RetroFedTrenching near tree advice
WxFisch
We discovered we have issues with our wastewater lateral and it needs to be replaced. Not to get too into the details but where we expected to find a 4” cast iron lateral that could be cleaned and lined we instead found a 6” terra cotta lateral with multiple issues that mainly stem from extensive root infiltration from the maple tree that was planted about 4 feet away from it.
The photo shows the tree and very close to where the line runs. The plan from our contractor is to dig up either side of the stairs and replace with PVC since lining isn’t possible. The excavation is planned to be only in the mulch beds shown, since the main runs in the grass about three feet away from the end of the bed. The existing terra cotta will be left under the stairs and to the main and lined then connected to the PVC.
Our concern is how close the excavation is to the tree and how it will impact the trees health. Ideally we would use trenchless but that isn’t really an option, and rerouting isn’t really possible due to needing to reuse the existing house and main connections. So what should I be sure our contractor is doing to best protect the tree, and how should we take care of it once everything is complete. We are expecting some die off in the canopy but it’s a really healthy tree so we are hoping that with good care we can save it overall.
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When I was a kid, I remember we had a raspberry bush in the garden that suddenly started giving spectacular amounts of incredibly juicy raspberries. It did that for a couple of years, and then we started having problems with the septic tank. When my Dad dug it up to find out what was wrong, he discovered the raspberry bush’s root had reached into the tank and the bush was having a field day with the nutrients in there.
I suspect your tree is doing well for the same reason. If it got used to the land of plenty, it might suffer from being cut off of it.
Sorry I don’t have any particular advice to give you with respect to your problem though - apart from digging up the pipe with a shovel and trying to work around the tree’s roots, which is not something your contractor will be willing to do that is.
I’m not saying laterals have no nutrients, but the concentration and type of nutrients are very different between laterals and septic tanks.
Sewage in laterals is pretty dilute. Septic tanks (the tank, not the drain fields) are where the solids collect. They break down a bit over time and particulate forms of nutrients become soluble and more easily taken up by plants.
The sewage in the fields is also generally more strong than sewage that goes to municipal or shared systems because it’s passing though the tank and taking up some of those newly solubilized nutrients on the way to the field.
The tree is absolutely going to get less water when it’s repaired, but I’d be doubtful that the nutrient level will change all that much.
I hadn’t considered this. I imagine soaps and such also don’t help things in a lateral since a lot of the water will have some sort of soap in it (anything other than a toilet flush, and those will be followed by at least a small amount from hand washing).
Maybe it’s because there’s always some water being pumped into a field, but the grass always grows like hell on a field. Effluent will also have quite a bit of nitrogen because urine=urea.
Yeah, I’ve had that same thought. About 30 linear feet of 6” pipe chock full of tree roots tells me it’s been feeding on that buffet for a little while. That said we live in an area where trees do really well anyways, there’s another tree about 20 feet away that’s also does fantastic and it’s not even close to anything as great as a sewer pipe so I do have hope that after a year or two it will bounce back, but it looks like we will end up cutting around 1/4 to 1/3 of its roots out. Luckily the house blocks the predominant wind and the hill slopes away from the house so worst case it shouldn’t be a risk to the house.
This happened when I was a kid as well, also terracotta, but the tree was a cedar, my father did exactly what you plan to do and the tree wasn’t the same after, but did live. Maples are top feeders(?) and compete with the grass for nutrients AFAIK, so probably will be rather hard on it. My arborist came out for free and took an hour talking about each of the trees in the property before his crew came out to do trimming and take one down, I’d assume that’s common practice, so I’d get a pro out and get their advice. Good luck.
Interesting, about 3/4 of the drip area is mulched with very few plants in it and honestly the grass doesn’t do great under the canopy so maybe it won’t need to compete as hard. I’ll have to see if I can get our borough tree guy to take a look at it, otherwise I’ll need to find a tree company near us.
Typing in with my semi-related thought. That is a crimson King Norway maple. If you’re in North America it is a subpar tree. If you take a swing at the work but the tree gets damaged in your project, could always replace it with something native to provide for our long-suffering wild friends. Doesn’t solve your problem but adds an extra wrinkle of consideration.
Seconding this. While a mature tree is worth something, Norway maples are generally miserable alternatives to a native maple. There certainly are worse trees but so many nicer ones. Their only benefit is they’re hardy, like a Norway rat.
Thanks! TIL and have a rabbit hole to dive down. This one at least has not pushed out anything native at least since it’s in a yard in a suburb, and the wooded areas around us are chock full of native trees.
It also seems to be at least tolerated by the birds and such around us, we regularly see nests in it every year and the birds are always flitting around it. We offer quality bird feed as well to keep our cardinals and titmouses (titmice?) happy year round. But if it dies and needs replaced we will for sure look at native options.
Yes, definitely check it out.
Important thing is that Norway maple won’t provide food for caterpillars, which are 100% necessary for many birds to have babies around these parts. So it takes care of one part of a birds needs whereas a native tree would produce the full spectrum of characteristics that they need to persist.
Cool to think about how complex the food web really is. Good luck on the project! 🤙🤙
Utility engineer here.
Find a new contractor, yours is working with the tools they have have, but a specialist will be able to cut the roots that have infiltrated the pipe, then run a structural epoxy liner through the old one (called CIPP).
Tree roots look for oxygen, so once you have a solid cured in place pipe, they’ll grow around it instead of trying to intrude.
From an arborist perspective, usually limiting the trenching to 30% of the root zone (a radius based on the drip line of the tree) will leave keep the tree alive, but it’s still a gamble.
The 30% will include the arc of the circle it cuts off, and if the tree is large enough that it could fall on a house, it’s not worth the risk.
CIPP was the original plan for the entire run until they got into it. The existing pipe doesn’t have the right fall over the run, being flat in a few places with it seeming as though it rises in at least one spot. They were able to clear the roots from 85% of the line with one area towards the very end giving them the most trouble.
While I have issues with our contractor, the scope of work isn’t really one of them. They are using CIPP for the last few feet to the city main tap, and for the section under the steps to avoid needing to dig that up, as well is along the interior portion before the trap where it is clear 4” cast iron. The only trenchless option we might have in this case is pipe bursting and I’ve not seen anyone in our area that really does that, and it would mean pulling a new 6” pipe which we don’t really. I appreciate the opinion but in this case trenching is really the right option unfortunately for the job being done.
Oooof, sucks about your lateral.
My experience is limited to construction standards for utility work so I can’t speak to how much safety buffer is built in or anything. That said, I typically see a requirement for 10x tree diameter to be protected as the critical root zone.
I’ve seen 3x the drip edge but that’s a pretty similar area. This is under the drip edge so not a great spot.
Im just happy we caught the issue before it was really bad. A little backup in the basement let us find a partially collapsed cast iron house trap (which is what was originally dug up, that’s the pile of dirt in the picture) and a lateral that was so full of roots I’m surprised we didn’t have bigger problems. Luckily our HO policy includes service line coverage so at the end of the day if we can keep the tree it’s really not that bad.
You probably don’t need me to tell you this but it would be a great opportunity to get a backwater valve and install it somewhere you can maintain and test it.
Good luck!
Thanks for the idea, our main is about 3’ lower than the first drain so code at least doesn’t stipulate one on our line. We haven’t really had backup issues and this was fully caused by root encroachment (and related issues like seam separation on the terra cotta and loss of proper drainage angle). The line is at least 55 years old so I’m not concerned with backups after we get a clear run going again with a proper functioning house trap.
I certainly don’t know what I’m talking about with respect to your local collections system but backwater valves also protect things like sewer backups caused by downstream clogs (think: farbergs) and backflow when city sewers are being cleaned (more annoying than disastrous). Also for overland flooding.
I’m sure you’ve done research and got good local advice but I wanted to throw that in there for others who may be reading and not know why they are helpful. A nearby city was hit with record rains earlier this week and there were 2000 flooded basements. They weren’t on combined sewers either, the water table was just too high it was getting in the sanitary pipes via cracks and other means.
I do appreciate the viewpoint, and there are areas around us I’d fully consider installing one (both areas with still combined storm/sewer systems and those with challenging topography and less than well maintained systems). Our borough does a great job keeping our system clear and I’ve never talked to anyone around us who has a backup for anything other than a clogged or more commonly collapsed lateral.
It’s a good thing to be thinking of though for others with sewer issues!
Generally per 1” caliper of the tree you want about 1’ of clearance if you are going to cut the roots for the health/structural stability of the tree. Also if using a trencher they typically are not going to make a smooth cut of the root.
If possible a root pruning machine should be used or if not feasible, expose the roots and make a clean cut with a reciprocating saw. Then feel free to go to town outside of that cut with the trencher. This will allow the new roots to easily grow out of that cut.
Thanks, they are not using a trencher but rather an excavator so I’m sure it won’t be clean cuts of the larger roots. I’ll have to ask them to cleanly cut what they can as they work. We don’t have the luxury working any further out though since the lateral is where it is.