Good Practices In Maintaining Hand Pumps & Production WellsBy Upul WickramaratneHydrogeologist / Manager (Groundwater)Groundwater SectionNational Water Supply & Drainage BoardChilaw RoadWariyapola

Groundwater ??

Animals and Villagers are using same Water in Drought Affected Tanks in Pothanegama

Dug well Constructed on Dry Tank-Warawewa

Dry Dug Well at Weewalayaya Village Distributed among common place in village by Social Service Department and Water Supply by Bowser.

Dug Well Constructed on Dry Stream - Polpithigama

Construction of Dug Well, blasting rocks Andarayaya, Polpitigama

Relevance to an Emergency

Groundwater can be developed quickly in some situations shallow tube wells/ Deep tube wells available drilling equipment (eg. Manika Farm 2009)If deep wells may be available Could be included in emergency water supply solutionNeed to understand capacity, condition, constraints on use Potential for future development later in emergency

What is groundwater?Groundwater is water that is found underground in the cracks and spaces in soil, sand, and rocks.Groundwater is stored inand moves slowly throughgeologic formations called AQIFERS which capable of yielding enough water to supply peoples' uses.

How does groundwater move?Underground, water slowly moves from an aquifers recharge areas (areas where water seeps into the aquifer from rain fall to its discharge area (like streams, springs and lakes).Groundwater is always moving (this is called groundwater flow) and moves very slowly--only inches per year.groundwater flowdischarge areaevaporationrecharge areaprecipitationcondensationrunofftranspirationaquiferwater tableinfiltrationHydrologic Cycle

Hydrogeology: Science which treats of occurrence distribution and movement of water under the earth surface

Major Features of the GW System to Remember

Porosity: is defined as the ratio of the volume of voids to the volume of aquifer material. It refers to the degree to which the aquifer material possesses pores or cavities which contain air or water. Permeability: The capacity of a porous rock, sediment, or soil to transmit ground water. It is a measure of the inter-connectedness of a material's pore spaces and the relative ease of fluid flow under unequal pressure.Pores, Porosity and PermeabilityPores: The spaces between particles within geological material (rock or sediment) occupied by water and/or air.

Primary Porosity

Secondary Porosity (Hard Rock Aquifers) Hard Rock Lime Stone CavitiesFracture

Aquifers are replenished by the seepage of Precipitation that falls on the land, but there are many geologic, meteorologic, topographic, and human factors that determine the extent and rate to which aquifers are refilled with water.Rocks have different porosity and permeability characteristics, which means that water does not move around the same way in all rocks. Thus, the characteristics of ground-water recharge vary all over the world

How can we trap the groundwaterBy dug wellsShallow tube wellsDeep Tube wellNatural springs

Well installation methodsHand excavation / boringHand drilling incl auguring and jettingMachine drilling Rotary, percussion, down hole hammerDrilled wellsReach greater depthsPenetrate wider range of rocks

Drilling

Summary of Types of Wells

Cross section of fractured aquiferHigh yield TW

Maintaining Of Tube wellsShould be a proper design and construction

Fractured AquiferFractures form conduits through which groundwater and pollution can moveRock matrix stores waterBoreholes intercepting fractures can have high yields

FractureRock Matrix

Water LevelSand & ClaySand & ClayHard Clay (Brown)Gravel Sand Clay & Calcareous Rock FragmentsGravel & ClayBlank PVC Casing 225mm (1000T)Gravel Pack (Filter Pack)Clay filledScreen PVC Casing 225mm (1000T)Sandy clayGravel & ClayHard Clay (White)Main AquiferTW design..Hard rockOpen hall22.4m27.8m31.0m14.2m

Test pumping of wellsCompleted after well developmentTests the potential pumping rate and resulting drawdownAssists in determining :Long term pumping rate and water levelSuitable pumpImpact on surrounding wells or environment

Pumping testsStep drawdown test short periods of pumping at progressively higher rates and measuring drawdown in the wellhelps work out achievable pumping rateConstant rate testPumping at constant rate (could be for days or weeks)Measure drawdown in well and nearby observation wellsHelps assess pumping impacts on the aquifer under different pumping scenarios

Pumping Test

Step Drawdown TestQ = 3,000 gpmDrawdown = 17 ftSpecific Capacity = 176 gpm/ft

Time Drawdown Test

Failures Being operating HPTW or PW performance of wells such as WQ variation and quantity could be declinedDue to Construction failure, Formation failure, Aquifer failure, Clogging or Scaling of Ca, iron & iron + magnesiumOVER PUMPING

OVER PUMPINGWhat is Over pumpingWhen exceed the given recommendation of pumping rate and duration

Is that Pumping Test recommendation everlasting No, because more than 80% of groundwater recharge from directly precipitation. If any change of rain fall pattern then recommendation could be changed.

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Specific Capacity of a WellThe rate of discharge of water well per unit of drawdown, usually expressed as m3/d/m.Allows a check of well efficiencyHelps indicate bore deterioration eg blocked screensReduced capacity (greater drawdown to pumping rate) indicates reduced well efficiency

Decline In Specific CapacitySTATIC WATER LEVEL130 GPMOriginal Drawdown, 40 ft SC = 50 gpm/ft Specific Capacity, gpm/ftTIME ---->504030201060 FT SC = 33 gpm/ft80 FT SC = 25 gpm/ftAQUIFERPumping Level ---->Clogging Of Screen SlotsDue To ScalePumping Level ---->Pumping Level ---->Loss In Specific Capacity

Degradation Of Water Quality

Pumping Excess Sand

Pumping Any Gravel

Pumping AirTime to Rehabilitate Well

Discharge Rate, gpmDrawdown, ftDesign Discharge

Design Drawdown

Analysis Of Well Efficiency - Specific Capacity DiagramWell Efficiency, %100

0Well Efficiency

Cones of Depression

Cone of depression forms in the water table when water is pumped from a well

The pumping of wells can have a great deal of influence on water levels below ground, especially in the vicinity of the well, as this diagram shows. If water is withdrawn from the ground at a faster rate that it is replenished by precipitation infiltration and seepage from streams, then the water table can become lower, resulting in a "cone of depression" around the well. Depending on geologic and hydrologic conditions of the aquifer, the impact on the level of the water table can be short-lived or last for decades, and the water level can fall a small amount or many hundreds of feet. Excessive pumping can lower the water table so much that the wells no longer supply waterthey can "go dry."

How intensive ground-water pumping can cause salt-water intrusion in coastal aquifers. Theoretically 1m drawdown creates 40m uplift

What Causes The Well To Need Rehabilitation?Clogging of PerforationsCorrosion Enlargement of Perforations Holes in Casing or ScreenCementation in the Near-well Zone (Eg. Filter Pack)Sand Sealing

When the Well Screen Slot Opening Is Too Small, Fine-grained Material Which Normally Migrates Through the Filter Pack on Start Up, Consolidate Near the Well Screen Creating a Low Permeability Zone Which Greatly Accelerates Well Losses.Well ScreenFilter PackAquiferSand SealingLow Permeability ZoneAdjacent to Well ScreenDue to too small a slot size

How Do I Know If My Loss In Production Is Due To My Well Or Is It A Well-field Problem?Well-field InterferenceRegional lowering of ground water levels leaving the most productive aquifers High And DrySeasonal Fluctuations in Recharge

Do All Wells Need Rehabilitation ?Experience in the Industry has shown that approximately 10% of all Large-capacity Water Supply Wells will be relined at some time during their lifeRehabilitation Percentage is much higher -- 70%It is rare that a well will operate without some rehabilitation during its life

Clogging IronIron Magnesium Clogging process could increased due depletion of water level by creating aerobic environment

HCL 10%HCL 5%Well Klean 20%HCl 5%Citric 1%Citric 10%Phosphoric 8.5%Laboratory ResultsAfter Dissolving Scale In Acid

Decision Tree For RehabilitationARE POTENTIAL BENEFITS INSUFFICIENTORREHABILITATION COSTS > REDRILLING COSTSREDRILLREHABILITATIONPOTENTIAL BENEFITS SUFFICIENTANDREHABILITATION COSTS < REDRILLING COSTSEVALUATE POTENTIAL BENEFITS AND COST OF REHABILITATIONIS WELL APPROPRIATE FOR REHABILITATION?(design, age, operational history, location)IF SOIDENTIFY PROBLEM AND CAUSE

The development of tube well is essential process to obtain an efficient and long lasting well. The main objectives of well development are as under: Repair to damage done to the formation by drilling operation and restore the original hydraulic conductivity of the aquifer. To increase the porosity and permeability of the water bearing formation in the vicinity of the well by removing finer material of aquifer Tube well development

Tube well development cont..

To stabilize the formation around well screen to yield sand free discharge.All the new wells should be developed before being put into production well. It well achieve highest specific capacity and ensure energy efficient well.We know that Tube well is an important and costlier structure in water supply schemes.

Well development Methods Surging and pumping with air-compressorRe-drilling with air-compressorOver pumping Back washing High velocity water jetting Use of explosive Use of acidHydro fracturing

Life time of TWDeveloped countries (Sweden, Denmark, Norway, UK, USA) 30 to 60 yearsSri Lanka - 4 to 10 years

If proper maintenance system implemented could be improved- 20 to 30 years

GROUNDWATER MONITORING is very IMPORTANT to avoid this problem

Thank you

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