Septic Discharge Pipe -Freeze Potential?
I’m building in northern VT on a saddle shaped lot <about a 4 ft drop in the middle of the saddle and also sloping front to back> with a septic plan already permitted. The septic location is on the lot line on high side of one saddle. The house will be roughly in the middle about 75-80 ft to the septic location. I want to run the discharge pipe out from the foundation <about 1.5-2ft below grade or whatever is typical> and under an unpaved driveway to minimize the run and maximize the ability to gravity drain the main floor <the basement will require a pump>.
I’m told I should NOT do that because it may freeze if the drive is plowed in winter. Temps can be minus 30. Placing it elsewhere will increase the run and cause a) either pumping the main floor, not desired or b) cause the septic field to be deeper, if that’s even allowed or practical.
Is this freezing concern warranted? What limits <within reason> are there to how deep a tank and field can be placed. Would 5ft or 6ft below grade be unreasonable <tank would need access collars obviously>?
Thanks….Charlie
Replies
in all common sense, there is nothing in the pipe till you flush
Here is my own experience, living at 2000 feet of elevation in the northern Adirondacks, across the lake from you.
We pump our sewage out of the basement lift station tank through a forced main. That line discharges into a 3.5" PVC line that is only about 1.5' underground at its high end, then pitches over to the understreet sewer main about 30 feet away, where it discharges.
The PVC line into which our pumped line discharges is only "wet" whenever the tank's float calls for a pumpout, which may occur every couple days. The line thus sees 5 minute surges every 48 hours or so.
In the two coldest of the last five winters, some kind of ice obstruction has built up in the PVC line, causing enough blockage that our pump heads out and sounds its alarm. The town water guys come out with a jetpump hose and jet out the line.
What gets discussed each time is the fact that the road under which the PVC line runs is plowed, and that a string of -28F nights puts a deep enough chill into the like that something like a small wad of solids freezes, attracts more, turns into a frozen glob, and the next thing we know, we're a solid frozen plug somewhere in there, or mostly.
You can probably do what you plan by being careful to pitch the line at a nice constant, say 1/4" to the foot, not more nor less, and providing a cleanout access on the uphill side of the drive for the possibility of jetting out some ice.
In our situation, our pump system sounds the alarm for us when the line is blocked and the pump cannot push. In a gravity situation, however, you'll only know when something, whatever is lowest, cannot drain. You might have the situation of having a high stack discharge causing backflow in downstairs fixtures. Yuk.
Good luck!
There is potential for water vapor in the pipe to condense and then freeze even when there is no liquid in the pipe.
I would box the pipe in a double layer of 2" styrofoam. Rip the strips and wire them together to make a tight fitting 4" thick box around the tube.
You should be able to do this with 10 sheets of styrofoam. It will be the best insurance money you spent.
We install water, sewer and septic lines in our business and I would definitely be worried about the line freezing in your situation.
The foam will help.But you don't want to box it in.You want a wide sheet over it.You want to allow "heat" from below get to it.Much like frost proof shallow foundation system, the foam acts as artifical dirt..
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
That's the way, not the box.
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With all due respect, I don't think either you or Bill live in an area where the temps get to 30 below or have actually done much, if any, of this type of work??
I liverd most of my life in pl;aces with temps running as cold as sixty below and have been involved in repairs to these lines several times.Your sprinkler lines have a design tolerance for movement with heaving up and down as frost lifts the soil. A waste line needs to stay at the level where it is placed to have the pitch it needs to drain. I have seen three waste lines under driveways snapped right off from the soils moving at the transition from plowed to not plowed. I also had to dig up a waste line for my plumber to get to where somebody had insulated similar to what you describe. They wrapped it with that foil bubble wrap and sprayed it with foam. It was quite a mess to fix that leak.Now, about that question I asked you....
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Temps get to 30 below here on occasion. (Used to be a regular thing before GW.) Our frost depth for footings is 42 inches. Generally anything below four feet is considered safe except when there's no snow cover and a long cold snap, stuff below five is perfectly safe.
The real question here is what is the local standard frost depth?? Knowing the temp can get to 30 below occasionally tells us very little.
And how come no one's focused on the pipe leaving the house at 1.5-2 feet?
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
Dan, Sewer pipes exiting a house at 2' or less is very common when you are using septic systems. Many times the tank is 10' away from the house, but many times we have to install them much farther away and often the line has to run under a drive or other area that is plowed. If they are not insulated properly, they will freeze.
The water and sewer lines coming in to my own home from the street are only 18" deep for the first 80' because of rock ledge. Dealing with shallow lines is a common problem where I live.
BTW, about every 10 years or so, we have frost depths under drives and roads that exceeds 10'.
To all, thanks for all the opinions and comments. You all do a great service to those of us who are trying to do things right but don't have the knowledge and experience needed. No where else on the planet could I access the talent and experience you all offer. Thanks! Allow me to answer some further information to answer some questions posed in the responses:
1. My letter size copy of the original permit plan indicate that the primary field and reserve field <we have to have that in VT> are approx 15 ft from the lot line.
2. The 1.5 - 2ft depth of the discharge pipe was just my guesstimate from others I've seen <many of which are older designs and probably not done properly, although they seem to work>. Bottom line, no science here.
3. This will be a septic tank system similar to what BoJangles describes, though without the ledge. I do have, I believe, the option of setting the tank a) near the house before the driveway, about 10 ft from the house, or b) on the other side of the driveway, probably 30-35 ft from the house. Opinions?
4. My neighbor has his tank, believe it or not, under his deck on the side of his small ranch style house, and his field is under the front lawn which he has plowed all winter. He's not had any problems. However the distances between the tank and field are less than 50 ft, if that make any difference.
5. I'll have to research the true frost depths, etc. This is northeast VT, Canadian Border territory. My anecdotal experience from 20 years of visiting occasionally in winter is they often have several weeks where it doesn't get above zero, and often see morning temps ranging from minus 25 to minus 40, though it often warms to the minus single digits during the day. Last few years these conditions have been much less severe (GW???) I'm fairly certain the local practice <believe it or not there is NO building code there> for frost walls etc is to go down 48inches.
If I need depth, any opinions on sinking the field deeper? Probably a drywell type field vs a pipe and gravel bed <assuming the former is an acceptable method).
Guess I'll have to see what the local guys think about the foam "box" vs "blanket". Decisions, decisions. What's clear is that if I do it wrong I'm in for nasty time.
Charlie
If you have the option, I would locate the tank close to the house. The 10' pipe between the tank and the house will not freeze if your tank is working properly and you use the system normally. Locating the tank as close as possible to the house always minimizes problems with clogs or freezing.
As for the pipe from the tank....be sure you install a removeable cleanout filter on the outlet of the tank. This will keep solids from ever getting into your drainfield.
Insulate the outlet pipe from the tank as I described where it passes under areas that are not normally covered with snow. If you want to lay a piece of foam over the line too, go for it, but be sure you completely box the line or it will freeze at that shallow depth in the temperature conditions you describe.
Be sure you bed and fill any dug out areas around the pipe and tank with clean sand. We have never had issues with frost heaving of pipe causing problems. The ground will not freeze within several feet of the tank.
Do not install the drainfield any deeper than you absolutely have to. There is nothing to be gained by installing a tank or drainfield any deeper than necessary. Be sure you don't drive over or plow over the drainfield.
The only place you have to worry about is the line between the tank and the drywells where it passes under exposed areas, and you can insulate this to prevent any problems.
I'm not sure about VT, but here, you could not sink a field deeper or bury it more. They are designed to work by evaporation. Likewise, the design location of the tank is more specific than "about ten feet" away from the foundation. Code requires that it be a minimum of at least ten feet from the foundation and that no structure be built over it. Maybe your neighbor is grandfathered or maybe he ignored the rules, accidentaly or otherwise.The thinking behind this one is that if the tank should leak, methane gas (unhealthy and explosive) can seep into a cellar or crawlspace and that it will eventually need to be serviced, so building over it is a dumb move there. Besides, so many decks become porches, and so many porches then get closed it to become three season rooms that in another generation get to be insulated....methan and all!Where I am going with all that - is when you decide whether to place tankl ten feet from the house or not, think ahead to wheteher you or anyone is ever likely to add onto the house in that direction.
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I'll start by saying that I'm pretty much in agreement with everything you've said in this message, but I'd like to add a couple of comments, because the situation is more complicated. That is, there are more reasons for the requirements that those you mention.
Onsite sewage disposal codes and requirements vary from locality to locality, but most still reflect work that was done by the Public Health Service back in the fifties, so there are also many similarities among localities.
The required depth of the drainfield is typically based on the need to maintain an adequate depth of suitable soil between rock or seasonally saturated soils and the drainfield. Although evaporation is a consideration, the potential for evaporative disposal of septic tank effluent depends on local climate. Some areas have a negative evaporation potential--they get more rain than is evaporated from the soil. Still, systems installed relatively shallow do tend to function better because shallow soils tend to have better aeration, which increases biological activity and better treatment of effluent and potentially less clogging of soil pores. In any case, if a permit specifies an installation depth, it is likely not permissible to arbitrarily install the system at a different depth.
A minimum 10' separation between the septic tank and the foundation is typical. In addition to the potential for migration of gas, there is a potential for migration of effluent if the tank leaks, potential for damage to either the foundation or the tank if enough force from the foundation acts upon the tank or the tank should fail.
Building over the septic tank is usually prohibited. Doing so often means that the tank can never be serviced. It does happen, but I have seen one real disaster caused by the practice. A concrete patio was placed over the septic tank. The owner had enough foresight to leave access to the inlet and outlet of the tank. Later, a concrete block foundation was laid around the patio, and the patio was enclosed. At some point, it was finished on the interior, creating a sunken living room. The day that I saw it, a leaky toilet had caused the tank to back-up out of the inlet and outlet access ports. The sewage pumper had to pump a couple of inches of sewage out of the living room, before being able to deal with the tank. I know that sounds like a fisherman's tale, but I swear it's true.
Thanks for filling in that generic rule about elevation re aeration and drainage.Here, we have damp clay soils. It is hard to find the required 18" deep non-hydric soil to base a field on to get a permit to begin with.the designs here are very specific and elevation is indicated to a colour marked nail in a tree generally and referenced in the plan. Deviating from plan re elevation is the quickest and most expensive way to get a septic syustem to fail inspection.I believe there is a maximum of X inches of extra fill or topsoil that can be placed over the designed system once built. Soil is so expensive here on this island that it has not been an issue - especially since these mounds are so gawd-awfull ugly to see!
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Bill, I have been doing this for over 30 years. I have put sewer lines under lawns, parking lots, driveways, bridges and everywhere else you could think of. Laying a layer of styrofoam as you suggest will work up to a point. When the ground freezes 6 or 8 feet deep, as it can easily do in a situation such as his, the frost is going to form under that styrofoam and freeze the line.
I have boxed in sewer and water lines like this where the lines are only 18" under ground and they won't freeze.
I have also done it using the method you describe. It freezes and I have to fix it. You learn those lessons the hard way!
How did you do it when it froze?It should be 18" down and extend 4' to either side of the pipe. That traps the heat from below and keeps the heaving from being a problem too. Your box can still get trapped in an ice lens and lift.
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When it freezes, you get the steam sewer cleaner out and thaw it out. You do this several times perhaps during the winter. It is not fun. Eventually, you dig it up and do it right.
Putting styrofoam over the top of a sewer line passing at shallow depth under a plowed drive or parking lot is not going to keep frost from eventually engulfing the whole pipe when the temps are low for a long time. It will eventually freeze completely around the pipe and then you have freezing inside the pipe. 2" of foam is not going to stop the ground below it from freezing when it is 30 below outside!
The foam on top may work in a milder winter or if there is snow cover on the ground, but it is only helpful for so long in exposed areas.
Our sewer trenches are always backfilled with clean sand to promote drainage.
I'm not saying you shouldn't put styrofoam over the top. Every bit of insulation helps, but you must have the pipe totally wrapped with styrofoam to insure that it won't freeze in the most extreme conditions ( which is apparently what he has )
A single family home is the most vulnerable to sewer line freezing because of the relatively low usage, but we have redone dozens of sewer lines from commercial sites that froze every year under parking lots. This usually happens in late January or early February. The last one we did had 2"of styrofoam 8' wide and about 24" under the parking lot. This was spec'd by the engineering firm. It would freeze every winter out near the end of the parking lot.
Of course, the deeper you can get the line, the better your chances of making it through the winter.
I would also suggest to the homeowner that they install cleanout risers frequently wherever possible along the line. In case they do have a freezing problem, it makes the steam out much easier to have closer access to the problem area(s)
"It will eventually freeze completely around the pipe and then you have freezing inside the pipe. 2" of foam is not going to stop the ground below it from freezing when it is 30 below outside!"I beg to differ. We do it here a lot and ou5r frost depth for footings is four feet.Ground and water temps at ten feet down remain 54-56 degrees year round. The earth is constantly radiating heat out towards the surface, so when you trap that heat under the insulation at 18" down, you don't get the frost. Roughly, each inch of insulation is equivalent to 14" of soil, depending on soil type and how dry or damp it is.The University of Maine in Bangor/Orono did astudy on this subject and that is their conclusion and the result applies to a lot up here. They placed a lot of different foams in differnt soils at different depths and installed thermocouples to record the actual temperature differentials throughout the winter.Now, I still don't hear your answer to my question. You assert that done this way it will freeze and you know this because you have done it this way and it has frozen.But I ask about the details of how you did it, because your results fly in the face of my experience, others experiences and the University scientific study. So I have to assume that your way of trying this had some details that were different. by explaining this, you can help us to understand what errors to avoid.Again, their recommendation was to place 2" of EPS foam at 18" deep, extenmdiong 4' beyond each side of the pipe.I can understand that if your normal frost depth is six feet, you might want thicker insulation, but four feet is the norm here.
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Installing styrofoam as you described is a common practice here. My experience shows me that it may or may not work depending on the kind of winter we have.
I do know that a sewer line 2 or 3 feet under a parking lot will freeze when insulated that way when we have spells where it is way below zero for days on end. I have dug plenty of them up and redone them with the pipe boxed with 4" of foam. I have never had to go back because of a problem doing it that way.
I try and do a job once and never have to go back and redo something because I screwed up the first time. I'm sure you operate the same way. I have learned what works and what doesn't in our severe winters.
Your original statement that boxing around the pipe doesn't work is simply not true. It is the one foolproof way I have found to stop shallow lines from freezing. It also uses only half the amount of styrofoam as the other method.
Actually, that sounds like an interesting study they did and I'm going to try and see if I can find it. If you know where it is, why don't you post the link.
"Your original statement that boxing around the pipe doesn't work is simply not true. "Maybe we have been arguing about something non-existant.Go back and read me again. I did not say that your line itself will freeze.What I was saying is that when you encapsule the line in a box, while the interior of the box may not freeze, it is possible (I have seen it that once) for the whole box to be encapsulated in the ice lense and be heaved up as the ground moves from the frost. That movement can break the line off.I can see about finding a link on that study. I did not read it - rather I heard it.
We have a saturday morning radio program here called "Hot and Cold" One of the two primaries of the show hosting is Professor Dick Hill. The guy is in his eighties and has pretty much seen it all inasfar as heating and insulation issues. It is a passion and a hobby as well as a career for him. One program a few years back was devoted to ground frost issues like this and frost protected shallow foundations. He spent quite some time citing this study which had been done not terribly long before that. IIRC, the primary reason for the study was because the university was having trouble with the light posts in their parking lots. In spite of a typical four foot deep pier and footing supporting the 20' tall light, the fact the ground was plowed and paved meant that the frost was lifting them out. The frost lens was an issue and the foam was the best way to prevent that, but the findings went further...
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I have written Proffesor Hill an E-mail to see if he can lead me to that study in print or online.
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I hope he gets back to you. Have a good week!
It's gonna be worse with gravity flow vs pumped, since gravity flow is more of a trickle. But there are a lot of variables. How deep under the drive would this pipe be running?
If you have temps of minus 30 I'd think that the pipe coming out of the house would have to be more than two feet below grade. I'd think three minimum, maybe four.
Pump lines are generally 2" diameter and stay full due to a check valve at the lift pump. So there is a serious freezing hazard where the drive way is plowed in the winter that is more than the hazard to a gravity line that is empty except when sewage is running through it.
Hartmans idea about covering the pipe with a heavy layer of foam over the top only is very good in my opinion. Similar in concept to a frost protected shallow foundation.
M
------------------
"You cannot work hard enough to make up for a sloppy estimate."
Depends on how the pump line is sloped, and whether there's a vacuum break.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
My concern would not be water freezing in the line if it has enough drop. Bacterial action in the tank creates heat that is going to be venting up too.
But what can and does happen isthat the soils of the driveway will freeze harder and deeper and can heave up more than surronding. If they take the line with them in the ice lens, then it can get snapped off. The results of that can be unpleasent to repair.
So provide well for drainage as you design the driveway so water doesn't settle into the sopil in that proximity, and when you trench the line in, go wide so you can cover it with 2" EPS foam 4' out to either sie.
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BTW, here the toe of a field has tobe fifteen feet back from the property line. Are you sure that you are legal going right onto th eproperty line with your design?
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My 'Rule of Thumb' for pipes
Frost depth (in feet) minus Trench depth (in feet) = foam thickness (in inches)
(Frost depth (in feet) minus Trench depth (in feet) ) x 2 = width of foam (in feet)
Example: Frost at 3' and trench at 1 1/2' = 1 1/2" x 3' foam
Example: Frost = 8', trench = 1.5', foam = 6.5" x 13' wide
SamT
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Edited 5/6/2007 9:00 am by SamT
The tests done at the U of M showed to run out parrallel to th eground the same distance that you normally count frost depth. That way you don't have the cold creeping in from the sides.
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My ROT does that too. Run out on both sides the distance from the foam to the frost depth.SamT
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