WURZEL 2001 Drilling Boreholes for Handpumps

Author: Dr Peter Wurzel

Desktop Publishing: Erich Baumann, SKAT

Illustrations: Source of Illustrations is credited in the respective chapters

Copyright: © SKAT, 2001

Copyright waver: Permission is granted to use the material found in thisvolume for educational and development purposes.Acknowledgement is requested.

First edition: 2001, 200 copies

Published by: SKATSwiss Centre for Development Cooperationin Technology and Management

Vadianstrasse 42CH-9000 St.GallenSwitzerland

Tel: +41 71 228 54 54Fax: +41 71 228 54 55email: [email protected]

Distributed by: ITDG Publishing103-105 Southampton RowLondon WC1B 4HL, UK

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ISBN: 3-908156-02-5

Drilling Boreholes for Handpumps

Foreword

HTN, the global Network for Cost-effective Technologies in Water Supply, aims to facilitate theprovision of safe water to the poor and unserved through the promotion of affordable technologies.HTN’s scope includes the sustainable exploitation of groundwater resources, with a specific focuson the following topics:

• Handpumps,• Supply chains of goods and services that support system sustainability, and• Development of efficient drilling operations.

Especially in African countries, the provision of underground water supplies has suffered for manyyears from a mismatch between the water source (the borehole) and the pumping device (thehandpump). This uneven correlation has often led to the construction of costly and unsustainablesystems based on imported technology. In Africa, drilling costs are 5-10 times higher than they arein Asia.

Optimisation of the processes for producing boreholes can reduce well drilling costs and thus helpto accelerate production. Well costs can be diminished by optimising methods employed during thefollowing stages of construction:

• Finding groundwater,• Borehole design,• Drilling techniques, and• Well development and construction

Drilling equipment that is light and easy-to-maintain can be used for drilling boreholes. Itssuccessful application requires rather sound procedures and skilful operations than highinvestments. This allows making use of the resources that lay in the local private sector.This booklet seeks to suggest ways in which funds can be better used for making safe wateravailable to the poor by illustrating how drilling costs can be reduced without compromising waterquality, water quantity, or the productive life of the borehole. These arguments are directedtowards the rural water supply sector as a whole. Those directly addressed are primarily decisionmakers, government civil servants, planners and implementers of water projects who are notexperts in drilling, as well as technical people, project leaders, technical aid personnel etc. Thispublication is neither a detailed drilling manual nor a methodology of drilling methods.The author draws on his extensive experience as a member of the UNICEF Water andEnvironmental Sanitation community. He hopes that his views and proposals will be a catalyst forchange, and that this contribution will stimulate interest in experimenting with ideas on low costdrilling of boreholes for handpumps.

This publication was made possible thanks to support and contributions made by UNICEF NYHQand the Water and Infrastructure Section of SDC. Although both organisations are committed tothe provision of safe water, the interesting and valid views expressed in this booklet are primarilyintended to stimulate discussion and do not necessarily reflect the official policies of either UNICEFor SDC.


Acknowledgements:

I would like to record my gratitude to my former colleagues and good friends in UNICEFMozambique (1991-95) whose input has been invaluable in arriving at the conclusions reached inthis booklet. The ideas mooted were jointly developed over several years of discussion, analysisand field trips, I thank Edward Karczewski, a skilful, hands-on driller with a M.Sc. in hydrogeology(an unusual combination), who played a pivotal role phasing in the low cost drilling fleet inMozambique. To the Water and Environmental Sanitation section in UNICEF New York whofunded this work, and particularly Gourisankar Ghosh who recognised that a ‘drilling revolution’ isoverdue, my grateful thanks. I also acknowledge The Swiss Centre for Development Cooperationin Technology and Management (SKAT), and especially Erich Baumann who provided thehospitality of his home, wise counsel and, additionally, took the risk of allowing me to carry severalSKAT library books around the world. A word of thanks to two friends and UNICEF stalwarts,Rupert Talbot and Ken Gray who (mostly) cheerfully put up with an endless stream of requests,questions and argument. In Zimbabwe, Zambia, Lesotho and Mozambique I spoke to many of thelocal experts, all of whom gave generously of their time and to whom I am most grateful. Finally Ithank my wife, Pauline for her enthusiastic interest in this somewhat dry topic, her critical reviewand her special talent for transforming my words and thoughts into language that is grammaticallycorrect.


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TABLE OF CONTENTS:Low Cost Drilling Methods ............................................................................................................ 3Matching depth of borehole to required yield ................................................................................ 4Borehole Diameter........................................................................................................................ 4Casing and Screens ..................................................................................................................... 4Borehole development .................................................................................................................. 4Artificial gravelpacks ..................................................................................................................... 4Borehole Pump Testing ................................................................................................................ 5Borehole Siting - Can the ‘experienced eye’ and science see eye to eye?................................... 5Data Collection, Record Keeping and the Low Yield Water Source .............................................. 5Environmental aspects.................................................................................................................. 5Lessons from India ....................................................................................................................... 5Rural Water Supply and Drilling Case Histories from Africa.......................................................... 5

1 INTRODUCTION....................................................................................................................... 62 A brief history of drilling ............................................................................................................. 83 The occurrence and disposition of underground water .............................................................. 9

3.1 Water level fluctuations........................................................................................................ 143.2 Groundwater and the environment....................................................................................... 153.3 Geology/hydrogeology of the African continent.................................................................... 16

3.3.1 Groundwater in Africa - the Resource of the Future...................................................... 174 Drilling methods-a brief description. ........................................................................................ 18

4.1 Overview.............................................................................................................................. 18Manually constructed Wells ........................................................................................................ 18

4.2.1 Dug wells. ..................................................................................................................... 184.2.2 Hand drilled boreholes.................................................................................................. 194.2.3 The hand dug-well versus the hand-drilled borehole..................................................... 19

4.3 Machine drilled boreholes .................................................................................................... 204.3.1 Cable Tool/Percussion Method..................................................................................... 204.3.2 Rotary Rigs................................................................................................................... 224.3.3 Rotary-percussion or Down-the-Hole Hammer method................................................. 23

4.4 Dug well versus hand bored (drilled) borehole versus machine drilled borehole .................. 234.5 Pollution and Shallow Groundwater ..................................................................................... 25

5 The low cost borehole-design and costing .............................................................................. 265.1 Overview.............................................................................................................................. 265.2 Borehole Diameter............................................................................................................... 265.3 Matching depth of the borehole to required yield ................................................................. 265.4 Borehole development. ........................................................................................................ 275.5 The use of PVC casing and screening................................................................................. 295.6 Artificial gravelpack - when and where needed? .................................................................. 31


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5.7 Borehole Pump Testing........................................................................................................325.8 Locating Groundwater - Can the ‘experienced eye’ and science see eye to eye? ................33

5.8.1 Costs of Finding Groundwater.......................................................................................345.9 Drill type - which is best?......................................................................................................37

5.9.1 Rotary versus percussion?............................................................................................375.10 Data Collection, Record Keeping and the Low Yield Water Source. .................................395.11 Quality versus costs - low yield, hence low cost, is NOT low quality. ................................40

6 Case studies from African Countries........................................................................................416.1 Case Studies from Mozambique ..........................................................................................41

6.1.1 CASE STUDY 1 – .........................................................................................................41Government of Mozambique/UNICEF drilling programme .......................................................416.1.2 CASE STUDY 2 ............................................................................................................44State Drilling Company, Mozambique ......................................................................................446.1.3 CASE STUDY 3 ............................................................................................................44Commercial Drilling in Mozambique.........................................................................................446.1.4 Lessons Learned from the 3 case histories in Mozambique ..........................................45

6.2 Case histories from Zimbabwe.............................................................................................456.2.1 Manual drilling in Zimbabwe ..........................................................................................456.2.2 The Government of Zimbabwe-Rural Water Development............................................46

6.3 Case histories from Zambia .................................................................................................486.3.1 Machine drilled holes before 1992 and 1992 to 95 ........................................................486.3.2 The UNICEF Water and Sanitation and Health Education (WASHE) programme.........49

6.4 Lesotho Case History...........................................................................................................517 Drilling for Rural Water Supplies in India .................................................................................54

Terminology. The terms ‘borehole’ and ‘well’ are used interchangeably, in contradistinction to‘hand dug well’ or ‘hand/manually-drilled well’. A full glossary of terms is found in Appendix 1.


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FAST TRACK

Jump on the fast track for a quick preview ofthe book and see the framework of the costsaving ideas expanded in the text. We hopethat it whets your appetite to investigate inmore detail the new drilling philosophy.“The Handpump Option” was one of the mostnotable developments of the InternationalDrinking Water Supply and SanitationDecade, which recognised the ‘triad’ of cleanwater together with sanitation and health,and hygiene education as fundamental toimproved health in rural communities. TheVillage Level Operation and Maintenanceconcept (VLOM) applied to the handpumpunderlined the desirability of designstandardisation within countries and regionsand saw handpump costs plummet. Thecosts of construction of the water source,however, have remained several timesmore expensive than the handpump,sanitation facilities and health educationcosts combined. The impetus now mustbe to reduce the costs of constructionand development of the water source.Since the absolute maximum yield of ahandpump is 1m3/hr, savings can be madeby tailoring depth and other parameters tothis, in groundwater terms, small yield,through the application of low cost drillingmethods and design criteria adaptedspecifically to handpump mounted boreholes.In many circumstances andhydrogeological settings, borehole-drilling costs can be reduced by a factorof 2 - 3 in Africa.Cost savings can be made withoutjeopardising quality in design areasincluding: depth and diameter of theborehole, both of which can be limited forhandpump yields, casing and screens,borehole development, gravel packs,borehole sitting and pumping tests.The recommendations below are notinviolate and may not be appropriate in allgeological settings since nature, andparticularly geology and groundwaterhydrology, are infinitely variable.Nevertheless, the rural water supplypersonnel should be cognisant that drillingprocedures and techniques for handpump

specific boreholes can be simplified, withoutcompromising quality, by relaxing theirdesign criteria. Even so, there is much scopeand need for experimentation and innovation.

Low Cost Drilling MethodsDug well vs. hand bored (drilled) boreholevs. machine drilled boreholeIf the water table is shallow and the rock issoft then manual techniques should befavoured. Both hand dug and hand drilledmethods are least cost solutions in shallowwater table areas (generally up to 15 or 20metres). If, however, speed is important thenmachine drilling in such an area is justified.The hydrogeology and relative cost aspectsof dug wells and hand-drilled boreholes aredealt with in the main text on pages 18through 25.What is the best drill type? Horses forCourses! For the small yield boreholeselect the small drill! Drilling methods usingmachine-mounted rigs are essentially of twotypes, the cable tool method (percussion) orone of several rotary methods. Both haveparticular advantages and disadvantageswhich are discussed in the main text (pages19 through 23) but the message is: modern,light manoeuvrable rotary/down the hole rigs(DHT) should be used if and only if trainedcrews and a supportive infrastructure-logistics are available. If not, simple old-fashioned percussion rigs are moreappropriate. They are simple, rugged (manyin Africa are over 50 years old), easy tomaintain and admirably suited to low costdrilling. Simplicity of design means easyservicing and relatively short training periodsfor crews. The payment of drilling bonuseshas been shown to have benefits waybeyond their costs.The cost defining decision for handpumpequipped borehole design is to aim for alimited yield of 1 - 2m3/hr, the most thatthe handpump can deliver. The modifieddesign guidelines are discussed below:


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Matching depth of borehole torequired yield

See 5.3 p. 26 of main textHistorically boreholes have been drilled onthe precept of “the greater the depth, up to acritical level, the greater the yield”. If we take1.5m3/hr. as being the upper limit of thehandpump’s delivery ability (a generousfigure) then drilling should stop 10m or sobeyond the depth at which the required yieldis obtained. This provides a reserve columnthat will allow for seasonal variations andexcessive drawdown.Once the required yield of 1.5m3/hr. isattained, drill a further 10m to allow forseasonal water level fluctuations anddrawdown levels. The yield can beestablished with a simple bailer test (ifpercussion drilling is used) as drillingproceeds in integrals of 2 or 3m after water isfirst struck,Areas where seasonal water levelfluctuations exceed 10m are relatively rare,but if the area is hydrogeologically ‘known’ tohave large fluctuations then clearly a reservecolumn of 15 - 20m will be necessary. In sub-artesian conditions, the borehole can beconsiderably deeper than the norm forhandpumps of the 50-60m, because thewater level will rise. It should be noted thatthe shallower the water table the greater thedanger of groundwater pollution, henceproperly constructed well aprons aremandatory.

Borehole DiameterSee 5.2 of main text

Six inch diameter was the historical standardin Africa and in many countries still is, but asthe cost differential, particularly with rotarydrilling, is negligible, there is a case for 8” asstandard,If the hole is to be artificially gravel packedfor hydraulic reasons, i.e. a very fine, wellsorted aquifer, then an 8” diameter hole is inany event essential.

Casing and ScreensSee 5.5 p. 29 of main text

For handpump supplies, low cost (locallymanufactured) PVC casing and screeningshould be utilised. The slot size of the

screens is not critical for low yields in normalconditions, although it can be critical in fine-grained aquifers. Primitive machine sawnslots with a total opening of 5% (slot size 0.5-1mm) are appropriate. PVC casing andscreens can be joined by either the bell andsocket (male/female) joint with solventcement, or threaded joints.

Borehole developmentSee 5.4 p. 27 of main text

The development of the borehole (pumpingand surging) results in the finer fractions ofmaterial being drawn from theunconsolidated aquifer (and from fissures inconsolidated and semi-consolidated aquifers)leaving behind a stable envelope of thecoarser, and therefore more permeable,material of the aquifer. This naturalgravelpack is not to be confused with anartificial gravelpack.Development of a borehole is a crucialadjunct to a properly completed hole,For low yield boreholes pumping, or betterstill over-pumping, is the best method ofdevelopment. Rule of thumb pumpingperiods vary from 2-24 hours or until thepumped water is clear, often within an houror two,The bailer (standard equipment on thepercussion rig) can be effectively employedfor development in the process of surging,and even for pumping if a submersible pumpis not available,Pumping and surging will create a naturalgravelpack around a borehole drilled inunconsolidated sediment that is crucial to thelong and productive life of the borehole,

Artificial gravelpacksSee 5.6 p. 31 main text

From a hydraulic viewpoint an artificialgravelpack is seldom required in low yieldingboreholes, and screen open areas can below (5%),Despite the fact that, in hydraulic terms, anartificial gravelpack is not required nearly asfrequently as it is used, the widespreadpractice in many countries of routinelyplacing an artificial gravelpack shouldcontinue given its low cost and possible‘anchoring’ action of screens and casing.


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In hard rock boreholes neither a gravelpacknor a screen and casing are needed butseveral countries routinely use them,primarily for mechanical purposes such asthe protection of the handpump rising main,which in turn anchors the screen. Stabilisersor centralisers would do the same job for lesscost. Exceptions to this rule exist (seeZambia case history).

Borehole Pump TestingSee 5.7 p. 32 of main text

Pump tests are a fundamental procedure toassess both borehole and aquiferperformance.In low yielding limited depth boreholesclassical extended pump tests are frequentlymeaningless and certainly unnecessary on aroutine basis.A simple test using either a bailer or smallsubmersible pump to determine the yieldover a 2-3 hour pumping period is all that isneeded. Timed water level depthmeasurements should be taken if possible.

Borehole Siting - Can the‘experienced eye’ and science see eyeto eye?

See 5.8 p. 33 main textThe author considers that the use and cost-effectiveness of geophysics in low cost watersupply is debatable since, in most cases, lowyield boreholes do not justify relativelyexpensive geophysical investigation. Mostcurrent drilling programmes support this view(India is the most important example).However, there is an important role forgeophysics in geologically difficult areas andalso in virgin groundwater regions.

Data Collection, Record Keeping andthe Low Yield Water SourceIt is vital for accurate records to be kept onevery borehole drilled and well dug. Somedegree of monitoring should subsequentlytake place so that a rigorous and completedatabase and groundwater inventory ismaintained and/or built up. But there has tobe a compromise between the extent of datacollection and record keeping of limiteddepth, low yielding boreholes and the time,money and effort expended in obtaining suchinformation.

Environmental aspectsThese are discussed throughout the text -low yield shallow water sources aresusceptible to surface pollution. The issue oflarge-scale irrigation schemes affecting ruralwater sources is also discussed; as is thefact that groundwater is the water source ofthe future, particularly in Africa.

Lessons from IndiaA brief chapter (Chap. 7, page 54) is devotedto a comparison of drilling costs in India andAfrica. Clearly, the economies of scale inIndia can never be achieved in Africa butthere are many lessons to be learned.

Rural Water Supply and Drilling CaseHistories from Africa.(Chapter 6, p. 41) is devoted to drilling casehistories from several African countries.The different drilling approaches arehighlighted and areas of possible costreduction are discussed. Examples of lowcost drilling programmes (possibly the bestmethod of convincing sceptics!) are cited, asare conditions where the low cost approachis somewhat limited.The ‘handpump option’ of the 1980’srevolutionised rural water supply andsanitation programmes worldwide. Byimplementing at least some of the costsaving drilling and development ideassuggested in this document more rural areaswould be able to benefit from the provision ofpotable water together with sanitationprogrammes and health and hygieneeducation.


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1 INTRODUCTIONOne of the most significant developments ofthe International Drinking Water Supply andSanitation Decade (IDWSSD) was therecognition within the rural water supplysector of the critical importance of what hasbecome known as 'THE TRIAD' of (a) Water,(b) Sanitation and (c) Health and Hygieneeducation. Classical studies by Feacham andothers showed that whilst the provision ofclean water within rural areas improved thequality of life of the beneficiaries, it did not,on its own, make a real impact on childmorbidity and mortality. Only when cleanwater was combined with sanitation andhealth and hygiene education - ‘THE TRIAD’,did health significantly improve.The pioneering work of Arlosoroff et al(1987), which focused initially on themechanical aspects of the 'the handpumpoption', led to improved handpump designscompatible with the evolving Village LevelOperation and Management of maintenanceconcept (VLOM) and underlined thedesirability of design standardisation withincountries and regions. A new philosophy ofcommunity driven Community Water Supply(CWS) was emerging: a demand basedapproach, which emphasised the importanceof ‘the triad’ as a unit.The cost of handpumps has plummeted overthe past decade but machine-drilling costs,although decreasing in some countries,remain, in general, inappropriately andunnecessarily high. The ratio can behighlighted on an example fromMozambique; for a village of 210 people thecost of the handpump is USD 870, (includinginstallation, sanitation facilities and healtheducation costs). Yet, the cost ofconstruction of the water source (in particularthe machine drilled borehole) is USD 5,000-6,000, several times more expensive thanthe handpump. Published data indicate thatin Africa drilling costs range from USD 3,000-USD 15,000. It is now time for a concertedfocus on the water source; an area wherelarge savings could be generated in a sectornotoriously strapped for global funds andwhere low cost does not imply low quality.Drilling for water in Africa is still largelytradition bound: drilling deeper than

necessary to obtain the maximum possibleyield from the water source, regardless ofwhether the water-lifting device (in mostcases the handpump) can take advantage ofthat yield.

Savings can be made by tailoring depth,diameter and other parameters to yield,through the application of low cost drillingmethods and design criteria adapted tohandpump mounted boreholes. In manycircumstances and hydrogeological settings,borehole drilling-costs can be reduced by afactor of 2 - 3 in Africa.This publication will attempt to define howdrilling costs can be reduced withoutcompromising water quality, water quantity,or the productive life of the borehole. To freefunds not only for more boreholes but alsofor the other two essential elements of theCommunity Water Supply ‘triad’. It isaddressed to the Rural Water Supply sectoras a whole, primarily decision makers,government civil servants, planners andimplementers of water projects who are notexperts in drilling, as well as technicalpeople, project leaders, technical aidpersonnel etc. It is neither a detailed drillingmanual nor a methodology of drillingmethods (although a brief resume is given).Hopefully, the views and proposals outlinedwill be a catalyst for change, and will arouseinterest in experimenting with some of theideas about drilling of boreholes forhandpumps.The fundamental premise of this booklet isthat groundwater, particularly in Africa, is andwill continue to be the primary source ofwater for the rural areas. Further, thathandpumps will be the water liftingtechnology of choice. In 'Community WaterSupply: the Handpump Option’ by Arlosoroffet al (1987) the authors foresaw thatevaluation of drilling methods andmanagement would be an importantcomponent of future research, requiring the

The impetus now must be to correct themismatch between the water liftingdevice and the water source.


same concentrated attention on this majorcost element as had already been focusedon handpump development.In the last years progress has been madetowards lowering drilling costs, with severalAfrican countries reporting significantreductions; but these results have beeninsufficiently studied and the progress madeso far has not perhaps received therecognition it deserves. Hopefully some ofthe suggestions to be found in this work mayspur the ‘drilling revolution’ on to the heightsand intensity achieved in ‘the handpumprevolution’. Hand dug wells and hand drilled boreholes,for which several excellent texts areavailable, will be dealt with only briefly.Instead we will focus on the details of designoptimisation of machine drilled boreholes toavoid over-design and wasteful expenditurewhen drilling for a small yield.

A groexbode

Drderai

etc., and indeed there may be circumstanceswhere local geology may not allow theadoption of all the low cost solutionssuggested. More experimentation, fieldtesting, research and, possibly, modificationare required in these situations.The focus in this text is on low cost solutionsusing machine-drilled boreholes, in marginalgroundwater areas other low costtechnologies such hand drilled or hand dugwells can be more cost-effective. The maxim'if you can dig, don't drill' is not inviolate andcalls for judgement on the part of thedecision-maker. In shallow water table areas,hand drilled boreholes are cheaper andfaster to construct and can be more costeffective and efficient than dug wells.However, where low soil permeability resultsin excessively low yields, the hand dug well isthe only appropriate technology. In suchcases, the well acts as a reservoir into whichwater can leak slowly but continuously inorder to fulfil a peak demand much greaterthan the instantaneous yield of the aquifer. Inother words, the inherent yield can be as lowas 0.25 m3/hr but water accumulated during

The absolute maximum yieldof a handpump is 1m3/hr!

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handpump can pump 1m3/hr (in classicalundwater hydrology/hydraulics this is an

tremely small yield) yet; traditionallyreholes for handpumps have been over-signed.

illing costs are obviously criticallypendent on the topography, geology,nfall frequency and intensity, soil profile,

the night will be sufficient for extraction of1m3/hr during several daylight hours.While the benefits of optimising boreholedesign to a small yield of 1-2m3/hr can bedemonstrated, there is a drawback. If thedesign is optimised on such a limited yield, itwill not be possible, in the future, to easilyincrease the level of service to includemotorised pumps in areas that perhaps couldhave yielded supplies larger than the 1m3/hrinitially sought. The response to this validargument is that ten years after the end ofthe IWASSD, and despite ongoing intenseadvocacy for ‘the handpump option’; thesector is currently unable to keep pace withpopulation growth in Africa. The number ofpeople worldwide who lack access to potablewater is still in the order of 1.2 billion. Thus,in the author’s opinion, the primary sectorfocus at this time should be to minimisecosts and at the same time increase the rateof production of completed boreholes, so asto reach the greatest number of people,albeit at a low level of service.

If the borehole design is optimised tothe small yield cost savings can be

made without jeopardising quality orproductive life. Areas where cost

savings can be made include: depthand diameter of the borehole, both ofwhich can be limited for handpump

yields, casing and screens, boreholedevelopment, gravel packs, boreholesiting, the extensiveness of pumpingtests, water level monitoring and the

need to keep records.


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2 A BRIEF HISTORY OF DRILLINGIt is axiomatic that man's existence on earthis dependent upon water. Every earlycivilisations - Mesopotamia, China, Egypt,India, Greece, and Rome - centred aroundsources of this life-giving liquid. In these hot,populous areas so often parched by drought,water was precious. No wonder, then, thatthe village well, the oasis in a desert,became a focal point for human activity.History tells us that the Egyptians used drillbits made of gemstones and quartz to grindrock beds, and records indicate that theChinese and Persians constructed wells asearly as 2000 BC by methods other thandigging.

The most significant progress in design andmanufacture of drilling equipment and inwater well construction methods has beenmade within the last 100 years. Primarily forthe oil industry, sophisticated truck mountedhydraulic/pneumatic rigs capable of drillingrapidly through the hardest rocks weredeveloped. Although not as large as the oildrilling industry, the water drilling industry,using these new rigs, has become 'big

business'.While the development of the modern 'super-rigs' is interesting, the focus here will bemore on the simple, less sophisticated andless costly machines because the boreholefitted with a handpump can be relativelyshallow, of limited yield, and of smalldiameter. Unless ultra fast progress isimportant, the use of large sophisticated rigshas to be carefully weighed in Africa. But thisdoes not mean that modern rigs (especiallythe small versions) have no place in low yieldborehole drilling programmes. They do, inspecial circumstances; an extended drought,a large emergency resettlement programmeas well as in an environment where a highdegree of managerial and technicalcompetence exists. Fierce private enterprisecompetition can reduce drilling costsdramatically also for the use of the modernrotary/DTH drill. India best illustrates thislatter situation, as will be seen in Chapter 7.An examination of drilling methods in Zambiaillustrates that because mining is the majorindustry, skilled drillers are available and thewater drilling fleet is made up primarily ofsmall DTH rigs. Good logistics are in placeand technical expertise is available. In thehard rock setting of Zambia the new modernDTH drills are cost effective and much fasterthan percussion rigs.

Figure 1. Early drilling rigs.

The Chinese were drilling boreholes by thepercussion method over 2000 years ago,great depths were reached (1800 ft) with

bamboo rods as the drill stem.There is no reference to costs!


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3 THE OCCURRENCE AND DISPOSITION OF UNDERGROUND WATER

A brief resume for the non-technical reader.Central to an understanding of groundwaterhydrology is the global water circulatorysystem known as the hydrological cycle;depicted in Figure 2 below.

FIGURE 2. The Global water cycle or Hydrologicalcycle

Precipitation falling on the land surfacerepresents the source of fresh water for allliving things. A part of the precipitation runsoff the surface into streams that dischargeinto larger streams that finally dischargeback into the oceans. Part of the precipitationenters or soaks into the soil. Much of thewater that enters the soil is detained in theplant root zone and eventually is drawn backinto the atmosphere by plants(evapotranspiration) or direct evaporationfrom the soil abetted by soil capillarity.However, part of the water that soaks intothe soil passes through the soil root zoneand, under the influence of gravity, continuesmoving downward until it enters thegroundwater reservoir.The quantity of water entering thegroundwater reservoir, known as recharge,depends on the soil type, rainfall amount andrainfall intensity. Water-bearing formations ofthe earth crust act as conduits fortransmission and as reservoirs for thestorage of water. Water enters theseformations as recharge and travels slowly

underground (from a fraction of a metre tohundreds of metres per year) until it returnsto the surface, sometimes several tens ofthousands of years later, by way of naturalflow (springs) and human enterprise (wellsand boreholes).At this point a few terms need to be defined(a full glossary of terms will be found inAppendix 1:Permeability: the ability of a rock orformation to transmit water. Gravel, anunconsolidated rock, has a high permeability,whereas granite, a consolidated rock, has alow permeability and generally, unlessfractured, equally low porosity.Porosity: those portions of a rock or soil notoccupied by mineral matter that can beoccupied by groundwater. These spaces areknown as voids, interstices, pores and porespace. Sand and gravel have a high porosityand a high permeability, decomposed rockhas a high porosity and a reasonablepermeability. Surprisingly clay has a veryhigh porosity (the reason being that clay ismade up of minuscule grains where the porespace is 40-50%) but a very low permeability. Aquifer: a formation that contains sufficientsaturated permeable material to yieldsignificant quantities of water for wells,boreholes and springs. The term ‘aquifer’implies an ability to store and transmit water.Unconsolidated rocks, sands and gravelmaking the best aquifers.Aquiclude: an impermeable formation, ofwhich clay is the best example.Some aquifers, called confined or artesianaquifers, are overlain by a confining layer ofrock. Water in the aquifer under the confininglayer is under pressure; the potentiometricsurface for a confined aquifer is the surfacerepresentative (height) of the level to whichwater will rise in a borehole drilled into theaquifer.


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Figure 3. Examples of rock interstices and the relation of rock texture to porosity.a) Well-sorted sedimentary rock having high porosity,b) Poorly-sorted sedimentary rock having low porosity,c) Well-sorted sedimentary deposits consisting of pebbles that are themselves porous so that the deposit as a whole

has a very high porosity,d) Well-sorted sedimentary deposit where porosity has been diminished by the deposition of mineral in the interstices,e) Rock rendered porous by solution,f) Rock rendered porous by fracturing.(after Meinzer)

Figure 4. Disposition of groundwater and the borehole.On the centre is a flowing or artesian borehole while on the right is the sub-artesian borehole referred to in thenomenclature of this book. A simple borehole is seen on the left.


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There are 3 types of rock in which groundwater can be stored:1. Crystalline Rock - this is a solid, dense rock wheregroundwater is stored in joints, crevices, cracks and mini-faults. See Figures 3 and 6.In crystalline rock groundwater yields are generally small(except for limestone and possibly basalt in specialstructures). Such rocks would include igneous rocks(granite), metamorphic rocks and consolidatedsedimentary rocks.

Figure 5. An example of the decrease in yield of boreholes with depthin crystalline rocks in North Carolina, United States. Numbers near points on curve indicate the number of boreholesused for each average shown. (after Davies & DeWiest)

Figure 6 shows how water occurs in non-weathered crystalline rock. It reveals different groundwaterdispositions in non-weathered crystalline rock. The intensity of fracturing, fracture size and the degree of fractureinterconnection govern the yield of the borehole (after Davies & DeWiest). (For an understanding of the term ‘drawdown’see Figure 8).a) Borehole drawing water from small fractures near the surface. A safe pumping rate for this hole is less than 1.4m

3/hr, but still enough for a handpump.b) Extensive small fractures connect this borehole with a nearby source of recharge. A safe pumping rate is more than

1m3/hr.c) This borehole is a failure except as a source for very small amounts of water. The drawdown curve reflects

dewatering of the hole and a large isolated fracture intercepted by the hole.d) Large fractures that drain the porous weathered rock maintain a moderate yield of about 1m3/hr in this hole. (after

DeWiest)


12

2. Decomposed Weathered Rock - Whencrystalline rock weathers over thousands ofyears water occurs in interstices of thethoroughly weathered mantle as well as inthe lower semi-decomposed layer. Watermay also occur in jointing in the underlyingfresh rock. The term, ‘basins ofdecomposition’, in vogue in Southern Africaduring the fifties related to areas of deeperdecomposition. Low yield supplies werefrequently found in such ‘basins’ that couldvary in aerial extent from a few hundredsquare yards to several square kilometres,occurring typically in the granitic areas of theregion (see 3.3 below). The model lookedupon the upper thicker weathered layer oflow permeability but high porosity as ‘thesponge’, while the lower, thinner semi-decomposed and highly permeable layer wasthe ‘conduit’. Below this lies the fresh countryrock or bedrock, which may or may not befissured and thus may or may not containwater.The concept of ‘basins of decomposition’ isno longer fashionable. Instead, considerable

data has accumulated on the Africanregolith, which is summarised by Wright andBurgess (1992). Generally, water is obtainedfrom all 3 elements, the regolith, the zone ofsemi decomposition and the bedrock. Clearlyratios vary considerably. It is now evidentthat boreholes in Zimbabwe draw primarilyfrom the bedrock and, interestingly, theredoes not appear to be a correlation betweenyield and regolith thickness, contrary toprevious thinking. In other parts of theAfrican crystalline basement, according toWright & Burgess, ‘yield correlations aremainly apparent in relation to mean valuesand are negative with relief and positive withregolith thickness’. The complexity of thenew emerging data on the African regolith issuch that the interested reader should referto ‘The Hydrogeology of CrystallineBasement Aquifers in Africa’, Wright &Burgess (1992). A rather detailed vertical profile throughregolith overlying crystalline rock is shown inFigure 7.

Figure 7. Vertical profile through regolith showing variation of weathering, storage capacity and permeability (afterAcworth 1987 quoted by Barker et al in Wright and Burgess 1992)


13

Unconsolidated Rock - Examples are gravel and alluvial sands and these form the best aquifers.(See figure 8, well type 7)

Figure 8.In an attempt to summarise geology and expected borehole yield this figure shows the relationship between geologicalfeatures and expected yield in a hypothetical region. (after Davies & De Wiest)

Type ofwell

Use Depth (m) Source of water

1. Drilled Farm 70 Lower part of weathered granite and fault zone. Small amount fromjoints.

2. Drilled None 70 Very small amount from joints3. Drilled Stock 10 Small amount from joints. Water is artesian.4. Drilled Observation 40 Lower part of alluvium and fractures and joints near dyke5. Drilled Domestic 35 Lower part of colluvium and schist6. Drilled Domestic 45 Cavernous zone in small body of marble7. Dug Stock 7 Alluvium8. Drilled Industry 55 Lower part of alluvium and same fault as in borehole no. 1.9. Dug None 5 Small amount from joints. Well dry during droughts

10. Dug Stock 8 Weathered granite GEOLOGIC UNITSA Residual soil on

granite.C Granite E Alluvium G Colluvium. I Dyke

B Fault. D Joints in granite F Contact betweengranite and schist

H Schist. J Marble


14

3.1 Water level fluctuationsSeasonal water level fluctuations(fluctuations of the general water table) are afunction of local variables such as watertable depth, the permeability of the overlyinglocal soils, recharge, climate, rainfall intensityand frequency. It is difficult to predictgeneralised water table fluctuations as theshallower the water table the greater thefluctuation. Only systematic water levelrecording over several years in a particularlocality allows knowledge of the possiblerange of fluctuation. Such records are veryimportant, the data obtained leading to abetter understanding of the localhydrogeology. Yet in many areas, particularlyin Africa, limited funds and manpower oftenrestrict data collection and record keeping.The practical aspects of generalisedseasonal water level fluctuations relative toborehole depth must be considered by theproject manager (or more realistically by thedrilling supervisor and drilling crew). Theseimportant topics are discussed in 3.6.4.Apart from seasonal fluctuations there arealso water level fluctuations in the boreholeitself because of pumping the borehole or asa result of pumping nearby boreholes. Assoon as water is pumped out of a boreholethere is an immediate drop in water level inthe borehole and the area surrounding theborehole. The drop in water level in theborehole is known as the drawdown.Clearly in any given situation the lessdrawdown the better. Drawdown isessentially dependent on 3 parameters: thedischarge, the permeability of the aquifer andborehole design.If large amounts of water (in excess of10m3/hr) are being pumped then (and onlythen) borehole design particularly in relationto screen length, type of screen, screenslots, gravelpack, diameter etc. is veryimportant and must adhere stringently tocertain criteria. The screen must have largepercentage openings yet screen slot sizesmust be small. An artificial gravelpack (hencea large diameter hole more than 250-300mm) is mandatory and the hole must bethoroughly developed using specialised tools.These design features will ensure minimaldrawdown and no sand/silt ingress forsignificant pumping rates. But borehole

design can be relaxed where a small amountof water (maximum 1m3/hr) is being pumped.

Figure 9. A high yielding borehole (motorised pump)shown here to emphasise significant drawdown, largescreens and terminology (after Johnson)

The drawdown in a borehole can also beaffected by the pumping of nearbyboreholes, a phenomenon known asborehole interference. In a typical rural watersupply setting where all the boreholes arehandpump mounted and a reasonabledistance apart from each other (50-100m),borehole interference is very unlikely.However, as soon as motorised pumpsappear (a nearby irrigation project pumpinglarge amounts) interference and, in theworst-case scenario, the drying up ofhandpump mounted boreholes is apossibility. Therefore known proximity to anirrigation scheme or a proposed irrigationscheme means that depth of drillingbecomes critically important. See Chapter 5.


3.2 Groundwater and theenvironment

Water stored in aquifers is almost always ofexcellent microbiological and chemicalquality, requiring minimal treatment (in theauthor's experience of Africa newly drilledboreholes never require treatment).Groundwater is naturally protected fromevaporation (particularly important in Africawhere evaporation rates are high, mean2m/annum) and the volume storedunderground in certain areas and regionscan be immense. Groundwater can offerwater supply security in areas prone tofrequent and extended droughts.

Polluenvia grif thyearrechConturntensannuthe becopollucomChivcapidecatimeHaraprevpollutooka gresepracThisSevof tpollupumpolluboreof m

The handpump, with its maximum yield of1m3/hr, is environmentally friendly, takingenough but seldom too much from theaquifer. The World Health Organisationdefines the minimum water requirement fordrinking and personal hygiene purposescombined as 20 litres per person per day.Observations show that the time it takes awoman to fill a 7litre bucket from ahandpump is approximately 1 minute. Ifwomen were lined up at the pump to createmaximum demand the well could supply 60 xm

If a groundwater reservoir becomesheavily polluted, in practical terms it

remains polluted forever.

Groundwater is mostly of excellenticrobiological and chemical quality.

tion of groundwater is a seriousronmental concern. The turnover time ofoundwater reservoir is measured in yearse reservoir is small, and in hundreds ofs if it is large, because the ratio ofarge to the volume stored is small.versely, a surface water dam has aover time of only months (small dam) to of years (large dam) because the meanal run-off into the dam is in the order of

total volume stored. Therefore, if a dammes polluted (and action to stop thetion is taken) it will clear within aparatively short time. A case in point isero Dam, which supplies Harare, thetal of Zimbabwe, with drinking water. Ade ago the dam, which has a turnover of 12 months, became polluted. There Municipality took legal steps toent pollutants going into the dam and thetion cleared within 2-3 years, the time it to turn over the total volume. Not so withroundwater reservoir. If a groundwaterrvoir becomes heavily polluted, intical terms it remains polluted forever! danger cannot be over-emphasised.eral of the large groundwater reservoirshe United States now showing nitratetion are forever ruined. Immediateping can probably rectify localisedtion within the circle of influence of thehole (in the order possibly of hundredsetres).

7 = 420 litres per hour. Assuming 10 hoursper day continuous pumping a total of 4,200litres of water would be supplied by onehandpump. This is sufficient for a village of210 people. The reality is that frequently onehandpump has to serve 500 people andmore meaning that the WHO definedminimum requirement is not met.

In terms of water wastage, the handpumpis singularly environmentally friendly.

Seldom, if ever, is there water wastage orover-pumping in areas where handpumps

are used.

15


16

3.3 Geology/hydrogeology of theAfrican continent

Wright (1992) reproduced a simplifiedgeohydrological map of the African continent(after Dijon - Les Eaux Souterraines del’Afrique), which reflects the groundwaterregions of Africa, shown below.

Figure 10. A simplified hydrogeological map ofAfrica. Note that Africa is made up primarily ofcrystalline igneous rocks (synonymous generally withsmaller yields); only in a few areas where there areunconsolidated sedimentary rocks/alluvial plains canlarge yields can be obtained. There are also a fewlimestone areas where large yields are possible.

Geohydrological provinces are delineated.As can be seen from the map, the crystallinebasement rocks of the so-called ‘continentalshield’ underlie extensive areas of Africa.Here relatively small low yielding aquifers aredeveloped in weathered mantle and infractures and fissures below the mantle inthe bedrock. Below the mantle ofdecomposed rock is semi-decomposed rockwhich is usually of high permeability butlimited depth, say 1-2 meters, leading tofresh bedrock where there may be limitedwater bearing fissures and cracks (SeeFigure 7). The crux here is that large yieldingaquifers are unlikely to occur in the vastareas of crystalline rock in Africa.One of the prime challenges in present dayhydrogeology is, according to Foster (1984),

the need to reach ‘... a fuller understandingof the evolution of the weathered mantleaquifer, leading to a unified conceptualmodel of its hydrogeology andhydrochemistry which in turn will allowimproved criteria for borehole siting andconstruction.’It is aquifers in the major sedimentary basinsand valley areas containing a variablethickness of unconsolidated material thatyield the substantive groundwater suppliesneeded for major irrigation schemes or urbansupplies. Groundwater yields in suchaquifers can be very large, for example in theSabi Valley in South Eastern Zimbabwe theSabi Alluvial Aquifer has boreholes that yield6-8m3/minute but such yields are outside thedomain of this work. It is the decomposed/weathered mantle in the crystalline rocksand the consolidated sedimentary rocks thatare of interest here. In consolidatedsedimentary rocks the weathered mantle isgenerally not so well developed but smallsupplies can be found in the interstices, ifany.Yields sufficient to justify motorised pumps inboreholes drilled in crystalline rock are notcommon, but when they do occur then thelevel of service can be improved andsupplies sufficient for supplementaryirrigation can be considered. Generally thelikelihood of such increased supplies is afunction not only of geology (as is the casewith all boreholes) but also of rainfall anddepth of borehole. Here we will consider onlyboreholes to be fitted with handpumps. Theycan therefore have a limited yield, whichusually means a limited depth. Groundwaterhydrology, while theoretically highlymathematical, is actually a remarkablyimprecise science and there have beencases where, when drilling has reached adepth of say 40m the yield is only 0.5m3/hrand yet, by drilling just half a metre more, theyield is suddenly 10m3/hr. Predictions aredifficult. It is therefore advocated that drillingshould only be deep enough to obtain a flowinto the borehole sufficient to support thedischarge of a handpump, plus enough extradepth to account for seasonal water levelfluctuations and drawdown into the borehole.


In the early eighties Chilton and Grey madereference to the construction of low costboreholes for handpump yields. They notedthat, in Malawi, drillers invariably 'cased off'the weathered mantle and sought waterbelow the mantle in the semi-decomposedlayer or even deeper in the fresh bedrock inthe hope of intersecting joints or fissures andcracks containing water. Chilton and Greyargued that the mantle contained sufficientwater for handpump supplies and should beutilised, thus eliminating the need for deeperdrilling. They concluded that boreholes in themantle should be screened and that withartificial gravel packing and thoroughdevelopment, productive, low yielding (butsufficient for handpumps) low cost boreholescould be drilled. Unfortunately this pioneeringwork did not reach a wide audience. In anyevent the focus of the sector at that time wason the development of the most appropriatewater raising device, the handpump, and theevolving concept of Village Level Operationand Maintenance (VLOM). Our purpose hereis to develop the ideas of Chilton and Greyand give to drilling the concentrated focusthat Arlosoroff et al foresaw would be thenatural follow-on from the extremelysuccessful ‘handpump option revolution'.

3.3.1 Groundwater in Africa - theResource of the Future

In rural Africa groundwater is the resource ofthe future given its many advantages oversurface water supplies. Yet, until fairlyrecently, engineers tended to prefer todevelop surface water supplies where thehydrology was better understood and theirvisibility made them more susceptible toprecise calculation. Groundwater wasconsidered 'out of sight out of mind'.In Africa groundwater is virtually ubiquitous,where only small yields are requiredgroundwater can generally be found close tothe surface and close to the area of demand.

The capital costs of groundwaterdevelopment are relatively modest (and ifsome of the 'philosophy' of this book isaccepted, can be further cut where onlysmall yields are needed), and compared tolarge dams the land requirements areminimal. Additionally, in rapidly developingareas where larger yields are sought and areavailable, the resource lends itself to phaseddevelopment to meet rising demand.

Aimpthuwthw

Groundwater hydrology, whiletheoretically highly mathematical, is inpractical terms remarkably imprecise.

Where only small yields are requiredgroundwater can generally be found close

to the surface and close to the area ofdemand.

Groundwater is always of excellent quality,close to the area of demand, protected fromevaporation and, in many regions, volumesstored underground are immense, providing

security of water supplies during droughtyears. The capital costs of groundwater

development are relatively low.

17

frica's rural population is dispersed overmense areas in discrete and isolated

ockets as small as 100-200 people. It is not,erefore, surprising that groundwater,

niquely suited to this setting, is the primeater supply source for the near future, as ise case in most of the rural developingorld.


18

4 DRILLING METHODS-A BRIEF DESCRIPTION.

4.1 OverviewFor the Government or Aid Agency watersupply manager planning a national orregional water supply strategy, the followingdiscussion on manual and machine drilling orexcavation with hand tools is intended to bea generalised orientation to what isessentially a complex topic. Familiarity withthe various technology options, their relativeadvantages and disadvantages, is anessential aspect of planning.Water can be extracted from the groundeither from a hand dug well or a hand drilledor machine drilled borehole and there are avariety of techniques in each case. Selectionof a particular method depends on thequantity of water required, depth togroundwater, geological conditions, andeconomic factors.Shallow wells, generally less than 15 metres,are constructed by digging, boring, driving orjetting. Deeper boreholes are usually drilledby a machine rig. Driving and jettingtechniques are not relevant to the Africancontinent and will therefore not be discussed.Digging and hand boring are very importantlow cost options in high (or shallow) watertable environments and deserve someamplification. Machine drilling will bediscussed in 4.3

4.2 Manually constructed Wells4.2.1 Dug wells.Dug wells are ubiquitous throughout theworld and, since biblical times, have providedcountless water supply points. They rangefrom a simple unprotected hole in the groundto a properly constructed facility equippedwith a handpump as depicted in Figure 11.

Figure 11 - A modern domestic dug well with a rocklining, concrete seal and handpump (after Todd).

The advantages:• The level of community involvement is

very high,• Skilled labour (unless blasting takes

place) is not required,• Until recently, it was considered the most

inexpensive technology available,although data from some Africancountries reveal this is not universally thecase,

• Most of the construction materials areavailable locally,

• The rejuvenation of an old hand dug wellis frequently the first step towards a safewater supply for the community,

• Water can continue to be drawn from a


19

well equipped with a handpump, even ifthe pump fails,

• Storage capacity allows wells to producesufficient water even when aquiferpermeability is extremely low,

• Horizontal drilling can improve yield,• Reliable maintenance of a well requires

little technical skill.The disadvantages:• Hand dug wells are usually shallow and

thus can tap only the upper levels of theaquifer, where water level fluctuations arerelatively large,

• The technology is only suitable for softgeological formations and shallow watertables thus restricting it to specific areasand regions,

• Wells are susceptible to bacteriologicalcontamination,

• A shallow water table generally meanslarge water level fluctuations and thepossibility of the well drying up, especiallyduring drought periods.

Digging is relatively easy in unconsolidatedrock (alluvial deposits). During the earlyeighties in the hard rock terrain of SouthWest Zimbabwe, shallow wells were thechosen technology because no drillingequipment was available. The expensivetechnique of rock blasting was used todeepen the wells when they dried up at theend of the dry season.After digging or blasting, loose material ishauled to the surface in a container bymeans of pulleys and lines. As diggingproceeds casing is inserted forming apermanent lining to prevent caving in. Casingcan be of wood, brick, metal, or concrete(pre-cast rings) and should contain openingsfor the entry of water. Dug wells must extendseveral metres below the water table(although it cannot be too far because, evenin a moderately permeable rock, dewateringneeds to take place to enable digging tocontinue, thus limiting the depth attained). Inextended drought years, shallow dug wellsfrequently dry up and the possibility of beingable to ‘chase the water down’ is attractive.Thereafter only particularly severe droughtswill cause the well to fail.

4.2.2 Hand drilled boreholesAsia has had a long and successful historywith hand drilling techniques but it is only inthe last twenty years or so that small, handoperated drilling machines have been usedin Africa. Due largely to the efforts andachievements of the International DrinkingWater Supply and Sanitation Decade small,hand operated drilling rigs have been usedwith varying success in such Africancountries as Zimbabwe, Mozambique,Malawi, and particularly Tanzania. There are3 types of hand operated drills: the auger,the percussion and the rather specialised'palm and sludger' method. In Africa, theauger is most commonly used while the other2 have for many years proved successful inseveral Asian countries.

Figure 12. The auger method

4.2.3 The hand dug-well versus thehand-drilled borehole

Drilling a borehole with the manual drill rigs isconsidered easier than digging a 1mdiameter hole. Whilst digging has the greatadvantage of involving virtually the whole


20

community, hand-drilled holes now alsoinvolve them. Only in a particular region orarea where well digging is an accepted,competently practised and well-understoodtechnique, is it perhaps better not toencourage change. In a new area, however,where the rock permeability is notexcessively low and a shallow water tableexists, there is merit in encouraging thehand-drilled borehole technique.Where the reservoir capacity of the hand-dugwell is not needed, i.e., areas with a shallowwater table and a reasonably highpermeability, the relatively low cost of themanually drilled borehole (see below), thepotential for substantial communityinvolvement, low maintenance, fasterpenetration and better inherent protectionagainst surface pollution makes the hand-drilled borehole a more attractive propositionthan the hand-dug well.In Tanzania, for example, it takes 2-7 weeksto dig a well depending on depth and soilconditions, whereas a hand-drilled boreholeis normally constructed in 3-5 days(Blankwaardt, 1984). The portability of handdrills has improved markedly and for smalldistances they can be carried by hand,whereas pre-cast concrete lining rings forwells need a truck.Data from Tanzania clearly shows thatinvestment costs for hand-drilled boreholesare less than dug wells and the differentialincreases with depth.Advantages of the manually drilled well:• More cost effective than the hand-dug

well,• Far speedier completion,• High potential for community

involvement,• Lower capital costs,• Can usually go somewhat deeper than

hand-dug wellsDisadvantages• Unlike the hand-dug well, pump failure

renders the manually drilled wellunserviceable,

• In extremely low permeability terrainhandpump yields may not be sufficient,

• In very fine grained, well-sorted sands orsilt, even a gravelpack and small slotscreen may not be able to stop abrasivesand ingress harming the pump, althoughthis is unusual.

• Decision-makers should be well versed inthe advantages and benefits of eachtechnology in specific environments andable to discuss them thoroughly with thecommunity at the planning stage.

Key Points of hand-dug and hand-drilledboreholes• Hand-dug wells have been known since

biblical times and are ubiquitous in Africa,• The old rule in rural water supply "dig

before you drill", is still true where diggingis a well-established method. In lowpermeability areas the storage capacityof a dug well is critical,

• Compelling evidence of the advantage ofthe hand-drilled borehole in Africa is welldocumented,

• Hand drilling a borehole is easier thandigging a 1 metre diameter well as theequipment is more portable, the cost issignificantly less and it provides aninherently better seal against the dangerof polluted surface water entering thegroundwater reservoir.

4.3 Machine drilled boreholesDrilling methods using machine-mounted rigsare essentially of two types, the cable toolmethod (percussion) or one of several rotarymethods. Both methods have particularadvantages, but here the drill type anddrilling approach suitable for low yieldingholes will be emphasised.

4.3.1 Cable Tool/Percussion MethodThe cable tool or percussion method is oneof the oldest and still one of the most populardrilling techniques. In Africa, there arehundreds of percussion rigs, some stilloperating effectively after 50 years.The essential parts of a cable tool rig areshown in figure 13.


21

Figure 13 - Typical truck mounted percussion drill. Itcan also be mounted on a two-wheel bogey (afterTodd).

Drilling is accomplished by the regular liftingand dropping of a string of tools made up ofa swivel socket, a set of jars, a drill stem anddrilling bit, the total weight being up toseveral tons. The drilling bit, which does theactual drilling, is essentially a chisel. It canweigh a ton or two and is variously shapedfor drilling in different rock formations. Thedrill bit is worked up and down in the holepulverising the rock until 1-2 metres of loosematerial fills the hole. The cuttings areremoved from the borehole by a bailer orsand bucket.

Figure 14. Basic drilling tools for the percussiondrilling method (after Todd).

To monitor drilling progress the experienceddriller holds the drilling cable to ‘feel’progress. The 'feel of the cable' as 'oldtimers' generally refer to it, can giveinformation as to the hardness of the rock,whether water has been struck, whether thebit is blunt, etc.Percussion rigs are mechanically simplemachines able to drill holes of 100mmdiameter (150mm is most common insouthern Africa) to as much as 400mmdiameter through consolidated rock materialsto depths in excess of 600 metres. Whilstpercussion rigs are less effective inunconsolidated sand and gravel, especiallyquicksand because the loose materialslumps around the bit, drilling rates in looseflowing sand, while slow, can reach 3-6m/day. These rigs also provide the onlymethod of drilling through material containingboulders, usually associated withunconsolidated alluvial material.The cable tool is highly versatile in its abilityto drill effectively over a wide variety ofgeological conditions. There is no consensuson the limitations of the percussion rig.Several authoritative drilling texts insist thatin hard rock it is not effective, while othersmaintain that in dense, very hard rock themethod offers no unusual difficultiesalthough clearly penetration is usually slow.Casing is not required when drilling in hardrock (except for the top few metres wherethe soil is loose). If the material being drilledis loose, it is necessary to advance casingduring drilling to prevent caving. In theauthor's experience it is surprising howinfrequently this occurs. In Zambia (1992-94), however, the borehole collapse rate inhard rock was approximately 20%, due tosoft, loose intervening layers in the hardrock. Casing is now invariably used in allboreholes in Zambia.

Key Points of percussion drilling:Advantages:• The cable tool is simple to operate and

maintain,• It has relatively low capital costs,• There is a great deal of experience with

this method in Africa,


22

• It is suitable for a wide spectrum ofgeological conditions,

• The majority run on a Lister engine andspare parts are generally available,

• For water chemistry studies this methodproves superior.

Disadvantages:• When compared to other methods it is

slow,• Problems can occur with exceedingly

loose formations

4.3.2 Rotary RigsIn the recent past, rotary rigs have becomeincreasingly popular in the sector due to thespeed of drilling and the fact that casing israrely needed during drilling.

Figure 15. The principle of rotary drilling: arrowsindicate direction of mud circulation. (after Davies &DeWiest)

Cutting of rock is achieved by rotating bits ofvarious types. The power is delivered to therotating bit by a rotating hollow steel tube ordrill pipe. Pre-mixed mud is forced down thedrill pipe and out of the bit. The role of themud is to carry the rock fragments upwardsand then deposit them in a settling tank. Italso supports the hole wall and minimisesfluid loss into the aquifer, which, perversely,means it seals off the aquifer! Drilling mud

consists of a suspension of water, bentonite,clay, and various organic additives. Themaintenance of the correct mud in terms ofweight, viscosity, jellying strength isimportant to ensure trouble free drilling andrequires considerable skill. Generally nocasing is required because the hole is filledwith the mud slurry and, once drilling stopsand the water level goes down, the mud cakekeeps the walls intact.Rotary drilling is difficult in cavernous highlypermeable rocks (basalt and limestone)because there can be a total loss of drillingfluid into the rock. Furthermore the mud cakeleft on the wall in unconsolidated aquiferssignificantly reduces the inherentpermeability of the aquifer. For large yieldsconsiderable development must take place toremove the cake and mud that has enteredthe aquifer itself. It is not easy to determinewhen water is struck and what the yield is,but an experienced driller will be able tomake a reasonable ‘guesstimate’.Below in Figure 16 is a schematic diagram ofa large direct rotary rig illustrating the majoroperational components of a truck-mountedmachine. It operates either with air-based orwater-based drilling fluid.

Figure 16. The ‘monster’ ‘super rig’. In theseventies there were many such ‘monsters’ drilling forwater in Africa, but not for long. A lack of spare partsand maintenance soon decimated these rigs - a ratherinappropriate tool for a low yield borehole often farfrom an accessible road. Today, much smaller versionsof this drill are available.


23

Key Points:Advantages:• Most rock formations can be drilled,• Relatively fast for semi-decomposed

rock,• Water and mud supports unstable

formations,• Small manoeuvrable rigs now availableDisadvantages:• High capital costs,• Complex and sophisticated, operational

logistics can be difficult in Africa,• Drillers need lengthy training and

experience for best results due to thecomplexity of the technique,

• Water is required for drilling, posing aproblem in arid areas,

• Mud reduces aquifer permeability,necessitating the efficient removal of themud cake,

• It is not easy to determine yield whiledrilling.

4.3.3 Rotary-percussion or Down-the-Hole Hammer method

This is a recently developed technique on therotary principle where air is used as thedrilling fluid and the rotary bit has the actionof a pneumatic hammer delivering 10-15impacts/second, known as down-the-hole-hammer (DTH). It is particularly suited todense, hard rock where penetration rates of0.3 m/min have been achieved (equivalent tosay 30-100m/day, which is very fast in hardrock). If large yields are required (which areseldom to be expected in hard rock but therule proves the exception in limestone andsome volcanic rocks) another method mustbe chosen because DTH is suitable only forsmall to moderate yields.

Key Points of the Rotary-percussion methodAdvantages:• Very fast in hard rock with moderate

water yields,• Small manoeuvrable rigs are now

available.

Disadvantages:• High equipment costs,• Requires experience to operate and

maintain,• Air compressor mandatory, complex

equipment.

4.4 Dug well versus hand bored(drilled) borehole versus machinedrilled borehole

A frequently reproduced table from ‘thehandpump option’, Arlosoroff et al (1987)showing cost comparisons for differenttechnologies plus other parametercomparisons is shown in the table below.The capital cost figures are now outdated,and while the cost comparison between thevarious technologies is still valid; absolutevalues will have increased.Interestingly 200mm holes are considered asstandard by the authors, clearly so that anartificial gravelpack can be placed.


24

Table 1.WELL CONSTRUCTION TECHNOLOGIES

Handdigging

Handdrilling

Cable-tool rig Small airflush rotary

Multipurposerotary

Approx. capital cost range USD 1000 USD1000-5000

USD20,000-100,000

USD100,000-250,000

USD200,000-500,000

Running cost very low low low medium very high

Training needs for operation very low low low-medium medium very high

Repair skills very low low low-medium medium very high

Back-up support very low low low-medium medium very high

Approx. range of penetrationrates in metres/ 8-hr day

0.1-2.0 1-15 1-15 20-100 20-100

200mm holes to 15m inunconsolidated formations

- fast fast impossible very fast

200mm holes to 50m inunconsolidated formations

- slow anddifficult

fairly fast impossible very fast

200mm holes to 15/50m in semiconsolidated formation

- Impossible fairly fast impossible very fast

100mm holes to 15/50m inconsolidated (hard) formation(not gravel packed)

- Impossible very slow very fast very fast

Another valuable and more recent cost study by The Swiss Centre for Development Cooperation inTechnology and Management (SKAT) attempts costing the various technologies in Table 2.Table 2.

Type of Technology Targetedpersons

persource

Investmentcosts(USD)

Cost/capita(USD)

Runningcost

(USD)

Cost/m3

(USD)Runningcosts/m3

(USD)

Dug well 150 1,650 11 50 0.35 0.06

Dug well with direct actionpump

200 2,700 14 125 0.49 0.11

Borehole with handpump 300 13,500 45 224 1.29 0.14

Borehole with electricpump

2,400 84,000 35 1,960 0.63 0.11

Borehole with diesel pump 2,400 68,000 28 3,900 0.79 0.22

Borehole with solar pump 2,400 72,000 30 1,435 0.76 0.10

Quite unexpected is the cost/capita ranking,the handpump mounted borehole having thehighest cost/capita. Clearly the water sourcehere is costed at a high figure, which istypical for West Africa.If the water table is shallow and the rock issoft then manual techniques should befavoured. Deciding which method is the mostappropriate can be difficult. Both hand-dugand hand-drilled methods are least cost

solutions in shallow water table areas. If,however, speed is the main factor thenmachine drilling in such an area is justified.All variables must be considered but thegeneral statement can be made; in shallowwater table areas manual digging or drilling isthe most appropriate technique. Thedefinition of shallow water table will vary, buta reasonable figure is up to 15 or 20 metres.


25

Matabeleland, the dry South-Westernprovince of Zimbabwe, where hand dug wellsare often employed, provides an interestingcase study of how past tradition frequentlydictates a certain approach. The water tableis relatively shallow but the weathered mantleis extremely thin and, in order to producesufficient water, expensive rock blasting isused in the wells. If, as at first sight, machinedrilling would appear more appropriate, whyis blasting chosen? The reason is thatmachine drills were not available at the timeimmediately after Independence when anaccelerated water supply programme beganin the early eighties. Consequently, there isnow a large cadre of trained well diggers andexplosives experts therefore wellconstruction continues to be the major watertechnology. It should, however, be noted thatwhile a machine-drilled borehole might seemto be more appropriate in such hard rock,there is no guarantee that it would be. Thepermeability of the rock (i.e. the amount ofwater which the rock will yield) may be so lowthat a borehole may not have sufficientreservoir capacity. A hand-dug well will berecharged during the night by water slowlyseeping into the well. By morning, it will haveperhaps 3-4 m3 of water in it, which can bepumped out.Costs are calculated based on an average offigures obtained from several countries inAfrica. Cost considerations will usuallydominate in rural water supplies wherefunding is limited and demand is great butthere are other factors, which will influencethe choice of drilling method. If, for example,cost and community participation areparamount (and there is a shallow watertable in soft terrain with low permeability)then the hand-dug well is the technique ofchoice. If the same criteria apply but the rockhas a relatively high permeability then thehand-drilled borehole may be moreappropriate. If, alternatively, speed is theoverriding factor then the machine-drilledborehole is clearly the answer.

4.5 Pollution and ShallowGroundwater

In shallow water table conditions the dangerof bacteriological pollution is ever presentand mandates the need for properconstruction of the well/borehole, particularlyof the surface apron that seals the aquiferfrom surface water pollution. The well isusually completed with a sealing slab and thesurrounding apron with a drain. It is the areaimmediately adjacent to the well thatprimarily determines whether pollution cantake place. If apron construction, and thussealing is poor, then pollutant can easilymake its way into the groundwater reservoiralong the wall of the well. Cleanliness nearthe well must be encouraged at all times,notwithstanding proper apron construction,and excess water should drain somedistance away from the well.

The shallower the water table the greaterthe danger of groundwater pollution. Properly constructed well aprons are

mandatory.


26

5 THE LOW COST BOREHOLE-DESIGN AND COSTING

5.1 OverviewWe now come to the central theme of thiswork - how to ensure economic optimisationof a handpump mounted borehole designthus reducing the current cost incompatibilitybetween the water source and the otherelements of ‘the triad’. Design andconstruction should be guided on common-sense guidelines to avoid over-design whereonly small yields are needed. Yield being theonly variable; design is critically dependenton yield.In large yielding boreholes, especially inunconsolidated material, stringent designand construction parameters are required.Large yields lead to high velocity water flow(entrance velocity) into the borehole, which inturn requires screens with high percentageopenings and a thick artificial gravelpack.The thickness required depends on themaximum velocity and aquifer material.Where large yields are sought, detailedhydrological and geophysical fieldinvestigations are justified because theborehole will most likely be deep, of largediameter, cased, gravel packed, expensivelyscreened and thoroughly developed;resulting in a high cost but high productionhole.Boreholes drilled specifically for handpumpsshould be viewed differently. The requiredyield is extremely small, the entrance velocityis low, and flow hydraulics simplified so thatseveral of the expensive requirements oflarge yielding boreholes fall away. It must beemphasised that the ‘downscaling ofboreholes’ does not and should not suggesta lowering of borehole construction quality.Even for very small water yields, boreholequality must be maintained or improved sothat productive life is long and trouble free.The new departure point for the design of ahandpump equipped borehole is therefore alimited yield of 1-2m3/hr. Design guidelinesare discussed below:

5.2 Borehole DiameterThe most commonly used handpump inAfrica has a rising main of 50mm and theborehole is normally drilled at 150mm with a100mm casing if required. Should asubstantial artificial gravelpack be required ina particular area then the 150mm hole canbe reamed out to 200mm. When rotarydrilling is used there is virtually no costdifferential between 150 and 200mm. Manyexperts believe that 200mm give moreleeway and are thus preferable to 150mm. Athin gravelpack is routinely used inMozambique, the annulus between the100mm screen and the 150mm bore beingpacked with gravel to just above the screen.While its hydraulic efficacy is negligible, thegravelpack has the advantage of anchoringthe screen in the hole, although centraliserswould do equally well.Key Points:• 150mm diameter is suggested as

standard, but as the cost differential,particularly with rotary drilling, isnegligible, some feel there is a case for200mm as standard,

• If the hole is to be artificially gravelpacked for hydraulic reasons, i.e. a veryfine, well sorted aquifer, then an 200mmdiameter hole is mandatory,

• In Mozambique 150mm boreholes areroutinely gravel packed, even though theannulus is only 25 mm.

5.3 Matching depth of the boreholeto required yield

Whilst it cannot always be said that 'thegreater the depth the greater the yield' it is areasonable rule of thumb up to a criticaldepth. If we consider 1 -1.5m3/hr to be theupper limit of the handpump's requirement (agenerous figure) then drilling should stop10m or so beyond the depth at which thisyield is obtained. This reserve column willallow for seasonal variations and excessivedrawdown in aquifers with low permeabilityor, more correctly, transmissibility. Areas


27

where seasonal water level fluctuationsexceed 10m are rare, but if the area ishydrogeologically 'known' to have largefluctuations then clearly a reserve column of15 - 20m will be necessary.In practical terms the drill crew (only if apercussion rig is used), once they havestruck water, should carry out a rapid bailertest (an eminently appropriate methodologyin this type of work) to establish the yield.The bailer test saves time and money andgives a good indication of what can beexpected from the borehole.If the test shows a yield less than 1m3/hr,drilling should continue with testing in depthintegrals of, for example, 2 metres. When therequired yield is attained drilling mustcontinue for a further 10m and then stop,although in Zambia the drilling is stopped 5mafter a yield of 0.8m3/hr is obtained. Adrawdown of more than 10m with handpumpyields is uncommon but, if the aquifer haslow permeability, then the borehole must bedeeper. Experienced drillers can at times‘gauge’ or ‘feel’ the permeability of theaquifer.In 90% of cases, groundwater yields suitablefor handpumps exist within 50m of thesurface. In any event handpumps have amaximum practical lifting capability of 60m(new developments currently beingresearched may increase this figure to 80m)so generally drilling should stop at 70m. Insome regions, however, first water may bepenetrated only at a relatively deep level, i.e.80-100m. Because there is a possibility thatit may be sub-artesian (and therefore underpressure and able to rise to a level which canbe pumped by the handpump), it is worthdrilling to such depths in areas where sub-artesian conditions are known to occur, e.g.in the so-called ‘basins of decomposition’ ingranite areas.In some areas in Zimbabwe there areinstances where local politics overtaketechnological acumen. In the mid-eighties acycle of droughts hit Zimbabwe and manyboreholes dried up. There is now theperception in these areas that onlyexceptionally deep boreholes will not besubject to drought.Key Points:• Once the required yield of 1.5 m3/hr is

attained, drill a further 10m to allow forseasonal water level fluctuations anddrawdown levels,

• The yield should be established with asimple bailer test as drilling proceeds inintegrals of 2 or 3 m after water is firststruck,

• In sub-artesian conditions the boreholewater first struck can be considerablydeeper than the norm for handpumps of50-60m, but it may rise to these levels.

5.4 Borehole development.In percussion drilling in unconsolidated rockthe inherent permeability is reduced;permeability is lost through vibration andcompaction, but the loss is minimal. This is incontradistinction to boreholes drilled by therotary method, where mud or bentonite isused, resulting in a dramatic fall inpermeability. In a fissured aquifer the mudmay be forced into the fissures cutting themoff from the borehole. To produce high yieldsin a potentially high yield aquifer, boreholedevelopment is required to eliminate the'skin' effect or 'cake' from the wall or extractthe 'mud' from blocked fissures. In essence,therefore, the action of drilling will lead tosome damage to the aquifer immediatelyadjacent to the hole and a reduction ofborehole performance. By developing theborehole, damage is reduced and long-termperformance improved. Thoroughdevelopment also ensures the acceleratedegress of sand and fine material from theaquifer. If a borehole is not developed, andthe handpump is mounted, then the pumpedwater may contain sand and/or silt which candamage handpump seals and valves.Development procedures are varied andinclude pumping, surging, use ofcompressed air, hydraulic jetting, the additionof chemicals (an important advance in rotarydrilling is the use of a biodegradable mudinstead of bentonite or clay), hydraulicfracturing and the use of explosives. Theseare specialised techniques and details canbe found in specialised drilling texts.For small yields the 'cake' effect is not socritical and, in any event, development by thevarious methods available (excludingpumping and surging) all have a minimaleffect with screens that have a small


28

percentage opening appropriate for smallyields. In large yielding boreholes, screenopenings of 30-50% are common and withsuch a large percentage of open area thevarious development methods are relativelyefficient. Low yielding boreholes with screenopenings of 1-5% (sufficient for handpumpyields) render the more sophisticateddevelopment techniques grossly ineffective.The most economical method of developingthe low yield borehole is to use a bailer topump or over-pump the hole until ingress offine material stops. In the low yield borehole,an effective method of development, apartfrom pumping and over-pumping, is the useof the same simple bailer to surge theborehole. Surging is a process that attemptsto set up a washing action by forcing thewater backwards and forwards through thematerial to be cleaned, i.e. the screen, thegravelpack (if there is one) and the aquifermatrix. The simplest way of surging aborehole is to use a bailer, taking it up anddown rapidly. The bailer acts as a piston inthe screen to pull loose material into theborehole for subsequent pumping out.The development of a borehole (pumpingand surging) results in the finer fractions ofmaterial being drawn from theunconsolidated aquifer (and from fissures insemi-consolidated aquifers) leaving behind astable envelope of the coarser, and thereforemore permeable, material of the aquifer. Thisnatural gravelpack is not to be confused withan artificial gravelpack.

Figure 17. Natural gravelpack development, (afterClarke 1988)

The grain size distribution of anunconsolidated aquifer dictates howefficiently development creates a naturalgravelpack. The D number, or moreimportantly the sorting or uniformitycoefficient expresses the grain sizedistribution. The D number is related to thegrain size; for example D40 relates to thesieve mesh diameter through which 40% ofthe aquifer material will pass (how sedimentsieving is carried out is explained in severaltexts marked in the list of references). An ill-sorted aquifer has a sorting or uniformitycoefficient (D60/D40) of more than 2.5. Thegrain size and sorting of sediments areillustrated by grain size distribution curves,which are used for the design of screen slotsize and artificial gravelpacks. Thisdiscussion will not be taken further intechnical terms, suffice to note that if largeyields are required in unconsolidatedaquifers the design of screen slot size andgravelpack are critical to the long life of theborehole.There are instances where, even followingpumping and surging, pumped water maytake weeks to clear up completely. If sandand silt continue to ingress after such aperiod, a possibility in very fine-grainedaquifer material, an artificial gravelpack ismandatory. Even in fine-grained material,however, an artificial pack is oftenunnecessary. For example, in the TharpakarDesert in Pakistan with a drilling programmethat did not include gravel packing despitefine-grained material, sand ingress severalweeks after drilling was reported in only 1borehole out of 75. This one-off case did notwarrant a change in design strategy, i.e., togravelpack all boreholes; the particular holewas simply abandoned.Key Points:• Development of a borehole is a crucial

adjunct to a properly completedinstallation,

• For low yield boreholes pumping, orbetter still over-pumping, is the bestmethod of development. Rule of thumbpumping periods vary from 2-24 hours oruntil the water pumped is clear, which isfrequently within an hour or two,


29

• The bailer (standard equipment on thepercussion rig) can be effectivelyemployed for development in the processof surging, and even for pumping if asubmersible pump is not available,

• Pumping and surging will create a naturalgravelpack around a borehole drilled inunconsolidated sediment which is criticalto the long productive life of the borehole,

• The brief technical discussion aboverelating to distribution curves and sortingcoefficient is not essential reading butillustrates the complexity of boreholedesign for large yields,

• Despite the fact that, in hydraulic terms, agravelpack is not required nearly asfrequently as it is used, the widespreadpractice in some countries of routinelyplacing an artificial gravelpack should beallowed to continue given its low cost and‘anchoring’ action.

5.5 The use of PVC casing andscreening

In boreholes designed for large flowsscreens have the effect of:• Stabilising the sides of the hole,• Preventing sand movement into the well,• Allowing a maximum amount of water to

enter the hole with minimum hydraulicresistance.

The choice of a particular screen type willdepend on a combination of factors includingstrength and corrosion resistance as well asslot size and design and open area (which isthe proportion of a screen face made up ofopen slots).An important design criterion relating to theopen area of a screen is the entrancevelocity, which is the discharge of theborehole divided by the effective open areaof the screen. It is widely accepted that theentrance velocity should be kept below thecritical value of 0.3m/min. If the entrancevelocity is higher than the critical value(assuming for the purposes of this discussionan unconsolidated aquifer, typical porousmedia), sand and silt or even finer materialwill enter the borehole and turbulent flow willcause a loss of head. The loss of head withthe onset of turbulent flow into the borehole

will not be considered here; it is onlyimportant when large yields are pumped.Inflowing sand or silt after development canoccur and the only way to stop it is to slowdown the water flowing into the borehole.This can be achieved by means of a highscreen open area and a natural or artificialgravelpack, which creates a highpermeability zone around the borehole. Thesmall handpump yield of 1 m3/hr translates toa very low entrance velocity, well below thecritical velocity concept in borehole design,above which sand/silt may be carried into theborehole. High percentage opening, smallslot size screens (which are expensive) arenot required; they are only needed whenyields are high and inflow velocities areconsequently large.Screens are manufactured from a variety ofmaterials, PVC, mild steel, stainless steeland various alloys. Slot designs are manyand varied, stainless steel screens and spiralwound wire being extremely expensive,although allowing an open area of 40-50%.For handpump supplies, low cost (locallymanufactured) PVC casing and screeningcan be utilised. The slot size of the screensis not critical for low yields in normalconditions, although it can be critical in fine-grained aquifers. In aquifers requiringscreens, primitive machine sawn slots with atotal opening of 5% (slot size 0.5-1 mm) areappropriate. Casing and screens can be oflow cost PVC. PVC casing and screens canbe joined by two methods, either bell andsocket (male/female) joint with solventcement, or threaded joints. In most areas,and certainly in the developed world,threaded joints are significantly moreexpensive than the bell/socket. Recentdevelopments in Southern Africa, however,show that local manufacturers are charginglittle more for threaded flush joints than thebell/socket joints. For a price differential ofUSD 1-3 per joint, threaded flush joints areprobably a better choice than the bell andsocket joint. In those regions, however,where the use of threaded joints wouldsignificantly increase costs in low capacityboreholes, bell and socket joints should beused. It could be argued that while the casingis being inserted the solvent cement jointcould come apart. As a safeguard againstthis unlikely event, two small self-tapping


30

screws inserted at every joint guarantee thatthere will be no problems. Interestingly, thedrilling industry in much of Africa has longbeen suspicious of solvent cement joints,however in Asia there is considerableexperience of effective use of this type ofcasing. In South Africa, irrespective of thesmall cost differential between the two typesof joints, most commercial drillers now usethe bell and socket joints routinely andsuccessfully. In addition, recent research

work carried out in the United Kingdom onsolvent cements has resulted in theavailability of improved products on themarket.It has taken time for drillers to ‘adapt’ to theuse of PVC casing and screening. In thepast, steel casing and screens were thenorm and, while much more expensive, thetoughness of steel meant that less care wasrequired in its handling.

Table 3. Cost of different casing and screens and effect on total cost of borehole. (Based on 5m of screen and 45 m ofcasing in a 50m hole).

Cost/m

(USD)

Cost of Screen /Casingin a 50m borehole

(USD)Steel screen with flame cut slots used in Zambia, pre 1995 50Steel casing used in Zambia, pre-1995 40 2050PVC screens (bell socket joint) manufactured and used inZimbabwe 7.3PVC casing (bell and socket joint) manufactured and usedin Zimbabwe 5.3 280Steel screen used in Zimbabwe, low percentage opening,large slots

20

Steel casing used in Zimbabwe 15 775PVC screen used in Mozambique, imported from Holland 28PVC casing used in Mozambique, imported from Holland 18 1040PVC screen manufactured and used in Pakistan 6,50PVC casing manufactured and used in Pakistan 5.50 280PVC screen manufactured in South Africa used in Zambia 10PVC casing manufactured in South Africa used in Zambia 8 390The table reveals how dramatically costs can be reduced with locally manufactured PVC screensand casing; imported PVC is expensive.

The collapse resistant rating is an importantfigure for screens and casing as itdetermines the permissible installation depthand likelihood of failure. Usually the highestexternal pressure load occurs duringdevelopment and gravel packing. Forboreholes with handpumps development isnormally carried out by pumping and/or bythe bailer acting as a surging tool. Light, lowcost screens are safe but care must be takenin raising and lowering the bailer. The heavydevelopment tools used in large yielding

holes such as a surge block, which exertsconsiderable pressure on the screens, areinappropriate for low yield holes.Generally casing and screens are notrequired in hard rock and seldom in semi-decomposed rock, (except the top fewmetres of overburden) yet many countries(e.g. Mozambique) use them despite the factthat there is no reason to do so. Theexplanation is sometimes proffered thatcasing protects the rising main in a hard rock


31

borehole from rubbing on the wall of theborehole. It is an unsatisfactory explanationsince the problem can be overcome easilyand cheaply by using PVC piping cut in halflengthways as stabilisers or centralisers.There are, however, exceptions. In hard rockterrain in Zambia the drills sometimes cutthrough a soft, loose decomposed layer atdepth, only to go through hard rock againafter a few metres. Previously such holeswere left uncased but it was discovered that,in time, 10-30% of such holes collapsed.Consequently, hard rock holes in Zambia arenow routinely cased. Research work isplanned on the thin decomposed layers lyingwithin fresh rock so that clear guidelines maybe established as to when and when not tocase.In the decomposed mantle in Malawi whereChilton and Grey did their early work,screens, some casing and gravel packingwere routinely used. Conversely, inZimbabwe, under very much the sameconditions, the policy was to case off theoverburden, usually the top 10-15m, drill intothe decomposed zone and the fresh rockand leave it open. Screens and gravelpacking were seldom used. No harmfuleffects such as silting or decreasing yieldwere experienced. The few screens usedwere made of mild steel with torch cut slots(at least 3mm wide) resulting in an open areaof only 1-2%. Although it must be said thatChilton and Grey suggested tapping theoverburden.Key Points:• Two important design criteria are

discussed in relation to screens.Entrance velocity and critical velocity. Itbecomes apparent that the lowhandpump yield means a low entrancevelocity well below the critical velocity;again emphasising the significantdifference that yield makes in boreholedesign requirements,

• PVC screens and casing are appropriatefor low yields,

• In some countries and regions there is asignificant cost differential between thejointing mechanism for PVC screens andcasing. Threaded joints are preferablebut, if the cost differential is significant,bell and socket joints should be used.

• PVC casing and screens are low costand can be easily transported andhandled,

• The smallest slot size of about 0.5mm isgenerally acceptable. For low yields, anopen screen area of 5% is sufficient,

• Boreholes drilled in either hard ordecomposed rock generally do notrequire screens and casing; the use ofstabilisers or centralisers is effective andlow cost but further experimentation isdesirable. Note the Zambian experience(see 6.3.1).

5.6 Artificial gravelpack - when andwhere needed?

At a typical discharge rate of a handpump of750 l/h, a 3-metre screen with only a 5percent opening, and no gravelpack, istheoretically “safe” in terms of sand ingress.The average velocity of the water passingthrough the screen is at least a factor 3below the critical velocity where turbulentflow may be generated and 0.5mm sandgrains begin to move. In large capacityboreholes sited in aquifer material that isfine-grained and well sorted, an artificialgravelpack is mandatory. The advantage of agravelpack is that, because the pack materialis coarser than the formation, screens withlarger slot sizes can be used and, bysurrounding the screen with highlypermeable material, inflow velocities arereduced.In terms of hydraulic theory, it is clear that forsmall yields an artificial gravelpack is notessential. Yet, in practice, even whenboreholes have gravelpacks, movement ofsand into boreholes can still occur. Althoughinfrequent, the fact that it happens at allillustrates how the theoretical aspects ofgroundwater hydraulics can and do divergefrom field reality. Such sand may actually findits way into handpump plungers andaccelerate the wear of seals and washers.This rare, but inconvenient ingress of sandinto low capacity boreholes dictates thatsome of the possible causes should beexamined before adopting a blanket policy of‘no gravelpack use’. Possible explanationsfor the presence of sand in handpumpplungers include physical and hydraulicfactors. The physical factors relate to the


32

grain size of the sand and, more importantly,the grain size distribution; the finer thesand/silt and the greater the uniformitycoefficient the more sand migration is likely.The hydraulic aspects are that theoryassumes a completely porous media withwater flowing through all pores at the samevelocity. In practice, however, porosity variesand so do flow velocities. Additionally, flowcaused by ‘handpumping’ is not constant butpulsing, which will also increase flowvelocities over short spans of time. In fact, afaulty footvalve may even cause a smallscale jetting action within the screen if thehandpump plunger is inserted.The author believes that the abovediscussion demonstrates that in mostsituations low yield boreholes (meaningentrance velocity well below the criticalvelocity) do not require an artificialgravelpack on hydraulic grounds. InZimbabwe, there are well over 25,000documented boreholes in a variety of terrainand rock types with no gravelpack and noscreens. Some boreholes have primitivescreens with ‘wide’ flame cut slots and anopen area of 1-2%. From a purist’s designviewpoint nothing could be worse, yet manyof these bores are 40-50 years old and showno sign of deterioration.Nevertheless, in several countries agravelpack is frequently installed in the beliefthat it is needed, even in hard rock boreholeswhere it definitely is not. In suchcircumstances the gravelpack has amechanical effect; it helps to anchor thescreen and casing in the borehole, but,perversely, this too is unnecessary in a hardrock borehole!Geotextile is a new material now beingexperimentally used instead of an artificialgravelpack, and sometimes in addition tosuch a pack. Unlike the gravelpack, whichreduces water velocity, geotextile acts as afilter, letting water in but excluding sand/siltand other fines. Data on its long-termefficacy is still lacking.Key Points:• From a hydraulic viewpoint, it is

concluded that an artificial gravelpack isseldom required in low yieldingboreholes, and screen open areas can below (5%),

• In hard rock boreholes neither agravelpack nor a screen and casing areneeded but several countries routinelyuse them, primarily for mechanicalpurposes such as the protection of thehandpump rising main. Stabilisers orcentralisers would do the same job forless cost.

• There is compelling evidence that thegravelpack can be eliminated but its lowcost, mechanical, and at times evenhydraulic advantage, coupled withwidespread practice, probably meansthat its use should not be discontinued incountries that routinely place agravelpack.

5.7 Borehole Pump TestingThere are two main reasons usually cited forpump testing a borehole:a) To measure the well performance and

efficiency with a varying discharge,b) To measure the aquifer characteristics

of storativity and permeability (for theaquifer as a whole it is calledtransmissibility).

Pump tests are fundamental in groundwaterhydrology. Boreholes are pumped forextended periods and the drawdown ismeasured over time, thus enablingassessment of well performance and aquifercharacteristics. Pump tests normally varyfrom 6-72 hours and at times are evenlonger. The tests are conducted with avarying discharge and/or constant discharge.The flow equations describing water flow intoa borehole are complex and analysis of thedepth/time data to obtain the requiredfunctions used to be intricate. Now, with theadvent of the computer, analysis is muchsimpler. Notwithstanding, for low yieldingholes of limited depth it is needless to carryout a ‘sophisticated’ test. In these holesneither theoretical well performance noraquifer characteristics can easily beobtained. All that needs to be established iswhether the borehole has a yield of 1-2m3/hr. Pumping for 2-3 hours at 1-2m3/hrcan do this. If, at the same time water depthmeasurements are taken, all the better; afirst order approximation of thetransmissibility is now available for future


33

reference. No more is required! To attemptextensive pump tests on low yield boreholesis woefully extravagant! Nonetheless theobligation for a particular region or country tobuild up a comprehensive groundwaterdatabase can sometimes colour theperception of the hydrogeologist tasked withcollecting such data.Pump test results are most valid inunconsolidated aquifers; in hard rock theyare an approximation at best. A privatecontractor in Mozambique gets around thedifficulty by combining a simple pump testwith development of the borehole (see casestudy). In Zambia formal pump tests are nolonger carried out on handpump mountedboreholes. But what if, when drilling for anormal low yield, a large yield is struck? Inthis situation a comprehensive pump test isjustified.In India simple two-hour pump tests arecarried out on handpump mountedboreholes. Water is air-pumped (usingcompressed air) to the surface and ledthrough a ‘v’ notch that measures the yield. Itmay not satisfy the purists but it is simple,low cost and appropriate.Key Points:• Pump tests are a fundamental procedure

to assess both borehole and aquiferperformance. In low yielding, limiteddepth boreholes classical extended pumptests are frequently meaningless andunnecessary on a routine basis.

• A simple test using either a bailer orsmall submersible pump to determine theyield over a 2-3 hour pumping period isall that is needed. Timed water leveldepth measurements should be taken ifpossible.

• Often the yield of the test pump is greaterthan the yield of the hole (5m3-10m3 /hrvs. 1m3/hr, so that the water is rapidlydrawn down to the pump. If that happens,the yield of the test pump should bereduced so that the rate of drawdown canbe measured for an hour or so.

5.8 Locating Groundwater - Can the‘experienced eye’ and sciencesee eye to eye?

A 1994 UNDP-World Bank funded reportentitled ‘Finding Groundwater, A ProjectManager’s Guide to Techniques and How toUse Them’ provides valuable insights intothis controversial topic.Boreholes sites should be chosen principallyon hydrogeological grounds, yet an importantcornerstone of the new philosophy ofcommunity water supplies is the completeinvolvement of the community is all aspectsof water supply, including the decision onsiting of boreholes. Quite naturally thecommunity will usually prefer that the watersource be sited as near as possible to thevillage, a location which may be at variancewith the ‘scientifically’ chosen site.The Bank study suggests that a logical andlow cost approach to borehole siting shouldhave the following sequential levels ofinvestigation:

Level 1: Inventory of Existing DataGeological DataHydrological and Climatic DataExisting Well Data

Level 2: Remote Sensing InterpretationSatellite ImageryAerial Photography

Level 3: Hydrogeological FieldworkGeomorphological AnalysisWater Point Inventory and MonitoringHydro-Climatic Monitoring

Level 4: Geophysical SurveyingElectrical ResistivitySeismic RefractionElectromagnetic Profiling (EM)

Level 5: Exploratory DrillingHand DrillingMachine DrillingGeological LoggingGeophysical LoggingTest PumpingWater Pumping


34

The approach above is sensibly systematicbut perhaps it should also include a zerolevel that allows ‘the experienced eye’ to sitethe borehole since groundwater in smallquantities is ubiquitous.The ‘experienced eye’ refers to thehydrogeologist who draws upon his scientifictraining and experience to assess the naturalclues for siting a borehole: the type ofvegetation, rock outcrops, soil colour,topography, valleys and drainage areas,existing nearby wells or boreholes andsprings. Negative indicators such as highground, areas of mudstone or basaltoverburden etc., etc. are also considered.For low yields and shallow depth, this is apowerful location method.The author (a geophysicist) has felt for manyyears that the use and cost-effectiveness of

geophysics in low cost water supply isdebatable since in most cases low yieldboreholes do not justify relatively expensivegeophysical investigation. In his view castingthe ‘experienced eye’ and ‘throwing of thehat’, or bones (more appropriate in Africa) onto the spot to be drilled is the method ofchoice in many (but clearly not all)hydrogeological situations.

5.8.1 Costs of Finding GroundwaterThe 1994 UNDP World Bank study hasattempted to evaluate costs of groundwaterassessment studies and borehole location inAfrica. These costs show tremendousvariation as can be seen below:

Table 4.

Category/regionAverage well

construction cost(USD)

Average cost ofinvestigation per site

(USD)

Low cost rural water suppliesWest AfricaEast AfricaSouthern Africa

12,00010,095 2,766

1,053 359 182

Compare these figures withConstruction and siting high yield boreholes 81,091 2,254

The variation in construction costs perborehole between the regions of West, Eastand Southern Africa is extraordinary. Inseveral East African projects the inclusion ofsanitation and health and hygiene education,etc., obviously raises costs. In West Africacosts are very high because of deeperdrilling and the use of more expatriate staff.Note too the far higher siting costs in WestAfrica. In Southern Africa a highlycompetitive commercial drilling industrykeeps costs lean. Nonetheless there aremany unanswered questions and suchregional differences deserve closer scrutiny.Interestingly, the percentage cost of siting inrelation to construction for low yieldboreholes in West Africa is significantlygreater (8%), than in East Africa (3.5%). In

absolute terms though these figures are verylow in East and Southern Africa. With suchlow figures, geophysics is certainlyworthwhile but once construction costs godown the issue is more debatable.The Case Study I, (Mozambique, see 6.1.1)shows geophysical siting cost of USD 250-500 (in 1994) is 17%-30% of total drillingcosts. The critical question is; would themoney saved by omitting scientific boreholesiting have made up for the loss involved indrilling 11 dry boreholes? The MozambiqueCase Study shows that it did, even assumingan unlikely 100% success rate hadgeophysics been used. The summing up ofFarr et al. is applicable here; ‘Groundwatersearch techniques are only justified if theyincrease the chances of subsequent


35

boreholes being successful, such that theoverall saving in drilling cost, in the long run,is greater than the cost of the search’.The evaluation of actual costs to determinethe extent of the investigation depends onlocal circumstances. Information on theexisting success rate without siting and thelikely increase in success rates withinvestigation must, if available, be acquiredfrom earlier projects in the area with

comparable conditions. The UNDP/WB study shows significantsavings in several large-scale projects, inparticular in high yielding borehole siting, butalso in low cost projects. An excellentexample is shown in the table below,although so dramatic is the improvement thatperhaps it is too good to be entirely true;perhaps another look at the results iswarranted?

Table 5.Rock type Number of

boreholesSuccess

rate%

Meandepth(m)

Meanyield

(m3/d)

Drilling cost perproductive well

(USD)Existing boreholes.Tertiary volcanic 38 44 126 140 17,700Nyanzian volcanic 19 68 116 95 10,600Granites 7 43 70 48 10,200ProgrammeboreholesTertiary volcanic 60 78 66 340 5,400Nyanzian volcanic 11 91 54 94 3,700Granites 10 60 61 140 6,350

In areas of high rainfall and unconsolidatedsediments, groundwater is usually shallowand in such cases the UNDP/World Bankstudy agrees that no investigation isnecessary for determining precise well sitesand that the community can select thedigging/drilling sites. The UNDP/World Bankstudy also allows that in areas where ‘...groundwater is known to be present atshallow depth, such as in many alluvialaquifers or areas with significant rechargefrom rainfall or surface water resources, thelimited abstraction needs of handpumps onlyrequire a very basic hydrologicalinvestigation...’However, over the vast crystalline rock areasof Africa where groundwater occurs in theweathered mantle, the study suggests thatgeophysical techniques are useful, ‘...especially where the subsurface conditionsare simple...’. Subsurface conditions,however, are seldom simple, and for some

50 years, until a decade ago whencompeting methods were introduced,geophysical methods in Africa centredaround an electrical resistivity depth profileused after the geophysicist had selected thesite based on his experience. For 40 yearsborehole sites were thus located inZimbabwe. No cost figures for such surveysare available and an estimate would not bemeaningful. The author has long beensceptical of the ‘confirmatory sounding’, andhas found ‘the experienced eye’ alone tosuffice. Witness the following success ratefrom a recent low yield borehole-drillingprogramme in Mozambique. Out of a totalnumber of 145 boreholes, 129 weresuccessful, (10 were dry and 6 saline) - asuccess rate of 89%. The most striking factis that only 60 (40%) of these were sited byan experienced hydrogeologist (using hisexperienced eye and throwing his hat), therest were sited by newly trained mediumlevel technicians with little experience of


36

hydrogeology. The boreholes were drilledover a large area covering 7 of the 10provinces in the country and, while most ofthe hydrogeology was relatively simple, inManica province, which is known as a verydifficult area, the drillers (all newly recruited)themselves sited 6 holes of which 3 weresuccessful.There is little doubt that in virgin areas thefirst two levels of investigation (UNDP/WBstudy): desk study, aerial photographs usedfor a photogeological study, geological maps,bulletins, reports and records of nearby wellsetc, are mandatory and, in areas known to bedifficult, systematic and thoroughinvestigation leading up to level 4 canincrease drilling success rates significantly.For example, in an accelerated drought reliefprogramme in Zimbabwe, a rapid surveytechnique that included systematicelectromagnetic profiling together withelectrical resistivity soundings increased thesuccess rate by 10-20%.The crux is that if geophysical surveys are tobe used (notwithstanding the author’s viewthat the ‘experienced eye’ can and should beutilised more often) then the surveys must becarried out systematically and sequentially.This should include working up the 5 levelsof investigation listed, rather than the ad hocelectrical resistivity depth soundings that areoften still practised by both government andprivate geophysicists. In Zimbabwe andmuch of Southern Africa over the past 50years the reality was that the ‘experiencedeye’ was utilised as the primary ‘locator’.Once the geophysicist had used his‘experienced eye’ and decided on a site hewould carry out a ‘confirmatory‘ electricalresistivity depth sounding; a debatably costeffective procedure.In terms of a cost benefit analysis wherelarge yields are sought with attendant high-cost borehole design, a full geophysicalinvestigation is well justified. Such aninvestigation is of doubtful value for smallyields, although the real expense starts atlevel 4 and leaps up at level 5.To complicate matters we have the frequentcase, as emphasised by Arlosoroff et al(1987), of a drilled borehole sited purelybased on a geophysical survey, irrespectiveof the community’s wishes. Consequently,‘...few people make use of the new facility,

regarding it as inconvenient’. The need toshare information with the community (andlisten to their opinion, including potentiallyuseful information about local water and soilconditions) at all phases of the planning,siting and designing of the proposed watersupply system is of paramount importance.Finally, (Blankwaardt, 1984) presents aninteresting finding in the Tanzanianenvironment; ‘The best method for siteinvestigation has proved to be the drilling byhand of small test boreholes followed by asimple pump test whenever a prospectiveaquifer is found’. There is no mention of howthe aquifer is found but clearly it must be in ashallow water table area.

Key Points• Finding groundwater is a mixture of

experience and science,• For the extremely low yields required by

the handpump, ‘the experienced eye’ canoften be enough; it is less expensive andfrequently as effective as moresophisticated options,

• A recent publication by the UNDP/WBWater and Sanitation Program addressesitself to the role of hydrogeology andgeophysics in locating small yields,

• The UNDP/WB study indicates that inSouthern Africa the siting cost (includingall 5 levels of investigation) is USD 150-180/borehole. Estimates in otherliterature are considerably higher.

• For the water supply manager the crux iswhether the cost of a geophysical searchcan be justified by an anticipatedincrease in drilling success rates to offsetthe cost of failed boreholes. In each areatime and experience will tell, but this is a"catch-22" situation requiring a decisionto be made before knowing the answer.

• Completed boreholes, sited purely upongeophysical surveys without reference tothe wishes of the community, arefrequently ignored by them.


37

5.9 Drill type - which is best?The answer is that there is no ideal all-purpose rig! The maxim ‘horses for courses’applies to the choice of rig. Therefore, for thesmall yield borehole select the small drill rig.Table 1 summarises several aspects of thedifferent drill types. As noted, this table hasnot been updated and costs are currentlygreater than the table suggests, although therelative costs remain approximately thesame.Several factors are recognised by Talbot,1992, as fundamental to the success of adrilling rig design. These include:• Access to the drilling site and

manoeuvrability over rough terrain -generally smaller rigs are moremanoeuvrable,

• Reliability,• Maintainability - with limited or virtually no

access to a workshop, design must allowmaximum field maintenance,

• Cost effectiveness-’the right drill for thejob’.

5.9.1 Rotary versus percussion?The choice is between differing models ofeach type; but at least there can be noargument about size, for handpump mountedboreholes drilling equipment must be small,mobile and compact.Percussion rigs are simple, rugged (many inAfrica are over 50 years old), easy tomaintain and admirably suited to low costdrilling. Simplicity of design means easyservicing (most have the ubiquitous Listerengine) and relatively short training periodsfor crews because the equipment is sostraightforward to operate. (Neverthelessonly long experience makes a proficientdriller). Recent design advances, in whichUNICEF has played a significant role, havefocused upon size. Compact cable rigs arenow available with specifications that allowdrilling to depths of 90m (150mm diameter)and 55m (400mm diameter). The drill ishighly manoeuvrable, vital in countries withfew roads and possibly a 5-month rainyseason.The Government of Mozambique purchased

10 of these rigs in 1993 (for the price of 2large rotary rigs) and an analysis of their fieldperformance will be found in one of the casestudies from that country. The rigs provedcost effective and reliable, cost/m was 60%less than the normal drilling costs at the time.Drilling covered a wide spectrum of rocktypes, from unconsolidated to hard rock, butdrilling rates were slow.The rotary/pneumatic drill is a speedyalternative in all types of terrain with rates of100m/day not uncommon. In hard, denserock the DTH can achieve a similar figure.Here too, designers and manufacturers haverecognised the need for compact, lesscomplex units and several well knownmanufacturers produce high qualityequipment that is manoeuvrable and mobileand which, while still expensive, costs lessthan the ‘monsters’ of a decade ago.In Africa logistical support is extraordinarilyexpensive, making sophisticated machinesinappropriate. Logistics are crucial with eventhe less sophisticated models tending tohave long down times awaiting spares and/orservicing. The pneumatic rig requires acompressor, useful for development (andpump testing of the hole!) but difficult tomaintain, with high capital costs. Theattendant disadvantages of this type oftechnical complexity warrant seriousconsideration before purchase, although thedays of fleets of large, sophisticated drillingrigs lying idle and broken down over much ofAfrica have largely disappeared.Several African countries, notably the Sudan,Ethiopia, Zambia and Nigeria, have achievedsubstantial reductions in drilling costs withrotary rigs. Appropriately managed to ensuremaximum utilisation, with technicallycompetent and experienced crews and goodlogistics, the unit costs of rotary rigs comparefavourably with percussion rigs. This isespecially so if the operation is commerciallyrun in a competitive environment as inZambia in the past two years (see casehistory, 6.3).At first sight the choice of a drilling rig for anew CWS project manager may appearconfusing, although at least size is no longera variable. If logistical support and technicalcompetence is available there is little doubtthat the small rotary/DTH is the most cost-effective rig. But the simplicity and


38

ruggedness of the cable tool, especially thenewer and more compact models, make itstill the best and most cost-effectivealternative in developing Africa where thereis little logistical support. As has been notedabove, several countries have reduced

drilling costs with the use of hydraulic rotaryand pneumatic rigs, but an objective analysisof the costing reveals that, while relativecosts have fallen, absolute values are stillhigh.

Some of the quoted figures for borehole construction in Africa are reported by Skinner andFranceys (1993):

Nigeria USD 3,700- 28,000Sudan USD 2,800Zimbabwe USD 6,000Angola USD 7,500Senegal USD 18,000Namibia USD 8,250South Africa USD 6,000Togo USD 9,700Zambia USD 2,700Burkina Faso USD 16,150 (including USD 4,400 administration costs!)Mozambique USD 4,000

Unfortunately in most of these examples thecost/m cannot be easily estimated and hencethere is no direct comparison and, further, itis not clear what is included in each costing.Nonetheless these statistics can beconsidered first order approximations andrough comparisons can be made.The Mozambique figure is that given by thegovernment drilling company (GEOMOC),which operates mostly large rotary rigs, andpercussion rigs, as well as privatecontractors, mostly operating large rotaryequipment. The figure does not actuallycorrespond to GEOMOC costing and privateenterprise costing researched by the authorin January 1998. In addition the author foundborehole costs in Zimbabwe (March 1998)unexpectedly low (to be discussed below).Contrast these costs with the recent casestudy in Mozambique, where, utilising anewly purchased fleet of small percussionrigs, a figure of USD 1,330/ borehole or USD37/m is quoted (although this figure does notinclude the cost of 11 unsuccessful holes).The decision as to whether a country shouldstandardise on a particular rig or purchase amix of rigs has obvious long-term

implications, complicated by the multifactorissues involved.Key Points• The choice of drilling rig in the African

setting is crucial in terms of subsequentproject costs.

• There is a wide variety of types andmodels of rigs available - although therecan no longer be any debate as to size -for low capacity boreholes compact rigsare the answer.

• The degree of sophistication is animportant criterion; the choice liesbetween the modern, versatile fastrotary/pneumatic rigs which allow rapiddrilling through the whole spectrum ofrock types, and the simple but slow cabletool machine.

• If logistics are a problem, technicalsophistication has no place in a drillingprogramme.

• A brief analysis of drilling costs revealsthat costs for handpump mountedboreholes are falling in several Africancountries. Mozambique is one suchsuccess story, where the costs of drilling


39

utilising a fleet of small percussion rigs isseen to be lower than most of thosereported from the rest of Africa. InZambia small DTH rigs demonstrated lowcost, rapid and cost effective drillingcapability.

• While the type and size of drillingequipment is a vital factor affecting cost,(apart from the invariable of geology andtopography), the importance of humanresources cannot be overstated. Trainingand experience are prerequisites, alongwith commitment, and, as has beenshown in the Sudan and Mozambiqueamong other countries, the payment ofproduction related bonuses could reapproduction benefits way beyond theircost.

5.10 Data Collection, Record Keepingand the Low Yield Water Source.

It is vital to keep accurate records on everyborehole and well dug to ensure for somedegree of subsequent monitoring. Thedegree to which this should be done, and atwhat stage it ceases to be cost effective, aremoot points. Most Ministries of WaterDevelopment have a section charged withrecording the details of the nation’sgroundwater in order to better understandthe occurrence and disposition of theresource. Data collection from each boreholeand record keeping of selected parametersallows the creation of a database forgroundwater research and study in aparticular region or country. From thetheoretical hydrogeologist’s viewpointexhaustive data collection is obligatory. Thismay explain the routine (but flawed)procedure in Mozambique whereby anextended pump test is done in every lowyield borehole (from which a meaningfulanalysis of aquifer parameters is seldomachieved). There has to be a compromisebetween the extent of data collection andrecord keeping and the time and effortexpended for obtaining such information inlimited depth low yield holes.A comprehensive record of drilling progressand hole details is important. Most countrieshave a protocol in the form of a boreholecompletion record, in which drilling data isrecorded, preferably by the drilling supervisor

or by the drill crew themselves. Details suchas depth at which water is first struck,penetration rate of drilling, depth of borehole,yield at various depths, static water level etc.,etc. are noted. This information wouldnormally be entered into a database and thusbe available for the Ministry, for the major aidagencies and University researchdepartments. Equally important is thecollection by the crew of drilling samplestaken at pre-determined depth increments.As a rule, if the geology is new, sample every1m, if not, every 5m is sufficient. Thedescription of the samples is best done in thefield, if possible by the supervisor/hydrogeologist. A geological depth profile iscrucial to determine if screens are required,as proper placement of the screens requiresanalysis of the rock samples taken duringdrilling. There are also times when it isnecessary to do a simple sieve analysis inthe field to decide whether a gravelpack isneeded. After analysis the samples shouldbe bagged and kept by the GroundwaterSection in the Ministry, where more detaileddescriptions may be done in the future ifrequired.Data collection from low yield boreholes neednot be exhaustive but it should be accurate,thorough and uniform. The same recordsMUST be collected for every hole drilled.There is seldom justification for logging theborehole with sophisticated geophysicalequipment, as the cost does not justify thedata captured from a limited depth borehole. Two parameters should be monitored overtime. Firstly the yield, although strictlyspeaking this does not need monitoring sinceit is being continuously ‘self monitored’ by thesimple act of pumping. A progressivedecrease in yield is soon evident. Thesecond parameter that should be monitoredis water level fluctuation, both seasonal anddrawdown. Both are important, the former forregional groundwater studies, the latter forthe localised setting. For example, if ahandpump stops pumping water and thedrawdown is known, it is simple to diagnosewhether the fault is in the handpump orborehole.Water level measurements are important forseveral reasons. Natural water levelfluctuations are a response to eitherrecharge or evapotranspiration or pumping.


40

Serial measurements over a number of years(statistics of natural events) are critical andcan be obtained by the establishment ofregional monitoring networks. Water levelmeasurements are particularly important inlarge yielding boreholes but are also of valuein low yielding holes. From such data it ispossible to compute approximate figures forwater in storage and aquifer yield, toestablish whether an aquifer is being over-pumped or recharged, etc. In large yieldingaquifers, measurements are taken on aweekly or monthly basis in what are knownas ‘open boreholes’ that are used solely formeasuring purposes.

5.11 Quality versus costs - low yield,hence low cost, is NOT lowquality.

The assumption that low cost equals poorquality tends to colour perceptions withregard to the projected productive life of lowcost boreholes. Low cost is in fact a relativeterm used to compare the cost of boreholesyielding several hundred m3 /hr with thoserequired to produce but a fraction of such ayield (in the order of less than 0.5% of thatfigure). Low cost must not be correlated withlow quality but rather low yield. Low cost inthis text is related to design features and notinferior materials. High quality, long lived butlow cost boreholes are eminently possible.Casing and screens, the major hardwarecomponent of a borehole (which are large

cost elements but which are NOT movingparts), can be made of low cost PVC, asthere is little wear and tear.Correct methodology and procedures willensure the construction of quality low costboreholes. The borehole must be drilledstraight. Screens and gravelpacks, if needed,should be accurately positioned. The apronmust be properly designed and constructedto prevent pollution. ‘Quality’ here is afunction of how carefully and diligently a drillcrew works, which in turn is related to thethoroughness of training and thecommitment and enthusiasm of the crew. Ahigh level of quality can only be maintainedwith an adequate supervision of work andeffective quality control.Despite all that has been said, there will bethose sceptics who will continue with steelcasing, expensive screens, deep holes,extensive pump tests, mandatorygeophysics, gravelpacks in hard rock holes,etc. etc., in the belief that this is at least triedand tested methodology. The shortage ofboth TIME (even The Decade did not catchup with population growth in providing ruralwater supplies) and FUNDS, however,suggests that, at the very least, projectmanagers and decision-makers in watersupply programmes should experiment withsome of the ideas discussed, so that drillingrates may be increased and costs reduced. Atrial sub-programme with close monitoring ofthe medium term (1 - 5 years?) performancecould be considered.


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6 CASE STUDIES FROM AFRICAN COUNTRIES

6.1 Case Studies from Mozambique6.1.1 CASE STUDY 1 –

Government of Mozambique/UNICEFdrilling programmeObjective of programme - To drill low yieldinghandpump mounted boreholes using newsmall percussion rigs.Drill type: 10 small light and manoeuvrablepercussion rigs were selected, the purchasebeing based on 4 factors, i. Suitability and cost effectiveness.

Because the yield sought was only 1-2m3/hr and the depth would thereforebe limited, many borehole designparameters could be relaxed andsmall, simple and relatively low costdrills could be used.

ii. Transport difficulties during theMozambique civil war.

A small rig could easily be packedinto an Antonov cargo aircraft, oftenthe only means of travelling aroundthe country during the war.

iii. Logistics.The decision to select a Lister enginepower plant for the Dando 3000 wasbased on the availability of spares.

iv. Ease of training.The simplicity of the drill allowed forrelatively easy training of newlyrecruited crews who readily acceptedthe concept that only low yieldingboreholes were to be drilled. Older,more experienced crews tended tothink in terms of larger yields.

Results and Analysis:Total number of boreholes drilled(1994-5)

145

Total metres drilled 5,152Average depth in metres 35.5Mean yield in m3/hr 3.7

Drilling rates: Drilling rates in hard rock varied from 1-3m/d, whilerates of 20-30m/d were achieved in fine to mediumsands.

The accompanying map and table (Figure18) reveal that the 10 drills operated in 7provinces over a wide geographicaldistribution, essentially in the unconsolidatedsediments of the coastal belt, extending insome areas as far inland as 150km. In Teteand Manica Province drilling took place inQuaternary alluvial sediments andCretaceous sandstone and conglomerates.

Two major aspects determined drilling rates:a) Geology;90% of all boreholes were drilled in theunconsolidated to semi-consolidatedsediments for which the small percussion drill

is suitable. Nevertheless, several boreholeswere drilled in hard, siliceous sandstone. Thesmall percussion rig can drill in hard rock butprogress is slow, primarily because the smallmast height of 5.2 metres means that jarscannot be used to loosen a stuck drill bit, anot unusual occurrence in jointed fresh rock.Additionally, the lack of a spudding armmakes drilling in hard rock difficult and slow.b) Competent field management;

Only one experienced hydrogeologistsupervised the drilling operation of 10 rigs,(compare this with Lesotho where 1hydrogeologist normally supervises 2 drillsalbeit that they are both rotary drills). To


42

optimise the operation of a drilling fleet is askilful managerial and technical task; leap-froging and operating in ‘packs’ of 3-4 rigsminimises costs and increases drilling rates.

Figure 18. Geographical distribution of boreholesdrilled by the small percussion rigs.

Costs Detailed costs are summarised below:

COSTED ITEMS AMOUNTUSD

Crew (5-6 workers/drill) 100Food for crew 30Fuel, lubricants (rig compressorand vehicle)

85

Drill cable for 15 boreholes 33PVC casing and screens 245Depreciation of rig over 10years

287

Depreciation of compressorover 10 years

100

Depreciation of vehicle, ToyotaLand Cruiser, over 5 years.

154

Depreciation of water tank (10years)

12

Depreciation on centrifugalpump (10 years)

4

Camping equipment (10 years) 10Percentage on administrationand a ‘profit’ for Govt. ofMozambique based on 25% ofthe cost of borehole.

265

TOTAL PER BOREHOLE 1,330

It must be stated that the rigs werepurchased before some of the suggestionsas to borehole construction discussed in thistext were formulated. The rigs were equippedwith small compressors, which meant thatdevelopment pumping was done with air.The PVC screens and casing were importedand drilling cable and bailer valves needed tobe imported more than once during a 2-yearperiod. Costs of drilling cable are based onthe assumption that cable will need to berenewed every 15 boreholes. With greatercrew experience the useful cable lifeincreases to 25 boreholes.Drilling stopped once a yield of 1-3m3/hr wasobtained, and after allowing several metresfor a reserve water column. Pump tests wereshort, 2-4 hours. Development was by over-pumping until the water was clear and an

Competent drill management andsupervision is as critical to success asthe correct choice of drill. Leap-froggingand operating in ‘packs’ of 2-4 rigs willminimize costs and increase drillingrates.


43

artificial gravelpack was installed in eachborehole.The cost per borehole of USD 37/m is basedon 2 boreholes drilled per month to anaverage depth of 35m. This was 30% of theusual drilling costs in Mozambique in 1995. Ifa 50% production bonus were paid to thedrilling crew, a production rate of 4 boreholesa month would be realistic which in turnreduces the cost per borehole by 22%.Moving costs for a small percussion drillwere low, USD 2/km as opposed to the USD11/km charged by the government drillingcompany for a large drill.

The Human AspectIt takes many years of experience to becomea proficient driller and the crews working withthe Dando 3000s were all new to the drill.Despite initial enthusiasm, low pay and lackof incentive bonuses tended to sapcommitment, as shown by an experimentalattempt to increase output by paying aproduction bonus, which resulted in a rise inproductivity of 100%!Because of the high esteem in which drillersare held in most African village communitiesthey should be widely used to train villagersin handpump maintenance, in promoting theVLOM concept and even in health/hygieneeducation. By so doing the drillers couldaugment their salaries (which in any case areunacceptably low) whilst providing valuablebenefits to the communities.

Drilling Success RateOut of 145 holes, 10 were dry and 6 weresaline. The success rate was 89%. The drillswere scattered countrywide and thehydrogeology in many areas was simple.Nonetheless the high success rate iscompelling evidence of what can be achievedby experience and minimal investigationswithout the use of geophysics. Anexperienced hydrogeologist sited 60 of theholes, the rest being sited by medium leveltechnicians with minimal experience.Community siting preferences wereconsidered (where the hydrogeologypermitted) and local knowledge of the areadrawn upon.The mean yield of the boreholes was

3.7m3/hr with a range of 0-25. This is arelatively high yield and, with experience, thedrilling crews will learn to stop drilling earlier,although with an average depth of only 30ma few metres more will make little costdifference.

Conclusions:• Small, simple, relatively low cost,

manoeuvrable percussion rigs provedsuccessful in Mozambique in a variety ofrock types, essentially soft orunconsolidated rock, semi-decomposedand hard,

• Costs were reasonably low, at USD 37/mper borehole, based on drilling 2boreholes/month. This is 10% of theprevailing drilling rate in Africa (figurebased on UNDP-WB Geophysicsdocument) and 35% of prevailing costs inMozambique,

• With a 50% production bonus the crewincreased their production two-fold to anaverage 4 boreholes per month. Thisreduces the cost per borehole by 22%.

• Success was critically dependent oncompetent field management andsupervision,

• Costs can be further reduced and drillingrates increased if the drills work in‘packs’, leap-froging each other and ascrews gain more experience and as moreof the guidelines suggested in this textare adopted by the decision makers inthe country,

• The Government of Mozambique newdrilling tender document revealsenlightened thinking that recognises theneed to drill specifically for low yieldboreholes.


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6.1.2 CASE STUDY 2

State Drilling Company, MozambiqueGEOMOC is the state drilling company inMozambique.A typical costing schedule (1996) is givenbelow:Borehole drilled for handpump supplies inAugust 1996 in Tete Province.

COSTED ITEMS AMOUNTUSD

Drill mobilisation 380Transport and packingequipment

268

Unpacking equipment andpreparing drill site

251

Drilling 24m 15” diameterhole in hard rock

836

Drilling 16m, not so hardrock

512

Drilling 28m very hard rock 1,1006m PVC screen 14024m PVC casing 432Gravelpack (13m) 156Air lift development 280Air lift pump test 10 hours 42330% Regional coefficient 1,433TOTAL 6,221Cost/m 91

Static water level 22mDynamic water level 34m

Observations:• Note depth of borehole (68m) and static

water level. The borehole is too deep.• Dynamic water level was measured with

an airlift pump, the yield of which is notconstant but which is well above 1-2m3/hr. The drawdown of 12m caused byairlift pumping is more than would occurwith a handpump of lower yield.

• The regional coefficient covers

depreciation and administrative costs.• The cost of mobilisation quoted is small.

Private companies charge an initialmobilisation fee of USD 10,000

• Pump test of 10 hours is grosslywasteful, particularly with an inconstantyield, although development is takingplace,

• Note the diameter of 15 inches, which isunnecessarily large.

• The drill was a Schram, DTH.• Geophysical siting is not included.• The community was not involved in

design and siting.The cost/m is average for the country atpresent (excluding the small Dando holes).Commercial drilling costs surprisingly (seenext case study) are only 10-15% lower, withbetter supervision and management beingoffset by very high mobilisation fees. Many ofthe drills have to be brought in from outsidethe country.Geophysics in Mozambique is carried out bythe Water Ministry. They cost USD 250-400/site. This generally will include someelements of level 1 and 2 investigation (asmentioned in the UNDP/World Bank study)and several electrical resistivity soundingsand profiling traverses. Success rates arenot convincingly demonstrated.

6.1.3 CASE STUDY 3

Commercial Drilling in MozambiqueBelow are brief details of the costs ofcontracting a commercial company tomanage a drilling programme:The project was in Sofala Province in 1996and had 2 sub contracts, 1 for theengineering consultants and 1 for the drillingcontractors. It was a large, all encompassingproject. The consultants worked throughout1996 conducting geophysical investigations,inspecting the drilling work, installinghandpumps, supervising training ofcommunity health and hygiene workers andpump maintenance mechanics.A total of 54 holes were drilled by thecommercial drilling company, of which 32


45

were successful (59% success rate). Thecontractor costs averaged USD 5,200 perattempt, or USD 7,926 per successfulborehole. Average depth was 60m at USD87/m. Drill type was a Schram DTH.Geophysical costs are not included.The pump test and development werecombined. A submersible pump was used inwhich the yield of the pump was greater thanthat of the borehole, so for an hour or so theborehole was over-pumped. The pump wasthen stopped and the water level recovered.The sequence was repeated several times,an excellent development procedure.Following development the pump yield wasreduced so that the rate of drawdown couldbe measured over 1 hour. After 1 hour thepump was stopped and water recoveryreadings were taken.Geophysical work was carried out on allboreholes drilled in 13 villages. This includedinvestigations up to level three including 69electrical resistivity depth soundings and 28fixed depth profiles. The total cost for thiswork was USD 23,000. The cost/site wasUSD 500. The success rate was low, (59%)but the area is known to be difficult.Community responsibilities included clearingaccess roads for the drilling rig, forming amaintenance group to receive training inhandpump maintenance and repair andaccepting responsibility for the full cost ofpurchasing spares and hiring a localmechanic to effect repairs. Drilling was carried out in accordance withthe new (1996) Government of Mozambiquetender document. This document specifiesseveral of the ideas discussed in this booklet;namely drilling to continue until a yield of 1-1.5m3/hr is obtained and then an extra 10mbe drilled, PVC screen and casing to beused, only a rudimentary pump test to becarried out, and strict and thoroughsupervision of drilling and sample collectionto take place. ObservationsDespite a new and sensible Governmenttender document, costs were relatively high.Drilling and transportation difficulties, thehigh drill mobilisation costs, the broad rangeof the project, which included long trainingtimes for the community on handpumpmaintenance, all contributed to outlay.

Overall costs, which included training ofhealth education workers, communityhandpump maintenance training, geophysicsetc., brought the cost per borehole to USD10,500.

6.1.4 Lessons Learned from the 3case histories in Mozambique

a) Case history 1 reveals that a fleet ofsmall percussion rigs performedexceptionally well at a cost of 35% ofcurrent drilling rates, although progresswas slow.

b) Case history 2 shows the high costsassociated with the State DrillingCompany, which has large drills andcrews still imbued with the ‘large yieldsyndrome’. Progress rates were littlefaster than using a small percussion fleet.

c) A new government tender document thatspecifies low yield drilling for handpumpmounted boreholes is an enlightenedattempt to reduce drilling costs.

d) Above all, the 3 case histories show that,while an improved mechanical approachto drilling can reduce costs dramatically,the non-technical, human aspect iscrucial if costs are to be lowered.Competent supervision and managementof individual drills as well as the drillingfleet itself together with forward planningof the drilling programme are essential.Training and more training is imperative.

6.2 Case histories from Zimbabwe6.2.1 Manual drilling in ZimbabweOne of the new types of hand drill, which hasperformed successfully in several Africancountries, the Wonder Rig, costing USD 600,was invented and produced in Zimbabwe.Ironically, it has found more favour andsuccess outside Zimbabwe than within. It was first manufactured in Zimbabwe in1982 and the Government, particularly theMinistry of Health, bought several units.Several hundred holes were drilled in theearly eighties in soft, decomposed granitewith exceptionally shallow water levels, idealconditions for the drill. Drilling was usuallystopped 1m after striking water, average


46

depth of boreholes being 10-15 m, themaximum depth being 35 m. The holes were100mm in diameter, 3 m of PVC screen wasinserted and gravel packed. The screens andcasing had bell and socket joints and thehole was mounted with either the Blairhandpump or the Bush pump, both of whichwere developed and manufactured inZimbabwe. Not surprisingly drill penetrationrates were low although at such small depthsthis was of no great consequence. The costof each borehole was USD 150.As noted above, the manual drill techniquebecame popular in Zimbabwe in the earlyeighties but it appears to have beenintroduced to the sector at the wrong time, atime, which saw several years of consecutivedrought. Within a few years many of theshallow hand drilled boreholes had dried-up,and with that, the technique of hand drillingfell from favour. The practice at the time wasto cease drilling 1m after striking water;which proved problematical in Zimbabwewhere seasonal shallow water tablefluctuations can be in the order of severalmetres. Many of the boreholes drilled weretoo shallow to cope with the extendeddrought. Deeper boreholes are lesssusceptible to drought since the deeper thewater table/level the less dramatic theseasonal water level fluctuations.By the mid-eighties hand drilling wasreplaced by the hand dug ‘family well’. Handdug wells by the thousands were constructed(simply and cheaply in the soft over-burdenof the granitic areas on the high plateau ofZimbabwe). The family well was successfulbecause the water level could be ‘chased’down during drought years and the conceptas practised in Zimbabwe is a fascinatingdevelopment deserving of study by sectorpersonnel. In his paper “The change ofattitude of the Government of Zimbabwe tothe ‘family well’” (1990) Morgan illustratesclearly how political will is crucial to success.While the hand drill has had a chequeredhistory in Zimbabwe, in Tanzania and Malawithe low cost and simple, user-friendlytechnology, along with a normal rainfallsequence of years, was a singular success.It behoves the sector to look closely atmanual drilling technologies in suitablesituations i.e., shallow water table areas indecomposed to semi-decomposed rock.

6.2.2 The Government of Zimbabwe-Rural Water Development

a) Drilling operationsThe Government of Zimbabwe (GOZ)operates approximately 100 drills (50-60medium sized air drills and the restpercussion machines). The private drillingsector has about 100 drills, mostlypercussion rigs.Drilling operations are directed specificallyfor handpumps with a cut off yield of only0.7m3/hr. Yet there is an obsession inZimbabwe that government drills should notstop at too shallow a depth - the vulnerabilityto drought and the possible drying-up of theborehole is a source of some frictionbetween the political functionaries and thewater-drilling technologists. The perceptionamongst the water professionals is thatpolitical influence is far too wide-ranging andentrenched and that many boreholes aredrilled deeper than necessary. In a sensethis is understandable in areas that haveexperienced the ‘drought stricken dryborehole’, but slowly a compromise is beingachieved whereby technical conviction canreverse political demands. In the RuralDistrict Councils where previously politicalpower frequently overruled technologicalknow-how, many examples can be foundwhere the static water level is 5-20m yet theborehole was drilled to 80m.

The GOZ specifies 2 borehole designs.• Type A-hard rock formations where the

regolith (upper 3-4 m) is screened off andthe borehole is left open, the norm forhard rock areas (see though the Zambianexperience).

• Type B-soft formations, where casingand screening is used, gravel packing isstandard.

The cost of a GOZ type A borehole is USD3,000-4,000, type B is usually drilled to200mm costs USD 5,000. Steel casing andscreening is preferred to PVC, despite atwofold increase in cost. Steel casing costsUSD 20/m and screening USD 21/m. Toreduce costs drillers make their own screens


from steel casing by flame cutting 2-3mmwide vertical slots. The resulting screens areprimitive, with a low percentage opening (1-2%). In terms of hydraulic design they arefutile. PVC casing and screens manufacturedin Zimbabwe cost USD 7/m and USD 8/mrespectively, a relatively low cost. Theantipathy of the Zimbabwe drilling industry(surprisingly not only Government drillers butalso the private drillers) towards PVC isdifficult to rationalise.

Gcophrearcob)reGmcocohadawreofSeevdainprabgrisgrIt prinon

c) Private sector drilling operations.The private drilling industry in Zimbabwe isvigorous, innovative and successful,illustrating perhaps more clearly thananywhere else in Africa, the benefits ofcompetition.

Typical costing from a private driller in

In Zimbabwe, perhaps more thananywhere else in Africa, the benefits of

a competitive environment are mostclearly illustrated.

The antipathy of the Zimbabwe drillingindustry towards PVC is difficult to

rationalize

47

eophysics is routine, although mostly itmprises only a desk study, some aerialoto interpretation and examination of thecords of previously drilled boreholes in theea, all appropriate and sensible minimalst measures.. Countrywide groundwater data base-cord keeping.OZ has recognised the advantages ofeticulous and rigorous efforts to collect andllate data from all boreholes drilled in theuntry. By law every borehole drilled mustve a borehole completion form in whichta such as location, rock type, depth, yield,

ater first struck, static water level etc. arecorded and the form is sent to the Ministry Water Development, Groundwaterction; giving the government a record ofery borehole drilled in the country. Theta from the completion form is transferred

to the standard groundwater data baseogramme providing invaluable informationout the occurrence and disposition ofoundwater in all areas of Zimbabwe. This a powerful tool for planning futureoundwater development in specific areas.also plays an important role in the ever-esent ‘battle’ in Zimbabwe between politicalfluences and technological wisdom based rigorous long-term data.

Zimbabwe is as follows (March 1998):

Drilling (0-100m) USD 13/mCasing, steel USD 20/mScreen (steel with flame slots) USD 24/mMobilisation USD 60Pump test (cable tool) USD 65

Thus, for a 50m hole, in hard rock (open holewith overburden casing) the cost isapproximately USD 800-900. The currentpractice, as with Government drills, is that allholes are now commenced at 200mmthrough the regolith reducing to 150mm aftera few metres.Geophysics is not routine, the ‘experiencedeye’ often does the job, although in areaswhere the rainfall is less than 600mm/annumsome drilling contractors consider scientificsiting essential. They use electrical-electromagnetic- geomagnetic-techniques.The siting is not systematic; readings aretaken on sites that ‘look promising’ for thecontractor. Such soundings are looked uponas ‘essentially confirmatory in nature’ - aneminently debatable point!During drought years in Zimbabwe, thecompetition becomes even more acute withan influx of South African drilling teams - aninflux understandably resented by the localindustry.The private drilling companies the authorinterviewed confirmed the strong politicalinvolvement in technical aspects of drilling forwater. More experience with optimal depth of

The groundwater data base built up overtwo decades in Zimbabwe is crucial to abetter understanding of the occurrenceand disposition of underground water in

all areas of Zimbabwe.


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drilling in drought prone areas and carefulmeasurements of regional water levels will,hopefully in the not too distant future,weaken the hold of the political catchphrase -’drill as deep as possible...’!In post independence Zimbabwe there isconsiderable sophistication, knowledge andmuch data available to the drilling industry;good use has been made of the availableresources thus far - but there is still much tolearn. Borehole prices are relatively low, butoptimal drilling depths, diameters, design,failure rates, optimal rigs, etc., require furtherstudy and experimentation.

6.3 Case histories from ZambiaThe Zambia case history can be divided intothree elements, before 1992, the droughtyears of 1992-5 and post 1995. Of the24,020 water points in the rural areas only3,174 (data as at April 1998) are machine-drilled, 320 are jetted wells, 169 handaugured tube wells and the rest are dugwells.

6.3.1 Machine drilled holes before1992 and 1992 to 95

Before 1992, drilling was mostly done by theMinistry of Water and Energy, through theirDepartment of Water Affairs (DWA) in 8provinces using a range of drilling rigs,mostly down the hole combination rigs and afew percussion rigs. The weak private sectorwas primarily engaged in drilling forcommercial farmers.The cost per borehole was in the order ofUSD 5-6,000. The annual rate of drilling was200-300 holes with an average of around 10per district. The drilling depth was frequentlya standard depth; 60m regardless of waterlevel or yield (see figure 19 that showsborehole depths and casing/screens depths).Also, as figure 19 reveals, the lengths ofscreens were extraordinarily large.The casing was steel 150mm as was thescreen, which was cut with large flame slotsor hacksaw. The cost of casing was USD40/m and the screen USD 50 /m. Boreholediameter was 175 mm but 228 mm was alsodrilled. A gravelpack was used at times but,clearly, with 150mm casing in 175 mmdiameter hole its efficacy was minimal.

Geophysics carried out on an ad-hoc basis,principally electrical resistivity, cost USD300/site. DWA staff was mostly responsiblefor surveying. In hard rock areas the policywas to leave the hole uncased except for theupper few metres.

Figure 19. Borehole depths and casing/screensused.

In summary therefore drilling in Zambia wasexpensive prior to 1992. There was nostandard design, the drilling fleet was costlyto operate and many rigs were often notoperational. Waiting for spare parts andrepairs were the norm (an average of 15-20borehole/year with the large drills wasnormal, with weak monitoring andsupervision). There was no boreholeinventory and thus no groundwater databank, no guidelines, no central policy, norbasic sector principles. The ‘standard’ depthof drilling was 60m irrespective of water first


49

struck and the yield.This situation was compounded by thedrought of 1992-1995 when an expandeddrilling programme was initiated with minimalguidelines and the same generalisedspecifications as described above. Boreholestatistics during the emergency droughtperiod were poorly recorded. During thedrought period the limited Governmentdrilling capacity was recognised and largedrilling contracts were awarded to the privatedrilling industry. Many of these private drillingcompanies were South African, operatingwith local partners. During the 3 years ofdrought, the target was 2,000 boreholes. TheDWA lacked the capacity to manage thisaccelerated borehole drilling programme.Again, supervision was weak and with someof the work reported complete had in fact notbeen done.In 1995 a systematic and rational low costdrilling approach in which UNICEF played animportant role was introduced. The crucialimportance of a rigorous borehole inventorythroughout the country was early recognisedand there is now (April 1998) a completedata bank of all water points andconsiderable knowledge of the occurrenceand disposition of groundwater in Zambiahas been accumulated.

6.3.2 The UNICEF Water andSanitation and Health Education(WASHE) programme

Using available countrywide data and thelessons from the past, appropriatetechnology was promoted. With well diggingremaining by far the major rural water supplysource over much of Zambia.The drilling programme incorporates thefollowing guidelines:• Drilling to halt when a yield of only

0.7m3/hr is reached, a further 5 m thenbeing drilled to allow for water levelfluctuations,

• Casing and screens to be PVC class 10,with 110mm nominal diameter,

• Screen slot sizes of 0.5 mm and screenlengths installed to be left to thediscretion of the drillers.

• All boreholes drilled in hard rock to bescreened and cased,

• All drilling for handpumps to be carriedout by commercial drillers operating thenew small and manoeuvrable DTH rigs.Government drills are being phased outto form private semi-autonomous bodies.

• Each drill to have a compressor forefficient development, by airlift pumpingfor three hours.

• No formal pump test.Siting the borehole involves close co-operation between the village and the drillingcontractor. The village designates 3 sitesbased on social factors, which are thenassessed for suitability by the drillingcontractor. Should he reject all 3 on technicalgrounds he has then to select an alternativesite as close as possible to the village usingeither geophysics or the ‘experienced eye’,the choice is left to him. Electrical resistivity soundings are used inmost cases. In Southern Province the failurerate is very high, especially in 2 districtswhere the failure rate is in excess of 50%. In1997, assisted by UNICEF, 330 boreholeswere drilled country wide, of which 70% weresited using electrical resistivity soundings.Some interesting data is available on thefrequency of the use of geophysics anddivining shown in the table below.Regrettably the relative success of eachtechnique is not available. Geophysicsmeans in most cases several ad hocelectrical resistivity depth soundings at a‘likely’ location, which this author interpretsas: the prime location is sited by ‘theexperienced eye’ and ‘confirmed’ bygeophysics!


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Table 6.Relative use of geophysics and water divining for site location.

Driller Water points Number of sites selected using:Nos. Geophysics Divining

Coratom 80 0 80Foradex 20 0 20Zarus 70 70 0Aquanova 145 145 0Desons 15 15 0Total 330 230 100

(70%) (30%) (Data: From UNICEF assisted programme in 10 districts in Southern and Eastern Provinces).

It is interesting to note that 30% of all thesites were divined by traditional methods,now commonly used by drillers in Zambia.The success rate for either technique is notknown. Although, in hard rock areas wherethe decomposed mantle is thin, geophysicsis generally considered important.Drilling quality is internally controlled byinteraction between the client (e.g. aidagency), the community and the contractor.Frequent meetings are necessary and theimportance of careful and thorough work isstressed. The community, too, has a‘supervisory’ role, whereby they keep an eyeon depth of drilling, type of casing insertedand so on in a long-term participatoryprocess that they themselves evaluate.The Results: The results of the low costdrilling endeavour appear promising; the datafrom the recently drilled 330 boreholesindicate:a) Average depth of drilling has

decreased from 60m to 44 m, andaverage casing used is 33 m and 25 mof screen.

b) Mean yield is 1m3/hr,c) the number of boreholes now being

drilled has increased dramatically to400/year, 330 in 1997 by UNICEFalone.

d) The drilling tender document whichevolved as a result of the UNICEFWASHE program is now the standarddocument for drilling handpump

mounted boreholes.e) the philosophy of drilling specifically for

low yielding boreholes rather than apotential future upgraded level ofservice is accepted in Zambia. The factthat, globally, only about 0.1% ofhandpump mounted boreholes areeventually converted to motorisedhigher yield pumping holes underlinesthe appropriateness of this precept.

f) Geophysics success rates are poor.Traditional divining (which probably hasa high component of the ‘experiencedeye and throw the hat’ has provedsuccessful.

g) Most important of all; the cost perborehole has decreased by almost afactor 2, from USD 5,000 in 1994 toUSD 2,800 in December 1997. (Seefigure 20). These figures apply to theGOZ/UNICEF assisted programme.

Figure 20. Cost reduction of borehole drilling in


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Zambia.

6.4 Lesotho Case HistoryLesotho case history-a dramatic ‘turn-about’strategyLesotho holds a special place in the annalsof rural water supply and sanitation. It wasthere that the first interdisciplinary teamapproach to rural water supply wasundertaken with the evaluation ‘Water,Health and Development’ published byFeacham et al (1978). Considerable changeshave taken place and lessons clearly learnedsince the pioneering work of the Feachemteam in 1978.In April 1998 the author found a distinct butunderstandable antipathy towardshandpumps by the Government of Lesotho(GOL). An analysis of a 1996 HandpumpTrial Project revealed: at any one time 60 -70% of the handpumps in Lesotho were notworking. The capital costs of the (Mono)handpumps were considerable and theirrepair costs were very high. Current thinkingof the Department of Rural Water Supplyleans towards submersible and dieselpumps, both incompatible with VLOMphilosophy. The reason for such highhandpump failure rates, according to GOL, isthat general water levels are too deep inLesotho for present handpump technology.Figure 21 reveals that 70% of all boreholeshad water levels of 60-70 metres; thegreatest number of repairs occur at that orgreater depth.

Figure 21. Depth of borehole versus number ofrepairs in Lesotho.

The effect on borehole drilling routines of amove towards ‘high yield’ pumping systemsis that yields now need to be in the region of4-5m3/hr, rather than 1m3/hr. Clearlytherefore, drilling depths must generally begreater in order to locate the higher yieldsrequired for motorised pumping. Sensibly,GOL has built into the pumping schemecosts a drilling success rate of only 40%.

Current (1998) costs of drilling a typicalborehole for handpump supplies (1m3/hr) arecontrasted with the cost of a ‘high capacity’borehole drilled to produce a minimum of3m3/h, considered the lower limit for amotorised pump. These costs are shown inthe table below.

Lesotho has turned its back on thehandpump and the VLOM approach-

higher yield boreholes and hence higherservice level technology is the new

strategy.


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Table 7.APPROXIMATE COST ESTIMATES FOR VARIOUS PUMPING SYSTEMS

Handpump Quantity Unit Unit Price USD Amount USDDrilling (average depth 60m) 60 metres 23.00 1,380.00Additional cost of failure (success rate60%)

552.00

Casing 150mm ID/SABS, supplied &installed

20 metres 23.00 460.00

Cleaning, development 1 per BH 580.00 580.00Base plates and cover plates 1 each 114.00 114.00Pump testing (6 hours) 6 Hours 27.00 162.00contingencies @ 15% 425.50Total for Drilling only 3,260.00Handpump (average cost)Head 1 each 250.00 250.00Cylinder 1 each 360.00 360.00Connecting rods including sockets,stabilisers, bobbin rubbers, couplingetc

15 each 33.00 495.00

Installation costs 1 each 150.00 150.00Contingencies @ 10% 125.00Total for handpump only 1,380.00TOTAL FOR DRILLING AND INSTALLATION OF HANDPUMP 4,640.00

Table 8:

High Capacity Borehole (<3m3/hr) Quantity Unit Unit Price USD Amount USDDrilling (average depth 70m) 70 metres 23.00 1,610.00Additional cost of failure (success rate40%)

966.00

Casing 150mm ID/SABS 62, suppliedinstalled

70 metres 23.00 1,610.00

Cleaning & development 1 per BH 580.00 580.00Base plates and cover plates 1 each 114.00 114.00Pump testing (48 hours) 48 Hours 33.00 1,584.00contingencies @ 15% 1,020.00TOTAL COST FOR DRILLING ACTIVITIES 7,484.00


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The geology of Lesotho is essentially hardrock and therefore the cost per borehole isnot unreasonable in the context of Africa (forthe handpump borehole approx. USD 3,000,April 1998). The most significant saving to besought is in lowering the failure rate ofdrilling. But significant savings could beconsidered for the 1m3/hr borehole - if hardrock, reduce diameter; the pump test of 6hours is too long, and development andcleaning costs appear very high. A possiblecost reduction of 50% is not unreasonable.For the high capacity holes the extensivepump test and development costs arejustified.The statistical data on borehole successrates was essentially anecdotal and theauthor saw no actual data during his visit.The main question is to reduce the drillingfailure rate. Thus far it has not been possibleto demonstrate in Lesotho the superiority ofany one of the location techniques(geophysics, traditional divining or ‘the

experienced eye’) over another. Methodicaldata collection of success related to locationtechnique over a period of years couldprovide a comparison.

The dramatic new approach taken by theGovernment of Lesotho in the rural watersector will provide an important observationopportunity for the sector in other countries.Rigorous records should be kept of costs inall aspects of the programme, rates ofprogress, consistency and reliability of watersupply etc. If there are lessons to be learnedfrom the non-handpump, high yield approachthe sector will have ample data that can beused in other areas where water levels aretoo deep for today’s handpumps.

Relatively deep water levels andhandpump unreliability at such depths

are the factors behind the LesothoGovernment’s change of strategy.


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7 DRILLING FOR RURAL WATER SUPPLIES IN INDIAAre there lessons for Africa in the Indian experience?

Drilling costs in India are much lower than inAfrica. In this text the UNDP/ World Bankstudy is taken as the definitive costing forAfrican boreholes. The large regionaldifferences in costs are averaged out and anapproximate figure for drilling in Africa isaccepted as USD 100/m. An approximatefigure for India ranges between USD 4-6/m(although according to UNICEF there areexamples in India where drillers are drillingfor USD 3/m). These figures apply to hardrock holes, which are left open (no casing orscreens except a few metres of casingholding the overburden). So, using thefigures above we have a factor 20 differentialin costs. There are, however, pitfalls inapproximating drilling costs and makingcomparisons based on such figures. Clearlysuch an attempt cannot be more than arough comparison given the differences ingeology and hence rock hardness, depth,diameter, use of casing, etc., butnevertheless the significant cost differentialbetween holes drilled in Africa and those inIndia requires analysis and discussion.Some of the factors that help to explain thedrilling cost differential are as follows:1. India has a well established,

competitiveness private drilling industryand most importantly, economies ofscale. There are several millionboreholes in India and such largenumbers foster lower costs. Productivityis high, for example, a drill rig with anoutput of 150 boreholes of 60m meanborehole depth per annum drilled over aperiod of 10 years (many of the rigs inIndia are still drilling efficiently after 15years) 90,000 metres. The amortisedcapital investment costs are very low permetre.To further emphasise the competitivenature of drilling in India; in the summer itis not unusual for drilling to take placeovernight so that in a 24 hour period 2-3boreholes can be drilled with a DTH rig.In addition, a rather surprising aspect ofthe low drilling costs in India is that, in

general terms, the rocks in India, mostlybasalt, are harder than those in Africa,which are mostly granite/gneiss.

2. Drilling contractors in a sovereign regionas large as India are not constrained byborders and customs regulations. Toillustrate the difficulties involved withcross border and customs regulationsconsider here the attempt byMozambique (1994) to establish anexperimental regional co-operationstructure in order to reduce handpumpmanufacturing costs. Focusing on thestrengths of each country (a steel factoryin Mozambique, rubber in Malawi, PVC inZimbabwe) to the mutual advantage ofthe countries involved should have beeneconomically advantageous for regionalhandpump manufacturing. Unfortunatelysuch was not the case. Politicaljealousies and customs bureaucracytorpedoed the attempt and handpumpcosts continue to be relatively high. Thissame lack of mutual co-operation affectsdrilling costs in Africa. In India drillers cantraverse the length and breadth of thecountry ‘without let or hindrance’.Conversely, in Africa the large number ofborders within the continent means thatcommercial drillers willing to drill in otherAfrican countries have to pay large sumsin taxes and customs guarantees, thuslimiting competition.

3. The long established road and railinfrastructure in heavily populated India issuperior to that in Africa. Where still largeareas are sparsely populated.

4. The industrial infrastructure in India isMUCH larger and better developed thanthat in Africa. India has the capacity tomanufacture drilling rigs and thiscapability has allowed the Government,working together with UNICEF, to evolveover the past several decades the ‘ideal’drill design. Because large numbers areproduced costs are relatively low. InAfrica all drills are imported withconcomitant high capital costs, with theexception of South Africa where a


55

fledging drill manufacturing industry doesexist.The immense scale of the rural watersupply programme in India has forged aclose relationship between the Indiangovernment and UNICEF during the past3 decades. They were jointly responsiblefor the considerable experimentation andinnovation with types and sizes of drillingrigs, which has led to the development ofthe near ideal rig for India. This evolutionof the ‘ideal’ drill in India means thatsince the mid-eighties there has been abalance reached between drill capital andrunning cost and performance; the drillrigs are neither too fragile nor ofexcessively large capacity.The impact on costs of the importantaspect of drill reliability deservesdiscussion. Because, in general, the drillrigs in India have now the idealspecifications, new rigs enjoy highreliability. But even with very old and lessreliable drill rigs, low cost drilling in Indiais still possible. A contractor in Karnatakais presently drilling with old equipment forUSD 3/metre. Whilst reliability is low,such is the infrastructure in India that thecontractor can get the required spares inthe local market and with frequent rapidrepairs can still make a profit, albeit aslim one!

5. Paragraphs 3 and 4 indicate thatlogistical support in India is much furtheradvanced than in Africa.

6. As a result, sophisticated rigs(rotary/DHT) can operate cost effectivelyand are routinely used, resulting in rapiddrilling rates (especially in hard rock),which in turn translate into lower drillingcosts.

7. Casing and screens are imported inAfrica (often from Europe) and aretherefore expensive. Local manufacturein India plus large volume localproduction of casing and screens (eventhough most boreholes are only minimally

lined) enables dramatic cost reductions tobe made. Although some countries inAfrica have local manufacturing capacity(viz. South Africa and Zimbabwe), evenso prices are higher than in India. Infuture, however, the relatively largeindustrial and manufacturing capacity ofSouth Africa, if utilised by other Africancountries, may lower prices.

8. Unlike Africa, India has numerouspractical, hands on, training institutions -an invaluable asset.

So, what are the lessons for Africa from thebrief Africa/India comparison above? Clearlythe economy of scale factor in India isunlikely to be duplicated in Africa. The issueof competition is, however, somethingalready being swiftly assimilated in Africa.Additionally in Africa there is a general moveto scale down the size of drilling rigs and, inthe case of South Africa, there is even anattempt to manufacture drills in-country.Customs and cross-border bureaucracy willhopefully improve in an era of greaterregional co-operation. Better transportinfrastructure is not only dependent upon agreater allocation of resources but also onco-operation between countries.Standardisation of rail gauges would facilitatetransport from country to country and takepressure off roads, but peace and stability inthe region are paramount if theseimprovements are to take place. Training isan area where Africa can learn a lot fromIndia and more hands-on training facilities fordrillers are an urgent requirement. It iscritical, too, that such institutions fullyrecognise the importance of cost reductionand increased drilling rates and that some ofthe other elements discussed in this textform part of the training courses. The formaldrilling curricula seen by the author in anAustralian drilling school focus on large yieldholes only and are patently unsuitable for theubiquitous low yield handpump mountedborehole found in Africa.


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Appendix 1 Glossary/terminology

Terminology is not standardised globally, and some confusion exists as a result of differingnomenclature in British and American texts.

The terminology used in this text is defined below:Borehole - small diameter hole (usually 150mm but can be up to 1.2 metre) machine drilled(machine can be motorised or operated manually) drilled for the principal purpose of obtaining awater supply. Synonyms are, tubewell (US terminology), water well, production well or even justwell.Hand-dug well - A large diameter (usually 1m but there are examples of 6m), shallow water table,well constructed by digging manually. Synonyms are: open well, dug well, shallow well.An aquifer is a water-bearing geological formation capable of yielding groundwater in significantamounts.Alluvium - Sediments deposited by flowing rivers.Gravel packing - placing graded gravel on outside of borehole screen to allow water to enter andprevent ‘fines’ from entering the borehole.Permeability - the capacity of a porous medium to transmit water.Geophysics - the location of underground water by the use of indirect surface electrical andseismic techniques and the measurement of magnetic variation over the surface.Static water level - is the level at which water stands in a borehole or unconfined aquifer when nowater is being pumped.Dynamic water level - is the level at which water stands in a borehole when pumping is inprogress.Hydrogeology - the study of the interrelationship of geologic materials and processes with water,especially groundwater.Porosity, primary - the porosity that represents the original pore openings when the rock orsediment formed.Porosity, secondary - the porosity that has been caused by fractures or weathering in a rock orsediment after it has been formed.Well development - the process whereby a well is pumped or surged to remove any fine materialthat may be blocking the well screen or the aquifer outside the well screen.


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REFERENCES

Arlosoroff S., Tschannerl G., Grey D., Journey W., Karp A., Langenegger O., and Roche R.,(1987), Community Water Supply - The Handpump Option, The World Bank, Washington, D.C.,USAConsidered the ‘bible’ of the sector, bristles with original ideas, well illustrated and succinctlywritten.

Beale, G., Water Management Consultants (1990), Development of the Drilling Industry in Nigeria- An Overview, (unpublished), quoted by de Rooy (1992)Blankwaardt, Bob (1984), Hand Drilled Wells - A Manual on Siting, Design, Construction andMaintenance, Rwegarulila Water Resources Institute, Dar es Salaam, Tanzania (contact TOOLFoundation, Amsterdam)A detailed hands-on text on this topic, full of outstanding diagrams and photographs.Chauvin J., Plopper S. and Malina A., (1992), Final Evaluation of the Benin Rural Water Supplyand Sanitation Project, WASH Field Report No. 349, Water and Sanitation for Health Project(WASH), USAID, Washington, D.C., USA.Chilton P.J. and Smith-Carrington A.K. (1984) Characteristics of the Weathered Basement Aquiferin Malawi in Relation to Rural Water Supply. In Challenges in African Hydrology and WaterResources, Ed. Walling D.E et al. IAHS Publ. 144. U.K. An admirable discussion on low costboreholes in Malawi.Clark L. (1988) The Field Guide to Water Wells and Boreholes. Open University Press. UK. Aconcise, excellent text, some technical knowledge assumed.DHV (1985), Low Cost Water Supply - For Human consumption, cattle watering, mall scaleirrigation, Part 1: Survey and Construction of Wells, DHV Consulting Engineers, Amersfoort, TheNetherlands.Feachem, Richard, et al. (1978). Water, Health and Development. Tri-Med Books Ltd. London.The first interdisciplinary evaluation in the sector; historically important.Foster S.S.D (1984). African Groundwater Development-The Challenges for HydrogeologicalScience. In Challenges in African Hydrology and Water Resources, Ed. Walling D.E et al. IAHSPubl. 144. U.K.Franceys R.W.A. (1987), Handpumps - Technical brief No. 13, Waterlines, Vol. 6, No. 1Intermediate Technology Publications, London, UK., pages 15 - 18, (also in ITP (1991).Lefort L, and Marchal J (?), Les Forages a Faibles Couts.- Research Technology Group, Paris.The non-French speaker will not be disadvantaged because the text is in French because thediagrams are so outstanding, numerous and easily understood that the text is of secondary import.Laver, Sue, (1987), Well Sinking - a step by step guide to the construction of wells using theblasting method, UNICEF, Harare, Zimbabwe. The illustrations are remarkably easy to understand.Lewis, Clark, (1988), The Field Guide to Water Wells and Boreholes. Open University Press, UK.A comprehensive but succinct text addressed to practicing geologists and engineers responsiblefor designing and implementing drilling projects.Meinzer, Oscar, (1946) Hydrology. U.S. Geological Survey, USA.An early classic-good on the history of hydrology and water suplies.Morgan, Peter, (1989), Upgraded Well Manual for Field Workers, Blair Research Laboratory andMinistry of Health, Zimbabwe.Morgan, Peter, (1990), Rural Water Supplies and Sanitation, Macmillan, London, UK. A classic, byone of the pre-eminent workers in the sector.


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Rowles, Raymond (1990), Drilling for Water. Cranfield Press. U.K.A well illustrated and clearly written practical driling manual.Skinner, Brian and Franceys, Richard. (second draft 1993). Cost Effective Technologies for WaterSupply in Guinea Worm Endemic Areas. Loughborough University of Technology. A Report forUNICEF New York.An interesting, well written and illustrated text covering the whole gamut of water supplytechnologies.Todd, David, (1989), Groundwater Hydrology. John Wiley and Sons. NY.Probably the best short text on the topic for the qualified engineer/geologist.Valentine, H.R. (1967), Water in the Service of Man. Penguin Books, London.Whilst the section on underground water is brief this delightful , illuminating and thoughtful bookdeserves to be read by all in the Sector.van Dongen P. and Woodhouse M. (1994) Finding Groundwater A project Manager’s Guide toTechniques and How to Use Them. (1994) UNDP-World Bank Water and Sanitation Program.Washington D.C. Recommended reading for project supervisors and the non-technical layman.Best brief discussion of methodology this author has seen. Chapter on results disappointing; tablesand graphs difficult to understand.Watt, S.B. and Wood, W.E. (1976), Hand Dug Wells and their Construction, IntermediateTechnology Publications, London, U.K. One of the definitive texts on the topic.Wright E.P. and Burgess W.G (1992), The Hydrogelogy of Crystalline Basement Aquifers in Africa.The Geological Society, London. The most up to date research on the topic-more for theprofessional geologist/geophysisct.Wright E.P. and Herbert R., (1985), Collector Wells in Basement Aquifers, Waterlines, Vol. 4, No.2, Intermediate Technology Publications, London, U.K., pages 8 - 11. Interesting research andpractical methodology on augmenting the yield of dug wells.Wurzel P. and de Rooy C., (1994), The Handpump versus Borehole, Addressing a Mismatch.Waterfront Issue 4, UNICEF, New York.Wurzel P. (1994), Water Level Measurements in Boreholes-a Gap in Our Knowledge. WaterfrontIssue 5, UNICEF New York.

WURZEL 2001 Drilling Boreholes for Handpumps

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