Low Yield or Good Strike? : A Borewell & Some questions - Chennai
Submitted by Muthukumaran on December 30, 2009 - 23:36
I had purchased land in Nandivaram Village, Gudavanchery, Chennai and last week attempted to sink a borewell with a local borewell contractor. A lot of variation was observed along the same street with some people striking water at 598ft and others at 350 or 400ft.
I went ahead with boring and reached hardrock level at 60ft and my contracter informed that we need to use PVC pipe until 60 feet. I have used 6.5 inch bore and 6kgf pipe.
Boring went until 350 ft, still hard rock particles seen after 450 feet hard particles changed to powederd soil with some moisture content but without water coming out.Then after 550ft it changed again with a lot of dust coming out until 614 ft and we stopped the drill.
Even after 614 feet we did not see water seepage, only at 500ft we could see powder sand with moisture, accompanied by a low level of dust.
My contractor confirms that we can get considereable water for 2 houses from this bore itself due to top level water at 60ft and 450 to 500ft powder soil with moisture.
Would like to get answers for below questions:
Is it a successful bore?
Is it a low yield bore?
Can i use this bore for 2 houses or do I need to go for another?
Should I try another bore with water diviner/ other technique?
My contractor advices against the use of a submersible pump, and recommends that a compressor motor can be used. Are there any particular recommendations regarding the same?
Please advise me,
Muthukumaran
Comments
1. A Borewell & Some questions
Dear Muthukumaran,
Here are the answers to the questions raised by you, these have been based on what information has been provided by you. If you have missed out something please feel to add to this response.
answers for below questions:
Is it a successful bore?
- success of a bore well is determined by the quantity of water you can get from it and if it fulfils the requirement it has been drilled for.
As there has been no mention of the quantity of water that was struck, or the level the water rose up in the bore well within 24 hours of completion of the drilling activity- so I really will refrain from commenting as regards its sucess or failure.
Is it a low yield bore?
-From the description it definitely is a low yielding bore
Can i use this bore for 2 houses or do I need to go for another?
-Unless you had measured the level of water in the bore well within a couple of hours of the drilling activity getting over and then after 24 hours we could have made some kind of estimate how much water you could get in 24 hours or per hour. and then decide if it was ok for one house of will be sufficient for two.
Should I try another bore with water diviner/ other technique?
-Before you try out another bore well with any divining or scientific technique, I would advise you to subject the bore well to a pump test. Get a test pump installed and test the performance for a week. and see how much water you get in 24 hours, or if you pump it every 4 hours or every 8 hours.
While doing this please measure the water level in the bore well before you do any of this, only if the water level is within 100 ft you could carry out the pump test.
My contractor advices against the use of a submersible pump, and recommends that a compressor motor can be used. Are there any particular recommendations regarding the same?
-Because you did not really strike a good quantity of water that could have been measured while drilling the contractor probably feels that the pump could rund dry and cause problems, on the other hand a compressor pump would definitely not be the right choice as it is the most inefficient system, an should be installed only on pumps which have problems of fine silt coming into the bore well with the water.
IF after the testing it is confirmed that you do have sufficient quantity of water to meet your daily requirements, then install a Submersible pump with a automatic level control unit based on a timers or level probes.- Whatever you do please ensure that the pump panel has a very good quality current sensing cut-off system inbuilt as additional safety.
I hope I have managed to clear your doubts.
Regards
Anil Lalwani
www.wellwaterworks.com
contactus@wellwaterworks.com
2. Dear Muthukumaran, Of couse
Dear Muthukumaran,
Of couse it is a low yieldig well but it can provide 1000 or 2000 litres of water per day. It can be aseessed by monitoring the water level of the well and conducting a pumping compressor pump is suitable since the low yield.
Pradeep
State Ground Water Department
3. Thanks
Thanks for the input.
Can you specify the suitable pump for this bore.
What is the spec of the pump?(BHP, III phase etc).
Regards,
Muthu
4. Dear Muthukumaran, I would
Dear Muthukumaran,
Actually the yield during the course of drilling is not a dependable estimate. Sometimes the yield during the drilling is very good, while ultimately the actual yield by pumping may not be that good, and similarly, there may be very little water apparently coming out during the course of drilling, while if you lower the pump, the yield may be sufficiently good. There are many hydro-geological reasons for such yields. Therefore the pump test would give you the actual performance of the borewell.
Pump tests can be detailed as well as simple. Go for a simple yield test in which the pump is lowered up to a certain depth (say at 200 feet) and run for sometime. Once the water dries out, the pump is lowered further (another 100 feet), and run again. The process is repeated till you reach about 30 feet from the bottom.
The level at which motor is lowered, the time run, and the approximate yield as well as the water level at the beginning of each stage is recorded. Please collect this data and communicate to me.
I will analyze the data for you, and though very accurate hydrogeological calculations may not be possible (nor they are required) a rough estimate about the yield of the bore can be drawn.
Therefore I would advice you to go for a pump test, which can be done by your local pump test people who have their own arrangements for testing pumps, and pipes, temporary electrical connections etc. They would charge you around Rs 6 to 10 per ft depending on the local market rates.
With regards,
Sudhindra Mohan Sharma
Hydro-geologist
Indore
Madhya Pradesh
5. FAILURE OR SUCCESS
Dear Sir,
Would like to get answers for below questions:
In my opinion it is a failed bore well. But since you got some micro cracks at about 500 feet there is some hope of getting a trickling yield over long seepage period.
How about the quality of the water. Is it o.k. for house hold purposes. Please check the quality.
Since the water level is at 60 feet, if your contractor has cleaned the bore well with some external water poured into the bore and flushed all the sticky powder and cleaned up or opened up the micro cracks, then you will get standing water of about 50 to 550 feet that is about 2800 to 2900 liters of water ( 165 X17.65).
If you fit the compressor pump then only about 65% you will be able to draw out. In case if you put a submersible pump then you may be able to pump out about 90 % of the water, by putting the pump at appropriate depth.
Should I try another bore with water diviner/ other technique?
Since your neighbourhood have good water yielding bore wells and there will be joints / fractures in the nearby spot also and unfortunately you have missed it. Either you can drill a new bore well or else you can try to refurbish the bore well by blasting at different depths.
As you informed in the nearby places you get sufficient yield any where between 350 to 600 feet. If you can find a professional blaster then you are assured of good supply, as the geohydrology which you indicates is favorable for connecting the nearby water flowing fractures with your bore well.
Hydro-fracturing and horizontal drilling for water is a costly affair. If you find it is cheaper then you may try out the hydro fracturing technique to increase the yield.
With best wishes,
A. Raja Mohamed Ambalam
Geophysicist.
Coastal Energy Pvt Ltd
Chennai. bismi1234786@gmail.com 09443619352.
A. RAJAMOHAMED AMBALAM GEOPHYSICIST COASTAL ENERGY Pvt Ltd, CHENNAI +919443619352
6. Thanks
Thanks for your advice.
Request you to give the details for pump test to understand better about the bore well yield.
Who does pump test in & around guduvanchery??
What is the cost for pump test.
Need details to do the test at my bore.
My contractor informs me for such high depth bore well and low yield,sumersible is not suitable.
Need your comments.
7. Thanks Submitted by Muthukumaran on January 13, 2010 - 13:43
Dear Sir,
For yo0ur bore well there is no need for conducting a pump test. As it is not going to sustain more than 5 or 10 minutes of pumping, as you are going to pump out the storage of about 2500 or 3000 liters per day in all. If you get more it is good.
Suppose if you want the bore to run for 10 minutes and fill your 2000 liters tank. Then you may need about 5 or 7.5 h.p pump thtg discharges about 200 liters per minute at a depth of about 600 feet.
Texmo groups based at Coimbatore has the low discharge, high depth withdrawal pumps. A 2 hp pump that may discharge about 50 liters per minute may be sufficient to empty your bore well.
Texmo pumps are Branded company and you do not need any address to search. Simply talk to any submersible pump distributor or retailer.
If you meet them you will have variety of chances that the shop owners will advise. You can choose a cost effective one.
This is for your kind inflrmation.
I am sorry for the delayed reply as I was abroad for a a quite a bit of period.
With best wishes,
A. Raja Mohamed Ambalam
Geophysicist
bismi123786@gmail.com; 09443619352
A. RAJAMOHAMED AMBALAM GEOPHYSICIST COASTAL ENERGY Pvt Ltd, CHENNAI +919443619352
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