Finding a water main leak with a metal detector

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by scrunchielaura, Sep 2, 2011.

  1. scrunchielaura

    scrunchielaura New Member

    Messages:
    10
    Location:
    California
    There's a water main leak under my street. It's been leaking for more than 10 years, though much worse in the last year. The water company has finally been contacted - they sent someone out - and they deny a leak! This is California. It hasn't rained in months. All seasonal springs and seeps have dried up. But something's keeping several thousand square feet of hillside damp beneath the surface. I think I know exactly where the leak is, and have a good idea of what's leaking. I'm posting this to see if someone finds a flaw in my logic.

    I'm on a hillside that slopes from the south down to the north. Our short private road goes east - west. The road climbs slightly to a high spot at it's midpoint. The suspected leak is at this high spot. The east half of the road has a 30 to 40 year old 6 inch asbestos-concrete water main. The west half has a 20 year old 6 inch PVC main. The PVC replaced a leaking World War I surplus 2 inch outside diameter steel pipe. The 6 inch main is fed at it's midpoint by another 2 inch steel line that comes down the hillside via people's side yards. There's also a plastic natural gas pipeline under the street.

    I have a metal detector. More specifically, it is an iron detector meant for finding property markers and buried steel pipes. It works by detecting changes in the earth's magnetic field caused by iron in any form (iron, steel, rust). Supposedly, it can detect buried pipelines 20 feet deep. It does not detect copper, aluminum, nor coins. And certainly not plastic.

    I wanted to dig a test/percolation pit abeam of the feed point of the 6 inch main. I hoped my metal detector could find the connection. Instead, there is a large area where the detector goes nuts! I mapped out the edges of this area: It is a 15 by 30 foot blob with a narrow (30 degree?) wedge shaped bulge that points uphill. Sort of like a dialog bubble from a comic strip. Other than perhaps the feed connection, I shouldn't have been able to detect anything in that area. (The disused 2 inch main is still present, but uphill from the blob.)

    Beyond the blob, my detector finds a wide diffuse fluctuating band that follows the natural gas line's (historical) trench downhill to both ends of the street. Remember, the gas line is plastic so I can't detect it. The disturbed soil of the trench is probably easier for water to flow through. The west end of the street is next to a ditch/stream. Several years ago I saw a new water seep there that included lots of "orange goop". (That area is now too overgrown with weeds to see.)

    My theory is that the metal detector is detecting a rust plume. Ten+ years of hundreds to maybe a thousand gallons a day of water has flushed lots of rust out of the water system. The wedge shaped bulge is like an arrow pinpointing the source of the leak. Does this sound plausible?

    The suspected leak is not over the 6 inch main, nor over the supply coming down the hill. It might be an end of the disused main, but I can't detect any iron/steel pipe running beyond the wedge. It is however right over the likely route of a defunct service connection. I've seen the water company use soft copper tubing to connect water meters to the main. (Remember, I can't detect copper.) I suspect the defunct connection is copper and it has a break!

    Today I finally finished breaking a small hole in the asphalt road right over the tip of the "wedge". The base rock (i.e. gravel) under the asphalt seemed dry. Beneath that is the sandy clay (loam) common to this area. I've dug about an inch into the loam and already encountered dampness. I'm thinking of hand digging further into the loam. Or maybe hydraulically drilling with a pipe attached to a garden hose. How should I proceed? (To get the water company to react, I apparently have to produce running water.)

    PS I would love it if the water company has to come out here on Labor Day to fix the leak!
    Last edited: Sep 2, 2011
  2. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    You should proceed straight to the looney bin...or go directly to jail! IF you succeed in finding a leak, or CREATING a larger leak, you will possibly encounter a much bigger surprise than you were expecting! And you will surely be BLAMED for it! There was a hillside washed away here in San Diego a couple of years ago, took 6 houses with it. The lawyers are still fighting over whether leaking mains, sewers, or storm drains caused the leak.

    If the water is as obvious as you say, get the channel 10 news girl out there with a camera crew. Contact your city council person, county supervisor, whoever your local elected official is. Those things can get the water company interested.
  3. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,825
    Location:
    Cave Creek, Arizona
    1. YOU CANNOT dig in the street without an "encroachment" permit, which ONLY a licensed plumber or utility contractor can get AFTER posting the proper bond and insurance documents.
    2. If they utility is not worried about it now, then they may NOT be worried about it even if you do find "moisture" in the area.
    3. You can be issued a citation and fined for doing ANYTHING in the street without approval.

    Many people have be fined for "improving" their roads and alleys without permission.
  4. scrunchielaura

    scrunchielaura New Member

    Messages:
    10
    Location:
    California
    It's a private road - and actually just an access easement over various parcels.
  5. johnjh2o1

    johnjh2o1 Plumbing Contractor for 49 years

    Messages:
    1,143
    Location:
    South*East
    If you break into the main I'm sure the water company will come out on labor day for overtime pay. But I'm also sure it will be on your dime.

    John
  6. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    In general, I think you will find this forum to be about as friendly as they come in terms of helping out homeowners. When 4 people come over the top on you as has happened here, I suggest there is a message in that......
    As well intentioned as you may be....the potential for VERY bad things to happen just can't be ignored.
  7. Terry

    Terry Administrator Staff Member

    Messages:
    15,124
    Location:
    Bothell, Washington
    Reading the story I become curious. If it is rust in the soil causing a signal that would be good detective work on your part.

    Finding underground leaks has always been difficult though. You might mention your theory to them, but I don't think I would consider digging it up on your own.
  8. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,139
    Location:
    New England
    My sister works for a municipal water system. One of her older jobs was leak detection/location. She got pretty good at it. They used a fancy microphone. She could usually pinpoint a leak within about 6", even feet underneath a roadway.
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