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.
High Purity & Ultrapure Water Piping Guide
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The following high purity piping guide, developed by Industrial Water Solutions, is a series of piping recommendations for corresponding high purity and ultra high purity water treatment applications as well as the maximum temperatures that the piping can accommodate. It is also very important that high purity or ultrapure water pipe fitting joints must not utilize chemical (solvent) bonding techniques or threads for assembly. Fitting joints must be accomplished with a heat-based process. The suggested water velocity within the pipes for ultrapure water is 3-6 fps (feet per second).
The quality of water degrades as it is stored and is highly susceptible to bacterial growth. Recirculation of the water at the above velocities reduces the likelihood of the establishment of colonies and biofilm. Installing a UV system and .2 micron or smaller filter helps prevent bacterial growth. Smaller storage tanks, which don’t allow water to sit statically for long as well as spray balls or spray bars also reduce likelihood of bacterial growth. Lastly, deadlegs should be eliminated or minimized.
Due to the reduction or removal of ions, treated water can sometimes become “aggressive” and corrode some kinds of piping. Therefore, when utilizing a water treatment system, it is important to consider the piping that will be used for water’s transport.
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Water Treatment System
Acceptable Piping
Particle Filtration
Most piping can be used
Microfiltration
Most piping can be used, but avoid copper piping
Ultrafiltration
PVC, CPVC, PP, PVDF, 304 or 316 stainless steel
Nanofiltration
PVC, CPVC, PP, PVDF, 304 or 316 stainless steel
Reverse Osmosis Filtration
PVC, CPVC, PP, PVDF, 304 or 316 stainless steel
Mixed Bed Deionization
Virgin PP, 316L SS (PVC, CPVC not recommended)
PP = Polypropylene PVC = Polyvinyl chloride type 1, grade 1 CPVC = Chlorinated Polyvinyl Chloride PVDF = Polyvinylidene Fluoride
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Temperature (‘F):
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140′
185′
250′
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