ASTM D7048-04(2010)
(Guide)Standard Guide for Applying Statistical Methods for Assessment and Corrective Action Environmental Monitoring Programs
Standard Guide for Applying Statistical Methods for Assessment and Corrective Action Environmental Monitoring Programs
SIGNIFICANCE AND USE
The principal use of this standard is in assessment, compliance and corrective action environmental monitoring programs (for example, for any facility that could potentially contaminate groundwater). The significance of the guidance is that it presents a statistical method that allows comparison of groundwater data to regulatory and/or health based limits.
Of course, there is considerable USEPA support for statistical methods applied to detection, assessment and corrective action monitoring programs that can be applied to environmental investigations. For example, the 90 % upper confidence limit (UCL) of the mean is used in SW846 (Chapter 9) for determining if a waste is hazardous. If the UCL is less than the criterion for a particular hazardous waste code, then the waste is not a hazardous waste even if certain individual measurements exceed the criterion. Similarly, in the USEPA Statistical Analysis of Groundwater Monitoring Data at RCRA Facilities Addendum to the Interim Final Guidance (1992) (2), confidence intervals for the mean and various upper percentiles of the distribution are advocated for assessment and corrective action. Interestingly, both the 1989 and 1992 USEPA guidance documents (2, 3) suggest use of the lower 95 % confidence limit (LCL) as a tool for determining whether a criterion has been exceeded in assessment monitoring. The latest USEPA guidance in this area (that is, the draft USEPA Unified Statistical Guidance) calls for use of the LCL in assessment monitoring and the UCL in corrective action. In this way, corrective action is only triggered if there is a high degree of confidence that the true concentration has exceeded the criterion or standard, whereas corrective action continues until there is a high degree of confidence that the true concentration is below the criterion or standard. This is the general approach adopted in this guide, as well.
There are several reasons why statistical methods are essential in assessment and correctiv...
SCOPE
1.1 The scope and purpose of this guidance is to present a variety of statistical approaches for assessment, compliance and corrective action environmental monitoring programs. Although the methods provided here are appropriate and often optimal for many environmental monitoring problems, they do not preclude use of other statistical approaches that may be equally or even more useful for certain site-specific applications.
1.2 In the following sections, complete details of select statistical procedures used in assessment and corrective action programs for environmental monitoring (soil, groundwater, air, surface water, and waste streams) are presented.
1.3 The statistical methodology described in the following sections should be used as guidance. Other methods may also be appropriate based on site-specific conditions or for monitoring situations or media that are not presented in this document.
1.4 This practice offers an organized collection of information or a series of options and does not recommend a specific course of action. This document cannot replace education, experience and professional judgements. Not all aspects of this practice may be applicable in all circumstances. This ASTM standard is not intended to represent or replace the standard of care by which the adequacy of a given professional service must be judged without consideration of a project's many unique aspects. The word Standard in the title of this document only means that the document has been approved through the ASTM consensus process.
1.5 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 requirements prior to use.
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Designation: D7048 − 04(Reapproved 2010)
Standard Guide for
Applying Statistical Methods for Assessment and Corrective
Action Environmental Monitoring Programs
This standard is issued under the fixed designation D7048; 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.
1. Scope 2. Referenced Documents
1.1 The scope and purpose of this guidance is to present a 2.1 ASTM Standards:
variety of statistical approaches for assessment, compliance D5092Practice for Design and Installation of Groundwater
and corrective action environmental monitoring programs. Monitoring Wells
Although the methods provided here are appropriate and often D5792Practice for Generation of Environmental Data Re-
optimal for many environmental monitoring problems, they do lated to Waste Management Activities: Development of
not preclude use of other statistical approaches that may be Data Quality Objectives
equally or even more useful for certain site-specific applica- D6250Practice for Derivation of Decision Point and Confi-
tions. dence Limit for StatisticalTesting of Mean Concentration
in Waste Management Decisions
1.2 In the following sections, complete details of select
D6312Guide for Developing Appropriate Statistical Ap-
statistical procedures used in assessment and corrective action
proaches for Groundwater Detection Monitoring Pro-
programsforenvironmentalmonitoring(soil,groundwater,air,
grams
surface water, and waste streams) are presented.
1.3 The statistical methodology described in the following
3. Terminology
sections should be used as guidance. Other methods may also
3.1 Definitions:
be appropriate based on site-specific conditions or for moni-
3.1.1 assessment monitoring—investigative monitoring that
toring situations or media that are not presented in this
is initiated after the presence of a contaminant has been
document.
detected in groundwater above a relevant criterion at one or
1.4 This practice offers an organized collection of informa- morelocations.Theobjectiveoftheprogramistodetermineif
tion or a series of options and does not recommend a specific
there is a statistical exceedance of a standard or criteria at a
course of action. This document cannot replace education,
Potential Area of Concern (PAOC) or at the groundwater
experienceandprofessionaljudgements.Notallaspectsofthis
discharging to surface water interface, and/or to quantify the
practice may be applicable in all circumstances. This ASTM
rateandextentofmigrationofconstituentsdetectedinground-
standard is not intended to represent or replace the standard of
water above applicable criteria.
care by which the adequacy of a given professional service
3.1.2 compliance monitoring—as specified under 40 CFR
must be judged without consideration of a project’s many
264.99, compliance monitoring is instituted when hazardous
uniqueaspects.ThewordStandardinthetitleofthisdocument
constituents have been detected above a relevant criterion at
only means that the document has been approved through the
the compliance point during RCRA detection monitoring.
ASTM consensus process.
Groundwater samples are collected at the compliance point,
1.5 This standard does not purport to address all of the
facilitypropertyboundary,andupgradientmonitoringwellsfor
safety concerns, if any, associated with its use. It is the
analysis of hazardous constituents to determine if they are
responsibility of the user of this standard to establish appro-
leaving the regulated unit at statistically significant concentra-
priate safety and health practices and determine the applica-
tions above background.
bility of regulatory requirements prior to use.
3.1.3 corrective action monitoring—under RCRA, correc-
tive action monitoring is instituted when hazardous constitu-
ents from a RCRA regulated unit have been detected at
ThisguideisunderthejurisdictionofASTMCommitteeD18onSoilandRock
and is the direct responsibility of Subcommittee D18.21 on Groundwater and
Vadose Zone Investigations. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved July 1, 2010. Published September 2010. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 2004. Last previous edition approved in 2004 as D7048–04. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/D7048-04R10. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7048 − 04 (2010)
statistically significant concentrations between the compliance 3.1.13 nonparametric prediction limit—the largest (or sec-
point and the downgradient facility property boundary as ond largest) of n background samples. The confidence level
associatedwiththenonparametricpredictionlimitisafunction
specified under 40 CFR 264.100. Corrective action monitoring
of n, m and k.
is conducted throughout a corrective action program that is
implemented to address groundwater contamination. At non-
3.1.14 normal distribution—a frequency distribution whose
RCRA sites, corrective action monitoring is conducted
plot is a continuous, infinite, bell-shaped curve that is sym-
throughout the active period of corrective action to determine
metrical about its arithmetic mean, mode and median (which
the progress of remediation and to identify statistically signifi-
are numerically equivalent). The normal distribution has two
cant trends in groundwater contaminant concentrations. parameters, the mean and variance.
3.1.15 outlier—a measurement that is statistically inconsis-
3.1.4 detection limit, DL—the true concentration at which
tent with the distribution of other measurements from which it
there is a specified level of confidence (for example, 99%
was drawn.
confidence) that the true concentration is greater than zero.
3.1.16 parametric—a term referring to a statistical tech-
3.1.5 detection monitoring—a program of monitoring for
nique in which the distribution of the constituent in the
the express purpose of determining whether or not there has
population is assumed to be known.
been a release of a contaminant to groundwater. Under RCRA,
3.1.17 quantification limit, QL—a lower limit on the con-
Detection Monitoring involves collection of groundwater
centration at which quantitative determinations of an analyte’s
samples from compliance point and upgradient monitoring
concentration in the sample can be reliably made during
wells on a semi-annual basis for analysis of hazardous con-
routine laboratory operating conditions. The QL is typically
stituentsofconcern,asspecifiedunder40CFR264.98.Results
described quantitatively as the true concentration at which the
are evaluated to determine if there is a statistically significant
signal to noise ratio of measured concentration or instrument
exceedance of the groundwater protection criterion and/or
response is 10:1. The signal to noise ratio is often determined
background.At non-RCRAsites, monitoring is conducted in a
by a percent relative standard deviation of 10%.
similar manner and results are compared to criteria to deter-
3.1.18 potential area of concern—areas with a documented
mine if there is a statistically significant exceedance.
release or likely presence of a hazardous substance that could
3.1.6 direct push sampling—groundwater sampling con-
pose an unacceptable risk to human health or the environment.
ductedwithadevicethatistemporarilypushedintotheground
3.1.19 phase I environmental site assessment—non-
with a hydraulic system or with a hammer.After groundwater
intrusive investigation that identifies PAOCs which may re-
sample collection, the device is removed from the ground.
quire further investigation in subsequent phases of work.
Examples include Geoprobe®, Hydropunch® direct push, and
3.1.20 phase II environmental site assessment, ESI—
environmental soil probe.
intrusive survey to confirm or deny existence of a release into
3.1.7 false negative rate—the rate at which the statistical
the environment at a PAOC at levels which may adversely
procedure does not indicate contamination when contamina-
impact public health or the environment.
tion is present.
3.1.21 upperconfidencelimit,UCL—anupperlimitthathas
3.1.8 false positive rate—the rate at which the statistical
a specified probability (for example, 95%) of including the
procedure indates contamination when contamination is not
true concentration (or other parameter). Taken together with
present.
the lower confidence limit, the UCL forms a confidence
intervalthatwillincludethetrueconcentrationwithconfidence
3.1.9 lognormal distribution—a frequency distribution
level that accounts for both tail areas.
whose logarithm follows a normal distribution.
3.1.22 upper prediction limit, UPL—a statistical estimate of
3.1.10 lowerconfidencelimit,LCL—alowerlimitthathasa
the maximum concentration that will not be exceeded by the
specified probability (for example, 95%) of including the true
next series of k measurements from that distribution, or the
concentration (or other parameter). Taken together with the
meanofmnewmeasurementsforeachofksamplinglocations,
upper confidence limit, forms a confidence interval that will
with specified level of confidence (for example, 95%) based
include the true concentration with confidence level that
on a sample of n background measurements.
accounts for both tail areas (for example, 90%).
3.2 Symbols:
3.1.11 lower prediction limit, LPL—a statistical estimate of
µ=the true population mean of a constituent
theminimumconcentrationthatwillprovidealowerboundfor
x¯ =the sample-based mean or average concentration of a
the next series of k measurements from that distribution, or the
constituentcomputedfromnbackgroundmeasurementswhich
meanofmnewmeasurementsforeachofksamplinglocations,
differs from µ because of sampling variability, and other error
with specified level of confidence (for example, 95%). 2
σ =the true population variance of a constituent
3.1.12 nonparametric—a term referring to a statistical tech-
s =the sample-based variance of a constituent computed
nique in which the distribution of the constituent in the from n background measurements
populationisunknownandisnotrestrictedtobeofaspecified
s=the sample-based standard deviation of a constituent
form. computed from n background measurements
D7048 − 04 (2010)
y¯ =the mean of the natural log transformed data (also the been exceeded in assessment monitoring. The latest USEPA
natural log of the geometric mean) guidance in this area (that is, the draft USEPA Unified
s =the standard deviation of the natural log transformed Statistical Guidance) calls for use of the LCL in assessment
y
data monitoring and the UCL in corrective action. In this way,
n=the number of background (offsite or upgradient) mea- corrective action is only triggered if there is a high degree of
surements confidence that the true concentration has exceeded the crite-
k=the number of future comparisons for a single monitor- rion or standard, whereas corrective action continues until
ing event (for example, the number of downgradient monitor- there is a high degree of confidence that the true concentration
ing wells multiplied by the number of constituents to be is below the criterion or standard.This is the general approach
monitored) for which statistics are to be computed adopted in this guide, as well.
α=the false positive rate for an individual comparison (that
5.3 There are several reasons why statistical methods are
is, one sampling location and constituent)
essential in assessment and corrective action monitoring pro-
m=the number of onsite or downgradient measurements
grams. First, a single measurement indicates very little about
used in computing the onsite mean concentration
the true concentration in the sampling location of interest, and
α*=the site-wide false positive rate covering all sampling
with only one sample there is no way of knowing if the
locations and constituents
measured concentration is a typical or an extreme value. The
t = the 100(1 − α) percentage point of Student’s
objectiveistocomparethetrueconcentration(orsomeinterval
t-distribution on n − 1 degrees of freedom
thatcontainsit)totherelevantcriterionorstandard.Second,in
H =the factor developed by Land (1971) (1) to obtain the
L
many cases the constituents of interest are naturally occurring
lower 100(α)% confidence limit for the mean of a lognormal
(for example, metals) and the naturally existing concentrations
distribution
may exceed the relevant criteria. In this case, the relevant
H =the factor developed by Land (1971) (1) to obtain the
U
comparison is to background (for example, off-site soil or
upper 100(α)% confidence limit for the mean of a lognormal
upgradient groundwater) and not to a fixed criterion.As such,
distribution
background data must be statistically characterized to obtain a
statistical estimate of an upper bound for the naturally occur-
4. Summary of Guide
ring concentrations so that it can be confidently determined if
4.1 The guide is summarized as Figs. 1-7. These figures
onsiteconcentrationsareabovebackgroundlevels.Third,there
provides a flow-chart illustrating the steps used in computing
is often a need to compare numerous potential constituents of
the comparisons to regulatory or health based groundwater
concern to criteria or background, at numerous sampling
protection standard (GWPS) in assessment and corrective
locations. By chance alone there will be exceedances as the
action environmental monitoring programs.
numberofcomparisonsbecomeslarge.Thestatisticalapproach
to this problem can insure that false positive results are
5. Significance and Use
minimized.
5.1 The principal use of this standard is in assessment,
5.4 Statistical methods for detection monitoring have been
compliance and corrective action environmental monitoring
wellstudiedinrecentyears(seeGibbons,1994a,1996,USEPA
programs (for example, for any facility that could potentially
1992 (2, 4, 5)andPracticeD6312,formerlyPS64-96authored
contaminate groundwater). The significance of the guidance is
by Gibbons, Brown and Cameron, 1996). Although equally
that it presents a statistical method that allows comparison of
important, statistical methods for assessment monitoring,
groundwater data to regulatory and/or health based limits.
Phase I and II investigations, on-going monitoring and correc-
5.2 Of course, there is considerable USEPA support for
tive action monitoring have received less attention, (Gibbons
...
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