PurposeAs with other classes of wells, adequate residential well water production, potability, and overallwater quality is enhanced by appropriate and regular service of the well system, including clean-ing of the well. Consumer confdence in residential water well systems for drinking water pur-poses can be enhanced by appropriate and regular service of the well system, including cleaningof the well to assure water potability, in addition to maintaining adequate water production fromthe well. For the purposes of this best suggested practice, the National Ground Water Associationdefnes cleaning as the removal from the well system of biological slime growths, naturalencrustations, and other debris.*Although it is critical to adequately clean a well before disinfectinga well system, this document distinguishes well cleaning from well disinfection. This documentintends to assist the professional water well system contractor in understanding how to effectivelyclean a residential water well system. The professional servicing residential well systems shouldunderstand that most residential well system owners are not accustomed to performing preventiveor routine maintenance on wells. Well owners, however, can be shown routine well and pumpcleaning and maintenance procedures that can provide a more dependable as well as a higherquality water source.IntroductionWater well systems, like other engineered structures, can deteriorate over time, and thereforerequire periodic maintenance.It is a requirement that the well system owner should assure the system is regularly and appro-priately maintained so as to maximize the quality and quantity of the systems water, as well as theoverall long-term use of the well system. The value in servicing the water well regularly is that itextends the life of the water well system, which in turn saves the homeowner replacement costs.A professional water well system contractor should be engaged to:a) Conduct annual inspection of the pumping system such as pump performance, wellseal/cap, storage tanks, controls, and water treatment equipment.b)Appropriately clean the well if cleaning is indicated as a need from the anaerobic bacteriasample evaluation.c) Appropriately disinfect the well following cleaning.Phone/ Toll-free 800 551.7379/ 614 898.7791Fax/ 614 898.7786Web/ www.ngwa.org and www.wellowner.orgAddress/ 601 Dempsey Road/ Westerville, Ohio 43081-8978 U.S.AResidential Well CleaningCompiled: April 2008NGWABestSuggestedPracticeAlthough it iscritical to adequatelyclean a well beforedisinfecting awell system,this documentdistinguishes wellcleaning fromwell disinfection.*For the purposes of this best suggested practice, the National Ground Water Association definescleaning as the removal from the well system of biological slime growths, naturalencrustations, and other debris.8/12/2008Approved by NGWABoard of Directors:2While water well system contractors are not necessarily specialists in analyzing water quality,they are a good point of contact for arranging water quality tests to check for deterioration.The well system owner can contribute to the well systems overall best condition by recognizingthese responsibilities: Always use licensed or certifed water well drillers and pump installers when a well isconstructed, a pump is installed, or the system is serviced and cleaned. An annual well maintenance check, including recommended water quality tests, is recom-mended. Any source of drinking water should be checked anytime there is a change in taste,odor, or appearance or anytime a water supply system is serviced. Keep hazardous chemicals such as paint, fertilizer, pesticides, and motor oil far away fromthe well. Periodically check the well cover, seal, or well cap on top of the casing (well) to ensure it isin good repair. Always maintain proper separation between the well and buildings, waste systems, orchemical storage facilities. When mixing pesticides, fertilizers, or other chemicals, dont immerse the hose inside thetank or container. This should prevent back-siphoning of chemicals into the water supply. When landscaping, keep the top of the well casing at least 1 foot above the ground. Slopethe ground away from the well for proper drainage. Avoid planting shrubs or trees (both ofwhich send down deep roots) around wells, and keep mulch away from wells. Take care in working around the well. A damaged casing could jeopardize the sanitaryprotection of the well. Homeowners should not pile snow, leaves, or other materials aroundthe well. Keep well records in an appropriate place that is secure and accessible. These include theconstruction report or well log, as well as annual water well system maintenance and watertesting results, other reports such as for site inspections, and manuals and data on pumps,tanks, and water treatment equipment. Be aware of changes in the well, the area around the well, surrounding land and properties(for example, sinkholes or new constructions), or the quality or quantity of water the wellprovides. If or when a residential well has come to the end of its serviceable life, have a qualifedwater well contractor properly decommission the well.Whenever a well shows signs of turbidity, loss of capacity, or taste and odor problems, or espe-cially if a bacteriological test is total coliform positive, it should be checked for overall bacterialpresence as these symptoms usually indicate high biological activity.*High biological activitygenerally means accumulation of organic matter and dictates a need for a good cleaning withremoval of accumulated debris.*Chlorination alone might temporarily prevent gas production or other taste and odor problems,but it leaves behind all the debris or accumulated organics which are a food source for future bac-terial growth. Cleaning, followed by disinfection, returns the well closer to the original conditions.Well cleaning must include removal of the pump with complete removal of debris from the wellbottom and should include brushing and cleaning of the well casing and well intake zones, withremoval of the pump. The contractor should also clean and fush the gravel pack and formationsurrounding the well. This fushing with proper chemicals will remove large volumes of bacteriaand their debris, thus removing many of the spaces sheltering coliforms, or in some instances,pathogenic bacteria. Once the heavy accumulation has been removed, the disinfection process isWhenever a wellshows signs ofturbidity, loss ofcapacity, or tasteand odor problems,or especially if abacteriological testis total coliformpositive, it should bechecked for overallbacterial presenceas these symptomsusually indicate highbiological activity.*In subtropical and tropical ground water, both total coliforms and high biological activity aretypically present.3more effective and the well can be returned to a near new condition with cleaner water brought tothe surface.A qualifed professional ground water contractor will best clean a water well system by follow-ing the procedures listed as follows.Understanding the Condition of the Natural Geologic Formationsat the WellPrior to implementing strategies for restoring a water well systems potability and production(volume of water or fow rate), it is critical to understand the condition of the well and borehole,as well as the natural geologic formation immediately surrounding the well borehole. Start bycollecting available well records, including the well construction log or record, as available.The drawdown caused by the well operation brings air (oxygen) into the well and encouragesvadose zone water to move more quickly toward the well. This introduction of oxygen encouragesgrowth of aerobic bacteria (bacteria requiring oxygen to grow) and oxidation of metals such asiron, especially in the upper reaches of the well. This is a normal operating condition of a well.Aerobic bacteria tend to cause clogging by the production of large amounts of slime and theentrapment of oxides of iron and manganese as well as other minerals. An anaerobic action isencouraged within the well as the water in the lower levels becomes depleted of oxygen as chemicalreactions and bacterial activity use up the oxygen present. Lower levels (especially sumps) mayhave no water fow and therefore no way to replace the oxygen in these areas. In addition, theseareas tend to accumulate materials brought into the well as well as the organic debris of bacterialactivity in the upper zones. As bacterial populations cycle in the oxygenated zones, the debrissinks to the lower levels, there becoming a food source for bacteria able to live in the anoxic(without oxygen) environment, the anaerobes. These bacteria, natural to the aquifer, which inhabitthe wellbore and the surrounding formation are responsible for the hydrogen sulfde (rotten eggodor), methane, fshy taste, and odors. These bacteria are also responsible for low pH resulting iniron taste and color to the water.The condition of the well may deteriorate as populations increase and byproducts of bacterialactivity, corrosion, and minerals accumulate. In addition, accumulation of heavy biofouling activ-ity from bacterial growth gives excellent areas for coliform to reside and proliferate, especially inthe anaerobic zone.Economics of Well Cleaning for the Residential CustomerAs with many decisions for infrastructure systems, there are certain decisions that the homeowner,in cooperation with the professional water well system contractor, must consider when striving toachieve a level of water quality and water quantity from the residential well system. Money is afactor; in general, residential customers do not budget for water supply maintenance. However,proper maintenance offers a positive payoff in extended pump and water treatment system life andreduced impacts on plumbing fxtures and appliances. Quality of life is enhanced as people enjoyhigh-quality water. In areas where ground water quality is challenging, regular maintenance maybe the only strategy that keeps rural water wells viable as a water source option.The age of the well can be a signifcant factor. The passage of time, coupled with changes innatural water quality and the need for maintenance, can impact the decisions to be reached as tohow much money the homeowner should invest to achieve a desired level of water quality andwater quantity.Certain cleaning options have the potential to damage the mechanical structures of an existingwell. For instance, if the wells water intake areas, or the well casing, have weakened over time,These bacteria,natural to the aquifer,which inhabit thewellbore and thesurrounding forma-tion are responsiblefor the hydrogensulfde (rotten eggodor), methane,fshy taste, and odors.These bacteria arealso responsible forlow pH resulting iniron taste and colorto the water.4they may be damaged or destroyed by more aggressive cleaning practices. In these instances, thewell owner and the contractor may decide to proceed directly to new well construction, or preparefor that option if cleaning causes irreparable damage.There are a number of means available to a professional water well system contractor cleaningwater wells. These are arranged into two categories: mechanical processes and chemical processes.Either the mechanical or the chemical processes are most effective when used in concert.Mechanical Processes Inventory for Residential Well CleaningAirburst: (Frazier Technologies Inc.) A specialized method of cleaning employing an air orgas (typically nitrogen)-actuated seismic tool to loosen both hardened deposits andbiofouling as part of a cleaning process.Airlift: Lifts fuid in a well to the land surface using compressed air, often associated withairlift development or an airlift test.1Bailer: A cylindrical device suspended from a wire rope or cable, which is used toremove sediment or other material from a well or open borehole. Bailers maybe equipped with various types of valves or trap doors at their base to allowsediment to enter the bailer and be retained within it while the bailer is pulled tothe land surface. Types of bailers include dart valve bailers, fapper valve bailers,suction bailers, and scows.2Carbon dioxide: Either in its solid dry ice form or as part of a specialized process using liquidand carbon dioxide gas, is used as part of a well cleaning process that employschemical, thermal, and mechanical activity to loosen deposits.Casing scraper: May be used to remove deposits on the casing. Probably more universallythought of as a tight-ftting swab or surge block with a brush.Develop the well: To surge, bail, pump, swab, airlift, jet, or otherwise conduct operations at a wellthat will increase the wells specifc capacity by removing fne sediment anddrilling fuids, and create a well-packed and graded flter pack envelope aroundthe well.2Hooded or shrouded pumps: Pipe, larger in diameter than the well pump, is inserted over thepump to increase suction in given areas to improve the removal of debris.Hydraulic fracturing (hydrofrac): Stimulate (improve) well production by increasing the second-ary porosity and permeability of the producing formation. During a hydraulicfracturing operation, a fuid, typically clean water for residential wells, is intro-duced into the borehole under high hydraulic pressure such that the fracturegradient of the formation material is exceeded, and the rock formation yieldsmore water.Injected water: Any injected water must be from a potable source (not pond water) and freefrom undesirable microorganisms and debris. All injections and cleaninggenerates dirty water that must be properly contained, treated, or hauled offfor disposal.5Jetting: Developing a well by applying high-velocity horizontal streams (jets) of waterto the well screen. Although used in the past, compressed air jets are discour-aged due to the encouragement of increased aerobic bacterial activity. Jet devel-opment can be conducted using the application of chemical additives, and withsimultaneous pumping or airlifting.2Pump-and-surge*: Well development process that involves alternately pumping and surging awell. This is accomplished by pumping the well at sequentially increasingpumping rates to allow the water in the pump column to backfow into the wellto provide a surging action that helps to fush out fne-grained sediment andaugment the well development process. To accommodate the pump-and-surgedevelopment process, the pump equipment is installed without a foot valve(jet pumping system) or an in-line check valve (submersible pumping system).Also known as backwashing development, overpumping development, andpumping development.2Rawhiding*: A method of developing a well by pumping the well without a foot valve (jetpumping system) or an in-line check valve (submersible pumping system)installed to prevent backfow through the pump, to allow backwashing of thewell through the pumps column pipe (see pump-and-surge).2Recirculation*: Using the standing water in the well and recirculating it to remove debris andbiological material in the well.Sand pumps: A type of bailer used to remove sediment from a borehole or well. The sedimentis kept in the bailer with a hinge fap valve and a plunger located within the bar-rel of the sand pump. Also termed a moran bucket and suction bailer.2Sonar jet: A technique for cleaning scale from a well casing by use of sonic waves that areemitted from sequentially timed blasts in the well.Surge block: A plunger-like tool consisting of solid or perforated pipe sandwiched betweenleather or rubber discs that is used in well development.2Wire brush To remove scale from a well casing by scraping it off with a steel or stiff plasticbrushing tool. The brushing tool is often constructed of partially uncoiled wirerope or cable or a similar very stiff material.2Chemical Processes Inventory for Residential Well CleaningAcidize: To add or circulate acid in a well or open borehole to clean scale or open theaquifer to improve water production characteristics. This is currently the primarycleaning chemistry used to remove mineral deposits from the well screen, gravelpack, and the immediate formation. Acids that are typically used to acidize wellsinclude citric acid, sulfamic acid, food-grade phosphoric acid, and hydrochloricacid (HCl). The acid used should be chosen carefully in combination with therock formation to maximize effciency or productivity. Acidizing limestone*Pump-and-surge, rawhiding, and recirculation are often used in place of pulling the pump and donot allow thorough cleaning of the well and removal of the debris from the well bottom or sumpzone. Further, rawhiding, recirculation, and pump-and-surge often develop and clean the higherzones but often pack the lower region with even more debris, encouraging poor anaerobic andcontaminant accumulation.6with HCl (the most effective choice for this application) to open pore spaces andfractures is more commonly used, but it is not effective if the carbonate rock isdolomitic or shaly. Acid is a dangerous material and the practice of acidifcationcan be hazardous; therefore, only people trained in these procedures with theproper equipment should perform acid cleaning of wells. While chemicalinhibitors can and should be used to limit corrosion of the well structure,extreme care should be used in the use of this type of chemistry. Only NSF-approved inhibitors should be used due to their often extreme toxicity.2Acid blends: A blend of two or more acids, typically with dispersants or surfactants, toimprove the cleaning procedure. Usually a mineral acid is used to remove orloosen the mineral deposits while a range of organic acids used appropriatelycan be used to improve the removal of iron, manganese, and biofouling. Theseare often available (National Science Foundation 60 listed) in convenient pack-ages with instructions from well equipment and material suppliers.Hydrochloric: A very aggressive liquid mineral acid very corrosive to stainless steel. But it is agood solvent for iron and sulfate minerals. However, if carbonates are present itmore typically will dissolve those frst. Its fumes are very acidic and often causesevere deterioration of electrical components, as well as being hazardous to softtissue. If combined with chlorine in solution, chlorine gas is generated. WhenHCl is used on iron sulfde clogs, dangerous levels of hydrogen sulfde may begenerated. Both chlorine and H2S are at best irritating and at worst lethal, espe-cially in confned spaces. Limited numbers of National Science Foundation(NSF)-listed formulations are available, and commercial or industrial productsare often highly contaminated with heavy metals. The acid is relatively ineffec-tive against biofouling. The cleaner forms of HCl, such as NSF approved andfood grade quality, should only be used.Phosphoric: A strong, primarily food-grade, liquid mineral acid that is effective against metaland mineral hydroxides and somewhat effective against biofouling. It is anexcellent iron control acid and effective against both carbonates and sulfateminerals. If left in the formation, phosphorus-containing compounds or productscan form minerals which have been implicated in increased bacterial activity.Dispersants should be used to prevent this formation. Phosphorus can attach toclays and a variety of rock minerals and promote bioflm regrowth; therefore,it is necessary to remove spent phosphoric acid from the well.Sulfamic: Solid granular tablet or powdered acid often used in blends that are relativelyeffective against carbonates, weakly effective against sulfate minerals and irondeposits. Sulfamic is used in blends to keep pH down during cleaning procedures.As with all blending, this should be performed at the surface.Muriatic: Industrial name for hydrochloric acid, usually a lower concentration of 20% orless acid. Often of substandard purity, industrial grade muriatic (such as sold formasonry cleaning) can contain heavy metals. This is no longer recommended forwell cleaning use.7Glycolic acid (hydroxyacetic acid): An organic acid especially effective against biofouling andcarbonate clogging. NSF lists 60 products available, often as a blend. While thisacid has some bactericidal activity, it must be maintained at 5% concentration todo so. Hydroxyacetic has been known to leave signifcant organic salts in theaquifer which lead to enhanced bacterial growth. As with any of the potentialdownsides of chemical choices, proper dosage, careful application, andthorough post-dosage development serve to maximize benefts and minimizedisadvantages.Acetic: An organic acid that is the active compound in vinegar which can be as high as90%. As with any acid, mixing and treating in closed unventilated areas is notrecommended. The high concentration form of the acid has a pungent and oftendangerous off-gassing which can lead to lung and eye damage. However, whenmixed at recommended levels, it is much safer to handle than mineral acids.Laboratory testing has shown only limited effectiveness against biofouling atambient temperatures. It has been successfully used for many years for this pur-pose, although hydroxyacetic acid is generally preferred. More so than hydroxy-acetic (glycolic), however, residual of acetic can be a source of organic carbonfor regrowth. Acetates remaining after cleaning are typically a small fraction ofthe assimilable organic carbon (AOC) found in ground water if good develop-mental practices are used.Citric: A weak organic acid, usually in a granular form. It provides increased control ofiron redeposition during acid cleaning with a strong mineral acid. It has consid-erable organic carbon and is an excellent food source for bacterial growth. Thisacid should not be used in ground water with signifcant calcium content as itforms calcium citrate.Oxalic: A very strong organic acid in crystalline form. It is very effective in dissolvingiron and manganese deposits. Care should be used as byproducts of cleaning canform oxalates which are known rodent poisons.Hypochlorites: Salts of hypochlorous acid that are powerful oxidizers. Calcium and sodiumhypochlorite are used as a disinfectant for water wells. The sodium form isthe best disinfectant due to its better solubility and penetration rate. Calciumhypochlorite is the powdered form and is considerably less soluble in hard waterareas. Calcium hypochlorite is a strong oxidizer and as such should not be storeddamp or mixed with organic material of any type. The product can be explosiveeven mixed with a simple organic detergent or motor oil.Biodispersants: Organic polymers that are designed specifcally to disperse the polysaccharideslime produced by bacterial cells. They also provide control of mineral depositcomponents once they have been dissolved by acid cleaner. This dispersantaction provides for a substantial increase in the washout of the debris from thewell and the surrounding formation following the cleaning procedure.Surfactants: Surface-active agents allow penetration and easy movement in cracks andcrevices that require cleaning by reducing the friction between the cleaning solu-tion and the surfaces of the screen and mineral formation. Surfactants are neces-sary for preventing air locks or the plugging of fow pathways by air bubbles.8The decision to cleanthe well should bebased on one or morefactors, such as poorproduction, observa-tional reports dealingwith water quality,or feld or laboratoryanalysis.Caustics: Chemicals which raise pH to alkaline range (7.0+). Caustics are useful in emul-sifying oils, neutralizing acids, removing bacterial slime, and are main compo-nents of certain chemistries which degrade biocides.Sodium hydroxide: Caustic material sold industrially as Liquid Caustic, a 50% solution.Potassium hydroxide: Caustic sold industrially as Liquid Potash, a 45% solution.Magnesium hydroxide: Caustic material sold commercially as a 50% to 60% slurry. As a causticit is often used to neutralize acid cleaners. It is diffcult to overtreat the productbecause solutions of the material will not exceed a pH of 9.5.Corrosion protection: Using cathodic protection or corrosion-inhibiting chemicals to protectcasing and equipment while acidizing.Acid enhancers: Special polymers, usually mineral dispersants, which increase the effectivenessof an acid by improving the solubility of the mineral deposit as initiated by anacid reaction.Steps in Residential Well CleaningLocal geologic conditions will impact on the wells condition, so the contractor will most likelyneed to employ a range of options to accomplish the best work for the customer.Let us discuss open borehole open hole and cased completions in wells. The open boreholewells are holes drilled into the aquifer with the casing placed in the upper portion of the hole tostabilize unconsolidated formation materials and facilitate the installation of grout for the sealingof the well to prevent surface contamination. The second type is the screened well which consistsof a casing and screen or perforated pipe in the water bearing zones.Specifcally, wells are constructed to ft the geology of the area, with the open borehole wellbeing placed in consolidated formations and the screened well placed where geology is unconsoli-dated, such as alluvial deposits, plains, or river basins.The construction of the well will necessitate some changes in the technology of well cleaning.The decision to clean the well should be based on one or more factors, such as poor production,observational reports dealing with water quality, or feld or laboratory analysis. Because biologicalfouling can lead to heavy blockage with mineral accumulation, taste and odor problems, red water,and possible coliform or pathogen contamination, a simple assessment of biological activity can besuffcient to determine the need for cleaning. The simplest assessment for biological fouling is todirect the testing to the anaerobic bacterial population. When the anaerobic bacterial community isabundant in the well, the well sanitation is in poor condition and in urgent need of cleaning. If thecontractor suspects that the well problem is due to the sanitary condition of the well, he shouldtake along a test kit or the means to sample the well water to provide evidence to the well owner ofbiological buildup in the well. If he performs his own testing, he should be trained in appropriatemethods.Several versions of user-friendly tests can provide a useful assessment of biological activity andfouling within the well structure. This fouling leads to blockage through mineral precipitation andthe accumulation of contaminants of both a chemical and biological nature. This precipitation andaccumulation of contaminants also enhances corrosion of the well structure and taste and odor inthe water. The well contractor should consult with a microbiologist familiar with biofouling andbiocorrosion on how to choose and use the right tests. The sample for biofouling analysis ideallyshould be drawn from a tap between the well and the systems tank, so as to establish the condition9All wells willrequire the temporaryremoval of the pumpand isolation ofwater treatmentor conditioningequipment toaccomplishcomplete cleaning.of the water in the well. The sample can also be taken from open pump discharge or from a sterilebailed sample. However, if such options are not available, the test can be taken from any tap withinthe system under evaluation, recognizing that the sample quality is compromised.The sample should be collected in a sterile glass or plastic container. The container should beflled completely and capped immediately. The contractor must not cough or touch the water sam-ple, the containers neck, or inside of the cap. The sample should be collected in midstream andthe faucet or orifce should not come in contact with the sample container. The sample should becollected in the morning or at a time when the well has sat idle for at least eight hours. Water fromthe down piping should be discharged and the water representing casing water should be collected.This may require running the pump for 10 to 30 seconds or a calculated period of time beforecollecting the sample. The sample should be delivered to a laboratory or used in a feld kit within12 hours. The sample should be kept at ambient ground water to room temperature and in a darkspace.The water well system contractor should conduct a fow test to check fow and (if possible) thedrawdown. If the contractor is unfamiliar with these, NGWA recommends consulting the Manualof Water Well Construction Practices. It is essential that well tests be performed properly to obtainvalid information.All wells will require the temporary removal of the pump and isolation of water treatment orconditioning equipment to accomplish complete cleaning. Any equipment removed from the wellshould be secured from exposure to bacterial or chemical contamination. When this equipment isready to be reinstalled, it should be cleaned and disinfected appropriately, as well.Check the apparent structural integrity of the casing and screen with a downhole camera.Determine the real bottom of the well compared to the assumed bottom of the well so as to beable to determine that all accumulated well debris has been removed.A mechanical process or combination of mechanical processes should be used to begin the wellcleaning. The water well system contracting professional will use his experience to determine thebest selection from among many options.Brushing and surge block surging is used for cased and screened wells. Jetting is the method ofchoice in open borehole wells in some friable formations as surge blocks and brushes can harmsome of the more fragile borehole formations, such as Cretaceous or Triassic rocks in the centralstates. Over much of the North American Great Lakes region, surge blocks and brushing are pre-ferred methods that are used very successfully in open rock boreholes (carbonates and sandstone-shale sequences) and screened wells alike. Water or chemical jetting is preferred. Air jettingshould be avoided, although single-pipe air development is successfully used in open boreholecompletions.Where these methods are not readily available, economical, or feasible (as with very smalldiameter wells) to deploy, airlift surging is a highly effective cleaning method for residential wellsthat can be accomplished with rental-class compressors available in many communities. Airliftingis also an effective adjunct to surge block cleaning. Surging should be accomplished with a lightpulsing that moves water up and down inside the well. Other methods such as Airburst or Sonar Jetmay be used as well.Once the surging (airlift or surge block or both) has been completed, the water in the boreholeshould be evacuated immediately to prevent settlement of suspended debris in the well environ-ment. Evacuate or pump all the loosened debris from the well bottom. It is imperative that thisaction be completed to the bottom of the well.Following or in conjunction with a mechanical process, the water well system contracting pro-fessional should use an appropriate chemical cleaning process.10When using a chemical cleaning process, the prepared cleaning solution should be equal to 1.5to 2 times the standing well volume (SWV). The contractor will need to be familiar with formationcharacteristics as many rock formations will not accept more than 1.5 times SWV, while in morecavernous formations, 2 times may not be nearly enough. Most screened wells will accept 2 timesSWV. This solution should be tremied into the well evenly throughout the well. It is excellentpractice to use approximately 20% of the solution to clean the area above the water line.All chemicals mixed for well cleaning should always be neutralized above ground when pumpedback out after cleaning.When using an acid solution, be sure to maintain a pH of 3 or lower throughout the duration ofcleaning. Additional acid should be added if the pH rises above 3 before the solution is pumpedfrom the well. If the pH rises above 4, more than half of the dissolved debris will drop out of solu-tion and be prevented from being pumped from the well.If the solution is to be left in the well overnight to improve dissolution of contaminants, thensome surging should be applied the following day prior to pumping out any residual cleaningsolution.A water well system contractor may elect to conduct a downhole inspection of the cleaned wellprior to disinfection.Well DisinfectionWell cleaning should then be followed by a thorough disinfection of the well and its immediateenvironment.It is diffcult to test following the cleaning process and prior to well disinfection. It is recom-mended to move directly from cleaning right to disinfection as testing for bacteria is diffcult atthis point due to disturbance in the well. Warning: Be sure all the acid is pumped from the well ashypochlorite used for disinfection may release chlorine gas if the pH is 5 or below. The pH of thedischarge water should be checked several times to ensure that pockets of acid do not remain.The water well system contracting professional should consult the National Ground Water Asso-ciations Manual of Water Well Construction Practices for guidelines for well disinfection.Ricky LaymanJames C. Hefty, CWD/PILawrence H. LaChance, MGWCKevin B. McCray, CAEJohn H. Schnieders, Ph.D.Stuart A. Smith, CGWPGilman G. VioletteNeil MansuyTodd E. HunterJames R. SparrowMichael VaughtTom PlatzerStephen OrdwayClifford L. GrievesMichael WiedornMichael Barcelona, Ph.D.Tom SmithAbnel EstabaKieth LarrimoreJohn W. Pitz, CPIRobert W. Masters (NGWA staff)Compiled by: Jonathan Jenkins (NGWA staff)When using a chemi-cal cleaning process,the prepared cleaningsolution should beequal to 1.5 to 2times the standingwell volume (SWV).The contractor willneed to be familiarwith formation char-acteristics as manyrock formations willnot accept more than1.5 times SWV, whilein more cavernousformations, 2 timesmay not be nearlyenough. Mostscreened wells willaccept 2 times SWV.This document was prepared as the result of regular meetings of a task group composed ofrepresentatives from among the NGWA membership and dually affected individuals. Thesevolunteers included:11References1NGWAs Illustrated Glossary of Drillers Terms, NGWA Press, 20042Ibid.Disclaimer:This publication is a collaborative effort to try to set forth best suggested practices on this topicbut individual situations and local conditions may vary, so members and others utilizing thispublication are free to adopt differing standards and approaches as they see fit. The Associationassumes no liability or responsibility for the contents of the publication.Copyright 2008 by National Ground Water Association PressISBN 1-56034-079-7Published by: NGWA PressNational Ground Water Association601 Dempsey Rd.Westerville, OH 43081-8978Phone/ 614 898.7791Fax/ 614 898.7786Email/ customerservice@ngwa.orgN G WA P r e s sRevised 11/2009