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Question DetailsAsked on 1/26/2018

How far down does a pvc pipe have to be burried underground

The pvc piping is outside in backyard attatched to a sump pump , which in freezing weather freezes, so we are thinking of burying it and would like to know who to call for this project. Thank you

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1 Answer


Depends on frost penetration depth in your area - you can google for that or for a more accurate number check your local building code website - they usually have a page on it.

Note the ENTIRE pipe has to be below frost depth to prevent freezing - meaning coming out across the top of the foundation and then down into the ground will not work unless it is VERY well insulated from outside temps but exposed to house heating at that point.

Also consider the outlet - you have to take special measures to be sure the outlet does not freeze up - and with the typically pretty sporadic flow from sump pumps, for that reason (freezing at the outlet or in the pipe itself near the outlet end) generally, using below-ground drainage for sump pumps is NOT recommended- or at least assume it will freeze up and provide a good secondary surface discharge path. In some cases you can use perforated drain pipe (assuming this is above groundwater level) to let the water mostly or totally drain into the ground before it ever comes to the end of the pipe. Putting a stone pack with exterior filter fabric around it can also increase the infiltration ability - assuming water in that area will not cause damage, infiltrate to your well, or saturate a leach field. Commonly, to prevent exit point freezeup you have to deeply bury the outlet section in an outlet stone drain field to prevent glaciering and freezeup - because it does you no good to run the pipe below frost level just to have it daylight through frozen ground to freezing air conditions, especially where the flow is sproadic so there is no continuing flow to keep it thawed out.

Thaw cables can be used to alleviate this - but you then need a freeze alarm on it to tell you when it fails, and of course you have no protection during power outages (assuming your sump pump has backup system to operate in power outages). I have also seen a fan system, with a small fan blowing into the sump pump discharge pipe from inside the house, blowing a low flow of heated air through the pipe to keep it thawed - though of course that is not energy efficient.

Also, because of the intermittent flow, ensure the portions at/outside the heated house environment have a very good downward slope so they drain out slowly, instead of dribbling along or pooling in a low spot and possibly freezing up in the pipe - at least 2% and preferably 5-10% slope or steeper in that section.

This issue of frozen-ground drainage issues is why a lot of people in areas with deep frost penetration, with sump pumps whose operation is sporadic - not a near-continuous flow - run the discharge (with proper air breeaker and trap) into their septic system.

Couple of other thoughts - to handle the contingency of the pipe getting plugged, where the sump pump discharge goes into the below-ground pipe there should be an opening that the water can exit above-ground so there is always an exit point - and the discharge should be at a point where the water will flow away from the house, not pool up against the foundation.

I recommend, if going to the trouble of burying it deep, go with standard 4" drainfield pipe, not a smaller pipe - much easier to clean or snake, does not plug up nearly as easily, can be looked into with a flashlight and mirror and actually see through it, etc.

Also - be sure to put in a sweeping curved cleanout at the inlet so you can run a hose with a jet nozzle in there to clean it out as needed - and preferably from the outlet end as well.

Answered 2 years ago by LCD

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