Well Drilled - Results

[Valveman]

My well was drilled today:

Drilling Type = Air Rotary
Well Depth = 505 feet
Static Water Level - 220 feet
Water GPM = 20
Perforated Pipe = 280 feet - 500 feet (20' pipe sections every 20 feet - 100 feet total of perforated PVC pipe)

The well driller said that the 20GPM is "conservative" since they measure the GPM during drilling by taking a bucket and timing how long it takes to fill. He said the well will produce more GPM since the drilling rig is blowing air into the well and this prevents the well from filling normally. He also said that debris can clog the water vains during drilling and that can reduce GPM.

Is the above true?

The well driller claims the only true test is once the well pump is installed one then can get a proper GPM reading.

It's a 6.5" bore hole with a 4.5" PVC casing

400 feet is solid PVC while 100 feet is perforated PVC

I missed this part. Do I understand correctly that the perforations start at 280’, and that there is 20’ of blank and 20’ of perf the rest of the way down?

If so, then the way the well was tested you have no idea which 20’ section of perf is letting the water in the well. It could be at 280’ to 300’ or 480’ to 500’ or all of the above. Then with 4.5” casing there is not enough room to put a shroud on the 3HP pump/motor. So to go by the Franklin and Goulds engineers, which I agree with in this instance, the end of the motor should be set no deeper than 279’. That motor needs a minimum of 5 GPM flow from below to remain cool. Any deeper than 279’ and you cannot guarantee there will be any flow past the motor. If all the water is coming into the well from 280’ to 285’, if you set the motor deeper than 286’ it won’t last long.

I would have used 5” casing so I could have gotten a 4” shroud on the motor, and been able to set it close to the bottom.

Like the well driller said, the only way to really tell the volume of the well is after the pump is installed. And with 4.5” casing it is also the only way to tell where to set the pump. If while pumping 13 GPM the water level never drops below say 370’, just to pick a number, then I would pull the pump up to 380’ and hope it gets the cooling flow from below that it needs.

If you only set the pump at 279’ (above perf) and the static is at 220’, a 1.5HP pump would deliver the 13 GPM you want, as long as the well will produce that much from 270’. Once you have tested the well you may find that the pumping level and the installed depth can and should be much higher. Then a 13 GPM, 3HP is way more pump than you need, and 480’ is deeper than it should be set, especially with perf starting at 280’.

 

[Egon]

Deep sump maybe??

 

[Pettrix]

I missed this part. Do I understand correctly that the perforations start at 280? and that there is 20 of blank and 20 of perf the rest of the way down?

If so, then the way the well was tested you have no idea which 20 section of perf is letting the water in the well. It could be at 280 to 300 or 480 to 500 or all of the above.

The perforations start at the 500' level and then every stick (20 feet lengths) up from there they alternate between 20' solid sticks and 20' perforated sticks. There is a total of 100' of perforated PVC pipe.

For example;

500 feet depth to 480 feet depth = perforated PVC
480 feet depth to 460 feet depth = solid PVC
460 feet depth to 440 feet depth = perforated PVC
440 feet depth to 420 feet depth = solid PVC
420 feet depth t0 400 feet depth = perforated PVC
ETC.

this continues and the last perforated PVC is located around 280 feet depth

That's what I remember them telling me. I measured the well water static depth and I hit water around 210-220 feet but the water goes down to the 500 foot level. So the pump will sit at around 480 feet and there will be 260 feet of water sitting above it.

This is the way they do wells out here and have been doing them that way for decades without any issues. All the well drilled out here use the same methodology.

The well was drilled with a 6.5 inch borehole and cased with a 4.5 inch PVC pipe.

I am not understanding what you are saying they did wrong.

 

[Haoleguy]

Hi Pettrix - Interesting well casing. Must be a reason behind it. In my neck of the woods the code is to supply metal casing up to the bedrock layer and then 10 ft into it. After that there is no well casing as the bedrock is considered stable.

 

[Valveman]

The well was drilled with a 6.5 inch borehole and cased with a 4.5 inch PVC pipe.

I am not understanding what you are saying they did wrong.

Some areas do things differently, but that is still pretty weird. The problem is setting a 3HP pump down below the perforations without having a shroud on it. Franklin says their 2HP and smaller motors will work fine without a shroud, but I still don't like putting them in a top feeding well situation. 3HP and larger motor should never be top fed. They need .5 fps flow past the motor to stay cool. If you don't know where the water is coming into the well, you can't set the pump above that point.

If you set the pump at 480' and the water is coming into the well anywhere above that, the motor will not get the cooling it needs. With perf like that the water could be coming in anywhere up to 280'. You cannot fit a shroud in 4.5" casing, but you could have in 5".

I have tested wells like that where the motor only lasted 4-6 hours. But if when sat at 480', the motor will last long enough to get a good test on the well, you maybe able to raise the pump where the motor will get the proper cooling. Like I said, if the water level stays higher in the well while pumping hard, you can raise the pump to just under that level. This is to try and make as much water come into the well from below the pump as possible.

A sump pump has the impeller on the bottom and pumps water up around the motor for cooling, so they can be set in a top feeding sump. But a well pump has impellers on top and the motor on the bottom. So to get water flow past the motor, all the perfs need to be below the motor, or it needs a cooling shroud. Like I said you maybe able to get a 2HP to work in a top feeding well, even though I don't like doing that, but a 3HP or larger needs flow past the motor, which means the well needs to feed in from below the motor.

Also with perf like that you have the chance of having a problem with cascading water. If any or all of the water comes in from up high in the perfs, it can fall a long ways down to the pumping level. When this happens the cascading water will churn up and aerate the water until the pump loses prime. The only way to prevent this is to not pump hard enough to pull the water level down. And if you don't pump hard enough to pull the water level down to 480' or so, then you don't need to set the pump that deep, and you don't need a pump large enough to pump from that depth.

If you can only pump the well hard enough to maintain a water level of say 350' to keep the water from cascading, then you would not need to set the pump any deeper than 360' or use a pump any larger than needed from 350'. Then you could probably use a 2HP, which the manufacturer claims can work without a shroud.

But all manufacturers will tell you that a 3HP or larger motor needs .5 fps flow past the motor. This means they must be installed with a shroud, above any perforations, or at least above the point where the water enters the well.

 

[Egon]

Are you saying all downhole pumps should be st above the perforations?

 

[Valveman]

Are you saying all downhole pumps should be st above the perforations?

Yes! Either that or above the point where the water enters the well, which has to be tested to find out. Or if the casing is large enough for a 4" motor shroud, you can put the pump as deep as you want.

 

[Egon]

Thank you.

 

[Qapla]

The perforations start at the 500' level and then every stick (20 feet lengths) up from there they alternate between 20' solid sticks and 20' perforated sticks. There is a total of 100' of perforated PVC pipe.

For example;

500 feet depth to 480 feet depth = perforated PVC
480 feet depth to 460 feet depth = solid PVC
460 feet depth to 440 feet depth = perforated PVC
440 feet depth to 420 feet depth = solid PVC
420 feet depth t0 400 feet depth = perforated PVC
ETC.

this continues and the last perforated PVC is located around 280 feet depth

That's what I remember them telling me. I measured the well water static depth and I hit water around 210-220 feet but the water goes down to the 500 foot level. So the pump will sit at around 480 feet and there will be 260 feet of water sitting above it.

This is the way they do wells out here and have been doing them that way for decades without any issues. All the well drilled out here use the same methodology.

The well was drilled with a 6.5 inch borehole and cased with a 4.5 inch PVC pipe.

I am not understanding what you are saying they did wrong.

Hi Pettrix - Interesting well casing. Must be a reason behind it. In my neck of the woods the code is to supply metal casing up to the bedrock layer and then 10 ft into it. After that there is no well casing as the bedrock is considered stable.

Perhaps this is where some of the confusion is coming from.

In your description, there may be a bit of confusion as to exactly which pipe has the perforations. Are you saying the well casing has the perforations or the drop pipe (the pipe the pump is fastened to).

In our area the well casing only extends to the "hard pan" (usually a layer of hard lime rock) and the "well" (the hole in the ground) continues to whatever depth was needed. The drop pipe usually sits somewhere in the casing portion of the well, not in the "hole in the ground" below the bottom of the casing. The well casing here can be metal or PVC.

It is quite common for a household well to be 100' - 200' deep with the casing only being 60' to 80' and the drop pipe to be 20' short of the bottom of the casing - but then, our static water level in a good well is commonly around 30-40 feet in a well that is not artesian.


So, I would guess that your actual well (the hole in the ground) is 500' deep and that your casing is also 500' deep. I would also think, by your description, that it is the well casing that has the perforations in it. With that in mind, I would then conclude that your drop pipe holding the pump extends down to 480' and that the drop pipe does NOT have perforations.

 

[Valveman]

Perhaps this is where some of the confusion is coming from.

In your description, there may be a bit of confusion as to exactly which pipe has the perforations. Are you saying the well casing has the perforations or the drop pipe (the pipe the pump is fastened to).

In our area the well casing only extends to the "hard pan" (usually a layer of hard lime rock) and the "well" (the hole in the ground) continues to whatever depth was needed. The drop pipe usually sits somewhere in the casing portion of the well, not in the "hole in the ground" below the bottom of the casing. The well casing here can be metal or PVC.

It is quite common for a household well to be 100' - 200' deep with the casing only being 60' to 80' and the drop pipe to be 20' short of the bottom of the casing - but then, our static water level in a good well is commonly around 30-40 feet in a well that is not artesian.


So, I would guess that your actual well (the hole in the ground) is 500' deep and that your casing is also 500' deep. I would also think, by your description, that it is the well casing that has the perforations in it. With that in mind, I would then conclude that your drop pipe holding the pump extends down to 480' and that the drop pipe does NOT have perforations.

What we call "Rock Wells" are drilled in rock or hard material all the way down. With this kind of well you only have to case at the surface like 50'-100' down. Then the rest of the well is open hole. Some people even set the pump below the casing down in the open hole. But technically you should never put the pump below the casing so the flow goes past the motor and so you don't get the pump stuck under the casing when you try to pull it up

Sand or gravel wells would collapse and not stay open. They are cased to the bottom and perfs are used in the water bearing strata on the way down. But the water still needs to come to the pump from below to keep the motor cool. So normally you would set the pump above the highest perforations or use a cooling shroud on the pump/motor.