Will a sewage pump system freeze?

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Old 08-08-19, 05:53 PM
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Will a sewage pump system freeze?

I built an in-law apartment off the garage of my main home, I can't get enough pitch from the apartment to the septic tank so I'm going to have to use a sewage pump system. My main septic tank line comes out of an open craw space in my basement of the main house, in order to connect the 2" sewage pump line to the 4" main septic pipe is to go through the block wall just above the concrete floor in the craw space. My problem is I'll only be 28 inches below ground with my 2" pump line, I know at least 3 feet is recommended to prevent freezing. I have to pump upgrade for about 20 feet, any ideas how I can insulate this 2" sewage line to keep it from freezing? If I was to run this 2" pvc line through a 3" pvc line would that help, or wrap heating tape around the 2" line and then put it inside 3" pipe? Any ideas would be helpful, thanks...
 
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Old 08-09-19, 04:42 AM
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When laying the 2" pipe back fill around the pipe and tamp the soil firm and flush with the top of the pipe. Then lay rigid foam in the trench. Make sure the foam is much wider than the pipe so the cold can't work it's way around the edges.
 
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Old 08-09-19, 07:05 AM
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Never even thought of that, it's hell getting old, lol. What thickness of foam board would I need?
 
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Old 08-09-19, 09:35 AM
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How much foam you need I don't know but I would use a good bit of it since you'll only be 2/3 the way down to the frost line. The big thing is to remember that cold travels in all directions. So if your pipe is at 24" and the frost line is at 36" then you need to keep the frozen earth at least 12" away laterally from your pipe. You'd need foam at least 24" wide so the cold that makes it down around the foam has to travel at least 12" sideways to get to the pipe.

We did this foam on top method on a water line at my brother in laws place in Alaska and it worked quite well. He had normal soil, not permafrost, and we insulated only the top side of the pipe allowing the warmth of the earth below to get to the pipe. In his case we put down 4" of rigid foam 48" wide. This water line went to an outbuilding and where he lived there were no codes or inspections so we were free to come up with our own solution to the problem.

The big problem for you will be satisfying your inspectors. I would talk with them about whatever you do and make sure you have a plan they will approve since technically your pipe will be above the frost line. That's normally not an issue for a drain line since they are normally mostly empty but since yours will be full all the time you have to treat it more like a water line.
 
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Old 08-09-19, 02:35 PM
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Nothing will freeze in a pipe as long as the pitch is sufficient to move the water from the source to the destination regardless of the temp.

Example, I have sump pump, GEO thermal furnace, and gutter drain pipes all running to my creek.

The pitch of all exceeds 1/4" per ft except the one downspout in the front of the house.

It froze in the Polar Vortex in 2014 but none of the others have ever frozen and non of the pipes are below 24" deep.

So, the depth is not an issue, insulation will do nothing, but you must keep the pitch to move the water!
 
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Old 08-10-19, 04:15 AM
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Marq1, this is a sewage ejectment system not a gravity drain system. The pipe will always be full because of the check valve at the pump. And, the pump only runs intermittently so for long periods the water will not be moving in the pipe.
 
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Old 08-10-19, 12:02 PM
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Understand, was providing insight that if underground pipes are sloped correctly they will not freeze in any temp.

If you have material in a pipe that is not moving, it's going to freeze regardless of what is done!
 
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Old 08-11-19, 05:20 AM
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I can only go 28 inches down max in order to get the ejector pump line into the basement of my main home to connect it to my septic line. Next year there will also be 4 inches of concrete over the top of it when I put in a patio if that helps any. We also get a lot of snow here to help as a frost blanket, between the snow, 6 inches of foam board, and the concrete pad over the top of it, you think I'll be safe? I can wrap the 2" pvc pipe with heating tape first and put it inside 3" pvc pipe and bury it that way with the foam board over it, would that be any better? I only have to go about 10 feet with it at 28 inches, the rest of the pipe will be below the frost line..
 
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Old 08-11-19, 04:09 PM
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Winters when you get snow aren't usually the problem. It's when you get bitter cold without the insulating blanket of snow that are a problem. I would plan for the worst as long as you have the ground opened up and it's easy to install insulation and heat.

Heating the pipe certainly wouldn't hurt and could provide a lot of peace of mind. You could install it and only turn it on during extreme weather.
 
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Old 08-11-19, 05:18 PM
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It seems to be the only option I have. I'll give it a try and see what happens this winter, thanks for all the help..
 
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