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4. Understanding Groundwater & Wells in Manual Drilling

1. y PRACTICA Foundation Manual drilling series Understanding Groundwater amp Wells in manual drilling Figure 2 permeability 66666 66666 sand and gravel clay and loam mixed soil very permeable impermeable semi permeable Mixed formations In most cases the formation consists of a mixture of clay silt and sand or gravel particles For example clay and sand sandy clay can exist as a homogeneous layer clay and sand are mixed or in alternating thin layers layered small sand and clay layers on top of each other When those soils are put in a bucket and a cup of water is added the water slowly flows through the soil fig 1 Conclusion Water flows slowly through mixed soils and they are therefore described as semi permeable When a well screen is placed in a mixed or layered layer the discharge of the well will be low fig 2 Field tricks Sometimes it might be difficult to determine the difference between permeable or impermeable layers This is a small trick to help you Take a representative sample of the soil paragraph 4 2 and squeeze it into a ball between your hands Then drop the ball from a height of one meter above ground level The ball falls down on the ground 1 If the ball consists of non cohesive non sticky particles the ball totally falls apart In this case the material is permeable The particles of sand or gravel will be easily visible 2 lf the ball falls apart only partially t
2. SSSSSSSSSSSSSSSSSSS Technical training handbooks on affordable manual well drilling These practical handbooks create awareness of manual drilling for affordable water supply anda roadmap for implementation of manual drilling programs The manuals provide an extensive and detailed guide for trainers and drilling teams in the use of various drilling techniques for making affordable boreholes The techniques are explained in simple and understandable language using clear illustrations and drawings UNDERSTANDING 5 GROUNDWATER amp WELLS in manual drilling Manual drilling series J ETTING This handbook describes in detail the various jetting techniques that can be used to drill wells in loose and soft soil formations With this technique wells are drilled in a number of hours rather than days Manual drilling series PERCUSSION This handbook describes in detail the percussion technique Although the technique is slower than other drilling techniques it is the only manual drilling technique that is able to drill through consolidated rock layers Manual drilling series HAND AUGER This handbook describes the hand auger technique This cheap and effective technique is very suitable for sinking shallow wells in soft soils and is excellent for soil surveys Many drilling teams have this technique in their toolkit to complement other drilling techniques Manual drilling series SLUDG ING This handbook describes the sludging techni
3. manual including the illustrations and technical drawings may be copied to meet local needs without permission from the author or publisher provided the parts are distributed free not for proft and reference to the source is made The author would appreciate receiving notice and a copy of any materials in which original text or pictures have been used For any reproduction with commercial ends written permission must be obtained in advance from the PRACTICA Foundation This instruction manual is available in English and in French and Swahili and has been developed for use in technical training courses organised for the intended users In case you want to organize such training you may contact the PRACTICA Foundation for further information and support The first edition of this publication was made possible by a financial contribution from the Technical Training Programme of the ETC Foundation in the Netherlands and the United Nations Children s Fund UNICEF office in Chad An updated version of this publication the second edition was made possible by a financial contribution from the United States Agency for International Development USAID as part of the West Africa Water Initiative WAWI The United Nations International Children s Fund UNICEF PRACTICA Foundation and Enterprise Works Vita have developed a toolkit for African countries wishing to embark on the professionalization of manual drilling This toolkit includ
4. Infectious agent that can cause disease bacteria viruses parasites A measure of the ability of a material to transmit water through it Material that easily allows water to flow through its pores PRACTICA Foundation Manual drilling series Rest water level Sand Sanitary seal Screen Sedimentary layers Silt Sump Unconsolidated layer Viscosity Water Quality Water table Weathering Well Well casing Well construction Well development Well screen Well yield Working water Understanding Groundwater amp Wells in manual drilling Groundwater level measured in the well before pumping starts Particles in a diameter between 0 063 mm and 2 mm Very coarse sand 2 mm Coarse sand 0 5 1 mm Medium sand 0 25 0 5 mm Fine sand 0 125 0 25 mm Very f ne sand 0 063 0 125 mm Seal made of bentonite or cement which is placed in the annular space between the casing and the formation borehole wall to stop poor quality water from contaminating the well See gt Well screen Layers formed by the weathering transport by wind or rivers and deposition sediment of particles Fine particles with a size between 0 004 mm and 0 063 mm Silt is larger than clay and smaller than sand 1 2 meter of plain casing pipe closed at the bottom end attached to the bottom end of the well screen Layer consisting of loose particles such as clay silt sand and gravel Measure of the thi
5. Sand coarse yellow Sand coarse yellow Sand coarse yellow Sand coarse yellow Sand coarse yellow Sandy Clay grey brown Sandy Clay grey brown Sandy Clay grey brown Sandy Clay grey brown Sand i yellow brown Sand i yellow brown Sand i yellow brown Sand i yellow brown Sand i groundwater Sand i yellow brown Sandy Clay brown Sandy Clay brown x Oo00 loOo00 AOUN ge pig a e a I CH O OD ar Oe CY RO Ou FAS DIC LO CD COR OR es TC yn ye g r I au cau afl y y Cly Ol gun OOo lt Ooc0oc0o wo0o AWN TUTOO Sr ae ee UN UJ ee LL LI ymau gi gos a yu Sal TD cA cu cy a ga CUO Cie Che ie tel o ee OQQA SECC SS Ne eRe aa Moooooooooooo DODODOOODODODDDDDDDODDODODOD neu ON O O O O O i O O CC Cr TG OG OT Gt Cy E O CYH CY O oooooooo o oo oo doo ooco Moi o o OcoDOsDOODSDODDDODDDDODDOD DD In this example a 6 meter well screen was installed between 15 and 21 meter below ground level And a 1 5 meter sump Cuttings was attached to the bottom end of the well screen Sanitary seal B Blind PVC casing pipe and sump Well screen tS Note This drilling log is designed to be filled in by both people who can wrife and who cannot write The drawings Gravel pack are intended to assist in visualizing the geological layers and well completion details PRACTICA Foundation Manual drilling series Understanding Groundwater amp Wells in manual drilling I Using the drilling log and drawing the soil ty
6. Step 3 Then quickly remove the pump and monitor the rise of the ground water level by measuring the water level every frequently The shorter time it takes to return to the rest level the better the aquifer During the test write down as much information as possible water level at start and end time and discharge monitored from time to time A basic form for a simple yield test is attached in appendix D Final step Conclusion If the pump didn t run dry during pumping and the water level returns to its rest level measured before the test within 6 12 hours then the flow rate will be sufficient for the installation of a hand pump PRACTICA Foundation Manual drilling series Understanding Groundwater amp Wells in manual drilling 7 3 WATER QUALITY TESTING Good quality potable drinking water is free from pathogens disease causing bacteria etc and excessive above the standard amounts of harmful chemicals The taste and smell should be good and the water should be clear and free of color To ensure the water quality of the well is suitable for drinking water the water should be tested Drinking water should be tested on a large number of parameters To give you a broad idea just a few examples of parameters 1 Chemical parameters Hardness calcium magnesium pH acidity electrical conductivity to indicate the total salt content iron heavy metals cadmium lead etc nutrients nitrogen phosphorus artificial threats p
7. and annular backfill The drilling log shown above is used in the explanation below Well screen position and length The well screen usually does not exceed a length of 6 meter for manually drilled boreholes Fine materials are often present in the extreme upper and lower parts of an aquifer Also thin clay layers might exist in the aquifer To prevent the fines which may cause turbidity and pump damage from entering the well screen it is important NOT to install the well screen at the same level as these fines in the aquifer In other words be sure that the whole screen length is installed in a permeable layer consisting of sand or gravel To achieve this in some cases the screen length might be less than 6 meters but should generally never be less than 3 meter see par 6 2 I Although carefully taken the exact depth of origin of the soil samples might not always be accurate To avoid fines from entering it is wise to install the well screen and backfill with a safety margin of at least 1 meter In the drilling log above the well screen was placed in the middle of the aquifer leaving a 1 meter margin of sand at each end Sump After the installation and during the use of a well some soil particles may still enter the well screen The bigger particles which can cause damage to the pump settle down to the bottom of the well by gravity To prevent loss of well screen surface area a sump of 1 2 meter in length with a closed bottom end is
8. at an example we all know A bag of water 1 Fill a transparent bag long with water for instance one of those drinking water bags which are commonly sold on the street see photo Now sgueeze the lower part of the bag between your thumb and f ngers lt takes very little effort to press the plastic inwards Then again release the bag As you see the plastic returns to its former shape What happened The weight of the water in the upper part of the bag pushed the plastic bag back into its former shape What you just felt is water pressure 2 Now put the bag in the middle of a bucket and f ll the bucket with very wet sand to one third the height of the plastic bag so that two thirds of it emerges above the sand Pour water into the bucket until the water level is just on top of the sand The wet sand in the bucket simulates the aguifer The hole and our plastic bag simulate the borehole What is happening Simulation of water pressure in the borehole bucket The weight of the water in the upper part of the bag is pushing against the sides of the plastic bag Due to this pushing pressure the bag remains in shape and holds back the sand in the bucket by water pressure 3 Next cut the plastic bag with a pair of scissors at the same height as the water level in the bucket You will see that the borehole collapses What happened By cutting the bag the weight of the water from the upper part of the bag is no lo
9. be small to fit a treadle pump suction hose and the water quality for irrigation is not critical shallow well first aquifer This well will be cheap for the farmer 2 Fora potable water well for use by a single household or a few households equipped with a rope pump or other low cost hand pump a deeper hole may be needed to protect water quality so preferably drilled to a second aquifer In this case a self slotted 4 inch PVC pipe can be used no maximum yield required In doing so the well stays affordable for the users 3 In large water projects for Governments or NGOs for communal potable water wells equipped with a India or Afridev pump also a deeper hole is needed and 4 to 5 inch standard factory slotted PVC well casing pipes are often required to maximize yield to ensure high construction quality and to accommodate the pump These wells will be significantly more expensive but of better quality As these examples show the choice of pipes depends on Outer diameter of the pump pump should fit into the inner diameter of the casing pipe Type of the well irrigation or potable water Users intensity household or communal Users budget cheap or expensive METRIC ENGLIS Diameter and wall thickness of well casing Approx Approx There are two main internationally accepted standards for pipe Nominal Outside Inside Outside Inside inch size Diameter Diameter Diameter Diameter size metric meters
10. borehole wall it is very difficult to remove it and has to be removed by chemicals or heavy pumping equipment during the well development If the bentonite is not properly removed it can badly affect the discharge of the well Therefore it is NOT recommended to use bentonite for manual low cost drilled boreholes In some countries its use as a drilling fluid additive is not permitted Other natural clays Natural clay found during drilling in termite hills or elsewhere works like bentonite only less sticky Natural clay is cheap but shares the same disadvantage as bentonite It clogs up the aquifer Sa Polymers POLY SAU The best working water additives are polymers When mixed with water they i vs wonin AACR POLI thicken the working water into a very viscous fluid Natural polymers are also used l re a y as stabilizers and thickeners in the food industry MUD sn dd Advantage Polymers work extremely well and natural polymers are a 1 yma En biodegradable In other words they disappear naturally in a ws tL few days time er Example of a biodegradable polymer Disadvantage In most countries they are difficult to obtain and rather expensive Although expensive polymers are recommended for manually drilled boreholes Further research on low cost natural polymers will be done shortly by the publisher of this manual PRACTICA Foundation Manual drilling series Understanding Groundwater amp Wells in man
11. groundwater came from Imagine a latrine close to a well which is to be used for drinking water The last thing you want is that bacteria viruses and parasites disease causing micro organisms called pathogens originating from the latrine will flow together with the groundwater to your well par 3 1 latrines Although it can be difficult to detect the flow direction without detailed surveys in the case of shallow groundwater examination of the landscape can help For instance when a latrine is located on the slope of a hill or a mountain the groundwater contaminated with bacteria is likely to flow in the same direction as the slope of the hill In this case it would not be good to place the well down slope downstream of the latrine but rather on the same level or higher up up slope of the latrine PRACTICA Foundation Manual drilling series Latrine and flow of water Understanding Groundwater amp Wells in manual drilling When the area is less hilly a good indicator can be the presence of a gully stream or river Rivers always flow through the lowest lying parts of the area And groundwater in turn generally flows to rivers Be careful this only counts for a naturally present river not for man made channels It is NOT preferable to construct the well down stream of the latrine Catchment area Groundwater is fed by the infiltration of rain through the soil and it eventually flows to lower areas and rivers
12. in manual drilling Let us assume the groundwater level is at 5 meter below Step 4 ground level In this example we can see a second aquifer Once the well screen and PVC casing are hatched in the between 14 and 21 5 meter first column the exact depths for the annular backfill i e gravel pack sanitary seal and cuttings can be determined Step 3 by use of the drawings on the drilling log Now the well screen length and depth can be determined which is further explained on the next page in paragraph 4 5 Drilling log Drilling log Drawing Depth Description hard soft Color s Drawing Depth Description hard soft Color s meter of the formation fine coarse ofthe sample meter of the formation fine coarse ofthe sample PVC Back Formation PVC Back Formation pipe fill type pipe fill type Q OD OOo DY O CO Sand i yellow brown Sand i yellow brown Sand i yellow brown Sand i yellow brown Sand i groundwater Sand i yellow brown Sandy Clay brown Sandy Clay brown Sandy Clay brown Sandy Clay brown Clay compact grey a Clay compact grey Clay compact grey Clay compact grey Clay compact grey Clay compact grey Clay compact grey Clay compact grey Clay compact grey Clay compact grey Clay compact grey Clay compact grey Sand coarse yellow Sand coarse yellow Sand coarse yellow Sand coarse yellow Sand coarse yellow Sand coarse yellow Sand coarse yellow Sand coarse yellow Sand coarse yellow Sand coarse yellow Sand coarse yellow
13. in their countries Machine drilled wells are often very expensive and not affordable by large parts of the population in developing countries Another option is to drill shallow water wells Up to about 35 meter depth by hand so reducing the price of a well by a factor 4 10 compared to a machine drilled borehole This cost reduction not only enables NGOs and Governments to construct more water wells but also opens the door to villagers farmers schools and small communities to have a well constructed independently through the private sector Although most of the existing manual drilling enterprises are technically able to drill boreholes mistakes are easily made during the construction and development of the wells Furthermore good well construction alone does not ensure good water quality and sustained yield from the well over many years In order to achieve that know how on geology and groundwater is important However many technical workers of manual drilling enterprises may have limited education Much of the available literature on geology hydrogeology and hygiene cannot easily be understood without an advanced education Technical workers are used to learn through experience and repetition Of course training could be given to these workers but classroom training alone is known to be insufficient for drilling teams They need to relate theoretical information to the real practical problems which occur regularl
14. may simply have an open end or a drill bit can be added and partial or full rotation of the drill pipe can be used Thickeners additives can be added to the water in order to prevent hole collapse and reduce loss of working water drill fluid Jetting with rotation is generally used up to depths of 35 45 meters Advantage very quick in sand Disadvantage a lot of working is needed at once The level of the water table is not known during drilling Jetting Geological application limited to sand and thin layers of soft clay MANUAL PERCUSSION uses a heavy cutting or hammering bit attached to a rope or cable and is lowered in the open bore hole or inside a temporary casing Usually a tripod is used to support the tools By moving the rope or cable up and down the cutting or hammering bit loosens the soil or consolidated rock in the borehole which is then extracted by using a bailer Just as with hand augering a temporary casing of steel or plastic may be used to prevent the hole from collapsing When the permanent well screen and casing are installed this temporary casing has to be removed Manual percussion drilling is generally used up to depths of 25 meters Advantage drills hard formations Disadvantage the equipment can be heavy and expensive The method is slow compared to other methods Geological application Sand silt stiff clays sandstone laterite gravel and small stones Various other techniq
15. pumping and the pumping water level at any time during pumping is called the drawdown Step 4 Increase the flow rate step by step Each time after the flow rate is increased you may note some cloudiness in the water as fines are still being removed from the well Only increase the flow rate after the water becomes clear and the water level has stabilized Note down the water level flow rate and time Note the water level should not drop below the top of the well screen If the water level has stabilized just above the top of the well screen then the flow rate should not be increased any further PRACTICA Foundation Manual drilling series Understanding Groundwater amp Wells in manual drilling Step 5 Increase the flow rate until the desired discharge for the pump to be installed is reached Typically for the average hand pump this discharge would be about 1000 1500 liters per hour 1 1 5 m h Pump at this flow rate for several hours until the water level in the well is stable and the water is clear Final step Conclusion If the water level stabilizes with the water level still above the top of the well screen the water level should not drop below the top of the well screen the well s discharge is sufficient for the installation of a hand pump If the water level has dropped below the top of the well screen in step 4 or 5 then the answer is to stop pumping let the water level recover wait until the water level bec
16. the drilling f uid These materials block the pores of coarse layers and help together with the additives to prevent working water loss However fibers are difficult to remove Use of fibers is therefore not recommended in the well screen zone of the borehole Typical examples of fibers are sawdust and grain husk 5 3 REMOVAL OF ADDITIVES FROM THE BO REHO LE After the drilling and installation of the well screen and casing the drilling fluid additives have to be removed to maximize the yield of the well This is done by rinsing surging and over pumping of the well in the process known as well development chapter 7 PRACTICA Foundation Manual drilling series Understanding Groundwater amp Wells in manual drilling 6 WELL CONSTRUCTION 6 1 W ELL DESIGN The first and most important step in achieving a good well design is to complete a drilling log chapter 4 during the actual drilling process NB be sure to describe the drilling samples at least every break as samples can easily get lost or being transformed into nice little clay puppets by playing children From the drilling logs the exact depth and length of the well screen and the depth and thickness of the gravel pack and sanitary seal can be determined par 4 5 Borehole diameter The internal diameter of the PVC well casing is selected to fit the outer diameter of the pump that is going to be installed The drilled diameter of the borehole in turn depends on the
17. the sanitary seal can be installed par 6 4 Prepare the cement grout natural swelling clay or bentonite and pour it into the borehole in the same way if cement grout is used for the sanitary seal remember to use clay for the first half meter on top of the gravel pack Measure to ensure the sanitary seal was installed at the right depth Step 6 Filling the annular space Depending on the country regulations see appendix A the rest of the annular space is filled up by cuttings and cement grout see below Always pour in the material slowly while moving the casing to prevent bridging of the material Step 7 Installation of the top seal A sanitary top seal of 3 5m thickness should be placed from 3 5m below ground to the surface The top seal is usually made of cement grout Step 9 Construction of the head works apron and the choice of hand pumps See chapter 8 Note If the well is left alone before the installation of the hand pump the top of the PVC casing should be protected closed children often drop stones in the well to hear the water splash PRACTICA Foundation Manual drilling series Understanding Groundwater amp Wells in manual drilling 7 WELL DEVELOPMENT AND TESTING 7 1 W ELL DEVELO PM ENT Well development is necessary to maximize the yield of the well and optimize the filter capacity of the gravel pack This is achieved by removing the fines and drilling fluid additives and settlement of the gravel pac
18. the well to remove the loosened fines and clean the sump Once the water becomes clear the surge block is used once again This process is repeated until the water remains clear Next the pump is installed just above the well screen Then start discontinuous pumping Discontinuous start stop pumping is carried out by having the pump run for 5 minutes and then shut off for 2 minutes Once the water becomes clearer the pump can be left running until the water is clear When an electrical or motorized pump is used it is advised to pump at least 2 3 times the design discharge unless the well runs dry When a hand pump is used try to create a maximum flow rate until the water is clear please find more country specific well development requirements in appendix A Pumps for well development For well development different pumping techniques can be used The best options for well development are electrical deep well pumps and airlifting However these pumps are expensive It is recommended to use these pumps for communal water wells which require a maximum flow rate For household wells which often have to be low cost to stay affordable hand operated pumps can be used for well development Electrical deep well pump submersible pump A good option is to use an electrical deep well pump High flow rates can be established However electricity probably from a generator is needed and the pump and generator are expensive Airlifting The s
19. the well screen it is advised to attach a 1 meter sump at the bottom of the well screen into which any particles entering the well screen from the aquifer can settle without blocking the well screen and pump par 4 5 The sump simply consists of a 1 meter plain PVC pipe which is closed at the bottom end To close the bottom of the sump a factory made wooden or PVC cap can be inserted Alternatively the bottom end of the sump pipe can also easily be closed by some cutting and bending Make 4 cuts in the bottom part of the sump pipe and heat nM tte the pipe end Fold the four parts inside and allow the parts to cool see photo Bottom end closed by cutting and Alternatively cut out 6 9 triangular parts The remaining parts can be bent together bending to a point Making a point will reduce the risk of scraping the borehole wall when the well screen is lowered into the borehole To completely seal the bottom of the sump 10 cm of cement mortar should be poured in the sump Pipe joints Casing and well screen pipes are usually joined by glued sockets The more expensive purpose made casings and well screens with a wall thickness of at least 5 mm are threaded When the pipes are glued together it is very important to clean and roughen both ends the inside of the socket and the outside of the pipe to be glued Then put sufficient glue ALL around on both ends and put the pipes together in one move Threaded socket joints I Effectiv
20. Although this might be difficult to see on the surface without detailed investigations always try to imagine where the groundwater would flow to especially during the dry season On top of a mountain for instance the groundwater level can drop dramatically during the dry season because at that time the groundwater that flows out of the pores of the formation to lower areas is not replaced by infiltrating water from rainfall Only when the rains start the groundwater level will rise again 2 3 AQUIFERS The word aquifer simply means a water bearing layer A good aquifer for the installation of a well screen is a permeable layer below the groundwater table par 1 3 During drilling you may come across different aquifers at different depths separated by impermeable layers Phreatic aquifer The upper aquifer is called the phreatic aquifer Rainwater directly infiltrates the soil The water moves down and when it reaches the water level it is added to this aquifer The water can take contamination such as bacteria or pesticides down into the groundwater Therefore a phreatic aquifer is prone to pollution from activities taking place on surface par 3 1 Phreatic groundwater exists in a permeable layer above an impermeable layer If this phreatic groundwater layer is just a few meters thick it may run dry during the dry season leaving your well empty Different aquifers Second aquifer The next aquifer covered by an imp
21. Igneous rock Impermeable Laterite Manual drilling Mechanized drilling Natural polymers Pathogen Permeability Permeable Understanding Groundwater amp Wells in manual drilling Permeable water bearing layer below the groundwater level The material gravel sanitary seal and cuttings which is placed in the space between the well screen and casing and the formation Treated natural clay swelling clay Extremely fine particles smaller than 0 004 mm in size Layer of clay deposits sediment The characteristic of particles that makes particles stick together Particles such as sand clay and gravel cemented together into rock Pollution Sediment Written record of the formations soil layers and characteristics drilled according to depth Formed rock types sedimentary layers under the surface of the earth The study of the earth formation of rocks and sedimentary layers Particles ranging from 2 mm up to 64 mm in diameter Particles from 4mm up to 64 mm are also called pebble Coarse sand around the well screen The study of groundwater Rocks formed when molten material has cooled Material that does not transmit water through it Hard formation with high iron content in tropical area Drilling boreholes with hand powered drilling tools and drilling rigs Drilling boreholes with machines or mechanised drilling rigs Biodegradable thickeners Mixed with water makes an excellent drilling fluid
22. Measuring tools Before the actual well construction starts par 6 5 it is important to double check the final depth of the borehole with a measuring tape Sometimes the length of drill pipes which are used during the drilling process for measuring can vary or there is contusion among the drilling team members about the number of drill pipes already in the ground For the latter it is important to count all your drill pipes beforehand Depth measurements should be done with a measuring tape or specially made measuring tool A cheap and accurate measuring tool is easily made A meter length of reinforcement bar bent into a loop is attached to a long piece of a 4mm thick rope At exact meter intervals knots are At exact meter intervals knots are tied in the rope The final depth of the borehole tied in the rope or depth of backfilling can be measured by counting the knots PRACTICA Foundation Manual drilling series _________ 25 Understanding Groundwater amp Wells in manual drilling 6 2 MATERIALS PVC W ELL SCREEN AND CASING In many countries several different PVC pipes exist varying from cheap drain pipes to expensive high class slotted well screens and casing pipes Which pipes you use out of this range will depend on different aspects Three examples l For a shallow irrigation well equipped with a treadle pump a cheap 2 inch self slotted drain pipe will be sufficient In this case the diameter can
23. UNDERSTANDING GROUNDWATER amp WELLS In manual driling Pe em dn for manual drilling w hydro geology for well drilling well installation and well development N A i N i y SNE i Ro nT if NA vee a f MPN g y DA unicef UNDERSTANDING GROUNDWATER amp WELLS IN Manual dniling Instruction handbook for manual drilling teams on hydro geology for well dniling well installation and well development Published by the PRACTICA Foundation Author Arjen van der Wal Peer reading Richard C Carter Structural support Wouter Jan Fellinga Melanie Stallen French translation Julien Labas St phan Abric R gis Garandeau Swahili translation Walter Mgina Ester Mgina van Vugt lllustrations Franck Nederstigt Photos Arjen van der Wal Layout Marijke Kreikamp 4colour design First edition April 2008 Second edition June 2010 PRACTICA Foundation develops and disseminates low cost appropriate technology in water and renewable energy in developing countries We focus on technology that responds to local cultural contexts can be locally produced and maintained and supports existing markets n p _______f_____ PRACTICA foundation Oosteind 47 NL 3356 AB Papendrecht The Netherlands t 31 0 786150125 info practicatoundation nl www practicafoundation n Disclaimer This manual is free of charge Any parts of this instruction
24. ack to settle equally around the screen leaving at least l inch of gravel all around the well screen Centralization can be achieved by attaching spacer rings or centralizers with an interval of every 3 meter around the well screen The spacer rings can be made of PVC rings which can be attached on 4 sides around the well screen see picture PRACTICA Foundation Manual drilling series Understanding Groundwater amp Wells in manual drilling Step 2 Installation of the PVC pipes A practical method of lowering the PVC pipes into the borehole is to use a rope see picture One end of the rope is attached to the drill rig and the other end is wrapped three times around the pipe to forma self closing loop The rope is used to prevent the casing and screen slipping into the borehole while adding a new length of pipe Install all the prepared pipes and leave meter see step 1 of pipe above ground level to so that the well screen is placed at the correct depth Use of rope during installation Step 3 Cleaning and flushing the well screen When the well screen has been installed at the correct depth the pipes and screen should be flushed in the case of fluid drilled boreholes Pour water into the PVC pipes and allow the dirty water to overflow out of the borehole If the added water only enters the well slowly or not at all this could indicate blockage of the well screen slots by clay or fine material from the borehole wall Extra water
25. al Ministry of Water Resources PRACTICA Foundation Manual drilling series Understanding Groundwater amp Wells in manual drilling 8 FINALIZATION 8 1 CONCRETE SLAB APRON Finally after pump testing the head works or concrete apron should be installed This apron will prevent surface water and contamination to flow into the borehole directly The apron also provides a solid and clean base for the hand pump and the collection of water The apron is usually 2 3 meter in diameter with a small wall around the outside There are many different designs for the concrete apron and the choice may depend on factors such as national standards type of pump to be installed price and need for protection against floods in some areas etc Finally it is important that the users are comfortable with the design too A fence can be constructed around the well to keep animals away and in some places to control access to the well 8 2 SOAK PIT As we have seen in paragraph 3 1 it is for hygienic reasons important that the apron dries up every now and then Doing so the sunlight will disinfect the well surroundings causing most pathogens to die To make drying of the apron possible it is advised to construct the apron under a small slope A drain a small outlet or channel is constructed at the lowest part of the apron which will carry the water away from the well The drained water can then soak away in a so called soak pit The soak pit is ge
26. al the soil from the hole and c if necessary provide support to the walls of the hole to prevent collapse during drilling A short overview of techniques PRACTICA Foundation Manual drilling series ____________ _ 3 Understanding Groundwater amp Wells in manual drilling THE HAND AUGER consists of extendable steel rods rotated by a handle A number of different steel augers drill bits can be a attached at the end of the drill rods The augers are rotated into the ground until they are f lled then lifted out of the borehole to be emptied Specialized augers can be used for different formations soil types Above the water table the borehole generally stays open without the need for support Below the water table a temporary casing may be used to prevent borehole collapsing Drilling continues inside the temporary casing using a bailer until the desired depth is reached The permanent well casing is then installed and the temporary casing must be removed Augers can be used up to a depth of about 15 25 meters depending on the geology Advantage easy to use above groundwater table Cheap equipment Disadvantage it may be difficult to remove the temporary casing Hand auger Geological application Sand silt amp soft clay SLUDGING or Rota sludging when the drill bit is rotated uses water circulation to bring the drilled soil up to the surface The drill pipes are moved up and down On the down stroke
27. ame applies to airlifting Airliffing is a very suitable development tool by which high flow rates and shock waves can be established However this reguires a big compressor which is very expensive Motorized centrifugal pump A cheaper option with substantial flow rates for development is a motorized centrifugal or mud flow pump However these pumps are suction pumps and only operate if the dynamic groundwater level water level during pumping is less than 7 meter below ground level Manual operated pumps For household wells also hand pumps which are cheaper can be used although development in this way will be less effective Nevertheless when hand pumps are used for well development and are operated to the maximum flow rate for a period of time until the water is clear they can be sufficient Re development After a well has been in use for several years and the yield decreases becomes Understanding Groundwater amp Wells in manual drilling less re development of the well can be considered Re developing a well is easily performed using the same procedure as described above by surge block and discontinuous pumping 7 2 PUMPING TEST W ELL YIELD Once a well has been developed and is free of any fines the well should be test pumped Test pumping gives useful information about both the well and the aquifer In particular it can indicate whether the well yield will be sufficient for its intended purpose Note Reliable test
28. and English inch However in each country i Armm 491mm the actual size in millimeters differs from the size given in inches 2 63mm 55mm 60 2mm _ 52mm by the factory As an indication you can make use of the table on MU 75mm A 88 7mm 114 1mm _ a mm 5 140mm I Important The wall thickness of the pipes should always be 160mm 148mm 168mm more than 3 mm If a smaller wall thickness is used in deeper 19mm wells the pipes might break during use Table 6 1 Comparison between Metric amp English uPVC pipe sizes Slots Slots are the openings in the well screen which allow groundwater to flow into the well In theory the slot size width should be smaller than the mean size of the Factory slotted pipe soil particles However in some countries only 1 factory made slot size Imm is i available For low cost wells one can make the slots by hand using a hacksaw see below Self slotted pipe PRACTICA Foundation Manual drilling series Understanding Groundwater amp Wells in manual drilling For a 4 inch screen 6 parallel lines are drawn along the full length of the pipe with an in between distance of about 4 5 and 6 7 cm see drawing Within the 6 7 cm lineation the slots are sawn see picture The distance between the slots should be about one centimeter The distance between slots and parallel lines depend on the wall thickness of the pipe prevent braking Sump To increase the lifetime of
29. ants are a threat to the quality of the drinking water When a well is placed in the shade bacteria and algae will flourish see photo Presence of bacteria indicated by If the well surroundings can dry up daily the sunlight will disinfect the well algae surroundings causing all pathogens to die PRACTICA Foundation Manual drilling series Understanding Groundwater amp Wells in manual drilling 3 2 MIG RATION OF PATHOGENS BACTERIA As we have seen in the previous paragraph pathogens bacteria viruses and parasites and chemicals move downward with the infiltrating rain water through permeable soil layers to the groundwater Once in the groundwater the pathogens and chemicals not only spread horizontally left right but also vertically up down deeper into the aquifer see par 2 3 Different aquifers figure 4 ee In par 1 3 we have seen that groundwater easily flows through permeable layers da aquifers like sand and gravel Pathogens and chemicals which are suspended mixed with or dissolved in this groundwater also easily migrate move through permeable i pe ar layers aw io ar i Water with pathogens has to be stopped before reaching the surroundings of the well screen Fortunately often impermeable layers can be found Water and thus the pathogens in this water does not easily flow through these impermeable layers Due to their fine texture very fine particles impermeable layers prevent pathogens fr
30. ater amp Wells in manual drilling lron The same approach may help when iron is found in the water Sometimes water has a bad metallic taste and the color of the water turns brown when it is left in a bucket or boiled The water may create rusty looking spots on clothes and cooking material This indicates the presence of high iron concentrations The presence of high levels of iron may cause people to reject the water source Iron is a very common element of groundwater Peat When during drilling remains of old plants are found it is recommended not to install a well screen in this layer Plant remains below the water table are decomposing very slowly and create an acidic environment A common example is peat Groundwater extracted from a peat layer smells like decomposed plant material is very acid and looks brown see photo Peat water Acidic groundwater low pH The pH is a measure of the acidity of water If the pH of the water is low the water is considered acid In areas of acidic groundwater with a low pH the acid in the water may cause corrosion to the steel and cast iron components parts of a hand pump In such cases a type of pump made of PVC plastic or stainless steel components may be considered Hard water hardness of the water If water from the well has a high content of the minerals calcium for example when drilling in limestone and chalk and magnesium it is called hard water Hard water is generally n
31. attached to the well screen for details on PVC casing and well screen see par 6 2 PRACTICA Foundation Manual drilling series Understanding Groundwater amp Wells in manual drilling Thickness of the gravel pack Once the well screen position is recorded hatched on the drilling log the position and thickness of the gravel pack can be determined The annulus open space around the well screen is filled with coarse sand or fine gravel of specific size gravel pack up to about 1 2 meter above the top of the well screen The extra meters are necessary because during the development of the well the gravel pack will settle and shrink It is therefore good practice to include at least 1 2 meter safety margin above the well screen during installation of the gravel pack for details see par 6 3 Thickness of the sanitary seal When an impermeable layer is drilled through it is advised to seal close again that whole impermeable layer with clay bentonite or cement par 3 3 To be sure the layer is sealed properly the thickness of this seal should be at least 3 5 meter If no impermeable layer was found and the well is thus placed in the first aquifer the sanitary seal should be installed directly on top of the gravel pack 1 2 meter above the well screen and should have a thickness of at least 5 meter for details see par 6 4 Cuttings On top of the sanitary seal backfilling of the drilling hole is done by using the cuttings soi
32. ckness of a fluid Term that tells whether water is safe or not safe polluted or not polluted for drinking The upper surface of the groundwater groundwater table Breakdown of rocks through contact with atmospheric conditions such as heat water ice and pressure A hand dug or drilled hole to access groundwater Blind pipe of PVC The construction drilling installation and backfilling of a well Removing f nes and drilling f uid additives from the well and the surrounding aguifer and settlement of the gravel pack Slotted PVC pipe through which water from the aquifer flows into the well The volume of water produced by the well generally measured in m day or liter second Water with or without drilling fluid used during the drilling process PRACTICA Foundation Manual drilling series Understanding Groundwater amp Wells in manual drilling ACKNOW LEDG EM EN TS Literature used Drilled Wells Peter Ball SKAT Switzerland 2001 Groundwater and Wells F G Driscoll Johnson Screens US 1986 Developing Groundwater Alan Mac Donald Jeff Davies Roger Calow John Chilton ITDG publishing United Kingdom 2005 Technical notes on Well Construction internet Lifewater Canada Simple drilling methods Bob Elson and Rod Shaw WEDC United Kingdom Hydrogeology l A Dassargues Leuven University Belgium 1998 Hand augered garden wells Jonathan Naugle Lutherean World Relief Niger 1996 Borehole and hand pump imple
33. ds 8 EE Figure blue is water white is soil sand and gravel clay and loam mixed soil Sand and Gravel When coarse sand or gravel is put into a bucket of which the bottom is perforated and a cup of water is added on top of it the water moves easily through the sand to the bottom of the bucket fig 1 The water flows easily through the pores open space between the grains Conclusion water easily flows through sand and gravel Sand and gravel are thus very permeable When a well screen is placed in a sand or gravel layer the water flow through the sand into the well will be high because the water easily flows through the sand to the well screen fig 2 However when drilling with water pressure see paragraph 5 1 working water also easily flows out of the bore hole into the sand layer Clay and loam The opposite is seen with clay and loam When wet clay is put in a bucket compressed as in a layer of soil and a cup of water is added the water will remain on top fig 1 Clay particles are very small and sticky as are the pore spaces between the particles Conclusion Water does NOT easily flow through clay Clay is therefore described as not permeable or impermeable If a well screen is placed in a clay layer the water flow into the well will be very low fig 2 in this case when drilling with water pressure paragraph 5 1 no additives par 5 2 are necessary
34. e the borehole might collapse especially when the drilling is done in gravel or sand non cohesive materials To avoid collapse it is necessary to keep the drilled borehole full of water during drilling and construction of the well To prevent our working water the water in the upper part of the borehole from seeping away into a sand or gravel layer a substitute for the plastic bag is needed so that we do not loose our water pressure For this reason drilling fluid additives are used 22 ___________ PRACTICA Foundation Manual drilling series Understanding Groundwater amp Wells in manual drilling 5 2 DRILL FLUID ADDITIVES When an additive is mixed with our working water drilling fluid and circulated through the borehole the walls of the borehole become plastered like paint on a wall This temporary plaster plays the same role as the plastic bag in the example of the bucket Additives also make the drilling fluid more viscous thicker so that it is better able to carry cuttings upward from the borehole A number of possible drilling fluid additives exist Bentonite Other natural clays Polymers Cow dung Fibers and other solids Bentonite Bentonite is a treated natural clay which when mixed with water will increase the viscosity of the working water In most countries bentonite is expensive Advantage Bentonite works extremely well Disadvantage Once the bentonite has plastered the
35. e le ng th Be aware that sockets and threads influence the total length of the pipe In other words a 6 meter pipe could become 5 80 meter when glued together W hen installing the pipes ina 30 meter deep borehole over 1 meter of difference might be created affecting the actual position of the filter screen 6 3 MATERIALS G RAVEL PACK The gravel pack fills the soace between the aquifer sand particles and the well screen preventing the wall of the hole from collapsing on to the well screen and may serve to filter some of the fine sand particles from entering the well par 4 5 The gravel should consist of a grain size generally 1 5 3mm which is just larger than and no more than twice to three times the slot size of the well screen Good size gravel looks more like coarse sand rather than gravel The grains are best Minimum and maximum sieve when round in shape Such material can often be found on river beds or lake shores The best way to prepare suitable gravel is using maximum and minimum sized sieves grains which are too small or too big are sieved out PRACTICA Foundation Manual drilling series 7 Understanding Groundwater amp Wells in manual drilling mara na yeyr igur ae Li ir P ean Bag of cement Self made spacer rings attached to the filter screen 6 4 MATERIALS SANITARY SEAL As we have seen in chapter 3 par 3 3 it is essential to install a sanitary seal if the well needs t
36. ermeable layer on top for example a clay layer is called the second aquifer The impermeable layer above this water bearing layer forms a barrier for bacteria and pollution and prevents them from traveling down to the second aquifer please see par 3 2 I If there is a second aquifer present It is generally best to install the well screen in this second aquifer Below the second aquifer again an impermeable layer and a third aquifer may be present One aguifer Sometimes only one aquifer is present In this case it is recommended to drill as deep as possible to prevent bacteria and pollution from entering the well Drilling deep also reduces problems of wells drying up because of seasonal fluctuations difference between wet and dry season of the water table One aquifer I For further explanation and important information on aquifers and hygiene see chapter 3 PRACTICA Foundation Manual drilling series Understanding Groundwater amp Wells in manual drilling 2 4 SEA WATER INTRUSION In coastal areas a deeper aquifer could contain salty sea water Also during the dry season when the water table is lower salty sea water could move inland When this happens it is called saltwater intrusion Salt water is heavier than fresh water This means fresh water tends to float on top of the salt water layer When a well is drilled in a coastal area where saltwater intrusion exists the salty water may move up due to the
37. es Technical Notes Technical Manuals including this publication Advocacy Materials Mapping of suitable areas for manual drilling Case Studies and Implementation and Training Manuals This initiative builds the capacity of the local private sector in order to respond to the ever increasing demand for safe water in rural areas The Technical Training Program TTP ofthe ETC Foundation contributed with structural support in the educational aspects of this manual While every care has been taken to ensure accuracy of the information given in this manual neither the publisher s nor the author s can be held responsible for any damage resulting from the application of the described methods Any liability in this respect is excluded 6 Note to those considering translation or modiftation before beginning any translation or modification and in order to avoid duplication of efforts and unintended mistakes please contact the PRACTICA Foundation This document or parts of this document may not be copied or published under a new name or author without permission from PRACTICA Foundation e PRACTICA Foundation Manual drilling series Foreword Context Over the years much literature on geology hydrogeology and hygienic aspects has been written and in a lot of countries this information is used by policy makers project managers engineers and technicians to construct machine drilled wells
38. esticides from farms hydrocarbons from fuel etc and natural chemicals chloride sodium fluoride arsenic etc 2 Biological parameters pathogens bacteria E coli form viruses Hepatitis parasites worms Amoeba etc Often E coli bacteria are analyzed to indicate a faecal contamination latrines 3 Physical parameters Turbidity color odor smell etc Most of the water quality analyses have to be done ina laboratory but some of these analyses can be done in the field For more information on water quality testing and for country specific requirements please refer to your National Ministry of Water Resources Representative water samples When taking water samples for testing wait until the whole development process and pump testing is finished Preferably then wait another few weeks to allow some parameters contents originating from drilling fluid working water or cement to disperse disappear Do not take a sample immediately after well disinfection because the result will be predictable no pathogens but will not be useful Well disinfection chlorination After the completion of the well it can be disinfected in order to kill harmful organisms pathogens that may have entered the well through the working water annular backfill or pump during the installation process A well can be disinfected by chlorination For more information on chlorination see appendix E For country specific requirements refer the Nation
39. gh an impermeable layer is a little like taking the plug out of the sink so enabling contaminants to flow down from the polluted layer to the clean second aquifer and enter the well screen fig 6 PRACTICA Foundation Manual drilling series Understanding Groundwater amp Wells in manual drilling I To prevent pathogens and chemicals from entering the filter screen and polluting the second aquifer a sanitary seal has to be placed please see paragraph 6 4 6 Bacteria migration in different 7 Bacteria migration in different aquifers aquifers with installed well and sanitary seal When a borehole is drilled a well screen will be installed and a gravel pack placed par 6 5 Then the impermeable layer has to be sealed closed to prevent contaminants from traveling down into the second aquifer This is done by a sanitary seal The sanitary seal par 6 4 is made of cement or bentonite natural clay which swells to many times its dry volume when wetted which will seal close again the impermeable layer see fig 7 n When only ONE aquifer exists fig 8 a sanitary seal with a thickness of at least 3 5 meter has to be installed above the gravel pack to prevent the contaminants from entering the well screen fig 9 Water and pathogens can travel faster down the loose material in the borehole than though undisturbed soil An impermeable seal will force the water to flow through the normal undisturbed soil thus increasing the t
40. he soil contains some silt or clay and sand The formation will have a low permeability 3 If the ball only deforms and or remains more or less in shape it is composed of clay and is described as impermeable Porosity Sedimentary layers consist of many particles such as sand silt and clay Between these particles there is still a lot of open space called pores The porosity is a measure for the percentage of free space in the formation A porosity of 30 means that 30 of the total volume of the sample is open space while the remaining 70 is filled with particles The pores can be filled with air or water This does not always mean that the water easily flows through the soil For example clay has a high porosity but low permeability PRACTICA Foundation Manual drilling series G Understanding Groundwater amp Wells in manual drilling Turbidity Turbidity is a difficult word for the cloudiness of water caused by very small particles in the water called suspended particles rather like smoke of a fire in the air Clay and silt sized particles are very fine When these particles are found in water they cause it to be turbid or cloudy If well water is extracted from a clay or silt layer some of the fine particles in the formation may be transported by the flow and get suspended mixed in the water As a result the water will look cloudy Bottles of water showing low and high turbidity Conclusion Always continue drilling
41. ion PVC Back Formation pipe fill Sand i yellow brown Sand i yellow brown Sand i yellow brown Sand i yellow brown Sand i yellow brown Sand i yellow brown Sandy Clay brown Sandy Clay brown Sandy Clay brown Clay compact grey Clay compact grey Sand i yellow brown Sand i yellow brown Sand i yellow brown Sand i yellow brown Sand i yellow brown Sand i yellow brown Sandy Clay brown Sandy Clay brown Sandy Clay brown Clay compact grey Clay compact grey Clay compact grey ip iy ia ery I Oo OO Oa Geo me N eh Clay compact grey Clay compact grey Clay compact grey Clay compact grey Clay compact grey Clay compact grey Clay compact grey Sand coarse yellow Sand coarse yellow Sand coarse yellow Sand coarse yellow Sand coarse yellow Sand coarse yellow Sand coarse yellow Sand coarse yellow Sand coarse yellow 5 Sand coarse yellow Sandy Clay grey brown Sandy Clay grey brown Sandy Clay grey brown Sandy Clay grey brown Sand coarse yellow Sand coarse yellow Sand coarse yellow Sand coarse yellow Sand coarse yellow Sand coarse yellow Py Vii we Saw aww Ca Co Go Oe Gio i iG i OOO i Le La to ON Ong a to By hatching now the permeable semi permeable and impermeable layers become visible Following hatching styles are used o Permeable a Low permeable Impermeable PRACTICA Foundation Manual drilling series 1 Understanding Groundwater amp Wells
42. k After drilling some of the fines and drilling fluid additives remain behind in the borehole and are blocking the pores of the surrounding aquifer par 5 2 and the new installed gravel pack After they have been removed by well development the water will be able to move freely from the aquifer to the well screen During well development also the gravel pack will settle and become more compacted ensuring that there are no large voids holes into which aquifer material sand could later collapse The settled gravel pack will filter out some of the fines from the aquifer Some well development has already started during step 3 of the well installation process during f ushing of the well screen and the borehole already some of the f ne particles and drilling fluid additives were removed However normally this first well development is not enough and more extensive development needs to be carried out after completing the installation process The remainder of well development takes place after the backfill has been placed and the cement grout of the sanitary seal has hardened this hardening process takes at least 24 hours Several techniques are available for well development and sometimes a combination of these techniques is used to get the best development results Useful techniques are e Surge block or plunger e Discontinuous pumping start stop cycle pumping e Continuous pumping with large flows Surge block or plunger By the use of a
43. king water soil determination logging well installation well development water quality and well yield flow rate of the well These problems may occur when the drilling process is not completely understood and important steps are missed This instruction manual describes many of the subjects and problems which you may come across during drilling The manual will help you to understand the drilling process at ground level and far below ground level in the drilled hole With the information provided you will be able to understand what is taking place in the hole during drilling and perform a professional job as you construct high quality water wells THE MANUAL How does this instruction manual work In the table of contents see previous page an overview is given of the subjects and where to find them Chapter to chapter 8 contains all the information needed for a good understanding of the drilling process and correct well installation In the Appendix you will find country specific regulations These are regulations designed for communal wells and defined by the government or NGO you are working for In the Appendix you will also find some specific geological conditions which are unique for the area or country you work in Furthermore simple blank drilling logs are included which can be copied for use in the field ADDITIONAL INFORMATION For more detailed background information for policy makers project managers implementing NGO
44. l which was drilled up during the drilling process Sanitary top seal Also a sanitary top seal of 3 5m thickness should be placed from 3 5m below ground to the surface for details see par 6 5 Drilling team filling in the drilling log PRACTICA Foundation Manual drilling series Understanding Groundwater amp Wells in manual drilling 2 WATER PRESSURE AND DRILLING FLUIDS 5 1 DRILLING W ITH WATER PRESSURE In paragraph 1 2 we have seen different manual drilling techniques Some techniques like the auger and percussion methods make use of a temporary casing when the groundwater table is reached to prevent the borehole from collapsing during drilling Other techniques like sludging and jetting use water pressure Temporary casing It is easy to understand how a temporary casing protects the hole from collapsing The casing pipe is strong and acts like a wall Soil from the sides of the borehole simply can not pass through the casing However the only drawback is that it has to be removed afterwards when the well screen is installed This can be very difficult or it can even become impossible when a drilling was made through a clay layer the casing can become stuck in the sticky clay Water pressure While a casing pipe is strong and solid water is just soft and liquid How is it then possible for water to hold open a borehole while drilling in wet sands To find the answer to this question let s first take a close look
45. length of the well screen 3 Depth and thickness of the gravel pack 4 _ Location of the sanitary seal Database Besides the direct use of drilling logs in the field drilling logs are also very important to record the hydro geological information of the drill site For example if at a later stage other wells have to be drilled in the same village or area it is very useful for the drilling team to know the geology depth of the water table and likely total drilling depth Previous drilling logs are an essential source of information for these purposes before the new drilling starts This information could be important for the choice of the drilling equipment The drilling logs can be kept together ina file which is called a database By taking care to record and preserve good drilling logs the drilling team will present itself as a professional and skilled team to their clients 4 2 TAKING SOIL SAMPLES The first step in making a drilling log is to take representative samples of the soil geological formations encountered in drilling This means the sample should be a pure piece of the layer that is being drilled at the moment of sampling avoiding mixing the sample with soil from other layers Samples should be taken every meter and or every time the formation soil type changes The samples should be put on a plastic sheet write down the depth if the sample is not immediately described away from the drilling activities Then desc
46. ling in the drilling logs Determine the depth of the filter screen and backfilling Well screen position and length Sump Thickness of the gravel pack Thickness of the sanitary seal Cuttings Sanitary top seal 5 WATER PRESSURE AND DRILLING FLUIDS sl o 5 9 Drilling with water pressure Temporary casing Water pressure Borehole Drill fluid additives Bentonite Other natural clays Polymers Fresh cow dung Fibers and other solids Removal of additives from the borehole 6 WELLCONSTRUCTION 6 Well design Borehole diameter Borehole depth Completion of the borehole Measuring tools PRACTICA Foundation Manual drilling series 16 16 16 16 17 25 25 Z9 Z9 25 25 6 2 Materials PVC well screen and casing 26 APPEN DIX Diameter and wall thickness of well casing Slots Sump Pipe joints 6 3 Materials Gravel pack 6 4 Materials Sanitary seal 6 5 Well construction 7O A Country specific regulations 26 B Country specific geological conditions 27 C Drilling logs of D Test pumping form E Chlorination 2 28 28 7 WELL DEVELOPMENT AND TESTING 31 f Welldevelopment Surge block or plunger Discontinuous pumping start stop cycle pumping Pumps for well development Re development 7 2 Pumping test Well yield Dip tape Yield test with motorized or deep well pumps Yield test with hand pumps Water level measuring fape or measuring rope 7 3 Water quality testing Rep
47. mentation Connect International Netherlands 2004 Oae OA Feedback This manual is based on the experience with a number of local NGO s and micro drilling enterprises trained and or evaluated during projects in Tanzania Chad Ghana Senegal Ethiopia Madagascar India and Nicaragua The contents of the manual can be used as a guide during training sessions including training sessions by local trainers and as a reference book for drilling supervisors NGOs manual drilling teams and enterprises during the entire drilling and well installation process The manual treads essential subjects like geology in relation to hygiene related to manual drilling in simple and understandable language We are keen to continue improving the manual Therefore we would appreciate it enormously to receive your feedback and suggestions for improvements so that we can take these up in future editions of the manual Please send them to the PRACTICA Foundation by e mail info practicatoundation nl ee PRACTICA Foundation Manual drilling series APPEN DIX A Country specific regulations B Country specific geological conditions C Drilling logs D Test pumping form yield test E Chlorination Understanding Groundwater amp Wells in manual drilling PRACTICA Foundation Manual drilling series
48. nerally constructed 4 6 meter away from the well The construction of a soak pit is simple It isa 1 by 1 by 1 meter drain pit filled with pebbles coarse gravel and stones YCH YNYR ss uu me ee e i n AYNAN Se AAA Hn rh gt gt gt Th rh gt gt gt XX mr gt gt gt gt Frh md mass ED Cross section of a well concrete apron soak pit and hand pump 8 3 PUMP CHOICE There are many types and models of good pumps but the choice of hand pump the type of pump to install on the well is very important The correct choice of a hand pump will depend on a number of factors such as the national standards the availability of spare parts the ease of maintenance the price the depth of the water table and the pH of the groundwater see par 2 5 It may be difficult to make the right choice and there are other manuals that deal with this subject Therefore hand pumps are not discussed in this manual PRACTICA Foundation Manual drilling series Understanding Groundwater amp Wells in manual drilling GLOSSARY OF TERMS Latrine Borehole Pathogen Pollution Well casing Aquiter Sanitary seal Impermeable layer Gravel pack Filter screen Sd aguifer Sump PRACTICA Foundation Manual drilling series 0 Aquifer Annular backfill Bentonite Clay Clay layer Cohesive Consolidated rock Contaminant Deposition Drilling log Geological formation Geology Gravel Gravel pack Hydrogeology
49. nger present and cannot push against the plastic any more The water level in the bag is now egual to the water level in the bucket There is no additional water pressure Collapse of the borehole bucket PRACTICA Foundation Manual drilling series 11 Understanding Groundwater amp Wells in manual drilling Borehole We have seen how to keep open a hole in wet sand when the sand was in a bucket But how does it work in a borehole during drilling Cios serdiorot ihe bucket Cross section of the borehole OSN The drawing on the left shows a cross section of the bucket with wet sand and a plastic bag On the right a cross section of the borehole is shown Let us compare our bucket borehole with the real borehole 1 _ The water level in the bucket represents the water table in our borehole 2 _ The upper part of the plastic bag above the water level in the bucket is similar to the part of the borehole filled with water which lies above the groundwater table 3 The wet sand in the bucket represents the water bearing sand layer in the aquifer However the plastic bag is absent in the real borehole In the bucket we have seen that when the plastic bag was cut the result was that the water level in the simulated borehole and the bucket became the same the simulated borehole collapsed In other words I f the water level in a real borehole falls towards and becomes equal to the water tabl
50. o yield good quality water par 4 5 The sanitary seal can consist of cement or bentonite pellets the volume of the bentonite pellets will increase many times when it gets wet and so it seals the hole by expanding Also natural swelling clays can be used but they are more difficult to handle than processed bentonite In many countries bentonite pellets are expensive In these cases it is recommended to use a cement water mixture cement grout The water and cement are mixed until a thick slurry is created 26 liters of water to one 50 kg bag of cement will make about 33 liters of cement grout If cement grout is used as a sanitary seal first a half meter of clay should be backfilled on top of the gravel pack to prevent the grout from penetrating the gravel pack 6 5 W ELL CONSTRUCTION I Note Fluid drilled boreholes must be kept full of water during the entire installation process Step 1 Preparations Prepare all materials needed for the installation and backfilling Measure out the effective length of the PVC pipes and cut the last pipe to a length allowing meter to be left above ground level after installation Number the pipes in order of installation Centralization of the well screen To prevent the slots from becoming blocked with clay due to scraping of the well screen against the borehole wall during installation the well screen should be centralized Centralizing the well screen in the borehole also allows the gravel p
51. om further vertical migration down into the underlying aquifer Because the impermeable layer blocks the pathogens from downward migration the next lower aquifer contains water without the harmful pathogens and chemicals originating from the surface fig 4 4 Bacteria migration in different aquifers a One aguifer figure 5 Ui Sometimes however only one aguifer exists within reach of manual drilling i a equipment for instance a 50 meter thick permeable sand layer W E Although there is no impermeable layer in this case further down into the sand layer the number of living pathogens will decrease gradually every meter down fewer pathogens will be present It takes time for the pathogens to travel down and while doing so they die off over time However there is no impermeable layer to prevent downward movement of pathogens and other contaminants which marks the exact depth at which contaminants are not further present fig 5 Therefore it is recommended to drill as deep as possible at locations where only ONE aquifer exists 5 Bacteria migration in one aquifer 3 3 SANITARY SEAL In the previous paragraph we have learned to drill through the impermeable layer to the second aquifer in order to find clean drinking water But by doing so a new problem is being created By drilling through the impermeable layer a connection a short cut is created between the first and the second aquifer Drilling a hole throu
52. om the human LE TH waste in the latrines move downwards through permeable layers and so locally PN ee N contaminate the groundwater see figure 3 Although pathogens will not survive long outside the human body it will take a while before they die off completely Therefore groundwater close to latrines can contain living and harmful pathogens In selecting a good site for the well it is recommended to construct the well NOT down stream or down hill par 2 2 from a latrine If it is difficult to determine the groundwater flow direction construct the well at least 30 meter away from the latrine 3 Pollution of the aquitet Waste dump areas farms fire places and fuel stations The same applies to areas where waste is dumped and burned or where fuel or other contaminants for example pesticides or animal waste on farms may seep into the groundwater which then will become contaminated Chemicals in drinking water can cause serious damage to health failure of body functions and deformations Sun or shade While drillers may prefer to drill in the shade it is NOT the best location for a well A lot of people will visit the well to fetch water unaware that harmful pathogens are traveling on the soles of their feet For example the bacteria can be picked from street refuse or from a latrine if someone has just been to the toilet These contaminants will be washed off the feet in the well surrounding which is often wet These contamin
53. omes equal to the earlier measured rest water level This will take from several hours up to one day and re test at a lower flow rate When only a small flow rate less than the estimated flow rate of the pump to be installed can be maintained the well is not successful Together with the owner and sometimes the donor a decision should be taken on what to do next Yield test with hand pumps Step 1 Before the yield test takes place it is very important to measure the rest water level in the well When measuring use a fixed reference point for instance the top of the well casing To measure the water level a measuring rope can be made Water level measuring tape or measuring rope Take a 6 cm long piece of 4 inch galvanized pipe Close one end by welding and weld an eye on top of it Attach the eye to a rope which is knotted every meter like the measuring rope used for checking backfilling Move this tool up and downward when it is lowered in the well When the galvanized pipe touches the water level a plopping sound can be heard Count the knots to measure the depth Step 2 Water level measuring rope Install the hand pump and pump at a steady rate maximum flow rate for as long asZpossible Ask the villagers users to assist Pump at a steady flow rate Don t start too enthusiastic and don t stop not even for a few minutes in between Continue pumping for 4 hours and measure every hour the flow rate with a bucket and stopwatch
54. ot harmful safe for drinking However it may give some problems while washing your clothes Soap lathers gives foam easily in soft water but not in hard water In other words if the hardness of the water is high it may be difficult to use soap 2 ________ PRACTICA Foundation Manual drilling series Understanding Groundwater amp Wells in manual drilling o HYGIENE IN RELATION TO GEOLOGY 3 1 SITE SELECTION Before the drilling of a new well starts a good drilling site has to be found In most cases the villagers or owner of the new well will point out a location which is suitable for them as users But this may NOT necessarily be the best location to get the best quality of water As a professional driller you will have the responsibility to inform your clients about hygiene and the most hygienic location for the well There are two important aspects to keep in mind The presence of sources of pollution such as latrines waste dump areas fire places and fuel stations Sun or shade at the location of the well Latrines Some people may find it practical to have their well constructed close to their house or latrine Unfortunately in doing so they may not realize that a well close to a latrine could be contaminated with micro organisms such as bacteria viruses and parasites Some of these organisms can cause disease like diarrhea when the water is used for drinking and are called pathogens The pathogens fr
55. outer diameter of the PVC well casing par 6 2 For the diameter of the borehole it is important to realize the following The drilled diameter of the borehole should be at least 2 inch larger than the outer diameter of the PVC well casing to be able to place the grave pack and sanitary seal If this rule is not applied and the space between the PVC well casing and the borehole wall is too small it is almost impossible to place the gravel pack and sanitary seal at the correct depth Furthermore the backfill may get stuck on its way down this is called bridging and end up in the wrong position Borehole depth When the final depth for the bottom of the well screen in the aquifer is reached par 4 3 an additional two meter should be drilled This is to allow for fine soil particles suspended mixed with the water in the borehole to settle prior to and during the installation of the well screen and casing by doing so the determined well screen depth can be maintained and to accommodate a sump par 4 5 Completion of the borehole Finally before the drilling pipes are lifted the fluid drilled borehole should be flushed with clean water to remove all fine particles that are suspended in the hole If this is not done the particles will settle at the bottom of the well influencing the final installation depth or enter the well screen during the installation of the well casing already filling up the sump par 4 5 and 6 2
56. pes i e permeable low permeable and impermeable will therefore simplify determination of the exact location for the well screen and annular backfill To resume filling in the drilling logs is a 4 step process Describe the samples and depth 2 Indicate permeable and impermeable layers 3 Mark the casing screen and sump in the column PVC pipe 4 Mark the backfilling and sanitary seal s in the column backfill Groundwater level Whena borehole is drilled dry meaning without the use of drilling fluid the depth of the water table can easily be determined during drilling The soil that comes out during drilling will be wet when the groundwater level is reached With a fluid drilled borehole see chapter 5 the borehole is kept full of water to maintain water pressure In such cases the groundwater level will not always be known from the hole drilled It then can help to have local people indicate where the water table is likely to be on the basis of a hand dug well other completed boreholes or river in the neighborhood In an area which is new to the drilling team it is advised to drill the first well to the maximum possible depth in a good aquifer and measure and record the water level after the well construction 4 5 DETERMINE THE DEPTH OF THE W ELL SCREEN AND BACKFILLING Once the soil descriptions are hatched on the drilling log the visible information can be used to determine the exact depth of the well screen
57. pressure in the casing and well screen should then be created by adding a plunger or surge block or simply a plug of cloth which is then moved up and down in the casing Repeat this process until the water directly flows away when added Continue flushing with clean water until the water which is coming out of the borehole is clean Only then the gravel pack should be installed Step 4 Installation of the gravel pack The gravel pack is now poured in the annular space around the pipe At the same time the PVC pipe is moved from side to side to guarantee an easy passage for the gravel down to the screen Pour in the gravel slowly to prevent bridging gravel getting stuck at the wrong level Use the measurement tape or tool to measure the depth to the top of the gravel and fill to 1 2 meter above the top of the well screen par 4 5 In fluid drilled holes water will overflow from the PVC casing pipe as the gravel is dropped around the well screen Water will stop overflowing the PVC casing pipe when the entire length of the well screen has been backfilled Pouring gravel in the borehole water will overflow the pipe PRACTICA Foundation Manual drilling series Understanding Groundwater amp Wells in manual drilling Backfilling has finished The top of the pipe is protected Step 8 Well development See chapter 7 Step 5 Installation of the sanitary seal When the gravel pack has settled to the right depth always measure
58. pumping can only be done when the groundwater level has returned to normal after the well development The well should rest for at least 24 hours after development before test pumping is started There are two ways of testing the well yield use of electrical deep well or motorized pumps or use of hand operated pumps Dip tape In both cases the water level should be measured For mechanized pumping tests this can be done by using a relatively expensive electrical dip tape which produces an electrical signal when the water level is reached see photo For low cost pumping test with hand operated pumps a simple measuring tape or self Electrical dip tape made measuring rope can be used Yield test with motorized or deep well pumps Step 1 Before the yield test starts it is very important to measure the water level in the well This level is called the rest level or static level When measuring use a fixed reference point for instance the top of the well casing Step 2 Insert the pump or suction hose for the motor pump at a maximum depth of 1 meter above the well screen Step 3 Start pumping initially at a minimal flow rate for example 0 2 or 0 5 m h Measure with bucket and stopwatch and write down the flow rate and monitor the water level during pumping Continue pumping at the same flow rate until the water level stabilizes Note down the water level flow rate and time The difference between the rest water level before
59. que and in greater detail the ROTA sludge technique It is a combination of sludging and percussion and is particularly useful due to its versatile application for a range of soil formations Manual Understanding Groundwater and Wells in manual drilling The manual Understanding Groundwater amp Wells in manual drilling complements the 4 technical training handbooks and highlights those essential subjects which are relevant to manual drilling geo hydrology hygiene well installation and well development in practice in simple and understandable language PRACTICA Foundation Manual drilling series Table of contents Introduction Making a well The Manual Additional information 1 BASIC GEOLOGY 1 1 Geology 1 2 Manual drilling techniques Hand augers Sludge Rota sludge Jetting Percussion and bailer other techniques 1 3 Soil classification and determination Permeability Field tricks Porosity Turbidity 2 HYDROLOGY 2 1 Hydrology 2 2 Groundwater flow 2 3 Aquifers 2 4 Sea water intrusion 2 5 Salt iron and minerals 3 HYGIENE IN RELATION TO GEOLOGY 3 1 Site selection Latrines Waste dump areas fire places and fuel stations Sun or shade 3 2 Migration of pathogens bacteria Different aguifers One aguifer 3 3 Sanitary seal NO MO MO MW CONNOWOaAAA KR KR W W 10 1 1 4 DRILLING LOGS 4 4 2 4 3 4 4 4 5 Why drilling logs Taking soil samples Drilling depths Fil
60. raveling time the pathogens die off over time from the surface to the filter screen 8 Bacteria migration in one aquifer and the borehole 9 Bacteria migration in one aquifer with installed well and sanitary seal PRACTICA Foundation Manual drilling series Understanding Groundwater amp Wells in manual drilling 4 DRILLING LOGS 4 1 WHY DRILLING LOGS In chapter we learned to install our well screen in a permeable layer Chapter 2 showed the existence of different aquifers In chapter 3 we have seen the necessity for the installation of a sanitary seal above the gravel pack which surrounds the well screen and or to seal off the impermeable layer above the second aquifer These are all important aspects of the construction of a well with a good yield of clear and clean water which is free of contaminants I lt is therefore very important to determine the exact location depth of permeable layers aquifers and the location of any impermeable layers in our borehole To do this simple but accurate drilling logs should be created A drilling log is a written record of the geological formations soil layers drilled according to depth Soil samples should be taken at regular depths e g every meter and described during the drilling process The soil description is then recorded in the form of a drilling log The drilling log will help us to determine 1 _ The right aquifer for installation of the well screen 2 Depth and
61. resentative water samples Well disinfection chlorination 8 FINALIZATION 8 1 Concrete slab apron 8 2 Soak pit 8 3 Pump choice GLOSSARY OF TERMS ACKNO W LEDG EM EN TS eZ 32 J2 33 33 33 34 34 95 35 35 36 36 36 36 37 40 PRACTICA Foundation Manual drilling series 41 4 4 4 4 4 PRACTICA Foundation Manual drilling series Understanding Groundwater amp Wells in manual drilling INTRODUCTION MAKING A WELL The construction of a well using manual drilling techniques is a complicated process Before drilling starts a good drilling site has to be selected where experience suggests that there will be an adequate quantity of good quality groundwater During the drilling process there are a lot of different aspects which require attention to prevent things from going wrong Besides the practical drilling skills which are executed at ground level at the same time attention has to be paid to important processes which are happening below ground level during drilling Water used in drilling working water could flow away or worse the borehole could collapse burying part of the drilling equipment And finally once the hole has been drilled the well casing screen and sanitary seals have to be installed at the right depth preventing contaminated water from entering and ensuring a sufficient yield In many countries manual drilling teams experience problems with site selection loss of wor
62. ribed and recorded on the drilling log see appendix C with the depth at which the soil sample was taken 4 3 DRILLING DEPTHS In the previous chapters we have learned to install a well screen in a permeable layer chapter 1 which is ideally an aguifer underlying an impermeable layer chapters 2 amp 3 Soil samples The f nal drilling depth is reached when at least 4 6 meter has been drilled into a water bearing permeable sand or gravel layer It is then recommended to drill two extra meters for installation of the sump see par 4 5 and 6 2 and as a reservoir for paricles in the borehole to settle down in during the well casing installation process par 6 5 Coarse sand sample PRACTICA Foundation Manual drilling series Understanding Groundwater amp Wells in manual drilling 4 4 FILLING IN THE DRILLING LOGS Step 1 Step 2 Describe samples during every break in the drilling process Then especially important for those who can not write and write down the depth name and characteristics on the hatch the formation column and show the difference drilling log see par 1 3 between permeable semi permeable and impermeable layers by different hatching Drilling log Drilling log Drawing Depth Description hard soft Color s Drawin Depth Description hard soft Color s meter of the formation fine coarse of the sample g p p s meter of the formation fine coarse ofthe sample PVC Back Format
63. rticles were deposited sediment settled down in still water for example a lake In the same way a sand or gravel layer could have been deposited The sand and gravel particles may have been transported by a river and were deposited along the river bed Although now there may not be a river or a lake present the deposition of particles could have happened thousands or even millions of years ago Another way to transport particles is by wind Particles can be blown to another location by the wind When a mixture of sand and fine particles has been compacted by pressure created by the weight of layers on top of it and cemented by minerals present in the mixture sandstone is created Sandstone is hard and may look like solid stone but is in fact consolidated sediment and may be possible to drill through These are just some basic examples It goes too far to describe the deposition of all sedimentary layers in detail The sedimentary surface layers of the earth are most important to manual drillers Especially hard layers such as sandstone compacted clay fragments of un weathered rock and laterite pose challenges to manual drilling because of their hardness 1 2 MANUAL DRILLING TECHNIQUES To drill through all these different types of formation soil a whole range of different manual drilling techniques have been developed and used around the world In each case the drilling technique must a break or cut the formation b remove the cut materi
64. s trainers and supervisors some useful titles of existing books and manuals are given at the end of this instruction manual G PRACTICA Foundation Manual drilling series Understanding Groundwater amp Wells in manual drilling I BASIC GEOLOGY 1 1 GEOLOGY Geology is the study of the earth It describes the origins and formation of the rock types under the surface of the earth The original material or building blocks of the earth are the hard rocks such as granites and volcanic formations formed when molten material cooled beneath or at the surface of the earth These are known as the igneous rocks made by fire It is from these rocks that sedimentary layers have been formed Sedimentary layers are formed by the weathering transport by wind or rivers and deposition sediment of particles broken down from rocks Those particles can range in size from extremely fine clay particles through silt sized to the larger sand and gravel particles Sedimentary layers may be unconsolidated loose such as clay and sand or consolidated cemented together to form harder rocks such as sandstones and lime stones Some examples The clay particles of the clay layer that you have encountered during drilling may have arrived from somewhere else The clay particles were formed by the weathering of rocks Then they may have been eroded and transported to your drilling location by a river or the sea Finally the clay pa
65. suction of the well see drawing Therefore in coastal areas drilling deeper will NOT always be the best option Salt water intrusion 2 5 SALT IRON AND MINERALS Besides pollution from the surface bacteria and chemicals par 3 1 or salt from the sea par 2 4 water can taste bad or be damaging to health due to natural minerals in the aquifer These minerals have been present since the formation of the different geological layers and are now dissolved in the groundwater Some well known examples of natural minerals natural chemicals in groundwater are Calcium Chloride Carbonate Arsenic Fluoride and Iron but many more exist Some minerals like Arsenic and Fluoride can damage health badly and therefore a sample of the groundwater has to be analyzed ina laboratory to find out if these chemicals are present Luckily in most places concentrations of these minerals are low and so the water is safe for drinking Some examples Salt When well water in a non coastal area tastes salty it is important to determine the origin of the salt For example if in the same area two other wells are drilled and completed at different depths deeper or shallower fresh or less salty water may be found just taste the difference between the water from the different wells Look for different colors or crystals in the soil samples these may be the origin of the salt PRACTICA Foundation Manual drilling series i Understanding Groundw
66. surge block or plunger creating shock waves through the gravel pack the fines and drilling fluid additives are washed loose from the well screen the gravel pack and the surrounding aquifer and voids in the gravel pack disappear Then the water containing the fines is pumped out A surge block consists of a set of wooden discs with rubber valves or alternatively a flexible flat seal for example made of a thick rubber sheet A surge block closely fits in the PVC casing and is operated as a plunger It is brought beneath the water level in the well Then by moving the surge block up and down water is forced into and out of the aquifer shock waves washing the aquifer and gravel pack and mobilizing the fines which they contain see drawings below Down stroke of the surge block Up stroke of the surge block PRACTICA Foundation Manual drilling series i Understanding Groundwater amp Wells in manual drilling The down stroke should be gentle not forcing the fines and fluid additives further into the aquifer The upstroke should be rapid with the result that fines and fluid additives end up in the PVC well casing which then can be cleaned by pumping see below Motorized centrifugal pump Well development by hand Re development by airlifting G PRACTICA Foundation Manual drilling series Discontinuous pumping start stop cycle pumping After the surge block is used a pump can be lowered to the bottom of
67. the impact of the drill bit loosens the soil and on the up stroke the top of the pipe is closed by hand or valve drawing up the water through the pipe and transporting the cuttings to the surface On the next down stroke the hand valve opens the top of the pipe and the water sguirts into a pit in front of the well In this pit the cuttings separate from the water and settle out while the water overflows from the pit back into the well The borehole stays open by water pressure Thickeners additives can be added to the water to prevent hole collapse and reduce loss of working water drill f uid Sludging can be used up to depths of about 35 meters Advantage easy to use and temporary casing is not needed Rota sludge Disadvantage working water has to be maintained during the drilling process The level of the water table is not known during drilling Geological application Sand silt clay stiff clay and softer consolidated rock formations weathered laterite O PRACTICA Foundation Manual drilling series Understanding Groundwater amp Wells in manual drilling JETTING is based on water circulation and water pressure As opposed to sludging water is pumped down the drilling pipes The large volume of water has an erosive effect at the bottom and the slurry water and cuttings are transported up between the drill pipe and the borehole wall A motor pump is used to achieve an adequate water flow The drill pipe
68. ual drilling Fresh cow dung It might sound dirty but fresh cow dung shares many of the advantages of natural polymers It works extremely well and is biodegradable Besides fresh cow dung is widely available in most countries and very cheap to get However there is resistance to the use of cow dung for water well drilling purposes Cow dung also contains the E coli bacteria and other animal pathogens par 7 3 The E coli bacteria is used as an indicator for the presence of fecal contamination bacteria coming from latrines that can cause human disease Studies so far have shown that cow dung indicated by Nitrates and E coli both disappear within a few weeks after the construction of the well However still more work needs to be done on the health and safety implications of the use of cow dung It is generally recommended that a newly drilled well in which cow dung has been used is not used for drinking during the first month of operation Mixing cow dung with working water Advantage Cow dung works extremely well is biodegradable cheap and widely available Disadvantage Carries animal pathogens Chlorination of the well after development and test pumping is recommended Further research in the health aspects of use of cow dung will be done shortly by the publisher of this manual Fibers and other solids To increase the effectiveness of additives in coarse sand and gravel aquifers fibers and other solids can be mixed in with
69. ues All existing manual drilling methods can be divided into four main Percussion drilling principles Hand Auger Manual Percussion Sludging and Jetting Within these four main drilling principles a wide range of variations have been developed in various countries PRACTICA Foundation Manual drilling series Understanding Groundwater amp Wells in manual drilling 1 3 SOIL CLASSIFICATION AND DETERMINATION An essential quality of a professional driller is his ability to lt 0 004 mm recognize and describe different types of soil formation material 0 004 0 06 mm encountered during drilling For the classification of the different Sand fine medium 0 06 2 mm COarse Gravel and pebbles detailed description is given in the glossary of terms in the back of Se and ponlders this manual particles in a soil sample the following table can be used a more For the construction of a good quality well it is essential to know the characteristics of different soils and their influence on the yield water discharge water quality and performance of the well In fact knowing the characteristics of the soil is even more important than to name different soils exactly itself First of all it is very important to know whether the types of soil drilled are permeable or impermeable Permeability Permeability is a measure of the ability of a soil or formation type to transmit water through it In other wor
70. until a large permeable layer sand or gravel is reached and install the entire well screen in this layer If the layer is permeable the water flow to the well will be high the yield of the well will be high In addition when the layer consists of sand and does not contain very small particles the water will be very clear not turbid PRACTICA Foundation Manual drilling series Understanding Groundwater amp Wells in manual drilling 2 HYDROLOGY 2 1 HYDROLOGY Hydrology describes the cycle of water as it rises from the sea and the earth s surface as water vapor This vapor forms clouds which fall somewhere else to the earth as rain Part of the water penetrates in the ground and becomes part of the groundwater while another part flows through streams and rivers back into the sea From here the whole cycle can start all over again For drillers it is important to know in particular about the location and movement flow direction of groundwater in permeable water bearing layers aquifers and factors affecting the quality of groundwater 2 2 GROUNDWATER FLOW Just as surface water moves ina river also groundwater flows although much slower through the pores and cracks of the formation groundwater does not stand still It is not always easy to determine the flow direction of groundwater Still it can be of great importance for the water quality of the well to know in which direction the groundwater is flowing and where the
71. y while working on drilling sites This book therefore only deals with those essential subjects which are relevant to manual drilling and well installation in practice in simple and understandable language O N ote Technical terms and the way in which subjects are explained are based on the average expected educational level of the intended users Sometimes the use of complicated geological and technical terms has been avoided to create better understanding Some words for example soil or gravel pack have been used because they are known by the intended users although these words are not always the terms that are used by geologists Please keep in mind that the objective of the handbook is to create better understanding of well drilling in practice aimed at technical workers of manual drilling teams who may have a limited educational background READERSHIP This handbook can be used as a guide during training sessions for well drillers local trainers and quality controllers It also serves as a reference for drilling supervisors NGOs development agencies manual drilling teams and enterprises during the entire drilling process The handbook consists of three sections that can be read together or used and printed separately for the various target groups SS ee PRACTICA Foundation Manual drilling series Colophon AVAILABLE MANUALS IN THIS SERIES _ __________ _ _ _ S _ _ _ SSSSSSS SSSSSSS

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4. Understanding Groundwater & Wells in Manual Drilling