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fullermatt 05-20-2013 07:21 AM

Trench in sump drain
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My wife and I have a house in SE Wisconsin where we have a high water table. Our sump pump runs about every 8 min during the winter and spring. Right now the 1.5" drain pipe goes through a crawl space, through the exterior wall to grade. In the crawl space there is also a Y in the line to another line that goes through the wall. I think this is for a vent to allow the line to drain when the check valve closes. I suspect this serves two purposes, one to get water out of the line so it does not freeze, and to allow for an alternative path if something does freeze or gets clogged.

The problem is that it puts a lot of water into the yard which is a muddy mess. My plan is to trench in the main line to a drainage ditch which is about 100ft away. I have the go ahead from the county, but need some guidance from the experts. . How deep should I trench it? Do I really need to get below the frost line? The deeper I go, the less pitch I am going to be able to put in. If I keep it at about 18", I should be able to pitch it pretty good.

Thanks in advance,

fullermatt 05-20-2013 09:19 PM

No comments from anyone? I thought I might bump this up a bit.

iamrfixit 05-20-2013 11:53 PM

Bury a larger diameter pipe, I like 3" pvc as a minimum, 4" is even better for longer runs. You don't want to have to pump the water the whole distance, you want the water to drain away by gravity. Pitch this pipe downward the entire distance, 1/8" per foot at a minimum. It doesn't take very much fall, but unlike a sewer line this is only water so if you have even more fall it won't hurt anything. Make sure you dig the trench so the pipe lays straight, you don't want some areas to settle and make low places for water to collect and freeze. If you over dig the trench in places you can pack gravel in the low areas to keep the pipe laying straight and prevent settling. If done correctly the pipe will drain empty each time so it does not need to be that deep. Larger diameter pipe is a bit more forgiving if minor settling occurs.

Avoid connecting your sump discharge line solid to your new line. I install a standpipe just outside the basement wall and insert the discharge line several inches into it . The air gap between the two pipes prevents a siphon from forming. You don't want a siphon to form because it will pull all the water out of the pit and create gurgling on each pump cycle. You can reduce the size of the standpipe for appearance, a 4" standpipe is not very attractive.

(Since you already have a secondary vent line you may be able to get away with connecting yours up solid without a standpipe.)

I have installed several this way including the one on my own house. It runs 70 feet across the yard into a storm water intake at the curb. My yard is very flat so the pipe has only minimal fall, it is just below the ground up near the house and just over a foot deep at the storm drain. It has been put to the test over the last 6 years, it easily handles the sump even when running continuous. Shortly after installation I placed 2 garden hoses fully on into the standpipe while the pump was running continuously just to see if I could get it to back up, it took it fine. I live in a lower area so we often have lots of water to deal with.

fullermatt 05-21-2013 05:43 AM

Great input! I had not thought of the pipe settling. Had you not said anything I would have used loose dirt to get things straight, instead of gravel. A larger pipe also makes sense. Thanks.

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