ISO 5667-17:2000

INTERNATIONAL ISO
STANDARD 5667-17
First edition
2000-07-01
Water quality — Sampling —
Part 17:
Guidance on sampling of suspended
sediments
Qualité de l'eau — Échantillonnage —
Partie 17: Lignes directrices pour l'échantillonnage des sédiments en
suspension
Reference number
ISO 5667-17:2000(E)
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ISO 5667-17:2000(E)
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ISO 5667-17:2000(E)
Contents Page
1 Scope . 1
2 Terms and definitions . 1
3 Sampling equipment . 1
4 Sampling procedure . 4
5 Interpretation of data . 6
6 Safety precautions . 7
Annex
A Information on suspended solids and their sampling. 9
A.1 Relationship of certain analytes to suspended solids . 9
A.2 Relationship of suspended solids concentration to analyte concentration . 9
A.3 Problems inherent in conventional analyses of suspended solids analyte concentration . 9
A.4 Centrifuge types . 10
Bibliography. 11
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ISO 5667-17:2000(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 com-
mittees. 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 liai-
son 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 3.
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 part of ISO 5667 may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 5667-17 was prepared by Technical Committee ISO/TC 147, Water quality,Subcommit-
tee SC 6, Sampling (general methods).
ISO 5667 consists of the following parts, under the general title Water quality — Sampling:
— Part 1: Guidance on the design of sampling programmes
— Part 2: Guidance on sampling techniques
— Part 3: Guidance on the preservation and handling of samples
— Part 4: Guidance on sampling from lakes, natural and man-made
— Part 5: Guidance on sampling of drinking water and water used for food and beverage processing
— 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 from sewage and water-treatment works
— Part 14: Guidance on quality assurance of environmental water sampling and handling
— Part 15: Guidance on preservation and handling of sludge and sediment samples
— Part 16: Guidance on biotesting of samples
— Part 17: Guidance on sampling of suspended sediments
— Part 18: Guidance on sampling of groundwater at contaminated sites
Annex A of this part of ISO 5667 is for information only.
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ISO 5667-17:2000(E)
Introduction
This part of ISO 5667 reflects the important role of suspended solids in flowing water, especially of the silt + clay
(< 63m) component and associated carbon, as a transport medium for nutrients (especially phosphorus), trace
metals, and certain classes of organic compounds (see A.1).
Although analysis of suspended solids has been carried out for many years, there are no standard methods for field
sampling of suspended solids for water quality purposes. While standard methods exist for sampling of suspended
mineral sediment for sedimentological purposes these are often not appropriate for the chemical analysis of sus-
pended solids. Because of the lack of standards for sampling of suspended solids for water quality purposes and the
improbability of achieving complete standardization because of differences in the objectives of water quality pro-
grammes and the lack of standard apparatus, this part of ISO 5667 provides guidance to the various sampling pro-
cedures, their biases, and alternatives. This part of ISO 5667 excludes sampling protocols that apply to conventional
water sampling. Field and laboratory filtration procedures that are conventionally used to measure the quantity of
suspended solids are also excluded. Any reference to these methods is solely for the purpose of demonstrating their
profound limitations for sediment quality purposes.
The objectives of a water quality programme will dictate the size of sample required and, therefore, the type of appa-
ratus to be used. Generally, however, the analysis of physical, chemical, biological and toxicological properties may
require gram-size samples. Examples of programme objectives that require bulk collection of suspended solids in-
clude:
a) ambient monitoring for water quality assessment, control or regulation;
b) in-river monitoring of effluents for regulatory or control purposes, especially for chemical and toxicological prop-
erties;
c) research into water quality, including physico-chemical processes that affect the pathways, fate and effects of
suspended solids and their associated nutrient and contaminant chemistry;
d) recovery of suspended solids for purposes of physical analysis, including particle size, organic content including
particulate organic carbon, sediment geochemistry, inorganic and organic chemistry of suspended solids, and
toxicity of suspended solids.
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INTERNATIONAL STANDARD ISO 5667-17:2000(E)
Water quality — Sampling —
Part 17:
Guidance on sampling of suspended sediments
1 Scope
This part of ISO 5667 is applicable to the sampling of suspended solids for the purpose of monitoring and investigat-
ing freshwater quality, and more particularly to flowing freshwater systems such as rivers and streams. Certain ele-
ments of this part of ISO 5667 may be applied to freshwater lakes, reservoirs and impoundments, however field
sampling programmes may differ and are not necessarily covered here.
2 Terms and definitions
For the purposes of this part of ISO 5667, the following terms and definitions apply.
2.1
suspended solids
solids removed by filtration or centrifuging under specified conditions
[ISO 6107-2]
2.2
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
[ISO 6107-2]
3 Sampling equipment
3.1 General
There are a number of different sampling techniques with differing apparatus for the bulk collection of suspended sol-
ids. Many of these samplers are specific to site conditions and may require deployment from boats, bridges or by
wading.
3.2 Passive samplers
This class of samplers includes the conventional suspended solids samplers such as depth integrating and point
samplers. Passive samplers are placed in the water column where they fill under ambient conditions using isokinetic
sampling methods. These samplers are generally used in conjunction with standard sampling protocols for the col-
lection of the most representative mineral solids sample in a given riverine cross-section, such as the equal dis-
charge increment and equal width increment methods [9], [10], [11].
The majority of standard samplers described by the National Handbook of Recommended Methods for Water-Data
Acquisition [11] were developed for quantity and not quality determinations of suspended solids. Their use is not rec-
ommended for solids quality sampling, due to small sample volumes, contamination of the sample by the materials
used in the construction of these samplers, and other technical and methodological factors [16].
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3.3 Bag sampler
The large-bag passive sampler (6,5 l) described in [12] was developed specifically for suspended solids quality due
to its large capacity and construction from chemically inert materials. Multiple bag samples were generally compos-
ited to produce a sample of sufficient volume to obtain enough suspended solids for subsequent chemical analysis.
The bag sampler is also used in conjunction with bulk samplers described in 3.4.
3.4 Bulk samplers
3.4.1 General
Bulk samplers are used for dewatering large (bulk) quantities of suspended solids. Field bulk samplers include tan-
gential-flow filtration and centrifugation. These both require a large volume of solids-water mixture to be taken, or
pumped, from the water column to the bulk sampler. This part of ISO 5667 refers only to those methods that can be
deployed in the field. Therefore, bench centrifuges and other laboratory methods of dewatering such as sedimenta-
tion, are not dealt with here.
3.4.2 Pumping requirements
3.4.2.1 General
Most bulk samplers require that the sediment-water mixture be pumped from the water column into the bulk sampler
or into a storage container. There are numerous types of pump ranging from submersible to peristaltic pumps, which
have been used for water quality sampling. The composition [plastics, metal, polytetrafluoroethylene (PTFE), etc.] of
pump parts that are in contact with the water, and the composition of the hosing that carries the water to the sampling
apparatus can be important, depending on the type of chemical analyses required in the sampling programme. Sub-
mersible pumps should be magnetically driven so that there is no chance of leakage of lubricating and cooling oil
from the submersible electric motor into the impeller housing.
Pumped samples are appropriate for all aquatic environments, providing that isokinetic sampling (2.2) is not a re-
quirement of the sampling protocol. Very few pumps can sample isokinetically. However, in practice, this is not gen-
erally a problem, especially as:
a) in many rivers the majority of suspended solids are silt + clay particles; and
b) the particle-size range of interest in the chemistry of suspended solids is usually the< 63m fraction [24].
Pumps are difficult to use for depth-integrated sampling. Therefore, if a river transports a significant proportion of
sand particles, then pump samplers are likely to under-sample this population (sand is generally transported near the
bed). For environmental chemistry this may not be critical, because chemical enrichment of solids is mainly in the silt-
clay (< 63m) fraction.
3.4.2.2 Operational considerations for pumping to bulk samplers
There are a number of practical advantages to using pumps.
a) Pumps are the only practical means of moving large volumes of water to the bulk sampler, and can be easily de-
ployed in any aquatic environment.
b) Because of the length of time involved, they average out any short-term temporal variations in solids chemistry
that are commonly observed in the water column.
c) Pumps are relatively inexpensive and are easily dismantled for cleaning.
d) Fine sediment in water is usually transported as flocculated solids [13], however pumps break up these flocs.
While not important for solids chemistry, this is important if the sampling programme is interested in measuring
the natural particle sizes that exist in the water column.
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e) Particle sizes sampled may be biased due to the non-isokinetic nature of most pump samplers.
f) The chemical composition of the hose material (e.g. rubber) and pump construction can affect the sediment
chemistry. Hosing can be obtained in stainless steel, PTFE and other non-contaminating materials.
3.4.3 Clarifiers/centrifuges
3.4.3.1 General
Centrifugal samplers can be referred to both as clarifiers and as centrifuges These types of centrifuge operate in
continuous-flow mode whereby the water medium is pumped continuously through the centrifugal force field where
the solids are separated from the aqueous medium. While there are a number of different types of continuous-flow
centrifuge (see clause A.4), they all function under the same principles. All require:
a) power (electrical or gas motor) in order to rotate the centrifuge bowl at a high speed;
b) a pump to deliver the sediment/water mixture to the centrifuge bowl;
c) a centrifuge bowl which retains the dewatered sediment.
All centrifuge components that come in contact with the water/solids should be of stainless steel construction or
PTFE-coated to avoid sample contamination. This is especially critical if the water discharge from the clarifier (efflu-
ent) is to be used for water quality analysis. In centrifuges, the raw water is pumped into the centre of the bowl from
the top or bottom. The denser sediment (relative to water) is pushed out to the side of the bowl by centrifugal force
and the clear water (effluent) passes out of the bowl. These systems are effective in dewatering suspended solids
provided that the organic matter concentration is not excessive [14]. The smallest size of sediment retained by the
centrifuges is dependent on bowl geometry, bowl rotation speed, and the physical characteristics of the suspended
particles (size distribution, composition and density) [15].
The recovery efficiency also depends on the above three characteristics as well as on the suspended solids concen-
tration and the amount of organic matter in the sample. Retention of more than 90 % of the suspended solids in the
solids-water mixture is described by [14]. Also, the percentage of retained solids that was less than 0,45m in diam-
eter was often more than 50 % of the solids sample.
3.4.3.2 Operational considerations for continuous-flow centrifuges
a) Bulk samples provide sufficient quantities for sediment quality analysis. The alternative, the analysis of trace ele-
ments and organic micropollutants on filtering media involves use of microsamples which are very easily contam-
inated in the field and laboratory. Although the ability to carry out quantitative analysis of organic micropollutants
on microsamples has made great progress, the amount of sample required for certain types of analysis is gener-
ally larger than can be obtained by filtration.
b) Bulk samples are less prone to field and handling contamination than are microsamples, except where micro-
samples are collected in prepackaged and sterile cartridges or capsules.
c) The ability to carry out replicate analyses or several different types of analyses on the same sample are limited
or impossible with conventional methods (e.g. particulate-P, particle size and organic carbon, or an organic
micropollutant analyte and toxicity). Multiple analysis is possible only when there is a bulk sample from which to
draw subsamples for the different analyses. [Reference to ISO/TC 190 International Standards on physical
methods may give some useful guidance.]
d) Sampling for bulk collection typically takes from 30 min to several hours, depending on the concentration of sus-
pended solids in the sampled medium. This can smooth out temporal variations in suspended solids concentra-
tions and their associated chemistry.
e) The collection efficiency of continuous-flow centrifuges depends on the specific gravity of the solids, internal tur-
bulence of the apparatus, gravitational forces produced by the apparatus, etc. Small “portable” tubular clarifiers
tend to be very poor at recovering silts and clays, which are the most important constituent for water quality pur-
poses.
f) There is no source of commercially-produced field-useable continuous-flow centrifuges. However, commercial
centrifuges have been successfully adapted for field use. Continuous-flow centrifuges are heavy, are slow to de-
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ploy in the field, and some units have large power requirements. These units use high rotational speeds and can
be dangerous if used incorrectly.
3.4.4 Tangential-flow filtration
3.4.4.1 General
This type of particle/fluid separation, also known as ultra-filtration, is generally used for the separation of the< 3m
fraction including colloids. However, this size is dependent upon the nominal pore size of the filters used, flowrate and
other factors. A sample is initially collected using other samplers, such as those from the passive category or by
pumping into a storage container. The system employs a stack of membrane filters, separated by gaskets, that chan-
nel the flow across the surface of the membranes. The sediment/water mixture is pumped (generally with a peristaltic
pump) across the filters with the retained sediment (that larger than the nominal pore size of the filters) swept tangen-
tially across the filter stack and out into the original sampler container where it is recycled through the system again.
Filtrate and sediment which is small enough to pass through the pores of the filters is removed from the system. This
recycling process is generally continued until the original sample volume is reduced to less than one litre [15], [16].
3.4.4.2 Operational considerations for tangential flow filtration
The following factors should be considered.
a) The final sediment sample can contain particle sizes into the colloidal size range, depending on the filter pore
size employed. This size fraction, because of its large surface area, has the highest concentration of adsorbed
chemical substances. However, sediment separation is relatively slow (slower than continuous-flow centrifuga-
tion).
b) Filter clogging can result in a downward shift in nominal pore size, resulting in better retention of very small par-
ticles, but at reduced flowrates.
c) Frequent filter replacement is often required, depending on the manufacturer and nature of use, and may involve
significant cost and generally has a greater clean-up time required than for other methods.
d) This technique has not been widely used in routine field situations. Thus, there is relatively little known of the op-
erational problems associated with tangential flow apparatus from different manufacturers.
e) This system is much smaller than continuous-flow systems and is less expensive to purchase, but may be more
expensive to operate because of cost of replacement filters [16].
4 Sampling procedure
4.1 General
No definitive guidance can be given on the methods to be used for sampling of suspended solids for chemical deter-
minations because of the lack of standard protocols in this field. It is therefore important to maintain consistency of
technique in order to retain the value of long-term monitoring. Unlike the non-cohesive sediment load (sand-sized
material), there is no unifying theory on cohesive solids transport that can be used as the basis for developing a
standard methodology.
The following factors [17] are essential to consider in deciding on the sampling regime:
a) horizontal variations in suspended solids and associated contaminants;
b) vertical variations in suspended solids and associated contaminants;
c) variations in suspended solids and associated contaminants in space and time during periods of constant dis-
charge (base flow) and during periods when discharge changes quickly (storm flow).
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d) variations in suspended solids and associated contaminants induced by differences in sampling strategy or meth-
odology; and
e) the volume of sample required to minimize the error-producing effects of inhomogeneities in the aquatic system,
and to meet analytical requirements.
All of these factors can be accommodated by using bulk-collection techniques (see 3.4) provided that the river and
solids chemical regimes are not dominated by sand-sized solids transport, for the reasons given in annex A.
4.2 Pumps
For research purposes, the deployment of sampling pumps depends upon the questions to be resolved by the data
collected by the pumping programme. However, for routine monitoring purposes the following protocol is recom-
mended, especially when there are constraints of time and budget.
— For small rivers (< 10 m in width), one pump should be located in the middle (or in zone of maximum velocity) of
the channel, at approximately 0,5 m from the surface of the water or at mid-depth whichever is less. The success
of this simplistic technique is based on the fact that, in many instances (but not always), the fine-grained< 63m
fraction (the chemically active fraction) is generally evenly distributed in the vertical section, although this may not
be true in the cross-section [18], [19]), depending on the nature of inputs of solids upstream.
— For larger rivers, several pumps should be placed at equal intervals across the river and at depths as above. The
pumped water should be integrated into a single sample (either in one container, or combined into a single hose
feeding into the bulk sampler). For very large rivers, pumps may have to be deployed sequentially in time across
the section.
— Any portable electrical generator should be placed downwind of all sampling apparatus, to avoid contamination
of equipment and sample by engine exhausts.
— It is essential that hoses be cleaned after use, to avoid sample contamination. A recommended operating proce-
dure is to pump water under field conditions through the hosing for 15 min prior to taking the sample.
— Long hose lengths should be avoided, especially under hot field conditions. Temperature rise in the hose, espe-
cially if there is a long transit time from water column to bulk sampler, can affect chemical partitioning between
sediment and water.
4.3 Centrifuges
4.3.1 General
Details on deployment, strategies for continuous-flow centrifuges and pumps can be found in [15], [16], [20] and [21].
Operation of the centrifuge should always be in accordance with manufacturer's specifications. Safety is particularly
important and is covered in clause 6. Recovering sediment from the bowl or tubular chamber is not covered in man-
ufacturer's instructions. Sediment should be removed either by PTFE or stainless steel spatulas (bowl-type centri-
fuges) or by removing a PTFE liner (tubular chambers). In all cases, great care is essential not to contaminate the
sample.
4.3.2 Quality assurance specific to centrifuges
This guidance is independent of the quality assurance required for laboratory analysis of samples. No standardized
quality assurance programme exists for centrifuges. Evaluations of internal contamination of the sample from contact
with metal or non-metallic parts, oils and greases, etc. have been carried out [16], [20]. Quality assurance pro-
grammes that have been used by various practitioners include pumping suspensions of laboratory clays, for which
the chemical composition is known, into the centrifuge (this includes all hosing, pumps and any other apparatus used
as part of the field centrifuge set-up), followed by analysis of the collected sediment for comparison with the original
sediment. This is not, however, a procedure that can be easily carried out and is usually reserved for ensuring, on an
occasional basis, that there is no sample contamination caused by the apparatus itself.
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Field cleaning of apparatus is essential to ensure that there is no carry-over of oils and greases or other materials
that may have been sampled at other sites. Rigorous cleaning of the centrifuge bowl with acetone should be carried
out at each site. Approximately 15 min of pumping a field sample through connecting hoses (but not through the cen-
trifuge) prior to discharge into the cleaned centrifuge prevents cross-contamination from hosing used at previous
sites. However, consideration should be given to using separate pump and hose apparatus when the field pro-
gramme includes both very contaminated and very clean conditions. If one set of apparatus has to be used, then the
cleanest site should be sampled first, followed by successively more contaminated sites.
All apparatus should be cleaned when returned to the laboratory by pumping suitable cleaning solutions through all
apparatus. Solvent cleaning of the centrifuge bowl is also essential.
4.4 Tangential-flow filtration units
Deployment strategies for tangential flow filtration can be found in [15] and [16]. Operation of the unit should be ac-
cording to manufacturer's specifications. There is no published literature on quality assurance of tangential-flow
units. However, re-use of filters and attached tubing requires cleaning, probably with reagent or pesticide-grade sol-
vents. Handling and disposal of such solvents requires great care and should be in accordance with national regula-
tions.
4.5 Quality assurance of field samples
Samples taken with bulk sampling apparatus should conform to the following guidance:
— Precision: One field sample should be split and analysed in duplicate for every sampling day. These samples
should not be analysed consecutively in the laboratory in order to limit any bias that may be introduced by their
position in the analytical run. Precision is based on the relative percent differences in analytical values between
the samples with an acceptable limit of no more than 10 %.
— Accuracy: Accuracy is derived by the analysis of a standard reference material (SRM) in the laboratory and
cannot be determined as part of the field programme.
— Field method blanks: Field blanks, commonly used in conventional water quality sampling, are not feasible. It
is neither practical nor realistic to carry enough “blank” water to run through a centrifuge to check for field con-
tamination or potential contamination of metals from stainless steel (or other metallic) apparatus; hence good
field practice that emphasizes cleanliness of apparatus, connecting hosing, etc. is essential.
5 Interpretation of data
5.1 General
The chemical nature of suspended solids is generally used for two purposes — one is to determine presence and
amount of the chemical parameters at the time of sampling; the second is to calculate chemical loadings that are be-
ing transported over some designated period of time.
Interpretation of suspended solids data is never exact because of the impossibility of knowing the actual distribution
of total sus
...