Question about sediment from newer well

[IAm_Not_Lost]

Hello,
New member to this forum, have used it many times to find answers to my questions, so thank you all!

Today though I could not find the answer so I thought I would ask it myself.

I am in Arizona and last year had a well installed, 250 feet deep with pvc casing, 5” OD with slotted 1/8”x6” sections at 160-180ft, 200-220ft, and 240-250ft.

My pump is a solar Grundfos SQflex pump with a sand protector, and it pumps directly into a surface cistern whenever the float valve indicates it needs to fill it. From there a surface pump moves the water into a pressure tank.

Yesterday I noticed a thin layer of very fine silt/sand on the bottom of my cistern (I am not regularly checking, so this isn’t a sudden new thing). Enough silt that you can’t generally see the black plastic bottom of the cistern if looking in with a flashlight. It’s only a 550 gallon tank and has about a 5’ diameter.

I set my pump to be around 15’ off the bottom of the well. At least that was my goal. My concern and question is; should I be worried my pump is somehow set too low, or is this a typical finding regardless of where the well pump is when you are dealing with an Arizona well.

Obviously most wells are on AC current and just kick on when the pressure tank needs to be filled, and you have a sediment filter you change every so often, so I am wondering if the sediment I am seeing sitting on the bottom of my cistern is just normal, and if it is, should I install a sediment filter between my solar well pump and the cistern.

Long post, I know, but I really appreciate any responses or first hand experiences with folks that have a similar setup.

 

[Valveman]

The silt is coming in because the slots are too big. 1/8" slots are way to wide to be able to use small enough gravel to stop the sediment. I use .020" or .035" slots and gravel that is almost as small as the sediment I am trying to filter out. Raising the pump may help. But you can't raise it too much or it can't access the water. Who decided on 1/8" slots?

 

[Sponsor]

 

[Reach4]

Yesterday I noticed a thin layer of very fine silt/sand on the bottom of my cistern (I am not regularly checking, so this isn’t a sudden new thing). Enough silt that you can’t generally see the black plastic bottom of the cistern if looking in with a flashlight. It’s only a 550 gallon tank and has about a 5’ diameter.

After a year the rate does not sound concerning. If it bothers you, you could probably find or build a mini pool cleaner to pick that up. You should see the rocks that I pulled out of my water heater. I since have filters to keep that from happening again.

Sorry about the big slots. I hope the sand does not build up in the bottom of the well.


Do you have problems with things growing in there? That seems as if that could be a problem.

 

[IAm_Not_Lost]

The silt is coming in because the slots are too big. 1/8" slots are way to wide to be able to use small enough gravel to stop the sediment. I use .020" or .035" slots and gravel that is almost as small as the sediment I am trying to filter out. Raising the pump may help. But you can't raise it too much or it can't access the water. Who decided on 1/8" slots?

The well drilling company decided on slot size. Never was brought up as a question or option, and I was not educated enough on the subject at the time. I am not sure if they just always use the same slot size or if they actually size it based on what is coming out as they are digging.

 

[Valveman]

The well drilling company decided on slot size. Never was brought up as a question or option, and I was not educated enough on the subject at the time. I am not sure if they just always use the same slot size or if they actually size it based on what is coming out as they are digging.

Then I would be asking the drilling company how THEY are going to make sediment stop coming in the well?

 

[IAm_Not_Lost]

After a year the rate does not sound concerning. If it bothers you, you could probably find or build a mini pool cleaner to pick that up. You should see the rocks that I pulled out of my water heater. I since have filters to keep that from happening again.

Sorry about the big slots. I hope the sand does not build up in the bottom of the well.


Do you have problems with things growing in there? That seems as if that could be a problem.

Thanks for the reply. Yes my main concern was just kind of figuring out what the “norm” is in this region. I did also call a well pump company to ask them if that seemed normal and he said all the cisterns in our area developed sediment on the bottom.

 

[IAm_Not_Lost]

Then I would be asking the drilling company how THEY are going to make sediment stop coming in the well?

You raise a good point. I will probably make a few calls to hear different opinions on the matter from other companies as well as contacting the folks who drilled mine.

There may be more specific reasoning or information than meets the eye. Of additional note the rock size where they placed the slots was listed as 5/8-3/4” fractured granite/weathered granite.

 

[Valveman]

Granite dust is hard to filter no matter what you do. These are usually called "rock wells" and are rarely even cased to the bottom. Usually you just have to develop the well by pumping it hard for a long period of time to basically pump out all the sediment. If /when gravel pack is used in a well the size of slots and the size of gravel pack is usually determined by sizing the particles in the water bearing formation. I don't really know if you can put in small enough slots and gravel to filter granite dust? I know it seems like a waste, but you have to pump a lot of water on the ground to develop a well properly.

 

[IAm_Not_Lost]

Granite dust is hard to filter no matter what you do. These are usually called "rock wells" and are rarely even cased to the bottom. Usually you just have to develop the well by pumping it hard for a long period of time to basically pump out all the sediment. If /when gravel pack is used in a well the size of slots and the size of gravel pack is usually determined by sizing the particles in the water bearing formation. I don't really know if you can put in small enough slots and gravel to filter granite dust? I know it seems like a waste, but you have to pump a lot of water on the ground to develop a well properly.

Yeah, I think for now it seems like a bit of sand/sediment is fairly normal in these AZ wells, and probably a bit more noticeable since it is a newer well and because I can see any sediment that comes in just resting on the bottom of my cistern versus having it accumulate in a sediment trap/filter that is cleaned every couple months. I may consider removing the little bit of sediment that has accumulated in my cistern and then installing a spin down sediment filter that has something like a 100 micron filter to act as a pre-filter that removes things like fine sand.

 

[Valveman]

Again, developing a well is more important than drilling it. Pump out what you can before you start trying to filter and clean.