ASTM D6051-96
(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: D 6051 – 96
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 responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
1.1 Compositing and subsampling are key links in the chain
bility of regulatory limitations prior to use.
of sampling and analytical events that must be performed in
compliance with project objectives and instructions to ensure
2. Referenced Documents
that the resulting data are representative. This guide discusses
2.1 ASTM Standards:
the advantages and appropriate use of composite sampling,
C 702 Practice for Reducing Samples of Aggregate to
field procedures and techniques to mix the composite sample
Testing Size
and procedures to collect an unbiased and precise subsample(s)
D 1129 Terminology Relating to Water
from a larger sample. It discusses the advantages and limita-
D 4439 Terminology for Geosynthetics
tions of using composite samples in designing sampling plans
D 4547 Practice for Sampling Waste and Soils for Volatile
for characterization of wastes (mainly solid) and potentially
Organics
contaminated media. This guide assumes that an appropriate
D 4687 Guide for General Planning of Waste Sampling
sampling device is selected to collect an unbiased sample.
D 5088 Practice for Decontamination of Field Equipment
1.2 The guide does not address: where samples should be
Used at Nonradioactive Waste Sites
collected (depends on the objectives) (see Guide D 6044),
D 5792 Practice for Generation of Environmental Data
selection of sampling equipment, bias introduced by selection
Related to Waste Management Activities: Development of
of inappropriate sampling equipment, sample collection proce-
Data Quality Objectives
dures or collection of a representative specimen from a sample,
D 6044 Guide for Representative Sampling for Manage-
or statistical interpretation of resultant data and devices de-
ment of Wastes and Contaminated Media
signed to dynamically sample process waste streams. It also
E 856 Definitions of Terms and Abbreviations Relating to
does not provide sufficient information to statistically design an
Physical and Chemical Characteristics of Refuse-Derived
optimized sampling plan, or determine the number of samples
Fuel
to collect or calculate the optimum number of samples to
composite to achieve specified data quality objectives (see
3. Terminology
Practice D 5792). Standard procedures for planning waste
3.1 Definitions:
sampling activities are addressed in Guide D 4687.
3.1.1 composite sample, n—a combination of two or more
1.3 The sample mixing and subsampling procedures de-
samples. D 1129
scribed in this guide are considered inappropriate for samples
3.1.2 sample, n—a portion of material taken from a larger
to be analyzed for volatile organic compounds. Volatile organ-
quantity for the purpose of estimating properties or composi-
ics are typically lost through volatilization during sample
tion of the larger quantity. E 856
collection, handling, shipping and laboratory sample prepara-
3.1.3 specimen, n—a specific portion of a material or
tion unless specialized procedures are used. The enhanced
laboratory sample upon which a test is performed or which is
mixing described in this guide is expected to cause significant
taken for that purpose. D 4439
losses of volatile constituents. Specialized procedures should
3.1.4 subsample, n—a portion of a sample taken for the
be used for compositing samples for determination of volatiles
purpose of estimating properties or composition of the whole
such as combining directly into methanol (see Practice
sample.
D 4547).
3.1.4.1 Discussion—a subsample, by definition, is also a
1.4 This standard does not purport to address all of the
sample.
safety concerns, if any, associated with its use. It is the
1 2
This guide is under the jurisdiction of ASTM Committee D34 on Waste Annual Book of ASTM Standards, Vol 04.02.
Managementand is the direct responsibility of Subcommittee D34.01.01 on Plan- Annual Book of ASTM Standards, Vol 11.01.
ning for Sampling. Annual Book of ASTM Standards, Vol 04.09.
Current edition approved Dec. 10, 1996. Published February 1997. Annual Book of ASTM Standards, Vol 11.04.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
D 6051
4. Summary of Guide 6.2.2 Reduce costs for estimating a total or mean value,
especially where analytical costs greatly exceed sampling costs
4.1 This guide describes how the collection of composite
(also may be effective when analytical capacity is a limitation),
samples, as opposed to individual samples, may be used to:
6.2.3 Efficiently determine the absence or possible presence
more precisely estimate the mean concentration of a waste
of hot spots or hot containers and, when combined with
analyte in contaminated media, reduce costs, efficiently deter-
retesting schemes, identify hot spots, as long as the probability
mine the absence or possible presence of a hot spot (a highly
of hitting a hot spot is low,
contaminated local area), and, when coupled with retesting
schemes, efficiently locate hot spots. Specific procedures for 6.2.4 Be especially useful for situations, where the nature of
mixing a sample(s) and collecting subsamples for transport to contaminant distribution tends to be contiguous and non-
a laboratory are provided. random and the majority of analyses are “non-detects” for the
contaminant(s) of interest, and
5. Significance and Use
6.2.5 Provide a degree of anonymity where population,
5.1 This guide provides guidance to persons managing or
rather than individual statistics are needed.
responsible for designing sampling and analytical plans for
6.3 Improvement in Sampling Precision—Samples are al-
determining whether sample compositing may assist in more
ways taken to make inferences to a larger volume of material,
efficiently meeting study objectives. Samples must be compos-
and a set of composite samples from a heterogeneous popula-
ited properly, or useful information on contamination distribu-
tion provides a more precise estimate of the mean than a
tion and sample variance may be lost.
comparable number of discrete samples. This occurs because
5.2 The procedures described for mixing samples and ob-
compositing is a “physical process of averaging.” Averages of
taining a representative subsample are broadly applicable to
samples have greater precision than the individual samples.
waste sampling where it is desired to transport a reduced
Likewise, a set of composite samples is always more precise
amount of material to the laboratory. The mixing and subsam-
than an equal number of individual samples. Decisions based
pling sections provide guidance to persons preparing sampling
on a set of composite samples will, for practical purposes,
and analytical plans and field personnel.
always provide greater statistical confidence than for a com-
5.3 While this guide generally focuses on solid materials,
parable set of individual samples.
the attributes and limitations of composite sampling apply
6.3.1 If an estimated precision of a mean is desired, then
equally to static liquid samples.
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
estimated when there are data to show the relationship between
6.1 In general, the individual samples to be composited
the precision of the individual samples that comprise the
should be of the same mass, however, proportional sampling
composite sample and that of the composite sample. The
may be appropriate in some cases depending upon the objec-
precision (standard deviation) of the composite sample is
tive. For example, if the objective is to determine the average
approximately the precision of the individual samples divided
drum concentration of a contaminant, compositing equals
by the square root of the number of individual samples in the
volumes of waste from each drum would be appropriate. If the
composite.
objective is to determine average contaminant concentration of
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:
analytical costs (3). These main advantages are discussed in the
Number of Individual Precision (standard deviation 4 n )
=
Samples in Composite of One Composite Sample
following paragraphs. However, a principle assumption needed
2 0.35
to justify compositing is that analytical costs are high relative
3 0.29
to sampling costs. In general, appropriate use of sample 4 0.25
5 0.22
compositing can:
6 0.20
6.2.1 Reduce inter-sample variance, that is, improve the
precision of the mean estimation while reducing the probability
Thus, if six samples are included in a composite, the
of making an incorrect decision, composite concentration of 0.6 mg/kg is two standard devia-
tions below the regulatory limit. Therefore, if the composite
6 concentration is actually observed to be in the neighborhood of
The boldface numbers in parentheses refer to a list of references at the end of
this guide. 0.6 mg/kg, we can be reasonably confident (approximately
D 6051
95 %) that the concentration of the site is below the regulatory
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
relatively small, say 0.1 mg/kg. Then the standard deviation of
a composite of 6 individual samples is 0.04 mg/kg (0.1 mg/kg
divided by the square root of 6 = 0.04 mg/kg), a very small
number relative to the regulatory limit of 1 mg/kg. In this case,
simple comparison of the composite concentration to the FIG. 2 Example of Within Cell Compositing
regulatory limit is often quite adequate for decision-making
especially pronounced when the cost of sample analysis is high
purposes.
relative to the cost of sampling, compositing, and analyzing.
6.5.1 The effectiveness of compositing depends on the
6.7 Hot Container/Hot Spot Identification and Retesting
relative magnitude of sampling and analytical error. When
Schemes—Samples can be combined to determine whether an
sampling uncertainty is high relative to analytical error (as is
individual sample exceeds a specified limit as long as the
usually assumed to be the case) compositing is very effective in
action limit is relatively high compared with the actual
improving precision. If analytical errors are high relative to
detection limit and the average sample concentration. Depend-
field errors, sample compositing is much less effective.
ing on the difficulty and probability of having to resample, it
6.5.2 Because compositing is a physical averaging process,
may be desirable to retain a split of the discrete samples for
composite samples tend to be more normally distributed than
possible analysis depending on the analytical results from the
the individual samples. The normalizing effect is frequently an
composite sample.
advantage since calculation of means, standard deviations and
6.8 Example 3—One hundred drums are to be examined to
confidence intervals generally assume the data are normally
determine whether the concentration of PCBs exceeds 50
distributed. Although environmental residue data are com-
mg/kg. Assume the detection limit is 5 mg/kg and most drums
monly non-normally distributed, compositing often leads to
have non-detectable levels. Compositing samples from ten
approximate normality and avoids the need to transform the
drums for analysis would permit determining that none of the
data.
drums in the composite exceed 50 mg/kg as long as the
6.5.3 The spatial design of the compositing scheme can be
concentration of the composite is <5 mg/kg. If the detected
important. Depending upon the locations from which the
concentration is >5 mg/kg, one or more drums may exceed 50
individual samples are collected and composited, composites
mg/kg and additional analyses of the individual drums are
can be used to determine spatial variability or improve the
required to identify any hot drum(s). The maximum number of
precision of the parameter being estimated. Fig. 1 and Fig. 2
samples that can theoretically be composited and still detect a
represent a site divided into four cells. Composite all samples
hot sample is the limit of concern divided by the actual
with the same number together. The sampling approach in Fig.
detection limit (for example, 50 mg/kg 4 5 mg/kg = 10).
1 is similar to sample random sampling, except they are now
6.9 Example 4—Assume background levels of dioxin are
composite samples. Each composite sample in this case is a
non detectable, and the analytical detection limit is 1 μg/kg and
representative sample of the entire site, eliminates cell-to-cell
the action level is 50 μg/kg. The site is systematically gridded
variability, and leads to increased precision in estimating the
(the most efficient sampling design for detecting randomly
mean concentration of the site. If there is a need to estimate the
distributed hot spots) using an appropriate design, and cores to
cell-to-cell variability, then
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