II 2007 Johnson ,'>cJree11s All ed. a Weatherford CCillliJ n t ~ r1. Introduction and Acknu:>wlecla :n"'"'""'r 2.Occurrence of Groundwater and"'"""""""' GroundwaterFlow Permeameters Field Penneameters v 1 7 13 15 Hi 20 23 24 31 34 38 43 Sonic Water Production Method Methods Dual-\Vall Percussion Hammer llollow-Stem Groundwater or Fonnation Unconsolidatedl\1Ta1erials Hardness Bedrock Color Water Content Other Water"Level Data Software 1'he Borehole Environment Third 49 52 54 55 56 )7 "' 5'7 "' 57 61 63 66 68 70 72 7"1"75 76 76 80 80 81 82 8'1 ,k 83 83 85 89 97 Tableur Contents [(eat-Pulse Flow Meter f1uid Wen-Construction Evaluation llltroduction Chemical' " ' ~ - ~ "...."'" of GroundVi'ater Conservative Elements Dissolved Gases Radio:mu:lides Bar 108 Ill I 12 IJ 115 117 1.8 11.9 121 121 23 124 125 25 127 27 128 133 135 135 136 138 166 168 169 172 viiiGroundwater and Data Collection and Overview """'-"''""'''Flowin Confined and Um::ont1ned Transient F1ovvin Confined Vertical Infiltration and Filtei'-Puck 1 .ttw,F>nruand Well Loss "'"'''"'""'''"'Data Methods DirectMethods Air and Mud Numerical Codes Edition 177 1 179 179 I 184 190 190 197 198 198 202 211. 215 21.5 220 224 224 226 227 231 23 236 24:! 245 246 249 253 254 254 TableofCn1nt1'1of Steel Pressures for 9,H.Recommended Minimum Thickness for Carbon Steel Well Abbreviations and Svimhnl!ll Reference List Index Edition 725 733 741 745 747 753 775 795 societiesare asaresultof energyandmineral Theseevaluationsincludedetenninationof them ~ n ' ' ' " resource. Johnsona Weatherford company, for more than l 00 years has thewater-wellwithwellscree:ns, forthe A copy of.each issue of the Drillers ]oumal book'sDVD. 2Third and vVells.The editionwa!land itsrelease foundworldwide use-because il\Vas a handbook that could be taken into field. newthird editioni.s"'"'''-"""'"' Theof this thirdedition of Groundwater and Wells ratherthanthe-oretical.Thematerial of well of thebook. most '-LI\A.U.U.I!.,.IIl()[ Individual.pores in ''"'"',,.,.,, cmnhi.nedvolumeof the of isirreversible andcanlead unitsdosome water but which meet even modest demands associated with nuclear waste ......have SOIIlC low.To 2.Groundwater as wal:er-tahle or zero-gauge pressure. Groundwater also can occur water is isolated from the andtheconfined confined conditions. Conti ned materi al.s of low '"''"'"'"'"" in 2.2illustratesunconfinedand conditions .. Confi.nedalsoarereferredto artesianbecauseelevationof theviaterlevelintheis thanthebottom ofunitIfthepressureintheconfined issuftlcient that theelevation in awell isthan the the well is called aartesian welL In two primary environments: confined, 14Third H+ Where: P=pressure; yof water; g=acceleration ofand elevation above a certain datmR as statesunder conditions of sible fluid tainedpres:mre.The fromthemovementof thewater" if thewaterisallmvedtoelevationenergycanbe to or pressureAswater moves, it losesof its energy due to friction.This energycan bethe Pt + 2.Occurrence of 5 energy contained in aBernoulli "4'"'"'"'-'"" therefore can be +zl=+zl + yy pressure Groundvvater locationof lowertotal situation occurs in aarea; total 2.3 the water level in well Bis less than that the water Figure 2.3. The water level Ina well rises to the elevation of the mH1ra1.mc headtheat the intake end of the weltwater levelB Is the same because both wells terminate on the !ooten,tlalllnefrom C.W.Fetter, Jr. 2001). 16Groundwater the water table canseve.ral feet water and Theupper surface of the Perched water streams, and \\'Cl11>reduces the volume of water held in '"'"'' """"""'tiooCM Water levels in wellsscreened elevations in wens that are screened near the water water-tahle map orsurface.the 2, water rises. in a wen that calledUnder confined I.'UJilUlUI-'u"'" reoresemmg the artesian welL 'l'hestatic \Vater levelinthis case isabove the land surface can bemeasuredthe well nearlevel and thenpressure head withapressure gauge,For every pre:>ilure above the gauge. Justasinanunconfinedsurface in a eonfined isabletoriseand fallin responsetothevolume withintheWhenawellacon11ned of the unconfinedis created, water frontthe pores of an unconfinedis easy to under drained fron1Tile unconfined water is atpressure, so the volume of water drained from the volumethatexistsintheporesminusthewaterthatadheresto up thewhich therefore is not removal of water from a confinedismore could be removed fhnn a well toward thewelL Meinzer 18 moves Gmundwaler and devised ate:r-tlea.nrtg "''".u'u""'"material act as of anetwork of conduits.Groundwater -..vu;:...:uru and ratesof movement can vary from feetper that rm;;related to thewater formationisthe amount of open space within volume ofmateriaLftisdefined asthevolume of voids pertotalunitvolumemateriaL1.sbulk volume of the material. of thatcontainwater. Unconsolidated Sediments11Clav Silt Sand Gravel Sand & !travelmix Glacial till When waterdrained. fromsaturated rnaterial under the force of material rdeasesof thetotal volume stored inits pores. The of water that a unit. volume is termed Occurrenceand Number of '"'"'"''"'";;,,.,..,:;,..,.,..,..,Area (mm2) Diameter ofParticles Ina Sphere(mm)1-mm Cube*One Particle Allp.,.,,,.,.,., I. I3, I3.1 0.0624.1.10!1.2 . 10""49 0.004L7. 10's.o ws850 Cubic pack.ing is assumed. (Baver 1956) coefficient is the volume of water taken into or released from storage, in head per unit area.In thecase of anunconfinedlhc andcoefficients for coeffi-tech 22Groundwater andThird k 2J).Unit prisms of unconfined and confined in storage coefficients, Fordeclines in head, theWhere: from an unconfinedIs muchthan the yield from a .............., aquifer (HeathTrainer 1968). illustrates 24 Groundwa.ter and 25 Figure 2,7.Hydraulic conductivity is affectedsize of interconnections between pores in storage takeswlleneveradifferenceintotalhead \Vater moves from locations 2.8showsa Watl)r 26 ThirdEdition 2.Occurrence of27 2.9,Schematicof laminar flowand turbulent flow Ina granular depoait, "u'""'"'"''' whileto estimatelhe volume conducted a series learned that the rate Where: QFlow rate A Oi:!!,orlll'mof a constant-rate used to estimate the ""'"'""''"' ... "'"'''uu'""'""'of sediments.Is calculated by measuring the area of theand the nffri .. cti .. on.thewater thepores.statesenergyloss tionalto theof flow under laminar conditions-the fas.ter the energy loss.the onset of turbul.ent flow near whereh1 K a well are discussed :28 ' L qKf the thecross-sectional ill'ea Q the QKIA eEdition the toflowtimes the size and character ofthe ,,,.,,"'''''"'le but the amount of soap needed to reduce the calcium and ma:gne:stuJrnwith themineral content. Laundries and other industries Chapter 5.Groundwater Chemistry155 of soap generally tind it cost effective to reduce hardness to about 50but find that furtherofwater isnot economical. Numericalvaluesforhardnesshave meaning only ina relativesense.An in New England (U.S.A.)-where waters nonnally contain only small amounts ofdissolved solids-might consider water with 100 mgle hardness to be very hard. In contrast,states such as Iowa, Minnesota, or Nebraskaconsider water having100hardness to be soft. Calcium andcan contribute tothat develops when hardwaterundergoesintemperatureandpressure.Thistypeof incrustation results from a change in the solution chemistry that facilitatesthe precipitation of carbonate or sulfate minerals.in water pH,tempera-ture,or pressure,or theaddition of water-treatmentallcould trigger scale-fonnationissues.The problemof scaledepositsinfor example, is familiar and generally causes little concern. Scale deposits in evaporators(suchascooling towers)and inwater wellscanleadto complete operational failure. Saturation Index Theprimarychemicalindicationof whethermineralswillprecipitateisthe saturation index. When a water is at equilibrium with a mineral, the concentra- . tionsof theionsraised tothepower of eachmolar abundance in the mineral multiplied together are equal to theconstant (Ksp).The forn1ationof fluorite (calcium fluoride) can be shown by the foUowing equation. (solid)(5.7) At equilibrium and 25C, the following equation then is satisfied. (5.8) Where[Ca+]and[F] are the activities of calcium and fluoridein solution. Note that these are theactivities of thenot their absolute concentrations. Indiluteactivitiescan be almost.thesame asbut in morewatersmorecltlenlistlrvare alteredthe formationof complex ions in solution. Theindex is based on the solubility product. SJ=lo{ lAP] (5.9) 156 158 Third Phosphorus Silica Siliconis the second-most abundant element in thecrust va .... the mostSilicon in combination with oxygen is called silica The conunonmineralin itsmanyispuresilicon dioxide.Silicon and oxygen combineelements SUCh as Hli:I.)I,,UCii.IUIIII,"'''"'"uu, a sometimes contains as much asl 00 20of "'"'thri,.o of silicate minerals.water move-and the presencenatural acids such as carbonic acid and theto which silicain a sm,citic Silicadoesnotcontributetothehardnessof water.It JIDJ)Orltantconstituentofthematerialorscalefanned AsthescalecornmtDnlj 159 silicate. Silicate scale is notdissolvedacids or other chemicals that are used for chemicaltreatment of wells.Therefore silica-rich water to be used in in gf1,,,,,.,, ... Redox-Sensitive Elements and Compounds andoxygenbasa inward fromthesurface of the earthinto theshowsthat oxygen concentrationsdecreaseand the environment becomes more redluci:ng. A familiarof this is the difference betweenwater at the a lake and the oftenconditionswith the sediment at the bot-tom of thelake. The anoxic environment of thesediments is characterized the presenceandhas associated elevated levels of methane andsulfideinthe sediment pore water.The differences betweenthesetwoenvironmentsisduetobothmediatedand abiotic oxidation-reductionreferred to as redox reactions. '-"Uillltil!t:liinoxygencontenthavechemicaleffectonsomeredox-and Lefoundin8.E fDVD) rolift coarse- sand or forline sand .fluidloss can be controlled\vitha thmcoating on the wall of theborehole.(FigureAthich.'r be required to achtew thefluid-loss thanthefilter cakes creatcJ are the same. t I I a I i 8.Fluids 313 .... '..... .. .. A.used as drilling fluid additives, thin boreholeand lnsol particlesplastered the wall of the fnm:oti ..n The filtration ratet1uid can be determinedfiltration test device8.10).Such de\ ices c:an measure the 'nlumc of t1uid that helost to the formatkmandthe onthecellulose isticswithfiltration UliJlU::-ui:i:>CU fluid 314 Th1rdEdition (e.g., full-area press left side, half-area press right side) can bemeasure the flow rate ofa specific thickness of filter cake (Quality Drilling Figure. 8.11. Examples of filter cake thickness. A well-maintained drilling fluida thin filter cake on the borehole wall Inadequatelymaintained fluid, or amud, aeiPOlms muchside) (Quality Drilling Fluids). t 8.Drilling Fluids Figure 8.12. A thick filter cake aliows mace contact with the drillpipe and can result in differentially stuck pipe (0 2005 Baroic'. a Halliburton PSL). 315 316 initiated.More bentonite Groundwater andThirdEdition of the averagecapacities after three deveiDplnel1t eJDIShowthe COirDP'On.cntsOfSandSilt Driven /!Iarcachieved minimum pressure on the bott,mof lhe borehcle. removalof the roc l C'\ erburdenthebecometooff Fluids 8.22. Effect of downhole pressure on drilling rate.was tne drillers in Indiana limestonea1,000 lb 2-cone rock bit operating at 50 rpm&1958). RLducedb; r wear Reduced Reduced sell-induced ;'lui,!loss with scnsiti\ e 332Groundwater andThirdEd1lion fonnationandofleither a roller adownholeair-hammerbit.Borehole,arethemmular Air u'ed ft/min orair-fmm1Lost-circulation toanair howe\ er,canoccur whenair c"'"'"'"'"areusedtodn IIsanJstone.InthistylKof fom1ation.so velocitiesbe m.;ufficknt tolift theTu anJ water Sfwater enll'r th.::bore-Watermixeswithsmallestrock rilefornutionandlitnitthepotential\Ieldof the toformondrillor restrided or \\ hc1 drilling resumes must besufficient to over-any head of fluidaccumulated in the'T'hethen the !C'\ c;and there are no frictionl(h\Csin the drillpipe,rhermnimumpressure (in LSunitsJrnrestarttheair-ftabllshed for the nHht c.:ritic:al annulus ust ahovethe bit. At thitPrvelocities Effortsshould bemade to reduce s:rounclwllter oxygentoanaerobicbacteria ...........,., .. , and facultative bacteria can.li ve i.n environments with or without oxygen.thereare three mainof bacteria that cause . mostin water wells andslimeiron vAJ.uJ"""'""' and anaerobes well screen. Dissolved gases such a'> oxygen, carbon .. and methane-wheninwater-increase corrosion rates. electrochemical corrosion can cause losson sections of well screens andwith some of these corrosion "'""""""'"'elsewhere in.thewellor wAt.. r .. tiu:tntnl 362 Groundwater and Wells, ThirdEdition Slime Formers Slimefonnerscomprisethelargestgroupandareprolificproducersof exo-polymer (slime). This type of bacteria can be found in practically all areas of a well system. Iron Oxidizers Iron oxidizers include many slime formers. Particularly problematic are stalked sheath-forming bacteria that oxidize iron (or manganese), and which can leave dense deposits in screen intakes and gravel packs. Anaerobes Themostcommonanaerobesaresulfate-reducingbacteria (SRB)whichcan produce corrosive hydrogen sulfide gas (giving off the familiar rotten-egg that accumulate in dead zones of well systems. Dead zones are areas that recetve little or nowater movement on a regular basis. The most common is the sump (blank casing at total depth),which is part of many well designs. WellDesign and Bacteria Management Design consideration begins with an understanding that bacteria exist, potentially can cause problems, and require future periodic control measures. Key areas of design consideration to better manage well bacteria include the following. Nature of Aquifer The chemical nature of anaquifer provides nutrients for bacteria, therefore the compositionandfeaturesof individualaquifersshouldbeunderstoodand aquifers that provide rich food sources should be blanked off and not be allowed accesstothewell.Geologiczonesof highhydraulicconductivityoftenare responsible for carrying large amounts of dissolved oxygen to the well, encour-aging bacterialgrowth.Well design.should not encourage the introduction of vadosewater(whichoftenisrichinoxygen)viacascadingwater or another means of entry. Chapter 9.Production Water-WellDesign363 Well Head Design Consideration should be given to future maintenance and rehabilitation, access, clearances, diameters, and chemical feed for cleaning. Annular Thickness Annular thickness has a direct bearing on the ability toclean the borehole wall during development and future redevelopment-thinner is better. Screen Geometry Openareadirectly impactswelldevelopment(evenmoresowellredevelop-ment); high open-area, continuous-slot screens allow for consideration of more development tool options. Popular jetting methods, for example, arenot effec-tivewhen used with louver, bridge-slot, or mill-slot screen designs. Sump The occurrence of little or nowater movement is ideal for the accumulation of anaerobic bacteria over time. When possible the sump should be eliminated. If a sumpis needed,then using a short sump(5ft(1.5m}to10ft (3.1m))isa more practical approach than use of the typical 20-ft (6.1-m) length. Even better would be to make provisions to fill the sump area once development is complete and before the permanent pump is placed inthe well. Development Chemicals such asNuWellnn cemented sandstone aqt1itersthe screen. 410Groundwater and Wells, Third Edition Figure 9.23. Filter pack dealgn In an underreamed borehole. The hydraulic conductivity of a filter pack generally is several times greater than that of even ageological unit, because the pack has a more uniform distribution of sediments. Filter-pack material should consist of clean, }Yell-rounded grains of a uniform size, composed mostly of siliceous particles. An allowable limit of calcareous material isupto5% (by weight). Table.?.l7 lists the desirable physic!'\! and chemical characteristics for a filter pack and the advantages of using these materials. All filter-pack material that is delivered to thewellsiteshouldbe protectedfromcontaminationatthewellsiteprior to installation. Chapter 9.Production Water-Well Design Table 9.17. Desirable Filter-Pack Characteristics and Derived Advantages CharacteristicAdvantages Clean Little loss of material during development Less development time Greater hydraulic conductivity and porosity Well-rounded grains Reduced drawdown Higher yield More-effective development 90% to 95% quartz grains No loss of volume caused by dissolution of minerals Unifonnity coefficient ofLess separation during installation 2.5 or lessLower head lossthrough filter pack Steps InDesigning a Filter Pack 411 1.Choosethelayerstobescreenedandconstructsievecanalysiscurvesfor these formations. 2.Basethefilterpack gradingonananalysisof thelayer composed of the finestmaterial.(Figure 9.24showsthegrading of twosamples, the finest material lies between 75ft (22.9 m)and 90ft (27.4 m).) 3.Multiply the 70% retained size of the sediment by a factor of between 3 and 8 (see the selection criteria below). Place theof themultiplication on the graph as the 70%size of the filter material. a.As a general rule, for unconsolidated sand use a 4 to 6 multiplier. b.Use a 3 to 6 multiplier if the formation is uniform and the 40% retained size is 0.010 in (0.25 mm) or smaller. c.Use a 6 to 8 multiplier for semiconsolidated or unconsolidated aquifers whenformationsediment ishighlynon-uniformandincludessiltor thin clay stringers to aid in complete development. d.Using multipliers greater than 8 could result in creating a sand-pumping well. 4.In Figure9.24,0.005in(0.127mm)is the 70%size of thesand between 75ft {22.8 m)and 90ft (27.4 m).Multiplying by 5 produces a 70%size of the filtermaterial as0.025in (5 0.005) {0.65mm).Thisis the firstpoint on the curve that represents thegrading for thefilter-packmaterial. 412Groundwater and Wells,Third Edition 5.Through thisinitial point, draw a smooth curve representing material with auniformity coefficient of approximately 2.5or less.(In Figure 9.24,the solid-line curvehas auniformity coefficient of 1.8,the dashed-linecurve acoefficientof2.5.)Alwaysdrawthefilter-packcurveasuniformas pmctical, thus in this example the material indicated by the solid-line curve is more desirable. 6.Select a commercial filter pack that fulfillsthe dimensionaland chemical requirements listed in Table 9.17. 7.As a finalstep, select a screen slot size that will retain 90% or more of the filter pack material. In the present example, the correct slot size is 0.018 in (0.46mm). 8.Calculatethevolumeof filterpack requiredusingdata fromTable 9.18. Thepackshouldextendwellabovethescreentocompensateforany settling occurring during development. Using a caliper log could reveal the presence of washoutsin the borehole,necessitatingadditional filter pack. It is good practice to have extra filter pack on the site, especially if the size and stability of the borehole is questionable. 300madd 7 psi/30 m Note: If slot < lmm, then multiply the valueslisted above by1.20. 20"> 0.66 0.49 0.33 Screen Length The determination of theoptimum length of a well screen is based on aquifer thickness,availabledrawdown,andthestratificationof theaquifer.Placing screens opposite layers of highest hydraulic conductivity is a typical practice for production-welldesign.Theselayersareidentifiedfromdriller'slogs,lost circulation,penetrationrate,andgeophysical-loganalysis.Recommended criteria for determining screen lengths in various hydrogeological situations are given below. An economical alternative to stainless-ste.el pipe-when leakage to the well is acceptable-is a tightwind screen.A tightwind screen commonly is used to make short sumps and casing extensions that attach to K-packers (Figure 9.29). Unconfined .Aquifers Experience demonstrates that screening the lower third to the lower half of anaquifer provides the optimum design. If the aquifer is non-homogenous, selectively placing screens in the mostpermeable layersof thelower portionsof the aquifer maxi-mizes avaihlble drawdown and yield. Chapter 9.Production Water-Well Design429 Figure 9.29. Tlghtwlnd screen with Kpa.ckers. Selectingascreenlengthinvolvesa compromisebetween(1)obtaining higher specific capacity with the longest screen possible, and (2) utilizing more availabledrawdownwiththeshortestscreenpossible.Anefficientscreen addresses both issues by minimizing head losses as drawdown increases. Figure 9.30showsthat,froma theoretical(hydraulic)standpoint,it isimpracticalto pump a well in an unconfined aquifer at a drawdown that exceeds two-thirds of the thickness of the water-bearing sediment. 430Groundwater and Wells,Third Edition 100m 90 I' eo 1---.i70f-t-t-t---H,t-+-70"j, :::60 I 601---i---r--+-rr-"-+--+-i ttt ' 1---.1 4llf-t-l+--+-+--+--+- +-+-+--1 l301--Ht-t-+--t--l--l--t--t---l 50 40 30I 'l5 20 100 010 20 304ll 50 50 70 110Percent d!l'awdownFigure 9.30. Relatlonahlpa between percent drawdown and yield, and between percent drawdown and apecltlc capacity tor a water-table well located In a homogeneoua unconfined aquifer. 90100 Confined Aquifers Whereamaterialishomogenous,80%to90%oftheaquifer shouldbescreened(assumingthatthepumpingwater level remains above the aquifer). Whereamaterialisnon-homogenous,80%to90%of themost-permeable thickness should be screened. Optimum results are obtained by centering the screen section in the aquifer. Maximumavailabledrawdownshouldbethedistancefromthe potentiometric surface to thetop of the aquifer. If available draw-down is limited, then drawing the pumping level below the bottom of the upper confining layer could be necessary.When this occurs the aquifer responds like an unconfined aquifer during pumping. Using these niles forenables the obtaining of fmm 90% to 95% of the specific capacity that would be obtained by screening the entire aquifer. Chapter 9.Production Water-Well Design431 ScreenDiameter Unless dictated by a well's casing size and completion (single string), a screen diameterisselectedtoprovideampleopenareasothattheentrancevelocity generallydoesnotexceedthedesignstandardof 0.1ft/sec(0.03mlsec).To minimizefrictionlossestheupholevelocity shouldbe5ft/sec( 1.5m/sec)or less. The diameter can be adjusted within narrow limits after the length and slot size are selected. Well yields areaffected by screen diameter, but the impact is far less than that of screen length. The theoretical increase gained by enlarging thediametercanbecalculatedusingtherelationshipgivenin equation 9.22. Chapter 2 and Chapter 6 discuss hydraulic conductivity. K(H2 -h2) Q I 055 log R I r(9.22) This equation can be stated as follows. Q=c logRjr Where: K= hydraulic conductivity (liT); Hand h= heads (L); Rand r= radii edge of drawdown and of well (respectively) (in L); and C = allthe constant terms. Table 9.22lists the figures obtained when the radius (R) is 400ft (122m), whichisatypicalradiusof influenceforunconfmedconditions.Thetable showsthat-with other factorsremaining constant-doubling the diameter of a 6-in well creates an approximate 10% increase in yield (tripling size increases yield by about 17%). In confined aquifers the yield increase is less (about 7%), because theradius ismuchlarger. These comparisons indicate that there isno substantialenhancement of specificcapacityor yieldgainedbyincreasinga well's diameter.Insome cases, however,it might beworthwhiletoincreasea well's diameter for even a 15% to25% yield increase, depending on need and cost factors. Groundwater andEdition ratios alsowell hasabout 7%morethandoesa well has about 12% more. Screen Open Area Screenmanufacturerstablesshowtheopenarea screen for each size of screen and for various widths of slot area forslotvaries continuous-slotscreenshavemuch lnuver1-.r1orscreens. openareasthandoDflllle-sJct. screenis deter--.. ---- 9.23. 100 or mill-slot screen Where: slslot wslot n D kconstantU.S. If a well screen has a maximum open area, 433 ren1ovmg viscous and nutstlc-tvt>e ......... areaswheredebrisha."'been mineral isin the on well-de'\ielorpmientr..... ,nnnn"'In.the last ten years,theof open area has rehabilitation and disinfection ofwells. 434Groundwater and Wells,ThirdEdition Figure 9.31. The open area of the screen and the configuration of the slot openings are Important factors controlling the effectiveness of development procedures using water jetting. Entrance Velocity Fieldexperienceandlaboratorytestshavedemonstratedthattheaverage entrance velocity of water moving into the screenshouldnot exceed 0.1ft/sec (3em/sec).Atthisvelocity,laminarflowconditionsnearthescreenare probable, with negligible occurrence of friction losses through the screen itself. Higher entrancevelocitiesinduceturbulentflow,resultinginaless-efficient welloperation.Anexperimentwhichstudiedaspectsofwelldevelopment (e.g.,particlemovement,gradients,time,hydraulicproperties,slot size)was conducted. The data collected confirmed that a maximum entrance velocity of 0.1ftlsec (3 ern/sec) to 0.2 ftlsec (6 em/sec) is required to maintain laminar flow in a well (Wendling, Chapuis & Gilll997). ,iiiChapter 9.Production Water-Well Design435 The average entrance velocity iscalculated by dividing the well's yield by thetotalareaof thescreenopenings.If thevelocityisgreater than 0. lftlsec (3 em/sec), the screen length-and possibly the diameter-should be increased to provide enough open area so that the entrance velocity is 0.1 ft/sec (3 em/sec) or slower.Lengtheningascreeninanunconfinedaquifermight decreasethe availabledrawdownthereby reducingtheyield.Conversely,ascreenthat is fully penetrating a confined aquifer enhances yields, as long as the aquifer is not dewatered.Occasionally it canbepossible tovary the constructioncharacter-istics of a screen toincrease the open area.For example,the wire width could be decreased inacontinuous-slot screen if strength requirements are met.An exampleof awelldesignandthevariationsthat can bemadeiscontainedin Appendix 9.0 (DVD). Transmitting Capacity Well-screen transmitting capacity, expressed as gpmlft (cm3/minlm or 11/minlm) of screen, iscalculated from open area. Multiplying the square inches (square centimeters) of open area, 0.31gpm in2 (0.18a/min cm2), gives the transmit-ting capacity at the recommended velocityof 0.1ftlsec (3em/sec). 0.31gpm =0.1ftlsec 60 sec/m 7.5 gal/ftl/144 in2/ft2 (9.25) An8-in(20.32-cm),60-slotwire-wrapscreenwith135in2/ftopenarea (Table9 .15),forexample,hasatransmittingcapacityof42gpm/ft (522 . ~ / m i n i m )at an entrance velocity ofO.l ftlsec(3 em/sec). When aquifer characteristics areavailable and well yieldsare anticipated, well-screen transmitting capacity can beused to select a proper screen length. The transmitting capacity of a well screen is not an indicator of the formation's ability to yield water. In non-homogeneous aquifers, some sediment layers have greater hydraulicconductivitythanthatof other layers,andwater fromsuch zonescanenterthescreenatavelocitygreaterthantheaveragecalculated. Similarly,entrancevelocitiesfromfiner-grainedlayerswillbelowerthan average.Experience shows that these velocity differences along the screenare not of significant concern if the overall screen is designed toinsure the recom-mended average entrance velocity of 0.1ftlsec(3em/sec). Edition 437 ---""'"with pump The conclusions str;ateJg:tC;aJJ)pu1"u1xthe pump intake into the screen etttct,enl..!Ohf drill t1uid volume and nrc:ss1Jre thusthe screen to sink thescreenandinsidethe inside uuJ,Juu1u in the screen could sand lock the wash 10. Water-Well Construction and Abandonment479 10.28. A waeh-down bottom tool with eprlngloaded valve. restsinaconicalseat in A.,..,.,, ... -,""'''"' 482Groundwater and Wells,Third Edition Before driving a well point, all the sediment in the casing is removed to pre-vent sand locking. If there is a chance that the sediments might heave, the casing should be kept full of water while the point is set. A K-packer is attached to the top of the well point andis placed through the casing. A driving bar, drill stem, or other tool is raised and lowered to drive the well point through the bottom of thecasing.Tominimize potential damage tothe screen, using a weight that is less than 250 lb (113 kg)together with a 2-ft (0.6-m) stroke is recommended. Carefulmeasurementsmustbemadesothatthedrillingprofessionalknows when the screen has been driven the correct distance. Use of a 3-ft (1-m) to 5-ft (1.5-m) riser pipe also isadvised. Some well points are manufactured to include a drive plate (Figure10.29) so that the driving force is directed at the point; however not all drive points are created towithstand driving from thebottom,so it is important toconfirm the specifications when ordering the points from the manufacturer. Driving a point frominsidea casingisrecommendedfor pointslonger than 5 ft ( 1.5m);but attempting this procedure without having a drive plate in place can cause severe damage to the bottom of the screen. Figure 10.29. A driving bar can be uaed to drive well polntalnslde the casing. Chapter 10. Water-Well Construction and Abandonment483 Pull-Back Installation Method The pull-back installation method reduces problems such assetting the screen atthewrongdepth,theheavingof sediment,andthesloughingof borehole walls caused by swelling clays or low hydrostatic pressure within the borehole. Thepull-backprocedureenablesscreenremovalandreplacementwithout disturbingthecasingseal,andthecost(ofpulling,cleaning,orreplacing) usually is small ascompared to thecost of drilling a new well. The pull-back installation procedure is particularly suited for rotary rigs that can drill and drive casing, and for cable tool drilling rigs. This method involves installing casing tothe total depth,telescoping the screen inside tofulldepth, and then extracting (pulling back) the casing far enough to expose the screen to the water-bearing formation {Figure10.30). The casing must be strong enough to be set to full depth and then be pulled back the entire length of the screen. Flgure10.30. Basic operations In setting a well screen using the pull-back method: (1) driving, balling, or lowering the casing to the full depth of the well; (2) lowering the screen Inside the casing; and (3) pulling the casing back to expose the screen to the aquifer. 484 Groundwater and op:po!ntethefonnation-notupinsidethe listed below . ThirdEdition ,_,..,..... '"'......6sediment movement into th.ebottom of the if thescreenhasseveralslotsizes or bas blankbetween screen zones. If sediment heav-is athewith water or afluid tocontrolfluidloss.If necessary,canbecontrolled """'''c"'''"cthefluid.Sudden verticalmovementof..IY bailers-increases theof u.., ... """ protJ,IenlS hole pressure. Aftersedimentisremovedfromthethe sional must determine whether thecan be withdrawn. If it cannot, then the drivean insideto reduce res1sUmc,e, and thebackfewinches. The screenthenisbottom ofmeans can be used to lower the screen, ......... e. andbackoff wash-down bottoms and Abandonment485 on the sand line is set on the puueDollottu of the suxncJtemres1tstance to hold the screenThe As the screen. is exJ:>os;ea, If no riser the 486Groundwater and Wells,Third Edition FILTER PACKING WELLS Many wells are designed to use an artificial filter pack. A filter-packed well has apredeterminedthickness,whereasanaturallydevelopedwellhasa graded permeable zone that is produced by the development process. Both types, when properly constructed, are efficient and stable. Filter-pack thickness has a direct impact oneffective development at the formation-pack interface.The optimal thickness for a pack is 3 in(76 mm), and packs thicker than 5 in (127 mm)are not recommended because the effectivenessof the development procedures is impaired severely. Installing a filter pack that is less than 2 in (50 mm) thick is preferred, but isnot practical: All filter-pack materials and equipment should be treated with bactericide-usually sodium or calcium hypochlorite-and all water usedinthe filter-pack operationshouldbetreatedwith50m g l ~free-chlorinesolutionbeforeuse. Whenpossible,thedrillingfluidshouldbethinnedandberelativelyfreeof solids before placement. Thegrainsizeswithinfilter-packmaterialshouldnotsegregateduring placement.Dissimilar-sizedparticlesfallthoughwater atdifferent velocities, thuswell-sortedmaterial(limitedsizedistributions)islessapttosegregate during placement. Tremle Pipe Using a tremie pipe minimizes the tendency for particle separation and bridging wheninstallingpackswithhighuniformitycoefficients.Pipethatis2in (51rnm) or larger works in shallow to moderately deep wells ( 1,000 ft (305 m) to1,500 ftm)) when gr.tvity-fed at approximatelylftl (0.03 m3)of pack material per 5(190 to10 gal(380 of water.In deeper wells, filterpack should be pumped througha tremie pipe, which typically is placed before the screenandThetremiepipeis raised periodically asthe filtermaterial builds up around the well screen, and also can be used to feel the top of the filter pack (or a weighted line can be inserted through the tremie). Chapter 10. Water-Well Constructionand Abandonment487 Telltale Screen Another filter-pack placement method incorporates use of a short telltale screen thatisinstalledabovetheproductionscreen(seeFigure10.32).Filterpack material ispumped into the annulus,andwater flowsinto the screen and back tothe surface through the drillpipe. The topof the casing must be sealed to the drillpipe so that the steadily increasing pressure can be monitored as the screen is covered. Surface pumping stops when an abrupt pressure spike occurs, which indicatesthatthetelltalescreeniscovered.Suspendedfilterpackstillfalls, however the depth to the top of the pack can be calculated using the filter-pack volume in suspension and the water volume in the annular space. Reverse Circulation Packing large-diameter wells by using reverse circulation often is performed in a manner similar to packing a telltale screen. The borehole iskept fullof fluid andpackmaterialiscarried.downwardoutsidetheinnercasingandscreen. Sometimes a stinger pipeand dual-swab tool (with a perforated pipe between two rubber swabs) that forces water to the bottom of the screen before returning to the surface is used (this is particularly advantageous for use with long strings or unstable boreholes where use of a tremie pipe is not practical) (Figure 10.32). Direct Circulation Direct circulation of clean water can reduce bridging problems, and is an option to consider if pack materialiscontaminated by organicmaterial(e.g.,leaves, grass) or contains too many fines. The low up hole velocity allows gravity settle-ment, but still is ample tofloat organic material or finesediment to the surface and thereby reducedevelopment time.During circulation,makesure to avoid removing the filter cake and causing the borehole to become unstable. 488Groundwater and Wells,Third Edition Flgure10.32. When filter packing a long screen, a stinger pipe is installed to force water to flow to the bottom of the screen. A more comf!licated direct-circulation method used in small-diameter deep wells is pumping through a crossover tool. The crossover tool generally is used for adeepwater well thathasasmall annulus.Figure10.33showsthebasic features and flow paths during placement of the filter pack. The crossover tool is connected between the drillpipe and thetop of the riser pipe. The top of the riser pipe can be sealed to the casing with a suitable packer (e.g., K-packer) after the filter pack is placed. The stinger pipe extends to within 3 ft (0.9 m) of the bottom of the screen. Thepumpingpressurewillincreasesuddenlywhenthefilterpackmaterial reachesthetopof thescreen.Theupperportionof thesandinjectionpipe (above the crossover sub) is equipped with a left-threaded backoff sub, so it can beremovedaftersandinstallation.Carefulobservationisnecessaryandthe procedure requires elaborate equipment and considerable skill.The operation must becoordinatedtoinsure continuousflowat arate thatwill not plugthe drillpipe or cause a bridge to form in the borehole. Chapter 10. Water-WellConstruction and Abandonment Flgure10.33. Diagram of essential feature& of crouover tool (Suman et al. 1983). 489 Filter-Pack Procedure for Telescoping Well Completion Filterpackingatelescopingwellcompletiontypicallyrequiresthatanouter casing firstbe set to full depth.The inner casing and screenthenare installed using centeringguides,and the filterpack isplaced(usu,allyinstages)in the annular space around the screen-extending highenough above thescreen to accommodate settlement as the outer casing is pulled back (Figure 10.34). The filterpack should extend above thetopof thescreenabout one-fourthof the total screen length. 490Groundwater and Wells,ThirdEdition Figure 10.34. llluatratlon of lnner-caalng method. Screen assembly Ia centered In a cased borehole, and the outer caalng Ia pulled back as filter pack Ia placed. The depth to the top of the filter pack is monitored carefully so that it never drops below the bottom of the outer casing. A pack height of5 ft (1.5m) should be maintained above the screen during withdrawal. To prevent bridging, screen sectionsoftenaredevelopedascasingiswithdrawn.Overfillingtheannulus during withdrawal can lead to sand locking of the outer casing to the screen. Chapter 10. Water-Wen Construction and Abandonment491 Asdevelopment proceeds, settlement occursandmore filter pack mustbe added to keepthe top of the filter pack above the screen. Permanent filter-pack tubessometimesareinstalled toallow gravelpack tobeadded to a well after completion if settling occurs(e.g.,subsidence,pack quality,acid treatments). These tubes are not necessary if the filler pack issealed usingbentonite pellets or cement grout. The outer (surface) casing can be either removed or left in place. Filter-Pack Procedure for Single-String Well Completion In most rotary-drilled wells the screenand casing areplaced asa single string (Figure10.35). Centralizersgenerally areattachedevery 20ft (6.1m)on the screen body and every 40ft (12.2m)on thecasing.The drilling righolds the a.'!sembly in tension at thesurface while the drilling-fluid viscosity isreduced as much aspossible without allowing collapse of the wellbore.Breaking down thedrillingfluidreducesdevelopmenttime,minimizesflotationeffects,and increases the settlement rate forpack materials. Downwarddragforcesonthescreen andcasingassemblyduringfilter packingarenoticeable,especiallyinlarger-diameterdeepwells.Finerpack materialsexertmoredragthandocoarsermaterials,inpartduetolarger surface-areacontact.Forcesinexcessof20,000lb(9,072kg)havebeen recorded during filter packing. These dynamic loads should be factored into any deep-string assembly calculations toprevent casing or screen failure. Filter-packmaterialsusuallyextendsomedistanceabovethetopof the screen,andpackmaterialshouldbeaddedasrequiredduringdevelopment. After development and backfilling of the borehole, tension forces on the and screen are released. Edition10. Water-Well Construction and Abandonment493 to remove a screen. u.:;I,uuuvlh however on a bail bottom unless the screen the sedi1mer1t. Screens that are 4 inin diameterare best removed aof smaller diameter that is sand locked inside the screen and which transmits theforce to the well screen.sandbetween the and screen becomes locked when lift isto the 10.35. A screen andcan be placed Into the borehole a,s a unit. 10.38. Dlagra1m of sarldIIDCk:lng method 494Groundwater and Wells, ThirdEdition Twoorthreeslotscanbecutinthepullingpipejustabovetheburlap (Figure 10.36), so that the sand joint can be loosened from inside if the below-ground connectionmustbebroken.Slotsalsocan be cut inthe pullingpipe, level to the upper part of the screen, so that excess sand runs into the pipe and to prevent overfilling the screen (which could sand lock the drill string) . .If sand lockingoccursthen,todisengagethedrillstring,installright- andleft-hand couplings between thebottom of the drillpipe and the pulling pipe. The screen and partof thepulling pipethenremainintheground.Sometimesattaching weld rings attwoor three different levels on thepulling pipe helps evenly dis-tributesandfriction.Aseriesofpipenipplesjoinedbypipecouplingsis especially practical for pulling 6-in (152-mm) diameter (and smaller) screens. Alternately,if thescreenisequippedwitha. sumppipethenthepulling force can be concentrated there. An elliptical plate that hasbeen cut in half and hinged together foldswhen lowered and,when lifted, unfolds and locks in the sump pipe. The folding plate should not be so large that it causes bulging of the sump pipe, which could lead to interlocking of the sump-pipe casing. Size of Telescope Screen In 4 5 6 8 Table 10.7. Sizes of Pulling Pipe Inside Diameter of Screen Size of Pulling Pipe Chapter 10. Water-Well Construction and Abandonment495 WELL PLUMBNESS AND ALIGNMENT Waterwellsshouldbeboth straightandplumb,although-inpractice-any borehole of substantial depth is not perfectly straight or perfectly plumb. A well isstraight when each casing section connectswhile maintaining perfect align-ment. A borehole is plumb when its center does not deviate fromthe (theoreti-cal) vertical line that runs from the earth's surface to its center (Figure 10.37). A wellbore sometimes can be straight but not plumb; but if it isplumb then it must be straight. Borehole neither straight nor plumb Borehole strelglit but not plumb I I I I I I I I: I ~ B o r e h o l e :straight Iend Iplumb I I I I I I I I ' Figure 10.37. A borehole should be both straight and plumb. Sometoleranceinstraightness(alignment)andplumbnessnormallyis allowable. Typically, a deviation from plumb of two-thirds the inside diameter per100 ft(30.5m)of antic.ipatedpumpsettingisallowedandisreasonable (AmericanWaterWorksAssociation2006).TheAWWAStandardAlOOis reasonableforcasingdiameterslargerthan12in(30.5em),but forsmaller casingdiametersthisstandardmight be toostringent.Table10.8showsthe allowable limits of deviation for various depths. 496Groundwater and Wells,ThirdEdition Table 10.8. Well-Deflection Limits for Drift-Indicator Survey Allowable DethDeviation Straightness of the well bore is most important when a vertical turbine pump is being considered for use.If alignment deviatesbeyond a certain limit,then thepump cannot beset.A pump can be installed in a well that isstraight but Chapter 10. Water-Well Construction and Abandonment497 which is notplumb; however too much vertical deviationaffects theoperation and life of some pumps. In general, turbine pumps require a reasonably straight well bore, whereas submersible pumps can be set in wellbores that are somewhat misaligned. Conditionsthat cancauseaboreholetobemisalignedandout of plumb include the following. Characterofthesubsurfacematerial(faults,bouldersinthe borehole, dipping strata) Placementof toomuchor toolittleweightonthedrillbit when drilling Trueness of the casing and drillpipe Pull-downforceappliedtothetopof thedrillpipeduringrotary drilling (as opposed to weight on the bit that is derived strictly from drill-collar weight) Gravity tends to make a drill bit cut a vertical hole, but varying hardness of formations encountered deflects a bit from following a truly vertical course. The edge of a boulder can deflect a cable tool,rotary bit,or even a well casing that is being driven, thus causing drift. Too much forceapplied atop a rotating drill stem bends the slender column of drill pipe causing an off-center cut. Rea vy drill collars(located justabovethebit)concentrateweightatthebit,tendingto overcome drift from true vertical. Collars are more rigid than ordinary drillpipe and stiffenthelower part of thedrillstring.Large stabilizersalso areusedto help drill straight holes. Sectionsof casingcan beslightly bowed,forexample,or a joint's center line might not coincide exactly with the casing's center line. Commercial toler-ances permitsomedeviationinstraightnessandtheaccuracyof threads,and thesemustbeconsideredwhenspecifyingtheallowabledeviationofa completed well. Borehole alignment should be checkedseveral times when drilling a deep well, especially when using the cable-tool drilling method. Immediately correct-ing any misalignment that is discovered saves both t i m ~ eand money. The align-ment often is checkedatpredeterminedintervalswith aninclinometer survey toolduringrotary(e.g.,100ft(30.5m),500ft(152m),1,000ft (305m)). In many cases, however, the alignment is checked only after the well has been completed. 498Groundwater and Wells,Third Edition Specialdeviationinstrumentsareavailabletomeasuremisalignment.A magneticorgyroscopicdeviationsurveycommonlyisrecordedalongwith standardgeophysicallogs.Specialcentralizerskeeptheinstrumentcentered, andreadings(givendirectlyasdisplacement)aretransmittedtothesurface. Chapter 4 contains additional information on alignment loss. UNDERGROUND "PITLESS" DISCHARGE Asanitary,practicalundergrounddischargeisaccomplishedusingeithera pitlessunitor apitlessadaptor.Thisdeviceisconnectedtothewellcasing below ground level through a hole cut into the side of the well casing (Figure 10.38, Figure10.39).Apitlessunit isinstalled by firstcuttingoff the casing below ground and thenwelding the spool-unit directly to the casing. The unit extends above ground level and provides a watertight subsurface connection for buried pump discharge or suction lines. To prevent freezing, the pipes must be buriedbelowthefrostline.Additionalinformationonpitlessadaptersis contained in AppendixlO.B(DVD). Insomecases,theentirewatersystemislocatedin or nearthewell.A buried pressure tank provides cooler water, eliminates moisture condensation, and does not take up space in the house (Figure 10.39). Chapter 10. Water-Well Construction and Abandonment Flgure10.38. Diagram of a typical domestic-well pltleaalnatallatlon equipped with a aubmeralble pump. Figure 10.39. Diagram of a pltleaa adaptor connected to underground pre!laure tank. 499 500Groundwater and Wells, ThirdEdition SUMMARY It isascritical toproperly plan and execute thephases of well construction as itistoconsider andaccomplishalltheelementsof design.Therealwaysare unforeseen circumstancesthat canarisetocomplicate construction-which is whyrelianceonan experienced drillingprofessional alwaysisa good invest-ment. A properly constructed well delivers years of dependable service and safe, quality water. ACKNOWLEDGMENTS Mr. Marvin F. Glotfelty, RG, Principal Hydrogeologist with Clear Creek Asso-ciates, and Mr.Tom Downey,President, Downey Drilling Inc., provided valu-able review and comments on this chapter. Their work isgreatly appreciated. CHAPTER 11 Development of Water Wells Thomas M. Hanna, PG Johnson Screens Well development includes procedures that are designed to maximize well spe-cific capacity, and has two broad objectives: (1} to repair aquifer damage near the borehole that was caused by the drilling operation, so that thenatural hydraulic properties are restored; and (2) to alter the basic physicalcharacteristics of the aquifer near the borehole so that water flows more freely to a well. These objec-tives are accomplished by applying some form of energy to the aquifer. Every new well should be developed-before being put into production-to achieve the goal of producing sediment-free water atthehighest possible spe-cific capacity. Older wells often require periodic redevelopment to maintain-or even improve-the original spec.ific capacity of thewell. Aquiferstimulationisanothertypeof "development"thatisperformed when the aquifer doesnotyield sufficient water,even after the applicationof typicalwell-developmentprocedures.Thistypeofdevelopmentusuallyis limited touse in semi-consolidated or consolidated aquifers. Thischapterdiscusseswell-developmenttechniquesbeforeitaddresses aquifer-stimulationprocedures,becausedevelopmentappliestoeverywell regardless of the geologic materials present. 501 500ThirdEdition 501 502Groundwater and Wells,ThirdEdition AQUIFER DAMAGE ANDDEVELOPMENT OBJECTIVES Aquifer Damage All drilling operations alter the geologic characteristics of the aquifer materials inthevicinityof theborehole.Suchalterationsoftenresultinasignificant reduction of the aquifer's hydraulic conductivity near the wellbore-even that of a well drilled without using drilling fluids(Hanna et al. 2003) (Figure 11.1 ). Figure 11.1. A significant reduction In hydraulic conductivity of the sediments surrounding a borehole can occur due to drilling. Somecommoncausesofboreholeandaquiferdamageincludethe following. A casingdriventhroughclay or very fine-grainedsediments can entrainsome of thesediments and carry them down the borehole, coating the borehole in the area adjacent to the aquifer. Inwellsdrilledusingdrillingfluids(especiallybentonite),the aquifercanbecomesealedduetotheinvasionof fine-grained particles.Suchinvasionminimizeswatermovementfromthe aquifer (Figure 11.2). Inconsolidatedorcrystallineaquifers,fine-grainedcuttingscan plug interstices or fractureopenings. Chapter 11. Development of Water Wells Inwellsdrilledwithfreshwater,naturallyoccurringdayscan become incorporated into the drilling fluid and plug the pore space of aquifers.Permeablegeologicmaterialsaremoresusceptible to drilling-fluid penetration. Figure 11.2. When using drilling fluids, some of the fluid flows Into the moat pervious parts of the aquifer. 503 Aquifer damage to some degree is unavoidable regardless of which drilling method is used. Development ObJectives The objectives of development procedures are to: Reducethe co01:pactionandintermixingof grainsizesproduced duringdrillingbyremovingfinesedimentfromporespaces adjacent to the borehole; Increasethe hydraulicconductivity of the previously undisturbed aquifer near the borehole by selectively removing the ftner fraction of aquifer material; 504Groundwater and Wells,ThirdEdition Remove the filter cake or drilling fluid that coats the borehole; Remove the drilling fluid and solids that have invaded the aquifer; Form a graded zone of sediment aroundthescreenin anaturally developedwell,therebystabilizingtheaquifersothatthewell yields water attaining a suspended sediment load criterion; Createanenvironmentthatreducesthepotentialforbacteria growth thereby increasing the life of the well; and Remove fine-grained cuttings fromtheborehole wall and fracture openings. Studies conducted by the State of Michigan (U.S.A.} concluded that wells that were properly developed hadfewer problems with positive coliform tests {Schneiders 2003). Further work by Schneiders (2003} confirmed the findings of the Michigan study, and showed that no-flow areas (e.g., zones clogged with drillingfluids) thatarenearthescreenarelocationsforenhancedbacterial growth.Thus,wellsthatarenot properlydevelopedtendtohavebiofouling problems more frequently than do properly developed wells. Properwelldevelopmentinsurestheproductionof waterof acceptable sediment concentration,maximizes well efficiency, reduces awell'smainten-ance costs, and increases the service life of a well. FACTORS THAT AFFECT DEVELO,PMENT Well-Completion Methods The most common well completion methods used after the casing and screen are installed are natural development, filter packing, use of prepacked screens (e.g., Muni.,Pakrn),and open borehole (no screen is used). The particular completion methodisselectedbasedonthegeologiccharacter of theaquifer.Tosome degree, the completion method determines the. effectiveness of specific develop-ment methods. Chapter 11. Development of Water Wells505 NaturalDevelopment The goal of natural development is to create a more-permeable zone around the screenintheaquifers.Thisprocessisbestunderstoodbyexaminingwhat happensthroughout aseriesof concentriccylindrical zonesinasand aquifer surroundingascreen.Inthezonejust outsidethewellscreen,development removesmostparticlessmallerthanthescreenopenings,leavingonlythe coarsest sedimentin place.Fartherout fromthescreen,somemedium-sized grains remainmixed with the coarsesediment; beyond that zone,the material graduallygradesback totheoriginalcharacter of theaquifer(Figure11.3). Finer particles brought into .the screen during natural development are removed bybailingor pumping,anddevelopmentcontinuesuntilthereisnegligible movement of fine sediments from the aquifer into the well. Figure 11.3. Natural development removes most particles near the well screen that are smaller than the screena slot openlnga. Filter Packing Inthefilter-packingprocess,aspeciallygradedsandor gravel-having high porosityandhydraulicconductivity-isplacedintheannulusbetweenthe screen and the aquifer. The selection of a filter pack is described in Chapter 9. Groundwater andThird Edition havethe ad,rant:al!:ederivedfrom Thisof sut1sec1Uellt developme111t reiCtifi.esthedantaae creatiilll an efficient well. 11.4. 507 508Third 509 the twoadditives used.After "'"u"''"' fluidshouldberemovedfrombothborehole Iaeffective when the the energydirected Into the filter 510 enhanceenergyinto and out of the should. be a method. that removes rme2raJJ11ea lift pun11pin1g,"',......,.,,pillmlnng:). ThirdEdRion air fluids that are in with air-to remove rates of water flow into the well. Theinitialprocessisthe removaloffluidsand.natural :finesfromthewell.removal of the .............. "' and withoutthere is the J.IV''"'" ....... and screen.If theintheannulusarenotpnJpe:dy cannot enter the well as fast as fluids arecan result in a fluidin the insidethewell(di:tteJrenltiaJJ!!o;;.,.,u.t"'J 511 512Groundwater and Wells,ThirdEdition the introduction ofNW-220 and the beginning of the well's development, so the clay masses can become completely disaggregated.After theNW -220 is jetted or surged into thescreen, clean water should be added tothe well todrive the solution farther into the aquifer. Its unique polymer formula allows NW-220 to disperseandtohold finesinsuspensionuntil the fluidscan be removedfrom the well. Typicalbentonite drilling fluidscan be broken down usingthe following procedures (provided in U.S. customary units). Add sodium hypochlorite (10% concentration) to the drilling fluids at a concentration of about15 gal per 1,000 gal of drilling fluid to achieve achlorine concentration in the well. AddNW-220to the drillingfluidata concentrationof 1 galfor every 500 gal of drilling fluid in the well. Keep the solution in the well for12 hr to 24 hr before agitating the solution. Agitate the solution vigorously for several hours using mechanical means (approximately one half hour per 20 linear ft (6.1 m) of well screen), until theviscosity of the solution-drilling fluid mixture is reduced to 27-sec funnelviscosity. Agitateandremove theremainder of thedrilling fluidsfromthe well.' MechanicalSurging Mechanicalsurging forceswater toflowinto and out of a screen by moving a plunger upanddown in the casingandscreen(similar tothemovement of a piston in a cylinder).The tools normally used are called a surge block (Figure 11. 7), surge plunger, or swab. Surge blocks are constructed so that the outside diameter of therubber edges is equal to the inside diameter of the screen.The solid part of the block is1 in (25.4 mm) smaller in diameter than the screen. A heavybailercanbeusedtoproducethesurgingaction,butisnotas effectiveastheclose-fittingsurgeblock.Asisthecaseinallmechanical development processes, fine-grained material should be removed from the well asfrequently as possible. Best results are obtained when thismethod is used in conjunction with pumping to remove fines from theChapter 11. Development of Water Wells Figure 11.7. Typical surge block made of 2 rubber dlaca sandwiched between 3 steel or wooden dlacs. 513 Before beginning a surge, drilling fluids should be removed from the well and water shouldbeflowinginto it.Thesurge block isloweredinto the well untilit is10ft (3m)to15ft (5m)beneath thestaticwaterlevel,but stillis above the screen (Figure11.8). The water column effectively can transmit the action of theblock to thescreen section. The initial surging motion should be relativelygentle,sothatanymaterialblockingthescreencanbreakup,be suspended, and then be moved into the well. The surge block (or bailer) should beoperatedwithcare-particularlyif theaquiferabovethescreenconsists mainly of fine sand, silt, or soft clay that could slump into the screen if a filter pack is not used.Surging also should be started slowly and relatively gently to avoid differential pressures that can cause collapse of the casing or well screen. 514Groundwater and Well$,ThirdEdition Figure 11.8. A surge block can be an effective tool for well development. Whenwaterbeginstomoveeasilybothintoandoutof thescreen,the surging tool usually is lowered (insteps) and positioned just above the screen. As the block is lowered the force of the surging movement increases. In a well that is equipped with a long screen, it can be more effective to operate the surge blockinthescreentoconcentrateitsactionat variouslevels.Development should begin above the screen and move progressively downward to prevent the tool from becoming sand locked. The force exerted on the aquifer depends on the length of the stroke and the vertical velocity of the surge block. The speed of retraction and length of pull are governed by thephysical characteristics of the rig. Surging should be continued for several minutes, and then the block should be pulled from the well.Air can be used tolift thesediment out of the well if Chapter 11. Development of Water Wells515 developmentisdonewitharotaryrigorif anaircompressorisavailable. Sediment can beremovedbya bailer or sand pumpwhenacable toolrigis used. The surging action is concentrated at the top of the screen, and this effect is accentuated if the lower part of the screen is continually blocked by the sand brought in by the surging process.Occasionally, if the washing action disrupts the seal around the casing formed by the overlying sediments, surging can cause upward movement of water outside the well casing. When this occurs, use of the surge block must be discontinued or sediment from the overlying materials can invade the screened zone. When used in certain aquifers, surge blocks sometimes produce unsatisfac-tory results--especially when the aquifer contains many clay lenses-because the action of the block can cause clay to plug the aquifer, resulting in a reduc-tion in yield rather than an increase. Surge blocks also are less useful when the particles comprising the aquifer are angular, because such particles do not sort themselvesasreadily asdo roundedgrains.Additionally,if large amounts of mica are present in the aquifer,the flat or tabular mica flakescan align them-selvesperpendicular tothedirectionof flowand clog the outer surface of the screen andtheaquifer zone adjacent to thescreen.Cloggingby mica canbe minimized when surging procedures are performed gently. Anothertypeof surgingtoolisaswab.Thesimplesttypeof swab-a rubber-flanged mud scow or bailer-is lowered into the casing to any selected pointbelowthewaterlevelandthenispulledupwardatabout3ftlsec (1mlsec), and no attempt is made to reverse the flow and cause a surging effect (Figure11.9). The lengthof the swabbing stroke usually is much greater than that of surging. As the bailer is raised a pressure differential is created near the topof thebailer;thisdifferentialallowswater to flowfromthewellinto the aquifer.Water,sand,andsilt aredrawnback intothewell beneaththeswab because the pressure is lower in the bottom of the well.The bailer usually has avalveat the bottom that opens toincrease the fallrate in the borehole. This method of swabbing, called line swabbing, often is used to cleanmaterial from deep wells that are drilled in consolidated rock Care must be taken when swabbing wells that have plastic casing or screens. In particular,screens that havescreen-slotsizesabout 0.010 in(0.25mm)or smaller can become blocked. These wells and associated screens can be particu-larly troublesomebecausedifferentialfluidpressurescreated by theswabby removing fluidsfrom inside thewell can collapse PVC casings. Groundwater andThird "Edition 517 toolfor 1G-In dla,ma'll'la.allvand 1 bottom jet never should contain sediment. Sediment circulated toolcan causeerosionnozzleina nrcln"'''"'""'"'J'orcvtdletoocanresult in pressuredifferentialsbetweenthe airand Third 527 nPt'"'"'''nP., ......... u.i!!itoo close to an air-dis;c:harge DlDe--tne d.lschalfgeshould be directed intomudorchannelorinstalled.Thisenablesestimationof the sediment content. When flowhasestablished the ..(1.5of the bottom of the screen or, ifcan start near theof thescreen.Air isand thewellisuntilthewater of sand. Thevalve then is closedwhile theairlineisloweredto1 ftor sobelowthe 43 the valve drives water outward thf;ouJ!:h water blows from theand ..n.....,,,, lineintotheeductor are re1leau'd DoubleBlock withAir SomedriUersuseadoubleblockor isolationtooltoremovesediment COlll,)UOCtlOOWiththe 528 Groundwater and Wells,ThirdEdition Figure 11.15. Double surge blocks are used to focus the energy of air bursts on a specific part of the aquifer and to remove sediment by air lifting. The double surge block with air-lift method is especially effective in long screens because it can concentrate the development energy on short sections of the aquifer. It is important to start the procedure at the top of the screen to avoid sand locking the assembly. The double surge block isa cost-effective tool for use in deeper wells, because multiple development techniques can be employed without removing the tools from the well. Chapter 11. Development of Water Wells Figure 11.16. When surging or injecting using the double surge block, water moves Into the filter pack and aquifer. 529 Double Surge Block withHigh-Pressure Jetti-ng Combination asadoublesurgeblockwithhigh-pressure jetting tool-are used m deeper wells because the time to install and remove tooling for developmentcanbesignificant(Figure11.17).Usingthistool,wellsare byhigh-pressurejettingandair-liftpumping.During htgh-pressure Jettlllg, the check-valve in thetool remains closed, forcing all of the water through thenoz.zles.After jetting approximately 20ft (6m) to 30ft (8 m) of screen, the same interval is swabbed and pumped by air-lifting without tooling. When air-lifting, the check-valve opens, allowing water and to move through the screens and up the drillpipe. The packers on the tooltsolate a 6-ft (2 m) to 10-ft (3m)section of the screen so that the full force of airlifting is focused on a smaller section to remove any sediment. 530 11.17. Double surge block with hlf.llh!llreiiSU11111 deep wells. Third 531 used In 532Groundwater and Wells,ThirdEdition To avoidpump damagethe controlboxshould be equipped with a starter lockout, sothat thepump cannot be engaged when it isback-spinning.During rawhiding,thefluidproducedoccasionallyshouldbepumpedtoawaste-holdingtanktoremovethesedimentthathasenteredthewellviasurging. Rawhidingrequiresremovalof acheckvaluethatnormallyisinstalled just abovethe pump-bowl sections. The permanent pump never should be used for rawbiding because the highsediment content accelerates pump wear.A com-parison of three development methods is contained inAppendixll.B {DVD). DEVELOPMENT OF OPEN-BOREHOLE WELLS The combination of water jetting and air-lift pumping is reconu:iiended for open-borehole or bedrock wells. Inflatable packers can be used to isolate productive zonessothatdevelopmenteffortscanbefocusedoncertainportionsof the borehole.It hasbeen shown that much of the water entering an open borehole in bedrock enters through fracturezones. One technique for cleaning wells completed in sandstone aquifers combines air-lift pumping,air jetting, and rawbiding; this overcomes development diffi-culties in stratified aquifers having layers cemented by silica, calcium, iron, or fine material such as clay. A borehole of this nature is depicted in Figure 11.19. Ledges form where the sandstone is most resistant and well-cemented, and bore-holeenlargementoccurswheremorefriablelayerserode.Asshowninthe figure, erodable sand lies on top of the ledges. If the well is put into production after bailing or air development,it often continuestoproducesediment.This problem stems from the inability to remove all of the loose material inthe well, because thedevelopment procedures donot extendfar enough fromthewell-bore. Borehole-camera surveys have shown that this loose sediment is removed wellaway from the borehole when air-lift pumping, air jetting, and rawhiding are used in combination. Chapter 11. Development of Water Wells Figure 11.19. Borehole configuration caused by drilling In weakly consolidated sandstone containing well-cemented layars. Loose sand collects on the upper surface of the cemented layars. ALLOWABLE SEDIMENT CONCENTRATION IN WELL WATER 533 Sediment in water supplies can be destructive to pumps arid to water-discharge fittingssuch as valves and irrigation nozzles. One of the requirements of a pro-ductionwell isthat itnotproducesediment;however,occasionally sediment productionoccurs.TheAmericanWaterWorksAssociation(A WWA2006) that, for municipal-supply wells, water should contain less than 5 ppm of total suspended solids by volume. For many applications, however,varying concentrations can be required. Pump manufactures suggest that less than l ppm by volume is acceptable to minimize pump damage and increase service life. Theconcentrationofsuspendedsedimentusuallyisestimatedusinga centrifugal sand sampler (Figure11. 20), or an Imhoff cone (Figure 11.21). The Imhoff cone is considered less accurate because of the small and instantaneous sample volume used. Accuracy of the Imhoff-cone method can be improved by increasing the frequency of sampling. The sediment concentration is determined 534 min After After start of test 4.Afterthetotal Near the end of the necessary. Groundwater andThirdEdition thewell sediment can be estimated mounted on thepipe. To obtainaccuratemeasurements,a u.s. Wells Figure 11.21. An Imhoff cone Iaused to estimate sediment concentration, but the small volume of the cone limits Ita accuracy. The recommended volume of water to be tested for sediment is determined the300 gpm, theis 300 times volume should be 50for 535 536Groundwater and Wells,ThirdEdition amount of sediment.Particle counters commonly arefoundinmunicipalwater supplies andwater-treatment plants. The acceptable sedi1nent concentration depends on theuse of the water. 'I'he National Ground Water Associati.on (NGWA)hasrecommended thefollowing limits,mostofwhicharewidelyacceptedinthewater-wellindustry (NGW A1998). Sediment concentration of Ippm (byvolume) for water tobeused directly incontact with, or inthe processing of, food and beverages. Sedimentconcentrationof lessthan2ppm(byvolume)forwells discharging directly intomunicipalwater-treatment or distribution mains. Sediment concentration of 5 ppm (byvolume) for water forhomes, instituti.ons,municipalities, andindustries. Sedimentconcentrationof10ppm(byvolume)forwaterfor sprinkler irrigation systems, industrial evaporative cooling systems, andanyotherusewhereamoderateamountof sedimentisnot especially harmful. Sediment concentration of 15ppm (byvolume) forwater fornood-typeirrigationinapplicationswherethe amount of sandpumping willnot harm thewellandpump. Inmanyinstances, anImhofl' cone or sand tester isnot availablt: at the well however a( 19-Q)bucket canbeused tocollect sediment and obtain a roughestimate of sand content.Ina( 19-9) bucket,l 0 ppm(byvolume) equalsapproximately0.04(tsp)(0.18ml)of sediment,whichis approximately theamount of sandthat cancover a dime (or a circle that has a 0.7-in( 18-mm) diameter)(FigureII Chapter 11. Development of Water Wells Figure 11.22. Amount of sand collected In a 5-gal ( 1 9 ~ )bucket sample of water that is equivalent to 1 0 ppm of sand by volume. AQUIFER-STIIIIIULATION TECHNIQUES 537 In many parts of the world, the only groundwater available comes from bedrock. Assumingthatthebedrock containssufticientwater storagetoservea water-suppl.yneed,the shortfallof a well's actualyield comparedwith thebedrock's potentia.!yieldcanarisefromeither thewell'sconstructionorthewell'scon-nectivitytonaturalwater-conductingfeatures.Methodsforimprovingthe performance of thewellitself throughwelldevelopmentarediscussed above. Thissectionaddressesselectmethodsof .improvingthepedbrmanceof the bedrockviastimulation. Wellsti.mulationisa techniqueusedtoimprove theconnectivity of a well tothewater conductorsinthebedrock.If thewatertransmissionintherock comesfromsparsefractures,thenthewellcouldpassthroughthefracture networkwithoutaconductorhavingsuffici.enttransrnissivityto produce thedesired yields. This effect canbea consequence of either thewell having anunfavorable orientation withrespect to the conducting fractures or the well'spassagethmugha portionof aconductivefracturethat haspoorl.ytransmissivity.Ineithercase,aquift:rstimul.ationisanattemptto improve theconnectivity of thewelltofracturesbyopening natural or existing fractures,or byartificial fractures. Hydrofracturing(asofferedbywater-wellismostapplicable lomaterial.sthatarehard,co1npetent,andindurated;andthatult.irnatelyderive 538Groundwater andThirdEdition Where: Tthe fracturetraJ!lsnus1nvtty or the di.stancebetween assumed tosmoothits essentialfractureswherea10-foldincrease .vuv-1u1uincreaseinwellprllowingrequirements. Flow rate= 120 gpm Pumping water level(PWL)10ft Suctionpipe length= 30ft Discharge and suctiondiameter3 in El.evationfrompumptodischarge20ft DischargedistanceI 00 ft Discharge pressure= 40 psi Chapter 12. Groundwater Pumps583 Fmmdiagram(a)in tion12.2. 12.25the followingcanbe statedusingequa-TDHh" + h,+ t ~+ I ~ +Vh From the example thefollowingcanbe determined. h,1 = Elevationfrompumptodischargeplusdischargepressure required( ft) = 20ft+ 92ft (40psi 2.31ft of water per psi) =112ft h, =Suctionlift (ft) = I 0 ft(PWL) fd= Discharge frictionhead (ft) =100ftof pipe3 ftfrictionlossper100ft of 3-inpipe(from frictionloss tables for3-in pipe) =3ft t:= Suction frictionhead (ft) 303ftfrictionlossper100ftof 3-inpipe(fromfrictionloss tables for 3-in pipe) 1 ft The centrifugal suction pump example yieldsthe foHowing. TDH112ft + 10ft+ 3ft+ .I ft =126ft For pumps that have a suction head instead of a suction lift, the TDH calcu-lationissimi.lar,asshowninthefollowingexampleofatypicaldomestic subrnersible-pump(FigureI 584Groundwater and Wells,ThirdEdition 10011level Check Valve Well Screen Submersible Pump SubmersibleMotor Figure 12.26. Typical domestic submersible-pump system (Servtech). Submersible Well Pump TDHSample Calculation This exampleshowshowtocalculatethe TDH of a simpl.c submersiblewell-pump app.licationthat hasthefollowingcharacteristics. Flowrate :::: 120 gpm Pumping water levelI 00 ft Pump set depth200 ft pipe diameter pipe distance pressure60 psi Elevationfromtopof30ft Chapter 12. Groundwater Pumps585 Asnotedondiagram(b)inFigureItheappropriatecalculationof TDHfor a pumpwitha suctionheadisasshowninequation12.3. TDHhdh,+ fd+ f,+ V11Verti.caldistancefrompumpintaketodischarge+discharge pressure requ.ired Pumpsetdepth+elevationfrompumptodischarge+discharge pressure required 200ft+ 30ft+ 139ft (60 psi. 2.31ft per psi)= 369n h,=Vertical di.stance fromthewellwater to thepumpintake =Pump set depth -pumping water level =200ft100 ft =I 00 ft ( 1=Discharge frictionheadinft (Pumpsetdepth+dischargepipedistance)frictionlossftper IOOftofpipe (200 ft + 200 ft) 3 ft frictionloss perI 00 ft of 3-inpipe 12ft f,Suction frictionhead inft :::: Not significant for submersible groundwater pumps For this example the followingcalculationresults. TDH369 ft + I 00 ft + 12ft48 I ft COMMON GROUNDWATER WELL PUMPS 1.2.27showsvarioustypesof centrifugalpumpsandconfi.gurat.ions. 'I'able12.2il.lustratessomeof themostcommontypesof groundwater pumps, their flow and head abilities, andthetype and size wellwhere they typically are used.'I'hesubsequentsect.ionsdescribethecommonpumptypes.Appendix 12.A(DVD) prov.ides a r r 1 o r ~ : : ~in-depthdiscussi.on. 586GroLmdwater and Wells,ThirdEdition CENTRIFUGAL PUMP TYPES u Figure 12.27. Centrifugal pump types and configurations. Chapter 12. Groundwater Pumps587 Table 12.2. Groundwater Pump and Well Comparison Type ol Well Envin)l'l mcnt.al; Sampling Domt,stic; Residen-tial Domestic; Residen-tial Nominal Well Dla-meter(ln) 2 to4 4to M Nominlll Well Depth (It) In IO 200 10 to :1030 to 2,000 Type ol Pump Multi slngcs.uh-1nersihle Shallow-well stage Multi-stagesub-mersible Nominal Flow (gpm} 0.5to 2 5!n 255to90 Impeller Type l'.ndnscd; Radialllow Enclosed; Radialnow

Radialllow Pump Selec-lion Con111ider-atlons Clmtanlinanl-free t:l>tlslmclinstruction matcriuls; Suit.ahlefor l)()tnhlew.;dcr; Max.lmmn suctionlift 25l'tLcud-fre" Cl)Ustmctlon materials; for pot.ul>lcwater; Allowablellow range; Sol itls-related wear I"C,-1\isLunce;NEMAstandard moto1 baseand resistance Motor Selel:ltion Considerations 2-into:!.75-in max.OD limits HP 121Ho240VAC single-phast llOWCftypical limits maxHI' Minimum cooling now past the motor casing; Sul>mcrsiblc cablevoltage

4-in 1notors max 10 liP; NEMAstundard base, shall; Lightning protection 588 Groundwater andThirdEdition12.Groundwater589 diameter 590Groundwater andThirdEdition 12. Figure 12.28. Shallow-well jet pump flow. Figure Tube Pressure Pipe Foot Valve Intake Pipe Deep-well jet pump. 591 592 ThirdEdition12. Groundwater593 contained Water-1 ubrlcated Sources for Additional Information electricalpower. 597 598 Groundwater andWells,ThirdEdition THEORY OF WELL BLOCKAGE Water flowing toward a well comes into contact with more surfaces and collides withmoreions,crystals,and colloids;thisprovidesopportunities forwaterto pairwithdissimilar chargesandformconglomerateandmineralcompounds. The compoundsthatoccurultimatelyformcrystalsthat areparticulatemauer too heavy to stayin solution.Eventually falling out of solution, the crystals con-tinueto growuntiltheflowpaths for groundwater areblocked.Thisphenom-enon canbeunif(xm, such as the fonnationof calcite (calcium carbonate), or it can be anaccumulation of separate crystals that are held together withclays or organicmatter also deposited bythenow of thewater. The major accumulation-which isthe truer definitionof incrustation-is theattachmentofthenewlyformedcrystalstothesurfacebytheadhesive action of a polysaccharide material produced by bacteria. The production of this naturalpolymer (sticky slime)bythebacteriaisthebeginningor theforming ol' incrustation.Allbacteria produce exopolymer and attach to a surface so that thebacterialcolonyisnotswept awaybytheflowof water.Thisattachment servestoformahabitat forthebacteria.Itisacollectionof bacteriaandthe polysaccharide exopolymer (or biofilm), and provides a place where the bacteria canmultiply andlive. The sticky polysaccharide is not water-soluble and isnot easily washedfromthe area.Oxygendiffusesthroughthe surface of the struc-ture for the aerobic organisms and water t1owsthrough thelatticework carrying oxygenand foodand removing waste products, enabling the biofilm colony to grow.Theslimealsoisaprotectivemechanismofthebacteriaandcanbe producedinamounts from30 to100 times the weight of the organism. IncrustationistheC(lmbination of mineraland biological depositsforming a complexmatrix. This matrix at times also can include natural clays, bentonite, andothercolloidal-likematerialfilteredfromtheflowof water.Additional discussionof incrustationiscontainedinthesectiontitled,of Block-age."Toassessthelikelihoodofmineralorbiologicalincrustation,water samplesfromthewellshouldbecollectedAppendix13.A(DVD) fora descriptionof sampling and a sampling form). Chapter 13. WellBlockage andRehabilitation599 ANALYSIS OF GROUNDWATER Overview of Laboratory Analysis A groundwater analysisshouldcover alltheinorganicparametersthatusually areassociatedwithastandardwater-qualityanalysis,andalsoshouldinclude a profile of bacterial activity. Consider including microscopic evaluation of the waterfordetectingsandsor silicacrystals,clays,andbacteriathataremore easilyidentifiedvisually.Table13.1andTable13.2showtypicalstandard commercial-laboratoryanalyses-including allof the elements of a laboratory report-to enable evaluation of the potential type and degree of incrustation that could be foundinthe well. Table 13.1. Typical Water Analysis and Control Report Well No.1WellNo.1 Casing After 3min*-(mam Aquifer Pumping 3-4 hr (malef Phenolphthalein al kall nlty*00 Total alkalinitY"*148172 Hydroxide alkalinity00 Carbonate alkalinity()0 Bicarbonate alkallnltv1481.72 pHValue7.67.8 Chlorides (as Cl)4549 Total Dissolved Solids291297 Conductivity (IJSIS)454464 Total Hardness184180 Carbonate hardness148172 Non-Carbonate hardness368 Calcium128116 Magnesium5664 Sodium (as Na)5366 Potassium (as K)2.63.0 ~ 0.20.3 .)0.00.0 0.50.4 Copper (as Cu)0.00.0 600 i\(luirer Low Groundwater and Well No.1 ThirdEdition Well No.1 601 the test for adenosine of bacteriamilliliter,Bothof these the 602 Groundwater andThirdEdition thebacteriainawater thinkthat this many labsdo use standardand therandomnatureofthenthetestsshouldthe the well. Whenincreases and numericalincreaseinthe count determinestheamount of ac.llt:n