A typical 250 foot (76 meter) deep well costs about $12,000 to install but provides clean, sustainable drinking water to 500-1,500 people. The actual number of people helped by each well varies based on how productive the water bearing zone is at each well location, as well as other factors. After installing our first six wells we found that community wells on average serve about 750 people per well.
That is 4,500 total people who now have a dependable source of clean, sustainable drinking water. That is 4,500 people who can now go to school, seek out employment opportunities, and have improved health because of clean water. For $16, one person’s life is changed because they can access clean, sustainable drinking water from a community well.
Drilling and Installing Wells in Kenya
Selecting the well location
Prior to mobilizing and drilling, we first determine the best location to drill the well. This is done by conducting secondary research and through contacts in the local area that is interested in obtaining a well for their community. To ensure accuracy of information, we have local contacts gather borehole (well) logs conducted within the area. These logs contain useful information, but because boreholes can be meters to miles away from the desired well location, the data, including water depth, can be old. Because of this, once we have determined that it may be possible to install a shallow well (<250 feet deep) in an area, we conduct a hydrogeologic study for the desired location to confirm data and to comply with Kenyan law.
A hydrogeologic study must be conducted by a qualified professional. It typically consists of conducting a resistivity study or survey to understand the potential water bearing zones present at the desired well location (the depth to water in the area and the depth and thickness of potential water bearing zones), and whether any aquitards or other detrimental layers might be avoided or not penetrated. The hydrogeologic study is also required to obtain the well permit to install a well, as required by the Kenyan Water Act
Conducting the hydrogeologic study
Electrical resistivity surveying methods are widely used to determine the thickness and resistivity of layered media for the purpose of assessing groundwater potential and siting boreholes in fractured, unconfined aquifers.
Electrical resistivity is commonly used because it is efficient, cheap, and gives valuable information about the aquifer potential. Resistivity works by employing an artificial source of electricity which is introduced into the subsurface using resistivity electrodes. This technique measures vertical variations of resistivity with depth. It is also commonly known as Vertical Electrical Sounding (VES). Resistivity depends on the lithology, air content, porosity (and/or fracture density in rock), and pore water ion concentration. The electrical sounding gives information on water bearing structures and determines the vertical variation of the earth electrical properties, which can be related to the geology and hydrogeology (depth to water and abundance of water) for the area.
Traveling to the drilling location
As with any water project, nothing is simple, and this includes physically traveling to drilling locations. Although it is legal to tow a trailer-mounted drilling rig and air compressor behind our vehicle, the reality is that it is a huge challenge. This is because it allows excessive scrutiny at checkpoints on the way to a drilling location, allowing each officer to determine whether the trailer is “fit and [in] proper condition for the purpose for which it is intended”. This often results in delays, fines, and other fees. Instead, we use a flatbed truck with a crane to load, and once at the destination, unload the drilling rig and air compressor and transport them to the drilling location. This transportation alone costs between $800-1,000 depending on distance to the destination. Once we drill in an area, we are able to carefully move the rig and compressor between drilling locations without problem. To optimize mobilization costs, we are currently drilling three wells in one area.
How we drill
Water For Life Charity and our partners use the BoreMaster™ 2600 drilling rig to drill boreholes by operating a down-the-hole (DTH) pneumatic air hammer with a 6-inch or 8-inch diameter drilling bit at the end of the drilling stem. The air hammer is operated using an industrial trailer-mounted air compressor capable of producing 375 cubic feet per minute (cfm) of compressed air at appropriate 125 psi.
The air hammer and drilling bit breaks down the rock formation at the bottom of the borehole as a large anvil or weight inside the air hammer is raised and then forced downward by the compressed air onto the drilling bit at a rate of a several hundred blows per minute. Borehole (i.e. drilling) cuttings are removed by continuously blowing them out of the borehole at approximately 32 mph as the DTH air hammer bit penetrates the formation. The drilling stem is connected to the drilling head or swivel of the drilling rig, which is the drive train of the drilling operation. The drilling swivel rotates, but only at about 20- 30 rpm. It is not the rotation but the pulverization of the rock that advances the drilling. The rotation helps keep the borehole straight. The compressed air is pushed down through the hollow drilling stem/rods by the air compressor to the DTH hammer and drilling bit. The cuttings are then blown upward in the space between the drilling stem and the borehole to the surface where the cuttings drop out of the air. The pulverized formation is then shoveled away from the opening of the borehole during drilling.
Once the drilling rig is at the selected borehole location and is leveled with the four manual jacks, the drilling head (swivel) is raised to a sufficient height (approximately 2 meters or 6.56 feet) to allow installation of the air hammer by turning the air hammer by hand to thread it onto the swivel’s threads until it is attached and hand-tight. The “table” that is used to hold and install or remove individual drilling rods is then removed to allow the larger diameter air hammer to contact the soil at the boring location. Technicians then dig a hand-dug guide hole about 6-12 inches (15.2 cm-30.5 cm) deep where the drilling bit naturally hangs vertically from the swivel. The air hammer and drilling bit are then lowered into the prepared hand-dug guide hole. Slowly the air hammer, which is now connected to the drilling bit, rotates clockwise above the bottom of the guide hole. Technicians start and run the air compressor and continue the slow rotation of the air hammer. While they do this they very slowly lower the air hammer until it engages the soil within the guide hole and slowly advance the air hammer as it begins the hammering process and the soil is blown out of the borehole.
Once the air hammer has been advanced to below the table height, technicians stop the drilling action and reinstall the table to help keep the air hammer and drilling stem (rods) plume, or vertical. Then, they use the table and its associated fork–a wrench-like tool that fits into slots on either end of each drilling rod–to hold the air hammer and break or unscrew the connection with the swivel by reversing the swivel and rotating it counterclockwise. Technicians then raise the swivel high enough to allow the installation of a two meter (6.56 foot) long drilling rod by first threading the drilling rod by hand into the top of the air hammer, then lowering the swivel slowly into the top of the drilling rod. Lastly, the drilling rod is threaded onto the swivel shafts by slowly rotating the swivel clockwise until it is tightly secured.
Drilling then continues by removing the fork inserted into the table to allow the drilling stem (air hammer and rods) to move up and down and rotate, followed by rotating and advancing the drilling stem into the borehole while blowing out the resulting cuttings. This continues until the borehole has been advanced another two meters (6.56 feet), the slot in the top of the last drilling rod lines up with the table and fork, and the cuttings have been blown out of the borehole. Then, this process repeats.
A slight downward pressure is be maintained on the drilling stem to allow for a steady drilling penetration speed, or vertical penetration rate. Rock penetration rates of 3.3-16.4 feet (1-5 meters) per hour, depending on the hardness of the rock, are typical. In very hard rock, a drilling rate of 1-5 feet per hour (0.3-1.5 meters per hour) is expected. Caution is used to avoid excessive down pressure exerted on the drilling stem because it can result in crooked holes, bent drilling rods, and jammed drill bits. Rotation speed is slowed from 30 to 20 rpm as down pressure increases from light to high.
Two types of lubricating need to be done each time a new rod is threaded onto the drilling stem.
- The threads of the next drilling rod need to be lubricated with thread grease.
- The air hammer needs to be lubricated with air hammer oil that is poured down the inside of the drilling stem each time a new rod is added (approximately 12 ounces of oil is used for each hour of drilling)
In addition, all of the grease fittings on the drilling rig are greased at least once a day during drilling, and the swivel is greased hourly during drilling. The chain drives that raise and lower the swivel are also lubricated at least twice daily during drilling operations to ensure safety and efficiency of drilling.
Well casing installation
Typically, we drill using six-inch drilling bits to create a pilot borehole until reaching the water table and hitting water. After this we ream, or enlarge, the six inch (15.2 cm) diameter borehole to eight inches (20.3 cm) using an eight-inch drilling bit down to the water table. Once the boring is reamed, a three meter (9.8 foot) long, eight-inch diameter steel casing with two three inch by three inch tabs is welded perpendicular to the length of the casing. This is done so that when the steel casing is placed into the borehole it does not fall into the borehole and the top of the casing is approximately 20 cm (eight inches) above grade, as required by the Kenyan Water Act guidelines. Six-inch (152 mm or 15.2 cm) PVC well casing is then installed through the steel casing to the bottom of the borehole.
Typical well casing comes with one flared bell end and one straight pipe end that come in either three-meter (9.8 foot) or six-meter (19.7 foot) lengths. PVC solvent welding techniques are used to glue/weld the pipes together. It is important to install the casing with the bell end up so that the smooth part of the coupler or connection is facing into the borehole to help reduce the chances of the connectors hanging up on the surface of the borehole.
Two well casing clamps are generally used to prevent losing the well casing down the borehole. One clamp is placed on the casing suspended in the borehole and the other clamp is placed on the length of casing to be joined to the casing in the borehole. There are two basic styles of clamps and both are used as appropriate to hold onto the casing during the construction of a well.
The first is a clamp that fastens to the casing with a mechanical clamping or vise-like mechanism. The other supports the well casing by the couplers but does not actually clamp onto the pipe. This type of “clamp” is known as a casing elevator. As long as there is a coupler above the casing elevator, the casing cannot be dropped down the borehole. Pipe wrenches can be used to support and/or lower the well casing at times but are not relied on for clamping the well casing to prevent it from going down the borehole and being lost.
The drilling head (swivel) can be utilized to lower the casing into place by attaching the chains of the clamp to it. One at a time we wipe clean and use PVC solvent primer and PVC solvent cement to glue/weld the well casing pipes together and lower the well string into the borehole. We then continue to add and lower casing until the well casing reaches the bottom of the borehole.
Once the casing is at the borehole bottom, the top is cut off if it sticks above the steel casing. The next step is to mix one 50-gallon batch of neat cement grout using six gallons (22.8 liters) of water for every 94-pound (42.6 Kg) bag of Portland cement. The grout is then carefully poured down the borehole on the outside of the casing and is left overnight to seal and plug the lower portion of the well casing to minimize the amount of grout at the bottom of the casing. Approximately 0.8 gallons (three liters) of grout are needed to seal the outside of the casing to the borehole wall, or the annular space. Grout is then mixed up to fill the annular space for the remainder of the borehole. Care must be taken in this step to not grout more than 100 feet of annular space without allowing the previous batch of grout to harden. This can lead to pressure issues from grout outside of the PVC casing, potentially leading to the collapsing of the casing and ruining the well.
Completing well drilling
After allowing the cement to harden, we continue to drill through the well casing using a 4- 5.875-inch (10.2 or 14.9 cm) DTH air hammer system for a typical open borehole well. An open borehole well is just that: the well is completed below the water table without any casing, well screen to allow the water to enter the well, or gravel pack to allow water to enter the well screen. Instead this well uses the borehole itself as the well screen and gravel pack. The advantage of this type of well completion is that it allows the well to be deepened in the future if the well goes dry due to water dropping too low to allow for continued operation of the well pump.
A fully-cased well cannot be deepened and a new well would need to be drilled and installed in this water scenario. The disadvantage of an open borehole well is that a rock could fall into the well from the boring wall and prevent the pump from being removed for servicing.
Drilling is typically continued until sufficient water is produced by the well. This is at least one gallon per minute (gpm) but hopefully greater than three gpm, or until the drilling rig’s capabilities are exhausted at about 242 feet (74 meters). The best practice is to have more than 50 feet (15.2 meters) of well below where water was first struck in the boring. Water often rises above the depth it was first struck, but the bedrock above the struck depth does not produce the water.
A one gpm well can help approximately 200 people each day to have clean sustainable water, whereas a three gpm well can help about 600 people per day
Well development and testing
Once well drilling is completed, the well must be developed. Well development involves removing the remaining drilling cuttings in the well and any sediment that may have been forced into the rock during drilling. Typically this is accomplished by using high pressure air to blow out the sediment and water until the water blowing out of the well is clear.
Once the well is properly developed, a pumping test is completed to determine the sustainable yield (approximately 60% of the absolute yield) of the well, or the highest rate at which the well should be pumped based on continuous usage. Without following this, a well can be over utilized and depleted. It is also required by the Kenyan Water Act.
To perform this pumping test, we blow all water out of the well using an air compressor and quickly use our water level indicator (a probe attached to a spool of measuring tape with dual conductor wire such that when the probe contacts water, the circuit is closed and a light and audible buzzer activates) to take rapid measurements of the rising water level in the well compared to the time it returns to the non-pumping water level. The sustainable yield is calculated using a spreadsheet using available or estimated values for the physical and hydrogeologic conditions of the well and bedrock formation.
Pump and tank installation
Typically, the type of pump that is installed at a well location is selected before drilling based on several factors. These include cost, electricity availability, and estimated production rate of the well.
Electric submersible pump
- These pumps are great, lower-cost options where electricity is readily available. We typically use Grundfos brand model 15 SQ15-290 2.5 Hp (2.46 kW) pumps, which are capable of pumping at 10-15 gpm from depths of up to 290 feet (88 meters).
- Where electricity is not readily available, we may install hand pumps. However, hand pumps are more expensive and require more operation and maintenance.
- To offset maintenance costs with hand pumps, we can install SUNFLO-B 1000C solar pumps. This is a solution that has been recommended by a local drilling contractor we often partner with in Kenya. While maintenance is extremely limited and there is no additional electric cost,solar pumps are the most expensive option. This is, however, the most requested well option by locals. The other challenge is that the typical pump required due to the depth of the wells we install only produce at about 3.5 gpm and only operate about 8-9 hours (when solar availability is ideal). In order to increase this water flow rate, the cost per well increases significantly. This is one reason why electric pumps maximize the water available to the overall community.
Because of the high efficiency of electric pumps, they are often a great option to serve larger communities. The challenge with this is coming up with a mechanism to collect a small fee from each person benefiting from the well to collect the approximate $4 per day in electrical costs. For a typical well, the electrical usage fee would be about $2-4 per person per year or half to one cent per day, which is very affordable even for the average Kenyan. The Kenyan government also suggests that each person should be willing to pay $5 per person per year to have water. However, communities we have worked with have also communicated that they are unable to pay these fees.
Once the type of pump is determined due to local needs and is installed, an electrician then comes to set up the pump to make sure the connections are waterproof and up to local code, including the installation of the electric meter for the electric pump.
To make sure our support and efforts can benefit as many families and communities as possible and to help communities take ownership of their water project, our agreement with local communities is that they provide a tank (typically holding 5,000-10,000 liters [1,300-2,600 gallons]) and a raised (about 18 inches high) tank pad to hold the water from the well, which will have spigots attached to it to allow dispensing of the water into people’s containers.
Water well cost
The typical 250-foot well costs about $12,000 to install. This is based on the installation of a solar pump; however, there could be a slight cost savings (about $800) if an electric pump is installed and electricity is available immediately adjacent to the well location.