Good Practices In Maintaining Hand Pumps & Production Wells

1. Good Practices In Maintaining Hand Pumps & Production Wells By Upul Wickramaratne Hydrogeologist / Manager (Groundwater) Groundwater Section National Water Supply & Drainage Board Chilaw Road Wariyapola

2. Groundwater ??

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

4. Dug well Constructed on Dry Tank-Warawewa

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

6. Dug Well Constructed on Dry Stream - Polpithigama

7. Construction of Dug Well, blasting rocks – Andarayaya, Polpitigama

8. 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 solution • Need to understand capacity, condition, constraints on use • Potential for future development later in emergency

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

10. How does groundwater move? • Underground, water slowly moves from an aquifer’s recharge areas (areas where water seeps into the aquifer from rain fall to it’s discharge area (like streams, springs and lakes). • Groundwater is always moving (this is called groundwater flow) and moves very slowly--only inches per year. Hydrologic Cycle condensation transpiration precipitation evaporation recharge area runoff infiltration water table aquifer groundwater flow discharge area

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

12. Major Features of the GW System to Remember

13. Pores, Porosity and Permeability Pores: The spaces between particles within geological material (rock or sediment) occupied by water and/or air. 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.

14. Primary Porosity

15. Secondary Porosity (Hard Rock Aquifers) Cavities Lime Stone Fracture Hard Rock

16. 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

17. How can we trap the groundwater • By dug wells • Shallow tube wells • Deep Tube well • Natural springs

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

19. Drilling…

20. Summary of Types of Wells

21. Cross section of fractured aquifer High yield TW

22. Maintaining Of Tube wells • Should be a proper design and construction

23. Fractured Aquifer • Fractures form conduits through which groundwater and pollution can move • Rock matrix stores water • Boreholes intercepting fractures can have high yields

24. Fracture Rock Matrix

25. TW design.. Sandy clay Blank PVC Casing 225mm (1000T) Hard Clay (Brown) Clay filled Hard Clay (White) Gravel & Clay Water Level 14.2m Sand & Clay Gravel & Clay Sand & Clay 22.4m Screen PVC Casing 225mm (1000T) Gravel Sand Clay & Calcareous Rock Fragments Main Aquifer Gravel Pack (Filter Pack) 27.8m Hard rock Open hall 31.0m

27. 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 • Suitable pump • Impact on surrounding wells or environment

28. 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

29. Pumping Test……

30. SWL 280 ft TD = 830 ft Step Drawdown Test Q = 3,000 gpm Drawdown = 17 ft Specific Capacity = 176 gpm/ft

31. Time Drawdown Test

32. Failures • Being operating HPTW or PW performance of wells such as WQ variation and quantity could be declined Due to • Construction failure, • Formation failure, • Aquifer failure, • Clogging or Scaling of Ca, iron & iron + magnesium • OVER PUMPING

33. OVER PUMPING • What is Over pumping When 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. .

34. Specific Capacity of a Well • The rate of discharge of water well per unit of drawdown, usually expressed as m3/d/m. • 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. Decline In Specific Capacity Time to Rehabilitate Well 130 GPM STATIC WATER LEVEL • Loss In Specific Capacity • Degradation Of Water Quality • Pumping Excess Sand • Pumping Any Gravel • Pumping Air Original Drawdown, 40 ft SC = 50 gpm/ft Pumping Level ----> 50 Pumping Level ----> 60 FT SC = 33 gpm/ft 80 FT SC = 25 gpm/ft 40 Pumping Level ----> Specific Capacity, gpm/ft 30 Clogging Of Screen Slots Due To Scale AQUIFER 20 10 TIME ---->

36. Analysis Of Well Efficiency - Specific Capacity Diagram Discharge Rate, gpm 100 Design Drawdown Well Efficiency, % Drawdown, ft Design Discharge Well Efficiency 0

37. Cones of Depression

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

39. 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 water—they can "go dry."

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

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

42. “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. Low Permeability Zone Adjacent to Well Screen Due to too small a slot size Well Screen Filter Pack Aquifer

43. How Do I Know If My Loss In Production Is Due To My Well Or Is It A Well-field Problem? • Well-field Interference • Regional lowering of ground water levels leaving the most productive aquifers “High And Dry” • Seasonal Fluctuations in Recharge

44. 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 life • Rehabilitation Percentage is much higher -- 70% • It is rare that a well will operate without some rehabilitation during its life

45. Clogging • Iron • Iron Magnesium • Clogging process could increased due depletion of water level by creating aerobic environment

46. Laboratory Results After Dissolving Scale In Acid HCL 10% HCL 5% Well Klean 20% HCl 5% Citric 1% Citric 10% Phosphoric 8.5%

47. Decision Tree For Rehabilitation IDENTIFY PROBLEM AND CAUSE IS WELL APPROPRIATE FOR REHABILITATION? (design, age, operational history, location) IF SO EVALUATE POTENTIAL BENEFITS AND COST OF REHABILITATION ARE POTENTIAL BENEFITS INSUFFICIENT POTENTIAL BENEFITS SUFFICIENT OR AND REHABILITATION COSTS > REDRILLING COSTS REHABILITATION COSTS < REDRILLING COSTS REDRILL REHABILITATION

48. Tube well development • 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  

49. 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.

50. Well development Methods    • Surging and pumping with air-compressor • Re-drilling with air-compressor • Over pumping    • Back washing   • High velocity water jetting • Use of explosive • Use of acid • Hydro fracturing