How large and how many holes in a Sump basin?

Discussion in 'Pumps and Tanks Well Forum & Blog. Water is life.' started by jrgallant, Apr 5, 2008.

  1. jrgallant

    jrgallant New Member

    Apr 5, 2008
    I'm installing a sump in my basement to help neutralize a recent water problem that I've had. I have the hole hammered out and I've dug down deep enough to put in the basin. I'm wondering how high up on the basin I should start drilling weep holes and also how many and how large should the holes be. The water table is quite high here - the water level right now in the hole is about 8 inches below the surface of my slab. I'm also going to drain my foundation drain tile into my sump as well. Just wondering if I should drill the holes in some kind of a grid or at random and if in a grid, how far apart and how far up the basin should I start. Any suggestions would be greatly appreciated. Thanks.
  2. Bob NH

    Bob NH In the Trades

    Oct 20, 2005
    New Hampshire
    I suggest digging the hole deep enough to set the basin on some 1.5" thick "patio blocks" for support.

    Then I would drill a ring of holes around the bottom of the basin, just above the radius at the bottom. The idea is to drill enough holes so the pump can run continuously as long as there is water to pump. That will reduce the cycling of the pump. You don't want the pump to be running 15 seconds on and 15 seconds off because the water can't get into the sump as fast as the pump can pump.

    If you have enough holes the pump will operate continuously until the water table at the sump is reduced to within a couple of inches of the holes in the basin. Then it will run only as often as necessary to keep the water level down.

    I would put at least one 5/8" hole for each GPM of the pump at the discharge head of the installation. For example, if the pump is rated at 20 GPM at 10 ft head and the discharge is about 10 ft above the pump, then put in 20 holes equally spaced around the bottom. If you use 1/2" holes, put in 30 holes for 20 GPM. More holes is always better if you have enough room without destroying the strength of the basin.

    If one row would put the holes closer than about 2.5" spacing, then put a second row about 1.5" above the first row so they won't have to be so close together.

    Put some larger stones around the bottom to allow the water to get access to the holes, and then fill the space around the rest of the tank with smaller stone, like 3/4" or 1/2".

    Set the pump on the bottom of the tank.
  3. Sponsor

    Sponsor Paid Advertisement

  4. gregr

    gregr New Member

    Apr 8, 2015

    To reduce pump cycling, wouldn't it work better to have a larger capacity basin without "weep" holes? The larger basin takes longer to fill and the pump cycles less. The "weep" holes are only adding water that is well below my foundation. When the ground water is lower than my foundation I see no reason to pump it out.
  5. Reach4

    Reach4 Well-Known Member

    Sep 25, 2013
    The gravel outside of the tank for me would be pea gravely. I would put the holes in roughly a grid about 4 to 7 inches from the top, maybe 1 inch apart. Your concrete has rock under the concrete I presume. I would do my drilling about even with that layer, figuring that layer will be supplying some movement path for water.

    I would use 1/4 or 3/16 holes -- small enough to not let smaller gravel in but still allow water trickles. You can make a hole bigger if you like.

    How will you dig the hole? How will keep the basin in place while you make the weep hole connection? Working during the dry season would help. A strut or jack post could push the bottom against the joists above. Bricks or other heavy removable items plus some water will help as you work and as you poke the pea gravel around the outside and down.

    When I cut my big hole, I found I had reinforcing wire in the concrete. I was using an electric hammer. I used a small bolt cutter to cut the wire. Rather than cut the wire right at the perimeter, I left a few inches of wire just bent up. I was then able to bend that over the rim to help hold the basin down while working. I did not bring in a side pipe. I only relied on water through the rocks. In retrospect, I drilled holes lower than best I think. I wish I had stayed higher, so the pump would only run during wetter times.

    After cramming in as much pea gravel as I could, I filled the basin with water for weight. I then bent the wires helping to hold down the basin to the outside rim. I applied fiber-filled mortar if I remember correctly. Covered the concrete with plastic for a few days to keep the mortar from drying out during hardening.
    Last edited: May 2, 2016
  6. cacher_chick

    cacher_chick Test, Don't Guess!

    Jan 5, 2008
    Test, Don't Guess!
    Land of Cheese
    You want to keep the solids outside of the basin, so a lot of really small holes is going to accomplish this the best. It does not really matter how low you place them in the basin, as the height the pump is positioned in the basin and the switch ajustment is what determines the high and low level setpoints. Also consider that it is really easy to go back and drill more holes or enlarge some of the holes after you have operated the system and see how things are working.
Similar Threads: large many
Forum Title Date
Pumps and Tanks Well Forum & Blog. Water is life. New, larger well pump installed - too large for current wiring Jul 5, 2019
Pumps and Tanks Well Forum & Blog. Water is life. Is a flow inducer on 4" pump really needed with large holding tank? Jun 4, 2019
Pumps and Tanks Well Forum & Blog. Water is life. CSV operation with large volume or small volume tanks Oct 3, 2018
Pumps and Tanks Well Forum & Blog. Water is life. Friction loss in reverse: Small pipe to Large. Sep 13, 2018
Pumps and Tanks Well Forum & Blog. Water is life. Help boosting flow up large hill into tank Aug 17, 2018

Share This Page