Having unknown well problems: debris

Discussion in 'Pumps and Tanks Well Forum & Blog' started by mikeywell, Jun 22, 2011.

  1. mikeywell

    mikeywell New Member

    Messages:
    5
    Location:
    FL
    Last week my sand filter near the well head started clogging completely with just one run of the sprinkler system (in FL near Sarasota). Well driller came out and didn't uncap the well and look: just said it looked more like limestone and not sand and I should wait for it to clear because with it being dry here, the water tables can change and cause limestone debris. Started hearing water hammer type thumping while near the well head even with me keeping the filter clear so had a pump guy pull the pump and check things out. The specifics:

    Type: residential well with PVC casing
    Area: west central FL, ground is mostly sandy
    Depth: 265 ft.
    Water table: 112 ft.
    Old pump: 1.5hp set at 180 ft.
    Conditions: well feeds both the house and sprinklers on a 1 acre lot so demand can be quite high especially with the sprinklers pulling full pump duty for up to 10 hours twice a week

    With the system 11 years old now, I told him I'd like a better pump anyway because my sprinklers always have had low pressure and don't have good coverage. I figured if he's gonna pull everything out: might as well replace it. So he did. Put in a 2hp 25 GPM pump and set it a little lower (200 ft versus the old 180 ft). He also said that what was clogging the filter looked more like stringy/slimy bacteria so he chlorinated the well while he had it open.

    Now with the new setup and my question/concern... The sprinklers certainly have enough power now. Nice pressure and it can finally keep up with demand. That's nice. BUT... the pump is bringing up sand and tiny pebbles: the biggest being between 1/16 and 1/8 inch. I guess a size just small enough to make it past the screen on the brand new pump. Pump guy said it wouldn't hurt the pump. The water is generally clear but with that pebbly sand. If I run just one zone of sprinklers (about 50 minutes), there's quite a bit of pebbly sand spinning around the end of my Rusko spinner sand filter: the filter is in no danger of being "full" but I'm not used to being able to HEAR the sand/pebbles spin around in there. If I release the debris with a purge, I'd say there's maybe 1/2 teaspoon of sand and small pebbles in there after a 50 minute zone run.

    So I'm concerned. My question is: could the new pump depth be too low? I called the pump guy and he said it's quite common when you put a stronger pump in for this to happen and it usually clears up in a few days to two weeks. He said the debris could be coming from the bottom. I doubt that. He measured the well at 265 feet and the pump is at 200 feet. I can't see 1/16 inch pebbles (which readily sink) being stirred up and rising 65 feet to the pump. Sounds to me more like it is coming from above or AT the pump. Could the pump be hitting the edge of the well and kicking up debris? I assume the casing doesn't go that deep so the pump must be sitting in an open rock hole? Could the pump vibrations be knocking some pebbles off the wall of the well down there? I don't know the internals of a well so I don't know what could be happening. Can anyone give me a scenario that makes sense because I hate not knowing how things work. :)

    Edit: Oh, I forgot that he also replaced all the down-piping from the well head to the pump. Old was 1.25 inch. Replaced with new 2 inch.

    Thanks,
    Mike
    Last edited: Jun 22, 2011
  2. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    4,143
    Location:
    NW Ontario, Canada
    I don't recall you mentioning the size of your well casing. If it has room, a Lakos sand separator down in the well should do the trick.

    www.lakos.com
  3. mikeywell

    mikeywell New Member

    Messages:
    5
    Location:
    FL
    The outside of the PVC casing measures 5.5 inches so I guess that makes the ID 5 inches? Local driller recommended some sort of screen but wanted to charge $2500 installed. Already paid $3245 to get the new pump and piping (which I assume would have to come back out if I install a screen), so I can't imaging the astronomical cost of that. Am I right?

    Mike
  4. valveman

    valveman Moderator Staff Member

    Messages:
    4,549
    Location:
    Lubbock, Texas
    I am amazed that pebbles that size will get to the top of 200' of 2" pipe. I would think you need to pump at least 30 GPM to have enough velocity in 2" pipe to get rocks to the surface. That is why drop pipe is usually smaller than undergroound pipe, because it is pointed straight up. I would take it loose at the well head and let it pump a full 2" pipe for a while. The increased volume will help clear up the well, and the increaed velocity will help get the pebbles to the top of the well.
  5. mikeywell

    mikeywell New Member

    Messages:
    5
    Location:
    FL
    Thanks for the reply! The pump guy ran it full bore for about 15 minutes after he had installed it. Might need more I guess. You bring up a good point though. I wonder if there is a LOT more pebbly debris near the bottom of the pipe that never makes it up the pipe. Will that stuff just sit in there forever and possibly damage the check valve or pump. Jeez I'm a worry wart. Something else to worry about. :(

    Mike
  6. valveman

    valveman Moderator Staff Member

    Messages:
    4,549
    Location:
    Lubbock, Texas
    Heavy debris with too large of drop pipe is something to worry about. Yes it will just settle back in the pump and check valve. 15 minutes is not enough. It will be enough when you can turn the pump on and off and no more debris comes up.
  7. mikeywell

    mikeywell New Member

    Messages:
    5
    Location:
    FL
    Sounds like you are saying the guy hosed me by installing a down pipe that is too large. Not sure about that. We are getting 20-25 GPM at the head (before he connected the plumbing) and it can easily lift pebbles 1/16 to almost 1/8 inch in just a few seconds. If I turn my sprinklers on AND open the valve on the sand filter, I get a half dozen of those pebbles spinning around in the filter within about 8-10 seconds. The system runs at about 10 PSI like that so obviously there is some restriction but I don't want to redo the plumbing on the head so that's the best I can do.

    Mike
  8. valveman

    valveman Moderator Staff Member

    Messages:
    4,549
    Location:
    Lubbock, Texas
    Nothing wrong with larger drop pipe unless you have debris. You need a velocity of about 3 feet per second for heavy debris to get to the top. My book says that is about 28 GPM. You are only seeing the pebbles that make it to the top. There maybe heavier ones that never make it.
  9. mikeywell

    mikeywell New Member

    Messages:
    5
    Location:
    FL
    OK. I don't think much bigger would make it past the pump screen. I saw the pump screen and honestly, I don't know how pebbles almost 1/8 inch are even making it into the pipe (past the pump screen)! Oh well... I used your advice and I've been cycling it full/off and I think it is helping. If I open the filter and let it run full open for about 30 seconds, I get maybe 6-10 of those little pebbles and some sand. Flush those and repeat 1 or 2 more times and by about the 3rd time doing this it is clear and no more debris comes up. So not denying there could be something larger down there but it looks like these purges are enough to clear what will come up and each time I do it I get fewer pebbles. So I'll keep an eye on it and maybe I'm OK.

    Mike
  10. valveman

    valveman Moderator Staff Member

    Messages:
    4,549
    Location:
    Lubbock, Texas
    You would be surprised how large of stuff can come through that screen. It is not the size of the pebbles so much as the weight that matters. Larger pebbles will actually stick in the screen, which makes the flow rate gradually taper off. They will usually fall off when the pump stops, but not always.
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