Why does water appear just below my basement slab in one location and not another?

Question

We recently purchased a house and inherited a "5 gallon lowes bucket shoved into a hole with gravel" sump pit. It sits approximately halfway across the width of our basement. There is consistently water in it 12 inches down from the slab. The water level rises and falls with rainfall/seasons, doesn't appear to be any sort of water leak. If I pump it to empty, it immediately returns to where it was before. Okay, cool, water table is 12 inches down, got it.

I finally got the motivation to dig a larger sump pit in the corner under the front side of our basement, in one of the lowest points I measured in basement. It's around 20 feet away from the current bucket-pump. I dug 35 inches down. No water. As I write this there's still water 12 inches from slab in old spot, no water 35 inches down from slab in new spot. There's no drain tiles or anything leading to the old spot, and the ground is like dirt, not particularly clay-like. Does gravity not exist under my house? Is the first pit like, supersaturated or something and acting as a mini-pond that's collected during rainy season?

I hope someone has the answer, it's driving me crazy!

Answer 1

Yes, gravity exists under your house and I’m pretty sure Sir Isaac Newton would agree, but I don’t think he could explain this...

But here are some ideas: 1) a small underground spring, 2) a bearing wall between the two locations, 3) Major addition separates areas

1) Because there’s different soil conditions at the two locations, it makes me think the original builder knew of a small spring and installed some gravel and a discharge pipe. The pipe is located about 12” down so the water never gets too high.

I’d check around your house and see if a pipe extends to a ditch, street gutter, etc. (Follow the roof drains too.)

2) If your house has a major wall separating the two areas, it could be keeping moisture from infiltrating your new hole.

3) Likewise, a major addition could have added a new foundation area, which is separate from the wet area.

I’ll check with Newton and see if he has revised any of his theories regarding basements...and then get back to you.

Answer 2

David, There are many good ideas listed above. Allow me to add my 2-cents. I have dealt with, seen and repaired this very problem in my customer's houses before.

Ground water is a funny and fickle thing. I wouldn't try telling it what to do. You are likely to lose.

First buy an off the shelf sump basin and float activated sump pump. They come as a package and are available in the plumbing houses or on-line. I would get a fairly good sized basin, 50-gallons. Dig out your hole (where you have a ground water problem) half again as large as you need. Fill the bottom of the hole with 6" of 1.5" minus round river/drainage rock. Drill a couple of hundred 1/4" holes in the sides of the basin to allow ground water to find its way into the basin. (these basins are made of heavy duty plastic.) Drop the basin into the hole to set on the new rock. Ensure the rim of the basin sits flush with the surface of the basement floor. Now back fill around the rest of the basin with the round rock to a level about 3" below floor surface. Finish the fill-in with hand mixed and poured concrete. Level with the surface of the existing floor. Now build a partition near the sump location, or install a column to house the utilities. I have systems built on this design that have successfully operated for years.