BS ISO BRITISH STANDARD 5667-20:2008 Water quality - Sampling - Part 20: Guidance on the use of sampling data for decision making Compliance with thresholds and classification systems ICS 13.060.45 BSi British Standards BSISO5667-20:2008 National foreword This British Standard is the UK implementation of IS0 5667-20:2008. The UK participation in its preparation was entrusted by Technical Committee EH/3, Water quality,to Subcommittee EH/3/6, Sampling (of technical committeeEH/3Waterquality). A list of organizations represented on this committee can be obtained on request to its secretary. This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Standard cannot confer immunity from legal obligations. This British Standard was Amendments/corrigenda issued since publication published under the authority of the Standards Policy and Date Comments Strategy Committee on 30April 2008 BSI 2008 ISBN9780580553523 BS ISO 5667-20:2008 INTERNATIONAL ISO STANDARD 5667-20 First edition 2008-03-15 Water quality Sampling - Part 20: Guidance on the use of sampling data for decision making Compliance with thresholds and classification systems QualitedeI'eau-Echantillonnage- Partie 2o: Lignes directrices relatives a I'utilisation des donnees d'echantillonnagepourla prise de decisionConformite avecles limitesetsystemesdeclassification Reference number ISO 5667-20:2008(E) ISO ii BSISO5667-20:2008 Contents Page Foreword iv Introduction vi 1 Scope 2 Summaryofkeypoints 3 Types oferrorandvariation 3.1 General.... 3.2 Analytical error... 3.3 Overalluncertainty 4 Activities..... 4.1 Estimationofsummarystatistics 4.2 Thresholds for water quality and compliance ... 4.3 Confidence of failure ................. 4.4 Methodsforthresholdsexpressedaspercentiles. 4.5 Non-parametricmethods..... 4.6 Look-up tables. 5 Definition of thresholds. 5.1 General...... 4 5.2 Ideal thresholds 14 5.3 Absolute limits. 5.4 Percentageoffailed samples 5.5 Calculating limits for effluent discharges.. 18 6 Declaring that a substance has been detected 19 7 Detecting change. 20 8 Classification..... 23 8.1 General..... 8.2 Confidence that class has changed.. 25 AnnexA (informative)Calculationofconfidencelimits.. 27 Annex B (informative) Calculation forthebinomial distribution... .29 Annex C (informative)Sample results with high error or reported as less than a limit of detection .....32 Bibliography.. ..34 ili BSISO5667-20:2008 Foreword Iso (the International Organization for Standardization) is a worldwide federation of national standards bodies InternationalElectrotechnicalCommission(lEC)onallmattersofelectrotechnicalstandardization. International Standards are drafted in accordance with the rules given in the ISO/lEC Directives, Part 2 adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75% of the member bodies casting a vote. rights. IsO shall not be held responsible for identifying any or all such patent rights. ISO5667-20waspreparedbyTechnicalCommittee ISO/TC147,Waterquality,Subcommittee SC6, Sampling (general methods). Iso 5667 consists of the following parts, under the general title Water quality -Sampling Part 1:Guidance on the designof samplingprogrammes and sampling techniques Part3:Guidanceonthepreservationandhandlingofwatersamples Part4:Guidanceonsamplingfromlakes, naturalandman-made Part 5:Guidanceon sampling of drinkingwater from treatment worksandpipeddistribution systems Part6:Guidanceon sampling of rivers and streams Part 7:Guidance on sampling ofwater and steam in boiler plants Part 8:Guidanceonthe samplingofwetdeposition Part9:Guidanceonsamplingfrommarinewaters Part10:Guidanceonsamplingofwastewaters Part 11: Guidance on sampling of groundwaters Part12:Guidanceonsamplingofbottomsediments Part13:Guidanceonsamplingof sludgesfromsewageandwatertreatmentworks Pa