8 ¼” bit for 5” casing should be good. That gives you about 1 ½” of space for gravel all the way around the casing. I don’t know about not using mud? Mud is what keeps the hole open until you get the casing and gravel down. You need a consistent layer or thickness of gravel all the way around the perforated casing. If you push perf casing into sand, you will always pump sand.
Air rotary rigs don’t usually drill very well when they encounter a water-bearing zone, because it caves in without mud to hold it open.
Silica sand comes in bags and can be sized to filter the particular size particles in the well. Smaller water-bearing sands need smaller gravel as a filter. And smaller gravel needs smaller slot size to keep the gravel out of the well. Skill saw perforations are very large, requiring large gravel, and then you get a sandy well.
The 20’ of rat hole to catch the sand is not a good idea.
Here is a link to some Silica sand I found.
http://www.targetproducts.com/UserContent/SpecSheets/fltwatwlAB.pdf
First off, your driller is not a well driller.
That will make a big difference when it come time to develop the well.
There is a lot more to a well than just digging a hole in the ground.
Drilling in large sand and gravel needs to be done with a mud rotary rig. Without mixing mud to hold the sand and gravel back, it is like trying to keep a hole open in a box of marbles.
((
This is to help me understand a little about what you have.
Why is the well you have 160' deep? Has it always pulled in air or is this a recent occurrence?
And why would the driller go 250' if there is water at 40 to 60 feet?))
If your well will be in sand or gravel, you would need to buy a screen that is sized for the sand where the water is going to come from.
The size of the screen can go from .006 and up to
? it just depends on the sand the well is being developed in. Most of ours around here are in the .010 to .014 range (that is in thousandths)
Unless you are trying to keep out small kids and animals, cutting them with a saw is never a good idea.
The casing you use should be (well casing) not just sch40 pipe. There is a difference.
Water well dude,
Thanks for the reply. Let me restate the situation.
The well driller is a person that regularly drills 250 foot deep, 8 inch boreholes for closed loop geothermal applications in our area. The geology here in central Oklahoma is that the bore holes will not quickly collapse. There is time to put in the vertical loop or, in the case of a water well, to place a PVC casing and then pour sand/gravel around the casing. I called him again tonight and sometimes he does use mud, but many (most) times he can drill the borehole without it.
The existing 160 foot well (40-50 years old) is recently (last summer) drawing air and due to the extreme drout, the water table is lowering. In the summer, when I irrigate around the house, the water looks "milky" indicating that the pump is cavitating due to the water table being unable to provide enough water to replenish the water being pumped out of the well. Last fall I had to replace the 1 HP pump, lower the pump placement by an additional 10 feet (to within 15 feet of the well bottom) and this winter the project is to put in a deeper well.
Yes, there is some water at 40-60 feet down, but the quantity of water is low and getting lower due to long term low rainfall. In this area, most all water well drillers now recommend putting in a 250 foot well as there are more water bearing gravels down lower. The geology is that there are water sands and then shale/clay layers and then more water sands with more and more available water the deeper you go.
I also understand that the casing should be 160 # PVC and I can get 5 inch diameter locally for about $2.50 a foot (20 foot lengths with bell ends). I can also get some sections of perforated 5 inch, 160 # PVC casing pipe and a woven "sock" to slide on the perforated casing to prevent sand intrusion into the casing (all from local pump water well supply house in Oklahoma City).
Many local drillers do not use perforated pipe, but cut it themselves in the PVC casing with a hacksaw blade so the cut is only about 20% around the casing diameter and many cuts being put in. The well drillers do not use a sock, but just washed gravel/stone outside the liner. The well supply house thinks this is "old school" and strongly prefer the pre made perforated pipe for the lower 40-80 feet and the use of the sock. Obviously, sections of the casing higher up are solid casing and not perforated.
The cost of the borehole digger is $ to dig a 250 foot deep 8 inch borehole. I would have the PVC casing on hand and he helps me put it in borehole, glue up the joints, fill the cavity space with sand/gravel and grout the upper twenty feet with cement. Well drillers that do all the above, are charging $20 or more a foot to drill and place PVC casing. Then the extra expense for electric submersible pump . . .
Once I have a PVC cased well, I can install a 1 HP submersible pump.
Does the above explain the situation?
Thanks for your help.
Steve
Excuse my ignorance but what are the differences between a geothermal hole driller and a well driller? Don't they use the same equipment?
Water wells need to be designed, constructed, and developed properly to make good, clean, drinking water. Geo wells are just a deep posthole with a geo loop thrown in and filled to the top with grout. People think $20 a foot is outrageous for digging a hole in the ground. But there is a lot more than deep postholes involved in making good water wells. The hole is just the first step in constructing a good well. There is some skill involved with drilling the hole, but real skill is needed to install the right casing, perforations, gravel, seal, and develop the well as needed.
Many a farmer has told me they have too many wells to hire out the work. So they purchase and old drilling rig and try it on their own. Then they start calling with the questions. How do I know how thick of mud to use, what kind of mud, how much volume, pressure, pull down force, rotation speed, what kind of bit, how do you keep the hole straight, how do you know when you are deep enough, do you wash out the mud, etc.? Why is my bit stuck in the ground, how do you get it out, how long can I wait to install the casing, what kind of casing, perfs, cap on bottom or not, what size gravel, surface seal, etc.? Then if they get that far the next questions are, how do you get the water cleaned up, how do you determine how much water you can get, what depth to set the pump, what is the best pump size, brand, shroud, splice, drop pipe, wire, controls, etc.?
The only reason I answer some of these questions is that I no longer make my living in the pump and drilling business. It would be crazy for a well driller who has spent years, untold thousands of dollars, and made all the mistakes possible learning these things the hard way, to just show you how to construct the perfect well. Many so-called professional well drillers still haven’t figured it out. There are no schools for this except the school of hard knocks.
I am not saying that paying $20 a foot means you have a driller that knows how to do these things properly. But at least charging you for a properly installed potable water well makes him obligated to make it right. If the customer isn’t happy he could lose his license. But if someone is only contracted to drill a hole in the ground, then a hole in the ground is what you will get.
Use of fliter pipes during bore well rigging
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by palmut » March 29th, , 8:42 pm
If you are looking for more details, kindly visit SINCO.
All,
Recently heard quite a few incidents from my friends where in filter pipes are being used along with MS Casing and the regular PVC pipes during bore well rigging. Bore well guys attribute it to silt in the well or the lack of hard rock. Us not being in this business, it is very difficult to figure out whether it actually a true statement or not. Since, we were told that the silt or loose soil will cover the well, we always will go for the filter pipe for the entire bore well depth, which doubles the total cost. Just wondering whether any one had any such experience and are filter pipes really required in Bangalore.
I'm about to dig a bore well and wanted to hear the opinion of the fellow members here.
Thanks
Re: Use of fliter pipes during bore well rigging
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by Virtual-world » April 3rd, , 12:45 am
I also got bore drilled last week and the borewell person told that there are soft portions at 2-3 locations and filter pipes were recommended.They try to scare and insist on them. They tell that it will cost @ 150?ft, so the pipe alone will cost equal to the cost of borewell. So i refused and after 8 days got the borewell inspected using a camera, the water was still muddy so I am also in dilemma, as I do not spend so much for pipes+pump etc.but there was no loose soil in the visible portions. So I may go for a compressor pump to avoid the submersible pump getting jammed.
Re: Use of fliter pipes during bore well rigging
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by m3_07 » April 3rd, , 11:26 am
If you want to learn more, please visit our website Water Well UPVC Filter Pipe.
The muddy content in the water goes away only after a 15 day minimum usage - on a regular basis. Please do not expect the bore to deliver "evian" grade mineral water on Day 1 !!
Re: Use of fliter pipes during bore well rigging
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by ardesarchitects » April 3rd, , 7:28 pm
Hi
using filter pipes can only be decided by observing the soil while bore drilling.In general silt will look like almost sand.In a very recent case of my apartment project they drilled till 850 and found silt at 500' till 850' after 5 days they checked with camera for installation of filter pipes and realized that bore collapsed till 500'.Now if they need to re-bore will cost them more than actual.So take decision as soon as possible by camera inspection or observe while drilling.
It is recommended to use filter pipes if the soil is loose as you may loose your pump stuck in the bore if it collapses later .Since the pump vibrates a lot deep in the earth crust you cannot anticipate.
Regards
Ar.Praveen.N
Ardes Architects and Interior Designers
Re: Use of fliter pipes during bore well rigging
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by palmut » April 6th, , 3:37 pm
Praveen - you are right. I did the drilling and was asked to go for filter pipes. Couldn't make out whether there was silt/loose soil but didn't want to take the risk and went for the filter pipes.
Re: Use of fliter pipes during bore well rigging
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by Virtual-world » April 7th, , 9:44 am
Want more information on HDPE Dredging Pipes for Philippines? Feel free to contact us.
The cost of filter pipes is prohibitively expensive almost equal to bore cost. And most of the bore drillers they scare you about silt.In my case from 20' onwards to 650 ft it was stone only at 150 ft and 440 ft during bore drilling he was telling that loose soil is there.So what is the exact criterians for filter pipe necessity? The filter pipes can be independently purchased from dealers.
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