Borehole Failure

Hand pump animation,source:wikimedia commons

In my previous article, we discussed about borehole drilling, design and procedure which can be found in this link. It is not denying that there has been issues of failed borehole systems in most part of the world, but mainly some part of Nigeria. Hence, this article will serve as a guideline in building a functional water borehole without failure. There are a lot of factors that causes borehole failure which we will be looking into in this article.

Hydrological Failure

^{^{San Andreas fault, source : wikimedia commons}}

Due to poor siting, wells may tap aquicludes (formation capable of absorbing water but do not transmit significant amount of water). This is often caused by improper predrilling investigation. Another aspect of hydrological failure is water level fluctuations. This is attributable to excessive pumping which may result in movement of the fine materials in the aquifer, with possibility of clogging near the screen, sand entrance to the well as a result of high entrance velocities which may damage the pump and acceleration of incrustation (clogging of the water bearing formation around the well bore and the screen).

High velocity near the screen may decrease the pressure, thereby reducing the ability of water to hold dissolved salts, particularly calcium carbonate in solution.

Hydrlogical failure of borehole or wells may also arise from location of a well above the lowest water level. This results in failure of borehole to pump water during periods of low flows.

Construction Failure and Others

Boreholes may fail due to poor construction, improper pump selection and installation and pipeline problems. The above factors may create problems( e.g head losses, incessant burst pipes), resulting in hydraulic inefficiency and subsequent failure.

^{^{CH057 - Track D Reception Pit-Drilling Inclinometer Borehole , source:flickr}}

Low voltages, over voltages and outright power supply failure affect the pumps.

Incompetent or unprofessional drillers failure to carry out a proper geophysical survey to delineate the underlying formation(s) and it’s extensiveness, failure to use the appropriate rig/platform, Poor or lack of supervision during the drilling process, lack of application of recommended specifications and parameters for borehole drilling, improper installations, excessive usage through over pumping and formation characteristics (not all geological materials produce water).

The other factors which contribute to borehole or well failure include increasing use of chemical fertilizers which leach out of the topsoil. The chemical properties of some water may affect lining materials. At low pH there may be electrolytic action between the unlike metals.

Information collected on drilling and well performance on 256 boreholes in the crystalline rocks of Nigeria (South western Nigeria: Lagos, Ibadan, Ilorin, Ondo etc) attributed the major cause of failure of boreholes to tapping of aquiclude. Non-penetration into the real water bearing horizon or aquifer implied that the boreholes could not pump out significant amount of water. Other factors identified include seasonal variations in water level, improper casing pump failures and blocked pipes.

The problem of improper casing is significant because of the nature of the overburden in the basement complex. The overburdened is mainly composed of fine gray clay materials. These clay materials swell by water absorption and may enter the hole where the overburdened is not properly cased. This results in the borehole producing muddy water is unfit for consumption.

Solution to Borehole Problems

Cases of siting boreholes in aquiclude can be reduced by adopting a proper geological and geophysical investigations before drilling. Construction of boreholes into water bearing horizons will minimize the influence of seasonal variation in water level on yield. Adoption of correct procedures and effective maintenance management will enhance sustainable borehole performance.

Maintenance of Boreholes

^{^{toolbox, source pixabay CC0 Creative Commons}}

The problem of incrustation may be solved by surging the well with a plunger and causing alternating flow back and forth through the screen or in severe cases allowing hydrochloric acid to stand in the well for several hours. Vibrations as well as a series of small explosive charges exploded in sequence can force water violently in and put of the well and shake the encrustation loose. Bacterial clogging of wells is sometimes corrected by chlorination.

In case of a corroded screen or casing, the effective remedy will depend on the nature of the aquifer material. If it is unconsolidated material the well should be abandoned. If the well is in rocky stratum, a damaged casing can sometimes be withdrawn and replaced. A new case can be inserted within an old one if the well is large enough.

The maintenance of boreholes involves carrying out a monthly check on sanitation of the pump house and field, servicing of the power generators and submersible, pump motor, static water level, water quality test and the pumping rate of water.

It is very essential to conduct regular tests on technology well and monitor the performance of the pumps. Worn out parts of the pumps must be replaced promptly. Constant power supply should be ensured in order to sustain the life span of the pump.

Conclusion

The failure of a borehole can be as a result of
the reduction of water output compared to the water yield produced immediately during drilling and couldn't align with the pumping test data.
Solicit an advice from a hydro-geologist or geophysicist on selection of the borehole driller.