Sump Pump

[CanadianSal]

Based on feedback from the forum, there was a suggestion that a high water table might displace this basin once its put in place.
I took a look at the neighbour's setup, and he has a sump pump adjacent to the sewage pit.
So I am thinking I will do the same - as I have seen water rise and receed in this pit.

I am new to this - what would be the recommended approach - should I extend the current pit to also include a sump pump - or complete this one and cut a new hole AFTER I am finished with this one. Or Can I fit a sump pump in the current pit - outside the basin.

This is more a best practice suggestion. Appreciate your thoughts - I am guessing I will need to rent a jackhammer. Hopefully the kid at the homedepot has some wisdom on this.

 

[Mliu]

Why would you want to complete that pit, only to cut and dig another one next to it? Just enlarge the pit as needed to fit a sump pump basin next to your sewage basin.

Make sure the sump pump basin is large enough for the sump pump you will be using (larger is better because you may need to change your pump in the future and the replacement pump may be larger). The sump pump basin will have or need holes (5/16" or 3/8") around the sides near the bottom to allow water into the basin. There should be a lot of holes: I would have at least double the area in holes as the area of the pump discharge size (e.g., for a 1-1/2" pump discharge, I would have at enough holes to provide at least 4 square inches of opening for water to enter the basin = 52 holes at 5/16" diameter).

Get a large piece of geo-textile filter fabric, and line your open pit with the fabric covering the bottom and all the way up the sides. Fold the edges out onto the concrete floor and place some bricks on the fabric to hold it in place Put gravel (or crushed rock) in the bottom of your pit completely covering the filter fabric by a few inches. Then place your basins so they're flush with your floor (the sump basin can be a little lower if you want to slope the concrete down to it). After the basins are positioned, fill around them with gravel to the bottom of the concrete. You may need to place bricks in your basins to keep them in place while you fill in your pit.

After the pit is filled with gravel, take the top flaps of filter fabric and fold them over the top of the gravel. Cut off any excess. Then place a sheet of heavy plastic on top with cut-outs for the basins. Place your welded wire fabric (with cut-outs for the basins) ensuring that it's positioned about halfway down the thickness of the concrete pour. Now pour your concrete.

 

[Sponsor]

 

[Reach4]

Make sure the sump pump basin is large enough for the sump pump you will be using (larger is better because you may need to change your pump in the future and the replacement pump may be larger). The sump pump basin will have or need holes (5/16" or 3/8") around the sides near the bottom to allow water into the basin.

I would go the other way. I would concentrate the holes up higher, near the level of the bottom of the concrete. Let's say you had holes in a 3-inch high band, and the lower 75% of those holes carry all of the water. That's enough holes. I would also use 3/16 to 1/4 inch holes with pea gravel outside of the holes. If you used bigger holes, you would want bigger gravel and a thicker layer of gravel I think.

Only if the upper holes are carrying much of the flow, would add some more holes. Holes are very easy to add after install. The theory is that the job of my sump pump is not to lower the water table for the neighborhood, but to deliver water to the pump before it rises enough to threaten my basement. I presume that I mortar in the upper part of the sump, so the tendency of an empty sump 3/4 of the way into water to float is overcome. Even if I have holes at the bottom of the pit, the sump must be secured. When the pump runs, the sump will be pretty much empty despite holes. I am not saying putting holes at the bottom is wrong. I am saying I think holes at the top is usually the better of two right ways.

During construction, bottom holes help keep the sump from floating before you get it set in concrete. However you can fill the sump with water from a hose if that is a concern.

I definitely agree that bigger is much better.

 

[CanadianSal]

I would go the other way. I would concentrate the holes up higher, near the level of the bottom of the concrete. Let's say you had holes in a 3-inch high band, and the lower 75% of those holes carry all of the water. That's enough holes. I would also use 3/16 to 1/4 inch holes with pea gravel outside of the holes. If you used bigger holes, you would want bigger gravel and a thicker layer of gravel I think.

Only if the upper holes are carrying much of the flow, would add some more holes. Holes are very easy to add after install. The theory is that the job of my sump pump is not to lower the water table for the neighborhood, but to deliver water to the pump before it rises enough to threaten my basement. I presume that I mortar in the upper part of the sump, so the tendency of an empty sump 3/4 of the way into water to float is overcome. Even if I have holes at the bottom of the pit, the sump must be secured. When the pump runs, the sump will be pretty much empty despite holes. I am not saying putting holes at the bottom is wrong. I am saying I think holes at the top is usually the better of two right ways.

During construction, bottom holes help keep the sump from floating before you get it set in concrete. However you can fill the sump with water from a hose if that is a concern.

I definitely agree that bigger is much better.

 

[CanadianSal]

Thanks for your responses. With resopect to the gravel - does what I have in the picture work? This is what I excavated from the hole.

 

[Mliu]

The reason for the holes near the bottom is to minimize buoyancy that could cause the sewage basin to pop up out of the ground. For example, an 18" x 30" sewage basin could have up to 276 lbs of buoyancy trying to push it up out of the floor if the pit fills with water.

3/16" to 1/4" holes are too small. They will restrict flow too much and are more likely to be fully obstructed by a piece of gravel.

 

[Reach4]

Thanks for your responses. With resopect to the gravel - does what I have in the picture work? This is what I excavated from the hole.

I would buy pea gravel for the part next to the holes or next to potential future holes. The pea gravel is more uniform and the rocks are rounded. The rocks pass water readily. Crushed gravel is better for a for structural base.

The reason for the holes near the bottom is to minimize buoyancy that could cause the sewage basin to pop up out of the ground. For example, an 18" x 30" sewage basin could have up to 276 lbs of buoyancy trying to push it up out of the floor if the pit fills with water.

My concrete had steel mesh. I don't think 276 pounds was significant once the concrete cured. If there was no reinforcement wire, I think 276 would still be OK for the usual 4 inch basement floor. CanadianSal may have much thinner concrete.

Even with holes to the bottom, the float force would be just as strong when the pump shuts off.

 

[Mliu]

Pea gravel is the wrong material for drainage. It is too small and too round, so it packs tighter. Tightly packed gravel does not allow the water to flow well. What you want are voids between the gravel for the water to pass between the gravel. Pea gravel also contains a lot of sand and silt.

The recommended material is crushed rock or coarse gravel, ~3/4" in size, screened and washed. And with the larger gravel, you can have larger holes in your sump basin without fear of pea gravel getting into your sump and destroying your pump.

 

[Reach4]

https://www.zoellerpumps.com/content/literature/fm2125.pdf says

Dig a hole for the basin. The basin should be located in a very low
traffic area proximate to an appropriate electrical outlet. The hole
should be at least 8” larger in diameter than the basin in order to
leave 4” of backfill all the way around the perimeter. A minimum of 4”
of compacted subbase is also required. Backfill and subbase should
be 1/8” to 3/4” pea gravel or 1/8” to 1/2” crushed stone.
​

That is pretty darned permissive. I would be thinking something like this, but crushed rock is probably perfectly fine:

https://www.menards.com/main/buildi...-1-2-cu-ft/1891124/p-1444441405466-c-5784.htm

​

 

[Mliu]

My concrete had steel mesh. I don't think 276 pounds was significant once the concrete cured. If there was no reinforcement wire, I think 276 would still be OK for the usual 4 inch basement floor. CanadianSal may have much thinner concrete.

It's not so much a concern of the concrete lifting (although the patch could crack and separate unless holes are drilled into the sides of the existing slab and rebar epoxied in to the the new concrete to the old slab). The bigger concern is that the basin itself, which typically has smooth, tapered sides, can be forced up out of the concrete like a cork.

Even with holes to the bottom, the float force would be just as strong when the pump shuts off.

Only if you have your pump float set to not turn on until the sump basin is filled to the top with water. But if your sump basin is 30" deep and your sump pump has an integral float switch, the height of the water in the bottom of your pit will never get higher than ~6-10" depending on the pump (versus your design with the holes at the top which will allow the pit to always be 26" full of water).

 

[Mliu]

Does it make sense to use gravel as small as 1/8"? That means you're holes would have to be smaller than 1/8" or the basin would have to be wrapped in filter fabric (or your pump will be ingesting gravel).

That is NOT the right way to engineer drainage, which leads me to question Zoeller's instructions in its entirety. Just because a manufacturer printed it, doesn't mean it's gospel.

Look at the work of guys who do flood mitigation and French drain installation for a living (the real pros, not the handyman installers). You'll see they use the same design I described.