“The mystery of language was revealed to me. I knew then that 'W-A-T-E-R' meant the wonderful cool something that was flowing over my hand. That living word awakened my soul, gave it light, joy, set it free.”
~ Helen Keller, The Story of My Life~
Water is essential…but if there is no water and a well is to be dug or drilled, the first question to ask is, “How shall we sink the well?” The type of well a project chooses to sink depends on many factors: soil type, project cost, available technology, well depth, time requirements, community involvement and community economic strength. Some well projects use community members to complete the project, while others rely heavily on expert help and guidance. This expert help or the added cost of tricky soil types can add to project cost and strain the community’s coffers. Another factor for consideration is the method by which water is brought to the surface. Let’s start by looking at the various methods that can be used to dig a well.
Hand-dug Wells
Hand-dug wells are only suitable in areas where the ground will allow it and the supply of water is able to replenish itself. Soils such as clay, sand and gravel are ideal for hand-dug wells, as they often contain the least natural obstacles. Globally, projects commonly use either local expert diggers, or the community members themselves. The depth of hand-dug wells can be anywhere from 5 meters (shallow) to more than 20 meters (deep). In many cases, however, hand-dug wells aren't suitable when the water table is below 6 meters, or when a hand pump will be used with the well.
Hand-dug wells are normally 1.5 meters in diameter at the time of digging, which allows enough room for a digger to complete the work and still be a practical dimension after lining. For safety reasons, a hand-dug well has to be well supported during work. After construction, hand-dug wells are traditionally plugged with gravel in order to keep silt and sediment from intruding and covered with a concrete slab to protect against contaminants.
Hand-dug wells provide more water than tube wells, but are time consuming. When it is time to draw water from the well, it can be done by a rope pulley system (rope on a bucket) or by installing a hand pump. Once a hand-dug well is completed, it's important that the community be able to protect the well and the rope and pump mechanisms from contamination.
Tube wells and Boreholes
Other commonly used wells are tube wells and boreholes.
Tube wells are relatively fast to sink, don't need as much lining and are safer to construct. During sinking, a borehole has to be watched carefully by at least two trained individuals in order to maintain quality and avoid construction issues. When planning a borehole, a fair bit of time and energy goes into finding a water source that is worth the added expense that is required. However, boreholes are well suited to areas where hard rock is common or the water table is low.
Tube wells and boreholes require the use of a hand pump, which actually helps to protect the well from the types of contamination common with a rope and bucket style collection system. Tube wells and boreholes with hand pumps may be used in places where water must be accessed at a deep level from an aquifer.
Drilling a well
There are a number of different methods that can be used to drill a well and the technique used depends on a number of factors, the most obvious being the makeup of the soil (rocky or not) and the availability of water to aid in the drilling process. Each method has its own advantages and disadvantages. The simplest forms of drilling are auguring and sludging.
- Auguring cuts away at the soil using a circular motion. The discarded soil is driven up into the machine’s body and requires frequent emptying. It is inexpensive and simple to maintain, but it's also slow, requires water to carry out and is prone to problems should the workers encounter a stubborn rock.
- Sludging is a process involving driving a bore pipe into the ground using an up-down movement. Commonly used to sink tube wells that are small in diameter, sludging can take advantage of locally produced equipment, which is often low-cost and simple to use. Sludging is common is delta areas and river plains. It also demands water in order to drill in a “dry hole” and is much more difficult to carry out if well-formed rock formations are present in the drill field. A simple adjustment to the boring pipe can be made to break through the obstruction field, but it does require removing the bore pipe in order to avoid damage.
While the simplest form of drilling is often preferred, conditions sometimes require a more complicated approach, such as rotary-percussion drilling, rotary drilling with flush, jetting and percussion drilling. In order to break through most rock types, rotary-percussion or rotary drilling with flush are needed.
- Rotary-percussion drilling drives compressed air down the well shaft, pulverizing any rocks in its path. Rotary-percussion drilling is often used when it is expected that the diggers will encounter very hard rock.
- Rotary drilling with flush utilizes a rotating drill pipe and bit while also driving air, mud and water down the shaft to clear away blasted rock and debris up to 40m down. The debris used also helps to reinforce the shaft.
While rotary-percussion drilling and rotary drilling with flush are both fast and can be done above and below the water table, they are also much more expensive than other drilling types and require precise operation and maintenance.
- Jetting is less demanding of expertise, but requires water to function, is weak against rock formations and only suitable in the same areas where hand digging is ideal.
- Percussion drilling is less demanding of expertise and can take on large rocks fairly well, but is slow and drilling can still grind to a halt if the drillers encounter a difficult area full of rocks. Additionally, percussion drilling can also require water for the drilling process if they are digging into a “dry hole”.
Drawing Water
When discussing the various methods for drilling, handpumps play an important role. How the water is brought to the surface is crucial to a well's success. In many cases, access to water is done through a simple bucket-rope pulley system. Water being drawn from a well for human consumption can be much safer if a simple hand pump is installed. The type of pump used is directly related to the depth of the well. Here are some basic facts about the some of the pumps that can be used:
- Suction Pump (0-7m) - most commonly used hand pump because they are inexpensive. Suction pump seals can become dried out. If the dry seal is not replaced, water contamination can occur.
- Direct Action Pump (0-15m) - also fairly inexpensive compared to high lift pumps. Direct action pumps depend on operator strength to draw a column of water to the surface.
- High Lift Pump (0-45m) - designed to make it easier for the operator to draw water. Special components are required in order to compensate for the stress of drawing water to the surface.
- Diaphragm Pump (deep well pump) - uses a flexible diaphragm accompanied by a foot pedal to draw water. The use of a foot pedal greatly eases water drawing. The diaphragms need to be replaced fairly often and are expensive. This expense alone can undermine the economic sustainability of the well project since replacement costs are often far above what a community can afford.
Kara Fairchild
Environment Team, co-chair
Source: WaterAid: Technology Notes, www.wateraid.org
Images: WaterAid, Arkansas Valley Drilling