Standard Guide for Developing Appropriate Statistical Approaches for Ground-Water Detection Monitoring Programs

SCOPE
1.1 This guide covers the context of ground-water 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 gound-water monitoring programs for waste disposal facilities. The purpose of these methods is to detect a potential gound-water impact from the facility at the earliest possible time while simultaneously minimizing the probability of falsely concluding that the facility has impacted ground water when it has not.
1.3 When applied inappropriately existing regulation and guidance on statistical approaches to ground-water 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 gound water 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 fasle positive rates approach 100%.
1.4 The purpose of this guide is to illustrate a statistical ground-water 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 ground-water 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 ground water. 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 they completely eliminate the spatial component of variability. Due to the absence of spatial variability, the uncertainty in measured concentrations is decreased making intra-well comparisons more sensitive to real releases (that is, false negatives) and false positive results due to spatial variability are completely eliminated.
1.9 Finally, it should be noted that the statistical methods described here are not the only valid methods for analysis of ground-water monitoring data. They are, however, currently the most useful from the perspective of balancing site-wide false positive and false negative rates at nominal levels. A more complete review of this topic and the associated literature is presented by Gibbons (1).  
1.10 The values stated in both inch-pound and SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.11 This standard does not purport to address all of the safety conce...

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09-Sep-1998
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ASTM D6312-98 - Standard Guide for Developing Appropriate Statistical Approaches for Ground-Water Detection Monitoring Programs
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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.
Designation: D 6312 – 98
Standard Guide for
Developing Appropriate Statistical Approaches for Ground-
1
Water 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope 1.5 This guide is applicable to statistical aspects of ground-
water detection monitoring for hazardous and municipal solid
1.1 This guide covers the context of ground-water monitor-
waste disposal facilities.
ing at waste disposal facilities, regulations have required
1.6 It is of critical importance to realize that on the basis of
statistical methods as the basis for investigating potential
a statistical analysis alone, it can never be concluded that a
environmental impact due to waste disposal facility operation.
waste disposal facility has impacted ground water. A statisti-
Owner/operators must perform a statistical analysis on a
cally significant exceedance over background levels indicates
quarterly or semiannual basis.Astatistical test is performed on
that the new measurement in a particular monitoring well for a
each of many constituents (for example, 10 to 50 or more) for
particular constituent is inconsistent with chance expectations
eachofmanywells(5to100ormore).Theresultispotentially
based on the available sample of background measurements.
hundreds, and in some cases, a thousand or more statistical
1.7 Similarly, statistical methods can never overcome limi-
comparisons performed on each monitoring event. Even if the
tations of a groundwater monitoring network that might arise
false positive rate for a single test is small (for example, 1%),
duetopoorsitecharacterization,wellinstallationandlocation,
the possibility of failing at least one test on any monitoring
sampling, or analysis.
event is virtually guaranteed. This assumes you have done the
1.8 It is noted that when justified, intra-well comparisons
correct statistic in the first place.
aregenerallypreferabletotheirinter-wellcounterpartsbecause
1.2 This guide is intended to assist regulators and industry
they completely eliminate the spatial component of variability.
in developing statistically powerful ground-water monitoring
Due to the absence of spatial variability, the uncertainty in
programs for waste disposal facilities. The purpose of these
measured concentrations is decreased making intra-well com-
methods is to detect a potential ground-water impact from the
parisonsmoresensitivetorealreleases(thatis,falsenegatives)
facility at the earliest possible time while simultaneously
and false positive results due to spatial variability are com-
minimizing the probability of falsely concluding that the
pletely eliminated.
facility has impacted ground water when it has not.
1.9 Finally, it should be noted that the statistical methods
1.3 When applied inappropriately existing regulation and
described here are not the only valid methods for analysis of
guidance on statistical approaches to ground-water monitoring
ground-water monitoring data. They are, however, currently
often suffer from a lack of statistical clarity and often imple-
the most useful from the perspective of balancing site-wide
mentmethodsthatwilleitherfailtodetectcontaminationwhen
falsepositiveandfalsenegativeratesatnominallevels.Amore
itispresent(afalsenegativeresult)orconcludethatthefacility
complete review of this topic and the associated literature is
has impacted ground water when it has not (a false positive).
2
presented by Gibbons (1).
Historicalapproachestothisproblemhaveoftensacrificedone
1.10 The values stated in both inch-pound and SI units are
type of error to maintain control over the other. For example,
toberegardedasthestandard.Thevaluesgiveninparentheses
some regulatory approaches err on the side of conservatism,
are for information only.
keepingfalsenegativeratesnearzerowhilefalsepositiverates
1.11 This standard does not purport to address all of the
approach 100%.
safety concerns, if any, associated with its use. It is the
1.4 The purpose of this guide is to illustrate a statistical
responsibility of the user of this standard to establish appro-
ground-water monitoring strategy that minimizes both false
priate safety and health practices and determine the applica-
negative and false positive rates without sacrificing one for the
bility of regulatory limitations prior to use.
other.
1.12 This guide offers an organized collection of informa-
tion or a series of options and does not recommend a specific
1
This guide is under the jurisdiction of ASTM Committee D-18 on Soil and
Rockandisthedirectresponsibilityof
...

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