Fate Tectonics

Recently, my office decided to go deeper in search of groundwater. This is in Coimbatore and the existing borewell had been yielding water at 200 feet. Now the water table has fallen and they had to go down to 436 feet. Excessive drawdown, lack of rains, and overall poor water management has contributed to this.

Here are a few images of the drilling work:

 

Another sad story of a child who fell into a borewell and died.

Oh dear how many such gory deaths?

Okay most of the cases of children falling into borewells seem to occur in rural India. This says something about the borewell diameters. In the cities, borewells are dug for domestic purposes. These are lesser in diameter. So looks like the bigger borewells are the problem. Some manufacturing companies too dig large-diameter borewells. These might be typically located in the villages or suburbs.

However, this is not the primary reason – in the villages, people constantly seek groundwater. The moment a farm or company needs water, they try to dig a well. However, open wells are not always the solution (open wells are dug when you have groundwater available easily at shallow depths. Open wells are convenient. But then groundwater is not easily available – thus borewells are dug to a greater depth. Also companies need more water and wells won’t suffice).

People need water and where does that come from? River or lake water supplies is not always available to all areas. Thus, groundwater is the source. And people dig to great depths to get groundwater. Groundwater for various reasons – summer, over exploitation, less recharge etc at times goes down deeper (water table).

However, many of the borewells do not yield water and are “abandoned”. The driller might have used casing and partially sealed the hole. Mostly, though the moment there is no water, the drillers pack up and leave. Vegetation takes over and these borewells are forgotten.

Some day a child wanders over and falls. in. The diameter is enough for the child to fall in. However, it takes time to realize that the lost child could have fallen into the borewell.

The inside of the now defunct or not used borewell might have collapsed. Some bores are 300 feet deep (or more). The child might not always fall to the bottom but get stuck in the mud in between. This is not easy to find out as the hole is dark and deep. It is not a case of just pulling out the child through a vertical shaft.

So rescue operations begin and if the child is closer to the surface, a rescuer gets in and pulls them out. However, if the child has fallen to greater depths, a camera is sent into the hole and then a parallel bore is dug. From there another horizontal bore is dug. Quiet often the rescue succeeds but not always. A lot of Geology is involved and rescue plans must be fast and precise. But even with the best geophysical instruments, it is not easy to estimate the type and size of rock that blocks access to the point where the child is stuck. Moreover, drilling through rock can make the entire borewell collapse.

The simplest solution should be to seal all the holes the moment they are not used. Sadly, this negligence and ineptitude devours a child.

 

In Rameswaram, an Island on the South east coast of India, there is a well some distance into the sea that provides water which is not salty and can be drunk. This is  a holy place and according to Hindu mythology Lord Rama shot an arrow into the sea to get water to drink for his wife Sita. This is known as the Villundi Tīrtham well.  How is it possible that you get non-salty water amid the sea water?

The Earth has Oceans which occur in “basins”. Continents, that is land we live on, is higher than the water level in the Oceans. (If you are keen for more, read about Isostasy.)

On land, groundwater occurs beneath the surface in what geologists call as Aquifers. Aquifers are geologic formations that can store and transmit water. Note that geologic formations are rock strata that have similar properties (for example rocks of a certain chemical and mineral nature is one such property). These have been deposited over millions of years (if you are interested read about stratigraphy, erosion, landforms, geologic time, etc).

Under some instances water gets collected from rain, rivers, and other sources and is stored underground in aquifers.

Aquifers constantly interact with other water sources, atmosphere, and is governed by forces such as pressure and gravity. The geologic formations too determine the aquifer’s nature – porosity, permeability, storage capacity, etc.

Groundwater near the coast interacts with the sea water too. The figure (source: Solinst) shows theoretically how groundwater exists. In reality though it is very complex.

Groundwater is recharged by rain and lakes or rivers. Thus Groundwater is not stagnant and flows. The flow is described by Darcy’s law which in simple terms means “groundwater flows depending on pressure and the length of the aquifer medium”. This pressure is the reason we are able to dig wells. This is often the capillary pressure.

Groundwater can be confined within strata and be under pressure. Or it may not have a confining layer and could be seen close to the surface.

The level to which groundwater can raise is the water table. Of course this is only for groundwater that is not confined by impervious or semi impervious strata. The potentiomentric surface is used to describe the water table level.

On the coasts, groundwater exists in “dynamic and often transient equilibrium” with sea water. Sea water is denser and filtrates into the ground beneath the sea and on to the land.

Groundwater should flow – discharge into the sea – as long as the water table level is at a higher pressure gradient. Sea water in turn will try to flow in and contaminate the fresh groundwater. There is a seawater-freshwater interface (not a sharp line!) that is transient and keeps changing with rainfall, river or lake discharge, tides and evaporation.

If humans pump out water from the coastal areas, sea water intrudes the fresher groundwater. The Gyben-Herzberg equation governs the fresher groundwater aquifer-sea water interface. For every feet of water on the surface, some 40 feet of groundwater exists below sea level.

So what does it have to do with this freshwater well in the sea? If you dig a well in the sea you expect to get saline water. Yet, the well provides drinkable water because of these possible scenarios:- the freshwater-sea water interface extends far into the sea even beneath the waves. Highly unlikely as the water table pressure would need to be immensely high on the land!
– there is submarine discharge of groundwater from a confined aquifer beneath the sea at this place. The strata confining the aquifer prevents water from seeping out on the land side but there is a hidden interface on the sea side.This is possible.
– maybe seawater has “transgressed” only on the surface and below the surface is stopped from infiltering by impervious formations.

So this must be some kind of mix of these situations. The sea water here is pretty static – no waves in sight. Modeling coastal aquifers is a major headache. On Islands, the Fetter analytical solution applies better. I will not describe that here.

Usually, salt water intrusion into coastal aquifers is due to:

– lateral movement of salt water from the sea due to heavy water loss (withdrawals by humans) from the coastal aquifers
– “Saline zones” deep in the interface move up to cause “upconing” near coastal pumping wells

So is it possible? Yes. Fresh water is less denser than salt water and “floats” on salt water. This is important when you bore into the groundwater in islands. Rain water percolates into the ground and pushes the salt water beneath it. So you need to model the interface where freshwater and saltwater mix and take care not to disturb this by puncturing into sea water (when you drill).

Here is a citation that explains why this well gives freshwater:

“This natural movement of fresh water towards the sea prevents salt water from entering freshwater coastal aquifers (Barlow, 2003).”

Similar examples exist at Cuba and the Gulf of Mexico.

There are 22 wells in the Rameswaram temple – on a shallow coastal aquifer (unconfined) and close to the sea. The dissolved solids vary in each.

So even if shooting the arrow part is not an acceptable theory, one must note the intelligence behind these wells. There was no technology and yet, this well was predicted to yield non-salty water.

Ice formed it. Silurian-age rocks were covered by glacial ice that retreated and advanced over many cycles. Finally, the glaciers melted to leave huge volumes of water in the Great Lakes. Lake Ontario still has its annual rendezvous with ice – in winter. The lake is huge – is almost like a sea. The waves try to keep the ice at bay at Rochester…

As you move north from Bangalore (India), the landscape changes – vast areas of reddish soil dotted with plenty of trees, agricultural lands, and low hillocks now and then and…lots of forest cover. This is the Tumkur district and used to be full of nondescript towns and people leading a simple life.

Tumkur is also home to Iron ore.

Geologically speaking Tumkur is made up of rocks of Archaean Complex (Granitic Gneisses, and Schists) with some Deccan trappean and intertrappean formations.

Haematite is the most prominent iron ore in this area. The iron ore occurs within banded iron ore formations in massive, laminated, friable form.

The Cauvery and  Tungabhadra make the land fertile enough.

Iron ore is a gift of nature that brings in revenue and helps in technological advancement. However, in the name of mining, there has been exploitation. This has two aspects: 1. the country has been denied money from its own resources with some individuals resorting to fraud and 2. the environment has been severely affected as all norms have been flouted.

The mining scam as it has been called by the media has rocked the country. Iron ore mining was run by authorized mines and everything was fine. Suddenly after 2000, China was ready to pay for iron ore to meet its infrastructure needs. In India mining licenses meanwhile had been issued to private companies in keeping with the opening up of the economy. Some mine owners started mining and exporting a lot of Iron ore. They provided false data about the iron ore mines and the money actually they got. They bribed the right people to help their cause. This resulted in loss for the government, honest stakeholders, and people.

However, the people involved in illegal mining ranged from the top brass to the simple farmer. With the boom in mining, people started to sell their agricultural lands to mining companies. The companies would easily get a mining license and convert the agricultural land to a mining one. This dealt a blow the environment too.  Account books were cooked and mine reports had false data.

Many sold everything they had to invest in the so-called mining lands. Many millionaires were made. The money was never accounted for. Some waited too long to sell their lands and are desperate now – the losers at the end of the greed chain.

Elsewhere – to the northwest, the scenery is spectacular. The story is not. As the Arabian sea beckons, the “smell” of magnesite too seems to add to the salty air. This is the border between Goa and Karnataka. The entire karwar-shimoga belt is lovely. Here too there are mines of Iron ore and Magnesite. This area too has suffered a similar fate. I will point you to an article link in The Hindu, one of India’s leading newspapers: http://www.thehindu.com/arts/magazine/article2540038.ece

In photo: agricultural lands in Tumkur that a a farmer wants to sell as “mineable” land. Typically many people bought such lands close to mines and prepared false geochemical sheets and tried to sell their lands. Haematite ore is reddish with some “banded” striations while magnesite is black. Samples too may not be from the agricultural land that farmers sell. Samples are not always indication that ore is available in that land.