Sump Overflow Design

[PapaDisco]

I have a walkout basement with two sumps: one for groundwater under the slab, and the other for grey water (laundry, bathroom, kitchen). I've posted before about building an overflow so that a pump failure would not result in a flooded basement. And it occurred to me that it might be possible to locate the overflow outlet under the basin lid if I were to add an extension ring to the basins. This would make installation much easier than a tiled curb. Would there be any issue with the overflow drain acting as a vent? The grey water basin has a 3" vent in it already, and the overflow drain would of course slope down. Attached is a sketch of Version 1 (overflow is above the basin lid through an, as-yet-to-be built tile curb), and Version 2 (bolt on a gasket and basin extension and locate the overflow under the lid and through the side of the extension). The floats and fluid levels would stay the same in both versions so Version 2 would just have more head room.

 

[Reach4]

For ground water, it is usual to not have a vent. However for radon considerations, it makes sense. In fact you might plan to insert a radon fan if your radon test shows elevated levels.

You did not show a check valve for each pump. That is normal to have, but you may not have illustrated that.

For gray water, I am not sure what the rule is for taking that overflow line to the curb. If nobody is checking sounds good to me.

If you put in a radon pump, the high lid would prevent that negative pressure in the pit that you would be looking for. I am not a pro.

 

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[PapaDisco]

I do have check valves in both. Didn’t think to draw those in. Also adding a vent to the ground water sump is a good idea. This under slab drainage system would be an easy route for any radon to follow (plastic sheet, 6” drain rock to full perimeter trenches).

We’re rural, so this won’t drain to any curb. But I thought a big in ground catch basin outside would be good. The under slab de watering is no issue, but the gray water obviously is. Still, better to have it out of the house than in.

 

[Josiah Barnabas]

When adding sump overflow, make sure it doesn't interfere with the main sump. Check valves are important and if radon is a concern, consider venting or consulting a professional.

 

[louisvilleKYradon]

Raising the lid with an extension and routing the overflow under it is a good idea—just ensure it’s sealed, slopes to the drain, and won’t backflow.