Boreholes are necessary in areas where a steady supply of clean water is unavailable. Boreholes are drilled for many uses including industrial, irrigation and domestic consumption.
Many Kenyan developers have opted for ground water exploitation to attract tenants or buyers to their property due to unreliable or even non-existent supply of water by local authorities.
Although borehole drilling is seen by some as complex and expensive, players in the sector paint a different picture. The entire process including surveys, actual drilling and installation of pump may cost anything from Ksh 1.2 m to 4 million or even more. Factors affecting cost include physical distance from where the drilling company is located, their pricing policies, geological characteristics of the site, extent of the hole and pump used. There are also several licensing requirements that cost money.
The process of drilling a borehole begins with a hydrogeological survey. This survey is carried out to determine such factors as groundwater levels and hydraulic characteristics. It should be done by a qualified and registered geologist.
Once the geologist is satisfied with the ground water potential, authorization to proceed is obtained from the Water Resources Management Authority (WARMA). This is followed by an Environmental Impact Assessment (EIA). If the National Environmental Management Authority (NEMA) is satisfied that the proposed drilling will not have undesirable impact on the immediate environment, the organization then issues a licence. The drilling may then commence although in some cases one may require a no-objection letter from the local water services provider.
Mobilization of equipment then follows and the actual drilling gets underway.
Steps in Drilling:
Generally, the following steps are followed. They may however differ slightly from service provider to service provider. The client may also influence some elements.
- Drilling of 11” until loose top formation and installing 9” temporary casing, then drilling 8” up to recommended depth.
- Casing: Installation of 6” casing pipe – Class – B ( 4.5mm thickness ) up to bottom. Generally ratio of plain casing and screen casing is 70:30 but depends on the hole drilled.
- Gravel Pack: Inserting 2-4mm natural gravel outside the casing and inside the open hole for artificial filtration.
- Development: This is done by air jetting until clean water emerges. Generally, this can take up to 3 hours but may vary with the hole.
- Well head Slab: This is done using cement, sand and gravel in proper ratios to prevent contamination of the hole.
- Capping: A cap is fitted over the hole until installation of pump.
- Test pumping: This is done to measure the exact yield of the borehole. The water needs to be pumped out continuously for 24 hours. It is then possible to tell the yield of the well, rest level and pumping water level. This is important in determining the size of pump to be installed. On the basis of test pump report, one can decide the pump installation depth, size of pump, motor, delivery pipe, cable, control panel, water meter and other sundries.
- Water chemical and bacteriological analysis is then done by government chemist to assess if the water is suitable for domestic/industrial use or not.
- Completion Report: A completion report is then filed with WRMA and a copy availed to the client.
