Measuring water level in Well

THE_RB

Joined Feb 11, 2008
5,438
Echo return will be a no-go I think. The pipe is very thin and has perforations, which will increase the sound absorbing ability of the pipe walls. At 100 feet depth it will be like trying to get a sonic echo from a 3" object in an open field 100+ feet away (using a 3" speaker as your sound source). Actually it's worse than that, because of the other things in the pipe.

The resonant idea may pay off. You could sweep it through a freq range to suit the expected resonant freq of the pipe height with a microcontroller and look for some sort of "peaking" effect.

If the pump empties the bore, and then it fills back up, you could use the pipe and pressure sensor idea someone suggested like they use in a washing machine. That system works fine provided every now and then the water levels drops low enough to clear the bottom of the pipe so it re-equalises itself to atmospheric pressure, then will give an accurate reading when the bore fills back up. That could be a real good solution.
 

sirch2

Joined Jan 21, 2013
1,026
I would hope that his drillers knew enough about the local hydrogeology to get to an aquifer that is big enough not to be emptied by a 3" domestic pump. Also these pumps rely in being in water for cooling so generally should always be submerged.

To the OP, you said earlier that you were interested in the level shortly after the pump shuts off. Unless your aquifer has very low transmissivity, I would be surprised if there was much of a difference just before the pump shuts off and just after. Also, assuming that you can establish the pump characteristics reasonably well, it may be more interesting to monitor current/flow rate and see the change whilst the pump is running - i.e. how much is the well drawn down over the time the pump is running. The next pump run will start at the recovered level so give you some indication of recharge.
 

wayneh

Joined Sep 9, 2010
16,399
One big advantage of monitoring the pump, IMHO, is that it would start to give you data NOW, without any significant invasion into your system (except maybe a pressure transducer near the pump head). After you collect data for a while, you may discover you have the information you need, or decide you need a more precise method.
 

Thread Starter

MikeML

Joined Oct 2, 2009
5,444
Monitoring the pump will not tell me much. The pressure at the top of the pump line is controlled by the bladder tank and a pressure switch. The static air pressure above the bladder in the pressure tank depends on how much water is in the tank. If the tank is near full, the air above the bladder pushes down on the water at ~60psi. If the tank is near empty, the air/water pressure is ~42psi.

The pressure switch (which powers the pump) cuts-in at 42psi, and cuts-out at 65psi.
The pump is always pumping against the pressures cited above plus a head pressure of a column of water 280ft high (8.5 atmospheres).

The only thing monitoring the pump would do is tell me if it is cavitating, meaning that there is no water in the well....
 

BR-549

Joined Sep 22, 2013
4,938
This couldn't hurt. Put a run time counter on the pump. Record pump run time in milliseconds. This will always lets you know if head is higher or lower than previous cycle. Also, any deviation might indicate a possible maintenance problem. This one thing will show and verify if head is raising or falling.
 

wayneh

Joined Sep 9, 2010
16,399
The pump is always pumping against the pressures cited above plus a head pressure of a column of water 280ft high (8.5 atmospheres).
But that head is not constant - it varies with the height of the water column above it which you want to estimate. More height = less current draw at a given bladder pressure. Since you know the back pressure at each start and stop, the draw current during a pumping cycle will tell you how much head you started with. It would give you a snapshot of well level every time the pump runs.
 

Thread Starter

MikeML

Joined Oct 2, 2009
5,444
Yeah, but at pump start the standing water level in the bore above the pump intake may be 175ft one day and 174ft the next day (it is that 1 foot difference that I am trying to resolve).

As soon as the pump comes up to speed, the water level above the pump intake is going to drop to ~30ft or 40ft above the pump intake. Do you think that I can tell something about original static water level by monitoring only the start-up in-rush current to the motor winding? ( I don't)

The other thing is that there is a check valve at the top of the well to prevent water flowing backwards out of the pressure tanks. That check valve is 280ft above the pump. Since a perfect vacuum can only support 33 ft of water, some of the vertical sched 80 PVC pressure pipe is dry, so the pump has to run for a while just to refill that pipe to get the water to the top of the well. Again, the dynamics of refilling this pipe are going to cloud the issue of what the pump does in the first few seconds it comes up to speed.
 

wayneh

Joined Sep 9, 2010
16,399
Yeah, but at pump start the standing water level in the bore above the pump intake may be 175ft one day and 174ft the next day (it is that 1 foot difference that I am trying to resolve).
Yeah, resolving 1ft changes everything. I'd be back to the bubbler.
 

jpanhalt

Joined Jan 18, 2008
10,225
Going back to post #1:
MikeML said:
I am planning to get a coil of 3/8 PEX water pipe, and I will insert that down into the well. The PEX is stiff enough that I think it will push past the random coils of the pump cable, and strong enough that I could withdraw it from the well if I ever need to... I show the PEX pipe as the Standpipe on the drawing.
Why not use the PEX as a guide tube to pass a small SMD pressure sensor or attach the senor to the inside of the tube before you place it in the well? Alternatively, you could use it to pass/attach electrodes.

I checked Digikey, and both absolute and differential/gauge sensors in SMD sizes are available -- some are a bit expensive at DigiKey though. The Honeywell application note says sensors for direct liquid contact will be available "soon." If one could find one available now, would that be a viable option?

BTW, is your water contaminated with high dissolved air?

John
 

Thread Starter

MikeML

Joined Oct 2, 2009
5,444
Going back to post #1:
...
BTW, is your water contaminated with high dissolved air?
No, but I did measure the resistivity of my water. It came out to 1100Ω*cm.

Two 5" 0.125"dia stainless rods 0.655" apart exhibit an impedance (measured with 1Vp-p sine wave excitation at 10kHz) of less than 50Ω.

I have decided to use the bubbler, but instead of pumping air, I will use Nitrogen out of a high pressure Nitrogen tank with a two-stage pressure regulator. I am guessing that commercially produced Nitrogen will be cleaner than air out of a compressor. That should mitigate contaminating the well...
 

jpanhalt

Joined Jan 18, 2008
10,225
Sounds good. That is what I would have done or get a fluid-capable pressure sensor.

Nitrogen and argon are available quite pure and are relatively cheap. Both are relatively soluble in water. That was one thing what was in the back of my mind on the contamination question. I guess bubbly water is not desirable in municipal sources. I believe both gases are recovered by fractional distillation of liquefied air, and I have never read any specification regarding microbial contamination.

If your only concern is microbes, those filters are relatively cheap and should last quite awhile. An intake filter would probably be cheaper and less bother in the long run. The likelihood of getting enteric (coliform) bacteria or viruses from desert air would seem to be quite small, anyway. Coccidiomycosis is not water borne.

John
 

BR-549

Joined Sep 22, 2013
4,938
It's good that the check valve is on top. Are you saying that when then pump cycle finishes, and the check valve closes, that some water flows back to your well? Can you install pressure gauge upstream of valve and check pressure? When that check valve closes......there should be no flow. The discharge pipe should remain full. Does anyone disagree with this?
 

Thread Starter

MikeML

Joined Oct 2, 2009
5,444
It's good that the check valve is on top. Are you saying that when then pump cycle finishes, and the check valve closes, that some water flows back to your well? Can you install pressure gauge upstream of valve and check pressure? When that check valve closes......there should be no flow. The discharge pipe should remain full. Does anyone disagree with this?
Yes, I disagree. A tube sealed at the top but open at the bottom filled with water standing erect cannot have a water column any taller than 33ft no matter how long the tube. As the tube is lifted, a perfect vacuum forms at the top after the water column is 33ft...

In the case of the well, the check valve is right at ground level. The pump is 280ft down. The water table is about 110ft+, so the vacuum forms under the check valve, the water sinks, stopping about 33ft above the water table.

This might be yet another non-invasive way of measuring where the water table is, but it occurs to me that sound will not propagate in a perfect vacuum...
 
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BR-549

Joined Sep 22, 2013
4,938
I like to see that vacuum pulled on the upstream of check valve. Ok, I'll take your word for it. So your well is already back flushing to a good extent. Good.....now put solenoid actuated vent valve at top of well head. Vent discharge line. Install pinger at elbow. The only time you can't take soundings, is during pump time. Would that work for you?
 

wayneh

Joined Sep 9, 2010
16,399
A small filter to sterilize incoming air would be cheap and easy. Any bio or chem lab would have them. I'd probably use it for either gas source. Be sure it's rated to 0.2micron or less. Essentially nothing living will pass.
 

jpanhalt

Joined Jan 18, 2008
10,225
wayneh said:
Be sure it's rated to 0.2 micron or less. Essentially nothing living will pass.
Not quite clear what you mean by "rated to 0.2 micron or less." The typical rating for a HEPA filter is based on a functional test for removal of 0.3 micron particles. (http://en.wikipedia.org/wiki/HEPA). If you meant a pore size of ≤0.2 microns, it is a common misconception that a filter's pore size must be smaller than the particles being filtered (See: "Function," loc. cit.).

@MikeML

You can probably get something properly rated for your purpose from a scientific supply house or even HD/Lowes. If not, Dacron or cotton wool can make an effective filter. It is important to define what you are trying to filter. Some of the sites I reviewed that discussed well contamination from air mentioned viruses, but they were uselessly vague. I am not quite sure viruses are an issue in your situation, since you presumably don't have contamination from surface run-off.

John[/USER]
 

BR-549

Joined Sep 22, 2013
4,938
If Mike installs a bubbler, he will have very accurate, real time readings at all times. Mike is concerned with the aquafier dropping. Which is understandable, but I would be looking for pump efficiency. I'll bet there are a lot of farmers and ranchers would be interested in this. Just regular home owners out west would be interested in this because of global warming scare. If some one built a non intrusive system, that a home owner could install say for 2-300 dollars, one might make a little money. I installed a pump monitoring system on a catfish farm in Georgia about 15 years ago. Farmer saved $50k monthly on electric. To this day I still get Christmas cards from him.
And I would be curious if Mike can see a daily or perhaps monthly tidal effect?
 

Thread Starter

MikeML

Joined Oct 2, 2009
5,444
Thanks again to all that have contributed to this thread. The reason I want more-or-less real time measurement of the water-table is because our aquifer is being pumped (bigtime) for agricultural uses. My well and my neighbor's residential-use wells can only draw like 45gal/min. I am more concerned about two different agricultural wells that are pumped at ~thousands gal/min that are located within 1/2mi of my place.
 

wayneh

Joined Sep 9, 2010
16,399
Not quite clear what you mean by "rated to 0.2 micron or less." The typical rating for a HEPA filter is based on a functional test for removal of 0.3 micron particles.
I should have just referenced HEPA. Most of my filtration experience is with liquids, where 0.2µ is a standard value. I was guessing at the rating for air filters, but the point is that you want a "sterile" filter, not just a cattle catcher.
 
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