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Groundwater Development and Drilling

Groundwater Development and Drilling. Session 4 Developing Groundwater Sources. 1. Session Aims. Provide guidance on appropriate methods of developing groundwater resources. Clarify understanding of the development of groundwater by wells, boreholes, spring enhancement

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Groundwater Development and Drilling

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  1. Groundwater Development and Drilling Session 4 Developing Groundwater Sources 1 GWD4

  2. Session Aims • Provide guidance on appropriate methods of developing groundwater resources. • Clarify understanding of the development of groundwater by wells, boreholes, spring enhancement • Discuss excavation and drilling techniques appropriate to hydrogeological conditions. 2 GWD4

  3. Wells and Bores • Wells are holes in the ground that intersect groundwater and enable groundwater to be brought to the surface • Holes are dug by hand or by drilling machine • Walls of the hole usually supported • Depth depends on aquifer type, available yield 3 GWD4

  4. Drilling techniques • How do you……? GWD4

  5. Types of wells Shallow well Hand dug Unconfined water table aquifer Groundwater recovered by hand or low rate suction pump 5 GWD4

  6. Types of wells Deep well Machine drilled Confined and unconfined aquifers Groundwater recovered by pump 6 GWD4

  7. Well installation methods • Hand excavation / boring • Hand drilling • incl augering and jetting • Machine drilling • Rotary, percussion, down hole hammer • Drilled wells • Reach greater depths • Penetrate wider range of rocks 7 GWD4

  8. Hand completed wells • Hand augering a small hole • install narrow casing - tube well • Hand digging larger diameter (~1m diam) • Ground must be soft enough to penetrate • Shallow water table required 8 GWD4

  9. Application of hand completed wells • Likely in the very first phase of an emergency • equipment can be mobilised quickly • produced from available materials • Relatively low cost • Often local expertise available • Can be labour intensive 9 GWD4

  10. Hand Auger drilling • VIEW Video of hand augering: http://www.youtube.com/watch?v=qq0p_WPwSZo • Affordable Water Well Drilling in Sierra Leone - Fresh Hope Ministries International 7min http://www.youtube.com/watch?v=UYay9-2UMwM 10 GWD4

  11. Shallow hand auger wells A C B D 11 GWD4

  12. Hand dug Groundwater wells GWD4

  13. Lining of Hand Dug wells From Oxfam Manual on Hand Dug Well Equipment 13 GWD4

  14. Completion of Hand dug wells Simple open holes, no protection from contamination Sanitary surrounds with hand pump 14 GWD4

  15. Bore Drilling • Drilling equipment and technique is affected by: • rock type(s) encountered • depth to groundwater • aquifer pressure 15 GWD4

  16. Hand operated drilling • Narrow diameter (< 100mm diam) bores • Casing installed to construct tube wells (narrow diameter production wells). VIEW YOUTUBE FILES Shallow percussion: http://www.youtube.com/watch?v=N3CUnUrMo6s&feature=related Shallow percussion in Senegal: http://www.youtube.com/watch?v=VWaTBNt0n9o&feature=related Deep well in Dhaka slums 200ft (>60m) deep: http://www.youtube.com/watch?v=nIvgg6QTKj4 16 GWD4

  17. Jetting Techniques Use water pressure forced down a drill pipe through a nozzle to penetrate the soil Need a source of water and pump to provide the pressure Source: Water for the World, Constructed Jetted Wells, Technical Note No RWS 2.C.3 17 GWD4

  18. Jetting Techniques Use water pressure forced down a drill pipe through a nozzle to penetrate the soil Need a source of water and pump to provide the pressure 20m deep jetted well, near Matatuto, Timor Leste 18 GWD4

  19. Jetting Videos A jetting operation in Ethiopia: http://www.youtube.com/watch?v=cHu5yFQn660&feature=related Jetting in Indonesia: http://www.youtube.com/watch?v=D-pmZe2aQuY&feature=related A backyard well in USA : http://www.youtube.com/watch?v=FbGUV7GQpMM&feature=fvw 19 GWD4

  20. Machine Drilling Advantages Can reach great depths Can penetrate wide range of rock types Can produce high yielding wells Disadvantages 20 GWD4 Expensive Require highly skilled crews Can have long lead time from set up to completion May be privately or Govt owned and not available for an emergency

  21. Percussion Rigs crushes the rock under the weight of a tool dropped down the hole on a length of cable Suitable for unconsolidated and soft formations Relatively slow VIDEO: of cable tool operation :http://www.youtube.com/watch?v=vEIyPhQdqrw&feature=related Application in the Philippines: http://www.youtube.com/watch?v=mXAS0UUc7Ek&feature=related 21 GWD4

  22. Rotary Rigs Photo of Rotary rig, with drill bit and drilling rods visible – white tubing is PVC casing to be installed in the bore. Photo courtesy GHD Pty Ltd Can drill to great depths (1000+ m) Drill bits attached to the end of a segmented string of steel drilling rods As the drilling rods rotate, the bit grinds through the soil and rock Air, water or drilling mud used as a circulation fluid to remove cuttings of rock and soil 22 GWD4

  23. Rotary Rigs • VIDEO of a mud rotary rig http://www.youtube.com/watch?v=ZVlzCs3686s • Some rotary rigs require no mud and are powered by air to activate the drilling bit. This is shown on the following video: http://www.youtube.com/watch?v=Qa0SL6h3pF8&feature=related 23 GWD4

  24. Constructing a Well • In most drilled wells, the walls need support • Wells are cased with lengths of factory-made pipe • Casing can be steel or plastic (Eg PVC, PE, ABS) • Holes in very strong rock sometimes not cased Installation of plastic casing in rotary drilled bore, Photo Courtesy GHD Pty Ltd 24 GWD4

  25. Constructing a Well Highest flow from an aquifer into a drilled well is ? throughthe most permeable zones Identified through: Drill cores “Cuttings” pushed to surface during drilling 25 GWD4

  26. Opening the well to the Aquifer • Cased wells need to have a screen to allow water to flow from the aquifer into the well • Screens are a length of slotted or perforated pipe • Typically PVC, steel or stainless steel • Screens often have a filter pack to improve inflow to the well • Wells drilled in stable rock sometimes are not cased and have no screen – termed “open hole” 26 GWD4

  27. Positioning Screens in a well from Nkhoma and Baumle, (2007) 27 GWD4

  28. Display of constructing a well Insert narrow pipe / plastic bottle Casing Soil mixed with flour Drilled Bore (Plastic bottle) Flour to seal Gravel pack Aquifer Screen 28 GWD4

  29. Typical Well construction 29 GWD4

  30. Summary of Types of Wells Modified From Wikepedia 30 GWD4

  31. Well Development • Well development is undertaken after installing casing, screen and gravel pack • Improves well efficiency • Involves surging or jetting water or air in and out of the well screen to clean out residual drilling fluid. • May take several days. • Well developed wells have lower pump costs, longer pump life – sand and mud passing through screen damages pumps 31 GWD4

  32. Groundwater pumping effects 32 GWD4

  33. Test pumping of wells • Completed after well development • Tests the potential pumping rate and resulting drawdown • Assists in determining : • Long term pumping rate and water level • Size of pump • Impact on surrounding wells or environment 33 GWD4

  34. Pumping tests • Step drawdown test • short periods of pumping at progressively higher rates and measuring drawdown in the well • helps work out achievable pumping rate • Constant rate test • Pumping at constant rate (could be for days or weeks) • Measure drawdown in well and nearby “observation” wells • Helps assess pumping impacts on the aquifer under different pumping scenarios 34 GWD4

  35. Specific Capacity of a Well • Measures ratio of drawdown to pumped flow rate • Allows a check of well efficiency • Helps indicate bore deterioration eg blocked screens • Reduced capacity (greater drawdown to pumping rate) indicates reduced well efficiency 35 GWD4

  36. Relevance to an Emergency • Groundwater can be developed quickly in some situations – eg springs, shallow wells, available drilling equipment • Existing deep wells may be available • Could be included in emergency water supply solution • Need to understand capacity, condition, constraints on use • Potential for future development later in emergency 36 GWD4

  37. Springs • May be harvested in a number of ways • Should always be protected from degradation. From Oxfam technical brief Spring being protected, Zaire - S House / WEDC 37 GWD4

  38. Springs • A protective box that enables: • collection of water by hand • discharge to a tap for collection at the spring • discharge downhill by distribution pipe . Spring box with discharge pipe leading down hill, Nias, Indonesia 38 GWD4

  39. Estimating volume of groundwater available Q:How you might work out how much groundwater is available? • A: Factors to be considered • Area where rainfall might occur on aquifer • When does it rain • Will all of the rainfall enter the aquifer? • The rock type • Flows of existing bores / springs GWD4

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