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My job moved me cross country and we bought a house (3 yrs old) that sits on a hill. It has a walk-out basement and the hill slopes away from there, yet the house was built with basement drainage going to a centralized pit and sump pump.

We are going to finish the basement, so I want to make sure it never floods, but the power can easily go out in bad weather. Instead of buying a secondary pump, battery backup, etc, can I just tap into the current drainage bed and use gravity to drain down the hill? Could I dig down near the low corner of the house, find the drain pipe that feeds into the sump well and connect a drainpipe that goes away from the house and down the hill instead?

I know the drain pipes currently in place are sloped to drain toward the centrally located sump well, but as long as they are all below basement floor level, then they could “back up” to my new connection point and drain down the hill without the water level rising high enough to flood the basement, right?

The only negative I can think of is that the water in the sump well (and the other drain pipes leading to it) may get stagnant since they won’t ever empty (my downhill drain would essentially drain from the top of the current system), am I missing anything?

I guess I could break the concrete slab and dig a trench from the current low point (sump well) out that side of the house and drain down the hill, but I would like to avoid all that concrete work if possible.

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    One method to "avoid all that concrete work" and still get to the bottom of the sump would be horizontal boring - often used to avoid digging up a road to put some service crossing under it, for instance. Basically well-drilling, but sideways. – Ecnerwal Feb 28 '20 at 17:10
  • From the house's basement floor height to the bottom of the hill, how long is the hill and what is the estimated elevation drop? – UnhandledExcepSean Feb 28 '20 at 17:36
  • Ecnerwal - horizontal boring sounds useful, but two questions come to mind: Assuming it won’t fit down into a sump well as the starting point so I’ll have to start on the outside and drill in, how accurate is it? I would be aiming to hit a sump well that is pretty small. Also, would that bore through the gravel and drain pipes currently in place that feed the sump? – Luke Patterson Feb 28 '20 at 18:01
  • UnhandledExcepSean - from my basement floor to the bottom of the hill is probably about 60-70 ft and the bottom 3/4 are steep and wooded, I would probably just give it a shallow slope to ensure flow and drain it out via a French drain to the edge of the yard, then let it free flow down the hill – Luke Patterson Feb 28 '20 at 18:05
  • The slope may help but if the water table is high (and / or the hill continues to rise on the other side of the house) the risk of flooding remains. If gravity alone worked I would wonder why there's a pump -- does it raise water over some ledge, or drain somewhere unexpected? – Carl Witthoft Feb 28 '20 at 18:05
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I would say yes you should be able to get rid of the pump if it is not needed . I have had homes with a similar setup and no pump. I would probably seal the sump so if the water starts smelling it is not stinking up the house. With natural drainage I believe the system would be safer with regards to possible flooding with natural drainage especially in an area prone to power outages. Natural drainage will also have less impact on the power bill so for me that would be a win win.

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