
plotted against the corresponding flow rates, thereby enabling other travel times to be obtained by
extrapolation or interpolation. However, extrapolation outside 10 % of a measured flow rate value can
provide inaccurate information on time of travel.
Also note that time of travel can vary greatly between seasons in regions that experience seasonal
rainfall only.
[7]
ISO 5667-1 should be consulted for general guidance on time-of-travel and ISO/TR 8363 should be
consulted for guidance on the measurement of liquid flow in open channels.
5.1.4 Non-homogeneous sites
Problems arise in selecting suitable sampling sites whenever the determinands are not homogeneously
distributed throughout the water body of interest. In general, such sampling sites should be avoided if
possible, except when the sites themselves are of direct interest, as they might not yield representative
samples of the major part of the water body. If there is any possibility of a non-homogeneous distribution
of the determinands of interest at the chosen site, experimental tests on the nature and magnitude of
any heterogeneity in all three dimensions should be made. If such tests show that the determinands are
distributed homogeneously, any sampling point suffices. Otherwise another site should be sought where
the determinands are homogeneously distributed.
If it is impossible to find such a sampling site, samples should be taken from suffic
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