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Boreholes: Before the earth begins to quake

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Boreholes: Before the earth begins to quake



With the rate at which boreholes are indiscriminately dug in many cities across Nigeria, major disasters are lurking ahead, ALLWELL OKPI writes

After laying the foundation of his three-bedroom flat in Abule Egba area of Lagos State, Samson Adegbe’s next concern was how to get water running from the taps in the house when completed. Like many people in his shoes, his only option was to drill a borehole.

While Adegbe’s facility is still under construction in a relatively well built up area, a mechanised borehole is already completed in the premises and it is already sucking water from scores of metres below. The trend, however, is that virtually every house in his neighbourhood has its own borehole.

For every building in Lagos and other urban areas in the country, there is at least one near hole drilled in search of water. For some, it is a shallow hand-dug well often less than 10 metres deep, while the mechanised boreholes go as deep as 50 metres or more. The failure of public water supply systems across the country, including Lagos and Abuja, has contributed to this trend. A lot of people in whose homes potable water used to run are now drilling boreholes in their homes.

James Agbayi, a surveyor who resides in Ikeja, Lagos, says boreholes are a matter of necessity.

He says, “The situation is really bad. One keeps buying water every day, and if you calculate it you will see that we spend a lot of money on water monthly. So we have decided that getting a borehole is just the best thing to do. They said water used to run in the compound; that is pipe-borne water. But since I moved into this compound almost two years ago, tap water has not run for one day.”

As a result, more and more boreholes are being sunk with the business of borehole drilling becoming more lucrative.

However, scientists have warned that the ‘culture’ is having negative impact on the earth and can make the country susceptible to natural disasters among other possible dangerous outcomes. According to Mr. Adetayo Folorunsho, a geophysicist/environmental geoscientist, who lectures at the University of Lagos, the indiscriminate sinking of boreholes in Lagos and other parts of the country could make the earth unstable and susceptible to natural disasters that include earthquake.

He said, “Look at it this way.” “You have a piece of land made up of rock unit. You pierce it on this side and you also pierce it on the other side. I’m describing it in terms of a plot of land or half a plot. You know in Lagos, people build on less than half a plot. And each individual will want to have a borehole in his house. Let’s talk of earth tremor and earthquake. If you have a rock that is together and there is a shaking, the whole will shake together and it will give whatever is on it a kind of balance. But when this one is shaking and this other one is not responding because there is a disjoint, the impact on the things on the ground is higher.”

Fractures caused by borehole blasts

According to Folorunso, the impact of an earthquake will be less disastrous in a place like Lagos, which is underlain by sedimentary rocks and loose sand, than places like Ibadan underlain by hard rock. This, he says, is because when a wave passes through a fractured hard rock, it has a more disastrous effect than when it passes through a fractured ‘soft’ rock.

“If a tremor hits a place like Ibadan, it will be disastrous, because everybody now wants to have a borehole and shallow well in their house. Nowadays in Ibadan, they try to blast the rock to make the shallow well deeper. By doing that, you are disturbing the rock unit and you are creating fracture in the underlying rock. I was in the house of my uncle in Ibadan when his neighbour was blasting the rock to make their well deeper. The blast was shaking my uncle’s house seriously. Then you can imagine the effect of those blasts on the buildings around, especially if other people in the neighbourhood do the same thing” he says.

Similarly, an Abuja-based hydrogeologist, Mr. Idris Abdullahi, who has practised mostly in the northern parts of the country, explains that the increasing number of boreholes is having diverse negative effects that are still unknown to many.

He says, “Any time you drill into the rock, whether you are looking for water or any other mineral, you fracture the rock. And some of these fractures can get to far distances. Now, if it is in an estate with buildings, the foundations of the building where the fracture will run through will be affected. The effect might not be noticeable initially but after sometime it will show.

“Somewhere in Niger State, a man was finishing his four-bedroom flat, when he noticed a big crack on the wall of his sitting room, from top to bottom. People blamed the engineer that handled the project, and said they used weak materials. But it was later discovered that there was a big fracture in the rock under the house. Although that fracture might have been there for very many years, it might have been caused by a borehole drilling activity in that neighbourhood just a few years earlier.”

Such fractures in the bedrock can affect roads and other facilities built on the ground. But another way such an exercise can affect buildings in the neighbourhood, especially in a place like Lagos, is the ‘differential settlement’ of the foundations of the buildings. Folorunso explains that when a lot of water is pumped out of the ground at a rate that is higher than the rate at which it is replenished, the ground becomes hollow. When a building is erected on it, the ground compresses over time and sometimes it can result in the collapse of the building.

In cities where most of the residential buildings have boreholes, there is excessive pumping of groundwater. And considering occurrences in different parts of the world, it has been established that when the ground water in any neighbourhood or town is indiscriminately and excessively withdrawn, over time, there will be land subsidence, which is the lowering of the land surface.

While this often happens gradually, it also can occur more rapidly resulting in the destruction of properties and, perhaps, loss of lives. In San Francisco, for instance, lowering of the land surface by 2.4metres necessitated the construction of special dams to prevent water from the Bay from invading the shore.

In Tokyo, Japan, between 1900 and 1975, it was discovered that the earth surface had lowered by 4.7 metres, with many adverse consequences on public and private infrastructure. As a result, the Water Law was established to reduce the extraction of groundwater.

According to the Technology Institute of Indonesia, in 1994 the land in Jakarta had lowered by 0.5 metre due to uncontrolled extraction of groundwater through boreholes, resulting in flooding because sea water flowed into the land and damaged buildings. Last year, it was also reported that excessive groundwater withdrawal caused severe land subsidence in the Su-Xi-Chang area of China, even though there has been restriction and prohibition on groundwater pumping since the late 1990s. In case of Su-Xi-Chang, like in some other places, there was also earth fissure, similar to the types that occur during earthquakes.

However, in all of these places, when ground water extraction was reduced, the land subsidence was minimised.

Contamination of groundwater

Another problem with indiscriminate sinking of boreholes is that the groundwater is more likely to get contaminated.

A popular case is that of Diamond Estate, in Isheri, Egbe/Idimu Local Council Development Area, Lagos State, where residents were drawing petroleum from their boreholes. The stream of petrol flowing in the neighbourhood was widely reported in January this year.

Folorunso, who made efforts to find a solution to that situation, said the problem was that the pipeline that passed through the area was vandalised some years ago and petrol had been leaking into the ground over the years but it did not contaminate the groundwater until people packed into the estate and started drilling boreholes.

“When the first few packed in and drilled there boreholes, there was no problem. They were drawing clean water, until there was massive pumping of groundwater. You know, this house is drawing water, that house is drawing and so on, and then it became massive. When there was no more water to draw, then the petrol that was stored in the sediments got drawn into the wells, because a liquid will move from an area of higher concentration to an area of lower concentration,” Folorunso says.

By the same principle, boreholes in built-up areas within almost all the buildings - can be contaminated with effluents from septic tanks and other hazardous components in the earth. Another common contamination that occurs in the coastal regions is salt-water intrusion. This is a situation where sea water is drawn into the borehole mainly as a result of too many boreholes in the area.

According to Obinna Ozoemena, a resident of Lekki Peninsula, he and his co-residents do not drink water from their boreholes because it smells and has tastes like sea water. He says they started experiencing this last year, after using the borehole for over two years.

Folorunso says apart from the huge number of boreholes, another reason for these problem is that boreholes drilling is now being handled mainly by quacks. According to him, many of the people that drill boreholes are not professionals. They don’t know anything about the earth and how water moves in the earth.

He adds, “For example, they will just drill a borehole for you just anywhere without considering the location of your septic tank or maybe a nearby refuse dump in relation with direction of groundwater flow. If you drill your borehole in a place that is lower in elevation than your septic then it will be easy for contaminants to flow into your borehole.”

Probably the greatest challenge is that there are a few or no data available about the number of holes being drilled in the country and the amount of groundwater that is being extracted, or even the rate of land subsidence over the years. This means there is no way to find out how fast the country is running to some major disasters. Worse is the fact that there are no active laws regulating the drilling of borehole in the country.

With the only alternative - pipe-borne water - seeming almost impossible to achieve, since it is not even readily available in Abuja, a city well planned and built from the scratches in the late 20th century – the solution seems far away. So, despite all the dangers, it is boreholes as usual. - Nigerian news, lifestyle news, naija, Nigeria, West Africa

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Updated 8 Years ago

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