ASTM D6312-98(2012)e1
(Guide)Standard Guide for Developing Appropriate Statistical Approaches for Groundwater Detection Monitoring Programs
Standard Guide for Developing Appropriate Statistical Approaches for Groundwater Detection Monitoring Programs
SIGNIFICANCE AND USE
5.1 The principal use of this guide is in groundwater detection monitoring of hazardous and municipal solid waste disposal facilities. There is considerable variability in the way in which existing Guide USEPA regulation and guidance are interpreted and practiced. Often, much of current practice leads to statistical decision rules that lead to excessive false positive or false negative rates, or both. The significance of this proposed guide is that it jointly minimizes false positive and false negative rates at nominal levels without sacrificing one error for another (while maintaining acceptable statistical power to detect actual impacts to groundwater quality (4)).
5.2 Using this guide, an owner/operator or regulatory agency should be able to develop a statistical detection monitoring program that will not falsely detect contamination when it is absent and will not fail to detect contamination when it is present.
SCOPE
1.1 This guide covers the context of groundwater monitoring at waste disposal facilities. Regulations have required statistical methods as the basis for investigating potential environmental impact due to waste disposal facility operation. Owner/operators must perform a statistical analysis on a quarterly or semiannual basis. A statistical test is performed on each of many constituents (for example, 10 to 50 or more) for each of many wells (5 to 100 or more). The result is potentially hundreds, and in some cases, a thousand or more statistical comparisons performed on each monitoring event. Even if the false positive rate for a single test is small (for example, 1 %), the possibility of failing at least one test on any monitoring event is virtually guaranteed. This assumes you have done the correct statistic in the first place.
1.2 This guide is intended to assist regulators and industry in developing statistically powerful groundwater monitoring programs for waste disposal facilities. The purpose of this guide is to detect a potential groundwater impact from the facility at the earliest possible time while simultaneously minimizing the probability of falsely concluding that the facility has impacted groundwater when it has not.
1.3 When applied inappropriately, existing regulation and guidance on statistical approaches to groundwater monitoring often suffer from a lack of statistical clarity and often implement methods that will either fail to detect contamination when it is present (a false negative result) or conclude that the facility has impacted groundwater when it has not (a false positive). Historical approaches to this problem have often sacrificed one type of error to maintain control over the other. For example, some regulatory approaches err on the side of conservatism, keeping false negative rates near zero while false positive rates approach 100 %.
1.4 The purpose of this guide is to illustrate a statistical groundwater monitoring strategy that minimizes both false negative and false positive rates without sacrificing one for the other.
1.5 This guide is applicable to statistical aspects of groundwater detection monitoring for hazardous and municipal solid waste disposal facilities.
1.6 It is of critical importance to realize that on the basis of a statistical analysis alone, it can never be concluded that a waste disposal facility has impacted groundwater. A statistically significant exceedance over background levels indicates that the new measurement in a particular monitoring well for a particular constituent is inconsistent with chance expectations based on the available sample of background measurements.
1.7 Similarly, statistical methods can never overcome limitations of a groundwater monitoring network that might arise due to poor site characterization, well installation and location, sampling, or analysis.
1.8 It is noted that when justified, intra-well comparisons are generally preferable to their inter-well counterparts because...
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
´1
Designation: D6312 − 98 (Reapproved 2012)
Standard Guide for
Developing Appropriate Statistical Approaches for
Groundwater Detection Monitoring Programs
This standard is issued under the fixed designation D6312; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Editorial changes were made throughout in February 2012.
1. Scope 1.4 The purpose of this guide is to illustrate a statistical
groundwater monitoring strategy that minimizes both false
1.1 This guide covers the context of groundwater monitor-
negative and false positive rates without sacrificing one for the
ing at waste disposal facilities. Regulations have required
other.
statistical methods as the basis for investigating potential
environmental impact due to waste disposal facility operation. 1.5 This guide is applicable to statistical aspects of ground-
Owner/operators must perform a statistical analysis on a water detection monitoring for hazardous and municipal solid
quarterly or semiannual basis.Astatistical test is performed on waste disposal facilities.
each of many constituents (for example, 10 to 50 or more) for
1.6 It is of critical importance to realize that on the basis of
eachofmanywells(5to100ormore).Theresultispotentially
a statistical analysis alone, it can never be concluded that a
hundreds, and in some cases, a thousand or more statistical
waste disposal facility has impacted groundwater. A statisti-
comparisons performed on each monitoring event. Even if the
cally significant exceedance over background levels indicates
false positive rate for a single test is small (for example, 1%),
that the new measurement in a particular monitoring well for a
the possibility of failing at least one test on any monitoring
particular constituent is inconsistent with chance expectations
event is virtually guaranteed. This assumes you have done the
based on the available sample of background measurements.
correct statistic in the first place.
1.7 Similarly, statistical methods can never overcome limi-
1.2 This guide is intended to assist regulators and industry
tations of a groundwater monitoring network that might arise
in developing statistically powerful groundwater monitoring
duetopoorsitecharacterization,wellinstallationandlocation,
programs for waste disposal facilities. The purpose of this
sampling, or analysis.
guide is to detect a potential groundwater impact from the
1.8 It is noted that when justified, intra-well comparisons
facility at the earliest possible time while simultaneously
aregenerallypreferabletotheirinter-wellcounterpartsbecause
minimizing the probability of falsely concluding that the
they completely eliminate the spatial component of variability.
facility has impacted groundwater when it has not.
Due to the absence of spatial variability, the uncertainty in
1.3 When applied inappropriately, existing regulation and
measured concentrations is decreased, making intra-well com-
guidance on statistical approaches to groundwater monitoring
parisonsmoresensitivetorealreleases(thatis,falsenegatives)
often suffer from a lack of statistical clarity and often imple-
and false positive results due to spatial variability are com-
mentmethodsthatwilleitherfailtodetectcontaminationwhen
pletely eliminated.
itispresent(afalsenegativeresult)orconcludethatthefacility
1.9 Finally, it should be noted that the statistical methods
has impacted groundwater when it has not (a false positive).
described here are not the only valid methods for analysis of
Historicalapproachestothisproblemhaveoftensacrificedone
groundwatermonitoringdata.Theyare,however,currentlythe
type of error to maintain control over the other. For example,
most useful from the perspective of balancing site-wide false
some regulatory approaches err on the side of conservatism,
positive and false negative rates at nominal levels. A more
keepingfalsenegativeratesnearzerowhilefalsepositiverates
complete review of this topic and the associated literature is
approach 100%.
presented by Gibbons (1).
1.10 The values stated in both inch-pound and SI units are
1 toberegardedasthestandard.Thevaluesgiveninparentheses
ThisguideisunderthejurisdictionofASTMCommitteeD18onSoilandRock
and is the direct responsibility of Subcommittee D18.21 on Groundwater and
are for information only.
Vadose Zone Investigations.
Current edition approved Feb. 15, 2012. Published December 2012. Originally
approved in 1998. Last previous edition approved in 2005 as D6312 – 98 (2005). The boldface numbers given in parentheses refer to a list of references at the
DOI: 10.1520/D6312-98R12E01. end of the text.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
´1
D6312 − 98 (2012)
1.11 This standard does not purport to address all of the containthenextseriesofkmeasurementswithaspecifiedlevel
safety concerns, if any, associated with its use. It is the of confidence (for example, 99% confidence) based on a
responsibility of the user of this standard to establish appro- sample of n background measurements.
priate safety and health practices and determine the applica-
3.2.8 quantification limit (QL), n—the concentration at
bility of regulatory limitations prior to use.
which quantitative determinations of an analyte’s concentra-
1.12 This guide offers an organized collection of informa-
tion in the sample can be reliably made during routine
tion or a series of options and does not recommend a specific
laboratory operating conditions (3).
course of action. This document cannot replace education or
3.3 Definitions of Terms Specific to This Standard:
experienceandshouldbeusedinconjunctionwithprofessional
3.3.1 false negative rate, n—in detection monitoring, the
judgment.Notallaspectsofthisguidemaybeapplicableinall
rateatwhichthestatisticalproceduredoesnotindicatepossible
circumstances. This ASTM standard is not intended to repre-
contamination when contamination is present.
sent or replace the standard of care by which the adequacy of
3.3.2 falsepositiverate,n—indetectionmonitoring,therate
a given professional service must be judged, nor should this
at which the statistical procedure indicates possible contami-
documentbeappliedwithoutconsiderationofaproject’smany
nation when none is present.
unique aspects. The word “Standard” in the title of this
document means only that the document has been approved
3.3.3 nonparametric, adj—a term referring to a statistical
through the ASTM consensus process.
technique in which the distribution of the constituent in the
population is unknown and is not restricted to be of a specified
2. Referenced Documents
form.
2.1 ASTM Standards:
3.3.4 nonparametric prediction limit, n—the largest (or
D653Terminology Relating to Soil, Rock, and Contained
second largest) of n background samples.The confidence level
Fluids
associatedwiththenonparametricpredictionlimitisafunction
of n and k .
3. Terminology
3.3.5 parametric, adj—a term referring to a statistical tech-
3.1 Definitions:
nique in which the distribution of the constituent in the
3.1.1 For definitions of common technical terms in this
population is assumed to be known.
standard, refer to Terminology D653.
3.3.6 verification resample, n—in the event of an initial
3.2 Definitions of Terms Specific to This Standard:
statistical exceedance, one (or more) new independent sample
3.2.1 assessment monitoring program, n—groundwater
is collected and analyzed for that well and constituent which
monitoring that is intended to determine the nature and extent
exceeded the original limit.
of a potential site impact following a verified statistically
significant exceedance of the detection monitoring program. 3.4 Symbols:
3.4.1 α—thefalsepositiverateforanindividualcomparison
3.2.2 combined Shewhart (CUSUM) control chart, n—a
(that is, one well and constituent).
statisticalmethodforintra-wellcomparisonsthatissensitiveto
3.4.2 α*—thesite-widefalsepositiveratecoveringallwells
both immediate and gradual releases.
and constituents.
3.2.3 detection limit (DL), n—the true concentration at
3.4.3 k—the number of future comparisons for a single
which there is a specified level of confidence (for example,
monitoring event (for example, the number of downgradient
99% confidence) that the analyte is present in the sample (2).
monitoring wells multiplied by the number of constituents to
3.2.4 detection monitoring program, n—groundwater moni-
be monitored) for which statistics are to be computed.
toring that is intended to detect a potential impact from a
3.4.4 n—the number of background measurements.
facility by testing for statistically significant changes in geo-
3.4.5 σ —the true population variance of a constituent.
chemistry in a downgradient monitoring well relative to
3.4.6 s—the sample-based standard deviation of a constitu-
background levels.
ent computed from n background measurements.
3.2.5 intra-well comparisons, n—a comparison of one or
3.4.7 s —the sample-based variance of a constituent com-
more new monitoring measurements to statistics computed
puted from n background measurements.
fromasampleofhistoricalmeasurementsfromthatsamewell.
3.4.8 µ—the true population mean of a constituent.
3.2.6 inter-well comparisons, n—a comparison of a new
3.4.9 x¯—thesample-basedmeanoraverageconcentrationof
monitoring measurement to statistics computed from a sample
a constituent computed from n background measurements.
of background measurements (for example, upgradient versus
downgradient comparisons).
4. Summary of Guide
3.2.7 prediction interval or limit, n—a statistical estimate of
the minimum or maximum concentration, or both, that will 4.1 This guide is summarized in Fig. 1, which provides a
flowchart illustrating the steps in developing a statistical
monitoring plan. The monitoring plan is based either on
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
background versus monitoring well comparisons (for example,
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
upgradient versus downgradient comparisons or intra-well
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. comparisons, or a combination of both). Fig. 1 illustrates the
´1
D6312 − 98 (2012)
FIG. 1 Development of a Statistical Detection Monitoring Plan
´1
D6312 − 98 (2012)
FIG. 1 (continued)
´1
D6312 − 98 (2012)
FIG. 1 (continued)
´1
D6312 − 98 (2012)
FIG. 1 (continued)
´1
D6312 − 98 (2012)
FIG. 1 (continued)
´1
D6312 − 98 (2012)
various decision points at which the general comparative 6.1.1.9 If the background detection frequency equals zero,
strategy is selected (that is, upgradient background versus use the laboratory-specific QL (recommended) or limits re-
intra-well background) and how the statistical methods are to quired by applicable regulatory agency (8).
beselectedbasedonsite-specificconsiderations.Thestatistical 6.1.1.10 This only applies for those wells and constituents
methods include parametric and nonparametric prediction that have at least 13 background samples. Thirteen samples
limits for background versus monitoring well comparisons and providea99%confidencenonparametricpredictionlimitwith
combined Shewhart-CUSUM control charts for intra-well one resample for a single well and constituent (see Table 1).
comparisons. Note that the background database is intended to 6.1.1.11 If less than 13 samples are available, more back-
expand as new data become available during the course of ground data must be collected to use the nonparametric
monitoring. prediction limit.
6.1.1.12 AnalternativewouldbetouseaPoissonprediction
5. Significance and Use limit that can be computed from four or more background
measurements regardless of the detection frequency and can
5.1 The principal use of this guide is in groundwater
adjust for multiple wells and constituents.
detection monitoring of hazardous and municipal solid waste
6.1.1.13 If downgradient wells fail, determine cause.
disposal facilities. There is considerable variability in the way
6.1.1.14 Ifthedowngradientwellsfailbecauseofnaturalor
in which existing Guide USEPA regulation and guidance are
off-site causes, select constituents for intra-well comparisons
interpretedandpracticed.Often,muchofcurrentpracticeleads
(9).
to statistical decision rules that lead to excessive false positive
6.1.1.15 If site impacts are found, a site plan for assessment
or false negative rates, or both. The significance of this
monitoring may be necessary (10).
proposed guide is that it jointly minimizes false positive and
6.1.2 Intra-well Comparisons:
false negative rates at nominal levels without sacrificing one
6.1.2.1 For those facilities that either have no definable
error for another (while maintaining acceptable statistical
hydraulic gradient, have no existing contamination, have too
power to detect actual impacts to groundwater quality (4)).
few background wells to meaningfully characterize spatial
5.2 Using this guide, an owner/operator or regulatory
variability (for example, a site with one upgradient well or a
agency should be able to develop a statistical detection
facility in which upgradient water quality is either inaccessible
monitoring program that will not falsely detect contamination
or not representative of downgradient water quality), compute
whenitisabsentandwillnotfailtodetectcontaminationwhen
intra-well comparisons using combined Shewhart-CUSUM
it is present.
control charts (9).
6.1.2.2 For those wells and constituents that fail upgradient
6. Procedure
versus downgradient comparisons, compute combined
NOTE 1—In the following, an overview of the general procedure is
Shewhart-CUSUM control charts. If no volatile organic com-
described with specific technical details described in Section 6.
pounds (VOCs) or hazardous metals are detected and no trend
6.1 Detection Monitoring:
is detected in other indicator constituents, use intra-well
6.1.1 Upgradient Versus Downgradient Comparisons:
comparisons for detection monitoring of those wells and
6.1.1.1 Detection frequency ≥50%.
constituents.
6.1.1.2 If the constituent is normally distributed, compute a
6.1.2.3 If data are all non-detects after 13 quarter
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.