In my last post, I wrote about one of the ways through which we get #water for our domestic use here in Nigeria in the absence of government-provided pipe-borne water. I discussed extensively, with original pictures from a real-life experience, how #waterwells are manually dug with rings installed in order to get the water up to some standards. Today, I will be talking about how mechanical boreholes are dug from a real-life experience as well.
I said in my last post how digging mechanical #boreholes is more expensive than digging manual water wells. However, while manual wells might be cheaper, they simply do not work for all land terrains. Since they are manually dug, there is a limit to the depth that the diggers can go. Thus, digging manual wells in places with stony terrain or deep water tables is a huge waste of time and resources as the water levels will never be reached. Only mechanically dug boreholes can work in this case.
The first step in digging a #mechanicalborehole would be to carry out a survey of the land on which the borehole is to be sunk. This time, unlike manually dug wells, the survey is not just done arbitrarily based on experience. Professionals bring the necessary machines and equipment to test the soil of the site and locate the best point to maximize water source and minimize depth. Survey alone costs about $50 or twenty thousand Nigerian naira.
Analysis and results of surveying take about a week to be ready depending on how busy the surveyors are. The depth at which adequate water would be reached is recommended in the report and from this, the total cost for mechanical digging and the materials needed to sink the borehole is calculated. The current digging rate per meter varies between $8 to $10 or four to five thousand Nigerian naira.
Apart from the cost of digging, the type of soil in an area where a mechanical borehole is to be sunk determines if an extra cost would be incurred through the purchasing of pipes. According to the professionals I interviewed, an area with loose soil is said to have an overlay and will require pipes to prevent soil from removing and going into the water well. This can contaminate or block water channels and prevent the longevity of the borehole. Some soils have just a few meters of overlay while some will require pipe deep down into the well.
Surveying can be outsourced to any company, but preferably, the firm that is going to dig the borehole is best given the job so as to limit the chances of 'fake' survey reports. A good survey report should have, at least, 90 percent accuracy as far as the proposed water level is concerned. Asking a digging firm to dig a borehole based on a survey report generated by another firm might cause serious confusion and lead to more costs for the owner.
For example, a neighbour of mine outsourced his surveying to a firm and awarded the digging to another firm. The depth recommended by the surveying firm was dug and the water level was not reached. Since he was not financially prepared to pay for more depth to be dug in order to reach water, the whole exercise ended up being a white elephant project.
The digging process
The digging team along with their trucks came in around 10:00 am local time. with one truck having the #drillingrig attached while another truck carried the #drillingbits.
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The drilling commenced almost immediately with the drill bits being fixed unto the drilling machine one after the other. Each drilling bit is 5 meters. Hence, the drilling machine signals at every 5-meter depth, and a new drilling bit is fixed to it.
In this case, the survey recommended a depth of 100 meters. Thus, a total of, at least, 20 drilling bits are needed. More drilling bits were, however, brought to take care of any error margin.
After drilling up to 100 meters, no signs of water were seen. Fortunately, the owner was around to assure them of augmenting the payment to cater for any other additional depth drilled as long as the water level is reached. Thus, an additional 15 meters (3 drilling bits) were added to the well before the drilling was put to a halt. Still, no sign of water.
At this point, the project owner became worrisome but the leader of the team that came to drill assured him that water will come unfailingly. The owner was worried because there have been cases of mechanically drilled boreholes not getting water even after 100s of meters had been drilled.
The team lead explained that the pressure in the borehole during drilling often prevents water from coming immediately. This is why after drilling to some meters above the recommended depth by the survey, a resting period of about 10 to 20 minutes is required to know if the water level has been reached. In some extreme cases, water springs out from boreholes days after drilling and abandoning without any hope of water.
After waiting for like 10 minutes, drilling resumed and as predicted, it took only a few seconds for the water to gush out from the drilling bit. At this point, the operation was declared successful and finishing touches were put to the whole process. The drilling bits were removed one after the other and thick pipes were used to prevent the overlay regions from collapsing into the borehole.
It was my first time witnessing a mechanical borehole drilling process and it was an interesting and very educative encounter. I also learned that irrespective of how high the water table of a terrain is, the minimum depth that is drilled by the firm is 50 meters. Whether this is a firm-specific policy or a kind of rule is what I am yet to know.
