Boreholes are essential for modern water supply systems. Used for centuries, they allow water to be obtained from otherwise inaccessible supplies. Water pumps are used to force the fluid in a borehole to the surface. How are contemporary boreholes designed and constructed?
Modern Borehole Designs
Firstly, the hydrogeology of a site is surveyed. Principal among the data that is needed from a survey is the depth of the target water source. Only when this is estimated can the borehole be designed. Commercial borehole systems usually include grouted steel casing at the top to provide a degree of sanitation for the water. This is because it is important to prevent lower quality surface water which may be dirty from mixing with any water derived from bore pumps.
Under the top-layer casing, a borehole can be either unlined, also known as an open hole approach, or lined. Two factors affect whether one approach is taken over another. The first is how stable the borehole is likely to be, and the second is the nature of the target water formation. Where earth might pollute the water, a further casing is commonly part of the design.
The final part of a design stage assesses which drilling methods will be used. A number of commercial materials can be used for drilling a borehole, so makers don't need to stick to certain drilling products only. Depending on the depth and the type of geology that is expected, either more or less robust drilling methods will be used. There is always a balance to be struck between efficient drilling and using the least costly materials.
Borehole Construction Techniques
During the construction phase of a new borehole, drilling is conducted over two stages. The first of these two is when the permanent casing at the top of the borehole is installed. Only after this is the second drilling stage carried out to reach the completion depth at the water source. In situations where the geology may throw up unexpected problems, a field geologist is commonly employed to be on site. They assist contractors in determining the exact position of linings and, ultimately, the depth of the borehole.
After the drilling has been completed, a process of acidifying or surging may be conducted. These methods are used to improve the yield of the borehole by helping it to operate efficiently for years to come. Among borehole contracting firms, this part of construction is known as development.
Where a well screen or lining has been used, a process of back filling behind it is needed. This is commonly done by pouring sand in or using gravel to act as a formation stabiliser. Whichever material is chosen, the purpose is to make the borehole stable and to avoid future damage from forces at play deep beneath the ground. In some cases, a filter pack will also be fitted to prevent fine particles, such as sand, from entering the water supply.