Sump Pit Design and Necessity

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Richtdow

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Yesterday after a couple days of rain ending with a particularly heavy bout, my basement had a couple of inches of water in it from hydrostatic pressure. This happened once before two years ago under similar conditions. Since then I worked my surface drainage around the house (ground level gutters and a swale) and the basement had been bone dry until this weekend.


It was filling at a rate significantly less than 5 gpm as that was the rating of the pump I was using to empty the basement prior to troubleshooting the source. At best I could gauge the fill rate was in the ballpark of 15-20 gph.


I noticed that the water was coming in like a spring from small cracks around the foundation and plugged some up. However, I am thinking I need a sump system to catch the water next time the hydrostatic pressure builds up.


My questions:


1. Given that it will only run roughly once every two years based on previous experience, is a sump pit really the best option? If not, what?


2. How deep should a sump pit be in this situation? I have a hunch that if I go 30" deep I'll just be bringing in water from the ground and pumping it out. Normally this water doesn’t enter the basement anyway.



3. If I install a sump basin, can I put holes in only in about the upper ¼ in order to only capture significant soil saturation as it nears my basement floor?



4. What is the distance away from a sump pit that hydrostatic pressure is relieved? For example, the opposite wall where some leaking/seeping was occurring is about 15 ft away, will the sump pit alleviate this pressure?



5. I have sized the Wayne CDU790 as the most appropriate pump for my head and fill rate. Is this brand and model worth it? At the Wayne’s pump rate, is it too much?



6. What dimensions of a sump basin do you recommend for this application?
 

Reach4

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1. I think so.
2. I would only drill holes higher in the sump liner that you cement in place. I would make those holes correspond to the gravel under the concrete or maybe even a little higher. You will put new gravel in the space around the liner. So water only comes in when it reaches the holes.
I would probably go with 1/4 inch holes. I used pea gravel, but crushed gravel that will not go through the holes should be good. I know some prefer that.
3. I would say the upper 1/6 if that lets the water flow in enough.

4. Depends. Some would like you to put a lateral line in to intercept water. For me the flow through the gravel under the concrete was sufficient.

5. Don't know. Zoeller is good, and I expect Wayne is too. Some choose to pay the extra for an ejector pump, but especially for your occational use, that extra expense is not needed. More power does not mean better. I doubt you will need/want more than 1/4 to 1/2 HP. Bigger is not better for the pump.

6. Bigger is better for the sump. Find the sump liner. Make the hole a little bigger, and put gravel all around. You might even upgrade to a more rigid one made to be used with a sealed system. But you do have to plan for feeding the pipe and power. Secure the top with mortar. I used fiber-filled. If the hole fills with water, you may want to wait until the dry season.

You can just cut down part way, put in a pump as best you can for temporary in the unlined hole, and finish up later.
 

WorthFlorida

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You can chip away at the cracks and fill them in with hydraulic cement that may help stop any flow. I would drill some holes through the leaking cracks at the base of the wall and epoxy in some pipe to drain water into the old or new sump. This will help with any pressure that can build up on the other side of the wall that may cause more damage. It sounds for the most part that the water stays below the slab and as you stated only during extreme rain events does water come through the cracks.

For number 3 question it can get tricky. The basin will need to be anchored down pretty good with cement. When the water table gets above the bottom of the basin, it can pop up out of the ground. Same as trying to submerge a pail into water. It will just want to float up.
 
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Harpooner

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I had a similar problem, but this happened in one of my Airbnb apartments after a strong storm. It is located on the first level, but it is very easy for the water to come in once it's raining. For me, a sump pump helped a lot, and since then, I didn't have problems of this kind for almost one year. I think you have to do like me and search for the best sump pump in your area and contact them. I am sure they will help you with all the details you need, such as what type you need and how to use it correctly.
 
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