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Query : About borewell minimum distance from openwell

Hello,

My farm is in north Konkan - Raigad district. The soil is lateritic. It is on a plateau, but at the base of a 40m high ridge which forms the catchment area.

Eventually, I intend to dig an openwell, but due to some restrictions initially I decided on a borewell. The question is, how far should my borewell be from the proposed openwell so that it does not affect the inflows into the well. The openwell spot gets inflows from all directions (N, E, W, S) and the borewell is a little upstream on one of the sides of the openwell.

Do you think a distance of 200m is sufficient buffer between the 2 wells?

Looking forward to your advice.

Thanks.

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Comments

1. The minimum distance should be about 150 meters

Generally it is suggested that the distance should be about 150 meters for minimum disturbance to the surrounding wells. It was noted many times that the wells at less than 150 meters are not disturbed and the wells more than 150 metres of distance were disturbed. There are so many variations in aquifers along with strata length and width. So no one rule can be applied in groundwater quantity.

Ratilal Sudani,

Director, Bhoojalshree GeoTech

2. Well can be used to tap water

The answer to Mr. Shreesh's question would depend on the soil profile, the depth of the borewell and whether a plain or slotted casing pipe is put at shallow depths. If the soil is lateritic, even between the bottom most level of the open well and the borewell, then the water fed into the well will also be available to the borewell.

Since the borewell is stated to be upstream, the well can be used to tap water and only when it dries up (if it dries up), the deeper borewell can be tapped.

Indukanth Ragade (isragade@yahoo.com)

3. Thanks for your comments - More details

Thanks, Mr Sudani and Mr Ragade.

I drilled the borewell and following was the strata:

15ft of soil, followed by 65ft of solid laterite rock, followed by a conglomerate kind of strata which kept collapsing and hence could not drill further. Luckily, I got water at 40ft and by 60ft it had crossed 2-inches of water flow. I have put solid casing pipe only for the depth of the soil, i.e. 15 ft.

After the drilling, the water has come up to 10ft below ground level. The drilling guy tells me that the laterite and the conglomerate layer is usually a good source of water. Since the borewell cannot go any deeper and the water source is good, he is suggesting that I take an open well (about 30-40 ft deep) right on top of the borewell. He is saying that the water from the conglomerate layer will feed the open well.

Does that sound right? Especially because the better place for open well that I was hoping to get (150m away) is probably not going to be available for me.

4. You can stop even at 20-25ft if you hit water table

Dear Shreesh

You can put an open well around the borewell. You say the borewell digger recommends a 30-40 ft open well. If the soil is solid laterite rock from 15 ft onwards, how was the drilling done for the borewell? By pneumatic drilling or using a rotary rig?

How does he plan to dig the surface below 15 ft? What is the nature of the soil upto 15ft? You simply say it is 'soil'. Is it clayey or sandy?

I don't see why you have to go upto 30-40ft. If you hit the water table earlier, you can stop even at 20-25. You can charge the borewell also with rainwater by providing the bottom portion of the casing pipe with a slotted pipe, covering it with nylon mesh and tying it in with copper wire at the top, middle and bottom portions and winding polythene thread.

This way, the borewell also will be charged with rain water.

Indukanth Ragade

5. Thanks for your comments Mr Ragade

Dear Mr Ragade,

Thanks for your guidance.

I am not sure but it was probably a pneumatic drill. There was a compressor and lots of air release noises :)

I would say the soil is loamy - clay + fine silt.

He suggested 30-40 feet and I agreed because that is the level at which we hit water during drilling. Then later, the water column rose up to 10m. Of course, if we hit the water table before 30/40 ft, we will stop. The other consideration is water table level in the peak of summer will be lower than current.

If we have the open well connected to the borewell, my fear is, will the water in the open well go down the borewell and be unavailable for us? 

In unfavourable strata and water table conditions, is there a way to plug such borewells in an inexpensive fashion?

I find one problem with borewell recharge, when there is surplus water in the monsoon, the borewell water table is also very high and there is no scope for recharge. Later as winter/spring progresses, the water table does go down and is suitable for recharge, but then I don't have any excess water to recharge the borewell with.

Regards
Shreesh

6. Borewell connected to shallow aquifer

The borewell has been dug using a pneumatic drill only. If the borewell water level is rising sharply during the monsoon, it means it has a connection with the shallow aquifer. This being the case, whether the open well is around the borewell or some distance from it, the borewell will have an impact on it. Since both take the water from the same layers, how does the borewell digger say the well will get good water from them and not the borewell? Or is it that the water level in the borewell could have gone down but the yield would not have reduced?

You say that you got a conglomerate layer after 65ft. I am not clear what this means, particularly when he says that this layer which starts only at 65 ft will feed the open well.

You mention that you hit water at 30-40 ft and then in the monsoon it rose to 10m. 10m is equal to 33ft. Did you mean it rose up to 10ft?

When did you you dig the borewell? If it was in the summer season, the rise in the level in the monsoon explains it. But it will not be higher than 30-40ft if you dig the open well now in the summer. It will only be beyond 40 ft. However, if you dig the well in winter and stop at less than 30-40 ft, then it will dry up in the dry season.

Indukanth Ragade

7. More clarifications

Dear Sir,

The borewell was drilled in February. I was present during the drilling and that is why I know that we struck water first at 40 ft depth. When I say it rose up to 10ft (yes feet, not meters, my mistake) later, I meant that a few days after the boring we checked and the water had risen up to 10ft.

The reason I say the borewell might not do well but open well will is because we cannot drill beyond the conglomerate layer as it keeps collapsing. Hence the borewell does not have an appreciable water column to store the water. Whereas the open well will have large storage capacity. Since I need this water for irrigation purpose, I need large quantities, upto 75000 LPD.

Yes, I do understand that the two may have an impact on each other. But my main fear is that the water that would have collected in the open well should not go down the borewell into a deeper aquifer. Is this a possibility in my case? If yes, can I plug the borewell through some easy method?

Conglomerate starts at 80ft, after the 15ft soil and 65ft of laterite stone. He expects it to feed the open well via the borewell, at least thats what the borewell guy says. I would appreciate your views on this as well.

Regards

8. You can have large diameter irrigation well around the borewell

(I find one problem with borewell recharge, when there is surplus water in the monsoon, the borewell water table is also very high and there is no scope for recharge. Later as winter/spring progresses, the water table does go down and is suitable for recharge, but then I don't have any excess water to recharge the borewell with)

Dear Mr.Shreesh

You mention that the water level rises in the borewell during the monsoon but falls down in the dry season when it cannot be recharged.

This is your assumption as you dug the borewell only in February 2012 and you have yet to cross a monsoon. If the first 15 ft is mainly clay and silt, the scope for recharge of the borewell is limited as this layer will not be allowing much water to percolate to the lower favourable layers. Therefore your assumption that the borewell will get recharged during the monsoon is not correct. But you may still get a good yield throughout the year if the conglomerate and the laterite layers are rich aquifers. (My earlier statement that you may hit water even earlier than 40 ft is incorrect.)

The borewell digger's statement that the conglomerate layer will feed the dug well is based on the fact that the pressure of the deep aquifer is such that the water rises in the borewell to 10ft and given the fact that the water table was at 40ft in February, this is the level which ultimately matters. If you now dig a well around the borewell, the dug well and the borewell both will be drawing the same water table. There is no scope at all for the water to drain from the dug well into the borewell. 

Since you want to draw huge quantities of water daily. what you should do is to harvest rainwater and charge it into the soil to maintain the water table at 40ft or even raise it further!

I feel that you should get a clearer idea of what is the composition of the soil up to 15 ft in order to design the rainwater harvesting system.Contact me directly to progress this matter.

I have reduced the depth of some borewells by dropping hard balls of a mixture of blue metal chips, sand and cement with just the amount of water necessary to hold the ball together. This is, however, not a sure shot method. However, after analysing all the facts in your case, I see no problem in having a large diameter irrigation well around the borewell as it is at present.There is no way that the borewell poses a risk to the potential dug well. On the contrary. as the borewell guy says, the borewell will feed it as water will rise under pressure through its pipe from the deeper aquifer.

Indukanth Ragade(isragade@yahoo.com)

9. Borewell near municipality bore in Hosur-How deep should I dig?

Hi,

I am looking to purchase s piece of land. I have concerns about water source in that land because there was a Hosur municipality bore well located within a distance of 30 to 40 feet. As per the land owner, municipality bore is 900 feet and opposite to this bore the land owner has dug a bore of 450 feet. As per the land owner's update, they are getting water if they pump in the early morning 3 am.

The land owner suggested me to drill upto 750 feet. Please let me know whether it will affect me if I am purchasing the land which is distance of 30 to 40 feet near to municipality bore. If there is water source within 300 to 400 feet, Do I need to dig bore more than 900 feet? Else, is it sufficient to have extra 100 to 200 feet after getting water?

Expecting some clear clarification.

Thanks,
J. Manikandan.

10. Explore the option of shallow dug well before going for borewell

(Comment received from Indukanth Ragade)

The tendency today is to go in for borewells straightaway. We have forgotten that the traditional source of water was the shallow dug well. The shallow dug well has two major advantages over the borewell: 1. It requires much less electricity usage to pump water from it; 2. It can be sustained by draining rainwater into it and therefore it will provide long time water security whereas a borewell taps an exhaustible source and may dry up some day. I say this after having saved/introduced the dug well in more than 150 apt complexes built by the company with which I was associated.

I would therefore advise you to explore the scope for going in for a dug well. Fweor this, the soil layer at shallow depths has to be favourable i.e. It has to be reasonably sandy or made up of weathered rock(gravelly). One can get a test borehole for a few thousand rupees whereby one can find out if a sandy layer is available within 30 ft. If the layer is found to be gravelly also, it is worth going in for a well and drain the rainwater from the terrace directly into it. The rainwater falling on the open spaces around the building can also be diverted suitably into the well after filtration.

Indukanth Ragade (Ph: 2834 3506)

11. Please give me more details

Dear Mr.Pradeep

Mr.Shreesh has asked two relevant questions: 1.At what depth did this layer begin?2. At what depth did you hit water?

If you or your borewell digger have any data on the type of soil encountered at various depths, let me know the same. I have found benefit in several borewell cases where by lifting the suction pipe to a shallower level, the water quality improved. Give me whatever info you have and let me see.

Indukanth Ragade

12. Lot of mud in the borewell water

I am from Bangalore. We have borewell for the last 5 yrs now. Since the day of digging the borewell the water is brownish in colour. There is lot of mud which comes along with the water. Every clothes that is washed becomes brown in colour. This is a 4 and 5 inch bore. We have gone about 90ft in depth. The main reason that we could not go deeper is because the machine could not dig (bit was struck) as per the borewell company. Therefore we stopped digging at that point and it is not stopped at a rocky place. I have spent some few thousands of filters. But it is of no use.

My questions-
1) Can we stop this mud from coming out.
2) What are the alternative
3) Can we dig the existing borewell a little more deep so that we get a rock.

Regards,
Pradeep

13. I don't have much hope

Hi Pradeep

This sounds very much like my case. During drilling, you have encountered a layer which keeps collapsing and prevents further drilling. My borewell guy too, had given up at this stage. In fact he had a lot of trouble extracting his pipes, it kept getting stuck due to loose rocks falling on top of the drill bit. I see little hope, unless someone can share some technique to overcome this.

You may have to take a new hole which preferably stops drilling before you hit this layer. Do you remember at what depth this layer started? And what depth did you strike water?

14. Need to dig a borewell, water level at 30 ft, rock found at 60ft

The water levels in our area is very good. Water started oozing out at 7 to 10 ft it self. We initially had a well which was 25 ft deep. I think we stroked water at 30 to 35 ft and the soft soil/ rock started by 60 ft. Is there any alternative?

Pradeep

15. Try raising the intake pipe level to above 60ft

As Mr Ragade suggested - try raising the intake pipe level to above 60ft. That might reduce the turbidity of the water, but it will also reduce the available water for you to use. If this does not reduce turbidity you can try a new bore that goes to only 50ft . So that you don't encounter the soft layer at all but remember that even for this option the standing water column will be very less and hence you wlll be able to operate the pump for very small durations only.

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