ASTM_D_6312_-_98_2012e1.pdf

Designation:D631298(Reapproved 2012)1Standard Guide forDeveloping Appropriate Statistical Approaches forGroundwater Detection Monitoring Programs1This standard is issued under the fixed designation D6312;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,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.1NOTEEditorial changes were made throughout in February 2012.1.Scope1.1 This guide covers the context of groundwater monitor-ing at waste disposal facilities.Regulations have requiredstatistical methods as the basis for investigating potentialenvironmental impact due to waste disposal facility operation.Owner/operators must perform a statistical analysis on aquarterly or semiannual basis.A statistical test is performed oneach of many constituents(for example,10 to 50 or more)foreach of many wells(5 to 100 or more).The result is potentiallyhundreds,and in some cases,a thousand or more statisticalcomparisons performed on each monitoring event.Even if thefalse positive rate for a single test is small(for example,1%),the possibility of failing at least one test on any monitoringevent is virtually guaranteed.This assumes you have done thecorrect statistic in the first place.1.2 This guide is intended to assist regulators and industryin developing statistically powerful groundwater monitoringprograms for waste disposal facilities.The purpose of thisguide is to detect a potential groundwater impact from thefacility at the earliest possible time while simultaneouslyminimizing the probability of falsely concluding that thefacility has impacted groundwater when it has not.1.3 When applied inappropriately,existing regulation andguidance on statistical approaches to groundwater monitoringoften suffer from a lack of statistical clarity and often imple-ment methods that will either fail to detect contamination whenit is present(a false negative result)or conclude that the facilityhas impacted groundwater when it has not(a false positive).Historical approaches to this problem have often sacrificed onetype 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 ratesapproach 100%.1.4 The purpose of this guide is to illustrate a statisticalgroundwater monitoring strategy that minimizes both falsenegative and false positive rates without sacrificing one for theother.1.5 This guide is applicable to statistical aspects of ground-water detection monitoring for hazardous and municipal solidwaste disposal facilities.1.6 It is of critical importance to realize that on the basis ofa statistical analysis alone,it can never be concluded that awaste disposal facility has impacted groundwater.A statisti-cally significant exceedance over background levels indicatesthat the new measurement in a particular monitoring well for aparticular constituent is inconsistent with chance expectationsbased on the available sample of background measurements.1.7 Similarly,statistical methods can never overcome limi-tations of a groundwater monitoring network that might arisedue to poor site characterization,well installation and location,sampling,or analysis.1.8 It is noted that when justified,intra-well comparisonsare generally preferable to their inter-well counterparts becausethey completely eliminate the spatial component of variability.Due to the absence of spatial variability,the uncertainty inmeasured concentrations is decreased,making intra-well com-parisons more sensitive to real releases(that is,false negatives)and false positive results due to spatial variability are com-pletely eliminated.1.9 Finally,it should be noted that the statistical methodsdescribed here are not the only valid methods for analysis ofgroundwater monitoring data.They are,however,currently themost useful from the perspective of balancing site-wide falsepositive and false negative rates at nominal levels.A morecomplete review of this topic and the associated literature ispresented by Gibbons(1).21.10 The values stated in both inch-pound and SI units areto be regarded as the standard.The values given in parenthesesare for information only.1This guide is under the jurisdiction ofASTM Committee D18 on Soil and Rockand is the direct responsibility of Subcommittee D18.21 on Groundwater andVadose Zone Investigations.Current edition approved Feb.15,2012.Published December 2012.Originallyapproved in 1998.Last previous edition approved in 2005 as D6312 98(2005).DOI:10.1520/D6312-98R12E01.2The boldface numbers given in parentheses refer to a list of references at theend of the text.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 1.11 This standard does not purport to address all of thesafety concerns,if any,associat