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I'm encapsulating my crawl space and as a part of this I'm installing a sump pump with a perimeter drain around the inside of the crawl space that leads to the sump pump basin. I installed the sump pump in the back corner of my house. I have a Zoeller M53 sump pump and a 24" x 24" basin. 10" from the top of the basin, I drilled a 4" hole for the inlet pipe. I then made a bunch of smaller holes all around the basin and made them small enough that the gravel won't spill through. None of these holes go lower than 12" from the top. So none of the holes are lower than the inlet pipe.

My reasoning behind this was that I wanted all the water intake to happen above the switch on for the pump. In other words, I didn't think I would want my pump to be pumping out water that was already over a foot deep underground. I also didn't think I would want the holes to be within the range of the pump turn on and off levels. Otherwise, it might lead to short cycling. If the water was already low enough in the ground, I figured it didn't need to be pumped out.

A few questions I have regarding this:

  1. Should I be drilling the holes lower in the basin? Right now, the top 12" of the basin has holes, the bottom 12" doesn't.
  2. Should I drill holes in the bottom of the basin? I'm slightly concerned that the ground water pressure might cause my basin to "float." I was planning to put a 16x16 40lb paver at the bottom of the basin for the pump to sit on. With the weight of the paver and the water that will naturally sit at the bottom of the basin (because it's too low for the pump to kick on and pump out), there will be over 100 lbs of weight keeping the basin from floating I would think. But should I install some holes in the bottom? This would mean my basin would be filling up with water that is 2' underground already. Not entirely sure it's necessary.

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Generally you want the holes at the bottom. This allows you to remove the maximum amount of water from under your slab or foundation. You will not pump out the entire ground water supply as it takes a finite amount of time for ground water to move toward a low-pressure area.

So your sump pump will create a "dip" in the ground water level around the sump but that's what you want to happen.

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