1、Designation: D 6044 96 (Reapproved 2009)Standard Guide forRepresentative Sampling for Management of Waste andContaminated Media1This standard is issued under the fixed designation D 6044; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revis
2、ion, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide covers the definition of representativeness inenvironmental sampling, identifies sources t
3、hat can affectrepresentativeness (especially bias), and describes the at-tributes that a representative sample or a representative set ofsamples should possess. For convenience, the term“ represen-tative sample” is used in this guide to denote both a represen-tative sample and a representative set o
4、f samples, unlessotherwise qualified in the text.1.2 This guide outlines a process by which a representativesample may be obtained from a population. The purpose of therepresentative sample is to provide information about a statis-tical parameter(s) (such as mean) of the population regardingsome cha
5、racteristic(s) (such as concentration) of its constitu-ent(s) (such as lead). This process includes the followingstages: (1) minimization of sampling bias and optimization ofprecision while taking the physical samples, (2) minimizationof measurement bias and optimization of precision whenanalyzing t
6、he physical samples to obtain data, and (3) minimi-zation of statistical bias when making inference from thesample data to the population. While both bias and precisionare covered in this guide, major emphasis is given to biasreduction.1.3 This guide describes the attributes of a representativesampl
7、e and presents a general methodology for obtainingrepresentative samples. It does not, however, provide specificor comprehensive sampling procedures. It is the users respon-sibility to ensure that proper and adequate procedures are used.1.4 The assessment of the representativeness of a sample isnot
8、covered in this guide since it is not possible to ever knowthe true value of the population.1.5 Since the purpose of each sampling event is unique, thisguide does not attempt to give a step by step account of how todevelop a sampling design that results in the collection ofrepresentative samples.1.6
9、 Appendix X1 contains two case studies, which discussthe factors for obtaining representative samples.1.7 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and he
10、alth practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 3370 Practices for Sampling Water from Closed ConduitsD 4448 Guide for Sampling Ground-Water MonitoringWellsD 4547 Guide for Sampling Waste and Soils for VolatileOrgani
11、c CompoundsD 4700 Guide for Soil Sampling from the Vadose ZoneD 4823 Guide for Core Sampling Submerged, Unconsoli-dated SedimentsD 5088 Practice for Decontamination of Field EquipmentUsed at Waste SitesD 5792 Practice for Generation of Environmental DataRelated to Waste Management Activities: Develo
12、pment ofData Quality ObjectivesD 5956 Guide for Sampling Strategies for HeterogeneousWastesD 6051 Guide for Composite Sampling and Field Subsam-pling for Environmental Waste Management Activities3. Terminology3.1 analytical unit, nthe actual amount of the samplematerial analyzed in the laboratory.3.
13、2 bias, na systematic positive or negative deviation ofthe sample or estimated value from the true population value.3.2.1 DiscussionThis guide discusses three sources ofbiassampling bias, measurement bias, and statistical bias.There is a sampling bias when the value inherent in thephysical samples i
14、s systematically different from what isinherent in the population.There is a measurement bias when the measurement processproduces a sample value systematically different from that1This guide is under the jurisdiction of ASTM Committee D34 on WasteManagement and is the direct responsibility of Subco
15、mmittee D34.01.01 onPlanning for Sampling.Current edition approved Feb. 1, 2009. Published March 2009. Originallyapproved in 1996. Last previous edition approved in 2003 as D 6044 96(2003).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at servic
16、eastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.inherent in the sample itself, although the physical samp
17、le isitself unbiased. Measurement bias can also include any sys-tematic difference between the original sample and the sampleanalyzed, when the analyzed sample may have been altereddue to improper procedures such as improper sample preser-vation or preparation, or both.There is a statistical bias wh
18、en, in the absence of samplingbias and measurement bias, the statistical procedure produces abiased estimate of the population value.Sampling bias is considered the most important factoraffecting inference from the samples to the population.3.3 biased sampling, nthe taking of a sample(s) with priork
19、nowledge that the sampling result will be biased relative tothe true value of the population.3.3.1 DiscussionThis is the taking of a sample(s) basedon available information or knowledge, especially in terms ofvisible signs or knowledge of contamination. This kind ofsampling is used to detect the pre
20、sence of localized contami-nation or to identify the source of a contamination. Thesampling results are not intended for generalization to theentire population. This is one form of authoritative sampling(see judgment sampling.)3.4 characteristic, na property of items in a sample orpopulation that ca
21、n be measured, counted, or otherwise ob-served, such as viscosity, flash point, or concentration.3.5 composite sample, na combination of two or moresamples.3.6 constituent, n an element, component, or ingredient ofthe population.3.6.1 DiscussionIf a population contains several contami-nants (such as
22、 acetone, lead, and chromium), these contami-nants are called the constituents of the population.3.7 Data Quality Objectives, DQOs, nqualitative andquantitative statements derived from a DQO process describingthe decision rules and the uncertainties of the decision(s)within the context of the proble
23、m(s) (see Practice D 5792).3.8 Data Quality Objective Processa quality managementtool based on the Scientific Method and developed by the U.S.Environmental Protection Agency to facilitate the planning ofenvironmental data collection activities. The DQO processenables planners to focus their planning
24、 efforts by specifyingthe use of data (the decision), the decision criteria (actionlevel), and the decision makers acceptable decision error rates.The products of the DQO process are the DQOs (see PracticeD 5792).3.9 error, nthe random or systematic deviation of theobserved sample value from its tru
25、e value (see bias andsampling error).3.10 heterogeneity, nthe condition or degree of the popu-lation under which all items of the population are not identicalwith respect to the characteristic(s) of interest.3.10.1 DiscussionAlthough the ultimate interest is in thestatistical parameter such as the m
26、ean concentration of aconstituent of the population, heterogeneity relates to thepresence of differences in the characteristics (for example,concentration) of the units in the population. It is due to thepresence of fundamental heterogeneity (or fundamental error)3in the population that sampling var
27、iance arises. Degree ofsampling variance defines the degree of precision in estimatingthe population parameter using the sample data. The smallerthe sampling variance is, the more precise the estimate is. Seealso sampling error.3.11 homogeneity, n the condition of the population underwhich all items
28、 of the population are identical with respect tothe characteristic(s) of interest.3.12 judgment sampling, ntaking of a sample(s) based onjudgment that it will more or less represent the averagecondition of the population.3.12.1 DiscussionThe sampling location(s) is selectedbecause it is judged to be
29、 representative of the averagecondition of the population. It can be effective when thepopulation is relatively homogeneous or when the professionaljudgment is good. It may or may not introduce bias. It is auseful sampling approach when precision is not a concern.Thisis one form of authoritative sam
30、pling (see biased sampling.)3.13 population, nthe totality of items or units of mate-rials under consideration.3.14 representative sample, na sample collected in such amanner that it reflects one or more characteristics of interest (asdefined by the project objectives) of a population from whichit i
31、s collected.3.14.1 DiscussionArepresentative sample can be a singlesample, a collection of samples, or one or more compositesamples. A single sample can be representative only when thepopulation is highly homogeneous.3.15 representative sampling, nthe process of obtaining arepresentative sample or a
32、 representative set of samples.3.16 representative set of samples, na set of samples thatcollectively reflect one or more characteristics of interest of apopulation from which they were collected. See representativesample.3.17 sample, na portion of material that is taken fortesting or for record pur
33、poses.3.17.1 DiscussionSample is a term with numerous mean-ings. The scientist collecting physical samples (for example,from a landfill, drum, or monitoring well) or analyzing samplesconsiders a sample to be that unit of the population that wascollected and placed in a container. A statistician cons
34、iders asample to be a subset of the population, and this subset mayconsist of one or more physical samples. To minimize confu-sion, the term sample, as used in this guide, is a reference toeither a physical sample held in a sample container, or thatportion of the population that is subjected to in s
35、itu measure-ments, or a set of physical samples. See representative sample.3.17.1.1 The term sample size also means different things tothe scientist and the statistician.To avoid confusion, terms suchas sample mass/sample volume and number of samples areused instead of sample size.3Pitard, F. F., “P
36、ierre Gys Sampling Theory and Sampling Practice: Heteroge-neity, Sampling Correctness and Statistical Process Control,” 2nd ed., CRC PressPublishers, 1993.D 6044 96 (2009)23.18 sampling errorthe systematic and random deviationsof the sample value from that of the population. The systematicerror is t
37、he sampling bias. The random error is the samplingvariance.3.18.1 DiscussionBefore the physical samples are taken,potential sampling variance comes from the inherent popula-tion heterogeneity (sometimes called the “fundamental error,”see heterogeneity). In the physical sampling stage, additionalcont
38、ributors to sampling variance include random errors incollecting the samples.After the samples are collected, anothercontributor is the random error in the measurement process. Ineach of these stages, systematic errors can occur as well, butthey are the sources of bias, not sampling variance.3.18.1.
39、1 Sampling variance is often used to refer to the totalvariance from the various sources.3.19 stratum, na subgroup of the population separated inspace or time, or both, from the remainder of the population,being internally similar with respect to a target characteristic ofinterest, and different fro
40、m adjacent strata of the population.3.19.1 DiscussionA landfill may display spatially sepa-rated strata, such as old cells containing different wastes thannew cells. A waste pipe may discharge into temporally sepa-rated strata of different constituents or concentrations, or both,if night-shift produ
41、ction varies from the day shift. In this guide,strata refer mostly to the stratification in the concentrations ofthe same constituent(s).3.20 subsample, na portion of the original sample that istaken for testing or for record purposes.4. Significance and Use4.1 Representative samples are defined in
42、the context of thestudy objectives.4.2 This guide defines the meaning of a representativesample, as well as the attributes the sample(s) needs to have inorder to provide a valid inference from the sample data to thepopulation.4.3 This guide also provides a process to identify thesources of error (bo
43、th systematic and random) so that an effortcan be made to control or minimize these errors. These sourcesinclude sampling error, measurement error, and statistical bias.4.4 When the objective is limited to the taking of arepresentative (physical) sample or a representative set of(physical) samples,
44、only potential sampling errors need to beconsidered. When the objective is to make an inference fromthe sample data to the population, additional measurementerror and statistical bias need to be considered.4.5 This guide does not apply to the cases where the takingof a nonrepresentative sample(s) is
45、 prescribed by the studyobjective. In that case, sampling approaches such as judgmentsampling or biased sampling can be taken. These approachesare not within the scope of this guide.4.6 Following this guide does not guarantee that represen-tative samples will be obtained. But failure to follow this
46、guidewill likely result in obtaining sample data that are either biasedor imprecise, or both. Following this guide should increase thelevel of confidence in making the inference from the sampledata to the population.4.7 This guide can be used in conjunction with the DQOprocess (see Practice D 5792).
47、4.8 This guide is intended for those who manage, design,and implement sampling and analytical plans for waste man-agement and contaminated media.5. Representative Samples5.1 Samples are taken to infer about some statistical param-eter(s) of the population regarding some characteristic(s) of itsconst
48、ituent(s) of interest. This is discussed in the followingsections.5.2 SamplesWhen a representative sample consists of asingle physical sample, it is a sample that by itself reflects thecharacteristics of interest of the population. On the other hand,when a representative sample consists of a set of
49、physicalsamples, the samples collectively reflect some characteristicsof the population, though the samples individually may not berepresentative. In most cases, more than one physical sample isnecessary to characterize the population, because the popula-tion in environmental sampling is usually heterogeneous.5.3 Constituents and CharacteristicsA population canpossess many constituents, each with many characteristics.Usually it is only a subset of these constituents and character-istics that are of interest in the context of the stated problem.Ther
