Design for deep water well - Vertical turbine line shaft pump

[ccc123]

All,

I have a new project at which we have to install a vertical turbine line shaft pump for deep water well , the design condition for pump is : 450m head and 200m3/hr capacity . The well is drilled before two months , the contractor who driiled the well performed a pumping test at 60m3/hr and from the data of this test they got the value of specific capacity and transmassivity, depending on the test data, the owner of the well did his calculation and correlation to specify the above desing condition. My qustion : Can we depend on the data of the 60 m3/hr pumping test to specify a pump with much higher capacity (200m3/hr) or we have to conduct a pumping test at 200m3/hr and then to check the data if it's ok or not.

 

[EGT01]

CCC123,

It has been some time since I've worked with water wells but I don't think we would have ever accepted a pumping test at less than the specified design rate. In fact, seems like I remember we required a short test at greater than design rate just to make sure something odd wasn't lurking around the corner.

At any rate, without a pumping test at the full design rate, I don't think you will know for sure what the draw-down will be and whether the pump will be set deep enough.

You don't say where you are located or what type well you have but there is quite a bit of info available on the internet about wells. Here's a few...

http://www.usace.army.mil/publications/eng-manuals/em1110-2-1421/c-4.pdf

http://wwwdpla.water.ca.gov/sd/groundwater/california_well_standards/b74-81chap1f.html

http://www.epa.state.oh.us/ddagw/Documents/chapter04PUMPING.PDF

http://www.usgs.gov/

 

[ccc123]

EGT01 , Thanks alot

Thats what I need to know , the pumping test should be at full design rate or greater.

Some Engineers answered me that I can depend on the 60m3/hr pumping test if its operated long enough to obtain a stable fluid level, and other said that you might be able to estimate from the well recovery after pumping but be careful 3.5X is a stretch.

BUT what does it mean 3.5X is a stretch ?

 

[EGT01]

They were probably refering to the ratio of the design rate to the test rate (200/60=3.33) and rounded that value to 3.5. Trying to "predict" the results at the design rate from test results that are significantly different is usually not a good idea especially when it involves the unpredictability of nature.

 

[Artisi]

ccc123 (Mechanical)

It is a good idea to keep your postings to only 1 forum or to at least advise that you have also posted it in another forum.

Phitsanulok
Thailand

 

[thewellguy]

The formula for specific capacity on a well is G.p.m. divided by draw down(the difference between the non-[um[ing and pumping level.) In theory the idea should work, HOWEVER in field tests it does not. The reason is the relationship between GPM and draw down is not linaer. It may not be possible to set the pump deep enough to apply the specific capacity idea. Or the well just may not make enough water.

I would recommend the you test the well at a level higher than you actually want the run the well. Over time wells loose capacity. YOur are going to spend a lot of money on this. You need to make sure that it will function in the future.

P.S. Have you considered a submersible motor? The upfront instillation cost is much less and with the proper motor portection they last just as long.

 

[Impdrew]

ccc123,

I have come across some disastrous jobs where estimations have been made from insufficient well draw down tests, both in terms of abstraction rates and the time of tests. A number of these have lead to lowering of pumps at a later date, which is costly and usually an operational disaster (and an embarassment).

It is important to usually carry out step tests (e.g 40 m3/hr, 80 m3/hr....200 m3/hr) to get a good idea of the draw down profile and equilibrium levels. These however do not give you a long term idea of rest levels at abstraction rates, and a constant rate test at maximum rate needs to be carried out for at least two weeks/until a convergence (in the time frames ppl. usually test for, you will get different levels at different rates).

Are you expecting your pump to operate at different rates, are the pumps variable speed. Often when these go wrong, a comprimise has to be made for a lower standard abstraction rate and an emergency maximum rate.

Knowledge of your water sources, aquifiers / adits etc. is also important, and observation boreholes to give a profile of the "cone" is a useful trait.

It is important to note that rest levels, and hence constant rate draw down levels can change with groundwater conditions in terms of drought etc.

Hope it helps