Guide to Conducting Well Pumping Tests - GUIDE TO... · the test (i.e., person responsible for the pumping test, such as a qualified well pump installer) • information on the hydrogeologic

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

20

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

AMBER JONES

Highlight

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

AMBER JONES

Highlight

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**



• 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**







• Every200minutesfrom1000minutesto2000**


• Every24hoursfrom5000minutesonward**

• Finalwaterlevelmeasurementjustpriortoendofpumping

DurIng reCovery:

• Everyminuteforthefirst10minutesafterendofpumping***

• Every2minutesfrom10minutesto20minutesafterendof pumping***

• Every5minutesfrom20minutesto50minutesafterendof pumping***

• Every10minutesfrom50minutesto100minutesafterend ofpumping***






• 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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Documents

Guide to Conducting Well Pumping Tests - GUIDE TO... · the test (i.e., person responsible for the pumping test, such as a qualified well pump installer) • information on the hydrogeologic