Crawlspace water and sump pump

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by lemmy, Feb 13, 2020.

  1. lemmy

    lemmy Member

    Joined:
    Aug 26, 2013
    Location:
    knoxville, tn
    My crawlspace floor is mostly flat with rock that is covered by plastic. But about 25% of it is a pour slab where I store quite a bit of things. Then there is a section that is higher that is just dirt with plastic over it. It can be seen in the attached drawing. I have rarely had an issue with water getting in and it has never been bad. After a big rain I might see a 1' wide puddle about 1/8" deep on the plastic in a couple of places. But recently I have had issues with standing water after the big rains we have had. I can't find any place it is coming in and almost seems to be rising up from the ground as the water is more in the middle of the crawlspace and not near any wall. Of course I know it could leak in and just seek the lowest point.

    I plan on buying a basin and a sump pump, but I was wondering if I placed it in the worst spot and drilled several holes in the basin, would it help the entire crawlspace, or is digging a trench and putting in a french drain necessary. It seems that it is common to run the french drain around the perimeter of the wall, but I don't seem to have any water around most of the perimeter. Should I put in a french drain just to the problem spots and bring to the basin, or is just a basin with holes sufficient?

    I do have a footer drain on the outside of the house. When I had some downspout issues I found that 2 or 3 downspouts and a foundation drain come around the right side of the house and dump in to that deep gravel shown on my diagram. Then when the gravel pit fills up with water there is another pipe that empties deep in to my back yard. I wanted to dump the downspout drains down there too, but they are too deep (at the level of the footer drain) so they are already lower than the lowest point at the back of my property. So ultimately I put the gravel back and left it as is.

    Thanks

    2020-02-12-Sump Pump-B.jpg

    2020-02-12-Sump Pump-A.jpg
     
  2. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    You can use just the pit, but put gravel around the outside of the pit I would opt for small river gravel or round pea gravel, and others would prefer crushed stone.

    Another area of disagreement is where to drill the holes. I like the holes near the same height as the concrete or a couple inches below. I would be thinking 3/16 holes, with maybe 1 inch between holes. Lots of holes, maybe 5 offset rows. If the higher holes bring in less water than the lower holes, I think you have enough holes. If you need more holes, you could add more giving about 1/2 inch between holes.


    If the ground water is high enough, you may have a problem with the sump basin trying to float up before you anchor the top in place with mortar. Some would fill the basin with water. But you can also make a leg pushing on the joists or subfloor holding the basin down temporarily.
     
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  4. lemmy

    lemmy Member

    Joined:
    Aug 26, 2013
    Location:
    knoxville, tn
    Thanks. My basin will just be sitting in the ground with nothing holding it in. With holes up higher like that will I need to do something to keep it from floating (post installation). I was hoping the >20lb cast iron pump would hold it down, but maybe not if the holes are drilled up high.

    The pump I plan on using (Liberty 250) can handle 1/2" solids. Should I go up to 1/4 - 3/8 on the hole size or stick with 3/16?

    I plan to have the basin surround by rock and then the boundary between the soil and rock will be some sort of fabric to prevent the fines from migrating in to the rock.
     
  5. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    Maybe a piece of pvc with some fitting, such as a flange, as a foot could hold the bottom down. One cubic ft of air below water has about 60 pounds of lift.

    If you put holes lower, there is less lift to fight. On the other hand, you could end up pumping a lot to lower the water table when that deeper water is not really bothering you.

    You want the holes to hold back the gravel, and the gravel to hold back most of the soil. You can make holes bigger later if you like, but water molecules are really tiny. There is no 1/8 inch solid that you are trying to allow to reach the pump. Don't think you are wasting money if you don't utilize that solid-handling ability.

    Never tried that, but sounds interesting. I think landscaping fabric would not be porous enough.
     
  6. lemmy

    lemmy Member

    Joined:
    Aug 26, 2013
    Location:
    knoxville, tn
    That is a good point regarding the hole size. The only positive I can see to making the holes larger would be decreasing the likelihood of the holes getting clogged.
     
  7. lemmy

    lemmy Member

    Joined:
    Aug 26, 2013
    Location:
    knoxville, tn
    One other question if you don't mind. You suggest pea gravel, and I think (due to it's shape) it is a good solution, but isn't it too small? I am worried it could get through the holes I drill in the basin. I would like to find peak gravel that is sized 3/8 - 1/2", but I don't think I have ever seen it that big. There is a place near by that has different sized river rock, but their rocks are super dirty.
     
  8. lemmy

    lemmy Member

    Joined:
    Aug 26, 2013
    Location:
    knoxville, tn
    Actually, I found some "Pea Pebbles" at a local big box store that claims the stone size is 0.5" to 1.5". So I assume that should work??
     
  9. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    You want rocks/gravel to pass water, but block most solids. As solids from the dirt nearby get stopped, those add to the solid-blocking.

    You want your holes to pass water, but block rocks/gravel.
    I suggested 3/16 holes. Pea gravel is normally 1/4 to 3/8.

    Crushed stone vs pea gravel. I am not sure which is best. The rounded pea gravel/river rock I think cannot pack really tightly together, I figure. The spaces between pieces is good for this purpose.

    I have only put in one sump with pump, and that was into a basement floor. I used mortar to hold it in place

    Regarding dirty rock, I don't know that that would be a big deal. As water flows, the fine dirt will wash into the sump, and you pump it away.

    I don't know why you want bigger rock. That won't do the filtering aspect as nicely. I know you are thinking of having the cloth bag outside of the rock to do your main filtering. I don't know about that.
     
  10. lemmy

    lemmy Member

    Joined:
    Aug 26, 2013
    Location:
    knoxville, tn
    I just want the rock to be be large enough to not pass through the holes in the basin. The basin I had thought about purchasing has some pre-drilled 5/16" holes so I was worried about the 1/4" peak gravel getting in. I guess I might be better off getting a basin without holes so I can control the size and the location of the holes. The "Pea Gravel Pebbles" description at the big orange store claims to be 0.5" to 1.5", but from my experience they are much smaller than that (1/4 - 3/8 like you said). Thanks
     
  11. HydroAirJoe

    HydroAirJoe New Member

    Joined:
    Feb 18, 2020
    Location:
    06820
    You want washed, crushed, stone (about 1-2 inch). The larger stone creates more voids between the stones, thus more capacity. Pea gravel would not give you much capacity. Even though you are not too concerned with capacity since the stone will only surround your sump pit, I would still use the crushed washed stone.
     
  12. lemmy

    lemmy Member

    Joined:
    Aug 26, 2013
    Location:
    knoxville, tn
    River Pebbles Pond Pebbles
    I have had a difficult time finding washed stone around here unless I buy an enormous amount. I plan on getting some bags and dumping it out on the driveway and spraying them, then shoveling them back up in to the wheelbarrow.
     
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