Sewer and water lines in same trench
For a future home I am going to need either a very long sewer line (~1500 ft), or a shorter sewer one through more difficult terrain that requires an easement, or discharge septic. The water line will probably go along hthe same route as the long sewer line no matter what. Currently I’m evaluating the long sewer line option. My main question is about putting sewer and water lines in the same trench, but I wouldn’t mind volunteered advice on the other aspects.
I believe the 2015 IRC in my applicable code source, and that P2906.4.1 (https://up.codes/viewer/virginia/irc-2015/chapter/29/water-supply-and-distribution#P2906.4.1) is the applicable code. What I gather is that the sewer pipe must be one of several acceptable materials in order to put water and sewer in the same trench. I am poorly-versed on the subject, but it would seem that, mainly, they just don’t want you using clay pipe. Does anyone have any additional understanding? Furthermore, even if it is allowed, would anyone recommend against sewer and water lines in the same trench? Presumably both lines could develop leaks and lead to contaminated water. Why, by the code, is that not a concern for some materials? Am I missing the spirit of it?
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Replies
Paul,
Most codes allow the two in one tench as long as a few mitigating steps are taken. They are generally some separation either vertical or horizontal, and usually that the waterline not have joints or fittings in the trench. The acceptable materials typically coincide with the ones you would be using anyway, and preclude older ones like clay tiles, or corrugated plastic that even if installed correctly allowed some effluent to seep into the adjacent soil. If both pipes did develop leaks in the same area, contamination of water supply in a pressurized line is very difficult.
Thanks, and good point about contaminating a pressurized pipe.
Paul,
Our the years I've run couple of small community water systems. One of the worst parts of working on repairs is having to keep the system pressurized to avoid contamination.
Ah. Just to be clear, this isn't an argument against putting both lines in the same trench, is it? I assume the water lines must be kept under pressure when repaired whether they are near a sewer line or not.
They can get stuff into the system from the ground too. Lots of nasty little microbes live in the ground near the surface waiting to make you sick.
Whenever the water system loses pressure, that’s when you get those “boil water” advisories. Usually this happens after a major power outage or a rupture of one of the BIG water mains. Some of the big water mains are 6 foot diameter pipes.
Bill
Paul,
No, you are good.
As Bill said, lots of coliform etc. in soil - and turbidity can make treatment like UV ineffective.
Paul,
This may not be a code requirement, but consider bedding the water line in sand and then backfilling the trench with more of the same material. This was NOT done in my community, and, after less than 10 years, the HOA had to install new supply lines. Movement in the originally PVC was sufficient to cause constant leaks in the system.
Steve,
Good advice - and because of that it is now required here.
Thanks for the tip, I'll look into that.
You don’t want to use clay pipe. Clay pipe has issues with tree roots getting into it over time. You also will probably be a lot happier with a sewer connection than a septic system. While sewer systems connections come with monthly fees, they also come pretty much maintenance free.
I’d recommend using directional drilling to install such long lines so that you don’t have to open a massive trench. A good directional drilling contractor can do a 1500 foot run in two or three (probably three) setups. They’ll also use HDPE pipe, which is nearly indestructible, with thermally fused joints so no fittings to leak! They can run water and sewer lines, and they can put the sewer lines in with a pitch (slope), which you probably need. It’s MUCH easier to deal with a few bore pits than an entire 1500 foot trench needing to be backfilled!
Bill
Right, I had no intention of using clay and I agree about sewer over septic. Although even with as expensive as discharge septic is, it's possible the up-front cost of sewer could be enough to make me go with septic. I'm still working on estimates, though. What worries me is possibly running into some troublesome stone. The house will be near the top of a hill, where there is a lot of shale. I don't imagine that will pose much of a problem (correct me if I'm wrong, but it's pretty brittle stuff), but closer toward the sewer at the bottom we could find some limestone in the way. Does directional boring have any advantages/disadvantages in this regard?
The larger directional drilling rigs can go through rocky ground without much trouble. My contractor can even use the boring rig drill “bit” to enter precast concrete manholes — the bit cores right through. He says the bits don’t last as long that way.
One crew I worked with had worked in Alaska putting in pipelines to offshore oil terminals. He told me they were boring through solid rock in many places, but with a HUGE rig “the size of a locomotive”
You’ll probably find the boring crew will have less trouble than a backhoe in rocky ground, just gave them use thicker wall pipe to make sure it doesn’t get scored during installation.
Bill
Don't mean to hijack the thread, but I have very similar question regarding water and sewer pipe materials in the same trench. I'll be using HDPE for the main water line. Would gasketed PVC for the sewer pipe be ok in the same trench or should it be glued PVC (or something else)? My sewer line has two sections at 45° angel and about 40' each. Thermal expansion and contraction is probably not a huge deal in this case.
Vlad,
Like Paul, I think you are fine. You might consider using these code provisions as guidelines for good practice.
http://www.buildingcode.online/1019.html
Why not use HDPE for the sewer line too? HDPE offers a lot of advantages, and doesn’t have the potential for fracture that PVC does in an improperly prepared trench. HDPE is usually assembled from long sticks (in the larger diameters anyway), using a thermal fusion machine, so no gaskets to leak.
Bill
Bill, Thanks for the advise on HDPE. I'll see if I can find local contractor to do it for a reasonable price.
You’ll probably need a commercial contractor. Directional drilling companies usually work with utility companies so it’s hard for residential people to find them sometimes. I’d ask your city engineering department who they use (for water and sewer installs), and your local power/gas company engineering guys will know too. You can find a few directional drilling contractors just about anywhere, and most of them will have the thermal fusion machines for the pipe.
Bill
Definitely check with your LOCAL authority before you make any plans. On my latest build the one thing that they actually got on the phone and called me over was water supply line proximity to sewer line or septic. Even though the IRC allows it, this town doesn't.