guide to conducting well pumping tests - guide to... · the test (i.e., person responsible for the...
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3.Extendthewellcasingtoatleast12inches(0.30meters)abovethefinishedgroundlevel(seeFigure5).Inareaswithsnowconditions,astickupheightof24to36inches(0.6to0.9meters)isconsideredmoreappropriate.Beforethisisdone,theconditionandtypeofthewellcasingmustbechecked.Ifthewellhassteelcasing,anycorrodedsectionsshouldberemovedbeforeextendingthecasing.Extendingthesteelcasingcanbedonebythreadingorweldingametalcasingextensiontotheexistingwellcasing.Alternatively,apitlessconnectororrigidcouplershouldbeusedtojointheexistingwellcasingtothecasingextension.IftheexistingcasingisPVC,solventweldthePVCcasingextensiontotheexistingcasing.Allnewjointsmustbewatertight.
4. Installapitlessadapter(seeFigure6)ontothenewextendedcasingtoprovideasealedwaterlineentryatadepthsothatthewaterlinesareprotectedfromfreezing.Thepitlessadaptorshouldbeconstructedofcorrosionresistantmaterialssuchasbrass(seeFigure7).Thepumpandanyassociatedpipingmustbere-installed,including
aproperlyattachedconduitforelectricalworks.4 – Dig to uncover tankOncelocated,youwillprobablyonlyseethetopoftheseptic
tank(therestofthetankwillbeburied).Thetopoftheseptictankisnormallyaboutthesizeofa1.2mx2.4m(4x8foot)sheetofplywood.Septictankscanbeconcrete,plasticorfibreglassandeitherrectangular,sphericaloroblonginshape.Thelighterplasticorfibreglasstanksaresometimestheonlyfeasibleoptionforruralareas.Thelidofanewertank(seeFigure4)isoftenlocatedcentrally,whereasmanyoldertanks(seeFigure5)haveconcreteorwoodslabscoveringtheentiretop(generallytwoorthreelidslocatedovertheinletandoutletofthetankandonelargelidasacleanout).Thelidwillgenerallybewithinonemeter(approximatelythreefeet)ofthegroundsurface,butsometimescanbefoundmuchdeeper.
Alwayslookforgas,electrical,waterandutilitylinesbeforedigging.
Water Stewardship Information Series
Guide to Conducting Well Pumping Tests
PhotosbyVickiCarmichael,JimFyfeandMikeSimpson
ISBN 978-0-7726-7033-5
Further information and resources on pumping tests
Reference Books and Reports
Sterrett R. J., 2007. Groundwater and Wells,3rdedition.NewBrighton:JohnsonScreens
Allen, D.M., 1999. An assessment of the methodologies used for analyzing hydraulic test data in British Columbia. Queen’sPress.
Internet Resources
Ministry of Environment Pumping Test Report form-www.env.gov.bc.ca/wsd/plan_protect_sustain/groundwater/brochures_forms.html
Guidance document on conducting pumping tests for wells requiring a Certificate of Public Convenience and Necessity (CPCN)-www.env.gov.bc.ca/wsd/plan_protect_sustain/groundwater/library/eval_well/index.html
Checklist for Pumping Test Reports in Support of Certificate of Public Convenience and Necessity-www.env.gov.bc.ca/wsd/plan_protect_sustain/groundwater/library/eval_well/well-07.htm
Listing of Groundwater Consultants in BC-www.env.gov.bc.ca/wsd/plan_protect_sustain/groundwater/library/consultants.html
Provincial registry of qualified well drillers-www.env.gov.bc.ca/wsd/plan_protect_sustain/groundwater/wells/applications/well_drillers_reg.pdf
Provincial registry of qualified well pump installers-www.env.gov.bc.ca/wsd/plan_protect_sustain/groundwater/wells/applications/pump_install_reg.pdf
BC Water Resource Atlas for information on aquifers and wells-www.env.gov.bc.ca/wsd/data_searches/wrbc/index.html
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Table of Contents
What’sthedifferencebetweenawellyieldtestandapumpingtest?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Whenarepumpingtestsneeded?. . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Whocanconductapumpingtest?...........................3
Whatarethekeythingstoconsiderwhendesigningandplanningapumpingtest?. . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Whattimeofyearshouldapumpingtestbedone?. . . . . . . . . . . 4
Aretherenaturalvariationsinthegroundwaterlevels? . . . . . . . . 4
Shouldotherwellownersbenotifiedaboutthepumpingtest? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Whattypeofpumpshouldbeusedandatwhatdepthshoulditbeplaced?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Howmuchtimewillthepumpingtesttake? . . . . . . . . . . . . . . . . . . 6
Howisthepumpingrateselected? . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Howisthepumpingratecontrolledandmeasured?..........7
Howandatwhatintervalswillchangesinwaterlevelsbemeasured? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Whenshouldneighbouringwellsand/orstreamlevelsbemeasured? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Howisthepumpedwaterdischarged? . . . . . . . . . . . . . . . . . . . . . . 14
Isawatersamplerequiredforanalysis? . . . . . . . . . . . . . . . . . . . . . . 15
Aretherespecialconditionstobeawareofwhenconductingorinterpretingthepumpingtest? . . . . . . . . . . 16
Whocaninterpretpumpingtestdata?. . . . . . . . . . . . . . . . . . . . . . . 18
Whatshouldbeinapumpingtestreport? . . . . . . . . . . . . . . . . . . . 18
setting,pumpingrates,methodofflowmeasurement, observationsmadeduringthepumpingtest,durationof thetest,availabledrawdown,specificcapacity,methodof waterlevelmeasurementsandwaterlevels/timesrecorded duringthepumpingtestandrecoveryperiod;
• analysisandassessmentofthepumpingtestdataincluding anassessmentofthelong-termsustainableyieldand potentialimpactstoneighbouringwellsand/orstreams;
• thequalifiedprofessional’sopinionontheshortand long-termcapacityofthewellanditsabilitytomeetthe applicableproductioncriteria(e.g.,subdivisionby-lawfor privatesources,projecteddemandforwatersystems);
• assessmentofthewaterqualityresults,includingcopiesof laboratoryresults;and
• signatureandprofessionalsealofthequalifiedprofessional responsibleforthereport.
19
Thisguideprovidesgeneralinformationandguidanceonbestpumpingtestpracticesforqualifiedwelldrillersandqualifiedwellpumpinstallers.Inaddition,theguideoffersgeneralinformationtodevelopersandlocalgovernmentsonthepumpingtestrequirementsforprovingupwatersupplies(i.e.,todetermineifsufficientgroundwaterisavailableforresidentialdevelopments)andanexplanationofthebenefitsofaproperlyconductedpumpingtest.Thisguideisnotmeanttobeasubstituteforprofessionalguidanceandtheappropriatestandardsofcare.
What is the difference between a well yield test and a pumping test?
Awell yield testisashort(approximatelyonehour)flowtest,usuallydonebyaqualifiedwelldrilleroncethewelliscompletedtoprovidearoughestimateofthewell’syield.Itisgenerallyrecordedinthewellconstructionreportbythedriller.Wellyieldtestsaredoneusingbailing1orairlifting2methods.Wellyieldtestsarenotasreliableasapumpingtestinthefollowingsituations.
• whenwellyieldislow(e.g.typicalbedrockwell);
• wheremaximumyieldfromthewellisrequired;
• whenreliableestimatesofaquiferpropertiesareneeded; and
• whenassessingimpactsofproposedpumpingon neighbouringwells.
Apumping testisapractical,reliablemethodofestimatingwellperformance,wellyield,thezoneofinfluenceofthewellandaquifercharacteristics(i.e.,theaquifer’sabilitytostoreandtransmitwater,aquiferextent,presenceofboundaryconditionsandpossiblehydraulicconnectiontosurfacewater).Apumpingtestconsistsofpumpinggroundwaterfromawell,usuallyataconstantrate,andmeasuringwaterlevelsinthepumpedwellandanynearbywells(observationwells)orsurfacewaterbodiesduringandafterpumping(seeFigure1).ThesedataareusedtoplotdrawdownandrecoveryasshownonFigure2.Pumpingtestscanlastfromhourstodaysorevenweeksinduration,dependingonthepurposeofthepumpingtest,buttraditionalpumpingteststypicallylastfor24to72hours.
professional,pumpingshouldbestoppedifintrudingsaltwatercouldaffectthewaterqualityinthecoastalaquifer.
Who can interpret pumping test data?
Interpretationofpumpingtestdatashouldbedonebyaqualifiedprofessionalwithexpertiseinhydrogeology,especiallyinthefollowingsituations:
• whenrequiredbyanapprovingagency;
• wherethemaximumwellyieldisneeded;
• toassessimpactsofthepumpingwell;or
• whenestimatesofaquiferpropertiesareneeded.
Wherewellsaretestedsolelytoprovidegreaterconfidenceinthedriller’sestimatedyield,aqualifiedwelldrillerorpumpinstallerwithcompetencyinpumpingtestinterpretationmaybeabletointerpretthepumpingtestdata.
What should be in a pumping test report?
Theformalreportforapumpingtestshouldcontainthefollowing:
• informationonthewell(thewellconstructionreport,typeofwell andadiagramshowingthewell’slocationontheproperty,etc.);
• informationonfieldproceduresandpersonnelinvolvedin thetest(i.e.,personresponsibleforthepumpingtest,such asaqualifiedwellpumpinstaller)
• informationonthehydrogeologicsetting,including referencestomappedaquifers,whenavailable;
• pumpingtestinformationincludingthedateofthe pumpingtest,alldataonthepumptype,depthofpump
Static Water Level
Flow of Water to Well
PumpingWater Level
EncroachingSalt Water
Figure 11. Pumping test of a well adjacent to the ocean.
1Waterisremovedfromthewellinacylindricalbailerloweredfromthedrillingrigmast.2Compressedairisinjectedintothewelltoblowairandwateroutofthewell.
1 18
Figure 1. This figure shows the impact of a pumping well on the water level and on a neighbouring well (observation well) in an unconfined aquifer. As the water is pumped from the well, the original water level lowers, i.e., drawdown in the well. A cone of depression is formed in the aquifer around the pumping well as the water level declines due to pumping. Note that drawdown in the observation well is much less than in the pumping well.
Pumpingtestwaterlevelmeasurementsshouldbemadeprior
to,duringandimmediatelyfollowingthepumpingperiord(see
Figure2).Theinformationcollectedduringtherecoveryperiodis
usedtoverifytheresultsofthepumpingtest.
Figure 2. Graph showing the different phases of a constant rate pumping test – the pumping phase and the recovery phase.
Aqualifiedprofessionalhydrogeologistshouldbeconsultedifthemajorwater-bearingfracture(s)arenotknown.
Small unconsolidated (sand and gravel) aquifers(e.g.,coveringuptoafewkm2inarea)havealimitedstorageandrechargecapacityandareoftenboundedbylowpermeabilitydepositssuchassilt,clay,tillorbedrock(seeFigure10).Thedrawdownbehaviourintheearlypartofthepumpingtestmaygiveafalselyoptimisticimpressionofthelong-termyield.Theaquifer’slimitsarereachedwhenthedrawdownrateincreasesnoticeably(i.e.,animpermeablegeologicboundaryorbarriermayhavebeenreached).Wellspumpedincoastal aquifershavethepotentialforsaltwaterintrusion,particularlywherepumpingoccursonoceanwaterfrontproperties(seeFigure11).Inthiscase,aqualifiedprofessionalhydrogeologistshouldbeinvolved.Monitoringaparameterlikespecificconductancethroughoutthepumpingtestwillindicatewhethersaltwaterintrusionisoccurringduringthetest.Forexample,whenspecificconductancehasrisentogreaterthan1,000microSiemenspercentimetre(μS/cm)whichisequivalentto~250mg/Lofchloride,itislikelysaltwaterintrusionisbeinginitiated.Specificconductancecanbemonitoredusingaspecificconductanceprobeormeter.Aqualifiedprofessionalshouldbeconsulted.Thequalifedprofessionalwilldesignthepumpingtestanddeterminewhethersentinelorobservationwells(monitoringwellslocatedbetweentheforeshoreandfaultsorfracturezonesadjacenttoseawaterandthepumpingwell)shouldbeinstalledormonitored,aswellastheparameterstomonitorwherethereisareasonableconcernaboutsaltwaterintrusion.Ontheadviceofaqualified
Cone ofDepression
PumpingWater Level
PumpingWell
ObservationWell
Original (Static)Water Table
Distance from Pumping Wellto Observation Well
DrawdownPumping Rate
Land Surface
Aquifer
Aquitard
Wat
er D
epth
Bel
ow O
rigin
alPr
e-Pu
mpi
ng S
tatic
Wat
er L
evel
(met
res)
Elapsed Time Since Start Of Pumping (minutes)
PumpShutdown
PumpStart-up Pumping
PhaseRecoveryPhase
Original StaticWater LevelDrawdown
Recovery
PumpingWater LevelStatic Water
Level
Aquifer BEDROCK
Figure 10. Drawdown behaviour in small unconsolidated unconfined aquifer bounded by bedrock.
217
When are pumping tests needed?
Wellscanbepumptestedsolelytoprovideagreater
confidenceinthedriller’sestimatedwellyield.Thesetestsare
typicallyshorterinduration(4to12hours)andarecommonly
doneondomesticorsingle-residencewells.
Longerdurationpumpingtestsarecommonlyrequiredto:
• proveupwaterquantityunderlocalgovernmentbylawsfor
newresidentialdevelopmentsorregulatoryrequirements,
e.g.CertificateofPublicConvenienceandNecessity(CPCN);
• determinethemaximumsustainablewellyield;
• assessimpactsonneighbouringwellsorwaterbodiessuch
asstreamsfromtheproposeduseofthewell;and/or
• obtainaquiferpropertiessuchaspermeabilityand
boundaryconditions.
Who can conduct a pumping test?
UnderSection70oftheWater Act,thefollowingpersonscan
conductapumpingtest:
• aqualifiedwelldriller;
• aqualifiedwellpumpinstaller;or
• apersonworkingunderthedirectsupervisionofthe
qualifiedwelldriller,qualifiedpumpinstallerorqualified
professionalwithcompetencyinhydrogeology.
Aqualifiedprofessional3withcompetencyinhydrogeology
shouldberesponsibletoplan,design,implementandinterpret
thepumpingtestinthefollowingsituations:
• whereapumpingtestforawellisrequiredbyanapproving
agency;or
• wheretheyieldofthewellneedstobemaximized;or
• whendataneedstobeinterpreted,forexample:
- whenthereisaneedtoassesstheimpactofthepumping
wellonnearbysurfaceandgroundwaterresources;and
- whenestimatesofanaquifer’spropertiesarerequired.
toanalyze.Consultaqualifiedprofessionaliffieldmeasurementsarerequired(e.g.pH,temperature,conductivity,alkalinity,dissolvedoxygenandturbidity).Consultthelaboratoryforsamplingprocedures,samplingbottles,coolersandholdingtimesfordeliveryofwaterqualitysamplestothelaboratory.
Are there special conditions to be aware of when conducting or interpreting the pumping test?
Ifhydrofracturing(fracking)hasbeenusedtoincreasetheproductivityofthewell,itmayadvisabletowaituptoaweekbeforeconductingthepumpingtest.Hydrofracturinguseslargevolumesofwater(upto2,000U.S.gallonsor7.6m3/min)thateitherneedtobepumpedoutordissipateintothesurroundingrockbeforethepumpingtestisdone.Dissipationeffectsofhydrofracturingcanbecheckedbymeasuringthewaterlevelimmediatelyafterthehydrofracturinghasoccurredandoversubsequenthoursordays.
Infractured bedrock aquifersitisimportanttoknowthedepthofanymajorwater-bearingfracture(s)(usuallyfoundinthedriller’swellconstructionreport)to:
• ensurethewaterlevelisnotdrawndownbelowthe fractureduringthepumpingtest;and
• enablemeaningfulinterpretationofthepumpingtestand thewell’ssustainableyield.
Figure 9. Conveyance channel constructed to reduce erosion from discharged pumped water.
3QualifiedprofessionalswhoareregisteredwiththeAssociationofProfessionalEngineersandGeoscientistsofBritishColumbia
3 16
Inanurbansetting,thepumpedwatermaybedischargedtoastormsewerbutlocalgovernmentapprovalmayberequiredifthepumpingrateisaboveacertainthreshold.
Forlargeproductionwells,wheredisposalwillbetoanadjacentwaterbodyorwetland,thelocalMinistryofEnvironmentandDepartmentofFisheriesandOceans(DFO)officesmustbeadvisedasanapprovalmayberequired.Evenifthewellwaterispotable,dischargingthewatertoanadjacentwaterbodycouldmobilizesedimentandimpactfishhabitat.Toeliminateorminimizethis,aproperconveyancechannelshouldbeused.Ensurethechanneliseitherrock-linedorvegetatedtopreventerosion(seeFigure9)andthattheoutlettothereceivingwaterbodydoesnotharmfishhabitatbydestabilizingstreambanksorerodinginstreamhabitatsuchasriparianvegetation,riverbanksorbeds.
Is a water sample required for analysis?
Apumpingtestisagoodtimetocollectwaterqualitysamplestoassessthechemical,physicalandbacterialpropertiesofthewater.Watersamplesshouldbecollectedwhenconditionshavestabilized(usuallyneartheendofthepumpingtest).Sanitizethesamplingportorbibwithisopropylalcoholoradilutechlorinesolutionbeforecollectingasample,takingcarenottointroducethesanitizationfluidtothewatersample.Consultwiththequalifiedprofessionalresponsibleforthetestortheapprovingauthority(regionalhealthauthorityorlocalgovernment)todeterminewhatwaterqualityparameters
What are the key things to consider when designing and planning a pumping test?
Designingandplanningapumpingtestiscriticalpriortotesting.Lackofplanningcanresultindelays,increasedcosts,technicaldifficultiesandpoororunusabledata.
Somethingstoconsiderinthepre-planningstageare:
4 timeofyearthepumpingtestshouldbedone
4naturalvariationsinthegroundwaterlevelsthatoccur duringthetestthatneedstobeaccountedfor
4informingotherswhomaybeaffected
4depthofpumpsettingandtypeofpump
4pumpingduration
4pumpingrate
4controlandmeasurementofthepumpingrate
4frequencyofmeasurementsofthewaterlevels
4measuringwaterlevelsinneighbouringwellsand/or streams
4dischargeofpumpedwater
4collectionofwatersamplesforwaterqualityanalysis
4specialconditionstobeawareof,e.g.saltwaterintrusion incoastalaquifers
What time of year should a pumping test be done?
Anapprovingagencymayrequireapumpingtesttobeconductedduringalowrechargeperiod(e.g.dryperiod)orothertimeoftheyear.Forfracturedbedrockandotherlow-yieldingwells,apumpingtestshouldbedoneduringadryperiodwhenwatertablesareattheirlowestlevelstoallowforaconservativeestimateoflong-termyield.OptimaltimesfortestinginB.C.aresummerandfallincoastalareasandfallandwinterintheInterior.
Are there natural variations in the groundwater levels?
Naturalvariationsinwaterlevelscausedbytidal,riverandbarometricchangescaninfluencewaterlevelsduringpumpingandrecovery.Evendiurnalvariationcanoccurinshallowwater
Figure 8. Discharge pipe for a large volume pumping test in Merritt.
15 4
tablesduetothegreatdifferencebetweennightanddayevapotranspiration.Pre-pumpingandpost-pumping(recovery)waterlevelmeasurementsinthepumpingwellandanyobservationwell(s),canbeusedbythequalifiedprofessionalhydrogeologisttofilteroutnaturalfluctuations.
Should other well owners be notified about the pumping test?
Ifthepumpingtestinvolvespumpingalargevolumeofwaterforalongduration(e.g.,24to72hours),ownersofneighbouringwells(i.e.,anywellwithin300feetor100metersofthepumpingwell)shouldbenotified.Pumpingoftheseneighbouringwellsduringthepumpingtestcouldaffecttheresultsofthetest,especiallyiftheneighbouringwellsaretobeusedasobservationwells.
What type of pump should be used and at what depth should it be placed?
Thepumpisnormallyplacedabovethewellscreentomaximizetheamountofdrawdownforthepumpingtest.Theintakeofthepumpshouldnotbeplacedwithinthewellscreenasthismaycauseincreasedvelocitiesresultinginsandingandpotentialcasingdeteriorization,alongwithscreenplugging.Forbedrockwellsthepumpissetatorjustabovetheuppermostmajorwater-bearingfracture(refertothedriller’swellconstructionreport).
Thereareseveralfactorstoconsiderwhendeterminingthetypeofpumptouseandthedepthatwhichitshouldbeset,including:
• welldiameter;
• desiredpumpingrate;
• totaldynamicheadincludingthepumpingwaterlevel,the abovegroundhead(ifapplicable)andallfrictionlossesin thecasing,pipes,fittings,etc.;
• reliabilityofpowersource;and
• horsepowerrequirements.
Aswell,considerwhetherthepumpissubmersibleandhasvariablespeeds.Powerneedstobecontinuouslyavailabletothepumpduringthetest.Ifpowerisinterrupted,itmaybenecessarytoterminatethetest,allowthewelltorecoverandrunanewtest.
• presenceofsedimentsinthepumpedwater;
• presenceofanysmellfromthedischargedwatere.g., rottenegg(H2S);and
• evidenceofcascadingwaterinsidethewell.
When should neighbouring wells and/or stream levels be measured?
Monitoringofwaterlevelsinneighbouringwells(observationwells)and/orstreamstoassesstheimpactofthepumpingwellshouldbespecifiedbythequalifiedprofessional,especiallywhere:
• thepumpingrateishigh;
• thereareregulatoryrequirements;and/or
• neighbouringwellsorstreamlevelscouldbeimpactedby thepumping.
Existingwellsmaybeusediftheyarewithinthesameaquiferformationandthewellownerhasprovidedconsent.Waterlevelsinatleastoneobservationwellneedtobemonitoredifanaquiferstorativityvalueisrequired.Theobservationwellshouldnotbepumpedduringthepumpingtest.Ifthisisunavoidable,thetimesandpumpingratesshouldberecorded.Often,waterlevelsmaynotvaryasmuchinobservationwellsastheywillinthepumpingwell,thereforeitisimportanttoestablishreliablebackgroundconditionspriortothepumpingtest.
How is the pumped water discharged?
Properdischargeofthepumpedwaterisimportanttoensurethereisnodamageduetoerosion,floodingorsedimentdepositsinstreams(seeFigure3).Itisimportanttoassessthevolumeofpumpedwater,ifstorageortreatmentareneeded,anddisposalalternativesearlyintheplanningprocess.Forlanddisposal,directthewaterfromthepumpingwellinadown-hilldirectionatasufficientdistancefromthepumpingwell.Thiswillpreventre-circulationofthepumpedwaterintothewelloraquiferandwillpreserveboththepumpingwaterlevelandtheintegrityofthepumpingtest.Severalhundredfeetormoreofdischargelinemaybeneeded(seeFigure8).Iftheaquiferisconfined(refertothelithologysectionofthedriller’swellconstructionreport),thewatercangenerallybeconveyedashorterdistanceawayfromthepumpingwellwithoutaffectingthepumpingwaterlevel.
5 14
loadingoftheaquiferduetoheavyequipment(trains,forexample).Itisimportanttoaccuratelynotedowndataandtorecordeventsthatoccurduringthepumpingtest.Keypointstonoteareasfollows:
• changesinthepumpingrate;
• anyperiodiccyclingonandoffofwellpumpsinthearea;
• staffchangesduringthepumpingandrecoverytests;
• ifandwhenequipment(e.g.,soundingprobe)was changedduringthetest;
• ifthepumpingtestwasconductedinawellfield,orwhen otherwellswerepumping;
• whenthepumpwaspulledout;
• timesandpumpingratesofanyobservationswells;
• precipitationthatoccurredduringthetest;
obServATIon Well*DurIng pumpIng:
• Every10minutesforthefirst100minutes**
• Every50minutesfrom100minutesto500minutes**
• Every100minutesfrom500minutesto1000minutes**
• Every500minutesfrom1000minutesto5000minutes**
• Every24hoursfrom5000minutesonward**
• Finalwaterlevelmeasurementjustpriortoendofpumping
DurIng reCovery:
• Every10minutesforthefirst100minutesafterendof pumping***
• Every50minutesfrom100minutesto500minutesafter endofpumping***
• Every100minutesfrom500minutesto1000minutes afterendofpumping***
• Every500minutesfrom1000minutesto5000minutes afterendofpumping***
• Every24hoursfrom5000minutesonward***
*If the observation well is located in close proximity to the pumping well it may be possible to take more frequent measurements
**Time since the real start time of the pumping or time immediately after a step change in pumping
*** Not required if time is beyond the specified duration of recovery measurements
How much time will the pumping test take?
Thedurationofthepumpingtestdependsonthepurposeofthewell,thetypeofaquiferandanypotentialboundaryconditions.Aquifertypesandpotentialboundaryconditionscanbeobtainedfrom:
• wellconstructionreportsforthepumpingwellandany neighbouringwell(s);
• informationontheaquiferandsurfacewaterbodies,such aslakesorriversinthevicinityofthewell;and
• qualifiedwelldrillersandprofessionalhydrogeologists.
Minimumdurationsoftraditionalpumpingtestsare24to72hoursunlessstabilizationoccurs.Localby-laws,regulatoryrequirementsoraqualifiedprofessionalcanstipulateminimumpumpingdurations.Durationisgenerallylonger,e.g.72hours,forbedrockwellsduetouncertaintiesassociatedwithbedrockaquifers,and48hoursforwellscompletedinunconfinedaquifersduetothedelayedreleaseofwaterasthewaterlevelgoesdownor“delayedyield”effect.
How is the pumping rate selected?
Thewellshouldbepumpedatorabovetherequiredyieldandthewellshouldnotberatedabovethepumpingrateusedduringthetest.
Otherconsiderationsforsettingthepumpingrateare:
• wellsshouldnotbepumpedataratehigherthanthe manufacturer’srecommendedtransmittingcapacityforthe wellscreentoavoiddamagetothewellandaquifernear thewell(checkthewellscreendetailsinthedriller’s constructionreportandrefertothesectiononentrance velocitiesinGroundwaterandWells);
• wellscompletedinunconsolidatedaquifers(e.g.,sandsand gravels)withanopenbottom(e.g.,nowellscreen)should notbepumpedataratewhichcouldcausetheheavingof aquifermaterialsintothewellandlockingupthepump;and
• bedrockwellsshouldnotbeoverpumped(i.e.,water levelsshouldnotbedrawndownpasttheuppermost waterbearingfracture)becauseturbulenceatthe borehole/wellinterfacecoulddamagetheaquifer formationandresultinexcessiveturbidityinthewater
13 6
Aqualifiedprofessionalinvolvedinthedesignofapumpingtestmaydetermineastepdrawdowntestisneededbeforetheconstantratepumpingtestisconducted.Ifastepdrawdowntestisdone,thewellshouldbe“rested”betweenthesteptestandtheconstant-ratepumpingtesttoallowforthewaterleveltorecover.Aqualifiedprofessionalshoulddeterminetheoptimumpumpingratefortraditionalpumpingandstepdrawdowntests.
Anotherconsiderationwhenselectingthepumpingrateisboreholestorage(waterstoredinthewellcasing).Inmostcases,forashortperiodafterpumpingbegins,allthepumpedwatercomesfromboreholestorage.However,insomecases,wherethewellisdeepandtherateofintendeduseislow,theboreholestoragemayneverbepumpedout.Intheseinstances,thepumpingratecanbeinitiallysethigherthantherateofintendedusetoremovetheboreholestorageandthenthepumpingrateiscutbacktomatchtherateofintendeduse.
How is the pumping rate controlled and measured?
Controlofthepumpingrateduringthetestisimportantasitallowsforreliabledrawdowndatatobecollectedtodeterminetheyieldofthewellandaquiferproperties.Controllingthepumpingratebyadjustingthepumpspeedisgenerallynotsatisfactory.Itisbettertouseagatevalvetoadjustthepumpingratetokeepitconstant.Thedischargepipeandthevalveshouldbesizedsothatthevalvewillbefrom½to¾openwhenpumpingatthedesiredrate.Thevalveshouldbeinstalledatasufficientdistancefromtheflowmeasurementdevicetoavoidanyimpactsfromturbulence.Measuringthedischargeofpumpedwateraccuratelyisalsoimportantandcommonmethodsofmeasuringdischargeincludetheuseofanorificeplateandmanometer(seeFigure3),aninlineflowmeter(see
Goodrecordkeepingiskeytointerpretingthedatacollectedfromapumpingtest.Occasionally,fluctuationsinthewaterlevelwilloccur,duetonearbypumpingofanotherwell,suddenrainfallevents,tidalvariationsorchangesinsurface
TaBle 1Recommended minimum intervals for water level
measurements for pumping tests.
Well beIng pumpeDDurIng pumpIng:
• Everyminuteforthefirst10minutes**
• Every2minutesfrom10minutesto20minutes**
• Every5minutesfrom20minutesto50minutes**
• Every10minutesfrom50minutesto100minutes**
• Every20minutesfrom100minutesto200minutes**
• Every50minutesfrom200minutesto500minutes**
• Every100minutesfrom500minutesto1000minutes**
• Every200minutesfrom1000minutesto2000**
• Every500minutesfrom2000minutesto5000minutes**
• Every24hoursfrom5000minutesonward**
• Finalwaterlevelmeasurementjustpriortoendofpumping
DurIng reCovery:
• Everyminuteforthefirst10minutesafterendofpumping***
• Every2minutesfrom10minutesto20minutesafterendof pumping***
• Every5minutesfrom20minutesto50minutesafterendof pumping***
• Every10minutesfrom50minutesto100minutesafterend ofpumping***
• Every20minutesfrom100minutesto200minutesafterend ofpumping***
• Every50minutesfrom200minutesto500minutesafterend ofpumping***
• Every100minutesfrom500minutesto1000minutesafter endofpumping***
• Every200minutesfrom1000minutesto2000minutesafter endofpumping***
• Every500minutesfrom2000minutesto5000minutesafter endofpumping***
• Every24hoursfrom5000minutesonward***
Figure 3. Water discharge during a pumping test
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Figure4),aninlinecalibratedpitottube,acalibratedweirorflume,orobservingthelengthoftimetakenforthepumpedwatertofillacontainerofknownvolume(seeFigure5).Theflowmeasurementdeviceshouldbecompatiblewiththeexpectedpumpingrate.Calibratedin-lineflowmetersandorificeweirsareusedtomeasurepumpingratesforhighproductionwells.Ifanorificeweirisused,thedischargepipeshouldbestraightandlevelforadistanceofatleastsixfeet(1.8meters)beforethewaterreachestheorificeplate.Forrelativelylowpumpingrates(e.g.<10USgpmor<0.6L/s),afivegallon(19L)bucketorgraduatedcylinderandastopwatchispracticalformeasuringflow(seeFigure5).
TheMinistryofEnvironmenthasdevelopedaPumpingTestReportformtorecordinformationanddatacollectedfromthepumpingandrecoverytest–www.env.gov.bc.ca/wsd/plan_protect_sustain/groundwater/brochures_forms.htm.AnExcelspreadsheethasalsobeendevelopedtorecordthetestdrawdownandrecoverydata.Therecommendedminimumintervalsforwaterlevelmeasurementsinboththepumpingandobservationwell(s)duringthepumpingandrecoveryphasesisshowninTable1aswellasonthebackofthePumpingTestReportform.Datacollectionattheminimumspecifiedintervalswillestablishconditionsthataffectgroundwaterflowtothewell.Itmaynotalwaysbepossibletotakethedrawdownmeasurementsatthespecifiedintervals.Inthesecases,waterlevelreadingswouldberecordedwiththeactualtimethedrawdownwasrecorded.
Monitoringwaterlevelrecoveryafterthepumphasstoppedisveryimportantbecauseitaidstheinterpretationofthepumpingtest.Recoverydataalsotendtosmoothoutvariationsinthepumpingrate,shouldvariationsoccur.Toobtainaccuraterecoverydata,acheckvalveshouldbeinstalledatthebottomofthepumpdischargepipetoeliminatebackflowofwaterintothewell.
Typically,thedurationoftherecoverytestisdirectedbythequalifiedprofessional.Ataminimum,recoverywaterlevelsinthewellshouldbemonitoredforthesamedurationofthepumpingtestoratleastuntil90percentrecoveryhasbeenachieved.Thepumpshouldnotberemovedfromthewelluntilthewaterlevelhasreturnedto85-90percentofthepre-pumpingorstaticwaterleveloruntilthesupervisingqualifiedprofessionalindicatesthepumpcanberemoved.However,generallyfora24-hourpumpingtest,90percentrecoveryoccurswithintwotothreehoursafterthepumpisstoppedandthepumpcanthenberemoved(thiseventshouldberecordedonthedatasheet).Ifthewaterdoesnotrecoverwithinthesametimedurationofthepumpingtest(e.g.,24hours)thewaterlevelshouldbemonitoreddailyforanadditionalweek.
Ifthewaterdoesnotreturnto90-95percentofthestartingwaterlevelafteraweek,thetestpumpingrateislikelyhigherthantheaquifer’scapacitytosustainthisrateandfurthertesting(i.e.,longerpumpingtimeandlowerpumpingrate)mayberequired.Ifthishappens,aqualifiedprofessionalshouldinterpretthepumpingtestandrecoverydataandrecommendacourseofaction.
Figure 5. A five gallon bucket (~20 liters) and a stop watch can be used to estimate low pumping rates.
Figure 4. In-line flow meter.
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How and at what intervals will changes in water levels be measured?
Priortothetest,allwatermonitoringinstrumentsshouldbecheckedtobesuretheyareworkingproperly.Freshreplacementbatteriesshouldbeavailableforallmanualsoundingprobes.Beforethetestbegins,synchronizethewatchesofallobserversanddatalogger’s“time-of-day”settings.Allstopwatchesshouldbestartedatthetimethepumpstartspumpingwater(orstoppedifdoingarecoverytest).
Establishinitialconditionsbymeasuringstaticwaterlevelsinthewellandanyobservationwell(s)foraperiodoftimebeforestartingthepumpingtest..Asageneralrule,theperiodofobservationbeforethestartofthetestshouldbeatleastoneweek.Allobserversshouldusethesamemeasuringpointonthetopofthewellcasingforeachwell.Ifstaticwaterlevelsintheaquiferarechangingduetorechargeorotherfactors,aqualifiedprofessionalshouldbeconsultedonestablishingthewaterlevelpriortothetest.
Asoundingtubeoraccesstube,typicallya¾”to1”(19to25mm)diameterPVCpipethatextendsfromthetopofthecasingdownto3to4feet(0.9to1.2meters)abovethepump,can
Duringaconstant-ratepumpingtestthepumpingratemustbemeasuredcorrectlyandrecordedregularly.Ingeneral,thelowerthepumpingrate,themoreaccurateandcarefultheflowmeasurementmustbe.Anunrecordedchangeofaslittleastwopercentinthepumpingratecanaffecttheinterpretationofthedata,i.e.,indicateafalsestabilizationoraboundarycondition.Atthebeginningofthetestthepumpingrateshouldbesetasquicklyandaccuratelyaspossibleandshouldremainconstantforthedurationofthetest.Forexample,thepumpingrateshouldnotvarybymorethanfivepercentandshouldgenerallybewithintwotothreepercentforhigherpumpingrates.Itisgoodpracticetomeasureandrecordpumpingratesfrequentlyatthebeginningofthetest(every15minutesforthefirsthour)andhourlythereafterfortestsofonetothreedays.Checkingthepumpingrateallowsforadjustmentstobemadeiftheratehasdrifted,andconfirmstheselectedpumpingratehasbeenmaintained.Adjustmentstothepumpingrateshouldberecordedalongwiththemeasuredrateandwaterlevelsduringthepumpingtest.Goodrecordkeepingiskeytointerpretingthepumpingtestresults.
beusedtotakewaterlevelmeasurementswithouttheprobegettingtangledinthepumpwiring.Waterlevelscanbemeasuredusingwaterlevelprobes(seeFigure6)orpressuretransducers(seeFigure7).Ifpressuretransducersareused,selecttypesthatcovertherangeofdrawdownanticipated.Pressuretransducersshouldbecalibratedbeforeandafterthetest.Takemanualreadingsofthewaterlevelpriortoandfollowingthetestandperiodicallythroughoutthetesttoconfirmthewaterlevelmeasurementsbythetransducer.Measurementsshouldbetakentothenearest1/8”or1/4”(0.3to0.6cm).
Figure 7. A pressure transducer can be used for automatic measurement and recording of water level and temperature, specific conductance or other parameters during the pumping test.
Figure 6. Water level measurement using water level probe and sounding tube.
Sounding Tube
WellWater Level Probe
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