Knowing What’s Below: Buried Utility Location

We humans have put an awful lot of effort into our infrastructure for the last few centuries, and even more effort into burying most of it. And with good reason — not only are above ground cables and pipes unsightly, they’re also vulnerable to damage from exposure to the elements. Some utilities, like natural gas and sanitary sewer lines, are also dangerous, or at least perceived to be so, and so end up buried. Out of sight, out of mind.

But humans love to dig, too, and it seems like no sooner is a paving project completed than some joker with a jackhammer is out there wrecking the pristine roadway. Before the construction starts, though, cryptic markings will appear on the pavement courtesy of your local buried utility locating service, who apply their rainbow markings to the ground so that nothing bad happens to the often fragile infrastructure below our feet.

Call Before You Dig

By law, every public utility company in the United States must participate in a “one-call locator service.” The Federal Communications Commission established 811 as the phone number to access the once-call system, which allows excavators to request location and marking of buried services. Location services are paid for by the utility companies, so there’s no direct charge to the customer.

Anyone doing any sort of excavation is required to call (or now, submit a request online) to schedule a location service to mark the intended work area. This applies to any digging — while the damage a backhoe with 40,000 pounds of breakout force can do to a gas main can be catastrophic, a homeowner with a posthole digger for that new mailbox can be just as dangerous. If you’re going more than 15″ deep, you need to call, because if you cause any damage to underground services, you’re on the hook for it. If you live, of course.

Beep, Beep, Beep

Once a ticket is entered, a location technician will usually come mark the job site within a couple of days. The caller is required to mark the general location with white spray paint. The tech isn’t coming in blind — he or she will have maps that indicate rough locations for the major utility lines. But the world beneath our feet is surprisingly dynamic, and coupled with the possibility of there being facilities that were never recorded properly, that makes physical verification of line locations a big part of the tech’s job.

Location techs have a wide range of tools to locate that which can’t be seen. Given that most underground facilities have some kind of metallic component — older water and sewer lines, natural gas pipes, and the copper wire in electrical or telecom cables — electromagnetic tools get the bulk of the work done.

Detectors can be active or passive. Passive methods are usually used to locate facilities that already have an AC signal on them, like power lines or telecom cables. These can be trickier since the signal strength depends a lot on what’s going on in the circuit. Passive methods can also include magnetometry to detect weak magnetic fields generated by utility lines, and even ground penetrating radar to probe beneath the surface and build an image of the buried structures.

Active detection applies a current to an above-ground section of a utility line, like a water or gas meter. An AC signal is applied to the line by the transmitter, which turns it into an antenna. Utility companies sometimes even lay copper wire alongside plastic lines as an aid to active detection. Handheld receivers with highly directional antennas are swept over the ground to pick up the signal, allowing the tech to mark the location. Sometimes a transmitter is even threaded into a pipe and a receiver is used to trace the signal as the probe is advanced through the pipe.

The Consequences

So what can happen if you fail to call before digging? Chances are, nothing. But when something happens, you can bet it won’t be good:

So next time you’re trenching for a power line to your shed or even driving a ground rod for a new antenna, make sure you make the call that could just save your life.

[Featured images: Positively Naperville]

54 thoughts on “Knowing What’s Below: Buried Utility Location

  1. regarding the video – “there’s this big-ass pipe with high-pressure gas in it sticking out of the ground, surely the underground part doesn’t go in the same direction then the top part”… This is a classic example of 0 critical thinking.

    1. More than likely they thought, or someone told them, the gas line was deeper than it is.
      Or possibly they used divining rods / witching sticks to ‘find’ the depth. Sadly I’ve seen it done by people in that line of work, thankfully they already had the utilities marked by someone with the right equipment so there was no risk, but it’s still baffling.

  2. I recently used 811’s web site to have them mark utilities so I could dig a trench for a new water supply line for my garage. It was a painless process. I had spent a bit of time worrying about it but in the end it was really easy. 811 acts to engage all of the involved utility companies so that they can come out and mark their lines. It is a neat process. Next article could be on the permitting process and what a permit actually means.

  3. Be certain that you know what the locator service is and is NOT locating. I live in the country. I have water lines from my well to my house & horse barn, electrical lines from the meter location to my house & from the house to the horse barn & well. The locator services only mark the services covered by their utility contracts. The rest of those underground utilities are generally located by the ‘braille’ method – i.e., dig gently until you locate the line and before you fire up the trencher!

        1. Find a survey shop that rents out equipment, and ask them for a pipe and cable locator kit. Most of these can detect both electrical and pipes passively. Plastic pipes (hdpe gas & water) are installed with a trace wire for detection. If you know that your water lines are iron and that your electrical lines are in RMC and less than 5 feet, you can get by with a magnetic locator. If you know that they’re extremely shallow (less than the diameter of the coil,) a metal detector will do the job.

          1. Good suggestion. In my case I was present when all of these were installed and I photographed the open trenches. My point to AKA was that it always eventually comes down to hand digging. Just have to watch your local utility company trench to within a foot or two of the locator mark, then get down in the trench with a spade to find the actual line.

          1. Depends on what you are digging around. Water or sewer line should be fine.
            Don’t do it anywhere near a 50 year old AC line. I’ve seen these with cracked insulation and even bare copper.
            Just don’t dig anywhere near AC lines if you cannot disconnect them, no matter what method.

        2. The alternative is being smart when you put them in.
          On my property all my lines are in an extra PVC pipe (example: waterline rated for burial inside PVC sewer pipe).
          a few inches of sand on top and around to seat the pipe, then 2 inches of gravel, some police tape and after that plane dirt.
          I also made a plan with all the lines and made lots of pictures from every trench.
          Now, if I dig and see gravel the alarms go off. And believe me, you don’t put a normal shovel through 2 inches of gravel by accident.

    1. There are many private utility location services. I don’t know how expensive they are but it barely takes an hour for them to wheel their lawnmower sized GPR around most properties. Time is obviously dependent on the extent/area of excavation.
      The same methods mentioned in the article are also used by them.

    2. I ran into a similar issue when I had to dig up my sewer line to replace it – all the utility locating services do is mark the location of their lines /up to the meter/, after the meter is considered your responsibility. Luckily only thing underground at my house is water and sewer, and I knew where the water line was.

  4. I have a project for which I need to dig a hole that I am pretty certain intersects the power line feeding my house.

    I find lots of information online about how to call 811. I have done this before and it is not hard. But… then what? They tell you what is where, not how to deal with it. Knowing the electric line is there is my project out of the question? Is it safe to dig up an electric line?

    Clearly I can’t use a backhoe or any kind of powered digger. Can I dig around it with a regular shovel? The kind one usually uses their feet for force? If not how about a hand held garden spade? (that would suck). When I expose the wire what will I find? A well protected conduit? Concrete? Just a wire? Just a wire with tough insulation or crappy insulation that is already falling apart? The house was built in 1992. I assume it was a new drop.

    Is this no big deal? Or instant death that shouldn’t even be considered?

    811 doesn’t seem to answer these kinds of questions. It would be much more useful if they did!

    1. If this is in USA and it’s a new drop from 1992, chances are it was run in “direct burial” underground wire. It’s cheaper and easier than running wire that thick in conduit (most houses in my area at least are provided either 2/0 or 4/0 awg service entrance conductors)……….

      This is a question that should be quickly answered by calling your power company or local authority having jurisdiction regarding electrical work — probably your local building department?? Odds are they will just tell you to hire someone who knows what they are doing :D

      Here’s the thing about digging it yourself… if it’s live with power, as the service lateral normally always is, then you must contact the power company to disconnect it before digging around it. You’d be foolish to attempt to dig out around a live UNFUSED high amp cable like this, even if it’s just with a tiny shovel or trowel. One little nick in the insulation and you could be toast if conditions are right, and it’s HARD to see what you’re doing when everything is covered in mud.

      In my area, the power company will come disconnect your power for times when you have to do work that requires the service lateral to be dead, BUT they won’t reconnect it without a sign off from the county inspector, and he won’t sign off on an inspection unless the work was done by a licensed contractor. YMMV

    2. >>They tell you what is where, not how to deal with it.

      At the risk of being pompous, if you’re asking this question you might want to reconsider doing your project yourself.
      The solution is don’t dig where utilities are.
      Unless there is some amazingly (life and death or millions of dollars) important reason that your project be at that location, just move the project. If your project can’t be in any other location your options are: 1) hire professionals so it’s their fault when things go wrong (they also have better suited equipment) or 2) Relocate the utility.
      The danger or damage from finding utilities the hard way can’t be worth whatever your project is.

    3. Thanks for the answers! I will probably just skip the project for now. The project was to add cleanout lines to my foundation drain. I have had problems in the past with basement flooding due to the line plugging. The thing is I now have a cleanout that lets me access the most important length of the drain. It’s a real PITA though because I have to fish my hose around a 90 degree bend to use it. Also, it only gets me access to the one side of the house where the original problem was. Adding a new line in the corner would give me access to the back section of the drain too plus I could put it in with much friendlier 45 degree angles.

      That being said.. it’s not big enough problem currently to justify paying a professional. The electrical feed comes right by that corner. Also, it’s a duplex. That feed is for both us and our neighbors who rent the other side from us. I don’t like inconveniencing the renters so getting the feed turned off is out of the question except in an emergency situation.

      Oh well. Better cleanouts would have made my life easier but it sounds like it’s just not worth it.

    4. A couple of times I’ve needed to trace hidden mains lines under ground. I plugged an open ended guitar lead with the centre conductor bared for about 12 inches in to my little Pignose portable amplifier, plugged in headphones and went wandering. It was really easy to find the mains lines under ground just by ‘divining’ with the bare wire.
      The hum is always there but reaches a peak near the wire. As suggeted in the video, I found it made a big difference when I turned on the electric oven. The extra load increased the induced signal.

  5. Where it gets fun is when you have utilities old enough to not be well documented. The pneumatic tubes in many downtown areas (NYC’s Wall Street comes to mind) that were once used for moving paper around are still down there.

    Someone proposed buying up the pneumatic tube right of ways and re-using them for fiber a while back.

    Turning up anything with an excavator can cause you a bit of a fright if you don’t know what it is.

  6. >15″? Where is that written? Not in my state. Call 811 for ANY excavation. Utilities can’t monitor/guarantee/maintaincover over a line once it’s buried. Lots of dangerous utilities are just a few inches deep due to excavation, erosion, etc. Always call 811. It’s free.

      1. It depends how big that flower is.
        Trees and shrubs have a tendency to grow roots down and outward nearly as big as the part you see up on top.
        Roots and pipes just love to cuddle up with each other despite your best efforts, and this can be devastating to the pipe.

        I’ll also add you should call not just planting a big flower, but also for tearing one out.
        It’s a bit strange with the timing, but I just had to call 811 two days ago, and they already came out today while I was at work leaving a bunch of blue and yellow flags in the ground for me (water and gas lines respectively)
        I’m having a tree cut down and the stump pulled as it’s starting to cause problems with the house foundation, and the gas line turns out to be not 2 feet away from the thing.
        Was hoping to pull the stump myself but now it’s clear I’m going to need professional help to avoid damaging the gas main.

        811 is free, takes only a couple days, and the worst possible case is you have a bunch of flags in the lawn to pull up because it turns out nothing is near your work area.
        Best case I just prevented exploding myself up this weekend!

        So yes, if your flower needs more than 12″ clearance below it, stop being lazy and call!

        (Now if you’ll excuse me I have some areal photographs to take with my drone so all the underground stuff can be retained for my own records in the future)

  7. Saw a docu about the British underground and they were doing work and came across a problem with a sewage pipe, but it was an Victorian age (or older) one, and although in active use there are no records on most of them it seems.
    Makes working in London a bit tricky I imagine, the only way to know is to carefully dig and see.

    I wonder if in some other countries they would send robots down the sewers to map it all out. Although they would have to be cleverly designed robots with all the various angles and materials used and the various clogs in the ancient pipes.

    1. London is a bit of a nightmare in this respect. Most of the water pipes are still Victorian as well and they have many leaks. This creates sinkholes and further damage to the utility lines.

      1. Interesting, but were all records really stored in a single spot during wartime? Seems a bit of a flawed setup. But I guess since they were all bits of paper of I expect various sizes with various ways of recording the info it was hard to copy them.

  8. So I run a geotechnical drill crew and I call miss utility like twice a week. Call if you are going deeper than 15 feet is lunacy. Maybe it was supposed to be 1.5′, which is about right. Legally if a tool penetrates the ground surface in an area not covered by a an active miss utility ticket the operator is liable for damages. 1.5′ seems like a pretty good rule. Most utilities are burried from 3-6 feet but there are always exceptions. A lot of plastic pipe gets buried without a locator and the location becomes lore at the utility company. Recently I had to hand excavate to find a 10in water main that connected to a 200,000 gallon tank with a broken shutoff valve, because the utility didn’t put a tracer with the plastic pipe and wasn’t sure where it was. To play it safe you want to give yourself 2′ from the outer bounds of the mark when digging. If you are within 2 feet of a mark you are suppose to hand excavate. I use an air spade (which you can rent) to loosen the soil and buckets to remove the loosened soil. I haven’t harmed a manually excavated utility yet. I have drilled through everything but if fiberoptic cable in areas where the utility was incorrectly marked, or not marked at all. Pipes are usually surrounded by fine gravel and if you are paying attention you can avoid damaging them. But there is no visual indication if something was installed by directional drilling or as a direct burial cable.

    1. ATT buried a line on my property at a depth of THREE INCHES, then failed to respond when the 811 people contacted them. If I hadn’t delayed digging for a week for unrelated reasons (giving them time to finally respond), I would have cut right through it.

  9. For those in Australia, the service you want is Dial Before You Dig and it has both a website and a special phone number. Never had a reason to use it or to do any digging of any sort, just letting anyone else in Australia know what they should do if they ever do need to dig :)

  10. Science is trying to determine what it is in an excavator that provides it with an affinity to find buried fiber optic cable. If that mechanism could be applied to cable locate technology, the benefits would be enormous.

    1. The PDF report is a great read (pictures!) https://assets.publishing.service.gov.uk/media/547c8fb940f0b60241000157/R032014_140213_Old_Street.pdf

      Basically they were drilling piles for support of a building and managed to ‘hole’ one of the london underground tube lines (they’re electrified using a third-rail system). Unfortunately, it would seem the auger can become detached from itself in some situations and so, when they came through the steel lining of the tunnel, they lost two sections of the auger into the tunnel itself, which fell across the line. “The piling team were unaware that they had penetrated a tunnel and attempted to locate the missing sections of auger by dropping metal bars down the hole.”

      Looking at the plans, if they’d actually done all of the piles, there would have been like a dozen strikes on the tube line, such was the location. So the most damming part (pertinent to the HaD article) is this point: “Searches undertaken on behalf of the Client prior to it purchasing the site did not include Network Rail.” (Network Rail maintain all the rail tracks in London and beyond.)

      1. Oh, I should add that the developers were not totally to blame as there appears to have been many professionals (from different companies) involved, many of whom should have caught this and the whole report does read like a clusterf**k of missed chances to avoid the problem.

  11. No list of flag identification? In US the flag color are:
    Red: electric
    Orange: communication (telephone, cable, and fiber optic)
    Yellow: natural gas
    Green: sewer
    Blue: water
    Purple: fiber optic (obsolete? been years since I saw purple and F.O. seems to be orange nowaday)
    Brown: storm drain water (if separate from sewer)
    Pink: property boundary.

  12. How incompetent is Qwest, or CenturyLink, or whatever the hell they are calling themselves these days? They dug a big hole in my front yard without even the courtesy of knocking on the door. Then, while they were trying to find their own damn TELEPHONE cable, they managed cut the TV CABLE (which as “a courtesy” to Cox they fixed with some electrical tape).

    Then after they sat on their ass for a week with a pile of dirt killing the lawn, they decided the buried short wasn’t under my lawn after all. So they buried the mess and put in a telephone pedestal by an existing tree. Then five years later they were complaining about the tree, having forgotten that with an entire front yard to choose from *they* had chosen to put the box next to the tree.

    Oh, yeah, and the guy insisted that the round black cable was TV COAX. Even after I showed him where it entered the wall and had four colored solid wires: red, green, black, yellow.

    That’s how incompetent CenturyLink is.

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