Solutions for Reducing Borehole Costs in Rural Africa - International ...

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Figures 5 & 6: Low cost borehole designs for crystalline rock and unconsolidated materialTOP SOILSANDSILTS & CLAYTYPICALLYDrilled 6" (150mm.)Dragbitwith 'Air, Form' or 'Mud'Flush4" (113 x 102 mm.) PVCcasingTypical water table risesabove water in fissuresSANDDrilled 6 1/2" (165mm.)Dragbit with 'Mud' flushonlySOFTWEATHEREDROCKCement / bentonitesealWATER TABLE4" (113X102mm.) PVCcasingGRANITEHand pump cylinder or4" submersible pumpSILTS & CLAY TYPICALLYHand pump cylinder or4" submersible pump.Cement / bentonite seal'crack' or'fissures'storing water113 x 63mm. PVC theadedadaptor2" (63 x 62mm.) well screenSlot size 0.5-1.0mm.Graded gravel packDrilled 100mm. Buttonbit3" DTH HAMMERSAND AQUIFER VERYFINE PARTICLESuse 0.7-1.5mm. gradedwashed sandto gravel pack for 0.5 slot size- use 1.0-2.0mm. gravel packfor 1.0 slot sizes113 x 63mm. PVC threadedadapterSump section 4" (113 x102mm.)PVC casing 3.6 meter long113 x 102mm. casing pointTypical depth 20-80 metersTypical depth 15-150 metersReduced diameter well screen for very fine sands requiring an even gravel packdiameters of drilled holes. Interestingly,telescoped designs would alsocontribute hugely to the enhancedperformance of bottom-supporteduPVC rising mains for deep-sethandpumps.Appropriate EquipmentBy defining the minimum requirementsof a community water supply basedon groundwater access rather than onthe equipment to be used, the localcontractor can then be left to determinehow the hole is constructed. Where thegroundwater is shallow and the waterlevel is relatively stable through dryseasons, a hand-dug well remains asound option.When groundwater is a little moredifficult to access, there are a numberof tripod-based drilling methods,largely hand operated, that producefully acceptable water supplies atvery modest costs up to depths of 20meters.As drilling gets deeper and involvesthe penetration of hard rock, largermachines are needed. These machinesshould be based on the boreholeconstruction required where the smallerthe borehole diameter, the lighterthe corresponding drilling rig (and itssupport equipment) can be.By definition, hard rock aquifersare fragile in terms of their rechargepotential. It is very easy to over pumpthem, as has happened in Indiaover the past two decades. Largediameter bore holes lend themselvesto power pumping, the abstractionof large volumes of water and heavydraw down – beyond the reachof most handpumps. Advocatingfor smaller diameter wells is alsomore environmentally friendly sincehandpumps do not damage aquifers.10
Solutions for ReducingBorehole Costs in Rural AfricaConclusionsThis analysis of borehole drillingtechniques suggests that the followingmeasures could make possible a hugeincrease in borehole construction, andrural water supply coverage throughoutAfrica.Relax the outdated nationalstandards that favorconservative borehole designsSmaller diameters holes shouldbe drilled to reduce the cost of theconstruction equipment and theinfrastructure needed to support them.Borehole designs need to embracevariations in geology, the occurrence ofgroundwater, and innovations in drillingtechnology.Develop an effective smallbusiness sector made up ofAfrican drilling contractors,based in rural areas, and spreadbetween the communities theyare required to serveThe alternative technology choice opensthe door to huge cost reductions inborehole drilling for water supplies, butthis technology needs skilful operationbased on both knowledge andexperience.An ideal world would see rurally basedsmall businesses operating drillingmachines for local community watersupplies. Such businesses would drillnew schemes, as well as have thecapacity to undertake well rehabilitation,pump improvements, and maintenanceduties.A portable drilling rig with DTH capacity.However, lack of specialized technicaland business skills hinders the abilityof local enterprise to undertake suchactivities. Seed schemes that couldprovide technical and business trainingto entrepreneurs, linked with credit forcapital equipment purchase, wouldimprove the success rate of such firms.Promote new, appropriatedrilling technologiesAcceptable borehole constructionsneed to be established and thenbroadened to the application of simplemachines capable of achieving thesestandards. Minimum quality controlthresholds for all new or modifiedborehole designs need to be developed.Provide continuity of work forlocal businessContractual frameworks that allow smallpracticing businesses some continuityof work should be created. Advantageswould include maximizing machineusage and availability within a fixedset of overheads, and increasing theconfidence levels of commercial lendinginstitutions in the local drilling industry.Such confidence would be increased bytraining and other methods designed tocontrol quality of drilling construction.11
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