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Sand in ground water and well casing  RSS feed

 
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The drilling crew and rig finally came out to my new place a couple weeks ago to drill a well for me. Hurray! They spend a couple days drilling and hit water at 190ft and went another 10ft. They found a great stand on non-sulfur water down there, with the driller guesstimating a useable rate of 50-60 gallons per minute, which is fantastic, except the water is full of sand and sediment. They sent a 10,000 slot screen down the well casing, which is PVC pipe with a bunch of slices around the circumference of the pipe and in two 20ft sections to help filter out the sand and provide a static column of water to set a pump in. The problem is the sand and sediment is so fine, it went right through the screen and filled it up. Bummer. So they pulled the PVC screen back out and sent the drill bit down to clean out the casing, but more sand keeps coming. They tried again, this time with some small gravel down the casing to act as a pre-filter to keep the sand from entering the screen. From what the driller said over the phone it kinda worked, but is only providing about 1 GPM, which they said is unsatisfactory.

My new homestead is sitting on an ocean of water that I currently can't use due to the sediment. Fortunately for me, there are some laws and regulations in place, and in the state of Tennessee, a well driller is required to "develop" a new well, removing any debris, sand or sediment and provide a working well to the customer. So the drillers can't abandon this unless they forego payment, but that's not what I care about. I want to be able to use this water for my new home and for livestock. The drillers are really great guys, have been very nice to me, and are trying to give me a working well so I'm happy and they get paid. But this has been going on for a few weeks now, which I know is really frustrating for the drillers, as they want to be done with this so they can move on to the next job. Last time I spoke to them, which was friday, they were trying to get ahold of a guy they know in the industry to bend his ear and see what he has to say.

I'm writing this to ask the people of the Permies community if they have any suggestions, or maybe someone here has dealt with a similar problem before, or maybe there is even a water resources engineer among us who might know a thing or two! I've got my fingers crossed on that last one. My wife and I have been talking about this and we've decided to let the drillers exhaust their options and if they come to us and say they can't provide a working well, we are open to them drilling deeper to see if there happens to be fractured bedrock (which I hope is where all this water is coming from) beneath this sand within a reasonable depth of another hundred or two hundred more feet.

City water, as I'm sure some of you reading this are thinking, is close to 2000ft away, and will cost about what the same as what we're sitting at right now with the well at 200ft. Besides, I don't want to be dependent on municipal water, but at the end of the day it is an option.

Does anyone here know how to keep sand & sediment in ground water from plugging up well casing pipe?

Here's a picture of the screens intended to filter out the sand and a picture of the sandy silty problem.


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I am definitely not an expert on this topic, have however played a bit with well drilling using primitive methods (not successful).

Could you flush the sand out periodically? (By placing a smaller hose/pipe in the well pipe and forcing enough water into it, that the uprise of the water is higher than the speed at which the sand falls down.)

Alternatively maybe a pump that tolerates sand? And then separating it above ground in a big tank?
 
James Freyr
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Sebastian Köln wrote:

Could you flush the sand out periodically? (By placing a smaller hose/pipe in the well pipe and forcing enough water into it, that the uprise of the water is higher than the speed at which the sand falls down.)

Alternatively maybe a pump that tolerates sand? And then separating it above ground in a big tank?



Well (no pun intended), I don't have the sort of equipment to pump water down 200ft with enough pressure and volume to come back up that 200ft with the debris. As far as the separation above ground, I'm looking at centrifugal sand/sediment filters, because I have a feeling no matter how good the well drillers get it, there will always be some amount of grit coming out of that well and into my pipes. I think a centrifugal sediment filter that has a valve at the bottom I can open to purge the collected sediment is a far more cost effective and less wasteful method of removing the sediment compared to using say, a 20 micron physical filter which will need frequent replacing.

I've been thinking about this a lot, becoming an armchair well expert full of layman speculation and looking on the googles for a possible solution. My brain thinks "use a finer screen to keep more of the sand and sediment out". I have no idea what size screen that pvc is they tried, but the slots look pretty big to me, like twenty five thousandths (0.025 inches or 0.635mm) and I wonder if maybe going much smaller like 0.005 inches but many more in number might be the solution. I also came across some well screens that have a gravel pack in them, and maybe this is a solution. Here's what they look like:

Edit: something went wrong with the image I tried to link, so let me try it as an attachment:



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Sebastian Köln
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The sand is very fine, so it sinks very slow. If you have a large tank and a pump that can deliver a modest pressure, it should work. (Keep in mind the the gravity induced pressure applies in both tubes, so it is really equivalent to pumping water 200ft on the horizontal.)

I have not used a centrifugal filter, so I can't comment on that.

I don't think regular filters can be a permanent solution, simply due to the amount of sand that will come out of the well over time. Another issue is that the finer the filter, the slower water gets through.
Depending on the volume of water needed (that has to be filtered), you could use two containers: One is filled and sits a day, while water is sourced from the other one. Once empty the sediment can be drained (optional).
For drinking water one container might be sufficient if the inflow rate is limited so that it does not disturb the sediment at the bottom and the clean layer at the top. (Assuming the container is kept slightly warmer than the well temperature, so the fresh water does not rise to the top.)

For reference, the clay I mix has a layer of clear water after about two days. Clay is far finer than your sand, so one day should suffice.
 
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Good luck James!  That is an expensive endeavor. 

I wonder how far down the bedrock is, too bad you can't have them punch through.
 
James Freyr
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Hey thanks Scott! I wish I knew how far down the bedrock is. I think the only way to find out is to send the drill bit back down and keep going, but unfortunately I don't have a blank check for this endeavor. I'm pretty confident that there is some sort of engineering solution to keeping the sand and sediment out of the casing and creating a column of good water I can pump out. I imagine this situation can't be unique and people have drilled sand holes before and found a way to deal with it. I'm just kinda ready for this to be finished and not keep dragging on. Hopefully a solution is found in the next couple weeks.
 
Scott Foster
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James Freyr wrote:Hey thanks Scott! I wish I knew how far down the bedrock is. I think the only way to find out is to send the drill bit back down and keep going, but unfortunately I don't have a blank check for this endeavor. I'm pretty confident that there is some sort of engineering solution to keeping the sand and sediment out of the casing and creating a column of good water I can pump out. I imagine this situation can't be unique and people have drilled sand holes before and found a way to deal with it. I'm just kinda ready for this to be finished and not keep dragging on. Hopefully a solution is found in the next couple weeks.





I'm sure you will find a solution!  Let us know how it turns out.

Cheers Scott
 
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James, Just wanted to do some brain storming but everything I ask might be really stupid so take this with a grain of...sand.

I am trying to visualize what this looks like underground. Seems that there is a formation that is almost like mud? Like an underground river or pond that has a lot of sand/silt in it? Does the sand/mud settle out or is the underground reservoir an emulsion of sorts?  I wonder if the drillers can pump the well at a max rate , one that would begin to suck the sand out forming a void underground. Moving a bunch of the sand/mud to the surface.  The recharge rate of the water would begin to refill the void. The trick would be to find a pumping rate that would not move sand from farther away from the well hole thus just refilling the void with sand. Seems to me that if you could ever create this void and then pump just enough water out to not create an underground flow, which would carry more sand with the water, you might be able to solve the problem?
 
James Freyr
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Miles Flansburg wrote:James, Just wanted to do some brain storming but everything I ask might be really stupid so take this with a grain of...sand.

I am trying to visualize what this looks like underground. Seems that there is a formation that is almost like mud? Like an underground river or pond that has a lot of sand/silt in it? Does the sand/mud settle out or is the underground reservoir an emulsion of sorts?  I wonder if the drillers can pump the well at a max rate , one that would begin to suck the sand out forming a void underground. Moving a bunch of the sand/mud to the surface.  The recharge rate of the water would begin to refill the void. The trick would be to find a pumping rate that would not move sand from farther away from the well hole thus just refilling the void with sand. Seems to me that if you could ever create this void and then pump just enough water out to not create an underground flow, which would carry more sand with the water, you might be able to solve the problem?



Hey Miles, I think your questions are great, I've been wondering the exact same things. So I don't think the formation is similar to mud. It looks like grey dirty water coming out of the hole. So if I had to guesstimate a number in my head based on what I saw, I would say it's 90% water and 10% particulate matter, I could be way off there but there was nothing thick and muddy about what was coming up. So the sandy silty stuff I think does settle out. I went there on a monday and everything had sat over the weekend. When the drillers sent a pipe down and started pushing compressed air down their pipe, I saw a column of clear water coming out of this 6 inch casing, which then turned grey, so to my mind the particles had settled out over the weekend. One problem that happened is during the settling, it's my understanding that the sand and silt then compacted inside the 6 inch casing under the weight of the water above it. (the static column of water the ground water pressure pushed up the casing is 100 feet tall.)

I had envisioned the same thing you did with the drillers hopefully creating a void at the bottom of the well casing where a pocket of clear water would be, but I don't think that is working. When I talked to them on the phone the other week, they mentioned they spent two days pumping it to no avail. I'm guessing they were thinking along those lines that maybe they can remove enough material to get a clear pocket of water at the bottom of the casing. I had also thought that possibly their machine is removing water at such a high rate that it's creating turbidity in a localized area deep underground that just keeps bringing in sand from farther away as the ground water moves along to replace what's being pumped out, which had me thinking what you mentioned about pumping just enough to avoid creating fast flow underground that disturbs the sand, which in my imagination is settling out. I mean, most particulate matter settles out with gravity. I know the sand particles are heavy enough to do that. I wonder if some of the very fine silty particles have the same "specific gravity" as water (if Im using that term correctly) and just stay suspended, but then I remember that column of water coming out of the casing that sat over the weekend and appeared clear to my eye.

I still hold faith that this can be solved with the right kind of screen and maybe a gravel pack too. Like I mentioned above, my situation can't be the first one ever, can it? Certainly drillers have come across similar situations before and found a solution.
 
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When they started pumping, after the sediment had settled for the weekend, where was the pump intake in terms of the height of the 100ft water column?

My thought is, if there's any amount of settlement, and you allow space for that to occur at the bottom of the well, and then have your pump intake above the level where the sediment enters the water column, all you have to do is ensure that the intake doesn't descend into where the silty water is entering.

You have your water column, and sedimentation will occur at the bottom. It is similar to the other suggestion I was going to make, regarding a cistern.

If you had a cistern into which you pumped, your well infrastructure would have to be able to deal with the sediment, but if your cistern capacity was large enough, and made of a substance with significant thermal mass itself, the cistern would be at a higher temperature than the incoming silty water, so theoretically, the incoming cold water, if introduced near the cistern floor, would stay there, and if the flow rate wasn't so high that it disturbed the sediment, the intake for your household water could be kept near the top.

You could periodically allow the cistern to run dry to clear out the sediment. Should the subterranean features change enough so that your well water runs clear, you could retain the cistern as is, for emergency use, or just plumb the well as you had originally intended. I would probably keep the cistern, though.

Sorry it wasn't as easy as drilling a hole and filling your glass. Keep us posted, and good luck.

-CK
 
James Freyr
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Hmm, I think I could have been more descriptive and my words may have been a little easy to misinterpret. When I mentioned they were pumping after things had settled for the weekend, they were pumping 350psi compressed air through a pipe down the PVC liner which was in the casing. From a glance, it looked like a 2inch pipe for compressed air going down the 4 inch PVC liner which has the 40ft of screen at the bottom (see picture above) which is going down the 6inch steel casing. They did not have a well water pump down in the column of water (yet). When they did this, all the water came up, and then it stopped. The sediment had plugged the casing somewhere near the bottom, preventing water from entering the casing. (that’s my understanding)

Days later they apparently did put a water pump down the well liner and the well was supplying the 1GPM flow.

Here’s a couple more pics. The first one is the discharge hose while drilling to give everyone some idea of the fierce amount of compressed air this rig sends down the hole. I can only imagine the amount of sediment it might stir up deep underground. The second pic is the initial flow of water emerging on that monday after things sat all weekend. The third pic is the end of that flow of water now all mixed with the compressed air their using to blow the water and sediment out.

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Bored wells have to be drilled into bedrock. In missouri the wells first 80 feet must be cased and grouted to prevent surface waters leaching into the deep aquifer, the case MUST extend into the bedrock.   My well is 465 ft deep. I pump it 3000 gallons per day. Have for a year almost. One day after a heavy heavy rain the water coming out of the ground turned to straight clay. There must have been a seam of clay they had drilled through and until the water level rose it wasn't a problem. After several days of pumping it cleared up but made a mess of my water tank and porcelain fixtures.  Long story short, I talked with some different well drillers and they told me to contact the department of natural resources, they have cameras they can send down into wells and inspect for seams like this and he said the repair is as simple as installing a sleeve inside the well to block the seam.  Perhaps your issue is you hit a seam of silt and you only need a sleeve as well, but it sounds like a second opinion is in order and I would look to your own states department of natural resources for that opinion.
 
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I realize this is probably a little late to resolve your issue...

The driller was on the right track with the gravel pack but the material size was wrong.  The slot size of the well screen should be based on the sediment size the well is installed in.  Then the filter pack particle size is based on the screen size and aquifer sediment size.

You mentioned 10,000 slot screen.  I think you are talking about ten thousandths of an inch slot (0.010") which is about the smallest slot size used in wells.  So that was appropriate.  However, the filter pack size sounds like it was way too big.  The filter pack should be the smallest size that has about 95% or more retained by the screen.  So a 0.010" slot screen with very fine sand or silt aquifer would have a filter pack mesh size of 20/40 (see attached chart).  That should hold back the fine aquifer material and still let water through.  The well driller will still need to develop the well to clear out the fines and get the filter pack as clean as possible.

This is pretty basic well design.  Though some drillers only know 'the way they have always done it'.  I've run into drillers who place pea gravel as a filter pack no matter what the aquifer sediment size is.  Not only does that mean you may be pumping sand forever, it can create voids that can put assymetric force on the screen and collapse it.

For what it is worth, I am a geologist/hydrologist and routinely design wells.
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Silica Sand Filter Pack chart
 
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As an interim solution a plain old sand filter will polish your water and remove the fines,

A sand filter is an above the ground vessel, (usually a plastic 55 gallon barrel) with the bottom 10 inches filled with course (1"+)  rocks, the next 10 inches filled with fine pea  (preferably pebbles rather than flake) gravel, and the last 10 inches filled with cleaned sand, a fine (removable) screen  suspended above the sand as a quick prefilter.

In use, the water is ran through the filter as slowly as possible to adequately supply demand, another pump is required from the bottom of the vessel to inject the cleaned water to a pressure tank, and from there to the rest of the system, a common 5 micron whole house filter installed before the pump is used as a final polish. When flow begins to diminish, clean the prefilter and scoop the accumulated muck from the top of the cleaned sand, and replenish the sand as necessary, the whole house filter should be changed yearly.

Obviously the fines will filter down through the system over protracted use and the sand filter will have to be rebuilt periodically, as determined by the quantity of sand caught in the whole house filter.....but usually the sand filter will last several months to several years depending on the fineness of your muck.

A sand filter needs to be kept in a dark area to discourage the growth of algae. If kept wet constantly via recirculation (when no demand is required) a healthy bacteria culture will form that aids in breaking down undesirable toxins.
 
James Freyr
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Ardilla- Thank you for the response and it's not too late! That's the kind of info I'm needing to hear. It makes sense to me, and now that I think about it, I think you're right and I mis-heard the driller when he said ten-thousandths slot screen and not 10,000 slot screen. (I'm deaf in one ear and I mis-hear shit all the time. It often makes for good laughs). My well has not been developed yet, and they also have not sent me a bill, so they haven't received one dime from me and I imagine they would like to get paid for their labors and materials as much as I would like to have a working well.

I did find 0.005 slot screens in the internet and thought that may be part of the solution as well as a different filter pack. I'll approach them about finding a solution so we can both be done with this well.

Red- I've been looking at sediment filters because I realize that no matter how good the well filter pack and screen is, some sediment will always make its way through the well pump. Instead of replacing physical media filters I've been looking at centrifugal sediment filters and all I have to do it open the clean out valve on the bottom of one and the water pressure blows the collected sediment out.
 
James Freyr
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I want to post an update: Finally, after four months, I have a working well. Interestingly, the well drillers abandoned the well they drilled (the black steel pipe), and drilled a new one (white pvc pipe) right next to it using a different kind of drilling rig. I'm not privy to the world of well drilling and and the different ways of drilling and can't remember what the type of rig was called, but apparently it uses a fluid to remove the debris as the well is drilled instead of compressed air like the other rig. Somehow with this difference, they were able to drill a stable hole and put a filter pack around a well screen. The new hole is 220 feet deep, has a 140 foot static column of water in the well casing, and the well guys were pumping out 20 gallons a minute and were unable to pump it dry with the size of pump they brought with them to test the well. The water is clear, no sulfur odor and I'm real happy with the outcome. My next step is to get a water analysis and I'll post those results here too.
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What was the cost in the end?
 

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