ASTM D6051-96(2001)
(Guide)Standard Guide for Composite Sampling and Field Subsampling for Environmental Waste Management Activities
Standard Guide for Composite Sampling and Field Subsampling for Environmental Waste Management Activities
SCOPE
1.1 Compositing and subsampling are key links in the chain of sampling and analytical events that must be performed in compliance with project objectives and instructions to ensure that the resulting data are representative. This guide discusses the advantages and appropriate use of composite sampling, field procedures and techniques to mix the composite sample and procedures to collect an unbiased and precise subsample(s) from a larger sample. It discusses the advantages and limitations of using composite samples in designing sampling plans for characterization of wastes (mainly solid) and potentially contaminated media. This guide assumes that an appropriate sampling device is selected to collect an unbiased sample.
1.2 The guide does not address: where samples should be collected (depends on the objectives) (see Guide D6044), selection of sampling equipment, bias introduced by selection of inappropriate sampling equipment, sample collection procedures or collection of a representative specimen from a sample, or statistical interpretation of resultant data and devices designed to dynamically sample process waste streams. It also does not provide sufficient information to statistically design an optimized sampling plan, or determine the number of samples to collect or calculate the optimum number of samples to composite to achieve specified data quality objectives (see Practice D5792). Standard procedures for planning waste sampling activities are addressed in Guide D4687.
1.3 The sample mixing and subsampling procedures described in this guide are considered inappropriate for samples to be analyzed for volatile organic compounds. Volatile organics are typically lost through volatilization during sample collection, handling, shipping and laboratory sample preparation unless specialized procedures are used. The enhanced mixing described in this guide is expected to cause significant losses of volatile constituents. Specialized procedures should be used for compositing samples for determination of volatiles such as combining directly into methanol (see Practice D4547).
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:D6051–96 (Reapproved 2001)
Standard Guide for
Composite Sampling and Field Subsampling for
Environmental Waste Management Activities
This standard is issued under the fixed designation D 6051; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 Compositing and subsampling are key links in the chain
responsibility of the user of this standard to establish appro-
of sampling and analytical events that must be performed in
priate safety and health practices and determine the applica-
compliance with project objectives and instructions to ensure
bility of regulatory limitations prior to use.
that the resulting data are representative. This guide discusses
the advantages and appropriate use of composite sampling,
2. Referenced Documents
field procedures and techniques to mix the composite sample
2.1 ASTM Standards:
andprocedurestocollectanunbiasedandprecisesubsample(s)
C 702 Practice for Reducing Samples of Aggregate to
from a larger sample. It discusses the advantages and limita-
Testing Size
tions of using composite samples in designing sampling plans
D 1129 Terminology Relating to Water
for characterization of wastes (mainly solid) and potentially
D 4439 Terminology for Geosynthetics
contaminated media. This guide assumes that an appropriate
D 4547 Practice for Sampling Waste and Soils for Volatile
sampling device is selected to collect an unbiased sample.
Organics
1.2 The guide does not address: where samples should be
D 4687 Guide for General Planning of Waste Sampling
collected (depends on the objectives) (see Guide D 6044),
D 5088 Practice for Decontamination of Field Equipment
selection of sampling equipment, bias introduced by selection
Used at Nonradioactive Waste Sites
of inappropriate sampling equipment, sample collection proce-
D 5792 Practice for Generation of Environmental Data
duresorcollectionofarepresentativespecimenfromasample,
Related to Waste ManagementActivities: Development of
or statistical interpretation of resultant data and devices de-
Data Quality Objectives
signed to dynamically sample process waste streams. It also
D 6044 Guide for Representative Sampling for Manage-
doesnotprovidesufficientinformationtostatisticallydesignan
ment of Wastes and Contaminated Media
optimized sampling plan, or determine the number of samples
E 856 Definitions of Terms and Abbreviations Relating to
to collect or calculate the optimum number of samples to
Physical and Chemical Characteristics of Refuse-Derived
composite to achieve specified data quality objectives (see
Fuel
Practice D 5792). Standard procedures for planning waste
sampling activities are addressed in Guide D 4687.
3. Terminology
1.3 The sample mixing and subsampling procedures de-
3.1 Definitions:
scribed in this guide are considered inappropriate for samples
3.1.1 composite sample, n—a combination of two or more
to be analyzed for volatile organic compounds. Volatile organ-
samples. D 1129
ics are typically lost through volatilization during sample
3.1.2 sample, n—a portion of material taken from a larger
collection, handling, shipping and laboratory sample prepara-
quantity for the purpose of estimating properties or composi-
tion unless specialized procedures are used. The enhanced
tion of the larger quantity. E 856
mixing described in this guide is expected to cause significant
3.1.3 specimen, n—a specific portion of a material or
losses of volatile constituents. Specialized procedures should
laboratory sample upon which a test is performed or which is
be used for compositing samples for determination of volatiles
taken for that purpose. D 4439
such as combining directly into methanol (see Practice
D 4547).
1 2
This guide is under the jurisdiction of ASTM Committee D34 on Waste For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Management and is the direct responsibility of Subcommittee D34.01.01 on contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Planning for Sampling. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Dec. 10, 1996. Published February 1997. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D6051–96 (2001)
3.1.4 subsample, n—a portion of a sample taken for the followingparagraphs.However,aprincipleassumptionneeded
purpose of estimating properties or composition of the whole to justify compositing is that analytical costs are high relative
sample. to sampling costs. In general, appropriate use of sample
3.1.4.1 Discussion—a subsample, by definition, is also a compositing can:
sample.
6.2.1 Reduce inter-sample variance, that is, improve the
precisionofthemeanestimationwhilereducingtheprobability
4. Summary of Guide
of making an incorrect decision,
4.1 This guide describes how the collection of composite
6.2.2 Reduce costs for estimating a total or mean value,
samples, as opposed to individual samples, may be used to:
especiallywhereanalyticalcostsgreatlyexceedsamplingcosts
more precisely estimate the mean concentration of a waste
(also may be effective when analytical capacity is a limitation),
analyte in contaminated media, reduce costs, efficiently deter-
6.2.3 Efficiently determine the absence or possible presence
mine the absence or possible presence of a hot spot (a highly
of hot spots or hot containers and, when combined with
contaminated local area), and, when coupled with retesting
retesting schemes, identify hot spots, as long as the probability
schemes, efficiently locate hot spots. Specific procedures for
of hitting a hot spot is low,
mixing a sample(s) and collecting subsamples for transport to
6.2.4 Be especially useful for situations, where the nature of
a laboratory are provided.
contaminant distribution tends to be contiguous and non-
random and the majority of analyses are “non-detects” for the
5. Significance and Use
contaminant(s) of interest, and
5.1 This guide provides guidance to persons managing or
6.2.5 Provide a degree of anonymity where population,
responsible for designing sampling and analytical plans for
rather than individual statistics are needed.
determining whether sample compositing may assist in more
6.3 Improvement in Sampling Precision—Samples are al-
efficiently meeting study objectives. Samples must be compos-
ways taken to make inferences to a larger volume of material,
ited properly, or useful information on contamination distribu-
and a set of composite samples from a heterogeneous popula-
tion and sample variance may be lost.
tion provides a more precise estimate of the mean than a
5.2 The procedures described for mixing samples and ob-
comparable number of discrete samples. This occurs because
taining a representative subsample are broadly applicable to
compositing is a “physical process of averaging.” Averages of
waste sampling where it is desired to transport a reduced
samples have greater precision than the individual samples.
amount of material to the laboratory. The mixing and subsam-
Likewise, a set of composite samples is always more precise
pling sections provide guidance to persons preparing sampling
than an equal number of individual samples. Decisions based
and analytical plans and field personnel.
on a set of composite samples will, for practical purposes,
5.3 While this guide generally focuses on solid materials,
always provide greater statistical confidence than for a com-
the attributes and limitations of composite sampling apply
parable set of individual samples.
equally to static liquid samples.
6.3.1 If an estimated precision of a mean is desired, then
more than one composite sample is needed; a standard devia-
6. Attributes of Composite Sampling for Waste
tion cannot be calculated from one composite sample. How-
Characterization
ever, the precision of a single composite sample may be
6.1 In general, the individual samples to be composited
estimatedwhentherearedatatoshowtherelationshipbetween
should be of the same mass, however, proportional sampling
the precision of the individual samples that comprise the
may be appropriate in some cases depending upon the objec-
composite sample and that of the composite sample. The
tive. For example, if the objective is to determine the average
precision (standard deviation) of the composite sample is
drum concentration of a contaminant, compositing equals
approximately the precision of the individual samples divided
volumes of waste from each drum would be appropriate. If the
by the square root of the number of individual samples in the
objective is to determine average contaminant concentration of
composite.
the waste contained in a group of drums, the volume of each
6.4 Example 1—An example of how a single composite
sample to be composited should be proportional to the amount
sample can be used for decision-making purposes is given
of waste in each drum. Another example of proportional
here. Assume a regulatory limit of 1 mg/kg and a standard
sampling is estimating the contaminant concentration of soil
deviation of 0.5 mg/kg for the individual samples. If the
overlying an impermeable zone. Soil cores should be collected
concentration of a site is estimated to be around 0.6 mg/kg,
from the surface to the impermeable layer, regardless of core
how many individual samples should be composited to have
length.
relatively high confidence that the true concentration does not
6.2 The principal advantages of sample compositing in-
exceed the regulatory limit when only one composite sample is
clude: reduction in the variance of an estimated average
used? Assuming the composite is well mixed, then the preci-
concentration (1), increasing the efficiency of locating/
sion of a composite is a function of the number of samples as
identifying hot spots (2), and reduction of sampling and
follows:
analyticalcosts(3).Thesemainadvantagesarediscussedinthe
Number of Individual Precision (standard deviation 4 n )
=
Samples in Composite of One Composite Sample
2 0.35
3 0.29
The boldface numbers in parentheses refer to a list of references at the end of
4 0.25
this guide.
D6051–96 (2001)
5 0.22
6 0.20
Thus, if six samples are included in a composite, the
composite concentration of 0.6 mg/kg is two standard devia-
tions below the regulatory limit. Therefore, if the composite
concentration is actually observed to be in the neighborhood of
0.6 mg/kg, we can be reasonably confident (approximately
95 %) that the concentration of the site is below the regulatory
FIG. 2 Example of Within Cell Compositing
limit, using only one composite sample.
6.5 Example 2—Another example is when the standard
deviation of the individual samples in the previous example is
of the cell is needed, multiple composite samples should be
relatively small, say 0.1 mg/kg. Then the standard deviation of
collected from that cell.
a composite of 6 individual samples is 0.04 mg/kg (0.1 mg/kg
6.6 Effect on Cost Reduction—Because the composite
divided by the square root of 6 = 0.04 mg/kg), a very small
samples yield a more precise mean estimate than the same
number relative to the regulatory limit of 1 mg/kg. In this case,
number of individual samples, there is the potential for
simple comparison of the composite concentration to the
substantial cost saving. Given the higher precision associated
regulatory limit is often quite adequate for decision-making
with composite samples, the number of composite samples
purposes.
required to achieve a specified precision is smaller than that
6.5.1 The effectiveness of compositing depends on the
requiredforindividualsamples.Thiscostsavingopportunityis
relative magnitude of sampling and analytical error. When
especiallypronouncedwhenthecostofsampleanalysisishigh
sampling uncertainty is high relative to analytical error (as is
relative to the cost of sampling, compositing, and analyzing.
usuallyassumedtobethecase)compositingisveryeffectivein
6.7 Hot Container/Hot Spot Identification and Retesting
improving precision. If analytical errors are high relative to
Schemes—Samples can be combined to determine whether an
field errors, sample compositing is much less effective.
individual sample exceeds a specified limit as long as the
6.5.2 Because compositing is a physical averaging process,
action limit is relatively high compared with the actual
composite samples tend to be more normally distributed than
detection limit and the average sample concentration. Depend-
the individual samples. The normalizing effect is frequently an
ing on the difficulty and probability of having to resample, it
advantage since calculation of means, standard deviations and
may be desirable to retain a split of the discrete samples for
confidence intervals generally assume the data are normally
possible analysis depending on the analytical results from the
distributed. Although environmental residue data are com-
composite sample.
monly non-normally distributed, compositing often leads to
6.8 Example 3—One hundred drums are to be examined to
approximate normality and avoids the need to transform the
determine whether the concentration of PCBs exceeds 50
data.
mg/kg.Assume the detection limit is 5 mg/kg and most drums
6.5.3 The spatial design of the compositing scheme can be
have non-detectable levels. Compositing samples from ten
important. Depending upon the locations from which the
drums for analysis would permit determining that none of the
individual samples are collected and composited, composites
drums in the composite exceed 50 mg/kg as long as the
can be used to determine spatial variability or improve the
concentration of the composite is <5 mg/kg. If the detected
precision of the parameter being estimated. Fig. 1 and Fig. 2
concentration is >5 mg/kg, one or more drums may exceed 50
represent a site divided into four cells. Composite all samples
mg/kg and additional analyses of the individual drums are
with the same number together. The sampling approach in Fig.
required to identify any hot drum(s). The maximum number of
1 is similar to sample random sampling, except they are now
samples that can theoretically be composited and still detect a
composite samples. Each composite sample in this case is a
hot sample is the limit of concern divided by the actual
representative sample of the entire site, eliminates cell-to-cell
detection lim
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