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Reviving a Failed Borewell - Detailed Query : Tirunelvelie, Tamil Nadu

Dear Experts

 

I am writing to seek the advice & suggestions of experts in retrieving my failed borewell. I have provided a detailed overview of my experience at http://www.indiawaterportal.org/ask/12636. A synopsis of the same is listed below

 

·         Location: Near Tenkasi, Tirunelveli District, Tamil Nadu

·         Foothills of the Western Ghats, I share a common boundary with the Western Ghats, the elevation of the mountains commences from the Northern boundary of our farm

·         Slopy terrain [gentle slope] from North to South, Extent of Slope from North to South – Approximately 15 Metres from highest to lowest point, spread over a distance of 620 metres

·         Ground Water survey carried out by the Geologist using an Electrostatic meter indicated good water potential at a depth of 150 feet

·         The borewell was drilled in the lowest point in the field

·         Hit hard rock at 63 feet and outer casing lodged at 63 feet

·         Borewell drilled to a depth of 450 feet

·         Water struck at 90 feet and we had very good force sufficient for a 2 inch pipe output between 110 feet to 150 feet; Drilling carried beyond 150 feet based on driller’s advice; dwindling water between 150 to 190 feet; beyond 190 feet till 450 feet we did not encounter water, and we just keep getting grey rock powder

·         We hit a single rock at 63 feet and kept going till 450 feet

·         Borewell drilling data

o   Upto 10 feet – Laterite with clay

o   10 TO 18 feet – Red Soil

o   18 – 30 feet – Highly weathered rock

o   30 – 40 feet – Weathered rock

o   40 - 50 feet – Boulders

o   50 – 120 feet – Jointed gneiss

·         Post drilling test carried out through hiring of a 5 HP motor and using an Air Compressor to check availability of water. There was no water despite trying to pump using the Air Compressor

·         We now realise that this is a locality where water is available at lower depths around 150 feet

 

I would like to seek the advice of experts in this forum for retrieval of this borewell and my queries are listed below;

 

1.      There was sufficient water between 110 to 150 feet, where has this water gone?

a.       Is the water lost to possible dry fracture openings between 150 / 190 feet downwards? I can confirm that from 190 feet onwards there was there was hardly any change in the rock layer, with a marginal change at around 400 feet]?

b.      Is there a possibility of us having hit a soft rock which is resulting in water seepage through this layer?

2.      Given that we hit water between 110 to 150 feet, is there merit in sealing / closing the borewell 150 feet or 190 feet downwards, and If yes, How should we seal it at a particular depth?

3.      There were also some suggestions on pulling out the PVC Pipe casing laid to the depth of 63 feet and creating slots in the pipe to capture potential surface level water and pushing the PVC pipe back. But I do not see merit in it as there was no water struck till 90 feet. Do the experts agree with my views of not pulling out the PVC pipe?

4.      On a different note, I would like to know about hydro fracturing, Is Hydro Fracturing relevant only for existing fractures or to create new fractures?

5.      I also read about creating rain water harvesting around the borewell to recharge the ground water and increase yield in my borewell. If yes, how can I create rainwater harvesting around the borewell, what should be the diameter and what should be the depth, and how do I create a rain water harvesting structure?

 

This is a long message with several questions. I shall appreciate the advice and suggestions of the experts in this forum

 

I look forward to hearing from you

 

Kind regards

 

KRISHNAN P S

CHENNAI

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Comments

1. Reviving a Failed Borewell -

Dear Mr KRISHNAN P S,

I remember advising  you in your earlier query it was worded differently, well any way now that you write again the answers to the queries put up by you based on what information you have given are as below.

 1.      There was sufficient water between 110 to 150 feet, where has this water gone?

a.       Is the water lost to possible dry fracture openings between 150 / 190 feet downwards?

b.      Is there a possibility of us having hit a soft rock which is resulting in water seepage through this layer?

Ans:  There is a possiblility but then there should be some water accumulating in the borewell and you hsoudl be getting some sound of water falling from top in to the borewell.

 

2.      Given that we hit water between 110 to 150 feet, is there merit in sealing / closing the borewell 150 feet or 190 feet downwards, and If yes, How should we seal it at a particular depth?

 

Ans: Pour cement in the borewell- but this is practical only if there is water falling in the borewell, if there was any water falling in it would have  mixed with the rock powder and would have been observed at the time of drilling

 

3.      There were also some suggestions on pulling out the PVC Pipe casing laid to the depth of 63 feet and creating slots in the pipe to capture potential surface level water and pushing the PVC pipe back. But I do not see merit in it as there was no water struck till 90 feet. Do the experts agree with my views of not pulling out the PVC pipe?

 Ans: pulling out the PVC pipe will be a waste of time and energy as it woudl really not help you in providing for water all through the year.

 

4.      On a different note, I would like to know about hydro fracturing, Is Hydro Fracturing relevant only for existing fractures or to create new fractures?

Ans: Hydrofracturing is usually done to open out the ezisting fracture ( microfractures), you could try Borehole blasting where new fractures and joints would be created, and it is much cheaper than hydrofracturing.

 

 

5.      I also read about creating rain water harvesting around the borewell to recharge the ground water and increase yield in my borewell. If yes, how can I create rainwater harvesting around the borewell, what should be the diameter and what should be the depth, and how do I create a rain water harvesting structure?

Ans: It will be a waste of money and time, it will not meet your requirements of cultivating 60 acres, if it manages to meet your drinking water requirements you will be lucky.

 

Sorry not very encouraging, but better this than some false hopes.

 

My advice is to check the elevation on which the other wells are located, and try to drill a test borewell at that elevation you probably will have better luck that way then going with the advice of the hydrogeologist who suggest a location in the lowest portion of your property.

 

All the best

 

Dr. Anil Lalwani

www.wellwaterworks.com

2. Dear Krishnan P

Dear Krishnan P S,


Geophysical well logging is recommended before meddling with the casing pipe or taking-up sealing work or initiating hydrofracturing work. Geophysical well logging facility must be available with State Ground water department or the nearest CGWB office. That will reveal exact depths to yielding fractures, thieving zones, if any, and also guide the hydrofracturing Specialist in his work.
In any case, it is unwise to remove the casing pipe lest the top soil and weathered material should collapse and seal the borewell.
If nothing mentioned above is possible, the borewell can be filled with cement slurry down to a depth of 175 feet and try test-pumping the borewell, preferably step-down test. One can select a pump based on the test pumping result.


With regards,


C. Udaya Shankar 
Geologists

3. failed borewel

The borewell site area is located very near to Western Ghat hills.The slope you have mentioned i.e North to South is local but general slope is towards eastern  and southeastern sides. In foot hill zones in valley fill areas, wells are suitable water abstraction structures. But your area doesn’t seem to be valley fill area but gradual slopy area towards Chittar river and finally towards Tamarabarani river basin.The site is located in run-off area (effluent flow)  as observed from the series of falls originate from Chittar river (named as Courtallam falls).In addition,as per CGWB Hydrogeology Map there is major Lineament (major fracture zone)passing from Tenkasi towards South East area.All these factors leads to the  conclusion it is not a groundwater potential zone.Beyond 150 feet there is no possibility of aquifer Zones as the site is located in almost catchment area. In middle and lower  command areas of river Basin we can expect deeper saturated zones. 

                                In the foot hill zones (in the northern portion of your site),series of ponds are to be constructed piercing through clay zone(pond base portion should not be clay layer).These ponds will act as recharge zones for the borewells constructed in the lower topography of area.For this task, efforts from Government side  or some NGO’ have to take initiative. In such situation only you could be able to irrigate 60 acres of irrigate land.

 

4. Borewell dried up all of sudden - Should I re-bore?

Hello

I'm Ramachandra seeking your valuable guidance on the sudden fail of borewell which was dug recently 4 months back. We had dug a bore well with a depth of 300ft where we had seen abundant water. Suddenly we noticed that the water is not available. Ampere reading of the submersible pump reads between 5-8 amps and there is no deflection of volt meter reading. We had called a pumpset expert who had pulled out the pump and checked the depth of the water level. It was informed that the water level is down to 250ft out of 290ft of borewell depth.

He said that the pump is working fine and water dried up, hence water is not pumping out!

Kindly advise what could be the reason for the sudden depletion of water level and if I opt for re-boring in the same point for further depth of 50-100 feet, would that restore the water level?Bore dia is 4 1/5 inches.

Recently some bore wells that were drilled nearly at around 100 ft distance from my borewell point. Is that the reason for my borewell drying up? In that case how should I go about restoring the water level in our borewell?

Kindly advise.

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