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Vertical separation distance between gas line and potable water main

  • 1.  Vertical separation distance between gas line and potable water main

    Posted 12-27-2019 11:57 AM
    ​Hi there,

    When a proposed water main is crossing perpendicular to an existing gas line, is there any requirement (in California) of the vertical separation distance?
    The proposed water main is a 12" ductile pipe, pressure class is 350 psi, operating pressure is 75 psi.
    The existing gas line is 2" natural gas line.
    Is 4" to 6" or vertical separation sufficient?
    Thank you for your thoughts.

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    Tsungchu Chien P.E., M.ASCE
    State Water Resources Control Board
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  • 2.  RE: Vertical separation distance between gas line and potable water main

    Posted 12-28-2019 11:10 AM
    I work in Tennessee.  Whenever possible, we maintain 2 feet of horizontal separation and 1 foot of vertical separation between our water main and a natural gas line.  That gives both gas and water main crews reasonable distance to perform any repairs that may be required at a later date.

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    Jonathan Hardin P.E., M.ASCE
    DIR OF WTR OPS
    Columbia TN
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  • 3.  RE: Vertical separation distance between gas line and potable water main

    Posted 01-02-2020 02:23 PM
    PLEASE design with maintenance in mind.  A little forethought now could save major headaches and repair costs later!

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    Maria Price P.E., M.ASCE
    Engineering Manager
    City of Chattanooga
    Chattanooga TN
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  • 4.  RE: Vertical separation distance between gas line and potable water main

    Posted 12-28-2019 03:27 PM
    Be careful of cathodic protection interference between the two pipelines.  I am aware of a case where, in a hill location, a gas street main crossed under a water street main within four to six inches.  The water main may not have been under cathodic protection.  The gas main probably was under cathodic protection.  Both pipelines had sand bedding.  The water main developed a pin-hole leak at a location closest to the gas line, possibly due to cathodic protection interference.  In this case, the escaping water, under pressure, and in the presence of the sand bedding, scoured a hole in the gas line and entered the gas pipe.  The  quantity of water in the gas pipe was sufficient  to cause interruption to its customers who were located at a lower elevation than the crossing pipelines.  I am not aware of any collateral damage due to the gas that may have escaped from the point of entry of the water, (i.e. the leak location).



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    Kenneth Salsman P.E., M.ASCE
    Retired
    Harbor City CA
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  • 5.  RE: Vertical separation distance between gas line and potable water main

    Posted 12-29-2019 09:59 AM
    Great! Thank you guys for the suggestions and sharing your experiences!
    -George





  • 6.  RE: Vertical separation distance between gas line and potable water main

    Posted 12-29-2019 04:03 PM
    Also, there should be specific ordinances,codes, and/or specifications for California that you are required to follow. It would be a good idea to contact the local municipality and inquire about the regulations as well as contacting State agencies to make sure you meet all requirements BEFORE you finalize your design and present it to the client.

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    Daniel Rosenberg P.E., M.ASCE
    AECOM
    Cleveland OH
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  • 7.  RE: Vertical separation distance between gas line and potable water main

    Posted 12-30-2019 11:19 AM

    Past years---12" minimum Clear-Outside to Outside was sufficient.

    However, we have encountered recently, this last year, for major gas lines, (So. CA. Gas),  18".

    Best to ask an Engineer at the Gas Company.

    Some of the agencies have required wrapping the D.I.  or enclosing and sealing (encasing) the piping in a secondary containment.

     

    Wendell Iwatsuru,  P.E. 

    Madole & Associates, Inc.

    9302 Pittsburgh Avenue, Suite 230

    Rancho Cucamonga, CA. 91730

    (909) 481-6322

     






  • 8.  RE: Vertical separation distance between gas line and potable water main

    Posted 12-30-2019 01:09 PM
    Mr. Chien: I assume you are with a regulatory organization. Let go back to the beginning. All of the comments are spot on, but somewhat incomplete. I would not install a water line unless there was sufficient knowledge about the soils. I have seen soils so hot that the plastic wrap looked like it was used for shotgun practice. Even sandy soil can have enough clay to create electrolysis. So consult a cathodic expert. I have seen soils that will cause DI leakage in less than 10 years.
    Crossing close to a gas line, probably protected with induced current, could cause corrosion in the metallic water line and there are other factors. If the water line has sacrificial anodes, are they installed correctly and spaced properly, and are the pipeline jumper connections (which carry current across gasketed joints to the anodes) welded sufficiently, and are there two jumpers in case one fails. Consider anodes on the pipe section that is crossing the gas line and install it so it is approximately in the middle of the waterline pipe section.
    Gas companies have been using the best cathodic technology for years. Their systems are strong and exists to protect the gas line, not the surrounding utilities. I have not seen where a water jet from a waterline pin hole punctured a gas line, but it sounds like a lot of liability for the water line owner. A lot of national standards addressing protection from electrolysis are available, but I am retired and have not kept current files, but they are worth looking at.

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    Bruce Yates P.E., M.ASCE

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  • 9.  RE: Vertical separation distance between gas line and potable water main

    Posted 01-02-2020 02:23 PM

    In San Bernardino county, I have seen gas companies requesting 12" vertical separation for standard distribution gas lines and as much as 24" vertical separation for high pressure gas transmission lines.  For standard gas distribution lines, I have experienced little resistance when requesting a variance for 9" vertical separation or as little as 6" vertical separation when it avoids an offset in either line.  However such a request must be made directly to the gas company's planning department which represents your jurisdictional boundaries (in my region the SCG transmission lines are represented by a different planning/design group than the distribution lines).  These contacts can be easily found through digalert design lookup.  They typically formally request 8 to 12 weeks for plan review of a 90% design set, but of course you want to know if a variance is acceptable much sooner than a 90% set and they typically are agreeable to advise as soon as you have a plan+profile for the crossing.  Good luck with your project.



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    Jonathon Schoenen EIT, Aff.M.ASCE
    Rialto CA
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