This project came via the Developing Technologies (DT) website as a request from a small community group, Rural Water Aid (RWA), working in the Bo region of Sierra Leone. RWA was attempting to hand- dig wells for local villages but meeting problems in penetrating rock to reach the water table. Help was requested to develop a low-cost percussion drill in which a heavy drill bit is repeatedly raised and dropped to bore the well. This was suggested as the most appropriate approach to overcoming this problem.
The vital need for improved water supplies in developing countries to reduce deaths from water-borne diseases is well documented. In sub-Saharan Africa it is estimated that 300 million people do not have access to a clean water supply. To meet the Millennium Goal to half this by 2015 will require almost a million new wells. Sierra Leone is one of the poorest countries in the World and has one of the greatest needs for improved water supply. The project therefore has the potential to greatly improve the lives of the local target communities and also to have an impact on a wider scale.
Most wells are drilled by large commercial rigs costing £100,000 or more and require large funding. Smaller percussion drill rigs are available but cost around £15,000 with all tools. It is therefore costly to set up small enterprises for local well- drilling programmes and it appeared there was a definite niche for a low-cost rig that could be largely manufactured locally
- Manual digging is slow and well-diggers have difficulty cutting through rock – making it impossible to reach groundwater in some locations. The new technology should be faster than manual digging and able to cut through all but the hardest rock.
- To reach the full potential market, the drilling-rig would need to be sufficiently portable to reach remote areas without access by paved or engineered road surfaces. There should be an upper limit on both weight and size, and a requirement for modularity. Other rigs cannot do this.
- Finally, for an enterprise to be sustainable, the drill-rig should be maintainable using spares and metalworking techniques available in a developing country.
A local team was trained to operate the drill and they can be seen in action in Figure 3. The pick-up shown was also used for transport of the rig. An initial well was drilled to 18m depth, just about reaching the water table, but then unfortunately the tool became stuck. This is an inherent problem of percussion drills that seems to increase in risk at deeper depths and when approaching the water table and techniques need to be developed to deal with this. A common method is to use an auxiliary winch with fishing hook to link onto the tool and lift it out. However, sometimes the tool becomes so firmly stuck that the cable breaks and the tool is lost, meaning a new well has to be started. This was the case with this first well but luckily enough data was obtained to estimate the cost of drilling wells to a depth of around 20m and to plan for further work. The estimated cost of a well was £1,000 with about 40% of this for the hand- pump. This is less than half the estimated cost of a hand-dug well that would take 2 to 3 months to dig compared to 3 to 4 days for the drilled well. Also there is a significant risk that hand-dug wells might not be completed due to striking rock.
A number of tools are used in drilling wells with a percussion drill; the most useful of which being the Clay cutter which is a heavy tube with a cutting edge ground around the circumference of its bottom end. This is used as a combined cutting tool and baler in clay, the cut clay being forced up inside the tube by the impact and then lifted out of the hole and removed through a slot cut in the side of the tube. The combined action significantly increases the drilling rate in clay. For low cost and ease of manufacture in Sierra Leone the tools were made from scrap steel pipe with the weight achieved by filling the tube with scrap steel embedded in concrete. The cutting blades were cut from scrap leaf springs from a vehicle.
Some pictures showing an overview of the drill, (clockwise from top left: A-frame, pulley and drilling rig arrangement; the heavy cutting tools that are repeatedly lifted and dropped; the diesel engine and drive with motorcycle-tyre/roller clutch). The choice of site can make the difference between providing a successful, sanitary water source, and a dry hole in the ground. But after all said and done nothing is guaranteed. Factors to consider included; community involvement, sensible even for technology-testing projects. A bore-hole may not be the solution people want. Existing knowledge about ground conditions, vegetation, surrounding hills and valleys, including river beds. It is also necessary to choose an slightly elevated place so that water will run away from it. 30m from animal pen, washing slab, animal trough and 40m from pit latrines. In an area so as many people as possible can benefit, too even out walking distance.